Synthesis of Rh(I) and Ir(I) metal complexes with the first two chiral dithiolate ligands derived from carbohydrates

New chiral dithiol compounds 1,2-O-isopropylidene-3,5-dithiol-alpha-D-ribofuranose RiSSH(2) and 1,2-O-isopropylidene-3,5-dithiol-alpha-D-xylofuranose XySSH(2) and their chiral dithiolate olefinic Rh(I) and Ir(I) complexes [M-2(mu-RiSS)(cod)(2)] (M = Rh 1, Ir 3) and [M-2(mu-XySS)(cod)(2)] (M = Rh 2, Ir 4) were synthesized and characterized. The Rh(I) complexes reacted with CO to give the corresponding binuclear tetracarbonyls [Rh-2(mu-RiSS)(CO)(4)] (5) and [Rh-2(mu-XySS)(CO)(4)] (6), which reacted with two equivalents of PPh3 to form mixed carbonyl-phosphine complexes [Rh-2(mu-RiSS)(CO)(2)(PPh3)(2)] (7) and [Rh-2(mu-XySS)(CO)(2)(PPh3)(2)] (8). The structures of [Rh-2(mu-RiSS)(CO)(4)] (5) and the two possible conformers of [Rh-2(mu-XySS)(CO)(4)] (6a) and (6b) were optimized and their relative stability determined by theoretical methods based on density functional theory (DFT). An interaction between one Rh atom and the oxygen atom of the ring was found in the most stable conformer of [Rh-2(mu-XySS)(CO)(4)]. The complexes [Rh-2(mu-RiSS)(cod)(2)] (1) and [Rh-2(mu-XySS)(cod)(2)] (2) were used as catalytic precursors in the hydroformylation of styrene. The results suggest that mononuclear rhodium hydride carbonyl species are responsible for the catalytic activity. (C) 1999 Elsevier Science S.A. All rights reserved.