Synthesis and spectroscopic properties of some new seven-coordinate thioacetamide complexes of molybdenum(II) and tungsten(II)

The compounds [MI₂(CO)₃(NCMe)₂] (M = Mo or W) react with one equivalent of SC(NH₂)Me in CH₂Cl₂ at room temperature to initially give the acetonitrile substituted products [MI₂(CO)₃(NCMe)- {SC(NH₂)Me}] which was isolated for M = W. However, the molybdenum complex rapidly dimerizes with loss of acetonitrile to give the iodide-bridged compound [Mo(σ-I)I(CO)₃ {SC(NH₂)Me}]₂. The tungsten complex does not appear to dimerize, even after stirring at room temperature for 72 h in CH₂Cl₂. Two equivalents of thioacetamide react with [MI₂- (CO)₃(NCMe)₂] in CH₂Cl₂ at room temperature to give the new bisthioacetamide compounds [MI₂- (CO)₃{SC(NH₂)Me}₂] via displacement of the labile acetonitrile ligands. The low temperature (−70 °C) ¹³C NMR spectrum of [WI₂(CO)₃{SC(NH₂)Me}₂] indicates that the geometry of the complex is capped octahedral with a carbonyl ligand in the unique capping position.     

Improved preparation of indenyl molybdenum(II) and tungsten(II) compounds

Oxidative addition of 1-bromo-1H-indene to [Mo(CO)₃(NCMe)₃] and [W(CO)₃(NCEt)₃] is a suitable method for preparation of the indenyl compounds [IndMo(CO)₃Br] and [IndW(CO)₃Br], respectively. These products were fully characterised using spectroscopic methods. Structure of [IndW(CO)₃Br] was determined by single crystal X-ray diffraction analysis.     

Synthesis and reactivity of cationic bipyridine tungsten(0) and molybdenum(0) nitrosyl complexes

A variety of Group 6 mono bipyridine (bpy) complexes were prepared, and substitution reactions of [(bpy)(MeIm)M(CO)₂(NO)]PF₆ complexes (MeIm = 1-methylimidazole, M = W or Mo) were investigated. Nitrosylation of complexes having the general formula (bpy)(L)M(CO)₃ (L = a variable ligand) gave cationic complexes of the form [(bpy)(L)M(CO)₂(NO)]PF₆. The structure of [(bpy)(MeIm)W(CO)₂(NO)]PF₆ was confirmed by single-crystal X-ray diffractometry. [(bpy)(MeIm)M(CO)₂(NO)]PF₆ complexes undergo facile substitutions with mono-, tri- and tetra-dentate ligands, yielding di- or mono-carbonyl mononitrosyl complexes. The structures of [(bpy)(PMe₃)₂W(CO)(NO)]PF₆ and [(dien)(PMe₃)W(CO)(NO)]PF₆ (dien = diethylenetriamine) were determined by X-ray diffraction.     

Reductive nitrosation of molybdenum and tungsten halides. III. Intramolecular redox reactions of molybdenum and tungsten halo nitrosyl complexes

Thermally initiated exothermic intramolecular redox reactions of [M(NO)₂Cl₂]_n and M(NO)₂CL₂L₂ (where M = Mo or W; L = PPh₃AsPh₃ or OPPh₃) type complexes were observed at definite temperatures. In these reactions the coordinated NO oxidizes M or L and N₂O or N₂ containing gases are formed. Thermal analysis was found to be a reliable supplementary method to differentiate between phosphine and phosphine oxide substituted halo nitrosyl complexes.     

Synthesis and structural characterization of five-, six-, and seven-coordinate mononuclear manganese(II) complexes with N-tridentate ligands

A series of four mononuclear manganese (II) complexes with the N-tridentate neutral ligands 2,2^′:6,2^′′-terpyridine (terpy) and N,N-bis(2-pyridylmethyl)ethylamine (bpea) have been synthesized and crystallographically characterized. The complexes have five- to seven-coordinate manganese(II) ions depending on the additional ligands used. The [Mn(bpea)(Br)₂] complex (1) has a five-coordinated manganese atom with a bipyramidal trigonal geometry, while [Mn(terpy)₂](I)₂ (2) is hexa-coordinated with a distorted octahedral geometry. Otherwise, the reactions of Mn(NO₃)₂ · 4H₂O with terpy or bpea afforded novel seven-coordinate complexes [Mn(terpy)(NO₃)₂(H₂O)] (3) and [Mn(bpea)(NO₃)₂] (4), respectively. 3 has a coordination polyhedron best described as a distorted pentagonal bipyramid geometry with one nitrate acting as a bidentate chelating ligand and the other nitrate as a monodentate one. 4 possesses a highly distorted polyhedron geometry with two bidentate chelating nitrate ligands. These complexes represent unusual examples of structurally characterized complexes with a coordination number seven for the Mn(II) ion and join a small family of nitrate complexes.     

Syntheses and structures of photochromic molybdenum(II) and rhodium(II) complexes with 1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene

Four novel Mo(II) and Rh(II) complexes with cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (cis-dbe) or closed-dbe were synthesized and characterized. Employing [M(O₂CCF₃)₄] (M = Mo, Rh) with cis-dbe or closed-dbe afforded complex [Mo₂(O₂CCF₃)₄(cis-dbe)](benzene) (1), [Rh₂(O₂CCF₃)₄(cis-dbe)](benzene) (2), [{Mo₂(O₂CCF₃)₄}₂(closed-dbe)] (3), and [Rh₂(O₂CCF₃)₄(closed-dbe)](p-xylene) (4). The structures of four metal complexes were revealed by X-ray crystallographic analyses and the correlation between the crystal structures and the photochromic performance was discussed. In all complexes, two cyano groups of the ligand bridged two dimetal carboxylates to give a 1-D zigzag infinite chain structure. Upon irradiation with 405 nm light, complex 1 turned into reddish purple from yellow, and the color reverted to initial yellow on exposure to 563 nm light, indicating the reversible cyclization/ring-opening reaction in the crystalline phase. However, the Rh(II) complex 2 did not display similarities in reaction induced by light, which is attributable to the lower ratio of photoactive anti-parallel conformers compared with complex 1 and coordination effect of metal ions on photochromism of diarylethenes. The complexes of Rh(II) ions did not exhibit the expected reversible photoinduced behavior.     

Ferrocenyl-substituted allenylidene complexes of chromium, molybdenum and tungsten: Synthesis, structure and reactivity

Bis(ferrocenyl)-substituted allenylidene complexes, [(CO)₅MCCCFc₂] (1a-c, Fc = (C₅H₄)Fe(C₅H₅), M = Cr (a), Mo (b), W (c)) were obtained by sequential reaction of Fc₂CO with Me₃Si-CCH, KF/MeOH, n-BuLi, and [(CO)₅M(THF)]. For the synthesis of related mono(ferrocenyl)allenylidene chromium complexes, [(CO)₅CrCCC(Fc)R] (R = Ph, NMe₂), three different routes were developed: (a) reaction of the deprotonated propargylic alcohol HCCC(Fc)(Ph)OH with [(CO)₅Cr(THF)] followed by desoxygenation with Cl₂CO, (b) Lewis acid induced alcohol elimination from alkenyl(alkoxy)carbene complexes, [(CO)₅CrC(OR)CHC(NMe₂)Fc], and (c) replacement of OMe in [(CO)₅CrCCC(OMe)NMe₂] by Fc. Complex 1a was also formed when the mono(ferrocenyl)allenylidene complex [(CO)₅CrCCC(Fc)NMe₂] was treated first with Li[Fc] and the resulting adduct then with SiO₂. The replacement route (c) was also applied to the synthesis of an allenylidene complex (7a) with a CC spacer in between the ferrocenyl unit and C_γ of the allenylidene ligand, [(CO)₅CrCCC(NMe₂)-CCFc]. The related complex containing a CHCH spacer (9a) was prepared by condensation of [(CO)₅CrCCC(Me)NMe₂] with formylferrocene in the presence of NEt₃. The bis(ferrocenyl)-substituted allenylidene complexes 1a-c added HNMe₂ across the C_α-C_β bond to give alkenyl(dimethylamino)carbene complexes and reacted with diethylaminopropyne by regioselective insertion of the CC bond into the C_β-C_γ bond to afford alkenyl(diethylamino)allenylidene complexes, [(CO)₅MCCC(NEt₂)CMeCFc₂]. The structures of 5a, 7a, and 9a were established by X-ray diffraction studies.     

Synthesis and structural characterization of a novel seven-coordinate cobalt(II) complex: 2,9-Bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II) chloride

Condensation reaction of 2,9-dicarboxaldehyde-1,10-phenanthroline with 2-aminoethanol followed by NaBH₄ reduction yielded the polydentate Schiff base ligand 2,9-bis(ethanolamine)-1,10-phenanthroline in its reduced form. This ligand was characterized by elemental analysis, LC-MS, IR, UV-Vis and NMR spectroscopy. Reaction of the reduced Schiff base ligand with aqueous solution of cobalt(II) chloride affords 2,9-bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II) chloride in high yield. Single crystals of the cobalt(II) complex were obtained from the crystallization in ethanol and its structure was elucidated by X-ray structural analysis. The cobalt(II) complex ion was found to be seven-coordinated in a pentagonal bipyramidal geometry, whereby cobalt(II) ion is surrounded by the six donor atoms in the ligand molecule and a chloride ion.     

NMR study of the complexation of D-gulonic acid with tungsten(VI) and molybdenum(VI)

By using multinuclear (1H, 13C, 17O, 95Mo, 183W) magnetic resonance spectroscopy (1D and 2D), D-gulonic acid is found to form ten and seven complexes, respectively, with tungsten(VI) and molybdenum(VI), in aqueous solution, depending on pH and metal-ligand molar ratios. Two isomeric 1:2 (metal-ligand) complexes involving the carboxylate and the adjacent OH group are present in the pH range 2-9. At intermediate and high pH, molybdate forms a 2:1 tetradentate complex involving the four secondary hydroxyl groups, whereas tungstate forms one 2:1 terdentate species. At low and intermediate pH values, three 2:1 complexes are found for both metals, involving the carboxylate group and three secondary hydroxyl groups, as well as a 5:2 species involving the carboxylate group and all the secondary hydroxyl groups; the concentration of this species increases in time mainly at the expense of 2:1 and 1:2 complexes. Tungstate can also form two additional species, probably a 5:2 species involving the carboxylate group and all the hydroxyl groups, and a 2:1 pentadentate species involving the carboxylate group and all the secondary hydroxyl groups. In alkaline solutions, tungstate is able to form an additional 2:1 pentadentate complex involving all the hydroxyl groups.     

Squarate complexes of diamine palladium(II) and platinum(II)

Reactions of cis-diaminediaqua palladium and platinum dinitrates and of trans-diaminediaqua platinum dinitrate give complexes of the type Pd(tmeda)(OH)(C₄O₄)Pd(tmeda)(C₄O₄H) (tmeda = tetramethylethylenediamine) (1), (en)M(C₄O₄)₂M(en) (en = ethylenediamine (M = Pd, Pt) and trans-[Pt- (NH₃)₂C₄O₄]_n, respectively. The structures of these compounds are discussed on the basis of their spectroscopic data.     

Nickel(II) and copper(II) complexes of mixed benzene-triazolehemiporphyrazines

The kinetics of substitution reactions of [η-CpFe(CO)₃]PF₆ with PPh₃ in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH)₄, 4-Ph, 3-Me, 2,3-(CH)₄, 2,6-Me₂, 2-Me), the reactions yeild the same product [η⁵-CpFe(CO)₂PPh₃]PF₆, according to a second-order rate law that is first order in concentrations of [η⁵-CpFe(CO)₃]PF₆ and of R-PyO but zero order in PPh₃ concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH^≠ = 13.4 ± 0.4 kcal mol⁻¹, ΔS^≠ = −19.1 ± 1.3 cal k⁻¹ mol⁻¹ for 4-PhPyO; ΔH^≠ = 12.3 ± 0.3 kcal mol⁻¹, ΔS^≠ = 24.7 ±1.0 cal K⁻¹ mol⁻¹ for 2-MePyO. For the various substituted pyridine N-oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N-oxide basicities, but decrease with increasing ¹⁷O chemical shifts of the N-oxides. Electronic and steric factors contributing to the reactivity of pyridine N-oxides have been quantitatively assessed.     

Squarato-metal(II) complexes. 1: Structural and magnetic characterization of squarato-bridged dinuclear nickel(II) and copper(II) complexes

A new series of dinuclear squarato-bridged nickel(II) and copper(II) complexes [Ni₂(2,3,2-tet)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (1), [Ni₂(aepn)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (2), [Cu₂(pmedien)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂.4H₂O (3) and [Cu₂(DPA)₂(μ_1,2-C₄O₄)(H₂O)₂](ClO₄)₂ (4) where is the dianion of 3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid), 2,3,2-tet = 1,4,8,11-tetraazaundecane, aepn = N-(2-aminoethyl)-1,3-propanediamine, pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine and DPA = di(2-pyridylmethyl)amine were synthesized and structurally characterized by X-ray crystallography. The spectral and structural characterization as well as the magnetic behaviour of these complexes is reported. In this series, structures consist of the groups as counter ions and the bridging the two M(II) centers in a μ-1,3- (1-3) and in a μ-1,2-bis(monodentate) (4) bonding fashions. The coordination geometry around the Ni(II) ions in 1 and 2 is six-coordinate with distorted octahedral environment achieved by N atoms of the amines and by one or two oxygen atoms from coordinated water molecules, respectively. In the Cu(II) complexes 3 and 4, a distorted square pyramidal geometry is achieved by the three N-atoms of the aepn or DPA and by an oxygen atom from a coordinated water molecule. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the M(II) centers. The complexes show weak antiferromagnetic coupling with ∣J∣ = 1.8-4.2 cm⁻¹ in the μ-1,3- bridged squarato compounds 1-3, and J = −16.1 cm⁻¹ in the corresponding μ-1,2- bridged squarato complex 4. The magnetic properties are discussed in relation to the structural data.     

Palladium(II) and platinum(II) complexes with polypyridylbenzene ligands

The ligands 1,3-bis(3-pyridyl)benzene (1), 1,3-bis(4-pyridyl)benzene (2) and 1,3,5-tris(4-pyridyl)benzene (3) have been prepared by Stille coupling of 3- or 4-trimethylstannylpyridine with the appropriate bromoarene. Ligands 1 and 2 react with [M(OTf)₂(dppp)] (M=Pd, Pt) to produce the dipalladium- or diplatinum-containing macrocycles [M₂(μ-1)₂(dppp)₂](OTf)₄ or [M₂(μ-2)₂(dppp)₂](OTf)₄. These have been characterized by NMR spectroscopy and mass spectrometry and, in the case of [Pd₂(μ-1)₂(dppp)₂](OTf)₄, by X-ray crystallography. The molecular structure of the [Pd₂(μ-1)₂(dppp)₂]⁴⁺ cation reveals a shallow arrangement of the aromatic rings, with the palladium atoms lying above and below. The tridentate ligand 3 reacts with [Pd(OTf)₂(dppp)] to produce a trimetallic species of the form [Pd₃(μ₃-3)₂(dppp)₃](OTf)₆.     

Reactivities of the coordinated organonitriles in molybdenum(0) and tungsten(0) phosphine complexes: protonation of the nitrile carbon and cleavage of the CN triple bond

The molybdenum and tungsten dinitrogen-organonitrile complexes trans-[M(N₂)(NCR)(dppe)₂] (2, M=Mo; 4, M=W; R=Ph, C₆H₄Me-p, C₆H₄OMe-p, Me; dppe=Ph₂PCH₂CH₂PPh₂) underwent double protonation at the nitrile carbon atom with loss of N₂ and a change in oxidation state to +4 on treatment with hydrochloric acid to afford the cationic imido complexes trans-[MCl(NCH₂R)(dppe)₂]⁺. The solid-state structure of trans-[WCl(NCH₂CH₃)(dppe)₂][PF₆]·CH₂Cl₂ was determined by single-crystal X-ray analysis. Protonation of complexes 2 by fluoroboric acid or hydrobromic acid also formed the similar imido complexes trans-[MoX(NCH₂R)(dppe)₂]⁺ (X=F, Br). In contrast, the dinitrogen complex trans-[Mo(N₂)₂(dppe)₂] reacted with two equiv. of benzoylacetonitrile, a nitrile with acidic CH hydrogen atoms, to give the nitrido complex trans-[Mo(N)(NKCCHCOPh)(dppe)₂] (12), which was accompanied by evolution of dinitrogen and the formation of 1-phenyl-2-propen-1-one in high yields. For complex 12, the zwitterionic structure, where the anionic enolate ligand PhC(O⁺)=CHCN coordinates to the cationic Mo(IV) center through its nitrogen atom, was confirmed by spectroscopic measurements and single-crystal X-ray analysis. A unique intermolecular aromatic C---HO hydrogen bonding was observed in that crystal structure. Complex 12 is considered to be formed via the cleavage of the CN triple bond of benzoylacetonitrile on the metal. A reaction mechanism is proposed, which includes the double protonation of the nitrile carbon atom of the ligating benzoylacetonitrile on a low-valent molybdenum center.     

Trispyrazolylmethane piano stool complexes of iron(II) and cobalt(II)

A series of cationic trispyrazolylmethane complexes of the general form [Tm^RM(CH₃CN)₃]²⁺ (Tm = tris(pyrazolyl)methane, 1, R = 3,5-Me₂, M = Fe(II); 2, R = 3-Ph, M = Fe(II); 3, R = 3,5-Me₂, M = Co(II); 4, R = 3-Ph, M = Co(II)) with ‘piano-stool’ structures was prepared by the reaction of the N₃tripodal ligands (Tm^R)with [(CH₃CN)₆M](BF₄)₂ in a 1:1 stoichiometric ratio. Magnetic susceptibility measurements indicate that all four complexes with BF₄⁻ counter anions are paramagnetic, high-spin systems in the solid state with μ_eff at high temperatures of 5.2 (1, S = 2), 5.4 (2, S = 2), 4.9 (3, S = 3/2) and 4.6 (4, S = 3/2) BM, respectively. Comparisons of bond lengths from the metal centre to the Tm^R nitrogen donors, and from the metal centre to the acetonitrile nitrogen donors indicate that the neutral tripodal ligands appear to be more weakly coordinated to the metal centre than are the acetonitrile ligands. Reactions of these tripodal complexes with bidentate phosphine ligands, such as 1,2-diphosphinoethane or 1,2-bis(diallylphosphino)ethane leads to displacement of the tripodal ligand, or to the formation of more thermally stable bis-ligand complexes M(Tm^R)₂ (R = 3,5-dimethyl).     

Copper(II) PMDTA and copper(II) TMEDA complexes: precursors for the synthesis of dinuclear dicationic copper(II) complexes

Copper(II) cations coordinated with PMDTA (pentamethyldiethylenetriamine) and TMEDA (tetramethylethylenediamine) possess a high synthetic potential. The synthesis of these cations was carried out by metathesis reactions with silver salts. The cationic copper(II) complexes, [Cu(PMDTA)(Me₂CO)Cl]⁺, [Cu(PMDTA)(H₂O)Cl]⁺, [Cu(PMDTA)(DMF)]⁺, [Cu(PMDTA)Cl]⁺, [Cu(PMDTA)OAc]⁺, [Cu(PMDTA)(MeCN)₂]²⁺, [Cu₂(TMEDA)₂Cl₃]⁺ and [Cu(TMEDA)(MeCN)₃]²⁺ were synthesised as PF₆ salts, crystallised and characterised by single-crystal X-ray diffraction.     

Different reaction behaviour of molybdenum and tungsten - Reactions of the dichloro dioxo dimethyl-bispyridine complexes with thiophenolate

The reaction of the metal complexes MO₂Cl₂(mebipy) (M = Mo, W) with two equivalents thiophenol by the exact same procedure leads to two different products for molybdenum [Mo₂O₄(SPh)₂(mebipy)₂] and tungsten [WO₂(SPh)₂(mebipy)]. To understand why this is the case the redox potentials of the starting materials were measured showing that the redox potential for thiophenol is lower than the redox potentials (M^V ↔ M^VI) for both of the metal precursors. A reduction of the metal and oxidation of the sulfur should be possible for both reactions but occurs only for the molybdenum compound. Theoretical calculations show that different metal-sulfur bond strengths are as well and equally responsible for the differing reaction behaviour as are the redox potentials.