Chelating dicarbene

Several reports in which NHC-Pd complexes have been employed to catalyse the copolymerisation of alkenes with CO have appeared over the years. Herrmann and co-workers reported that the chelating dicarbene complex 38 (Fig. 4.14) is active for CO/ethylene [43], The highest TON [(mol ethylene + mol CO) mol Pd ] was 3 075 after a 4 h run. The modest TONs coupled with a very high molecular weight copolymer led the authors to conclude that only a small fraction of the pre-catalyst goes on to form an active species. Low molecular weight (M = 3 790) CO/norbomene copolymer resulted when complex 39 (Fig. 4.14) was tested by Chen and Lin [44]. The catalyst displayed only a very low activity, yielding 330 turnovers after 3 days. 

Some bidentate bis(imidazolin-2-ylidene)s 18 have been used for the preparation of complexes with chelating dicarbene ligands [75-80]. The synthesis, properties, and coordination chemistry of tripodal tris(imidazolin-2-ylidene) ligands like 19... 

The kinetics of formation of chelating dicarbene products from the reaction of the hexakisisonitrile complex [Fe(CNMe)6] with hydrazine and with methyl-... 

Chelating dicarbene ligands were found very useful for stabilizing technetium(V) dioxo species, forming complexes of structure 51, which turned out to be stable to water, a potentially very useful feature for the application of these compounds as radiopharmaceuticals/ ... 

C—H activation/functionalization reactions represent one of the classes of chemical transformations that have been most intensively studied in recent years. Poly-NHC metal complexes have a long-standing tradition of involvement as catalysts in these processes, which can be tracked back to their stability under the relatively harsh reaction conditions that are often needed to drive such reactions to completion in a reasonable time. For example, the group of Strassner reported already in 2002 that paUadium(II) complexes with chelating dicarbene ligands can catalyze the... 

Direct arylation can be very efficiently catalyzed also by other metal centers besides paUadium(II), in particular rhodium(III) and ruthenium(II). In 2009, the groups of Ozdemir and Bruneau jointly reported on the catalytic activity of ruthenium(II) compounds with o-xylylene-bridged, chelating dicarbene ligands for the direct arylation of 2-phenylpyridine. Good catalytic efficiencies were observed even with aryl chlorides as substrates, so that the process resulted in the predominant formation ofbis-o-arylated products (Fig. 20). ... 

Chelating dicarbene palladium(II) complexes have been found to catalyze the Nazarov cyclization of divinyl-beta-ketoesters to the corresponding cyclopentenones (Fig. 29). The reactivity of the complexes was generally... 

Cp -iridium(III) complexes with chelating dicarbene hgands have been successfully employed as water oxidation catalysts, both in the presence of a sacrificial oxidant (Ce(IV) or Nal04) or under photoactivated conditions with Ru(bpy)3 as photosensitizer and sodium persulfate as sacrificial acceptor of electrons catalytic efficiencies were comparable with the most efficient iridium-based catalysts reported to date. ... 

Recently, Venkatesan reported the platinum(II) complexes 108—110 (Fig. 37), whose structures are similar to complexes of type 100 the three complexes differ for the ancillary chelating dicarbene Hgand and for the phenylacetylide coordinated moieties.AH the complexes display a deep blue emission, in solution (dichloromethane at room temperature), in rigid matrix (2-methyltetrahydrofuran at 77 K), in soHd state, and in PMMA film (doped with 10% of the platinum complex). The emission maxima are in the... 

Biffis A, Tubaro C, Buscemi G, Basato M. Highly efficient alkyne hydroarylation with chelating dicarbene paUadium(II) and platinum(II) complexes. Adv Synth Catal. 2008 350 189-196. 

Biffis A, GazzolaL, Gobbo P, Buscemi G, Tubaro C, Basato M. Alkyne hydroarylations with chelating dicarbene paUadium(n) complex catalysts improved and imexpected reactivity patterns disclosed upon additive screening. Eur J Org Chem. 2009 2009 3189-3198. 

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