Synthesis, Structures and Properties of Calix[4]arenes Bearing Four Phosphanate or Phosphine Oxide Groups At The Upper Arm

Makoto Kyoda, Hirofumi Maekawa, Yoshiki Sadai and Ikuzo Nishiguchi

Copyright AD-TECH; licensee AZoM.com Pty Ltd.

This is an AZo Open Access Rewards System (AZo-OARS) article distributed under the terms of the AZo–OARS https://www.azom.com/oars.asp which permits unrestricted use provided the original work is properly cited but is limited to non-commercial distribution and reproduction.

AZojomo (ISSN 1833-122X) Volume 2 April 2006

Topics Covered

Abstract

Keywords

Introduction

Experimental

Typical Procedure for Arbuzov Reaction

Extractability of The Calix[4]arenes 5, 6, 7, and 8 For a Variety of Metal Chloride

Isolation and Properties of the Complex Between Calix[4]arenes 6c and FeCl₃

Results and Discussion

Acknowledgement

References and Notes

Contact Details

Abstract

Novel calix[4]arene derivatives 6-8 bearing four phosphonate or phosphine oxide groups at the upper rim and four alkyl ether groups at the lower rim were synthesized from Arbuzov reaction of the corresponding conformational isomers of tetrabromocalix[4]arene tetraalkyl ethers. It was found that the calix[4]arenes 5c, 6c, 7c, 8c with four diphenylphosphine oxide groups extracted only FeCl₃ in a highly selective manner, and the one 6c possessing four n-propyl ether groups displayed the largest extraction ability among them

Keywords

Calix[4]arenas, Phosphine Oxide Groups, Ferric Chloride, Extraction, Inclusion Complex

Introduction

Much attention has been focused on various functionalization of calix[4]arenes both at the phenolic oxygen atoms (the lower rim) and on the benzene rings (the upper rim) for the study on supramolecular host-guest chemistry based on the conformational analysis. [1,2]  Many derivatives of four hydroxyl groups at the lower rim of calix[4]arenes were prepared and studied on their functions and behaviors for binding and transport of metal and organic cations. [3-5]

On the other hand, phosphonate, phosphine and phosphine oxide derivatives have been known as useful extracting agents for metal ions [6] and / or as potent ligands of transition metal-catalysts in organic synthetic reactions. [7]  Therefore, it is quite valuable and useful to develop new calix[4]arenes possessing those phosphorus groups at the lower rim directly introduced to the benzene rings, which may be expected unprecedented specific functions and behaviors of including, transport and extraction agents of metals and organic cations, and catalysis in organic reactions.

However, only synthesis was reported for the calix[4]arenes possessing methoxy groups at the low rim and two diphenylphosphine oxide, [8] four phosphonate, [9] or four triphenylphosphine groups [10] at the upper rim directly substituted on the benzene rings, which were not studied on their conformational analysis, functions and behaviors.  It is well known that functions and behaviors of calix[4]arenes are largely influenced by a characteristic conformation (cone, partial cone, 1,2-alternate or 1,3-alternate) and a kind of a substituent at the low rim, and conformational stability of the calix[4]arenes possessing four methoxy groups at the low rim is generally relatively too low to characterize.  Some studies [11-14] have also done on chemistry of the calix[4]arenes possessing four phosphonate or phosphine groups at the upper rim with some functional substituents as spacers between those groups and the benzene ring although chemistry of the calix[4]arenes bearing four carboxylate [15, 16] and sulfonate groups [16, 17] were already well-known.

In this study, we wish to report synthesis of a variety of novel calix[4]arene derivatives 6-8 bearing four phosphonate or phosphine oxide groups at the upper rim and four alkyl ether groups at the lower rim.  Furthermore, the study on conformational analysis and extraction behaviors of these compounds showed high selectivity and large ability of a particular calix[4]arene (6c-cone18) with four diphenylphosphine oxide groups and propioxy groups for extraction of FeCl₃.

Figure 1. Cone and partial cone structure.

Experimental

Typical Procedure for Arbuzov Reaction

Typical Procedure for Arbuzov Reaction of Tetrabromocalix[4]arene Derivative 1-4 with Phosphites or Phosphinate

Each of tetrabromocalix[4]arene tetraalkylethers 1-4 [16] (1 mmol) was stirred in benzonitrile (8 ml) in the presence of nickel dibromide (1 mmol) at 180˚C.  A benzonitrile (2 ml) solution of trialkyl phosphite or ethyl diphenylphosphinate (20 mmol) was added and the whole was stirred for 30 min. at 180˚C.  After a solution was cooled to room temperature, toluene (100 ml) was added and washed with 5%-NH₃ aqueous soution (100 ml x 2) and dried (MgSO₄).  After removal of the drying agent by filtration, the solvent was evaporated by distillation.  The residue was purified by flash column chromatography on silica gel using acetone as an elute to give the desired products as almost pure solids in the yields, as shown in Table1.  All of the products, the calix[4]arene derivatives with four diphenyl phosphine oxide or four dialkyl phosphinate groups 5a, 6a-c, 7a-c and 8a-c, were characterized by spectroscopic analyses (IR, 1H-NMR, 13C-NMR, MASS) and elemental analysis as shown below.  Calix[4]arene 5b-c with four methoxy groups at the lower rim and four dipropyl phosphonate or four diphenyl phosphine oxide groups at the upper rim were identified by comparison with their spectroscopic behaviors with those of authentic samples.

5,11,17,23-Tetrakis(diethylphosphono)-25,26,27,28-tetramethoxycalix[4]arene [5a]:

IR(neat) 1260(P=O); 1H-NMR(400MHz, CDCl₃) δ: 7.78(d, 2H, J=13.2Hz, Ph), 7.58(d, 2H, J=13.2Hz, Ph), 7.43(d, 2H, J=12.7Hz, Ph), 7.00(d, 2H, J=13.2Hz, Ph), 4.39-3.16(m, 8H, ArCH₂Ar, OCH₂CH₃, OCH₃), 3.61(brs, 3H, OCH₃), 3.19(brs, 3H, OCH₃), 1.41-1.26(m, 15H, OCH₂CH₃), 1.18(t, 3H, J=7.0Hz, OCH₂CH₃), 1.03(brs, 6H, OCH₂CH₃); 13C-NMR (100MHz, CDCl₃) δ: 161.1, 161.0, 160.9, 160.8(d, 4JPC=3.7Hz), 136.2, 136.1, 136.0, 134.7(d, 2JPC=9.2Hz), 133.9(d, 3JPC=14.7Hz), 133.5, 133.3, 132.9(d, 2JPC=9.2Hz), 132.5(d, 2JPC=11Hz), 132.3(d, 2JPC=11.0Hz), 122.7, 122.6, 122.1, 122.0, 120.8, 61.9(s), 61.8(s), 60.7(s), 60.0(s), 58.5(s), 53.8(s), 36.4(s), 31.7(s), 30.8(s), 30.6(s), 30.5(s), 29.2(s), 16.3(s), 16.2(s), 15.9(s); MS(apci, M+): 1025. Anal: Calcd. for C₄₈H₆₈ O₁₆P₄ : C, 56.25; H, 6.69. Found: C, 56.45; H, 6.59.

Cone-5,11, 17, 23-Tetrakis(diethylphosphono)-25, 26, 27, 28-tetra-n-propoxy calix[4]arene [6a]:

m.p: 150-152˚C; IR(KBr) 1260(P=O); 1H-NMR(400MHz, CDCl₃) δ: 7.28(d, 8H, J=7.3Hz, Ph), 4.49(d, 4H, J=13.2Hz, ArCH₂Ar), 4.00-3.85(m, 24H, OCH₂CH₃, OCH₂CH₂CH₃ ), 3.31(d, 4H, J=13.2Hz, ArCH₂Ar), 1.97(qt, 8H, J=7.0Hz, OCH₂CH₂CH₃), 1.21(t, 24H, J=7.0Hz, OCH₂CH₃), 1.00(t, 12H, J=7.0Hz, OCH2CH2CH3); 13C-NMR (100MHz, CDCl3) δ: 159.6(d, 4JPC=3.7Hz), 134.6(d, 3JPC=14.7Hz), 132.2(d, 2JPC=11Hz), 122.2(d, 1JPC=191.2Hz), 77.2(s), 61.9(d, 2JPC=5.5Hz), 30.9(s), 23.1(s), 16.2(d, 3JPC=5.5Hz), 10.1(s); 31P-NMR (160MHz, CDCl₃) δ: 13.7; MS(apci, M++1): 1138.  Anal: Calcd. for C₅₆H₈₄ O₁₆P₄ : C, 59.15; H, 7.45. Found: C, 59.23; H, 7.59.

Cone-5,11,17,23-Tetrakis (diisopropylphosphono)-25,26,27,28-tetra-n-propoxy-calix[4]arene [6b]:

m.p: 153-155˚C; IR(KBr) 1260(P=O); 1H-NMR(400MHz, CDCl3) δ: 7.28(d, 8H, J=13.3Hz, Ph), 4.60-4.54(m, 8H, OCH(CH₃)₂), 4.59(d, 4H, J=12.7Hz, ArCH₂Ar), 3.94(t, 8H, J=7.0Hz, OCH₂CH₂CH₃), 3.32(d, 4H, J=12.7Hz, ArCH₂Ar), 2.00-1.93(m, 8H, OCH₂CH₂CH₃), 1.27(d, 24H, J=6.0Hz, OCH(CH₃)₂), 1.00(t, 12H, J=7.5Hz, OCH₂CH₂CH₃); 13C-NMR (100MHz, CDCl₃) δ: 159.5(d, 4JPC=3.7Hz), 134.4(d, 3JPC=16.5Hz), 132.4(d, 2JPC=9.2Hz), 122.8(d, 1JPC=95.6Hz), 77.2(s), 70.4(d, 2JPC=2.6Hz), 31.2(s), 24.0(s), 23.8(s), 23.8(s), 23.1(s), 10.2(s); 31P-NMR (160MHz, CDCl₃) δ: 11.5; MS(apci, M++1): 1250.  Anal: Calcd. for C₆₄H₈₅O₁₆P₄ : C, 61.53; H, 8.07. Found: C, 61.45; H, 7.99.

Cone-5,11,17,23-Tetrakis (diphenyl-oxo-phosphino)-25,26,27,28-tetra-n-propoxycalix[4]arene [6c]:

m.p: >300˚C; IR(KBr) 1260(P=O); 1H-NMR(400MHz, CDCl₃) δ: 7.42-7.21(m, 48H, Ph), 4.53(d, 4H, J=13.2Hz, ArCH₂Ar), 3.94(t, 8H, J=7.3Hz, OCH₂CH₂CH₃), 3.26(d, 4H, J=13.2Hz, ArCH₂Ar), 1.98(qt, 8H, J=7.3Hz, OCH₂CH₂CH₃), 0.99(t, 12H, J=7.3Hz, OCH₂CH₂CH₃); 13C-NMR (100MHz, CDCl₃) δ: 159.2, 134.8(d, 3JPC=12.9Hz), 132.7(d, 1JPC=103.0Hz), 132.7(d, 2JPC=9.2Hz), 131.7(d, JPC=9.2Hz), 128.5(d, JPC=12.9Hz), 125.6(d, 1JPC=106.6Hz), 77.1(s), 31.2(s), 23.1(s), 10.1(s); 31P-NMR (160MHz, CDCl₃) δ: 22.3; MS(apci, M++1): 1394.  Anal: Calcd. for C₈₈H₈₄O₈P₄: C, 75.85; H, 6.08. Found: C, 75.53; H, 6.09.

Partial-Cone-5,11,17,23-Tetrakis (diethylphosphono)-25,26,27,28-tetra-n-propoxy-calix[4]arene [7a]:

m.p: 150-151˚C; IR(KBr) 1260(P=O); 1H-NMR(400MHz, CDCl₃) δ: 7.72(d, 2H, J=13.7Hz, Ph), 7.61(d, 2H, J=13.2Hz, Ph), 7.41(d, 2H, J=13.2Hz, Ph), 6.98(d, 2H, J=13.7Hz, Ph), 4.28-3.38(m, 30H, ArCH₂Ar, OCH₂CH₃, OCH₂CH₂CH₃ ), 3.21(d, 2H, J=13.2Hz, ArCH₂Ar), 1.99-1.81(m, 8H, OCH₂CH₂CH₃), 1.40(t, 6H, J=7.0Hz, CH3), 1.38(t, 6H, J=7.0Hz, CH3), 1.25(t, 6H, J=7.0Hz, CH3), 1.03(t, 6H, J=7.0Hz, CH3), 0.95(t, 3H, J=7.0Hz, CH3), 0.73(t, 3H, J=7.0Hz, CH₃); 13C-NMR (100MHz, CDCl₃) δ: 160.9(s), 160.1(s), 159.4(d, 4JPC=3.7Hz), 136.5(d, 3JPC=16.6Hz), 134.7(d, 2JPC=11.0Hz), 133.9(d, 3JPC=16.5Hz), 133.6(d, 2JPC=9.2Hz), 133.1(d, 3JPC=16.5Hz), 133.1(d, 2JPC=11.0Hz), 132.9(d, 2JPC=11.0Hz), 132.6(d, 2JPC=11.0Hz), 121.8(d, 3JPC=16.6Hz), 122.7(d, 1JPC=193.1Hz), 121.2(d, 1JPC=194.8Hz), 121.0(d, 1JPC=191.2Hz), 76.6(s), 75.6(s), 73.8(s), 62.0(d, 2JPC=5.5Hz), 61.8(d, 2JPC=5.5Hz), 61.7(d, 2JPC=5.5Hz), 61.6(d, 2JPC=5.5Hz), 36.9(s), 30.4(s), 23.4(s), 22.9(s), 21.1(s), 16.4(s), 16.4(s), 16.3(s), 16.2(s), 16.0(s), 16.0(s), 10.6(s), 10.1(s), 9.2(s); 31P-NMR (160MHz, CDCl₃) δ: 19.0, 18.6, 18.4; MS(apci, M++1): 1138.  Anal: Calcd. for C₅₆H₈₄ O₁₆P₄ : C, 59.15; H, 7.45. Found: C, 59.32; H, 7.49.

Partial-Cone-5,11,17,23-Tetrakis (diisopropylphosphono)-25,26,27,28-tetra-n-propoxycalix[4]arene [7b]:

m.p: 125-128˚C; IR(KBr) 1260(P=O); 1H-NMR (400MHz, CDCl₃) δ: 7.69(d, 2H, J=13.7Hz, Ph), 7.59(d, 2H, J=13.2Hz, Ph), 7.41(d, 2H, J=13.2Hz, Ph), 7.05(d, 2H, J=12.2Hz, Ph), 4.85-4.60(m, 6H, OCH(CH3)2), 4.37(m, 2H, OCH(CH₃)₂), 4.14(d, 2H, J=13.2Hz, ArCH₃Ar), 3.87-3.75(m, 6H, ArCH₂Ar, OCH₂CH₂CH₃), 3.63(t, 2H, J=8.0Hz, OCH₂CH₂CH₃), 3.53-3.41(m, 4H, OCH₂CH₂CH₃), 3.22(d, 2H, J=13.2Hz, ArCH₂Ar), 1.96-1.74(m, 6H, OCH₂CH₂CH₃), 1.40-1.20(m, 47H, OCH₂CH₂CH₃, OCH(CH3)2), 1.01(t, 6H, J=7.3Hz, OCH₂CH₂CH₃), 0.92(t, 3H, J=7.3Hz, OCH₂CH₂CH₃), 0.75(t, 6H, J=6.0Hz, OCH(CH₃) ₂); 13C-NMR (100MHz, CDCl₃) δ: 160.6(d, 4JPC=3.7Hz), 159.9(d, 4JPC=3.7Hz), 159.3(d, 4JPC=3.7Hz), 136.1(d, 3JPC=16.5Hz), 134.6(d, 2JPC=9.2Hz), 133.9(d, 3JPC=16.6Hz), 133.3(d, 2JPC=11.0Hz), 132.8(d, 3JPC=16.5Hz), 132.8(d, 2JPC=9.2Hz), 132.7(d, 2JPC=11.0Hz), 132.6(d, 3JPC=16.6Hz), 124.2(d, 1JPC=193.0Hz), 122.7(d, 1JPC=194.8Hz), 76.5(s), 75.5(s), 73.3(s), 70.4(d, 2JPC=5.5Hz), 70.3(d, 2JPC=5.5Hz), 70.2(d, 2JPC=5.5Hz), 70.0(d, 2JPC=5.5Hz), 37.2(s), 30.6(s), 24.1(s), 24.0(s), 23.9(s), 23.1(s), 23.1(s), 22.6(s), 20.9(s), 10.6(s), 10.3(s), 9.4(s); 31P-NMR (160MHz, CDCl₃) δ: 12.8, 12.3, 11.9; MS(apci, M++1): 1250.  Anal: Calcd. for C₆₄H₈₅ O₁₆P₄: C, 61.53; H, 8.07. Found: C, 61.65; H, 8.25.

Partial-Cone-5,11,17,23-Tetrakis(diphenyl-oxo-phosphino)-25,26,27,28-tetra-n-propoxycalix[4]arene [7c]:

m.p: 186-188˚C; IR(KBr) 1260(P=O); 1H-NMR(400MHz, CDCl₃) δ: 7.77-7.72(m, 4H, Ph), 7.58-7.25(m, 42H, Ph), 7.15(d, 2H, J=11.7Hz, Ph), 4.17(d, 2H, J=12.7Hz, ArCH₂Ar), 3.74(s, 4H, ArCH₂Ar), 3.57(t, 4H, J=8.0Hz, OCH₂CH₂CH₃), 3.46(t, 4H, J=8.0Hz, OCH₂CH₂CH₃), 3.43(t, 4H, J=8.0Hz, OCH₂CH₂CH₃), 3.16(d, 2H, J=12.7Hz, ArCH2Ar), 1.59-1.53(m, 6H, OCH2CH2CH3), 1.26-1.22(m, 2H, OCH₂CH₂CH₃), 0.90-0.80(m, 9H, OCH₂CH₂CH₃), 0.52(t, 3H, J=7.6Hz, OCH₂CH₂CH₃); 13C-NMR (100MHz, CDCl₃) δ: 160.9(d, 4JPC=3.7Hz), 159.5(d, 4JPC=4.3Hz), 136.5(d, 3JPC=12.9Hz), 135.0(d, 2JPC=11Hz), 134.0(d, JPC=12.9Hz), 133.6, 133.5, 133.4, 133.3, 133.2, 133.1, 133.1, 132.9, 132.9, 132.8, 132.4, 132.4, 132.1, 132.0, 131.9, 131.8, 131.7, 131.6, 128.7, 128.6, 128.5, 128.4, 128.4, 128.4, 128.2, 126.9(d, 1JPC=104.8Hz), 124.7(d, 1JPC=108.4Hz), 124.4(d, 1JPC=108.4Hz), 76.5(s), 75.3(s), 74.2(s), 37.4(s), 31.5(s), 31.0(s), 23.2(s), 23.1(s), 22.6(s), 21.3(s), 14.1(s), 10.3(s), 9.6(s); 31P-NMR (160MHz, CDCl₂) δ: 23.2, 22.6, 22.3; MS(apci, M++1): 1394.  Anal: Calcd. for C₈₈H₈₄ O₈P₄ : C, 75.85; H, 6.08. Found: C, 76.06; H, 5.98.

Cone-5,11,17,23-Tetrakis(diethylphosphono)-calix[4]arene Bis(crown ether) [8a]:

m.p: 231-232˚C; IR(KBr) 1260(P=O); 1H-NMR(400MHz, CDCl₃) δ: 7.46(d, 4H, J=11.2Hz, Ph), 7.43(d, 4H, J=11.2Hz, Ph), 5.16(d, 2H, J=12.2Hz, ArCH₂Ar), 4.52(d, 2H, J=12.2Hz, ArCH₂Ar), 4.35(d, 4H, J=10.7Hz, OCH₂CH₂O), 4.35(s, 4H, OCH₂CH₂CH₃), 4.24(s, 4H, J=10.7Hz, OCH₂CH₂O), 4.01-3.86(m, 20H, OCH₂CH₂O, OCH₂CH₃), 3.37(d, 2H, J=12.2Hz, ArCH₂Ar), 3.32(d, 2H, J=12.2Hz, ArCH₂Ar), 1.16-1.11(m, 24H, OCH₂CH₃); 13C-NMR(100MHz, CDCl₃) δ: 158.7(d, 4JPC=3.7Hz), 135.5(d, 3JPC=16.5Hz), 135.3(d, 3JPC=16.5Hz), 132.9(d, 2JPC=11.0Hz), 132.0(d, 2JPC=11.0Hz), 123.6(d, 1JPC=123.6Hz), 76.3(s), 73.9(s), 62.0(s), 30.5(s), 29.7(s), 16.1(d, 3JPC=3.7Hz); 31P-NMR (160MHz, CDCl₃) δ: 13.2; MS(apci, M+): 1109.  Anal: Calcd. for C₅₂H₇₂ O₁₈P₄ : C, 56.32; H, 6.54. Found: C, 56.55; H, 6.49.

Cone-5,11,17,23-Tetrakis(diisopropylphosphono)-calix[4]arene Bis(crown ether) [8b]:

m.p: 185-186˚C; IR(KBr) 1260(P=O); 1H-NMR(400MHz, CDCl₃) δ: 7.43(d, 4H, J=13.2Hz, Ph), 7.42(d, 4H, J=13.2Hz, Ph), 5.15(d, 2H, J=12.7Hz, ArCH₂Ar), 4.58-4.50(m, 10H, ArCH₂Ar, OCH(CH₃) ₂), 4.35(d, 4H, J=11.2Hz, OCH₂CH₂O), 4.24(d, 8H, J=5.4Hz, OCH₂CH₂O), 3.87(m, 4H, OCH₂CH₂O), 3.36(d, 2H, J=12.7Hz, ArCH₂Ar), 3.30(d, 2H, J=12.2Hz, ArCH₂Ar), 1.25(d, 12H, J=6.0Hz, OCH(CH₃) ₂), 1.23(d, 12H, J=6.0Hz, OCH(CH₃) ₂), 1.09(d, 12H, J=6.0Hz, OCH(CH₃)₂), 1.05(d, 12H, J=6.0Hz, OCH(CH₃)₂); 13C-NMR(100MHz, CDCl₃) δ: 158.5(d, 4JPC=3.7Hz), 135.2(d, 3JPC=16.6Hz), 135.0(d, 3JPC=16.6Hz), 132.8(d, 2JPC=11Hz), 132.0(d, 2JPC=11Hz), 125.1(d, 1JPC=193Hz), 76.2(s), 73.9(s), 70.5(d, 2JPC=5.5Hz), 30.7(s), 29.8(s), 23.9(s), 23.8(d, 3JPC=3.7Hz), 23.7(d, 3JPC=3.7Hz); 31P-NMR (160MHz, CDCl₃) δ: 11.1; MS(apci, M++1): 1221.  Anal: Calcd. for C₆₀H₈₄O₁₈P₄ : C, 59.01; H, 7.26. Found: C, 58.93; H, 7.19.

Cone-5,11,17,23-Tetrakis(diphenyl-oxo-phosphino)-calix[4]arene Bis(crown ether) [8c]:

m.p: 187-189˚C; IR(KBr) 1260(P=O); 1H-NMR(400MHz, CDCl₃) δ: 7.45-7.22(m, 48H, Ph), 5.22(d, 2H, J=12.2Hz, ArCH₂Ar), 4.55(d, 2H, J=12.2Hz, ArCH₂Ar), 4.35(d, 4H, J=10.8Hz, OCH₂CH₂O), 4.24(d, 8H, J=4.9Hz, OCH₂CH₂O), 3.89-3.84(m, 4H, OCH₂CH₂O), 3.27(d, 2H, J=12.2Hz, ArCH₂Ar), 3.23(d, 2H, J=12.2Hz, ArCH₂Ar); 13C-NMR (100MHz, CDCl₃) δ: 158.4(s), 135.6(d, 3JPC=12.9Hz), 135.4(d, 3JPC=12.9Hz), 133.1(d, 2JPC=11Hz), 132.3(d, 1JPC=117.7Hz), 132.2(d, 2JPC=11Hz), 131.8(s), 131.6(s), 131.5(s), 128.5(d, JPC=14.7Hz), 126.9(d, 1JPC=104.8Hz), 76.2(s), 73.7(s), 69.3(s), 30.7(s), 29.9(s); 31P-NMR (160MHz, CDCl₃) δ: 23.1; MS(apci, M++1): 1366.  Anal: Calcd. for C₈₄H₇₂ O₁₀P₄ : C, 73.89; H, 5.32. Found: C, 74.13; H, 5.69.

Extractability of The Calix[4]arenes 5, 6, 7, and 8 For a Variety of Metal Chloride

The extractability of the calix[4]arenes 5, 6, 7 and 8 for a variety of metal chlorides were measured using a double layer system according to the following procedure: A chloroform solution (20 ml) of a sample of 5-8 (1.0 mmol dm^-3) and an aqueous solution (20 ml) containing 4N-hydrochloric acid and 0.1 mmol dm^-3 of metal chloride were magnetically stirred at 30˚C for 20h. An aliquot of the upper aqueous solution was withdrawn, and analyzed by inductively coupled plasma (ICP) emission spectrometry.  A similar extraction experiment was performed without any sample.  The extractability was determined on the basis of the concentration of metal chloride in the aqueous solution by means of the following equation:

Extractability (%)=[(A₀ - A) / A₀ ] x 100

Where A₀ and A are the aqueous concentration of metal chloride in the absence (the initial concentration) and the presence (the final concentration) of the sample, respectively.

Isolation and Properties of the Complex Between Calix[4]arenes 6c and FeCl3

The complex between calix[4]arenes 6c and FeCl₃ was successfully isolated from a chloroform solution of a double layer used for extractability experiment., and was subjected to spectroscopic (UV and 31P-NMR), electrochemical (cyclic voltammetry) and mp measurements.

Results and Discussion

Tetrabromocalix[4]arene derivatives 1-4 {1 (R=Me-paco (= partial cone)18), 2 (R=n-Pr-cone), 3 (R=n-Pr-paco), 4 (R=-CH₂CH₂OCH₂CH₂- -cone)} were prepared according to the modified procedure of the reported methods.15,19,20 Arbuzov reaction of tetrabromocalix[4]arene tetra-n-propylether 2 (cone ) and 3 (paco) with trialkyl phosphite ( P(OR)₃ ) or ethyl diphenylphosphinate ( Ph₂P(OEt) ) using NiBr₂ as a Lewis acid catalyst in benzonitrile at 180˚C smoothly proceeded to give the corresponding new calix[4]arenes 6a-c (cone) and 7a-c (paco), possessing a dialkyl phosphonate ( PO(OR)₂ ) or a diphenylphosphine oxide ( Ph₂PO) group at the para-position of each of the benzene rings in excellent yields (51~97%), as shown in Table 1.

Table 1. Synthesis of tetraphosphono- ( or phosphino) calix[4]arene derivatives through Arbuzov reaction.

On the other hand, the novel calix[4]arenes 8a (cone) and 8c (cone) were obtained in low yield from the reaction of tetrabromocalix[4]arene 4 (cone), having two diethylene glycol groups, with P(OEt)₃ and Ph₂P(OEt), while the reaction of 4 (cone) with P(O_iPr)₃ gave the corresponding product 8b (cone) in 81% yield.

Measurement of the extractability of the calix[4]arenes 5, 6, 7 and 8 for a variety of metal chlorides was conducted as follows.  A double layer consisted of a chloroform solution of 1.0 mmol dm^-3 of 5-8 and an aqueous 4N-hydrochloric acid solution containing 0.1 mmol dm^-3 of metal chloride was magnetically stirred at 30˚C for 20 h.  Then the aqueous concentration of metal chloride in an aliquot of the upper aqueous solution was analyzed by inductively coupled plasma (ICP) emission spectrometry.

As a result, it was found that none of the calix[4]arenes 5a,b, 6a,b, 7a,b and 8a,b possessing four dialkyl phosphonate groups showed any extractability of metal salts such as FeCl₃, CoCl₂, NiCl₂, ZnCl₂ and LaCl₃ .  On the other hand, those bearing diphenylphosphine oxide groups 5c, 6c, 7c and 8c displayed the highly selective and excellent extraction behaviors for only FeCl₃ even in an aqueous solution containing a same concentration of various metal chlorides (FeCl₃, CoCl₂, NiCl₂, ZnCl₂), as shown in Table 3.

Table 2. P-NMR spectrum of calix[4]arene derivatives.

It may be also noteworthy that the one 6c with four diphenylphosphine oxide groups showed the highest extractability among 5c, 6c, 7c and 8c, possibly because the n-propyl ether groups at the lower rim made the conformation more rigid and the hole size was more suitable for [FeCl₄^-] anion, as shown in Table 3 and 4.

Table 3. Extraction of FeCl₃ in mixed solution with Calix[4]arene derivatives 5c-8c and 7a,b.

Table 4. Extraction of FeCl₃ in mixed solution with Calix[4]arenas and TPPO

¹Extract condition: [Organic Phase]: 1mM-CHCl₃, 20ml [Aqueous Phase]:0.1mM of FeCl₃, 20ml, c[HCl]: 4N, 20h, 30jC
²TPPO: triphenylphosphine oxide

Furthermore, triphenylphosphine oxide (TPPO) did not show any extractability under the extract condition (entry 4), which indicated a specific structural feature of the calix[4]arenes.

It is quite interesting that increase in pH of the aqueous solution of the double layer system brought about gradual increase in the extractability (E%) of FeCl₃ up to almost 100%, when 8N-HCl aq. was used in this extraction, as shown in Figure 2.

Figure 2. Extraction of FeCl₃ by HCl Concentration Change for Calix[4]arene 6c.

Furthermore, a white solid isolated from an organic layer in the double layer system by extraction using calix[4]arene 6c with four diphenylphosphine oxide groups showed peculiar electrochemical and spectroscopic behaviors. Thus, the solid shows melting point at 80-81° (mp of 6c : >300°), and small but characteristic absorption at λmax:  370 nm in its ultraviolet spectrum.  The calix[4]arene 6c and the solid show their reduction potentials at -1.43 V and -1.92 V (vs. Ag/Ag+), respectively, in their cyclic voltammetry, and a broad singlet peak was observed at δ=41.2 ppm in the 31P-NMR spectrum of the solid while 6c shows a singlet peak at δ=22.3 ppm.

From these experimental results of extraction behaviors and characteristic properties, this solid seems to consist of a complex between calix[4]arene 6c and FeCl₃, as shown in Figure 3, where the oxygen atoms of four diphenylphosphine oxide groups are protonated , and a molecule of FeCl₄ anion is included into a cationic cavity surrounded by the four diphenylphosphine oxide groups of 6c.  The cone conformation and the four Oi-Pr groups at the lower rim may be responsible to generate suitable size of the cavity for a guest molecule of FeCl₄ anion.

Figure 3. Complex between calix[4]arene 6c and FeCl_3.

As a conclusion, novel calix[4]arene derivatives bearing a diphenylphosphine oxide group on the p-position of each of four benzene rings 6c, 7c, and 8c were synthesized through Arbzov reaction of tetrabromocalix[4]arene derivatives with ethyl diphenylphosphinate retaining each of the original conformations. All of them shows high selectivity and large ability of ion pair extraction for only FeCl₃, and the one 6c possessing four n-propyl groups at the rim showed the highest extractability.

Figure 4. Arbuzov Reaction.

Acknowledgement

This research was supported by the 21st Century COE Program and a Grant-in-Aid for Scientific Research on Priority Areas (No. 13029038) from Ministry of Education, Science, Sports and Culture, Japan.

References and Notes

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12.   Also some studies have done on chemistry (synthesis, conformational analysis and/or properties) of the calix[4]arenes possessing some functional groups as spacers between phosphonate groups and the benzene rings. See references 13-14.

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19.   Cone is cone conformation, and paco is partial cone conformation.

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21.   A. Soi, W. Bauer, H. Mauser, C. Moll, F. Hampel and A. Hirsch, “Investigations on the Dynamic Properties of 25,26,27,28-Tetraalkoxycalix[4]arenes: Para-substituent- and Solvent-dependent Properties of Paco Conformers and Determination of Thermodynamic Parameters of the Pinched Conelpinched Cone Conversion“, J. Chem. Soc., Perkin Trans. 2 (1998) 1471-1478.

Contact Details

Makoto Kyoda, Hirofumi Maekawa, Yoshiki Sadai and Ikuzo Nishiguchi

Department of Chemistry
Nagaoka University of Technology
Japan

E-mail: [email protected]

This paper was also published in print form in “Advances in Technology of Materials and Materials Processing”, Vol. 6 [1] 29-36 (2004)