A Dimetalloxycarbene Bonding Mode and Reductive Coupling Mechanism for Oxalate Formation from CO 2

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