Aspects of chirality retention in rearrangements of pseudooctahedral molybdenum and tungsten complexes

Abstract

A mechanistic analysis of the rearrangements and structural investigation of a series of p3-allyl molybdenum and tungsten dicarbonyl bisphosphine complexes are presented. A three-dimensional crystallographic analysis revealed the structure of (p3-C3H5)Mo(CO)2(diphos)Cl to be unlike that of the analogous diether and diamine chelates. Analysis of variabletemperature *H, 13C, and 3IP NMR spectra have allowed the elucidation of the dynamic properties of these complexes. A trigonal twist rearrangement is proposed for the dynamic behavior of these complexes in which a rotation of the triangular face formed by the halogen and two phosphorus atoms relative to the face formed by the aliyl and two carbonyl groups is involved. Barriers for this process are between 10 and 12 kcal/mol in the iodide derivatives. The twist process interconverts certain pairs of isomers while retaining particular elements of chirality, indicating that when complexes of this type rearrange a pathway for racemization may not necessarily be present.

Carbonyl complexes of manganese, rhenium and molybdenum with ethynyliminopyridine ligands

“…This implies that the inequivalency of the two allyl termini is maintained in solution at room temperature. Nevertheless this would be compatible with the existence of a trigonal twist involving the ''triangular'' face formed by the g 3 -methallyl and the two carbonyls [22]. This concerted rotation would maintain the relative orientation of the allyl and carbonyl ligands, keeping the inequivalency of the two allyl halves.…”

Fluxional Processes in Diamagnetic and Paramagnetic Allyl Dicarbonyl and 2-Methylallyl Dicarbonyl Molybdenum Histidinato Complexes as Revealed by Spectroscopic Data and Density Functional Calculations

“…[34,35,39,40] Also, the activation barriers of interconversion are in the range reported for trigonal twists of other pseudooctahedral Mo(allyl)(CO) 2 compounds. [39,40] Unlike all previous examples with a higher symmetry, three different positions of the allyl ligand with respect to the Mo(His) plane are possible in 1 ± 4. Even in very clean 1 H NMR spectra we could not detect signals of a third isomer in solution.…”

Syntheses, structures, and dynamic properties of M(CO)2(η3-C3H5)(en)(X) (M=Mo, W; X=Br, N3, CN) and [(en)(η3-C3H5)(CO)2M(μ-CN)M(CO)2(η3-C3H5)(en)]Br (M=Mo, W)

“…Among the group 6 metal allyl complexes M(CO) 2 (g 3 -C 3 H 5 )(L-L)(X) with a non-rigid bidentate ligand those with 1,2-bis(diphenylphosphino)ethane (dppe) are the most studied [15,22,32]. Due to their fluxional behavior one could observe only averaged NMR signals for these compounds at room temperature, the fluxional behavior being observed even at À100°C [15].…”

“…In general, when L-L is a rigid bidentate ligand the complex adopts conformation A (Scheme 1) in the solid state and displays non-fluxional behavior in solution [13,14]. When L-L is a non-rigid bidentate ligand, the complex adopts conformation C (Scheme 1) in the solid state and is fluxional in solution [15][16][17]. Although most of these allyl compounds can be classified into these two categories based on the rigidity of the bidentate ligand, exceptions have been found.…”

“…The dppe-containing compounds M(CO) 2 (g 3 -C 3 H 5 )(dppe)(X) have always been found to adopt conformation C in the solid state and display fluxional behavior in solution [16][17][18]. A trigonal twist rearrangement involving a rotation of the triangular face formed by the ligand X and the chelating diphosphine ligand P-P with respect to the face formed by the allyl and two carbonyls has been proposed to explain their fluxional behavior in solution [15,21,22]. In contrast to the dppecontaining compounds, those with 1,2-ethylenediamine (en) have not been studied extensively.…”