Aluminium-catalysed isocyanate trimerization, enhanced by exploiting a dynamic coordination sphere

Main-group metals are inherently labile, hindering their use in catalysis. We exploit this lability in the synthesis of isocyanurates. For the first time we report a highly active catalyst that trimerizes alkyl, allyl and aryl isocyanates, and di-isocyanates, with low catalyst loadings under mild conditions, using a hemi-labile aluminium-pyridyl-bis(iminophenolate) complex.

Reactivities of zero-valent group 10 complexes toward organic isocyanates: synthesis of metallacycles containing dimeric isocyanate units, isocyanate cyclotrimerization, and computational chemistry

Five-membered metallacycles involving dimeric isocyanate units converted into cyclic tetramers and isocyanurates, depending on the central metal or organic isocyanates, and their synthetic and theoretical studies were carried out.

Yttrium dialkyl supported by a silaamidinate ligand: synthesis, structure and catalysis on cyclotrimerization of isocyanates

A four-coordinate yttrium dialkyl complex with a sterically demanding silaamidinate ligand exhibited high activity and excellent functional group tolerance for the catalysis of isocyanate cyclotrimerization.

Cycloaddition versus Cleavage of the C=S Bond of Isothiocyanates Promoted by Digallane Compounds with Noninnocent α-Diimine Ligands

Whereas the chemistry of single-bond activation by compounds of the main group elements has undergone some development in recent years, the cleavage of multiple bonds remains underexplored. Herein, the reactions of two digallanes bearing α-diimine ligands, namely, [L¹ Ga-GaL¹ ] (1, L¹ =dpp-dad=[(2,6-iPr₂ C₆ H₃ )NC(CH₃ )]₂ ) and [L² Ga-GaL² ] (2, L² =dpp-bian=1,2-[(2,6-iPr₂ C₆ H₃ )NC]₂ C₁₀ H₆ ), with isothiocyanates are reported. Reactions of 1 or 2 with isothiocyanates in 1:2 molar ratio proceeded with [2+4] cycloaddition of the C=S bond across the C₂ N₂ Ga metallacycle with formation of C-C and S-Ga single bonds to afford [L¹ (RN=C-S)Ga-Ga(S-C=NR)L¹ ] (3, R=Me; 4, R=Ph) and [L² (RN=C-S)Ga-Ga(S-C=NR)L² ] (8, R=allyl; 9, R=Ph). In the cases of 8 and 9, this cycloaddition is reversible. The digallanes reacted with 2 equiv of PhNCS in the presence of Na metal or at high temperatures through a unique reductive cleavage of the C=S bond to yield the disulfide-bridged digallium species [Na(THF)₃ ]₂ [L¹ Ga(μ-S)₂ GaL¹ ] (5), [L² Ga(μ-S)₂ GaL² ] (10), and [Na(DME)₃ ][L² Ga(μ-S)₂ GaL² ] (11). Moreover, products 4 and 5 can further react with an excess of isothiocyanate, through cleavage of the C=S bond or cycloaddition, to give the bis- or mono-S-bridged complexes [Na(THF)₂ ]₂ [L¹ (PhN=C-S)Ga(μ-S)₂ Ga(S-C=NPh)L¹ ] (6) and [L¹ (PhN=C-S)Ga(μ-S)Ga(S-C=NPh)L¹ ] (7). All the newly prepared compounds were characterized by elemental analysis, single-crystal X-ray diffraction, IR spectroscopy, NMR (3-9) or ESR spectroscopy (11), and DFT calculations.

Cyclotrimerisation of isocyanates catalysed by low-coordinate Mn(ii) and Fe(ii) m-terphenyl complexes

Isocyanurates can be synthesised through the cyclotrimerisation of primary isocyanates catalysed by low-coordinate manganese(ii) and iron(ii) m-terphenyl complexes under mild conditions.