Metallacyclic yttrium alkyl and hydrido complexes: synthesis, structures and catalytic activity in intermolecular olefin hydrophosphination and hydroamination

Abstract

Metallacyclic neutral and ionic yttrium alkyl complexes coordinated by a dianionic ene-diamido ligand ([2,6-iPr₂C₆H₃NC(Me)C(Me)NC₆H₃iPr₂-2,6] = L¹) [L¹]Y(CH₂SiMe₃)(THF)₂ (2), {[L¹]Y(CH₂SiMe₃)₂}⁻{Li(THF)₄}⁺ (3), [L¹]Y(OEt₂)(μ-Me)₂Li(TMEDA) (4) were synthesized using a salt-metathesis approach starting from the related chloro complex [L¹]Y(THF)₂(μ-Cl)₂Li(THF)₂ (1) in 70, 85 and 72% yields respectively. The reactions of 2 with H₂ or PhSiH₃ afford the dimeric hydride {[L¹]Y(THF)(μ-H)}₂(μ-THF) (5) containing two μ-bridging hydrido and one μ-bridging THF ligands (91 and 85% yields). The X-ray studies of complexes 2, 3 and 5 revealed η²-coordination of the CC fragment of an ene-diamido ligand to a Y cation. DFT calculations were carried out to give an insight into the metal–ligand bonding and especially the interaction between the metal and the ene-diamido ligand. The observed bonding of the ene-diamido fragment is found to reflect the acidity of the metal center in the complex that is partially overcome by a better donation from the double bond (better overlap with an empty d orbital at the yttrium center). The treatment of complex 4 with DME resulted in the C–O bond cleavage of DME and afforded a three nuclear methoxide oxide complex [{[L¹]Y}₃(μ²-OMe)₃(μ³-O)]²⁻[Li(DME)₃]⁺₂ (6). Complexes 2, 3, 5 and 7 proved to be efficient precatalysts for the intermolecular hydrophosphination of styrene, 4-vinylpyridine, and 1-nonene with PhPH₂ and Ph₂PH as well as hydroamination of styrene and pyrrolidine.