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

Abstract

Neugiergetriebene Forschung wird in der modernen Welt der Chemie gelegentlich als überflüssig angesehen. Clusterchemiker wurden nur allzu oft in diese Kategorie verwiesen, dürfen sich nun aber dank einer Reihe neuer Ergebnisse, die hauptsächlich von Beller et al. sowie einigen anderen Gruppen erzielt wurden, für ihre beharrlichen Bemühungen belohnt sehen. [1] In diesen Studien wurde gezeigt, dass so einfache Clusterkomplexe wie [Fe 3 (CO) 12 ] die besten und einfachsten Katalysatorvorstufen (d. h. die nützlichsten Quellen aktiver, ungesättigter Fragmente) für eine Reihe schwieriger Reaktionen sind, deren Mechanismen noch immer unklar sind.Allerdings wollen wir derlei reale Probleme der Clusterkatalyse, die in wichtigen Monographien ausführlich diskutiert wurden, [2] an dieser Stelle außer Acht lassen. Unser Fokus gilt vielmehr den fundamentalen Aspekten der Chemie polymetallischer Cyclopentadienyl-Rutheniumpolyhydride, die gegenwärtig von Suzuki und Mitarbeitern in Japan erforscht und entwickelt werden. Das zunehmende Aufkommen der Nanowissenschaften verschafft der Clusterchemie neue Perspektiven, z. B. zur Modellierung chemischer Reaktionen in der Peripherie von Nanopartikeln oder an Metalloberflächen heterogener Systeme.In unserem ersten Beispiel (Schema 1) [3] nimmt 1,3-Ditert-butylimidazol-2-yliden, ein repräsentatives N-heterocyclisches Carben (NHC), [4] an einer reversiblen Additions-Aktivierungs-Sequenz mit dem zweikernigen Aggregat 1 teil. Der anfänglichen Bildung des hypothetischen Addukts 2 [5]

Bimetallic Activation of 2‐Alkanones through Photo‐Induced α‐Hydrogen Abstraction Mediated by a Dinuclear Ruthenium Tetrahydride Complex

“…[2] Some remarkable reactions performed on the reaction sites of these polyhydride clusters were recently highlighted by Lavigne. [3] To extend our research to a new area, we began a project on the photochemistry of a polyhydride cluster which we anticipated to possess increased structural stability.…”

Bimetallic Activation of 2‐Alkanones through Photo‐Induced α‐Hydrogen Abstraction Mediated by a Dinuclear Ruthenium Tetrahydride Complex

“…Although there are a vast number of studies on the photochemistry of mononuclear complexes, multimetallic systems remain unexplored. [3] To extend our research to a new area, we began a project on the photochemistry of a polyhydride cluster which we anticipated to possess increased structural stability.We report herein an unusual photochemical reaction of a diruthenium tetrahydride complex, [(Cp*Ru)(m-H) 4 -(RuCp*)] (1) (Cp* = h 5 -C 5 Me 5 ), with 2-alkanones, which produces dinuclear oxatrimethylenemethane (OTMM) complexes.Upon irradiation with UV light (365 nm) at 10 8C for 48 h under an argon atmosphere, the red suspension of diruthenium tetrahydride (46.1 mg, 96.7 mmol) in acetone (15 mL) became a blue-purple solution. Whereas mononuclear polyhydride complexes often eliminate hydride ligands as dihydrogen, the elimination of dihydrogen upon photoirradation is hindered in hydride-bridged clusters.…”

“…[2] Some remarkable reactions performed on the reaction sites of these polyhydride clusters were recently highlighted by Lavigne. [3] To extend our research to a new area, we began a project on the photochemistry of a polyhydride cluster which we anticipated to possess increased structural stability.We report herein an unusual photochemical reaction of a diruthenium tetrahydride complex, [(Cp*Ru)(m-H) 4 -(RuCp*)] (1) (Cp* = h 5 -C 5 Me 5 ), with 2-alkanones, which produces dinuclear oxatrimethylenemethane (OTMM) complexes.Upon irradiation with UV light (365 nm) at 10 8C for 48 h under an argon atmosphere, the red suspension of diruthenium tetrahydride (46.1 mg, 96.7 mmol) in acetone (15 mL) became a blue-purple solution. Removal of the solvent under reduced pressure, followed by purification of residual solids by column chromatography on alumina (Merck Aluminium Oxide 90 standardized) with a toluene/tetrahydrofuran (5:1) mixture afforded a dinuclear OTMM complex of ruthenium, [(Cp*Ru){m-h 3 :h 1 -(CH 2 ) 2 CO}(m-H) 2 (RuCp*)] (2 a), in 91 % yield (46.8 mg, 88.2 mmol; Scheme 1).The 1 H NMR spectrum of 2 a recorded in [D 6 ]benzene at 25 8C exhibited two singlet signals at d = 1.67 and 1.80 ppm, which were assignable to the Cp* groups.…”

“…[2] Some remarkable reactions performed on the reaction sites of these polyhydride clusters were recently highlighted by Lavigne. [3] To extend our research to a new area, we began a project on the photochemistry of a polyhydride cluster which we anticipated to possess increased structural stability.…”

“…Molecular structure of 2 b with thermal ellipsoids set at 30 %. Relevant bond lengths [] and angles [8]: Ru1-Ru2 2.8322(3), Ru2-O1 2.0618(18), Ru1-C1 2.173(3), Ru1-C2 2.189(3), Ru1-C3 2.216(3), C2-O1 1.339(3), C1-C2 1.420(4), C2-C3 1.429(4), C3-C4 1.507(4); O1-C2-C1 120.8(3), O1-C2-C3 121.8(3), C1-C2-C3 115.7(3).…”