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Reactions of trans-chloro(cyanomethyl)bis(triphenylphosphine)palladium(II), trans-[PdCl(CH2CN)(PPh3)2] (1), with an equimolecular amount of Tl(β-dik) (β-dik=etac, acac, tfac, bzac, and dbm) in dichloromethane afforded the O,O′-chelated β-dik complexes [Pd(CH2CN)(β-dik)(PPh3)] (3). Hydrogen peroxide oxidation and chloride abstraction by AgClO4or AgBF4of 1gave the neutral [PdCl(CH2CN)PPh3]nand the cationic [Pd(CH2CN)(PPh3)2]mXm(X=ClO4or BF4), respectively, from either of which complexes 3were also obtained by the reactions with the β-dik anions. No pure product corresponding to 3was isolated by a similar treatment of 1with Tl(hfac). On the other hand, chloro(cyanomethyl){1,2-bis(diphenylphosphino)ethane}palladium(II), [PdCl(CH2CN)(dppe)] (2), reacted only with Tl(hfac) in refluxing acetone to give the cationic [Pd(CH2CN)(dppe)]2(hfac)2, which was also derived from 2via[Pd(CH2CN)(dppe)]2X2(X=ClO4or BF4).

Complexes of a novel type, [(PP)Pd(O,O'-ß-dik(2–)-C1–C3)Pd(PP)](ClO4)2containing dianions of acetylacetone and ethyl acetoacetate as a bridging ligand and diphosphines (PP) were prepared and characterized mainly by IR and 1H, 13C, and 31P NMR spectroscopy.

When diketene and sodium tetrachloropalladate(II) are mixed in aqueous solution, color of the solution changes promptly from dark red to yellow. During this fast primary reaction about one equivalent of diketene is consumed and acetoacetic acid (H2A) is retained as a trihapto ligand in [PdCl2(HA)]-(2). The succeeding steady hydrolysis of diketene (S) proceeds as a pseudo first-order reaction, obeying the rate law: –d[S]/dt=kobsd[S]=(k0+kcat)[S], kcat=kobsd–k0=(k1+k2/[H+])[PdII]/[Cl-], where k1=2.0×10-5s-1and k2=2.96×10-6mol dm-3s-1at 0 °C and µ=1.0 mol dm-3(HClO4and NaClO4). A mechanism which postulates complex 2as the effective catalyst is proposed to explain the observed two-term rate equation.

The reaction of sodium tetrachloropalladate(II) with ethyl acetoacetate in aqueous alkaline solution afforded a key intermediate Pd(C6H9O3)2·\frac12H2O [1]. The compound 1reacts with a base L such as pyridine, 2-methylpyridine, n-butylamine, benzylamine, or 2,2′-bipyridine, resulting in Pd(1-ethoxycarbonylacetonato-c1)2L2[2]. The central-carbon-bonding of ethyl acetoacetate to palladium has been deduced from the IR and NMR spectra, and finally ascertained by the X-ray analysis of a compound with 2-methylpyridine as L.

The dinuclear palladium(II) complexes [(PP)Pd(C1–C3-β-dik(2−)-O,O′)Pd(PP)](ClO4)2containing a β-diketonate dianion as a bridging ligand were prepared by the reactions of the mononuclear complexes [Pd(β-dik(2−)-C1–C3)(PP)] with [Pd(PP)(H2O)2](ClO4)2. In the reactions of [Pd(etac(2−)-C1–C3)(dpe)] with [Pt(PPh3)2(H2O)2](ClO4)2and [Ni(acac)2] in the 1:1 mole ratio, similar dinuclear complexes [(dpe)Pd(C1–C3-etac(2−)-O,O′)Pt(PPh3)2](ClO4)2and [(dpe)Pd(C1–C3-etac(2−)-O,O′)Ni(acac)2] were produced, respectively, while the reactions of [Pd(β-dik(2−)-C1–C3)(PP)] with Ni(ClO4)2·6H2O and Mg(ClO4)2in the 2:1 mole ratio afforded the trinuclear complexes [M{O,O′-β-dik(2−)-C1–C3Pd(PP)}2](ClO4)2(M=Ni(II) and Mg(II)). The trihapto coordination to palladium(II) and O,O′-chelation to another metal atom of the β-diketonate dianion in these complexes were deduced mainly by IR and NMR spectroscopy.

The bis(β-diketonato)platinum(II) complexes react with various nitrogen bases (L) to afford [Pt(β-dik)L2](β-dik), [Pt(β-dik-O)2L2], [PtL4](β-dik)2, and [Pt(β-dik)(β-dik-C)L] depending on the natures of the β-diketonate anions and L. All of these complexes are stable in solution, showing no sign of isomerization and dissociation of L. The platinum(II) complexes containing the O-unidentate β-diketonate ligand are much more stable than the corresponding palladium(II) complexes and [Pt(acac)(piperidine)2](acac) and [Pt(acac-O)2(piperidine)2] constitute a pair of linkage isomers. The complexes containing the 2,4-pentanedionate anion (acac) in the outer sphere readily undergo the H-D exchange of the methine proton of acac and the NH protons of coordinated amines with CDCl3.

Bis(β-diketonato)palladium(II) and -platinum(II) readily react with tertiary phosphines (L) to afford [M(β-dik)(β-dik-O)L], [M(β-dik)L2](β-dik), [ML4](β-dik)2, [M(β-dik-O)2L2], and [M(β-dik)(β-dik-C)L] complexes, which were characterized mainly by infrared and 1H and 13C NMR spectroscopy. Factors influencing the relative stability of each bonding mode of β-diketonate anions were investigated.

Bis (β-diketonato)palladium(II) reacts with excess amines(L) to afford [Pd(β-dik)L2] (β-dik) or [PdL4] (β-dik)2depending upon whether L is a secondary or a primary amine, respectively. These reactions are reversible and the relative stability in solution of the complexes containing the β-diketonate anion in the outer sphere is in the order: acac < tfac < hfac.

The 2,4-pentanedionate dianion acts as a bridging ligand in [Be(acac)L] and [Pd(acac)L] which were prepared by the reactions of (2,2'-bipyridine)chloro(2,4-pentanedionato-C1)palladium(II) (HL) with [Be(acac)2] and [Pd(acac)2]. On the other hand the 1,1,1-trifluoro-2,4-pentanedionate dianion is chelating to the metal atom in [Pt(C5H3O2F3)L2'] (L'= PPh3and AsPh3).

A novel type of palladium(II) complexes, [Pd(ß-dik)(pyridyl)(PPh3)] and [Pd(ß-dik)(pyridyl)]2containing a chelating acetylacetonate, trifluoroacetylacetonate, or hexafluoroacetylacetonate anion and 2-, 3-, or 4-pyridyl radical as the coexisting ligands were prepared and characterized by elemental analysis and molecular weight determination as well as 1H and 13C NMR spectroscopy. [Pd(acac)(C5H3(6-Cl)N–C2)(PPh3)] is stereochemically rigid in solution but undergoes the coordination-site exchange reaction catalyzed by nitrogen and phosphorus bases and donor solvents. Similar reaction of [Pd(acac)(C5H4N–C2)(PPh3)] is catalyzed by triphenylphosphine liberated by the dinuclear-complex formation reaction (autocatalysis). Intact molecules of [Pd(acac)(C5H4N–C3and –C4) (PPh3)] catalyze mutually their own coordination-site exchange (self-catalysis).

Five-coordinate complexes [M(hfac)2L] (M=Pd, Pt; hfac=1,1,1,5,5,5-hexafluoro-2,4-pentanedionate anion) were produced by the reactions of [M(hfac)2] with equimolar amounts of tertiary phosphines, phosphites, and triphenylarsine. They were characterized by 1H, 13C, 19F, and 31P NMR spectra in solution and several complexes containing bulky phosphines as L were isolated, and structures of [Pd(hfac)2{P(o-tolyl)3}] and [Pt(hfac)2{P(cyclohexyl)3}] were determined by X-ray analysis. Both complexes have very distorted square-pyramidal structures, one of the two hfac anions in either of them spanning the apical and basal coordination sites. NMR spectra at various temperatures disclosed the fluxional behaviors of these complexes which retain the solid-state structures at such low temperatures as -60 °C. Two kinds of twist mechanisms were proposed.

Palladium(II) complexes of the [Pd(ß-dik-O)(pyridyl)(PEt3)2] type containing an O-unidentate acetylacetonate, trifluoroacetylacetonate, or hexafluoroacetylacetonate anion and a 2-, 3-, 4-pyridyl or 6-chloro-2-pyridyl group as ligands were prepared and characterized mainly by 1H and 13C NMR spectroscopy. The acetylacetonate and hexafluoroacetylacetonate ligands in the [Pd(ß-dik-O)(C5H3(6-Cl)N-C2)(PEt3)2] complexes undergo the head-to-tail donor-atom exchange reaction, to which an intramolecular mechanism is proposed.

The reactions of [M(ß-dik)2] (M=Pt(II), Pd(II); ß-dik=acetylacetonate (acac), dipivaloylmethanate (dpm), hexafluoroacetylacetonate (hfac) ions) with dppm (dppm=Ph2PCH2PPh2) and mdppm (mdppm=Ph2PCH(Me)PPh2) have been investigated. [M(hfac)2] complexes react with dppm to afford the stable cationic complexes, [M(dppm)2](hfac)2. By contrast, [M(acac)2] complexes react to give the homoleptic bis(diphenylphosphino)methanido complexes, [M(Ph2PCHPPh2)2], through deprotonation of dppm by the displaced acac anions. The analogous complexes, [M(Ph2PC(Me)PPh2)2], are obtained using mdppm, instead of dppm. A complete reaction scheme leading to these products is proposed, based on the IR and 1H, 13C, and 31P NMR spectral data. Some consideration is given to the dependence of these reactions on the metals and the ß-diketonate ligands, employed.

Oxidative-addition reactions of excess 2-(chloromethyl) and 2,6-bis(chloromethyl)pyridines with [RhCl(PPh3)3] in toluene at room temperature afforded (2-pyridylmethyl)- and {2-(6-chloromethyl)pyridylmethyl}rhodium(III) complexes, cis(PP)-[RhCl2{C5H3(6-R)N-2-CH2}(PPh3)2] (R = H, 1-cis; R = CH2Cl, 2-cis), respectively, which isomerized to the corresponding trans(PP) complexes at elevated temperature. In refluxing toluene, the reactions thus resulted in the trans(PP) complexes (R = H, 1-trans; R = CH2Cl, 2-trans) exclusively. A novel dinuclear rhodium(III) complex [Rh2Cl4{C5H3N-2,6-(CH2)2}(PPh3)2], in which the 2,6-dimethylpyridine-α,α′-diyl ligand is C,N-chelated to one rhodium atom and bound to the second one in an η3-pseudo-1-azaallylic fashion, was obtained by reactions of 2,6-bis(chloromethyl)pyridine with [RhCl(PPh3)3] (1 : 2 in mole) and of the 2-ciswith [RhCl(PPh3)3] (1 : 1 in mole), both in refluxing toluene. These were characterized by 1H, 13C, and 31P NMR spectroscopy and mass spectrometry as well as an elemental analysis and a molecular-weight determination.

Reactions of the bis(β-diketonato)palladium(II) complexes with various nitrogen bases (L) afforded [Pd(β-dik)L2](β-dik), [PdL4](β-dik)2, or [Pd(β-dik)(β-dik-C)L] according to the natures of L and β-diketonate anions. Less basic ligands such as 1,1,1,5,5,5-hexafluoro- and 1,1,1-trifluoro-2,4-pentanedionates are readily removed by L to the outer sphere. Tendency of preferring the central-carbon-bonded state of the β-diketonate anion is related with the keto-favoring nature of its conjugate acid. Excess primary amines and pyridines can displace both of the β-diketonate ligands but secondary amines only one. These two types of compounds containing the 2,4-pentanedionate anion in the outer sphere undergo prompt deuteration of methine and amine protons by CDCl3. Tribenzylamine and 2,6-diphenylpyridine react with bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)palladium(II) to afford orthometallated products.

The title complex crystallizes in the monoclinic space group C2/c with a=24.900(6) Å, b=8.272(2) Å, c=30.437(9) Å, and β=97.23(2)°. The structure analysis, which converged at R=0.061 and Rw=0.083 with 3017 reflections for which Fo2>3σ(Fo2), showed that the palladium has a complete square-planar coordination geometry. While one of the tfac ligands is chelating, the other is bound to the metal only through the carbonyl oxygen adjacent to CH3. The O-unidentate tfac ligand lies trans to the CF3CO moiety of chelating tfac and has a planar structure in which the dangling CF3CO group is situated trans to the bonding oxygen atom with respect to the C=C bond. The ab initioMO calculation for the Z,Z-form of the tfac anion indicated that the coordination ability of the acetyl oxygen is higher than that of the trifluoroacetyl oxygen in consistence with the observed structure.

The reactions of [Pd(hfac)2] with aniline and its derivatives (L) in benzene at room temperature afforded [Pd(hfac)(hfac-C3)L], [Pd(hfac)L2](hfac), and [PdL4](hfac)2depending on the reactants mole ratio. On the other hand, the reactions of various [Pd(β-dik)2] complexes with L in refluxing benzene (in most cases) gave rise to the aniline-bridged dinuclear complexes [Pd(β-dik)(L–H)]2, which in turn reacted with primary amines and pyridine (L′) to produce [PdL′2(L–H)]2(β-dik)2.

A platinum(II)complex containing a 2,4-pentanedionate dianion as a trihapto ligand [Pt(acac(2–)-C1–C3){P(p-ClC6H4)3}2] was prepared by the reaction of [Pt(acac)2] with tris(p-chlorophenyl)phosphine and reacted with pyridinium perchlorate to afford [Pt(acac-C1)(py){P(p-ClC6H4)3}2](ClO4). A similar terminal-carbon-bonded complex of 1,1,1-trifluoro-2,4-pentanedionate monoanion with platinum(II) was also derived from [Pt(tfac(2–)C,O)(AsPh3)2] by the reaction with pyridinium perchlorate. These novel platinum(II) complexes were characterized mainly by IR and NMR spectroscopy.

A number of palladium(II) and platinum(II) bis-chelates have been prepared which contain one kind of symmetric or unsymmetric ß-diketonate anions, or involve two different ß-diketonate anions. Existence of the cisand transisomers in solution of the binary chelates of unsymmetric ß-diketones was confirmed by 1H and 13C NMR spectroscopy. Geometrical isomerization of the palladium(II) complexes to attain equilibrium in solution is fast, while the platinum(II) complexes are quite inert. The mixed-ligand chelates are stable in solution, showing no sign of disproportionation. The isomeric pairs of bis(1-phenyl-1,3-butanedionato)palladium(II), bis(2,4-hexanedionato)palladium(II), and bis(1,1,1-trifluoro-2,4-pentanedionato)platinum(II) were isolated, and molecular structure of the cisisomer of the first complex was determined by X-ray analysis.

Reactions of bis(trifluoroacetylacetonato)palladium(II), [Pd(tfac)2], with tertiary phosphines followed by pyridine or its derivatives afforded a series of the [Pd(tfac(2–)-C,O)LL']-type complexes which contain a C,O-chelating trifluoroacetylacetonate dianion and a couple of tertiary phosphine and/or heterocyclic nitrogen base ligands (L and L'). Their structures in solution were studied by 1H, 13C, 19F, and 31P NMR spectroscopy and the molecular structure in a crystal of [Pd(tfac(2–)-C,O)(PPh3)(2,6-Me2-py)]·C6H6containing triphenylphosphine and 2,6-dimethylpyridine as L and L' was determined by means of X-ray diffraction.