Phenylamino ( diphenyl ) phosphine selenide : supramolecular aggregation via weak NH ... Se , C-H ... π and ... interactions

Phenylamino (diphenyl)phosphine selenide 1 was synthesized and analyzed by X-ray. The analysis revealed a deformation of the phosphorus tetrahedron, the planar geometry around the nitrogen atom, and the torsion angle Se1-P1-N1-C11, corresponding to a synclinal conformation (-46.7(4)). It has been postulated that the conformation of 1 is stabilized by short intramolecular C-HN, C-HSe interactions, which generate rings of motifs S(5) and aromatic hydrogen bonds C-H. The crystal structure is stabilized by the weak N-HSe intermolecular interactions, generating infinite chains, parallel to the c axis, of graph-set motif C(4). Additionally, there have been observed the C-H interactions, connecting chains N-HSe into the sheet, parallel to (100), producing binary graph set   10 C N 2 2 2  (with ab sequence) and   24 R N 4 4 2  motifs (with abab sequence). The weak  interactions stack the layers in the crystal lattice.


Introduction
For more than 50 years the Wadsworth-Emmons reaction of dialkyl(aryl)phosphoramidate anions with carbonyl electrophiles and their analogues has been as a convenient synthetic route to a plethora of unsaturated nitrogen derivatives, usually of cumulene-type. 1 Additionally, from the mid seventies, this reaction has been commonly applied for the synthesis of P-chiral phosphoramidates. 2 The exploration of synthetic applications of the P-chiral phosphoramidates led Stec and coworkers to be aware of the potential offered by the Wadsworth-Emmons reaction in the synthesis of disubstituted phosphates, phosphorothioates and phosphoroselenoates, with special focus upon the stereochemical consequences of the PN → PX conversions. 3 turned out that the development of a synthetic approach involving the preparation of the Pchiral phosphoramidates (mostly anilidates) followed by replacement of an amidate function by oxygen or sulfur opened the way to the stereospecific preparation of a variety of P-chiral derivatives of phosphorus acids, including numerous biophosphates and their analogues. 4his approach resulted in successful solution of the problem of a waste free, stereoconvergent synthesis of a single isomer of either R P or S P dinucleoside (3',5')methanephosphonates from both isomers of diastereomerically pure R P and S P 5'-O-DMT nucleoside -3'-O-methylphosphonoanilidates. 5 In the course of our studies we also synthesized and characterized several model phosphoroand phosphono selenoamidates, which have been used to investigate the mechanism of the Stec reaction by NMR and DFT molecular modeling. 6Numerous studies carried out with different enantiomeric and diastereomeric amidates confirmed stereoretentive pathway for this reaction, however, still an involvement of postulated PV intermediates or transition states has not been verified experimentally. 4ere we present the X-ray analysis of phenylamino (diphenyl)phosphine selenide 1.This selenoanilidate, in contrast to the catechol analogue, 2-aniline-2-seleno-1,3,2benzodioxaphospholane reported previously, 6 could be easily obtained in almost quantitative yields, and almost spontaneously crystallizes from non-polar solvents.
We postulate that high tendency to crystallization and high stability of 1 is a result of supramolecular aggregation through weak N-H … Se and C-H … π and π … π interactions.The parameters received from the X-ray analysis will be of importance for theoretical modeling of the Stec reaction.The title compound 1 was prepared by reaction of chlorodiphenylphosphine 2 with 2.2 molar excess of aniline in toluene at room temperature under argon, and without isolation of phosphinoamidite 3, followed by an addition of excess of elemental selenium (overnight reaction at ambient temp.).
Selenoanilidate 1 was obtained in very high yield (<90%), and after aqueous workup crystallized from toluene.This compound has already been reported in the literature but without experimental part and with incomplete spectral data. 7

X-Ray analysis
In the crystal structure of molecule 1 there was observed a deformation of the phosphorus tetrahedron.The smallest angle N1-P1-C31 101.88 (15)º is probably result of intermolecular interaction N1-H1 ... Se1.Similar deformation has been previously reported for P,P'-iminobis (diphenylselenophosphine) tetrahydrofuran solvate. 8The valence angles N1-P1=Se in this tetrahedron range from 113.77 (11)º to 114.39 (12)º and are comparable with those found there.The observed significant difference between Se=P-C angles and others in the environment of central phosphorus observed in 1 (Table 1) stays in agreement with literature data. 9The value of the Se1-P1-N1-C11 torsion angle is -46.7(4)º, and suggests a -synclinal conformation.
From the above X-ray data the importance of weak N-H … Se intermolecular interactions and C-H … π interactions in formation of the aggregates is clear.Further studies are continued to support the inter-and intramolecular hydrogen bonding supramolecular network by means of DFT/Gaussian calculations.

X ray analysis
Crystal and molecular structure of 1 was determined on a Xcalibur 3 CCD area-detector diffractometer with graphite monochromatized MoKα radiation up to a resolution of (sinθ/λ)max=0.6268Å -1 .The crystal structure was solved by a conventional direct method using the SHELXL-97 program package, followed by the least squares structural refinement and calculated difference density.Compound 1 crystallized in monoclinic system in space group P21/c with the unit cell consisting of four molecules, without molecules of solvent(s) used for crystallization.An empirical absorption correction was applied by the use of the ψ-scan method.The structure was solved by the direct methods with total of 1888 reflections with I>2σ(I) used and refined by the full matrix least squares using F 2 .The final refinement converged to R[F 2 >2σ(F 2 )] =0.040 for 3560 reflections.Non-H atoms were refined anisotropically, while H atoms (with the exception of N-H proton, whose positions were determined from a difference map) were positioned geometrically at C-H distances of 0.93 (Csp 2 -H), and were refined using a riding model, with U iso (H) = 1.2Ueq(C).Symmetry codes: (i) x, 1/2-y, 1/2+z; (ii) 1-x, 0.5+y, 1.5-z; (iii) -x,1-y,1-z Note: Cg1 is the centroid of the of the C11-C16 aromatic ring, Cg2 is the centroid of the of the C21-C26 aromatic ring.

Crystal data
Crystallographic data for 1 have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 792807.Copies of these data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44(0)-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk)

Figure 1 .
Figure 1.(a) The molecular structure of 1 showing 50% probability displacement ellipsoids and the atomic numbering.The red dashed lines indicate intramolecular hydrogen bonds.(b) Packing of the molecule 1 in the unit cell, with the network of N1-H1 ... Se1 (red dashed lines).