Synthesis and Structure of Dinuclear Silver(I) and Palladium(II) Complexes of 2,7-Bis(methylene)naphthalene-Bridged Bis-N-Heterocyclic Carbene Ligands

Abstract

The chemistry of transition-metal complexes containing N-heterocyclic carbenes (NHCs) has been extensively studied, and a large number of compounds have been reported. Among various metal complexes, the Ag-NHC complexes turned out to be very unique, since they are fluxional molecules and also efficient carbene-transferring reagents. The structures of these complexes were also interesting, and many examples have been reported in the literature. 1 The compounds could be readily prepared by the reaction of the imidazolium salt with Ag 2 O, and it is not necessary to isolate NHC, which is a less stable species. Interestingly, few 1:1 complexes were reported, 2 while a series of 2:1 (Ag 2 (bis-NHC)) complexes 3,4 and 2:2 (Ag 2 (bis-NHC) 2 ) complexes 5-7 were characterized. Even cyclic bisimidazolium salts reacted with Ag 2 O to give interesting 2:2 complexes. 8 Many of these Ag-NHC complexes were known as good carbenetransfer agents, and various metal-NHC complexes have been synthesized. Among the complexes, the Pd-NHC complexes 9 have been extensively studied since the complexes are potentially useful catalysts for organic synthesis. In contrast to the corresponding Ag-NHC complexes, a limited number of dinuclear Pd complexes have been reported in the literature. 10 We have been interested in the chemistry of metal-bis-NHC and metal-NHC-oxazoline complexes and synthesized some Pd complexes with unique structures. 11 In this paper we report the synthesis and structure of new dinuclear silver and palladium complexes that are connected with 2,7-dimethylnaphthalenebridged bis-NHC ligands. 11 The catalytic activities of the Pd complexes were also examined.

Di‐ and Tricationic Organic Salts: An Overview of Their Properties and Applications

“…Diimidazolium‐based salts 27 containing rigid aromatic spacers, such as a naphthalene ring, and having bromide as counter anion have been used by Saito et al to prepare silver(I) complexes that were subsequently converted into palladium complexes 52. These were used as catalysts in a study of the Mizoroki–Heck reaction in DMF solution (Scheme ).…”

Heterocyclic Carbene–Metal-catalyzed Csp2–Csp2 and Csp–Csp2 Couplings Using Nonmetallic Substrates

“…Moreover, dinuclear complexes 118120 (Chart 8) were prepared bridging the imidazole moieties with a 2,7-bis(methylene)naphtalene unit. 36 An NHC based on 1,10-phenanthroline has been employed in the preparation of bis(NHC) complex 121 (Chart 9), which was shown to be active in the MizorokiHeck reaction catalyzing (with 2 mol % of 121) the coupling of 4-bromoanisole with n-butyl acrylate in 90% yield. 37 The preparation of complex the 122 (Chart 9) bearing two NHC-tetracyclic rings has been also reported, and its catalytic activity in the Mizoroki Heck reaction has been tested with similar results.…”

3,3′-Dibenzyl-1,1′-[naphthalene-1,4-diylbis(methylene)]di(1H-imidazol-3-ium) bis(hexafluorophosphate)

“…For the first free carbenes isolated, see: Arduengo et al (1991). For the application of N-heterocyclic carbene ligands in transmetalation, see: Lin et al (2009); Saito et al (2011); Wang et al (2005). For the synthesis of the title compound, see: Saito et al (2011).…”

“…For the application of N-heterocyclic carbene ligands in transmetalation, see: Lin et al (2009); Saito et al (2011); Wang et al (2005). For the synthesis of the title compound, see: Saito et al (2011). For related structures, see: Saito et al (2011).…”