Toward the Synthesis of Indenyl Molybdenum Compound [(η3‑Ind)(η5‑Cp)Mo(CO)2]: Modified Compounds and Structure of a Previously Unrecognized Intermediate

The mechanism of synthesis of [(η3-Ind′)­(η5-Cp)­Mo­(CO)2] was studied on methyl-substituted derivatives (Ind′ = 2-MeC9H6; 4,7-Me2C9H5). It was observed that the initial step involving reaction with HCl gives dimeric chloride species [{(η5-Ind′)­Mo­(CO)2(μ-Cl)}2]. This outcome differs from the structure suggested in the literature. Furthermore, it was demonstrated by various examples that compounds of the formula [{(η5-Ind′)­Mo­(CO)2(μ-Cl)}2] are convenient starting materials giving [(η3-Ind′)­(η5-Cp′)­Mo­(CO)2] through the reaction with appropriate cyclopentadienides. The variability of this method was demonstrated on several examples including weakly donating Cp ligands bearing strong electron-withdrawing functional groups [C5H4COOMe, (1,2-MeOCO)2C5H3, and 1,2-(tBuNHCO)2C5H3] as well as Cp ligands bearing a pendant amine arm (C5H4CH2CH2NMe2). Similar η3-indenyl complexes are formed when using other univalent six-electron ligands such as carbaborane (9-Me2S-7,8-nido-C2B9H10) or scorpionate (Tp, Tp*). The attempts to synthesize [(η3-Ind)­(η5-Cp)­Mo­(CO)2] from [(η3-C3H5)­(η5-Cp)­Mo­(CO)2] have failed because the initial reaction with HCl does not give the expected [{(η5-Cp)­Mo­(CO)2­(μ-Cl)}2] but trivial [(η5-Cp)­Mo­(CO)3Cl].