Inducing ring distortions in unsubstituted metallophthalocyanines using axial N-heterocyclic carbenes

Abstract

A series of metallophthalocyanine (PcM) complexes with axial N-heterocyclic carbene ligands (NHC; 1,3-diisopropylimidazol-2-ylidene (DIP) and 1,3-dimethylbenzimidazol-2-ylidene (DMB)) were prepared and structurally characterized. PcCo^II(DIP), PcZn^II(DIP), and PcZn^II(DMB) are five-coordinate complexes with mild dome-type Pc-ring distortions, while PcFe^II(DIP)₂ is six-coordinate and has a very large ruffle-type ring-distortion with respect to typical PcM(L)₂ systems. The distortion is induced by the highly steric axial DIP ligands. The distortions were quantified and classified by their bond lengths and torsion angles, and according to the normal-coordinate structural decomposition (NSD) analysis. Upon ligation of the NHC, the insoluble PcM materials were solublized in common organic solvents, with typical UV-visible Q-band maxima observable between 658 and 677 nm; the increased solubility is rationalized in terms of the reduced solid-state aggregation of the complexes, attributable to the axial ligation.