Molecular Transformations of Bicyclic Nitrogen Heterocycles on Triosmium Clusters

The reactions of indoline (I) and tetrahydroquinoline (THQ) with Os 3 (CO) 10 (CH 3 CN) 2 (1) have been studied. Reaction of 1 with I at ambient temperatures gives Os 3 (CO) 10 (μ-H)(μ-η 2 -C 8 H 7 NH) ( 2 ), which decarbonylates thermally to give a mixture of the tautomeric complexes Os 3 (CO) 9 (μ-H) 2 (μ 3 -η 2 -C 8 H 7 N) ( 3 and 4 ) whose structures differ by having a μ-alkylidene−imino bonding mode ( 3 ) vs a μ-amido−aryl bonding mode ( 4 ). The conversion of 2 to 3 and 4 follows strictly first-order kinetics and the equilibrium constant K( 4 / 3) = 6. Further thermolysis of 3 or 4 yields the dehydrogenated cluster Os 3 (CO) 9 (μ-H) 2 (μ 3 -η 2 -C 8 H 4 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 (μ-H)(μ 3 -η 2 -C 9 H 9 N) ( 6 and 7 ) are obtained. In addition, the product Os 3 (CO) 10 (μ-H)(μ-η 1 -C 9 H 10 N(CH 3 )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 (μ-H)(μ-η 2 -C 9 H 8 N) ( 10 ), which maintains the η 2 -C(8)−N bonding to the metal core, in sharp contrast to 5 . Thermolysis of 8 yields Os 3 (CO) 8 (μ-H) 2 (μ 3 -η 2 -C 9 H 9 N(CH 3 )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 CF 3 SO 3 H or CF 3 CO 2 H 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 7 H + gradually rearranges to 6 H + 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 μ-imidoyl cluster Os 3 (CO) 10 (μ-H)(μ-η 2 -C 9 H 8 N) ( 13 ), which decarbonylates to give the μ 3 -imidoyl cluster Os 3 (CO) 9 (μ-H)(μ 3 -η 2 -C 9 H 8 N) ( 14 ). The thermal behavior and dynamics of these complexes are discussed in the context of current models for hydrodenitrification.