Synthesis, molecular structure and palladium(II) and platinum(II) complex chemistry of 3-(ferrocen-1-yl)-1-(pyridin-2-yl)pyrazole

Less, Robert J.; Wicks, Joseph L. M.; Chatterton, Nicholas P.; Dewey, Michael J.; Cromhout, Natalie L.; Halcrow, Malcolm A. and Davies, John E. (1996). Synthesis, molecular structure and palladium(II) and platinum(II) complex chemistry of 3-(ferrocen-1-yl)-1-(pyridin-2-yl)pyrazole. Journal of the Chemical Society, Dalton Transactions(21) pp. 4055–4061.



Treatment of the potassium salt of 3(5)-(ferrocen-1-yl)pyrazole L1 with 2-bromopyridine in diglyme (2,5,8-trioxononane) at 130 °C for 3 d, followed by an aqueous quench, yielded the compound 3-(ferrocen-1-yl)-1-(pyridin-2-yl)pyrazole L2 in 37% recrystallised yield. A single-crystal structure determination of L2 confirmed the proposed 1,3-disubstitution pattern at the pyrazole ring, the substituted cyclopentadienyl and two heterocyclic rings being approximately coplanar. Treatment of L2 with a stoichiometric amount of [{MCl(C3H5)}x](M = Pd, x= 2; M = Pt, x= 4) and NH4PF6 gave [M(η3-C3H5)(L2)]PF6(M = Pd 1 or Pt 2) while a similar reaction with [PdCl2(NCPh)2] afforded [PdCl2(L2)]3. Treatment of 3 with 1 molar equivalent of K2C2O4, Na2(cat) or Na(acac)–NH4PF6 yielded [Pd(L)L2][L = C2O42–4 or catecholate (cat)5] and [Pd(acac)(L2)]PF66(acac = acetylacetonate) as analytically pure solids. The 1H NMR behaviour of 4–6 is complex and suggestive of extensive ligand dissociation in solution; molecular models imply that this may reflect steric interactions between the pendant ferrocenyl moiety and metal-bound anionic chelate O-donors. The UV/VIS and electrochemical data show that the ferrocenyl group becomes significantly electron-poorer upon co-ordination of L2, reflecting an inductive interaction with the co-ordinated M2+(M = Pd or Pt) electrophiles.

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