Crystal structure of (3,5-dimethyl-1H-pyrrol-2-yl)di-phenyl-phosphine oxide.

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 ethyl-ene oligomerization. In the crystal, mutual pairs of N-H⋯O=P hydrogen bonds link two mol-ecules into a dimer with individual mol-ecules 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 inter-actions between the dimers, linking the mol-ecules into a three-dimensional network structure.

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.

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 + ] 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 + ] hydrogen bonds (dashed lines).

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N19—H19⋯O2i	0.862 (19)	1.92 (2)	2.757 (2)	164.7 (18)

Symmetry code: (i) .

Figure 3

Part of the crystal structure of (I), showing mol­ecules linked by inter­molecular N—H⋯O hydrogen bonds (dashed lines).

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

Crystal data
Chemical formula	C18H18NOP
M r	295.30
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	296
a, b, c (Å)	10.656 (6), 14.765 (8), 20.757 (11)
β (°)	98.378 (8)
V (Å3)	3231 (3)
Z	8
Radiation type	Mo Kα
μ (mm−1)	0.17
Crystal size (mm)	0.29 × 0.27 × 0.25
Data collection
Diffractometer	Bruker SMART CCD area-detector
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 ▸)
T min, T max	0.943, 0.967
No. of measured, independent and observed [I > 2σ(I)] reflections	14781, 3961, 3196
R int	0.027
(sin θ/λ)max (Å−1)	0.670
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.046, 0.136, 1.07
No. of reflections	3961
No. of parameters	196
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)	0.32, −0.24

Computer programs: SMART and SAINT (Bruker, 2002 ▸), SHELXS97 (Sheldrick, 2008 ▸), SHELXL2013 (Sheldrick, 2015 ▸) and ORTEP-3 for Windows and (Farrugia, 2012 ▸).

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

Click here for additional data file.

Supporting information file. DOI: 10.1107/S2056989017010994/wm5405Isup4.cml

CCDC reference: 1564683

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

C18H18NOP	F(000) = 1248
Mr = 295.30	Dx = 1.214 Mg m−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 10.656 (6) Å	Cell parameters from 6973 reflections
b = 14.765 (8) Å	θ = 2.4–28.0°
c = 20.757 (11) Å	µ = 0.17 mm−1
β = 98.378 (8)°	T = 296 K
V = 3231 (3) Å3	Block, orange
Z = 8	0.29 × 0.27 × 0.25 mm

Bruker SMART CCD area-detector diffractometer	3196 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.027
ω scans	θmax = 28.4°, θmin = 2.0°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −14→14
Tmin = 0.943, Tmax = 0.967	k = −19→19
14781 measured reflections	l = −27→27
3961 independent reflections

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.046	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.136	w = 1/[σ2(Fo2) + (0.069P)2 + 1.3679P] where P = (Fo2 + 2Fc2)/3
S = 1.07	(Δ/σ)max = 0.001
3961 reflections	Δρmax = 0.32 e Å−3
196 parameters	Δρmin = −0.24 e Å−3

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.

	x	y	z	Uiso*/Ueq
P1	0.71878 (4)	0.57612 (3)	0.33110 (2)	0.03972 (14)
O2	0.65623 (12)	0.55565 (10)	0.26460 (6)	0.0621 (4)
C3	0.82519 (14)	0.48606 (10)	0.36150 (8)	0.0429 (4)
C4	0.7970 (2)	0.42449 (12)	0.40734 (11)	0.0602 (5)
H4	0.7259	0.4330	0.4278	0.072*
C5	0.8752 (2)	0.34969 (14)	0.42287 (13)	0.0780 (7)
H5	0.8565	0.3088	0.4542	0.094*
C6	0.9787 (2)	0.33576 (14)	0.39253 (13)	0.0744 (7)
H6	1.0294	0.2850	0.4025	0.089*
C7	1.0074 (2)	0.39616 (16)	0.34775 (14)	0.0796 (7)
H7	1.0786	0.3871	0.3274	0.096*
C8	0.93109 (19)	0.47160 (14)	0.33202 (11)	0.0655 (5)
H8	0.9518	0.5127	0.3013	0.079*
C9	0.81251 (15)	0.67828 (11)	0.33328 (8)	0.0451 (4)
C10	0.92531 (18)	0.69087 (13)	0.37448 (11)	0.0597 (5)
H10	0.9568	0.6453	0.4033	0.072*
C11	0.9917 (2)	0.77160 (16)	0.37289 (14)	0.0814 (7)
H11	1.0678	0.7798	0.4005	0.098*
C12	0.9455 (3)	0.83877 (15)	0.33103 (17)	0.0933 (9)
H12	0.9906	0.8926	0.3301	0.112*
C13	0.8345 (3)	0.82778 (15)	0.29083 (15)	0.0909 (9)
H13	0.8031	0.8744	0.2630	0.109*
C14	0.7680 (2)	0.74766 (14)	0.29101 (11)	0.0688 (6)
H14	0.6927	0.7401	0.2626	0.083*
C15	0.60482 (15)	0.58994 (10)	0.38423 (8)	0.0400 (3)
C16	0.60900 (17)	0.60509 (11)	0.45053 (8)	0.0468 (4)
C17	0.48236 (18)	0.60914 (13)	0.46181 (9)	0.0558 (5)
H17	0.4559	0.6182	0.5021	0.067*
C18	0.40454 (17)	0.59763 (12)	0.40420 (10)	0.0516 (4)
N19	0.47866 (13)	0.58591 (9)	0.35719 (8)	0.0435 (3)
H19	0.4501 (18)	0.5756 (12)	0.3169 (10)	0.049 (5)*
C20	0.7239 (2)	0.61602 (16)	0.50077 (10)	0.0675 (5)
H20A	0.7544	0.5574	0.5158	0.101*
H20B	0.7020	0.6504	0.5368	0.101*
H20C	0.7888	0.6472	0.4820	0.101*
C21	0.26291 (19)	0.59778 (19)	0.38760 (13)	0.0812 (7)
H21A	0.2255	0.6017	0.4269	0.122*
H21B	0.2357	0.5429	0.3650	0.122*
H21C	0.2367	0.6489	0.3603	0.122*

	U11	U22	U33	U12	U13	U23
P1	0.0339 (2)	0.0405 (2)	0.0439 (3)	0.00439 (15)	0.00249 (17)	−0.00102 (16)
O2	0.0492 (7)	0.0831 (9)	0.0507 (7)	0.0116 (6)	−0.0035 (6)	−0.0094 (6)
C3	0.0362 (8)	0.0360 (7)	0.0547 (9)	0.0020 (6)	0.0006 (7)	−0.0045 (6)
C4	0.0564 (11)	0.0451 (9)	0.0800 (14)	0.0051 (8)	0.0132 (10)	0.0097 (9)
C5	0.0836 (15)	0.0466 (10)	0.1029 (18)	0.0115 (10)	0.0107 (14)	0.0217 (11)
C6	0.0588 (12)	0.0449 (10)	0.1140 (19)	0.0165 (9)	−0.0059 (12)	0.0015 (11)
C7	0.0557 (12)	0.0658 (13)	0.121 (2)	0.0215 (10)	0.0242 (13)	−0.0065 (13)
C8	0.0590 (11)	0.0559 (11)	0.0861 (14)	0.0154 (9)	0.0255 (11)	0.0074 (10)
C9	0.0429 (8)	0.0394 (8)	0.0549 (10)	0.0045 (6)	0.0142 (7)	0.0037 (7)
C10	0.0547 (11)	0.0456 (9)	0.0776 (13)	−0.0055 (8)	0.0049 (10)	−0.0012 (9)
C11	0.0661 (13)	0.0582 (13)	0.122 (2)	−0.0174 (11)	0.0226 (14)	−0.0215 (13)
C12	0.0905 (18)	0.0440 (11)	0.159 (3)	−0.0099 (12)	0.0644 (19)	−0.0032 (14)
C13	0.0995 (19)	0.0523 (12)	0.131 (2)	0.0178 (12)	0.0516 (18)	0.0377 (13)
C14	0.0633 (12)	0.0595 (12)	0.0867 (15)	0.0154 (10)	0.0213 (11)	0.0258 (10)
C15	0.0353 (8)	0.0376 (7)	0.0462 (8)	0.0033 (6)	0.0024 (7)	0.0008 (6)
C16	0.0515 (10)	0.0433 (8)	0.0449 (9)	0.0027 (7)	0.0048 (7)	0.0043 (7)
C17	0.0603 (11)	0.0588 (11)	0.0517 (10)	0.0065 (9)	0.0198 (9)	0.0071 (8)
C18	0.0433 (9)	0.0500 (9)	0.0641 (11)	0.0036 (7)	0.0165 (8)	0.0097 (8)
N19	0.0361 (7)	0.0444 (7)	0.0493 (8)	0.0015 (5)	0.0038 (6)	−0.0002 (6)
C20	0.0699 (13)	0.0776 (14)	0.0510 (11)	0.0019 (11)	−0.0045 (10)	−0.0015 (9)
C21	0.0436 (11)	0.1053 (18)	0.0982 (18)	0.0040 (11)	0.0225 (11)	0.0118 (14)

P1—O2	1.4740 (15)	C12—C13	1.354 (4)
P1—C15	1.7672 (18)	C12—H12	0.9300
P1—C3	1.8011 (17)	C13—C14	1.380 (3)
P1—C9	1.8059 (18)	C13—H13	0.9300
C3—C8	1.377 (3)	C14—H14	0.9300
C3—C4	1.380 (3)	C15—N19	1.381 (2)
C4—C5	1.392 (3)	C15—C16	1.388 (2)
C4—H4	0.9300	C16—C17	1.404 (3)
C5—C6	1.363 (3)	C16—C20	1.497 (3)
C5—H5	0.9300	C17—C18	1.363 (3)
C6—C7	1.355 (4)	C17—H17	0.9300
C6—H6	0.9300	C18—N19	1.353 (2)
C7—C8	1.390 (3)	C18—C21	1.498 (3)
C7—H7	0.9300	N19—H19	0.862 (19)
C8—H8	0.9300	C20—H20A	0.9600
C9—C10	1.383 (3)	C20—H20B	0.9600
C9—C14	1.387 (2)	C20—H20C	0.9600
C10—C11	1.389 (3)	C21—H21A	0.9600
C10—H10	0.9300	C21—H21B	0.9600
C11—C12	1.362 (4)	C21—H21C	0.9600
C11—H11	0.9300
O2—P1—C15	110.49 (9)	C11—C12—H12	119.8
O2—P1—C3	110.63 (8)	C12—C13—C14	120.3 (2)
C15—P1—C3	108.75 (8)	C12—C13—H13	119.9
O2—P1—C9	111.57 (9)	C14—C13—H13	119.9
C15—P1—C9	108.41 (8)	C13—C14—C9	120.4 (2)
C3—P1—C9	106.87 (8)	C13—C14—H14	119.8
C8—C3—C4	118.62 (16)	C9—C14—H14	119.8
C8—C3—P1	118.29 (14)	N19—C15—C16	107.38 (15)
C4—C3—P1	122.60 (14)	N19—C15—P1	117.27 (13)
C3—C4—C5	120.0 (2)	C16—C15—P1	135.35 (13)
C3—C4—H4	120.0	C15—C16—C17	106.22 (15)
C5—C4—H4	120.0	C15—C16—C20	127.80 (17)
C6—C5—C4	120.6 (2)	C17—C16—C20	125.97 (17)
C6—C5—H5	119.7	C18—C17—C16	108.97 (16)
C4—C5—H5	119.7	C18—C17—H17	125.5
C7—C6—C5	119.78 (18)	C16—C17—H17	125.5
C7—C6—H6	120.1	N19—C18—C17	107.71 (16)
C5—C6—H6	120.1	N19—C18—C21	120.57 (19)
C6—C7—C8	120.4 (2)	C17—C18—C21	131.71 (19)
C6—C7—H7	119.8	C18—N19—C15	109.72 (16)
C8—C7—H7	119.8	C18—N19—H19	124.2 (13)
C3—C8—C7	120.6 (2)	C15—N19—H19	126.0 (13)
C3—C8—H8	119.7	C16—C20—H20A	109.5
C7—C8—H8	119.7	C16—C20—H20B	109.5
C10—C9—C14	118.60 (18)	H20A—C20—H20B	109.5
C10—C9—P1	123.76 (13)	C16—C20—H20C	109.5
C14—C9—P1	117.65 (15)	H20A—C20—H20C	109.5
C9—C10—C11	120.0 (2)	H20B—C20—H20C	109.5
C9—C10—H10	120.0	C18—C21—H21A	109.5
C11—C10—H10	120.0	C18—C21—H21B	109.5
C12—C11—C10	120.2 (2)	H21A—C21—H21B	109.5
C12—C11—H11	119.9	C18—C21—H21C	109.5
C10—C11—H11	119.9	H21A—C21—H21C	109.5
C13—C12—C11	120.5 (2)	H21B—C21—H21C	109.5
C13—C12—H12	119.8
O2—P1—C3—C8	66.62 (17)	C10—C11—C12—C13	0.3 (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—C9	1.4 (4)
O2—P1—C3—C4	−105.19 (17)	C10—C9—C14—C13	−0.7 (3)
C15—P1—C3—C4	16.33 (17)	P1—C9—C14—C13	179.28 (17)
C9—P1—C3—C4	133.17 (16)	O2—P1—C15—N19	−3.94 (14)
C8—C3—C4—C5	0.0 (3)	C3—P1—C15—N19	−125.55 (12)
P1—C3—C4—C5	171.80 (16)	C9—P1—C15—N19	118.61 (12)
C3—C4—C5—C6	−0.9 (3)	O2—P1—C15—C16	176.30 (16)
C4—C5—C6—C7	1.3 (4)	C3—P1—C15—C16	54.69 (18)
C5—C6—C7—C8	−0.8 (4)	C9—P1—C15—C16	−61.15 (18)
C4—C3—C8—C7	0.5 (3)	N19—C15—C16—C17	0.45 (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—C20	0.7 (3)
C15—P1—C9—C10	92.73 (17)	C15—C16—C17—C18	−0.5 (2)
C3—P1—C9—C10	−24.33 (18)	C20—C16—C17—C18	178.98 (18)
O2—P1—C9—C14	34.61 (17)	C16—C17—C18—N19	0.4 (2)
C15—P1—C9—C14	−87.28 (16)	C16—C17—C18—C21	−178.5 (2)
C3—P1—C9—C14	155.66 (14)	C17—C18—N19—C15	−0.10 (19)
C14—C9—C10—C11	−0.1 (3)	C21—C18—N19—C15	178.96 (18)
P1—C9—C10—C11	179.85 (16)	C16—C15—N19—C18	−0.23 (18)
C9—C10—C11—C12	0.4 (3)	P1—C15—N19—C18	179.95 (11)

D—H···A	D—H	H···A	D···A	D—H···A
N19—H19···O2i	0.862 (19)	1.92 (2)	2.757 (2)	164.7 (18)