C−N Bond Formation on Addition of Aryl Carbanions to the Electrophilic Nitrido Ligand in TpOs(N)Cl2

• Published in: Journal of the American Chemical Society 2001-02, Vol.123 (6), p.1059-1071
• Main Authors: Crevier, Thomas J, Bennett, Brian K, Soper, Jake D, Bowman, Julie A, Dehestani, Ahmad, Hrovat, David A, Lovell, Scott, Kaminsky, Werner, Mayer, James M
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0028424

The osmium(VI) nitrido complex TpOs(N)Cl2 (1) has been prepared from K[Os(N)O3] and KTp in aqueous ethanolic HCl. It reacts rapidly with PhMgCl and related reagents with transfer of a phenyl group to the nitrido ligand. This forms Os(IV) metalla-analido complexes, which are readily protonated to give the analido complex TpOs(NHPh)Cl2 (4). The nitrido-phenyl derivatives TpOs(N)PhCl and TpOs(N)Ph2 react more slowly with PhMgCl and are not competent intermediates for the reaction of 1 with PhMgCl. Reactions of 1 with alkyl- and arylboranes similarly result in transfer of one organic group to nitrogen, leading to isolable borylamido complexes such as TpOs[N(Ph)(BPh2)]Cl2 (11). This is an unprecedented insertion of a nitrido ligand into a boron−carbon bond. Hydrolysis of 11 gives 4. Mechanistic studies suggest that both the Grignard and borane reactions proceed by initial weak coordination of Mg or B to the nitrido ligand, followed by migration of the carbanion to nitrogen. The hydrocarbyl group does not go to osmium and then move to nitrogenthere is no change in the atoms bound to the osmium during the reactions. It is suggested that there may be a general preference for nucleophiles to add directly to the metal−ligand multiple bond rather than binding to the metal first and migrating. Ab initio calculations show that the unusual reactivity of 1 results from its accessible LUMO and LUMO + 1, which are the Os⋮N π* orbitals. The bonding in 1 and its reactivity with organoboranes are reminiscent of CO.