Diaminocarbene complex

Chiral diaminocarbene complexes of copper were used in asymmetric conjugate addition of diethylzinc to Michael acceptors. Achiral copper carbene complexes derived from imidazolium salts were synthesized and characterized for the first time by Arduengo in 1993 [43]. In 2001, Woodward reported the use of such Arduengo-type carbene in copper-catalyzed conjugate addition and showed their strong accelerating effect [44]. The same year, Alex-... 

This group showed that isolable silver(I) diaminocarbene complexes can be use in situ instead of free carbenes, to generate the copper carbene complex. The silver salts that precipitates during the formation of the copper complex have not any negative effect on the conversion. This method is advantageous since most of the silver complexes are isolable, air-stable and easily obtained by treatment of the corresponding imidazohnium salt by 0.5 equiv of silver oxide (Scheme 53). The solid structure of 78 was analyzed by X-ray diffraction. 

Roland S, Mangeney P (2005) Chiral Diaminocarbene Complexes, Synthesis and Application in Asymmetric Catalysis. 15 191-229... 

Diaminocarbene complexes were reported as early as 1968 [152], Preparation and applications of such complexes have been reviewed [153], Because of 7t-electron donation by both nitrogen atoms, diaminocarbenes are very weak tt-acceptors and have binding properties towards low-valent transition metals similar to those of phosphines or pyridines [18,153]. For this reason diaminocarbenes form complexes with a broad range of different metals, including those of the titanium group. Titanium does not usually form stable donor-substituted carbene complexes, but rather ylide-like, nucleophilic carbene complexes with non-heteroatom-substituted carbenes (Chapter 3). 

The most practical approach is the direct treatment of azolium salts with metal complexes under neutral or basic conditions [39,154-159]. Alternatively, the free carbenes can be generated in the presence of a suitable metal complex by reduction of a carbene precursor, e.g. a thiourea [160]. Stable, uncomplexed imidazoline-2-ylidenes, isolated for the first time in 1991 by Arduengo [161] (for further examples see [162-166]), are also convenient starting materials for the preparation of carbene complexes [167,168]. The corresponding diaminocarbene complexes can be obtained by treatment of the stable diaminocarbenes with transition metal complexes. Finally, at high temperatures many transition metal complexes catalyze the carbon-carbon bond scission of tetraaminoethylenes, forming carbene complexes [169-171]. Examples of such preparations are given in Table 2.8. 

Photolysis of cationic alkoxycarbene iron complexes [193] or alkoxycarbene manganese complexes [194] has been used to replace carbonyl groups by other ligands. The alkylidene ligand can also be transferred from one complex to another by photolysis [195], Transfer of alkylidene ligands occurs particularly easily from diaminocarbene complexes, and has become a powerful synthetic method for the preparation of imidazoline-2-ylidene complexes [155,196]. 

Rogers MM, Stahl SS (2006) N-Heterocyclic Carbenes as Ligands for High-Oxidation-State Metal Complexes and Oxidation Catalysis. 21 21-46 Roland S, Mangeney P (2005) Chiral Diaminocarbene Complexes, Synthesis and Application in Asymmetric Catalysis. 15 191-229 Roll R, see Behr A (2008) 23 19-52... 

A mechanism for asymmetric induction has been discussed based on the merry-go-round mechanism proposed for Ni(II)-catalyzed polymerization, and discussed earlier. In the initial stages, a chiral amine attacks one of the four isocyanide ligands (C1) on the nickel to form a diaminocarbene complex I, whose structure has been elucidated in detail [60]. Among the possible conformations, the one that involves weak interaction between the Ph group and Ni was presumed to have the most favorable conformation (Scheme 37). The structure of the intermediate I has also been discussed in... 

Bicyclic bisamidines can be prepared from tra i-A, A( -dunethyl-l,2-diaminocyclohexane and a palladium bis(arylisocyanide) complex [38] (Scheme 3.22). Oxidation of the initially-formed palladium bis(acyclic diaminocarbene) complex with air or idosobenzene (Phi = O) followed by treatment with excess amounts of methylisonitrile (MeNC) yields bicyclic bisamidines. The structure of the product obtained in each step is unequivocally determined by X-ray crystallographic analysis. 

Wanniarachchi, YA. and Slaughter, L.M. (2007) One-step assembly of a chiral palladium bis (acyclic diaminocarbene) complex and its unexpected oxidation to a bis(amidine) complex. 

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