Platinum(II) and Palladium (II) Complexes with Group 14 and 15 Donor Ligands. Synthesis, Structure and Substitution Mechanisms

Sammanfattning: The present thesis deals with Pd(II) and Pt(II) complexes with group 14 and 15 donor ligands. Such complexes have been prepared and investigated mainly with regard to their ground state structures and the mechanism according to which they undergo substitution. The main conclusions are:The trans influence of the donor atoms in group 14 and 15 decreases in the following order in platinum(II) complexes: Si>Ge>C>Sn>P>As>Sb>N. Tetrakis(nitrile) complexes of palladium(II) and platinum(II) can be synthesised from the corresponding bis(acetylacetonato) complex, by protonation of the acetylacetonato ligands in the presence of free nitrile. The nitrile complexes undergo solvent exchange with a rate contribution from a pathway independent of free nitrile concentration. This can be rationalised as a solvent path and as an outer-sphere complex formation with triflate (the counter-ion) followed by rate-determining, intramolecular exchange within the ion pairs formed. The complexes trans-PtPhCl(SMe2)2 (1), trans-PtPhCl(SEt2)2 (2), trans-Pt(mesityl)Cl(SMe2)2 (3), trans-Pt(p-anisyl)Cl(SMe2)2 (4), [PtI3(PPh3)]- (5), [PtI3(SbPh3)]- (6) and trans-PtCl(SiPh3)(PMe2Ph)2 (7) undergo substitution via five-coordinate transition states both along the direct and the solvent path. The degree of bond breaking in the transition state increases in the order 6<5<1,4<3<2<7, and along this series the intimate mechanism changes from strongly Ia to slightly Id. The reactivity decreases in the order 7>6>5>1,4>3>2. The solvento complex of 7 reacts with rates that are among the highest ones reported for platinum(II). The introduction of a silyl ligand makes the platinum(II) centre "hard" in acetonitrile, the thermodynamic stability sequence of the halide complexes being Cl>Br>I. The high trans effect of the triphenylstibine ligand is explained by its better p-accepting ability as compared to phosphines and arsines. The p' orbital of the stibine is proposed to be predominantly of 5d character.cis-Pt(SiPh2Me)2(PMe2Ph)2 is strongly tetrahedrally distorted in the solid state with a dihedral angle of 39° between the planes Si-Pt-Si and P-Pt-P. It undergoes substitution and phosphine exchange via a 3-coordinate 14-electron intermediate. Both these features can be explained by the high electron density at the metal centre, giving "pseudo d10" behaviour.