Coordinate bonding

Bond lengths and infrared spectra support the multiple-bond character of the M—CO bonds. Coordination of a CO molecule to a metal center can change the C—O bond order. According to the description of ( - and TT-bonding given herein, increased ( -bonding between a metal and CO results in a... 

Chemical shift (isotropic component) 5. ISO Magic-angle spinning Chemical bonding coordination number... 

The most favorable coordination sites in thiophenes are the C2C3 and C4C5 double bonds ( -coordination, 38). This type of coordination greatly enhances the nucleophilic power of the sulfur atom, which then gives rise to two new modes of binding the metal atoms, as in the V, S-p.2-, 42, and V, S-p.3-species, 43. 

The cocondensation of nickel atoms and CS2 at 12 K resulted in the formation of three binary, mononuclear, nickel/CS complexes, NKCSjln, n = 1-3 (145). Mixed CS2/ CS2 isotopes were used to identify the lowest stoichiometry species. An interpretation of the IR and UV-visible spectra, as well as normal-coordinate analyses (144), suggested that these species are best considered as normal 7r-complexes, with the nickel atom coordinated to the C=S bond in a manner analogous to C=C bond coordination (123). 

In the case where the bond coordinate can be treated as classical, and when the electronic interaction A is much smaller than the solvent reorganization, the energy of activation can be calculated explicitly in Saveant s [1993] model ... 

Obviously, the NMR pattern of the QM moiety depends on its coordination mode. As expected, in case of ring coordination, such as r -coordination or r -coordination,16 17 the ring signals are affected, while in the case of exocyclic bond coordination, the signals of the exocyclic bond are influenced.6 14 18 19... 

The X-ray structure of the dibromine complex with toluene (measured at 123 K) is more complicated, and shows multiple crystallographically independent donor/acceptor moieties [68]. Most important, however, is the fact that in all cases the acceptor shows an over-the-rim location that is similar to that in the benzene complex. In both systems, the acceptor is shifted by 1.4 A from the main symmetry axis, the shortest Br C distances of 3.1 A being significantly less than the sum of the van der Waals radii of 3.55 A [20]. Furthermore, the calculated hapticity in the benzene/Br2 complex (x] = 1.52) is midway between the over-atom (rj = 1.0) and over-bond (rj = 2.0) coordination. In the toluene complex, the latter varies from rj = 1.70 to 1.86 (in four non-equivalent coordination modes) and thus lies closer to the over-bond coordination model. Moreover, the over-bond bromine is remarkably shifted toward the ortho- and para-carbons that correspond to the positions of highest electron density (and lead to the transition states for electrophilic aromatic bromination [12]). Such an experimental location of bromine is in good agreement with the results of high level theoretical... 

The weak supramolecular interactions (H-bonds, coordination or van der Waals interactions, etc.) positioning the molecular components to give the supramolecular architectures are typically several orders of magnitude less robust than the cross-linked covalent bonds formed in a specific polymerization process. Accordingly, the sole solution to overcome these difficulties is to improve the binding (association) efficiency of the molecular components generating supramolecular assemblies. At least in theory, an increased number of interaction moieties and the selection of the... 

The presence of a remote C=C double bond in the alkyl halide was critical saturated analogs underwent nickel-catalyzed halogen-zinc exchange.248 It has been suggested that the double bond coordinates to the nickel atom. As a 7r-acceptor, the C=C bond removes some electron density from the metal, thus facilitating the reductive coupling (Scheme 154).246... 

The two stereoisomers of the bis(r 3-anti),A-trans intermediate 7b confirmed by NMR (References 20, 21) are distinguished by the Irons double bond coordination of opposite enantiofaces. Different from experiment, the major stereoisomer (established by NMR) with a parallel orientation of the trans double bond is predicted to be 0.6 kcal mol 1 (AG) less favorable than the minor stereoisomer with a nonparallel double bond arrangement. 

If we now assume, following Lewis, that each monovalent bond coordination is associated with an electron pair, we can write the total number (ebf) of valence bond-pair electrons as... 

This scheme disregards mass transfer limitations and represents only a simplified model. Formation of A S may involve specific interactions, such as hydrogen bonds, coordination, or ir-complex formation, or non-specific interactions, such as van der Waals or hydrophobic bonds. Non-specific interactions are insignificant for small polar molecules, but may contribute significantly to the surface complex formation if the hydrophobic moiety is large ( 5, 6) ... 

HC1 is the acid, because it is donating an H+ and the H+ will accept an electron pair from ammonia. Ammonia is the base, accepting the H+ and furnishing an electron pair that the H+ will bond with via coordinate covalent bonding. Coordinate covalent bonds are covalent bonds in which one of the atoms furnishes both of the electrons for the bond. After the bond is formed, it is identical to a covalent bond formed by donation of one electron by both of the bonding atoms. 

Products deriving from cyclization-alkoxycarbonylation are instead formed through the general mechanism shown in Scheme 19, involving exo (path a) or endo (path b) intramolecular nuclophilic attack by YH to the triple bond coordinated to Pd(II) followed by CO insertion and nucleophilic... 

On the other hand, when the oxidative carbonylation of a ,a -disubstituted propynylamines was carried out in the presence of an excess of CO2, the intermediate carbamate species could undergo cyclization with incorporation of CO2 into the five-membered cycle, either by direct nucleophilic attack of the carbamate oxygen to the triple bond coordinated to Pd(II) (Scheme 33, path a) or through the intermediate formation of a palladium carbamate complex followed by triple bond insertion (Scheme 33, path b). Carbon monoxide insertion into the Pd - C bond of the resulting stereoisomeric vinylpalladium intermediates then led to the final oxazolidi-none derivatives. 

An alternative approach, developed by van Roosmalen et al. (1982, 1983a), is based on the use of the bond coordinates, and treats bent molecules still keep-... 

When it comes to polyatomic molecules, there are two problems that complicate the issue, as already discussed in Note 1 of Chapter 3. One is the separation of the overall rotation of the molecule (Jellinek and Li, 1989). The other is that, depending on the choice of internal coordinates, certain coupling terms can be assigned to be kinetic or potential terms. A simple and familiar case is a linear triatomic, when one uses bond coordinates versus Jacobi coordinates. The case for Fermi coupling for a bending motion is discussed in Sibert, Hynes, and Reinhardt (1983). 

Figure 5. Stacking interaction proposed in the reaction between bipy and Ni(phen)(H20)k2 immediately prior to the first bond coordination of bipy.

When a second equivalent of trimethylphosphine was reacted with 140.e, the ketene functionality of the vinylketene ligand was displaced leaving only the C = C bond coordinated in an if fashion (142). This product could also be isolated by the direct treatment of vinylcarbene 139 with 2 equiv... 

In both compounds the dioxygen coordination is side-on terminal and the 0-0 distance falls within the typical range of a peroxide bond coordinated to a single metal ion. In both cases the geometry can be viewed as either distorted trigonal-pyramidal or distorted octahedral, depending on whether one considers the oxygen molecule to occupy one or two positions. 

The set of molecules for which the relationship of Eq. (3.3) has been tested with the reported accuracy, has certain sinq>lifying features in common They all have standard bonding coordinations around each atom and the shortfall of the SCF energy is entirely due to dynamic correlations. Modifications are to be expected for systems where these premises are not satisfied. Even with these limitations, however, the molecules in Table 2 represent a variety of atom and bond combinations. It is therefore remarkable that, for all of them, the correlation energy can be recovered by a sinq>le system-independent formula that allows for a physically meaningful interpretation. 

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