Benzene complex with

Mercaptobenzothiazole [149-30-4] M 167.2, m 182°, pK 7.5 (50% aq AcOH). Crystd repeatedly from 95% EtOH, or purified by incomplete pptn by dilute H2SO4 from a basic soln, followed by several crystns from acetone/H20 or benzene. Complexes with Ag, Au, Bi, Cd, Hg, Ir, Pt, and Tl. 

An intriguing annulation has been observed upon treatment of a Zr(II)-borata-benzene complex with an alkyne (Scheme 23).38 This reaction is believed to proceed through generation of the normal metallacyclopentadiene intermediate, followed by migration of the Zr—C bond to the electrophilic boron, and then formation of the C—C bond. Both the starting Zr(II) complex and the annulation product have been crystallographically characterized. 

As a 3-step mechanism, the electron-transfer paradigm provides a pair of discrete intermediates [D, A] and D+, A for the prior organization and the activation, respectively, of the donor and the acceptor. The quantitative evaluation of these intermediates would allow the overall second-order reaction (k2) to be determined. Although the presence of [D, A] does not necessarily imply its transformation to D+, A-, a large number and variety of donor/ acceptor couples showing transient charge-transfer absorptions associated with [D, A] have now been identified. In each case, the product can be predicted from the expected behavior of the individual ion radicals D+ and A-. Consider for example, the labile 1 1 benzene complex with bromine that has been isolated at low temperatures and characterized crystallographically (Chart 9).256... 

The nitrosonium cation bears a formal relationship to the well-studied halogens (i.e. X2 = I2, Br2, and Cl2), with both classes of structurally simple diatomic electron acceptors forming an extensive series of intermolecular electron donor-acceptor (EDA) complexes that show well-defined charge-transfer absorption bands in the UV-visible spectral region. Mulliken (1952a,b 1964 Mulliken and Person, 1969) originally identified the three possible nonbonded structures of the halogen complexes as in Chart 7, and the subsequent X-ray studies established the axial form II to be extant in the crystals of the benzene complexes with Cl2 and Br2 (Hassel and Stromme, 1958, 1959). In these 1 1 molecular complexes, the closest approach of the... 

The same conclusion is not applicable to the NO+ complexes, in which the magnitudes of the formation constants are much more strongly dependent on the ionization potential of the arene donor (see Fig. 10A). Thus the factor of >104 that separates the formation constant of the benzene complex with NO+ from that of the hexamethylbenzene complex corresponds to more than 5 kcal mol-1 of extra stabilization energy in the... 

The increased importance of charge transfer in proceeding up the series of NO+ complexes with the enhanced donor strength of arenes that vary from benzene with IP = 9.23 eV to the electron-rich hexamethylbenzene (IP - 7.85 eV) has its chemical consequences with respect to thermal (adiabatic) electron transfer. Thus the benzene complex with Z = 0.52 is persistent in acetonitrile solution for long periods, provided the solution is protected from adventitious moisture and light. By contrast, the hexamethylbenzene complex with Z = 0.97 slowly liberates nitric oxide under... 

Note that despite the death of the carbene-alkene complex in the study of benzylchlorocarbene (53) (see above), benzene is able to modulate the intramolecular reactivity of ferf-butylcarbene. ° Some sort of complex must be involved here. Benzene complexes with carbenes have been proposed before. Kahn and Goodman found a transient species on photolysis of diazomethane in benzene, and attributed it to a complex. Moss et al. found that benzene modulated the ratio of intramolecular rearrangement to intermolecular addition for three different carbenes (53), chloropropylcarbene, and chlorocyclopropylcarbene, and proposed that a carbene-benzene complex 70 favored the intramolecular rearrangement (Scheme 7.31). Their proposal was bolstered by ab initio calculations that found such stable complexes for CCI2 and CH3CCI. 

In the oxidative aromatic substitution of benzene with the nitrosonium cation (NO+), the benzene complex with symmetry 12 has been calculated as a local minimum at the B3LYP/6-31G(d) level of theory with an energy of 48 kcal mol-1 above that of the 7t-complex 13 <1999PCA4261> therefore, the former should not be relevant for the nitrosation mechanism as was previously proposed (Figure 3) <1985RJOC842>. 

U Propagation In a classical study of solvent effect on propagation, Hatada et,al found that the polymerization of vinyl acetate is subjected to significant influence by the solvent. With benzene as solvent essentially no branching was observed. However, in ethyl acetate 0.7 branch per chain (for Mn = 20000) was observed. The reason postulated is that the benzene complexes with the propagating radical to make it more selective. 

The combination of the (CuOTf)2 benzene complex with CS2CO3 also catalyzes C-N bond formation. Coupling of aryl... 

Table 5 Intermolecular interaction energies of the benzene complex with water, amm-nonia and methane ...

Fig. 16 MP2/cc-pVTZ interaction energies of benzene complexes with some halogenated methanes...

Fig. 17 Structures of benzene complexes with hydrocarbon molecules...

The CH/tt interaction is very weak in most cases. The interaction energies of benzene complexes with methane, ethane and ethylene are around -2 kcal/mol, as summarized in Table 6. The attraction is enhanced when electronegative substituents (chlorine and fluorine atoms) are attached to the carbon atom of the C - H bond [112]. The interaction energy of the benzene-chloroform complex (- 5.6 kcal/mol) is considerably greater than that of the benzene-methane complex (- 1.5 kcal/mol). The enhancement of the attraction was explained by the increased electrostatic interaction. The substituent increases the positive charge on the hydrogen atom of the C - H bond and thereby increases the attractive electrostatic interaction. The electrostatic energy in the benzene-chloroform complex (- 2.4 kcal/mol) is 2.2 kcal/mol... 

The sizes of the electrostatic interactions in benzene complexes with methane, ethane and ethylene (interactions with nonsubstituted sp and sp C - H bonds) are very small (absolute values are less than 1 kcal/mol), as shown in Table 6. The electrostatic interaction in the benzene-chloromethane complex (interaction with a monosubstituted sp C-H bond) is also around - 1 kcal/mol. Dispersion is the major source of attraction in these complexes. The only exceptions are the benzene-acetylene complex (interactions with an sp C - H bond) and dichloromethane and chloroform complexes (interactions with a dihalogenated or a trihalogenated sp C - H bond), where the electrostatic interaction is more negative than - 1 kcal/mol [16,112]. Although dispersion is still the major source of the attraction in these complexes, the contribution of the electrostatic interaction is not negligible. 

The strong attraction between a cation and a n system is denoted as a cation/TT interaction. The size of the interaction energy for a cation/zr interaction is considerably larger than that for interactions between aromatic molecules and neutral molecules (tt/tt, OH/tt, NH/tt and CH/n interactions), as shown in Table 7. The experimental interaction energies of benzene complexes with Li, Na and K" " shown in Fig. 18 are -38.5, - 22.1 and - 17.5kcal/mol, respectively [24]. The importance of the cation/ 7r interaction in biological structures and molecular recognition processes has been... 

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