Ligands CCC pincer

The monoanionic CCC pincer ligand 7 was introduced by Hollis [15] (Figure 9.3). Metallation of the ligand precursor was achieved by deprotonation with tetraamido zirconium(IV) complexes. Modifications were done by Chianese [16] who used stronger donating benzimidazolin-2-ylidene moieties in 8, and by... 

Rh complexes with the monoanionic CCC pincer ligand 7 were first synthesized by Hollis et al. [ 15,31] in a rather unusual way. They first synthesized the Zr... 

Scheme 9.5 Synthesis of monometallic complex 36 and the dimers 37 and 39 bearing a monoanionic CCC pincer ligand (According to Hollis [15, 31, 32].) and the preparation of iridium complex 38. (According to Braunstein [33].)...

Similar reasons seem to count also for the promising catalytic experiments with the dimeric Rh and Ir complexes 37 and 39 which bear the same CCC pincer ligand in the intramolecular hydroamination of terminal olefins. Up to now, the air- and water-stable catalyst system is limited to the intramolecular reaction of P-disubstituted secondary amines. 

Zhang Y-M, Shao J-Y, Yao C-J, Zhong Y-W. Cyclometalated ruthenium(II) complexes with a bis-carbene CCC-pincer ligand. Dalton Trans. 2012 41 9280-9282. 

The Rh CCC pincer complex 36 tested by Hollis in the hydrosilylation of acetylenes shows a high activity and selectivity for the Z-product, which is also found for a bimetalUc NHC complex bearing the same ligand in a bridging... 

A similar complex bearing a normal and an abnormal coordinated carbene moiety was reported by Zuo and Braunstein its catalytic activity in the transfer dehydrogenation of cyclooctene was however markedly lower than that of the complexes by Chianese/ Remarkably, CCC pincer complexes of iridium(III) developed by Chianese and by the gyoup of Herrmann and Kuhn " turned out to be active catalysts also for another C—H functionalization reaction, namely theborylation of arenes. Activities were however low compared to iridium(III) complexes with other ligands which were extensively optimized over the years. 

Several metal complexes with CCC pincer-type dicarbene ligands have been investigated over the years by the group of Hollis as catalysts for the intramolecular hydroamination/cychzation of unactivated alkenylamines. Initial studies concerned rhodium(III) and iridium(III) complexes of type 75, but later investigations were extended to complexes of the same ligands with group 4 metals such as zirconium, hafnium, and tita-... 

A series of cyclometalated Ru(II) complexes, 91 and 92, with a CCC pincer dicarbene ligand have been also proposed in this regard. However, only complex 91b in acetonitrile solution at room temperature shows an emission band at 808 nm, although with a very low quantum yield (0en.[Pg.255]

Huckaba AJ, Hollis TK, Howell TO, Valle HU, Wu Y. Synthesis and characterization of a 1,3-phenylene-bridged N-alkyl bis(benzimidazole) CCC-NHC pincer ligand precursor homobimetaUic silver and rhodium complexes and the catalytic hydrosilylation of phenylacetylene. Organometallics. 2013 32 63-69. 

Some other intermolecular C-H activations involving the NHC ligand have been observed during the synthesis of particular NHC-containing pincer -type complexes also called CCC-NHC complexes. In addition to zirconium- and rhodium-based complexes (210) and (211)/ several examples involving palladium of general structure (271) have been synthesized. Whereas Faller... 

Some of the most stable NHC-Pd complexes reported to date feature a pincer type CNC or CCC ligands, where the two terminal ligands are NHCs (Figure 3.2). For example, complex 63 decomposed in refluxing A, A -dime-thylacetamide (DMA) (bp = 165 °C) depositing Pd black after 8 h, while 55 was unchanged after 24 h at this temperature. In Heck reactions catalyst 55 had no induction period and no loss of catalytic activity was found in the presence of metallic mercury. 

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