CYCLOADDITION AND NUCLEOPHILIC-SUBSTITUTION REACTIONS OF THE MONOMERIC TITANOCENE SULFIDO COMPLEX (ETA(5)-C5ME5)(2)(C5H5N)TI=S

The titanocene sulfide complex Cp-2(py)Ti=S (1, py = pyridine) reacts reversibly with terminal alkynes to give the thiametallacyclobutenes Cp-2Ti(SC(R)=CH) (R = H (2), Ph (3), Tol (4), TMS (5)). Complex 1 als o reacts with alkyl halides to give products derived from formal 1,2-a ddition across the titanium-sulfur bond. Treatment of 1 with allyl hal ides results in the formation of Cp-2Ti(X)SCH2CHCH2 (X = Cl (10), F ( 16), Br (17), I (18)). Reaction of 1 with alkyl-substituted allyl chlo rides showed that displacement of the halide anion occurs with S(N)2' regiochemistry. A kinetic study of the conversion of 1 to 10 is consis tent with a mechanism in which pyridine dissociation from the metal ce nter precedes reaction of allyl chloride with the Cp-2Ti=S fragment. The S(N)2' regiochemistry of the reaction is explained by postulating coordination of the halogen atom to the metal center in the reaction t ransition state. Complex I also reacts with allyl tosylate, but labeli ng experiments show (in contrast to the allyl chloride reaction) that substitution of the tosylate functionality occurs via a S(N)2 pathway. Heterocycles formed from the reaction of 1 with alpha,beta-unsaturate d aldehydes were also isolated and characterized.