Stepwise coordination reaction

On the basis of DFT calculations, a catalytic cycle involving a copper vinylidene intermediate has been proposed (Scheme 9.22) [44]. The reaction is initiated by copper acetylide (138) formation. Sharpless and coworkers next invoke an unusual [3 + 3]-cycloaddition that would be forbidden by orbital symmetry, were it not stepwise. Coordination of an azide to complex 138 generates a zwitterionic complex (139). Internal nucleophilic attack of the acetylide moiety of 139 on the electrophilic... 

A proposed mechanistic sequence involves stepwise coordination of two molecules of C02 to CpFe(CO)2, followed by formation of Na2C03 and transient formation of CpFe(CO)3+ which quickly reacts with more of the anion to form the dimer. Support for this mechanism comes from the observation that reaction with labeled C02 results in extensive and rapid incorporation of labeled CO in the product dimer. 

We describe here that the redox oligomer wires fabricated with the stepwise coordination method show characteristic electron transport behavior distinct from conventional redox polymers. Redox polymers are representative electron-conducting substances in which redox species are connected to form a polymer wire.21-25 The electron transport was treated according to the concept of redox conduction, based on the dilfusional motion of collective electron transfer pathways, composed of electron hopping terms and/or physical diffusion.17,18,26-30 In the characterization of redox conduction, the Cottrell equation can be applied to the initial current—time curve after the potential step in potential step chronoamperometry (PSCA), which causes the redox reaction of the redox polymer film ... 

While molecular assembly has proven to be effective for a photoelectric conversion system, coordination reactions are possibly a simple approach for connecting such functional molecules, as presented in the previous section. We applied the stepwise coordination method to prepare a photoelectric conversion system. Since the molecular wire exhibits redox conduction through the wire,11,13 efficient photo-electron transport through the redox sites in the wire is also expected. In this section, we demonstrate the fabrication of a photoelectric conversion system using ITO electrodes modified with M(tpy)2 (M = Co, Fe, Zn) complex wires with a terminal porphyrin moiety as a photosensitizer. The behavior of photo-electron transfer from porphyrin to ITO through the molecular wire was investigated by changing the metal element in the M(tpy)2 moieties.14... 

We fabricated the modified ITO electrodes4 by a combination of SAM formation with a terpyridine derivative and stepwise metal-terpyridine coordination reactions in a similar manner as that described in the previous section (Fig. II).11,13 A cleaned ITO was immersed in a 0.1 M solution of 4-[2,2 6, 2"-terpyridin]-4 -yl-benzoic acid (tpy-BzA) in chloroform for 12 h to anchor the carboxyl group to ITO. Subsequently, the modified ITO was immersed in an aqueous solution of 0.1 M CoCl2, Fe(BF4)2 or Zn(BF4)2 for 2—3 h to form metal-terpyridine coordination reactions. Finally, the metal-coordinated ITO was immersed in a 0.1 M acetonitrile solution of a terpyridine-functionalized porphyrin, tpy-ZnTPP, providing the target molecular wires, [M-ZnTPP], on electrodes (Fig. 11). In addition, a cleaned ITO was immersed in a 0.1 M ethanol solution of carboxylate-functionalized porphyrin, C10ZnTPP, to afford a modified ITO as a reference. 

Stepwise coordination by phosphinoalkynes has also been used to build up butterfly clusters. For example, reaction of [Co2(/t,-MeC=CMe)(CO)6] and Ph2PC=CPh affords [Co2(/r.-MeC=CMe)(T71-Ph2PC=CPh)(CO)5] (41), which reacts with [Co2(CO)8] to afford [Co2(/i.-MeC=CMe)(CO)5(/x3-7j3-Ph2PC=CPh)Co2(CO)6] (42), which upon thermolysis rearranges to give the butterfly tetracobalt cluster 43 illustrated in Scheme 16.157... 

Precipitation equilibria are described in part in Chapter 7. An important type of precipitation equilibrium considered here involves a coordination reaction of a metal ion with univalent anions to form an uncharged chelate that is insoluble. In general, it is necessary to consider stepwise equilibria ... 

Asymmetric SBs (65i) having an additional amine nitrogen on one lateral chain to provide a four- and a potential five-coordinate binding site have been prepared by a stepwise template reaction to give mixed CunPbn complexes. The amine nitrogen is involved in coordination to the Pb11 ion. The CunPbn complexes are good precursors for the preparation by transmetallation reactions of CunMn complexes (M = Mn, Fe, Co, Ni, Cu, Zn).180 A series of NinMn (M = Fe, Mn, Co, Ni, Cu, Zn) have also been described.181... 

One of the interesting things about the redox polymers is their use in the creation of the molecular electronic devices.3-5 Redox polymer films on electrodes have been fabricated using chemical modification, electrochemical polymerization, polymer coating, and so on.88 Recently, stepwise complexation methods have been employed to fabricate multiple complex layers.89,90,91 In this section, the stepwise preparation of bis(tpy)metal polymer chains by combining terpyridine (tpy) ligand self-assembled monolayer (SAM) formation and metal-tpy coordination reactions is described as an example. This method realized the formation of a desired number of polymer units and a desired sequence of Co-Fe heterometal structures in the polymer chain.92... 

An example of this approach is represented by the growth of 3-D coordination polymers with SCO properties via stepwise adsorption reactions for multilayer films based entirely on intra- and interlayer coordination bonds Fe(pyrazine) [Pt(CN) ] [218, 219], Indeed, after functionalization of the surface with the appropriate anchoring layer the coordination polymer is built in a stepwise fashion, alternating the metal ion (Fe "), the platinum salt ([Pt(CN) ] ), and pyrazine. The polymer shows many interesting properties, with the SCO transition accompanied by a variation in the dielectric constant of the material accompanied by a room temperature hysteresis of the dielectric constants. This dielectric hysteretic property may be useful in building molecular memory devices that can store information by high- and low-capacitance states. What must be remarked here is that these appealing properties cannot be exploited in bulk materials, but only in thin films. 

The major developments of catalytic enantioselective cycloaddition reactions of carbonyl compounds with conjugated dienes have been presented. A variety of chiral catalysts is available for the different types of carbonyl compound. For unactivated aldehydes chiral catalysts such as BINOL-aluminum(III), BINOL-tita-nium(IV), acyloxylborane(III), and tridentate Schiff base chromium(III) complexes can catalyze highly diastereo- and enantioselective cycloaddition reactions. The mechanism of these reactions can be a stepwise pathway via a Mukaiyama aldol intermediate or a concerted mechanism. For a-dicarbonyl compounds, which can coordinate to the chiral catalyst in a bidentate fashion, the chiral BOX-copper(II)... 

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