Hydroalumination of carbon dioxide, carbon disulfide, and phenyl isocyanate with an aluminum ketiminate compound

The reaction of MeC(O)C(H)=C(Me)NHAr (Ar = 2,6-diisopropylphenyl) (1) with excess LiAlH₄ in diethyl ether at -78 °C generates [AlH(OCMeCHCMeNAr)₂] (2) in 76% yield. The aluminum formate compound [Al(OCMeCHCMeNAr)₂(OCOH)] (3) can be isolated from the reaction of 2 with CO₂ in 93% yield. Compound 3 is thermally stable and remains unchanged when heated under vacuum at 100 °C for 24 h. Similarly, a solution of 2 in dichloromethane reacts with carbon disulfide or phenyl isocyanate at room temperature to yield the insertion products [Al(OCMeCHCMeNAr) ₂(SCHS)] (4) and [Al(OCMeCHCMeNAr)₂(OCH=NPh)] (5), respectively, in 80% and 92% yield. Reaction of 2 with 1 equiv. of urethane in toluene at refluxing temperature for 1 h yields the aluminum isocyanate compound [Al(OCMeCHCMeNAr)₂(NCO)) (6). The molecular structures of compounds 2-6 have been determined by X-ray crystallography. Density functional calculations show that the isomer of compound 2 with an N-N frans arrangement is 3.1 kcal·mol^-1 lower in energy than the O-O trans isomer. Inserting CO₂ into the Al-H bond of compound 2 results in the formation of the formate compound 3; this reaction is predicted to be exothermic by 29.8 kcal·mol^-1.