4 years ago

Weak M····H-C interactions in Neutral Complexes, Anions and Cations of Palladium(II) and Rhodium (I) containing the iso-Quinoline ligand - Anagostic or Preagostic?

Alastair James Nielson, Arif Sajjad, Peter Schwerdtfeger, John Harrison
DFT-D calculations show that the above-plane M····H-C separations in square-planar complexes of palladium (II) and Rh(I) containing the iso-quinoline ligand are influenced by whether the complexes are neutral, anionic or cationic due mainly to changes in atomic charge on the metal, H and C atoms but the nature of the cis-ligands also plays a part because of the development of weak intramolecular interactions. The Pd····H-C separations are effected by strong σ-withdrawing or π-donating substituents placed at C7 of the iso-quinoline ligand with the shortest anagostic Pd····H separation of 2.218 Å achieved using the π-donating S- substituent in an anionic complex. The same substituent on the cationic complex leads to Pd-C covalency. Lack of flexibility of the iso-quinoline ring system prevents the anagostic carbon approaching the metal when the electrostatics are favourable. Instead of an anagostic/preagostic divide it is suggested that all complexes with above plane Pd····H-C close approaches are termed anagostic and where some agostic covalency develops below an NBO E(2) value of 5 kcal mol-1 they be regarded as having an emerging preagostic condition.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/ejic.201701094

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