Triethynylphosphine oxide

In the solid state, the title compound, C₆H₃OP, lies on a crystallographic mirror plane, with the P=O as well as one of the acetyl­ene units bis­ected by this plane. The central P atom exhibits pseudo-tetra­hedral geometry. The crystallographic packing is dominated by C—H...O hydrogen bonds between all of the acetyl­ene H atoms and the O atom, which form a heavily inter­connected hydrogen-bonding network. Two of the hydrogen bonds, related by the mirror plane, are coplanar with each other and with the P=O unit, while the third C—H...O hydrogen bond is at an angle of 67.49 (7)° to this plane; the H...P=O angles are 134 and 112°, respectively. The three-dimensional structure formed by the hydrogen-bond inter­actions consists of two independent inter­penetrating networks.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.030
• wR factor = 0.084
• Data-to-parameter ratio = 19.1

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT230_ALERT_2_B Hirshfeld Test Diff for    P1     -   C1      ..       9.96 su

Alert level C
ABSTM02_ALERT_3_C  The ratio of expected to reported Tmax/Tmin(RR') is < 0.90
            Tmin and Tmax reported:      0.708     0.930
            Tmin(prime) and Tmax expected:      0.853     0.930
            RR(prime) =      0.831
            Please check that your absorption correction is appropriate.
PLAT061_ALERT_3_C Tmax/Tmin Range Test RR' too Large .............       0.83
PLAT125_ALERT_4_C No _symmetry_space_group_name_Hall Given .......          ?
PLAT230_ALERT_2_C Hirshfeld Test Diff for    P1     -   C3      ..       5.54 su

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

As an aspect of our research into the Diels-Alder chemistry of electron poor alkynyl phosphonates we attempted the synthesis of bis(2,2,2-trifluoroethyl)(trimethylsilyl)ethynyl phosphonate by reacting lithium trimethylsilyl acetylide with bis(2,2,2-trifluoroethyl)phosphorochloridate as shown in Figure 1. Displacement of not only the chlorine but also of the two –OCH₂CF₃ groups resulted, after aqueous workup and loss of the trimethylsilyl group, in the unplanned formation of triethynylphosphine oxide in 25% yield. While the triethynylphosphine oxide is mentioned in some spectroscopic publications (Yang et al., 1992; Rosenberg & Drenth, 1972) no synthesis is reported in the scientific literature.

In the solid state the title compound is found to be located on a crystallographic mirror plane with the P=O as well as one of the acetylene units bisected by this plane (Figure 2). The phosphorus center exhibits pseudo-tetrahedral geometry with three acetetylene substituents and the double bonded oxygen atom. The bond distances and angles are unexceptional.

Crystal packing is dominated by hydrogen bonds between the acetylenic H atoms and the P=O oxygen with all three acetylene units forming relatively strong C—H···O hydrogen bonds. Two of the three hydrogen bonds towards each oxygen atom are symmetry related by the crystallographic mirror plane and are coplanar with each other and the P=O unit. The third C—H···O hydrogen bond is at an angle of 67.49 (7) ° to this plane (as given by the angles between the lines defined by P1—O1 and O1—C4ⁱⁱⁱ (symmetry code iv = x - 1, y, z). (Figure 3)

The Cambridge crystallographic database does not have any other entries for hydrogen bonds between acetylene and O=P units, but the parameters observed here are in good agreement with those listed for hydrogen bonds towards other O=X units such as ketones or aldehydes (Cambridge Structural Database, V5.28; Allen 2002). The H···P=O angles of the title compound are 133.70° for H2^v···O1—P1 and 112.35° for H4^iv···O1—P1, respectively (symmetry code v = 1/2 - x, 1 - y, 1 - z).

The three dimensional crystal structure thus formed by the hydrogen bonding interactions actually consists of two interpenetrating networks that are each heavily interconnected via H-bonding, but that are not connected via such interactions with each other (Figures 4 and 5).

Related literature

For geometry, see: Allen (2002); Herbstein (2000). For NMR data, see: Yang et al. (1992); Rosenberg & Drenth (1972).

S2. Experimental

To a solution of trimethylsilylacetylene (5 mmol, 0.71 ml) in anhydrous pentane (5 ml) and anhydrous ether (5 ml), was added n-BuLi (1.6 M) solution in hexane (6 mmol, 3.8 ml) in a dropwise manner at 195 K (-78 °C). The reaction solution was stirred continuously for 1 h. Then bis(2,2,2-trifluoroethyl)phosphorochloridate was added dropwise at the same temperature and the mixture was stirred for an additional hour. The reaction solution was stirred overnight at ambient temperature and was then quenched with a saturated aqueous solution of ammonium chloride. The organic layer was separated and washed with water. The aqueous layers were washed with ether, and the organic fractions were combined, washed with saturated NaCl solution and dried over MgSO₄. The oxide was purified by column chromatography (hexane/ethyl acetate, 1/1) and crystals of sufficient quality for single-crystal diffraction analysis were obtained from ethyl acetate by slow evaporation. ¹H NMR (400 MHz, CDCl₃) δ 3.30 (d, 3H, J = 12.45 Hz), ¹³C NMR (100 MHz) δ 92.12 (d, 3 C, J = 45.45 Hz), 77.35 (d, 3 C, J = 233.88 Hz), ³¹P NMR (162 MHz) δ -55.3..

S3. Refinement

Treatment of hydrogen atoms: All hydrogen atoms were added in calculated positions with a C—H bond distance of 0.95 Å and were refined with U_iso(H) = 1.2U_eq(C).

The e.s.d. values of the cell parameters are taken from the software recognizing that the values are unreasonably small (Herbstein, 2000).

Computing details

Data collection: SMART (Bruker, 2002); cell refinement: SAINT-Plus (Bruker, 2003); data reduction: SAINT-Plus (Bruker, 2003); program(s) used to solve structure: SHELXTL (Bruker, 2003); program(s) used to refine structure: SHELXTL (Bruker, 2003); molecular graphics: SHELXTL (Bruker, 2003); software used to prepare material for publication: SHELXTL (Bruker, 2003).

Figures

	Fig. 1. Synthesis of the title compound.
	Fig. 2. Molecular structure showing 50% probability displacement ellipsoids (symmetry code i: x, -y + 3/2, z).
	Fig. 3. Hydrogen bonding environment for one P=O unit, 50% probability displacement ellipsoids. Hydrogen bonds are indicated by dotted lines (symmetry codes: ii = x + 1, y, z; iii = -x + 1/2, -y + 1, z + 1/2; vi = -x + 1, y + 1/2, z + 1/2).
	Fig. 4. Packing view along the b axis, 50% probability displacement ellipsoids. Hydrogen bonds are indicated as dotted lines. Left: both interpenetrating networks shown, right: only one of the interpenetrating networks shown.
	Fig. 5. Packing view along the a axis, 50% probability displacement ellipsoids. Hydrogen bonds are indicated as dotted lines. Left: both interpenetrating networks shown, right: only one of the interpenetrating networks shown.

Triethynylphosphine oxide

Crystal data

C6H3OP	Dx = 1.294 Mg m^−3
Mr = 122.05	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pnma	Cell parameters from 7248 reflections
a = 6.8646 (9) Å	θ = 3.0–30.6°
b = 9.7823 (13) Å	µ = 0.33 mm^−1
c = 9.3277 (12) Å	T = 100 K
V = 626.37 (14) Å^3	Block, colorless
Z = 4	0.48 × 0.23 × 0.22 mm
F(000) = 248

Data collection

Bruker SMART APEX CCD diffractometer	821 independent reflections
Radiation source: fine-focus sealed tube	796 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.018
ω scans	θmax = 28.3°, θmin = 3.0°
Absorption correction: multi-scan (SADABS in SAINT-Plus; Bruker, 2003)	h = −9→9
Tmin = 0.708, Tmax = 0.930	k = −13→13
7459 measured reflections	l = −12→12

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)] = 0.030	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.084	H-atom parameters constrained
S = 1.12	w = 1/[σ^2(Fo^2) + (0.049P)^2 + 0.2795P] where P = (Fo^2 + 2Fc^2)/3
821 reflections	(Δ/σ)max = 0.001
43 parameters	Δρmax = 0.45 e Å^−3
0 restraints	Δρmin = −0.33 e Å^−3

Special details

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.

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

	x	y	z	Uiso*/Ueq
P1	0.42049 (6)	0.7500	0.53431 (4)	0.01596 (17)
O1	0.29767 (18)	0.7500	0.40356 (13)	0.0205 (3)
C1	0.37974 (17)	0.60900 (12)	0.64477 (12)	0.0199 (2)
C4	0.8405 (3)	0.7500	0.47595 (18)	0.0235 (4)
H4	0.9760	0.7500	0.4552	0.028*
C3	0.6715 (3)	0.7500	0.50180 (18)	0.0191 (3)
C2	0.33869 (17)	0.51443 (13)	0.71937 (12)	0.0230 (3)
H2	0.3060	0.4390	0.7788	0.028*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0142 (2)	0.0159 (2)	0.0178 (2)	0.000	−0.00015 (13)	0.000
O1	0.0186 (6)	0.0219 (6)	0.0209 (6)	0.000	−0.0035 (4)	0.000
C1	0.0181 (5)	0.0199 (5)	0.0217 (5)	0.0000 (4)	0.0004 (4)	−0.0012 (4)
C4	0.0196 (9)	0.0248 (9)	0.0261 (9)	0.000	0.0001 (6)	0.000
C3	0.0190 (8)	0.0182 (7)	0.0200 (7)	0.000	0.0007 (6)	0.000
C2	0.0227 (6)	0.0222 (6)	0.0242 (6)	−0.0002 (4)	0.0022 (4)	−0.0001 (5)

Geometric parameters (Å, º)

P1—O1	1.4826 (12)	C1—C2	1.1914 (17)
P1—C1	1.7443 (12)	C4—C3	1.185 (3)
P1—C1^i	1.7443 (12)	C4—H4	0.9500
P1—C3	1.7495 (18)	C2—H2	0.9500
O1—P1—C1	113.25 (5)	C1^i—P1—C3	105.09 (5)
O1—P1—C1^i	113.25 (5)	C2—C1—P1	175.54 (11)
C1—P1—C1^i	104.52 (8)	C3—C4—H4	180.0
O1—P1—C3	114.67 (8)	C4—C3—P1	178.24 (17)
C1—P1—C3	105.09 (5)	C1—C2—H2	180.0

Symmetry code: (i) x, −y+3/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C4—H4···O1^ii	0.95	2.26	3.210 (2)	179
C2—H2···O1^iii	0.95	2.30	3.2433 (14)	174

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