Ligand-controlled synthesis of vanadium(i) β-diketiminates and their catalysis in cyclotrimerization of alkynes?

Dalton Transactions Pub Date: 2010-12-13 DOI: 10.1039/C0DT01061H

Abstract

Three dimeric vanadium(I) β-diketiminates [V{μ-(η6-ArN)C(Me)CHC(Me)C(N–Ar)}]2 (Ar = 2,6-Me2C6H3 (2), 2,6-Et2C6H3 (3), 9-anthracenyl (4)) were prepared and isolated upon reduction of their corresponding dichloro precursors VCl2(Nacnac). Compounds 2–4 all show a structure with each vanadium atom being η2 bonded to the β-diketiminate framework and η6 bonded to a flanking ring of a β-diketiminato ligand, attached to the other vanadium centre within the dimer. No metal–metal bonding interactions are observed in these dimers due to long vanadium–vanadium separations. Compounds 2–4 display an antiferromagnetic exchange between the two vanadium centres. An imido azabutadienyl complex (η2-PhCC(H)C(Ph)NC6H3-2,6-iPr2)VN(C6H3-2,6-iPr2)(OEt2) (5) was isolated from the reduction of VCl2(HC(C(Ph)NC6H3-2,6-iPr2)2) by KC8. Compounds 2–4 and the inverted-sandwich divanadium complex (μ-η6:η6-C6H5Me)[V(HC(C(Me)NC6H3-2,6-iPr2)2)]2 (1) reduce Ph2S2 to give two vanadium dithiolates V(SPh)2[(HC(C(Me)NC6H3-2,6-R2)2)] (R = Et (6), iPr (7)) through an oxidative addition. Most notably, 1 and 3 catalyze the cyclotrimerization of alkynes, giving tri-substituted benzenes in good yields and a 1,3,5-triphenylbenzene coordinated intermediate 8 was isolated and characterized.

Graphical abstract: Ligand-controlled synthesis of vanadium(i) β-diketiminates and their catalysis in cyclotrimerization of alkynes
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