(Pentamethylcyclopentadienyl)indium(I) and -indium(III) compounds. Syntheses, reactivities, and X-ray diffraction and electron diffraction studies of In(C5Me5)

Article abstract of DOI:10.1021/om00104a012

The golden yellow compound In(C₅Me₅) has been prepared in 62% yield from InCl and Li(C₅Me₅) in diethyl ether and fully characterized according to its physical and solubility properties, its reaction with dilute aqueous HCl, a cryoscopic molecular weight study in cyclohexane, IR and ¹H NMR spectroscopic properties, a single-crystal X-ray diffraction study, and a gas-phase electron diffraction study. The other products of this reaction have been identified as In(C₅Me₅)₂Cl, indium metal, and (C₅Me₅)₂ in 5.0, 21, and 2.5% yields, respectively. The identity of the yellow indium(III) product In(C₅Me₅)₂Cl was confirmed by its independent synthesis from InCl₃ and Li(C₅Me₅) in a 1:2 mol ratio and full characterization. The orange-yellow compound In(C₅Me₅)Cl₂ has also been synthesized from InCl₃ and Li(C₅Me₅) in a 1:1 mol ratio in order to distinguish it from In(C₅Me₅)₂Cl. However, the attempted preparation of In(C₅Me₅)₃ from InCl₃ and either Li(C₅Me₅) or Na(C₅Me₅) was unsuccessful. A noteworthy observation of the chemical properties of the (pentamethylcyclopentadienyl)indium(I) and -indium(III) compounds was their decomposition in benzene solution to form (C₅Me₅)₂ and other products. Additional studies of prepurified In(C₅Me₅) confirmed decomposition in THF and pyridine but demonstrated its stability in cyclohexane. The compound In(η⁵-C₅Me₅) crystallizes in the rhombohedral space group R3 (C_3i²; No. 148) with unit cell parameters (hexagonal setting) a = 20.182 (4) A?, c = 13.436 (3) A?, V = 4739 12) A?³, and Z = 18. Single-crystal X-ray diffraction data (Mo Kα, 2θ = 4.5-50.0°) were collected with a Syntex P2₁ automated four-circle diffractometer; the structure was solved and refinement converged with R_F = 3.6%. and R_wF = 3.3% for all 1870 symmetry-independent data (none rejected) and R_F = 2.5% and R_wF = 2.9% for those 1444 reflections with |F_o| > 6σ(|F_o|). The η⁵-C₅Me₅ ligand is symmetrically bound to indium with In-C = 2.581 (4)-2.613 (4) A? (average = 2.595 A?) and In?centroid = 2.302 A?. The In(η⁵-C₅Me₅) units are arranged about centers of 3 (S₆) symmetry, with indium atoms on the interior and η⁵-C₅Me₅ units on the exterior of hexameric units in which In-In distances are 3.942 (1)-3.963 (1) A?. The centroid → indium vectors do not point toward the center of the hexaindium cluster as in other main-group clusters. The molecular structure of In(C₅Me₅) in the gas phase consists of discrete monomeric units with the indium(I) atom being situated 2.288 A? above the ring centroid. Ab initio calculations were carried out on In(C₅H₅) and In(C₅Me₅) in an attempt to understand the effects of methyl groups on the bonding between indium(I) and the cyclopentadienyl ring.