Metathesis Reaction of Hydrocarbyl Ligands across the Triruthenium Plane

Abstract

Carbon-chain recombination, similar to that observed during the cracking of alkanes and in the Shell higher olefin process, is one of the most important reactions in the chemical industry. There has been a continuous demand for a process that can yield hydrocarbons of desired chain length. Recently, a method for converting lower alkanes into higher alkanes, which is referred to as alkane metathesis, has been reported. [1] Alkane metathesis has considerable scientific and industrial importance because it can convert gaseous hydrocarbons into liquid fuels. Such interconversion involves three catalytic reactions: activation of the alkane CÀH bond, olefin metathesis, and hydrogenation of the formed olefins. However, because of the cross-metathesis of the alkenes during the recombination process, the product will have a molecular weight distribution to some extent.Coupling reactions between two hydrocarbyl ligands placed on both faces of a trimetallic plane have often been seen in organometallic chemistry, [2] as has CÀC bond scission on a cluster.[3] These reactions have attracted considerable attention and are considered to be characteristic of cluster compounds. We have studied C À C bond formation on a triruthenium cluster by directing our attention to the roles of an MÀM bond.[4] Recently, we reported the synthesis of 2 using the coupling reaction of m 3 -benzyne and m 3 -vinylidene ligands separated by the Ru 3 plane of 1 (Scheme 1).[4c] In this reaction, the formation of the ruthenacyclopentadiene skeleton was accompanied by the rupture of a Ru À Ru bond. We also reported the scission of a CÀC bond in a ruthenacyclopentadiene skeleton in which a Ru 3 triangle was reconstructed.[4a] Such flexibility in a cluster skeleton would enable a novel recombination of hydrocarbons. Herein, we report an unprecedented selective interconversion of two C 5 fragments into C 8 and C 2 fragments on a triruthenium cluster.The thermolysis of 4, which was obtained by the sequential treatment of 3 with 1-pentene and 1-pentyne, [5] resulted in the quantitative formation of an equilibrated mixture of 5 a and 5 b (Scheme 2). At ambient temperature, the motion of the hydrido ligand was so rapid that the signals of 5 a and 5 b coalesced. For simplification, we denote this equilibrated mixture as 5.[6] The structures of 4 and 5 were determined by X-ray diffraction studies (Figure 1 and Figure 2, respectively).[7] These results clearly indicate that the m 3 -pentylidyne and m 3 -pentyne ligands in 4 were respectively transformed into the m 3 -ethylidyne and m 3 -octyne ligands in 5.This rearrangement required the migration of the C 3 fragment across the Ru 3 plane. In order to elucidate the mechanism, we monitored the reaction by means of NMR spectroscopy. Upon heating at 80 8C, formation of the m 3 -butylidyne-m 3 -hexyne complex 6 was observed (Path a in Scheme 3). For the formation of 6, a carbyne group must Scheme 1. CÀC bond formation in a trimetallic cluster accompanied by MÀM bond breaking. Cp* = pentamethylcyclopentadienyl. Sche...

Die hohe Kunst der bimetallischen Aktivierung: Pendeln von Carbenen, Kohlenwasserstoffen und Hydridliganden zwischen Metallzentren

“…[10] Dies ist in Schema 4 veranschaulicht: Komplex 7 reagiert glatt mit einem Olefin (1-Penten) und dann mit einem Alkin (1-Pentin) zum Komplex 8, der als Mischung der Isomere 8 a,b vorliegt, die sich in der Stellung der Hydride unterscheiden. [10] Dies ist in Schema 4 veranschaulicht: Komplex 7 reagiert glatt mit einem Olefin (1-Penten) und dann mit einem Alkin (1-Pentin) zum Komplex 8, der als Mischung der Isomere 8 a,b vorliegt, die sich in der Stellung der Hydride unterscheiden.…”

“…[8] Dies Bestimmte Umwandlungen ungesättigter Kohlenwasserstoffe an dem dreikernigen Pentahydrid-Komplex 7 sind sogar noch spektakulärer, weil sie selektiv sind und die Flexibilität der Clusterstruktur voll ausnutzen. [10] Dies ist in Schema 4 veranschaulicht: Komplex 7 reagiert glatt mit einem Olefin (1-Penten) und dann mit einem Alkin (1-Pentin) zum Komplex 8, der als Mischung der Isomere 8 a,b vorliegt, die sich in der Stellung der Hydride unterscheiden. [10] Die zwei Liganden werden an unterschiedlichen Clusterflächen in Form eines m 3 -Pentylidins [11] (obere Fläche) bzw.…”

“…[10] Dies ist in Schema 4 veranschaulicht: Komplex 7 reagiert glatt mit einem Olefin (1-Penten) und dann mit einem Alkin (1-Pentin) zum Komplex 8, der als Mischung der Isomere 8 a,b vorliegt, die sich in der Stellung der Hydride unterscheiden. [10] Die zwei Liganden werden an unterschiedlichen Clusterflächen in Form eines m 3 -Pentylidins [11] (obere Fläche) bzw. eines…”

The Subtle Art of Bimetallic Activation: Juggling Carbenes, Hydrocarbons, and Hydride Ligands Between Metals

“…Certain transformations of unsaturated hydrocarbons onto the trinuclear pentahydride complex 7 are even more spectacular because they are selective and take full advantage of the flexibility of the cluster skeleton. [10] This is illustrated in Scheme 4: Complex 7 is prone to react sequentially with an olefin (1-pentene) and an alkyne (1-pentyne) in a selforganized manner at room temperature to give cleanly complex 8 (existing as a mixture of isomers 8 a,b differing in the position of hydrides). [10] The two ligands are each activated on a different cluster face (Scheme 4), as a m 3 -pentylidyne [11] (upper face), and a m 3 -pentyne (lower face).…”

Anorganische Chemie 2010

“…Zu einer Serie von C‐C‐Bindungsspaltungen und ‐knüpfungen kommt es bei der Thermolyse eines μ3‐Pentylidin‐μ3‐Pentin‐Trirutheniumkomplexes 2_30. Dabei wandert ein C3‐Fragment von einer Seite der Ru3‐Ebene des Clusters auf die andere, wodurch zwei C5‐Einheiten in ein C2‐ und ein C8‐Fragment umgewandelt werden.…”