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 = 1,5-cyclooctadiene) are presented. Treatment of 1 with two equivalents of the phosphines PMe₃, PEt₃ and P<i>n</i>Bu₃, and the N-heterocyclic carbene 1,3,4,5-tetramethyl-imidazolin-2-ylidene (IMe^Me) 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), P<i>n</i>Bu₃ (4), IMe^Me (5)) in good yields. The reaction of [Ni(Mes₂NHSi)₂(COD)] with IiPr^Me (1,3-diisopropyl-4,5-dimethyl-imidazolin-2-ylidene) and the reaction of [Ni(IiPr^Me)₂(η²-COE)] (COE = cyclooctene) with Mes₂NHSi afforded mixtures of heteroleptic three-coordinated nickel complexes [Ni(Mes₂NHSi)₂(IiPr^Me)] (6) and [Ni(Mes₂NHSi)(IiPr^Me)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 also 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.