Steric and electronic control of an ultrafast isomerization

Chelating Phosphine-N-Heterocyclic Carbene Platinum Complexes via Catalytic Asymmetric Hydrophosphination and Their Cytotoxicity Toward MKN74 and MCF7 Cancer Cell Lines

A series of activated vinyl azoles was hydrophosphinated in the presence of a chiral palladacycle catalyst under mild conditions to give enantioenriched phosphine azoles with moderate enantioselectivities and yields. The racemic phosphine azoles were transformed into eleven novel chelating phosphine-N-heterocyclic carbene (NHC) platinum complexes. The drug efficacies of nine selected phosphine-NHC platinum(II) chlorides in two cancer cell lines (MKN74 and MCF7) were evaluated, and two were found to exhibit activities comparable to that of cisplatin.

Full Conformational Analyses of the Ultrafast Isomerization in Penta-coordinated Ru(S2C2(CF3)2)(CO)(PPh3)2: One Compound, Two Crystal Structures, Three CO Frequencies, 24 Stereoisomers, and 48 Transition States

The stereodynamics of an ultrafast (picosecond) isomerization in a penta-coordinated ruthenium complex, Ru(S₂C₂(CF₃)₂)(CO)(PPh₃)₂, were characterized by density functional theory (DFT). The ruthenium complex crystallizes in two almost-square pyramidal (SP) forms. The violet form has an apical PPh₃ ligand, the orange form has an apical CO ligand, and their solution displays three CO stretching frequencies. With 4 possible centers of chirality (1 ruthenium, 2 phosphines, and 1 dithiolate), there are 24 stereoisomers. DFT calculations of these stereoisomers show structures ranging from almost-perfect SP (τ₅ ≈ 0) to structures significantly distorted toward trigonal bipyramidal (TBP) (τ₅ ≈ 0.6). The stereoisomers fall neatly into three groups, with ν_CO ≈ 1960 cm^-1, 1940 cm^-1, and 1980 cm^-1. These isomers were found to interconvert over relatively small barriers via Ru-S bond twisting, CF₃ rotation, phenyl twisting, PPh₃ rotation, and, in some cases, by coupled motions. The composite energy surface for each CO frequency group shows that interconversions among the low-energy structures are possible via both the direct and indirect pathways, while the indirect pathway via isomers in the ν_CO ≈ 1980 cm^-1 group is more favorable, which is a result consistent with recent experimental work. This work provides the first complete mechanistic picture of the ultrafast isomerization of penta-coordinated, distorted SP, d⁶-transition-metal complexes.