Tungsten oxo complexes containing pi-acid ligands

Reaction of Tp′W(O)(I)(CO) (1 ) (Tp′ = hydridotris(3,5-dimethyl)pyrazolyl borate) with MeLi followed by trapping of the resultant anion by ClSiPh₂Me leads to the formation of a single isomer of the tungsten(VI) heteroatom-substituted carbene complex, Tp′W(O)(I)(=C(Me)OSiPh₂Me) (5a). The connectivity of complex 5a was confirmed by x-ray crystallography and spectral data. The acyl intermediate in the reaction, [Li][Tp′W(O)(I)(C(O)Me)] (6), was observed by spectroscopic techniques. Trapping of the acyl intermediate 6 with H+ yields the neutral hydroxy carbene complex, Tp ′W(O)(I)(=C(Me)OH) (5c). Reaction of complex 1 with PhLi generates the anionic phenyl-acyl complex [Li] [Tp ′W(O)(I)(C(O)Ph)] (8) which may be trapped with ClSiPh₂Me, yielding the phenyl carbene complex Tp′ W(O)(I)(=C(Ph)OSiPh₂Me) (7). Reaction of complex 1 with [Li][HBEt₃] at low temperature generates the anionic formyl complex [Tp′W(O)(I)(C(O)H)][Li] (9). Complex 9 can be trapped with ClSiPh₂Me to form the neutral carbene complex Tp′W(O)(I)(=C(H)OSiPh₂Me) (10). Alternatively, warming of a solution of 9 generates the tungsten hydride complex Tp′W(O)(H)(CO) (11). Carbene complex 5a reacts with [Ag][SO ₃CF₃] to form silver iodide and a coordinated triflate complex, Tp′W(O)(OSO₂CF₃)(=C(Me)OSiPh ₂Me) (13). Complex 13 reacts with Me ₂Mg to give the corresponding methyl complex Tp′W(O)(Me)(=C(Me)OSiPh ₂Me) (15). Deprotonation of carbene complex 5a generates the parent vinylidene complex Tp′W(O)(I)(=C=CH ₂) (16) in low to moderate yields.; In contrast to the acyl product formed with MeLi and 1, combining LiCuMe₂ with 1 leads to the replacement of iodide by a methyl group to form Tp′W(O)(Me)(CO) ( 2). Protonation of this methyl tungsten complex (2) in CH₂Cl₂ in the presence of acetonitrile yields methane and the cationic nitrile adduct [Tp′W(O)(CO)(NCMe)] + (3) while protonation of 2 in neat acetonitrile produces a cationic hydroxy carbene complex, [Tp ′W(O)(NCMe)(=C(Me)OH)]+ (4).; Reaction of complex 1 with [Ag][SO₃CF₃] in neat CH₂Cl₂ generates the coordinated triflate complex Tp′W(O)(OTf)(CO) (19). Dissolution of 19 in acetonitrile immediately produces the cationic nitrile complex [Tp′W(O)(NCMe)(CO)][OTf] (20a). Metathesis of the triflate anion for the large, non-coordinating [BAr₄ ′−] anion produces the isolable complex [Tp′ W(O)(NCMe)(CO)][BAr₄′] (20b ). Photolysis of 1 in acetonitrile generates the neutral nitrile complex Tp′W(O)(I)(NCMe) (21). Spectroscopic data for 20a, 20b and 21 are consistent with formation of η2-bound nitrile ligands. Attempts to chromatograph monomeric complex 21 have led to the formation of the tungsten dimer Tp′(O)(I)W=N...