A Dimetalloxycarbene Bonding Mode and Reductive Coupling Mechanism for Oxalate Formation from CO₂

Abstract

We describe the stable and isolable dimetalloxycarbene [(TiX3 )2 (μ2 -CO2 -κ(2) C,O:κO')] 5, where X=N-(tert-butyl)-3,5-dimethylanilide, which is stabilized by fluctuating μ2 -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 μ2 -κ(1) O:κ(1) O' bonding mode of the free dimetalloxycarbene compared to the μ2 -κ(2) C,O:κ(1) O' bonding mode of the masked dimetalloxycarbene. The parent cationic bridging formate complex [(TiX3 )2 (μ2 -OCHO-κO:κO')][B(C6 F5)4], 4[B(C6 F5)4], was simply deprotonated with the strong base K(N(SiMe3 )2 ) to give 5. Complex 5 reacts smoothly with CO2 to generate the bridging oxalate complex [(TiX3 )2 (μ2 -C2 O4 -κO:κO'')], 6, in a C-C bond formation reaction commonly anticipated for oxalate formation by reductive coupling of CO2 on low-valent transition-metal complexes.

How easy is CO2 fixation by M–C bond containing complexes (M = Cu, Ni, Co, Rh, Ir)?

“…Despite the very recent large number of experimental [47][48][49][50][51][52] and theoretical [53][54][55][56][57][58][59] studies focusing on CO 2 insertion, reports on direct comparison between theoretical and experimental results remain very limited. 53,60,61 Based on the experimental findings, a plausible mechanism for CO 2 insertion into the M-X bonds (X = O or N) proposed by Nolan et al is outlined in Scheme 2. Considering complex A, the nucleophilic attack of the heteroatom X onto CO 2 does not proceed via the oxygen atoms but through the carbon atom, involving a four-membered cyclic center, hypothetically structure B, i.e.…”

Reaction of CO2 with a Vanadium(II) Aryl Oxide: Synergistic Activation of CO2/Oxo Groups towards H‐Atom Radical Abstraction

“…We also considered the possibility that the starting V II species might afford a dianonic dinuclear CO 2 complex. Although DFT predicts for this hypothetical complex the same bridging arrangement as observed by Maron, Okuda, Cummins, and co‐workers, the energy profile was less favorable with respect to the simple deoxygenation. The scenario provided by ts6 is therefore somewhat reminiscent of a frustrated Lewis pair, whose high reactivity is sufficient to perform dihydrogen activation among other remarkable transformations .…”

Photolytic and Reductive Activations of 2‐Arsaethynolate in a Uranium–Triamidoamine Complex: Decarbonylative Arsenic‐Group Transfer Reactions and Trapping of a Highly Bent and Reduced Form

“…The U1ÀO1, U1ÀAs1, U2ÀAs1 bond distancesa re 2.294 (7), 2.895(4), and 2.923(4) ,r espectively,a nd are unexceptional. The U1ÀC1 distance of 2.54(2) ,i se ssentially the same as in I, [7] and compares to distances of 2.576(12)-2.598(11) and 2.672 (5) in the mesoionic and N-heterocyclic carbene complexes [U{CN(Me)C(Me)N(Me)CH}(N") 3 ] and [U{C(NMeCMe) 2 }(N") 3 ][ N" = N(SiMe 3 ) 2 ], [14] which together with the acute O-C-As angle suggests, analogously to some reduced CO 2 and CS 2 complexes, [15] that the C-atom in 5 possess some carbene character when highly reduced. The UÀN amide (av.2 .324 (9) )a nd UÀN amine (av.2 .776 (7) )d istances are averaged by the disorder,a nd towards the high end of such distances.…”