'Pincer' pyridine dicarbene complexes of nickel and their derivatives. Unusual ring opening of a coordinated imidazol-2-ylidene

Pugh, David, Boyle, Aimee and Danopoulos, Andreas A. (2008) 'Pincer' pyridine dicarbene complexes of nickel and their derivatives. Unusual ring opening of a coordinated imidazol-2-ylidene. Dalton Transactions, (8), 1087-1094. (doi:10.1039/b715769j).

Abstract

The reaction of NiBr2(DME), DME = 1,2-dimethoxyethane, with the pincer pyridine dicarbene ligands (C-N-C) ( 2) and (C-NMe-C) ( 2Me), (C-N-C = 2,6-bis-[(DiPP)imidazol-2-ylidene]pyridine, C-NMe-C = 2,6-bis-[(DiPP)imidazol-2-ylidene]-3,5-dimethylpyridine, DiPP = 2,6-diisopropylphenyl) gave the square planar complexes [Ni(C-N(Me)-C)Br]Br, 3·( Br)- and 3Me·( Br)- respectively. Transmetallation from [(C-NMe-C)2Ag2](Ag6I8), 6Me·( Ag6 I8)2- to NiBr2(DME) gave [Ni(C-NMe-C)Br](AgI2), 3Me·( AgI2)-. Reaction of 3·( Br)- with KPF6 resulted only in exchange of the ionic bromide, however the reaction of 3·( Br)- with AgBF4 in MeCN or AgOTf in THF resulted in the exchange of both coordinated and ionic bromides, giving rise to the square planar 4·( BF4)-2 and octahedral 5, respectively. In contrast, the reaction of 3Me·( AgI2)-, with excess AgOTf resulted in an unusual reverse transmetallation leading to 6Me·( OTf)-. The substitution of tmeda in Ni(CH3)2(tmeda), tmeda = N,N,N,N-tetramethylethylenediamine, by 2 produced the complex 7, in which ring opening of the heterocyclic imidazole ring of one of the NHC functional groups has taken place.

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