1296 Inorganic Chemistry, Vol. 17, No. 5, 1978
Elder, Kennard, Payne, and Deutsch Contribution from the Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 4522 1
Synthesis and Characterization of Bis(ethylenediamine)cobalt(III) Complexes Containing Chelated Thioether Ligands. Crystal Structures of [(en)2Co(S(CH3)CH2CH2NH2)][Fe(CN)6] and [(~II)~C~(S(CH~C~H~)CH~COO)](SCN)~ R. C . ELDER, GREGORY J. KENNARD, M. DIANE PAYNE, and EDWARD DEUTSCH*
Received October 3, 1977 A general synthesis of coordinated thioethers via alkylation of coordinated thiols in N,N-dimethylformamide is described. with R = methyl, ethyl, cyclohexylmethyl, benzyl, 4-fluorobenzyl, The series of complexes [(en)zCo(S(R)CH2CHzNH2)]3+, 4-methylbenzyl, 1-naphthylmethyl, 2-naphthylmethyl, carboxymethyl, methylcarboxymethyl, carboxyethyl, and carboxypropyl, are characterized. Single-crystal x-ray structure analyses of ((methyl and the complex [(en)2Co(S(CH2C6H5)CH2coo)]2+ 2-aminoethyl thioether)-N,S)bis(ethylenediamine)cobalt(III) hexacyanoferrate(II1) tetrahydrate and ((benzyl 2-carboxymethyl thioether)-O,S)bis(ethylenediamine)cobalt(III) thiocyanate, refined to conventional R factors of 0.042 and 0.037, respectively, are reported. Both cobalt(II1) centers are approximately octahedrally coordinated with one coordination site occupied by a thioether sulfur atom. The salient structural feature of both complexes is that the coordinated thioether sulfur does not induce a significant structural trans effect (STE). This result is ascribed to the lack of a formal negative charge on the thioether sulfur atom inasmuch as other sulfur atoms which do carry a formal charge also exert significant STE’s. The visible-UV spectra of the thioether complexes are discussed in relation to the spectra of the analogous thiolato complexes.
Introduction Our long-standing interest in the chemistry of coordinated sulfur’-14 has led us to a consideration of coordinated thioethers, a divers class of ligands which may readily be prepared via alkylation of coordinated thiols.15-17 Recent reports have indicated that when coordinated to cobalt(III), thioether sulfur induces remarkable effects upon the kinetics of electron transfer to ~ o b a l t ’ ~and - ~ ’ on the kinetics of ligand substitution trans to sulfur.22 In this context, complexes of the type [(en)2Co(S(R)CH2CH2NH2)]3+and [(en),Co(S(R)CH2C00)]’+ are of special interest since we have previously studied the parent thiolato complexes,23as well as the analogous ~ u l f e n i cand ~ ~ sulfinic3 acid complexes [ (en)&o(S( 0 ) C H 2 C H 2 N H 2 ) ] and [ (en)2Co(S(0)2CH2CH2NH2)] 2+. The sulfur atoms of all of these complexes are known to induce structural trans effects (Le., the Co-N bond that is trans to the coordinated sulfur is significantly longer than the average of the Co-N bonds that are cis to sulfur). It has been s ~ g g e s t e dthat ~ ~ ~this J ~structural trans effect may be correlated with many of the kinetic phenomena associated with coordinated sulfur. W e therefore desired to determine whether or not thioether sulfur exerts a structural trans effect when coordinated to cobalt(III), and also to prepare a series of [(en)2Co(S(R)CH2CH2NH2)]3+ complexes in which the R group is systematically varied in a manner designed to explicate kinetic phenomena. This paper describes the preparation and characterization of this series of complexes, as well as single-crystal x-ray determinations of the structure of two specific thioether complexes. Our studies25 on the kinetics and mechanism of electron transfer to the title complexes will be detailed in subsequent papers. Experimental Section
’+
General Data. All common laboratory chemicals were of reagent grade. (2-Mercaptoethylamine-N,S)bis(ethylenediamine)cobalt(III) perchlorate and (mercaptoacetato-O,S)bis(ethylenediamine)cobalt(III) chloride were available from previous s t ~ d i e s . ’ ~Dowex . ~ ~ , ~50W-X2 ~ (200-400 mesh) cation-exchange resin was cleaned by a previously detailed procedure.26 Elemental analyses were performed by Galbraith Laboratories, Knoxville, Tenn. Visible-UV spectra were recorded on a Cary 14 spectrophotometer at ambient temperature. IH N M R spectra were obtained on Varian T-60 and A-60 instruments. ((Alkyl 2-aminoethylthioether)-N,S)bis(ethylenediamine)cobalt(III) Salts, [(en)2Co(S(R)CHzCHzNHz)]X3, X = CIO,, I-, 1/3[Fe(CN),]3-, ’/s[Co(CN)6)]3-. These compounds are readily prepared via the alkylation of [(en)2Co(SCH2CH2NH2)](C104)2.1z~25 W e have synthesized complexes with R = methyl, ethyl, cyclohexylmethyl, benzyl, 4-fluorobenzyl, 4-methylbenzyl, 1 -naphthylmethyl, 2-
0020-166Y/78/1317-1296$01.00/0
naphthylmethyl, carboxymethyl, methylcarboxymethyl, carboxyethyl, and carboxypropyl. Our general procedure, using alkyl halides as alkylating agents and N,N-dimethylformamide (DMF) as reaction solvent, is detailed here for the preparation of the complex with R = benzyl. Twenty-two millimoles of [(en)zCo(SCH2CH2NH2)](ClO4)z was dissolved in 50 mL of D M F to give a black solution. Benzyl chloride (12 mL, ca. 100 mmol, Aldrich) was added. Within 12 h (reaction time depends on the specific alkyl halide used) the solution turned deep red-orange and the product complex precipitated. The DMF and excess benzyl chloride were extracted into diethyl ether leaving a red-black oil which was dissolved in a minimum amount of warm (30 “C) water. After filtration, this solution was treated with an equal volume of 72% HC104 and then slowly cooled to give an essentially quantitative yield of [ ( ~ I I ) & O ( S ( C H ~ C ~ H ~ ) CHzCH2”2)1 (c104)3. The general procedure succeeds when cyclohexylmethyl bromide is used as alkylating agent, but the reaction time is excessively long (50% completion in ca. YO days). Therefore the complex with R = cyclohexylmethyl was prepared using the more reactive alkylating agent cyclohexylmethyl trifluoromethanesulfonate. Over a period of 1 h, with cooling, a solution of trifluoromethanesulfonic anhydride (177 mmol, Cationics Chemicals) in 50 mL of dry dichloromethane was added dropwise to a solution of (hydroxymethyl)cyclohexane (1 50 mmol, Aldrich) and N,N-diisopropylethylamine (200 mmol, Aldrich, dried over CaH,) in 200 mL of dry CHZCl2.The resulting solution of ester was added to 22 mmol of [(en)zCo(SCH2CH2NHz)](C104)2 dissolved in 300 mL of D M F and this mixture was stirred overnight at ambient temperature. After removal of volatile components by rotary evaporation, the resulting orange-red oil was dissolved in water and absorbed on a Dowex 50W-X2 cation-exchange column. The desired 3+ product band was eluted with 50% (v/v) ethanol-water which was 6 M in HC10,; the central 80% of this band yielded 4.0 g of red-orange solid after treatment with large volumes of 2-butanol and diethyl ether. Recrystallization from water-NaC10, yielded 1.1 (C104)3 g of the desired [(en)2Co(S(CH2C6H11)CH2CH2NH2)] complex. All perchlorate salts, with the exception of the naphthylmethyl complexes, were recrystallized three times from water-HC104 or water-NaC104 solutions; the naphthylmethyl complexes were recrystallized three times from 50% (v/v) ethanol-water and HCIO,. It should be noted that it is very difficult to remove bromide and iodide ions (resulting from alkylation with alkyl bromides and iodides) by successive recrystallizations of the perchlorate salts. This problem may be circumvented by the use of alkyl chlorides in the original reaction (however, alkyl chlorides react more slowly than do the corresponding bromides and iodides) or by treatment of the thioether complex with excess AgC104 solution. After removal of the silver halide, excess silver ion is readily removed by recrystallization of the thioether complex from water-HCIO,. Iodide salts of the thioether complexes may be prepared either by using a saturated aqueous solution of N a I rather than 72% HC104
0 1978 American Chemical Society
Thioether Ligands
Inorganic Chemistry, Vol. 17, No. 5, 1978 1291
Table I. Elemental Analyses for Thioether Complexes Complex Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found
%Ca
%H
%N
%Co
%S
% c1
14.78 14.55 12.92 12.79 28.01 28.20 24.22 22.50 20.46 20.66 28.72 28.51 30.07 30.33 23.99 24.49 16.99 16.76 15.68 15.56 17.24 17.24 17.75 17.28 23.56 22.13 25.52 24.81 16.49 16.37 37.81 37.83
4.43 4.59 3.87 4.16 5.97 5.87 4.53 4.74 4.35 4.30 5.09 4.88 5.18 5.12 5.42 5.58 4.34 4.30 4.11 4.33 4.34 4.42 4.91 4.88 4.26 4.83 4.14 4.77 4.67 5.00 5.29 5.61
12.32 11.86 10.76 10.46 27.64 27.81 10.86 11.09 9.17 9.17 9.30 9.33 9.23 9.90 10.76 11.20 10.86 10.82 11.43 11.56 11.18 11.17 10.34 9.90 10.57 10.85 10.63 10.59 12.02 12.16 17.64 17.71
10.36 9.85
5.64 5.43 4.93 4.94 5.75 5.67 4.91 4.90 4.20 3.84 4.26 4.18 4.22 4.23 4.93 5.19 4.97 4.94 5.23 5.20 5.12 5.05 4.74 4.03 4.84 4.54 4.87 4.59 5.50 5.19 20.19 19.95
18.70 18.03 58.48b 58.26
21.14 20.71 9.14 9.42 7.12 7.69 7.83 7.44 7.77 7.69 9.06 9.14 9.14 9.19 9.62 9.74 9.40 9.31 8.71 8.77 8.89 8.50 8.95 8.92 10.11 9.77 12.37 12.17
17.36 17.54 16.97 17.16
a % C analyses of perchlorate salts are often low due to the explosive nature of these compounds. % I. See results of crystal structure on Fe(CN), 3 - salt. Iodide salt prepared by metathesis from perchlorate salt. e 1-Naphthylmethyl derivative. 2-Naphthylmethyl derivative; molecules of solvation confirmed by 'H NMR.
Table 11. Visible-UV Spectrophotometric Parameters for Selected Ethylenediaminecobalt(II1) Complexesa Complex [(en),Co I [(~~),CO(SCH,CH,NH,)]~+
Amax (E)
Xmin ( E )
Amax
(€1
Xmin
(€1
465 482 600 518
(87.5) (142) (44) sh (152)
387 (9.2) 423 (95)
339 (79) 282 (13 800)
250 (1550)
430 (73)
282 (11 700)
255 (4270)
R = CH,COOCH, R = CH,COOH R = CH,CH,COOH R = CH,CH,CH,COOH R = CH,C,HI1 R = CH,C,H, R =p-CH,C,H,F
487 487 490 489 489 488 489 487 486
(177) (182) (153) (170) (186) (175) (194) (182) (196)
405 405 405 405 405 406 410 405 409
257 (4140) 258 (4640) 258 (4720) 258 (4760) 258 (4890) 258 (4460) 261 (5330) 255 (5100) 256 (5500)
R =p-CH,C,H,CH,C
488 (212)
421 (51)
480 (222) 484 (238)
460 (213) 446 (178)
282 (8380) 283 (9040) 280 (8060) 282 (8410) 282 (8920) 282 (8930) 286 (9480) 291 (9920) 290 (10 300) 274 (8220) sh 285 (9390) 278 (9230) 288 (18 100) 283 (17 300)
499 (168) 504 (175)
420 (36)
280 (7300) 293 (10 200)
+ ,
,
[(en) Co(SCH,COO) ]' [ (en), Co(S(R)CH, CH, ",)I3+ R =C H , ~ R = CH,CH,
R = l-CH,C,,H, R = 2-CH,CI,H, [( ~ ~ ) , C O ( ~ R ) C H , C O O ) ] ~ + R = CH, R = CH,C,H,
(18) (20) (19) (19) (19) (19) (35) (20) (25)
257 276 256 254
(5440) (9150) (7490) (9490)
225 (8600)
Wavelengths, A, of maxima (max), minima (min), and shoulders (sh) are in nm. Molar extinction coefficients, E , given in parentheses, are in M-' cm-'. Spectra are recorded in dilute aqueous perchloric acid. Average of determinations on three independently prepared samples. The charge-transfer band is split into two components separated by a shallow minimum. See Figure 2. Data from ref 17. a
in the above general procedure or by simple metathesis from the perchlorate salts. Crystals of [(en)2Co(S(CH3)CH2CH2NH2)][Fe(CN)6].4H20 and [(en)2Co(S(C H 3 ) C H 2 C H 2 N H 2 )[]Co(CN)6].4H20 were grown by allowing layers of 0.01 M [(en)&o(S(CH3)CH2CH2NH2)]13and 0.02 M K3M(CN)6 (M = Fe, Co) to slowly diffuse together; these crystals, which are isomorphous, form as hollow needles. They were cleaved to yield pieces suitable for the x-ray diffraction experiment. Data confirming the characterization of these complexes by elemental analyses, visible-UV spectrophotometry, and IH NMR
spectrometry are given in Tables I, 11, and I11 respectively. ((Benzyl 2-carboxymethyl thioether)- O,S)bis(ethylenediamine)cobalt(II1) Salts. [(en)2Co(S(CH2C~H5)CH~COO)]X2, X = Cl; SCN-. The chloride salt was prepared from [ (en)2Co(SCH2COO)]C123and benzyl chloride in D M F according to the general procedure outlined above and then recrystallized from water-isopropyl alcohol mixtures containing LiC1. Crystals of the thiocyanate salt suitable for x-ray diffraction measurements were grown by allowing to slowly diffuse together layers of (a) a saturated aqueous solution of the chloride salt that had been diluted 1:6 with 50% (v/v) ethanol-water and (b)
1298 Inorganic Chemistry, Vol. 17, No. 5, 1978 Table 111. H NMR Spectral Parameters for [(en),Co(S(R)CH,CH,NH,)131 Thioether Complexesa
Elder, Kennard, Payne, and Deutsch
monitored to check crystal stability and to account for long-term drift. The drift correction varied from 0.994 to 1.038 and was random in behavior. Absorption corrections were not applied since fi = 14.5 cm-' Inteand the maximum relative error in the measured intensities was s Character gral -R Protonsb estimated to be less than 4%. Within the sphere 28 < 55', 2892 Broad 10 A 4.4-5.4 -CH,CH3 reflections were measured in the forms hkl and h k c 2760 unique 14 B 2.4-3.1 Broad reflections were obtained by averaging.28 Of these, 2025 had I > 2 4 4 , Under Hg SCH,~ ~ .was ~ ~ set equal where p the ignorance factor used to ~ a l c u l a t eu(I) 3 Triplet 1.45 -CH3 to 0.02. Broad 10 4.1-5.2 A -CH2C6H11 X-Ray Characterization, [(en)2Co(SCH2C6H,)CH2COO)](SCN)2. 14 2.2-3.1 Broad B A deep red, plate-shaped crystal of approximate dimensions 0.25 X Under HB SCH,0.18 X 0.12 mm was generally characterized as above, with the Multiplet 11 0.8-2.2 -C6H11 following differences in procedures and data. Preliminary precession 10 4.4-5.5 Broad A -CH,C6H, photographs indicated a crystal of the triclinc class. Cell constants 12 2.4-2.9 Broad B (13 reflections) are a = 6.976 (1) A, b = 7.884 (1) A, c = 20.358 2 Singlet 2.0 SCH,(2) A, CY = 99.48 (l)', fi = 90.94 (l)', and y = 107.91 (l)', these 5 Singlet 7.5 -C6H5 parameters corresponding to the reduced primitive cell obtained by 10 4.4-5.4 Broad A -CH,C,H,F the method of B ~ e r g e r . ~ ' ,With ~ ' Z = 2, dcald= 1.54, dmeasd = 1.52 12 Broad 2.4-3.0 B (1) g ern-). The 8/28 scan rate varied between 2.0 and 8.0°/min, 2 Doublet SCH,4.0 and the scan ranged from 0.6' in 20 below the calculated K a l peak 4 7.2-7.8 Multiplet -C,H,position to 0.8' above that calculated for Ka2. The drift correction 10 4.4-5.4 Broad A -CH,C, H4CH3 12 Broad B 2.4-3.0 varied from 1.013 to 0.990 and was random in behavior. Absorption 2 Doublet SCH,4.0 corrections were not applied since fi = 11.87 cm-' leading to an 5 Singlet -C6H,7.4 estimated maximum relative error of 3 2.4 Singlet -CH, 45', 3629 reflections were measured in the forms h k l , hkl, hkl, and 10 4.7-5.8 Broad A -CH,Cl,H, hkl. From these, 2729 were obtained by averaging and in this set 14 Broad 2.4-3.1 (1-Naphthylmethyl) B 2229 had I > 2 4 with p set equal to 0.04. Under HB SCH,Structure Solution and Refinement, [(en)2Co(S(CH3)7 7.6-8.6 Multiplet -'loH, CH2CH2NH2)][Fe(CN)6]-4H20. This structure was solved using 0 4.6-5.8 Broad A normal Patterson techniques and refinement proceeded without 4 B 2.6-3.1 Broad difficulty. Hydrogen atoms, fixed at calculated positions (N-H = Under HB SCH,0.87 A; C-H = 0.97 A; tetrahedral geometry), were assigned isotropic 7 7.6-8.5 Multiplet -ClOH, temperature parameters32of B = 4.0 A2. In the final cycles of 2 Quartet -CH,OH 3.62 least-squares refinement, 278 parameters were varied including the 3 1.12 Triplet -CH3 overall scale factor, positional parameters, and anisotropic thermal 0 4.4-5.4 Broad A -CH,CO,CH, parameters for all nonhydrogen atoms, but excluding hydrogen atom 2 B 2.4-3.2 Broad positional and thermal parameters. Convergence was achieved with 2 Singlet 3.95 SCH,R1 = 0.042 and R2 = 0.036,33with all correlation coefficients
