Ancillary Steric Effects on the Activation of SiH Bonds in Arylsilazido Rare-Earth Compounds

Three new hydridosilazido ligands, ?N(SiHMe2)Aryl (Aryl = Ph, 2,6-C6Me2H3 (dmp), 2,6-C6iPr2H3 (dipp)) and their rare-earth complexes Ln{N(SiHMe2)Aryl}3(THF)n (Ln Sc, Y, Lu; Aryl n 2; dmp, 1; dipp, 0) were synthesized to study the relationships among ligand steric properties, secondary Ln?H–Si bonding, reactivity of amide SiH groups. In these compounds, encumbrance aryl group was systematically increased from phenyl 2,6-dimethylphenyl 2,6-diisopropylphenyl. NMR, IR, X-ray diffraction studies characterize number interactions additional THF ligands coordinated centers. The with smallest phenylsilazido Ln{N(SiHMe2)Ph}3(THF)2, contain features associated three nonbridging 2-center-2-electron (2c-2e) Si–H bonds. Characterization intermediate-sized Ln{N(SiHMe2)dmp}3THF reveals two for yttrium lutetium analogues, respectively, both metals having one per complex. Ln{N(SiHMe2)dipp}3 is formed solvent-free, all adopt bonding modes. reaction between ketones provides hydrosilylated product via addition C?O bonds, which occurs rapidly even at low temperature. This proposed occur through an associative mechanism on basis negative activation entropy measured substitution pyridine in Ln{N(SiHMe2)dipp}3·NC5H5.