Rhodium and Iridium Complexes of N-Heterocyclic Carbenes via Transmetalation:  Structure and Dynamics

Abstract

Rhodium and iridium complexes of N-heterocyclic carbenes (3a-c and 4a-c) were obtained by transmetalation from the corresponding Ag(I) complexes. The structure of 3b was verified by X-ray diffraction. The compounds display restricted rotation about the metal-carbene bond, the rate of which can be controlled by altering the steric bulk of the auxiliary ligands. Infrared spectroscopy provides an estimate of the electron-donor power of the carbene ligands from ν(CO) of the carbonyl derivatives.

C4-bound imidazolylidenes: from curiosities to high-impact carbene ligands

“…3(b). Accordingly, C4-bound carbenes in complexes 21-24 induce a considerably lower stretch frequency (n av (CO) 1999-2015 cm À1 ) than sterically similar C2-bound carbenes in 25-27 (n av (CO) 2017-2020 cm À1 ), 43 which in turn are lower than the most basic alkyl phosphines (e.g. n av (CO) 2028 cm À1 for L = PCy 3 in 28).…”

Rhodium(I) Complexes of the Conformationally Rigid IBioxMe4Ligand: Preparation of Mono-, Bis-, and Tris-ligated NHC Complexes

“…22 In particular, these complexes allow the determination of the Tolman electronic parameter (TEP) 23 for the NHC ligand from the carbonyl stretching frequencies of cis-[M(NHC)(CO) 2 Cl], avoiding the need to prepare toxic nickel adducts. 24,25 Using this approach the calculated TEP for IBioxMe 4 using 4 (2053 cm -1 ) is in good agreement with that determined using the previously reported iridium analogue cis-[Ir(IBioxMe 4 )(CO) 2 Cl] (2052 cm -1 ) 11 and both are marginally larger in magnitude than those of (13); 5 -Rh1-Cl2, 2.3642(15); Rh1-C3, 2.048(6); Rh1-C18, 2.197(6); Rh1-C19, 2.182(6); Rh1-C21, 2.098(6); Rh1-C22, 2.105(6); Θ NHC (@C3), 177.2 (4). 29 33.8 25 a Tolman electronic parameter calculated from regression using the average ν(CO) value.…”

Application of 1,2,3-triazolylidenes as versatile NHC-type ligands: synthesis, properties, and application in catalysis and beyond

“…The CO stretch vibrations of iridium complexes of the form [(NHC)Ir(CO) 2 Cl] provide a direct probe for the donor properties of the ligand, as a linear 15 correlation between the average CO stretch frequency, ν av (CO) and the Tolman electronic parameter (TEP) has been established by Crabtree and co-workers. 43 The 1,2,3-triazolylidene iridium complexes, 25a-f exhibit ν av (CO) stretch frequencies between 2018 cm -1 and 2021 cm -1 (Table 1), just slightly higher than the 20 normal triazolylidene complex 30d (ν av (CO) = 2017 cm -1 ), thus suggesting that the normal/abnormal nomenclature overemphasises the difference in this case. According to the measured data, the donor ability of 1,2,3-triazolylidenes is stronger than the most donating normal 2-imidazolylidenes, 33, 25 yet weaker than abnormal 4-imidazolylidenes, 34.…”