Zinc, Cadmium and Mercury Complexes of Redox-active Cyanomanganese Carbonyl Ligands: Intramolecular Electron Transfer Through Tetrahedral d10 Metal Centres

The redox-active cyanomanganese carbonyl ligands cis- and trans-[Mn(CN)(CO)2{P(OR)3}(dppm)] (R = Ph or Et dppm = Ph2PCH2PPh2) reacted with ZnBr2, CdI2 and Hg(NO3)2 to give the tetrahedral (at M) complexes [X2M{(-NC)MnLx}2] [MX2 = ZnBr2, CdI2 or Hg(NO3)2; Lx = cis- or trans-(CO)2{P(OR)3}(dppm); R = Ph or Et]; similarly [Mn(CN)(NO)PPh3)(-C5H4Me)] gives [X2M{(-NC)MnLx}2] {MX2 = ZnBr2 or CdI2 Lx = (NO)-(PPh3)(-C5H4Me)}. Treatment of [Br2Zn{(-NC)MnLx}2] [Lx = trans-(CO)2{P(OEt)3}(dppm)] 4 with TlPF6 in the presence of 1 or 2 equivalents of trans-[Mn(CN)(CO)2{P(OEt)3}(dppm)] gave the tetra- and penta-metallic complexes [BrZn{(-NC)MnLx}3][PF6] 13 and [Zn{(-NC)MnLx}4][PF6]2 14 [Lx = trans-(CO)2{P(OEt)3}(dppm)] respectively. Differential pulse volammetry showed that 4, 13 and 14 are oxidised to weakly interacting mixed-valence complexes. The reaction of trans-[Mn(CN)(CO)(dppm)2] with ZnBr2 or CdX2 (X = Br or I) in thf gave the bimetallic species [X2(thf)M(-NC)Mn(CO)(dppm)2] (MX2 = ZnBr2 or CdI2) and [Br2Cd(-NC)Mn(CO)(dppm)2] which are oxidised by [Fe(-C5H5)2][PF6] to the MnII complexes [X2(thf)M(-NC)Mn(CO)(dppm)2][PF6] and [Br2Cd(-NC)Mn(CO)(dppm)2][PF6]. The crystal structures of the tetrahedral polynuclear complexes [I2Cd{(-NC)MnLx}2] [Lx = trans-(CO)2{P(OEt)3}(dppm)] 9 and [Br2(thf)Zn(-NC)Mn(CO)(dppm)2] 15 are reported, and the importance of steric effects (as quantified by cone angles) in the behaviour of cyanomanganese carbonyl ligands is noted