Fate of dimethylsilanediol (DMSD) via indirect photolysis in water.

Dimethylsilanediol (DMSD) is the common degradation product of ubiquitous polydimethylsiloxane (PDMS) and volatile methylsiloxanes (VMS) in water and soil. Given the high solubility of DMSD in water, the further degradation of DMSD in this compartment is of particular importance. While DMSD appears relatively resistant to degradation in standard hydrolysis or biodegradation studies, it may degrade by indirect photolysis in surface waters through oxidation by hydroxyl radicals.

Volatilization of dimethylsilanediol (DMSD) under environmentally relevant conditions: Sampling method and impact of water and soil materials.

Dimethylsilanediol (DMSD) is the common breakdown product of methylsiloxanes such as polydimethylsiloxane (PDMS) and volatile methylsiloxanes (VMS) in soil. In this work, we first present a sorbent selection experiment aiming to identify a sorbent that can trap gas-phase DMSD without causing DMSD condensation and VMS hydrolysis at environmentally relevant humidities. With a proper sorbent (Tenax) identified, the volatilization of DMSD from water and various wet soil and soil materials were measured in a controlled environment.

Fate of dimethylsilanediol (DMSD) in outdoor bare surface soil and its relation to soil water loss.

Dimethylsilanediol (DMSD) is a primary degradation product of silicone materials in the environment. Due to its low air/water partition coefficient and low soil/water distribution coefficient, this compound is not expected to undergo sorption and volatilization in wet soil. In an accompanying paper, we confirm that under controlled indoor conditions in test tubes, there is little to no volatilization of DMSD from soil and soil constituents if soil is wet.

Fate of dimethylsilanediol (DMSD) in soil-plant systems.

Dimethylsilanediol (DMSD) is the degradation product of methylsiloxane polymers and oligomers such as volatile cyclic methylsiloxanes (cVMS). To better understand the environmental fate of this key degradation product, we conducted a three-part study on the movement of DMSD in soil. The objective of this third and final study was to determine the fate of DMSD in soil-plant systems under constant irrigation.

Frustrated Lewis Pair Mediated Csp -H Activation.

The cleavage of a Csp -H bond by an N/B frustrated Lewis pair (FLP) is reported. Upon mild heating, the ambiphilic molecule (2-NMe -C H ) BH activates the C-H bond of a methyl group in α position of a nitrogen atom to generate an unprecedented N-B heterocycle. Upon further heating, the novel species rearranges through a hydride abstraction/1,2-aryl shift sequence.

Phosphinidene Reactivity of a Transient Vanadium P≡N Complex.

Toward the preparation of a coordination complex of the heterodiatomic molecule PN, P≡N-V(N[Bu]Ar) (1, Ar = 3,5-MeCH), we report the use of ClPA (A = CH, anthracene) as a formal source of phosphorus(I) in its reaction with Na[NV(N[Bu]Ar)] (Na[4]) to yield trimeric cyclo-triphosphane [PNV(N[Bu]Ar)] (3) with a core composed exclusively of phosphorus and nitrogen. In the presence of NapS (peri-1,8-naphthalene disulfide), NapSP-NV(N[Bu]Ar) (6) is instead generated in 80% yield, suggesting trapping of transient 1. Upon mild heating, 3 readily fragments into dimeric [PNV(N[Bu]Ar)] (2), while in the presence of bis(trimethylsilyl)acetylene or cis-4-octene, the respective phosphirene (Ar[Bu]N)VN-PC(SiMe) (7) or phosphirane (Ar[Bu]N)VN-P(CH) (8) compounds are generated.

Reversible hydrogen activation by a bulky haloborane based FLP system.

The FLP species bis(2-(TMP)phenyl)chloroborane (TMP = 2,2,6,6-tetramethylpiperidine)(1) was prepared and crystallized as a monomeric Frustrated Lewis Pair (FLP) displaying no apparent B-N interaction. Species 1 readily reacts with H2 at room temperature to generate reversibly the zwitterionic H2 activation product 2. Interestingly, in the presence of a base, 2 releases HCl, generating the novel FLP species 3 which is also monomeric.

Synthesis and Properties of Rhomboidal Macrocyclic Subunits of Graphdiyne-Like Nanoribbons.

Rhomboidal macrocyclic subunits of graphdiyne-like nanoribbon (GDNR) bearing both alkyne and diyne units, allowing for multichannel π-conjugation, were synthesized using an oxidative Glaser-type ring closing reaction. These subunits, called the "meshes" of the nanoribbon, possess phenyl groups with decyloxy solubilizing chains on each corner. The yields of the ring closing reaction highly depend on the metal (Cu or Pd) catalyst used for the macrocyclization step.

BORON CATALYSIS. Metal-free catalytic C-H bond activation and borylation of heteroarenes.

Transition metal complexes are efficient catalysts for the C-H bond functionalization of heteroarenes to generate useful products for the pharmaceutical and agricultural industries. However, the costly need to remove potentially toxic trace metals from the end products has prompted great interest in developing metal-free catalysts that can mimic metallic systems. We demonstrated that the borane (1-TMP-2-BH2-C6H4)2 (TMP, 2,2,6,6-tetramethylpiperidine) can activate the C-H bonds of heteroarenes and catalyze the borylation of furans, pyrroles, and electron-rich thiophenes.

Ambiphilic Frustrated Lewis Pair Exhibiting High Robustness and Reversible Water Activation: Towards the Metal-Free Hydrogenation of Carbon Dioxide.

The synthesis and structural characterization of a phenylene-bridged Frustrated Lewis Pair (FLP) having a 2,2,6,6‑tetramethylpiperidine (TMP) as the Lewis base and a 9-borabicyclo[3.3.1]nonane (BBN) as the Lewis acid is reported.

Intramolecular B/N frustrated Lewis pairs and the hydrogenation of carbon dioxide.

The FLP species 1-BR2-2-NMe2-C6H4 (R = 2,4,6-Me3C6H2, 2,4,5-Me3C6H2) reacts with H2 in sequential hydrogen activation and protodeborylation reactions to give (1-BH2-2-NMe2-C6H4)2. While reacts with H2/CO2 to give formyl, acetal and methoxy-derivatives, reacts with H2/CO2 to give C6H4(NMe2)(B(2,4,5-Me3C6H2)O)2CH2. The mechanism of CO2 reduction is considered.

Phosphazenes: efficient organocatalysts for the catalytic hydrosilylation of carbon dioxide.

Phosphazene superbases are efficient organocatalysts for the metal-free catalytic hydrosilylation of carbon dioxide. They react with CO2 to form the respective phosphine oxides, but in the presence of hydrosilanes, CO2 can be selectively reduced to silyl formates, which can in turn be reduced to methoxysilanes by addition of an extra loading of silanes. Activities reach a TOF of 32 h(-1) with a TON of 759.

Lewis base activation of borane-dimethylsulfide into strongly reducing ion pairs for the transformation of carbon dioxide to methoxyboranes.

The hydroboration of carbon dioxide into methoxyboranes by borane-dimethylsulfide using different base catalysts is described. A non-nucleophilic proton sponge is found to be the most active catalyst, with TOF reaching 64 h(-1) at 80 °C, and is acting via the activation of BH3·SMe2 into a boronium-borohydride ion pair.

Reducing CO₂ to methanol using frustrated Lewis pairs: on the mechanism of phosphine-borane-mediated hydroboration of CO₂.

The full mechanism of the hydroboration of CO2 by the highly active ambiphilic organocatalyst 1-Bcat-2-PPh2-C6H4 (Bcat = catecholboryl) was determined using computational and experimental methods. The intramolecular Lewis pair was shown to be involved in every step of the stepwise reduction. In contrast to traditional frustrated Lewis pair systems, the lack of steric hindrance around the Lewis basic fragment allows activation of the reducing agent while moderate Lewis acidity/basicity at the active centers promotes catalysis by releasing the reduction products.

Transition-metal-free catalytic reduction of carbon dioxide.

Metal-free systems, including frustrated Lewis pairs (FLPs) have been shown to bind CO2. By reducing the Lewis acidity and basicity of the ambiphilic system, it is possible to generate active catalysts for the deoxygenative hydroboration of carbon dioxide to methanol derivatives with conversion rates comparable to those of transition-metal-based catalysts.

A highly active phosphine-borane organocatalyst for the reduction of CO2 to methanol using hydroboranes.

In this work, we report that organocatalyst 1-Bcat-2-PPh2-C6H4 ((1); cat = catechol) acts as an ambiphilic metal-free system for the reduction of carbon dioxide in presence of hydroboranes (HBR2 = HBcat (catecholborane), HBpin (pinacolborane), 9-BBN (9-borabicyclo[3.3.1]nonane), BH3·SMe2 and BH3·THF) to generate CH3OBR2 or (CH3OBO)3, products that can be readily hydrolyzed to methanol.

Ambiphilic molecules for trapping reactive intermediates: interrupted Nazarov reaction of allenyl vinyl ketones with Me2PCH2AlMe2.

The addition of the ambiphilic molecule Me(2)AlCH(2)PMe(2) (1) to the allenyl vinyl ketone 2 gave a trapped Nazarov reaction product. Under kinetic control, the addition of the phosphine was on the methylated carbon, contrary to expected steric and electronic considerations. Computational data pointed to hydrogen bonding between the phosphine and the methyl group guiding the regiochemistry of this reaction.

Design, synthesis, and applications of potential substitutes of t-Bu-phosphinooxazoline in Pd-catalyzed asymmetric transformations and their use for the improvement of the enantioselectivity in the Pd-catalyzed allylation reaction of fluorinated allyl enol carbonates.

The design, synthesis, and applications of potential substitutes of t-Bu-PHOX in asymmetric catalysis is reported. The design relies on the incorporation of geminal substituents at C5 in combination with a substituent at C4 other than t-butyl (i-Pr, i-Bu, or s-Bu). Most of these new members of the PHOX ligand family behave similarly in terms of stereoinduction to t-Bu-PHOX in three palladium-catalyzed asymmetric transformations.

Reactivity of Lewis pairs (R2PCH2AlMe2)2 with carbon dioxide.

Species R(2)PCH(2)AlMe(2) (R = Me, Ph) are stable Lewis adducts but still react with CO(2) both in solution and in the solid state. The CO(2) adducts undergo a rearrangement unprecedented for ambiphilic molecules to form aluminium carboxylates. A new spirocyclic compound was also obtained by double Lewis pair activation of CO(2).