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

aDepartment of Chemistry, Chungnam National University, Daejeon 34134, Republic of Korea
*Correspondence e-mail: kson@cnu.ac.kr

Edited by M. Weil, Vienna University of Technology, Austria (Received 12 July 2017; accepted 26 July 2017; online 28 July 2017)

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.

1. 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[Fliedel, C. R., Ghisolfi, A. & Braunstein, P. (2016). Chem. Rev. 116, 9237-9304.]). 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[Agapie, T. (2011). Coord. Chem. Rev. 255, 861-880.]; McGuinness, 2011[McGuinness, D. S. (2011). Chem. Rev. 111, 2321-2341.]). 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.

[Scheme 1]

2. Structural commentary

The mol­ecular structure of the title compound, (I)[link], is shown in Fig. 1[link]. 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[Al-Farhan, K. (1992). J. Crystallogr. Spectrosc. Res. 22, 687-689.]], which is not involved in hydrogen bonding as is the case in the structure of (I)[link]. In general, the P=O bond appears to be elongated when involved in hydrogen-bonding inter­actions (Kunz et al., 2011[Kunz, P. C., Huber, W. & Spingler, B. (2011). J. Chem. Crystallogr. 41, 105-110.]). In the pyrrole heterocyclic ring of (I)[link], 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)[link] (Vélez del Burgo et al., 2016[Vélez Del Burgo, A., Ochoa de Retana, A. M., de Los Santos, J. M. & Palacios, F. (2016). J. Org. Chem. 81, 100-108.]). The dihedral angle between the O2/P1/C15 plane and the pyrrole ring in (I)[link] is small, 3.89 (5)°.

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

3. Supra­molecular features

Two mutual inter­molecular N19—H19⋯O2i [symmetry code; (i) –x + 1, y, −z + [{1\over 2}]] hydrogen bonds between the amino group and the O=P group link two mol­ecules into a dimer (Fig. 2[link], Table 1[link]). 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)[link] (Fig. 3[link]).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N19—H19⋯O2i 0.862 (19) 1.92 (2) 2.757 (2) 164.7 (18)
Symmetry code: (i) [-x+1, y, -z+{\script{1\over 2}}].
[Figure 2]
Figure 2
Dimeric structure of (I)[link], showing mol­ecules linked by inter­molecular N19—H19⋯O2i [symmetry code: (i) −x + 1, y, −z + [{1\over 2}]] hydrogen bonds (dashed lines).
[Figure 3]
Figure 3
Part of the crystal structure of (I)[link], showing mol­ecules linked by inter­molecular N—H⋯O hydrogen bonds (dashed lines).

4. Database survey

A search of the Cambridge Structural Database (Version 5.38, update February 2017; Groom et al., 2016[Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171-179.]) 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[Vélez Del Burgo, A., Ochoa de Retana, A. M., de Los Santos, J. M. & Palacios, F. (2016). J. Org. Chem. 81, 100-108.]).

5. 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[Moloy, K. G. & Petersen, J. L. (1995). J. Am. Chem. Soc. 117, 7696-7710.]). 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[Nyamato, G. S., Alam, M. G., Ojwach, S. O. & Akerman, M. P. (2015). J. Organomet. Chem. 783, 64-72.]). 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.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link]. 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 Uiso(H) = 1.2Ueq(C) for aromatic-H and 1.5Ueq(C) for methyl-H atoms, respectively.

Table 2
Experimental details

Crystal data
Chemical formula C18H18NOP
Mr 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)
V3) 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[Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3-10.])
Tmin, Tmax 0.943, 0.967
No. of measured, independent and observed [I > 2σ(I)] reflections 14781, 3961, 3196
Rint 0.027
(sin θ/λ)max−1) 0.670
 
Refinement
R[F2 > 2σ(F2)], wR(F2), 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[Bruker (2002). SAINT and SMART. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]), SHELXL2013 (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. C71, 3-8.]) and ORTEP-3 for Windows and (Farrugia, 2012[Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849-854.]).

Supporting information


Computing details top

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).

(3,5-Dimethyl-1H-pyrrol-2-yl)diphenylphosphine oxide top
Crystal data top
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 top
Bruker SMART CCD area-detector
diffractometer
3196 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 = 1414
Tmin = 0.943, Tmax = 0.967k = 1919
14781 measured reflectionsl = 2727
3961 independent reflections
Refinement top
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) = 0.136 w = 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 top

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) top
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) top
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) top
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—C8171.86 (15)C11—C12—C13—C141.1 (4)
C9—P1—C3—C855.02 (17)C12—C13—C14—C91.4 (4)
O2—P1—C3—C4105.19 (17)C10—C9—C14—C130.7 (3)
C15—P1—C3—C416.33 (17)P1—C9—C14—C13179.28 (17)
C9—P1—C3—C4133.17 (16)O2—P1—C15—N193.94 (14)
C8—C3—C4—C50.0 (3)C3—P1—C15—N19125.55 (12)
P1—C3—C4—C5171.80 (16)C9—P1—C15—N19118.61 (12)
C3—C4—C5—C60.9 (3)O2—P1—C15—C16176.30 (16)
C4—C5—C6—C71.3 (4)C3—P1—C15—C1654.69 (18)
C5—C6—C7—C80.8 (4)C9—P1—C15—C1661.15 (18)
C4—C3—C8—C70.5 (3)N19—C15—C16—C170.45 (18)
P1—C3—C8—C7171.64 (18)P1—C15—C16—C17179.78 (14)
C6—C7—C8—C30.1 (4)N19—C15—C16—C20179.03 (18)
O2—P1—C9—C10145.38 (16)P1—C15—C16—C200.7 (3)
C15—P1—C9—C1092.73 (17)C15—C16—C17—C180.5 (2)
C3—P1—C9—C1024.33 (18)C20—C16—C17—C18178.98 (18)
O2—P1—C9—C1434.61 (17)C16—C17—C18—N190.4 (2)
C15—P1—C9—C1487.28 (16)C16—C17—C18—C21178.5 (2)
C3—P1—C9—C14155.66 (14)C17—C18—N19—C150.10 (19)
C14—C9—C10—C110.1 (3)C21—C18—N19—C15178.96 (18)
P1—C9—C10—C11179.85 (16)C16—C15—N19—C180.23 (18)
C9—C10—C11—C120.4 (3)P1—C15—N19—C18179.95 (11)
Hydrogen-bond geometry (Å, º) top
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 information

Funding for this research was provided by: Chungnam National University .

References

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