Generator coordinate

A new generation coordination catalysts are metallocenes. The chiral form of metallocene produces isotactic polypropylene, whereas the achiral form produces atactic polypropylene. As the ligands rotate, the catalyst produces alternating blocks of isotactic and atactic polymer much like a miniature sewing machine which switches back and forth between two different kinds of stitches. 

The spectroscopy, reaction kinetics, and photophysics of coordinatively unsaturated metal carbonyls generated in the gas phase via UV photolysis are probed via transient infrared spectroscopy. The parent compounds that have been used to generate coordinatively unsaturated species are Fe(CO)5, Cr(C0)5 and Mn2(CO)io- In contrast to what is observed in solution phase, photolysis of these compounds produces a variety of coordinatively unsaturated photoproducts. 

Nevertheless, we were able to develop a transient absorption apparatus involving IR probe radiation that is suitable for gas phase studies, as have a number of other groups either coincident with or subsequent to our work [1]. In the remainder of this article we will discuss the apparatus and the results of our studies on three prototypical metal carbonyl species Fe(C0>5, Cr(C0>5 and Mn2(CO)] o The discussion in this article will center on the nature of the photolytically generated coordinatively unsaturated species, their kinetic behavior and photophysical information regarding these species. This latter information has enabled us to comment on the mechanism for photodissociation in these systems. Since most of the results that will be discussed have been presented elsewhere [3-10], we will concentrate on a presentation of data that illustrates the most important features that have come out of our research and directly related research regarding the kinetics, photophysics and photochemistry of coordinatively unsaturated metal carbonyls. 

A point of interest at this stop in our tour is that fragmentation of organometallic ions in ESI-MS often proceeds via ligand dissociation (e.g., phosphane loss) to generate coordinatively unsaturated organometallic ions [1-9]. One of the strengths of this technique is that such unsaturated ions are typically proposed as reactive intermediates in catalytic reactions carried out in solution (vide infra), allowing ESI-tandem-MS systems to study directly the gas-phase reactivity of such species. 

Lathouwers, L., Van Leuven, P., Deumens, E., and Ohm, Y. (1987), Applications of the Generator Coordinate Approximation to Diatomic Systems. II. Dunham Analysis of Vibration-Rotation Spectra, /. Chem. Phys. 86, 6352. 

Van Leuven, P., and Lathouwers, L. (1980), The Generator Coordinate Method in Molecular Physics, in Quantum Dynamics of Molecules, R. G. Woolley (Ed.), Plenum, New York. 

DR. WILLIAM TR0GLER (Northwestern University) I wish to make a brief presentation of some results which relate to Dr. Geoffroy s talk. We have been employing a different approach to generate coordinatively unsaturated centers, utilizing a reduc-... 

Although authors [74,75] have claimed that a generator-coordinate theory yields an expression for spectral terms exactly of Dunham s form, as in formula 8, in which however term coefficients encompass intrinsically elfects of at... 

We thank Dr. S.P.A. Sauer of University of Copenhagen for fruitful collaboration in a project since 1994 of which this article is an overview, and Professor P. van Leuven for helpful comments about the generator coordinate approach. Much preparation of this article occurred whilst JFO was a visiting professor in Kemisk Institut at Syddansk Universitet, for which hospitality he is grateful. 

We present a new mapping procedure from fermion onto boson spaces. The procedure is based on the Generator Coordinate Method. We show an application of this technique to systems of nucleons moving in a single j-orbit. The extension of this microscopic investigation to many j-orbit systems is also examined. 

The procedure we are going to expose is based on the Generator Coordinate Method (GCM). The GCM looks for solutions of the Schrodinger equation of the form... 

The M(CO)6 (M = Cr, Mo, W) photocatalyzed hydrogenation140 and hydro-silation139 of 1,3-dienes is another example where the role of the light is to generate coordinative unsaturation. The reactions (58) and (59) can be carried out on a synthetic scale and represent very selective transformations. The facts that... 

Mito, Y. and Kamimura, M. (1976). The generator coordinate method for composite-particle scattering based on the Kohn-Hulth6n variational principle,... 

The latter complex undergoes CO loss to generate coordinatively unsaturated 4.28. Conversion of 4.28 to 4.30 is the crucial step that is responsible for the formation of the branched isomer. Obviously this reaction is possible only when propylene is present as one of the reactants, or under reaction conditions where propylene from //-propanol is generated in situ. Conversion of 4.28 to 4.30 is an example of alkene insertion into an M-H bond in a Markovnikov manner (see Section 5.2.2 for a discussion on Markovnikov and anti-Markovnikov insertion). The anti-Markovnikov path leads to the formation of 4.29, which is in equilibrium with 4.24. Complexes 4.25 and 4.26 are analogues of 4.4 with //-butyl and /-butyl groups in the place of methyl. They reductively eliminate the linear and branched acid iodides. In the presence of water the acid iodides are hydrolyzed to give //-butyric and / -butyric acids. 

There have been a few reports of first generation coordination complex structural models for the phosphatase enzyme active sites (81,82), whereas there are some examples of ester hydrolysis reactions involving dinuclear metal complexes (83-85). Kim and Wycoff (74) as well as Beese and Steitz (80) have both published somewhat detailed discussions of two-metal ion mechanisms, in connection with enzymes involved in phosphate ester hydrolysis. Compared to fairly simple chemical model systems, the protein active site mechanistic situation is rather more complex, because side-chain residues near the active site are undoubtedly involved in the catalysis, i.e, via acid-base or hydrogenbonding interactions that either facilitate substrate binding, hydroxide nucleophilic attack, or stabilization of transition state(s). Nevertheless, a simple and very likely role of the Lewis-acidic metal ion center is to... 

These features can be exploited in synthesis and catalysis. Acidic ionic liquids have proved to be particularly useful as they strip away halide ligands attached to catalysts thereby generating coordinatively unsaturated species that are more reactive towards the substrates. Ionic liquids based on chlorocuprates are prepared in a similar manner from the direct reaction of... 

The proposed mechanism for a standard Heck reaction is depicted in Scheme 6.5. Generally, a haloalkene or haloarene undergoes oxidative addition to an in situ generated, coordinatively unsaturated 14-electron palladium(O) complex, but other substrates such as tosylates, triflates or diazonium salts can also be applied. Subsequent, sy -insertion into the C=C double bond of a complexed olefin yields a t7-(j -alkenyl) or (j- aryl)alkylpalladium complex. If no hydrogen atom in a pseudo cis-position relative to the palladium is present, an internal rotation step is required prior to syw-elimination of the olefin to afford the traws-olefin product and a palladium(II) hydride complex. The latter is restored to the initial Pd(0) species by base-induced reductive elimination.137"401... 

The condensation reactions of carbonyl metallates with neutral species, which are either coordinatively unsaturated or which will readily generate coordinatively unsaturated fragments, have also yielded a variety of mixed-metal clusters. The square-based pyramidal dianion [Fe5C(CO)i4] , for example, has been shown to react with a number of such species to yield octahedral FcjMC cluster compounds (Scheme 9) 269, 381). In some cases. 

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