A new ONO3− trianionic pincer ligand with intermediate flexibility and its tungsten alkylidene and alkylidyne complexes†
Abstract
This report details the synthesis and characterization of the semi-flexible [ONCH2O]H3 (1) ligand and its W(VI)-alkylidene and alkylidyne complexes. The alkylidyne complex [ONHCH2O]WCtBu(OtBu) (2) forms as a result of alcoholysis of 1 with (tBuO)3W
CtBu. Complex 2 evolves to [ONCH2O]W
CHtBu(OtBu) (3) through proton migration from the N atom of the pincer ligand to the W
Cα bond. Deprotonation of 2 or 3 with Ph3PCH2 affords the anionic alkylidyne {CH3PPh3}{[ONCH2O]W
CtBu(OtBu)} (4). Complex 4 exhibits pincer-ligand-centered reactivity with electrophiles (H+, Me+, and TMS+), in spite of its enhanced inorganic enamine interaction. Addition of 2 equiv. of HCl to 4 yields the W(VI)-neopentyl complex [ONCH2O]W(CH2tBu)(OtBu)(Cl) (5). MeOTf or TMSOTf addition to 4 generates the dianionic pincer ligated alkylidynes [ONRCH2O]W
CtBu(OtBu) (R = Me (6-Me); TMS (6-TMS)). Complexes 2–5 were characterized by multinuclear NMR spectroscopy, and combustion analysis. Complexes 4 and 5 were also characterized by single crystal X-ray diffraction. This work bridges the gap in the series involving W(VI)-alkylidynes ligated to the rigid [CF3-ONO]3−, and the flexible [OCH2NCH2O]3− ligands. DFT computations permit comparison of the inorganic enamine effect within alkylidynes supported by all three trianionic-pincer type ONO ligands.