Search

The investigations conducted on the synthesis and structural characterization of a series of alkyl, aryl, and benzo-annulated [B.sub.2][N.sub.2][C.sub.2] triphenylene analogues are reported. The incorporation of boron and nitrogen heteroatoms in the central ring has a striking effect on these properties.

Comparative studies on the catalytic dehydricoupling of the amine-borane adduct Me(sub 2)NH.BH(sub 3) with a variety of [MeN-BH(sub 2)](sub2)) and the phosphine-borane adduct Ph2Ph.Bh3 with a variety of Rh (pre) catalysts such. Results suggest that the catalytic dehydrocoupling of Me(sub 2)NH.BH(sub 3) is heterogenous in nature involving Rh(O) collids, while that of Ph(sub 2)PH.BH(sub 3) proceeds by a homogeneous mechanism even when starting with Rh(O) precursors such as Rh/Al(sub 2)O(sub 3).

The borazine derivative is an outcome of the catalytic dehydrocoupling of NH3.BH3, MeNH2.BH3, and PhNH2.BH3 and the same is discussed. The TEM evaluation of the components of the reaction results in the catalyzed dehydrocoupling of Me2NH.BH3 along with Hg venomous test indicating a heterogenous catalytic method consisting of Rh(O) colloids.

A mechanism involving the formation of Rh-Ga bonds on the Rh colloid surface based on the catalytic dehydrocoupling of a secondary phosphine-gallane adduct with either Rh(I) or Rh(0) leading to release of [H.sub.2] gas and decomposition to Ga(0) metal is presented.

The synthesis and characterization of a series of planar and twisted heteroaromatic quaterphenyl analogues containing BN ring linkages were observed to show unique excited-state dimer (excimer) fluorescnece.

A report presents the findings on the poisoning behavior of BH3.THF (THF = tetrahydrofuran) and other related group 13 hydride species with heterogeneous transition metal catalysts used for the dehydrocoupling of Me2-NH.BH3.The results obtained suggest that although the poisoning behavior is not a universal phenomenon, the observation that such boron layers are formed needs to be considered when boron reagents are used for the generation of metal colloids.

Me2NH.BH3 acts as a reducing agent to generate catalytically active Rh colloids and a stoichiometric hydrogen source for the hydrogenation of alkenes in a one-pot procedure at 25 degree C is demonstrated.

The operation of a heterogeneous mechanism involving colloidal Rh(0) metal is described. Detailed comparative studies of the catalytic dehydrocoupling of a phosphine-borane adduct and an amine-borane adduct, which suggest that the mechanism for the former involves homogeneous catalysis, are presented.

The linear hybrid Aminoborane/Phosphinoborane chains are described. Thermolysis of Aminoborane/Phosphinoborane chains at 130 C, gives polymeric species such as the polyphosphinoborane and the six-membered ring [BH2-Ch2-PPh2]2.

Attempts to induce the catalytic dehydrocoupling of the phosphine-gallane adduct Cy2PH·GaH3 (Cy = cyclohexyl) (1) by treatment with ca. 5 mol % of either the Rh(I) complex [{Rh(μ-Cl)(1,5-cod)}2] (cod = cyclooctadiene) or the Rh(0) species Rh/Al2O3 and [Oct4N]Cl-stabilized colloidal Rh led to catalytic P-Ga bond cleavage to generate the phosphine, H2, and Ga metal. Interestingly, subsequent treatment of the reaction mixtures with Me2NH·BH3 failed to lead to the formation of [Me2N-BH2]2 via Rh-catalyzed dehydrocoupling, which suggested that catalyst deactivation was taking place. Poisoning studies involving the treatment of the active Rh(0) catalyst with Cy2PH, PMe3, or GaH3·OEt2 showed that deactivation indeed occurred as the dehydrocoupling of Me2NH·BH3 either dramatically decreased in rate or did not take place at all. The X-ray photoelectron spectroscopy analysis of colloidal Rh(0) that had been treated with Cy2PH and PMe3 confirmed the presence of phosphorus on the catalyst surface in each case, consistent with catalyst poisoning via phosphine ligation. A mechanism for the Rh-catalyzed P-Ga bond cleavage reaction of 1 and Me3P·GaH3 (2) is proposed and involves the initial reaction of Ga-H bonds with the Rh colloid surface, which weakens and ultimately breaks the P-Ga bond. The reasonable nature of this mechanism is supported by a model reaction between the zerovalent group 9 complex Co2(CO)8 and 2 which afforded Me3P·Ga[Co(CO)4]3 (3). Consistent with the elongated and thus weakened P-Ga bond in 3, solutions of this species in Et2O subsequently form the known complex [(Me3P)Co(CO)3]2 (4) and Ga metal after 4 h at 25 °C. [ABSTRACT FROM AUTHOR]

A series of planar and twisted heteroaromatic quaterphenyl analogues containing BN ring linkages has been synthesized using primarily difunctional Lewis acidic diborabiphenyl moieties as molecular cores. Crystal structure analyses indicated the presence of large twist angles between adjacent aromatic rings in 1 and 3, which were also observed to possess nonfluorescent behavior due to a lack of molecular rigidity and insufficient BN character in the excited state. In contrast, the incorporation of one or two bridging ethylene groups between the adjacent rings (installed via an ethynyl cycloisomerization) was found to afford planar phenanthrene or pyrene moieties, which resulted in weak fluorescence behavior (ΦF = 0.02-0.16) for the n-Bu and Ph derivatives 5-12. Emission colors ranged from green (λem = 521 nm) to red (λem = 630 nm) and depended primarily on the conformation (2,2′- as 4,4′-), the extent of chromophore conjugation (phenanthrene as pyrene), and the type of exocyclic substituent present (n-Bu as Ph). Communication between the two phenanthrene or pyrene moieties was observed in some cases, which was characterized by bathochromically shifted emission bands relative to that of monomeric phenanthrene or pyrene species. Unique excited-state dimer (excimer) fluorescence was observed for the 2,2′-isomer 8, which was characterized by broad, low-energy emission bands bathochromically shifted from that of the corresponding monomer. [ABSTRACT FROM AUTHOR]

A series of alkyl (1–3), aryl (6), and benzo-annulated (4, 5) heteroaromatic triphenylene analogues with B2N2O2 cores have been synthesized via chelation of pyridazine derivatives using difunctional Lewis acidic diborabiphenyl precursors. In contrast to triphenylene, NICS(1) calculations on 1 suggested high aromaticities for the central (-11.3 ppm) and outer borabenzene rings (-7.7 ppm), along with nonaromatic behavior for the pyridazine ring (-0.7 ppm). Crystal structure analyses supported this analysis. When the a- and c-faces of the pyridazine moiety were free of substitution (1,3), planar structures resulted, but upon substitution, a twisted B2N2O2 core was observed due to steric repulsion of neighboring hydrogen atoms (e.g., 5). The increase of steric bulk from H (1) to iPr (3) in the planar species was found to result in a dimeric, head-to-tail herringbone packing motif, held together by close intermolecular B⋯N interactions of 3.39 Å. One-electron reduction by Cp*2Co was found to afford the radical anions of 3 and 5, which were characterized by broad, featureless singlets in the EPR spectra; [3]·-[Cp*2Co]+ was characterized by X-ray crystallography. While the planar structures (1–4) were observed to possess weak fluorescence (ΦF = 0.02–0.08) with either yellow-orange (ca. 555 nm) or green emission (521 nm), the twisted structures (5, 6) were found to be nonfluorescent. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Focuses on the role of transition metal catalysis in organic synthesis. Use of metal complexes to catalyze ring-opening polymerization reactions; Analysis of the catalytic dehydrocoupling of phosphine-borane adducts; Synthesis of polyphosphinoboranes.

In the title compound, [Pt2(C6H6P)2(C26H48P2)2]Cl2·2CH2Cl2·C6H14, the cation crystallizes as a phosphido-bridged PtI dimer [Pt(dcype)(μ-PPhH)]2Cl2, with crystallographic 2/ m symmetry [dcype is 1,2-bis­(di­cyclo­hexyl­phosphino)­ethane]. The Pt2P2 core forms a planar distorted square capped by chelating bis-phosphine ligands, resulting in a distorted square-planar geometry for the Pt atoms. In the Pt2P2 core, the Pt—P bond length is 2.3403 (9) Å, with a narrow P—Pt—P angle of 76.87 (6)° and a wide Pt—P—Pt angle of 103.13 (6)°. The bite angle of the dcype ligand is 85.70 (6)°, with a Pt—P bond length of 2.2993 (11)°. [ABSTRACT FROM AUTHOR]

[structure: see text]. Phenanthrene analogues with internalized B-N moieties were found to afford blue light emission with good quantum efficiencies, whereas the isomeric species with peripheral B-N moieties displayed only UV emission behavior, like the all-carbon framework.

The reaction of the Pt(II) dihydride complex cis-[PtH2(dcype)](dcype = 1,2-bis(dicyclohexylphosphino)ethane) with the primary or secondary phosphine-borane adducts PhRPH x BH3(R = H, Ph) was found to exclusively afford the mono-substituted complexes cis-[PtH(PPhR x BH3)(dcype)](1: R = H; 2: R = Ph)via a dehydrocoupling reaction between Pt-H and P-H bonds. Similar reactivity was observed between the uncoordinated phosphines PhRPH (R = H, Ph) and cis-[PtH2(dcype)], which gave cis-[PtH(PPhR)(dcype)](4: R = H; 5: R = Ph). The complexes were characterized by 1H, 11B, 13C and 31P NMR spectroscopy, IR, MS and, in the case of 2, X-ray crystallography that confirmed the cis geometries. The di-substituted complex cis-[Pt(PhPH x BH3)2(dcype)](3) was prepared from the reaction of cis-[PtCl2(dcype)] with two equivalents of Li[PPhH x BH3]. This suggested that steric reasons alone cannot be used to explain the lack of reactivity with respect to a second dehydrocoupling reaction involving the remaining Pt-H bond in complexes 1, 2, 4 and 5.

Highly active Rh colloids, generated in situ during the catalytic dehydrocoupling of Me2NH.BH3 using [{Rh(cod)(mu-Cl)}2] as a precatalyst, are capable of efficiently hydrogenating alkenes at 25 degrees C in a one-pot procedure using only the evolved H2 from the initial dehydrocoupling reaction.

Reaction of [Pt(PEt(3))(3)] with the primary and secondary phosphine-borane adducts PhRPH x BH(3) (R=H, Ph) resulted in oxidative addition of a P-H bond at the Pt(0) center to afford the complexes trans-[PtH(PPhR x BH(3))(PEt(3))(2)] (1: R=H; 2: R=Ph). The products 1 and 2 were characterized by (1)H, (11)B, (13)C, (31)P, and (195)Pt NMR spectroscopy, and the molecular structures were verified by X-ray crystallography. In both cases, a trans arrangement of the hydride ligand with respect to the phosphidoborane ligand was observed. When 2 was treated with PhPH(2) x BH(3), a novel phosphidoborane ligand-exchange reaction occurred which yielded 1 and Ph(2)PH x BH(3). Treatment of 2 with one equivalent of depe (depe=1,2-bis(diethylphosphino)ethane) resulted in the formation of the complex cis-[PtH(PPh(2) x BH(3))(depe)] (3), in which the hydride ligand and the phosphidoborane ligand are in a cis arrangement. Treatment of 3 with PhPH(2) x BH(3) was found to result in an exchange of the phosphidoborane ligands to give the complex cis-[PtH(PPhH x BH(3))(depe)] (4) and Ph(2)PH x BH(3). Complex 4 was found to undergo further reaction in the presence of PhPH(2) x BH(3) to give meso-cis-[Pt(PPhH x BH(3))(2)(depe)] (5) and rac-cis-[Pt(PPhH x BH(3))(2)(depe)] (6).