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)₂L] (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 ΔE_int are larger for olefins than for phosphanes indicating that olefins may be better ligands than the latter under special conditions.