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

Abstract

Reactions of [(Me 3 Si) 2 N] 3 RE(μ-Cl)Li(THF) 3 with aminomethylene-substituted pyridine 2- Pr(2c), Nd(2d), Sm(2e), Dy(2f), Er(2g), and Lu (2h)). However, reaction of [(Me 3 Si) 2 N] 3 Y(μ-Cl)Li(THF) 3 with pyridin-2-ylmethyl-substituted amines such as 2-(RNHCH 2 )C 5 H 4 N (R = t Bu (3a) and 2,6-i Pr 2 Ph (3b)) or benzyl-substituted amine O(CH 2 CH 2 ) 2 NCH 2 CH 2 NHCH 2 C 6 H 5 (5) afforded the corresponding yttrium complexes containing monoanionic ligands [2-(RNCH 2 )C 5 H 4 N] 2 YN(SiMe 3 ) 2 (R = t Bu (4a) and 2,6-i Pr 2 Ph (4b 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.

Syntheses of Rare-Earth Metal Alkyl Complexes Bearing a Dianionic α-Iminopyridyl Ligand and Their Catalytic Activities toward Polymerization of 2-Vinylpyridine

“…Similar to the process of [(Me 3 Si) 2 N] 3 RE­(μ-Cl)­Li­(THF) 3 with compound 1 , reactions of RE­(CH 2 SiMe 3 ) 3 (THF) 2 with compound 1 gave the α-iminopyridyl rare-earth metal alkyl complexes 2a – 2f through the double deprotonations of 2-aminomethylpyridine (Scheme ). In order to explore the formation mechanism of the rare-earth metal alkyl complexes bearing a dianionic α-iminopyridyl ligand, reaction of Sc­(CH 2 SiMe 3 ) 3 (THF) 2 with compound 1 was examined in a shortened reaction time to afford the scandium dialkyl complex 3f .…”

“…The NCCN backbones of the ligand in complexes 2a – 2f (C(6)–N(2) 1.41–1.44 Å, C(5)–N(1) 1.38–1.41 Å, C(5)–C(6) 1.37–1.40 Å, Table ) are similar to those of (C–N (iminyl) 1.41–1.45 Å, C–N (pyridyl) 1.38–1.40 Å, C–C 1.37–1.41 Å) in the dianionic α-iminopyridyl rare-earth amido complexes {μ-η 2 :σ 1 :κ 1 :κ 1 -2-[O­(CH 2 CH 2 ) 2 NCH 2 CH 2 NCH]­C 5 H 4 N} 2 RE 2 [N­(SiMe 3 ) 2 ] 2 , and different from the complex 3f (C(6)–N(2) 1.425(4) Å, C(5)–N(1) 1.334(4) Å, C(5)–C(6) 1.486(5) Å, Figure ). The bonding situation within the planar diimino fragment NCCN in 2a – 2f is also consistent with the dianionic form of the ligand (C–N (iminyl) 1.37 Å, C–N (pyridyl) 1.41 Å, C–C 1.38 Å) .…”

“…In complexes 2a – 2f , the RE(1)–N(1) distance is close to the RE(1)–N(2) distance and were all shorter than the RE(1)–N(3) distance. The Dy(1)–N(1) distance of 2.407(3) Å is similar to the corresponding values in the rare-earth amido complexes (Dy(1)–N (pyridyl) 2.399(2) Å) with dianionic α-iminopyridyl ligand and is slightly shorter than the complex Dy­(IPy •– ) 3 (Dy(1)–N (pyridyl) 2.424(2) Å) with radical-anionic α-iminopyridine ligand . These results indicated that the ligands in 2a – 2f are in dianionic form with unusual μ-η 2 :σ 1 :κ 1 binding modes.…”

“…However, the rare-earth metal complexes bearing the dianionic α-diimine ligand were usually synthesized through reduction of α-diimine with alkali metal or divalent rare-earth complexes . Recently, we reported synthesis of the rare-earth metal amido complexes bearing the dianionic α-iminopyridyl ligand in a unusual μ-η 2 :σ 1 :κ 1 coordinated mode through the double deprotonations of [(Me 3 Si) 2 N] 3 RE­(μ-Cl)­Li­(THF) 3 with the functionalized donor group 2-aminomethylpyridine, which displayed high catalytic activities for dehydrogenation coupling of hydrosilanes and amines . In order to further explore general synthesis of the dianionic α-iminopyridyl rare-earth metal complexes and expand their application, we herein report the synthesis of rare-earth metal alkyl complexes bearing the dianionic α-iminopyridyl ligand in μ-η 2 :σ 1 :κ 1 or μ-η 4 :η 2 coordinated mode, and these rare-earth metal alkyl complexes as catalysts for polymerization of 2-VP were examined.…”

“…Solvents were refluxed and distilled over sodium/benzophenone under argon prior to use. RE­(CH 2 SiMe 3 ) 3 (THF) 2 , and 2-[O­(CH 2 CH 2 ) 2 NCH 2 CH 2 NHCH 2 ]­C 5 H 4 N ( 1 ) were prepared according to the literature methods. IR spectra were recorded on a Bruker INVENIO S spectrometer.…”