'Pincer' dicarbene complexes of some early transition metals and uranium

Pugh, David, Wright, Joseph A., Freeman, Sandra and Danopoulos, Andreas A. (2006) 'Pincer' dicarbene complexes of some early transition metals and uranium. Dalton Transactions, (6), 775-782. (doi:10.1039/b512133g).

Abstract

The complexes [(C-N-C)MXn(thf)(m)] with the 'pincer' 2,6-bis(imidazolylidene)pyridine, (C-N-C) = 2,6-bis(arylimidazol-2-ylidene)pyriditie, aryl = 2,6-(Pr2C6H3)-C-1, M = V, X = Cl, n = 2, to = I 1a; M = Cr, X = Cl, n = 2, m = 0, 2a, X = Br, 2b; M = Mn, X = Br, n = 2, m = 0, 3; M = Nb, X = Cl, n = 3, m = 0, 4; and M = U, X = Cl, n = 4, m = 0, 5, were synthesised by (a) substitution of labile tined (1a), thf (2a, 3, 5) or dine (4) by free (C-N-C) or by (b) reaction of the bisimidazolium salt (CH-N-CH)Br-2 with {Cr[N(SiMe3)(2)](2)(thf)(2)} followed by amine elimination (2b). Attempted alkylation of 1a, 2, 3a and 4 with Grignard or alkyl lithiums gave intractable mixtures, and in one case [reaction of 1a with (mesityl)MgBr] resulted in exchange of Cl by Br (1b). Oxidation of 1a or [(C-N-C)VCl3] with 4-methylmorpholine N-oxide afforded the trans-V(C-N-C)(=O)Cl-2, 6, which by reaction with AgBF4 in MeCN gave trans-[V(C-N-C)(=O)(MeCN)(2)][BF4](2), 7. Reaction of 1a with p-tolyl azide gave trans-V(C-N-C)(=N-p-tolyl)Cl-2 8. The complex trans-Ti(C-N-C)(=NBu1)Cl-2, 9, was prepared by substitution of the pyridine ligands in Ti(NBu1)Cl-2(py)(3) by C-N-C.

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