Inhibierung der [2+2+2]‐Cyclisierung durch Chelatbildung: Alkin‐ und Vinylidenkomplexe mit Cyclopentadienylcobalt(I)

Abstract

Die Alkintrimerisierung zu Arenen, die üblicherweise bei der Umsetzung von Cyclopentadienylcobalt (I)‐Komplexen mit Alkinen beobachtet wird, läßt sich durch Chelatbildung mit einem an den Cyclopentadienylliganden gebundenen „Phosphanarm”︁ unterbinden. Statt dessen können Alkinkomplexe in sehr guten Ausbeuten erhalten werden. der Einsatz von Ethin selbst führt in 88 % Ausbeute zum Vinylidenkomplex 1, einem möglichen Vorläufer für carbencobaltkomplexe.

Half-sandwich cyclopentadienyl rhodium complexes bearing pendant sulfur or oxygen ligands and their catalytic behaviors in ethylene polymerization

“…In the 1 H NMR spectrum of 3 in CDCl 3 , the cyclopentadienyl triplets [17] are observed at 5.84 and 5.62 ppm, the ethylenic side-chain protons (CH 2 S and CH 2 CH 2 S) appeared at 3.82, 2.96 and 2.65, 2.47 ppm, the SCH 2 CH 3 multiplet is at 3.54 ppm, and the CH 2 CH 3 triplet is at 1.35 ppm. A halogen-bridged dimmer structure with a decoordinated sulfide arm can be excluded on the basis of the observation of two doublets of multiplet of the ethylenic protons by NMR spectroscopy [18].…”

The first metal complexes of bicyclopropylidene, a unique tetrasubstituted alkene ligand

“…It is instructive to compare these numbers with those of ethene and the ethene complex corresponding to 7. The bond length of ethene is 1.330 Å, in the ethene complex corresponding to 7 this value is 1.396 Å, 24 an increase of only 5.0%. The bonds in 2 and 7 adjacent to the double bond are of similar length, whereas the single bond opposite the double bond is significantly shortened from 1.544 Å in 2 to 1.499 Å in complex 7.…”

“…22 Complexation of sensitive ligands without subsequent reactions is also possible with the {[2-(di-tert-butylphosphanyl)-P-ethyl]-h 5 -cyclopentadienyl}cobalt(i) fragment (CoCp#), with which the cyclopentadienyl ligand and the pending phosphane side arm coordinate at the metal to form a rather stable chelate. [23][24][25] For oligomerization reactions, frequently observed at normal cyclopentadienyl cobalt, to occur with this complex fragment, an advance decomplexation of the phosphane side arm would be necessary. In this case the phosphane side arm normally wins the competition with an external ligand for entropic reasons.…”

Reactions of a Chelated Cyclopentadienylcobalt(I) Complex with 3,3-Disubstituted Cyclopropenes: Formation of Isoprene, Vinylcarbene, and 1-Phosphadiene Ligands at the Metal

“…As the Cp # Co system, in contrast to CpCo, does not facilitate cyclooligomerization reactions of alkynes, alkyne complexes are easily obtained with Cp # Co , Reactions with tert -butylphosphaethyne resulted in complete cleavage of the P⋮C bond with formation of a phosphido cluster, whose phosphido ligand could be oxidized to a PO or PS ligand . Cyclopropenes form complexes with transition metals or react with transition metal complexes to form oligomers − or vinylcarbene complexes. , Because only a few vinylcarbene complexes of cobalt are known , and in light of the role of vinylcarbene complexes in catalysis, we undertook the preparation of such species by treatment of Cp # Co complexes such as 1 or 2 with cyclopropenes. …”