Rare Earth Ion Size Effects in Structures of Rare Earth <i>N,N′</i> ‐bis(2‐trifluoromethylphenyl)formamidinates

The complexes, [RE(CF 3 Form) 3 ] (RE = Ce, 1, or Pr, 2 ) and [Y(CF 3 Form) 3 (thf)] 3, have been prepared by protolysis of the corresponding RE[N(SiMe 3 ) 2 ] 3 complexes with N , N ′‐bis(2‐trifluoromethylphenyl)formamidine (CF 3 FormH) in tetrahydrofuran ( 1–3 ) or by redox transmetallation/protolysis between the RE metal, bis(pentafluorophenyl)mercury (Hg(C 6 F 5 ) 2 ), and CF 3 FormH in tetrahydrofuran ( 1 , 2 ), and are characterized by 1 H NMR and 19 F NMR spectroscopy. X‐ray crystallography established 1 and 2 to contain 12‐coordinate RE metals with three tetradentate F,N,N′,F′‐CF 3 Form ligands, whereas 3 has an eight coordinate Y atom with two bidentate N,N′‐ and one tridentate N,N′,F‐CF 3 Form ligands and coordinated thf, and with a further F atom within the sum of Y and F van der Waals radii but &gt;0.25 Å more distant from Y. In 1 and 2 , every CF 3 group forms a F 2 CFRE bond, and the extensive FRE bonding is preferred over coordination of thf.