SYNTHESIS, SOLID-STATE STRUCTURE, SOLUTION DYNAMICS, AND REACTIVITY OF THE TRINUCLEAR OPEN CLUSTER ANION [RE-2(CO)(9)((MU-H)REH(CO)(4))](-)

The addition of [M(CO)(5)](-) anions (M = Re, Mn) to the electronicall y unsaturated [Re-2(mu-H)(2)(CO)(8)] complex rapidly and selectively g ives the trinuclear anions [ReM(CO)(9){(mu-H)ReH-(CO)(4)}](-) (M = Re, 2; M = Mn, 3), The single-crystal X-ray analysis of[NEt(4)]2 has reve aled a fully staggered L-shaped structure. The anion 2 has been obtain ed with good selectivity also by reacting (i) [Re-2(CO)(9)(THF)] with [H2Re(CO)(4)](-) and (ii) [HRe2(CO)(9)](-) with [HRe-(CO)(5)]. The las t reaction can be reversed upon treatment with CO. The reaction of the trinuclear open cluster [Re-2(CO)(9){(mu-H)Re(CO)(5)}] with [H2Re(CO) 4](-) affords 2 as well, even if not quantitatively. H-1 and C-13 NMR spectra of 2 show conformational freedom around both the Re-Re interac tions and a dynamic process exchanging the two hydrides and the carbon yls trans to them (E(a) = 67(2) kJ/mol). This last is attributable to a windshield-wiper motion of the H2Re(CO)(4) fragment around the two t rans diaxial carbonyls. The exchange of the hydrides with comparable D elta G(double dagger) has been observed also for 3, suggesting that th e same type of motion is occurring, C-13-NMR. studies of the related [ Re-2(CO)(9){(mu-H)Re(CO)(5)}] complex have shown the facile mobility o f the bridging hydride between the two metal-metal interactions (at va riance with the anion 2), resulting in a ''dynamic'' C-2 upsilon symme try of the molecule in solution, Upon heating, the anion 2 looses CO a nd gives irreversibly,the previously known triangular cluster anion [R e-3(mu-H)(2)(CO)(12)](-). The addition of a strong acid (CF3SO3H) resu lts in fragmentation of the trinuclear skeleton of 2, affording [HRe(C O)(5)] and [Re-2(mu-H)2(CO)(8)].