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Logo of actae2this articlesearchopen accesssubmitActa Crystallographica Section E: Crystallographic CommunicationsActa Crystallographica Section E: Crystallographic Communications
 
Acta Crystallogr E Crystallogr Commun. 2017 July 1; 73(Pt 8): 1268–1270.
Published online 2017 July 28. doi:  10.1107/S2056989017010994
PMCID: PMC5598863

Crystal structure of (3,5-dimethyl-1H-pyrrol-2-yl)di­phenyl­phosphine oxide

Abstract

The title compound, C18H18NOP, was obtained during a search for new P,N-containing ligands with the potential to generate precatalysts with chromium(III) for selective ethyl­ene oligomerization. In the crystal, mutual pairs of N—H(...)O=P hydrogen bonds link two mol­ecules into a dimer with individual mol­ecules related by a twofold rotation axis. The P=O bond length of 1.4740 (15) Å is not elongated although the O atom is involved in hydrogen bonding. The crystal structure is further stabilized by van der Waals inter­actions between the dimers, linking the mol­ecules into a three-dimensional network structure.

Keywords: crystal structure, pyrrole, phosphine oxide, catalysis

Chemical context  

Mixed bi- and tridentate ligands containing phospho­rus and nitro­gen atoms are highly useful in chromium(III)-catalysed selective ethyl­ene oligomerization (Fliedel et al., 2016  ). Several variations of the ligands introduced by chemical modifications can tune the steric and electronic properties of the catalysts, affecting the catalytic behavior in ethyl­ene oligomerization (Agapie, 2011  ; McGuinness, 2011  ). In search of new P,N-containing ligands, we obtained the title compound from the reaction of 2,4-di­methyl­pyrrole and chloro­diphenyl­phosphine. Herein we present the synthesis and the crystal structure of the title compound, (3,5-dimethyl-1H-pyrrol-2-yl)di­phenyl­phosphine oxide, C18H18NOP, that was obtained by an accidental oxidation reaction.

An external file that holds a picture, illustration, etc.
Object name is e-73-01268-scheme1.jpg

Structural commentary  

The mol­ecular structure of the title compound, (I), is shown in Fig. 1  . The P=O bond length of 1.4740 (15) Å is virtually identical to that of tri­phenyl­phosphine oxide [1.479 (2) Å; Al-Farhan, 1992  ], which is not involved in hydrogen bonding as is the case in the structure of (I). In general, the P=O bond appears to be elongated when involved in hydrogen-bonding inter­actions (Kunz et al., 2011  ). In the pyrrole heterocyclic ring of (I), the C15—C16 [1.388 (2) Å] and C17—C18 [1.363 (3) Å] bonds are shorter than the C16—C17 [1.404 (3) Å] bond, even though the pyrrole ring has a delocalized π-system. The bond length of P1—C15 [1.767 (2) Å] to the pyrrole moiety is shorter than those of P1—C3 [1.801 (2) Å] and P1—C9 [1.806 (2) Å] to the C atoms of phenyl rings. Such a slight difference is also observed in the crystal structure of a compound containing the same entity as in (I) (Vélez del Burgo et al., 2016  ). The dihedral angle between the O2/P1/C15 plane and the pyrrole ring in (I) is small, 3.89 (5)°.

Figure 1
The mol­ecular structure of (I), showing the atom-numbering scheme and displacement ellipsoids at the 30% probability level.

Supra­molecular features  

Two mutual inter­molecular N19—H19(...)O2i [symmetry code; (i) –x + 1, y, −z + An external file that holds a picture, illustration, etc.
Object name is e-73-01268-efi1.jpg] hydrogen bonds between the amino group and the O=P group link two mol­ecules into a dimer (Fig. 2  , Table 1  ). The two mol­ecules of the dimer are related by a twofold rotation axis. Apart from van der Waals inter­actions between dimers, there are no other inter­molecular inter­actions that stabilize the three-dimensional crystal packing of (I) (Fig. 3  ).

Figure 2
Dimeric structure of (I), showing mol­ecules linked by inter­molecular N19—H19(...)O2i [symmetry code: (i) −x + 1, y, −z + An external file that holds a picture, illustration, etc.
Object name is e-73-01268-efi1.jpg] hydrogen bonds (dashed lines).
Figure 3
Part of the crystal structure of (I), showing mol­ecules linked by inter­molecular N—H(...)O hydrogen bonds (dashed lines).
Table 1
Hydrogen-bond geometry (Å, °)

Database survey  

A search of the Cambridge Structural Database (Version 5.38, update February 2017; Groom et al., 2016  ) for compounds containing the (3,5-dimethyl-1H-pyrrol-2-yl)di­phenyl­phosphine oxide skeleton revealed only one structure, viz. AVPL146MP (Vélez del Burgo et al., 2016  ).

Synthesis and crystallization  

The title compound was prepared by salt elimination after 2,4-di­methyl­pyrrole was treated with tri­methyl­amine and then chloro­diphenyl­phosphine (Moloy & Petersen, 1995  ). The ease of in situ oxidation of the resulting pyrrole­phosphine derivative led to the formation of the corresponding phosphine oxide ligand (Nyamato et al., 2015  ). This new compound was characterized by single crystal X-ray analysis as well as 1H, 13C, 31P NMR, high resolution mass spectrometry, and infrared spectroscopy (see supplementary Figs. S1-S5).

2,4-Di­methyl­pyrrole (0.2 ml, 2 mmol), tri­ethyl­amine (0.34 ml, 3 mmol), and 5 ml of diethyl ether were charged into a Schlenk flask under inert atmosphere. To this solution, chloro­diphenyl­phosphine (0.18 ml, 1 mmol) in 1 ml diethyl ether was added dropwise at 273 K. A colorless precipitate formed immediately. The reaction mixture was then stirred for 10 min at 273 K and heated under reflux for a further 24 h. The precipitate that formed was removed by filtration, and the filtrate was evaporated to dryness under vacuum. The resulting oil was re-dissolved in hexane and filtered. The solvent was removed under vacuum to give the product as a red solid (0.21 g, 0.72 mmol, yield 72%). Single crystals of the title compound were obtained by slow diffusion of hexane into a concentrated solution of the product in tetra­hydro­furan at room temperature. 1H NMR (300 MHz, CDCl3): δ = 2.17 (s, 3H), 2.18 (s, 3H), 5.86 (s, 1H), 7.27–7.35 (m, 11H). 13C NMR (150 MHz, CDCl3): δ = 12.25 (d, J = 10.2 Hz), 13.34 (s), 110.08 (d, J = 5.6 Hz), 117.32 (d, J = 13.5 Hz), 128.40 (s), 128.70 (d, J = 6.5 Hz), 132.39 (s), 132.83 (d, J = 18.5 Hz), 138.03 (d, J = 8.8 Hz). 31P NMR (242 MHz, CDCl3): δ = −35.08 (s). HRMS (ESI) calculated for C18H19ONP ([M + H]+): 296.12043, found: 296.1228. Melting point: 352 K.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 2  . The H atom of the NH group was located in a difference-Fourier map and refined freely. The C-bound H atoms were positioned geometrically and refined using a riding model, with d(C—H) = 0.93–0.96 Å, and with U iso(H) = 1.2U eq(C) for aromatic-H and 1.5U eq(C) for methyl-H atoms, respectively.

Table 2
Experimental details

Supplementary Material

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989017010994/wm5405sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989017010994/wm5405Isup2.hkl

spectroscopic analysis of the title compound. DOI: 10.1107/S2056989017010994/wm5405sup3.pdf

CCDC reference: 1564683

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

C18H18NOPF(000) = 1248
Mr = 295.30Dx = 1.214 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 10.656 (6) ÅCell parameters from 6973 reflections
b = 14.765 (8) Åθ = 2.4–28.0°
c = 20.757 (11) ŵ = 0.17 mm1
β = 98.378 (8)°T = 296 K
V = 3231 (3) Å3Block, orange
Z = 80.29 × 0.27 × 0.25 mm

Data collection

Bruker SMART CCD area-detector diffractometer3196 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.027
ω scansθmax = 28.4°, θmin = 2.0°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)h = −14→14
Tmin = 0.943, Tmax = 0.967k = −19→19
14781 measured reflectionsl = −27→27
3961 independent reflections

Refinement

Refinement on F20 restraints
Least-squares matrix: fullHydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.046H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.136w = 1/[σ2(Fo2) + (0.069P)2 + 1.3679P] where P = (Fo2 + 2Fc2)/3
S = 1.07(Δ/σ)max = 0.001
3961 reflectionsΔρmax = 0.32 e Å3
196 parametersΔρmin = −0.24 e Å3

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 (Å2)

xyzUiso*/Ueq
P10.71878 (4)0.57612 (3)0.33110 (2)0.03972 (14)
O20.65623 (12)0.55565 (10)0.26460 (6)0.0621 (4)
C30.82519 (14)0.48606 (10)0.36150 (8)0.0429 (4)
C40.7970 (2)0.42449 (12)0.40734 (11)0.0602 (5)
H40.72590.43300.42780.072*
C50.8752 (2)0.34969 (14)0.42287 (13)0.0780 (7)
H50.85650.30880.45420.094*
C60.9787 (2)0.33576 (14)0.39253 (13)0.0744 (7)
H61.02940.28500.40250.089*
C71.0074 (2)0.39616 (16)0.34775 (14)0.0796 (7)
H71.07860.38710.32740.096*
C80.93109 (19)0.47160 (14)0.33202 (11)0.0655 (5)
H80.95180.51270.30130.079*
C90.81251 (15)0.67828 (11)0.33328 (8)0.0451 (4)
C100.92531 (18)0.69087 (13)0.37448 (11)0.0597 (5)
H100.95680.64530.40330.072*
C110.9917 (2)0.77160 (16)0.37289 (14)0.0814 (7)
H111.06780.77980.40050.098*
C120.9455 (3)0.83877 (15)0.33103 (17)0.0933 (9)
H120.99060.89260.33010.112*
C130.8345 (3)0.82778 (15)0.29083 (15)0.0909 (9)
H130.80310.87440.26300.109*
C140.7680 (2)0.74766 (14)0.29101 (11)0.0688 (6)
H140.69270.74010.26260.083*
C150.60482 (15)0.58994 (10)0.38423 (8)0.0400 (3)
C160.60900 (17)0.60509 (11)0.45053 (8)0.0468 (4)
C170.48236 (18)0.60914 (13)0.46181 (9)0.0558 (5)
H170.45590.61820.50210.067*
C180.40454 (17)0.59763 (12)0.40420 (10)0.0516 (4)
N190.47866 (13)0.58591 (9)0.35719 (8)0.0435 (3)
H190.4501 (18)0.5756 (12)0.3169 (10)0.049 (5)*
C200.7239 (2)0.61602 (16)0.50077 (10)0.0675 (5)
H20A0.75440.55740.51580.101*
H20B0.70200.65040.53680.101*
H20C0.78880.64720.48200.101*
C210.26291 (19)0.59778 (19)0.38760 (13)0.0812 (7)
H21A0.22550.60170.42690.122*
H21B0.23570.54290.36500.122*
H21C0.23670.64890.36030.122*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
P10.0339 (2)0.0405 (2)0.0439 (3)0.00439 (15)0.00249 (17)−0.00102 (16)
O20.0492 (7)0.0831 (9)0.0507 (7)0.0116 (6)−0.0035 (6)−0.0094 (6)
C30.0362 (8)0.0360 (7)0.0547 (9)0.0020 (6)0.0006 (7)−0.0045 (6)
C40.0564 (11)0.0451 (9)0.0800 (14)0.0051 (8)0.0132 (10)0.0097 (9)
C50.0836 (15)0.0466 (10)0.1029 (18)0.0115 (10)0.0107 (14)0.0217 (11)
C60.0588 (12)0.0449 (10)0.1140 (19)0.0165 (9)−0.0059 (12)0.0015 (11)
C70.0557 (12)0.0658 (13)0.121 (2)0.0215 (10)0.0242 (13)−0.0065 (13)
C80.0590 (11)0.0559 (11)0.0861 (14)0.0154 (9)0.0255 (11)0.0074 (10)
C90.0429 (8)0.0394 (8)0.0549 (10)0.0045 (6)0.0142 (7)0.0037 (7)
C100.0547 (11)0.0456 (9)0.0776 (13)−0.0055 (8)0.0049 (10)−0.0012 (9)
C110.0661 (13)0.0582 (13)0.122 (2)−0.0174 (11)0.0226 (14)−0.0215 (13)
C120.0905 (18)0.0440 (11)0.159 (3)−0.0099 (12)0.0644 (19)−0.0032 (14)
C130.0995 (19)0.0523 (12)0.131 (2)0.0178 (12)0.0516 (18)0.0377 (13)
C140.0633 (12)0.0595 (12)0.0867 (15)0.0154 (10)0.0213 (11)0.0258 (10)
C150.0353 (8)0.0376 (7)0.0462 (8)0.0033 (6)0.0024 (7)0.0008 (6)
C160.0515 (10)0.0433 (8)0.0449 (9)0.0027 (7)0.0048 (7)0.0043 (7)
C170.0603 (11)0.0588 (11)0.0517 (10)0.0065 (9)0.0198 (9)0.0071 (8)
C180.0433 (9)0.0500 (9)0.0641 (11)0.0036 (7)0.0165 (8)0.0097 (8)
N190.0361 (7)0.0444 (7)0.0493 (8)0.0015 (5)0.0038 (6)−0.0002 (6)
C200.0699 (13)0.0776 (14)0.0510 (11)0.0019 (11)−0.0045 (10)−0.0015 (9)
C210.0436 (11)0.1053 (18)0.0982 (18)0.0040 (11)0.0225 (11)0.0118 (14)

Geometric parameters (Å, º)

P1—O21.4740 (15)C12—C131.354 (4)
P1—C151.7672 (18)C12—H120.9300
P1—C31.8011 (17)C13—C141.380 (3)
P1—C91.8059 (18)C13—H130.9300
C3—C81.377 (3)C14—H140.9300
C3—C41.380 (3)C15—N191.381 (2)
C4—C51.392 (3)C15—C161.388 (2)
C4—H40.9300C16—C171.404 (3)
C5—C61.363 (3)C16—C201.497 (3)
C5—H50.9300C17—C181.363 (3)
C6—C71.355 (4)C17—H170.9300
C6—H60.9300C18—N191.353 (2)
C7—C81.390 (3)C18—C211.498 (3)
C7—H70.9300N19—H190.862 (19)
C8—H80.9300C20—H20A0.9600
C9—C101.383 (3)C20—H20B0.9600
C9—C141.387 (2)C20—H20C0.9600
C10—C111.389 (3)C21—H21A0.9600
C10—H100.9300C21—H21B0.9600
C11—C121.362 (4)C21—H21C0.9600
C11—H110.9300
O2—P1—C15110.49 (9)C11—C12—H12119.8
O2—P1—C3110.63 (8)C12—C13—C14120.3 (2)
C15—P1—C3108.75 (8)C12—C13—H13119.9
O2—P1—C9111.57 (9)C14—C13—H13119.9
C15—P1—C9108.41 (8)C13—C14—C9120.4 (2)
C3—P1—C9106.87 (8)C13—C14—H14119.8
C8—C3—C4118.62 (16)C9—C14—H14119.8
C8—C3—P1118.29 (14)N19—C15—C16107.38 (15)
C4—C3—P1122.60 (14)N19—C15—P1117.27 (13)
C3—C4—C5120.0 (2)C16—C15—P1135.35 (13)
C3—C4—H4120.0C15—C16—C17106.22 (15)
C5—C4—H4120.0C15—C16—C20127.80 (17)
C6—C5—C4120.6 (2)C17—C16—C20125.97 (17)
C6—C5—H5119.7C18—C17—C16108.97 (16)
C4—C5—H5119.7C18—C17—H17125.5
C7—C6—C5119.78 (18)C16—C17—H17125.5
C7—C6—H6120.1N19—C18—C17107.71 (16)
C5—C6—H6120.1N19—C18—C21120.57 (19)
C6—C7—C8120.4 (2)C17—C18—C21131.71 (19)
C6—C7—H7119.8C18—N19—C15109.72 (16)
C8—C7—H7119.8C18—N19—H19124.2 (13)
C3—C8—C7120.6 (2)C15—N19—H19126.0 (13)
C3—C8—H8119.7C16—C20—H20A109.5
C7—C8—H8119.7C16—C20—H20B109.5
C10—C9—C14118.60 (18)H20A—C20—H20B109.5
C10—C9—P1123.76 (13)C16—C20—H20C109.5
C14—C9—P1117.65 (15)H20A—C20—H20C109.5
C9—C10—C11120.0 (2)H20B—C20—H20C109.5
C9—C10—H10120.0C18—C21—H21A109.5
C11—C10—H10120.0C18—C21—H21B109.5
C12—C11—C10120.2 (2)H21A—C21—H21B109.5
C12—C11—H11119.9C18—C21—H21C109.5
C10—C11—H11119.9H21A—C21—H21C109.5
C13—C12—C11120.5 (2)H21B—C21—H21C109.5
C13—C12—H12119.8
O2—P1—C3—C866.62 (17)C10—C11—C12—C130.3 (4)
C15—P1—C3—C8−171.86 (15)C11—C12—C13—C14−1.1 (4)
C9—P1—C3—C8−55.02 (17)C12—C13—C14—C91.4 (4)
O2—P1—C3—C4−105.19 (17)C10—C9—C14—C13−0.7 (3)
C15—P1—C3—C416.33 (17)P1—C9—C14—C13179.28 (17)
C9—P1—C3—C4133.17 (16)O2—P1—C15—N19−3.94 (14)
C8—C3—C4—C50.0 (3)C3—P1—C15—N19−125.55 (12)
P1—C3—C4—C5171.80 (16)C9—P1—C15—N19118.61 (12)
C3—C4—C5—C6−0.9 (3)O2—P1—C15—C16176.30 (16)
C4—C5—C6—C71.3 (4)C3—P1—C15—C1654.69 (18)
C5—C6—C7—C8−0.8 (4)C9—P1—C15—C16−61.15 (18)
C4—C3—C8—C70.5 (3)N19—C15—C16—C170.45 (18)
P1—C3—C8—C7−171.64 (18)P1—C15—C16—C17−179.78 (14)
C6—C7—C8—C3−0.1 (4)N19—C15—C16—C20−179.03 (18)
O2—P1—C9—C10−145.38 (16)P1—C15—C16—C200.7 (3)
C15—P1—C9—C1092.73 (17)C15—C16—C17—C18−0.5 (2)
C3—P1—C9—C10−24.33 (18)C20—C16—C17—C18178.98 (18)
O2—P1—C9—C1434.61 (17)C16—C17—C18—N190.4 (2)
C15—P1—C9—C14−87.28 (16)C16—C17—C18—C21−178.5 (2)
C3—P1—C9—C14155.66 (14)C17—C18—N19—C15−0.10 (19)
C14—C9—C10—C11−0.1 (3)C21—C18—N19—C15178.96 (18)
P1—C9—C10—C11179.85 (16)C16—C15—N19—C18−0.23 (18)
C9—C10—C11—C120.4 (3)P1—C15—N19—C18179.95 (11)

Hydrogen-bond geometry (Å, º)

D—H···AD—HH···AD···AD—H···A
N19—H19···O2i0.862 (19)1.92 (2)2.757 (2)164.7 (18)

Symmetry code: (i) −x+1, y, −z+1/2.

Funding Statement

This work was funded by Chungnam National University grant .

This paper was supported by the following grant(s):

Chungnam National University .

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