Tripod coupling

In order to gain more direct access to these bicyclic ligands, methods have been developed which allow the formation of the macrobicycle in one step. The tripod-tripod coupling is an example of this method (Fig. 5.2) which may be performed without the need for high-dilution conditions. The synthesis of the bis-tren macrobicycle, 17, illustrates this approach.3... 

The first reported synthesis of this compound involved the stepwise procedure described in Scheme 5.8.5 One can note that there are two cyclization reactions which were accomplished in 59% and 60% yields. The synthesis required ten steps and the overall yield was 7%. In order to gain more direct access to the macrobicyclic compound a shorter route involving a tripod-tripod coupling sequence was developed (Scheme 5.9). 

The following procedure for the synthesis of macrobicycle 16 is representative of the tripod-tripod coupling reaction. 

Some major strategies (45) developed for the synthesis of cryptands are illustrated in Scheme 1 and are termed (1) stepwise, (2) tripodal coupling,... 

Synthesis of macrobicycUc polyamines by direct macrohicyclisation via tripode-tripode coupling. Helv Chim Acta 68 289-299... 

Scheme 12.82 Synthesis under high-dilution conditions of the macrobicyclic products 230-232 by a tripod-coupling reaction of preorganized trisphenol 229...

In the bifunctional radiopharmaceuticals, Tc and Re complexes that are suitable for coupling to antibodies are almost square-pyramidal oxo complexes of tetradentate ligands, as mentioned earlier. Spies et al. [65] recently studied the syntheses and structures of rhenium complexes with a tetradentate NS3 tripod ligand 2, 2,, 2"-nitrilotris(ethanethiol) (l in Fig. 9) as an interesting alternative to the oxo complex. Such ligands could lead to weakly polar, trigonal-bipyramidal complexes in which the metal atom is more strongly shielded than in the square-pyramidal oxo complexes. Schemes for the syntheses... 

The presence of two types of titanium sites in TS-1 (tetra- and tripodal) was also suggested by the cyclic voltametry experiments of Bodoardo et al. (158). The tripodal Ti(OSi)3(OH) showed a redox couple at 0 V and the tetrapodal Ti(OSi)4... 

We have performed Spin-Coupled calculations on a series of selected carbonium ions (55). The Spin-Coupled calculations allow the study of chemical structure of die molecule, since chemical structure and connectivity are central features of VB theory. Spin-Coupled calculations for CHS+ in CSI show the system as bonded by the intuitively proposed 3c2e bond, which connects the carbon atom to two hydrogens, and three ordinary 2c2e bonds between the carbon and the other hydrogens, commonly called the tripod (Figure 3). 

The structures of the bis-ligand iron(II) complexes of the tripodal ligands tris(pyrazol-l-yl)methane and bis(pyrazol-l-yl)(pyridin-2-yl)methane have been determined the former is a spin cross-over complex." " Polybis(pyrazolateiiron(II) has a ID chain structure with the Fe " " ions doubly bridged by pyrazolates the Fe + ions (-S = 2) are weakly antiferromagnetically coupled. ... 

The accurate calculation of the resonance frequencies of a tripod scanner is a complicated problem. The flexing modes are effectively coupled with the stretching modes. An evaluation of the lowest resonance frequency of the flexing mode provides an order-of-magnitude estimation of the lowest resonance frequency of the tripod scanner. For a piezo made of PZT-5A, 20 mm long and 2 mm thick, the radius of gyration is 2 mm/y/ 2 = 0.577 mm. The speed of sound is about 2.8 km/sec. Using Eq. (9.44), the resonance frequency is found to be 3.3 kHz, which is close to the values often observed experimentally. 

The following synthesis of OBISTREN is carried out by the coupling of two tripodal subunits, by triple C—N bond formation without the use of high-dilution conditions. The procedure was first described by Dietrich et al.14 and was later modified by Motekaitis et al.3 It had previously been synthesized by a stepwise procedure requiring a high-dilution step.10 The tripodal synthetic method has been used to synthesize several analogs of OBISTREN.14 The procedure used here is described in detail by Chen et al.15... 

Si-Si coupling and Si-X functionalization had to be modified and extended. The preparation of CH3Si[Si(CH3)3]3 is based on the procedure reported by Marsmann et al.6 The functionalization of the branched-chain silane occurs by the method introduced by Ishikawa et al.7,8 and leads to the desired trichloro-derivative,9 which can easily be converted to a tripodal amine by aminolysis with a primary amine.5... 

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