Synthesis, Structure, and Reactivity of Organometallic Osmium(VI) Hydroxo Compounds

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)(PiPr3)]OTf (1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene, OTf = CF3SO3) reacts with acetonitrile and benzonitrile to give [OsH{κ2-C,O-[C(Ph)NHC(R)O]}(NCR)(IPr)(PiPr3)]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{κ2-C,O-[C(Ph)NHC(CH2Ph)O]}(NCCH3)(IPr)(PiPr3)]OTf (4). The deprotonation of the osmaoxazolium ring of 2 and 4 leads to the oxazole derivatives OsH{κ2-C,O-[C(Ph)NC(R)O]}(IPr)(PiPr3) (R = Me (5), CH2Ph (6)). Complexes 2 and 4 add their Os-H and Os-C bonds to the C-C triple bond of phenylacetylene to afford [Os{η3-C 3 ,κ1-O-[CH2C(Ph)C(Ph)NHC(R)O]}(NCCH3)2(IPr)]OTf (R = Me (7), CH2Ph (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 OsH2(C≡CPh){κ2-C,O-[C(Ph)NC(R)O]}(IPr)(PiPr3) (R = Me (9), CH2Ph (10)), which reductively eliminate H2 to yield the acetylide-osmaoxazoles Os(C≡CPh){κ2-C,O-[C(Ph)NC(R)O]}(IPr)(PiPr3) (R = Me (11), CH2Ph (12)).