Reactions of [Cp2Ti(η2-Me3SiC2SiMe3)] with 1,4-Bis(diphenylphosphanyl)but-2-yne: Coupling and Isomerization versus Phosphorylation

The reactions of [Cp2Ti((2)-Me3SiC2SiMe3)] (1; Cp = (5)-cyclopentadienyl) with 1,4-bis(diphenylphosphanyl)but-2-yne (2) have been investigated and found to yield a mixture of products. From these, through the coupling of 2, the tetrasubstituted titanacyclopentadiene [Cp2Ti(CCH2PPh2)(4)] (3) was isolated. In addition, small amounts of very unusual complexes were obtained and characterized. In one case, the substrate 2 isomerized to the allene Ph2PC(H)=C=C(H)CH2PPh2, which formed the complex [Cp2Ti{(3)-Ph2PC(H)=C=C(H)CH2PPh2}] (4) through the coordination of a double bond and one of the phosphorus atoms. Another complex, [Cp2Ti{-C(CH2PPh2)=C(CH2PPh2)P(Ph-2)H-}] (5), was identified to be the result of a formal hydrophosphorylation of the substrate 2 by HPPh2, and features a Ti-H-P bridge. It is not clear how HPPh2 was formed. One possible explanation is the dehydrophosphorylation of the substrate with the formation of HPPh2 and the butatriene H2C=C=C=C(H)PPh2 [tautomer of the but-2-en-3-yne HCC-CH=C(H)PPh2]. The molecular structures of complexes 4 and 5 were determined by X-ray analysis.