Phosphine 13C and 31P NMR spectra are discussed for the compounds Pt(PPh 3) 2(η 2-olefin), with olefin CH(CN) CH 2, trans-CH(CN)CH(CN), C(CN) 2=CH(CN), C(CN) 2 C(CN) 2, CH(COOCH 3)CH 2, trans-CH(COOCH 3)CH(COOCH 3), C(COOCH 3) 2CH(COOCH 3), C(COOCH 3) 2C(COOCH 3) 2, C(CN) 2C(CH 3) 2. The chemical shifts of the phosphine para carbons reveal that CN or COOCH 3 groups bound to the olefin extend their electron-withdrawing effects as far as these carbons. The 195Pt NMR spectrum of the last compound and the 31P NMR spectrum of Pt(PPh 3) 2[C(CN) 2CH(OCH 3)] are also reported. For Pt(PPh 3) 2[C(COOCH 3) 2CH(COOCH 3)] the solid state structure, as determined by X-ray diffraction methods, is described. Cell parameters are: a = 14.275(5), b= 14.464(4), c= 12.172(4) Å, α=84.29(2), β=81.44(2), γ=63.86(2)°, space group P 1 . Substituents bending back occurs and conjugation results allowed only for the two trans carbonyls. A structural analysis is made for all of the title compounds so far studied by diffraction methods. This indicates that the PPtP bond angle and the dihedral angle between the PPtP and CPtC planes are governed by intramolecular contacts between the olefin substituents and the phosphine ligands. For acyclic olefins, the PPtP bond angle increases in the order CX 2CX 2‘CX 2CY 2< trans- CHXCHX < CH 2CH 2.