Four-membered group 13 metal(I) N-heterocyclic carbene analogues: synthesis, characterization, and theoretical studies

The synthesis, spectroscopic and structural characterization of the monomeric, four-membered group 13 metal(I) heterocycles ([:M{eta2-N,N'-(Ar)NC(NCy2)N(Ar)}], M = Ga or In, Ar = C6H3Pri2-2,6) and an isomeric thallium complex are reported. Theoretical studies on these complexes, which are analogues of four-membered N-heterocyclic carbenes, suggest they should act as good sigma-donor ligands.     

Theoretical investigations of the reactivities of four-membered N-heterocyclic carbene analogues of the group 13 elements

The potential energy surfaces for the chemical reactions of four‐membered N‐heterocyclic group 13 heavy carbeneoid species have been studied using density functional theory (Becke, 3‐parameter, Lee‐Yang‐Parr (B3LYP)/Los Alamos National Laboratory 2‐Double‐Zeta (LANL2DZ)). Five four‐membered group 13 heavy carbeneoid species, iPr₂NC(NAr)₂E:, where E = B, Al, Ga, In, and Tl, have been chosen as model reactants in this work. Also, three kinds of chemical reactions, C? H bond insertion, alkene cycloaddition, and dimerization, have been used to study the chemical reactivities of these group 13 four‐membered N‐heterocyclic carbeneoid species. In principle, our present theoretical work predicts that the larger the ∠NEN bond angle of the four‐membered group 13 iPr₂NC(NAr)₂E: species, the smaller the singlet–triplet splitting, the lower the activation barrier, and, in turn, the more rapid its chemical reactions to various chemical species. Moreover, our theoretical investigations suggest that the relative carbenic reactivity decreases in the following order: B > Al > Ga > In > Tl. That is, the heavier the group 13 atom (E), the more stable its four‐membered carbeneoid toward chemical reactions is. As a result, our computations predict that the four‐membered heavy group 13 iPr₂NC(NAr)₂E: species (E = Al, Ga, In, and Tl) should be both kinetically and thermodynamically stable, and can be readily synthesized and isolated at room temperature. Furthermore, the singlet–triplet energy splitting of the four‐membered group 13 iPr₂NC(NAr)₂E: species, as described in the configuration mixing model attributed to the work of Pross and Shaik, can be used as a diagnostic tool to predict their reactivities. The results obtained allow a number of predictions to be made. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Synthesis, characterisation and theoretical studies of amidinato-indium(I) and thallium(I) complexes: isomers of neutral group 13 metal(I) carbene analogues

The synthesis and characterisation of the monomeric amidinato-indium(I) and thallium(I) complexes, [M(Piso)].PisoH, M = In or Tl, Piso- = [ArNC(Bu(t))NAr]-, Ar = C6H3Pr(i)2-2,6, are reported. These complexes, in which the metal centre is chelated by the amidinate ligand in an N,eta3-arene-fashion, can be considered as isomers of four-membered group 13 metal(I) carbene analogues. Theoretical studies have compared the relative energies of both isomeric forms of a model complex, [In{PhNC(H)NPh}].     

Synthesis of N-heterocyclic carbene rhenium(I) carbonyl complexes

Reaction of aminophosphinimine [RHN(CH(2))(2)N[double bond, length as m-dash]PPh(3)] (R = H, Et) with Re(2)(CO)(10) provided the NH-functionalized carbene rhenium complex [Re(2)(CNHCH(2)CH(2)NR)(CO)(9)] (3a, R = H, 3b, R = Et). Treatment of 3 with Br(2) provided the mono nuclear [Re(CNHCH(2)CH(2)NR)(CO)(4)Br] (1, R = H, 2, R = Et). However, NH-functionalized carbene complexes 1-3 did not undergo N-alkylation with alkyl halides to yield the N-substituted NHC complexes. The direct ligand substitution of [Re(CO)(5)Br] with a carbene donor was employed to prepare [Re(IMes(2))(CO)(4)Br] (6a, IMes(2) = 1,3-di-mesitylimidazol-2-ylidene; 6b, IMes(2) = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene). Analyses of spectroscopic and crystal data of 6a and 6b show similar corresponding data among these complexes, suggesting the saturated and unsaturated NHCs have similar bonding with Re(I) metal centers. Reduction of 6a and 6b with LiEt(3)BH yielded the corresponding hydrido complexes 7a-b [ReH(CO)(4)(IMes(2))], but not 1 and 2. Ligand substitution of 1, 6a and 6b toward 2,2'-bipyridine (bipy) was investigated. Crystal structures of 1, 3a-b, 6a-b and 7b were determined for characterization and comparison.     

Direct functionalisation of group 10 N-heterocyclic carbene complexes for diversity enhancement

The synthesis of alkyne-substituted N-heterocyclic carbene complexes of Pd(II) and Pt(II) is reported. Catalyzed 1,3-dipolar cycloaddition with azides has been applied as a modular way of functionalisation of group 10 transition metal NHC complexes to generate potentially new metallodrugs.     

4-Vinylbenzyl-substituted silver(I) N-heterocyclic carbene complexes and ruthenium(II) N-heterocyclic carbene complexes: synthesis and transfer hydrogenation of ketones

4-Vinylbenzyl-substituted Ag(I) N-heterocyclic carbene (NHC) complexes and Ru(II) NHC complexes have been synthesized. The Ag(I) complexes were synthesized from the imidazolium salts and Ag₂O in dichloromethane at room temperature. The Ru(II) complexes were prepared from Ag(I) NHC complexes by transmetallation. The six 4-Vinylbenzyl-substituted Ag(I) NHC complexes and six 4-Vinylbenzyl-substituted Ru(II) NHC complexes have been characterized by spectroscopic techniques and elemental analyses. The Ru(II) NHC complexes show catalytic activity for the transfer hydrogenation of ketones.     

Dendrimer N-heterocyclic carbene complexes with rhodium(I) at the core

Novel dendrimer N-heterocyclic carbene complexes with rhodium(I) located at the core were synthesized, and a positive dendrimer effect was found in the hydrosilylation of ketones catalyzed by them.     

Facile synthesis of metal N-heterocyclic carbene complexes

A novel electrochemical procedure for the preparation of metal complexes of N-heterocyclic carbenes using imidazolium salts or corresponding silver-NHC complexes as carbene sources and electrolytes, and metal plates as the sacrificial anodes is described. The procedure is simple and good yielding without the use of expensive or air-sensitive reagents.     

N-heterocyclic carbene stabilized dichlorosilylene transition-metal complexes of V(I), Co(I), and Fe(0)

Reactions of N-heterocyclic carbene stabilized dichlorosilylene IPr·SiCl(2) (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with (η(5)-C(5)H(5))V(CO)(4), (η(5)-C(5)H(5))Co(CO)(2), and Fe(2)(CO)(9) afford dichlorosilylene complexes IPr·SiCl(2)·V(CO)(3)(η(5)-C(5)H(5)) (2), IPr·SiCl(2)·Co(CO)(η(5)-C(5)H(5)) (3), and IPr·SiCl(2)·Fe(CO)(4) (4), respectively. Complexes 2-4 are stable under an inert atmosphere, are soluble in common organic solvents, and have been characterized by elemental analysis and multinuclear ((1)H, (13)C, and (29)Si) NMR spectroscopy. Molecular structures of 2-4 have been determined by single crystal X-ray crystallographic studies and refined with nonspherical scattering factors.     

Structural motifs of Au(I)-Cu(I) N-heterocyclic carbene halide complexes

A series of Au(I)–Cu(I) N-heterocyclic carbene (NHC) halide complexes [AuCu₂(im(CH₂py)₂)₂X]²⁺ where X?=?Cl (1), Br (2), I (3) was prepared by refluxing [AuCu₂(im(CH₂py)₂)₂(NCCH₃)₄]³⁺ with the appropriate halide in acetonitrile. The compounds were characterized by NMR, absorption, and fluorescence spectroscopy. They feature similar solution behavior and solid-state photoemissions. The solid-state structures feature a rhomboidal [AuCu₂X]²⁺ core which is influenced by the type of halide. Compared to other Au(I)–Cu(I) NHC complexes, 1–3 comprise a new structural motif containing a bridging halide. The benzimidazolium analog of 1 was also characterized crystallographically. The structure of [AuCu₂(benzim(CH₂py)₂)₂Cl]²⁺(4) features different coordination modes of the NHC ligands with the carbenic carbon bonded to both gold and copper and the pyridyl groups bonded to the same copper(I) ion.     

Synthesis and characterisation of anionic and neutral gallium(I) N-heterocyclic carbene analogues

A high yield synthesis of a new, extremely bulky anionic gallium(I) N-heterocyclic carbene analogue, [(DAB*)Ga:](-) (DAB* = {N(Ar*)C(H)}(2), Ar* = C(6)H(2){C(H)Ph(2)}(2)Me-2,6,4) has been developed and four monomeric sodium complexes of the heterocycle have been crystallographically characterised. The gallium(I) heterocycle has been utilised in the preparations of the heteroleptic zinc and cadmium gallyl complexes, [(DAB*)GaMX(tmeda)] (M = Zn or Cd, X = Br or I), which were crystallographically characterised. In addition, [(DAB*)Ga:](-) was oxidatively coupled to give the diamagnetic digallane(4), [(DAB*)GaGa(DAB*)]. The moderate yield synthesis of the six-membered gallium(I) heterocycle, [((But)MesNacnac)Ga:] ((But)MesNacnac = [(MesNCBu(t))(2)CH](-), Mes = mesityl), is described, and the compound found to be a monomer in the solid state by an X-ray crystallographic analysis. A low yield by-product from this synthesis, [Ga(5)I(4)((But)MesNacnac)(3)], was also isolated and shown by X-ray crystallography to be a rare example of a compound bearing a group 13 metal-metal bonded chain stabilised by β-diketiminate ligands. A preliminary analysis of the bonding in the compound was carried out using DFT calculations.     

Four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes with brightly luminescence properties

Three four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes, [Cu(Py-Im)(POP)](PF₆) (P1), [Cu(Py-BenIm)(POP)](PF₆) (P2), and [Cu(Py-c-BenIm)(POP)](PF₆) (P3) (Py-Im = 3-methyl-1-(pyridin-2-yl)-1H-imidazolylidene, Py-BenIm = 3-methyl-1-(pyridin-2-yl)-1H-benzo[d]imidazolylidene, Py-c-BenIm = 3-methyl-1-(pyridin-2-ylmethyl)-1H-benzo[d]imidazolylidene, POP = bis([2-diphenylphosphino]-phenyl)ether), have been synthesized without transmetalation of the NHC–Ag(I) complex for the first time. The photophysical properties of the resultant NHC–Cu(I) complexes have been systematically investigated via spectroscopic methods. All complexes exhibit good photoluminescence properties with long excited-state lifetimes and moderate quantum yields. Density functional theory and time dependent density functional theory calculations were employed to rationalize the photophysical properties of the NHC–Cu(I) complexes.     

Synthesis and anticancer properties of gold(I) and silver(I) N-heterocyclic carbene complexes

Bis(1,3-dimethylimidazol-2-ylidene)silver(I) nitrate and bis(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)silver(I) nitrate were prepared by reacting the corresponding imidazolium nitrate salts with silver oxide. Bis(1,3-dimethylimidazol-2-ylidene)gold(I) nitrate and bis(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)gold(I) nitrate salts were prepared via transmetallation of their silver precursors with chloro dimethylsulfide gold. The anticancer properties were determined using NCI-H460 lung cancer cells. Efficacy was established by comparison of the gold and silver compounds with cisplatin.     

Stable nitridorhenium(V) complexes with an N-heterocyclic carbene

Nitridorhenium(V) complexes with the nucleophilic cyclocarbene 1,3,4-triphenyl-1,2,4-triazol-5-ylidene have been synthesised and are the first representatives of a new class of high-valent metallocarbenes.     

Silver(I) N-heterocyclic carbene halide complexes: A new bonding motif

Two new NHC silver halide salts have been synthesised and structurally characterised, and they show the two most common structural forms for such salts: the (NHC)AgX and the forms (both have a stoichiometry of 1 NHC:1 Ag:1 halide). A third new compound has been synthesised and structurally characterised: this compound has an unprecedented 2 NHC:1 Ag:1 halide stoichiometry and exhibits a planar arrangement of two coordinating NHCs, and a coordinating bromide about the central silver. The Ag-Br bond is long in the solid state and, together with solution NMR data, this suggests that a formulation of (NHC)₂Ag⁺Br⁻ might be more appropriate.     

Synthesis and structural characterisation of linear Au(I) N-heterocyclic carbene complexes: New analogues of the Au(I) phosphine drug Auranofin

The synthesis and characterisation of a series of neutral Au(I) N-heterocyclic carbene complexes [(NHC)AuX] (X = Cl and 2′,3′,4′,6′-tetra-O-acetyl-β-d-glucopyranosyl-1-thiolato) are reported. The chloro complexes were synthesised either by reaction of the appropriate 1,3-dialkylimidazol-2-ylidene with [(Me₂S)AuCl] or by transmetallation between the appropriate Ag(I)–NHC complex and [(Me₂S)AuCl]. The 2′,3′,4′,6′-tetra-O-acetyl-β-d-glucopyranosyl-1-thiolato complexes were prepared from the appropriate [(NHC)Au(I)Cl] complex and 2′,3′,4′,6′-tetra-O-acetyl-1-thio-β-d-glucopyranose under basic conditions. A cationic Au(I)–NHC triphenylphosphine adduct was also prepared. Structural studies (X-ray diffraction) of a number of the complexes show that in each case the gold atom is (quasi-) linearly two-coordinate, having C–Au–Cl, C–Au–S or C–Au–P coordination. In one case, a new phase of [(Cy₂Im)AuCl], the molecules pack pair-wise with a close Au⋯Au interaction (3.1566(6) Å). Preliminary studies show this complex is luminescent in the solid state.     

Homo- and heteroleptic mercury(II) complexes with monoamino complexones in aqueous solution

Reactions of mercury(II) with iminodiacetic (H₂Ida), 2-hydroxyethyliminodiacetic (H₂Heida), and nitrilotriacetic acids (H₃Nta) were studied by spectrophotometry and pH potentiometry. The resulting complexes included [HgIda], [Hg(OH)Ida]^?, [HgIda₂]^2?, [HgHeida], [Hg(OH)Heida]^?, [Hg(Heida)₂]^2?, [HgNta]^?, [HgNta₂]^4?, [Hg(Ida)Heida]^2?, [Hg(Ida)Nta]^3?, and [Hg(Heida)Nta]^3?. The logarithms of their stability constants calculated for I = 0.1 (NaClO₄) and T = 20 ± 2°C were 11.14 ± 0.07, 20.33 ± 0.08, 19.40 ± 0.10, 11.42 ± 0.04, 19.68 ± 0.11, 18.48 ± 0.09, 13.42 ± 0.05, 20.80 ± 0.08, 19.05 ± 0.06, 20.64 ± 0.11, and 20.53 ± 0.16, respectively. The experimental data were analyzed in terms of the mathematical models that predict the existence of a wide spectrum of complex species in solution and allow one to consider only those species that are sufficient for accurate reproduction of the observed pattern.     

Nickel(0)/N-heterocyclic carbene complexes catalysed arylation of aromatic diamines

Nickel complexes of N-heterocyclic carbenes were examined for effecting C–N coupling reactions between aromatic diamines and aryl chlorides of varying electron density. The Ni(0) · 2IPr (IPr = N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) complex associated to t-BuONa allowed N,N′-diarylation at 100 °C in 1,4-dioxane with excellent yields. Selective monoarylation of diamines could be performed in THF at 65 °C.