- Competitive aryl-fluorine and aryl-halogen (Halogen = Cl, Br) bond cleavage with iridium porphyrin complexes
-
Base-promoted competitive Ar-F and Ar-X (X = Cl, Br) bond cleavage with iridium porphyrin complexes was investigated. Mechanistic studies suggested that Ir(ttp)- (ttp = 5,10,15,20-tetra-p-tolylporphyrinato dianion) cleaves the Ar-F bond via nucleophilic aromatic substitution and Ir 2(ttp)2 cleaves the Ar-X (X = Cl, Br) bond via metalloradical ipso substitution. Therefore, a stronger base, polar solvent, lower temperature, and iridium anion precursor favor Ar-F bond cleavage, while a weaker base, nonpolar solvent, higher temperature, and Ir2(ttp) 2 precursor favor Ar-X (X = Cl, Br) bond cleavage.
- Qian, Ying Ying,Li, Bao Zhu,Chan, Kin Shing
-
supporting information
p. 1567 - 1570
(2013/05/08)
-
- Base-promoted selective aryl C-Br and C-I bond cleavage by iridium(III) porphyrin: Reduction of IrIII-OH to IrII for metalloradical ipso substitution of aryl-halogen bonds
-
Base-promoted selective aryl carbon-bromine and carbon-iodine bond (Ar-X, X = Br, I) cleavage by iridium(III) porphyrin carbonyl chloride (Ir III(ttp)(CO)Cl) was achieved in the presence of base (K 2CO3, NaOH) to give iridium(III) porphyrin aryls (Ir III(ttp)Ar). Mechanistic studies revealed that the base undergoes ligand substitution with Ir(ttp)(CO)Cl to yield an iridium(III) hydroxo species (IrIII(ttp)OH). The hydroxo ligand most likely reduces the Ir(III) center to give iridium(II) porphyrin dimer ([IrII(ttp)]2) and H2O2. In a competitive pathway, [Ir II(ttp)]2 disproportionates in the presence of base and residual water to give an iridium(III) hydride (IrIII(ttp)H) and Ir(ttp)OH. In a productive process, [Ir(ttp)]2 undergoes Ir II(ttp) metalloradical-mediated ipso substitution of Ar-X via an addition-elimination pathway to form Ir(ttp)Ar and Ir(ttp)X. Ir(ttp)X is recycled by reacting with base to regenerate [Ir(ttp)]2 for subsequent Ar-X cleavage.
- Cheung, Chi Wai,Chan, Kin Shing
-
experimental part
p. 4269 - 4283
(2011/10/03)
-
- Scope and mechanism of carbonyl carbon and α-carbon bond cleavage of ketones by Iridium(III) porphyrin complexes
-
Chemoselective carbonyl carbon and α-carbon bond activation (CCA) of ketones (RCOR) was successfully achieved with various iridium(III) tetrakis-4-tolylporphyrinato complexes Ir(ttp)X (X = (BF4)(CO), Cl(CO), and Me) to give the corresponding Ir(ttp)COR (R = Ar, Me, or Et) and Ir(ttp)R (R = Me or Et) complexes. Ir(ttp)(BF4)(CO) exhibited the highest reactivity toward CCA, as it possesses a higher Lewis acidity in catalyzing the aldol condensation of ketones to give water, which hydrolyzes the kinetic products, C-H bond activation (CHA) complexes, into the proposed Ir(ttp)OH for a subsequent CCA process. The CCA step is nonregioselective in giving both Ir(ttp)R and Ir(ttp)COR. However, Ir(ttp)R was kinetically less stable toward hydrolysis to give Ir(ttp)OH. Thus, only Ir(ttp)COR was observed as the sole CCA product.
- Li, Bao Zhu,Fung, Hong Sang,Song, Xu,Chan, Kin Shing
-
p. 1984 - 1990
(2011/05/06)
-
- Base-promoted selective aryl carbon-bromine bond cleavage by Iridium(III) porphyrin for Iridium(III) porphyrin aryl synthesis: A metalloradical Ipso addition-elimination mechanism
-
K2CO3 was found to promote selective aryl carbon-bromine bond (Ar-Br) cleavage by a high-valent iridium(III) porphyrin carbonyl chloride (IrIII(ttp)(CO)Cl, ttp = 5,10,15,20-tetra-p- tolylporphyrinato dianion) in benzene so
- Cheung, Chi Wai,Chan, Kin Shing
-
scheme or table
p. 1768 - 1771
(2011/06/22)
-
- Cleavage of carbonyl carbon and α-carbon bond of acetophenones by iridium(III) porphyrin complexes
-
Selective carbonyl carbon (C( - O)) and α-carbon (C(methyl)) bond activation of acetophenones was discovered by the high-valent, iridium(III) 5,10,15,20-tetrakis-4-tolylporphyrinato carbonyl chloride (Ir(ttp)Cl(CO)), which also acted as a Lewis acid in catalyzing the aldol condensation of acetophenones together with release of the coproduct water. Preliminary mechanistic studies suggest that both aliphatic and aromatic carbon-hydrogen bond activation products are kinetic products, which can be converted by reaction with water to iridium porphyrin hydride (Ir(ttp)H) via iridium porphyrin hydroxide (Ir(ttp)OH). Both Ir(ttp)OH and Ir(ttp)H were the possible intermediates to cleave the C( - O)-C(methyl) bond of acetophenones and to generate iridium porphyrin acyl complexes as the thermodynamic products.
- Li, Bao Zhu,Song, Xu,Fung, Hong Sang,Chan, Kin Shing
-
p. 2001 - 2003
(2010/06/18)
-
- Reactivity studies of iridiuni(III) porphyrins with methanol in alkaline media
-
Ir(ttp)Cl(CO) (la; ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dianion) was found to cleave the C-O bond of CH3OH at 200 C to give Ir(ttp)CH3 (3a). Addition of KOH promoted the reaction rate and gave a higher yield of Ir(ttp)CH3 in 70% yield in 1 day. Mechanistic studies suggest that, in the absence of KOH, Ir(ttp)Cl(CO) reacts with CH 3OH initially to give Ir(ttp)OCH3, which then undergoes β elimination to produce Ir(ttp)H (4a). Ir(ttp)H further reacts slowly to cleave the C-O bond of CH3OH, likely via cr-bond metathesis, to give Ir(ttp)CH3. In the presence of KOH, Ir(ttp)Cl(CO) initially reacts with KOH more rapidly to give Ir(ttp)OH, which then cleaves the 0-H bond of CH3OH by metathesis to give Ir(ttp)OCH3. Ir(ttp)OCH 3 further isomerizes via /3-hydride elimination/reinsertion to give Ir(Up)CH2OH and concurrently undergoes base-assisted /3-proton elimination to give Ir(ttp)-K+ (5a). Ir(ttp)CH.20H subsequently condenses with CH3OH to form. Ir(Up)CH2OCH3 (2). Finally, Ir(ttp)-K+ cleaves the C-O bond in CH3OH, most probably via nucleophilic substitution, to give Ir(ttp)CH3. Ir(ttp)CH 2OCH3 also serves as the precursor of Ir(ttp)-K+ as it undergoes nucleophilic substitution by KOH to give Ir(ttp)-K+.
- Cheung, Chi Wai,Fung, Hong Sang,Lee, Siu Yin,Qian, Ying Ying,Chan, Yun Wai,Chan, Kin Shing
-
p. 1343 - 1354
(2010/05/14)
-
- Base-promoted silicon-hydrogen bond activation of silanes by iridium(III) porphyrin complexes
-
Iridium(III) porphyrin silyls were synthesized in moderate to high yields conveniently from the reactions of iridium(III) porphyrin carbonyl chloride and methyl with silanes, via silicon-hydrogen bond activation (SiHA) in solvent-free conditions and nonpolar solvents. Base was found to promote the SiHA reactions. Specifically, K3PO4 accelerated the SiHA with iridium porphyrin carbonyl chloride, while KOAc promoted the SiHA by iridium porphyrin methyl. Mechanistic experiments suggested that iridium(III) porphyrin carbonyl chloride initially formed iridium porphyin cation, which then reacted with silanes likely via heterolysis to give iridium porphyrin hydride. Iridium porphyrin hydride further reacted with silanes to yield iridium porphyrin silyls. On the other hand, iridium(III) porphyrin methyl and silyls underwent either oxidative addition or σ-bond metathesis to form the products. In the presence of base, a pentacoordinated silicon hydride species likely formed and reacted with iridium porphyrin methyl to form iridium porphyrin anion, which could further react with silanes to yield iridium porphyrin hydride after protonation. Ir(ttp)H finally reacted with excess silanes to give iridium porphyrin silyl complexes.
- Li, Baozhu,Chan, Kin Shing
-
p. 4034 - 4042
(2009/02/06)
-
- Base-promoted selective activation of benzylic carbon-hydrogen bonds of toluenes by iridium(III) porphyrin
-
K2CO3 and NaOPh promoted the rate of benzylic carbon-hydrogen bond activation (BnCHA) of toluenes with iridium(III) porphyrin carbonyl chloride (Ir(ttp)Cl(CO)) to give iridium porphyrin benzyls in high yields. Mechanistic studies sug
- Cheung, Chi Wai,Chan, Kin Shing
-
p. 3043 - 3055
(2009/02/05)
-