Electronic and Steric Manipulation of the Agostic Interaction in benzo[h]quinoline Complexes of Pd(II) and Implications for the Formation of η1-Pd-C Bonds

Structures and properties were obtained by density functional (DFT) calculations for the complexes [PdCl2(L)] (L = benzo[h]quinolines) containing aromatic ring agostic interactions. The inflexibility of the benzenoid rings of the ligands keep the structures of the complex relatively constant when electron withdrawing substituents are added to the aromatic ringparato the agostic carbon but electron donation causes a change to eta(1)-Pd-C bond complexes in which agostic donation is significantly reduced and pi-syndetic donation no longer features. Increasing the steric size at the alpha-carbon through the series H, Me, CHMe2, CMe(3)or Ph, changes the manner in which the ligand sits in relation to the coordination plane but a change in the way the nitrogen atom of the ligand tilts in relation to the coordination plane does not effectively reduce the agostic or syndetic donations. CPh(3)reduces the agostic donation but not the syndetic donation and C(Ph-2,6-Me-2)(3) turns both donations off and installs eta(2)pi-donation on one aromatic ring. Placingortho-substituents on the ring can influence the interplay of electronic and steric effects when eta(1)-Pd complexes are formed.