Masood Parvez

Tandem Frustrated Lewis Pair/Tris(pentafluorophenyl)borane-Catalyzed Deoxygenative Hydrosilylation of Carbon Dioxide

The frustrated Lewis pair system consisting of 2 equiv of 2,2,6,6-tetramethylpiperidine (TMP) and tris(pentafluorophenyl)borane [B(C(6)F(5))(3)] activates carbon dioxide to form a boratocarbamate-TMPH ion pair. In the presence of triethylsilane, this species is converted to a silyl carbamate and the known ion pair [TMPH](+)[HB(C(6)F(5))(3)](-), which recently was shown to react with CO(2) via transfer of the hydride from the hydridoborate to form the formatoborate [TMPH](+)[HC(O)OB(C(6)F(5))(3)](-). In the presence of extra B(C(6)F(5))(3) (0.1-1.0 equiv) and excess triethylsilane, the formatoborate is rapidly hydrosilated to form a formatosilane and regenerate [TMPH](+)[HB(C(6)F(5))(3)](-). The formatosilane in turn is rapidly hydrosilated by the B(C(6)F(5))(3)/Et(3)SiH system to CH(4), with (Et(3)Si)(2)O as the byproduct. At low [Et(3)SiH], intermediate CO(2) reduction products are observed; addition of more CO(2)/Et(3)SiH results in resumed hydrosilylation, indicating that this is a robust, living tandem catalytic system for the deoxygenative reduction of CO(2) to CH(4).

Dihydrogen Activation by Antiaromatic Pentaarylboroles

Facile metal-free splitting of molecular hydrogen (H(2)) is crucial for the utilization of H(2) without the need for toxic transition-metal-based catalysts. Frustrated Lewis pairs (FLPs) are a new class of hydrogen activators wherein interactions with both a Lewis acid and a Lewis base heterolytically disrupt the hydrogen-hydrogen bond. Here we describe the activation of hydrogen exclusively by a boron-based Lewis acid, perfluoropentaphenylborole. This antiaromatic compound reacts extremely rapidly with H(2) in both solution and the solid state to yield boracyclopent-3-ene products resulting from addition of hydrogen atoms to the carbons alpha to boron in the starting borole. The disruption of antiaromaticity upon reaction of the borole with H(2) provides a significant thermodynamic driving force for this new metal-free hydrogen-splitting reaction.

Activation of Water, Ammonia, and Other Small Molecules by PCcarbeneP Nickel Pincer Complexes

Nickel complexes of a PC(carbene)P pincer ligand framework are described. Dehydrobromination of the precursor (PC(sp)(3)P)NiBr in the presence of a donor (PPh3 or NC(t)Bu) leads to the title complexes, which feature a rare nickel-carbene linkage as the pincer ligand anchor point. This strongly donating, nucleophilic carbene center engages in a variety of E-H bond activations (E = H, C, N, O), some of which are reversible. This represents a new mode of bond activation by ligand cooperativity in nickel pincer complexes.

Highly Selective Guest Uptake in a Silver Sulfonate Network Imparted by a Tetragonal to Triclinic Shift in the Solid State

The silver sulfonate network presented herein, silver 3-pyridinesulfonate, reversibly and selectively absorbs MeCN while undergoing a major structural rearrangement. The origin of this structural flexibility is a coupling of the weak coordinating ability of the SO3 group with the geometrically pliant silver(I) center. Single crystal and powder X-ray structures of both the desolvated and solvated forms are presented in addition to the mechanism of their reversible interconversion. A heterogeneous gas chromatographic study showing selective extraction of the MeCN is also presented. Extended solid frameworks which reorder to any extent are not common but the structure presented herein transforms from a tetragonal to a triclinic crystal system. The results indicate that cooperative interactions in systems based on supposedly weaker interactions can yield softer yet functional networks with behavior unlike that observed in more rigid inorganic frameworks.

Reaction of pentaarylboroles with carbon monoxide: an isolable organoboron carbonyl complex

The highly Lewis acidic perfluoropentaphenylborole forms a stable, isolable adduct with the weak Lewis base carbon monoxide. A similar adduct with the unfluorinated borole is observed at low temperature, but this adduct undergoes reaction involving insertion into the B–C bonds due to the greater nucleophilicity of the α-carbons. Together these observations provide concrete chemical evidence for long held presumptions regarding the observed reactivity of organoboranes with carbon monoxide.

Benzo- and Naphthoborepins: Blue-Emitting Boron Analogues of Higher Acenes†

Unsaturated rings containing boron have been of fundamental and practical interest for many years. Five-membered borole rings I are isoelectronic to the antiaromatic cyclopentadienyl cation and have been important in addressing concepts of aromaticity. The six-membered borabenzene and boratabenzene compounds II (Nu = nucleophile), however, are aromatic and have found application as cyclopentadienide-like ligands with substantial tunability at the boron substituent. More recently, these cores have been tested as organic materials, finding application as fluoride sensors.

9‐Boraanthracene Derivatives Stabilized by N‐Heterocyclic Carbenes

2009: A boraanthracene odyssey: General routes to boraanthracene derivatives--long proposed, but never observed--are disclosed, along with the structural and photophysical properties of these compounds and their remarkable reactivity towards oxygen.

Characterization of β-B-Agostic Isomers in Zirconocene Amidoborane Complexes

The reaction of Cp(x)(2)ZrCl(2) (Cp(x) = Cp, Cp*) with ammonia borane in presence of n-butyllithium yielded Cp(2)Zr(Cl)NH(2)BH(3) and Cp(x)(2)Zr(H)NH(2)BH(3). These derivatives are isoelectronic with the ethyl zirconocene chloride and hydride, respectively, and feature a chelating amidoborane ligand coordinating through a Zr-N bond and a Zr-H-B bridge. In solution, each of the complexes consists of an equilibrium mixture of two isomers differing in the orientation of the amidoborane ligand with respect to the Zr-X bond (X = H, Cl), while in the solid state, only one isomer was observed. Such isomers have not been characterized for any metal complexes containing the isoelectronic beta-agostic ethyl ligand or any other agostic alkyl group.

BN‐Dibenzo[a,o]picenes: Analogues of an Unknown Polycyclic Aromatic Hydrocarbon

Reflecting on synthetic pinnacles: Whereas the parent hydrocarbon is not readily accessible, several examples of BN substituted-dibenzo[a,o]picenes can be prepared in two steps from known starting materials. These non-linear heptacene analogues are water-stable materials. Their preparation utilizes a potentially general method for preparing extended BN analogues of difficult-to-synthesize polycyclic aromatic hydrocarbon frameworks.

Synthesis, structural characterization and reactivity of the amino borane 1-(NPh2)-2-[B(C6F5)2]C6H4

Abstract The bright red title compound 1 was synthesized from (2-lithiophenyl)diphenylamine and bis(pentafluorophenyl)boron chloride. Its reactions with small acids like H2O and HCl proceeded easily giving zwitterionic compounds. For 1 and its water adduct 2 the crystal structures were determined, the latter featuring an ammonium borate structure containing a short intramolecular hydrogen bond bridge. Treatment of 1 with Jutzis acid, [H(OEt2)2][B(C6F5)4], did not result in protonation of the nitrogen, but reaction of 1 with LiH in the presence of 12-crown-4, led to the isolation of the aminoborate [1-(Ph2N)-2-{B(H)(C6F5)2}C6H4][Li(12-crown-4)] (3). Borohydride 3 reacted with Jutzis acid to regenerate 1 and liberate hydrogen.