A convenient access to N-phosphonio-substituted NHC metal complexes [M = Ag(i), Rh(i), Pd(ii)]

Abstract

A series of NHC pre-ligands featuring a pendant phosphonium moiety attached to N' position through a propyl linker was readily obtained upon quaternization of N-mesityl- and N-methyl-imidazole, or N-mesityl-imidazoline using (3-bromo-propyl)-triphenylphosphonium bromide. Reactions of the resulting dicationic salts with [PdCl(allyl)] in the presence of KCO afforded the anticipated NHC-ligated Pd(ii) metal complexes in high yields. Further treatment of the latter complexes with tBuOK induced a deprotonation of the carbon atom adjacent to the phosphonium moiety and the formation of the corresponding C,C-chelating NHC-phosphonium ylide Pd(ii) complexes. Investigation of an alternative synthetic route involving a silver transmetallation reaction incidentally allowed isolation and full characterization of an unusual dimeric tetranuclear NHC Ag(i) complex of general formula [(NHC∼P)(AgBr)].

Phosphine‐NHC Manganese Hydrogenation Catalyst Exhibiting a Non‐Classical Metal‐Ligand Cooperative H2 Activation Mode

“…Themost thermodynamically stable isomer of NHC-ylide complexes fac-6b,yet being destabilized by + 7.5 kcal mol À1 relative to 6a,i sd epicted in Figure 2( right). [19] According to ETS-NOCV study,the PÀMn bond in fac-6b is significantly stronger than that in complexes 2-3 featuring ac onventional phosphinemetal dative bond (see the Supporting Information for details). [19] According to ETS-NOCV study,the PÀMn bond in fac-6b is significantly stronger than that in complexes 2-3 featuring ac onventional phosphinemetal dative bond (see the Supporting Information for details).…”

Carbeniophosphines versus Phosphoniocarbenes: The Role of the Positive Charge

“…The N ‐phosphonio‐substituted NHC precursors 39 a , b were then obtained in near‐quantitative yield by N‐ and P‐methylation of neutral precursors 38 a , b (Scheme , top). However, N ‐phosphonio‐substituted imidazolium salts 41 a – c exhibiting a C 3 propyl linker were readily prepared (71–89 % yield) upon N‐quaternization of the corresponding imidazole precursors 40 a – c by (3‐bromopropyl)triphenylphosphonium bromide (Scheme , middle) . Using the same strategy, double quaternization of bis(imidazol‐1‐yl)methane ( 42 ) afforded the bis(imidazolium), bis(phosphonium) salt 43 in 64 % overall yield (Scheme , bottom) …”

“… Preparation of N ‐phosphonio‐substituted NHC precursors 39 a , b , 41 a – c , and 43 from neutral imidazole‐type derivatives 37 a , b , 40 a – c , and 42 , respectively.…”

“…In both series, N ‐phosphonio NHC complexes were selectively prepared by addition of a metal precursor to the dicationic salts in the presence of a weak base (NEt 3 , K 2 CO 3 ), as illustrated with the formation of N ‐phosphonio‐substituted NHC metal complexes 59 (M=Rh I ) and 61 a – c (M=Pd II ) (Scheme ). Further treatment of the latter complexes with a stronger base such as t BuOK induced the deprotonation of the carbon atom adjacent to the phosphonium moiety, thereby affording in good yield the corresponding C,C‐chelating NHC‐phosphonium ylide metal complexes 60 (M=Rh I ) and 62 a – c (M=Pd II ), respectively (Scheme ). In Pd II complexes 62 a – c , the coordination of the stereogenic ylidic carbon atom and the slow rotation of the π‐allyl co‐ligand account for the existence of two diastereoisomers in solution.…”

“…In Pd II complexes 62 a – c , the coordination of the stereogenic ylidic carbon atom and the slow rotation of the π‐allyl co‐ligand account for the existence of two diastereoisomers in solution. In the latter case, the sequential synthetic strategy was shown to tolerate different N‐heterocycles, unsaturated or saturated, allowing the first access of a NHC‐phosphonium ylide complex bearing a strongly donating imidazolidin‐2‐ylidene . By using the same sequential strategy, the bis(NHC) PdCl 2 complex 63 featuring two pendant phosphonium moieties was prepared in 90 % yield.…”