Platinum n

Platinum(n).—Aquationy Solvolysis, and Anation. Kinetic parameters have been determined for the forward and reverse reactions of equation (2). Mercury(ii) 

Aquation of the [PtClJ - anion is catalysed by Zeise s salt, KfPtClafCjHJ]. This catalysis is inhibited by adding chloride, suggesting that the active catalyst may be [PtCl2(C2H4)(OH2)], with (3) being the dinuclear intermediate produced in the rate- 

Similar reactions in which the acetonitrile is replaced by amides or uracil derivatives produce analogous platinum blues. The ultimate product in the aquation of the [PtCl4] anion is the Ptaq cation, whose preparation and properties have been described, and whose anation kinetics can be now studied (c/. Pd q ). 

The affinity of DMSO for platinum(ii) makes this an attractive solvent for solvolysis studies. Pt N.m.r. spectroscopy has shown that six products result from the solvolysis of cw-[PtCl2(NH3)2] in this medium, indicating a complicated mechanism. The stereochemistry and kinetics of solvolysis of the [PtCUCgly)] anion have also been probed by n.m.r. spectroscopy. Discrepancies between this and earlier work on amino-acid complexes [PtCl2(aa)] have been rationalized by further n.m.r. studies of the configurational changes involved en route to the products (4).  

The kinetics of solvolysis of complexes cis- and // a 5-[Pt(N02)2L2] (L=ammonia, pyridine, or triethylphosphine) in acetic acid-sulphuric acid mixtures have been compared with those in aqueous sulphuric acid. The mechanism is loss of a nitro-sonium ion from the protonated complex. Whether this protonation takes place at the nitrito-ligand or at the metal is not known, but definitive evidence favouring the latter could not be obtained. Platinum-carbon bond cleavage in cw-[Pt(C6H4Y)2-(PEt3)2], studied in methanol and methanol-water mixtures, takes place by electrophilic attack by a proton, 

Platinum(n).—General The normal rate law for nucleophilic substitution at platinum(n) complexes, as at other square-planar rf complexes, is 

The values of the rate constants kx and k of equation (4) for any given reaction are solvent-dependent. One way of probing some effects of the tetra-gonally interacting solvent molecules would be to replace one of them by 

Normally, substitution at platinum(ii) in solution is nucleophilic in character. It is interesting therefore to note the first report of an Sb.2 substitution at platinum(ii), which is reported for the reactions of cw-tPtRgLa], where R = Me, Et, CHaPh, or CHaSiMeg and L = a phosphine, with OBu or SPh radicals. Indeed this is the first report of radical substitution at any transition-metal centre. 

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Gilman S. 1964. The mechanism of electrochemical oxidation of carhon monoxide and methanol on platinum, n. The reactant-pair mechanism for electrochemical oxidation of carhon monoxide and methanol. J Phys Chem 68 70-80. 

C10HuN4OsPs, 2.88 Na+16 HjO 0.86 C20H28N10O16P2Pt2-0.28 5 -phosphate, hexadecahydrate Sodium diammine-bis(inosine 5 -phosphate)-platinum(n)- IMPPTS 43 308... 

CijH NioOigPjPtj 2 HjO iodide, dihydrate Bis(cytidine 5 -phosphate) bis[ethylenediamine-platinum(n)], CMPEPT 38 527... 

The dimeric 2,3-dihydro-l,2,4-oxadiazole palladium(n) complex 182 (Equation 27) reacts with aqueous methylamine to liberate the ligand 183 <2003JCD2544>. A similar process has also been applied to platinum(lv)-bound complexes 184, using pyridine to liberate the 2,3-dihydro-l,2,4-oxadiazole <2000JA3106>. Reduction of the platinum(iv) complexes 184 (Equation 28) gives the corresponding platinum(n) complexes 185 <2001IC264>. 

A closely related dicationic platinum complex has been shown to transform efficiently /3-citronellene into cis-thujane in a highly diastereoselective manner, which mimics terpene biosynthesis.362 Also, using platinum(n) catalysis, Widenhoefer has reported an intramolecular alkylation of indoles with unactivated olefins, which can be carried out in an enantioselective fashion (Scheme 99).363... 

The proposed mechanism starts with a methyl group abstraction on platinum complex 416 with the borane reagent in the presence of diyne 414 (Scheme 105). The square-planar cationic diyne-platinum(n) complex 417 is converted to the octahedral platinum(rv) hydride intermediate 418 through oxidative addition of the hydrosilane. This complex decomposes rapidly with methane release to form another tetracoordinated platinum(n) species 419, followed by platinasilylation of the triple bond. The resulting vinylplatinum 420 undergoes an intramolecular carboplatination to... 

In contrast to the palladium-catalyzed reactions, little attention has been paid to other transition-metal catalysts. Recently some efficient reactions using copper(i or 11), gold(m), platinum(n), and tungsten(O) have been developed for the synthesis of nitrogen-heterocycles. The copper-catalyzed cyclizations of 2-alkynylaniline derivatives into... 

In relation to the mechanistic proposal, an interesting reactivity of (boryl)(silyl)platinum(n) complex has been reported.223 The complex is prepared by the reaction of silylborane with Pt(cod)2 complex via oxidative addition (Scheme 46). The (boryl)(silyl)platinum complex undergoes insertion of alkynes at the B-Pt bond to give (/3-borylalkenyl)(silyl)platinum(n) complex in high yield. Importantly, the insertion takes place regioselectively, with Pt-G bond formation at the internal. -carbon atom. This result may indicate that the boron-transition metal bond is more prone to undergo insertion of unsaturated molecules. 

THE FORMATION OF THE HYDRIDO(METHANOL)BIS(TRIETHYL-PHOSPHINE)PLATINUM(n) CATION AND ITS REACTIONS WITH UNSATURATED HYDROCARBONS... 

Figure 8-23. The formation of a five-co-ordinate platinum(n) complex after the addition of hydroxide ion to [Pt(bpy)2]2+. This is thought to be the final product of the reaction.

Enyne 190 undergoes platinum(n)-catalyzed ring closures to afford the cyclopropyl-fused 3,4-dihydropyran 191. The reaction is thought to proceed via formation and rearrangement of the intermediate cyclobutyl cation 192 (Scheme 59) <2000JA6785, 2001JA11863>. 

Platinum (n)—Group VII and Hydride Donors. SCF—Xa calculations have been made for the ions [MC14]2 (M = Pd or Pt) (see p. 384).13 In addition the extended Hiickel MO method has been employed to calculate activation energies of the halide-... 

Two catalyzed reactions have been reported for the addition to the carbon-heteroatom bonds. Rhodium(i) or platinum(n) complexes catalyzed the addition of B2cat2 to C-S241 and C-N242,243 double bonds (Equations (37) and (38)). 

When 2 forms a complex with Pt(PF6>2, the Pt2+ lies at an inversion center surrounded by a distorted square planar array of four atoms. The two oxygen atoms lie trans to each other and oriented away from the Pt center, precluding any Pt-O interactions. In the complex, the S-O-S unit adopts a meridional rather than facial coordination mode. The Pt-O distances in 2-Pt(PF6)2 complex is 3.730(5) A and the Pt-S bond lengths average 2.317(2) A. In this structure, the platinum(n) ion lies 0.018 A above the mean plane of the four sulfur atoms. 

Notably, it is not just heteroatom-functionalized alkenes that can behave as dienophiles with metal-bound phospholes. It has been demonstrated that reaction of 2equiv of 3,4-dimethyl-l-phenylphosphole with a cationic platinum(n) complex of an enantiomerically pure cyclometallated A, A -dimethyl-l-(l-naphthyl)ethylamine ligand affords, following decomplexation with cyanide, the novel optically pure diphosphine (-f)-267 quantitatively as an air-sensitive oil (Scheme 93) <2000CC167>. The high-frequency chemical shift of one of the phosphoms centers (5 4.9 and 104.2 ppm (7pp = 43.9 Hz)) is indicative of rwt>-jy -stereochemistry. Similar reactivity has been... 

Write formulas for (a) platinum(n) monohydrogen phosphate and (b) platinum(II) dihydrogen phosphate. 

The square-planar coirfiguration of platinum(n) was proven by the same methods bnt with a different chronology and a difference in interpretation of the resolntions. Three symmetrical configurations for the coordination number four are theoretically possible (see Figure 6). 

Selenourea is less stable than urea or thiourea, as it is sensitive to air and light, particularly in solution, and tends to dimerize in certain systems. In general, the donor properties of selenourea are similar to those of thiourea,2.3 and complexes with cobalt(II),4,5 palladium(II), platinum(n), zinc, cadmium, and mercury acceptors can be obtained by appropriate modification of the methods used for the preparation of the analogous thiourea derivatives. 

The synthesis of platinum(n) complexes has also been studied by Urriolabeitia and co-workers <20010M1424>. Treatment of PtCl2(NCPh)2 with [Ph3PCH2COCH2PPh3]Cl2 (1 1 molar ratio, 2-methoxyethanol, reflux, 22 h) resulted in the formation of the C,C-ortio-meta htcd derivative 100, characterized by elemental analysis and mass spectrometry (Equation 15). 

A more complex intramolecular hydrogen bond system is built in the platinum(II) complex 33 (O Fig. 8) in which the central f/trco-configured diol is the chelation site. A y and a S hydrogen bond, each starting at one of the terminal donor hydroxyl functions, end at one and the same alkoxido function. The other one is an acceptor in a more strained p hydrogen bond [22]. Affirmed by DPT calculations, the completion of an octahedral coordination sphere of trimethyl-platinum(n) in a dinuclear complex is accomplished with facial tridentately bonded D-mannitol (coordination mode , 0, 0 k 0, 0, 0 ) [38]. 

G. Strukul, R. A. Michelin, Catalytic epoxidation of 1-Octene with diluted hydrogen peroxide. On the basic role of hydroxo complexes of platinum(n) and related species, J. Am. Chem. Soc. 107 (1985) 7563. 

Zbllner, P., Zenker, A., Galanski, M., Keppler, B. K., Lindner, W. Reaction monitoring of platinum(n) complex 5 -guanosine monophosphate adduct formation by ion-exchange liquid chromatography/electrospray ionization mass spectrometry. J Mass Spectrom 2001, 36, 742-753. 

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