The Emergence of Zerovalent Carbon Compounds from Structural Curiosities to Organocatalysts

Low-valent main group compounds have reactivity patterns and properties reminiscent of transition metals. While divalent carbon compounds such as carbenes are widely studied ligands and organocatalysts, zerovalent carbon species have received considerably less attention. This perspective highlights the properties and reactivity of zerovalent carbon compounds, focusing on their first applications as organocatalysts for small molecule reduction and polymerization reactions

Ketone Hydrosilylation Studies Using a Carbodiphosphorane Catalyst

The objective of this research is to discover an effective, safe, and low-cost catalyst for ketone hydrosilylation reactions, which involve the addition of a silicon–hydrogen bond across a C=O double bond. Improving catalyst efficiency could benefit the organic synthesis industry, as carbonyl hydrosilylation is used industrially in the synthesis of alcohol products. Use of the carbodiphosphorane catalyst as a replacement for toxic heavy-metal-containing catalysts could reduce waste and emissions harmful to the environment, while also providing an alternative means for accomplishing ketone reduction. Using a cyclic carbodiphosphorane catalyst, we have compared catalytic activity toward acetophenone hydrosilylation for a range of 18 silanes, the most effective of which was diphenylsilane. A range of 24 alkyl and aryl ketones have also been investigated. The carbodiphosphorane catalyst was more active in ketone hydrosilylation reactions compared to other nucleophilic organic catalysts tested

Crystal Structure of 2-(2,6-diisopropylphenyl)-N,Ndiethyl- 3,3-dimethyl-2-azaspiro[4.5]decan-1- amine: A Diethylamine Adduct of a Cyclic(alkyl)- (amino)carbene (CAAC)

The structure of the title compound, C27H46N2, at 93 K has monoclinic (P21/n) symmetry. The title compound was prepared by treatment of 2-(2,6-diiso­propyl­phenyl)-3,3-dimethyl-2-aza­spiro­[4.5]dec-1-en-2-ium hydrogen dichloride with two equivalents of lithium di­ethyl­amide. Characterization of the title compound by single-crystal X-ray diffraction and 1H and 13C NMR spectroscopy is presented. Formation of the di­ethyl­amine adduct of the cyclic(alk­yl)(amino)­carbene (CAAC) was unexpected, as deprotonation using lithium diiso­propyl­amide results in free CAAC formation

Group 14 Metallocene Catalysts for Carbonyl Hydroboration and Cyanosilylation

A series of six Group 14 metallocene compounds (M = Ge, Sn, Pb) were studied as catalysts for carbonyl hydroboration and cyanosilylation reactions at room temperature. Both bis(pentamethylcyclopentadienyl) and tetramethyldisiloxa[3]metallocenophane compounds were compared. The tin and lead metallocenophanes exhibited the highest reactivity in hydroboration and cyanosilylation reactions. Hammett analysis of aldehyde hydroboration provided a ρ value of 0.73, suggesting a buildup of negative charge during the turnover-limiting step, consistent with the transition state for hydride transfer to the carbonyl center. NMR studies of Lewis acidity indicate that the Ge, Sn, and Pb tetramethyldisiloxa[3]metallocenophane compounds are weak Lewis acids

Crystal Structure of 2-(2,6-diiso­propyl­phen­yl)-N,N-diethyl-3,3-dimethyl-2-aza­spiro­[4.5]decan-1-amine: A Di­ethyl­amine Adduct of a Cyclic(alk­yl)(amino)­carbene (CAAC)

The structure of the title compound, C27H46N2, at 93 K has monoclinic (P21/n) symmetry. The title compound was prepared by treatment of 2-(2,6-diiso­propyl­phenyl)-3,3-dimethyl-2-aza­spiro­[4.5]dec-1-en-2-ium hydrogen dichloride with two equivalents of lithium di­ethyl­amide. Characterization of the title compound by single-crystal X-ray diffraction and 1H and 13C NMR spectroscopy is presented. Formation of the di­ethyl­amine adduct of the cyclic(alk­yl)(amino)­carbene (CAAC) was unexpected, as deprotonation using lithium diiso­propyl­amide results in free CAAC formation

Olefin Hydroarylation Catalyzed by (Pyridyl-Indolate)Pt(II) Complexes: Catalytic Efficiencies and Mechanistic Aspects

A series of Pt(II) complexes of the type (N–N)PtPh(SR_2) (N–N = 2,2′-pyridyl-indolate) were prepared, and their performance as catalysts for the hydroarylation of olefins was assessed. Evidence that the catalysis is homogeneous and is Pt-mediated is provided by control experiments with added hindered base (2,6-di-tert-butyl-4-methylpyridine) and Hg(0). Two potential catalytic intermediates, (^tBuPyInd)PtPh(C_2H_4) and (^tBuPyInd)Pt(CH_2CH_2Ph)(C_2H_4), were synthesized, and their catalytic efficacy was explored. Additionally, decomposition and deactivation pathways, including styrene formation via β-hydride elimination and ligand reductive demetalation, were identified

Measurement of 10B concentration through autoradiography images in polycarbonate nuclear track detectors

The determination of the local concentration of boron in the different regions of tissue samples treated by Boron Neutron Capture Therapy (BNCT) could be made through the evaluation of the number of tracks forming autoradiography images. It is necessary to get a "standard" material containing a known amount of 10B, to correlate the number of tracks and boron concentration, i.e. to be used as a reference. Different systems were tested in order to find a suitable standard. Films made of 2% agarose in boron solutions showed a homogeneous distribution of the 10B atoms in the material structure. This system is easy handled and its physical properties are satisfactory. On the other hand, a small volume polycarbonate box was designed to contain 10B solutions of known concentration. This system showed a reduced number of background tracks and a promising behavior in many aspects. There is proportionality between track numbers per surface unit and 10B concentration, and between track numbers per surface unit and neutron fluence. Experimental results were compared to calculated values through formulas developed for thick samples autoradiography.Fil: Portu, Agustina Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Bernaola, Omar Alberto. Comisión Nacional de Energía Atómica. Gerencia de Area de Aplicaciones de la Tecnología Nuclear. Gerencia de Radiobiología (Centro Atómico Constituyentes); ArgentinaFil: Nievas, Susana Isabel. Comisión Nacional de Energía Atómica; ArgentinaFil: Liberman, Sara. Comisión Nacional de Energía Atómica; ArgentinaFil: Saint Martin, María Laura Gisela. Comisión Nacional de Energía Atómica. Gerencia de Area de Aplicaciones de la Tecnología Nuclear. Gerencia de Radiobiología (Centro Atómico Constituyentes); Argentin

Carbodiimide and Isocyanate Hydroboration by a Cyclic Carbodiphosphorane Catalyst

We report hydroboration of carbodiimide and isocyanate substrates catalyzed by a cyclic carbodiphosphorane catalyst. The cyclic carbodiphosphorane outperformed the other Lewis basic carbon species tested, including other zerovalent carbon compounds, phosphorus ylides, an N-heterocyclic carbene, and an N-heterocyclic olefin. Hydroborations of seven carbodiimides and nine isocyanates were performed at room temperature to form N-boryl formamidine and N-boryl formamide products. Intermolecular competition experiments demonstrated the selective hydroboration of alkyl isocyanates over carbodiimide and ketone substrates. DFT calculations support a proposed mechanism involving activation of pinacolborane by the carbodiphosphorane catalyst, followed by hydride transfer and B−N bond formation