Cyclopentadienyl Yttrium Ene-Diamido Complexes: Coupling of the Ene-Diamido Ligand with Isocyanate

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.

Gallium "Shears" for C=N and C=O Bonds of Isocyanates

Digallane [L¹ Ga-GaL¹ ] (1, L¹ =dpp-bian=1,2-[(2,6-iPr₂ C₆ H₃ )NC]₂ C₁₂ H₆ ) reacts with RN=C=O (R=Ph or Tos) by [2+4] cycloaddition of the isocyanate C=N bonds across both of its C=C-N-Ga fragments to afford [L¹ (O=C-NR)Ga-Ga(RN-C=O)L¹ ] (R=Ph, 3; R=Tos, 4). The reactions with both isocyanates result in new C-C and N-Ga single bonds. In the case of allyl isocyanate, the [2+4] cycloaddition across one C=C-N-Ga fragment of 1 is accompanied by insertion of a second allyl isocyanate molecule into the Ga-N bond of the same fragment to afford compound [L¹ Ga-Ga(AllN- C=O)₂ L¹ ] (5) (All=allyl). In the presence of Na metal, the related digallane [L² Ga-GaL² ] (2; L² =dpp-dad=[(2,6-iPr₂ C₆ H₃ )NC(CH₃ )]₂ ) is converted into the gallium(I) carbene analogue [L² Ga:]^- (2 A), which undergoes a variety of reactions with isocyanate substrates. These include the cycloaddition of ethyl isocyanate to 2 A affording [Na₂ (THF)₅ ]{L² Ga[EtN-C(O)]₂ GaL² } (6), cleavage of the N=C bond with release of 1 equiv. of CO to give [Na(THF)₂ ]₂ [L² Ga(p-MeC₆ H₄ )(N-C(O))₂ -N(p-MeC₆ H₄ )]₂ (7), cleavage of the C=O bond to yield the di-O-bridged digallium compound [Na(THF)₃ ]₂ [L² Ga-(μ-O)₂ -GaL² ] (8), and generation of the further addition product [Na₂ (THF)₅ ][L² Ga(CyNCO₂ )]₂ (9). Complexes 3-9 have been characterized by NMR (¹ H, ¹³ C), IR spectroscopy, elemental analysis, and X-ray diffraction analysis. Their electronic structures have been examined by DFT calculations.

Yttrium dialkyl supported by a silaamidinate ligand: synthesis, structure and catalysis on cyclotrimerization of isocyanates

A four-coordinate yttrium dialkyl complex with a sterically demanding silaamidinate ligand exhibited high activity and excellent functional group tolerance for the catalysis of isocyanate cyclotrimerization.

Cycloaddition versus Cleavage of the C=S Bond of Isothiocyanates Promoted by Digallane Compounds with Noninnocent α-Diimine Ligands

Whereas the chemistry of single-bond activation by compounds of the main group elements has undergone some development in recent years, the cleavage of multiple bonds remains underexplored. Herein, the reactions of two digallanes bearing α-diimine ligands, namely, [L¹ Ga-GaL¹ ] (1, L¹ =dpp-dad=[(2,6-iPr₂ C₆ H₃ )NC(CH₃ )]₂ ) and [L² Ga-GaL² ] (2, L² =dpp-bian=1,2-[(2,6-iPr₂ C₆ H₃ )NC]₂ C₁₀ H₆ ), with isothiocyanates are reported. Reactions of 1 or 2 with isothiocyanates in 1:2 molar ratio proceeded with [2+4] cycloaddition of the C=S bond across the C₂ N₂ Ga metallacycle with formation of C-C and S-Ga single bonds to afford [L¹ (RN=C-S)Ga-Ga(S-C=NR)L¹ ] (3, R=Me; 4, R=Ph) and [L² (RN=C-S)Ga-Ga(S-C=NR)L² ] (8, R=allyl; 9, R=Ph). In the cases of 8 and 9, this cycloaddition is reversible. The digallanes reacted with 2 equiv of PhNCS in the presence of Na metal or at high temperatures through a unique reductive cleavage of the C=S bond to yield the disulfide-bridged digallium species [Na(THF)₃ ]₂ [L¹ Ga(μ-S)₂ GaL¹ ] (5), [L² Ga(μ-S)₂ GaL² ] (10), and [Na(DME)₃ ][L² Ga(μ-S)₂ GaL² ] (11). Moreover, products 4 and 5 can further react with an excess of isothiocyanate, through cleavage of the C=S bond or cycloaddition, to give the bis- or mono-S-bridged complexes [Na(THF)₂ ]₂ [L¹ (PhN=C-S)Ga(μ-S)₂ Ga(S-C=NPh)L¹ ] (6) and [L¹ (PhN=C-S)Ga(μ-S)Ga(S-C=NPh)L¹ ] (7). All the newly prepared compounds were characterized by elemental analysis, single-crystal X-ray diffraction, IR spectroscopy, NMR (3-9) or ESR spectroscopy (11), and DFT calculations.