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Influence of ring-expanded N-Heterocyclic Carbenes on the structures of half-sandwich Ni(I) complexes: An X-ray, electron paramagnetic resonance (EPR), and electron nuclear double resonance (ENDOR) study

Pelties, Stefan, Carter, Emma, Folli, Andrea, Mahon, Mary F., Murphy, Damien Martin, Whittlesey, Michael K. and Wolf, Robert 2016. Influence of ring-expanded N-Heterocyclic Carbenes on the structures of half-sandwich Ni(I) complexes: An X-ray, electron paramagnetic resonance (EPR), and electron nuclear double resonance (ENDOR) study. Inorganic Chemistry 55 (21) , pp. 11006-11017. 10.1021/acs.inorgchem.6b01540

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Abstract

Potassium graphite reduction of the half-sandwich Ni(II) ring-expanded diamino/diamidocarbene complexes CpNi(RE-NHC)Br gave the Ni(I) derivatives CpNi(RE-NHC) (where RE-NHC = 6-Mes (1), 7-Mes (2), 6-MesDAC (3)) in yields of 40%–50%. The electronic structures of paramagnetic 1–3 were investigated by CW X-/Q-band electron paramagnetic resonance (EPR) and Q-band 1H electron nuclear double resonance (ENDOR) spectroscopy. While small variations in the g-values were observed between the diaminocarbene complexes 1 and 2, pronounced changes in the g-values were detected between the almost isostructural species (1) and diamidocarbene species (3). These results highlight the sensitivity of the EPR g-tensor to changes in the electronic structure of the Ni(I) centers generated by incorporation of heteroatom substituents onto the backbone ring positions. Variable-temperature EPR analysis also revealed the presence of a second Ni(I) site in 3. The experimental g-values for these two Ni(I) sites detected by EPR in frozen solutions of 3 are consistent with resolution on the EPR time scale of the disordered components evident in the X-ray crystallographically determined structure and the corresponding density functional theory (DFT)-calculated g-tensor. Q-band 1H ENDOR measurements revealed a small amount of unpaired electron spin density on the Cp rings, consistent with the calculated SOMO of complexes 1–3. The magnitude of the 1H A values for 3 were also notably larger, compared to 1 and 2, again highlighting the influence of the diamidocarbene on the electronic properties of 3.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Publisher: American Chemical Society
ISSN: 0020-1669
Funders: Deutsche Forschungsgemeinschaft and the German Academic Exchange Service and EPSRC
Date of First Compliant Deposit: 14 October 2016
Date of Acceptance: 28 September 2016
Last Modified: 29 Jun 2019 16:21
URI: http://orca.cf.ac.uk/id/eprint/95338

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