Organic Functional Group Transformations in the Periphery of a Group-4 Metallocene Complex: 2H-Pyrrole Formation at a Pendant Boron Lewis Acid

Abstract

The allyl-substituted ansa-zirconocene dichloride [Me2Si(C 5H4)(C5H3CH2CH=CH 2)ZrCl2] (1) cleanly adds the borane 9-BBN to the allyl C=C double bond to yield the corresponding hydroboration product 2. The borane HB(C6F5)2 (3) is also added regioselectively to 1 to yield [Me2Si(C5H4){C5H 3(CH2)3B(C6F5) 2}ZrCl2] (4). The strongly electrophilic boron Lewis acid in 4 adds 2-methyl-4,5-dihydrooxazole to yield 6. Treatment of 4 with pyrrole results in the formation of the respective borane adduct 7 of the pyrrole tautomer 2H-pyrrole. The 2H-pyrrole ligand in 7 is deprotonated at C-2 upon treatment with pyridine, followed by proton transfer and replacement of pyrrole with formation of the corresponding pyridine adduct 12. The complexes 1, 4 and 7 were characterized by X-ray diffraction. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.