Water soluble phosphine rhenium complexes

Reduction of [NMe₄]₂[ReBr₅(NO)] (1) with zinc in acetonitrile leads to the known trisacetonitrile compound [ReBr₂(CH₃CN)₃(NO)] (2). Attempts to turn 2 into a dihydrogen or a hydride complex applying direct reaction with H₂ or with H₂ and a base were unsuccessful. Complex 2 could be transformed into [ReBr(BF₄)mer-(CH₃CN)₃(NO)] (2a) with AgBF₄ in acetonitrile and was used as a starting material in a ligand exchange reaction with the water soluble phosphine 1,3,5-triaza-7-phosphadamantane (PTA) to obtain the complex [ReBr₂(NO)(PTA)₃] (3). When the reduction of 1 with zinc was carried out in the presence of PTA in acetonitrile, the disubstituted complex [ReBr₂(CH₃CN)(NO)(PTA)₂] (4) was formed. The olefin-coordinated rhenium complexes [ReBr₂(NO)(CH₂CH₂)(PTA)₂] (5a) and [ReBr₂(NO)(PhCHCH₂)(PTA)₂] (5b) were obtained from the reaction of 4 with the corresponding olefins. Complex 4 reacts further with NaHBEt₃ in THF to give the dihydride [ReH₂(THF)(NO)(PTA)₂] (6). In the presence of ethylene 6 is transformed into the ethyl hydride complex [ReH(CH₂CH₃)(η²-C₂H₄)(NO)(PTA)₂] (7). Complexes 6 showed catalytic activity in the hydrogenation of olefins.     

New complexes of the fac-{(CO)3Re} fragment bearing a diaminediphosphine ligand

The mono- and binuclear hydride compounds fac-[ReH(CO)₃L] (1a) and [{ReH(CO)₄}₂(μ-L)] (1b) have been prepared by reaction of [ReH(CO)₅] with Ph₂PN(CH₃)(CH₂)₂N(CH₃)PPh₂ (L) under UV light. Protonation reactions of the hydride compound 1a with equimolar amounts of HSO₃CF₃ or HCl yielded the triflato or the chlorido compounds fac-[Re(OSO₂CF₃)(CO)₃L] (2) and fac-[ReCl(CO)₃L] (3), respectively. The compounds have been characterised by elemental analysis, IR and NMR spectroscopic data, and mass spectrometry. Their structures have been confirmed by X-ray crystallography.     

The Re(I) coordination chemistry of a series of pyrido[2,3-b]pyrazine-derived ligands: Syntheses,characterisation and crystal structures

Reaction of 2,3-diaminopyridine with one equivalent of a functionalised vicinal diketone, in ethanol, yields a series of ligands based upon the pyrido[2,3-b]pyrazine core. The ligands were characterised by ¹H, ¹³C–{¹H} NMR, MS and UV–Vis spectroscopy. Reaction of the ligands with one equivalent of {ReBr(CO)₅} gave a series of Re-Lⁿ complexes based upon the general formula fac-{ReBr(CO)₃(L)} (where L = pyrido[2,3-b]pyrazine-derived ligands, L¹–L⁶). Solution IR studies confirmed the retention of the facially capped, tri-carbonyl coordination geometry at rhenium, and ¹H NMR studies confirmed coordination of the ligand to Re(I). EI HR MS data were obtained for each complex confirming the proposed formulation and stoichiometry. Single crystal X-ray structures were obtained for three of the complexes (Re-L¹, Re-L², Re-L⁶), with each demonstrating that the ligands coordinate to Re(I) in a bidentate manner, via a four-membered chelate ring, which was unsymmetrical in the former two cases. The electronic absorption spectra of the complexes showed absorption into the visible region ca. 375–500 nm, (the complexes are orange-red in appearance). Following irradiation at 350–450 nm, the complexes display a solid-state broad emission peaking between 600–700 nm. The complexes were not sufficiently luminescent in solution to allow further investigation into the origin of this emission band, although with reference to related 1,8-naphthyridine complexes of Re(I) it is likely to incorporate significant ³MLCT character.     

Structural and theoretical studies of (E,E)-benzaldehyde azine and its rhenium(IV) complex

The azine bridged dicatechol ligand (E,E)-benzaldehyde azine (H₄L) was fully characterized by X-ray analysis. The reaction of [ReCl₆]²⁻ with this compound was studied and the novel Re(IV) complex (HNEt₃)(NBu₄)[ReCl₄(H₂L)] was prepared and characterized. The structure and spectroscopy of the compound H₄L and its Re(IV) complex were studied experimentally and by means of density functional calculations.     

Synthesis and reactivity of η-tetramethylcyclopentadienyl-propenyl rhenium complexes: Molecular structure of [(η:η-C5Me4CH2CHCH2)Re(CO)2]

The fulvene complexes [(η⁶-C₅Me₄CH₂)Re(CO)₂(R)] (1a, RI; 1b, RC₆F₅) react at the exocyclic methylene carbon with a vinylmagnesium bromide solution to produce the anionic species [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(R)]⁻. Protonation with HCl at 0 °C produces the hydride complexes [trans-(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(R)(H)] (2a, RI; 2b, RC₆F₅). Thermolysis of an hexane solution of the iodo-hydride (2a) under a CO atmosphere yields the complex [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₃] (3) and [Re(CO)₅I] as by-product. Thermolysis of 2b produced three new products, mainly the chelated complex [(η⁵:η²-C₅Me₄CH₂CHCH₂)Re(CO)₂] (4) and complex 3, with a non-coordinated olefin group, in moderated yield, and traces of [Re(CO)₅(C₆F₅)]. Thermolysis of an hexane solution of 2 in presence of an excess of PMe₃, afforded the phosphine derivative [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(PMe₃)] (5). All the complexes were characterized by IR, ¹H, ¹³C and ³¹P NMR spectroscopies and mass spectrometry. The molecular structure of 4 has also been determined. The molecule exhibits a formal three-legged piano-stool structure, with two CO groups, and the third position corresponding to the η²-coordination of the propenyl side arm of the η⁵-C₅Me₄ ring.     

Copper(II) complexes with the N,N,O-tridentate ligand 6-amino-5-formyl-1,3-dimethyluracilato-(N6)-benzoylhydrazone: synthesis, spectral and XRD studies

From reactions between different Cu(II) salts and the Schiff base 6-amino-5-formyl-1,3-dimethyluracil-benzoylhydrazone (H₂BEZDO) in alcohol, six new copper complexes with simplified formulas [Cu(HBEZDO)(H₂O)(MeOH)]NO₃ (1), [CuCl(HBEZDO)(DMF)] (2), [CuBr(HBEZDO)]·2H₂O (3), CuBr(HBEZDO) (4), Cu(ClO₄)(HBEZDO)·H₂O (5), and Cu(SO₄)_1/2(HBEZDO)·1 H₂O (6) were isolated. The structures of compounds 1, 2 and 3 have been established by means of XRD diffraction methods. In the three compounds, the Schiff base acts as a tridentate monodeprotonated ligand through the N(6), N(51) and O(52) atoms, making two five- and six-membered chelate rings. In the structure of 1 and 2, the solvent molecules are coordinated giving square-based pyramidal environments, with the basal plane completed by a MeOH (1) or Cl (2) and the apical positions occupied by the oxygen atom of a water (1) or a DMF molecule (2). The molecular unit of the complex [CuBr(HBEZDO)]·2H₂O (3) is defined by a square-plane containing the three donor atoms of the organic ligand and a bromide ligand (Cu–Br 2.384 Å), but there is a stronger tetragonally elongated pyramidal geometry around the metal, the apical position of the polyhedron being occupied by a weakly bound-to-copper bromine atom (3.086 Å) of a neighbouring molecule. This fact gives the appearance of an apparent dimer with very asymmetric bromine bridges, in which there are no exchange interactions between metal centres. Also, infrared, magnetic and EPR data of the isolated complexes are reported.     

Direct Synthesis of a Dimeric Mixed-Anions Bismuth(III) Complex: Synthesis and Structural Characterization of [Bi2(Phen)4(No3)4.4I0.6]I3 (A New Dimeric Compound)

A direct synthetic method of mixing Bi(NO₃)₃ and NaI with 1,10-phenanthroline yielded red crystals of [Bi₂(phen)₄(NO₃)_4.4I_0.6]I₃. In this complex the cationic part is in fact binuclear and contains two [Bi(phen)(NO₃)_1.7I_0.3] groups linked via a bridging NO^? ₃ anion. The I^? ₃ anion was not coordinated to bismuth(III) and the lone pair of valence electrons of the bismuth(III) ions appears to be stereochemically inactive. There are two independent NO^? ₃ anions, one coordinated to bismuth but another shares a position with I^? anion. The final results of crystallography show that 40% of these positions are occupied by NO^? ₃ anions and 60% by I^? anions that are coordinated to bismuth atom in bidentate fashion (NO^? ₃) and in unidentate fashion (I^?). An interesting point is that the I^? ₃ anion was produced by direct synthetic method (Branched tube method). There is a π-π stacking interaction between the parallel aromatic rings around the Bi(III) ion.     

First-principles study of electronic structure of transition metal nitride: ReN under normal and high pressure

First-principles calculation was performed using tight-binding LMTO method with local density approximation (LDA) and atomic sphere approximation (ASA) to understand the electronic properties of rhenium nitride. The equilibrium geometries, the electronic band structure, the total and partial DOS are obtained under various pressures and are analyzed in comparison with the available experimental data. The most stable structure of ReN is NiAs like structure. Our results indicate that ReN can be used as a super-hard conductor. We estimated the average electron-phonon coupling constant to be 1.65 and superconducting transition temperature (T_c) is 5.1 K. The T_c value increases with the increase in pressure.     

Rhenium complex-catalyzed acylative cleavage of ethers with acyl chlorides

It was found that rhenium complex was an efficient catalyst for the acylative cleavage of C-O bond of ethers with acyl chlorides. When acyclic ethers were allowed to react with acyl chlorides in the presence of a catalytic amount of ReBr(CO)₅, acylative cleavage of C-O bond of acyclic ethers smoothly proceeded to give the corresponding esters in moderate to good yields. Similarly, cyclic ethers were acylative cleaved by acyl chlorides to give the corresponding chloro substituted esters in good yields by the use of Re₂O₇ catalyst.