Pt and Pd

Allyl Complexes and Complexes Derived from Monoolefins 1. Ni, Pd and Pt 

Calculations confirm a singlet ground state for Ni(C2H ) with 

C2H ) indicate the greater importance of back-bonding binding energies follow the order 02 2 2 2 4 Ni Pd Pt.  

Reaction of MeLi/TMED with Ni(C2H )3 yields the iCH Ni(C2H )2I ion as its Li(TMED)2 salt 2 1 may be displaced by CO to give 

Ni(C2H )3 though reactivities indicate an order of acceptor strength for the metal fragment of Ni(CO)3 Ni(1,5,9-cdt)  

A crystal structure determination of (C2H )2Pt02 reveals the expected trigonal planar (in-plane) coordination. In (cod)Nl[methyl-trans-B-(phenylsulfonyl)acrylate], the cod and olefin bonds are mutually perpendicular in a trigonal planar geometry. The 

A variety of CpNi(olefin)R complexes (olefin = ethene, propene) have been prepared by reaction of Cp2Ni with RMgX in the presence of olefin. Olefin rotation in the propene complexes occurs 

A single crystal polarized electronic absorption study of 

Olefin rotational barriers are larger in the CpPt(PPh )(olefin) case, and crystal structure determinations show that olefin is coordinated perpendicular to the plane defined by Pt, P and the 

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Small metal clusters are also of interest because of their importance in catalysis. Despite the fact that small clusters should consist of mostly surface atoms, measurement of the photon ionization threshold for Hg clusters suggest that a transition from van der Waals to metallic properties occurs in the range of 20-70 atoms per cluster [88] and near-bulk magnetic properties are expected for Ni, Pd, and Pt clusters of only 13 atoms [89] Theoretical calculations on Sin and other semiconductors predict that the stmcture reflects the bulk lattice for 1000 atoms but the bulk electronic wave functions are not obtained [90]. Bartell and co-workers [91] study beams of molecular clusters with electron dirfraction and molecular dynamics simulations and find new phases not observed in the bulk. Bulk models appear to be valid for their clusters of several thousand atoms (see Section IX-3). 

In the presence of [PtC ] and a base. 2-aminothiazole undergoes ring cleavage of the C-S bond to give PtLCF (L=HSCH=CHNHCN) (699). The Pd and Pt complexes of 2-aminothiazoles show biological activity (1596i. 

Hydrogenolysis of propylene oxide yields primary and secondary alcohols as well as the isomeri2ation products of acetone and propionaldehyde. Pd and Pt catalysts favor acetone and 2-propanol formation (83—85). Ni and Cu catalysts favor propionaldehyde and 1-propanol formation (86,87). 

Full eomplexation with Pt(II) is reaehed at the presenee of an aseorbie aeid (optimum 4 mg/em ) during 10-15 min at 65 5°C. At these eonditions eomplexes of Pd lose stability and within a day there is their full destmetion aeeompanying with deeolouration of solutions. That makes possible definition of a Pd and Pt at joint presenee, ineluding at H SO media. 

A particularly elegant route to metallacarbor-anes is the direct oxidative insertion of a metal centre into a c/oso-carborane cluster the reaction uses zero-valent derivatives of Ni, Pd and Pt in a concerted process which involves a nett transfer of electrons from the nucleophilic metal centre to the cage ... 

Arsine complexes are especially stable for b-class metals such as Rh, Pd and Pt, and such complexes have found considerable industrial use in hydrogenation or hydroformylation of alkenes. 

Incorporation of a third heteroatom into S-N compounds is now well established, e.g. for C, Si P, As O Sn and Pb, together with the S2N2 chelates of Fe, Co, Ni, Pd and Pt mentioned on p. 725. The field is very extensive but introduces no new concepts into the general scheme of covalent heterocyclic molecular chemistry. Illustrative examples are in Fig. 15.44 and fuller... 

The nine elements, Fe, Ru, Os Co, Rh, Ir Ni, Pd and Pt, together formed Group VIII of Mendeleev s periodic table. They will be treated here, like the other transition elements, in vertical triads, but because of the marked horizontal similarities it is not uncommon for Fe, Co and Ni to be distinguished from the other six elements (known collectively as the platinum metals) and the two sets of elements considered separately. 

Although estimates of their abundances vary considerably, Pd and Pt (approximately 0.015 and 0.01 ppm respectively) are much rarer than Ni. They are generally associated with the other platinum metals and occur either native in placer (i.e. alluvial) deposits or as sulfides or arsenides in Ni, Cu and Fe sulfide ores. Until the 1820s all platinum metals came from South America, but in 1819 the first of a series of rich placer deposits which were to make Russia the chief source of the metals for the next century, was discovered in the Urals. More recently however, the copper-nickel ores in South Africa and Russia (where the Noril sk-Talnakh deposits are well inside the Arctic Circle) have become the major sources, supplemented by supplies from Sudbury. 

Also in the divalent state, Pd and Pt show the class-b characteristic of preferring CN and ligands with nitrogen or heavy donor atoms rather than oxygen or fluorine. Platinum(IV) by contrast is more nearly class-a in character and is frequently reduced to Pt by P- and Aj-donor ligands. The organometallic chemistry of these metals is rich and varied and that involving unsaturated hydrocarbons is the most familiar of its type. 

Violet, easily hydrolysed, PdFp is produced when Pd [Pd F(sl s refluxed with SCF4 and is notable as one of the very few paramagnetic compounds of Pd. The paramagnetism arises from the configuration of Pd which is consequent on its octahedral coordination in the rutile-type structure (p. 961). The dichlorides of both Pd and Pt are obtained from the elements and exist in two isomeric forms which form i.s produced depends on the exact experimenial conditions used. The more usual a form of PdCb is a red material with... 

This is undoubtedly the most prolific oxidation state for this group of elements. The stereochemistry of Ni" has been a topic of continuing interest (see Panel), and kinetic and mechanistic studies on complexes of Pd" and Pt" have likewise been of major importance. It will be convenient to treat Ni" complexes first and then those of Pd" and Pt"... 

Figure 27-10 Anhydrous acetates of Pd" and Pt" (a) trimeric [Pd(02CMe)2h involving square-planar coordinated Pd but no metal-metal bonding (average Pd -Pd = 315pm), and (b) tetrameric [Pt(02CMc)2]4 involving octahedrally coordinated Pt and metal-metal bonds (average Pt-Pi = 249.5 pm). llie four bridging ligands in the Pt,j plane are much more labile than the others.

On the basis of the 18-electron rule, the d s configuration is expected to lead to carbonyls of formula [M(CO)4] and this is found for nickel. [Ni(CO)4], the first metal carbonyl to be discovered, is an extremely toxic, colourless liquid (mp —19.3°, bp 42.2°) which is tetrahedral in the vapour and in the solid (Ni-C 184pm, C-O 115 pm). Its importance in the Mond process for manufacturing nickel metal has already been mentioned as has the absence of stable analogues of Pd and Pt. It may be germane to add that the introduction of halides (which are a-bonded) reverses the situation [NiX(CO)3] (X = Cl, Br, I) are very unstable, the yellow [Pd"(CO)Cl2]n is somewhat less so, whereas the colourless [Pt (CO)2Cl2] and [PtX3(CO)] are quite stable. 

Palladium forms clusters of these types far less readily than nickel and platinum, unless they are stabilized by o-donor ligands such as phosphines. This may be due to the lower energy of Pd-Pd bonds as reflected in the sublimation energies, 427, 354 and 565 kJ mol for Ni, Pd and Pt. 

The solid metals all have the fee structure, like their predecessors in the periodic table, Ni, Pd and Pt, and they continue the trend of diminishing mp and bp. They are soft, and extremely malleable and ductile, gold more so than any other metal. One gram of gold can be beaten out into a sheet of 1.0m only 230 atoms thick (i.e. 1 cm to 18 m ) likewise Ig Au can be drawn into 165 m of wire of diameter 20/um. The electrical and thermal conductances of the... 

Alkylation lo yield a leriiary amine may occur easily if the formation involves cyclization (ii). Catalysts may have a marked influence. In reductive alkylation of ammonia wilh cyclohexanones, more primary amine was formed over Ru and Rh and more secondary amine over Pd and Pt. Reduction of the ketone to an alcohol is an important side reaction over ruthenium. 

Highly expl decompd by ferrous salts, Ag, Pd and Pt stable in storage distillable under vacuum... 

Pyridine complexes of Pd- and Pt-pincer ligands are also suitable substrates for olefin metathesis [116]. The first-generation catalyst 9 efficiently mediates the RCM of diallylphosphines and diallyl sulfide when the heteroatom is com-plexed by a cationic [C5H5(NO)(PPh3)Re] moiety [117]. This principle has been exploited in the same study for tungsten, rhodium, and platinum complexes. 

Reactions involving the catalytic reduction of nitrogen oxides are of major environmental importance for the removal of toxic emissions from both stationary and automotive sources. As shown in this section electrochemical promotion can affect dramatically the performance of Rh, Pd and Pt catalysts (commonly used as exhaust catalysts) interfaced with YSZ, an O2 ion conductor. The main feature is strong electrophilic behaviour, i.e. enhanced rate and N2 selectivity behaviour with decreasing Uwr and , due to enhanced NO dissociation. 

Information about the structure of Pd and Pt is provided by the paramagnetic susceptibility of the metals, interpreted by the Weiss equation... 

In Fig. 4 there are shown the lines representing x 1 as a function of T for Ni, Pd, and Pt. It is seen that the slopes, which give the values of C l, are essentially the same, and that accordingly Pd and Pt have the same number of unpaired electrons as Ni. We accordingly conclude that they have the same valence, 6. 

Fig. 4. Curves showing the reciprocal of the molar paramagnetic susceptibility of Ni, Pd, and Pt as a function of the temperature.

Very few studies on complexes of palladium and platinum with 1,1-dithiolato ligands have been reported recently. The electronic absorption spectra of the Et2dtc complexes of Pd and Pt, as well as Zn, Cu, Fe, Co, and Mn, have been measured in MeCN, EtOH, and -heptane, with diffuse-reflectance spectra also being determined (401). In 1969 and... 

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