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 N2-derived diazenido complex Me3SiNNMo(N[t-Bu]Ar)3 with 4-RC6H4CHO and 2 equiv of AlCl3. The structures of [1-H][AlCl4] and [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 σ parameter. This reduction process forms the C−C bonded dimer, μ-(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.