A Dimetalloxycarbene Bonding Mode and Reductive Coupling Mechanism for Oxalate Formation from CO21. Issue 31 (25th June 2015)

• Record Type: Journal Article
• Authors: Paparo, Albert; Silvia, Jared S.; Kefalidis, Christos E.; Spaniol, Thomas P.; Maron, Laurent; Okuda, Jun; Cummins, Christopher C.
• Is Part Of: Angewandte Chemie international edition. Volume 54:Issue 31(2015)
• Page Start: 9115
• Page End: 9119
• Publication Date: 2015-06-25
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201502532
• Languages: English
• ISSNs: 1433-7851

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>We describe the stable and isolable dimetalloxycarbene [(TiX<sub>3</sub>)<sub>2</sub>(μ<sub>2</sub>‐CO<sub>2</sub>‐κ<sup>2</sup><italic>C</italic>, <italic>O</italic>:κ<italic>O</italic>′)] <bold>5</bold>, where X=<italic>N</italic>‐(<italic>tert</italic>‐butyl)‐3, 5‐dimethylanilide, which is stabilized by fluctuating μ<sub>2</sub>‐κ<sup>2</sup><italic>C</italic>, <italic>O</italic>:κ<sup>1</sup><italic>O</italic>′ coordination of the carbene carbon to both titanium centers of the dinuclear complex <bold>5</bold>, as shown by variable‐temperature NMR studies. Quantum chemical calculations on the unmodified molecule indicated a higher energy of only +10.5 kJ mol<sup>−1</sup> for the μ<sub>2</sub>‐κ<sup>1</sup><italic>O</italic>:κ<sup>1</sup><italic>O</italic>′ bonding mode of the free dimetalloxycarbene compared to the μ<sub>2</sub>‐κ<sup>2</sup><italic>C</italic>, <italic>O</italic>:κ<sup>1</sup><italic>O</italic>′ bonding mode of the masked dimetalloxycarbene. The parent cationic bridging formate complex [(TiX<sub>3</sub>)<sub>2</sub>(μ<sub>2</sub>‐OCHO‐κ<italic>O</italic>:κ<italic>O</italic>′)][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>], <bold>4</bold>[B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>], was simply deprotonated with the strong base K(N(SiMe<sub>3</sub>)<sub>2</sub>) to give <bold>5</bold>. Complex <bold>5</bold> reacts smoothly with CO<sub>2</sub> to generate the bridging oxalate complex [(TiX<sub>3</sub>)<sub>2</sub>(μ<sub>2</sub>‐C<sub>2</sub>O<sub>4</sub>‐κ<italic>O</italic>:κ<italic>O</italic>′′)], <bold>6</bold>, in a CC bond formation reaction commonly anticipated for oxalate formation by reductive coupling of CO<sub>2</sub> on low‐valent transition‐metal complexes.</p> </abstract>