The dithiol­ene ligand and tetra­thia­fulvalene precursor mol­ecules 4,5-bis­(bromo­meth­yl)-1,3-dithiol-2-one and 4,5-bis­[(dihy­droxy­phosphoryl)meth­yl]-1,3-dithiol-2-one

The crystal structures of 4,5-bis­(bromo­methyl)-1,3-dithiol-2-one, C₅H₄Br₂OS₂, (I), and 4,5-bis[(dihydroxyphosphoryl)methyl]-1,3-dithiol-2-one, C₅H₈O₇P₂S₂, (II), occur with similar unit cells in the same monoclinic space group. Both mol­ecules reside on a twofold symmetry axis coincident with the C=O bond, so that the substituents in the 4- and 5-positions project above and below the plane of the 1,3-dithiol-2-one ring. In both structures, the mol­ecules align themselves in a head-to-tail fashion along the b axis, and these rows of mol­ecules then stack, with alternating directionality, along the c axis. For (II), an extensive network of inter­molecular hydrogen bonds occurs between mol­ecules within the same stack and between adjacent stacks. Each -CH₂P(O)(OH)₂ group participates in four hydrogen bonds, twice as donor and twice as acceptor.

S1. Comment

Molecules including the 1,3-dithiol-2-one moiety are useful both as protected forms of dithiolene ligands (Rauchfuss, 2004; Rowe et al., 1985) and as precursors to tetrathiafulvalene-type compounds, which are of interest for their potential application as superconducting (Dressel & Drichko, 2004; El-Wareth & Sarhan, 2005) or magnetic materials (El-Wareth & Sarhan, 2005), sensors (El-Wareth & Sarhan, 2005; Moonen et al., 2005), light-harvesting materials (Martín et al. 2007) and other electronic devices (Rovira, 2004) designed from a bottom-up approach. We recently described an improved synthesis (Chandrasekaran & Donahue, 2009) and crystal structure (Chandrasekaran et al., 2009) of 4,5-dimethyl-1,3-dithiol-2-one, one of the simplest molecules of this type. An underappreciated aspect of this particular compound is the facility with which it is converted to variants that are more richly functionalized. Following a literature protocol (Crivillers et al., 2007), 4,5-dimethyl-1,3-dithiol-2-one is readily transformed into 4,5-bis(bromomethyl)-1,3-dithiol-2-one, (I), a molecule from which a panorama of synthetic options then unfolds. For example, a straightforward Michaelis–Arbuzov reaction (Gorgues et al., 2004; Gautier et al., 2004) with triethyl phosphite yields 4,5-bis[(diethoxyphosphoryl)methyl]-1,3-dithiol-2-one, (III) (see Scheme). In turn, classical Wittig chemistry provides a means by which this molecule can be elaborated, with the appropriate carbonyl compound, to include any of a broad variety of substituents linked to the 1,3-dithiol-2-one ring via an olefinic bond (see Scheme) (Gautier et al., 2004). Alternatively, dealkylation with BBr₃ (Gauvry & Mortier, 2001) affords the corresponding 4,5-bis[(dihydroxyphosphoryl)methyl]-1,3-dithiol-2-one, (II), a molecule which is of some interest for its utility as precursor to a robust water-soluble dithiolene ligand whose metal complexes should be similarly water soluble. We report here the structures of (I) and derivative (II) as part of an ongoing effort aimed at creating facile synthetic access to new types of dithiolene ligands.

Compound (I) (Fig. 1a) crystallizes in the monoclinic space group C2/c on a twofold symmetry axis coincident with the C═O bond. The Br atoms of the bromomethyl groups thus project themselves above and below the plane defined by the 1,3-dithiol-2-one ring, thereby maximizing their separation. Molecules of (I) arrange themselves in a head-to-tail fashion into one-dimensional rows in the direction of the b axis (Fig. 2a). These rows then stack along the c axis, with alternating directionality of the head-to-tail alignment of the molecules in the row. Although intermolecular hydrogen bonding is not present within this crystal packing pattern, relatively short intermolecular Br1···H3ⁱ [symmetry code: (i) -x+1/2, -y+1/2, -z+2] and Br1···S1ⁱⁱ [symmetry code: (ii) -x+1/2, y-1/2, -z+3/2] contacts of 3.06 (Fig. 2b) and 3.6266 (6) Å (Fig. 2a), respectively, are made between adjacent rows of molecules. Within a row along the b axis, short nonbonding O1···H3ⁱⁱⁱ [symmetry code: (iii) x, y-1, z] distances of 2.40 Å are observed between neighboring molecules (Fig. 2a).

The crystal structure of (II) is similar to that of bromomethyl compound (I) in that it crystallizes on a twofold axis in the space group C2/c with an up and down (C₂) disposition of the (dihydroxyphosphoryl)methyl substituents (Fig. 1b). A further similarity is the head-to-tail alignment of the molecules into rows parallel to the b axis, stacked along the c axis and alternating in the orientation of the molecules between rows by 180° (Fig. 3a). The principal difference between the two structures arises from a dense network of intermolecular hydrogen bonding in (II). Each phosphoryl group participates in four P—OH···O═P hydrogen bonds, two as donor and two as acceptor. The two lone pairs on the terminal O atom of each –CH₂P(O)(OH)₂ group enable it to act twice as a hydrogen-bond acceptor. The intermolecular hydrogen bonding occurs both between molecules within the same stack and between molecules in adjacent c-axis stacks (Figs. 3a and 3b).

Structurally characterized molecules having the 1,3-dithiol-2-one moiety are not uncommon, although it is noteworthy that the majority of such examples incorporate this fragment as part of a tetrathioethylene group, the opposing side of which is either chelated to a transition metal (Yang et al., 1991; Kobayashi et al., 1992; Fourmigué et al., 1998; Keefer et al., 1998; Smucker et al., 2003; Llusar et al., 2005; Faulmann et al., 2006; Rabaça et al., 2006; Nomura & Fourmigué, 2007; Llusar et al., 2008) or heavy main group element (Chohan et al., 1999; Avarvari & Fourmigué, 2003), or is alkylated (Simonsen et al., 1990; Xue et al., 2003; Nomura et al., 2009) or arylated (Yu et al., 1995). Of the crystallographically identified molecules that might be compared with (I) and (II), the nearest and best comparison is given by 4,5-dicarbomoyl-1,3-dithiol-2-one, (IV) (Baudron et al., 2003). Like both (I) and (II), it is a molecule that is symmetrically substituted in the 4- and 5-positions with a functional group that allows for further synthetic modification and which confers both water solubility and the opportunity for extensive hydrogen bonding in its corresponding metal complexes (Oku et al., 1997; Baudron et al., 2005). Like (II), (IV) engages in multiple hydrogen bonds with neighboring molecules, but it does so strictly within a two-dimensional sheet network. Compound (II) provides for a rather different pattern of hydrogen bonding that involves molecules above, below and to either side of the plane of the 1,3-dithiol-2-one (Figs. 3a and 3b). It is likely that a pattern of intermolecular hydrogen bonding similar to that observed for (II) will be asserted in the crystal structures of simple metal complexes with the unmasked -ene-1,2-dithiolate form of this molecule, such as square-planar bis(dithiolene) complexes of the group 10 metals.

Related literature

For related literature, see: Avarvari & Fourmigué (2003); Baudron et al. (2003, 2005); Chandrasekaran & Donahue (2009); Chandrasekaran, Arumugam, Jayarathne, Pérez, Mague & Donahue (2009); Chohan et al. (1999); Crivillers et al. (2007); Dressel & Drichko (2004); El-Wareth & Sarhan (2005); Faulmann et al. (2006); Fourmigué et al. (1998); Gautier et al. (2004); Gauvry & Mortier (2001); Gorgues et al. (2004); Keefer et al. (1998); Kobayashi et al. (1992); Llusar et al. (2005, 2008); Martín et al. (2007); Moonen et al. (2005); Nomura & Fourmigué (2007); Nomura et al. (2009); Oku et al. (1997); Rabaça et al. (2006); Rauchfuss (2004); Rovira (2004); Rowe et al. (1985); Simonsen et al. (1990); Smucker et al. (2003); Xue et al. (2003); Yang et al. (1991); Yu et al. (1995).

S2. Experimental

Compound (I) was prepared according to the method of Crivillers et al. (2007). Colorless plates were grown by slow evaporation of a dichloromethane solution at ambient temperature. Compound (II) was prepared by dealkylation of the corresponding methyl phosphonic acid diethyl ester (0.50 g), according to the procedure of Gauvry & Mortier (2001). Pale-yellow plates were obtained by diffusion of diisopropyl ether vapor into a methanol solution (yield 0.079 g, 22%; m.p. 528 K). ¹H NMR (CD₃OD, δ, p.p.m.): 3.24 (m, –CH₂–). ³¹P NMR (CD₃OD, δ, p.p.m.): 21.01. Analysis, calculated for C₅H₈O₇P₂S₂: C 19.61, H 2.63%; found: C 20.70, H 2.99%.

S3. Refinement

For both compounds, the methylene H atoms were placed in calculated positions (C—H = 0.99 Å) and included as riding contributions, with U_iso(H) = 1.2U_eq(C) atoms. In (II), H atoms attached to O atoms were placed in locations derived from a difference map (O—H = 0.84–0.86 Å) and included as riding contributions, with U_iso(H) = 1.2U_eq(O).

Computing details

For both compounds, data collection: APEX2 (Bruker, 2008). Cell refinement: SAINT-Plus (Bruker, 2006) for (I); SAINT (Bruker, 2008) for (II). Data reduction: SAINT-Plus (Bruker, 2006) for (I); SAINT (Bruker, 2008) for (II). For both compounds, program(s) used to solve structure: SHELXS97 (Sheldrick, 2008a); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008a); molecular graphics: SHELXTL (Sheldrick, 2008a). Software used to prepare material for publication: SHELXL97 (Sheldrick, 2008a) for (I); SHELXTL (Sheldrick, 2008a) for (II).

Figures

	Fig. 1. The molecular structures of (a) (I) and (b) (II), with the atom-numbering schemes. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. (a) A packing diagram for (I), with the b axis coincident with the horizontal axis. (b) A packing diagram with the b axis orthogonal to the plane of paper. The stacking of molecules is coincident with the c axis. Hydrogen bonds are shown as dashed lines. [Please confirm added text] (In the electronic version of the paper, Br atoms are illustrated in maroon, S atoms in gold–yellow and O atoms in red.)
	Fig. 3. (a) A packing diagram for (II), viewed down the c axis. The alternating disposition of the one-dimensional rows of molecules along the (horizontal) b axis is seen. (b) A packing diagram showing the intermolecular hydrogen bonding between methyl phosphonic acid groups in different rows of (II). The b axis is coincident with the horizontal axis. Hydrogen bonds are shown as dashed lines. [Please confirm added text] (In the electronic version of the paper, S atoms are illustrated in gold–yellow, P atoms in purple and O atoms in red.)

(I) 4,5-bis(bromomethyl)-1,3-dithiol-2-one

Crystal data

C5H4Br2OS2	F(000) = 576
Mr = 304.02	Dx = 2.403 Mg m^−3 Dm = 0 Mg m^−3 Dm measured by not measured
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 3880 reflections
a = 14.9026 (15) Å	θ = 2.8–29.4°
b = 7.8804 (8) Å	µ = 10.07 mm^−1
c = 7.4012 (7) Å	T = 100 K
β = 104.836 (1)°	Plate, colourless
V = 840.20 (14) Å^3	0.16 × 0.13 × 0.09 mm
Z = 4

Data collection

Bruker APEXII CCD area-detector diffractometer	1062 independent reflections
Radiation source: fine-focus sealed tube	1005 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.027
ϕ and ω scans	θmax = 28.5°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 2008b)	h = −19→19
Tmin = 0.307, Tmax = 0.464	k = −10→10
7166 measured reflections	l = −9→9

Refinement

Refinement on F^2	Primary atom site location: heavy-atom method
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.016	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.044	H-atom parameters constrained
S = 1.11	w = 1/[σ^2(Fo^2) + (0.0223P)^2 + 0.8485P] where P = (Fo^2 + 2Fc^2)/3
1062 reflections	(Δ/σ)max = 0.001
47 parameters	Δρmax = 0.44 e Å^−3
0 restraints	Δρmin = −0.44 e Å^−3

Special details

Experimental. The diffraction data were obtained from 3 sets of 400 frames, each of width 0.5° in ω, collected at ϕ = 0.00, 90.00 and 180.00°, and 2 sets of 800 frames, each of width 0.45° in ϕ, collected at ω = -30.00 and 210.00°. The scan time was 15 sec/frame.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. H-atoms were placed in calculated positions (C—H = 0.99 Å) and included as riding contributions with isotropic displacement parameters 1.2 times those of the attached carbon atoms.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br1	0.193908 (12)	0.36865 (2)	0.75618 (3)	0.01797 (8)
S1	0.09409 (3)	−0.03052 (5)	0.87598 (6)	0.01129 (10)
O1	0.0000	−0.3084 (2)	0.7500	0.0200 (4)
C1	0.0000	−0.1545 (3)	0.7500	0.0131 (5)
C2	0.04303 (12)	0.1667 (2)	0.8081 (2)	0.0105 (3)
C3	0.09766 (13)	0.3204 (2)	0.8879 (3)	0.0135 (3)
H3A	0.1272	0.3018	1.0223	0.016*
H3B	0.0555	0.4191	0.8766	0.016*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.01267 (11)	0.01707 (11)	0.02387 (12)	−0.00362 (7)	0.00413 (8)	0.00491 (7)
S1	0.0099 (2)	0.00922 (19)	0.0145 (2)	0.00188 (15)	0.00272 (15)	0.00139 (14)
O1	0.0228 (10)	0.0083 (8)	0.0282 (11)	0.000	0.0054 (8)	0.000
C1	0.0155 (12)	0.0116 (11)	0.0134 (12)	0.000	0.0059 (10)	0.000
C2	0.0116 (8)	0.0073 (7)	0.0139 (8)	0.0004 (6)	0.0054 (7)	0.0002 (6)
C3	0.0120 (8)	0.0113 (7)	0.0172 (9)	−0.0019 (7)	0.0038 (7)	−0.0013 (6)

Geometric parameters (Å, º)

Br1—C3	1.9667 (18)	C2—C2^i	1.349 (4)
S1—C2	1.7467 (17)	C2—C3	1.494 (2)
S1—C1	1.7664 (14)	C3—H3A	0.9900
O1—C1	1.213 (3)	C3—H3B	0.9900
C1—S1^i	1.7664 (14)
C2—S1—C1	96.42 (9)	C2—C3—Br1	110.72 (12)
O1—C1—S1	123.58 (7)	C2—C3—H3A	109.5
O1—C1—S1^i	123.58 (7)	Br1—C3—H3A	109.5
S1—C1—S1^i	112.85 (13)	C2—C3—H3B	109.5
C2^i—C2—C3	125.80 (10)	Br1—C3—H3B	109.5
C2^i—C2—S1	117.15 (6)	H3A—C3—H3B	108.1
C3—C2—S1	117.03 (13)

Symmetry code: (i) −x, y, −z+3/2.

(II) 4,5-bis[(dihydroxyphosphoryl)methyl]-1,3-dithiol-2-one

Crystal data

C5H8O7P2S2	F(000) = 624
Mr = 306.17	Dx = 1.999 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 6382 reflections
a = 15.078 (3) Å	θ = 2.7–28.3°
b = 8.1736 (14) Å	µ = 0.86 mm^−1
c = 8.3628 (15) Å	T = 100 K
β = 99.188 (2)°	Plate, gold
V = 1017.4 (3) Å^3	0.23 × 0.22 × 0.06 mm
Z = 4

Data collection

Bruker APEXI CCD area-detector diffractometer	1269 independent reflections
Radiation source: fine-focus sealed tube	1196 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.030
ϕ and ω scans	θmax = 28.3°, θmin = 2.7°
Absorption correction: multi-scan (SADABS; Sheldrick 2008b)	h = −20→20
Tmin = 0.829, Tmax = 0.955	k = −10→10
8625 measured reflections	l = −11→11

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.024	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.069	H-atom parameters constrained
S = 1.12	w = 1/[σ^2(Fo^2) + (0.0335P)^2 + 1.4614P] where P = (Fo^2 + 2Fc^2)/3
1269 reflections	(Δ/σ)max = 0.001
74 parameters	Δρmax = 0.48 e Å^−3
0 restraints	Δρmin = −0.34 e Å^−3

Special details

Experimental. The diffraction data were obtained from 3 sets of 400 frames, each of width 0.5° in ω, collected at ϕ = 0.00, 90.00 and 180.00°, and 2 sets of 800 frames, each of width 0.45° in ϕ, collected at ω = -30.00 and 210.00°. The scan time was 10 sec/frame.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. H-atoms were placed in calculated positions (C—H = 0.99 Å) and included as riding contributions with isotropic displacement parameters 1.2 times those of the attached carbon atoms. H-atoms attached to oxygen were placed in locations derived from a difference map and included as riding contributions with isotropic displacement parameters 1.2 times those of the attached oxygen atoms.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
P1	0.32403 (2)	0.13964 (4)	0.70802 (4)	0.01285 (12)
S1	0.41730 (3)	0.55257 (4)	0.63065 (5)	0.01697 (12)
O1	0.36348 (8)	0.11939 (13)	0.88925 (13)	0.0175 (2)
H1O	0.3328	0.0816	0.9591	0.021*
O2	0.24844 (7)	0.26862 (14)	0.68676 (13)	0.0197 (2)
H2O	0.2461	0.3343	0.7640	0.024*
O3	0.28874 (8)	−0.01573 (13)	0.62326 (13)	0.0173 (2)
O4	0.5000	0.8216 (2)	0.7500	0.0267 (4)
C1	0.41638 (9)	0.21256 (18)	0.61670 (16)	0.0138 (3)
H1A	0.4613	0.1237	0.6202	0.017*
H1B	0.3942	0.2370	0.5013	0.017*
C2	0.46251 (10)	0.36220 (17)	0.69418 (17)	0.0129 (3)
C3	0.5000	0.6739 (3)	0.7500	0.0186 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0129 (2)	0.0136 (2)	0.01207 (19)	−0.00119 (12)	0.00219 (14)	−0.00057 (12)
S1	0.0163 (2)	0.01379 (19)	0.0207 (2)	0.00286 (13)	0.00258 (14)	0.00322 (13)
O1	0.0194 (6)	0.0210 (6)	0.0120 (5)	−0.0027 (4)	0.0018 (4)	0.0019 (4)
O2	0.0174 (5)	0.0236 (6)	0.0177 (5)	0.0056 (4)	0.0016 (4)	−0.0034 (4)
O3	0.0204 (5)	0.0158 (5)	0.0162 (5)	−0.0060 (4)	0.0047 (4)	−0.0034 (4)
O4	0.0346 (10)	0.0128 (7)	0.0337 (9)	0.000	0.0086 (8)	0.000
C1	0.0138 (6)	0.0152 (7)	0.0125 (6)	−0.0017 (5)	0.0023 (5)	−0.0010 (5)
C2	0.0137 (7)	0.0120 (6)	0.0139 (6)	0.0005 (5)	0.0047 (5)	0.0011 (5)
C3	0.0201 (10)	0.0157 (10)	0.0214 (10)	0.000	0.0076 (8)	0.000

Geometric parameters (Å, º)

P1—O3	1.5093 (11)	O2—H2O	0.8450
P1—O2	1.5418 (12)	O4—C3	1.207 (3)
P1—O1	1.5460 (11)	C1—C2	1.5019 (19)
P1—C1	1.7936 (15)	C1—H1A	0.9900
S1—C2	1.7472 (15)	C1—H1B	0.9900
S1—C3	1.7712 (13)	C2—C2^i	1.346 (3)
O1—H1O	0.8585
O3—P1—O2	108.82 (7)	C2—C1—H1A	108.5
O3—P1—O1	114.96 (6)	P1—C1—H1A	108.5
O2—P1—O1	110.35 (6)	C2—C1—H1B	108.5
O3—P1—C1	108.61 (7)	P1—C1—H1B	108.5
O2—P1—C1	109.48 (7)	H1A—C1—H1B	107.5
O1—P1—C1	104.46 (7)	C2^i—C2—C1	125.37 (8)
C2—S1—C3	97.01 (8)	C2^i—C2—S1	117.03 (5)
P1—O1—H1O	122.8	C1—C2—S1	117.57 (10)
P1—O2—H2O	117.8	O4—C3—S1	124.05 (6)
C2—C1—P1	115.11 (10)	S1—C3—S1^i	111.89 (12)

Symmetry code: (i) −x+1, y, −z+3/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···O3^ii	0.86	1.70	2.5538 (16)	170
O2—H2O···O3^iii	0.84	1.68	2.4959 (16)	161

Symmetry codes: (ii) x, −y, z+1/2; (iii) −x+1/2, y+1/2, −z+3/2.