RATES OF RING-OPENING OF 2,2,4,7,7-PENTAMETHYL-3,6-DITHIAOCTANE TETRACARBONYL TUNGSTEN (0)

Abstract

Ring displacement from η²-PDOW(CO)₄ (PDO = 2,2,4,7,7-pentamethyl-3.6-dithiaoctane) by L (L = P(0-i-Pr)₃ and P(OEt)₃) produces a mixture of cis- and trans- (L)₂W(CO)₄. Results from kinetics experiments are consistent with the results observed for the structurally-related η²-DTOW(CO)₄ complex (DTO = 2,2,7,7-tetramethyl-3,6-dithiaoc-tane). A smaller value for the rate constant (k₁) for the ring-opening step of η²-PDOW(CO)₄ reflects the shorter W-S bond distances observed in η²-PDOW(CO)₄. This observation is consistent with the trend observed for a series of η²-DTAW(CO)₄ complexes (DTA = Dithiaalkanes) in which the value of k₁ increases with the size of the chelate ring. Since the species η²-PDOW(CO)₄ and η²-DTOW(CO)₄ are five-membered chelate complexes, differences in their molecular and kinetic parameters are being ascribed to the methyl group in the chelate backbone of η²-PDOW(CO)₄. Our observations confirm earlier findings that small differences in the structure of DTA greatly affect the rates of ring-opening in η²-DTAW(CO)₄ complexes.     

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]^?.     

A stable carbonyl-pyrazine-metal(0) complex: Synthesis and characterization of cis-tetracarbonylpyrazinetrimethylphosphitetungsten(0)

Pentacarbonylpyrazinetungsten(0), (CO)₅W(pyz), is not stable in solution in polar solvents such as acetone or dichloromethane and undergoes conversion to a bimetallic complex, (CO)₅W(pyz)W(CO)₅ plus free pyrazine. These three species exist at equilibrium. Using the quantitative ¹H NMR spectroscopy, the equilibrium constant could be determined to be K_eq = (5.9 ± 0.8) × 10⁻² at 25 °C. Introducing a second pyrazine ligand into the molecule does not stabilize the complex, as cis-W(CO)₄(pyz)₂ was found to be less stable than W(CO)₅(pyz) and, therefore, could not be isolated. However, introducing trimethylphosphite as a donor ligand into the complex leads to the stabilization of the carbonyl-pyrazine-metal(0) complexes, as shown by the synthesis of cis-W(CO)₄[P(OCH₃)₃](pyz). This complex could be isolated from the reaction of the photogenerated W(CO)₄[P(OCH₃)₃](tetrahydrofuran) with trimethylphosphite upon mixing for 2 h at 10 °C in tetrahydrofuran and characterized by elemental analysis, IR, MS, ¹H, ¹³C, and ³¹P NMR spectroscopy.     

The syntheses and coordination properties of M(CO)3X(DAB) (M = Mn,Re; X = Cl,Br, I; DAB = 1,4-diazabutadiene)

M(CO)₅X (M = Mn, Re; X = Cl, Br, I) reacts with DAB (1,4-diazabutadiene = R₁N=C(R₂)C(R₂)′=NR′₁) to give M(CO)₃X(DAB). The ¹H, ¹³C NMR and IR spectra indicate that the facial isomer is formed exclusively. A comparison of the ¹³C NMR spectra of M(CO)₃X(DAB) (M = Mn, Re; X = Cl, Br, I; DAB = glyoxalbis-t-butylimine, glyoxyalbisisopropylimine) and the related M(CO)₄DAB complexes (M = Cr, Mo, W) with Fe(CO)₃DAB complexes shows that the charge density on the ligands is comparable in both types of d⁶ metal complexes but is slightly different in the Fe-d⁸ complexes. The effect of the DAB substituents on the carbonyl stretching frequencies is in agreement with the A′(cis) > A″ (cis) > A′(trans) band ordering.Mn(CO)₃Cl(t-BuNCHCHNt-Bu) reacts with AgBF₄ under a CO atmosphere yielding [Mn(CO)₄(t-BuNCHCHN-t-Bu)]BF₄. The cationic complex is isoelectronic with M(CO)₄(t-BuNCHCHNt-Bu) (M = Cr, Mo, W).     

The nature of the lowest excited state and photosubstitution reactivity of tetracarbonyl-1,10-phenanthrolinetungsten(0) and related complexes

Absorption and emission spectral studies of M(CO)₄L complexes (M = Cr Mo, W; L = 2,2′-bipyridine, 1,10-phenanthroline, 5-CH₃-, 5-Cl-, 5-Br-, 5-NO₂-1,10-phenanthroline) have been carried out and reveal that the lowest excited state in every case is charge-transfer (CT) in character, M→ CT in absorption, and in no case do the ligand field (LF) excited states cross below the CT state. Minimum energies of the LF states have been established by the spectroscopic study of cis-bis(pyridine)- and cis-bis(aliphatic amine)-tetracarbonylmetal(0) complexes which all have LF lowest excited states for M = Mo, W. For the M(CO)₄L complexes emission is detectable for M = Mo or W and occurs in the range 14.40-15.66 kK with lifetimes of 7.9-13.3 μsec and quantum yields of 0.02–0.09 all in EPA solution at 77 K. For the bis-pyridine and -aliphatic amine complexes emission occurs only from the W complexes and is of the order of 3.0–4.0 kK higher in energy than for the M(CO)₄L complexes. Photosubstitution of pyridine is efficient in cis-W(CO)₄(py)₂ (py = pyridine): Φ_436nm = 0.23; Φ_405nm = 0.27; and Φ_366nm = 0.23. The M(CO)₄L complexes have strongly wavelength dependent, but modest, quantum yields for CO substitution and show that the lowest CT state is unreactive. Typical values for CO substitution for M = W and L = 1,10-phenanthroline are: Φ_436nm = 1.6 × 10^?4; Φ_405nm = 1.2 × 10^?3; Φ_366nm = 9.2 × 10^?3; and Φ_313nm = 2.2 × 10^?2.     

Tetracarbonyl group 6 complexes containing secondary and tertiary phosphines

The mixed ligand tetracarbonyl derivatives, cis-M(CO)₄(PPh₂H)(PPh₃) (M  Cr, Mo, W) and cis-W(CO)₄(PPh₂H)(L) (L  PEt₃, PEt₂Ph, PEtPh₂) have been prepared from the reaction of M(CO)₅PPh₂H with L in THF in the presence of potassium t-butoxide. These reactions are accompanied in most instances by the formation of [W(CO)₅PPh₂]⁻, [(OC)₅M(μ-PPh₂)M(CO)₅]⁻, [(OC)₅M(μ-PPh₂)-M(CO)₄(PPh₂H)]⁻, [(OC)₄M(μ-PPh₂)₂M(CO)₄]²⁻, (OC)₄M(μ-PPh₂)₂M(CO)₄, and cis-M(CO)₄(PPh₂H)₂.     

Reactivity of tungsten(0) and molybdenum(0) pentacarbonyl thiobenzoate anions: thiobenzoate as a cis-CO labilizing ligand

The [Et₄N][M(CO)₅SCOPh] complexes (1a, M = Mo; 2a, M = W) have been prepared at ambient temperatures by reacting the photogenerated M(CO)₅ THF intermediate with [Et₄N][SCOPh] in THF. Kinetic studies of the reactions of the anions [M(CO)₅SCOPh]^– with the tri(iso-propyl)phosphite (L) ligand under pseudo-first-order conditions indicate that these reactions are first-order in substrate and are independent of the P(OPr-i)₃ concentration. It is thus envisaged that these CO substitutions proceed via a mechanism which involves initial cis-M—CO bond-breaking, followed by fast attack of the incoming nucleophile on the resulting intermediate to give [cis-M(CO)₄{P(O-Pri)₃}SCOPh]^–. This facile displacement of cis-CO indicates the labilizing nature of the thiobenzoate ligand, most probably by virtue of distal oxygen atom participation. Activation parameters for the reactions are: [M(CO)₅SCOPh]^– + L cis-[M(CO)₄(L)SCOPh]^– + CO M = Mo, H = 24.6(2) kcal mol^–1, S = 8.2(6) eu; M = W, H = 28.4(2) kcal mol^–1, S = 11.3(5) eu. Kinetic data and the mechanism of these ligand-substitutions are discussed.     

A mass spectral study of intramolecular rearrangements in cis-M(CO)4(13CO)piperidine (M = Cr,W) derivatives

Low voltage mass spectra of cis-M(CO)₄(¹³CO)piperidine (M = Cr,W) show the initial loss of CO to proceed with complete scrabling of the label between axial and equatorial sites.     

Kinetic characterization of the interactions of trans-dichloro-platinum(IV) anticancer prodrugs and a model compound with thiosulfate

Sodium thiosulfate has been utilized as a rescuing agent for relief of the toxic effects of cisplatin and carboplatin. In this work, we characterized the kinetics of reactions of the trans-dichloro-platinum(IV) complexes cis-[Pt(NH₃)₂Cl₄], ormaplatin [Pt(dach)Cl₄] and trans-[PtCl₂(CN)₄]^2? (anticancer prodrugs and a model compound) with thiosulfate at biologically important pH. An overall second-order rate law was established for the reduction of trans-[PtCl₂(CN)₄]^2? by thiosulfate, and varying the pH from 4.45 to 7.90 had virtually no influence on the reaction rate. In the reactions of thiosulfate with cis-[Pt(NH₃)₂Cl₄] and with [Pt(dach)Cl₄], the kinetic traces displayed a fast reduction step followed by a slow substitution involving the intermediate Pt(II) complexes. The reduction step also followed second-order kinetics. Reductions of cis-[Pt(NH₃)₂Cl₄] and [Pt(dach)Cl₄] by thiosulfate proceeded with similar rates, presumably due to their similar configurations, whereas the reduction of trans-[PtCl₂(CN)₄]^2? was about 1,000 times faster. A common reduction mechanism is suggested, and the transition state for the rate-determining step has been delineated. The activation parameters are consistent with transfer of Cl⁺ from the platinum(IV) center to the attacking thiosulfate in the rate-determining step.     

Aminobis(phenolate)s of imidomolybdenum(VI) and -tungsten(VI)

The reactions of trans-[MoO(ONO^Me)Cl₂] 1 (ONO^Me = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) dianion) and trans-[MoO(ONO^tBu)Cl₂] 2 (ONO^tBu = methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) with PhNCO afforded new imido molybdenum complexes trans-[Mo(NPh)(ONO^Me)Cl₂] 3 and trans-[Mo(NPh)(ONO^tBu)Cl₂] 4, respectively. As analogous oxotungsten starting materials did not show similar reactivity, corresponding imido tungsten complexes were prepared by the reaction between [W(NPh)Cl₄] with aminobis(phenol)s. These reactions yielded cis- and trans-isomers of dichloro complexes [W(NPh)(ONO^Me)Cl₂] 5 and [W(NPh)(ONO^tBu)Cl₂] 6, respectively. The molecular structures of 4, cis-6 and trans-6 were verified by X-ray crystallography. Organosubstituted imido tungsten(VI) complex cis-[W(NPh)(ONO^tBu)Me₂] 7 was prepared by the transmetallation reaction of 6 (either cis or trans isomer) with methyl magnesium iodide.     

Komplexe mit Antimon‐Liganden: [tBu2(Cl)SbW(CO)5], [tBu2(OH)SbW(CO)5], O[SbPh2W(CO)5]2, E[SbMe2W(CO)5]2 (E = Se,Te), cis‐[(Me2SbSeSbMe2)2Cr(CO)4]

Complexes Containing Antimony Ligands: [^tBu₂(Cl)SbW(CO)₅], [^tBu₂(OH)SbW(CO)₅], O[SbPh₂W(CO)₅]₂, E[SbMe₂W(CO)₅]₂ (E = Se, Te), cis‐[(Me₂SbSeSbMe₂)₂Cr(CO)₄] Syntheses of [^tBu₂(Cl)SbW(CO)₅] ( 1 ), [^tBu₂(OH)SbW(CO)₅] ( 2 ), O[SbPh₂W(CO)₅]₂ ( 3 ), Se[SbMe₂W(CO)₅]₂ ( 4 ), cis‐[(Me₂SbSeSbMe₂)₂Cr(CO)₄] ( 5 ) Te[SbMe₂W(CO)₅]₂ ( 6 ) and crystal structures of 1 – 5 are reported.     

The kinetics and mechanism of diene exchange in (η4-enone) Fe(CO)2L complexes (L = phosphine,phosphite)

Kinetic data for the exchange of 1,3-cyclohexadiene with (η⁴-benzylideneacetone)Fe(CO)₂L complexes (L = CO, PPh_3-xMe_x (x = 0-2) or P(OPh)₃) to give (η⁴-1,3-cyclohexadiene)Fe(CO)₂L derivatives indicate a mechanism involving stepwise competing D and I_d opening of the ketonic M-CO π-bond. Rates increase in the order CO ? PPh₃ ≈ P(OPh)₃ > PPh₂Me ? PPhMe₂, and both steric and electronic factors appear to be important. (η⁴-1,3-cyclohexadiene)Fe(CO)₂L complexes of potential use in enantioselective synthesis (L=(+)-Ph₂P(menthyl) or (+)-Ph₂PCH₂CH(Me)Et) may be prepared via their (η⁴-benzylideneacetone)Fe(CO)₂L complexes.     

Some catalytic properties of Rh(diphos)(η-BPh4)

The covalent complex Rh(diphos)(η-BPh₄) (I) reacts with CO in polar solvents to afford the cationic dicarbonyl cis-[Rh(diphos)(CO)₂](BPh₄). I is an effective catalyst for methylacetylene oligomerization and allene polymerization. In the presence of CO₂ and methylacetylene, I affords 4,6-dimethyl-2-pyrone.     

The vibrational spectra of isotopically substituted metal carbonyls : V. C18-O-substituted cis-Mn(CO)4LBr (L = PPh3, AsPh3, SbPh3)

The reactions of cis-Mn(CO)₄LBr (L = PPh₃, AsPh₃, SbPh₃) with 96%¹⁸O-enriched CO in cyclohexane solution at 35°C have been investigated by IR spectroscopy in the ν(CO) region and the vibrational modes of the parent molecules and the various C¹⁸O-substituted species produced have ben assigned with the aid of approximate force field calculations for the energy-factored CO stretching blocks of the (FG) matrices. The IR data for the reaction of the triphenylphosphine complex indicate that, while all four carbonyl groups are eventually replaced by C¹⁸O, there is initially a stereochemical preference for axial CO substitution. For the other two complexes, both carbonyl and L substitution take place.     

Kinetics of substitution atcis-tetracarbonylbis(4-methylpyridine)-tungsten(0)

Summary Rate constants have been obtained for reactions ofcis-tetracarbonylbis(4-methylpyridine)tungsten(0),cis-[W(CO)₄(4Mepy)₂], with 1, 10-phenanthroline, 2,2-bipyridyl, and related diimine ligands in toluene solution at 298.2K. Effects of varying the nature and concentration of the entering ligand, and of addition of 4-methylpyridine, indicate the operation of a limiting dissociative (D) mechanism. This is confirmed by the establishment of an activation volume of + 8 cm³ mol^–1, in toluene at 298.2K.     

Kinetics and mechanism of the anation of cis (aquo)(ammine) bis(ethylenediamine) Co(III) by oxalate

The kinetics of the anation of cis (aquo)(ammine)bis(ethylenediamine)Co(III) by H₂C₂O₄, HC₂O₄⁻ and C₂O₄²⁻ have been investigated at 50–60°C and I = 1.0 mol dm⁻³ (ClO₄⁻). Association of the aquo cation with oxalic acid could not be identified. The association constants of the aquo-HC₂O₄⁻ and aquo-C₂O₄²⁻ ion-pairs are essentially temperature independent and have values 1.5 and 5.8 dm³ mol⁻¹ (50–60°C) respectively. The interchange reactions of the ion-pairs to yield the innersphere complexes, cis[(en)₂(NH₃)CoC₂O₄]⁺ or its acid form, are assigned a dissociative mechanism, Id, involving CoO bond breaking. The mechanism of the anation of the aquo cation by H₂C₂O₄ may be Id but the possibility of rate limiting addition of oxalic acid to the CoO bond can not be completely ruled out.     

Synthesis and structure of stable cis-dimethyl complex of oxotungsten(VI)

Oxotungsten(VI) complex cis-[WO(L^tBu)Me₂] (L^tBu = methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) was prepared by the transmetallation reaction of [WO(L^tBu)Cl₂] (either cis or trans isomer) with methyl magnesium iodide. This unexpectedly stable dialkyl complex can be activated by Et₂AlCl to catalyze the ring-opening metathesis polymerization of norbornene.     

Reductive elimination of halogens assisted by phosphine ligands in Fe(CO)4X2 (X = I, Br) complexes

Fe(CO)₄X₂ complexes [X = I (1), Br(1′)] react with phosphine ligands L (L = PMe₃, PEt₃, PMe₂Ph, PMePh₂, PPh₃) via a two-step mechanism: in the first step fac-Fe(CO)₃LX₂ complexes are formed; in the second step two parallel pathways, a and b, are observed; in pathway a, reductive elimination with formation of equimolar amounts of Fe(CO)₃L₂ (5) and phosphonium salts [LX]⁺X⁻ is observed; in pathway b, disubstituted dihalide complexes cis,trans,cis-Fe(CO)₂L₂X₂ are formed. The relative weights of pathways a and b depend on the basicity, steric hindrance and concentration of ligand L, on the nature of the halogen and on temperature. A radical mechanism which accounts for most of the experimental results is proposed.     

Octahedral metal carbonyls: XL. Rates of olefin coordination via chelate ring-closure in cis-[(η1-4-pentenyldiphenylphosphine)tetracarbonyltungsten(0)] created through flash photolysis

Ring-closure via olefin coordination in coordinatively-unsaturated cis-[(η¹-pdpp)W(CO)₄], (pdpp = CH₂CH(CH₂)₃P(C₆H₅)₂, 4-pentenyldiphenylphosphine) produced via pulsed laser flash photolysis of cis-(pip)(η¹-pdpp)W(CO)₄ (pip = piperidine) in chlorobenzene has been identified unequivocally. Rates and activation parameters for this pathway and for competitive bimolecular interaction of pip at the solvated coordination site have been measured.     

Improved syntheses of Ru(CO)2 (O3SCF3)2 (bidentate) complexes and their conversion into new [Ru(CO)2 (bidentate)2]2+ complexes

Reaction of the complexes Ru(CO)₂Cl₂L [L = 2,2′-bipyridyl (bpy) or 1,10-phenanthroline (phen)] with trifluoromethanesulphonic acid under carefully controlled conditions yields Ru[cis-(CO)₂] [cis-(O₃SCF₃)₂] (bidentate complexes. From reactions of the trifluoromethanesulphonates with the appropriate bidentate ligands, the new complexes [cis-Ru(CO)₂-L(L′)]²⁺ (L as above; L′ = 4,4′-dimethyl-2,2′-bipyridyl or 4,4′-diisopropyl-2,2′-bipyridyl) as well as the known [_cis-Ru(CO)₂L₂]²⁺ and [cis-Ru(CO)₂bpy(phen)]²⁺ have been prepared.