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Ligand assisted carbon dioxide activation and hydrogenation using molybdenum and tungsten amides


Chakraborty, Subrata; Blacque, Olivier; Berke, Heinz (2015). Ligand assisted carbon dioxide activation and hydrogenation using molybdenum and tungsten amides. Dalton Transactions, 44(14):6560-6570.

Abstract

The hepta-coordinated isomeric M(NO)Cl3(PNHP) complexes {M = Mo, 1a(syn,anti); W, 1b(syn,anti), PNHP = (iPr2PCH2CH2)2NH, (HN atom of PNHP syn and anti to the NO ligand)} and the paramagnetic species M(NO)Cl2(PNHP) (M = Mo, 2a(syn,anti); W, 2b(syn,anti)) could be prepared via a new synthetic pathway. The pseudo trigonal bipyramidal amides M(NO)(CO)(PNP) {M = Mo, 3a; W, 3b; [PNP]− = [(iPr2PCH2CH2)2N]−} were reacted with CO2 at room temperature with CO2 approaching the M[double bond, length as m-dash]N double bond in the equatorial (CO,NO,N) plane trans to the NO ligand and forming the pseudo-octahedral cyclic carbamates M(NO)(CO)(PNP)(OCO) (M = Mo, 4a(trans); W = 4b(trans)). DFT calculations revealed that the approach to form the 4b(trans) isomer is kinetically determined. The amine hydrides M(NO)H(CO)(PNHP) {M = Mo, 5a(cis,trans); W, 5b(cis,trans)}, obtained by H2 addition to 3a,b, insert CO2 (2 bar) at room temperature into the M–H bond generating isomeric mixtures of the η1-formato complexes M(NO)(CO)(PNHP)(η1-OCHO), (M = Mo, 6a(cis,trans); M = W, 6b(cis,trans)). Closing the stoichiometric cycles for sodium formate formation the 6a,b(cis,trans) isomeric mixtures were reacted with 1 equiv. of Na[N(SiMe3)2] regenerating 3a,b. Attempts to turn the stoichiometric formate production into catalytic CO2 hydrogenation using 3a,b in the presence of various types of sterically congested bases furnished yields of formate salts of up to 4%.

Abstract

The hepta-coordinated isomeric M(NO)Cl3(PNHP) complexes {M = Mo, 1a(syn,anti); W, 1b(syn,anti), PNHP = (iPr2PCH2CH2)2NH, (HN atom of PNHP syn and anti to the NO ligand)} and the paramagnetic species M(NO)Cl2(PNHP) (M = Mo, 2a(syn,anti); W, 2b(syn,anti)) could be prepared via a new synthetic pathway. The pseudo trigonal bipyramidal amides M(NO)(CO)(PNP) {M = Mo, 3a; W, 3b; [PNP]− = [(iPr2PCH2CH2)2N]−} were reacted with CO2 at room temperature with CO2 approaching the M[double bond, length as m-dash]N double bond in the equatorial (CO,NO,N) plane trans to the NO ligand and forming the pseudo-octahedral cyclic carbamates M(NO)(CO)(PNP)(OCO) (M = Mo, 4a(trans); W = 4b(trans)). DFT calculations revealed that the approach to form the 4b(trans) isomer is kinetically determined. The amine hydrides M(NO)H(CO)(PNHP) {M = Mo, 5a(cis,trans); W, 5b(cis,trans)}, obtained by H2 addition to 3a,b, insert CO2 (2 bar) at room temperature into the M–H bond generating isomeric mixtures of the η1-formato complexes M(NO)(CO)(PNHP)(η1-OCHO), (M = Mo, 6a(cis,trans); M = W, 6b(cis,trans)). Closing the stoichiometric cycles for sodium formate formation the 6a,b(cis,trans) isomeric mixtures were reacted with 1 equiv. of Na[N(SiMe3)2] regenerating 3a,b. Attempts to turn the stoichiometric formate production into catalytic CO2 hydrogenation using 3a,b in the presence of various types of sterically congested bases furnished yields of formate salts of up to 4%.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2015
Deposited On:21 Mar 2016 10:59
Last Modified:24 Apr 2016 06:14
Publisher:Royal Society of Chemistry
ISSN:1477-9226
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1039/C5DT00278H
PubMed ID:25756332

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