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(SiMe3)(2)](2) (THF)(2) (M = Yb and Ca) and Y(CH2SiMe3)(3)(THF)(2) proceed with the opening of the dihydrobenzoxazole ring and the elimination of HN (SiMe3)(2) or SiMe4. Besides, in the case of Yb[N(SiMe3)(2)](2)(THF)(2), an electron transfer from Yb(s) to L takes place and Yb(iii) complex 1 is coordinated by a dianionic phenolate ligand containing a pendant radicalanionic diazabutadiene fragment form. When LH is reacted with Ca[N(SiMe3)(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(CH3)-C (=CH2) NR'](-) (R = 2,4-tBu(2)-C6H2O; R' = 2,6-iPr(2)C(6)H(3)). In situ generated ate-complex {Na(Et2O)(n))(Ca[N(SiMe3)(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(=CH2)-C(CH3)=NR'](-) featuring the sequence of N-C and N=C bonds opposite to that in 2. The reaction of Y(CH2SiMe3)(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)(CH2SiMe3)-C(Me)=NR']. 4 undergoes slow intramolecular C-H bond activation of the residual CH3 group to afford a yttrium complex coordinated by a trianionic diamido-phenolate ligand [R-N-C(Me)(CH2SiMe3)-C(=CH2)NR'].

Automated summary

The reactions of 2-imino-2,3-dihydrobenzoxazole with compounds containing Yb, Ca, and Y result in the formation of various coordination complexes, involving the opening of the dihydrobenzoxazole ring, elimination of nitrogen sources, and activation of C-H bonds.