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

Abstract

[EN]The perfluorothiolate dinuclear compounds [Rh( ]A,-SC6E5XCOD)] 2 1 and [Rh( ]J~-SC6F5XCO)2] 2 2 react with PPh 3 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 PPh 3 renders cis-7 and trans-[Rh(/x-SC6Fs)((CO)(PPh3)] z 8, while with 4 moles of PPh 3 trans[Rh(SC6FsXCO)(PPh3)E]lOa is obtained. This latter product can otherwise be prepared by C1 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 PPh 3 is used, a mixture of compounds 11a and llb is formed. An X-ray crystal structure study shows trans[Rh(SC6Fs)(CO)(PPh3) 2] to exit as two polymorphs. 11a crystallises in the space group P2t/n of the monoclinic system with a = 12.489(1), b = 15.430(5), c = 19.719(1) A, te = y= 90, /3 = 92.84(1) °, and llb is triclinic, space group P1 with a = 9.764(2), b = 12.197(6), c = 17.880 ]k, a = 100.18(5), /3 = 101.92(2), T= 113.61(2) °. Both PPh 3 ligands are mutually trans and the difference in u(CO) stretching frequencies, 1989 and 1939 cm -1, can be explained in terms of o-phenyl H... CO interactions in the latter. The [Rh(/z-SC6Fs)(COD)] 2 1 and [Rh(/.£-SC6FsXCO)2] 2 2/nPPh 3 systems have been studied as catalyst precursors for the hydroformylation of l-heptene in toluene at 30 bar and 343 K. Selectivity towards the linear aldehyde is enhanced when dimeric complexes are used.