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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.


Plot of Si–M(M = Tm, Ho, Tb, Gd) versus covalent radii.62 Si–M is the average bond length in 2a–2d.
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fig4: Plot of Si–M(M = Tm, Ho, Tb, Gd) versus covalent radii.62 Si–M is the average bond length in 2a–2d.

Mentions: Because 2a–2d and 3 are the first structurally characterized complexesbearing a Ce–Si, Tm–Si, Ho–Si, Tb–Si,or Gd–Si bond, no data for comparison are available. The moststriking features of these molecular structures are the values forthe lanthanide–silyl bond lengths, which are in good agreementwith the sum of the covalent radii (Figure 4).62 The distances between Ln and Si decreaseincrementally with decreasing metal size, as expected. This indicatesthat the Ln–Si bond is rather polar but might possess at leastsome covalent character.63 The bond angleSi–Ln–Si varies only slightly from 94.15° in 2a (Tm) to 94.68° in 2b (Ho) to 95.47°in 2c (Tb) to 94.84° in 2d (Gd).


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)

Plot of Si–M(M = Tm, Ho, Tb, Gd) versus covalent radii.62 Si–M is the average bond length in 2a–2d.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: Plot of Si–M(M = Tm, Ho, Tb, Gd) versus covalent radii.62 Si–M is the average bond length in 2a–2d.
Mentions: Because 2a–2d and 3 are the first structurally characterized complexesbearing a Ce–Si, Tm–Si, Ho–Si, Tb–Si,or Gd–Si bond, no data for comparison are available. The moststriking features of these molecular structures are the values forthe lanthanide–silyl bond lengths, which are in good agreementwith the sum of the covalent radii (Figure 4).62 The distances between Ln and Si decreaseincrementally with decreasing metal size, as expected. This indicatesthat the Ln–Si bond is rather polar but might possess at leastsome covalent character.63 The bond angleSi–Ln–Si varies only slightly from 94.15° in 2a (Tm) to 94.68° in 2b (Ho) to 95.47°in 2c (Tb) to 94.84° in 2d (Gd).

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.