Synthesis, characterization and crystal structures of isothiocyanate and carbodiimide complexes derived from organomagnesium reagents: insertion into Mg–X (X = C or N) bonds

A series of magnesium–isothiocyanate and –carbodiimide insertion products, Mg(SCPhNBu t ) 2 (thf) 2 1, Mg(SCPhNPh) 2 (thf) 2 2, Mg(Pr i NCRNPr i ) 2 (thf) 2 (R = Ph 3, Et 4 or Pr i 5) and Mg(Bu t NCEtNBu t ) 2 (thf) 2 6 have been prepared by the stoichiometric reaction between MgR 2 (R = Ph, Et or Pr i ) and various isothiocyanates and carbodiimides in tetrahydrofuran (thf) solution. The 1∶1 reaction between bis(diisopropylamido)magnesium and 1,3-diisopropylcarbodiimide gave a dinuclear complex Mg 2 (µ-NPr i 2 ) 2 [(Pr i N) 2 CNPr i 2 ] 2 7 and a mononuclear complex Mg[(Pr i N) 2 CNPr i 2 ] 2 (thf) 8 when the stoichiometry is 1∶2. The mononuclear complexes Mg[SC(NPh)NR 2 ] 2 (thf) 2 (R = Pr i 9 or Et 10) were obtained using phenyl isothiocyanate and bis(diethylamido)- or bis(diisopropylamido)-magnesium in 1∶1 stoichiometric ratio. A plausible mechanism for the formation of 7 and 8 is suggested. Reaction between MgEtBr and PhNCS in diethyl ether gave the dinuclear complex Mg 2 (SCEtNPh) 4 (OEt 2 ) 2 11. All of the complexes were characterized by 1 H, 13 C NMR and IR spectroscopy as well as elemental analysis. The crystal structures of 1, 3, 8, 9 and 11 were determined by single-crystal X-ray diffraction. The reaction of complex 1 with an excess of PhNCO resulted in the cyclotrimerization of phenyl isocyanate to give (PhNCO) 3 ·thf.