Small steric variations in ligands with large synthetic and structural consequences

The reaction of ytterbium metal with the aminopyridines 2,6-(diisopropylphenyl)-[6-(2,6-dimethylphenyl)pyridin-2-yl]amine (1, Ap'H) and (2,4,6-trimethylphenyl)-[6-(2,4,6-trimethylphenyl)pyridin-2-yl]amine (2, Ap(Me)H) at elevated temperature under vacuum in the presence of mercury gave rise to divalent [Yb(Ap')(2)] (3) and trivalent [Yb(Ap(Me))(3)] (4), respectively. The single-crystal X-ray structure analysis of 3 revealed a four-coordinate ytterbium atom with two chelating (N,N') Ap' ligands inclined to each other at an angle of 126.93(7)degrees (Cl-Yb-C26). Additionally the complex forms intermolecular C-Aryl-H agostic interactions [Ybl center dot center dot center dot C17 2.981(2) angstrom and Yb1 center dot center dot center dot H17 2.56(3) angstrom] (all H atoms refined). Complex 4 contains a six-coordinate ytterbium atom having three chelating (N,N') Ap(Me) ligands and has distorted octahedral stereochemistry. The reaction of the potassium salts of Ap'H (5) and Ap(Me)H (6) with [Ybl(2) (thf)(4)] in thf gave rise to the divalent lanthanoid complexes [Yb(Ap')(2)(thf)] (7), and [Yb(Ap(Me))(2)(thf)(2)] (8), respectively, and 7 was also obtained by redox transmetallation/ligand exchange from Yb metal, HgPh2 and Ap'H. X-ray crystal structures show that 7 and 8 have five- and six-coordinate ytterbium atoms and distorted trigonal-bipyramidal and distorted octahedral stereochemistry, respectively, the difference in coordination number reflecting the difference in steric demand of the Ap' and Ap(Me) ligands. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).