David Gau

Stable phosphonium sila-ylide with reactivity as a sila-Wittig reagent.

The silicon congeners of well-known phosphonium ylides have been considered only as short-lived reactive intermediates. We successfully synthesized a remarkably stable phosphonium sila-ylide. Its X-ray structure reveals a long Si-P bond and a strongly pyramidalized silicon center, indicating a very weak P-Si pi interaction. In addition, it exhibits an alpha,beta-ambiphilic character with a nucleophilic silicon center, similar to its carbon-congener phosphonium ylides. This property of the phosphonium sila-ylide allows its use as a sila-Wittig reagent with carbonyl derivatives.

Diastereoselective synthesis of bulky, strongly nucleophilic, and configurationally stable P-stereogenic tricyclic phosphines.

A very simple, one-step highly diastereoselective synthesis of bulky, configurationally and air-stable P-chiral tricyclic phosphines 3, showing an exceptionally strong nucleophilic character, has been developed. This method involves the reaction of the stable phosphonium sila-ylide 1 with aryl- and alkyl-substituted acetylene derivatives. Starting from commercially available chiral (R,S)-(+)-endo-2-norborneol, the corresponding enantiomerically pure phosphines were obtained with excellent enantioselectivities (ee ≥ 99%) and high chemical yields.

A Stable Monomeric SiO2 Complex with Donor–Acceptor Ligands

Isolation of a monomeric SiO2 compound 3 as a stable donor-acceptor complex with two different ligands -a σ-donating ligand (pyridine, dimethylaminopyridine, N-heterocyclic carbene) and a donor-acceptor ligand (iminophosphorane)-is presented. The SiO2 complex 3 is soluble in ordinary organic solvents and is stable at room temperature in solution and in the solid state. Of particular interest, 3 remains reactive and can be used as a stable and soluble unimolecular SiO2 reagent.

Donor-Stabilized 1,3-Disila-2,4-diazacyclobutadiene with a Nonbonded Si⋅⋅⋅Si Distance Compressed to a Si=Si Double Bond Length

A donor-stabilized 1,3-disila-2,4-diazacyclobutadiene presents an exceptionally short nonbonded Si⋅⋅⋅Si distance (2.23 Å), which is as short as that of Si=Si bonds (2.15-2.23 Å). Theoretical investigations indicate that there is no bond between the two silicon atoms, and that the unusual geometry can be related to a significant coulomb repulsion between the two ring nitrogen atoms. This chemical pressure phenomenon could provide an alternative and superior way of squeezing out van der Waals space in highly strained structures, as compared to the classical physical methods.