Benzene metal interaction

I.4.2.6. 1-Deuterio Aldehydes Asymmetric hydrogenation of 1-deuterio benzaldehydes with Ru(OCOCH3)2[(5)-binap] in the presence of 5 equiv. of HC1 gives the corresponding chiral 1-deuterio alcohols with up to 89% ee (Scheme 1.75) [280]. The heteroatom substitution at the C2 position in the benzene ring tends to increase the enantioselectivity due to the heteroa-tom/metal interaction. This catalyst is less reactive in deuteration of benzaldehyde. 

Dienes are four-electron donors. Alkynes are four-electron donors when they use one 7r bond to form a cr bond and the other ir bond to form a 7r bond to metal orbitals of the proper symmetry. When only two of the three 7r bonds in a benzene ring interact with a metal, the ring is a four-electron donor. 

Taylor came to the conclusion that the olefin exchange and related reactions occurred by the associative mechanism. On the other hand in the case of the benzene-deuterium interaction on metal films he quoted the work of Anderson and Kemball (80-82) which indicated the validity of the dissociative mechanism for the exchange. 

Reaction of 3 with dialkylating agents such as 1,2-dibromoethane or l,4-bis(bromomethyl)-benzene allows to produce protected bis-macrocycles of type 4, the tosyl groups of which can then be cleaved off to give the polyamines 5. The interest in these ligands comes from the fact that the two rings are kept at different distances, thus allowing to study the effect of metal-metal interactions as a function of their separation. 

For the current discussion, RVS analysis has been carried out on cation-jt complexes of benzene-metal complexes. An overview of the results obtained for the RVS analysis carried out at the HF/6-31G level on the cation-jt complexes of benzene with monovalent and bivalent metal ions such as LP, Na, K, Mg and Ca + is presented in Figure 15.5. Generally, cation- t complexes are held by pure electrostatic effects due to strong attraction between opposite charges. Hence, bivalent metal ions show stronger interaction than the monovalent metal ions. However, the contribution of ion-quadrupole interactions in complex stabilization is still being... 

The metal-ion complexmg properties of crown ethers are clearly evident m their effects on the solubility and reactivity of ionic compounds m nonpolar media Potassium fluoride (KF) is ionic and practically insoluble m benzene alone but dissolves m it when 18 crown 6 is present This happens because of the electron distribution of 18 crown 6 as shown m Figure 16 2a The electrostatic potential surface consists of essentially two regions an electron rich interior associated with the oxygens and a hydrocarbon like exterior associated with the CH2 groups When KF is added to a solution of 18 crown 6 m benzene potassium ion (K ) interacts with the oxygens of the crown ether to form a Lewis acid Lewis base complex As can be seen m the space filling model of this... 

In the case of ions, the repulsive interaction can be altered to an attractive interaction if an ion of opposite charge is simultaneously adsorbed. In a solution containing inhibitive anions and cations the adsorption of both ions may be enhanced and the inhibitive efficiency greatly increased compared to solutions of the individual ions. Thus, synergistic inhibitive effects occur in such mixtures of anionic and cationic inhibitors . These synergistic effects are particularly well defined in solutions containing halide ions, I. Br , Cl", with other inhibitors such as quaternary ammonium cations , alkyl benzene pyridinium cations , and various types of amines . It seems likely that co-ordinate-bond interactions also play some part in these synergistic effects, particularly in the interaction of the halide ions with the metal surfaces and with some amines . 

Borazine is isoelectronic and isostructural with benzene and may act as a six-electron donor in complex chemistry. In contrast to arene ligands of arene-transi-tion-metal complexes, coordinated borazines lose their planarity and are slightly puckered . Nevertheless, the B atoms show interactions with metal atoms. 

Supercomputers become more and more useful, and the Insights they can generate become more and more unique, as the complexity of the system modelled Is Increased. Thus Interfaclal phenomena are a very natural field for supercomputation. In addition to the examples In this volume It may be useful to mention the work of Llnse on liquid-liquid benzene-water interfaces, which he studied with 504 H2O molecules, 144 CgHg molecules, and 3700 Interaction sites. He generated over 50 million configurations In 56 hours on a Cray-lA, and he was able to quantitatively assess the sharpness of the Interfaclal density gradient, which Is very hard to probe experimentally. Similarly Spohr and Helnzlnger have studied orientational polarization of H2O molecules at a metallic Interface, which is also hard to probe experimentally. 

---