American Chemical Society
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A Homologous Series of Regioselectively Tetradeprotonated Group 8 Metallocenes:  New Inverse Crown Ring Compounds Synthesized via a Mixed Sodium−Magnesium Tris(diisopropylamide) Synergic Base

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posted on 2004-09-22, 00:00 authored by Prokopis C. Andrikopoulos, David R. Armstrong, William Clegg, Carly J. Gilfillan, Eva Hevia, Alan R. Kennedy, Robert E. Mulvey, Charles T. O'Hara, John A. Parkinson, Duncan M. Tooke
Subjecting ferrocene, ruthenocene, or osmocene to the synergic amide base sodium−magnesium tris(diisopropylamido) affords a unique homologous series of metallocene derivatives of general formula [{M(C5H3)2}Na4Mg4(i-Pr2N)8] (where M = Fe (1), Ru (2), or Os (3)). X-ray crystallographic studies of 13 reveal a common molecular “inverse crown” structure comprising a 16-membered [(NaNMgN)4]4+ “host” ring and a metallocenetetraide [M(C5H3)2]4- “guest” core, the cleaved protons of which are lost selectively from the 1, 1‘, 3, and 3‘-positions. Variable-temperature NMR spectroscopic studies indicate that 1, 2, and 3 each exist as two distinct interconverting conformers in arene solution, the rates of exchange of which have been calculated using coalescence and EXSY NMR measurements.