Platinum Intermediates Research Articles

Stability and C-H Bond Activation Reactions of Palladium(I) and Platinum(I) Metalloradicals: Carbon-to-Metal H-Atom Transfer and an Organometallic Radical Rebound Mechanism.

One-electron oxidation of palladium(0) and platinum(0) bis(phosphine) complexes enables isolation of a homologous series of linear d9 metalloradicals of the form [M(PR3)2]+ (M = Pd, Pt; R = tBu, Ad), which are stable in 1,2-difluorobenzene (DFB) solution for >1 day at room temperature when partnered with the weakly coordinating [BArF4]- (ArF = 3,5-(CF3)2C6H3) counterion. The metalloradicals exhibit reduced stability in THF, decreasing in the order palladium(I) > platinum(I) and PAd3 > PtBu3, especially in the case of [Pt(PtBu3)2]+, which is converted into a 1:1 mixture of the platinum(II) complexes [Pt(PtBu2CMe2CH2)(PtBu3)]+ and [Pt(PtBu3)2H]+ upon dissolution at room temperature. Cyclometalation of [Pt(PtBu3)2]+ can also be induced by reaction with the 2,4,6-tri-tert-butylphenoxyl radical in DFB, and a common radical rebound mechanism involving carbon-to-metal H-atom transfer and formation of an intermediate platinum(III) hydride complex, [Pt(PtBu2CMe2CH2)H(PtBu3)]+, has been substantiated by computational analysis. Radical C-H bond oxidative addition is correlated with the resulting MII-H bond dissociation energy (M = Pt > Pd), and reactions of the metalloradicals with 9,10-dihydroanthracene in DFB at room temperature provide experimental evidence for the proposed C-H bond activation manifold in the case of platinum, although conversion into platinum(II) hydride derivatives is considerably faster for [Pt(PtBu3)2]+ (t1/2 = 1.2 h) than [Pt(PAd3)2]+ (t1/2 ∼ 40 days).

Interconversion of Atomically Dispersed Platinum Cations and Platinum Clusters in Zeolite ZSM-5 and Formation of Platinum gem-Dicarbonyls.

Catalysts composed of platinum dispersed on zeolite supports are widely applied in industry, and coking and sintering of platinum during operation under reactive conditions require their oxidative regeneration, with the platinum cycling between clusters and cations. The intermediate platinum species have remained only incompletely understood. Here, we report an experimental and theoretical investigation of the structure, bonding, and local environment of cationic platinum species in zeolite ZSM-5, which are key intermediates in this cycling. Upon exposure of platinum clusters to O2 at 700 °C, oxidative fragmentation occurs, and Pt2+ ions are stabilized at six-membered rings in the zeolite that contain paired aluminum sites. When exposed to CO under mild conditions, these Pt2+ ions form highly uniform platinum gem-dicarbonyls, which can be converted in H2 to Ptδ+ monocarbonyls. This conversion, which weakens the platinum-zeolite bonding, is a first step toward platinum migration and aggregation into clusters. X-ray absorption and infrared spectra provide evidence of the reductive and oxidative transformations in various gas environments. The chemistry is general, as shown by the observation of platinum gem-dicarbonyls in several commercially used zeolites (ZSM-5, Beta, mordenite, and Y).

Ambipolar Discotic Liquid Crystals Built Around Platinum Diimine-Dithiolene Cores.

Platinum diimine dithiolene complexes bearing mesogenic groups on one or both ligands have been prepared through an original ligand metathesis reaction to introduce the dithiolene ligand. The neutral diimine ligands, the intermediate platinum dichloride diimine complexes, and the target compounds were characterized by a combination of electronic (electrochemistry, absorption and emission spectroscopy, DFT calculations) and structural (SAXS, DSC) tools. Several novel liquid crystalline platinum diimine-dithiolene were identified over a large temperature range, and the systems were endowed with ambipolar properties, associated with the high reversibility of both oxidation and reduction processes.

Fast Cryomediated Dynamic Equilibrium Hydrolysates towards Grain Boundary-Enriched Platinum Scaffolds for Efficient Methanol Oxidation.

Although platinum nanocrystals have been considered as potential electrocatalysts for methanol oxidation reaction (MOR) in fuel cells, the large-scale practical implementation has been stagnated by their limited abundance, easy poisoning, and low durability. Here, grain boundary-enriched platinum (GB-Pt) scaffolds are produced in large scale via facilely reducing fast cryomediated dynamic equilibrium hydrolysates of platinum salts. Such plentiful platinum grain boundaries are originated from the fast fusion of short platinum nanowires during reduction of the individually and homogeneously dispersed platinum intermediates. These grain boundaries can provide abundant active sites to efficiently catalyze MOR and meanwhile enable to oxidize the adsorbed poisonous CO during the electrocatalytic process. As a consequence, the as-synthesized GB-Pt scaffolds exhibit an impressively high mass activity of 1027.1 mA mgPt−1 for MOR, much higher than that of commercial Pt/C (345.2 mA mgPt−1), as well as good stability up to 5000 cycles. We are confident that this synthetic protocol can be further extended to synthesize various grain boundary-enriched metal scaffolds with broad applications in catalysis.

Ligand-Controlled Synthesis of [3]- and [4]Cyclo-9,9-dimethyl-2,7-fluorenes through Triangle- and Square-Shaped Platinum Intermediates.

The syntheses of [3]- and [4]cyclo-9,9-dimethyl-2,7-fluorenes ([3] and [4]CFRs), cyclic trimer, and tetramers of 9,9-dimethyl-2,7-fluorene (FR), respectively, were achieved by the platinum-mediated assembly of FR units and subsequent reductive elimination of platinum. A triangle-shaped tris-platinum complex and a square-shaped tetra-platinum complex were obtained by changing the platinum ligand. The structure of the triangle complex was unambiguously determined by X-ray crystallographic analysis. Reductive elimination of each complex gave [3] and [4]CFRs. Two rotamers of [3]CFR were sufficiently stable at room temperature and were separated by chromatography. The physical properties of the CFRs were also investigated theoretically and experimentally.

Heterometallic complexes with cube-type [MTi3N4] cores containing Group 10 metals in a variety of oxidation states.

Treatment of [{Ti(η5-C5Me5)(μ-NH)}3(μ3-N)] (1) with one equivalent of [Ni(cod)2] (cod = 1,5-cyclooctadiene) in toluene at 60–80 °C and subsequent addition of diphenylacetylene, trans-stilbene or triphenylphosphane afforded the nickel(0) complexes [LNi{(μ3-NH)3Ti3(η5-C5Me5)3(μ3-N)}] (L = PhCCPh (2), PhCH≡CHPh (3), PPh3 (4)). The nickel(II) complex [I2Ni{(μ3-NH)3Ti3(η5-C5Me5)3(μ3-N)}] (5) was prepared by analogous addition of iodine to the solution obtained from the heating of 1 and [Ni(cod)2]. Treatment of 1 with one equivalent of [Pd(dba)2] (dba = dibenzylideneacetone) in toluene at room temperature led to the palladium(0) complex [(dba)Pd{(μ3-NH)3Ti3(η5-C5Me5)3(μ3-N)}] (6). Compound 6 reacted immediately with chloroform-d1 to give the palladium dichloride derivative [Cl2Pd{(μ3-NH)2Ti3(η5-C5Me5)3(μ-NH)(μ3-N)}] (7), which was prepared by treatment of 1 with [PdCl2(cod)] at room temperature. Addition of iodine to a toluene solution of 6 afforded the analogous palladium(II) derivative [I2Pd{(μ3-NH)2Ti3(η5-C5Me5)3(μ-NH)(μ3-N)}] (8). Complex 6 reacted with two equivalents of dimethylacetylenedicarboxylate (dmad) to give the metallacyclopentadiene palladium(II) complex [{(MeOOC)4C4}Pd{(μ3-NH)2Ti3(η5-C5Me5)3(μ-NH)(μ3-N)}] (9) via oxidative coupling. The treatment of 1 with [Pt(nbe)3] (nbe = norbornene) in toluene at room temperature gave the platinum(0) complex [(nbe)Pt{(μ3-NH)3Ti3(η5-C5Me5)3(μ3-N)}] (10). Compound 10 reacted with excess iodine to afford the platinum(IV) ionic derivative [I3Pt{(μ3-NH)3Ti3(η5-C5Me5)3(μ3-N)}]2(I3)(I5) (11) via an intermediate platinum(II) complex [I2Pt{(μ3-NH)2Ti3(η5-C5Me5)3(μ-NH)(μ3-N)}] (12). The X-ray crystal structures of 5, 8, 9 and 11 have been determined.

Selective and Random Syntheses of [n]Cycloparaphenylenes (n = 8–13) and Size Dependence of Their Electronic Properties

[n]Cycloparaphenylenes (n = 8-13, CPPs) were synthesized, and their physical properties were systematically investigated. [8] and [12]CPPs were selectively prepared from the reaction of 4,4'-bis(trimethylstannyl)biphenyl and 4,4''-bis(trimethylstannyl)terphenyl, respectively, with Pt(cod)Cl(2) (cod = 1,5-cyclooctadiene) through square-shaped tetranuclear platinum intermediates. A mixture of [8]-[13]CPPs was prepared in good combined yields by mixing biphenyl and terphenyl precursors with platinum sources. Products were easily separated and purified by using gel permeation chromatography. In (1)H NMR spectra, the proton of the CPPs shifts to a lower field as n increased due to an anisotropic effect from the nearby PP moieties. Although the UV-vis spectra were rather insensitive to the size of the CPPs, the fluorescence spectra changed significantly in relation to their size. A larger Stokes shift was observed for the smaller CPPs. Redox properties of the CPPs were measured for the first time by using cyclic voltammetry, and the smaller CPPs had lower oxidation potentials. The results are consistent with the HOMO energies of CPPs, of which the smaller CPPs had higher energies.

Abstract 1714: Chemoresistance in patients with papillary serous carcinoma of the ovary

Abstract The majority of patients with ovarian carcinoma present at an advanced stage, with metastatic disease throughout the peritoneal cavity. Therefore, patients commonly undergo platinum-based chemotherapy. Even though the initial response rates can be high, the majority of patients will have recurrent disease and the 5-year survival rate is only 10-20%. The human lung resistance protein (LRP) is a multidrug resistance protein that has been shown to be overexpressed in models of chemotherapy resistance, but has not been adequately explored in platinum-resistant epithelial ovarian cancer (EOC). The primary aim of this study was to compare LRP expression in the tumor cells from ascitic fluid with tumor cells from omental metastasis in chemotherapy-naïve patients with advanced EOC. The secondary aim was to explore possible mechanisms in which LRP might cause drug resistance. After IRB approval, patient ascites and metastatic implants were collected and evaluated for platinum sensitivity and expression of LRP, phospho-ERK, and AKT using western blots and immunohistochemistry (IHC). Both ascites and omental metastatic implants were treated with 50 uM carboplatin for 48 hours and cell viability was analyzed. LRP, phospho-ERK, and AKT were analyzed using IHC on samples treated with 50 uM carboplatin or phosphate buffered saline. Of 20 patients who had matched ascites and omental metastatic implants adequate for analysis, 4 were platinum resistant, 3 were platinum sensitive, and 13 displayed intermediate platinum sensitivity. Overall, the malignant cells in ascites were more resistant to carboplatin than the metastatic implants (p=0.001) and the malignant cells in ascites showed higher expression of LRP than the omental metastatic implants by IHC and western blotting. IHC and western blotting also demonstrated that the malignant cells in ascites had lower expression of phospho-ERK and higher expression of AKT than the metastatic implants. After treatment with 50 uM carboplatin, the platinum resistant patients had decrease in phospho-ERK and an increase in AKT versus the platinum sensitive patients who had an increase in phopho-ERK and a decrease in AKT and LRP. High expression of LRP in the tumor cells in ascitic fluid may indicate platinum resistance prior to initiation of platinum-based chemotherapy. Also, changes in phospho-ERK and AKT following platinum based therapy may indicate the extent of response of EOC to this therapy. Supported in part by the Kaleidoscope of Hope ovarian cancer foundation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1714. doi:10.1158/1538-7445.AM2011-1714

Formation Mechanism of Oriented Pb(Zr,Ti)O3 Thin Films on Platinum Bottom Electrodes from Amorphous Films Prepared by Liquid Delivery Metalorganic Chemical Vapor Deposition

Ferroelectric Pb(Zr,Ti)O3 (PZT) thin films with 111- and 001/100-orientations were fabricated on silicon substrates covered with platinum (Pt). Amorphous PZT (a-PZT) films were deposited on Pt bottom electrodes by liquid delivery metalorganic chemical vapor deposition and subsequent postannealing by a special heating stage equipped with an X-ray diffraction system. Variations in the 111 d-space of Pt and the crystallization behavior of PZT layers were in situ measured in postannealing processes. The existence or absence of lead platinum intermediates in a-PZT layers near Pt bottom electrodes at the beginning of crystallization are suggested to be the key factor for obtaining 111- or 001/100-oriented crystalline PZT thin films.

Photophysical Properties of Platinum(II)−Acetylide Complexes: the Effect of a Strongly Electron-Accepting Diimine Ligand on Excited-State Structure

The compounds [Pt(MesBIAN)(C[triple bond]CR)2] (R = C6H4-CN-p, 1; SiMe3, 2; C6H4-CF3-p, 3; C6H5, 4; C6H4-CH3-p 5) {MesBIAN = bis(mesitylimino)acenaphthene} have been synthesized; the X-ray crystal structure determinations of 4 and 5 and the starting material [Pt(MesBIAN)Cl2] are reported. Chemical oxidation of 4 with diiodine leads to generation of an intermediate platinum(IV) bis(acetylide) diiodide complex, which then couples and reductively eliminates the acetylide ligands as a diyne, leading to the generation of [Pt(MesBIAN)I2] 6. Compound 2 readily forms an adduct 2a with copper(I) chloride, in which the copper atom is bonded to the two acetylide triple bonds. 1-5 each undergo an irreversible oxidation, and a reversible one-electron reduction to generate a stable anion. ESR studies of 1(-)-5(-) show that the unpaired electron is localized mainly on the pi* orbital of the coordinated MesBIAN ligand, with about 10% platinum contribution to the singly occupied molecular orbital (SOMO). The compounds show a strong absorption at around 500 nm in the UV/visible spectrum, which is assigned to a "mixed metal-ligand to ligand charge transfer" (MMLL'CT) transition; this assignment is supported by time-dependent density-functional theory (TD-DFT) calculations on 5. 1-5 emit in the near-infrared region from a (3)MMLL'CT excited state, with lifetimes ranging from 8 to 36 ns. Picosecond and nanosecond time-resolved infrared (TRIR) spectroscopy has been used to probe directly the nature and dynamics of the excited state of 5. The TRIR data show a decrease of the energy of the C[triple bond]C vibration upon excitation, by about 90 cm(-1) in comparison to the ground state, and formation of a new, very intense, and very broad band at 1820 cm(-1). We propose that the excited-state structure contains some contribution from a pseudo-cumulenic form of the platinum-acetylide moiety, which is supported by TD-DFT calculations. Picosecond TRIR allowed determination of the rate of vibrational relaxation (14 ps) of the vibrationally "hot" electronic excited state of 5 formed upon initial laser excitation.

Photochemistry of PtBr6 2− in aqueous solution

Photochemistry of the PtBr62− complex in aqueous solution was studied by steady-state and laser flash photolysis (308 nm). The multistep photoaquation of the complex occurs in the nano-and microsecond time intervals without the formation of intermediate platinum(III) complexes.

Protonolysis of a toluidinoalkyl platinum(ii) complex derived from the insertion of the CC bond into the Pt–NHR (amido) bond: the role of amine in Pt-catalyzed hydroamination of acrylonitrile

The complex Pt{2,6-(R2PCH2)2C6H3}(OTf) [R = Ph (1a), Cy (1b)] catalyzes the hydroamination of acrylonitrile with p-toluidine to produce CH2(CN)CH2NH(Tol-p), exclusively. In the catalyzed reactions, platinum intermediates were detected by NMR spectroscopy. The p-tolylamido platinum complex Pt{2,6-(Ph2PCH2)2C6H3}{NH(Tol-p)} (4), containing the pincer ligand, was synthesized from the reaction of 1a and NaNH(Tol-p). Complex 4 reacted with acrylonitrile to yield the regiospecific insertion product Pt{2,6-(Ph2PCH2)2C6H3}{CH(CN)CH2NH(Tol-p)} (5), quantitatively. Reaction of 5 with HX (X = Cl, OTf) generated free acrylonitrile, p-toluidine and Pt{2,6-(Ph2PCH2)2C6H3}X. Reacting 5 with a proton source having a non-coordinating counter anion, [NH3(Tol-p)]BPh4, also produced free acrylonitrile along with a cationic amine complex [Pt{2,6-(Ph2PCH2)2C6H3}{NH2(Tol-p)}]+. On the other hand, reaction of 5 with [NH3(Tol-p)]BPh4 in the presence of excess p-toluidine (ca. 30 equiv.) generated the hydroaminated product CH2(CN)CH2NH(Tol-p), predominantly. Treatment of 5 with [NH2Me2]BPh4 in the absence of amine bases also released the hydroaminated product. These results apparently reveal that the amine substrate plays a critical role in driving the catalytic cycle.

Investigation of the interfacial structure of ultra-thin platinum films using X-ray reflectivity and X-ray photoelectron spectroscopy

Ultra-thin films of platinum deposited on highly polished 100 silicon have been investigated using X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS) as part of a study on the interface structure of multilayers used for X-ray mirrors. In this paper results are presented for films deposited by electron beam evaporation and by DC-magnetron sputtering. The reflectivity was fitted by assuming an intermediate platinum silicide layer exists between the platinum and the silicon. XPS data clearly confirmed the existence of such a platinum silicide layer. According to the XRR data this layer was estimated to be approximately 10 Å thick for e-beam samples and approximately 30 Å thick for magnetron samples. For e-beam films the fitted density for the platinum silicide layer was found to decrease from 16.4 g·cm −3 for a nominal 80 Å film down to 2.65 g·cm −3 for a nominal 20 Å film. For magnetron sputtered films the fitted density was always within the range of 6.1–6.8 g·cm −3. The fitted density of the platinum layer from the e-beam results was always within 5% of the density of bulk platinum whereas for the magnetron sputtered films the density decreased uniformly with decreasing film thickness for films with a nominal thickness less than 30 Å. The XPS data show that the magnetron deposited platinum penetrates through the native oxide layer and into the silicon substrate to a far greater degree than the e-beam deposited platinum.

Reaction of DNA oligonucleotides with [Pt(dien)GSMe]2+ (GSMe = S-methylated glutathione) and cis-[Pt(NH3)2(GSMe)2]2+: evidence of oligonucleotide platination via sulfur-coordinated platinum intermediates.

To study the possibility of DNA platination via platinum-sulfur coordinated intermediates, the reactions of the complexes [Pt(dien)GSMe]2+ (GSMe=S-methylated glutathione) and cis-[Pt(NH3)2(GSMe)2]2+ with the synthetic oligonucleotides d(ATATGCATAT), d(ATTACCGGTAAT), and d(ATCCTATTTTTTTTAGGAT) have been investigated. The reactions were studied using FPLC, NMR, and mass spectrometry. It was found that the sulfur atom of the platinum-thioether adduct is substituted by these oligonucleotides. For the reactions with [Pt(dien)GSMe]2+ at 310 K, half-lives were determined to be t 1/2 =147+/-7 h for d(ATATGCATAT), t 1/2 =84+/-4 h) for d(ATTACCGGTAAT), and t 1/2 = 21+/-1 h for d(ATCCTATTTTTTTTAGGAT. This study clearly shows that it is indeed possible for oligonucleotides to be platinated via Pt-thioether coordinated intermediates. The rates at which such substitutions occur, however, makes it improbable that such a mechanism contributes significantly to the antitumor activity of cisplatin.

Platinum-Catalyzed Silaborative Coupling of 1,3-Dienes to Aldehydes: Regio- and Stereoselective Allylation with Dienes through Allylic Platinum Intermediates

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTPlatinum-Catalyzed Silaborative Coupling of 1,3-Dienes to Aldehydes: Regio- and Stereoselective Allylation with Dienes through Allylic Platinum IntermediatesMichinori Suginome, Hiroshi Nakamura, Takanori Matsuda, and Yoshihiko ItoView Author Information Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering Kyoto University, Kyoto 606-01, Japan Cite this: J. Am. Chem. Soc. 1998, 120, 17, 4248–4249Publication Date (Web):April 22, 1998Publication History Received3 February 1998Published online22 April 1998Published inissue 1 May 1998https://doi.org/10.1021/ja980373oCopyright © 1998 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1049Altmetric-Citations65LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (109 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Aldehydes,Hydrocarbons,Molecular structure,Platinum,Stereoselectivity Get e-Alerts

Laser pulse photolysis study of the reaction of the intermediate platinum(III) complex PtCl 2−5 and 4-(2- p-dimethylaminophenyl ethynil)-6,6-dimethyl-3-cyano-5,6-dihydro-2(1H)-pyridone

Laser flash photolysis was used to investigate the fast reaction of 4-(2- p-dimethylaminophenyl ethynil)-6,6-dimethyl-3-cyano-5,6-dihydro-2(1H)-pyridone (DHP) with the intermediate complex of platinum(III), PtCl 2− 5, appearing in the photoreduction of PtCl 2− 6 in methanol. Kinetic and spectroscopic parameters of the new-formed complex PtCl 2− 5|DHP were determined. DHP in this complex is coordinated by an −N(CH 3) 2 group nitrogen atom since a similar molecule with this group substituted by −O(CH 3) does not react with PtCl 2− 5. Steady-state photolysis has shown that the transformation Pt(III) å Pt(II) involves escape of DHP from the coordination sphere since the final complex Pt(II)|DHP is not formed.

Photochemistry of the PtCl 62− complex in methanol solution

In the laser flash photolysis of PtCl 6 2− in methanol, a non-linear dependence of the yields of the trivalent platinum intermediates PtCl 6 3− and PtCl 5 2− on laser pulse intensity is observed. The non-linearity is due to the absorption of photons by PtCl 6 3− which is a primary product resulting from the electron transfer from a methanol molecule to excited PtCl 6 2−. Photodissociation of PtCl 6 3− yields PtCl 5 2−. However, PtCl 6 3− in the ground state also dissociates into PtCl 5 2− and Cl −. This monomolecular process proceeds with an activation energy of 29.7 kJ mol −1 and a rate constant of 1.05 × 10 6 s −1 at 300 K. The parameters of the reverse reaction between Cl − and PtCl 5 2− which yields PtCl 6 3− have also been measured (activation energy, −9.6 kJ mol −1; rate constant at 300 K, 7.6 × 10 6 M −1 s −1). When free Cl − is present in methanol at a concentration of more than 0.1 – 0.2 M, electron transfer from Cl − to excited PtCl 6 2− is also possible. The chlorine atom formed reacts with Cl − yielding the radical ion Cl 2 − which is detected by an intense absorption band with a maximum at 340 nm.

A newly proposed cycle for the water gas shift reaction homogeneously catalyzed by platinum and tin chloride

Data previously reported by Cheng and Eisenberg for catalysis of the water gas shift (WGS) reaction by platinum and tin chlorides have been reviewed. A new catalytic cycle for the WGS catalysis that is consistent with more recent studies and the experimental data for the Pt-Sn system is presented. It appears to be likely that the platinum intermediates have the trichlorotin ligand, but the exact nature of the catalytic intermediates is still unknown. 16 refs., 2 figs.

Bimetallic systems. Part 12. Mixed rhodium(I)–platinum(II) acetylide complexes containing bridging Ph2PCH2PPh2. Crystal structures of [(MeCC)Pt(µ-dppm)2(σ,η-CCMe)Rh(CO)]PF6and of [ClPt(µ-dppm)2(σ,η-CCMe)Rh(CO)]PF6

Treatment of [Pt(CCMe)2(dppm-P)2] with [Rh2Cl2(CO)4] gave [(MeCC)Pt(µ-dppm)2(σ,η-CCMe)Rh(CO)]Cl readily converted into the corresponding PF6– salt (1b) the crystal structure of which was determined. Other complexes of the type [(RCC)Pt(µ-dppm)2(σ,η-CCR)Rh(CO)]Cl were made similarly; with R = Ph, p-tolyl, CH2CH2Ph, or C(Me)CH2. The complexes are fluxional with the low-temperature limiting 1H-{31P} n.m.r. spectrum showing non-equivalent pseudoequatorial and pseudo-axial CH2 protons, He coupled to 195Pt and Ha not. The fluxional process corresponds to interchange of He and Ha and interchange of terminal and bridging CCR. When heated in toluene for 3 h, [(RCC)Pt(µ-dppm)2(σ,η-CCR)Rh(CO)]Cl (R =p-tolyl or Ph) was converted into [(RCC)Pt(µ-dppm)2(σ,η-CCR) RhCl]. With CO, [(p-MeC6H4CC)Pt(µ-dppm)2(σ,η-CCC6H4Me-p)RhCl] rapidly gave back [(p-MeC6H4CC)Pt(µ-dppm)2(σ,η-CCC6H4Me-p)Rh(CO)]Cl. Treatment of [Pt(CCR)2(dppm-P)2] with [Rh2Cl2(C8H14)4](C8H14= cyclo-octene) also gave [(RCC)Pt(µ-dppm)2(σ,η-CCR)RhCl](R =p-tolyl or Ph) but the complexes were not isolated pure. Treatment of [(PhCC)2Pt(µ-dppm)2HgCl2] with [Rh2Cl2(CO)4] caused rapid and complete displacement of HgCl2, giving [(PhCC)Pt(µ-dppm)2(σ,η-CCPh)Rh(CO)]+; similarly treatment of [(PhCC)2Pt(µ-dppm)2AgCl], [(PhCC)2Pt(µ-dppm)2Cul], or [(PhCC)2Pt(µ-dppm)2Au]Cl with [Rh2Cl2(CO)4] gave [(PhCC)Pt(µ-dppm)2(σ,η-CCPh)Rh(CO)]+. Treatment of [Cl(RCC)Pt(µ-dppm)2AgCl] with [Rh2Cl2(CO)4] gave [ClPt(µ-dppm)2(σ,η-CCR)Rh(CO)]+(R = Me, Ph, or p-tolyl) isolated as PF6– or AgCl2– salts. These complexes could also be made in ‘one-pot’ syntheses, viz. successive treatment of [Pt(dppm-PP′)2]Cl2 with AgO2CMe–PhCCH followed by treatment with [Rh2Cl2(CO)4], without isolation of the intermediate platinum–silver complex. The crystal structures of [(MeCC)Pt(µ-dppm)2(σ,η-CCMe)Rh(CO)]PF6(1b) as the dichloromethane solvate and of [ClPt(µ-dppm)2(σ,η-CCMe)Rh(CO)]PF6(5a) were determined. Crystals of (1b) are orthorhombic, space group Pbca, a= 19.212(7), b= 27.364(6), c= 21.468(5)A, and Z= 8; those of (5a) are orthorhombic, space group Pn21a, a= 43.39(1), b= 25.178(9), c= 10.164(6)A, and Z= 8. Final R factors were 0.088 for 4 500 and 0.058 for 6 320 observed reflections, respectively. In each complex cation the two metal centres [Pt ⋯ Rh 3.099(2) for (1b) 3.066(2) and 3.086(2)A for (5a)] are bridged by a methylacetylide group σ-bonded to Pt and π-bonded in an unsymmetrical side-on fashion to Rh [mean Rh–CPt 2.24(2), mean Rh–CMe 2.44(2)A], giving rise to an A-frame structure.