Reactions of tungsten phosphonium carbyne complexes with aryloxide nucleophiles to form aryloxycarbyne and η2-ketenyl complexes

Tungsten phosphoranylideneketene complexes of the type Tp′(CO)(p-OC6H4R)W(η2-(C,C)OCCPR′2Ph) (R=NO2, R′=Me (6a); R=NO2, R′=Ph (6b); R=CN, R′=Me (7a); R=CN, R′=Ph (7b); R=Cl, R′=Ph (8b)) have been synthesized from phosphonium carbyne precursors in a reaction that reflects coupling of carbonyl and carbyne ligands. In addition to these products, aryloxycarbyne complexes Tp′(CO)2WCO(p-C6H4NO2) (9a), Tp′(CO)2WCO(p-C6H4CN) (9b), and Tp′(CO)2WCO(p-C6H4Cl) (9c)) have been prepared via substitution of the phosphonium carbyne phosphine with an aryloxide nucleophile. The product ratio of substitution at the carbyne carbon to carbonyl–carbyne coupling can be tuned by variation of the aryloxide para-substituent. Aryloxy carbyne complexes are the favored products with stronger nucleophiles, while weaker nucleophiles result in a mixture of aryloxy carbyne complexes and η2-ketenyl coupled complexes. Formation of η2-ketenyl complexes is favored for the least nucleophilic aryloxides. Ketenyl complexes 6a and 6b were methylated at the ketenyl oxygen to form cationic alkyne complexes [Tp′(CO)(p-OC6H4NO2)W(η2-(C,C)CH3OCCPR2Ph)][OTf] (R=Me (10a), R=Ph (10b)). The structures of η2-ketenyl complexes 6a and 7b and the structure of cationic alkyne complex 10a were determined by X-ray crystallography.