Cyclic (Alkyl)(Amino)Carbene Complexes of Rhodium and Nickel and Their Steric and Electronic Parameters

Abstract

N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (CAACs) are of great interest, as their electronic and steric properties provide a unique class of ligands and organocatalysts. Herein, substitution reactions involving novel carbonyl complexes of rhodium and nickel were studied to provide a deeper understanding of the fundamental electronic factors characterizing CAAC(methyl) , which were compared with the large array of data available for NHC and sterically more demanding CAAC ligands.

Tris(imidazolin‐2‐ylidenamino)phosphine: A Crystalline Phosphorus(III) Superbase That Splits Carbon Dioxide

“…This is consistent with Tolman's substituent additivity rule stating that each substituent at the P atom has an individual contribution to the overall donor strength of the phosphine . Phosphine 3 has the lowest reported TEP value among the known phosphines and is a better donor ligand than well‐established carbene ligands such as the N ‐heterocyclic carbene NHC1 (2051.5 cm −1 ), the cyclic alkylaminocarbene NHC2 (2046.1 cm −1 ) or the abnormal N ‐heterocyclic carbene NHC3 (2038.5 cm −1 ) …”

“…[a] Literature values determined from [ L Ni(CO) 3 ] . [b] Literature value determined from [ L IrCl(CO) 2 ] .…”

“…This is consistentw ith To lman's substituenta dditivity rule stating that each substituent at the P atom has an individual contribution to the overall donor strength of the phosphine. [4a] Phosphine 3 has the lowest reported TEP value among the known phosphines and is ab etter donor ligand than well-established carbene ligands such as the N-heterocyclic carbene NHC1 (2051.5 cm À1 ), [21] the cyclic alkylaminocarbene NHC2 (2046.1 cm À1 ) [22] or the abnormal N-heterocyclic carbene NHC3 (2038.5 cm À1 ). [23] X-ray diffraction (XRD) studies were performed on single crystalso f3 and 3·LiCl (Figure 2 [23] [c] Values taken from Tolman et al [4b] and Yang et al [8] [d] Kilocalories per mole (1 kcal mol À1 = 4.184 kJ mol À1 ), calculated using PW6B95-D3//TPSS-D3/def2-TZVP.…”

Cyclic (Alkyl)(amino)carbenes (CAACs): Recent Developments

“…Within the set of cyclic carbenes that have been investigated, it can be concluded that the p-accepting ability of CAACs is among the strongest, and is only surpassed by diamidocarbenes XVIII and XXIV.Note that, unlike the TEP values,l arge differences of 31 Pc hemical shifts are observed (Dd > 150 ppm). [56,57] Shortly after our group reported the "Pscale," Ganter et al established ar anking of the p-accepting ability of carbenes using the 77 Se NMR chemical shift of carbene-selenium adducts. [58] As imilar order of carbenes electrophilicity was obtained.…”

Reversible oxidative Addition an Kohlenstoff

“…Verglichen mit NHCs weisen cAACs einen kleineren HOMO‐LUMO‐Abstand auf und stellen somit gleichzeitig stärkere Elektrophile und stärkere Nukleophile dar . Diese Eigenschaften befähigen cAACs zur Aktivierung kleiner Moleküle, wie CO, H 2 und P 4 , sowie zur Aktivierung anderer enthalpisch starker Einfachbindungen, wie B‐H, C‐H und C‐F . Dieser elektrophilere Charakter der cAACs und ihre erhöhte Stabilität gegen eine Ringerweiterung motivierten uns dazu, diese Moleküle für Kohlenstoff‐Element‐Bindungsaktivierungen zu untersuchen .…”