Theoretical Aspects of Metal-Dihydrogen Bonding and Calculational Methodologies

DEVELOPMENT OF THE THEORETICAL ASPECTS OF METAL-DIHYDROGEN BONDING AND CALCULATIONAL METHODOLOGIES 

The existence of a complex between H2 and a metal is one of the few notable examples in all of science of the nearly simultaneous and independent derivation of theory and fact. Neither the theoreticians nor the experimentalists involved were aware of the seminal research being carried out in their respective fields during 1979-1983 when H2 activation was initially studied computationally and W(CO)3(P Pr3)2(H2) was first prepared and later proven to contain aH2 ligand (see Chapter 2). This is marvelously exemplified by the classic theoretical paper by Saillard and Hoffmann in 1984 presenting extended Huckel calculations on the bonding of H2 and CH4 to metal fragments10 that appeared only months after the 

As discussed in an excellent review by Maseras et. al.,9 the study of H2 on metal complexes, including classical hydride ligands, has many advantages  

H is the smallest ligand and the only one to form a pure single bond to a metal, Le., a crucial computational benchmark r ligand. 

The H atom is easy to locate computationally but difficult experimentally even neutron diffraction (see Chapter 5) often cannot pinpoint the exact position of the hydrogens in H2 ligands. Computational crystallography is a low-cost, high-quality technique for structural location and prediction of classical versus nonclassical structures. 

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