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 LiAlH 4 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 CO 2 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 trans arrangement is 3.1 kcal·mol −1 lower in energy than the O−O trans isomer. Inserting CO 2 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 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)