Reductive Cyclotetramerization of CO to Squarate by a U(III) Complex:  The X-ray Crystal Structure of [(U (η-C₈H₆{SiⁱPr₃-1,4}₂)(η-C₅Me₄H)]₂(μ-η²: η²-C₄O₄)

Abstract

The U(III) mixed-sandwich compound [U(eta-C5Me4H)(eta-C8H6{SiiPr3-1,4}2)(THF)] 1 may be prepared by sequential reaction of UI3 with K[C5Me4H] in THF followed by K2[C8H6{SiiPr3-1,4}2]. 1 reacts with carbon monoxide at -30 degrees C and 1 bar pressure in toluene solution to afford the crystallographically characterized dimer [(U(eta-C8H6{SiiPr3-1,4}2)(eta-C5Me4H)]2(mu-eta2: eta2-C4O4) 2, which contains a bridging squarate unit derived from reductive cyclotetramerization of CO. DFT computational studies indicate that addition of a 4th molecule of CO to the model deltate complex [U(eta-COT)(eta-Cp)]2(mu-eta1: eta2-C3O3)] to form the squarate complex [U(eta-COT)(eta-Cp)]2(mu-eta2: eta2-C4O4)] is exothermic by 136 kJ mol-1.

UIII‐Induced Reductive Co‐Coupling of NO and CO to Form UIV Cyanate and Oxo Derivates

“…2 :h 2 -C 4 O 4 )], [3] and the stoichiometric dimerisation of CO to afford the linear yne diolate complex…”

“…[2][3][4] However, the m-oxo bridge in 2 is significantly bent (U1-O1-U2 154.5(3)8), in marked contrast to the less sterically congested tris-cyclopentadienyl derivatives [ [9] which display the expected linear U-O-U geometry. Nonetheless, the U À O distances in 2 (U1ÀO1 2.113(5), U2ÀO1 2.105(6) ) are only marginally longer than that in (2) ).…”

Homologation and functionalization of carbon monoxide by a recyclable uranium complex

“…The high reduction potentials of low valent f-element complexes suggests a promising approach for the reductive activation of C 1 -small molecules such as CO (19)(20)(21)(22) and CO 2 (23); however, only a handful of f-element complexes can affect the reductive homologation of CO under ambient conditions (24,25). Organometallic uranium complexes can effect reductive homologation of CO to C n -oligomers (n ¼ 2-4) (26)(27)(28), and a small number of uranium triamide and triaryloxide complexes also reductively dimerize CO (29,30). More recently, an organometallic uranium complex was shown to effect the simultaneous reduction and hydrogenation of CO to give a coordinated methoxide that could be liberated as CH 3 OSiMe 3 (31); however, there have been no reports of successful homologation, functionalization, and removal of C n -oligomers (n ≥ 2) under mild conditions with retention of a metal complex that may be recycled for reuse in a synthetic cycle as has been demonstrated for CO 2 (32, 33), P 4 (34), and carbodiimides (35).…”

Hydrierung von CO an einem Uran(III)‐Zentrum

“…[3] Neueste Befunde lassen außerdem vermuten, dass Uran ein geeigneter Promotor im Fischer-Tropsch-Verfahren sein kçnnte, in dem CO und H 2 zu flüssigen Kohlenwasserstoffen umgewandelt werden. [1,[4][5][6][7] Trotz des offensichtlichen Potenzials von Uran sind Reaktionen der f-Elemente mit CO, vor allem verglichen mit denen der Übergangsmetalle, nur unzureichend erforscht. Diese Tatsache dürfte auf die schwachen p-Rückbindungen in Komplexen der f-Elemente zurückzuführen sein.…”

“…[14] Bis 2006 war die Synthese des trigonalen Deltat-Dianions (Abbildung 1, B) [4] Geringe sterische Veränderungen im Ligandensystem ermçglichten die Isolierung eines cyclotetramerisierten Produkts in Form eines über ein C 4 O 4 2À -Quadrat verbrückten Urankomplexes. [5] Der Mechanismus dieser Reaktion verläuft vermutlich über ein relativ langlebiges "Zickzack"-Intermediat, U-C 2 O 2 -U, das mit CO weiterreagiert (Schema 1). [6] [6] Seitdem gab es zwei weitere Verçffentlichungen, die die reduktive Kupplung von CO durch Uran zum Alkindiolat belegen.…”