Reaction of the Schiff base ligands CpFe[η5-C5H2{C(H)O(CH2)3O}C(H)NR]
(R = 2,4,6-Me3C6H2, a; R = Cy, b) derived from the 1,2-disubstituted formylferrocene
CpFe[(CHO){C(H)O(CH2)3O}-η5-C5H3] 1, with Li2[PdCl4] in methanol at room temperature for 48 h, gave the chlorine-bridged
complexes [Pd{CpFe[η5-C5H2{C(H)O(CH2)3O}C(H)NR]}(Cl)]2, 1a and 1b, after C–H activation of the cyclopentadienyl
ring bearing the cyclic acetal. The reactions of 1a and 1b with the Ph2P(CH2)
n
PPh2 diphosphines in a 1:2 ratio, plus addition
of ammonium hexafluorophosphate, gave the dinucelar compounds [Pd{CpFe[η5-C5H2{C(H)O(CH2)3O}C(H)NR]}-(Ph2P(CH2)
n
PPh2-P,P)][PF6] 2a, 3a and 2b, 3b with the diphosphine in a chelating mode, as 1:1 electrolytes.
Treatment of the latter with aqueous acetic acid gave the corresponding
functionalized compounds with transformation of the 1,3-dioxane ring
into a formyl group on the metalated ring, 4a, 5a and 4b, 5b.
The Schiff
base condensation reaction of 5b with 2-(methylthio)aniline
in refluxing chloroform gave [Pd(Ph2P(CH2)2PPh2){(CpFe)η5-C5H2[C(H)NCy][C(H)N(2-SMeC6H4]}][PF6] 6b, with regeneration of the CN
double bond, which, when treated with lithium tetrachloropalladate
in methanol for 48 h, gave the novel compound [Pd(Ph2P(CH2)2PPh2){(CpFe)η5-C5H[C(H)NCy][C(H)N(2-SMeC6H4]}PdCl][PF6] 7b, which is the first ferrocene
metallacycle displaying 1,3-double cyclopalladation.