Rhodium complexes pincer-type

Following this observation, a general approach for the synthesis of pincer-type methylene arenium compounds was developed (Scheme 3.4). Upon reaction of the methyl rhodium (or iridium) complexes 5 with a slight excess of triflic acid, dihydrogen (not methane ) was evolved to form the methylene arenium complexes 4a.11 Thus, the methylene arenium form is clearly preferred over the benzylic M(III) form, in which the positive charge is localized at the metal center. 

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... 

Diphosphine pincer-type PCP-rhodium complexes were found to be robust precursors for the synthesis of carbene complexes such as 311 and 312 by reaction with phenyldiazomethane. ... 

Ozerov reported the synthesis of rhodium pincer complexes of types 89 and 90 with aryl/bis(phosphinite) POCOP ligands. Their donating ability was assessed by IR spectroscopy. Furthermore, all surveyed Rh complexes were applied as catalysts in dimerization reactions of terminal allynes, such as 4-ethynyltoluene, l-he)yne and trimethysilylacelylene. 

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-... 

Tridentate bis(oxazolinyl)pyridinyl rhodium and ruthenium pincer complexes are useful as catalysts for hydrosilylations and cyclopropanations. These NNN-type inorganic pincer complexes are not as stable, however, as phosphine or salen-type pincer complexes. On the other hand, an organometallic tridentate bis(oxazolinyl) phenyl NCN-type complex is stable. These optically active NCN-type pincer complexes act as efficient catalysts for enantioselective hetero Diels-Alder reactions of Danishefsky s diene with glyoxylates [26]. 

For example, several pincer ligands with a central amido moiety, such as those of type 11, have been developed by several groups and their complexes with metal centers such as paUadium(II), platinum(II), and rhodium(I) have been characterized. The aim was on the one hand to synthesize robust, electron-rich organometaUic compounds which easily undergo oxidative addition at the metal center and, on the other hand, to develop bifiinctional catalysts in which the central amido moiety can cooperatively act with the metal center in a catalytic event, for example, by accepting/releasing protons... 

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