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Low Coordinated Group 13 Chelates

  1. Samuel Dagorne

Published Online: 15 MAR 2006

DOI: 10.1002/0470862106.ia291

Encyclopedia of Inorganic Chemistry

Encyclopedia of Inorganic Chemistry

How to Cite

Dagorne, S. 2006. Low Coordinated Group 13 Chelates. Encyclopedia of Inorganic Chemistry. .

Author Information

  1. Chimie de la Matière Condensée (CNRS), Ecole Nationale Supérieure de Chimie de Paris, Paris, France

Publication History

  1. Published Online: 15 MAR 2006

Abstract

Recent developments in the area of low-coordinate group 13 chelates are the focus of this article. Emphasis is placed on the synthesis and reactivity of two new classes of compounds, that is, tri-coordinate cationic chelates and monovalent two/three-coordinate chelate species.

Unknown 10 years ago, tri-coordinate chelate cations {L-X}MR+ (M = Al, Ga, In; R = Me, Et, Pr) could be obtained by reaction of the neutral precursors {L-X}MR2 with a strong Lewis acid such as [Ph3C][B(C6F5)4], provided an extremely crowded L-X bidentate ligand and an inert counterion are used. Reactivity studies on the Al derivatives show that these highly electrophilic species are potent Lewis acids as expected by the combination of the cationic charge and a low-coordination number, but are less reactive than neutral AlR3 compounds with regard to insertion of unsaturated substrates into the Al[BOND]C bond.

The use of bulky tri- and bidentate ligands has also allowed access to unprecedented monovalent and monomeric low-coordinate group 13 compounds. Tri-coordinate Ga(I) and In(I) complexes incorporating a sterically encumbered HB(PzR, R′) tridentate ligand were obtained and are quite stable. Similarly, the use of the very crowded HC(CMeNAr)2 and tBuNC[DOUBLE BOND]CNtBu2− dinitrogen ligands with an appropriate synthetic methodology has opened the way to stable two-coordinate and monovalent species: {HC(CMeNAr)2}M (M = Al, Ga) and the {tBuNC[DOUBLE BOND]CNtBu}Ga anion, respectively. Such species may behave either as Lewis acids or as Lewis bases due to the intrinsic properties of the metal center (a sextet configuration and the presence of a lone pair of electrons). Reactivity studies on these two-coordinate complexes have just begun but have already permitted the synthesis of the first monomeric Al and Ga imide complexes {HC(CMeNAr)2}M(N-Trip) (M = Al, Ga).

Finally, representative examples of recent new catalytic applications of tri-coordinate Al(III) neutral species containing a chiral or achiral X22−-type chelating ligand, used as catalysts, are mentioned.

Keywords:

  • low-coordinate;
  • chelate;
  • cationic;
  • monovalent;
  • aluminium;
  • gallium;
  • indium;
  • catalysis