A homologous series of regioselectively tetradeprotonated group 8 metallocenes: New inverse crown ring compounds synthesized via a mixed sodium-magnesium tris(diisopropylamide) synergic base

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 1-3 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.