Coordinated olefins, H2C=CHR, and phosphanes, PH2R:: a theoretical study of the R substituent effect

Five olefin complexes and five phosphane platinum(0) complexes of the type [Pt(PH3)(2)L] (L = H2C=CHR or PH2R, R = H, CN, F, OH, NH2) were investigated by DFT methods using the B3LYP functionals to investigate the effects of the substituent R on the donation and back-donation in the bonding of these ligands. A charge decomposition analysis (CDA) proved to be particularly useful in this respect. Some expected trends are well reproduced, i.e. for olefins. particularly for H2C=CHCN, back-donation is important while for phosphanes, particularly for PH2NH2, electron donation prevails. The variation of the substituent R has a larger effect in phosphane complexes indicating that the electronic properties of a transition metal complex may be more easily controlled by changing the substituent via a coordinated phosphane than via an olefin. Interestingly. the intrinsic interaction energies DeltaE(int) are larger for olefins than for phosphanes indicating that olefins may be better ligands than the latter under special conditions. (C) 2002 Elsevier Science B.V. All rights reserved.