Synthesis of an oxorhenium(V) corrolate from porphyrin with detrifluoromethylation and ring contraction

摘要

N N N N CF3 CF3 CF3 F3C N N N N CF3 CF3 F3C Re O H H 1 2 1. Re2(CO)10 2. air, reflux - room temp. 9 PhCN, reflux N2, 1 h 1 h F(2) F(1) F(3) C(20) C(5) C(4) C(3) C(7) C(2) C(8) C(6) N(1) C(1) N(2) C(9) C(10) O Re F(6) C(21) N(4) N(3) F(4) C(18) C(11) C(16)C(14) C(15) C(12) C(17) C(13) C(22) F(8) F(7) F(9) ( a) ( b) F(5) C(19) Synthesis of an oxorhenium(v) corrolate from porphyrin with detrifluoromethylation and ring contraction Man Kin Tse, Zeying Zhang, Thomas C. W. Mak and Kin Shing Chan*dagger; Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong Metallation of highly electron deficient 5,10,15,20-tetrakis( trifluoromethyl)porphyrin 1 with Re2(CO)10 in refluxing PhCN resulted in a novel synthesis of oxorhenium(V) 5,10,15-tris(trifluoromethyl)corrolate 2 characterized by single crystal X-ray crystallography. A new family of porphyrins having highly electron deficient perfluoroalkyl groups in the meso-positions has been efficiently synthesized recently by the acid-catalyzed condensation of perfluoro-1-(2A-pyrrolyl)alkan-1-ols.1 Metallo-perfluoroalkylporphyrins have attracted considerable interest owing to their special non-planar conformation,1 unusual electronic features,2 and catalytic properties.3 In order to explore the chemistry of these electron deficient metalloporphyrins, we have prepared the metal complexes of the porphyrin 5,10,15,20-tetrakis(trifluoromethyl) porphyrin (H2TCF3P, 1).In the course of metallation of 1 with Re2(CO)10, we have discovered a novel oxorhenium( v) corrolate 2, Re(TCF3C)(O), with concomitant detrifluoromethylation and ring contraction of the porphyrin 1 (Scheme 1).When 1 was refluxed with Re2(CO)10 in benzonitrile in N2 for 1 h, the brown solution changed to pink. After cooling in air for 1 h, the solution turned to a muddy green suspension. A diamagnetic red product 2 was obtained in ca. 9 yield after chromatographic separation in air, together with other uncharacterized side products.The diamagnetic 1H NMR spectrum of 2 showed a doublet at d 9.88 (J 4.8 Hz) and a multiplet at d 10.09 with integration ratio of 1 to 3, respectively. The b-pyrrolic protons were therefore non-equivalent. Moreover, the molecular ion appeared at 702 in the mass spectrum and was too low for any expected carbonyl or oxorhenium porphyrin.Dagger; The structure of 2 was obtained from a single crystal X-ray study.sect; The structure was shown to be an oxorhenium corrolate 2 Fig. 1(a) with detrifluoromethylation and ring contraction having taken place at one of the meso-carbons of 1. C(1) and C(19) of 1 were bonded together with a distance of 1.417(4) Aring; to form a corrole skeleton. The distances between the opposite nitrogens N(1)middot;middot;middot;N(3) and N(2)middot;middot;middot;N(4) were 3.751 and 3.754 Aring;, respectively, and were shorter than that of the free base porphyrin 1 by ca. 30.para; The central rhenium lay in a square pyramidal environment in which the corrolate trianion constructed the basal square and the oxygen acted as the axial ligand with ReNO bond length of 1.662(2) Aring;.4 The characteristic ReNO stretching frequency appeared at about 994 cm21 in the IR spectrum.5 Owing to the contraction of the porphyrin to corrole, the large central rhenium deviated from the mean plane of the nitrogens by 0.701 Aring; Fig. 1(b) toward the oxygen to accommodate the typical Rendash;N bond distance of 2 Aring;.5 To the best of our knowledge, it is the first oxorhenium porphyrin like macrocycle to be characterized by X-ray crystallography.Scheme 1 Fig. 1 (a) ORTEP view of Re(TCF3C)(O) showing the atom labelling. The thermal ellipsoids are drawn at a 35 probability level and hydrogen atoms have been omitted for clarity. (b) Simplified diagram of the side view of Re(TCF3C)(O). Chem. Commun., 1998 1199The novel oxorhenium corrolate likely arose from the reduction of 1 by Re2(CO)10 via a cyclopropane intermediate.The formation of cyclopropane product has been reported in the reaction of octaethylporphyrinogen with transition metals.6 The driving force for corrole formation is probably due to the release of steric hindrance in this and other non-planar porphyrin-like macrocycles.7 However, the mechanism of novel detrifluoromethylation and ring contraction to form a corrole from a porphyrin remains unclear. Further studies of the electron deficient corrole are in progress.We thank Direct Grant of the Chinese University of Hong Kong and Shell Chemical Company of Hong Kong for financial support. Notes and References dagger; E-mail: ksc@cuhk.edu.hk Dagger; The molecular ion of meso-tetrakis(trifluoromethyl)porphyrinato rhenium, ReTCF3P+ occurs at m/z 767. UVndash;VIS (CH2Cl2): lmax/nm (log e) 429 (4.64), 549 (3.71), 589 (3.87). sect; Single crystals suitable for X-ray crystallographic studies were obtained by slow evaporation of a CHCl3ndash;MeOH solution of 2. Crystal data for oxorhenium(v) 5,10,15-tris(trifluoromethyl)corrolate 2, C22H8F9N4ReO: red prism, monoclinic, space group C2, a = 19.219(4), b = 13.798(3), c = 8.112(2) Aring;, b = 111.59(3)deg;, Z = 4, m = 6.186 mm21, 2465 reflections collected T = 293(2) K, 2396 independent reflections (Rint = 0.0315) observed.The structure was solved by direct methods and refinement was by full-matrix least squares. In the final refinement, calculated H atom positions were included using a riding model with fixed isotropic U.R1 I 2s(I) = 0.0388, wR2 = 0.1101. Programs used: Siemens SHELXTL PLUS (PC Version). CCDC 182/857. para; The distances between opposite nitrogens of 1 were found to be 4.159 and 4.180 Aring;. The crystal structure of 1 will be published elsewhere. 1 H. Ogose, H. Kuroda and H. Murase, Jpn. Pat., Kokai Tokkyo Koho JP 02 311 478 90 311 478 (Cl. C07D487/22), 27 Dec. 1990, Appl. 89/133,037, 26 May 1989; T. P. Wijeseera and R. W. Wagner, US Pat., 5 241 062 (Cl. 540ndash;145 C07d487/22), 31 Aug. 1993, Appl. 5,702, 19 Jan. 1993; S. G. Dimagno, M. J. Therien and R. A. Williams, J. Org. Chem., 1994, 59, 6943. 2 S. G. Dimagno, A. K. Wertsching and C. R. Ross, J. Am. Chem. Soc., 1995, 117, 8279; J. G. Goll, K. T. Moore, A. Ghosh and M. J. Therien, J. Am. Chem. Soc., 1996, 118, 8344. 3 In Metalloporphyrins in Catalytic Oxidations, ed. R. A. Sheldon, Marcel Dekker, New York, 1994; B. Meunier, Chem. Rev., 1992, 92, 1411; P. E. Ellis Jr.and J. E. Lyons, Coord. Chem. Rev., 1990, 105, 181; T. P. Wijesekera, J. E. Lyons and P. E. Ellis Jr. Catal. Lett., 1996, 36, 69. 4 M. Tsutsui, C. P. Hrung, D. Ostfeld, T. S. Srivastava, D. L. Cullen and E. F. Meyer Jr., J. Am. Chem. Soc., 1975, 97, 1975; A.-M. Lebuis and A. L. Beauchamp, Can. J. Chem., 1993, 71, 2060; C. Bolzati, F. Tisato, F. Refosco, G. Bandoli and A. Dolmella, Inorg. Chem., 1996, 35, 6221; B. Noll, S. Noll, P. Leibnitz, H. Spies, P. E. Schulze, W. Semmler and B. Johannsen, Inorg. Chim. Acta, 1997, 255, 399; S. B�elanger, S. Fortin and A. L. Beauchamp, Can. J. Chem., 1997, 75, 37; B. Dirghangi, K. Menon, M. A. Pramanik and A. Chakravorty, Inorg. Chem., 1997, 36, 1095. 5 For the diphosphine rhenium porphyrin, average Rendash;N bond length was 2.059(5) Aring;; J. P. Collman, J. M. Garner, K. Kim and J. A. Ibers, Inorg. Chem., 1988, 27, 4513; for the nitridorhenium(v) porphyrins, Rendash;N bond lengths range from 2.074(4) to 2.086(4) Aring;; J. W. Buchler, A. D. Cian, J. Fischer, S. B. Kruppa and R. Weiss, Chem. Ber., 1990, 123, 2247. 6 J. Jubb, C. Floriani, A. Chiesi-Villa and C. Rizzoli, J. Am. Chem. Soc., 1992, 114, 6571; U. Piarulli, C. Floriani, A. Chiesi-Villa and C. Rizzoli, J. Chem. Soc., Chem. Commun., 1994, 895. 7 R. Paolesse, S. Licoccia, G. Bandoli, A. Dolmella and T. Boschi, Inorg. Chem., 1994, 33, 1171; S. Licoccia, E. Tassoni, R. Paolesse and T. Boschi, Inorg. Chim. Acta, 1995, 235, 15. Received in Cambridge, UK, 13th March 1998; 8/02033G 1200 Chem. Commun., 19