Thioether platinum

Catalytic hydrogenation with platinum liberates the hydrocarbon from methylcobalamin (57) and from alkyl-Co-DMG complexes (161), but not from pentacyanides with primary alkyl, vinyl, or benzyl ligands, though the cr-allyl complex yields propylene (109). Sodium sand gives mixtures of hydrocarbons with the alkyl-Co-salen complexes (64). Dithioerythritol will liberate methane from a variety of methyl complexes [cobalamin, DMG, DMG-BF2, G, DPG, CHD, salen, and (DO)(DOH)pn] (156), as will 1,4-butanedithiol from the DMG complex (157), and certain unspecified thiols will reduce DMG complexes with substituted alkyl ligands (e.g., C0-CH2COOH ->CH3C00H) (163, 164). Reaction with thiols can also lead to the formation of thioethers (see Section C,3). 

A combination of bromide ions and methyl octyl sulphide is able to oxidise secondary alcohols at the potential necessary to fonn bromine. Conversion of the alcohol to the ketone follows the Scheme 8.2 and uses an undivided cell with benzo-nitrile as the solvent containing 2,6-lutidine as base and tetraethylamnionium bromide. The reaction occurs using a platinum anode at 1.1 V vs-, see [28], Thio-anisole alone, in absence of bromide, will function as a catalyst for the oxidation of secondary alcohols but in these cases a more positive anode potential of 1.5 V vs. see is needed to oxidise the thioether [29]. 

Platinum(II) thiolates can be decomposed in strong acid because of protonation at sulfur (equation 509). This reaction is similar to electrophilic alkylation at the coordinated thiolate, although in this case the thioether complex may be isolable (equation 510). Thiolato ligands are unreactive to nucleophiles, and only under the most forcing conditions does ligand replacement occur. 

Bis(phoshacyclopentadienyl)titanium(II) complexes, preparation and reactivity, 4, 265 Bisphosphanes on DIOP modification, 10, 7 in hydrogenations, 10, 7 in hydrogenations, P-chiral ligands, 10, 11 Bisphosphinidenes, with platinum(II), 8, 453 -54 Bisphosphinites, in hydrogenations, 10, 14 Bis(phosphinoalkyl-thioether)arenes, in ruthenium isocyanides, 7, 138... 

Transplatin reacts 360 times faster than cisplatin with glutathione [27], a reaction likely to remove platinum from the cell, through ATP-dependent efflux [28]. It has been shown that a thioether ligand on a platinum triamine complex can be slowly replaced by a guanine-N(7), suggesting a possible platinum transporter role for such thioether compounds towards DNA [6], (This topic is discussed in the contribution by J. Reedijk and J. M. Teuben.)... 

From the studies reviewed above it has become evident that competion studies between thiols/thioethers and intact double-helical DNA are required, to find out whether or not the formation of the Pt-GG chelate is a driving force that can overcome the Pt-S interactions. Even then, one should realize that we are only dealing with a model, as in the cell other metals might also play a role in the disruption of Pt-S bonds. In this respect it should be mentioned that it was recently reported that addition of transition metals such as Zn11 or Cu11 can cleave even the Pt-S bond in thiolated terpyridine-platinum complexes at neutral pH [87],... 

A number of other groups can be used for the protection of thiols benzyl thioethers of amino acids and peptides have been cleaved electrochemically at a platinum cathode in liquid ammonia [121], at mercury in MeOH-TMACl [122], and in DMF [123,124], and the trityl group has been used to protect cysteine cysteine was recovered in 90% yield after reduction in DMF [124]. The 4-pyridylmethyl [125,126] and diphenyl-4-pyridylmethyl groups can be cleaved in acid solution [124] at a mercury cathode. 

These fluxional complexes have been fully characterized in solution by multinuclear NMR techniques. The data are consistent with a c -arrangement of the hydride and the silyl ligand. In the H NMR spectrum of 2a (in CDCI3 at 243 K) the hydride resonance is found at 6 = -2.66 ppm and consists of a doublet of doublets (Vp-h = 19.6, 152.7 Hz), which is flanked by platinum satellites ( pt-H = 972.3 Hz). A single crystal X-ray determination performed on 2a revealed that intramolecular short contacts between a thioether group and the platinum center are absent in the solid state. 

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