Formation and Reactivity of a Tantalocene Trihydride Containing an Aminoethyl‐Functionalised Ligand

The complex [Cp*{C 5 H 4 (CH 2 CH 2 NMe 2 )}TaCl 2 ] ( 1 ) was synthesised by reaction of the lithium salt LiC 5 H 4 (CH 2 CH 2 NMe 2 ) with the tantalum compound [Cp*TaCl 3 (PMe 3 )]. Reduction of 1 with NaAl(H) 2 (OCH 2 CH 2 OMe) 2 leads to the trihydride derivative [Cp*{C 5 H 4 (CH 2 CH 2 NMe 2 )}TaH 3 ] ( 2 ). The oxidation of 2 in THF with ferrocenium ion leads to a cationic dihydride intermediate [Cp*{C 5 H 4 (CH 2 CH 2 NMe 2 )}TaH 2 ]PF 6 ( 3 ) with an intramolecular stabilization by the aminoethyl side‐chain of the cyclopentadienyl ligand. The hemilabile character of the functionalised cyclopentadienyl ligand was checked by treating 3 with electron‐donating ligands (e.g. phosphanes, sulfides, anions); in all cases, no displacement of the amino group was observed. When treated with HBF 4 , 2 undergoes a loss of the hydride and the resulting cation can be isolated as a solvento adduct by carrying out the reaction in dimethyl sulfide. Acidolysis of 2 in the presence of an excess of trifluoroacetic acid affords the compound [Cp*{C 5 H 4 (CH 2 CH 2 NHMe 2 )}TaH(OCOCF 3 ) 2 ](CF 3 COO) ( 5 ). Microanalytical and NMR spectroscopic data for these complexes are given. The X‐ray crystal structures are reported for [Cp*{C 5 H 4 (CH 2 CH 2 NMe 2 )}TaH 2 ]PF 6 ( 3 ) and [Cp*{C 5 H 4 (CH 2 CH 2 NHMe 2 )}TaH(OCOCF 3 ) 2 ](CF 3 COO) ( 5 ). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)