Mercury center

Hawthorne and co-workers have also produced a series of macrocyclic Lewis acid hosts called mercuracarborands (156, 157, and 158) (Fig. 84) with structures incorporating electron-withdrawing icosahedral carboranes and electrophilic mercury centers. They were synthesized by a kinetic halide ion template effect that afforded tetrameric cycles or cyclic trimers in the presence or absence of halide ion templates, respectively.163 These complexes, which can bind a variety of electron-rich guests, are ideal for catalytic and ion-sensing applications, as well as for the assembly of supramolecular architectures. 

Figure 84 Macrocyclic mercuracarborands (156, 157, and 158) with structures incorporating electron-withdrawing icosahedral carboranes and electrophilic mercury centers. (Adapted from ref. 163.)... 

Organolithium reagents stabilized by ct-silyl groups have been recently used for the synthesis of mononuclear derivatives such as compounds 8, 9 which the bulky (PhMe2Si>3C and (Me3Si>3C as ligands directly attached to the mercury center.30 Other examples include the dialkylmercury products shown in Equations (2) and (3).31 32... 

In the solid state, the pyridine nitrogen atom of compound 10 forms secondary interactions with the mercury center. Intramolecular coordination of the nitrogen atom is, however, not observed in derivative 11 in which N —> Si 7t-bonding possibly monopolizes the nitrogen lone pair. 

The mercuration of ferrocenylimines with Hg(OAc)2 has been studied. - 6 Mercuration occurs selectively at the a-position relative to the imine group to afford compounds 86a-i (Scheme gy107,108 The regioselectivity of these reactions points to the directing role of the Lewis-basic imine functionality. Similar factors probably play a role in the formation of the ferrocenylketone and ferrocenylaldehyde derivatives 87a-f and 87g-j, respectively. These derivatives readily react with amines to afford the corresponding imines (Scheme 9). Presumably, the Lewis-acidic mercury center of the monomercurated ferrocenylketones and ferrocenylaldehydes activates the carbonyl functionality toward nucleophilic attack by the amine. 

The centrosymmetrical complex 154, formed by interaction of the quinolyl ligand with HgCl2, features intramolecular coordination of one of the cyclopentadiene C=C bonds to the mercury center. The resulting Hg-C(sp2) distances of 2.81 and 2.88 A are longer than typical Hg-C c-bonds but remain much shorter than the sum of the van der Waals radii. This dihapto interaction does not result in a significant lengthening of the coordinated C=C... 

The reaction of tetraethynylplatinum derivatives with mercury dihalide in acetone affords complexes 156 and 157 in which the mercury centers are coordinated to two neighboring mercury alkynyl functionalities.194 195 In turn, each alkynyl functionality interacts with the mercury center in an 7]Z-fashion. For complexes 156 and 157, the resulting Hg-Cjp bonds, which range from 2.41 to 2.77 A, are longer than typical Hg-C cr-bonds but shorter that those observed in 154. In 156, the greater flexibility of the structure allows for the formation of shorter Hg-C(.r/>) bonds than in 157 (av. Hg-C(.r/>) = 2.52 A for 156 and 2.64A for 157). The formation of such complexes is not limited to the case of... 

Another remarkable example of a mercuracarborand halide adduct has been obtained by reaction of the octamethyl tetranuclear derivative 165 with [NMe4]F. This reaction affords complex [165-F]- in which the fluoride is coordinated to the four mercury centers in an approximate square-planar arrangement (Equation (57)). The Hg-F distances, which range from 2.56 to 2.65 A, are slightly longer than those found in [163-/i2-F]2. The 9Hg NMR resonance of the complex indicates coupling to the fluorine atom with 1Jug-F = 698 Hz.215... 

The reaction of the tetranuclear mercuracarborand 166 with 2 or 3 equiv. of KNO3/I8-C-6 in acetone affords two different nitrate complexes namely [166-(N03)2(H20)]2 and [166-(N03)2]2 (Figures 15 and 16). In both cases, the nitrate anions are ligated to the mercury centers by Hg-O interactions ranging from 2.60 to 3.08 A. In [166-(N03)2]2, the two anions coordinate with all four mercury atoms in a face-on trihapto fashion from either side of the plane.216... 

Polynuclear organomercurials featuring proximal mercury centers have often been considered as multidentate Lewis acids. This research area has witnessed some noteworthy developments which will be summarized in the following sections. 

Interaction of 137 with dimethyl sulfide in 1,2-dichloroethane leads to the formation of the polymeric adduct [137-/t6-Me2S] , which features sandwiched dimethyl sulfide molecules (Figure 22).233 The sulfur atom of the latter interacts simultaneously with the mercury centers of two neighboring molecules of 137 and thereby achieves hexacoordination. 

Polyfunctional organomercurials have emerged as useful building blocks for the construction of supramolecular species. Compound 137, for instance, was shown to complex benzene, yielding extended binary stacks where the two components alternate (Figure 25).235 These stacks are rather compact (centroid distance of 3.24 A), so that secondary 7t-interactions occur between the benzene molecule and the mercury centers. Each of the six C-C bonds of the benzene molecule interacts with one of the six mercury centers of the two juxtaposed molecules of 137. As a result, the benzene is hexacoordinated in a fashion. The strength of the Hg-C interactions must... 

The Moon center, the pituitary body, is situated just beneath the pineal gland (the Mercury center), which represents the Philosopher s Stone. The Stone is sometimes called the Seed of the Sun and, in sacred art, is often portrayed as a flaming disc. On the ceremonial crowns of certain high lamas, there is often shown the symbol of a lunar crescent, lying on its back, holding a radiant disc. This refers to the crown-wearer s realization of the ultimate nature of reality and their ability to... 

One of the purposes for attaining the Stone of the Wise enshrined in the Mercury center (astrologically, Mercury rules communication) is to produce a receptor capable of receiving the more rarefied spiritual influences and an organism capable of transmitting them. Selfish salvation there is none. It is for all others, as well as for ourselves, that we undertake the Work. Likewise, in Mahayana Buddhism, all rituals and meditations end with the dedication that Whatever benefits are accrued may help all beings to reach Enlightenment. ... 

Mercury Center (Quicksilver) Yellow square charged with a second yellow square. 

Turning our attention to the Turret Room of Da ath, to the right of the eastern serpent-framed window, there is a purple pull-rope. It is used to lower or raise a trapdoor in the ceiling ornamented with the Prithivi-Prithivi symbol of the Mercury center, and from it comes a ladder that enables one to ascend to the battlements of the tower, which correspond to the crown center, the Sahasrara-padma, the thousand-petaled Lotus. 

Yang, X. G., Knobler, C. B., Zheng, Z. P., Hawthorne, M. F., Host-guest chemistry of a new class of macrocyclic multidentate lewis-acids comprised of carborane-supported electrophilic mercury centers. J. Am. Chem. Soc. 1994,116, 7142-7159. 

All of these complexes display a strong visible luminescence under UV excitation, which is sensitive to the interaction of the gold atoms with the mercury centers. Thus in Hg(-C,C-C6F4 ]3([AuC(0-R)=NR ]3)2 and Hg (p.-C,C-C6F4)3([Au(p,-C2,N3-Rim)]3)2 ra an increase of the intensity upon coordination of mercury to the starting gold materials was observed. 

Thus, the toxicity of DMM is mediated by its dealkylation. Cleavage of the carbon-mercury bond generates MMM metabolites, which can form covalent bonds with cellular ligands with amphiphilic properties. The mercury center reacts with sulfur and sulfur-containing thiol groups of enzymes and thereby inhibits them. The metal center of DMM acts as a soft acid, and binds tightly to polarizable donor atoms in soft bases. Within cells, mercury may interact with a variety of proteins, particularly microsomal and mitochondrial enzymes. This can severely impair cell function. 

Recently, a hexamethyl[9]mercuracarborand-3 derivative has been reported (105). This receptor showed smaller shifts in its 199Hg NMR peaks on anion complexation, probably due to the methyl groups making the mercury centers less electron deficient. Chloride ions formed 1 1 complexes, while bromide and iodide formed complexes of 2 1 stoichiometry. 

A tetraphenyl substituted derivative of [12]mercuracarborand-4 (40), which binds one iodide ion in its cavity due to steric hinderance, has been reported. The stereochemistry of the phenyl groups was found to depend on the mercury counteranion used during the synthesis (106). This observation provided yet further evidence for a direct anion templating effect in mercuracarborane syntheses. Most recently, the C—Hg—C link in this type of host has been replaced with a B—Hg—B link, which alters the electron demands of the mercury centers (reducing their electron deficiency) and apparently switches off anion complexation (107). 

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