Syntheses and Characterizations of Platinum Complexes with New Pyrene-based Salicylaldiminato-type Ligand Substituted at 7-Position of Pyrene

Many experimental data show that bulky substituents on the molecules enhance solubility, catalytic activity, and photophysical properties due to the prevention of π-π stacking in metal salicylaldimines. In order to understand the effect of bulkiness of substituents on the properties of the obtained molecules, the author researched and synthesized two new pyrene-based salicylaldiminato-type ligands that were substituted at 7-position and functionalized on imine group with bulky substituents. After the introduction of the tert-butyl group at 7-position of pyrene by Friedel-Crafts reaction, the syntheses of new ligands 1-hydroxy-2-[((2,6-dimethylphenyl)-imino)methyl]-7-(tert-butyl)-pyrene 3, 2-hydroxy-1- [((2,6-dimethylphenyl)imino)methyl]-7-(tert-butyl)-pyrene 4 and corresponding platinum complexes 3(Pt), 4(Pt) were performed in the different ways with the synthetic processes of the complexes 1(Pt) and 2(Pt). The new ligands and complexes were characterized by 1H NMR, IR spectroscopy, mass spectroscopy, elemental analysis and X-ray diffraction, only for 3(Pt). In addition to measurements of the absorption and emission spectra, TDDFT calculations using the B3LYP functions were also performed. The complexes 3(Pt) and 4(Pt) exhibit good solubility and red-shift in absorption and emission spectra because of tert-butyl group at 7-position of pyrene and extension of the delocalized π-orbitals to the 2,6-dimethylphenyl on imine group. The change of functional groups also induces the upfield shift of the protons affected by ring currents of phenyl groups Ar-3, Ar-4 on imine groups. Introduction of t-butyl groups in pyrene moieties can stabilize radical forms in oxidation processes.

Radical-mediated sulfonyl alkynylation, allylation, and cyanation of propellane

Bicyclo[1.1.1]pentane (BCP) is widely applied as the bioisostere for aryl, internal alkynes, and tert-butyl group in medicinal chemistry. We herein disclose an efficient and practical preparation of sulfonyl alkynyl/allyl/cyano-substituted BCP...

Raise the anchor! Synthesis, X-ray and NMR characterization of 1,3,5-triazinanes with an axial tert-butyl group

N-t-Bu-N′,N′′-Disulfonamide-1,3,5-triazinanes were synthesized and studied by X-ray single crystal structure analysis and dynamic low-temperature NMR.

Tripeptide-Catalyzed Asymmetric Aldol Reaction Between α-ketoesters and Acetone Under Acidic Cocatalyst-Free Conditions

Here, we report the tripeptide-catalyzed asymmetric aldol reaction between α-ketoesters and acetone under acidic cocatalysts-free conditions. H-Pro-Tle-Gly-OH 3g-catalyzed reactions between α-ketoesters and acetone resulted in up to 95% yield and 88% ee. Analysis of the transition state using density functional theory (DFT) calculations revealed that the tert-butyl group in 3g played an important role in enantioselectivity.

Steric Protection of Rhodium-Nitridyl Radical Species

In an attempt to synthesize a mononuclear rhodium nitridyl complex with a reduced tendency to undergo nitridyl radical N-N coupling we synthesized a bulky analog of Milstein’s bipyridine-based PNNH ligand, bearing a tert-butyl group at the 6’ position of the bipyridine moiety. A three-step synthetic route toward this new bulky tBu₃PNNH ligand was developed, involving a selective nucleophilic substitution step, followed by a Stille coupling and a final hydrophosphination step to afford the desired 6-(tert-butyl)-6'-((di-tert-butylphosphino)methyl)-2,2'-bipyridine (tBu₃PNNH) ligand. This newly developed tBu₃PNNH ligand was incorporated in the synthesis of the sterically protected azide complex [Rh(N₃)(tBu₃PNNH)]. We explored N₂ elimination form this species using photolysis and thermolysis, hoping to synthesize a mononuclear rhodium complex with a terminal nitrido moiety. Characterization of the reaction product(s) using NMR, coldspray HR-ESI-MS and EPR spectroscopy shows that the material is both EPR and NMR silent, and data obtained by MS spectrometry revealed masses corresponding with both monomeric and dimeric nitrido/nitridyl complexes. The combined data point to formation of a paramagnetic [(tBu₃PNN)Rh(µ-N)Rh(tBu₃PNN)] species. It thus seems that despite its three tBu groups the new ligand is not bulky enough to prevent formation of Rh-N-Rh bridged species. However, the increased steric environment does prevent further reaction with carbon monoxide, which is unable to coordinate to rhodium.<br>

Steric Protection of Rhodium-Nitridyl Radical Species

In an attempt to synthesize a mononuclear rhodium nitridyl complex with a reduced tendency to undergo nitridyl radical N-N coupling we synthesized a bulky analog of Milstein’s bipyridine-based PNNH ligand, bearing a tert-butyl group at the 6’ position of the bipyridine moiety. A three-step synthetic route toward this new bulky tBu₃PNNH ligand was developed, involving a selective nucleophilic substitution step, followed by a Stille coupling and a final hydrophosphination step to afford the desired 6-(tert-butyl)-6'-((di-tert-butylphosphino)methyl)-2,2'-bipyridine (tBu₃PNNH) ligand. This newly developed tBu₃PNNH ligand was incorporated in the synthesis of the sterically protected azide complex [Rh(N₃)(tBu₃PNNH)]. We explored N₂ elimination form this species using photolysis and thermolysis, hoping to synthesize a mononuclear rhodium complex with a terminal nitrido moiety. Characterization of the reaction product(s) using NMR, coldspray HR-ESI-MS and EPR spectroscopy shows that the material is both EPR and NMR silent, and data obtained by MS spectrometry revealed masses corresponding with both monomeric and dimeric nitrido/nitridyl complexes. The combined data point to formation of a paramagnetic [(tBu₃PNN)Rh(µ-N)Rh(tBu₃PNN)] species. It thus seems that despite its three tBu groups the new ligand is not bulky enough to prevent formation of Rh-N-Rh bridged species. However, the increased steric environment does prevent further reaction with carbon monoxide, which is unable to coordinate to rhodium.<br>