Palladium complexes diketonates

Unsymmetrical oc-diketones RCOCOR have been prepared by treatment of an acyl halide RCOCl with an acyltin reagent R COSnBus, with a palladium complex catalyst. 

Several combinatorial approaches to the discovery of transition metal based catalysts for olefin polymerization have been described. In one study Brookhart-type polymer-bound Ni- and Pd-(l,2-diimine) complexes were prepared and used in ethylene polymerization (Scheme 3).60,61 A resin-bound diketone was condensed with 48 commercially available aminoarenes having different steric properties. The library was then split into 48 nickel and 48 palladium complexes by reaction with [NiBr2(dme)] and [PdClMe(COD)], respectively, all 96 pre-catalysts being spatially addressable. 

Hydrolysis of Pd(MeCOCHMe)2 in aqueous methanol is considered to involve Pd(0,0-MeCOCHCOMe)(0-MeCOCHCOMe)(MeOH) as an intermediate from which the monodentate acetylacetonate ligand is then solvolyzed.221 Subsequent studies on Lewis base complexes of palladium bis(diketonate) complexes provide ample support for the proposed intermediate. A pulse radiolysis study of the kinetics of aquation of M(MeCOCHCOMe) " (M = Cr, Co) indicates that an 17,-172 equilibrium involving one or more of the acetylacetonate ligands occurs, associated with an acid-catalyzed removal of the monodentate ligand.222 Treatment of Cu(MeCOCHCOMe)2 with picric acid in moist dichloromethane affords a partially hydrolyzed material, Cu(MeCOCHC-0Me)(H20)2[C6H2(N02)30], proposed to contain square pyramidal five-coordinate copper with the oxygen atom from the picrate moiety at the apex.223... 

Tschierske synthesized the butterfly mesogens 132-134 (Scheme 72, Table 9). These compounds are based on a macrocyclic crown-like para-cyclophane ring containing two 2-phenylpyrimidine units. Of/to-palladation and subsequent treatment with substituted half-disks like (5-diketones gave the desired dinuclear palladium complexes with 4 (132), 8 (133), and 12 (134) peripheral alkyl chains [127]. 

A number of metal / -diketonates have been used to catalyze the oxidation of sulfides to sulfoxides, important synthetic intermediates for the construction of various biologically active molecules . For example, an elegant study by Ishii and coworkers demonstrated that VO(acac)2 (35) selectively catalyzed the sulfoxidation of adamantane (41) by SO2/O2 to give 1-adamantane sulfonic acid (42) (equation 10) . Although a number of metal acac complexes were examined as catalysts for this reaction, all but the vanadium compound failed to promote the sulfoxidation. The catalytic oxidation of triarylphosphines using the palladium complex Pd(acac)2 (29) has also been investigated . 

Asymmetric alkylations can be performed in the presence of catalytic amounts of chiral phase transfer catalysts or through the intermediacy of 7t-allyl-palladium complexes bearing chiral ligands. Both methods normally require relatively acidic carbon acids (pKa 5 17) such as (3-diketones, P-keto- or cyanoesters or malonic acid derivatives. 

The widest columnar mesophase temperature ranges were obtained for the bis-[l,3-di-(substi-tuted-phenyl)-/3-diketonate] metal complexes bearing ten and twelve chains ((55) R = H or OC H2 +i). The ten-chain copper, palladium, and oxovanadium(IV) complexes ((55) M = Cu, Pd, VO R = H, = 6, 8, 10, 12, 14) were all mesomorphic and the enantiotropic mesophases were identified by optical texture and variable-temperature X-ray diffraction as columnar phases (Table 34). The copper and palladium complexes displayed a Coh phase for short chain length ( = 6, 8 for M = Cu = 6, 8, 10 for M = Pd), which transformed to a Coin phase as the chain length was increased. Surprisingly, no direct Cok-to-Colh phase transition was observed within the same compound, but weakly first-order Cok-to-Cok and Colh-to-Colh phase transitions were found for compounds with intermediate chain lengths. In contrast, the vanadyl complexes exhibited only one Coh mesophase. Infrared studies indicated that the VO complexes possessed a linear V=0—V=0 linear polymeric chain structure in the crystal phase, while no... 

Diaryl-a-diketones were obtained in the carbonylation of diaryliodonium salts catalyzed by Pd(OAc)2 in the presence of zincJ In addition to diketones, formation of diaryl ketones, biaryls, and aryl iodides was also found. A synthetic method to yield a-diketones has been developed by carbonylative coupling between diorganozincs and acid halides promoted by palladium complexes (Eq. 26). A diacylpalladium intermediate was proposed in the course of formation of a-diketone. 

Palladium complexes with an heterocyclic N-containing ligand have been used in the carbonylation of aromatic nitro compounds with cocatalysts such as cyclopentadienyl halides or oxyhalides of transition metals belonging to group V e.g. CP2VCI) [168], a cyclopentadienyl halide or oxyhalide together with phosphorus oxytrichloride [169], or a 1,3-diketone derivative of vanadium [170], even also in the presenee of phosphorus oxychloride [171]. 

Reaction of butadiene with aldehydes in the presence of palladium(o)-triphenylphosphine species leads to two products (80) and (81), whose formation can be explained by the mechanism outlined in Scheme 4. Whereas butadiene reacts with active-hydrogen-containing compounds such as a-cyano-esters or jS-diketones in the presence of palladium complexes of unidentate phosphines, in the presence of palladium complexes of bidentate phosphines addition of the butadiene to the active-hydrogen compound takes place. ... 

The first jS-diketonate, 21, examined for mesophase behavior was the palladium complex of Bulkin et al. [55]. They suggested that it may be mesomorphic but have been unable to confirm this. 

It has been shown that a j8-diketonate liquid crystal containing palladium(II) and oxo-vanadium(IV), analogous to known copper complexes (which display discotic lamellar and columnar mesophases), has been prepared and characterized palladium complexes are mesomorphic but their identification is difficult due to their decomposition in the isotropic phase the complex n = 10 seems to present a Nj phase on the basis of optical microscopy. The vanadium complexes are enantiotropic discotic [75], while the vanadium complex, 30, presented by Styring et al. [76] (n= 10), exhibited a short monotropic columnar discotic phase. 

Template syntheses of P macrocycles are a new area. In fact, a 1978 review93 of template synthesis made no mention of P macrocycles. Template syntheses have been developed by Stelzer and co-workers.94 Firstly, two molecules of the bidentate secondary phosphine are complexed with a nickel(II) or palladium(II) salt (Scheme 6) and the resultant secondary phosphine complex is then condensed with a diketone to form the macrocyclic metal complex. Unfortunately, these macrocycles are strong field ligands and no method has yet been devised to remove the metal from the ring. On the other hand, Cooper and co-workers95 have used a template synthesis to produce a [l4]aneP2N2 macrocycle (Scheme 7). 

Backwall and coworkers have extensively studied the stereochemistry of nucleophilic additions on 7r-alkenic and ir-allylic palladium(II) complexes. They concluded that nucleophiles which preferentially undergo a trans external attack are hard bases such as amines, water, alcohols, acetate and stabilized carbanions such as /3-diketonates. In contrast, soft bases are nonstabilized carbanions such as methyl or phenyl groups and undergo a cis internal nucleophilic attack at the coordinated substrate.398,399 The pseudocyclic alkylperoxypalladation procedure occurring in the ketonization of terminal alkenes by [RCC PdOOBu1], complexes (see Section 61.3.2.2.2)42 belongs to internal cis addition processes, as well as the oxidation of complexed alkenes by coordinated nitro ligands (vide in/ra).396,397... 

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