Synthesis and reactivity of cationic vinylidene and allenylidene ruthenium(II) complexes containing the phosphinoether Pri2PCH2CH2OMe as chelating ligand

Abstract

An efficient method for the preparation of the chelate complex [RuCl₂(κ²P,O-Prⁱ₂PCH₂CH₂OMe)₂]2, using [{RuCl₂(C₈H₁₂)}_n]1 as starting material, has been developed. Compound 2 reacts with terminal alkynes HCCR (R = Ph, C₆H₄Me-p or C₆H₄CCH-m) in the presence of Ag(O₃SCF₃) to give the octahedral cationic vinylidene complexes [RuCl(CCHR)(κ²P,O-Prⁱ₂PCH₂CH₂OMe)₂][O₃SCF₃]4–6 in 70–80% yield. The parent derivative 3(R = H) has been prepared analogously but is stable only under an acetylene atmosphere. Crystal structural analysis of 4(R = Ph) confirms a cis arrangement of the chloro and vinylidene ligands. Treatment of 4 with basic Al₂O₃ produces, by deprotonation, a mixture of two isomers [RuCl(CCPh)(κ²P,O-Prⁱ₂PCH₂CH₂OMe)₂]7, 8 with the alkynyl and chloro ligands in either cis or trans disposition. Compounds 7, 8 easily react by partial cleavage of the chelate bonds to give the corresponding dicarbonyl derivatives [RuCl(CCPh)(CO)₂(κP-Prⁱ₂PCH₂CH₂OMe)₂]9, 10. The isomeric mixture can be completely converted into the thermodynamically preferred species 9 with the two CO and the alkynyl and chloro ligands cis disposed. The neutral vinylidene complexes [RuX₂(CCHPh)(κP-Prⁱ₂PCH₂CH₂OMe)(κ²P,O-Prⁱ₂PCH₂CH₂OMe)](X = CN, I or Br) were obtained from 4 and KCN, NaI and LiBr, respectively. The reaction of 2 with propargylic alcohols HCCCR(Ph)OH in the presence of Ag(O₃SCF₃), followed by treatment with acidic Al₂O₃, afforded the cationic allenylidene compounds [RuCl{CCC(Ph)R}(κ²P,O-Prⁱ₂PCH₂CH₂OMe)₂][O₃SCF₃](R = Ph or C₆H₄Me-o) in moderate yields. The crystal structure where R = Ph has been determined and reveals an almost linear RuCCC chain with one of the methoxy groups trans to the allenylidene ligand. While the R = C₆H₄Me-o derivative reacts with CO to give the cationic carbonyl compound [RuCl(CO)(κ²P,O-Prⁱ₂PCH₂CH₂OMe)₂][O₃SCF₃], the reaction of 4 with CO gives a mixture of this complex, 9/10, and trans,trans,trans-[RuCl₂(CO)₂(κP-Prⁱ₂PCH₂CH₂OMe)₂]. The latter is formed quantitatively from 2 and carbon monoxide.