Strained and Unstrained Sandwich Compounds: From Small Molecules to Polymers

The synthesis and characterization of aluminum, gallium, and indium dichlorides decorated with the bulky Mamx [Mamx = 2,4-tBu2-6-(Me2NCH2)C6H2] ligand are described. The salt-metathesis reaction of (Mamx)ECl2 (E = Al, Ga) with dilithioferrocene and dilithioruthenocene yielded strained [1]ferrocenophanes ([1]FCPs) and [1]ruthenocenophanes ([1]RCPs), respectively, with aluminum and gallium as bridging elements. Galla[1]ruthenocenophane was isolated from the reaction mixture, while other aluminum- and gallium-bridged [1]FCPs and [1]RCPs spontaneously ring-open polymerized under conditions of their formation reactions and produced metallopolymers. Galla[1]ruthenocenophane was polymerized using Karstedt’s catalyst, which yielded poly(ruthenocenylgallane). Aluminum- and gallium-bridged bis(ferrocenyl) species were prepared by reacting lithioferrocene with respective dichlorides. DFT calculations were performed to study the structure and reactivity of these new [1]metallocenophanes. Particularly, the role of the bulky Mamx ligand and its influence on the high reactivity of these strained sandwich species was investigated. (Mamx)InCl2 was reacted with dilithioferrocene and resulted in indium-bridged [1]FCP, [1.1]FCP and oligomers. However, the reaction of (Mamx)InCl2 with dilithioferrocene, substituted with two isopropyl groups ortho to lithium atoms, resulted in inda[1]ferrocenophane selectively. However, this inda[1]ferrocenophane could not be isolated as it spontaneously polymerized under conditions of its formation reaction. The synthesis and characterization of aluminum and gallium dichlorides decorated with the slim p-SiMe3Ar′ [p-SiMe3Ar′ =5-Me3Si-2-(Me2NCH2)C6H3] and Mpysm [Mpysm = (2-C5H4N)Me2SiCH2] ligands are described. These dichlorides were utilized to synthesize group-13-bridged [1.1]FCPs and bis(ferrocenyl) species. Bis(ferrocenyl) species with SiMe2- and SiEt2-bridges were described as well. Two similar species, bis(1'-bromoferrocenyl)dialkylsilane (alkyl = Me, Et) were also prepared. The reaction of bis(1'-lithioferrocenyl)dialkylsilane with tin and gallium dichlorides resulted in unsymmetrically bridged [1.1]FCPs as well as poly(ferrocene)s with two different elements as altering bridges. These poly(ferrocene)s consist of a series of linear and cyclic species. Using either crystallization or column chromatography, some species were isolated. The reactions of dilithioferrocene with dialkyltin dichlorides also yielded polymers that contained a mixture of linear and cyclic species. Some species were isolated by column chromatography. These [1.1]FCPs, bis(ferrocenyl) species and other isolated species with heavier group 13 and/or group 14 element bridges contained two or more iron redox centers. The electronic communication between these redox centers were investigated using several electrochemical methods