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Synthesis and Structural Characterization of Organophosphorus Ylide-1-(3-nitrophenyl)-2-(triphenyl phosphoranylidene)ethanone①

Alireza Dadrassa②Ali RamazanibAhmad Poursattar MarjaniaHojjatollah RahchamaniaHassan Nasri KourehaAli SouldozicSepideh SamieedKatarzyna ?lepokuraeTadeusz Lise

a(57153-165,)b(49195-467)c(969)d()e(,)

The title compound Ph3P=C(H)C(O)PhNO2(L) has been prepared by the addition of triphenylphosphine in acetone as solvent to 2-bromo-1-(3-nitrophenyl)ethanone followed by the addition of alkaline solution of sodium hydroxide. The yellow crystals of the title ylide were grown in methanol/chloroform solution by drop method without stirring at room temperature. The solid state structure of ylide has been established by X-ray crystallography analysis. In the molecule of the title compound, the geometry around the P atom is nearly tetrahedral and the O atom is in synperiplanar orientation to the P atom. The nitrophenyl ring is twisted with respect to the plane of the carbonyl group through an angle of 36.6(1)°. The crystal (C26H20NO3P,M= 425.40) belongs to the monoclinic system, space group21/with= 10.889(3),= 14.467(3),= 13.872(4) ?,= 103.08(3)°,= 2128.6(10) ?3,= 4,= 100(2) K,= 0.059 and= 0.163 for 3984 observed reflections with> 2().

crystal structure, phosphorus ylide, 2-bromo-1-(3-nitrophenyl)ethanone, triphenylphosphine;

1 INTRODUCTION

Ylides are reactive nucleophiles in organic che- mistry especially in the synthesis of naturally occurring products with biological and pharmaco- logical activities[1]. Ylides, in which the heteroatom is N, P, As, S or Se, are well known. Other ylides containing Sb, Bi, O, Te, I or Br are also known, but they are rarely used as ligands since they are very unstable, and they will not be treated here. AW Johnson[2]stated that "a ylide is a carbanion directly bonded to a heteroatom with a high degree of formal positive charge. This charge arises from the number of sigma bonds between the heteroatom and its substituents". Formally, ylides could be represented in two extreme canonical forms, one without formal charges (ylene) and one zwitterio- nic (ylide), both shown in Scheme 1. In practice, the chemical behaviour of the ylides can be explained just considering the polar ylide form. The presence of a negative charge at the ylidic carbanionic center is the source of the nucleophilic behaviour of the ylides and, hence, the origin of their ability to behave as ligands. The nature of substituents R1and R2could allow the delocali- zation of charge through auxiliary functional groups (Scheme 1). In the present work, the phosphorus ylide was prepared and structurally characterized in the solid state by X-ray crystallo- graphy. Its structure was also determined by theoretical method.

Scheme 1

2 EXPERIMENTAL

All solvents were dried and distilled prior to use. 2-Bromo-1-(3-nitrophenyl)ethanone and triphenyl- phosphine were purchased from either Merck or Aldrich companies. The ylide L was prepared according to the literature methods[3, 4].

2.1 Computational method

The geometry of ligand L determined by X-ray crystal structure analysis was fully optimized using density functional theory (DFT) calculations at the B3LYP/CEP-121G level of theory[5, 6].The obser- ved geometry of L was used as a basis of DFT calculations. The latter basis set includes effective core potentials (ECP) for L. All calculations were performed using the G03 package[7].

2. 2 Crystal structure determination

Data collection for X-ray structure determination of the phosphorus ylide was performed at 100(2) K on an Xcalibur PX four-circle diffractometer (scan) equipped with an Onyx CCD detector, with graphite monochromatized Curadiation. Data were corrected for Lorentz and polarization effects. Data collection, cell refinement, data reduction and analysis, and absorption correction were carried out with the Xcalibur PX software, CryAlis CCD and CrysAlis RED, respectively[8]. Analytical absorp- tion correction was applied to the data with the use of CrysAlis RED. The structure was solved by direct methods with the SHELXS-97 program[9], and refined on2by a full-matrix least-squares technique using SHELXL-2013 with anisotropic thermal parameters for the non-H-atoms. All H atoms were found in difference Fourier maps, but in the final refinement cycles they were reposi- tioned in their calculated positions and refined using a riding model, with C–H = 0.95 ? andiso(H) = 1.2eq(C).The figures presenting the molecular and crystal structures were made using the Diamond program[10].

Crystal data C26H20NO3P,M= 425.40, yellow block, crystal size 0.32mm ×0.24mm×0.20mm, monoclinic, space group21/,= 10.889(3),= 14.467(3),= 13.872(4) ?,= 103.08(3)°,= 2128.6(10) ?3,= 100(2) K,= 4,calc= 1.327 g·cm-3,= 1.38 mm-1(for Cu,= 1.5418 ?), absorption correction: analytical,min= 0.725,max= 0.796, 15867 reflections measured, 4391 unique (int= 0.047), 3984 observed (2()),range 4.48～78.02°, parameters = 280, restraints = 0,= 0.059,= 0.163 (observed refl.),== 1.10, (Δmax) = 0.43 and (Δmin)= –0.64 e·?-3.

3 RESULTS AND DISCUSSION

The synthesis of ylides is achieved through several preparative methods, most of which have been comprehensively reviewed (Scheme 2)[11-19].

Scheme 2

Comparison of the calculated and single-crystal X-ray structures of the title ylide reveals the similar geometrical structures for this compound in both solid and gas phases (Fig. 1, Table 1).

Table 1. A Comparison between the Selected Calculated Bond Lengths (?) and Bond Angles (°) for the Ylide with Corresponding Experimental Values

The values of bond lengths and bond angles (Table 1) correspond well with those typical for the respective types of chemical connections[20]. The distances of C(7)–O(3) (slightly longer than the typical carbonyl), C(7)–C(8) (longer than the typi- cal C=C, but shorter than C2–C2) and P(1)–C(8) (shorter than the single P+–C) prove the resonance delocalization within the ylide molecule. The value of P(1)–C(8)–C(7)–O(3) torsion angle (10.6(2)°) reveals that the molecule adopts cisoid form about partially double C(7)–C(8) bond. Both nitro and ketone groups are slightly twisted relative to the phenyl ring, which is reflected in the O(1)– N(1)–C(1)–C(6) and O(3)–C(7)–C(5)–C(6) torsion angles amounting to 11.4(2)° and 31.7(2)°, respec- tively. As a result, the nitrophenyl ring is twisted with respect to the plane of the carbonyl group through an angle of 36.6(1)°.

Intermolecular interactions in the crystal lattice of ylide are dominated by weak C–H···O and van der Waals contacts. C(3)–H(3)···O(3)iinteractions join the adjacent molecules to form chains (black and grey in Fig. 2), which are further organizedC(25)–H(25)···O(1)iicontacts (orange dashed lines), giving rise to layers parallel to the (10) plane (For the geometry and symmetry codes, see Fig. 2 caption.).

The observed geometry of L was used as a basis forcalculations. Moreover, the structure of ylide was also fully optimized at the B3LYP/ CEP-121G level of theory. A comparison between the calculated bond lengths (?) and bond angles (°) with corresponding experimental values are shown in Fig. 2 and Table 1. As it can be seen in Table 1, there is a good agreement between the calculated bond lengths for this compound in gas phase with those derived from the X-ray crystal structure.

The HOMO-LUMO gap is an important para- meter to characterize the electronic structure of molecule. It is well known that the energy gap retains close connection to some molecular pro- perties[21]. The energy gap and hardness of L are given in Table 2. The hardnessof a molecule is defined as Eq. (1):

whereandare the ionization potential and electron affinity of the system, respectively. Ob- viously the energy gap between the highest occu- pied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is equal to (?), as shown in Fig. 3. Thus, we can easily calculate the hardness of the present ligand using equation Eq. (2)[21, 22].

(2)

HOMO??????????????????LUMO

Fig. 3 . Structures of HOMO and LUMO of L

Table 2. Calculated Energies for HOMO and LUMO Molecular Orbitals, Energy Gap between the HOMO and LUMO and Hardness of Ylide

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10 September 2014; accepted 28 November 2014 (CCDC 915835)

①This project was supported by Urmia University

(A. R. Dadrass). E-mail: dadrassi@yahoo.com

10.14102/j.cnki.0254-5861.2011-0504