Ferrocene-based P-chiral amidophosphinate: stereoselective synthesis and X-ray structural study.

Racemic and enantiopure ferrocene-based P-chiral amidophosphinates have been simply and stereoselectively synthesized by ortho-lithiation of rac- or (R)-Ugi's amine and further reaction with amidochlorophenylphosphinate Cl-P(O)(Ph)NEt2. This is the first example of an asymmetric reaction of ortho-lithiated Ugi's amine with tetracoordinated phosphorus(V) chlorides. The structures of rac- and (R)-Ugi's amine ferrocenyl(phenyl)phosphinic acid N,N-diethylamide have been extensively studied experimentally (NMR, X-ray analysis, electrochemistry). The CV first peak refers to the oxidation of the amine fragment, which is clearly seen when (R)-Ugi's amine ferrocenyl(phenyl)phosphinic acid N,N-diethylamide reacts with anhydrous acid. The addition of two equivalents of CF3COOH leads to the protonation of nitrogen atoms, and a classical reversible wave of oxidation of Fe(II) to Fe(III) is observed.

Sterically Hindered Phosphonium Salts: Structure, Properties and Palladium Nanoparticle Stabilization.

A new family of sterically hindered alkyl(tri-tert-butyl) phosphonium salts (n-CnH2n+1 with n = 2, 4, 6, 8, 10, 12, 14, 16, 18, 20) was synthesized and evaluated as stabilizers for the formation of palladium nanoparticles (PdNPs), and the prepared PdNPs, stabilized by a series of phosphonium salts, were applied as catalysts of the Suzuki cross-coupling reaction. All investigated phosphonium salts were found to be excellent stabilizers of metal nanoparticles of small catalytically active size with a narrow size distribution. In addition, palladium nanoparticles exhibited exceptional stability: the presence of phosphonium salts prevented agglomeration and precipitation during the catalytic reaction.

3D Ni and Co redox-active metal-organic frameworks based on ferrocenyl diphosphinate and 4,4'-bipyridine ligands as efficient electrocatalysts for the hydrogen evolution reaction.

New 3D Ni and Co redox-active metal-organic frameworks based on ferrocenyl diphosphinate and 4,4'-bipyridine ligands have been synthesized, characterized by single crystal X-ray diffraction and spectroscopic techniques and explored as stable electrocatalysts capable of meeting two important parameters: the overpotential and Tafel slope (TS) in the hydrogen evolution reaction (HER). The electrochemical studies suggest that the reaction kinetics of a Ni-MOF (1) catalyst is more favorable than that of a Co-MOF (2) catalyst. Particularly, Ni-MOF exhibits better HER performance with an overpotential of 350 mV at a current density of 10 mA cm-2, a small TS of 60 mV dec-1 and superior long-term durability (of up to 10 000 cycles), ranking it among the most active non-noble metal-based molecular electrocatalysts. The introduction of a 4,4'-bpy linker in 2 significantly changes the catalytic properties in an organic or aqueous environment compared to 1D cobalt polymers based on ferrocenyl diphosphinate. For Co-MOF 2, there is a significant decrease in the overvoltage by ∼440 mV in comparison with the 1D Co polymer in an organic medium and by 50 mV in an aqueous medium. The TS changes from 120 to 65 mV dec-1 when moving from 1D CofcdHp to a 3D structure of 2. Thus, a 4,4'-bpy linker reduces the overvoltage and gives more favorable HER kinetics (lower TS). These results provide important guidelines for the rational design of non-precious metal electrocatalysts.

Electrochemical Properties and Structure of Multi-Ferrocenyl Phosphorus Thioesters.

The reaction of triferrocenylthiophosphite with elemental sulfur leads to triferrocenyltetrathiophosphate. The molecule of tetrathiophosphate adopts propeller-like all synclinal-conformation of the ferrocenyl fragments respective to the P=S bond. All ferrocenyl groups have nearly ideal eclipsed conformation of the cyclopentadienyl fragments. The Fc3S3P (1), Fc3S3P=O, (2) and Fc3S3P=S (3) demonstrate three reversible and well-separated ferrocenyl-based redox events. The electronic structures of 1-3 have been studied quantum-chemically; the energies and composition of frontier orbitals have been calculated.

Excellent supercapacitor and sensor performance of robust cobalt phosphinate ferrocenyl organic framework materials achieved by intrinsic redox and structure properties.

A new redox active coordination polymer [Co(H2O)2(Fc(PHOO)2)·2H2O]n (Fc = ferrocene) was synthesized by the diffusion method and characterized by single-crystal X-ray diffraction. Phosphinate fragments formed infinite chains connected through ferrocene fragments to 2D PCP associated with cobalt atoms. Additional strong hydrogen bonding via the participation of coordinated and lattice water molecules resulted in the formation of a 3D network. The polymer exhibited water-induced crystal-to-amorphous transformation with chromotropism, as confirmed by spectroscopic techniques, elemental analysis, TGA and XRPD. The explosion of the amorphous phase [Co(Fc(PHOO)2)]n to form water vapor readily led to its conversion into the initial crystalline [Co(H2O)2(Fc(PHOO)2)·2H2O]n with a reverse change of color. The dehydrated form of the polymer selectively sorbed water and could be used as a material with the function of an express dehydrator. Moreover, a modified electrode could qualitatively determine the water content in the solvent at a concentration of 0.05%. Both hydrated and dehydrated forms were evaluated as electrode materials for supercapacitors. The [Co(Fc(PHOO)2)]n (dehydrated form) electrode exhibited high specific capacitance and excellent cycling stability. Its maximum specific capacitance was 2517 F g-1 at a current density of 2 A g-1, and the specific capacitance retention was about 90.1% after 1000 cycles.

Zn and Co redox active coordination polymers as efficient electrocatalysts.

New redox active 1D helical coordination polymers M(fcdHp) (M(ii) = Zn(1), Co(2)) have been obtained by utilizing the 1,1'-ferrocenylenbis(H-phosphinic) acid (H2fcdHp) ligand and Zn or Co nitrate salts. Complexes 1 and 2 are isomorphic, crystallizing in the chiral space groups P4122 and P4322, respectively. Their redox, electrocatalytic and other properties are described. These compounds incorporated into carbon paste electrodes and exhibited reversible redox reactions, arising from the ferrocenyl moiety. These coordination polymers are efficient as electrocatalysts for the reduction of protons to hydrogen. Using N,N-dimethylformamidium ([DMF(H)+]) as the acid in the acetonitrile solution, Co CP (2) displays a turnover frequency of 300 s-1, which is among the fastest rates reported for any CP electrocatalyst in CH3CN. This high rate of catalytic reaction comes at the cost of the 820-840 mV overpotential at the potential of catalysis. As the hydrogen evolution reaction (HER) catalysts, the CPs exhibited in 0.5 M H2SO4 the overpotential η10 of 340 or 450 mV, onset overpotential of 220 or 300 mV (vs. RHE), Tafel slope of 110 or 120 mV dec-1, correspondingly for 1 and 2, and considerable long-term stability for the HER.

Ferrocene-Containing Sterically Hindered Phosphonium Salts.

The synthesis and physical properties of the series of the ferrocenyl-containing sterically hindered phosphonium salts based on di(tert-butyl)ferrocenylphosphine is reported. Analysis of voltamogramms of the obtained compounds revealed some correlations between their structures and electrochemical properties. The elongation of the alkyl chain at the P atom as well as replacement of the Br- anion by [BF4]- shifts the ferrocene/ferrocenium transition of the resulting salts into the positive region. DFT results shows that in the former case, the Br- anion destabilizes the corresponding ion pair, making its oxidation easier due to increased highest occupied molecular orbital (HOMO) energy. Increased HOMO energy for ion pairs with the Br- ion compared to BF4- are caused by contribution of bromide atomic orbitals to the HOMO. The observed correlations can be used for fine-tuning the properties of the salts making them attractive for applications in multicomponent batteries and capacitors.

Novel enantiopure monophospholes: synthesis, spatial and electronic structure, photophysical characteristics and conjugation effects.

A rational and highly efficient method to access lithium 2,3,4,5-tetraphenylphospholide directly from white phosphorus, diphenylacetylene and lithium has been developed. This novel, convenient synthetic route has allowed the incorporation of various chiral substituents into 2,3,4,5-tetraarylphospholes. The spatial and electronic structures of the obtained novel enantiopure phospholes, their oxides and sulfides have been characterized both experimentally (single-crystal X-ray diffraction) and computationally (DFT). The experimental vibrational Raman spectra and electronic absorption and emission spectra of the synthesized compounds have been interpreted using quantum chemical calculations. A moderate impact of the substituent at the P-atom on the photophysical properties of the phospholes was demonstrated both experimentally and theoretically, while the oxidation/thionation of the phosphorus center was shown to influence remarkably both absorption and emission spectral characteristics. The latter effect is ascribed to the increase of conjugation strength of the oxidized/thionated species with exocyclic Ph rings.

Mechanism of intramolecular transformations of nickel phosphanido hydride complexes.

In solution, nickel phosphanido hydride complexes ([NiH{P(Ar)(H)}(dtbpe)], Ar = Dmp, Mes*) undergo a degenerate intramolecular exchange, with the Ni-H and P-H hydrogens and both halves of the dtbpe moiety interchanging. This intramolecular rearrangement was shown to occur in three steps: first, the hydride proton migrates to phosphorus, then the P-Aryl moiety rotates around the P-Ni bond, and finally the back migration of one proton to Ni completes the process. Both migration and rotation were determined to be characterized by high barriers (on the NMR time scale) and to depend on the type of aryl group at the terminal phosphorus. Compared to that observed for the Ni complexes, the same isomeric preference, but with a slower rate of intramolecular rearrangement, is predicted for the corresponding Pt complexes. An opposite isomeric preference, however, is expected for the corresponding Pd complexes. Thus, it is likely that some of the catalytic reactions of Pd and Pt complexes are driven by the relative thermodynamic stabilities of their main forms.

Conjugation in and optical properties of 1-R-1,2-diphospholes and 1-R-phospholes.

The strength of conjugation between the diene moieties of 1-R-1,2-diphospholes and 1-R-phospholes and exocyclic phenyl groups of these P-heteroles has been quantitatively characterized by the use of Raman activities of the bands of the phenyl substituents. It is shown that conjugation in both types of phospholes is very similar to the conjugation of phenyl groups with the diene system of cyclopentadiene. Introduction of substituents (-OMe, -C(═O)H, -NO2, -NMe2, and -CH═CH2) in the para-position of the phenyl groups of 1-R-1,2-diphospholes extends π-delocalization of exocyclic groups into the electronic system of the 1,2-diphosphole ring, producing bathochromic shifts of the absorption bands up to 63 nm. In contrast, hypsochromic shifts up to 40 nm can be achieved by introduction of SnMe3 or SiMe3 groups at the phosphorus(III) atom of the 1,2-diphosphole and concomitant increase of aromaticity of the P-heterole. Conjugation shifts the "centre of gravity" of the whole electronic absorption spectrum, whereas positions of separate absorption bands are not simply dependent on conjugation lengths.