Synthesis, structure, and reactivity of eta(2)-phosphabenzyne-zirconocene dimers

The extrusion of methane from (2-phosphininyl)(methyl) zirconocenes 3a-c at 80 degrees C in benzene affords the corresponding eta(2)-phosphabenzyne-zirconocene dimers 4a-c, one of which has been characterized by X-ray crystal structure analysis. The parameters of the C-C-Zr three-membered ring are exactly similar to those found in the eta(2)-benzyne-zirconocene complex: C-C, 1.361(2); C-Zr, 2.238 and 2.250(2) Angstrom. The P-Zr distances are normal at 2.6857(5) and 2.6922(5) Angstrom. The reaction of these eta(2)-phosphabenzyne complexes with acetonitrile, Ph3P=S, (diphenylphosphino)- and (trimethylsilyl)alkynes, aldehydes, and (+)-camphor have been investigated. In all cases, an insertion into the C-2-Zr bond is observed. Hydrolysis of the intermediate zirconacycles thus obtained yielded several new 2-functional phosphinines, including a thiol (6), a vinylphosphine (8), two secondary alcohols (14 and 15), and an homochiral phosphinine-substituted alcohol (17). The regiospecificity of the insertion is ascribed to the huge concentration of negative charge at the alpha-position of the phosphinine ring.