Coordination and reactivity of acetonitrile in tungsten(IV) complexes: oxidation, methylation and dimerization of coordinated acetonitrile

Abstract

Reaction of Tp′W(O)(CO)(I) ( 1) with silver trifluoromethanesulfonate (silver triflate, AgOTf) in dichloromethane generates Tp′W(O)(CO)(OTf) ( 2) with triflate in the coordination sphere. Dissolution of neutral triflate adduct 2 in acetonitrile immediately produces the cationic tungsten(IV) nitrile complex [Tp′W(O)(NCMe)(CO)][OTf] ( 3). Exchange of the triflate anion in 3 for the large, non-coordinating tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion, [BAr′ 4] −, produces the isolable salt [Tp′W(O)(NCMe)(CO)][BAr′ 4] ( 4). Photolysis of Tp′W(O)(CO)(I) complex ( 1) in acetonitrile promotes loss of carbon monoxide and generates the neutral tungsten(IV) nitrile complex Tp′W(O)(I)(NCMe) ( 5). Spectroscopic data for 5 is consistent with formation of an η 2-bound nitrile ligand. Chromatography of complex 5 on alumina led to oxidation to form an acylimido complex, Tp′W(O)(I)(NC(O)Me) ( 6). A dimeric complex, Tp′(O)(I)W(NC(Me)C(Me)N)W(I)(O)Tp′ ( 7) resulting from reductive coupling of two nitrile ligands was also isolated following alumina chromatography. Methylation of η 2-nitrile complex 5 by MeOTf generates the cationic η 2-iminoacyl complex [Tp′W(O)(I)(MeNCMe)][OTf] ( 9).