Fe(III), Cu(II), and Ag(II) porphyrin complexes are active catalysts for benzylic and ring C−H insertions by carbene fragments transferred from methyl diazomalonate, 2. Temperatures above 100 °C are required, and yields greater than 70% have been achieved. C−H insertions with cyclohexane and tetrahydrofuran are catalyzed at a lower temperature of 60 °C with 60% yields when para-substituted methyl 2-phenyldiazoacetates, 15a−d, are used as carbene sources. The rate for Fe(TPP)Cl-catalyzed insertion into the C−H bond of cyclohexane was found to be first-order in the concentration of methyl 2-(pchlorophenyl)diazoacetate, p-Cl-MPDA, indicating that formation of a carbene complex is the ratedetermining step. Competition reactions for cyclohexane insertion with para-substituted methyl 2-phenyldiazoacetates correlated linearly with σ+ Hammett parameters with a ρ value of -1.11 ± 0.05 when Fe(TPP)Cl was used as a catalyst, demonstrating that electron-donating para-substituents on the phenyl group of the methyl 2-aryldiazoacetates enhanced reactivity. These data are consistent with the involvement of an electrophilic iron−carbene complex in the catalytic cycle. A mechanistic model for the iron-mediated C−H insertion reactions is proposed. Disciplines Chemistry CommentsReprinted (adapted) with permission from Organometallics 27 (2008): 637, ABSTRACT: C−H insertion reactions between different substrates and diazo reagents were catalyzed by tetratolylporphyrinato methyliridium (Ir(TTP)CH 3 ). The highest yields were achieved for reactions between the bulky diazo reagent methyl 2-phenyldiazoacetate (MPDA) and substrates containing electron-rich C−H bonds. An intermediate metalloporphyrin complex was identified as a metal−carbene complex, Ir(TTP)(C[Ph]CO 2 CH 3 )(CH 3 ) (4), using 1 H NMR and UV/vis absorption spectroscopy. The presence of 4 was further supported by computationally modeling the absorption spectra with time-dependent DFT (6-31G(d,p)/ SBKJC basis set, PBE0 functional). Kinetic studies for C−H insertion reactions using different substrates showed substantial differences in the rate of MPDA consumption, suggesting that carbene transfer is rate-limiting. Furthermore, primary kinetic isotope effects of 3.7 ± 0.3 and 2.7 ± 0.4 were measured using toluene and cyclohexane, respectively. These data are consistent with a mechanism that involves direct C−H insertion rather than a radical rebound pathway.

A series of metalloporphyrin complexes were surveyed as catalysts for carbene insertion from ethyl diazoacetate into the N−H bonds of amines. Iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl, was found to be an efficient catalyst for N−H insertion reactions with a variety of aliphatic and aromatic amines, with yields ranging from 68 to 97%. Primary amines were able to undergo a second insertion when another equiv of EDA was added by slow addition. N-Heterocyclic compounds were poor substrates, giving low yields or no N−H insertion products. Competition reactions and linear free energy relationships provided mechanistic insights for the insertion reaction. The relative rates for N−H insertion into para-substituted aniline derivatives correlated with Hammett σ+ parameters. Electron-donating groups enhanced the reaction, as indicated by the negative value of ρ (ρ = −0.66 ± 0.05, R2 = 0.93). These results are consistent with a ratedetermining nucleophilic attack of the amine on an iron carbene complex. In addition, the decomposition of EDA catalyzed by FeII(TPP) or FeIII(TPP)Cl was examined with various amounts of added pyridine. The Fe(II) catalyst is strongly inhibited by the presence of pyridine. In contrast, catalysis by the Fe(III) porphyrin is accelerated by amines. These experiments suggested that an iron(III) porphyrin carbene complex is the active catalyst.

Iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl , efficiently catalyzed the insertion of carbenes derived from methyl 2-phenyldiazoacetates into O-H bonds of aliphatic and aromatic alcohols, with yields generally above 80%. Although the analogous N-H insertions are rapid at room temperature, the O-H insertion reactions are slower and required heating in refluxing methylene chloride for about 8 hours using 1.0 mol.% catalyst. Fe(TPP)Cl was also found to be effective for tandem N-H insertion/cyclization reactions when 1,2-diamines and 1,2-alcoholamines were treated with diazo reagents to give piperazinones and morpholinones and related analogs such as quinoxalinones and benzoxazin-2-ones. This approach provides a new one-pot route for synthesizing these classes of heterocyclic compounds.

Chloro(tetraphenylporphyrinato)iron, Fe ( TPP ) Cl , is an active catalyst for the Büchner addition of para-substituted methyl 2-phenyldiazoacetates, 1a–d, to substituted benzenes. Yields greater than 70% have been achieved at temperatures ranging from 60–100°C. Reactions of substituted methyl 2-phenyldiazoacetates with benzene gave rapidly equilibrating mixtures of norcaradienecycloheptatriene valence isomers, 2a–d/2′a–d, in yields over 70%. Treatment of chlorobenzene with methyl 2-phenyldiazoacetate produced a regio-isomeric mixture of 7-carbomethoxy-2-chloro-7-phenylnorcaradiene/7-carbomethoxy-2-chloro-7-phenylcycloheptatriene, 3a/3′a, and 7-carbomethoxy-3-chloro-7-phenylnorcaradiene/7-carbomethoxy-3-chloro-7-phenylcycloheptatriene, 4a/4′a. When p-methylanisole was treated with methyl 2-phenyldiazoacetate at 80°C, a product that largely favored a fused cyclopropane structure, 7-carbomethoxy-2-methoxy-5-methyl-7-phenylnorcaradiene, 12a, was obtained along with the benzylic C–H insertion product methyl 3-(p-methoxyphenyl)-2-phenylpropionate, 13a. Heating the norcaradiene product 12a at 110°C yielded the ring-opened diarylacetate, 14a. The diene forms of the fluxional norcaradiene-cycloheptatriene systems were trapped with benzyne to give one stereoisomer of 3,3-disubstituted benzhomobarralenes, 18a–d. The norcaradiene-cycloheptatriene valence isomers were quantitatively converted into ring-opened diaryl acetate products upon acidification in acetonitrile. Rates for the addition of methyl (p-chlorophenyl)diazoacetate to benzene were first order with respect to the diazo reagent. A concerted mechanism involing an iron carbene complex is proposed for these iron porphyrin-catalyzed Büchner reactions.

In order to help curtail or imposesustained control to the offensive water hyacinth plant, it is essential to explore ways of generating water remediation materials from it. In the current study, the capacity and efficacy of water hyacinth ash (WHA), its insoluble residue (WHAR) and rice husk ash (RHA) to remove cadmium ions and methylene blue from contaminated water was investigated. Mixtures of the two ashes were used to formulate zeolitic materials by hydrothermal reactions. Material A, ZMA was prepared by using rice husk ash and the soluble portion of WHA while for material B, ZMB a mixture of equal amounts the two ashes including the insoluble fraction of WHA were used. Batch experiments was carried out to determine the effect of metal ion concentration, initial PH, contact time (t), temperature (T), shaking speed and adsorbent dose on percentage removal of Cd on RHA, ZMA, and ZMB was found to best fit in the Langmuir isotherm model while WHA and WHAR data best fitted in the Freundlich model. Adsorption capacities for cadmium on RHA, WHA, WHAR, ZMA and ZMB adsorbents ions were 3.745, 52.00, 56.89, 11.24 and 22.22 mg/g respectively. The findings showed that incorporating the WHAR during synthesis of the zeolitic material enhanced its adsorption capacity and efficiency for Cd (II) ions and methylene blue.