RESUMEN
Secondary phosphines are important building blocks in organic chemistry as their reactive P-H bond enables construction of more elaborate molecules. In particular, they can be used to construct tertiary phosphines that have widespread applications as organocatalysts, and as ligands in metal-complex catalysis. We report here a practical synthesis of the bulky secondary phosphine synthon 2,2,6,6-tetramethylphosphinane (TMPhos). Its nitrogen analogue tetramethylpiperidine, known for over a century, is used as a base in organic chemistry. We obtained TMPhos on a multigram scale from an inexpensive air-stable precursor, ammonium hypophosphite. TMPhos is also a close structural relative of di-tert-butylphosphine, a key component of many important catalysts. Herein we also describe the synthesis of key derivatives of TMPhos, with potential applications ranging from CO2 conversion to cross-coupling and beyond. The availability of a new core phosphine building block opens up a diverse array of opportunities in catalysis.
RESUMEN
An aqueous suspension of silica nanoparticles or nanofluid can alter the wettability of surfaces, specifically by making them hydrophilic and oil-repellent under water. Wettability alteration by nanofluids has important technological applications, including for enhanced oil recovery and heat transfer processes. A common way to characterize the wettability alteration is by measuring the contact angles of an oil droplet with and without nanoparticles. While easy to perform, contact angle measurements do not fully capture the wettability changes to the surface. Here, we employed several complementary techniques, such as cryo-scanning electron microscopy, confocal fluorescence and reflection interference contrast microscopy, and droplet probe atomic force microscopy (AFM), to visualize and quantify the wettability alterations by fumed silica nanoparticles. We found that nanoparticles adsorbed onto glass surfaces to form a porous layer with hierarchical micro- and nanostructures. The porous layer can trap a thin water film, which reduces contact between the oil droplet and the solid substrate. As a result, even a small addition of nanoparticles (0.1 wt %) lowers the adhesion force for a 20 µm sized oil droplet by more than 400 times from 210 ± 10 to 0.5 ± 0.3 nN as measured by using droplet probe AFM. Finally, we show that silica nanofluids can improve oil recovery rates by 8% in a micromodel with glass channels that resemble a physical rock network.
RESUMEN
To be effective enhanced oil-recovery (EOR) agents, nanoparticles must be stable and be transported through a reservoir. However, the stability of a nanoparticle suspension at reservoir salinity and temperature is still a challenge and how it is affected by reservoir rocks and crude oils is not well understood. In this work, for the first time, the effect of several nanoparticle treatment approaches on the stability of silica nanoparticles at reservoir conditions (in the presence of reservoir rock and crude oil) was investigated for EOR applications. The stability of nanoparticle suspensions was screened in test tubes at 70 °C and 3.8 wt. % NaCl in the presence of reservoir rock and crude oil. Fumed silica nanoparticles in suspension with hydrochloric acid (HCl), polymer-modified fumed nanoparticles and amide-functionalized silica colloidal nanoparticles were studied. The size and pH of nanoparticle suspension in contact with rock samples were measured to determine the mechanism for stabilization or destabilization of nanoparticles. A turbidity scanner was used to quantify the stability of the nanoparticle suspension. Results showed that both HCl and polymer surface modification can improve nanoparticle stability under synthetic seawater salinity and 70 °C. Suspensions of polymer-modified nanoparticles were stable for months. It was found that pH is a key parameter influencing nanoparticle stability. Rock samples containing carbonate minerals destabilized unmodified nanoparticles. Crude oil had limited effect on nanoparticle stability. Some components of crude oil migrated into the aqueous phase consisting of amide-functionalized silica colloidal nanoparticles suspension. Nanoparticles modification or/and stabilizer are necessary for nanoparticle EOR application.
RESUMEN
Reaction of the amido-bridged zirconium complex (CpSiMe(2)NSiMe(2)Cp)ZrCH(3) (1) (Cp = C(5)H(4)) with half an equivalent of B(C(6)F(5))(3) or Ph(3)CB(C(6)F(5))(4) afforded the binuclear zirconium complexes [(CpSiMe(2)NSiMe(2)Cp)Zr)(2)(mu-CH(3))][RB(C(6)F(5))(3)] (2a, R = CH(3), 2b, R = C(6)F(5)) with a methyl group as the bridge between the two zirconium atoms. In the presence of one equivalent of B(C(6)F(5))(3) or Ph(3)C(C(6)F(5))(4), 1 was transformed to the zwitterionic complexes [(CpSiMe(2)NSiMe(2)Cp)Zr][RB(C(6)F(5))(3)] (3a, R = CH(3), 3b, R = C(6)F(5)) which are free of a metal-bound sigma-alkyl ligand. 2b is stable with Me(3)Al while 3b combined with Me(3)Al to form a hetero-binuclear complex [(CpSiMe(2)NSiMe(2)Cp)Zr(mu-CH(3))]Al(CH(3))(2)][B(C(6)F(5))(4)] (4) as shown by NMR spectroscopy at room temperature. Treatment of 2a or 3a with an excess of Me(3)Al led to (CpSiMe(2)NSiMe(2)Cp)Zr(C(6)F(5)) (5) through a group exchange process. 2b, 3a and 5 have been characterized by X-ray diffraction studies. 2b, 2b, 3a and 3b were highly active catalysts for ethylene polymerization and copolymerization with 1-octene in the presence of trialkylaluminium, but the binuclear zirconium complexes (2a and 2b) showed higher activities than their mononuclear counterparts 3a and 3b. Polymerization activities varied with the trialkylaluminiums and increased with the trialkylaluminium concentration applied in the system. The product existed mainly in the form of Al(PE)(3) with polymeric chains, and its molecular weight and distribution were greatly influenced by the type and amount of trialkylaluminium applied in the catalytic system.
RESUMEN
A novel methodology for random copolymer functionalization based on a noncovalent, one-step, multifunctionalization strategy has been developed. Random copolymers possessing both palladated-pincer complexes and diaminopyridine moieties (hydrogen-bonding entities) have been synthesized using ring-opening metathesis polymerization. Noncovalent functionalization of the resultant copolymers is accomplished via (1) directed self-assembly, (2) multistep self-assembly, and (3) one-step orthogonal self-assembly. This system shows complete specificity of each recognition motif for its complementary unit, with no observable changes in the association constants regardless of the degree of functionalization.
RESUMEN
Polymers containing terminal hydrogen-bonding recognition motifs based on diaminotriazine and diaminopyridine groups in their side chains for the self-assembly of appropriate receptors have been prepared by ring-opening metathesis polymerization (ROMP) of norbornenes. A new synthetic method for the preparation of norbornene monomers based on pure alkyl spacers is introduced. These monomers show unprecedented high reactivity using ROMP. To suppress self-association of diaminotriazine-based polymers, polymerizations were run in presence of N-butylthymine. The butylthymine acts as a protecting group via self-assembly onto the hydrogen-bonding sites of the polymeric scaffold, thereby solubilizing the polymer. Diaminopyridine monomers do not require the presence of a protecting group due to their low propensity to dimerize. In addition, they exhibit a high affinity for hydrogen-bonded receptors on both monomeric and polymeric level. These polymers present our first building blocks towards the design and synthesis of a "universal polymer scaffold".
