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1. Creating Well-Defined monolayers of phosphine linkers incorporating ethoxysilyl groups on silica surfaces for superior immobilized catalysts

   https://doi.org/10.1016/j.apsusc.2023.156380  

   Shakeri, Ehsan; Blümel, Janet (April 2023, Applied Surface Science)

   Many applications of catalysts immobilized on solid supports like silica via bifunctional phosphine linkers are still hampered by their decomposition, leaching, agglomeration, and uncontrolled nanoparticle formation, all of which change their activities and selectivities. In general, the success of an immobilized catalyst is crucially dependent on the linker and its attachment to the oxide support. In this contribution, an improved method for covalently binding phosphine linkers to silica via ethoxysilane groups is described. This method leads to well-defined sub-monolayers of linkers on silica surfaces without cross-linking of the linkers, which typically leads to clogged pores and metal agglomeration during catalysis, thus entailing less active and selective catalysts. The novel immobilization method has been supported by multinuclear classical CP/MAS solid-state NMR spectroscopy, as well as suspension NMR of slurries. It has been demonstrated by TEM that nickel complexes coordinated by immobilized phosphine linkers in a well-defined sub-monolayer coverage do not form larger aggregates or nanoparticles during the catalytic cyclotrimerization of phenylacetylene under various conditions, in contrast to analogous complexes in homogeneous catalytic runs. 

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2. Synthesis of diphenyl-(2-thienyl)phosphine, its chalcogenide derivatives and a series of novel complexes of lanthanide nitrates and triflates

   https://doi.org/10.1039/d2dt01570f  

   Luster, Troy; Van de Roovaart, Hannah J.; Korman, Kyle J.; Sands, Georgia G.; Dunn, Kylie M.; Spyker, Anthony; Staples, Richard J.; Biros, Shannon M.; Bender, John E. (June 2022, Dalton Transactions)

   A novel synthesis of diphenyl(2-thienyl)phosphine, along with its’ oxide, sulfide and selenide derivatives, is reported here. These phosphines have been characterized by NMR, IR, MS and X-Ray crystallography. The phosphine oxide derivative was reacted with a selection of lanthanide( iii ) nitrates and triflates, LnX 3 , to give the resultant metal–ligand complexes. These complexes have also been characterized by NMR, IR, MS and X-Ray crystallography. Single crystal X-Ray diffraction data shows a difference in metal–ligand complex stoichiometry and stereochemistry depending on the counteranion (nitrate vs. triflate). The [Ln(Ar 3 PO) 3 (NO 3 ) 3 ] ligand–nitrate complexes are nine-coordinate to the metal in the solid state (bidentate nitrate), featuring a 1 : 3 lanthanide–ligand ratio and bear an overall octahedral arrangement of the six, coordinated ligands. Our [Ln(Ar 3 PO) 3 (NO 3 ) 3 ] ligand–nitrate complexes gave three examples of fac -stereochemistry, where mer -stereochemistry is almost universally observed in the literature of highly related [Ln(Ar 3 PO) 3 (NO 3 ) 3 ] complexes. For the Tb complexes, two different arrangements of the ligands around the metal were observed in the solid state for [Tb(Ar 3 PO) 3 (NO 3 ) 3 ] and [Tb(Ar 3 PO) 4 (OTf) 2 ] [OTf]. [Tb(Ar 3 PO) 3 (NO 3 ) 3 ] is strictly nine-coordinate, ligand mer -stereochemistry in the solid state, and [Tb(Ar 3 PO) 4 (OTf) 2 ] [OTf] is strictly octahedral, six-coordinate, with a square-planar stereochemical arrangement of the phosphine oxide ligands around the metal. 

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3. Reaction Chemistry at Discrete Organometallic Fragments on Black Phosphorus

   https://doi.org/10.1002/anie.202311575  

   Mitra, Kendahl L. Walz; Riehs, Michael; Draguicevic, Andrei; Swann, William A.; Li, Christina W.; Velian, Alexandra (November 2023, Angewandte Chemie International Edition)

   Abstract Black phosphorus (bP) is a two‐dimensional van der Waals material unique in its potential to serve as a support for single‐site catalysts due to its similarity to molecular phosphines, ligands quintessential in homogeneous catalysis. However, there is a scarcity of synthetic methods to install single metal centers on the bP lattice. Here, we demonstrate the functionalization of bP nanosheets with molecular Re and Mo complexes. A suite of characterization techniques, including infrared, X‐ray photoelectron and X‐ray absorption spectroscopy as well as scanning transmission electron microscopy corroborate that the functionalized nanosheets contain a high density of discrete metal centers directly bound to the bP surface. Moreover, the supported metal centers are chemically accessible and can undergo ligand exchange transformations without detaching from the surface. The steric and electronic properties of bP as a ligand are estimated with respect to molecular phosphines. Sterically, bP resembles tri(tolyl)phosphine when monodentate to a metal center, and bis(diphenylphosphino)propane when bidentate, whereas electronically bP is a σ‐donor as strong as a trialkyl phosphine. This work is foundational in elucidating the nature of black phosphorus as a ligand and underscores the viability of using bP as a basis for single‐site catalysts. 

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4. X-ray crystallographic, luminescence and NMR studies of phenacyldiphenylphosphine oxide with the Ln( iii ) ions Sm, Eu, Gd, Tb and Dy

   https://doi.org/10.1039/c7dt02678a  

   G. Leach, Erin; Shady, Justin R.; Boyden, Adam C.; Emig, Anne-lise; Henry, Alyssa T.; Connor, Emily K.; Staples, Richard J.; Schaertel, Stephanie; Werner, Eric J.; Biros, Shannon M. (January 2017, Dalton Transactions)

   We report here the characterization in solution (NMR, luminescence, MS) and the solid-state (X-ray crystallography, IR) of complexes between phenacyldiphenylphosphine oxide and five Ln( iii ) ions (Sm, Eu, Gd, Tb, Dy). Four single crystal X-ray structures are described here showing a 1 : 2 ratio between the Ln 3+ ions Eu, Dy, Sm and Gd and the ligand, where the phosphine oxide ligands are bound in a monodentate manner to the metal center. A fifth structure is reported for the 1 : 2 Eu(NO 3 ) 3 -ligand complex showing bidentate binding between the two ligands and the metal center. The solution coordination chemistry of these metal complexes was probed by 1 H, 13 C and 31 P NMR, mass spectrometry, and luminescence experiments. The title ligand has the capability to sensitize Tb 3+ , Dy 3+ , Eu 3+ and Sm 3+ leading to metal-centered emission in solutions of acetonitrile and methanol and in the solid state. 

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5. 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. 

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