2,2′-Bipyridyl formation from 2-arylpyridines through bimetallic diyttrium intermediate

Abstract

An alkylyttrium complex supported by an N,N′-bis(2,6-diisopropylphenyl)ethylenediamido ligand, (ArNCH 2 CH 2 NAr)Y(CH 2 SiMe 3)(THF) 2 (1, Ar = 2,6- i Pr 2 C 6 H 3), activated an ortho-phenyl C-H bond of 2-phenylpyridine (2a) to form a (2-pyridylphenyl)yttrium complex (3a) containing a five-membered metallacycle. Subsequently, a unique C(sp 2)-C(sp 2) coupling of 2-phenylpyridine proceeded through a bimetallic yttrium intermediate, derived from an intramolecular shift of the yttrium center to an ortho-position of the pyridine ring in 3a, to yield a bimetallic yttrium complex (4a) bridged by two-electron reduced 6,6′-diphenyl-2,2′-bipyridyl. Aryl substituents at the ortho-position of the pyridine ring were key in order to destabilize the μ,κ 2 -(C,N)-pyridyldiyttrium intermediate prior to the C(sp 2)-C(sp 2) bond formation.