Organotransition-metal complexes of multidentate ligands: XII. Crystal structure of allyl[ N,N-bis(pyrazol-1-ylmethyl)aminomethane]dicarbonylchromium(II) hexafluorophosphate; the symmetric orientation of the η 3-allyl group with respect to the pyrazole-derived tridentate ligand

Abstract

The structure of [Cr(bpam)(CO) 2(η 3-allyl)]PF 6 (bpam  N,N-bis(pyrazol-1-ylmethyl)aminomethane) has been determined by X-ray diffraction methods. The crystals are orthorhombic, space group Pbca, with cell dimensions: a = 13.430(3), b = 18.530(4), c = 15.565(3) Å and Z = 8. This structure was refined to give R = 0.055 and R w = 0.044 using 1720 reflections with I > 2σ( I) in the range of 2 ≤ 2θ ≤ 50° (Mo- K α). As expected previously from NMR studies, the compound named in the title is now confirmed to contain, in the solid state, an η 3-allyl group symmetric with respect to the nitrogen tridentate ligand, bpam. This symmetric structure is also compared with the unsymmetric structure reported for [Mo(bpam)CO) 2(η 3-allyl)]PF 6 and a new five-stage process is proposed for the stereochemically nonrigid behaviour of this compound and of its tungsten analogue in solution at room temperature.