Cleavage of Carbonyl Carbon and α-Carbon Bond of Acetophenones by Iridium(III) Porphyrin Complexes

Li, Bao Zhu; Xu, Song; Fung, Hong; Chan, Kin Shing

doi:10.1021/om1000887

Cited by 23 publications

(33 citation statements)

References 29 publications

(22 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It was proposed that iridium(III) was initially inserted into the macrocycle, and subsequent introduction of a benzyl ligand took place to give 301 (Scheme ). In fact, this type of chemistry had previously been observed for iridium(III) porphyrins. , Oxidation by trace amounts of molecular oxygen would afford a peroxide derivative ( 302 ) that could eliminate water to produce the observed benzoyl ligand …”

Section: Azuliporphyrins and Heteroazuliporphyrinsmentioning

confidence: 99%

“…DFT calculations were used to compare the relative stabilities for tautomers of unsubstituted benziporphyrin 354 and naphthiporphyrin 355 (Figure ). Tautomer 354′ was shown to be 7.21–7.91 kcal/mol higher in energy than 354 , while the aromatic form 354 A was calculated to be 42.75–48.01 kcal/mol higher in energy. The aromatic form is destabilized by the loss of the 6π arene subunit, as well as by significant lone pair–lone pair interactions within the macrocyclic cavity.…”

Section: Benziporphyrins Heterobenziporphyrins and Related Systemsmentioning

confidence: 99%

See 1 more Smart Citation

Carbaporphyrinoid Systems

2016

View full text Add to dashboard Cite

Following immediately after the serendipitous discovery of N-confused porphyrins, remarkably diverse carbaporphyrinoid systems have been synthesized and investigated. By replacing a pyrrolic unit within the porphyrin framework with cyclopentadiene, indene, azulene, cycloheptatriene, or benzene, new families of porphyrin-like macrocycles were produced. True carbaporphyrins are fully aromatic structures, while benziporphyrins are essentially devoid of macrocyclic aromatic character, and azuliporphyrins fall midway between the two extremes. Monocarbaporphyrinoids are superior organometallic ligands and form stable complexes with copper(III), silver(III), gold(III), nickel(II), palladium(II), platinum(II), rhodium(III), iridium(III), and ruthenium(II). Unusual oxidation reactions have also been discovered, commonly leading to derivatization of the internal carbon atom. In addition, structural rearrangements have been uncovered that allow the conversion of azuliporphyrins into benzocarbaporphyrins, and benziporphyrins into carbaporphyrins. Although less well studied, many examples of dicarbaporphyrinoids have been reported, and these show equally intriguing characteristics. Furthermore, contracted and expanded carbaporphyrinoids have been investigated. Studies in this area provide fundamental insights into the aromatic properties, tautomerization, and reactivity of porphyrins and related macrocyclic systems.

show abstract

Section: Azuliporphyrins and Heteroazuliporphyrinsmentioning

confidence: 99%

Section: Benziporphyrins Heterobenziporphyrins and Related Systemsmentioning

confidence: 99%

Carbaporphyrinoid Systems

2016

View full text Add to dashboard Cite

show abstract

“…From the absence of PhBr coproduct, bromine atom must react with [M II (ttp)] 2 very rapidly and have a very short lifetime. In the extreme case, this pathway is the nonchain pathway d. The nearly 1:1 ratios of the reactions shown in Table favor pathway d over c. The role of OH – is as both a ligand and a single-electron reductant. ,,, …”

Section: Resultsmentioning

confidence: 57%

“…Four M(ttp) (M = Ir, Rh) species, M I (ttp) − , M II (ttp), M III (ttp)H, and M III (ttp)OH, have been reported to exist in equilibria under basic conditions. ,,− For the case of cobalt porphyrin species, which is the least reactive and reducing among M II (por) (M = Ir, Rh, Co), Co III (por)OH with a weaker Co(por)–OH bond is likely to be very unstable. The stronger M(ttp)–OH (M = Rh, Ir) decomposes at 120 °C to give H 2 O 2 and [M II (ttp)] 2 . , The intermediacy of M(por)H is also not considered by the stoichiometry of the reaction, as no hydrogen is introduced into the products.…”

Section: Resultsmentioning

confidence: 99%

“…This mechanism is analogous to the well-known halogen atom transfer mechanism by analogous Co II (CN) 5 3– chemistry with alkyl halides . KOH then reduces Co(ttp)Br via the intermediate Co(ttp)OH to give Co II (ttp) and H 2 O 2 for further reaction. , However, the absence of any product in the reaction without base highly disfavors this mechanism (Table , entry 1).…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Base-Promoted Vinyl Carbon–Bromine Bond Cleavage by Group 9 Metalloporphyrin Complexes

2016

Self Cite

View full text Add to dashboard Cite

Base-promoted vinyl carbon−bromine bond cleavage of styryl bromide by group 9 metalloporphyrin complexes was achieved to give the metal(III) porphyrin styryls M(ttp)(styryl) (ttp = 5,10,15,20-tetra-p-tolylporphyrinato dianion). Mechanistic studies suggest that [M II (ttp)] 2 (M = Rh, Ir) cleaves the vinyl C−Br bond via an addition− elimination mechanism. The much less reactive Co II (ttp) undergoes a radical recombination with styryl radical which is generated by the hydroxide reduction of styryl bromide to give a radical anion with subsequent C−Br cleavage. ■ INTRODUCTIONVinyl halides are useful materials in organic synthesis, and the C−C bond formations of vinyl halides with alkyl halides, 1a heteroaromatic halides, 1a aryl halides, 1b,c heteroarenes, 1d alkynes, 1c,e and amides 1c,f have been reported. Moreover, the stereoselective conversion of vinyl halides to the corresponding hydrocarbons is an important synthetic procedure. 1g−jThe comprehensive C(sp 2 )−halogen bond cleavage of aryl halides by group 9 metalloporphyrin complexes has been reported by us. Iridium 2 and rhodium 3 porphyrin complexes cleave the aryl−halogen (ArX; X = I, Br) bond via an ipsosubstitution mechanism to give Ir(ttp)Ar and Rh(ttp)Ar (ttp = 5,10,15,20-tetra-p-tolylporphyrinato dianion) in good to high yields. We have proposed that, in the presence of base, Ir(ttp)(CO)Cl and Rh(ttp)Cl undergo ligand substitution with OH − to generate M(ttp)OH (M = Ir, Rh) followed by reductive dimerization to give [M II (ttp)] 2 . M II (ttp) metalloradicals, which exist in equilibria with [M II (ttp)] 2 , attack the ipso carbon of ArX to give the M(ttp)−cyclohexadienyl radical intermediates. The radical intermediates then eliminate a halogen atom to give Ir(ttp)Ar and Rh(ttp)Ar.Cobalt(II) porphyrins, however, cleave the aryl−bromine bond by a distinctly different mechanism, via a key bromine atom transfer. 4 Co II (ttp) abstracts the bromine atom from ArBr through halogen atom transfer to give an aryl radical and Co(ttp)Br. The aryl radical then combines with another Co II (ttp) to form Co(ttp)Ar.To expand the substrate scope and gain a more comprehensive understanding of C(sp 2 )−halogen bond cleavage, C(sp 2 )−bromine bond activation of styryl bromide by iridium, rhodium, and cobalt porphyrin complexes have been investigated.

show abstract

Transition‐Metal‐Mediated Cleavage and Activation of C–C Single Bonds

2012

View full text Add to dashboard Cite

The activation and cleavage of C–C single bonds mediated by transition metal complexes is one of the most challenging reactions, both practically and in terms of understanding, in the field of metal organic chemistry. In this review the fundamental reactions – oxidative addition, β‐carbon elimination, retro‐allylation, and radical cleavage – so far successfully applied for this transformation are discussed in terms of their mechanisms, their intrinsic problems, and their published examples, which are still fairly rare. Decarbonylation, as another fundamental reaction, is only touched briefly. This group of reactions is today poised to set aside its shadow existence as an exotic reaction class. Meanwhile the number of catalytic and even enantioselective processes involvingC–C single bond cleavage is slowly increasing, although the substrates used in these reactions are still limited to quite special connection patterns. The basic challenges for the future and the paradigms concerning this reaction are presented.

show abstract

Cleavage of Carbonyl Carbon and α-Carbon Bond of Acetophenones by Iridium(III) Porphyrin Complexes

Cited by 23 publications

References 29 publications

Carbaporphyrinoid Systems

Carbaporphyrinoid Systems

Base-Promoted Vinyl Carbon–Bromine Bond Cleavage by Group 9 Metalloporphyrin Complexes

Transition‐Metal‐Mediated Cleavage and Activation of C–C Single Bonds

Contact Info

Product

Resources

About