Studies on the Coordination Patterns of Diamine-Bridged Tetraphenoxy Ligands with Group 3 and 4 Metals.

Alkane elimination reactions between the diamino- and dianilino-bridged tetrakis(phenolate) proligands 1a,b-H 4 and precursors M(CH 2 SiMe 3 ) 3 (THF) 2 , M(CH 2 C 6 H 4 - o -NMe 2 ) 3 (M = Sc and Y), and Hf(CH 2 Ph) 4 were investigated. The diamino-bridged 1a-H 4 afforded nonsymmetric complex 2a-Y 2 incorporating two metal centers in different coordination environments. This one and other dinuclear compounds 2b-Sc 2 , 2a-Hf 2 , and 2b-Hf 2 were characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction study (for 2a-Y 2 and 2b-Sc 2 ) and turned out to be symmetric in solution. Compound 2a-Y 2 , upon treatment with 2 equiv of 2-phenylpyridine, afforded symmetric bis(aryl) product 3a-Y 2 , which was authenticated by NMR spectroscopy and X-ray crystallography. The mechanism of its formation was studied by DFT computations and presumably involves a cooperative reorganization process within the nonsymmetric parent 2a-Y 2 to afford a symmetric isomer prior to its reaction with 2-phenylpyridine.