Structural and theoretical insights into metal-scorpionate ligand complexes

The syntheses of the complexes [M(Tm-Me)(CO)(2)(NO)] (M = Mo, W) by reaction of NOBF4 with [M(Tm-Me) (CO)(3)](-) are reported and their spectroscopic characterisation and crystal structures are described. The analogous Cr complex could not be prepared by this methodology. The complexes adopt the expected pseudo-octahedral geometry. Complexes [M(L)(CO)(2)(NO)] (M = Cr, Mo, W; L = Cp, Tp and Tm-Me) together with the hypothetical [MO(CO)2(NO)]' cation were subjected to DFT calculations. Geometry-optirmsed structures closely parallel the crystallographic determinations and indicate that the complex [Cr(Tm-Me)(CO)2(NO)] is not inherently unstable. The DFT calculations allow the assignment of the C-O and N-O stretches in the IR spectrum and give insight into both the M-NO bonding and the metal to tripodal ligand bonding. The electron-donor strengths are confirmed to lie in the order Tm-Me > Tp > Cp. A side reaction of the B-H moiety of the Tm-Me anion with NO+ results in the isolation of the dimethylformamide adduct of (trismethimazolyl)borane, providing further evidence that the reaction pathways of the Tm' ligands are more varied and less passive than in the chemistry of the nitrogen-based scorpionates. (c) Wiley-VCH Verlag GmbH & Co. KGaA.