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. Dipp(2)NHSi (1,3-bis(2,6-diisopropyphenyl)-1,3-diaza-4-silacyclopent-4-en-2-yliden) reacts with [{(eta(5)-C5H5)Fe(CO)(2)}(2)] and [(eta(5)-C5H5)(2)Ni] to yield, in contrast to the results obtained for analogous transformations with NHCs, the dinuclear silylene-bridged complexes [{(eta(5)-C5H5)Fe(CO)}(2)(mu-CO)(mu-Dipp(2)NHSi)] (1) and [{(eta(5)-C5H5)Ni(mu-Dipp(2)NHSi)}(2)] (2). The reaction with [(eta(5)-C5H5)Ni(PPh3)(Cl)] leads with insertion of the silylene into the nickel-chloride bond to [(eta(5)-C5H5)Ni(PPh3)(Dipp(2)NHSi-Cl)] (3). [Mn(CO)(5)(Cl)] reacts with 2 equiv of Dipp(2)NHSi to afford [Mn(CO)(4)(Dipp(2)NHSi)(Dipp(2)NHSi-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 Dipp(2)NHSi with the corresponding iodide complex [Mn(CO)(5)(I)] leads to formation of the bis-silylene complex [Mn(CO)(3)(Dipp(2)NHSi)(2)(I)] (4).