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
Abstract
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)Å, and Z= 8; those of (5a) are orthorhombic, space group Pn21a, a= 43.39(1), b= 25.178(9), c= 10.164(6)Å, 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)Å 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)Å], giving rise to an A-frame structure.