Dinitrogen Reduction by Titanium PCP Complexes

Reduction of ^RPCP pincer-supported titanium dichloride (R = Cy <b>1a</b>, ^<i>t</i>Bu <b>1b</b>) under a N₂ atmosphere affords the respective bridging dinitrogen complex [{(^RPCP)TiCl}₂{μ-N₂}] (R = Cy <b>2a</b>, ^<i>t</i>Bu <b>2b</b>). N₂ is bound in an end-on fashion in both <b>2a</b> and <b>2b</b>, though much stronger activation is observed in <b>2b</b>, as evidenced by Raman spectroscopy. Surprisingly, <b>2a</b> is paramagnetic, whereas <b>2b</b> is diamagnetic. Exchanging the chloride for a methyl group in <b>2</b> affords [{(^RPCP)TiMe}₂{μ-N₂}] (R = Cy <b>3a</b>, ^<i>t</i>Bu <b>3b</b>); both being diamagnetic and displaying equally strong N₂ activation. The effect coordination sphere has on N₂ activation was further investigated: halide abstraction of <b>2b</b> yields cationic Ti(III) [{(^<i>t</i>BuPCP)Ti(Et₂O)}₂(μ-N₂)] [BAr^F₄]₂ <b>4</b>; and reduction with 5% K/KI delivers a further reduced species <b>5</b>. Complexes <b>1</b>, <b>2</b>, and <b>5</b> are capable of stoichiometric dinitrogen silylation.