N-Heterocyclic Silylene Complexes of Nickel(0)

Reactivity studies on the nickel complex [Ni(Mes2NHSi)2(COD)] (1), ligated with the N-heterocyclic silylene 1,3-bis(2,6-dimesityl)-1,3-diaza-2-silacyclopent-4-en-2-ylidene (= Mes2NHSi; COD = cyclooctadiene) are presented. Treatment of 1 with two equivalents of the phosphines PMe3, PEt3, PnBu3, and the N-heterocyclic carbene 1,3,4,5-tetramethyl-imidazolin-2-ylidene (IMeMe) led to substitution of the COD (and not the NHSi) ligand to yield the heteroleptic substituted complexes [Ni(Mes2NHSi)2(L)2] (L = PMe3 (2), PEt3 (3), PnBu3 (4), IMeMe (5)) in good yields. The reaction of [Ni(Mes2NHSi)2(COD)] with IiPrMe (1,3-diisopropyl-4,5-dimethyl-imidazolin-2-ylidene) and the reaction of [Ni(IiPrMe)2(η2-COE)] (COE = cyclooctene) with Mes2NHSi afforded mixtures of heteroleptic three-coordinated nickel complexes [Ni(Mes2NHSi)2(IiPrMe)] (6) and [Ni(Mes2NHSi)(IiPrMe)2] (7). Complex 1 reacts with carbon monoxide also under substitution of the COD ligand to afforded mixtures of mononuclear [Ni(Mes2NHSi)2(CO)2] (8) and dinuclear, silylene-bridged [{Ni(μ-Mes2NHSi)(CO)2}2] (9). Treatment of [Ni(CO)4] with Mes2NHSi led to formation of the complexes 8 and 9, and, in addition, to the trinuclear Chini-type cluster complex [Ni3(μ-Mes2NHSi)2(μ-CO)2(CO)3] (10). In contrast to known related complexes of NHCs, complex 1 does not react with aryl fluorides and aryl chlorides and decomposes in the reaction with organyl bromides and iodides.