Reactions of Scorpionate-Anchored Yttrium and Lutetium Dialkyls with Terminal Alkynes: From Bimetallic Complexes with Bridging Enynediyl Ligands to Monomeric Terminal Dialkynyl Complexes

Abstract

The reactions of scorpionate-anchored yttrium and lutetium dialkyls with terminal alkynes were investigated, and the nature of the complexes was found to depend on both the ancillary scorpionate ligand and the alkyne substituent. Reaction of (TpMe2)Ln(CH2SiMe3)2(THF) (1; Ln = Y, Lu) with the terminal alkynes HC≡CR (R = Ph, SiMe3, tBu, adamantyl (Ad)) afforded dimeric complexes. The solid-state structures, determined by single-crystal X-ray diffraction, showed the two metal centers bridged by two asymmetric alkynyl ligands and a coupled dialkynyl ligand, the latter exhibiting the unusual enyne bonding motif: [{(TpMe2)Ln(μ-C≡CR)}2(μ-RC4R)] (Ln = Y, Lu, R = Ph (3), SiMe3 (4), tBu (5); Ln = Y, R = Ad (6-Y)). Protonolysis of complexes 3-Y and 4-Y with 2,4,6-trimethylphenol gave a 2:1 mixture of free alkyne and (Z)-enyne; however, with 5-Y and 6-Y both enyne and butatriene were obtained in addition to the free alkyne. Dissolution of dimeric 3-Lu and 4-Y in THF resulted in cleavage of the bridging units to give (TpMe2)Ln(C≡CR)2(THF) (Ln = Lu, R = Ph (7); Ln = Y, R = SiMe3 (8)); however, the putative monomers could not be isolated, as they were only stable in THF solution. In the presence of 1 equiv of 2,2′-bipyridine, 1-Lu reacted with HC≡CtBu to give the monomeric bipyridine adduct (TpMe2)Lu(C≡CtBu)2(bipy) (9-Lu). Compound 9-Lu is seven-coordinate in the solid state with the metal center coordinated to a κ3-TpMe2 ligand, two terminal alkynyl ligands, and a κ2-bipyridine ligand. Reaction of (TptBu,Me)Ln(CH2SiMe3)2 (2; Ln = Y, Lu) with 2 equiv of HC≡CPh yielded the terminal dialkynyl complexes (TptBu,Me)Ln(C≡CPh)2 (10), on the basis of characteristic NMR spectroscopic data. Complexes 1-Y and 1-Lu reacted with HC≡CTrit* (Trit* = tris(3,5-di-tert-butylphenyl)methyl) to give the corresponding monomeric complexes (TpMe2)Ln(C≡CTrit*)2(THF) (11; Ln = Y, Lu). The monomeric nature and the presence of terminal alkynyl ligands in 11-Lu was verified by X-ray crystallography. The complex adopts a six-coordinate distorted-octahedral structure, with the Lu center coordinated to a κ3-TpMe2 ligand, two terminal alkynyl ligands, and a THF molecule. NMR-tube reactions of the dimeric complexes 3-Y and 4-Y and the dialkyl complexes 1-Y and 1-Lu with excess terminal alkynes showed that the complexes are able to dimerize terminal alkynes, albeit with low activity.