REACTION OF IRON DICARBONYL PHOSPHINE COMPLEXES OF 2-(PHENYLAZO)PYRIDINES WITH DIMETHYL ACETYLENEDICARBOXYLATE - SYNTHESIS AND CRYSTAL-STRUCTURE OF A 2,3,1-DIAZAFERROLE COMPLEX

The complexes Fe(CO)(2)(P(n)Bu(3))L (L = 2-(phenylazo)pyridine, 4-meth yl-2-(phenylazo)pyridine, and 4,6-(dimethyl)-2- (phenylazo)pyridine) u ndergo a [3 + 2] cycloaddition reaction with dimethyl acetylenedicarbo xylate (DMAD), RC=CR' (R=R'= COOCH3), to produce the complexes )(P(n)B u(3))(C(COOCH3)=C(COOCH3)N(X-py)N(Ph))(X=H, 4-CH3, 4,6-(CH3)(2)), whic h contain a 2,3,1-diazaferrole ring. This reaction is very sensitive t o the acetylene used and to the electron density at the iron center. N o reaction occurs with an acetylene unless R and R' are both ester gro ups, and DMAD does not react with Fe(CO)(2)(P(n)Bu(3)) (5-(trifluorome thyl)-2-(phenylazo)pyridine) or with the tricarbonyls Fe(CO)(3)L. The complexes Fe(CO)(2)(PPh(3))L do not react with DMAD, presumably due to steric effects, but e(CO)(2)(P(OCH3)(3))(4-methyl-2-phenylazopyridine ) reacts to give (OCH3)(3))(C(COOCH3)=C(COOCH3)N(4-CH3-2-py)N(Ph)). Th is complex crystallizes in the space group P2(1)/c with a = 15.027(4) Angstrom, b = 8.244(1) Angstrom, c = 22.560(5) Angstrom, beta = 108.03 (2)degrees, V = 2651.1(10) Angstrom(3) and Z = 4. The iron atom is in an approximate square pyramidal environment with P(OCH3)(3) in the axi al 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 pi system. The results obtaine d in this study are compared with similar studies on analogous alpha-d iimine complexes.