Organoindium(III) cyclopentadienide compounds and their chemistry

A new synthetic methodology for the preparation of In(C₅H ₅)₃ has been developed. Isolation of analytically pure In(C ₅H₅)₃ afforded the opportunity to study the ligand redistribution reactions between In(C₅H₅)₃ with InMe₃ and In(CH₂CMe₃)₃ with the goal of preparing the heteroleptic organoindium compounds R_nIn(C ₅H₅)_3−n (R = Me and CH₂CMe ₃, n = 1, 2). These compounds were characterized as completely as possible. It is of note that although all of these heteroleptic compounds were isolated as pure single compounds in the solid state, they redistributed their ligands to form equilibrium mixtures of compounds in tetrahydrofuran solution. Another aspect of interest with regards to the nature of these compounds is their thermal decomposition at relatively moderate temperatures, below 150°C, to form the indium(I) derivative In(C₅H₅). For example, (Me₃CCH2)₂In(C₅H₅) was isolated as a polymer in the solid state, as determined by an X-ray structural study, but its ligands redistributed in THF solution to form an equilibrium mixture of In(C₅H₅)₃, In(CH₂CMe₃ )₃, (Me₃CCH₂)₂In(C ₅H₅), and Me₃CCH₂In(C₅H ₅)₂ as THF adducts. This equilibrium was investigated thoroughly by variable temperature 1H NMR spectroscopy. In the melt, (Me ₃CCH₂)₂In(C₅H₅) redistributed its ligands to form In(C₅H₅)₃ and (Me ₃CCH₂)₂In(C₅H₅). The In(C ₅H₅)₃ then decomposes at 150°C to give the indium(I) compound In(C₅H₅) and C₅H ₆. Thus, the isolable indium products from the thermal decomposition were In(C₅H₅) and (Me₃CCH₂) ₂In(C₅H₅). Similarly, In(C₅H₅ )₃ was observed independently to decompose to form In(C ₅H₅) and C₅H₆ at 150°C.; A comparison of the reactivities of the Me₂In(C₅H ₅) and (Me₃CCH₂)₂In(C₅H ₅) with t-butanol, acetylacetone, triphenylsilylthiol, t-butylamine and diphenylphosphine found the cyclopentadiene elimination reaction to be an efficient method for the preparation the corresponding organoindium alkoxide (R₂InOR′), β-diketonate (R₂In(acac)), thiolate (R₂InSR′) and phosphide (R₂ InPR′₂) derivatives. However, the reaction between Me₂In(C₅H₅) with H₂N(t-Bu) for the formation of Me₂InNH(t-Bu) required elevated temperatures and longer reaction times. The reaction between In(C₅H₅) ₃ with t-BuOH in a 1:1 mol ratio led to the formation of [(C₅H ₅)₂InO(t-Bu)]₂. Interestingly, the reaction between of In(C₅H₅)₃ and HPPh₂ in a 1:2 mol ratio in diethyl ether gave the very unexpected result of a reductive elimination reaction with formation of the indium(I) compound In(C₅H ₅) and tetraphenylbisphosphine (P₂Ph₄).