Influence of bidentate phosphine ligands on the chemistry of [FeFe]-hydrogenase model: insight into molecular structures and electrochemical characteristics

Substitution of carbonyl ligands of the hydrogenase model complex [Fe₂(μ-SeCH₂CH(Me)CH₂Se-μ)(CO)₆] ( A ), by 1,1′-bis (diphenylphosphino)ferrocene (dppf), 1,2-bis (diphenylphosphino)benzene (dppbz) or 1,2-bis (diphenylphosphino)acetylene (dppac) is investigated. It is found that the reaction product depends on the diphosphine used. In the case of dppf, the product is an intramolecular bridged disubstituted complex [Fe₂{μ-SeCH₂CH(Me)CH₂Se-μ}(CO)₄{μ,κ¹,κ¹(P,P)-dppf}] ( 1 ), while the dppac-reaction produces an intermolecular bridged tetra-iron model [Fe₂{μ-SeCH₂CH(Me)CH₂Se-μ}(CO)₅]₂{μ,κ¹,κ¹(P,P)-dppac} ( 2 ). However, the dppbz-reaction gives [Fe₂{μ-SeCH₂CH(Me)CH₂Se-μ}(CO)₄{κ²(P,P)-dppbz}] ( 3 ) in which the dppbz ligand is bonded to one Fe atom in a chelated manner. The newly prepared complexes ( 1 – 3 ) have been characterized by elemental analysis, IR, ¹H-, ¹³C{H}-, ³¹P{H}-, ⁷⁷Se{H}-NMR spectroscopy and X-ray structure determination. The electrochemical behavior of 2 and 3 , in absence and presence of acid, is described by cyclic voltammetric measurements in CH₂Cl₂.     

Synthesis and EPR/UV/Vis‐NIR Spectroelectrochemical Investigation of a Persistent Phosphanyl Radical Dication

The reaction of the bis(imidazoliumyl)‐substituted P^I cation [(2‐Im^Dipp)P(4‐Im^Dipp)]⁺ ( 10 ⁺) (2‐Im=imidazolium‐2‐yl; 4‐Im=imidazolium‐4‐yl; Dipp=2,6‐di‐isopropylphenyl) with trifluoromethanesulfonic acid (HOTf) or methyl trifluoromethylsulfonate (MeOTf) yields the corresponding protonated [(2‐Im^Dipp)PH(4‐Im^Dipp)]²⁺ ( 11 ²⁺) and methylated [(2‐Im^Dipp)PMe(4‐Im^Dipp)]²⁺ ( 12 ²⁺) dications, respectively. EPR/UV/Vis‐NIR spectroelectrochemical investigation of the low‐coordinated P^I cation 10 ⁺ predicted a stable and “bottleable” P‐centered radical dication [(2‐Im^Dipp)P(4‐Im^Dipp)]^2+. ( 13 ^2+.). The reaction of 10 ⁺ with the nitrosyl salt NO[OTf] yields the persistent phosphanyl radical dication 13 ^2+. as triflate salt in crystalline form. Quantum chemical investigation revealed an exceptional high spin density at the P atom.     

Reductive Catenation of Phosphine Antimony Complexes

Reactions of triarylphosphines with fluoroantimony(III) triflates give phosphine antimony(III) complexes, which undergo spontaneous reductive elimination of fluorophosphonium cations. The resulting phosphine antimony(I) complexes catenate to give the first examples of cationic antimony bicyclic compounds, [(R₃P)₄Sb₆]⁴⁺, featuring a bicyclo[3.1.0]hexastibine framework stabilized by four phosphine ligands. The unprecedented 14‐electron redox process illustrates the generality of the reductive catenation method.     

Facile synthesis of potassium tetrathiooxalate – The “true” monomer for the preparation of electron-conductive poly(nickel-ethylenetetrathiolate)

Herein, aiming at optimization of the polymerization process leading to a family of hole- and electron-conducting 1,1,2,2-ethenetetrathiolate-based polymers, such as poly(nickel-1,1,2,2-ethenetetrathiolate), poly[K_x(Ni-ett)], we investigated transformations of the monomer precursor 1,3,4,6-tetrathiapentalene-2,5-dione (TPD) occurring under polymerization conditions. We found that only one ring of TPD opens upon its reaction with potassium methoxide under inert conditions at room temperature which leads to the formation of potassium 2-oxo-1,3-dithiol-4,5-dithiolate (K₂[3]). Heating of K₂[3] under reflux in methanol solution under inert conditions opens the second ring, however the resulting product is not potassium ethenetetrathiolate (K₄[2]), the product of an exhaustive methanolysis of TPD, but potassium tetrathiooxalate (K₂[4]), the product of the decarbonylation of K₂[3]. Preliminary experiments reveal that the involvement of K₂[4] in the polymerization process is beneficial for reproducible formation of high quality 1,1,2,2-ethenetetrathiolate-based polymers suitable for thermoelectric applications.