| Research Abstract |
In this research project, we have investigated (1) synthesis of transition-metal complexes with unsaturated bonding between metal and main group elements such as silylene and germylene complexes and (2) reactivities of the unsaturated bonding, especially sigmatropic rearrangement between the M-E and M=E bonds (M = transition metal, E = main group element).
Silyl(silylene) complexes have been proposed as key intermediates in many transformations of organosilicon compounds mediated by transition metal compounds. However, such complexes are too unstable to isolate due to the electron-deficient nature of the silylene ligand. We have succeeded to stabilize the silyl(silylene) complexes kinetically using bulky Mes substituents (Mes = 2,4,6-C_6H_2Me_3) and isolated the first silyl(silylene)tungsten, molybdenum, and iron complexes. Reaction of the isolated silyl(silylene)iron complex with 'BuNC afforded a disilanyliron complex produced by 1,3-substituent migration from silyl to silylene ligand followed by 1,2-silyl migration from iron to silylene ligand.
Photo-irradiation of Cp^*W(CO)_3Me (Cp^* = η-C_5Me_5) in the presence of (2-N,N-dimethylaminophenyl)dimethylsilane gave a silyl complex in which the amino group was coordinated to the tungsten atom. Further irradiation of the silyl complex caused 1,2-aryl migration from silyl to tungsten to form abase-stabilized silylene complex.
Irradiation of phosphinosilyliron complex CpFe(CO)_2SiMe_2PPh_2 afforded a novel metallacycle complex with Fe-Si-P three-membered ring. The Fe-Si bond bears unsaturated character due to the contribution of a resonance form with a phosphino-coordinated silylene ligand. Thus reaction of the complex with acetone proceeded via coordination of acetone oxygen to the silylene ligand followed by insertion into the Si-P bond to form a Fe-Si-O-C-P five-membered ring.
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