Limits...
Open-shell lanthanide(II+) or -(III+) complexes bearing σ-silyl and silylene ligands: synthesis, structure, and bonding analysis.

Zitz R, Arp H, Hlina J, Walewska M, Marschner C, Szilvási T, Blom B, Baumgartner J - Inorg Chem (2015)

Bottom Line: Density functional theory calculations were carried out for complexes 2a-2d, 5, and 6 to elucidate the bonding situation between the Ln(II+) or Ln(III+) centers and Si.In particular, a decrease in the Mayer bond order (MBO) of the Ln-Si bond is observed in the series 2a-2d in moving from the lighter to the heavier lanthanides (Tm = 0.53, Ho = 0.62, Tb = 0.65, and Gd = 0.75), which might indicate decreasing covalency in the Ln-Si bond.In accordance with the long bond lengths observed experimentally in complexes 5 and 6, comparatively low MBOs were determined for both silylene complexes (5, 0.24; 6, 0.25) .

View Article: PubMed Central - PubMed

Affiliation: †Institut für Anorganische Chemie, Technische Universität Graz, Stremayrgasse 9, 8010 Graz, Austria.

ABSTRACT
Complexes featuring lanthanide (Ln)-Si bonds represent a highly neglected research area. Herein, we report a series of open-shell Ln(II+) and Ln(III+) complexes bearing σ-bonded silyl and base-stabilized N-heterocyclic silylene (NHSi) ligands. The reactions of the Ln(III+) complexes Cp3Ln (Ln = Tm, Ho, Tb, Gd; Cp = cyclopentadienide) with the 18-crown-6 (18-cr-6)-stabilized 1,4-oligosilanyl dianion [(18-cr-6)KSi(SiMe3)2SiMe2SiMe2Si(SiMe3)2K(18-cr-6)] (1) selectively afford the corresponding metallacyclopentasilane salts [Cp2Ln({Si(SiMe3)2SiMe2}2)](-)[K2(18-cr-6)2Cp](+) [Ln = Tm (2a), Ho (2b), Tb (2c), Gd (2d)]. Complexes 2a-2d represent the first examples of structurally characterized Tm, Ho, Tb, and Gd complexes featuring Ln-Si bonds. Strikingly, the analogous reaction of 1 with the lighter element analogue Cp3Ce affords the acyclic product [Cp3CeSi(SiMe3)2SiMe2SiMe2Si(SiMe3)2-Cp3Ce](2-)2[K(18-cr-6)](+) (3) as the first example of a complex featuring a Ce-Si bond. In an alternative synthetic approach, the aryloxy-functionalized benzamidinato NHSi ligand Si(OC6H4-2-tBu){(NtBu)2CPh} (4a) and the alkoxy analogue Si(OtBu){(NtBu)2CPh} (4b) were reacted with Cp*2Sm(OEt2), affording, by OEt2 elimination, the corresponding silylene complexes, both featuring Sm(II+) centers: Cp*2Sm ← :Si(O-C6H4-2-tBu){(NtBu)2CPh} (6) and Cp*2Sm ← :Si(OtBu){(NtBu)2CPh} (5). Complexes 5 and 6 are the first four-coordinate silylene complexes of any f-block element to date. All complexes were fully characterized by spectroscopic means and by single-crystal X-ray diffraction analysis. In the series 2a-2d, a linear correlation was observed between the Ln-Si bond lengths and the covalent radii of the corresponding Ln metals. Moreover, in complexes 5 and 6, notably long Sm-Si bonds are observed, in accordance with a donor-acceptor interaction between Si and Sm [5, 3.4396(15) Å; 6, 3.3142(18) Å]. Density functional theory calculations were carried out for complexes 2a-2d, 5, and 6 to elucidate the bonding situation between the Ln(II+) or Ln(III+) centers and Si. In particular, a decrease in the Mayer bond order (MBO) of the Ln-Si bond is observed in the series 2a-2d in moving from the lighter to the heavier lanthanides (Tm = 0.53, Ho = 0.62, Tb = 0.65, and Gd = 0.75), which might indicate decreasing covalency in the Ln-Si bond. In accordance with the long bond lengths observed experimentally in complexes 5 and 6, comparatively low MBOs were determined for both silylene complexes (5, 0.24; 6, 0.25) .

No MeSH data available.


HOMO (left) and HOMO–1 (right)of 2c calculated at the B3PW91/Basis1 level of theory(isovalue: 0.02). White, gray, blue, and teal refer to H, C, Tb, andSi atoms, respectively.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4389698&req=5

fig11: HOMO (left) and HOMO–1 (right)of 2c calculated at the B3PW91/Basis1 level of theory(isovalue: 0.02). White, gray, blue, and teal refer to H, C, Tb, andSi atoms, respectively.

Mentions: The analogous Gd complex, 2d, features a half-filledf shell (S = 7/2), and theGd–Si bond distances (3.025 and 3.030 Å) in the optimizedgeometry also show agreement with the experimentally characterizeddistances (3.018 and 3.038 Å, respectively). HOMO (−0.77eV) and HOMO–1 (−0.97 eV) (Figure 10) depict more covalent character than that in the case of 2a because HOMO–1 exhibits uniform extension betweenthe Gd and Si atoms. MBOs of Gd–Si bonds (0.73 and 0.75) arelarger than that of Tm–Si bonds (0.53), although NBO analysisstill suggests lone pairs on the Si atoms. For 2b and 2c, the calculated bond distances, bond orders, and charges(Table 3) are between the discussed theoreticalresults of 2a and 2d; therefore, the calculatedparameters follow the experimentally characterized series of bondlengths, providing further evidence of the partial covalent characterof the Ln–Si bonds as HOMO and HOMO–1 also suggest (Figures 9–11). The calculated data in the series of 2a–2d might also indicate, in agreement with the previously suggestedrelationship of bond lengths, some covalency in the bonding character(Figure 4).39


Open-shell lanthanide(II+) or -(III+) complexes bearing σ-silyl and silylene ligands: synthesis, structure, and bonding analysis.

Zitz R, Arp H, Hlina J, Walewska M, Marschner C, Szilvási T, Blom B, Baumgartner J - Inorg Chem (2015)

HOMO (left) and HOMO–1 (right)of 2c calculated at the B3PW91/Basis1 level of theory(isovalue: 0.02). White, gray, blue, and teal refer to H, C, Tb, andSi atoms, respectively.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4389698&req=5

fig11: HOMO (left) and HOMO–1 (right)of 2c calculated at the B3PW91/Basis1 level of theory(isovalue: 0.02). White, gray, blue, and teal refer to H, C, Tb, andSi atoms, respectively.
Mentions: The analogous Gd complex, 2d, features a half-filledf shell (S = 7/2), and theGd–Si bond distances (3.025 and 3.030 Å) in the optimizedgeometry also show agreement with the experimentally characterizeddistances (3.018 and 3.038 Å, respectively). HOMO (−0.77eV) and HOMO–1 (−0.97 eV) (Figure 10) depict more covalent character than that in the case of 2a because HOMO–1 exhibits uniform extension betweenthe Gd and Si atoms. MBOs of Gd–Si bonds (0.73 and 0.75) arelarger than that of Tm–Si bonds (0.53), although NBO analysisstill suggests lone pairs on the Si atoms. For 2b and 2c, the calculated bond distances, bond orders, and charges(Table 3) are between the discussed theoreticalresults of 2a and 2d; therefore, the calculatedparameters follow the experimentally characterized series of bondlengths, providing further evidence of the partial covalent characterof the Ln–Si bonds as HOMO and HOMO–1 also suggest (Figures 9–11). The calculated data in the series of 2a–2d might also indicate, in agreement with the previously suggestedrelationship of bond lengths, some covalency in the bonding character(Figure 4).39

Bottom Line: Density functional theory calculations were carried out for complexes 2a-2d, 5, and 6 to elucidate the bonding situation between the Ln(II+) or Ln(III+) centers and Si.In particular, a decrease in the Mayer bond order (MBO) of the Ln-Si bond is observed in the series 2a-2d in moving from the lighter to the heavier lanthanides (Tm = 0.53, Ho = 0.62, Tb = 0.65, and Gd = 0.75), which might indicate decreasing covalency in the Ln-Si bond.In accordance with the long bond lengths observed experimentally in complexes 5 and 6, comparatively low MBOs were determined for both silylene complexes (5, 0.24; 6, 0.25) .

View Article: PubMed Central - PubMed

Affiliation: †Institut für Anorganische Chemie, Technische Universität Graz, Stremayrgasse 9, 8010 Graz, Austria.

ABSTRACT
Complexes featuring lanthanide (Ln)-Si bonds represent a highly neglected research area. Herein, we report a series of open-shell Ln(II+) and Ln(III+) complexes bearing σ-bonded silyl and base-stabilized N-heterocyclic silylene (NHSi) ligands. The reactions of the Ln(III+) complexes Cp3Ln (Ln = Tm, Ho, Tb, Gd; Cp = cyclopentadienide) with the 18-crown-6 (18-cr-6)-stabilized 1,4-oligosilanyl dianion [(18-cr-6)KSi(SiMe3)2SiMe2SiMe2Si(SiMe3)2K(18-cr-6)] (1) selectively afford the corresponding metallacyclopentasilane salts [Cp2Ln({Si(SiMe3)2SiMe2}2)](-)[K2(18-cr-6)2Cp](+) [Ln = Tm (2a), Ho (2b), Tb (2c), Gd (2d)]. Complexes 2a-2d represent the first examples of structurally characterized Tm, Ho, Tb, and Gd complexes featuring Ln-Si bonds. Strikingly, the analogous reaction of 1 with the lighter element analogue Cp3Ce affords the acyclic product [Cp3CeSi(SiMe3)2SiMe2SiMe2Si(SiMe3)2-Cp3Ce](2-)2[K(18-cr-6)](+) (3) as the first example of a complex featuring a Ce-Si bond. In an alternative synthetic approach, the aryloxy-functionalized benzamidinato NHSi ligand Si(OC6H4-2-tBu){(NtBu)2CPh} (4a) and the alkoxy analogue Si(OtBu){(NtBu)2CPh} (4b) were reacted with Cp*2Sm(OEt2), affording, by OEt2 elimination, the corresponding silylene complexes, both featuring Sm(II+) centers: Cp*2Sm ← :Si(O-C6H4-2-tBu){(NtBu)2CPh} (6) and Cp*2Sm ← :Si(OtBu){(NtBu)2CPh} (5). Complexes 5 and 6 are the first four-coordinate silylene complexes of any f-block element to date. All complexes were fully characterized by spectroscopic means and by single-crystal X-ray diffraction analysis. In the series 2a-2d, a linear correlation was observed between the Ln-Si bond lengths and the covalent radii of the corresponding Ln metals. Moreover, in complexes 5 and 6, notably long Sm-Si bonds are observed, in accordance with a donor-acceptor interaction between Si and Sm [5, 3.4396(15) Å; 6, 3.3142(18) Å]. Density functional theory calculations were carried out for complexes 2a-2d, 5, and 6 to elucidate the bonding situation between the Ln(II+) or Ln(III+) centers and Si. In particular, a decrease in the Mayer bond order (MBO) of the Ln-Si bond is observed in the series 2a-2d in moving from the lighter to the heavier lanthanides (Tm = 0.53, Ho = 0.62, Tb = 0.65, and Gd = 0.75), which might indicate decreasing covalency in the Ln-Si bond. In accordance with the long bond lengths observed experimentally in complexes 5 and 6, comparatively low MBOs were determined for both silylene complexes (5, 0.24; 6, 0.25) .

No MeSH data available.