title: 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.
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-band1H 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-band1H 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 the1H 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.
authors.affiliation: Institute of Inorganic Chemistry, University of Regensburg , 93040 Regensburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Pelties
authors.affiliation: School of Chemistry, Cardiff University , Park Place, Cardiff CF10 3AT, United Kingdom.
authors.forename: Emma
authors.initials: E
authors.lastname: Carter
authors.affiliation: School of Chemistry, Cardiff University , Park Place, Cardiff CF10 3AT, United Kingdom.
authors.forename: Andrea
authors.initials: A
authors.lastname: Folli
authors.affiliation: Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, United Kingdom.
authors.forename: Mary F
authors.initials: MF
authors.lastname: Mahon
authors.affiliation: School of Chemistry, Cardiff University , Park Place, Cardiff CF10 3AT, United Kingdom.
authors.forename: Damien M
authors.initials: DM
authors.lastname: Murphy
authors.affiliation: Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, United Kingdom.
authors.forename: Michael K
authors.initials: MK
authors.lastname: Whittlesey
authors.affiliation: Institute of Inorganic Chemistry, University of Regensburg , 93040 Regensburg, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Wolf