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Phosphaferrocene Analogues of Calixpyrroles Rongqiang Tian and Franc- ois Mathey* Division of Chemistry & Biological Chemistry, School of Physical & Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
bS Supporting Information ABSTRACT: Two new heterocalixpyrroles are described in which two opposite pyrrole rings are replaced by either two phosphaferrocene or one phosphaferrocene and one thiophene unit to give PNPN or PNSN macrocycles.
C
ore-modified porphyrins and related macrocycles have been intensively studied during the last decades in view of their fascinating coordination properties.1 But it must be stressed that the successful replacement of pyrroles by phospholes in these structures has been achieved only very recently by Matano and co-workers.2 In line with this breakthrough, it was logical to consider the further replacement of phospholes by phosphaferrocenes. In so doing, while keeping the five-membered heterocyclic structure, we replace a poorly by a highly aromatic ring,3 a tricoordinate by a dicoordinate phosphorus, and a electrondonating by an electron-accepting heteroatom. In addition, the CpFe complexing group introduces steric protection and differentiation of the two sides of the central cavity. Thus, a dramatic modification of the coordinating properties of the resulting porphyrin-related macrocycles can be expected. We first decided to address the problem of phosphaferrocene analogues of calixpyrroles. From a synthetic standpoint, one of the possible starting products was the recently described 2,5-diester 1.4 The 2,5-bis(pyrrolylmethyl) derivative 3 was prepared according to eq 1.
Figure 1. X-ray crystal structure of the P2N2 macrocycle 4a. Main bond lengths (Å) and angles (deg): Fe1P1 2.2956(10), P1C9 1.784(3), C9 C8 1.429(3), C8C8A 1.435(5), C9C10 1.512(4), C10C11 1.513(3), C11N1 1.371(3), C11C12 1.360(4), C12C12B 1.428(5); C9 P1C9A 89.14(16), C9C10C11 112.5(2), C11N1C11B 110.9(3).
The intermediate 2,5-bis(hydroxymethyl) derivative 2 is not very stable and was directly converted in situ into 3 by reaction with an excess of pyrrole in 43% overall yield. Then, 2 was allowed to react with either 3 or the 2,5-bis(pyrrolylmethyl)thiophene derivative 55 to give either the bis(phosphaferrocene) r 2011 American Chemical Society
macrocyle as a 65:35 mixture of the two possible isomers (4a,b) in 11% yield or the P,N2,S-macrocycle 6 in 23% yield (eq 2). Received: May 18, 2011 Published: June 13, 2011 3472
dx.doi.org/10.1021/om200393a | Organometallics 2011, 30, 3472–3474
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[Ir(COD)Cl]2 at room temperature in toluene. The structure of the resulting complex [Ir(6)(COD)Cl] (7) is shown in Figure 2. The coordination of iridium induces a sharp distortion of the central macrocycle. The two pyrrole rings form an angle of 30.3°. The phospholyl plane forms angles of 77.7° and 74.9° with the two pyrrole planes. The thiophene ring forms an angle of 17.5° with the phospholyl plane. The N 3 3 3 N distance is 5.2 Å, and that of P 3 3 3 S is 4.5 Å. On the NMR spectra, the two pyrroles and the two sides of the thiophene ring appear to be inequivalent. The coordination of P by iridium induces the disappearance of the 1 JCP coupling. The sharp decrease of 1JCP upon coordination of phosphaferrocene is known.6 The NMR data of all of the new compounds are presented hereafter.7 A more complete description of the syntheses is given in the Supporting Information. As a final note, we must stress that the classical oxidative aromatization of the central rings of 4 and 6 to the porphyrin-like species needs special care since the phosphaferrocene units are easily oxidized to the poorly stable phosphaferricinium cations.
’ ASSOCIATED CONTENT
bS Figure 2. X-ray crystal structure of the PN2S macrocycle iridium complex 7. Main bond lengths (Å) and angles (deg): Ir1P1 2.3047(7), Ir1Cl1 2.391(5), P1Fe1 2.262(5), P1C19 1.775(3), P1C22 1.782(3), C19 C20 1.420(4), C20C21 1.432(4), C21C22 1.428(4), C19C44 1.515(4), C44C43 1.501(4), C43N2 1.373(4), N2C40 1.376(3), C40C41 1.365(4), C41C42 1.426(5), C42C43 1.367(4), C40C37 1.514(4), C37C36 1.516(4), C36S1 1.727(3), S1C33 1.735(3), C33C34 1.358(4), C34C35 1.420(5), C35C36 1.360(4); P1Ir1Cl1 90.35(17), C19P1C22 91.76(12), C40N2C43 110.4(2), C33S1C36 93.17(14).
We were able to grow crystals of the major isomer from a solution of 4 in dichloromethane/hexane. The structure is shown in Figure 1. The two pyrrole rings are strictly coplanar. The two phospholyl rings stand face to face in a head-to-tail disposition and are strictly parallel. They form an angle of 79° with the pyrrole plane. The N 3 3 3 N distance is 5.2 Å, and the P 3 3 3 P distance is 5.6 Å.
In order to get a first idea of the coordination chemistry of 4 and 6, we prepared an iridium complex of 6 by reaction with
Supporting Information. Complete experimental section. X-ray crystal structure analysis of compounds 4a and 7. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT The authors thank the Nanyang Technological University in Singapore for the financial support of this work and Dr. Li Yong Xin for the X-ray crystal structure analyses. ’ REFERENCES (1) Recent reviews: Latos-Grazy nski, L. In The Porphyrin Handbook; Kadish, K. M.; Smith, K. M.; Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 2, p 361. Gupta, I.; Ravikanth, M. Coord. Chem. Rev. 2006, 250, 468. (2) Review: Matano, Y.; Imahori, H. Acc. Chem. Res. 2009, 42, 1193. Recent references:Ochi, N.; Nakao, Y.; Sato, H.; Matano, Y.; Imahori, H.; Sakaki, S. J. Am. Chem. Soc. 2009, 131, 10955. Matano, Y.; Fujita, M.; Miyajima, T.; Imahori, H. Organometallics 2009, 28, 6213. Nakabuchi, T.; Nakashima, M.; Fujishige, S.; Nakano, H.; Matano, Y.; Imahori, H. J. Org. Chem. 2010, 75, 375. Nakabuchi, T.; Matano, Y.; Imahori, H. Org. Lett. 2010, 12, 1112. (3) Mattmann, E.; Mathey, F.; Sevin, A.; Frison, G. J. Org. Chem. 2002, 67, 1208. Frison, G.; Mathey, F.; Sevin, A. J. Phys. Chem. A 2002, 106, 5653. (4) Escobar, A.; Mathey, F. Organometallics 2010, 29, 1053. (5) Nagarajan, A.; Ka, J.; Lee, C. Tetrahedron 2001, 57, 7323. (6) Mathey, F. J. Organomet. Chem. 1978, 154, C13. (7) 2: Purified by chromatography on silica gel at 0 °C, orange solid, yield 61%. 31P NMR (CDCl3): δ 61.7. 1H NMR (CDCl3): δ 1.74 (s, 15H, CH3 Cp*), 1.98 (s, 6H, CH3), 4.064.18 (m, 4H, OCH2). 13C NMR (CDCl3): δ 10.56 (s, Cp* Me), 11.01 (s, Me PFc), 60.48 (d, 2JCP = 23.1 Hz, O-CH2), 82.87 (s, Cp* C), 93.46 (d, 2JCP = 4.8 Hz, dC-Me), 95.27 (d, 1JCP = 55.9 Hz, dC-P). HRMS: calcd for C18H28O2PFe (M þ H)þ 363.1176, found 363.1172. 3: Purification by chromatography on silica gel at 0 °C using 1:2 dichloromethane/hexane; orange oil (43.6%). 31P NMR (CDCl3): δ 63.3. 1H NMR (CDCl3): δ 1.83 (s, 15H, Me Cp*), 3473
dx.doi.org/10.1021/om200393a |Organometallics 2011, 30, 3472–3474
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1.89 (s, 6H, Me), 3.283.46 (m, 4H, CH2), 5.89 (s, 2H, CH), 6.076.09 (m, 2H, CH), 6.596.61 (m, 2H, N-CH), 7.88 (s, 2H, N-H). 13C NMR (CDCl3): δ 10.44 (s, Cp* Me), 11.49 (s, Me), 26.54 (d, 2JCP = 22.2 Hz, CH2), 82.38 (s, Cp* C), 92.36 (d, 2JCP = 3.9 Hz, d C-Me), 94.12 (d, 1JCP = 54.9 Hz, dC-P), 105.01 (s, Py CH), 108.09 (s, Py CH), 116.42 (s, Py CH), 131.64 (s, Py C). HRMS: calcd for C26H34N2PFe (M þ H)þ 461.1809, found 461.1814. 4a,b: Purification by chromatography on silica gel at 0 °C using 1:2 dichloromethane/ hexane; red solid (11%). 31P NMR (CDCl3): δ 64.22 (65%, 4a), 62.88. 1H NMR (CDCl3): δ 1.57 (s, Me PFc minor), 1.75 (s, 30H, Me Cp*), 1.79 (s, Me PFc major), 3.173.36 (m, 8H, CH2), 5.725.75 (dd, 4H, CH), 7.25 and 7.39 (2s, NH). 13C NMR (CDCl3): δ 10.23 (s, Cp* Me major), 10.27 (s, Cp* Me minor), 10.84 (s, Me PFc minor), 11.10 (s, Me PFc major), 25.73 (d, 2JCP = 21.1 Hz, CH2), 82.32 (s, Cp* C), 82.36 (s, Cp* C), 92.42 (br s, dC-Me minor), 92.68 (d, 2JCP = 5.0 Hz, d C-Me major), 93.48 (d, 1JCP = 55.3 Hz, dC-P major), 93.55 (d, 1JCP = 56.3 Hz, dC-P minor), 103.69 (s, Py CH), 129.11 (s, Py C), 129.19 (s, Py C). HRMS: calcd for C44H57N2P256Fe2 (M þ H)þ 787.2696, found 787.2686. 6: Purification by chromatography on silica gel at 0 °C using 1:2 dichloromethane/hexane; yellow solid (23.7%). 31P NMR (CDCl3): δ 70.59. 1H NMR (CDCl3): δ 1.60 (s, 6H, Me), 1.65 (s, 6H, Me), 1.77 (s, 21H, Me), 3.103.29 (m, 4H, CH2), 5.73 (m, 2H, CH Py), 5.80 (m, 2H, CH Py), 6.78 (s, 2H, CH Th), 7.34 (s, 2H, N-H). 13C NMR (CDCl3): δ 10.35 (s, Cp* Me), 11.09 (s, Me), 25.70 (d, 2JCP = 20.1 Hz, CH2), 30.95 (s, Me), 31.16 (s, Me), 37.88 (s, C-Me), 82.33 (s, Cp* C), 91.85 (d, 2JCP = 4.0 Hz, dC-Me), 94.86 (d, 1JCP = 53.3 Hz, dC-P), 101.48 (s, Py CH), 103.70 (s, Py CH), 122.65 (s, Th CH), 130.08 (s, Py C), 139.23 (s, Py C), 151.90 (s, Th C). HRMS: calcd for C36H46N2PSFe (M þ H)þ 625.2469, found 625.2462. 7: Purification by chromatography on silica gel at 0 °C using 1:10 ethyl acetate/hexane; red solid (84%). 31P NMR (CDCl3): δ 32.30. 1H NMR (CDCl3): δ 1.55 (s, 5H, 3H, Me þ 2H CH2 COD), 1.63 (s, 7H, 6H Me þ 1H CH2 COD), 1.71 (s, 4H, 3H Me þ 1H CH2 COD), 1.78 (s, 6H, Me), 1.84 (s, 15H, Me Cp*), 1.982.04 (m, 2H, CH2 COD), 2.142.18 (m, 2H, CH2 COD), 3.153.25 (m, 2H, CH2), 3.52 (br s, 2H, dCH COD), 3.733.78 (m, 2H, CH2), 4.90 (br s, 2H, dCH COD), 5.72 5.805.88 (3m, 4H, CH Py), 6.69 (s, 1H, CH Th), 6.75 (s, 1H, CH Th), 7.97 (s, 2H, N-H). 13C NMR (CDCl3): δ 10.99 (s, Cp* Me), 11.04 (s, Me), 11.07 (s, Me), 25.67 (s, CH2), 25.78 (s, CH2), 29.57 (s, Me), 29.64 (s, COD CH2), 30.86 (s, Me), 31.99 (s, Me), 34.08 (s, COD CH2), 37.82 (s, C-Me), 37.90 (s, C-Me), 53.60 (s, COD dCH), 84.86 (s, Cp* C), 86.48 (s, dC-P), 90.57 (s, COD dCH), 90.74 (s, COD dCH), 92.09 (d, 2JCP = 6.7 Hz, dC-Me), 101.85 (s, Py CH), 102.39 (s, Py CH), 103.87 (s, Py CH), 121.11 (s, Th CH), 122.12 (s, Th CH), 129.77 (s, Py C), 139.37 (s, Py C), 139.93 (s, Py C), 152.94 (s, Th C), 153.93 (s, Th C). HRMS: calcd for C44H58N2PS57Fe191Ir (M þ H Cl)þ 925.3018, found 925.3042
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dx.doi.org/10.1021/om200393a |Organometallics 2011, 30, 3472–3474
