Rhenium(V) Complexes with Bidentate N,O-Donor Imidazole Derivatives

The reaction of a two-fold molar excess of the potential N,O-donor ligand 2-(hydroxymethyl)-1-methylimidazole (Hmi) with trans-[ReOCl₃(PPh₃)₂] led to the isolation of cis-[ReOCl₂(mi)(PPh₃)]. An X-ray structure determination indicated that the complex has distorted octahedral geometry, and that mi coordinates as a bidentate with the alcoholate oxygen trans to the oxo group. A similar reaction with 2-(1-ethyloxomethyl)-1-methylimidazole (eomi), the ethyl substituted analogue of Hmi, led to the formation of the oxo-bridged dinuclear complex [(μ-O){ReOCl₂(eomi)₂}₂]. The ligand eomi coordinates as a monodentate via the imidazole nitrogen, with the "hard" ether oxygen uncoordinated. An X-ray crystal structure indicates that the chlorides are trans to each other in the ReN₂Cl₂ planes, which are orthogonal to the O=Re-O-Re=O backbone.     

Monodentate imido and bidentate aminophenolate coordination of 2-aminophenol in rhenium(V) complexes

Reactions of trans-[ReOCl₃(PPh₃)₂] and trans-[ReO(OEt)I₂(PPh₃)₂] with 2-aminophenol (H₂ap) in acetonitrile led to the formation of cis-[ReOCl₂(Hap)(PPh₃)] (1) and trans-[Re(ap)(Hap)I(PPh₃)₂]I (2), respectively. The X-ray crystal structures show that Hap is coordinated as a bidentate chelate via the neutral amino nitrogen and deprotonated phenolate oxygen, and ap is coordinated as a monodentate through the imido nitrogen. The complexes have been characterized by IR spectroscopy, NMR spectrometry and X-ray crystallography. The bite angle of the Hap chelate is 76.9(1)° and 76.0(1)° in 1 and 2, respectively.     

Complexes of Oxorhenium(V) with Aromatic 2-Amino-Alcohols

Monooxo complexes of rhenium(V) with 2-aminophenol and some of its derivatives (H₂nod), containing the N,O donor-atom set, have been synthesized. Square-pyramidal complexes [ReO(nod)₂]^? were isolated by reaction with (n-Bu₄N) [ReOCl₄] in ethanol. In benzene the neutral species [ReOCL(Hnod)₂] were obtained. In the presence of hydrochloric acid in ethanol, the anionic complexes (n-Bu₄N) [ReOCl₃(Hnod)] were produced. Trans-[ReOCl₃(PPh₃)₂] was also reacted with some of the H₂nod ligands to yield [ReOCL₂(Hnod)(PPh₃]. The crystal structure of [ReOCl₂(Hmap)(PPh₃)] (H₂map = 2-aminobenzylalcohol) was determined; crystals are monoclinic, P2₁/n, with a = 15.065(6), b = 11.253(7), c = 15.850(7) Å, β = 94.27(4)°, U = 2680(2) &Aringsup3; and Z = 4. The structure was solved by the Patterson method and refined by full-matrix least-squares techniques to R = 0.042. The monoanionic Hmap^? ligand is coordinated as a bidentate through a neutral amino nitrogen and an anionic alcoholate oxygen atom, with the latter trans to the oxo group.     

A trigonal-bipyramidal oxorhenium(V) complex with a bidentate nitrogen-donor ligand

The oxorhenium(V) complex [ReO(Hapb)(apb)] (1) (H₂apb =?2-(2-aminophenyl)-1-benzimidazole) was prepared by reaction of trans-[ReO₂(py)₄]Cl with a twofold molar amount of H₂apb. The complex was characterized by spectroscopy and X-ray crystallography. The results show that the rhenium atom lies in a distorted trigonal-bipyramidal environment, with the two imidazole nitrogen atoms in apical positions, and the oxo and two amido nitrogens in the trigonal plane.     

Oxorhenium(V) Complexes with Thiosemicarbazones

Neutral oxorhenium(V) complexes with thiosemicarbazones derived from 2‐pyridine formamide, HL¹, are formed when [ReOCl₃(PPh₃)₂] reacts with equimolar amounts of the ligands. Reduction of the metal and the formation of rhenium(III) complexes of the composition [Re(L¹)₂]⁺ occurs when an excess of thiosemicarbazones is used and the reaction is performed in boiling toluene for a prolonged period of time. The thiosemicarbazones deprotonate and act as tridentate ligands as has been confirmed by an X‐ray structure of [ReOCl₂(L^1b)], where HL^1b is 2‐pyridineformamide‐N(4)‐ethylthiosemicarbazone and the ligand occupies the equatorial coordination sphere of the complex together with one of the chloro ligands.     

Technetium(V) complexes of dithiocarbazate derivatives

The neutral complex [TcOCl(hdc)] (1) (hdc?=?S-methyl-β-N-(2-hydroxyphenylethylidene)dithiocarbazate) was prepared by reaction of (n-Bu₄N)[TcOCl₄] with an equimolar amount of H₂hdc in ethanol/dichloromethane at room temperature. With a fourfold mol excess of H₂hdc in methanol/acetone, the ‘3?+?2’ complex [TcO(hdc)(adc)] (2) (adc?=?S-methyl-β-N-(prop-2-ylidene)dithiocarbazate) was isolated. Adc was formed by ketone exchange between solvent acetone and the hydroxyacetophenone fragment of hdc. Compounds 1 and 2 were characterized by infrared spectroscopy, ¹H NMR spectrometry, elemental analysis and single-crystal X-ray crystallography. Complex 1 has square-pyramidal geometry with the SNO-donor atoms of the tridentate chelate hdc and chloride forming a square plane, with the oxo oxygen atom in the apical position. Complex 2 has a distorted octahedral geometry, with an S₂N₂ donor set in the equatorial plane and the oxo and phenolate oxygen atoms in trans apical positions.     

Synthesis and Structural Characterization of Dinuclear Oxorhenium(V) Complexes with Bidentate Imidazole Derivatives

The oxo-bridged dinuclear complexes [(μ-O){ReOCl₂(L)}₂] [L = 2-(1-ethylaminomethyl)-1-methylimidazole (eami); 2-(1-methylaminomethyl)-1-methylimidazole (mami); 2-(1-ethylthiomethyl)-1-methylimidazole (etmi)] were prepared by reaction of trans-[ReOCl₃(PPh₃)₂] with L in acetone. X-ray crystallographic studies of the eami and etmi complexes show that these ligands coordinate in a bidentate manner, and that the cis, cis-N₂Cl₂ and cis, cis-NSCl₂ equatorial planes are nearly orthogonal to the O=Re-O-Re=O backbone.     

Monodentate imido coordination of 2-aminodiphenylamine to rhenium(V)

The complex trans-[Re(ada)Cl₃(PPh₃)₂] (H₂ada?=?2-aminodiphenylamine) was prepared from the reaction of trans-[ReOCl₃(PPh₃)₂] with H₂ada in acetonitrile. The ligand ada is coordinated to the rhenium(V) centre solely through a dianionic imido nitrogen, with distorted octahedral coordination geometry around the metal ion. Surprisingly, the Re–Cl bond trans to the Re=N bond is shorter than the two equatorial Re–Cl bonds. The Re?=?N–C bond angle of the phenylimido moiety equals 178.7(4)°.     

Monodentate imido coordination of 1,2-diaminobenzene to rhenium(V)

The complex trans-[Re(dab)Cl₃(PPh₃)₂] (H₂dab?=?1,2-diaminobenzene) was prepared from the reaction of trans-[ReOCl₃(PPh₃)₂] with H₂dab in ethanol. The ligand dab is coordinated to the rhenium(V) centre only through a dianionic imido nitrogen to give a distorted octahedral coordination geometry around the metal ion.     

Imido,amino and amido coordination of diaminouracil to rhenium(V)

Reaction of equimolar quantities of cis-[ReO₂I(PPh₃)₂] with 5,6-diamino-1,3-dimethyl-2,4-dioxopyrimidine (H₂ddd) in acetonitrile led to the formation of [Re(ddd)(Hddd)I(PPh₃)₂] (ReO₄) (1). A single-crystal X-ray crystal structure shows that ddd is coordinated as a monodentate through the doubly deprotonated amino nitrogen and is therefore present as an imide. The chelate Hddd is coordinated as a bidentate via a neutral amino nitrogen atom, trans to the imido nitrogen, and a singly deprotonated amido nitrogen atom, trans to the iodide.     

NUCLEOPHILIC ADDITION OF WATER AND ETHANOL TO COORDINATED DI-(2-PYRIDYL)KETONE IN RHENIUM(V) AND TECHNETIUM(V) COMPLEXES. THE CRYSTAL STRUCTURE OF DICHLORO(HYDROXY-DI-(2-PYRIDYL)METHOXIDE)OXORHENIUM(V)

Abstract

Complexes of general formula MOCl₂[(C₅H₄N)₂C(O)(OR)] (M = Re, Tc; R = H, Et) were prepared by the reaction of trans-ReOCl₃(PPh₃)₂ and (n-Bu₄N)[TcOCl₄] with di-(2-pyridyl)ketone (DPK) in ethanol (R = Et) under nitrogen and in benzene, containing trace amounts of water, in air (R = H). The compounds were characterized by elemental analysis, vibrational, optical and proton nuclear magnetic resonance spectroscopy. The evidence suggests that the coordinated DPK ligand has undergone addition of water and ethanol at the carbonylic carbon atom, and that the (C₅H₄N)₂C(o)(OR) moiety acts as a uninegative, terdentate N,O,N-donor ligand. The X-ray crystal structure of the complex ReOCl₂[(C₅H₄N)₂C(O)(OH)] is also reported. Crystal data: C₁₁H₉N₂O₃Cl₂Re, orthorhombic, space group Pcca; a = 14.935(5), b = 11.896(8), c = 14.937(11)Å, and U = 2653.8 (2.7)ų to give Z = 8 for D _calc = 2.37 g cm_?3. The structure was solved by Patterson and Fourier methods and refined by least-squares methods to R = 0.076. The complex has an Re = O bond distance of 1.67(2)Å, and a deprotonated diolate oxygen of the ligand is coordinated in the position trans to the oxo group.     

Formation of an oxo-free rhenium(v) complex with 2-aminothiophenol

The reaction of a twofold molar excess of 2-aminothiophenol (H₂L) with trans-[ReOCl₃(PPh₃)₂] in benzene led to the isolation of the oxo-free rhenium(V) complex [ReCl(PPh₃)L₂] (1). IR, ¹H NMR and X-ray crystallographic results indicate that the ligands L coordinate in a dianionic amidothiolate form to the metal and that the complex has the unusual skew-trapezoidal bipyramidal geometry. The ligands L have an average bite angle of 78.8(1)°, with average Re–N and Re–S bond lengths equal to 1.978(5) and 2.297(1)?Å, respectively.     

Synthesis and characterization of a neutral rhenium(V) complex containing a tridentate chelate with an imido donor atom

The six-coordinate complex cis-[Re(mps)Cl₂(PPh₃)] (1) (H₃mps?=?N-(2-amino-3-methylphenyl)-salicylideneimine) was prepared the reaction of trans-[ReOCl₃(PPh₃)₂] with a twofold molar excess of H₃mps in benzene. The compound was characterized by spectroscopy and single-crystal X-ray crystallography. Mps coordinates as a tridentate chelate via the doubly deprotonated 2-amino nitrogen (which is present in 1 as an imide), the neutral imino nitrogen and the phenolate oxygen atoms. The imide and phenolate oxygen atoms coordinate trans to each other in a distorted octahedral geometry around the rhenium(V) centre, with the two chlorides in cis positions.     

Coordination of a tridentate imido-amino-phenolate chelate to rhenium(V)

The complex cis-[Re(apa)Cl₂(PPh₃)] (1) (H₃apa?=?N-(2-aminophenyl)salicylideneamine) was prepared by reaction of trans-[ReOCl₃(PPh₃)₂] with H₃apa in ethanol. Apa acts as a tridentate chelate ligand via the doubly deprotonated amino nitrogen (which is coordinated as an imide), the amino nitrogen and the deprotonated phenolic oxygen atoms. The two chlorides lie cis to each other in a distorted octahedral geometry around the rhenium(V) centre.     

2,2′-dipyridylamine complexes of rhenium(V)

The reactivity of oxorhenium(V) precursors with the potentially N,N-donor ligand 2,2′-dipyridylamine (dpa) has been investigated. Reaction of a two-fold molar excess of dpa with trans-[ReO(OEt)Cl₂(PPh₃)₂] in ethanol led to the isolation of [ReOCl₂(OEt)(dpa)] (1). Spectroscopic measurements indicate that dpa is coordinated as a bidentate in the equatorial plane cis to the oxo group, with the ethoxide in the trans position. Treatment of trans-[ReOCl₃(PPh₃)₂] with a tenfold molar excess of dpa in ethanol at reflux yielded the trans-dioxo complex [ReO₂(dpa)₂]Cl (2), but with a twofold molar excess (μ-O)[{ReOCl₂(dpa)}₂] (3a) was isolated. The latter reaction with (n-Bu₄N)[ReOCl₄] as starting material in ethanol at room temperature led to a dark green product, also with the formulation (μ-O)[{ReOCl₂(dpa)}₂] (3b). These compounds were characterised by common spectroscopic techniques, and the crystal structures of 2·3H₂O, 3a and 3b·2DMSO were determined. The structure of 3b presents a nearly linear O=Re–O–Re=O group, with the two [ReOCl₂(dpa)] halves of the dimer rotated by 180.0° about the Re–O–Re fragment away from an eclipsed conformation. In 3a, the two halves are only rotated by 61.4°.     

Synthese und Struktur von [(Me2PhP)3Cl2ReN]2ReCl4, [(Me2PhP)3Cl2ReN]2ReCl4 · 2 SbCl3 und [Re(NH)Cl2(PMe2Ph)3][SbCl6]

Synthesis and Structure of [(Me₂PhP)₃Cl₂ReN]₂ReCl₄, [(Me₂PhP)₃Cl₂ReN]₂ReCl₄ · 2 SbCl₃ and [Re(NH)Cl₂(PMe₂Ph)₃][SbCl₆] The reaction of ReNCl₂(PMePh)₃ with SbCl₅ in toluene yields the trinuclear complex [(Me₂PhP)₃Cl₂Re≡N]₂ReCl₄ · 2 SbCl₃ ( 1 · 2 SbCl₃). It forms triclinic crystals with the composition 1 · 2 SbCl₃, as well as monoclinic crystals 1 · 2 SbCl₃ · 4 C₇H₈. The monoclinic crystals with the space group P2₁/c, and a = 1212.3(2), b = 2098.5(4), c = 1827.7(3) pm, β = 95.51(1)°, Z = 2, have been used for a crystal structure determination. In the centrosymmetric complex 1 two complexes ReNCl₂(PMe₂Ph)₃ coordinate with their nitrido ligands a square planar, central unit ReCl₄. The SbCl₃ molecules are coordinated by chlorine bridges to Cl atoms of 1 , and, in addition, connect the complexes 1 with each other. The SbCl₃ free compound 1 is obtained in good yield by the reaction of ReNCl₂(PMePh)₃ with ReCl₄(NCEt)₂. It crystallizes in the triclinic space group P1 with a = 1037.7(3), b = 1153.0(2), c = 1393.8(3) pm, α = 72.31(2)°, β = 74.06(2)°, γ = 67.94(2)°, and Z = 1. The bond lengths of the Re–N triple bonds are 172 pm in 1 and 170 pm in 1 · 2 SbCl₃. By the reaction of ReNCl₂(PMePh)₃ with SbCl₅ in CH₂Cl₂ the solvent is decomposed forming HCl which protonates the nitrido ligand to afford the imido complex [Re(NH)Cl₂(PMe₂Ph)₃][SbCl₆] ( 2 ) crystallizing in the monoclinic space group P2₁/n with a = 1221.4(2), b = 1358.6(2), c = 2177.3(1) pm, β = 92,72(1)° and Z = 4. The Re–N distance in the almost linear unit Re≡N–H is 169,1 pm.     

Nucleophilic addition of water to coordinated dipyridylethylene in rhenium(V) complexes

Complexes of general formula [ReOX₂{(C₅H₄N)CH(O)CH₂(C₅H₄N)}] (X?=?Cl,?I) were prepared by reaction of trans-[ReOCl₃(PPh₃)₂] and trans-[ReOI₂(OEt)(PPh₃)₂] with cis-1,2-di-(2-pyridyl)ethylene (DPE) in ethanol and benzene in air. The coordinated DPE ligand undergoes addition of water at the ethylenic carbon atoms, and the (C₅H₄N)CH(O)CH₂(C₅H₄N) moiety acts as a uninegative terdentate N,O,N-donor ligand. X-ray crystal structures of both complexes have been determined and show distorted octahedral geometry at the rhenium(V) centre.     

Synthesis,characterization, and crystal structures of cobalt(II), copper(II), and zinc(II) complexes of a bidentate iminophenol

A bidentate iminophenol (HL = 2-((4-methoxyphenylimino)methyl)-4,6-di-tert-butylphenol derived from condensation of 4-methoxyaniline and 3,5-di-tert-butyl-2-hydroxybenzaldehyde) was mixed with divalent metal salts to form the corresponding mononuclear metal complexes [M^II(L)₂] (M = Co (1), Cu (2), and Zn (3)). The complexes are characterized by different spectroscopic and analytical tools. X-ray crystal structures of the complexes revealed homoleptic mononuclear complexes with MN₂O₂ coordination. The cobalt(II) (1) and zinc(II) (3) complexes display a pseudo-tetrahedral coordination geometry, whereas the copper(II) complex (2) exhibits a distorted square-planar coordination. The zinc(II) complex (3) emits at 460 nm with a twofold enhancement of emission with respect to the free iminophenol.     

Syntheses and Structures of Tris-(1,2-Benzosemiquinone DIimine) Complexes of Rhenium(IV)

Reactions of trans-[ReO₂(py)₄Cl] and cis-[ReO₂I(PPh₃)₂] with 2,3-diaminophenol (H₂dab-OH) and 1,2-diaminobenzene (H₂dab), respectively, in ethanol under aerobic conditions led to the corresponding isolation of [Re(sbqdi-OH)₃]Cl (1) and [Re(sbqdi)₃]I (2). Crystallographic data show that the ligand sbqdi represents the monoanionic N,N-coordinated π-radical form of the 1,2-benzosemiquinone diimine of H₂dab. The ligands in Complex 1 clearly show semiquinoid character; e.g., the two C-N and two Re-N bondlengths differ considerably. In 2, the phenyl rings display typical quinoid distortions with two localized double bonds, and the C-N bondlengths are short, approaching double bonds. Rhenium is formally in the +IV oxidation state.