Time-resolved infra-red spectroscopy reveals competitive water and dinitrogen coordination to a manganese(I) carbonyl complex

Time-resolved infra-red (TRIR) spectroscopy has been used to demonstrate that photolysis of [Mn(C<^>N)(CO)(4)] (C<^>N = bis-(4-methoxyphenyl)methanimine) in heptane solution results in ultra-fast CO dissociation and ultimate formation of a rare Mn-containing dinitrogen complex fac-[Mn(C<^>N)(CO)(3)(N-2)] with a diagnostic stretching mode for a terminal-bound N?N ligand at 2249 cm(-1). An isotopic shift to 2174 cm(-1) was observed when the reaction was performed under N-15(2) and the band was not present when the experiment was undertaken under an atmosphere of argon, reinforcing this assignment. An intermediate solvent complex fac-[Mn(C<^>N)(CO)(3)(heptane)] was identified which is formed in less than 2 ps, indicating that CO-release occurs on an ultra-fast timescale. The heptane ligand is labile and is readily displaced by both N-2 and water to give fac-[Mn(C<^>N)(CO)(3)(N-2)] and fac-[Mn(C<^>N)(CO)(3)(OH2)] respectively. The fac-[Mn(C<^>N)(CO)(3)(heptane)] framework showed a significant affinity for N-2, as performing the reaction under air produced significant amounts of fac-[Mn(C<^>N)(CO)(3)(N-2)]. Kinetic analysis reveals that the substitution of heptane by N-2 (k = (1.028 +/- 0.004) x 10(9) mol(-1) dm(3) s(-1)), and H2O is competitive on fast (<1 mu s) time scales. The binding of water is reversible and, under an atmosphere of N-2, some fac-[Mn(C<^>N)(CO)(3)(OH2)] converts to fac-[Mn(C<^>N)(CO)(3)(N-2)].