Reactions of Os(CO)4(η2-C2H2) with Phosphines: Substitution and Facile CO Insertion into Osmium−Alkyne Bonds. Combined Synthetic and Kinetic Studies

Rhodium-Catalyzed [2+2+1+1] Cyclocarbonylative Coupling of Alkynes with Carbon Monoxide Affording Tetrasubstitutedp-Benzoquinones

In this strategy, the tetrasubstituted benzoquinones have been prepared directly by a [2+2+1+1] cyclocarbonylative coupling reaction of internal alkynes with CO in the presence of [RhCl(CO)2]2. The low concentration of CO in the reaction is the crucial point for the chemoselective formation of tetrasubstituted benzoquinones in good to high yields. Functional groups such as chloro, methoxy, cyano, vinyl, fluoro, and carboxylate are tolerated under the reaction conditions.

Reaction of [Fe(CO)4(η2-Me3SiC≡CSiMe3)] with PMe3 — CO rather than alkyne substitution

Reaction of [Fe(CO)4(η2-BTMSA)] (1) (BTMSA = Me3SiCCSiMe3) with trimethylphosphine proceeds by stepwise loss of CO ligands yielding [Fe(CO)3(PMe3)(η2-BTMSA)] (2) and [Fe(CO)2(PMe3)2(η2-BTMSA)] (3), respectively. This demonstrates the CO dissociative nature of substitution in 1 toward PMe3, as established in analogous M(CO)4(η2-alkyne) (M = Fe, Ru, Os) compounds. The structures of all three compounds have been determined by X-ray crystallography to assess the effect of CO substitution by PMe3 on the metal–alkyne bonding in these molecules.Key words: iron, carbonyl, alkyne, substitution, phosphine, steric effects.