Dimolybdenum complexes of bis(2-pyridyl)amine (Hdpa) ligand and its anion (dpa −); transformation of chelating η 2-Hdpa to bridging η 2-dpa −

Abstract

The reaction of trans-Mo 2(O 2CCR 3) 2X 2(PPh 3) 2 with 1 equiv. of Hdpa (Hdpa=bis(2-pyridyl)amine) in CH 2Cl 2 afforded the complex cis-Mo 2(O 2CCR 3) 2X 2(η 2-Hdpa) (R=H, X=Cl, 1; R=H, X=Br, 2; R=F, X=Cl, 3, R=F, X=Br, 4). Layering of a Mo 2(O 2CCF 3) 4 solution in CH 2Cl 2 with Hdpa in ether produced red and yellow crystals, which were characterized as Mo 2(η 2-dpa) 4 ( 5), and Mo 2(O 2CCF 3) 4(η 1-HO 2CCF 3) 2 · 2Hdpa ( 6), respectively. Complex 5 can also be prepared by reaction of trans-Mo 2(O 2CCR 3) 2X 2(PPh 3) 2 with excess Hdpa. Their UV–Vis and IR spectra have been recorded and the structures of 4, 5 and 6 have been determined. The Hdpa ligand in 4 is coordinated to the metal centers via two terminal pyridine nitrogen atoms with a cis-N conformation. The dpa − ligands in 5 are bridged to the metal centers via one terminal nitrogen atom and the central nitrogen atom. The aligned-N conformation of the dpa − ligand is stabilized by both the intramolecular Mo⋯N and C–H⋯N interactions. In 6, the CF 3COOH ligands coordinate to the metal centers in the axial positions with η 1-bonding modes and the Hdpa molecules adapt cis-N conformations.