Crystal structure and Hirshfeld surface analysis of dimeth­yl(phen­yl)phosphine sulfide

The title compound, C₈H₁₁PS, which melts below room temperature, was crystallized at low temperature. The P—S bond length is 1.9623 (5) Å and the major contributors to the Hirshfeld surface are H⋯H (58.1%), S⋯H/H⋯S (13.4%) and C⋯H/H⋯C contacts (11.7%).

1. Chemical context

The structure of the title compound, C₈H₁₁PS, 11, is inter­esting for two reasons: firstly, the crystals are very temperature sensitive and secondly the chemical background of the substance itself. Although 11 has been known since 1962 (Monsanto Chemicals, 1962) and even commercially available, no crystal structure has been obtained until now. This might be due to its low melting point, which made measurements very difficult and only feasible with X-Temp 2 (Stalke, 1998), which makes crystal picking and mounting possible at very low temperatures. Phospho­rus-based mol­ecules are used in a large variety of different chemical applications as chiral ligands for enanti­oselective catalysis (Grabulosa, 2011). Compound 11 is a prochiral building block for P-stereogenic biphosphine ligands, which are used for transition-metal-catalyzed asymmetric reactions (Tang & Zhang, 2003). This application makes an enanti­oselective synthesis indispensable, which is why different approaches have been reported. For the chemically similar phosphine–boranes, the desired enanti­omer can be synthesized either under kinetic control with sec-BuLi and (−)-sparteine via an asymmetric deprotonation (Muci et al., 1995) or a thermodynamically controlled reaction with n-BuLi and (−)-sparteine via dynamic resolution (Wolfe & Livinghouse, 1998) (Fig. 1). For phosphine sulfides like compound 11, the synthetic approach is quite similar. Using n-BuLi and (−)-sparteine in Et₂O results in an enanti­ometric ratio (e.r.) of 88:12 via a kinetically controlled reaction (Gammon et al., 2010) (Fig. 2). By trapping the li­thia­ted inter­mediate, not only has a higher enanti­oselectivity of e.r. = 93:7 been achieved, but it has also been discovered that the enanti­omers can inter­convert at temperatures above 253 K. One of the most recent synthetic approaches for phosphine–boranes relies on the much cheaper (R,R)-TMCDA instead of (−)-sparteine and crystallization-induced dynamic resolution (CIDR). This synthesis achieves up to 80% yield and enanti­oselectivity of 98:2 (Kuzu et al., 2024).

Figure 1 Kinetic and thermodynamic approaches to synthesize chiral phosphine boranes.

Figure 2 More recent synthetic approaches for chiral phosphine sulfides and boranes.

2. Structural commentary

Compound 11, which was crystallized from toluene at 193 K, forms colorless needles in the monoclinic space group P2₁/n. The P-tetra­hedral mol­ecule consists of two methyl groups and one phenyl group bound to the phosphine sulfide unit. The P1—S1 bond length of 1.9623 (5) Å matches the typical bond length for this species (Verschoor-Kirss et al., 2016; Blake et al., 1981). The phospho­rus bond angles vary from 105.58 (6)° for C1—P1—C3 to 113.55 (5)° for C2—P1—S1. These angles are slightly distorted from the nominal angle of 109.5°, which is probably caused by the different steric effects of the substituents. The bond lengths and angles of the C3–C8 phenyl ring match with the typical lengths and angles for this familiar group (Lide, 2005). Atom S1 is displaced from the plane of the C3–C8 ring by −0.549 (1) Å with corresponding deviations for atoms C1 and C2 of the methyl groups of 1.839 (2) and −0.781 (1) Å, respectively; the C4—C3—P1—S1 torsion angle is 23.85 (12)°.

3. Supra­molecular features

To better understand the inter­molecular inter­actions of 11, a Hirshfeld surface analysis was performed. In Fig. 3 the Hirshfeld surface analysis is mapped over d_norm in the range of −0.07 to 1.20 a.u. (Spackman & Jayatilaka, 2009) and generated by CrystalExplorer21 (Spackman et al., 2021) using red dots to represent close contacts. Atom S1 has close contacts to atoms H1A (H⋯S = 2.87 Å) and H2C (2.95 Å) of the methyl groups of a neighboring mol­ecule displaced by translation in the a-axis direction. For further visualization of the percentage of the respective inter­actions, two-dimensional fingerprint plots (McKinnon et al., 2007) were generated and these are shown in Fig. 4. The most significant contacts in the solid state are the H⋯H inter­actions, contributing 58.1% of the total surface (Fig. 5). The S⋯H/H⋯S (13.4%) and C⋯H/H⋯C inter­actions (11.7%) are less impactful in comparison.

Figure 3 The mol­ecular structure of 11 showing 50% displacement ellipsoids.

Figure 4 Hirshfeld surface analysis of 11 showing close contacts in the crystal.

Figure 5 Two-dimensional fingerprint plots for compound 11, showing (a) all contributions and (b)–(d) contributions between specific inter­acting atom pairs.

4. Database survey

Similar mol­ecules to 11 can vary either in the attached heteroatom such as the previously discussed phosphine boranes (Muci et al., 1995; Kuzu et al., 2024) or they can vary in their organic substituents (Gammon et al., 2010). A search in the Cambridge Structural Database (WebCSD, March 2024; Groom et al., 2016) for phosphine sulfides lead to many similar structures with different organic substituents. Some of those structures contain aromatic substituents such as three phenyl rings (CSD refcode BAQTOC; Arca et al., 1999) or even larger substituents like an anthracene group (BARWEA; Schillmöller et al., 2021). Structures with smaller substituents are also known, for example, butyro­nitrile (KADJEE; Blake et al., 1981).

5. Synthesis and crystallization

In a round-bottom flask equipped with a condenser dimeth­yl(phen­yl)phosphane (1.00 g, 7.24 mmol, 1 eq.) and sulfur (2.23 g, 8.69 mmol, 1.2 eq.) were dissolved in 20 ml of toluene. While stirring, the mixture was heated under reflux to 373 K and then stirred overnight without heating. The resulting mixture was filtered through 3 cm of celite and washed with diethyl ether. The organic phase was dried with magnesium sulfate and the solvent was removed in vacuo, yielding a slightly yellow oil of dimeth­yl(phen­yl)phosphine sulfide (1.04 g, 85%). The oil was dissolved in hot toluene and recrystallized at 193 K, forming colorless needles.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms were geometrically placed (C—H = 0.95–0.98 Å) and refined as riding atoms with U_iso(H) = 1.2U_eq(C) or 1.5U_eq(methyl C).

Table 1
Experimental details

Crystal data
Chemical formula	C8H11PS
Mr	170.20
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	100
a, b, c (Å)	6.2805 (2), 7.6549 (2), 19.3578 (8)
β (°)	99.372 (2)
V (Å^3)	918.23 (5)
Z	4
Radiation type	Cu Kα
μ (mm^−1)	4.17
Crystal size (mm)	0.14 × 0.13 × 0.10
Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015)
Tmin, Tmax	0.465, 0.587
No. of measured, independent and observed [I > 2σ(I)] reflections	12606, 1886, 1745
Rint	0.029
(sin θ/λ)max (Å^−1)	0.626
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.024, 0.064, 1.06
No. of reflections	1886
No. of parameters	93
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å^−3)	0.34, −0.23
Computer programs: APEX2 and SAINT (Bruker, 2018), SHELXT (Sheldrick, 2015a), SHELXL2014/7 (Sheldrick, 2015b) and OLEX2 (Dolomanov et al., 2009).

Supporting information

Computing details

Dimethyl(phenyl)phosphanethione

Crystal data

C8H11PS	F(000) = 360
Mr = 170.20	Dx = 1.231 Mg m^−3
Monoclinic, P21/n	Cu Kα radiation, λ = 1.54178 Å
a = 6.2805 (2) Å	Cell parameters from 3458 reflections
b = 7.6549 (2) Å	θ = 4.6–79.2°
c = 19.3578 (8) Å	µ = 4.17 mm^−1
β = 99.372 (2)°	T = 100 K
V = 918.23 (5) Å^3	Needle, colourless
Z = 4	0.14 × 0.13 × 0.10 mm

Data collection

Bruker APEXII CCD diffractometer	1745 reflections with I > 2σ(I)
φ and ω scans	Rint = 0.029
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θmax = 74.7°, θmin = 4.6°
Tmin = 0.465, Tmax = 0.587	h = −7→7
12606 measured reflections	k = −9→7
1886 independent reflections	l = −24→23

Refinement

Refinement on F^2	Primary atom site location: dual
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.024	H-atom parameters constrained
wR(F^2) = 0.064	w = 1/[σ^2(Fo^2) + (0.031P)^2 + 0.342P] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max = 0.001
1886 reflections	Δρmax = 0.34 e Å^−3
93 parameters	Δρmin = −0.23 e Å^−3
0 restraints

Special details

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

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

	x	y	z	Uiso*/Ueq
P1	0.42807 (5)	0.75930 (4)	0.57224 (2)	0.02071 (10)
S1	0.73232 (5)	0.79603 (5)	0.56424 (2)	0.02966 (11)
C3	0.3919 (2)	0.57849 (16)	0.62992 (6)	0.0225 (3)
C8	0.1928 (2)	0.49493 (18)	0.62617 (7)	0.0280 (3)
H8	0.0754	0.5285	0.5913	0.034*
C2	0.2586 (2)	0.71634 (18)	0.48984 (7)	0.0267 (3)
H2A	0.3014	0.6055	0.4708	0.040*
H2B	0.2743	0.8110	0.4570	0.040*
H2C	0.1078	0.7091	0.4968	0.040*
C1	0.3115 (2)	0.94645 (17)	0.60830 (7)	0.0268 (3)
H1A	0.1620	0.9205	0.6133	0.040*
H1B	0.3142	1.0466	0.5769	0.040*
H1C	0.3950	0.9741	0.6543	0.040*
C4	0.5618 (2)	0.52745 (19)	0.68113 (7)	0.0320 (3)
H4	0.6990	0.5816	0.6836	0.038*
C7	0.1657 (2)	0.36298 (19)	0.67315 (8)	0.0331 (3)
H7	0.0303	0.3056	0.6700	0.040*
C6	0.3345 (3)	0.31482 (19)	0.72440 (8)	0.0357 (3)
H6	0.3152	0.2250	0.7567	0.043*
C5	0.5320 (3)	0.3975 (2)	0.72876 (8)	0.0398 (4)
H5	0.6477	0.3654	0.7645	0.048*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.01838 (17)	0.02128 (17)	0.02246 (17)	0.00095 (11)	0.00330 (12)	0.00012 (12)
S1	0.01915 (17)	0.03201 (19)	0.0385 (2)	0.00062 (12)	0.00678 (13)	0.00507 (14)
C3	0.0253 (6)	0.0205 (6)	0.0223 (6)	0.0025 (5)	0.0058 (5)	−0.0015 (5)
C8	0.0261 (7)	0.0248 (6)	0.0337 (7)	−0.0002 (5)	0.0066 (5)	−0.0004 (5)
C2	0.0266 (7)	0.0291 (7)	0.0238 (6)	0.0010 (5)	0.0021 (5)	−0.0011 (5)
C1	0.0285 (7)	0.0236 (6)	0.0293 (6)	0.0023 (5)	0.0075 (5)	−0.0008 (5)
C4	0.0304 (7)	0.0315 (7)	0.0321 (7)	−0.0014 (6)	−0.0011 (6)	0.0027 (6)
C7	0.0377 (8)	0.0251 (7)	0.0396 (8)	−0.0021 (6)	0.0152 (6)	−0.0005 (6)
C6	0.0553 (10)	0.0250 (7)	0.0300 (7)	0.0032 (6)	0.0165 (7)	0.0035 (6)
C5	0.0478 (9)	0.0368 (8)	0.0319 (7)	0.0039 (7)	−0.0027 (7)	0.0077 (6)

Geometric parameters (Å, º)

P1—S1	1.9623 (5)	C1—H1A	0.9800
P1—C3	1.8158 (13)	C1—H1B	0.9800
P1—C2	1.7977 (13)	C1—H1C	0.9800
P1—C1	1.8004 (13)	C4—H4	0.9500
C3—C8	1.3957 (19)	C4—C5	1.390 (2)
C3—C4	1.3893 (18)	C7—H7	0.9500
C8—H8	0.9500	C7—C6	1.379 (2)
C8—C7	1.388 (2)	C6—H6	0.9500
C2—H2A	0.9800	C6—C5	1.383 (2)
C2—H2B	0.9800	C5—H5	0.9500
C2—H2C	0.9800
C3—P1—S1	112.26 (4)	P1—C1—H1A	109.5
C2—P1—S1	113.55 (5)	P1—C1—H1B	109.5
C2—P1—C3	106.91 (6)	P1—C1—H1C	109.5
C2—P1—C1	105.68 (6)	H1A—C1—H1B	109.5
C1—P1—S1	112.28 (5)	H1A—C1—H1C	109.5
C1—P1—C3	105.58 (6)	H1B—C1—H1C	109.5
C8—C3—P1	121.21 (10)	C3—C4—H4	119.9
C4—C3—P1	119.64 (10)	C3—C4—C5	120.24 (14)
C4—C3—C8	119.08 (12)	C5—C4—H4	119.9
C3—C8—H8	119.9	C8—C7—H7	119.9
C7—C8—C3	120.25 (13)	C6—C7—C8	120.26 (14)
C7—C8—H8	119.9	C6—C7—H7	119.9
P1—C2—H2A	109.5	C7—C6—H6	120.1
P1—C2—H2B	109.5	C7—C6—C5	119.89 (13)
P1—C2—H2C	109.5	C5—C6—H6	120.1
H2A—C2—H2B	109.5	C4—C5—H5	119.9
H2A—C2—H2C	109.5	C6—C5—C4	120.26 (14)
H2B—C2—H2C	109.5	C6—C5—H5	119.9
P1—C3—C8—C7	−176.66 (10)	C8—C7—C6—C5	−0.4 (2)
P1—C3—C4—C5	175.48 (12)	C2—P1—C3—C8	−34.24 (12)
S1—P1—C3—C8	−159.38 (10)	C2—P1—C3—C4	148.99 (11)
S1—P1—C3—C4	23.85 (12)	C1—P1—C3—C8	77.98 (12)
C3—C8—C7—C6	0.8 (2)	C1—P1—C3—C4	−98.79 (12)
C3—C4—C5—C6	1.7 (2)	C4—C3—C8—C7	0.1 (2)
C8—C3—C4—C5	−1.4 (2)	C7—C6—C5—C4	−0.8 (2)