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. 2017 Jan 19;56(4):1069-1072.
doi: 10.1002/anie.201610679. Epub 2016 Dec 21.

C-H and C-N Activation at Redox-Active Pyridine Complexes of Iron

K Cory MacLeod  1 , Richard A Lewis  1 , Daniel E DeRosha  1 , Brandon Q Mercado  1 , Patrick L Holland  1
Affiliations

C-H and C-N Activation at Redox-Active Pyridine Complexes of Iron

K Cory MacLeod et al. Angew Chem Int Ed Engl. .

Abstract

Pyridine activation by inexpensive iron catalysts has great utility, but the steps through which iron species can break the strong (105-111 kcal mol-1 ) C-H bonds of pyridine substrates are unknown. In this work, we report the rapid room-temperature cleavage of C-H bonds in pyridine, 4-tert-butylpyridine, and 2-phenylpyridine by an iron(I) species, to give well-characterized iron(II) products. In addition, 4-dimethylaminopyridine (DMAP) undergoes room-temperature C-N bond cleavage, which forms a dimethylamidoiron(II) complex and a pyridyl-bridged tetrairon(II) square. These facile bond-cleaving reactions are proposed to occur through intermediates having a two-electron reduced pyridine that bridges two iron centers. Thus, the redox non-innocence of the pyridine can play a key role in enabling high regioselectivity for difficult reactions.

Keywords: bond cleavage; iron; pyridine; redox-activity.

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Figures

Figure 1
Figure 1
The molecular structures of 1 (left) and 2 (right), with thermal ellipsoids shown at 50% probability. H atoms (except for the hydride) and the ortho-methyl groups on the supporting ligands are omitted for clarity.
Figure 2
Figure 2
The molecular structure of 4, with thermal ellipsoids shown at 50% probability. Only one of two independent molecules in the asymmetric unit is shown. The hydrogen atoms have been omitted for clarity.
Figure 3
Figure 3
The molecular structure of 6, with thermal ellipsoids shown at 50% probability. One of the two possible orientations is shown for the bridging pyridinyl ligands. Hydrogen atoms and 2,6-Me2C6H3 groups omitted for clarity.
Scheme 1
Scheme 1
C-H activation of tert-butylpyridine, and functionalization of the hydride product.
Scheme 2
Scheme 2
C-H activation of 2-phenylpyridine.
Scheme 3
Scheme 3
C-N activation in DMAP.
Scheme 4
Scheme 4
Proposed mechanism for C-H and C-N activation.
See this image and copyright information in PMC

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