Alternative Transformations of N-Heterocyclic Carbene Complexes of the Group 11 Metals in Transmetalation Reactions (A Review)

Abstract

The carbene transfer from N-heterocyclic carbene complexes of Group 11 metals (NHC-M C ) (especially silver and copper) to other metals is considered a convenient and universal, sometimes having no alternative, method for the synthesis of a wide range of important N-heterocyclic carbene complexes of transition metals. As the number of successful examples of transmetalation with the formation of the target product has increased, the data were accumulated on alternative or unexpected results of the interaction of NHC-M C complexes with compounds of other metals. This review considers the examples of NHC-M C reactions with compounds of other metals which proceed with a change in the metals oxidation state, conversion of (NHC)M C X into cationic homoleptic [(NHC) 2 M C ] + forms, transmetalation retaining the other metal in the coordination sphere of the product, or formation of heterometallic adducts preserving the M C -C carbene bond, rather than these occurring according to the standard reaction pathway. Unusual "reverse" carbene transfer reactions have been considered separately. The review material reveals a promising new synthetic potential of NHC-M C in the reactions with other metals and discusses the possible mechanisms and driving forces of such transformations. The most important aspects of the application of the obtained products, primarily in various catalytic processes, have been considered as well.

Dibromo–Isonitrile and N-acyclic Carbene Complexes of Platinum(II): Synthesis and Reactivity

“…In the 31 P NMR spectra, the disappearance of signals due to the isocyanido precursors was accompanied by the presence of new signals with satellites (J P-Pt ≈ 4000 Hz), which could be ascribed to the carbene species. In the case of benzyl derivative 5, a single signal was observed both in 31 P-and 195 Pt NMR spectra, indicating the stereoselectivity of the process towards the formation of a single isomer, to which a cis geometry was assigned for analogy with the analogous chlorinated system [9]. In the case of the 4-methoxyphenyl derivative 6, a mixture of carbene products was observed, as indicated by the presence of two distinct signals with satellites in the 31 P NMR spectrum and of two doublet signals in the 195 Pt NMR one.…”

“…The dinuclear brominated precursor was prepared according to a convenient reported procedure, starting from the easily available [PtCl2(NCMe)2] [45] (see Supplementary Material for the synthesis), while the chosen isonitrile ligands were commercially available. The ring-opening reaction of the dinuclear precursor was carried out in 1,2-dichloroethane (1,2-DCE) and was followed by TLC or 31 P nuclear magnetic resonance (NMR) spectroscopy. The isonitrile ([ligand]/[Pt] = 2.0 molar ratio) was dissolved in 1,2-DCE and the addition was made at 0 °C to avoid any further substitution by the nucleophile.…”

“…Isolated yields and percentage compositions at equilibrium in solution are indicated in Table 1. Cis,trans percentages were calculated by integrating the corresponding 31 The ring-opening reaction of the dinuclear precursor was carried out in 1,2-dichloroethane (1,2-DCE) and was followed by TLC or 31 P nuclear magnetic resonance (NMR) spectroscopy. The isonitrile ([ligand]/[Pt] = 2.0 molar ratio) was dissolved in 1,2-DCE and the addition was made at 0 • C to avoid any further substitution by the nucleophile.…”

“…Isolated yields and percentage compositions at equilibrium in solution are indicated in Table 1. Cis,trans percentages were calculated by integrating the corresponding 31 The coordination of isonitrile ligands to the platinum center was evidenced in 31 P NMR spectra by the presence of satellites, with 1 J P-Pt coupling constants within 3310-3380 Hz for both isomers, in agreement with previous results [2,9,45]. In the 195 Pt NMR spectra, doublet signals were observed in the −4180-−4600 ppm spectral zone, with the same 1 J PPt coupling constants measured in the 31 P NMR spectra.…”

“…In addition to the neutral ligands, the leaving groups as well can play an important role in modulating the properties of anticancer complexes [11,12]. Considering the wide applications described for carbene metal complexes in both bioinorganics [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and catalysis [31][32][33][34][35][36][37][38][39][40][41][42][43][44], we hereby describe the synthesis of new [PtBr 2 (PPh 3 )(CNR)] and [PtBr 2 (PPh 3 )(NAC)] compounds, in order to compare their properties with those of their chlorinated counterparts.…”