DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2159–2169 2159 Heterobimetallic alkoxysilyl cationic complexes: investigations into the displacement of a Ï-Á2-Si,O bridge by functional phosphine ligands Joël Blin,a Pierre Braunstein,a Jean Fischer,b Guido Kickelbick,c Michael Knorr,a Xavier Morise a and Tobias Wirth a a Laboratoire de Chimie de Coordination (UMR 7513 CNRS), Université Louis Pasteur, 4 rue Blaise Pascal, F-67070 Strasbourg Cédex, France b Laboratoire de Cristallochimie et de Chimie Structurale (UMR 7513 CNRS), Université Louis Pasteur, 4 rue Blaise Pascal, F-67070 Strasbourg Cédex, France c Institut für Anorganische Chemie, Technische Universität Wien, Getreidemarkt 9/153, A-1060 Wien, Austria Received 13th January 1999, Accepted 5th May 1999 The lability of the SiOÆM interaction unique to some bimetallic complexes may confer hemilabile properties to the Si(OR)3 ligand and various bifunctional phosphines P–Z have been used in order to evaluate the possible competition for co-ordination between the bridging SiOÆM interaction and P–Z chelation.Thus, treatment of the heterobimetallic complexes [(OC)3Fe{m-Si(OMe)2(OMe)}(m-dppm)MCl] (M = Pd 4 or Pt 6; dppm = Ph2PCH2PPh2) and [(OC)3Fe{m-Si(OMe)2(OMe)}(m-dppa)PdCl] 5 (dppa = Ph2PNHPPh2) with TlPF6 in the presence of P–Z aVorded the corresponding cationic compounds [(OC)3Fe{m-Si(OMe)2(OMe)}(m-dppm)M(P–Z)PF6 (M = Pd 1 or Pt 3) and [(OC)3Fe{m-Si(OMe)2(OMe)}(m-dppa)Pd(P–Z)]PF6 2 (P–Z = Ph2PC6H4(o-OMe), a P{C6H4(o-OMe)}3, b Ph2PCH2C(O)Ph, c Ph2PCH2CH]] CH2, d Ph2P(CH2)2CN, e or Ph2PCH2C(O)NPh2, f ).These complexes are stabilized by the occurrence of a Fe–Si-OÆM four-membered ring and the pre-existent SiOÆM interaction in 4–6 was not displaced by the donor function of the incoming P–Z ligand. Complexes 1b and 1f were obtained as mixtures of two isomers, the P–Z ligands acting either as monodentate or as a P,O chelate. In the latter cases formation of fiveco- ordinated palladium species is proposed.Displacement of the SiOÆPd interaction originally present in 4 was observed when the diphosphines (Ph2P)2NR (R = Me or (CH2)3Si(OEt)3) were used, since the two phosphorus atoms co-ordinate to the Pd. Surprisingly these diphosphine ligands show diVerent co-ordination modes, depending on whether dppa or dppm is used as the assembling ligand. In the former case, chelation to the Pd is observed, which leads to complex [(OC)3{(MeO)3Si}Fe(m-dppa)Pd{Ph2PN(Me)PPh2}]PF6 2g, whereas in the latter case, oligomeric entities of the type [{(OC)3{(MeO)3Si}Fe(m-dppa)Pd[Ph2PN(R)PPh2]}n][PF6]n 1g,1h (n probably equals two) were formed.The molecular structures of [PdCl(dppm-P,P9){Ph2PC6H4(o-OMe)}]PF6 g and [Pd2Cl2(m-CO)- (m-dppm)2] 10, obtained during this work, have been determined by X-ray diVraction. Introduction During the past decades both complexes containing metal silicon bonds 1 and heteronuclear clusters 2 have attracted increasing attention owing to their fundamental interest and their catalytic and physico-chemical properties.With the objective of combining the potential of these two classes of compounds, we have investigated the synthesis and the reactivity of heterobimetallic complexes bearing a SiR3 ligand.3a This led to the discovery that a Si(OMe)3 unit, which was originally only known as a terminal ligand, could bridge two metal centres.3b,c We have synthesized a series of Fe–M heterobimetallic complexes of type A (M = Pd, Pt, Rh, In, Zn, Cd, etc.), which display a m-h2-Si,O bridge between the two metal centres.The bifunctional phosphine P–Y acts as an assembling ligand and thus contributes to the stabilization of the entire molecule.4 Surprisingly, the dative OÆM interaction is usually not displaced by two-electron donor ligands such as phosphines or amines. However, it is kinetically labile as shown by variable temperature 1H NMR experiments which revealed the hemilability of the Si(OMe)3 ligand.The equivalence of the OMe groups above the coalescence temperature results from rapid rotation of the ligand about the Fe–Si axis. This behaviour may represent an interesting tool for catalytic processes where the storage of a “masked” co-ordination site plays an important role. Indeed we have observed insertion reactions under mild conditions of small molecules such as CO, isocyanides or olefins into the Pd–C or Pt–C bond of such bimetallic complexes. 5 These reactions proceed via the following pattern: opening of the SiOÆPd interaction, co-ordination of the incoming substrate, cis migration, isomerization and closing of the Fe-Si- OÆPd ring. This is depicted in Scheme 1 in the case of CO insertion into a Pd–Me bond, followed by olefin insertion into the resulting palladium–acyl bond. Repetition of these successive steps results in sequential insertion of CO and olefins (OC)3Fe Ph2P Si Y MLn O MeO MeO Me M = Pd, Pt, Rh, In, Zn, Cd, etc.A CH2PPh2 (dppm), NHPPh2 (dppa), CH2C(O)Ph, 2-pyridine, etc. Y =2160 J. Chem. Soc., Dalton Trans., 1999, 2159–2169 leading to polyketone formation.3a,5a A related mechanism has also been proposed for the dehydrogenative coupling of stannanes catalysed by Fe–Pd complexes.6 The above observations prompted us to study the behaviour of the SiOÆPd interaction in the presence of various donor ligands which may compete with it.Infrared monitoring of the reactions in Scheme 1 has evidenced the formation of intermediates in which the oxygen atom of the ketone function of the growing chain co-ordinates to the palladium centre and generates a new Pd–C–C–C–O five membered ring.5a Thus we found it of interest to investigate whether similar displacements occur when ligands containing ketone or olefin functionalities, such as phosphines Ph2PCH2C(O)Ph c and Ph2PCH2CH]] CH2 d respectively, are present in the palladium co-ordination sphere.More generally we were interested in introducing in the coordination sphere of the metal M (Pd or Pt) nucleophilic functionalities Z which could potentially form a P,Z chelate, with retention or displacement of the SiOÆPd interaction. It was hoped that such studies could provide useful information about the chelate-assisted co-ordination of unsaturated functional groups which could also mimic the behaviour of substrates during catalytic cycles.We report here investigations on the synthesis and characterization of a series of cationic heterobimetallic Fe–Pd and Fe–Pt complexes 1–3 containing the closely related assembling ligands dppm and dppa (dppm = Ph2PCH2PPh2; dppa = Ph2PNHPPh2) and the functional phosphines P–Z shown below. Results and discussion The approach used for the preparation of the target complexes 1–3 is outlined in eqn. (1). It involves treatment of the corre- Scheme 1 (OC)3Fe Ph2P (MeO)2Si PPh2 Pd O Me Me (OC)3Fe (MeO)3Si Pd O Me C (OC)3Fe (MeO)3Si Pd Me (OC)3Fe (MeO)3Si Pd C Me O O Me Ph2P PPh2 (OC)3Fe (MeO)3Si Pd Me C O Ph2P PPh2 Ph2P PPh2 Ph2P PPh2 (OC)3Fe Pd (MeO)3Si Ph2P PPh2 O Me C O + CO norbornadiene + CO n cis-migration isomerization (OC)3Fe Ph2P Si X PPh2 M O MeO MeO P Z Me 1-3 4 X = CH2, M = Pd 5 X = NH, M = Pd 6 X = CH2, M = Pt ? + P–Z (1) TlPF6, - TlCl (OC)3Fe Ph2P Si X PPh2 M O MeO MeO Me Cl PF6 – sponding neutral chloro derivatives 4–6, which contain the m-h2-Si,O bridge between the metals, with TlPF6 in the presence of the appropriate P–Z phosphine. The driving force for this reaction is the formation of insoluble TlCl.The counter ion PF6 2 is a reliable probe in 31P-{1H} NMR spectroscopy (septuplet centered at ca. d 2144, JPF = ca. 700 Hz). Note that when silver salts were used as halide abstractors secondary reactions led to decomposition products such as [Fe(CO)3(dppm-P,P9)] or [Fe(CO)3(dppa-P,P9)]. Cationic complexes displaying a Ï-Á2-Si,O bridge Complexes with EPh3 (E 5 P or As) 7,8.We first prepared cations 7 and 8 from EPh3 (E = P or As) and 4 or 6 eqn. (2), in which the Fe–Si-OÆPd four-membered ring is retained. Thus their NMR and IR data could be used for comparison with those of complexes 1–3 and help determine the structures of the latter. Complex 7a has been obtained as a red-orange powder in an analytically pure form after a CH2Cl2 solution of 4 and PPh3 was treated with TlPF6, the volatiles removed in vacuo and the residue washed with Et2O and pentane. In addition to the characteristic PF6 2 signal (septuplet at d 2143.5, 1JPF = 710 Hz), the 31P-{1H} NMR spectrum consists of three doublets of doublets, the three phosphorus atoms being coupled to each other (Table 1, Fig. 1). The signals at lower field, d 41.4 and 31.0, are assigned by comparison with 4 to the P atoms of the dppm ligand, P(Fe) and P(Pd), respectively (213JPP = 45 Hz). The signal at d 21.5 is ascribed to the PPh3 ligand (Table 1).In the 1H NMR spectrum the methoxysilyl ligand gives rise to a very broad signal centered at d 3.47 as the result of its hemilability and the successive involvement of the diVerent oxygen atoms in co-ordination to the Pd. Upon cooling to 273 K, two (OC)3Fe Ph2P Si X PPh2 M O MeO MeO P Z Me 1 X = CH2, M = Pd 2 X = NH, M = Pd 3 X = CH2, M = Pt ? + Ph2P Ph2 P O Ph Ph2P O NPh2 Ph2P CN Ph2 P N PPh2 CH3 Ph2P OMe Ph2P N PPh2 (CH2)3Si(OEt)3 P OMe a c d g f e h b 3 P–Z = (OC)3Fe Ph2P Si PPh2 M O MeO MeO EPh3 Me (OC)3Fe Ph2P Si PPh2 M O MeO MeO Me Cl 7a M = Pd, E = P3 7b M = Pd, E = As 8a M = Pt, E = P3 8b M = Pt, E = As 4 M = Pd 6 M = Pt + CH2Cl2 –40 °C to RT 1 2 (2) TlPF6, EPh3 PF6 –J.Chem. Soc., Dalton Trans., 1999, 2159–2169 2161 Table 1 Selected 31P-{1H} NMR and IR data of cationic complexes 7 and 8 and their corresponding neutral complexes 4 and 6 Chemical shifts (J/Hz) Coupling constants/Hz Complex PFe a (JP-Pt) PM b (JP-Pt) PPh3 (JP-Pt) JP1–P2 JP1–P3 JP2–P3 n& (CO)c/cm21 4 7a 7b 6 8a 8b 48.0 41.4 40.1 52.9 44.5 (37) 44.4 (40) 34.9 31.0 30.2 7.7 (4756) 6.4 (4676) 5.3 (4593) 21.5 36.5 (2806) 55 45 47 47 39 42 16 13 42 12 1985m, 1925s, 1905s 2000s, 1950m, 1930s 2004s, 1950m, 1932s 1995m, 1935s, 1910s 2000s, 1947m, 1916s 2004s, 1954m, 1925s a P atom of the dppm ligand co-ordinated to the Fe.b P atom of the dppm ligand co-ordinated to the Pd in complex 7 or Pt in 8.c Recorded in CH2Cl2. signals are observed at d 3.40 and 3.71 with relative intensities of 2 : 1 (DG‡ = 55.6 ± 1.1 kJ mol21 for a coalescence temperature of 278 K). In the IR spectrum (CH2Cl2) three n(CO) absorptions typical for a meridional arrangement of the CO ligands around the iron centre are observed at 2000s, 1950m and 1930s cm21. These values are at higher wavenumbers than those of neutral 4, indicating that in 7a the eVect of the positive charge of the complex prevails over the donor properties of the PPh3 ligand (Table 1).Complex 7b displays a similar AX pattern in the 31P-{1H} NMR spectrum and its IR characteristics are similar to those of 7a. The 1H NMR spectrum of the former, however, shows for the methoxysilyl ligand two singlets at d 3.77 and 2.89 with relative intensities of 2 : 1, the latter being assigned to the three methyl protons of the OMe group co-ordinated to the Pd. In this complex rotation of the silyl ligand about the Fe–Si axis is therefore not observed on the NMR timescale at room temperature. It is interesting to contrast this behaviour with that of 7a and this may be due to the lower donor ability of AsPh3 vs.PPh3. The platinum complexes 8 exhibit IR spectra in the n(CO) region similar to those of their palladium counterparts 7, with absorption bands being at higher wavenumbers than in the case of the parent neutral complex 6 (Table 1). In the 31P-{1H} NMR spectrum of 8a the chemical shift of PPh3 is observed at lower field than in 7a (d 36.5 vs. 21.5) whereas the JP-P coupling constants are similar in both cases, except for Jcis between the two phosphorus atoms co-ordinated to M: 12 Hz for 8a (M = Pt) vs. 42 Hz in 7a (M = Pd). The 1JP-Pt coupling constants between the diVerent P atoms and Pt are very diVerent: 4676 Hz in the case of the P atom of the dppm ligand and 2806 Hz in the case of PPh3. This should be related to the fact that the former is trans to a relatively weak ligand whereas the latter phosphine experiences the trans influence of the metal–metal bond.In the 1H NMR spectra of 8a,8b the methoxy protons of the Si(OMe)3 unit give rise to two singlets in a 1 : 2 ratio, thus showing the Fig. 1 The 31P-{1H} NMR spectrum of the cation in complex 7a. rigidity of this ligand on the NMR timescale, as already observed for 6.3b Dppm–Fe–Pd and Fe–Pt complexes 1a and 3a with P–Z 5 Ph2PC6H4(o-OMe). We have been interested in preparing complexes 1a and 3a from Ph2PC6H4(o-OMe), since the methoxy donor function thus introduced in the co-ordination sphere of the palladium atom would be of a similar nature to that of the bridging alkoxysilyl ligand.Depending on whether or not the pre-existent Si–O bridge is retained, isomers a–g could be envisaged. In the case of isomer b, co-ordination of the oxygen atom of the anisyl group to the Pd or Pt would generate a five-membered ring expected to be thermodynamically more favorable than the Fe–Si–OÆPd four-membered ring retained in isomer a.Furthermore, the possibility of forming isomer g with a five-co-ordinated centre should also be considered (Scheme 2). Both the IR and NMR spectra of complex 1a show great similarities with those of 7a (see Tables 1–3). In the 31P-{1H} NMR spectrum the signal assigned to co-ordinated Ph2PC6- H4(o-OMe) occurs at d 14.7. Although it is at higher field than that of PPh3 in 7a (d 21.5), the diVerences in chemical shifts between “free” and co-ordinated ligands are similar: Dd = 127 and 130 for 7a and 1a, respectively.In the 1H NMR spectrum the four methoxy groups give rise to two signals at d 3.39 and 3.74, with relative intensities of 3 : 1. The latter is a sharp singlet, assigned to the methyl protons of the anisyl group which does not appear to chelate the Pd since the chemical shift is the same as for the free phosphine. The former signal is broad and ascribed to the three OMe groups of the silyl ligand, which appear equivalent on the NMR timescale, as the result of Scheme 2 (OC)3Fe Si M O MeO MeO P3Ph2 Me O Me (OC)3Fe (MeO)3Si M P3Ph2 O Me + + a b M = Pd, Pt Ph2P P2Ph2 1 Ph2P P2Ph2 1 (OC)3Fe Si M O MeO MeO P3Ph2 Me O Me + g Ph2P P2Ph2 12162 J.Chem. Soc., Dalton Trans., 1999, 2159–2169 the hemilabile behaviour of this ligand (see above). Variable temperature 1H NMR experiments confirmed these attributions: the signal at d 3.39, which is slightly shifted towards lower field upon cooling, splits into two signals at d 3.60 and 3.79, with relative intensities of 2 : 1, below coalescence temperature (245 K).The IR and NMR data are thus in favour of a structure for 1a similar to that of 7a and only isomer a is observed. Thus competition for co-ordination to palladium between the methoxy groups of the silyl ligand and that of the phosphine Ph2PC6H4(o-OMe) is not observed, the Fe–Si–OÆPd fourmembered ring remaining entropically favoured.Attempts to obtain suitable crystals of 1a for X-ray analysis led to the formation of decomposition products, amongst which the new cationic complex [PdCl(dppm-P,P9){Ph2PC6H4(o-OMe)}]PF6 9 and the known but not yet structurally characterized [Pd2Cl2(m-CO)(m-dppm)2] 10.7 Both these compounds have been isolated and structurally characterized (see below). The platinum complex 3a has also been prepared, from 6 and Ph2PC6H4(o-OMe), by using the method described above.Both the IR and NMR data (Tables 2 and 3), which are comparable to those of 1a and 8,8b, are consistent with this complex having a structure similar to that of 1a, with isomer a being the only one observed (Scheme 2). Note that when CO gas was passed through solutions of these complexes for 15 to 30 min the IR spectra in the n(CO) region were not modified; co-ordination of CO was not observed. This is similar to previous observations made on the neutral complexes 4–6.3 dppm Fe–Pd complex 1b with P–Z 5 P{C6H4(o-OMe)}3.In the n(CO) region the IR spectrum of complex 1b which contains the tris(o-anisyl)phosphine shows great similarities with that of 1a (Table 2). In the room temperature 31P-{1H} NMR spectrum two doublets of doublets are observed at d 40.5 (213JP1–P2 = 45 and 314JP1–P3 = 16 Hz) and 27.4 (2JP2–P3 = 37 Hz), which are ascribed to the P(Fe) and P(Pd) atoms of the dppm ligand, respectively. The signal corresponding to coordinated P{C6H4(o-OMe)}3 occurs as a very broad signal around d 0, which hardly emerges from the baseline and suggests a dynamic process.Upon cooling, a splitting of the above resonances was observed and signals corresponding to two isomers 1b and 1b9, in a 85 : 15 ratio, appeared below 263 K (Table 3, Fig. 2). Note that the 1H NMR spectrum contains complicated sets of signals, in the d 3.21–3.83 region, due to the numerous methoxy groups. More specific assignments were not attempted. We have previously reported that 213JP1–P2 values ranged from 40 to 56 Hz for bimetallic complexes stabilized by a Fe–Si- OÆM four-membered ring (M = Pd, Pt, etc.) and from 80 to 110 Hz in the absence of the latter (this has also been noticed in the present study, see below and Table 3).3,8 Thus, the observed Table 2 Selected IR data (cm21) for the cationic complexes 1 and 2a Complex n(CO), mer-Fe(CO)3 Other 1a 1b, 1b9 1c 1d 1e 1f, 1f9 1g 1h 2c 2g 3a 1995vs, 1941 (sh), 1918vs 1999vs, 1949 (sh), 1931vs b 2000vs, 1947 (sh), 1925vs 1992vs, 1944 (sh), 1918vs 2001vs, 1947 (sh), 1928vs 1992vs, 1945 (sh), 1925vs 1978vs, 1925 (sh), 1907vs 1977vs, 1924 (sh), 1908vs 2007vs, 1955 (sh), 1942vs 1977vs, 1924 (sh), 1907vs 1995vs, 1940 (sh), 1912vs 1670s c 2258wd 1659s,c 1591m,e 1555mc 1670s c a Recorded as KBr disk.b Recorded in CH2Cl2. c n(CO) vibration of the ketone/amide functionality. d n(C–N) vibration. e n(C–N) of the amide functionality. 213JP1–P2 values for the two isomers 1b (45 Hz) and 1b9 (44 Hz) are consistent with the presence of a SiOÆPd interaction in both cases.The only diVerence between the two 31P-{1H} NMR AMX spin systems concerns the chemical shifts assigned to the tris(o-anisyl)phosphine. In the case of the major isomer 1b, the Dd between “free” (d 239.5) and co-ordinated phosphine is 134.2 ppm. Since this downfield shift is in the same range as that observed for Ph2PC6H4(o-OMe) in 1a or for PPh3 in 7a, we suggest for 1b the same structure as for 1a and 7a, the tris(oanisyl) phosphine acting as a monodentate ligand eqn.(3). On the other hand, in the case of the minor isomer 1b9 the chemical shift of co-ordinated phosphine occurs at lower field than for 1b (Dd = 115.5 ppm). This suggests a diVerent co-ordination mode and a possible MeOÆPd interaction involving the phosphine ligand. Chelation of this phosphine to the Pd would generate a P–C–C–OÆPd five-membered ring, eqn. (3), which would contribute to the downfield shift observed.Thus a structure with two OÆPd interactions, involving both the phosphine and the silyl ligand, can be envisaged for 1b9. We have recently structurally characterized the bimetallic complex [(OC)3- Fe{m-Si(OMe)2(OMe)}(m-Ph2NHPPh2)Pd{C9H9NO3C(]] O)- Me}] B in which five-co-ordination of the palladium centre is achieved by dative interactions with the ketone function in the apical position of a square-based pyramid (C]] OÆPd 2.769(5) Å) and the alkoxysilyl ligand (SiOÆPd = 2.240(3) Å).5e Our structural proposal is also consistent with the fact that five- and even six-co-ordinate palladium centres have been reported and that phosphine ligands containing o-anisyl groups are commonly used as P,O chelating ligands 9 (see also below the crystal structure of 9).Although a crystal structure of complex 1b/1b9 is not available it is reasonable to assume that a species of type 1b9 best represents the static structure of this complex.Modeling studies with Chem3D (see Fig. 3) support this view and indicate that even a six-co-ordinated species might be envisaged since PdÆO distances of 2.553 and 2.825 Å are found (Fig. 3). This suggests a potential, incipient tridentate behaviour for ligand P{C6H4(o-OMe)}3. dppm and dppa Fe–Pd complexes 1c–1e and 2c. The cationic complexes 1c–1e have been obtained following the same procedure as that described above for the synthesis of 1a. On the basis of the IR and 31P-{1H} NMR data, which are given in Tables 2 and 3 respectively, it appears that the ketone or alkene (OC)3Fe Si Pd O MeO MeO P3{C6H4( o-OMe)}3 Me (OC)3Fe Si Pd O MeO MeO P3{C6H4( o-OMe)}2 Me O Me + 1b low temp.room temp + 1b' (3) Ph2P P2Ph2 1 Ph2P P2Ph2 1 PF6 – PF6 – (OC)3Fe Pd (MeO)2Si Ph2P PPh2 HN C Me O O OAc C O Me N BJ. Chem. Soc., Dalton Trans., 1999, 2159–2169 2163 Table 3 31P-{1H} NMR data (d, J/Hz) of cationic complexes a Fe M P3 P2 P1 P4 Complex P1 P2 P3 P4 213JP1 –P2 314JP1–P2 2JP2–P3 314JP1–P4 2JP2–P4 2JP3–P4 1a 1b b 1b9 b 1c 1d 1e 1f 1f9 1g 1h 2c 2g 3a 41.5 40.8 42.0 40.1 41.7 39.4 40.4 66.1 64.4 64.6 94.2 108.0 43.9 c 28.5 28.8 26.8 25.6 29.4 26.4 25.7 30.6 23.1 25.4 78.2 70.5 4.3 d 14.7 25.3 10.2 6.7 12.8 9.4 10.6 52.9 124.6 124.9 5.6 45.5 33.1 e 90.7 92.2 50.5 45 45 44 47 45 46 44 45 85 81 41 85 41 23 16 15 14 16 14 13 18 70 71 13 10 13 40 33 31 40 40 44 41 27 30 33 46 12 f 27 27 30 535 536 506 90 94 105 a In CD2Cl2; P1, P2, P3 and P4 refer to the diVerent phosphorus atoms in complexes 1 and 2.b Recorded at 243 K. c 1JP-Pt not observed. d 1JP-Pt = 4747 Hz. e 1JP-Pt = 2862 Hz. f Not observed. functionality does not co-ordinate to the palladium centre, neither by displacing the Fe–Si–OÆPd four-membered ring nor by giving a five-co-ordinated species. Indeed, in both cases, the 1H NMR spectrum shows two signals for the alkoxysilyl protons in a 2 : 1 ratio, indicating the non-equivalence of the OMe groups and the persistence of the SiO bridge between the Fe and Pd.For 1c the n(C]] O) absorption of the ketone function (1670 cm21) is identical to that of the free phosphine, whereas chelation of Ph2PCH2C(O)Ph to palladium usually causes a shift towards lower wavenumbers by ca. 100 cm21.10 Similarly the phosphinonitrile Ph2PCH2CH2CN behaves as a monodentate ligand in complex 1e in which the m-h2-Si,O bridge is retained. The n(CN) vibration is observed at the same value (2258 cm21) as for the unco-ordinated phosphine.In order to evaluate the influence of chemical modifications in the assembling ligand, we have prepared the Ph2PNHPPh2 (dppa) complex 2c, from 5 and Ph2PCH2C(O)Ph. The spectroscopic data are given in Tables 2 and 3. In the 31P-{1H} NMR spectrum the two signals at lower field d 94.2 and 78.2 are assigned to the P(Fe) and P(Pd) atoms of the dppa ligand, respectively. By comparison with neutral 5, a slight upfield shift of ca. 6 ppm is noticed for these two signals, as in the dppm series (Tables 1 and 3). In the IR spectrum, the n(C]] O) absorption of the ketone is observed at 1670 cm21, as for Ph2PCH2- Fig. 2 The 31P-{1H} NMR spectra of the cation in complex 1b/1b9 at (a) 298 K, (b) 243 K in CD2Cl2. C(O)Ph. Here again, the ketone functionality in 2c does not displace the SiOÆPd interaction. dppm Complex 1f (P–Z 5 Ph2PCH2C(O)NPh2). The NMR and IR data of cation 1f which contains a amidophosphine ligand being similar to those of 1c (Tables 2 and 3), we assume that their structures are comparable.However, 1f was accompanied by a second species 1f9 (ratio 1f : 1f9 = 70 :30) which displays in the 31P NMR spectrum a set of three doublets of doublets, at lower field than those of 1f (Table 3 and Fig. 4). The main feature is the large downfield shifts, compared with 1f, observed for the signals (a) of the P atom of the dppm ligand co-ordinated to the iron centre (125.7 ppm) and (b) of Ph2PCH2C(O)NPh2 (142.3 ppm).The IR spectrum shows an additional n(C]] O) vibration at 1555 cm21, which may be assigned to an amide function co-ordinated by its O atom to the electron deficient Pd.11 The 1H NMR spectrum of the mixture 1f, 1f9 contains three signals in a 4:1:1 ratio at d 3.74, 3.58 and 3.55, respectively, for the OMe protons. This would be consistent with the presence of two isomers containing a m-h2-Si,O bridging interaction. Therefore on the basis of the spectroscopic data, we propose that in 1f9 the functional phosphine ligand Ph2PCH2C(O)NPh2 Fig. 3 Chem3D model of complex 1b9 produced by using the following parameters inspired by the structure determination of [(OC)3- Fe{m-Si(OMe)2(OMe)}(m-dppm)PdSnPh3]3c or of 9 (for Pd–P(3)): Pd– P(2) 2.19, Pd–P(3) 2.370, Pd-Fe 2.670, Pd–O(1) 2.148, Pd–O(2) 2.825, Pd–O(3) 2.553, Fe–Si 2.260, Fe–P(1) 2.200, Si–O(1) 1.685, O(1)–C 1.38, O(2)–C 1.38, O(3)–C 1.38 Å; Si–Fe–P(1) 171.0, Si–O(1)–Pd 96.7, O(1)–Pd–P 175.0, Fe–Pd–P(2) 175.0, P(2)–Pd–P(3) 93.08.2164 J.Chem. Soc., Dalton Trans., 1999, 2159–2169 chelates the Pd and aVords a five-co-ordinated species. This is supported by observations made with related, structurally characterized Fe–Pd complexes in which a ketone function acts as a fifth ligand toward the Pd.5e Clearly, the protons of the SiOMe bridge are more sensitive to the change in co-ordination at the palladium than those of the other methoxy groups which resonate at d 3.74 in both cases.The two isomers 1f, 1f9 could not be separated, perhaps owing to the existence of an equilibrium of the type (4), which would be slow on the NMR timescale since no dynamic behaviour was observed by VT NMR within the stability range of the complex (<323 K). The contrasting behaviour of Ph2PCH2C(O)Ph and Ph2PCH2- C(O)NPh2 may be due to the slightly better donor properties of the amide vs. the ketone function.11 Cationic complexes in which the Ï-Á2-Si,O bridge is displaced dppm Complexes 1g,1h (P–Z 5 Ph2PN(R)PPh2).Diphosphines such as dppm or dppa also appeared to be interesting candidates for competition with the SiOÆPd bond. However, despite numerous attempts, reactions of complex 4 with dppm or dppa in the presence of an halide abstractor led to decomposition and/or mixtures of products; the desired complexes were not detected. Reasons for these observations remain speculative although in the case of dppa its low solubility may represent a drawback. In order to circumvent this problem we have used the more soluble N-methyl derivative (Ph2P)2NMe.Preliminary observations revealed that in the absence of halide abstractor complex 4 reacted with (Ph2P)2NMe to yield decomposition products, probably owing to displacement of the Pd-bound dppm P atom by (Ph2P)2NMe. In order to prevent this pathway, 4 was first treated with TlPF6 in acetonitrile, below 273 K, to generate in situ [(OC)3- Fe{m-Si(OMe)2(OMe)}(m-dppm)Pd(NCMe)]PF6 before the phosphine was added.The latter displaced the acetonitrile ligand, which aVorded 1g as the sole product (see Scheme 3). Its 31P-{1H} NMR spectrum shows, apart from the signal due to PF6 2, four signals, two for each of the diphosphine ligands. The pattern of these signals, doublets of doublets of doublets, indicates that all the phosphorus atoms are coupled to each other (Table 3, Fig. 5). The signals at d 124.6 (P3) and 90.7 (P4) are assigned to the P atoms of ligand (Ph2P)2NMe, whereas the two signals at higher field, d 64.4 (P1) and 23.1 (P2), are ascribed to the P atoms of the bridging dppm ligand, P(Fe) and P(Pd) respectively.In comparison with complexes 1a, 1c–1f, the P(Fe) Fig. 4 The 31P-{1H} NMR spectrum of the cation in complex 1f/1f9. (OC)3Fe Ph2P Si PPh2 Pd O MeO MeO Me O NPh2 Ph2 P (OC)3Fe Ph2P Si PPh2 Pd O MeO MeO Me O NPh2 Ph2 P + 1f 1f' + (4) ? signal is shifted towards lower field by ca. 24 ppm, whereas the P(Pd) signal is shifted in the opposite direction. These observations indicate for 1g a diVerent structure. The most striking feature is the very large JP-P value of 535 Hz between P2 and P4, which indicates a trans disposition of these two atoms. In the 1H NMR spectrum the nine methoxy protons appear equivalent since a sharp singlet is observed at d 3.59. In the IR spectrum of 1g the n(CO) vibrations occur at lower wavenumbers than for 1a, 1c–1f (Table 2), thus indicating a higher electron density in the former.This would be expected if the two phosphorus atoms of ligand (Ph2P)2NMe were co-ordinated to the Pd. On the basis of these spectroscopic data, we therefore conclude that the SiOÆPd interaction has been displaced. Nevertheless, a chelating co-ordination mode for (Ph2P)2NMe, as depicted in Scheme 3, is not corroborated by the observed 31P NMR chemical shifts (d 124.6 and 90.7). In such a case, these should be high field shifted in comparison to that of unco-ordinated (Ph2P)2NMe (d 72), owing to the chelate eVect.12 The data are more in accordance with a bridging co-ordination mode of ligand (Ph2P)2NMe between two Pd, one of the P atoms (P3) being trans to the Fe–Pd bond in one bimetallic unit, the other one (P4) being trans to the P2 atom of the dppm ligand in another bimetallic unit.The exact structure of 1g could not be determined by X-ray analysis, since, as for the other cationic bimetallic complexes described above, suitable crystals could not be obtained owing to slow decomposition in solution.However, mass spectroscopy using electrospray (1g) or FAB1 (1h) techniques showed the presence of isotopic patterns consistent with dinuclear Fe–Pd monocationic and tetranuclear Fe2Pd2 dicationic species. The latter is best explained by a dimeric form for these complexes (Scheme 3). Higher nuclearity cyclic species could be envisaged but were not detected.With the combined objectives of confirming the above observations and of obtaining complexes of potential use in sol–gel processes, we have prepared complex 1h from 4 and the phosphine (Ph2P)2N{(CH2)3Si(OEt)3}, following the same procedure as for 1g. Complex 1h was obtained as a burgundyred powder. Both its IR and NMR data are similar to those of Fig. 5 The 31P-{1H} NMR spectrum of the cation in complex 1g. Scheme 3 Representations of structures discussed for complexes 1g,1h (phenyl, carbonyl and methoxy groups have been omitted for clarity).Fe P1 Si P2 Pd P4 N P3 N P4 Fe P1 Si P2 Pd P3 Fe P1 Si P2 Pd P4 N P3 Me R R Chelate Dimeric form + 2+J. Chem. Soc., Dalton Trans., 1999, 2159–2169 2165 1g (Tables 2 and 3), thus indicating a similar structure (Scheme 3). The 1H NMR spectrum shows the expected signals for the (CH2)3Si(OEt)3 moiety. dppa Complex 2g (P–Z 5 Ph2PN(Me)PPh2). For comparison, we have also prepared the dppa analogue of complex 1g from 5 and phosphine (Ph2P)2NMe.The IR spectrum of this new complex is similar to that of 1g, 1h in the n(CO) region (Table 2). In the 31P-{1H} NMR spectrum the P(Fe) and P(Pd) signals of the bridging dppa ligand appeared at lower and higher field, respectively, than for 2c (Fig. 6). Similar trends were observed between the dppm complexes 1a, 1c–1f and 1g, 1h (see above). The similarity between the 213JP1-P2 values of 81–85 Hz for 2g and 1g, 1h is noteworthy and contrasts with those for the other cationic complexes where they range from 41 to 47 Hz.This would suggest the absence of a m-h2-Si,O bridge in the former, by analogy with observations made previously with related, neutral bimetallic complexes.3,8 Interestingly, the signals assigned to co-ordinated (Ph2P)2- NMe occurred at d 45.5 (P3) and 50.5 (P4) (Fig. 6), at high field compared to that of the “free” phosphine (d 72), and thus suggest a chelating co-ordination mode for this ligand.This contrasts with the situation in 1g where the phosphine does not chelate but acts as a bridging ligand. Furthermore, for both mononuclear neutral and cationic palladium complexes in which (Ph2P)2NMe has been found to chelate the metal centre, the 31P NMR chemical shifts also occurred in the d 40–50 region.13 That the JP1-P3 and JP2-P3 values are much smaller for 2g than for 1g, 1h (Table 3) is again consistent with diVerent structures for these complexes. The trans arrangement of P2 and P4 is confirmed by the large coupling constant between these two nuclei (506 Hz).Clearly, the co-ordination mode of (Ph2P)2NMe is strongly influenced by the nature of the assembling ligand (dppm or dppa). Unfortunately, the reactions of 5 with dppa or dppm carried out for comparison did not allow isolation of any well defined complex. Crystal structures of complexes 9 and 10 X-Ray quality crystals of complexes 9 and 10 were obtained from adventitious decomposition of 1a in a CH2Cl2–toluene– hexane mixture.However, 9 was then prepared in a rational way (62% yield) by treatment of a mixture of [PdCl2(dppm- P,P9)] and Ph2PC6H4(o-OMe) with TlPF6, eqn. (5), whereas 10 is easily prepared by carbonylation of [Pd2Cl2(m-dppm)2].7 The molecular structure of the cation of complex 9 is shown in Figs. 7 and 8 and selected bond distances and angles are listed in Table 4. The Pd atom has a square planar coordination environment involving the Cl and the three P atoms.The bond distances to Pd are in the normal range. The Pd–P(3) distance of 2.372(1) Å is slightly longer than the Pd–P(1) (2.281(1) Å) and Pd–P(2) (2.262(1) Å) distances involving the P (OC)3Fe P1 N P2 Pd P4 N P3 Me H PF6 – (MeO)3Si + Ph2P Ph2P Pd Cl Cl Ph2P Ph2P Ph2P O Me Cl Pd –TlPF6, a -40 °C to RT 9 + (5) PF6 – atoms of the chelating dppm ligand. The methoxy oxygen atom is oriented towards the metal centre, almost residing in an apical position, with a Pd–P(3)–C(38) angle of 108.8(1)8 and a P(3)–C(38)–C(39)–O(1) torsion angle of 1.0(5)8. This leads to a pseudo-five-co-ordinated palladium complex, with a long range Pd ? ? ? O interaction (3.172(3) Å).Although complex 10 has been known since 1978,7 it has not been characterized by X-ray diVraction. Its molecular structure is shown in Fig. 9 and belongs to the expected “A frame” type 15 in which the two palladium centres are held together by mutually trans dppm ligands and share a common carbonyl ligand.Selected bond angles and distances are given in Table 4 and lie within the range of those found for related systems such as [Pd2Cl2(m-CO)(dmpm)2] (dmpm = Me2PCH2PMe2),16 [Pd2Cl2(m-CO)(dam)2] (dam = Ph2AsCH2AsPh2),17 [Pd2Cl2- (m-SO)(dppm)2],17 [ Pd2{OC(O)CF3}2(m-CO)(dppm)2] 18 or [Pd2- Cl2(m-CH2)(dmpm)2].19 The Pd ? ? ? Pd separation of 3.190 Å suggests no direct metal–metal interaction. There is a slight deviation from square geometry around the almost planar Pd atoms, as shown by the P(1)–Pd(1)–P(3) and P(2)–Pd(2)–P(4) Fig. 6 The 31P-{1H} NMR spectrum of the cation in complex 2g (* denotes minor impurities). Fig. 7 An ORTEP14 view of the structure of the cation in complex 9. Thermal ellipsoids are drawn at the 50% probability level. Fig. 8 View of the palladium environment in complex 9 illustrating incipient five-co-ordination (see text).2166 J. Chem. Soc., Dalton Trans., 1999, 2159–2169 angles of 171.48(4) and 171.33(4)8, respectively.The bridging CO is symmetrically bound to the metal atoms, with bond distances Pd(1)–C(1) 1.974(4) and Pd(2)–C(1) 1.971(4) Å and bond angles Pd(1)–C(1)–O 125.27(5), Pd(2)–C(1)–O 126.79(5) and Pd(1)–C(1)–Pd(2) 107.93(5)8. The C(1)–O distance is 1.184(5) Å. The Pd–Cl distances of 2.445(1) and 2.427(1) Å are within the same range as those found in [Pd2Cl2(m-CO)- (dmpm)2] (2.444 and 2.446 Å)16 and [Pd2Cl2(m-CH2)(dmpm)2] (2.429 and 2.419 Å)19 and slightly longer than those in [Pd2Cl2(dpmMe)2] (dpmMe = Ph2PCH(Me)PPh2) (2.420 and 2.401 Å) in which the Cl atoms are trans to the Pd–Pd bond.20 Conclusion In order to study the availability of the masked co-ordination site on the palladium centre in bimetallic complexes containing a bridging m-h2-Si(OMe)3 ligand, such as 4 and 5, we have examined the behaviour of various donor functions held in proximity to the palladium centre by a phosphorus donor atom.We have found that donor functionalities such as methoxy, Fig. 9 An ORTEP view of the structure of complex 10. Thermal ellipsoids are drawn at the 30% probability level. Table 4 Selected bond distances (Å) and angles (8) for complexes 9 and 10 9 10 Pd–Cl Pd–P(1) Pd–P(2) Pd–P(3) P(1)–C(13) P(2)–C(13) C(39)–O O–C(44) Cl–Pd–P(1) Cl–Pd–P(2) Cl–Pd–P(3) P(1)–Pd–P(2) P(1)–Pd–P(3) P(2)–Pd–P(3) P(1)–C(13)–P(2) Pd–P(3)–C(38) C(38)–C(39)–O(1) C(39)–O(1)–C(44) 2.3344(8) 2.2804(7) 2.2617(7) 2.3724(7) 1.893(3) 1.835(3) 1.356(4) 1.413(5) 92.85(3) 166.18(3) 89.39(3) 73.34(3) 174.55(3) 104.34(3) 95.2(1) 108.76(3) 115.0(3) 120.3(3) Pd(1)–Cl(1) Pd(1)–C(1) Pd(1)–P(1) Pd(1)–P(3) Pd(2)–Cl(2) Pd(2)–C(1) Pd(2)–P(2) Pd(2)–P(4) C(1)–O Pd(1) ? ? ? Pd(2) Cl(1)–Pd(1)–C(1) P(1)–Pd(1)–Pd(3) Pd(1)–C(1)–O P(1)–Pd(1)–C(1) P(3)–Pd(1)–C(1) Cl(2)–Pd(2)–C(1) P(2)–Pd(2)–P(4) Pd(2)–C(1)–O P(2)–Pd(2)–C(1) P(4)–Pd(2)–C(1) Pd(1)–C(1)–Pd(2) 2.445(1) 1.974(4) 2.340(1) 2.341(1) 2.427(1) 1.971(4) 2.335(1) 2.336(1) 1.184(5) 3.190(4) 174.8(1) 171.48(4) 125.27(5) 86.5(1) 85.8(1) 178.8(1) 171.33(4) 126.79(5) 86.1(1) 87.1(1) 107.93(5) ketone, amide, olefin or nitrile, present in phosphines, do not displace the pre-existent Fe–Si–OÆPd four-membered ring. With the ligands tris(o-anisyl)phosphine and the amidophosphine Ph2PCH2C(O)NPh2, an additional interaction between an oxygen donor and palladium was evidenced, leading to incipient five- or even six-co-ordination in the case of P{C6H4- (o-OMe)}3.It is notable that the ligands (Ph2P)2NMe and (Ph2P)2- N{(CH2)3Si(OEt)3} are able to displace the SiOÆPd interaction.The nature of the resulting product depends upon the assembling ligand since with dppm these ligands assume a bridging behaviour whereas with dppa chelation is observed. These features might be related to the dppa ligand being less electron donating than dppm.4h Experimental General procedures All the reactions and manipulations were carried out under an inert atmosphere of purified nitrogen using standard Schlenk tube techniques.Nitrogen (Air liquide, R-grade) was passed through BASF R3-11 catalyst and 4 Å molecular sieves columns to remove residual oxygen and water. Solvents were dried and distilled under nitrogen before use: pentane, hexane and toluene over sodium, tetrahydrofuran and diethyl ether over sodium–benzophenone, acetonitrile and dichloromethane over calcium hydride. Elemental C, H and N analyses were performed by the Service de microanalyses du CNRS.Infrared spectra were recorded on a Bruker IFS 66 FT-IR spectrometer in the 4000–400 cm21 region and on a Bruker IFS 113V FT-IR spectrometer in the 500–90 cm21 region, 1H, 31P-{1H} and 13C- {1H} NMR spectra at 300.1, 121.5 and 75.5 MHz, respectively, on a Bruker AM300 instrument. Phosphorus chemical shifts were externally referenced to 85% H3PO4 in water with down- field chemical shifts reported as positive. Preparations The heterobimetallic complexes 4 and 63b and the ligands Ph2PCH2C(O)Ph,10 Ph2PCH2C(O)NPh2,11 (Ph2P)2NMe,21 (Ph2P)2N{(CH2)3Si(OEt)3} 22 and Ph2P(CH2)2CN23 were prepared according to published procedures. The ligand Ph2P{C6H4(o-OMe)} was obtained by treatment of Ph2PCl with MgBr{C6H4(o-OMe)} whereas P{C6H4(o-OMe)}3 was purchased from Lancaster Ltd and used without purification.[(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd{Ph2P(C6H4[o- OMe])}]PF6 1a. A solution of complex 4 (225 mg, 0.286 mmol) and Ph2P{C6H4(o-OMe)} (87 mg, 0.300 mmol) in 20 ml of CH2Cl2 was stirred for 5 min at room temperature.It was then cooled to 230 8C and TlPF6 (120 mg, 0.343 mmol) added. The reaction mixture was allowed to return slowly to ambient under vigorous stirring. Meanwhile the initial orange colour turned dark red and TlCl precipitated. After filtration over a Celite pad, the solvent was removed under reduced pressure. The residue was washed with diethyl ether (2 × 20 ml) and pentane (2 × 20 ml) and then vacuum dried.Complex 1a was obtained as a red powder in 71% yield (240 mg) (Found: C, 50.64; H, 4.10. C50H48F6FeO7P4PdSi requires C, 50.50; H, 4.07%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.39 (s, 9 H, Si(OMe)3), 3.74 (s, 3 H, OMe phosphine), 4.33 (t, 2 H, PCH2P, 2JPH = 11 Hz) and 6.5–7.5 (m, 34 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd{P(C6H4[o- OMe])3}]PF6 1b and 1b9. Treatment of complex 4 (100 mg, 0.13 mmol) with P{C6H4(o-OMe)}3 (50 mg, 0.14 mmol) and TlPF6 (52 mg, 0.15 mmol), according to the procedure described for 1a, aVorded a red powder, in 81% yield (132 mg) consisting of a mixture of 1b and 1b9 (see text) (Found: C, 47.96; H, 4.16.C52H42F6FeO9P4PdSi?CH2Cl2 requires C, 47.72;J. Chem. Soc., Dalton Trans., 1999, 2159–2169 2167 H, 4.08%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.21, 3.25, 3.40, 3.60, 3.75 and 3.83 (18 H, OMe), 4.15 (broad, 2 H, PCH2P) and 6.4–8.1 (m, 32 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd{Ph2PCH2C(O)- Ph}]PF6 1c.Complex 1c was prepared as described for 1a from 500 mg of 4 (0.635 mmol), 195 mg of Ph2PCH2C(O)Ph (0.640 mmol) and 250 mg of TlPF6 (0.716 mmol). It was obtained as a red-orange powder in 78% yield (595 mg) (Found: C, 51.11; H, 4.08. C51H48F6FeO7P4PdSi requires C, 51.00; H, 4.08%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.45 (s, 6 H, Si(OMe)2), 3.55 (d, 2 H, PCH2C(O), 2JPH = 11), 3.73 (s, 3 H, MeOÆPd), 4.26 (t, 2 H, PCH2P, 2JPH = 10 Hz) and 6.5–7.9 (m, 35 H, aromatics).[(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd(Ph2PCH2CH]] CH2)]PF6 1d. Complex 1d was prepared as described for 1a from 250 mg of 4 (0.317 mmol), 75 mg of Ph2PCH2CH]] CH2 (0.33 mmol) and 130 mg of TlPF6 (0.37 mmol). It was obtained as a burgundy-red powder in 75% yield (268 mg) (Found: C, 49.67; H, 4.02. C46H47F6FeO6P4PdSi requires C, 49.15; H, 4.21%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.56 (dd, 2 H, PCH2C, 2JPH = 8 or 6, 3JHH = 6 or 8 Hz), 3.50 (s, 3 H, MeOÆPd), 3.58 (s, 6 H, Si(OMe)2), 4.25 (t, 2 H, PCH2P, 2JPH = 11), 4.99 (dd, 1 H, CH]] CHAHB, 3JHHtrans = 18, 2JHAHB = 2.5), 5.16 (dd, 1 H, CH]] CHAHB, 3JHHcis = 11, 2JHAHB = 2.5 Hz), 5.63 (m, 1 H, CH]] ) and 6.8–7.8 (m, 30 H, aromatics).[(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd(Ph2PCH2CH2- CN)]PF6 1e. This complex was prepared as described for 1a from 250 mg of 4 (0.317 mmol), 79 mg of Ph2PCH2CH2CN (0.33 mmol) and 130 mg of TlPF6 (0.37 mmol). It was obtained as a red powder in 85% yield (320 mg) (Found: C, 48.91; H, 4.12; N 1.49.C46H45F6FeNO6P4PdSi requires C, 48.63; H, 3.99; N, 1.23%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 1.62 (m, 2 H, PCH2), 2.08 (m, 2 H, PCH2CH2), 3.49 (s, 6 H, Si(OMe)2), 3.57 (s, 3 H, MeOÆPd), 4.36 (t, 2 H, PCH2P, 2JPH = 11 Hz) and 7.0–7.7 (m, 30 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)(Ï-dppm)Pd{Ph2PCH2C(O)- NPh2}]PF6 1f and 1f9. Treatment of 300 mg of complex 4 (0.38 mmol) with 154 mg of Ph2PCH2C(O)NPh2 (0.39 mmol) and 140 mg of TlPF6 (0.40 mmol), according to the procedure described for 1a, aVorded a red powder in 72% yield (353 mg) consisting of a mixture of 1f and 1f9 (see text) (Found: C, 53.14; H, 4.46; N, 1.23.C57H54F6FeNO7P4PdSi requires C, 52.94; H, 4.21; N, 1.08%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.45 (d, PCH2C(O), 2JPH = 7), 3.55 (s, OMe), 3.58 (s, OMe), 3.74 (s, OMe), 3.95 (t, PCH2P, 2JPH = 10), 4.08 (d, PCH2C(O), 2JPH = 10), 4.27 (t, PCH2P, 2JPH = 12 Hz) and 6.6–7.7 (m, 35 H, aromatics). [(OC)3{(MeO)3Si}Fe(Ï-dppm)Pd{Ph2PN(Me)PPh2}]n[PF6]m 1g.A solution of complex 4 (150 mg, 0.19 mmol) in 20 ml of MeCN was cooled to 240 8C and TlPF6 (70 mg, 0.20 mmol) added. The resulting suspension was stirred for 1 h while the temperature was maintained below 230 8C. Then solid (Ph2P)2NMe (80 mg, 0.20 mmol) was added, the temperature was allowed to warm to ambient and the mixture further stirred for 14 h. The initial orange-red colour turned dark red and TlCl precipitated. After filtration over a Celite pad, the solvent was removed under reduced pressure and the residue extracted with CH2Cl2.The filtrate was dried in vacuo, aVording a redbrown sticky material which was washed with diethyl ether (10 ml) and pentane (2 × 10 ml) and then vacuum dried. Complex 1g was obtained as a red-brown powder in 58% yield (143 mg) (Found: C, 49.50; H, 4.09; N, 1.27. C56H54F6FeNO6P5PdSi? CH2Cl2 requires C, 49.89; H, 4.20; N, 1.08%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.47 (s, 3 H, NMe), 3.59 (s, 9 H, Si(OMe)3), 3.74 (t, 2 H, PCH2P, 2JPH = 11 Hz) and 6.6–7.9 (m, 40 H, aromatics).Mass spectrum (electrospray, acetonitrile, 40 V): m/z 1066.0 (M1 2 PF6 2 3CO, 100), 705.8 [2(M1) 2 2PF6 2 dppaMe 2 2Ph 2 5MeO 2 Me, 50] and 698.3 [2(M1) 2 2PF6 2 dppaMe 2 2Ph 2 5MeO 2 2Me, 27%]. [(OC)3{(MeO)3Si}Fe(Ï-dppm)Pd{Ph2PN(R)PPh2}]n[PF6]m 1h (R 5 (CH2)3Si(OEt)3). Complex 1h was obtained as described for 1g from 4 (102 mg, 0.13 mmol), (Ph2P)2N{(CH2)3Si(OEt)3} (77 mg, 0.13 mmol) and TlPF6 (49 mg, 0.14 mmol) as a burgundy-red powder in 58% yield (143 mg) (Found: C, 52.12; H, 5.20; N, 0.82.C64H72F6FeNO9P5PdSi requires C, 51.71; H, 4.88; N, 0.94%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 0.11 (m, 2 H, SiCH2), 0.93 (t, 9 H, 3JHH = 6 Hz, OCH2CH3), 1.12 (m, 2 H, SiCH2CH2), 2.82 (m, 2 H, NCH2), 3.43 (m, 15 H, Si(OMe)3 and SiOCH2), 3.88 (t, 2 H, PCH2P, 2JPH = 11 Hz) and 6.5–7.9 (m, 40 H, aromatics). Mass spectrum (FAB1): m/z 2142 [2(M1 2 PF6 2 2(CH2)3Si(OEt)3 2 3MeO 2 Me, 13], 1284 (M1 2 PF6 2 2CO, 30), 1256 (M1 2 PF6 2 3CO, 100), 1207 (M1 2 PF6 2 2CO 2 Ph, 85), 1135 (M1 2 PF6 2 (CH2)3- Si(OEt)3, 15), 1079 (M1 2 PF6 2 (CH2)3Si(OEt)3 2 2CO, 25), 1002 (M1 2 PF6 2 (CH2)3Si(OEt)3 2 2CO 2 Ph, 34) and 997.7 [2(M1) 2 2PF6 2 2(CH2)3Si(OEt)3 2 3MeO 2 Me, 14%].[(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppa)Pd{Ph2PCH2C(O)- Ph}]PF6 2c. This complex was prepared as described for 1g from 100 mg of 5 (0.127 mmol), 39 mg of Ph2PCH2C(O)Ph (0.128 mmol) and 50 mg of TlPF6 (0.14 mmol).It was obtained as a red-brown powder in 76% yield (116 mg) (Found: C, 47.89; H, 3.83; N, 1.03. C50H47F6FeNO7P4PdSi?CH2Cl2 requires C, 47.59; H, 3.84; N, 1.09%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.45 (s, 6 H, Si(OMe)2), 3.65 (s, 3 H, MeOÆPd), 5.10 (broad, 1 H, NH) and 6.8–7.7 (m, 35 H, aromatics). [(OC)3{(MeO)3Si}Fe(Ï-dppa)Pd{Ph2PN(Me)PPh2}]PF6 2g. This complex was prepared as described for 1g from 100 mg of 5 (0.127 mmol), 52 mg of (Ph2P)2NMe (0.13 mmol), and 50 mg of TlPF6 (0.14 mmol).It was obtained as a red-brown powder in 66% yield (108 mg) (Found: C, 50.57; H, 4.04; N, 2.17. C55H53F6FeN2O6P5PdSi requires C, 50.92; H, 4.12; N, 2.16%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.10 (s, 3 H, NMe), 3.03 (s, 9 H, Si(OMe)3), 4.72 (broad, 1 H, NH) and 6.7–7.9 (m, 40 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pt{Ph2PC6H4(o- OMe)}]PF6 3a. This complex was prepared in a similar manner to 1a from 200 mg of 6 (0.228 mmol), 67 mg of Ph2P{C5H4- (o-OMe)} (0.23 mmol), and 87 mg of TlPF6 (0.25 mmol).It was obtained as a yellow-brown microcrystals in 79% yield (230 mg) (Found: C, 46.00; H, 3.75. C50H48F6FeO7P4PtSi?0.5CH2Cl2 requires C, 45.94; H, 3.74%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.88 (s, 3 H, MeOÆPt), 3.47 (s, 3 H, OMe phosphine), 3.73 (s, 6 H, Si(OMe)2), 3.96 (t, 2 H, PCH2P, JPH = 10 Hz) and 6.8–7.7 (m, 34 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppa)PdCl] 5. The hydrido complex [FeH{Si(OMe)3}(CO)3(dppa-P)] was formed in situ by photochemical oxidative addition of HSi(OMe)3 (1.15 ml, 9 mmol) to [Fe(CO)5] (0.4 ml, 3 mmol) in hexane (100 ml) followed by addition of 0.646 g (Ph2P)2NH (dppa, 2.8 mmol).This procedure is similar to that previously described for [FeH{Si(OMe)3}(CO)3(dppm-P)].4b Addition of NEt3 (0.4 ml, 0.28 mmol) caused precipitation of [HNEt3][Fe{Si(OMe)3}- (CO)3(dppa-P)]. The reaction mixture was kept at 220 8C for 2 d. The solvent was then decanted and the residue dried under reduced pressure and redissolved in dichloromethane.2168 J.Chem. Soc., Dalton Trans., 1999, 2159–2169 The solution was cooled to 230 8C and [PdCl2(COD)] (0.77 g, 2.7 mmol) added. After the solution had been stirred at room temperature for 1 h it was filtered through a 3 cm pad of silica and Celite. The solvent was then removed under reduced pressure and 5 was obtained as a yellow powder in 62% yield based on Pd (1.32 g) (Found: C, 45.48; H, 4.07; N, 1.80. C30H30ClFeNO6P2PdSi requires C, 45.71; H, 3.84; N, 1.78%).n(CO) (hexane) 2002s, 1955s and 1918w cm21. 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.70 (br, 9 H, Si(OMe)3) and 4.5 (br, NH). 31P-{1H} NMR (CD2Cl2, 121 MHz, 298 K): d 85.8 (d, 213JPP = 51, P(Pd)) and 100.8 (d, 213JPP = 51 Hz, P(Fe)). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd(PPh3)]PF6 7a. This complex was prepared in a similar manner to 1a from 150 mg of 4 (0.19 mmol), 52 mg of PPh3 (0.20 mmol), and 76 mg of TlPF6 (0.22 mmol).It was obtained as a red powder in 80% yield (175 mg) (Found: C, 50.31; H, 4.08. C49H46F6FeO6P4PdSi requires C, 50.77; H, 4.00%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.47 (broad, 9 H, Si(OMe)3), 4.19 (t, 2 H, PCH2P, 2JPH = 10.5 Hz) and 6.8–7.9 (m, 35 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd(AsPh3)]PF6 7b. This complex was prepared as described for 1a from 150 mg of 4 (0.19 mmol), 61 mg of AsPh3 (0.20 mmol), and 76 mg of TlPF6 (0.22 mmol). It was obtained as a red powder in 74% yield (170 mg) (Found: C, 48.65; H, 4.14. C49H46AsF6- FeO6P3PdSi requires C, 48.92; H, 3.85%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.89 (s, 3 H, MeOÆPd), 3.77 (s, 6 H, Si(OMe)2), 4.13 (t, 2 H, PCH2P, 2JPH = 10.5 Hz) and 7.0–7.9 (m, 35 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pt(PPh3)]PF6 8a. This complex was prepared as described for 1a from 200 mg of 6 (0.228 mmol), 60 mg of PPh3 (0.23 mmol), and 84 mg of TlPF6 (0.24 mmol). It was obtained as a yellow powder in 71% yield (200 mg) (Found: C, 47.42; H, 3.76.C49H46F6FeO6P4PtSi requires C, 47.17; H, 3.71%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.88 (s, 3 H, MeOÆPt), 3.79 (s, 6 H, Si(OMe)2), 3.94 (t, 2 H, PCH2P, 2JPH = 10.5 Hz) and 6.8–7.9 (m, 35 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pt(AsPh3)]PF6 8b. This complex was prepared as described for 1a from 200 mg of 6 (0.228 mmol), 70 mg of AsPh3 (0.23 mmol), and 84 mg of TlPF6 (0.24 mmol). It was obtained as a red powder in 77% yield (225 mg) (Found: C, 44.07; H, 3.19.C49H46AsF6- FeO6P3PtSi requires C, 43.62; H, 3.51%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.13 (s, 3 H, MeOÆPt), 3.81 (s, 6 H, Si(OMe)2), 3.95 (dd, 2 H, PCH2P, 2JPH = 9.8 and 11.2 Hz) and 7.0–7.8 (m, 35 H, aromatics). [PdCl(dppm-P,P9){Ph2P{C6H4(o-OMe)}]PF6 g. A mixture of 150 mg of [PdCl2(dppm-P,P9)] (0.267 mmol) and 78 mg of Ph2P{C6H4(o-OMe)} (0.267 mmol) in CH2Cl2 (20 ml) was cooled to 240 8C and treated with 95 mg of TlPF6 (0.27 mmol).The reaction mixture was allowed to warm to room temperature, stirred for 1 h at this temperature, filtered over a Celite pad and concentrated to ca. 3 ml. Addition of Et2O aVorded a yellow-orange precipitate. The solvent was removed via a canula and the residue washed with pentane (2 × 10 ml) and dried in vacuo. Complex g was obtained as a yellow-orange powder in 62% yield (160 mg) (Found: C, 54.96; H, 3.94. C44H39ClF6FeOP4Pd requires C, 54.85; H, 4.08%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.74 (s, 3 H, OMe), 3.79 (t, 2 H, PCH2P, 2JPH = 11 Hz) and 6.8–7.8 (m, 34 H, aromatics). 31P-{1H} NMR (CD2Cl2, 298 K): d 2143.6 (sept, PF6, 1JPF = 709), 248.2 (dd, dppm, P trans P, 2JPPtrans = 484, 2JPP = 81), 238.3 (d, dppm, P trans Cl, 2JPP = 81) and 16.04 (d, Ph2PC6H4(o-OMe), 2JPPtrans = 484 Hz). Collection of the X-ray data and structure determination for complexes 9 and 10 Single crystals suitable for X-ray diVraction were obtained from CH2Cl2–toluene–hexane. Data were collected on a Nonius MACH-3 diVractometer using Mo-Ka graphite monochromated radiation (l = 0.7107 Å), q–2q scans.The structures were solved using direct methods and refined against |F|. Absorption corrections were computed from the y scans of four reflections. For all computations; the Nonius MoLEN package 24 was used. Crystal data for complex 9. Yellow crystals, data collected at 293 K (crystal dimensions 0.35 × 0.40 × 0.40 mm): C44H39ClF6OP4Pd?C7H8, M = 1055.7, monoclinic, space group P21/c, a = 11.500(3), b = 20.814(6), c = 21.055(6) Å, b = 97.92(2)8, V = 4991.4 Å3, Z = 4, Dc = 1.405 g cm23, m(Mo-Ka) = 6.028 cm21.A total of 15846 reflections were collected, 2 < q < 308, 8137 having I > 3s(I). Absorption factors 0.98/ 1.00, 542 parameters. Final R(F) = 0.051, Rw(F = 0.080, Goodness of fit = 1.528, maximum residual electron density 1.26 e Å23. All non-hydrogen atoms were refined anisotropically with the exception of the toluene C atoms.The hydrogen atoms were introduced as fixed contributors (dC-H = 0.95 Å, BH = 1.3Bequiv(C) Å2); toluene protons were omitted. Crystal data for complex 10. Red crystals, data collected at 173 K (crystal dimensions 0.60 × 0.40 × 0.20 mm): C51H44OP4- Cl2Pd2?3CH2Cl2?H2O, M = 1353.3, tetragonal, space group P41, a = 21.171(6), c = 14.309(4) Å, V = 6413.4 Å3, Z = 4, Dc = 1.402 g cm23, m(Mo-Ka) = 10.228 cm21. A total of 9185 reflections were collected, 2 < q < 298, 7135 having I > 3s(I ).Absorption factors 0.89/1.00, 639 parameters. Final R(F) = 0.036, Rw(F) = 0.053, Goodness of fit = 1.167, maximum residual electron density 0.12 e Å23. All nonhydrogen atoms were refined anisotropically. The hydrogen atoms were introduced as fixed contributors (dC-H = 0.95 Å, BH = 1.3Bequiv(C) Å2); water protons were omitted. CCDC reference number 186/1457. See http://www.rsc.org/suppdata/dt/1999/2159/ for crystallographic files in .cif format.Acknowledgements We are grateful to T. Faure for preliminary studies on complex 1b and thank the SOCRATES Mobility Scheme between RWTH Aachen, Germany and Université Louis Pasteur, Strasbourg, France for a grant to T. W. 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