Cycloaddition and Nucleophilic Substitution Reactions of the Monomeric Titanocene Sulfido Complex (η5-C5Me5)2(C5H5N)TiS

Abstract

The titanocene sulfido complex Cp*2(py)TiS (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 also reacts with alkyl halides to give products derived from formal 1,2-addition across the titanium−sulfur bond. Treatment of 1 with allyl halides 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 chlorides showed that displacement of the halide anion occurs with SN2‘ regiochemistry. A kinetic study of the conversion of 1 to 10 is consistent with a mechanism in which pyridine dissociation from the metal center precedes reaction of allyl chloride with the Cp*2TiS fragment. The SN2‘ regiochemistry of the reaction is explained by postulating coordination of the halogen atom to the metal center in the reaction transition state. Complex 1 also reacts with allyl tosylate, but labeling experiments show (in contrast to the allyl chloride reaction) that substitution of the tosylate functionality occurs via a SN2 pathway. Heterocycles formed from the reaction of 1 with α,β-unsaturated aldehydes were also isolated and characterized.