Mononuclear tantalum (V) pentalene complexes:: synthesis of [Ta{η8-C8H4(1,4-SiiPr3)2}X3] (X = CH3, Cl, I) and the X-ray crystal structures of [Ta{η8-C8H4(1,4-SiiPr3)2}(CH3)3], [Ta{η8-C8H4(1,4-SiiPr3)2}(CH3)2Cl], [Ta {η8-C8H4(1,4-SiiPr3)2}(CH3)Cl2] and [Ta{η8-C8H4(1,4-SiiPr3)2}I3]

The reaction between [TaMe3Cl2] and the potassium salt of the silylated pentalene dianion [K-2{C8H4(1,4-Si'Pr-3)(2)}] gives the eta(8)- pentalene complex [Ta{eta(8)-C8H4(1,4-Si'Pr-3)(2)}(CH3)(3)] (1). Sequential protonolysis of 1 with [Et3NH]Cl affords [Ta{eta(8)-C8H4(1,4Si'Pr-3)(2)}(CH3)(2)Cl] (2), [Ta{eta(8)-C8H4(1,4-Si'Pr-3)(2)}(CH3)Cl-2] (3) and [Ta{eta(8)-C8H4(1,4-Si'Pr-3)(2)}Cl-3] (4). An alternative and cleaner route to 4 involves treatment of 1 with BCl3; in an analogous fashion, the reaction of 1 with BI3 gives [Ta{eta(8)-C8H4(1,4-Si'Pr-3)(2)}I-3] (5). The X-ray crystal structures of 1, 2, 3 and 5 are reported. (C) 2004 Elsevier Ltd. All rights reserved.