Tethered Boryl and Base-Stabilized Borylene Osmium Complexes from the Reaction of Os(BCl₂)Cl(CO)(PPh₃)₂ with 2-Aminopyridine

Reaction between Os(BCl 2 )Cl(CO)(PPh 3 ) 2 and 2-aminopyridine in the presence of ethanol leads to a mixture of two products. In the first, replacement of one chloride on the dichloroboryl ligand through condensation with the amino function and coordination of the pyridine nitrogen atom to osmium leads to the tethered, six-coordinate boryl complex ( 1 ). In the second, the direction of addition of the aminopyridine is reversed, leading to the tethered, pyridine-stabilized borylene complex ( 2 ). The five-membered chelate ring formed in 1 is stable and persists through reactions involving replacement of chloride both at osmium and at boron. When 1 is treated with NaBr or with NaBH 4, replacement of chloride at osmium occurs exclusively, leaving the B−Cl bond intact and giving ( 3 ) or ( 4 ), respectively. Replacement of chloride at boron requires the assistance of AgSbF 6, and the following derivatives of 1 have been characterized: ( 5 ) (with 1 equiv of AgSbF 6 ), ( 6 ) (with 2 equiv of AgSbF 6 in MeCN), and ( 7 ) (with 2 equiv of AgSbF 6 and CO in the presence of EtOH). Reaction between Os(BCl 2 )Cl(CO)(PPh 3 ) 2 and 2-(methylamino)pyridine leads to only one product, the tethered, pyridine-stabilized borylene complex ( 8 ). Four further pyridine-stabilized borylene complexes have been derived from 8 . Reaction of 8 with NaBH 4 gives ( 9 ), and 9 is hydrolyzed by water to ( 10 ). Ethanol converts 8 to ( 11 ), and 2 equiv of AgSbF 6 in acetonitrile converts 8 to ( 12 ). Crystal structures of complexes 2 − 6 and 9 are reported.