Trifluoromethyl-Containing β-Diketiminato-Magnesium Complexes: Synthesis, Structures, and Catalysis for the Hydroboration of Carbodiimides

Trifluoromethyl-containing β-diketiminate ligands (CF 3 )BDI Et -H = (2,6-di-Et 2 C 6 H 3 )N=C (CF 3 )CH=C (CF 3 )NH(2,6-di-Et 2 C 6 H 3 ), (CF 3 )BDI i Pr -H = (2,6-di- i Pr 2 C 6 H 3 )N=C (CF 3 )CH=C (CF 3 )NH(2,6-di- i Pr 2 C 6 H 3 ) react with Mg n Bu 2 readily to provide THF-ligated four-coordinate monomeric magnesium butyl complexes (CF 3 )BDI Et Mg n Bu (THF) ( 1 ) and (CF 3 )BDI i Pr Mg n Bu (THF) ( 2 ) in THF, and three-coordinate monomeric complexes (CF 3 )BDI Et Mg n Bu ( 3 ) and (CF 3 )BDI i Pr Mg n Bu ( 4 ) in toluene, respectively. The alkane elimination between 4 and NH (SiHMe 2 ) 2 gives silylamido complex 5 in toluene. Treatments of 4 with heterocumulene tert-butyl isothiocyanate, tert-butyl isocyanate, and N,N′-diisopropylcarbodiimide produce single insertion derivatives (CF 3 )BDI i Pr MgN ( t Bu)C ( n Bu)S ( 6 ), (CF 3 )BDI i Pr MgN ( t Bu)C ( n Bu)O ( 7 ), and (CF 3 )BDI i Pr MgN ( i Pr)C ( n Bu)N ( i Pr) ( 8 ), respectively. All these new compounds were characterized by NMR spectroscopy, and the molecular structures of complexes 1 , 2 , 4 – 7 were further confirmed by single-crystal X-ray diffraction analyses. Moreover, representative complexes 2 – 5 were employed as pre-catalysts for the hydroboration of commercially available carbodiimides bearing aliphatic and aromatic substituents with pinacol borane HBpin, including diisopropylcarbodiimide (DIC), dicyclohexylcarbodiimide (DCC), di- tert -butylcarbodiimide, 2,6-diisopropylphenylcarbodiimide, and unsymmetric 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDCI), in which the three-coordinate monomeric complexes 3 and 4 showed better efficiency giving corresponding N -boryl formamidine products in high yields. A possible mechanistic pathway of the hydroboration reaction has been proposed.