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 ORCID: https://orcid.org/0000-0001-8913-6606, Mahon, Mary F., Murphy, Damien M. ORCID: https://orcid.org/0000-0002-5941-4879, 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:	28 Nov 2024 03:15
URI:	https://orca.cardiff.ac.uk/id/eprint/95338

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