J. Am. Chem. SOC.1982, 104, 137-141
137
Synthesis of a Chiral 0-Bound Sulfoxide from an S-Bound Sulfenate Ion Graeme J. Gainsford,'" William Gregory Jackson,lb and Alan M. Sargeson*lC Contribution from the Chemistry Division, Department of Scientific and Industrial Research, Petone, New Zealand, the Department of Chemistry, University of New South Wales, Royal Military College, Duntroon, Canberra, A.C.T., Australia, and the Research School of Chemistry, Australian National University, Canberra, A.C.T.. Australia. Received March 6. 1981. Revised Manuscript Received July 13, 1981 Abstract: Methylation of the chelated sulfenate ion bis(ethane- 1,2-diamine)(cysteamine sulfenate-S)cobalt(III) occurs at sulfur with complete retention of chirality at the S center. The crystal and molecular structures of one of the racemic diastereoisomeric products, A(R),A(S)-bis(ethane- 1,2-diamine)(cysteamine sulfoxide-O)cobalt(III) triiodide hydrate, have been determined by single-crystal X-ray diffraction techniques ( R = 0.040, orthorhombic crystals, space group Pbca with a = 23.755 (2) A, b = 12.531 (2) A, c = 13.453 (1) A). The structure consists of centrosymmetrically related enantiomers and iodide ions with one water molecule hydrogen bonded to an amino nitrogen of the cations. The sulfoxide moiety forms a six-membered ring with the oxygen bonded to cobalt. A rearrangement from S- to 0-bonded sulfoxide following the alkylation is implied with a concomitant increase in ring size. The mechanism is discussed.
to remove unreacted sulfenato complex. Elution with 3 mol dm-, HCI eluted the pink-red sulfoxide product. After removal of most of the HCI by evaporation, the addition of HC104 (70%) and cooling (5 O C , 12 h) produced pink crystals (4.1 g, 60%) of the triperchlorate hydrate salt. They were recrystallized twice from H20/HC104. Anal. Cacld for C7H27C13C~N5014S: C, 14.0; H, 4.5; N, 11.6; S, 5.3; CI, 17.7. Found: C, 13.9; H, 4.3; N, 11.1; S, 5.4; CI, 18.1. The chloride salt was obtained from the perchlorate by anion exchange (Dowex 1-X8, CI- form) and crystallization from H20/HCI/MeOH/Me2C0. The triiodide salt was obtained by metathesis using NaI in water. 'H NMR (D20) 6 2.77, s, SCH,; "C NMR (D2O) 6 -21.28, -21.74, -21.88, -22.14 (4C, NCH2 of en), -23.01 (lC, SCH,), -31.98 (lC, NCH,), -31.99 ( l e , SCH,); vis max €513 98.1 (H20). Anal. Calcd for C7H2SCoI,N50S:C, 12.6; H, 3.8; N, 10.5; S, 4.8; I, 57.1. Found: C, 12.8; H, 3.9; N, 10.5; S, 4.8; I, 56.1. A(S),A(R)[CO(~~),(SO(CH,)(CH~)~NH,)IS+ Salts. A procedure similar to the above was followed with A(R),A(S) [Co(en),(SO(CH2)2NH2)](CI04), (5.0 g) in place of A(S).A(R)[Co(en),(SO(CH2)2NH2)]N03C104.The red complex was crystallized as the hydrated trichloride salt from H20/MeOH/Me2C0 (2.90 g, 65%). Anal. Experimental Section C, 20.0; H, 6.7; N, 16.7;S, 7.6; C1, 25.3. Calcd for C7H28C13C~Ns02,5S: Found: C, 20.0; H, 6.1; N, 16.1; S, 7.8; CI, 25.4. The perchlorate and Visible spectra were measured with a Cary 118C spectrophotometer. 'H NMR spectra were recorded by using Varian T60 or JEOL Minimar iodide salts were obtained by metathesis in H 2 0 (HC104 or NaI). Anal. Calcd for C7H27C~13NS02S: C, 12.3; H, 4.0; N, 10.2; S, 4.7; I, 55.6. 100-MHz spectrometers with an internal Me4Si reference. Proton-deFound: C, 12.5; H, 4.0; N, 10.3; S, 4.8; I, 55.7. 'H NMR (D,O) 6 2.80, coupled I3C NMR spectra were obtained with a Varian FX60 specS, SCH,; I3C NMR (D2O) 6 -21.28, -21.48, -21.81, -22.34 (4C, NCH2 trometer using an internal deuterium lock. Positive chemical shifts are of en), -22.67 (lC, SCH,), -30.98 ( l e , NCH,), -31.12 (lC, SCH,); vis reported in ppm downfield from an internal dioxane reference. Solutions max tdg985.9 (H,O). were evaporated under reduced pressure (- 15 mmHg) by using a Biichi Product Analyses. We were unable to separate mixtures of the sulfrotary evaporator so that the solution temperature did not exceed 25 OC. The hydrogen peroxide oxidation of [Co(en),(S(CH2)2NH,)](C10,), oxide isomers satisfactorily by ion-exchange chromatography. Therefore gave major (80%) A(S),A(R) [CO(~II)~(SO(CH~)~NH~)]NO~CIO~ and the products from the two methylation reactions above ('/5th scale) were isomeric minor (20%) A(R),A(S)[CO(~~)~(SO(CH~),NH,)](CIO~)~ sampled and examined by "C NMR and 'H NMR spectroscopy (D20). sulfenato products. The separation, purification, and characterization A single 0-bound sulfoxide diastereoisomer (>95%) was observed in each of these diastereoisomers will be given e l s e ~ h e r e . ~ case. A(R),A(S)[CO(~~),(SO(CH,)(CH,),NH~)]~+ Salts. Methyl iodide Chlorine Oxidation. Solutions of the CI- salts of each of the O-sulf(15 mL) was added to the orange-brown solution of A(S),A(R)[Cooxides in D 2 0 were saturated with C12 (ca. 0.04 mol dm-') and sealed. No changes in the 'H and I3C NMR spectra were observed after 3 days (en)2(SO(CH2)2NH2)]N03C104 (5.0 g) in Me2S0 (80 mL), and the mixture was allowed to stand overnight at ca. 20 OC. The orange-pink at 20 O C . X-ray Diffraction Study of A(R),A(S)-Bis(ethane-1,t-diamine) (mesolution was diluted with water (400 mL), extracted with chloroform (3 thylcysteamine sulfoxide-O)cobalt(II) Triiodide Hydrate. The crystals X 30 mL) to remove I2 and excess CH,I, and then sorbed on a column of Dowex 50W-X2 (Hc form, 200-400 mesh) cation-exchange resin. were grown from water as orange rectangular needles. The crystals The column was washed (H20, 500 mL) and eluted (2 mol dm-' NaCI) appeared to have the same habitat, and all from a random selection were crystallographically identical. The crystal employed for data collection was of dimensions 0.32 X 0.19 X 0.04 mm mounted with a goniometer (1) (a) Department of Scientific and Industrial Research, Petone, New and [0, 1, 11 directions coincident. Approximate unit cell constants and Zealand. (b) University of New South Wales, Royal Military College, group absences were determined from Weissenberg and precession phoDuntroom, Canberra, A.C.T., Australia. (c) Australia National University, tographs. The absences hOl, I = 2n + 1, Okl, k = 2n + 1, and hkO, h Canberra, A.C.T., Australia. = 2n + 1, are consistent with the space group p b ~ a ( 6 1 ) . ~Unit cell (2) (a) Jackson, W. G.;Sargeson, A. M.; and Whimp, P. 0. J. Chem. Soc., dimensions were adjusted by a least-squares treatment' of the setting Chem. Common. 1976, 934 and references therein. (b) Adzamli, I. K.; Deutsch, E. Inorg. Chem. 1980, 19, 1366, and references therein. (3) Jackson, W. G.; Sargeson, A. M., unpublished data. (4) Elder, R. C.; Kennard, G . J.; Payne, M. D.; Deutsch, E. Inorg. Chem. (6) "International Tables for X-ray Crystallography"; Kynoch Press: 1978 17, 1296. Birmingham, England, 1962. ( 5 ) Jackson, W. G . ;Sargeson, A. M., to be published. (7) Busing, W. R.; Levy, H. A. J . Chem. Phys. 1957 26, 563. Thiolate ion coordinated to cobalt(II1) retains some of the nucleophilic character of the sulfur center of the parent ion, RS-.2a-4 For example, [(en)2Co(S(CH2)2NH2)]2+readily undergoes the electrophilic addition of H202,2bBr+, or CP3 in water to give the coordinated sulfenate [(en)2Co(SO(CH2)2NH2)]2+ and ultimately the sulfinate [(en)2Co(S02(CH2)2NH2)]z+ ion. Similarly it readily attacks alkyl halides to give thioethers of the type [(~~),CO(SR(CH~)~NH~)]~+.~~~ A feature of the chemistry is the control and stability imparted by the metal complex. For example, free sulfenate ions are notoriously unstable while their S-bonded metal complexes are apparently very stablesb Futhermore, chiral cobalt(II1) centers can direct the stereochemistry of the oxidation to give the chiral sulfur center which remains bonded to the metal i ~ n . ~WJe were interested in utilizing these properties to prepare stereospecifically the first sulfur-bonded Co(II1)-sulfoxide complex. In these attempts we found some unexpected and unusual reactions which are reported herein.
9002-7863/82/1504-Ol37$01.25/0
0 1982 American Chemical Society
138 J. Am. Chem. SOC.,Vol. 104, No. 1, 1982
Gainsford. Jackson, and Sargeson Table I. Atomic Positional Parameters for
Scheme I
A(R),A(S)Bis(ethane-1,2-diamine)(cysteamine 1
sulfoxide-O)cobalt(III) Iodide Hydrate anisotropic atoms atoms
104~ 2103.0 (5) 3310.7 (5) 5003.6 (5) 3599.3 (8) 3526 (2) 3432 (5) 3792 (8) 4156 (11) 384 (9) 223 (18) 700 (44)
I
104y
1042
1796 (1) 3735 (1) 1791 (1) -108 (2) 130 (4) -401 (9) 1421 (14) -470 (18) 158 (22) -690 (41) 260 (33)
1004.7 (8) 3068.4 (9) 4690.7 (9) 3083 (2) 720 (3) 1725 (8) 1034 (13) 273 (17) 2540 (21) 3260 (32) 1990 (81)
isotroDic atoms angles of 12 reflections centered automatically on a Hilger and Watts Y290 diffractometer, controlled by a PDP8/I computer. Crystal data (20 lo): a = 23.755 (2), b = 12.531 (2), and c = 13.453 (1) A: formula C7H2,Co13N502S;M 685.0; cell volume 4004 A'; Z = 8; D,= 2.27 g cm-3; F(000) 2576; p(Mo K,) 56.7 cm-I; X(Mo K,) 0.7107 A. Details of Data Collection. The intensities were measured by using the 0 and 20 scan technique, with a scan step in 0 of 0.01' and a counting time of 1 s. Each reflection was scanned through a range of 0.72' centered on the Mo K, peak. The local background was measured for 18 s at each end of the scan range using the stationary-crystal, stationary-counter technique. For monitoring of the crystal and electronic stability, the intensities of three strong reflections well separated in reciprocal space were measured periodically throughout the experiment; only random fluctuations (5*3%) in their mean values were observed. All independent reflections in the sphere with 0 5 23' were measured; the integrated intensities and their standard deviations were derived as described previously' with an 'uncertainty" factor, p , of 0.05. The 1394 reflections having greater I than 3a(I), used in the subsequent analysis, were corrected for absorption by the analytical method: transmission coefficients on I ranging from 1.25 to 2.76. Solution and Refmement of the Structure. The structure was solved1o by conventional Patterson and difference Fourier calculations; the initial R, where R is xllFol - lFcll/EIFol and F,, F, are the observed and calculated structure factors, for the cobalt and iodine atoms was 0.20. All nonhydrogen atoms were located on the following difference Fourier map. Full matrix least-squares refinement was carried out minimizing the function xw(lFol IFc1)2,where w was initially l/G(Fo). The atomic scattering factors for Co, I, N, 0, and C were taken from the usual tabulation6 and those for H from Stewart et al." The initial refinement without the water oxygen, in which all nonhydrogen atoms were refined with isotropic vibrational parameters, gave R = 0.115 and R'(weighted R factor) = 0.133 where R, = [Cw(lFol - IFcl)2/xwlFp12]'/2. The iodine and cobalt atoms were then refined with anisotropic thermal parameters leading to R 0.086, R' = 0.093. Analysis of the minimized function over ranges of lFol and A-I sin j indicated the "diffractometer" weights were unsatisfactory. Absorption corrections were carried out and the weights recalculated as w = 1/(170.0 + IFoI + 5 I lod lF0I3), Refinement with 18 atoms now converged in three cycles to R = 0.052, R' = 0.078. The difference Fourier map showed three distinct peaks with relative integrated heights of 7:3:2 with the largest about 0.6 of the height of the last oxygen atom located. Several different refinement models were tried for these distinct atomic positions; all were consistent with the disorder of one oxygen atom into the three closely related sites. The water oxygens were included with population parameters fixed at 0.58, 0.25, and 0.17 (0(2), 0(3), and 0(4), respectively). Atoms S, 0(1), C(1), and C(7) in the six-membered chelate also showed anisotropy in the map, and along with O(2) and O(3) were therefore refined with anisotropic thermal parameters. Hydrogen atoms were included but not refined in their calculated positions (C-H 0.95 A, N-H 0.87 A, with B temperature factors of 4 A2);all corresponded to regions of positive density in the map. The refinement with 46 atoms and 379 variables converged in four cycles to a final R of 0.040 and R' of 0.044. The maximum shift/estimated
*
atoms
-
(8) Corfield, P. W. R.; Doedens, R. J.; Ibers, J. A. Inorg. Chem. 1967,6, 197. (9) De Meulenaer, J.; Tampa, H. Acta Crystallogr. 1965, 19, 1014. (10) "The X-ray System-Version of June, 1972"; Stewart, J. M., Ed.; Computer Science Center, University of Maryland; Technical Report TR-192. (11) Stewart, R. F.; Davidson, E. R.;Simpson, W. T. J. Chem. Phys. 1%5, 42, 3175.
103x 400.1 366.5 288.0 430.2 322.4 422.7 326.5 214.6 414.4 366.3 428 377 44 2 454 34 8 3 93 401 359 341 321 257 24 9 26 2 290 450 453 446 407 351 377 300 301 43 2 446 404
(5) (6) (5) (5) (5) (7) (7) (7) (7) (7)
103~ 122.7 (11) 16.1 (11) 63.8 (10) -92.9 (10) -149.6 (9) 147.1 (12) 100.4 (13) 80.4 (14) -207.2 (13) -231.0 (13) 127 175 216 96 184 175 36 -4 2 167 101 17 138 27 126 -87 70 -255 - 220 -300 - 234 166 146 -10 -49 -115
-
-
1032 280.0 (9) 451.0 (10) 319.8 (9) 302.3 (10) 331.9 (8) 181.5 (12) 479.9 (13) 426.7 (13) 285.5 (12) 346.1 (12) 3 24 293 184 168 126 44 467 485 460 54 8 454 436 290 290 359 255 303 216 328 4 14 281 3 85 -31 75 9
Partial occupancy; see text. Scheme I1
standard deviation ratio was 0.4 (for atom O(4)) with the overall mean 0.03. Average values of the minimized function showed little dependence on lFol and X-' sin 8. Examination of the final difference Fourier showed no significant features with all peaks within 1.3 A of heavy atom positions. The positional and vibrational parameters and their esd's obtained from the final cycle are listed in Table I.
Results and Discussion W e sought to construct the S-bound sulfoxide stereospecifically on the metal ion by using two different approaches, the oxidation
Chiral 0Bound Sulfoxide Synthesis
J . Am. Chem. Soc., Val. 104, No. 1, 1982 139
Scheme I11
Table 11. Borid 1,engths 2t
3+
3+
distance, A
distance, A
1.906 (11) 1.956 (14) 1.963 (13) 1.524 (12) 1.78 ( 3 ) 1.47 (2) 1.50 (2) 1.48 (2) 1.44 (2)
1.963 (13) 1.953 (14) 1.980 (12) 1.79 ( 2 ) 1.46 (2) 1.49 (2) 1.47 (2) 1.45 (2)
of the thioether (Scheme I) and the alkylation of the sulferiate ion (Scheme 11). The chiral sulfur center in the thioether complex is not optically stable, but the methyl group is known to be stereospecifically oriented,' as shown in Scheme I. A similar Table 111. Bond Angles (Degrees) orientation was observed in the S-methyl-(@-cysteine analogue12 (axially, between the en chelates). Therefore it was anticipated atoms angle atoms angle that oxidation at sulfur would lead to one epimer of the S-bonded OIl)-Co-N( 1 ) 94.6 (5) N(l)-Co-N(2) -90.3 (6j sulfoxide product, the specificity arising from the presence of the O( l)-Co-N(2) 172.4 (6) N(l)-Co-N(3) 91.9 ( 5 ) chiral c i ~ - C o ( e n moiety. )~ These expectations were not realized. O( l)-Co-N(3) 89.2 (5) N(l)-Co-N(4) 91.4 (5) The thioether complex failed to oxidize with H z 0 2 and N O( l)-Co-N(4) 92.2 (6) N(l)-Co-N(5) 176.8 (5) bromosuccinimide or even with chlorine (over 3 days). UncoO( l)-Co-N(5) 83.7 (5) N(2)-Co-N(4) 93.6 (6) N(3)-Co-N(4) 176.3 (6) N(2)-Co-N(5) 91.7 (5) ordinated thioethers RSR are oxidized very readily by these N(3)-Co-N( 5) 90.8 (5) N(4)-Co-N(5) 85.9 (5) reagents to give first the sulfoxide RSOR and then the sulfone O(l)-S-C( 1) 103.7 (8) Co-O(l)-S 137.4 (7) RS02R. While coordination must block the path to the sulfone, O(l)-S-C(7) 103.8 (9) Co-N(1)€(2) 122 (1) it is apparent that it also protects the thioether from oxidation, C( 1 )-S-C(7) 100 (1) Co-N( 2)-C(3) 109 (1) despite the availability of a lone pair on sulfur. C*N(3)-C(4) 109 (1) Co-N(4)-C(5) 107 ( 1 ) The second approach, addition of CH3+to coordinated sulfenate Co-N(5)-C(6) 108 (1) s-C( l)-C( 2) 117 (1) ion, gave unexpected and interesting results. The chiral sulfur N(l)-C(2)-C(l) 112 (1) N(2)-C(3)-C(4) 107 (1) center of the starting material [CO(~~)~(SO(CH~)~NH~)]~+ is N(3)4(4)-C(3) 109 (1) N(4)-C(5)-C(6) 108 (1) and the two S-bonded sulfenate known to be stable to inver~ion,~,' N(5)-C(6)-C(5) 110 (1) diastereoisomers have been i ~ o l a t e d . ~The reaction of either sulfenate with Me1 in Me$O produced a pink solution from which some unreacted orange-brown sulfenate (2+ ion, -40%) and the pink-red product ( 3 + ion, -60%) were separated easily by ionexchange chromatography. The products were crystallized readily as C1-, I-, or C104- salts, and the elemental analyses and 'H and 13CN M R spectra were all consistent with the addition of one methyl group. A single but different product was obtained from each of the sulfenate diastereoisomers. Two reaction pathways were envisaged: methylation at sulfur to give an S-bound sulfoxide (Scheme 11) or methylation at oxygen to produce an 0-bound sulfenate ester (Scheme 111). In either case two diastereonieric products would be expected. The visible spectra of the two products were similar, and both the ' H and "C N M R spectra indicated essentially identical chemical environments for the Me group in the two molecules, indicating that the products were diastereoisomers of essentially the same chemical species, Neither visible spectrum resembled that of the corresponding sulfenate c o m p l e ~ ,implying ~ ~ * ~ alkylation of the donor sulfur rather than at the more remote oxygen center. Sulfurbonded cobalt(II1) complexes typically show only one of the expected two ligand field band^;^^-^ the second band is usually obscured by an intense charge transfer absorption in the near-UV which extends into the far-visible region. However the present complexes showed both ligand field bands and lacked the UV absorption characteristic of CoIII-S-charge transfer. The only reasonable structure consistent with these data is 0-bonded sulfoxide or, much less likely," 0-bonded sulfenate ester. The visible spectra of the products closely resembled that of the ~is-[Co(en)~(NH,)(OSMe2)1~+ ion,14 while the chemical shifts for the methyl group in the ' H N M R spectrum were also conFigure 1. The molecular structure of the A(R)bis(ethane-1,2 disistent with 0-bonded sulfoxide. However, neither of the isomeric amine)(cysteamine sulfoxide-O)cobalt(III) cation. products reacted with aqueous chlorine (0.04 mol dm-3, 3 days), (NHJ50SMe2]'+ reacts under the conditions above with t1,2 ca. and this remarkable insensitivity to oxidation is atypical of 02 s.15 This conflicting chemical evidence led us to determine the bonded s ~ l f o x i d e . ' ~ J ~For example, the complex [Comolecular structure of one of the isomers by X-ray crystallography. Description of the Structure. Bond lengths and angles are given -in Tables I1 and 111, intermolecular contacts of significance in (12) Gainsford, G. J.; Jackson, W. G.; Sargeson, A. M. J . Chem. SO~., Chem. Commun. 1979, 802. Table IV, and torsion angles and least-squares planes in Tables (13) 0-bonded sulfenate ester is expected to hydrolyze very rapidly, by V and VI. I_-__ 1 1 "
analoav with studies on free and 0-coordinated NH,CH,C(0)OR.15 (14j Absorption maxima for cis-(Co(en)z(NH3)(MezS6)~'are observed at 506 and 353 nm. (15) Buckingham, D. A,; Foster, D. M.; Sargeson, A. M. J . 4 m . Chem. Soc. 1970, 92, 5701.
~~
~
~~~~
(16) Harrowfield, J. N.; Sargeson, A. M.; Singh, B.; Sullivan, J. C. Inorg. Chem. 1975, 14, 2864. (17) Jackson, W. G.; Sargeson, A. M. Inorg. Chem. 1978, 17, 1348.
140 J. Am. Chem. SOC.,Vol. 104, No. 1, 1982
Gainsford, Jackson, and Sargeson
Table IV. Close Intermolecular Contacts I. Hydrogen Bonds
A-B-H."O
LA-B-.O, deg
Co-N(4)-H( 16)-0(2) Co-N(4)-H(16)."0(3)
120 129
-
LB-H-0, 136 137
symmetry operation
B...O, A
H-.O, A
deg
2.30 1.97
3.00 2.81
0.5+~,~,0.5-~ 0.5 + X , y , 0.5 - z
11. Other Contacts (to 3.5 A )
A...B
distance, A
H(4)...0(2) H(24)...0(3) H(23)...0(3) H(1)...1(3) H(7).*.1(3) H( 2)...I( 2)
2.4 8 2.25 2.4 1 2.69 2.97 2.72
symmetry operation
-
0.5 + X , Y , 0.5 z 0.5 t X, y , 0.5 z 0.5-~,~,~-0.5 X,Y,Z X,Y,Z X,Y,Z
A-B-C-D
Q
R
S
Co2 O(1)-4 s4 C(1)-2 N(1)32 C(2) 82 C(7) 176
21.16 -5.42 -1.89 1.17
Co-8 S-9 N(l) 10 C(l)-ll 0(1)-2 C(2) 64
X,Y,Z X,Y,Z X,Y,Z X,Y,Z X,Y,Z X,Y,Z
,s
