ACTIVATION OF 1-ALKYNES BY HEXAMETHYLBENZENE RUTHENIUM(II) DERIVATIVES - SYNTHESIS AND CHARACTERIZATION OF ALKOXYALKYLCARBENE RUTHENIUM(II) COMPLEXES VIA HIGHLY REACTIVE VINYLIDENE INTERMEDIATES

Hexamethylbenzene-ruthenium complexes (eta-6-C6Me6)(L)RuCl2 [L = PMe3 (1), PMe2Ph (2), PPh3 (3)] react with a variety of 1-alkynes RC = CH (R = Ph, Me, t-Bu) in several alcohols (R'OH = MeOH, EtOH, i-PrOH) to produce alkoxyalkylcarbene complexes [(eta-6-C6Me6)(L)(Cl)Ru = C(OR')(CH2R)]PF6 (4-8). Reaction of 1 with (trimethylsilyl)acetylene in methanol yields the methoxymethylcarbene complex 9a. Treatment of 1 with 3-butyn-1-ol in methanol exclusively produces [(eta-6-C6Me6)(PMe3)(Cl)Ru = activated COCH2CH2CH2)]PF6 (10a). Carbene derivatives 4-10 are formed via an electrophilic vinylidene intermediate, which has been characterized for R = Ph: the reaction of 1 with PhC = CLi or PhC = CH/Et3N gives [(eta-6-C6Me6)(PMe3)(Cl)Ru-C = CPh] (11), which affords the vinylidene complex [(eta-6-C6Me6)(PMe3)(Cl)(Ru = C = CHPh]PF6 (12) by addition of HBF4.OEt2 or CF3CO2H. Addition of methanol to 12 readily yields the methoxymethylcarbene complex 4a. Cyclic voltammetry studies of complexes 1-3 and of isoelectronic ruthenium complexes (C5H5)(L)(PPh3)RuCl (L = PPh3, CO) are reported and show that the electron deficiency of the [(C6Me6)(PR3)(Cl)Ru] fragments can explain the greatest reactivity of the corresponding vinylidene intermediates toward nucleophilic additions.