Polyhedron Vol. 9, No. 21, pp. 264-2645, 1990 Printed in Great Britain

0277-5387/90 $3X13+ ~30 0 1990 Pergamon Press plc

IRON MACROCYCLIC COMPLEXES : THE SYNTHESIS AND SINGLE CRYSTAL X-RAY STRUCTURE OF

Fe([lt#]aneN&J](BPQ l 2MeCN l 1/2MeOH {[lS]aneN,S, = 1,4,10,13- TETRATHIA-7,16-DIAZACYCLOOCTADECANE)

NIGEL ATKINSON and AIDAN J. LAVERY

Department of Physical Sciences, The Polytechnic, Queensgate, Huddersfield HDl 3DH, U.K.

and

ALEXANDER J. BLARE, GILLIAN REID and MARTIN SCHRODER”

Department of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 355, U.K.

(Received 17 May 1990 ; accepted 20 July 1990)

Abstract-Reaction of FeCl, with one molar equivalent of [ 18]aneN,S, in refluxing MeOH- H,O for 15 min affords a deep blue solution containing the complex cation [Fe([18] aneN,&)] . *+ Addition of excess BF4- or BPh,- counterions gives the complex as a blue solid. A single crystal X-ray structure determination of [Fe([l8]aneN,S,)](BPh,), * 2MeCN. 1/2MeOH shows iron(I1) bound to all six macrocyclic donor atoms in a distorted octahedral geometry, Fe-N = 2.022(4), 2.037(5), Fe-S = 2.2578(17), 2.2588(16), 2.2673(16), 2.2674(15) A. The macrocycle binds to give a rat configuration with each SCH2CH2NCH2CH2S linkage bound meridionally to the metal centre. Solutions of [Fe([l8]aneN,S,)](BF,), show two irreversible, overlapping oxidations at Epa = +0.78 and +0.88 V vs Fc/Fc+.

We have recently been investigating the coor- dination chemistry of the potentially hexadentate macrocycles [ 18]aneN,S, (1,4,10,13-tetrathia-7,16- diazacyclooctadecane) and Me,[ 18]aneN,S, (7,16- dimethyl- 1,4,10,13-tetrathia-7,16-diazacycloocta- decane). I In the course of this work we have ob- served that these macrocycles bind readily to transition metal centres, leading to unusual stereo- chemical and electrochemical properties. Im- portantly, we have found that [18]aneN,S, binds octahedrally to metal centres to give exclusively the rat isomer, as originally proposed by Black and McLean. 1*2 As a continuation of these studies we report herein the synthesis and single crystal struc- ture of [Fe([18]aneN2S,)](BPh,),.2MeCN* 1/2Me OH.

*Author to whom correspondence should be addressed.

RESULTS AND DISCUSSION

Treatment of FeCl, * M-I20 with one molar equi- valent of [18]aneN2S4 in refluxing MeOH-H,O (1: 1 v/v) under N2 for 15 min affords a deep blue solution. Addition of excess NaBF, or NaBPh, yields a blue precipitate, which can be recrystallized

Cl83 aneN.&: R = H

Mr2C183 aneN&,: R = Me

Scheme 1.

2641

2642 N. ATKINSON et al.

from MeCN. Prolonged refluxing results in decomposition giving an insoluble orange pre- cipitate.

The IR spectrum of the tetratluoroborate salt shows peaks at 3240 and 3080 cm- ’ corresponding to N-H stretching vibrations, v(N-H), as well as other peaks indicative of the presence of coor- dinated [18]aneN2S4. Peaks at 1050, 535 and 520 cm-’ are characteristic of the BF4- counterion. The FAB mass spectrum of this product shows molecular ion peaks at m/z = 469, 401 and 381, assigned to [56Fe([18]aneN,S,)BFd]+, [56Fe([18] aneNzSd)*H,O+H]+ and [56Fe([18]aneN,S,-H)]+, respectively. The ‘H NMR spectrum measured in CD,NO, shows a complex second-order multi- plet in the range 6 = 2.15-3.85 ppm assigned to the methylene protons of the coordinated macro- cycle. The ’ 3C NMR spectrum of the complex, measured in CD3N02 at 298 K, exhibits 12 distinct resonances, indicating the presence of two differ- ent isomers in solution in a ratio of roughly 3~2, (6 = 52.26, 51.90, 39.82, 39.46, 33.56 and 32.96 ppm for one isomer; 52.41, 51.80, 38.90, 38.08, 35.46 and 34.94 ppm for the other isomer). These results are consistent with the presence of two alternative forms of the rut configuration. These diastereoisomers, I and II, differ in the rela- tive orientations of the N-H functions (Fig. 1) and each gives rise to six methylene carbon reson- ances.3 The UVvis spectrum of the product shows absorption bands at A,,,, = 572 nm (h,, = 171 M-i cm-‘), 424 (152) and 344 (103) which are assigned as d-d transitions on the basis of the magnitudes of their extinction coefficients and their solvent independence. In addition, there is a much more intense band at 238 nm (19,570) which is assigned tentatively as a S -+ Fe charge-trans- fer transition. This evidence, together with micro- analytical data, indicates the product to be the low-spin iron(I1) species [Fe([18]aneN,S,)](BF,),. The corresponding BPh,- salt, [Fe([l8]aneN&)] (BPhJz, can be prepared by using NaBPh, in place of NaBF, in the above synthesis.

I II

Fig. 1. Isomers I and II for rat-[M([18]aneN,S,)y+.

Deep blue, columnar crystals of suitable quality for a single crystal X-ray structure determination were obtained by slow evaporation from a solution of [Fe([l8]aneN&)](BPh& in MeCN-EtOH. The structure confirms a rat configuration for [Fe([18]aneN&,)]2+ (Fig. 2), with all six macro- cyclic donor atoms bound to the Fe” centre, Fe-S( 1) = 2.2674( 15), Fe-S(4) = 2.2673( 16), Fe-S(lO) = 2.2578(17), Fe-S(13) = 2.2588(16), Fe-N(7) = 2.037(5), Fe-N(16) = 2.022(4) A. Thus, the two Fe-S bond lengths in one SCH2 CH2S chain are essentially equal, but different from those in the other SCHzCH2S linkage. This is consistent with predictions based on the influence of the N-H functions which give rise to approximate non-crystallographic C2 symmetry [Fig. 2(b)] and six distinct methylene carbon resonances. Further- more, the orientations of the two N-H groups confirm that the complex exists as isomer I in the crystal selected. 3 The rat configuration observed probably reflects the preference for gauche torsions at C-S linkages and anti torsions at C-N (secondary amine) linkages.4 There is a small, but significant, tetrahedral distortion of the sulphur-donor atoms out of the least-squares S, coordination plane, with S( 1) and S( 13) lying 0.137 and 0.139 A, respectively, above the plane, while S(4) and S(10) lie 0.137 and 0.139 A, respectively, below. The structure also shows that the N-H groups in [Fe([18]aneN2S4)12+ par- ticipate in strong hydrogen-bonding interactions with the two MeCN molecules : H(7). . . N(6S) = 2.079(9) A, angle N(7)---H(7). . * N(6S) = 137.4(5)“, H(7)...N(6Sw(5S) = 171.1(7)“; H(16)+..N(3S) = 2.078(9) A, angle N(16)--H(16)~~~N(3S) = 139.4(4)“, H(16). . . N(3S)-C(2S) = 166.5(7)“.

Cyclic voltammetry of [Fe([18]aneN2S4)](BF4),, measured in MeCN (0.1 M “Bu,NBF4 supporting electrolyte) at platinum electrodes, shows two over- lapping, irreversible oxidations at Epa = + 0.78 and +0.88 V vs Fc/Fc+, assigned tentatively to Fe”/ Fe”’ couples for the two rat isomers. The irreversi- bility may be due to deprotonation of the oxidation product. The Fen/Fe”’ couple for the related low- spin, bis-trithia and bis-triaza macrocyclic species,

Fe(PlanW~12+ and [Fe([9]aneN,),]‘+, occur at E,,2 = +0.9S5 and -0.59 V vs Fc/Fc+, respec- tively.’

EXPERIMENTAL

IR spectra were recorded as KBr and CsI discs using a Perkin-Elmer 598 spectrometer over the range 2004000 cm-‘. UV-vis spectra were mea- sured in quartz cells using Perkin-Elmer Lambda 9 and Pye Unicam SP8-400 spectrophotometers. Microanalyses were performed by the Edinburgh

Iron macrocyclic complexes 2643

Fig. 2. Two views of the single crystal structure of [Fe([l8]aneN,S,)]*+: (a) showing hydrogen- bonded MeCN solvent molecules, with numbering scheme adopted ; (b) view along the approximate,

non-crystallographic C,-axis.

University Chemistry Department Microanalytical service. Electrochemical measurements were per- formed on a Bruker E310 Universal Modular Polarograph. All readings were taken using a three- electrode potentiostatic system in acetonitrile con- taining 0.1 M “Bu4NPFh or “Bu4NBF4 as sup- porting electrolyte. Cyclic voltammetric measure- ments were carried out using a double platinum electrode and an Ag/AgCl reference electrode. All potentials are quoted vs ferrocene/ferrocenium, Fc/Fc+ . Mass spectra were measured by electron impact on a Kratos MS 902 and by fast atom bom- bardment on a Kratos MS 50TC spectrometer. ‘H and 13C NMR spectra were obtained on Bruker WP80 and WP200 instruments.

(a) Synthesis of [Fe([18]aneN,S4)](BF,)2

Reaction of FeCl,-4H,O (22 mg, 0.107 mmol) and [18]aneN,& (35 mg, 0.107 mmol) in refluxing, degassed MeOH-H,O (35 cm3, 1 : 1 v/v), for 15 min under N,, afforded a deep blue solution. Cooling, reducing the volume to 10 cm3 and filtering the reaction mixture into a solution of excess NaBF4 in MeOH gave a blue precipitate which was recrys- tallized from MeCN and diethyl ether (Yield: 40 mg, 83%). Found : C, 26.0 ; H, 4.8 ; N, 5.0. Calc. for [C,2H26N2S4Fe](BF4)2: C, 25.9; H, 4.7; N, 5.0%. FAB mass spectrum (3-NOBA matrix): Found

m/z = 469, 401 and 381. Calc. for Cs6Fe([18]aneN, S4)BF4]+, M+ = 469; [56Fe([18]aneN&)*H20]+, M+ = 400; [S6Fe([18]aneNzS,)]f, M+ = 382. UV- vis spectrum (MeCN) : A,,,,, = 572 nm (smax = 171 M-’ cm-‘), 424 (152), 344sh (103) 238 (19,570). ‘H NMR spectrum (80.13 MHz, CD3N02, 298 K) : 6 = 2.15-3.85 ppm (m, CH2, 24H). 13C DEPT NMR spectrum (50.32 MHz, CD3NOz, 298 K): 6 = 52.26, 51.90 (2 xNCHJ; 39.82, 39.46 (2 x NCH,CH,S); 33.56, 32.96 ppm (2 x SCH&H$) major isomer ; 6 = 52.40, 51.80 (2 x NCH,) ; 38.90, 38.08 (2 x NCH,CH$) ; 35.46, 34.94 ppm (2 x SCH&H$) minor isomer. IR spectrum (KBr disc): 324Om, 3080m, 2920m, 1460m, 1420m, 138Ow, 132Ow, 1295w, 1050~s b, 93Ow, 790m, 535m, 520m cm- ‘.

(b) Synthesis of [Fe([l8]aneN&)](BPh,),

Method as for (a), using NaBPh, in place of NaBF,. Recrystallization from MeCN-EtOH gave the product as blue crystals. FAB mass spectrum (3-NOBA matrix): Found m/z = 381. Calc. for [s6Fe([18]aneN,S,)]+, M+ = 382. IR spectrum (KBr disc) : 3180m, 304Om, 298Ow, 292Ow, 1575m, 1475m, 1460m, 1420m, 1405m, 138Ow, 1305w, 126Ow, 117Ow, 112Ow, 108Ow, 106Ow, 103Ow, 99Ow, 97Ow, 92Ow, 84Ow, 82Ow, 785w, 755m, 735vs, 710~s 61Ovs, 470~ cm- ‘.

2644 N. ATKINSON et al.

Single crystal X-ray structure determination of (0.69 x 0.27 x 0.27 mm) was sealed in a glass capil-

[Fe([l8]aneN,S,)](BPh,), -2MeCN. 1/2MeOH lary to prevent solvent loss. Crystal data: [C,2H26N,S4Fe]Z+ - 2(C24H2,,B-) * 2MeCN *

Slow evaporation from a solution of the complex 1/2MeOH, M = 1119.0, triclinic, space group Pi, in a 1: 1 v/v mixture of MeCN-EtOH gave deep a = 11.8615(8), b = 15.4285(12), c = 17.9412(13) blue, columnar crystals. The selected crystal A, c1 = 67.301(3), /3 = 78.542(4), y = 76.696(3)“,

Table 1. Bond lengths, angles and torsion angles for [Fe([l8]aneN,S,)]*+

Fe-S( 1) Fe-S(4) Fe-N(7) Fe-S( 10) Fe-S(13) Fe-N(16)

S(l)--c(2) S(l>--c(l8) ~(2~c(3) C(3)-S(4) S(4)--c(5) C(5>--c(6)

S( l)-Fe-S(4) S( 1 jFe-N(7) S(l)---Fe-S(l0) S(l)-Fe-S(13) S(l)--Fe-N(16) S(4)-Fe-N(7) S(4)-Fe-S( 10) S(4)---Fe-S( 13) S(4)-Fc+N( 16) N(7)--Fe--S( 10) N(7)-Fe-S( 13) N(7)-Fe-N( 16) S(lO)--Fe-S(13) S(lO)--Fe-N(16) S( 13)-Fe-N( 16)

Fe-S(l)--C(2) Fe-s(l)--c(18)

C(2)-S(l)----c(l8) S(l)--c(2)+3) C(2k---c(3)_S(4) Fe-S(4)--C(3) Fe-S(4)-C(5)

C(3)_S(4)--c(5)

Bond lengths (A) with standard deviations

2.2674( 15) C(6)_N(7) 2.2673( 16) N(7)--C(8) 2.037(5) C(8yC(9) 2.2578(17) C(9)_S(lO) 2.2588( 16) S(lOk-c(ll) 2.022(4) C(1 lF(l2) 1.826(6) C(12)--S(13) 1.826(6) S(l3)--c(l4) 1.503(8) C(l4)--c(l5) 1.823(6) C(15)-N(16) 1.843(6) N(16)--C(17) 1.528(8) C(l7)--c(l8)

Angles (“) with standard deviations

90.66(5) S(4)--c(5)--c(6) 92.50(13) C(5)-C(6tiN(7) 90.16(6) Fe-N(7)--C(6)

172.77(6) Fe-N(7)-C(8) 86.02(13) C(6)-N(7)--c(8) 85.61(13) N(7)_-C(8)--C(9)

173.20(6) C(8HX9W(lO) 90.46(6) Fe-S( 10)-C(9) 91.94(13) Fe-S( IO)-C( 11) 87.62(13) 94.71(13)

177.13(18) 89.56(6) 94.85(13) 86.80(13)

103.46(20) 100.00(19) 101.4(3) 112.8(4) 113.5(4) 103.29(20) 99.95(19)

101.3(3)

C(9~S(lO)--c(ll) s(1o)---c(1l~c(12) C(ll)-C(12)---S(13) Fe-S(l3)-C(12) Fe-S(13)---C(14) C(12)-S(13bC(14) s(13)--c(14)--c(15) C(14jC(15)-N(16) Fe-N(16)-C(15) F+N(16)-C(17) C(15)---N(16w(17)

N(l6V(l7W(l8) S(l)--c(l8)--c(l7)

Torsion angles (“) with standard deviations

1.485(7) 1.498(8) 1.524(9) 1.819(7) 1.822(6) 1.526(9) 1.817(6) 1.804(6) 1.532(9) 1.477(8) 1.503(7) 1.518(8)

108.6(4) 108.2(5) 112.1(3) 114.0(4) 111.2(4) 108.0(S) 112.1(4) 98.06(21)

106.55(20) 104.0(3) 114.5(4) 114.7(4) 106.68(20) 98.99(21)

103.3(3) 110.5(4) 108.7(5) 114.4(4) 112.1(3) 111.4(4) 108.7(4) 109.3(4)

-68.8(5) 130.8(4)

-46.8(5) -69.1(5) 130.7(4)

- 50.8(5) - 175.9(5) - 172.7(5)

49.2(6)

C(8yC(9)_S(lO)_-ct 11) ~(9)-S(lO)-cxl l)--c(l2) S(lO)-C(ll)--C(l2)--S(13) C(11)--C(12)-+(13~(14) C(12)---S(13 )--C(14)-C(15) S(13)-C(14)-C(15)---N(16) C(14)--C(15)-N(16)-C(17) C(15)-N(16~(17)--C(18) N(16)--C(17)---C(18)-S(1)

79.1(5) -78.3(5) - 32.6(6) - 79.6(5)

79.8(5) 49.2(6)

- 174.2(5) - 177.0(5)

-49.6(5)

Iron macrocyclic complexes 2645

V = 2925.6 A’ [from 28 values for 27 reflections measured at +0(32 < 28 < 35”, A = 1.54184 A, T = 298 K)], Z = 2, D, = 1.270 g cmm3, ~(CU- K,) = 3.712 cm- ‘, F(OOO) = 1186.

Data collection and processin.q. Stoe STADI-4 four-circle diffractometer, graphite-monochrom- ated Cu-K, radiation, o-28 scans using the learnt- profile method.7 8245 reflections measured (20,,, = 120”, h -13+12, k -15+17, I -18-20) giving 6110 with F > 6a(F). No significant crystal decay.

Structure analysis and refinement. The iron pos- ition was deduced from a Patterson synthesis. Iter- ative cycles of least-squares refinement and differ- ence Fourier syntheses* located the positions of all other non-hydrogen atoms. Corrections for absorp- tion (max. 0.356, min. 0.171) were applied using II/ scans. Two fully-occupied MeCN molecules and one half-occupied MeOH molecule from the solvent were found to be associated with each [Fe([18]aneN,S,)]2+ cation. Strong hydrogen- bonding interactions between the macrocyclic N-H functions and the two MeCN molecules may account for the well-ordered nature of these solvent molecules, whereas the MeOH molecule is dis- ordered and does not participate in significant hydrogen-bonding interactions. Hydrogen atoms were included in fixed, calculated positions, and the phenyl rings of the BPh4- counteranion were refined as rigid groups.8 Anisotropic thermal par- ameters were refined for Fe, S, N, B and C atoms. The weighting scheme w- ’ = 02(F) +0.000509F2 gave satisfactory agreement analyses. At final con- vergence, R = 0.0668, R, = 0.0947, S = 1.232 for 591 independent parameters, and the final differ- ence Fourier synthesis showed no feature above 0.60 or below -0.61 e A- 3. Illustrations were pre- pared using ORTEPII,’ molecular geometry cal- culations utilized CALC,” and scattering factor data were inlaid’ or taken from ref. 11. Bond lengths, angles and torsion angles are given in Table 1. Fractional atomic coordinates and thermal par-

ameters, together with observed and calculated structure factors have been deposited with the Editor, from whom copies are available on request. Atomic coordinates have also been deposited with the Cambridge Crystallographic Data Centre.

Acknowle&ement-We thank the SERC for support.

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11.

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