Nickel(II)-SNS Thiolate Complexes: Reactivity and Solution Dynamics.

Abstract

Nickel coordination chemistry with a biomimetic thiolate-imine-thioether SNSMe ligand is accompanied by diverse reactivity and multidentate ligand dynamics. Reaction of Ni(acac)2 with 2 equiv of 2-(methylthio)-phenyl-benzothiazolidine (MPB) affords the bis(arylimino-phenylene-thiolate) complex Ni(κ2-SNSMe)2 (1; acac = acetylacetonate). Thermolysis of 1 in refluxing toluene is accompanied by imine C-C bond formation, yielding [Ni(N2S2)] (2) with a redox-active ligand. Protonation of 1 with NHTf2 at a low temperature released 1 equiv of MPB, yielding crystals of the dimeric dication {[Ni(μ-κ3-SNSMe)]2}(NTf2)2 (3; Tf = SO2CF3) in high yield. In contrast, the same reaction at room temperature gave also paramagnetic complexes {Ni[μ-Ni(κ3-SNSMe)2]2}(NTf2)2 (4) and {Ni[μ-Ni(κ3-SNSMe)2]3}(NTf2)2 (5) that feature coordination of two or three pseudo-octahedral, paramagnetic Ni(κ3-SNSMe)2 units to a central Ni(II) dication via thiolate bridges. Remarkably, dissolution of 3 in a variety of solvents, including weakly coordinating CH2Cl2, rapidly generates a mixture of 4 and Ni(NTf)2. Treatment of this mixture with Lewis bases L gave high yields of dimers {[Ni(μ-κ3-SNSMe)L]2}(NTf2)2 for L = CNXylyl (6a) and {[Ni(μ-κ3-SNSMe)]2(μ-dmpm)}(NTf2)2 (6b; dmpm = bis(dimethylphosphino)methane) or monomers [Ni(κ3-SNSMe)L](NTf2) for L = PMe3 (7a) and P(OMe)3 (7b). Addition of 2 equiv of the strong donor N-heterocyclic carbene ligand, IPr, to 3, however, led to thioether demethylation, affording neutral dithiolate complex Ni(κ3-SNS)(IPr) (8). Reaction products were characterized by NMR and mass spectrometry and complexes 1-5, 6a, 6b, 7a, and 8 by single-crystal X-ray diffraction.