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Homoleptic σ‐bonded uranium–alkyl complexes have been a synthetic target since the Manhattan Project. The current study describes the synthesis and characterization of several unprecedented uranium–methyl complexes. Amongst these complexes, the first example of a homoleptic uranium–alkyl dimer, [Li(THF)4]2[U2(CH3)10], as well as a seven‐coordinate uranium–methyl monomer, {Li(OEt2)Li(OEt2)2UMe7Li}n were both crystallographically identified. The diversity of complexes reported herein provides critical insight into the structural diversity, electronic structure and bonding in uranium–alkyl chemistry. [ABSTRACT FROM AUTHOR]

The combination of simple cobalt salts and N-heterocyclic carbene (NHC) ligands has been highly effective in C–H functionalization, hydroarylation and cross-coupling catalysis, though displaying a strong dependence on the identity of the NHC ligand. In addition, reactions effective with NHC ligands are often ineffective with phosphine ligands, further motivating the evaluation of the fundamental electronic structure and bonding differences in well-defined distorted tetrahedral Co(ii) complexes. Magnetic circular dichroism (MCD) studies indicate that Co(ii)–bisphosphines have larger ligand fields than Co(ii)–NHC complexes. Theoretical density functional theory (DFT) calculations were performed on an expanded set of L2CoCl2 complexes (L2 = NHC, bisphosphine and diamine) to study the electronic structure and relative ligation properties of NHCs compared to bisphosphine and diamine ligands. Mayer bond order and charge decomposition analyses indicate that NHC ligands are slightly stronger donor ligands than bisphosphines but also result in a weakening of Co–Cl bonds in a trans-like influence. From MCD and DFT studies, changing the NHC N-substituent has a larger effect on the ligand field of Co(ii)–NHC complexes than saturating the backbone. Overall, these studies provide detailed insight into the electronic structure and bonding effects in Co(ii) complexes with ligand types commonly explored in catalysis. [ABSTRACT FROM AUTHOR]

Iron complexes containing pincer ligands that incorporate N-heterocyclic carbene (NHC) moieties are of significant interest in organometallic catalysis in order to generate more oxidatively robust complexes that may exhibit novel catalytic properties. In order to define the effect that introducing NHC moieties into pincer ligands has on electronic structure and bonding in iron(II)-pincer complexes, MCD and DFT studies of (iPrCDA)FeBr2, (iPrPDI)FeBr2, and (iPrCNC)FeBr2 were performed. These studies quantify the electronic structures and bonding interactions as a function of pincer ligand variation. They also demonstrate that the observed ligand fields (and, hence, spin states) directly correlate to the increased Fe-C bonding and pincer-donating abilities that result from introducing NHC moieties into the pincer ligand. However, the net donor abilities of the pincers and the strength of the Fe-pincer interaction do not directly correlate to the number of NHC moieties present, but instead are determined to be due to differences in Fe-C and overall Fe-pincer bonding as a result of the position of the NHC moieties in the pincer ligand and the overall geometric constraints of the pincer architecture. [ABSTRACT FROM AUTHOR]