ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Activation of c-h bonds by metal complexes

Dioxygen activation at mononuclear nonheme iron active sites: enzymes, models, and intermediates.

Iron-sulfur proteins are found in all life forms. Most frequently, they contain Fe2S2, Fe3S4, and Fe4S4 clusters. These modular clusters undergo oxidation-reduction reactions, may be inserted or removed from proteins, can influence protein structure by preferential side chain ligation, and can be interconverted. In addition to their electron transfer function, iron-sulfur clusters act as catalytic centers and sensors of iron and oxygen. Their most common oxidation states are paramagnetic and present significant challenges for understanding the magnetic properties of mixed valence systems. Iron-sulfur clusters now rank with such biological prosthetic groups as hemes and flavins in pervasive occurrence and multiplicity of function.

http://science.sciencemag.org/content/sci/277/5326/653.full.pdf

Iron-Sulfur Clusters: Nature's Modular, Multipurpose Structures

Desulfovibrio desulfuricans iron hydrogenase: the structure shows unusual coordination to an active site Fe binuclear center.

Artificial photosynthesis: molecular systems for catalytic water oxidation.

Two neutral complexes [(L634M)Fe2Cl4]*2H2O*2CHCl3 (1) and [(L634M)Mn2Cl4]*CH3CN (2) have been synthesized {L634M = N,N,N′,N′-tetrakis[(6-methyl-2-pyridyl)methyl]propane-1,3-diamine} and their molecular structures established by X-ray crystallography. Both structures are similar, with each metal center in a trigonal-bipyramidal environment. No magnetic coupling is observed between the metal centers. UV/Vis spectra and cyclic voltammograms were recorded in CH2Cl2 and CH3CN solutions. Both complexes are stable in CH2Cl2, whereas only 2 is stable in CH3CN. On the contrary, 1 is in equilibrium with another FeII species in CH3CN. When this last solution is aerated, monocrystals of the neutral linear tetranuclear complex [(L634M)Fe4(μ-O)3Cl6]*2CH3CN (3) can be isolated. Its structure is unusual with two FeIII ions pentacoordinate and the two others tetracoordinate with only chloro ligands and oxo bridges. The magnetic properties reveal that two consecutive metal centers are strongly antiferromagnetically coupled. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Synthesis, structure and characterizations in solid state and solution of dinuclear pentacoordinated FeII and MnII complexes and of a linear tetranuclear FeIII complex obtained with the ligand N,N,N',N'-tetrakis[(6-methyl-2-pyridyl)methyl]propane-1,3-diamine

Tautomeric changes in guanfacine and its copper(II) complex as revealed by X-ray crystallography; synthesis and EPR

Menkes disease is a lethal genetic disorder of copper transport in humans. Its current treatment is the administration of copper–l-histidine complex. However, this therapy is only effective in some cases and when started early in life. In order to develop an improved treatment, copper(II) mixed ligand amino acid complexes were studied because these complexes play an important role in the physiological copper pathway. A promising strategy is the administration of l-histidine–copper(II)–l-glutamine complex, which has been reported to be the predominant low molecular-weight copper(II) complex in human blood serum. Before the biopharmaceutical studies of l-histidine–copper(II)–l-glutamine complex, a physicochemical study of this ternary system must be performed. The stoichiometry and the stability of l-histidine–copper(II)–l-glutamine relative to copper(II)–l-histidine and copper(II)–l-glutamine were established at pH 7 in solution by polarography and UV–visible spectroscopy. Nevertheless, it has bee...

Jean-Jacques Girerd

Papers

Synthesis, structure and characterizations in solid state and solution of dinuclear pentacoordinated FeII and MnII complexes and of a linear tetranuclear FeIII complex obtained with the ligand N,N,N',N'-tetrakis[(6-methyl-2-pyridyl)methyl]propane-1,3-diamine

Tautomeric changes in guanfacine and its copper(II) complex as revealed by X-ray crystallography; synthesis and EPR

Copper Complexation by Amino Acid: l-Glutamine–Copper(II)–l-Histidine Ternary System

Synthesis and structure of a new iron(III) complex with a doubly positively charged ligand. Oxidative study of the related catecholato adduct

Mechanismus der Sauerstoffaktivierung durch einkernige, Häm-freie Eisenproteine