N-heterocyclic carbine

Fig. 1 Structure of hydrid scorpionate complex 6 and N-heterocyclic carbine complex 7.

Keywords Ketones, trisilyl enols, THF, room temperature, silyl transfer, N-heterocyclic carbine (NHC), silyl enol ethers... 

Y. Suziiki, M. Murofushi, K. Manabe, One-pot synthesis of unsymmetrical benzhs and N-heteroarenes through nucleophilic aroylation catalyzed by N-heterocyclic carbine. Tetrahedron 69 (2013) 470-473. 

A facile synthesis of y-ketophosphonates (589) has been realised by intermolecular cross-coupling reaction of aromatic aldehydes (587) with vinylphosphonates (588), catalysed by N-heterocyclic carbine (589) in moderate to good yields (Scheme 171). ... 

Non-metallic homogeneous catalyst systems were also reported for methanol synthesis. Recently, Ashley et al. [49] demonstrated the selective hydrogenation of COj to methanol using a FLP-based nomnetal mediated procedure at low pressures (1-2 atm). N-Heterocyclic carbine (NHC) was found to be an elFective organic catalyst for methanol synthesis from CO2 reduction with silane. Compared to transition metal catalyst, NHC is more efficient at ambient reaction conditions [50,51]. Table 5.1 lists catalytic activities of different heterogeneous catalysts employed for methanol synthesis from CO. It shows that maximum CO conversion of 25.9%, methanol selectivity of 99.5% and methanol yield of378 mg/g-cat h could be achieved. The space velocities were tried between 1800 and 18,000 h and the temperature from 170 to 270 C. 

TON= moles formic acid formed per mole of metal [DAMI] [TfD] = l,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium trifluoromethanesulfonate NHC = N-heterocyclic carbine, Tp=hydrotris(pyrazolyl)borate. 

They differ, both in the imidazoline or imidazolidine-derived Ai-heterocyclic carbine and in the substituents R on the N-atoms, as well as in the alkylidene fragment. Most importantly, the activity of the catalysts 27-29 is significantly higher than that of the parent Grubbs carbene 19 and comes close to that of Schrock s Mo alkylidene complex 18. In combination with exceptional thermal stability and resistance towards oxygen and moisture, together with compatibility with many... 

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