Dinitrogen Reduction by Titanium PCP Complexes
Sara Belazregue1, Liam Parkin1, George Britovsek1
1Department of Chemistry, Imperial College London, MSRH, 82 Wood Lane, London W12 0BZ, U.K.
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Reduction of RPCP pincer-supported titanium dichloride (R = Cy 1a, tBu 1b) under a N2 atmosphere affords the respective bridging dinitrogen complex [{(RPCP)TiCl}2{μ-N2}] (R = Cy 2a, tBu 2b). N2 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 [{(RPCP)TiMe}2{μ-N2}] (R = Cy 3a, tBu 3b); both being diamagnetic and displaying equally strong N2 activation. The effect coordination sphere has on N2 activation was further investigated: halide abstraction of 2b yields cationic Ti(III) [{(tBuPCP)Ti(Et2O)}2(μ-N2)] [BArF4]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.
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