Bis zincs

Reek, van Leeuwen et al. have also reported the template-induced generation of bidentate ligands onto a rigid bis-zinc(II) salphen platform. Homobidentate [41] or heterobidentate [42] P,P-ligands have been prepared and tested in hydroformylation and hydrogenation reactions. 

Kuil, M., Goudriaan, P.E., Kleij, A.W, Tooke, D.M., Spek, A.L., van Leeuwen, P.W.N.M. and Reek, J.N.H. (2007) Rigid bis-zinc(ll) salphenbuilding blocks forthe formation of template-assisted bidentate ligands and their application in catalysis. Dalton Trans, 2311-2320. 

The reaction of 1,4-bis-zinc derivatives with CuCN-2LiCl allows the preparation of a range of new polyfunctional zinc-copper reagents.309 They undergo selectively 1,4-additions on a,/3-ethylenic ketones in the presence of TMSC1 providing a new zinc-copper reagent, which can react with another electrophile (Equation (175)). 

Most chemical reactions and spectroscopic work are carried out in solution. However, recent investigations have shown great potential for solid-state chemistry. First, supramolecular systems consisting of more than one kind of molecule exhibit characteristics that are different from those of the individual molecules. We have recently reported inverted supramolecular chirality of bis(zinc octae-thylporphyrin), an enantiopure monoamine system in solution and in the solid phase [3]. Secondly, solid-state reactions occur more frequently than previously envisaged [4-7], and they may give products in high yield that are unobtainable by reaction in solution. They are kind to the environment because of their solvent-free nature and hence are currently attracting attention from the industrial sector as well. Compared with thermal or chemical reactions, photochemistry is particularly... 

B sub group metals are rather more covalent in character, those of Gps IIB and IIIB being nearer true metals than Se, Te, As, Sb and Bi. Zinc and cadmium, for example, have distorted, close-packed hexagonal arrangements in which the axial ratios are about 1.87 instead of the ideal 1.63 (Fig. 80). Aluminium and indium have approximately face-centred cubic lattices, and thallium has a close-packed hexagonal one. In Gp.VIB, white tin possesses a character between that of lead and silicon its co-ordi-... 

The first double-helical metal complex described was the tetrahedral bis(zinc formylbiliverdinate) (Figure 5.34). The helical dimer forms spontaneously, if the planar monomeric zinc complex, which carries an axial water ligand, is dehydrated by HCl" . 

Ojida, A. Mito-oka, Y. Sada, K. Hamachi, I., Molecular recognition and fluorescence sensing of monophosphorylated peptides in aqueous solution by bis(zinc(II)-dipicolylamine)-based artificial receptors,./. Am. Chem. Soc. 2004, 126, 2454-2463... 

Synthesis and molecular structure of two bis(zinc-dioxolene) complexes have been also described.186 The [ Zn(TpCum,Me) 2(L-H2)] derivative in Fig. 3.39 has two protonated catecholate ligands, whereas [ Zn(TpCum,Me) 2(L-H)] has one protonated catecholate and one semiquinone ligand. 

Rotaxanes made of a pendant gold-porphyrin macrocycle threaded inside a bis zinc-porphyrin stoppered dumbbell were built using a template approach, in order to assemble the two parts of the system, the dumbbell and the macrocycle. The template principle of construction is depicted in Fig. 11. 

A similar design led Hunter to the porphyrin pentamer 91 in which a free base bearing four articulated pyridyl arms is chelated twice by bis-zinc porphyrin tweezers . The stmcture depicted in Figure 13.52 shows a high association constant of 2.0 0.5 X 10 (vs. 10 for usual ZnP-Py coordination). Upon excitation at 562 nm, isolated species have rather usual fluorescence decay times of 1,330 ps for the zinc porphyrin tweezers, and 9,500 ps for the free base tetradentate. After complete assembly, an energy transfer is observed at the rate of 2 x 10 s , with a 73% quantum yield. 

Table 13.13. Transient Absorption Maxima and Decay Lifetime of bis-(zinc porphyrins).

Bis(zinc porphyrin)-oxoporphyrinogen [(ZnTPP)2-OxP] is an example of a donor-acceptor-type triad. Excitation of the zinc porphyrin gronps leads to an efficient energy or electron transfer in the triad and this process depends on the polarity of the solvent used. Further elaboration of this system was accomplished by complexing this compound and other derivatives with fullerene-containing compounds capable of coordinating at the porphyrin zinc metal ions. The structures of the complexes are shown in Figure 14. 

Furan-Benzene. Pelter et al. [811,812] have chemically prepared structural isomers of furan-phenylene copolymers by reacting bis-zinc chlorides of l,4-bis(2-furanyl)phenylenes with 1,3- and 1,4-dibromobenzene. The group of Reynolds has also investigated these copolymers [817,821] (Fig. 56). 

Twyman and King [77] constructed a (AA - BB) -type coordination polymer from a rigid bis(zinc porphyrin) imit 22 and a flexible ditopic pyridine... 

Pd-catalyzed cross-coupling of the bis-zinc homoenolate 391 with o-tolylbromide ... 

Based on this hypothesis, we had developed an asymmetric Simmons- mith reaction to allylic alcohols. When allylic alcohol 1 was treated successively with diethylzinc, diethyl (R,R)-tartrate [(RJ )-DET], and a second diethylzinc, the dinucleating intermediate 2 possessing an ethylzinc moiety might be generated. To the intermediate is added diiodomethane, ethyl-zinc moiety acts as a reductant resulting in the formation of the bis-zinc containing intermediate 3, which has an iodomethyl zinc moiety. Ensuing Simmons mith reaction within this complex is expected to proceed enantioselectively (Eq. 11.2). 

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