Tripod scheme

Figure 3.16 Left panel Sketch of the tripod scheme involving three discrete states coupled via a common continuum by three lasers. Right panel Population of the discrete states and the ionization probability versus the pulse width of the pump and Stokes pulses within the counter-intuitive pulse order. Taken from Ref. [95].

A tripodal imidazolium salt 13 was obtained by Howarth from enantiopure imidazoles 14 (Scheme 10) by reaction with l,3,5-tris(bromomethyl)-2,4,6-trimethyl benzene [19]. 

Iron(II) complex of tris(N -tert-butylurea-ylato)-N-ethylene]aminato activates dioxygen at room temperature to afford an iron(III) complex containing a single terminal oxo ligand. X-ray structures show that the three urea molecules act as a tridentate N,N,N-hgand [52]. The tripodal ligand was also used to synthesise complexes of cobalt, iron or zinc with terminal hydroxo ligands (Scheme 8) [53]. 

The tripodal ligand (550) with N2OS donor set reacts with Ni(0Ac)2 4H20 or Ni(C104)2 6H20 to give multinuclear Ni11 complexes (Scheme 7). 

Fig. 9. Scheme for syntheses of rhenium complexes with tetradentate NS, tripod ligands (R-NC R = CH2COOCH3)... 

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... 

Another example of selective C=C bond hydrogenation has arisen from mechanistic studies on an iron m-hydride dihydrogen complex, [Fe(PP3)(FI)(H2)](BF4) [PP3 = P(CH2CH2PPh2)3], a catalyst inactive with alkene substrates. Scheme 6 shows that no decoordination of dihydrogen is required in any step of the cycle and that the vacant site is created by unfastening of one of the P-donor atoms (species (16)).50 Extensive studies on catalytic alkene hydrogenation by analogous tripodal (polyphosphine) Rh, Os, and Ir complexes have been carried by Bianchini and co-workers.51,52... 

Scheme 28 Synthesis of sulfide tripod-terminated polysilanes.

A homochiral tripod ligand thus can be obtained from a C2 symmetric precursor without additional separation of enantiomers or diastereomers. As an example for this concept we chose bis(camphor-pyrazol-l-yl)methane as starting material to afford an enantiopure but C2 symmetric bidentate ligand which is obtained in three steps from (-l-)-camphor (Scheme 17). 

To examine the chemical behavior of these new ligands 48-50 in coordination chemistry, tricarbonyl complexes with manganese and rhenium were synthesized from [MnBr(CO)s] and [ReBrCCOls] as described earlier for the other heteroscorpionate ligands (Scheme 28). The purpose of these tricarbonyl complexes was to verify tripodal binding of the solid-bound ligand. The protected OH linker in 50 acts as model for the solid phase bound ligand. 

SiO)3Ti-H and (=SiO)3Ti species react very easily with alcohols to give titanium tris-siloxy mono-alkoxy. Step by step, following the methods described in Scheme 2.10, it is thus possible to obtain well-defined mono-, bi- or tripodal complexes that have been characterized by chemical analysis and by chemical and spectroscopic methods such as IR and solid-state NMR ( H and C). 

The tripodal tin surface complex MsSnBu has been isolated on a Pt/Si02 catalyst [124]. EXAFS measurements carried out at the SnK edge indicated that tin was surrounded by three platinum atoms (0.2716 nm) and one carbon atom (0.212 nm) (Scheme 2.39). 

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