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] 4-RC subscript 6 H subscript 4 C(H)NNMo(N[t-Bu]Ar) subscript 3] [AlCl subscript 4]], [1-R][AlCl4] (R = NMe2, Me, H, Br, CN; Ar = 3,5-C6H3Me2) [[1-R][AlCl subscript 4] (R = NMe subscript 2, Me, H, Br, CN; Ar = 3,5-C subscript 6 H subscript 3 Me subscript 2)] has been prepared by treatment of the N2-derived [N subscript 2 derived] diazenido complex Me3SiNNMo(N[t-Bu]Ar)3 [Me subscript 3 SiNNMo(N[t-Bu]Ar) subscript 3] with 4-RC6H4CHO [4-RC subscript 6 H subscript 4 CHO] and 2 equiv of AlCl3 [AlCl subscript 3]. The structures of [1-H][AlCl4] [AlCl subscript 4] and [1-NMe2][AlCl4] [[1-NMe subscript 2][AlCl subscript 4]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] [AlCl subscript 4] was shown to be linear with the Hammett σ [delta] parameter. This reduction process forms the C−C bonded dimer, [μ-(4-RC6H4C(H)NN)2[Mo(N[t-Bu]Ar)3]2 [μ [mu]-(4-RC subscript 6 H subscript 4 C(H)NN) subscript 2 [Mo(N[t-Bu]Ar) subscript 3] subscript 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 [4-RC subscript 6 H subscript 4 C(H)NNMo(N[t-Bu]Ar) subscript 3], 1-R, that is an intermediate in the formation of [1-R]2 [[1-R] subscript 2]. The C−C bond in [1-R]2 [[1-R] subscript 2] is redox-noninnocent and is broken upon oxidation. This reaction was used to prepare [1-H][A] (A = PF6−, OTf−) [(A = PF subscript 6-,OTf-)], and possible uses of this property in charge-storage devices are discussed.National Science Foundation (U.S.) (Grant CHE-719157