Synthesis and characterization of Pd/NHC_F complexes with fluorinated aryl groups

Abstract

The series of novel Pd/NHCF complexes were synthesized via a straightforward approach from fluorine-containing anilines. Computational and structural studies were performed to assess the effect of fluorine on the Pd–NHC bond.

Synthesis and a combined experimental/theoretical structural study of a comprehensive set of Pd/NHC complexes witho-,m-, andp-halogen-substituted aryl groups (X = F, Cl, Br, CF3)

“…Thus, the crystal structures of complexes without substituents at Ph rings are still unknown. Structures of complexes bearing only o - or m -substituents are limited to two recent structures of 3a and 3b , 26 whereas seven crystal structures of complexes with 4 different p -substituents have been reported (CSD 49 refcodes are BILDUY, 50 KIFCAG, KIFCEK, KIFCIO, KIFCOU, 51 MOBVOR, 52 and XEKFEZ 53 ).…”

“…Notably, the Im-C 6 H 4 X angle (see Tables 3 and S11†) gradually increases while going from unsubstituted 3 (25.8(5)–50.72(5)°) through m -/ p -substituted 3b , 3e , 3k , 3i , 3l (39.14(5)–45.60(5)°) and o -F 3a 26 (50.55(7)–63.02(5)°) to o -Cl/Br/CF 3 3d , 3g and 3j (64.32(10)–67.53(6)°). Since sterically hindered Pd/NHC complexes of types Hal 2 Pd(1,3-(2,6-R 2 C 6 H 4 ) 2 Im) 2 and [HalPd(1,3-(2,6-R 2 C 6 H 4 ) 2 Im)] 2 (μ-Hal) 2 exhibit Im-C 6 H 4 X dihedral angle values of up to 90° (see the CSD, ver.…”

“…The same is observed for 3a . 26 The insignificant weakening of the Pd–N py bond might be explained by the electronic influence of the NHC-ligand located in the trans -position: either by a decrease in its π-acceptor ability for an o -substituted NHC-ligand or by a noticeable increase in its σ-donor ability with respect to an increase in the Im-C 6 H 4 X angle, while its π-acceptor ability should not change considerably. The latter is not evident but is in good agreement with DFT calculations for Pd 0 -NHC complexes, which reveal the dependence between the Im-C 6 H 4 X angle value and σ-donor and π-acceptor abilities of the NHC ligand (see below).…”

“…aPd–C NHC interatomic distance, Å.bDihedral angle between N 2 C 3 and Ph cycles, degrees.c 3b is highly disordered in the crystal structure, 26 therefore Pd–X bond distances cannot be used for comparison.…”

Arylation of aldehydes catalyzed by fluorinated NHC–Rh(i) complexes

“…Based on the above, we decided to study the effect of fluorine atoms on the catalytic activity of a series of fluorinated-NHC complexes of the type [RhCl(NHC)(COD)]. The well-known electron-withdrawing properties of the fluorine atoms may allow us to fine-tune the electronic properties of the NHC ligands, 38 and consequently their catalytic performance. [39][40][41][42][43] Furthermore, fluorinated-organic compounds exhibit interesting supramolecular interactions, for instance, they form hydrogen bonds with H-Y donors, [44][45][46][47][48][49] and in the case of aromatic fluorinated-molecules, they promoted the formation of p-p interactions with electron rich arenes.…”