Cobalt-59 NMR spectroscopy of organocobalt(I) and -cobalt(III) compounds and its relation to chemical properties of the complexes

Abstract

59Co NMR parameters of various organocobalt(I) and -cobalt(III) complexes with ir-ligands have been determined in solution in order to find out whether they provide a measure for complex properties. The 59Co shifts of (?)1 23-allyl) (^-cyclopentadienyl)ComR complexes (R = Br, benzyl, methyl) range from 1100 to -1300 ppm. (r)3-Allyl)3Co ( 1) and (tj3-2-methylallyl)3Co (2) yield 59Co signals close to the region typical for organocobalt(I) compounds. Even at -50 and -30 °C the line width of their resonances is relatively narrow (3750 and 13000 Hz, respectively). In (olefinLCo^complexes 5("Co) is sensitive to the type of R ligand and increases in the series alkyl-substituted-j/1-cyclopentadienyl, ^-cyclopentadienyl, r)6-indenyl, and 7j3-allyl. In the (^-cyclopentadienyl)Co^series, <5("Co) increases within the sequence L = cyclobutadiene, (CO)2, jj4-cyclohexadiene, ?;4 *-butadiene, ij4-cyclopentadiene, and (ethylene)2. These orderings resemble the strength of complexation of the ir-ligand. Extended Hiickel molecular orbital calculations were performed to compare (cyclopentadienyl)cobalt dicarbonyl and (cyclopentadienyl)cobalt bis(ethylene) with respect to their HOMO/LUMO gap and their frontier MO composition, in order to probe the influence of different paramagnetic screening terms upon "Co shifts in these complexes. The increased shielding of the Co nucleus in the dicarbonyl complex can be rationalized by its 0.3-eV larger HOMO/LUMO energy separation and its smaller Co contribution in the LUMO wave function. Chemical applications and the relevance of "Co NMR data are pointed out. Additionally, structures and dynamic behavior of these complexes have been investigated by !H and 13 *C NMR spectroscopy.

The Anion [Co(C8H12)2]–. A Comparative Study of the Crystal Structures of [{K(18-crown-6)}2(C5H5)][Co(C8H12)2] and Co(C8H12)(C8H13)

“…The 59 Co NMR resonance of anion 3a appears as a single, broad signal at −1737 ppm (∆ V 1/2 = 1376 Hz, at 25 • C), while the signal of compound 2 is observed at −280 ppm, in accordance with reported data [18].…”

“…Due to the relatively high magnetic moment and a natural abundance of 100 % of the quadrupolar nucleus, a large number of 59 Co NMR data are available [18]. The 59 Co NMR resonance of anion 3a appears as a single, broad signal at −1737 ppm (∆ V 1/2 = 1376 Hz, at 25 • C), while the signal of compound 2 is observed at −280 ppm, in accordance with reported data [18].…”

Synthesis, multinuclear NMR, and solution conformation of (η5-indenyl)CoIRfL complexes (L = CO, P-donor)

“…TIndenyl complexes are known for cobalt in formal oxidation states 111, 11, and I with the very air-sensitive Co(1) derivatives formulated as ( q 5 -i n d e n y l )~o~2 (L = ethylene (23,24), CO (25,26), PPh, (27), PMe, (28), P(OR), (29) or L, = cyclic and acyclic dienes (3,4,23) or vinylketenes (27)) being the most numerous. Fewer Co(II1) complexes have been re orted (21,27,28,30) and only one crystal P.…”

Organometallic Chemistry

“…Following a three-month visiting professorship in Berkeley in 1980, he was appointed to a visiting professorship in Munich in 1981 that was converted into a permanent academic position. Working with Ernst Otto Fischer, the chemistry Nobel laureate of 1973, he benefited from an ideal research environment that enabled him to compare his theoretical analyses and predictions with experimental data [34][35][36][37][38]40,42,43,[45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60]62,63,65,74]. As an accomplished communicator of his research results, Peter Hofmann was a much sought-after visiting professor in the following years, which led to stints at the Universities of Bern, Ulm, TU and FU Berlin, Heidelberg, Rennes, Strasbourg, and Madison Wisconsin.…”