C˭O···π Interaction: A Rare Noncovalent Binding in RC(O)NHP(O)[NR¹R²]₂ Phosphoric Triamide Structures

Abstract

In the structure of C 6 F 5 C(O)NHP (O)[N(C 2 H 5 )(C 6 H 11 )] 2 , in addition to N-H···O═P hydrogen bond, the oxygen atom of P═O group is involved in the P═O···π interaction (O P ···Cg = 3.507 Å, Cg is the centroid of C 6 F 5 ring). Moreover, a noncovalent C═O···π interaction takes part in the crystal packing, O c ···Cg = 3.159 Å. The C═O···π interaction is the interesting feature of this structure, as a Cambridge Structural Database analysis (CSD; Allen, Acta Cryst. 2002, B58, 380-388) of 149 structures with a C(O)NHP(O)[N] 2 skeleton shows that such an interaction exists only in 4 structures. The dihedral angle between the aromatic ring and the plane defined by the atoms of [C][N]C═O segment is 66.66°. The C═O bond length in the present structure (of 1.2148(18) Å) is within the expected range for compounds with a C(O)NHP(O)[N] 2 segment; however, due to the electronic effect caused by C 6 F 5 group, it is in the region of the short bond lengths for analogous structures deposited in the CSD (1.18 to 1.26 Å). The P═O (1.4831(10) Å) Downloaded by [Umeå University Library] at 11:56 01 April 2015 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 and P-N (1.6340(12) Å and 1.6424(12) Å) bond lengths are standard for a phosphoric triamide structure and the P-N bond of C(O)NHP(O) segment (1.6980(12) Å) has an expected longer value relative to the other P-N bonds. The bond-angle sums around the tertiary nitrogen atoms (SUM = 2 × P-N-C + C-N-C) are 357.8° and 352.0° that show few deviations from the planar value of 360°. The more pyramidal N atom is oriented so that the corresponding lone electron pair is anti with respect to the P═O group.

Evaluation of N—H...S and N—H...π interactions inO,O′-diethylN-(2,4,6-trimethylphenyl)thiophosphate: a combination of X-ray crystallographic and theoretical studies

“…The S atom has been known to act as a hydrogen-bond acceptor (Cocinero et al, 2005;Freitas & Galembeck, 2006;Biswal & Wategaonkar, 2009), but normally has a weaker hydrogen-bond acceptor capability than an O atom. Recently, we discussed P XÁ Á ÁH-N (X = S or O) hydrogen bonds in different families of phosphoramide and thiophosphoramide compounds (Chaijan et al, 2015;Alamdar et al, 2015;Keikha et al, 2016).…”