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1. On the Nature of the Bonding in Metal-Silane sigma-Complexes

Author

McGrady, G. Sean, Sirsch, Peter, Chatterton, Nicholas P., Ostermann, Andreas, Gatti, Carlo, Altmannshofer, Sandra, Herz, Verena, Eickerling, Georg, and Scherer, Wolfgang

Subjects
Physics - Chemical Physics
Abstract

The nature of metal silane sigma-bond interaction has been investigated in several key systems by a range of experimental and computational techniques. The structure of [Cp'Mn(CO)2(eta2-HSiHPh2)] 1 has been determined by single crystal neutron diffraction, and the geometry at the Si atom is shown to approximate to a trigonal bipyramid. This complex is similar to [Cp'Mn(CO)2(eta2-HSiFPh2)] 2, whose structure and bonding characteristics have recently been determined by charge density studies based on high-resolution X-ray and neutron diffraction data. The geometry at the Si atom in these sigma-bond complexes is compared with that in other systems containing hypercoordinate silicon. The Mn-H distances for 1 and 2 in solution have been estimated using NMR T1 relaxation measurements, giving a value of 1.56(3) AA in each case, in excellent agreement with the distances deduced from neutron diffraction. DFT calculations have been employed to explore the bonding in the Mn-H-Si unit in 1 and 2 and in the related system [Cp'Mn(CO)2(eta2-HSiCl3)] 3. These studies support the idea that the oxidative addition of a silane ligand to a transition metal center may be described as an asymmetric process in which the Mn-H bond is formed at an early stage, while both the establishment of the Mn-Si bond and also the activation of the eta2-coordinated Si-H moiety are controlled by the extent of Mn-> sigma*(X-Si-H) back-donation, which increases with increasing electronwithdrawing character of the X substituent trans to the metal-coordinated Si-H bond. This delocalized molecular orbital (MO) approach is complemented and supported by combined experimental and theoretical charge density studies including the source function S(r,Omega)., Comment: 39 pages, 7 figures, 4 tables

Published
2008

2. Valence Shell Charge Concentrations at Pentacoordinate d0 Transition Metal Centers: Non-VSEPR Structures of Me2NbCl3 and Me3NbCl2

Author

McGrady, G. Sean, Haaland, Arne, Verne, Hans Peter, Volden, Hans Vidar, Downs, Anthony J., Shorokhov, Dmitry, Scherer, Wolfgang, and Eickerling, Georg

Subjects
Physics - Chemical Physics
Abstract

The molecular structures of the monomeric, pentacoordinated ethylchloroniobium(V) compounds Me3NbCl2 and Me2NbCl3 have been determined by gas electron diffraction (GED)and Density Functional Theory (DFT) calculations, and, for Me3NbCl2, by single crystal X-ray diffraction. Each of the molecules is found to have a heavy-atom skeleton in the form of a trigonal bipyramid (TBP) with Cl atoms in the axial positions, in accord with their vibrational spectra. The TBP is somewhat distorted in the case of Me2NbCl3 with the two axial Nb-Cl bonds bent away from the equatorial, slightly shorter Nb-Cl bond. In the case of Me3NbCl2, moreover, the X-ray model suggests structural distortions away from the idealized C3h geometry, in line with the results of quantum chemical calculations. The electronic structures of Me2NbCl3 and Me3NbCl2 have been explored by rigorous analysis of both the wavefunction and the topology of the electron density, employing DFT calculations. Hence the structures of these compounds are shown to reflect repulsion between the Nb-C and Nb-Cl bonding electron density and charge concentrations induced by the methyl ligands in the valence shell of the Nb atom and arising mainly from use of Nb(4d) functions in the Nb-C bonds., Comment: 32 pages, 8 figures, submitted to Chem. Eur. J

Published
2005

13. Molecular structures of two metal tetrakis(tetrahydroborates), Zr(BH (sub)4) (sub)4 and U(BH (sub)4) (sub)4: equilibrium conformations and barriers to internal rotation of the triply bridging BH (sub)4 groups

Author

Haaland, Arne, Shorokhov, Dmitry J., Tutukin, Andrey V., Volden, Hans Vidar, Swang, Ole, McGrady, G. Sean, Kaltsoyannis, Nikolas, Downs, Anthony J., Tang, Christina Y., and Turner, John F. C.

Subjects
Chemistry, Inorganic -- Research, Borates, Chemical equilibrium -- Research, Molecular rotation -- Research, Zirconium, Hydrogen, Uranium, Boron, Density functionals -- Usage, Diffraction -- Analysis, Chemistry
Abstract

Research has been conducted on Zr(BH (sub)4) (sub)4 and U(BH (sub)4) (sub)4. The study of compounds' molecular structures carried out via the use of density functional theory calculations and gas electron diffraction is presented.

Published
2002

14. Electron delocalization in acyclic and n-heterocyclic carbenes and their complexes: A combined experimental and theoretical charge-density study

Author

Tafipolsky, Maxim, Ofele, Karl, Scherer, Wolfgang, Artus, Georg, Pedersen, Bjorn, Herrmann, Wolfgang, and McGrady, G. Sean

Subjects
Charge density waves -- Analysis, Heterocyclic compounds -- Structure, Aliphatic compounds -- Structure, Chemistry
Abstract

The study explains a combination of experimental and theoretical charge-density studies on free and metal-coordinated N-heterocyclic carbenes. An analysis of the topology of the total density and its laplacian obtained through the results are explained.

Published
2002

15. On the nature and incidence of beta-agostic interactions in ethyl derivatives of early transition metals: ethyltitanium trichloride and related compounds

Author

Haaland, Arne, Scherer, Wolfgang, Ruud, Kenneth, McGrady, G. Sean, Downs, Anthony J., and Swang, Ole

Subjects
Complex compounds -- Research, Transition metal compounds -- Research, Chemical reactions -- Research, Chemical bonds -- Research, Density functionals -- Usage, Chemistry
Abstract

Agostic interactions of ethyltitanium trichloride, with valence count of 8, and its complex, with valence count of 12, were studied since these types of interactions involved the donation of a C-H bonding electron pair to the metal atom M. The analyses of interactions were undertaken through density functional theory. Calculations established that agostic stabilization was generated from delocalization of the M-C bond and not from the C-H->M electron donation. The bonding between the ethyl group and the metal atom was produced by one electron pair and one orbital of the metal.

Published
1998

16. Molecular structures of methyldifluoroarsine, CH3AsF2, and dimethylfluoroarsine, (CH3)2AsF, in the gas phase as determined by electron diffraction and ab initio calculations

Author

Downs, Anthony J., Greene, Tim M., McGrady, G. Sean, Townson, Neil, Brain, Paul T., Pulham, Colin R., Rankin, David W.H., Robertson, Heather E., Smart, Bruce A., and Alberts, Ian L.

Subjects
Molecular structure -- Research, Fluorine compounds -- Research, Chemistry
Abstract

The molecular structures of gaseous CH3AsF2 and (CH3)2AsF were determined by electron-diffraction experiments and ab initio computations. Findings indicated that both As-C and As-F bond lengths are shortened by increasing numbers of fluorine atoms but that the angles CAsF and FAsF are almost invariant in the series (CH3)3As, (CH3)2AsF, CH3AsF2, and AsF3.

Published
1996

17. Molecular structure of dimethyldichlorotitanium(IV) by gas-phase electron diffraction, IR and NMR spectroscopies, and density functional theory calculations. Unexpected distortion from tetrahedral coordination geometry

Author

McGrady, G. Sean, Downs, Anthony J., McKean, Donald C., Haaland, Arne, Scherer, Wolfgang, Verne, Hans-Peter, and Volden, Hans Vidar

Subjects
Nuclear magnetic resonance spectroscopy -- Usage, Infrared spectroscopy -- Usage, Density functionals -- Usage, Titanium compounds -- Research, Chemistry
Abstract

The gas-phase electron diffraction (GED) and density functional theory (DFT) calculations analyze the molecular structure of dimethyldichlrotitanium(IV) ((CH3)2TiCl2). The bond distances for Ti-C and Ti-Cl are 205.8(4) pm and 219.6(3) pm, respectively. The valence angles for Cl-Ti-C, Cl-Ti-C, and C-Ti-C are 117.3(3) degrees,108.9(2) degrees, and 102.8(9) degrees, respectively show that more electronegative substituents traverse larger valence angles at Ti. The GED structure, DFT calculations, or the infrared and NMR spectra fail to explain the agostic interactions.

Published
1996

18. [(Triphos)Ni(eta(super 2)-BH4)]: An unusual nickel(I) borohydride complex

Author

Kandiah, Mathivathai, McGrady, G. Sean, Decken, Andreas, and Sirsch, Peter

Subjects
Nickel compounds -- Chemical properties, Chemistry
Abstract

Reduction of [(triphos)NiCI2] with an excess of NaBH4 in THF produces the paramagnetic Ni(I) complex [(triphos)Ni(eta(super 2)-BH4)]. X-ray crystallography shows [(triphos)NiCI2] to be a square-planar Ni(II) species in which the phosphine ligand is bidentate, whereas [(triphos)Ni(eta(super 2)-BH4)] has pseudotetrahedral geometry at the Ni(I) center, with a tridentate phosphine and the borohydride ligand occupying a single coordination site.

Published
2005

19. Insights into metal borohydride and aluminohydride bonding: x-ray and neutron diffraction structures and a DFT and charge density study of [Na(15-crown-5)][E[H.sub.4]] (E = B, Al)

Author

Sirsch, Peter, Clark, Natascha L. N., Onu, Lenua, Burchell, Richard P. L., Decken, Andreas, McGrady, G. Sean, Daoud-Aladine, Aziz, and Gutmann, Matthias J.

Subjects
Sodium compounds -- Chemical properties, Sodium compounds -- Structure, Density functionals -- Usage, Electrostatic interactions -- Analysis, Hydrogen bonding -- Analysis, Neutrons -- Diffraction, Neutrons -- Usage, X-rays -- Diffraction, X-rays -- Usage, Chemistry
Published
2010

20. Facile cycling of Ti-doped LiAl[H.sub.4] for high performance hydrogen storage

Author

Xiangfeng Liu, McGrady, G. Sean, Langmi, Henreitta W., and Jensen, Craig M.

Subjects
Aluminum -- Chemical properties, Aluminum -- Electric properties, Lithium compounds -- Chemical properties, Lithium compounds -- Electric properties, Semiconductor doping -- Analysis, Solvation -- Analysis, Titanium -- Chemical properties, Chemistry
Abstract

LiH and Ti-doped Al has reacted quantitatively with [H.sub.2] in [Me.sub.2]O solution to form LiAl[H.sub.4] under mild conditions. The solvent is vented along with excess [H.sub.2] on completion, leaving dry Ti-doped LiAl[H.sub.4] and releasing [H.sub.2] with excellent kinetics.

Published
2009

21. Nature of the bonding in metal-silane ?-complexes

Author

McGrady, G. Sean, Sirsch, Peter, Chatterton, Nicholas P., Ostermann, Andreas, Gatti, Carlo, Altmannshofer, Sandra, Herz, Verena, Eickerling, Georg, and Scherer, Wolfgang

Subjects
Silane -- Properties, Silane -- Structure, Silane -- Research, Chemical bonds -- Research, X-rays -- Diffraction, X-rays -- Usage, Chemistry
Published
2009

28. Nature of the bonding in metal-silane σ-complexes

Author

McGrady, G. Sean, Sirsch, Peter, Chatterton, Nicholas P., Ostermann, Andreas, Gatti, Carlo Gatti, Altmannshofer, Sandra, Herz, Verena, Eickerling,Georg, and Scherer, Wolfgang

Subjects
Models, Molecular, Silicon, Neutron diffraction, chemistry.chemical_element, Source Function, 010402 general chemistry, 01 natural sciences, Inorganic Chemistry, chemistry.chemical_compound, Coordination Complexes, Atom, ddc:530, Physical and Theoretical Chemistry, Bonding, Metal-silane complexes, Molecular Structure, 010405 organic chemistry, Spin–lattice relaxation, Charge density, Silanes, Silane, 0104 chemical sciences, Crystallography, Trigonal bipyramidal molecular geometry, Neutron Diffraction, X-ray charge Density, chemistry, Single crystal
Abstract

The nature of metal silane σ-bond interaction has been investigated in several key systems by a range of experimental and computational techniques. The structure of [Cp′Mn(CO)2(η2-HSiHPh2)] 1 has been determined by single crystal neutron diffraction, and the geometry at the Si atom is shown to approximate a trigonal bipyramid; salient bond distances and angles are Mn−H(1) 1.575(14), Si−H(1) 1.806(14), Si−H(2) 1.501(13) Å, and H(1)−Si−H(2) 148.5(8)°. This complex is similar to [Cp′Mn(CO)2(η2-HSiFPh2)] 2, whose structure and bonding characteristics have recently been determined by charge density studies based on high-resolution X-ray and neutron diffraction data. The geometry at the Si atom in these σ-bond complexes is compared with that in other systems containing hypercoordinate silicon. The Mn−H distances for 1 and 2 in solution have been estimated using NMR T1 relaxation measurements, giving a value of 1.56(3) Å in each case, in excellent agreement with the distances deduced from neutron diffraction. Density functional theory calculations have been employed to explore the bonding in the Mn−H−Si unit in 1 and 2 and in the related system [Cp′Mn(CO)2(η2-HSiCl3)] 3. These studies support the idea that the oxidative addition of a silane ligand to a transition metal center may be described as an asymmetric process in which the Mn−H bond is formed at an early stage, while both the establishment of the Mn−Si bond and also the activation of the η2-coordinated Si−H moiety are controlled by the extent of Mn → σ*(X−Si−H) back-donation, which increases with increasing electron-withdrawing character of the X substituent trans to the metal-coordinated Si−H bond. This delocalized molecular orbital (MO) approach is complemented and supported by combined experimental and theoretical charge density studies: the source function S(r,Ω), which provides a measure of the relative importance of each atom’s contribution to the density at a specific reference point r, clearly shows that all three atoms of the Mn(η2-SiH) moiety contribute to a very similar extent to the density at the Mn−Si bond critical point, in pleasing agreement with the MO model. Hence, we advance a consistent and unifying concept which accounts for the degree of Si−H activation in these silane σ-bond complexes.

Published
2009

50. Nature of the Bonding in Metal-Silane σ-Complexes

Author

McGrady, G. Sean, primary, Sirsch, Peter, additional, Chatterton, Nicholas P., additional, Ostermann, Andreas, additional, Gatti, Carlo, additional, Altmannshofer, Sandra, additional, Herz, Verena, additional, Eickerling, Georg, additional, and Scherer, Wolfgang, additional

Published
2009
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