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

[Image: see text] 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)).