Halides dimeric

In their work [58], GY demonstrated that a standard Lennard-Jones model grossly over-predicted the well-depth of rare gas-halide ion dimer potential energy curves when they were parametrized to reproduce the neutral rare gas-halide dimer curves. They further showed that the OPNQ model performed just as badly when the charge dependence of the expressions were ignored, but the potential energy curves for both the neutral and ionic dimers could be simultaneously be reproduced if the charge dependence is considered. 

The insoluble complexes (27) have been prepared by the room-temperature reaction of the appropriate cyclo-octa-1.5-diene cuprous halide dimer with [(Tt-CpljTilSR),], in toluene, under an atmosphere of nitrogen. The existence of a Ti—Cu bond is suggested from comparative spectral studies with [(7t-Cp)2-... 

With primary halides, dimers (R—R) are formed predominantly, while with tertiary halides, the disproportionation products (RH, R(—H)) prevail. Both alkyl nickel(III) complexes, formed by electrochemical reduction of the nickel(II) complex in presence of alkyl halides, are able to undergo insertion reactions with added activated olefins. Thus, Michael adducts are the final products. The Ni(salen)-complex yields the Michael products via the radical pathway regenerating the original Ni(II)-complex and hence the reaction is catalytic. In contrast to that, the Ni(III)-complex formed after insertion of the activated olefin into the alkyl-nickel bond of the [RNi" X(teta)] -complex is relatively stable. Thus, further reduction leads to the Michael products and an electroinactive Ni"(teta)-species. 

Infrared spectroscopy is not as inherently informative with regard to metal interactions in highly symmetrical metal-metal bound dimers as is Raman spectroscopy, since the totally symmetric metal-metal stretch is a forbidden absorption in the infrared experiment. Oldham and Ketteringham have prepared mixed-halide dimers of the type Re2ClxBr 2xto lower the symmetry and hence introduce some infrared allowedness into the Re-Re stretching mode (206). Indeed, the appearance of a medium-intensity band at 274 cm 1 in the infrared spectrum of the mixed-halo species was considered to be the result of absorption by the metal—metal stretching vibration, which was also observed in the Raman spectrum at 274 cm ". ... 

The inert gas hydrogen halide dimers have been extensively used in calculations whose goal is to fit a vibrational potential energy surface to a variety of experimental... 

As demonstrated by Kahn and co-workers, Phillips-Kleinman types of EPs often yield poor results when computing molecular properties (23). This was found to be particularly true for the halide dimers. Figures 2 and 3 show dissociation curves for F2 and Cl2 computed using all-electron and EP two-configuration wave functions. The shape-consistent and all-electron results are in excellent agreement, whereas the curves obtained using Phillips-Kleinman (PK) types of EPs (23) ( Kahn E.P. ), and even those based on a corrected PK EP (24) ( Hay E.P. ), show dramatic deviations, particularly at short bond lengths. It should be noted that the discrepancies between the... 

A number of di- or trimerization reactions of aryl and vinyl halides, which are mechanistically related to those in Eqs. 47-49, have been reported. Interestingly, in the reaction of o-tert-hutyl- and o-methoxyiodobenzenes, the aliphatic C-H bonds in the orf/20-substituents are intramolecularly activated to give di- and trimerized products, respectively, with good yields (Eqs. 51 and 52) [111-114]. These reactions can also be applied to the cross-coupling of different halides. Dimerization of vinyl halides has also been reported [115,116]. 

See Jordan, K. D. Kurtz, H. A. "Theory of Metal Atom-Water Interactions and Alkali Halide Dimers" ACS Symp. Series,... 

Such plots are shown In references Aa and Ab for a range of stoichiometries. These Include the alkali halides, alkali halide dimers, diatomic oxides, nitrides, and sulfides, and molecules of the type MX2. Good agreement with the model is obtained with many species. Including those which are non-lonlcal-ly bonded. 

Milne and Cubicciotti(14) have applied ionic models to calculate the heats of dimerization for gaseous alkali halide dimer molecules, and the results are as follows ... 

The ultraviolet photoelectron spectra of diatomic alkali halide molecules are reviewed and interpreted. Data for lithium halide dimers, 112X2> are presented and it is shown that the dimers have significantly larger ionization thresholds than the corresponding monomers. Some historical controversies regarding the presence of dimers and their ionization energies are clarified. Photoionization mass spectrometry is used to determine the adiabatic ionization potential of lithium chloride trimer, in order to probe the trend of I.P. with cluster size. The predictions of Hartree-Fock, Xa and ionic model calculations on this point are presented. 

The numerical values for these quantities have been extracted and summarized in Table V. These results did not surprise us, since they were predicted by ionic model calculations (19) as well as one ab initio Hartree-Fock calculation for lithium fluoride (20) (a subsequent one is also shown in Table V) which treated both monomer and dimer. However, the trend is opposite to that observed with metal and noble gas dimers, whose I.P. s are lower than the corresponding monomers. It is simply a consequence of the relative bonding strengths of the two units in the neutral and ionic forms. Alakll halide dimers are more stable as neutrals metal and noble gas dimers are generally more stable as ions. 

We have performed Xa calculations on the various lithium halide dimers, from which we have determined the sequence of molecular orbitals, their sjmnnetries and the energy span of the valence band. These calculations [summarized elsewhere (18)] are in reasonable agreement with experiment, and also Indicate that the dimers have a higher first I.P. than the monomers. The geometries chosen for these calculatians were the well-established planar-rhombic structures, with angles and distances taken from electron diffraction and infrared matrix isolation results. 

Electric Dipole Polarizabilities of Alkali Halide Dimers... 

In Figure 3 we show a typical deflection pattern for one of the alkali halide-dimer combinations (RbCl). 

In fact, the situation with regards to the excited states of the monomers Is not much better. The first values for polar-zabllltles of some of the alkali halide dimers were reported at this Symposium by Bederson and co-workers (18). Experimental values of the polarizabilities of the monomers are not available and would be difficult to determine by deflection studies due to contributions resulting from the permanent dipole moments. 

It appears unlikely that the cyclic dimers will have stable anions. Calculations (32) on cyclic (L1H)2 failed to give a stable anion. It Is likely that the quadrupole fields of the cyclic alkali halide dimers are also too small to bind an electron. (Be0)2, which has a much larger quadrupole field, has been shown (33) to have a stable anion. The dissociative attachment process ... 

The remainder of this section will be devoted largely to a summary of recent results from our group on the polarizabilities of LIF and (L1F)2- These represent, respectively, the first calculation of an alkali halide polarizability In which electron correlation effects have been included and the first calculation of a polarizability of an alkali halide dimer. The section concludes with a summary of recent theoretical results for the Ionization potentials for (LlF)jj, n 1-4. 

J., "Electric Dipole Polarizabilities of Alkali Halide Dimers", presented at 181st National ACS Meeting, Atlanta, 1981. 

Zeng, Y. R, Sharpe, S. W., Shin, S. K., Wittig, C., and Beaudet, R. A., Infrared spectroscopy of C02 D(H)Br Molecular structure and its reliability, J. Chem. Phys. 97, 5392-5402 (1992). Muenter, J. S., Potential functions for carbon dioxide-hydrogen halide and hydrogen halide dimer van der Waals complexes, J. Chem. Phys. 103, 1263-1273 (1995). 

The reactions are very fast, and halide ion addition always leads to 77-allylpalladium halide dimers. The cyclopentadienyl moiety has been isolated in the form of cyclopentadiene (reaction with hydrogen chloride), or as a carboxylic acid dimer (reaction with BuLi -f CO2). That part of the attacking reagent bearing positive charge always combines with the C5H5... 

The molecular structure and K-F bond distance were determined by Akishin and Rambidi (2), using electron diffraction with sector microphotoraetry. The bond angles are estimated by comparison with other alkali halide dimers. The vibrational frequencies are taken from Berkowitz (3 ) which were calculated based on an ionic model. The three principal moments of... 

White, et al., ( ) from their spectral data have assigned two observed frequencies and estimated the remaining frequencies using the ionic model calculations of Berkowitz (2) as a guide. They proposed a planar rhombic structure of symmetry, similar to the alkali halide dimers, for the previously undetected LigO molecule, and estimated the angle, 116 , and bond distance, 1.90... 

Benzylic and allylic halides dimerize (homo-couple) readily in the presence of a number of metal species. Synthetically useful yields of homo-coupled products have been obtained using chlorotris(tri-phenylphosphine)cobalt(I), nickel(O) complexes generated in situ, ° Te " species, VCb/LAH, CrCh/LAH and TiCb or TiCl4/LAH. Representative examples are given in equations (37) and (38). Treatment of 8-bromocrotonates with zinc(O) in DMSO leads to dimerization. ... 

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