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Functionalized Cyclic Disilenes via Ring Expansion of Cyclotrisilenes with Isocyanides

The reaction of cyclotrisilenes <b>1</b> with 1 equiv of alkyl and aryl isocyanides at 25 °C affords the four-membered trisilacyclobutenes <b>2</b> with an exocyclic imine functionality as the major products of formal insertion into one of the Si–Si single bonds of <b>1</b>. Minor quantities of the iminotrisilabicyclo[1.1.0]­butanes <b>3</b> are obtained as side products, formally resulting from [1 + 2] cycloaddition of the isocyanides to the Si–Si double bond of <b>1</b>. The bicyclo[1.1.0]­butanes <b>3</b> become dominant at lower temperatures and may react with an additional 1 equiv of isonitriles to give the diiminotrisilabicyclo[1.1.1]­pentanes <b>4</b>

Functionalized Cyclic Disilenes via Ring Expansion of Cyclotrisilenes with Isocyanides

The reaction of cyclotrisilenes <b>1</b> with 1 equiv of alkyl and aryl isocyanides at 25 °C affords the four-membered trisilacyclobutenes <b>2</b> with an exocyclic imine functionality as the major products of formal insertion into one of the Si–Si single bonds of <b>1</b>. Minor quantities of the iminotrisilabicyclo[1.1.0]­butanes <b>3</b> are obtained as side products, formally resulting from [1 + 2] cycloaddition of the isocyanides to the Si–Si double bond of <b>1</b>. The bicyclo[1.1.0]­butanes <b>3</b> become dominant at lower temperatures and may react with an additional 1 equiv of isonitriles to give the diiminotrisilabicyclo[1.1.1]­pentanes <b>4</b>

Iridium N-Heterocyclic Carbene Complexes as Efficient Catalysts for Magnetization Transfer from <i>para</i>-Hydrogen

While the characterization of materials by NMR is hugely important in the physical and biological sciences, it also plays a vital role in medical imaging. This success is all the more impressive because of the inherently low sensitivity of the method. We establish here that [Ir(H)₂(IMes)(py)₃]Cl undergoes both pyridine (py) loss as well as the reductive elimination of H₂. These reversible processes bring <i>para</i>-H₂ and py into contact in a magnetically coupled environment, delivering an 8100-fold increase in ¹H NMR signal strength relative to non-hyperpolarized py at 3 T. An apparatus that facilitates signal averaging has been built to demonstrate that the efficiency of this process is controlled by the strength of the magnetic field experienced by the complex during the magnetization transfer step. Thermodynamic and kinetic data combined with DFT calculations reveal the involvement of [Ir(H)₂(η²-H₂)(IMes)(py)₂]⁺, an unlikely yet key intermediate in the reaction. Deuterium labeling yields an additional 60% improvement in signal, an observation that offers insight into strategies for optimizing this approach