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1.
Dalton Trans ; 45(3): 1055-62, 2016 Jan 21.
Article in English | MEDLINE | ID: mdl-26649782

ABSTRACT

Polyaminoboranes [N(R)H-BH2]n (1: R = H, 2: R = Me) were pyrolyzed on a range of substrates: silicon, metal foils (stainless steel, nickel, and rhodium), and sapphire wafers, as well as on Al2O3 and AlN powders. The pyrolysis of 2 on a Si-wafer resulted in porous nanostructures containing hexagonal-boron nitride (h-BN). In the case of 1 or H3N·BH3 as precursor, using rhodium foil as substrate afforded amorphous B and N-containing nanostructures, and polydisperse spherical nanoparticles, respectively. Switching the substrate to sapphire wafers, as well as to Al2O3 or AlN powders, resulted in formation of crystalline Al5BO9 nanostructures (nanowires, nanotubes, and nanoribbons). For sapphire wafers, the size of the resulting nanowires was influenced by modifying the surface defect density.

2.
Angew Chem Int Ed Engl ; 54(16): 4836-41, 2015 Apr 13.
Article in English | MEDLINE | ID: mdl-25712707

ABSTRACT

The catalyst loading is the key to control the molecular weight of the polymer in the iron-catalyzed dehydropolymerization of phosphine-borane adducts. Studies showed that the reaction proceeds through a chain-growth coordination-insertion mechanism.

3.
J Am Chem Soc ; 137(6): 2375-85, 2015 Feb 18.
Article in English | MEDLINE | ID: mdl-25585041

ABSTRACT

We have found that the width and shape (from rectangular to elliptical, to almost circular in cross-section) of the crystalline core of fiberlike micelles of polyferrocenyldimethylsilane (PFDMS) diblock copolymers can be varied by altering the degree of polymerization of PFDMS, and also the chemistry of the complementary corona-forming block. This enabled detailed studies of living crystallization-driven self-assembly (CDSA) processes that involved the addition of unimers with a short, crystallizable core-forming PFDMS block to a seed solution of short micelles with a large diameter crystalline core, derived from block copolymers with a longer PFDMS block. The morphology of resultant micelles was found to be highly dependent on the polarity of the solvent and temperature. For example, linear micelles were formed in less polar solvents (which are moderately poor solvents for PFDMS) and/or at higher temperatures. In contrast, the formation of branched structures could be "switched on" when the opposite conditions were used. Thus, the use of more polar solvents (which are very poor solvents for PFDMS) and ambient or subambient temperatures allowed the formation of branched micelles and block comicelles with variable and spatially distinct corona chemistries, including amphiphilic nanostructures. Rapid crystallization of added unimers at the seed micelle termini under nonequilibrium self-assembly conditions appears to facilitate the formation of the branched micellar structures as a kinetically trapped morphology. This is evidenced by the transformation of the branched micelles into linear micelles on heating at elevated temperatures.


Subject(s)
Micelles , Polymers/chemistry , Crystallization , Kinetics , Microscopy, Electron, Transmission , Polymerization
4.
J Am Chem Soc ; 135(47): 17739-42, 2013 Nov 27.
Article in English | MEDLINE | ID: mdl-24188009

ABSTRACT

We report the preparation of branched micelles by the growth of thinner-core cylindrical micelles at the termini of the thicker-core cylindrical micelle seeds through crystallization-driven self-assembly of polyferrocenylsilane block copolymers. The branched micelles possessed structures with monodisperse middle segments and, in most cases, two branches at the seed terminus. After cross-linking of the coronas, the branched micelles become resistant to dissolution in good solvents for both blocks and can be manipulated as colloidally stable nanomaterials.

5.
Dalton Trans ; 41(8): 2346-53, 2012 Feb 28.
Article in English | MEDLINE | ID: mdl-22186899

ABSTRACT

Reaction of Ti(OiPr)(4) with various bis(ß-diketones) and bis(ß-ketoesters) (LH(2)) results in the formation of dimeric complexes [Ti(OiPr)(2)L](2), where each metal centre is coordinated by two terminal OiPr ligands and two bridging ß-diketonate or ß-ketoesterate groups (L). Macrocycles containing two M(OiPr)(2) moieties are thus formed. Reaction of Zr(OiPr)(4) with the same bis(ß-diketones) and bis(ß-ketoesters) results in different compounds, depending on the organic spacer connecting the two functional groups. With shorter spacers, the compounds [ZrL(OiPr)(2)](2)·2iPrOH are obtained, with the same structures as the corresponding titanium complexes. With longer spacers, however, complexes with a higher degree of substitution are formed, such as (ZrL(2))(2) and Zr(2)L(3)(OiPr)(2)·2iPrOH. The molecular weight and structure of all compounds was elucidated by ESI-MS. MS/MS of the corresponding [M+Na](+) precursor ions confirmed the proposed structures based on structure-specific product ions. Solution NMR experiments and DFT calculations additionally supported the proposed structures.

6.
Chem Commun (Camb) ; 46(45): 8549-51, 2010 Dec 07.
Article in English | MEDLINE | ID: mdl-20972509

ABSTRACT

Evidence is provided that thermal decomposition of Co(CO)(4)SiCl(3) adsorbed on silica in a hydrogen atmosphere results in the formation of metallic cobalt nanoparticles covered with a Co(2)SiO(4)/CoO shell instead of cobalt silicide nanoparticles, as had been reported previously.

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