More Like this

1. Di(hydroperoxy)adamantane adducts: synthesis, characterization and application as oxidizers for the direct esterification of aldehydes

   https://doi.org/10.1039/d1dt03243g  

   Arp, Fabian F.; Ashirov, Rahym; Bhuvanesh, Nattamai; Blümel, Janet (November 2021, Dalton Transactions)

   The di(hydroperoxy)adamantane adducts of water (1) and phosphine oxides p -Tol 3 PO·(HOO) 2 C(C 9 H 14 ) (2), o -Tol 3 PO·(HOO) 2 C(C 9 H 14 ) (3), and Cy 3 PO·(HOO) 2 C(C 9 H 14 ) (4), as well as a CH 2 Cl 2 adduct of a phosphole oxide dimer (8), have been created and investigated by multinuclear NMR spectroscopy, and by Raman and IR spectroscopy. The single crystal X-ray structures for 1–4 and 8 are reported. The IR and 31 P NMR data are in accordance with strong hydrogen bonding of the di(hydroperoxy)adamantane adducts. The Raman ν (O–O) stretching bands of 1–4 prove that the peroxo groups are present in the solids. Selected di(hydroperoxy)alkane adducts, in combination with AlCl 3 as catalyst, have been applied for the direct oxidative esterification of n -nonyl aldehyde, benzaldehyde, p -methylbenzaldehyde, p -bromobenzaldehyde, and o -hydroxybenzaldehyde to the corresponding methyl esters. The esterification takes place in an inert atmosphere, under anhydrous and oxygen-free conditions, within a time frame of 45 minutes to 5 hours at room temperature. Hereby, two oxygen atoms per adduct assembly are active with respect to the quantitative transformation of the aldehyde into the ester. 

   more » « less
2. Immobilized di(hydroperoxy)propane adducts of phosphine oxides as traceless and recyclable oxidizing agents

   https://doi.org/10.1016/j.apsusc.2023.157333  

   Hoefler, John C.; Vu, Anh; Perez, Arturo J.; Blümel, Janet (August 2023, Applied Surface Science)

   Oxidations represent important reactions that are ubiquitous in academia and industry. Hydrogen peroxide (H2O2) is a common source of active oxygen for oxidations. H2O2 is usually diluted in water as it is too unstable to be used in pure form. However, the presence of water can complicate reactions because biphasic mixtures with organic solvents form. Furthermore, secondary reactions with water may lead to side products. Therefore, alternative forms of H2O2, such as peroxide adducts, are an active area of research. Di(hydroperoxy)alkane adducts of phosphine oxides are one attractive solution because they are soluble in organic solvents, crystallizable, shelf-stable and active towards a variety of oxidation reactions. The only drawback is that the phosphine oxide carrier has to be removed after the reaction. In this contribution, the bifunctional ligand (EtO)3Si(CH2)2PPh2 is immobilized on a silica (SiO2) support which is subsequently end-capped with EtOSi(CH3)3. The new surface-bound di(hydroperoxy)propane adduct is then generated with the immobilized phosphine oxide as carrier. The adduct and a deuterated analog are characterized with solid-state and solution NMR spectroscopy. It has been demonstrated that substrates in organic solvents easily access the surface-bound peroxide and are oxidized quantitatively. The phosphine oxide carrier remains bound to the surface and can be removed easily by settling of the silica. Using the oxidative esterification of nonyl aldehyde it is proven that the immobilized peroxide adduct does not leach from the silica support and is active and reusable over multiple cycles. 

   more » « less
3. A new supramolecular bonding motif involving NH bonds of ammonium salts and macrocycles derived from platinum corners and butadiynediyl linkers

   https://doi.org/10.1039/D2DT02680E  

   Collins, Brenna K.; Bhuvanesh, Nattamai; Gladysz, John A. (November 2022, Dalton Transactions)

   CuI catalyzes reactions of cis -(R 2 C(CH 2 PPh 2 ) 2 )Pt(CCCCH) 2 and cis -(R 2 C(CH 2 PPh 2 ) 2 )PtI 2 in secondary amine solvents HNR’ 2 to give the title adducts [(R 2 C(CH 2 PPh 2 ) 2 )Pt(CCCC)] 4 ·(H 2 NR’ 2 + I − ) n (R/R’/ n = Me/Et/1, Me/((CH 2 CH 2 ) 2 O) 0.5 /3, Et/Et/1, Et/CH 2 CHCH 2 /1; 92–42%). Crystal structures of these or closely related species establish folded Pt 4 cores containing ammonium cation guests, with NH/ and NCH/CC hydrogen bonding. DOSY NMR experiments show that the host/guest relationship can be maintained in solution. 

   more » « less
4. Counterintuitive torsional barriers controlled by hydrogen bonding

   https://doi.org/10.1039/d0cp03285a  

   Barbero, Héctor; Meunier, Antoine; Kotturi, Kondalarao; Smith, Ashton; Kyritsakas, Nathalie; Killmeyer, Adam; Rabbani, Ramin; Nazimuddin, Md; Masson, Eric (September 2020, Physical Chemistry Chemical Physics)

   null (Ed.)

   The torsional barriers along the C aryl –C aryl axis of a pair of isosteric disubstituted biphenyls were determined by variable temperature 1 H NMR spectroscopy in three solvents with contrasted hydrogen bond accepting abilities (1,1,2,2-tetrachloroethane-d 2 , nitrobenzene-d 5 and dimethyl sulfoxide-d 6 ). One of the biphenyl scaffolds was substituted at its ortho and ortho ′ positions with N ′-acylcarbohydrazide groups that could engage in a pair of intramolecular N–H⋯O=C hydrogen bonding interactions at the ground state, but not at the transition state of the torsional isomerization pathway. The torsional barrier of this biphenyl was exceedingly low despite the presence of the hydrogen bonds (16.1, 15.6 and 13.4 kcal mol −1 in the three aforementioned solvents), compared to the barrier of the reference biphenyl (15.3 ± 0.1 kcal mol −1 on average). Density functional theory and the solvation model developed by Hunter were used to decipher the various forces at play. They highlighted the strong stabilization of hydrogen bond donating solutes not only by hydrogen bond accepting solvents, but also by weakly polar, yet polarizable solvents. As fast exchanges on the NMR time scale were observed above the melting point of dimethyl sulfoxide-d 6 , a simple but accurate model was also proposed to extrapolate low free activation energies in a pure solvent (dimethyl sulfoxide-d 6 ) from higher ones determined in mixtures of solvents (dimethyl sulfoxide-d 6 in nitrobenzene-d 5 ). 

   more » « less
5. Non-covalent assembly of proton donors and p- benzoquinone anions for co-electrocatalytic reduction of dioxygen

   https://doi.org/10.1039/D1SC01271A  

   Hooe, Shelby L.; Cook, Emma N.; Reid, Amelia G.; Machan, Charles W. (July 2021, Chemical Science)

   The two-electron and two-proton p -hydroquinone/ p -benzoquinone (H 2 Q/BQ) redox couple has mechanistic parallels to the function of ubiquinone in the electron transport chain. This proton-dependent redox behavior has shown applicability in catalytic aerobic oxidation reactions, redox flow batteries, and co-electrocatalytic oxygen reduction. Under nominally aprotic conditions in non-aqueous solvents, BQ can be reduced by up to two electrons in separate electrochemically reversible reactions. With weak acids (AH) at high concentrations, potential inversion can occur due to favorable hydrogen-bonding interactions with the intermediate monoanion [BQ(AH) m ]˙ − . The solvation shell created by these interactions can mediate a second one-electron reduction coupled to proton transfer at more positive potentials ([BQ(AH) m ]˙ − + n AH + e − ⇌ [HQ(AH) (m+n)−1 (A)] 2− ), resulting in an overall two electron reduction at a single potential at intermediate acid concentrations. Here we show that hydrogen-bonded adducts of reduced quinones and the proton donor 2,2,2-trifluoroethanol (TFEOH) can mediate the transfer of electrons to a Mn-based complex during the electrocatalytic reduction of dioxygen (O 2 ). The Mn electrocatalyst is selective for H 2 O 2 with only TFEOH and O 2 present, however, with BQ present under sufficient concentrations of TFEOH, an electrogenerated [H 2 Q(AH) 3 (A) 2 ] 2− adduct (where AH = TFEOH) alters product selectivity to 96(±0.5)% H 2 O in a co-electrocatalytic fashion. These results suggest that hydrogen-bonded quinone anions can function in an analogous co-electrocatalytic manner to H 2 Q. 

   more » « less