Anionic N‐Heterocyclic Carbenes That Contain a Weakly Coordinating Borate Moiety

Abstract

Scheme 1. Reactivity of a frustrated carbene-borane Lewis pair. Scheme 2. Selected examples of anionic N-heterocyclic carbenes. Mes = 2,4,6-trimethylphenyl.

Coordination chemistry of ditopic carbanionic N-heterocyclic carbenes

“…25). This reactivity is different to that observed for the lithiated ditopic NHC-borane reported by the Tamm group which is discussed in greater detail in Section 4.3.3 and affords a complex that is only metallated at the C2 position [117]. 46 consists of a ditopic carbanionic carbene whereby a formally cationic Au PPh 3 fragment has coordinated to the anionic C4 backbone and the C2 position coordinates a formally neutral Au Cl fragment with loss of Zn t Bu 2 and NaCl.…”

“…Tamm then explored the reactivity of the anionic species and synthesized the gold(I) complexes 55a and 55b by a transmetallation reaction with (Ph 3 P)AuCl (Fig. 28) [117].…”

Some insights into the gold-catalysed A 3 -coupling reaction

“…The use of NHC gold(I) complexes containing weakly coordinating counteranions, has been proposed as a way to overcome the low catalytic activity frequently observed with N-heterocyclic carbene gold(I) chloride complexes. [72][73][74][75] Given the low reactivity of naphthyl complex 12, we wondered if exchange of the chloride ligand for the more weakly bound bis(trifluoromethanesulfonyl)imidate moiety would afford a NHC complex with an improved reactivity profile in A 3 -couplings. To this end 12 was reacted with one equivalent of silver bis(trifluoromethanesulfonyl)imide in CH 2 Cl 2 , according to the general method outlined by Gagosz et al, 75 to give the NHC gold(I) triflimide complex 17 (Scheme 5).…”

Transition Metal Complexes of Anionic N‐Heterocyclic Dicarbene Ligands

“…[14] A related anionic NHC which can be rationalized as an adduct of a dicarbene and B(C 6 F 5 ) 3 was also recently reported. [15] Whereas lanthanide complexes of an N-heterocyclic dicarbene have previously been isolated, [16] to our knowledge no examples of transition metal complexes of N-heterocyclic dicarbenes have been reported to date. Related neutral dicarbenes based on 1,2,4-triazole-3,5-diylidenes were first identified in coordination polymers of silver(I) salts.…”