Thienyl-Substituted Allenylideneruthenium(II) Complexes: Synthesis, Spectroscopic Characterization, and Electrochemical Studies

Two propargylic alcohols incorporating a thienyl moiety were synthesized, and their subsequent reaction to form allenylideneruthenium(II) complexes is reported. The alkynol 4-hydroxy-4-ethynylcyclopenta[2,1-b:3,4-b']dithiophene (4) reacts with cis-[RuCl2(P boolean AND P)(2)] (P boolean AND P = dppm, dppe) to afford the allenylidene complexes trans-[RuCl(P boolean AND P)(2){=C=C=C(4-cyclopentadithiophene)}]PF6 (P boolean AND P = dppm, 5a; dppe, 5b). Similar reactions of cis-[RuCl2(P boolean AND P)(2)] with 1,1-di(2'-thienyl)prop-2-yn-1-ol (2) yield products consistent with formulation as an allenylideneruthenium(II) complex, although with no identifiable counteranion. In contrast the reaction of 2 with [RuClCp(dppe)] readily affords the deep purple complex [RuCp-(dppe){=C=C=C(2-thienyl)(2)}]PF6. The complexes have been characterized by spectroscopy and mass spectrometry, and a single-crystal X-ray structural determination of complex 5a was undertaken. The allenylidene complexes obtained in a pure state have also been investigated through cyclic voltammetry, and preliminary investigations illustrate their potential as synthons for organometallic polymers via electropolymerization.