Organometallics最新文献

We investigated the low-valent chemistry of Al and Ga with the ligand ^tBuDPM, a dipyrromethene ligand scaffold with two large tBu groups in the flanking 1- and 9-positions and a mesityl group in the backbone 5-position. Attempted synthesis of (^tBuDPM)Al^I by reduction of (^tBuDPM)AlI₂ with KC₈ failed. However, reduction of (^tBuDPM)GaI₂ (1) with K/KI led to successful isolation of (^tBuDPM)Ga^I (3). The Ga^II intermediate in the reduction process crystallized as a digallane: [(^tBuDPM)GaI]₂ (2). Also, 3 crystallized as a dinuclear complex with a Ga–Ga bond. However, in a benzene solution, the 3 dissociates into two mononuclear complexes. Reaction of a benzene solution of (^tBuDPM)Ga^I with excess Me₃SiN₃ gave the tetrazagallole product (^tBuDPM)Ga[N₄(SiMe₃)₂] (4) and not the alternative azide-amide product (^tBuDPM)Ga(N₃)[N(SiMe₃)₂], which according to calculations is thermodynamically considerably more stable. Theoretical investigations on the nature of the Ga–Ga bonds in 2 and 3 and the mechanism for selective formation of 4 have been included.

We report the conversion of anisoles and olefins to alkenyl anisoles via a transition-metal-catalyzed arene C–H activation and olefin insertion mechanism. The catalyst precursor, [(η²-C₂H₄)₂Rh(μ-OAc)]₂, and the in situ oxidant Cu(OPiv)₂ (OPiv = pivalate) convert anisoles and olefins (ethylene or propylene) to alkenyl anisoles. When ethylene is used as the olefin, the o/m/p ratio varies between approximately 1:3:1 (selective for 3-methoxystyrene) and 1:5:10 (selective for 4-methoxystyrene). When propylene is the olefin, the o/m/p regioselectivity varies between approximately 1:8:20 and 1:8.5:5. The o/m/p ratios depend on the concentration of pivalic acid and olefin. For example, when using ethylene, at relatively high pivalic acid concentrations and low ethylene concentrations, the o/m/p regioselectivity is 1:3:1. Conversely, again for use of ethylene, at relatively low pivalic acid concentrations and high ethylene concentrations, the o/m/p regioselectivity is 1:5:10. Mechanistic studies of the conversion of anisoles and olefins to alkenyl anisoles provide evidence that the regioselectivity is likely under Curtin–Hammett conditions.

A series of ferrocenyl- and ruthenocenyl-containing β-diketonato (triphenylphosphine)gold(I) complexes of the type [(RCO)(R′CO)-H^αC-AuPPh₃] were synthesized via the reaction of appropriate β-diketones, RCOC^αH₂COR′, with [(Ph₃PAu)₃][OBF₄]. Complexes with R = R′ = CH₃ (1), or R = Fc = Fe^II(η⁵-C₅H₄)(η⁵-C₅H₅), and R′ = CF₃ (2), CH₃ (3), Ph = C₆H₅ (4), or Fc (5), as well as R = Ru^II(η⁵-C₅H₄)(η⁵-C₅H₅) and R′ = CF₃ (6), CH₃ (7), Ph (8), Rc (9), or Fc (10), were obtained. The Au–^αC bonding mode between gold and β-diketonato ligands was spectroscopically (NMR, FTIR, and XPS) identified as the only bonding mode for all complexes lacking a CF₃ moiety, while a mixture of Au–^αC- and Au–(^κO,^κO)-bonded isomers in equilibrium with each other was observed for CF₃-containing complexes 2 and 6. This experimental observation is supported by a theoretical study utilizing density functional theory. Cyclic and square wave voltammetric studies in CH₂Cl₂/[N(ⁿBu)₄][B(C₆F₅)₄] displayed only the metallocene-based redox processes of 2–10 as reversible, well-resolved ferrocenyl and irreversible ruthenocenyl one-electron transfer steps. XPS spectra for each element in the complexes were measured, and an uncommon indirect proportionality between Au 4f_7/2 binding energies and the sum of R group electronegativities, Σχ_R, as well as between the Fe 2p_3/2 binding energies and formal ferrocenyl reduction potentials, E°′, was obtained.

Rubidium and cesium are the least studied naturally occurring s-block metals in organometallic chemistry but are in plentiful supply from a sustainability viewpoint as highlighted in the periodic table of natural elements published by the European Chemical Society. This underdevelopment reflects the phenomenal success of organometallic compounds of lithium, sodium, and potassium, but interest in heavier congeners has started to grow. Here, the synthesis and structures of rubidium and cesium bis(amido)alkyl magnesiates [(AM)MgN′₂alkyl]_∞, where N′ is the simple heteroamide ^–N(SiMe₃)(Dipp), and alkyl is nBu or CH₂SiMe₃, are reported. More stable than their nBu analogues, the reactivities of the CH₂SiMe₃ magnesiates toward 1,4-cyclohexadiene are revealed. Though both reactions produce target hydrido-magnesiates [(AM)MgN′₂H]₂ in crystalline form amenable to X-ray diffraction study, the cesium compound could only be formed in a trace quantity. These studies showed that the bulk of the ^–N(SiMe₃)(Dipp) ligand was sufficient to restrict both compounds to dimeric structures. Bearing some resemblance to inverse crown complexes, each structure has [(AM)(N)(Mg)(N)]₂ ring cores but differ in having no AM-N bonds, instead Rb and Cs complete the rings by engaging in multihapto interactions with Dipp π-clouds. Moreover, their hydride ions occupy μ₃-(AM)₂Mg environments, compared to μ₂-Mg₂ environments in inverse crowns.

While the reduction of unsaturated bonds is well established by catalytic hydrogenation reactions using H₂, alternative approaches are appealing for environmental and safety reasons. One of these methods is the catalytic hydrosilylation reaction, which becomes environmentally very friendly when using polymethylhydrosiloxane (PMHS), a waste product from the silicon industry, as a hydrosilylation agent. Here, we report the synthesis and catalytic activity of a range of iron triazolylidene complexes for the hydrosilylation of carbonyls using PMHS with unprecedented turnover numbers up to 72,000. Various functional groups on the substrate aromatic ring are tolerated, including CN, Br, OMe, and NMe₂ substituents. The hydrosilylation is not restricted to benzylic ketones and aldehydes, esters, and amides are also converted. Rather remarkable for hydrosilylation, ketones are converted faster than aldehydes. Intermolecular competition experiments suggest that the active catalyst is formed by the coordination of a ketone, which rationalizes the origin of this untypical substrate reactivity trend.

Herein, we report a simple, very fast, and efficient method for the synthesis of a library of organofunctional alkoxysilanes based on an amine-catalyzed thiol-isocyanate click reaction. At first, systematic studies were carried out to select the most active catalyst and its concentration for the model reaction involving 3-isocyanatopropyltriethoxysilane (ICPTES) and 1-octanethiol. Six tertiary amines were studied using an in situ FT-IR technique. After an effective catalytic system was selected, a set of alkoxysilanes containing various functional groups were synthesized. In addition, new thiols and thioacetates (sequentially reduced to thiols) were obtained as a result of the thiol–ene reaction. Two synthetic routes were applied to obtain alkoxysilanes, the reaction between ICPTES and functional-group-containing thiols or between 3-mercaptopropyltriethoxysilane (MPTES) and functional-group-containing isocyanates. The developed procedure permitted the synthesis of 13 new organosilicon compounds. The silanes obtained contain various functional groups, i.e. long alkyl or fluoroalkyl chain, phenyl, trisiloxane, naphthyl, trisilylamine, or polyether.