172099-74-0Relevant articles and documents
Synthesis and reactivities of pyrrolylimido complexes of molybdenum and tungsten: Formation of pyrrole and N-aminopyrrole from molecular nitrogen
Seino, Hidetake,Ishii, Youichi,Sasagawa, Takao,Hidai, Masanobu
, p. 12181 - 12193 (2007/10/03)
Hydrazido(2-) complexes trans-[MX(NNH2)(dppe)2]+ (M = Mo, W; X = F, Cl; dppe = Ph2PCH2CH2-PPh2) and cis,mer-[WX2(NNH2)(PMe2Ph)3] (X = Cl, Br), which are readily derived from trans-[M(N2)2(dppe)2] (1) and cis-[W(N2)2(PMe2Ph)4] by protonation, condensed with 2,5-dimethoxytetrahydrofuran to afford pyrrolylimido complexes of the type trans-[MX(NNCH=CHCH=CH)(dppe)2]+ (3+) and cis,mer-[WX2(NNCH=CHCH=CH)(PMe2-Ph)3] (6), respectively. Their structures were characterized spectroscopically and further confirmed by X-ray diffraction study. Electrophilic substitution reactions at the pyrrole ring in complexes 3+ occurred selectively at the β-position to give the corresponding β-substituted pyrrolylimido complexes trans-[MX(NNCH=C(E)CH=CH)(dppe)2]+ (E = Br, CN, SO3-, COR), although only chlorination of 3+ with N-chlorosuccinimide in THF took place predominantly at the α-position. This β-regioselectivity is in sharp contrast to the α-regioselectivity of free pyrrole and is probably caused by the steric effect of the dppe ligands. Complexes 3+ were readily reduced under ambient conditions with LiAlH4 to liberate pyrrole and N-aminopyrrole in high yields. Further, the tetrahydrido complexes [MH4(dppe)2], which can be converted back into the original dinitrogen complexes 1, were recovered in moderate yields after the reduction. This accomplishes the synthetic cycle for pyrrole and N-aminopyrrole starting from the dinitrogen complexes 1. β-Heptylpyrrole was also prepared by starting from 3c+ (M = W, X = Cl) by the β-selective heptanoylation followed by the reduction with LiAlFL;. On the other hand, reduction of 6b (X = Br) with LiAlH4 predominantly produced pyrrole, whereas treatment of 6b with KOH/EtOH liberated N-aminopyrrole in a high yield.
