N-杂环卡宾钯催化剂

2010年，Michael G. Gardiner 和他的同事合成了新型的氮杂环卡宾化合物，A colorless solution of 1 over anhydrous Na2CO3 in dry MeOH was heated at 508C for two hours to give a red solution, from which red crystals of 2 were obtained in 84%

yield after filtration and concentration (Scheme 1).[8] Complex 2 has high stability as a solid (more than one year) and in MeOH and THF (several months). The complex is tolerant to moisture, but reacts quickly with atmospheric oxygen in solution and the solid state.

Peter D. W. Boyd, Alison J. Edwards, Michael G. Gardiner, Angew. Chem. Int. Ed. 2010, 49, 6315 –6318.

2008年，Takeshi Makino和他的同事得到了具有二齿氮杂环配体的钯配合物，The bidentate NHC-palladium complexes 4a–e were prepared by the reaction of 1-(4-iodoaryl)-3-aryl-4,5-dihydroimidazolinium salt (1)[16] and xanthenediboronic acid (2)[17] in the presence of Pd(PPh3)4 and Ag2O followed by palladation[18] (Scheme 1). The bis(imidazolidene) derivative 6 was also synthesized in a similar way (Scheme 2).

Takeshi Makino, Hyuma Masu, Kosuke Katagiri, Ryu Yamasaki, Isao Azumaya,

and Shinichi Saito，Eur. J. Inorg. Chem. 2008, 4861–4865.

There are many examples of monodentate NHCs, but only a few examples of alkane-bridged chelating biscarbene ligands. Chelated carbenes are expected to be more stable since one possible decomposition pathway, reductive elimination of the carbene, should be slower for this conformationally restricted case. A chelating coordination is one way to obtain highly stable catalysts capable of tolerating harsher reaction conditions than traditional phosphine catalysts. Sebastian Ahrens 和他的同事化合物长链烷烃桥联配体的钯配合物，

Sebastian Ahrens, Alexander Zeller, Maria Taige, and Thomas Strassner Organometallics, Vol. 25, No. 22, 2006

N-Heterocyclic carbenes (NHCs), first prepared independently by Wanzlick and Schnherr[1] and fele[2] in 1968, attracted little interest from the chemical community until 1991, when Arduengo et al. revealed the first stable, crystalline NHC

(1, IAd).[3] The potential of this class of compounds to serve as spectator ligands in transition-metal complexes was recognized in 1995 by Herrmann et al.[4] Soon thereafter, the exploitation of the remarkable potential of NHC ligands in catalysis began. The above seminal works led to the development of a variety of other NHC platforms (see right column)[5] and their transition-metal complexes for catalytic applications. However, only NHCs derived from imidazolium or 4,5-dihydroimidazolium salts have found wide-spread use in homogeneous catalysis to date. The most important example is the ruthenium metathesis catalyst developed

by Grubbs and co-workers, for which the Nobel Prize was awarded. Replacement of one of the two tricyclohexyl phosphane ligands in the generation I Grubbs catalyst with the bulky carbene SIMes (3) led to significant improvements in terms of catalyst stability, activity, and substrate range in subsequent generations.[6] Palladium is another transition metal capable of directing a wide range of useful transformations,[7] in particular C-C and C-heteroatom cross-coupling and carbopalladation reactions.[8] The use of bulky carbenes, in particular IPr (4) and SIPr (5), as ligands in these transformations has also resulted in significant improvements in catalyst performance compared to the more traditional phosphane ligands.

[1] H.-W. Wanzlick, H.-J. Schnherr, Angew. Chem. 1968, 80, 154; Angew. Chem. Int. Ed. Engl. 1968, 7, 141– 142.

[2] K. fele, J. Organomet. Chem. 1968, 12, P42– P43.

[3] A. J. Arduengo III, R. L. Harlow, M. Kline, J. Am. Chem. Soc.1991, 113, 361– 363.

[4] W. A. Herrmann, M. Elison, J. Fischer, C. Kchter, G. R. J. Arthus, Angew. Chem. 1995, 107, 2602– 2605; Angew. Chem. Int. Ed. Engl. 1995, 34, 2371– 2373.