Synthesis and structural and reactivity studies of thiatitanacyclopropane complexes [CpTi(SCHCH2CH2S)]2 (Cp = Cp, MeCp)

Abstract: The complexes [CpTi(SCHCH2CH2S)]2 (Cp = Cp (3), MeCp (4)) are readily prepared from reaction of CpTi(SCH2CH2CH2S)Cl (Cp = Cp (1), MeCp (2)) with MeLi, AlMe3, or t-BuLi. Both compounds are centrosymmetric dimers in the solid state containing strained thiatitanacyclopropane rings. PMe3 cleaves these dimers, establishing equilibria between 3 and 4 and CpTi(SCHCH2CH2S)(PMe3) (Cp = Cp (5), MeCp (6)), while compound 3 undergoes facile acidolysis with HCl, acetic acid, PhSH, and propanedithiol affording CpTiCl3, CpTi(O2CMe)3 (7), CpTi(SCH2CH2CH2S)(SPh), and H+[CpTi(SCH2CH2CH2S)2]-?THF (8), respectively. The thiametallacycles react with benzophenone to give CpTi(SCH(CPh2O)CH2CH2S) (Cp = Cp (9); MeCp (10)) while reaction with cyclohexanone gives the dimeric species [CpTi(SCH(C6H10O)CH2CH2S)]2 (Cp = Cp (11); MeCp (12)). Analogous reactions with 2-methylcyclohexanone, menthone, and nopinone give related addition products with varying degrees of diastereoselectivity. The complex 3 also reacts with a series of imines to give complexes of the form CpTi(SCH(CHRNR)CH2CH2S), where the diastereoselectivity observed is a function of the steric demands of the substrate substituents. Reaction of 3 with nitriles, methyl isocyanate, dicyclohexylcarbodiimide, and phenyl thioisocyanate results in insertion of the substrate and subsequent enolization to give species of the form CpTi(SC=(C(R)NH)CH2CH2S). The analogous reaction with phenyl isocyanate yields the bimetallic complex CpTi(SC(PhNCO)CH2CH2S)TiCp(SCH2CH2CH2S) (27). Crystallographic characterization of a number of these reaction products is reported. Kinetic studies of the formation of 10 and 12 are consistent with initial formation of ketone complex adducts and subsequent intra- and intermolecular C-C bond formation reactions. The nature of the products, reaction mechanisms, and reactivity of strained thiatitanacyclopropane rings are discussed in the light of EHMO calculations.