Phosphine Exchange Research Articles

Cyclotribenzylene alkynylgold(I) phosphine complexes: synthesis, chirality, and exchange of phosphine.

Two different alkynyl-substituted C3-symmetric cyclotribenzylenes (CTB) were synthesized in racemic and enantiomerically pure forms, and six gold(I) phosphine complexes differing by the nature of the CTB and the phosphine were prepared and characterized, in particular by NMR spectroscopy, DOSY, electronic circular dichroism (ECD), and electrospray ionization mass spectrometry (ESI-MS). Their ECD patterns depended on the substitution of the starting CTBs and were shifted bathochromically by comparison with the latter. ESI-MS in the presence of HCO2H allowed us to detect the complexes as proton adducts. The intensities of the signals were stronger when the phosphine was more electron-rich. This technique was also used to investigate the exchange of phosphine betweeen pairs of CTB complexes. The scrambling reaction was demonstrated by the higher intensity of the signals of the complexes subjected to the exchange of a single phosphine ligand by comparison with the intensity of the signals of the starting complexes.

Gold(I) and Silver(I) π-Complexes with Unsaturated Hydrocarbons.

Gold π-complexes have been studied largely in the past 2 decades because of their role in gold-catalyzed reactions. We report an experimental and theoretical investigation of the interaction between a wide range of unsaturated hydrocarbons (alkanes, alkynes, alkadienes, and allenes) and triphenylphosphine-gold(I), triphenylphosphine-silver(I), and acetonitrile-silver(I) cations. The bond dissociation energies of these complexes were determined by mass spectrometry collision-induced dissociations and their structures were studied by density functional theory calculations and infrared photodissociation spectroscopy. The results show that with the same phosphine ligand, gold binds stronger to the π-ligands than silver and thereby activates the unsaturated bond more effectively. Ligand exchange of phosphine by acetonitrile at the silver complexes increases the binding energy as well as the activation of the π-ligands. We also show that the substitution of an unsaturated bond is more important than the bond type.

Phosphinoborylenes as stable sources of fleeting borylenes.

Base-stabilised borylenes that mimic the ability of transition metals to bind and activate inert substrates have attracted significant attention in recent years. However, such species are typically highly reactive and fleeting, and often cannot be isolated at ambient temperature. Herein, we describe a readily accessible trimethylphosphine-stabilised borylborylene which was found to possess a labile P–B bond that reversibly cleaves upon gentle heating. Exchange of the labile phosphine with other nucleophiles (CO, isocyanide, 4-dimethylaminopyridine) was investigated, and the binding strength of a range of potential borylene “ligands” has been evaluated computationally. The room-temperature-stable PMe3-bound borylenes were subsequently applied to novel bond activations including [2 + 2] cycloaddition with carbodiimides and the reduction of dichalcogenides, revealing that PMe3-stabilised borylenes can effectively behave as stable sources of the analogous fleeting dicoordinate species under mild conditions.

Synthesis and characterization of [Rh(PP)(PP)]X complexes (PP = DPPE or DPPP, X = Cl− or BF4-). Phosphine exchange and reactivity in transfer hydrogenation conditions

The synthesis of heteroleptic monomeric cationic Rh(I) bis-diphosphine complex [Rh(dppe)(dppp)]Cl (dppe = 1,2-bis-(diphenylphosphino)ethane and dppp = 1,3-bis-(diphenylphosphino)propane) was achieved by reaction between the neutral dimeric complex [Rh2(dppe)2(μ2-Cl)2] and the dppp ligand. The corresponding complex [Rh(dppe)(dppp)]BF4 was instead obtained from reaction between [Rh(dppe)(nbd)]BF4 (nbd = bicyclo-[2.2.1]-hepta-2,5-diene) and the dppp ligand. Previous protocols had extended to the synthesis of the analogous homoleptic complexes containing two dppe or two dppp ligands. The structural analysis of such complexes conducted in the solid state by single-crystal x-ray crystallography and in solution by 31P and 1H NMR revealed a distorted square planar geometry where the anion and the cation are not bonded each other. Nevertheless, important differences in reactivity can be found if same complexes with different anions are compared, as in the case of the phosphine exchange reaction between [Rh(dppp)2]X (X = Cl−, BF4−) and the dppe ligand or in the case of the employment of such complexes as catalytic precursors for the transfer hydrogenation reaction from 2-propanol to acetophenone.

A magnetic spin transfer NMR study of tertiary phosphine exchange in rhodium(I) complexes

Magnetic spin transfer NMR was used to investigate phosphine exchange reactions in complexes of the type [Rh(N,O-Bid)(CO)(PPh3)] (where N,O-Bid is a derivative of 4-(phenylamino)pent-3-en-2-onate, Phony−). Chlorido and methyl substituted rhodium phenyl β-enaminoketonato complexes, [Rh(2,6-Cl2-Phony)(CO)(PPh3)] and [Rh(2,6-Me2-Phony)(CO)(PPh3)], were chosen as study subjects allowing for a comparison of the influence of electronic properties on the rate of exchange. Moreover, a non-coordinating solvent, dichloromethane, was employed to minimize the effect of the solvent pathway. The rate of PPh3 exchange in [Rh(2,6-Cl2-Phony)(CO)(PPh3)] (k1 = 218 ± 16 M−1 s−1) was found to be approximately three times faster than the rate of reaction for the methylated counterpart (k1 = 82 ± 7 M−1 s−1). The methyl substituents increase the electron density of the d-orbitals of the rhodium atom and stabilize the five-coordinate distorted pyramidal intermediate, while the opposite is true for the complex with the chlorido-containing ligand. The activation parameters of the exchange reactions of both complexes correlate well with one another and an associative mechanism is indicated by the negative values for the entropy of activation, ΔS‡, −117 ± 9 and −124 ± 12 J K−1 mol−1. The activation process is primarily controlled by entropy as opposed to enthalpy (58% and 61% at 25 °C for the respective complexes) and involves the formation of a stable, well-ordered transition state while bond weakening is less important.

Structure and dynamic NMR behavior of rhodium complexes supported by Lewis acidic group 13 metallatranes.

Monovalent Rh was installed into the group 13 metallatranes, M[N(o-(NCH2P(iPr)2)C6H4)3] (where M = Al and Ga, abbreviated as ML) to generate Rh → M bonds in the parent complexes, Cl-RhAlL (1-Cl) and Cl-RhGaL (2-Cl). The electron-withdrawing nature of the group 13 metalloids was probed by cyclic voltammetry, and Rh-Ga was found to be more electron-deficient than Rh-Al (Epc = -2.07 and -1.95 V vs. Fc+/Fc for 1-Cl and 2-Cl, respectively). Both 1-Cl and 2-Cl were further functionalized through metathesis reactions using MeLi to generate 1-CH3 and 2-CH3, respectively, or using LiHBEt3 to form 1-H and 2-H, respectively. The solid-state structures of all Rh-M bimetallics feature Rh-M bond lengths that are less than the sum of the covalent radii of Rh and M (Rh-M: 2.50-2.54 Å for 1-X and 2.49-2.46 Å for 2-X, where X = Cl, CH3, and H). In the Rh-M structures, the Rh center is distorted from square pyramidal geometry due to steric interactions between X and the isopropyl substituents of L. Finally, all the Rh-M bimetallics exhibit fluxionality that involves phosphine exchange. Of note, the two phosphines cis to the X ligand become inequivalent at low temperature. The activation barrier to exchange these two phosphine donors is: 14.9, 14.2, 10.9, and 11.5 kcal mol-1 for 1-Cl, 2-Cl, 1-H, and 2-H, respectively. The activation barriers for 1-CH3 and 2-CH3 are both >15.2 kcal mol-1. At high temperature, 2-Cl was also found to exchange all three phosphine donors. Mechanisms for the different types of phosphine exchange are proposed.

Reaction of a polyphosphino ruthenium(II) acetate complex with Grignard reagents: Halogenation, alkylation and β-elimination

(PMe3)4Ru(H)OAc has been prepared from (PPh3)3Ru(H)OAc via phosphine exchange followed by solvent partitioning between acetonitrile and pentane. Complexes of the type (PMe3)4Ru(H)R (R = Et, nPr, nBu, iBu, H) have been synthesized through reaction with the corresponding Grignard reagents, RMgCl, and were found to be moderately stable provided the alkyl group is primary. Treatment with bulkier alkylmagnesium chlorides led instead to the dihydrido complex (PMe3)4RuH2. In some cases, the reaction was complicated by transfer of halide from the Grignard reagent to form, for example, (PMe3)4Ru(H)Cl.

Evidence for a SN2-type pathway in the exchange of phosphines at a [PhSe]+ centre.

A range of thio- and seleno-phosphonium cationic complexes [RE(PR'3)](+)[X](-) (R = Me, Ph; E = S, Se; X = GaCl4, SbF6) have been synthesised and structurally characterised. Reaction of [PhSPPh3][GaCl4] and [PhSePPh3][GaCl4] with P(t)Bu3 results in the ready transfer of the "RS(+)" and "RSe(+)" fragments from PPh3 to the stronger electron donor P(t)Bu3. NMR experiments combined with an Eyring analysis on the corresponding degenerate phosphine exchange reaction allowed the thermodynamic values for the phosphine exchange reaction of the sulfur cation (ΔH(‡) 18.7 ± 12.0 kJ mol(-1); ΔS(‡) -99.3 ± 36.3 J mol(-1) K(-1)) to be compared with the corresponding values (ΔH(‡) 2.4 ± 1.1 kJ mol(-1) and ΔS(‡) -58.1 ± 5.0 J mol(-1) K(-1)) for the [PhSePPh3](+) system. Importantly, the large negative entropy of activation and linear dependence on the rate of exchange are compatible with an SN2-type exchange process. This conclusion is supported by DFT calculations which confirm that the phosphine exchange process occurs via an associative mechanism. The rate of exchange was found to increase from sulfur to selenium and those with aryl substituents underwent exchange faster than those with alkyl substituents.

Synthesis and characterization of mono- and dinuclear aryl palladium(II) complexes: oxidative additions of 1,4-dihalogenated benzene or 4,4′-dibromobiphenyl to Pd(PR3)4

Mononuclear palladium(II) complexes 1–12, (C6H4X-4)PdXʹ(PR3)2 (X = I, Br, or Cl; Xʹ = I or Br; R = Ph, Cy, Et, or Me), were synthesized by oxidative addition of 1,4-dihalogenated benzene to Pd(PR3)4; dinuclear palladium(II) complexes 13–15, (Me3P)2XPd(C6H4-1,4)PdXʹ(PMe3)2 (X, Xʹ = I or Br), could be obtained only using trimethylphosphine. Another method to prepare 13–15 is via re-oxidative addition of the corresponding mononuclear palladium(II) complexes and Pd(PMe3)4. Using 4,4′-dibromobiphenyl as the starting material, the mononuclear palladium(II) complexes [C6H4(C6H4Br-4)-4]PdBr(PPh3)2 (16) and [C6H4(C6H4Br-4)-4]PdBr(PCy3)2 (17) with bulky phosphines could be synthesized at relative low temperature, while dinuclear 18, (Cy3P)2BrPd(C6H4C6H4-4,4ʹ)PdBr(PCy3)2, was prepared by bis-oxidative addition at higher temperature. The re-oxidative addition of 16 and Pd(PMe3)4 gave dinuclear 19, (Me3P)2BrPd(C6H4C6H4-4,4ʹ)PdBr(PMe3)2, accompanying phosphine exchange. X-ray diffraction analysis revealed that formation of dinuclear palladium(II) complexes depends on the reaction temperature, phosphine ligands, and bridging groups.

Immobilization of [Pt2(μ-S)2(PPh3)4] on Polymeric Supports by Sulfide Alkylation and Phosphine Exchange Reactions

The immobilization of the dinuclear platinum(II) sulfido complex [Pt2(μ-S)2 (PPh3)4] on solid supports has been investigated. Reaction with haloalkyl functionalized polymers [Merrifield's resin (chloromethylated polystyrene), chloropropyl silica, chloropropyl controlled pore glass, and bromopropyl polysiloxane] gives complexes immobilized through alkylation of one of the sulfide ligands, forming a μ-thiolate ligand acting as an anchor to the polymer support, akin to well-established reactions of [Pt2(μ-S)2(PPh3)4] with molecular alkylating agents. The model complex [Pt2(μ-S)(μ-SCH2SiMe3)(PPh3)4]PF6 was prepared as the first molecular silicon-containing derivative of [Pt2(μ-S)2(PPh3)4] and was fully characterized by NMR spectroscopy, electrospray ionization-mass spectrometry, and single-crystal X-ray diffraction. Immobilization of [Pt2(μ-S)2(PPh3)4] by phosphine exchange reactions was also achieved using commercial polystyrene-grafted triphenylphosphine or a new immobilized phosphine [derived by sequential functionalization of Merrifield's resin with a polyether amine and then Ph2PCH2OH].

Unusual Structure, Fluxionality, and Reaction Mechanism of Carbonyl Hydrosilylation by Silyl Hydride Complex [(ArN)Mo(H)(SiH2Ph)(PMe3)3

The reactions of bis(borohydride) complexes [(RN=)Mo(BH4)2(PMe3)2] (4: R = 2,6-Me2C6H3; 5: R = 2,6-iPr2C6H3) with hydrosilanes afford new silyl hydride derivatives [(RN=)Mo(H)(SiR'3)(PMe3)3] (3: R = Ar, R'3 = H2Ph; 8: R = Ar', R'3 = H2Ph; 9: R = Ar, R'3 = (OEt)3; 10: R = Ar, R'3 = HMePh). These compounds can also be conveniently prepared by reacting [(RN=)Mo(H)(Cl)(PMe3)3] with one equivalent of LiBH4 in the presence of a silane. Complex 3 undergoes intramolecular and intermolecular phosphine exchange, as well as exchange between the silyl ligand and the free silane. Kinetic and DFT studies show that the intermolecular phosphine exchange occurs through the predissociation of a PMe3 group, which, surprisingly, is facilitated by the silane. The intramolecular exchange proceeds through a new non-Bailar-twist pathway. The silyl/silane exchange proceeds through an unusual Mo(VI) intermediate, [(ArN=)Mo(H)2(SiH2Ph)2(PMe3)2] (19). Complex 3 was found to be the catalyst of a variety of hydrosilylation reactions of carbonyl compounds (aldehydes and ketones) and nitriles, as well as of silane alcoholysis. Stoichiometric mechanistic studies of the hydrosilylation of acetone, supported by DFT calculations, suggest the operation of an unexpected mechanism, in that the silyl ligand of compound 3 plays an unusual role as a spectator ligand. The addition of acetone to compound 3 leads to the formation of [trans-(ArN)Mo(OiPr)(SiH2Ph)(PMe3)2] (18). This latter species does not undergo the elimination of a Si-O group (which corresponds to the conventional Ojima's mechanism of hydrosilylation). Rather, complex 18 undergoes unusual reversible β-CH activation of the isopropoxy ligand. In the hydrosilylation of benzaldehyde, the reaction proceeds through the formation of a new intermediate bis(benzaldehyde) adduct, [(ArN=)Mo(η(2)-PhC(O)H)2(PMe3)], which reacts further with hydrosilane through a η(1)-silane complex, as studied by DFT calculations.

A Mechanistic Description of Unexpected Room Temperature C-H and P-C Bond Activation by Wilkinson's Catalyst

Abstract The Wilkinson's catalyst, (PPh3)3RhCl dissolved in benzene under nitrogen or under high vacuum undergoes a series of unreported reactions at room temperature. The preliminary mechanistic description involves a series of consecutive intramolecular and intermolecular phosphine exchanges, benzene oxidative addition, and biphenyl reductive elimination.

Facile synthesis of rhodium and iridium complexes bearing a [PEP]-type ligand (E = Ge or Sn) via E–C bond cleavage

Rhodium and iridium complexes bearing a tridentate [PEP] type ligand ([PEP] = {o-(Ph(2)P)C(6)H(4)}(2)E(Me); E = Ge or Sn) were synthesized through the phosphine exchange reaction accompanied by selective E-C bond cleavage. The ligand precursors {o-(Ph(2)P)C(6)H(4)}(2)EMe(2) (E = Ge or Sn) were readily obtained in excellent yields by treating {o-(Ph(2)P)C(6)H(4)}(2)Li with 0.5 equivalents of Me(2)ECl(2). Tris(triphenylphosphine)rhodium(I) carbonyl hydride M(H)(CO)(PPh(3))(3) (M = Rh, Ir) cleaved one of the E-Me bonds of {o-(Ph(2)P)C(6)H(4)}(2)EMe(2) exclusively to afford the trigonal bipyramidal (TBP) complexes, [PEP]M(CO)(PPh(3)). Square-planar rhodium complexes [PEP]Rh(PPh(3)) were also prepared from the reactions of tetrakis(triphenylphosphine)rhodium(I) hydride Rh(H)(PPh(3))(4) with {o-(Ph(2)P)C(6)H(4)}(2)EMe(2). Further, the trans influence of group 14 elements E (E = Si, Ge, Sn) in [PEP]Rh(PPh(3)) is discussed in terms of the (1)J(Rh-P) coupling constants, indicating that E exhibited a stronger trans labilizing effect in the order Sn < Ge < Si.

Phosphine Complexes of an Enantiomerically Pure, Atropisomeric Arsenium Ion

The first enantiomerically pure secondary iodoarsine has been prepared by ring closure of (aR)-[{Li(TMEDA)}2{2,2′-bis(methylene)-1,1′-binaphthylyl}] with dichlorophenylarsine, followed by disproportionation of the resulting seven-membered (aR)-phenylarsepine with triiodoarsine in boiling toluene. The corresponding (aR)-chloroarsepine was prepared from the (aR)-iodoarsepine by halide metathesis with silver chloride in dichloromethane. The crystal structures of the two air-stable (aR)-haloarsepines have been determined. A series of phosphine-stabilized arsenium hexafluorophosphates has been prepared from the (aR)-iodoarsepine by reactions with trimethylphosphine, dimethylphenylphosphine, and [2-(methoxymethyl)phenyl]dimethylphosphine in dichloromethane in the presence of aqueous potassium hexafluorophosphate. The crystal structures of the three complexes have been determined. The structure in each case revealed the significant twist in the (aR)-binaphthyl framework of the seven-membered arsepinenium ion and the coordination of the phosphine approximately orthogonal to the trigonal AsC2 plane of the arsepinenium ion. The 1H{31P} NMR spectrum of the dimethylphenylphosphine complex in dichloromethane-d2 at 25 °C contains broadened singlets for the diastereotopic PMe groups and a multiplet for the methylene protons of the arsepinenium ring because of phosphine exchange. At the slow exchange limit (ca. −50 °C), the complex cation is devoid of symmetry, as indicated in the 1H NMR spectrum by the sharp resonances for the PMe groups and separate AB and A′B′ spin systems for the two pairs of methylene groups in the arsepinenium ring. The 1H{31P} NMR spectrum of the closely related [2-(methoxymethyl)phenyl]dimethylphosphine–arsenium complex in dichloromethane-d2 at 25 °C is sharp, however, which is in agreement with additional stabilization of the complex by coordination of the 2-methoxymethyl group to the phosphorus and arsenic atoms, as indicated in the crystal structure. The resolution of (±)-[2-(methoxymethyl)phenyl]methyl(2-naphthyl)phosphine was achieved by complexation to the enantiomerically pure (aR)-arsenium hexafluorophosphate auxiliary. The crystal structure of the less soluble aR,RP diastereomer of the phosphine–arsenium complex confirmed the absolute configuration of the resolved P-chiral phosphine.

P–H activation using alkynylgold substrates: steric and electronic effects

The susceptibility of a prototypical hydrogen phosphonate to undergo P-H activation upon treatment with alkynylgold complexes has been studied. Dynamic solution behavior was observed during reactions involving triphenylphosphine ligated substrates and was attributed to rapid phosphine exchange between the alkynylgold starting material and the gold phosphonate product. The use of bulky biaryldialkylphosphine ligands eliminated the fluxional behavior, but did not significantly slow the rate of P-H activation. Similarly, changing the supporting ligand to an N-heterocyclic carbene did not significantly slow the rate of the reaction. Despite a number of reports outlining the functionalization of propargyl alcohols using gold catalysts, incorporating these groups into the architecture of the alkynylgold substrates did not alter the product distributions. Although the chemistry tolerated a range of supporting ligands, incorporating electron donating groups into the alkyne increased the rate of the reaction while electron-withdrawing groups slowed the reaction. A possible mechanism for the process includes a transition state containing significant pi-contribution from the alkyne. Due to the high yields of gold phosphonates obtained in this chemistry as well as the mild conditions of the reactions, the interception of intermediates/catalysts by substrates or ligands containing labile P-H donors is an issue that must be circumvented when designing or developing a gold catalyzed reaction that proceeds through alkynylgold intermediates.

Synthesis, Structural Characterization, and Photophysical Study of Luminescent Face-to-Face Dinuclear Platinum(II) Alkynyl Phosphine Complexes and Their Tetranuclear Mixed-Metal Platinum(II)−Silver(I) and −Copper(I) Complexes

A series of luminescent face-to-face dinuclear platinum(II) alkynyl phosphine complexes with trimethoxyphenyl and carbazole moieties have been synthesized by phosphine exchange reaction. Two mixed-metal tetranuclear platinum(II)−silver(I) and −copper(I) complexes have also been synthesized. The complexes are well characterized by 1H, 13C, and 31P NMR spectroscopy, positive ion FAB mass spectrometry, IR spectroscopy, and elemental analysis. Most of them have been structurally characterized by X-ray crystallography. All the complexes are found to show emissive behavior. Correlations of the emissive property with the Pt···Pt distance, the nature of the alkynyl and bridging phosphine ligands, and the nature of the encapsulated metal ions on the alkynyl ligands have been made. TDDFT/CPCM calculations have been performed to provide further insight into the origin of the absorption and emission properties.

ChemInform Abstract: Highly Chemoselective Catalytic Hydrogenation of Unsaturated Ketones and Aldehydes to Unsaturated Alcohols Using Phosphine-Stabilized Copper(I) Hydride Complexes.

Abstract A base metal hydrogenation catalyst composed of the phenyldimethylphosphine-stabilized copper(I) hydride complex provides for the highly chemoselective hydrogenation of unsaturated ketones and aldehydes to unsaturated alcohols, including the regioselective 1,2-reduction of α,β-unsaturated ketones and aldehydes to allylic alcohols. The active catalyst can be derived in situ by phosphine exchange using commercial [(Ph 3 P)CuH] 6 or from the reaction of copper(I) chloride, sodium tert -butoxide, and dimethylphenylphosphine under hydrogen. The catalyst derived from 1,1,1-tris(diphenylphosphinomethyl)ethane is mechanistically interesting but less synthetically useful.

Tertiary arsine-stabilised arsenium salts: syntheses and comparisons with phosphine analogues

The first tertiary arsine-stabilised arsenium salts, [(L)AsMePh]OTf (L = Ph3As, Me2PhAs, [2-(MeOCH2)C6H4]Ph2As, [2-(MeOCH2)C6H4]Me2As), have been prepared by chloride abstraction from chloromethylphenylarsine with trimethylsilyl triflate in the presence of the arsine. The complexes have been characterised by crystallography and 1H NMR spectroscopy. The chiral cations in the complexes have structures based on the trigonal pyramid in which the arsine is coordinated orthogonally to the prochiral, six-electron MePhAs+ ion that forms the base of the pyramid. The NMR data for the complexes in dichloromethane-d2 are consistent with rapid exchange of the arsine on the arsenium ion, even at 183 K. The corresponding phosphine-stabilised complexes are considerably more stable than their arsine counterparts in dichloromethane-d2 with the free energy of activation DeltaG = ca. 60 kJ mol(-1) being calculated for phosphine exchange in [(Me2PhP)AsMePh]OTf at 281 K; for [(Me2[2-(MeOCH2)C6H4]P)AsMePh]OTf in the same solvent, DeltaG = ca. 70 kJ mol(-1) at 323 K.

Polyhedral metallathiaborane chemistry: Synthesis and characterisation of metallathiaboranes based on the twelve-vertex icosahedral closo-{MSB 10H 10} unit, where M is Rh or Ir

The reaction of [ nido-7-SB 10H 12] with [RhCl(PPh 3) 3] in the presence of N, N, N′ N′-tetramethylnaphthalene-1,8-diamine (tmnd) in CH 2Cl 2 gives twelve-vertex [2,2-(PPh 3) 2-2-H- closo-2,1-RhSB 10H 10] ( 1) and eleven-vertex [8,8-(PPh 3) 2- nido-8,7-RhSB 9H 10] ( 2), as major products, plus the dimeric species [{(PPh 3)- closo-RhSB 10H 10} 2] ( 3) as a minor product. Reaction of 1 with PMe 2Ph in CH 2Cl 2 results in phosphine exchange and hydride substitution, affording the chloro analogue of 1, [2,2-(PMe 2Ph) 2-2-Cl- closo-2,1-RhSB 10H 10] ( 4). By contrast, reaction between [IrCl(PPh 3) 3] and [ nido-7-SB 10H 12] in CH 2Cl 2 with tmnd affords only one product, twelve-vertex [2,2-(PPh 3) 2-2-H- closo-2,1-IrSB 10H 10] ( 5). [RhCl 2(η 5-C 5Me 5)] 2 with [ nido-7-SB 10H 12] under the same conditions gives twelve-vertex [2-(η 5-C 5Me 5)- closo-2,1-RhSB 10H 10] ( 6). All the compounds are characterised by NMR spectroscopy, and by mass spectrometry, and the molecular structure of [2,2-(PMe 2Ph) 2-2-Cl- closo-2,1-RhSB 10H 10] ( 4) was established by single-crystal X-ray diffraction analysis. This last rhodathiaborane 4 is fluxional in solution through a process that involves a reversible partial rotation of the {RhCl(PMe 2Ph) 2} unit above the {SB 4} pentagonal face of the {SB 10H 10} fragment.

Kinetic investigation of a ruthenium metathesis catalyst

The complex [(IMesH 2)(PPh 2Cy)Cl 2Ru CHPh] was synthesised and shown to be an active catalyst in ring-closing metathesis of a diallylmalonate. Its phosphine exchange was investigated in C 6D 6 using magnetisation transfer 31P NMR spectroscopy and it was found to operate via a dissociative mechanism with k 353 = 4.1 ± 0.9 s −1, Δ H ‡ = 84 ± 10 kJ mol −1 and Δ S ‡ = 4 ± 28 J mol −1 K −1.