Dinitrogen Reduction by Titanium PCP Complexes

Reduction of R PCP pincer-supported titanium dichloride (R = Cy 1a, t Bu 1b ) under a N 2 atmosphere affords the respective bridging dinitrogen complex [{( R PCP)TiCl} 2 {μ-N 2 }] (R = Cy 2a, t Bu 2b ). N 2 is bound in an end-on fashion in both 2a and 2b, though much stronger activation is observed in 2b, as evidenced by Raman spectroscopy. Surprisingly, 2a is paramagnetic, whereas 2b is diamagnetic. Exchanging the chloride for a methyl group in 2 affords [{( R PCP)TiMe} 2 {μ-N 2 }] (R = Cy 3a, t Bu 3b ); both being diamagnetic and displaying equally strong N 2 activation. The effect coordination sphere has on N 2 activation was further investigated: halide abstraction of 2b yields cationic Ti(III) [{( t Bu PCP)Ti(Et 2 O)} 2 (μ-N 2 )] [BAr F 4 ] 2 4; and reduction with 5% K/KI delivers a further reduced species 5 . Complexes 1, 2, and 5 are capable of stoichiometric dinitrogen silylation.