Electronic ground states and isotropic proton NMR shifts of manganocene and its derivatives

Versatile Routes to Mono- and Bis(alkynyl) Manganese(II) and Manganese(III) Complexes via Manganocenes

“…To manganese complexes paramagnetic NMR has been applied in just a few instances, e.g. to the parent manganocenes and their substituted derivatives. , The chemical shifts of the methyl and methylene protons of the dmpe ligands are especially suited for assigning different spin states. For the high-spin complexes (MeC 5 H 4 )Mn(dmpe)I 14 and Mn(dmpe) 2 X 2 (X = Br, I) two broad downfield signals are observed for the methylene and the methyl groups of the dmpe ligand, while for the low-spin complexes Mn(dmpe) 2 X 2 (X = Me, C⋮CR‘ 16 ) these resonances are shifted to higher field strengths and the width at half-height of these signals is much smaller.…”

“…Young valve to ensure long-term exclusion of oxygen and moisture. The assignment of the 1 H NMR signals for paramagnetic compounds is principally based on the investigations of Köhler et al , Chemical shifts for 1 H and 13 C{ 1 H} NMR spectra are given in ppm with respect to the signals of residual solvent protons ( 1 H) or 13 C atoms of the deuterated solvents. 31 P{ 1 H} NMR spectra and 119 Sn{ 1 H} NMR spectra were referenced to 85% external H 3 PO 4 and external (CH 3 ) 4 Sn, respectively.…”

“…The first representatives of the manganocene family (C 5 H 5 ) 2 Mn and (MeC 5 H 4 ) 2 Mn have been known for around 40 years . Their electronic properties, especially the high-spin/low-spin crossover, have attracted much attention and have been studied extensively by photoelectron and EPR , spectroscopy, by magnetic measurements in solution, by electron diffraction, and by NMR spectroscopy. , The manganocenes have the longest M−C distances and exhibit the highest reactivity of all metallocenes of the 3d transition-metal series . They are pyrophoric, hydrolyze instantaneously in contact with water and acids,1b undergo facile ring exchange reactions characteristic of ionic cyclopentadienide compounds, and allow substitution of one cyclopentadienyl ligand by three two-electron donors, e.g.…”

Steric Influence on the Structure, Magnetic Properties, and Reactivity of Hexa- and Octaisopropylmanganocene

“…Methylation of cyclopentadienyl rings has consistently been found to favor the low-spin form of manganocenes. Manganocene itself is essentially high-spin at room temperature and above (5.50 μ B at 373 K). ,,, In contrast, gaseous 1,1‘-(MeC 5 H 4 ) 2 Mn is a mixture of both low- and high-spin states in almost equal proportions, and (Me 4 C 5 H) 2 Mn is entirely low-spin up to 400 K …”

“…Manganocene itself is essentially high-spin at room temperature and above (5.50 µ B at 373 K). 5,6,24,38 In contrast, gaseous 1,1′-(MeC 5 H 4 ) 2 Mn is a mixture of both low-and high-spin states in almost equal proportions, 39 and (Me 4 C 5 H) 2 Mn is entirely low-spin up to 400 K. 7 Measurements on solid decamethylmanganocene indicate Curie behavior from 4 to 116 K with an effective magnetic moment of 2.16 ( 0.1 µ B , while measurements by the Evans' method gave a magnetic moment of 1.97 ( 0.1 µ B in toluene-d 8 at 313 K. 9 Magnetic susceptibility measurements and X-ray data confirm that (Cp 3i ) 2 Mn continues the trend previously observed with the methylated manganocenes; i.e., the six electron-donating isopropyl substituents substantially stabilize the low-spin electronic ground state relative to Cp 2 Mn. The slow increase in the magnetic moment with temperature suggests that the influence of the lattice is minimal, which may be a consequence of the heavily substituted cyclopentadienyl rings.…”