2-Imino-2,3-dihydrobenzoxazole-a useful platform for designing rare- and alkaline earth complexes with variable di- and trianionic O,N,N, ligands.

The reactions of 2-imino-2,3-dihydrobenzoxazole LH with M[N(SiMe 3 ) 2 ] 2 (THF) 2 (M = Yb and Ca) and Y(CH 2 SiMe 3 ) 3 (THF) 2 proceed with the opening of the dihydrobenzoxazole ring and the elimination of HN(SiMe 3 ) 2 or SiMe 4 . Besides, in the case of Yb[N(SiMe 3 ) 2 ] 2 (THF) 2 , an electron transfer from Yb(II) to L takes place and Yb(III) complex 1 is coordinated by a dianionic phenolate ligand containing a pendant radical-anionic diazabutadiene fragment form. When LH is reacted with Ca[N(SiMe 3 ) 2 ] 2 (THF) 2 , C-H bond activation of a methyl fragment by imino nitrogen occurs and affords a dimeric calcium complex 2. In 2, the phenolate ligand is dianionic due to the presence of the amido-imino fragment [R-NC(CH 3 )-C(CH 2 )-NR'] - (R = 2,4- t Bu 2 -C 6 H 2 O; R' = 2,6-iPr 2 C 6 H 3 ). In situ generated ate-complex {Na(Et 2 O) n }{Ca[N(SiMe 3 ) 2 ] 3 } also enables C-H bond activation, however the dianionic phenolate ligand in the resulting complex 3 contains an amido-imino fragment [R-N-C(CH 2 )-C(CH 3 )NR'] - featuring the sequence of N-C and NC bonds opposite to that in 2. The reaction of Y(CH 2 SiMe 3 ) 3 (THF) 2 with LH affords mono(alkyl) yttrium complex 4. 4 contains a dianionic amido-imino phenolate ligand resulting from the migration of one alkyl group to the CN bond [R-N-C(Me)(CH 2 SiMe 3 )-C(Me)NR']. 4 undergoes slow intramolecular C-H bond activation of the residual CH 3 group to afford a yttrium complex coordinated by a trianionic diamido-phenolate ligand [R-N-C(Me)(CH 2 SiMe 3 )-C(CH 2 )NR'].