Pd II complexes

Following some earlier observations [18], the chemistry of cyclopalladated complexes has been greatly developed in the last ten years [31]. Recently, systematic investigations on the luminescence of cyclometallated Pd(II) complexes have also appeared. Most of the available data are gathered in Table 2. 

For Pd(bhq)2, the luminescence emission can be assigned to an essentially 3LC excited state on the basis of the following considerations  

the emission spectrum is only slightly red-shifted (650 cm x) with respect to the spectrum of the free C-protonated ligand  

the relative intensities of the vibrational features are quite similar to those of the ligand  

the radiative lifetime (estimated from the experimental lifetime and quantum yield) is 0.25 s, a value expected for slightly metal-perturbed 3LC emissions. 

---

Carbon monoxide also reacts with olefins such as ethylene to produce high molecular weight polymers. The reaction of CO with ethylene can be initiated by an x-ray irradiator (62) or transition-metal cataly2ed reactions (63). The copolymeri2ation of ethylene with carbon monoxide is cataly2ed by cationic Pd (II) complexes such as Pd[P(CgH )2] (CH CN) (BF 2 where n = 1-3. With this catalyst, copolymeri2ation can be carried out at 25°C and pressures as low as 2.1 MPa. 

With soft Lewis acids, phenotellurazines 43 form molecular complexes in which the tellurium center serves as the ligating atom [82DOK(266)1164 85KGS757]. The 1 1 complexes 49 are formed with salts of Hg(II) and Ag(I). PdCb reacts with 43 to give 1 2 complexes 50. Whereas the Hg(II) and Pd(II) complexes are stable on exposure to air, the Ag(I) complexes rapidly decompose when isolated from their solutions. 

MeS(0)CHMe2, Et2S=0] support the S-bonded structures and configurations of the complexes shown in Scheme 15. Far-IR studies indicate that the Pd(II) complexes have uniformly the trans structure while the Pt(II) complexes have the cis one196 197. 

Tetrakis(tripheiiylphosphine)palladium(0) is often used for this reaction. However, Pd(II) complexes such as bis(triphenylphosphine)palladium dichloride or palladium acetate are also commonly employed for convenience, as they are stable in ah. The base is typically a secondary or tertiary amine such as triethy-lamine. Weak bases such as sodium (potassium) acetate, bicarbonate, or carbonate are also used. 

Ph3P)4Pd and certain Pd(II) complexes in the presence of an excess of a tertiary phosphine also function as active catalysts (128). This indicates that palladium species may have potential provided they are protected from destructive reduction by the choice of suitable ligands. A complex species [(Ph3P)2Pd]jf gradually forms in the PhjP—Pd metal mixture ( 28). 

Mikami M, Hatano M, Akiyama K (2005) Active Pd(II) Complexes as Either Lewis Acid Catalysts or Transition Metal Catalysts. 14 279-322 Minatti A, DOtz KH (2004) Chromium-Templated Benzannulation Reactions. 13 123-156 Miura M, Satoh T (2005) Catalytic Processes Involving b-Carbon Elimination. 14 1-20 Miura M, Satoh T (2005) Arylation Reactions via C-H Bond Cleavage. 14 55-84 Mizobe Y, see Hidai M (1999) 3 227-241... 

The coupling of terminal alkynes with aryl or alkenyl halides catalysed by palladium and a copper co-catalyst in a basic medium is known as the Sonogashira reaction. A Cu(I)-acetylide complex is formed in situ and transmetallates to the Pd(II) complex obtained after oxidative addition of the halide. Through a reductive elimination pathway the reaction delivers substituted alkynes as products. 

More recently, a study with di- and mono-carbene Pd(II) complexes has demonstrated that the Sonogashira coupling of activated and non-activated aryl iodides can be carried out in an aqueous, aerobic medium and in the absence of amines. These results suggest that the moisture-sensitive copper-acetylide may not be present in this particular transformation, and that a Pd-acetyhde could be formed by deprotonation of the coordinated alkyne instead of transmetallation [130]. 

Table 7.2 Chiral NHC-Pd(II) complexes in asymmetric oxidative Heck reaction...

Extended linear chain inorganic compounds have special chemical and physical properties [60,61], This has led to new developments in fields such as supramolecular chemistry, acid-base chemistry, luminescent materials, and various optoelectronic applications. Among recent examples are the developments of a vapochromic light emitting diode from linear chain Pt(II)/Pd(II) complexes [62], a luminescent switch consisting of an Au(I) dithiocarbamate complex that possesses a luminescent linear... 

Johnson, T. W. Kostic, N. M. Steric effect on the rate of hydrolysis by Pd(II) complexes of the C-terminal amide bond in a series of dipeptides Ac-Met-AA, American Chemical Society, Washington, D. C. In Book of Abstracts, 212th ACS National Meeting, Orlando, FL, August 25-29, 1996. 

A novel phosphinito dipeptido ligand series were prepared, and fully characterized. These ligands readily form metal complexes with Pd(H) and Pt(II) precursors. The Pd(II) complexes were investigated for their suitability in asymmetric Heck reaction using 3,4-dihydrofuran as a substrate. 

Transition metal isocyanide complexes can undergo reactions with nucleophiles to generate carbene complexes. Pt(II) and Pd(II) complexes have been most extensively investigated, and the range of nucleophilic reagents employed in these reactions has included alcohols, amines, and thiols (56) ... 

An addition-elimination reaction of substituted trimethylsi-lylphosphines with vinylic bromides catalyzed by Pd(II) complexes has been found to be of use for the preparation of vinylic phosphines (Equation 4.31).95... 

---