Density Functional Theory Study of the Reaction between d0 Tungsten Alkylidyne Complexes and H2O: Addition versus Hydrolysis

Effective destruction of perfluorooctanoic acid by zero-valent iron laden biochar obtained from carbothermal reduction: Experimental and simulation study

This study investigated the degradation of perfluorooctanoic acid (PFOA) on zerovalent iron-laden biochar (BC-ZVI) prepared by carbothermal reduction. Results show that over 99% PFOA can be removed by BC-ZVI in hydrothermal conditions under 240 °C within 6 h. The maximum defluorination rate of 63.2% was achieved after 192 h, and this outcome was significantly better than biochar (BC) and zero-valent iron (ZVI) alone. The short-chain perfluorinated compounds (PFCs) and perfluoroheptanal were detected in the liquid phase after degradation, suggesting that the degradation of PFOAs by BC-ZVI followed the Kobel decarboxylation process. XRD and SEM-EDS analyses strongly suggested that carbothermal reduction could avoid the agglomeration of ZVI loaded onto biochar, which helped make the PFOA degradation more efficient. The frontier molecular orbital theory calculated by density functional theory revealed there were two possibilities for ZVI loading on BC (edged or internal loading), while the edge loaded ZVI had a greater tendency to provide electrons for the defluorination of PFOA than internally loaded ZVI.

"Canopy Catalysts" for Alkyne Metathesis: Molybdenum Alkylidyne Complexes with a Tripodal Ligand Framework

A new family of structurally well-defined molybdenum alkylidyne catalysts for alkyne metathesis, which is distinguished by a tripodal trisilanolate ligand architecture, is presented. Complexes of type 1 combine the virtues of previous generations of silanolate-based catalysts with a significantly improved functional group tolerance. They are easy to prepare on scale; the modularity of the ligand synthesis allows the steric and electronic properties to be fine-tuned and hence the application profile of the catalysts to be optimized. This opportunity is manifested in the development of catalyst 1f, which is as reactive as the best ancestors but exhibits an unrivaled scope. The new catalysts work well in the presence of unprotected alcohols and various other protic groups. The chelate effect entails even a certain stability toward water, which marks a big leap forward in metal alkylidyne chemistry in general. At the same time, they tolerate many donor sites, including basic nitrogen and numerous heterocycles. This aspect is substantiated by applications to polyfunctional (natural) products. A combined spectroscopic, crystallographic, and computational study provides insights into structure and electronic character of complexes of type 1. Particularly informative are a density functional theory (DFT)-based chemical shift tensor analysis of the alkylidyne carbon atom and ⁹⁵Mo NMR spectroscopy; this analytical tool had been rarely used in organometallic chemistry before but turns out to be a sensitive probe that deserves more attention. The data show that the podand ligands render a Mo-alkylidyne a priori more electrophilic than analogous monodentate triarylsilanols; proper ligand tuning, however, allows the Lewis acidity as well as the steric demand about the central atom to be adjusted to the point that excellent performance of the catalyst is ensured.

Syntheses of Molybdenum Oxo Benzylidene Complexes

The reaction between Mo(O)(CHAr_o)(OR_F6)₂(PMe₃) (Ar_o = ortho-methoxyphenyl, OR_F6 = OCMe(CF₃)₂) and 2 equiv of LiOHMT (OHMT = O-2,6-(2,4,6-Me₃C₆H₂)₂C₆H₃) leads to Mo(O)(CHAr_o)(OHMT)₂, an X-ray structure of which shows it to be a trigonal bipyramidal anti benzylidene complex in which the o-methoxy oxygen is coordinated to the metal trans to the apical oxo ligand. Addition of 1 equiv of water (in THF) to the benzylidyne complex, Mo(CAr_p)(OR)₃(THF)₂ (Ar_p = para-methoxyphenyl, OR = OR_F6 or OC(CF₃)₃ (OR_F9)) leads to formation of {Mo(CAr_p)(OR)₂(μ-OH)(THF)}₂(μ-THF) complexes. Addition of 1 equiv of a phosphine (L) to Mo(CAr_p)(OR_F9)₃(THF)₂ in THF, followed by addition of 1 equiv of water, all at room temperature, yields Mo(O)(CHAr_p)(OR_F9)₂(L) complexes in good yields for several phosphines (e.g., PMe₂Ph (69% by NMR), PMePh₂ (59%), PEt₃ (69%), or P( i-Pr)₃ (65%)). The reaction between Mo(O)(CHAr_p)(OR_F9)₂(PEt₃) and 2 equiv of LiOHMT proceeds smoothly at 90 °C in toluene to give Mo(O)(CHAr_p)(OHMT)₂, a four-coordinate syn alkylidene complex. Mo(O)(CHAr_p)(OHMT)₂ reacts with ethylene (1 atm in C₆D₆) to give (in solution) a mixture of Mo(O)(CHAr_p)(OHMT)₂, Mo(O)(CH₂)(OHMT)₂, and an unsubstituted square pyramidal metallacyclobutane complex, Mo(O)(CH₂CH₂CH₂)(OHMT)₂, along with ethylene and Ar_pCH═CH₂. Mo(O)(CHAr_p)(OHMT)₂ also reacts with 2,3-dicarbomethoxynorbornadiene to yield syn and anti isomers of the "first-insertion" products that contain a cis C═C bond.

Syntheses of Molybdenum Oxo Alkylidene Complexes through Addition of Water to an Alkylidyne Complex

Addition of one equiv of water to Mo(CAr)[OCMe(CF3)2]3(1,2-dimethoxyethane) (2, Ar = o-(OMe)C6H4) in the presence of PPhMe2 leads to formation of Mo(O)(CHAr)[OCMe(CF3)2]2(PPhMe2) (3(PPhMe2)) in 34% yield. Addition of one equiv of water alone to 2 produces the dimeric alkylidyne hydroxide complex, {Mo(CAr)[OCMe(CF3)2]2(μ-OH)}2(dme) (4(dme)) in which each bridging hydroxide proton points toward an oxygen atom in an arylmethoxy group. Addition of PMe3 to 4(dme) gives the alkylidene oxo complex, (3(PMe3)), an analogue of 3(PPhMe2) (95% conversion, 66% isolated). Treatment of 3(PMe3) with two equiv of HCl gave Mo(O)(CHAr)Cl2(PMe3) (5), which upon addition of LiO-2,6-(2,4,6-i-Pr3C6H2)2C6H3 (LiOHIPT) gave Mo(O)(CHAr)(OHIPT)Cl(PMe3) (6). Compound 6 in the presence of B(C6F5)3 will initiate the ring-opening metathesis polymerization of cyclooctene, 5,6-dicarbomethoxynorbornadiene (DCMNBD), and rac-5,6-dicarbomethoxynorbornene (DCMNBE), and the homocoupling of 1-decene to 9-octadecene. The poly(DCMNBD) has a cis,syndiotactic structure, whereas poly(DCMNBE) has a cis,syndiotactic,alt structure. X-ray structures were obtained for 3(PPhMe2), 4(dme), and 6.

Hydrolysis of organometallic and metal–amide precursors: synthesis routes to oxo-bridged heterometallic complexes, metal-oxo clusters and metal oxide nanoparticles

Organometallic and metal amide reagents react with –OH groups to generate metal–oxygen connectivity, yielding metal-oxo heterobimetallics, clusters and nanoparticles.

Syntheses of Molybdenum Adamantylimido and t-Butylimido Alkylidene Chloride Complexes Using HCI and Diphenylmethylphosphine

Reactions between Mo(N-t-Bu)₂(CH₂-t-Bu)₂ or Mo(NAdamantyl)₂(CH₂CMe₂Ph)₂ and 3 equiv of HCl in the presence of 1 equiv of PPh₂Me yield Mo(NR)(CHR')(PPh₂Me)Cl₂ complexes, from which Mo(NR)(CHR')(PPh₂Me)(OAr)Cl complexes (OAr = a 2,6-terphenoxide) can be prepared. The Mo(NR)(CHR')(PPh₂Me)(OAr)Cl complexes were evaluated as cross-metathesis catalysts between cyclooctene and Z-1,2-dichloroethylene. The efficiencies of the test reaction for complexes in which OAr = OTPP, OHMT, OHIPT, or OHTBT (where OTPP is 2,3,5,6-tetraphenylphenoxide, OHMT is hexamethylterphenoxide, OHIPT is hexaisopropylterphenoxide, and OHTBT is hexa-t-butylterphenoxide) maximize when OAr is OHMT or OHIPT. Mo(N-t-Bu)(CH-t-Bu)(PPh₂Me)Cl₂ is essentially inactive for the reaction between cyclooctene and Z-1,2-dichloroethylene. X-ray structural studies were carried out on Mo(NAd)(CHCMe₂Ph)(PPh₂Me)Cl₂, Mo(N-t-Bu)(CH-t-Bu)(PPh₂Me)(OHMT)Cl, Mo(NAd)(CHCMe₂Ph)(Cl)(OHTBT)(PMe₃), and [Mo(NAd)(CHCMe₂Ph)(PMe₃)(Cl)]₂(μ-O), the product of the reaction between Mo(NAd)(CHCMe₂Ph)(Cl)(OHTBT)(PMe₃) and 0.5 equiv of water.