Karen Temple

Rhodium-catalyzed formation of boron–nitrogen bonds: a mild route to cyclic aminoboranes and borazines

Secondary amine–borane adducts R2NH·BH3, which are stable to H2 elimination below 100 °C, undergo efficient catalytic dehydrocoupling at 25–45 °C in the presence of RhI or RhIII complexes to quantitatively form cyclic aminoboranes [NR2–BH2]2 (1: R = Me or 2: cyclo-C4H8); under similarly mild conditions, the analogous adducts NH3·BH3 and MeNH2·BH3 yield borazines [RN–BH]3 (3: R = H or 4: R = Me) in yields limited by intermolecular coupling reactions.

Supramolecular Organometallic Polymer Chemistry: Multiple Morphologies and Superstructures from the Solution Self‐Assembly of Polyferrocene‐block‐Polysiloxane‐block‐Polyferrocene Triblock Copolymers

The solution self-assembly of an organometallic-inorganic triblock copolymer, poly(ferrocenyldimethylsilane)-block-poly(dimethylsiloxane)-block-poly-(ferrocenyldimethylsilane) (PFDMS-b-PDMS-b-PFDMS, 3b; block ratio 1:13:1; Mn = 2.88 x 10(4) gmol(-1), polydispersity (PDI) 1.43 (gel permeation chromatography, GPC)) was studied in n-hexane, a PDMS block selective solvent. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and TEM with negative staining analysis of these micellar solutions after solvent evaporation revealed the presence of multiple micellar morphologies including spheres, cylinders, and novel flower-like supramolecular aggregates. TEM analysis of samples fractionated by ultracentrifugation and preparative size-exclusion chromatography suggest that the formation of multiple morphologies is a consequence of compositional variations. When micellar solutions were prepared at 50 degrees C (above the glass transition of the PFDMS core-forming block) flower-like micellar aggregates similar to those present in micellar solutions prepared at room temperature also formed. However, after solvent evaporation, TEM analysis of micellar solutions prepared in decane at about 150 degrees C, above the melt temperature of the PFDMS core (ca. 120-145 degrees C), revealed the presence of spherical micelles (when decane solutions at 150 degrees C were rapidly cooled to room temperature) and rod-like cylindrical micelles (when decane solutions at 150 degrees C were slowly cooled to room temperature). In contrast, poly(ferrocenylmethylethylsilane)block-poly(dimethylsiloxane)-block-poly(ferrocenylmethylethylsilane) (PFMES-b-PDMS-b-PFMES, 4; block ratio 1:16:1; Mn=2.90x10(4)g mol(-1), PDI= 1.42 (GPC)) and poly(ferrocenylmethylphenylsilane)-block-poly(dimethylsiloxane)-block-poly(ferrocenylmethylphenylsilane) (PFMPS-b-PDMS-b-PFMPS, 5; block ratio 1:15:1; Mn=3.00 x 10(4) gmol(-1), PDI = 1.38 (GPC)), which possess completely amorphous organometallic core-forming blocks, formed only spherical micelles in hexane at room temperature. These observations indicate that crystallinity of the insoluble polyferrocenylsilane block is a critical factor in the formation of the nonspherical micelle morphologies.

Strained, ring tilted dicarbon-bridged [2]ferrocenophanes and ferrocene revisited: 57Fe Mössbauer spectroscopic study of bonding, hyperfine interactions, and lattice dynamics

Abstract The temperature dependencies of the nuclear hyperfine interactions (isomer shift, quadrupole splitting and resonance effect magnitude) for two [2]ferrocenophanes have been studied by 57Fe Mossbauer effect spectroscopy over the temperature range from 90 K to above room temperature, and compared to analogous data for both staggered and eclipsed forms of unbridged ferrocene. The effect of the two-atom bridge, as well as the possibility of a direct metal atom-olefin moiety interaction have been examined in detail. The temperature dependence of the quadrupole splitting is not uniquely related to the tilt angle of the two Cp rings, and is distinct from that observed for related [1]ferrocenophanes.

Living Anionic Ring-Opening Polymerization of Unsymmetrically Substituted Silicon-Bridged [1]Ferrocenophanes; A Route to Organometallic Block Copolymers with Amorphous Poly(ferrocenylsilane) Blocks

Living anionic ring-opening polymerization methodology for silicon-bridged [1]ferrocenophanes has been extended to unsymmetrically substituted monomers. This permits access to well-defined amorphous poly(ferrocene) homopolymers and organometallic block copolymers, such as polystyrene-b-poly(ferrocenylmethylphenylsilane), with an amorphous poly(ferrocenylsilane) block. This allows phase separation to occur at lower temperatures, which should facilitate applications in which organometallic nanodomains are desirable.

CATALYTIC DEHYDROCOUPLING OF AMINE-BORANE ADDUCTS TO FORM AMINOBORANES AND BORAZINES

A mild, catalytic dehydrocoupling route to aminoboranes and borazine derivatives from either primary or secondary amine-borane adducts has been developed using late transition metal complexes as precatalysts. The dehydrocoupling of Me 2 NH·BH 3 was found to be catalyzed by 0.5 mol% [Rh(1,5-cod)(μ-Cl)] 2 in solution at 25°C to give [Me 2 N─BH 2 ] 2 (1) quantitatively after ca. 8 h. This new catalytic method was extended to other secondary adducts RR ′NH·BH 3 which afforded the dimeric [(1,4-C 4 H 8 )N─BH 2 ] 2 (2) and [PhCH 2 (Me)N─BH 2 ] 2 (3) or the monomeric aminoborane i Pr 2 N═BH 2 (4) under mild conditions. The catalytic dehydrocoupling of NH 3 ·BH 3 , MeNH 2 ·BH 3 , and PhNH 2 ·BH 3 at 45°C affords the borazine derivatives [RN─BH] 3 (5: R = H; 6: R = Me; 7:R = Ph). TEM analysis of the contents of the reaction solution for the [Rh(1,5-cod)(μ-Cl)] 2 catalyzed dehydrocoupling of Me 2 NH·BH 3 together with Hg poisoning experiments suggested a soluble heterogeneous catalyst involving Rh(0) nanoclusters.

Isolation and characterisation of a well defined precatalyst for the ring-opening polymerisation of silicon-bridged [1]ferrocenophanes

Reaction of the silicon-bridged [1]ferrocenophane [Fe(η-C 5 H 4 ) 2 SiMe 2 ] with [Pt(cod) 2 ] (cod = cycloocta-1,5-diene) yields a [2]platinasilaferrocenophane [Fe(η-C 5 H 4 ) 2 Pt(cod)SiMe 2 ] which functions as a precatalyst for the ring-opening polymerisation of the silicon-bridged [Fe(η-C 5 H 4 ) 2 SiMe 2 ] to yield the poly(ferrocenylsilane) [{Fe(η-C 5 H 4 ) 2 SiMe 2 } n ]; a key step in the mechanism is believed to involve dissociation of the cod ligand.