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Site-Selective
Coupling of Pyridines Mediated by Low-Valent
Aluminum Compounds: 4,4′- versus 2,2′-Coupling
Weixing Chen (3729784)
Li Yang (6520)
Yihu Zhang (11834675)
Fangfeng Chen (23485261)
Zhenzhou Sun (14185336)
Yanxia Zhao (303724)
Shi-Lu Chen (1428979)
Igor L. Fedushkin (1612696)
Biao Wu (523665)
Xiao-Juan Yang (1850356)
Biophysics
Biochemistry
Physical Sciences not elsewhere classified
Medicine
Microbiology
Molecular Biology
Pharmacology
Evolutionary Biology
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Immunology
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Plant Biology
unique molecular square
give mononuclear complexes
dme )][ lal
promoting reductive coupling
2 ′- dihydro
2 ′- bipyridine
valent aluminum compounds
bulky group (<
2 ′- coupling
thf solution rearranged
1 ′- diyl
1 molar ratio
dme )< sub
relatively small 4
4 ′- dihydro
4 ′- bipyridine
}] (< b
bn (< b
9 </ sub
8 </ sub
5 </ sub
10 </ sub
2 </ sub
al – al
thf )< sub
l )( μ
bu )< sub
1 </ b
py )< sub
ii )– al
py ), 4
selective coupling
(< b
para </
α-Diimine
dianion ligated dialumane [L(THF)Al–Al(THF)L]
(<b>1</b>), in cooperation with Na metal, readily mediates dearomatizing
C–C coupling of pyridines with high regioselectivity. Treatment
of <b>1</b> with pyridine (Py) and Na in a 1:1:1 molar ratio
in toluene at room temperature afforded coupled complex [Na(THF)<sub>6</sub>]<sub>2</sub>[LAl–Al(L)(μ-C<sub>10</sub>H<sub>10</sub>N<sub>2</sub>)Al(L)–AlL] (<b>2</b>), which features
a bridging 4,4′-dihydro-4,4′-bipyridine-1,1′-diyl
(C<sub>10</sub>H<sub>10</sub>N<sub>2</sub><sup>2–</sup>) unit
while retaining the Al(II)–Al(II) bond. However, when 4 equiv
of Py and 2 equiv of Na were used, the Al(II) center in <b>1</b> and Na both participated in promoting reductive coupling of Py,
yielding Al(III) complex [Na(Py)<sub>3</sub>(Et<sub>2</sub>O)][Na⊂{LAl(μ-C<sub>10</sub>H<sub>10</sub>N<sub>2</sub>)<sub>2</sub>AlL}] (<b>3a</b>), which in a THF solution rearranged to a unique molecular square
[Na(THF)<sub>4</sub>]<sub>4</sub>[{LAl(μ-C<sub>10</sub>H<sub>10</sub>N<sub>2</sub>)}<sub>4</sub>] (<b>3b</b>). With a relatively
small 4-substituent on pyridine (4-Me-Py or 4-benzyl-Py), 4,4′-coupling
still occurred to form products [Na(Solv)<sub><i>n</i></sub>]<sub>2</sub>[LAl–Al(L)(μ-C<sub>10</sub>H<sub>8</sub>N<sub>2</sub>R<sub>2</sub>)Al(L)–AlL] (R = Me (<b>4</b>) or Bn (<b>5</b>)). In contrast, when the <i>para</i> position is equipped with a bulky group (<i>t</i>Bu) or
is incorporated within a ring (tetrahydroisoquinoline), the thermodynamically
less favored 2,2′-coupling was observed to give mononuclear
complexes [Na(DME)<sub>3</sub>][LAl(NC<sub>5</sub>H<sub>4</sub><i>t</i>Bu)<sub>2</sub>] (<b>6</b>) and [Na(DME)][LAl(NC<sub>9</sub>H<sub>11</sub>)<sub>2</sub>] (<b>7</b>) with a chelating
2,2′-dihydro-2,2′-bipyridine-1,1′-diyl ligand.
Such selective C–C couplings of pyridines have not been reported
for Al compounds before, and the regioselectivity of 4,4′-
versus 2,2′-coupling is verified by DFT computations.
2026-10-02T00:00:00Z
Dataset
Dataset
10.1021/acs.inorgchem.6c03154.s002
https://figshare.com/articles/dataset/Site-Selective_Coupling_of_Pyridines_Mediated_by_Low-Valent_Aluminum_Compounds_4_4_-_versus_2_2_-Coupling/34055080
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