Platinum-palladium, isocyanides

Since the initial report on the addition reactions of palladium(II) and platinum(II) isocyanide complexes by Badley et al. (S), a rather substantial number of further examples have been reported. These are summarized in Table II. 

Chemical routes to palladium(I) and platinum(I) isocyanide complexes have been devised. Addition of CNMe to an aqueous solution of [MC14]2-(M = Pd, Pt) resulted in the rapid formation of [M(CNMe)4]2+ cations, which were isolated as the hexafluorophosphate salts. On standing, however, the cations [M(CNMe)4]2+ slowly converted over 18 hr to [M CNMe ]2 ... 

An extension to work on platinum(i) isocyanides discussed above has been undertaken, showing that it is possible to coordinate metals other than platinum. In the first instance, platinum and palladium compounds were added to the dinuclear Pt(i) compound 103 to give either the linear trinuclear complex 105 (when a -M(0) source was used), or a combined dimer-monomer complex 124 (when a -M(ii) source was added) (Scheme 28). An A-frame complex 125 results when the -source is added to 102. 

A few isocyanides of palladium and platinum are known in the zerovalent oxidation state. The best characterized compounds involve triangular M3 clusters with M-M bonds. 

Substantially more work has been done on reactions of square-planar nickel, palladium, and platinum alkyl and aryl complexes with isocyanides. A communication by Otsuka et al. (108) described the initial work in this area. These workers carried out oxidative addition reactions with Ni(CNBu )4 and with [Pd(CNBu )2] (. In a reaction of the latter compound with methyl iodide the complex, Pd(CNBu )2(CH3)I, stable as a solid but unstable in solution, was obtained. This complex when dissolved in toluene proceeds through an intermediate believed to be dimeric, which then reacts with an additional ligand L (CNBu or PPh3) to give PdL(CNBu )- C(CH3)=NBu I [Eq. (7)]. 

Coco, S., Cordovdla, C., Donnio, B., Espinet, P., Garda-Casas, M.J. and Gudlon, D. (2008) Self-Organization of Dendritic Supermolecules, Based on Isocyanide-Gold(I), -Copper(l), -Palladium(II), and -Platinum(ll) Complexes, into Micellar Cubic Mesophases. Chemistry - A European Journal, 14, 3544-3552. 

The hexakis(methyl isocyanide) dimers, [Pt2(CNMe)6], undergo photolytic cleavage of the Pt—Pt bond to give 15-electron radicals, Pt(CNMe)3.94 Mixtures of platinum and palladium dimers give rise to heteronuclear complexes under photolytic conditions. Mixtures of normal and deuterium-labeled methyl isocyanide complexes reveal that the metal-ligand bonds undergo thermal redistribution.94... 

To date, only nickel, palladium, and platinum have formed homoleptic metal(O) isocyanide clusters. This may be due to two factors, either the greater tendency to nucleation in the group or simply the ready access to the highly labile metal(O) precursors M(COD)2 [M = Ni (137), Pt (138)]. 

The complexes M3(CNR)6 [M = Pd, R = Bu (22,60), M = Pt, R = alkyl (23, 140)], containing a triangle of palladium and platinum atoms, were synthesized by treating [CpPdC3H5]2 or Pt(COD)2 with isocyanides. The multinuclear isocyanide cluster Pt7(CNXylyl),2 was formed from reactions of Pt(COD)2 and xylyl isocyanide in a 1 2 ratio or from reduction of PtCl2(CNXylyl)2 with sodium amalgam (20). 

For alcohol additions, mono- and dicarbene complexes have been synthesized, for palladium, platinum (487-489), and gold (475, 490- 493), from methanol, ethanol, or ethanethiol (494) additions to the isocyanide precursor. The stability of the gold(I) carbenes can be gauged from reactions with halogens which gave the oxidative addition product without loss of the carbene ligand (492). 

Although thiols on gold and silanes on silicon are the most prominent examples, they are not the only self-assembling systems. Various substrates beside gold and silicon oxide are capable of binding SAMt s such as silver, copper, palladium, platinum and metal oxides as zirconium oxides and indium tin oxide (ITO). As organic molecules alcohols ( OH), amines ( NH2), organic acids ( COOH), or isocyanides ( NCO) have been used. 

Iron-only hydrogenase, dithiolate-bridged compounds as biomimetic models, 6, 239 Iron oxide films, synthesis, 12, 51 Iron-palladium nanoparticles, preparation, 12, 74 Iron-platinum bimetallic clusters, with isocyanide clustes,... 

J. S. Miller, and A. L. Balch, Preparation and Reactions of Tetrakis(methyl isocyanide) Complexes of Divalent Nickel, Palladium, and Platinum, Inorg. Chem. 11, 2069-2074 (1972). 

A. Burke, A. L. Balch, and J. H.Enemark, Palladium and Platinum Complexes Resulting from the Addition of Hydrazine to Coordinated Isocyanide, J. Am. Chem. Soc. 92,2555-2557 (1970). 

Basato, M., Benetollo, F., Facchin, G., Michelin, R. A., Mozzon, M., Pugliese, S., Sgarbossa, P., Sbovata, S. M., Tassan, A The Staudinger reaction of platinum(ll)- and palladium(ll)-coordinated 2-(azidomethyl)phenyl isocyanide. X-ray structure of [cyclic] trans-[RCI CN(H)C6H4-... 

Isocyanide insertion reactions have been studied extensively for nickel, palladium, and platinum complexes. As early as 1968, cyclohexylisocyanide was reported to insert into the nickel-carbon bond of Ni(fj -C5Hs)R(PPh3), giving the following cyclo-hexylimino derivatives ... 

Polymerization of isocyanides is a thermodynamically feasible process, in agreement with the stoichiometric multiple insertion observed in reactions between metal-alkyl complexes and isocyanides. The entropy loss in the case of isocyanides is lower than for insertion of CO. Isocyanide insertions into palladium-alkyl a bonds are faster than those for the platinum(II) analogues. The latter, on the other hand, usually lead to more stable and better defined products. Insertion of isocyanides into platinum-carbon bonds has been studied extensively Reaction (j) is typical the ionic product was strongly suggested by observation that the compounds isolated under mild conditions are 1 1 electrolytes. 

Scheme 8. Polymerization of Isocyanides by a Dinuclear Palladium—Platinum //-Ethynediyl Complex...

In the last few years the design and use of various disilane compounds has gained importance because of the reactivity of the Si-Si bond and the large potential for organic synthesis involved with it. Many publications offer us numerous examples of possible reactions at the silicon-silicon bond such as addition reactions with C-C double bonds or C-C triple bonds [1, 2], addition reactions with C-element multiple bonds (e.g. aldehydes, quinones, isocyanides) [3-5] or metathesis [6, 7] and cross-metathesis [8]. In the most cases the existence of a catalyst (palladium, platinum or nickel complexes) for activation of the silicon-silicon a bond is indispensable for a successful transformation [9-11]. 

The additions of bimetallic reagents such as the silicon-metal and tin-metal compounds to the carbon-carbon multiple bonds have been extensively studied however, there are few reports concerning the metal-boron compounds as shown above. Miyaura and co-workers have examined the addition reaction of tetraafkoxydiboron to alkynes and found that only the platinum complexes such as Pt(PPh3)4 exhibited excellent catalytic activity (Scheme 24). Pd(PPh3)4 and Pd(OAc)2-isocyanide complexes, which have been the best catalysts for the silyl- and stannyhnetallation, were ineffective because their oxidative addition to palladium(0)-phosphine complexes is very slow. ... 

Facchin, M. Mozzon, and L. Zanotto, Inorg. Chim. Acta, 1992,198-200, 883-897. Synthesis of Heterocyclic Systems by Activation of Isocyanide, Carbonyl, Trifuluo-rmethyl, and Nitrile Ligands in Platinum(II) and Palladium(II) Complexes. 

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