15 The noble metals Peter Thornton Department of Chemistry, Queen Mary andWestfield College, Mile End Road, London, UK E1 4NS 1 Introduction As with previous contributors to this series, this year’s survey concentrates on preparative and structural chemistry, with fewer reports on solution work, kinetic studies, and catalytic and biological activity or papers without experimental work. There is a concentration on work which may not appear in other sections and on results that will be of interest to readers beyond the specialist circle directly addressed by the original authors.Much excellent work has been excluded for space reasons in order to describe the best work adequately. Reviews and general interest articles The latest volume of Inorganic Syntheses1 contains many valuable contributions, including ligands for water soluble organometallics, convenient quick syntheses for cisplatin and other familiar Pt, Ru, Ag and Au complexes and syntheses for [M 3 (CO) 11 ]2~ (M\Ru, Os) and other carbonyl clusters. A collection of papers on nanoparticles includes many accounts of noble metals.2 One of these papers specially deals with bimetallic nanoparticles containing Pd, Pt and Au and their use in homogeneous catalysis.3 Many good reviews of general interest have appeared.One covers activities from 1985 to 1995 in Ag and Au chemistry with Group 15, 16 and 17 donors.4 The formation and structure of polymers and dendrimers containing Au and Pt are reviewed.5 Other series of co-ordination compounds reviewed include boryl complexes6 and chiral phosphine complexes, with emphasis on catalysis and 2-D NMR studies.7 Among many reviews on organometallic chemistry, general readers will find interesting matter in those on photochemistry in a special issue of Journal of Organometallic Chemistry,8 on allenylidene [:C–– C––CR 2 ] and cumulenylidene [other CnR 2 ] complexes,9 the use of electrospray mass spectrometry in organometallic chemistry, 10 the use of organometallics in the synthesis of biologically significant molecules (the field is dubbed ‘bioorganometallic chemistry’),11 and organometallic reactions in the solid state.12 Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 2132 Ruthenium Simple compounds Ruthenium metal can be formed in single walled carbon nanotubes by the H 2 reduction of deposited RuCl 3 .13 The a-form of RuCl 3 has become another of the few lattices to support intercalative redox polymerization, in this case of aniline.14 High pressure converts the rutile form of RuO 2 to a new cubic phase, whose short O–O distance explains the very low compressibility which is comparable to that of diamond.15 Co-ordination compounds EXAFS shows aqueous Ru4` is indeed tetranuclear, with an adamantyl Ru 4 O 6 4` cage structure rather than rectangular with OH bridges.16 The first aqua dihydrogen complex, [Ru(H 2 O) 5 (H 2 )]2`, has been identified by 1H and 17O NMR spectroscopy, from the reaction between [Ru(H 2 O) 6 ]2` and H 2 under pressure.17 Tetrachlorocatechol (H 2 L) reacts with [Ru 2 (O 2 CCH 3 ) 4 Cl] to give [Ru 2 L 4 ]3~, the first structurally characterised unbridged Ru–Ru bonded complex; this can be oxidised by Ag` to the Ru 2 6` analogue.18 Synthetic and magnetochemical studies of [NBu 4 ]- [MRu(ox) 3 ] show these are isostructural with the known Cr complexes; for M \Fe, Cu the complexes are ferrimagnetic, but whenM\Mn the material is ferromagnetic.It is asserted that simple orbital rules for magnetic interactions are not as valid for Ru as for 3d metals.19 Ru is found to follow the example of Rh in forming IR-detectableN 2 complexes such as [Ru(N 2 ) 2 ]2` or [Ru(N 2 ) 2 (CO)n]2` (n\1 or 2) on zeolite DAY.20 The oxidation of Ru(II) ammines by Br 2 proceeds by outer sphere one-electron transfer to Br 2 to make reactive [Br 2 ]~, inhibition by Br~ being attributed to the formation of inert [Br 3 ]~.21 The observation that the antitumor active [RuCl 4 (Him) 2 ]2~ loses its imidazoles as well as its chlorides in the presence of histidine or glutathione suggests extra subtleties in the interpretation of its biological activity.22a In a classic study, a combination of X-ray crystallographic and NMR methods shows the all cis-[RuCl 2 (dmso)(L)(1,2- Me 2 Him)] (L\3,5-dimethylpyridine) has the same mixture of conformers in the solid state as in the solution equilibrium.22b [Ru(Me 3 [9]aneN 3 )Cl 3 ] has been used to prepare various g5:g6 half sandwich compounds.23 Polyaminopolycarboxylate complexes of Ru have been reviewed with emphasis on substitution mechanisms and applications to electrocatalysis.24a 1H NMR spectroscopic evidence suggests pyrimidine co-ordinates through a C–– N bond in solution in [Ru(hedta)(pym)(H 2 O)] ~.24b The reaction of P(CH 2 OH) 3 with hydrated RuCl 3 to make a water-soluble catalyst gave elimination of HCHO to form [RuMP(CH 2 OH) 3N2MP(CH 2 OH) 2 HN2 Cl 2 ].25 A new convenient synthesis of [RuHX(dppm) 2 ] (X\H, Cl) from [RuCl 2 (dppm) 2 ] is reported.26 [Ru(H) 2 (dmpe) 2 ] is converted by N 2 O into [RuH(OH)(dmpe) 2 ], whose reactions include the formation of carboxylate complexes by reaction with 4- CH 3 C 6 H 4 CHO or (CF 3 ) 2 CO.27 [RuHX(dmpe) 2 ] (X\Cl, OH) may be used to make low oxidation state amide complexes by reaction with NH 3 and NaNH 2 to give [RuH(NH 2 )(dmpe) 2 ].28 The co-ordination chemistry of 2,6-(Ph 2 PCH 2 ) 2 C 5 H 3 N(pnp) Annu. Rep.Prog.Chem., Sect. A, 1999, 95, 213–238 214has been extended by the synthesis of the meridional complexes [RuHX(PPh 3 )(pnp)] (X\H, Cl, O 2 CCH 3 ).29 The hydrazine derivative Ph 2 PNMeNMePPh 2 (L) reacts with [RuCl 2 (cod)]x and NaOMeto give [RuH 2 L 2 ], whose wide reactivity was studied, e.g. the reaction with S 8 to give [RuL 2 (S 2 )] with a slightly short S–S bond of 205 pm.30 The vitality of research into Ru stibine complexes has been confirmed by mass spectral evidence that the compound assigned the formula [RuCl 2 (SbPh 3 ) 3 ] is most probably [RuCl 2 (SbPh 3 ) 4 ] and by the benchmark crystal structure determination for [Ru(NO)Cl 3 (SbPh 3 ) 2 ].31 Polypyridyl complexes This field continues to be very active, with much good work having to be excluded. An analysis of [Ru(bipy) 3 ]n` (n\0,2,3) structures shows these normally involve six face to face interactions, given the soubriquet Sextuple Aryl Embrace, with other cations, each of the pair of participants needing to have opposite chirality.32 A review of the time-resolved vibrational spectra of Ru(II) [and Os(II)] polypyridyl complexes shows how e§ective these are as a way of studying excited state structure and bonding.33 The time-resolved IR spectra of [Ru(phen) 3 ]2`* favour a description having Ru(III) and one anionic ligand rather than a delocalised negative charge.34a The time-resolved resonance Raman spectrum also leads to this conclusion.34b The synthesis of heteroleptic tris(chelate) complexes of Ru(II) has been improved by using pairwise replacement of ligands in [RuCl 2 (dmso) 4 ].35 A discussion of synthetic methodologies for polynuclear cyclometallated complexes makes special reference to Ru(III) complexes of bipy units linked by diphenyl moieties in which cyclometallation occurs.36 The use of [Ru(CN) 3 (terpy)]~ for photochemical studies, including solvatochromism, shows that the lifetime of the MLCT state is two orders of magnitude longer lasting than for [Ru(terpy) 2 ]2`.37 The contentious issue of the binding of diimine complexes to DNA now leans toward intercalation in the minor groove of the protein after 1H NMR studies of [Ru(phen) 2 (dpq)]2` (crystal structure) and other complexes with oligonucleotides.38 The use of [(phen) 2 RuM4-Mebipy(CH 2 )nbipyMe-4NRu(phen) 2 ]4` to co-ordinate to double stranded DNA gives more stable complexes than [Ru(phen) 3 ]2`, with best results for n\7.39 Among studies of mixed ligand complexes, it is found that, in addition to prolonging the lifetime of the excited state, immobilising such complexes as [Ru(bipy) 2 (py) 2 ]Cl 2 in, for example, polymethylmethacrylate also inhibits photochemical ligand loss.40 When an excess of 4,4@-bipy reacts with [RuCl 2 (dmso)([9]aneS 3 )] the product is cubic [MRu([9]aneS 3 )N8 (4,4@-bipy) 12 ]16`, with Ru at the cube corners and 4,4@-bipy along the edges.41 Complexes containing a bis(pyridyl) and a tris(pyridyl) type ligand with CO can be formed by a new and improved photochemical method; the CO can be substituted by many monodentate ligands, with consequent changes in CT spectra and redox potentials.42 Complexes containing [Ru(4,4@-Bu5 2 bipy) 2 ]` units linked by semiquinone bridges may be diradicals or diamagnetic depending on the points of attachment of conjugated chains at the aromatic rings in the bridge.43 The use of cationic exchange resin chromatography with SP Sephadex C-25 allows separation of the stereoisomers of [Ru 2 (4,4@-Me 2 bipy) 4 (l-bipym)]4`.44 A redox and EPR study Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 215of [MRu(NH 3 ) 4N2 (l-bipym)]4` showed the 3] cation involved Ru(II) and [bipym]~, but the EPR-inactive 5]ion might be Ru(II,III).45 Carboxylates and other bridged complexes All aspects of [Ru 2 (O 2 CR) 4 ]n` chemistry have been comprehensively reviewed.46 Various [Ru 2 (O 2 CR) 4 ] have been prepared by the Zn–Hg reduction of [Ru 2 Cl(O 2 CR) 4 ], but the phenylglyoxylate complex was made from [Ru 2 Cl(O 2 CCH 3 ) 4 ] and PhOCCO 2 H; all are spin doublets.47 Temperature control of the reaction of [Ru 2 Cl(O 2 CCH 3 ) 4 ] with 2-amino-4,6-dimethylpyridine gave controlled stepwise replacement of one bridging ligand by the other; the d* orbital is raised in energy during this to give a change from a quartet spin state to a doublet when complete substitution is achieved.48 Magnetic studies of various [Ru 2 Cl(O 2 CR) 4 ], including some which are mesomorphic, show they are antiferromagnetic in addition to having a very high zero field splitting; the magnitude of the antiferromagnetism depends on the RuClRu angle.49 The technique of liquid secondary ion mass spectrometry may be useful for distinguishing between binuclear and polymeric structures, as in [Ru 2 Cl(O 2 CR) 4 L] (L\monodentate ligand).50a The use of O 3 –O 2 mixtures for convenient preparations of many high oxidation state compounds is exemplified by the synthesis of the new [Ru 2 (l-O)(l-O 2 CC 2 H 5 ) 2 Cl 6 ]2~.50b The determination of the crystal structure of [Ru 2 (chp) 4 (thf)][BF 4 ] prompted comparison with that of the neutral Ru(II) complex; the Ru 2 5` core has a longer Ru–Ru bond than does Ru 2 4`, in line with the relationship of the pentacation to Ru 2 6`.51 Porphyrins and other related macrocylic complexes The synthesis of Ru(II) complexes of tetraazaporphyrins (porphyrins with N instead of CH bridges between the pyrrole rings) is described, including polymers with such bridging ligands as 1,4-(NC) 2 C 6 Me 4 .52 The use of Ru to isolate analogues of unstable Fe porphyrin derivatives from nitrosations is shown by the demonstration that RSNO add across [Ru(oep)] to give nitrosyl thiolate complexes (R\penicillamine residue). 53 The crystal structure, magnetism and EPR studies of [Ru 2 (tpp) 2 ][PF 6 ] con- firm this is a spin doublet, not the quartet found normally in bridged Ru(II,III) dimers; the Ru–Ru distance of 229pm agrees with the EXAFS result for the oep analogue.54 Placing a 4-pyridyl group in one meso position of a tetraarylporphyrin allows the formation of a cyclic tetramer based on an Ru 4 square.55 Such complexes have distinctive redox properties and electronic spectra.56 Mononuclear organometallics P(C 7 H 7 ) 3 (L) forms [Ru(CO) 4 L] on reaction with [Ru 3 (CO) 12 ], but irradiation of this gives loss of one or two CO ligands, with one or two C 7 H 7 rings co-ordinating as alkene or diene with further loss of CO.57 A thorough study of hydrosilation catalysed by [RuHCl(CO)(PPh 3 ) 3 ] shows involvement of both the Chalk–Harrod and the so-called modified Chalk–Harrod mechanisms, their connecting processes and the identification of some key intermediates.58 The discovery of the stability of Ru(II) Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 216stibine complexes prompted the synthesis of [RuHCl(CO)(SbPr* 3 ) 3 ], for example, from which useful intermediate many interesting complexes may be made, including the allenylidene [RuCl 2 (––C–– C––CPh 2 )(CO)(SbPr* 3 ) 2 ].59 Tp shows i2N,N@ co-ordination in [RuH(CX)(PPh 3 ) 2 Tp] (X\O,S); this finding is supplemented by reactivity studies involving conversion to the j3N,N@,NA mode with displacement of PPh 3 .60 Treating cis-[Ru(phen) 2 (CO) 2 ]2` with [NEt 4 ][BH 4 ] gave the new formyl complex [Ru(phen) 2 (CO)(CHO)]`, whose reactions include the formation of the bridged CO 2 complex [MRu(phen) 2 (CO)N2 (l-C,O-CO 2 )]2` with H 2 O and O 2 .61 The first cyclometallated hydridoruthenium(II) complex is claimed to be formed when [RuH 2 (CO)(PPh 3 ) 3 ] reacts with 2-phenylpyridine or N-benzylideneaniline and triethoxyvinylsilane.62 The new phosphaalkenyl complex [RuMP(O)CBu5C(O)N- (CNBu5) 2 (PPh 3 ) 2 ] is formed from the reaction of [Ru(P––CHBu5)Cl(CO)(PPh 3 ) 2 ] or its CNBu5 adduct with CNBu5 in air.63 Nucleophilic attack at Cc in [Ru(PPh 3 ) 2 (–– C––C––C––CH 2 )Cp]` gives, for example, [Ru(PPh 3 ) 2M––C–– C––C(CH 3 )NPh 2NCp]` and [Ru(PPh 3 ) 2 (CCCH––CHCl)Cp].64 The porphyrin carbene complex [Ru(tpp)MC(CO 2 Et) 2N] has been prepared, and its formation of six-co-ordinate complexes in solution studied.65 The macrocyclic complex of Ru with dibenzotetramethyltetraazaannulene (L1) forms five-co-ordinate carbene complexes with various –– CRR@.With CO these give bridges across to the macrocycle, notably for CPh(MeO 2 C), which forms an ester bond to Ru and an alkenyl bond to the ring.66 NMe MeN NMe MeN L1 The first stable Ru(III) alkene complexes have been made by using chelating alkenes to give, for example, [Ru(acac) 2 (2-CH 2 ––MeCC 6 H 4 NMe 2 )]`.67 The versatility of the ligand CH 2 ––CHPPh 2 , known to show g3 or g1 co-ordination, is matched by CH 2 ––CHCH 2 PPh 2 (L), which gives both modes in [RuL 2 Cp*]`.68 The useful synthetic intermediate [Ru(SbPr* 3 ) 2 (g3-C 3 H 5 ) 2 ] reacts with acetic acid to give the binuclear Ru(II) complex [Ru 2 (O 2 CCH 3 ) 5 (H 2 O)(SbPr* 3 ) 2 ], with bridging by acetates and the water molecule.69 The ‘open ruthenocene’ complex [Ru(C 7 H 11 ) 2 ], containing two 2,4-dimethylpentadienyl ligands, reacts with [Ru 3 (CO) 12 ] to give the first homoleptic metallabenzene complex [RuMC 7 H 11 Ru(CO) 3N2 ].70 Various new complexes derived from dialkynes include [MRu(dppm) 2 ClN2 (l-CCC 6 H 4 CC)], its quinonoid cation and the monodentate [Ru(dppm) 2 Cl(––C––C––CHC 6 H 5 )]`, with an allenylidene ligand.71 A thermochemical study has shown that the stability of diphosphine (L) complexes [RuClLX] (X\Cp, Cp*) depends on good ligand p-acceptor properties, the best being (PhO) 2 PNMeNMeP(OPh) 2 .72 One of many flash vacuum thermolysis studies in this area shows that a complete set of [Ru(C 5 HnF 5~n)Cp*] is obtained from application of this technique to the products of the reaction between [Ru(NCMe) 3 Cp*]` with the Tl salts of fluorinated phenols.73 The new benzothiaborolide ligand (L2) forms an Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 217B S NPri 2 L2 g5 complex [Ru(L2)Cp*].74 The Me 2 N donor function from [Ru(dppm)MC 5 H 4 (CH 2 )nNMe 2N]` (n\2,3) is displaced from Ru by H 2 to give a dihydrogen complex believed to be in equilibrium with an isomer containing hydride and C 5 H 4 (CH 2 )nNMe 2 ` ligands.75 The range of organometallic clusters containing polyoxometalate ligands is extended by the synthesis of [MRu(cym)N4 (Mo 4 O 16 )], for example, but the Ru fragments do not interact.76 [RuCl 2Mg6-C 6 H 5 (CH 2 ) 3 PPh 2N] is the first chelating arene Ru complex.77 Binuclear organometallics The bridging carbonyl in [Ru 2 (CO) 5 (dppm) 2 ] reacts with S or Se (E) to give [Ru 2 (CO) 4 (l-E)(dppm) 2 ], and with SO 2 to give bridging SO 2 , all these having single Ru–Ru bonds.78 [Ru(CO) 3 (dppe)], with intermediate five-co-ordinate geometry, is oxidised by the ferrocenium ion to the Ru–Ru bonded fluxional dimer [Ru 2 (CO) 6 (dppe) 2 ]2`.79 The reaction of [Ru 3 (CO) 9 (Ph 2 PC 5 H 4 N-4) 3 ] with Hg or Cd halides resulted in Ru–Ru bond cleavage to give, for example, [Ru 2 (CO) 4 I 2 (l- Ph 2 PC 5 H 4 N-4) 2 ] rather than co-ordination of the free pyridine N atom to the new metal.80 1,8-Diphenyloctatetraene forms complexes with two [RuClCp*] or [Ru(acac) 2 ] moieties, the former having s-cis, the latter s-trans structures.81 The products from the reaction of N 2 H 4 with [Ru 2 (l-H) 3 (C 6 Me 6 ) 2 ]` include the amide complex [Ru 2 (C 6 Me 6 ) 2 (l-H)(l-g1:g1-N 2 H 4 )(l-NH 2 )]2` and [Ru 2 (C 6 Me 6 ) 2 (l-H)(l-g1:g1- N 2 H 4 )(l-g1:g1-N 2 H 3 )]2`.82 The first g4-naphthalene complexes have been isolated, most spectacularly [Ru(cod)(l-g6,g4-C 10 H 8 )Ru(cod)(PEt 3 )].83 [HgMRu(CO) 4N2 ]2~, prepared from 2 K 2 Ru(CO) 4 and HgCl 2 in thf, has linear Hg and trigonal bipyramidal Ru, but a 1: 1 ratio of reactants gives polymeric HgRu(CO) 4 ; the Os analogues were also made.84 Reacting [MRu(CO) 2 CpN2 (l-CC)] with [Mo 2 (CO) 4 Cp 2 ] gave the carbide complex [MoRu 2 (l-CO) 3 Cp 2Ml3 -CC[Ru(CO) 2 - Cp]N, the first l3 -carbide outside Cu and Li.85 The use of [Ru(NCMe) 3 Cp]` as a capping agent gives many heterometallic complexes, including [Ru 2 Os 3 (CO) 11 - Cp 2 ].86 Polynuclear organometallics Anumber of reviews have appeared in this area.Topics include linked arene clusters,87 nitrene complexes,88 structures and statistical analysis of penta- and hexa-nuclear Ru and Os complexes containing g6-arene or g5-Cp ligands,89a and those containing [2.2]paracyclophane.89b A new convenient synthesis of [Ru 3 (l-H)(l-X)(CO) 10 ] (X\Br, Cl, I) is achieved by the photochemical reaction of [Ru 3 (CO) 12 ] with HX in diethyl ether.90 The neglected co-ordination chemistry of melamine, C 6 H 3 (NH 2 ) 3 -1,3,5, is augmented by a study of Annu.Rep. Prog. Chem., Sect.A, 1999, 95, 213–238 218its reaction with [Ru 3 (CO) 12 ] to give, inter alia, two isomers of [MRu 3 (l- H)(CO) 9N2Ml3 ,l3 -(NH) 2 C 3 H 3 (NH 2 )N].91 The stabilisation of unusual structures by bulky phosphines is exemplified by the formation of the 44-electron [Ru 3 H 2 (CO) 6 (PCy 3 ) 3 ] from [Ru 3 H(CO) 11 ]~ and PCy 3 .92 The electrochemical oxidation of many [Ru 3 H 3 (CX)(CO) 6 (PPh 3 ) 3 ] (X\OMe, SEt, Ph, etc.) gave 47-electron monocations of remarkable stability.93 The useful synthon [Ru 3 (CO) 9 (NCMe) 3 ] gives a good e¶cient route to ruthenaboranes.For example, B 3 H 8 ~ followed by acid gives [Ru 3 H(CO) 9 (B 2 H 5 )].94 Another ruthenaborane is obtained when [MRuCl 2 Cp*Nn] and LiBH 4 give the capped nido-[Ru 3 (B 3 H 8 )Cp* 3 ], showing the e§ect of bridging hydrogens opening a cluster in comparison with isoelectronic [Co 3 (B 3 H 5 )Cp* 3 ].95 The reaction of [Ru 3Ml3 -HC 2 (CO 2 Me)N(l-dppm)(CO) 8 ] with C 2 Ph 2 gave alkyne coupling, and isomers of [Ru 3Ml3 -C 2 Ph 2 CHC(CO 2 Me)N(l-dppm)(CO) 6 ].96 The structure of [Ru 4 H 2 (CO) 12 ]2~, obtained as the [NaL]` salt (L\cryptand 221), has two l-H and three l-CO ligands.97 [Ru 3 (CO) 12 ] reacts with but-3-yn-2-ol to give five cluster complexes with four to seven Ru atoms and including metallocyclic ketone rings.98 New phosphinidene complexes include [Ru 4 (CO) 11 (PPh)(PNPr* 2 )] (62 electrons) and [Ru 4 (CO) 12 (PNPr* 2 )] (64 electrons).99 All isomers of diphenyl(pyrrolyl)phosphine react with [Ru 3 (CO) 12 ] to give two isomers of [Ru 4 (CO) 11 (l4 -PPh)(l4 -C 4 H 3 N)], containing C–CorC–Npyrrolyne.100 Me 3 PBMe 3 unexpectedly extracts Cl from [MRuClCp*N4 ] and [MRuCl 2 Cp*N2 ] to give [Ru(PMe 3 )(g2-HnBCl 4~n)Cp*] (n\2,3).101 The first l4 -PF and -PO complexes are formed by modification of [Ru 5 (CO) 15 (l4 - PNCy 2 )], by reaction with HBF 4 ·OEt 2 and HBF 4 ·H 2 O respectively.102 A minor product from [Ru 3 (CO) 12 ] and 1-naphthyldiphenylphosphine is [Ru 6 (CO) 14 (C 10 H 6 )(PPh)], which has l6 -naphthalenediyl, with both r- and p-interactions. 103 Under anaerobic conditions electrochemical reduction of [Ru 6 C(CO) 17 ] gives [Ru 6 C(CO) 16 ]2~, but ifO 2 is present about one mole of CO 2 is also formed, with some cluster degradation.104 The reactivity of C 6 H 6 in [Ru 6 C(CO) 14 (g6-C 6 H 6 )] includes reaction with LiMe followed by [CPh 3 ]`, giving conversion to an g6-xylene complex.105 Two benzocrown ethers (L) react with [Ru 6 C(CO) 17 ] to give [Ru 6 C(CO) 14 L], one of which can complex to sodium or ammonium ions with modification of the electrochemistry.106 The attractive square antiprismatic cluster [Ru 8 (l8 -P)(CO) 22 ]` is formed as the [N(PPh 3 ) 2 ]` salt after reaction of [Ru 3 (l-H)(l-NC 5 H 4 )(CO) 10 ] with PClPh 2 .107 In one of many similar studies, allene formed l-g2:g2 complexes with [Ru 10 C 2 - (CO) 24 ]2~, progressively replacing pairs of CO by one or two C 3 H 4 ligands.108 The new potentially useful synthon nido-[Ru 3 (l3 -Se) 2 (CO) 7 (PPh 3 ) 2 ] gives closo bicapped square planar clusters [Ru 2 M 2 (l4 -Se) 2 (CO) 10 (PPh 3 ) 2 ] (M\Mo, W) with [M(CO) 3 (NCMe) 3 ].109 Studies of the reactivity of Cp* in cluster complexes include the thermolysis of [Ru 3 Rh(l-H) 2 (CO) 10 Cp*] to give products including [Ru 3 Rh 2 (l3 - H)(l-CO)(l3 -CO) 2 (CO) 6 (l-g1:g5-CH 2 C 5 Me 4 )Cp*] in which the modified Cp* coordinates g5 to Rh and through r-bonding by CH 2 to Ru.110 Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 2193 Osmium Simple and co-ordination compounds The crystal structures, IR and Raman spectra are reported for trans-[OsO 2 (ox) 2 ]2~ and its malonate analogue.111New reactions of the nitride complex [Os(terpy)Cl 2 N]` include that with azide in MeCN to form an MeCN complex which further reacts to give [Os(terpy)Cl 2 (L)] (L\methyltetrazolate), but reacting with azide and CS 2 gives [Os(terpy)(NS)][NCS].112 Varying the conditions gave a wider range of products, including trans-[Os(terpy)Cl 2 (py)] and [Os(terpy)Cl 2 (NS)].113 The action of Se on [OsCl 2 NTp] gives the first metal selenonitrosyl complex [OsCl 2 (NSe)Tp].114 The X-ray crystal structure determination identified the cis form of [OsF 4 Br 2 ]2~ as its dipyridiniomethane salt, having a shorter Os–Br bond than [OsBr 6 ]2~.115 A better synthesis of [Os 2 X 10 ]2~ (X\Cl, Br) uses the reaction of [OsX 6 ]2~ withCF 3 CO 2 Hat 40 °C; magnetochemistry shows these have k[1.5 kB per Os and electrochemistry shows that anions having one to five charges can be made.116 Both chlorides in [OsH 2 Cl 2 (PPr* 3 ) 2 ] can be substituted by acetate; the product, which has both monoand bi-dentate acetate, is a useful synthon, for [Os(CO) 2 (O 2 CCH 3 )(PPr* 3 ) 2 ]` for example.117 [Os(acac) 3 ] can be made from aqueous pentane-2,4-dione and [OsCl 6 ]2~; reactions using [OsX 3 Y 3 ]2~ (X, Y\Cl, Br, I) give all six isomers of [OsXY(acac) 2 ].118 When [OsBr 4 (acac)]~ reacts with EPh 3 (L; E\P, As), the product [OsBr 2 (acac)L 2 ] has cis-Br and trans-L.119 The crystal structure shows that the dmso ligands in both isomers of [OsCl 2 (dmso) 4 ] are fully S-bonded, despite solutions of the cis-form being believed to have one O-bonded.120 Studies of various hydrazine complexes [OsH(RNHNH 2 )- L 4 ]` (L\tertiary phosphine or phosphite) led to variants such as complexes of amidrazone, NH––CRNR@NH 2 .121 The first clearly described synthesis of [OsH 2 (dmpe) 2 ] uses the reaction of the dichloro analogue with sodium and hydrogen; laser flash photolysis generates square planar [Os(dmpe) 2 ].122 Nitrosylation of [OsH 3 Cl(PPr* 3 ) 2 ] gives a new route to [OsH 2 Cl(NO)(PPr* 3 ) 2 ]; this complex loses chloride to give [OsH 2 (NO)(PPr* 3 ) 2 ]`, which reversibly binds H 2 , forming [Os(H) 2 H 2 (NO)(PPr* 3 ) 2 ].123 The pyrazine-bridged [MOs(CN) 5N2 (pyz)]6~ has been synthesised and oxidised to the mixed-valence pentaanion in which the charge is thought to be more localised than in the ammonia analogue.124 Polypyridyl complexes The isotope e§ect found in solvent dependence studies of [Os(bipy) 3 ]2` and [Os(phen) 3 ]2` radiationless transitions from the excited MLCT triplet state is attributed to hydrogen bonding between water molecules and ligands.125 IR spectra of [MOs(bipy) 2 ClN2 (l-pyz)]3` give the curious conclusion that the bipy vibrations suggest valence delocalisation, but the pyz vibrations indicate localisation.126 The synthesis, structure and properties of [OsM4,4@-(MeO) 2 bipyN3 ]2`, apparently a good sensor for glucose oxidase, are described.127 The use of 1,2,4,5-(Ph 2 P) 4 C 6 H 2 (L) to make linear trinuclear complexes [Os(bipy) 2 LNiLPdM1,2-(Ph 2 P) 2 C 6 H 4N]6` gives a Annu. Rep.Prog. Chem., Sect. A, 1999, 95, 213–238 220switchable photochemical electron transfer ion, with the Os catching the light, the Ni acting as the switchable tracer and the Pd as the electron acceptor.128 Porphyrins The use of Os to make stable compounds not isolable for Fe is shown by the characterization of [Os(oep)(NO)X] (X\OBu, O 2 PF 2 ) and [Os(oep)(SPh) 2 ].129 Other new Os oep complexes include [Os 2 (l-O)(oep) 2 (NO) 2 ], curiously obtained as an HCl solvate, from NOCl and [Os(oep)(CO)].130 Various bis(tosylimido) (NTs) Os porphyrin (por) complexes are made from [Os(por)(CO)(MeOH)] and PhI––NTs, but the Ru analogues decompose in solution.131 Mononuclear organometallics The limited range of Os carbonyl fluoride complexes is extended by the conversion of [Os(CO)Br 5 ]2~ to [Os(CO)Br 3 F 2 ]2~ by reaction with TlF; the [Os(CO)F 5 ]2~ which is also formed can be oxidised by chlorine to the monoanion [Os(CO)F 5 ]~.132 New hydride complexes such as [OsH 3 (CO)(PPr* 3 ) 2 ]~ can be prepared from [OsHCl(CO)(PPr* 3 ) 2 ], hydrogen,KHand 1-aza-crown-6, and are stabilised by hydrogen bonds between co-ordinated hydride and H on the crown N.133 The crystal structure of the rare boryl complex [Os(CO)(B-1,2-O 2 C 6 H 4 )Cl(PPh 3 ) 2 ] is reported, together with its substitution of chloride, by NCMe for example, to give cationic boryl complexes.134 The scanty OsCp chemistry is expanded by the synthesis of inter alia the remarkably nucleophilic [OsCl(PPr* 3 )(––C––C––CPh 2 )Cp] allenylidene complex.135 The reaction between [Os(–– CCl 2 )Cl 2 (CO)(PPh 3 ) 2 ] and naphthyllithium (LiR) gives [Os(CR)Cl(CO)(PPh 3 ) 2 ]; its reactions with CO, HX and PhICl 2 are discussed.136 The reaction of [OsH 2 Cl 2 (PPr* 3 ) 2 ] and terminal alkenes like styrene gives [OsHCl 2 (CCH 2 Ph)(PPr* 3 ) 2 ], with the first formation of a carbyne from an alkene.137 The reaction of this complex with CO is accompanied by migration to give carbene complexes [Os(CO)Cl 2 (––CHCH 2 R)(PPr* 3 ) 2 ]; with R\Ph, excess of CO gives HCl elimination and [Os(CO) 2 ClM(E)-CH––CHPhN(PPr* 3 ) 2 ].138 [OsBr(CO) 2 (g5-C 5 Ph 5 )], formed from [Os 3 (CO) 12 ] and C 5 Ph 5 Br, is the first Os pentaphenylcyclopentadienyl complex.139 Polynuclear organometallics Activation of biphenylene with metal carbonyls gives, with [Os 3 (CO) 12 ] for example, [Os 2 (CO) 6Ml-g2,g4-(C 6 H 4 ) 2N], suggested to be a metallacyclopentadienylg5 bonding an [Os(CO) 3 ] unit.140 Reviews of polynuclear Os complexes include one on heterometallic clusters and trinuclear alkylidyne complexes,141 and another on penta- and hexa-nuclear carbonyls with arene and Cp type ligands.89a Fluoride complexes in very low oxidation states are exemplified by [Os 3 (l-H)(CO) 10 (AsPh 3 )F], made by substitution of F for ON(CF 3 ) 2 using HF.142 The photochemical reaction of [Os 3 (CO) 12 ] is better than thermal methods for making [Os 3 H(CO) 10 (l-L)] (LH\pz, 3,5-Me 2 pz) for example, with appropriate choice of solvent.143 Further studies of the products of Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 221the reactions of quinolines with [Os 3 (CO) 10 (NCMe) 2 ] gave mechanistic results and crystal structures of some hydride-bridged trinuclear cyclometallated compounds.144 The synthesis and photochemistry of various new [Os 3 (CO) 10 (a-diimine)] complexes are reported.145 Photochemistry is also a good method for synthesising heterometallic clusters, as shown by the preparation of [Os 3 (CO) 10 (l-Cl)Ml-Au(PPh 3 )N] from [Os 3 (CO) 12 ] and [AuCl(PPh 3 )].146 Reaction of [Os 3 (CO) 9 (l-C 4 Ph 4 )] with phosphines having cone angles less than 143° gives carbonyl substitution, but bulkier phosphines break down the cluster.147 4 Rhodium This section includes discussions of iridium chemistry when the reported research includes both Rh and Ir.Simple and co-ordination compounds New antiferromagnetic mixed valence Sr 6 Rh 5 O 15 is synthesised by heating rhodium with SrCO 3 ; it has RhO 6 octahedra linked as linear tetramers, which are then linked together by RhO 6 trigonal prisms to give RhO 3 chains.148 The known Cr(III)Rh(III) aqua complexes have now been joined by [CrRhM(l-OH) 4 (H 2 O) 9 ]5` (M\Cr, Rh)149 and [(H 2 O) 4 M(l-OH) 2 Ir(H 2 O) 4 ]4` (M\Cr, Rh).150 [RhCl(PW 11 O 39 )]5~, synthesised from RhCl 3 and [PW 11 O 39 ]7~, forms [Rh 2 (PW 11 O 39 ) 2 ]10~ on controlled potential reduction; this has an Rh–Rh bond and characteristic spectroscopy and reactivity.151 New Rh(III) complexes of the unfamiliar class of distibine ligands have been prepared and studied by X-ray di§raction and 103Rh NMR spectroscopy, including [RhMPh 2 Sb(CH 2 ) 3 SbPh 2NCl 2 ]`.152 The RhH 3 complex of the triphosphine CH(CH 2 PPh 2 ) 3 (L) reacts with P 4 to give PH 3 and [RhL(g3-P 3 )] through the intermediate [RhL(g1: g2-HP 4 )]; for the analogous Ir system the intermediate [IrL(P 4 )H] was also found.153 [Rh(PPh 3 ) 2 Tp], formed from KTp and [RhCl(PPh 3 ) 3 ], is a useful synthetic intermediate, giving [RhMg2-C 2 (CO 2 Me) 2N(PPh 3 )Tp], [RhCl 2M––C(SMe) 2NTp] and [Rh(g2-SCNMe 2 )(PPh 3 )Tp]`.154 The synthesis of the first monomeric Rh(0) complex, by using a very hindered phosphine, has been claimed.155 All four heterodinuclear porphyrins of Rh(I) with Tl(III) using tpp and oep have been prepared and characterized (UV, 1H, 13C and 205Tl NMR spectroscopy); pyridine adds to the Rh, but the dimer is split by I 2 or MeI.156 The porphyrin H 2 L with four meso-(4-Bu5C 6 H 4 ) groups forms [RhClL(NCC 6 H 5 )], which can be converted to [RhL(CH 2 CH 2 C 6 H 5 )], which rearranges to [RhLMCH(CH 3 )C 6 H 5N] after the manner of vitamin B 12 , possibly through formation of cis bis adducts on the same side of the porphyrin ring.157 Reduction of [MCl 2 (pc)]~ (M\Rh, Ir) with [NBu 4 ][BH 4 ] gives the M(I) species [M(pc)]~.158 Mononuclear organometallics The unusually stable monomeric Rh(II) complex [RhH(CO)(PPh 3 ) 3 ]` is prepared by Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 222the electrochemical oxidation of [RhH(CO)(PPh 3 ) 3 ] and is shown by EPR spectroscopy to have square pyramidal geometry; it can be further oxidised to the dication, which loses a proton to give [Rh(CO)(PPh 3 ) 3 ]`.159 The use of para-enriched hydrogen revealed the exceptionally rich reaction of H 2 with [RhI(CO)(PMe 3 ) 2 ], five reaction products being found.160 New amine (L) complexes [RhCl(CO)(PPh 3 )L] are made by the reaction of L with [MRh(CO)(PPh 3 )N2 (l-Cl) 2 ]; some undergo oxidative addition with CX 4 .161 Mesomorphic [Rh(CO) 2 (diket)] containing up to 29-atom chains at the c-position of the diketonate are unusual in not having the metal atom at the centre of the molecule.162 [Rh(SiHPh 2 )(PMe 3 ) 4 ] is formed from Ph 2 SiH 2 and the analogous Rh methyl complex, but use of the mesityl reagent gave metallation of one Me ortho to Si, forming [RhHMSiH(mes)C 6 H 2 (CH 3 ) 2 CH 2N(PMe 3 ) 4 ].163 A variety of products is given from the reaction of MgCl(C 6 Cl 5 ) with [RhCl 3 (tht) 3 ], namely [Rh(C 6 Cl 5 ) 3 ], [Rh(C 6 Cl 5 ) 2 (tht) 2 ] and [Rh(C 6 Cl 5 )(C 12 Cl 8 )(tht) 2 ]; these include chelating C 6 Cl 5 ~ and a biphenylene ligand.164 Carbene chemistry of Rh has been very active.Azide migrates from [RhN 3 (––C–– C––CRR@)(PPr* 3 ) 2 ] in the presence of CO, losing N 2 to give [Rh(CO)MC(CN)––CRR@N(PPr* 3 ) 2 ].165 The synthesis of [Rh(OH)(––C––CRR@)(PPr* 3 ) 2 ] allowed further reaction of co-ordinated hydroxide to give notably [Rh 2 (–– C––CRR@) 2 (PPr* 3 ) 4 (l-C 4 )] with (Ph 3 Sn) 2 C 4 (R\H, R@\Ph; R, R@\Me).166 Migratory insertion occurs when [RhM––C(C 6 H 5 ) 2N(PPr* 3 ) 2 Cp] is treated with PF 3 , HCl or CF 3 CO 2 H to give [Rh(PPr* 3 )(PF 3 )MC 5 H 4 CH(C 6 H 5 ) 2N] or [Rh(PPr* 3 )(H)XMC 5 H 4 CH(C 6 H 5 ) 2N]; more acid gives [Rh(PPr* 3 )X 2MC 5 H 4 CH- (C 6 H 5 ) 2N].167 The useful new synthons [Rh(C 2 H 4 ) 2 X] (X\Tp, Tp@) have been prepared and their reactivity by substitution of ethene studied.168 Arylallenes form r-complexes such as [RhClMg2-C 6 H 4 C(H)––C–– CH 2 -pN(PMe 3 ) 3 ], which allows study of isomerisation at the unco-ordinated alkene.169 The reaction of [RhCl(PPh 3 ) 3 ] with various NaOAr gives [Rh(OAr)(PPh 3 ) 3 ] with r-bonded phenoxide, but in solution this is in equilibrium with [Rh(g4-OAr)(PPh 3 ) 2 ] and free phosphine.170 The photochemical displacement of ethene from [Rh(PPh 3 )(C 2 H 4 )Cp] can be a useful method for preparing [RhH(SiPr* 3 )(PPh 3 )Cp] for example.171 Polymeric complexes such as [MRh(C 2 O 4 )Cp*Nn] are given by the reaction of [(RhCp*) 2 Cl 4 ] and a silver salt; these are depolymerized by monodentate ligands, to give for example [Rh(C 2 O 4 )(PPh 3 )Cp*], which photochemically loses CO 2 in CHX 3 (X\Cl, Br) to give [RhX 2 (PPh 3 )Cp*].172 The polymeric arene borole complex cation [Rh(l-g5:g6- C 4 H 4 BPh)]` is made from [MRhI(C 4 H 4 BPh)N4 ] via [Rh(C 4 H 4 BPh)(NCMe)]`.173 Polynuclear organometallics [Rh 2 Cl 2 (CO) 4 ] reacts with a range of hydrazines to give [MRhCl(CO) 2N2 (l-g1:g1- H 2 NNHMe)] and [RhCl(CO) 2 ClMN(Ph)–– NPh)N] for example.174 Studies of Rh carbonyl halide complexes showed the occurrence of six-co-ordinate Rh(I) in compounds such as [Rh 2 Cl 2 (l-CO) 3 (py) 4 ] and [Rh 2 (l-Cl) 2 (CO) 2 (py) 2 (C 2 H 4 ) 2 ].175 Heating [Rh 2 H 3 Cl(SiPh 3 ) 2 (PPr* 3 ) 2 ] gives [Rh 2 H 2 Cl(––SiPh 2 )(SiPh 3 )(PPr* 3 ) 2 ]; both of the silyl ligands are bridging, this being the first symmetrical bridge by an SiR 3 group.176 The time-resolved resonance Raman spectrum shows the triplet excited state of [Rh 2 (tmb) 4 ]2` has a stronger Rh–Rh bond than the ground state.177 The use of Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 223[Rh 2 (l-OH) 3 Cp* 2 ]` to deprotonate [Rh 2 (l-CH 2 ) 2 (l-SH)Cp* 2 ]` gave the first coupling of two methylenes to form the alkyne complex [Rh 3 (l3 -g2-C 2 H 2 )(l3 -S)- Cp* 3 ]2`.178 The reaction of [Rh(NCMe) 3 Cp*]2` with [Rh(CN) 3 Cp*]~ gives [Rh 7 Cp* 7 (CN) 12 ]2`, whose structure is an Rh 8 cube with one vacant vertex and cyanide bridges.Using [Ir(CN) 3 Cp*]~ gives [Ir 4 Rh 3 Cp* 7 (CN) 12 ]2`.179 5 Iridium Some iridium chemistry has been mentioned in the previous section when papers referred to both Rh and Ir.Ion-exchange chromatography allowed the separation of [Ir(SCN) 6 ]3~ from its isomers, leading to X-ray crystallographic, IR and Raman studies.180 A reinterpretation of the electronic spectrum of [IrCl 5 (NCMe)]2~ suggests all the transitions are spin-allowed.181 A convenient new synthesis of [IrCl 2 (tn) 2 ]` and [Ir(tn) 3 ]3` starts with [IrCl 3 (tht) 3 ]; the cation of [Ir(tn) 3 ][Co(CN) 6 ]·5H 2 O has the chair configuration. 182 Me 3 SiX reagents are used for substitution of F in [Ir(H) 2 F(PBu5 2 Ph) 2 ] to give, for example, [Ir(H) 2 (NHCOCH 3 )(PBu5 2 Ph) 2 ].183 The new water-soluble complex [IrMe(CO)(tppms) 2 ] and its K analogue were prepared and their reactivity with H 2 , CO and O 2 studied, involving hydrolysis of the Ir–Me bond.184 H 2 oxidatively adds to the Ir(II) complex of the dianion of 1,8- diaminonaphthalene (X), [Ir 2 (l-X)(CO) 2 (PPr* 3 ) 2 ], to give ultimately [Ir 2 (l-X)(l- H)(H) 2 (CO) 2 (PPr* 3 ) 2 ]` andH`, implying heterolytic activation of H 2 .185 New metallacyclobutenes include [IrCl(CO)MCH 2 C(PPh 3 )CHN(PPh 3 )]`.186 O L3 The first o-quinone methide complexes are reported using L3, e.g.[Ir(L3)Cp*]`, with co-ordination by the ring in g4-diene mode.187 The elusive late transition metal alkoxides may be obtained by using RCH 2 ONa (R\Me, Bu5, Np) with RCH 2 OH in the reaction with [IrPh(OH)(PMe 3 )Cp*] to give substitution of OH with OCH 2 R.188 The g6-mode of co-ordination by hydroquinone is stabilised by complexation with the electron-rich IrCp*2` moiety, allowing isolation and reactivity studies.189 Thus, deprotonation gives g5-semiquinone and g4-quinone complexes.190 The S and Se atoms (E) in [Ir(CO)(EPh) 2 Cp*], made by photochemical reaction of [Ir(CO) 2 Cp*] with Ph 2 E 2 , can co-ordinate further to give such heterometallic complexes as [MIr(CO)Cp*N(l-SePh) 2 Mo(CO) 4 ].191 [Ir 2 (l-pyz) 2 (CNBu5) 4 Cl(CH 2 C 6 H 5 )] shows a new form of tautomerism, one isomer having chloride and benzyl on the same Ir atom, and the other on di§erent metals.192 The unfamiliar tellurophenoxide ligand forms cluster complexes in [Ir 6 (CO) 14 (l-TePh)]~ and [Ir 6 (CO) 13 (l-TePh) 2 ].193 Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 2246 Palladium Co-ordination compounds In this section monomeric compounds are dealt with before polymeric compounds and within this division entries are given in order of decreasing hardness of the dominant ligand. The limited range of ROO~ complexes has been extended by the synthesis of [Pd(OOR)(py)(TpP32)] (R\H, Bu5).194 [Pd 2 (O 2 CCH 3 ) 4 (dmso) 2 ] has two bridging acetates and S-bonded dmso.195 In crystals [PdPh(PPh 3 ) 2 (O 2 CC 6 H 4 SEt)] shows monodentate O-bonded carboxylate, but in solution the S atom can displace one phosphine ligand.196 Pd(II) complexes have been prepared with new 2-acylphenolates, analogues of diketonates.197 The reaction of Na 2 PdCl 4 and 1-methyluracil (HL) at pH 9–10 produces [Na 2 PdL 4 (H 2 O)]n, with a columnar structure having one water molecule acting as a guest molecule and the host lattice being sustained by p–p interactions and hydrogen bonds.198 The first platinum metal penicillamine (HL) complexes include [Pd 2 L 2 Cl 2 ] and [Pd 3 L 3 ]·0.875KCl·2.375H 2 O, which has a triangular structure with bridging anions.199 The undeveloped field of metallocarbohydrate chemistry may expand following identification of structures, including ligand conformation changes, of complexes formed by the interaction of [Pd(OH) 2 (en) 2 ] with anhydroerythritol, anhydroglucose and glucose.200 [Pd(dppe)(S 2 CNEt 2 )]` was prepared as halogenometalate salts by reacting [PdX 2 (dppe)] with metal dithiocarbamates, but no heterometallic complexes were formed.201 Cysteine hydrochloride and [PdCl 4 ]2~ react to give the first polynuclear Pd(II) amino acid complex [Pd 4 Cl 4 (l-Cys) 4 ] with all the S atoms bridging two Pd.202 The role of the cation in determining which complex a metal–polyanion system may adopt is highlighted in a study of the formation of Pd polyselenide salts such as [MeN(CH 2 CH 2 ) 3 N] 2 [Pd(Se 6 ) 2 ].203 [Pd(SePh) 2 (PBu/ 3 ) 2 ] is the first structurally characterized Pd(II) selenolate complex.204 Kinetic studies showed that substitution of en for Cl~ in [PdCl 2 - MRR@N(CH 2 ) 2 NRAR@@@N2 ] (R,R@,RA,R@@@\H, alkyl, aryl) was promoted by the electron withdrawing properties of phenyl substituents and retarded by steric e§ects of alkyl groups, but that substitution of en for bipy in [Pd(bipy)MRR@N(CH 2 ) 2 NRAR@@@N2 ]2` was faster with more alkyl groups, possibly due to hydrogen bonding e§ects between solvent water and co-ordinated diamine hydrogens.205 The reaction of [Pd(NO 3 ) 2 (en) 2 ] with either 4-pyridylmethyl acetate or 2,4,6-tris(3-pyridyl)triazine gave cluster molecules containing six Pd(en) 2 moieties and four of either ligand.206 The co-ordination chemistry of Ph 3 P––NCN shows the terminal N atom is the better donor, as in [PdCl 2 (NCNPPh 3 ) 2 ].207 New co-ordination compounds of pyridine-2-selenolate (L) include [Pd 2 Cl 3 L(PR 3 ) 2 ], in which one Pd is co-ordinated by L through N and Se and the other by Se.208 The first binuclear Pd(III) compound has been claimed; palladium(II) acetate reacts with the anion of HL4 giving [Pd 2 L4 4 ], which undergoes two-electron oxidation with PhICl 2 to give [Pd 2 L4 4 Cl 2 ], which has the shortest Pd–Pd bond yet (239.1 pm).209 Stoichiometric mixtures of the appropriate pyridylporphyrins gave a square array containing nine ligands and twelve PdCl 2 moieties.210 A review on the design of cyclic nanostructures uses Pd compounds as the most frequent metallic Annu. Rep.Prog. Chem., Sect. A, 1999, 95, 213–238 225NH N N HL4 building unit.211 The unexpected synthesis of the double A-framed complex [MPd 2 Br 2 (l-PPh 2 )(l-dppm)N2 (l-CN) 2 ] arose from the NaBH 3 CN reduction of [Pd 2 (Np) 2 Br(dppm) 2 ]`.212 The variability of the Pd–Pd single bond length in Pd(I) dimers is exemplified by its length (318.5 pm) in [Pd 2 (C 4 H 6 ) 2 (PPh 3 ) 2 ]2` and its shortness (248.8 pm) in [Pd 2 (PPh 3 ) 2 (NCMe) 4 ]2` (equatorial PPh 3 ), made from the former on dissociation in MeCN.213 The terminal phosphines were found to be more readily substituted by other phosphines than their bridging sibling in [Pd 2 (l-PBu5 2 )(l- PBu5 2 H)(PBu5 2 H) 2 ]`.214 [Pd 2 (l-OH) 2 (PPh 3 ) 2 ]2` forms [Pd 3 (PPh 3 ) 4 ]2` in alcoholic CH 2 Cl; the product has a linear structure with two phenyl rings showing l-g2:g2 co-ordination.215 Another of the relatively rare type of rectangular Pd 4 complexes, [Pd 4 (l-Cl) 2 (l-dppm) 4 ][ClO 4 ] 2 ·dpe, has been prepared from [Pd 2 Cl 2 (l-dppm) 2 ], AgClO 4 and dpe, the last not being co-ordinated.216 Organometallic compounds The first stable Me 2 PdIV units have been formed from the reaction of [PdMe 2 (bipy)] and Ph 2 Se 2 , giving [PdMe 2 (SePh) 2 (bipy)], and from other similar reactions.217 The trans to cis isomerization of [Pd(C 6 Cl 2 F 3 ) 2 (tht) 2 ] is catalysed by [Au(C 6 Cl 2 F 3 )(tht)] with intermediates involving aryl exchange between Pd and Au.218a The oxidative addition of C 6 Cl 2 F 3 I to [Pd(PPh 3 ) 4 ] gave the unusually stable cis- [Pd(C 6 Cl 2 F 3 )I(PPh 3 ) 2 ], whose slow isomerization to the trans form was studied kinetically.218b The new ligand 2,6-bis(pyrimidin-2-yl)pyridine (L) forms [PdMeL]`, which gives an acetyl derivative; the fluxionality of the diimine ligand was studied.219 The reaction of palladium(II) acetate, phen, nitromethane and CO gave the Pd(phen) complex of MeN(CO)CO 2 2~, shown by powder X-ray methods to be co-ordinated through two C atoms.220 Pd 6 hexagons occur in [Pd 6 (4,7-phen) 3MC 6 H 2 (CH 2 SR) 4 - 1,2,4,5N3 ]6` (R\Bu, Ph).221 The reaction of CO with methyl Pd(II) complexes of a diphosphine and various PhC––NR gave acyl formation followed by formation of chelating CH 3 CONRCHPh.222 Reviews on mononuclear Pd organometallics include one on the use of [Pd(L)(solv)]2` (L\triphosphine) as catalysts for reducing CO 2 to CO,223 and a wide ranging survey of carbonyl–ylide complexes which emphasises the role of the ylide C co-ordination.224 Tris(1-naphthyl)phosphine (HL) gives various cyclometallated Pd complexes, including [Pd 2 L 2 (O 2 CCH 3 ) 2 ], a good catalyst for the Heck reaction (aromatic alkenation).225 A new mechanism for the Heck reaction involves nucleophilic attack on the Pd-co-ordinated alkene.226 The crystal structures and fluxionality in solution (29Si and 31P NMR) have been studied for various [ML 2 X 2 ] (M\Pd, L\PMe 2 Ph, X\SnMe 3 ; M\Pt, L\PEt 3 , PMe 2 Ph, X\SiMePh 2 , SiF 2 Me).227 Many new examples of [PdL(g2-1,6-diene)] complexes have been reported, including [Pd(PMe 3 )M(g2-CH 2 ––CHCH 2 ) 2 ON] (X-ray di§raction).228 The photochemistry of Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 226[PdCl 2 (cod)] gives the cod radical cation and [PdCl 2 ]~, which in MeCN gives isomerization to 1,3-cod and in ethanol decomposition to Pd and acetaldehyde.229 Various Pd(II) allyl diketonates act as good Pd CVD precursors, some of them being liquid, e.g.[Pd(C 3 H 5 )MBu5C(O)CHC(O)C 3 F 7N].230 Palladium(II) acetate and [Ni 6 (CO) 12 ]2~ give a Ni–Pd heterometallic cluster which reacts with PMe 3 to give, inter alia, [Pd 59 (CO) 32 (PMe 3 ) 21 ], which has 11 interior Pd atoms and is described as the largest crystallographically determined metal atom core with direct metal–metal bonding.231 7 Platinum Co-ordination compounds In this section complexes of oxidation state IV are considered before those of oxidation state II.Within each section the order is of decreasing hardness of the dominant ligand.The crystal structures and IR, Raman and 195Pt NMR spectra have been reported for [PtCl 5 (SCN)]2~, cis-[PtCl 4 (SCN) 2 ]2~,232 both isomers of [PtCl 3 (SCN) 3 ]2~, cis- [PtCl 2 (SCN) 4 ]2~, [PtCl(SCN) 5 ]2~,233 and [Pt(SCN) 6 ]2~.234 The reaction of halogens with [Pt(ox) 2 ]2~ gives [PtX 2 (ox) 2 ]2~, also described by crystallographic and spectral studies.235 Reacting [9]aneN 3 with [PtCl 2 (dmso) 2 ] in air results in oxidation to Pt(IV) and the formation of a peroxide complex [MPt 2 Cl 2 ([9]aneN 3 )N2 (l-O 2 ) 2 ]2`.236 [Pt(OH) 2 (ox) 2 ]2~, though long known, has now been obtained for X-ray study as the [(py) 2 CH 2 ]2` salt of the double complex with [Pt(OH)(ox) 2 (H 2 O)]~.237 New Pt(IV) amino acid complexes characterized by crystallography include cis-[PtCl 4 (Ala)- H 2 O]·18-crown-6, with the zwitterion co-ordinated through O, and the glycinium salt of [PtCl 4 (Gly)]2~·2(18-crown-6)·1.25H 2 O, with N,O-chelating glycinate.238 [Pt(L)Me 3 ]` (L\glucopyranoside) complexes show a new co-ordination mode for carbohydrate by using the 2- and 4-hydroxyls and the pyranose acetal oxygen.239 POCl 3 oxidises Pt(II) to Pt(IV) giving, for example, [Pt(en)(NO 2 )Cl 3 ] from [Pt(en)(NO 2 ) 2 ].240 Reacting [Pt 2 (l-SO 4 ) 4 (H 2 O) 2 ] with acetic acid gave [Pt 4 (l-O 2 CCH 3 ) 4 (H 2 O) 8 ]4`, which reacts with py to give the square structured [Pt 4 (l-O 2 CCH 3 ) 6 (py) 4 ]2`.241 New polymeric Pt(II) complexes based on repeating Pt 4 units include K 4 [Pt 4 (NO 2 ) 6 (OH) 4 (ox)]·2(MeO) 3 PO.242 Various new binuclear Pt (and Pd) diphenylphosphinate complexes described include [Pt 2 Cl 2 (l-O 2 PPh 2 ) 2 (PMe 2 Ph) 2 ] (crystal structure).243 In studies involving biochemical ligands, the trans-[Pt(NH 3 ) 2 ]2` complex with trimethyladenine and 9-ethylguanidine forms three intermolecular H bonds with the ion of the complex with deprotonated guanine, the two guanine entities interacting to give a Z-shaped structure.244a AWAXS (anomalous wide angle X-ray scattering) studies on Pt 5-fluorouridine green sulfate suggest this has binuclear and mononuclear Pt components.244b [PtCl(dien)]` forms an S-bonded methionine complex at pH 7, which becomes N-bonded at pH 8; at pH 3 the triamine is monoprotonated, and methionine becomes bidentate, four diastereoisomers being identified.245 The bridging ligand bptz is particularly e§ective at stabilising mixed valence com- Annu. Rep.Prog. Chem., Sect. A, 1999, 95, 213–238 227N N N N N N bptz plexes formed by reduction and oxidation of [MPt(mes) 2N2 (l-bptz)].246 Time-resolved IR spectra have been used for the first time to study various photochemical processes involving [Pt(N 3 ) 2 L 2 ] (L\PPh 3 , 1/2 dppp).247 Carbazole oxidatively adds across its N–H bond to [Pt(PR 3 ) 2 ] (R\Me, Et), in contrast to dibenzothiophene, which gives insertion into the C–S bond.248 The alkyne bond in PhSCCSiMe 3 is broken by [PtH(MeOH)(PEt 3 ) 2 ]` to give the benzenethiolate complex [MPt(PEt 3 ) 2N2 (l- SPh) 2 ]2`.249 Among reactions of 2,3-dppn is that with [PtCl 2 (NCC 6 H 5 ) 2 ] and Ag`, giving [Pt(1,2-dppn) 2 ]2`, one of many such ligand isomerizations.250 The determination of the crystal structures of cis-[PtCl 2 (SbPh 3 ) 2 ] and trans- [PtI 2 (SbPh 3 ) 2 ] indicated that SbPh 3 has a similar static trans-e§ect to PPh 3 .251 The protonation of [PtHX(PCy 3 ) 2 ] depends on the trans ligand X, the reaction occuring at H (X\H, Me, Ph), Pt (X\Cl, Br, I) or X (X\CN).252 Organometallic compounds [PtMe 2 (cod)] undergoes photochemical oxidative addition of MeI to give [MPtMe 3 IN4 ],253a while the elusive [MPtMe 3 FN4 ] has finally been made by the reaction of the iodide with XeF 2 .253b The rare aryl halide oxidative addition process to Pt(II) has been achieved by using Schi§ bases of the type RN––CHC 6 H 4 X-2 (X\Br, Cl) and [Pt 2 Me 4 (l-SMe 2 ) 2 ].254 The limited range of Pt cyclopentadienyl compounds has been extended by the synthesis of [PtMe 2 (CO)Cp*]` and [PtMe 2 (SC 6 H 4 CH 3 -4)- Cp*].255 The first crystal structure of a Pt acetonyl complex, [Pt(bipy)MCH 2 C(O)CH 3N2 ], has been reported.256 In a new reaction of the fairly unfamiliar chloride bridged platina-b- diketone, [Pt 2M(COCH 3 ) 2 HN(l-Cl) 2 ] reacts with bipy and its derivatives to give Pt(IV) acyls [Pt(bipy)HCl(COCH 3 ) 2 ] which may eliminate acetaldehyde at the low temperature of 180 °C to give [Pt(bipy)Cl(COCH 3 )].257 a-(Diisopropylphosphino)isodurene (HL) forms cis-[PtMeL(HL)] which gives selective C–Si coupling with various HSiR 3 to give MeSiR 3 and [PtHL(HL)].258 [Pt(PPr* 3 ) 2 Me(OTf)] undergoes metallation of the phosphine when catalytic amounts of HCl are added, giving a phosphacyclobutane complex with Cl replacing Me.259 The thermolysis of many Pt(0) PPh 3 complexes gave [Pt 2 (PPh 3 ) 2 (l-PPh 2 )Ml-C 6 H 4 (PPh 2 ) 2 -1,2N], which is probably what was previously formulated as [Pt 2 (PPh 3 ) 4 ] or [Pt 2 (l-PPh 2 ) 2MC 6 H 4 (PPh 2 ) 2 -1,2N2 ].260 [Pt(CNMe) 4 ]- [Pt(mnt) 2 ] 2 occurs in three di§erent lattice structures depending on the crystallization solvent, each having di§erent magnetochemistry.261 Li 2 [Pt(CCBu5) 4 ] and HPPh 2 in acetone–ethanol gives [LiMOC(CH 3 ) 2N] 2 - [Li 2 (H 2 O) 2 ][Pt(CCBu5) 2 (PPh 2 O)] 2 , the phosphinyl O bridging two types of Li.262 The diplatinum complex [Pt 2 (dppf) 2 (l-CHCH 2 C 6 H 4 OMe)(l-H)]` has the rare combination of bridging hydride and alkylidene.263 [Pt(acac) 2 ] and PPh 3 give [Pt 2 (l- L)(PPh 3 ) 4 ]`, in which the deprotonated acac, L, co-ordinates one Pt through both oxygens and the other Pt in an allyl mode.264 The range of rare five-co-ordinate alkyne complexes is extended by the synthesis of [PtI 2 (2,9-Me 2 phen)(g2-C 6 H 5 CCC 6 H 5 )] and Annu.Rep.Prog. Chem., Sect. A, 1999, 95, 213–238 228some analogues.265 The elusive benzyne complex [Pt(PPh 3 ) 2 (g2-C 6 H 4 )] is made from [Pt(PPh 3 ) 2 (C 2 H 4 )], chlorobenzene and base, but is only isolated as derivatives such as [Pt(PPh 3 ) 2 (g1:g1-C 6 H 4 C 6 H 4 )].266 Dry etching of Pt can be obtained using a chlorine–COgas mixture, with the benefit of the easy removal of sublimable [PtCl 2 (CO) 2 ].267 The first crystallographically characterised ‘buckybowl’ complex, [Pt(C 30 H 12 )(PPh 3 ) 2 ], is prepared (10% yield) by reacting the hydrocarbon with [Pt(PPh 3 ) 2 (C 2 H 4 )]; the ligand co-ordinates by oxidatively adding a C–C bond in an outside pentagon.268 Unlike its PEt 3 analogue, [Pt(PMe 2 Ph) 2 (g5-7-CB 10 H 11 )]~ gives a complex mixture of products on protonation with HCl, including [Pt 2 (PMe 2 Ph) 4 (l-CB 10 H 10 ) 2 ], which has g5-co-ordination supplemented by B–B and Pt–B links.269 Two new bipyridyl thiocarborane Pt complexes act as powerful oxidising agents in their photochemical excited states.270 A new synthesis of [PtMe 2 (PMe 2 Ph) 2 ] using MeLi and [PtCl 2 (PMe 2 Ph) 2 ] facilitates the use of this as a synthon for big metalloboranes such as [PtHMg4- B 18 H 19 (PMe 2 Ph)N(PMe 2 Ph)].271 The oxidative addition of B 2 F 4 to [Pt(PPh 3 ) 2 (C 2 H 4 )] gives the first Pt–BF 2 complex, cis-[Pt(BF 2 ) 2 (PPh 3 )].272 The first neutral Pt silylene complexes [PtMSi(mes) 2N(PR 3 ) 2 ], (R\Cy, Pr*), made by the photolysis of [Pt(PR 3 ) 2 ] with (Me 3 Si) 2 Si(mes) 2 , has a 69° dihedral angle between the C 2 Si and P 2 Pt planes.273 The germyl complex [PtMGe[N(SiMe 3 ) 2 ] 2N(PEt 3 ) 2 ] reacts with O 2 to form [Pt(l-g2-O 2 )MGe[N(SiMe 3 ) 2 ] 2N(PEt 3 ) 2 ], which is transformed by light into the germanate isomer [PtO 2MGe[N(SiMe 3 ) 2 ] 2N(PEt 3 ) 2 ] and by SO 2 into [Pt(l- g2-SO 4 )MGe[N(SiMe 3 ) 2 ] 2N(PEt 3 ) 2 ].274 In a typical result from many thermochemical studies on various terminal phosphide complexes [Pt(dppe)Me(PRR@)], prepared from [Pt(dppe)Me(OMe)] and HPRR@, the Pt–P bond strength depends on both steric and electronic e§ects.275 In other zerovalent Pt studies, reacting cyclopropene (L) complexes of the type [PtL(PPh 3 ) 2 ] with HCl gave either cyclopropane (L\C 3 H 4 ) or propene (L\3,3- Me 2 C 3 H 2 ).276 New Pt 2 M 2 square clusters include [MPt(PPh 3 ) 2N2MMXN2 Se 2 ] (M\Cu, Ag, X\Cl; M\Au, X\SeH).277 [Pt(C 6 H 5 CCCCC 6 H 5 )(PPh 3 ) 2 ], con- firmed (crystal structure) as having one triple bond co-ordinated, forms trinuclear complexes [Pt 2 M(l3 -g1:g1: g2-(C 6 H 5 CCCCC 6 H 5 )(PPh 3 ) 2 (CO) 5 ], still with only one triple bond involved.278 8 Silver In this section compounds are discussed in decreasing order of oxidation state.For each oxidation state the order is of decreasing hardness of the dominant ligand. MAgF 4 (M\K, Li) has been made by the photochemical reaction of AgF 2 with MF and fluorine in HF. Treating KAgF 4 with GeF 4 and fluorine in HF gives the purest AgF 3 yet and K 2 GeF 6 .279 The elusive potential proton conductor AgHSO 4 has been made from Ag 2 O or Ag 2 SO 4 and sulfuric acid; it absorbs CO reversibly in concentrated H 2 SO 4 .280 The rare category of Ag–Hg complexes has been augmented by the synthesis of [MAg 2 Hg(mes) 2 X 2N2 (X\OTf, ClO 4 ), from AgX and Hg(mes) 2 ; the triflate shows the first tridentate mode for this ligand.281 A low temperature synthesis of Ag 2 E (E\S, Se, Te) has been achieved by the reaction of E with silver oxalate in organic solvents at Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 213–238 229140–180 °C.282 The new complex [Ag 4 (SPh) 4 (PPh 3 ) 4 ] has a chair configuration which is suggested to include Ag–Ag connections from correlation e§ects after the manner of Au(I) compounds.283 The first l4 -sulfide ligand outside Cu chemistry is found in the polymeric zwitterionic complex [Ag 8 (SC 2 H 4 NH 3 ) 6 Cl 8 ].284 Thianthrene (L5) forms [Ag 2 (L5) 2 (ClO 4 ) 2 ], with each Ag co-ordinated by 2S from one ligand, one C––C of another and a perchlorate O atom.285 The first co-ordination by S in di-2-pyridylsulfide (L) has been found in [Ag 2 L 2 (NO 3 ) 2 ], with 2N on one Ag and the S on the other.286 The reaction of AgS 2 CNEt 2 with Na 2 Se or [MoSe 4 ]2~ gives [Ag 11 Se(S 2 CNEt 2 ) 9 ], containing l5 -Se.287 The protecting action of phosphine ligands in forming large clusters is emphasised in various Ag–Se examples, giving up to [Ag 172 Se 40 (SeBu) 92 (dppp) 4 ].288 S S L5 [Ag(pym)]` forms as cyclic tetranuclear cations which stack to give channels in which the oxyanions can be located.289 Earlier work on terpy derivative Cu(I) complexes has found some analogies in the probable formation in solution of a double helical complex, but only planar [Ag(terpy)(NCMe)]` was isolated; this has Ag–Ag contacts of 317 pm, comparable to many macrocyclic Ag 2 complexes.290 Two chiral derivatives (L) of terpy form [AgL(NCMe)]` complexes in acetonitrile, but in less co-ordinating solvents double helicates [Ag 4 L 4 ]4` were indeed found.291 A new cage structure with approximately an Ag 6 octahedron was found in [Ag 6 (triphos) 4 (OTf) 4 ]2`.292 3,6-Bis(diphenylphosphino)pyridazine (L) forms zigzag chains [Ag 2 L(NCMe) 2 ]2` with each L co-ordinated to four Ag and each Ag bonded to anNfrom one ligand and a P from another.293 Aqueous co-crystallisation of Ag 2 C 2 with AgClO 4 gives corner-shared Ag 6 clusters encapsulating acetylide units and generating cavities for ClO 4 ~ and H 2 O; there are many examples of similar channeled structures this year.294 Adding Ag 2 C 2 to AgF in water gave [Ag 10 F 8 C 2 ] with an exohedral Ag outside an Ag 9 cage again encapsulating an acetylide and with F bridges to other cages.295 The structure of Tl[Ag(CN) 2 ] shows an Ag–Ag separation of 311 pm, but no Tl–Ag bonding.296a The luminescence of this complex is interpreted as showing Ag–Ag interactions, said to imply the first solid state metal–metal bound exciplex.296b The reaction of AgCN or AgSCN with [SnMCH(SiMe 3 ) 2N2 ] gave dinuclear complexes with the pseudo-halide N-bonded to Sn, and showing the first coupling to 109Ag or 107Ag in an 119Sn NMR spectrum.297 The first Ag–Sn compound was claimed in Rb 4 Sn 4 Ag 4 (P 2 Se 6 ) 3 .298 9 Gold In this section, compounds are discussed in decreasing order of oxidation state.For each oxidation state the order is of decreasing hardness of the dominant ligand. [AuF 6 ]~ has been prepared by the oxidation of [AuF 4 ]~ byO 2 F formed fromO 2 ~ in anhydrous HF.299 Annu. Rep.Prog. Chem., Sect. A, 1999, 95, 213–238 230[AuBr(C 6 F 5 ) 3 ]~ reacts with NaSH to give the first Au hydrosulfide complex [Au(SH)(C 6 F 5 ) 3 ]~, which in turn leads to other derivatives, such as [MAu(C 6 F 5 ) 3N2 SMM(PPh 3 )N]~ (M\Ag, Au).300 [Au(Se 3 ) 4 ]5~ is the first Au(III) chalcogenide mononuclear anion; its square planar configuration has bent Se 3 chains which give the overall anion structure the appearance of a swastika.301 Gold dissolves in alkali polysulfide solutions to form MAuS, (M\Li, Na), with [AuS] chains which, in the Na compound, interweave after the manner of chicken wire.302 [Au 3 S 2 ]~ has been found together with [Au 3 Sb 4 S 8 ]~, which is better formulated as [(Au 3 S)`·(Sb 4 S 7 )2~], in Rb 2 Au 6 Sb 4 S 10 .303 Colourless [AuMS 2 CN(C 5 H 11 ) 2N] becomes orange when solvated by various aprotic organic molecules, with a decrease in the intermolecular Au–Au separation from 814pm to about 300 pm; this is suggested to imply potential as a sensor.304 Heating calcium nitride with gold in nitrogen gave Ca 2 AuN, having a new structure with Au zigzag chains between Ca 6 N octahedra.305 Determining the structure of new [MM(PPh 2 )Au(C 6 F 5 ) 3N]~ (M\Ag, Au) showed the Au(I)–P bonds were shorter by 69pm than Ag–P bonds.306a A similar conclusion arose when determination of the structure of [Ag(PPh 3 ) 2 ][BF 4 ] induced a comparison of 14 isostructural pairs of Ag and Au compounds, with Au` deduced to have a smaller ionic radius by about 10 pm.306b The phenylborole complex [FeH(CO) 2 (g5-C 4 H 4 BPh)]~ reacts with [AuCl(PPh 3 )] to give first [Fe(CO) 2MAu(PPh 3 )N2 (C 4 H 4 BPh)] with an Au–Au separation of 273.7 pm, and then [Fe(CO) 2MAu(PPh 3 )N3 (C 4 H 4 BPh)] with tetrahedral FeAu 3 .307 [AuMPOPh) 3N]` and some similar cations are said to be unusual among gold compounds in showing catalytic activity, in this case for the addition of alcohols to alkynes.308 S L6 The Au–Au contacts of solid [(AuCl) 3 (PhPMC 6 H 4 (PPh 2 )-2N2 )] appear to be retained in solution.309 [AgMAu 2 (CH 2 SiMe 3 ) 2 (l-dppm)N2 ]` contains the first unsupported Ag–Au bonds.310 The chemistry of phenylacetylide complexes has been extended by reacting [Au(C 2 C 6 H 5 ) 2 ]~ with Au and Cu phenylacetylides giving [Au 3 Cu 2 (C 2 C 6 H 5 ) 6 ]~, containing linear Au co-ordination and with each triple bond co-ordinated to a copper atom.311 Tetramethylthiacycloheptyne (L6) forms the first g2-Au alkyne complex in [MAu(L7)ClNn].312 Au catalysts for CO oxidation can be prepared by decomposition of [Au(NO 3 )(CNEt)] (crystal structure) on Fe(OH) 3 .313 Various new complexes [AuX(CNxyl-o)], (X\Cl, Br, I, CN), have di§erent structures but are all luminescent.314 Powder neutron di§raction shows AuCN has polymeric chains with each Au at the centre of an Au 6 hexagon, but that there are no Ag–Ag interactions in AgCN, in which the chains are di§erently arranged.315 [(Ph 3 P)Au(l- C 4 H 9 CO)MRe 2 (l-PPh 2 ) 2 (CO) 7N], the first gold acyl, has the acyl C bonded to Au and the O to Re.316 The improbable procedure of the photolysis of a mixture of [AuCl(PPh 3 )], Annu.Rep. 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