A MALDI-TOF MS analysis study of the binding of 4-(N, N-dimethylamino)pyridine to amine-bis(phenolate) chromium(III) chloride complexes: mechanistic insight into differences in catalytic activity for CO2/epoxide copolymerization

作者：Kozak Christopher M^*; Woods April M; Bottaro Christina S; Devaine Pressing Katalin; Ni Kaijie

来源：Faraday Discussions, 2015, 183: 31-46.

DOI：10.1039/c5fd00046g

Amine-bis(phenolato) chromium(III) chloride complexes, [LCrCl], are capable of catalyzing the copolymerization of cyclohexene oxide with carbon dioxide to give poly(cyclohexane) carbonate. When combined with 4-(N, N-dimethylamino) pyridine (DMAP) these catalyst systems yield low molecular weight polymers with moderately narrow polydispersities. The coordination chemistry of DMAP with five aminebis( phenolato) chromium(III) chloride complexes was studied by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The aminebis( phenolato) ligands were varied in the nature of their neutral pendant donor-group and include oxygen-containing tetrahydrofurfuryl and methoxyethyl moieties, or nitrogen-containing N, N-dimethylaminoethyl or 2-pyridyl moieties. The relative abundance of mono and bis(DMAP) adducts, as well as DMAP-free ions is compared under various DMAP : Cr complex ratios. The [LCr](+) cations show the ability to bind two DMAP molecules to form six-coordinate complex ions in all cases, except when the pendant group is N, N-dimethylaminoethyl (compound 3). Even in the presence of a 4 : 1 ratio of DMAP to Cr, no ions corresponding to [(LCr)-Cr-3(DMAP)(2)](+) were observed for the complex containing the tertiary sp(3)-hybridized amino donor in the pendant arm. The difference in DMAP-binding ability of these compounds results in differences in catalytic activity for alternating copolymerization of CO2 and cyclohexene oxide. Kinetic investigations by infrared spectroscopy of compounds 2 and 3 show that polycarbonate formation by 3 is twice as fast as that of compound 2 and that no initiation time is observed.

• 出版日期2015