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 [ON(CH2)O]H3 (1) ligand and its W(vi)-alkylidene and alkylidyne complexes. The alkylidyne complex [ONH(CH2)O]W[triple bond, length as m-dash]C(t)Bu(O(t)Bu) (2) forms as a result of alcoholysis of 1 with ((t)BuO)3W[triple bond, length as m-dash]C(t)Bu. Complex 2 evolves to [ON(CH2)O]W[double bond, length as m-dash]CH(t)Bu(O(t)Bu) (3) through proton migration from the N atom of the pincer ligand to the W[triple bond, length as m-dash]Cα bond. Deprotonation of 2 or 3 with Ph3PCH2 affords the anionic alkylidyne {CH3PPh3}{[ON(CH2)O]W[triple bond, length as m-dash]C(t)Bu(O(t)Bu)} (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 [ON(CH2)O]W(CH2(t)Bu)(O(t)Bu)(Cl) (5). MeOTf or TMSOTf addition to 4 generates the dianionic pincer ligated alkylidynes [ONR(CH2)O]W[triple bond, length as m-dash]C(t)Bu(O(t)Bu) (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 [O(CH2)N(CH2)O](3-) ligands. DFT computations permit comparison of the inorganic enamine effect within alkylidynes supported by all three trianionic-pincer type ONO ligands.

Synthesis and Characterization of Tungsten Alkylidene and Alkylidyne Complexes Featuring a New Carbazole-Based Rigid Trianionic ONO3– Pincer-Type Ligand

“…The downfield resonance at 288.7 ppm in the 13 C­{ 1 H} NMR spectrum of 4 provides strong support for its assignment as an alkylidyne. Four other reported [ONO] 3– trianionic pincer ligand supported anionic W alkylidyne α carbons resonate at 280.6, 286.0, 290.6, and 301.1 ppm. ,,− In addition, a single methyl resonance at 2.48 ppm in the 1 H NMR spectrum and two quartets at −70.62 and −75.47 ppm in the 19 F NMR spectrum are consistent with the C s -symmetric structural assignment.…”

Synthesis and Characterization of a Molybdenum Alkylidyne Supported by a Trianionic OCO3– Pincer Ligand

“…Trianionic pincer and pincer-type ligands confine three anionic donors to a meridional coordination sphere thereby creating metal complexes with both electronic and coordination unsaturation. When ligated to group 6 high oxidation state W-alkylidynes, − trianionic pincer and pincer-type ligands engender unique reactivity not seen among similar group 6 alkylidynes bearing monodentate ligands. For example, the W-alkylidyne complex [ t BuOCO]­WC t Bu­(THF) 2 reacts with phenylacetylene to afford the tetraanionic pincer W-alkylidene, [O 2 C­( t BuC)­W­(η 2 -CHCPh)­(THF)], which catalyzes the polymerization of alkynes into high molecular weight cyclic polyalkynes .…”

Density Functional Theory Study of the Reaction between d0 Tungsten Alkylidyne Complexes and H2O: Addition versus Hydrolysis

“…Metal complexes have also been grafted onto a support material, such as silica or alumina, to develop supported heterogeneous catalysts. , Protonolysis of ligands on the metal complexes by surface hydroxyl groups is a strategy commonly used to immobilize a metal complex on a support medium. − Investigation of the hydrolysis of metal precursors may therefore shed light on the formation of a catalytically active site of the heterogeneous catalysts . Tungsten alkylidyne complexes are very important precursors for preparing metathesis catalysts, − and efforts have been devoted to achieving a desirable supported tungsten metathesis catalyst. , …”