You are here:
ORGANONICKEL CHEMISTRY IN THE CATALYTIC HYDRODECHLORINATION OF POLYCHLOROBIPHENYLS (PCBS): LIGAND STERIC EFFECTS AND MOLECULAR STRUCTURE OF REACTION INTERMEDIATES. (R823526)
Citation:
King, CM, R. B. King, N. K. Bhattacharyya, AND M. G. Newton. ORGANONICKEL CHEMISTRY IN THE CATALYTIC HYDRODECHLORINATION OF POLYCHLOROBIPHENYLS (PCBS): LIGAND STERIC EFFECTS AND MOLECULAR STRUCTURE OF REACTION INTERMEDIATES. (R823526). AMERICAN JOURNAL OF INDUSTRIAL MEDICINE. American Chemical Society, Washington, DC, 600(1-2):63-70, (2000).
Description:
Abstract
Soluble homogeneous organophosphorus¯¯nickel complexes have been used to detoxify polychlorinated biphenyls (PCBs) by catalyzed hydrodechlorination using NaBH2(OCH2CH2OCH3)2 as the hydrogen source. The reactions appear to proceed by NiL3 oxidative addition into C---Cl bonds followed by hydrogenolysis of the metal---carbon bond. In model experiments with decachlorobiphenyl, the cone angle of the organophosphorus ligand L was shown to be a key factor controlling the magnitude and position of chlorine displacement. Hence, ligands leading to para displacement (e.g. (o-MeC6H4O)3P), meta¯¯para displacement (e.g. (EtO)3P and (PhO)3P), and ortho¯¯meta¯¯para displacement (e.g. Me3P and Et3P) were found. Significantly, the highly toxic, coplanar dioxin precursor 3,3',4,4'-tetrachlorobiphenyl, a meta¯¯para chlorine-substituted congener, was dechlorinated quantitatively with the Et3P catalyst system. Evidence for the presence of organonickel intermediates in the reaction mixtures was obtained by mass spectroscopic and X-ray diffraction studies. Of particular interest is the isolation of square planar complexes p-C6Cl5C6Cl4Ni(PEt3)2Cl from the reaction of decachlorobiphenyl with NaBH2(OCH2CH2OCH3)2¯¯(Et3P)2NiCl2 as the catalyst precursor and m-C6Cl5C6Cl4Ni(PEt3)2Cl from decachlorobiphenyl¯¯Ni(1,5-C8H12)2¯¯PEt3 at room temperature. All are oxidative addition intermediates and precursors for decachlorobiphenyl hydrodechlorination.
Author Keywords: Nickel complexes; Alkoxyborohydrides; Hydrogenolysis; Polychlorinated biphenyls; Catalysis; X-ray structures