Cyclometallated [C,N,O] Complexes as Metalloligands: Synthesis and Structural Characterisation of New Di-, Tri-, Tetra- and Pentanuclear Heterometallic Complexes

Reaction of the Schiff-base ligands 4-(4-NC5H4)C6H4C-(H)=N(C6H3OH-2-tBu-5) (a) and (4-NC5H4)C(H)=N(C6H3-OH-2-tBu-5) (b) with palladium(II) acetate in toluene at 60 degrees C gave the tetranuclear orthometallated palladium complexes la and 1b, respectively, as air-stable solids. Treatment of la and 1b with triphenylphosphane gave the mononuclear species 2a and 2b upon splitting of the polynuclear structure. Reaction of la with the tertiary diphosphanes Ph2P(CH2)(4)-PPh2 (dppb), Fe(C5H4PPh2)(2) (dppf), Ph(2)pC(H)=C(H)PPh2 (t-dppe) and Ph2P(CH2)(6)PPh2 (dpph), and 1b with dppb and dppf, in a 1:2 molar ratio gave complexes 3a-6a and 3b and 4b, respectively. Reaction of 2a, 4a and 6a with hexacarbonylchromium or -tungsten and 2b and 3b with hexacarbonylchromium, -molybdenum or -tungsten in thf under UV activation gave complexes 7a-12a and 5b-10b, respectively, which contain an M(CO)(5) fragment coordinated to the pyridine nitrogen atom. Treatment of 2b with [RuCl2(CO)(dmf)-(PPh3)(2)] in chloroform at room temperature for 2d afforded 11b. Treatment of ligands (2- NC5H4)C(H)=N(C6H4OH-2) (c) and (2-NC5H4)C(H)=N(C6H3OH-2-tBu-5) (d) with palladium(II) acetate yielded the mononuclear palladium acetate complexes 1c and Id, respectively. Treatment of 1c and 1d with aqueous sodium chloride, or, alternatively, treatment of c and d with K-2[PdCl4], gave chloropalladium complexes 2c and 2d, respectively. Treatment of 2c and 2d with silver perchlorate and triphenylphosphane in acetone gave the mononuclear phosphane complexes 3c and 3d, respectively. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)