The synthesis, structures, and electrochemistry of 1′-heteroaryl-2,5-dimethylazaferrocenes

Reaction of an iron(IV) nitrido complex with cyclohexadienes: cycloaddition and hydrogen-atom abstraction

The iron(IV) nitrido complex PhB(MesIm)₃Fe≡N reacts with 1,3-cyclohexadiene to yield the iron(II) pyrrolide complex PhB(MesIm)₃Fe(η⁵-C₄H₄N) in high yield. The mechanism of product formation is proposed to involve sequential [4 + 1] cycloaddition and retro Diels–Alder reactions. Surprisingly, reaction with 1,4-cyclohexadiene yields the same iron-containing product, albeit in substantially lower yield. The proposed reaction mechanism, supported by electronic structure calculations, involves hydrogen-atom abstraction from 1,4-cyclohexadiene to provide the cyclohexadienyl radical. This radical is an intermediate in substrate isomerization to 1,3-cyclohexadiene, leading to formation of the pyrrolide product.

The iron(IV) nitrido complex PhB(MesIm)₃Fe≡N reacts with both 1,3- and 1,4-cyclohexadiene to yield the iron(II) pyrrolide complex, PhB(MesIm)₃Fe(η⁵-C₄H₄N). In the case of 1,3-cyclohexadiene, product formation is proposed to occur by sequential [4 + 1] cycloaddition and retro Diels−Alder reactions. In the case of 1,4-cyclohexadiene, initial hydrogen-atom abstraction isomerizes the substrate to 1,3-cyclohexadiene, providing a pathway to the pyrrolide product.

New polydentate trimethylsilyl chalcogenide reagents for the assembly of polyferrocenyl architectures

A series of polychalcogenotrimethylsilane complexes Ar(CH2ESiMe3)n, (Ar = aryl; E = S, Se; n = 2, 3, and 4) can be prepared from the corresponding polyorganobromide and M[ESiMe3] (M = Na, Li). These represent the first examples of the incorporation of such a large number of reactive -ESiMe3 moieties onto an organic molecular framework. They are shown to be convenient reagents for the preparation of the polyferrocenylseleno- and thioesters from ferrocenoyl chloride. The synthesis, structures, and spectroscopic properties of the new silyl chalcogen complexes 1,4-(Me3SiECH2)2(C6Me4) (E = S, 1; E = Se, 2), 1,3,5-(Me3SiECH2)3(C6Me3) (E = S, 3; E = Se, 4) and 1,2,4,5-(Me3SiECH2)4(C6H2) (E = S, 5; E = Se, 6) and the polyferrocenyl chalcogenoesters [1,4-{FcC(O)ECH2}2(C6Me4)] (E = S, 7; E = Se, 8), [1,3,5-{FcC(O)ECH2}3(C6Me3)] (E = S, 9; E = Se, 10) and [1,2,4,5-{FcC(O)ECH2}4(C6H2)] (E = S, 11 illustrated; E = Se, 12) are reported. The new polysilylated reagents and polyferrocenyl chalcogenoesters have been characterized by multinuclear NMR spectroscopy ((1)H, (13)C, (77)Se), electrospray ionization mass spectrometry and, for complexes 1, 2, 3, 4, 7, 8, and 11, single-crystal X-ray diffraction. The cyclic voltammograms of complexes 7-11 are presented.