Chip Nataro’s research while affiliated with Lafayette College and other places

The importance of electron deficient Tp ligands motivates the introduction of electron-withdrawing substituents into the scorpionate framework. Since perfluorophenyltris(pyrazol-1-yl)borate affects significant anodic shifts in half-cell potentials in their metal complexes relative those of phenyltris(pyrazol-1-yl)borate analogues, the tuning opportunities achieved using 3,4,5-trifluorophenyl- and 3,5-bis(trifluoromethyl)phenyl(pyrazol-1-yl)borates were explored. Bis(amino)boranes ((3,4,5-F)C6H2)B(NMe2)2 and ((3,5-CF3)C6H3)B(NMe2)2 are precursors to fluorinated tris(pyrazol-1-yl)phenylborates. Thallium salts of these scorpionates exhibit bridging asymmetric κ3-N,N,N coordination modes consistent with the reduced π-basicity of the fluorinated phenyl substituents relative those of other structurally characterized tris(pyrazol-1-yl)phenylborates. While a comparative analysis of the spectral and X-ray crystallographic data for classical Mo(0), Mo(II), Mn(I), Fe(II) and Cu(II) complexes of [((3,4,5-F)C6H2)Bpz3]- and [((3,5-CF3)C6H3)Bpz3]- could not differentiate these ligands with respect to their metal-based electronic impacts, cyclic voltammetry suggests that 3,4,5-trifluorophenyl- and 3,5-bis(trifluoromethyl)phenyl(pyrazol-1-yl)borates affect similar anodic shifts within their metal complexes, with coordination of [((3,5-CF3)C6H3)Bpz3]- rendering metal centers more difficult to oxidize, and sometimes even more difficult to oxidize than their [C6F5Bpz3]- analogues. These data suggest that the extent of phenyl substituent fluorination necessary to minimize metal center electron-richness in phenyltris(pyrazol-1-yl)borate complexes cannot be confidently predicted.

The catalytic activity of a series of [(AuCl)2(μ-PP)] (PP = 1,1'-bis(phosphino)metallocene ligands) compounds in the presence of Na[BArF24] (BArF24 = tetrakis(3,5-bis(trifluoromethyl)phenyl borate)) was examined in the formation of disubstituted furans from pyridine-N-oxide and terminal alkynes. The products of these reactions were typically the 2,5-disubstituted furans, but in the case of using 2-ethynylpyridene, the 2,4-disubstituted furan formed. The catalytic efficiency was dependent upon both the nature of the terminal alkyne and the 1,1'-bis(phosphino)metallocene ligands. During the course of this study, two new compounds, [(AuCl)2(μ-dppr)] and [(AuCl)2(μ-dppo)] (dppr = 1,1'-bis(diphenylphosphino)ruthenocene; dppo = 1,1'-bis(diphenylphosphino)osmocene), were prepared and characterized by NMR. X-ray crystal structures of both compounds were determined and the oxidative electrochemistry of these new compounds was examined.

1,1′-bis(phosphino)ferrocene ligands are commonly employed in a variety of catalytic systems. These ligands are of particular interest as the steric and electronic properties of the phosphorus donor atoms can be altered by changing the substituents of the phosphines. In addition, the ferrocene backbone of the ligands provides unique electronic and conformational flexibility to these ligands. Previous investigations in this lab have examined catalytic ring closing reactions using a series of gold compounds with bis(phosphino)ferrocene ligands, [Au2Cl2(μ-PP)]. These gold compounds were shown to react with sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate, Na[BArF24], to generate a cationic species with the general formula [Au2(μ-Cl)(μ-PP)][BArF24] that are much more efficient catalysts than the [Au2Cl2(μ-PP)] compounds. In this study, a series of [Au2Cl2(μ-PP)] (μ-PP = 1,1′-bis(diphenylphosphino)ferrocene (dppf), 1,1′-bis(diiso-propylphosphino)ferrocene (dippf), 1,1′-bis(dicyclohexylphosphino)ferrocene (dcpf), 1,1′-bis(ditert-butylphosphino)ferrocene (dtbpf), 1-diphenylphosphino-1′-ditert-butylphosphinoferrocene (dppdtbpf) or 1,1ʹ-bis(5-methyl-2-furanylphosphino)ferrocene (dfurpf)) compounds were examined as catalysts for the intramolecular ring-closing hydroamination of 3-(vinyloxy)propan-1-amine and the intermolecular hydroamination of phenylacetylene with a variety of phenylamine reagents. The catalytic activity of the corresponding [Au2(μ-Cl)(μ-PP)][BArF24] compounds that were generated in situ was also explored. Two new [Au2Cl2(μ-PP)] compounds with chiral bis(phosphino)ferrocene ligands (PP = 1,1′-bis(2R,5R-dimethylphospholanyl)ferrocene (R-dMeplf) or 1,1′-bis(2S,5S-dimethylphospholanyl)ferrocene (S-dMeplf)) were prepared, characterized spectroscopically and electrochemically, and evaluated as catalysts in the ring-closing hydroamination reaction. In addition, the X-ray structures of [Au2Cl2(μ-PP)] (PP = dppdtbpf, R-dMeplf and S-dMeplf) were determined.

The efficiency of various gold compounds containing bis(phosphino)ferrocene ligands for catalyzing ring-closing reactions was examined. Six commercially available bis(phosphino)ferrocene ligands: 1,1′-bis(ditert-butylphosphino)ferrocene (dtbpf), 1,1′-bis(diphenylphosphino)ferrocene (dppf), 1,1′-bis(dicylohexylphosphino)ferrocene (dcpf), 1,1′-bis(diiso-propylphosphino)ferrocene (dippf), 1-diphenylphosphino-1′-di-tert-butylphosphinoferrocene (dppdtbpf) and 1,1′-bis(5-methyl-2-furanylphosphino)ferrocene (dfurpf) were employed in this study. In addition to the previously reported [Au 2 Cl 2 (μ-PP)] (PP = dtbpf, dppf, dcpf, dippf or dppdtbpf) compounds, [Au 2 Cl 2 (μ-dfurpf)] was synthesized and characterized by NMR spectroscopy, cyclic voltammetry and X-ray crystallography. All of these gold compounds react with Na[BArF 24 ] (BArF 24 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) to remove a chloride and yield the cationic monochlorides, [Au 2 (μ-Cl)(μ-PP)] ⁺ . The effectiveness of the [Au 2 Cl 2 (μ-PP)] and [Au 2 (μ-Cl)(μ-PP)][BArF 24 ], either pre-formed or generated in situ, compounds for the catalytic intramolecular alkyne hydroalkoxylation of (Z)-3-methylpent-2-en-4-yn-1-ol was examined in CDCl 3 and toluene-d 8 . The ring-closing of N-(prop-2-yn-1-yl)benzamide was also examined and was efficiently carried out in toluene-d 8 using [Au 2 (μ-Cl)(μ-PP)][BArF 24 ] (PP = dtbpf, dppf, dcpf, dippf, dppdtbpf or dfurpf). In addition, [Au 2 Cl 2 (μ-dppe)] and [Au 2 (μ-Cl)(μ-dppe)][BArF 24 ] were examined as catalysts for these ring-closing reactions in order to determine if the ferrocene backbone of the bis(phosphino)ferrocene ligands was important for catalysis.

ACS Examinations provide a lens through which to examine historical changes in topic coverage via analyses of course-specific examinations. This study is an extension of work completed previously by the ACS Exams Research Staff and collaborators in general chemistry, organic chemistry, and physical chemistry to explore content changes in the principal courses of the postsecondary chemistry curriculum. In this study, we consider how inorganic chemistry content coverage has varied over a 55-year period since the first inorganic chemistry ACS Examination was released in 1961. A total of 860 items was evaluated on the basis of problem type (i.e., algorithmic, conceptual, or recall), use of visual-spatial or reference components, and content coverage. Our analyses identify core content areas in the inorganic chemistry curriculum, consistent with those reported in faculty surveys. Each examination also contained questions addressing a variety of specialty areas that vary widely within the discipline between 1961 and 2016. Unlike the results from historical reviews of general chemistry and organic chemistry ACS Examinations, we observe great variability across the 13 inorganic chemistry examinations with an absence of strong trends in inclusion or exclusion of problem types, visual-spatial or reference components, or content across the 13 exams analyzed. Our results offer a framework for using historical ACS Examinations as a tool to make decisions about the future of content coverage in postsecondary inorganic chemistry education.

A variety of gold compounds containing bis(phosphino)ferrocene ligands were examined as catalysts in the ring closing reaction of (Z)-3-methylpent-2-en-4-yn-1-ol