The synthesis and dynamic structures of multinuclear complexes of large porphyrinoids expanded by phenylene and thienylene spacers

Abstract

1,3-Bis(2-pyrryl)benzene was used to prepare dibenziamethyrin, in which two pyrrole units of [24]amethyrin(1.0.0.1.0.0) are replaced by benzene. 1,4-Bis(2-pyrryl)benzene, 2,5-bis(2-pyrryl)thiophene, and 4,4'-bis(2-pyrryl)biphenyl were also used in place of 2,2'-bipyrrole to give expanded analogues of [24]rosarin(1.0.1.0.1.0) and [32]octaphyrin(1.0.1.0.1.0.1.0). These large porphyrinoids can incorporate multiple metal units of Rh(CO)2 and Pd(π-allyl) with considerable deviation of the metal atoms from the dipyrrin planes, evidenced by X-ray crystallography. The coordinated Rh(CO)2 group shuttled between both sides of the macrocycle; the rate was dependent on the spacer, ring size, and number of metal atoms. Variable temperature (1) H NMR spectroscopy showed that the tris-rhodium complexes of the expanded rosarins with 1,4-phenylene or 2,5-thienylene spacers adopt a C3v -symmetric form and a Cs -symmetric form as a result of the Rh(CO)2 groups hopping through the macrocycle cavity. The C3v -symmetric form has a greater dipole moment and, therefore, is favored in solvents of greater polarity. The Rh(CO)2 groups in the tris-rhodium complex of the expanded rosarin with 4,4'-biphenylene spacers hop so fast that an averaged spectral pattern (D3h ) was seen in the (1) H NMR spectrum, even at -60 °C. Expanded octaphyrins with 1,4-phenylene and 2,5-thienylene spacers bind four Rh(CO)2 groups outside the macrocycle cavity to form a D2d -symmetric saddle-shaped structure that did not show any dynamic behavior on the NMR timescale, even at 80 °C. This tetranuclear complex is one of the largest porphyrinoid metal complexes characterized by X-ray crystallography to date.

Keywords: amethyrin; multinuclear complexes; octaphyrin; porphyrinoids; rosarin; ruthenium.