Reactions of MO 2(O 2CMe) 4with amines and diamines: A structural and thermal study of stepwise acetate displacement and hydrogen bonding

Abstract

MO 2(O 2CMe) 4 ( 1) reacts with the neat bidentate diamines Me(H)NCH 2CH 2 N(H)ME ( N, N′-dmed), H 2NCH 2CH 2CH 2NH 2 (pda), H 2NCH 2CH 2NMe 2 ( N, N-dmed), and H 2NCH 2CH 2N(H)Me ( N-med) to form the compounds 1 ∞ [MO 2(O 2CMe) 4( N, N′-dmed)] ( 4), ∞[MO 2(O 2CMe) 4(pda)] ( 5), {[Mo 2(O 2CMe) 3( N, N-dmed) 2] +[(O 2CMe)] −} 2 ( 6), and {[MO 2(O 2CMe) 3( N-med) 2] +[(O 2CMe)] −} 2· N-med ( 7), respectively. Compounds 4- 7 possess MoMo quadruple bonds (MoMo = 2.11(2) Å, ave) and weak axial MoN bonds (MoNa ax = 2.7(1) Å, ave). Compound 4 exhibits a kinked, one-dimensional chain structure comprising MO 2(O 2CMe) 4 units linked by N, N′-dmed ligands. The amine hydrogens are weakly hydrogen-bonded to adjacent O 2CMe oxygens (N ⋯ O = 3.09(9) Å). Compound 5 crystallizes in a linear one-dimensional chain structure with a four-fold disorder in the pda chain. Conversely, compounds 6 and 7 display structures resulting from acetate displacement from the MO 2 centre. Each Mo atom possesses a chelating diamine with the NH 2 group bound in the equatorial position previously occupied by the displaced acetate moiety. Two [MO 2(O 2CMe) 3(diamine) 2] + units are linked together via hydrogen bonding between the equatorial NH 2 diamine hydrogens and the oxygens of the displaced acetate groups. The polar monoamines MeNH 2 and NH 3 do not affect acetate displacement presumably due to their inability to overcome entropic effects of the bidentate acetate ligands. Compounds 4- 7 expel the diamine ligands in the solid state and reform crystalline 1 (XRD). The temperatures of amine expulsions occur at or below the boiling points of the pure diamine liquids. Crystal data for 4 at 20°C: triclinic P 1 , a = 8.784(3); b = 12.945(6), c = 8.663(3) Å; α = 91.73(3)°, β = 97.23(3)°, γ = 101.45(4)°;