Insertions, transition metals

Teixidor F, Leutkens ML Jr, Rudolph RW (1983) Transition-metal insertion into naked cluster polyanions. J Am Chem Soc 105 149-150... 

Another chemical approach to the chemical conversion of methane involves organometallic reactions.85-89 Interesting work with iridium complexes and other transition metal insertion reactions (rhodium, osmium, rhenium, etc.) were carried out. Even iron organometallics were studied. These reactions take place in the coordination spheres of the metal complexes, but so far the reactions are stoichiometric and noncatalytic.77 In terms of synthetic hydrocarbon chemistry, these conversions are thus not yet practical, but eventually it is expected that catalytic reactions will be achieved. 

In the sixth period is a subset of 14 metallic elements (numbers 58 to 71) that are quite unlike any of the other transition metals. A similar subset (numbers 90 to 103) is found in the seventh period. These two subsets are the inner transition metals. Inserting the inner transition metals into the main body of the periodic table, as in Figure 2.30, results in a long and cumbersome table. So that the table can fit nicely on a standard paper size, these elements are commonly placed below the main body of the table, as shown in Figure 2.31. 

M. Gozin, A. Weisman, Y. Ben-David, and D. Milstein, Activation of a Carbon-Carbon Bond in Solution by Transition-Metal Insertion, Nature 364, 699-701... 

In certain instances (Ir, Pt, Au), the carbon-transition-metal-mercury complexes are actually isolable. They also decompose in the manner indicated. When organomercury halides are employed in such reactions, similar oxidation-reduction processes occur, but evidence suggests that the transition metal inserts primarily into the mercury-halogen bond followed by loss of mercury " ... 

When the terminal carbonyl group on the Fe atom is replaced by a ligand such as PPhj, P(OPh)3, or PMcs, no isolable insertion products can be obtained . Other mixed transition metal insertion products such as CpCr(CO)3SnBr2CpMo(CO)3 and CpFe(CO)2SnCl2Co(CO)4 are prepared by reacting the trihalotin derivative of one of the metals with the metal-metal-bonded dimer of the other, but not by a direct insertion reaction ... 

In the present study, we consider the bond analysis in metal porphyrins. In the following discussion, the porphyrin will be often indicated as phy. We apply Electron Localization Function (ELF) analysis and Maximum Probability Domains (MPDs) analysis for understanding the eventual differences between transition metal and non-transition metals inserted into the porphyrin ring. As an example of nontransition metal, we consider Be, Mg, and Zn (a d metal, so d orbitals can be considered core-Uke). For transition metals, we consider Fe, Co, and Ni. Due to the difficulties in finding experimental examples of pure square planar coordination... 

That is, the atom of the transitional metal inserts into a C-C bond and a C-H bond to form a reaction intermediate. The metal-carbon (M-C) bond in the reaction intermediate is considerably weaker and will subsequently rupture to yield methyl or H radicals. The methyl radical will combine with a hydrogen radical to form methane. Therefore, the metal insertion becomes the rate-determining step and has to be understood. 

Apart from carbene transfer from early transition metals, insertion of isocyanides into a palladium alkyl bond, followed by alkylation, has been found to lead to palladium(ii) amino carbene complexes (Equation (21)). Isocyanide insertion first leads to an iminoacyl complex, from which the carbene is generated by alkylation or protonation of the nitrogen. The molecular structure of 55 has been determined and a Pd-G bond length of 1.97(1) A observed. 

Contents Comparison of synthetic reactions by transition metal complexes with those by Grignard reagents. -Formation of a-bond involving transition metals. -Reactivities of a-bonds involving transition metals. -Insertion reactions. - Liberation of organic compounds from the a-bonded complexes. - Cyclization reactions, and related reactions. - Concluding remarks. 

The transition metal structures consist of close-packed (p. 26) arrays of relatively large atoms. Between these atoms, in the holes , small atoms, notably those of hydrogen, nitrogen and carbon, can be inserted, without very much distortion of the original metal structure. to give interstitial compounds (for example the hydrides, p. 113). 

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

Transition metals have also been inserted into the aziridine ring affording derivatives (295). Stereochemical studies suggest that transfer of a proton is followed by bimolecular attack on the ring with subsequent closure on the carbonyl group (76AG(E)495). 

Numerous examples oF metal carbonyls will be found in later chapters dealing with the chemistry of the individual transition metals. CO also has an unrivalled capacity for stabilizing metal clusters and for inserting into M-C bonds (p. 309). Synthetic routes include ... 

Stable transition-metal complexes may act as homogenous catalysts in alkene polymerization. The mechanism of so-called Ziegler-Natta catalysis involves a cationic metallocene (typically zirconocene) alkyl complex. An alkene coordinates to the complex and then inserts into the metal alkyl bond. This leads to a new metallocei e in which the polymer is extended by two carbons, i.e. 

The general understanding of the electronic structure and the bonding properties of transition-metal silicides is in terms of low-lying Si(3.s) and metal-d silicon-p hybridization. There are two dominant contributions to the bonding in transition-metal compounds, the decrease of the d band width and the covalent hybridization of atomic states. The former is caused by the increase in the distance between the transition-metal atoms due to the insertion of the silicon atoms, which decreases the d band broadening contribution to the stability of the lattice. 

The strained bicyclic carbapenem framework of thienamycin is the host of three contiguous stereocenters and several heteroatoms (Scheme 1). Removal of the cysteamine side chain affixed to C-2 furnishes /J-keto ester 2 as a possible precursor. The intermolecular attack upon the keto function in 2 by a suitable thiol nucleophile could result in the formation of the natural product after dehydration of the initial tetrahedral adduct. In a most interesting and productive retrosynthetic maneuver, intermediate 2 could be traced in one step to a-diazo keto ester 4. It is important to recognize that diazo compounds, such as 4, are viable precursors to electron-deficient carbenes. In the synthetic direction, transition metal catalyzed decomposition of diazo keto ester 4 could conceivably furnish electron-deficient carbene 3 the intermediacy of 3 is expected to be brief, for it should readily insert into the proximal N-H bond to... 

The diazo function in compound 4 can be regarded as a latent carbene. Transition metal catalyzed decomposition of a diazo keto ester, such as 4, could conceivably lead to the formation of an electron-deficient carbene (see intermediate 3) which could then insert into the proximal N-H bond. If successful, this attractive transition metal induced ring closure would accomplish the formation of the targeted carbapenem bicyclic nucleus. Support for this idea came from a model study12 in which the Merck group found that rhodi-um(n) acetate is particularly well suited as a catalyst for the carbe-noid-mediated cyclization of a diazo azetidinone closely related to 4. Indeed, when a solution of intermediate 4 in either benzene or toluene is heated to 80 °C in the presence of a catalytic amount of rhodium(n) acetate (substrate catalyst, ca. 1000 1), the processes... 

The Structural Stability of Transition Metal Oxide Insertion Electrodes for Lithium Batteries... 

This review focuses on the structural stability of transition metal oxides to lithium insertion/extraction rather than on their electrochemical performance. The reader should refer to cited publications to access relevant electrochemical data. Because of the vast number of papers on lithium metal oxides that have been published since the 1970s, only a selected list of references has been provided. 

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