Impact of Ligand Modification on Structures and Catalytic Activities of Chelating Bis-Carbene Rhodium(I) Complexes

Abstract

A series of novel chelating N-heterocyclic bis-carbene rhodium(I) complexes based on 1,2,4-triazoles, benzimidazoles, and imidazoles with varying bridge length and N substituents has been synthesized. In addition to their structural characterization, their catalytic activity in the hydrosilylation of 4-fluoroacetophenone with diphenylsilane has been examined. The results reveal that selectivities and turnover frequencies (TOFs) are influenced by bridge length, steric demand of the N substituents, and electronic properties of the heterocycle. † Part of the Dietmar Seyferth Festschrift. Dedicated to Dietmar Seyferth.

Synthesis of palladium(0) and -(ii) complexes with chelating bis(N-heterocyclic carbene) ligands and their application in semihydrogenation

“…The complexes with the bulkier mesityl substituents, which have been used previously to ensure stability of palladium complexes bearing these ligands, 32,37,38 were stable in solution and resistant against air and moisture at room temperature for at least a week. In contrast to the findings of Riederer et al, 3 we did not observe a relation between stability and linker length.…”

“…1). 1 In addition to the advantages regarding stability, bis-NHCs are good candidates for the fine-tuning of catalytic properties by altering the wingtips, backbone and linker, 3 the first of which is explored in this contribution. The influence of the linker length is briefly studied as well.…”

“…Bis-NHCs have been coordinated to many transition metals: ruthenium, 4 rhodium, 3,5 iridium, 6 palladium, 7 platinum, 8,9 and more recently also the first row metals such as nickel [10][11][12] and iron. 13,14 We are interested in the properties and reactivity of low-valent late transition metal complexes, notably electron rich zero-valent palladium NHC complexes, as these often play a vital role in the catalytic cycles of many reactions.…”

Synthesis and characterization of κ-2-bis-N-heterocyclic carbene rhodium(I) catalysts: Application in enantioselective arylboronic acid addition to cyclohex-2-enones

“…Despite possessing a strong M-NHC bond, NHCs can reductively eliminate from corresponding metalhydrido and alkyl species to give imidazolium salts [18,54e63]. A systematic study by Hermann et al provides some insight into the effects of achiral diNHC ligand bridge length, N-substituent, and heterocycle composition on Rh(I) catalyzed hydrosilylation of ketones [64]. Considering the limited models available for designing effective chiral catalysts using diNHCs, it is important that a chosen ligand platform permit rapid and facile modification.…”

Synthesis and Structural Characterization of New Chiral (Biscarbene)platinum(II) Complexes

“…As observed for phosphanes, the introduction of chelating ability to carbenes confers additional stabilizing character to the ligand. [1][2][3] Over the past two decades, N-heterocyclic carbenes (NHCs) have emerged as a new class of ancillary ligands for a broad range of transition-metal-mediated catalytic reactions. [4][5][6][7][8] NHCs are excellent σ-donors and form strong M-C bonds, often giving rise to complexes with a higher stability compared to complexes containing phosphanes.…”