The dinuclear gem-dithiolato bridged compounds [Rh-2(mu-S(2)Cptn)(cod)(2)] (1) (CptnS(2)(2-) = 1,1-cyclopentanedithiolato), [Rh-2(mu-S(2)Chxn)(cod)(2)] (2) (ChxnS(2)(2-) = 1,1-cyclohexanedithiolato), [Rh-2(mu-S2CBn2)(cod)(2)] (3) (Bn2CS22- = 1,3-diphenyl-2,2-dithiolatopropane) and [Rh-2(mu-(S2CPr2)-Pr-i)(cod)(2)] (4) ((Pr2CS22-)-Pr-i = 2,4-dimethyl-2,2-dithiolatopentane) dissolved in toluene in the presence of monodentate phosphine or phosphite P-donor ligands under carbon monoxide/hydrogen (1: 1) atmosphere are efficient catalysts for the hydroformylation of oct-1-ene under mild conditions (6.8 atm of CO/H-2 and 80 degrees C). The influence of the gem-dithiolato ligand, the P-donor co-catalyst and the P/Rh ratio on the catalytic activity and selectivity has been explored. Aldehyde selectivities higher than 95% and turnover frequencies Lip to 245 h(-1) have been obtained using P(OMe)(3) as modifying ligand. Similar activity figures have been obtained using P(OPh)(3) although the selectivities are lower. Regioselectivities toward linear aldehyde are in the range 75-85%. The performance of the catalytic systems [Rh-2(mu-S2CR2)(CO)(2)(PPh3)(2)]/PPh3 has been found to be comparable to the systems [Rh-2(mu-S2CR2)(cod)(2)] at the same P/Rh ratio. The system [Rh-2(mu-S2CBn2)(cod)(2)] (3)/P(OPh)(3) has been tested in the hydroformylation-isomerization of trans-oct-2-ene. Under optimized conditions tip to 54% nonanal was obtained. Spectroscopic studies under pressure (HPNMR and HPIR) evidenced the formation of hydrido mononuclear species under catalytic conditions that are most probably responsible for the observed catalytic activity. (C) 2008 Elsevier B.V. All rights reserved.