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The synthesis, coordination and electrochemical studies of metallocene bis(crown ether) receptor molecules. Single-crystal x-ray structure of a ferrocene bis(crown ether) potassium complex
Po/ykdmn Vol.&No. 7,p~. 87%886, 1989 Printedin Great Britain
0277-5381189 $3.00+.00 0 1989 Pergamon Press pk
TI-IE SYNTHESIS, COORDINATION AND ELECTROCHEMICAL STUDIES OF METALLOCENE BIS(CROWN ETHER) RECEPTOR MOLECULES. SINGLE-CRYSTAL X-RAY STRUCTURE OF A FERROCENE BIS(CROWN ETHER) POTASSIUM COMPLEX PAUL D. BEER* and HARRISON
SIKANYIKA
Department of Chemistry, University of Birmingham, P.O. Box 363, Birmingham B15 2TT, U.K. and ALEXANDRA
Chemical Crystallography
M. Z. SLAWIN
and DAVID
J. WILLIAMS
Laboratory, Department of Chemistry, Imperial College, London SW7 2AY, U.K.
(Received 3 October 1988 ; accepted 31 October 1988) Abstract-The condensation of 1, 1‘-bis(chlorocarbonyl)ferrocene and l,l’-bis(chlorocarbonyl)ruthenocene with 4-aminobenzo-15-crown-5 gives the metallocene bis(crown ether) ligands l,l’-bis[(2,3,5,6,8,9,1 1,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin15-yl)amino]carbonylferrocene (4) and the ruthenocene analogue (5). 13C NMR titrations of 4 and 5 with Na+, K+ and Cs+ alkali metal salts lead to titration curves interpreted as suggesting 1 : 1 stoichiometry. The single-crystal X-ray structure of [4K]PF6 * 4MeOH reveals an intramolecular sandwich complex with the potassium guest cation in the solid state. Competition fast atom bombardment (FAB) mass spectrometry selectivity experiments show 4 and 5 to exhibit exclusive K+ selective complexation over either Na+ or Cs+.
Responsive macrocyclic receptor molecules whose binding strength and/or selectivity towards guest species can be influenced by physical and chemical means, have been the subject of many recent reports in the chemical literature. I-5 Examples include pHresponsive crown ethers,2,3,6,7 which change their cation binding ability in response to medium pH and photoresponsive crown ethers, ‘*8 azoarenecapped oxygen macrocycles which undergo photoinduced reversible interconversion between the tram and cis azo linkages resulting in substantial changes in their cation binding properties. Particular attention has been focused on the synthesis of redox-responsive macrocycles that contain redox-active functions such as quinone,g-‘4 nitro*Author to whom correspondence
should be addressed.
benzenei and metallocene moieties’“23 in close proximity to a cation binding site. We are currently interested in preparing metallocene redox-active macropolycyclic host molecules designed to be selective as well as being redox-responsive to the host binding of inorganic and organic guest species. ‘9-22 One application of such receptors lies in their potential development as components of new chemical sensory devices. We report here the synthesis, coordination and electrochemical studies of two new metallocene bisbenzo-crown ethers, 4 and 5, and the single-crystal X-ray structure of [4K]PF6 - 4MeOH, which, to our knowledge, is the$rst structural example of a bisbenzo-crown ether potassium intramolecular sandwich complex. A preliminary report on this work has recently been published. l9 879
P. D. BEER et al.
880
RESULTS
AND DISCUSSION
Synthesis of 4 and 5 The condensation carbonyl)metallocenes
Table 1. ‘H NMR data for 4 (solvent CDCl, ; reference TMS) Assignment
6 Cm-W of respective l,l’-bis(chloro1 and 224 with 2 mol of 4-
aminobenzo-15-crown-5 (3)25 in the presence of triethylamine gave, after column chromatography (alumina, 99% CH2C12, 1% MeOH), the ferrocene bis(crown ether) (4 :80% yield) and the ruthenocene analogue (5: 75% yield), Scheme 1 (preparative details are given in the Experimental). The structures of both new air-stable metallocene bis(crown ethers) were characterized by elemental analysis, mass spectrometry and ‘H (Tables 1 and 2) and 13C NMR spectroscopy (Tables 3 and 4).
3.73-4.13 4.39”
4.60” 6.82 7.20
(m, 32 H) (t, J 1.8 Hz, 4H) (t, J 1.8 Hz, 4H) (d, J 8.7 Hz, 2H (d of d, J 8.7 Hz, J 2 Hz, 2H) (d, J 2 Hz, 2H) (.s, broad, 2H)
Crown protons Ferrocenyl
j
7.55 8.87
Aromatics NH
“‘Apparent triplet’ assigned as an AA’BB’ system.
Table 2. ‘H NMR data for 5 (solvent CDC13 ; reference TMS)
Coordination studies ‘%2 NMR spectroscopy investigate the complexation
was used initially to of 4 and 5 with alkali
Assignment
6 (Ppm)
metal cations sodium, potassium and caesium.26 The stepwise addition of an alkali metal nitrate salt to a methanol (65%)-acetone (35%) solution of 4 and a methanol (65%)dichloromethane (35%) solution of 5 led to considerable shifts of the 0CH2 carbons of the respective bis(crown molecules). In all cases the A6 ppm versus [alkali metal salt]/ [metallocene bis(crown ether)] titration curves can
3.72-4.10 4.72” 5.01” 6.75 7.09
7.42 8.38
(m, 32H) (t, J 1.7 Hz, 4H) (t, J 1.7 Hz, 4H) (d, J 8.7 Hz, 2H j (d of d, J 8.7 Hz, J 2 Hz, 2H) (d, J 2 Hz, 2H) (s, broad, 2H)
“Apparent
Crown protons Ruthenocenyl
Aromatics NH
triplet’ assigned as an AA’BB’ system.
Table 3. 13CNMR data for 4 from broad band decoupled and DEPT spectra (solvent CDC13 ; reference TMS) 6 (.Ppm) (I) (2)
M’=Fe M’=Ru
I
2 Et,N
(4)
M’= Fe
(51 M’=Ru
Scheme 1.
68.83 69.39 69.62 69.71 70.38 70.53 70.88 70.96 71.07 79.27
Assignment
OCH,
1)
112.32 114.94 132.78 145.60 149.30 107.01 I 168.65 DRelative integration.
Ferrocene-C Ferrocene-C(ipso)
c---o
881
Metallocene bis(crown ether) receptor molecules Table 4. ’3C NMR data for 5 from broad band decoupled and DEPT spectra (solvent CDCl, ; reference TMS)
6 (pw-4 68.74 69.38 69.61 69.65 70.36 70.52 70.87 70.96 I 72.66 (2) 73.25 (2) 1 83.35 107.01 112.38 114.78 132.53 145.54 149.19 167.05
Assignment
OCH,
Ruthenocene-C Ruthenocene-C(ipso)
Aromatics
C=o
r?Relative integration.
be interpreted as suggesting 1 : 1 stoichiometry of metallocene bis(crown ether) to guest alkali metal cation (Fig. 1). This result may lead to the proposition that both 4 and 5, in solution, are adopting a conformation in which the amido-benzo-15 crown-5 units are lying either cofacial or in close proximity to one another and are acting co-operatively to form intramolecular sandwich complexes with the alkali metal cation guest species. In contrast to this observation, a recent publication
reports the 18-crown-6 units of a related ferrocene bis(crown ether) to be acting independently of one another and complexing two alkali metal guest ions.27 Refluxing aqueous-methanolic solutions of 4 with an excess amount of sodium or potassium hexafluorophosphate led to the successful isolation of the respective [4M]PF6* H20, M = Na, K, complexes (see Table 5 for elemental analyses). The single-crystal structure of [4K]PF, -4MeOH is illustrated in Fig. 2 with the space-filling representation of the structure in Fig. 3. The structure confirms the intramolecular sandwich complex with the potassium guest cation in the solid state. Selected bond lengths and bond angles are listed in Tables 6 and 7, respectively. The torsional angles associated with the crown ether rings are shown in Table 8. These values are similar to those of benzo-15crown-5 itself28 and one conformer in the NaClO, (benzo-l5-crown-5), sandwich.29 The potassium guest cation is coordinated to all 10 oxygen atoms of the two benzo-crown ether moieties in an irregular pentagonal antiprismatic configuration with K-O contact distances ranging
Table 5. Microanalytical
(%y data
Compound
C
H
N
4 5 [4K]PFs.H,0 [4Na]PF, - Hz0
59.9(59.7) 56.6(56.4) 47.7(47.7) 48.5(49.4)
5.8(6.0) 5.8(5.6) 5.0(4.9) 5.5(5.5)
3.3(3.5) 3.4(3.3) 2.8(2.9) 2.7(2.8)
a Calculated values are in parentheses.
-
[ KN0,1/141
Fig. 1. 13C NMR titration curve of 4 and potassium nitrate.
P.
882
D. BEER et al.
^,^.
Cc261
cm C(23)
.n
KV .-
_
A,^#\
C(26') Fig. 2. The skeletal representation of the solid-state structure of [IK]PF, * 4MeOH.
from
Fig. 3. The space-filling representation of the solid-state structure of the 1: 1 complex formed between 4 and potassium.
2.82 to 2.97 8, (Table 9). These distances compare with 2.78-2.96 A in the KI (benzo-15crown-5), crystal structure reported by Truter.30 In contrast to Truter’s structure, it is noteworthy that the two shortest K-O contact distances are not those from the catechol oxygens but are from K-O(4) and K-O(7) (Table 9). Unlike the centrosymmetrical arrangement of the two benzocrown ligands in the KI (benzo-15-crown-5)2 structure,30 here the two components of the sandwich are related by a two-fold axis that passes through the Fe and K atoms with the benzo-crown moieties of 4 being gauche to each other. The cyclo-
Table 6. Bond lengths (A) with ESDs in parentheses Fc--C(21) Fe-C(23) Fe-C(25) Fc-C!(22a) Fe-C(24a) 0(1)-C(2) C(2t--c(3) 0(4)-C(5) C(6tW7) C(8)_C(9) O(lOY-Jl1) C(12)--0(13) C(14)--c(f5) C(15)--c(16) C(17t_C(18) c(1o)-c(19) C(2OWX20) C(21)-C(22) C(22)-C(23) C(24)--C(25) 0(27)-C(27)
2.043(4) 2.043(5) 2.040(4) 2.038(5) 2.020(5) 1.412(5) 1.503(7) 1.416(6) 1.436(7) 1.484(9) 1.416(6) 1.435(6) 1.399(6) 1.367(6) 1.379(7) 1.388(7) 1.224(6) 1.413(7) 1.418(7) 1.413(7) 1.391(10)
Fe--C(22) Fe-C(24) Fe-C(2la) Fe-C(23a) Fe-C(25a) W)--c(15) C(3WX4) C(5tC(6) 0(7)-C(8) C(9)--0(10) C(1 l)-C(12) 0(13)-C(14) C(l4)--c(l9) C(l6>--c(l7) C(17)-N(17) N( 17)-X(20) C(20)-C(21) C(21)-C(25) C(23)-C(24) 0(26)-C(26) P-F( 1)
2.038(5) 2.020(5) 2.043(4) 2.043(5) 2.040(4) 1.377(5) 1.416(6) 1.465(7) 1.411(6) 1.435(6) 1.487(7) 1.356(5) 1.380(7) 1.407(7) 1.404(6) 1.355(6) 1.483(7) 1.435(7) 1.399(7) 1.396(8) 1.576(5)
Metallocene
bis(crown
ether) receptor
883
molecules
Table 7. Bond angles (“) with ESDs in parentheses
w9-wk--w5) W-W-W) 0(4)--c(5)--c(6) C(6)--0(7)--C(8) C(8)--C(9FWO) W0k-W ltc(l2) C(12)--0(13)--c(~4) W3+C(l4F-C(19) 0(1)--c(15)-c(14) C(l4)--C(l5)--c(l6) C(16j-C(17)--C(18) C(lQ-C(17)-N(17) C(14)--C(19)--C(18) N( 17)--C(20)--O(20) 0(2O)--c(2Ok-C(2 C(2O)--c(2l)--c(25) C(2l)--c(22)-~(23) C(23)--C(24bC(25)
1)
119.4(3) 109.3(4) 113.9(4) 110.7(4) 113.3(4) 109.5(4) 118.6(3) 125.9(4) 113.5(4) 122.1(4) 119.0(4) 117.4(4) 119.8(4) 123.0(4) 120.7(4) 129.6(4) 108.9(4) 109.6(4)
Table 8. Torsional angles (“) associated with the crown ether rings with ESDs in parentheses C(15) C(2) C(2) O(1) C(2) C(3) O(4) C(5) C(6) O(7) C(8) C(9) O(l0) C(l1) C(12) C(12) O(l3) O(l3) C(19) C(19) O(l3) O(1) CU4) C(15) C(16) C(17)
O(l) O(l) O(1)
C(2) C(3) O(4) C(5) C(6) O(7) C(8) C(9) O(l0) C(l1) C(12) O(l3) O(l3) C(14) C(14) C(14) C(14) C(14) C(15) C(15) C(16) C(17) C(18)
C(2) C(15) C(l5) C(3) O(4) C(5) C(6) O(7) C(8) C(9) O(l0) C(l1) C(12) O(l3) C(14) C(14) C(15) C(15) C(15) C(15) C(19) C(16) C(16) C(17) C(18) C(19)
Table 9. K-O K--O(l) K--o(4) K--o(7) K-0(10) K-0( 13)
contact
C(3) C(14) C(16) O(4) C(5) C(6) O(7) C(8) C(9) O(l0) C(11) C(12) O(l3) C(14) C(15) C(19) 00) C(16) O(1) C(16) C(18) C(17) C(17) C(18) C(19) C(14)
distances 2.97(l) 2.88( 1) 2.82( 1) 2.86( 1) 2.91(l)
167.8(4) 176.5(4) - 5.0(6) 61.3(4) - 163.5(4) 85.3(6) 66.9(6) - 177.7(4) 172.1(4) -64.1(5) -79.8(5) 165.5(4) - 62.5(5) - 168.2(4) 178.2(4) - 2.3(6) 0.1(5) - 178.4(4) - 179.4(4) 2.0(7) 178.9(4) - 178.3(4) 0.0(6) -2.5(6) 3.0(7) - 0.9(7)
(A)
o(l)--c(2~(3) C(3)--0(4)-C(5) C(5)--c(6F(7) 0(7)--c(8yC(9) c(9)-0(10~c(11) C(ll)--c(l2)--o(l3) 0(13)--c(14~(15) C(l5)--c(l4)--W9) W)--c(l5)_C(l6) C(l5)--c(l6)--c(l7) C(16)-C(17)-N(17) C(17~C(18)--C(19) C(17)-N(17)-C(20) N(l7)--C(2O)--C(21) C(2O)--c(21 )--c(22) C(22)--c(2 v--~(25) C(22)-C(23)--C(24) C(2lW(25>--c(24)
105.7(4) 114.3(4) 108.7(4) 109.3(4) 113.1(4) 106.1(4) 115.5(4) 118.5(4) 124.4(4) 119.0(4) 123.5(4) 121.4(5) 128.6(4) 116.3(4) 123.2(4) 107.2(4) 107.2(4) 107.0(4)
rings of the ferrocene unit are almost parallel (3.4” between their mean planes and a mean inter-ring separation of 3.3 A) and rotated from an eclipsed orientation by ca 7” (Fig. 4). Similar geometries are found in low temperature triclinic,2g orthorhombic3’ forms of ferrocene, l-acetyl-l’benzoyl-ferrocene, 3’ acetyl-ferrocene, 32 diacetylferrocene33 and ferrocene-carboxylic acid34 where ring orientations range from eclipsed (O”) to 14” from eclipsed. 31 The cyclopentadienyl ring, the amide group and the benzo ring are not all coplanar there being small torsional rotations about the C(20)-C(21) [N(17), C(20), C(21), C(22) torsion angle 174.1(4)“] and the C(17)-N(17) [C(lS), C(17), N(17), C(20) torsion angle - 176.8(4)“] bonds. There are four molecules of methanol for each molecule of the complex, forming strong hydrogen bonds to each other and more weakly to the amido linkages of the ligand. It is noteworthy that X-ray quality crystals of the complex rapidly degrade in air indicating that the methanol molecules are essential to the structure of the crystal. pentadienyl
Fast atom bombardment tivity studies
mass spectrometry
selec-
Fast atom bombardment (FAB) mass spectrometry, a new powerful semi-quantitative technique, has been used to study the selectivity of monocyclic crown ethers for metal cations in competition experiments. 37It seemed reasonable to apply this method for the first time to bis(crown) ethers. Individual FAB mass spectrometric experiments
P. D. BEER et al.
884
HC26) 1
O(27’)
\
O(26)
H(27’)
Fig. 4. View of the complex normal to the plane of the upper (“heavy bonds”) cyclopentadienyl ring. Hydrogenbondinggeometries: 0z0..=02,2.71 A,0z0...H2, 1.79&O...H-0 < 154°,026...027 2.71 A, Hz69 . . 027 1.73 A, O...H--O < 175”, N,,...0z6 3.13 A, H,,...0z6 2.19 ii, N-H...0 < 161”.
of 4 (5 x lop3 M; 0.5 cm3 65% methanol-35% acetone) and 5 (5 x 10e3 M; 0.5 cm3 65% methanol-35% dichloromethane) with the nitrates of sodium, potassium and caesium (5 x lop3 M ; 0.5 cm3 water-l.0 cm3 glycerol) gave gas-phase [bis(crown ether) +metal]+ ions at m/z values of 1 : 1 stoichiometric formulations. Analogous competition experiments of 4 and 5 with an aqueous solution of sodium, potassium and caesium nitrates each at a concentration of 5 x 1O- 3 M gave the respective [4+potassium]+ ion (m/z 843) and [5 + potassium]+ ion (m/z 889), exclusively. The exclusive selectivity exhibited by both 4 and 5 towards potassium suggests that a well-defined cavity exists between the amido-benzo-15-crown-5 units which provides an optimal spatial fit3* for the potassium guest cation (see Figs 2 and 3). It is interesting to note that related bis(benzo-15crown-5) and bis(benzo- 18-crown-6) ether ligands linked together by various alkyl and alkoxy moieties, preferentially extract alkali metal cations larger than the hole size of the respective benzocrown ether unit39g40(K+ and Cs+, respectively) ; this change of selectivity has been called the “bis crown effect”. 41 Electrochemical
studies
The results of cyclic voltammetry measurements in acetonitrile of 4 and 5 are reported in Table 10. Addition of one or more equivalents of sodium or
Table 10. Electrochemical data Compound 4 5
E,,z”
0’)
AE,b (mV)
0.79 0.55’
lOO(70)
“Obtained from cyclic voltammetry studies in acetonitrile solvent containing 0.2 M [Bu”4NJBF4 as supporting electrolyte. Solutions were ca 2 x 10m3 M in the compound and measurements were made at 21+ 1°C at 0.2 V s- ’ scan rate using a Pt bead working electrode with ferrocene internal reference. Values are quoted relative to the saturated calomel reference electrode. bSeparation between anodic and cathodic peak potentials, values for ferrocene under the same conditions in parentheses. No compensation was made for internal cell resistance. ’ Anodic peak potential for an irreversible process. potassium hexafluorophosphate chemical acetonitrile solutions
to
the
electro-
of 4 had little effect (A&,, .< 20 mV) on the reversible ferrocenyl oxidation wave. This result implies that the alkali metal cation complexed at the benzo-crown ether coordinating sites, is too far away to influence the electron density at the ferrocene iron atom, either inductively or through space. We are currently synthesizing related Group 1A selective metallocene receptor molecules designed to have the cation binding site in closer proximity to the redox-active centre.
885
Metallocene bis(crown ether) receptor molecules EXPERIMENTAL Reactions were carried out under an atmosphere of dry nitrogen and solvents were distilled prior to use from an appropriate drying agent. ‘H NMR spectra were recorded at 400 MHz and 13C NMR spectra at 100 MHz using tetramethylsilane (TMS) as internal standard. Electrochemical measurements were performed on a PAR 174A polarographic analyser. Positive ion FAB mass spectrometry was performed using a primary atom beam of Ar (6 keV) on a Kratos MS80 RF mass spectrometer coupled to a Kratos DS55 data system. 1,l ‘-Bis(chlorocarbonyl)ferrocene, I,1 ‘-bis(chloro4-aminobenzo- 15and carbonyl)ruthenocene crown-5 were prepared according to literature procedures.24,25
product which was chromatographed on an alumina column using 99% dichloromethane-I % methanol. A pale yellow band was collected and removal of solvents followed by recrystallization from dichoromethane-hexane gave 5 (0.98 g, 75%) as pale yellow crystals, m.p. 206-207°C ; m/z 850. Preparation
of sodium
and potassium
complexes
of 4
To a methanolic solution of 4 (1 mmol) was added an excess amount of alkali metal hexafluorophosphate salt (5 mmol). The resulting solution was refluxed for 30 min and upon cooling an orange precipitate was collected and dried in uacuo. Recrystallization from methanol gave the respective complexes in quantitative yields. ‘3C NA4R titration experiments
l,l’-Bis([(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13benzopentaoxacyclopentadecin - 15 - yl) - amino]carbonyllferrocene
(4)
A solution of 1, I’-bis(chlorocarbonyI)ferrocene (1) (0.5 g, 1.61 mmol) in dry toluene (70 cm’) was added dropwise over 30 min to a stirred solution of 4-aminobenzo-15-crown-5 (3; 0.91 g, 3.2 mmol) in toluene (100 cm’) containing triethylamine (0.32 g, 3.2 mmol). When addition was complete stirring was continued for 1 h and the solution filtered. After removal of solvent the crude product was chromatographed on a column of alumina using 99% dichloromethane-I % methanol eluant. An orange band was collected and after solvents were removed recrystallization from dichloromethanehexane gave 4 (1.03 g, 80%) as orange crystals, m.p. 198199°C ; m/z 804. 1,1’-Bis([(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13- 15 - yl) - aminol-
benzopentaoxacyclopentadecin carbonyljruthenocene (5)
The procedure for the preparation of 5 followed that described for 4. A solution of l,l’-bis(chlorocarbonyl)ruthenocene (2) (0.6 g, 1.68 mmol) in dry toluene (50 cm3) was added dropwise over 30 min to a stirred solution of 4-aminobenzo-15-crown-5 (0.95 g, 3.3 mmol) in toluene (70 cm3) containing triethylamine (0.34 g, 3.3 mmol). When addition was complete stirring was continued for 1 h and the solution filtered. Removal of solvent gave the crude * The atomic co-ordinates for this work are available on request from the Director of the Cambridge Crystallographic Data Centre, University Chemical Laboratory, Lensfield Road, Cambridge CB2 lEW, U.K.
The experimental procedure consisted of measuring Adobsas a function of changing alkali metal nitrate salt concentrations while the metallocene bis(crown ether) ligand’s concentration was kept constant. In a typical experiment, 4 (30 mg, 0.373 mmol) was dissolved in 65% methanol-35% acetone (4 cm3) and the resulting solution transferred to a 13CNMR tube. The 13CNMR chemical shifts were measured versus tetramethylsilane (TMS) as internal standard after each addition of NaNO,, KN03 and CsN03, respectively. Titration curves were obtained by plotting A&b, (ppm) versus [MN0,]/[4]. See Fig. 1 in Results and Discussion. Crystal data*
C4,,H48N2012KFe*PF6.(CH30H)4, M = 1116.9, monoclinic, space group C2/c, a = 14.283(3), b = 25.726(5), c = 14.438(2) A, /I = 101.53(2)“, V = 5198 A3, Z = 4 (the complex is disposed about a two-fold axis), D, = 1.43 g cm- 3, p = 41 cm-’ , F(OOO)= 2332. Data collection. 2672 unique independent rehections (28 < 1OOC) were measured on a Nicolet R3m diffractometer with Cu-K, radiation (graphite monochromator, 1 = 1.54178 A) using the o-scan measuring routine. Of these, 2022 had [IF,1 > 3@J)] and were considered observed. Structure solution and rejinement. The structure was solved by direct methods. A numerical absorption correction, based on a face-indexed crystal, was applied. The non-hydrogen atoms were refined anisotropically. The PF; group was disordered, and refined as two distinct orientations, of occupancy 70 and 30%, respectively. The hydroxy hydrogen atoms on the methanols and the amide
P. D. BEER et al.
886
proton were located from a AF map and refined isotropically. The leading hydrogen atoms on the methyls of the methanols were also located from a AF map, and the groups refined as rigid bodies. The positions of the remaining hydrogen atoms were idealized (C-H 0.96 A), assigned isotropic thermal parameters U(H) = 1.2 U,, (C), and allowed to ride on their parent carbon atoms. Refinement converged to R = 0.051, R, = 0.046 [w- ’ = 02(F’) + 0.00032F2]. Refinement was by block-cascade full-matrix least-squares, carried out on an Eclipse S140 computer using the SHELXTL program system.40 Acknowledgements-We thank the British Council for financial support (to H.S.), NATO, the Research Corporation Trust for additional financial support and the SERC for use of the high field NMR service at the University of Warwick.
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Gatto, R. A. Schultz, T. P. Clearly, C. R. Morgan, D. M. Goli, A. M. Rios and G. W. Gokel, J. Am. Chem. Sot. 1985, lCn, 1958. 16. S. Akabori, Y. Habata, M. Sato and S. Ebine, Bull. Chem. Sot. Jpn 1983,56,
1459.
17. B. Czech and A. Ratajczak, Pol. J. Chem. 1980, 54, 767.
18. T. Saji, Chem. Lett. 1986, 275. 19. P. D. Beer, J. Chem. Sot., Chem. Commun.
1985,
1115.
20. P. D. Beer, J. Organomet. Chem. 1985,297, 313. 21. P. D. Beer and A. D. Keefe, J. Organomet. Chem. 1986,306, ClO. 22. P. D. Beer, C. G. Crane, A. D. Keefe and A. R. Whyman, J. Organomet. Chem. 1986,314, C9. 23. P. D. Beer, P. J. Hammond, C. Dudman, I. P. Danks and C. D. Hall, J. Organomet. Chem. 1986,306,367. 24. H. J. Lorkowski, R. Pannier and A. Wende, J. Prakt. Chem. 1967,35, 149. 25. R. Ungaro, B. El Haj and J. Smid, J. Am. Chem. Sot. 1977,98,5198. 26. E. Amble and E. Amble, Polyhedron 1983,2, 1063. 27. B. Czech, A. Czech, S. I. Kang and R. A. Bartsch, Chem. Lett. 1984, 37. 28. I. R. Hanson, Actu Crystallogr. 1978, B34, 1026. 29. J. D. Owen, J. Chem. Sot., Dalton Trans. 1980, 1066. 30. P. R. Mallinson and M. R. Truter, J. Chem. Sot., Perkin Trans. 2 1972, 1818. 31. P. Seiler and J. D. Dunitz, Acta Crystallogr. 1979, B35,2020. 32. P. Seiler and J. D. Dunitz, Acta Crystallogr. 1982, B38, 1741. 33. G. Calvarin and D. Weigel, Acta Crystullogr. 1971, B27, 1253. 34. K. Sato, M. Katada, H. Sano and M. Kono, Bull. Chem. Sot. Jpn 1984,57,2361. 35. G. J. Palenik, Znorg. Chem. 1970, 9, 2424. 36. F. A. Cotton and A. H. Reid Jr, Acta Crystallogr. 1985, C41,686. 37. R. A. W. Johnstone and M. E. Rose, J. Chem. Sot., Chem. Commun. 1983, 1268. 38. E. Weber and F. Vogtle, Top. Curr. Chem. 1981,
98, 1. 39. M. Bourgoin, K. H. Wong, J. Y. Hui and J. Smid, J. Am. Chem. Sot. 1975,97,3462.
40. K. Kikukawa, G. X. He, A. Abe, T. Goto, R. Arata, T. Ikeda, F. Wada and T. Matsuda, J. Chem. Sot., Perkin Trans. 2 1987, 135.
41. K. Kimura, H. Sakamoto, Y. Koseki and T. Shono, Chem. Lett. 1985, 1241.
42. G. M. Sheldrick, SHELXTL, An Integrated System for Solving, Refining and Displaying Crystal Structures from Diffraction Data. University of Gijttingen (1978) ; revised version (1984).
0277-5381189 $3.00+.00 0 1989 Pergamon Press pk
TI-IE SYNTHESIS, COORDINATION AND ELECTROCHEMICAL STUDIES OF METALLOCENE BIS(CROWN ETHER) RECEPTOR MOLECULES. SINGLE-CRYSTAL X-RAY STRUCTURE OF A FERROCENE BIS(CROWN ETHER) POTASSIUM COMPLEX PAUL D. BEER* and HARRISON
SIKANYIKA
Department of Chemistry, University of Birmingham, P.O. Box 363, Birmingham B15 2TT, U.K. and ALEXANDRA
Chemical Crystallography
M. Z. SLAWIN
and DAVID
J. WILLIAMS
Laboratory, Department of Chemistry, Imperial College, London SW7 2AY, U.K.
(Received 3 October 1988 ; accepted 31 October 1988) Abstract-The condensation of 1, 1‘-bis(chlorocarbonyl)ferrocene and l,l’-bis(chlorocarbonyl)ruthenocene with 4-aminobenzo-15-crown-5 gives the metallocene bis(crown ether) ligands l,l’-bis[(2,3,5,6,8,9,1 1,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin15-yl)amino]carbonylferrocene (4) and the ruthenocene analogue (5). 13C NMR titrations of 4 and 5 with Na+, K+ and Cs+ alkali metal salts lead to titration curves interpreted as suggesting 1 : 1 stoichiometry. The single-crystal X-ray structure of [4K]PF6 * 4MeOH reveals an intramolecular sandwich complex with the potassium guest cation in the solid state. Competition fast atom bombardment (FAB) mass spectrometry selectivity experiments show 4 and 5 to exhibit exclusive K+ selective complexation over either Na+ or Cs+.
Responsive macrocyclic receptor molecules whose binding strength and/or selectivity towards guest species can be influenced by physical and chemical means, have been the subject of many recent reports in the chemical literature. I-5 Examples include pHresponsive crown ethers,2,3,6,7 which change their cation binding ability in response to medium pH and photoresponsive crown ethers, ‘*8 azoarenecapped oxygen macrocycles which undergo photoinduced reversible interconversion between the tram and cis azo linkages resulting in substantial changes in their cation binding properties. Particular attention has been focused on the synthesis of redox-responsive macrocycles that contain redox-active functions such as quinone,g-‘4 nitro*Author to whom correspondence
should be addressed.
benzenei and metallocene moieties’“23 in close proximity to a cation binding site. We are currently interested in preparing metallocene redox-active macropolycyclic host molecules designed to be selective as well as being redox-responsive to the host binding of inorganic and organic guest species. ‘9-22 One application of such receptors lies in their potential development as components of new chemical sensory devices. We report here the synthesis, coordination and electrochemical studies of two new metallocene bisbenzo-crown ethers, 4 and 5, and the single-crystal X-ray structure of [4K]PF6 - 4MeOH, which, to our knowledge, is the$rst structural example of a bisbenzo-crown ether potassium intramolecular sandwich complex. A preliminary report on this work has recently been published. l9 879
P. D. BEER et al.
880
RESULTS
AND DISCUSSION
Synthesis of 4 and 5 The condensation carbonyl)metallocenes
Table 1. ‘H NMR data for 4 (solvent CDCl, ; reference TMS) Assignment
6 Cm-W of respective l,l’-bis(chloro1 and 224 with 2 mol of 4-
aminobenzo-15-crown-5 (3)25 in the presence of triethylamine gave, after column chromatography (alumina, 99% CH2C12, 1% MeOH), the ferrocene bis(crown ether) (4 :80% yield) and the ruthenocene analogue (5: 75% yield), Scheme 1 (preparative details are given in the Experimental). The structures of both new air-stable metallocene bis(crown ethers) were characterized by elemental analysis, mass spectrometry and ‘H (Tables 1 and 2) and 13C NMR spectroscopy (Tables 3 and 4).
3.73-4.13 4.39”
4.60” 6.82 7.20
(m, 32 H) (t, J 1.8 Hz, 4H) (t, J 1.8 Hz, 4H) (d, J 8.7 Hz, 2H (d of d, J 8.7 Hz, J 2 Hz, 2H) (d, J 2 Hz, 2H) (.s, broad, 2H)
Crown protons Ferrocenyl
j
7.55 8.87
Aromatics NH
“‘Apparent triplet’ assigned as an AA’BB’ system.
Table 2. ‘H NMR data for 5 (solvent CDC13 ; reference TMS)
Coordination studies ‘%2 NMR spectroscopy investigate the complexation
was used initially to of 4 and 5 with alkali
Assignment
6 (Ppm)
metal cations sodium, potassium and caesium.26 The stepwise addition of an alkali metal nitrate salt to a methanol (65%)-acetone (35%) solution of 4 and a methanol (65%)dichloromethane (35%) solution of 5 led to considerable shifts of the 0CH2 carbons of the respective bis(crown molecules). In all cases the A6 ppm versus [alkali metal salt]/ [metallocene bis(crown ether)] titration curves can
3.72-4.10 4.72” 5.01” 6.75 7.09
7.42 8.38
(m, 32H) (t, J 1.7 Hz, 4H) (t, J 1.7 Hz, 4H) (d, J 8.7 Hz, 2H j (d of d, J 8.7 Hz, J 2 Hz, 2H) (d, J 2 Hz, 2H) (s, broad, 2H)
“Apparent
Crown protons Ruthenocenyl
Aromatics NH
triplet’ assigned as an AA’BB’ system.
Table 3. 13CNMR data for 4 from broad band decoupled and DEPT spectra (solvent CDC13 ; reference TMS) 6 (.Ppm) (I) (2)
M’=Fe M’=Ru
I
2 Et,N
(4)
M’= Fe
(51 M’=Ru
Scheme 1.
68.83 69.39 69.62 69.71 70.38 70.53 70.88 70.96 71.07 79.27
Assignment
OCH,
1)
112.32 114.94 132.78 145.60 149.30 107.01 I 168.65 DRelative integration.
Ferrocene-C Ferrocene-C(ipso)
c---o
881
Metallocene bis(crown ether) receptor molecules Table 4. ’3C NMR data for 5 from broad band decoupled and DEPT spectra (solvent CDCl, ; reference TMS)
6 (pw-4 68.74 69.38 69.61 69.65 70.36 70.52 70.87 70.96 I 72.66 (2) 73.25 (2) 1 83.35 107.01 112.38 114.78 132.53 145.54 149.19 167.05
Assignment
OCH,
Ruthenocene-C Ruthenocene-C(ipso)
Aromatics
C=o
r?Relative integration.
be interpreted as suggesting 1 : 1 stoichiometry of metallocene bis(crown ether) to guest alkali metal cation (Fig. 1). This result may lead to the proposition that both 4 and 5, in solution, are adopting a conformation in which the amido-benzo-15 crown-5 units are lying either cofacial or in close proximity to one another and are acting co-operatively to form intramolecular sandwich complexes with the alkali metal cation guest species. In contrast to this observation, a recent publication
reports the 18-crown-6 units of a related ferrocene bis(crown ether) to be acting independently of one another and complexing two alkali metal guest ions.27 Refluxing aqueous-methanolic solutions of 4 with an excess amount of sodium or potassium hexafluorophosphate led to the successful isolation of the respective [4M]PF6* H20, M = Na, K, complexes (see Table 5 for elemental analyses). The single-crystal structure of [4K]PF, -4MeOH is illustrated in Fig. 2 with the space-filling representation of the structure in Fig. 3. The structure confirms the intramolecular sandwich complex with the potassium guest cation in the solid state. Selected bond lengths and bond angles are listed in Tables 6 and 7, respectively. The torsional angles associated with the crown ether rings are shown in Table 8. These values are similar to those of benzo-15crown-5 itself28 and one conformer in the NaClO, (benzo-l5-crown-5), sandwich.29 The potassium guest cation is coordinated to all 10 oxygen atoms of the two benzo-crown ether moieties in an irregular pentagonal antiprismatic configuration with K-O contact distances ranging
Table 5. Microanalytical
(%y data
Compound
C
H
N
4 5 [4K]PFs.H,0 [4Na]PF, - Hz0
59.9(59.7) 56.6(56.4) 47.7(47.7) 48.5(49.4)
5.8(6.0) 5.8(5.6) 5.0(4.9) 5.5(5.5)
3.3(3.5) 3.4(3.3) 2.8(2.9) 2.7(2.8)
a Calculated values are in parentheses.
-
[ KN0,1/141
Fig. 1. 13C NMR titration curve of 4 and potassium nitrate.
P.
882
D. BEER et al.
^,^.
Cc261
cm C(23)
.n
KV .-
_
A,^#\
C(26') Fig. 2. The skeletal representation of the solid-state structure of [IK]PF, * 4MeOH.
from
Fig. 3. The space-filling representation of the solid-state structure of the 1: 1 complex formed between 4 and potassium.
2.82 to 2.97 8, (Table 9). These distances compare with 2.78-2.96 A in the KI (benzo-15crown-5), crystal structure reported by Truter.30 In contrast to Truter’s structure, it is noteworthy that the two shortest K-O contact distances are not those from the catechol oxygens but are from K-O(4) and K-O(7) (Table 9). Unlike the centrosymmetrical arrangement of the two benzocrown ligands in the KI (benzo-15-crown-5)2 structure,30 here the two components of the sandwich are related by a two-fold axis that passes through the Fe and K atoms with the benzo-crown moieties of 4 being gauche to each other. The cyclo-
Table 6. Bond lengths (A) with ESDs in parentheses Fc--C(21) Fe-C(23) Fe-C(25) Fc-C!(22a) Fe-C(24a) 0(1)-C(2) C(2t--c(3) 0(4)-C(5) C(6tW7) C(8)_C(9) O(lOY-Jl1) C(12)--0(13) C(14)--c(f5) C(15)--c(16) C(17t_C(18) c(1o)-c(19) C(2OWX20) C(21)-C(22) C(22)-C(23) C(24)--C(25) 0(27)-C(27)
2.043(4) 2.043(5) 2.040(4) 2.038(5) 2.020(5) 1.412(5) 1.503(7) 1.416(6) 1.436(7) 1.484(9) 1.416(6) 1.435(6) 1.399(6) 1.367(6) 1.379(7) 1.388(7) 1.224(6) 1.413(7) 1.418(7) 1.413(7) 1.391(10)
Fe--C(22) Fe-C(24) Fe-C(2la) Fe-C(23a) Fe-C(25a) W)--c(15) C(3WX4) C(5tC(6) 0(7)-C(8) C(9)--0(10) C(1 l)-C(12) 0(13)-C(14) C(l4)--c(l9) C(l6>--c(l7) C(17)-N(17) N( 17)-X(20) C(20)-C(21) C(21)-C(25) C(23)-C(24) 0(26)-C(26) P-F( 1)
2.038(5) 2.020(5) 2.043(4) 2.043(5) 2.040(4) 1.377(5) 1.416(6) 1.465(7) 1.411(6) 1.435(6) 1.487(7) 1.356(5) 1.380(7) 1.407(7) 1.404(6) 1.355(6) 1.483(7) 1.435(7) 1.399(7) 1.396(8) 1.576(5)
Metallocene
bis(crown
ether) receptor
883
molecules
Table 7. Bond angles (“) with ESDs in parentheses
w9-wk--w5) W-W-W) 0(4)--c(5)--c(6) C(6)--0(7)--C(8) C(8)--C(9FWO) W0k-W ltc(l2) C(12)--0(13)--c(~4) W3+C(l4F-C(19) 0(1)--c(15)-c(14) C(l4)--C(l5)--c(l6) C(16j-C(17)--C(18) C(lQ-C(17)-N(17) C(14)--C(19)--C(18) N( 17)--C(20)--O(20) 0(2O)--c(2Ok-C(2 C(2O)--c(2l)--c(25) C(2l)--c(22)-~(23) C(23)--C(24bC(25)
1)
119.4(3) 109.3(4) 113.9(4) 110.7(4) 113.3(4) 109.5(4) 118.6(3) 125.9(4) 113.5(4) 122.1(4) 119.0(4) 117.4(4) 119.8(4) 123.0(4) 120.7(4) 129.6(4) 108.9(4) 109.6(4)
Table 8. Torsional angles (“) associated with the crown ether rings with ESDs in parentheses C(15) C(2) C(2) O(1) C(2) C(3) O(4) C(5) C(6) O(7) C(8) C(9) O(l0) C(l1) C(12) C(12) O(l3) O(l3) C(19) C(19) O(l3) O(1) CU4) C(15) C(16) C(17)
O(l) O(l) O(1)
C(2) C(3) O(4) C(5) C(6) O(7) C(8) C(9) O(l0) C(l1) C(12) O(l3) O(l3) C(14) C(14) C(14) C(14) C(14) C(15) C(15) C(16) C(17) C(18)
C(2) C(15) C(l5) C(3) O(4) C(5) C(6) O(7) C(8) C(9) O(l0) C(l1) C(12) O(l3) C(14) C(14) C(15) C(15) C(15) C(15) C(19) C(16) C(16) C(17) C(18) C(19)
Table 9. K-O K--O(l) K--o(4) K--o(7) K-0(10) K-0( 13)
contact
C(3) C(14) C(16) O(4) C(5) C(6) O(7) C(8) C(9) O(l0) C(11) C(12) O(l3) C(14) C(15) C(19) 00) C(16) O(1) C(16) C(18) C(17) C(17) C(18) C(19) C(14)
distances 2.97(l) 2.88( 1) 2.82( 1) 2.86( 1) 2.91(l)
167.8(4) 176.5(4) - 5.0(6) 61.3(4) - 163.5(4) 85.3(6) 66.9(6) - 177.7(4) 172.1(4) -64.1(5) -79.8(5) 165.5(4) - 62.5(5) - 168.2(4) 178.2(4) - 2.3(6) 0.1(5) - 178.4(4) - 179.4(4) 2.0(7) 178.9(4) - 178.3(4) 0.0(6) -2.5(6) 3.0(7) - 0.9(7)
(A)
o(l)--c(2~(3) C(3)--0(4)-C(5) C(5)--c(6F(7) 0(7)--c(8yC(9) c(9)-0(10~c(11) C(ll)--c(l2)--o(l3) 0(13)--c(14~(15) C(l5)--c(l4)--W9) W)--c(l5)_C(l6) C(l5)--c(l6)--c(l7) C(16)-C(17)-N(17) C(17~C(18)--C(19) C(17)-N(17)-C(20) N(l7)--C(2O)--C(21) C(2O)--c(21 )--c(22) C(22)--c(2 v--~(25) C(22)-C(23)--C(24) C(2lW(25>--c(24)
105.7(4) 114.3(4) 108.7(4) 109.3(4) 113.1(4) 106.1(4) 115.5(4) 118.5(4) 124.4(4) 119.0(4) 123.5(4) 121.4(5) 128.6(4) 116.3(4) 123.2(4) 107.2(4) 107.2(4) 107.0(4)
rings of the ferrocene unit are almost parallel (3.4” between their mean planes and a mean inter-ring separation of 3.3 A) and rotated from an eclipsed orientation by ca 7” (Fig. 4). Similar geometries are found in low temperature triclinic,2g orthorhombic3’ forms of ferrocene, l-acetyl-l’benzoyl-ferrocene, 3’ acetyl-ferrocene, 32 diacetylferrocene33 and ferrocene-carboxylic acid34 where ring orientations range from eclipsed (O”) to 14” from eclipsed. 31 The cyclopentadienyl ring, the amide group and the benzo ring are not all coplanar there being small torsional rotations about the C(20)-C(21) [N(17), C(20), C(21), C(22) torsion angle 174.1(4)“] and the C(17)-N(17) [C(lS), C(17), N(17), C(20) torsion angle - 176.8(4)“] bonds. There are four molecules of methanol for each molecule of the complex, forming strong hydrogen bonds to each other and more weakly to the amido linkages of the ligand. It is noteworthy that X-ray quality crystals of the complex rapidly degrade in air indicating that the methanol molecules are essential to the structure of the crystal. pentadienyl
Fast atom bombardment tivity studies
mass spectrometry
selec-
Fast atom bombardment (FAB) mass spectrometry, a new powerful semi-quantitative technique, has been used to study the selectivity of monocyclic crown ethers for metal cations in competition experiments. 37It seemed reasonable to apply this method for the first time to bis(crown) ethers. Individual FAB mass spectrometric experiments
P. D. BEER et al.
884
HC26) 1
O(27’)
\
O(26)
H(27’)
Fig. 4. View of the complex normal to the plane of the upper (“heavy bonds”) cyclopentadienyl ring. Hydrogenbondinggeometries: 0z0..=02,2.71 A,0z0...H2, 1.79&O...H-0 < 154°,026...027 2.71 A, Hz69 . . 027 1.73 A, O...H--O < 175”, N,,...0z6 3.13 A, H,,...0z6 2.19 ii, N-H...0 < 161”.
of 4 (5 x lop3 M; 0.5 cm3 65% methanol-35% acetone) and 5 (5 x 10e3 M; 0.5 cm3 65% methanol-35% dichloromethane) with the nitrates of sodium, potassium and caesium (5 x lop3 M ; 0.5 cm3 water-l.0 cm3 glycerol) gave gas-phase [bis(crown ether) +metal]+ ions at m/z values of 1 : 1 stoichiometric formulations. Analogous competition experiments of 4 and 5 with an aqueous solution of sodium, potassium and caesium nitrates each at a concentration of 5 x 1O- 3 M gave the respective [4+potassium]+ ion (m/z 843) and [5 + potassium]+ ion (m/z 889), exclusively. The exclusive selectivity exhibited by both 4 and 5 towards potassium suggests that a well-defined cavity exists between the amido-benzo-15-crown-5 units which provides an optimal spatial fit3* for the potassium guest cation (see Figs 2 and 3). It is interesting to note that related bis(benzo-15crown-5) and bis(benzo- 18-crown-6) ether ligands linked together by various alkyl and alkoxy moieties, preferentially extract alkali metal cations larger than the hole size of the respective benzocrown ether unit39g40(K+ and Cs+, respectively) ; this change of selectivity has been called the “bis crown effect”. 41 Electrochemical
studies
The results of cyclic voltammetry measurements in acetonitrile of 4 and 5 are reported in Table 10. Addition of one or more equivalents of sodium or
Table 10. Electrochemical data Compound 4 5
E,,z”
0’)
AE,b (mV)
0.79 0.55’
lOO(70)
“Obtained from cyclic voltammetry studies in acetonitrile solvent containing 0.2 M [Bu”4NJBF4 as supporting electrolyte. Solutions were ca 2 x 10m3 M in the compound and measurements were made at 21+ 1°C at 0.2 V s- ’ scan rate using a Pt bead working electrode with ferrocene internal reference. Values are quoted relative to the saturated calomel reference electrode. bSeparation between anodic and cathodic peak potentials, values for ferrocene under the same conditions in parentheses. No compensation was made for internal cell resistance. ’ Anodic peak potential for an irreversible process. potassium hexafluorophosphate chemical acetonitrile solutions
to
the
electro-
of 4 had little effect (A&,, .< 20 mV) on the reversible ferrocenyl oxidation wave. This result implies that the alkali metal cation complexed at the benzo-crown ether coordinating sites, is too far away to influence the electron density at the ferrocene iron atom, either inductively or through space. We are currently synthesizing related Group 1A selective metallocene receptor molecules designed to have the cation binding site in closer proximity to the redox-active centre.
885
Metallocene bis(crown ether) receptor molecules EXPERIMENTAL Reactions were carried out under an atmosphere of dry nitrogen and solvents were distilled prior to use from an appropriate drying agent. ‘H NMR spectra were recorded at 400 MHz and 13C NMR spectra at 100 MHz using tetramethylsilane (TMS) as internal standard. Electrochemical measurements were performed on a PAR 174A polarographic analyser. Positive ion FAB mass spectrometry was performed using a primary atom beam of Ar (6 keV) on a Kratos MS80 RF mass spectrometer coupled to a Kratos DS55 data system. 1,l ‘-Bis(chlorocarbonyl)ferrocene, I,1 ‘-bis(chloro4-aminobenzo- 15and carbonyl)ruthenocene crown-5 were prepared according to literature procedures.24,25
product which was chromatographed on an alumina column using 99% dichloromethane-I % methanol. A pale yellow band was collected and removal of solvents followed by recrystallization from dichoromethane-hexane gave 5 (0.98 g, 75%) as pale yellow crystals, m.p. 206-207°C ; m/z 850. Preparation
of sodium
and potassium
complexes
of 4
To a methanolic solution of 4 (1 mmol) was added an excess amount of alkali metal hexafluorophosphate salt (5 mmol). The resulting solution was refluxed for 30 min and upon cooling an orange precipitate was collected and dried in uacuo. Recrystallization from methanol gave the respective complexes in quantitative yields. ‘3C NA4R titration experiments
l,l’-Bis([(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13benzopentaoxacyclopentadecin - 15 - yl) - amino]carbonyllferrocene
(4)
A solution of 1, I’-bis(chlorocarbonyI)ferrocene (1) (0.5 g, 1.61 mmol) in dry toluene (70 cm’) was added dropwise over 30 min to a stirred solution of 4-aminobenzo-15-crown-5 (3; 0.91 g, 3.2 mmol) in toluene (100 cm’) containing triethylamine (0.32 g, 3.2 mmol). When addition was complete stirring was continued for 1 h and the solution filtered. After removal of solvent the crude product was chromatographed on a column of alumina using 99% dichloromethane-I % methanol eluant. An orange band was collected and after solvents were removed recrystallization from dichloromethanehexane gave 4 (1.03 g, 80%) as orange crystals, m.p. 198199°C ; m/z 804. 1,1’-Bis([(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13- 15 - yl) - aminol-
benzopentaoxacyclopentadecin carbonyljruthenocene (5)
The procedure for the preparation of 5 followed that described for 4. A solution of l,l’-bis(chlorocarbonyl)ruthenocene (2) (0.6 g, 1.68 mmol) in dry toluene (50 cm3) was added dropwise over 30 min to a stirred solution of 4-aminobenzo-15-crown-5 (0.95 g, 3.3 mmol) in toluene (70 cm3) containing triethylamine (0.34 g, 3.3 mmol). When addition was complete stirring was continued for 1 h and the solution filtered. Removal of solvent gave the crude * The atomic co-ordinates for this work are available on request from the Director of the Cambridge Crystallographic Data Centre, University Chemical Laboratory, Lensfield Road, Cambridge CB2 lEW, U.K.
The experimental procedure consisted of measuring Adobsas a function of changing alkali metal nitrate salt concentrations while the metallocene bis(crown ether) ligand’s concentration was kept constant. In a typical experiment, 4 (30 mg, 0.373 mmol) was dissolved in 65% methanol-35% acetone (4 cm3) and the resulting solution transferred to a 13CNMR tube. The 13CNMR chemical shifts were measured versus tetramethylsilane (TMS) as internal standard after each addition of NaNO,, KN03 and CsN03, respectively. Titration curves were obtained by plotting A&b, (ppm) versus [MN0,]/[4]. See Fig. 1 in Results and Discussion. Crystal data*
C4,,H48N2012KFe*PF6.(CH30H)4, M = 1116.9, monoclinic, space group C2/c, a = 14.283(3), b = 25.726(5), c = 14.438(2) A, /I = 101.53(2)“, V = 5198 A3, Z = 4 (the complex is disposed about a two-fold axis), D, = 1.43 g cm- 3, p = 41 cm-’ , F(OOO)= 2332. Data collection. 2672 unique independent rehections (28 < 1OOC) were measured on a Nicolet R3m diffractometer with Cu-K, radiation (graphite monochromator, 1 = 1.54178 A) using the o-scan measuring routine. Of these, 2022 had [IF,1 > 3@J)] and were considered observed. Structure solution and rejinement. The structure was solved by direct methods. A numerical absorption correction, based on a face-indexed crystal, was applied. The non-hydrogen atoms were refined anisotropically. The PF; group was disordered, and refined as two distinct orientations, of occupancy 70 and 30%, respectively. The hydroxy hydrogen atoms on the methanols and the amide
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proton were located from a AF map and refined isotropically. The leading hydrogen atoms on the methyls of the methanols were also located from a AF map, and the groups refined as rigid bodies. The positions of the remaining hydrogen atoms were idealized (C-H 0.96 A), assigned isotropic thermal parameters U(H) = 1.2 U,, (C), and allowed to ride on their parent carbon atoms. Refinement converged to R = 0.051, R, = 0.046 [w- ’ = 02(F’) + 0.00032F2]. Refinement was by block-cascade full-matrix least-squares, carried out on an Eclipse S140 computer using the SHELXTL program system.40 Acknowledgements-We thank the British Council for financial support (to H.S.), NATO, the Research Corporation Trust for additional financial support and the SERC for use of the high field NMR service at the University of Warwick.
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