UNEXPECTED SYNTHESIS OF ORTHO-SUBSTITUTED DISELENOPHENYLENEZIRCONOCENES FROM THE PARASUBSTITUTED DIPHENYLZIRCONOCENES - CHEMICAL AND STRUCTURAL EVIDENCE OF THE PARTICIPATION OF A CYCLOMETALATED INTERMEDIATE THAT BEHAVES AS A BENZYNE ZIRCONOCENE EQUIVALENT

Heating grey selenium with [eta(5)-C5H4(t-Bu)]Zr-2(C6H4(p-OCH3))(2) in boiling octane affords the diselenophenylenezirconocene complex containing a methoxy group in the ortho position. A similar reaction, although less selective, occurs when starting from [eta(5)-C5H4(t-Bu)]Zr-2(C6H4(p-CH3))(2). (C6H4(p-CH3))(2). The structures of the diselenophenylenezirconocenes obtained were confirmed by NMR spectroscopy and definitively proved by comparison with the authentic orthosubstituted derivatives prepared from the corresponding methyl-o-anisyl- and methyl-o-tolylzirconocene. The mechanism proposed to explain this transformation involves the activation of a tert-butyl C-H bond by a transient benzynezirconocene species. The cyclometalation product, which is obtained by heating the diphenylzirconocene, reacts toward selenium and unsaturated organic compounds like the benzynezirconocene but the reaction takes place at room temperature. The cyclometalation pathway allows a more sterically hindered selenium-containing derivative [eta(5)-C5H4(t-Bu)]2ZrSe2C6H3(o,o'-(CH3)(2)) to be prepared. The new diselenophenylenezirconocenes described are good precursors to generate benzodiselenagermoles and related spiro compounds by a zirconium-germanium transmetalation reaction. All the new products synthesized, zirconocene complexes and cyclometalated derivatives, benzodiselenagermoles, and spirobisbenzodiselenagermoles, were identified by the multinuclear NMR methods and mass spectrometry. The structure of the cyclometalated product [eta(5)-C5H4(t-Bu)]Zr[(2,5-(CH3)(2)C6H3)(eta(1):eta(5)-CH2C(CH3)(2)C5H4)] was determined by X-ray diffraction analysis. This compound crystallizes in the monoclinic space group P2(1)/c with two molecules per asymmetric unit with cell dimensions a = 8.278(3) Angstrom, b = 20.113(9) Angstrom, c = 27.661(9) Angstrom, and beta = 93.13(2)degrees at 295 K. Least-squares refinement led to a value for the final R index of 0.0642 for 2701 reflections with I > 2 sigma(I).