Reactions of [Cp 2 Ti(η 2 ‐Me 3 SiC 2 SiMe 3 )] with 1,4‐Bis(diphenylphosphanyl)but‐2‐yne: Coupling and Isomerization versus Phosphorylation

The reactions of [Cp 2 Ti(η 2 ‐Me 3 SiC 2 SiMe 3 )] ( 1 ; Cp = η 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 [Cp 2 Ti(CCH 2 PPh 2 ) 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 Ph 2 PC(H)=C=C(H)CH 2 PPh 2 , which formed the complex [Cp 2 Ti{η 3 ‐Ph 2 PC(H)=C=C(H)CH 2 PPh 2 }] ( 4 ) through the coordination of a double bond and one of the phosphorus atoms. Another complex, [Cp 2 Ti{‐C(CH 2 PPh 2 )=C(CH 2 PPh 2 )P(Ph 2 )H‐}] ( 5 ), was identified to be the result of a formal hydrophosphorylation of the substrate 2 by HPPh 2 , and features a Ti–H–P bridge. It is not clear how HPPh 2 was formed. One possible explanation is the dehydrophosphorylation of the substrate with the formation of HPPh 2 and the butatriene H 2 C=C=C=C(H)PPh 2 [tautomer of the but‐2‐en‐3‐yne HC≡C‐CH=C(H)PPh 2 ]. The molecular structures of complexes 4 and 5 were determined by X‐ray analysis.