Synthesis of a base-free titanium imido and a transient alkylidene from a titanocene dinitrogen complex. Studies on Ti=NR hydrogenation, nitrene group transfer, and comparison of 1,2-addition rates

The synthesis and reactivity of the end-on bound dinitrogen complex [(eta(5)-C5H3-1,3-(SiMe3)(2))(2)Ti](2)(mu(2),eta(1),eta(1)-N-2) is described. The solid state structure of the dinitrogen compound reveals a weakly activated end-on bound N-2 ligand with an N-N bond length of 1.164(5) Angstrom. Displacement of the N2 ligand by organic azides has been used to prepare monomeric, base-free titanocene imido complexes, (eta(5)-C5H3-1,3-(SiMe3)(2))(2)Ti=NR (R = SiMe3, 2,4,6-Me-3-C6H2). While unreactive toward C-H bonds, the Ti-N linkage is readily hydrogenated and participates in group transfer reactions with unsaturated organic molecules such as carbon monoxide and benzophenone. Reaction of the N-2 complex with Ph2CN2 allowed isolation of (eta(5)-C5H3-1,3-(SiMe3)(2))(2)Ti(N2CPh2), which exists as a mixture of interconverting eta(2) and eta(1) isomers in solution. The diazoalkane complex also participates in "imido-like" reactivity, producing (eta(5)-C5H3-1,3-(SiMe3)(2))(2)Ti(NHN=CPh2)H upon addition of H-2. Changing the diazoalkane to Me3SiCHN2 resulted in isolation of the double cyclometalated titanocene (eta(5)-C5H3-eta(1)-1-SiMe2CH2-3-SiMe3)(2)Ti, arising from facile intramolecular C-H activation of the cyclopentadienyl substituent by a transient titanocene alkylidene.