Platinum macrocycles

Bett JS, Kunz HR, Aldykiewicz AJ Jr, Eenton JM, Bailey WS, Me Grath DV. 1998. Platinum-macrocycle co-catalysts for the electrochemical oxidation of methanol. Electrochim Acta 43 3645-3655. 

Figure 4.30. Effect of Pt-FeTSPcad anode catalyst in a direct formic acid fuel cell 333 K, atmospheric pressure, 6 M HCOOH. Anode Pt loading 0.5 mg cm, fuel flow rate 1.0 ml min Cathode Pt loading 1.5 mg cm, 100 cm min of dry O2 at STP [164]. (Reproduced from Electrochemistry Communications, 9(7), Zhou X, Xing W, Liu C, Lu T, Platinum-macrocycle co-catalyst for electrooxidation of fonnic acid, 469-73, 2007, with permission from Elsevier.)...

Zhou X, Xing W, Liu C, Lu T. Platinum-macrocycle co-catalyst for electro-oxidation of formic acid. ElectrochemComm 2007 9 1469-73. 

Mukheijee S, Zyla R, Atanassov P. Non-platinum macrocycle electrocatalysts based on pyrolzed transition metal macrocycles. AIChE - Aim Meet Arch 2002 2436—43. 

Bauerle et al. have recently published a noncatalytic procedure allowing the isolation of a bis-platinum macrocycle which was transferred to a conjugated system with two 1,3-butadiyne units by a reductive elimination process [34]. This technique was used to prepare cyclotetracosa-l,3-ll,13-tetrayne (15) (Scheme 7.4) [35]. The reaction of dichloro-l,3-bis(diphenylphosphinopropane)platinum(ii) (12) with 1,11-dodecadiyne yielded 13(11). This species was reacted again with 12 to afford the cyclic system 14(11) which was oxidized with iodine to obtain cyclotetrayne 15. 

With their preference for square planar coordination, palladium(II) and platinum(II) are well suited to binding to porphyrins and related N4 donor macrocycles. Therefore, Pd(octaethylporphyrin) is readily synthesized starting from the labile PhCN complex (like the platinum analogue) [92]... 

Mononuclear complexes of palladium and platinum in the +3 oxidation state have only recently been unequivocally characterized [157]. The major advance has come in complexes with macrocyclic ligands such as 1,4,7-trithiacyclononane (ttcn) and 1,4,7-triazacyclononane (tacn) (Figure 3.96). 

Figure 3.96 Macrocyclic ligands used to stabilize palladium(III) and platinum(III).

Reaction of iodine with Pt(phen)Cl2 gives compounds with the unusual stoichiometries Pt(phen)I (a = 5,6) these contain Pt(phen)I4 molecules and free iodine molecules in the lattice. Pt(bipy)I4 has also been made [172], Macrocyclic complexes of platinum(IV) are readily made by oxidation ... 

The first structurally characterized example of a platinum(II) derivative containing a saturated tetraamine macrocycle, 6,13-dimethyl-l,4,8,ll-tetraazacyclotetradecane-6,13-diamine has been reported (80).251 The species crystallizes as the colorless tetra-cationic complex from dilute HC104 solution by slow evaporation, where the two pendant primary amines are protonated. Other macrocyclic tetraamine complexes including [Pt([14]aneN4)]Cl2 have also been described.252... 

The synthesis, X-ray structure, NMR, and UV-visible spectroscopy, and electrochemistry of a macrocyclic platinum(II) complex containing the tetradentate 1,4,7,10-tetrathiacyclodecane ligand, [12]aneS4 (144) have been reported.350 Related complexes including [Pt([13]aneS4)]2+ and [Pt([16]aneS4)]2+ have also been prepared, and molecular mechanics calculations complemented... 

As it follows from Table 5, many catalysts contain metallic platinum. We have developed bi-layer porous hydrophobic air electrodes, which do not contain platinum metals, are active and can be cycled [24, 25] (Figures 4-6). These bifunctional catalysts are pyrolized Co - macrocyclic compounds. Said catalyst has high catalytic activity for the oxygen reduction and also features acceptable stability, however its activity for the oxygen evolution is not high enough. 

The present volume is the fourth in the series and covers the topics lithium in biology, the structure and function of ceruloplasmin, rhenium complexes in nuclear medicine, the anti-HIV activity of macrocyclic polyamines and their metal complexes, platinum anticancer dmgs, and functional model complexes for dinuclear phosphoesterase enzymes. The production of this volume has been overshadowed by a very sad event—the passing away of the senior editor, Professor Robert W. Hay. It was he who conceived the idea of producing this series and who more than anyone else has been responsible for its continuation. A tribute by one of his many friends, Dr. David Richens, is included in this Volume. 

Although platinum is the metal of choice for PEM fuel cell cathodes, Paul Matter, Elizabeth Biddinger, and Umit Ozkan (Ohio State University) show that nonprecious metals will have to be developed for this type of fuel cell to become practical and widely used. Although few materials have the electrochemical properties needed to replace platinum, this review discusses candidates such as macrocycle compounds, non-marcrocyclic pyrolyzed carbons, conducting polymers, chalcogen-ides, and heteropolyacids. 

Despite the uncertainty regarding the exact nature of the active site for oxygen reduction, researchers have managed to produce catalysts based on heat-treated macrocycles with comparable activities to state-of-the-art platinum catalysts. In numerous cases researchers have shown activity close to or better than platinum catalysts.64,71,73,103,109 Since the active site for the ORR in these materials is not fully understood, there is still potential for breakthrough in their development. Another advantage of this class of materials that should be mentioned is their inactivity for methanol oxidation, which makes them better suited than platinum for use in direct methanol fuel cell cathodes where methanol crossover to the cathode can occur.68,102,104,122-124 While the long-term activity of heat treated materials is... 

Scheme 9.1. Oxidation of aldehydes at a platinum anode catalysed by macrocycle 5 in methanol.

These electrodes modified with metal complexes could have been substitutes for expensive platinum if they had been usable under conditions compatible with requirements for efficient fuel cells. However, they are not stable, particularly in contact with acidic media, which results from demetallation. This is known since the early works with N4 macrocycles and heat treatment has been proposed to enhance the durability of the carbon... 

Although there has heen a great deal of research concerning how platinum(II) complexes hind to biological molecules and the hkely mechanism of antitumor activity of these platinum-containing species, far less attention has heen paid to the properties of other metal complexes in this arena. Recent attention has fallen on cohalt(II)-Schiff hase complexes, as several have heen discovered to have promise as antiviral agents. A review of recent work has appeared elsewhere [64], so the topic will not he covered here however, in addition to focusing on recent developments, emphasis is placed on the introduction of the new head unit, 3,6-diformylpyridazine (13), into Schiff-hase macrocyclic electrochemistry. 

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