Mechanistic and Structural Studies of Electron-Deficient Quinoline Triosmium Clusters

Deuterium-labeling experiments on the sequential reactions of the previously reported electron-deficient complexes Os 3 (CO) 9 (μ 3 -η 2 -C 9 H 4 NRR‘)(μ-H)(R = R‘ = H, 1a; R = 4-Me, R‘ = H, 1b; R = H, R‘ = 6-CH 3, 1c ) with X - /X + (X = H or D) reveal that initial attack of H - is at the 5-position of the quinoline ring and that the reduction of the C(5)−C(6) double bond to yield Os 3 (CO) 9 (μ 3 -η 3 -C 9 H 6 RR‘N)(μ-H) ( 2a − c ) is not stereoselective. Related experiments with 2a − c reveal that hydride attack at the 7-position is followed by protonation at the metal core to yield Os 3 (CO) 9 (μ 3 -η 2 -C 9 H 7 RR‘N)(μ-H) 2 ( 3a − c ). The conversion of 2a to 3a is also achieved by reaction with H 2 at 75 °C and 100 psi. When this reaction is carried out with excess D 2, deuterium incorporation is observed at C(7) and at the metal core, suggesting a concerted, irreversible hydrogen addition or a radical chain reaction. The related 46-electron cluster Os 3 (CO) 9 (μ 3 -η 2 -C 9 H 8 N)(μ-H) ( 5 ) containing a C N bond in a partially reduced heterocyclic ring, as well as the three-center two-electron bond at C(8), undergoes H - attack at C(2) and not at C(5), as for 1a − c, followed by protonation at the metal core to yield Os 3 (CO) 9 (μ 3 -η 2 -C 9 H 9 N)(μ-H) 2 ( 4 ). Photolysis or thermolysis of the previously reported Os 3 (CO) 9 (μ-η 2 -(4-Me)C 9 H 5 N)(μ-H)(P(OEt) 3 ) ( 6b ) does not yield the phosphite-substituted 46-electron clusters related to 1a − c but leads only to nonspecific decomposition. Partially selective incorporation of 13 CO into 1a − c is observed to yield the corresponding decacarbonyl derivatives, and the pattern of 13 CO incorporation helps to elucidate the interconversion of the nona- and decacarbonyl derivatives. The electrochemical behavior of 1a, the dynamical behavior of 2b, and the solid-state structures of 2b, 3a, 5, and 6b are reported.