Reaction of iron dicarbonyl phosphine complexes of 2-(phenylazo)pyridines with dimethyl acetylenedicarboxylate. Synthesis and crystal structure of a 2,3,1-diazaferrole complex

Abstract

The complexes Fe(CO) 2(P nBu 3)L (L = 2-(phenylazo)pyridine, 4-methyl-2-(phenylazo)pyridine, and 4,6-(dimethyl)-2-(phenylazo)pyridine) undergo a [3 + 2] cycloaddition reaction with dimethyl acetylenedicarboxylate (DMAD), RCCR′ (R  R′  COOCH 3), to produce the complexes Fe(CO) 2(P nBu 3)(C (COOCH 3C(COOCH 3)N(X-py)N (Ph)) (X  H, 4-Ch 3, 4,6-(CH 3( 2), which contain a 2,3,1-diazaferrole ring. This reaction is very sensitive to the acetylene used and to the electron density at the iron center. No reaction occurs with an acetylene unless R and R′ are both ester groups, and DMAD does not react with Fe(CO) 2(P nBu 3) (5-(trifluoromethyl)-2-(phenylazo)pyridine) or with the tricarbonyls Fe(CO) 3L. The complexes Fe(CO) 2(PPh 3)L do not react with DMAD, presumably due to steric effects, but Fe(CO) 2(P(OCH 3) 3)(4-methyl-2-phenylazopyridine) reacts to give Fe(C O) 2(P(OCH 3) 3) (C (COOCH 3C(COOCH 3)N(4-CH 3-2-py)N (Ph)). This complex crystallizes in the space group P2 l / c with a = 15.027(4) A ̊ , b = 8.244(1) A ̊ , c = 22.560(5) A ̊ , β = 108.03(2)°, V = 2651.1(10) A ̊ 3 and Z = 4 . The iron atom is in an approximate square pyramidal environment with P(OCH 3) 3 in the axial position. The 2,3,1-diazaferrole ring is essentially planar with sp 2 hybridization for all C and N ring atoms, and bond length data are consistent with a possible delocalized π system. The results obtained in this study are compared with similar studies on analogous α-diimine complexes.