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On the unprecedented level of dinitrogen activation in the calix[4]arene complex of Nb(III)
journal contribution
posted on 2023-05-17, 11:14 authored by Terrett, R, Cavigliasso, G, Stranger, R, Brian YatesBrian YatesThe calix[4]arene niobium(III) complex ([L]Nb–NN–Nb[L] where [L] = p-tert-butylcalix[4]arene), reported to bind N2 in a μ2-linear dimeric capacity and to activate the N2 triple bond to 1.39 Å, corresponding to the longest N2 bond known in the end-on coordination mode, was subjected to a computational investigation involving both density functional and wavefunction based methods to establish the basis for the unprecedented level of activation. Replacement of the calix[4]arene ligand with hydroxide or methoxide ligands reveals that the organic backbone structure of the calix[4]arene ligand exerts negligible electronic influence over the metal centre, serving only to geometrically constrain the coordinating phenoxide groups. A fragment bonding analysis shows that metal-to-dinitrogen π* backbonding is the principal Nb–N interaction, providing a strong electronic basis for analogy with other well-characterised three- and four-coordinate complexes which bind N2 end-on. While the calculated structure of the metallacalix[4]arene unit is reproduced with high accuracy, as is also the Nb–Nb separation, the calculated equilibrium geometry of the complex under a variety of conditions consistently indicates against a 1.39 Å activation of the N2 bond. Instead, the calculated N–N distances fall within the range 1.26–1.30 Å, a result concordant with closely related three- and four-coordinate μ2–N2 complexes as well as predictions derived from trends in N–N stretching frequency for a number of crystallographically characterized linear N2 activators. A number of potential causes for this bond length discrepancy are explored.
Funding
Australian Research Council
History
Publication title
Dalton TransactionsVolume
40Issue
42Pagination
11267-11275ISSN
1477-9226Department/School
School of Natural SciencesPublisher
Royal Society of ChemistryPlace of publication
Thomas Graham House, Science Park, Milton Rd, Cambridge, England, Cambs, Cb4 0WfRights statement
Copyright 2011 The Royal Society of ChemistryRepository Status
- Restricted