Reactive sulfur species: aqueous chemistry of sulfenyl thiocyanates

Sulfenyl thiocyanate (RSSCN) derivatives of penicillamine (PENSCN) and glutathione (GSSCN) have been synthesized in situ at pH = 0 from equilibrium mixtures that consists of hypothiocyanous acid (HOSCN), thiocyanogen ((SCN)2), and trithiocyanate ((SCN)3-). The electrophilic thiocyanating agent N-thiocyanatosuccinimide (NTS) also reacts with PEN and GSH to yield the corresponding RSSCN derivatives. PENSCN and GSSCN were characterized by NMR, ES-MS, and IR spectroscopy. While stable at pH = 0, at higher pH the RSSCN derivatives decompose to give products that are consistent with hydrolysis and formation of reactive sulfenic acids.     

Bioorganic Chemistry of Hypothiocyanite

Abstract

Hypothiocyanite (OSCN^?) plays an important role in the human host defense system as a nonimmunological antimicrobial agent. Although many conjugate reactions of proteins have been attributed to OSCN^?, there is little precedence for such reactions in small-molecule chemistry. We will discuss the derivative species that are in equilibrium with OSCN^?, including hypothiocyanous acid (HOSCN), thiocyanogen [(SCN) ₂ ], and trithiocyanate [(SCN) ₃ ^?], the first organic derivatives of this mixture to be fully characterized, and we will describe a new method of synthesizing hypothiocyanite.     

Dinuclear metal complexes of Schiff base ligands as catalysts for oxidation and epoxidation reactions

Dinuclear copper(II) complexes (Cu₂ L_nCl₃), nickel(II) complexes (Ni₂ L_nCl₃) and cobalt(II) complexes (Co₂L ₂ ⁿ Cl₂) from Schiff base ligands are synthesised, characterised and used as catalysts for oxidation of 3,5-DTBC to 3,5-DTBQ. (Cu₂L_nCl₃) are found to be more efficient than the other complexes. Dinuclear iron(III) complexes of composition (Fe₂L₂Cl₂) and ruthenium (III) complexes of composition Ru₂L ₂ ⁿ Cl₆(PPh₃)₂ and Ru₂L ₂ ⁿ Cl₂(PPh₃)₂ catalyse epoxidation of styrene and cyclohexene. Catalytic activities of ruthenium(III) complexes are much greater than those of analogous iron(III) complexes.     

A fluorobenzene adduct of Ti(IV), and catalytic carboamination to prepare alpha,beta-unsaturated imines and triaryl-substituted quinolines

A rare fluorobenzene adduct of group 4, [(nacnac)Ti=NAr(FC6H5)][B(C6F5)4] (nacnac- = [ArNC(tBu)]2CH, Ar = 2,6-iPr2C6H3), has been isolated and structurally characterized. This highly electron-deficient system engages readily in imine metathesis and catalyzes carboamination reactions involving diphenylacetylene and aldimines to afford alpha,beta-unsaturated imines as well as triaryl-substituted quinolines. The latter product results from cyclization of the corresponding electron-rich alpha,beta-unsaturated imine.     

Neutral and zwitterionic low-coordinate titanium complexes bearing the terminal phosphinidene functionality. Structural, spectroscopic, theoretical, and catalytic studies addressing the Ti-P multiple bond

Alpha-hydrogen abstraction and alpha-hydrogen migration reactions yield novel titanium(IV) complexes bearing terminal phosphinidene ligands. Via an alpha-H migration reaction, the phosphinidene ((tBu)nacnac)Ti=P[Trip](CH(2)(tBu) ((tBu)nacnac(-) = [Ar]NC((t)Bu)CHC((t)Bu)N[Ar], Ar = 2,6-(CHMe2)(2C6H3, Trip = 2,4,6-(i)Pr3C6H2) was prepared by the addition of the primary phosphide LiPH[Trip] to the nucleophilic alkylidene triflato complex ((tBu)nacnac)Ti=CH(t)Bu(OTf), while alpha-H abstraction was promoted by the addition of LiPH[Trip] to the dimethyl triflato precursor ((tBu)nacnac)Ti(CH)(2)(OTf) to afford ((tBu)nacnac)Ti=P[Trip](CH3). Treatment of ((tBu)nacnac)Ti=P[Trip](CH3) with B(C6F5)(3) induces methide abstraction concurrent with formation of the first titanium(IV) phosphinidene zwitterion complex ((tBu)nacnac)Ti=P[Trip]{CH3B(C6F5)(3)}. Complex ((tBu)nacnac)Ti=P[Trip]{CH3B(C6F5)(3)} [2 + 2] cycloadds readily PhCCPh to afford the phosphametallacyclobutene [((tBu)nacnac)Ti(P[Trip]PhCCPh)][CH3B(C6F5)(3)]. These titanium(IV) phosphinidene complexes possess the shortest Ti=P bonds reported, have linear phosphinidene groups, and reveal significantly upfielded solution 31P NMR spectroscopic resonances for the phosphinidene phosphorus. Solid state 31P NMR spectroscopic data also corroborate with all three complexes possessing considerably shielded chemical shifts for the linear and terminal phosphinidene functionality. In addition, high-level DFT studies on the phosphinidenes suggest the terminal phosphinidene linkage to be stabilized via a pseudo Ti[triple bond]P bond. Linearity about the Ti-P-C(ipso) linkage is highly dependent on the sterically encumbering substituents protecting the phosphinidene. Complex ((tBu)nacnac)Ti=P[Trip]{CH3B(C6F5))(3)} can catalyze the hydrophosphination of PhCCPh with H(2)PPh to produce the secondary vinylphosphine HP[Ph]PhC=CHPh. In addition, we demonstrate that this zwitterion is a powerful phospha-Staudinger reagent and can therefore act as a carboamination precatalyst of diphenylacetylene with aldimines.