Syntheses and structures of dicyanobis(oxazolidin-2-ylidene)palladium(II) and platinum(II) complexes

Synthesis of β-Aminoenones via Cross-Coupling of In-Situ-Generated Isocyanides with 1,3-Dicarbonyl Compounds

An efficient and practical strategy for the synthesis of β-aminoenones from a three-component reaction was developed. Ethyl bromodifluoroacetate serves as a C1 source in this strategy, forming isocyanides in situ with primary amines. This reaction represents the first example of utilization of readily available starting materials to generate isocyanides in situ and sequentially fully converted to β-aminoenones, avoiding the generation of byproduct imines and overinsertion products. The mechanism study suggested that this method involves activation of two C(sp³)-F bonds and the formation of isocyanides, which might nourish both isocyanide chemistry and fluorine chemistry.

Synthesis and coordination chemistry of macrocyclic ligands featuring NHC donor groups

Poly-NHC (NHC = N-heterocyclic carbene) ligands emerged almost immediately after the first stable NHCs had been described. Macrocyclic ligands, featuring NHC donor groups and their metal complexes, however, remained rare until recently. This perspective highlights modern developments in the fields of synthesis and coordination chemistry of macrocyclic poly-NHC ligands. These include the synthesis of tetracarbene ligands which were obtained from complexes of β-functionalized isocyanides followed by cyclization of the coordinated iscocyanide ligands to NH,NH-functionalized NHCs and the subsequent metal template controlled bridging alkylation of the NH,NH-NHCs to yield the macrocycle. The template synthesis of ligands featuring a mixed NHC/phosphine donor set like [11]ane-P(2)C(NHC) and [16]ane-P(2)C(NHC)(2) by linkage of NH,NH-NHCs to different phosphines is also presented. Finally, methods for the preparation of cyclic polyazolium salts, their deprotonation and metalation and the different modes of coordination of such macrocyclic poly-NHC ligands are discussed.

Heterocyclic carbenes: synthesis and coordination chemistry

The chemistry of heterocyclic carbenes has experienced a rapid development over the last years. In addition to the imidazolin-2-ylidenes, a large number of cyclic diaminocarbenes with different ring sizes have been described. Aside from diaminocarbenes, P-heterocyclic carbenes, and derivatives with only one, or even no heteroatom within the carbene ring are known. New methods for the synthesis of complexes with N-heterocyclic carbene ligands such as the oxidative addition or the metal atom template controlled cyclization of beta-functionalized isocyanides have been developed recently. This review summarizes the new developments regarding the synthesis of N-heterocyclic carbenes and their metal complexes.

Synthesis of BenzannulatedN-Heterocyclic Carbene Ligands by a Template Synthesis from 2-Nitrophenyl Isocyanide

The reaction of 2-nitrophenyl isocyanide 2 with [M(CO)5(thf)] (M=Cr, Mo, W) yields the isocyanide complexes [M(CO)5(2)] (3: M=Cr; 4: M=Mo; 5: M=W). Complexes 3-5 react with elemental tin under reduction of the nitro function of the isocyanide ligand to give the complexes with the unstable 2-aminophenyl isocyanide ligand. The coordinated 2-aminophenyl isocyanide ligand in all three complexes reacts spontaneously under intramolecular nucleophilic attack of the primary amine at the isocyanide carbon atom to yield the complexes with the NH,NH-benzimidazol-2-ylidene ligand (6: M=Cr; 7: M=Mo; 8: M=W). An incomplete reduction of the nitro group in 3-5 is observed when hydrazine hydrate is used instead of tin. Here the formation of complexes with a coordinated 2-hydroxylamine-functionalized phenyl isocyanide [(CO)5M-CN-C6H(4-)-2-N(H)-OH] is postulated and this unstable ligand again undergoes intramolecular cyclization to give the NH,NOH-stabilized benzimidazol-2-ylidene complexes 9-11. The tungsten derivative 11 can be allylated stepwise by a deprotonation/alkylation sequence first at the OH and then at the NH position to yield the monoallylated and diallylated species 12 and 13. The molecular structures of 3-5 and 12-13 were established by X-ray crystallography.