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 degreesC generates [AIH(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 degreesC 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(C)CMeCHCMeNAr)(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 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). ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).