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

摘要

Three dimeric vanadium(i) β-diketiminates [V{μ-(η~6- ArN)C(Me)CHC(Me)C(N-Ar)}]_2 (Ar = 2, 6-Me_2C _6H_3 (2), 2, 6-Et_2C_6H_3 (3), 9-anthracenyl (4)) were prepared and isolated upon reduction of their corresponding dichloro precursors VCl_2(Nacnac). Compounds 2-4 all show a structure with each vanadium atom being η~2 bonded to the β-diketiminate framework and η~6 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 (η~2-PhCC(H)C(Ph)NC_6H_3-2, 6- ~iPr_2)VN(C_6H_3-2, 6-~iPr _2)(OEt_2) (5) was isolated from the reduction of VCl _2(HC(C(Ph)NC_6H_3-2, 6-~iPr _2)_2) by KC_8. Compounds 2-4 and the inverted-sandwich divanadium complex (μ-η~6:η~6- C_6H_5Me)[V(HC(C(Me)NC_6H_3-2, 6- ~iPr_2)_2)]_2 (1) reduce Ph _2S_2 to give two vanadium dithiolates V(SPh) _2[(HC(C(Me)NC_6H_3-2, 6-R_2) _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.