121393-39-3Relevant academic research and scientific papers
Determination of Rh-C bond dissociation energy in methyl(porphyrinato)rhodium(III) complexes: A new application of photoacoustic calorimetry
Li, Gang,Zhang, Fei Fei,Pi, Na,Chen, Hui Lan,Zhang, Shu Yi,Chan, Kin Shing
, p. 284 - 285 (2001)
The photolysis of RhCH3(ttp) and RhCH3(tmp) (ttp = 5,10,15,20-tetratolylporphyrin, tmp = 5,10,15,20-tetramesitylporphyrin) was studied in methanol at ambient temperature: the quantum yields for photolysis were determined to be 0.51 and 0.54, respectively, and the Rh-C bond dissociation energies (227 and 219 kJ mol-1, respectively) were measured by photoacoustic calorimetry, which were larger than those of Co-C bond.
Activation of unstrained aliphatic carbon-carbon bonds by a transition metal complex
Tse, Man Kin,Chan, Kin Shing
, p. 510 - 511 (2001)
The activation of unstrained aliphatic carbon-carbon bonds by a transition metal complex was discussed. The intermolecular activation of aliphatic carbon-carbon bonds by transition metal complexes were found to be demonstrated in the reaction of nitroxides with a rhodium(II) porphyrin radical. The analysis showed that the methyl group in the nitroxide was cleaved to give Rh(tmp)Me.
Reduction of rhodium(III) porphyrin hydroxide to rhodium(II) porphyrin
Choi, Kwong Shing,Lai, Tsz Ho,Lee, Siu Yin,Chan, Kin Shing
, p. 2633 - 2635 (2011)
Highly reactive rhodium(III) porphyrin hydroxides were formed from the ligand substitution of rhodium porphyrin halides in benzene and were rapidly reduced to rhodium(II) porphyrins and hydrogen peroxide. Thus hydroxide acted as the reducing agent. Oxidat
Excited state dynamics of Rh(II) tetramesityl porphyrin monomer from nanosecond transient absorption and emission spectroscopy
Vitols,Friesen, Duane A.,Williams, Darryl S.,Melamed, Dan,Spiro, Thomas G.
, p. 207 - 213 (1996)
The excited states of [tetrakis(2,4,6-trimethylphenyl)porphyrinato]rhodium(II), Rh(II)TMP, have been studied using nanosecond transient absorption spectroscopy, emission spectroscopy, and electrochemistry. Rh(II)-TMP has a long-lived excited state, with a 460 nm absorption band, that decays with a time constant of 180 ± 22 ns, in benzene and 205 ± 28 ns in 1,3-difluorobenzene. No transient absorption features are seen between 600 and 700 nm, but weak phosphorescence is detected at 743 nm at 77 K. Thus, the excited state has the characteristics of a triplet (π,π*) state, although a low lying, charge transfer state had been expected from iterative extended Huckel calculations. The phosphorescence is biphasic, and highly temperature dependent, consistent with a trip-quartet [4T] lowest excited state, lying not far below a trip-doublet [2T] state. Electrochemistry establishes that the Rh(II)/(I) reduction potential is more negative than -1.5 V versus SSCE while the porphyrin cation reduction potential is +0.55 V. These potentials place the lowest LMCT state at >2.05 V, well above the triplet states. In addition to elucidating the photophysics of a novel type of metalloporphyrin, these results have significant bearing on the feasibility of using Rh(II) porphyrins in photoinduced catalytic systems.
Carbon-carbon bond activation of 2,2,6,6-tetramethyl-piperidine-1-oxyl by a RhII metalloradical: A combined experimental and theoretical study
Kin, Shing Chan,Xin, Zhu Li,Dzik, Wojciech I.,De Bruin, Bas
, p. 2051 - 2061 (2008)
Competitive major carbon-carbon bond activation (CCA) and minor carbon-hydrogen bond activation (CHA) channels are identified in the reaction between rhodium(II) meso-tetramesitylporphyrin [RhII(tmp)] (1) and 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) (2). The CCA and CHA pathways lead to formation of [RhIII(tmp)Me] (3) and [RhIII(tmp)H] (5), respectively. In the presence of excess TEMPO, [RhII(tmp)] is regenerated from [RhIII(tmp)H] with formation of 2,2,6,6-tetramethyl- piperidine-1-ol (TEMPOH) (4) via a subsequent hydrogen atom abstraction pathway. The yield of the CCA product [RhIII(tmp)Me] increased with higher temperature at the cost of the CHA product TEMPOH in the temperature range 50-80°C. Both the CCA and CHA pathways follow second-order kinetics. The mechanism of the TEMPO carbon-carbon bond activation was studied by means of kinetic investigations and DFT calculations. Broken symmetry, unrestricted b3-lyp calculations along the open-shell singlet surface reveal a low-energy transition state (TS1) for direct TEMPO methyl radical abstraction by the RhII radical (SH2 type mechanism). An alternative ionic pathway, with a somewhat higher barrier, was identified along the closed-shell singlet surface. This ionic pathway proceeds in two sequential steps: Electron transfer from TEMPO to [RhII(por)] producing the [TEMPO] +[RhI(por)]- cation-anion pair, followed by net CH3+ transfer from TEMPO+ to RhI with formation of [RhIII(por)Me] and (DMPO-like) 2,2,6-trimethyl-2,3, 4,5-tetrahydro-1-pyridiniumolate. The transition state for this process (TS2) is best described as an SN2-like nucleophilic substitution involving attack of the dz2 orbital of [RhI(por)]- at one of the CMe-Cring σ* orbitale of [TEMPO] +. Although the calculated barrier of the open-shell radical pathway is somewhat lower than the barrier for the ionic pathway, R-DFT and U-DFT are not likely comparatively accurate enough to reliably distinguish between these possible pathways. Both the radical (SH2) and the ionic (S N2) pathway have barriers which are low enough to explain the experimental kinetic data.
Superoxo, peroxo, and hydroperoxo complexes formed from reactions of rhodium porphyrins with dioxygen: Thermodynamics and kinetics
Cui, Weihong,Wayland, Bradford B.
, p. 10350 - 10351 (2006)
Rhodium(II) porphyrin complexes react with dioxygen to form terminal superoxo and bridged μ-peroxo complexes. Equilibrium constants for dioxygen complex formation with rhodium(II) tetramesitylporphyrin ((TMP)Rh?) and a m-xylyl-tethered dirhodium(II) diporphyrin complex (?Rh(m-xylyl)Rh?) are reported. (TMP)Rh-H reacts with oxygen to form a transient hydroperoxy complex ((TMP)Rh-OOH), which reacts on to form the rhodium(II) complex ((TMP)Rh?) and water. Kinetic studies for reactions of (TMP)Rh-H with O2 suggest a near concerted addition of dioxygen to the (TMP)Rh-H unit. Reactivity studies for mixtures of H2/O2 and CH4/O2 with the dirhodium(II) complex (?Rh(m-xylyl)Rh?) are reported. Copyright
Ligand effect on the rhodium porphyrin catalyzed hydrogenation of [2.2]paracyclophane with water: Key bimetallic hydrogenation
Tam, Chun Meng,To, Ching Tat,Chan, Kin Shing
, p. 10057 - 10063 (2017/08/09)
Rhodium porphyrin catalyzed hydrogenation of the aliphatic carbon-carbon σ-bond of [2.2]paracyclophane with water has been examined with a variety of tetraarylporphyrins and axial ligands. Mechanistic investigations show that RhIII(ttp)H, which can be derived from the reaction of [RhII(ttp)]2 with water without a sacrificial reductant, plays an important role in promoting bimetallic reductive elimination to give the hydrogenation product.
Metalloradical-Catalyzed Selective 1,2-Rh-H Insertion into the Aliphatic Carbon-Carbon Bond of Cyclooctane
Chan, Yun Wai,De Bruin, Bas,Chan, Kin Shing
, p. 2849 - 2857 (2015/06/30)
The selective aliphatic carbon-carbon activation of cyclo-octane (c-octane) was achieved via the RhII(ttp)-catalyzed 1,2-addition of Rh(ttp)H to give Rh(ttp)(n-octyl) (ttp = tetratolylporphyrinato dianion) in good yield under mild reaction conditions. This mechanism is further supported by DFT calculations. The reaction worked only with the sterically accessible Rh(ttp) porphyrin complex but not with the bulky Rh(tmp) system (tmp = tetrakismesitylporphyrinato dianion), thus showing the highly steric sensitivity of carbon-carbon bond activation by transition metal complexes. (Chemical Equation Presented).
Metalloradical-catalyzed aliphatic carbon-carbon activation of cyclooctane
Chan, Yun Wai,Chan, Kin Shing
supporting information; experimental part, p. 6920 - 6922 (2010/08/06)
The aliphatic carbon-carbon activation of c-octane was achieved via the addition of Rh(ttp)H to give Rh(ttp)( n-octyl) in good yield under mild reaction conditions. The aliphatic carbon-carbon activation was RhII(ttp)- catalyzed and was very se
Activation of aliphatic carbon-carbon bonds of esters and amides by rhodium(II) porphyrin
Zhang, Lirong,Chan, Kin Shing
, p. 2021 - 2027 (2007/10/03)
Aliphatic carbon-carbon bonds of esters and amides were activated successfully with rhodium(II) porphyrin radical to give rhodium(III) porphyrin alkyls in moderate yields.
