Synthesis and crystal structures of mononuclear half-sandwich complexes of Ni and Co containing Kläui’s tripodal ligand, [M{κ3-(η5-C5H5)Co[P(O)(OCH3)2]3}(κ2-NO3)(L)] (M = Ni or Co)

Abstract

Synthesis of L_ORM–X-type 1∶1 mononuclear adducts containing Kläui’s tripodal ligands {L_OR = CpCo[P(O)(OR)₂]₃} was studied. Addition of NaL_OMe to an excess amount of CoCl₂ did not afford a mononuclear product but the dinuclear complex [Co(µ-L_OMe)₂CoCl₂] 1, which results from co-ordination of the two PO oxygen atoms in the initially formed 1∶2 adduct, Co(L_OMe)₂, to a second molecule of CoCl₂. In contrast, similar reaction of nitrate salts M(NO₃)₂·6H₂O followed by crystallization from acetone produced 1∶1 mononuclear complexes, [ML_OMe(κ²-NO₃)(Me₂CO)] M = Ni 3 or Co 4], with octahedral co-ordination geometry. Before crystallization from acetone the dinuclear adduct [Ni(µ-L_OR)₂(µ-NO₃)₂Ni(NO₃)] 2 was isolated from a reaction mixture and subsequent treatment with acetone gave the mononuclear product 3. Thus, for synthesis of L_ORM–X-type complexes, it is essential to use a potentially κ²-co-ordinating ligand (e.g. NO₃) in the presence of a donor (e.g. acetone). The labile acetone ligand in 3 is replaced by P- and N-donors to give the substituted products [NiL_OMe(κ²-NO₃)(L)] (L = PPh₃ 5a, 2,5-dimethylpyridine 5b or 3,5-diisopropylpyrazole 5c) and [NiL_OMe(κ²-NO₃)(py)₃]NO₃ 6. Complexes 1, 2b, 2c, 3, 4, 5a–5c, 6, and [NiL_OMe(κ²-NO₃)(MeOH)] were characterized by X-ray crystallography.