Displacement kinetics of eta(2)-bound furan and 2,3-dihydrofuran from Mn and Cr centers: evidence for the partial dearomatization of the furan ligand.

The displacement of eta(2)-coordinated ligands from the photolytically generated CpMn(CO)(2)L and BzCr(CO)(2)L [Cp = eta(5)-C(5)H(5), Bz = eta(6)-C(6)H(6), L = 2,3-dihydrofuran (DHF), furan] complexes by pyridine has been studied. The displacement reactions span a wide range of time scales from microseconds to hours and were studied using a range of time-resolved IR spectroscopic techniques. The substitution reactions follow a dissociative pathway and the measured activation enthalpies provide an estimate for the strength of the metal-(eta(2)-furan) and metal-(eta(2)-DHF) interactions. In these complexes, the Cr center binds both ligands weaker than the Mn center. There is a approximately 6-10 kcal/mol difference in the binding enthalpies of eta(2)-furan and eta(2)-DHF to both metals suggesting that this difference is the result of a partial loss of resonance energy in the case of the aromatic furan ligand upon interaction with the metal.

Investigations into the coupling of cyclohexene oxide and carbon disulfide catalyzed by (salen)CrCl. Selectivity for the production of copolymers vs. cyclic thiocarbonates.

The synthesis of poly(thiocarbonates) has been achieved via the (salen)CrCl/[PPN]Cl (salen = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-ethylenediamino) and PPN(+) = bis(triphenyl-phosphoranylidene)ammonium) catalyzed coupling of carbon disulfide and cyclohexene oxide. Optimal catalytic activity was observed at 50 degrees C and a 1:1 carbon disulfide to cyclohexene oxide loading ratio to afford copolymers with molecular weights ranging from 14,000-34,000 g mol(-1) with narrow molecular weight distributions. The exchange of sulfur and oxygen atoms was observed in both the copolymer and cyclic products. In situ infrared monitoring of the coupling reactions revealed an initiation period followed by formation of copolymers enriched in oxygen content, and concomitantly cyclic thiocarbonates enriched in sulfur content. By way of contrast, the copolymerization of cyclohexene sulfide and carbon disulfide was found to be highly selective and effective for producing cyclohexylene trithiocarbonate vs. the all-sulfur copolymer at 30 degrees C. Density functional theory calculations were carried out on the possible cyclic materials from the coupling of cyclohexene oxide and CS(2), which revealed cyclohexylene trithiocarbonate to be the most stable cyclic species.

Switchable-polarity solvents prepared with a single liquid component.

Known liquids that can reversibly switch their polarity at atmospheric pressure are all prepared as mixtures of two liquid components; we now report a series of switchable-polarity solvents that consist, in their low-polarity form, of only a single liquid component, a secondary amine. These solvents operate in a polarity range that is significantly lower than those of previously reported switchable solvents. Application to the separation and purification of a polymer and recovery of a catalyst is described.