NH HN N HN N N N N Me Me Me Me Me Me Et Et Et Me Me Me Et Me Me Me + 1 2 P OH Cl – 350 400 450 500 550 600 650 l / nm Absorbance Phosphorus complex of corrole Roberto Paolesse,* a Tristano Boschi, a Silvia Licoccia, a Richard G. Khoury b and Kevin M. Smith b † a Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, Roma, 00133, Italy b Department of Chemistry, University of California, Davis, CA 95616, USA Reaction of 8,12-diethyl-2,3,7,13,17,18-hexamethylcorrole (1) with POCl 3 in pyridine affords the first non-metal derivative of corrole; in this compound, 2, the phosphorus is in a pentavalent state and is different from analogous complexes of porphyrins. Non-porphyrin polypyrrolic macrocycles represent a novel field of research which has experienced impressive expansion in the last few years. 1 These compounds are particularly intriguing for both theoretical and experimental reasons. For example, they can enable studies of the way in which skeletal variations influence the aromaticity and the chemical properties of the macrocycles, thereby opening potential applications of these molecules in different fields, ranging from catalysis to bio- medical sciences. Among porphyrin analogues, corrole (e.g. 1) was one of the first examples to be reported in the literature; it was synthesized more than 30 years ago by Johnson and Kay during their attempts to approach the corrin nucleus of vitamin B 12 . 2 But recent investigations using the corrole macrocycle have re- vealed interesting differences in its coordination behavior compared with the analogous porphyrin complexes. Corrole, for example, is able to stabilize high oxidation states for co- ordinated metals, and to retain a planar conformation even when the peripheral positions are fully substituted. 1a,b Despite these interesting properties, the coordination chemistry of corrole is substantially limited to the first row transition metals; expansion of the so-called ‘periodic table’ of metallocorrolates should allow researchers to study, in more detail, the coordination behavior of this macrocycle. In particular, coordination of phosphorus can be intriguing due to the non-metal character of this element and because it is, in its pentavalent state, the smallest ion so far coordinated to a porphyrin. 3 Herein we report the synthesis and characterization of the first example of a phosphorus corrole derivative. Reaction of 8,12-diethyl-2,3,7,13,17,18-hexamethylcorrole (1; H 3 EMC) 2 with POCl 3 in pyridine at room temperature showed an immediate spectrophotometric change, with the formation of the spectrum of the characteristic corrole mono- cation. 4 When the mixture was heated at reflux the optical spectrum quickly changed (indicating the formation of a complex), with the complete disappearance of the absorbance characteristic of the corrole; Fig. 1 shows the optical spectra of the corrole monocation and the phosphorus complex. Evapora- tion of the solvent and recrystallization from CH 2 Cl 2 –hexane afforded a purple powder. In complexes with porphyrins, phosphorus has been reported to be hexacoordinated in a +v oxidation state; 3 in the case of octaethylporphyrin a transient +iii state has been reported to be an intermediate during the metallation reaction. 3 In the present case of corrole, the electronic absorption spectrum is similar to those of other main group metallocorrolates. 5 By analogy with porphyrins it can be classified as ‘normal’, 6 thereby indicating the presence of the +v oxidation state for the coordinated phosphorus. The 1 H NMR spectrum of the phosphorus corrole was also typical of a metallocorrolate, with the absence of internal NH resonances and the expected pattern for peripheral substituents. 31 P NMR spectroscopy showed a resonance for coordinated phosphorus at 2102.5 ppm (relative to external H 3 PO 4 ), which is significantly different from phosphorus complexes of por- phyrins in which the phosphorus signal is at ca. 2200 ppm. 7 This feature indicated that the diamagnetic ring current effect is less influential in determining the phosphorus resonance in the corrole derivative compared with porphyrin complexes. This difference can be attributed to two major factors: (i) the diminished aromatic character of corrole relative to porphyrin, and/or (ii) a different coordination geometry of phosphorus in the corrole complex. Both 1 H and 13 C NMR spectra ruled out the first hypothesis because resonances of the corrole derivative have almost the same chemical shifts as do the analogous porphyrinates. 8 A different coordination geometry seems more likely because the EI mass spectrum of the corrole complex showed a molecular peak at m/z 483, indicating the presence of only one ligand at an axial position. Analogous phosphorus porphyrinates are hexacoordinated. 3 X-Ray characterization‡ performed on a single crystal of the phosphorus corrolate 2 allowed its unambiguous structural identification. The molecular structure is shown in Fig. 2. The phosphorus atom exhibits pentacoordinated geometry, lying more than 0.4 Å out of the mean corrole plane toward the oxygen atom of the axial hydroxy group. The P–O bond distance of 1.531 Å can be attributed to a single bond and is similar to the observed P–O distance in an analogous porphyrin complex. 3 The P–N bond lengths average 1.80 Å. These lengths Fig. 1 Optical spectra, in CH 2 Cl 2 , of [H 4 EMC] + (– – –), and [(EMC)- P(OH)]Cl (2), (––––) Chem. Commun., 1998 1119 Published on 01 January 1998. Downloaded on 26/10/2014 17:37:25. View Article Online / Journal Homepage / Table of Contents for this issue