Phenyl iodide, activation

Abstract In this chapter, a perspective on how the field of applied computational organometallic chemistry has developed since the nud-1980s is presented. We describe the way in which the modelling of chenucal systems has evolved over time, using metallocene chenustiy as an example, and highlight the successes and limitations of simple models that were mandatory in the early days of the discipline. A number of more recent case studies are then presented where the full experimental system is now employed and a more quantitative outcome is sought. This includes examples from the Ce-mediated hydrogenation of pyridine, Rh-catalysed C-H bond activation and functionalization, Pd-catalysed azidocarbonylation and phenyl iodide activation at Ru(II) complexes. We conclude with our take on the title question. 

Recently, the high activity of palladium/NHC complexes in the Heck reaction was combined with an efficient recyclability process [63]. Bis-carbene pincer complexes of palladium(II) were immobilized on montmorillonite K-10. The catalytic activity of the heterogeneous system is similar to that displayed by their homogeneous counterparts. The stability of the catalyst was tested in the reaction of phenyl iodide and styrene. The product yield decreases from 99 to 79% after ten cycles. 

El-Sayed and co-workers more recently reported on the catalytic activity of PVP-stabUized aqueous palladium colloids in Suzuki reactions (substrates 2-iodo-thiophene or phenyl iodide and 2-thiophene boronic add or phenylboronic acid 0.3 mol% palladium 12 h reflux) (Table 1) [20]. They did not find such a clear... 

Miura has also published examples of arylation reactions directed by intramolecular C-H activation. Reaction of o-phenylphenol and phenyl iodide in the presence of palladium(ll) leads to arylation of the remote ring (Equation Reaction of n-phenylphenol and methyl acrylate in the presence of palladium, copper, and... 

A related process was characterised for the exchange of an allyl with an aryl group at the C2 position of an imidazolium cation and involved the reaction of [( IMe)Pd(r -C3H5)(PMe3)] with phenyl iodide. In this case, transmetala-tion between a NHC-Pd and a Pd-iodo intermediate and the C C reductive elimination both had similar activation energies of around + 20kcalmol ... 

Reactions.—Alkaline Hydrolysis. The first total resolution of a heterocyclic phosphonium salt containing an asymmetric phosphorus atom (128) has been reported, providing ready access to optically active phospholan derivatives of value for studies of the stereochemistry of nucleophilic displacement at phosphorus.124 Alkaline hydrolysis of (128) proceeds with retention of configuration at phosphorus to form the oxide (129). Stereochemical studies in the phospholan series have also been facilitated by the X-ray investigation125 of an isomer of l-iodomethyl-l-phenyl-3-methylphospholanium iodide, which is shown to have the structure (130). 

Sulfoxides are known to form both 0-alkyl and S-alkyl derivatives. The latter are obtained when so-called soft alkylating agents are employed. This behavior of sulfoxides was utilized (172) in the stereospecific synthesis of chiral 135. The reaction of the optically active (+)-ethyl phenyl sulfoxide 136 with methyl iodide in the presence of mercuric iodide followed by anion exchange was found to give the optically active salt 135. 

Arylation of benzene 128 with aryl iodides 129 via direct C—H bond activation was achieved in the presence of [Cp lrHCl]2 and KO Bu to afford corresponding biaryl 130 (Equation 10.33) [56]. The phenyl radical would participate as an intermediate in this reaction. 

As an alternative to addition of anionic nucleophiles followed by reoxidation, rhodium(l)-catalyzed C-H activation allowed the nucleophilic addition of alkenes to the intermediate Rh(i) carbene complex <2002JA13964, 2004JOC7329>. Purine behaved anomalously compared to other heterocycles, for which selective monoalkylation was observed, and underwent sequential substitution first at C-8 and then at C-6 (Equation 8). Caffeine was monoalkylated at C-8 in low yield (15%). Selectivity for C-8-arylation was also observed in the palladium-catalyzed C-H activation of 6-phenyl-9-benzylpurine (aryl iodides, 0.05 equiv Pd(OAc)2, 3 equiv Cul, 2.5 equiv CS2CO3, DMF, 160 °C, 60 h, 48-95% yields) <2006OL5389>. 

Alkyl halides possessing / -hydrogens are usually poor substrates for carbonylative cross-coupling due to competitive / -hydride elimination/ Allyl chlorides can be used in carbonylative cross-coupling with allylstannanes/ phenyl-, 3-furyl, or vinylstannanes " to afford allylketones in modest to good yields. Divinylketones can be accessed through the reaction of vinylstannanes with vinyl iodides or vinyl triflates, with the latter requiring the addition of LiCl. Synthetic potential of this method has been proved in the formation of macrocyclic ketone jatrophone. In the reaction of vinyl triflates with tetramethyltin or aryltrimethylstannanes the additional activation by ZnCle is required. 

By contrast, for iodide 18 having the triple bond activated by a phenyl group, conversion to the cyclic organozinc species 25 occurred effectively and the latter could be efficiently functionalized, provided that traces of moisture were excluded by pre-treatment of zinc powder with Mel. The substituted benzylidene cyclopentanes 26 and 27 were respectively obtained after iodinolysis and palladium-catalyzed cross-coupling reaction with benzoyl chloride (equation 10). However, it could not be assessed whether the formation of organozinc 25 was attributable to an anionic or a radical cyclization pathway (or both) as, had iodide 26 been produced by a radical iodine atom-transfer, it would have been converted to 25 by reaction with metallic zinc due to the presence of the activating phenyl group21. 

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