Latent Nucleophilic Carbenes

Using DFT and ab initio calculations, we demonstrate that noncyclic formamidines can undergo thermal rearrangement into their isomeric aminocarbenes under rather mild conditions. We synthesized the silylformamidine, for which the lowest activation energy in this process was predicted. Experimental studies proved it to serve as a very reactive nucleophilic carbene. The reactions with acetylenes, benzenes, and trifluoromethane proceeded via insertion into sp, sp², and sp³ CH bonds. The carbene also reacted with the functional groups, such as CHO, COR, and CN at double or triple bonds, displaying high mobility of the trimethylsilyl group. The obtained silylformamidine can be considered as a latent nucleophilic carbene. It can be prepared in bulk quantities, stored, and used when the need arises. Calculation results predict similar behavior for some other silylated formamidines and related compounds.

Rh(i) and Ru(ii) phosphaamidine and phosphaguanidine (1,3-P,N) complexes and their activity for CO2 hydrogenation

Phosphaamidine metal complexes Rh₂Cl₂[Ph₂PC(Ph)[double bond, length as m-dash]NPh]₂μ-CO (1), RuCl₂[Ph₂PC(Ph)[double bond, length as m-dash]N(Ph)]₂ (2), [Rh{ⁱPr₂PC(Ph)[double bond, length as m-dash]NⁱPr}(COD)]BF₄ (3), and RuCl₂[ⁱPr₂PC(Ph)[double bond, length as m-dash]NⁱPr](DMSO)₂ (4) are prepared by combining phosphaamidines Ph₂P-C(Ph)[double bond, length as m-dash]NPh and ⁱPr₂P-C(Ph)[double bond, length as m-dash]NⁱPr (1,3-P,N) with their corresponding metal ions. Complexes 1 and 2 are stable in air while 3 and 4 are stable under inert conditions. For further comparison of structure and stability, a Ru(ii) phosphaguanidine complex, RuCl₂[Me₂NC(PPh₂)[double bond, length as m-dash]NⁱPr](DMSO)₂ (6) was prepared. Complex 6 is stable in air and in the presence of water. The structures of the phosphaamidine and phosphaguanidine complexes, determined using single crystal X-ray diffraction, revealed P,N bidentate coordination. While all five complexes have some activity as precatalysts, complex 6 was the most active.

1,2-Migration of N-Diarylboryl Imidazol-2-ylidene through Intermolecular Radical Process

1,2-Boryl migration of N-boryl N-heterocyclic carbene to 2-boryl imidazole is proposed to proceed through generation and recombination of two radical intermediates, namely, a neutral diarylboron radical and a N-heterocyclic carbene radical. Crossover experiments suggest that these two radical species are stable enough to escape solvent cages and recombine intermolecularly. The presence of radical intermediates is further supported by spin trapping experiments. Besides, the coordination of Li⁺ cation is found to be critical for the stability of the NHC radical.

The phosphinoboration of carbodiimides, isocyanates, isothiocyanates and CO2

The transition metal-free addition of phosphinoboronate ester Ph₂PBpin (pin = 1,2-O₂C₂Me₄) to heterocumulenes including carbodiimides, isocyanates, isothiocyanates and carbon dioxide proceeds with remarkable selectivity to give products in high yield.

Palladium(ii) complexes with chelating N-phosphanyl acyclic diaminocarbenes: synthesis, characterization and catalytic performance in Suzuki couplings

Novel palladium(ii) complexes with the title ligands have been prepared and tested as precatalysts in Suzuki couplings of aryl chlorides.

1,2-migration in N-phosphano functionalized N-heterocyclic carbenes

1,2-Migration of the phosphano-group to the carbene center in N-phosphano functionalized N-heterocyclic carbenes has been studied by density functional theory (DFT) calculations. An intramolecular mechanism with a three-center transition state structure seems to be most plausible for the isolated carbenes, while an intermolecular pathway catalyzed by azolium salts may be preferable for a migration proceeding in the course of generating the carbenes in situ. Our calculations show that amino-substitution at the phosphorus atom and an enhanced nucleophilicity of the heterocycle scaffold facilitate the phosphorus shift. Calculated singlet-triplet energy gaps do not correlate with thermodynamic stability of the studied carbenes and their disposition toward the 1,2-rearrangement.