Ammonia Formation Catalyzed by Dinitrogen-Bridged Dirhenium Complex Bearing PNP-Pincer Ligands under Mild Reaction Conditions

A series of rhenium complexes bearing a pyridine-based PNP-type pincer ligand are synthesized from rhenium phosphine complexes as precursors. A dinitrogen-bridged dirhenium complex bearing the PNP-type pincer ligands catalytically converts dinitrogen into ammonia in the reaction with KC₈ as a reductant and [HPCy₃]BAr^F₄ (Cy = cyclohexyl, Ar^F = 3,5-(CF₃)₂C₆H₃) as a proton source at –78 °C to afford 8.4 equiv of ammonia based on the rhenium atom of the catalyst. The rhenium-dinitrogen complex also catalyzes silylation of dinitrogen in the reaction with KC₈ as a reductant and Me₃SiCl as a silylating reagent under ambient reaction conditions to afford 11.3 equiv of tris(trimethylsilyl)amine based on the rhenium atom of the catalyst. These results demonstrate the first successful example of catalytic nitrogen fixation under mild reaction conditions by using rhenium-dinitrogen complexes as catalysts.

Ammonia Formation Catalyzed by Dinitrogen-Bridged Dirhenium Complex Bearing PNP-Pincer Ligands under Mild Reaction Conditions

A series of rhenium complexes bearing a pyridine-based PNP-type pincer ligand are synthesized from rhenium phosphine complexes as precursors. A dinitrogen-bridged dirhenium complex bearing the PNP-type pincer ligands catalytically converts dinitrogen into ammonia in the reaction with KC₈ as a reductant and [HPCy₃]BAr^F₄ (Cy = cyclohexyl, Ar^F = 3,5-(CF₃)₂C₆H₃) as a proton source at –78 °C to afford 8.4 equiv of ammonia based on the rhenium atom of the catalyst. The rhenium-dinitrogen complex also catalyzes silylation of dinitrogen in the reaction with KC₈ as a reductant and Me₃SiCl as a silylating reagent under ambient reaction conditions to afford 11.3 equiv of tris(trimethylsilyl)amine based on the rhenium atom of the catalyst. These results demonstrate the first successful example of catalytic nitrogen fixation under mild reaction conditions by using rhenium-dinitrogen complexes as catalysts.

Neutral Rhenadicarbaboranes with Re(CO)2(NO) Vertices: A Theoretical Study of Building Blocks for Rhenacarborane-Based Drug Delivery Agents

The rhenadicarbaborane carbonyl nitrosyls (C2Bn−3Hn−1)Re(CO)2(NO), (n = 8 to 12), of interest in drug delivery agents based on the experimentally known C2B9H11Re(CO)2(NO) and related species, have been investigated by density functional theory. The lowest energy structures of these rhenadicarbaboranes are all found to have central ReC2Bn−3 most spherical closo deltahedra in accord with their 2n + 2 Wadean skeletal electrons. Carbon atoms are found to be located preferentially at degree 4 vertices in such structures. Furthermore, rhenium atoms are preferentially located at a highest degree vertex, typically a vertex of degree 5. Only for the 9-vertex C2B6H8Re(CO)2(NO) system are alternative isocloso deltahedral isomers found within ~8 kcal/mol of the lowest energy closo isomer. Such 9-vertex isocloso structures provide a degree 6 vertex for the rhenium atom flanked by degree 4 vertices for each carbon atom.

enantio-Enriched CPL-active helicene–bipyridine–rhenium complexes

Incorporation of a rhenium atom within an extended helical π-conjugated bi-pyridine system leads to the first examples of rhenium-based phosphors that exhibit circularly polarized luminescence.

Reactivity of [M4(co)12(µ-pyms)4] (M = Mn, re; pymS = pyrimidine-2-Thiolate) with bis(triphenylphosphino)nickel(ii) dicarbonyl: X-ray crystal structure of [Re(Co)3(?2-pymS)(PPh3)]

The reaction between the tetranuclear compound [Mn4(CO)12(µ -pymS)4] (1) and (PPh3)2Ni(CO)2 at room temperature resulted in the cleavage of the square to afford the dinuclear complex [Mn2(CO)5(µ -pymS)2(PPh3)] (2) (19%) along with two mononuclear complexes fac- [Mn(CO)3(?2-pymS)(PPh3)] (3) (43%) and [Mn(CO)2(?2-pymS)(PPh3)2] (4) (24%). In contrast, a similar reaction of [Re4(CO)12(µ-pymS)4] (5) with (PPh3)2Ni(CO)2 at 25oC did not afford any dinuclear compound leading instead to the monophosphine substituted mononuclear compound fac- [Re(CO)3(?2-pymS)(PPh3)] (6) (72%). Compound 4 is also formed when a toluene solution of 3 is treated with PPh3 at elevated temperature (100oC). A similar treatment of 6 with triphenylphosphine in refluxing toluene gave [Re(CO)2(?2-pymS)(PPh3)2] (7) (60%). All the new compounds have been characterized by elemental analysis, IR, 1H NMR and 31P{1H} NMR spectroscopy and mass spectrometry along with single crystal X-ray diffraction analysis for 6. Compound 6 consists of a single rhenium atom with three carbonyls, a triphenylphosphine ligand and a chelating pyrimidinethiolate ligand. DOI: http://dx.doi.org/10.3329/jbas.v38i2.21340 Journal of Bangladesh Academy of Sciences, Vol. 38, No. 2, 155-165, 2014

N10-(2′-Mercaptoethanoyl)-2,2,5,5-tetramethyl-3,4-diathia-7,10-diaza-bicyclo[5.3.0]decane and its reaction with oxotrichlorobis(triphenylphosphine)rhenium(V)

The ligand molecule N10-(2′-mercaptoethanoyl)-2,2,5,5-tetramethyl-3,4-dithia-7,10-diazabicyclo[5.3.0]decane has been prepared and characterized by 1H and 13C NMR spectroscopy and by mass spectrometry. The protected analogue, N10-[(2′-triphenylmethylthio)ethanoyl]2,2,5,5-tetramethyl-3,4-dithia-7,10-diazabicyclo[5.3.0]decane dimethanol hemihydrate, was examined by the same techniques and also by X-ray crystallography. Crystals were triclinic, P-1, a = 11.125(2), b = 11.986(2), c = 13.562(3) Å, α = 103.54(3)°, β = 90.29(3)°, γ = 107.11(3)°, and Z = 2. The crystal was unstable in air at room temperature, so measurements were made on a crystal sealed in a tube that contained methanol vapour Intensities were measured with a Rigaku AFC6R diffractometer and monochromated CuKα radiation (λ = 1.54178 Å). The structure was solved by direct methods and refined to R = 0.1497, wR = 0.0655 based on 5000 independent reflections. The high residuals were caused by solvent disorder. Bond lengths and angles were normal. The reaction of the ligand with oxotrichlorobis(triphenylphosphine)rhenium(V) yielded an unexpected asymmetric complex, oxo(1,1-dimethyl-1,8-dimercapto-3,6-diazaoctan-7-onato-N3,N6,S1,S8) rhenium(V). Crystals were monoclinic, P21/n, a = 10.633(2), b = 11.221(2), c = 11.678(1) Å, β = 116.10(1)°, Z = 4. Intensities were measured with a Siemens P4 diffractometer and monochromated MoKα radiation (λ = 0.71073 Å). The structure was solved by the heavy atom method and refined to R = 0.0471, wR = 0.0340 based on 2866 unique reflections. Most bond lengths and angles were normal. The Re≡O distance of 1.681(5) Å was longer than normal. It is postulated that this was caused by competitive π bonding between the deprotonated amidic nitrogen atom and the rhenium atom, as shown by the short Re—N distance (1.997(6) Å) compared to the equivalent distance for the amine nitrogen atom (Re—N, 2.151(4) Å). Key words: N2S2 ligands, rhenium, crystal structure.

Synthese von Nitrenkomplexen mit N-Trimethylsilylanilin I. Charakterisierung und Kristallstruktur von [Re(NPh)Cl3(Et2PhP)2] und [Re(NPh)Cl3(Ph3P)2] ·1/2 CHCl3 / Synthesis of Nitrene Complexes with N –T rimethylsilylaniline I. Characterisation and Crystal Structure of [Re(NPh)Cl3(Et2PhP)2] and [Re(N Ph)Cl3(Ph3P)2] · 1/2CHCl3

trans-mer--Trichlorobis(diethylphenylphosphine)phenylnitrene rhenium(V), [Re(NPh)Cl3- (Et2PhP)2], has been synthesized from [ReOCl3 (Et2 PhP)2 ] and N-trimethylsilylaniline, while trans-mer-trichlorophenylnitrenebis (triphenylphosphine) rhenium(V), [Re(NPh)Cl3 (Ph3P)2] has been obtained via a novel route, from (Bu4N)[ReOCl4 ] and N-trimethylsilylanilin. The products were studied by mass spectrometry, IR spectroscopy and X-ray diffraction.trans-mer-[Re(NPh)Cl3(Et2PhP)2 ] crystallizes in the monoclinic space group P21/n with a = 1498.5(3), b = 1068.6(1), c = 1784.0(4) pm and β = 91.28(1)°, Z = 4. The rhenium atom exhibits a distorted octahedral coordination with the phosphine groups in trans positions, and the Cl ligands in a meridional arrangement. The Re ≡N -C moiety is linear with a bond angle o f 169,4(5)°and a Re= N bond length o f 171.8(6) pm.[Re(NPh)Cl3(Ph3P)2 ]· 0.5 CHCI3 crystallizes in the triclinic space group P 1̄ with a = 1232.1 (4), b= 1431.6(5), c = 2236.6(8) pm, a = 89.19(2)°, β = 80.50(2)°and γ = 88.26(2)°, Z = 4. The asymmetric unit contains two symmetry independent complex molecules of approximately the same structure, with Cl atoms meridionally arranged and the phosphine groups in trans positions. The coordination geometry is a distorted octahedron. The almost linear Re≡N -C moieties have Re≡N bond lengths of 170.2(7) and 170.8(7) pm, respectively, and Re≡N -C angles of 173.3(6)°and 175.0(7)°.

Thiocarbonyl Complexes of Rhenium. Part I.

Novel rhenium complexes with terminal thiocarbonyl groups have been synthesized from ReCl3(Me2PhP)3 and sodium diethyldithiocarbamate. mer-(Diethyldithiocarbamato)tris-(dimethylphenylphosphine)(thiocarbonyl)rhenium(I), mer-[Re(CS)(Me2PhP)3(Et2dtc)], and tris(diethyldithiocarbamato)(thiocarbonyl)rhenium(III), [Re(CS)(Et2dtc)3] have been studied by infrared and NMR spectroscopy, mass spectrometry and X-ray diffraction.mer-[Re(CS)(Me2PhP)3(Et2dtc)] crystallizes orthorhombic in the space group Pna21 with a = 1516.1(2), b = 2189.8(2) and c = 1035.6(1) pm. Structure solution and refinement converged at R = 0.042. The coordination geometry is a distorted octahedron. The Re—C bond length is found to be 184(2) pm.[Re(CS)(Et2dtc)3] crystallizes monoclinic in the space group P21/c with a = 962.2(6), b = 1744.0(2), c = 1537.4(6) pm and β = 96.21(1)°. The final R value is 0.028. In the monomeric complex the rhenium atom is seven-coordinate with an approximate pentagonal-bipyramidal coordination sphere and a rhenium-carbon distance of 181(1) pm.

Reaktionen von Oxo-Rhenium(VII und V)-Verbindungen mit Thiobenzoylhydrazin. Kristall- und Molekülstrukturen von Re(NHNC(S)Ph)3 · DMF, Re(NHNC(S)Ph)3 · OPPh3 und [Re(NHNC(S)Ph)(NHNHC(S)Ph)2]Cl · 1/3 C2H5OH · 1/3 H2O / Reactions of Oxorhenium(VII and V) Complexes with Thiobenzoylhydrazine. Crystal and Molecular Structures of Re(NHNC(S)Ph)3 · DMF, Re(NHNC(S)Ph)3 · OPPh3 and [Re(NHNC(S)Ph)(NHNHC(S)Ph)2]Cl · 1/3 C2H5OH · 1/3 H2O

The reaction of NaReO4 with thiobenzoylhydrazine yields Re(NHNC(S)Ph)3- DMF (1). With ReOCl3(PPh3)2 thiobenzoylhydrazine reacts to give Re(NHNC(S)Ph)3 · OPPh3 (2) and in the presence of HCl to yield [Re(NHNC(S)Ph)(NHNHC(S)Ph),]Cl · 1/3 C2H5OH -1 /3 H2O (3). The structures of 1-3 have been determined. 1: monoclinic, space group P2,/c, a = 1150.1(9), b = 2050.0(9), c = 1181.0(8) pm, β = 109.62(5)°, Z = 4, 2980 reflections, R = 0.055; 2: trigonal, space group R 3, a = 1399.8(1), c = 1684.0(1) pm, Z = 3, 1419 reflections, R = 0.033; 3: monoclinic, space group P2,/c, a = 1446.8(3), b = 3220.7(5), c = 1727.1(4) pm, β = 108.42(2)°, Z = 12, 6112 reflections, R = 0.062. In 1 and 2 three N,S-chelating ligands NHNR (R = C(S)Ph) are coordinated to the central rhenium atom. The ligand structure is intermediate between a diazene and a hydrazido(2–) structure. In 3 each rhenium atom is coordinated by one NHNR and two NHNHR ligands, all N,S-chelating. The latter can be considered as protonated diazene ligands. The unit cell contains three isomeric coordination polyhedra.