Substitution reactions of [MBr(π allyl)(CO)2(LL)] complexes (M = Mo,W; L-L = 2,2 -bipyridine 1,2-bis(diphenylphosphine)ethane) with xanthates and dithiocarbamates

The complexes [MBr(π-allyl)(CO)₂(bipy)] (M = Mo, W, bipy = 2,2′-bipyridine) react with alkylxanthates (M^IRxant), and N-alkyldithiocarbamates (M^IRHdtc) (M^I = Na or K), yielding complexes of general formula [M(S,S)- (π-allyl)(CO)₂(bipy)] (M = Mo, (S,S) = Rxant (R = Me, Et, t-Bu, Bz), RHdtc (R = Me, Et); M = W, (S,S) = Extant). A monodentate coordentate coordination of the (S,S) ligand was deduced from spectral data. The reaction of [MoBr(π-allyl)(CO)₂(bipy)] with MeHdtc and Mexant gives the same complexes whether pyridine is present or not. The complexes [Mo(S,S)(π-allyl)(CO)₂(bipy)] ((S,S) = MeHdtc, Mexant) do not react with an excess of (S,S) ligand and pyridine.No reaction products were isolated from reaction of [MoBr(π-allyl)(CO)₂(dppe)] with xanthates or N-alkyldithiocarbamates.     

Gehinderte Ligandenbewegungen in Übergangsmetallkomplexen : VII. Rotation der olefinliganden L = malein- und furmarsäuredimethylester in komplexen des typs C5H5Mn(CO)2L und C5H5Cr(CO)(NO)L

The restricted rotation of the olefin ligands L = dimethyl maleate and dimethyl fumarate in complexes of the type C₅H₅Mn(CO)₂L and C₅H₅Cr(CO)-(NO)L, respectively, has been investigated on the basis of their temperature-dependent ¹H NMR spectra. The olefinic ligand is arranged preferably in a position where the CC double bond is parallel to the plane of the cyclopentadienyl ring. The possible stereoisomers are discussed using this model. The ¹H NMR spectra of C₅H₅Cr(CO)(NO)(trans-CH₃OOCCHCHCOOCH₃) provide direct evidence that the configuration (R or S) at the metal is stable up to 120°C, and that the restricted motion of the olefin is exclusively rotation around the metal—olefin bond. The activation barriers of the olefin rotation are found to be appreciably lower in the C₅H₅Mn(CO)₂L complexes (ΔG^≠(T_C) 11–12 kcal mol^?1) than in the isoelectric C₅H₅Cr(CO)(NO)L compounds (ΔG^≠(T_C) 15–20 kcal mol^?1).     

Anionic carbonyl complexes of the group VI transition metals with sulfur containing ligands

Anionic complexes of the type [M(CO)₄(dpet)]^? (where M is Cr, Mo or W and dpet is the anion of 2-(diphenylphosphino)ethanthiol) are readily prepared by the reaction of the Tl(dpet) and [M(CO)₅X]^? anions (X = halogen). These complex anions appear to have the normal octahedral geometry with the dpet ligand coordinated through both the P and S atoms. When treated with methyl or allyl halides, neutral complexes of the type M(CO)₄(dpet—R) are formed (where R is an allyl or methyl group now bound to the sulfur atom). By treating Tl^I salts of o-aminothiophenol (atp), o-methylmercaptophenol (nmp) and methylxanthic acid (mxt), with [M(CO)₅]^? anions, the respective complexes [M(CO)₄(atp)]^?, [M(CO)₄(mmp)]^? and [M(CO)₅(mxt)]^? are formed.     

Elektronische effekte in cyclopentadienyl-chrom-komplexen,die mehrere akzeptorliganden enthalten

The coordinative properties of the acceptor ligand CS are discussed on the basis of the new thiocarbonyl complexes CpCr(CO)(CS)(NO) (I), [CpCr(CS)(NO)₂]PF₆ (II), CpCr(CS)(L)(NO) (L = pyridine (III) or trimethylphosphane (IV) and related carbonyl complexes. The IR and NMR spectra (¹H, ¹³C, ³¹P) of the complexes indicate ligand—ligand interactions between CS and both the nitrosyl group and the cyclopentadienyl ring. An attempt is made to compare CS with other sulphur-containing acceptor ligands such as NS (in CpCr(CO)₂(NS)) and CS₂ (in CpCr(CS₂)(PMe₃)(NO)).     

Correlation between solvatochromism and back-bonding in four isomeric (α-diimine)M(CO)4 complexes,M = Cr,Mo, W

Long-wavelength charge transfer absorption energies of isomeric complexes (bidiazine)M(CO)₄, (bidiazine = 3,3′-bipyridazine, 2,2′- and 4,4′-bipyrimidine, 2,2′-bipyrazine; M = Cr, Mo, W) were measured in various solvents and compared with those for corresponding 2,2′-bipyridine complexes. Linear correlations of energies of absorption maxima with solvent parameters E_MLCT revealed that the solvent dependence Δυ/gDE_MLCT within the bidiazine series increases with decreasing absolute charge transfer transition energy in a given solvent, i.e. with increasing back-donation into the ligand π orbital. Complexes of the most strongly back-bonding ligand, 4,4′-bipyrimidine, thus display by far the most pronounced solvent dependence, with Δυ/gdE_MLCT 4100 cm ⁻¹ for the molybdenum system.     

The thermochemistry of M(CO)6−xLx (M = Cr,Mo, W; L = piperidine,pyridine, pyrazine,pyrazole, thiazole; x = 1, 2, 3)

A number of M(CO)_6?xL_x complexes (M = Cr, Mo, W; L = piperidine, pyridine, pyrazine, pyrazole, thiazole; x = 1, 2, 3) are shown to undergo both disproportionation and substitution in a CO atmosphere, when heated on a thermobalance. Using a DSC, reaction enthalpies have been determined from which enthalpies of formation were calculated. Combined with the sublimation enthalpies of these complexes, individual metal—ligand bond enthalpies were evaluated and discussed.     

Preparation and NMR spectroscopy of [Hg{(μ-PEt2)Cr(CO)5}3]−

The new tetranuclear phosphido-bridged compound [Hg{(μ-PEt₂)Cr(CO)₅}₃]⁻ has been obtained by reaction of [Hg{(μ-PEt₂)Cr(CO)₅}₂] with Li[Cr(CO)₅PEt₂]. The coordination of [Cr(CO)₅PEt₂]⁻ results in an unprecedented increase in J(Hg,P), whereas an increase in the number of phosphorus ligands coordinated to mercury is usually accompanied by a decrease in the magnitude of J(Hg,P). This anomaly is interpreted in terms of CrHg donor acceptor interactions.     

N-Heterocyclic Silylenes as Ligands in Transition Metal Carbonyl Chemistry: Nature of Their Bonding and Supposed Innocence

A study on the reactivity of the N-heterocyclic silylene Dipp₂NHSi (1,3-bis(diisopropylphenyl)-1,3-diaza-2-silacyclopent-4-en-2-yliden) with the transition metal complexes [Ni(CO)₄], [M(CO)₆] (M=Cr, Mo, W), [Mn(CO)₅(Br)] and [(η⁵-C₅H₅)Fe(CO)₂(I)] is reported. We demonstrate that N-heterocyclic silylenes, the higher homologues of the now ubiquitous NHC ligands, show a remarkably different behavior in coordination chemistry compared to NHC ligands. Calculations on the electronic features of these ligands revealed significant differences in the frontier orbital region which lead to some peculiarities of the coordination chemistry of silylenes, as demonstrated by the synthesis of the dinuclear, NHSi-bridged complex [{Ni(CO)₂(μ-Dipp₂NHSi)}₂] ( 2 ), complexes [M(CO)₅(Dipp₂NHSi)] (M=Cr 3 , Mo 4 , W 5 ), [Mn(CO)₃(Dipp₂NHSi)₂(Br)] ( 9 ) and [(η⁵-C₅H₅)Fe(CO)₂(Dipp₂NHSi-I)] ( 10 ). DFT calculations on several model systems [Ni(L)], [Ni(CO)₃(L)], and [W(CO)₅(L)] (L=NHC, NHSi) reveal that carbenes are typically the much better donor ligands with a larger intrinsic strength of the metal–ligand bond. The decrease going from the carbene to the silylene ligand is mainly caused by favorable electrostatic contributions for the NHC ligand to the total bond strength, whereas the orbital interactions were often found to be higher for the silylene complexes. Furthermore, we have demonstrated that the contribution of σ- and π-interaction depends significantly on the system under investigation. The σ-interaction is often much weaker for the NHSi ligand compared to NHC but, interestingly, the π-interaction prevails for many NHSi complexes. For the carbonyl complexes, the NHSi ligand is the better σ-donor ligand, and contributions of π-symmetry play only a minor role for the NHC and NHSi co-ligands.     

Transition Metal Cation Salts in Organic Synthesis

Reaction of lithium diisopropylamide (LDA) with (η⁴-1,3-cyclohexadiene)Fe(CO)₃ complexes bearing functionalized side chains at C-5, under an atmosphere of carbon monoxide, gives bridged bicyclo[3,2,1]octene and bicyclo[3,3,1]nonene systems after electrophilic quenching. Under the same reaction conditions, intramolecular cyclization of acyclic (η⁴- 1,3-butadiene)Fe(CO)₃ complexes with functionalized side chains at the terminal position of the diene ligands furnishes fused bicyclo[3.3,0]octanone and bicyclo[4.3.0]nonanone derivatives after acid quenching. The addition of a variety of the highly functionalized zinc-copper reagents RCu(CN)ZnI to the (η⁷-cycloheptatrienyl)Cr(CO) gives (η⁶-cyclohepta-1,3,5-triene)Cr(CO)₃ complexes with a functionalized side-chain at the C-7 position of the ring. Intramolecular cyclization of ester-subsbtuted adducts using lithium diisopropylamide generates fused bicyclo[5.3.0]decane and bicyclo[5.4.0]undecane derivatives. The addition of a variety of the highly functionalized zinc-copper reagents RCu(CN)Znl to the (η⁴-cyclohexa-1,3-diene)Mo(CO)₂(Cp) at the terminus of the coordinated diene ligand gives [Mo(π-allyl)(CO)₂(Cp)](Cp = cyclopentadienyl) complexes with the functionalized side-chain at the C-4 position of the ring. Intramolecular cyclization of the (π-allyl)molybdenum complex containing a pendant propanoic acid unit generates the δ-lactone derivative.     

Synthesis of the pentacarbonyl(chalcocarbonyl)chromium(0) complexes,Cr(CO)5(CX) (X = S,Se)

The arene complexes, (η⁶-C₆H₆)Cr(CO)₂(CX) (X = S, Se), react with excess CO gas under pressure in tetrahydrofuran at about 60° C to produce the Cr(CO)₅(CX) complexes in high yield. The IR and NMR (¹³C and ¹⁷O) spectra of these complexes are in complete accord with the expected C_4v molecular symmetry. Like the analogous W(CO)₅(CS) complex, both compounds react with cyclohexylamine to give Cr(CO)₅(CNC₆H₁₁). However, while W(CO)₅(CS) undergoes stereospecific CO substitution with halide ions (Y^? to form trans-[W(CO)₄(CS)Y]^?, the two chromium chalcocarbonyl complexes apparently undergo both CO and CX substitution to afford mixtures of [Cr(CO)₅Y]^? and trans-[Cr(CO)₄(CX)Y]^?.     

Zur elektronischen struktur von trans-chloro-methylcarbin-tetracarbonyl-chrom ClCr(CO)4CCH3

By means of an extension of the CNDO formalism the donor/acceptor properties of the methylcarbyne ligand are investigated. Apparently this ligand has electronic properties similar to the NO radical. Furthermore the assumption of a carbon metal triple bond in the title compound as well as the possibility of a hyperconjugative coupling of the methyl group to the carbyne carbon atom is confirmed. for trans-CO-substituted carbyne complexes a weak metalCO bond is found in accordance with the special thermal instability of these compounds. Finally the electronic structure of ClCr(CO)₄CCH₃ is compared with those of Cr(CO)₆, Mn(CO)₅Cl and of a hypothetic (CO)₅VCCH₃.     

A carbon-13 NMR study of some metal carbonyl compounds containing one-electron ligands

Carbon-13 NMR spectral data for complexes having the general formula CpM(CO)_nX (Cp = η⁵-C₅H₅; M = Mo or W, n = 3; M = Fe, n = 2; X = halogen, methyl or acetyl) and their phosphine and isocyanide substitution products are reported. For CpM(CO)₃X complexes two carbonyl resonances (1 : 2 ratio) are observed in all cases, consistent with the retention of the “piano-stool” geometries observed in the solid state. Substituted complexes CpM(CO)₂(L)X (M = Mo or W; L = PR₃ or cyclohexyl isocyanide) are unequivocally assigned cis or trans geometries on the basis of the number of observed carbonyl resonances and values of ²J(PC) for the phosphine substituted derivatives. Spectral data for [M(CO)₅X]^? (M = Cr, Mo or W; X = Cl, Br or I) and η⁷-C₇H₇Mo(CO)₂X and the halide derivatives above generally show an increase in the shielding for carbonyls adjacent to the halide ligand in the order Cl < Br < I. Carbonyl resonances are more shielded in isostructural complexes in the order Cr < Mo < W (triad effect).     

Theoretical study of solvent and substituent effects on the structure, <Superscript>14</Superscript>N NQR and electronic spectra of [Cr(CO)<Subscript>5</Subscript>py]

The structure, ¹⁴N NQR parameters, electronic spectra, and hyperplarizability of [Cr(CO)₅py] in seven different solvents were theoretically computed with MPW1PW91 method based on Polarizable Continuum Model (PCM). The substituent effects in para- substituted Cr(CO)⁵–pyridine complexes have been evaluated. The results indicate that both polarity of solvents and the substituents have played a significant role on the structures and properties of complexes. The study also shows that the structural and solvent modification change the NLO properties.     

Diazene ligand geometry effects on the formation and properties of metal carbonyl complexes. Group vib pentacarbonyl complexes of cis- and trans-1,2-diisopropyldiazene and 1,2-diisopropylhydrazine

The Group VIB complexes M(CO)₅L have been synthesized for the cases L= cis-1,2-diisopropyldiazene (c-DIPD) with M = Cr, Mo, W, L = trans-1,2-diisopropyldiazene (t-DIPD) with M = Or, W, and L, = 1,2-diisopropylhydrazine (DIPH) with M = Cr, W. Failure to obtain any bimetallic complexes is discussed in terms of steric interactions of these and related complexes. The significance of diazene ligand geometry is demonstrated by the differences in properties of the c-DIPD and t-DIPD complexes. The available evidence indicates that cis diazenes are better ligands than their trans isomers. Complex stability decreases in the order W > Cr > Mo and c-DIPD > t-DIPD. Infrared, visible, and NMR spectra are interpreted in terms of bonding in the complexes. A 30–60 cm^?1 reduction of v(NN) of the diazenes upon coordination is attributed to metal-ligand π-bonding with c-DIPD being a better π-acceptor than t-DIPD. The NMR spectra of the c-DIPD complexes are temperature dependent and show that the M(CO)₅ moiety undergoes coordination site exchange between the two nitrogen atoms. No exchange occurs in the t-DIPD complexes. Coalescence temperatures of 10, ?48, and 60°C were recorded for the Cr, Mo, and W complexes of c-DIPD respectively, with the Gibbs free energy barriers of 15.0, 11.5 and 15.0 kcal/ mol. A comparison with exchange in other M(CO)₅(cis-diazene) complexes is made and the role of the diazene structure on the reaction rate is discussed. The M(CO)₅(DIPH) (M = Cr, W) complexes have been oxidized by H₂O₂/Cu²⁺ and by activated MnO₂ to DIPD complexes in low yield. The tungsten DIPH complex gives only W(CO)₅(t-DIPD) but the chromium system gives predominantly Cr(CO)₅(c-DIPD).     

Chrom-, molybdän-, wolfram- und mangan-komplexe von 1-phenyl-4,5-dihydroborepin

1-Phenyl-4,5-dihydroborepin (I) reacts with suitably substituted carbonyls of Cr, Mo, and W to yield stable complexes LM(CO)₄ with L = I and M = Cr, Mo, W. Irradiation of (C₅H₅)Mn(CO)₃ in the presence of I produces labile (C₅H₅)MnL(CO). Large upfield ¹¹B NMR shifts in these complexes with respect to I indicate that the born atom participates in the metalligand bonding.     

Stibinidenkomplexe: Verbindungen mit trigonal planar koordiniertem antimon

Intensively coloured stibinidene complexes (L_nM)₂SbR (L_nM = (CO)₅Cr; R = ^tBu, Cl, I, EtS. L_nM = C₅H₅(CO)₂Mn; R = Cl. L_nM = CH₃C₅H₄(CO)₂Mn; R = Br) which contain trigonally planar coordinated Sb(+1) with the stibanediyl ligand stabilized by M $\text{?}$ Sb(R) $\text{?}$ M-π-bonding have been obtained. Their synthesis and properties as well as an X-ray structure determination of [CH₃C₅H₄(CO)₂Mn]₂SbBr are described.     

[N‐(Benzyl­idene)­aniline‐N]­pentacarbonyl­chromium(0)

In the title compound, [Cr(C₁₃H₁₁N)(CO)₅], the imino ligand displays weak π‐acceptor capabilities and, in contrast to Fischer‐type carbene complexes, is not positioned on the bisecting line of the angle between two CO ligands.     

1,3-diaryltriazenido complexes of ruthenium(I), (II) and (III), and of osmium(III), rhodium(III) and iridium(III)

The synthesis and characterization of the platinum metal—1,3-diaryltriazenido complexes [Ru(ArNNNAr)(CO)₃]₂, [Ru(ArNNNAr)₂]₂, cis-Ru(ArNNNAr)₂(CO)₂, MX₂(ArNNNAr)(PPh₃)₂ (M = Ru, Os; X = Cl, Br) and M′(ArNNNAr)₃ (M′= Ru, Os, Rh and Ir) are reported. Axial ligand substitution in [Ru(ArNNNAr)(CO)₃]₂ and adduct formation by [Ru(ArNNNAr)₂]₂ are described. In contrast to other known Ru(II)/Ru(II) “lantern” molecules, the species [Ru(ArNNNAr)₂]₂ have measured magnetic moments equivalent to ca one unpaired electron per dimer, which are presumably due to population of the spin states σ²π⁴δ²π^*4 and σ²π⁴δ²π^*3σ^*1.     

Substituent Effect Parameters: Extending the Applications to Organometallic Chemistry

Typically, metal complexes are constituted of an acceptor metal ion and one or more Iigands containing the donor atoms. Accordingly, the properties of a metal complex are equally dependent on the nature of the metal ion and the ligands. Minute structural variations in the ligand will may result in linear changes in the respective energetic parameters and such linear relationships have paramount importance in organometallic chemistry. The variation in ligands is virtually limitless and substantial because of the extent of organic chemistry available for the modelling of desirable ligands, apart from the variation in metal ions. Anyhow, there is still a need for new parameters for the design and quantification of new ligands which in turn leads to the synthesis of metal complexes with possibly predictable chemical properties. Previous studies have demonstrated that quantum chemically derived molecular electrostatic potential (MESP) parameters can be listed as one of the superior quantifiers in this regard, which can act as an effective ligand electronic parameter. The interaction between the ligand part and metal-containing part will be crucial in assessing the reactivity of organometallic complexes. Here we are applying MESP based substituent constants derived from substituted benzenes to forecast the interaction energies in (pyr^*)W(CO)₅, (NHC^*)Mo(CO)₅ and (η⁶-arene^*)Cr(CO)₃ complexes. Ligands and metal ions are varied in each case for better understanding and transparency.     

Synthesis of Re(I) complexes bearing tridentate 2,6-bis(7-azaindolyl)phenyl ligand with green emission properties

The Re(I) complexes bearing 2,6-bis(7^′-azaindolyl)phenyl ligand as a tridentate ligand were synthesized by treatment with Re₂(CO)₁₀. The structures of the complexes were confirmed by X-ray crystallography. Both 7-azaindolyl ligands of Re(I) complexes are present in butterfly forms. The Re-C_ipso bonds showed a partial double bond character by π back-donation between the phenyl moiety and Re atom. In THF solution at room temperature, these complexes exhibited green emission (λ_em=510 nm), which is considered to be attributable to MLCT (dz²(Re) →π^* (7^′-azaindolyl group)) transition containing π→π^* (7^′-azaindolyl group) transition.