Metallacyclobutan-3-one [slipped oxodimethylenemethane] complexes of platinum[II] and palladium[II].

Chapter 1 reviews the literature concerning trimethylenemethane and oxodimethylenemethane (oxoallyl) metal complexes, containing 144 references. This review briefly details the uses of these complexes in organic synthesis, emphasising their similarities. The preparation and characterisation of metallacyclobutan-3-one (slipped oxodimethylenemethane) complexes [M(CH{lcub}COR{rcub}COCH{lcub}COR{rcub})L2] (where M = Pt or Pd) are presented in Chapter 2, and details the molecular structure of five of these complexes, establishing the highly puckered nature of the ring and the presence of an allylic contribution in the bonding of the oxodimethylenemethane ligand to the metal. In solution these complexes undergo rapid ring inversion at roan temperature and the activation energies for these processes have been calculated. The law temperature 1H n.m.r. spectra shows the expected features for the static structure, the magnitude of the 2J (PtH) and 3J (PH) coupling for the CH protons depend on the CH bond orientation. Preliminary investigation into the reactivity of metallacyclobutan-3-ones is detailed in Chapter 3. The triphenylarsine ligands of the complexes [M(CH{lcub}COR{rcub}COCH{lcub}COR{rcub}) (ASPh3)2] are easily displaced by tertiary phosphines to the corresponding phosphorus ligand complexes. Similarly t-butylisocyanide displaces either triphenylarsine or triphenylphosphine from the parent metallacyclobutan-3-ones to give the monosubstituted complexes [M(CH{lcub}CO2Me{rcub}COCH{lcub}CO2Me{rcub}) (CNBut)L]. With excess t-butyliso-cyanide the platinacyclobutan-3-ones afford the zwitterion complexes [Pt(CH{lcub}COR{rcub}COC{lcub}COR{rcub}C:NHBut)(CNBut)2] (where R=OMe or Me). The final chapter examines the chemistry of 3-oxopentanedioic acid dimethyl ester and heptane-2,4,6-trione with other platinum metal centres. Treatment of osmium, ruthenium, and rhodium metal chloride complexes with either of these ketones in the presence of a base afforded the oxygen bound chelate complexes of the type "MOCRCHCOCH2COR", however, with cis-[PtCl2(PPh3)2] only the platinacyclobutan-3-one complexes are obtained. Similarly palladium salts react readily with these ketones to afford a number of complexes depending on the ketone used and the conditions. Interestingly a few of these palladium complexes can be converted to palladacyclobutan-3-ones on treatment with a donor ligand.