The perfluorothiolate dinuclear compounds [Rh(μ-SC6F5)(COD)[2 1 and [Rh(μ-SC6F5)(CO)2[2 2 react with PPh3 to give monomeric and dimeric complexes, the particular product depending upon the PR3/Rh ratio and reaction conditions. Reaction of 2 with 2 moles of PPh3 renders cis-7 and trans-[Rh(μ-SC6F5)((CO)(PPh3)[2 8, while with 4 moles of PPh3 trans[Rh(SC6F5)(CO)(PPh3)2[10a is obtained. This latter product can otherwise be prepared by Cl metathesis from trans-[RhCl(CO(PPh3)2[ in toluene. This same reaction in dichloromethane however yields the cis isomer 10b. When a larger excess of PPh3 is used, a mixture of compounds 11a and 11b is formed. An X-ray crystal structure study shows trans[Rh(SC6F5)(CO)(PPh3)2[ to exit as two polymorphs. 11a crystallises in the space group P21/n of the monoclinic system with a = 12.489(1), b = 15.430(5), c = 19.719(1) Å, α = γ = 90, β = 92.84(1)°, and 11b is triclinic, space group P1¯ with a = 9.764(2), b = 12.197(6), c = 17.880 Å, α = 100.18(5), β = 101.92(2), γ = 113.61(2)°. Both PPh3 ligands are mutually trans and the difference in v(CO) stretching frequencies 1989 and 1939 cm−1, can be explained in terms of o-phenyl H…CO interactions in the latter. The [Rh(μ-SC6F5)(COD)[2 1 and [Rh(μ-SC6F5)(CO)2[2 2/nPPh3 systems have been studied as catalyst precursors for the hydroformylation of 1-heptene in toluene at 30 bar and 343 K. Selectivity towards the linear aldehyde is enhanced when dimeric complexes are used.

We gratefully acknowledge financial support from the CE (Programme ALAMED) Project CI1"--CT93-0329 and Dr. A. Antifiolo for recording the NMR spectra.