Synthesis, Reactivity, and Computational Studies of [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiMe]+: Aromatic C−H Bond Activation at −50 °C

Abstract

The titanocene compound [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiMe2] (1) was prepared from the titanocene dichloride precursor [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiCl2] (1a). The solid-state structures of 1a and 1 were determined and are similar to other titanocene compounds. The reaction of compound 1 with B(C6F5)3 in CD2Cl2 was monitored by NMR spectroscopy. At −60 °C the expected cationic compound [η5-C5H5(η5:η1-C5H4CMe2C6H4Me)TiMe]+ (2) with a coordinated tolyl group was observed. Warming the samples to −50 °C leads to evolution of methane, indicating C−H bond activation of the coordinated tolyl moiety. The so-formed titanacycles form with the anion [MeB(C6F5)3]− the inner sphere ion pair (ISIP) [η5-C5H5-(η5:σ1-C5H4CMe2C6H3Me)Ti-μ-MeB(C6F5)3] (3) and is in exchange with an outer sphere ion pair η5-C5H5-(η5:σ1-C5H4CMe2C6H3Me)Ti]+[MeB(C6F5)3]− (4), with the free coordination site probably occupied by a solvent molecule. The structure of 4 could not be determined unambiguously. The homoleptic bimetallic compound [{η5-C5H5-(η5-C5H4CMe2C6H4Me)Ti}2-μ-Me]+ (5) was prepared by reaction of 2 equiv of 1 with 1 equiv of B(C6F5)3 in CD2Cl2 at −50 °C and monitored by NMR spectroscopy. Detailed density functional theory (DFT) studies of the formation of 3 and 4 from 2 corroborate the NMR results.