Multicenter Bonding

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Multicenter.png


LIST OF PARTICIPANTS

Bernard Silvi (not attending)



DISCUSSION

(Bernard Silvi) Why is multicenter bonding challenging?

1. There is no acknowledged representation of multicenter bonding in expanded structures. Although the space-filling model provides a realistic picture, the ball and stick model is misleading.

2. The QTAIM molecular graphs do not account for multicenter bonding because bond paths link two nuclear attractors. They are confusing because one unconsciously associate a Lewis electron pair to a bond path.

3. The fourth postulate of Lewis (two atomic shells are mutually interpenetrable) has to be generalized (Several atomic shells are mutually interpenetrable). The synaptic order concept has been introduced by the ELF community to account for the possibility of a valence basin to belong to n≥ 1 atomic valence shells[1].

4. Multicenter bond involving a hydrogen is conceptually interesting. Hydrogen is a special case because its Lewis kernel is reduced to a proton, A-H bonds can be considered as "protonated lone pairs". In the case of diborane, there are accordingly two "protonated bonding pairs" (see K. Pitzer[2]). With this two generalizations of the Lewis's rules B2H6, C2H7+ and Al2H6[3] satisfy the octet rule around the B,C or Al centres and the duet rule for hydrogens.

Is this a way to define agostic hydrogens?


Some relevant literature [4] [5] [6] [7]


RELEVANT REFERENCES


  1. B. Silvi, Journal of Molecular Structure, 2002, 614, 3-10. DOI: [1]
  2. K. Pitzer, Journal of the American Chemical Society, 1946, 67, 1126--1132
  3. C Lepetit, P Fau, K. Fajerwerg, M. L. Kahn, B. Silvi, Coord. Chem. Rev., 2017, 345, 150-181, DOI: [2]
  4. M. Giambiagi, M.S. de Giambiagi, K.C. Mundim, Structural Chemistry, 1990, 1, 423-427. DOI: 10.1002/poc.922
  5. P. Bultinck, R. Ponec, S. Van Damme, Journal of Physical Organic Chemistry, 2005, 18, 706-718. DOI: 10.1002/poc.922
  6. R. Ponec, G. Yuzhakov, D. J. Tantillo, Journal of Organic Chemistry, 2004, 69, 2292-2996. DOI: 10.1021/jo035506p
  7. E. Matito, M. Solà, Coordination Chemistry Reviews, 2009, 253, 647-665. DOI: 10.1016/j.ccr.2008.10.003

http://dx.doi.org/doi:10.1039/C5CS00066A