Pseudo coordination modes

Molybdenum imido alkylidene complexes have been prepared that contain bulky carboxylate ligands such as triphenylacetate [35]. Such species are isola-ble, perhaps in part because the carboxylate is bound to the metal in an r 2 fashion and the steric bulk prevents a carboxylate from bridging between metals. If carboxylates are counted as chelating three electron donors, and the linear imido ligand forms a pseudo triple bond to the metal, then bis(r 2-carboxylate) species are formally 18 electron complexes. They are poor catalysts for the metathesis of ordinary olefins, because the metal is electronically saturated unless one of the carboxylates slips to an ri1 coordination mode. However, they do react with terminal acetylenes of the propargylic type (see below). 

The FIR spectrum is proportional to the Fourier transform of the dipole correlation function, (M(t) -M(0). As discussed above, at short times the correlation function is dominated by pseudo-oscillatory modes. Insofar as the dipole moment of the liquid is relatively weakly dependent on these pseudo-oscillatory coordinates, it is generally safe to truncate Eq. (1) after the second term in describing this short-time behavior. Thus, an IR-active intermolecular mode is considered to be one for which M-1 0. 

The complex [Mn4(S2)2(CO)i5l contains two disulfide ligands and has been obtained by oxidation of [Mn2(SSnMe3)2(CO)8] " Similar to [Mn3(S2)2(CO)9(SH)] (see Chapter 1.10.5), the disulfide groups are coordinated in different coordination modes. Each manganese atom is coordinated pseudo-ociahedx Wy by six ligands, but the coordination spheres of the individual atoms differ with respect to the total number of sulfur ligands. Two of them are coordinated to three sulfur atoms, the other ones to two and one, respectively. The family of tetranuclear complexes... 

The NMR spectra of the compounds la-d clearly indicate a chelating coordination mode of the amidinate ligands. Both R groups show only one set of signals in the temperature range from +30 to -90 C ( h, C NMR), indicative for a fast pseudo-rotation of the molecular skeleton in each case, whereas the Si NMR resonances confirm the presence of a pentacoordinate silicon centers. The... 

Pseudo-oxocarbons coordination chemistry has hardly been described in the chemical literature. Croconate violet 17 exhibits four different coordination modes as can be inferred from Table 5.5. 

Oxocarbons, pseudo-oxocarbons, and squaraines are a very versatile class of compounds, being useful in a wide range of areas, from model compounds to medicinal chemistry. Their role in coordination of metal ions appears to be their most important property. For the coming years, oxocarbons and their derivatives will be very important in crystal engineering. For this application, their impressive ability to provide several different coordination modes is particularly important. 

Define an adequate TS structure and for such a structure define the pseudo-normal mode of vibration corresponding to the reaction coordinate. 

Examination of cyclopropanation through RT6 and RT7 reveals that a less conventional explanation may be required to rationalize the high reactivity of zinc car-benoids (Fig. 3.29). The structure of RT6 represents a pseudo-dimer as shown in RTS that has been further activated by coordination of zinc chloride to the oxygen of the chloromethylzinc alkoxide. This mode of activation is reminiscent of that observed in RTl. Cyclopropanation proceeding from RT6 through TS3 has an activation energy of 27.8 kcal mol . This represents a negligible decrease in the barrier to methylene transfer when compared to reaction from RTS. 

ESI and APCI produce predominantly pseudo-molecular ions [M + H] + species in a positive mode and [M — H] in negative ion mode, with variable fragmentation depending upon the cone voltage used and, in the case of APCI, on the temperamre used. Adduct ions are very often seen in ESI, and it is these that can cause most problems to inexperienced users, but they can be useful. Their formation depends on the coordinating properties, polarity and concentration of the analyte and to some extent on the solvent being used. 

Hydrogen bonding to substrates such as carbonyl compounds, imines, etc., results in electrophilic activation toward nucleophilic attack (Scheme 3.1). Thus, hydrogen bonding represents a third mode of electrophihc activation, besides substrate coordination to, for example, a metal-based Lewis acid or iminium ion formation (Scheme 3.1). Typical hydrogen bond donors such as (thio)ureas are therefore often referred to as pseudo-Lewis-acids. ... 

The coordination behavior as well as the tautomerization equilibria of the new pyridone ligands was studied in detail by NMR and computational methods. For all three the data obtained strongly support a pseudo-bidentate hydroxypyridine-pyridone binding mode. 

Bader 46) considered the implications of the pseudo Jahn-Teller theorem for this and deduced that the bond stretching E mode would be the most likely reaction coordinate, and one can see from Fig. 10 that this would lead to the required products if continued to dissociation. 

A parameterization method of the Hamiltonian for two electronic states which couple via nuclear distortions (vibronic coupling), based on density functional theory (DFT) and Slaters transition state method, is presented and applied to the pseudo-Jahn-Teller coupling problem in molecules with an s2-lone pair. The diagonal and off-diagonal energies of the 2X2 Hamiltonian matrix have been calculated as a function of the symmetry breaking angular distortion modes and r (Td)] of molecules with the coordination number CN = 3... 

The photodissociation of trifluoromethyl iodide, CF3I —> CF3 + I/I, which was briefly discussed in Section 6.4, seems to illustrate case (a) of Figure 9.4 while the photo dissociation of methyl iodide, CH3I —> CH3 + I/I, appears more to represent case (b). In both examples, the 1/2 umbrella mode, in which the C atom oscillates relative to the Irrespectively F3-plane, is predominantly excited. Following Shapiro and Bersohn (1980) the dissociation of CH3I and CF3I may be approximately treated in a two-dimensional, pseudo-linear model in which the vibrational coordinate r describes the displacement of the C atom from the H3-/F3-plane and the dissociation coordinate R is the distance from iodine to the center-of-mass of CH3/CF3 (see Figure 9.6).t... 

A transition state theory formalism (Equation 9.10) was used to calculate the lsO KIE from the reaction coordinate frequency (rrc), defined as the mode that converts the 0—0 vibration into a translation, and the pseudo-equilibrium constant for forming the transition state (KTs). In the expression for the latter (Equation 9.11), the one vibration that becomes the reaction coordinate has been removed. 

A (molecular) crystal polymorph is a solid crystalline phase of a given compound resulting from the possibility of at least two different arrangements of the molecules of that compound in the solid state Conformational polymorphs are formed by molecules that can adopt different conformations in different crystal structures formed by coordination complexes where ligands bound in delocalized bonding modes adopt different relative orientations Concomitant polymorphs are polymorphic modifications of the same substance obtained from the same crystallisation process Pseudo-polymorphs are ... 

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