Search

The coordination chemistry of the stiboranes Ph4Sb(OTf) ( 1 a, OTf = OSO2CF3) and Ph3Sb(OTf)2 ( 3) with Lewis bases has been investigated. The significant steric encumbrance of the Sb center in 1 a precludes interaction with most ligands, but the relatively low steric demands of 4-methylpyridine- N-oxide (OPyrMe) and OPMe3 enabled the characterization of [Ph4Sb(OPyrMe)][OTf] ( 2 a) and [Ph4Sb(OPMe3)][OTf] ( 2 b), rare examples of structurally characterized complexes of stibonium acceptors. In contrast, 3 was found to engage a variety of Lewis bases, forming stable isolable complexes of the form [Ph3Sb(donor)2][OTf]2 [donor=OPMe3 ( 6 a), OPCy3 ( 6 b, Cy=cyclohexyl), OPPh3 ( 6 c), OPyrMe ( 6 d)], [Ph3Sb(dmap)2(OTf)][OTf] ( 6 e, dmap=4-(dimethylamino)pyridine) and [Ph3Sb(donor)(OTf)][OTf] [donor=1,10-phenanthroline ( 7 a) or 2,2′-bipy ( 7 b, bipy=bipyridine)]. These compounds exhibit significant structural diversity in the solid-state, and undergo ligand exchange reactions in line with their assignment as coordination complexes. Compound 3 did not form stable complexes with phosphine donors, with reactions instead leading to redox processes yielding SbPh3 and products of phosphine oxidation. [ABSTRACT FROM AUTHOR]

The cyclo-diphosphinophosphonium salt [(PfBu)3Me][OTf] (2) has been shown to be highly reactive toward Lewis bases, exhibiting diverse reactivity with phosphines, 4-(dimethylamino)pyridine (dmap) and chlorophosphines, providing approaches to new open-chain and cyclic catena-phosphorus frameworks. Reaction of 2 with R3P (R = Me or nPr) or dmap led to the ring-opened adducts [R3P—PfBu—PfBu—P(Me)fBu] [OTf] (R = Me (4a), nPr (4b)) and [(dmap)-PtBu-PtBu-P(Me)tBu][OTf] (6), respectively. The complicated 31P{1H} NMR spectra of the three compounds were simulated, evidencing the presence of two diastereomeric forms of 4a, and single diastereomers of 4b and 6. This ring-opening reactivity of the cation in 2 parallels the reactivity of isolobal epoxides with nucleophiles under acidic conditions. Compound 2 was also shown to react with a 2:1 mixture of Me2PCl and TMSOTf to form the unexpected cyclo-diphosphino-1,2-diphosphonium salt [(Me2P)2(PfBu)2] [OTf]2 (8), which is postulated to result from two consecutive ring-opening and ring-closing steps. In contrast, reaction with MePCl2 furnished [(MeP)(PtBu)2(P(Me)tBu)][OTf] (9), consistent with insertion of a “MeP” moiety into the cationic phosphorus framework of 2. The importance of ring strain on the reactivity of the cation in 2 was illustrated by comparative studies of the corresponding cyclo-tetraphosphorus cation in [(PfBu)4Me][OTf] (10), which exhibits no reactivity under analogous conditions. [ABSTRACT FROM AUTHOR]

Protonation of MeRNH⋅BH3 (R = Me or H) with HX (X = B(C6F5)4, OTf, or Cl), followed by immediate, spontaneous H2 elimination, yielded the amine-boronium cation salt [MeRNH⋅BH2(OEt2)][B(C6F5)4] and related polar covalent analogs, MeRNH⋅BH2X (X = OTf or Cl). These species can be deprotonated to conveniently generate reactive aminoborane monomers MeRN=BH2 which oligomerize or polymerize; in the case of MeNH2⋅BH3, the two step process gave poly(N-methylaminoborane), [MeNH-BH2]n. [ABSTRACT FROM AUTHOR]

The syntheses of salts containing ligand-stabilized Ph3Sb2+ and Ph3Bi2+ dications have been realized by in situ formation of Ph3Pn(OTf)2 (Pn=Sb or Bi) and subsequent reaction with OPPh3, dmap and bipy. The solid-state structures demonstrate diversity imposed by the steric demands and nature of the ligands. The synthetic method has the potential for broad application enabling widespread development of the coordination chemistry for PnV acceptors. [ABSTRACT FROM AUTHOR]

We report the first insertion step at a metal center for the catalytic dehydropolymerization of H3B·NMeH2 to form the simplest oligomeric species, H3B·NMeHBH2·NMeH2, by the addition of 1 equiv of H3B·NMeH2 to [Ir(PCy3)2(H)2(η2-H3B·NMeH2)][BArF4] to give [Ir(PCy3)2(H)2(η2-H3B·NMeHBH2·NMeH2)][BArF4]. This reaction is also catalytic for the formation of the free linear diborazane, but this is best obtained by an alternative stoichiometric synthesis. [ABSTRACT FROM AUTHOR]

The article focuses on developments in the study and application of amine and phosphine borane adducts. According to the authors, amine and phosphine are prominent as classic examples of compounds that are produced by the reactions between Lewis bases and Lewis acids. These class of compounds have been increasingly used as reagents, hydrogen storage materials, polymer precursors, and have been examined for their coordination chemistry.

The coordination of Me2E(OTf)2 (E = Si, Ge, Sn) acceptors by dmap or 2,2'-bipy furnishes two series of complexes which exhibit distinct structural trends that correlate with the covalent radii of the tetrael elements, and which contrast complexes of these ligands with EX4 (X = Cl or Br). [ABSTRACT FROM AUTHOR]

Efficient catalysts for the dehydrocoupling or dehydropolymerisation of H3B·NMexH(3−x)(x= 1, 2) have been developed by variation of the P–Rh–P angle in {Rh(Ph2P(CH2)nPPh2)}+fragments (n= 2–5). [ABSTRACT FROM AUTHOR]

The catalytic dehydrocoupling/dehydrogenation of N-methylamine-borane, MeNH2∙BH3 (7), to yield the soluble, high molecular weight poly(N-methylaminoborane) (8a), [MeNH-BH2]n (Mw > 20 000), has been achieved at 20 °C using Brookhart's Ir(III) pincer complex IrH2POCOP (5) (POCOP = [μ3-1,3- (OPtBu2)2C6H3)) as a catalyst. The analogous reaction with ammonia-borane, NH3∙BH3 (4), gave an insoluble product, [NH2-BH2]n (8d), but copolymerization with MeNH2∙BH3 gave soluble random copolymers, [MeNH-BH2]n-r-[NH2-BH2]m (8b and 8c). The structures of polyaminoborane 8a and copolymers 8b and 8c were further analyzed by ultrahigh resolution electrospray mass spectrometry (ESI-MS), and Ba, together with insoluble homopolymer 8d, was also characterized by 11B and 1H solid-state NMR, IA, and wide- angle X-ray scattering (WAXS). The data indicate that 8a-8c are essentially linear, high molecular weight materials and that the insoluble polyaminoborane 8d possesses a similar structure but is of lower molecular weight (ca. 20 repeat units), presumably due to premature precipitation during its formation. The yield and molecular weight of polymer 8a was found to be relatively robust toward the influence of different temperatures, solvents, and adduct concentrations, while higher catalyst loadings led to higher molecular weight materials. It was therefore unexpected that the polymerization of 7 using 5 was found to be a chain- growth rather than a step-growth process, where high molecular weights were already attained at about 40% conversion of 7. The results obtained are consistent with a two stage polymerization mechanism where, first, the Ir catalyst 5 dehydrogenates 7 to afford the monomer MeNH=BH2 and, second, the same catalyst effects the subsequent polymerization of this species. A wide range of other catalysts based on Ru, Rh, and Pd were also found to be effective for the transformation of 7 to polyaminoborane 8a. For example, polyaminoborane 8a was even isolated from the initial stage of the dehydrocouplingldehydro-genation of 7 with [Rh(μ-Cl)(1 5-cod)]2 (2) as the catalyst at 20 °C, a reaction reported to give the N,N,N- trimethyl borazine, [MeN-BH]3, under different conditions (dimethoxyethane, 45 °C). The ability to use a variety of catalysts to prepare polyaminoboranes suggests that the synthetic strategy should be applicable to a broad range of amine-borane precursors and is a promising development for this new class of inorganic polymers. [ABSTRACT FROM AUTHOR]

[This corrects the article DOI: 10.1039/C5SC02423D.].

The dehydrocoupling/dehydrogenation behavior of primary arylamine-borane adducts ArNH(2)⋅BH(3) (3 a-c; Ar = a: Ph, b: p-MeOC(6)H(4), c: p-CF(3)C(6)H(4)) has been studied in detail both in solution at ambient temperature as well as in the solid state at ambient or elevated temperatures. The presence of a metal catalyst was found to be unnecessary for the release of H(2). From reactions of 3 a,b in concentrated solutions in THF at 22 °C over 24 h cyclotriborazanes (ArNH-BH(2))(3) (7 a,b) were isolated as THF adducts, 7 a,b⋅THF, or solvent-free 7 a, which could not be obtained via heating of 3 a-c in the melt. The μ-(anilino)diborane [H(2)B(μ-PhNH)(μ-H)BH(2)] (4 a) was observed in the reaction of 3 a with BH(3)⋅THF and was characterized in situ. The reaction of 3 a with PhNH(2) (2 a) was found to provide a new, convenient method for the preparation of dianilinoborane (PhNH)(2)BH (5 a), which has potential generality. This observation, together with further studies of reactions of 4 a, 5 a, and 7 a,b, provided insight into the mechanism of the catalyst-free ambient temperature dehydrocoupling of 3 a-c in solution. For example, the reaction of 4 a with 5 a yields 6 a and 7 a. It was found that borazines (ArN-BH)(3) (6 a-c) are not simply formed via dehydrogenation of cyclotriborazanes 7 a-c in solution. The transformation of 7 a to 6 a is slowly induced by 5 a and proceeds via regeneration of 3 a. The adducts 3 a-c also underwent rapid dehydrocoupling in the solid state at elevated temperatures and even very slowly at ambient temperature. From aniline-borane derivative 3 c, the linear iminoborane oligomer (p-CF(3)C(6)H(4))N[BH-NH(p-CF(3)C(6)H(4))](2) (11) was obtained. The single-crystal X-ray structures of 3 a-c, 5 a, 7 a, 7 b⋅THF, and 11 are discussed., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)