Diene complexes chelated

Dehydrogenation of alkanes 5.8.2.2.1 Diene complexes chelated reaction with nucleophiles 5.8.2.5.2 chelating... 

Several groups have reported the use of rare earth complexes as catalysts for asymmetric Diels-Alder reaction. Qian and Wang described thus the preparation and use of Yb complexes chelated by Pr-PyBOx to successfully achieve the hetero-Diels-Alder reaction of methyl glyoxylate with Danishefsky s diene in 77% ee and 73% yield (Scheme 37) [98]. 

However, the usual course of events in the isomerization of cycloalkadienes is to achieve conjugation where coordination is impossible. Thus cyclohexa-1,4-diene is isomerized to cyclohexa-1,3-diene by [RuC PPhsjs]. Nevertheless, RhCb 3H2O isomerizes cycloocta-1,3-diene, the most stable isomer, to a chelated cycloocta-1,5-diene complex (equation 6). Since no intermediate cycloocta-1,4-diene can be observed in the reaction, it was presumed to proceed via an... 

Both 1,4- and 1,5-dienes form stable complexes with Pd. For most 1,3-dienes, such as 1,3-butadiene, reaction with Pd° compounds leads to 7r-allyl formation. These reactions are described in Section 7. The coordinated double bonds in palladium diene complexes are reactive toward attack by many nucleophiles, and the resulting chelating alkene palladium alkyls are easily isolated. Many useful reactions of dienes were discovered by Jiro Tsuji in the 1960s and 1970s. These have been recently reviewed in a historical memoir. ... 

Many nncleophiles add to one of the double bonds of chelating palladium(diene) complexes to give a chelating Pd alkyl(alkene) derivative, as exemphfied by the reaction of PdCl2(l,5-cod) with methoxide (equation 41). In most cases, the direction of attack is exo. If the nucleophile is in a form that can undergo transmetalation with the Pd l bond, such as Ph2Hg, the nucleophihc group can be delivered endo. In this case, prior formation of a Pd nucleophile bond accounts for the direction of attack (equation 42). 

Within a series of a,t j-dienes, the 1,5-diene forms the most stable AgNOs complex (416), perhaps because it possesses the optimum configuration for chelation. As with monoolefins, the presence of alkyl substituents decreases the stability of the diene complexes (416). 

Qualitative photochemical studies concentrate on diene complexes because of their greater thermal inertness and ease of characterization. Formation of olefin complexes is induced in situ either by photochemical or thermal means and their presence determined by spectroscopy. The photocatalyzed hydrogenation and hydrosilation of 1,3-di-enes the photocatalyzed valence isomerization of norbomadiene to quadricyc-lane and the cis trans photoisomerization of coordinated olefins are potentially usefulHowever, these transformations are not photosubstitution reactions and are not discussed here the reader should consult ref. 1 and references cited therein. Photolysis of olefin complexes leads to olefin loss with high quantum efficiency unless the olefin is a chelating di- or polyene where, as with most chelating ligands, other reactions occur. 

Chelating Diene Complexes Reaction with Metal Complexes. 

I. Chelating Diene Complexes by Direct Reaction with Metal Complexes via Ligand Displacement. 

S.2. rj n-Alkyl Complexes by Nucleophilic Attack on Metal-Chelating Diene Complexes. 

Nucleophiles reactions with alkene complexes S.8.2.3.4 chelated diene complexes 5.S.2.5.2... 

Very few other t/4-diene complexes have been studied, apart from those also containing the cyclopentadienyl ligand (Section VII). In MeCN at platinum (264) or mercury (265), [M(L-L)(tj4-diene)]+ (M = Rh or Ir, L-L = bipy, o-phen, 2,2 -bipyrazine, etc. diene = 1,5-cod or nbd) are reduced in two reversible, one-electron stages [e.g., [Rh(bipy)(l,5-cod)]+, ° = -1.26 and -1.73 V] the chelate, L-L, is lost at more negative potentials and mercury-containing products are formed via irreversible... 

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