Acetylide-bridged organometallic oligomers via the photochemical metathesis of methyl-iron(II) complexes

The acetylido methyl iron(II) complexes, cis/trans-Fe(dmpe)(2)(Ctriple bond]CR)(CH(3))] (1) and trans-Fe(depe)(2)(Ctriple bond]CR)(CH(3))] (2) (dmpe = 1,2-dimethylphoshinoethane; depe = 1,2-diethylphosphinoethane), were synthesized by transmetalation from the corresponding alkyl halide complexes. Acetylido methyl iron(II) complexes were also formed by transmetalation from the chloride complexes, trans-Fe(dmpe)(2)(Ctriple bond]CR)(Cl)] or trans-Fe(depe)(2)(Ctriple bond]CR)(Cl)]. The structure of trans-Fe(dmpe)(2)(Ctriple bond]CC(6)H(5))(CH(3))] (1a) was determined by single-crystal X-ray diffraction. The methyl acetylido iron complexes, Fe(dmpe)(2)(Ctriple bond]CR)(CH(3))] (1), are thermally stable in the presence of acetylenes; however, under UV irradiation, methane is lost with the formation of a metal bisacetylide. Photochemical metathesis of cis- or trans-Fe(dmpe)(2)(CH(3))(Ctriple bond]CR)] (R = C(6)H(5) (1a), 4-C(6)H(4)OCH(3) (1b)) with terminal acetylenes was used to selectively synthesize unsymmetrically substituted iron(II) bisacetylide complexes of the type trans-Fe(dmpe)(2)(Ctriple bond]CR)(Ctriple bond]CR')] R = Ph, R' = Ph (6a), 4-CH(3)OC(6)H(4) (6b), (t)()Bu (6c), Si(CH(3))(3) (6d), (CH(2))(4)Ctriple bond]CH (6e); R = 4-CH(3)OC(6)H(4), R' = 4-CH(3)OC(6)H(4), (6g), (t)()Bu (6h), (CH(2))(4)Ctriple bond]CH (6i), adamantyl (6j)]. The structure of the unsymmetrical iron(II) bisacetylide complex trans-Fe(dmpe)(2)(Ctriple bond]CC(6)H(5))(Ctriple bond]CC(6)H(4)OCH(3))] (6b) was determined by single-crystal X-ray diffraction. The photochemical metathesis of the bis-acetylene, 1,7-octadiyne, with trans-Fe(dmpe)(2)(CH(3))(Ctriple bond]CPh)] (1a), was utilized to synthesize the bridged binuclear species trans,trans-(C(6)H(5)Ctriple bond]C)Fe(dmpe)(2)(mu-Ctriple bond]C(CH(2))(4)Ctriple bond]C)Fe(dmpe)(2)(Ctriple bond]CC(6)H(5))] (11). The trinuclear species trans,trans,trans-(C(6)H(5)Ctriple bond]C)Fe(dmpe)(2)(mu-Ctriple bond]C(CH(2))(4)Ctriple bond]C)Fe(dmpe)(2)(mu-Ctriple bond]C(CH(2))(4)Ctriple bond]C)Fe(dmpe)(2)(Ctriple bond]CC(6)H(5))] (12) was synthesized by the photochemical reaction of Fe(dmpe)(2)(Ctriple bond]CPh)(Ctriple bond]C(CH(2))(4)Ctriple bond]CH) (6e) with Fe(dmpe)(2)(CH(3))(2). Extended irradiation of the bisacetylide complexes with phenylacetylene resulted in insertion of the terminal alkyne into one of the metal acetylide bonds to give acetylide butenyne complexes. The structure of the acetylide butenyne complex, trans-Fe(dmpe)(2)(Ctriple bond]CC(6)H(4)OCH(3))(eta(1)-C(C(6)H(5))=CH(Ctriple bond]CC(6)H(4)OCH(3)))] (9a) was determined by single-crystal X-ray diffraction.