Cyclopentadienyl-allyl-palladium

The use of appropriate ligands for a given metal can permit one to obtain high purity deposits. The Tjballyl and T -cyclopentadienyl ligands coordinated to palladium seem to be especially attractive for the deposition of pure palladium on silica surfaces. It has been proposed that [Pd(T hC3H5)(T -C5H5)] under a helium atmosphere could easily react with a silica surface to produce a surface allyl palladium species and cyclopentadiene [57] (9.9) ... 

This surface reaction would involve a change in the cyclopentadienyl hapaticity prior to SiO-H activation by the metallic species. Loss of cyclopentadiene by reductive elimination would then occur to provide an allyl palladium(ll) surface species, probably stabilized by a silanol group, in which the oxygen atom acts as a 2e donating ligand. However, when the temperature is raised significant carbon contamination has been evidenced by TPD and TPO experiments. These results are consistent with the absence of further SiO-H activation to eliminate propene [57]. 

Cycloalkenes, into if-allyl palladium complexes, 8, 363 Cycloalkenyl rings, metal complex conformational interconversions, 1, 414 Cycloalkynes, in nickel complexes, 8, 147 (Cyclobutadiene)cyclopentadienyl complexes, with cobalt, polymercuration, 2, 435 Cyclobutadienes... 

Nesmeyanov s laboratory (22) found that t/3-allyl palladium cyclopentadienyl reacted with iron pentacarbonyl to produce [CpFe(CO)2]2 and Cp2Fe. The fate of the palladium was not revealed. In a similar fashion, Cp(f/3-C3Hj)Pd reacted with FeCl2 in THF to produce [(r/3-C3H5)PdCl]2 and Cp2Fe. No conversions or yields were given. 

Caution. (r)3-Allyl)(r)s-cyclopentadienyl)palladium is volatile and has an unpleasant odor. As the toxity is unknown, all manipulations should be carried out in an efficient hood. All solvents are dried over sodium metal and distilled under nitrogen. 

The allyl group itself may also be attached to a cyclopentadienyl-metal residue, giving compounds of the type (CjHsJMCCsHs). These are known for nickel (77, 152), palladium (232), and platinum (232a). The palladium and platinum compounds are remarkably stable the nickel derivative is. liquid at room temperature, and decomposes very readily in oxygen. 

In 1971 only two complexes of palladium(I) had been identified.65 Although the area has grown significantly, the relative paucity of palladium cluster compounds can be attributed, in part, to the surprising weakness of palladium-carbon monoxide bonds and in particular those where CO is bound terminally. In this chapter the chemistry of palladium(I) and clusters of palladium in other oxidation states will be considered. However, complexes containing organic ligands such as allyl and cyclopentadienyl will not be dealt with as this area has been reviewed recently in a companion volume.66... 

With 1,1-difluorocyclopropabenzene and a range of nickel(O) complexes, nickelabicy-clobutanes 118 (84—93%) are formed by loss of olefin or phosphane ligands and addition of the nickel atom across the bridge bond (Scheme 20)256-266. The products appear to be stable at ambient temperatures but are oxygen sensitive the majority revert to cycloproparene in solution even below -20 °C. With (j -allyl)( s-cyclopentadienyl(palladium in the... 

Chemical shifts have been reported for [Me3CCH2HgX] 203) (see Table XII), tr-allylic derivatives (see Table XIII), o-cyclopentadienyl derivatives (see Table XIV), and miscellaneous compounds (see Table XV). In the case of fluxional a-cyclopentadienyl derivatives, it has been shown that chemical shifts can be used to differentiate between fluxional o-cyclopentadienyl derivatives and w-cyclopentadienyl derivatives 103). The NMR spectrum of [Sb(cyclopropyl)s] has only two carbon resonances, showing that the molecule is fluxional (56) and the NMR spectrum of the naturally occurring organometallic compound, 5 -deoxyadenosylcobalamin, has been reported (65). For a number of norbornane and allylic derivatives of palladium and platinum, a number of linear relationships have been found between chemical shifts of various carbon atoms. It was suggested that a term due to paramagnetic shielding by the metal was dominant 52b). 

Allyl and 77-cyclopentadienyl ligands have been replaced by triphenylphosphine or cyclohexylisonitrile in 77-cyclohexenyl-77-cyclopentadienyl-palladium 152)... 

Wilkinson had observed an associative exchange of CjH, rings analogous to that of (77-allyl)(7r-cyclopentadienyl)palladium and other related complexes discussed below. 

The reactivity of such compounds has been studied in detail 201-212). Substitution of the 7r-cyclopentadienyl group has been investigated for monocyclopentadienyl halogen and alkoxytitanium derivatives, dicyclo-pentadienyltitanium halides and alkoxides 201-211), and for (77-a llyl) (77-cyclopentadienyl)palladium 212a). The stereochemistry of these complexes has been confirmed unequivocally by physical methods including X-ray studies. The structures of (77-allyl)(7T-cyclopentadienyl)palladium 213) and of (77-cyclopentadienyl)titanium trichloride 214) are shown. 

Other characteristic examples of easy substitution of the 77-C5H5 ring in coordinatively unsaturated complexes include cleavage and transfer of the 77-cyclopentadienyl ligand in (77-allyl)(77-cyclopentadienyl)palladium... 

Such a scheme has been proposed based on the UV spectrum and polaro-gram of (7r-allyl)(77-cyclopentadienyl)palladium (212). A complete X-ray study of this compound carried out by Struchkov et al. (213) revealed that the palladium atom has a vacant coordination site. In essence, the scheme proposed is a version of associative substitution via change in ligand bond character in the transition state. 

Similar to the nickel-catalyzed reactions, metallacycles of palladium are assumed to be intermediates of these conversions. They were isolable in some cases. Thus, 3,3-dimethylcyclopropene with -allyl( ) -cyclopentadienyl)palladium, on cyclizing oxidative addition, formed metallacyclopentanes 20 and metallacyclononanes 21, depending on the reaction conditions. Thermal decomplexation via reductive elimination gave cyclopropane systems and products thereof. ... 

A remarkable product selectivity is also observed in the case of methylenecyclopropanes with geminal diphenyl substitution. Whereas under nickel catalysis [Ni(cod)2 at SO-TO C] 18 is selectively dimerized to tra7w-l,l,6,6-tetraphenyldispiro[2.1.2.1]octane, which can be obtained in 28% yield at a conversion of 40%, substrate 18 reacts in a completely different manner with palladium(O) catalysts derived from (t/ -allyl)( -cyclopentadienyl)palladium(II) and triisopropylphosphane. Besides isomerization to 19, proceeding at temperatures above 85 °C, the monospiro derivative 20 is formed as the major product. Additionally, minor amounts of a formal [3 + 3] dimer 21 can be isolated. The latter probably arises from a palladium-mediated, stoichiometric reaction as the yield of 21 could not be improved under any conditions in catalytic runs. On prolonged heating, thermal isomerization of the methylenecyclopropanes to form... 

This reaction can be improved with respect to both yield and selectivity by the use of (> -allyl)( 7 -cyclopentadienyl)palladium/triisopropylphosphane (1 1) as catalyst. However, due to a metal-catalyzed C-C double-bond isomerization of the primary exocyclic methylene product 26, two isomeric trisubstituted alkenes 27 and 28 are formed in almost equal amounts. ... 

A solution of (> -allyl)(>7 -cyclopentadienyl)palladium (100 mg, 0.52 mmol), i-PfjP (83 mg, 0.52 mmol) and (diphenylmethylene)cyclopropane (7 4.78 g, 23.2 mmol) in anhyd toluene (10 mL), was placed in a stai nless steel autoclave which was then pressurized at rt with ethene (3000 Torr, ca. 30 mmol). The autoclave was heated to 100 C with magnetic stirring of the contents for 3 h. Excess ethene was removed and the red-brown product mixture (which also contained a black precipitate of palladium) was distilled in vacuo. After a forerun (bp up to 60"C/0.5 Torr) of essentially pure toluene, the cycloadduct was obtained as a yellow, viscous liquid yield 4.5 g (83%) bp 92-95°C/10 Torr. 

A solution of (t -allyl)(( -cyclopentadienyl)palladium, (403 mg, 1.9 mmol), i-PrjP (304 mg, 1.9 mmol) and methyl acrylate (2.25 g, 26 mmol) in o-xylene (10 mL) was heated to reflux with stirring under argon. A solution of l-methylene-2-(trimethylsilyl)cyclopropane (3.29 g, 26 mmol) in o-xylene (10 mL) was then added dropwise. After 4 h at reflux temperature, there was total consumption of 5 (as determined by GC). Fractionating distillation of the mixture in vacuo yielded a forerun of o-xylene, then the cycloadduct as a yellow liquid yield 4.31 g (78%), bp 30°C/10 Torr ratio ( /Z)47 53 (as determined by capillary GC). 

A 200-mL stainless steel autoclave was charged with DMF (15 mL) and heated to 165°C. It was then pressurized with 4 MPa of carbon dioxide at 165 °C. From a reservoir, prepressurized at 2.5 MPa with Nj, a solution of (f/ -allyl)(j -cyclopentadienyl)palladium (100 mg, 0.47 mmol), PhjP (550 mg, 2.1 mmol) and methyleneeyclopropane (20.6 g, 381 mmol) in DMF (90 mL) was slowly pumped into the autoclave within 1 h. This rate of addition was such that the temperature inside the autoclave was kept at 4 MPa. After the addition, the contents of the autoclave were stirred for an additional hour at 165 C. From this black mixture (145.7g), a distillate was obtained (142.7g bp up to 60°C/10 Torr). This fraction was redistilled using a 60-cm Vigreux colmnn to yield a forerun of DMF (109 g bp 50°C/6.8 Torr), then 17 (R = H) of 97% purity (as determined by GC analysis) yield 31 g (80%) bp 131-132°C/6.8 Torr. 

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