Reversible Transformation between Alkylidene, Alkylidyne, and Vinylidene Ligands in High-Valent Bis(phenolate) Tungsten Complexes

Abstract

A tungsten alkylidyne complex [{(OC6H2tBu2-4,6)2(SCH2CH2S)}W(≡CEt)X] (X = OtBu, 1a) with a bridged bis(phenolate) ligand was prepared from the alkoxy precursor (tBuO)3W≡CEt and the corresponding bis(phenol). The tert-butoxy ligand in 1a was substituted against chloride or trimethylsilylmethyl to give 1b (X = Cl) or 1c (X = CH2SiMe3). X-ray diffraction studies of 1a and 1c showed an octahedral cis α-configuration of the metal atom. Hydride abstraction from the β-position of the n-propylidyne ligand in 1a and 1c with [Ph3C][B(C6F5)4] gave high-valent cationic vinylidene complexes [{(OC6H2tBu2-4,6)2(SCH2CH2S)}W(═C═CHMe)X][B(C6F5)4] (2a: X = OtBu; 2c: X = CH2SiMe3), while protonation of 1a with [PhNMe2H][B(C6F5)4] gave the cationic n-propylidene complex [{(OC6H2tBu2-4,6)2(SCH2CH2S)}W(═CHEt)(OtBu)][B(C6F5)4] (3a). The alkylidyne complex 1a was regenerated from the alkylidene 3a by deprotonation with Ph3P═CH2, whereas 1c was regenerated from 2c by nucleophilic attack by a hydride at the β-carbon of the vinylide...