The Nature of Secondary Interactions at Electrophilic Metal Sites of Molecular and Silica-Supported Organolutetium Complexes from Solid-State NMR Spectroscopy

Abstract

Lu[CH(SiMe3)2]3 reacts with [SiO2-700] to give [(≡SiO)Lu[CH(SiMe3)2]2] and CH2(SiMe3)2. [(≡SiO)Lu[CH(SiMe3)2]2] is characterized by solid-state NMR and EXAFS spectroscopy, which show that secondary Lu···C and Lu···O interactions, involving a γ-CH3 and a siloxane bridge, are present. From X-ray crystallographic analysis, the molecular analogues Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 0-2) also have secondary Lu···C interactions. The (1)H NMR spectrum of Lu[CH(SiMe3)2]3 shows that the -SiMe3 groups are equivalent to -125 °C and inequivalent below that temperature, ΔG(⧧)(Tc = 148 K) = 7.1 kcal mol(-1). Both -SiMe3 groups in Lu[CH(SiMe3)2]3 have (1)JCH = 117 ± 1 Hz at -140 °C. The solid-state (13)C CPMAS NMR spectrum at 20 °C shows three chemically inequivalent resonances in the area ratio of 4:1:1 (12:3:3); the J-resolved spectra for each resonance give (1)JCH = 117 ± 2 Hz. The (29)Si CPMAS NMR spectrum shows two chemically inequivalent resonances with different values of chemical shift anisotropy. Similar observations are obtained for Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 1 and 2). The spectroscopic data point to short Lu···Cγ contacts corresponding to 3c-2e Lu···Cγ-Siβ interactions, which are supported by DFT calculations. Calculated natural bond orbital (NBO) charges show that Cγ carries a negative charge, while Lu, Hγ, and Siβ carry positive charges; as the number of O-based ligands increases so does the positive charge at Lu, which in turns shortens the Lu···Cγ distance. The change in NBO charges and the resulting changes in the spectroscopic and crystallographic properties show how ligands and surface-support sites rearrange to accommodate these changes, consistent with Pauling's electroneutrality concept.

Silica-Supported Organolanthanum Catalysts for C–O Bond Cleavage in Epoxides

“…19 The oxophilic lanthanide centers also form strong bonds to oxygen in metal oxides, which is a useful property for attaching these sites onto supports in heterogeneous catalysts. [20][21][22][23][24][25][26][27][28][29] Homoleptic compounds in particular, such as La(CH2Ph)3THF3 or La{CH(SiMe3)2}3, [30][31] have potential in surface organometallic chemistry (SOMC). 26,32 For example, lanthanum benzyl grafted onto silica is a catalyst for styrene and ethylene polymerization and alkyne dimerization.…”

“…[20][21][22][23][24][25][26][27][28][29] Homoleptic compounds in particular, such as La(CH2Ph)3THF3 or La{CH(SiMe3)2}3, [30][31] have potential in surface organometallic chemistry (SOMC). 26,32 For example, lanthanum benzyl grafted onto silica is a catalyst for styrene and ethylene polymerization and alkyne dimerization. 32 Unfortunately, the molecular precursors are limited by their typically difficult syntheses, tendency to tightly coordinate donors, such as THF or Cl as LiCl adducts, and thermal lability.…”

Efficient alkene hydrosilation with bis(8-quinolyl)phosphine (NPN) nickel catalysts. The dominant role of silyl-over hydrido-nickel catalytic intermediates

“…This insertion step yields an alkyl ligand with the silyl group in the b position, and results in a relatively short Ni/Si contact (2.66Å) indicative of a b-agostic C(b)-Si(g) bond, as has been observed for numerous alkyl complexes. [64][65][66][67][68][69] This silyl-substituted alkyl intermediate reacts with PhSiH 3 , to yield either the silyl or the hydride complex. As expected, the energetically more favourable transition state corresponds to a transfer of H (TSB2) and leads directly to the hydrosilation product Ph(C 5 H 11 )SiH 2 with regeneration of the silyl catalyst (cycle B of Scheme 3).…”

NMR spectroscopic study of the adduct formation and reactivity of homoleptic rare earth amides with alkali metal benzyl compounds, and the crystal structures of [Li(TMEDA)2][Nd{N(SiMe3)2}3(CH2Ph)] and [{Li(TMP)}2{Li(Ph)}]2

“…[1,3] Rare earth amides and organometallics, on the other hand, are not widely used throughout chemistry with their use mainly restricted to synthetic f-block chemistry. [8] Simple homoleptic starting materials, such as [Ln(N″)3] [9] and [Ln{CH(SiMe3)2}3], [10][11][12] and the THF solvated [Ln(CH2Ph)3(THF)n] (n = 2 [13,14] or 3 [13][14][15][16]) and [Ln(CH2SiMe3)3(THF)n] (n = 2 [17,18] or 3 [17,19]), are well known, although they are very air-and moisture-sensitive and can be non-trivial to synthesise.…”