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

The mono -benzaldimine (HN═CHPh) complex [( t Bu pyrpyrr 2 )Fe(HN═CHPh)] ( 1 -HN═CHPh) has been prepared by reaction of [( t Bu pyrpyrr 2 )Fe(OEt 2 )] ( 1 -OEt 2 ) ( t Bu 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 [( t Bu pyrpyrr 2 )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 Fe II center. Reaction of 1 with excess benzyl azide yields [( t Bu pyrpyrr 2 )Fe(HN═CHPh) 2 ·PhCHNCH(NH 2 )Ph] ( 2 -PhCHNCH(NH 2 )Ph), which contains an unstable benzylideneamino phenyl methanamine fragment, effectively hydrogen bonded to 2 . Thermolysis of 2 or 2 -PhCHNCH(NH 2 )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(NH 2 )Ph to the C-C and C-N coupled products. Reduction of 1 -HN═CHPh with KC 8 yields the reductively coupled benzylamide complex [K(OEt 2 )] 2 [( t Bu pyrpyrr 2 ) 2 Fe 2 (μ 2 -NHCHPhCHPhNH)] ( 3 ) as the result of a new C-C bond formed between two radical benzylamide fragments.