Monomeric Rare-Earth Metal Silyl-Thiophosphinoyl-Alkylidene Complexes: Synthesis, Structure, and Reactivity.

A series of monomeric rare-earth metal silyl-thiophosphinoyl-alkylidene complexes [LLn{C(SiR3 )PPh2 S}] (5: Ln=Lu, R=Me; 6: Ln=Lu, R=Ph; 7: Ln=Y, R=Me; 8: Ln=Y, R=Ph; 9: Ln=Sm, R=Ph; 10: Ln=Sm, R=Me; 11: Ln=La, R=Ph; L=[MeC(NDIPP)CHC(Me)(NCH2 CH2 N(Me)2 )]- , DIPP=2,6-(iPr)2 C6 H3 ) have been synthesized and structurally characterized. The influences of rare-earth metal ions, ancillary ligands, and alkylidene groups on the reactivity of complexes 5-11 and the related scandium complexes [LSc{C(SiR3 )PPh2 S}] (1: R=Me; 2: R=Ph) and [L'Sc{C(SiR3 )PPh2 S}] (3: R=Me; 4: R=Ph; L'=[MeC(NDIPP)CHC(Me)(NCH2 CH2 N(iPr)2 )]- ) have been studied. Reactions of these rare-earth metal alkylidene complexes with PhCN give four kinds of products, the formation of which is dependent on the rare-earth metal ions, ancillary ligands, and alkylidene groups of the complexes. In the reactions with tBuNC, unusual C-P bond cleavage of the alkylidene group and C≡C triple bond formation occur. Complexes 10 and 11 also react with PhSiH3 to form hydrides, which subsequently undergo Ln-H addition to the C=N bond of the ancillary ligand L. DFT calculations have been used to analyze the bonding in complex 10, which exhibits a polarized three centers Sm-C-P π interaction, and to rationalize the reactivity by computing reaction mechanisms. The difference in reactivity of PhCN and tBuNC is due to the electron density delocalization that is enabled by the phenyl group rather than the tBu group.