Rhodium(I) fluorothiolate complexes as hydroformylation catalyst precursors. Crystal structure of two polymorphs of trans-[Rh(SC6F5) (CO) (PPh3) 2]

Article abstract of DOI:10.1016/S0022-328X(97)00330-6

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) A, 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 A, 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.