Platinum Metals Review

UK ISSN 0032-1400

PLATINUM METALS REVIEW A Quarterly Survey of Research on the Platinum Metals and of Developments in their Application in Industry www.matthey.com and www.platinurn.matthey.com

VOL. 46 APRIL 2002 NO. 2 Contents

Palladium/Nucleophilic Carbene Catalysts for Cross-Couplmg Reactions 50 By Anna C. Hillier and Steven P. Nolan Automotive Fuel Cells: A U.K.Perspective 64 By D. M. Jollie

Fuel Cells: Science and Technology 2002 64

Catalysis for Low Temperature Fuel Cells 64

Catalysts & Catalysed Reactions 65 A review by Andrew P. E. York

Jewellery-Related Propefties of Platinum 66 By John C. Wright

Laser Drilling of Platinum Cavities 72

Heterogeneous Catalytic Hydrogenation 73 A review by M. Hayes

Two-Phase Iridium-Based Refractory Superalloys 74 By Y. Yamabe-Mitarai, Y. F. Gu and H. Harada

The Chemistry of the Platinum Group Metals: PGM8 81

2001 Nobel Prize in Chemistry 82 By Thomas J. Colacot

Abstracts 84

New Patents 89

Final Analysis: 5% Pd/C - Precise but Vague 92 By D. E. Grove

Communications should be addressed to: The Editor, Susan V. Ashton, Platinum Metals Review, [email protected] Johnson Matthey Public Limited Company, Hatton Garden, London EClN 8EE Palladium/Nucleophlic Carbene Catalysts for Cross-Coupling Reactions

By Anna C. Hillier and Steven P. Nolan' Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148, USA., 'E-mail: [email protected]

Palladium complexes bearing N-heterocyclic nucleophilic carbenes can,function as eificient and convenient mediators of C-C and C-N cross-coupling reactions. These phosphine-free systems are highly effective in coupling reactions of aryl bromides and aryl chlorides with a variety of coupling partners. Some applications of these palladium complexes in a range of coupling reactions are described here and catalysts, conditions and results are presented.

Palladium and nickel based catalysts have pro- number of processes mediated by palladium-bulky vided a plethora of new methodologies for phosphine systems (8, 9). Their success is synthetic organic chemistry. Palladium-catalysed explained by reference to the catalytic cyde depict- cross-coupling of aryl halides (or halide analogues) ed in Figure 2. The increased electron-richness with nudeophiles is firmly established as one of imparted to the metal centre by the electron-donat- the most important methods available for C-C and ing phosphine assists in the cleavage of an Ar-X C-N bond formation (14). These cross-coupling bond in the first, oxidative addition, step, while the reactions employ a range of transmetallating steric bulk of the hgand promotes the reductive agents, examples of which are shown in Figure 1. elimination of the Ar-Ar' coupling product fol- Palladium and nickel complexes containing lowing transmetallation with M-Ar'. While Heck phosphine hgands are among the most successful and amination (and CuI-free Sonogashira) reac- and widely used catalyst precursors for couphg of tions do not, strictly speaking, involve a sp2 carbons, and bulky electron-rich tertiary alkyl transmetallation step, they are generally included phosphines are particularly effective (5-7). in discussions of cross-couplug chemistry since Significant advances have been made in using their catalytic cycles possess essentially the same aryl chlorides as cross-couplug partners, with a features. Recently, alternatives to phosphines have been sought owing to certain of their 'user-unfriendly' properties, namely air- and moisture-sensitivity and thermal instability, which means that excess hgand is often required to stabilise low-valent Reaction Reagent, [MI-Ar' metal centres during the catalytic cycle. Highly promising and versatile alternatives to Suzuki-Miyaura phosphines have been found in the N-heterocyclic Kumada Ar'-MgX nudeophilic carbene (NHC) class of hgand (10) Negishi Ar'-ZnX (see Figure 3), often referred to as Arduengo car- Stille Ar'-SnR"3 I benes, following their isolation by Arduengo in Hiyama Ar'-Si(OR")s I I 1991 (11). These carbenes are neutral two electron Heck o-donors (12), generally bearing bulky and/or Sonogashira electron-donating N-substituents. Arduengo car- Hartwig-Buchwald Amination HN R "R"' benes exhibit greater thermal stability than Fig. I Coupling partners for cross-coupling with aryl phosphines and can bind more strongly to a metal halides centre (lOa), eliminating the need for excess ligand

Pbhnnm Metah b.,2002,46, (Z), 5064 50 commercial scale the Suzuki-Miyaura reaction is usually preferred to other C-C bond-forming processes since organoboronic acids are conve- niently synthesised reagents (18), and are generally thermally stable and inert to water and oxygen. NHC llgands have been employed with great success in this process (19). Our initial research in this area focused on the use of catalytic quantities of zerovalent PdZ(dba), as the precursor in conjunction with the carbene LMes and CsZCO3 as base (19e). This combination afforded a yield of 59% in the coupling of Cchlorotoluene with phenylboronic acid. The catalytic protocol could be simplified and improved by the use of air-stable IMes.HCl as hg- and precursor and deprotonating in sib with Fig. 2 Catalytic cycle for palladium complex-mediated Cs2C03. Other combinations of NHC and base cross-coupling reactions; where Ar'-M is organoboroni( acid, organostannane, organomagnesium, organosilicon, were less effective in this reaction. amine, etc. Subsequently a simpler catalytic system was achieved by using air-stable Pd(II) precursors, during catalytic processes. They have proven to be eliminating the need for a drybox to load the cat- extremely effective ancillary lpnds in a broad alytic components (20). The catalytic system was range of metal complex-catalysed processes (13), activated by heating at 80°C for 30 minutes under with reactivity often surpassing that observed with an argon atmosphere, during which time the base phosphine Itgation (another notable example being reacts with the PdQl) salt and IMes-HCIto gener- in ruthenium-catalysed olefin metathesis (14)). ate the NHC and the active Pd(0) catalyst, prior Some of our recent work, in the area of cross-cou- to ad- substtate. The catalytic activity of the pling chemistry employing palladium complexes with N-heterocyclic nudeophilic carbenes as catalyst precursors, is reviewed here. R, ;; /R NN \=/ Cross-Coupling via Transmetallation Suzuki-Miyaura Cross-Coupling of Aryl R L Halides or Pseudo-Halides with 2,4,6-trirnethylphenyI lMes Arylboronic Acids (15) 2,6-di-iso-propylphenyl IPr 4-rnethylphenyl ITol The couphng reaction of aryl and heteroaryl- 2,6-dimethylphenyl IXY boronic acids with aryl and heterocyclic halides or cyclohexyl ICY dates is a powerful method for preparing vari- adamantyl IAd ous biaryl systems and is .widely used in synthesising natural products (16). The importance of the palladium-catalysed Sd-Miyaura cross-coupling reaction cannot be overstated in view of its general use in a variety of C-C bond R L 2,4,6-trimethylp henyl SlMes formations and is underscored by the volume large 2,6-di-iso-propylphenyl SlPr of research published in the last year, includmg cyclohexyl SlCy extension to aqueous and supercritical COZ media and polymer-supported catalysts (17). Indeed, on a Fig. 3 N-Heterocyclic nucleophilic carbenes (NHCs)

51 R

Pd sourccl 2L-HCI

C s2COj(2 equiv.) dioxane, 80.C CI R' / R'

Table I Functional Group Tolerance of Suzuki-Miyaura Cross-Coupling Using PdAmidazoliurn Salt Catalystsa

Pd source R R' Time, h Yield, Yob

IMes-HCI IPr-HCI Pdz(dbaI3 4-CH3 H 1.5 90 95 Pdz(dbah 4-CH3 4-OCH3 1.5 99 99 Pdddbah 4-CH3 2-CH3 1.5 88 97 Pdz(dbah 4-CH3 3-OCH3 1.5 91 95 Pd4dbah 4-OcH3 H 1.5 93 99 Pdz(dbaI3 2,5-(CH3)2 H 1.5 95 95 Pdz(dhalo H 4-OCH3 1.5 99 7ge Pdz(dbaI3 4-C(O)OCH3 H 1.5 99 98 PdddbaI3 4-C( 0)CHJ H 1.5 ale 99' Pdz(dbah 4-CN H 1.5 80e 100' Pd(0AC)Z 4-CH3 H 2 99 - Pd( 0Ac)z 4-CH3 4-OCH3 2 80 - Pd(0AC)z 4-CH3 2-CH3 2 50 - Pd(0AC)Z 4-CH3 3- OCH, 19 93 - Pd(0Ac)z 4-C(O)OCH3 H 2 99 - Pd(0AC)z H - 4-CH3 8 85 Pd(0AC)z 3-N(CH3)7 H 2 989 - Pd( 0Ac)z 2,5-(CH& H 2 94 - Pd(0Ac)z 2,5-(CH3)7 H 2 9ah - Pd(0AC)z 2,5-(CH3)z H 2 6gg -

'Reaclion conditions: 1.0 mmol awl chloride, 1.5 mmol uiylhoronic acid, 2.0 ntmol Cs2CO1, 2 L/Pd. 80°C; lsolated yields; Pdz(dbu).q/lMe.s.HCl = (1.5 mo1%)/(3.0 mol%), Pd(OAc)?/IMes.HCI = (2.5 mo1%)/(2.5 mol%J: Pdz(dba)j/lPr.HCl = (1.0 mol%)/(2.0 mol%J: ' 16 hours; '3 hours: 5 mol% of IMes-HCI: Pd(OAc)?/lMe.sHCl = (5.0 mo1%)/(5.0 mol%J system was also investigated as a function of the ing substituents, with slightly lower yields imidazolium salt (NHC precursor). NHC N- observed for sterically-hindered ortho-substituted substituents comprising bulky orthesubstituted reagents, see Table I. This protocol could also be aryl groups (IMeseHCl, IPr-HCl, JXyHCl) dis- applied to the cross-coupling of aryl aiflates with played the highest activities, indicating that steric phenylboronic acids, as shown in Table II. factors dictate the catalytic system effectiveness. Both Pd(0) (Pd2(dba)3/IMes.HC1; Pdz(dba),/ Kumada-Tamao-Corriu Cross-Coupling of Pr-HCl) and PdQI) (Pd(OAc)z/Mes.HCl) sys- Aryl Chlorides with Aryl Grignard Reagents tems were found to be exceptionally tolerant to Arylboronic acids and other organometallic functional groups on the aryl chloride and boron- reagents employed in (3-c coup& reactions are ic acid. Excellent yields were obtained with some often prepared from the corresponding Grignard diverse electron-donatmg and electron-withdraw- or organolithium reagents (15a). Three years after

Phinwm Metab Reu., 2002,46, (2) 52 R

R Pd surce (2.5rnol -1.) IPr.HCI (2.5 rnol */a)

CszCO3 (2equiv.l dioxane, 80-C, 5h OTf R’ / -8R’

Table II Functional Group Tolerance of Pd SourceAPr-HCI-Catalysed Suzuki Cross-Coupling of Aryl Triflates with Phenylboronic Acid Derivativesa

Pd source R R’ Yield, Yob

Pd(0AC)z 4-OCH3 H 86 Pd(0AC)z 4-OCH3 4-OCH3 81 Pdddba)3 4-OCH3 H 97 Pdz(dbaI3 4-OCH3 4-CH3 98 Pd(0Ac)z H 4-OCH3 85 Pdddbah H 4-CH3 99 Pd(0Ac)z 4-c 0 CH3 H 76 Pd(0AC)z 4-c 0 CH3 4-OCH3 77 Pdz(dbaI3 4-c 0 CH3 4-CH3 97

Reaction conditions: 1.0 mmol of aryl trifklte, 1.5 mmol of arylboronic acid, 2.0 mmol of Csl COA2.5 mol% Pd source, 2.5 mol% IPr.HC1, 80°C; Isolatedyields the first reports, in 1972, of the Nio-catalysed (which is particularly inactive) afforded quantita- reaction of Grignards with akenyl or aryl halides tive conversion in three hours. Although (21, 22), the Pd-catalysed reaction was described oho-substituents on the aryl Grignard reagents (23). Several reports have appeared since, dew were tolerated well, ortho-substituted aryl chlorides phosphine-modified Pd- or Ni-mediated couphg required a larger excess of Grignard (1.8 equiva- of Grignards with aryl halides (5% 5b, 5n-5v). We lents) to achieve good yields. Steric congestion recently reported the first example of successful around both reactive centres (as encountered in couplmg involving unactivated aryl chlorides and the reactions of 2-chloro-mxylene or 2-bromo- an aryl Gngnard reagent (24). mesitylene with mesityl magnesium bromide) The reaction between 4-chlorotoluene and resulted in no conversion. phenylmagnesium bromide was selected for the initial screening of the Pd source and hgand. The Stille Cross-Coupling of Aryl Halides system Pd2(dba)3/IF’r-HC1in a l,Cdioxane/THF with Hypervalent Organostannanes solvent mixture at 80°C was found to be most The use of readily available, ait- and moisture- effective (quantitative convesion in 3 h), although stable organotin reagents, SnR”,R, as cross- replacing 1 mol% Pdz(dba)3 with 2 mol% coupling partners represents one of the most ver- Pd(0Ac)z afforded similar conversions. No addi- satile of couplug methods in organic chemistry. tional base was necessary as a small excess of One important advantage of tin reagents is their PhMgBr was utilised. The catalytic system was compatibility with a large variety of functional tested with a range of substituted aryl halide sub- groups. However, there are sgdicant disadvan- strates and Gngnard reagents Fable III)and tages to their use, most notably the difficulty of found to be extremely tolerant of electronic varia- removing tin from the product and there are con- tion in the substituents; even Cchloroanisole cerns regarding the toxicity of tin. A further

Phtinm Metah Rev., 2002, 46, (2) 53 Table 111 Palladium/lmidazolium Salt-Catalysed Cross-Coupling of Aryl Halides with Aryl Grignard Reagentsa

X R R' Time, h I Yield, Yob CI 3 99 CI 3 9gC Br 1 99 CI 3 97 CI 3 85 CI 5 87d Br 5 69 I 3 96e CI 5 95e CI 3 99 CI 3 83 CI 3 99 CI 3 95 CI 24 0 Br 24 0

rhe wactions were carried out according to the conditions indicated hv the ohove eyuution. 1.2 equivulenrs qfPhMgBr (1.0 Msolution in THF) used unless otherwise stated; Isolated vields (average of hvo runs) afierjlush chromatography: 2.0 mol% of Pd(OAc)> used instead of 1.0 mol% ofPd?(dba),; a 1.8 eyuivulents ofphen>hnugnesiumbromide weir used: 2.5 equivalents of phenylmagnesium bmmide were used limitation is their hgh stability which results in a TBAF appears to play a dual role in the cadytic slow transmetallation step in the catalytic cycle. To system, acting both as the base/nudeophile to avoid these limitations we investigated the use of deprotonate the NHC precursor imidazolium salt hypervalent stannate species. Fluorophilic organo- and as the fluorinating agent, accelerating the stannanes (25) react with fluoride anion to give transmetallation step via formation of the more hypervalent five-coordinate intermediates which reactive hypervalent organostannate. An addition- are more labile than the parent organostannanes al advantage of using TBAF is that it serves as a and thus expected to transmetallate more effec- fluorous medium for tin extraction, aidq the tively (26). removal of tin by simple water extraction. Both We identified a hypervalent fluorostannate the Pd(II)/IPr.HCl and Pd(II)/IAd-HCl systems anion by I9F NMR spectroscopy after treating were effective in the cross-coupling of electron- SnMe3Ph with 2 equivalents of tetrabutylammoni- neutral and electron-deficient aryl bromides with um fluoride 0.In the presence of catalytic SnMe3Ph or Sn(Bu")sPh (see Table IV). Electron- amounts of Pd(0Ac)z and IPr.HC1 this intermecl- rich 4-bromoanisole proved less facile and only ate coupled with Cchlorotoluene to afford the coupled rapidly with the more reactive SnMe3Ph desired biaryl cross-coupling product (27). Other employing IPr-HCl as ligand precursor. Odwsub- bases that were screened for activity (CsF, KOBu', stituted aryl bromides required longer reaction CszC03, NaOH) were essentially ineffective. The times with SnMe3Ph. Unactivated aryl chlorides

PMmm Metah Rm, 2002,46, (2) 54 L.HCI (3.0mol %)

TBAF (2 equiv.) R dioxane/THF

Table IV Pd(OAc)2/L.HCI-Catalysed Stille Couplinga

~ X R Tin reagent Time, h Yield, Yob

Br 4-CH3 SnMe3Ph IPr-HCI 1.5 90 Br 4-CH3 Sn(BU")3Ph IAd-HCI 3 91 Br 4-C( O)CHs SnMesPh IPr-HCI 0.5 92 Br 4-C(O)CH3 SnMe3Ph IAd*HCI 1 86 Br 2,4,6-(CH3)3 SnMe3Ph IPr-HCI 48 86 Br 4-OCH3 SnMe3Ph IPr-HCI 2 92 Br 2-CN SnMe3Ph IPr-HCI 48 80 CI 4-CH3 SnMe3Ph IPr-HCI 24 54 CI 4-CH3 Sn( Bu"),Ph IAd*HCI 12 45 CI 4-C( O)CHs SnMe3Ph IPr-HCI 1 91 GI 4-OCH3 SnMe3Ph IPr-HCI 48 35

Reaction conditions: 1.0 mmol ofaryl halide. 1.1 mmol of arylstannane. 2 mmol TBAE 3.0 mol% Pd(0Ac)a 3.0 mol% L.HC1. I ml dioxane, 80°C for awl bromides (100% for aryl chlorides); Isolated yie1d.v were unsuitable couplmg partners for this catalytic couphg of aryl bromides with vinylstannanes in system, although good yields were obtained with 4- good to moderate yields, (Table V) although for chloroacetophenone. the aryl chlorides, moderate conversion was The same catalytic method also effected the observed only with the electron-deficient

Table V Pd(OAc)2/1Pr.HCI-Catalysed Cross-Coupling of Aryl Halides with Vinylstannanea

X R Time, h Yield, Yob

Br 4-C(O)CH3 3 92 Br 4-OCH3 48 69 Br 2,4,6-(CH3)3 48 25 Br 4-CH3 48 98 CI 4-C(O)CH3 3 83 CI 4-OCH3 24 15 CI 4-CH3 12 41

Reaction conditions: 1.0 mmol aryl halide, 1.1 mmol vinylslannane, 2 mmol TBAE 3.0 mol% Pd(0Ac)a 3.0 mol% IPraHCI, I mi dioxane, 80°C for aryl bromides (100% for aryl chlorides): GCyields

PIpltiwwm Meitah h.,2002,46, (2) 55 Cchloroacetophenone. The results suggest that couplug of aryl chlorides is facilitated by electron- withdrawing substituents, consistent with a rate determining oxidative addition step.

I Organosilanes as Coupling Partners Fig. 4 Chelating carbene-phosphine (imidazolium salt Silicon-derived compounds are viable altema- depicted) tives to other transmetdating agents owing to their low cost, easy availability, low-toxicity affordmg moderate yields with longer reaction byproducts and stability to different reaction con- times. A further analogy with the tin chemistry is ditions (28). However, for electron-rich or -neutral suggested by a preliminary study which indicated aryl chlorides hgh yields are only obtained with that substituted styrenes are obtained in quantita- high catalyst and phosphine loadmgs. tive yield (after prolonged reaction times) &om the The reaction of one equivalent of aryl halide reaction of aryl halides with vinyltrimethoxysilane. with two of phenyltrimethoxysilane in the presence of 3 mol% each of Pd(OAc)z and IPr-HC1 Cross-Coupling with ALkenes: Heck Reaction and two equivalents (per Pd) TBm in 1,4-dioxane The Heck reaction involves initial oxidative at 80°C afforded both the desired couplug prod- addition of an aryl halide to generate ArPdX, fol- ucts and the homocouplug product (29,30). As in lowed by insertion of an alkene into the Pd-Ar Stille coupling, rapid, quantitative conversion was bond and subsequent liberation of the new akene achieved with aryl bromides and electron-deficient by P-hydrogen elimination (as with concomi- aryl chlorides (4chloroacetophenone, Cchloro- tant regeneration of the Pd(0) catalyst. Thus a base benzonitrile) but poor activity was observed with is required to promote the removal of HX and unactivated chlorides (4chlorotoluene, Cchloro- provide additional driving force for the reaction. anisole) despite prolonged reaction times. This Heck coupling of an aryl moiety to an alkene is protocol was also applicable to heteroaryl halides, widely employed in organic synthesis in the prepa-

Table VI Pd/Chelating Carbene-Phosphine-Catalysed Heck Reaction of Aryl Halides with n-Butyl Acrylatea

X R Time, h Yield, Yob

Br 4-C( 0)H 0.25 100 Br H 1 100 Br 4-CH3 1.5 100 Br 2-CH3 1 35 Br 3,5-CH3 1 99 Br 4-OCH3 3 99 Br 3-OCH3 2 99 GI H 2 13

a Reaction conditions: I mmol aryl halide: 1.4 mmol n-hutyl acrylate: GCvield (diethyleneglycol di-n-butyl ether as GC standard; average of two runs)

56 Pd(OAc)l (2molV.) I Mes. HCI (4 rnol%) flOBu" R COOB~" cs2co3(2 equiv.) R DMAc, 120.C

Table VII Pd(OAc)2/1Mes.HCI-Catalysed Heck Coupling of Aryl Bromides with n-Butyl Acrylatea

Yield, Yob

100 100 97 94 99 16 97 94 65 91 99 88 66 99

'Reaction condilions:1.0 mmol aryl bromide, 1.6 mmol n-buy1 aciylate, 2 ml ojDMAc; ' GC yield (diethyleneglycol di-n-buy1 ether as GC standard); an average oj'lwo runs; with addition of [Bun4NjBr(20 mol%); 2 mol% Pd(dba)> as Pd source; ' 4 mol% ICyHCl as ligand; 4 mol% SlPi-HCI as ligund ration of substituted olehns, dienes and precursors Optimal conditions were found using Pd(dba)z to conjugated polymers (50,31). While monoden- with one equivalent of L-HBr, & = the &and in tate phosphines have provided efficient catalyst Figure 4), two equivalents of CSZCO,, and the modifiers, in reactions with less reactive aryl bro- polar solvent Nfl-dimethylacetamide (DMAc) at mides and chlorides bulky electron-donating 120°C. Excellent yields were obtained with a range phosphines, such as PBu'3, are necessary (50). At of activated and unactivated aryl bromides (Table the elevated temperatures required for Heck chem- vI>. The protocol was, however, intolerant of ster- istty, both phosphines and their Pd complexes are icdy hindered orlho-substituted substrates and prone to decomposition, so %her catalyst load- ineffective for unactivated aryl chlorides, with pro- ings are needed. Increased stability can be imparted longed reaction times resulting in side reactions in by using chelating phosphines but only limited suc- both cases. cess has then been achieved in catalysis. These results were compared with those However, a hlgh degree of efficiency has been obtained employing non-chelating NHC hgands observed in Heck reactions mediated by palladium (35). Both Pd(0) and Pd(II) precursors were effec- carbene complexes (32). Following a recent theo- tive with IMes-HC1 and the system using 2 mol% retical study which suggested that mixed Pd(OAc)J4 mo1Yo IMes.HC1 was selected for carbene-phosphine chelates were suitable for the study owing to its greater ease of execution. When Pd-catalysed Heck reaction (33), we prepared the the same protocol was used as that for the chelat- carbene-phosphine chelating ligand shown in ing NHC-phosphine system, htgh yields of franr Figure 4 and investigated its eficacy in the cross- coupling products were obtained with a range of couphg of aryl bromides with n-butyl acrylate (34). aryl bromides (Table VIl). With 4bromoanisole,

Pbtinwm Metah h.,2002,46, (2) 57 Pd(OAc), (3 mol %I I Mes.HCI (6 mol%) Cul (2 mo1v.I.) (&X (&X + R CS.~CO) (2 equiv.) DMAC, 8O.C

Table Vlll Pd(OAc)2/1Mes.HCI-Catalysed Sonogashira Reaction of Aryl Halides with 1-Phenyl-2-(trimethylsily1)-acetylenea

X R Time, h Yield, Yob

Br 4-C(O)H 0.25 100 (92)' Br H 0.5 100 (91)' Br 4-CH3 0.5 96 (86)' Br 4-CH3 0.5 99 Br 2-CH3 0.5 100 (93) ' Br 4-OCH3 0.5 azc Br 4-OCH3 3 946 Br 4-OCH3 0.5 96 (88) Br 4-OCH3 1 43 '. Br 2-OCH3 0.5 100 (93) Br 2-OCH3 0.5 95' Br 2,4,6-(CH3)2 1 90 (82) CI H 1 51

O Reaction conditions: 1.0 mmol aryl halide, 1.4 mmol I-phenyl-2-(trimeth~lsilvl)-acehiene.2 ml of DMAc; GCyields based on aryl halide; Number in parenthesis is isolatedyield (average of two runs); Without Cul: Reaction temperature 60°C; ' 3 mol% Pd(dba)? as Pd source; 6 mol% IPr-HCI us ligund

4bromotoluene and 2-bromotoluene, the conver- Reductive elimination affords the arylalkyne cou- sion was improved when 20 mol?h Pun4N]Brwas pling product and regenerates the Pd(0) catalyst added to the reaction. Aryl chlorides proved and CuI. unsuitable for this system. A recent report described the unusually high activity of a palladium system modified by PBu'3 in Cross-Coupling with Terminal Alkynes: the Sonogashira coupling of aryl bromides (39). Sonogashira Reaction To our knowledge only a handful of Pd/NHC- Palladium complexes are active for the cou- mediated Sonogashira reactions have been phg of terminal alkynes with aryl or alkenyl reported, and these deal only with activated aryl halides to give arylalkynes or conjugated enynes. bromides (40, 41). After different ligands and These are important in assemblulg bioactive nat- bases were screened, a similar set of conditions to ural molecules and for new materials (36,37). The that used for Heck coupling was adopted, namely Sonogashira reaction of terminal alkynes with aryl the combination: Pd(OAc)2/IMes-HC1/Cs2CO3 in or alkenyl halides provides a straightforward and DMAc at 80°C. Nitrogen bases are commonly powerful method for their synthesis (37, 38). The used in the Sonogashira reaction but in this case Pd(0)-catalysed Sonogashira couplulg is most effi- produced inactive systems. Undesired dimerisa- cient when CuI is added as cocatalyst. CuI tion products were obtained when phenylacetylene activates the alkyne by forming copper acetylide, was employed as the alkyne source. This side reac- which transmetallates with an arylpalladium halide tion was suppressed by using l-phenyl-2- to form the alkynyl-arylpalladium species. (trimethylsily1)-acetylene as coupltng partner with

PIdnun Metals Rcv., 2002,46, (2) 58 Table IX Pd2(dba)3/1Pr-HCI-CatalysedAmination of Aryl Chloridesa

R I Amine, HNR'R" Yield, %b Kmethylaniline 99 piperidine 96 piperidine, 4-(tetrahydro-2H-pyran-Cyl) 86 morpholine 82 HN(Bu")~ 95 HzN(6i1') 86 aniline 96 mesitylaniline 59 2,6-(Pr')z-aniline 85 Kmethylaniline 91 aniline 91 morpholine 80 HN(Bu")z 98 Kmethylaniline 94

Reaction conditions: 1.0 mmol of aiyl chloride, 1.2 mmol of amine. 1.5 mmol of KOBu ', 1.0 mol% Pd2(dba)j. 4.0 mol% lPr.HCl(2 L/Pd). 3 ml ofdioxane, 100°C. Reactions were complete in 3-24 hours and reaction times were not minimised; Isolated yields aryl bromides (35). Under optimised conditions has proved very effective for amination of aryl excellent product yields were obtained; however, it chlorides (44). After the success of the Pd/NHC is noteworthy that these hgh yields were achieved system in mediating C-C bond formation we under Cd-free conditions. Ad- Cul increased turned out attention to C-N coupling processes. reaction rates, most notably with deactivated or The use of the bulky NHC precursor IPr-HC1with sterically encumbered aryl bromides. The catalytic KOBu' as base and 1,Cdioxane as solvent permit- system was even effective for chlorobenzene, ted the catalytic C-N couplulg of aryl iodides and although the yield was moderate. bromides at room temperature and the catalytic couplulg of aryl chlorides at elevated temperature. C-N Bond-Forming Reactions I-Qh conversions were achieved with primary and Hartwig-Buchwald Amination secondary, cyclic and acyclic amines with various Only recently has metal-catalysed displacement aryl halides. CChlorotoluene and ortho-substituted of aryl halides with primary and secondary alkyl- aryl halides were aminated in good to excellent and arylamines been developed as a useful synthet- yields. ic method (42). Pd- and Ni-mediated aminations The effective couplulg of Cchloroanisole with have attracted significant interest owing to the sterically unhindered amines makes this the most importance of this reaction in organic synthesis effective catalytic system to date (45,46). Data for and materials science. The careful selection of hg- the coupling of aryl chlorides with a variety of ands dictates the efficiency of a catalytic system, amines are presented in Table IX. with bulky monodentate and chelaring phosphines The scope of the Harrwig-Buchwald reaction giving the best results (43), although a recently was extended to the amination of heteroaromatic reported two-coordinate palladium-carbene system halides. No problems were encountered with

P/atnnm Metals Rev., 2002,46, (2) 59 Table X Pd2(dba)3/1Pr.HCI-Catalysed Amination of Chloropyridines and Bromopyridinesa

Aryl halide Arnine, HNR'R" Yield, Yob

2-chloropyridine morpholine 99 2-chloropyridine Nmethylaniline 97 2-chloropyridine aniline 88 3-chloropyridine rnorpholine 97 3-chloropyridine Nmethylaniline 91 3-chloropyridine aniline 98 4-chloropyridine-HCI rnorpholine 80 4-chloropyridine-HCI N-rnethylaniline 70 4-chloropyridine-HCI aniline 83 2-bromopyridine morpholine 95 2-bromopyridine N-rnethylaniline 99 2-bromopyridine aniline 96

a Reaction conditions: 1.0 mmol chloro- or hmmopyidine. 1.1 mmol arnine. 1.5 nimol KOBii'. I L/Pd. 3 ml diorarzr. 3 h. loo'%: Isolated ~vie1d.v coordinationof Ncontaining substrates to the metal, N-Arylation of Aryl Indoles and moderate to hgh conversions were achieved N-Aryl indoles themselves can be biologically with 2-chloro- and 2-bromopyridine (Table X). active (48), or can be useful intermediates in the synthesis of biologically active agents (49). As such Amination of Aryl Halides with an they are attractive synthetic targets. The involve- Ammonia Analogue ment of aromatic nitrogen in the reaction limits Benzophenone imine adducts have been pre- the use of the N-arylation of indoles to more reac- pared using benzophenone imine as an ammonia tive aryl iodides and bromides. While our general surrogate. This represents an efficient alternative amination procedure was ineffectual for the aryla- route to the synthesis of N-unsubstituted anilines tion of indoles, good results were obtained when owing to its low cost, availability of reagent and coupling a number of aryl bromides and indole stability to varied reaction conditions (42e, 47). derivatives using a Pd(OAc)2/SIPr-HCl/NaOH Under the conditions established for catalytic ami- catalytic system. This protocol additionally over- nation, benzophenone imine reacted readily with came a common problem in indole synthesis, unactivated and ortb~~substitutedaryl chlorides in namely the formation of C-arylation side products. high yield at 80°C. The reactions with Cchloro- Results are presented in Table XII. toluene and 4-chloroanisole were faster and cleaner at 100°C, as were reactions with aryl bro- Conclusions mides. However, activated aryl halides were NHCs have been shown to be hghly effective incompatible with the strong base KOBu' in this as supporting ligands in a range of catalytic process, resulting in base-promoted cleavage of processes. Their superior thermal stability, togeth- the substrate. Primary anilines were obtained in er with electronic and steric tunability imparted by good yields by acidic cleavage of the benzophe- facile variation of the N-substituents, and the ease none imine adducts, see Table XI. of manipulation (and in siiu deprotonation) of the

Phtinnm Metab b.,2002,46, (2) 60 Pd(dba)z(2Wl %) Ph IPr.HCI (211701 %) Ph ax+ H-N- R 7ph KOBu'(1.5equiv.) * g++ Ph dioxanc

Table XI Arnination of Aryl Chlorides and Bromides with Benzophenone lrninea

CI CI CI CI CI Br Br Br Br Br

a Reaction conditions: 1.0 mmol aryl halide, 1.0s mmol benzophenone imine, 1.5 mmol KOBU', 2.0 mol% Pd(dba)2, 2.0 mol% IPr.HC1, 3 ml dioxane. 80°C: Isolated yields; ' The reaction was performed at I00"C

NHC-precursor imidazolium salts, makes NHCs unprecedented catalytic activity has been observed the anahy llgands of choice in many pdadiun- in some cases, particularly with 'difficult' aryl catalysed cross-coupling processes. Indeed, chloride substrates.

Table XI1 Arnination of Aryl Bromides with lndolesa

R R' I Time, h Yield, Yob H 3.5 97 H 1 100 H 3.5 88 H 16 68 Ph 3 1ooc Ph 18 looc Ph 10 61 2-F-CsH4 3 97 2-F-CsH4 10 83'

a Reaction conditions: 1.0 mmol aryl bromide, 1.1 mmol indole. 2 mmol KOBU'. 2.0 mol% Pd(OAc)z. 2.0 mol% SIPr.HCl, 3 ml dioxane. I00"C; Isolated yields; The reaction was performed in toluene

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Platinum Me.& Rm.,2002,46, (2) 63 42 Recent reviews of palladim- and nickel-mediated 44 L. R. Titcomb, S. Caddick, F. G. N. Cloke, D. J. aryl aminations: (a) J. P. Wolfe, S. Wagaw, J.-F. Wilson and D. McKerrecher, Cbem. Commun., 2001, Marcoux and S. L. Buchwald, Ac. Cbem. Res., 1998, 1388 31, 805; (b) J. F. Hdg,Act. Chem. Ref., 1998, 31, 45 J. Huang, G. A. Grasa and S. P. Nolan, 0% Ltt., 852; (c) J. F. Hartwig, Angw. Cbem., Int. Ed Engl., 1999,1, 1307 1998, 37, 2046; (dl F. Hattwig, Gnktt,1997, 329; J. 46 G. A. Grass, M. Vidu, J. Huang and S. P. Nolan, J. (e) B. H. Ymg and s. L. Buchwald, ]. ofgunornet. ofg,,-hem,, 2001, 86, 7729 Cbem., 1999,576, 125 47 F. Paul, J. Pan and 1. F. Hdg,-- Oqunometulbcf, 1995,14,3030 43 For examples of amination of aryl chlorides, see: q. it., (Refs. 5b, 5n, 54; (a) J. P. Wolfe and S. L. 48 (a) P. Marchini, G. Liso and A. Reho,]. 0%.Cbem., 1975,40,3453; (b) Lane, Synthesis, 1975,135 Buchwald, Angew. Cbem, Znt. Ed, 1999,38,2413; (b) C. F. X. Bei, T. Uno, J. Norris, H. W. Turner, W. H. 49 J. Perregaard, J. ht,K. P. Bogrso, J. Hyttel and C. Weinburg, A. S. Guram and J. L. Petersen, Sinchez,]. Med Cbern., 1992,35,1090 O?ganomet&cs, 1999,18,1840, (c) E. Brenner and Y. Fort, Tetrubedmn Lett., 1998, 39, 5359; (d) T. The Authors Yamamoto, M. Nishiyama and Y. Kole, ibid, 2367; Anna Hillier is a Postdoctoral Research Associate at the (e) J. P. Wolfe and S. L. Buchwald,]. h.Cbem. Soc., University of New Orleans. Her main research interests are in 1997,119,6054; (0 T. H. Riermeir, A. Zapf and M. organolanthanides, organometallic chemistry and catalysis Beller, TL~.Cu#ul., 1997, 4301; @ N. P. Reddy and Steve Nolan is a University Research Professor in the M. Tan&, Tetrdedmn Lit.,1997,38,4807; (h) S. R. Department of Chemistry at the University of New Orleans. Stauffer, S. Lee, J. P. Stambuli, S. I. Hauck and J. F. His main research interests are organornetallic chemistry, Hartwig, Ox.Lit., 2000,2,1423 organometallic thermochemistry and catalysis. Automotive Fuel Cells: A U.I<. Perspective The Institution of Mechanical Engineers held a which lie even beyond the immediate technical hur- one-day conference in London on 28th February on dles. Fuel Cells for Automotive Applications. The main Finally, the motion: ‘This house believes that the topics discussed were technical issues, implementa- fuel cell electric vehicle will comprise 10% of a new tion of the technology and potential markets. car market in 2010’, was defeated, despite strong Melanie Sadler (QinetiQ) addressed challenges support from Gary Acres (Consultant) and many and developments across the entire spectrum of positive comments. Professor James Randle fuel cell vehicles, payjng attention to fuel storage (University of Birmingham) won the day. and cost reduction. Achieving lower costs has been Nonetheless, the impression was given of a market examined for many components, including the almost on the verge of expansion. D. M. JOLLIE noble metal content in electrodes. Careful use of David Jollie is Manager of the online resource Fuel Cell Today chemistry and engineering ought to optimise the (fuelcelltoday.com), sponsored by Johnson Matthey, Hatton platinum and ruthenium content in a fuel cell. Garden, London. David’s main interests are the industrial development and utilisation of fuel cells. Work with alkaline fuel cells was described by A. Willett (Fuel Cell Systems). These were the first fuel Fuel Cells: Science and Technology 2002 cells to be seriously demonstrated (by Francis The next Grove-organised fuel cell conference Bacon in 1959). NASA have used alkaline fuel cells ‘Scientific Advances in Fuel Cell Systems’ takes with platinum group metal electrodes since the place in Amsterdam on 25th and 26th September. Apollo programme. The low operating temperature Topics covered will include materials (and mem- provides some benefits for vehicles, but carbon branes), stack and cell engineering, electrochemisq dioxide has to be removed from the air intake. This and catalysis, fuel processing, hydrogen storage and technology has ‘trickle-charged’ an electric taxi. distribution and balance of plant. For further infor- Chris Dudfield (Intellgent Energy) gave details mation please contact Ms C. Norris, Fax: +44 (0)118 on more conventional platinum-based proton 377 4696; E-mail: [email protected]. exchange membrane technology for sole power in a car. He listed many prototypes using this technology. Catalysis for Low Temperature Fuel Cells A project underway to put a fuel cell into use in Unfortunately publication of the second part of the town of Woking, U.K., was described by J. this paper has had to be postponed until a later Kenna (Energy for Sustainable Development). He issue. We apologise to readers who were hoping to showed the logistical and regulatory challenges read this item in this issue of Phtinum Met& Wew.

Phhvurn Metah h.,2002, 46, (2) 64 Catalysts & Catalysed Reactions EDITOR IN CHIEF: E. G. DEROUANE, The Royal Society of Chemistry, Cambridge, Number 1, January 2002, Items 1-233, ISSN (printed version) 1474-9173, (online version) 1474-91 81, Subscription for 2002 (12 issues): f 395, U.S.$596

Initially I was skeptical when I heard of the pub- titles. Indeed, over one third of the abstracts in this lication of another new catalysis journal into this edition are drawn from 3 journals (Chemicaf already saturated field. But when I found out it was Communications, Journaf of Catabsis and Joutnaf of to be an abstracts journal I was optimistic. There is Mokmkar Cdysis) includhg all 25 from one issue now a wide range of sources containing literature of Joumd of Cata&k. All of these journals would of interest to the catalysis community, and often rank highly in any list of important journals for important catalysis-related research appears in catalysis research, and therefore it is more than obscure or non-specialised journals, outside the likely that most researchers would already be aware scope of usual searches, so any help in bringing of important papers in these journals long before these sources to light is greatly appreciated. the three months it takes for the editors to include The stated aim of the new journal, Cata&ts & and publish them in Catdysts Q Ca&ysed Reactions. Catdysed Reactions, is to alert catalysis researchers to Also, although the source list is certainly exten- new and interesang developments in the field. This sive, it was easy to think of a number of journals is done using graphical synopses of papers pub- that are not included. For example, Journal ofSolid lished in a wide range of relevant journals over the State Cbemistty, Chemishy ofMatetiah and Carbon, to past 2 to 3 months. name but three, all of which frequently contain The editors and publishers of the new journal papers of relevance to catalysis. Perhaps it is have been partially successful in their aim. The intended to expand the source list in the future? journal is well laid out, with section headlngs Of far more interest would be coverage of the allowing simple searches for areas of interest, and less well known journals, includmg more foreign covers a wide range of subjects: it does not appear journals sometimes containing published work in to have a bias towards one area. Most of the English (for example Shokubai gapan)), and abstracts are very informative. In particular, those obscure sources, such as solid state chemistry concerning organic transformations are well dis- titles. Abstracts from these could be included and, played with plenty of useful and relevant I would argue, should take precedence. information (such as solvent, yield) to supplement Certainly this journal does not replace the need the title. In these types of reactions the use of a for regular perusal of the literature and literature pictorial representation greatly aids in understand- searches, but it may, with the inclusion of more ing the subject matter of the paper. Nevertheless, a obscure journals, become a useful additional tool few of the abstracts are no- more than a direct for keeping aware of current developments in pictorial interpretation of the title, and give no catalysis research, alongside ChemWeb's forum on additional information on the content: perhaps a catalysis (http://catalysis.chemweb.com). pictorial abstract is not always required, and more Professor Eric Derouane, the Editor in Chief, would be gained by the inclusion of a couple of states in his hrst editorial that comments are wel- lines of relevant text. come. I hope that comments are forthcoming The inclusion of a Chemikaf Abstracts-style index from the catalysis community, so that in the future is a good feature, allowing quick and easy scanning this journal becomes a good source of information for subjects of interest. In particular, brealung the for its readers. (http://~.rsc.org/catalysts) index into separate sections for author, catalyst, ANDREW P. E. YORK reactant, product and journal is useful. However this also reveals the major favouritism of the jour- Andy York is a Research Scientist at the Johnson Matthey Technology Centre. His interests are in the development of nal to two or three sources, all of which are major computer models for diesel aftertreatment systems.

Phtinwn Metalr Rev., 2002,46, (2), 65 65 Jewellery-Related Properties of Platinum LOW THERMAL DlFFUSlVlTY PERMITS USE OF LASER WELDING FOR JEWELLERY MANUFACTURE

By John C. Wright Consultant, Wilson-Wright Associates, Solihull, West Midlands, 690 4LS, U.K.

The performance ofprecious metal alloys can be usefully compared by the application of engineering design theory and heat flow properties on the small scale that is required for jewellery production. Some of the physical and mechanical properties ofplatinum jewellery alloys differ sufficiently from typical gold and silver alloys to require modifications in the processing techniques, but these properties may allow for stronger slender designs. The thermal difsusivity ofplatinum jewellery alloys is significantly lower than that of other precious metal jewellery alloys. This explains why laser welding is so efficient when used in making platinum jewellery and why it also allows most of the cold work hardening to be retained in components.

Few jewellery designers or manufacturers start properties of the materials and their interaction with a design specification, outline a design, detail with the production process, but also has to take a materials specification and optimise the produc- into account how all these factors have to operate tion ability - which is the usual procedure in the in an acceptable economic and environmental manufacture of engineering components. Critical framework. Most of the worldwide jewellery engineering design not only integrates mechanical industry takes a traditional view that depends on a design (such as stress/strain behaviour) with the relatively narrow range of processes and materials and favours batch processing rather than mass production. By applying engineering design theory and heat flow physical properties on the small scale required for jewdery, the performances of precious metal alloys can be compared. For example, properties such as Young’s modulus, elastic limit stress and work hardenability of platinum jewellery alloys are significantly hgher than those of the other precious metal jewdery alloys. This combination of properties can explain the favourable ‘dead-set’ capability of platinum settings, that is, claws/

Fig. I A YAG laser used for jewellery welding (I). Most jewellery lasers are Class 1 lasers. The workpiece IS irradiated by the narrow laser beam which heats up a small, controllable surface area of the platinum or platinum alloy jewellery to well above the melting point (I 772-2000°C). Precise targeting allows welds to be made - 0.2 rnm,from heat-sensitiveparts. Jewellety to be welded is placed in the upper compartment: the stereomicroscope aids positioning Photo courtew of RoJin-Buosrl LIK Lld.

Phfinum Metah Rnr, 2002,46, (2), 6C72 66 Table I Typical Parameters of Jewellery Laser Welding Machines

Machine size, height x width x depth 700-1 350 x 250-550 x 650-860 mm Weight 85-1 50 kg Input power supply 115 or 200-240 V, 50-60 Hz Max average operating power 30-80 W' Focal spot diameter 0.2-2.0 mm Pulse energy 0.05-80 J (W S) Peak pulse power 4.5-10 kW Pulse duration 0.5-20 ms Pulse frequency single to 10 Hz Pulse energising voltage 200-400 V"

Average light bulb power but in-phase, so equivalent to much higher power density ** Voltage used to trigger xenon jlash. in turn, afects laser beam output power prongs and similar settings when pushed against The laser welding machine is easier to use if the gemstones tend to remain in position and show lit- shape of the beam in the worlung zone is cylindri- tle 'spring-back'. cal; this is because the spot diameter does not The thermal difhsivities of the platinm alloys change over a range of focus of several millime- used for jewellery are significantly lower than tres, see Figure 2. A typical laser pulse lasts from 1 those for gold and silver, which explains why laser to 20 milliseconds and suitable adjustments can be welding is so efficient and also why it allows more made for various materials through trial and error, of the cold work hardening of jewellery alloys to but certain heat flow data allow good predictions be retained in components. of suitable weldmg parameters. Material properties which need to be taken into account when welding Laser Welding of Jewellery jewellery alloys, includmg latent heats of melung Laser machines for jewellery are compact, low- and corresponding thermal conductivities, are powered and safe, see Figure 1. They weld most available but these values are more accurately alloys quickly, repeatably and precisely, but the known at or near room temperature than around efficiency of the laser process depends very much the melting point. Despite the hgh energy needed on the properties of the target material. The ener- to melt platinum alloys, their relatively low thermal gy that is effectively used in the welding depends on the surface absorption of the target and is controlled by adjusting pulse Good beam Bad beam intensity, duration and pulse frequency. quality quality The laser weldmg effectiveness depends on properties of absorption, reflection and any chemical reactions of the target material. Components to be joined, or Misalignment upgraded (repaired) in the case of cast- of work piece indue beam to manual direction-E=5!5 ings, are arranged under visual control or positioning Spot diameter Spot diameter jigged, and exposed to one or more laser remains nearly changes pulses. A stereomicroscope and cross constant dramatically hairs facilitate the positioning of the parts 2 A good quality laser beam is one where the beam shape in and help to target the exact position Fig. the working area is cylindrical so that the spot diameter is constant where the laser pulse will strike. over several millimetres of.focus.

Phtinum Metah REX, 2002, 46, (2) 67 Table II Typical Laser Welding Parameters For Some Jewellery Materials

Alloy Pulse energising Pulse duration, Comments composition voltage**, V ms

Platinum, All 200-300 1.5-1 0 Very good welding results Gold, 999 fine 300-400 10-20 Darken target area; high power necessary Gold, 18 ct yellow 250-300 2.5-1 0 Good welding results Gold, 18 ct white 250-280 1.7-5.0 Very good welding results Silver, 925, 835 300-400 7.0-20 Darken target area; high power necessary Titanium 200-300 2.0-4.0 Weld in inert gas inside the laser welding machine Stainless steel 200-300 2.0-15 Weld in inert gas inside the laser welding machine

I* Voltage used to trigger the xenonJ7ash affecfs the outpuf power of the laser heam used,for the diferent materials diffusivity allows the heat to be retained/concen- laser machines to achieve this. trated at the target, so they can be efficiently The very hgh intensity laser pulse generates a welded. However, platinum jewellery alloys have surface temperature well above the melting point casting temperatures around 2000°C and high of platinum over a very small diameter target spot. solidification rates, so the challenge is for compact This allows controlled welding, under ideal conditions, as close as 0.2 rnm from complicated and heat-sensitive component parts, such as hinges, 300V 350V 400V catches, fasteners, settings, most precious stones, and even, with care, pearls and organic materials. Provided that the heat flow away from the target is limited, it is possible to retain heat treated or cold

Beam diameter 0.2mm, Pulse 2.5ms worked hardness in most jewellery alloys; this works particularly well with platinum jewellery

2.5ms lOms 20ms alloys. The settings given in Table I1 are based on a beam diameter of about 0.5 mm on the materials stated and may need adjustment for other compo- sitions. The main control settings on the laser Beam diameter 0.2mm, Voltage 300V machine @ower/energy, beam diameter, dura-

0.25mm 2.5mm 4.5mm tions) have slightly different effects on any one material, as shown in Figure 3. Different materials can have very different values for thermal diffusivity, melting temperatures and latent heats of melting. The way these properties combine togeth- Pulse 2.5ms, Voltage 300V er has a marked effect on the energy intensity

Fig. 3 Effect of diflerent laser settings of voltage. needed to produce an effective weld. Welding is duration of beam pulse and beam diameter on the achieved only when adequate heat is absorbed cross-section of the heat affected zone. through the surface, not when the beam is reflect- (a) Increasing the voltage increases the penetration of the beam. ed off the surface, so surface colour and reflectivity (h) Increasing the duration of the pulse increases the have to be taken into consideration. Where there is total pulse energy and radial heat Jlow. (c) Increasing the beam diameter at constant pulse a combination of high reflectivity and high heat energy gives heat spread rather than penetration dispersion (for instance in silver and hgh carat

Phhinwm Met& Rev., 2002,46, (2) 68 golds), it is helpful to mark and darken the target be a little greyer) have little effect on the optimum spot or line with a dark blue or black felt tip pen settings. Gold and silver alloys have lower melting or permanent marker. This effectively increases points but five to seven times &her capacity to the absorption coefficient of the surface. transmit heat away from the target. The units used in Table I1 are c.g.s. units. This Why Platinum Responds Well is because they fit the scale of jewellery alloys bet- The efficiency of a laser welding machine dif- ter than SI units (which rates thermal diffusivity in fers from alloy to alloy. While the same set of J m2 s-') and the interest here is in the order of the control parameters will result in the same power effect rather than calculating the actual heat flow. delivered in each weldmg pulse, the melting effect The data for the pure metals are known most of each pulse depends on the proportion of the accurately around room temperature (2, 3) and heat energy absorbed and then on the rate at data for the alloys were calculated from the prop- which the heat is dissipated from the erties of the pure metals, based on alloy melting/welding zone. This is not simply a func- composition by weight. The fullest version of the tion of the thermal conductivity. Thermal data was used where available. For instance, data conductivity is defined as the rate of heat transfor platinum, gold and silver have been mwe ferred through a volume whose two extremes are extensively studied than for, say, ruthenium. at different but constant temperatures - a steady However, the data in Table ID have been ratio- state. However, what matters more in dependable nalised to two decimal places to give greater practical workshop technology, is how the heat is uniformity, while acknowledgmg that the accuracy transferred from a hot-spot, such as where a weld- at %her temperatures is questionable. ing torch touches a surface, through a mass whose The laser beam does its most effective work at temperature rises as a consequence, and thus or near the melting point of the target metal so we where the 'low' temperature end is not at constant should be more interested in data at and near melt- temperature. This property is best described by ing point temperatures. Thermal conductivity thermal diffusivity, stiu very dependent on con- increases with temperature: for platinum from ductivity but modified by the specific heat of the 0.171 at 300 K to 0.230 at 1800 IQ and at the melt- metal related to the volume: ing point it is around 0.24. Specific heat (more correctly, molar heat at constant pressure, C,) thermal conductivity Thermaldiffusivity = within a single-phase region also increases with specific heat x density temperature according to a polynomial function: The heat input parameters are: C, = a + bT + cT2 + dT'I2 + eT-' [a] Specific heat of solid up to the melting point [b] Melting (liquidus) temperature For platinum, a = 5.755, b = 0.001505, c = -0.185 [c] Latent heat of melting x lod, so the specific heat increases from 0.0316 [d] Specific heat of the superheated melt at 273 K to 0.0452 at 2046 K. [el Thermal diffusivity Density decreases by the cube of the coeffi- Melung points for most platinum alloys are cient of linear expansion with temperature, which hgh, but thermal diffusivities are relatively low for platinum is 8.9 x 10". This means that a cube Fable III) so the laser is able to deliver enough of platinum, sides of 1 cm, at 273 K (21.40 g) energy to melt a very small focused spot at each would expand to a 1.016 cn-sided cube at 2046 K, pulse but with only a small heat affected zone. or volume 1.049 an3,which is almost 5% less With the possible exception of palladium, all the dense - at 20.04. On these assumptions, the ther- platinum group jewellery alloys respond in the mal diffusivity of solid platinum at the melting same way to identical settings of a laser machine. point is approximately 0.265 instead of 0.245, Shght differences in surface colour when melting about an 8% increase. All the platinum jewellery in air (alloys containing copper and cobalt tend to alloys have thermal diffusivities of the order of

P&mm Metah Rev., 2002,46, (2) 69 Table 111 Melting Points and Thermal Diffusivities for Platinum Alloys and Other Jewellery Materials

MetaVAlloy Liquidus Density, Thermal Latent Mean Thermal temperature, g cm3 conductivity, heat, specific heat, diff usivity, OC cal (s T cm)-’ cal g-’ cal g-’ OC-’ cm2 s-’ at 50°C

999 Platinum 1772 21.45 0.17 27.13 0.03 0.25 990 Platinum 1772 21.45 0.17 27.13 0.03 0.25 Copper 1084.5 8.93 0.96 48.90 0.09 1.17 Pt-5% Copper 1745 20.38 0.21 28.22 0.04 0.29 Cobalt 1494 8.80 0.12 63.00 0.10 0.13 Pt-5% Cobalt 1765 20.34 0.17 28.68 0.04 0.23 Iridium 2447 22.55 0.14 51.09 0.03 0.20 Pt-5% Iridium 1795 21 51 0.1 7 28.33 0.03 0.24 Pt-10% Iridium 1800 21 56 0.17 29.53 0.03 0.24 Pt-15% Iridium 1820 21 62 0.17 27.31 0.03 0.24 Pt-20% Iridium 1830 21 67 0.16 31.92 0.03 0.24 Palladium 1554 12.00 0.17 38.00 0.06 0.24 Pt-5% Palladium 1765 20.98 0.1 7 27.67 0.03 0.24 Pt-10% Palladium 1755 20.51 0.1 7 28.22 0.04 0.24 Pt-15% Palladium 1750 20.03 0.17 28.76 0.04 0.24 Rhodium 1963 12.42 0.21 53.00 0.06 0.29 Pt-5% Rhodium 1820 21 .oo 0.17 28.42 0.03 0.25 Ruthenium 231 0 12.36 0.28 91.19 0.06 0.40 Pt-5% Ruthenium 1795 21 .oo 0.1 8 30.31 0.03 0.25 Tungsten 3387 19.25 0.35 61 .OO 0.03 0.54 Pt-5% Tungsten 1845 21.34 0.18 29.1 7 0.03 0.27 Fine Gold 1064.43 19.28 0.76 15.21 0.03 1.25 Fine Silver 961.93 10.50 1.02 25.30 0.06 1.74 Sterling Silver 893 10.40 1.oo 26.40 0.06 1.66

0.23 to 0.27. A similar argument applied to silver, operator can weld the surface without scarring and shows its thermal diffusivity decreases from 1.74 most components can be polished to ‘near finish‘ to 1.31 (near its melting point). before welding. Alternatively, components can be The heat energy contained within 1 cm3 cubes ‘tack welded’, adjusted to the correct position and of liquid platinum, gold and silver at 100 K above final welds made with laser settings that improve their respective melting points, are 1854, 956, and the cosmetic finish of the tack welds. 878 cal, respectively. Although the heat contents of Another feature of the localised heating effect molten platinum jewellery alloys are roughly double of the laser is that dissimilar alloys can be joined those of gold or silver, their thermal diffusivities more readily than when using bulk melting. There are about one fifth of that for gold and one seventh are incompatible pairs of metals, but a laser weld- of that of silver. So the rate of heat input to the ta+- ing machine can produce narrow weld zones get can still substantially exceed the rate of outward where the change in colour or texture between the heat diffusion. In effect this means that the laser two components is sharper and better delineated beam can be placed very close to delicate stones than in alternate technologies. The most obvious with platinum, and that normally it is unnecessary common feature of a typical range of laser welded to remove stones before malung repairs. A skilled platinm jewellery is that remarkably small sections,

PLatinum Metah Rev., 2002, 46, (2) 70 Fig. 4 Platinum jewellery (not to scale) by Tom Rucker, who used laser welding in its assembly: (a) A 16 ct beiylpendant (back view) made in platinum- 5% copper The beryl is held between 2 laser-welded rails. This design could only be achieved by laser welding. (b) This diamond brooch made in platinum-20% iridium and I8 ct yellow gold was complete!y laser welded. (c) Necklace with diamond brilliants. sapphires and pearls (2nd Prize, International Pearl Design Contest, Tokyo, 1999/2000) made in platinum-20% iridium and 18 ct yellow gold. The 0.6 mm diameter wire is assembled crosswise in two levels and laser welded. (d) The 'Sea ofLights ' necklace made in platinum and 18 ct yellow gold with a 1.3 ct diamond brilliant. In the centre ofthe gold bowl is a brilliant cut diamond held in tension by 4 crossing platinum wires - 0.7 mm thick. The setting is so secure that brilliants up to 2 ct are used. The bowl is surrounded at the back by a cage of0.4 mm platinum wire which also holds the bearing. (e) A necklace with pearl clasp made in platinum-20% iridium. Platinum wire was wound onto the surface ofa wooden ball and laser welded. The ball was then burned away. The wire balls appearfragile, but the strong Pt-Ir al1o.v structure gives a solid result

Phtinwr Metah Rev., 2002,46, (1) thin stampings and fine wire can be at least stitch ellery alloys when used with a laser machine, welded with precision. More extensive welds and whether for upgrading castings or for weldmg, are repairs of casting defects (see later section) can be virmally identical. made by a series of overlapping pulses. As the laser is limited to joints that can be hit by the direct Conclusion beam, deep and undercut sites should be avoided. Comparing jewellery alloys, the necessary heat inputs to melt platinum alloys are high compared Jewellery Design with gold and silver alloys, but thermal diffusivities Several components in the jewellery shown in are significantly lower. One effect is that heat is Figure 4 have been elastically stressed to give more localised around hot-spots than with gold springiness and rigidity. The tightly localised and and silver. limited heat diffusivity allows springy and hard Most platinum jewellery alloys show the rela- components to be joined with little or no soften- tively high stress necessary to exceed the elastic ing. This enables designs that make good use of limit, followed by a hgh rate of plastic work hard- lightweight springy sections or robust fasteners. ening which also raises the ‘bend-back‘ stress. The very limited heat affected zones also allow Components may have useful strength and springi- joining of more dissimilar alloys (assay rules per- ness in slender sections, and these extra properties mit~@than would be possible with large scale acquired before laser welding can be retained after melting. In good commercial practice all the com- assembly. ponents could have a high degree of finish prior to joining. Most of the high finish is preserved, and it Acknowledgements is clearly easier before welding to dean up and pol- I gratefully acknowledge technical advice from Michael Batchelor and David MacLellan of RofimBaasd UK Ltd.; ish separate components than finished pieces. www.rofin.com. I am indebted to Tom Rucker of Anton Rucker, Ottostrasse 80,85521, Ottobrunn, Germany, who puts Upgrading and Repairs the technology expressed in this paper into very effective artistic design, and for permission to use several of his designs. There are probably as many laser welding machines used for upgtadtng castings as there are References for makmg welded pieces. Some surface defects 1 Rofir-Baasel UK Ltd., (formerly Baasel Lasertech can be repaired at the fettllng stage but small pir- UK Ltd.), Drayton Fields, Daventry, “11 5RB holes sometimes show up later during polishing. 2 “Kempe’s Engineers Yearbook 2000”, Miller Freeman, Tonbridge, U.K., 2000 The expense to both the finisher and caster of 3 “CRC Handbook of Chemistry and Physics”, 76th returning such components for recasting is often Edn., CRC, Boca Raton, 1995-1996 avoidable by using the laser welder to upgrade the The Author castings, particularly when casting and finislung John Wright is a former Professor of Industrial Metallurgy at the University of Aston in Birmingham. Currently, he is a consultant for operations are on the same site. the jewellery industry worldwide with Wilson-Wright Associates. A small area of rough surface texture may be glossed by using a rapid repeat sequence of pulses Laser Drilling of Platinum Cavities with the laser beam set relatively wide and shallow. A copper laser has been used to etch and bore Small pinhole defects (around 0.25 mm) can be into coated platinum wire electrodes (outer diame- filled by similarly pdsing around the edge of the ter 50-150 pn) to form - 30 pn diameter cavities defect. Larger defects can be effectively filled with for storing enzymes, by P. M. Vadgama of the fine filler wire touched into the defect, cut to size University of Manchester (WotbiAppr! 01/13,102). with the laser beam striking the wire and then lev- Cavities are formed in and along the length of the elling the tiller down to the original surface. The active electrode core. The enzymes face laterally, colour of the filler can usually be matched accu- instead of being on a mechanically vulnerable tip, rately to that of the casting. The principle of which improves effectiveness and ease of use. The relatively low thermal diffusivities of platinum jew- electrodes are for in yivo biological sensors.

PLdnwn Metals h.,2002,46, (2) 72 Heterogeneous Catalytic Hydrogenation HANDBOOK OF HETEROGENEOUS CATALYTIC HYDROGENATION FOR ORGANIC SYNTHESIS BY SHIGEO NISHIMURA, John Wiley & Sons, New York. 2001,700 pages, ISBN 0-471-39698-2, US. $185. €217.70, f 137

Catalytic hydrogenation is widely applied for supported Pd (the Lindlar catalyst) is active in the the reduction of a variety of functional groups. It selective hydrogenation of alkynes to alkenes. The has been and will continue to be a very substantial catalyst can be further modified for this reaction by market for platinum group metal (pgm)catalysts as addition of a nitrogen base such as quinoline or they tend to be more active for a given transfor- pyridine. This inhibition of the catalyst prevents mation than their base metal equivalents. This further hydrogenation of the alkene product and permits the use of less severe reaction conditions. results in an increase in selectivity. It is important, In the main, though not exclusively, the reactions however, to adjust the concentration of the are carried out over a heterogeneous catalyst. inhibitor to avoid complete poisoning of the cata- Unsupported catalysts have found application in lyst. Another example of selective poisoning is small-scale laboratory use, though on an industrial described in Chapter 13 where a BaSO4-supported scale use of a supported catalyst is usually advanta- Pd catalyst when treated with a sulfur-containing geous. The rather diffidt-to-handle Raney Ni poison, such as thioquinanthrene, becomes selec- catalyst is one of the few unsupported materials tive in the hydrogenation of acid chlorides to give which has been utilised industrially. aldehydes (the Rosenmund reduction). Addition of A diversity of materials can be used as a support the inhibitor prevents further hydrogenation of the to the hydrogenation catalyst and numerous tech- labile aldehyde product. niques are used to deposit and anchor the active The specialist nature of this book is reflected metal on this material. This results in a vast array not only in the price (an eye-watering E137) but of catalysts, each of which may be optimal for a also in the fact that technical terms (explanations given reaction operating under appropriate condi- being beyond its scope) are used liberally through- tions. Correlating this data to produce a reference out. The reference lists for each chapter, while not book, to enable a researcher to ascertain quickly meant to be comprehensive, could perhaps benefit the favoured catalyst and reaction conditions for from an update as they tend to be biased towards the hydrogenation step of a particular functional earlier work, sometimes even towards unsupport- group is an ambitious and hghly laudable endeav- ed catalysts. our. This is exactly what Professor Nishimura has In conclusion, this book is easy to use to find attempted to do with this book. information quickly on the hydrogenation of a The book is divided into thirteen chapters. The given functional group. In conjunction with other first chapter gives an overview of hydrogenation texts (1, 2) it adds to a useful armoury for dealulg catalysts, subdivided into sections on base metal with most queries on hydrogenation. It is therefore catalysts and one on pgm catalysts. Details are good value for the specialist practitioner. given of methods by which both supported and unsupported catalysts can be prepared. The recipes References provide a useful starting point for preparation of 1 R L. Augustine, “Heterogeneous Catalysis for the an optimised catalyst. The second chapter deals Synthetic Chemist”,Marcel Dekker, New York, 1995 2 “Fine Chemicals through Heterogeneous Catalysis” briefly with reactors, then with catalyst inhibitors ed. R. A. Sheldon and H. Van Bekkum, Wiley-VCH, and poisons, the judicious use of which is seen in weinheim, 2000 the subsequent chapters on hydrogenation chem- M. HAYES istries to be a good control of catalyst selectiviq. Martin Hayes is a Senior Chemist, Process Catalyst Development For example, in Chapter the hydrogena- Department, Johnson Matthey, Royston. His interests are in the 4 on development of heterogeneous platinum group metals catalysts tion of alkynes we see that Pb-doped CaC03- for commercial production of added value chemicals.

Plnttaum Me.& Rev., 2002, 46, (2), 13 73 Two-Phase Iridum-Based Refractory Superalloy s THEIR DEVELOPMENT AND POSSIBILITIES AS HIGH TEMPERATURE STRUCTURAL MATERIALS

By Y. Yamabe-Mitarai, Y. F. Gu and H. Harada High-Temperature Materials Group, NIMS, Sengen 1-2-1, Tsukuba. lbaraki 305-0047, Japan

A new class of alloys based on platinum group metals. which are called rejractoty superallo.vs, is proposed. These refractory superalloys have aJc.c. and L 12 coherent two-phase structure (similar to that of nickel-based superalloys). high melting temperatures, and good potential as structural materials for use at temperatures up to 1800°C. In this paper. we report our results on the strength behaviour. creep property, ductility and,fracture mode of iridium-based refractory superalloys.

Iridium has a high melting temperature Much work has been done over the past three (2447"C), the highest room temperature elastic decades in attempts to prevent brittle fracture of Ir modulus (570 GPa) (1) and is one of the most sta- and its alloys and to improve their mechanical ble elements against corrosion (2). Its main use is properties. Alloying (by macro-addition or micro- for crucibles for growing single crystals of hh dopais believed to be one of the most effective melting temperature oxides, but it is also used in ways to achieve this. Liu and colleagues found that catalysts and in ignition devices (spark plugs). adding a trace amount (below 60 ppm) of thorium Over the last few decades, the possibility of (Th) to an Ir-0.3W alloy (the alloy currently used as using iridium Q as a hgh temperature structural a fuel-clad- material in radioisotope thermo- material has been evaluated. Several Ir-based inter- electric generators) could improve its strength and metallics have been noted as having melting ductility, and change the fracture mode from inter- temperatures above 2000"C, such as IrNb with a granular to transgranular (15). A cerium-doped Ir Llo structure (3), IrAl with a B2 structure (4), and alloy has also shown several similarities to Th- Ir,Nb or Ir3Zr with a L12 structure (5-6). doped alloys (16). Wolff and coworkers reported However, Ir is an anomalous metal with a face cen- that the addition of 0.5 at.% boron (B) to an Ir- tred cubic (f.c.c.) lattice that fails due to cleavage 16Nb alloy could raise its strength and ductility at (7,s). lower temperatures but caused a rapid fall in Iridium single crystals fail in a brittle manner strength above 1100°C (17). Recently, Heatherly under tensile tests after an elongation of about 80 and colleagues investgated the effects of impuri- per cent at room temperature (9). However, poly- ties in Ir and found that iron, nickel pi), crystalline Ir and its alloys normally exhibit chromium or aluminium (Al) at levels ranging intergranular or mixed intergranular and transgran- from 50 to 5000 ppm do not embrittle Ir, whereas ular cleavage with limited ductility over a wide high levels of silicon cause severe embrittlement temperature range (10-1 2). Some researchers (18). believe that intergranular fracture in polycrystalline While these research projects concentrated on Ir is caused by non-metallic impurities, such as car- single-phase alloys based on Ir (which may be less bon (C) and oxygen, or that it is environmentally resistant to creep deformation than two-phase induced (13). Other reports have proposed that the alloys) we focused on two-phase Ir-based alloys intergranular brittleness in polycrystalline Ir is consisting of f.c.c. and L12 phases (19). We have intrinsic and not due to impurities at the grain proposed a new class of alloys based on Ir with a boundary (14). f.c.c. and Llz coherent two-phase structure similar

Pkzfinum Metalr Rev., 2002, 46, (2), 74-81 74 Fig. 1 Phase diagrams of iridium alloys, determined experimentally: (a) Nb (a) the tertiary system Ir-Nb-Ni at 1300°C (b) the quaternary system Ir-Nb-Ni-A1 at 1300°C

Atomic percent of Ni, at.%

I to that of Ni-based super- I f.&. f.c.c. + Ir3Nb + Ni3Al alloys, and named them Atomic percent d Ni, at.% ‘refractory superalloys’ (20, 21). The coherent interface in the alloys appears to play an important strength at hgh temperature. Such an alloy could role in strengthening alloys by preventing disloca- then be used at hgh temperawe in situations tion movements. We considered that if the where Ni-based superalloys cannot be used. A Ir-based alloys (with melting temperature above brief introduction to our primary work was given 2000°C) have a f.c.c. and L12 two-phase coherent in this Journal by Wolff and W (22). Here, our structure, then the alloys should show high recent results on the strength behaviour, creep

Phtinnm Me& h.,2002,46, (2) 75 Fig. 2 Precipitate shape of (u) lr-I5 ut.% Nb und (h) Ir-I5 at.% Zr alloys. These durk+eid images were takeii.jrom sirperlattice rejlectionsfrom the L12 phase. (c) Bright$eld image qf'un Ir-15 at. % ZI- ulloy property, ductility and fracture mode of Ir-based to stabilise the grain boundary. Therefore B and C alloys developed under the High-Temperature were expected to improve grain boundary strength Materials 21 Project are reported. in Ir-based alloys. In addition to these trials, platinum (Pt), Ni and rhodium @) were also added Design Concept of Ir-Based to Ir-Nb alloys to characterise the structural con- Refractory Superalloys nection and to find a suitable quantity of each to According to the Ir binary phase diagrams replace some of the Ir. These added elements may given in Massalski (23), the f.c.c. and LlZ two- help to improve ductility. phase region exists, for example, in the Ir-V, Ir-Ti, Another trial involved combining the two- Ir-Nb, Ir-Ta, Ir-Hf and Ir-Zr systems. We investi- phase Ir-Nb and Ni-Al alloys and also the gated the strength behaviour and deformation two-phase Ir-Nb-Ni and Rh-Nb-Ni alloys in order structure in these alloys (24,25), and Ir-Nb and Ir- to check the two-phase regions in the combined Zr were found to be the most promising alloys for systems. These two quaternary alloys can be study with regard to their strength and microstruc- expected to have the advantages of both systems - ture up to 1200°C. However, the strength of these Qhstrength at high temperature from the Ir-Nb two binary alloys dropped off drastically above and Ir-Nb-Ni alloys, and good ductility and low 1200°C. In attempts to improve the high-tempera- density from the Ni-Al and Rh-Nb-Ni alloys. ture strength, additions of molybdenum (Mo), These quaternary alloys could be described, tantalum pa) and tungsten (W) with hgh melting respectively, as an Ir-Ni-based alloy or as an Ir-Rh- temperatures (261 7,2977 and 3380"C, respectively) based alloy, containing some f.c.c. or L1, phase- were added to the Ir-Nb alloy. forming elements. Another problem is that Ir-based alloys are very Experimentally determined phase diagrams of brittle and break by the intergranular fracture Ir-Nb-Ni and Ir-Nb-Ni-Al at 1300°C are shown in mode (26). In attempts to improve their ductility Figure 1 (27,28). In the Ir-Nb-Ni system, the f.c.c. and change the fracture mode, different elements and L12 two-phase region expanded on addition of were added as the third element to the Ir-Nb alloy. Ni. However, when too much Ni was added a In Ni-based superalloys, B is the element added to third phase, Qr, Ni),,Nb,, was formed. In the Ir- improve grain boundary strength and C is added Nb-Ni-Al system, contrary to our expectations,

Pkzhn#m Metah b.,2002, 46, (2) 76 Fig. 3 Comparisons of Ihe temperature dependence of the compressive strengths of 2000 four iridium-based alloys: Ir-12Zc Ir-l7Nb, Ir-ISNb-5Ni and Ir-13.5Nb-8Ni-2AI; with the nickel-based alloy (CMSX-10) (29), a niobium-based alloy (Nh-Si-Mo- W) (30). and a tungsten-based alloy (31)

1500

a 4

v)- 1000 v) LL cv) s3 LL zs

the f.c.c. and Llz two-phase region 500 lo00 1500 2000 was not connected from the Ni-Al TEMPERATURE, *C side to the Ir-Nb side. Instead, a three- phase region, the f.c.c. and Llz-Ir3Nb and L12-Ni& appeared. However, there was no Figure 2a. However, plate-like precipitates formed other phase of different structure in addition to the in the Ir-Zr alloys where there was a large lattice f.c.c. and Llz phase in the alloys that were tested. misfit of 2% (Fiie 2b), and a sern-coherent The quaternary Ir-Nb-Ni-Al alloy is very promis- structure with many misfit dislocations also ing from the point of view of phase structure. formed (Figure 2c). Plots of the temperature Although exact phase diagrams for the Ir-Nb-Mo, dependence of the strength showed that the Ir-Nb-Ta, Ir-Nb-W, Ir-Nb-Pt, Ir-Nb-B and Ir-Nb- strengths of the Ir-Nb and Ir-Zr alloys were very C systems cannot be provided yet, the f.c.c. and hgh (> 1000 MPa) below 1200"C, although the Llz two-phase structure was confirmed in the strengths decreased dramatically above 1200°C following alloys: Ir-15Nb-5M0, Ir-l5Nb-Ta, (Figure 3). (Figure 3 also shows the strengths of a Ir-lSNb-lOW, Ir-15Nb-30Pt (all measured in typical commercial Ni-based superalloy, CMSX-10 at.%) and in Ir-15 at.% Nb-500 ppm B, and Ir-15 (29), a Nb alloy (30) and a W alloy (31) plotted for at.% Nb-500 ppm C, by observation of their comparison as other hgh-temperature materials.) microstructure. For the Ir-Rh-Nb-Ni system, the In both the Ir alloys the volume fraction of the L11 f.c.c. and L11 two-phase region was observed over precipitates was 50%. Below 1200"C, the strength a wide area. of the Ir-Zr alloy was higher than that of the Ir-Nb alloy. In these two alloys, solid-solution hardening High-Temperature Strength and precipitation-hardening effects were both Precipitate Morphology Effect observed (32), with precipitation hardening being Precipitate morphology depends on the lattice larger in the Ir-Zr alloy. misfit between the f.c.c. matrix and the Llz precip- The deformation mode in the Ir-Zr alloy was by itates (21). Typical microstructures are shown in she- (25); on the other hand, shearing did not Figure 2. In the Ir-Nb alloy with a small lattice mis- occur in the Ir-Nb alloy (33). In the Ir-Zr alloy, fit of 0.4%, cuboidal Llz precipitates formed, see when a dislocation moves in the f.c.c. matrix, it

77 Fig. 4 The temperature dependence 140 of the speciJk strength of (I6 Rh)rsNblsNiIn allo.vs. Small udditions of rhodium produce the 120 strongest alloy

0 .-‘E, 100 tm 2 = 80 I‘ GJ 60 u +u) U IT- 40 U aW u) 20

500 1000 1500 201 TEMPERATURE, *C meets numerous interfaces in the maze structure. phase Ir-based alloy as a structural material at The coherent interface has high-coherency strain ultra-high temperatures may come from its lower energy in the maze structure, and a large number specific strength (normalised strength to density), of misfit dislocations will prevent the movement which is mainly caused by its higher density. of dislocations in a semi-coherent structure. This To reduce the density, we med replacing Ir by Rh could be attributed to the high precipitation in an Ir-15Nb-1ONi alloy, which has higher hardening of the Ir-Zr alloy. strength at both room and high temperature. The effects of the replacement on the strength and The Effect of Element Addition ductility are shown in Figure 4. The quaternary In attempts to improve the high-temperature (Ir75Rh25)75Nb15Nilotwo-phase alloy had the high- strength of Ir-based alloys above 1200”C, we est specific strength of all the tested Qr, added Mo, Ta and W to a two-phase 11-15Nb Rh)7sNb15Niloalloys: 126 MPa g-’ cm-’ at room alloy. Only Ta, at concentrations C 20 at.%, was temperature, 81 MPa g-’ cm-’ at 1200°C, and 24 found to be effective at improving the high-tem- MPa g-’ cm-3at 1600°C. perature strength. Additions of Ta > 20 at.% made In the trial described previously, after the Ir-Nb the Ir-15Nb lose the f.c.c. and L12 two-phase alloy had been combined with the Ni-Al alloy, the structure, causing the alloy strength to drop great- density decreased; for example, the density of the ly at 1200°C. Ad* W and Mo to the Ir-15Nb Ir-lONb-42Ni-8Al alloy with three phases was alloy only slightly improved its high-temperature 14.8 g cm-’. However, the strength and melting strength even though W has a higher melting tem- temperature also decreased drastically. perature and larger atomic size than Ta. Similar behaviour was also observed in the Ir-Nb-Ni and Creep Properties Ir-Nb-Ni-Al alloys (Figure 3). These results Compressive creep curves of the Ir binary and showed that a third element is not very effective at ternary alloys at 1500 and 1650°C are shown in improving the strength at temperatures over Figure 5. Although the strength of the Ir-based 1200°C. binary alloys above 1500°C was not very high, the One of the biggest obstacles to using a two- creep strain was below 2% and tertiary creep was

PIatinrrm Met& Rey., 2002,46, (2) ia Fig. 5 Creep curves (a) for the binary iridium alloys (a) Ir-12.3 and Ir-17Nb at 1500°C 1MO *C under I3 7 MPa (b) for Ir-17Nb alloy and nickel- containing iridium-niobium alloys at 1650%, also under 137 MPa. The alloy containing the least -?.31 amount (I at.%) of nickel shows 5 2. the best creep property LL Li. Ir-12Zr

Ir-17Nb

100 200 3bO TIME, HOURS

(b) 1650.C

Ir-15Nb-1ONi 3- not observed until 300 hours. z z- The creep resistance was %her 1 a in the It-Nb alloy than in the Ir- I-v) Zr alloy because discontinuous coarsening occurred from the 1- grain boundary in the Ir-Zr alloy \ and its microstructure changed to I I a coarse structure during creep 100 200 300 (34). This was due to the large lat- TIME, HOURS tice misfit in the h-Zr alloy. In the Ir-Zr alloys, the coherency strain energy of the interface was very hgh and binary Ir-17Nb alloy 1 o-~ d).The values of the coarsening of the maze structure was difficult to steady-state creep rates for the Ir-15Nb-5Ni and achieve. Discontinous coarsening was also Ir-15Nb-1ONi alloys were 2.1 X lo4 sd and 1.2 x observed in the lamellar structure of the Ti-Al lo-' s-', respectively. The great improvement in alloy, for example (35). When the lamellae are very creep resistance of the Ir-15Nb alloy on adding fine, coarsening often occurs by migration of the Ni might be due to the effect of Ni on improving grain boundary (36). the grain-boundary strength and reducing the At 1650°C, a tertiary creep was observed dear- coarsening process. ly in the binary Ir-Nb alloy after 20 hours, but ad- Ni to this alloy improved its creep resis- Ductility and Fracture Mode tance dramatically. As long as the Ni content is Our previous investigation showed that poly- below 5 at.%, tertiary creep is not observed. The crystalline binary Ir-based two-phase alloys creep strains were below 2% after 300 hours for Ir- normally exhibit intergranular fracture with limited 15Nb-xNi alloys (x e 5). The steady-state creep ductility even in compression tests, as does pure Ir rate for the Ir-15Nb-ZNi was 1.2 x 10" s-I, about and its single-phase alloys (26). This result implies three orders of magnitude lower than that of the that the grain boundary in binary Ir-based two-

Phtinnm Me& &., 2002,46, (2) 79 phase alloys is still a weak point. The large differ- ature. On the other hand, the creep property of ence between the cohesion of the grain boundary the Ir-based alloys is remarkable. We tested a Ni- and of the bulk is likely to cause the grain bound- based superalloy, TMS-75,which has a rupture life ary to break before any dislocations form, as of 196 hours under 98 MPa in a tensile condition discussed by Hack et ul. (37). at 1150°C (38). Under compressive stress at An interpretation of the enhanced ductility in 1200”C, the sample buckled, and the strain could alloys prone to intergranular fracture (which hap- not be measured accurately. Another comparative pens in many intermetallic alloys and other alloy test indicated that the compressive creep strain systems) based on improved grain-boundary cohe- rates of an IrAl single-phase alloy with a B2 struc- sion caused by B segregation has been at least ture at 1100°C were between lo4 and 1 o-~ s-’ partially successful. The fracture behaviour and under 100 to 220 MPa (39). The strain rate of ItAl compression properties of the 11-15Nb alloy at 1100°C was one or two orders of magnitude doped with 80 to 2000 wppm B were investigated. larger than that of our alloys (lo-’ s-’) at 1500°C. The results showed that doping with B can change This shows that our alloys, with the f.c.c. and the fracture mode from intergranular (for the bina- L12 two-phase structure are more promising ry Ir-l5Nb alloy) to transgranular (for the B-doped materials because of their high creep resistance. alloys). However, we found that doping with B We also found that the creep life of Ir-Nb only shghtly improves the ductility of the alloy. We increased dramatically at 1650°C by addition of a also found that even though the fracture mode for third element, such as Ni. This shows that the Ir- Ir-15Nb can be changed from intergranular to based refractory superalloys may possibly be transgranular by adding Ni, W, Ta, Pt or Ni-Al, regarded as ultra-high temperature materials. there is no obvious improvement in compression Furthermore, the change in fracture mode on ductility by this change. The main reason is that the addition of Ni showed that there is a potential for Ir-15Nb alloy, despite having additions of various designing high-temperature Ir-based alloys with elements, stiU fractures by transgranular cleavage both htgh-temperature strength and good ductility at room temperature. This is due to apparently by addition of a suitable element. very strong and directed atomic bin- forces. To stabilise the structure of polycrystalline Ni- Acknowledgement based superalloys against high-temperature This work was conducted as part of the High-Temperature Materials 21 Project. We thank Dr X. H. Yu from Manitoba deformation, carbide formation is required. University, who did part of this work during her stay at NIMS. However, C is reported to be the main impurity We also thank Mr S. Nishikawa and Mr T. Maruko of Furuya causing polycrystalline Ir to crack in intergranular Metal Co.,Ltd. for the iridium. fracture (13). Our research has found harmful no References effects due to C additions on the properties of the 1 “International Tables of Selected Constants”, two-phase Ir-Nb refractory superalloy, even when Vol. 16, ‘Metals: Thermal, and Mechanical Data’, ed. the C additions were up to 2000 wppm. The com- S. Allatd, Pergamon, Oxford, 1969 pression ductility for C-free and C-doped alloys 2 “Metals Handbook”, 9th Edn., ASM, Metals Park, OH, 1979, Vol. 2 had almost the same value. 3 R. L. Fleisher, R D. Field, K. K. Denke and R J. Zabala, Metal Truns. A, 1990,2lA, 3063 Possibilities for Ir-Based 4 P. J. W, L. A. Cornish and M. J. Witcomb,]. A/&s Refractory Superalloys co,.qd, i99a,280,240 5 M. Bruemmer, J. Brimhall and C. H. Heneger, The high-temperature strength of Ir-based Mater. Res. SOC.Symp. Proc., 1990,194, pp. 257-262 refractory superalloys above 1200°C did not 6 A. M. Gyurko and J. M. Sanches, M&. Sci Eng., improve on addition of a third element. Compared 1993, A170, 169 7 C. Gandhi and M. F. Ashby, Ada Metal., 1979,27, in with the Nb-Si-Mo-W doy Figure 3, the 1565 strength of the Ir-based alloys above 1200°C is not 8 P. Pantilov and A. Yermakov, Platinum Metalr h., remarkable considering their high melang temper- 2001, 45, (4), 179

Phtinum Metalj Rev., 2002, 46, (2) 80 9 C. A. Brooks, J. H. Greenwood and J. L. Routbort, 29 G. L. Elickson, “Superalloys 1996”, TMS, J. Appl Ply.., 1968,39,2391 Warrendale, PA, 1996, pp. 35-44 10 C. A. Brooks, J. H. Greenwood and J. L. Routbort, 30 C. L. Ma, A. Kasama, Y. Tan, H. Tankaka, R J. IM. Met., 1970, 98,27 Tanaka, Y. Mishima and S. Hanada, Report of the 11 R W. Douglass and R I. Jaffee, Proc. ASTM, 1962, 123rd Committee on Heat-Resisting Materials and 62,627 Alloys, JSPS, Tokyo, 1999,40, (3), pp. 349-360 12 D. L. Rohr, L. E. Mutr and S. S. Hecker, Metall 31 W. F. Brown, H. Mindin and N. C. Ho, “Aerospace Tmns., 1979, 104 399 Structural Metals Handbook”, CIDAS/Purdue 13 J. R Handley, PkdnumMetOLr Rev., 1986,30, (l), 12 University, Weat Lafayette, IN, 1992, Vol. 5, p. 5502 14 S. P. Chen, Phil Mag. A, 1992,66, 1 32 Y. Yamabe-Mitarai, Y. Ro, T, Maruko and H. Harada, Intmetaficf, 1999, 7, 49 15 C. T. Liu, H. Inouye and A. C. Schaffhauser, Met& Trans. A, 1981,12A, 993 33 Y. Yamabe-Mitarai, Yuefeng Gu, Y. Ro, S. Nakazawa, T. Maruko and H. Harada, Sm Mafm., 16 A. N. Gubbi, E. P. George, E. K. Ohriner and R H. Zee, Metdl Mah. Tmns. A, 1997,28,2049 1999, 41, (3), 305 17 I. M. Wolff and G. Sauthoff, Metal Trans. A, 1996, 34 Y. Yamabe-Mitarai, S. Nakazawa and H. Harada, Sm 27,2642 Mater., 2000,43,1059 18 L. Heatherly and E. P. George, A& Muter., 2001,49, 35 Y. Yamabe, N. Honjo and M. Kikuch~,JIMIS-6, 289 Proc. Int. Symp. on Intermetallic Compounds, ed. 0. Izumi, Japan Inst. Metals, Sen& 1991, p. 821 19 Y. Ro, Y. Koizumi and H. Harada, Muter. Sci Eng., 1997, A223,59 36 J. D. Livingston and J. W. Cahn, Ada Metau., 1974, 22,495 20 Y. Yamabe, Y. Koizumi, H. Murakarm, Y.Ro, T. Maruko and H. Harada, Sm Muter., 1996,35, (2), 211 37 J. E. Hack, S. P. Chen and D. J. Srolovitz, Ada Me&’., 1989,37,1957 21 Y. Yamabe-Mtarai, Y. Ro, T. Maruko and H. Harada, Metdl Ma&. Trans. A, 1998,294 537 38 Y. Koizumi, T. Kobayashi, T. Kimwa, M. Osawa and H. Harada, ‘Waterials for Advanced Power 22 I. M. Wolff and P. J. W, Phtnum Metals Rm, 2000, Engineering 1998”, Forschungszentrum,Jiilich, pp. 44, (4), 158 1089-1098 23 “Binary Alloy Phase Diagrams”, 2nd Edn. Suppl., A. Chiba, X. G. and ed. T. B. Massalski, ASM, Materials Park, OH, 1992 39 T. Ono, Li S. Takahashi, Intemehakcs, 1998, 6, 35 24 Y. Yamabe-Mitarai, Y.Ro, T. Maruko, T. Yokokawa, and H. Harada, “Structural Intermetallics 1997, Authors TMS, Seven Springs, 1997, pp. 805-814 Dr Yoko Yamabe-Mitarai is a Senior Researcher at the National 25 Y. Yamabe-Mitarai, Y. Ro, S. Nakazawa, T. Maruko Institute for Materials Science in Tsukuba. Her main professional and H. Harada, Dcf.ct D&. Foam, 2001, 188-190, interests are in high temperature materials, applications of the 171 platinum group metals and intermetallics. 26 Yuefeng Gu, Y. Yamabe-Mtarai, Y. Ro and H. Dr Y. Gu is a Senior Researcherat the National Institute for Harada, Sm Muter., 1999,40, (ll), 1313 Materials Science in Tsukuba. His main professional interests are 27 Yuefeng Gu, Y. Yamabe-Mtarai, Y. Ro, T. in high temperature materials, applications of the platinum group Yokokawa and H. Harada, Sm Matm., 1998,39, (6), metals and in intermetallics. 723 Professor H. Harada is Project Director at the National Institute for 28 X H. Yu, Y. Yamabe-Mitarai and H. Harada, Scr Materials Science in Tsukuba. His main professional interests are Muter., 1999,41, (ll), 1153 in high temperature materials, especially nickel-based superalloys. The Chemistry of the Platinum Group Metals: PGM8 The eighth conference in this series takes place [email protected], Tel: +44 (0)20 7440 3322; at Southampton University, U.K, from 7th to 12th Fax: +44 (0)20 7734 1227; or from the website: July. Internationally-recognised speakers from the http://www.rsc.org/lap/confs/PGM8.hm. chemistry community will present their work on a wide range of platinum group metals chemistry. The Invitation to Students ~~ -~ main themes include: organometallic chemistry; Students attending the conference are invited to coordination and supramolecular chemistry; biolog- write an article of 300 words for Pkzfinum Metah ical and medicinal chemistry; surfaces, materials and Reyien, on one of the following a presentation, a crystal enginee-, photochemistty and electro- series of presentations or an interview with a respect- chemistry; catalysis and organic synthesis; and ed academic attending the conference. The winning theoretical chemistry and physical methods. article will be published in Ph’iinum Mehah lZeview. More information may be obtained from Ms P. Further details will be available later and at the Mohamed, Royal Society of Chemistry, E-mail: Ph’inum Metah Review desk at the conference.

Pfatinzm Metah h.,2002,46, (2) 81 2001 Nobel Prize in Chemistry TIMELY RECOGNITION FOR RHODIUM, RUTHENIUM AND OSMIUM-CATALYSED CHIRAL REACTIONS

William S. Knowles, a retired chemist from able to hydrogenate a-phenylacrylic acid to (+)- Monsanto Company, USA., and Professor Ryoji hydratropic acid in 15% ee. These results, along with Noyori, Nagoya University, Japan, shared one half reports by Homer, H. B. Kagan, J. D. Morrison and of the 2001 Nobel Prize for Chemistry for their B. Bosnich, prompted him to investigate the prop- work on chiral-catalysed hydrogenation reactions. er match between ligand, metal and substrate to Professor K. Barry Sharpless, Scripps Research enhance selectivity. After much systematic work Institute, U.S.A., received the other half of the prize Knowles and colleagues at Monsanto were able to for his work on chiralcatalysed oxidation reactions. make the rare amino acid, L-DOPA, in 100% yield In nature, molecules, such as hormones, DNA, with 95% ee, using [Rh((R,R)-DiPAMP)COD]BF4 antibodies and enzymes, display the property of (Fiie 1). Monsanto commercialised the process in chirality. Such molecules have the same chemical 1974. It is recognised as the first industrial process formula but different spatial orientations, ma& a using catalytic asymmetric synthesis. In the catalytic significant difference to their biological properties; chiial hydrogenation cycle, Rho becomes Rho for example, (R)-limonene smells of oranges, (S)- by oxidative addition of two H atoms. These H limonene smells of lemons. Chiral molecules in our atoms are later transferred to the double bond in nasal receptors can recognise these differences. the substrate, and the catalyst is regenerated. Biochemical reactions are sensitive to chirality and the activity of a drug depends on the nature of the Noyori’s Rh and Ru Catalysed Hydrogenations enantiomer. Many drugs are chiral, and it is essen- Ryoji Noyori has worked in the area of chiral tial that a drug is matched to the receptor in the cell catalysis from the mid-1960s and has sought to which it is directed. Mismatch will reduce the throughout his career to understand chiral hydro- potency of the drug and could be extremely ham- genation. The co-discovery of the ligand BINAP ful. (S)-(+)-Ibuprofen is an example of a drug (3) and its applications in chiral synthesis was of where only the (S) isomer is efficacious for anti- great help. Other powerful ligands are now avail- inflammatory use (1). able, but BINAP is still one of the most versatile in Enantioselective syntheses involve two major chiral synthesis. Noyori’s enantiopure isomerisa- approaches: resolution or asymmetric synthesis. In tion reaction of allylic amines to (R)-(-)-ðyl- resolution the mixture of chiral compounds is sep- (E)-citronellalenamine in the presence of [Rh-(-)- arated by physical means whereas in chiral BINAP(COD)]ClO, resulted in commercialisation syntheses the novel concept is that a very small of a multi-ton L-menthol process (Figure 2). amount of catalyst can drive chemical selectivity Noyori also used Rh-BINAP catalysts for the towards the desired isomer. As an active catalyst chiral hydrogenation of several a-(acy1amino)- can produce millions of molecules of optically pure acrylic acids or esters, and his work on BINAP- compound, the waste associated with racemate res- Ru(II) complexes is used for the enantioselective olution can be minimised. hydrogenation of a,P- and P,y-unsaturated carboxylic acids. The anti-inflammatory drug (S)-(+)- Knowles’ Rh Catalysed Chiral Hydrogenation naproxen (Figure 3) is synthesised in very high ee In the 1960s G. Wilkinson with J. A. Osbom (2) and yield using ~u(OAC)~((S)-(BINAP)]. synthesised the hydrogenation catalyst RhCl(Ph3P)3. A wide range of ketones has also been hydro- At the same time L. Homer and K. M. Mislow syn- genated with the aid of [RuX(arene)BINAP]X or thesised optically active phosphines. Knowles p&(BINAp)] (X = halogen) complexes. The anti- combined these two discoveries. Using a Rh com- bacterial agent levofloxacin is produced indusmally plex of (-)-methylpropylphenylphosphine he was this way. Ru(II) BINAP complexes are also used in

PbfiwmMetub &., 2002, 46, (2). 82-83 82 Me0 [Rh((R,R)-(DiPAMP)COD]BFt, -HO NHAc lobar H2, 25.C AcO ' AcO ' NHAc no ton 20.000, tof 1000 ti' yield;95.1aee L-DOPA Fig. I Industrial production of L-DOPA developed by Knowles using [Rh((R,R)-DiPAMP)COD]BF4'

Fig. 2 [Rh-(-)-BINAP(COD)]ClO4' 100.C

manufactureis'Curalysr the catalyst dotu.Jtom: of used L-menthol. in the ~NEt~h-~-)-~~Azlclo~-tof 440 h-' OH H. U Blaser. F. Spindler and M.Studer. bNE- bA 94% ee Appl Caral. A. Gen.. 2001. 221. (1-2). 119 ... allylamine ...enamine L- menthol

Fig. 3 (S)-(+)-Naproxen is c-0~ [Ru(OAC),((S)-BINAP)] COO" produced using Noyori k * catalyst [Ru(OAC)Z((S)-BINAP)] Me0 Me0 (S)-(+)-naproxen (92.1. yield; 97% ec)

cinchona alkaloid (0.13 equiv.) Fig. 4 Catalyst oso4 as used in Sharpless' chiral dihydroxylation production of chiral propanediol, and for an enan- resulted. Glycidol is used to produce P-blockers. tiopure azetidinone for carbapenem synthesis. The Sharpless epoxidation is also used industrially In recent years, Noyori has demonstrated to produce the pheromone (7R,8S)-disparlure. asymmetric hydrogen transfer reactions in simple Sharpless also introduced 'hgand accelerated ketones, such as acetophenone. Addtng ethylene- catalysis' where catalytic amounts of OsO4 and diamine in the presence of KOH in isopropanol cinchona alkaloid were used with a stoichiometric enhances the activity of the Ru catalysts. The syn- amount of co-oxidant, N-methylmorpholine N- thetically challenging substrates a,P-unsaturated oxide, to give asymmetric dihydroxylation (Figure 4). ketones have been reduced with hgh ees and The platinum metals catalysts used in these yields. The modified Ru BINAP complex, RuC12- reactions have contributed to their success and (xylylbinap)(diamine) transforms enone to chiral efficacy, and have formed an essential part of this ally1 alcohol with hgh turnover number. Noyori's most presugious award to Knowles, Noyori and work has been used in the pharmaceutical, agro- Sharpless (4). Organometallic chemistry now sits chemical, flavours and hechemical industries. Myin the main-stream of modem chemistry.

References Sharpless' Oxidation Chemistry 1 S. C. Stinson, Cbem. Eng. News, 2001, 79, (a),79; In the 1980s, Sharpless centred his work on the ibid., 2001, 79, (20), 45 chiral oxidation of allyfic alcohols to epoxides, use- 2 M. L. H. Green and W. P. Griffith, Phtinam Met& ful synthons for various organic compounds. Rey., 1998, 42, (4). 168 Transformation utilises Ti0tetraisopropoxide, 3 H. Nozaki, S. Moriuti, H. Takaya and R Noyori, Tetrahedron Lett., 1966,5239 t&-butylhydroperoxide, and enantiomerically pure 4 http://www.nobel.se ddkyltartrate. Choice of the appropriate tartrate THOMAS J. COLACOT hgand permits oxygen addition either to the top Thomas Colacot is Senior Development Associate for Chemicals & or bottom face of the ole&. Production methods Catalysts, Johnson Matthey, West Deptford, USA. His interests are high throughput screening of catalysts for organic reactions, supported for (R)-and (9-glycidol and methylglycidol have homogeneous catalysts and process development for new products.

Phtinum Metolr Rev., 2002, 46, (2) 83 ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES Tris(pyrazoly1)methanesulfonate (Tpms) - Palladium Nanoparticles Stabilised by A Versatile Alternative to Tris(pyrazoly1)borate in Polyfluorinated Chains Rhodium(1) Chemistry M. MORENO-MARAS, R PLEIXATS and s. VILLARROYA, Chem. w. UUI,D. SCHRAMM, w. PETERS, G. RHEINWALD and Cornman., 2002, (l), 6Ul H. m~,Ear.]. Inotg. Cbem., 2001, (6), 1415-1424 Pd nanoparticles can be prepared by reduction of TlTpms (Tpms = tris@yrazol-1-y1)methanesul- Naz(Pd2Ch) in the presence of compounds having fonate) reacts with m(LL)CI]z (LL = (C0)2, cod and long perfluorinated C chains (1) such as 1,5-bis(4,4'- nbd) to give TpmsRh(LL) complex. In solution, bis@e~uor00ayl)-l,4-pentadien-3~1ne.The reduction TpmsRh(C0)z (1) reversibly forms TpmsRh@-CO)3- is performed in MeOH at 60°C. (1) is the only RhTpms. TpmsRh(CO)(PR3) (PR3 = PPh3, PMe3, constituent of the stabilising layer. PCy3, P(Ph)2(PhS031C))were obtained by reaction of (1) with the correspondmg phosphanes. IR studies Influence of the Thermal Annealing on the indicate that Tpms is a weakly donating ligand. Electrical Resistivity and Thermal Diffusivity of Synthesis of Chloro(2-methylimidazole)ruthenium(lll) Pd:Ag Nanocomposites c. A. s. LIMA, R. OLIVA, G. CARDENAS T., E. N. SILVA and Complexes and Their Aqueous Solution Chemisby, and L. C. M. MIRANDA, &futm ha.,2001,51, (4), 357-362 the Crystal Structure of [2-MelmHl2[RuCl52-MeIm1 Nanocrystalline Pd:Ag powder was formed by sol- CANDEMON, Can.J. Chem., 2001,79, (lo), 1477-1482 vent evaporation of metal colloids. The obtained 2-Methylimidazole reacts with RuCl3 in HCI-HzO- Pd:Ag powder was then compressed into compacts of EtOH to give (2-MeImH)2~uCl@MeIrn)] and - 250 pthick, 10 mm diameter wafers, and annealed (2-MeImH) puCl@MeIm)~] (2-MeImH = protonat- at different temperatures for - 1 h. The electrical ed 2-methylimidazole). The ratio of the products resistivity exhibited a sharp exponential decrease with depends on the reacuon conditions employed. increasing annealing temperature I 400°C. At > 400"C, electrical resistivity remained almost constant. The dependence of thermal diffusivity on increasing ELECTROCHEMISTRY annealing temperature is complex. Temperature-Dependent Surface Electrochemistry on Pt Single Crystals in Alkaline Electrolyte: CHEMICAL COMPOUNDS Part 1: CO Oxidation Oxidation of [Pt"Cl2(ethane-l,2-diamine-N,N'- T. J. SCHMIDT, P. N. ROSS and N. M. MARKOVIC. J. Pbys. Chem. B, 2001,105,(48), 12082-12086 dicarboxylic Acid)] and Ligand Ring Closure in the The continuous electrooxidation of CO in 0.1 M Platinum(1V) Oxidation State KOH electrolyte (cob) on Pt(h4 at 275 and 333 K P. N. WONG, M. s. DAVIES and T. w. HAMBLEY, Aust. J. Chem., was investigated. Significant reaction rates were 2001,54, (5), 303-306 observed even in the potential region for H underpo- Oxidation of [Pt"Cl~(H~enda)]using HZOZgives rise tentid deposition (Hued). The cob oxidation on to a variety of products, including three crystal and Pt(h4 involves a Langmuit-Hinshelwood type reac- two isomeric forms. The major product is the ring tion between the adsorbed states of CO and 0H.d. closed [pt'"Clz(enda)] and if the solution is heated under reflux for 24 h, this is the only product. Electrochemical Properties of Pt-Modified Kinetics of Substitution of Aqua Ligands from cis- Nano-Honeycomb Diamond Electrodes K HONDA, M. YOSHIhiURA, T. N. RAO, D. A. TRYK, A. FUJISHIMA, Diaqua(ethylenediamine)platinum(ll) Perchlorate K. YASUI, Y. SAKAMOTO, K. NISHIO and H. MASUDA, by DL-Penicillamine in Aqueous Medium J. EIectounuL Chem., 2001,514,(1-2), 35-50 P. s. SENGUFTA, R SMHA and G. s. DE, Trunsition Met. Chem., B-doped nanoporous honeycomb diamond films 2001,26,(6), 63%643 modified with Pt nanoparticles (10-150 nm) were The kinetics of the interaction of DL-penidlamine studied with CV and electrochemical impedance spec- with [Pt(en)(HzO)Z]" were studied spectrophotomet- troscopy in acid solution. These electrodes showed rically at pH 4.0. The reaction proceeds via rapid high electroactivity for H adsorption and oxidation of outer-sphere-association complex (1) formation, fol- MeOH, EtOH and 2-propanol. The current density lowed by two slow steps. The first is the conversion (geometric basis) in the CV for MeOH oxidation at a of (1) into the inner-sphere complex, independent of Pt-modified porous film of pore diameter 400 nm and ltgand concentration, and the second is a slower pore depth 3 p was enhanced by a factor of 16 chelation step, where another aqua ltgand is replaced. compared to values obtained with a bulk Pt electrode.

PhfinamMetub Rev., 2002,46, (Z), 8688 84 An Electrochemical Impedance Study of the Photochromic Atropisomer Generation and Electrochemical Doping Process of Platinum Conformation Determination in a Ruthenium Phthalocyanine Microcrystals in Non-Aqueous Bis( bipyridine) Phosphonite y-Cyclodextrin Electrolytes System J. JIANG and A. KUCERNAK, J. Ekchand Cbem., 2001,514, D. HESEK, G. A. HEMBURY. M. G. B. DREW, V. V. BOROVKOV (1-2), 1-15 and~.~~ou~,J.h.&. Soc,2001,l23, (49), 1223Z12237 The electrochemical doping process (1) of Pt Irradiation of ra~-~u@py)~(PhP(OMe);)(CI)]Cl (1) phthalocyanine microcrystalline film (2) in MeCN at h > 460 nrn results in the photochromic genera- was studied using electrochemical impedance spec- tion of a new atropisomer and chirality inversion, via troscopy. At low doping levels of (l), the rate of the rotation of PhP(0Me)z around the Ru-P bond. The first electrochemical step is slow and determined by formation of a supramoleculai complex between (1) the conductivity of (2). Once (2) becomes conduc- and y-cydodextrin allows the stabilisation of the new tive, the electrochemical reaction is accelerated atropisomeric conformation. abruptly. Further increases in doping potential trigger another slow oxidation process. Ruthenium Polypyridine Complexes. On the Route to Biomimetic Assemblies as Models for the Formation of Palladium Complex at Carbon Paste Photosynthetic Reaction Center Surface in Chloride Solution as Studied by Cyclic H. DURR and S. BOSSMA", Acc. Ck.h~., 2001,34, (ll), Voltammetry 905-917 IC-H. LUBERT, M. GU?TMA" and L. BEER, CoUect. Cpcb. Photophysical data and the preparation of RI& Ck.Co-n., 2001,66, (lo), 1457-1472 complexes (1) from simple or more complicated The deposition and dissolution of Pd at a non-mod- bipyridine ligands, L, are reported. (1) with polyether ified C paste electrode was studied by CV in C1- bipyridines as building blocks, such as in Ru podates solutions Q 0.5 M KCl and pH 3-6).Pdo was deposit- and coronates, were shown to be among the most ed from Pd"CL]% solution by potential cycling from photostable Ru complexes. Two-shell biomimetic E 2 0 V (vs. Ag/AgCl) or application of positive model systems have more efficient electron transfer potentials or by potentiostatic treatment at E I0 V. than one-shell systems. Covalently linked assemblies [pdnC1.] was formed on applying anodic potentials. are more efficient in electron transfer. (41 Refs.)

PHOTOCONVERSION ELECT R 0 D EPO S ITI 0 N AN D S U R FACE Photochemistry of v-Hydrido-tetrakis(tertiary COATINGS ph0sphine)diplatinum Complexes Nanostructured Pt-Doped Tin Oxide Films: R. BOARETTO, S. SOSTERO and 0. TRAVERSO, J. Pbotocbem. Sol-Gel Preparation, Spectroscopic and Electrical Photobid A Cbem., 2001,144, (2-3), 101-106 The primary photoprocessesof trm-trum monohy- Characterization drido-bridged [(PEt3),HPt(p-H)PtH(PEt3)~][SPh,] F. MORAZZONI. C. CANEVALI, N. CHIODINf, C. MARI, R RUFFO, R. SCOITI. L. ARMELAO. E. TONDELLO, L. E. DEPERO and and &u~J-& dihydrido-bridged [(PEt&HPt(p- E. BONTEMF'I, Cbem. Ma&.., 2001,13, (11), 43554361 H2)Pt(PEt3)2][SPh4] are homolyses of their Pt-Pt Nanostructured (3-6 nm) (80 nm) of bonds. The Pt-Pt bond dissociation leads to cleavage thin films SnO, and Pt-doped SnOz (1) were obtained by a of Pt(p-H)Pt and Pt(p-Hz)Pt yieldmg the reactive sol-gel route using [Sn(OBu'),] and pt(acac)z] pre- complexes [(PEt3)~PtHzl and [(PEt3)zPtH(S)][SPb] cursors. Glancing incidence X-ray diffraction (S = solvent). measurements showed that Pto substituted for Snoin the lattice of the air annealed films. XPS Dendrimers Based on Ruthenium(l1) and established that the reaction of (1) with CO reduces Osmium(l1) Polypyridine Complexes and the Ptoto PtO at 373 K and to Pt(0) at 673 K. Approach of Using Complexes as Ligands and Complexes as Metals Computed Depth Profile Method of X-Ray S. SERRONI, S. CAMPAGNA, F. PUNTORIERO, C. DI PIETRO, Diffraction and Its Application to NiPd Films N. D. MCCLENAGHAN and F. LOISEAU, Cbm. SOC.Rm, 2001, H. WU. B. LI, W. ML40. X InJ and K TAO, Sw$ Cod. Tecbnol, 30, (6), 367-375 2002,149, (2-3), 198-205 The use of the 'complexes as hgands and complex- A method based on parallel beam XRD for profil- es as metals' synthetic strategy for the preparation of ing structure and phase distributions along with luminescent and redox-active Os(Il) and Ru(II) den- depth was used to characterise Ni/Pd thin films (1) hers is reviewed. The photophysical and redox and to obtain their phase depth profile. (1) were properties of such dendrimers containing 2,3-dpp annealed at 380°C for 30 min. In the data analysis (2,3-bis(2-pyridyl)pyrazine) bridges are included. procession, the non-negative least squares algorithm Alternative approaches to polypyridine dendrimers was employed to resolve the ill-posed inverse prob- are briefly discussed. (27 Refs.) lem that emerged in the solving procession.

Pldinnm Mekdr Rm, 2002,46, (2) a5 APPARATUS AND TECHNIQUE Electrochemical Evaluation of the Morphology Glucose Sensor Based on Au-Pt Black Electrode- and Enantioselectivity of Pt/Graphite Preparation of Functionally Different Sites on G. A. ATTARD, J. E. GII.LIES, C. A. HARRIS, D. J. JENKINS, P. JOHNSTON, M. A. PRICE, D. J. WATSON and P. B. WELLS, Electrode Surface Appl. Cai'al. A: Gen., 2001,222, (1-2), 39-5 1405 0. TAKEI. S. TOYAMA, M. SOMEYA, T. KUROKAWA, R USAMI, Cinchona-modifiedPt/graphite (1) is enantioselec- ICHORIKOSI and Y.Il(ARIyAMA, Ek&cb&try flpn.), 2001, tive for the hydrogenation of ethyl pyruvate to ethyl 69, (12), 956-958 lactate at 1 bar pressure and 293 K. CV was used to A glucose sensor has been developed based on a investigate surface morphology, alkaloid adsorption composite metal (Au and Pt) black electrode, fabri- and morphology change on sintering. CVs of (1) were cated by simultaneous codeposition of Au and Pt. interpreted using literature data for Pt single crystals. Enzyme was immobilised at Au sites on the electrode 0-induced surface reconstruction is lifted by reduc- surface, while enzymatic product was oxidised at Pt tion. Adsorption rates for cinchona alkaloids on (1) sites. a60moWo Au:Pd gave the largest response. are: cinchonine > cinchonidine > dihydrocinchoni- dine. Cinchonidine adsorption is site selective during Sputtered, Electroless, and Rolled uptake from the acidic electrolyte solution. Sintering Platinum-Ceramic Membranes increases particle size. S. TOSTI, L. BETTINALI, S. CASTELLI, F. SARTO, S. SCAGLIONE and V. VIOLANTE,]. Membrane Sci, 2002,196, (2), 241-249 Kinetics of Hydrogenation of 4-Chloro-2-nitrophenol Sputtering, electroless deposition and rolling of thin Catayzed by Pt/Carbon Catalyst Pd-Ag alloy films over ceramic porous tubes were s. B. HALLIGUDI ands.s. KHAIREJ Chem. Technol. Biotechnot!, used to produce Pd-ceramic composite membranes 2002,77, (l), 2528 for Hz separation and production. In the sputtered Hydrogenation of 4-chloro-2-nitrophenol (CNP) (0.5-5 p)and electroless (2.5-20 p)membranes, catalysed by 1% Pt/C at 300 K and 21.3 am Hz in a thermal cydulg of the hydrogenated metallic layer stirred pressure reactor gave 4-chloro-2-aminophenol produces membrane failures. Rolled (50-70 p) (CAP) exclusively. Pdly-AlZO3 is also active in membranes, however, have a complete Hz selectivity the hydrogenation; however, dechlorination of CNP and good chemical and physical stability. or CAP occurs forming 2-nitrophenol and 2- aminophenol, respectively. From an Arrhenius plot of In rate vs. 1000/Tfor the Pt/C reaction an appar- HETERO G EN EO US CATALYSIS ent activation energy of 22 kJ mol-I was estimated. The Effect of Metal Order on the Oxidation of a Hydrocarbon Mixture over Alumina-Supported Molecular Weight Effects in the Hydrogenation of Combined Platinum/Rhodium Catalysts Model Polystyrenes Using Platinum Supported on M. J. PATIERSON, D. E. ANGOVE and N. w. CANT, Appl. Catal. Wide-Pore Silica B: Envimn., 2001,35, (l),5>58 J. s. NESS, J. c. BRODIL, F. s. BATES, s. F. HAHN, D. A. HUCUL and The oxidation of a mixture of benzene, toluene, 1- M. A. HILLMYER, Mammokaks, 2002,35, (3), 602-609 hexene and isooctane in the absence and presence of A kinetic study of the hydrogenation of model CO was investigated over Pt/Al203 and Rh/AlzO, polystyrenes (PS) (molecular weight Mw = 1.5276 monolith catalysts arranged singly and in various 1:l kg mol-') using Pt/wide-pore SiOz catalyst was car- and 41 combinations. Physical mixtures of the Pt ded out. The initial rate of hydrogenation, r,, was and Rh are more active than the individual metals for found to be inversely proportional to the PS MW. complete removal of hydrocarbons when CO is pre- For MW I 102 kg mol-I, r, scaled with the number- sent. Without CO, Pt is more active than Rh for average degree of polymerisation, X,, to the -0.15 aromatic and isooocme oxidation. Removing CO on power. The two highest MW samples, 190 and 276 kg Rh facilitates oxidation of benzene and isooctane on mol-', had significantly slower initial rates of hydro- Pt. If Rh is put ahead of Pt in a sequential bed genation and did not follow this trend. arrangement, the effect is maximised. Effect of Transition Metals on Catalytic Adsorption and Decomposition of NO on Carbon Performance of Ru/Sepiolite Catalyst for and Carbon-Supported Catalysts Methanation of Carbon Dioxide J. ZAWADZKI and M. WI~NIEWSKI, Carbon, 2002, 40, (l), L. LUO, S. Ll andJ.GUO, Chin.]. Cai'd, 2002,23, (I), 85-87 119-124 The effects of adding Mo, Mn and Zr to Ru/sepio- The interactions of NO with C and C-supported lite (1) catalyst was investigated for methanation of catalysts have been studied by means FlTR spec- COz. The activity of (1) is closely associated with the troscopy. Direct decomposition of NO over electronic state on the Ru surface. Mo increases the C-supported catalysts (Pt, Cu) was investigated at active surface area, Ru dispersity, number of active 47-23 K NO conversion increased with increasing sites, and poisoning resistance. When TI674 K, the reaction temperature. Pt/C has a very hgh activity energy factor predominates and results in S (CHd)/S for NO decomposition, even in the absence of 02. (CO) decreasing. Otherwise steric factors dominate.

PhfinumMetah Rev., 2002, 46, (2) 86 H0 M 0 G EN EO US CATALYSIS Rhodium-Catalyzed Conjugate Addition of Aryl- Stability and Thermodynamics of the PtCh Type and Alkenyl-Stannanes to a,p-Unsaturated Catalyst for Activating Methane to Methanol: Carbonyl Compounds s. 01,M. MORO, H. ITO, Y. HONMA, s. MIYANO and Y. INOUE, A Computational Study Te@abedmn,2002,58, (l), 91-97 KUA, x. xu, R. A. PERIANA and w. A. GODDARD, J. Addition of aryl- or to O~unom~fa~,2002,21, (3), 511-525 alkenyl-trimethylstannanes The relative stability and reaction mechanism of a,P-unsaturated carbonyl compounds in the presence a catalytic amount of P(cod)(MeCN)z]BF, and Pt(NH&Clz and Pt@pym)Clz @pym = bipyrimidine) of HzO affords the conjugate addition products in good in concentrated H2SO4were studied. The mechanism was found to involve a series of steps beginning with yields. The use of HzO allowed the reaction to pro- GH activation to form an intermediate ion-pair ceed smoothly. The ary- or alkenyl-Rh complex, Pt(Il)-C& complex prior to a PtO-CH3 which is generated by the transmetallation from forming the organo-Sn compound, is proposed as the active complex. The calculated relative activation barriers for C-H activation are in good agreementwith exper- catalytic species. imentally observed H/D ratios. Subsequent oxidation to a Ptocomplex can occur with reduc- Catalyst Screening by Electrospray Ionization tion of SO,. Release of methyl bisulfate regenerates Tandem Mass Spectrometry: Hofmann Carbenes the Pt(II) catalyst. for Olefin Metathesis M. A. 0. VOLLAND, c. ADLHART, c. A. KIENER, P. CHEN and Microwave Promoted Palladium-Catalyzed P. HOFMA", Cbem. EIK I.,2001,7, (21), 4621432 Phenylation of Aroyl Chlorides and Sodium In sitrr synthesis of complexes combined with an Tetraphenylborate assay by electrospray ionisation tandem mass spec- J.-X WANG, B. WFJ, Y. HU,Z. LIU and Y. YANG, Jptb. cornrun.., trometry has been employed to investigate 2001,31, (24), 3885-3890 [{R~P(CH~),PR~-K~P}XRU=CHR~+in ring-opening Unsymmemcal ketones (1) can be synthesised from metathesis polymerisation. The most reactive com- sodium tetraphenylborate and aroyl chlorides using plex for acyclic olefin metathesis utilised chloride as Pd(pPh3)~Cl~as the catalyst under microwave iitadia- the anionic ligand X, had a small chelating angle (n = tion. KF was the best base for the reaction. This l), and reduced steric demand of the substituents R method is simple, fast and affords good yield (Cy vs. t-Bu). Variation of the carbene moiety CHR' (8748%) of (1). The results show that the synthesis had little influence. of (1) under microwave irradiation was 133 times faster than with conventional heating. Ring-Closing Metathesis, Kharasch Addition and Enol Ester Synthesis Catalysed by a Novel Class Synthetic Process Development and Scale Up of of Ruthenium(ll) Complexes Palladium-Catalyzed Alkoxycarbonylation of B. DE CLERCQ and F. VERPOORT, Tetrabedmi h#.,2001, Chloropyridines 42, (51), 89594963 R CRE~AZ,J. WASER and Y. BESSARD, 0%.Pmte~s Res. Dw., Ru Schiff base complexes were shown to be good 2001,5, (6), 572-574 catalysts for the Kharasch addition of CCL across Mono- or dicarbonylation of 2,3-dichloropyridines olehns. The yields depended on the catalyst and the in the presence of CO, EtOH and Pd(OAc)z/dppf or substrate used. Also, ring-closing metathesis of PdCL(ph3P)~/dppbcatalyst, gives selectively either diolehns was achieved. The best catalytic system was alkyl 3-chloropyridine-2-carboxylatesor dialkyl pyri- able to form tri- and tetrasubstituted double bond dine-2,3-dicarboxylates in good yields, depending on products. Stereoselective formation of enol esters or the reaction conditions. The process was used for the enynes in excellent yields was also achieved. scale up of the monoalkoxycarbonylation of 2,3- dichloro-5-(trifluoromethyI)pyridine, giving ethyl 3- Highly Efficient Use of NaOCl in the Ru-Catalysed chloro-5-(trifluoromethyl)pyridine-2-carboxylatewith Oxidation of Aliphatic Ethers to Esters high selectivity and yield. L. GONSALVI, I. W. C. E. ARENDS and R A. SHELDON, Chem. Commun., 2002, (3), 202-203 Palladium-Catalyzed Intramolecular adrylation Ru-catalysed bleach a-oxidation of ethers was of a-Amino Acid Esters achieved without the need of an excess of oxidant by 0. GAERTZEN and S. L. BUCHWALD, J. erg. Chm., 2002,67, careful pH control during the reaction. Fast complete (2), 465475 conversions (as short as 3 h) and high yields in esters A simple route to dihydroisoindole and tetrahy- (I95%) were obtained by efficient reoxidation of Ru droisoindole carboxylic acid derivatives involves the to the active catalytic species (Ru04) by optimal use use of Pd-catalysed intramolecular a-arylation of a- of the terminal oxidant, NaOCl. CH2ClZand EtOAc amino acid esters. The best results in the cyclisation were employed as solvents. Using a stoichiometric reactions used a slight excess of biphenyl-based, ster- amount of NaOCl, high substrate to catalyst ratios ically hindered phosphines together with Pdz(dba),. were possible in biphasic media at room temperature.

Pkdnzm Metah Rm, 2002, 46, (2) 87 FUEL CELLS The Influence of Surface Cleaning on the Stability Chemical and Electronic Effects of Ni in Rlwi and of Pd/GaAs Contacts P. MACHAt, A. KANTA and v. PE~INA,J. Muter. Sci.: Muter. Pt/Ru/Ni Alloy Nanoparticles in Methanol Ekctmn., 2001,12, (ll), 649-653 Electrooxidation The thermal stability of Pd/n’-GaAs ohmic con- K.-W. PARK, J.-H. CHOI, B.-K. KWON, S.-A. LEE, Y.-E. SUNG, tacts with Ge and Sn layers was studied at 300 and H.-Y. HA, S.-A. HONG, H. KIM and A. WIECKOWSKI, J. Phy. 400°C. The Pd/Ge contact structures have better Chem. B, 2002,106, (8), 1869-1877 thermal stability than Pd/Sn. The Ge(20 nm)/Pd(lO The electrooxidationof MeOH in H2SO4was stud- nm) structure has two optimum annealing tempera- ied using Pt, Pt/Ni (1:l and 3:1), Pt/Ru/Ni (541and tures, the higher one producing ohmic contacts with 6:3.5:0.5) and Pt/Ru (1:l) alloy nanoparticle catalysts, slightly lower contact resistivity and better stability. in relation to MeOH oxidation processes in a DMFC. Ge/Pd contact structures are based on solid phase Pt/Ni and Pt/Ru/Ni exhibited excellent catalytic regrowth mechanisms. The annealing mechanism is activities compared to pure Pt and Pt/Ru. completely different in the Sn/Pd structures. Etching the GaAs wafers before metal deposition in HzS04: Synthesis and Characterization of Osmium H202:HZO (1:8:500) followed by HC1:HzO (1:l) or in Carbonyl Cluster Compounds with Molecular concentrated HC1 gives the best thermal stability. Oxygen Electroreduction Capacity R. H. CASTELLANOS, A. L. OCAMPO, J. MOREIRA-ACOSTA and Characterization of Hydrous Ruthenium P. J. SEBASTIAN, Int. 1. Hydrogen Energy, 2001, 26, (12), Oxide/Carbon Nanocomposite Supercapacitors 1301-1306 Prepared by a Colloidal Method A cluster electrocatalyst (1) is based on Os&O). (2) H. KIM andB. N. POPOV,]. Po~erso#ms,2002,104, (I), 52-61 and Vulcan C; (2) was prepared by pyrolysis of Amorphous nanostructured composite electrodes Os3(CO)l2 in 1,2di&lorobenzene under Nz.The elec- based on RuOz (1) were loaded on C using a colloidal trocatalytic parameters of the 0 reduction reaction for method. The colloids were synthesised from solu- (1) were studied with a rotating disk electrode in 0.5 M tions containing various amounts of RuCl3.xH~0 H2S04 electrolyte. (1) used in a H2/02PWC cath- adjusted with NaHC03to pH 5. The electrochemical ode is reported to perform nearly as well as a Pt one. performance of the composite material depends on the annealing temperature and the particle size of (1). ELECTRICAL AND ELECTRONIC ENGINEERING MEDICAL USES Impacts of Postannealing Ambient Atmospheres Voltammetric Studies of the Effect of Cisplatin- on Pt/SrBi2.2Ta209/PtCapacitors Liposome on Hela Cells A.-D. LI, T. w, H.-Q. LING, D. wu, 2.-G. MU and N.-B. MING, Y.-X.CI, Q. ZHAI, S. WANG, W.-B. CHANG, C.-Y. ZHANG, H. hiA, J. Muter. Ref., 2001,16, (12), 35263535 D.-Y. CHEN, M.-Z. ZHAOand s.-w.HU, Tuhntu, 2001,55, (4), Films of SrBizTa20p (SBT) were formed on 69M98 Pt/TiOZ/SiO2/Si substrates at 750°C in 02.SBT film The effect of cisplatin-liposome on HeLa cells was capacitors were postannealed in Ar (Nz) at 356750°C studied using a voltammetric method (1). The peak and then reannealed in OZ at 750°C. Composition current decreased with both cisplatin-liposome con- analyses show that Ar- or Nz-annealing at 750°C leads centration and increasing treatment time. The to Bi evaporation and 0 loss. After 550°C 100% Ar decrease of peak current was in accordance with dam- or Nz postannealing, the remnant polarisation age to the nucleus and loss of mitochondrial decreases and the coercive field increases significant- membrane potential. (1) may be a useful way to study ly. The subsequent 02 annealing can only partly the electron-transfer mechanism in drug-treated cells. restore the SBT phase; the ferroelectric properties cannot be rejuvenated. Study on the Microstructure and the Phase Composition of Two Precious Metal Dental Preparation of Pt-PtO, Thin Films as Electrode for Casting Alloys Memory Capacitors x ZHAO, x LAN and z. SHANG, Preciour Met. (Chin.),2001, K KURIBAYASHI and s. KITAMURA, Thin Solid Film, 2001, 22, (4), 13-16 400, (1-2), 160-164 Dental alloys Ag-30Au-15Pd-llCu (1) and Ag- Pt-PtO, thin films (1) were deposited on Si(100) at 1 lAu-23Pd-9Cu (2) in the as-cast conditions consist of substrate temperatures of 36700°C by reactive r.f. two phases: Ag-Pd-rich f.c.c. solid solution (a,) and magnetron sputtering with a Pt target. (1) mainly con- Cu-rich f.c.c. solid solution (012). Au is evenly distrib- sisted of amorphous PtO and Pt30, (or Pt203) at < uted throughout both phases. The as-cast micro- 400°C. The amorphous Pt in (1) increased as deposi- structure of (1) consists of equiaxed gains of aland tion temperature increased to 600°C. Pure Pt fhsof a small amount of lamellar eutectic structure (a, + (1 11) orientation were formed at 700°C. The electr- a2).(2) consists mainly of lamellar eutectic structure cal resistivity of (1) was of the order 10-’-10-5 C2 cm. (a,+ a2)and a small amount of (al).

Phdnum Met& Rev., 2002, 46, (2) 88 NEW PATENTS ELECTROCHEMISTRY APPARATUS AND TECHNIQUE Electrode for Water Purification Water Denitrification H. E. ODONNELL et d US.&pL 2001 /0,042,682 SUD CHEMIE MT Sfl Eampean&pL 1,178,017 An electrode (1) for HzO purification, includes an Nitrates are removed from H20 by making it flow intermediate layer and a protective pre-coat layer over a transition metal catalyst, preferably 0.01-5 (containing a Pt group metal). The former decreases wt.% Pd, on a porous carrier which can activate leakage of current from an electrolyte solution direct- applied Hz, forming metallic hydrides (1). Denitr- ly to the latter. A method to produce (1) is claimed. fying bacteria, which can survive in the presence of (1) has a longer service life and good current yield. Hz, adhere to (1). COZis used to adjust the pH to 4.57.8. 0,is fed into the tank to convert nitrites. ELECTRODEPOSITION AND SURFACE Detecting Nitric Oxide COATINGS UNIV DUKE U.S. Patent 6,280,604 Chemical Vapour Deposition of Ruthenium Films An electrode (1) for rapid in vim detection of NO in APPLIED MATERIALS INC Ewupean&pL 1,178,131 biological samples, such as blood, urine, synovial Thin Ru films are deposited on a substrate by liquid fluid, lymph, surgical dramage fluid, etc., has a surface source CVD using bis(ethylcyclopentadienyl)Ru, made of material containing Ru and at least one oxide which is at room temperature. Deposition occurs in of Ru which complexes with NO when exposed to a the kinetic-limited temperature regime. The bis(ethy1- NO-containing fluid. (1) exhibits maximal NO cyclopentadieny1)Ru is vaporised at 100-300°C to response after pre-conditioning. Direct response to form a CVD source material gas (1). Deposition onto NO has been observed for the Ru electrodes at the substrate is performed in a reaction chamber potentials I +675 mV vs. Ag/AgCl,while the para- using (1) and 0 source reactant gas at - 10&500"C. doxical response of the Ru electrodes to NO occurs at potentials > +675 mV vs. Ag/AgCl. High-Purity Bis(ethylcyclopentadieny1)ruthenium TANAKA KIKINZOKU KOGYO KK wWkJ&pL 01/42,261 Material for a Deflecting Colour Filter High purity bis(ethy1cyclopentadienyI)Ru is pro- NATL INST ADV IND SCI TECHNOL duced by hydrogenating bis(acetylcyclopentadieny1)- Japane~e&pL 2001 /147,326 Ru (1) without causing corrosion. (1) is prepared by Material for a deflecting colour filter comprises a reacting bis(cyclopentadieny1)Ru (2) with acetic anhy- planar organic metal complex of Pd, Pt or Ni. Lght dride and H3P04 as catalyst, while (2) is prepared by transmittance can be changed, depending on the reacting cyclopentadiene with Ru chloride and Zn viewing angle. By gradually increasing the angle of powder. CVD formation of thin Ru or Ru compound incidence, light transmittance is decreased. For light films is also claimed for use in capacitors for ICs. hitting vertically to the film surface, transmittance is - 90%. Light transmittance at a spedc wavelength Fabrication of X-Ray Masks depends on the incident angle of the hght. INT BUSINESS MACHINES cow U.S.Patent 6,287,434 An apparatus, for electroplating one side of a sub- Gas Sensor to Measure NOx Concentration strate for use in fabricating X-ray masks, has an anode NGK SPARK PLUG CO LTD ]apanese AppL2001/153,834 positioned in an electrolyte. A Pt inhibitor electrode (1) A gas sensor, for accurate measurement of NOx is attached to the inner surface of the dielectric plate concentrations in ICES, motor vehicles, aeroplanes of the cathode. A Si substrate is attached to the inner and boilers, comprises an exterior electrode and an surface of the cathode. (1) allows electroplating on internal electrode formed on an 0 ion conducting one side of the substrate using a rack plating system. layer. The internal electrode comprises (ii wt.O/o): 0.1-25 Pd, 0.1-30 Au and remainder Pt An 0 pump Palladium Plating Solution cell controls the 0 concentration in the sensor void. KOJIMA KAGAKU YAKUHIN KK 0 pumping capability is maintained for a long time. Japanese AppL 2001/192,885 A Pd plating solution (l), for decorative and elec- Ozone Generator sonic uses, comprises (ii g P, as metal equiv. amount): KI SAN JET PLASMA CO LTD banAppL 2001/007,966 0.14soluble Pd salt, 0.01-10 of pyridine carboxylic An 03generator using low activity plasma ion dis- acid (Pa)and/or 0.002-1 of soluble salt of Fe, Zn, charge effects to produce purified 03has a discharge 'l3, Se or Te, 0.005-10 of amine group derivative of plate for low activity plasma ions. The discharge plate PCA, and 0.001-1.2 of aldehyde benzoic acid deriva- is prepared from a composite powder of Zr, Y, Ti, Al tive, and anionic or amphoteric group surfactant. (1) oxides and balance SiN. SiOzglass is added to form has stable properties and corrosion resistance and and sinter the synthetic ceramic sheets. Molten metal the Pd film has high purity, a mirror-like gloss and between the sheets contains 1.8-2.2 wt.% of Mo and plasticity. Crack generation is suppressed. 0.3-0.7 wt.% of Pt group elements.

Pkatinum Mehh Rm, 2002,46, (2), 89-91 89 HETE R 0 G EN EO US CATALYSIS Hydrogenation Catalyst for Anthraquinones ASAHI KASEI KOGYO KK Japanese AppL 2001/170,485 Production of Epoxycyclododecane Compound A highly active hydrogenation catalyst (1) for UBE IND LTD Eumpean AppL 1,125,934 anthraquinones is formed from a Pd component on An epoxycydododecane compound (1) for produc- support particles of diameter < 200 pn and bulk ing the resin component for paints and adhesives, is density 0.7-1.5 g ml The support is a SOz-based produced by hydrogenating 1,2-epoxy-5,9-cyclodo- '. composition, with Alz03 and MgO in atomic ratio decadiene with HZ at 0.8-9 MPa pressure, in the MgAI > 1/2. The Pd distribution is controlled presence of a long-life catalyst of Pt supported on and has surface area of 40-300 mz g-'. (1) is almost activated C, Alz03,SO,, etc. (1) are produced in high free from Pd loss and has excellent durability. The yield at a high reaction rate. (1) can also be used to support has superior abrasion resistance. produce a lactam compound which is an intermediate for polyamide 12 and polyesters, useful for producing synthetic resins and fibres. Hydrogenation of Carbonyl Compounds BASF AG GennaneL 1/00/09,817 Purification of Naphthalenic Carboxylic Acid A catalyst (1) used in hydrogenation of carbonyl compounds to alcohols at relatively low temperature BP cow NORTH AMERICA mc WodiAPp/; 01/56,967 (< 140°C) contains (in part wt.): 0.0001-0.5 Re, A naphthalenic carboxylic acid, especially 2,6-naph- 0.00014.5 Pt and 0-0.25 of Ru, Zn, Cu, Au, thalene dicarboxylic acid (2,6-NDA), is purified by Ag, Ni, Fe, Mn, Cr, Mo, W and V on activated C, sub- contacting with a purification solvent in the presence jected to non-oxidative pretreatment. (1) has higher of Hz and a Group VIII catalyst, such as Ru/C, at total selectivity for the hydrogenation of carbonyl 52&575"F. 2,6-NDA is useful as a monomer in the compounds to alcohols, without ether formation. production of dimethyl-2,6-naphthalene dicarboxy- late-based polymers for use in films and food and Catalyst Preparation by Chemical Vapour Deposition beverage containers. Reduced amounts of organic HYOSUNG T & c co LTD Korean Appl 2001 /046,425 impurities are obtained in the purified acid. A catalyst for the dehydration of hydrocarbons comprises (in wt.Yo): 0.1-2.0 Pt, 0.0-1.0 K, 0.1-1.0 Palladium Hydrogenation Catalyst Sn, and 0.0-1 .O Eu or Yb on an A1203-Alborate sup- SUED-CHEMIE AG WodillppL 01/58,590 port. The support is prepared by mixing Al(N03)~ A catalyst for hydrogenation of unsaturated hydro- and H3BO3 with NH3 solution. The support has pore carbons, such as selective hydrogenation of diolefins volume 0.4-1.0 cc g-', mean pore size 20&3000 A to monoolefins or of acetylenes to olefins, contains a and surface area 25-1 50 mzg-'. CVD impregnates the catalytically-effectiveamount of Pd and optionally Ag catalyst active species onto the support by spray on a support. The support comprises a moulding of injection of the chemicals in the reactor at 800°C. tdlobal cross-section with holes through the lobes. Catalysts on a ailobal support have higher activiq and selectivity than usual and can be used at gas H0 M0 G EN EO US CATALYSIS hourly spatial velocities of - 12,00&15,000, com- Carbonylation of Unsaturated Compounds pared with only 3000-8000 when beads, tablets or SHELL INT RES MIJ BV WorM &pL 01 /68,583 extrudates are used. The pressure drop is also lower. Carbonylation of 3C or more ethylenically unsaturated compounds used in the preparation of Production of Epoxide detergents, involves reacting CO and hydroxyl- ARC0 CHEM TECHNOL LP WorMAppL 01/62,380 group-containing compounds in the presence of a An epoxide, such as propylene oxide, is produced catalyst system (1) in an aprotic solvent. (1) compris- by reacting an olefin, HZ and 02in the presence of a es a source of Pd cations, bidentate diphosphine and catalyst of Ti zeolite, Pd and Au promoter. The Ti a source of anions derived from an acid having pK, zeolite is impregnated with a solution of a Pd com- < 3 at 18°C in an aqueous solution. High regioselec- pound and Au compound in a solvent, followed by tivity towards a linear product is obtained. solvent removal and diymg. Adding the Au promoter increases productivity and selectivity to epoxide. Manufacture of Cyclic Polyether Compounds KAGAKU GIJUTSU SHINKO JIGYODAN Jet Engine Catalytic Converter Japanese AppL 2001/199,987 P. BOURGON Canadian Appr 2,299,746 The manufacture of a cyclic polyether compound A catalytic converter for a jet engine is built into the used as starting material for the synthesis of natural engine and uses Pt anodised onto all the metal parts substances, such as ciguatoxin, comprises cross-cou- of the combustion chamber and turbine, except for pling an alkyl borane and cyclic enol phosphate, in any bearings used in these stages. The anodised Pt the presence of a basic aqueous solution containing a catalyses some of the &/fuel mixture in the engine. Pd(0) compound which has a phosphine ligand, The engine becomes more responsive, smoother, as the catalyst. The method can be used to manufac- gains more thrust across the power band, and lasts ture cyclic polyether product, which is suitable longer as there are fewer contaminating byproducts. for the synthesis of cyclic compounds larger than six- Fuel economy is increased. membered rings.

Pkafinwv Metals Rev., 2002, 46, (2) 90 FUEL CELLS ELECTRICAL AND ELECTRONIC Electrode Catalyst for Fuel Cells ENGINEERING NE CHEMCAT COW Eunpan AppL 1,156,543 Ceramic Capacitor Electrode-Forming Paste A h@ly active electrode catalyst (1) for a fuel cell NGK INSULATORS LTD Eun@an&I. 1,178,493 electrode, such as for SPEFCs, comprises 20-70 A paste to form a ceramic capacitor electrode con- wt.% Pt on conductive C, which has 0 chemically tains (in wt.?h): 10-14 of an organic vehicle and bonded to it, at an atomic ratio of 0.7-3 to the Pt. 8690 of Pt powder. The Pt powder contains pow- Also claimed is an alloy catalyst prepared by deposit- ders of spherical, flaky and indefinitely-shaped ing a metal component which alloys with Pt in a Pt particles. The electrode layer film formed with the precursor, which is then reduced to form the alloy. paste has density of 1 8W?, surface roughness of (1) is also used in a membrane electrode assembly. 0.44.6 pn and adhesion strength of 2 2 kg. There is improved adhesion to the dielectric layer and small Proton Conducting Polymer Membrane through-holes can be made in the electrode layer. JOHNSON MAmYPLC WdAppL 01/69,706 A proton conducting polymer membrane of thick- Oxidation Stabilisation of Semicondutors ness < 100 p,for a membrane electrode assembly MICRON TECHNOLOGY INC U.S. P&t 6,291,364 (MEA) and a fuel cell, comprises channels and/or A catalyst matrix is used in high pressure, high tem- capillaries (< 50 p)arranged in the z-direction of perature oxidation in Nz0 of a gate dielectric layer or the membrane. Tow or yarn or Pt or Nb wires are cell dielectric layer on Si to stabilise the semiconduc- placed or inserted into the membrane during its for- tor. Oxidation at 5-250 atm pressure and 600-750°C mation, The tow or yarn is subsequently removed to occurs in the presence of a catalyst selected from Pt, form channels; and/or the Pt or Nb is left in J-& to Ir, Pd, Rh, Pb, Ni or Ag and their oxides. The form capillaries. The membrane allows the supply of method and apparatus prevent N20 from becoming additional HzO to the system to sustain H20 elec- supercritical; temperature and pressure spikes are trolysis during cell reversal in a MEA or fuel cell. The prevented. The exposure of semiconducting wafers hfEA exhibits improved performance at low reactant to high temperature is minimised and undesirable gas pressure. diffusion prevented. Generation of a Hydrogen-Rich Fuel Gas Stream Chip-Type Multilayer Electronic Part UOP LLC U.S. Patent 6,299,995 TDK COW U.S. Patent 6,342,732 A H-rich fuel gas stream (1) is generated by passing A chip-type laminated electronic part, for a multi- a fuel stream over an 0-contahhg preferential oxi- layered ceramic capacitor, comprises internal metal dation catalyst at 70-160°C. The catalyst comprises electrodes and terminal electrodes (l), which contain Ru metal dispersed on an A1203 carrier with apparent Ag and Pd as their main ingredients (&Pd = 73 to bulk density of 0.2-0.4 g cm-3 and high porosity 3:7 wt. ratio). (1) also contain 0.1-1.0 wt% B. (1) are (average pore size 800-1500 A). (1) containing < 50 prevented from oxidising when the electrical part is ppm of CO is passed to a fuel cell for electric power joined to the substrate, so that improved electtical generation for a motor vehicle. CO is converted and bonding to the internal electrodes is attained. high selectivity to COZis maintained. High Output Piezoelectric Ceramic Platinum-Ruthenium Alloy Electrodes for Fuel Cells NEC HYOGO LTD J+anese Appl. 2001 /146,470 ISHIFUKU KINZOKU KOGYO KK A high output piezoelectric ceramic composition ]+aneseAppl 2001/205,086 for oscillators, piezoelectric actuators, and ultrasonic Catalysts loaded with Pt-Ru alloys, for fuel cell elec- motors, consists of ternary composite oxide system trodes, are prepared by reducing Pt ammine type of Pb-Mn-Sb, Pb-Zr, and Pb-Ti. Piezoelecmc ceram- complexes and Ru salts (not containing Cl) to a state ics with a hgh exothermic threshold of oscillating where Ru bonds to C powder. Very fine Pt-Ru velocity can be manufactured by sintering at low alloy particles are dispersed uniformly on the C temperature together with Ag-Pd electrodes. powder support, and poisoning by CO is inhibited. Reflecting Film for Liquid Crystal Display Elements Selective Oxidation Catalyst for Fuel Cell FURIJYA KINZOKU KK [email protected] @I. 2001 /226,765 MATjUSHITA ELEcTRlC WORKS LTD A heat-resistant reflecting film (1) for a LCD ele- J@anueAPpl2001/212,458 ment, consists of Ag alloy material containing 0.1-3.0 A selective oxidation catalyst (1) used for fuel cells, wt.% Pd. Also claimed are: a laminate of one or more particularly SPFCs, contains Ru and Pt on a porous layers of (1); a LCD element using the laminate; and carrier, such as a-Alz03, at a Ru:Pt weight ratio of a portable device which can use the LCD element as 0.1-9.5. The Ru and/or Pt are localised in a layer 4 reflector, reflecting film or bddmg glass material. (1) 100 punder the outer surface of the porous carrier. has improved heat-resistance, reliability and optical (1) selectively oxidises CO in a reformed gas, at low reflecting rate. (1) has enhanced bondmg with the temperature, by an 02-contahhg gas. Improved fuel substrate layer, glass substrate or resin substrate. and electricity generation efficiencies are obtained. Brightness is improved, due to reduced optical loss.

Phtinum Me& Rcv., 2002,46, (2) 91 5% Pd/C - Precise but Vague For liquid phase batch hydrogenations catalysed metal distribution. At the other extreme the Pd can by supported platinum group metals (pgms), the be evenly distributed throughout the particle: uni- most frequently used combination of metal and form distribution. Somewhere between these two support is 5% palladium/carbon (Pd/C) paste (1). extremes is the intermediate distribution. It does Catalytic hydrogenation is very widely used in not follow that catalysts with eggshell distributions industrial organic chemistry and includes reactions are invariably the most active. For example: as diverse as carbon-carbon multiple bond reduction; aromatic ring saturation; reduction of carbonyl 5'1. w/c groups to alcohols or hydrocarbons; ocoo"150%. 100tur H2- oc -. reduction of nitro and nitroso com- Pd distribution Eggshell Intermediate Uniform pounds,pounds, iminesimines andand nitrilesnitriles toto amines;amines; reductivereductive aminations/alkylations;amhadons/alkylations; % Conversion after 1 hour 10 60 a5 hydrogenolysis, for example, hydro- dehdogenation, removal of protecting groups; etc. At higher pressures, catalysts with the same For some pgm catalysed hydrogenations, Pd total metal loading but deeper metal locations tend would not necessarily be the metal of choice. For to be more active than those with eggshell distrib- example, the reduction of aliphatic aldehydes to utions because of their &her metal dispersions. primary alcohols is best performed with a rutheni- In some extreme cases, certain 5% Pd/C paste um catalyst (2). formulations have no catalytic activity whatsoever However, in practice, about three quarters of all and others can show a wide variation in reaction liquid phase batch hydrogenations which use a het- rate. For the reaction below, performed in an aka- erogeneous pgm catalyst are in fact performed line methanol solvent, the following relative with 5% Pd/C paste. Some of the variables reaction rates have been observed: exploited in the manufacture of any given 5% Pd/C paste include: source of the acti- fi vated carbon support; pretreatment (if any) of the support; the nature of the soluble PdPd saltsalt used used to to impregnate impregnate the the support; support; Types of 5% Pd/C paste catalyst 1 2 3 4 5 thethe nature nature and and formform ofof thethe reducingreducing Relative reaction rate 0 38 10 7 4 agent used to produce the Pd metal crystallites on the support; pH and temperature of To achieve reproducible results, it is absolutely both the Pd salt impregnation and reduction steps; essential therefore to ensure that the same catalyst rate and order of addition of the reagents; efficien- formulation, identified by the manufacturer's code, cy of the final washing/filtration step; etc. be used throughout any evaluation programme. Clearly a vast number of combinations of the D. E. GROVE above is possible, all capable of yielding an end References product that could accurately be described as '5% 1 D. E. Grove, P&nwnMetalsReu., 2002,46, (l), 48 Pd/C paste' with each being assigned some unique 2 See for example, "The Catalyst Technical identification code by the manufacturer. Handbook", Johnson Matthey, 2001 One of the key parameters that can be controlled is the location of the Pd on the support. At David E. Grove is a former Marketing Manager in Johnson Matthey Catalysts and Chemicals Division. His many years experience of one extreme the Pd can be entirely located at the the platinum group metals catalyst industry gives him a unique surface of the individual carbon particle: eggshell insight into typical user problems.

Phz'inum Metals Rev., 2002, 46, (Z), 92 92