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DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 285–290 285 Reactions of a diruthenium complex with sulfur, selenium and sulfur dioxide Joshi Kuncheria, Hameed A. Mirza, Hilary A. Jenkins, Jagadese J. Vittal and Richard J. Puddephatt* Department of Chemistry, University of Western Ontario, London, N6A 5B7, Canada Reaction of the complex [Ru2(CO)4(m-CO)(m-dppm)2] 1 (dppm = Ph2PCH2PPh2) with sulfur or selenium gave the corresponding [Ru2(CO)4(m-E)(m-dppm)2] (E = 2 or 3) in high yield.Both 2 and 3 reacted with an excess of sulfur to give the disulfido, m-sulfido complex [Ru2(CO)2(m-CO)(m-S)(S2)(m-dppm)2] 4. Complex 1 reacted readily with SO2 to give [Ru2(CO)4(m-SO2)(m-dppm)2] 5, containing a bridging S-bonded SO2 ligand. The complexes 1, 4 and 5 have been characterized by crystal structure determinations and are shown to contain Ru]Ru single bonds. The complex [Ru2(CO)4(m-CO)(m-dppm)2] 1 (dppm = Ph2- PCH2PPh2),1–3 like related diphosphine derivatives of the unstable [Ru2(CO)9],4 displays high reactivity towards both electrophilic and nucleophilic reagents and so is an interesting reagent for study of co-ordination chemistry at a diruthenium centre.1–4 Although this topic is of current interest and though there are many examples of ruthenium complexes with bridging sulfur- or selenium-donor ligands,5–10 there appear to be no reports on complexes derived from 1 with sulfur or selenium reagents.4 Since it seemed probable that interesting chemistry relevant to the role of RuS2 in catalytic hydrodesulfurization 5 would result, such a study was initiated and this article reports the reactions of 1 with the reagents sulfur (and some other potential sulfur atom donors), selenium, and sulfur dioxide.Results and Discussion The chemistry below leads to a series of complexes [Ru2(CO)4- (m-E)(m-dppm)2] (E = S, Se or SO2) by displacement in complex 1 with E = CO. It was of interest to compare the properties of these complexes. The structure of 1 as a solvate with 1,2- C2H4Cl2 has been determined but the data were of poor quality,2 so we have therefore redetermined it, this time as the acetone solvate.Whilst this work was in progress the structure of 1 as the acetonitrile solvate was reported.1 The new structure is shown in Fig. 1 and selected distances and angles are given in Table 1. The structure contains a trans,trans-Ru2(m-dppm)2 unit in the extended boat conformation with the methylene flaps directed away from the bridging carbonyl ligand.Hence, the axial phenyl groups are all directed towards the bridging carbonyl, which is small enough to fit between them (Fig. 1). The bond distances and angles are similar to those found in the other solvates.1,2 Thus, the Ru]Ru distance is 2.903(2), 2.903(2) and 2.907(9) Å in the acetone, 1,2-dichloroethane 2 and acetonitrile 1 solvates respectively. Reactions with sulfur and selenium When [Ru2(CO)4(m-CO)(m-dppm)2] 1 was treated with elemental sulfur in a ratio Ru2:S = 1 : 1 the bridging sulfido complex [Ru2(CO)4(m-S)(m-dppm)2] 2 was obtained by displacement of the bridging carbonyl by the sulfide ligand.The reaction was complete in 10 min at room temperature and the product was obtained as an air-stable, orange-brown solid in high yield. The same product 2 was obtained by reaction of 1 with either of the sulfur atom donors H2S or propylene sulfide, with evolution of hydrogen or propene respectively as well as CO (Scheme 1).No intermediates were observed when the reactions were monitored by 1H and 31P NMR spectroscopy, though, at least with H2S as reagent, they must be formed transiently. Complex 2 did not react further with either H2S or with propylene sulfide, but did react with an excess of sulfur as described later. Complex 2 was readily characterized by analytical and spectroscopic methods. The significant feature which differentiated the IR spectrum from that of its precursor was the four terminal carbonyl stretching bands but no bridging carbonyl band (observed at 1701 cm21 for 1).2 The 1H NMR spectrum was typical of an ‘A-frame’ complex, containing two multiplets due to the CHaHb protons of the dppm ligands at d 5.1 and 3.1.The 31P NMR spectrum showed a singlet at d 27.5 as expected for a symmetrical compound. The reaction of complex 1 with grey selenium proceeded in an analogous way to give the bridging selenido complex 3 (Scheme 1), which was isolated as a stable, dark brown solid.Its spectroscopic properties were very similar to those of 2. In addition, it gave a parent ion in the FAB mass spectrum, as well as peaks due to fragments from sequential loss of the four carbonyl ligands. The reaction of complex 1 or 2 with an excess of sulfur gave a new complex characterized as [Ru2(CO)2(m-CO)(m-S)(S2)- (m-dppm)2] 4 (Scheme 1), and this could be isolated as air-stable red crystals.The reaction with 1 proceeded sequentially to give 2 and then 4, as monitored by 1H and 31P NMR spectroscopy. Fig. 1 View of the structure of [Ru2(CO)4(m-CO)(m-dppm)2] 1286 J. Chem. Soc., Dalton Trans., 1998, Pages 285–290 The IR spectrum of 4 contained three carbonyl bands at 2020, 1960, and 1836 cm21, consistent with the presence of two terminal carbonyls and one bridging carbonyl group. The 1H NMR spectrum contained two broad multiplets at d 2.8 and 4.5 due to the CHaHb protons of the dppm ligands, while the 31P NMR spectrum contained two multiplets of equal intensity at d 10.5 and 18.0, indicating the inequivalence of the two ruthenium centres.The FAB mass spectrum showed the parent peak for [Ru2(CO)2(m-CO)(m-S)(S2)(m-dppm)2]1 at m/z = 1151 and fragmentation peaks at m/z = 1087, 1059, 1031 and 1003, attributed to ions formed by sequential loss of S2, followed by one, two, and three CO groups respectively. The spectroscopic data did not define the nature of the sulfur-donor ligands in complex 4 so it was also characterized by a crystal structure determination.A view of the structure is given in Fig. 2 and selected bond distances and angles are in Table 2. There was disorder between the m-S and m-CO ligands of 4, but this was successfully resolved; Fig. 2 shows only one of the two arrangements. Scheme 1 Reagents: (i) S8, 2CO; (ii) Se, 2CO; (iii) S8, 2CO; (iv) S8, 2CO, 2Se; (v) SO2, 2CO P Ru S Ru P P P OC OC CO CO P Ru S Ru P P P OC OC CO CO P Ru S Ru P P P S S CO CO P Ru Se Ru P P P OC OC CO CO P Ru C Ru P P P OC OC CO CO O O (iii) (iv) (ii) (v) (i) O C O 2 5 4 3 1 Table 1 Selected bond lengths (Å) and angles (8) for complex 1?0.5Me2CO Ru(1)]C(1) Ru(1)]C(5) Ru(1)]P(2) Ru(2)]C(3) Ru(2)]C(5) Ru(2)]P(4) O(2)]C(2) O(4)]C(4) C(2)]Ru(1)]C(1) C(1)]Ru(1)]C(5) C(1)]Ru(1)]P(1) C(2)]Ru(1)]P(2) C(5)]Ru(1)]P(2) C(2)]Ru(1)]Ru(2) C(5)]Ru(1)]Ru(2) P(2)]Ru(1)]Ru(2) C(4)]Ru(2)]C(5) C(4)]Ru(2)]P(4) C(5)]Ru(2)]P(4) C(3)]Ru(2)]P(3) P(4)]Ru(2)]P(3) C(3)]Ru(2)]Ru(1) P(4)]Ru(2)]Ru(1) O(1)]C(1)]Ru(1) O(3)]C(3)]Ru(2) O(5)]C(5)]Ru(1) Ru(1)]C(5)]Ru(2) 1.98(2) 2.13(2) 2.352(4) 1.96(2) 2.13(2) 2.327(4) 1.13(2) 1.13(2) 115.8(7) 145.3(7) 85.1(5) 89.5(5) 93.8(4) 145.8(5) 47.0(4) 91.2(1) 107.9(7) 87.1(5) 89.7(4) 90.3(5) 117.2(2) 86.9(5) 91.1(1) 178(2) 178(2) 138(1) 86.0(6) Ru(1)]C(2) Ru(1)]P(1) Ru(1)]Ru(2) Ru(2)]C(4) Ru(2)]P(3) O(1)]C(1) O(3)]C(3) O(5)]C(5) C(2)]Ru(1)]C(5) C(2)]Ru(1)]P(1) C(5)]Ru(1)]P(1) C(1)]Ru(1)]P(2) P(1)]Ru(1)]P(2) C(1)]Ru(1)]Ru(2) P(1)]Ru(1)]Ru(2) C(4)]Ru(2)]C(3) C(3)]Ru(2)]C(5) C(3)]Ru(2)]P(4) C(4)]Ru(2)]P(3) C(5)]Ru(2)]P(3) C(4)]Ru(2)]Ru(1) C(5)]Ru(2)]Ru(1) P(3)]Ru(2)]Ru(1) O(2)]C(2)]Ru(1) O(4)]C(4)]Ru(2) O(5)]C(5)]Ru(2) 1.90(2) 2.346(4) 2.903(2) 1.87(2) 2.347(4) 1.11(2) 1.14(2) 1.18(2) 98.9(6) 91.3(5) 92.8(4) 88.4(5) 173.1(2) 98.4(5) 91.9(1) 118.1(7) 133.9(7) 90.3(5) 90.2(5) 91.8(4) 154.9(6) 47.0(4) 91.7(1) 177(2) 177(2) 136(1) The structure contains the expected trans,trans-Ru2(m-dppm)2 unit in an extended chair conformation. This conformation results in the presence of two axial phenyl groups on each side of the molecule, and so to two similarly sized cavities for the m-S and m-CO ligands to fit into.Atom Ru(1) is bonded to a terminal h2-disulfide ligand while Ru(2) is bonded to two terminal carbonyls. There is a bridging sulfide ligand and a bridging carbonyl. The Ru]Ru distance of 2.935(3) Å indicates the presence of a metal–metal bond; although the distance is at the long end Fig. 2 View of the structure of [Ru2(CO)2(m-CO)(m-S)(S2)(m-dppm)2] 4. Only one of the arrangements of the disordered m-S and m-CO groups is shown Table 2 Selected bond distances (Å) and bond angles (8) in [Ru2(CO)2(m-CO)(m-S)(S2)(m-dppm)2]?Me2CO Ru(1)]C(1) Ru(1)]P(2) Ru(1)]S(2) Ru(1)]Ru(2) Ru(2)]C(2) Ru(2)]P(3) Ru(2)]S(1) C(2)]O(2) C(1)]Ru(1)]P(1) P(1)]Ru(1)]P(2) P(1)]Ru(1)]S(1) C(1)]Ru(1)]S(2) P(2)]Ru(1)]S(2) C(1)]Ru(1)]S(3) P(2)]Ru(1)]S(3) S(2)]Ru(1)]S(3) P(1)]Ru(1)]Ru(2) S(2)]Ru(1)]Ru(2) C(3)]Ru(2)]C(2) C(2)]Ru(2)]C(1) C(2)]Ru(2)]P(3) C(3)]Ru(2)]P(4) C(1)]Ru(2)]P(4) C(3)]Ru(2)]S(1) C(1)]Ru(2)]S(1) P(4)]Ru(2)]S(1) C(2)]Ru(2)]Ru(1) O(1)]C(1)]Ru(1) Ru(1)]C(1)]Ru(2) S(2)]S(3)]Ru(1) O(3)]C(3)]Ru(2) 2.18(3) 2.403(6) 2.430(7) 2.935(3) 1.86(3) 2.415(6) 2.535(9) 1.15(3) 95(2) 174.0(2) 90.9(3) 107.1(7) 92.8(2) 156.6(8) 82.1(2) 51.8(3) 93.3(1) 156.0(2) 92(1) 171(2) 87.4(8) 89.3(8) 96(2) 174.6(8) 98.8(7) 85.5(3) 137.9(9) 134(2) 83(1) 64.0(3) 177(2) Ru(1)]P(1) Ru(1)]S(1) Ru(1)]S(3) Ru(2)]C(3) Ru(2)]C(1) Ru(2)]P(4) S(2)]S(3) C(3)]O(3) C(1)]Ru(1)]P(2) C(1)]Ru(1)]S(1) P(2)]Ru(1)]S(1) P(1)]Ru(1)]S(2) S(1)]Ru(1)]S(2) P(1)]Ru(1)]S(3) S(1)]Ru(1)]S(3) C(1)]Ru(1)]Ru(2) P(2)]Ru(1)]Ru(2) S(3)]Ru(1)]Ru(2) C(3)]Ru(2)]C(1) C(3)]Ru(2)]P(3) C(1)]Ru(2)]P(3) C(2)]Ru(2)]P(4) P(3)]Ru(2)]P(4) C(2)]Ru(2)]S(1) P(3)]Ru(2)]S(1) C(3)]Ru(2)]Ru(1) Ru(1)]S(1)]Ru(2) O(1)]C(1)]Ru(2) S(3)]S(2)]Ru(1) O(2)]C(2)]Ru(2) 2.395(6) 2.404(9) 2.434(7) 1.80(2) 2.25(3) 2.415(6) 2.13(1) 1.22(2) 90(2) 105.1(7) 91.5(3) 82.3(2) 147.5(3) 92.1(2) 97.1(3) 49.5(7) 92.6(2) 152.2(2) 83(1) 91.3(8) 85(2) 91.8(8) 179.0(2) 86.7(9) 93.8(3) 130.1(9) 72.9(2) 143(2) 64.2(3) 177(3)J. Chem.Soc., Dalton Trans., 1998, Pages 285–290 287 of the Ru]Ru single bond range [2.707(6)–3.02(1)],1–4 there are precedents for the elongation of metal–metal bonds when they are bridged by sulfur.11 Hence each ruthenium atom can be considered to be seven-co-ordinate with highly distorted pentagonal bipyramidal stereochemistry.Since Ru(1) is bound to three sulfur atoms and Ru(2) is bound to only one, the simplest way of dealing with the electron configuration is to consider that Ru(1) and Ru(2) carry a negative and a positive charge respectively; each ruthenium is then co-ordinatively saturated and has a formal oxidation state of II. If the ruthenium atoms are initially considered to be neutral, the formal oxidation states are RuIII(1) and RuI(2) and then a donor–acceptor bond(2)ÆRu(1) must be invoked in order for each ruthenium to attain the 18-electron configuration, leading to effectively the same electron configuration as in the situation above.The bridging sulfide ligand is bound asymmetrically, as indicated by the distances Ru(1)]S(1) and Ru(2)]S(1) of 2.404(9) and 2.535(9) Å respectively. The disulfide ligand is bound in a symmetrical h2-chelate mode with Ru(1)]S(2) and Ru(1)]S(3) distances of 2.430(7) and 2.434(7) Å respectively.The S]S distance S(2)]S(3) 2.13(1) Å is at the long end of the range found in other disulfido complexes for which the S]S distances range between the S]] S double bond (1.88 Å) and S]S single bond (2.09 Å) distances.5–7,12 Although h2 chelation by disulfide ligands is common for many transition metals,5 complex 4 appears to be the first example for a diruthenium complex.4–7 In the known disulfido complexes of ruthenium, the disulfido group bridges in the bridging h2-|| bonding mode and there is evidence for partial SS and RuS double bonding.For example, the complex [Ru2(m-S2)(m-SPri)2(h-C5Me5)2] has Ru]S 2.215(4) and 2.209(5) and S]S 2.008(6) Å, all significantly shorter than the corresponding distances in 4.6 Attempts were made to prepare mixed chalcogenide complexes but without success. Thus complex 2 failed to react with an excess of selenium.Complex 3 did react with an excess of sulfur but the only product formed in detectable quantity was 4; hence this reaction leads to displacement of the bridging selenide ligand in 3 by sulfide. Reaction of complex 1 with sulfur dioxide Complex 1 reacts readily with sulfur dioxide to give [Ru2(CO)4- (m-SO2)(m-dppm)2] 5, which was isolated as air-stable yellow crystals (Scheme 1). The reaction involves the displacement of the bridging carbonyl of 1 by a bridging S]bonded SO2 ligand.Complexes 5 and 2 are closely related, but efforts to prepare 5 by oxidation of the sulfide ligand in 2 using hydrogen peroxide or trimethylamine N-oxide were unsuccessful. The symmetrical nature of complex 5 is shown by the 31P NMR spectrum, which contains a sharp singlet at d 34.7 due to the equivalent phosphorus atoms of the dppm ligands. The 1H NMR spectrum exhibited two resonances at d 2.7 and 4.6 due to the CHaHb protons of the dppm ligands, as expected for an A-frame structure.The IR spectrum contained only terminal carbonyl stretching bands at 2070, 2007, 1972 and 1943 cm21. The n(SO) bands were observed at 1210 (sym. stretch) and 1050 cm21 (asym. stretch), and their separation of 160 cm21 indicates a symmetrical S-bonded co-ordination of the SO2 ligand.13 Complex 5 was further characterized by a crystal structure determination of a solvate 5?EtOH?H2O. A view of the structure is given in Fig. 3 and selected bond distances and angles are in Table 3. The structure contains the trans,trans-Ru2(m-dppm)2 unit in the extended boat conformation.This conformation with the methylene flaps towards the m-SO2 ligand creates a larger cavity on this side of the molecule, since the phenyl substituents are all equatorial, as needed to accommodate the SO2 ligand. Note that in 1, with the smaller m-CO ligand, the extended boat conformation is also observed but with the methylene flaps away from the bridging ligand (Fig. 1). In 5 each ruthenium has two terminal carbonyl ligands and the SO2 ligand adopts the symmetrical bridging mode, as predicted from the spectroscopic data. Nevertheless the arrangement of the carbonyl ligands is much less symmetrical and this appears to be due to steric effects with the axial phenyl substituents of the dppm ligands. Note for example the large differences in bond angles C(2)]Ru(1)]Ru(2) 82.8(5) and C(4)]Ru(2)]Ru(1) 120.7(5), and C(1)]Ru(1)]Ru(2) 166.6(6) and C(3)]Ru(2)] Ru(1) 142.4(6)8.In order to avoid the axial phenyl groups C(2)O(4) moves from its natural position towards Ru(2) while C(4)O(6) moves away from Ru(1). The Ru]Ru separation of 2.925(2) Å indicates the presence of a metal–metal single bond.1–4 The acute Ru]S]Ru angle of 76.2(1)8 also indicates compression along the Ru]Ru axis and is comparable to other such values where SO2 bridges a metal–metal bond [69.6(1)– 79.8(1)8];14 the M]S]M angle is significantly larger [91.2(1)– Fig. 3 View of the structure of [Ru2(CO)4(m-SO2)(m-dppm)2] 5 Table 3 Selected bond distances (Å) and angles (8) in [Ru2(CO)4- (m-SO2)(m-dppm)2]?EtOH?H2O Ru(1)]C(1) Ru(1)]S Ru(1)]P(1) Ru(2)]C(3) Ru(2)]S Ru(2)]P(4) S]O(2) C(2)]O(4) C(4)]O(6) C(1)]Ru(1)]C(2) C(2)]Ru(1)]S C(2)]Ru(1)]P(2) C(1)]Ru(1)]P(1) S]Ru(1)]P(1) C(1)]Ru(1)]Ru(2) S]Ru(1)]Ru(2) P(1)]Ru(1)]Ru(2) C(3)]Ru(2)]S C(3)]Ru(2)]P(3) S]Ru(2)]P(3) C(4)]Ru(2)]P(4) P(3)]Ru(2)]P(4) C(4)]Ru(2)]Ru(1) P(4)]Ru(2)]Ru(1) O(1)]S]Ru(2) O(1)]S]Ru(1) Ru(2)]S]Ru(1) O(4)]C(2)]Ru(1) O(6)]C(4)]Ru(2) 1.90(2) 2.386(4) 2.393(4) 1.91(2) 2.354(4) 2.402(4) 1.53(1) 1.16(2) 1.21(2) 110.6(7) 134.2(5) 91.3(4) 85.8(5) 91.0(1) 166.6(6) 51.4(1) 93.5(1) 90.0(6) 92.4(5) 91.6(2) 89.8(4) 175.1(1) 120.7(5) 89.1(1) 114.7(6) 120.3(5) 76.2(1) 176(1) 169(2) Ru(1)]C(2) Ru(1)]P(2) Ru(1)]Ru(2) Ru(2)]C(4) Ru(2)]P(3) S]O(1) C(1)]O(3) C(3)]O(5) C(1)]Ru(1)]S C(1)]Ru(1)]P(2) S]Ru(1)]P(2) C(2)]Ru(1)]P(1) P(2)]Ru(1)]P(1) C(2)]Ru(1)]Ru(2) P(2)]Ru(1)]Ru(2) C(3)]Ru(2)]C(4) C(4)]Ru(2)]S C(4)]Ru(2)]P(3) C(3)]Ru(2)]P(4) S]Ru(2)]P(4) C(3)]Ru(2)]Ru(1) P(3)]Ru(2)]Ru(1) O(1)]S]O(2) O(2)]S]Ru(2) O(2)]S]Ru(1) O(3)]C(1)]Ru(1) O(5)]C(3)]Ru(2) 1.90(2) 2.391(4) 2.925(2) 1.95(2) 2.386(4) 1.48(1) 1.16(2) 1.13(2) 115.2(6) 86.4(5) 91.1(1) 92.7(4) 172.1(2) 82.8(5) 93.8(1) 96.9(8) 173.0(5) 87.1(4) 91.8(5) 91.0(1) 142.4(6) 89.2(1) 108.5(7) 114.8(5) 119.2(5) 174(2) 176(2)288 J.Chem. Soc., Dalton Trans., 1998, Pages 285–290 118.0(2)8] when SO2 bridges two non-bonded metal atoms.13,14 Thus, each ruthenium atom is considered to have distorted octahedral stereochemistry.The symmetrical bridging of the SO2 is illustrated by the similarity of the Ru]S distances Ru(1)]S and Ru(2)]S of 2.386(4) and 2.354(4) Å respectively, while the S]] O distances S]O(1) 1.48(1) and S]O(2) 1.53(1) Å are significantly different although within the range for other m-SO2 complexes.13,14 The elongation of the S]] O bonds compared to those in free SO2 [1.432(3) Å] is expected since the orbital used for M]SO2 back bonding is S]O antibonding in nature.7,13–15 These are few other binuclear SO2 complexes of ruthenium. 7,10,13–15 The complex [Ru2(m-SO4)2(SO2)2(PPh3)4] contains a sulfur dioxide molecule co-ordinated to each ruthenium as a terminal S]bonded ligand.10 The closest analogy to 5 appears to be [Ru2(CO)2(h-C5Me5)2(m-SO2)], which is characterized as having a bridging SO2 group from its spectroscopic properties.10 Complex 5 is thus the first Ru2(m-SO2) complex to be characterized crystallographically.Conclusion The reactions described between complex 1 and sulfur or selenium lead to formal oxidation of the complexes from the initial Ru0Ru0 state. Thus, 2 and 3 are considered as RuIRuI complexes, while 4 can be considered either as RuIIRuII or RuIRuIII. The SO2 complex 5 would normally be considered as Ru0Ru0, with its formation involving a simple ligand displacement. However, all the complexes contain a metal–metal single bond whose distance appears to depend primarily on the nature of the bridging group(s).Thus, 1, which has a bridging carbonyl only, has the shortest Ru]Ru distance of 2.903(2) Å, while 4 and 5, which each have a sulfur donor bridge, have approximately equal but longer Ru]Ru distances of 2.935(3) and 2.925(2) Å respectively. The bonding in complex 4 is of interest since the metal atoms have high co-ordination numbers for a M2(dppm)2 complex.If the axes are defined as in 4A, the ruthenium atoms use the orbitals 4dyz, 4dx22y2, 4dz2, 5s, 5px, 5py, 5pz primarily for s bonding, while 4dxy and 4dyz are used in p bonding. Strong interactions are expected between the p orbitals of the sulfide ligand and the filled p* orbitals of the disulfide ligand with the metal orbitals of p symmetry.5–7 Extended Hückel molecular orbital calculations indicate that the HOMO (highest occupied molecular orbital) is an antibonding combination of such filled orbitals as shown in 4B, while the LUMO (lowest unoccupied molecular orbital) is a combination of the metal–metal s* orbital (mostly dz2–dz2) and p* orbitals of the carbonyl ligands shown as 4C.Another interesting feature of the structures is that the dppm ligands adopt different conformations in the complexes 1, 4 and 5. Complexes with the trans,trans-M2(m-dppm)2 group usually adopt an envelope conformation of each M2(m-dppm) group with the CH2 flap directed towards the side of the molecule where the bulkier ligands are located. This naturally leads to the phenyl groups on this side of the molecule being equatorial and there is a larger natural cavity in which the other ligands must Ru1 S C Ru2 C C S S P P P P O O O – + y x z 4A S C C S S P P P P O O C C C P P P P O O O C O S S S 4B 4C fit.In complex 4 the m-S and m-CO groups have about equal size (thus allowing them to be disordered on either side) and there is also one S and one CO on either side.Hence, the elongated chair conformation is adopted, leading to equal sized cavities on each side of the Ru2(m-dppm)2 plane. In complexes 1 and 5 there is a m-CO and m-SO2 group respectively on one side of the molecule and two terminal axial carbonyls on the other. Both adopt the extended boat conformation, but in 1 the methylene flaps are away from the m-CO ligand whereas in 5 they are towards the m-SO2 ligand. We suggest that this occurs because the steric effects follow the series m-SO2 > 2 × terminal CO > m- CO.In 5 it seems that steric effects with the axial phenyl groups cause a major distortion of the angles involving the terminal carbonyl ligands. In terms of reactivity complex 1 is electron-rich and is airsensitive. All the complexes 2–5 are air-stable and presumably all have lower electron density at ruthenium. This can be attributed to formal oxidation in the case of 2, 3 and, especially, 4, but to the better electron-withdrawing ability of m-SO2 compared to m-CO in 5.Experimental Complex 1 was synthesized as reported elsewhere,2 and all experiments were carried out using Schlenk techniques with an atmosphere of nitrogen. The NMR spectra were recorded by using a Varian Gemini 300 MHz spectrometer and chemical shifts are given with respect to SiMe4 (1H) or phosphoric acid (31P). Preparations [Ru2(CO)4(Ï-S)(Ï-dppm)2] 2. The complex [Ru2(CO)4(m-CO)- (m-dppm)2] (0.11 g) was mixed with elemental sulfur (0.0032 g) and CH2Cl2 (15 cm3) added.The reaction mixture was stirred under nitrogen for 0.5 h. Solvent was then removed under reduced pressure. The orange-brown compound thus obtained was washed with pentane (5 cm3) and dried under vacuum. Yield = 96%. It was recrystallized from CH2Cl2– pentane (Found: C, 57.5; H, 4.0. Calc. for C54H44O4P4Ru2S: C, 58.2; H, 3.9%). IR (Nujol): n& (CO) 2035, 1980, 1943 and 1916 cm21. NMR (acetone): d(1H) 3.1 (m, 2 H, 2JHH = 13, JPH = 4, CHaHb), 5.1 (m, 2 H, 2JHH = 13, JPH = 5 Hz, CHaHb) and 7.0– 8.0 (m, 40 H, C6H5); d(31P) 27.3 (s, dppm).To a stirring solution of [Ru2(CO)4(m-CO)(m-dppm)2] (0.15 g) in tetrahydrofuran (thf) (20 cm3) was injected H2S (10 cm3). The reaction mixture was then stirred for 3 h after which the solvent was removed under vacuum. The brown solid thus obtained was characterized as [Ru2(CO)4(m-S)(m-dppm)2] by IR, 1H and 31P NMR spectroscopy. Yield = 94%. Propylene sulfide (10 ml) was added to a solution of [Ru2- (CO)4(m-CO)(m-dppm)2] in thf (20 cm3) After stirring the reaction mixture for 3 h it was evaporated to dryness. The resulting orange-brown solid was then washed with hexane (10 cm3) and dried in vacuo.The product was identified as [Ru2(CO)4(m-S)- (m-dppm)2] by its IR, 1H and 31P NMR spectra. Yield = 96%. [Ru2(CO)4(Ï-Se)(Ï-dppm)2] 3. To a mixture of [Ru2(CO)4- (m-CO)(m-dppm)2] (0.15 g) and elemental grey selenium (0.035 g) was added thf (25 cm3).The reaction mixture was then stirred for 5 h. The unchanged selenium (excess) was filtered off. Removal of solvent yielded the product as a dark brown solid. Yield = 97%. It was recrystallized from CH2Cl2–pentane (Found: C, 56.2; H, 3.9. Calc. for C54H44O4P4Ru2Se: C, 55.8; H, 3.8%). IR (Nujol): n& (CO) 2036, 1981, 1944 and 1921 cm21. NMR (acetone): d(1H) 3.5 (m, 2 H, 2JHH = 13, JPH = 4, CHaHb), 5.5 (m, 2 H, 2JHH = 13, JPH = 6 Hz, CHaHb) and 7.0–7.8 (m, 40 H, C6H5); d(31P) 27.8 (s, dppm).FAB mass spectrum: m/z = 1161 (M1), 1133, 1105 and 1049. [Ru2(CO)2(Ï-CO)(Ï-S)(S2)(Ï-dppm)2] 4. The complex [Ru2(CO)4(m-CO)(m-dppm)2] (0.11 g) was mixed with an excessJ. Chem. Soc., Dalton Trans., 1998, Pages 285–290 289 Table 4 Crystal data and structure refinements* for complexes 1, 4 and 5 Formula MT /K Space group a/Å b/Å c/Å b/8 U/Å3 Dc/Mg m23 m/mm21 Tmin, Tmax F(000) No. observations [I > 2s(I)] No parameters R1, wR2 1?0.5(CH3)2CO C56.5H47O5.5P4Ru2 1139.96 295 P21/c 11.989(2) 22.496(3) 22.188(5) 104.94(3) 5782(2) 1.310 0.676 0.312, 0.339 2312 6620 632 0.0834, 0.1931 4?(CH3)2CO C56H50O4P4Ru2S3 1209.16 298 P21/n 12.877(5) 37.69(1) 13.303(5) 117.46(1) 5729(4) 1.402 0.790 0.844, 0.896 2456 3515 348 0.1146, 0.2334 5?C2H5OH?H2O C56H52O8P4Ru2 1211.06 298 P21/n 20.700(3) 12.944(2) 22.913(4) 91.08(1) 6138(2) 1.284 0.695 0.723, 0.827 2416 4864 402 0.0963, 0.2715 * In each case the wavelength of X-rays was 0.710 73 Å, monoclinic, Z = 4.of elemental sulfur (0.026 g) and thf (20 cm3) added. The reaction mixture was stirred overnight upon which a yellow-brown precipitate was formed. This was filtered off, washed with pentane (2 × 5 cm3) and dried under vacuum. Recrystallization from CH2Cl2 gave red crystals. Yield = 55% (Found: C, 55.0; H, 4.0. Calc. for C53H44O3P4Ru2S3: C, 55.2; H, 3.8%). IR (Nujol): n& (CO) 2020, 1960 and 1836 cm21. NMR (CD2Cl2): d(1H) 2.82 (m, 2 H, CHaHb), 4.5 (m, 2 H, CHaHb) and 6.9–8.0 (m, 40 H, C6H5); d(31P) 10.5 and 18.0 (m, dppm).FAB mass spectrum: m/z = 1151, 1087, 1059, 1031 and 1003. Alternatively, [Ru2(CO)4(m-Se)(m-dppm)2] (0.10 g) was mixed with elemental sulfur (0.025 g) to which thf (15 cm3) was added. The reaction mixture was stirred under nitrogen overnight. Solvent was than removed under reduced pressure. The brown solid product thus obtained was crystallized from CH2Cl2, and identified by its IR and 1H and 31P NMR spectra.Yield = 32%. [Ru2(CO)4(Ï-SO2)(Ï-dppm)2] 5. Sulfur dioxide was bubbled into a greenish yellow solution of [Ru2(CO)4(m-CO)(m-dppm)2] (0.15 g) in CH2Cl2 (15 cm3) for 5 min. Ethanol (40 cm3) was added to the resulting wine-red solution and the mixture was set aside. The product, which slowly deposited as yellow needles, was filtered off, washed with ethanol and vacuum dried. Yield = 61% (Found: C, 55.2; H, 4.4. Calc. for C54H44O6P4- SRu2?C2H5OH?H2O: C, 55.5; H, 4.3%).IR (Nujol): n& (CO) 2070, 2007, 1972 and 1943 cm21. NMR (CDCl3): d(1H) 2.68 (m, 2 H, 2JHH = 12, JPH = 4, CHaHb), 4.6 (m, 2 H, 2JHH = 12, JPH = 6 Hz, CHaHb) and 6.6–7.6 (m, 40 H, C6H5); d(31P) 34.7 (s, dppm). X-Ray crystallography The structure determinations were carried out using a Siemens P4 diffractometer, with XSCANS software and the crystals were sealed in glass capillary tubes. The data processing, solution by direct methods and refinements were carried out using SHELXTL programs.16 For complexes 1 and 5 an empirical absorption correction was made using y scans, while for 4 a Gaussian absorption correction was applied to the data.Full details are given in Table 4. In refinement of the structure of complex 1 an acetone molecule with occupancy of 0.5 was located and refined, but a second area of residual electron density (1.44 e Å23) could not be modelled; it may due to partial occupation by a disordered water molecule. During the least-squares cycles refinement for complex 4 the positions of the bridging groups S(1) and C(1)]O(1) were found to be disordered. This disorder was successfully resolved by refining site occupancy factors to each bridging unit 0.6 : 0.4.The sulfur atom S(1) having occupancy of 0.6 was refined anisotropically whereas only isotropic refinement was possible for S(1a), C(1), O(1), C(1a) and O(1a). The C]O distances C(1)]O(1) and C(1a)]O(1a) were fixed at 1.20 Å. Isotropic thermal parameters were refined for all the phenyl carbon atoms and a C2 symmetry restraint was imposed on all the phenyl rings.All hydrogen atoms were placed in the calculated positions for the purpose of structure-factor calculations only. The Fourier-difference map revealed two regions of disordered acetone. In one region the disordered methyl carbons were related by rotation along the C]] C bond and in the other region the carbonyl carbon atom was found at the origin (crystallographic disorder).The site occupancies of these disorder models are arbitrary and were not refined in the least-squares cycles. Ideal constraints were imposed on the geometry (C]C 1.54 and C]] O 1.20 Å). Common isotropic thermal parameters were refined for each set of disordered solvent molecules and no hydrogen atoms were included for the solvent molecules. The crystals of complex 5 diffracted weakly. In the neutral molecule all the non-hydrogen atoms except the phenyl carbons were assigned anisotropic thermal parameters and refined.Isotropic thermal parameters were refined for all the phenyl carbon atoms. A C2 symmetry restraint was imposed on all these phenyl rings. All hydrogen atoms were placed in the calculated positions for the purpose of structure-factor calculations only. The Fourier-difference map revealed the regions of highly disordered solvent molecule and they were assigned to be one ethanol (in three regions with occupancies of 0.5, 0.25 and 0.25) and one water molecule (in four positions in the crystal lattice with occupancy of 0.25 each).Ideal constraints were imposed on the geometry of ethanol molecules (C]C 1.54, C]O 1.40 Å). Common isotropic thermal parameters were refined for each set of disordered solvent molecules and no hydrogen atoms were included for them. CCDC reference number 186/783. See http://www.rsc.org/suppdata/dt/1998/285/ for crystallographic files in .cif format. Acknowledgements We thank the Natural Sciences and Engineering Research Council of Canada for financial support.References 1 D. W. Engel, K. G. Moodley, L. Subramony and R. J. Haines, J. Organomet. Chem., 1988, 349, 393; G. M. Ferrence, P. E. Fanwick, C. P. Kubiak and R. J. Haines, Polyhedron, 1997, 16, 1453.290 J. Chem. Soc., Dalton Trans., 1998, Pages 285–290 2 H. A. Mirza, J. J. Vittal and R. J. Puddephatt, Inorg. Chem., 1993, 32, 1327. 3 H. A. Mirza, J. J. Vittal and R. J. Puddephatt, Can.J. Chem., 1995, 73, 903; Organometallics, 1994, 13, 3063. 4 R. J. Haines, in Comprehensive Organometallic Chemistry, eds. D. F. Shriver and M. I. Bruce, Pergamon, Oxford, 1995, vol. 7, ch. 11. 5 See, for example, A. Muller, W. Jaegermann and J. H. Enemark, Coord. Chem. Rev., 1982, 46, 245; A. Muller and E. Diemann, Adv. Inorg. Chem., 1987, 31, 89; R. D. Adams, Polyhedron, 1985, 4, 2003; R. D. Adams and I. T. Horvath, Prog. Inorg. Chem., 1985, 33, 127; J. W. Kolis, Coord.Chem. Rev., 1990, 105, 195; L. C. Roof and J. W. Kolis, Chem. Rev., 1993, 93, 1037. 6 Y. Mizobe, M. Hozomizu, S. Kuwata, J. I. Kuwabatha and M. Hidai, J. Organomet. Chem., 1996, 513, 231; S. Kuwata, Y. Mizobe and M. Hidai, J. Am. Chem. Soc., 1993, 115, 8499; H. Matsuzaka, Y. Hirayama, M. Nishio, Y. Mizobe and M. Hidai, Organometallics, 1993, 12, 36; H. Matsuzaka, Y. Mizobe, M. Nishio and M. Hidai, J. Chem. Soc., Chem Commun., 1991, 1011; Y. Mizobe, M. Hosomizu, J. Kawabata and M.Hadai, J. Chem. Soc., Chem. Commun., 1991, 1226; A. Takahashi, Y. Mizobe, H. Matsuzaka, S. Dev and M. Hidai, J. Organomet. Chem., 1993, 456, 243. 7 P. L. Andrew, J. A. Cabeza, D. Miguel, V. Riera, M. A. Villa and S. Garcia-Granda, J. Chem. Soc., Dalton Trans., 1991, 533; K. Seitz and U. Behrens, J. Organomet. Chem., 1988, 345, 351; J. Amarasekera, T. B. Rauchfuss and S. R. Wilson, J. Chem. Soc., Chem. Commun., 1989, 14; T. B. Rauchfuss, D. P. S. Rodgers and S. R. Wilson, J.Am. Chem. Soc., 1986, 108, 3114; A. Amarsekera, T. B. Rauchfuss and S. R. Wilson, Inorg. Chem., 1987, 26, 3328; H. Brunner, N. Janietz, J. Wachter, B. Nuber and M. L. Ziegler, J. Organomet. Chem., 1988, 356, 85; M. A. E. Hinnawi, M. L. Sumadi, F. T. Esmadi, I. Jibril, W. Imhof and G. Huttner, J. Organomet. Chem., 1989, 377, 373; J. Wachter, Angew. Chem., Int. Ed. Engl., 1989, 28, 1613. 8 D. Cauzzi, C. Graiff, M. Lanfranchi, G. Predieri and A. Tiripicchio, J. Chem. Soc., Dalton Trans., 1995, 2321; A. P. Ginsberg, W. E. Lindsell, C. R. Sprinkle, K. W. West and R. L. Kohen, Inorg. Chem., 1982, 21, 3666; L. Y. Goh, C. Wei and E. Sinn, J. Chem. Soc., Chem. Commun., 1985, 462; I. Jibril, F. T. Esmadi, H. Al-Masri, L. Zsolnai and G. Huttner, J. Organomet. Chem., 1996, 510, 109; R. S. Bates and A. H. Wright, J. Chem. Soc., Chem. Commun., 1990, 1129. 9 D. M. P. Mingos, Transition Met. Chem., 1978, 3, 1; S. L. Randall, C. A. Miller, T. S. Janik, M. R. Churchill and J. D. Atwood, Organometallics, 1994, 13, 141; G. J. Kubas, Acc. Chem. Res., 1994, 27, 183. 10 D. L. Davies, S. A. R. Knox, K. A. Mead, M. J. Morris and P. Woodward, J. Chem. Soc., Dalton Trans., 1984, 2293; I. Ghatak, D. M. P. Mingos, M. B. Hursthouse and K. M. A. Malik, Transition Met. Chem., 1979, 4, 260. 11 P. Thometzek, K. Zenkert and H. Werner, Angew. Chem., Int. Ed. Engl., 1985, 24, 516. 12 W. D. Bonds and J. A. Ibers, J. Am. Chem. Soc., 1972, 94, 3413; A. Caron and J. Donohue, Acta Crystallogr., 1965, 18, 562; A. Muller and W. Jaegermann, Inorg. Chem., 1979, 18, 2631. 13 W. A. Schenk, Angew. Chem., Int. Ed. Engl., 1987, 26, 98; G. J. Kubas, Inorg. Chem., 1979, 18, 182; R. R. Ryan, G. J. Kubas, D. C. Moody and P. G. Eller, Struct. Bonding (Berlin), 1981, 46, 47. 14 M. R. Churchill and K. L. Kalra, Inorg. Chem., 1973, 12, 1650; M. Angoletta, P. L. Bellon, M. Manassero and M. Sansoni, J. Organomet. Chem., 1974, 81, C40; D. C. Moody and R. R. Ryan, Inorg. Chem., 1977, 6, 1052; L. S. Benner, M. M. Olmstead, H. Hope and A. L. Balch, J. Organomet. Chem., 1978, 153, C31. 15 D. Seyferth, G. B. Womack and C. M. Archer, Organometallics, 1989, 8, 443. 16 To be supplied. Received 16th September 1997; Paper 7/06728C

ISSN:1477-9226    

DOI:10.1039/a706728c

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 291–300 291 A theoretical study of [M(PH3)4] (M 5 Ru or Fe), models for the highly reactive d8 intermediates [M(dmpe)2] (dmpe 5 Me2PCH2- CH2PMe2). Zero activation energies for addition of CO and oxidative addition of H2 ‡ Stuart A. Macgregor,*,†,a Odile Eisenstein,a Michael K. Whittlesey b and Robin N. Perutz b a Laboratoire de Chimie Théorique, Bâtiment 490, Université de Paris-Sud, 91405 Orsay, France b Department of Chemistry, University of York, York, UK YO1 5DD Density functional calculations have been carried out on [M(PH3)4] species as models for transient [M(dmpe)2] formed from the photolysis of [M(dmpe)2H2] (M = Ru or Fe, dmpe = Me2PCH2CH2PMe2).Calculations have also been performed on [Rh(PH3)4]1 as a model for the relatively inert [Rh(dmpe)2]1. The singlet electron configurations of [Ru(PH3)4] and [Rh(PH3)4]1 were found to have D2d geometries with trans P]M]P angles of 159 (M = Ru) and 1728 (M = Rh1).Singlet [Fe(PH3)4] was computed to have a C2v structure with trans P]M]P angles of 137 and 1608 at Fe. The triplet configurations of [Fe(PH3)4] and [Ru(PH3)4] were predicted to adopt C2v geometries with angles of ca. 155 and 958 for both species. Singlet [Ru(PH3)4] is calculated to be 11.7 kcal mol21 more stable than the triplet, but the triplet form of [Fe(PH3)4] is the more stable by 8.0 kcal mol21. The addition of CO and oxidative addition of H2 to [M(PH3)4] (M = Ru or Fe) were calculated to be highly exothermic.In contrast, the reaction between [Rh(PH3)4]1 and H2 is less thermodynamically favoured, consistent with the lower reactivity of experimental Rh1 analogues. Both the oxidative addition of H2 and addition of CO were calculated to proceed without activation energy for [Ru(PH3)4], but only once the ‘end-on’ approach of H2 and an angled approach of CO at long ruthenium–substrate separations are considered. The calculations on [Ru(PH3)4] also reproduced the UV/VIS spectrum and geometry of [Ru(dmpe)2] satisfactorily.The reaction of singlet [Fe(PH3)4] with CO was calculated to be barrierless, while the oxidative addition of H2 required a very small activation energy (ª1 kcal mol21) at long Fe]H2 distances. The reaction of [Rh(PH3)4]1 with H2 has a somewhat larger activation barrier (ª3 kcal mol21) and is predicted to pass through a product-like C2v transition state. The problem of the geometry and reactivity of d8 ML4 complexes is longstanding and complex.Geometries close to tetrahedral with triplet spin states are found for first-row transition metals of Groups 9 and 10, while square-planar geometries with singlet spin states are common for second- and third-row metals of the same groups. The ML4 complexes of Group 8 metals are highly reactive molecules which have only a transient existence under conventional conditions. The importance of such molecules lies in their ability to undergo a large number of reactions, including co-ordination of an additional ligand, oxidative addition with reagents such as dihydrogen, and formation of metal–metal bonds.The isolobal analogy between d8 ML4 and carbenes1 highlights the problem of spin state and geometry as well as the high reactivity of these molecules. The first such molecule to be studied in detail was [Fe(CO)4].2 Matrix infrared and gas-phase time-resolved infrared (TRIR) experiments showed that this molecule adopts a C2v structure with C]Fe]C angles of 147 and 1208 and two unpaired electrons.As a result of a triplet ground state, the rate constants for its reaction with CO and H2 in the gas phase are 2–3 orders of magnitude lower than for the corresponding reactions of [Cr(CO)5].3 When xenon or methane matrices are used in place of argon, triplet [Fe(CO)4] is replaced by a species identified as [Fe(CO)4S] (S = Xe or CH4) which has a trigonal-bipyramidal structure with S in the equatorial plane.The C]Fe]C angles are now 174 and 1258; it is thought that the electrons are spin- † Present Address: Department of Chemistry, Heriot-Watt University, Riccarton, Edinburgh, UK EH14 4AS. ‡ Supplementary data available: calculated coordinates and energies. For direct electronic access see http://www.rsc.org/suppdata/dt/1998/ 291/, otherwise available from BLDSC (No. SUP 57317, 12 pp.) or the RSC Library. See Instructions for Authors, 1998, Issue 1 (http.//www.rsc.org/dalton). Non-SI unit employed: cal = 4.184 J.paired.2 Far less is known about the nature of [Fe(CO)4] as a transient species in solution. A recent summary of experimental results, collated by Grevels,4 indicates that the first species to be observed after laser flash photolysis of [Fe(CO)5] in cyclohexane is [Fe(CO)4(C6H12)], i.e. the analogue of [Fe(CO)4S], which is formed within the instrumental risetime of 3 ms. Any triplet [Fe(CO)4] must have a much shorter lifetime in solution.Thus the results indicate that three ML4 species need to be considered: a triplet, a singlet and a solvent adduct, ML4S. The structures of the triplet and singlet may both be far from the tetrahedral and square-planar limits. The ruthenium analogue, [Ru(CO)4], has been studied by TRIR in the gas phase, but the spectral data do not permit the structure to be determined. However, the high rate constant for reaction with CO indicates that [Ru(CO)4] has a singlet ground state.5 The combination of matrix isolation and time-resolved absorption spectroscopy in solution has recently been applied with considerable success to ML4-type complexes with chelating phosphine ligands, [M(dmpe)2] (M = Fe or Ru, dmpe = Me2PCH2CH2PMe2).6,7 These complexes are usually generated by photolysis of the corresponding dihydrides, [M(dmpe)2H2].The ruthenium complex, [Ru(dmpe)2], shows a three-band UV/ VIS spectrum and reacts with both H2 and CO at rates close to the diffusion limit (>1 × 109 dm3 mol21 s21).The spectrum suggests that it adopts a geometry very close to square planar. The large rate constants indicate that there is no barrier to reaction created by spin-state interconversion, and hence that [Ru(dmpe)2] has a singlet ground state. The NMR evidence demonstrates that [Ru(dmpe)2] undergoes oxidative-addition reactions with benzene, but not with alkanes.8 Recently, [Ru(CO)2L2] (L = PBut 2Me) was isolated in a singlet ground state and shown by X-ray crystallography to have a C2v structure with C]Ru]C 133.38 and P]Ru]P 165.68.292 J.Chem. Soc., Dalton Trans., 1998, Pages 291–300 Like the other d8 RuL4 complexes, it reacts very rapidly with several molecules.9 The analogue with L = PMe3 has been studied in low-temperature matrices and shown to have C]Ru]C larger than 1308 and to form adducts of the type [Ru(CO)2(PMe3)2S] (S = Xe or CH4).10 Ab initio second-order Møller-Plesset perturbation (MP2) calculations on [Ru(CO)2- (PH3)2] have revealed a C2v structure, indicating that the C]Ru]C bond angle is not constrained either by steric effects or the presence of S.9 The iron complex [Fe(dmpe)2],6 exhibits very different characteristics from its ruthenium analogue.The lowest-energy absorption is in the near-UV region at ca. 28 000 cm21, the rate constant for reaction with H2 is a factor of 7500 smaller than for [Ru(dmpe)2], whereas the rate constant for reaction with CO is only a factor of two slower.Oxidative-addition reactions with arenes and with alkanes compete effectively with the back reaction with H2. The NMR investigations provide decisive evidence that even methane reacts with [Fe(dmpe)2].11 Thus [Fe(dmpe)2] is substantially less reactive than [Ru(dmpe)2] towards H2, but more reactive towards hydrocarbons. The differences in spectra and reactivity between [Fe(dmpe)2] and [Ru(dmpe)2] suggest that [Fe(dmpe)2] is not square planar. Although the high rate constant for reaction with CO makes a singlet ground state for [Fe(dmpe)2] likely, it is not close enough to the diffusion limit to be decisive.The experimental data show that any effect of specific complexation by the solvent on the kinetics of reaction of [Fe(dmpe)2] is very slight. The structures of d8 ML4 species have also been investigated extensively by theoretical methods. Burdett 12 predicted on the basis of extended Hückel calculations that high-spin d8 [M(CO)4] complexes should adopt a C2v structure with angles of 110 and 1358.He noted that the square-planar geometry was preferred for low-spin d8, but that a D2d distortion was preferred over a C3v distortion. The conclusions from Burdett’s angular overlap analysis paralleled those from the extended Hückel calculations. 13 Since the angular overlap arguments were based solely on s interactions, they should be applicable (in a first approximation) to metal phosphine as well as metal carbonyl complexes.Elian and Hoffmann,14 who included the metal– ligand dp/pp interactions in their calculations, predicted a D2d geometry (angle ca. 1508) for a d8 low-spin [M(CO)4] molecule, but a square-planar geometry for the corresponding MCl4 complex. They did not consider the high-spin case. Ziegler and co-workers 15 returned to these problems with density functional calculations. This work predicts that [Fe(CO)4] and [Ru(CO)4] would have C2v structures both in their singlet and in their triplet states, that the angles in the singlet states should be ca. 175 and 1308, and that the angles in the triplet states should be ca. 155 and 958. The singlet state was strongly favoured for [Ru(CO)4], but the two states were almost equienergetic for [Fe(CO)4]. Ziegler et al.15a also examined the pathways for reaction of [Ru(CO)4] with H2 and CH4. Notable features were: (i) formation of s complexes as reaction intermediates albeit with very shallow potential wells, (ii) oxidative addition of H2 with an activation energy of ca. 2.6 kcal mol21 and (iii) oxidative addition of methane with a barrier of 19 kcal mol21. Wang and Weitz 16a have re-examined both singlet and triplet [Fe(CO)4] and published a critique of the various estimates of the singlet– triplet energy separation. Many other theoretical studies of the addition of small molecules to unsaturated transition-metal species have been performed at various levels of theory.17–27 These calculations have repeatedly demonstrated the existence of potential minima for s complexes of H2 and CH4 prior to full oxidative addition. The importance of s complexes is supported by a large body of experimental evidence.28 We report a theoretical study designed to reveal the molecular structure and ground electronic configuration of [Fe(dmpe)2] and [Ru(dmpe)2] and to examine the pathways for co-ordination of CO and oxidative addition of H2 to these molecules.We have employed [M(PH3)4] (M = Ru or Fe) as model compounds and used density functional methods29 which have proved to be particularly effective in reproducing the molecular geometries, dissociation energies and reactivity trends of transition-metal systems.30 The present study also includes a number of calculations on the isoelectronic model system [Rh(PH3)4]1. Many tetrakis- (phosphine)rhodium(I) species are known experimentally and several have been characterised crystallographically, including [Rh(dmpe)2]1.31,32 In the absence of structural information on the ruthenium and iron systems, this provides us with an experimental standard against which we can compare our computed results.In addition, whereas [Fe(dmpe)2] and [Ru(dmpe)2] are both extremely reactive species, their rhodium(I) analogue is relatively unreactive. We should therefore expect our computed results to reflect this large difference in reactivity before we can tackle the subtler distinctions between the ruthenium and iron systems with confidence.Jones et al.32 reported that [Rh(PMe3)4]1 undergoes oxidative addition with H2. The reactivity of [Rh(PR2R9)4]1 with H2 has been studied by Schrock and Osborn.33 They found when R = Me and R9 = Ph that oxidative addition occurred with the formation of [Rh(PMe2Ph)4H2]1. However, when R = Ph and R9 = Me or R = OMe and R9 = Ph no reaction was observed. Clearly the reactivity of these rhodium(I) systems is very sensitive to the steric and electronic properties of the phosphine.In the following we use the oxidative addition of H2 to [M(PH3)4] (M = Ru, Fe or Rh1) as a test of our computational approach. Computational Details All calculations used the Amsterdam Density Functional program (ADF, version 2.0.1) developed by Baerends et al.34 and employed the numerical integration scheme of te Velde and Baerends.35 For Ru, Fe and Rh a triple-z-STO (Slater type orbital) basis set was employed. For P, O, C and PH3 hydrogen atoms a double-z-STO basis set extended by a polarisation function was used.All hydrogen atoms directly involved in bonding to a metal were described using a triple-z-STO basis set extended with two polarisation functions. An auxiliary set of s, p, d, f and g STO basis functions centred on all nuclei was used in order to fit the molecular density and describe accurately the Coulomb and exchange potentials in each SCF (selfconsistent field) cycle.36 Core electrons (up to and including 3d for Ru and Rh, 2p for Fe and P and 1s for C and O) were treated using the frozen-core approximation.34 The calculations incorporated the quasi-relativistic corrections of Ziegler et al.37 Geometry optimisation was carried out using the local density approximation (LDA) employing the parameterisation of Vosko et al.38 and made use of the optimisation procedure developed by Versluis and Ziegler.39 Geometries were fully optimised under the appropriate symmetry constraints.Test calculations on the C2v geometries of singlet and triplet [M(PH3)4] species (M = Fe or Ru) in which symmetry constraints were relaxed first to Cs and then C1 symmetry gave very similar results. Energies of all optimised structures were recalculated with the BP86 functional, including the non-local (NL) corrections of Becke 40 (exchange) and Perdew41 (correlation). Electronic transition energies and ionisation potentials were calculated using the DSCF method.Total computed energies (at both local and non-local levels of calculation) and cartesian coordinates for all optimised structures are available as supplementary information (SUP 57317). Results Structures of M(PH3)4 species Singlet electronic configuration (M 5 Ru, Fe or Rh1). The geometries of [M(PH3)4] (M = Ru, Fe or Rh1) were optimisedJ. Chem. Soc., Dalton Trans., 1998, Pages 291–300 293 for a singlet electronic configuration under the C2v symmetry constraint, corresponding to a staggered arrangement of the PH3 ligands.The optimised structures of all three species exhibit distortions away from a square-planar geometry (see Fig. 1). For [Ru(PH3)4] and [Rh(PH3)4]1 the MP4 cores are close to overall D2d symmetry with the M]P bonds being displaced away from a square-planar geometry by an average of 10.7 (M = Ru) and 3.98 (M = Rh1). For [Fe(PH3)4] we calculate a C2v structure with angles of 137.0 and 159.78 at the metal.The calculated average M]P bond length for [Rh(PH3)4]1 is 2.239 Å. This is somewhat shorter than the distance found experimentally in the crystal structure of [Rh(dmpe)2]1 (Rh-P 2.282 Å) in which the geometry at the metal is very close to square planar.31 In the crystal structure of [Rh(PMe3)4]1 the trans P]Rh]P angles average 1508; this larger distortion is probably due to steric crowding of the phosphine ligands.32 The Rh]P distances in this species average 2.297 Å.Comparison of the two experimental structures suggests that one effect of the chelating phosphine may be to force the geometry nearer to square planar. Thus, in the case of [Ru(PH3)4] the deviation away from square-planar geometry may be a consequence of the inability of PH3 to model fully the dmpe ligand, especially its steric bulk and the consequences of its bidentate binding mode. The calculated average Ru]P distance in this species (2.239 Å) is again shorter than those found experimentally in related species, for example [Ru- (dmpe)2(CO)], in which the Ru]P distances average 2.297 Å.42 The underestimation of metal–ligand bond lengths is usually found when the LDA (local density approximation) level of theory is employed.30 § Optimising [Ru(PH3)4] in C2v symmetry but constraining the RuP4 core to a square-planar geometry yielded an average Ru]P bond distance of 2.246 Å and a calculated energy only 2 kcal mol21 higher than the global D2d minimum.As has been suggested previously,14 the deformation of the d8 MP4 core appears relatively facile. The calculated C2v structure of [Fe(PH3)4] has Fe]P bonds of 2.103 (axial) and 2.088 Å (equatorial). These calculated distances are somewhat shorter than expected, even given the usual underestimation of metal–ligand bonds with the LDA. A review of structures contained in the Cambridge Structural Database gave Fe]PR3 distances of 2.246 (R = Me, average of 20 systems) and 2.237 Å (R = Ph, average of 31 systems).43 The Fig. 1 Geometries (distances in Å, angles in 8) of singlet [M(PH3)4] species (M = Fe, Ru or Rh1) § Reoptimisation of [Ru(PH3)4] including non-local gradient corrections yielded an equivalent (to within 0.58) D2d structure with an average Ru]P bond length of 2.268 Å. short calculated Fe]P distances may arise from the lack of steric crowding around the small iron metal centre in our model compounds. Triplet electronic configuration (M 5 Ru or Fe).Optimisations for the triplet structures of [M(PH3)4] species (M = Ru or Fe) were based upon a bent C2v structure. The deformation of square-planar d8 ML4 species towards such a structure is known to lead to a reduction in the HOMO–LUMO (highest occupied–lowest unoccupied molecular orbital) gap.44 A formally nonbonding (neglecting p effects) metal-based d orbital is strongly destabilised while, at the same time, an unoccupied metal p orbital is stabilised (see Fig. 2). Geometries for the triplet electronic configuration were therefore optimised for single occupation of the appropriate b2 and a1 orbitals (Fig. 2, right-hand side) under the C2v symmetry constraint. The geometries obtained (see Fig. 3) are similar to those of the triplet forms of [M(CO)4] (M = Fe or Ru) calculated by Ziegler and co-workers 3 and that obtained more recently by Wang and Weitz 16a for [Fe(CO)4]. Using an equivalent method to that used here, both sets of authors calculated triplet [Fe(CO)4] to be slightly more stable (< 2 kcal mol21) than the singlet,¶ in accord with the experimental evidence that ‘naked’ [Fe(CO)4] exists as a triplet.2,3 The singlet form of [Ru(CO)4] was calculated to be significantly more stable than Fig. 2 Schematic representation of ML4 valence orbital changes upon C4v to C2v distortion Fig. 3 Geometries of triplet [M(PH3)4] species (M = Fe or Ru) ¶ It has been pointed out that calculated singlet–triplet separations can be dependent on the density functional employed and that the B3LYP functional exhibits a greater preference for the higher spin-state species than does the BP86 functional used here.16a Recently, Ruiz et al.16b have found the B3LYP functional to be especially effective at reproducing the singlet–triplet energy difference in hydroxy- and alkoxo-bridged copper(II) binuclear complexes.294 J.Chem. Soc., Dalton Trans., 1998, Pages 291–300 the triplet.15 For [Ru(PH3)4] the singlet is more stable by 11.7 kcal mol21, but for [Fe(PH3)4] the triplet was more stable than the singlet by 8.0 kcal mol21.The singlet–triplet energy gap is therefore significantly larger for [Fe(PH3)4] than for [Fe(CO)4]. UV/VIS spectra. The experimental evidence for the structure of [Ru(dmpe)2] is based mainly on its UV/VIS spectrum which exhibits three low-energy absorption bands and is consistent with a square-planar geometry. The lowest-energy band is assigned as a dz2 > pz transition on the basis of its absorption coefficient and occurs experimentally at 13 800 cm21 in pentane solution. The equivalent transition occurs at 25 600 cm21 for square-planar [Rh(dmpe)2]1 in methanol.7 The calculated energies of these transitions in the [M(PH3)4] model species are 13 900 and 26 200 cm21 for M = Ru and Rh1 respectively. Thus, we find remarkably good reproduction of the experimental trend.For [Fe(dmpe)2] in pentane solution a single band has been observed at 28 200 cm21.6 The dz2 > pz transition in singlet [Fe(PH3)4] is calculated to occur at 2530 cm21, and so the lowest-energy excitation would be expected to occur in the IR region of the spectrum.However, as we have seen, the dmpe ligand appears to favour a planar structure. Recalculation of this transition energy for square-planar [Fe(PH3)4] [optimised under C2v symmetry, Fe-P (average) = 2.107 Å] gives a value of 6600 cm21. This suggests a low-lying band would be seen in the visible/near-IR spectrum of square-planar singlet [Fe(dmpe)2].Following this prediction, we measured the spectrum of [Fe(dmpe)2] in an argon matrix from 4000 to 12 500 cm21, a region which has not been examined previously. No absorptions were detected. In summary, our calculations on [Ru(PH3)4] support the experimental evidence that [Ru(dmpe)2] has a singlet electronic configuration in the ground state and a structure close to square planar.For [Fe(PH3)4] the calculations favour the triplet structure. The experimental data on [Fe(dmpe)2] do not provide direct evidence for or against a triplet state, nor do they preclude a spin-state equilibrium. Reactivity of [M(PH3)4] species with H2 and CO The reactivity of [M(dmpe)2] species was modelled by computing the reaction profiles for the approach of the substrate molecules towards the [M(PH3)4] model species in the singlet electronic configuration. The energy of each point on the reaction profile was then plotted relative to that of the reactants in their optimum singlet-state geometries.We do not include any correction for zero-point energies. The difference in zero-point energy between products and reactants for the oxidative addition of H2 is estimated to be about 2.2 kcal mol21 based on two M]H stretching frequencies at 1770 cm21 and four deformations modes at 600 cm21. Oxidative addition of H2 to [M(PH3)4] (M 5 Ru, Fe or Rh1). The geometries of the octahedral products of oxidative addition of H2 to [M(PH3)4] are shown in Fig. 4 along with the calculated energies of formation (DEform) for the products. As expected, the two (equatorial) phosphine ligands in the plane of addition bend away from the hydride ligands while the other two (axial) phosphines incline slightly towards the H ? ? ?H midpoint. The optimised M]H bond lengths compare well with available neutron diffraction data: in [Fe(dppe)2H(H2)]1 the Fe]H bond is 1.535 Å 45 and the Fe]H distance averages 1.526 Å in [Fe(PEtPh2)3H2(H2)] 46 compared with a computed value of 1.511 Å.The Rh]H distance in [Rh(h5-C5Me5)H2(SiEt3)2] 47 average 1.581 Å compared with the calculated Rh]H value of 1.598 Å, while the computed Ru]H distance of 1.643 Å compares to experimental values of 1.630 Å in [Ru(h5-C5H5)- (PMe3)2H] and 1.602 Å (average) in [Ru(h5-C5H5)(PMe3)2H2]1.48 In all three structures the trans influence of the hydride ligand causes the equatorial M]P bonds to be slightly longer than both the M-P axial bonds and the M]P distances calculated for the four-co-ordinate singlet reactants.Little elongation of the axial M]P bonds is seen. The large negative values obtained for DEform with singlet [Fe(PH3)4] and [Ru(PH3)4] (242.6 and 237.6 kcal mol21 respectively) suggest a strong thermodynamic drive for the addition of H2. With triplet [Fe(PH3)4] DEform is calculated to be 234.4 kcal mol21. For [Rh(PH3)4]1 the thermodynamic driving force is much smaller (DEform = 215.6 kcal mol21).The calculated values of DEform are therefore consistent with the high reactivity of the experimental ruthenium and iron analogues and with the relatively lower reactivity of Rh1 experimental analogues towards oxidative addition of H2. In order to understand the origin of the high reactivity of the neutral [M(PH3)4] systems toward H2, we have computed reaction profiles for the oxidative-addition process.Previous studies have found that an ‘end-on’ (or h1) approach of H2 is energetically favoured over a ‘side-on’ (or h2) approach at long M](H2) separations.18–20 Two reaction profiles corresponding to these two different orientations of the H2 moiety relative to the [M(PH3)4] reactant were therefore considered. Both were computed within C2v symmetry and defined by the M]x distance, x being the H ? ? ? H midpoint (Scheme 1). All other variables were optimised. Profiles for the reaction of [Ru(PH3)4] 1 H2 (Fig. 5) compare the h1 and h2 approaches calculated both at the LDA level and with the inclusion of non-local corrections, LDA 1 NL. At the LDA level the h1 approach is indeed favoured at long Ru]x distances (>2.4 Å) and, within C2v symmetry, a [Ru(PH3)4- (h1-H2)] adduct is formed with Ru]x 2.25 Å. This species is calculated to be 9.0 kcal mol21 more stable than the isolated reactants. At shorter Ru]x distances the h1 approach is rapidly destabilised.When the geometry of the C2v adduct is reoptimised in Cs symmetry the H2 moiety moves off the local C2 axis Fig. 4 Geometries of singlet [M(PH3)4H2] species (M = Fe, Ru or Rh1) Scheme 1 M H x H M x H H h1 approach h2 approachJ. Chem. Soc., Dalton Trans., 1998, Pages 291–300 295 and the optimised structure of the final [Ru(PH3)4H2] species is obtained. The addition of H2 to [Ru(PH3)4] via an h2 approach is calculated to proceed without any activation barrier at the LDA level.Similar trends are seen in the reaction profiles calculated at the LDA 1 NL level [Fig. 5(b)]. The h1 approach remains favoured at long Ru]x distances and, within C2v symmetry, a [Ru(PH3)4(h1-H2)] adduct is formed without any activation barrier. This species is only 1 kcal mol21 more stable than the isolated reactants. Significantly, at this level of calculation the h2 approach of H2 towards [Ru(PH3)4] is computed to have a small activation barrier (ª 2 kcal mol21).This result is inconsistent with the kinetic data for the oxidative addition of H2 to [Ru(dmpe)2] which indicate the absence of an activation barrier for this reaction. As we have only included non-local corrections as a perturbation on the LDA results and not selfconsistently in the computation of the reaction geometries, we cannot be certain that the [Ru(PH3)4(h1-H2)] adduct corresponds to a local minimum at the LDA 1 NL level. Likewise, true transition states involved in these processes have not been optimised (as no transition state is calculated in the LDA reaction profiles) and so we only provide estimates of the energies associated with these species from the shape of the LDA 1 NL reaction profiles.The reaction profiles calculated at the LDA level for the reactions of [Fe(PH3)4] and [Rh(PH3)4]1 with H2 are similar to those described above for [Ru(PH3)4]. For [Fe(PH3)4] at the LDA 1 NL level a small activation barrier (ª 1 kcal mol21) is associated with both the h1 and h2 approaches of H2 at Fe]x separations greater than 3 Å (Fig. 6).Within C2v symmetry we compute the presence of an h1 adduct with Fe]x 2.1 Å at this level. In contrast, for [Rh(PH3)4]1 1 H2 (Fig. 7) no h1 adduct is predicted: the LDA 1 NL curve for h1 approach is weakly repulsive at long Rh]x distances and is destabilised above the h2 approach at Rh]x ª 2.3 Å. An activation energy of approximately 3 kcal mol21 is required for the h2 approach of H2 in this case and the transition state occurs with an Rh]x distance of approximately 2.3 Å.Note that at the LDA level the h2 Fig. 5 Reaction profiles for the h1 and h2 approaches of H2 towards singlet [Ru(PH3)4] calculated at the LDA level (a) and including nonlocal corrections (LDA 1 NL) (b) approach of H2 towards [Rh(PH3)4]1 is calculated to proceed without any activation barrier. This result is inconsistent with the relatively low reactivity of experimental rhodium(I) analogues and stresses the need to include non-local corrections in the computation of reaction profiles.For all three systems therefore, the optimum reaction coordinate for addition of H2 may involve an h1 approach early in the reaction. As the M]x distance decreases further the H2 fragment must swing round into an h2 conformation. To investigate this process we have calculated a third reaction pro- file defined by the M]H]H angle, q. The h1 adducts described above have q = 1808, while at the other extreme the final octahedral oxidative-addition products have q ª 488.Fig. 8 shows this reaction profile for [Ru(PH3)4], computed at the LDA 1 NL level, as well as a schematic representation of the changes in r(H]H), r(Ru]H) and the Peq]Ru]Peq angle during the approach of H2 toward [Ru(PH3)4]. Most significantly, the h1/h2 swing proceeds without activation energy for the Ru(PH3)4 1 H2 reaction. This contrasts with the reaction pro- file computed for the oxidative addition of H2 to [Ru(CO)4] which displayed a distinct activation barrier.15a However, only the h2 approach of H2 was considered in that study, whereas the results presented here indicate that the orientation of the H2 moiety during the oxidative-addition reaction can be important in determining activation barriers.Fig. 8 shows that the steep fall in energy begins when r(Ru]H) ª 1.77 Å and q = 1408. At this stage Peq]Ru]Peq also starts to decline rapidly. However, the value of r(H]H) remains little changed until q = 1008 at which r(Ru]H) = 1.65 Å is close to its final value of 1.64 Å.Only then elongation of H]H occurs. Similar results were obtained with [Fe(PH3)4]. In contrast, for [Rh(PH3)4]1 the h1/h2 swing requires an activation energy of >4 kcal mol21. Addition of CO to [M(PH3)4] (M 5 Ru or Fe). The addition reaction with CO was studied with [Ru(PH3)4] and [Fe(PH3)4]. Fig. 6 Reaction profiles for the h1 and h2 approaches of H2 towards singlet [Fe(PH3)4] (LDA 1 NL) Fig. 7 Reaction profiles for the h1 and h2 approaches of H2 towards singlet [Rh(PH3)4]1 (LDA 1 NL)296 J. Chem. Soc., Dalton Trans., 1998, Pages 291–300 Since the experimental analogues of [Rh(PH3)4]1 undergo phosphine substitution with CO rather than forming an addition product,32 this system was not studied. The geometries of the five-co-ordinate product species optimised in C2v symmetry are shown in Fig. 9. As for the dihydride species, the equatorial M]P bonds are somewhat longer than the axial M]P bonds. The calculated Ru]C bond distance (1.870 Å) is comparable to that found experimentally for [Ru(dmpe)2(CO)] (1.850 Å).42 The calculated Fe]C bond length (1.714 Å) is shorter than those found in the structure of [Fe(dppm)(CO)3] (dppm = Ph2PCH2PPh2) in which the average Fe]C bond distance is 1.76 Å.49 The energy of formation for the two products (259.5 and 243.5 kcal mol21 for M = Fe and Ru Fig. 8 Reaction profile and schematic representation of geometrical changes for the h1/h2 swing of H2 with singlet [Ru(PH3)4] (LDA 1 NL).Energies are relative to the sum of the isolated reactants set to zero, as indicated at the extreme right of the profile Fig. 9 Geometries of [M(PH3)4(CO)] species (M = Fe or Ru) respectively) shows that addition of CO to the model species is a strongly thermodynamically favoured process. An ab initio study of addition of CO to Vaska’s compound has found a transition state featuring a non-linear Ir]C]O unit to be more stable than its linear equivalent.19a Reaction profiles for the addition of CO to [M(PH3)4] species, defined by the M]C distance, were therefore computed in both C2v and Cs symmetry, the latter allowing the CO moiety to move off the local C2 axis of the [M(PH3)4] fragment if it was energetically favourable to do so.The computed reaction profiles are shown in Fig. 10 for M = Ru. Similar results were obtained for M = Fe.The addition of CO to [M(PH3)4] species is computed to proceed without an activation barrier for both M = Fe and Ru once the non-linear approach of CO is taken into account. These results are consistent with the experimental rate constant obtained for the addition of CO to [M(dmpe)2] species which exceeded 109 dm3 mol21 s21 for both metals and, in the case of Ru, was near diffusion control (i.e. very little, if any, activation energy).6 At long M]C separations (>2.5 Å) we found that geometries with M]C]O angles of approximately 1078 were favoured for both metals.Imposing a linear approach of CO (C2v symmetry) resulted in a small activation barrier (ª2 kcal mol21) for both metals at long M]C separations (M]C > 3.5 Å). Discussion Structure and ground-state electronic configuration of [M(dmpe)2] species The UV/VIS spectrum of [Ru(dmpe)2] suggests that this species has a geometry which is square planar or close to it.7 The rate constants for reaction with CO and H2 are close to the diffusion limit suggesting that [Ru(dmpe)2] has a singlet electronic state.The calculations on [Ru(PH3)4] show that a near square-planar D2d geometry with a singlet-state configuration is 11 kcal mol21 more stable than the triplet configuration (C2v geometry). The calculated energy of the dz2 > pz transition is also consistent with the experimental results and the computed profiles for reaction with both H2 and CO do not feature any activation barrier.Thus both experiment and calculation are in agreement with a near square-planar, singlet ground state for [Ru(dmpe)2]. For the iron system neither experiments nor calculations are so clear. Experimentally, the lack of correspondence in spectra and the different rates of reaction relative to the ruthenium system point to a change in structure. The reaction with CO is extremely rapid, but not close enough to the diffusion limit to exclude a triplet configuration.The experimental evidence for the role of specific solvation is inconclusive. The calculations on [Fe(PH3)4] show that a C2v triplet is more stable than a C2v singlet structure by 8.0 kcal mol21. The dz2 æÆ pz transition of singlet [Fe(PH3)4] is predicted to occur in the visible/near-IR Fig. 10 Reaction profiles for the addition of CO to singlet [Ru(PH3)4] allowing for linear (C2v) and non-linear (Cs) approaches of CO (LDA 1 NL)J. Chem. Soc., Dalton Trans., 1998, Pages 291–300 297 region of the spectrum, but no absorptions are observed within this spectral range.The calculations predict a small barrier for the addition of H2 to singlet [Fe(PH3)4] but no barrier for addition of CO. Overall the reactivity of singlet [Fe(PH3)4] is predicted to be similar to that of singlet [Ru(PH3)4]. The experimental and theoretical evidence both argue therefore against a square-planar singlet ground state. Since the reaction may involve singlet [Fe(dmpe)2], triplet [Fe(dmpe)2] and the solvent adduct [Fe(dmpe)2S], calculations including this solvated species would therefore be necessary for a full understanding of the reactivity of the iron system.If one assumes a triplet structure for [Fe(dmpe)2] the activation energies for addition of CO and oxidative addition of H2 can be estimated from the difference in energy between the triplet and singlet states to increase by 8.0 kcal mol21. Influence of the L group on the singlet and triplet states of ML4 The energy patterns computed for singlet and triplet [M(PH3)4] are similar to those calculated previously for analogous [M(CO)4] species (M = Ru or Fe).15 The geometries calculated here for singlet [Fe(PH3)4] and triplet [M(PH3)4] are also similar to their carbonyl analogues.However, our calculations predict a D2d structure for singlet [Ru(PH3)4] with angles of about 1608 at Ru whereas singlet [Ru(CO)4] was computed to have a C2v geometry with angles of about 175 and 1308 at the metal.The mixed-ligand species [Ru(CO)2(PH3)2], appears to be closer to the tetracarbonyl complex since it adopts a singlet ground state with C]Ru]C and P]Ru]P angles of 133 and 1738 respectively (MP2 optimisation).9 These structural trends in the ruthenium systems are consistent with the conclusions of Elian and Hoffmann, 14 who showed that the tendency for d8 ML4 systems to deviate from square-planar geometry is associated with the presence of p-acceptor ligands and is consistent with the relatively weak p-acceptor capability of phosphine ligands.Distortion away from a square-planar geometry is also a reflection of the metal centre. The C2v structure of [Ru(CO)2- (PH3)2] is promoted by strong p-back donation from the highlying metal-based orbitals. In contrast, [Rh(CO)2(PH3)2]1, in which the metal-based orbitals are much lower in energy, adopts a square-planar geometry.9 The deviations from square planarity calculated for singlet [Fe(PH3)4] and [Ru(PH3)4] in the present study suggest that p-back donation from high-lying metal-based orbitals is important in these systems with lowoxidation- state metal centres as well.The near square-planar structure computed for [Rh(PH3)4]1 is consistent with these ideas. Reactivity of singlet [M(PH3)4] species Oxidative addition of H2. The oxidative addition of H2 to [M(PH3)4] species has been studied for three metal systems where M = Fe, Ru or Rh1. Experimental data demonstrate that the iron and ruthenium experimental analogues, [Fe(dmpe)2] and [Ru(dmpe)2], are highly reactive species.In contrast, [Rh(dmpe)2]1 is unreactive enough to be characterised crystallographically. Starting from a singlet geometry, product formation is calculated to be strongly favoured thermodynamically with the iron and ruthenium model complexes. In contrast, addition of H2 to [Rh(PH3)4]1 is much less exothermic. We attempt to account for the greater reactivity of the neutral [M(PH3)4] systems by employing an energy-decomposition scheme 50 to analyse the bonding between the [M(PH3)4] and {H ? ? ? H} fragments within [Rh(PH3)4H2]1 and [Ru(PH3)4H2].The major interactions between these two fragments are summarised in Fig. 11 in which the orbital numbering employed in the following discussion is also indicated. The decomposition approach allows the bonding energy between two closed-shell fragments to be split up into a stericrepulsion term (DEsteric) and an orbital-interaction term (DEoi); DEsteric is made up of the four-electron destabilising interactions between occupied orbitals (exchange repulsion) and the electrostatic interaction between the nuclear and electronic distributions of the two fragments.The orbital-interaction term can be further divided into contributions from each symmetry representation. We also consider the energy required to distort each of the two isolated reactants to arrive at the geometries found in the optimised structure of the product (DEprep).The results of the energy decomposition analysis are given in Table 1. On comparing the ruthenium and Rh1 systems, we find DEprep to be 8.4 kcal mol21 higher for [Rh(PH3)4]1–{H ? ? ? H}, the majority of this difference resulting from the higher energy required to distort the [Rh(PH3)4]1 moiety away from a squareplanar geometry. Analysis of the DEsteric term indicates that the electrostatic interaction is more stabilising by 15 kcal mol21 for [Rh(PH3)4]1–{H ? ? ? H}, as would be expected for a cationic fragment.In contrast, the exchange repulsion term is less destabilising for [Ru(PH3)4]–{H ? ? ? H} by 34 kcal mol21. Finally the orbital interaction contribution is larger for [Rh(PH3)4]1–{H ? ? ? H} by 5 kcal mol21. The major difference in DEform therefore originates from DEsteric (19 kcal mol21) and can be traced to the much larger exchange repulsion seen in the Rh1 system.The origin of the larger exchange repulsion calculated in [Rh(PH3)4H2]1 compared with [Ru(PH3)4H2] must arise from Fig. 11 Schematic representation of major interactions between [M(PH3)4] and {H ? ? ? H} fragments. The 3a2 and 6b, metal-based valence orbitals which are non-bonding with respect to the {H ? ? ? H} fragment have been omitted for clarity Table 1 Energy decomposition data (kcal mol21) for [M(PH3)4H2] (M = Ru or Rh1) DEsteric Exchange repulsion Electrostatic Total DEoi a1 b2 Total Total bonding energy DEprep * DEform [Ru(PH3)4]– {H ? ? ? H} 206.3 2208.2 22.0 248.2 2119.4 2168.1 2170.1 14.2 1 115.0 237.6 [Rh(PH3)4]1– {H ? ? ? H} 240.2 2223.3 16.9 259.7 2113.1 2173.3 2156.4 25.3 1 112.5 215.6 * The two figures refer to DEprep terms for the [M(PH3)4] and {H ? ? ? H} fragments298 J.Chem. Soc., Dalton Trans., 1998, Pages 291–300 the interaction of the occupied sg orbital of {H ? ? ? H} with occupied metal fragment orbitals of a1 symmetry, in particular the metal-based 9a1 orbital.In general, one would expect the metal-based orbitals of a ruthenium(0) species to lie to much higher energy than those of an isoelectronic Rh1 cation.9 This should result in a larger energy gap between sg {H ? ? ? H} and the 9a1 orbital of the ruthenium fragment, leading to reduced exchange repulsion in that case. Although DEoi between the [M(PH3)4] and {H ? ? ? H} fragments in the final product molecules is rather similar for both ruthenium and Rh1 systems the contributions from the different symmetry representations depend on the nature of the metal centre.Thus for [Ru(PH3)4]–{H ? ? ? H} we find the a1 and b2 orbital interactions contribute 248 and 2119 kcal mol21 respectively. The corresponding figures for [Rh(PH3)4]1– {H ? ? ? H} are 260 and 2113 kcal mol21. These differences can again be understood in terms of the higher energy of the metalbased orbitals of the [Ru(PH3)4] fragment.The high energy of the 6b2 orbital of [Ru(PH3)4] should result in it acting as a better donor into su*{H ? ? ? H} than the equivalent low-lying 6b2 orbital of the [Rh(PH3)4]1 fragment. For similar reasons the acceptor capabilities of the 10a1 orbital will be relatively poor in [Ru(PH3)4] compared to [Rh(PH3)4]1. These conclusions are supported by the calculated orbital populations of the sg and su* orbitals of the {H ? ? ? H} fragment in the final [M(PH3)4H2] species (see Table 2).The stronger acceptor nature of [Rh(PH3)4]1 results in the more efficient depopulation of the sg orbital in this case while back donation into su* is greater for [Ru(PH3)4]. However, in terms of the overall orbital interaction these two effects approximately cancel out. A similar comparison between the iron and ruthenium systems is hampered by the different geometries of the species involved. This results in large changes in DEprep and DEsteric which may simply reflect these geometrical changes rather than any difference in the intrinsic electronic properties of the iron and ruthenium centres.We shall therefore not use this fragmentation approach for the comparison of the first- and second-row transition-metal species. Reaction with CO. The reactions of [M(PH3)4] with CO (M = Fe or Ru) are both computed to be highly exothermic, consistent with the high reactivity of their M(dmpe)2 experimental analogues. In this case DEform can be equated to a M]CO bond dissociation enthalpy, DH, and is computed to be slightly larger for the iron system.This conclusion, that DH3d > DH4d, is consistent with the results of previous theoretical 15,51 determinations of M]CO bond dissociation in related polycarbonyl systems, including a recent study employing highlevel ab initio calculations.52 However, an experimental study of the first M]CO bond-dissociation enthalpy in Group 6 M(CO)6 species gave the order DH5d > DH4d > DH3d.53 We shall not pursue this issue further in the present paper but note that DEform for the oxidative addition of H2 to [Fe(PH3)4] and [Ru(PH3)4] is again computed to be larger for the first-row metal.For reasons discussed in the previous section we do not attempt a more detailed comparison of the 3d and 4d M(PH3)4(CO) systems. Reaction profiles. The different reaction profiles computed for the oxidative-addition reaction of H2 to [M(PH3)4] species allow us to propose the likely course of these reactions.For [Ru(PH3)4] both the initial h1 approach of H2 and subsequent Table 2 Orbital populations (e) for the {H ? ? ? H} fragment in [M(PH3)4H2] species (M = Ru or Rh1) M sg su* Ru 1.34 1.03 Rh1 1.15 0.91 h1/h2 swing can occur without any activation barrier. For singlet [Fe(PH3)4] both the h1 and h2 approaches appear equally probable, both requiring small activation energies (ª1 kcal mol21) at long Fe]x separations (>3.0 Å). The h1/h2 swing is again barrierless in this case.For [Rh(PH3)4]1 the h1 approach is favoured at long Rh]x separations, but we estimate the activation energy required for the h1/h2 swing to be at least comparable and possibly slightly larger than that estimated for the h2 approach. The transition state in this case may well have a ‘product-like’ C2v geometry with Rh]x ª 2.3 Å. The different reaction profiles can be understood in terms of the fragmentation analysis performed above. For example, the absence of a barrier for the reaction between [Ru(PH3)4] and H2 is a result of the donor/acceptor characteristics of the metal species.The linear approach of H2 is stabilised by good donation from the high-lying 9a1 into su*(H2) while any 9a1/sg destabilisation is relatively small due to the large energy mismatch between these orbitals. This reduced destabilisation coupled with the strong p-donor power of the metal 6b2 orbital, which is further enhanced by the distortion of the [Ru(PH3)4] moiety,18–20 allows the reorientation and cleavage of the H2 moiety to proceed without any activation barrier.The similar form of the reaction profile calculated between [Fe(PH3)4] and H2 suggests a comparable series of orbital interactions with decreasing Fe]x distances, although in this case we calculate a small activation barrier for the h1 approach at Fe]x ª 3.5Å. This may simply be due to reduced overlap arising from the more contracted Fe-based orbitals in this case.The small activation barrier calculated for the reaction between singlet [Fe(PH3)4] and H2 may contribute to the slower reaction rate observed with [Fe(dmpe)2] compared to [Ru(dmpe)2]. However, as the precise nature of the transient species formed in the case of the iron complex is not known, the role played by this activation barrier in determining the overall reaction rate is not clear. As for [Fe(CO)4] 1 H2,45 the triplet ground state of [Fe(PH3)4] complicates any analysis of reaction profiles. For the reaction of [Rh(PH3)4]1 with H2 the linear approach is again preferred at long Rh]x separations.However, reorientation of the H2 moiety entails a significant activation barrier due to the low energy of the metal 9a1 orbital (greater 9a1/sg destabilisation) and the lower p-donor ability of the metal 6b2 orbital in this case. Overall an h2 approach may be favoured in this case as this maximises the donation from sg (H2) into the low-lying 10a1 acceptor orbital of the [Rh(PH3)4]1 fragment.Similar considerations apply to the addition of CO to [M(PH3)4] species (M = Fe or Ru). In this case the four-electron destabilisation occurs between the lone pair of CO and the 9a1 metal-based orbital. However, as has been described previously for the addition of CO to trans-[Ir(PH3)2(CO)Cl],19a this destabilisation can be reduced by a non-linear approach of CO towards the metal fragment. The early stages of this reaction have been described as a nucleophilic attack of the metalbased a1 HOMO on the p* acceptor orbital of CO.For the addition of CO to [M(PH3)4] species the computed reaction curves indicate that the non-linear approach of CO can completely override the effect of any four-electron destabilisation early in the reaction profile. The subsequent reaction then proceeds without any activation barrier. This is in contrast to the above study of the reactivity of Vaska9s complex where an activation barrier of 4.6 kcal mol21 was calculated.This difference is again probably a reflection of the high energy of the metal-based orbital in our systems which results in better MÆCO p donation and reduced four-electron destabilisation compared to the equivalent interactions involving trans- [Ir(PH3)2(CO)Cl]. Conclusion Density functional calculations have been carried out onJ. Chem. Soc., Dalton Trans., 1998, Pages 291–300 299 [M(PH3)4] as models for transient [M(dmpe)2] species which are formed from the photolysis of [M(dmpe)2H2] (M = Fe or Ru).Calculations have also been performed on [Rh(PH3)4]1 as a model for the relatively inert [Rh(dmpe)2]1. The singlet electron configurations of [Ru(PH3)4] and [Rh(PH3)4]1 were found to have D2d geometries with trans] P]M]P angles of 159 and 1728 respectively. Singlet [Fe(PH3)4] was computed to have a C2v structure with angles of 137 and 1608 at Fe. The structure of [Ru(PH3)4] differs, therefore, from the isoelectronic [Ru(CO)4] and [Ru(CO)2L2] species while the computed structure of singlet [Fe(PH3)4] is similar to that calculated for singlet [Fe(CO)4].The triplet configurations of [Fe(PH3)4] and [Ru(PH3)4] were predicted to adopt C2v geometries with P]M]P angles ca. 155 and 958 and thus resemble analogous [M(CO)4] triplet species (M = Fe or Ru). For [Ru(PH3)4] the singlet structure is calculated to be 11 kcal mol21 more stable than the triplet, while the triplet form of [Fe(PH3)4] is 8 kcal mol21 more stable in this case.The singlet/triplet energetic preferences have therefore now been calculated for the two known pairs of homoleptic ML4 species (M = Fe or Ru, L = CO or PH3). The calculations on [Ru(PH3)4] and [Rh(PH3)4]1 reproduce the UV/VIS spectra, geometries and relative reactivities of these species towards H2 satisfactorily. For [Ru(PH3)4] the reaction with H2 is calculated to be highly exothermic and to proceed without an activation barrier.For [Rh(PH3)4]1 the reaction with H2 is much less thermodynamically favoured and proceeds with an activation barrier of approximately 3 kcal mol21. The reaction between H2 and singlet [Fe(PH3)4] is also highly exothermic and proceeds with a small activation barrier at long Fe]H2 separations. An h1 approach of H2 to [M(PH3)4] (M = Fe or Ru) is preferred at large M ? ? ?H2 separations, but H2 is predicted to tilt to an h2 orientation in the later stages of reaction.Elongation of the H ? ? ? H distance occurs very late in the reaction profile. Although the h1 approach is computed to be more stable at long Rh1 ? ? ?H2 separations, the transition state formed with [Rh(PH3)4]1 is likely to have an h2-H2 geometry. The addition of CO to [M(PH3)4] (M = Fe or Ru) is calculated to be highly exothermic. With an angled approach of CO, the activation energy for reaction with both species is zero. The zero {or, in the case of singlet [Fe(PH3)4] 1 H2, minimal} activation energies computed for the reactions of [M(PH3)4] species (M = Fe or Ru) with H2 and CO reflect the high energies of the metal-based valence orbitals of these systems.This allows the metal centre to act as a strong electron donor and reduces the four-electron destabilisation that occurs upon approach of the substrate molecule. The high energy of the metal-based valence orbitals results in these species being relatively poor acceptors of electron density.However, any acceptor capabilities will be enhanced by a small HOMO– LUMO gap and will further promote low activation barriers. Acknowledgements We thank the EPSRC for a Western European NATO Fellowship (S. A. M.) and support (R. N. P., M. K. W.). The Laboratoire de Chimie Théorique is associated with the Centre National de la Recherche Scientifique (URA 506) and is a member of Institut de Chimie Moléculaire d’Orsay and Institut de Physico-Chimie Moléculaire. S.A. M. also thanks the EU Human Capital and Mobility Network (CHRX CT 93 0152) for a travel grant and Professor E. J. Baerends and his group for useful discussions. We thank Dr. A. J. Downs for providing facilities for measuring the NIR spectrum of [Fe(dmpe)2]. References 1 R. Hoffmann, Angew. Chem., Int. Ed. Engl., 1982, 21, 711. 2 M. Poliakoff, Chem. Soc. Rev., 1978, 7, 527. 3 M. Poliakoff and E. Weitz, Acc. Chem. Res., 1987, 20, 408; R. J. Ryther and E. Weitz, J. Phys. Chem., 1991, 95, 9841; W.Wang, A. A. Narducci, P. G. House and E. Weitz, J. Am. Chem. Soc., 1996, 118, 8654. 4 F. W. Grevels, in Photoprocesses in Transition-metal Complexes, Biosystems and Other Molecules. Experiment and Theory, ed. E. Kochansky, Kluwer, Dordrecht, 1992. 5 P. L. Bogdan and E. Weitz, J. 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ISSN:1477-9226    

DOI:10.1039/a706081e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 301–309 301 Boron–boron bond oxidative addition to rhodium(I) and iridium(I) centres William Clegg,a Fiona J. Lawlor,b Todd B. Marder,*,c Paul Nguyen,c Nicholas C. Norman,*,b A. Guy Orpen,b Michael J. Quayle,b Craig R. Rice,b Edward G. Robins,b Andrew J. Scott,a Fabio E. S. Souza,c Graham Stringer c and George R. Whittell b a The University of Newcastle, Department of Chemistry, Newcastle upon Tyne, UK NE1 7RU b The University of Bristol, School of Chemistry, Bristol, UK BS8 1TS c The University of Waterloo, Department of Chemistry, Waterloo, Ontario, N2L 3G1, Canada The reaction between the diborane(4) compound B2(1,2-O2C6H4)2 and either of the rhodium(I) complexes [RhCl(PPh3)3] or [{Rh(m-Cl)(PPh3)2}2] afforded the colourless rhodium(III) bis(boryl) species [RhCl(PPh3)2- {B(1,2-O2C6H4)}2]. Similar reactions have been carried out with the diborane(4) compounds B2(1,2-O2-4- ButC6H3)2, B2(1,2-O2-3,5-But 2C6H2)2, B2(1,2-O2-3-MeC6H3)2, B2(1,2-O2-4-MeC6H3)2, B2(1,2-O2-3-MeOC6H3)2, B2(1,2-S2C6H4)2, B2(1,2-S2-4-MeC6H3)2 and B2[R,R-1,2-O2CH(CO2Me)CH(CO2Me)]2 affording analogous rhodium complexes all of which have been characterised spectroscopically.The complexes derived from the reactions with B2(1,2-O2C6H4)2 and B2(1,2-O2-3-MeC6H3)2 have also been characterised by X-ray crystallography, the structures comprising a five-co-ordinate rhodium centre with a square-based-pyramidal geometry in which the apical site is occupied by a boryl group and the phosphines are mutually trans in basal positions.Reactivity studies have also been carried out for [RhCl(PPh3)2{B(1,2-O2C6H4)}2]. Hydrolysis or alcoholysis with catechol afforded [RhH2Cl(PPh3)3] and either B2(1,2-O2C6H4)2(m-O) or B2(1,2-O2C6H4)3 and addition of the phosphines PMe3, PEt3 and PMe2Ph afforded the new bis(boryl) compounds cis,mer-[RhCl(PMe3)3{B(1,2-O2C6H4)}2], [RhCl(PEt3)2- {B(1,2-O2C6H4)}2] and cis,mer-[RhCl(PMe2Ph)3{B(1,2-O2C6H4)}2], the PEt3 complex having been characterised by X-ray crystallography and shown to be similar to the PPh3 complex.The iridium analogue [IrCl(PEt3)2- {B(1,2-O2C6H4)}2] was also prepared from the reaction between [IrCl(PEt3)3] and B2(1,2-O2C6H4)2 and shown by X-ray crystallography to be isomorphous with the rhodium complex. Reactions between [RhCl(PPh3)2- {B(1,2-O2C6H4)}2] and the phosphines PPri 3, P(C6H11)3, 1,2-bis(diphenylphosphino)ethane (dppe) and 1,2- bis(dicyclohexylphosphino)ethane (dcpe) are also described although these do not result in new rhodium boryl complexes.The reaction between [{RhCl(dppe)}2] and B2(1,2-O2C6H4)2 afforded a compound tentatively assigned as [Rh(dppe)2{B(1,2-O2C6H4)}] with analogous compounds being formed with the diborane(4) compounds B2(1,2-O2-3-MeC6H3)2 and B2(1,2-O2-4-MeC6H3)2. Finally, the reaction between [Rh(PMe3)4]Cl and the diborane(4) compound B2(1,2-O2C6H4)2 is described which affords cis,mer-[RhCl(PMe3)3{B(1,2-O2C6H4)}2].Analogous reactions with B2(1,2-O2-3,5-But 2C6H2)2, B2(1,2-O2-3-MeC6H3)2 and B2[R,R-1,2-O2CH(CO2Me)CH- (CO2Me)]2 afforded similar products. Transition-metal-catalysed diborations of alkenes,1 alkynes 2 and 1,3-dienes 3 are now well established, particularly in the case of alkynes, and an important mechanistic feature is the oxidative addition of the B]B bond in diborane(4) compounds (R2B]BR2) to a low-valent transition-metal centre resulting in metal boryl species, M]BR2. These species have also been implicated in the palladium catalysed cross-coupling of diborane(4) compounds with halogenoarenes.4 Structurally characterised examples of metal boryls deriving from B]B bond oxidative addition to tungsten(II),5 iron(0),6 cobalt(0),7 rhodium(I),8 iridium(I) 9 and platinum(0) 2b,c,e, f centres have now been described with additional examples also having been characterised for complexes of tantalum,10 tungsten,11 manganese, 12 iron,13 rhodium14 and iridium.15 Herein we describe details of reactions involving the oxidative addition of B]B bonds to rhodium(I) and iridium(I) centres, some of which has been the subject of a preliminary communication,8a concentrating on aspects of synthesis, structure and ligand-exchange reactivity.Studies dealing with the rhodium-catalysed diboration of alkenes will be reported separately. Results and Discussion In ref. 8(a) we described the reactions between the diborane(4) compounds B2(1,2-O2C6H4)2 Ia, B2(1,2-O2-4-ButC6H3)2 Ib and B2(1,2-O2-3,5-But 2C6H2)2 Ic and the rhodium(I) complexes [RhCl(PPh3)3] 1 or [{Rh(m-Cl)(PPh3)2}2] 2 which cleanly afforded the colourless rhodium(III) bis(boryl) species [RhCl(PPh3)2{B(1,2-O2C6H4)}2] 3a, [RhCl(PPh3)2{B(1,2-O2-4- ButC6H3)}2] 3b and [RhCl(PPh3)2{B(1,2-O2-3,5-But 2C6H2)}2] 3c as shown in Scheme 1; full experimental details and spectroscopic data are provided here in the Experimental section.Corresponding reactions with the catecholato and dithiocatecholato diborane(4) compounds B2(1,2-O2-3-MeC6H3)2 Id, B2(1,2-O2-4-MeC6H3)2 Ie, B2(1,2-O2-3-MeOC6H3)2 If, B2(1,2- S2C6H4)2 Ig and B2(1,2-S2-4-MeC6H3)2 Ih 16 afforded the analogous boryl complexes [RhCl(PPh3)2{B(1,2-O2-3-MeC6H3)}2] 3d, [RhCl(PPh3)2{B(1,2-O2-4-MeC6H3)}2] 3e, [RhCl(PPh3)2- {B(1,2-O2-3-MeOC6H3)}2] 3f, [RhCl(PPh3)2{B(1,2-S2C6H4)}2] 3g and [RhCl(PPh3)2{B(1,2-S2-4-MeC6H3)}2] 3h respectively (Scheme 1).The reaction between 1 and the tartrate derivative B2{R,R-1,2-O2CH(CO2Me)CH(CO2Me)}2 Ii 17 also afforded a bis(boryl) complex, namely [RhCl(PPh3)2{B[R,R-1,2-O2CH- (CO2Me)CH(CO2Me)]}2] 3i. Spectroscopic and analytical data for all complexes were consistent with their formulation and the structures of 3a and 3d were confirmed by X-ray crystallography, the results of which are shown in Figs. 1 and 2 respectively; selected bond length and angle data are given in Table 1 and crystallographic data are presented in Table 2.Compound 3a crystallises as the tetra-CH2Cl2 solvate 3a?4CH2Cl2 from this solvent with no short intermolecular contacts. Its molecular structure may be302 J. Chem. Soc., Dalton Trans., 1998, Pages 301–309 described as comprising a five-co-ordinate rhodium centre in a distorted square-based pyramidal environment with one of the boryl groups occupying the apical site and the other in one of the basal sites trans to the chlorine; the mutually trans PPh3 ligands occupy the remaining two basal positions.The Rh]B bond distances differ slightly with that to the apical boron [Rh]B(1) 1.954(4) Å] being somewhat shorter than the basal Rh]B bond [Rh]B(2) 2.008(4) Å] although both distances are similar to those of other rhodium(III) boryls.8c,14,18 Of particular Scheme 1 O B O O B O Rn Rn Rh B(cat) Cl Ph3P PPh3 (cat)B Rh B(cat) Cl Ph3P PPh3 (cat)B MeO2C MeO2C O B O O B O Rh B(tart) Cl Ph3P PPh3 (tart)B 3a cat = 1,2-O2C6H4 3b cat = 1,2-O2-4-ButC6H3 3c cat = 1,2-O2-3,5-But 2C6H2 3d cat = 1,2-O2-3-MeC6H3 3e cat = 1,2-O2-4-MeC6H3 3f cat = 1,2-O2-3-MeOC6H3 1 + Ia R n = H4 Ib R n = 4-But-3,5,6-H3 Ic R n = 3,5-But 2-4,6-H2 Id R n = 3-Me-4,5,6-H3 Ie R n = 4-Me-3,5,6-H3 If R n = 3-MeO-4,5,6-H3 [{Rh(m-Cl)(PPh3)2}2] + Ia–Ii 3a–3i + PPh3 + PPh3 1 Ig R n = H4 Ih R n = 4-Me-3,5,6-H3 3g cat = 1,2-S2C6H4 3h cat = 1,2-S2-4-MeC6H3 [RhCl(PPh3)3] CO2Me CO2Me 1 [RhCl(PPh3)3] + 3i tart = R,R-1,2-O2CH- (CO2Me)CH(CO2Me) S B S S B S Rn Rn Ii + PPh3 + [RhCl(PPh3)3] 2 Fig. 1 View of the molecular structure of complex 3a with key atoms labelled. Hydrogen atoms are omitted for clarity. Atoms are drawn as spheres of arbitrary radius note for comparison, however, is the structure of another crystalline modification of 3a, which had previously been isolated from a reaction between 1 and HB(1,2-O2C6H4), as the tris(1,2- dichloroethane) solvate, 3a?3C2H4Cl2-1,2.8b The molecular structures of 3a in the two crystal forms are essentially identical although the present structure is better determined, data for comparison being given in Table 1.The bond angles about the rhodium centre in 3a?4CH2Cl2 support the description of the co-ordination geometry as distorted square-based pyramidal with the P(1)]Rh]P(2) and B(2)]Rh]Cl angles being 169.75(3) and 162.07(11)8 respectively, i.e. both similar and reasonably close to linear [the Rh resides 0.270 Å above the average basal plane towards B(1)], and angles between the apical boron B(1) and the four contact atoms in the basal plane ranging from 78.9(2)8 for the B(1)]Rh]B(2) angle to 118.89(11)8 for B(1)]Rh]Cl.The acute B]Rh]B angle results in a B ? ? ? B separation of 2.517 Å, although this is more than 0.8 Å longer than typical values for B]B bonds in bis(catecholate) diborane(4) compounds, which are generally about 1.68 Å.16b,19 Any residual B ? ? ? B interaction is therefore necessarily very weak.Moreover, the relative orientations of the boryl ligands are such as to preclude any interaction between the boron p orbitals since the boron catecholate planes are close to orthogonal as shown in A. An alternative configuration for two mutually cis boryl groups, shown in B and observed in, for example, the platinum complexes of general formula cis-[Pt(PR3)2{B(1,2-O2C6H4)}2] 2b,c,e, f and the cobalt compound [Co(PMe3)3{B(1,2-O2C6H4)}2],7 does allow for the possibility of residual B ? ? ? B 2p ? ? ? 2p bonding but while any such interaction is still open to question in the platinum compounds2f,20 the possibility of B ? ? ? B bonding in the cobalt species has been discussed 7 in view of the short B]B distance (2.185 Å) observed and theoretical studies are in progress to address this issue further.Compound 3d also crystallises as a solvate with three molecules of CH2Cl2 and one half molecule of n-hexane per asymmetric unit and with no short intermolecular contacts. The gross molecular structure of 3d (Fig. 2) is very similar to both those of 3a including the conformations of the two boryl ligands which are again close to perpendicular as illustrated in A. Relevant bond-length data reveal that the apical Fig. 2 View of the molecular structure of complex 3d. Details as in Fig. 1 O B O M O B O O B O M BO O B AJ. Chem. Soc., Dalton Trans., 1998, Pages 301–309 303 Table 1 Selected bond lengths (Å) and angles (8) for compounds 3a, 3d, 8 and 9 a 3a?4CH2Cl2 3a?3 1,2-Cl2C2H4 b 3d?3CH2Cl2?0.5C6H14 8 9 B(1)]Rh B(2)]Rh B(1)]Rh]B(2) B(1)]Rh]Cl B(1)]Rh]P(1) B(1)]Rh]P(2) B(2)]Rh]Cl B(2)]Rh]P(1) B(2)]Rh]P(2) Cl]Rh]P(1) Cl]Rh]P(2) P(1)]Rh]P(2) 1.954(4) 2.008(4) 78.9(2) 118.89(11) 93.90(11) 94.45(11) 162.07(11) 86.68(10) 89.12(10) 89.38(3) 91.77(3) 169.75(3) B(2)]Rh B(1)]Rh B(1)]Rh]B(2) B(2)]Rh]Cl B(2)]Rh]P(1) B(2)]Rh]P(2) B(1)]Rh]Cl B(1)]Rh]P(1) B(1)]Rh]P(2) Cl]Rh]P(1) Cl]Rh]P(2) P(1)]Rh(1)]P(2) 1.956(8) 2.008(7) 79.0(3) 117.5(2) 93.5(2) 95.8(2) 163.4(2) 92.2(2) 85.7(2) 88.09(6) 91.14(6) 169.88(7) B(2)]Rh B(1)]Rh B(2)]Rh]B(1) B(2)]Rh]Cl B(2)]Rh]P(1) B(2)]Rh]P(2) B(1)]Rh]Cl B(1)]Rh]P(1) B(1)]Rh]P(2) Cl]Rh]P(1) Cl]Rh]P(2) P(1)]Rh]P(2) 1.906(13) 2.034(12) 80.9(5) 118.9(3) 93.4(3) 93.8(3) 160.2(4) 88.4(4) 87.2(4) 91.1(1) 90.3(1) 170.8(1) B(1)]Rh B(2)]Rh B(1)]Rh]B(2) B(1)]Rh]Cl B(1)]Rh]P(1) B(1)]Rh]P(2) B(2)]Rh]Cl B(2)]Rh]P(1) B(2)]Rh]P(2) Cl]Rh]P(1) Cl]Rh]P(2) P(1)]Rh]P(2) 1.973(2) 1.994(2) 75.3(1) 132.29(7) 94.91(7) 94.69(7) 152.34(7) 89.16(7) 93.92(7) 86.52(2) 86.53(2) 170.37(2) B(1)]Ir B(2)]Ir B(1)]Ir]B(2) B(1)]Ir]Cl B(1)]Ir]P(1) B(1)]Ir]P(2) B(2)]Ir]Cl B(2)]Ir]P(1) B(2)]Ir]P(2) Cl]Ir]P(1) Cl]Ir]P(2) P(1)]Ir]P(2) 1.991(6) 2.004(6) 76.6(6) 132.9(2) 94.5(2) 94.8(2) 150.4(2) 89.8(2) 93.8(2) 86.09(6) 86.53(6) 170.56(6) a This table is organised such that comparable bond lengths and angles for the five structures occur in any given line although the atom labelling schemes vary for different structures.b Data taken from ref. 8(b). Rh–B bond [Rh]B(2) 1.906(13) Å] is shorter than the corresponding basal bond [Rh]B(1) 2.034(12) Å] as found for 3a, and the transoid P]Rh]P and B]Rh]Cl angles in the basal plane [170.8(1) and 160.2(4)8 respectively] are also consistent with a square-based pyramidal rhodium geometry; the B ? ? ? B distance is 2.56 Å. An alternative description of the structures of complexes 3a and 3d can be given in terms of the discussion presented by Eisenstein and co-workers 21 for d6 ML5 complexes.In the specific case of one of their model compounds, [IrH2Cl(PH3)2], the so-called T-shaped geometry, shown in C, and the alternative Y-shaped geometry (D) are calculated to be the lowestenergy structures on the potential-energy surface for this system (the more symmetrical trigonal-bipyramidal geometry is calculated to be a maximum) with the Y-shaped geometry being the actual minimum.The model complex [IrH2Cl(PH3)2] is a particularly apposite example here since it contains two phosphines and a chlorine, as found in 3a/3d, and two high-trans-influence hydrides which are probably good models for boryl groups which are also known to exhibit a high trans influence.2e,8c,9 We will not reiterate here the details of the discussion given by Eisenstein concerning the precise electronic origins of these structural preferences (the reader is referred to the original papers given in ref. 21) but note that the structures of 3a and 3d are about midway between the limiting T- and Y-shaped geometries (C and D) although significantly distorted from a regular trigonal-bipyramidal geometry as expected.21 Having established the generality of the reaction between the bis(catecholato) diborane(4) compounds Ia–Ih and either 1 or 2 affording the rhodium(III) bis(boryls) 3a–3h, we next turned our attention to a study of the reactivity of the rhodium boryl complexes, largely that of 3a.The first point to note concerns the stability of 3a in solution. Thus, the reaction to produce 3a described above using 2 as the rhodium source (and that for the other complexes 3b–3i) was generally carried out in CH2Cl2 solution. Monitoring this reaction by 31P NMR spectroscopy revealed that it was essentially complete within 15 min (somewhat longer in the case of 3c and 3i) and that, once formed, 3a was stable in this solvent for about 1 week, the major phosphorus-containing decomposition product being the rhodium(III) dihydride cis,mer-[RhH2Cl(PPh3)3] 4 22,23 for which H Ir H Cl PH3 PH3 Cl Ir H H PH3 PH3 C D 180° 80° a doublet was observed at d 34.0 and a broad singlet at d 14.6.† In the 11B NMR spectrum signals were observed, in variable ratios depending on the particular reaction, for the species B2(1,2-O2C6H4)2(m-O) II (d 18.1),24 B2(1,2-O2C6H4)3 III (d 16.6) 25 and the anion [B(1,2-O2C6H4)2]2 IV (d 12.3).‡,26 If the synthesis of complex 3a was carried out in the same solvent but using 1 as the rhodium source, decomposition was observed to give the same products but somewhat more quickly with complete disappearance of signals due to 3a occurring after 2–3 d.A similar set of observations was made when benzene was used as the reaction solvent, but when thf was used complete decomposition of 3a took place after about 2–3 d if 2 was used as the precursor and after only 24 h if 1 was employed.In all cases the same major decomposition products were produced as evidenced by 31P and 11B NMR spectroscopy. The implication is that 3a is apparently much less stable in solution in the presence of a two-electron donor such as thf or free PPh3 (produced when 1 is used as the rhodium starting material). The mechanism of these decompositions remains unclear in detail, but the nature of the products indicated that, despite stringent precautions being taken to exclude moisture, some form of hydrolysis was likely especially in (donor) solvents such as thf.§ That compound 3a was particularly susceptible to hydrolysis was confirmed in a separate experiment wherein it was exposed to small quantities of water.Following the reaction by 31P and 11B NMR spectroscopy revealed exclusive and rapid formation O B O O B O O O B O O B O O O O O BO O III IV II † At room temperature the 31P-{1H} NMR spectrum of cis,mer- [RhH2Cl(PPh3)3] 4 23b shows a doublet at d 34.0 (JRhP = 115 Hz) and a broad singlet at d 14.6 due to rapid intermolecular exchange involving the unique PPh3 ligand.At 260 8C this exchange is essentially frozen out and the spectrum expected for this structure is observed: d 34.0 (dd, 2 P, PPh3, 1JRhP = 115, 2JPP = 20) and 14.6 (dt, 1 P, PPh3, 1JRhP = 92, 2JPP = 20 Hz).22 ‡ Chemical shifts for compounds II–IV are reported for samples in tetrahydrofuran (thf) solution. Values can vary slightly depending on the solvent used.§ A related degradation of HB(1,2-O2C6H4) in the presence of PPh3 has been described in ref. 22 and refs. therein which affords, as one product III, the mechanism for which is also unknown.304 J. Chem. Soc., Dalton Trans., 1998, Pages 301–309 of 4 and II according to equation (1) (the presence of the PPh3 [RhCl(PPh3)2{B(1,2-O2C6H4)}2] 1 PPh3 1 H2O æÆ 3a [RhH2Cl(PPh3)3] 1 B2(1,2-O2C6H4)2(m-O) (1) 4 II derives from the in situ formation of 3a from 1), the presence of II being confirmed by mass spectrometry.We note that the sensitivity of 3a to hydrolysis is in contrast to the recently reported ruthenium(II) and osmium(II) boryls described by Roper and co-workers 27 which are stable to hydrolysis. The susceptibility of the Rh]B bonds in complex 3a to protolysis was also established from reaction (2) [as with equation [RhCl(PPh3)2{B(1,2-O2C6H4)}2] 1 PPh3 1 1,2-(HO)2C6H4 æÆ 3a [RhH2Cl(PPh3)3] 1 B2(1,2-O2C6H4)3 (2) 4 III (1), the presence of the PPh3 in (2) derives from the in situ formation of 3a from 1] whereby catechol was observed cleanly to afford 4 and III; the precise origin of the anion IV remains unclear (as does the nature of its associated cation) although it is a very commonly observed decomposition product in all reactions involving metal boryls (see later).The reactivity of complex 3a towards phosphine exchange was also investigated with a variety of phosphines. Treatment of 3a in CH2Cl2 solution with 3 equivalents of PMe3 cleanly afforded a complex formulated as cis,mer-[RhCl(PMe3)3{B(1,2- O2C6H4)}2] 5 on the basis of multinuclear NMR data.Thus, the 31P-{1H} NMR spectrum indicated two inequivalent phosphorus environments with a 2 : 1 occupancy ratio whilst the 11B-{1H} spectrum revealed two boron signals of equal intensity in the metal boryl region indicating a mutually cis configuration for the boryl groups (the alternative cis, fac isomer would have equivalent boryl groups and hence only one 11B resonance).Further confirmation of the structure of 5 is provided by comparison with the iridium analogue cis,mer-[IrCl(PMe3)3- {B(1,2-O2C6H4)}2] 69 which has been crystallographically characterised and exhibits almost identical NMR spectra to those of 5 (allowing for the absence of coupling to 103Rh). Compound 5 was also formed quantitatively (and more readily isolated as a pure material) in stoichiometric reactions between either Ia and [RhCl(PMe3)3] in benzene solution or between Ia and [Rh(PMe3)4]Cl 7 in thf [further reactions between 7 and diborane(4) compounds will be described later]. Treatment of 3a with a large excess of PMe3 resulted in the formation of 7 as the only rhodium–phosphorus containing species as evidenced by 31P NMR spectroscopy, although when carried out in CH2Cl2 solution rapid overall decomposition occurred since 7 reacts with this solvent.28 In contrast to the reaction with PMe3, treatment of complex 3a in CH2Cl2 solution with 3 equivalents of PEt3 afforded the colourless crystalline bis(phosphine) complex [RhCl(PEt3)2- {B(1,2-O2C6H4)}2] 88a rather than a tris(phosphine) species analogous to 5.The formula of 8 was apparent from multi- Cl Me3P PMe3 Rh O B O O B O PMe3 5 nuclear NMR studies but was confirmed by X-ray crystallography the results of which are shown in Fig. 3; selected bond length and angle data are given in Table 1 and crystallographic data in Table 2.The molecular structure is broadly similar to that of 3a in that the boryl groups are cis with an acute B]Rh]B angle [B(1)]Rh]B(2) 75.3(1)8], a type A orientation of the boryl groups (see above), and trans phosphines [P(1)]Rh]P(2) 170.37(2)8]. The main difference between 8 and 3a lies in the angles about the rhodium centre within the plane defined by the atoms Cl, B(1) and B(2). Thus although the B]Rh]B angles are similar in both structures [8 75.3(1), 3a?4CH2Cl2 78.9(2)8)], the Cl]Rh]B(1) [8 132.29(7), 3a?4CH2Cl2 118.89(11)] and Cl]Rh]B(2) [8 152.34(7), 3a?4CH2Cl2 162.07(11)8] angles each differ by about 10–148, being more nearly equal in 8.A description of the geometry of 8 as square-based pyramidal is therefore less appropriate here, a better description being in terms of the Y-shaped geometry (D) mentioned above in connection with the structures of 3a/3d. However, the fact that the boryl groups are still in different environments (in the sense that the Cl]Rh]B angles still differ by 208) is reflected in different Rh]B bond lengths [Rh]B(1) 1.973(2), Rh]B(2) 1.994(2) Å].Furthermore, it is the boryl with the shorter Rh]B bond and the smaller Cl]Rh]B angle [B(1)] which lies parallel to the P(1)]Rh]P(2) vector in 8 as is also the case for 3a; in the event that the boryl groups were in equivalent environments, i.e. the Cl]Rh]B angles were the same, such a distinction would be lost. The iridium analogue of complex 8, [IrCl(PEt3)2{B(1,2-O2- C6H4)}2] 9, has also been prepared, although by a different route involving the direct reaction between [IrCl(PEt3)3] and Ia, and structurally characterised and is included here for comparison with 8; a view of the molecular structure of 9 is shown in Fig. 4 with selected bond length and angle data in Table 1 and crystallographic data in Table 2. In fact the structure of 9 is isomorphous with 8 such that the description given above for 8 is also appropriate for 9, no further discussion being warranted.In solution, however, the Ir]PEt3 system differs slightly from the Rh]PEt3 system. Thus in the rhodium case, as described above, there is no evidence for the presence of a tris(phosphine) derivative analogous to 5 whereas for the iridium example solution NMR studies did indicate the presence of the tris- (phosphine) species [IrCl(PEt3)3{B(1,2-O2C6H4)}2] 10. Thus, at room temperature all 31P NMR resonances were broad but at 255 8C a doublet and triplet spectrum was observed consistent with a cis,mer-tris(phosphine) arrangement analogous to 5.Whether or not the exchange process is intra- or inter- Fig. 3 View of the molecular structure of complex 8. Details as in Fig. 1J. Chem. Soc., Dalton Trans., 1998, Pages 301–309 305 molecular cannot be ascertained from these data but the fact that it is the bis(phosphine) species which was isolated in crystalline form indicates that one of the PEt3 ligands in 10 is labile, most likely the one trans to boron in view of the known high trans influence of the boryl group.2e,8c,9 The reaction between complex 3a and 3 equivalents of PMe2Ph quantitatively afforded the tris(phosphine) complex [RhCl(PMe2Ph)3{B(1,2-O2C6H4)}2] 11 characterised on the basis of multinuclear NMR spectroscopy, and by analogy with the tris-PMe3 complex 5; it is also assumed to have the cis,mer configuration shown in the diagram.At room temperature the 31P-{1H} NMR spectrum showed a doublet at d 23.9 (1JRhP = 101 Hz) for the equivalent, mutually trans phosphines and a broad singlet at d 222.7 for the unique phosphine trans to a boryl group. In the latter case broadening of phosphorus signals trans to boron is commonly observed [see, for example, ref. 2(e)], but some degree of dissociation was also indicated by the fact that the resonance at d 23.9 showed no phosphorus– phosphorus coupling. Such a dissociation process would be consistent with the known high trans influence of boryl groups2e,8c,9 and this was confirmed by low-temperature 31P- {1H} NMR spectroscopy.Thus at 260 8C the 31P-{1H} spectrum of 11 becomes fully resolved with the mutually trans pair of phosphines appearing as a doublet of doublets [d 23.6 (dd, 1JRhP = 99, 2JPP = 28 Hz)] and the unique phosphine resonating as a doublet of triplets [d 221.1 (dt, 1JRhP = 69, 2JPP = 28 Hz)], the small value of the 1JRhP coupling constant in the latter case being indicative of the relatively weak Rh]P bond resulting from the aforementioned trans influence of the boryl group.2e,8c,9 The reaction between complex 3a and the phosphine PMePh2 in CH2Cl2 solution proceeded somewhat differently from the reactions described above involving the phosphines PMe3, PEt3 and PMe2Ph.Thus even when a large excess of PMePh2 was added to solutions of 3a a proportion of 3a remained unchanged Fig. 4 View of the molecular structure of complex 9.Details as in Fig. 1 M Cl Et3P PEt3 O B O O B O Cl Et3P PEt3 Ir O B O O B O PEt3 10 8 M = Rh; 9 M = Ir although signals due to unco-ordinated PPh3 and two new rhodium–phosphine species were observed [d 19.1 (d, 1JRhP = 109) and 2.8 (d, 1JRhP = 141 Hz)]. The former signal has a chemical shift and rhodium–phosphorus coupling constant consistent with a new bis(boryl) species [RhCl(PMePh2)2{B(1,2- O2C6H4)}2] 12 analogous to 3a and 8, but we were not able to isolate this compound as a pure material.The compound giving rise to the signal at d 2.8 remains unidentified, although the large value of 1JRhP is indicative of a rhodium(I) species, but the fact that the 11B-{1H} NMR spectrum of the reaction mixture showed signals corresponding to compounds II–IV, indicated that considerable decomposition was occurring. When CH2Cl2 solutions of 3a were treated with an excess of either PPri 3 or P(C6H11)3 no reaction took place as evidenced by 31P-{1H} NMR spectroscopy which showed, in both cases, unchanged 3a and free phosphine even after several days.In view of the fact that the structures of the bis(phosphine) complexes 3a, 3d and 8 all have mutually trans phosphines, we were interested in preparing bis(phosphine) complexes in which the two phosphorus centres were part of a chelating diphosphine. With this in mind we treated CH2Cl2 solutions of 3a with 1 equivalent of either dppe [1,2-bis(diphenylphosphino)ethane] or dcpe [1,2-bis(dicyclohexylphosphino)ethane]. In both cases, however, it was clear from following the reactions by 31P-{1H} NMR spectroscopy that no new metal boryl species were obtained.Rather, in the former case, the only two rhodium– phosphorus containing products formed (in approximately equal amounts) were the rhodium(I) species [Rh(dppe)2]Cl 13 [d 58.5 (d, 1JRhP = 133 Hz)] 29 and the rhodium(III) species trans- [RhH(Cl)(dppe)2][B(1,2-O2C6H4)2] 14 [d 52.6 (d, 1JRhP = 94 Hz].30 Compound 14 was characterised by X-ray crystallography, details of which, together with full experimental and spectroscopic data, are reported in ref. 30. The formation of 13 from 3a can be envisaged as proceeding according to equation (3) but the mechanism of formation of 14 remains unclear [RhCl(PPh3)2{B(1,2-O2C6H4)}2] 1 2 dppe æÆ 3a [Rh(dppe)2]Cl 1 2 PPh3 1 B2(1,2-O2C6H4)2 (3) 13 Ia although we note that the reaction was fully reproducible. The analogous reaction between complex 3a and dcpe likewise afforded compounds identified as the rhodium(I) species [Rh(dcpe)2]Cl 15 [d 67.0 (d, 1JRhP = 129 Hz)] 31 and the ionic rhodium(III) species trans-[RhH(Cl)(dcpe)2][B(1,2-O2C6H4)2] 16 [d 61.3 (d, 1JRhP = 90 Hz)].30 Compound 16 was also characterised by X-ray crystallography, full structural, experimental and spectroscopic data for which are given in ref. 30. As an alternative route to metal bis(boryls) containing a chelating diphosphine ligand, the compound [{RhCl(dppe)}2] 17 was treated with 1 equivalent of Ia in CH2Cl2 solution.Monitoring the reaction by 31P-{1H} NMR spectroscopy revealed a quantitative conversion over a period of 24 h into a single new phosphorus-containing species [d 64.2, 1JRhP = 153 Hz] which was subsequently isolated, albeit in low yield, as a pale yellow crystalline powder. We were not able to obtain Cl PhMe2P PMe2Ph Rh O B O O B O PMe2Ph 11306 J. Chem. Soc., Dalton Trans., 1998, Pages 301–309 X-ray-quality crystals of this product or satisfactory analytical data, but multinuclear NMR studies were consistent with a formulation as a rhodium(I) mono(boryl) species [Rh(dppe)2- {B(1,2-O2C6H4)}] 18.The 1H NMR spectrum was particularly informative, the integration of which showed two dppe ligands to one B(1,2-O2C6H4) group. Moreover the boryl catecholate resonances had chemical shift values characteristic of rhodium boryls such as 3a, these resonances being shifted to higher field compared to those of species such as Ia and II–IV.Furthermore, the CH2 resonances of the dppe ligands were split into two sets consistent with different environments above and below the Rh(dppe)2 plane. The value of 1JRhP is also consistent with a rhodium(I) species although we were not able to observe a resonance for the boryl group in the 11B NMR spectrum. Analogous reactions between 17 and Id and Ie proceeded in a similar fashion affording complexes formulated as [Rh(dppe)2- {B(1,2-O2-3-MeC6H3)}] 19 and [Rh(dppe)2{B(1,2-O2-4-Me- C6H3)}] 20.Clearly the reaction between 17 and the diborane(4) compounds Ia, Id and Ie is complicated and the formulation of the compounds 18–20 must be considered as tentative, any mechanistic speculation being unwarranted at this time. The reaction between compound Ia and the cationic rhodium(I) complex [Rh(PMe3)4]Cl 7 in thf affording 5 has been described above. Compound 7 also reacts cleanly in thf solution with the diborane(4) compounds Ic, Id, Ii and the neopentyl glycolate derivative B2(OCH2CMe2CH2O)2 Ij 16a,b affording the bis(boryl) complexes cis,mer-[RhCl(PMe3)3- {B(1,2-O2-3,5-But 2C6H2)}2] 21, cis,mer-[RhCl(PMe3)3{B(1,2-O2- 3-MeC6H3)}2] 22, cis,mer-[RhCl(PMe3)3{B(tart)}2] 23 and cis,mer-[RhCl(PMe3)3{B(OCH2CMe2CH2O)}2] 24 all of which were characterised by multinuclear NMR studies and found to be analogous to 5 described in detail above.Finally we mention that the reaction between complex 3a and the isocyanide CNC6H3Me2-2,6 proceeds according to equation (4) as described in ref. 8(b). An analogous reaction between [RhCl(PPh3)2{B(1,2-O2C6H4)}2] 1 CNC6H3Me2-2,6 æÆ 3a [RhCl(CNC6H3Me2-2,6)(PPh3)2] 1 B2(1,2-O2C6H4)2 (4) Ia 3a and CO afforded [RhCl(CO)(PPh3)2] as the rhodiumcontaining product although the boron-containing species was not identified. We also note that no reaction was observed between compound Ia and the rhodium(I) and iridium(I) com- Rh P P O B O Ph Ph Ph Ph P P Ph Ph Ph Ph 18 Cl Me3P PMe3 Rh O B O O B O PMe3 Me Me O B O B O O Me Me O O Ij = 1,2-O2-3,5-But 2C6H2 21; 1,2-O2-3-MeC6H3 22; tart 23; OCH2CMe2CH2O 24 plexes [RhCl(PMe2Ph)3], [RhCl(PMePh2)3], [RhCl(CO)- (PPh3)2], [IrCl(CO)(PMe2Ph)2] and [IrCl(PPh3)3].Experimental General procedures All reactions were performed using standard Schlenk or glovebox techniques under an atmosphere of dry, oxygen-free dinitrogen or argon. All solvents were distilled from appropriate drying agents immediately prior to use (sodium–benzophenone for Et2O, CaH2 for chlorinated solvents and sodium or sodium–benzophenone for toluene and hexanes).Microanalytical data were obtained at The University of Bristol. The NMR spectra were recorded on JEOL GX 270, GX 400, Lambda 300 and Bruker WP 200 spectrometers and were referenced to SiMe4, SiMe4, 85% H3PO4 and BF3?Et2O for 1H, 13C, 31P and 11B nuclei respectively. Mass spectra (high and low resolution) were obtained in electron impact (EI) mode on a Micromass Autospec spectrometer.The compounds 1,32 2,32 [RhCl- (PMe3)3],33 7,33 [ IrCl(PEt3)3] 34 and 17 35 were prepared by literature methods. Preparations and reactions [RhCl(PPh3)2{B(1,2-O2C6H4)}2] 3a. In a typical preparation CH2Cl2 (2–4 cm3) was added to a mixture of solid complex 2 (0.015 g, 0.011 mmol) and Ia (0.005 g, 0.023 mmol) at room temperature resulting in an orange suspension (2 is only sparingly soluble in this solvent).After stirring for 15 min all of compound 2 had dissolved/reacted and the resulting pale yellow solution was cooled to 278 8C using a solid CO2–ethanol bath. Addition of n-hexane (15 cm3) resulted in the formation of a white precipitate which was then allowed to settle and the solvent was removed by syringe. The remaining solid was washed with n-hexane (2 × 5 cm3) and finally dried under vacuum affording crude 3a as a dry white powder (0.015 g, 72%). For any subsequent reactivity studies 3a was used in this form but analytically pure samples and X-ray-quality crystals were obtained by redissolving the crude product in CH2Cl2 (3 cm3), adding n-hexane (10 cm3) as an overlayer and allowing solvent diffusion to occur over a period of days at 230 8C.Compound 1 can also be used as a starting rhodium material as described in the text, although this is less desirable since traces of the liberated PPh3 were sometimes found to contaminate the crude product.Compounds 3b–3e were prepared in an analogous fashion and with similar yields although in the case of 3b and 3c the increased solubility deriving from the But groups resulted in lower isolated yields. Compounds 3f–3h were characterised on the basis of 31P-{1H} NMR spectroscopy of their respective reaction mixtures (which indicated quantitative yields in solution as with all other reactions) but were not isolated. [RhCl(PPh3)2{B[R,R-1,2-O2CH(CO2Me)CH(CO2Me)]}2] 3i.Compound 3i was prepared and isolated as described for 3a except that the reaction took much longer to go to completion and was stirred for 2–3 h at room temperature rather than 10– 15 min. Complex 3a: NMR (CD2Cl2) 1H, d 7.66 (m, 12 H, PPh3), 7.15 (m, 18 H, PPh3), 6.68 (m, 4 H, 1,2-O2-3,6-C6H4) and 6.60 (m, 4 H, 1,2-O2-4,5-C6H4); 13C-{1H}, d 149.5 (s, 1,2-O2-1,2-C6H4), 134.9 (t, o-C of PPh3), 132.4 (t, ipso-C of PPh3), 130.4 (s, p-C of PPh3), 128.2 (t, m-C of PPh3), 121.3 (s, 1,2-O2-3,6-C6H4) and 111.1 (s, 1,2-O2-4,5-C6H4); 31P-{1H}, d 31.1 (d, PPh3, 1JRhP = 113 Hz); 11B-{1H}, d 38.4 (Found: C, 56.00; H, 3.40. C48H38B2ClO4- P2Rh?2CH2Cl2 requires C, 56.10; H, 3.95%).The crystal structure reveals the presence of four molecules of CH2Cl2 of crystallisation per molecule of 3a. Some of this solvent is readily lost from the crystals and the best for fit for the analyticalJ. Chem. Soc., Dalton Trans., 1998, Pages 301–309 307 data obtained is for two remaining molecules of CH2Cl2 per molecule of 3a.Complex 3b: NMR (CD2Cl2) 1H, d 7.74 (m, 12 H, PPh3), 7.27 (m, 18 H, PPh3), 6.72 (m, 6 H, 1,2-O2-4-But-3,5,6-C6H3) and 1.27 (s, 18 H, But); 13C-{1H}, d 149.5 and 147.3 (s, 1,2-O2-4-But- 1,2-C6H3), 135.0 (t, o-C of PPh3), 132.6 (t, ipso-C of PPh3), 130.4 (s, p-C of PPh3), 128.3 (t, m-C of PPh3), 145.1, 117.8, 110.0 and 108.8 (s, 1,2-O2-4-But-3,4,5,6-C6H3), 34.9 (s, CMe3) and 31.9 (s, CMe3); 31P-{1H}, d 33.7 (d, PPh3, 1JRhP = 115 Hz); 11B-{1H}, d 38.9.Complex 3c: NMR (CD2Cl2) 1H, d 7.76 (m, 12 H, PPh3), 7.28 (m, 18 H, PPh3), 6.82 (d, 2 H, 1,2-O2-3,5-But 2-6-C6H2, 4JHH = 2), 6.66 (d, 2 H, 1,2-O2-3,5-But 2-4-C6H2, 4JHH = 2 Hz), 1.30 (s, 18 H, But) and 1.07 (s, 18 H, But); 13C-{1H}, d 149.7 and 145.3 (s, 1,2-O2-3,5-But 2-1,2-C6H2), 135.1 (t, o-C of PPh3), 132.6 (t, ipso- C of PPh3), 130.4 (s, p-C of PPh3), 128.4 (t, m-C of PPh3), 144.3, 133.6, 115.2 and 106.7 (s, 1,2-O2-3,5-But 2-3,4,5,6-C6H2), 35.0 and 34.2 (s, CMe3), 32.0 and 30.0 (s, CMe3); 31P-{1H}, d 31.9 (d, PPh3, 1JRhP = 116 Hz); 11B-{1H}, d 42.6.Complex 3d: NMR (CD2Cl2) 1H, d 7.70 (m, 12 H, PPh3), 7.22 (m, 18 H, PPh3), 6.64 (t, 2 H, 1,2-O2-3-Me-5-C6H3, 3JHH = 8), 6.58 (d, 2 H, 1,2-O2-3-Me-6-C6H3, 3JHH = 8), 6.52 (d, 2 H, 1,2- O2-3-Me-4-C6H3, 3JHH = 8 Hz) and 1.86 (s, 6 H, Me); 13C-{1H}, d 149.5 and 148.5 (s, 1,2-O2-3-Me-1,2-C6H3), 135.2 (t, o-C of PPh3), 132.9 (t, ipso-C of PPh3), 130.7 (s, p-C of PPh3), 128.6 (t, m-C of PPh3), 123.0, 121.7, 121.2 and 109.0 (s, 1,2-O2-3-Me- 3,4,5,6-C6H3) and 14.6 (s, Me); 31P-{1H}, d 31.0 (d, PPh3, 1JRhP = 114 Hz); 11B-{1H}, d 40.3 (Found: C, 64.60; H, 4.80.C50H42B2ClO4P2Rh requires C, 64.65; H, 4.55%). Complex 3e: NMR (CD2Cl2) 1H, d 7.68 (m, 12 H, PPh3), 7.26 (m, 18 H, PPh3), 6.54 (m, 6 H, 1,2-O2-4-Me-3,5,6-C6H3) and 2.21 (s, 6 H, Me); 13C-{1H}, d 149.6 and 147.5 (s, 1,2-O2-4-Me- 1,2-C6H3), 135.0 (m, o-C of PPh3), 132.5 (t, ipso-C of PPh3), 130.4 (s, p-C of PPh3), 128.2 (m, m-C of PPh3), 124.2, 121.4, 111.8 and 110.4 (s, 1,2-O2-4-Me-3,4,5,6-C6H3) and 21.3 (s, Me); 31P-{1H}, d 31.4 (d, PPh3, 1JRhP = 113 Hz); 11B-{1H}, d 37.0.Complex 3f: NMR (CD2Cl2) 31P-{1H}, d 31.2 (d, PPh3, 1JRhP = 114 Hz). Complex 3g: NMR (CD2Cl2) 31P-{1H}, d 33.8 (d, PPh3, 1JRhP = 117 Hz); 11B-{1H}, d 56.1. Complex 3h: NMR (CD2Cl2) 31P-{1H}, d 32.8 (d, PPh3, 1JRhP = 112 Hz). Complex 3i: NMR (CD2Cl2) 1H, d 7.68 (m, 12 H, PPh3), 7.34 (m, 18 H, PPh3), 4.97 (s, 4 H, CHCO2Me) and 3.80 (s, 12 H, CHCO2Me); 13C-{1H}, d 170.0 (s, CHCO2Me), 135.2 (m, o-C of PPh3), 130.3 (s, p-C of PPh3), 128.2 (m, m-C of PPh3), 78.1 (s, CHCO2Me), 52.8 (s, CHCO2Me), ipso-C of PPh3 not observed; 31P-{1H}, d 32.0 (d, PPh3, 1JRhP = 117 Hz); 11B-{1H}, d 36.3.Satisfactory analytical data for the isolated compounds 3b, 3c, 3e and 3i were difficult to obtain due to extremely facile loss of some solvent of crystallisation. Reaction between complex 3a and water.In a typical reaction, complex 1 (0.035 g, 0.038 mmol) and Ia (0.009 g, 0.038 mmol) were codissolved in thf (2 cm3) and the mixture stirred for 20 min. After this time the only product present was 3a as evidenced by 31P and 11B NMR spectroscopy. A solution of water in thf (0.5 cm3 of a 0.05 M solution) was then added resulting in an immediate change from pale yellow to orange. The 31P NMR analysis revealed the presence of 4 and free PPh3 as the sole phosphorus-containing species whilst 11B NMR spectroscopy showed the presence of II.The latter was also confirmed by mass spectrometry; m/z 254 (C12H8B2O5, M1) with the correct isotope pattern. Reaction between complex 3a and catechol. A sample of complex 3a was prepared in thf solution as for the analogous hydrolysis experiment. A solution of catechol (0.004 g, 0.036 mmol) in thf (0.5 cm3) was then added which also resulted in an immediate change from pale yellow to orange. The 31P NMR analysis revealed the presence of 4 and free PPh3 as the sole phosphorus-containing species whilst 11B NMR spectroscopy showed the presence of III.The latter was also confirmed by mass spectrometry; m/z 346 (C18H12B2O6, M1) with the correct isotope pattern. [RhCl(PMe3)3{B(1,2-O2C6H4)}2] 5. Method A. Complex 3a (0.013 g, 0.014 mmol) was dissolved in CD2Cl2 (0.6 cm3) at room temperature affording a pale yellow solution to which PMe3 (ca. 5 ml, 0.045 mmol) was added resulting in an immediate change to bright yellow.Analysis by multinuclear NMR spectroscopy confirmed the formation of 5 in essentially quantitative yield although it was not readily isolated from this particular reaction due to the presence of the PPh3 produced. Method B. The compounds [RhCl(PMe3)3] (0.037 g, 0.100 mmol) and Ia (0.024 g, 0.100 mmol) were codissolved in benzene (0.8 cm3) at room temperature and n-hexane (4 cm3) was then added. This mixture was stirred for 15 min resulting in the formation of a pale yellow precipitate.After removal of the solvent by syringe and drying under vacuum, the crude 5 obtained was recrystallised from toluene–n-hexane mixtures affording 5 as a colourless crystalline solid (67%), m.p. 170 8C (decomp.). Method C. Complex 7 (0.030 g, 0.063 mmol) and Ia (0.015 g, 0.063 mmol) were codissolved in thf (5 cm3) at room temperature and the mixture stirred for 30 min during which time it changed from pale orange to colourless. After this time the solvent volume was reduced by about 50% by vacuum and then cooled by means of a solid CO2–ethanol bath.Subsequent addition of n-pentane (15 cm3) afforded a white precipitate from which the remaining solvent was removed by syringe. Further washing with pentane (2 × 5 cm3) and drying by vacuum afforded 5 as a white crystalline solid (0.03 g, 76%). NMR (C6D6): 1H, d 7.21 (m, 4 H, 1,2-O2-3,6-C6H4), 6.96 (m, 4 H, 1,2- O2-4,5-C6H4), 1.52 (t, 18 H, PMe3, 2JHP = 3) and 1.22 (d, 9 H, PMe3, 2JHP = 7 Hz); 13C-{1H}, d 138.0 (s, 1,2-O2-1,2-C6H4), 137.9 (s, 1,2-O2-1,2-C6H4), 134.2 (s, 1,2-O2-3,6-C6H4), 134.0 (s, 1,2-O2-3,6-C6H4), 128.8 (s, 1,2-O2-4,5-C6H4), 128.7 (s, 1,2-O2- 4,5-C6H4), 20.0 (t, PMe3, 1JCP = 16) and 18.0 (d, PMe3, 1JCP = 18 Hz); 31P-{1H}, d 29.4 (d, PMe3, 1JRhP = 100 Hz) and 230.4 (br unresolved m, PMe3); 11B-{1H}, d 44.1 and 40.8.NMR (CD2Cl2): 31P-{1H}, d 29.7 (dd, PMe3, 1JRhP = 101, 2JPP = 30 Hz) and 229.7 (br unresolved m, PMe3); 11B-{1H}, d 44.3 and 39.8 (Found: C, 41.60; H, 5.85.C21H35B2ClO4P3Rh requires C, 41.75; H, 5.85%). [RhCl(PEt3)2{B(1,2-O2C6H4)}2] 8. A sample of PEt3 (0.095 g, 0.81 mmol) was added dropwise to a solution of complex 3a (0.230 g, 0.26 mmol) in CH2Cl2 (5 cm3). Monitoring the reaction by 31P NMR spectroscopy showed that quantitative conversion into 8 occurred after 30 min. After this time all volatiles were removed by vacuum and the crude product was recrystallised initially from toluene–n-hexane mixtures and subsequently from pentane affording 8 as a pale yellow powder (0.043 g, 28%), m.p. 85 8C (decomp.). Colourless, X-ray-quality crystals were obtained by slow evaporation of the solvent from the crude reaction mixture. NMR (C6D6): 1H, d 6.85 (m, 8 H, 1,2- O2C6H4), 2.04 [m, 12 H, P(CH2CH3)3] and 0.99 [m, 18 H, P(CH2CH3)3]; 13C-{1H}, d 149.8 (s, 1,2-O2-1,2-C6H4), 121.9 (s, 1,2-O2-3,6-C6H4), 111.4 (s, 1,2-O2-4,5-C6H4), 17.1 [t, P(CH2CH3)3, 1JCP = 14 Hz] and 8.6 [s, P(CH2CH3)3]; 31P-{1H}, d 29.0 (d, PEt3, 1JRhP = 106 Hz); 11B-{1H}, d 39.7 (Found: C, 47.10; H, 6.40.C24H38B2ClO4P2Rh requires C, 47.05; H, 6.25%). [IrCl(PEt3)2{B(1,2-O2C6H4)}2] 9/[IrCl(PEt3)3{B(1,2-O2C6- H4)}2] 10. Samples of [IrCl(PEt3)3] (0.058 g, 0.100 mmol) and Ia (0.024 g, 0.100 mmol) were codissolved in C6D6 (1 cm3) and stirred for 12 h which resulted in a gradual fading of the solution from red to pale yellow. Multinuclear NMR studies indicated essentially quantitative conversion into complex 10 although colourless, X-ray-quality crystals of 9 were obtained308 J.Chem. Soc., Dalton Trans., 1998, Pages 301–309 Table 2 Crystallographic data for complexes 3a, 3d, 8 and 9 Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 m/mm21 F(000) Crystal size/mm qmax/8 Maximum indices h, k, l Reflections measured Unique reflections Rint Transmission factors Number of refined parameters Extinction parameter x Weighting parameters a, b R9 (all data, on F2) R [data with F2 > 2s(F2)] Goodness of fit on F2 Largest difference-map features/e Å23 3a?4CH2Cl2 C52H44B2Cl9O4P2Rh 1238.4 Triclinic P1� 11.2003(6) 13.5606(7) 19.0819(10) 83.551(2) 83.064(2) 79.373(2) 2815.6(3) 2 1.461 0.83 1252 0.62 × 0.20 × 0.18 25.5 12, 16, 22 24 661 9306 0.0385 0.422–0.502 644 0.0018(2) 0.0372, 5.1991 0.1022 0.0402 (8469) 1.054 11.00, 20.75 3d?3CH2Cl2?0.5C6H14 C56H55B2Cl7O4P2Rh 1166.6 Triclinic P1� 10.939(4) 13.843(6) 19.916(7) 80.34(3) 81.99(3) 77.63(3) 2887(2) 2 1.342 0.72 1194 0.50 × 0.20 × 0.05 27.5 14, 17, 25 17 737 12 337 0.0883 0.288–0.526 642 0 0.1355, 8.18 0.3042 0.1083 (4356) 0.899 12.63, 21.84 8 C24H38B2ClO4P2Rh 612.5 Monoclinic P21/n 13.9618(14) 10.4578(11) 19.219(2) 92.337(3) 2803.8(5) 4 1.451 0.85 1264 0.38 × 0.24 × 0.24 28.4 18, 13, 25 16 886 6439 0.0258 0.739–0.862 314 0.001 33(12) 0.0242, 1.7283 0.0646 0.0289 (5463) 1.042 10.56, 20.66 9 C24H38B2ClIrO4P2 701.8 Monoclinic P21/n 13.970(2) 10.551(2) 19.155(3) 92.819(3) 2819.9(7) 4 1.653 4.97 1392 0.50 × 0.44 × 0.12 28.5 17, 13, 24 17 064 6382 0.0644 0.148–0.408 314 0.000 12(8) 0.0336, 11.7717 0.0982 0.0381 (5081) 1.067 11.44, 21.68 by slow evaporation of the solvent over a period of 18 months; 10 was not isolated.NMR (C6D6) for complex 10: 1H, d 6.93 (m, 8 H, 1,2-O2C6H4), 2.10 and 1.92 [br m, 12 H, P(CH2CH3)3] and 0.96 [br m, 18 H, P(CH2CH3)3]; 13C-{1H}, d 150.6 (s, 1,2-O2-1,2- C6H4), 121.4 (s, 1,2-O2-3,6-C6H4), 111.2 (s, 1,2-O2-4,5-C6H4), 19.2 and 18.4 [t, P(CH2CH3)3, 1JCP = 14 Hz], 9.1 and 8.7 [s, P(CH2CH3)3]; 11B-{1H}, d 30.1; 31P-{1H} (255 8C), d 231.2 (t, 1 P, PEt3, 2JPP = 25) and 218.4 (d, 2 P, PEt3, 2JPP = 25 Hz).Satisfactory analytical data for 9 were not obtained since only a small quantity of crystals were isolated. [RhCl(PMe2Ph)3{B(1,2-O2C6H4)}2] 11. Complex 2 (0.053 g, 0.040 mmol) and Ia (0.021 g, 0.088 mmol) were dissolved in CH2Cl2 (2 cm3) and the resulting pale yellow mixture stirred for 1 h after which time the quantitative formation of 3a was con- firmed by 31P-{1H} NMR spectroscopy.A sample of PMe2Ph (0.023 cm3, 0.16 mmol) was then added, resulting in no colour change, and the mixture stirred for 3 h. Analysis by 31P-{1H} NMR spectroscopy showed essentially quantitative conversion into 11. In order to isolate a solid sample of 11, the reaction mixture was cooled in a solid CO2–ethanol bath and n-hexane (5 cm3) added resulting in the formation of a white precipitate.The remaining solution was removed by syringe and the white solid washed with n-hexane (3 × 5 cm3). Difficulties in removing all traces of PPh3 prevented satisfactory analytical data from being obtained. NMR (CD2Cl2) (room temperature): 1H, d 7.31 (m, 6 H, PMe2Ph), 7.20 (m, 9 H, PMe2Ph), 7.04 (m, 4 H, 1,2-O2- 3,6-C6H4), 6.90 (m, 4 H, 1,2-O2-4,5-C6H4), 1.57 (t, 12 H, PMe2Ph, 2JHP = 4) and 1.07 (d, 6 H, PMe2Ph, 2JHP = 7 Hz); 31P- {1H}, d 23.9 (d, 2 P, PMe2Ph, 1JRhP = 101 Hz) and 222.7 (br s, 1 P, PMe2Ph); 11B-{1H}, d 40.3; 31P-{1H} (260 8C), d 23.6 (dd, 2 P, PMe2Ph, 1JRhP = 99, 2JPP = 28) and 221.1 (dt, 1 P, PMe2Ph, 1JRhP = 69, 2JPP = 28 Hz).[Rh(dppe)2{B(1,2-O2C6H4)}] 18. Complex 17 (0.015 g, 0.014 mmol) and Ia (0.007 g, 0.028 mmol) were dissolved in CH2Cl2 (5 cm3). In fact 17 is not particularly soluble in this solvent such that initially the reaction mixture consisted of an orange suspension but after stirring at room temperature for 12 h all materials had dissolved and the colour had changed to pale yellow.After this time the solvent volume was reduced by about 50% by vacuum and then the solution was cooled using a solid CO2–ethanol bath. On addition of n-hexane (15 cm3) a pale yellow precipitate formed which was allowed to settle. The remaining solvent was removed by syringe and the solid washed with n-hexane (2 × 5 cm3) and then dried under vacuum (0.011 g, 34%).Compounds 19 and 20 were prepared in an analogous manner and in similar yields from 17 and either Id or Ie respectively. Complex 18: NMR (CD2Cl2) 1H, d 7.95 (m, 16 H, Ph), 7.50 and 7.35 (m, 12 H, Ph), 7.15 and 7.00 (m, 12 H, Ph), 6.96 (m, 2 H, 1,2-O2-3,6-C6H4), 6.55 (m, 2 H, 1,2-O2-4,5-C6H4), 2.87 (br m, 4 H, CH2) and 2.23 (br m, 4 H, CH2); 31P-{1H}, d 64.2 (d, dppe, 1JRhP = 153 Hz). Complex 19: NMR (CD2Cl2) 1H, d 7.90 (m, 16 H, Ph), 7.45 and 7.35 (m, 12 H, Ph), 7.15 and 7.05 (m, 12 H, Ph), 6.70 (m, 1 H, 1,2-O2-3-Me-6-C6H3), 6.60 (m, 2 H, 1,2-O2-3-Me-4,5-C6H3), 2.85 (br m, 4 H, CH2), 2.20 (br m, 4 H, CH2) and 2.15 (s, 3 H, 1,2-O2-3-MeC6H3); 31P-{1H}, d 66.4 (d, dppe, 1JRhP = 150 Hz).Complex 20: NMR (CD2Cl2) 1H, d 7.80 (m, 16 H, Ph), 7.45 and 7.35 (m, 12 H, Ph), 7.05 and 6.95 (m, 12 H, Ph), 6.35 (m, 2 H, 1,2-O2-4-Me-3,6-C6H3), 6.30 (m, 1 H, 1,2-O2-4-Me-5-C6H3), 2.80 (br m, 4 H, CH2), 2.20 (br m, 4 H, CH2) and 2.10 (s, 3 H, 1,2-O2-4-MeC6H3); 31P-{1H}, d 66.2 (d, dppe, 1JRhP = 151 Hz).cis,mer-[RhCl(PMe3)3{B(1,2-O2-3,5-But 2C6H2)}2] 21, cis,mer- [RhCl(PMe3)3{B(1,2-O2-3-MeC6H3)}2] 22, cis,mer-[RhCl- (PMe3)3{B(tart)}2] 23 and cis,mer-[RhCl(PMe3)3{B(OCH2CMe2- CH2O)}2] 24. Compounds 21–24 were prepared from 7 and the corresponding diborane(4) compound Ic, Id, Ii and Ij according to method C described above for the preparation of 5 and with similar yields. Complex 21: NMR (C6D6) 31P-{1H}, d 29.8 (dd, PMe3, 1JRhP = 101, 2JPP = 30 Hz) and 230.3 (br unresolved m, PMe3); 11B-{1H}, d 42.0.Complex 22: NMR ([2H8]toluene) 1H, d 7.22 (m, 2 H, 1,2-O2- 3-Me-6-C6H3), 7.05 (m, 2 H, 1,2-O2-3-Me-5-C6H3), 6.97 (m, 2 H, 1,2-O2-3-Me-4-C6H3), 2.57 (s, 6 H, 1,2-O2-3-MeC6H3), 1.69J. Chem. Soc., Dalton Trans., 1998, Pages 301–309 309 (t, 18 H, PMe3, 2JHP = 4) and 1.40 (t, 9 H, PMe3, 2JHP = 6 Hz); 31P-{1H}, d 28.6 (d, PMe3, 1JRhP = 103 Hz) and 230.3 (br unresolved m, PMe3); 11B-{1H}, d 44.2 and 41.4. Complex 23: NMR (C6D6) 31P-{1H}, d 210.9 (d, PMe3, 1JRhP = 93 Hz) and 230.2 (br unresolved m, PMe3); 11B-{1H}, d 43.3 and 38.2.Complex 24: NMR (C6D6) 31P-{1H}, d 28.3 (d, PMe3, 1JRhP = 92 Hz) and 227.0 (br unresolved m, PMe3); 11B-{1H}, d 39.0. X-Ray crystallography Crystallographic data for crystals containing complexes 3a, 3d, 8 and 9 are presented in Table 2. Measurements were made at 160 K (173 K for 3d) on Siemens SMART CCD area-detector diffractometers with Mo-Ka radiation (l � = 0.710 73 Å).36 Intensities were integrated 36 from several series of exposures, each exposure ng 0.38 in w, and the total data set being more than a hemisphere in each case.Absorption corrections were applied, based on multiple and symmetry-equivalent measurements.37 The structures were solved variously by heavyatom and direct methods, and refined by least squares on F2 values for all reflections, with weighting w21 = s2(Fo 2) 1 (aP)2 1 (bP), where P = [max(Fo 2, 0) 1 2Fc 2]/3.An isotropic extinction parameter x was refined, whereby Fc9 = Fc/[1 1 (0.001xFc 2l3/sin 2q)]� �4 . The crystal for which data were collected on 3d?3CH2Cl2? 0.5C6H14 was the best of many tried but still of poor quality. The sample was prone to solvent loss and whilst this was minimised, the resulting peak profiles were less than ideal making accurate integration difficult. A half molecule of hexane solvent was present in the crystal structure although the third atom was not found in the electron-density difference map.Unresolved disorder was apparent in some of the phenyl rings. Hydrogen atoms were placed in idealised positions. CCDC reference number 186/769. See http://www.rsc.org/suppdata/dt/1998/301/ for crystallographic files in .cif format. Acknowledgements We thank the EPSRC for support (to W. C. and N. C. N.) and for studentships (for F. J. L., E. G. R., A. J. S., M. J. Q. and G. R. W.) and Natural Sciences and Engineering Research Council (NSERC) of Canada for research funding (for T.B. M.) and for a postgraduate scholarship (for P. N.). This collaboration was also supported by the NSERC/Royal Society (London) Bilateral Exchange Program (T. B. M., W. C. and N. C. N.), the British Council (Ottawa) (F. J. L. and P. N.) and the University of Newcastle upon Tyne through a Senior Visiting Research Fellowship to T. B. M. The latter also thanks the University of Bristol for a Faculty of Science Visiting Fellowship.Finally we thank Johnson Matthey for loans of rhodium and iridium salts. References 1 R. T. Baker, P. Nguyen, T. B. Marder and S. A. Westcott, Angew. Chem., Int. Ed. Engl., 1995, 34, 1336; T. Ishiyama, M. Yamamoto and N. Miyaura, Chem. Commun., 1997, 689; C. N. Iverson and M. R. Smith, Organometallics, 1997, 16, 2757. 2 (a) T. Ishiyama, N. Matsuda, N. Miyaura and A. Suzuki, J. Am. Chem. Soc., 1993, 115, 11018; (b) T. Ishiyama, N. Matsuda, M. Murata, F. Ozawa, A.Suzuki and N. Miyaura, Organometallics, 1996, 15, 713; (c) C. N. Iverson and M. R. Smith, J. Am. Chem. Soc., 1995, 117, 4403; (d) C. N. Iverson and M. R. Smith, Organometallics, 1996, 15, 5155; (e) G. Lesley, P. Nguyen, N. J. Taylor, T. B. Marder, A. J. Scott, W. Clegg and N. C. Norman, Organometallics, 1996, 15, 5137; ( f ) W. Clegg, F. J. Lawlor, G. Lesley, T. B. Marder, N. C. Norman, A. G. Orpen, M. J. Quayle, C. R. Rice, A. J. Scott and F. E. S. Souza, J. Organomet. Chem., 1997, in the press. 3 T. Ishiyama, M. Yamamoto and N. Miyaura, Chem. Commun., 1996, 2073. 4 T. Ishiyama, M. Murata and N. Miyaura, J. Org. Chem., 1995, 60, 7508; T. Ishiyama, M. Yamamoto and N. Miyaura, Chem. Lett., 1996, 1117. 5 J. F. Hartwig and X. He, Angew. Chem., Int. Ed. Engl., 1996, 35, 315; Organometallics, 1996, 15, 5350. 6 X. He and J. F. Hartwig, Organometallics, 1996, 15, 400. 7 C. Dai, G. Stringer, J. F. Corrigan, N. J. Taylor, T. B. Marder and N. C. Norman, J. Organomet.Chem., 1996, 513, 273. 8 (a) P. Nguyen, G. Lesley, N. J. Taylor, T. B. Marder, N. L. Pickett, W. Clegg, M. R. J. Elsegood and N. C. Norman, Inorg. Chem., 1994, 33, 4623; (b) R. T. Baker, J. C. Calabrese, S. A. Westcott, P. Nguyen and T. B. Marder, J. Am. Chem. Soc., 1993, 115, 4367; (c) C. Dai, G. Stringer, T. B. Marder, A. J. Scott, W. Clegg and N. C. Norman, Inorg. Chem., 1997, 36, 272. 9 C. Dai, G. Stringer, T. B. Marder, R. T. Baker, A. J. Scott, W. Clegg and N. C.Norman, Can. J. Chem., 1996, 74, 2026. 10 D. R. Lantero, D. H. Motry, D. L. Ward and M. R. Smith, J. Am. Chem. Soc., 1994, 116, 10811. 11 J. F. Hartwig and S. R. De Gala, J. Am. Chem. Soc., 1994, 116, 3661. 12 K. M. Waltz, X. He, C. Muhoro and J. F. Hartwig, J. Am. Chem. Soc., 1995, 117, 11357. 13 J. F. Hartwig and S. Huber, J. Am. Chem. Soc., 1993, 115, 4908. 14 S. A. Westcott, N. J. Taylor, T. B. Marder, R. T. Baker, N. J. Jones and J. C. Calabrese, J. Chem. Soc., Chem. Commun., 1991, 304. 15 S. A. Westcott, T. B. Marder, R. T. Baker and J. C. Calabrese, Can. J. Chem., 1993, 71, 930; P. Nguyen, H. P. Blom, S. A. Westcott, N. J. Taylor and T. B. Marder, J. Am. Chem. Soc., 1993, 115, 9329; J. R. Knorr and J. S. Merola, Organometallics, 1990, 9, 3008; R. T. Baker, D. W. Ovenall, J. C. Calabrese, S. A. Westcott, N. J. Taylor, I. D. Williams and T. B. Marder, J. Am. Chem. Soc., 1990, 112, 9399. 16 (a) F. J. Lawlor, N. C. Norman, N. L. Pickett, E. G. Robins, P. Nguyen, G. Lesley, T. B. Marder, J. A. Ashmore and J. C. Green, Inorg. Chem., in the press; (b) W. Clegg, M. R. J. Elsegood, F. J. Lawlor, N. C. Norman, N. L. Pickett, E. G. Robins, A. J. Scott, P. Nguyen, N. J. Taylor and T. B. Marder, Inorg. Chem., in the press. 17 N. C. Norman and C. R. Rice, unpublished work. 18 C. Dai, G. Lesley, T. B. Marder, N. C. Norman, C. R. Rice, E. G. Robins, W. R. Roper, F. E. S. Souza and G. R. Whittell, Chem. Rev., manuscript in preparation. 19 G. Lesley, T. B. Marder, N. C. Norman and C. R. Rice, Main Group Chem. News, 1997, 5, 4. 20 S. Sakaki and T. Kikuno, Inorg. Chem., 1997, 36, 226; Q. Cui, D. G. Musaev and K. Morokuma, Organometallics, 1997, 16, 1355. 21 I. El-Idrissi Rachidi, O. Eisenstein and Y. Jean, New J. Chem., 1990, 14, 671; J.-F. Riehl, Y. Jean, O. Eisenstein and M. Pélissier, Organometallics, 1992, 11, 729. 22 K. Burgess, W. A. van der Donk, S. A. Westcott, T. B. Marder, R. T. Baker and J. C. Calabrese, J. Am. Chem. Soc., 1992, 114, 9350. 23 (a) A. Sacco, R. Ugo and A. Moles, J. Chem. Soc. A, 1966, 1670; (b) W. MacFarlane, N. C. Norman and N. L. Pickett, unpublished work. 24 W. Gerrard, M. F. Lappert and B. A. Mountfield, J. Chem. Soc., 1959, 1529. 25 S. A. Westcott, H. P. Blom, T. B. Marder, R. T. Baker and J. C. Calabrese, Inorg. Chem., 1993, 32, 2175. 26 W. Clegg, T. B. Marder, N. C. Norman, N. L. Pickett, E. G. Robins and A. J. Scott, Acta Crystallogr., Sect. C, manuscript in preparation and refs. therein. 27 G. J. Irvine, W. R. Roper and L. J. Wright, Organometallics, 1997, 16, 2291. 28 T. B. Marder, W. C. Fultz, J. C. Calabrese, R. L. Harlow and D. Milstein, J. Chem. Soc., Chem. Commun., 1987, 1543. 29 B. Bogdanovic, W. Leitner, C. Six, U. Wilczok and K. Wittmann, Angew. Chem., Int. Ed. Engl., 1997, 36, 502. 30 W. Clegg, M. R. J. Elsegood, T. B. Marder, N. C. Norman, N. L. Pickett, E. G. Robins and A. J. Scott, Acta Crystallogr., Sect. C, in preparation. 31 T. B. Marder, unpublished work. 32 J. A. Osborn, G. Wilkinson and J. J. Mrowca, Inorg. Synth., 1972, 10, 67. 33 R. A. Jones, F. M. Real, G. Wilkinson, A. M. R. Galas, M. B. Hursthouse and K. M. A. Malik, J. Chem. Soc., Dalton Trans., 1980, 511. 34 J. R. Bleeke and W.-J. Peng, Organometallics, 1987, 6, 1576; see also A. van der Ent and A. L. Onderdelinden, Inorg. Synth., 1990, 28, 91. 35 D. P. Fairlie and B. Bosnich, Organometallics, 1988, 7, 936. 36 SMART (control) and SAINT (integration) software, Siemens Analytical X-Ray Instruments Inc., Madison, WI, 1994. 37 G. M. Sheldrick, SHELXTL version 5, Siemens Analytical X-Ray Instruments Inc., Madison, WI, 1995. Received 25th July 1997; Paper 7/05

ISSN:1477-9226    

DOI:10.1039/a705374f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 311–315 311 Synthesis and characterisation of hexa- and hepta-ruthenium carbido carbonyl clusters containing arenes derived from 1,1-diphenylethene Brian F. G. Johnson,*,a Douglas S. Shephard,a Dario Braga,b Fabrizia Grepioni b and Simon Parsons c a Department of Chemistry, The University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW b Dipartimento di Chimica ‘G. Ciamician’, dell’Università di Bologna, Via Selmi 2, 40126 Bologna, Italy c Department of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh, UK EH9 3JJ The three ruthenium arene clusters [Ru6C(CO)14(h6-PhCHMePh)] 1, [Ru6C(CO)14(h6-PhC]] CH2Ph)] 2 and [Ru7C(CO)14(m3-k:h6 :h6-C6H4CH2C6H4)] 3 have been synthesized by reaction of 1,1-diphenylethene with triruthenium dodecacarbonyl in octane under reflux.Compound 1 is a 1,1-diphenylethene hexaruthenium carbido cluster (Ru6C) derivative wherein the organo-group, hydrogenated at the olefinic centre, is bound to the cluster by a single phenyl ring in an h6 manner.Compound 2 is a similar Ru6C derivative wherein the 1,1-diphenylethene ligand remains unsaturated, whilst the third, and minor, product is the first example of a metal carbonyl cluster chelated by a diphenyl ligand and is one of the few examples of an Ru7C ‘spiked’ octahedron. The subtle electronic effects of the Ru6C co-ordination in 2 have been probed by 1H NMR spectroscopy. The solid-state structures of both the hydrogenated derivative 1 and the Ru7C ‘spiked’ octahedral cluster 3 have been determined by singlecrystal X-ray analysis.The supramolecular architecture of 3 has been examined in depth. Further to our continuing interest in the construction of organometal cluster networks and arene clusters, we have synthesized and fully characterised several compounds containing hydrocarbon frameworks derived from the ligand 1,1-diphenylethene. In the design of these potentially interesting materials we wish to introduce an unsaturated link between redox-active cluster centres thus increasing electronic communication between the metal-containing units.Dehydrogenation (and hydrogenation) of alkenes of the type RCH]] CHR9 in thermolysis reaction of [Ru3(CO)12] is a commonly observed phenomenon, usually yielding alkyne moieties co-ordinated to clusters of various nuclearities.1a Hence, for the synthesis of [Ru6C(CO)14{h6-Ph(CH)2Ph}] a direct carbonyl substitution reaction on the parent cluster [Ru6C(CO)17] was chosen.1b To avoid these problems in the thermolysis reaction and still produce an unsaturated linking group connecting the arene rings 1,1-diphenylethene was used in the production of a further group of Ru6C (arene) type compounds (Scheme 1).Results and Discussion The three Ru6C derivatives 1, 2 and 3 respectively were prepared from the reaction of [Ru3(CO)12] with an excess of 1,1- diphenylethylene in n-octane under reflux.The reaction proceeded to give moderate yields of the three products together with a small amount of [Ru6C(CO)17]. No evidence was found for the production of hydrocarbon-linked clusters. The cluster compounds were purified by TLC on silica plates, using an eluent based on the mixture 30% dichloromethane–70% hexane. Crystals of 1 and 3 suitable for X-ray determination were nucleated from dichloromethane–pentane slow diffusion. The three derivatives 1, 2 and 3 were observed as red-brown, black and brown-black bands on the thin-layer chomatographic plates respectively.After separation the yields of 1 and 2 were similar and substantially higher than that of 3 which could only be isolated in small amounts. The IR spectra of 1 and 2 in the CO region were consistent with that of an Ru6C (arene) compound bound in an h6 mode. The FAB mass spectra of 1, 2 and 3 showed molecular ion peaks at m/z 1192 (calc. 1193), 1190 (1191) and 1290 (1291) respectively, with a carbonyl regression typical of these systems, showing the loss of several CO units. 1H NMR spectra of compounds 1 and 2 The 1H NMR spectrum of compound 1 in CDCl3 under ambient conditions showed a more complex set of proton resonances than previously observed for similar systems. A multiplet centred at d 7.26 and a doublet at d 7.05 correspond to the p/m- and o-protons of the unco-ordinated phenyl ring respectively. At lower frequencies a set of five signals due to the co-ordinated ring protons may be identified.A series of decoupling experiments identified the origins of the resonances. The ortho signals, at d 5.89 and 5.34, are in distinct environments. While the meta signals are also differentiated at d 5.56 and 5.51. The para resonance overlaps with the low-frequency Scheme 1 Thermolysis products of 1,1-diphenylethene and [Ru3- (CO)12]312 J. Chem. Soc., Dalton Trans., 1998, Pages 311–315 ortho signal and is centred at d 5.32.The existence of these individual proton environments is a consequence of the proximal chiral centre, which (whether in its R or S form) denies mirror symmetry to the co-ordinated phenyl. The aliphatic protons show two signals: a quartet centred at d 3.84 corresponding to a single hydrogen attached to the tertiary carbon and a doublet at d 1.43 due to a methyl group. This led us to conclude that the double bond in the 1,1-diphenylethene ligand had undergone hydrogenation during the thermolysis reaction.This was later confirmed by the solid-state structure as determined by a single-crystal X-ray diffraction study. The source of the hydrogen remains unclear, but was postulated as being from small amounts of water in the reaction mixture. Therefore in order to evaluate this hypothesis an experiment was undertaken. The reactants were further purified; [Ru3(CO)12] was sublimed prior to use, 1,1-diphenylethene distilled and octane distilled from Na/K alloy.The reaction was then repeated as before with added D2O (0.5 cm3). Isolation of the products showed a greater degree of breakdown to metallic ruthenium than usual and reduced yields of the products. A 1H NMR spectrum of 1 in CDCl3 under ambient conditions together with a positive-ion FAB mass spectrum showed no decrease in the presence of 1H at the site of hydrogenation. The 1H NMR spectrum of compound 2 in CDCl3 under ambient conditions showed that the ligand had remained unsaturated, consistent with the positive-ion FAB mass spectrum, although the C]] C stretch could not be conclusively identified from the solution IR spectrum.The nuclear Overhauser effect NOE NMR spectrum of 2 along with the spin assign- Fig. 1 The NOE NMR spectrum of compound 2; * = solvent ments is shown in Fig. 1. As in 1 five separate environments can be identified for the co-ordinated arene protons. However they span a much greater frequency range (ca. 2.5 ppm). The large chemical shift difference between the protons Hi and Ho indicates very different environments for them. This is probably due to the steric control exercised by the C]] C double bond, holding Hi close to the carbonyl cluster and Ho away from it. Equivalence of the Hx hydrogen atoms suggests the pendant phenyl is free to rotate. However, rotation is hindered according to the NOE data, about the Phcoor]C axis. This may be due to the steric requirements of the ligand or due to some hyperconjugative effect involving the Phcoor and the alkene p system.There is evidence in the IR spectrum to suggest this may be so. A shift to lower energy of the two principal absorptions (cf. 1), indicates a larger degree of MÆCO p* back donation and therefore increased electron density in the cluster core. Solid-state molecular structure of compound 1 The solid-state structure of compound 1 is shown in Fig. 2 and some structural parameters are in Table 1.In common with the other compounds the cluster core consists of an octahedral arrangement of ruthenium metal atoms encapsulating the interstitial carbido atom. The substituted arene is co-ordinated in an h6 mode which is predominant in compounds of this type. Fourteen carbonyl ligands make up the remaining coordination sphere of the hexaruthenium cluster. The twelve ruthenium contacts lie in the range Ru(2)]Ru(4) 2.799(1) to Ru(1)]Ru(6) 3.143(1) Å. This is a similarly wide range to that observed in the parent cluster [Ru6C(CO)17].The shortest Ru]C (carbide) distance is to the metal carrying the arene [Ru(3)]C 1.921(8) Å], a phenomenon commonly observed in these systems. The Ru(3)]C (arene) distances vary little and lie in the range Ru(3)]C(1A) 2.21(1) to Ru(3)]C(3A) 2.28(1) Å whilst the co-ordinated arene carbon–carbon distances lie in the range C(4A)]C(5A) 1.38(1) to C(3A)]C(4A) Fig. 2 Solid-state molecular structure of compound 1, showing the atomic labelling scheme; the C atoms of the CO groups bear the same numbering as that of the corresponding O atomsJ.Chem. Soc., Dalton Trans., 1998, Pages 311–315 313 Table 1 Selected bond distances (Å) with estimated standard deviations (e.s.d.s) for compound 1 Ru(1)]Ru(2) Ru(2)]Ru(4) Ru(3)]Ru(6) Ru(1)]C Ru(5)]C Ru(3)]C(3A) C(3A)]C(7A) C(1A)]C(2A) C(5A)]C(6A) 2.823(1) 2.799(1) 2.862(1) 2.045(9) 2.084(8) 2.28(1) 1.52(1) 1.41(1) 1.43(1) Ru(1)]Ru(5) Ru(2)]Ru(3) Ru(4)]Ru(6) Ru(2)]C Ru(6)]C Ru(3)]C(4A) C(8A)]C(7A) C(2A)]C(3A) 2.844(1) 2.883(1) 2.907(1) 2.092(9) 2.052(9) 2.23(1) 1.53(1) 1.40(1) Ru(1)]Ru(3) Ru(2)]Ru(5) Ru(4)]Ru(5) Ru(3)]C Ru(3)]C(1A) Ru(3)]C(5A) C(7B)]C(7A) C(3A)]C(4A) 2.888(1) 2.967(1) 2.923(1) 1.921(8) 2.21(1) 2.24(1) 1.52(1) 1.44(1) Ru(1)]Ru(6) Ru(3)]Ru(4) Ru(5)]Ru(6) Ru(4)]C Ru(3)]C(2A) Ru(3)]C(6A) C(1A)]C(6A) C(4A)]C(5A) 3.143(1) 2.856(1) 2.811(1) 2.084(9) 2.25(1) 2.24(1) 1.40(1) 1.38(1) Table 2 Selected bond distances (Å) with e.s.d.s for compound 3 Ru(1)]Ru(1I) Ru(1)]Ru(4) Ru(3)]Ru(4) Ru(2)]C Ru(1)]C(1) Ru(2)]C(4) Ru(5)]C(7) C(2)]O(2) C(5)]O(5) C(8)]O(8) Ru(3)]C(10) Ru(3)]C(13) 2.9042(10) 2.8425(9) 2.8491(9) 2.079(8) 1.894(7) 1.837(7) 1.957(7) 1.132(7) 1.107(11) 1.144(13) 2.196(6) 2.216(6) Ru(1)]Ru(2) Ru(2)]Ru(3) Ru(3)]Ru(3I) Ru(3)]C Ru(1)]C(2) Ru(4)]C(5) Ru(5)]C(8) C(3)]O(3) C(6)]O(6) Ru(3)]C(9) Ru(3)]C(11) Ru(3)]C(14) 3.0486(9) 2.8599(9) 2.7832(10) 1.961(6) 1.917(7) 1.950(11) 1.882(12) 1.145(9) 1.137(7) 2.187(6) 2.246(6) 2.198(6) Ru(1)]Ru(3) Ru(2)]Ru(5) Ru(1)]C Ru(4)]C Ru(1)]C(3) Ru(4)]C(6) C(1)]O(1) C(4)]O(4) C(7)]O(7) Ru(5)]C(9) Ru(3)]C(12) 2.8497(11) 2.9174(12) 2.068(6) 2.095(8) 1.887(7) 1.907(6) 1.146(8) 1.157(8) 1.132(8) 2.113(6) 2.219(6) 1.44(1) Å.Of importance in this determination is the structural confirmation of the hydrogenation of the olefinic part of the 1,1-diphenylethene ligand. The chiral centre C(7A) displays a distorted tetrahedral geometry consistent with that of a saturated hydrocarbon together with three bond lengths to C(3A), C(8A) and C(7B) of single-bond character.However, no enantiomeric excess is observed since the space group is centrosymmetric. This may not however be the case for the bulk compound although no measurements were undertaken to ascertain this. Twelve carbonyls show terminal bonding with bond parameters typical of this type. Whilst CO(3) displays a bridging mode triangulating the Ru(1)]Ru(2) vector and CO(10) occupies a semibridging mode to Ru(4) and Ru(2) [Ru(2)]C(10) 2.37(1), Ru(4)]C(10) 1.99(1) Å].Solid-state molecular structure of compound 3 The solid-state structure of compound 3 is shown in Fig. 3 and some structural parameters are in Table 2. A crystallographic mirror plane passes through Ru(5), Ru(2) and Ru(4), making the two phenyl rings and their cluster interaction identical. The Fig. 3 Solid-state molecular structure of compound 3. Details as in Fig. 2 arrangement of the seven ruthenium metal atoms may be described as a ‘spiked’ octahedron, produced by the addition of a single ruthenium carbonyl fragment to the more orthodox hexaruthenium carbido cluster core. This arrangement of metal atoms is relatively rare, the only examples displaying stabilisation of the ruthenium ‘spike’ in an unsaturated metallocycle.2 The ‘spike’ Ru(5) is s co-ordinated to both C6 rings along with three carbonyls, which including the interaction with the cluster core produces an essentially octahedral co-ordination geometry.It is immediately apparent that the 1,1-diphenylethene ligand has been substantially transformed. The C]] C bond has been cleaved and the remaining ‘carbene’ [C(15)] hydrogenated to give a simple CH2 link between the C6 rings. Hydrogens at both C(9) positions have been replaced by an orthometallation by Ru(5) at these sites. The hydrocarbon moiety spans two cis-ruthenium cluster core atoms with each C6 ring displaying co-ordination in an h6 mode.The cluster-core metal–metal contacts span a large range. The smallest of these is between Ru(3) and its symmetryequivalent Ru(3I) (2.7832 Å), which is spanned by the hydrocarbon ligand. Whilst the longest, Ru(1)]Ru(2) 3.0486(11) Å, is an unbridged edge between an equatorial metal and the apical metal with a metal connectivity of five, which is repeated twice, due to symmetry. The ‘spike’ bond length lies in the normal range for a ruthenium metal–metal bond [Ru(2)]Ru(5) 2.9174(12) Å].Of the metal–carbide distances, the smallest is that to the arene carrying Ru(3) at 1.961(6) Å. The bonding mode of the hydrocarbon ligand is novel. The chelating diphenylmethane donates a total of fourteen electrons: twelve p electrons to the cluster core and a further two in s co-ordination to Ru(5). These s bonds to the ruthenium ‘spike’ are the shortest metal–ligand interaction at 2.113(6) Å and produce an angle of 87.3(3)8 at Ru(5).The h6-co-ordinated C6 rings are closely bound to the cluster core and give a range of metal–carbon bond lengths; Ru(3)]C(9) 2.187(6) to Ru(3)]C(11) 2.246(6) Å. The C6 rings are essentially planar and produce a dihedral angle of 110.3(8)8 at C(15). A representation of the hydrocarbon bond lengths is given in Fig. 4. The shortest C]C bond is between carbons C(11) and C(12) which, at the same time, have the longest cluster–arene bond lengths. Fourteen terminal carbonyl ligands make up the remaining coordination sphere of the cluster core and ‘spike’ and donate a total of 28e2 to the system.Together with the electrons donated by the hydrocarbon ligand this gives a total electron count of314 J. Chem. Soc., Dalton Trans., 1998, Pages 311–315 102 for the ‘spiked’ octahedron, which is in accordance with the rules for condensed polyhedra [86(Oh.closo) 1 34(M2) 2 18(one vertex shared) = 102e2].3 It is apparent that in the formation of compound 3 hydrogenolysis of the C]] C bond has occurred. A source of hydrogen for such a reaction is orthometallation of the phenyl groups and may in turn be transferred to the olefinic bond.We may exclude the possibility of 3 being the result of adventitious diphenylmethane since no 3 was isolated in the reaction of [Ru3(CO)12] with diphenylmethane.1b We are presently undertaking experiments which should shed more light upon this fascinating mechanism. Solid-state supramolecular architecture of compound 3 The solid-state architecture of compound 3 also shows some interesting intermolecular interactions.A projection through the bc plane shown in Fig. 5 shows a packing motif constructed of interlocking snakes of molecules displaying two dominant interactions which extend along the a axis. First, there is a ‘graphitic’ interaction between arenes of adjacent molecules; Fig. 6 shows a projection through the aligned C6 rings displaying the type of overlap produced.The distance between the two planes in this interaction is 3.45 Å, which is comparable to values previously observed in similar bis(arene) systems.4 Secondly, there is a short contact of the CO ? ? ?H]C type between the snake-like chains of the previously mentioned ‘graphitic’ interactions. Owing to the high symmetry of the crystal structure this short contact is repeated four times for each molecule. The O ? ? ? H distance is quite short for interactions of this type, falling in the lower range of C]H? ? ?OCO ‘hydrogen bonds’.The multibonded network thus produced is shown in Fig. 7 along with a summary of the interaction parameters. The ‘snake’ arrangement closely resembles that observed in the Fig. 4 Representation of the carbon framework in compound 3; bond lengths in Å Fig. 5 Solid-state architecture of compound 3. The carbonyls have been removed for clarity and cluster cores are represented by large spheres positioned by their centre of mass solid-state structure of [Ru6C(CO)11(h6-C6H6)(m3-h2 :h2 :h2- C6H6)]. The geometry of the two ligands with respect to the cluster, albeit very different from that of 3, generates similar steric requirements and makes the molecules very similar in shape hence in packing requirements.Conclusion Compound 1 is an interesting example of metal carbonylmediated hydrogenation. Whilst the source of the hydrogen has not been pinpointed it is likely that reforming-type reactions may take place with the hydrocarbon solvent even at this low temperature.Compound 2 may serve as a precursor to a cluster network connected by the unsaturated C]] C link. Compound 3 is the first example of a chelating diphenyl ligand on a carbonyl cluster; it is also one of a very rare collection of spiked octahedral cluster compounds. Experimental All reactions were carried out with the exclusion of air using solvents distilled under an atmosphere of nitrogen.Subsequent work-up of products was achieved without precautions to exclude air. Infrared spectra were recorded on a Perkin-Elmer 1710 series FTIR instrument in CH2Cl2 using NaCl cells (0.5 nm path length). Positive-ion fast atom bombardment mass spectra were obtained using a Kratos MS50TC spectrometer, with CsI as calibrant, 1H NMR spectra in CDCl3 using a Bruker AM400 instrument, referenced to internal SiMe4. Products were separated by thin-layer chromatography using plates supplied by Merck (0.25 mm layer of Kieselgel 60 F254).The compound [Ru3(CO)12] was prepared by the literature procedure. 5 1,1-Diphenylethylene from Aldrich was used without further purification. Fig. 6 Projection through the C6 rings in compound 3 showing the overlap geometry [interplanar angle 0(2)8 with an offset distance of 1.88(4) Å] Fig. 7 The CO ? ? ?H]C type interactions between molecules of compound 3; distances in ÅJ. Chem. Soc., Dalton Trans., 1998, Pages 311–315 315 Synthesis and characterisation of [Ru6C(CO)14(Á6-PhCHMe- Ph)] 1, [Ru6C(CO)14(Á6-Ph]] CH2Ph)] 2 and [Ru7C(CO)14- (Ï3-Í:Á6 :Á6-C6H4CH2C6H4)] 3 The compound [Ru3(CO)12] (1.00 g) was refluxed in n-octane (40 cm3) with 1,1-diphenylethene (300 mg) for 6 h.Infrared spectroscopy indicated complete consumption of the starting material. The solvent was removed in vacuo and the residue separated by TLC using dichloromethane–hexane (3 : 7) as eluent. Two major red-brown bands and a minor darker band were extracted with dichloromethane and characterised (average yields) (75 1), (100 2) and (ca. 5 mg 3). Spectroscopic data: 1, IR (CH2Cl2) n(CO) 2076m, 2035 (sh), 2025vs, 1985w, 1968w and 1816w (br) cm21; 1H NMR (CDCl3) d 7.26 (m, 3 H), 7.05 (m, 2 H), 5.89 (m, 1 H), 5.56 (m, 1 H), 5.51 (m, 1 H), 5.34 (m, 1 H), 5.32 (m, 1 H), 3.84 (q, 1 H) and 1.43 (d, 3 H); m/z 1192 (M1; calc. 1193) (Found: C, 30.1; H, 1.2. Calc. for C29H14O14Ru6: C, 29.2; H, 1.18%); 2, IR (CH2Cl2) n(CO) 2070m, 2033 (sh), 2023vs, 1996m (br) and 1816w (br) cm21; 1H NMR (CDCl3): d 7.52 (m, 2 H), 7.39 (m, 3 H), 6.31 (m, 1 H), 6.01 (m, 1 H), 5.81 (m, 1 H), 4.71 (m, 1 H), 4.47 (m, 1 H), 3.88 (m, 1 H) and 2.57 (m, 1 H); m/z 1190 (M1, calc. 1191) (Found: C, 31.2; H, 1.15. Calc. for C29H12O14Ru6: C, 29.25; H, 1.02%); 3, IR (CH2Cl2) n(CO) 2067m, 2055 (sh), 2023vs and 1970s cm21; m/z 1278 (M1, calc. 1279). Crystallography Crystal data for compound 1. C29H12O14Ru6, M = 1192.82, monoclinic, space group P21/a, a = 11.644(4), b = 16.546(3), c = 17.650(2) Å, b = 105.56(3)8, U = 3275.8(13) Å3, Z = 4, Dc = 2.419 Mg m23, l = 0.710 73 Å, T = 150(2) K, m = 2.764 mm21.Data were collected on a Stöe-Stadi four-circle diffractometer equipped with an Oxford Cryosystems low-temperature device, using a crystal of dimensions 0.16 × 0.20 × 0.15 mm, mounted directly from solution, by the q–w method (3 < 2q < 508). Of a total of 6127 reflections collected, 5740 were independent (Rint = 0.0397).Data were corrected for absorption using y scans (Tmax = 0.659, Tmin = 0.559).6 The structure was solved by direct methods (SHELXTL PLUS)7 and refined by full-matrix least-squares analysis on F2 with R1 [F > 4s(F)] and wR2 (all data) to 0.0499 and 0.0946, respectively. The pendant phenyl [C(8A) to C(13A)] shows considerable disorder over several positions. Since a satisfactory model could not be produced the AFIX 66 command was used to fit the C atoms with a regular hexagon in the highest-occupancy orientation.Hydrogen atoms were placed in fixed calculated positions. Largest peak and hole in final difference map 12.033 and 21.671 e Å23. The residual peaks were all in the proximity of the metal atoms, indicating an only partially successful experimental absorption correction. Crystal data for compound 3. C28H10O14Ru7, M = 1277.85, orthorhombic, space group Pbcm, a = 9.664(3), b = 21.556(6), c = 14.748(3) Å, U = 3072.3(14) Å3, Z = 4, Dc = 2.763 Mg m23, l = 0.710 73 Å, T = 150(2) K, m = 3.419 mm21.Data were collected as for compound 1 using a crystal of dimensions 0.10 × 0.12 × 0.15 mm. Of a total of 4622 reflections collected, 2108 were independent (Rint = 0.0607). The structure was solved and refined as for 1 to R1 and wR2 0.0336 and 0.0912, respectively. The H atoms were placed in fixed calculated positions. Largest peak and hole in final difference map 10.850 and 21.495 e Å23. CCDC reference number 186/772. Acknowledgements We gratefully acknowledge financial support from NATO, EPSRC and The University of Edinburgh. References 1 (a) C. M. Martin, Ph.D. Thesis, University of Edinburgh, 1995 and refs. therein; J. Wang, M. Sabat, L. J. Lyons and D. F. Shriver, Inorg. Chem., 1991, 30, 382; (b) A. J. Blake, P. J. Dyson, B. F. G. Johnson, D. Reed and D. S. Shephard, J. Chem. Soc., Dalton Trans., 1995, 843. 2 D. Braga, F. Grepioni, E. Parisini, P. J. Dyson, D. Reed, P. E. Gaede, J. J. Byrne and B. F. G. Johnson, Organometallics, 1995, 14, 4892; A. J. Blake, P. J. Dyson, P. E. Gaede, D. Braga, E. Parisini and B. F. G. Johnson, J. Chem. Soc., Dalton Trans., 1995, 3431. 3 D. M. P. Mingos, J. Chem. Soc., Chem. Commun., 1983, 706. 4 D. Braga, P. J. Dyson, F. Grepioni, B. F. G. Johnson and M. J. Calhorda, Inorg. Chem., 1994, 33, 3218. 5 B. F. G. Johnson, J. Lewis and P. A. Kilty, J. Chem. Soc. A, 1968, 2859. 6 A. C. T. North, D. C. Phillips and F. S. Mathews, Acta Crystallogr., Sect. A, 1968, 24, 351. 7 G. M. Sheldrick, SHELXTL PLUS, Siemens Analytical Instruments, Madison, WI, 1990. Received 6th October 1997; Paper 7/07179E

ISSN:1477-9226    

DOI:10.1039/a707179e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 317–320 317 Synthesis and characterization of Group 11 and 12 complexes containing a new thioether-functionalized and pyridine-based bis(phosphine) ligand, 2,6-bis[2-(diphenylphosphino)ethylsulfanylmethyl] pyridine Shan-Ming Kuang,a Zheng-Zhi Zhang *,b and Thomas C. W. Mak*,a a The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong b Elemento-Organic Chemistry Laboratory, Nankai University, Tianjin, China The new ligand 2,6-bis[2-(diphenylphosphino)ethylsulfanylmethyl]pyridine, 2,6-(Ph2PCH2CH2SCH2)2C5H3N (L1), has been synthesized.Reaction of [Cu(MeCN)4][CF3SO3] or AgNO3 with 1 molar equivalent of L1 gave [CuL1][CF3SO3] 1 or [AgL1][NO3] 2, in good yield. Reaction of equimolar quantities of L1 and AuI, followed by precipitation with AgO3SCF3, gave [AuL1][CF3SO3] 3. In the crystal structure of 2?H2O, L1 co-ordinates to Ag via a P2S2 donor set in a distorted tetrahedral geometry.Reaction of M(O3SCF3)2 (M = Zn or Cd) with 1 molar equivalent of L1 gave [ML1(O3SCF3)2] (M = Zn 4 or Cd 5). Crystal structure analysis of 5 showed that the molecule has symmetry 2, with all five donor atoms of L1 and a pair of monodentate CF3SO3 2 ligands arranged in an unusual distorted pentagonal bipyramidal co-ordination geometry about the cadmium centre. Acyclic phosphine ligands are well known to form stable complexes with many metal ions, whereas acyclic thioether complexes tend to be less stable and often hydrolyse readily.1 As the NS2 donor set in 2,6-bis(R-sulfanylmethyl)pyridine has been found to be good for the stabilization of transition-metal ions,2 we reasoned that the incorporation of heteroatom donors, such as nitrogen or sulfur, on sites within a diphosphine bridge might result in transition-metal complexes co-ordinated by sulfur (or nitrogen) and the phosphorus centres.We anticipated that, as phosphines are better s donors compared to thioethers, stabilization of a mixed phosphine–thioether co-ordination complex could be achieved by inhibiting decomplexation of the more weakly bound thioether in solution. In this context, recent reports by Darensbourg and co-workers 3 and Reid and coworkers 4 have demonstrated the development and coordination chemistry of dithiobis(phosphine) chelates.We report here the synthesis and characterization of Group 11 and 12 complexes with a new thioether-functionalized and pyridine-based bis(phosphine) ligand, 2,6-bis[2-(diphenylphosphino) ethylsulfanylmethyl]pyridine, 2,6-(Ph2PCH2CH2SCH2)2- C5H3N (L1), which displays an unusual co-ordination mode toward Cd21.Experimental General procedure, measurement and materials All reactions were routinely carried out under a nitrogen atmosphere using Schlenk techniques. The solvents were puri- fied by standard methods. The 1H and 13C-{1H} NMR spectra were recorded on a Bruker-300 spectrometer using SiMe4 as the external standard and CDCl3 as solvent, 31P-{1H} NMR spectra on a Bruker-500 spectrometer at 202.45 MHz using (PhO)3P as the external standard and CDCl3 as solvent and mass spectra on a Hewlett-Packard 5989B spectrometer. The compounds [Cu(MeCN)4][CF3SO3] 5 and M(O3SCF3)2 (M = Zn or Cd)6 were prepared by the literature procedures.Preparations 2,6-Bis[2-(diphenylphosphino)ethylsulfanylmethyl]pyridine, L1. A solution of LiBun in hexane (1.60 M, 17.0 cm3) was added dropwise to a solution of Ph2PH (4.65 g, 25 mmol) in tetrahydrofuran (thf, 50 cm3) at 278 8C.To this mixture, a solution of ethylene sulfide (thiirane) (1.50 cm3, 25 mmol) in thf (20 cm3) was added. The resulting solution was continuously stirred until 0 8C was reached, and a solution of 2,6-bis(chloromethyl)- pyridine (2.20 g, 12.5 mmol) in thf (80 cm3) was then added over a period of 3 h with the temperature maintained at 0 8C. After the addition the mixture was stirred at room temperature for 48 h.The thf was removed in vacuum and water (100 cm3) added. The water phase was next extracted with diethyl ether (3 × 50 cm3) and the organic phase dried with anhydrous Na2SO4 overnight. Most of the diethyl ether was removed in vacuum and hexane (100 cm3) was added. Cooling to 230 8C for 8 h yielded a colourless solid. Recrystallization from CH2Cl2–hexane afforded L1 as an analytically pure product, 5.30 g (71%) (Found: C, 70.24; H, 5.88; N, 2.27. C35H35NP2S requires C, 70.56; H, 5.92; N, 2.35%), m.p. 52–53 8C. 1H NMR (CDCl3): d 7.52 (t, J = 3.5, 1 H), 7.36–7.25 (m, 20 H), 7.05 (d, J = 2.2 Hz, 2 H), 3.73 (s, 4 H), 2.50 (m, 4 H) and 2.26 (m, 4 H). 13C-{1H} NMR (CDCl3): d 28.73 (d, J = 20.3), 28.96 (d, J = 14.9 Hz), 38.56 (s) and 121.65–138.57 (m). 31P-{1H} NMR: d 24.54. FAB mass spectrum: m/z = 596; Calc. 595 for (Ph2PCH2CH2- SCH2)2C5H3N. [CuL1][CF3SO3] 1. To a solution containing compound L1 (0.30 g, 0.5 mmol) in CH2Cl2 (20 cm3) was added solid [Cu- (MeCN)4][CF3SO3] (0.19 g, 0.5 mmol).The resulting solution was stirred at room temperature for 2 h. Subsequent diffusion of diethyl ether into the concentrated solution gave complex 1 as air-stable colourless crystals (yield 0.34 g, 84%) (Found: C, 53.21; H, 4.71; N, 1.78. C36H35CuF3NO3P2S3 requires C, 53.49; H, 4.36; N, 1.73%). 31P-{1H} NMR: d 34.72. [AgL1][NO3] 2. The procedure used was similar to that above, except that AgNO3 (0.09 g, 0.5 mmol) was employed instead of [Cu(MeCN)4][CF3SO3].Recrystallization of the product from CH2Cl2–diethyl ether afforded complex 2?H2O as colourless crystals. Yield: 0.29 g (76%) (Found: C, 54.99; H, 4.61; N, 3.55. C35H35AgN2O3P2S2?H2O requires C, 54.86; H, 4.72; N, 3.57%). 31P-{1H} NMR: d 43.14. [AuL1][CF3SO3] 3. The complex K[AuCl4]?2H2O (0.10 g, 0.25 mmol) was reduced to AuI by 2,29-thiodiethanol (0.06 g, 0.5318 J. Chem. Soc., Dalton Trans., 1998, Pages 317–320 mmol) in methanol (20 cm3) for 30 min.Compound L1 (0.15 g, 0.25 mmol) in CH2Cl2 (10 cm3) was added and stirred for 10 min, and then AgO3SCF3 (0.26 g, 1.0 mmol) in methanol (20 cm3) was added to the mixture and stirred for 30 min. Filtration followed by solvent removal and subsequent recrystallization from CH2Cl2–hexane afforded complex 3 as colourless crystals. Yield: 0.15 g (81%) (Found: C, 45.78; H, 3.77; N, 1.41. C36H35AuF3NO3P2S3 requires C, 45.91; H, 3.75; N, 1.49%). 31P- {1H} NMR: d 42.91.[ZnL1][CF3SO3]2 4. To a solution containing compound L1 (0.30 g, 0.5 mmol) in CH2Cl2 (20 cm3) was added solid Zn(O3- SCF3)2 (0.18 g, 0.5 mmol). The resulting solution was stirred at room temperature for 2 h. Subsequent diffusion of diethyl ether into the concentrated solution gave complex 4 as air-stable colourless crystals (yield 0.40 g, 77%) (Found: C, 43.95; H, 3.67; N, 1.33. C37H35F6NO3P2S4Zn?CH2Cl2 requires C, 43.71; H, 3.57; N, 1.34%). 31P-{1H} NMR: d 56.53. [CdL1(O3SCF3)2] 5.The procedure used was similar to that above, except that Cd(O3SCF3)2 (0.21 g, 0.5 mmol) was used instead of Zn(O3SCF3)2. Recrystallization of the product from CH2Cl2–hexane afforded complex 5 as colourless crystals. Yield: 0.32 g (64%) (Found: C, 43.37; H, 3.49; N, 1.34. C37H35- CdF6NO6P2S4 requires C, 44.16; H, 3.51; N, 1.39%). 31P-{1H} NMR: d 55.09. X-Ray crystallography Intensity data for complexes 2?H2O and 5 were collected at 294 K in the variable w-scan mode on a four-circle diffractometer (Siemens R3m/V) using Mo-Ka radiation (l = 0.710 73 Å, 50 kV, 25 mA; 2qmin = 3, 2qmax = 558).Empirical absorption corrections were applied by fitting a pseudo-ellipsoid to the y-scan data of 25 selected strong reflections over a range of 2q angles.7a Structure solution by the direct method yielded the positions of all non-hydrogen atoms, which were refined using anisotropic thermal parameters. Hydrogen atoms were all generated geometrically (C]H bond lengths fixed at 0.96 Å), assigned appropriate isotropic thermal parameters, and allowed to ride on their parent carbon atoms.All the H atoms were held stationary and included in the structure-factor calculation in the final stage of full-matrix least-squares refinement. All computations were performed on an IBM-compatible 486 personal computer with the SHELTX PC, version 5.03, program package.7b Information concerning X-ray data collection and structure refinement of all compounds is summarized in Table 1.CCDC reference number 186/780. Results and Discussion The synthesis of a new thioether-functionalized and pyridinebased bis(phosphine) ligand, namely 2,6-bis[2-(diphenylphosphino) ethylsulfanylmethyl]pyridine (L1), was accomplished in two steps in good yield, as outlined in Scheme 1. Reaction of Ph2PLi (prepared ‘in situ’ from Ph2PH and LiBun) with ethylene sulfide at low temperature gave the lithium 2-diphenylphosphinoethanethiolate salt, which then reacted with 2,6-bis- (chloromethyl)pyridine to give the designed phosphine ligand.The structure of 2,6-(Ph2PCH2CH2SCH2)2C5H3N, L1, was confirmed by elemental analysis and 1H, 13C-{1H}, 31P-{1H} NMR spectroscopy and FAB mass spectrometry. In the 1H NMR spectrum the SCH2C5H3N methylene protons appeared as a singlet at d 3.73 and two groups of signals attributed to the SCH2CP and SCCH2P methylene protons coupled with the phosphorus atoms were observed at d 2.50 and 2.26.In the 13C- {1H} NMR spectrum the SCC5H3N carbon atom appeared as a singlet at d 38.56, whereas the SCCP carbon atoms appeared as a pair of doublets centred at d 28.73 (J = 20.3) and 28.96 (J = 14.9 Hz). On the basis of literature data for P]C coupling constants 8 and the observed chemical shifts for related phosphine-containing ligands, we assigned the first and second doublets to the carbon atoms located in the a and b positions, respectively, with respect to the phosphorus atom.The FAB mass spectrum showed the molecular ion at m/z = 596, and the 31P-{1H} NMR spectrum exhibited a singlet at d 24.54. Reaction of [Cu(MeCN)4][CF3SO3] or AgNO3 with 1 molar equivalent of L1 in degassed dichloromethane, followed by precipitation with diethyl ether, gave [CuL1][CF3SO3] 1 or [AgL1][NO3] 2, as white solids in good yield. Reaction of equimolar amounts of L1 and AuI, generated in situ by the reduction of K[AuCl4] with 2,29-thiodiethanol in methanol, gave a colourless solution at room temperature.Addition of AgO3SCF3 to the solution precipitated [AuL1][CF3SO3] 3, as a white solid. The 31P-{1H} NMR spectra of complexes 1 and 2 at 298 K showed a singlet at d 34.72 and 43.14, respectively, and no Ag]P coupling was observed for 2. For complex 3 the 31P-{1H} NMR spectrum displayed a high-frequency shift of 47.4 ppm relative to the free phosphine. This shift is similar to those of the complexes [Au{(Ph2PCH2CH2SCH2)2}][PF6] (49.2 ppm) and [Au{(Ph2PCH2CH2SCH2)2CH2}][PF6] (46.1 ppm),4b both of which involve averaged P2 co-ordination in solution.In view of the similarity of these species, we expect that in the solid state 3 also adopts a similar primary P2 co-ordination about AuI and a distorted linear geometry. Crystals of [AgL1][NO3]?H2O suitable for single-crystal Xray study were obtained by layering a solution of the complex in CH2Cl2 at ca. 220 8C with toluene. The structure of the molecular cation with the atom numbering scheme is depicted in Fig. 1. The co-ordination geometry around silver(I) may be described as a very distorted tetrahedron with a P]Ag]P angle of 144.4(1)8 (Table 2), far higher than the idealized value of 109.58. This is certainly caused by the repulsion between two phenyl rings [C(26) ? ? ? C(36) 3.690 Å] which has the further consequence of narrowing the S]Ag]P bond angles to 80.2(1) and 81.3(1)8. A similar effect has been reported in [Ag(Ph2PScheme 1 S N Cl Cl Ph2PH Ph2PLi Ph2P SLi N S PPh2 S PPh2 LiBun Fig. 1 Perspective view of the cation in [Ag{(Ph2PCH2CH2SCH2)2- C5H3N}][NO3]?H2O, 2?H2O. The atoms are shown as 35% thermal ellipsoidsJ. Chem. Soc., Dalton Trans., 1998, Pages 317–320 319 CH2CH2SEt)2][ClO4] with a P]Ag]P angle of 148.9(1)8.9 The Ag(1) ? ? ? N(1) distance of 2.689 Å, much longer than the corresponding distance of 2.368(6) Å in [AgL2][PF6] [L2 = 6,9,12- trioxa-3,15-dithia-21-azabicyclo[15.3.1]henicosa-1(21),17,19- triene],10 indicates that the Ag ? ? ? N interaction is very feeble, which is consistent with the fact that the nitrogen lone pair does not point directly toward the silver atom (Fig. 1). The Ag]P distances of 2.455(3) and 2.448(3) Å are within the expected range for silver tertiary phosphine complexes. The Ag]S distances of 2.869(3) and 2.846(3) Å, which are longer than 2.694(2) Å in [Ag(Ph2PCH2CH2SEt)2][ClO4] 9 and 2.589(2) Å (average) in [Agn(PhSCH2CH2CH2SPh)2n][BF4]n?0.5nH2O,11 suggest that the silver ion is weakly bound to the sulfur atoms.Reactions of M(O3SCF3)2 (M = Zn or Cd) with 1 molar equivalent of L1 in dichloromethane at room temperature gave a colourless solution which on addition of diethyl ether gave [ML1(O3SCF3)2] (M = Zn 4 or Cd 5). The 31P-{1H} NMR spectra of 4 and 5 at 298 K showed a singlet at d 56.53 and 55.09, respectively, and no Cd]P coupling was observed for 5. Diffraction-quality crystals of [CdL1(O3SCF3)2] 5 were obtained by vapour diffusion of diethyl ether into a solution of the complex in CH2Cl2 at room temperature. A perspective view of the molecular structure of 5, which possesses a crystallographically imposed two-fold axis passing through Cd, N and C(6), is illustrated in Fig. 2. The co-ordination geometry about the cadmium centre is a distorted pentagonal bipyramid, with Table 1 Crystal and structural data for complexes 2?H2O and 5 Formula M Crystal system Space group a/Å b/Å c/Å U/Å3 ZF (000) Dc/g cm23 m/cm21 Goodness of fit No.unique reflections (Rint) No. observed reflections [|F | > 4s(F)] No. variables, p RF a R9F 2 b C35H35AgN2O3P2S2? H2O 2?H2O 783.6 Orthorhombic P212121 9.875(1) 12.585(5) 28.362(3) 3524.7(12) 4 1608 1.477 0.821 1.22 4909 (0.027) 3183 410 0.053 0.087 C37H35CdF6NO6P2S4 5 1006.2 Trigonal P3221 18.072(3) 18.072(3) 12.099(2) 3425(2) 3 1524 1.464 0.797 1.10 4876 (0.030) 4561 263 0.049 0.052 a S(|Fo| 2 |Fc|)/S|Fo|. b {w[S(|Fo| 2 |Fc|)2]/S|Fo|2}� �� .Table 2 Selected bond lengths (Å) and angles (8) of complexes 2?H2O and 5 2?H2O Ag]P(1) Ag]S(1) P(1)]Ag]P(2) P(1)]Ag]S(2) S(1)]Ag]S(2) 2.455(3) 2.869(3) 144.4(1) 110.5(1) 142.7(1) Ag]P(2) Ag]S(2) P(1)]Ag]S(1) P(2)]Ag]S(1) P(2)]Ag]S(2) 2.448(3) 2.846(3) 80.2(1) 111.2(1) 81.3(1) 5 Cd]P(1) Cd]O(1) P(1)]Cd]S(1) S(1)]Cd]O(1) S(1)]Cd]N P(1)]Cd]P(1a) O(1)]Cd]O(1a) P(1)]Cd]O(1a) 2.590(1) 2.455(2) 79.9(1) 75.8(1) 70.1(1) 166.8(1) 69.5(2) 93.8(1) Cd]S(1) Cd]N(1) P(1)]Cd]O(1) P(1)]Cd]N O(1)]Cd]N S(1)]Cd]S(1a) P(1)]Cd]S(1a) S(1)]Cd]O(1a) 2.821(1) 2.695(3) 97.1(1) 83.4(1) 145.2(1) 140.1(1) 95.6(1) 143.7(1) coplanar O(1), S(1), N, S(1a) and O(1a) atoms at the equatorial sites, and P(1) and P(1a) occupying the axial positions.The seven-co-ordinate geometry observed in this complex is largely a result of the constraints imposed by the pentadentate ligand. Since there is no ligand-field stabilization effect in Cd21, the stereochemistry of its complexes is in general determined by ionic size, electrostatics, and covalent bonding energies.13 Owing to its size, Cd21 commonly has a co-ordination number of six as in CdCl2, [CdCl2(NH3)2], [CdCl(OH)], K4[CdCl4], CdI2 and Cd(OH)2.14 However, a seven-co-ordinate, distorted pentagonal bipyramidal complex of Cd21 containing a thioether ligand is known, namely [Cd([15]aneS5)][ClO4]2?H2O ([15]- aneS5 = 1,4,7,10,13-pentathiacyclopentadecane).15 The P(1)]Cd]S(1) and P(1)]Cd]N angles are somewhat acute [79.9(1) and 83.4(1)8, respectively], while P(1)]Cd]S(1a) and P(1)]Cd]O(1) are somewhat obtuse [95.6(1) and 97.1(1)8].This distortion is attributable to the geometrical constraints imposed by the ligand, as the ethylene bridges between S and P atoms do not allow P(1) and P(1a) to pull away far enough from each other. The P(1)]Cd]P(1a) angle of 166.8(1)8 is accordingly less than the ideal value of 1808. The P]Cd bond length of 2.590(1) Å is close to the sum of covalent radii for cadmium and phosphorus (1.48 1 1.10 = 2.58 Å) 16 and also comparable to 2.602(2) Å found in [Cd{P(C6H11)3}2][NO3]2?CH2Cl2.17 The Cd]S bond length of 2.821(1) Å is comparable to those of [Cd([15]aneS5)][ClO4]2?Cd]Sav 2.76 Å) 15 and significantly longer than 2.703(1) Å in the six-co-ordinate complex [{CdL2Cl2?H2O}2] [L2 = 2,6- bis(ethylsulfanylmethyl)pyridine] 18 and four-co-ordinate complex [Cd([16]aneS4)][ClO4]2 (Cd]Sav 2.65 Å) ([16]aneS4 = 1,5,9,13-tetrathiacyclohexadecane).19 It has been observed that in mercury(II) thioether complexes 20 the metal–sulfur bond lengths are a function of the number of donor atoms.As the co-ordination number of the metal centre goes up, its bonds to sulfur are lengthened. Hence it is not surprising that the seven-co-ordinate complex 5 has such long Cd]S bonds compared to those of an analogous six- or four-co-ordinate complex. The Cd]N bond distance of 2.695(3) Å is also longer than 2.380(3) Å in the six-co-ordinate, dimeric complex [{CdL2Cl2?H2O}2].18 Acknowledgements This work is supported by Hong Kong Research Grants Council Earmarked Grant Ref.No. CUHK 311/94P and the National Natural Science Foundation of China. Fig. 2 An ORTEP12 view of the [Cd{(Ph2PCH2CH2SCH2)2C5H3N}- (O3SCF3)2] molecule, 5. The atoms are shown as 35% thermal ellipsoids. Note that a two-fold symmetry axis passes through the Cd, N and C(6) atoms320 J. Chem. Soc., Dalton Trans., 1998, Pages 317–320 References 1 S.G. Murray and F. R. Hartley, Chem. Rev., 1981, 81, 365. 2 See, for example, F. Teixidor, L. Escriche, J. Casabó, E. Molins and C. Miravitlles, Inorg. Chem., 1986, 25, 4060; J. Casabó, L. Escriche, S. Alegret, C. Jaime, C. Perez-Jimenez, L. Mestres, J. Rius, E. Molins, C. Miravitlles and F. Teixidor, Inorg. Chem., 1991, 30, 1893; F. Teixidor, G. Sánchez-Castelló, N. Lucena, L. Escriche, R. Kivekäs, M. Sundberg and J. Casabó, Inorg. Chem., 1991, 30, 4931; G.Ferguson, K. E. Matthes and D. Parker, Angew. Chem., Int. Ed. Engl., 1987, 26, 1162; M. J. Gunter, L. N. Mander, K. S. Murray and P. E. Clark, J. Am. Chem. Soc., 1981, 103, 6784; B. Girmay, J. D. Kilburn, A. E. Underhill, K. S. Varma, M. B. Hursthouse, M. E. Harman, J. Becher and G. Bojesen, J. Chem. Soc., Chem. Commun., 1989, 1406. 3 Y. Hsiao, S. S. Chojnacki, P. Hinton, J. H. Reibenspies and M. Y. Darensbourg, Organometallics, 1993, 12, 870. 4 (a) N. R. Champness, R.J. Forder, C. S. Frampton and G. Reid, J. Chem. Soc., Dalton Trans., 1996, 1261; (b) A. M. Gibson and G. Reid, J. Chem. Soc., Dalton Trans., 1996, 1267. 5 G. J. Kubas, Inorg. Synth., 1979, 19, 90. 6 J. R. Lockemeyer, A. L. Rheingold and J. E. Bulkowski, Organometallics, 1993, 12, 256. 7 (a) G. Kopfmann and R. Huber, Acta Crystallogr., Sect. A, 1968, 24, 348; (b) J. A. Ibers and W. C. Hamilton, in International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4, pp. 55, 99, 149; vol. 3, p. 278. 8 L. M. Green and D. W. Meek, Polyhedron, 1990, 9, 35. 9 P. D. Bernardo, M. Tolazzi and P. Zanonato, Inorg. Chim. Acta, 1994, 215, 199. 10 G. Ferguson, A. Craig, D. Parker and K. Matthes, Acta Crystallogr., Sect. C, 1989, 45, 741. 11 J. B. Black, N. R. Champness, W. Levason and G. Reid, J. Chem. Soc., Chem. Commun., 1995, 1277. 12 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 13 F. A. Cotton and G. Wilkinson, Advanced Inorganic chemistry, 5th edn., Wiley, New York, 1988, p. 598. 14 A. F. Wells, Structural Inorganic Chemistry, Oxford Press, 3rd edn., 1962. 15 W. N. Setzer, Y. Tang, G. J. Grant and D. G. VanDerveer, Inorg. Chem., 1992, 31, 1116. 16 L. Pauling, The Nature of the Chemical Bond, Cornell University Press, New York, 3rd edn., 1960. 17 D. Dakternieks and B. F. Hoskins, Aust. J. Chem., 1986, 39, 7. 18 F. Teixidor, L. Escriche, I. Rodriguez, J. Casabó, J. Rius, E. Molins, B. Martínez and C. Miravitlles, J. Chem. Soc., Dalton Trans., 1989, 1381. 19 W. N. Setzer, Y. Tang, G. J. Grant and D. G. VanDerveer, Inorg. Chem., 1991, 30, 3652. 20 W. N. Setzer, Q. Guo, G. J. Grant, J. L. Hubbard, R. S. Glass and D. G. VanDerveer, Heteroatom Chem., 1990, 1, 317. Received 8th September 1997; Paper 7/06543D © Copyright 1998 by the Royal Society of Chemistry

ISSN:1477-9226    

DOI:10.1039/a706543d

出版商:RSC    

年代:1998

数据来源: RSC