Synthesis and redox properties of crowded triarylphosphines possessing ferrocenyl groups

Crowded triarylphosphines possessing ferrocenyl groups [(4-ferrocenyl-2,6-diisopropylphenyl)(n)(2,4,6-triisopropylphenyl)(3-n)P (5a, n = 1; 5b, n = 2; 5c, n = 3)] were synthesized by the reaction of the corresponding arylcopper(I) reagents with the diarylchlorophosphines. Structures of the triarylphosphines were studied by 1H, 13C, and 31P NMR spectroscopies, and the characteristic patterns of the proton signals of the 2,6-isopropyl groups and upfielded 31P chemical shifts suggest structural similarities of the triarylphosphine moiety to the previously reported tris(2,4,6-triisopropylphenyl)phosphine (2). X-ray crystallography of 5c also revealed that the structure around the phosphorus is similar to that of 1, where the average bond angle and length around the phosphorus atom are 110.8 degrees and 1.854 A, respectively. According to the electrochemical measurements, phosphines 5a, 5b, and 5c are reversibly oxidized in two, three, and four steps, respectively, which suggests significant electronic interaction among the triarylphosphine and the ferrocene redox centers as well as weak interaction among the ferrocene redox centers. The EPR spectra obtained at cryogenic temperature after oxidation of phosphines 5a, 5b, and 5c are superpositions of those for the cation radicals of the crowded triarylphosphine and ferricinium. The solution spectra obtained at 293 K, which consist of two lines typical of the cation radical of the crowded triarylphosphines, become weaker as the number of the ferrocenyl groups increases and the cation radical of 5c does not show EPR signals. These findings suggest not only instability of the tetra(cation radical) of 5c but also the course of oxidation where the ferrocenyl groups in the periphery of the molecules are oxidized at first.     

ESCA STUDIES OF A DIPHOSPHENE

Abstract

The nature of the P[dbnd]P bond in E-bis(2,4,6-tri-tert-butylphenyl)diphosphene was studied by means of ESCA, indicating that the phosphorus 2p binding energy is the lowest among those for common organophosphorus compounds.     

Construction of Stable Redox Systems Composed of the Crowded Triarylphosphines

Extremely crowded triarylphosphines were synthesized by the reaction of arylcopper(I) reagents with chlorophosphines, and the relationship between molecular structure and redox properties was studied by X-ray crystallography and cyclic voltammetry. As the substituent on phosphorus became bulkier, bond lengths and angles around phosphorus atom became longer and larger, and oxidation potential was significantly lowered. Especially, tris(2,4,6-triisopropylphenyl)phosphine had an extremely crowded structure and was oxidized to a stable radical cation at an extraordinarily low oxidation potential. Novel redox systems possessing the crowded triarylphosphine structure as one of the redox sites were designed and synthesized.     

A very crowded molecule: formation of bis(2,4,6-tri-t-butylphenyl)phosphinic chloride

Reaction of 2,4,6-ri-t-butylphenyllithium with phosphoryl trichloride gave a very crowded compound, bis(2,4,6-tri-t-butylphenyl)phosphinic chloride ($\text{1}$), and 2,4,6-tri-t-butylchlorobenzene ($\text{3}$), while the reaction with thiophosphoryl trichloride afforded $\text{3}$.     

Ligand promoted reductive elimination from Zr(IV). The preparation of zirconacycles from alkylzirconium(IV) hydrides and alkynes

Alkynes induce reductive elimination of alkane from Cp₂Zr(H)(R); zirconacyclopentadienes are formed as well.     

Formation and electrochemical properties of a 1,4-diphosphafulvene including formal dimerization of phosphaallene

Reactions of sterically protected 2-bromo-3-phenyl-1-phosphapropenes with bases such as tert-butyllithium and potassium tert-butoxide successfully afforded a bulky 1,4-diphosphafulvene (Mes = 2,4,6-tBu(3)C(6)H(2)) through a novel and formal dimerization pathway of 1-phosphaallene, together with small amounts of 3-phenyl-1-phosphaallene and 3,4-diphosphanylidenecyclobutene. The structure of the 1,4-diphosphafulvene was confirmed by X-ray crystallography indicating somewhat flattened phosphorus atoms due to the bulky Mes groups. The electrochemical properties of the 1,4-diphosphafulvene were investigated to show promising suitability as an electron donor, and indeed, it afforded a charge-transfer complex with TCNQ. Preparation and structural elucidation of an alkoxy-functionalized 1-phosphaallene was also performed, and the effect of the alkoxy group on the 1-phosphaallene moiety was characterized.     

Preparation and coordination properties including catalytic activities of a bulky 2-methyl-3-thioxo-1,3-diphosphapropene

[reaction: see text] 2-Methyl-3,3-diphenyl-3-thioxo-1-(2,4,6-tri-tert-butylphenyl)-1,3-diphosphapropene, which bears a P=C-P=S skeleton, was prepared and used as a ligand of transition-metal complexes. The palladium complexes containing the ligated 3-thioxo-1,3-diphophapropene were stable and used for catalytic reactions such as cross-couplings and direct conversion of allyl alcohol to allylaniline.