Synthesis and reactivity of μ-bis(carbene)dimanganese complexes. X-ray structures of {Cp′(CO)2Mn}2{μ-C(OEt)CH2CH2(EtO)C}, (E)-{Cp′(CO)2Mn}2{μ-C(OEt)CHCH(EtO)C} and {Cp′(CO)2Mn}2{μ-H}

Abstract

The carbene anions resulting from in situ deprotonation of the Fischer-type carbene complexes Cp′(CO)2MnC(OEt)CH2R (1; 1a: R=H; 1b: Me) undergo an oxidative coupling in the presence of Cu(I), Cu(II) or Fe(III) salts to produce the corresponding μ-bis(carbene)dimanganese complexes {Cp′(CO)2Mn}2{μ-C(OEt)CH(R)CH(R)(OEt)C} (2; 2a: R=H; 2b: Me). Double deprotonation of 2a gives a dianionic species that undergoes an oxidation in the presence of Fe(III) chloride to afford the μ-bis(vinylcarbene)dimanganese complex (E)-{Cp′(CO)2Mn}2{μ-C(OEt)CHCH(OEt)C} (3). The controlled electro-reduction of the latter gives a radical anion whose ESR spectrum is consistent with a type III Mn0/MnI mixed valence complex. When reacted with BCl3 followed by benzylideneaniline complex 2 afford a mixture of the mixed μ-(alkylalkoxy carbene/azetidinylidene)dimanganese complex {Cp′(CO)2Mn}2{μ-C(OEt)CH2CHCH(Ph)N(Ph)C} (4) and the μ-bis(azetidinylidene)dimanganese complex {Cp′(CO)2Mn}2{μ-CN(Ph)CH(Ph)CHCHCH(Ph)N(Ph)C} (5). Complex 4 is the product of a net [2+2] cycloaddition reaction between the mixed μ-(alkylalkoxy carbene/carbyne)dimanganese complex {Cp′(CO)2Mn}2{μ-C(OEt)CH2CH2C}+ [6]+ and the imine, whereas 5 results from a net 2×[2+2] cycloaddition between the μ-bis(carbyne)dimanganese complex {Cp′(CO)2Mn}2{μ-CCH2CH2C}2+ [7]2+ and imine. The treatment of complex 4 by BCl3 followed by reaction with benzylideneaniline afford the mixed μ-(vinylidene/azetidinylidene)dimanganese complex {Cp′(CO)2Mn}2{μ-CCHCHCH(Ph)N(Ph)C} (8). Finally, the oxidative coupling-type reaction observed from the alkylalkoxy carbene complex 1 could be extended to the azetidinylidene complex [Cp′(CO)2MnCN(Ph)CHPhCH2] (10) to yield 5 in a selective manner.