Dissimilarity in the Chemical Behavior of Osmaoxazolium Salts and Osmaoxazoles: Two Different Aromatic Metalladiheterocycles.

The preparation of aromatic hydride-osmaoxazolium and hydride-oxazole compounds is reported and their reactivity toward phenylacetylene investigated. Complex [OsH(OH)(≡CPh)(IPr)(P i Pr 3 )]OTf ( 1 ; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene, OTf = CF 3 SO 3 ) reacts with acetonitrile and benzonitrile to give [OsH{κ 2 - C,O -[C(Ph)NHC(R)O]}(NCR)(IPr)(P i Pr 3 )]OTf (R = Me ( 2 ), Ph ( 3 )) via amidate intermediates, which are generated by addition of the hydroxide ligand to the nitrile. In agreement with this, the addition of 2-phenylacetamide to acetonitrile solutions of 1 gives [OsH{κ 2 - C,O -[C(Ph)NHC(CH 2 Ph)O]}(NCCH 3 )(IPr)(P i Pr 3 )]OTf ( 4 ). The deprotonation of the osmaoxazolium ring of 2 and 4 leads to the oxazole derivatives OsH{κ 2 - C,O -[C(Ph)NC(R)O]}(IPr)(P i Pr 3 ) (R = Me ( 5 ), CH 2 Ph ( 6 )). Complexes 2 and 4 add their Os-H and Os-C bonds to the C-C triple bond of phenylacetylene to afford [Os{η 3 - C 3 , κ 1 - O -[CH 2 C(Ph)C(Ph)NHC(R)O]}(NCCH 3 ) 2 (IPr)]OTf (R = Me ( 7 ), CH 2 Ph ( 8 )), bearing a tridentate amide-N-functionalized allyl ligand, while complexes 5 and 6 undergo a vicarious nucleophilic substitution of the hydride at the metal center with the alkyne, via the compressed dihydride adduct intermediates OsH 2 (C≡CPh){κ 2 - C,O -[C(Ph)NC(R)O]}(IPr)(P i Pr 3 ) (R = Me ( 9 ), CH 2 Ph ( 10 )), which reductively eliminate H 2 to yield the acetylide-osmaoxazoles Os(C≡CPh){κ 2 - C,O -[C(Ph)NC(R)O]}(IPr)(P i Pr 3 ) (R = Me ( 11 ), CH 2 Ph ( 12 )).