| 1. |
- Andersson, Ingegärd, et al.
(författare)
-
Speciation in the aqueous H+/H2VO4–/H2O2/picolinate system relevant to diabetes research
- 2004
-
Ingår i: Dalton Transactions. - Cambridge : Royal Society of Chemistry, Thomas Graham House. - 1477-9226 .- 1477-9234. ; :3, s. 421-428
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the quaternary aqueous H+/H2VO4−/H2O2/picolinate (Pi−) system has been performed at 25 °C in 0.150 M Na(Cl) medium using quantitative 51V NMR (500 MHz) and potentiometric data (glass electrode). In the ternary H+/H2VO4−/Pi− system, six complexes have been found in the pH region 1–10. In the quaternary H+/H2VO4−/H2O2/Pi−system, eight additional complexes have been found. Generally, equilibria are fast in both systems. The rate of peroxide decomposition depends on the species in solution. Chemical shifts, compositions and formation constants for the species are given. Equilibrium conditions and the fit of the model to the experimental data are illustrated in distribution diagrams. Possible formation of mixed ligand species with imidazole, lactic acid and citric acid have been investigated and ruled out under the same experimental conditions. Structural proposals are given, based on 13C NMR data and available crystal structures.
|
|
| 2. |
|
|
| 3. |
- Desroches, C., et al.
(författare)
-
Design and synthesis of multifunctional thiacalixarenes and related metal derivatives for the preparation of sol-gel hybrid materials with non-linear optical properties
- 2003
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :10, s. 2085-2092
-
Tidskriftsartikel (refereegranskat)abstract
- Thiacalixarenes bearing phenylazo or ethynylic groups on the lower rims were prepared and fully characterized. The functional groups were chosen for their ability to increase the electron delocalisation over the molecule and to form metal complexes. The formation of complexes between phenylazothiacalixarenes and metal salts (Zn2+, Ag+...), and the synthesis of platinum acetylides from ethynylthiacalixarenes were investigated. Preliminary studies on optical limiting properties for both ligands and complexes is reported. Clamping levels of ~4 µJ at 532 nm, were observed for both tetra(pentylphenylethynyl)tetrapropoxythiacalix[4]arcne (150 mM in THF, 99% transmission) and the platinum complex (30 mM in THF, 83% transmission). A second functionalisation (upper rims) with metal alkoxide groups has also been investigated in order to prepare hybrid materials incorporating the optically active molecule. The same macrocycle core was thus bifunctionalised, and used for its optical properties on one side and as a precursor of an inorganic network for hybrid materials on the other. © The Royal Society of Chemistry 2003.
|
|
| 4. |
- Gorzsás, András, et al.
(författare)
-
A speciation study of the aqueous H+/H2VO4–/H2O2/L--alanyl-L-serine system
- 2003
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; , s. 1161-7
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the quaternary aqueous H+/H2VO4–/H2O2/L--alanyl-L-serine (Alaser) system has been performed at 25 °C in 0.150 M Na(Cl) medium, representing the ionic strength of human blood, using quantitative 51V NMR and potentiometric data (glass electrode). Data were evaluated with the computer program LAKE, which is able to treat combined EMF and NMR data. The pKa-values for Alaser were determined as 8.04 ± 0.01 and 3.07 ± 0.01. The errors given are 3. In the ternary H+/H2VO4–/Alaser system, two complexes, (H+)p(H2VO4–)q(Alaser)r, having (p, q, r) values (0, 1, 1) and (–1, 1, 1) with log0,1,1= 2.42 ± 0.01 and log–1,1,1=–5.80 ± 0.05 explain all data in the pH region 2.5–9.5. Equilibrium conditions are illustrated in distribution diagrams and structure proposals are given based on 1H and 13C NMR investigations. In the quaternary H+/H2VO4–/H2O2/Alaser system, six complexes could be found in addition to all binary and ternary complexes over the pH region 2.6–11.1, four with a V/X/Alaser ratio 1 1 1 and two with a ratio 1 2 1 (X = peroxo ligand). The formation of the monoperoxo vanadium species is very slow, requiring up to 10 days for complete equilibrium. Significant decomposition of peroxide occurs only in acidic solutions. Chemical shifts, compositions and formation constants for the six quaternary complexes are given, and equilibrium conditions are illustrated in distribution diagrams. The H+/H2VO4–/H2O2/Alaser/Alahis system, where Alahis denotes L--alanyl-L-histidine, was briefly investigated and no mixed ligand species were detected.
|
|
| 5. |
- Gorzsás, András, et al.
(författare)
-
Speciation in the aqueous H+/H2VO4–/H2O2/citrate system of biomedical interest
- 2004
-
Ingår i: Dalton Transactions. - Cambridge : Royal Society of Chemistry, Thomas Graham House. - 1477-9226 .- 1477-9234. ; :18, s. 2873-2882
-
Tidskriftsartikel (refereegranskat)abstract
- The speciation in the quaternary aqueous H+/H2VO4–/H2O2/citrate (Cit3–) and H+/H2VO4–/Cit3–/L-(+)-lactate (Lac–) systems has been determined at 25 °C in the physiological medium of 0.150 M Na(Cl). A combination of 51V NMR integral intensities and chemical shift (Bruker AMX500) as well as potentiometric data (glass electrode) have been collected and evaluated with the computer program LAKE, which is able to treat multimethod data simultaneously. The pKa-values for citric acid have been determined as 2.94, 4.34 and 5.61. Altogether six vanadate–citrate species have been found in the ternary H+/H2VO4–/Cit3– system in the pH region 2–10, only two of which are mononuclear. Reduction of vanadium(V) becomes more pronounced at pH < 2. Solutions, in which reduction occurred to any extent, were excluded from all calculations. In the quaternary H+/H2VO4–/H2O2/Cit3– system, eight complexes have been found in addition to all binary and ternary complexes over the pH region 2–10, including three mononuclear species. Equilibria in general are fast, but the significant and rapid decomposition of peroxide in acidic solutions limited the final model to pH > 4. In the quaternary H+/H2VO4–/Cit3–/Lac– system, two mixed-ligand species have been determined, with the compositions V2CitLac2– and V2CitLac3–(pKa= 5.0). To our knowledge, this is the first time such complexes have been reported for vanadium(V). 51V NMR chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. When suitable, structural proposals are given, based on 13C NMR measurements and available literature data of related compounds.
|
|
| 6. |
- Gorzsás, András, et al.
(författare)
-
Speciation in the aqueous H+/H2VO4–/H2O2/L-(+)-lactate system
- 2003
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). ; , s. 2503-11
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the quaternary aqueous H+/H2VO4–/H2O2/L-(+)-lactate (Lac–) system has been performed at 25 °C in 0.150 M Na(Cl) medium, representing the ionic strength of human blood, using quantitative 51V NMR and potentiometric data (glass electrode). Data were evaluated with the computer program LAKE, which is able to treat combined EMF and NMR data. The pKa-value for lactic acid was determined as 3.653 ± 0.002. The error given is 3. In the ternary H+/H2VO4–/Lac– system, eight complexes were found in the pH region 1.1–10.9; only half of them are mononuclear. Owing to the fast reduction of vanadium(V) in acidic solutions and to the slow equilibria of the inorganic vanadates under certain conditions, the final model of this ternary system presented in the study is limited to pH > 3.1. Solutions, in which reduction occurred to any extent, were excluded from all calculations, hence the study is limited to vanadium(V). In the quaternary H+/H2VO4–/H2O2/Lac– system, seven complexes could be found in addition to all binary and ternary complexes over the pH region 2.1–10.0, only two of which were mononuclear. Equilibrium is fast, but significant decomposition of peroxide occurs in acidic solutions over very short time, limiting the final model to pH > 4. Chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. Simple biological tests were carried out to check the resistance of different peroxovanadate complexes (including the ones with Lac–) against human catalase and the results are being presented here.
|
|
| 7. |
- Grachova, E V, et al.
(författare)
-
The structure and dynamic behaviour of disubstituted derivatives of Rh6(CO)16 containing heterobidentate bridging phosphine ligands
- 2003
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; :12, s. 2468-2473
-
Tidskriftsartikel (refereegranskat)abstract
- The solution structures and dynamic behaviour of [Rh6(CO)14(µ-PX)][PX = diphenyl(2-pyridyl)phosphine, (PN); diphenyl(2-thienyl)phosphine, (PS); diphenyl(vinyl)phosphine, (PV)] have been studied by multinuclear NMR and the X-ray structure of [Rh6(CO)14(µ,3-PV)] is reported. In solution, the above clusters undergo a variety of localised CO-exchanges and the mechanisms of these are discussed. The PV ligand in [Rh6(CO)14(µ,3-PV)] is hemilabile and exhibits facile exchange/reorientation of the vinyl group.
|
|
| 8. |
- Kjellström, Johan, et al.
(författare)
-
Similar rates for platination of hairpin loops and single-stranded DNA
- 2003
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234. ; :14, s. 2867-2871
-
Tidskriftsartikel (refereegranskat)abstract
- The presence of ribonucleic acid hairpin structures is important for proper processing of the genetic information in living cells. Recent studies indicate that interactions between platinum based anticancer active metal complexes and hairpin motifs result in a change of their three-dimensional structure combined with a decrease of the melting temperature. We here report a study of the reaction between two platinum complexes, cis-[PtCl(NH3)(2)(OH2)](+) I and, cis-[PtCl(NH3)(c-NH2C6H11)(OH2)](+) II, and a series of short DNA hairpins which all exhibit a documented preference for adduct formation with donor groups located in the loop region; d(CGCGTTXTTCGCG), where X = G-N7, p(S), I-s6 or U-s4. The binding kinetics of adduct formation with the hairpins have been compared with that of binding to similar size single-stranded DNA; d(T6XT6), where X = G, p(S), I-s6 or U-s4. The overall picture reveals rather similar reactivity of the platinum complexes towards these two DNA secondary structures. However, the smaller complex I exhibits a tendency for preferential interaction with the hairpins, whereas the more bulky complex II shows a higher reactivity towards the single-stranded structures.
|
|
| 9. |
- Otto, Stefanus, et al.
(författare)
-
Bridge-splitting Kinetics, Equilibria and Structures of trans-bis-cyclooctene Complexes of Platinum(II)
- 2003
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; :12, s. 2519-2525
-
Tidskriftsartikel (refereegranskat)abstract
- Cyclooctene (C8H14, cot) complexes of platinum(II) have been synthesised and characterised by means of multinuclear NMR, UV-Vis spectroscopy and X-ray crystallography. The bridge-splitting equilibrium constants of the dinuclear, chloride-bridged trans-[PtCl2(cot)]2, 1, in dichloromethane solvent at 298 K with MeOH, MeCN and cot, yielding trans-[PtCl2(cot)(MeOH)], 2, trans-[PtCl2(cot)(MeCN)], 3, and trans-[PtCl2(cot)2], 4, were determined by UV-Vis measurements as K12= 0.0169 ± 0.0015, K13= 9.7 ± 0.9 and K14= 2.05 ± 0.06 mol–1 dm3, respectively. Substitution of one cyclooctene from 4 by MeOH gives K42= 0.110 ± 0.009 and by MeCN K43= 2.25 ± 0.03. The bis-cyclooctene complexes 1 and 4 react quantitatively with chloride to give [PtCl3(cot)]–, 5. The kinetics for bridge-splitting of 1 with MeOH, MeCN and cot was studied by conventional and cryo-stopped-flow spectroscopy. Second-order rate constants at 298 K are 0.128 ± 0.003, 4.93 ± 0.02 and 0.0637 ± 0.0009 mol–1 dm3 s–1, respectively. The corresponding activation parameters are H= 43.7 ± 1.8, 42.0 ± 0.8 and 39.6 ± 0.9 kJ mol–1 and S=–115 ± 6, –91 ± 3 and –135 ± 3 J K–1 mol–1, indicating associative activation with a relatively large -TS contribution to G. Crystal and molecular structures of 1, 4, and the tetraphenylphosphonium salt of 5 have been determined, indicating a moderate ground-state trans influence of cyclooctene. The molecular structure of 4 with two CC double bonds coordinated trans to each other and perpendicular to the platinum coordination plane, features a significant Pt–C bond lengthening compared to cyclooctene complexes with chloride or nitrogen trans to cyclooctene, leading to high reactivity and thermodynamic instability. Equilibrium data confirm that the thermodynamic stability of a cyclooctene coordinated trans to another cyclooctene is much lower than trans to a ligand with less -back-bonding capacity.
|
|
| 10. |
- Pettersson, Lage, et al.
(författare)
-
17O NMR study of aqueous peroxoisopolymolybdate equilibria at lower peroxide/Mo ratios
- 2003
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; , s. 146-52
-
Tidskriftsartikel (refereegranskat)abstract
- Aqueous peroxomolybdates have been studied using 17O NMR together with equilibrium measurements and calculations, over a wide range of conditions. Ten peroxo species are identified, mostly in more than one state of protonation. Some are already known in the solid state, or from equilibrium analysis, but structural information is also obtained for MoO3(HO2)– and the new or previously tentative species Mo2O5(O2)22–, HpMo7O23(O2)2p–6 and HpMo7O23(O2)p–6(p= 0–2). Sites of protonation are identified, as are 17O resonances from both bidentate and monodentate peroxide. Several oxygen exchange processes are also seen, including a probable dimer–tetramer exchange.
|
|
| 11. |
- Taube, Fabian, 1967
(författare)
-
17O NMR study of aqueous peroxoisopolymolybdate equilibria at lower peroxide/Mo ratios. Electronic supplementary information (ESI) available: concentrations of total Mo, total H2O2 and other species expressed as [Mo]
- 2003
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234.
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Aqueous peroxomolybdates have been studied using 17O NMR together with equilibrium measurements and calculations, over a wide range of conditions. Ten peroxo species are identified, mostly in more than one state of protonation. Some are already known in the solid state, or from equilibrium analysis, but structural information is also obtained for MoO3(HO2)− and the new or previously tentative species Mo2O5(O2)22−, HpMo7O23(O2)2p−6 and HpMo7O23(O2)p−6 (p = 0–2). Sites of protonation are identified, as are 17O resonances from both bidentate and monodentate peroxide. Several oxygen exchange processes are also seen, including a probable dimer–tetramer exchange.
|
|
| 12. |
- Taube, Fabian, et al.
(författare)
-
Equilibria and dynamics of some aqueous peroxomolybdophosphate catalysts: a potentiometric and 31P NMR spectroscopic study
- 2003
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; , s. 2512-2518
-
Tidskriftsartikel (refereegranskat)abstract
- The equilibrium speciation in the pH++qMoO42–+rH2O2+sH2PO4–+tSO42–(H+)p(MoO42–)q(H2O2)r(H2PO4–)s(SO42–)tp–2q–s–2t system in 0.300 M Na2(SO4) medium at 25 °C and [H2O2]tot/[Mo]tot > 2 has been determined from potentiometric data and 31P NMR integral and chemical shift data in the range 1.0 pH 9.0, 2.0 [MoO42–]tot/mM 293, 32 [H2O2]tot/mM 640, 2 [H2PO4–]tot/mM 60 and 200 [SO42–]tot/mM 380. Species with the following compositions were obtained: MoX2P3–(0,1,2,1,0), MoX2P2–(1,1,2,1,0), MoX2P–(2,1,2,1,0), Mo2X4P3–(2,2,4,1,0), Mo2X4P2–(3,2,4,1,0), Mo3X6P3–(4,3,6,1,0), Mo3X6P2–(5,3,6,1,0) and Mo4X8P3–(6,4,8,1,0). The numbers and charges of molybdenum (Mo), peroxide (X), phosphate (P) and sulfate (S) in each species are given in the abbreviated formula MoqXrPsStp–2q–s–2t. The numbers in parentheses refer to the values of p, q, r, s and t in the formula above. The following formation constants with 3 were obtained; log0,1,2,1,0= 5.16 ± 0.09, log1,1,2,1,0= 12.73 ± 0.02 (pKa= 7.63), log2,1,2,1,0= 16.14 ± 0.03 (pKa= 3.42), log2,2,4,1,0= 25.03 (± 0.04), log3,2,4,1,0= 29.54 ± 0.02 (pKa= 4.51), log4,3,6,1,0= 42.30 ± 0.03, log5,3,6,1,0= 44.06 ± 0.08 (pKa= 1.76), log6,4,8,1,0= 57.30 ± 0.07. pKa values for H3PO4 and H2PO4– were determined to 2.00 and 6.48, respectively. Chemical exchange processes were detected by 31P NMR 2D EXSY and selective magnetisation transfer experiments between the complexes. An averaged lifetime, (X2Mo–OP) 30 ms, can be estimated for the MoX2P and Mo2X4P species at pH = 5.5 and 5 °C.
|
|
| 13. |
- Tunik, S P, et al.
(författare)
-
Chiral hexarhodium clusters containing heterobidentate phosphine ligands, a structural and reactivity study
- 2003
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234. ; :12, s. 2457-2467
-
Tidskriftsartikel (refereegranskat)abstract
- Some intrinsically chiral [Rh6(CO)14(µ,2-PX)] clusters have been synthesized, beginning with reactions of [Rh6(CO)16–x(NCMe)x](x= 1, 2) with PX, where PX represents the bidentate bridging ligands diphenyl(benzothienyl)phosphine (1), diphenyl(2-thienyl)phosphine (2), di(2-thienyl)phenylphosphine (3), tris(2-thienyl)phosphine (4), diphenyl(2-pyridyl)phosphine (5) and diphenylvinylphosphine (6). The ligand tris(2-furyl)phosphine (7) shows no bridging capability. When x= 1 the initial products are the clusters [Rh6(CO)15(1-PX)] which undergo spontaneous CO loss to form [Rh6(CO)14(µ,2-PX)]. The structures of the [Rh6(CO)15(1-PX)] clusters have been elucidated by IR, NMR spectroscopy and FAB-MS spectrometry, and have been found to involve phosphorus atom coordination to a rhodium atom. In addition, the solid state structures of the [Rh6(CO)14(µ,2-Ph2P(2-benzothienyl))](8), [Rh6(CO)14(µ,2-Ph2P(2-thienyl))](9), [Rh6(CO)14(µ,2-PhP(2-thienyl)2)](10) and [Rh6(CO)14(µ,2-Ph2P(pyridyl))](12) clusters have been determined by X-ray crystallography. The various types of chirality exhibited by these clusters are discussed. A simple model is proposed to account for the ratios of stereochemical isomers found in the Rh6(CO)14(µ,2-PhP(2-thienyl)2 cluster. The kinetics of formation of the bridged clusters from the monosubstituted [Rh6(CO)15(1-PX)] clusters have been studied.
|
|
| 14. |
- Vallet, V., et al.
(författare)
-
Experimental and quantum chemical studies of structure and reaction mechanisms of dioxouranium(VI) complexes in solution
- 2004
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :22, s. 3799-3807
-
Tidskriftsartikel (refereegranskat)abstract
- This perspective article describes the combination of experimental data and quantum chemical methods for the determination of structure and reaction mechanisms of uranyl( VI) complexes in aqueous solution. The first part assesses the accuracy of the chemical and thermodynamic properties of solvated uranyl( VI) complexes as obtained by various quantum chemical methods. The second part discusses structure determination, mechanisms for ligand exchange and the lability of coordinated water molecules for various uranyl( VI) complexes using a combination of NMR and quantum chemical data.
|
|
| 15. |
|
|
| 16. |
- Öhrström, Lars, 1963, et al.
(författare)
-
What kinds of three-dimensional nets are possible with tris-chelated metal complexes as building blocks?
- 2004
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). ; 4:3, s. 347-353
-
Tidskriftsartikel (refereegranskat)abstract
- Tris-chelated metal complexes with octahedral geometry are sometimes used as building blocks for "self assembly" and "crystal engineering". These versatile building blocks easily form honey-comb type 2D nets. However, in this Perspective we discuss the different types of 3D nets that can be formed with these starting materials using Wells classification, and concentrate on the ( 10,3) nets. We show that several of these, and not only the ( 10,3)-a net, are possible by analysing the geometrical requirements of each net. We note that each possible net implies a specific assembly order of Delta or Lambda chirality of the building blocks.
|
|
| 17. |
- Deeming, Antony J, et al.
(författare)
-
Oxidative addition of silanes R3SiH to the unsaturated cluster [Os3(µ-H){µ3-Ph2PCH2PPh(C6H4)}(CO)8]: Evidence for reversible silane formation in the dynamic behaviour of [Os3(µ-H)(SiR3)(CO)9(µ-dppm)]
- 2004
-
Ingår i: Dalton Transactions. - 1477-9234. ; 2004:21, s. 3709-3714
-
Tidskriftsartikel (refereegranskat)abstract
- Oxidative addition of the silanes R3SiH (R3= Ph3, Et3, EtMe2) to the unsaturated cluster [Os3(µ-H){µ3-Ph2PCH2PPh(C6H4)}(CO)8] leads to the saturated clusters [Os3(µ-H)(SiR3)(CO)9(µ-dppm)](SiR3= SiPh31, SiEt32 and SiEtMe23) and the unsaturated clusters [Os3(µ-H)2(SiR3){µ3-Ph2PCH2PPh(C6H4)}(CO)7](SiR3= SiPh34, SiEt35 and SiEtMe26). Structures are based on spectroscopic evidence and a XRD structure of [Os3(µ-H)(SiPh3)(CO)9(µ-dppm)]1 in which all non-CO ligands are coordinated equatorially and the hydride and the silyl groups are mutually cis. From variable-temperature 1H NMR spectra of the SiEt3 compound 2, exchange of the P nuclei is clearly apparent. Simultaneous migrations of the SiEt3 group and of the hydride from one Os–Os edge to another generate a time-averaged mirror plane in the molecule. VT 1H NMR spectra of the somewhat less bulky compound [Os3(µ-H)(SiMe2Et)(CO)9(µ-dppm)]3 have been analysed. Two isomers 3a and 3b are observed with the hydride ligand located on different Os–Os edges. Synchronous migration of the hydride and SiMe2Et groups is faster than the observed interconversion of isomers which occurs by hydride migration alone. The synchronous motion of H and SiR3only occurs when these ligands are mutually cis as in the major isomer 3a and we propose that this process requires the formation of a transient silane complex of the type [Os3(2-HSiR3)(CO)9(µ-dppm)]. Turnstile rotation within an Os(CO)3(2-HSiR3) group leads to the observed exchange within the major isomer 3a without exchange with the minor isomer. This process is not observed for the minor isomer 3b because the hydride and the silyl group are mutually trans. Protonation to give [Os3(µ-H)2(SiR3)(CO)9(µ-dppm)]+ totally suppresses the dynamic behaviour because there are no edge vacancies.
|
|
| 18. |
- Otto, Stefanus, et al.
(författare)
-
Pseudo-rotation mechanism for fast olefin exchange and substitution processes at orthometalated C,N-complexes of platinum(II)
- 2004
-
Ingår i: Dalton Transactions. - 1477-9234. ; :21, s. 3662-3668
-
Tidskriftsartikel (refereegranskat)abstract
- Bridge splitting in chloroform of the orthometalated chloro-bridged complex [Pt(mu-Cl)(2-Me2NCH2C6H4)](2) (1), with ethene, cyclooctene, allyl alcohol and phosphine according to 1 + 2L --> 2 [PtCl(2-Me2NCH2C6H4)(L)], where L = C2H4 (3a), C8H14, (3b), CH2CHCH2OH (3c), and PPh3 (4a and 4b) gives monomeric species with L coordinated trans or cis to aryl. With olefins the thermodynamically stable isomer with L coordinated cis to aryl is formed directly without an observable intermediate. With phosphine and pyridine, the kinetically controlled trans-product isomerizes slowly to the more stable cis-isomer. Bridge splitting by olefins is slow and first-order in 1 and L, with largely negative DeltaS(double dagger). Substitution of ethene cis to aryl by cyclooctene and allyl alcohol to form 3b and 3c, and substitution of cot from 3b by allyl alcohol to form 3c are first order in olefin and complex, ca. six orders of magnitude faster than bridge cleavage due to a large decrease in DeltaH(double dagger), and with largely negative DeltaS(double dagger). Cyclooctene exchange at 3b is first-order with respect to free cyclooctene and platinum complex. All experimental data for olefin substitution and exchange are compatible with a concerted substitution/isomerization process via a turnstile twist pseudo-rotation in a short-lived labile five-coordinated intermediate, involving initial attack on the labile coordination position trans to the sigma-bonded aryl. Bridge-cleavage reactions of the analogous bridged complexes occur similarly, but are much slower because of their ground-state stabilization and steric hindrance.
|
|
