Synthesis, Solid-State Structure, Solution Dynamics, and Reactivity of the Trinuclear Open Cluster Anion [Re2(CO)9{(μ-H)ReH(CO)4}]-

The addition of [M(CO) 5 ] - anions (M = Re, Mn) to the electronically unsaturated [Re 2 (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 [NEt 4 ] 2 has revealed a fully staggered L-shaped structure. The anion 2 has been obtained with good selectivity also by reacting (i) [Re 2 (CO) 9 (THF)] with [H 2 Re(CO) 4 ] - and (ii) [HRe 2 (CO) 9 ] - with [HRe(CO) 5 ]. The last reaction can be reversed upon treatment with CO. The reaction of the trinuclear open cluster [Re 2 (CO) 9 {(μ-H)Re(CO) 5 }] with [H 2 Re(CO) 4 ] - affords 2 as well, even if not quantitatively. 1 H and 13 C 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 ( E a = 67(2) kJ/mol). This last is attributable to a windshield-wiper motion of the H 2 Re(CO) 4 fragment around the two trans diaxial carbonyls. The exchange of the hydrides with comparable Δ G ⧧ has been observed also for 3, suggesting that the same type of motion is occurring. 13 C-NMR studies of the related [Re 2 (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” C 2 v symmetry of the molecule in solution. Upon heating, the anion 2 looses CO and gives irreversibly the previously known triangular cluster anion [Re 3 (μ-H) 2 (CO) 12 ] - . The addition of a strong acid (CF 3 SO 3 H) results in fragmentation of the trinuclear skeleton of 2, affording [HRe(CO) 5 ] and [Re 2 (μ-H) 2 (CO) 8 ].