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.