Metal ligand system

The Fenske-Hall method is a modification of crystal held theory. This is done by using a population analysis scheme, then replacing orbital interactions with point charge interactions. This has been designed for the description of inorganic metal-ligand systems. There are both parameterized and unparameterized forms of this method. 

A lot of research has been published on hydroformylation of alkenes, but the vast majority of the effort has been focused on the chemistry of various metal-ligand systems. Quantitative kinetic studies including modeling of rates and selectivities are much more scarce. In this work, we present the approach to modeling of hydroformylation kinetics and gas-solubility. Hydroformylation of 1-butene with a rhodium-based catalyst was selected as a case study. 

Armentrout, R B., Kickel, B. L., 1996, Gas-Phase Thermochemistry of Transition Metal Ligand Systems Reassessment of Values and Periodic Trends in Organometallic Ion Chemistry, Freiser, B. S. (ed.), Kluwer, Amsterdam. 

M[pz(A4)] A = S2ML2. The octakis(.V-R)porphyra/,ines reported by Schramm and Hoffman (2), M[pz(S-R)8 (M = Ni, Cu), (60), can be converted to the octathiolate M[pz(S )g] (Scheme 11) via reductive cleavage of the sulfur-carbon bond when R = benzyl (Bn), and this tetra-bis(dithiolate) can then be peripherally capped with metal-ligand systems to yield peripherally tetrametalated star porphyrazines. The benzyl dinitrile 57 can be macrocyclized around magnesium butoxide to form [Mg[pz(S-Bn)8] (58) (35-40%), which can then be demetalated with trifluoroacetic acid to form 59 (90%), which is subsequently remetalated with nickel or copper acetate to form 60a (95%) and 60b (70%) (Scheme 11) (3, 23, 24). Deprotection of 60a or 60b with sodium in ammonia yields the Ni or Cu tetra-enedithiolates, 61a or 61b to which addition of di-ferf-butyl or n-butyl tin dinitrate produces the peripherally metalated star porphyrazines 62a (37%), 62b (80%), and 62c (41%). 

Serve as a eollecting point for reactants. Sec. 6.1 Promote electron shifts in the metal-ligand system. Secs. 6.2-6.S... 

Many factors play a role in establishing the value of the stability constants of a particular metal-ligand system. J. Bjerrum [4] considered such factors and their effect on the successive stability constants. The ratio of two stepwise constants is defined as ... 

There are two major routes of formation of an unstable metal-ligand system (a) The metal ion in its given state of oxidation interacts with the ligand to give an unstable system (via Mechanisms 1 or 2). (b) The metal-ligand system is stable... 

Reduction of Ligands. In contrast to the many systems where the oxidation of a ligand by the central atom could be demonstrated, there are relatively few examples of unstable metal-ligand systems that result in the reduction of the ligand... 

Fission of the ligand molecule may take place during the redox process of the metal-ligand system. This is generally true of systems in which the ligands are bound to the metal through an oxygen atom. 

Stable Metal Ligand Systems with Oxidants or Reductants,... 

The interaction of stable metal-ligand systems with oxidizing or reducing reactants, resulting in a redox change in the ligand. 

The formation of ligated transition metal ions at unstable high states of oxidation, its implications in the mechanisms of metal-catalyzed autoxidation, and the effect of configuration of a metal-ligand system on its redox stability have been pointed out. These considerations may be helpful in interpreting more complex metal-ligand systems including metal-enzyme reactions. 

Normal coordinate analyses of a series of Cr(R2Dtc)3 complexes have been reported (81). In these analyses the complexes were treated as planar 1 1 metal-ligand systems of C2 symmetry and only the 11 in-plane vibrations (6At +5B2) were considered (81). The alkyl groups were treated as point masses. One interesting result of these studies was that the observed decrease in v(C-N) in the sequence R = Me > Et > Pr Bu, is paralleled by the calculated sequence obtained by increasing the point mass of the alkyl group... 

In 1978, Ashworth and the present author recognized that molecules containing either unsaturated carbon-metal or unsaturated metal-metal bonds should complex with other metal-ligand systems, as do alkenes or alkynes, provided the metal centers were electron rich yet had a vacant coordination site (4). This concept is illustrated in Scheme 1, with platinum (d10) as the paradigm metal center. 

Coordination of a ligand to a metal reduces the ligand flexibility and therefore the number of conformations available to the metal-ligand system is reduced. 

In this chapter we have seen the three ways in which co-ordination to a metal ion may modify the properties of a ligand. In any real metal-ligand system, the observed reactivity is expected to be a subtle blend of all three. In the remainder of this book we will consider the ways in which these various effects work in real complexes. 

The substituted ferrocenes 757 are widely used as metal-ligand systems. These compounds have a great variety of chelating groups (R) (1-diketones (a) [458], semicarbazones and thiosemicarbazones (b) [458], azomethines and their analogues (c) [458-462], oximes (d), carbonic, thiocarbonic (e), and amino acids (f) [458] ... 

While the examples described above highlight the impressive results that can be achieved with protein as scaffolds for catalyst design, this approach is not without problems. Firstly, there is the issue of cavity size. It would be useful to incorporate large metal-ligand systems into this protein system to generate catalysts for a plethora of... 

Results for Metal-Ligand Systems Phthalimide-On-Copper... 

There are a number of metal-ligand systems that will provide the proper activation for nucleophile coupling, but the Pd system is by far the most well developed and useful. In recent years, asymmetric allylic alkylation reactions have received the most interest for organic synthesis apphcations (see Asymmetric Synthesis by Homogeneous Catalysis). Metals other than Pd have also received some additional attention. 

Halide Substitution using Activation with Other Metal-Ligand Systems... 

Another technique which has been used to prepare 3-D polyhedra is Raymond s symmetry-interaction method.19 This strategy derives from the realization that many natural supramo-lecular assemblies are formed in a symmetry-driven process which relies on incommensurate lock-and-key interactions. By closely examining a desired polyhedral structure, one may establish the relevant symmetry interactions and their associated geometric relationships, and then design metal-ligand systems capable of fulfilling them. 

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