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The mechanisms of formation, decomposition, and isomerisation of platinacyclobutane complexes [PtCl2(C3H6)L2] (L is typically pyridine) are discussed on the basis of density functional theory (DFT). The isomerisation and decomposition reactions occur through 5-coordinate intermediates [PtCl2(C3H6)L] that cannot be directly detected. These 5-coordinate complexes are predicted to have distorted square pyramidal structures, but a pinched trigonal bipyramidal (PTBP) stereochemistry is easily accessible. Both α- and β-elimination from these complexes to give hydride complexes [PtHCl2(C3H5)L] are predicted to have high activation energies. The isomerisation of [PtCl2(C3H6)L2] to the ylide complex [PtCl2{CH(L)CH2CH3)L] is instead predicted to occur after cleavage of a Pt–C bond to give an intermediate that can be considered as a corner platinated cyclopropane, leading to 1,3-hydrogen transfer without a hydridoplatinum intermediate. The reaction of [PtCl2{CH(L)CH2CH3}L] to give the alkene complex [PtCl2(CH2 = CHCH3)L] involves dissociation of the C–L bond followed by a 2,1-hydrogen transfer. The selectivity of related reactions from phenylcyclopropane follows naturally from these mechanisms.

Cecil Bawn was a physical chemist with particular expertise in chemical kinetics. Early in his career he made pioneering studies of free radical reactions in the gas phase and, during the war years, on the chemistry of high explosives. From mid career, he was one of the pioneers of polymer chemistry and established and led a strong and diverse group of polymer scientists at the University of Liverpool. He was a private and enigmatic person, with a strong sense of duty. His caring and helpful attitude was greatly appreciated locally by his students and younger faculty members. Nationally, he made outstanding service contributions to physical chemistry and polymer chemistry.

The reactions of dimethylamine-borane with platinum(II) or platinum(IV) triflate complexes gave, not the anticipated σ-complexes, but the respective hydridoplatinum complexes. The reaction with [Pt(OTf)Me3(NN)], with NN = 2,2′-bipyridine (bipy) and 4,4′-di-t-butyl-2,2′-bipyridine (bu2bipy), gave the rare stable bridging hydridoplatinum(IV) complexes [μ-H{PtMe3(NN)}2][OTf] and the reaction with [Pt(O2CCF3)Me(NN)] gave the unstable hydridoplatinum(II) complex [PtHMe(NN)]. The unstable hydridoplatinum(II) complexes could be trapped by reaction with methyl acrylate by forming the insertion products [PtCl(CHMeCO2Me)(bipy)] and [Pt(CHMeCO2Me)2(bipy)]. The complex [PtCl(CHMeCO2Me)(bipy)] reacted with methyl iodide to give [PtClIMe(CHMeCO2Me)(bipy)], by cis oxidative addition, and the presence of two chiral centers in the product platinum(IV) complex allowed a detailed stereochemical pathway to be proposed.

A new di-2-pyridylamine ligand with an appended azobenzene group (2-C5H4N)2N-4-C6H4-NN-Ph, dpaa, is reported. This ligand readily forms the platinum(II) complexes [PtMe2(dpaa)], 1, and [PtCl2(dpaa)], 2. Complex 1 is electron-rich and it undergoes oxidative addition with I2, MeI or PhCH2Br to give the corresponding organoplatinum(IV) complexes [PtI2Me2(dpaa)], [PtIMe3(dpaa)] or [PtBrMe2(CH2Ph)(dpaa)]. Both the ligand dpaa and its platinum complexes undergo photoswitching by trans–cis isomerization about the NN linkage.

The isomerization and reductive elimination reactions from octahedral organometallic complexes of palladium(IV) and platinum(IV) usually occur through five-coordinate intermediates that cannot be directly detected. This paper reports a computational study of five-coordinate complexes of formulae [PtMe3(bipy)]+, [PtMe2Ph(bipy)]+, and [PtMe(CH2CMe2C6H4)(bipy)]+ (M = Pd or Pt, bipy = 2,2′-bipyridine), particularly with respect to reactivity and selectivity in reductive elimination. All of the complexes are predicted to have square pyramidal structures with the bipy and two R groups in the equatorial positions and one R group in the axial position, and axial–equatorial exchange occurs by a pairwise mechanism, with the transition state having a pinched trigonal bipyramidal (PTBP) stereochemistry, with one nitrogen and two R groups in the trigonal plane. The activation energy for isomerization is lower than that for reductive elimination in all cases. For the complexes [MMe2Ph(bipy)]+, the activation energies for reductive elimination with Me–Me or Me–Ph coupling are similar. For the complexes [MMe(CH2CMe2C6H4)(bipy)]+, the reductive elimination with Me–C6H4 bond formation from the isomer with the methyl group in the axial position is predicted and is attributed to it having the best conformation of the Me and C6H4 groups for C–C bond formation. In all cases, the selectivity for reductive elimination is similar for M = Pd or Pt, but reactivity is higher for M = Pd. The relevance of this work to selectivity in catalysis is discussed.

Unusual features are observed in studies of oxidative addition to cycloneophylplatinum(II) complexes [Pt(CH2CMe2C6H4)(NN)], 2, NN = 3,4,7,8-tetramethyl-1,10-phenanthroline (phen*) or 3, NN = 4,4′-di-t-butyl-2,2′-bipyridine (bubipy). The oxidative addition of 4-nitrobenzyl bromide to 2 or of HgCl2 to 3 occurs with cis stereochemistry to give [PtBr(CH2-4-C6H4NO2)(CH2CMe2C6H4)(phen*)] or [PtCl(HgCl)(CH2CMe2C6H4)(bubipy)], whereas similar reactions with dimethylplatinum(II) complexes occur with trans stereochemistry. The reaction of 2 with CH2Cl2 occurs, with formal insertion of methylene into the arylplatinum bond, to give [PtCl2(CH2CMe2C6H4CH2)(phen*)], the first time such a reaction has been observed with the reagent CH2Cl2. Hydrogen peroxide reacts with 2 to give oxidative addition with trans stereochemistry to give [Pt(OH)2(CH2CMe2C6H4)(phen*)] and reaction with chlorinated solvent then gives [PtCl(OH)(CH2CMe2C6H4)(phen*)]. Depending on the reaction conditions, the peroxyacid m-ClC6H4CO3H reacts with 2 to give [Pt(OH2)2(CH2CMe2C6H4)(phen*)](m-ClC6H4CO2)2, [{Pt(OH2)2(CH2CMe2C6H4)(phen*)}.{Pt(OH)(OH2)(CH2CMe2C6H4)(phen*)}](m-ClC6H4CO2)3, or [PtCl{OOC(=O)C6H4Cl-m}(CH2CMe2C6H4)(phen*)]. Computational studies indicate that the stereochemistry of oxidative addition may be determined by kinetic or thermodynamic factors in different cases, and that the unique CH2 insertion reaction with CH2Cl2 occurs by a radical mechanism. X-ray structure determinations are reported for eight of the platinum(IV) complexes.

The platinum(II) complexes [PtCl(SMe2)(κ2-N,N′-L)]Cl and [PtMe(SMe2)(κ2-N,N′-L)]Cl, L = 2-C5H4NCH2NH-x-C6H4OH (x = 2, 3, or 4), have been prepared and structurally characterized. In all cases, the complexes form supramolecular polymers in the solid state by NH··Cl and OH··Cl hydrogen bonding to the chloride anion. The ligands are chiral at the amine nitrogen atom, and in all cases, the polymers are isotactic, formed by self-recognition or narcissistic self-assembly. The structures in the crystalline state all have the Me2S ligand trans to pyridyl, but in solution, the methylplatinum(II) complexes isomerise slowly to give an equilibrium with the isomers having the methyl group trans to the pyridyl donor.

The role of NH and OH groups in the oxidative addition reactions of the complexes [PtMe2(κ2-N,N′-L)], L = 2-C5H4NCH2NH-x-C6H4OH [3, x = 2, L = L1; 4, x = 3, L = L2; 5, x = 4, L = L3], has been investigated. Complex 3 is the most reactive. It reacts with CH2Cl2 to give a mixture of isomers of [PtMe2(CH2Cl)(κ3-N,N′,O-(L1-H)], 6, and decomposes in acetone to give [PtMe3(κ3-N,N′,O-(L1-H)], 7, both of which contain the fac tridentate deprotonated ligand. Complex 3 reacts with MeI to give complex 7, whereas 4 and 5 react to give [PtIMe3(κ2-N,N′-L2))], 8, or [PtIMe3(κ2-N,N′-L3)], 9, respectively. Each complex 3, 4, or 5 reacts with either dioxygen or hydrogen peroxide to give the corresponding complex [Pt(OH)2Me2(κ2-N,N′-L)], 10, L = L1; 11, L = L2; 12, L = L3. The ligand L3 in complexes 9 and 12 is easily oxidized to the corresponding imine ligand 2-C5H4NCH=N-4-C6H4OH, L4, in forming the complexes [PtIMe3(κ2-N,N′-L4)], 13, and [Pt(OH)2Me2(κ2-N,N′-L4)], 14, respectively. The NH and OH groups play a significant role in supramolecular polymer or sheet structures of the complexes, formed through intermolecular hydrogen bonding, and these structures indicate how either intramolecular or intermolecular hydrogen bonding may assist some oxidative addition reactions.

The reaction of RCH2X with [PtMe2(DPA)], 1, (DPA = di-2-pyridylamine) has given [PtXMe2(CH2R)(DPA)] by cis oxidative addition to give 2a, when R = 6-uracil, X = Cl, or 3a, when R = CO2H, X = Br, but by a mixture of cis and trans oxidative addition to give 4a/4b when R = 4-C6H4CO2H, X = Br. The unusual cis stereochemistry of oxidative addition is rationalized thermodynamically by the formation of an intramolecular hydrogen bond in 2a and 3a but not 4a, and kinetically by the role of the ligand DPA NH group in hydrogen bonding to halide. Complex 2a in the solid state forms an unusual supramolecular syndiotactic polymer by forming two different intermolecular NH..O=C hydrogen bonds to neighbouring molecules.

The oxidant diphenyldiselenide reacts with MIIMe2(bipy) (bipy = 2,2′-bipyridine) to form a pre-equilibrium involving weak adducts, from which [MMe2(bipy)]2·Ph2Se2 undergoes rate-limiting dissociation of phenylselenide preceded by the oxidative addition step to obtain [Me2(bipy)M-MMe2(bipy)(SePh)]+. Coordination of PhSe− gives the neutral MIII–MIII bonded dimers [MMe2(bipy)(SePh)]2. The dimers fragment in the presence of light to give radicals [MIIIMe2(bipy)(SePh)]˙. After reorientation in the solvent cage, the radicals interact to form triplet adducts [MIIIMe2(bipy)(SePh)·(bipy)MIIIMe2(SePh)]˙˙ with π-stacked ‘SePh·bipy’, followed by transformation via a Minimum Energy Crossing Point allowing [SePh]˙ transfer to give MIIMe2(bipy) and MIVMe2(bipy)(SePh)2. The regenerated MII reagent reacts with Ph2Se2 through the above sequence, allowing completion of reaction to give the MIV product only. The reaction of PtMe2(bipy) with diphenyldisulfide has been studied in an analogous manner to assist with interpretation of DFT results for reactions of diphenyldiselenide. In short, this study shows that photochemical cleavage of metal–metal bonds (Pd, Pt) via excitation to an M–M antibonding orbital facilates disproportionation of the MIII–MIII complex to MII and MIV complexes.

A new route to cycloneophylplatinum(II) complexes is reported and the selectivity of protonolysis of the platinum–aryl and −alkyl bonds has been determined. Reaction of [PtCl2(SMe2)2] with neophylmagnesium chloride gives the binuclear cycloneophylplatinum(II) complex [Pt2(CH2CMe2C6H4)2(μ-SMe2)2], 1, which is shown to exist as a mixture of syn and anti isomers. Complex 1 reacts reversibly with SMe2 to give [Pt(CH2CMe2C6H4)(SMe2)2], 2, and irreversibly with bidentate ligands NN = 3,4,7,8-tetramethyl-1,10-phenanthroline (phen*) or 4,4′-di-t-butyl-2,2’bipyridine (bubipy) to give the corresponding complexes [Pt(CH2CMe2C6H4)(phen*)], 3, and [Pt(CH2CMe2C6H4)(bubipy)], 4, respectively. Complex 2 reacts with HCl initially by cleavage of the aryl–platinum bond to give mostly trans-[PtCl(CH2CMe2Ph)(SMe2)2], which then rearranges to an equilibrium mixture with trans-[PtCl(C6H4-2-t-Bu)(SMe2)2], while 3 and 4 react to give [PtCl(CH2CMe2Ph)(phen*)] and [PtCl(CH2CMe2Ph)(bubipy)], which do not undergo the isomerization re...

The complexes [PtMe2(L)], L = 2-C5H4NCH2NH-x-C6H4OH (x = 2, 3, or 4), react with iodine to form [PtI2Me2(L)], by trans oxidative addition, when x = 3 or 4, and they are shown to have polymeric or sheet structures formed through NH···I hydrogen bonding. However, ligand dissociation occurs when x = 2 to give [(PtI2Me2)n] and, with methyl group transfer, the complex [(PtIMe3·PtI2Me2)2]. This tetraplatinum cluster complex is shown to have a double cubane structure, thus solving a longstanding puzzle.

The photolysis of the allylplatinum(IV) complex [PtBr(C3H5)(4-MeC6H4)2(bipy)], 1, bipy = 2,2'-bipyridine, in air yielded [{PtBr(4-MeC6H4)2(bipy)}2(μ-O2)], 2, the first diplatinum(IV) complex containing a single bridging peroxide ligand. The PtO-OPt bond distance in 2 is 1.481(3) A. Complex 2 is thought to be formed by homolysis of the allyl-platinum bond of 1, followed by reaction of the platinum(III) intermediate [PtBr(4-MeC6H4)2(bipy)] with oxygen.

The oxygen atom transfer reactions of 2-pyridyl-N-t-butyloxaziridine, pyox, with the dimethylplatinum(II) complex [Pt2Me4(μ-SMe2)2], 1, have been studied. In the presence of methanol or water, proton coupled oxygen atom transfer occurs, with displacement of dimethylsulfide ligands by the product ligand 2-pyridyl-N-t-butylmethanimine, pyim, to give initially the complexes [Pt(OH)(OR)Me2(pyim)], R = Me or H, respectively, which were slowly oxidized further to give the binuclear picolinate complexes [Pt2(μ-OR)2Me4(2-pyCO2)2], R = Me or H, respectively, and t-butylamine. The complex [Pt(OH)2Me2(pyim)] is also formed by oxidative addition of H2O2 to [PtMe2(pyim)], and the complex [Pt2(μ-OMe)2Me4(2-pyCO2)2] is also formed by reaction of 2-pyridyl-N-t-butylnitrone, pyNO, with complex 1 in methanol solution. The structures of several of the above complexes, as well as model complexes [PtXRMe2(pyim)], X = R = Cl; X = Cl or I, R = Me; X = Cl, R = CH2Cl, [PtMe(2-pyCO2)(dmso)] and [PtCl2(SMe2)(pyNO)], were determined to aid in characterization of new compounds. In the absence of a protic solvent, the oxaziridine group is still activated on reaction of pyox with complex 1 but a more complex mixture of products is formed.

The ligands RN(CH2-2-C5H4N)2, L1, R = CH2C6H4-2-OH; L2, R = CH2C6H3-4-Me-2-OH; L3, R = CH2C6H3-5-Cl-2-OH; L4, R = CH2C6H3-5-NO2-2-OH; give dimethylplatinum(II) complexes that activate dioxygen in the absence of a protic solvent. The initial reaction with [Pt2Me4(SMe2)2] gives [PtMe2(κ2-N,N’-L)], and these react with oxygen to give [Pt(OH)Me2(κ3-N,N’,N”-L-H)], which exist as a mixture of isomers. The factors influencing reactivity and mechanism in these reactions are elucidated, and the presence of both a free pyridyl donor (push group) and a free hydroxyl (pull group) is suggested to give a synergy for dioxygen activation. Some platinum(II) complexes and trimethylplatinum(IV) complexes with these ligands are also reported.

A bidentate nitrogen-donor ligand with an appended phenol group, C5H4NCHN-2-C6H4OH, H(L1) was treated with a palladium cycloneophyl complex [Pd(CH2CMe2C6H4)(COD)], with both Pd-aryl and Pd-alkyl bonds, to give a Pd-alkyl complex, [Pd(CH2CMe2C6H5)(κ3-N,N′,O-OC6H4NCH(2-C5H4N))], 1. The cleavage of the Pd-aryl bond and the deprotonation of the ligand phenol to afford a bound aryloxide, indicates facile Pd-aryl bond protonolysis. Deuterium labelling experiments confirmed that the ligand phenol promotes protonolysis and that the reverse, aryl C-H activation, occurs under very mild reaction conditions (within 10 min at room temperature). An unusual isomerization of the Pd-alkyl complex 1 to a Pd-aryl complex, [Pd(C6H4(2-t-Bu))(κ3-N,N′,O-OC6H4NCH(2-C5H4N))], 2, was observed to give an equilibrium with [2]/[1] = 9 after 5 days in methanol. The isomerization requires that both aryl C-H activation and Pd-alkyl protonolysis steps occur. The very large KIE value (kH/kD = ca. 40) for isomerization of 1 to 2, suggests a concerted SE2-type mechanism for the Pd-alkyl protonolysis step.

The ligand N(CH2-2-C5H4N)2(CH2CH2CH2OH), L1, reacted with [Pd(CH2CMe2C6H4)(COD)] to give a new fluxional "cycloneophyl" organopalladium complex [Pd(CH2CMe2C6H4)(κ2-L1)], 1, which on attempted recrystallization from THF gave the monodentate carbonate complex [Pd(CO3)(κ3-L1)], 2. Complex 2 was prepared in designed syntheses by reaction of [PdCl(κ3-L1)]+ with silver carbonate or by reaction of [Pd(OH)(κ3-L1)]+ with CO2. Complex 1 reacted with aqueous CO2 to give the cationic neophylpalladium complex [Pd(CH2CMe2C6H5)(κ3-L1)]+(HCO3)-, 6. Complex 6 reacts with hydrogen peroxide to give complex 2 with release of a mixture of organic products, the major one being 2-phenyl-2-butanol, PB. The formation of PB involves a neophyl rearrangement with the unprecedented preference for methyl over phenyl migration. A mechanistic basis for this unexpected reaction is proposed, involving β-carbon elimination at a palladium(IV) center.

The ligands RN(CH2-2-C5H4N)2 (L1, R = CH2CH2OH; L2, R = CH2CH2CH2OH; L3, R = 2-C6H4OH) have been designed to give dimethylplatinum(II) complexes that can activate dioxygen in the absence of a protic solvent. The ligands react with [Pt2Me4(SMe2)2] to give an equilibrium mixture, with the major constituent being [PtMe2(κ2-N,N′-L)] (1a, L = L1; 1b, L = L2; 1c, L = L3). In the absence of air, 1a reacts with solvent CH2Cl2 to give [PtMe2(CH2Cl)(κ3-N,N′,N″-L1]Cl, while 1c decomposes with loss of methane to give [PtMe(κ3-N,N′,N″-L3-H)] and then, by reaction with solvent, the binuclear complex [{PtMe(κ3-N,N′,N″-L3-H)}2(μ-H)]Cl. In the presence of oxygen the complexes 1 in CH2Cl2 solution react to give [Pt(OH)Me2(κ3-N,N′,N″-L)]Cl, when L = L1 or L2, or [Pt(OH)Me2(κ3-N,N′,O-L-H)], when L = L3. The complex [Pt(OH)Me2(κ3-N,N′,N″-L2)]Cl decomposed in the presence of air to give the binuclear complex [{PtMe2(2-C5H4NCO2)(μ-OH)}2]. The factors influencing reactivity and mechanism in these reactions are elucidated, and th...

A review is given of the chemistry of compounds containing platinum-metal bonds, focussed on the research developed in the author's group. The synthetic methods, structures and bonding, and reactivity are treated, as well as the ability of some compounds to mimic the reactivity of platinum-containing bimetallic catalysts, which are widely used in petroleum reforming.

Notable differences are observed in reactions of platinum(II) precursor complexes with pyridine-imine ligands of formula 2-C5H4NCH = NCH2-C6H4OR with R = Me or H. The ligand 2-C5H4NCH = N-2-C6H4OMe, L1, gave simple complexes [PtXY(L1)], XY = Me,Me; Me,Cl; Cl,Cl. However, the ligand 2-C5H4NCH = NCH2-2-C6H4OH, L2, gave either [PtCl(κ3-N,N,O-2-C5H4NCH2N = CH-2-C6H4O)], in which the ligand L2 had undergone a proton migration and a deprotonation, or a more complex product arising from reaction with solvent. The ligand 2-C5H4NCH = NCH2-4-C6H4OH, L3, gave a complex [PtCl2(L3)], which formed a polymer in the solid state through intermolecular OH..Cl hydrogen bonding.

The reactions of methylene halides, CH2X2, with cycloneophylplatinum(II) complexes [Pt(CH2CMe2C6H4)(NN)], NN = 4,4’-di-t-butyl-2,2’-bipyridine or 3,4,7,8-tetramethyl-1,10-phenanthroline, gave either the product of cis oxidative addition [PtX(CH2X)(CH2CMe2C6H4)(NN)] or of cis oxidation with methylene insertion [PtX2(CH2CMe2C6H4CH2)(NN)]. By monitoring the reactions by NMR spectroscopy, it was shown that the major route to the methylene insertion product was by rearrangement of the initial product of oxidative addition. When X = I and NN = 4,4’-di-t-butyl-2,2’-bipyridine, the products of trans oxidative addition and methylene insertion were also detected in solution at intermediate stages of reaction. The methylene insertion step was strongly retarded in the presence of free halide, indicating that reaction occurred by way of a cationic intermediate formed by halide dissociation from [PtX(CH2X)(CH2CMe2C6H4)(NN)]. The chemistry gives useful insight into the possible mechanisms operating in catalytic chemistry involving methylene halides as methylene insertion reagents.

The synthesis of four new bis(phosphine-amide) ligands E{NHC( O)-4-C6H4PPh2}2, E = 1,4-C6H4, 1,3-C6H4, 1,4-C6H4(CH2)2 or 1,4-C6H10, is reported along with a preliminary study of their properties. The ligands are slowly oxidized in solution to give the corresponding phosphine oxides, and they form complexes with gold(I) with bridged structures [Au2Cl2{μ-E(NHC( O)-4-C6H4PPh2)2}] or large macrocyclic structures [Au2{μ-E(NHC( O)-4-C6H4PPh2)2}2]X2, with X− = triflate or nitrate. A macrocyclic platinum(II) complex cis,cis-[Pt2Cl4{μ-1,4-C6H4 (NHC( O)-4-C6H4PPh2)2}2], was prepared but an attempt to isolate a related cationic complex [Pt2(dppp)2{μ-E(NHC( O)-4-C6H4PPh2)2}](OTf)4 led to ligand hydrolysis, with formation of the unusual phosphine-carboxylate bridged complex [Pt2(dppp)2{μ-O2C-4-C6H4PPh2)2}](OTf)2, dppp = Ph2P(CH2)3PPh2. The amide groups of the bis(phosphine-amide) ligands take part in hydrogen bonding, which may lead to self-assembly of more complex structures.

The chiral diphosphine ligand R,R-cyclo-C6H10-trans-1,2-{NHC(=O)C6H4-2-PPh2}2, 1, forms complexes with gold(I) of formula [Au(1)]Cl, 2, and [(ClAu)2(µ-1)], 3, in which the diphosphine acts as a trans-chelate and bridging ligand, respectively. Oxidation of these gold(I) complexes leads to dissociation and oxidation of the diphosphine ligand to form the corresponding diphosphine dioxide R,R-cyclo-C6H10-1,2-{NHC(=O)C6H4-2-P(=O)Ph2}2, which has been crystallized in its protonated form and as complexes with Na+ and Fe2+, with [AuBr2]− or [AuBr4]− anions. Some of these compounds form supramolecular polymers by intermolecular hydrogen bonding.

The oxidative addition reactions of platinum(II) complexes [PtMe 2 (RN=CH-2-C 5 H 4 N)], especially when R = CH 2 CH 2 OH or CH 2 CH 2 CH 2 OH, have been studied. Both complexes react with R’X (MeI or PhCH 2 Br) by trans oxidative addition to give [PtXMe 2 R′(RN=CH-2-C 5 H 4 N)]. They also react with oxygen in methanol solution or with hydrogen peroxide to give [Pt(OH)(OMe)Me 2 (RN=CH-2-C 5 H 4 N)] or [Pt(OH) 2 Me 2 (RN=CH-2-C 5 H 4 N)], respectively, but the reactions are complicated in the case with R = (CH 2 ) 3 OH by partial cyclization of the imine ligand to give the corresponding oxazine complex. When R = CH 2 CH 2 OH, the complex [PtMe 2 (RN=CH-2-C 5 H 4 N)] reacts with oxygen in acetone solution to give the platinum(IV) complex [Pt(OH)Me 2 {κ 3 - N , N , O -RNH-CH(2-C 5 H 4 N)(CH CMeO)}], but no reaction occurs when R = CH 2 CH 2 CH 2 OH or CH 2 CH 2 NMe 2 . It is suggested that the hydroxyethyl substituent plays a key role in the dioxygen activation and subsequent reactions of a coordinated acetone molecule.

The coordination chemistry of mercury(II) halides, HgX2, X = Cl, Br, I, with N-methyl-α-(2-pyridyl)nitrone, L1, and N-t-butyl-α-(2-pyridyl)nitrone, L2, is reported. The structures of 1 : 1 complexes [HgX2L], X = Cl, L = L1; X = Br, L = L2, 2 : 1 complexes [(HgX2)2L], X = Br or I, L = L1; X = Cl or I, L = L2, and a unique compound [(HgBr2)5(L2)3] have been determined. In the 1 : 1 and 1 : 2 complexes, the ligand L1 adopts the anti conformation, and is either monodentate or bridging, while the ligand L2 adopts the syn conformation and acts as a chelate ligand. In the compound [(HgBr2)5(L2)3] the ligand L2 is present in both syn-chelate and anti-bridging bonding modes. Secondary intermolecular bonding, involving O⋯Hg or X⋯Hg interactions, can lead to association of the molecular compounds to form polymers of several kinds. In solution, the complexes are labile and the crystalline products do not necessarily reflect the reaction stoichiometry.

Malcolm Chisholm was one of the most creative and distinguished inorganic chemists of his generation. He was particularly renowned for his chemistry of compounds containing multiple metal–metal bonds and for showing how they could give insights into catalysis or be used in functional materials. Very early in his independent career he reported the remarkable compounds M 2 X 6 , with M = molybdenum or tungsten and X = alkoxide or dialkylamide, which contain metal–metal triple bonds, and his group showed how they could activate organic compounds in unusual ways, often with changes in the metal–metal bond order. He was a master of synthetic chemistry, but he also made notable discoveries in theory, spectroscopy and catalysis. Personally, he was outgoing, friendly and fun-loving. He was faithful and supportive of his family, students, colleagues and his many friends around the globe, and took great pleasure in their successes.

The self-assembly of [Au2(μ-(±)binap)X2], which have weakly coordinated anions X− = trifluoroacetate, triflate or nitrate, with bis(amidopyridyl) ligands (NN) has given three different macrocyclic complexes of general formula [Au4(μ-(±)binap)2(μ-NN)2]X4, an open complex [Au2(μ-(±)binap)(κ1-NN)2]X2, and a polymer [{Au2(μ-(±)binap)(μ-NN)}n]X2n. Macrocycles with both homochiral (RR/SS) and heterochiral (RS/SR) combinations of the two binap ligands in the cations [Au4(μ-binap)2(μ-NN)2]4+ have been structurally characterized. The polymeric complex has the syndiotactic (heterochiral) architecture. The donor ability of the anion X− is shown to affect both the degree of self-assembly in solution, through competition with the bis(amidopyridyl) ligand for coordination to gold(I), and the conformation of the bis(amidopyridyl) ligand in the products, through hydrogen bonding effects. In solution, there is a rapid equilibrium between cyclic and open chain oligomers, as determined by ESI-MS and NMR studies.

The aerobic oxidation of the binuclear ruthenium(0) carbonyl complexes [Ru2(CO)5(μ-dppm)2], dppm = Ph2PCH2PPh2, 1, and [Ru2(μ-H) (CO)5(μ-dppm)2]+X−, 2, has been studied. In acidic solution a 4-electron oxidation of 2 occurs to give [Ru2(μ-OH)2CO)4(μ-dppm)2]X2, X = ReO4 or BF4. However, in neutral solution aerobic oxidation occurs in 2-electron steps, with parallel 2-electron oxidation of a carbonyl ligand. The reaction of complex 1 in acetone solution gave a diruthenium(I) formate derivative [Ru2(μ-OH) (O2CH) (CO)3(μ-dppm)2], while reaction in dichloromethane solution gave a diruthenium(II) carbonate derivative [Ru2(CO3) (CO) (Cl) (μ-OH) (μ-CO) (μ-dppm)2]. The aerobic oxidation of 1 in the presence of methyl isocyanide and NH4[PF6] gave [Ru2(CO)2(CNMe)4(μ-dppm)2][PF6]2. The structural characterization of the products is described, and likely mechanisms of reaction are discussed.

The coordination chemistry of palladium(II) with bis(3-amidopyridine) ligands [LL = 2,6-C5H3N(CONH-3-C5H4N)2, 1; 1,3-C6H4(CONH-3-C5H4N)2, 2; 1,3-C6H4(CONMe-3-C5H4N)2, 3; 2,5-C4H2S(CONMe-3-C5H4N)2, 4] has been investigated. Neutral binuclear macrocyclic complexes trans,trans-[Pd2X4(μ-LL)2] have been characterized with X = Cl or Br and LL = 1. Cationic complexes have been characterized as mononuclear bis(chelate) derivatives [Pd(LL)2]2+, when LL = 3 or 4, but a lantern complex [Pd2(μ-LL)4]4+, when LL = 2. The tendency for chelation versus bridging coordination of the flexible ligands 1–4 is analyzed in terms of substituent effects on the preferred ligand conformations. In the dipalladium complexes, the macrocycle or lantern structure can accommodate guest molecules.

The bis(pyridine) ligand thiophene-2,5-dicarboxylic acid bis(N-methyl-N-4-pyridyl-amide), 1, reacts with [Pt2Me4(μ-SMe2)2], with displacement of Me2S, to give the chelate complex [PtMe2(1)], 2, which then reacts with methyl iodide to give [PtIMe3(1)], 3. Complex 3 spontaneously dimerizes to give a macrocyclic complex [{PtIMe3(μ-1)}2], 4, which exists as a mixture of anti and syn isomers 4a and 4b, as characterized by both NMR spectroscopy and X-ray structure determination. In the complex 4*, formed by oxidative addition of CD3I, the CH3 and CD3 ligands are scrambled between the axial and equatorial coordination sites at platinum(IV). The dimerization can be considered as a model for the first step in a dynamic ring-opening polymerization and occurs to give a new conformation of the flexible ligand.

The oxidation of [PtMe2(bu2bipy)] with XeF2 in dichloromethane or acetonitrile solution has given crystals of trans-[PtFClMe2(bu2bipy)] or trans-[PtF{NHC( O)Me}ClMe2(bu2bipy)] respectively, but none of the expected product [PtF2Me2(bu2bipy)]. It is suggested that the initial reaction occurs with solvent participation to give xenon and trans-[PtF(S)Me2(bu2bipy)]+ F−, S = solvent. When S = CH2Cl2, this is followed by rapid nucleophilic attack by fluoride on the coordinated solvent to give trans-[PtFClMe2(bu2bipy)] and CH2FCl, but, when S = MeCN, by slow hydrolysis to give trans-[PtF{NHC( O)Me}Me2(bu2bipy)] and HF. The evidence is based on monitoring of the reactions by 1H and 19F NMR spectroscopy in CD2Cl2 or CD3CN solvent. The mechanistic conclusions are significant in the context of the current interest in the use of XeF2 as a reagent in C–F and C–C coupling reactions.

A rare example of the oxidation of a monomethylplatinum(II) complex with dioxygen is reported, aided by an appended phenol group. The ligands X-2-HO-C6H3CH2N(CH2-2-C5H4N)2 (L1, X = H; L2, X = 5-Cl; L3, X = 5-NO2; L4, X = 4-Me) react with [PtClMe(SMe2)2] to give the corresponding complexes [PtMe(κ3-N,N’,N’’-L)]Cl in which L acts as a tridentate pincer ligand, binding through all three nitrogen donors with the phenol group not coordinated. When L = L1 – L3, the complexes react rapidly with hydrogen peroxide and slowly with dioxygen from air to give the corresponding platinum(IV) complexes [Pt(OH)Me(κ4-N,N’,N”,O-L-H)]Cl, in which the deprotonated phenol group is coordinated trans to the hydroxo ligand. The structures of three of these complexes are determined and all are shown to self-assemble with water molecules to form hydrogen-bonded supramolecular polymers. The mechanisms of the oxidation reactions are discussed.

The reactions of halogens or their equivalent with the cycloneophylplatinum (II) complex [Pt (CH2CMe2C6H4) (phen*)], phen* = 3,4,7,8-tetramethyl-1,10-phenanthroline, are reported. The reactions occur by kinetically controlled trans oxidative addition to form trans-[PtX2(CH2CMe2C6H4) (phen*)], X = Cl, Br, I, and, when X = Br or I, these equilibrate slowly with the products of cis oxidative addition cis-[PtX2(CH2CMe2C6H4) (phen*)], X = Br, I. The complex cis-[PtCl2(CH2CMe2C6H4) (phen*)] was prepared by reaction of [PtCl(CH2CMe2C6H5) (phen*)] with chlorine equivalent, in a reaction that involves a cyclometalation step at platinum (IV). The unusual complex [PtCl(CH2CMe2C6H4) (CH2CMe2C6H5) (phen*)], which contains both a neophyl and a cycloneophyl group, was isolated as a minor product from reaction of [Pt (CH2CMe2C6H4) (phen*)] with HCl. The mechanisms of several of these reactions are elucidated and seven structure determinations are reported.

The oxidative addition chemistry of cycloneophylplatinum (II) complexes containing ligands with an appended phenol group is reported. The platinum (II) complexes [Pt (CH2CMe2C6H4) (L)] with L = 2-C6H4NCH N-2-C6H4OH (L1) or 2-C6H4NCH2–NH-n-C6H4OH (L2, n = 2; L3, n = 3; L4, n = 4) react with MeI or H2O2 to give the corresponding platinum (IV) complexes [PtIMe(CH2CMe2C6H4) (L)] or [Pt (OH)2(CH2CMe2C6H4) (L)], respectively. NMR studies indicate that methyl iodide initially gives trans oxidative addition, but the initial products isomerize rapidly, often to give complex mixtures. The crystalline products all have structures with cis orientation of the PtIMe unit, whose formation is thought to require two isomerization steps after the initial oxidative addition. In contrast, the oxidative addition of H2O2 occurs with trans stereochemistry and no subsequent isomerization is observed. The iodoplatinum (IV) complexes [PtIMe(CH2CMe2C6H4) (L)] form intramolecular OH.I hydrogen bonds (L1) or intermolecular OH.I hydrogen bonds to give head-to-tail dimers (L2 or L4), or a hydrogen bond to solvent (L3). The complex [Pt (OH)2(CH2CMe2C6H4) (L4)] forms an unusual racemic supramolecular polymer with multiple OH.O and NH O hydrogen bonds.

This work has established the double and quadruple cyclometalation of the ligands 1,3- or 1,4-C6H4(CONHCH2CH2PPh2)2 (dpipa or dppeta respectively) by either reagent [Pt2Me4(μ-SMe2)2], 1, or [Pt(O2CCF3)2(SMe2)2], 2b, to give complexes containing new PNC-pincer ligands. The major product formed depends primarily on the stoichiometry of the reaction, but also on the reaction conditions. Reaction of a 1:1 mixture of dppeta and 1 followed by crystallization from a solvent mixture containing dmso, gave remarkable quadruple metalation of dppeta in the product [Pt2(dmso)2(μ-κ6-C,C′,N,N′,P,P′-C6H2{C( O)N(CH2)2PPh2}2)], which contains two PNC-pincer groups. Reaction of a 1:1 mixture of dpipa and 2b gave double metalation of dpipa in the dimeric product [Pt2{μ-κ4-C,N,P,P′-C6H3(CONH(CH2)2PPh2)(CON(CH2)2PPh2)}2], which contains one PNC-pincer group for each dpipa ligand used. Related reactions were monitored by NMR spectroscopy and gave insight into the reaction sequences involved in the cyclometalation steps. It is argued that phosphine coordination directs a first N–H bond activation and then, in a faster step, that the amido group formed in this step directs an aryl C–H bond activation step, to give double cyclometalation of one arm of the dicarboxamide-diphosphine ligand and that, if stoichiometry allows, this can be followed by similar double cyclometalation of the second arm to give the quadruply cyclometalated ligand.

The chemistry of the heterobinuclear platinum-iridium complex [PtIr(CO)3(μ-dppm)2][PF6], 1, dppm = Ph2PCH2PPh2, is described. The reaction of a hydride with 1 gave [HPtIr(CO)2(μ-dppm)2], by displacement of the carbonyl ligand from platinum, while reaction of 1 with dihydrogen, hydrogen chloride or Ph2MeSiH gave the fluxional complex [PtIrH4(CO)(μ-dppm)2][PF6], [PtIrH2Cl2(CO)(μ-dppm)2][PF6], or [PtIrH(SiMePh2)(CO)2(μ-dppm)2][PF6], respectively, by oxidative addition at iridium. Complex 1 reacted, often regioselectively, with several alkynes to give the μ-η(1),η(1) bridging alkyne complexes [PtIr(μ-RCCR')(CO)2(μ-dppm)2][PF6], R = H, R' = Ph, 4-C6H4Me, CO2Me; R = Ph, R' = CO2Me; R = R' = CO2Me. The complex [PtIr(μ-HCC-4-C6H4Me)(CO)2(μ-dppm)2][PF6] reacted reversibly with CO to give [PtIr(μ-HCC-4-C6H4Me)(CO)3(μ-dppm)2][PF6] and [PtIr(CO)3(μ-dppm)2][PF6], 1. With HCl, [PtIr(μ-HCC-4-C6H4Me)(CO)2(μ-dppm)2][PF6] reacted to give [PtIrHCl(μ-HCC-4-C6H4Me)(CO)2(μ-dppm)2][PF6], by oxidative addition at iridium, and then the alkenylplatinum derivative [PtIrCl{HC=CH(4-C6H4Me)}(CO)2(μ-dppm)2][PF6]. [PtIr(μ-HCC-4-C6H4Me)(CO)2(μ-dppm)2][PF6] reacted slowly with dihydrogen to give 4-MeC6H4CH=CH2 and [PtIrH4(CO)(μ-dppm)2][PF6]. The complex [PtIr(μ-HCCPh)(CO)2(μ-dppm)2][PF6] is intensely luminescent in solution at room temperature, with features characteristic of a d(8)-d(8) face-to-face complex.

The oxidative addition of alkyl bromides, RBr, to the dimethylplatinum(II) complex [PtMe 2 (bpox)], 1,bpox ¼ 2,5-bis(2-pyridyl)-1,3,4-oxadiazole gave the corresponding organoplatinum(IV) complexes[PtBrMe 2 (R)(bpox)], R ¼ CH 2 e4-C 6 H 4 C(]O)NHCH 2 Ph, 2;R¼ CH 2 e4-C 6 H 4 C(]O)NHe4-C 6 H 4 et-Bu, 3;R ¼ CH 2 e4-C 6 H 4 C(]O)NHe3,5-C 6 H 3 et-Bu 2 , 4;R¼ CH 2 e2-C 6 H 4 CH 2 OH, 5, which contain amide oralcohol functional groups. Several of these complexes form supramolecular polymers in the solid statethrough intermolecular hydrogen bonding. In complex 2 there is complementary hydrogen bondingbetween amide groups, while in complexes 3 and 5 the hydrogen bonding involves the oxygen atom ofthe bpox ligand as acceptor.© 2014 Elsevier B.V. All rights reserved. IntroductionThe oxidative addition of alkyl halides, RX, to organo-platinum(II)complexes[PtMe 2 L 2 ]isaversatilemethodtointroducemany functional alkyl groups to the organoplatinum(IV) products[PtXRMe 2 L 2 ] [1e6]. In particular, the alkyl group R may containhydrogen bonding groups such as carboxylic acids, amides, orphenols [7e13]. The chemistry is possible because alkylplatinu-m(IV)bondsareusuallystabletoprotonolysis,andalsobecausetheoxidative addition reactions occur more rapidly than protonolysisof the methylplatinum(II) bonds in the precursor complex [9e13].Thefunctional organoplatinum(IV)complexes canthen takepart infurther reactions, and they can self-assemble to give supramolec-ular polymers or network materials in a similar way as for organiccompounds or inorganic complexes containing analogous func-tional groups [14e24]. For example, the incorporation of an ami-doalkyl group into an organoplatinum complex by oxidativeaddition, and the formation of a supramolecular polymer on crys-tallization, is illustrated in Scheme 1 [24].In earlier papers, it has been shown that the complex[PtMe2(bpox)], 1, Scheme 2, can give organoplatinum(IV) com-plexes containing carboxylic acid or boronic acid groups (A, B,Scheme 2)and that the freeoxygenand nitrogen atoms of the bpoxligand can participate as hydrogen bond acceptors in forming su-pramolecular polymers [25,26]. This paper reports the formationand structures of organoplatinum(IV) complexes derived fromcomplex 1 that contain amide or alcohol groups as hydrogen bonddonors.Results and discussionThree organoplatinum(IV) complexes 2e4 containing ami-doalkyl groups were prepared by oxidative addition of the BreCH

Several platinum(II) complexes with ligands containing azo groups have been prepared and structurally characterised, and their photoswitching between trans and cis azo group isomers has been studied. The azo groups in the cationic complexes [PtMe(bipy)(4-NC5H4-NN-4-C6H4X)][PF6], X = H, OH or NMe2, and in the dicationic complex [Pt(bipy)(4-H2NC6H4-NN-C6H5)2][OTf]2 undergo trans to cis photoswitching on irradiation at 365 nm. The complex [PtMe(bipy)(4-NC5H4-NN-4-C6H4NMe)2][PF6] also exhibits a reversible halochromic effect on protonation to give the dicationic complex [PtMe(bipy)(4-NC5H4-NHN-4-C6H4NMe2]2+. The nature of the frontier orbitals in the platinum(II) complexes depends on the charge on the complex and on the degree of metal–ligand π-bonding.

The ligand 1,4-di-2-pyridyl-5,6,7,8,9,10-hexahydrocycloocta[d]pyridazine (6-dppd) contains two potential chelate groups, but it coordinates to only one dimethylplatinum group in forming the complex [PtMe2(6-dppd)], 1. Complex 1 contains a free pyridyl and a free pyridazine nitrogen donor, but it fails to coordinate to ZnCl2 or to CuCl to give a bimetallic complex. Complex 1 reacted with mercury(II) salts HgX2 (X = Cl, Br, OAc), not by coordination but by oxidative addition to the dimethylplatinum(II) center to give the platinum(IV) complexes [PtX(HgX)Me2(6-dppd)]. Complex 1 reacted with bromine or iodine by trans oxidative addition to give [PtX2Me2(6-dppd)], X = Br or I, but, when X = I, a more complex sequence of reactions also gave rise to products of cis oxidative addition and to the products [PtIMe3(6-dppd)] and [PtI3Me(6-dppd)], which arise through a methyl group transfer reaction. Complex 1 reacted with alkyl halides RX by trans oxidative addition to give [PtXRMe2(6-dppd)], R = Me, X = I; R = CH2Ph,...