Excess PPh3 Research Articles

Multi-phosphine-chelated iron-carbide clusters via redox-promoted ligand exchange on an inert hexa-iron-carbide carbonyl cluster, [Fe6(μ6-C)(μ2-CO)4(CO)12]2.

We report the reactivity, structures and spectroscopic characterization of reactions of phosphine-based ligands (mono-, di- and tri-dentate) with iron-carbide carbonyl clusters. Historically, the archetype of this cluster class, namely [Fe6(μ6-C)(μ2-CO)4(CO)12]2-, can be prepared on a gram-scale but is resistant to simple ligand substitution reactions. This limitation has precluded the relevance of iron-carbide clusters relating to organometallics, catalysis and the nitrogenase active site cluster. Herein, we aimed to derive a simple and reliable method to accomplish CO → L (where L = phosphine or other general ligands) substitution reactions without harsh reagents or multi-step synthetic strategies. Ultimately, our goal was ligand-based chelation of an Fe n (μ n -C) core to achieve more synthetic control over multi-iron-carbide motifs relevant to the nitrogenase active site. We report that the key intermediate is the PSEPT-non-conforming cluster [Fe6(μ6-C)(CO)16] (2: 84 electrons), which can be generated in situ by the outer-sphere oxidation of [Fe6(μ6-C)(CO)16]2- (1: closo, 86 electrons) with 2 equiv. of [Fc]PF6. The reaction of 2 with excess PPh3 generates a singly substituted neutral cluster [Fe5(μ5-C)(CO)14PPh3] (4), similar to the reported reactivity of the substitutionally active cluster [Fe5(μ5-C)(CO)15] with monodentate phosphines (Cooke & Mays, 1990). In contrast, the reaction of 2 with flexible, bidentate phosphines (DPPE and DPPP) generates a wide range of unisolable products. However, the rigid bidentate phosphine bis(diphenylphosphino)benzene (bdpb) disproportionates the cluster into non-ligated Fe3-carbide anions paired with a bdpb-supported Fe(ii) cation, which co-crystallize in [Fe3(μ3-CH)(μ3-CO)(CO)9]2[Fe(MeCN)2(bdpb)2] (6). A successful reaction of 2 with the tripodal ligand Triphos generates the first multi-iron-chelated, authentic carbide cluster of the formula [Fe4(μ4-C)(κ3-Triphos)(CO)10] (9). DFT analysis of the key (oxidized) intermediate 2 suggests that its (μ6-C)Fe6 framework remains fully intact but is distorted into an axially compressed, 'ruffled' octahedron distinct from the parent closo cluster 1. Oxidation of the cluster in non-coordinating solvent allows for the isolation and crystallization of the CO-saturated, intact closo-analogue [Fe6(μ6-C)(CO)17] (3), indicating that the intact (μ6-C)Fe6 motif is retained during initial oxidation with [Fc]PF6. Overall, we demonstrate that redox modulation beneficially 'bends' Wade-Mingo's rules via the generation of electron-starved (non-PSEPT) intermediates, which are the key intermediates in promoting facile CO → L substitution reactions in iron-carbide-carbonyl clusters.

Cyclic Diplatinum Complex with a Tröger's Base Ligand and Reductive Elimination of a Highly Strained Ring Molecule

AbstractDistannylated Tröger's base Me3Sn−C6H3−C3N2H6−C6H3−SnMe3 (TB‐(SnMe3)2) reacted with PtCl2(cod) (cod=1,5‐cyclooctadiene) to yield a mixture of macrocyclic diplatinum complex composed of two Tröger's base ligands and two Pt(cod) units (1) and oligomers of the −C6H3−C3N2H6−C6H3−Pt(cod)‐ units (2). Heating a toluene solution of isolated complex 1 and excess PPh3 caused reductive elimination of a cyclic dimer of Tröger's base. The product is obtained in a diastereoselective manner. 1H NMR and DFT studies suggested the molecular structure having the Tröger's base units with smaller arylene rings (ϕ=65–66°) than that reported for dimethyl Tröger's base (ϕ=103°).

Promotional effect of CH3I on hydroxycarbonylation of cycloalkene using homogeneous rhodium catalysts with PPh3 ligand

The reaction mechanism of the hydroxycarbonylation of cyclohexene with formic acid to form cyclohexanecarboxylic acid using organorhodium complexes was investigated both experimentally and computationally. It was found that excess CH3I and PPh3 promote this reaction. The active catalyst species was determined to be a five-coordinated rhodium hydride 16-electron complex derived from a mononuclear rhodium 16-electron complex (Vaska-type complex). PPh3 and CH3I played the following roles: i) to promote the formation of the Vaska-type Rh complex from Rh2Cl2(CO)4 (1), ii) to aid the elimination of the PPh3 ligand from the Vaska-type complex by stabilizing the free energy of formation of a mononuclear three-coordinated rhodium 14-electron complex through the formation of phosphonium iodide ([Ph3P(CH3)]I), and iii) to generate the active rhodium hydride species.

Monomeric and Oligomeric Metal Selenide Complexes from Structural Transformation of the Tetraselenotungstate Anion

Treatment of W(CO)6 with Na2Sex (x = 2–4) at 90 °C, prepared from heating selenium powder and sodium in DMF solution, afforded (Et4N)2[WSe4] (1) in a relatively high yield. Interaction of 1 with one equiv. [Me3NCH2Ph]Br in MeCN gave a cation exchanging product (Et4N)(Me3Ph2CH2N)[WSe4] (2) in a quantitative yield. Reaction of 1 with excess grey selenium in DMF produced monomeric polyselenide complex (Et4N)2[WO(Se4)2] (3). Treatment of 1 with equal equiv. anhydrous FeCl2 and excess PPh3 in DMF gave a dimeric complex (Fe(DMF)6)[W2Se4(μ-Se)2] (4). Similar reaction using MnCl2·4H2O salt easily gave rise to isolation of a trimeric complex (Mn(DMF)6)[WO(DMF)(μ-WSe4)2] (5). Reaction of 1 with anhydrous ZnCl2 in a mixed DMF/MeCN at 40 °C afforded a mixed-metal selenide complex (Et4N)2[Zn(μ-WSe4)2] (6). All complexes are well characterized by electronic, infrared, mass and NMR spectroscopies in this paper, and the solid-state structures of complexes 1–6 have been also established by X-ray crystallography. Interactions of tetraselenotungstate anion [WSe4]2− and first-row transition metal ions (Fe2+, Mn2+ and Zn2+) in the heating dimethylformide resulted in isolation of monomeric and oligomeric metal selenide complexes (Fe(DMF)6)[W2Se4(μ-Se)2] (Mn(DMF)6)[WO(DMF)(μ-WSe4)2] and (Et4N)2[Zn(μ-WSe4)2].

Thiol-Induced Synthesis of Phosphine-Protected Gold Nanoclusters with Atomic Precision and Controlling the Structure by Ligand/Metal Engineering.

Efficient synthesis of atomically precise phosphine-capped gold nanocluster (with >10 metal atoms) is important to deeply understand the relationship between structure and properties. Herein, we successfully utilize the thiol-induced synthesis method and obtain three atomically precise phosphine-protected gold nanoclusters. Single-crystal X-ray structural analysis reveals that the nanoclusters are formulated as [Au13(Dppm)6](BPh4)3, [Au18(Dppm)6Br4](BPh4)2, and [Au20(Dppm)6(CN)6] (where Dppm stands for bis(diphenylphosphino)methane), which are further confirmed by electrospray ionization mass spectrometry, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Meanwhile, [Au18(Dppm)6Br4](BPh4)2 could be converted into [Au13(Dppm)6](BPh4)3 and [Au20(Dppm)6(CN)6] by engineering the surface ligands under excess PPh3 or moderate NaBH3CN, respectively. Furthermore, according to the different binding ability of silver with halogen, we successfully achieved target metal exchange on [Au18(Dppm)6Br4](BPh4)2 with Ag-SAdm (where HS-Adm stands for 1-adamantane mercaptan) complex and obtained [AgxAu18-x(Dppm)6Br4](BPh4)2 (x = 1, 2) alloy nanoclusters. Our work will contribute to more intensive understanding on synthesizing phosphine-protected nanoclusters as well as shedding light on the structure-property correlations in the nanocluster range.

Molecular and Electronic Structures of Ruthenium Complexes Containing an ONS-Coordinated Open-Shell π Radical and an Oxidative Aromatic Ring Cleavage Reaction.

The coordination chemistry of 2,4-di-tert-butyl-6-[(2-mercaptophenyl)amino]phenol (LONSH3), which was isolated as a diaryl disulfide form, (LONSH2)2, with a Ru ion is disclosed. It was established that the trianionic LONS3- is redox-noninnocent and undergoes oxidation to either a closed-shell singlet (CSS), LONS-, or an open-shell π-radical state, LONS•2-, and the reactivities of the [RuII(LONS•2-)] and [RuII(LONS-)] states are different. The reaction of (LONSH2)2 with [Ru(PPh3)3Cl2] in toluene in the presence of PPh3 affords a ruthenium complex of the type trans-[Ru(LONS)(PPh3)2Cl] (1), while the similar reaction with [Ru(PPh3)3(H)(CO)Cl] yields a LONS•2- complex of ruthenium(II) of the type trans-[RuII(LONS•2-)(PPh3)2(CO)] (2). 1 is a resonance hybrid of the [RuII(LONS-)Cl] and [RuIII(LONS•2-)Cl] states. It is established that 2 incorporating an open-shell π-radical state, [RuII(LONS•2-)(CO)], reacts with an in situ generated superoxide ion and promotes an oxidative aromatic ring cleavage reaction, yielding a α-N-arylimino-ω-ketocarboxylate (LNS2-) complex of the type [RuII(LNS2-)(PPh3)(CO)]2 (4), while 1 having a CSS state, [RuII(LONS-)Cl], is inert in similar conditions. Notably, 2 does not react with O2 molecule but reacts with KO2 in the presence of excess PPh3, affording 4. The redox reaction of (LONSH2)2 with [Ru(PPh3)3Cl2] in ethanol in air is different, leading to the oxidation of LONS to a quinone sulfoxide derivative (LONSO0) as in cis-[RuII(LONSO0)(PPh3)Cl2] (3), via 1 as an intermediate. The molecular and electronic structures of 1-4 were established by single-crystal X-ray crystallography, electron paramagnetic resonance spectroscopy, electrochemical measurements, and density functional theory calculations. 1+ is a resonance hybrid of [RuIII(LONS-)(PPh3)2Cl ↔ RuIV(LONS•2-)(PPh3)2Cl]+ states, 2- is a LONS3- complex of ruthenium(II), [RuII(LONS3-)(PPh3)2(CO)]-, and 2+ is a ruthenium(II) complex of LONS- of the type [RuII(LONS-)(PPh3)2(CO)]+, where 35% diradical character of the LONS- ligand was predicted.

Improving the Catalytic Activity in the Rhodium‐Mediated Hydroformylation of Styrene by a Bis(N‐heterocyclic silylene) Ligand

For the first time, a significant boost in catalytic activity in the rhodium‐catalysed hydroformylation of an alkene by using a bidentate bis(N‐heterocyclic silylene) ligand is reported. This is shown by the hydroformylation of styrene at 30 bar CO/H2 pressure in the presence of [HRh(CO)(PPh3)3] with an excess of the ferrocenediyl‐based bis‐NHSi ligand 4, [({η5‐C5H4{PhC(NtBu)2}Si})2Fe], which results in superior catalytic activity, compared with the bidentate diphosphines DPPF (3a) and xantphos (3b). In contrast, the hydroformylation of styrene in the presence of [HRh(CO)(PPh3)3] with excesses of the monodentate NHSi ligands [{PhC(NtBu)2}SiNMe2] (1) and [{C2H2(NtBu)2}Si:] (2) at 30 bar CO/H2 pressure revealed considerably slower conversion to the aldehyde products than [HRh(CO)(PPh3)3], with or without an excess of PPh3, showing catalyst deactivation. Surprisingly, the germanium analogue of 4 is shown to be virtually catalytically inactive. The superior activity of 4, compared with the xantphos‐containing benchmark system, is rationalized on the basis of solution NMR spectroscopic studies, and the comparative catalyst cycles are elucidated using density functional theory (DFT) methods. The latter quantum‐chemical studies explain very well the favourable energy pathway for the hydroformylation of styrene using 4 versus xantphos.

Positional isomers of mononuclear silver(I) anionic complex [Ag(Ph3P)2[B10H10−xClx]]− (x = 0 or 1) with apically and equatorially coordinated decahydrido-closo-decaborate and 2-chlorononahydrido-closo-decaborate ligands

Attempts to separate the two dianions [B10H10]2− and [B10H9Cl]2− from mixtures with silver nitrate and PPh3 gave two novel compounds, [Ag(PPh3)4][Ag(PPh3)2[B10H9.15Cl0.85]] (1) and [Ag(PPh3)4][Ag(PPh3)2[B10H9.5Cl0.5]] (2), instead. They were selectively prepared using different synthetic approaches: 1 was prepared by the reaction of a mixture of [B10H10]2− and [B10H9Cl]2− salts [Bu4N]2[B10H10−xClx] (x=0, 1) with AgNO3 followed by dissolution of the resulting precipitate in an acetonitrile solution in an excess of PPh3, whereas 2 was prepared by the reaction of the same mixture [Bu4N]2[B10H10−xClx] with AgNO3 and an excess of PPh3 in a DMF solution. The X-ray diffraction studies showed that complex anions [Ag(Ph3P)2[B10H10−xClx]]− in 1 and 2 are positional isomers with the 10-vertex boron cluster ligands coordinating silver atoms by an apical and an equatorial edge, respectively. Crystals 1 and 2 are isostructural; in both, the anionic silver(I) complexes with [B10H10]2− and [B10H9Cl]2− cocrystallize in the same lattice. The chlorine substituents are not involved in silver coordination. Anionic complex in 2 provides the first example of silver(I) decahydrido-closo-decaborate with uncoordinated apical boron atoms of the boron cage. Possible mechanisms of the formation of complexes 1 and 2 are supposed.

A Synthetic Oxygen Atom Transfer Photocycle from a Diruthenium Oxyanion Complex.

Three new diruthenium oxyanion complexes have been prepared, crystallographically characterized, and screened for their potential to photochemically unmask a reactive Ru-Ru═O intermediate. The most promising candidate, Ru2(chp)4ONO2 (4, chp = 6-chloro-2-hydroxypyridinate), displays a set of signals centered around m/z = 733 amu in its MALDI-TOF mass spectrum, consistent with the formation of the [Ru2(chp)4O](+) ([6](+)) ion. These signals shift to 735 amu in 4*, which contains an (18)O-labeled nitrate. EPR spectroscopy and headspace GC-MS analysis indicate that NO2(•) is released upon photolysis of 4, also consistent with the formation of 6. Photolysis of 4 in CH2Cl2 at room temperature in the presence of excess PPh3 yields OPPh3 in 173% yield; control experiments implicate 6, NO2(•), and free NO3(-) as the active oxidants. Notably, Ru2(chp)4Cl (3) is recovered after photolysis. Since 3 is the direct precursor to 4, the results described herein constitute the first example of a synthetic cycle for oxygen atom transfer that makes use of light to generate a putative metal oxo intermediate.

Advantages of the solventless hydroformylation of olefins

The hydroformylation of olefins using Rh(acac)(CO)2 as a catalyst with the excess of PPh3 was investigated at the temperature of 80°C within the pressure range from 4 to 12bar in a neat substrate, without a solvent. The conversion of 1-hexene was complete, with a linear-to-branched aldehyde ratio of ca. 10. Very good results were also obtained for 1-pentene and 1-octene. The catalytic performance of the Rh(acac)(CO)2/PPh3 catalytic system in hydroformylation under solventless conditions was better than that in toluene, owing to the high concentration of the reactants. Recycling experiments confirmed the good stability of the catalyst and its constant activity.

Novel synthetic approach to charge-compensated phosphonio-nido-carboranes. Synthesis and structural characterization of neutral mono and bis(phosphonio) nido-ortho-carboranes.

A number of monosubstituted n-(triphenylphosphonio)-7,8-dicarba-nido-undecaboranes (2a, n = 1; 2b, n = 3; 2c, n = 5; 2d, n = 9) were prepared via a cross-coupling reaction between the tetrabutylammonium iodo-7,8-dicarba-nido-undecaborates (1a-d) and PPh3 in the presence of a Pd(PPh3)4 catalyst. The substitution rate was found to depend on the iodine position in the carborane cage. Under similar conditions, the reaction of 5,6-diiodo- (3) and 9,11-diiodo-7,8-dicarba-nido-undecaborate (5) anions exclusively yielded the monosubstitution products 5-iodo-6-(triphenylphosphonio)-7,8-dicarba-nido-undecaborane (4) and 9-iodo-11-(triphenylphosphonio)-7,8-dicarba-nido-undecaborane (6), respectively. The reaction of tetrabutylammonium 6,9-diiodo-7,8-dicarba-nido-undecaborate (7) exclusively produced the phosphine substitution product in the open face of the nido-carborane, 6-iodo-9-triphenylphosphonio-7,8-dicarba-nido-undecaborane (8). The addition of a base (Cs2CO3, NaH) to the reactions of 3 and 5 with PPh3 afforded the corresponding bis(triphenylphosphonio)-7,8-dicarba-nido-undecaboranes, 9 and 10. Compound 10 was also prepared from 6 using the general procedure. The reaction of the triiodocarborane tetrabutylammonium 5,6,9-triiodo-7,8-dicarba-nido-undecaborate (11) with excess PPh3 in the presence of Cs2CO3 and Pd(PPh3)4 only produced neutral 5-iodo-6,9-bis(triphenylphosphonio)-7,8-dicarba-nido-undecaborane (12); no positively charged tris(phosphonio) species formed. The compositions of all prepared compounds were determined by multinuclear NMR spectroscopy and high-resolution mass spectrometry. The structures of compounds 2c, 6, 8, 9, and 12 were established by the X-ray diffraction analysis of single crystals.

Production of Additives with Antimicrobial Activity via Tandem Hydroformylation-amine Condensation of Soybean FAME Using an Ionic Liquid-Based Biphasic Catalytic System

A biphasic catalytic system based in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was employed for tandem hydroformylation-amine condensation reactions of soybean FAME using HRhCO(PPh3)3 as the catalyst precursor and n-butylamine. Using a tenfold excess of the ligand PPh3, the presence of the ionic liquid increased the selectivity for imine if compared to the reaction carried out under similar conditions, but in homogeneous media.The yield for imine reached 75% after 24 h. On the other hand, in the absence of a PPh3 excess, the effect of using the ionic liquid was opposite and the selectivity for imine decreased. This supposedly occurred due to the generation ofN-heterocyclics carbenes, which would coordinate to Rh to form species active for parallel and/or consecutive reactions. When an excess PPh3 is used, it suppress the carbenes coordination, maintaining the Rh complex in a form active for hydroformylation.The obtained imine products presented remarkable antimicrobial activity towards a set of fungi and bacteria commonly present in fuel storage tanks.

A detailed kinetic analysis of rhodium-catalyzed alkyne hydrogenation

Continuous monitoring using electrospray ionisation mass spectrometry (ESI-MS) shows that Wilkinson's catalyst hydrogenates a charge-tagged alkyne to the corresponding alkene, and at only a marginally slower rate, to the alkane. No rhodium-containing intermediates were observed during the reaction, consistent with the established mechanism which points at the initial dissociation of triphenylphosphine from Rh(PPh₃)₃Cl as being the key step in the reaction. A numerical model was constructed that the closely matched the experimental data, and correctly predicted the response of the reaction to the addition of excess PPh₃.

Mutual transformation between mono- and binuclear ruthenium complexes and their reactions with iminobis(diisopropylphosphinesulfide) ligand

Treatment of RuCl3·xH2O, PPh3 and HCHO in boiling 2-methoxyethanol led to isolation of complex [(PPh3)(CO)ClRu(μ-Cl)3Ru(CO)(PPh3)2] (1) and [RuCl2(CO)(CH3OH)(PPh3)2] (2), which could convert to each other under special conditions. 1 could turn to 2 in MeOH/Et2O solvent in the presence of excess PPh3, while 2 could transform to 1 in CH2Cl2/n-hexane solvent. Reactions of complex 1 or 2 with KN[iPr2P(S)]2 afforded complex [{RuCl(CO)(PPh3)}2(μ-Cl)(μ-η2(S),η2(S′)-N(iPr2PS)2)] (3), in which the N[P(S)iPr2]2− ligand acts as a dinucleating tetraconnective unit through both sulfur atoms between two Ru(II) atoms. Complexes 1, 2, and 3 have been characterized spectroscopically and by X-ray crystallography.

Interconversion of Metallabenzenes and Cyclic η2‐Allene‐Coordinated Complexes

Treatment of the osmabenzene [Os{CHC(PPh(3))CHC(PPh(3))CH}Cl(2)(PPh(3))(2)]Cl (1) with excess 8-hydroxyquinoline produces monosubstituted osmabenzene [Os{CH C(PPh(3))CHC(PPh(3))CH}(C(9)H(6)NO)Cl(PPh(3))]Cl (2) or disubstituted osmabenzene [Os{CHC(PPh(3))CHC(PPh(3))CH}(C(9)H(6)NO)(2)]Cl (3) under different reaction conditions. Osmabenzene 2 evolves into cyclic η(2)-allene-coordinated complex [Os{CH=C(PPh(3))CH=(η(2)-C=CH(2))}(C(9)H(6)NO)(PPh(3))(2)]Cl (4) in the presence of excess PPh(3) and NaOH, presumably involving a P-C bond cleavage of the metallacycle. Reaction of 4 with excess 8-hydroxyquinoline under air affords the S(N) Ar product [(C(9)H(6)NO)Os{CHC(PPh(3))CHCHC}(C(9)H(6)NO)(PPh(3))]Cl (5). Complex 4 is fairly reactive to a nucleophile in the presence of acid, which could react with water to give carbonyl complex [Os{CH=C(PPh(3))CH=CH(2)}(C(9)H(6)NO)(CO)(PPh(3))(2)]Cl (6). Complex 4 also reacts with PPh(3) in the presence of acid and results in a transformation to [Os{CHC(PPh(3))CHCHC}(C(9)H(6)NO)Cl(PPh(3))(2)]Cl (7) and [Os{CH=C(PPh(3))CH=(η(2)-C=CH(PPh(3)))}(C(9)H(6)NO)Cl(PPh(3))]Cl (8). Further investigation shows that the ratio of 7 and 8 is highly dependent on the amount of the acid in the reaction.

Reactions and properties of the dinuclear molybdenum complex [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)6

Reactions of the title complex (1), which features the rigid doubly-bridged biscyclopentadienyl ligand and the unusually long Mo–Mo bond in the structure, with a variety of classic substrates are explored. Complex 1 reacts with I2 in CH2Cl2 to give the expected Mo–Mo cleaved product [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)6I2 (2A) with a Mo–Mo distance of 5.329Å. While the same reaction in benzene forms the product 2B, which has the same structural formula as 2A but a different conformation, in which the Mo–Mo distance is 6.442Å. Reaction of 1 with Ph2E2 (E=S, Se) in refluxing toluene or under UV irradiation yields products with the carbonyls completely removed, [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(EPh)2(μ-EPh)2 (3a–b). Reaction of 1 with [Et2NC(S)S]2 results in the di-substituted product [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)4(Et2NC(S)S)2 (4). Reaction of 1 with C2Ph2 affords the acetylene-bridged derivative [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)4(μ-C2Ph2) (5). Reaction of 1 with an excess of PPh3 in refluxing toluene only provides the mono-substituted derivative [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)5(PPh3) (6), while the reaction of 1 with excess P(OPh)3 under the same conditions produces not only the mono-substituted derivative [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)5(P(OPh)3) (7), but also the di-substituted derivative [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)4(P(OPh)3)2 (8). The reactivity and properties of the doubly-bridged molybdenum complex 1 and the corresponding non-bridged and singly-bridged analogs are compared. The molecular structures of 2A, 2B, 3a, 5 and 8 have been determined by single crystal X-ray diffraction.

Rearrangements of phosphinoimines to phosphine–imines in ruthenium chelate complexes

Thermal reaction of 1:1 mixtures of the RuCl(2)(PPh(3))(3) and phosphinoimine R(2)PN=CPh(2) (R = Ph, iPr, Me) at 140 °C results in isolation of the dimeric species [RuCl(μ-Cl)(PPh(3))(C(6)H(4)(PPh(2))C(Ph)NH)](2) (R = Ph 1, iPr 2, Me 3) containing phosphine-imine chelating ligands. Subsequent reaction of 1 and 3 with one equivalent of pyridine at room temperature give RuCl(2)(PPh(3))(py)(C(6)H(4)(PR(2))C(Ph)NH) (R = Ph 4, Me 5). Excess pyridine reacts with 2 to give a mixture of the cis and trans-isomers of RuCl(2)(py)(2)(C(6)H(4)(PiPr(2))C(Ph)NH) 6 and 7 respectively. Treatment of 5 with excess PPh(3) affords RuCl(2)(PPh(3))(2)(C(6)H(4)(PMe(2))C(Ph)NH) 8. Aspects of the mechanism of the thermal rearrangements of the phosphinoimine to the phosphine-imine ligands are considered and the isolation of RuCl(2)(Ph(2)PN=CPh(2))(SIMes)(CHPh) 9 and RuCl(2)(PPh(3))(2)(HN=C(Ph)C(6)H(4)) 10 provide support for a proposed mechanism involving a intermediate containing a Ru-bound metallated aryl-imine fragment.

1-(2′-Pyridylazo)-2-naphtholate (PAN) complexes of rhodium(III): Synthesis, structure and spectral studies

The ligating properties 1-(2′-pyridylazo)-2-naphthol (HPAN) toward Rh(III) have been examined. The reaction of RhCl 3·3H 2O with HPAN in presence of excess PPh 3 afforded trans-[Rh(PAN)Cl(PPh 3) 2]PF 6 ( 3PF 6 ). Intermediate cis-[Rh(PAN)Cl 2(PPh 3)] ( 4) has also been isolated. Solid state structures were authenticated by X-ray analyses revealing that monoanionic PAN is coordinated to rhodium in meridional fashion. Both the compounds were spectroscopically characterized in both solution and solid states, which include IR, NMR ( 1H and 31P), and optical spectra. The diamagnetic complexes show multiple CT transitions in the visible region. Low-energy transitions ( λ ≈ 550–650 nm) occurred in the absorption spectra are predominantly ligand centered in nature. The rhodium(III)–PAN compounds are red emissive ( λ em ≈ 650 nm) at room temperature and the nature of the emission level is probably an ILCT level. Complexes are electro-active in acetonitrile and display irreversible oxidative and reductive waves and these responses are ascribed to be PAN ligand centered in character.

Oxidation of phosphine by sulfur or selenium involving a catalytic cycle in the interconversion of monomer and tetramer forms of copper-maleonitriledithiolate complexes

The addition of triphenylphosphine (PPh3), into [Et4N]4[Cu4(mnt)4] shifted its characteristic electronic spectral band at 377 nm to 372 nm which is identical to that of the monomeric species, [Et4N][Cu(mnt)(PPh3)]. This reaction was followed by electrochemical study and also by 31P NMR spectroscopy. Such interconversion with the participation of breaking of bridging copper-µ3-sulfur bond with the formation of new copper-phosphorous bond led to the development of a catalytic cycle using excess PPh3 and S or Se as the reacting substrates. The turnover number for the oxidation of PPh3 by S was found to be 0·8 × 10−2 s−1 and that with Se was 0·6 × 10−2 s−1 using this catalytic system.

A Novel Ligand Modification and Diamond-core Molybdenum(IV) 2,6-Bis(2,2-diphenyl-2-thioethyl)pyridinate(2-) Complex

The reaction of Mo(VI)O(2)(L-NS(2)) [L-NS(2) = 2,6-bis(2,2-diphenyl-2-thioethyl)pyridinate(2-)] or Mo(V)(2)O(3)(L-NS(2))(2) with excess PPh(3) in N,N-dimethylformamide at 70 degrees C results in the formation of gray-green (L-NOS)Mo(IV)(mu-O)(mu-S)Mo(IV)(L-NS(2)) [L-NOS = 2-(2,2-diphenyl-2-thioethyl)-6-(2,2-diphenyl-2-oxoethyl)pyridinate(2-)] (1). The crystal structure of 1 revealed a dinuclear complex comprised of two trigonal bipyramidal Mo centers bridged along an axial-equatorial edge (the mu-O-mu-S vector) such that the Mo-N bonds are trans to the bridging atoms and are anti with respect to the Mo-Mo bond (d(Mo-Mo) = 2.5535(5) A); the remaining coordination sites are occupied by the S- and O-donor atoms of the L-NOS and L-NS(2) ligands. The diamond core is asymmetric, with Mo(1/2)-O(1) distances of 1.845(2) and 2.009(2) A and Mo(1/2)-S(1) distances of 2.374(1) and 2.230(1) A. Compound 1 is unique in possessing a planar, diamond-core unit devoid of terminal oxo ligation and a new tridentate L-NOS ligand formed via a novel intramolecular modification of the original L-NS(2) ligand.