Cyclometalated phosphine-based pincer complexes: Mechanistic insight in catalysis, coordination, and bond activation

http://alpha.chem.umb.edu/chemistry/ch611/documents/C-Htransitionmetalbonds.pdf

Carbonhydrogen-transition metal bonds

C-H oxidation has a long history and an ongoing presence in research at the forefront of chemistry and interrelated fields. As such, numerous highly useful articles and reviews have been written on this subject. Logically, these are generally written from the perspective of the scope and limitations of the reagents employed. This Minireview instead attempts to emphasize chemoselectivity imposed by the nature of the substrate. Consequently, many landmark discoveries in the field of C-H oxidation are not discussed, but hopefully the perspective taken herein will allow C-H oxidation reactions to be more readily incorporated into synthetic planning.

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If C-H bonds could talk: selective C-H bond oxidation.

Owing to their high uptake capacity at low temperature and excellent reversibility kinetics, metal–organic frameworks have attracted considerable attention as potential solid-state hydrogen storage materials. In the last few years, researchers have also identified several strategies for increasing the affinity of these materials towards hydrogen, among which the binding of H2 to unsaturated metal centers is one of the most promising. Herein, we review the synthetic approaches employed thus far for producing frameworks with exposed metal sites, and summarize the hydrogen uptake capacities and binding energies in these materials. In addition, results from experiments that were used to probe independently the metal–hydrogen interaction in selected materials will be discussed.

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Hydrogen Storage in Microporous Metal-Organic Frameworks with Exposed Metal Sites

Use of the tritopic bridging ligand 1,3,5-benzenetristetrazolate (BTT3-) enables formation of [Mn(DMF)6]3[(Mn4Cl)3(BTT)8(H2O)12]2·42DMF·11H2O·20CH3OH, featuring a porous metal−organic framework with a previously unknown cubic topology. Crystals of the compound remain intact upon desolvation and show a total H2 uptake of 6.9 wt % at 77 K and 90 bar, which at 60 g H2/L provides a storage density 85% of that of liquid hydrogen. The material exhibits a maximum isosteric heat of adsorption of 10.1 kJ/mol, the highest yet observed for a metal−organic framework. Neutron powder diffraction data demonstrate that this is directly related to H2 binding at coordinatively unsaturated Mn2+ centers within the framework.

Hydrogen Storage in a Microporous Metal−Organic Framework with Exposed Mn2+ Coordination Sites

Reported were the first examples of isolable transition-metal complexes containing a coordinated dihydrogen molecule, characterized by a variety of spectroscopic and structural methods to possess n/sup 2/-bonded hydrogen. The dihydrogen ligand is symmetrically coordinated in an n/sup 2/ mode with average tungsten-hydrogen distances of 1.95 (23) angstroms (x-ray) and 1.75 angstroms (neutron, ..delta..F). The H-H separation is 0.75 (16) angstrom (x-ray) and 0.84 angstroms (neutron, ..delta..F), slightly larger than that obtained from free H/sub 2/ (0.74 angstroms). The H/sub 2/ ligand axis is approximately parallel to the trans phosphorous-phosphorus direction. Vibrational spectra of solid samples of the H/sub 2/, D/sub 2/, and HD forms (M = W) are consistent with coordination of molecular H/sub 2/. The H/sub 2/ complexes are significant in that they may represent an arrested form of oxidative addition of H/sub 2/ to metals. 1 table (DP)

Characterization of the first examples of isolable molecular hydrogen complexes, M(CO)3(PR3)2(H2) (M = molybdenum or tungsten; R = Cy or isopropyl). Evidence for a side-on bonded dihydrogen ligand

Structural characterization of both components of an electrochemically reversible couple in ((N - C/sub 5/H/sub 5/)/sub 2/ Fe/sub 2/(S/sub 2/) (SC/sub 2/H/sub 5/)/sub 2/)/sup +/ was used to derive an electron-pair coupling mechanism which is consistent with the observed structural and magnetic properties. (DLC)

Electrochemical synthesis and structural characterization of the iron-sulfur cluster cation bis(.eta.5-2,4-cyclopentadien-1-yl)[.mu.-(dithio)]bis[.mu.-(ethanethiolato)]diiron(1+)

Preparation par reaction de H 2 avec M(CO) 3 (PR 3 ) 2 . Etude RX et IR et Raman des structures

Characterization of the first examples of isolable molecular hydrogen complexes, M(CO)3(PR3)2(H2)(M=Mo, W; R=Cy, i-Pr): evidence for a side-on bonded H2 ligand

P. J. Vergamini

Papers

Characterization of the first examples of isolable molecular hydrogen complexes, M(CO)3(PR3)2(H2) (M = molybdenum or tungsten; R = Cy or isopropyl). Evidence for a side-on bonded dihydrogen ligand

Electrochemical synthesis and structural characterization of the iron-sulfur cluster cation bis(.eta.5-2,4-cyclopentadien-1-yl)[.mu.-(dithio)]bis[.mu.-(ethanethiolato)]diiron(1+)

Characterization of the first examples of isolable molecular hydrogen complexes, M(CO)3(PR3)2(H2)(M=Mo, W; R=Cy, i-Pr): evidence for a side-on bonded H2 ligand

Electrochemical synthesis and structural characterization of the iron-sulfur cluster cation bis(.eta.5-2,4-cyclopentadien-1-yl)[.mu.-(dithio)]bis[.mu.-(ethanethiolato)]diiron(1+)