Transition-metal mediated heteroatom removal by reactions of FeL+ [L=O,C4H6, c-C5H6, c-C5H5, C6H6, C5H4(=CH2)] with furan,thiophene, and pyrrole in the gas phase

Reactions of Fe⁺ and FeL⁺ [L=O, C₄H₆, c-C₅H₆, C₅H₅, C₆H₆, C₅H₄(=CH₂)] with thiophene, furan, and pyrrole in the gas phase by using Fourier transform mass spectrometry are described. Fe⁺, Fe(C₅H₅)⁺, and FeC₆H ₆ ⁺ yield exclusive rapid adduct formation with thiophene, furan, and pyrrole. In addition, the iron-diene complexes [FeC₄H ₆ ⁺ and Fe(c-C₅H₆)⁺], as well as FeC₅H₄(=CH₂)⁺ and FeO⁺, are quite reactive. The most intriguing reaction is the predominant direct extrusion of CO from furan by FeC₄H₆ ⁺, Fe(c-C₅H₆)⁺, and FeC₅H₄(=CH₂)⁺. In addition, FeC₄H ₆ ⁺ and Fe(c-C₅H₆)⁺ cause minor amounts of HCN extrusion from pyrrole. Mechanisms are presented for these CO and HCN extrusion reactions. The absence of CS elimination from thiophene may be due to the higher energy requirements than those for CO extrusion from furan or HCN extrusion from pyrrole. The dominant reaction channel for reaction of Fe(c-C₅H₆)⁺ with pyrrole and thiophene is hydrogen-atom displacement, which implies D^O(Fa(N₅H₅)⁺-C₄H₄X)>D^O(Fe(C₅H₅)⁺-H)=46±5 kcal mol^?1. D^O(Fe⁺-C₄H₄S) and D^O(Fe⁺-C₄H₅N)=D^O(Fe⁺-C₄H₆)=48±5 kcal mol^?1. Finally, 55±5 kcal mol^?1=D^O(Fe⁺-C₆H₆)>D^O(Fe⁺-C₄H₄O)>D^O(Fe⁺-C₂H₄)=39.9±1.4 kcal mol^?1. FeO⁺ reacts rapidly with thiophene, furan, and pyrrole to yield initial loss of CO followed by additional neutral losses. D^O(Fe⁺-CS)>D^O(Fe⁺-C₄H₄S)≈48±5 kcal mol^?1 and D^O(Fe⁺-C₄H₅N)≈48±5 kcal mol^?1>D^O(Fe⁺-HCN)>D^O(Fe⁺-C₂H₄)=39.9±1.4 kcal mil^?1.     

Reactivity of metal-bound peroxides; alkali triperoxovanadate(V) trihydrates,A[V(O2)3]·3H2O (A = Na or K), as oxidants resembling alkali—H2O2 reagent for some organic substrates

The efficacy of the triperoxovanadium(V) complexes, A[V(O₂)₃]·3H₂O (A = Na or K), as potential oxidants with respect to certain organic substrates has been investigated. Aqueous solutions of the complexes are basic (pH ca. 11) in nature. The complexes efficiently oxidise an α,β-unsaturated ketone to the corresponding epoxide and benzonitrile to benzamide. Such reactions are usually accomplished using alkaline-H₂O₂ reagent. The complexes are also capable of bringing about Bayer-Villiger-type oxidation and oxidise benzil to benzoic acid. The peroxo-depleted vanadium product, isolated after the oxidations, has been identified as a diperoxovanadate(V) complex, [VO(O₂)₂(H₂O)]⁻.     

Molecular structure of two dicyclopentadienylmolybdenum derivatives containing a four-membered ring [Mo(η5-C5H5)2(2-NHNC5H4)][PF6] and [Mo(η5C5H5)2(2-ONC5H4)][PF6]

The structure of the new compound [Mo(η⁵-C₅H₅)₂(2-NHNC₅H₄)][PF₆] (1) has been determined. The crystals are orthorhombic, space group Pca2₁ with a 20.807(1), b 8.0030(8), c 10.056(3) Å, V 1674.5 ų, Z = 4. The structure of [Mo(η⁵-C₅H₅)₂(2-ONC₅H₄)][PF₆] (2) has also been determined. The crystals are orthorhombic, space group Pnma with a 12.727(3), b 10.174(2), c 12.918(1) Å, V 1672.8 ų, Z = 4. The structures were solved by Patterson and difference electron density syntheses and refined by least-squares to R of 0.028 for 1287 reflections for 1 and 0.059 for 1178 reflections for 2.Although not isostructural the two cationic complexes have equivalent geometries with the normal bent bismetallocene structure. For 1 the MoN bond lengths are 2.160(8) and 2.142(9) Å, with a NMoN bond angle of 59.8(3)°, whereas for 2 MoO is 2.142(10), MoN is 2.138(11) Å, the NMoO angle is 61.2(4)°. These parameters are discussed and compared with the corresponding data for similar biscyclopentadienyl complexes of molybdenum(IV). Extended Hückel molecular orbital calculations have been carried out to throw light on the nature of the bonding between the metal and the bidentate ligand.     

Ru(II) complexes imparting N2O2 donor bis chelating ligand N,N-bis(salicylidine)-hydrazine in unusual coordination mode

The synthesis and characterization of binuclear ruthenium complexes [{(η⁶-C₆H₆)Ru}₂(μ-bsh)₂] (1), [{(η⁶-C₁₀H₁₄)Ru}₂(μ-bsh)₂] (2), [{(η⁶-C₆Me₆)Ru}₂(μ-bsh)₂] (3), and rhodium complex [{(η⁵-C₅Me₅)RhCl}₂(μ-bsh)] (4) (bsh=N,N^′-bis(salicylidine)-hydrazine dianion) are reported. The complexes have been fully characterized by analytical and spectral techniques and unusual coordination mode of the ligand H₂bsh has been confirmed by single crystal X-ray analysis of the complex 2. Structural data revealed extensive inter- and intra-molecular C-H?O and C-H?π interactions and involvement of methyl and isopropyl hydrogen from the p-cymene in hydrogen bonding.     

Synthesis,spectroscopic and structural characterisation of vanadium(IV) and oxovanadium(IV) complexes with arsenic donor ligands

The reaction of o-C₆H₄(AsMe₂)₂ with VCl₄ in anhydrous CCl₄ produces orange eight-coordinate [VCl₄{o-C₆H₄(AsMe₂)₂}₂], whilst in CH₂Cl₂ the product is the brown, six-coordinate [VCl₄{o-C₆H₄(AsMe₂)₂}]. In dilute CH₂Cl₂ solution slow decomposition occurs to form the V^III complex [V₂Cl₆{o-C₆H₄(AsMe₂)₂}₂]. Six-coordination is also found in [VCl₄{MeC(CH₂AsMe₂)₃}] and [VCl₄{Et₃As)₂]. Hydrolysis of these complexes occurs readily to form vanadyl (VO²⁺) species, pure samples of which are obtained by reaction of [VOCl₂(thf)₂(H₂O)] with the arsines to form green [VOCl₂{o-C₆H₄(AsMe₂)₂}], [VOCl₂{MeC(CH₂AsMe₂)₃}(H₂O)] and [VOCl₂(Et₃As)₂]. Green [VOCl₂(o-C₆H₄(PMe₂)₂}] is formed from [VOCl₂(thf)₂(H₂O)] and the ligand. The [VOCl₂{o-C₆H₄(PMe₂)₂}] decomposes in thf solution open to air to form the diphosphine dioxide complex [VO{o-C₆H₄(P(O)Me₂)₂}₂(H₂O)]Cl₂, but in contrast, the products formed from similar treatment of [VCl₄{o-C₆H₄(AsMe₂)₂}_x] or [VOCl₂{o-C₆H₄(AsMe₂)₂}] contain the novel arsenic(V) cation [o-C₆H₄(AsMe₂Cl)(μ-O)(AsMe₂)]⁺. X-ray crystal structures are reported for [V₂Cl₆{o-C₆H₄(AsMe₂)₂}₂], [VO(H₂O){o-C₆H₄(P(O)Me₂)₂}₂]Cl₂, [o-C₆H₄(AsMe₂Cl)(μ-O)(AsMe₂)]Cl·[VO(H₂O)₃Cl₂] and powder neutron diffraction data for [VCl₄{o-C₆H₄(AsMe₂)₂}₂].     

Thermochemistry of bis-arene- and arenetricarbonyl-chromium compounds containing hexamethylbenzene, 1,3,5-trimethylbenzene and naphthalene.

Microcalorimetric measurements at elevated temperatures of the heats of thermal decomposition and iodination have led to values of the standard enthalpies of formation of the following crystalline compounds (values given in kJ mol^?1) at 298K: [Cr(η⁶-1,3,5-C₆H₃(CH₃)₃)₂] = (63±12); [Cr(η⁶-C₆(CH₃)₆)₂] : -(88±12); [Cr(1,2,3,4,4a,8a-η-C₁₀H₈)₂] = (407±11); [Cr(CO)₃(1,2,3,4,4a,8a-η-C₁₀H₈)] = -(258±8). Separate measurements by the vacuum sublimation microcalorimetric technique gave the following values for the enthalpy of sublimation at 298K (kJ mol^?1) : [Cr(η⁶-1,3,5-C₆H₃(CH₃)₃)₂] = (104±1); [Cr(η⁶-C₆(CH₃)₆)₂] = (119±4); [Cr(CO)₃(1,2,3,4,4a,8a-η-C₁₀H₈)] = (107±3). From these and other data, the bond enthalpy contributions of the metal-ligand bonds in the gaseous metal complexes were evaluated as follows: [(η₆-C₆(CH₃)₆)-Cr] (155±7); [(η⁶-C₆H₃(CH₃)₃)-Cr] (151±6); [(1,2,3,4,4a, 8a-η-C₁₀H₈)-Cr](145±6) kJ mol^?1]The question of the transferability of the enthalpy contributions of chromium—ligand bonds between organochronium complexes is discussed with aid of information from structural and spectroscopic investigation. The limitations of the procedure are defined.The thermodynamic data are used to discuss various substitution, redistribution and exchange reaction of Cr(η-arene)₂ and [Cr(CO)₃(η-arene)] compounds.     

Carbon-13 NMR spectra of some group VIB and VIIB transition metal chalcocarbonyl complexes

The ¹³C NMR spectra of the five series of chalcocarbonyl complexes, (η⁶-C₆H₆)Cr(CO)₂(CX), (η⁶-C₆H₅CO₂Me)Cr(CO)₂(CX), (η⁵-C₅H₅)Mn(CO)₂(CX), (η⁵-C₅H₄Me)Mn(CO)₂(CX) and (η⁵-C₅H₅)Re(CO)₂(CX) (X = O, S, Se), and some of their derivatives including several ¹³C-enriched species have been investigated at ?30 to ?50°C. The chemical shift variations observed with changes in the CX ligand suggest that the π-acceptor/σ-donor capacity of these ligands increases in the order CO < CS < CSe. Changes in the nuclear charge and in the electronic density at the central metal atom affect δ(¹³CS) and δ(¹³CO) in the same manner. The increased downfield chemical shift for δ(¹³CX) in the chromium and manganese series on changing X from O to S and Se is in the direction expected from considerations of Pople's paramagnetic shielding expression.     

New η-allyl η-cyclopentadienylcobalt cations

[Co(R-η-C₃H₄)(η-C₅H₅)I] is a good precursor for the preparation of some new cationic complexes as the iodide can easily be replaced; thus addition of PEt₃ to the iodo-complex (R  H) gives [Co(η-C₃H₅)(η-C₅H₅)(PEt₃)]⁺. The reactions of [Co(R-η-C₃H₄)(η-C₅H₅))I] (R  H or 2-Me) with AgBF₄ give solutions containing the coordinatively unsaturated species [Co(R-η-C₃H₄)(η-C₅H₅)⁺. The presence of traces of water leads to the formation of [Co(R-ηC₃H₄)-(η-C₅H₅)(H₂O)]⁺. The addition of monodentate ligands L  PEt₃ PPh₃, AsPh₃, SbPh₃, CNCH₃ and bidentate ligands LL  Ph₂PCH₂CH₂PPh₂(dppe) and o-C₆H₄(AsMe₂)₂(diars), gives, respectively mononuclear [Co(2-Me-ηC₃H₄)-(η-C₅H₅)L]⁺ and binuclear ligand-bridged [(2-Me-ηC₃H₄)(η-C₅H₅)CoLLCo(2-Me-ηC₃H₄)(η-C₅H₅))]²⁺ complexes. Crystals of [Co(2-Me-ηC₃H₄)(η-C₅H₅)-(H₂O)]⁺[BF₄]^- are monoclinic, space group P2₁/c, with a 7.858(3), b 10.262(4), c 15.078(4) Å, β 98.36(1)°. The molecular structure contains the cobalt atom bonded to planar 2-Me-allyl and cyclopentadienyl substituents, which are almost parallel with the H₂O molecule in a staggered conformation with respect to the 2-Me group.     

Lineare oligophosphaalkane: XVIII. Addition Ph-funktioneller methylenbisphosphane an die MoMo-Dreifachbindun in (η5-C5H5)2Mo2(CO)4

By means of the addition of the PH-functional methylenebisphosphanes R¹R²-PCH₂PR³H (PCP) to the MoMo triple bond in (η⁵-C₅H₅)₂Mo₂(CO)₄(MoMo) the complexes (η⁵-C₅H₅)₂Mo₂(CO)₄(PCP) containing a five-membered ring system Mo₂P₂C are obtained. Starting with unsymmetrically substituted methylenebisphosphanes R′₂PCH₂PRH only one isomer is formed, while the disecondary derivatives RHPCH₂PHR (as the diastereomeric mixture) gave two isomers of (η⁵-C₅H₅)₂Mo₂(CO)₄(PCP) (A₂ and AB) as indicated by the ³¹P{¹H} and ¹³C{¹H} NMR spectra.X-ray structural analysis of the derivative of the racemate of t-BuHPCH₂PH(t-Bu) space group C2/c, monoclinic, a 18.034(2), b 14.909(1), c 11.106(1) Å, α 90, β 99.788(8), γ 90°) reveals a puckered Mo₂P₂C five-membered ring system (dihedral angle PMoMo′P′ 54.4(2)°) with square-pyramidal coordination geometry at the Mo atoms. Two of the CO ligands (C(6)O(1) and C(6′)O(1′)) are almost coplanar with the molybdenum atoms, while the terminal CO groups (C(7)O(2) and C(7′)O(2′)) are about orthogonal (dihedral angle C(7)MoMo′C(7′) 88.4(3), MoMo′ 3.2109(4), MoP 2.4567(8), PC(8) 1.834(3), PH(P) 1.37(3) Å).     

Cluster chemistry: XXX. Reaction of a triruthenium anion with [O{Au(PPh3)}3][BF4]: Synthesis and structure of Ru3Au3(μ3-2η1,η3-C12H15)(CO)8(PPh3)3

The cluster HRu₃(μ₃-C₁₂H₁₅)(CO)₉ is rapidly deprotonated by K[HBBu₃^sec] in tetrahydrofuran, generating the anion [Ru₃(μ₃-C₁₂H₁₅)(CO)₉]^? in high yield. Reaction between this anion and [O{Au(PPh₃)}₃][BF₄] gives Ru₃Au₃(μ₃-C₁₂H₁₅)(CO)₈(PPh₃)₃ (2) as the main product, shown by an X-ray study to contain a capped trigonal-bipyramidal Ru₃Au₃ core in which the C₁₂H₁₅ ligand is bonded in the μ₃-2η¹,η³ fashion to the Ru₃ face. An alternative formulation involving the cyclo-Au₃(PPh₃)₃ moiety acting as a three-electron donor to the Ru₃ cluster is discussed. Crystals of 2 are monoclinic, space group P2₁/c, a 13.574(1), b 40.634(4), c 14.617(2) Å, β 92.58(1)°, Z = 4; 3233 data with I > 3σ(I) were refined to R = 0.078, R_w = 0.084.     

Reactions of a phosphido-bridged unsymmetrical diiron complex (η-C5Me5)Fe2(CO)4(μ-CO)(μ-PPh2) with various alkynes

A phosphido-bridged unsymmetrical diiron complex (η⁵-C₅Me₅)Fe₂(CO)₄(μ-CO)(μ-PPh₂) (1) was synthesized by a new convenient method; photo-dissociation of a CO ligand from (η⁵-C₅Me₅)Fe₂(CO)₆(μ-PPh₂) (2) that was prepared by the reaction of Li[Fe(CO)₄PPh₂] with (η⁵-C₅Me₅)Fe(CO)₂I. The reactivity of 1 toward various alkynes was studied. The reaction of 1 with ^tBuCCH gave a 1:1 mixture of two isomeric complexes (η⁵-C₅Me₅)Fe₂(CO)₃(μ-PPh₂)[μ-CHC(^tBu)C(O)] (3) containing a ketoalkenyl ligand. The reactions of 1 with other terminal alkynes RCCH (R=H, CO₂Me, Ph) afforded complexes incorporating one or two molecules of alkynes and a carbonyl group. The principal products were dinuclear complexes bridged by a new phosphinoketoalkenyl ligand, (η⁵-C₅Me₅)Fe₂(CO)₃(μ-CO)[μ-CR¹CR²C(O)PPh₂] (4a: R¹=H, R²=H; 4b: R¹=CO₂Me, R²=H; 4c: R¹=H, R²=Ph). In the cases of alkynes RCCH (R=H, CO₂Me), dinuclear complexes having a new ligand composed of two molecules of alkynes, a carbonyl group, and a phosphido group; i.e. (η⁵-C₅Me₅)Fe₂(CO)₃[μ-CRCHCHCRC(O)PPh₂] (5a: R=H; 5b: R=CO₂Me), were also obtained. In all cases, mononuclear complexes, (η⁵-C₅Me₅)Fe(CO)[CR¹CR²C(O)PPh₂] (6a: R¹=H, R²=H; 6b: R¹=H, R²=CO₂Me; 6c: R¹=H, R²=Ph) were isolated in low yields. The structures of 1, 4c, 5b, and 6a were confirmed by X-ray crystallography. The detailed structures of the products and plausible reaction mechanisms are discussed.     

Studies of lambert's reaction: The formation of [Mn2(CO)8(μ-AsR2)2] complexes from tertiary arsines and [Mn2(CO)10] at high temperatures

Although very bulky ligands e.g.(o-MeC₆H₄)₃E or (μ-C₁₀H₇)₃E (E = P or As) are inert, the normal photochemical or thermal reaction of tertiary phosphines or arsines, L, with [Mn₂(CO)₁₀] is CO substitution with the formation of [Mn₂(CO)₈(L)₂] derivatives (I). At elevated temperatures some triarylarsines, R₃As, undergo Lambert's reaction with ligand fragmentation to give [Mn₂(CO)₈(μ-AsR₂)₂] complexes (II) (R = Ph, p-MeOC₆H₄, p-FC₆H₄, or p-CIC₆H₄) even though, in the absence of [Mn₂(CO)₁₀] R₃As are stable under the same conditions. Exceptional behaviour is exhibited by (p-Me₂NC₆H₄)_3- As which forms a product of type I; by some HN(C₆H₄)₂AsR which give a product of type II as a result of loss of the non-aryl groups R = PhCH₂, cyclo-C₆H₁₁, or MeO; and by Ph(α-C₁₀H₇₂P which is the only phosphine to form a product of type II, albeit in trace amounts only. The thermal decomposition of a n-butanol solution of [Mn₂(CO)₈(AsPh₃)₂] in a sealed tube gives C₆H₆ and [Mn₂(CO)₈(α-AsPh₂)₂], whilst in an open system in the presence of various tertiary phosphines, L, [Mn(H)(CO)₃(L)₂] are obtained. It is suggested that Lambert's reaction is a thermal fragmentation of [Mn(CO)₄(AsR₃]^* radicals, the first to be recognised. They lose the radical R^* which abstracts hydrogen from the solvent. The resulting [Mn(CO)₄(AsR₂)] moiety dimerises to [Mn₂(CO)_8-(α-AsR₂)₂]. the reaction is facilitated by the stability of the departing radical (e.g. PhCH₂ or MeO) and, as the crowding about As is relieved, by its size (e.g. Ph, cyclo-C₆H₁₁, o-MeC₆H₄, or α-C₁₀H₇). In general, phosphine-substituted radicals [Mn(CO)₄(PR)₃]^* do not undergo this decomposition, probably because the PC bonds are much stronger than AsC.     

Arene ruthenium bis-saccharinato complexes: Synthesis, molecular structure and catalytic oxidation properties in aqueous solution

Arene ruthenium complexes [(η⁶-arene)Ru(sacc)₂(OH₂)] (arene = para-cymeme, benzene) containing an aqua and two saccharinato ligands have been synthesized from [(η⁶-arene)RuCl₂]₂ and sodium saccharinate in a water-ethanol mixture (1:1). The aqua complex [(η⁶-MeC₆H₄Prⁱ)Ru(sacc)₂(OH₂)] reacts with acetonitrile to give the acetonitrile complex [(η⁶-MeC₆H₄Prⁱ)Ru(sacc)₂(NCMe)]. The corresponding benzene derivative [(η⁶-C₆H₆)Ru(sacc)₂(NCMe)] was obtained from [(η⁶-C₆H₆)RuCl₂]₂ and saccNa in an acetonitrile-methanol mixture (1:1). All new complexes show a piano-stool geometry with two mono-hapto nitrogen-bonded saccharinato ligands in addition to a H₂O or MeCN ligand. All complexes of the type [(η⁶-arene)Ru(sacc)₂(OH₂)] and [(η⁶-arene)Ru(sacc)₂(NCMe)] were found to catalyze the oxidation of secondary alcohols with tert-butyl hydroperoxide (Bu^tOOH) to give the corresponding ketones in aqueous solution.     

Synergistic complexes of uranyl ion with 1-phenyl-3-methyl-4-acetyl-pyrazolone-5 and some oxo-donors

Complexes of uranyl ion with 1-phenyl-3-methyl-4-acetyl-pyrazolone-5(PMAP) and various oxo-donors such as aliphatic sulphoxides [R₂SO, where R = i-C₅H₁₁(DISO), n-C₆H₁₃(DHSO), n-C₇H₁₅(DSSO), n-C₈H₁₇(DOSO), n-C₉H₁₉(DNSO), n-C_1OH₂₁(DDSO), n-C₁₁H₂₃(DUDSO) and n-C₄H₉(DBUSO)] tributylphosphate (TBP) and tri-n-octyl phosphine oxide (TOPO) have been synthesised and characterized. Analytical data establish that they have the stoichiometry UO₂(PMAP)₂X where X is the oxo-donor. The IR spectra of the sulphoxide complexes in the SO stretching region indicate that the ligands R₂SO are O-bonded. The methyl protons of the pyrazole ring and acetyl group in the PMAP ligand are equivalent giving rise to a single sharp peak in the PMR spectra, whereas in the synergistic complexes with the oxo-donors, two deshielded peaks of equal intensity are observed which indicate the non-equivalence of the methyl groups. The peak which is more deshielded has been ascribed to the methyl of the acetyl group. The higher deshielding of these methyl protons arises due to the transfer of electron density to the metal atom on complexation.     

Preparation and structural characterization of [(η5-C5H5)2Zr(SC6H5)]2O. A qualitative description of the bonding in oxo-bridged dicyclopentadienyl-transition metal dimers

The hydrolysis of (η⁵-C₅H₅)₂Zr(SC₆H₅)₂ was shown previously by IR spectroscopy to produce an oxo-bridged complex. The molecular structure of this material has been determined by X-ray diffraction methods and consists of two (η²-C₅H₅)₂Zr(SC₆H₅) units linked by an oxo bridge. The ZrOZr bond is nonlinear at 165.8(2)° with a Zr?Zr interatomic separation of 3.902(1)Å. The two independent SZrO bond angles of 98.7(1) and 103.3(1)° are consistent with a d° electronic structure for each zirconium atom. The relatively short ZrO distances of 1.968(3) and 1.964(3) Å support the presence of partial double-bond character arising from the donation of electron density from filled p_π-orbitals on the oxygen atom to unfilled d-orbitals on the electron deficient d⁰ metal atoms. This bonding feature requires based upon orbital symmetry arguments that the (ML)₂O molecular core in [(η⁵-C₅H₅)₂ML]₂O complexes must be nonplanar with a dihedral angle between the two LMO planes less than 90°. For [(η⁵-C₅H₅)₂Zr(SC₆H₅)]₂O, dihedral angle of 61.7° was observed. The compound crystallizes in an orthorhombic space group, Pbca, with refined lattices parameters a 16.458(4), b 20.281(5), and c 17.016(4) Å. Full-matrix least-squares refinement of 2613 diffractometry data I > σ(I) led to a final discrepancy index R(F₀²) = 0.044.     

Preparation, spectroscopic properties of 1,4-di (N,N-diisopropylacetamido)-2,3(1H,4H)-quinoxalinedione (L) lanthanide complexes and the supramolecular structure of [Nd2L2(NO3)6(H2O)2]·H2O

The reaction of lanthanide nitrate with 1,4-di (N,N-diisopropylacetamido)-2,3(1H,4H)-quinoxalinedione (L) yields six novel Ln(III) complexes ([Ln₂L₂(NO₃)₆(H₂O)₂]·H₂O) which are characterized by elemental analysis, thermogravimetric analysis (TGA), conductivity measurements, IR, electronic and ¹H NMR spectroscopies. A new quinoxalinedione-based ligand is used as antenna ligand to sensitize the emission of lanthanide cations. The lowest triplet state energy level of the ligand in the nitrate complex matches better to the resonance level of Eu(III) and Sm(III) than Tb(III) and Dy(III) ion. The f-f fluorescence is induced in the Eu³⁺ and Sm³⁺ complexes by exciting into the π-π* absorptions of the ligand in the UV. Furthermore, the crystal structures of a novel binuclear complex [Nd₂L₂(NO₃)₆(H₂O)₂]·H₂O has been determined by single-crystal X-ray diffraction. The binuclear [Nd₂L₂(NO₃)₆(H₂O)₂]·H₂O complex units are linked by the intermolecular hydrogen bonds and π-π interactions to form a two-dimensional (2-D) layer supramolecule.     

Facile synthesis of new polyolefinic ruthenium(0) complexes from ruthenium(II) precursors

The new ruthenium(II) complex [(C₈H₁₀)RuCl₂]_n (1) (C₈H₁₀ = 1,3,5-cyclooctatriene; n ⩾ 2) has been obtained from the reaction of RuCl₃·xH₂O with 1,3,5,7-cyclooctatetraene in refluxing ethanol. Reduction of [(C₈H₁₀)RuCl₂]_n and [(C₇H₈)RuCl₂]₂ (2) (C₇H₈ = 1,3,5-cyclooctatriene) by Na/Hg amalgam in the presence of isoprene (C₅H₈) gives the novel ruthenium(O) complexes [(η⁶-C₈H₁₀)Ru(η⁴-C₅H₈)] (3) and [(η⁶-C₇H₈)Ru(η⁴-C₅H₈)] (4). [(η⁶-C₇H₈Ru(η⁴-C₅H₈)] reacts with CO and HBF₄ to give [(η⁶-C₇H₈)Ru(η³-C₅H₉)(CO)][BF₄] (C₅H₉ = trans-1,2-dimethylallyl (5a); 1,1-dimethylallyl (5b)).     

Multiple C−H Bond Activations in Corannulene by a Dirhenium Complex

The reaction of Re₂(CO)₈(μ-C₆H₅)(μ-H), 1 with corannulene (C₂₀H₁₀) yielded the product Re₂(CO)₈(μ-H)(μ-η²-1,2-C₂₀H₉), 2 (65 % yield) containing a Re₂ metalated corannulene ligand formed by loss of benzene from 1 and the activation of one of the CH bonds of the nonplanar corannulene molecule by an oxidative-addition to 1 . The corannulenyl ligand has adopted a bridging η²-σ+π coordination to the Re₂(CO)₈ grouping. Compound 2 reacts with a second equivalent of 1 to yield three isomeric doubly metalated corannulene products: Re₂(CO)₈(μ-H)(μ-η²-1,2-μ-η²-10,11-C₂₀H₈)Re₂(CO)₈(μ-H), 3 (35 % yield), Re₂(CO)₈(μ-H)(μ-η²-2,1-μ-η²-10,11-C₂₀H₈)Re₂(CO)₈(μ-H), 4 (12 % yield), and Re₂(CO)₈(μ-H)(μ-η²-1,2-μ-η²-11,10-C₂₀H₈)Re₂(CO)₈(μ-H), 5 (12 % yield), by a second CH activation on a second rim double bond on the corannulene molecule. The isomers differ by the relative orientations of the coordinated Re₂(CO)₈(μ-H) groupings. All new products were characterized structurally by single crystal X-ray diffraction analysis.     

Octahapto cyclooctatetraene rings and metal-metal multiple bonds in binuclear niobium carbonyl chemistry

Theoretical studies on (C₈H₈)₂Nb₂(CO)_n (n = 6, 5, 4, 3, 2, 1) predict structures mainly with octahapto and tetrahapto C₈H₈ rings. In all cases, the lowest energy singlet spin state structures lie below the corresponding lowest energy triplet spin state structures. Thus the lowest energy (C₈H₈)₂Nb₂(CO)₄ structure has two η⁸-C₈H₈ rings and an unbridged Nb-Nb single bond of length ∼3.15 Å. The lowest energy (C₈H₈)₂Nb₂(CO)₂ structure has two η⁸-C₈H₈ rings but a doubly bridged NbNb triple bond of length ∼2.64 Å. The lowest energy structure of (C₈H₈)₂Nb₂(CO)₃ also has a formal NbNb triple bond of similar length (2.66 Å) but with only one of the rings fully coordinated as an octahapto η⁸-C₈H₈ ligand. The other C₈H₈ ring in this tricarbonyl has “slipped” to form a hexahapto η⁶-C₈H₈ ligand. The lowest energy structure of the monocarbonyl (C₈H₈)₂Nb₂(CO) again has two octahapto η⁸-C₈H₈ rings and an extremely short NbNb distance of 2.45 Å, suggesting a formal quadruple bond. The lowest energy structures for the carbonyl-richer species (C₈H₈)₂Nb₂(CO)_n (n = 6, 5) have one η⁸-C₈H₈ and one η⁴-C₈H₈ ring (n = 5) and two η⁴-C₈H₈ rings (n = 6). The qualitatively assigned Nb-Nb bond orders are consistent with the Wiberg bond indices obtained from the Weinhold natural bond orbital analysis. Comparison of the (C₈H₈)₂Nb₂(CO)_n (n = 6, 5, 4, 3, 2, 1) derivatives with the isovalent (C₇H₇)₂Mo₂(CO)_n is made.     

Syntheses and characterization of η-hexamethylbenzeneruthenium(II)-β-diketone complexes: their reactions with mono- and bidentate neutral ligands

The complex [(η⁶-C₆Me₆)Ru(μ-Cl)Cl]₂1 react with sodium salts of β-diketonato ligands in methanol to afford the oxygen bonded neutral complexes of the type [(η⁶-C₆Me₆)Ru(κ²-O,O′-R¹COCHCOR²)Cl] {R¹, R² = CH₃ (2), CH₃, C₆H₅ (3), C₆H₅ (4), OCH₃ (5), OC₂H₅ (6)}. Complex 4 with AgBF₄ yields the γ-carbon bonded ruthenium dimeric complex 7. Complex 4 also reacts with tertiary phosphines and bridging ligands to yield complexes of the type [(η⁶-C₆Me₆)Ru(κ²-O,O′-C₆H₅COCHCOC₆H₅)(L)]⁺ (L = PPh₃ (8), PMe₂Ph (9)) and [{η⁶-C₆Me₆)Ru(κ²-O,O′-C₆H₅COCHCOC₆H₅)}₂(μ-L)] L = 4,4′-bipyridine (4,4′-bipy) (11), 1,4-dicyanobenzene (DCB) (12) and pyrazine (Pz) (13). Complexes 2-4 react with sodium azide to yield neutral complexes [(η⁶-C₆Me₆)Ru(κ²-O,O′-R¹COCHCOR²)N₃] {R¹, R² = CH₃ (10a), CH₃, C₆H₅ (10b), C₆H₅ (10c). All these complexes were characterized by FT-IR and FT-NMR spectroscopy as well as analytical data. The molecular structures of complexes [(η⁶-C₆Me₆)Ru(κ²-O,O′CH₃COCH-COC₆H₅)Cl] (3) and [(η⁶-C₆Me₆)Ru(κ²-O,O′-C₆H₅COCHCOC₆H₅] (4) were established by single crystal X-ray diffraction studies. The complex 3 crystallizes in the triclinic space group, [a = 7.9517(4), b = 9.0582(4) and c = 14.2373(8) Å, α = 88.442(3)°, β = 76.6.8(3)° and γ = 81.715(3)°. V = 987.17(9) ų, Z = 2]. Complex 4 crystallizes in the monoclinic space group, P2₁/c [a = 7.5894(8), b = 20.708(2) and c = 29.208(3) Å,β = 92.059(3)° V = 4587.5(9) ų, Z = 8].