Bridged polymer

Titanium Tetrafluoride. Titanium tetrafluoride [7783-63-3] is a white hygroscopic soHd, density 2798 kg/m, that sublimes at 284°C. The properties suggest that it is a fluorine-bridged polymer in which the titanium is six-coordinate. The preferred method of preparation is by direct fluorination of titanium sponge at 200°C in a flow system. At this temperature, the product is sufficiently volatile that it does not protect the unreacted sponge and the reaction proceeds to completion. The reaction of titanium tetrachloride with cooled, anhydrous, Hquid hydrogen fluoride may be used if pure hydrogen fluoride is available. 

Several demonstrations of this concept have recently been published The first one is based on the pH dependence of redox transitions in oxide semiconductors that are connected with conductivity changes. If the bridging polymer layer in Fig. 6 is WO3 sputtered onto the electrode array or electrochemically deposited Ni(OH)j the transistor amplification is a function of the pH of the... 

The bridging polymer is a conducting poly(3-methyIthiophene) or polyaniline and the solid state redox conduction between all electrodes is accomplished by a common coating with poly(ethyleneoxide)/Li" CF3S03- or poly(vinyl alcohol)/ The polyaniline based molecular transistor proved as a very sensitive moisture detector it works well in a dry argon atmosphere but in water saturated argon the device cuts out... 

Figure 6 Steady state rotating ring-disk voltammograms of (A) compound (42) (B) compound (43) and (C) a Ru-bridged polymer of (43) each adsorbed to a graphite working electrode. Disk current shows reduction of 02 while ring current reveals the presence of H202 simultaneously reoxidised at the ring anode poised at +1.0 V (reproduced with permission of the American Chemical Society from Acc. Chem. Res., 1997, 30, 437-444).

A number of insoluble or immobilized catalysts have been developed and applied to the carbonyl-ene reaction. As is evidenced by the entries below, the enantioselectivities are variable. Sasai23 has utilized a titanium-bridged polymer to effect an enantioselective carbonyl-ene (Equation (14)). A single substrate was examined, and the polymer could be reused up to five times without loss of enantioselectivity in the ene reaction. 

Bunz UHF (2003) In Grubbs RH (ed) Handbook of metathesis. WUey-VCH, 3 354-370 Acyclic diyne metathesis utilizing in situ transition metal catalysts an efficient access to alkyne-bridged polymers... 

The reagent stoich. fran -Ru(0)3(0Ac)3(py)3/CH3CN oxidised Ph3P to Ph3PO giving what may be Ru" (0)(OAc)(py)3 or a p-oxo bridged polymer. Linear and cyclic alkenes were epoxidised with additional by-products hydrocarbons and... 

Potassium hexafluorovanadate(IV) can be prepared from [VF4] and KF in selenium tetrafluoride(III)416 or by fluorination of K2VF5 for example. K+, Rb+ and Cs+ salts obey the Curie-Weiss law with high values of 6. [VF4] reacts with py and NH3 forming [VF4L], probably fluorine-bridged polymers.416... 

Chromium(II) complexes of bipyridyls, terpyridyl and the phenanthrolines have been discussed in Section 35.2.2.1. Complexes of the ligands 2-aminomethylpyridine (pic, 2-picolyl-amine) and 8-aminoquinoline (amq), which have one heterocyclic and one amino nitrogen donor atom, have been prepared by methods similar to those in Scheme 10. The bis(amine) complexes are typical high-spin, distorted octahedral complexes, and the mono(amine) complexes, from their antiferromagnetic behaviour and reflectance spectra, are six-coordinate, halide-bridged polymers (Table 15).103 No tris(amine) complexes could be prepared so the attempt to find spin isomeric systems in octahedral chromium(II) systems was unsuccessful ([Cr(en)3]X2 are high-spin and [Cr(bipy)3]X3 and [CrX2(bipy)2] low-spin). 

When simple nickel(II) salts are treated with thiols, in most cases stable thiolate-bridged polymers are formed. In a number of cases, treating these polymers with either tertiary phosphines or isocyanides gave mononuclear mixed-ligand complexes (equation 204).1951 These mononuclear complexes, due to the presence of terminal thiolates which possess lone pairs, can further react with nickel(II) and give trinuclear complexes (equation 205).1952... 

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