Homologues of the Easily Ionized Compound Mo2(hpp)4 Containing Smaller Bicyclic Guanidinates

Abstract

Two bicyclic guanidinate ligands consisting of 5,5-membered (tbo) and 5,6-membered (tbn) rings have been used for the preparation of dimolybdenum compounds, such as Mo₂(tbo)₄ and Mo₂(tbo)₄Cl, and species containing Mo₂(tbn)₄ⁿ⁺ with n = 0−2. The compounds with quadruply bonded Mo₂⁴⁺ species are strong reducing agents and have potentials of about −1 V (vs Ag/AgCl) for the Mo₂^5+/4+ process. The structure of the THF solvate of Mo₂(tbo)₄ shows the longest Mo−Mo bond distance, 2.1453(4) Å, for a quadruply bonded species, and this is due to a large divergent angle induced by the geometry of the ligand. This distance increases to 2.2305(8) Å upon oxidation by CH₂Cl₂ to Mo₂(tbo)₄Cl. For the 5,6-membered-ring ligand tbn, even though the divergent angle is large compared to formamidinate ligands, it is not as large as that in tbo, and the Mo−Mo distance in Mo₂(tbn)₄, 2.082(1) Å, is in the normal range for paddlewheel Mo₂⁴⁺ compounds. This distance increases to 2.2233(8) Å upon oxidation by O₂ in CH₂Cl₂, which forms Mo₂(tbn)₄Cl₂·CH₂Cl₂.