| Summary: | Square-planar alkylidyne and five-coordinate alkylidene mixed iPr3P–Os–IPr (IPr = 1, 3-bis(diisopropylphenyl)imidazolylidene) complexes have been discovered and characterized, and their formation has been rationalized. The cationic five-coordinate hydride-alkylidyne compounds [OsHX(=CPh)(IPr)(PiPr3)]OTf (X = Cl (1), F (4); OTf = CF3SO3) undergo deprotonation with KOtBu to afford the trans-halide-alkylidyne square-planar derivatives OsX(=CPh)(IPr)(PiPr3) (X = Cl (2), F (5)). Oxidative addition of the C(sp)–H bond of phenylacetylene and methyl propiolate along the Cl–Os–CPh axis of 2 with the hydrogen atom directed to the alkylidyne leads to alkynyl-cis-hydride-alkylidyne intermediates, which rapidly evolve into the five-coordinate alkylidene complexes Os(C=CR)Cl(-CHPh)(IPr)(PiPr3) (R = Ph (6), CO2Me (7)) as a consequence of the migration of the hydride from the metal center to the Ca atom of the alkylidyne. Oxidative addition of the C(sp)–H bond of methyl propiolate along the X–Os–CPh axis of 2 and 5 with the hydrogen atom directed to the halide gives the alkynyl-trans-hydride-alkylidyne derivatives OsH(C=CCO2Me)X(=CPh)(IPr)(PiPr3) (X = Cl (8), F (9)). Complex 8 evolves into 7. However, complex 9 containing the stronger p-donor fluoride is stable. The oxidative addition of HCl to 2 selectively yields the cis-hydride-alkylidyne compound OsHCl2(=CPh)(IPr)(PiPr3) (10), which is also stable.
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