Probing organometallic structure and reactivity by transition metal NMR spectroscopy†

Abstract

Transition metal NMR chemical shifts are readily measured by modern 1D and 2D pulse techniques and serve as a probe into electronic and steric effects of ligands and substituents in metal complexes. Quantitative correlations of metal chemical shifts with reaction rates and catalytic activities, both experimental and as a result of quantum chemical calculations, give new mechanistic insights and permit reactivity predictions and a screening of homogeneous catalysts. A variety of such examples involving the spin-1/2 nuclei 57 Fe, 103 Rh, and 187 Os as well as the quadrupolar nuclei 51 V, 53 Cr, 55 Mn, 59 Co, and 91 Zr are discussed.

Synthesis and Structure of [Tp*Rh{P(C7H7)3}] - Competition between the Ligands Tris(3,5-dimethyl-1-pyrazolyl)borate (Tp*) and Tris(1-cyclohepta-2,4,6-trienyl)phosphane. Proof of the κ2(N,B-H) Coordination Mode of the Tp* Ligand

“…The trigonal planar geometry of 6 as a 14 e complex is tentatively proposed at present since the O 2 complex 7 could be isolated. The structure of the Rh(III) species 7 is in agreement with the NMR data, in particular with the extreme deshielding of the 103 Rh nuclei (d 103 Rh = +4540) [13]. The d 31 P value (20.8) indicates that none of the cycloheptatrienyl substituents is linked to the rhodium atom in 7 [7].…”

Computational Study of Structures and Properties of Metallaboranes: Cobalt Bis(dicarbollide)

“…Experimental 11 B NMR chemical shifts of 1 are reproduced to better than 5 ppm at the GIAO-B3LYP/II' level, and the computed d( 11 B) values are only little affected by rotational averaging or the presence of a polarizable continuum. Larger such effects are found for the as-yet unknown 59 Co chemical shift, for which a value in the range between À1800 and À2400 ppm is predicted. Even though the accuracy achieved for the theoretical d ( 11 B) values is somewhat lower than that for heteroboranes at conventional ab initio levels, the level of density functional employed can afford qualitatively reliable chemical shifts, which can be useful in assignments and structural refinements of heteroboranes containing transition metal.…”

“…Co: Among the transition metals, 59 Co is a relatively wellbehaved NMR nucleus, [57] which can be observed in a wide variety of compounds, including fairly large biomolecules such as vitamin B 12 . [58] In metallacarboranes such as 1, the presence of quadrupolar boron nuclei adjacent to 59 Co may render the observation of the latter nucleus difficult, if not impossible.…”

Thermal Effects and Vibrational Corrections to Transition Metal NMR Chemical Shifts

“…The possibility to probe with NMR the very centre of a transition-metal complex has opened many fruitful applications for this important class of compounds. [4] Whereas density functional theory (DFT) has been the workhorse for computational transition-metal chemistry for some time, [5] it was not until the mid-nineties that DFT calculations could be performed which describe the chemical shifts of transition-metal nuclei properly. [6][7][8][9] It has turned out that the quantum chemical investigation of transitionmetal nuclei is quite elaborate and far from being a blackbox method.…”