RESUMEN
Phosphorus-nitrogen (PN) adamantanoid cages are valuable precursors for materials chemistry, but their syntheses are based on harsh methods that sometimes require access to restricted reagents. We report a new and scalable synthesis of PN adamantanoid compounds by chlorosilane elimination between bis-silylated amines and phosphorus trichloride. We further study the mechanism of the recently-reported four-fold oxidation of such cages with Me3 SiN3 to yield tetravalent tetrahedral connectors for materials chemistry. Reaction monitoring and kinetic modelling revealed the key rate-limiting step, but attempts to accelerate this using Lewis acid additives were unsuccessful. Nevertheless, a new four-fold oxidized PN-adamantanoid cage has been prepared and structurally characterized.
RESUMEN
Geometric deformation in main group compounds can be used to elicit unique properties including strong Lewis acidity. Here we report on a family of planar bismuth(iii) complexes (cf. typically pyramidal structure for such compounds), which show a geometric Lewis acidity that can be further tuned by varying the steric and electronic features of the triamide ligand employed. The structural dynamism of the planar bismuth complexes was probed in both the solid and solution phase, revealing at least three distinct modes of intermolecular association. A modified Gutmann-Beckett method was used to assess their electrophilicity by employing trimethylphosphine sulfide in addition to triethylphosphine oxide as probes, providing insights into the preference for binding hard or soft substrates. Experimental binding studies were complemented by a computational assessment of the affinities and dissection of the latter into their intrinsic bond strength and deformation energy components. The results show comparable Lewis acidity to triarylboranes, with the added ability to bind two bases simultaneously, and reduced discrimination against soft substrates. We also study the catalytic efficacy of these complexes in the ring opening polymerization of cyclic esters ε-caprolactone and rac-lactide. The polymers obtained show excellent dispersity values and high molecular weights with low catalyst loadings used. The complexes retain their performance under industrially relevant conditions, suggesting they may be useful as less toxic alternatives to tin catalysts in the production of medical grade materials. Collectively, these results establish planar bismuth complexes as not only a novel neutral platform for main group Lewis acidity, but also a potentially valuable one for catalysis.
RESUMEN
Herein we exploit a catalytic amount of [Ph3C]+ to initiate B-X to B-H bond conversion with Et3SiH. This was applied to 6 haloboranes. However, 9-X-9-borabicyclo[3.3.1]nonane (B-X-9-BBN, X = F, Br) reacts directly with silane. Thus, C-F bond activation of benzyl fluorides in the presence of arenes afforded the Friedel-Crafts (FC) products using B-H-9-BBN in the presence of Et3SiH. This catalysis was probed with a range of arenes and several benzyl fluoride derivatives. The protocol is simple, cheap and a convenient route to 1,1-diarylmethanes from benzyl fluorides in good to excellent yields (up to 99%) under mild conditions.
RESUMEN
Diazaphospholenes are widely used as hydride transfer catalysts, however their use in radical reactions is a recently emerging area. Here, we show prior stoichiometric radical cyclizations of aryl iodides mediated by diazaphospholene hydrides are made catalytic by the combination of phenylsilane and alkali metal salts to regenerate the diazaphospholene hydride. The scope was expanded to include aryl bromides, which benefit from visible light irradiation. Twenty one substrates underwent cyclization, including a dearomative cyclization. Extension to six intermolecular radical hydroarylations with arenes, thiophenes, and a pyridine was also accomplished.
RESUMEN
Tetraarylmethanes and adamantanes are important rigid covalent connectors that play a four-way scaffolding role in molecular and materials chemistry. We report the synthesis of a new tetravalent phosphaza-adamantane cage, (PNSiMe3 )4 (NMe)6 (2), that shows high thermal, air, and redox stability due to its geometry. It nevertheless participates in covalent four-fold functionalization reactions along its periphery. The combination of a robust core and reactive corona makes 2 a convenient inorganic scaffold upon which tetrahedral molecular and macromolecular chemistry can be constructed. This potential is demonstrated by the synthesis of a tetrakis(bis(phosphine)iminium) ion (in compound 3) and the first all P/N poly(phosphazene) network (5).
RESUMEN
Reactions of the diborane(4) B2 (o-tolyl)4 and monohydridoboranes are shown to give B(o-tolyl)3 and (o-tolyl)BR2 (R2 =(C8 H14 ) 3, cat 4, pin 5, (C6 F5 )2 6) as the major products. The corresponding reaction with BH3 -sources gives complex mixtures, resulting from hydride/aryl exchange, dimerization and borane elimination. This led to the isolation of the first tetra-substituted pentaborane(9) HB[B(o-tolyl)(µ-H)]4 8. The reaction pathways are probed experimentally and by computations.
RESUMEN
The synthesis and isolation of the first stable C-B-N-substituted borinium [MesBNiPr2][B(C6F5)4] (2) is described. Compound 2 was shown to react with isothiocyanate and carbodiimides, effecting B-C insertion to afford nitrilium (4) and borenium amidinate salts, respectively. The borinium cation [MesBNiPr2]+ (2+) was also generated from reactions of MesB(Cl)NiPr2 (1) and GaCl3, and used to prepare stable borenium amidinate salts (5-6), while the triflate borane MesB(OTf)NiPr2 (7) reacts with carbodiimide to give the bis(amidinate) boronium salt [MesC(NiPr)2B((NiPr)2C)NiPr2][OTf] (8).
RESUMEN
The mechanochemical synthesis of tertiary and secondary alanes AlR3 (R = Np 1 or Mes 2; HAlR2 R = Np 3 or Mes 4) is described. These species are reacted with several α-diimines to give a series of aluminium-derived radicals of the form [(diimine)AlR2]Ë (6-11). EPR and several crystallographic studies are reported. These species are thought to form via hydro- or carboalumination and subsequent elimination reactions. This view is supported by the structural data for minor products C12H7(NHDipp)(NDipp)AliBu25 and C13H8(C(iBu)[double bond, length as m-dash]N(m-Xy)(NH(m-Xy)))AliBu212. In addition, the characterization of (C6F5)2B(OC(C6F5)OC12H8) indicates that such a carboboration pathway also provides access to related boron-derived radicals.
RESUMEN
Metal-free hydroarylation of alkynes with N-substituted pyrroles is shown to be most efficiently mediated by B(C6F5)3 to yield 12 variants of dipyrrole-alkanes, a mono-hydroarylation product and a tetrahydroarylation product of a bis-alkyne. These products were generally obtained in good to excellent yields (up to 95%). Control experiments suggest a mechanism involving FLP addition of the borane and pyrrole to alkyne.
RESUMEN
A rigid naphthalenediamine framework has been used to prepare antimony hydrides that feature LUMO shapes and energies similar to those found in secondary boranes. By exploiting this feature, we introduce the first examples of uncatalyzed hydrostibination reactions of robust C≡C, C=C, C=O, and N=N bonds as new elementary hydrometalation reactions analogous to hydroboration. These results endorse the notion of a diagonal relationship between the lightest p-block element and the heaviest Groupâ 15 elements and may lead to the conception of novel reaction chemistry.
RESUMEN
The reactions of CO2 with a series of phosphinoboranes, including R2 PBpin (R=Ph, tBu; pin=pinacol), R2 PBMes2 (R=Ph, tBu; Mes=2,4,6-Me3 -C6 H2 ), and R2 PBcat (R=Ph, tBu, Mes; cat=catechol) are described. Although R2 PBpin and R2 PBMes2 afford products of the form R2 PCO2 Bpin (R=Ph 1, tBu 4) and R2 PCO2 BMes2 (R=Ph 2, tBu 3), respectively, R2 PBcat lead to further reaction affording the diphospha-ureas, (R2 P)2 CO (R=Ph 5, tBu 6, Mes 7), together with O(Bcat)2 . Computational studies provide insight into the mechanism, revealing an intermediate derived from double phosphinoboration of CO2 .
RESUMEN
Friedel-Crafts benzylation of arenes with benzyl fluorides using 9-borabicyclo[3.3.l]nonane (9-BBN) as a mediator has been developed. This provides a simple and cheap route to the activation of C-F bonds to synthesize 1,1-diarylmethanes in good to excellent yields (up to 98%) under mild conditions. Functional group tolerance and the mechanism are considered.
RESUMEN
The borinium cation [(iPr2N)2B]+ (1+) is shown to react with PhCCH, PhCN, Ph2CO, and Ph2CN2 to effect a net hydroboration, affording borenium complexes of the form [(iPr2N)B(iPrN[double bond, length as m-dash]CMe2)(L)][B(C6F5)4] (L = CH[double bond, length as m-dash]CHPh 2, N[double bond, length as m-dash]CHPh 3, OCHPh24, NHNCPh25). The nature and reaction of 1+ with PhCCH was probed computationally and the reduction of these unsaturates is shown to occur via hydride transfer from an isopropyl group to the alkyne, thus effecting hydroboration without a B-H bond.
RESUMEN
Reaction of dihydrogen and the borinium cation salt [Mes2B][B(C6F5)4] gave an arene-stabilized mesityl-borenium cation, which isotopically scrambles HD. Similarly, reaction with triethylsilane gave the diboranium cation [MesB(µ-H)2(µ-Mes)BMes]+ featuring three bridge-bonds between two boron centers. Reaction of same (Mes2BH)2 with Brønsted acid also afforded the same diboranium whereas the corresponding reaction with (MesBH2)2 yielded the triboron cation [H2B(µ-H)(µ-Mes)B(µ-Mes)(µ-H)BH2]+.
RESUMEN
The stoichiometric reactions of the alkylfluorides 1-fluoroadamantane (Ad-F), fluorocyclohexane (Cy-F), 1-fluoropentane (Pent-F) and benzyl fluorides with secondary boranes pinacolborane (HBpin), catecholborane (HBcat), 9-borabicyclo(3.3.1)nonane (9-BBN) and Piers' borane (HB(C6 F5 )2 ) are described. While HBcat, 9-BBN and HB(C6 F5 )2 reduce Ad-F to Ad-H, the latter borane was shown to react with secondary and primary fluoroalkanes, affording C-F borylation, while benzyl fluorides undergo Friedel-Crafts chemistry.
RESUMEN
Reactions of [Cp*2 Fe] with the Lewis acid [Zn(C6 F5 )2 ] in the presence of [(PhC(S)S)2 ], 9,10-phenanthrenedione or 4,5-pyrenedione yield the salt [Cp*2 Fe][(PhC(S)S)Zn(C6 F5 )2 ] 1, [Cp*2 Fe][((C14 H8 O2 )Zn(C6 F5 )2 )â ] 4, and [Cp*2 Fe][((C16 H8 O2 )Zn(C6 F5 )2 )â ] 5, respectively. The latter two species represent the first examples of isolable zinc-containing radical anions. While [(PhC(S)S)2 ] binds weakly to [Zn(C6 F5 )2 ], the diones afford the isolable adducts [(C14 H8 O2 )Zn(C6 F5 )2 ] 2 and [(C16 H8 O2 )Zn(C6 F5 )2 ] 3. Cyclic voltammetry and computational studies support the view that 4 and 5 are formed via single electron transfer (SET) to the donor-acceptor adducts, 2 and 3, respectively. Subsequent treatment of 4 and 5 with [NC5 H4 NMe2 ] affords [Zn(C6 F5 )2 (NC5 H4 NMe2 )2 ] with liberation of the dione, and regeneration of [Cp*2 Fe].
RESUMEN
Redox active, or non-innocent, ligands containing O or N heteroatoms are frequently used in transition metal complexes, imparting unique catalytic properties, but have seen comparatively limited use in the chemistry of group 13 elements. In this article we report the frustrated Lewis pair (FLP) hydrogenation and hydroboration of an N-aryl-phenanthrene-o-iminoquinone and two N,N'-diaryl-phenanthrene α-diimines. These reactions exploit B(C6F5)3/H2, HB(C6F5)2 and H2BC6F5·SMe2 to give a series of derivatives including 1,3,2-oxaza- and diazaboroles and borocyclic radicals. The reaction pathways leading to these products are outlined and supported by DFT-calculations and experimental insight. The modular and unusual synthetic strategies described herein give access to new boroles as well as air-stable boron-containing radicals, thus extending the chemistry of redox active ligands in main group systems.
RESUMEN
A series of phosphinophosphonium cations ([R2PPMe3]+; R = Me, Et, i Pr, t Bu, Cy, Ph and N i Pr2) have been prepared and examined by collision-induced dissociation (CID) to determine the fragmentation pathways accessible to these prototypical catena-phosphorus cations in the gas-phase. Experimental evidence for fission of P-P and P-E (E = P, C) bonds, and ß-hydride elimination has been obtained. Comparison of appearance potentials for the P-P bond dissociation fragments [R2P]+ (P-P heterolysis) and [PMe3]+Ë (P-P homolysis) shows that heterolytic P-P cleavage is more sensitive than P-P homolysis towards changes in substitution at the trivalent phosphorus center. The facility of ß-hydride elimination increases with the steric bulk of R in [R2PPMe3]+. A density functional theory (DFT) study modelling these observed processes in gas-phase, counterion- and solvent-free conditions, to mimic the mass spectrometric environment, was performed for derivatives of [R2PPMe3]+ (R = Me, Et, i Pr, t Bu, Ph and N i Pr2), showing good agreement with experimental trends. The unusual observation of both homolytic and heterolytic cleavage pathways for the P-P and P-C bonds reveals new insight into the fundamental aspects of bonding in monocations and undermines the use of simplistic bonding models.