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. 2015 Oct 1;6(10):5394-5399.
doi: 10.1039/c5sc01599e. Epub 2015 Jul 17.

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

Yu Shibata  1 , Haruki Nagae  1 , Shiki Sumiya  1 , Raphaël Rochat  1 , Hayato Tsurugi  1 , Kazushi Mashima  1
Affiliations

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

Yu Shibata et al. Chem Sci. .

Abstract

An alkylyttrium complex supported by an N,N'-bis(2,6-diisopropylphenyl)ethylenediamido ligand, (ArNCH2CH2NAr)Y(CH2SiMe3)(THF)2 (1, Ar = 2,6- i Pr2C6H3), 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(sp2)-C(sp2) 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,κ2-(C,N)-pyridyldiyttrium intermediate prior to the C(sp2)-C(sp2) bond formation.

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Figures

Fig. 1
Fig. 1. Aggregated monoarylated and monoalkynylated metal species. A: π-coordination-bridged bimetallic species. B: 3-centered-2-electron Ph-bridged bimetallic species. C: dianionic biphenyl-bridged bimetallic lanthanide complex. D: dianionic diyne-bridged bimetallic lanthanide complex.
Scheme 1
Scheme 1. Pyridylyttrium-mediated 2,2′-bipyridyl formation. [Y] = (ArNCH2CH2NAr)Y.
Fig. 2
Fig. 2. Molecular structure of complex 4a with 30% thermal ellipsoids. All hydrogen atoms and isopropyl groups are omitted for clarity. Selected bond lengths (Å) and angles (°): Y1–N1, 2.344(5); Y1–C1, 2.746(5); Y1–C1*, 2.857(5); Y1–C2*, 2.661(5); N1–C1, 1.424(6); C1–C2, 1.476(7); C1–C1*, 1.396(10); Y1–N2, 2.194(4); Y1–N3, 2.192(5); N1–Y1–C2*, 70.68(16); N2–Y1–N3, 80.78(17). Dihedral angle between N1–Y1–C2* and N1–C1–C1*–C2* planes, 109.6.
Scheme 2
Scheme 2. Deuterium labelling experiment.
Scheme 3
Scheme 3. Stepwise metallacycle and C–C bond formation.
Scheme 4
Scheme 4. Effect of substituents on the aryl ring of 2-arylpyridine on the C–C bond formation step.
Scheme 5
Scheme 5. Reactions of alkylyttrium complex 1 with pyridine derivatives.
Fig. 3
Fig. 3. Molecular structure of complex 6a with 30% thermal ellipsoids. All hydrogen atoms are omitted for clarity. Selected bond lengths (Å): Y1–N1, 2.328(4); Y1–C1, 2.681(5); Y1–C1*, 2.560(5); Y1–N2, 2.216(4); Y1–N3, 2.219(4); Y1–O1, 2.422(3).
Scheme 6
Scheme 6. Plausible mechanism for the reductive dimerization of 2-phenylpyridine.
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