A Molecular Barium Hydrido Complex Stabilized by a Super-Bulky Hydrotris(pyrazolyl)borate Ligand

Carbon-Carbon Bond Formation from Carbon Monoxide and Hydride: The Role of Metal Formyl Intermediates

Current examples of carbon chain production from metal formyl intermediates with homogeneous metal complexes are described in this Minireview. Mechanistic aspects of these reactions as well as the challenges and opportunities in using this understanding to develop new reactions of CO and H2 are also discussed.

Anionic Magnesium and Calcium Hydrides: Transforming CO into Unsaturated Disilyl Ethers

The synthesis, characterisation and reactivity of two isostructural anionic magnesium and calcium complexes is reported. By X-ray and neutron diffraction techniques, the anionic hydrides are shown to exist as dimers, held together by a range of interactions between the two anions and two bridging potassium cations. Unlike the vast proportion of previously reported dimeric group 2 hydrides, which have hydrides that bridge two group 2 centres, here the hydrides are shown to be "terminal", but stabilised by interactions with the potassium cations. Both anionic hydrides were found to insert and couple CO under mild reaction conditions to give the corresponding group 2 cis-ethenediolate complexes. These cis-ethenediolate complexes were found to undergo salt elimination reactions with silyl chlorides, allowing access to small unsaturated disilyl ethers with a high percentage of their mass originating from the C₁ source CO.

Reactions of a Dilithiomethane with CO and N2 O: An Avenue to an Anionic Ketene and a Hexafunctionalized Benzene

Synthesis of value-added products from simple C1 feedstocks is an attractive alternative avenue to traditional fossil fuels. Hexa-substituted benzene derivatives are highly useful molecules but are often challenging to prepare. Herein, we report that the lithium complex [(Ph₂ P(S))₂ CLi₂ (THF)]₂ 1 reacts with CO lead to C-C bond formation and migration of a Ph₂ P(S)-fragment affording 2. Subsequent reaction with N₂ O results in oxidative cleavage of a P-C bond affording [Ph₂ P(S)OLi(THF)₂ ]₂ 4 and the anionic ketene-derivative Ph₂ P(S)CCOLi(THF)₂ 5. Heating 5 prompts cyclotrimerization giving the hexa-substituted benzene derivative [Ph₂ P(S)CCOLi(THF)₂ ]₃ 6 regioselectively. This transition metal-free protocol to a hexa-substituted benzene is viable on a gram scale and permits the incorporation of ¹³ C labels. The mechanisms of these reactions are detailed via extensive DFT computations.

Reaction of B2 (o-tol)4 with CO and Isocyanides: Cleavage of the C≡O Triple Bond and Direct C-H Borylations

The reaction of highly Lewis acidic tetra(o-tolyl)diborane(4) with CO afforded a mixture of boraindane and boroxine by the cleavage of the C≡O triple bond. ¹³ C labeling experiments confirmed that the carbon atom in the boraindane stems from CO. Simultaneously, formation of boroxine 3 could be considered as borylene transfer to capture the oxygen atom from CO. The reaction of diborane(4) with ^t Bu-NC afforded an azaallene, while the reaction with Xyl-NC furnished cyclic compounds by direct C-H borylations.