Silver(I)-mediated isomerisation of trans-[RuCl2(P-P)2] (P-P = four-membered ring chelate diphosphine ligand) to cis-[{Ru(P-P)2(μ-Cl)2}nAg]+ species, and applications in stereoselective syntheses of cis- and trans-[RuCl(L)(P-P)2]+ (L = neutral ligand)

When complexes trans-[RuCl2(diphos)(2)] (diphos=(Ph2P)(2)C=CH2, Ph2PCH2PPh2 or Ph2PNHPPh2) were treated with silver salts of poorly coordinating anions (e.g. AgBF4, AgO3SCF3) in 1,2-dichloroethane halide abstraction was slow, even at reflux, and the reaction proceeded by an interesting mechanism involving a trans to cis isomerisation. At room temperature, a complex, characterized as [RuCl(diphos)(2)(mu -Cl)Ag](+), forms. When heated to reflux for 5-10 min this reacts to give a mixture, which includes cis-[RuCl2(diphos)(2)], and species of the type [{Ru(diphos)(2)(mu -Cl)(2)}(n)Ag](+) (n=1 or 2) in which the exact coordination geometry at Ag-I is unknown. The reactions have been followed by P-31-{H-1} NMR spectroscopy, and electronic spectroscopy results also support the isomerisation. The ruthenium and silver K-edge EXAFS spectra of the solid isolated from the reaction of trans-[RuCl2(dppm)(2)] and AgO3SCF3 lend support to this formulation; in particular, the best fit for the silver(I) environment includes coordination to one oxygen (from the -O3SCF3; Ru-O 2.43 Angstrom), two Cl (2.79 Angstrom) and between one and two Ru (3.94 Angstrom). Over 30-40 min at reflux, AgCl precipitates, the signals due to cis-[RuCl2(diphos)(2)] disappear from the P-31-{H-1} NMR spectra, those due to the [{Ru(diphos)(2)(mu -Cl)(2)}(n)Ag](+) mixture diminish, and new resonances, attributed to five-coordinate [RuCl(diphos)(2)](+), appear. This reaction has been investigated for stereoselective ligand substitution. Treatment of trans-[RuCl2(diphos)(2)] with AgBF4 or AgO3SCF3 in DCE in the presence of CH3CN or CO yields exclusively trans-[RuCl(L)(diphos)(2)](+) (L=CH3CN or CO), but treatment of trans-[RuCl2(diphos)(2)] with AgBF4 or AgO3SCF3 in DCE, followed by treatment with L, usually gave exclusively cis-[RuCl(L)(diphos)(2)](+) (L=CH3CN or CO).