Solid-state structure and fluxional solution behavior of the ambident organometallic nucleophiles (. eta. sup 3 -C sub 7 H sub 7 )M(CO) sub 3 sup minus (M = Ru, Os)

The cycloheptatrienyl carbonyl anions (C{sub 7}H{sub 7})M(CO){sub 3}{sup {minus}} (M = Ru, 1b; M = Os, 1c) have been isolated and structurally characterized as their Ph{sub 4}As{sup +} salts. Both 1b and 1c crystallize in the centrosymmetric space group P{bar 1} with two molecules per unit cell. For 1b: a = 12.308 (4) {angstrom}, b = 12.017 (5) {angstrom}, c = 11.326 (4) {angstrom}, {alpha} = 71.18 (2){degree}, {beta} = 80.93 (2){degree}, {gamma} = 90.15 (2){degree}. For 1c: a = 12.314 (2) {angstrom}, b = 12.025 (2) {angstrom}, c = 11.331 (2) {angstrom}, {alpha} = 71.12 (2){degree}, {beta} = 80.87 (2){degree}, {gamma} = 90.08{degree}. The structures were refined to R(F) = 0.0567 and 0.0268 and R{sub w}(F) = 0.0575 and 0.0278 for 3,686 and 3,905 reflections with F > 3.0{sigma}(F) for 1b and 1c, respectively. In both cases the seven-membered ring is coordinated to the metal in an {eta}{sup 3} fashion. The low-temperature-limiting {sup 1}H and {sup 13}C NMR spectra of 1c have been obtained and show that the same bonding mode is also adopted in solution. A comparison of the spectroscopic, structural, and chemical properties for the series of complexes (C{sub 7}H{sub 7})M(CO){sub 3}{sup {minus}} (M = Fe, Ru, Os) is made and explained in terms of increasing metal basicity upon descending the triad.