N-Heterocyclic Silylenes as Metal-Metal Bridges and Metal-Halide Activators in Transition Metal Complexes.

Several examples are provided that NHSi (N-heterocyclic silylene) ligands are much better metal-metal bridging ligands as compared to NHCs and that NHSi also tends to insert much more easily into metal-halide bonds of transition metal complexes. Dipp2NHSi (1,3-bis(2,6-diisopropyphenyl)-1,3-diaza-4-silacyclopent-4-en-2-yliden) reacts with [{(η5-C5H5)Fe(CO)2}2] and [(η5-C5H5)2Ni] to yield, in contrast to the results obtained for analogous transformations with NHCs, the dinuclear silylene-bridged complexes [{(η5-C5H5)Fe(CO)}2(μ-CO)(μ-Dipp2NHSi)] (1) and [{(η5-C5H5)Ni(μ-Dipp2NHSi)}2] (2). The reaction with [(η5-C5H5)Ni(PPh3)(Cl)] leads with insertion of the silylene into the nickel-chloride bond to [(η5-C5H5)Ni(PPh3)(Dipp2NHSi-Cl)] (3). [Mn(CO)5(Cl)] reacts with 2 equiv of Dipp2NHSi to afford [Mn(CO)4(Dipp2NHSi)(Dipp2NHSi-Cl)] (5), in which one of the silylenes has inserted into the Mn-Cl bond and acts as a chloro silyl ligand. The reaction of 2 equiv of Dipp2NHSi with the corresponding iodide complex [Mn(CO)5(I)] leads to formation of the bis-silylene complex [Mn(CO)3(Dipp2NHSi)2(I)] (4).