Synthesis, Structure, and Reactivity of Rare-Earth Metallocene η³-Propargyl/Allenyl Complexes

The reaction of the alkyl complexes Cp* 2 LnCH(SiMe 3 ) 2 (Ln = Y 1-Y, Ce 1-Ce, La 1-La; Cp* = η 5 -C 5 Me 5 ) and Me 2 Si(η 5 -C 5 Me 4 ) 2 LnCH(SiMe 3 ) 2 (Ln = Ce 5-Ce ) with 1-methylalk-2-ynes CH 3 C≡CR (R = Me 3a, Et 3b, n Pr 3c, t Bu 3d, SiMe 3 3e, Ph 3f, C 6 H 4 Me-2 3g, C 6 H 3 Me 2 -2,6 3h, C 6 H 3 i Pr 2 -2,6 3i, C 6 F 5 3j ) affords the corresponding η 3 -propargyl/allenyl complexes Cp* 2 LnCH 2 CCR ( 4a−j-Ln ) and Me 2 Si(η 5 -C 5 Me 4 ) 2 CeCH 2 CCR ( 6a−j-Ce ) via propargylic metalation. The hydride complexes [Cp* 2 Ln(μ-H)] 2 (Ln = Y 2-Y, Ce 2-Ce, La 2-La ) react rapidly with 3 to produce mixtures of insertion and propargylic metalation products, and the relative rate of these processes depends on the metal and alkyne substituent. Selected η 3 -propargyl/allenyl complexes Cp* 2 YCH 2 CCR (R = Me 4a-Y, Ph 4f-Y ), Cp* 2 CeCH 2 CCR (R = Me 4a-Ce, Ph 4f-Ce ), Cp* 2 CeCH(Me)CCEt ( 9b-Ce ), Cp* 2 LaCH 2 CCR (R = Ph 4f-La, C 6 H 3 Me 2 -2,6 4h-La ) are obtained on a preparative scale and characterized by NMR spectroscopy, IR spectroscopy, and cryoscopy. Compounds 4f-Y and 4f-La are also characterized by single-crystal X-ray diffraction. The reactions of the η 3 -propargyl/allenyl complexes with Brønsted acids, such as alcohols and acetylenes, afford the corresponding substituted allenes (RCH═C═CH 2 ) and 1-methylalk-2-ynes (CH 3 C≡CR) as organic products. The reactions of 4f-Y and 4f-La with Lewis bases, such as pyridine and THF, yield the corresponding base adducts. The adduct 4f-La ·py is characterized by single-crystal X-ray diffraction, revealing an η 3 -coordinated propargyl/allenyl ligand.