Reactivity Studies of Phosphinines: The Selenation of Diphenyl-Phosphine Substituents and Formation of a Chelating Bis(Phosphinine) Palladium(II) Complex

Abstract

Phosphinines and donor-substituted phosphinines are of recent interest due to their use in homogeneous catalysis. In this article, a Pd(II) bis(phosphinine) complex was characterised and phosphorus–selenium coupling constants were used to assess the donor properties of the diphenylphosphine substituents of phosphinine ligands to promote their further use in catalysis. The selenation of 2,5-bis(diphenylphosphino)-3,6-dimethylphosphinine (5) and 2-diphenylphosphino-3-methyl-6-trimethylsilylphosphinine (6) gave the corresponding phosphine selenides 8 and 9, respectively, leaving the phosphinine ring intact. Multinuclear NMR spectroscopy, mass spectrometry and single crystal X-ray diffraction confirmed the oxidation of all the diphenylphosphine substituents with 1JP-Se coupling constants determined to be similar to SePPh3, indicating that the phosphinine rings were electronically similar to phenyl substituents. Solutions of 6 were found to react with oxygen slowly to produce the phosphine oxide 10 along with other by-products. The reaction of [bis{3-methyl-6-(trimethylsilyl)phosphinine-2-yl}dimethylsilane] (4) with [PdCl2(COD)] gave the chelating dichloropalladium(II) complex, as determined by multinuclear NMR spectroscopy, mass spectrometry and an elemental analysis. The molecular structure of the intermediate 2 in the formation of 4,6-di(tert-butyl)-1,3,2-diazaphosphinine (3) was also determined, which confirmed the structure of the diazaphosphacycle P(Cl){N=C(tBu)CH=C(tBu)-N(H)}.

Highly selective, reversible water activation by P,N-cooperativity in pyridyl-functionalized phosphinines

“…Atoms marked with 000 are symmetry generated using the following equation: +Y, 1-X, 2-Z. Selected bond lengths (Å) and angles (°): P(1)-O(1): 1.514(4); P(1)-C(1): 1.764 (5); P(1)-C( 5): 1.752 (5); O(1)-Li(1): 1.916 (8); O(1)-Li(1 0 ): 1.897 (9); N(3)-Li(1): 2.040 (10); N(4)-Li(1 0 ): 2.130 (9). C(1)-P(1)-C( 5): 105.0(2).…”

“…6 a Compound 1 also reacts with HCl under formation of a chlorodiazaphosphacycle. 9 However, so far only a single example was reported by Le Floch and co-workers, in which an SPS-based pincer-type “classical” phosphinine was found to react with H 2 O. 10 Initial, yet inconclusive calculations revealed, that the sulfur-functionality of the additional Ph 2 P S-groups in 2- and 6-position of the phosphorus heterocycle plays an important role in the addition of H 2 O across the P C double bond ( vide infra ).…”

“…The corresponding phosphinin-1-ol then undergoes fast tautomerization, leading to the experimentally observed 1,2-dihydrophosphinine oxide derivatives. 9 A direct oxidative addition at the phosphorus centre via a three-membered transition state was first considered and modelled, but subsequently discounted given the excessively high energy of the corresponding transition state, TS(OA) (+62.8 kcal mol −1 , Fig. S2d ‡ ).…”