Journal of Organometallic Chemistry 646 (2002) 4 – 14 www.elsevier.com/locate/jorganchem Account Organoaluminum chemistry with low valent aluminum — recent developments M.N. Sudheendra Rao 1 , Herbert W. Roesky *, G. Anantharaman Institut fu ¨r Anorganische Chemie der Uniersita ¨t Go ¨ttingen, Tammannstrasse 4, D-37077 Go ¨ttingen, Germany Received 8 January 2001; accepted 8 March 2001 Dedicated to Professor Franc ¸ois Mathey on the occasion of his 60th birthday Abstract The chemistry of mono and divalent aluminum has progressed very significantly in the last decade. Many fascinating and unusual results and novel structures of products have been realized. The monomeric form of divalent aluminum does not exist but dimers are well known and characterized. Stable Al(I) derivatives in both monomeric and tetrameric forms have been synthesized and structurally characterized. A common feature in these compounds is the use of bulky organic substituents. The chemistry of some of these compounds has also been explored. The monomeric Al(I) derivative, [HC(MeCNAr) 2 ]Al, very recently synthesized, exhibits interesting addition and insertion reactions with alkyne, carbon dioxide and silyl azide at room temperature. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Organo Al(I) and (II); Monomeric, dimeric and tetrameric forms; Syntheses; Structures; Reactions; CO 2 insertion 1. Introduction Low valent chemistry of polyvalent elements is a topic of considerable research interest in recent years. For a long time, it was a formidable challenge to prepare compounds with subvalent elements in a labo- ratory. Thanks to the advent of new and sophisticated synthetic methodologies, nowadays more success stories are reported on solutions to difficult synthetic prob- lems. Recent isolation and structural characterization of organometallic hydroxides [1], nonafluoromesityl tel- luride [2], metallasiloxanes from discrete silanetriols as building blocks [3] and a stable cyclotrigermenyl radical [4] are only a few examples of this development. How- ever, for most new developments the design and details of the synthesis of the desired target are still dependent on the skill of the chemist. Aluminum, the most abundant metal in the earth’s crust, is known to have a vast chemistry in its normal trivalent state [5,6]. Several organoaluminum com- pounds have found extensive use as selective reagents for a wide variety of organic transformations. On the industrial side, their most prominent applications are as polymerization cocatalysts, ceramic precursors and spe- cialty chemicals in electronic devices. Further, com- pounds of the type R 3 -x AlE x (where R is an organic group and E is halogen or hydrogen) have stimulated substantial interests for studies on structure and bond- ing concepts as well. The discovery that trialkyl alu- minum compounds play an important role in the Ziegler – Natta process of olefin polymerizations has given tremendous boost to the research and develop- mental work in aluminum chemistry. It currently runs almost parallel to organolithium and organomagnesium chemistry in terms of its versatility and usefulness. 2. Interests and importance of low valent aluminum Aluminum, a member of the main group metals, uses all the valence electrons (3s 2 ,3p 1 ) for its trivalent chem- istry. Its low valent chemistry is therefore to be charac- terized by the restricted use of its alence electrons in * Corresponding author. Tel.: +49-551-393001; fax: +49-551- 393373. E-mail address: hroesky@gwdg.de (H.W. Roesky). 1 On leave from The Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India. 0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0022-328X(01)00799-9