Synthesis, solid-state structure, solution dynamics, and reactivity of the trinuclear open cluster anion [Re2(CO)9μ-HReH(CO)4]

The addition of [M(CO)5]- anions (M = Re, Mn) to the electronically unsaturated [Re2(μ-H)2(CO)8] complex rapidly and selectively gives the trinuclear anions [ReM(CO)9(μ-H)ReH-(CO)4]- (M = Re, 2; M = Mn, 3). The single-crystal X-ray analysis of [NEt4]2 has revealed a fully staggered L-shaped structure. The anion 2 has been obtained with good selectivity also by reacting (i) [Re2(CO)9(THF)] with [H2Re(CO)4]- and (ii) [HRe2(CO)9]- with [HRe(CO)5]. The last reaction can be reversed upon treatment with CO. The reaction of the trinuclear open cluster [Re2(CO)9(μ-H)Re(CO)5] with [H2Re(CO)4]- affords 2 as well, even if not quantitatively. 1H and 13C NMR spectra of 2 show conformational freedom around both the Re-Re interactions and a dynamic process exchanging the two hydrides and the carbonyls trans to them (Ea = 67(2) kJ/mol). This last is attributable to a windshield-wiper motion of the H2Re(CO)4 fragment around the two trans diaxial carbonyls. The exchange of the hydrides with comparable ΔG‡ has been observed also for 3, suggesting that the same type of motion is occurring. 13C-NMR studies of the related [Re2(CO)9(μ-H)Re(CO)5] complex have shown the facile mobility of the bridging hydride between the two metal - metal interactions (at variance with the anion 2), resulting in a "dynamic" C2v symmetry of the molecule in solution. Upon heating, the anion 2 looses CO and gives irreversibly the previously known triangular cluster anion [Re3(μ-H)2(CO)12]-. The addition of a strong acid (CF3SO3H) results in fragmentation of the trinuclear skeleton of 2, affording [HRe(CO)5] and [Re2(μ-H)2(CO)8].