Chemistry of the PC^NHCP Ligand:  Silver and Ruthenium Complexes, Facial/Meridional Coordination, and Catalytic Transfer Hydrogenation

Abstract

The silver complex of PC NHC P was identified as [Ag 3 (µ-Cl)(PC NHC P) 2 ]Cl 2 (1). Anion exchange of 1 with AgNO 3 affords a white compound, which crystallizes into two forms, [Ag 3 (µ-Cl)-(PC NHC P)] 2 (NO 3 ) 2 (2a) and [Ag 3 (Cl)(NO 3 )(0.5DMF)(PC NHC P) 2 ]NO 3 (2b), from different solvent combinations. Their structural determination reveals interesting structural features, including a short Ag‚‚‚Ag interaction in both of them. Unlike the common preparation of ruthenium(II) NHC complexes in the literature, a novel silver carbene transfer reaction between 1 and RuCl 2 (PPh) 3 produces fac-[Ru 2 (µ-Cl) 3 (PC NHC P) 2 ]Cl (3) in good yield. The nonredox nature of the carbene transfer reaction is different from that of an earlier report and shows that the preparation of divalent ruthenium NHC complexes via silver carbene transfer is a feasible synthetic route. Significantly, complex 3 can also be prepared directly from PC NHC P‚HCl and RuCl 2 (PPh 3 ) 3 in the absence of base. Reactions of 3 with CO, phenylacetylene, and pyridine afford mer complexes mer,cis-RuCl 2 (CO)(PC NHC P) (4), mer-,trans-RuCl 2 (dCdCHPh)(PC NHC P) (6), and mer,trans-[RuCl(py) 2 (PC NHC P)]Cl (7), respectively. The fac complex, fac,cis-[RuCl(bipy)(PC NHC P)]Cl (8), was produced in reaction of either 3 or 7 with 2,2′-bipyridine. Treatment of 4 with excess NaBH 4 produced the hydride complex mer-RuHCl(CO)(PC NHC P) (5). Complex 7 is slowly oxidized to mer-[Ru III Cl 3 (PC NHC P)] ( 9) in the air. The structures of 2a, 2b, 3, 4, 7, 8, and 9 have been confirmed by X-ray crystallography. The reactivity study shows that PC NHC P is capable of accommodating extra steric requirement by readily switching from facial to meridional coordination mode, and the preliminary catalytic study indicates that 3 is effective in transfer hydrogenation of ketones.

Di‐ and Trinuclear Gold Complexes of Diphenylphosphinoethyl‐Functionalised Imidazolium Salts and their N‐Heterocyclic Carbenes: Synthesis and Photophysical Properties

“…Originally, Lee et al suggested a simple NHC-AgCl complex, [37] but a reinvestigation revealed that both phosphine units are actually involved in metal complexation. [64] This was finally proved by X-ray crystallography demonstrating a trinuclear silver species. Apart from this, the 31 In the 1 H NMR spectrum a broad singlet (9.87 ppm) is seen for the imidazolium proton.…”

“…Alkylation with dichloroethane and subsequent nucleophilic substitution of the side-chain chlorine atoms with potassium diphenylphosphide afforded (L2H)Cl. For this salt and the benzimidazolium analogue, silver complexes were described by Lee [64] and Hahn [63] for the preparation of pincertype palladium and ruthenium complexes by transmetallation. Originally, Lee et al suggested a simple NHC-AgCl complex, [37] but a reinvestigation revealed that both phosphine units are actually involved in metal complexation.…”

“…[64] In each case the in situ prepared [(L2) 2 Ag 3 Cl]Cl 2 species was directly treated with the corresponding solid gold precursor.…”

“…[64] The authors suggested that the reaction of the imidazolium salt with Ag 2 O leads to [(L2) 2 Ag 3 Cl]Cl 2 . With respect to the high yield, decomposition of the solvent CH 2 Cl 2 and the abstraction of one chloride atom was suggested by the authors, because both imidazolium salts only provide two chloride ions.…”

Carbohydrate– N -heterocyclic carbene metal complexes: Synthesis, catalysis and biological studies

“…When NHCs are synthesized from a pre-formed heterocycle, the substituents on N are typically limited to primary and secondary alkyl groups (including benzylic and allylic groups) [12,13]. If aryl or t-butyl substituents on N are required, the NHC can be constructed from the parent amine(s) via appropriate ring formation pathways [14][15][16].…”