Verknüpfung von Alkinen mit Carbenliganden zu Wolfram‐koordinierten Cyclopropenen und deren stereoselektive Isomerisierung zu Vinylcarben‐Komplexen

Abstract

Die Synthese von Cyclopropen‐Komplexen nicht über Ligandenverdrängungsreaktionen, sondern durch Verknüpfung eines Carbenliganden mit einem Alkin am Metall gelang erstmals für 1, R = H, Me. Bereits oberhalb von ‐ 40°C lagert sich 1 stereoselektiv in den Vinylcarben‐Komplex 2 um.

Mono- and binuclear 3-amino cyclobuten-2-one complexes of tungsten—facile migration of pentacarbonylmetal fragments in carbene complexes

“…The W(1) Ã/W(2) bond in 6 (3.193(2) Å ) compares well with that in other (CO) 9 W 2 L complexes {e.g. 3.119(1) Å (L 0/C(H)C 6 H 4 OMe [12]), 3.119(1) Å (L 0/CH Ã/C(Ph) Ä/ C(H)Ph [13]), and 3.189(1) Å (L 0/CH Ã/CH Ä/CMe 2 [14])}. The two carbonyl ligands C(3) Ã/O(3) and C(22) Ã/O(22) are located in the plane of the dimetallacycle formed by the atoms W(1), W 2, and C (6).…”

“…The 13 C-NMR spectrum shows all in all six resonances for the nine CO ligands indicating a rather rigid structure. The influence of the coordination of W(CO) 4 to 2 (to give 6) on the 13 C-NMR resonances of the various ring carbon atoms differs strongly. The peaks of the Wbonded carbon atom and the C (H) atom are shifted towards higher field by about 90 ppm [in 6: d 0/186.26 ppm (WC ) and 88.53 ppm (C H)] whereas the remaining two atoms C3 and C4 are less strongly affected (shift of 10 Á/15 ppm towards higher field).…”

“…IR: FTIR spectrophotometer (FTS70), Bio-Rad. All IR measurements were carried out at 298 K. 1 H-NMR, 13 C-NMR: Bruker AC 250, Bruker DRX 600. NMR spectra were recorded at room temperature (r.t.).…”

“…16 (s,3H,NCH 3 ), 3.38 (s, 3H, NCH 3 ), 9.22 (s, 1H, C Ä/CH). 13 The sequential reactions of 1.00 mmol (0.27 g) of 1b [1.00 mmol (0.32 g) of 1c] with 1.00 mmol of n -BuLi and 1.00 mmol (0.35 g) of [W(CO) 6 ] in 5 ml of THF were carried out analogously to those of Section 4.2.1. Chromatography and recrystallization of the product from 3 ml of CH 2 Cl 2 gave orange Á/red crystals of 2.…”

Dötz Benzannulation Reactions: Heteroatom and Substituent Effects in Chromium Fischer Carbene Complexes

“…[42,43] Another possibility for this initial part of the reaction is alkyne insertion into 1 leading to the 17-electron intermediate 2 b followed by CO dissociation to also give the species 3 (associative route). [44,45] In the central part of the reaction, under the Dçtz benzannulation mechanistic proposal, there is first a rearrangement of carbene 3 a into 3 b (bending of the Cr À C(a) bond to place one of the CO ligands closer to the acarbon atom) followed by a CO insertion to form 4, an h 3 -vinylketene (or phenylketene) complex. Then, electrocyclic ring closure of 4 to form 5 followed by tautomerization generates 6, an h 6 -benzenic (or naphthalenic) Cr(CO) 3 complex (Scheme 2).…”