Structural Correlations between the Tetraisopropylphosphonium Cation and Triisopropylphosphonium Isopropylide: An X-ray Diffraction Study

Hubert Schmidbaur, Annette Schier, Carlos M.F. Frazão, Gerhard Muller

Research output: Contribution to journalArticlepeer-review

62 Scopus citations

Abstract

Tetraisopropylphosphonium iodide (la) and tetraphenylborate (lb) were prepared in a three-step synthesis from triisopropylphosphine. Single-crystal X-ray diffraction data were collected for both salts, but only the structure of lb could be solved. Crystals of lb are orthorhombic, space group P212, 2a = 9.415 (1) Å, b = 15.199 (2) Å, c = 11.157 (1) Å, V = 1596.6 Å3, Z = 2, and Rw = 0.063 for 181 parameters and 2519 observed reflections (Fo≥ 4.0σ(Fo)). Both the tetra-isopropylphosphonium cations and the tetraphenylborate anions lie on a crystallographic twofold axis, but the actual cation symmetry approaches point group S4(4) symmetry, in agreement with theoretical predictions for tetrahedral species with four ligands of Cs(m) symmetry. The isopropyl groups are rotated pairwise in opposite directions (C1, C1*/C2, C2*) by 110° (av) away from the fully staggered D2d(42m) conformation. The triisopropylphosphonium isopropylide (2), obtained from la and NaNH2 in liquid ammonia, crystallizes in triclinic needles, space group P1, a = 7.587 (2) Å, b = 8.030 (2) Å, c = 11.521 (2) Å, a = 86, 17 (2)°, β = 106.08 (2)°, y = 104.66 (2)°, V = 652.5 Å3, Z = 2, and Rw= 0.055 for 154 parameters and 1654 observables. The individual ylide molecules have approximate Cs(m) symmetry, but the phosphorus-carbon skeleton is clearly reminiscent of a parent D2d(42m) symmetry. The relatively long ylidic bond P-C1 is complemented by the short aliphatic P-C4 bond. Distortions also arise from a large C—P=C angle (C3—P—Cl). The ylidic carbon atom Cl exhibits a pyramidal configuration. Through these effects, the steric interactions are reduced with retention of the basic symmetry. No intra- or intermolecular hydrogen bonds between carbon atoms are present, which could account for the facile proton transfer observed in solution.

Original languageEnglish
Pages (from-to)976-982
Number of pages7
JournalJournal of the American Chemical Society
Volume108
Issue number5
DOIs
StatePublished - 1986

Fingerprint

Dive into the research topics of 'Structural Correlations between the Tetraisopropylphosphonium Cation and Triisopropylphosphonium Isopropylide: An X-ray Diffraction Study'. Together they form a unique fingerprint.

Cite this