Reaction of carbon monoxide with tri-tert-butylgallium: The first example of CO insertion into a gallium-carbon bond

Reactions of ^tBu₃M (M = Al, Ga) with CO have been studied by density functional theory employing the B3PW91 functional. Calculations suggest that CO insertion into a M-C bond of ^tBu₃M is thermodynamically favorable at room temperature, whereas CO coordination to ^tBu₃M to form ^tBu₃M·CO is unfavorable due to an unfavorable entropy change. These results are in agreement with experimental observations. Reaction of carbon monoxide with ^tBu₃Ga at 50 °C and atmospheric pressure yields the dimeric tert-butylacyl complex [^tBu₂GaC(O)^tBu]₂ (1). Compound 1 has been characterized by X-ray crystallography and NMR and IR spectroscopy. Isotopic labeling with ¹³CO confirmed that the acyl carbon of 1 results from the CO starting material. CO insertion into a Ga-C bond does not occur for Me₃Ga or ⁿBu₃Ga under a range of reaction conditions.     

Norbornadiene complexes of molybdenum(II) and their transformation to a catalyst for ring-opening metathesis polymerization: DFT calculations - X-ray crystal structure of a new norbornadiene complex [MoCl(GeCl3)(CO)3(η-nbd)]

Photolysis of [Mo(CO)₄(η⁴-nbd)] (nbd = norbornadiene) in n-heptane solution containing GeCl₄ leads to the formation of a seven-coordinate compound with a direct Mo-Ge bond, [MoCl(GeCl₃)(CO)₃(η⁴-nbd)] (1). The molecular structure of compound 1 has been established by single-crystal X-ray diffraction studies. Similarly to the previously investigated heterobimetallic complexes of molybdenum(II), [MoCl(SnCl₃)(CO)₃(η⁴-nbd)] (2) and [MoCl(SnCl₃)(CO)₂(NCMe)(η⁴-nbd)] (3), the molybdenum-germanium compound 1 initiates the ring-opening metathesis polymerization (ROMP) of nbd. Density functional theory calculations at the B3LYP level have been performed to understand the mechanism of the rearrangement of the η⁴-nbd ligand to the species initiating the ROMP reaction in the coordination sphere of the molybdenum(II) complexes 2 and 3, which together with complex 1 are representative examples of experimental complexes in which such a transformation takes place.     

Insertion reactions of SnCl2 into Pt-Cl bonds in pentahalophenylplatinate(II) complexes

Several pentahalophenylplatinate complexes with Pt-Sn metal-metal bonds have been synthesized by facile insertion of SnCl₂ into Pt-Cl bonds of the starting platinum substrates. The complexes have been characterized spectroscopically and, in the case of (NBu₄)₂[trans-Pt(SnCl₃)₂(C₆F₅)₂] and (NBu₄)₂[trans-Pt₂(μ-Cl)₂(SnCl₃)₂(C₆F₅)₂], the structures have been analyzed by X-ray diffraction. The reactivity of these derivatives towards neutral ligands has been explored. The electronic spectra of some selected derivatives have also been examined.     

In-depth insight into metal–alkene bonding interactions

The relative alkene dissociation energies and the structures of Pd(PH₃)₂(η²-CH₂CHX), trans-[Pd(PH₃)₂Cl(η²-CH₂CHX)]⁺, trans-[Pd(PH₃)Cl₂(η²-CH₂CHX)], Cp₂Zr(PH₃)(η²-CH₂CHX) and [Cp₂Zr(CH₃)(η²-CH₂CHX)]⁺ (X = CN, Cl, Br, Me, OMe, NMe₂) were calculated with the B3LYP density functional theory. We examined the correlations between the partial charges of the coordinated alkenes and the relative alkene dissociation energies. Through these correlations, we have been able to see how the alkene(π)-to-metal(d) donation and metal(d)-to-alkene(π*) back-donation interactions affect the relative alkene dissociation energies. We also examined the calculated structures and found that the Zr(IV) and Pd(II) complexes have a rather asymmetric alkene coordination while the Zr(II) and Pd(0) complexes have an approximately symmetric alkene coordination. The effects of the alkene(π)-to-metal(d) donation and metal(d)-to-alkene(π*) back-donation interactions on the structural features have also been discussed.     

Studies of the fischer-tropsch process on uranium catalysts

In the study of the catalytic reaction of uranium powder, phenylacetylene and dimethylacetylenedicarboxylate were converted to polymers via linear-oligomerization and cyclo-oligomerization reactions [6]. Our results indicate a new synthetic pathway of the carbon-carbon bond formation through the participation of f-orbital elements. In this report, reactions of methylenediiodide, diazomethane and ketene were studied. The products of these reactions, i.e., C₁ and C₄ alkanes and alkenes, suggested that the bond could be formed by the insertion of methylene radicals. An interesting phenomenon, where the carbon number of products increased with the duration of reaction period, was found.The role of the uranium element in the Fischer-Tropsch process was studied. Hydrogen and carbon monoxide were catalyzed to methane (60–70%), CH₃OH (20–25%), C₂H₅OH and CH₃OCH₂OCH₃ at one atmosphere pressure and 250 °C. The Fischer-Tropsch process could proceed through uranium alkoxide intermediates. This oxide-formation machanism was tested by the pyrolysis of uranium alkoxides.     

Structural,infrared and Mössbauer studies of octahedral cis-dichlorobis(diketonate)tin(IV) complexes having anti-tumour activity

Two complexes, SnCl₂(bzac)₂ [Hbzac = benzoylacetone] and SnCl₂(bzbz)₂ [Hbzbz = dibenzoylmethane], have been prepared and characterised by analytical, infrared and Mössbauer studies. In addition, the X-ray crystal structure of SnCl₂(bzbz)₂ has been determined. The crystals are orthorhombic, space group Pbca with cell parameters a=18.767(9), b=17.611(8), c=16.563(8) Å. A total of 2116 reflections with I/σ(I)⩾3 gave R=3.0%. The tin is coordinated to two cis-chlorine and four oxygen atoms from the dibenzoylmethanato ligands in an approximately octahedral arrangement. The bond distances in the tin coordination sphere are SnCl 2.335(2) and 2.344(2) Å and SnO 2.062(4), 2.074(4), 2.063(4) and 2.063(4) Å and the ClSnCl angle is 95.1(1)°. The results of anti-tumour tests on these complexes are given and attempts are made to correlate the anti-tumour activity of SnCl₂(bzbz)₂ with its structure.     

Insertion reactions of carbonyl sulfide and carbon disulfide with [HRu(η5-C5H5)(EPh3)(E′Ph3)] (E,E′  P,As, Sb)

Monthioformate and dithioformate complexes of [HRu(η⁵-C₅H₅)(EPh₃)(E′Ph₃)] (E, E′  P, As, Sb) have been synthesized as a result of the insertion reactions of [HRu(η⁵-C₅H₅)(EPh₃)(E′Ph₃)] with carbonyl sulfide and carbon disulfide. The complexes were characterized by microanalytical, infra red, ¹H NMR, ¹³C NMR spectral data, molecular weight determination along with other studies.     

Synthesis and reactivity of mixed pentafluorophenyl platinum(I)-palladium(I) derivatives

XPd(μ-dppm)₂Pt(C₆F₅) (X = Cl (I), Br (II)) have been prepared by reacting Pd₂(dba)₃·CHCl₃ and PtX- (C₆F₅)(η¹-dppm)₂. Reaction of complex I with SnCl₂ gives the SnCl₃⁻ derivative, whilst ligands L (PPh₃, P(OPh)₃, SbPh₃) render the cationic complexes. The species R₂N⁺, SO₂ or MeOOC)CCCOOMe insert into the PdPt bond of I to give A-frame Pd(II)- Pt(II) complexes. The reactions of CIPd(μ-dppm)₂- Pt(C6F₅) with isonitriles CNR (R = p-Tol, Cy) lead to products containing either terminal or inserted isocyanide or both.     

Carbonyl trichlorostannate complexes of platinum: chemistry and 119Sn, 195Pt,and 13C NMR spectroscopy

The reactions of the carbonyl anion [PtCl₃(CO)]^- with SnCl₂ in the presence of CO in both methylene chloride and acetone are reported. In the former solvent, only Pt^II-SnCl₃ species are formed. These have been identified by ¹³C, ¹¹⁹Sn and ¹⁹⁵Pt NMR measurements as cis-[PtCl₂(SnCl₃)(CO)]^-, (I), trans- [PtCl(SnCl₃)₂(CO)]^-, (II), and [Pt(SnCl₃)₄(CO)]^2-, (III). Salts of these complexes have been isolated. In contrast, when acetone is the solvent, reduction of the platinum occurs to give two new complexes. On the basis of NMR measurements, we assign one of these as the Pt^I dimer [Pt₂(SnCl₃)₄(CO)₂]^2-, (IV), and the other as a platinum triangle (VI) containing terminal CO ligands and two types of Sn ligand. The Pt^II compound (IV) can also be generated by treating a CH₂Cl₂ solution of trans-[PtCl(SnCl₃)_2- (CO)]^-, (II), with dihydrogen. NMR spectroscopic data, including those from measurements on samples of the complexes containing ¹³C-enriched CO, are reported and discussed.     

Conversion of the reactive sulfhydryl groups of proteins to the S-trifluoroethyl derivatives: Application to human hemoglobin

The S-2,2,2-trifluoroethyl residue (-SCH₂CF₃) has been incorporated into human hemoglobin, Hb₄(SH)₂, as an extrinsic probe at Cys-β93 through formation of a disulfide bond. The thiol group was activated by reaction with 5,5′-dithiobis(2-nitrobenzoic acid), Hb₄(SSCH₂CF₃)₂ then being obtained by reaction with 2,2,2-trifluoroethanethiol. Both disulfide interchange reactions proceed to completion with a modest excess of reagents using dilute solutions of hemoglobin (0.005 m heme). The stoichiometry of each disulfide interchange reaction is readily determined by measurement of 5-thio-2-nitrobenzoic acid, a product of each reaction. The functional properties of Hb₄ (SSCH₂CF₃)₂ were found to be similar to those of Hb₄(SH)₂. At pH 7.0 and 20°C the partial pressure of oxygen required for half saturation was 0.45 mm Hg in 0.050 m 2,2-bis(hydroxymethyl)-2,2′,2″-nitrilo-triethanol, 4.1 mm Hg in 0.050 m potassium phosphate, and 16.5 mm Hg in 0.010 m inositol hexaphosphate. The n values of the Hill plots were 1.45, 1.80, and 2.3, respectively. The equilibrium constant for the tetramer-dimer dissociation reaction, K_4,2, of the carbon monoxide derivative was 2.1 × 10^?7m. The time course for combination with carbon monoxide was homogeneous at 432 nm. In the presence of inositol hexaphosphate the time course of combination with carbon monoxide was wavelength dependent.     

Preparation of trihydridostannyl complexes of rhenium stabilised by isocyanide ligands

Mixed-ligand complexes [ReBr(CO)₂(CNR)_nL_3−n] (1-4) [R = 4-CH₃OC₆H₄, 4-CH₃C₆H₄, C(CH₃)₃; L = P(OEt)₃, PPh(OEt)₂; n = 1, 2] were prepared by allowing carbonyl compounds [ReBr(CO)₄L] and [ReBr(CO)₃L₂] to react with an excess of isocyanide. Treatment of these bromocomplexes [ReBr(CO)₂(CNR)_nL_3−n] with SnCl₂ · 2H₂O yielded the trichlorostannyl derivatives [Re(SnCl₃)(CO)₂(CNR)_nL_3−n] (5-8). Trihydridestannyl complexes [Re(SnH₃)(CO)₂(CNR)_nL_3−n] (9-12) were prepared by allowing trichlorostannyl compounds 5-8 to react with NaBH₄ in ethanol. The trimethylstannyl derivative [Re(SnMe₃)(CO)₂(CNC₆H₄-4-CH₃){PPh(OEt)₂}₂] (13b) was also prepared by treating [Re(SnCl₃)(CO)₂(CNC₆H₄-4-CH₃){PPh(OEt)₂}₂] with an excess of MgBrMe in diethylether. Reaction of the tin trihydride complexes [Re(SnH₃)(CO)₂(CNR)_nL_3−n] (9-12) with CO₂ (1 atm) led to dinuclear OH-bridging bis(formate) derivatives [Re{Sn(OC(H)O)₂(μ-OH)}(CO)₂(CNR)_nL_3−n]₂ (14, 15). The complexes were characterised spectroscopically (IR, ¹H, ³¹P, ¹³C, ¹¹⁹Sn NMR) and by X-ray crystal structure determination of [Re(SnH₃)(CO)₂{CNC(CH₃)₃}{PPh(OEt)₂}₂] (10b).     

Benzene-1,2-dithiolate-induced assembly of reactive iridium fragments into tetranuclear octahydride complexes

The tetrametallic compound [Ir₄(μ-1,2-S₂C₆H₄)₂(μ-H)₂H₆(PⁱPr₃)₄(NCMe)] (1) has been obtained by treatment of the reactive cationic complex [IrH₂(PⁱPr₃)(NCMe)₃]BF₄ with the benzene-1,2-dithiolate anion. In the solid state, this tetrametallic compound exhibits an irregular nearly planar metal skeleton with the two dithiolate anions bridging the four metal centres from the same side of the tetrametallic plane. Even though all iridium atoms coordinate one PⁱPr₃ ligand, two bridging S atoms and, at least, two hydrides, they show different electronic and coordination environments. This unusual structure is maintained in solution, even after substitution of the labile acetonitrile ligand by other Lewis bases such as ethylene or carbon monoxide.     

Quantum chemical study of the mechanism of ethylene elimination in silylative coupling of olefins

Silylative coupling of olefins differs from olefin metathesis. Although in both these reactions ruthenium catalysts play a crucial role and ethylene product is detected, ruthenium-carbene intermediate is formed only in the course of the metathesis reaction. In this study quantum chemical calculations based on the density functional theory (DFT) have been carried out in order to examine the mechanism of the silylative coupling of olefins leading to ethylene elimination. In the first step of the catalytic cycle, a hydrogen atom from the ruthenium catalytic center is transferred preferentially to the carbon atom bound to Si in a vinylsilane. This H transfer is coupled with the formation of Ru-C bond. Next, the rotation around the newly formed C-C single bond occurs so that silicon atom is placed in the vicinity of the ruthenium center. The following step involves the migration of a silyl moiety, and leads to Ru-Si bond formation, coupled with ethylene elimination. The next reaction, that is the insertion of ethylene (alkene) into Ru-Si bond, has an activation barrier almost as high as the reaction of ethylene elimination. However, the posibility of removing gaseous ethylene from the reactive mixture together with the entropic fators suggests that the insertion of alkene that is larger than C₂H₄ is the rate limiting step in the silylative coupling of olefins. It also suggests that the substituents attached to the silicon atom or the carbon atoms of an alkene by electronic and steric effects may significantly affect silyl migration and thus the effectiveness of the catalytic reaction. Figure Insertion of alkene into Ru-Si bond seems to be rate limiting step in the silylative coupling of olefins Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

In situ high pressure FT-IR spectroscopy on alkene hydroformylation catalysed by RhH(CO)(PPh3)3 and Co2(CO)8

Catalytic hydroformylation of olefins has been carried out in a HP FT-IR cell using RhH(CO)(PPh₃)₃ catalytic precursor. A different behaviour was noticed between a terminal (hex-1-ene) and an internal alkene (cyclohexene) and different rate-determining steps of the catalytic cycle have been hypothesised. The hydroformylation of hex-1-ene has also been tested in the presence of Co₂(CO)₈ as catalyst. In this case, only the catalytic precursor is evidenced by HP FT-IR. Finally, the influence of an additional gas (helium, nitrogen or argon) in the reaction medium was evaluated: a high pressure of argon or nitrogen affects the initial rate of the reaction as shown by a decrease of the rate of the aldehyde formation.     

Effect of N-Guanyl Modifications on Early Steps in Catalysis of Polymerization by Sulfolobus solfataricus P2 DNA Polymerase Dpo4 T239W

Translesion DNA polymerases are more efficient at bypass of many DNA adducts than replicative polymerases. Previous work with the translesion polymerase Sulfolobus solfataricus Dpo4 showed a decrease in catalytic efficiency during bypass of bulky N²-alkyl guanine (G) adducts with N²-isobutylG showing the largest effect, decreasing ∼ 120-fold relative to unmodified deoxyguanosine (Zhang, H., Eoff, R. L., Egli, M., Guengerich, F. P. Versatility of Y-family Sulfolobus solfataricus DNA polymerase Dpo4 in translation synthesis past bulky N²-alkylguanine adducts. J. Biol. Chem. 2009; 284: 3563-3576). The effect of adduct size on individual catalytic steps has not been easy to decipher because of the difficulty of distinguishing early noncovalent steps from phosphodiester bond formation. We developed a mutant with a single Trp (T239W) to monitor fluorescence changes associated with a conformational change that occurs after binding a correct 2′-deoxyribonucleoside triphosphate (Beckman, J. W., Wang, Q., Guengerich, F. P. Kinetic analysis of nucleotide insertion by a Y-family DNA polymerase reveals conformational change both prior to and following phosphodiester bond formation as detected by tryptophan fluorescence. J. Biol. Chem. 2008; 283: 36711-36723) and, in the present work, utilized this approach to monitor insertion opposite N²-alkylG-modified oligonucleotides. We estimated maximal rates for the forward conformational step, which coupled with measured rates of product formation yielded rate constants for the conformational step (both directions) during insertion opposite several N²-alkylG adducts. With the smaller N²-alkylG adducts, the conformational rate constants were not changed dramatically (<  3-fold), indicating that the more sensitive steps are phosphodiester bond formation and partitioning into inactive complexes. With the larger adducts (≥  (2-naphthyl)methyl), the absence of fluorescence changes suggests impaired ability to undergo an appropriate conformational change, consistent with previous structural work.     

Deuterium isotope effect in bioactivation and hepatotoxicity of chloroform

Cytochrome P-450 appears to catalyze the $\text{in}$$\text{vitro}$ formation of phosgene (COCl₂) from chloroform (CHCl₃) in rat liver microsomes, since this reaction is NADPH dependent and inhibited by carbon monoxide and SKF 525-A. Moreover, the cleavage of the C-H bond appears to be the rate-determining step in this process since deuterium labeled chloroform (CDCl₃) is biotransformed into COCl₂ slower than is CHCl₃. CDCl₃ was also less hepatotoxic than CHCl₃ suggesting that a similar pathway of metabolism is responsible for the hepatotoxic properties of chloroform.     

Reaction of [Pt3(μ-CO)3(PBu3)3] with activated olefins and alkynes: the X-ray-structure of [Pt(CO)(PBu3)(CF3CCCF3)]

The reactions of the triangulo-cluster [Pt₃(μ-CO)₃(P^tBu₃)₃] with activated olefins and alkynes have been examined under various conditions. At low temperature, cluster fragmentation occurs yielding the Pt(0) complexes [Pt(CO)(P^tBu₃)(olefin)] (olefin = maleic anhydride and maleimide), while di(tert-butyl)acetylenedicarboxilate reacts quantitatively giving the dinuclear Pt(0) complex [Pt₂(CO)₂(P^tBu₃)₂(μ-η²:η²-^tBuO₂CCCCO₂^tBu)]. At higher temperature and in the presence of alkyne in large excess, the latter dimer converts quantitatively to the monomers [Pt(CO)(P^tBu₃)(alkyne)] (alkyne = CF₃CCCF₃ and ^tBuO₂CCCCO₂^tBu). The stereochemistry of these complexes has been established by NMR and IR measurements. The structure of [Pt(CO)(P^tBu₃)(CF₃CCCF₃)] was confirmed by X-ray diffraction analysis.     

Synthesis and reactivity of iron carbonyl clusters containing alkynethiolate ligands

The new cluster Li[Fe₃(μ₃,η¹-SCCFc)(CO)₉] reacts with ClAuPPh₃ to afford compound [Fe₃Au(μ₄,η²-CCFc)(CO)₉(PPh₃)], which exhibits an isomeric equilibrium in solution with the cluster [Fe₃Au(μ₃,η²-CCFc)(CO)₉(PPh₃)].The rupture of C-S bonds in the thioethers Me₃SiCCSCCR (R = Fc, SiⁱPr₃) in the presence of Fe₃(CO)₁₂, yields to the clusters [Fe₃(μ-SCCSiⁱPr₃)(μ-CCSiMe₃)(CO)₉] and [Fe₃(μ,η²-(SiⁱPr₃)CCCCSiMe₃)(μ₃-S)(CO)₉] together with the unexpected compounds [Fe₂(μ-SCC(H)R)(CO)₆] (R = SiMe₃, SiⁱPr₃).Additionally, the dinuclear derivatives [Fe₂(μ-SCCR)(μ-CCR′)(CO)₆] (R = Fc, R′ = SiMe₃; R = SiMe₃, R′ = Fc; R = SiMe₃; R′ = SiⁱPr₃) have also been obtained. These compounds have been spectroscopically characterized and the crystal structure of some of them has been solved.     

Antitumor activity of organotin compounds. Reaction,synthesis and structure of Et2SnCl2(phen) with 5-fluorouracil

The antitumor agent Et₂SnCl₂(phen) (phen = phenanthroline) reacts with 5-fluorouracil (UF) to form Et₂Sn(phen)UF)Cl by a basic catalytic process. The reaction may be characterized as nucleophilic attack on H⁺N(3) in the 5-fluorouracil ring by the cis-chloro in Et₂SnCl₂(phen). The product has been identified by microanalysis, IR, UV and NMR spectra and these results are consistent with the expected complex. The binding of the 5-fluorouracil ligand to the cis-chloro in Et₂SnCl₂(phen) not only enhances the antitumor activity of the complex, but also promotes studied aimed at understanding the mechanism of drug action.