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. 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