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ABSTRACT: We present an extensive study of a novel class of de novo designed tetrahedral M(4)L(6) (M = Ni, Zn) cage receptors, wherein internal decoration of the cage cavities with urea anion-binding groups, via functionalization of the organic components L, led to selective encapsulation of tetrahedral oxoanions EO(4)(n-) (E = S, Se, Cr, Mo, W, n = 2; E = P, n = 3) from aqueous solutions, based on shape, size, and charge recognition. External functionalization with tBu groups led to enhanced solubility of the cages in aqueous methanol solutions, thereby allowing for their thorough characterization by multinuclear ((1)H, (13)C, (77)Se) and diffusion NMR spectroscopies. Additional experimental characterization by electrospray ionization mass spectrometry, UV-vis spectroscopy, and single-crystal X-ray diffraction, as well as theoretical calculations, led to a detailed understanding of the cage structures, self-assembly, and anion encapsulation. We found that the cage self-assembly is templated by EO(4)(n-) oxoanions (n ≥ 2), and upon removal of the templating anion the tetrahedral M(4)L(6) cages rearrange into different coordination assemblies. The exchange selectivity among EO(4)(n-) oxoanions has been investigated with (77)Se NMR spectroscopy using (77)SeO(4)(2-) as an anionic probe, which found the following selectivity trend: PO(4)(3-) ≫ CrO(4)(2-) > SO(4)(2-) > SeO(4)(2-) > MoO(4)(2-) > WO(4)(2-). In addition to the complementarity and flexibility of the cage receptor, a combination of factors have been found to contribute to the observed anion selectivity, including the anions' charge, size, hydration, basicity, and hydrogen-bond acceptor abilities.
Journal of the American Chemical Society 04/2012; 134(20):8525-34. · 9.91 Impact Factor
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ABSTRACT: This study identifies how the amidoximate anion, AO, interacts with the uranyl cation, UO(2)(2+). Density functional theory calculations have been used to evaluate possible binding motifs in a series of [UO(2)(AO)(x)(OH(2))(y)](2-x) (x = 1-3) complexes. These motifs include monodentate binding to either the oxygen or the nitrogen atom of the oxime group, bidentate chelation involving the oxime oxygen atom and the amide nitrogen atom, and η(2) binding with the N-O bond. The theoretical results establish the η(2) motif to be the most stable form. This prediction is confirmed by single-crystal X-ray diffraction of UO(2)(2+) complexes with acetamidoxime and benzamidoxime anions.
Inorganic Chemistry 02/2012; 51(6):3855-9. · 4.60 Impact Factor
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ABSTRACT: This Viewpoint highlights creative ways that members of the Interactive Online Network of Inorganic Chemists (IONiC) are using journal articles from Inorganic Chemistry to engage undergraduate students in the classroom. We provide information about specific educational materials and networking features available free of charge to the inorganic community on IONiC's web home, the Virtual Inorganic Pedagogical Electronic Resource (VIPEr, www.ionicviper.org ) and describe the benefits of joining this community.
Inorganic Chemistry 07/2011; 50(13):5849-54. · 4.60 Impact Factor
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ABSTRACT: Density functional theory calculations have been used to evaluate the geometries and energetics of interactions between a number of uranyl complexes and hydrogen bond donor groups. The results reveal that although traditional hydrogen bond donors are repelled by the oxo group in the [UO(2)(OH(2))(5)](2+) species, they are attracted to the oxo groups in [UO(2)(OH(2))(2)(NO(3))(2)](0), [UO(2)(NO(3))(3)](-), and [UO(2)Cl(4)](2-) species. Hydrogen bond strength depends on the equatorial ligation and can exceed 15 kcal mol(-1). The results also reveal the existence of directionality at the uranyl oxo acceptor, with a weak preference for linear U═O---H angles.
Inorganic Chemistry 02/2011; 50(6):2599-605. · 4.60 Impact Factor
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ABSTRACT: Reaction of (PNP)Li with TaF5 produces pentagonal-bipyramidal (PNP)TaF4 (2). Alkylation of 2 with MeMgBr allows for the isolation of (PNP)TaMe4 (3). (PNP)TaMe4 (3) evolves thermally and/or photochemically into a bis(methylidene) complex (PNP)Ta(CH2)2 (4). The identity of the latter has been established by X-ray structural, NMR spectroscopic, and DFT computational studies. It does not appear that 4 possesses agostic interactions in solution.
08/2007;
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ABSTRACT: Operationally unsaturated (i.e., 16/18-electron) (PNPR)Re(H)4, where PNPR is N(SiMe2CH2PR2)2, is reactive at 22 degrees C with cyclic olefins. The first observed products are generally (PNPR)Re(H)2(cycloalkylidene), with hydrogenated olefin as the product of hydrogen abstraction from the tetrahydride. The tetrahydride complex with R = tBu generally fails to react (too bulky), that with R = cyclohexyl suffers a (controllable) tendency to abstraction of 3H from one ring, forming an eta3-cyclohexenyl compound, and that with R = iPr generally gives the richest bimolecular reactivity. The cyclic monoolefins studied show distinct reactivity, C6 giving first the carbene and then coordinated cyclohexadiene, C5 giving carbene, then diene, and then eta5-C5H5, C8 giving carbene and then eta2-cyclooctyne, and C12 giving an eta3-allyl. Norbornene gives a pi-complex of the norbornene in thermal equilibrium with its carbene isomer; at 90 degrees C, hydrocarbon ligand Calpha-Cbeta bond cleavage occurs to give, for the first time, a carbyne complex from an internal olefin. Two compounds synthesized here have the formal composition "(PNPR)Re + olefin", and each of these is capable of dehydrogenating the methyl group of a variety of alkanes at 110 degrees C to form (PNP)ReH triple bond (CR).
Journal of the American Chemical Society 06/2007; 129(18):6003-16. · 9.91 Impact Factor
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ABSTRACT: A Ru center ligated by a pincer bis(o-phosphinoaryl)amine (PNP) ligand in (PNP)RuH(H2) is sufficiently electron rich to break C−O and C−C bonds, resulting in the ultimate decarbonylation of hydrocarbonate and acetone, respectively, to give (PNP)RuH(CO). The decarbonylation of acetone is accompanied by hydrogenolysis of the C−C bonds to produce methane.
12/2004;
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ABSTRACT: The reaction of alkynes RCCH (R = H, Ph) with (PNP)RuCl, where PNP is (tBu2PCH2SiMe2)2N, occurs rapidly below 23 °C to give first an η2-alkyne adduct and then a final product with a vinylidene group, CCHR, inserted into the N−Ru bond. Characterization included X-ray diffraction (R = Ph) and DFT calculations to probe mechanistic aspects of the reaction.
09/2004;
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ABSTRACT: (PNPtBu)Re(H)4, where PNPtBu is (tBu2PCH2SiMe2)2N, reacts at 23 °C with RCCH (R = tBu, SiMe3, Ph) to give first H2 and mirror-symmetric (PNPtBu)ReH3(CCR), then H2 and C2ν symmetric (PNPtBu)Re(CCR)2. The diacetylide compounds show temperature-independent paramagnetism and 13C and 31P chemical shifts far beyond their normal values for other (PNPtBu)ReXn compounds. Single-crystal X-ray diffraction shows very similar structures for the cases R = Ph and R = SiMe3, each having an approximately C2v geometry with equivalent acetylides with C−Re−C approximately 108°. No hydride or H2 ligands are detected in final difference Fourier maps. DFT(B3PW91) calculations give minimum energy geometries of these species, of their products upon adding H2, and of mechanistically significant analogues [(H2PCH2SiH2)2N]ReHnR‘mH2-m, with n = 0, 2, m = 1, 2, and R‘ = H or Ph. These calculated geometries, when compared to those from X-ray diffraction, indicate that the isolated compounds have no hydride or H2 ligands and are thus (PNP)ReIII(CCR)2, making them more unsaturated than the reagent (PNP)ReV(H)4 by two electrons. Triplet state geometries of (PNP)ReXY are calculated and analyzed, as are their frontier orbitals.
09/2004;
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ABSTRACT: Synthesis of (PNP(R))ReOCl(2) (PNP(R) = (R(2)PCH(2)SiMe(2))(2)N, R = (i)()Pr, Cy, and (t)()Bu) from (Me(2)S)(2)ReOCl(3) and (PNP(R))MgCl is described. Magnesium and H(2) convert (PNP(R))ReOCl(2) first to (PNP(R))ReO(H)(2) and then to (PNP(R))Re(H)(4), the last being an operationally unsaturated species which can bind PMe(3) or p-toluidine. Acyclic alkenes react with (PNP(R))Re(H)(4) at 22 degrees C to give first (PNP(R))Re(H)(2)(olefin) and then (PNP(R))ReH(carbyne), in equilibrium with its eta(2)-olefin adduct. Re can also migrate to the terminal carbon of internal olefins to form a carbyne complex. Allylic C-SiMe(3) or C-NH(2) bonds are not broken, but OEt, OPh, and F vinyl substituents (X) are ultimately cleaved from carbon to give the ReC-CH(3) complex and liberate HX. DFT calculations, together with detection of intermediates for certain olefins, help to define a mechanism for these conversions.
Journal of the American Chemical Society 06/2004; 126(20):6363-78. · 9.91 Impact Factor
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ABSTRACT: Synthesis of (PNPR)ReOCl2 (PNPR = (R2PCH2SiMe2)2N, R = iPr, Cy, and tBu) from (Me2S)2ReOCl3 and (PNPR)MgCl is described. Magnesium and H2 convert (PNPR)ReOCl2 first to (PNPR)ReO(H)2 and then to (PNPR)Re(H)4, the last being an operationally unsaturated species which can bind PMe3 or p-toluidine. Acyclic alkenes react with (PNPR)Re(H)4 at 22 °C to give first (PNPR)Re(H)2(olefin) and then (PNPR)ReH(carbyne), in equilibrium with its η2-olefin adduct. Re can also migrate to the terminal carbon of internal olefins to form a carbyne complex. Allylic C−SiMe3 or C−NH2 bonds are not broken, but OEt, OPh, and F vinyl substituents (X) are ultimately cleaved from carbon to give the ReC−CH3 complex and liberate HX. DFT calculations, together with detection of intermediates for certain olefins, help to define a mechanism for these conversions.
04/2004;
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ABSTRACT: Both (PNP)Re(H)(4) and (PNP)ReH(cyclooctyne) (PNP(i)(Pr) = ((i)Pr(2)PCH(2)SiMe(2))(2)N) react with alkylpyridines NC(5)H(4)R to give first (PNP)ReH(2)(eta(2)-pyridyl) and cyclooctene and then, when not sterically blocked, (PNP)Re(eta(2)-pyridyl)(2) and cyclooctane. The latter are shown by NMR, X-ray diffraction, and DFT calculations to have several energetically competitive isomeric structures and pyridyl N donation in preference to PNP amide pi-donation. DFT studies support NMR solution evidence that the most stable bis pyridyl structure is one that is doubly eta(2)- with the pyridyl N donating to the metal center. When both ortho positions carry methyl substituents, cyclooctane and the carbyne complex (PNP)ReH(tbd1;C-pyridyl) are produced. Excess 2-vinyl pyridine reacts with (PNP)Re(H)(4) preferentially at the vinyl group, to give 2-ethyl pyridine and the sigma-vinyl complex (PNP)ReH[eta(2)-CH=CH(2-py)]. The DFT and X-ray structures show, by various comparisons, the ability of the PNP amide nitrogen to pi-donate to an otherwise unsaturated d(4) Re(III) center, showing short Re-N distances consistent with the presence of pi-donation.
Journal of the American Chemical Society 03/2004; 126(7):2105-13. · 9.91 Impact Factor
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ABSTRACT: Presented on the occasion of the 70th birthday of Prof J.J. Ziółkowski, in recognition of the great vision he has brought to the Institute of Chemistry in Wrocław. Abstract The reaction of NO with highly unsaturated, triplet spin state (PNP)Ru II Cl ("PNP" = (t Bu 2 PCH 2 SiMe 2) 2 N) in benzene at 20 • C is reported. The reaction proceeds through three major intermediate species, ultimately forming [(PNP)Ru(NO) 2 + ][Ru(NO)(OH)(NO 2) 2 Cl 2 − ], whose structure is determined by X-ray diffraction. The implications of PNP ligand loss, NO 2 − production, and partial oxidation of ruthenium to Ru(III) (the anion above) are discussed, together with the observed oxygen transfer which represents NO disproportionation. The two NO ligands in the cation are chemically inequivalent (one bent, NO − , and one linear, NO +), features which are studied by density functional theory (DFT) geometry optimization. Two isomers of (PNP)Ru(NO) 2 Cl, as well as (PNP)Ru(NO)Cl are evaluated as possible reaction intermediates by DFT geometry optimization.
Journal of Molecular Catalysis A Chemical 01/2004; 224:51-59. · 2.95 Impact Factor
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ABSTRACT: The molecule (PNPR)Re(H)4 (PNPR = (R2PCH2SiMe2)2N, R = iPr or cyclohexyl) reacts at 20 degrees C with 2 mol of cyclohexene to form equimolar cyclohexane and (PNPR)Re(H)2[=C(CH2)5]. This product is characterized by 1H, 13C, and 31P NMR and by X-ray diffraction as having one CH2 hydrogen (from a carbon located beta to Re) donating to the metal ("agostic CH"). This interaction occurs in preference to PNPR amide nitrogen pi-donation. DFT calculations confirm this agostic interaction, and show that the (PNPR)Re(H)2 fragment indeed reverses the greater stability of free olefin vs free carbene.
Journal of the American Chemical Society 09/2003; 125(32):9604-5. · 9.91 Impact Factor
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ABSTRACT: The ligand (tBu2PCH2SiMe2)2N1- (PNP) in [PNP]RuCl leads to an intermediate spin ground state, S = 1, which has been characterized by NMR and X-ray diffraction as having a planar structure. This spin state is attributed in part to N --> Ru pi donation. DFT calculations confirm that the singlet state lies higher in energy and is nonplanar. The molecule is converted to a diamagnetic product by addition of 2 mol of PhCN. The half-filled orbitals of the S = 1 state are suggested to be the reason agostic interactions do not compensate for the 14-valence electron count.
Journal of the American Chemical Society 08/2003; 125(28):8426-7. · 9.91 Impact Factor
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ABSTRACT: The reaction of (R(2)PCH(2)SiMe(2))(2)NM (PNP(R)M; R = Cy; M = Li, Na, MgHal, Ag) with L(2)ReOX(3) [L(2) = (Ph(3)P)(2) or (Ph(3)PO)(Me(2)S); X = Cl, Br] gives (PNP(Cy))ReOX(2) as two isomers, mer,trans and mer,cis. These compounds undergo a double Si migration from N to O at 90 degrees C to form (POP(Cy))ReNX(2) as a mixture of mer,trans and fac,cis isomers. Additional thermolysis effects migration of CH(3) from Si to Re, along with compensating migration of halide from Re to Si. DFT calculations on various structural isomers support the greater thermodynamic stability of the POP/ReN isomer vs PNP/ReO and highlight the influence of the template effect on the reactivities of these species.
Inorganic Chemistry 11/2002; 41(21):5615-25. · 4.60 Impact Factor
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ABSTRACT: The reaction of (R2PCH2SiMe2)2NM (PNPRM; R = Cy; M = Li, Na, MgHal, Ag) with L2ReOX3 [L2 = (Ph3P)2 or (Ph3PO)(Me2S); X = Cl, Br] gives (PNPCy)ReOX2 as two isomers, mer,trans and mer,cis. These compounds undergo a double Si migration from N to O at 90 °C to form (POPCy)ReNX2 as a mixture of mer,trans and fac,cis isomers. Additional thermolysis effects migration of CH3 from Si to Re, along with compensating migration of halide from Re to Si. DFT calculations on various structural isomers support the greater thermodynamic stability of the POP/ReN isomer vs PNP/ReO and highlight the influence of the template effect on the reactivities of these species.
09/2002;
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ABSTRACT: Consistent with the C−O cleavage behavior of vinyl ethers, vinyl fluoride reacts with Cp2ZrHCl to give Cp2ZrFCl and C2H4 as primary products. DFT (B3PW91) calculations show this reaction to be highly exoenergetic (−55 kcal/mol), and reveal a σ-bond metathesis mechanism to be unfavorable compared to a Zr−H addition across the CC bond, with regiochemistry placing F on Cβ of the resulting fluoroethyl ligand. β-F elimination (onto Zr) then completes the reaction. There is no η2-olefin intermediate on the reaction path. DFT calculations seeking the energy and structure of the two carbenes Cp2ZrHCl[CF(CH3)] and Cp2ZrFCl[CH(CH3)] are also described.
01/2001;
