Steric control of the reduction of carbodiimides by samarium(II) and the synthesis of very crowded samarium(III) complexes.

Reduction of N,N'-di(2,6-diisopropylphenyl)carbodiimide (DippNCNDipp) by [SmL(2)(thf)(2)] (1) (L = N,N'-bis(2,6-diisopropylphenyl)formamidinate, DippNC(H)NDipp) in PhMe gave [Sm(L)(3)] (2) in good yield. An analogous reaction of 1 with N,N'-dimesitylcarbodiimide (MesNCNMes) gave [SmL(2)(MesNC(H)NMes)] (3). In contrast, reduction of N,N'-dicyclohexylcarbodiimide (CyNCNCy) by 1 in PhMe gave mixture of products from which [SmL(2)(CyNC(CH(2)Ph)NCy)] (4) and [SmL(2)(CyNC(H)NCy)] (5) were isolated by fractional crystallisation. Using thf as the reaction solvent, solely compound 5 was crystallised. Reactions of [Sm(L)(2)(C[triple bond]CPh)(thf)] (6) with the carbodiimides RNCNR (R = Cy, Mes) gave [Sm(L)(2)(RNC(C[triple bond]CPh)NR)] (R = Cy (7) or Mes (8)) which are analogues of 4. No reaction was observed between 6 and DippNCNDipp.