David M. McEwan

Bimetallic systems. Part 2. Synthesis and interconversion of monodentate- and bridging-bis(diphenylphosphino)methane platinum, diplatinum, and mercury–platinum acetylides

Treatment of [PtCl2(dppm-PP′)][dppm = bis(diphenylphosphino)methane] with LiCCR gives good yields of the diplatinum ‘face-to-face’ complexes trans,trans-[Pt2(CCR)4(µ-dppm)2](2a), (2b), (2d), or (2e), with R = C6H4Me-p, Ph, CH2CH2Ph, or C(Me)CH2 respectively. These diplatinum complexes react with more dppm to give the mononuclear fluxional complexes trans-[Pt(CCR)2(dppm-P)2](3a), (3b), (3d), or (3e). A more convenient method of making the mononuclear complexes (3a)–(3e) is to treat [PtCl2(dppm-PP′)] with LiCCR in the presence of dppm. Treatment of [Pt(dppm-PP′)2]Cl2 with LiCCPh gives (3b) but deprotonation to give [Pt(Ph2PCHPPh2)2] also occurs. Treatment of [PtCl2(dppm-PP′)] with an excess of LiCCPh gives (3b) and [Pt(CCPh)4]2–, isolated as its [NBun4]+ salt. Treatment of [Pt(dppm-PP′)2]Cl2 with Hg(CCR)2 rapidly gives the platinum–mercury complexes [(RCC)2Pt(µ-dppm)2HgCl2](4a)–(4d) in very high yields, with R = C6H4Me-p, Ph, Me, or Prn respectively. Treatment of the platinum–mercury complexes (4a)–(4c) with Na2S·9H2O gives HgS and high yields of the mononuclear complexes trans-[Pt(CCR)2(dppm-P)2](3a)–(3c), with R = C6H4Me-p, Ph, or Me respectively. More conveniently, when [Pt(dppm-PP′)2]Cl2 is treated with Hg(O2CMe)2+ RCCH the platinum–mercury complexes (4a)–(4c) are formed in excellent yields. Preliminary work shows that [(HOCH2CH2CC)2Pt(µ-dppm)2HgCl2](4e) is formed from [Pt(dppm-PP′)2]Cl2+ Hg(O2CMe)2+ HOCH2CH2CCH. Treatment of the complex trans-[Pt(CCPh)2(dppm-P)2](3b) with HgCl2 gives [(PhCC)2Pt(µ-dppm)2HgCl2](4b). The fluxional monodentate-dppm complexes trans-[Pt(CCR)2(Ph2PCH2PPh2)2](3a)–(3c), R = C6H4Me-p, Ph, or Me respectively, are oxidised by hydrogen peroxide to give the non-fluxional phosphine oxide complexes trans-[Pt(CCR)2{Ph2PCH2P(O)Ph2}2](5a)–(5c) or quaternised by methyl iodide to give trans-[Pt(CCR)2(Ph2PCH2PMePh2)2]l2(6a)–(6c). Complex (6b; R = Ph) is deprotonated by lithium propan-2-oxide probably to give the di-ylide trans-[Pt(CCPh)2(Ph2PCHPMePh2)2](7) which hydrolyses to trans-[Pt(CCPh)2(PMePh2)2]. l.r., and 1H, 31P, and 195Pt n.m.r. data are given.

Syntheses and michael additions to vinylidene diphosphine complexes of type [M(CO)4{(Ph2P)2CCH2}] (MCr, Mo or W)

Treatment of [M(CO)4Ph2PCHPPh2]− with CH3- OCH2Cl at 20 °C gave the methoxymethyl derivations [M(CO)4{Ph2PCH(CH2OCH3)PPh2}] (MCr or W), but a similar treatment at 80 °C gave derivatives of a vinylidene diphosphine [M(CO)4(Ph2P)2C CH2]. Treatment of [M(CO)4Ph2PCHPPh2]−with CH3CHClOCH3 at 20 or 80 °C gave only [M(CO)4- (Ph2P)2CHCH(CH3)OCH3] (MCr or W). The vinylidene diphosphine complexes [M(CO)4(Ph2P)2- CCH2] (MCr, Mo or W) were even more easily prepared by treating [M(CO)6] with (Ph2P)2CCH2 (vdpp) in hot solvents such as CH3OCH2CH2OCH2- CH2OCH3. Treatment of [W(CO)4vdpp] with LiBun followed by methanol gave [W(CO)4(Ph2P)2CHCH2Bun] (1c), i.e. conjugate addition to the CCH2 occurs. 1c was also made by treating [W(CO)4(Ph2P)2CH]− with n-pentyl-iodide. Similarly LiMe was added to [W(CO)4(Ph2P)2CCH2]. Treatment of [M(CO)4- vdpp] with NaCH(COOEt)2 gave [M(CO)4(Ph2- P)2CHCH2CH(COOEt)2] (MW or Mo). Pyrrolidine added to the CCH2 bonds of [M(CO)4vddp] to give [M(CO)4(Ph2P)2CHCH2NC4H8]. 31p and 1H NMR and IR data are given.

Bimetallic systems. Part 12. Mixed rhodium(I)–platinum(II) acetylide complexes containing bridging Ph2PCH2PPh2. Crystal structures of [(MeCC)Pt(µ-dppm)2(σ,η-CCMe)Rh(CO)]PF6 and of [ClPt(µ-dppm)2(σ,η-CCMe)Rh(CO)]PF6

Treatment of [Pt(CCMe)2(dppm-P)2] with [Rh2Cl2(CO)4] gave [(MeCC)Pt(µ-dppm)2(σ,η-CCMe)Rh(CO)]Cl readily converted into the corresponding PF6– salt (1b) the crystal structure of which was determined. Other complexes of the type [(RCC)Pt(µ-dppm)2(σ,η-CCR)Rh(CO)]Cl were made similarly; with R = Ph, p-tolyl, CH2CH2Ph, or C(Me)CH2. The complexes are fluxional with the low-temperature limiting 1H-{31P} n.m.r. spectrum showing non-equivalent pseudoequatorial and pseudo-axial CH2 protons, He coupled to 195Pt and Ha not. The fluxional process corresponds to interchange of He and Ha and interchange of terminal and bridging CCR. When heated in toluene for 3 h, [(RCC)Pt(µ-dppm)2(σ,η-CCR)Rh(CO)]Cl (R =p-tolyl or Ph) was converted into [(RCC)Pt(µ-dppm)2(σ,η-CCR) RhCl]. With CO, [(p-MeC6H4CC)Pt(µ-dppm)2(σ,η-CCC6H4Me-p)RhCl] rapidly gave back [(p-MeC6H4CC)Pt(µ-dppm)2(σ,η-CCC6H4Me-p)Rh(CO)]Cl. Treatment of [Pt(CCR)2(dppm-P)2] with [Rh2Cl2(C8H14)4](C8H14= cyclo-octene) also gave [(RCC)Pt(µ-dppm)2(σ,η-CCR)RhCl](R =p-tolyl or Ph) but the complexes were not isolated pure. Treatment of [(PhCC)2Pt(µ-dppm)2HgCl2] with [Rh2Cl2(CO)4] caused rapid and complete displacement of HgCl2, giving [(PhCC)Pt(µ-dppm)2(σ,η-CCPh)Rh(CO)]+; similarly treatment of [(PhCC)2Pt(µ-dppm)2AgCl], [(PhCC)2Pt(µ-dppm)2Cul], or [(PhCC)2Pt(µ-dppm)2Au]Cl with [Rh2Cl2(CO)4] gave [(PhCC)Pt(µ-dppm)2(σ,η-CCPh)Rh(CO)]+. Treatment of [Cl(RCC)Pt(µ-dppm)2AgCl] with [Rh2Cl2(CO)4] gave [ClPt(µ-dppm)2(σ,η-CCR)Rh(CO)]+(R = Me, Ph, or p-tolyl) isolated as PF6– or AgCl2– salts. These complexes could also be made in ‘one-pot’ syntheses, viz. successive treatment of [Pt(dppm-PP′)2]Cl2 with AgO2CMe–PhCCH followed by treatment with [Rh2Cl2(CO)4], without isolation of the intermediate platinum–silver complex. The crystal structures of [(MeCC)Pt(µ-dppm)2(σ,η-CCMe)Rh(CO)]PF6(1b) as the dichloromethane solvate and of [ClPt(µ-dppm)2(σ,η-CCMe)Rh(CO)]PF6(5a) were determined. Crystals of (1b) are orthorhombic, space group Pbca, a= 19.212(7), b= 27.364(6), c= 21.468(5)A, and Z= 8; those of (5a) are orthorhombic, space group Pn21a, a= 43.39(1), b= 25.178(9), c= 10.164(6)A, and Z= 8. Final R factors were 0.088 for 4 500 and 0.058 for 6 320 observed reflections, respectively. In each complex cation the two metal centres [Pt ⋯ Rh 3.099(2) for (1b) 3.066(2) and 3.086(2)A for (5a)] are bridged by a methylacetylide group σ-bonded to Pt and π-bonded in an unsymmetrical side-on fashion to Rh [mean Rh–CPt 2.24(2), mean Rh–CMe 2.44(2)A], giving rise to an A-frame structure.

Bimetallic systems. Part 4. Synthesis and characterisation of mixed copper(I)–, silver(I)–, or gold(I)–platinum(II) acetylide complexes containing bridging Ph2PCH2PPh2

The bis(monodentate dppm)diacetylide complexes of type trans-[Pt(CCR)2(dppm-P)2](dppm = Ph2PCH2PPh2; R = Ph, p-tolyl, Me, etc.) react with silver nitrate or silver hexafluorophosphate to give mixed platinum–silver salts of the type [(RCC)2Pt(µ-dppm)2Ag]X (X = NO3– or PF6–) or with [{AgX(PPh3)}4](X = Cl or I) to give neutral platinum–silver complexes, [(RCC)2Pt(µ-dppm)2-AgX](X = Cl or I), in excellent yield. The salts and neutral complexes can be interconverted, e.g. the nitrate salt with NaI gives the neutral platinum–silver iodide complex and when the neutral platinum–silver chloride complex [(PhCC)2Pt(µ-dppm)2AgCl] is treated with [NH4][PF6] in acetone the corresponding [PF6]– salt is formed. A more convenient method of synthesis of the complex [(PhCC)2Pt(µ-dppm)2AgX] is to treat [Pt(dppm-PP′)2]X2(X = Cl or I) with two equivalents of AgO2CMe + PhCCH. Treatment of [Pt(dppm-PP′)2]X2 with one equivalent of AgO2CMe + RCCH gives platinum–silver monoacetylides of type [(RCC)ClPt(µ-dppm)2AgCl](R = Ph, p-tolyl, Me, CH2CH2Ph, or CMeCH2). In ‘one-pot’ reactions PtCl2(or K2[PtCl4]) was treated with two equivalents of dppm followed by one equivalent of AgO2CMe + PhCCH to give the complex [(PhCC)ClPt(µ-dppm)2AgCl] in 71% overall yield. This chloro-complex, when treated with LiBr or NaI in dichloromethane–acetone, gave the corresponding bromo- or iodo-complexes [(PhCC)XPt-(µ-dppm)2AgX](X = Br or I) in ca. 90% yields. Treatment of [Pt(CCC6H4Me-P)2(dppm-p)2] with [AuCl(PPh3)] gave the platinum–gold complex salt [(p-MeC6H4CC)2Pt(µ-dppm)2Au]Cl. Treatment of [Pt(dppm-PP′)2]Cl2 with Li[Cu(CCPh)2] gives [(PhCC)2Pt(µ-dppm)2CuCl], which in acetone solution + Na[BPh4] gives the corresponding salt [(PhCC)2Pt(µ-dppm)2Cu][BPh4]. All of the complexes were characterised by microanalysis, solution conductivity measurements, i.r. spectroscopy, and particularly 31P-{1H} and 1H-{31P} n.m.r. spectroscopy. The variable-temperature 1H-{31P} and 31P-{1H} n.m.r. spectra of the complexes are discussed.

Bimetallic systems. Part 14. Mixed iridium(I)–platinum(II) acetylide complexes containing bridging Ph2PCH2PPh2 ligands

Treatment of the cyclo-octene (C8H14) iridium(I) complex [Ir2Cl2(C8H14)4] with trans-[Pt(CCR)2(dppm-P)2](R = Ph or p-tolyl; dppm = Ph2PCH2PPh2) gave the dark green complexes [(RCC)Pt-(µ-dppm)2(µ-CCR)IrCl], which reacted with dihydrogen to give the dihydrides [(RCC)2Pt(µ-dppm)2(µ-H)IrH(Cl)]. [(PhCC)Pt(µ-dppm)2(µ-CCPh)IrCl] reacted with CO to give [(PhCC)Pt-(µ-dppm)2(µ-CCPh)Ir(CO)Cl], more conveniently prepared by treating trans-[IrCl(CO)(PPh3)2] with trans-[Pt(CCPh)2(dppm-P)2]. The p-tolylacetylide and methylacetylide analogues were prepared similarly. Treatment of [(RCC)Pt(µ-dppm)2(µ-CCR)Ir(CO)Cl] with large anions, e.g. PF6– or BPh4–, gave the corresponding red cationic species [(RCC)Pt(µ-dppm)(µ-CCR)Ir-(CO)]+, isolated as PF6– or BPh4– salts. The conversion was reversed by addition of Cl–. These cations (R = Me, Ph, or p-tolyl) reacted rapidly with dihydrogen to give the corresponding dihydrides [(RCC)Pt(µ-dppm)2(µ-CCR)(µ-H)IrH(CO)]+. I.r. and 1H, 31P, and 195Pt n.m.r. data are given.

Transition metal–carbon bonds. Part 56. Attack on allene complexes of type cis-[PtCl2(PR3)(C3H4)] by the ambident nucleophile, acetoxime: crystal structure of [PtCl(PMe2Ph){ON(CMe2)CH CMe}]

Treatment of cis-[PtCl2(PMe2Ph)(C3H4)] with Me2CNOH gives the title complex, the formation of which involves nucleophilic attack by nitrogen, a 1–3-hydrogen shift, and ring closure. Crystals are monoclinic, space group P21/c, with a= 10.208(3), b= 11.056(3), c= 15.305(2)A, β= 102.49(2)°, and Z= 4; the final R factor was 0.025 for 3 171 independent F0. A 31P-{1H} n.m.r. study of the conversion shows that some (unidentified) intermediates and minor products are formed.

Synthetic and nuclear magnetic resonance studies on dialkyl- and diaryl-platinum complexes containing chelating, monodentate, or bridging Ph2PCH2PPh2 ligands

Complexes of the type [PtR2(dppm-PP′)](R = Me, CH2CMe3, Et, CH2Ph, Ph, C6H4Me-p, C6H4OMe-2, C6H2Me3-2,4,6,1-naphthyl, C6F5, or C6H4Me-o; dppm = Ph2PCH2PPh2) have been prepared from [PtCl2(dppm-PP′)] and the corresponding alkyl-lithium or Grignard reagents. Equilibrium constants, K, for the conversion of [PtR2(dppm-PP)′] into cis-[PtR2(dppm-P)2] with dppm were studied using 31P n.m.r. spectroscopy at different temperatures. Equilibrium is rapidly established for R = Me, even at –60 °C, but more slowly for R = Ph, completion taking less than 1 h at –30 °C; for the sterically hindered (o-substituted) aryls equilibrium is only established after several days at 20 °C. The values of K increase as the temperature is lowered. Complexes of the type cis-[PtR2(dppm-P)2] were isolated for R = Me, C6H4Me-o, or 1-naphthyl. The o-tolyl or 1-naphthyl complexes exist as syn–anti mixtures in solution, due to restricted rotation around the platinum–aryl bonds. Treatment of several complexes of the type [PtR2(dppm-PP′)] with Mel gives [PtR2Me(I)(dppm-PP′)] with trans addition of Mel. Treatment of [PtR2(dppm-PP′)] with HCl gives [PtCl(R)(dppm-PP′)] for R = C6H2Me3-2,4,6,C6H4OMe-2, or 1-naphthyl, whereas [Pt(C6H4OMe-2)2(dppm-PP′)] with Mel appears to give [PtI(C6H4OMe-2)(dppm-PP′)]. The 1H, 31P, and 195Pt n.m.r. parameters for these complexes are discussed. For [PtR2(dppm-PP′)]δ(P) is much more negative (–30 to –40 p.p.m.) than for cis-[PtR2(dppm-P)2](+5 to +20) and the J values are much smaller. In contrast, platinum-195 chemical shifts are 600 p.p.m. to high frequency of those for complexes of type cis-[PtR2(dppm-P)2], similarly for 13C n.m.r. shifts. The δ(PCH2P) values for the chelates are 3.9–4.5 p.p.m., whereas for [PtR2(dppm-P)2] they are 1.8–3.0 p.p.m.

Simple, high yield syntheses of heterobimetallic complexes of Ph2PCH2PPh2(dppm) with platinum, mercury, and silver

Treatment of the readily available salts [Pt(dppm)2]2X (dppm = Ph2PCH2PPh2) with (i) Hg(CCR)2 or (ii) Hg(OAc)+ RCCH or (iii) Hg(CN)2 gives virtually quantitative yields of Y2Pt(µ-dppm)2 HgX2(Y = CCR or CN, R = Ph, p-tolyl, Me, or Prn, X = Cl) and with AgOAc + PhCCH, high yields of (PhCC)2Pt(µ-dppm)2AgX (X = Cl or I).

Systematic syntheses of heterobimetallic complexes of platinum with rhodium(I), iridium(I), iridium(III) or tungsten(0) bridged by Ph2PCH2PPh2

Complexes of type trans-[Pt(CCR)2(η1-Ph2PCH2PPh2)2](R = Me, Ph, or p-tolyl), are used to effect systematic, high-yield syntheses of heterobimetallic complexes with RhI, IrI, IrIII(bridging hydride), and Wo.