An official website of the United States government
The bis(aminophenol) 2,2′-biphenylbis(3,5-di- tert -butyl-2-hydroxyphenylamine) (ClipH 4 ) forms trans -(Clip)Os(py) 2 upon aerobic reaction of the ligand with {( p -cymene)OsCl 2 } 2 in the presence of pyridine and triethylamine. A more oxidized species, cis -β-(Clip)Os(OCH 2 CH 2 O), is formed from reaction of the ligand with the osmium( vi ) complex OsO(OCH 2 CH 2 O) 2 , and reacts with Me 3 SiCl to give the chloro complex cis -β-(Clip)OsCl 2 . Octahedral osmium and ruthenium tris-iminoxolene complexes are formed from the chelating ligand tris(2-(3′,5′-di- tert -butyl-2′-hydroxyphenyl)amino-4-methylphenyl)amine (MeClampH 6 ) on aerobic reaction with divalent metal precursors. The complexes’ structural and electronic features are well described using a simple bonding model that emphasizes the covalency of the π bonding between the metal and iminoxolene ligands rather than attempting to dissect the parts into discrete oxidation states. Emphasizing the continuity of bonding between disparate complexes, the structural data from a variety of Os and Ru complexes show good correlations to π bond order, and the response of the intraligand bond distances to the bond order can be analyzed to illuminate the polarity of the bonding between metal and the redox-active orbital on the iminoxolenes. The osmium compounds’ π bonding orbitals are about 40% metal-centered and 60% ligand-centered, with the ruthenium compounds’ orbitals about 65% metal-centered and 35% ligand-centered.
more »
« less
Slip to π Ru: structural distortions due to metal-iminoxolene π bonding
Both pseudo-octahedral and pseudo-square pyramidal bis-iminoxolene complexes trans -(Diso) 2 RuCl 2 and trans -(Diso) 2 Ru(PPh 3 ) are structurally distorted, with the ruthenium atom slipping off the twofold axis of the idealized coordination polyhedra. These distortions take place because they allow or enhance π interactions between ruthenium and the iminoxolene π orbitals.
more »
« less
- Award ID(s):
- 1955933
- PAR ID:
- 10443197
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 59
- Issue:
- 63
- ISSN:
- 1359-7345
- Page Range / eLocation ID:
- 9618 to 9621
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
A bstract An amplitude analysis of the D + → π − π + π + decay is performed with a sample corresponding to 1.5 fb − 1 of integrated luminosity of pp collisions at a centre-of-mass energy $$ \sqrt{s} $$ s = 8 TeV collected by the LHCb detector in 2012. The sample contains approximately six hundred thousand candidates with a signal purity of 95%. The resonant structure is studied through a fit to the Dalitz plot where the π − π + S-wave amplitude is extracted as a function of π − π + mass, and spin-1 and spin-2 resonances are included coherently through an isobar model. The S-wave component is found to be dominant, followed by the ρ (770) 0 π + and f 2 (1270) π + components. A small contribution from the ω (782) → π − π + decay is seen for the first time in the D + → π − π + π + decay.more » « less
-
Product Inhibition in Nucleophilic Aromatic Substitution through DPPPent-Supported π-Arene CatalysisNucleophilic aromatic substitution (SNAr) of fluorobenzene by morpholine at a bis(diphenylphosphino)pentane-supported ruthenim complex is investigated as a model system for π-arene catalysis through the synthesis and full characterization of proposed intermediates. The SNAr step proceeds quickly at room temperature, however the product N-phenylmorpholine binds tightly to the ruthenium ion. In the case examined, the thermodynamics of arene binding favor product N-phenylmorpholine over fluorobenzene binding by a factor of 2,000, corresponding to significant product inhibition. Observations of the catalyst resting state support this hypothesis and demonstrate an additive-controlled role for a previously-proposed ligand cyclometalation.more » « less
-
In proteins, proline-aromatic sequences exhibit increased frequencies of cis-proline amide bonds, via proposed C–H/π interactions between the aromatic ring and either the proline ring or the backbone C–Hα of the residue prior to proline. These interactions would be expected to result in tryptophan, as the most electron-rich aromatic residue, exhibiting the highest frequency of cis-proline. However, prior results from bioinformatics studies on proteins and experiments on proline-aromatic sequences in peptides have not revealed a clear correlation between the properties of the aromatic ring and the population of cis-proline. An investigation of the effects of aromatic residue (aromatic ring properties) on the conformation of proline-aromatic sequences was conducted using three distinct approaches: (1) NMR spectroscopy in model peptides of the sequence Ac-TGPAr-NH2 (Ar = encoded and unnatural aromatic amino acids); (2) bioinformatics analysis of structures in proline-aromatic sequences in the PDB; and (3) computational investigation using DFT and MP2 methods on models of proline-aromatic sequences and interactions. C–H/π and hydrophobic interactions were observed to stabilize local structures in both the trans-proline and cis-proline conformations, with both proline amide conformations exhibiting C–H/π interactions between the aromatic ring and Hα of the residue prior to proline (Hα-trans-Pro-aromatic and Hα-cis-Pro-aromatic interactions) and/or with the proline ring (trans-ProH-aromatic and cis-ProH-aromatic interactions). These C–H/π interactions were strongest with tryptophan (Trp) and weakest with cationic histidine (HisH+). Aromatic interactions with histidine were modulated in strength by His ionization state. Proline-aromatic sequences were associated with specific conformational poses, including type I and type VI β-turns. C–H/π interactions at the pre-proline Hα, which were stronger than interactions at Pro, stabilize normally less favorable conformations, including the ζ or αL conformations at the pre-proline residue, cis-proline, and/or the g+ χ1 rotamer or αL conformation at the aromatic residue. These results indicate that proline-aromatic sequences, especially Pro-Trp sequences, are loci to nucleate turns, helices, loops, and other local structures in proteins. These results also suggest that mutations that introduce proline-aromatic sequences, such as the R406W mutation that is associated with protein misfolding and aggregation in the microtubule-binding protein tau, might result in substantial induced structure, particularly in intrinsically disordered regions of proteins.more » « less
-
Biocompatible molecules with electronic functionality provide a promising substrate for biocompatible electronic devices and electronic interfacing with biological systems. Synthetic oligopeptides composed of an aromatic π-core flanked by oligopeptide wings are a class of molecules that can self-assemble in aqueous environments into supramolecular nanoaggregates with emergent optical and electronic activity. We present an integrated computational–experimental pipeline employing all-atom molecular dynamics simulations and experimental UV-visible spectroscopy within an active learning workflow using deep representational learning and multi-objective and multi-fidelity Bayesian optimization to design π-conjugated peptides programmed to self-assemble into elongated pseudo-1D nanoaggregates with a high degree of H-type co-facial stacking of the π-cores. We consider as our design space the 694 982 unique π-conjugated peptides comprising a quaterthiophene π-core flanked by symmetric oligopeptide wings up to five amino acids in length. After sampling only 1181 molecules (∼0.17% of the design space) by computation and 28 (∼0.004%) by experiment, we identify and experimentally validate a diversity of previously unknown high-performing molecules and extract interpretable design rules linking peptide sequence to emergent supramolecular structure and properties.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d3cc02943c
