Synthesis, reactivity, and computational studies of [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiMe]+:: Aromatic C-H bond activation at -50 °C

The titanocene compound [eta(5)-C5H5-eta(5)-C5H4CMe2C6H4Me)TiMe2] (1) was prepared from the titanocene dichloride precursor [eta(5)-C5H5-(eta(5)-C5H4CMC2C6H4Me)TiCl2] (1a). The solid-state structures of la 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 degrees C the expected cationic compound [eta(5)-C5H5 (eta(5): eta(1)-C5H4CMe2C6H4Me)TiMe](+) (2) with a coordinated tolyl group was observed. Warming the samples to -50 degrees 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) [eta(5)- C5H5-(eta(5):sigma(1)-C5H4CMe2C6H3Me)Ti-mu-MeB(C6F5)(3)] (3) and is in exchange with an outer sphere ion pair eta(5)-C5H5-(eta(5):sigma(1)-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. ne homoleptic bimetallic compound [{eta(5)-C5H5-(eta(5)-C5H4CMe2C6H4Me)Ti}(2)-mu-Me](+) (5) was prepared by reaction of 2 equiv of 1 with 1 equiv of B(C6F5)(3) in CD2Cl2 at -50 degrees 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.