Synthesis and Reversible Reductive Coupling of Cationic, Dinitrogen-Derived Diazoalkane Complexes

A series of cationic diazoalkane complexes [4-RC6H4C(H)NNMo(N[t-Bu]Ar)(3)][AlCl4], [1-R][AlCl4] (R = NMe2, Me, H, Br, CN; Ar = 3,5-C6H3Me2) has been prepared by treatment of the N-2-derived diazenido complex Me3SiNNMo(N[t-Bu]Ar)(3) with 4-RC6H4CHO and 2 equiv of AlCl3. The structures of [1-H][AlCl4] add [1-NMe2][AlCl4] were determined by X-ray crystallography. The C-N and N-N stretching modes were identified by a combined IR and Raman spectroscopy study, and other physical properties are discussed in detail. The electrochemical reduction potential for [1-R][AlCl4] was shown to be linear with the Hammett sigma parameter. This reduction process forms the C-C bonded dimer, mu-(4-RC6H4C(H)NN)(2)[Mo(N[t-Bu]Ar)(3)](2), that was characterized by X-ray crystallography for R = H. Possible mechanisms for the formation of this dimer are presented. Both electrochemical investigations and quantum chemical calculations are used to describe the odd-electron complex 4-RC6H4C(H)NNMo(N[t-Bu]Ar)(3), 1-R, that is an intermediate in the formation of [1-R](2). The C-C bond in [1-R](2) is redox-noninnocent and is broken upon oxidation. This reaction was used to prepare [1-H][A] (A = PF6-, OTf-), and possible uses of this property in charge-storage devices are discussed.