DFT methods were used to elucidate features of coordination environment of Pd(II) that could enable Ar-F reductive elimination as an elementary C-F bond-forming reaction potentially amenable to integration into catalytic cycles for synthesis of organofluorine compounds with benign stoichiometric sources of F(-). Three-coordinate T-shaped geometry of Pd(II)Ar(F)L (L = NHC, PR(3)) was shown to offer kinetics and thermodynamics of Ar-F elimination largely compatible with synthetic applications, whereas coordination of strong fourth ligands to Pd or association of hydrogen bond donors with F each caused pronounced stabilization of Pd(II) reactant and increased activation barrier beyond the practical range. Decreasing donor ability of L promotes elimination kinetics via increasing driving force and para-substituents on Ar exert a sizable SNAr-type TS effect. Synthesis and characterization of the novel [Pd(C(6)H(4)-4-NO(2))ArL(mu-F)](2) (L = P(o-Tolyl)(3), 17; P(t-Bu)(3), 18) revealed stability of the fluoride-bridged dimer forms of the requisite Pd(II)Ar(F)L as the key remaining obstacle to Ar-F reductive elimination in practice. Interligand steric repulsion with P(t-Bu)(3) served to destabilize dimer 18 by 20 kcal/mol, estimated with DFT relative to PMe(3) analog, yet was insufficient to enable formation of greater than trace quantities of Ar-F; C-H activation of P(t-Bu)(3) followed by isobutylene elimination was the major degradation pathway of 18 while Ar/F- scrambling and Ar-Ar reductive elimination dominated thermal decomposition of 17. However, use of Buchwald's L = P(C(6)H(4)-2-Trip)(t-Bu)(2) provided the additional steric pressure on the [PdArL(mu-F)](2) core needed to enable formation of aryl-fluoride net reductive elimination product in quantifiable yields (10%) in reactions with both 17 and 18 at 60 degrees over 22 h.

Silicon is the second most abundant element on the earths surface, whereby inorganic silanols (SiOH) make up the reactive hydroxyl groups on the surface of minerals, zeolites, and silica gel. The acidic silanol groups [1] are known to be capable of hydrogen bonding to small molecules for heterogeneous catalysis and separation chemistry, but the discrete surface-molecule interactions are not well understood.[2] Silanediols R 2 Si(OH) 2 are of particular interest as they contain a geminal diol bonding motif that is not commonly accessible for carbon analogues, but they represent a synthetic challenge due to their rapid rates of self-condensation. While condensation is advantageous for the synthesis of siloxane polymers, metallosiloxanes, and silesquioxanes, [3] it creates a barrier that may hinder researchers from exploring the properties and applications of discrete silanediols. [4] Recent studies demonstrate that silanols can function as isosteres and transition-state analogues in drug design, in which the enhanced acidity of the silanol can improve binding to a receptor.[5] Small molecules containing silanol and silanediol groups may be useful as models to understand local surface sites and reactivity of silica materials for catalysis, and also to design new homogeneous small-molecule catalysts.We seek to understand the hydrogen bonding patterns and interactions between organic silanediols with carbonyls for applications to catalysis and molecular recognition. Hydrogen bonding interactions play an important role in molecular recognition and metal-free catalysis, and are frequently used in nature for structural organization and enzyme activity.[6] Previous structural studies have demonstrated the hydrogen bonding networks that silanediols can attain through dual donor and acceptor interactions, [4, 7] and also the ability to hydrogen bond with chloride anions for molecular recognition.[8] Studies of silanetriols have shown that amines can complex with and stabilize silanetriols.[9]Here we describe the synthesis and structural studies of organic silanediols for small-molecule hydrogen bonding activation of carbonyl compounds.[10] We are particularly interested in studying bulky silanediols that do not readily undergo condensation reactions.[11] We have performed crystallization and NMR-binding experiments to investigate the hydrogen bonding interactions in both solid-state and solution for molecular recognition and the design of new catalysts. This is the first study of neutral Lewis basic carbonyl compounds with silanediols.We have synthesized a series of bulky silanediols 2-4 that incorporate electron-withdrawing groups to enhance acidity while incorporating steric effects to overcome condensation reactions. Due to the synthetic challenge, the chemical space for silanediols is largely unexplored, and silanediols 2-4 represent new structures.[4] The mesityl group (Mes) was incorporated to prevent formation of disiloxanediols and higher order siloxanes.[12] Incorporating a mesityl group also provides enhanced so...

The importance of cooperative hydrogen-bonding effects and SiOH-acidification is described for silanediol catalysis. NMR binding, X-ray, and computational studies provide support for a unique dimer resulting from silanediol self-recognition. The significance of this cooperative hydrogen-bonding is demonstrated using novel fluorinated silanediol catalysts for the addition of indoles and N,N-dimethyl-m-anisidine to trans-β-nitrostyrene.

Polydopamine coatings are of interest due to the fact that they can promote adhesion to a broad range of materials and can enable a variety of applications. However, the polydopamine-substrate interaction is often noncovalent. To broaden the potential applications of polydopamine, we show the incorporation of 3-aminopropyltriethoxysilane (APTES), a traditional coupling agent capable of covalent bonding to a broad range of organic and inorganic surfaces, into polydopamine coatings. High energy X-ray photoelectron spectroscopy (HE-XPS), conventional XPS, near-edge X-ray absorption fine structure (NEXAFS), Fourier transform infrared-attenuated total reflectance (FTIR-ATR), and ellipsometry measurements were used to investigate changes in coating chemistry and thickness, which suggest covalent incorporation of APTES into polydopamine. These coatings can be deposited either in Tris buffer or by using an aqueous APTES solution as a buffer without Tris. APTES-dopamine hydrochloride deposition from solutions with molar ratios between 0:1 and 10:1 allowed us to control the coating composition across a broad range.

Trimeric green [(i-PrNC)12Rh(I)3]Cl3.4.5H2O, monomeric [(C6H11NC)4Rh(I)](BPh4) and [(i-PrNC)4Rh(I)](BPh4) (both yellow), and red, dimeric [(C6H11NC)8Rh(I)2]Cl2.0.5C6H6.2H2O have been crystallized.

Numerous studies have focused on the remarkable adhesive properties of polydopamine, which can bind to substrates with a wide range of surface energies, even under aqueous conditions. This behavior suggests that polydopamine may be an attractive option as a surface treatment in structural bonding applications, where good bond durability is required. Here, we assessed polydopamine as a surface treatment for bonding aluminum plates with an epoxy resin. A model epoxy adhesive consisting of diglycidyl ether of bisphenol A (DGEBA) and Jeffamine D230 polyetheramine was employed, and lap shear measurements (ASTM D1002 10) were made (i) under dry conditions to examine initial bond strength and (ii) after exposure to hot/wet (63 °C in water for 14 days) conditions to assess bond durability. Surprisingly, our results showed that polydopamine alone as a surface treatment provided no benefit beyond that obtained by exposing the substrates to an alkaline solution of tris buffer used for the deposition of polydopamine. This implies that polydopamine has a potential Achilles' heel, namely, the formation of a weak boundary layer that was identified using X-ray photoelectron spectroscopy (XPS) of the fractured surfaces. In fact, for longer deposition times (2.5 and 18 h), the tris buffer-treated surface outperformed the polydopamine surface treatments, suggesting that tris buffer plays a unique role in improving adhesive performance even in the absence of polydopamine. We further showed that the use of polydopamine-3-aminopropyltriethoxysilane (APTES) hybrid surface treatments provided significant improvements in bond durability at extended deposition times relative to both polydopamine and an untreated control.

No abstract

The fundamental properties of a series of organic monosilanols, silanediols, disiloxanediols, and known hydrogen-bonding organocatalysts have been examined in the gas phase using computational and experimental mass spectrometry methods. The organosilicon diol molecules contain dual hydrogen-bonding groups that were designed as potential hosts and hydrogen-bonding catalysts. Newly measured acidities are reported, and implications regarding solvent effects, catalysis, and molecular recognition are discussed.