Metalation of aromatic heterocycles by yttrium alkyl complexes that contain a linked amido-cyclopentadienyl ligand: synthesis, structure and Lewis base adduct formation

The reaction of the half-sandwich alkyl complex [Y(η5:η1-C5Me4SiMe2NCMe3)(CH2SiMe3)(THF)] with furan and thiophene gives metalation products [Y(η5:η1-C5Me4SiMe2NCMe3)(μ-2-C4H3X)]2 (X=O, S) which are sparingly soluble in hydrocarbons due to the dimeric structure. Single crystal X-ray structure analysis of the 2-thienyl complex confirms a six-membered core with bridging sulfur atoms and trans-disposed amido-tetramethylcyclopentadienyl ligands. In contrast to THF and pyridine, 1,2-dimethoxyethane (DME) forms isolable, crystalline adducts [Y(η5:η1-C5Me4SiMe2NCMe3)(2-C4H3X)(DME)]. Single crystal X-ray structure analysis of the 2-furyl derivative shows a four-legged piano stool configuration. The reaction of [Y(η5:η1-C5Me4SiMe2NCMe3)(CH2SiMe3)(THF)] with excess DME gives the isolable, five-coordinate complex [Y(η5:η1-C5Me4SiMe2NCMe3)(CH2SiMe3)(DME)] that does not react with furan or thiophene, indicating an associative mechanism. [Y(η5:η1-C5Me4SiMe2NCMe3)(CH2SiMe3)(THF)] reacts with pyrrole to give the sparingly soluble pyrrolide that can be studied by crystallography as a DME adduct [Y(η5:η1-C5Me4SiMe2NCMe3)(η1-κN-C4H4N)(DME)]. The reaction of [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(CH2SiMe3)(THF)] that contains the longer CH2SiMe2-bridge reacts with furan to a mixture of a hydrocarbon-soluble dimer and the labile THF adduct, whilst the reaction with thiophene results in the selective formation of the monomeric [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(2-C4H3S)(THF)] which was characterized by crystallography.