Stereochemistry of some ligand substitution and insertion reactions in pseudotetrahedral ruthenium(II) complexes

Article abstract of DOI:10.1021/om00126a012

Pseudotetrahedral (S_Ru,R_C)-1 and (R_Ru,R_c)-(η-C₅H₅)Ru(prophos)Cl, 1′ (where prophos is (R)-1,2-propanediylbis(diphenylphosphine)). react with CH₃MgBr or C₂H₅MgBr to give the alkylation products (S_Ru,R_C)-2 and (R_Ru,R_C)-(η-C₅,H₅)Ru(prophos)R, 2′ (R = CH₃, a; R = C₂H₅, b), with stereospecific retention of configuration at the ruthenium atom. With C₂H₅MgBr also a competitive formation of the corresponding hydrides (S_Ru,R_C)-3 and (R_Ru,R_C)-(η-C₅H₅)Ru(prophos)H, 3′, takes place. Hydride formation is the only reaction observed when 1 or 1′ is reacted with sec-C₄H₉MgBr and, according to NOE experiments, takes also place with retention of configuration. Under the conditions of their formation (or even under more severe conditions) 2b and 2b′ do not thermally decompose to 3 or 3′. Hydride formation is therefore not a consequence of alkylation followed by β-hydrogen elimination but must arise from a different reaction pathway whose possible nature is discussed. Hydrides 3 and 3′ react with CH₂N₂ in the presence of catalytic amounts of Pd(CH₃COO)₂, to give the methyl derivatives 2a and 2a′ with retention of configuration. Stereospecific retention of configuration is also observed in the formation of 3 and 3′ when 1 and 1′ are treated with CH₃ONa. By contrast, the reaction of 1 and 1′ and that of (S_Ru,R_C)-4 and (R_Ru,R_C)-[(η-C₅H ₅)Ru(prophos)(CH₃CN)]PF₆, 4′, with HCOONa is stereoselective; in the first case 3 and 3′ were obtained in a 20:80 and in the second one in a 40:60 molar ratio. 1 and 1′ form from the hydrides 3 and 3′ when treated with CDCl₃ or CCl₄ in a stereoselective reaction. Predominant inversion of configuration is observed in the reaction of 4 and 4′ with (C₆H₅)₄AsCl to give 1 and 1′.