Main Group Organometallics and Sterically Demanding Aromatics
The research of the Organic and Organometallic Chemistry Group has always had a strong emphasis on main group organometallic chemistry,1 and one of the areas which has been developed in the last 20 years involves the use of metal alkoxides for modifying reactivity and properties of the more traditional organometallic reagents such as those of lithium, sodium, potassium and magnesium.2 Recent work has centered on the superbase system butyllithium-lithium potassium bis(dimethylaminoethoxide). This is a strong metallating agent which combines the activating effect of a tertiary amine with that of a potassium alkoxide. It is capable of readily abstracting allylic, benzylic and even olefinic protons.3 The choice of a mixed alkoxide was determined by the need to use saturated hydrocarbons as solvents; the solubility of the mixed alkoxide being much greater than that of the potassium alkoxide itself. Catalytic amounts of this reagent in combination with Mg(OCH2CH2OEt)2 promote the multiple and clean addition of ethylene to a series of alkylaromatics (see examples in the table).4
The introduction of the 3-pentyl group introduces steric crowding which for some of the molecules is quite considerable. This and the fact that these compounds can be produced on a large scale in good yields, makes them attractive for further study. Bulky molecules find applications in many areas of chemistry, e.g. for the stabilisation of molecules with unusual oxidation states or with novel types of bonding, for the preparation of stable homoleptic materials and as ligands for homogeneous catalysis. We are therefore pursuing the development of this methodology for the synthesis of functional aromatic molecules and this has been successful for certain ortho-methyl anilines and phenols. Functionalisation of the hydrocarbons is also being studied. Bromination and nitration reactions proceed as expected under suitable conditions and reduction of the nitro-compounds provides an alternative route to crowded anilines. These products should be useful starting materials for the preparation of organometallic compounds and bulky ligands for coordination complexes and further work in this area is being actively pursued.5-8
1. C.G. Screttas and M. Micha-Screttas, J. Org. Chem. 1978, 43, 1064-1071; ibid.1979, 44, 1471-1475; 1983, 48, 153-158; 1983, 48 , 252-254; and refs. therein
2. C.G. Screttas and B.R. Steele, Appl. Organomet. Chem. 2000, 14 , 653-659 and refs. therein.
3. C.G. Screttas and B.R. Steele, J. Organomet. Chem. 1993, 453 , 163-170
4. B.R. Steele and C.G. Screttas, J. Am. Chem. Soc.2000, 122, 2391-2392; B.R. Steele, C. Villalonga-Barber, M. Micha-Screttas, C.G. Screttas, Tetrahedron Lett.2006, 47 , 2093-2097
5. B.R. Steele, M. Micha-Screttas and C.G. Screttas, Tetrahedron Lett. 2004, 45 , 9537-9540
6. D.P. Catsoulacos, B.R. Steele, G.A. Heropoulos, M. Micha-Screttas and C.G. Screttas, Tetrahedron Lett., 2003, 44 , 4575-4578
7. S.V. Amosova, N.A. Makhaeva, A.V. Martynov, V.A. Potapov, B.R. Steele and I.D. Kostas, Synthesis, 2005, 1641-1648; I.D. Kostas, B.R. Steele, A. Terzis, S.V. Amosova, A.V. Martynov and N.A. Makhaeva, Eur. J. Inorg. Chem.2006 , 2642-2646
8. G.A. Heropoulos, S. Georgakopoulos and B.R. Steele, Tetrahedron Lett. 2005 , 46, 2469-2473.
9. B.R. Steele, S. Georgakopoulos, M.Micha-Screttas and C.G. Screttas, Eur. J. Org. Chem.. 2007, 3091-3094. -Synthesis of new sterically hindered anilines-
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