Oxidative homolysis of organochromium(III) macrocyclic complexes

Summary Organochromium complexes, [CrRL(H₂O)]²⁺] (L = 1,4,8,12-tetraazacyclopentadecane; R = 1°- or 2°-alkyl, or para-substituted benzyl), are oxidized to [CrRL(H₂O)]³⁺, which rapidly decomposes (k ₃ > 10² s^–1) by homolysis of the Cr-C bond. Rate constants of the oxidation of these complexes by [IrCl₆]^2– range from 2.20 × 10^–1 (R = Me) to 4.60 × 10⁵ (R = 4-MeC₆H₄CH₂)dm³ mol^–1 s^–1. A very negative reaction constant (–4.3) is found for the oxidation of para-substituted benzlchromium(III) complexes which, in conjunction with the results of product analysis, indicates a [Cr^III/R^.] type transition state.     

Rhodium(III) and palladium(II) complexes of some P-heterocycles; synthesis and X-ray structures

Deoxygenation of the syn-3-phosphabicyclo[3.1.0]hexane 3-oxides bearing a 3-phenyl or a 3-(4-methylphenyl) substituent (1a,b) by trichlorosilane took place already at mild condition and resulted in the corresponding phosphines (2a,b) with retention of configuration at phosphorus, while in the case of 3-(2-methylphenyl)-3-phosphabicyclo[3.1.0]hexane (2c), the inversion of the phosphorus atom was observed in solution under ambient conditions that was evaluated by quantum chemical calculations. A further phosphine ligand (5) was obtained by the reduction of 4-dichloromethylene-1,4-dihydrophosphinine oxide (4). The phosphine ligands (2 and 5) were used in the preparation of Rh(III) complexes (3 and 6). A Pd(II) complex of type PdCl₂(5)₂ (7) was also prepared. The stereostructures of a series of Rh(III) complexes of 3-aryl-3-phosphabicyclo[3.1.0]hexanes (3b-syn, 3c-syn and 3c-anti) were elucidated by single crystal X-ray analysis confirming the relative position of the dichlorocyclopropane and the P-substituent.     

Photolysis in aprotic solvents of some alkylcobalt(III) complexes; an ESR and spin-trapping technique study

Photolysis of several alkylcobalt(III) complexes in the visible region λ > 420 nm has been studied by ESR and spin-trapping techniques with nitrosuderene, phenyl-t-butylnitrone (PBN) and 5,5′-dimethylpyrroline-N-oxide (DMPO) and their mixtures. DMPO and PBN give spin adducts of two different radicals; the first is a hydrogen atom coming from the equatorial ligand, and the second is an alkyl-free radical coming from the axial position of the cobalt(III) complexes. This indicates that excitation of the complex is followed by the expulsion of one hydrogen atom and homolytic cleavage of the metalalkyl bond.     

Preparation and structures of some tetraazamacrocyclic complexes of In(III)

Treatment of the dibenzo-tetraaza macrocycle, C₂₂H₂₄N₄ (H₂tmtaa) (I), with triethylindium yields the diethylindium-macrocycle complex [Et₂In(Htmtaa)] (IV). On heating (IV) is converted quantitatively into the monoethyl complex [EtIn(tmtaa)] (V). A single crystal X-ray diffraction study on (V) shows the EtIn fragment to be bonded to the four planar nitrogen atoms of the macrocycle, with a square–pyramidal geometry around the metal. Reaction of the dilithio salt of (I), [Li₂(tmtaa)], with InCl₃ yields [ClIn(tmtaa)] (VI), and further reaction of (VI) with equimolar quantities of LiR [R=C₅H₅(Cp), Me, N(SiMe₃)₂, OSiMe₃] yields the corresponding [RIn(tmtaa)] derivatives [R=Cp (VII), Me (VIII), N(SiMe₃)₂ (IX), OSiMe₃ (X)]. An X-ray diffraction study on (VII) shows an η¹-bonded Cp group, with the metal atom also bound to the four nitrogen atoms of the tmtaa ligand.     

Synthesis and X-ray crystal structures of two cobalt(III) complexes with Schiff bases

Two new mononuclear cobalt(III) complexes, [Co(MP)₂(N₃)] (I) and [Co(BP)₂]NO₃ · 2H₂O (II), where MP is 2-methoxy-6-[(2-morpholin-4-ylethylimino)methyl]phenolate and BP is 4-bromo-2-[(2-methylaminoethylimino)methyl]phenolate, were prepared and structurally characterized by physicochemical methods and single crystal X-ray diffraction. Both complexes crystallize in the monoclinic space group P2₁/c. For I: a = 10.3526(18), b = 25.371(4), c = 11.3585(19) Å, β = 101.529(8)°, V = 2923.1(8) ų, Z = 4; for II: a = 9.801(2), b = 27.183(3), c = 10.846(2) Å, β = 114.269(2)°, V = 2634.2(8) ų, Z = 4. An X-ray structural analysis indicates that in both complexes the Co atoms adopt octahedral coordination. The hindrance effects of the Schiff bases can influence the coordination of the secondary ligands such as azide.     

Synthesis and X-ray crystal structures of some isothiosemicarbazone complexes

Transition Metal Chemistry - Four complexes of a new isothiosemicarbazone ligand have been prepared and characterized as μ2-pip-(NiL)2 (1), MnL2 (2), UO2L(BrSal)BuOH (3) and (μ2-MoO2L)2...     

Syntheses and X-ray structures of some pyrrolylaldiminate metal complexes

Several pyrrolylaldiminate complexes of Group 1, 4 and 13 metals are reported. The reaction of 5-tert-butyl-2-[(2,6-diisopropylphenyl)aldimino]pyrrole (HL) with NaH produced LNa(THF) (1). In situ lithiation of HL followed by addition of one equivalent of MCl_x (M=Zr, x=4; M=Hf, x=4, M=Al, x=3) afforded the corresponding pyrrolylaldiminate complexes, MLCl₂(μ-Cl)₂Li(OEt₂)₂ (M=Zr, 3; Hf, 4) and AlLCl₂ (5). Alkylation of 5 with MeMgBr generated AlLMe₂ (6). In addition to the spectroscopic data, complexes 3-6 were characterized by X-ray crystallography.     

Crystal structures of some lanthanide(III) complexes with acylhydrazone and their coordination chemistry

Three new lanthanide(III) complexes with N-(2-propionic acid)-salicyloylhydrazone (H₂L, C₁₀H₁₀N₂O₄) ligand [La(HL)₂(NO₃)(H₂O)₂]₃ ·4H₂O(I), [Gd(HL)₃] · 2(C₂H₅)₃ N(II) and [Er(L)(HL)(H₂O)₂] · 2H₂O(III) has been synthesized and characterized by elemental analyses, IR, UV, and molar conductivity. The crystal structures of three complexes have been determined by X-ray single-crystal diffractometer. In complex I, the La³⁺ ion is ten-coordinated by two tridentate ligands, one bidentate nitrate, and two water molecules. In complex II, the Gd³⁺ ion has a coordination number of nine by three tridentate ligands. In complex III, the Er³⁺ ion is eight-coordinated by two tridentate ligands and two water molecules. In all structures, tridentate ligands are coordinated by carboxyl O and acyl O atoms and azomethine N atom to form two stable five-membered rings sharing one side in the keto mode as indicated by the results of crystal structures and infrared spectral analysis.     

Mixed-ligand complexes of Ru(III) and Rh(III): ESR studies on some Ru(III) complexes

Reactions of 2-mercapto-3-phenyl-4-quinazolinone (LH) with RuCl₃·xH₂O and RhCl₃·xH₂O afforded the compounds [RuL₂Cl(H₂O)]H₂O, [RuL₂Cl·DMFI and RhL(LH)Cl₂·2H₂O. Reactions of LH with RuCl₃·xH₂O in the presence of N-heterocyclic bases led to the formation of complexes of type [RuL₂ClB]·H₂O (B = pyridine, 3-picoline or imidazole) and [RuLCl₂(o-phen)] H₂O (o-phen = 1, 10-phenanthroline). These complexes were characterized on the basis of analytical, conductivity, magnetic, IR and electronic spectral and ESR studies. Tentative structures for the complexes are proposed.     

Cis-influence of hydroporphyrin macrocycles on axial ligation equilibria and alkyl exchange reactions of alkylcobalt(III) porphyrin complexes

Stability constants are reported for the coordination of pyridine and substituted pyridines to the alkylcobalt(III) complexes of octaethylporphyrin (OEP), t-octaethylchlorin (OEC), and ttt-octaethylisobacteriochlorin (OEiBC) in toluene solution. The stability constants correlate with the base strength of the nitrogenous ligand. A cis-influence of the macrocycle saturation level on the stability constants is observed. Stability constants for coordination of a given pyridine ligand to an alkylcobalt(III) complex are roughly 10 times smaller than the stability constants for the corresponding cobalt(II) complex. Analysis of a thermodynamic cycle demonstrates that this leads to decreased stability of the complex with respect to Co-C bond homolysis upon ligand coordination, a "base-on" effect. Alkyl exchange occurs between cobalt complexes of different tetrapyrroles. Equilibrium data establish that the exchange is nonstatistical and that the Co-C bond is stabilized by increasing the saturation of the tetrapyrrole macrocycle.     

Dealkylation of alkylcobalt complexes by the mercury(II) electrophile

The dealkylation of a variety of RCo(BDMBg)⁺ complexes by Hg²⁺ is discussed. (The ligand BDMBg^- is formed by the condensation of two moles of 2,3-butanedionemonoxime with one mole of 1,3-propanediamine or 1,2-ethanediamine.) The products of the dealkylation reaction are Co^III(BDMBg)(H₂O)²⁺₂ and RHg⁺. All reactions are first order in the [Hg²⁺]. The second order rate constants (k₂) vary from 5.9 M^-1 sec^-1 (R = CH₃) to 5.7 x 10^-3M^-1 sec^-1 (R = n-C₃H₇). The relative rates for R are: CH₃ ? C₂H₅ τ C₆H₅CH₂ τ n-C₄H₉ ? n-C₃H₇. This order and other evidence are indicative of an S_E2 mechanism with an attack by Hg²⁺ on the carbon bonded to the cobalt.     

EPR spectra and structures of spin-variable iron(III) complexes

The structures of the spin-variable iron(III) complexes Fe(4-OCH₃-SalEen)₂X and FeL′₂X (L′ is oxysalicylidene-N′-ethyl-N-ethylenediamine; X = PF₆, NO₃, and SCN) were examined from their EPR spectra. The coordination units (CUs) of these complexes are a high-symmetry octahedron with a slight tetrahedral distortion or a low-symmetry pseudooctahedron with considerable tetragonal and orthorhombic distortions. When the complex passes from the high-spin to low-spin state, its CU changes. The energy level splittings caused by various types of distortions were estimated from the EPR data. The distortion of the CU depends on the outer-sphere anion. The magnetic resonance parameters of the complexes were analyzed. The fine structure parameters of the EPR spectra of high-spin complexes (the ground-state term is $^6 A_{1_g }$ ) depend on the CU distortion and the covalent bonding. The spin-orbital coupling makes an appreciable second-order contribution to the expressions for the Zeeman coupling parameters of low-spin complexes (the ground-state term is $^2 T_{2_g }$ ).     

Influence of the nature of an organic solvent on the kinetic parameters of the thermal homolysis of five-coordinate complexes of alkylcobalt

By the spectrophotometric method in solvents of different natures a study was made of the kinetics of the homolytic breakage of the axial cobalt-carbon bond in five-coordinate complexes with dianionic tetradentate equatorial ligands. The negative values obtained for the activation entropies of the processes investigated are explained by the existence of interaction between the components of the primary radical pair and the solvent molecules. The kinetic parameters of the redox-interaction reactions of some macrocyclic complexes of cobalt(II) with chloroform and carbon tetrachloride were determined. A scheme in which the autocatalytic homolysis of the Co-CH ₃ bond in the presence of chlorine-containing solvents is proposed.L. V. Pisarzhevskii Institute of Physical Chemistry, Ukrainian Academy of Sciences, Kiev 252028. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 838–844, April, 1992.     

Synthesis, characterisation and X-ray structures of diorganotin(IV) and iron(III) complexes of dianionic terdentate Schiff base ligands

Diorganotin(IV) complexes, [SnR₂L] (1)-(4), (R = Me, Ph), of the terdentate Schiff bases N-[(2-pyrroyl)methylidene]-N′-tosylbenzene-1,2-diamine (H₂L¹) and N-[(2-hydroxyphenyl)metylidene]-N′-tosylbenzene-1,2-diamine (H₂L²) have been synthesised. The complexes were obtained by addition of the appropriate ligand to a methanol suspension of the corresponding diorganotin(IV) dichloride in the presence of triethylamine. However, the reaction between the precursor [η⁵-C₅H₅Fe(CO)₂]₂SnCl₂ and the Schiff bases in the presence of triethylamine gave (5) and (6), respectively. The crystal structures of the ligands and complexes have been studied by X-ray diffraction. The structure of [SnR₂L] complexes shows the tin to be five-coordinate in a distorted square pyramidal environment with the dianionic ligand acting in a terdentate manner. In 5 and 6, the iron atom is in a slightly distorted octahedral environment and is meridionally coordinated by two ligands. Spectroscopic data for the ligands and complexes (IR, ¹H, ¹³C and ¹¹⁹Sn NMR and mass spectra) are discussed and related to the structural information.     

The development of highly selective approaches to sandwich-type heteroleptic double- and triple-decker lutetium(III) and europium(III) phthalocyanine complexes

The selective synthesis of heteroleptic (heteronuclear) sandwich-type lanthanide phthalocyanines has been accomplished. Double-decker complexes ^BuPcLnPc, and ^BuPcLnPc^Cl (Ln = Lu, Eu; ^BuPc = 2,3,9,10,16,17,23,24-octabutylphthalocyaninate; Pc = phthalocyaninate, ^ClPc = 2,3,9,10,16,17,23,24-octachlorophthalocyaninate) were obtained in good yields by a direct interaction of metal-free ligand ^BuPcH₂ with the monophthalocyanines PcLnOAc or ^ClPcLnOAc. Heteronuclear triple-decker phthalocyanines PcEu^RPcLu^RPc, ^ClPcEu^RPcLu^RPc and ^BuPcEu^RPcLu^RPc (^RPc = ^BuPc, ^tBuPc; ^tBuPc = 2(3),9(10),16(17),23(24)-tetra-tert-butylphthalocyaninate) were obtained from the corresponding mono-(PcEuOAc, ^ClPcEuOAc, ^BuPcEuOAc) and bisphthalocyanines (^RPc₂Lu) under similar conditions.     

Syntheses and structures of lanthanide(III) complexes with some bis(pyrazolyl)borate and tris(pyrazolyl)borate podand ligands

Two new poly(pyrazolyl)borate ligands have been prepared: potassium tris[3-{(4-^tbutyl)-pyrid-2-yl}-pyrazol-1-yl]hydroborate (KTp^BuPy) which has three bidentate arms and is therefore hexadentate; and potassium bis[3-(2-pyridyl)-5-(methoxymethyl)pyrazol-1-yl]-dihydroborate (KBp^(COC)Py) which has two bidentate arms and is therefore tetradentate. The crystal structures of their lanthanide complexes [La(Tp^BuPy)(NO₃)₂] and [La(Bp^(COC)Py)₂X] (X=nitrate or triflate) have been determined. In [La(Tp^BuPy)(NO₃)₂] the metal ion is ten-coordinate, from the hexadentate N-donor podand ligand and two bidentate nitrates. [La(Bp^(COC)Py)₂(NO₃)] is also ten-coordinate, from two tetradentate ligands and a bidentate nitrate, but in [La(Bp^(COC)Py)₂(CF₃SO₃)] the metal ion is nine-coordinate because the triflate anion is monodentate. Two unexpected new complexes which arose from partial decomposition of the poly(pyrazolyl)borate ligands have also been characterised structurally. In [La(^BuPypzH)₃(O₃SCF₃)₃] the metal ion is nine-coordinate from three bidentate pyrazolyl-pyridine arms (liberated by decomposition of KTp^BuPy) and three triflate anions; there is extensive NH· · · O hydrogen-bonding between the pyrazolyl and triflate ligands. [Nd(Tp^Py)(Bp^Py)][Nd(PypzH)(NO₃)₄] was isolated from the reaction of hexadentate tris[3-(2-pyridyl)-pyrazol-1-yl]hydroborate (Tp^Py) with Nd(NO₃)₃. One of the Tp^Py ligands has lost one bidentate pyrazolyl-pyridine ‘arm’ (PypzH) to leave tetradentate tris[3-(2-pyridyl)-pyrazol-1-yl]dihydroborate (Bp^Py). In this structure, the cation [Nd(Tp^Py)(Bp^Py)]⁺ is ten-coordinate from inter-leaved hexadentate and tetradentate ligands, and the anion [Nd(PypzH)(NO₃)₄]⁻ is also ten-coordinate from the bidentate N-donor ligand PypzH and four bidentate nitrates.     

Chromium(III) and oxovanadium (IV) complexes of some urea derivatives

Summary The preparation of eight new complexes of Cr^III and VO^IV with urea derivatives is reported here. The ligands used were 2-imidazolidinone (ethyleneurea, EU),N,N'-dimethyl-2-imidazolidinone (N,N -dimethylethyleneurea, DMEU), 2-imidazolidinethione (ethylenethiourea, ETU), andN, N, N, N -tetramethyl-2-imidazolidone (tetramethylurea, TMU). The previously reported complex VOCl₂(TMU)₂ was also prepared. All nine complexes were investigated with regard to conductimetry as well as visible and i.r. spectroscopy. All carbonyl-containing complexes exhibit a metal-oxygen bond, whereas in ETU complexes a metal-nitrogen bond seems to be favoured.     

The thermal decomposition of some Cr(III) complexes

The thermal decomposition reactions of the following chromium(III) complexes were investigated: Cr(CH₃COO)₃·2 H₂O, [C_r3O(CH₃COO)₆(H₂O)₃]Cl·2 H₂O and [Cr₃O(CH₂ClCOO)₆(H₂O)₃]Cl·6H₂O. Simultaneous TG/DTG/DTA were applied nonisothermal conditions. From the recorded curves, the activation energiesE _a were calculated for all the thermal decomposition steps. Appropriate chemical reactions were attributed to the thermal effects, with consideration to the X-ray diffraction and IR spectra results.

---

Zusammenfassung Für die Untersuchung der thermischen Zersetzungsreaktion der Chrom(III)-Komplexe Cr(CH₃COO)₃·2H₂O [C_r3O(CH₃COO)₆·(H₂O)₃]Cl2H₂O und [C_r3O(CH₂ClCOO)₆·(H₂O)₃]C₁₆H₂O wurde simultane TG/DTG/DTA unter nichtisothermen Bedingungen eingesetzt. Ausgehend von den aufgezeichneten Kurven wurden für alle Schritte der Zersetzungsreaktion die E_a-Werte berechnet. In Übereinstimmung mit röntgenographischen und IR-spektroskopischen Ergebnissen wurden den thermischen Effekten passende chemische Reaktionen zugeordnet.