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)] (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)(N)] with a diagnostic stretching mode for a terminal-bound N[triple bond, length as m-dash]N ligand at 2249 cm. An isotopic shift to 2174 cm was observed when the reaction was performed under N 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)(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 and water to give fac-[Mn(C^N)(CO)(N)] and fac-[Mn(C^N)(CO)(OH)] respectively. The fac-[Mn(C^N)(CO)(heptane)] framework showed a significant affinity for N, as performing the reaction under air produced significant amounts of fac-[Mn(C^N)(CO)(N)]. Kinetic analysis reveals that the substitution of heptane by N (k = (1.028 ± 0.004) × 10 mol dm s), and HO is competitive on fast (<1 μs) time scales. The binding of water is reversible and, under an atmosphere of N, some fac-[Mn(C^N)(CO)(OH)] converts to fac-[Mn(C^N)(CO)(N)].