Syntheses of vinylidene-bridged A-frame palladium complexes containing Ph2PCH2PPh2 or Ph2PCHMePPh2: protonation to give carbyne-bridged complexes
Abstract
Treatment of benzene solutions of [Pd(dba)2](dba = dibenzylideneacetone) or [Pd(PPh3)4] with Ph2PCH2PPh2(dppm) and X2CCH2(X = Cl or Br) gave the ‘A-frame’ vinylidene-bridged complexes of type [XPd(µ-dppm)2(µ-CCH2)PdX][X = Cl (1a) or Br (1b)] in high yield. Treatment of (1a), with LiBr, Nal, or KSCN in acetone gave [XPd(µ-dppm)2(µ-CCH2)PdX][X = Br (1b), I (1c), or NCS (1d)], respectively. Complex (1a) with TIO2CMe gave [(MeCO2)Pd(µ-dppm)2(µ-CCH2)Pd(O2CMe)](1e) and with LiCCC6H4Me-4 the diacetylide complex [(p-MeC6H4CC)Pd(µ-dppm)2(µ-CCH2)Pd(CCC6H4Me-p)](2a) was obtained in low yield. Better yields of the diacetylides of type [(RCC)Pd(µ-dppm)2(µ-CCH2)Pd(CCR)] were obtained by treating (1a) with HCCR, TIPF6, and NEt3 in dichloromethane; e.g. with R = C6H4Me-4 (2a), Ph (2b), or CMe2(OH)(2c). Treatment of (1a) with p-MeC6H4NC and NaBPh4 in ethanol gave [(p-MeC6H4NC)Pd(µ-dppm)2(µ-CCH2)Pd(CNC6H4Me-p)][BPh4]2(3). Treatment of [Pd(PPh3)4] with dppm and Cl2CCCl2 gave a mixture of [ClPd(µ-dppm)2(µ-CCCl2)PdCl](4) and [ClPd(µ-dppm)2PdCl] but (4) was obtained in high yield and purity when a mixture of [Pd(PPh3)4], dppm, and [PdCl(CClCCl2)(PPh3)2] was heated. A mixture of [Pd(PPh3)4] and Ph2PCHMePPh2(mdppm) when treated with Cl2CCH2 gave the “A-frame” vinylidene-bridged complex [ClPd-(µ-mdppm)2(µ-CCH2)PdCl](5a) or (5b). Treatment of (1a) or (5a)/(5b) with HBF4·Et2O or CF3CO2H gave [ClPd(µ-L–L)2(µ-CMe)PdCl]+[L–L = dppm (6) or mdppm (7)], characterized in solution by n.m.r. spectroscopy. Salts of these carbyne cations were not isolated pure. N.m.r. data are given and discussed.