Transition metal templates

The yield of 7 might have been higher had a transition metal template been used, but to our knowledge, this has not been tried. 

An 18-membered N3O3 macrocycle could not be synthesized with transition metal templates but the N402 analog (85) was successfully synthesized with a zinc template. This gave dinuclear /r-hydroxy bridged zinc complexes including a rare example of a single unsupported... 

Blanco, M.-J., Transition-Metal-Templated Synthesis of Rotaxanes, 23, 125. 

The use of transition metal templates represents a particularly intriguing strategy to selectively accomplish [6 + 4] cycloadditions, as was shown first in the Kreiter laboratories302. Chromium(O) has emerged as the metal of choice in this kind of cycloaddition reaction which is either thermally or photochemically activated291. 

Goral, V. Nelen, M. I. Eliseev, A. V. Lehn, J. M. Double-level orthogonal dynamic combinatorial libraries on transition metal template. Proc. Natl. Acad. Sci. U.S.A. 2001,98,1347-1352. 

B. M. Trost, Transition metal templates for selectivity in organic synthesis, Pure Appl. Chem. 53 2357 (1981). 

Some radical reactions occur under the control of transition metal templates. The first example of asymmetric creation of an asymmetric carbon with a halogen atom is shown by the a DIOP-Rh(I) complex-catalyzed addition of bromotrichloromethane to styrene, which occurs with 32% enantioselectivity (Scheme 99) (233). Ru(II) complexes with DIOP or BINAP ligands promote addition of arenesulfonyl chlorides to afford the products in 25-40% ee (234). A reaction mechanism involving radical redox transfer chain process has been proposed. 

Chambron, Jean-Claude, Rotaxanes From Random to Transition Metal-templated Threading of Rings at the Molecular Level, 5, 225. 

Rigby, J.H. and Henshilwood, J.A. (1991) Transition metal template controlled cydoaddition reactions. An efficient chromium(0)-mediated [6it + 2it] cydoaddition. Journal of the American Chemical Society, 113, 5122—5123. 

The early history of phthalocyanines is a quite bizarre and tragic. They are easily synthesized by a transition metal templated cyclocondensation of phthalonitrile, however, this was not how they were discovered. It is probable that a metal-free phthalocyanine was successfully prepared by Braun and Tcherniac in the early 1900s though it was not characterized [9], Given their synthetic methods it is also probable that de Diesbach and von der Weid were the first to prepare copper phthalocyanine but, again, their 1927 paper gives no characterization details [10]. 

Transition metal-templated formation of [2]-catenanes and [2]-rotaxanes... 

In the early 1980s, a transition-metal template strategy for the synthesis of catenanes was developed in our laboratory.9 It is based on the ability of Cu(I) to entwine two diphenylphenanthroline molecules in such a way that the coordination geometry around the metal is tetrahedral. Thus catenanes... 

This chapter will be concerned mainly with the transition-metal-templated synthesis of rotaxanes. General features of these compounds, including stereochemical issues, will be addressed at first. The intent, however, is not to... 

The earliest syntheses of rotaxanes were largely based on the statistical or directed methods.2,3 Statistical methods require very precise reaction conditions, and directed methods involve numerous chemicals steps. However, the use of templates allows high control of these synthetic methods resulting in efficient and precise assemblies of rotaxanes that incorporate a wide range of chemical functionalities. Two types of interactions occur in synthetic template methods (1) purely organic and (2) transition-metal-templated. In this latter case, the template can easily be removed at the end of the synthesis, whereas in the former, the interactions between the template and the components of the final rotaxane will often be maintained. Selected examples will now illustrate the statistical, the directed, and templated strategies outlined above. The transition-metal-templated route will be developed separately. 

III. TRANSITION-METAL-TEMPLATED SYNTHESIS A. Principle and Examples... 

Figure 2.22. Strategies for the transition metal-templated synthesis of catenanes. The metal (in) predisposes two fragments as open chelates (A) (strategy I) or as a macrocyclic chelate (E) and an open chelate (strategy II) in intermediates (B) and (F), respectively. Cyclization of these intermediate complexes with the chain fragments (C) provides the [2]-catenate complex (D).

---