Oligomerization and cis-trans isomerization equilibria in dichloropalladium(II) metallacrown ethers and a dichloropalladium(II) complex of 1,12-bis(diphenylphosphino)dodecane

Quantitative P-31{H-1} NMR spectroscopic studies of monomer-oligomer and ci s-trans equilibria in chloroform-d solutions of PdCl2{Ph2P(CH2CH2O)(n)CH2CH 2PPh2-P,P'}(n) n = 3, 4, 5) metallacrown ethers and of PdCl2{Ph2P(CH2)(12)P Ph2-P,P'} are reported. The NMR data for all of the complexes can be adequa tely modeled using a single cis-trans isomerization equilibrium and two ste p-polymerization (dimerization, oligomerization) equilibria. As expected, b oth the dimerization and oligomerization equilibrium constants for the meta llacrown ethers increase as n increases. However, the dimerization equilibr ium constants of the metallacrown ethers are much smaller than are the olig omerization equilibrium constants. In contrast, the dimerization and oligom erization equilibrium constants for PdCl2{Ph2P(CH2)(12)PPh2-P,P'} are nearl y identical and are significantly larger than are those of the metallacrown ethers. Kinetic studies of monomer-oligomer and cis-trans equilibria in so lutions of cis-PdCl2{Ph2P(CH2CH2O)(3)CH2CH2PPh2-P,P'} indicate that the tra ns monomer and trans oligomers are formed at approximately the same rates a nd that the reactions follow reversible first-order kinetics. The very diff erent dimerization constants for the metallacrown ethers and PdCl2{Ph2P(CH2 )(12)PPh2-P,P'}and the similar rates of formation for the trans monomer and trans oligomers suggest that the isomerization and dimerization reactions have a common rate-determining step that involves cleavage of a palladium-p hosphorus bond.