SYNTHESIS, MOLECULAR-STRUCTURE AND PALLADIUM(II) AND PLATINUM(II) COMPLEX CHEMISTRY OF 3-(FERROCEN-1-YL)-1-(PYRIDIN-2-YL)PYRAZOLE

Treatment of the potassium salt of 3(5)-(ferrocen-1-yl)pyrazole L(1) w ith 2-bromopyridine in diglyme (2,5,8-trioxononane) at 130 degrees C f or 3 d, followed by an aqueous quench, yielded the compound 3-(ferroce n-1-yl)-1-(pyridin-2-yl)pyrazole L(2) in 37% recrystallised yield. A s ingle-crystal structure determination of L(2) confirmed the proposed 1 ,3-disubstitution pattern at the pyrazole ring, the substituted cyclop entadienyl and two heterocyclic rings being approximately coplanar. Tr eatment of L(2) with a stoichiometric amount of [{MCl(C3H5)}(x)] (M = Pd, x = 2; M = Pt, x = 4) and NH4PF6 gave [M(eta(3)-C3H5)(L(2))]PF6 (M = Pd 1 or Pt 2) while a similar reaction with [PdCl2(NCPh)(2)] afford ed [PdCl2(L(2))] 3. Treatment of 3 with 1 molar equivalent of K2C2O4, Na-2(cat) or Na(acac)-NH4PF6 yielded [Pd(L)L(2)] [L = C2O42- 4 or cate cholate (cat) 5] and [Pd(acac)(L(2))]PF6 6 (acac = acetylacetonate) as analytically pure solids. The H-1 NMR behaviour of 4-6 is complex and suggestive of extensive ligand dissociation in solution; molecular mo dels imply that this may reflect steric interactions between the penda nt ferrocenyl moiety and metal-bound anionic chelate O-donors. The UV/ VIS and electrochemical data show that the ferrocenyl group becomes si gnificantly electron-poorer upon co-ordination of L(2), reflecting an inductive interaction with the co-ordinated M(2+) (M = Pd or Pt) elect rophiles.