4-Ethinyl-benzonitrile-ferrocenes bridged by a Pd(PPh3)2 unit; the solid-state structure of (η5-C5H5)Fe(η5-C5H4CCC6H4CN-1,4)

The trinuclear Fc–Pd–Fc complex [(FcCCC6H4CN-1,4)2Pd(PPh3)2](OTf)2 (5) [Fc=(η5-C5H5)Fe(η5-C5H4)] is accessible by the reaction of FcCCC6H4CN-1,4 (3) with (Ph3P)2Pd(OTf)2 (4) in a 2:1 molar ratio. In 5 the corresponding late transition metal centers are linked by C5H4CCC6H4CN-1,4 π-conjugated organic units. The result of the X-ray structure analysis of 3, which itself can be synthesised by a Sonogashira coupling of FcCCH (1) with BrC6H4CN-1,4 (2), is reported. Complex 3 crystallises in the monoclinic space group P21 with the following cell parameters: a=9.6598(6), b=7.3185(5), c=10.1910(7) Å, β=98.876(3)°, V=711.80(8) Å3 and Z=2. In 3 the cyclopentadienyl ligands are rotated by 4.1(2)° and therefore possess an almost eclipsed conformation. With respect to the η5-coordinated C5H4 group, the C6H4 unit is tilted by 69.87(13)°. Electrochemical studies on 3 show that the Fe(II)/Fe(III) oxidation process appears to be reversible and is shifted to a more positive value when compared to the FcH/FcH+ couple. An even more positive value is observed for 5. A reason for this behaviour is presented.