The effect of redox-active cyanomanganese(I) ligands on intramolecular electron transfer to, and alkyne alignment in, M(CO)(RCCR)Tp′ (M = Mo or W) units

Abstract

The complexes [(η-C₅Me₅)(ON)LMn(μ-CN)M(CO)(RCCR)Tp′]⁺ (L = CNXyl, M = Mo; L = CNBu^t, M = Mo or W, R = Ph or Me) and trans- or cis-[(dppm){(EtO)₃P}(OC)₂Mn(μ-CN)M(CO)(PhCCPh)Tp′]⁺, and their linkage isomers [(η-C₅Me₅)(ON)LMn(μ-NC)M(CO)(PhCCPh)Tp′]⁺ and trans- or cis-[(dppm){(EtO)₃P}(OC)₂Mn(μ-NC)M(CO)(PhCCPh)Tp′]⁺, undergo two one-electron oxidations. The complexes [(η-C₅Me₅)(ON)LMn(μ-XY)M(CO)(RCCR)Tp′]⁺ (XY = CN or NC) are oxidised first at the N-bound metal centre and then at the C-bound centre. For [(dppm){(EtO)₃P}(OC)₂Mn(μ-XY)M(CO)(PhCCPh)Tp′]⁺, the trans isomers are first oxidised at manganese whereas the cis isomers are first oxidised at M. Thus, the order of one-electron oxidation of the two series of binuclear monocations is influenced by linkage isomerisation of the cyanide bridge and cis-trans isomerisation of the Mn(CO)₂ group. IR spectroscopic changes on reaction of Ag⁺ with [(η-C₅Me₅)(ON)(Bu^tNC)Mn(μ-CN)W(CO)(MeCCMe)Tp′]⁺ are consistent with one-electron at the N-bound tungsten centre. Likewise, trans-[(dppm){(EtO)₃P}(OC)₂Mn(μ-NC)M(CO)(PhCCPh)Tp′]⁺ (M = Mo or W) give the stable dications [(dppm){(EtO)₃P}(OC)₂Mn(μ-NC)M(CO)(PhCCPh)Tp′]²⁺. Significantly longer Mn-P bond distances in trans-[(dppm){(EtO)₃P}(OC)₂Mn(μ-NC)Mo(CO)(PhCCPh)Tp′]²⁺ than in trans-[(dppm){(EtO)₃P}(OC)₂Mn(μ-NC)Mo(CO)(PhCCPh)Tp′]⁺ are consistent with one-electron oxidation first at Mn(I); the alignment of the (CN)Mn(CO)₂{P(OEt)₃}(dppm) fragment relative to the alkyne in trans-[(dppm){(EtO)₃P}(OC)₂Mn(μ-NC)Mo(CO)(PhCCPh)Tp′]⁺ suggests it acts as a π-acceptor, in contrast to related species such as trans-(NC)Mn(CO)₂{P(OEt)₃}(dppm) and (NC)Mn(NO){P(OPh)₃}(π-C₅H₄Me) which behave as simple N-donors.