Issue 14, 2015

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

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%.

Graphical abstract: Ligand assisted carbon dioxide activation and hydrogenation using molybdenum and tungsten amides

Supplementary files

Article information

Article type
Paper
Submitted
20 Jan 2015
Accepted
27 Feb 2015
First published
02 Mar 2015
This article is Open Access
Creative Commons BY-NC license

Dalton Trans., 2015,44, 6560-6570

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

S. Chakraborty, O. Blacque and H. Berke, Dalton Trans., 2015, 44, 6560 DOI: 10.1039/C5DT00278H

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