Iron(II) Mediated Deazotation of Benzyl Azide: Trapping and Subsequent Transformations of the Benzaldimine Fragment

The mono-benzaldimine (HN = CHPh) complex [((tBu)pyrpyrr2)Fe(HN = CHPh)] (1-HN.CHPh) has been prepared by reaction of [((tBu)pyrpyrr2)Fe(OEt2)] (1-OEt2) ((tBu)pyrpyrr(2) = 2,6-bis(3,5-di-tert-butyl-pyrrolyl)pyridine) with one equivalent of benzyl azide. Compound 1-HN = CHPh retains the cis-divacant octahedral coordination geometry akin to 1, as established by single crystal X-ray diffraction study. A bis-HN = CHPh complex [((tBu)pyrpyrr2)Fe(HN. CHPh)(2)] (2) was also prepared by the addition of two equivalents of benzyl azide to 1, and its molecular structure exhibits the two HN.CHPh ligands coordinated trans to each other, thereby forming a square pyramidal coordination geometry at the FeII center. Reaction of 1 with excess benzyl azide yields [((tBu)pyrpyrr(2))Fe(HN = CHPh)(2)center dot PhCHNCH(NH2)Ph] (2-PhCHNCH(NH2)Ph), which contains an unstable benzylideneamino phenyl methanamine fragment, effectively hydrogen bonded to 2. Thermolysis of 2 or 2-PhCHNCH(NH2)Ph releases the HN. CHPh self-coupling products hydrobenzamide (A), N-benzylidine benzylamine (B), and benzonitrile (C). Under catalytic conditions, free HN.CHPh (cis/trans-HN = CHPh mixture) is produced using 2.5 mol % of 1 in 90% spectroscopic yield. These studies provide a clearer understanding for the conversion of the HN = CHPh in 2 or 2-PhCHNCH(NH2)Ph to the C-C and C-N coupled products. Reduction of 1-HN = CHPh with KC8 yields the reductively coupled benzylamide complex [K(OEt2)](2)[((tBu)pyrpyrr(2))(2)Fe2(mu(2)-NHCHPhCHPhNH)] (3) as the result of a new C-C bond formed between two radical benzylamide fragments.

Automated summary

The synthesis and characterization of mono-benzaldimine and bis-benzaldimine complexes were investigated. It was found that the mono-benzaldimine complex can produce free HN.CHPh under catalytic conditions. The study also elucidated the conversion of HN = CHPh in the bis-benzaldimine complexes to C-C and C-N coupled products.