Trans influence of some ligands on the ethylene-platinum(II) bonding in trans-[Pt(C2H4)LC12] complexes

Abstract Pmr, cmr and vibrational spectra and extended Huckel molecular orbital calculations have been studied for a series of ethylene-platinum(II) π complexes. The spectroscopic parameters are discussed in terms of the trans influence of the ligand L on the ethylene-platinum(II) bonding. It was concluded that the coordination bonding of the ethylene-platinum(II) complexes is dominated by the σ donation from ethylene to platinum(II) and the bond strength increases in the order N ligand − ligand It has generally been accepted that the coordination bonding in olefin-metal complexes consists of both the σ donation from olefin to metal (σ bonding) and the π back donation from metal to olefin (π back bonding) (1). In order to elucidate the bonding characteristics of olefin-metal π complexes, systematic studies by varying either olefin substituents or ligands are necessary. Platinum complexes are favored for this purpose owing to the presence of 195 Pt nucleus ( I = 1 2 , natural abundance : 33.8%), since substantial information is afforded through nuclear spin coupling in nmr spectroscopy. In our recent publication (2), it was demonstrated that both the σ and π bonding between olefin and platinum(II) are weakened by the alkyl substitution at the olefic carbons on the basis of 13 C chemical shifts and 13 C- 195 Pt coupling constants of Zeise's type salts, K[Pt(olefin)Cl 3 ]. The reports on the ligand effect in olefin-platinum π complexes are rather limited (3,4). With regard to methylplatinum(II) complexes, however, extensive investigations have been made and the following trans influence (5) series was obtained: PR 3 > CN − > NR 3 > Cl − > OR 2 . The carbon-platinum(II) σ bonding of methylplatinum(II) complexes becomes stronger as the trans influence of ligands decreases in the above order (5a, 6). In the present paper, we have investigated the trans influence on the ethyleneplatinum(II) bonding by measuring pmr, cmr, vibrational spectra and by extended Huckel MO calculations for a series of π complexes, trans-[Pt(C 2 H 4 )LCl 2 ].