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

GRAPHICAL ABSTRACT

Abstract

In the structure of C₆F₅C(O)NHP(O)[N(C₂H₅)(C₆H₁₁)]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(1) Å, Cg is the centroid of C₆F₅ ring). Moreover, a noncovalent C˭O···π interaction takes part in the crystal packing, O_C···Cg = 3.159(1) 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 C₆F₅ group, it is in the region of the short bond lengths for analogous structures deposited in the CSD (1.18–1.26 Å). The P˭O (1.4831(10) Å) 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.

Keywords:

• CSD
• crystal structure
• phosphoric triamide
• C˭O···π