Probing the catalytic potential of chloro nitrosyl rhenium(i) complexes?

Dalton Transactions Pub Date: 2011-02-01 DOI: 10.1039/C0DT00842G

Abstract

The reduction of the mononitrosyl Re(II) salt [NMe4]2[ReCl5(NO)] (1) with zinc in acetonitrile afforded the Re(I) dichloride complex [ReCl2(NO)(CH3CN)3] (2). Subsequent ligand substitution reactions with PCy3, PiPr3 and P(p-tolyl)3 afforded the bisphosphine Re(I) complexes [ReCl2(NO)(PR3)2(CH3CN)] (3, R = Cy a, iPr b, p-tolyl c) in good yields. The acetonitrile ligand in 3 is labile, permitting its replacement with H2 (1 bar) to afford the dihydrogen Re(I) complexes [ReCl2(NO)(PR3)2(η2-H2)] (4, R = Cy a, iPr b). The catalytic activity of 2, 3 and 4 in hydrogen-related catalyses including dehydrocoupling of Me2NH·BH3, dehydrogenative silylation of styrenes, and hydrosilylation of ketones and aryl aldehydes were investigated, with the main focus on phosphine and halide effects. In the dehydrocoupling of Me2NH·BH3, the phosphine-free complex 2 exhibits the same activity as the bisphosphine-substituted systems. In the dehydrogenative silylation of styrenes, 3a and 4a bearing PCy3 ligands exhibit high catalytic activities. Monochloro Re(I) hydrides [Re(Cl)(H)(NO)(PR3)2(CH3CN)] (5, R = Cy a, iPr b) were proven to be formed in the initiation pathway. The phosphine-free complex 2 showed in dehydrogenative silylations even higher activity than the bisphosphine derivatives, which further emphasizes the importance of a facile phosphine dissociation in the catalytic process. In the hydrosilylation of ketones and aryl aldehydes, at least one rhenium-bound phosphine is required to ensure high catalytic activity.

Graphical abstract: Probing the catalytic potential of chloro nitrosyl rhenium(i) complexes
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