Molecular transformations of bicyclic nitrogen heterocycles on triosmium clusters

The reactions of indoline (I) and tetrahydroquinoline (THQ) with Os-3(CO)(10)(CH3CN)(2) (1) have been studied. Reaction of 1 with I at ambient temperatures gives Os-3(CO)(10)(mu-H)(mu-eta(2)-C3H7NH) (2), which decarbonylates thermally to give a mixture of the tautomeric complexes Os-3(CO)(9)(mu-H)(2)(mu(3)-eta(3)-C8H7N) (3 and 4) whose structures differ by having a mu-alkylidene-imino bonding mode (3) vs a mu-amido-aryl bonding mode (4). The conversion of 2 to 3 and 4 follows strictly first-order kinetics and equilibrium constant K(4/3)=6. Further thermolysis of 3 or 4 yields the dehydrogenated cluster Os-3(CO)(9)(mu-H)(2)(mu(3)-eta(2)-C8H4-NH) (5). In the case of THQ reacting with 1, no direct analog of 2 is observed but a directly analogous pair of tautomers Os-3(CO)(9)(mu-H)(mu(3)-eta(2)-C9H9N) (6 and 7) are obtained. In addition, the product Os-3(CO)(10)(mu-H)(mu-eta(1)-C9H10N(CH3)CN) (8) is obtained, which is the result of an apparent nucleophilic attack of THQ on the coordinated acetonitrile of 1. Thermolysis of 7 yields the dehydrogenation product Os-3(CO)(10)(mu-H)(mu-eta(2)-C9H8N) (10), which maintains the eta(2)-C(8)-N bonding to the metal core, in sharp contrast to 5. Thermolysis of 8 yields Os-3(CO)(8)(mu-H)(2)(mu(3)-eta(2)-C9H9N(CH3)CN) (11) in which the acetonitrile nitrogen caps the trimetallic core and the C-H bond at C(8) has been activated. Reaction of 3 and 6 with CF3SO3H or CF3CO2H reveals reversible protonation at the nitrogen of the coordinated I or THQ. Protonation of 7 on the other hand takes place at the metal core but 7H(+) gradually rearranges to 6H(+) which yields 6 on deprotonation. The solid-state structures of 4, 6, and 10 are reported. In sharp contrast to the above results, isotetrahydroquinoline (ITHQ) reacts with 1 to give the mu-imidoyl cluster Os-3(CO)(10)(mu-H)(mu-eta(2)-C9H8N)(13), which decarbonylates to give the mu(3)-imidoyl cluster Os-3(CO)(9)(mu-H)(mu(3)-eta(2)-C9H8N)(14). The thermal behavior and dynamics of these complexes are discussed in the context of current models for hydrodenitrification.