Bradford B. Wayland

RhRh, RhH, RhC and RhO bond energies in (OEP)Rh complexes: Thermodynamic criteria for addition of MH and MM bonds to CO and CC multiple bonds

Abstract Thermodynamic measurements and reactivity studies are used in estimating (RhRh), (RhH), (RhC) and (RhO) bond dissociation energies (BDE) in octaethylporphyrin rhodium, [(OEP)Rh], complexes. Temperature dependence of the proton NMR line broadening of [(OEP)Rh]2 is used as a kinetic method for estimating the (RhRh) BDE as 16.5±0.8 kcal mol−1. Thermodynamic cycles are presented that provide values for the (RhH) BDE in (OEP)RhH (62 kcal mol−1) and (RhC) BDE in (OEP)RhCHO (58 kcal mol −1). Transfer of bond energy values from organic compounds to the organic fragments in organometallic species is used as a means of establishing general thermodynamic criteria for addition reactions of metal hydrides and metal—metal bonded complexes, with compounds that contain CO and CC multiple bonds. Approximate bond energy analysis is applied to the (OEP)Rh system in anticipating reactivity, estimating (RhC) and (RhO) bond energies and in recognizing steric effects.

Rate constants and activation parameters for organo-cobalt porphyrin bond homolysis from NMR relaxation times

Abstract 1H NMR line broadening is found to be an effective complimentary method to chemical trapping for determining the rates and activation parameters for organo-metal bond homolysis events that produce freely diffusing radicals. Application of this method is illustrated by measurement of bond homolysis activation parameters for a series of organo-cobalt porphyrin complexes ((TPP)Co-C(CH3)2CN (ΔH≠ = 19.5±0.9 kcal mol−1, ΔS≠ = 12±3 cal°K−1 mol−1), (TMP)Co-C(CH3)2CN (ΔH≠ = 20±1 kcal mol−1,ΔS≠ = 13±2 cal°K−1 mol−1), (TAP)Co-C(CH3)2CO2CH3 (ΔH≠ = 18.2±0.5 kcal mol−1, ΔS≠ = 12±2 cal °K−1 mol−1), (TAP)Co-CH(CH3)C6H5 (ΔH≠ = 22.5±0.5, ΔS≠ = 17±2 cal °K−1 mol−1)). The line broadening method is particularly useful in determining activation parameters for dissociation of weakly bonded organometallics where the rate of homolysis can exceed the range measurable by conventional chemical trapping methods.

Activation of CH bonds by octaethylporphyrinrhodium dimer

Abstract Octaethylporphyrinrhodium dimer, [RhOEP] 2 , reacts thermally with arylmethyl CH bonds to produce octaethylporphyrinbenzylrhodium compounds.

Preparation of heterobimetallic compounds containing octaethylporphyrinrhodium and their reactions with hydrogen and carbon monoxide

Abstract Octaethylporphyrinrhodium dimer ([Rh(OEP)] 2 ) reacts with a series of transition metal dimers (M′M′; M′ = Mn(CO) 5 ; Mo(CO) 3 Cp; Ru(CO) 2 C 5 Me 5 ) to form metalmetal bonded heterobimetallic compounds ((OEP)RhM′). The heterobimetallic compounds reported in this paper react with H 2 and CO to produce M′H and equilibrium quantities of Rh(OEP)(H) and Rh(OEP)(CHO).

A comparison of AgMnO4 with permanganate and manganate salts

Abstract Electronic spectra for AgMnO 4 in frozen solution are broad and diffuse and are not characteristic of the permanganate anion. Approximate thermochemical calculations indicate only a small energy difference between the limiting ionic forms Ag + ; MnO 4 − and Ag 2+ ; MnO 4 2− . Vibrational analysis of AgMnO 4 , potassium permanganate and barium manganate were carried out and support an intermediate manganese oxidation state in AgMnO 4 .

SPECTROSCOPIC AND KINETIC STUDIES OF THE REACTIONS OF IRON(III) PORPHYRINS WITH ALKYL THIOLS

Abstract The reaction of toluene solutions of FeTPPCl with RSH (R = CH 3 or (CH 3 ) 3 C) in the presence of pyridine has been studied by epr and electronic spectra. The reaction results in the reduction of FeTPPCl to FeTPP(Py) 2 and the oxidation of RSH to R 2 S 2 . Kinetic data obtained for the reaction shows the observed rate law to be: −d[ Fe TTPCl]/I d t = k[ Fe TPPCl][ R SH][ Py ] 3 Epr studies show the involvement of two paramagnetic, S = 1/2, intermediates. The first intermediate is assigned as FeTPP(Py)(SR), while the second intermediate is postulated as FeTPP(Py) 2 (RS). Possible structures for this second intermediate are discussed. A mechanism is proposed which it consistant with the observed data. The intocatalytic nature of this system is also described.

Nitric oxide complexes of iron(II) and iron(III) porphyrins

The reversible formation of a nitric oxide adduct with tetraphenylporphyriniron(III) chloride formulated as [FeII(TPP)Cl–NO+] is observed in toluene, but reductive nitrosylation to give FeII(TPP)·NO occurs in the presence of a hydroxylic solvent, in reactions analogous to hemeprotein interactions with nitric oxide.

Macromonomer living character in the cobalt(II) porphyrin chain transfer catalysis for radical polymerization of methacrylic acid in water

Macromonomers formed by cobalt(II) porphyrin catalyzed chain transfer in the aqueous radical polymerization of methacrylic acid acquire living character by continual reinitiation through reaction with an intermediate cobalt hydride.

Observation of a neutral metallo-formyl complex formed by the reaction of rhodium octaethylporphyrin hydride with carbon monoxide

Rhodium octaethylporphyrin hydride, RhOEP-(H)(OEP = octaethylporphyrin),m reacts with carbon monoxide to form a neutral metallo-formyl complex.

Formation and ethene substrate reactions of iridium(II) porphyrin metal-centered dπ radicals

Monomeric iridium(II) porphyrin complexes of tetrakis(2,4,6-trialkylphenyl)porphyrin ligands that are generated by photolysis of the Ir–Me derivatives are found to have the dxy2 dz22 dxz,yz3 ground electron configuration which differs from the dxy2 dxz,yz4 dz21 configuration observed for the Co(II) and Rh(II) analogs; reactions of these Ir(II) species with ethene reflect both the metallo-radical reactivity and the varying steric demands for the series of porphyrin ligands.