Synthesis, Structure and Electrochemical Properties of Triarylamine Bridged Dicobaltdicarbon Tetrahedrane Clusters

Abstract

The reaction of [Co2(CO)6(dppm)] (1) with the ethynyl substituted triarylamines [N(C6H4-4-C≡CSiMe3)(C6H4Me-4)2] (2) or [N(C6H4-4-C≡CSiMe3)2(C6H4Me-4)] (3) affords [{Co2(CO)4(dppm)}{μ-(Me3SiC2-4-C6H4)N(C6H4Me-4)2}] (4) or a mixture of [Co2{μ-Me3SiC2-4-C6H4N(C6H4-4-C≡CSiMe3)(C6H4Me-4)}(CO)4(dppm)] (5) and [{Co2(CO)4(dppm)}2{μ-(Me3SiC2-4-C6H4)2N(C6H4Me-4)}] (6), respectively. A combination of electrochemical measurements in different electrolytes, and IR and NIR spectroscopic studies of these compounds, which feature both organometallic and organic redox active groups, indicates that the cluster centres are oxidised at significantly less positive potentials than the triarylamine moieties. Reaction of 6 with one or two equivalents of [Fe(η-C5H4COMe)Cp]PF6 gives [6][PF6]n (n = 1, 2), which are best described in terms of cluster-localised oxidation processes. Despite the presence of the substantial differences in the first and second cluster based oxidations in 6 (up to 220 mV in CH2Cl2/0.1 M [NBu4][BAr4F]), there is little ground state delocalisation between the cluster centres through the triarylamine bridge. The stabilisation of [6]+ with respect to disproportionation can be attributed to electrostatic effects.