Stanislav Ignatov - Academia.edu (original) (raw)
Uploads
Papers by Stanislav Ignatov
Journal of the Chemical Society, Dalton Transactions, 2001
ABSTRACT
Chemical communications (Cambridge, England), Jan 21, 2004
Coupling of silanes with the imido group of (Ar'N)2Mo(PMe3)3 gives either the silanimine dime... more Coupling of silanes with the imido group of (Ar'N)2Mo(PMe3)3 gives either the silanimine dimer (ArN-SiHCl)2 or Si-H agostic silylamido complexes which do not exhibit the commonly expected correlation between the nature of the substituents on silicon, the degree of Si-H addition and the value of the Si-H coupling constant.
Chemical Communications, 2004
ABSTRACT
Journal of the American Chemical Society, 2003
A series of hydridosilyl complexes of tantalum, Cp(ArN)Ta(PMe3)(H)(SiClnR3-n) (n = 0-3), was prep... more A series of hydridosilyl complexes of tantalum, Cp(ArN)Ta(PMe3)(H)(SiClnR3-n) (n = 0-3), was prepared and studied by 29Si NMR, X-ray diffraction, and DFT calculations. An unprecedented increase of the J(Si-H) coupling constant between the hydride and silyl ligands from 14 Hz for n = 0 to 50 Hz n = 3 was observed, which however, according to DFT calculations, does not correspond to stronger bonding interaction between silicon and hydride ligands, with the strongest interaction being for n = 1.
Inorganic Chemistry, 2009
Reactions of bis(imido) compounds (RN) 2 Mo(PMe 3 ) n (n = 2, R = t Bu; n = 3, R =2,6-dimethylphe... more Reactions of bis(imido) compounds (RN) 2 Mo(PMe 3 ) n (n = 2, R = t Bu; n = 3, R =2,6-dimethylphenyl (Ar 0 ) and 2,6-diisopropylphenyl (Ar)) and (RN) 2 W(PMe 3 ) 3 (R = 2,6-dimethylphenyl and 2,6-diisopropylphenyl) with silanes afford four types of products: the β-agostic silylamido compounds (RN)(η 3 -RN-SiR 0 2 -H 3 3 3 )MCl(PMe 3 ) 2 (M = Mo and W), mono(imides) (RN)MCl 2 (PMe 3 ) 3 (M = Mo and W), silyl hydride bis(imido) derivative (ArN) 2 W(PMe 3 )(H)(SiMeCl 2 ), and Si-Cl 3 3 3 W bridged product (ArN)(η 2 -ArN-SiHMeCl-Cl 3 3 3 )WCl(PMe 3 ) 2 . Reactions of molybdenum compounds (RN) 2 Mo(PMe 3 ) m (m = 2 or 3) with mono-and dichlorosilanes HSiCl n R 0 3-n (R 0 = Me, Ph; n = 1,2) afford mainly the agostic compounds (RN)(η 3 -RN-SiR 0 2 -H 3 3 3 )MoCl(PMe 3 ) 2 , accompanied by small amounts of mono(imido) derivatives (RN) MoCl 2 (PMe 3 ) 3 . In contrast, the latter compounds are the only transition metal products in reactions with HSiCl 3 , the silicon co-product being the silanimine dimer (RNSiHCl) 2 . The reaction of (ArN) 2 W(PMe 3 ) 3 with HSiCl 2 Me under continuous removal of PMe 3 affords the silyl hydride species (ArN) 2 W(PMe 3 )(SiMeCl 2 )H, characterized by NMR and X-ray diffraction. This product is stable in the absence of phosphine, but addition of catalytic amounts of PMe 3 causes a fast rearrangement into the Si-Cl 3 3 3 W bridged product (ArN)(η 2 -ArN-SiHMeCl-Cl 3 3 3 )WCl(PMe 3 ) 2 . The mechanism of silane addition to complexes (RN) 2 Mo(PMe 3 ) n has been elucidated by means of density functional theory calculations of model complexes (MeN) 2 Mo(PMe 3 ) n (n = 1-3). Complex (MeN) 2 Mo(PMe 3 ) 2 is found to be the most stable form. It undergoes facile silane-to-imido addition reactions that afford silylamido hydride complexes stabilized by additional Si 3 3 3 H interactions. The ease of this addition increases from HSiMe 2 Cl to HSiCl 3 , consistent with experimental observations. The most stable final products of silane addition are the agostic complexes (MeN)(η 3 -MeN-SiR 2 -H 3 3 3 ) MoCl(PMe 3 ) 2 (R 2 = Me 2 , MeCl, Cl 2 ) and Cl-bridged silylamido complexes (MeN)(η 2 -MeN-SiRH-Cl 3 3 3 )MoCl(PMe 3 ) 2 (R = Me or Cl). In the case of HSiMeCl 2 addition the former is the most stable, but for HSiCl 3 addition the latter is the preferred product. In all cases, the isomeric silyl hydride species (MeN) 2 Mo(PMe 3 )(H)(SiClR 2 ) are less stable by about 6 kcal mol -1 . Silane additions to the imido ligand of the tris(phosphine) (MeN) 2 Mo(PMe 3 ) 3 afford octahedral silylamido hydride derivatives. The different isomers of these addition products are destabilized relative to (MeN) 2 Mo(PMe 3 ) 3 only by 7-24 kcal mol -1 (for the HSiMe 2 Cl additions), but since the starting tris(phosphine) is 14.8 kcal mol -1 less stable than (MeN) 2 Mo(PMe 3 ) 2 , silane addition to the latter is a more preferred pathway. A double phosphine dissociation pathway via the species (MeN) 2 Mo-(PMe 3 ) was ruled out because this complex is by 24.7 kcal mol -1 less stable than (MeN) 2 Mo(PMe 3 ) 2 . † Dedicated to Prof. Dietmar Seyferth on the occasion of his 80th birthday.
Dalton Transactions, 2014
The bis(imido) complexes ((t)BuN[double bond, length as m-dash])2Mo(PMe3)(L) (L = PMe3, C2H4) rea... more The bis(imido) complexes ((t)BuN[double bond, length as m-dash])2Mo(PMe3)(L) (L = PMe3, C2H4) react with up to three equivalents of silane PhSiH3 to give the imido-bridged disilyl silyl Mo(vi) complex ((t)BuN){μ-(t)BuN(SiHPh)2}Mo(H)(SiH2Ph)(PMe3)2 (3) studied by NMR, IR and X-ray diffraction. NMR data supported by DFT calculations show that complex 3 is an unusual example of a silyl hydride of Mo(VI), without significant SiH interaction. Mechanistic NMR studies revealed that silane addition proceeds in a stepwise manner via a series of Si-H∙∙∙M agostic and silanimine complexes whose structures were further elucidated by DFT calculations.
Chemistry - A European Journal, 2008
Chemistry - A European Journal, 2004
The titanocene silyl hydride complexes [Ti(Cp)2(PMe3)(H)(SiR3)] [SiR3=SiMePhCl (6), SiPh2Cl (7), ... more The titanocene silyl hydride complexes [Ti(Cp)2(PMe3)(H)(SiR3)] [SiR3=SiMePhCl (6), SiPh2Cl (7), SiMeCl2 (8), SiCl3 (9)] were prepared by HSiR3 addition to [Ti(Cp)2(PMe3)2] and were studied by NMR and IR spectroscopy, X-ray diffraction (for 6, 8, and 9), and DFT calculations. Spectroscopic and structural data established that these complexes exhibit nonclassical Ti-H-Si-Cl interligand hypervalent interactions. In particular, the observation of silicon-hydride coupling constants J(Si,H) in 6-9 in the range 22-40 Hz, the signs of which we found to be negative for 8 and 9, is conclusive evidence of the presence of a direct Si-H bond. The analogous reaction of [Ti(Cp)2(PMe3)2] with HSi(OEt)3 does not afford the expected classical silyl hydride complex [Ti(Cp)2(PMe3)(H)[Si(OEt)3]], and instead NMR-silent titanium (apparently TiIII) complex(es) and the silane redistribution product Si(OEt)4 are formed. The structural data and DFT calculations for the compounds [Ti(Cp)2(PMe3)(H)(SiR3)] show that the strength of interligand hypervalent interactions in the chlorosilyl complexes decreases as the number of chloro groups on silicon increases. However, in the absence of an Si-bound electron-withdrawing group trans to the Si-H moiety, a silane sigma complex is formed, characterized by a long Ti-Si bond of 2.658 A and short Si-H contact of 1.840 A in the model complex [Ti(Cp)2(PMe3)(H)(SiMe3)]. Both the silane sigma complexes and silyl hydride complexes with interligand hypervalent interactions exhibit bond paths between the silicon and hydride atoms in Atoms in Molecules (AIM) studies. To date a classical titanocene phosphane silyl hydride complex without any Si-H interaction has not been observed, and therefore titanocene silyl hydrides are, depending on the nature of the R groups on Si, either silane sigma complexes or compounds with an interligand hypervalent interaction.
![Research paper thumbnail of Unusual structure, fluxionality, and reaction mechanism of carbonyl hydrosilylation by silyl hydride complex [(ArN=)Mo(H)(SiH2Ph) (PMe3)3]](https://attachments.academia-assets.com/45024495/thumbnails/1.jpg)
](
J. Phys. Chem. C 2011, 115, 9081–9089, 2011
The low-temperature interaction between methyl hydroperoxide CH3OOH (MHP) and the hexagonal wate... more The low-temperature interaction between methyl hydroperoxide CH3OOH (MHP) and the hexagonal water ice surface was studied using the DFT (BLYP/6-31++G(d,p)) calculations. The structures, energies, and some thermodynamic properties of the molecular complexes between MHP and the water clusters (H2O)48 (H2O)56, (H2O)72 representing the surface fragments of the (0001), , and crystallographic planes of the hexagonal oxygen lattice of the water ice Ih with proton ordering corresponding to Pisani’s P-ordered model were calculated. The various modes of coordination and intrusion were studied using the extended set (up to 192 points for each plane) of the structures optimized at the semiempirical (PM3) level. The validity of the surface models was verified by the stability of the results obtained in the cluster series (H2O)n, (n=48, 72, 192, 216) at semiempirical level as well as by DFT calculations of selected structures at the BLYP/6-311++G(2d,2p) level.
Journal of the Chemical Society, Dalton Transactions, 2001
ABSTRACT
Chemical communications (Cambridge, England), Jan 21, 2004
Coupling of silanes with the imido group of (Ar'N)2Mo(PMe3)3 gives either the silanimine dime... more Coupling of silanes with the imido group of (Ar'N)2Mo(PMe3)3 gives either the silanimine dimer (ArN-SiHCl)2 or Si-H agostic silylamido complexes which do not exhibit the commonly expected correlation between the nature of the substituents on silicon, the degree of Si-H addition and the value of the Si-H coupling constant.
Chemical Communications, 2004
ABSTRACT
Journal of the American Chemical Society, 2003
A series of hydridosilyl complexes of tantalum, Cp(ArN)Ta(PMe3)(H)(SiClnR3-n) (n = 0-3), was prep... more A series of hydridosilyl complexes of tantalum, Cp(ArN)Ta(PMe3)(H)(SiClnR3-n) (n = 0-3), was prepared and studied by 29Si NMR, X-ray diffraction, and DFT calculations. An unprecedented increase of the J(Si-H) coupling constant between the hydride and silyl ligands from 14 Hz for n = 0 to 50 Hz n = 3 was observed, which however, according to DFT calculations, does not correspond to stronger bonding interaction between silicon and hydride ligands, with the strongest interaction being for n = 1.
Inorganic Chemistry, 2009
Reactions of bis(imido) compounds (RN) 2 Mo(PMe 3 ) n (n = 2, R = t Bu; n = 3, R =2,6-dimethylphe... more Reactions of bis(imido) compounds (RN) 2 Mo(PMe 3 ) n (n = 2, R = t Bu; n = 3, R =2,6-dimethylphenyl (Ar 0 ) and 2,6-diisopropylphenyl (Ar)) and (RN) 2 W(PMe 3 ) 3 (R = 2,6-dimethylphenyl and 2,6-diisopropylphenyl) with silanes afford four types of products: the β-agostic silylamido compounds (RN)(η 3 -RN-SiR 0 2 -H 3 3 3 )MCl(PMe 3 ) 2 (M = Mo and W), mono(imides) (RN)MCl 2 (PMe 3 ) 3 (M = Mo and W), silyl hydride bis(imido) derivative (ArN) 2 W(PMe 3 )(H)(SiMeCl 2 ), and Si-Cl 3 3 3 W bridged product (ArN)(η 2 -ArN-SiHMeCl-Cl 3 3 3 )WCl(PMe 3 ) 2 . Reactions of molybdenum compounds (RN) 2 Mo(PMe 3 ) m (m = 2 or 3) with mono-and dichlorosilanes HSiCl n R 0 3-n (R 0 = Me, Ph; n = 1,2) afford mainly the agostic compounds (RN)(η 3 -RN-SiR 0 2 -H 3 3 3 )MoCl(PMe 3 ) 2 , accompanied by small amounts of mono(imido) derivatives (RN) MoCl 2 (PMe 3 ) 3 . In contrast, the latter compounds are the only transition metal products in reactions with HSiCl 3 , the silicon co-product being the silanimine dimer (RNSiHCl) 2 . The reaction of (ArN) 2 W(PMe 3 ) 3 with HSiCl 2 Me under continuous removal of PMe 3 affords the silyl hydride species (ArN) 2 W(PMe 3 )(SiMeCl 2 )H, characterized by NMR and X-ray diffraction. This product is stable in the absence of phosphine, but addition of catalytic amounts of PMe 3 causes a fast rearrangement into the Si-Cl 3 3 3 W bridged product (ArN)(η 2 -ArN-SiHMeCl-Cl 3 3 3 )WCl(PMe 3 ) 2 . The mechanism of silane addition to complexes (RN) 2 Mo(PMe 3 ) n has been elucidated by means of density functional theory calculations of model complexes (MeN) 2 Mo(PMe 3 ) n (n = 1-3). Complex (MeN) 2 Mo(PMe 3 ) 2 is found to be the most stable form. It undergoes facile silane-to-imido addition reactions that afford silylamido hydride complexes stabilized by additional Si 3 3 3 H interactions. The ease of this addition increases from HSiMe 2 Cl to HSiCl 3 , consistent with experimental observations. The most stable final products of silane addition are the agostic complexes (MeN)(η 3 -MeN-SiR 2 -H 3 3 3 ) MoCl(PMe 3 ) 2 (R 2 = Me 2 , MeCl, Cl 2 ) and Cl-bridged silylamido complexes (MeN)(η 2 -MeN-SiRH-Cl 3 3 3 )MoCl(PMe 3 ) 2 (R = Me or Cl). In the case of HSiMeCl 2 addition the former is the most stable, but for HSiCl 3 addition the latter is the preferred product. In all cases, the isomeric silyl hydride species (MeN) 2 Mo(PMe 3 )(H)(SiClR 2 ) are less stable by about 6 kcal mol -1 . Silane additions to the imido ligand of the tris(phosphine) (MeN) 2 Mo(PMe 3 ) 3 afford octahedral silylamido hydride derivatives. The different isomers of these addition products are destabilized relative to (MeN) 2 Mo(PMe 3 ) 3 only by 7-24 kcal mol -1 (for the HSiMe 2 Cl additions), but since the starting tris(phosphine) is 14.8 kcal mol -1 less stable than (MeN) 2 Mo(PMe 3 ) 2 , silane addition to the latter is a more preferred pathway. A double phosphine dissociation pathway via the species (MeN) 2 Mo-(PMe 3 ) was ruled out because this complex is by 24.7 kcal mol -1 less stable than (MeN) 2 Mo(PMe 3 ) 2 . † Dedicated to Prof. Dietmar Seyferth on the occasion of his 80th birthday.
Dalton Transactions, 2014
The bis(imido) complexes ((t)BuN[double bond, length as m-dash])2Mo(PMe3)(L) (L = PMe3, C2H4) rea... more The bis(imido) complexes ((t)BuN[double bond, length as m-dash])2Mo(PMe3)(L) (L = PMe3, C2H4) react with up to three equivalents of silane PhSiH3 to give the imido-bridged disilyl silyl Mo(vi) complex ((t)BuN){μ-(t)BuN(SiHPh)2}Mo(H)(SiH2Ph)(PMe3)2 (3) studied by NMR, IR and X-ray diffraction. NMR data supported by DFT calculations show that complex 3 is an unusual example of a silyl hydride of Mo(VI), without significant SiH interaction. Mechanistic NMR studies revealed that silane addition proceeds in a stepwise manner via a series of Si-H∙∙∙M agostic and silanimine complexes whose structures were further elucidated by DFT calculations.
Chemistry - A European Journal, 2008
Chemistry - A European Journal, 2004
The titanocene silyl hydride complexes [Ti(Cp)2(PMe3)(H)(SiR3)] [SiR3=SiMePhCl (6), SiPh2Cl (7), ... more The titanocene silyl hydride complexes [Ti(Cp)2(PMe3)(H)(SiR3)] [SiR3=SiMePhCl (6), SiPh2Cl (7), SiMeCl2 (8), SiCl3 (9)] were prepared by HSiR3 addition to [Ti(Cp)2(PMe3)2] and were studied by NMR and IR spectroscopy, X-ray diffraction (for 6, 8, and 9), and DFT calculations. Spectroscopic and structural data established that these complexes exhibit nonclassical Ti-H-Si-Cl interligand hypervalent interactions. In particular, the observation of silicon-hydride coupling constants J(Si,H) in 6-9 in the range 22-40 Hz, the signs of which we found to be negative for 8 and 9, is conclusive evidence of the presence of a direct Si-H bond. The analogous reaction of [Ti(Cp)2(PMe3)2] with HSi(OEt)3 does not afford the expected classical silyl hydride complex [Ti(Cp)2(PMe3)(H)[Si(OEt)3]], and instead NMR-silent titanium (apparently TiIII) complex(es) and the silane redistribution product Si(OEt)4 are formed. The structural data and DFT calculations for the compounds [Ti(Cp)2(PMe3)(H)(SiR3)] show that the strength of interligand hypervalent interactions in the chlorosilyl complexes decreases as the number of chloro groups on silicon increases. However, in the absence of an Si-bound electron-withdrawing group trans to the Si-H moiety, a silane sigma complex is formed, characterized by a long Ti-Si bond of 2.658 A and short Si-H contact of 1.840 A in the model complex [Ti(Cp)2(PMe3)(H)(SiMe3)]. Both the silane sigma complexes and silyl hydride complexes with interligand hypervalent interactions exhibit bond paths between the silicon and hydride atoms in Atoms in Molecules (AIM) studies. To date a classical titanocene phosphane silyl hydride complex without any Si-H interaction has not been observed, and therefore titanocene silyl hydrides are, depending on the nature of the R groups on Si, either silane sigma complexes or compounds with an interligand hypervalent interaction.
J. Phys. Chem. C 2011, 115, 9081–9089, 2011
The low-temperature interaction between methyl hydroperoxide CH3OOH (MHP) and the hexagonal wate... more The low-temperature interaction between methyl hydroperoxide CH3OOH (MHP) and the hexagonal water ice surface was studied using the DFT (BLYP/6-31++G(d,p)) calculations. The structures, energies, and some thermodynamic properties of the molecular complexes between MHP and the water clusters (H2O)48 (H2O)56, (H2O)72 representing the surface fragments of the (0001), , and crystallographic planes of the hexagonal oxygen lattice of the water ice Ih with proton ordering corresponding to Pisani’s P-ordered model were calculated. The various modes of coordination and intrusion were studied using the extended set (up to 192 points for each plane) of the structures optimized at the semiempirical (PM3) level. The validity of the surface models was verified by the stability of the results obtained in the cluster series (H2O)n, (n=48, 72, 192, 216) at semiempirical level as well as by DFT calculations of selected structures at the BLYP/6-311++G(2d,2p) level.