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Synthesis of (1-Adamantylimido)vanadium(V)-alkyl Complexes Containing a Chelate Alkoxo(imino)pyridine Ligand, and Reactions with Alcohols (ROH) That Proceed via Intermediates Formed by Coordination of ROH

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posted on 09.03.2009, 00:00 by Wenjuan Zhang, Shohei Katao, Wen-Hua Sun, Kotohiro Nomura
An (1-adamantylimido)vanadium(V)-dialkyl complex containing a chelate alkoxo(imino)pyridine ligand, V(NAd)(CH2SiMe3)2(L) [2, Ad = 1-adamantyl, L = 6-OC(Me)2-2-{(2,6-iPr2C6H3)NCMe}-C5H3N], has been prepared, and some reactions with (CF3)2(CH3)COH, (CF3)2CHOH, 2,6-Me2C6H3OH, and 2,6-Me2C6H3SH in C6D6 have been explored. Two alkyl groups in 2 take a trans form, as determined by the dichloride analogue V(NAd)Cl2(L) (1), and no reaction took place or afforded a negligible amount of the product even if the C6D6 solution containing 2 and PMe3 (13 equiv) or NHC [2.1 equiv, NHC = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] was heated at 80 °C for 72 h. The reaction of 2 with (CF3)2CHOH and (CF3)2(CH3)COH at 25 °C afforded intermediates V(NAd)(CH2SiMe3)2(L)[ROH] [R = CH(CF3)2, C(CF3)2(CH3)], and the resultant species were converted to the original complex 2 if the mixed solutions were placed in vacuo (to remove volatiles). The reactions with ROH upon heating or by stirring for longer hours afforded the monoalkyl-alkoxo species V(NAd)(CH2SiMe3)(L)(OR) [R = CH(CF3)2 (4), C(CF3)2(CH3) (5)]; complex 4 determined by X-ray crystallography has a distorted tetrahedral geometry around vanadium. It has thus been proposed that reactions of the dialkyl complex 2 with ROH proceeded via pentacoordinated intermediates formed by coordination of ROH, accompanied by dissociation of two neutral nitrogen donors in the chelate ligand.