Reductive Cyclotrimerization of Carbon Monoxide to the Deltate Dianion by an Organometallic Uranium Complex

Abstract

Despite the long history of the Fischer-Tropsch reaction, carbon monoxide has proven remarkably resistant to selective homologation under mild conditions. Here, we find that an organouranium(III) complex induces efficient reductive trimerization of carbon monoxide at room temperature and pressure. The result is a triangular, cyclic C3O(2-)3, or deltate, dianion held between two uranium(IV) units. The bonding within the C3O(2-)3 unit and its coordination to the two U centers have been analyzed by x-ray diffraction and density functional theory computational studies, which show a stabilizing C-C agostic interaction between the C3 core and one U center. Solution nuclear magnetic resonance studies reveal a rapid equilibration of the deltate unit between the U centers.

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).…”

Facile Conversion of CO/H2 into Methoxide at a Uranium(III) Center

“…The distances between the metal and the ring centroids in the U(h-C 8 H 6 {SiiPr 3 -1,4} 2 )(hCp*) fragment (U-M1 2.4887(2) and U-M2 1.95590(2) ) are identical within the estimated standard deviations (esds) to those for other U IV complexes incorporating this fragment, for example, [U(h-C 8 H 6 {SiiPr 3 -1,4} 2 )(h-Cp*)] 2 (m-h 1 :h 2 -C 3 O 3 ) (U-M1 2.480(8) and U-M2 1.950 (8) ), although the M1-U- M2 angle in 3 (135.809 (9)8) is slightly more acute than that in the latter (141.8 (2)8). [6] The U-OMe linkage in 3 is essentially linear (178.3 (5)8) with a U-O distance of 2.058(4) , and the structural features are comparable to those found in other (rare) examples of U IV terminal methoxide complexes. [10] To gain insight into the bonding situation in 3, computational studies were carried out at the DFT (B3PW91/SDD-(U,Si)-6-31G(d,p)(C,O,H)) level.…”

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.…”

“…[13] Das quadratisch-planare SquaratDianion (Abbildung 1, C) kann elektrochemisch bei sehr hohem CO-Druck erzeugt werden. [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).…”