skip to main content

Title: Cationic magnesium hydride [MgH] + stabilized by an NNNN-type macrocycle
A magnesium hydride cation [(L)MgH] + supported by a macrocyclic ligand (L = Me 4 TACD; 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) has been prepared by partial protonolysis of a mixed amide hydride [(L)MgH 2 Mg{N(SiMe 3 ) 2 } 2 ] and shown to undergo a variety of reactions with unsaturated substrates, including pyridine.
; ; ; ; ; ;
Award ID(s):
Publication Date:
Journal Name:
Chemical Communications
Page Range or eLocation-ID:
3199 to 3202
Sponsoring Org:
National Science Foundation
More Like this
  1. d -Proline ( D Pro, D P) is widely utilized to form β-hairpin loops in engineered peptides that would otherwise be unstructured, most often as part of a D PG sub-unit that forms a β-turn. To observe whether D PG facilitated this effect in short protonated peptides, conformation specific IR–UV double resonance photofragment spectra of the cold (∼10 K) protonated D P and L P diastereomers of the pentapeptide YAPGA was carried out in the hydride stretch (2800–3700 cm −1 ) and amide I/II (1400–1800 cm −1 ) regions. A model localized Hamiltonian was developed to better describe the 1600–1800more »cm −1 region commonly associated with the amide I vibrations. The CO stretch fundamentals experience extensive mixing with the N–H bending fundamentals of the NH 3 + group in these protonated peptides. The model Hamiltonian accounts for experiment in quantitative detail. In the D P diastereomer, all the population is funneled into a single conformer which presented as a type II β-turn with A and D P in the i + 1 and i + 2 positions, respectively. This structure was not the anticipated type II′ β-turn across D PG that we had hypothesized based on solution-phase propensities. Analysis of the conformational energy landscape shows that both steric and charge-induced effects play a role in the preferred formation of the type II β-turn. In contrast, the L P isomer forms three conformations with very different structures, none of which were type II/II′ β-turns, confirming that L PG is not a β-turn former. Finally, single-conformation spectroscopy was also carried out on the extended peptide [YAA D PGAAA + H] + to determine whether moving the protonated N-terminus further from D PG would lead to β-hairpin formation. Despite funneling its entire population into a single peptide backbone structure, the assigned structure is not a β-hairpin, but a concatenated type II/type II′ double β-turn that displaces the peptide backbone laterally by about 7.5 Å, but leaves the backbone oriented in its original direction.« less
  2. A C–H bond activation strategy based on electrochemical activation of a metal hydride is introduced. Electrochemical oxidation of ( tBu4 PCP)IrH 4 ( tBu4 PCP is [1,3-( t Bu 2 PCH 2 )-C 6 H 3 ] − ) in the presence of pyridine derivatives generates cationic Ir hydride complexes of the type [( tBu4 PCP)IrH(L)] + (where L = pyridine, 2,6-lutidine, or 2-phenylpyridine). Facile deprotonation of [( tBu4 PCP)IrH(2,6-lutidine)] + with the phosphazene base tert -butylimino-tris(pyrrolidino)phosphorane, t BuP 1 (pyrr), results in selective C–H activation of 1,2-difluorobenzene (1,2-DFB) solvent to generate ( tBu4 PCP)Ir(H)(2,3-C 6 F 2 H 3more »). The overall electrochemical C–H activation reaction proceeds at room temperature without need for chemical activation by a sacrificial alkene hydrogen acceptor. This rare example of undirected electrochemical C–H activation holds promise for the development of future catalytic processes.« less
  3. Cationic gold vinyl carbene/allylic cation complexes of the form ( E )-[(L)AuC(H)C(H)CAr 2 ] + OTf − {L = IPr, Ar = Ph [( E )- 5a ], L = IPr, Ar = 4-C 6 H 4 OMe [( E )- 5b ], L = P( t -Bu) 2 o -biphenyl, Ar = 4-C 6 H 4 OMe [( E )- 5c ]} were generated in solution via Lewis acid-mediated ionization of the corresponding gold (γ-methoxy)vinyl complexes ( E )-(L)AuC(H)C(H)C(OMe)Ar 2 at or below −95 °C. Complexes ( E )- 5b and ( E )- 5c were fully characterized inmore »solution employing multinuclear NMR spectroscopy, which established the predominant contribution of the aurated allylic cation resonance structure and the significant distribution of positive charge into the γ-anisyl rings. Complex ( E )- 5b reacted rapidly at −95 °C with neutral two-electron, hydride, and oxygen atom donors exclusively at the C1 position of the vinyl carbene moiety and with p -methoxystyrene to form the corresponding vinylcyclopropane. In the absence of nucleophile ( E )- 5a decomposed predominantly via intermolecular carbene dimerization whereas formation of 1-aryl-5-methoxy indene upon ionization of ( Z )-(IPr)AuC(H)C(H)C(OMe)(4-C 6 H 4 OMe) 2 [( Z )- 6b ] implicated an intramolecular Friedel–Crafts or electrocyclic Nazarov pathway for the decomposition of the unobserved vinyl carbene complex ( Z )-[(IPr)AuC(H)C(H)C(4-C 6 H 4 OMe) 2 ] + OTf − [( Z )- 5b ].« less
  4. Abstract The mechanisms by which the complexes CpCoL2 (Cp = C5H5; L = CO or CH2=CH2) mediate the cycloisomerizations of α,δ,ω-enynenes containing allylic ether linkages are probed by DFT methods. The outcomes corroborate experimental results and provide energetic and structural details of the trajectories leading to 3-(oxacyclopentyl or cycloalkyl)furans via the intermediacy of isolable CpCo-η 4-dienes. They comprise initial stereoselective complexation of one of the double bonds and the triple bond, rate-determining oxidative coupling to a triplet 16e cobalta-2-cyclopentene, and terminal double bond docking, followed by stereocontrolled insertion to assemble intermediate cis- and trans-fused triplet cobalta-4-cycloheptenes. A common indicator ofmore »the energetic facility of the latter is the extent of parallel alignment of the alkene moiety and its target Co–Cα bond. The cobalta-4-cycloheptenes transform further by β-hydride elimination–reductive elimination to furnish CpCo-η 4-dienes, which are sufficiently kinetically protected to allow for their experimental observation. The cascade continues through cobalt-mediated hydride shifts and dissociation of the aromatic furan ring. The findings in silico with respect to the stereo-, regio-, and chemoselectivity are in consonance with those obtained in vitro.« less
  5. Self-assembly of vertically aligned III–V semiconductor nanowires (NWs) on two-dimensional (2D) van der Waals (vdW) nanomaterials allows for integration of novel mixed-dimensional nanosystems with unique properties for optoelectronic and nanoelectronic device applications. Here, selective-area vdW epitaxy (SA-vdWE) of InAs NWs on isolated 2D molybdenum disulfide (MoS 2 ) domains is reported for the first time. The MOCVD growth parameter space ( i.e. , V/III ratio, growth temperature, and total molar flow rates of metalorganic and hydride precursors) is explored to achieve pattern-free positioning of single NWs on isolated multi-layer MoS 2 micro-plates with one-to-one NW-to-MoS 2 domain placement. The introductionmore »of a pre-growth poly- l -lysine surface treatment is highlighted as a necessary step for mitigation of InAs nucleation along the edges of triangular MoS 2 domains and for NW growth along the interior region of 2D micro-plates. Analysis of NW crystal structures formed under the optimal SA-vdWE condition revealed a disordered combination of wurtzite and zinc-blend phases. A transformation of the NW sidewall faceting structure is observed, resulting from simultaneous radial overgrowth during axial NW synthesis. A common lattice arrangement between axially-grown InAs NW core segments and MoS 2 domains is described as the epitaxial basis for vertical NW growth. A model is proposed for a common InAs/MoS 2 sub-lattice structure, consisting of three multiples of the cubic InAs unit cell along the [21̄1̄] direction, commensurately aligned with a 14-fold multiple of the Mo–Mo (or S–S) spacing along the [101̄0] direction of MoS 2 hexagonal lattice. The SA-vdWE growth mode described here enables controlled hybrid integration of mixed-dimensional III–V-on-2D heterostructures as novel nanosystems for applications in optoelectronics, nanoelectronics, and quantum enabling technologies.« less