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Repeated Dihydrogen Elimination from Boranes and Gallanes Stabilized by Guanidine‐Type Bases: A Quantum Chemical Study Motivated by Recent Experimental Results
Author(s) -
Ciobanu Oxana,
Himmel HansJörg
Publication year - 2007
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200700336
Subject(s) - chemistry , electronegativity , elimination reaction , guanidine , boranes , reductive elimination , intramolecular force , computational chemistry , medicinal chemistry , organic chemistry , catalysis , boron
Monomeric boranes and gallanes stabilized by guanidine derivatives undergo in certain cases H 2 elimination reactions leading in a first step to dinuclear E(III) hydrides (E = B or Ga) and in the second step upon elimination of further H 2 to dinuclear compounds with the elements in the formal oxidation state +II featuring a direct E–E bond. The thermodynamics for such H 2 elimination reactions were calculated applying several methods and basis sets. In addition the calculations provide information about possible mechanisms. Thus the calculations suggest the first step to be an intramolecular H 2 elimination followed by a cycloaddition reaction. The second H 2 elimination, in which E–E and H–H bonds are formed at the expense of E–H bonds, is almost energy neutral, as anticipated from the small differences in electronegativity between E and H. The reaction barriers are important indicators to answer the question if H 2 elimination can be made reversible. Reversible H 2 elimination and addition would make this class of compounds in principle interesting for hydrogen storage applications, although obviously the weight percentage of stored dihydrogen is in the special systems presented herein not sufficient for mobile applications. The compounds can also be applied for dehydrocoupling and transfer hydrogenation to deliver a stoichiometric amount of H 2 to olefins. Finally, the possibility of elimination of a third H 2 leading to a dinuclear E(I) species with an E–E double bond is discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)