Intermediate Complexes in the Octacarbonyl Dicobalt-Initiated Living Polymerization of 3-Methyl-1,2-butadiene

Abstract

In the reaction of octacarbonyl dicobalt with 3-methyl-1,2-butadiene at room temperature dinuclear η3-allyl-type complexes are formed which contain 2 + n (n = 0, 1, 2, 3, ···) five-carbon units depending on the applied molar ratio. These complexes are the individual compounds in the octacarbonyl dicobalt-initiated living polymerization of 3-methyl-1,2-butadiene. The first three members in this series of complexes containing two (1), three (2), and four (3) five-carbon units have been isolated and characterized by IR, Raman, 1H, and 13C NMR spectroscopies, molecular weight, and for 1 and 2 also by single-crystal X-ray diffraction. The first two molecules of 3-methyl-1,2-butadiene establish the formation of two (η3-3,3-dimethylallyl)cobalt tricarbonyl parts which are linked together at the central allylic carbon by a carbonyl group. By the addition of 3-methyl-1,2-butadiene in excess, the monomer inserts into the unsubstituted allylic carbon−cobalt bond in a 1,2-fashion, pushing the cobalt atoms further apart. The X-ray structures of 1 and 2 disclose that the 1,2-polymer chain grows in a helical manner. The rate of the insertion of the monomer is first order with respect of both the 3-methyl-1,2-butadiene and the dicobalt complex and is negative first order with respect of carbon monoxide. The observed rate constants of the formation of 1−3 at 30 °C are 14.3 × 10-4, 1.75 × 10-4, and 0.79 × 10-4 s-1, reproducible to within 5, 10, and 7%, respectively.

Enhanced Solubilization of Bovine Serum Albumin in Reverse Micelles by Compressed CO2

“…We expected to be able to construct new ligands by metal‐induced dimerization of 1,1‐difluoroallene and tetrafluoroallene on manganese and cobalt complex fragments, as reactions of allenes with decacarbonyldimanganese7 and octacarbonyldicobalt8 resulted in new ligand systems through C−C coupling. Furthermore the dimerization is the first step of a polymerization reaction which is not a metal‐catalyzed process in the case of fluorinated alkenes.…”

Fluorierte Bis(enyl)-Liganden durch metallinduzierte Dimerisierung fluorierter Allene

“…Wir hofften daher, durch metallinduzierte Dimerisierung von 1,1‐Difluorallen und Tetrafluorallen an Mangan‐ und Cobaltkomplexfragmenten neue fluorierte Liganden aufbauen zu können, da die Reaktionen von Allenen mit Decacarbonyldimangan7 und Octacarbonylcobalt8 unter C‐C‐Bindungsknüpfung neue Ligandensysteme liefern. Außerdem bildet die Dimerisierung den ersten Schritt einer Polymerisation, für die es im Falle der fluorierten Alkene keine Katalysatoren auf der Grundlage von Metallen gibt.…”

Recent Advances in the Pauson–Khand Reaction

“…[7] The reaction temperatures and solvents varied, but the cyclopentenones could often be isolated in reasonably good yields. The authors were unable to effect efficient cycloannulation from alkyne, allene and dicobalt octacarbonyl due to the propensity of Co 2 (CO) 8 to polymerize allenes, [8] necessitating the preformation of the alkyne-cobalt-hexacarbonyl complex. Allene itself was unreactive under all conditions examined.…”