Gehinderte Ligandbewegungen in Übergangsmetallkomplexen, XIX [1]. Oktaedrische Wolfram-Olefin-Komplexe mit Bisphospbinoethan-Liganden / Hindered Ligand Motions in Transition Metal Complexes, XIX [I]. Octahedral Tungsten Olefin Complexes with Bisphosphinoethane Ligands

Abstract

<jats:p>(OC-6-32)-W(CO)<jats:sub>3</jats:sub>[(CH<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub>PC<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub>P(CH<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub>] (olefin) complexes (9-14) were prepared photochemically from W(CO)<jats:sub>4</jats:sub>[(CH<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub>PC<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub>P(CH<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub>](l) via W(CO)<jats:sub>3</jats:sub>[(CH<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub>PC<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub>P(CH<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub>]- (THF) (2) and the electron poor olefins dimethyl inalonate(3), fumarate (4), inothylfumarate (5), fluorofumarato (6), chlorofumarato (7) and bromofumarate (8). The stereoche­mistry of 9-14 was elucidated by IR and NMR spectroscopy. The hindered rotations of the olefin ligands in 9-14 were studied by D-NMR spectroscopy. 11-14 form two diastereomeric isomers when the olefin rotation is freezed. The spectroscopic behaviour of the dimethyl fumarato complex 10 gives unambiguous proof for the rotation of the olefin ligand around the metal-olefin-bond. Alternative motions are ruled out.</jats:p>

Dissociative CO Photosubstitution in M(CO)4(1,4-diazabutadiene) Complexes (M = W, Mo) by an Olefin Affording Novel fac-M(CO)3(1,4-diazabutadiene)(η2-olefin) Derivatives

“…Olefin ligands in group 6 carbonylmetal complexes commonly prefer an orientation that minimizes competition with other ligands for π back-donation from the metal and, thus, favors the metal d(π)→olefin (π*) component of the metal−olefin bond in the best possible way. Illustrative examples are the trans-orthogonal arrangement of two η 2 -CC units in various trans -M(CO) 4 (η 2 -olefin) 2 40,77,78 and mer -M(CO) 3 (η 2 :η 2 -diene)(η 2 -olefin) 45,48 compounds, the coplanar arrangement of the η 2 -CC and carbene unit in a trans -M(CO) 4 (carbene)(η 2 -olefin) complex, the eclipsed orientation of the η 2 -CC unit to the L−M−L axis in compounds of the type mer -M(CO) 3 (L) 2 (η 2 -olefin), , and the eclipsed orientation of the η 2 -CC unit to a L−M−CO axis in mer -M(CO) 3 (L−L)(η 2 -olefin) ,, and cis -M(CO) 4 (L)(η 2 -olefin) , systems. With these precedents in mind, one might suspect that a mer -M(CO) 3 (iprop-dab)(η 2 -eco) geometry of 3 and 4 (where the η 2 -CC unit, if eclipsed to one of the N−M−CO axes, shares a metal d(π) orbital with only one carbonyl ligand) would be thermodynamically favored over the actually observed structure (Figure ), where the olefin experiences competitive demand for π back-donation from the metal by two carbonyls and by the α-diimine ligand.…”