124535-65-5Relevant academic research and scientific papers
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).
Room-temperature selective aliphatic carbon-carbon bond activation and functionalization of ethers by rhodium(II) porphyrin
Lee, Siu Yin,Lai, Tsz Ho,Choi, Kwong Shing,Chan, Kin Shing
scheme or table, p. 3691 - 3693 (2011/09/20)
Selective aliphatic carbon(α)-carbon(β) bond activation of ethers by (5,10,15,20-tetramesitylporphyrinato)rhodium(II) (Rh(tmp) (1)) was achieved at room temperature to yield corresponding rhodium porphyrin alkyls and the functionalized esters. Rh(tmp)OH was the proposed intermediate responsible for cleaving the C(α)-C(β) bond. The reaction is general for both straight- and branch-chain ethers.
Comparison of Rh-OCH3 and Rh-CH2OH bond dissociation energetics from methanol C-H and O-H bond reactions with rhodium(II) porphyrins
Sarkar, Sounak,Li, Shan,Wayland, Bradford B.
, p. 13569 - 13571 (2010/12/18)
Reaction of methanol in toluene with tetramesityl rhodium(II) porphyrin ((TMP)RhII·) produces a 1H NMR-observable equilibrium with rhodium methoxide ((TMP)Rh-OCH3(CH3OH)) and rhodium hydride ((TMP)Rh-H) complexes. Equilibrium concentrations for each of these species, obtained from integration of 1H NMR spectra, were used in determining the equilibrium constant, K(298K) = [Rh-OCH 3(CH3OH)][Rh-H]/[RhII·] 2[CH3OH]2 = 3.0(0.3), and free energy change, δG0(298K) = -0.65(0.5) kcal mol-1, for the reaction. Equilibrium thermodynamic measurements in CD2Cl2 give δG0(298K) = -5.5(0.2) kcal mol-1 for association of methanol with (TMP)Rh-OCH3 to form the six-coordinate 18-electron complex (TMP)Rh-OCH3(CH3OH). Equilibrium measurements in conjunction with (TMP)Rh-H and CH3O-H bond energetics are used to evaluate the (TMP)Rh-OCH3 bond dissociation free energy (Rh-OCH 3 BDFE(298K) = 38 (1.3) kcal mol-1), which is 15 kcal mol-1smaller than the Rh-H BDFE and approximately equal to the Rh-CH2OH BDFE.
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
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 (2008/09/16)
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.
Metalloradical activations of aliphatic carbon-carbon bonds of nitriles: Scope and mechanism
Chan, Kin Shing,Li, Xin Zhu,Zhang, Lirong,Fung, Chun Wan
, p. 2679 - 2687 (2008/10/09)
The C(sp3)-C(sp3) bonds of a series of α-alkylacetonitriles, 2-silylacetonitriles and 2-alkylbenzonitriles, have been activated by Rh(tmp) using Ph3P as the optimized promoter ligand at 130°C. Selective aliphatic-aliphatic carbon-carbon bond activation (CCA) occurred for α-alkylacetonitriles and 2-alkylbenzonitriles without aromatic-aliphatic or aromatic-cyanide bond activation. Competitive activations of C-Si and C-C bonds were observed for 2-silylacetonitriles. The yields of Rh(tmp) alkyls were affected by bond energy and steric hindrance of the nitriles. Kinetic studies for the carbon-carbon bond activation (CCA) of tBuCN at 130°C revealed the rate law: rate = k′K 1[Rh(tmp)]m[Ph3P]n + k 3K2(K1[Ph3P])/(1 + K 1[Ph3P])[Rh(tmp)][tBuCN]. The CCA is proposed to occur at the coordinated tBuCN with Rh(tmp) in a 1:1 ratio in the transition state.
Competitive O-H and C-H oxidative addition of CH3OH to rhodium(II) porphyrins
Li, Shan,Cui, Weihong,Wayland, Bradford B.
, p. 4024 - 4025 (2008/03/18)
Rhodium(II) porphyrins react with CH3OH in benzene by alternate mechanisms that give H-CH2OH and H-OCH3 bond activation in different methanol concentration regimes which is a rare example of transition metal reactivity with methanol. The Royal Society of Chemistry.
Formation and reactivity of (tetraarylporphyrinato)rhodium(II) monocarbonyls: Bent RhIICO complexes that react like acyl radicals
Wayland, Bradford B.,Sherry, Alan E.,Poszmik, George,Bunn, Andrew G.
, p. 1673 - 1681 (2007/10/02)
Reactions for a series of rhodium(II) porphyrins with CO are used in illustrating the use of ligand steric effects in both promoting and inhibiting CO coupling to form α-diketone complexes ((por)RhC(O)C(O)Rh(por)). [Tetrakis(2,4,6-trimethylphenyl)porphyri
