Synthesis and Catalysis of NHC Coordinated Cyclometalated Palladium(II) Complexes with Bridging Hydroxide Ligands

Abstract

1,2‐Addition reactions using organoboron compounds are one of the useful syntheses of various functionalized alcohols, but they generally require a large quantity of bases. In this study, we attempted to solve this problem by synthesizing unsymmetrical 1,3‐diarylimidazoline‐type N‐heterocyclic carbene (NHC)‐coordinated C^C* cyclometalated palladium(II) complexes with bridging hydroxide ligands (CYPOHs) in two steps and one pot from the corresponding Cl bridged dimer and using them as catalysts. 2,6‐di(pentan‐3‐yl)aniline (IPent)‐based NHC coordinated PhS‐IPent‐CYPOH acted as a highly efficient catalyst for the 1,2‐addition of (hetero)arylboronates to a large number of aldehydes and ketones, including unactivated ketones, under base‐free conditions.

Halogen-Substituted Mesoionic-Carbene/Palladium Complexes for Catalytic Arylation of Aldehydes

“…General Procedure for Br-e-TAP (5d)-Catalyzed Arylation of Formaldehyde: Br-e-TAP (5d) (1.0-3.0 μmol), (hetero)aryl boronate (7) or (hetero)aryl boronic acid (9) (0.50 mmol) and, Cs2CO3 or CsF (1.0 mmol) were charged in a 10 mL test tube sealed with a rubber septum. The test tube was evacuated and backfilled with argon, and this sequence was repeated five times.…”

“…[3] Recently, transition-metal-catalyzed addition reactions involving carbonyl compounds using aryl boron compounds as nucleophiles have drawn attention for the synthesis of highly functionalized alcohols because of their superiority to the Grignard reaction in terms of functional group tolerance. [4][5][6][7][8][9] Strong σ-donating ligands, such as tertiary phosphines and NHCs, are effective for this type of addition reaction, and the use of NHCs with greater donating attributes in Rh- [5,6] and Pd-assisted [7,8] catalysis tends to reduce catalyst loading. However, their catalysts are limited to Arduengo-type NHCs, and the catalytic activity is expected to be improved using the more donor-oriented MICs.…”

Halogen‐Substituted Mesoionic‐Carbene/Palladium Complexes for Catalytic Arylation of Aldehydes

“…[3] Recently, transition-metal-catalyzed addition reactions involving carbonyl compounds using aryl boron compounds as nucleophiles have drawn attention for the synthesis of highly functionalized alcohols because of their superiority to the Grignard reaction in terms of functional group tolerance. [4][5][6][7][8][9] Strong σ-donating ligands, such as tertiary phosphines and NHCs, are effective for this type of addition reaction, and the use of NHCs with greater donating attributes in Rh- [5,6] and Pdassisted [7,8] catalysis tends to reduce catalyst loading. However, their catalysts are limited to Arduengo-type NHCs, and the catalytic activity is expected to be improved using the more donor-oriented MICs.…”

Phthalimide‐tethered imidazolium salts: Synthesis, characterization, enzyme inhibitory properties, and in silico studies

“…[ 11 ] Metal complexes of NHC ligands have been extensively studied because many of these complexes are effective catalysts of various chemical reactions. [ 12–15 ] In recent years, biological properties of these complexes have been investigated for medical applications. Especially, Au and Ag complexes of NHC ligands have been found to be efficient anticancer and antibacterial agents against many various cancer cell lines and bacterial species.…”