Synthesis and Characterization of Tungsten(VI) Alkylidene Complexes Supported by an [OCO]3− Trianionic Pincer Ligand: Progress towards the [tBuOCO]W≡CC(CH3)3 Fragment

Abstract

The synthesis and characterization of trianionic [tBuOCO]3− pincer-supported tungsten alkylidene and alkylidyne complexes are described. The reaction of an equimolar ratio of (tBuO)3W≡CC(CH3)3 (where tBuO = tert-butoxide) with [tBuOCO]H3 (9) and 2,6-diisopropylphenol affords the alkylidene [tBuOCO]W═CHC(CH3)3(O-2,6-C6H3-iPr2) (10), with a five-coordinate tungsten center that adopts a distorted square-pyramidal geometry. Treatment of (Np)3W≡CC(CH3)3 (11) with 9 provides an equilibrium mixture of the two isomeric alkylidenes with the general formula [(tBuOCO)W═CHC(CH3)3(μ-tBuOCHO)W═CHC(CH3)3(tBuOCO)] (12kin and 12therm). Single crystals of the two isomers cocrystallize and were amenable to X-ray diffraction studies, which revealed subtle differences in their molecular structures, most notably the orientation of the bridging ligand. The complexes are each comprised of two square-pyramidal tungsten ions linked by the diphenolate form of the OCO ligand. Isomer 12kin could not be isolated independently; however...