Excess Methoxide Research Articles

Reactions of Grubbs Catalysts with Excess Methoxide: Formation of Novel Methoxyhydride Complexes

On exposure to NaOMe (≥3 equiv) in CH2Cl2–MeOH at 23 °C, the first-generation Grubbs catalyst RuCl2(PCy3)2(═CHPh) (1a) is immediately transformed into the six-coordinate methoxyhydride complexes RuH(OMe)(CO)2(PCy3)2 (4a) and RuH(OMe)(CO)(H2)(PCy3)2 (5a). Complex 5a can be recycled into 4a under conditions conducive to removal of H2. The second-generation catalyst RuCl2(IMes)(PCy3)(═CHPh) (1b; IMes = N,N′-bis(mesityl)imidazol-2-ylidene) reacts more slowly, requiring several hours even at 20 equiv of NaOMe, and terminates at five-coordinate RuH(OMe)(CO)(IMes)(PCy3) (3b). Experiments in the presence of added PCy3 reveal that consumption of 1a, but not 1b, proceeds via the four-coordinate intermediate formed by equilibrium loss of phosphine, a function of the lability of the PCy3 ligand at ambient temperatures. The poor accessibility of such an intermediate for 1b at 23 °C retards salt metathesis and inhibits further reaction of 3b. For the bis(PCy3) analogue 3a, fast transformation into 4a is proposed to inv...

Verdoheme reactivity. Remarkable paramagnetically shifted (1)H NMR spectra of intermediates from the addition of hydroxide or methoxide with Fe(II) and Fe(III) verdohemes.

Studies of the reaction of 5-oxaporphyrin iron complexes (verdohemes) with methoxide ion or hydroxide ion have been undertaken to understand the initial step of ring opening of verdohemes. High-spin [ClFe(III)(OEOP)] undergoes a complex series of reactions upon treatment with hydroxide ion in chloroform, and similar species are also detected in dichloromethane, acetonitrile, and dimethyl sulfoxide. Three distinct paramagnetic intermediates have been identified by (1)H NMR spectroscopy. These reactive species are formed by addition of hydroxide to the macrocycle and to the iron as an axial ligand. Treatment of low-spin [(py)(2)Fe(II)(OEOP)]Cl (OEOP is the monoanion of octaethyl-5-oxaporphyrin) with excess methoxide ion in pyridine solution produces [(py)(n)()Fe(II)(OEBOMe)] (n = 1 or 2) ((OEBOMe), dianion of octaethylmethoxybiliverdin), whose (1)H NMR spectrum undergoes marked alteration upon addition of further amounts of methoxide ion. An identical (1)H NMR spectrum, which is characterized by methylene resonances with both upfield and downfield paramagnetic shifts, is formed upon treatment of [Fe(II)(OEBOMe)](2) with methoxide in pyridine solution and results from the formation of [(MeO)Fe(II)(OEBOMe)](-).

The propensity of alkoxide and aryloxide derivatives of tungsten carbonyls to aggregate in solution. Synthesis and X-ray structures of dinuclear, trinuclear and tetranuclear complexes derived from the MeOW(CO) 5− anion

The complex [Et 4N][W(CO) 5OMe] ( 1) has been prepared from the reaction of the photochemically generated W(CO) 5THF adduct and [Et 4N][OH] in methanol. Complex 1 was shown to undergo rapid CO dissociation in THF to quantitatively provide the dimeric dianion, [W(CO) 4OMe] 2 2−. The resulting THF insoluble salt [Et 4N] 2[W(CO) 4OMe] 2 ( 2) has been structurally characterized by X-ray crystallography, with the doubly bridging methoxide ligands being in an anti configuration. Complex 2 was found to subsequently react with excess methoxide ligand in a THF slurry to afford the face-sharing octahedron complex [Et 4N] 3[W 2(CO) 6(OMe) 3] ( 3) which contains three doubly bridging methoxide groups. In the absence of excess methoxide ligand complex 2 cleanly yields the tetrameric complex [Et 4N] 4[W(CO) 3OMe] 4 ( 4) which has been structurally characterized as a cubane-like arrangement with triply bridging μ 3-methoxide groups and W(CO) 3 units. Although complex 3 was not characterized in the solid state, the closely related glycolate derivative [Et 4N] 3[W 2(CO) 6(OCH 2CH 2OH) 3] ( 5) was synthesized and its structure determined by X-ray crystallography. The trianions of complex 5 are linked in the crystal lattice by strong intermolecular hydrogen bonds. Crystal data for 2: space group P2 1/ n, a = 7.696(2), b = 22.019(4), c = 9.714(2) Å, β = 92.22(3)°, Z = 4, R = 6.43%. Crystal data for 4: space group Fddd, a = 12.433(9), b = 24.01(2), c = 39.29(3) Å, Z = 8, R = 8.13%. Crystal data for 5: space group P2 12 12 1, a = 11.43(2), b = 12.91(1), c = 29.85(6) Å, Z = 8, R = 8.29%. Finally, the rate of CO ligand dissociation in the closely related aryloxide derivatives [Et 4N][W(CO) 5OR] (R = C 6H 5 and 3,5-F 2C 6H 3) were measured to be 2.15 × 10 −2 and 1.31 × 10 −3 s −1, respectively, in THF solution at 5°C. Hence, the value of the rate constant of 2.15 × 10 −2 s −1 establishes a lower limit for the first-order rate constant for CO loss in the W(CO) 5OMe − anion, since the methoxide ligand is a better π-donating group than phenoxide.

Substitution Reactions of α-Alkyl 4- and 5-Nitropyrrol-2-ylmethyl Derivatives

The α-t-butyl 4- and 5-nitropyrrol-2-yl chlorides (5b) and (6b) react with azide, thiocyanate and p- toluenethiolate ions in dimethylformamide through cationic species in an SN 1-type process, rather than by the SRNl or SN(AEAE) processes, by which their analogues in the benzene, furan or thiophen systems react. These reactions are so facile that they take place in the aqueous dimethylformamide solutions produced during the workup of reaction mixtures. Solvolysis of (5b) or (6b) in methanol produces high yields of the corresponding methyl ethers (5f) and (6f) The chloride (6b) reacts with methoxide ion to produce the diene (33), which reacts reversibly with excess methoxide to give polymethoxylated derivatives. The mesitoic ester (3d) and the acetic ester (3c) are sufficiently unreactive by the cationic pathway, unlike the highly reactive chlorides (3b) and (4c), to allow reaction with the lithium salt (16) and the tetrabutylammonium salt (17) of 2-nitropropane to occur by an SRNl mechanism to give the C- alkylate (3e).

Nucleophilic activation of coordinated carbon monoxide. 3. Hydroxide and methoxide reactions with the trinuclear clusters M3(CO)12 (M = Fe, Ru, or Os). Implications with regard to catalysis of the water gas shift reaction

Reported are quantitative investigations of the reactions of the triangular clusters M/sub 3/(CO)/sub 12/ (M = Fe, Ru, or Os) with methoxide ion in solution. In methanol under a CO atmosphere, both the osmium and ruthenium species form stable 1:1 methoxycarbonyl adducts (M/sub 3/(CO)/sub 12/ + NaOCH/sub 3/ in equilibrium (M/sub 3/(CO)/sub 11/(CO/sub 2/CH/sub 3/))Na); however, for the triiron analogue this adduct undergoes fragmentation to give Fe(CO)/sub 4/(CO/sub 2/CH/sub 3/)/sup -/. Initial adduct formation in each case occurs with an equilibrium constant of about 10/sup 3/ M/sup -1/. In mixed tetrahydrofuran/methanol solutions, K/sub eq/ for Ru/sub 3/(CO)/sub 11/(CO/sub 2/CH/sub 3/)/sup -/ is much larger, an indication of the greater activity of NaOCH/sub 3/ in the less protic solvent. Notably, in such solvent mixtures, the presence of excess methoxide also led to the formation of 2:1 adducts. Rates of adduct formation were examined by using stopped-flow kinetics techniques, and it was shown that in methanol the second-order rate constants (25/sup 0/C) are 11.3 x 10/sup 3/, 2.1 x 10/sup 3/, and 0.6 x 10/sup 3/ M/sup -1/ s/sup -1/ for Fe/sub 3/(CO)/sub 12/, Ru/sub 3/(CO)/sub 12/, and Os/sub 3/(CO)/sub 12/, respectively. Rates were much higher in the mixed THF(tetrahydro-furan)/CH/sub 3/OH solutions;more » for example, k/sub 1/ (25/sup 0/C) for Ru/sub 3/(CO)/sub 12/ is 2.0 x 10/sup 5/ M/sup -1/ s/sup -1/ in 90/10 THF/CH/sub 3/OH (v/v). Monosubstitution of the ruthenium cluster with (CH/sub 3/O)/sub 3/P markedly reduced the reactivity toward the anionic nucleophile. The reaction of the triruthenium species with hydroxide (Ru/sub 3/(CO)/sub 12/ + OH/sup -/ in equilibrium Ru/sub 3/(CO)/sub 11/(CO/sub 2/H)/sup -/ ..-->.. HRu/sub 3/(CO)/sub 11//sup -/ + CO/sub 2/) was also investigated. Analysis of the reaction kinetics leads to the conclusion that formation of the initial hydroxycarbonyl adduct is somewhat less favorable and is slower than the analogous reaction of methoxide.« less

The reinvestigation of the kinetics of the reactions of fluorodi(4-nitrophenyl)ethanes with sodium methoxide in methanol

The procedure previously described for the preparation of 1-fluoro-2,2,-di(4-nitrophenyl)ethane actually yields 1,1,2-tri-(4-nitrophenyl)ethane. 1-Fluoro-2,2-di(4-nitrophenyl)ethane has been prepared and rate constants, isotope effects, and activation parameters for the β-elimination reaction with methoxide ion in methanol are reported. These parameters indicate a concerted E2 mechanism, with a fairly symmetrical transition state. The subsequent dimerization reaction of the olefin product to yield 1,1,3,3-tetra(4-nitrophenyl)butene-1 is described.The reaction of 1,1,1-trifluoro-2,2-di(4-nitrophenyl)ethane with methoxide ion in methanol has been reinvestigated and the reaction of the first product 1,1-difluoro-2,2-di(4-nitrophenyl)ethylene with excess methoxide, to give di(4-nitrophenyl)ketene dimethylacetal in a multistep reaction, is reported.