Synthesis and characterization of chiral phosphirane derivatives of [(μ-H)₄Ru₄(CO)₁₂] and their application in the hydrogenation of an α,β-unsaturated carboxylic acid

Ruthenium clusters containing the chiral binaphthyl-derived mono-phosphiranes [(S)-([1,1'-binaphthalen]-2-yl)phosphirane] (S)-1a, [(R)-(2'-methoxy-1,1'-binaphthyl-2-yl)phosphirane] (R)-1b, and the diphosphirane [2,2'-di(phosphiran-1-yl)-1,1'-binaphthalene] (S)-1c have been synthesized and characterized. The clusters are [(μ-H)₄Ru₄(CO)₁₁((S)-1a)] (S)-2, [(μ-H)₄Ru₄(CO)₁₁((R)-1b)] (R)-3, 1,1-[(μ-H)₄Ru₄(CO)₁₀((S)-1c)] (S)-4, [(μ-H)₄Ru₄(CO)₁₁((S)-binaphthyl-P_(s)(H)Et)] (S,S _p)-5, [(μ-H)₄Ru₄(CO)₁₁((S)-binaphthyl-P_(R)(H)Et)] (S,R _p)-6, [(μ-H)₄Ru₄(CO)₁₁((R)-binaphthyl-P_(s)(H)Et)] (R,S _p)-7, [(μ-H)₄Ru₄(CO)₁₁((R)-binaphthyl-P_(R)(H)Et)] (R,R _p)-8 and the phosphinidene-capped triruthenium cluster [(μ-H)₂Ru₃(CO)₉(PEt)] 9. Clusters 5-8 are formed via hydrogenation and opening of the phosphirane ring in clusters (S)-2 and (R)-3. The phosphirane-substituted clusters were found to be able to catalyze the hydrogenation of trans-2-methyl-2-butenoic acid (tiglic acid), but no enantioselectivity could be detected. The molecular structures of (S)-4, (R,S _p)-7 and 9 have been determined and are presented.