Exploring the Reactivity towards Acidic Protic Ligands of the Di-μ-hydroxo Complex [NBu4]2[Pd2{C4(COOMe)4}2(μ-OH)2]: A Convenient Precursor in the Preparation of New Palladacyclopentadiene Complexes

The dinuclear hydroxo complex [NBu4]2[Pd2{C4(COOMe)4}2(μ‐OH)2] (I) reacts in a 1:2 molar ratio with a wide variety of protic electrophiles H(L) bearing different sets of donor atoms (L = OO, NS or ON) to give the mononuclear anionic palladium(II) derivatives with the general formula [Pd{C4(COOMe)4}(L)]– [OO = salycilaldehydate (sal) (1), acetohydroxamate (ahx) (2) and benzohydroxamate (bhx) (3); NS = 2‐pyridinthiolate (spy) (4), 2‐pyrimidinthiolate (spym) (5), 3‐methyl‐2‐imidazolin‐thiolate (meimt) (6) and 2‐aminothiophenolate (2‐atp) (7); ON = N‐phenylsalycilaldiminate (N‐phsal) (8), N‐p‐chlorophenylsalycilaldiminate (N‐clsal) (9), N‐p‐tolylsalycilaldiminate (N‐tolsal) (10), 2‐aminophenolate (2‐atp) (11), 2‐pyrrole‐carboxaldeydate (2‐pcal) (12), 8‐hydroxiquinolinate (oxin) (13), picolinate (2‐pic) (14)]. Structural characterisation by X‐ray diffraction of complexes 5, 8 and 13 confirmed the proposed formula. Dinuclear complexes [NBu4]2 [Pd{C4(COOMe)4}(μ‐az)]2 (az = pyrazolate (pz) (15), triazolate (tz) (16) and 3,5‐dimethylpyrazolate (3,5‐Me2pz) (17) were obtained when treating I with azoles in the same molar ratio, and also treating the hydroxo complex with chloranilic acid (chl) (18) and squarate (sq) (19) in 1:1 proportion to yield compounds [NBu4]2[Pd{C4(COOMe)4}2{(μ‐O–O)}] with the ligands acting as bis‐bidentate ones. A related process takes place when (I) reacts with ammonium O,O'‐dialkyldithiophosphates in acetone under mild conditions and complexes [NBu4][Pd{C4(COOMe)4}{S(S)P(OR)2}] (R = Me (20), Et (21), iPr (22)) are obtained. Deprotonation of secondary amines Et2NH, Pr2NH, piperidine or morpholine by (I) in the presence of carbon disulfide leads to the corresponding dithiocarbamate complexes [Pd{C4(COOMe)4}(S2CNR2)] 23–26. (I) also promotes the nucleophilic addition of water to pyridine‐2‐carbonitrile and a mononuclear complex 27 containing the pyridine‐2‐carboxamidate ligand is formed. Its structure has been determined by a single‐crystal diffraction study. The new complexes were fully characterised by analytical and spectroscopic techniques (FAB‐MS, IR; 1H, 13C and 31P‐NMR). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)