Half-sandwich complexes of molybdenum-(III), -(IV) and -(V) with P–O and P–N bifunctional ligands Ph2PCH2X (X = 2-oxazolinyl, or C(O)NPh2)

Abstract

The reaction of the ligands Ph₂PCH₂X (X = 2-oxazolinyl, I; or C(O)NPh₂, II) with the half-sandwich molybdenum(III) precursors [Mo(η-C₅R₅)(μ-Cl)₂]₂ (R = H or Me) has been investigated. Ligand I reacts with both complexes to form the corresponding adducts [Mo(η-C₅R₅)Cl₂(Ph₂PCH₂C₃H₄NO)] (R = H, 1; or Me, 2). The reaction between I and [MoCp*Cl₄] (Cp* = η-C₅Me₅) affords [MoCp*Cl₄(Ph₂PCH₂C₃H₄NO-κ¹P)] as a kinetic isomer, which then transforms quantitatively to [MoCp*Cl₃(Ph₂PCH₂C₃H₄NO-κ²P,N)]⁺Cl⁻, 3. Ligand II reacts with [MoCp(μ-Cl)₂]₂ (Cp = η-C₅H₅) to afford the adduct [CpMoCl₂{Ph₂PCH₂C(O)NPh₂-κ²P,O}], 4, as an equilibrium mixture of two isomers. Longer reaction times in CH₂Cl₂ lead to the molybdenum(IV) by-product [MoCpCl₃{Ph₂PCH₂C(O)NPh₂-κ²P,O}], 5. While ligand II does not react with [MoCp*(μ-Cl)₂]₂, it does so in the presence of 1 equivalent of AgBF₄ to afford [MoCp*Cl₂{Ph₂PCH₂C(O)NPh₂-κ²P,O}][BF₄], 6. Further reaction with CH₂Cl₂ leads to [MoCp*Cl₃{Ph₂PCH₂C(O)NPh₂-κ²P,O}] [BF₄], 7. The direct reaction between [MoCp*Cl₄] and ligand II affords [MoCp*Cl₄{Ph₂PCH₂C(O)NPh₂-κ¹P}] 8 as a kinetic isomer which then slowly establishes a solvent-dependent equilibrium with the ionic isomer [MoCp*Cl₃{Ph₂PCH₂C(O)NPh₂-κ²P,O}]⁺ Cl⁻. The solid state structure of compounds 5 and 7 has been determined by single crystal X-ray diffraction. The chemical, spectroscopic, and electrochemical data indicate that ligand II has a greater hemilabile character than ligand I.