Ligand coupling processes

Scheme 2.8 ab initio model of a ligand coupling process... 

The survey of the literature of all the ligand coupling processes which have been described with the various heteroatomic main-group elements shows that they can be classified in two general categories, themselves subdivided into subclasses ... 

The type A ligand coupling processes (ipso-ipso), whether of the synchronous LCh type or of the polar LCn type, are the most frequently occurring mode of coupling. They are involved in a large number of reactions in the chemistry of sulfur, selenium, tellurium, phosphorus, antimony and iodine derivatives. 

The elementary phenylation reaction with pentavalent organobismuth reagents is itself a two-steps sequence which proceeds first by the formation of a covalent pentavalent substrate-bismuth intermediate. In the second step, this intermediate then undergoes a ligand coupling process. ... 

Triarylsulfonium halides reacted with sodium arylthiolates to afford mixtures of diarylsulfides. The reaction can be explained by a ligand coupling process taking place on a (arylthio)triarylsulfurane and is free of any competing free radical chain component as no diaryldisulfides were observed.25.39... 

With a large R group (such as 8-quinolinyl or 9-anthryl), release of the steric strain favours a ligand coupling process between one unit of the spirocyclic system and the fifth ligand to afford a 2,2 -biphenyldiyl system. 

When the W-trimethylsilyltris(2-pyridyl)phosphinimine (22) was treated with one equivalent of methyllithium at - 78°C, a lithium complex (23) binding a dipyridyl moiety with a trivalent amino-methyl (2-pyridyl)phosphane was isolated. This compound results from a ligand coupling process taking place on the pentacoordinate phosphorus intermediate formed by addition of methyllithium on the imine bond. 

The occurrence of two competing pathways was also observed in the reaction of some enol silyl ethers with diphenyliodonium fluoride (19), which afforded the mono- or the di-phenylated products in moderate to good yields. This C-phenylation reaction is likely to occur by a ligand coupling process. However, with some hindered silyl enol ethers, for example (20), diketone dimers (21) were also isolated, indicative of a free-radical component in the overall mechanistic picture. ... 

The reaction of the cyclic hindered iodonium perchlorate (46) with triphenylphosphine led unexpectedly to the vinyl iodide (75) as the major product, along with the expected vinylphosphonium salt (76). This result was explained by the formation of an iodophosphonium intermediate (77) which follows two different pathways for the ligand coupling process.i (Scheme 5.6)... 

These reactions were explained by the formation of an iodonium salt intermediate (133), which reacts with a second molecule of the substrate to yield a tricoordinate species (134). By a ligand coupling process, this iodane compound leads to the self-coupling product. 2,234 (Scheme 5.15)... 

Aromatic primary amines react with lead tetraacetate to give symmetrical azo compounds in varying yields, via hydrazo intermediates." " However, in the case of 2,4,6-tri-tert-butylaniline, reaction with lead tetraacetate in benzene at 5°C led to a mixture of three products, the formation of which can be explained by a ligand coupling process. (Scheme 7.2)... 

Although some other reactions may be viewed as typical ligand coupling processes, we will not consider them in this chapter, as they result from the classical sequence in transition organometallic chemistry oxidative addition - reductive elimination. For example, the reaction of organotin compounds (1) described by Reich is in accordance with a ligand coupling mechanism. ... 

Alkyl and vinylthallium(in) compounds are mostly obtained by oxythallation of alkenes or alkynes. They can also be formed by transmetallation between, for example, an organomercury compound and thallium(ni) salts. Various types of reactivity have been observed for these compounds. The evolution of the carbon-thallium bond into functionalised products usually takes place homolytically or heterolytically. The ligand coupling process has also been evoked to rationalize a small number of transformations. 

Organohalides (usually with Csp -X bonds) and Pd(0) readily participate in ligand coupling processes. Pd(0) is readily oxidised to Pd(ll), with simultaneous oxidative addition into the C-Br bond, to givea c/s-organopalladium complex, which rapidly equilibrates to the trans-system. 

Organohalides (usually with Csp -X bonds) and Pd(0) readily participate in ligand coupling processes. Pd(0) is readily oxidised... 

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