Metal-metal multiply-bonded complexes of technetium. Part 8. Synthesis andcharacterization of the alpha- and beta-isomers of Tc2Cl4(dppe)(2)

The alpha- (chelated) and beta- (bridged) isomers of Tc2Cl4(dppe)(2) (dppe = Ph2PCH2CH2PPh2) have been prepared and characterized. The reaction of Tc2 Cl4(PEt3)(4) or Tc2Cl4(PMe2Ph)(4) with dppe in refluxing toluene affords th e pale pink p-isomer, isostructural with both the analogous Mo and Re compo unds. When Tc2Cl4(PMePh2)(4) is refluxed in toluene with a large excess of dppe, the mauve alpha-isomer is produced. Spectral and electrochemical prop erties as well as reactivity of each isomer are reported. For each the X-ra y crystal structure is also reported. The alpha-isomer has average Tc-Tc = 2.15[1] Angstrom and an eclipsed conformation. For the beta-isomer there is a twict angle of 35(2)degrees and a Tc-Tc distance of 2.117(1) Angstrom. ( C) 1999 Elsevier Science S.A. All rights reserved.