Reductive Coupling of a Diazoalkane Derivative Promoted by a Potassium Aluminyl and Elimination of Dinitrogen to Generate a Reactive Aluminium Ketimide

The reaction of 9-diazo-9H-fluorene (fluN2) with the potassium aluminyl K[Al(NON)] ([NON]2– = [O(SiMe2NDipp)2]2–, Dipp = 2,6-iPr2C6H3) affords K[Al(NON)(κN1,N3-{(fluN2)2})] (1). Structural analysis shows a near planar 1,4-di(9H-fluoren-9ylidene)tetraazadiide ligand that chelates to the aluminium. The thermally induced elimination of dinitrogen from 1 affords the neutral aluminium ketimide complex, Al(NON)(N=flu)(THF) (2) and the 1,2di(9H-fluoren-9-yl)diazene dianion as the potassium salt, [K2(THF)3][fluN=Nflu] (3). The reaction of 2 with N,N'diisopropylcarbodiimide (iPrN=C=NiPr) affords the aluminium guanidinate complex, Al(NON){N(iPr)C(N=CMe2)N(CHflu)} (4), showing a rare example of reactivity at a metal ketimide ligand. Density functional theory (DFT) calculations have been used to examine the bonding in the newly formed [(fluN2)2]2– ligand in 1 and the ketimide bonding in 2. The mechanism leading to the formation of 4 has also been studied using this technique.