Heavy Heterodendralenes: Structure and Reactivity of Phosphabora[3]dendralenes.

The incorporation of phosphorus and boron into [3]dendralenes provides access to heavy heterodendralenes, a new class of main-group precursor to "doped" polycyclic hydrocarbons. []Dendralenes are a core class of unsaturated hydrocarbons built from geminally connected polyenes; the resulting arrangement of conjugated C═C bonds enables []dendralenes to undergo reactions that allow rapid access to complex polycyclic compounds. The increasing technological and synthetic importance of main-group-containing polycyclic hydrocarbons and their analogues makes new routes to access such systems highly attractive.

Transition Metal-Free Catalytic C-H Zincation and Alumination.

C-H metalation is the most efficient method to prepare aryl-zinc and -aluminium complexes that are ubiquitous nucleophiles. Virtually all C-H metalation routes to form Al/Zn organometallics require stoichiometric, strong Brønsted bases with no base-catalyzed reactions reported. Herein we present a catalytic in amine/ammonium salt (EtN/[(EtN)H]) C-H metalation process to form aryl-zinc and aryl-aluminium complexes.

Reversible Dissociation of a Dialumene*.

Dialumenes are neutral Al compounds with Al=Al multiple bonds. We report the isolation of an amidophosphine-supported dialumene. Our X-ray crystallographic, spectroscopic, and computational DFT analyses reveal a long and extreme trans-bent Al=Al bond with a low dissociation energy and bond order.

The Phospha-Bora-Wittig Reaction.

We report the phospha-bora-Wittig reaction for the direct preparation of phosphaalkenes from aldehydes, ketones, esters, or amides. The transient phosphaborene Mes*P═B-NR reacts with carbonyl compounds to form 1,2,3-phosphaboraoxetanes, analogues of oxaphosphetane intermediates in the classical Wittig reaction. 1,2,3-Phosphaboraoxetanes undergo thermal or Lewis acid-promoted cycloreversion, yielding phosphaalkenes.

Aluminium-Catalyzed C(sp)-H Borylation of Alkynes.

Historically used in stoichiometric hydroalumination chemistry, recent advances have transformed aluminium hydrides into versatile catalysts for the hydroboration of unsaturated multiple bonds. This catalytic ability is founded on the defining reactivity of aluminium hydrides with alkynes and alkenes: 1,2-hydroalumination of the unsaturated π-system. This manuscript reports the aluminium hydride catalyzed dehydroborylation of terminal alkynes.

Reversible Reductive Elimination in Aluminum(II) Dihydrides.

Oxidative addition and reductive elimination are defining reactions of transition-metal organometallic chemistry. In main-group chemistry, oxidative addition is now well-established but reductive elimination reactions are not yet general in the same way. Herein, we report dihydrodialanes supported by amidophosphine ligands.

Characterization of the Zwitterionic Intermediate in 1,1-Carboboration of Alkynes.

The reaction of a Lewis acidic borane with an alkyne is a key step in a diverse range of main group transformations. Alkyne 1,1-carboboration, the Wrackmeyer reaction, is an archetypal transformation of this kind. 1,1-Carboboration has been proposed to proceed through a zwitterionic intermediate.

Silyl Anion Initiated Hydroboration of Aldehydes and Ketones.

Hydroboration is an emerging method for mild and selective reduction of carbonyl compounds. Typically, transition-metal or reactive main-group hydride catalysts are used in conjunction with a mild reductant such as pinacolborane. The reactivity of the main-group catalysts is a consequence of the nucleophilicity of their hydride ligands.

Flexible Coordination of N,P-Donor Ligands in Aluminum Dimethyl and Dihydride Complexes.

Aluminum hydrides, once a simple class of stoichiometric reductants, are now emerging as powerful catalysts for organic transformations such as the hydroboration or hydrogenation of unsaturated bonds. The coordination chemistry of aluminum hydrides supported by P donors is relatively underexplored. Here, we report aluminum dihydride and dimethyl complexes supported by amidophosphine ligands and study their coordination behavior in solution and in the solid state.

Intercepting the Disilene-Silylsilylene Equilibrium.

The equilibrium between disilenes (R Si=SiR ) and their silylsilylene (R Si-SiR) isomers has previously been inferred but not directly observed, except in the case of the parent system H Si=SiH . Here, we report a new method to prepare base-coordinated disilenes with hydride substituents. By varying the bulk of the coordinating base and other silicon substituents, we have been able to control the rearrangement of disilene adducts to their silylsilylene tautomers.

Phenylene-bridged cross-conjugated 1,2,3-trisilacyclopentadienes.

1,2,3-Trisilacyclopentadienes are obtained from the reactions of cyclotrisilene c-Si3R4 (R = iPr3C6H2) with phenyl and diphenyl acetylene, respectively. With 1,4-diethynyl benzene the cross-conjugated bridging of two of the Si3C2 cycles by a para-phenylene linker is achieved. UV/vis spectroscopy indicates a small but significant effect of cross-conjugation, which is confirmed by TD-DFT calculations.

Aluminium-mediated carbon-carbon coupling of an isonitrile.

Cp*Al reacts with diphenylacetylene to form a Cp*-substituted 1,4-dialuminacyclohexene. The dialuminacyclohexene reacts with four equivalents of an isonitrile to couple the terminal carbon atoms, forming 6 new carbon-carbon bonds and resulting in a zwitterionic diamide ligand which contains a carbocationic backbone.

Preparation and Characterization of P BCh Ring Systems (Ch=S, Se) and Their Reactivity with N-Heterocyclic Carbenes.

Four-membered rings with a P BCh core (Ch=S, Se) have been synthesized by the reaction of phosphinidene chalcogenide (Ar*P=Ch) and phosphaborene (Mes*P=BNR ). The mechanistic pathways towards these rings are explained by detailed computational work that confirmed the preference for the formation of P-P, not P-B, bonded systems, which seems counterintuitive given that both phosphorus atoms contain bulky ligands. The reactivity of the newly synthesized heterocycles, as well as that of the known (RPCh) rings (n=2, 3), was probed by the addition of N-heterocyclic carbenes, which revealed that all investigated compounds can act as sources of low-coordinate phosphorus species.

Phosphaborenes: Accessible Reagents for the Synthesis of C-C/P-B Isosteres.

Formal exchange of C=C units with isoelectronic B=N or B=P units can provide access to molecules with unique electronic or chemical properties. Herein, we report the simple solution-phase generation of highly reactive phosphaborenes, RP=BR, and demonstrate their use for the introduction of P=B units into organic systems. Ring opening of a P-B-containing cyclobutene isostere provided access to unique 1,4-boraphosphabutadiene systems with conjugated main-group multiple bonds.

Aluminum Hydride Catalyzed Hydroboration of Alkynes.

An aluminum-catalyzed hydroboration of alkynes using either the commercially available aluminum hydride DIBAL-H or bench-stable Et Al⋅DABCO as the catalyst and H-Bpin as both the boron reagent and stoichiometric hydride source has been developed. Mechanistic studies revealed a unique mode of reactivity in which the reaction is proposed to proceed through hydroalumination and σ-bond metathesis between the resultant alkenyl aluminum species and HBpin, which acts to drive turnover of the catalytic cycle.

Ligand coordination modulates reductive elimination from aluminium(iii).

Oxidative addition of inert bonds at low-valent main-group centres is becoming a major class of reactivity for these species. The reverse reaction, reductive elimination, is possible in some cases but far rarer. Here, we present a mechanistic study of reductive elimination from Al(iii) centres and unravel ligand effects in this process.

Comparison of transradial coronary procedures via right radial versus left radial artery approach: A meta-analysis.

Introduction: Coronary angiography and angioplasty via transradial approach is shown to be associated with significant reduction in access site complications. Due to a lack of sufficient data, the use of the right or left radial approach is still operator-dependent. We performed a meta-analysis of prospective randomized studies to compare right versus left radial artery approach for coronary procedures.

Base-Stabilized Phosphinidene Boranes by Silylium-Ion Abstraction.

We report the preparation of N-heterocyclic carbene (NHC)-stabilized compounds containing P=B double bonds. The reaction of the highly functionalized phosphinoborane Mes*(SiMe3 )P-B(Cl)Cp* with Lewis bases allows access to base-stabilized phosphinidene boranes Mes*P=B(L)Cp* (L=4-dimethylaminopyridine (DMAP), NHC) by Me3 SiCl elimination. The formation of these species is shown to proceed through transient borylphosphide anions generated by Me3 Si abstraction.

Strategies for the hyperpolarization of acetonitrile and related ligands by SABRE.

We report on a strategy for using SABRE (signal amplification by reversible exchange) for polarizing (1)H and (13)C nuclei of weakly interacting ligands which possess biologically relevant and nonaromatic motifs. We first demonstrate this via the polarization of acetonitrile, using Ir(IMes)(COD)Cl as the catalyst precursor, and confirm that the route to hyperpolarization transfer is via the J-coupling network. We extend this work to the polarization of propionitrile, benzylnitrile, benzonitrile, and trans-3-hexenedinitrile in order to assess its generality.

The reaction of an iridium PNP complex with parahydrogen facilitates polarisation transfer without chemical change.

The short lived pincer complex [(C5H3N(CH2P((t)Bu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange. This catalyst formulation enables the efficient transfer of polarization from parahydrogen to be placed into just a single molecule of the hyperpolarisation target, pyridine. When the catalysts (1)H nuclei are replaced by (2)H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals.

Donor-acceptor adducts of a 1,3-disila-2-oxyallyl zwitterion.

In the presence of a Lewis acid or base, cyclotrisilene cSi3Tip4 (Tip = 2,4,6-triisopropylphenyl) reacts with CO to form stable adducts of a 1,3-disila-2-oxyallyl zwitterion. Coordination of an N-heterocyclic carbene (NHC) to one silicon center results in a localized Si=C bond, whereas B(C6F5)3 bonds to the carbonyl moiety leading to the delocalization of the positive charge over the oxyallyl moiety. Computational analysis of the electronic structure of the Lewis acid adduct reveals a considerable interaction between the two silicon atoms in 1,3-position and thus aromaticity akin to the homocyclopropenium cation.

Probing signal amplification by reversible exchange using an NMR flow system.

Hyperpolarization methods are used in NMR to overcome its inherent sensitivity problem. Herein, the biologically relevant target nicotinamide is polarized by the hyperpolarization technique signal amplification by reversible exchange. We illustrate how the polarization transfer field, and the concentrations of parahydrogen, the polarization-transfer-catalyst and substrate can be used to maximize signal amplification by reversible exchange effectiveness by reference to the first-order spin system of this target.

Contemporary antiplatelet therapy in patients undergoing percutaneous coronary intervention.

The proper use of antiplatelet agents in the cardiac catheterization laboratory is important for ensuring optimal results in patients undergoing percutaneous revascularization. Understanding the mechanisms by which these drugs exerts their effects is important for both interventional and non-interventional cardiologists. The effects of these agents on platelet function can be assessed and monitored using a variety of commercially available laboratory assays but so far these tests have not been adopted in routine clinical practice.

From disilene (Si=Si) to phosphasilene (Si=P) and phosphacumulene (P=C=N).

The generation of heavier double-bond systems without by- or side-product formation is of considerable importance for their application in synthesis. Peripheral functional groups in such alkene homologues are promising in this regard owing to their inherent mobility. Depending on the steric demand of the N-alkyl substituent R, the reaction of disilenide Ar2Si=Si(Ar)Li (Ar = 2,4,6-iPr3C6H2) with ClP(NR2)2 either affords the phosphinodisilene Ar2 Si=Si(Ar)P(NR2)2 (for R = iPr) or P-amino functionalized phosphasilenes Ar2(R2N)Si=Si(Ar)=P(NR2) (for R = Et, Me) by 1,3-migration of one of the amino groups.