Synthesis and Structure of a New Bulky Hybrid Scorpionate/Cyclopentadienyl Ligand and its Lithium Complex

The reaction of 5-(1-adamantyl)-3-methyl-1H-pyrazole with dibromomethane yields a product mixture of bis(3-adamantyl-5-methylpyrazolyl)methane (H2C(Pz(Ad,Me))(2), 2 a), (3-adamantyl-5-methylpyrazolyl)-(3-methyl-5-adamantylpyrazolyl)methane ((H2C(Pz(Ad,Me))(Pz(Me,Ad)), 2 b) and bis(3-methyl-5-adamantylpyrazolyl)methane (H2C(Pz(Me,Ad))(2), 2 c). Lithiation of sterically congested H2C(Pz(Ad,Me))(2) (2 a) and subsequent addition of diphenylfulvene yields lithium 1,1-bis(3-adamantyl-5-methylpyrazolyl)-2,2-diphenyl-2-ethyl-cyclopentadienide, [(thf)Li{Cp-CPh2-CHPz(Ad,Me)}] (3) which is unable to form a thf adduct but can be hydrolyzed to H5C5-CPh2-CHPz(Ad,Me) (4). Adamantyl groups in 5-position of bis(pyrazolyl)methane, i. e. 2 b and 2 c, prohibit formation of a fulvene adduct. For comparison reasons, [{H5C5-CPh2-CHPz(Me2)}LiI] (1 b) has been prepared via protolysis of (thf)lithium 1,1-bis(3,5-dimethylpyrazolyl)-2,2-diphenyl-2-ethyl-cyclopentadienide, [(thf)Li{Cp-CPh2-CHPz(Me2)}] (1 a), in the presence of calcium iodide.

Automated summary

The reaction of 5-(1-adamantyl)-3-methyl-1H-pyrazole with dibromomethane yields a mixture of three products. One of the products can undergo addition reaction with diphenylfulvene to form a lithium salt.