Styrene Aziridination by Iron(IV) Nitrides

Abstract

Thermolysis of the iron(IV) nitride complex PhB(tBuIm)3Fe≡N with styrene leads to formation of the high spin iron(II) aziridino complex PhB(tBuIm)3Fe-N(CH2CHPh). Similar aziridination occurs with both electron-rich and electron-poor styrenes, while bulky styrenes hinder the reaction. The aziridino complex PhB(tBuIm)3Fe-N(CH2CHPh) acts as a nitride synthon, reacting with electron poor styrenes to generate their corresponding aziridino complexes, i.e. aziridine cross-metathesis. Reaction of PhB(tBuIm)3Fe-N(CH2CHPh) with Me3SiCl releases the N-functionalized aziridine Me3SiN(CH2CHPh) while simultaneously generating PhB(tBuIm)3FeCl. This closes a synthetic cycle for styrene azirdination by a nitride complex. While the less hindered iron(IV) nitride complex PhB(MesIm)3Fe≡N reacts with styrenes below room temperature, only bulky styrenes lead to tractable aziridino products.

Boron‐Centered Scorpionate‐Type NHC‐Based Ligands and Their Metal Complexes

“…Although complex 64 does not react with aliphatic alkenes, the aziridino complex {PhB(Im t Bu ) 3 }Fe–N(CH 2 =CHCH 3 ) ( 81 ) can be obtained in high yield by treatment of [PhB(Im t Bu ) 3 Fe]Cl ( 60 ) with LiN(CH 2 CHCH 3 ) . Complexes 64 and 65 react with styrenes with the formation of high‐spin ( S = 2) Fe II ‐aziridino complexes 82 – 91 (Figure ).…”

“…Complexes 64 and 65 react with styrenes with the formation of high‐spin ( S = 2) Fe II ‐aziridino complexes 82 – 91 (Figure ). These reactions are dependent on the steric and electronic properties of the styrene substrate and of the tris(NHC)borate ligands, as well as on the reaction temperature . In fact, whereas complex 64 [{PhB(Im t Bu ) 3 }Fe≡N] requires heat in order to react with less hindered styrenes, complex 65 [{PhB(Im Mes ) 3 }Fe≡N] reacts usefully only with bulky styrenes at room temperature, giving intractable products with other styrenes.…”

“…In fact, whereas complex 64 [{PhB(Im t Bu ) 3 }Fe≡N] requires heat in order to react with less hindered styrenes, complex 65 [{PhB(Im Mes ) 3 }Fe≡N] reacts usefully only with bulky styrenes at room temperature, giving intractable products with other styrenes. In particular, by treatment of complex 65 with 3,5‐(CF 3 ) 2 C 6 H 3 CH=CH 2 and C 10 H 7 C(CH 3 )=CH 2 it is possible to obtain the corresponding aziridino complexes 90 and 91 . The Fe II ‐aziridino complex {PhB(Im t Bu ) 3 }Fe–N(CH 2 CHPh) ( 82 ) can be obtained by heating a solution of complex 64 with an excess of styrene .…”

“…In particular, by treatment of complex 65 with 3,5‐(CF 3 ) 2 C 6 H 3 CH=CH 2 and C 10 H 7 C(CH 3 )=CH 2 it is possible to obtain the corresponding aziridino complexes 90 and 91 . The Fe II ‐aziridino complex {PhB(Im t Bu ) 3 }Fe–N(CH 2 CHPh) ( 82 ) can be obtained by heating a solution of complex 64 with an excess of styrene . Aziridine cross‐metathesis reactions between 81 and ( p ‐XC 6 H 4 )CH=CH 2 (X = NO 2 , CF 3 , Cl) give complexes 83 – 85 and styrene.…”

“…Very interestingly, the Fe II ‐aziridino complexes could be used as synthons in styrene aziridinations; in fact, complex 82 reacts with Me 3 SiCl, leading to the formation of [{HB(Im t Bu ) 3 }Fe]Cl ( 60 ) and the N ‐silylated aziridine Me 3 SiN(CH 2 CHPh). Given that complex 82 can be synthesized by starting from compound 64 , and that this can in turn be obtained from complex 60 , this sequence creates a cyclic chain reaction process for the synthesis of N‐functionalized aziridines …”