Quinone Methide Stabilization by Metal Complexation

Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel 

Coordination of reactive and/or unstable molecules to metal centers is a useful approach for their stabilization,1 and it presents unique opportunities for their characterization by spectroscopic methods and for elucidation of their structure. Moreover, under appropriate conditions the coordinated species can be chemically modified. In addition, displacement of the coordinated compound from the metal and its trapping in solution by reactions with suitable substrates can form the basis for useful synthetic methodology. 

Quinone Methides, Edited by Steven E. Rokita Copyright 2009 John Wiley Sons, Inc., Publication. 

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Vigalok, A. Shimon, L. J. W. Milstein, D. Methylene arenium cations via quinone methides and xylylenes stabilized by metal complexation. J. Am. Chem. Soc. 1998, 120, 477 183. 

An alternative route for stabilization of quinone methides by metal coordination involves deprotonation of a ri5-coordinated oxo-dienyl ligand. This approach was introduced by Amouri and coworkers, who showed that treatment of the [Cp Ir(oxo-ri5-dienyl)]+ B1, 22 with a base (i-BuOK was the most effective) resulted in formation of stable Cp Ir(r 4-o-QM) complexes 23 (Scheme 3.14).25 Using the same approach, a series of r 4-o-QM complexes of rhodium was prepared (Scheme 3.14)26 Structural data of these complexes and a comparison of their reactivity indicated that the o-QM ligand is more stabilized by iridium than by rhodium. 

Quinone derivatives such as quinone methides (the monomethylene analogues of quinones) have also been extensively studied ([183] and references cited therein) because they possess biological activity, particularly as antitumor agents. The first thermally stable quinone methide having no substituents in the methylene group ( simple quinone methide ) was crystallographically characterized [183a], It was shown that stabilization of the quinone methide can be achieved by complexation to a transition metal center (5.25) ... 

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