Characterization of Dimeric and Tetrameric μ‐Hydroxide Ytterbium(III) Binaphtholate Complexes

Wooten, Alfred J.; Salvi, Luca; Carroll, Patrick J.; Walsh, Patrick J.

doi:10.1002/adsc.200600600

Cited by 18 publications

(16 citation statements)

References 30 publications

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“…The 1 H and 13 C{ 1 H} NMR spectra of ( S )-1-La , ( S )-1-Pr , and ( S )-1-Eu were recorded in THF- d 8 and were similar to reported spectra for the [Li 3 (THF) n ][(BINOLate) 3 RE(THF)] (RE = La ( ( S )-2-La ), Pr ( ( S )-2-Pr ), Eu ( ( S )-2-Eu )) complexes. − ,, As expected, ( S )-1-La is diamagnetic, with resonances ranging from 7.78 to −1.01 ppm, while ( S )-1-Eu and ( S )-1-Pr exhibit paramagnetically shifted and broadened resonances ranging from 18.78 to −7.98 ppm and 13.86 to −6.33 ppm, respectively (spectra are provided as Supporting Information). The resonances for the zinc-bound ethyl groups of ( S )-1-RE are diastereotopic due to the chiral environment of the BINOLate ligands.…”

Section: Results and Discussionsupporting

confidence: 74%

“…We have recently shown that the primary determinants in the ability of Shibasaki’s complexes [M 3 (THF) n ][(BINOLate) 3 RE] to bind substrate analogues and/or Lewis basic ligands at the lanthanide cation are dependent on the size of the main group metal cation and its ability to form π-arene type noncovalent interactions with the BINOLate ligands . When the main-group metal is lithium, binding of substrate analogues to the rare-earth cation occurs readily and can be observed both in the solid state by X-ray crystallography and in solution by NMR spectroscopy.…”

Section: Results and Discussionmentioning

confidence: 99%

“…Two routes to synthesize zinc derivatives of REMB complexes were envisioned. The first was a salt-metathesis reaction with REX 3 (X = halide, pseudohalide), and the second was protonolysis using RE[N(SiMe 3 ) 2 ] 3 . − , Our first approach to incorporate zinc into the REMB framework involved combining a THF solution of anhydrous RE(OTf) 3 and ( S )-BINOL with excess Et 2 Zn. We expected that diethylzinc would react rapidly with the acidic BINOL to generate BINOLate(ZnEt) 2 in situ.…”

Section: Results and Discussionmentioning

confidence: 99%

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Synthesis and Catalytic Activity of Heterobimetallic Rare Earth–Zinc Ethyl BINOLate Analogues of Shibasaki’s Catalysts

et al. 2013

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Shibasaki's heterobimetallic complexes [M 3 (THF) n ] -[(BINOLate) 3 RE] (BINOLate = 1,1′-bi-2-naphtholate; RE = Ln III , Y III ; M = Li + , Na + , K + ) are among the most general and highly enantioselective catalysts known. Their structures, however, have been limited to group I metals in the peripheral sites. We envisioned that the utility of this class of catalysts could be broadened by the synthesis of new members. Herein, we report the first synthesis of Shibasaki-type catalysts that incorporate divalent Zn 2+ ions in the peripheral positions. The compounds (EtZn) 3 (THF) 2 (BINOLate) 3 -RE(THF) (RE = La III , Pr III , Eu III ) are easily prepared from the corresponding tris(silylamide) precursors RE[N(SiMe 3 ) 2 ] 3 , 3 equiv of (S)-BINOL, and 3 equiv of ZnEt 2 in 68−86% crystalline yields. The compounds are isostructural with known [Li 3 (THF) 4 ]-[(BINOLate) 3 RE(THF)] catalysts. We have demonstrated that the (EtZn) 3 (THF) 2 (BINOLate) 3 RE(THF) complexes are catalytically active in the enantioselective addition of diethylzinc to benzaldehyde with moderate enantioselectivities.

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Section: Results and Discussionsupporting

confidence: 74%

Section: Results and Discussionmentioning

confidence: 99%

Section: Results and Discussionmentioning

confidence: 99%

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Synthesis and Catalytic Activity of Heterobimetallic Rare Earth–Zinc Ethyl BINOLate Analogues of Shibasaki’s Catalysts

et al. 2013

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“…19 On standing, solutions of K 3 (THF) 6 (BINOLate) 3 Yb formed Xray quality needles. Surprisingly, an unprecedented helical polymer, [K 3 (THF) 2 (BINOLate) 3 Yb] n , was observed ( Figure 5).…”

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confidence: 99%

Impact of Na− and K−C π-Interactions on the Structure and Binding of M₃(sol)_n(BINOLate)₃Ln Catalysts

2007

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Shibasaki's heterobimetallic complexes M 3 (THF) n (BINOLate) 3 Ln [M = Li, Na, K, Ln = lanthanide (III)] are among the most successful asymmetric Lewis acid catalysts. Why does M 3 (THF) n (BINOLate) 3 Ln readily bind substrates when M = Li but not when M = Na or K? Structural studies herein indicate Na-and K-C cation-π interactions and alkali metal radius may be more important than even lanthanide radius. Also reported is a novel polymeric [K 3 (THF) 2 (BINOLate) 3 Yb] n structure that provides the first evidence of interactions between M 3 (THF) n (BINOLate) 3 Ln complexes.Shibasaki's M 3 (THF) n (BINOLate) 3 Ln complexes (Figure 1) are among the most effective asymmetric Lewis acid catalysts known, exhibiting high enantioselectivities over a broad range of reactions. 1-3 Understanding how these heterobimetallic catalysts work, however, has proven challenging. 4-9 In particular, seemingly subtle alterations in the catalyst composition result in dramatic changes in selectivity. For example, in the nitro aldol reaction with M 3 (THF) n (BINOLate) 3 Ln, 94% ee was obtained when M = Li and 2% ee when M = Na. In contrast, the asymmetric Michael reaction gave 92% ee when M = Na and 29% ee for M = Li. 10 The first step in unraveling the factors that are responsible for these striking differences is understanding the impact of the alkali metal on substrate binding to the lanthanide centers.Reported herein are solution and solid state studies of M 3 (sol) n (BINOLate) 3 Ln complexes that illuminate dramatic differences in Ln binding ability when M = Li vs. Na and K. Also disclosed is an unprecedented helical polymer, [K 3 We recently demonstrated that DMF reversibly binds to paramagnetic lanthanides in Li 3 (THF) n (BINOLate) 3 Ln (Ln = Eu, Pr), exhibiting > 2 ppm lanthanide induced shift (LIS) in the formyl C-H resonance in the 1 H NMR spectrum. 8 Salvadori, on the other hand, reported 7 that Na 3 (THF) 6 (BINOLate) 3 Yb does not bind water in solution or the solid state, which was attributed to the small ionic radius of Yb (La = 1.17, Eu = 1.09, Yb = 1.01). This dichotomy prompted us to examine binding of the lithium analog, Li 3 (THF) n (BINOLate) 3 Yb, with DMF. In the presence of Li 3 (THF) n (BINOLate) 3 Yb, the formyl C-H shifted over 4 ppm, consistent with binding to Yb. Furthermore, crystallization of Li 3 (THF) n (BINOLate) 3 Yb from pyridine yielded 7-coordinate Li 3 (py) 5 (BINOLate) 3 Yb•py, the ORTEP of which is shown in Figure 2. We next examined binding of DMF to Na 3 (THF) 6 (BINOLate) 3 Ln [Ln = Yb, Eu] 11-13 and K 3 (THF) 6 (BINOLate) 3 Yb 14,7 under the same conditions. Surprisingly, no LISs (>0.1 ppm) were observed, indicating that binding to the lanthanide in the Na and K analogs is much less favorable than in the Li series.

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“…We found that the commercially available, inexpensive RE(NO 3 ) 3 ·(H 2 O) x salts could be used in the synthesis of RETMGHB up to a 25 g scale in combination with 3 equiv of ( S )-BINOL and 6 equiv of tetramethyl guanidine (TMG, Figure ). Remarkably, tetramethyl guanidinium cation-containing (TMGH + ) complexes [(TMGH) 3 ][RE III (( S )-BINOLate) 3 ] (RETMGHB) withstand hydrolysis, which we attribute to the strong directionality of H-bonding between TMGH + and BINOLate oxygens. This limits structural reorganization needed for water coordination, a key requirement for hydrolysis.…”

Section: Understanding and Expansion Of The Catalysis Of Shibasaki’s ...mentioning

confidence: 98%

Expanding the Rare-Earth Metal BINOLate Catalytic Multitool beyond Enantioselective Organic Synthesis

et al. 2021

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Metrics & MoreArticle Recommendations CONSPECTUS: Shibasaki's rare earth alkali metal BINOLate (REMB) framework has provided chemists with a general catalyst platform to access a range of enantioenriched small molecules from the single, commercially available pro-ligand (R)-or (S)-BINOL. A defining feature of these heterobimetallic frameworks is the high level of catalyst tunability, achieved through the simple modulation of the central rare-earth cation and peripheral alkali metal cations. While this family of multifunctional catalysts displays impressive generality and catalytic capability, detailed mechanistic understanding of these complex, multimetallic systems was lacking prior to our investigations. This backdrop served as initial inspiration for our investigations of this privileged class of complexes over the past decade, which have led to new and exciting advances in catalysis and beyond.In this Account, we describe our investigations using Shibasaki's framework focusing on the central metal-ion, the BINOLate ligands, and the secondary sphere cations. Our studies began with an investigation into the Lewis acidity of the complexes, where we demonstrated that Lewis bases readily coordinate to REMB frameworks when lithium occupies the secondary coordination sphere. This observation was contrasted by the complexes containing sodium or potassium in the secondary coordination sphere, as the rare earth cation is evidently less accessible for substrate binding. Our efforts in understanding the ligand exchange of the complexes enabled the discovery that associative processes dominate the mechanism of ligand exchange and LA/LA (Lewis acid/Lewis acid) and LA/BB (Lewis acid/Brønsted base) catalysis by the REMB frameworks.Replacing metal cations in the secondary coordination sphere with the N,N,N′,N′-tetramethylguanidinium cation delivered an effective precatalyst that is air and water stable over the course of 6 months.To expand the reactivity of the REMB, we investigated the ability of U IV cations to occupy the primary coordination sphere and ZnEt + and Cu(DBU) + cations to occupy the secondary coordination sphere. Synthesizing the REMB complexes using the thiol congener monothioBINOL provided an unusual anionic REMB framework, driven by the oxophilicity of the lithium cations. Using the REMB as a platform for investigating the Ce III /Ce IV redox couple, we demonstrated that, while oxidative cerium functionalization is observed in the case of lithium containing REMBs, salt elimination is observed in the sodium, potassium, and cesium containing REMBs. Furthermore, we found that while the rate of heterogeneous electron transfer for Ce III was k s (Cs I ) > k s (K I ) > k s (Na I ) > k s (Li I ), the rates of reaction with the oxidant trityl chloride trended in the opposite order with k obs (Li I ) ≫ k obs (Na I ) > k obs (K I ) > k obs (Cs I ). We attribute this to the ability to form inner-sphere complexes with the oxidant, rather than differences in redox potential or reorganization energies. Applying our knowle...

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Characterization of Dimeric and Tetrameric μ‐Hydroxide Ytterbium(III) Binaphtholate Complexes

Cited by 18 publications

References 30 publications

Synthesis and Catalytic Activity of Heterobimetallic Rare Earth–Zinc Ethyl BINOLate Analogues of Shibasaki’s Catalysts

Synthesis and Catalytic Activity of Heterobimetallic Rare Earth–Zinc Ethyl BINOLate Analogues of Shibasaki’s Catalysts

Impact of Na− and K−C π-Interactions on the Structure and Binding of M₃(sol)_n(BINOLate)₃Ln Catalysts

Expanding the Rare-Earth Metal BINOLate Catalytic Multitool beyond Enantioselective Organic Synthesis

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Characterization of Dimeric and Tetrameric μ‐Hydroxide Ytterbium(III) Binaphtholate Complexes

Cited by 18 publications

References 30 publications

Synthesis and Catalytic Activity of Heterobimetallic Rare Earth–Zinc Ethyl BINOLate Analogues of Shibasaki’s Catalysts

Synthesis and Catalytic Activity of Heterobimetallic Rare Earth–Zinc Ethyl BINOLate Analogues of Shibasaki’s Catalysts

Impact of Na− and K−C π-Interactions on the Structure and Binding of M3(sol)n(BINOLate)3Ln Catalysts

Expanding the Rare-Earth Metal BINOLate Catalytic Multitool beyond Enantioselective Organic Synthesis

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Impact of Na− and K−C π-Interactions on the Structure and Binding of M₃(sol)_n(BINOLate)₃Ln Catalysts