Photoresponsive Dioxazaborocanes-containing Oligomers: "A light Move".

The synthetic methodology for the preparation of photoresponsive dioxazaborocanes-containing oligomers is developed. It relies on the transformation of the (diisopropylamino)boryl group (-BH(NiPr2)) into a dioxazaborocane unit in the presence ß-aminodiols and involves a bis-borylated dithienylethene photochromic unit. The photophysical properties of the obtained oligomers are evaluated as well as their processability for the preparation of spin-coated films. The photomechanical behavior of the resulting films is assessed via displacement tracking profile.

Coordination of a Phosphine-Tethered Aminoborane to Group 10 Metals.

While π-complexes of C=C bonds are ubiquitous in organometallic chemistry, analogous complexes of the isoelectronic but strongly polarized B=N double bond of aminoboranes are extremely scarce. To address this gap, a diphosphine-aminoborane ligand (PhDPBAiPr) is introduced and its coordination with group 10 metals is investigated. The B=N bond does not coordinate to the metal in Pt(0) and Pd(II) complexes. In contrast, side-on coordination of the B=N bond is observed in the Ni(0) complex (PhDPBAiPr)Ni(NCPh), and the X-ray crystal structure reveals B-N bond elongation compared to the free ligand. The choice of co-ligand strongly influences the presence or absence of side-on coordination at Ni(0) as evidenced by NMR spectroscopy. While the B=N π-complex is geometrically similar to C=C analogues, a bonding analysis reveals that the interaction of the B=N motif with the electron-rich Ni(0) center is best described as 3c4e hyperbond, in which Ni and N are competing for the empty orbital on B.

Dynamic Covalent Optical Chirality Sensing with a Sterically Encumbered Aminoborane.

A sterically encumbered aminoborane sensor is introduced and used for quantitative stereochemical analysis of monoalcohols, diols and amino alcohols. The small-molecule probe exhibits a rigid ortho-substituted arene scaffold with a proximate boron binding site and a triarylamine circular dichroism (CD) reporter unit which proved to be crucial for the observed chiroptical signal induction. Coordination of the chiral target molecule produces strong Cotton effects and UV changes that are readily correlated to its absolute configuration, enantiomeric composition and concentration to achieve comprehensive stereochemical analysis within a 5 % absolute error margin. The sensing method was successfully applied in the chromatography-free analysis of less than one milligram of a crude asymmetric reaction mixture and the advantages of this chiroptical sensing approach, which is amenable to high-throughput experimentation equipment and automation, over traditional methods is discussed.

Magnesium-Catalyzed Tandem Dehydrogenation-Dehydrocoupling: An Atom Economical Access to Alkynylboranes.

Owing to the unusual reactivity of sterically hindered amine-borane complexes, a catalytic system based on magnesium salts was designed to perform a tandem dehydrogenation-dehydrocoupling between terminal alkynes and boranes. The reaction is providing pure alkynylboranes within few minutes at room temperature, with only two molecules of hydrogen as a byproduct.

Efficient Co-Catalyzed Double Hydroboration of Nitriles: Application to One-Pot Conversion of Nitriles to Aldimines.

The commercially available and bench-stable Co(acac)2 /dpephos system is employed as a precatalyst for selective and efficient room temperature hydroboration of organic nitriles with HBPin to produce a series of N,N-diborylamines [RN(BPin)2 ], which react in situ with aldehydes to give aldimines. Formation of aldimines from N,N-diborylamines does not require a dehydrating agent, is applicable to a wide range of N,N-diborylamine and aldehyde substrates and is highly chemoselective, being unaffected by various common functional groups, such as alkenes, alkynes, secondary amines, ketones, esters, amides, carboxylic acids, pyridines, nitriles, and nitro compounds. The overall transformation represents a synthetically valuable approach to aldimines from nitriles and can be performed in a sequential one-pot manner, tolerating ester, lactone, carboxamide and unactivated alkene functionalities.

Metal-like Ductility in Organic Plastic Crystals: Role of Molecular Shape and Dihydrogen Bonding Interactions in Aminoboranes.

Ductility is a common phenomenon in many metals but is difficult to achieve in molecular crystals. Organic crystals bend plastically on one or two face-specific directions but fracture when stressed in any other arbitrary directions. An exceptional metal-like ductility and malleability in the isomorphous crystals of two globular molecules, BH3 NMe3 and BF3 NMe3 , is reported, with characteristic tensile stretching, compression, twisting, and thinning. The mechanically deformed samples, which transition to lower symmetry phases, retain good long-range order amenable to structure determination by single-crystal X-ray diffraction. Molecules in these high-symmetry crystals interact through electrostatic forces (B- -N+ ) to form columnar structures with multiple slip planes and weak dispersive forces between columns. On the other hand, the limited number of facile slip planes and strong dihydrogen bonding in BH3 NHMe2 negates ductility. Our study has implications for the design of soft ferroelectrics, solid electrolytes, barocalorics, and soft robotics.

Readily Available Primary Aminoboranes as Powerful Reagents for Aldimine Synthesis.

Primary aminoboranes (RNHBR2 ), which are readily available by spontaneous dehydrocoupling of amines and boranes cleanly react at room temperature with aldehydes to give aldimines. The overall transformation from amines to aldimines can be conveniently performed by a sequential one-pot reaction. This synthetic strategy is especially useful for electron poor and bulky amines which are reluctant to react with aldehydes under dehydration conditions. Using a Glorius robustness screen, we show that this methodology is chemoselective, and functional group tolerant. Computational and experimental data support the irreversible formation of the aldimine product in marked contrast with traditional methods.

Borane Adducts of Hydrazoic Acid and Organic Azides: Intermediates for the Formation of Aminoboranes.

The reaction of HN3 with the strong Lewis acid B(C6 F5 )3 led to the formation of a very labile HN3 ⋅B(C6 F5 )3 adduct, which decomposed to an aminoborane, H(C6 F5 )NB(C6 F5 )2 , above -20 °C with release of molecular nitrogen and simultaneous migration of a C6 F5 group from boron to the nitrogen atom. The intermediary formation of azide-borane adducts with B(C6 F5 )3 was also demonstrated for a series of organic azides, RN3 (R=Me3 Si, Ph, 3,5-(CF3 )2 C6 H3 ), which also underwent Staudinger-like decomposition along with C6 F5 group migration. In accord with experiment, computations revealed rather small barriers towards nitrogen release for these highly labile azide adducts for all organic substituents except R=Me3 Si (m.p. 120 °C, Tdec =189 °C). Hydrolysis of the aminoboranes provided C6 F5 -substituted amines, HN(R)(C6 F5 ), in good yields.

Access to FeII Bis(σ-B-H) Aminoborane Complexes through Protonation of a Borohydride Complex and Dehydrogenation of Amine-Boranes.

Herein, we report on the first synthesis and structural characterization of the iron based aminoborane complexes [Fe(PNP)(H)(η2 :η2 -H2 B=NR2 )]+ (R=H, Me). These species are formed upon protonation of the borohydride complex [Fe(PNP)(H)(η2 -BH4 )] by ammonium salts [NH2 R2 ]+ (R=H, Me). For R=Me, the reaction proceeds via the cationic dinuclear intermediate [{Fe(PNP)(H)}2 (µ2 ,η2 :η2 -BH4 )]+ . A mechanism for the reaction is proposed based on DFT calculations that also indicate the final aminoborane complex as the thermodynamic product. All complexes were characterized by NMR spectroscopy, HRMS, and X-ray crystallography.

Direct Reductive N-Functionalization of Aliphatic Nitro Compounds.

The first general protocol for the direct reductive N-functionalization of aliphatic nitro compounds is presented. The nitro group is partially reduced to a nitrenoid, with a mild and readily available combination of B2 pin2 and zinc organyls. Thereby, the formation of an unstable nitroso intermediate is avoided, which has so far severely limited reductive transformations of aliphatic nitro compounds. The reaction is concluded by an electrophilic amination of zinc organyls.

Catalyst- and Template-Free Ultrafast Visible-Light-Triggered Dimerization of Vinylpyridine-Functionalized Tetraarylaminoborane: Intriguing Deep-Blue Delayed Fluorescence.

A photoredox-catalyst- and template-free sunlight-induced molecular dimerization of a vinylpyridine-functionalized tetraarylaminoborane (TAAB) has been accomplished for the first time. The reaction is quantitative, highly regioselective, and thermally irreversible. The presence of the propeller-shaped TAAB framework allows selective photodimerization of one of the two vinyl pyridine units. Monomer 1 and photodimer 2 exhibit distinct photophysical properties with delayed fluorescence (DF) both in solution and the solid state, which was confirmed by steady-state and time-resolved luminescence studies. Quantum mechanical calculations were performed to support the experimental observations. Our new approach using [2+2] cycloaddition chemistry paves the way for the development of highly sought-after deep-blue DF materials.

Solventless and Metal-Free Synthesis of High-Molecular-Mass Polyaminoboranes from Diisopropylaminoborane and Primary Amines.

The solventless reaction of diisopropylaminoborane with n-butylamine, at room temperature, leads to a mixture of B(sp2) H-, B(sp3) H2 -, and B(sp3) H3 -containing species. At low temperature, the reaction outcome is completely modified, thus leading selectively to the formation of high-mass polybutylaminoborane. When extended to a variety of primary amines, under solventless conditions and at low temperature, this reaction provides a new, efficient, and direct metal-free access to high-molecular-mass polyaminoboranes in good to high yields under mild reaction conditions.

Generation of High-Molecular-Weight Polymers with Diverse Substituents: An Unusual Metal-Free Synthesis of Poly(aminoborane)s.

A new concept has been introduced for the preparation of high-molecular-weight poly(aminoborane)s with diverse substituents on the nitrogen atom. Whereas previous methods were oxidative and relied largely on catalytic dehydrocoupling, the new process is based on an uncatalysed polymerisation reaction promoted by amine-aminoborane exchange, and should give access to previously inaccessible polymers.

Phenothiazinyl Boranes: A New Class of AIE Luminogens with Mega Stokes Shift, Mechanochromism, and Mechanoluminescence.

Phenothiazines with a dimesityl boron moiety, a new class of aminoboranes with B-N linkage, were synthesized. These aminoboranes exhibited interesting photophysical behavior including aggregation-induced emission (AIE), mechanochromism (MC), mechanoluminescence (ML), and a mega Stokes shift (up to 312 nm in hexane). The solid-state emission of the aminoboranes could be switched reversibly by grinding-fuming processes. Furthermore, the phenothiazine derivative with a bromo and an arylborane group at 3- and 7-positions exhibited bright mechanoluminescence.

Electrophilic Amination with Nitroarenes.

An exceptionally general electrophilic amination, which directly transforms commercially available nitroarenes into alkylated aromatic aminoboranes with zinc organyl compounds was developed. The reaction starts with a two-step partial reduction of the nitro group to a nitrenoid, which is used in situ as the electrophilic amination reagent. To facilitate isolation, the resulting air- and moisture-sensitive aminoboranes were reacted with a range of electrophiles. The method not only represents a direct transformation of nitro compounds into electrophilic amination reagents but also provides an elegant alternative to dehydrocoupling methods for the generation of aminoboranes.

Deeper Insight into the Factors Controlling H2 Activation by Geminal Aminoborane-Based Frustrated Lewis Pairs.

H2 activation mediated by geminal aminoborane-based frustrated Lewis pairs (FLPs; R2 N-CH2 -BR'2 ) has been computationally explored within the density functional theory framework. It is found that the activation barrier of this process as well as the geometry of the corresponding transition states strongly depend on the nature of the substituents directly attached either to the acidic or the basic centers of the FLPs. The physical factors controlling the whole activation path are quantitatively described in detail by means of the activation strain model of reactivity combined with the energy decomposition analysis method. This methodology suggests a highly orbital-controlled mechanism where the degree of charge transfer cooperativity between the most important donor-acceptor orbital interactions, namely LP(N)→σ*(H2 ) and σ(H2 )→pπ (B), along the reaction coordinate constitutes a suitable indicator of the reaction barrier.

Phosphoramidate-Supported Cp*Ir(III) Aminoborane H2 B=NR2 Complexes: Synthesis, Structure, and Solution Dynamics.

Reaction of aminoboranes H2 B=NR2 (R=iPr or Cy) with the cationic Cp*Ir(III) phosphoramidate complex [IrCp*{κ(2) -N,O-Xyl(N)P(O)(OEt)2 }][BAr(F) 4 ] generates the aminoborane complexes [IrCp*(H){κ(1) -N-η(2) -HB-Xyl(N)P(OBHNR2 )(OEt)2 }][BAr(F) 4 ] (R=iPr or Cy) in which coordination of a P=O bond with boron weakens the B=N multiple bond. For these complexes, solution- and solid-state, as well as DFT computational techniques, have been employed to substantiate B-N bond rotation of the coordinated aminoborane.

Intramolecular frustrated Lewis pair with the smallest boryl site: reversible H2 addition and kinetic analysis.

Ansa-aminoborane 1 (ortho-TMP-C6H4-BH2; TMP = 2,2,6,6-tetramethylpiperid-1-yl), a frustrated Lewis pair with the smallest possible Lewis acidic boryl site (-BH2), is prepared. Although it is present in quenched forms in solution, and BH2 represents an acidic site with reduced hydride affinity, 1 reacts with H2 under mild conditions producing ansa-ammonium trihydroborate 2. The thermodynamic and kinetic features as well as the mechanism of this reaction are studied by variable-temperature NMR spectroscopy, spin-saturation transfer experiments, and DFT calculations, which provide comprehensive insight into the nature of 1.

Low-valent iron(i) amido olefin complexes as promotors for dehydrogenation reactions.

Fe(I) compounds including hydrogenases show remarkable properties and reactivities. Several iron(I) complexes have been established in stoichiometric reactions as model compounds for N2 or CO2 activation. The development of well-defined iron(I) complexes for catalytic transformations remains a challenge. The few examples include cross-coupling reactions, hydrogenations of terminal olefins, and azide functionalizations. Here the syntheses and properties of bimetallic complexes [MFe(I) (trop2 dae)(solv)] (M=Na, solv=3 thf; M=Li, solv=2 Et2 O; trop=5H-dibenzo[a,d]cyclo-hepten-5-yl, dae=(N-CH2 -CH2 -N) with a d(7) Fe low-spin valence-electron configuration are reported. Both compounds promote the dehydrogenation of N,N-dimethylaminoborane, and the former is a precatalyst for the dehydrogenative alcoholysis of silanes. No indications for heterogeneous catalyses were found. High activities and complete conversions were observed particularly with [NaFe(I) (trop2 dae)(thf)3 ].

Alkoxide activation of aminoboranes towards selective amination.

Piece of the (inter)action: The interaction of alkoxides with the sp(2) Bpin (pin=pinacol) moiety in aminoboranes forms the in situ Lewis acid-base adduct [RO(-) →B(OR)2 N(R')2 ] which enables the amino moiety to react as a strong nucleophile with several electrophiles, thus providing amino alcohols, ß-enamino esters, and ß-hydroxy amides in a direct and remarkably selective way.