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Breaking Chemistry's Strongest Bond: Can Three‐Coordinate [M{N(R)Ar} 3 ] Complexes Cleave Carbon Monoxide?
Author(s) -
Christian Gemma,
Stranger Robert,
Petrie Simon,
Yates Brian F.,
Cummins Christopher C.
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200601643
Subject(s) - cleave , chemistry , bond cleavage , dimer , cleavage (geology) , exothermic reaction , reaction coordinate , carbon monoxide , crystallography , binding energy , carbide , stereochemistry , medicinal chemistry , catalysis , organic chemistry , materials science , physics , fracture (geology) , nuclear physics , composite material , enzyme
The reaction pathway for the interaction of CO with three‐coordinate Ta III , W III and Re III complexes (modelled on the experimental [M{N( t Bu)Ar} 3 ] system) has been explored by using density functional methods. Calculations show that CO binds without a barrier to [Re(NH 2 ) 3 ], forming the encounter complex [OCRe(NH 2 ) 3 ], which is stabilized by ≈280 kJ mol −1 relative to the reactants. The binding of [Ta(NH 2 ) 3 ] to the oxygen terminus of CO is inhibited by a barrier of only 20 kJ mol −1 and is followed by spontaneous cleavage of the CO bond to form the products [CRe(NH 2 ) 3 ] and [OTa(NH 2 ) 3 ]. The salient features of the potential energy surface are more favourable to CO cleavage than the analogous N 2 cleavage by [Mo(NH 2 ) 3 ], which is less exothermic (335 vs. 467 kJ mol −1 ) and is impeded by a significant barrier (66 kJ mol −1 ). The Re III /Ta III /CO system therefore appears to be an excellent candidate for cleaving the exceptionally strong CO bond under mild laboratory conditions. The related W III /Ta III dimer, which significantly weakens but does not cleave the CO bond, may be a suitable alternative when the chemistry is to be performed on activated CO rather than on the strongly bound oxide and carbide cleavage products.