N,N-Bis(diphenylphosphino)ethylamine

In the title compound, C26H25NP2, the diphenylphosphino groups are staggered relative to the PNP backbone, even though the ethyl substituent coordinated to the N atom is not sterically bulky. The N atom adapts an almost planar geometry with two P atoms and a C atom of the allyl group attached to it in order to accommodate the steric bulk of the phenyl groups and the alkyl group. The distortion of the trigonal-pyramidal geometry of the nitrogen is further illustrated by the bond angles which range between 114.0 (1) and 123.7 (1)°. There are no classical intermolecular interactions.

In the title compound, C 26 H 25 NP 2 , the diphenylphosphino groups are staggered relative to the PNP backbone, even though the ethyl substituent coordinated to the N atom is not sterically bulky. The N atom adapts an almost planar geometry with two P atoms and a C atom of the allyl group attached to it in order to accommodate the steric bulk of the phenyl groups and the alkyl group. The distortion of the trigonal-pyramidal geometry of the nitrogen is further illustrated by the bond angles which range between 114.0 (1) and 123.7 (1) . There are no classical intermolecular interactions.

Related literature
For similar diphosphineamine non-coordinated ligands with the P-N-P angle ranging between 113.3 (2) and 122.8 (3) , see: Keat et al. (1981); Cotton et al. (1996);Fei et al. (2003); Cloete et al. (2008). Financial assistance from the South African National Research Foundation (NRF), the Research Fund of the University of the Free State and SASOL is gratefully acknowledged. Dr A. J. Muller is also gratefully acknowledged for the collection of the crystallographic data. Part of this material is based on work supported by the South African National Research Foundation (GUN 2038915). Opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NRF.

Experimental
Two conformers are generally found for diphosphineamines and are described (Keat et al., 1981) as C 2v and C s . In C 2v conformer, the phosphorous lone pairs are cis with respect to the N-C bond while in the C s conformer the two lone pairs are trans relative to the N-C bond. It has been postulated (Keat et al., 1981) that the C s conformer is usually observed for diphoshineamines with relatively bulky substituents on the nitrogen atom. The title compound (I), however has a C s conformer in solid state even though the ethyl group is not particularly bulky.

Experimental
Ethylpropylamine (0.010 mol, 0.45 g) was dissolved in dichloromethane (30 ml) and placed on an ice bath and triethylamine (0.030 mol, 4.22 ml) was added to the solution while being stirred. Chlorodiphenylphosphine (0.020 mol, 3.62 ml) was slowly added to the reaction mixture. The ice bath was removed after 30 minutes and the reaction mixture was allowed to stir at room temperature for a further 12 h. The dichloromethane was removed under reduced pressure. A mixture of hexane (20 ml) and toluene (2 ml) was added to the remaining white powder and was passed through a column containing neutral activated alumina (35 g). The solvent of the eluent was removed under reduced pressure and the white precipitate was collected. The product was recrystallized from methanol. Single colourless crystals were obtained (yield 2.439 g, 59.0%) the next day which were suitable for X-ray crystallography.

Refinement
The methylene, methyl and aryl H atoms were placed in geometrically idealized positions with distances C-H = 0.99 0.98 and 0.95 Å, respectively and constrained to ride on their parent atoms, with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C-nonmethyl).