Chloro-bridged complexes

Palladium forms the largest series of ir-allylic complexes of any metal, and many of these complexes are readily prepared. The majority are chloro-bridged complexes of the type [PdCl(all)]2, where all = an allylic radical. 

Treatment of the chloro-bridged complex [PdCl(7r-C3H5)]2 with cyclo-pentadienylsodium gives 7r-al lyl-rr-cyclopentadienylpalladiu m (II) [Pd(ir-C3H6)(7r-C6H6)] as dark red, voltatile crystals, mp 64° (190). Its nmr spectrum (191) confirms the sandwich structure (L) in which the palladium has the electronic configuration of xenon. 

Diisopropylamino-dimethylphosphole also reacts with a source of Pd(ll) to form the chloro-bridged complex 347, which on addition of further quantities of phosphole generates the corresponding monometallic system 348 (Scheme 116). In contrast to the reactivity observed for complex 341, neither complex exhibits intramolecular cycloaddition processes upon heating <2002JOM19>. 

Dimeric, cyano-bridged-r -allylic derivatives of Pd(II) are prepared from the chloro-bridged complexes with NaCN. Reaction of the /i-cyano species with phosphines or arsines results in bridge splitting and formation of mononuclear sp>ecies . 

The reaction of palladium black with certain gem-dichlorocyclopropenes produces the cyclopropenylidene-palladium(II) chloro-bridged complexes 297 which have a significant contribution from the zwitterionic form " The unsaturated complex 298 can be... 

A series of the chloro-bridged complexes have been studied by X-ray diffraction and as a result of the shorter-than-theoretical molecular length, a model was proposed with the molecules containing a rigid core of about 11 A) with the longer of the two chains tending to fill the free space close to the shorter chain... 

The dinuclear, chloro-bridged complex can easily be cleaved by a diimin [68] ... 

Similarly, smectic mesophases were obtained in heteronuclear or/ o-palladated imine complexes based on various non-mesomorphic enaminoketone ligands ((263) to (265), Figure 104). The precursor chloro-bridged complex was also mesomorphic, showing an SmA phase between 238 and 248°C. ... 

As above (242), the dinuclear ort/ o-palladated complexes derived from (S)-2-(2-hydroxyaryl) oxazoline Schiflf-base ligands ((277) X = OAc, Cl x = 1 R = CHMez x = 1,2 R = C HCH3CH2CH3) showed a broad SmA phase. In the planar, chloro-bridged complexes (cis. trans mixture 1 2), the phase existed from 50 °C to 170 °C, and up to 250 °C for the biphenyl derivative as far as the non-planar acetato-bridged complexes (only tram isomer) were concerned, only the biphenyl derivative was mesomorphic (g 71 SmA 121 Cr 179 SmA 232 I). Used as chiral dopants (ca. lOmol.%), a chiral nematic phase was induced systematically in both the chloro- and acetato-ljridged series, with the suppression of the SmA phase in the chloro-bridged systems (x = 1). 

Tebbe s reagent 8.188 is a nucleophilic carbene (Scheme 8.53). It is made by treatment of titanocene chloride with trimethyl aluminium to give a chloro-bridged complex 8.187. The reagent is released in the presence of a Lewis base, such as pyridine or DMAP, which will coordinate the aluminium. Even THE can function as an effective Lewis base. 

Secondary benzylamines have been cyclopalladated and reactions of the chloro-bridged complexes with various ligands such as PPhs, acac, 1,1,2,2-tetraacetylethane, l-phenylazo-2-naphthol, and 2-hydroxy-3-/-butyl-5-methylbenzylidene-/)-chloroaniline have been carried out. Secondary and primary benzylamines were cyclopalladated in benzene using Pd(OAc)2. Bridge-splitting reactions with, for example, 3,5-lutidine, PPh3, and thallium acetylacetonate have been carried out. 

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