Low Symmetry in P(NR₂)₃ Skeletons and Related Fragments:  An Inherent Phenomenon

Abstract

A single-crystal X-ray diffraction study at 110 K and ab initio calculations up to the MP2/6-31G* level of theory showed that the ground state of P(NMe2)3 has C s symmetry, with two different coordination geometries at the nitrogen atoms (pyramidal and planar). The calculated and experimentally determined geometries are in good agreement. Steric strain could be ruled out as the predominant factor causing the deviation from the expected C 3 symmetry, because ab initio calculations on the model system P(NH2)3 (up to MP2/6-311G**) also indicate C s symmetry for the ground-state structure, whereas calculations on N(NH2)3 have predicted this molecule to have C 3 symmetry. The structure of the phosphorane H2CP(NMe2)3 has been elucidated by X-ray diffraction in the solid state (110 K) and by electron diffraction in the gas phase augmented by restraints derived from ab initio calculations up to the MP2/6-31G* level of theory. Solid-state and gas-phase structures are in good agreement showing again the C s arrangement to be the ground-state structure of the molecule. Ab initio calculations (MP2/6-311G**) indicate that H2CP(NH2)3 also has C s symmetry. The reasons for the preference for C s rather than C 3 symmetry adopted by the P(NR2)3 units are discussed in terms of steric repulsion, lone pair, and other electronic interactions. Literature reports of structures of derivatives containing P(NMe2)3 units are discussed in the light of the new results. Selected structural results include: P(NMe2)3 (XRD, average values); PN(1/2) 1.687, PN(3) 1.731 Å, N(1)PN(2) 110.8, N(3)PN(1/2) 97.7°, ∑∠ at N(1/2) 355.9, at N(3) 337.6°; H2CP(NMe2)3 (GED/XRD average without esd); PC(1) 1.620(5)/1.655(6), PN(1/2) 1.684(3)/1.668, PN(3) 1.718(6)/1.698(4) Å, N(1)PN(2) 115.2(13)/114.7(2), N(1/2)PN(3) 97.0(5)/99.6, C(1)PN(1/2) 110.0(5)/110.0, C(1)PN(3), 127.1(8)/122.4(4)°, ∑∠ at N(1/2) 359.5(11)/353.4, at N(3) 332.9(13)/337.3(6)°.

Reversible Intermolecular E–H Oxidative Addition to a Geometrically Deformed and Structurally Dynamic Phosphorous Triamide

“…Specifically, Mitzel et al have shown, 19 in accord with earlier spectroscopic studies, 20 that P(NMe 2 ) 3 is inherently nontrigonal, adopting molecular C s symmetry as determined by X-ray crystallography. The distortion away from 3-fold symmetry in this case, however, is modest; the difference in bond angles about phosphorus (Δ∠N x −P−N y ) is only ca.…”

A Phosphorus Bisylide: Exploring a New Class of Superbases with Two Interacting Carbon Atoms as Basicity Centers

“…TheP ÀCbond lengths (between 1.675(5) and 1.683(5) )are slightly longer than observed for the P-ylide (Me 2 N) 3 P = CH 2 (1.655(6) ) [15] or the azaphosphatrane N(CH 2 CH 2 NMe) 3 P = CH 2 (1.6585 (15) ). [16] Thec rystal structure as well as the theoretically calculated molecular structure of 1·p-TolSO 3 H (Figure 3 HMPN) and the non-bonding C-C distance is even longer than in the unprotonated bisylide (3.034(4) and 3.056(4) ).…”

Validating the Biphilic Hypothesis of Nontrigonal Phosphorus(III) Compounds

“…TheP N 3 framework of model tricoordinate phosphorous triamide P(NH 2 ) 3 was parameterized within C s symmetry (Figure 5a)a nd ar elaxed potential energy surface scan was conducted at the B3LYP/6-31G* level for two independent driving coordinates (bond angle q and dihedral angle f). At this level of theory,t he overall electronic energy plot (Figure 5b)d escribes am inimum for P(NH 2 ) 3 that is nearly trigonal (q = 938 8, f = 1138 8), [51] with electronic energy increasing upon planarization (f!1808 8)b ut varying only modestly for excursions of q from equilibrium. Whereas HOMO (i.e.…”