Parallel-stacked aromatic molecules in hydrogen-bonded inorganic frameworks.

By precisely constructing molecules and assembling these into well-defined supramolecular structures, novel physical properties and functionalities can be realized, and new areas of the chemical space can be accessed. In both materials science and biology, a deeper understanding of the properties and exploitation of the reversible character of weak bonds and interactions, such as hydrogen bonds and π-π interactions, is anticipated to lead to the development of materials with novel properties and functionalities. We apply the hydrogen-bonded organic frameworks (HOFs) strategy to inorganic materials science using the cubic octamer of orthosilicic acid, [Si8O12][OH]8, as a building block, and find that various types of hydrogen-bonded inorganic frameworks (HIFs). We succeed in parallel π-stacking pure benzene, thiophene, selenophene, p-benzoquinone, thiophene·p-benzoquinone, and benzene·p-benzoquinone polymers infinitely. These polymers interact via their π-systems by taking advantage of the flexible pores of the three-dimensional nano-honeycomb HIFs, which consist of periodic wide and narrow segments.

Treating octasilanol [Si8O12][OH]8 with tetramethoxysilane and trimethoxyvinylsilane: a halogen-free synthetic route to alkoxysilyl-substituted double-four-ring siloxanes.

The synthesis of methoxysilyl-substituted siloxanes with a double-four-ring (D4R) framework [Si8O12][OSiR(OMe)2]8 (R = OMe or vinyl) via the dealcoholative coupling between silanol [Si8O12][OH]8 and alkoxysilane was accomplished and achieved a halogen-free synthetic process. The solid-state structure of [Si8O12][OSi(OMe)3]8 was determined via a single-crystal X-ray diffraction analysis.

A catalyst- and additive-free synthesis of alkoxyhydrosiloxanes from silanols and alkoxyhydrosilanes.

A convenient method for the selective synthesis of alkoxyhydrosiloxanes that bear SiH and SiOR2 groups on the same silicon atom, R13Si-O-SiR32-n(OR2)nH (n = 0, 1, or 2), via a simple catalyst- and additive-free dealcoholization reaction between silanols and alkoxyhydrosilanes has been developed. These alkoxyhydrosiloxanes can be easily converted into Si(OR2)3-containing siloxanes by zinc catalyzed alkoxylation and alkoxy-containing silphenylene polymers by platinum catalyzed hydrosilylation.

Organocatalytic controlled/living ring-opening polymerization of cyclotrisiloxanes initiated by water with strong organic base catalysts.

Organocatalytic controlled/living ring-opening polymerization of cyclotrisiloxanes, such as hexamethylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane, and 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane, using water as an initiator and strong organic bases, such as amidines, guanidines, phosphazene bases, and proazaphosphatrane, as catalysts produced a variety of polysiloxanes with controlled number-average molecular weights (M n = 2.64-102.3 kg mol-1), narrow polydispersity (D = 1.03-1.16), and well-defined symmetric structures. Controlled syntheses of statistical copolymers and triblock copolymers were achieved by copolymerizations of two cyclotrisiloxanes. Various terminal functionalities were successfully introduced by the end-capping reaction of propagating polysiloxanes using functional chlorosilanes. Kinetic investigations demonstrated that the polymerization proceeded through the initiator/chain-end activation mechanism, namely activations of water in the initiation reaction and of terminal silanols in propagating polysiloxanes in the propagation reaction. Catalytic activities of strong organic bases were revealed to depend on their Brønsted basicity and efficiency of the proton transfer in the initiation and propagation reactions. Guanidines possessing an R-N[double bond, length as m-dash]C(N)-NH-R' unit, in particular 1,3-trimethylene-2-propylguanidine, showed excellent performance as a catalyst. In this system, even non-dehydrated solvents are usable for the polymerization.

Non-aqueous selective synthesis of orthosilicic acid and its oligomers.

Orthosilicic acid (Si(OH)4) and its small condensation compounds are among the most important silicon compounds but have never been isolated, due to their instability. These compounds would be highly useful building blocks for advanced materials if they became available at high purity. Here we show a simple procedure to selectively synthesize orthosilicic acid and its dimer, cyclic trimer and tetramer in organic solvents. Isolation of orthosilicic acid, the dimer and the cyclic tetramer as hydrogen-bonded crystals with tetrabutylammonium halides and the cyclic trimer as solvent-containing crystals is also described. The solid-state structures of these compounds are unambiguously clarified by single crystal X-ray and neutron diffraction studies. The usefulness of orthosilicic acid and its oligomers prepared by the new procedure is demonstrated by the synthesis of functionalized oligosiloxanes.Orthosilicic acid is essential to many natural and synthetic materials but notoriously difficult to isolate, limiting its use in materials synthesis. Here, the authors successfully synthesize and stabilize orthosilicic acid and its oligomers, making available a new family of building blocks for silicon oxide-based materials.

A convenient and clean synthetic method for borasiloxanes by Pd-catalysed reaction of silanols with diborons.

Selective O-borylation of silanols with diborons took place in the presence of Pd catalysts to give the corresponding boryl silyl ethers in high yields.

Cyclotrisilenylium ion: the persilaaromatic compound.

The highly crowded 3,3-bis(di-tert-butylmethylsilyl)-1,2-bis(tri-tert-butylsilyl)cyclotrisilene (3) was newly designed as a precursor of the cyclotrisilenylium ion and prepared by the reaction of 2 equiv of dilithiosilane (tBu2MeSi)2SiLi2 (1) with 2,2,3,3-tetrabromo-1,1,1,4,4,4-hexa-tert-butyltetrasilane. The reaction of 3 with triphenylmethylium tetraarylborate in toluene produced (di-tert-butylmethylsilyl)bis(tri-tert-butylsilyl)cyclotrisilenylium ion (4+), which was isolated in the form of the tetraarylborate salt as extremely air- and moisture-sensitive yellow crystals, representing the first isolable silicon congener of the cyclopropenylium ion. The molecular structure of 4+.TSFPB- (TSFPB- = tetrakis[4-(tert-butyldimethylsilyl)-2,3,5,6-tetrafluorophenyl]borate) was established by X-ray crystallographic analysis, showing that the three-membered ring constitutes an almost equilateral triangle with average Si-Si bond lengths of 2.216(3) A. The X-ray crystal structure and spectral data show that 4+ is not only a free silyl cation but also a 2pi electron aromatic species with delocalization of the positive charge over the three-membered skeleton.