Enantioselective Hydroboration of Ketones Catalyzed by Rare-Earth-Metal Complexes Supported with Phenoxy-Functionalized TsDPEN Ligands

Abstract

Six novel chiral rare-earth-metal complexes bearing the phenoxy-functionalized TsDPEN ligandwere synthesized successfully and well characterized. The solid-state structures of four tetranuclear rare-earth-metal complexes [RE 2 L 1 3 ] 2 (RE = Nd (1), Sm (2), Eu (3), Gd ( 4)) and the dual-core yttrium complex Y 2 L 1 3 (5) were determined by X-ray diffraction, respectively. The structure of lanthanum complex 6 was speculated by the 1 H DOSY spectroscopy in THF-d 8 together with DFT calculations. Complexes 1−5 were employed to catalyze the enantioselective hydroboration of ketones and α,β-unsaturated ketones using pinacolborane (HBpin) as a reductant, and complex 1 gave better outcomes in comparison to the others. The corresponding secondary alcohols were obtained in excellent yields and moderate ee values. The same results were also achieved using the combined catalyst system of the neodymium amide Nd[N(SiMe 3 ) 2 ] 3 with the phenoxy-functionalized TsDPEN ligand H 3 L 1 in a 1:1.5 molar ratio.

Synthesis and Structure of a Dimeric Yttrium Complex [LSi(BH3)(C5Me4)Y(CH2SiMe3)2]2 (L = PhC(NtBu)2) and Its Catalytic Application for Hydroboration of Ketones and Aldehydes

“…RE complexes have been successfully employed as catalysts for catalytic hydroelementation of unsaturated organic compounds. Catalytic hydroboration with RE complexes as catalysts have also been investigated . However, most of the catalysts are not efficient with high catalyst loadings.…”

“…Catalytic hydroboration of carbonyl compounds represents the most atom economy and selective method for the synthesis of organoboranes, which played important roles in organic synthesis as adjustable intermediates . Compared to the extensively employed main-group and transition metal catalysts, , the RE catalysts for hydroboration of unsaturated substrates are limited . In particular, high-efficiency RE catalysts are still lacking.…”

Chiral Bis(oxazoline) Ligand‐Supported Alkyl Aluminum Cations

“…All the analytical data were in accord with those reported in the literature. [30] 6 c: 1 H NMR (CDCl 3 ): δ 7. 32-7.28 (m, 2H), 6.90-6.87 (m, 2H), 4.86 (q, 3 J HÀ H = 6.4 Hz, 1H), 3.81 (s, 3H), 1.78 (br s, 1H), 1.48 (d, 3 J HÀ H = 6.4 Hz, 3H).…”

“…19 F{ 1 H} NMR (CDCl 3 ): δ −63.5 (s). HPLC analysis: [30] OD−H column (210 nm), method: nHex:IPA=99 : 1, flow 1.0 mL/min, t S =18.65 min, t R =19.25 min. All the analytical data were in accord with those reported in the literature [30] .…”

“…HPLC analysis: [30] OD−H column (210 nm), method: nHex:IPA=99 : 1, flow 1.0 mL/min, t S =18.65 min, t R =19.25 min. All the analytical data were in accord with those reported in the literature [30] . 6 c : 1 H NMR (CDCl 3 ): δ 7.32–7.28 (m, 2H), 6.90–6.87 (m, 2H), 4.86 (q, 3 J H−H =6.4 Hz, 1H), 3.81 (s, 3H), 1.78 (br s, 1H), 1.48 (d, 3 J H−H =6.4 Hz, 3H).…”