Synthesis, Structure, and Reactivity of η²-Phosphabenzyne−Zirconocene Dimers

The extrusion of methane from (2-phosphininyl)(methyl) zirconocenes 3a−c at 80 °C in benzene affords the corresponding η²-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 η²-benzyne−zirconocene complex:  C−C, 1.361(2); C−Zr, 2.238 and 2.250(2) Å. The P−Zr distances are normal at 2.6857(5) and 2.6922(5) Å. The reaction of these η²-phosphabenzyne complexes with acetonitrile, Ph₃PS, (diphenylphosphino)- and (trimethylsilyl)alkynes, aldehydes, and (+)-camphor have been investigated. In all cases, an insertion into the C₂−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 α-position of the phosphinine ring.