The hydroformylation of hex-1-ene and styrene with syngas (30 bar of 1:1 CO/H-2) in the presence of the alkoxycarbonylcyclopentadienyl rhodium(l) complexes [Rh{C5H4CO2X}(L,L)] [X = -CH2CH=CH2, -(CHR)(2)OH (R = H, Me); L,L = 2CO, NBD] has been studied and compared with the unsubstituted system [Rh(C5H5)NBD]. The influence of various reaction parameters on the catalytic activity and selectivity is presented and discussed. (C) 2003 Elsevier B.V. All rights reserved.