A theoretically oriented, structural and physical inorganic, bioinorganic, and organometallic chemist. Phone: +1 250 807-8346 Address: Department of Chemistry The University of British Columbia - Okanagan 1177 Research Dr, Kelowna, BC, CANADA
In this work, we demonstrate the potential of multi-edge X-ray absorption near-edge structure (XA... more In this work, we demonstrate the potential of multi-edge X-ray absorption near-edge structure (XANES) analysis in completely defining the ground state electronic structure of a prototypical biomimetic complex of the [2Fe]-subcluster of the catalytic H-cluster of FeFe-hydrogenase. The spectral features at the ionization thresholds for Fe, S, C, and O 1s (K-edge) and Fe 2p (L-edge) core electrons were considered simultaneously to obtain the atomic compositions of the unoccupied frontier molecular orbitals. A systematic error analysis was carried out at the most informative S K-edge for spectra collected by multiple detection methods, at various data collection temperatures, and different sample preparation protocols. As expected for the difference in bonding between bridging and terminal Fe-S(thiolate) coordination, the Fe-S bond is more covalent in the [2Fe]-biomimetic complex with formally iron(I) centers (36 ± 2% S character per Fe-S bond) than in the previously described [2Fe-2S] clusters (25 ± 3% S character per Fe-S bond) with formally iron(III) centers. An electron hole-based analysis of the pre-edge features at Fe K-, Fe L-, and S K-edges experimentally defines the composition of the first three frontier unoccupied molecular orbitals to contain 4% Fe 4p, 44% Fe 3d, and 24% S 3p contributions per electron hole, respectively. The complementary CO ligand contribution thus can be defined as 28% per electron hole. These experimental orbital covalency values are important in rationalizing redox properties, electrophilicity of the metals, or nucleophilicity of the ligands, and critically evaluating the absolute accuracy of electronic structure calculations.
Tris(pyrazolyl)hydroborate ligands have been utilized in the fields of inorganic and coordination... more Tris(pyrazolyl)hydroborate ligands have been utilized in the fields of inorganic and coordination chemistry due to the ease of introduction of steric and electronic substitutions at the pyrazole rings. The development and use of the tris(pyrazolyl)hydroborate ligand, called a `scorpionate', were pioneered by the late Professor Swiatoslaw Trofimenko. He developed a second generation for his ligand system by the introduction of 3-tert-butyl and 3-phenyl substituents and this new ligand system accounted for many remarkable developments in inorganic and coordination chemistry in stabilizing monomeric species while maintaining an open coordination site. Bismuth is remarkably harmless among the toxic heavy metal p-block elements and is now becoming popular as a replacement for highly toxic metal elements, such as lead. Two bismuth(III) complexes of the anionic sulfur-containing tripod tris(3-tert-butyl-2-sulfanylidene-1H-imidazol-1-yl)hydroborate ligand were prepared. By recrystalliza...
Tris(pyrazolyl)borate (scorpionate) ligands can be considered as the most prolific ligands in con... more Tris(pyrazolyl)borate (scorpionate) ligands can be considered as the most prolific ligands in contemporary coordination chemistry due to the availability of various steric and electronic substituents at the pyrazolyl rings that allow fine-tuning of the open-coordination site for metal centres. The thallium(I) complexes of anionic tridentate-chelating scorpionate ligands, namely [tris(3-mesityl-5-methyl-1H-pyrazol-1-yl-κN(2))hydroborato]thallium(I) monohydrate, [Tl(C39H46BN6)]·H2O, (I), and [bis(3-mesityl-5-methyl-1H-pyrazol-1-yl-κN(2))(5-mesityl-3-methyl-1H-pyrazol-1-yl-κN(2))hydroborato]thallium(I), [Tl(C39H46BN6)], (II), show a {Tl(I)N3} coordination, with average Tl(I)-N bond lengths of 2.53 and 2.55 Å in (I) and (II), respectively. The overall Tl(I) coordination geometry is distorted trigonal pyramidal, with the average N-Tl(I)-N angle being approximately 73° for both. The dihedral angle between the planes of the pyrazolyl and benzene rings of the mesityl group is 82° in (I), wh...
Sulfur K-edge X-ray absorption spectroscopy (XAS) spectra of the monodentate sulfate complexes [M... more Sulfur K-edge X-ray absorption spectroscopy (XAS) spectra of the monodentate sulfate complexes [M(II)(itao)(SO4)(H2O)0,1] (M = Co, Ni, Cu) and [Cu(Me6tren)(SO4)] exhibit well-defined preedge transitions at 2479.4, 2479.9, 2478.4, and 2477.7 eV, respectively, despite having no direct metal-sulfur bond, while the XAS preedge of [Zn(itao)(SO4)] is featureless. The sulfur K-edge XAS of [Cu(itao)(SO4)] but not of [Cu(Me6tren)(SO4)] uniquely exhibits a weak transition at 2472.1 eV, an extraordinary 8.7 eV below the first inflection of the rising K-edge. Preedge transitions also appear in the sulfur K-edge XAS of crystalline [M(II)(SO4)(H2O)] (M = Fe, Co, Ni, and Cu, but not Zn) and in sulfates of higher-valent early transition metals. Ground-state density functional theory (DFT) and time-dependent DFT (TDDFT) calculations show that charge transfer from coordinated sulfate to paramagnetic late transition metals produces spin polarization that differentially mixes the spin-up (α) and spin-d...
JBIC Journal of Biological Inorganic Chemistry, 2016
The linear nickel-nitrosyl complex [Ni(NO)(L3)] supported by a highly hindered tridentate nitroge... more The linear nickel-nitrosyl complex [Ni(NO)(L3)] supported by a highly hindered tridentate nitrogen-based ligand, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (denoted as L3), was prepared by the reaction of the potassium salt of the ligand with the nickel-nitrosyl precursor [Ni(NO)(Br)(PPh 3 ) 2 ]. The obtained nitrosyl complexes as well as the corresponding chlorido complexes [Ni(NO)(Cl)(PPh 3 ) 2 ] and [Ni(Cl)(L3)] were characterized by X-ray crystallography and different spectroscopic methods including IR/far-IR, UV-Vis, NMR, and multi-edge X-ray absorption spectroscopy at the Ni K-, Ni L-, Cl K-, and P K-edges. For comparative electronic structure analysis we also performed DFT calculations to further elucidate the electronic structure of [Ni(NO)(L3)]. These results provide the nickel oxidation state and the character of the Ni-NO bond. The complex [Ni(NO)(L3)] is best described as [Ni (II) (NO (-) )(L3)], and the spectroscopic results indicate that the phosphane complexes have a similar [Ni (II) (NO (-) )(X)(PPh 3 ) 2 ] ground state.
Dalton transactions (Cambridge, England : 2003), Jan 11, 2016
Potential energy surface mapping was completed for the entire catalytic cycle of palladium-cataly... more Potential energy surface mapping was completed for the entire catalytic cycle of palladium-catalysed cyanoesterification onto norbornene (NBE) using density functional theory calculations. We found that after the oxidative addition step of the reagent methyl cyanoformate, the reaction proceeds through an insertion of olefin into a Pd(II)-COOMe bond first. Subsequently, reductive elimination occurs by transferring the cyanide group from the Pd center to NBE. This rearrangement is triggered by the rotation of the ester group into a π-interaction with the Pd(II) centre. The regioselectivity of olefin insertion is controlled by ionic and covalent interactions in the precursor π-complex formation step. Importantly, all of the intermediates and transition states along the exo pathway were found to be more stable than the corresponding structures of the endo pathway without any sign of crossing over between the two surfaces via isomerization. The rate-determining step is the reductive elim...
The journal of physical chemistry. A, Jan 20, 2015
X-ray absorption spectroscopy is a unique experimental technique that can provide ground state el... more X-ray absorption spectroscopy is a unique experimental technique that can provide ground state electronic structure information about transition metal complexes with unoccupied d-manifold. The quantitative treatments of pre-edge and rising-edge features have already been developed for the sulfur- and chlorine-ligand K-edge excitations. The complementarity of using multiple core excitation edges from hard, tender, and soft X-ray energy regions has been defined for the first paper of this series. The given study provides compelling evidence for the transferability of the empirical transition dipole integral from ligand K-edge to metal L-edge and back to ligand K-edge in the tender X-ray energy range. The case study was performed for a series of homoleptic chloropalladium compounds at the chlorine K- and palladium L-edges. We propose the method described here to be generally applicable for other core level excitations, where complementarity of ground state electronic structural informa...
The α-ketocarboxylatocopper(II) complex [{Cu(L1)}{O2CC(O)CH(CH3)2}] can be spontaneously converte... more The α-ketocarboxylatocopper(II) complex [{Cu(L1)}{O2CC(O)CH(CH3)2}] can be spontaneously converted into the binuclear oxalatocopper(II) complex [{Cu(L1)}2(μ-C2O4)] upon exposure to O2/CO2 gas. (13)C-labeling experiments revealed that oxalate ions partially incorporated (13)CO2 molecules. Furthermore, the bicarbonatocopper(I) complex (NEt4)[Cu(L1){O2C(OH)}] in an Ar atmosphere and the α-ketocarboxylatocopper(I) complex Na[Cu(L1){O2CC(O)CH(CH3)2}] in an O2 atmosphere were also transformed spontaneously into the oxalato complex [{Cu(L1)}2(μ-C2O4)].
One-electron-oxidized Ni(III)-phenoxide complexes with salen-type ligands, [Ni(salen)py2](2+) ([1... more One-electron-oxidized Ni(III)-phenoxide complexes with salen-type ligands, [Ni(salen)py2](2+) ([1(en)-py](2+)) and [Ni(1,2-salcn)py2](2+) ([1(cn)-py](2+)), with a five-membered chelate dinitrogen backbone and [Ni(salpn)py2](2+) ([2(pn)-py](2+)), with a six-membered chelate backbone, have been characterized with a combination of experimental and theoretical methods. The five-membered chelate complexes [1(en)-py](2+) and [1(cn)-py](2+) were assigned as Ni(III)-phenoxyl radical species, while the six-membered chelate complex [2(pn)-py](2+) was concluded to be a Ni(II)-bis(phenoxyl radical) species with metal-centered reduction in the course of the one-electron oxidation of the Ni(III)-phenoxide complex [2(pn)-py](+). Thus, the oxidation state of the one-electron-oxidized Ni(III) salen-type complexes depends on the chelate ring size of the dinitrogen backbone.
In this work, we demonstrate the potential of multi-edge X-ray absorption near-edge structure (XA... more In this work, we demonstrate the potential of multi-edge X-ray absorption near-edge structure (XANES) analysis in completely defining the ground state electronic structure of a prototypical biomimetic complex of the [2Fe]-subcluster of the catalytic H-cluster of FeFe-hydrogenase. The spectral features at the ionization thresholds for Fe, S, C, and O 1s (K-edge) and Fe 2p (L-edge) core electrons were considered simultaneously to obtain the atomic compositions of the unoccupied frontier molecular orbitals. A systematic error analysis was carried out at the most informative S K-edge for spectra collected by multiple detection methods, at various data collection temperatures, and different sample preparation protocols. As expected for the difference in bonding between bridging and terminal Fe-S(thiolate) coordination, the Fe-S bond is more covalent in the [2Fe]-biomimetic complex with formally iron(I) centers (36 ± 2% S character per Fe-S bond) than in the previously described [2Fe-2S] clusters (25 ± 3% S character per Fe-S bond) with formally iron(III) centers. An electron hole-based analysis of the pre-edge features at Fe K-, Fe L-, and S K-edges experimentally defines the composition of the first three frontier unoccupied molecular orbitals to contain 4% Fe 4p, 44% Fe 3d, and 24% S 3p contributions per electron hole, respectively. The complementary CO ligand contribution thus can be defined as 28% per electron hole. These experimental orbital covalency values are important in rationalizing redox properties, electrophilicity of the metals, or nucleophilicity of the ligands, and critically evaluating the absolute accuracy of electronic structure calculations.
Tris(pyrazolyl)hydroborate ligands have been utilized in the fields of inorganic and coordination... more Tris(pyrazolyl)hydroborate ligands have been utilized in the fields of inorganic and coordination chemistry due to the ease of introduction of steric and electronic substitutions at the pyrazole rings. The development and use of the tris(pyrazolyl)hydroborate ligand, called a `scorpionate', were pioneered by the late Professor Swiatoslaw Trofimenko. He developed a second generation for his ligand system by the introduction of 3-tert-butyl and 3-phenyl substituents and this new ligand system accounted for many remarkable developments in inorganic and coordination chemistry in stabilizing monomeric species while maintaining an open coordination site. Bismuth is remarkably harmless among the toxic heavy metal p-block elements and is now becoming popular as a replacement for highly toxic metal elements, such as lead. Two bismuth(III) complexes of the anionic sulfur-containing tripod tris(3-tert-butyl-2-sulfanylidene-1H-imidazol-1-yl)hydroborate ligand were prepared. By recrystalliza...
Tris(pyrazolyl)borate (scorpionate) ligands can be considered as the most prolific ligands in con... more Tris(pyrazolyl)borate (scorpionate) ligands can be considered as the most prolific ligands in contemporary coordination chemistry due to the availability of various steric and electronic substituents at the pyrazolyl rings that allow fine-tuning of the open-coordination site for metal centres. The thallium(I) complexes of anionic tridentate-chelating scorpionate ligands, namely [tris(3-mesityl-5-methyl-1H-pyrazol-1-yl-κN(2))hydroborato]thallium(I) monohydrate, [Tl(C39H46BN6)]·H2O, (I), and [bis(3-mesityl-5-methyl-1H-pyrazol-1-yl-κN(2))(5-mesityl-3-methyl-1H-pyrazol-1-yl-κN(2))hydroborato]thallium(I), [Tl(C39H46BN6)], (II), show a {Tl(I)N3} coordination, with average Tl(I)-N bond lengths of 2.53 and 2.55 Å in (I) and (II), respectively. The overall Tl(I) coordination geometry is distorted trigonal pyramidal, with the average N-Tl(I)-N angle being approximately 73° for both. The dihedral angle between the planes of the pyrazolyl and benzene rings of the mesityl group is 82° in (I), wh...
Sulfur K-edge X-ray absorption spectroscopy (XAS) spectra of the monodentate sulfate complexes [M... more Sulfur K-edge X-ray absorption spectroscopy (XAS) spectra of the monodentate sulfate complexes [M(II)(itao)(SO4)(H2O)0,1] (M = Co, Ni, Cu) and [Cu(Me6tren)(SO4)] exhibit well-defined preedge transitions at 2479.4, 2479.9, 2478.4, and 2477.7 eV, respectively, despite having no direct metal-sulfur bond, while the XAS preedge of [Zn(itao)(SO4)] is featureless. The sulfur K-edge XAS of [Cu(itao)(SO4)] but not of [Cu(Me6tren)(SO4)] uniquely exhibits a weak transition at 2472.1 eV, an extraordinary 8.7 eV below the first inflection of the rising K-edge. Preedge transitions also appear in the sulfur K-edge XAS of crystalline [M(II)(SO4)(H2O)] (M = Fe, Co, Ni, and Cu, but not Zn) and in sulfates of higher-valent early transition metals. Ground-state density functional theory (DFT) and time-dependent DFT (TDDFT) calculations show that charge transfer from coordinated sulfate to paramagnetic late transition metals produces spin polarization that differentially mixes the spin-up (α) and spin-d...
JBIC Journal of Biological Inorganic Chemistry, 2016
The linear nickel-nitrosyl complex [Ni(NO)(L3)] supported by a highly hindered tridentate nitroge... more The linear nickel-nitrosyl complex [Ni(NO)(L3)] supported by a highly hindered tridentate nitrogen-based ligand, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (denoted as L3), was prepared by the reaction of the potassium salt of the ligand with the nickel-nitrosyl precursor [Ni(NO)(Br)(PPh 3 ) 2 ]. The obtained nitrosyl complexes as well as the corresponding chlorido complexes [Ni(NO)(Cl)(PPh 3 ) 2 ] and [Ni(Cl)(L3)] were characterized by X-ray crystallography and different spectroscopic methods including IR/far-IR, UV-Vis, NMR, and multi-edge X-ray absorption spectroscopy at the Ni K-, Ni L-, Cl K-, and P K-edges. For comparative electronic structure analysis we also performed DFT calculations to further elucidate the electronic structure of [Ni(NO)(L3)]. These results provide the nickel oxidation state and the character of the Ni-NO bond. The complex [Ni(NO)(L3)] is best described as [Ni (II) (NO (-) )(L3)], and the spectroscopic results indicate that the phosphane complexes have a similar [Ni (II) (NO (-) )(X)(PPh 3 ) 2 ] ground state.
Dalton transactions (Cambridge, England : 2003), Jan 11, 2016
Potential energy surface mapping was completed for the entire catalytic cycle of palladium-cataly... more Potential energy surface mapping was completed for the entire catalytic cycle of palladium-catalysed cyanoesterification onto norbornene (NBE) using density functional theory calculations. We found that after the oxidative addition step of the reagent methyl cyanoformate, the reaction proceeds through an insertion of olefin into a Pd(II)-COOMe bond first. Subsequently, reductive elimination occurs by transferring the cyanide group from the Pd center to NBE. This rearrangement is triggered by the rotation of the ester group into a π-interaction with the Pd(II) centre. The regioselectivity of olefin insertion is controlled by ionic and covalent interactions in the precursor π-complex formation step. Importantly, all of the intermediates and transition states along the exo pathway were found to be more stable than the corresponding structures of the endo pathway without any sign of crossing over between the two surfaces via isomerization. The rate-determining step is the reductive elim...
The journal of physical chemistry. A, Jan 20, 2015
X-ray absorption spectroscopy is a unique experimental technique that can provide ground state el... more X-ray absorption spectroscopy is a unique experimental technique that can provide ground state electronic structure information about transition metal complexes with unoccupied d-manifold. The quantitative treatments of pre-edge and rising-edge features have already been developed for the sulfur- and chlorine-ligand K-edge excitations. The complementarity of using multiple core excitation edges from hard, tender, and soft X-ray energy regions has been defined for the first paper of this series. The given study provides compelling evidence for the transferability of the empirical transition dipole integral from ligand K-edge to metal L-edge and back to ligand K-edge in the tender X-ray energy range. The case study was performed for a series of homoleptic chloropalladium compounds at the chlorine K- and palladium L-edges. We propose the method described here to be generally applicable for other core level excitations, where complementarity of ground state electronic structural informa...
The α-ketocarboxylatocopper(II) complex [{Cu(L1)}{O2CC(O)CH(CH3)2}] can be spontaneously converte... more The α-ketocarboxylatocopper(II) complex [{Cu(L1)}{O2CC(O)CH(CH3)2}] can be spontaneously converted into the binuclear oxalatocopper(II) complex [{Cu(L1)}2(μ-C2O4)] upon exposure to O2/CO2 gas. (13)C-labeling experiments revealed that oxalate ions partially incorporated (13)CO2 molecules. Furthermore, the bicarbonatocopper(I) complex (NEt4)[Cu(L1){O2C(OH)}] in an Ar atmosphere and the α-ketocarboxylatocopper(I) complex Na[Cu(L1){O2CC(O)CH(CH3)2}] in an O2 atmosphere were also transformed spontaneously into the oxalato complex [{Cu(L1)}2(μ-C2O4)].
One-electron-oxidized Ni(III)-phenoxide complexes with salen-type ligands, [Ni(salen)py2](2+) ([1... more One-electron-oxidized Ni(III)-phenoxide complexes with salen-type ligands, [Ni(salen)py2](2+) ([1(en)-py](2+)) and [Ni(1,2-salcn)py2](2+) ([1(cn)-py](2+)), with a five-membered chelate dinitrogen backbone and [Ni(salpn)py2](2+) ([2(pn)-py](2+)), with a six-membered chelate backbone, have been characterized with a combination of experimental and theoretical methods. The five-membered chelate complexes [1(en)-py](2+) and [1(cn)-py](2+) were assigned as Ni(III)-phenoxyl radical species, while the six-membered chelate complex [2(pn)-py](2+) was concluded to be a Ni(II)-bis(phenoxyl radical) species with metal-centered reduction in the course of the one-electron oxidation of the Ni(III)-phenoxide complex [2(pn)-py](+). Thus, the oxidation state of the one-electron-oxidized Ni(III) salen-type complexes depends on the chelate ring size of the dinitrogen backbone.
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Papers by Robert Szilagyi