A tris(alkyl)yttrium compound containing six β-agostic Si–H interactions

Yan, KaKing; Pawlikowski, Andrew V.; Ebert, Chris; Sadow, Aaron D.

doi:10.1039/b818630h

Cited by 30 publications

(42 citation statements)

References 29 publications

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“…The La … Si distances in the b-SiC agostic Cp*La{CH(SiMe 3 ) 2 } 2 of 3. 35(1) and 3.42(1) Å are longer than in 1a. 42 Additional structural evidence for a multicenter interaction between La and the C(SiHMe 2 ) 3 ligands comes from ÐLa-C-Si, which are ≤90° for the SiHMe 2 groups with close La … H and La … Si contacts.…”

Section: Resultsmentioning

confidence: 86%

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Homoleptic Trivalent Tris(alkyl) Rare Earth Compounds

et al. 2017

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Homoleptic tris(alkyl) rare earth complexes Ln{C(SiHMe)} (Ln = La, 1a; Ce, 1b; Pr, 1c; Nd, 1d) are synthesized in high yield from LnITHF and 3 equiv of KC(SiHMe). X-ray diffraction studies reveal 1a-d are isostructural, pseudo-C-symmetric molecules that contain two secondary Ln↼HSi interactions per alkyl ligand (six total). Spectroscopic assignments are supported by comparison with Ln{C(SiDMe)} and DFT calculations. The Ln↼HSi and terminal SiH exchange rapidly on the NMR time scale at room temperature, but the two motifs are resolved at low temperature. Variable-temperature NMR studies provide activation parameters for the exchange process in 1a (ΔH = 8.2(4) kcal·mol; ΔS = -1(2) cal·molK) and 1a-d (ΔH = 7.7(3) kcal·mol; ΔS = -4(2) cal·molK). Comparisons of lineshapes, rate constants (k/k), and slopes of ln(k/T) vs 1/T plots for 1a and 1a-d reveal that an inverse isotope effect dominates at low temperature. DFT calculations identify four low-energy intermediates containing five β-Si-H⇀Ln and one γ-C-H⇀Ln. The calculations also suggest the pathway for Ln↼HSi/SiH exchange involves rotation of a single C(SiHMe) ligand that is coordinated to the Ln center through the Ln-C bond and one secondary interaction. These robust organometallic compounds persist in solution and in the solid state up to 80 °C, providing potential for their use in a range of synthetic applications. For example, reactions of Ln{C(SiHMe)} and ancillary proligands, such as bis-1,1-(4,4-dimethyl-2-oxazolinyl)ethane (HMeC(Ox)) give {MeC(Ox)}Ln{C(SiHMe)}, and reactions with disilazanes provide solvent-free lanthanoid tris(disilazides).

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Section: Resultsmentioning

confidence: 86%

“…YCl 3 , however, reacts with KC(SiHMe 2 ) 3 to afford Y{C(SiHMe 2 ) 3 } 3 . 35 The identities of 1a-d are unambiguously established by single crystal X-ray diffraction studies (see below) and elemental analysis. The selectively isotopically-labeled compounds Ln{C(SiDMe 2 ) 3 } 3 (1a-d-d 9 ) are synthesized from KC(SiDMe 2 ) 3 .…”

Section: Resultsmentioning

confidence: 99%

Homoleptic Trivalent Tris(alkyl) Rare Earth Compounds

et al. 2017

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“…31 In addition, the reaction of Y{N(SiHMe 2 ) 2 } 3 THF 2 and ImMe 2 (1,3-dimethylimidazol-2-ylidene) gives a carbene-coordinated, THF-free compound that also shows Y↼H−Si close contacts. 32 All three alkyl ligands in Y{C(SiHMe 2 ) 3 } 3 contain two secondary interactions, as characterized by low-temperature NMR studies, 33 but a solution to X-ray diffraction data was not found. In addition to the unusual diagostic-like structure in 4a, it is also notable that the other ligand does not contain any other secondary interactions with the Yb center.…”

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confidence: 99%

Homoleptic Divalent Dialkyl Lanthanide-Catalyzed Cross-Dehydrocoupling of Silanes and Amines

2016

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The rare-earth bis(alkyl) compound Sm{C-(SiHMe 2 ) 3 } 2 THF 2 (1b) is prepared by the reaction of samarium(II) iodide and 2 equiv of KC(SiHMe 2 ) 3 . This synthesis is similar to that of previously reported Yb{C-(SiHMe 2 ) 3 } 2 THF 2 (1a), and compounds 1a,b are isostructural. Reactions of 1b and 1 or 2 equiv of B(C 6 F 5 ) 3 afford SmC(SiHMe 2 ) 3 HB(C 6 F 5 ) 3 THF 2 (2b) or Sm{HB-(C 6 F 5 ) 3 } 2 THF 2 (3b), respectively, and 1,3-disilacyclobutane {Me 2 Si-C(SiHMe 2 ) 2 } 2 as a byproduct. Bands from 2300 to 2400 cm −1 assigned to ν BH in the IR spectra and highly paramagnetically shifted signals in the 11 B NMR spectra of 2b and 3b provided evidence for Sm-coordinated HB(C 6 F 5 ) 3 . Compounds 1a,b react with the bulky N-heterocyclic carbene (NHC) 1,3-di-tert-butylimidazol-2-ylidene (ImtBu) to displace both THF ligands and give three-coordinate monoadducts Ln{C-(SiHMe 2 ) 3 } 2 ImtBu (Ln = Yb (4a), Sm (4b)). Complexes 4a,b catalyze cross-dehydrocoupling of organosilanes with primary and secondary amines at room temperature to give silazanes and H 2 , whereas 1a,b are not effective catalysts under these conditions. Second-order plots of ln{[Et 2 NH]/[Ph 2 SiH 2 ]} vs time for 4a-catalyzed dehydrocoupling are linear and indicate first-order dependences on silane and amine concentrations. However, changes in the experimental rate law with increased silane concentration or decreased amine concentration reveal inhibition by silane. In addition, excess ImtBu or THF inhibit the reaction rate. These data, along with the structures of 4a,b, suggest that the bulky carbene favors low coordination numbers, which is important for accessing the catalytically active species.

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“…This b-SiH strategy may also be applied to alkyls, and the ligand C(SiHMe 2 ) 3 supports trivalent yttrium and divalent ytterbium and samarium homoleptic alkyls containing secondary Ln(H-Si interactions. 15,16 Recently, we reported Ce{C(SiHMe 2 ) 3 } 3 as a precursor to a zwitterionic hydrosilylation catalyst. 17 New chemistry might be accessed with alkyl ligand variations that include both b-SiH and benzylic functionalities, and these groups could compete to enhance the homoleptic compounds' resistance to undesired ligand elimination pathways.…”

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confidence: 99%