Boron Complexes with Propiolamidinato Ligands: Synthesis, Structure, and Photophysical Properties

Two series of boron derivatives with propiolamidinato ligands, [BPh2{C(C≡CAr)(NR)2}] (Ar = Ph, p-MeOPh, p-FPh, p-Me2NPh, or phen; R = iPr or p-tolyl), were synthesized and structurally characterized. The corresponding propiolamidine (or propargylamidine) proligands have been obtained through sustainable methods. One is the catalytic hydroalkynylation of diisopropylcarbodiimide with different terminal alkynes, using simple ZnEt2 as a precatalyst. Alternatively, to obtain propiolamidines with aromatic groups on the nitrogen atoms, the formation of lithiated derivatives of terminal alkynes by reaction with n-BuLi in air and at room temperature, and subsequent addition to the di-p-tolylcarbodiimide, under the same conditions and using 2-MeTHF as a sustainable solvent, has been used for the first time. After reaction with BPh3, the corresponding boron amidinates were obtained, which are emissive in the solution state. The influence of the different substituents introduced into the ligands on the photophysical properties of the boron compounds has been studied. One of the obtained compounds can be used as a ratiometric fluorescent pH sensor in the acidic range.

Synthesis and characterization of rare-earth metallate amido complexes bearing 2-amidate-functionalized indolyl ligand and their application in the hydroboration of esters with pinacolborane

The reactions of 2-amidate-functionalized indolyl proligand 2-(2,6-iPr2C6H3NHC=O)C8H5NH (H2L) with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 were studied leading to the synthesis and characterization of a series of novel discrete trinuclear rare-earth metal metallate amido complexes...

Asymmetric epoxidation of α,β-unsaturated ketones catalyzed by rare-earth metal amides RE[N(SiMe3)2]3 with chiral TADDOL ligands

The first application of rare-earth metal catalyst combined with TADDOLs in the asymmetric epoxidation of α,β-unsaturated ketones is disclosed.

Dehydrogenative Coupling of Terminal Alkynes with O/N-Based Monohydrosilanes Catalyzed by Rare-Earth Metal Complexes

Newly synthesized rare-earth metal alkyl complexes bearing a tripyrrolyl ligand act as excellent precatalysts for the cross-dehydrogenative coupling between various terminal alkynes and O/N-based monohydrosilanes of HSi(OEt)₃/HSi(NMe₂)₃, leading to the formation of a variety of alkoxysilylalkyne and aminosilylalkyne derivatives in good to high yields. The precatalysts LRE(CH₂SiMe₃)(thf)₂ (RE = Y(1a), Er(1b), Yb(1c), L = 2,5-[(2-C₄H₃N)CPh₂]₂(C₄H₂NMe), thf = tetrahydrofuran) were easily prepared in high yields via the reactions of RE(CH₂SiMe₃)₃(thf)₂ with the proligand H₂L in a single step. Mechanistic studies reveal that treatment of 1 with phenylacetylene could generate the active catalytic species: dinuclear rare-earth metal alkynides (L(thf)_n[RE(μ-C≡CPh)]₂L) (RE = Y(5a), n = 1; Yb(5c), n = 0), which could react with HSi(OEt)₃ to produce the coupling product 4aa and the dinuclear rare-earth metal hydrides (L (thf)[RE(μ-H)]₂L) (RE = Y(6a); Yb(6c)). By contrast, prior treatment of 1c with HSi(OEt)₃ proceeds via cleavage of the Si-O bond to produce the dinuclear ytterbium alkoxide (LYb(μ-OEt))₂ 7c, which is inert in the dehydrogenative coupling reaction. The results of the mechanistic studies are consistent with the observation that the reaction is greatly influenced by the addition sequence of precatalyst/alkynes/silanes.

Enantioselective Hydroboration of Ketones Catalyzed by Rare-Earth Metal Complexes Containing Trost Ligands

Four chiral dinuclear rare-earth metal complexes [REL¹]₂ (RE = Y(1), Eu(2), Nd(3), La (4)) stabilized by Trost proligand H₃L¹ (H₃L¹ = (S,S)-2,6-bis[2-(hydroxydiphenylmethyl)pyrrolidin-1-ylmethyl]-4-methylphenol) were first prepared, and all were characterized by X-ray diffraction. Complex 4 was employed as the catalyst for enantioselective hydroboration reaction of substituted ketones, and the corresponding secondary alcohols with excellent yields and high ee values were obtained using reductant HBpin. The same result was also achieved using the combination of lanthanium amides La[N(SiMe₃)₂]₃ with Trost proligand H₃L¹ in a 1:1 molar ratio. The experimental findings and DFT calculation revealed the possible mechanism of the enantioselective hydroboration reaction and defined the origin of the enantioselectivity in the current system.

Syntheses of Dianionic α-Iminopyridine Rare-Earth Metal Complexes and Their Catalytic Acitivities toward Dehydrogenative Coupling of Amines with Hydrosilanes

Reactions of [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ with aminomethylene-substituted pyridine 2-[O(CH₂CH₂)₂NCH₂CH₂NCH₂]C₅H₄N (1) gave the dianionic α-iminopyridine rare-earth metal amido complexes {μ-η²:σ¹:κ¹:κ¹-2-[O(CH₂CH₂)₂NCH₂CH₂NCH]C₅H₄N}₂RE₂[N(SiMe₃)₂]₂ (RE = Y(2a), La(2b), Pr(2c), Nd(2d), Sm(2e), Dy(2f), Er(2g), and Lu (2h)). However, reaction of [(Me₃Si)₂N]₃Y(μ-Cl)Li(THF)₃ with pyridin-2-ylmethyl-substituted amines such as 2-(RNHCH₂)C₅H₄N (R = ^tBu (3a) and 2,6-ⁱPr₂Ph (3b)) or benzyl-substituted amine O(CH₂CH₂)₂NCH₂CH₂NHCH₂C₆H₅ (5) afforded the corresponding yttrium complexes containing monoanionic ligands [2-(RNCH₂)C₅H₄N]₂YN(SiMe₃)₂ (R = ^tBu (4a) and 2,6-ⁱPr₂Ph (4b)) or [O(CH₂CH₂)₂NCH₂CH₂NCH₂C₆H₅][(Me₃Si)₂N)]Y(μ-Cl)(μ-η³-O(CH₂CH₂)₂NCH₂CH₂NCH₂C₆H₅)Li(THF) (6). Dianionic α-iminopyridine rare-earth metal amido complexes showed high catalytic activities for the dehydrogenation coupling reaction of hydrosilanes and amines providing a variety of silylamines in high yields.