Bond Insertion Products Research Articles

CuSO 4-catalyzed diazo decomposition in water: a practical synthesis of β-keto esters

CuSO 4 was found to be an efficient catalyst for the diazo decomposition of β-hydroxy α-diazoesters in water. 1,2-H shift occurred efficiently to give β-keto esters in high yields. No O–H bond insertion products were identified.

Intermolecular Coupling Reaction of Cyclic Amines and Alkenes Catalyzed by a Ruthenium-Hydride Complex (PCy3)2(CO)RuHCl

The ruthenium-hydride complex (PCy3)2(CO)RuHCl (1) was found to be an effective catalyst for the dehydrogenative coupling reaction of cyclic amines and alkenes. The reaction of secondary cyclic amines with unactivated alkenes preferentially gave the C−H bond insertion products in which both C−H and N−H bonds of amines have been selectively activated. In contrast, the reaction of amines with vinylsilane gave the N-silylation products. The catalytically active anionic ruthenium-amido complex was isolated from the reaction mixture, and its structure was established by X-ray crystallography. The preliminary mechanistic studies suggested that both C−H and N−H bond activation steps are mediated by a highly unsaturated ruthenium species.

Insertion of a stable dialkylsilylene into silicon-chlorine bonds

The reactions of a stable dialkylsilylene with chlorosilanes such as tetrachlorosilane, dimethyldichlorosilane, and dichlorosilane occurred smoothly at room temperature in hydrocarbon solvents to give the corresponding Si-Cl bond insertion products. In the reaction of the silylene with dichlorosilane, only the Si-Cl bond insertion product was obtained, while a similar reaction with dimethylchlorosilane gave only the Si-H insertion product, emphasizing the remarkable difference in the steric requirements between these two insertion reactions. No reaction took place during the treatment of the silylene with trimethylchlorosilane. The Si-Cl insertion reactions are expected to be applied in the synthesis of new organosilicon frameworks that cannot be obtained by conventional methods.

Coupling of Cyclobutenediones with Fischer Carbene Complexes: A One-Step Synthesis of Cyclopentenediones and/or 5-Alkylidenefuranones via Net Insertion of the Carbene Unit into a C−C Bond1

The reaction of Fischer carbene−chromium complexes with 3-cyclobutene-1,2-diones has been investigated. In most cases, the major product of the reaction is the C−C bond insertion product, a 2-alkoxy-4-cyclopentene-1,3-dione, accompanied by a minor amount of the partial deoxygenation product, a 4-cyclopentene-1,3-dione. In some cases, 5-alkylidenefuranones are also formed. A mechanism involving oxidative addition of the coordinatively unsaturated Fischer carbene complex followed by acyl migration and reductive elimination was proposed to account for cyclopentenedione formation. Furanone formation was thought to arise via demetalation of the acyl migration product, followed by O-acylation. An electronic dependence was noted for cyclopentenedione/alkylidene−furanone ratio, which was evaluated using the Hammett equation.

Insertion and C−H Bond Activation of Unsaturated Substrates by Bis(benzamidinato)yttrium Alkyl, [PhC(NSiMe3)2]2YR (R = CH2Ph·THF, CH(SiMe3)2), and Hydrido, {[PhC(NSiMe3)2]2Y(μ-H)}2, Compounds

The reactivity of benzamidinate-stabilized yttrium complexes [PhC(NSiMe(3))(2)](2)YR (R = CH(2)Ph . THF, CH(SiMe(3))(2) and {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) have been investigated. The complexes are thermally stable showing no sign of decomposition, ligand or solvent metalation or H/D exchange after hours of 100 degrees C in cyclohexane-d(12) or benzene-d(6). The alkyls are also stable in ethereal solvents. However, {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) induces C-O cleavage in THF solutions. The complexes [PhC(NSiMe(3))(2)](2)YCH(2)Ph . THF and {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) are modestly active in ethylene polymerization but are inactive toward propylene and 1-hexene. Terminal alkynes react stoichiometrically with [PhC(NSiMe(3))(2)]2YCH(SiMe(3))(2) and {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) to give mu-acetylide dimers, {{PhC(NSiMe(3))(2)]Y-2(mu-C=CR)}(2) (1, R = H; 2, R = Me; 3, R = n-Pr, 4, R = SiMe(3); 5, R = Ph; 6, R = CMe(3)). Treatment with THF leads to cleavage of these dimers, yielding [PhC(NSiMe(3))(2)]2YC=Cr . THF (7, R = H; 8, R = CMe(3)). [PhC(NSiMe(3))(2)]Y-2(mu-Me)(2)Li . TMEDA reacts with HC=CCMe(3) to afford [PhC(NSiMe(3))(2)]Y-2(mu-C=CCMe(3))(2)Li . TMEDA. [PhC(NSiMe(3))(2)]2YCH(SiMe(3))(2) catalyzes the regioselective dimerization of bulky 1-alkynes. With small 1-alkynes, HC=CR (R = H, Me, n-Pr), no dimerization was observed and the reaction stops with the formation of the alkynyl dimers {PhC(NSiMe(3))(2)]Y-2(mu-C=CR)}(2) (1-3). Treatment of [PhC(NSiMe(3))(2)](2)YR with acetonitrile gives either C-H bond activation or insertion. For R = CH(SiMe(3))(2), C-H bond activation occurs, yielding {[PhC(NSiMe(3))(2)]Y-2(mu-(N,N')-N(H)C(Me)=C(H)C=N)}(2) (10). For R = CH(2)Ph . THF a mixture of C-H bond activation (10, 10%) and insertion products, {[PhC(NSiMe(3))(2)]Y-2(mu-N=C(Me)CH(2)Ph)}(2) (11a, 50%) and {[PhC(NSiMe(3))(2)]Y-2(mu-N(H)C(Me)=C(H)Ph)}(2) (11b, 40%), was obtained. The hydride {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) exclusively gives insertion of acetonitrile, affording {[PhC(NSiMe(3))(2)]Y-2(mu-N=C(H)Me)}(2) (12). With pyridine, [PhC(NSiMe(3))(2)]2YCH(SiMe(3))(2) gives C-H bond activation, whereas [PhC(NSiMe(3))(2)](2)YCH(2)Ph . THF and {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) undergo insertion yielding [PhC(NSiMe(3))(2)]Y-2(NC(5)H(5)R) (13, R = H; 14, R = CH(2)Ph). In contrast with alpha-picoline, [PhC(NSiMe(3))(2)](2)YR (R = CH(SiMe(3))(2), Ch(2)Ph . THF) and {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) afford the alpha-picolyl derivative, [PhC(NSiMe(3))(2)]Y-2(eta(2)-(C,N)-2-CH2NC5H4 (15). The difference in reactivity of the bis(benzamidinate)-stabilized complexes compared to the corresponding Cp*(2)YR systems, e.g. the low tendency to catalyze C-C bond formation, the reduced or even the absence of C-H/C-O activation properties, and the enhanced nucleophilic and Bronsted base reactivities, is interpreted in terms of the high ionicity of the benzamidinate-stabilized yttrium complexes. The contracted yttrium orbitals are less exposed than in the dicyclopentadienyl derivatives and therefore not suited to establish the first initiating interaction with substrate molecules.

Proton NMR studies of syn‐ and anti‐tricyclo [5.1.0.03,5]octanes and their dichloromethyl derivatives

AbstractThe carbon and proton NMR spectra of syn‐ and anti‐tricyclo[5.1.0.03,5]octanes and their dichlorocarbene CH bond insertion products were determined by conventional 1D and 2D methods. Partially relaxed proton spectroscopy was carried out in some instances to aid in the separation of badly overlapped multiplets. A detailed analysis of the spectra was carried out with the aid of a new equation relating both the torsion angles and the CCH angles to the vicinal proton coupling constants. These values were combined with molecular modeling to draw conclusions regarding the conformational preferences for these molecules.

Photophysics of atomic magnesium isolated in solid methane and perdeuteromethane. III. Evidence for a kinetic isotope effect in the competitive process of atomic magnesium insertion into a C–H bond

The formation of the C–H bond insertion product methylmagnesium hydride (CH3MgH) and the simultaneous emission of atomic triplet magnesium are observed following photoexcitation of the first allowed singlet resonance transition of atomic magnesium isolated in solid methane matrices at 12 K. Isotopic variation of the solid methane hosts produces observable differences in the relative branching ratios into the photophysical (atomic triplet emission) and photochemical (insertion product formation) channels. In solid perdeuteromethane (CD4), the intensity of the atomic emission is approximately five times that in solid methane (CH4) while the rate of formation of the insertion product shows the opposite behavior in the two solids. No singlet atomic magnesium emission is observed in the solid Mg/methane systems and the rise time of the atomic triplet emission is deduced to occur on a time scale of less than 10 ns. A simple model derived from spin and orbital correlations between reactants and products is presented which considers the effect of the low symmetry of an insertive reaction coordinate in the approach geometry of atomic magnesium to methane yielding the linear product CH3MgH. Using this model, the absence of the singlet atomic emission is explained in terms of the attractive nature of the singlet surface with respect to the formation of a bent, inserted intermediate. The observation of an enhanced rate of atomic magnesium intersystem crossing is thought to occur as a result of the symmetry-induced participation of the repulsive triplet surface in the process leading to the linear insertion product. The model also suggests an origin for the observed kinetic isotope effects. Differences in the observed behavior of the 1P state of atomic magnesium in gas-phase and solid-phase quenching experiments (explicitly the formation of fragmented products only with no unreacted atomic triplet in the former case and the formation of the insertion product with intense atomic triplet emission in the latter) are discussed in relation to the presence of efficient relaxation pathways in the solid phase and the absence of such pathways in the single-collision conditions of the gas-phase experiments.

Donoraddukte des Silanimins Me 2SiNSi tBu 3: Darstellung, Stabilität, Reaktivität

Silaneimine Me 2SiNSi tBu 3 ( 1), which is unstable under normal conditions with regard to dimerization, forms metastable adducts D · Me 2SiNSi tBu 3 ( 1 · D ≙ 3 with D = Et 2O, THF, NEt 3, NMe 2Et), which can be decomposed thermally to give 1 and D and, can thus serve as sources of 1. Adducts 1 · D result from Me 2SiXNLi(Si tBu 3) (X = halogen, amides formed by reaction of Me 2SiXNH-(Si tBu 3) with RLi) under LiX elimination in the presence of D and CF 3SO 3SiMe 3. Lewis basicity of D, relative to 1, increases in the order Et 2O < THF < NEt 3, Cl − < NMe 2Et < F −. Similarly resistance of 1 · D to decompose into the dimer of 1 and D also increases. Adducts 1 · D also decompose by action of excess donor, (viz. 1 · OEt 2 decomposes in Et 2O into ethylene and Me 2SiOEtNHSi tBu 3, 1 · NMe 2Et decomposes in NMe 2Et under Stevens migration into EtMeNCH 2Si-Me 2NHSi tBu 3). Reaction of adducts 1 · D with water, alcohols and amines, or with organic enes (propene, isobutene, dimethylbutadiene, cyclopentadiene), or with silyl azides (Me n tBu 3− n SiN 3), or with benzophenone, respectively, gives the OH and NH bond insertion products, or ene reaction products, or [2 + 3] cycloaducts, or a [2 + 2] cycloadduct of 1, respectively.

Reaction of ethoxycarbonylcarbene with n-hexadecane and n-docosane

The reaction of both thermally and photolytically generated ethoxycarbonylcarbene with high molecular weight n-alkanes (> C10) gives the expected C–H bond insertion products, e.g., ethyl esters of isomeric C18 acids in the case of n-hexadecane. The thermally generated species gave much higher yields, up to 75% based on the carbene precursor, ethyl diazoacetate; possible explanations are discussed. A novel variation in reactivity of the carbene towards the secondary positions of an n-alkane has been observed. In the photolyses, the relative rate of insertion of ethoxycarbonylcarbene for secondary C–H:primary C–H was found to be 2·1 at position 2, steadily falling to ca. 1·4 at the secondary positions in the middle of the chain. Similar trends were noted in thermal reactions. Other products of the reactions are described.