Ferrocenyl-substituted allenylidene complexes of chromium, molybdenum and tungsten: Synthesis, structure and reactivity

Bis(ferrocenyl)-substituted allenylidene complexes, [(CO)₅MCCCFc₂] (1a-c, Fc = (C₅H₄)Fe(C₅H₅), M = Cr (a), Mo (b), W (c)) were obtained by sequential reaction of Fc₂CO with Me₃Si-CCH, KF/MeOH, n-BuLi, and [(CO)₅M(THF)]. For the synthesis of related mono(ferrocenyl)allenylidene chromium complexes, [(CO)₅CrCCC(Fc)R] (R = Ph, NMe₂), three different routes were developed: (a) reaction of the deprotonated propargylic alcohol HCCC(Fc)(Ph)OH with [(CO)₅Cr(THF)] followed by desoxygenation with Cl₂CO, (b) Lewis acid induced alcohol elimination from alkenyl(alkoxy)carbene complexes, [(CO)₅CrC(OR)CHC(NMe₂)Fc], and (c) replacement of OMe in [(CO)₅CrCCC(OMe)NMe₂] by Fc. Complex 1a was also formed when the mono(ferrocenyl)allenylidene complex [(CO)₅CrCCC(Fc)NMe₂] was treated first with Li[Fc] and the resulting adduct then with SiO₂. The replacement route (c) was also applied to the synthesis of an allenylidene complex (7a) with a CC spacer in between the ferrocenyl unit and C_γ of the allenylidene ligand, [(CO)₅CrCCC(NMe₂)-CCFc]. The related complex containing a CHCH spacer (9a) was prepared by condensation of [(CO)₅CrCCC(Me)NMe₂] with formylferrocene in the presence of NEt₃. The bis(ferrocenyl)-substituted allenylidene complexes 1a-c added HNMe₂ across the C_α-C_β bond to give alkenyl(dimethylamino)carbene complexes and reacted with diethylaminopropyne by regioselective insertion of the CC bond into the C_β-C_γ bond to afford alkenyl(diethylamino)allenylidene complexes, [(CO)₅MCCC(NEt₂)CMeCFc₂]. The structures of 5a, 7a, and 9a were established by X-ray diffraction studies.     

Improved preparation of indenyl molybdenum(II) and tungsten(II) compounds

Oxidative addition of 1-bromo-1H-indene to [Mo(CO)₃(NCMe)₃] and [W(CO)₃(NCEt)₃] is a suitable method for preparation of the indenyl compounds [IndMo(CO)₃Br] and [IndW(CO)₃Br], respectively. These products were fully characterised using spectroscopic methods. Structure of [IndW(CO)₃Br] was determined by single crystal X-ray diffraction analysis.     

Heptacoordinate dithiophosphate W(II) and Mo(II) complexes of diphosphines and iodide

New complexes [MI(CO)₂(dppe){S₂P(OEt)₂}] (M=W, 1a; M=Mo, 1b), [MI(CO)₂(dppm){S₂P(OEt)₂}] (M=W, 2a; M=Mo, 2b) and [W(CO)(dppe){S₂P(OEt)₂}₂][O₂dppe] (3a), were synthesised from [MI₂(CO)₃(NCMe)₂] (M=Mo, W), after treatment with ammonium diethyldithiophosphate and phosphine under different conditions. The structure of the tungsten complexes was determined by single crystal X-ray diffraction. During the synthesis of 3a, oxidation of the phosphine took place and a molecule of oxidised phosphine occupies channels in the crystal. DFT/B3LYP calculations on models of 1a and 2a showed the capped octahedron structure, observed in most dicarbonyl complexes of this family, to be preferred by 1.4 and 2.6 kcal mol⁻¹ for the dppm and the dppe complexes, respectively. Strong steric repulsions can reverse this trend, as happens with the rigid dppm ligand. Complex 1a adopts a pentagonal bipyramidal geometry, which is often found in related monocarbonyl complexes.     

The propensity of alkoxide and aryloxide derivatives of tungsten carbonyls to aggregate in solution. Synthesis and X-ray structures of dinuclear, trinuclear and tetranuclear complexes derived from the MeOW(CO)5 anion

The complex [Et₄N][W(CO)₅OMe] (1) has been prepared from the reaction of the photochemically generated W(CO)₅THF adduct and [Et₄N][OH] in methanol. Complex 1 was shown to undergo rapid CO dissociation in THF to quantitatively provide the dimeric dianion, [W(CO)₄OMe]₂²⁻. The resulting THF insoluble salt [Et₄N]₂[W(CO)₄OMe]₂ (2) has been structurally characterized by X-ray crystallography, with the doubly bridging methoxide ligands being in an anti configuration. Complex 2 was found to subsequently react with excess methoxide ligand in a THF slurry to afford the face-sharing octahedron complex [Et₄N]₃[W₂(CO)₆(OMe)₃] (3) which contains three doubly bridging methoxide groups. In the absence of excess methoxide ligand complex 2 cleanly yields the tetrameric complex [Et₄N]₄[W(CO)₃OMe]₄ (4) which has been structurally characterized as a cubane-like arrangement with triply bridging μ³-methoxide groups and W(CO)₃ units. Although complex 3 was not characterized in the solid state, the closely related glycolate derivative [Et₄N]₃[W₂(CO)₆(OCH₂CH₂OH)₃] (5) was synthesized and its structure determined by X-ray crystallography. The trianions of complex 5 are linked in the crystal lattice by strong intermolecular hydrogen bonds. Crystal data for 2: space group P2₁/n, a = 7.696(2), b = 22.019(4), c = 9.714(2) Å, β = 92.22(3)°, Z = 4, R = 6.43%. Crystal data for 4: space group Fddd, a = 12.433(9), b = 24.01(2), c = 39.29(3) Å, Z = 8, R = 8.13%. Crystal data for 5: space group P2₁2₁2₁, a = 11.43(2), b = 12.91(1), c = 29.85(6) Å, Z = 8, R = 8.29%. Finally, the rate of CO ligand dissociation in the closely related aryloxide derivatives [Et₄N][W(CO)₅OR] (R = C₆H₅ and 3,5-F₂C₆H₃) were measured to be 2.15 × 10⁻² and 1.31 × 10⁻³ s⁻¹, respectively, in THF solution at 5°C. Hence, the value of the rate constant of 2.15 × 10⁻² s⁻¹ establishes a lower limit for the first-order rate constant for CO loss in the W(CO)₅OMe⁻ anion, since the methoxide ligand is a better π-donating group than phenoxide.     

Synthesis and reactivity of cationic bipyridine tungsten(0) and molybdenum(0) nitrosyl complexes

A variety of Group 6 mono bipyridine (bpy) complexes were prepared, and substitution reactions of [(bpy)(MeIm)M(CO)₂(NO)]PF₆ complexes (MeIm = 1-methylimidazole, M = W or Mo) were investigated. Nitrosylation of complexes having the general formula (bpy)(L)M(CO)₃ (L = a variable ligand) gave cationic complexes of the form [(bpy)(L)M(CO)₂(NO)]PF₆. The structure of [(bpy)(MeIm)W(CO)₂(NO)]PF₆ was confirmed by single-crystal X-ray diffractometry. [(bpy)(MeIm)M(CO)₂(NO)]PF₆ complexes undergo facile substitutions with mono-, tri- and tetra-dentate ligands, yielding di- or mono-carbonyl mononitrosyl complexes. The structures of [(bpy)(PMe₃)₂W(CO)(NO)]PF₆ and [(dien)(PMe₃)W(CO)(NO)]PF₆ (dien = diethylenetriamine) were determined by X-ray diffraction.     

Synthesis and characterization of organomolybdenum and organotungsten halides containing the η-pentabenzylcyyclopentadienyl ligand η-Bz5C5M(CO)3X (M = Mo, W; X = Cl, Br, I). The X-ray molecular structure of η-Bz5C5Mo(CO)3I

An improved synthetic procedure for pentabenzylcyclopentadiene Bz₅C₅H was developed. Six new organomolybdenum and organotungsten halides η⁵-Bz₅C₅M(CO)₃X(M = Mo, W; X = Cl, Br, I) were syntesized through the reaction of η⁵-Bz₅C₅M(CO)₃Li (derived from Bz₅C₅H, n-BuLi and M(CO)₆) with PCl₃, PBr₃ or I₂ and characterized by elemental analysis, IR and ¹H NMR spectroscopy. The structure of η⁵-Bz₅C₅Mo(CO)₃I was determined by single-crystal X-ray diffraction techniques. It crystallized in the monoclinic space groupp P2/c with cell parameters a = 13.294(4), B = 15.147(4), C = 19.027(3) Å, β = 108.32(2)°, V = 3637(2) ų, Z = 4 and D_x = 1.50 g cm⁻³. The final R value was 0.035 for 4564 observed reflections.     

Carbonylmolybdenum complexes with di(imino)pyridine and related ligands: Reduction of a di(imino)pyridine to an aminoiminopyridine system under mild conditions

The reactions of [Mo(CO)₆] towards a 2,6-di(imino)pyridine L¹ and related ligands were studied. The reaction with L¹ afforded two new complexes, [Mo(CO)₄L¹] (1) and [Mo(CO)₄L²] (2), where L² is the 2-amino-6-iminopyridine ligand arising from the hydrogenation of one imine function of L¹; similar reaction with a 2-acetyl-6-iminopyridine ligand L³ afforded [Mo(CO)₄L³] (3). Compounds 1, 2 and 3 have been fully characterised by IR, ¹H NMR and X-ray crystallography; they present a metal ion in a pseudo-octahedral environment, the three organic ligands acting with bidentate N₂ coordination modes. One of the imine functions in 1, the amine function in 2, and the ketone function in 3 are uncoordinated.     

The ReH6[P(C6H5)3]2 ion as a ligand: complexes with M(CO)3 fragments (M = Cr, Mo, W)

The reactions of [(H₅C₆)₃P]₂ReH₆⁻ with (CH₃CN)₃Cr(CO)₃, (diglyme)Mo(CO)₃ or (C₃H₇CN)₃W(CO)₃ led to the formation of [(H₅C₆)₃P]₂ReH₆M(CO)₃⁻ (M = Cr, Mo, W) complexes. These have been characterized by IR and NMR spectroscopies, as well as elemental analyses. A single crystal X-ray diffraction study has also been carried out for the M = Cr complex as a K(18-crown-6)⁺ salt. The complex crystallizes as a THF monosolvate in the monoclinic space group P2₁/n with a = 22.323(6), B = 9.523(2), C = 27.502(5) Å, β = 104.98(2)⁰ and V = 5648 ų for Z = 4. The Re---Cr separation is 2.5745(12) Å, and the two phosphine ligands are oriented unsymmetrically. Although the hydride ligands were not found, the presence of three bridging hydrides and a dodecahedral coordination geometry about rhenium could be inferred. Low temperature ¹H and ³¹P NMR spectroscopic studies did not reveal the low symmetry of the solid state structure.     

Different reaction behaviour of molybdenum and tungsten - Reactions of the dichloro dioxo dimethyl-bispyridine complexes with thiophenolate

The reaction of the metal complexes MO₂Cl₂(mebipy) (M = Mo, W) with two equivalents thiophenol by the exact same procedure leads to two different products for molybdenum [Mo₂O₄(SPh)₂(mebipy)₂] and tungsten [WO₂(SPh)₂(mebipy)]. To understand why this is the case the redox potentials of the starting materials were measured showing that the redox potential for thiophenol is lower than the redox potentials (M^V ↔ M^VI) for both of the metal precursors. A reduction of the metal and oxidation of the sulfur should be possible for both reactions but occurs only for the molybdenum compound. Theoretical calculations show that different metal-sulfur bond strengths are as well and equally responsible for the differing reaction behaviour as are the redox potentials.     

Synthesis and characterization of thiocyanato and chlorodioxo tungsten(VI) compounds: Comparative oxygen atom transfer capability with molybdenum analogs

Four new tungsten-oxo(VI) complexes have been synthesized, characterized spectroscopically and their molecular structure established by X-ray diffraction analysis. These bear identical environment as previously reported molybdenum-oxo(VI) complexes, which allowed direct comparison of their spectroscopic properties. Their capability as oxygen atom transfer agents was found to be significantly lower than their molybdenum analogs.     

Lightinduced sulfur-dealkylation of phosphino-thioether nickel(0) complexes

The observation of homolytic S---CH₃ bond cleavage in (Ph₂P(o-C₆H₄)SCH₃)₂Ni⁰ under photochemical conditions has prompted further investigation of nickel(0) complexes and their stability. Tetradentate P₂S′₂ donor ligands (S′ = thioether type S donor) with aromatic rings incorporated into the P to S links, Ph₂P(o-C₆H₄)S(CH₂)₃S(o-C₆H₄)PPh₂ (arom-PSSP), or the S to S links, Ph₂P(CH₂)₂SCH₂(o-C₆H₄)CH₂S(CH₂)₂PPh₂ (PS-xy-SP), have been used to form four-coordinate, square planar nickel(II) complexes, [(arom-PSSP)Ni](BF₄)₂ (2) and [(PS-xy-SP)Ni](BF₄)₂ (3). The bidentate and tetradentate ligands, Ph₂P(o-C₆H₄)SCH₂CH₃ (arom-PSEt) and Ph₂P(CH₂)₂S(CH₂)₃S(CH₂)₂PPh₂ (PSSP), give similar complexes, [(arom-PSEt)₂Ni](BF₄)₂ (1) and [(PSSP)Ni](BF₄)₂ (4), respectively. Cyclic voltammograms of the Ni¹¹ complexes in CH₃CN show two reversible redox events assigned to and . The one-electron reduction product produced by stoichiometric amounts of Cp₂Co can be characterized by EPR. At 100 K rhombic signals show hyperfine coupling to two phosphorus atoms. Complete bulk chemical reduction of complexes 1, 2, 3 and 4 with Na/Hg amalgam provided the corresponding nickel(0) complexes 1^R, 2^R, 3^R and 4^R which were isolated as red solutions or solids characterized by magnetic resonance properties and reaction products. Photolysis of these nickel(0) complexes leads to S-dealkylation to produce alkyl radicals and dithiolate nickel(II) complexes. Complex 3 crystallized in the monoclinic space group P_2t/c with a=20.740(5), B=9.879(3), C=17.801(4) åA, ß=92.59(2)°, V=3644(2) ų and Z=4; complex 4: P2₁/c with A=13.815(4), B=13.815(4), C=15.457(5) åA, V=3365.4(14) ų and Z=4.     

Syntheses, characterisation, infrared and Mo NMR spectroscopy of some coordinated oxo—molybdenum(VI) complexes

Adducts with MoO₄²⁻ tetrahedra coordinated to Cr(III) or Co(III) complexes have been synthesized and studied by IR and high resolution ⁹⁵Mo NMR spectroscopy. The ⁹⁵Mo chemical shifts of the adducts with cobalt(III) lie in the range −33.2 to + 49.4 ppm. This may be compared with an overall known chemical shift range in excess of 7000 ppm and implies a similarity in the molybdenum environment in all cases. For adducts with chelated cobalt(III) complexes several rather broad ⁹⁵Mo singnals are obtained with linewidths up to 260 Hz.     

1,2-Borotropic shifts and B-N bond cleavage reactions in molybdenum hydrotris(3-isopropylpyrazolyl)borate chemistry: Mixed-valence MoMo2 and pyrazole-rich oxo-Mo complexes

Red-black [Tp^iPr∗Mo^VO]₂(μ-O)(μ-Mo^VIO₄) (1, Tp^iPr∗ = hydrobis(3-isopropylpyrazolyl)(5-isopropylpyrazolyl)borate) has been isolated as a by-product in the synthesis of NEt₄[Tp^iPrMo(CO)₃] (Tp^iPr = hydrotris(3-isopropylpyrazolyl)borate) and characterized by spectroscopic and X-ray crystallographic techniques. The trinuclear, mixed-valence complex contains two distorted octahedral anti-Tp^iPr∗Mo^VO centers bridged by bent oxo (Mo-O-Mo av. 158.7°) and tetrahedral κO,κO′-molybdate ligands. The complex contains a six-membered, non-planar Mo₃(μ-O)₃ core and two 1,2-borotropically-shifted Tp^iPr∗ ligands (with the shifted pyrazolyl trans to Mo^V=O). Aerial decomposition of solid NEt₄[Tp^iPrMo(CO)₃] produces sky-blue, diamagnetic Tp^iPrMoO(ⁱPrpz)(ⁱPrpzH) (2, ⁱPrpz^- = 3-isopropylpyrazolate, ⁱPrpzH = 3-isopropyl-2H-pyrazole). Molecules of 2 feature a tridentate fac-Tp^iPr ligand and mutually cis terminal oxo (MoO = 1.665(2) Å) and monodentate ⁱPrpz⁻ and ⁱPrpzH ligands. The latter are formed by B-N bond cleavage of Tp^iPr. The complex can also be synthesized by reacting NEt₄[Tp^iPrMo(CO)₃] with excess 3-isopropylpyrazole and dioxygen at 100 °C. Cleavage of the B-N bond(s) of Tp^iPr was also observed in the formation of Tp^iPrMoO(SPh)(ⁱPrpzH) (3) as a by-product in the synthesis of Tp^iPrMoO₂(SPh). In the monohydrate, 3 exhibits a distorted octahedral geometry defined by a tridentate fac-Tp^iPr ligand and mutually cis terminal oxo (MoO = 1.676(3) Å) and monodentate SPh⁻ and ⁱPrpzH ligands. The pyrazole β-NH group is observed to participate in a hydrogen-bond to the lattice water molecule. The complex can be synthesized in high yield by reducing Tp^iPrMoO₂(SPh) by HSPh or PPh₃ in the presence of excess 3-isopropylpyrazole.     

Chemistry of tris(2,4,6-trimethoxyphenyl)phosphine with rhodium(I) and iridium(I) olefin complexes

Rh(I) and Ir(I) complexes of the type [Rh(cod)(η²-TMPP)]¹⁺ (1) and M(cod)(η²-TMPP-O) (M = Rh (2), Ir (3); cod = cyclooctadiene; TMPP = tris(2,4,6-trimethoxyphenyl)phosphine; TMPP-O = mono-demethylated form of TMPP) have been isolated from reactions of [M(cod)Cl]₂ with M′BF₄ (M′ = Ag⁺, K⁺, Na⁺) followed by addition of the tertiary phosphine ligand. This chemistry is dependent on the identity of the metal, as both the cationic phosphine complex and the neutral phosphino-phenoxide compound are stable for Rh(I), whereas only the latter is stable for Ir(I). The three complexes have been characterized by IR and NMR (¹H and ³¹P) spectroscopies as well as by cyclic voltammetry. The ¹H NMR spectrum of [Rh(cod)(η²-TMPP)]¹⁺ (1) is in accord with the formula and reveals that the TMPP phenyl rings are undergoing rapid exchange between coordinated and non-coordinated modes; the corresponding spectra of 2 and 3 support free rotation about the P---C bonds of the unbound phenyl rings with no fluxionality of the bound demethylated ring. The ³¹P{¹H} NMR spectrum of the neutral species 2 exhibits a significant upfield shift with respect to the analogous cationic compound 1. This shielding is the result of improved electron donation to the metal from a phenoxide group as compared to an ether substituent. In situ addition of CO to the reaction between TMPP and [Rh(cod)Cl]₂ or [Ir(cod)Cl]₂ in the presence of M′BF₄ results in the isolation of the monocarbonyl species [Rh(TMPP)(η²-TMPP)(CO)][BF₄] (5) and the stable dicarbonyl compound [Ir(TMPP)₂(CO)₂][BF₄] (4), respectively. Single crystal X-ray data for

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. The geometry of 4 is square planar, with essentially ideal angles for the mutually trans disposed phosphine and carbonyl ligands, as found in earlier studies for the analogous Rh dicarbonyl compound. The ¹H NMR spectrum of 4 supports the assignment of magnetically equivalent phosphorus nuclei in solution. The results of this study indicate that cyclooctadiene is a particularly strong ligand for monovalent late transition metals ligated by TMPP, to the extent that it is inert with respect to substitution in the absence of π-acceptor ligands such as carbon monoxide.     

Syntheses, redox and UV-Vis spectroelectrochemical properties of mono- and dinuclear tris(pyrazolyl)borato-oxomolybdenum(IV) complexes with pyridine ligands

Reaction of [Mo^VI(Tp^Me,Me)(O)₂Cl] with a variety of pyridine-based ligands [pyridine (py), 4,4′-bipyridine (bpy), 4-phenylpyridine (phpy) and 1,2′-bis(4-pyridyl)ethene (bpe)] in toluene in the presence of Ph₃P affords the mononuclear oxo-Mo(IV) complexes [Mo(Tp^Me,Me)(O)Cl(L)] (L=py, phpy or monodentate bpy; abbreviated as Mo(py), Mo(phpy) and Mo(bpy), respectively) and the dinuclear complexes [{Mo(Tp^Me,Me)(O)Cl}₂(μ-L)] (L=bpy, bpe; abbreviated as Mo₂(bpy), Mo₂(bpe), respectively). The complex Mo₂(bpy), together with the by-product [{Mo(Tp^Me,Me)(O)Cl}₂(μ-O)], have been crystallographically characterised. Electrochemical studies on the oxo-Mo(IV) complexes reveal the presence of reversible Mo(IV)/Mo(V) couples at around −0.3 V versus ferrocene/ferrocenium in every case. For the dinuclear complexes Mo₂(bpy) and Mo₂(bpe) these redox processes are coincident, indicating that they are largely metal-centred and not significantly delocalised across the bridging ligand. In contrast, Mo₂(bpe) alone shows two reversible reductions, separated by 320 mV; these could be described as ligand-centred reductions of the bpe bridge, or as Mo(IV)/Mo(III) couples which—because of their separation—are substantially delocalised onto the bridging ligand. UV-Vis spectroelectrochemical studies using an OTTLE cell at 243 K revealed that oxidation of the complexes results in spectral changes (collapse of the Mo(IV) d-d transitions, loss in intensity of the Mo→pyridine MLCT transition) consistent with the formation of a Mo(V) state following metal-centred oxidation, but that one-electron reduction of Mo₂(bpe) results in appearance of numerous intense transitions more characteristic of a ligand radical following ligand-centred reduction.     

Kinetics and mechanisms of ligand substitution reactions of molybdenum SO2 complexes. Synthesis and X-ray structure of trans-Mo(CO)2 (dmpe) (PPh3) (SO2)

Kinetic results are reported for intramolecular PPh₃ substitution reactions of Mo(CO)₂(η¹-L)(PPh₃)₂(SO₂) to form Mo(CO)₂(η²-L)(PPh₃)(SO₂) (L = DMPE = (Me)₂PC₂H₄P(Me)₂ and dppe=Ph₂PC₂H₄PPh₂) in THF solvent, and for intermolecular SO₂ substitutions in Mo(CO)₃(η²-L)(η²-SO₂) (L = 2,2′-bipyridine, dppe) with phosphorus ligands in CH₂Cl₂ solvent. Activation parameters for intramolecular PPh₃ substitution reactions: ΔH^≠ values are 12.3 kcal/mol for dmpe and 16.7 kcal/mol for dppe; ΔS^≠ values are −30.3 cal/mol K for dmpe and −16.4 cal/mol K for dppe. These results are consistent with an intramolecular associative mechanism. Substitutions of SO₂ in MO(CO)₃(η²-L)(η²-SO₂) complexes proceed by both dissociative and associative mechanisms. The facile associative pathways for the reactions are discussed in terms of the ability of SO₂ to accept a pair of electrons from the metal, with its bonding transformations of η²-SO₂ to η¹-pyramidal SO₂, maintaining a stable 18-e count for the complex in its reaction transition state. The structure of Mo(CO)₂(dmpe)(PPh₃)(SO₂) was determined crystallographically: P2₁/c, A=9.311(1), B = 16.344(2), C = 18.830(2) Å, ß=91.04(1)°, V=2865.1(7) ų, Z=4, R(F)=3.49%.     

Synthesis, platinum(II) complexes and structural aspects of the new tetradentate phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane

Several novel dimers of the composition [M₂Cl₄(trans-dppen)₂] (M=Ni (1), Pd (2), Pt (3)) containing trans-1,2-bis(diphenylphosphino)ethene (trans-dppen) have been prepared and characterized by X-ray diffraction methods, NMR spectroscopy (¹⁹⁵Pt{¹H}, ³¹P{¹H}), elemental analyses, and melting points. The intramolecular [2+2] photocycloaddition of the two diphosphine-bridges in 3 produces [Pt₂Cl₄(dppcb)] (4), where dppcb is the new tetradentate phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane. Neither 1 nor the free diphosphine trans-dppen shows this reaction. In the case of 2 the photocycloaddition is slower than in 3. This difference can be explained by the shorter distance between the two aliphatic double bonds in 3 than in 2, but also different transition probabilities within ground and excited states of the used metals could be involved. Furthermore, variable-temperature ³¹P{¹H} NMR spectroscopy of 2 or 3 reveals a negative activation entropy of 2 for the [2+2] photocycloaddition, but a positive of 3. The removal of chloride from 4 by precipitating AgCl with AgBF₄, and subsequent treatment with 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) leads to [Pt₂(dppcb)(bipy)₂](BF₄)₄ (5) and [Pt₂(dppcb)(phen)₂](BF₄)₄ (6), respectively. In an analogous reaction of 4 with PMe₂Ph or PMePh₂, [Pt₂(dppcb)(PMe₂Ph)₄](BF₄)₄ (7) and [Pt₂(dppcb)(PMePh₂)₄](BF₄)₄ (8) are formed. Complexes 1–8 show square–planar coordinations, where the compounds 4–8 have also been characterized by the above mentioned methods together with fast atom bombardment mass spectrometry (7, 8). The crystal structure of 4 reveals two conformations, which arise from an energetic competition between the sterical demands of dppcb and an ideal square–planar environment of Pt(II). The free tetraphosphine dppcb can be obtained easily from 4 by treatment with NaCN. It has been characterized fully by the above methods including ¹³C{¹H} and ¹H NMR spectroscopy. The X-ray structure analysis shows the pure MMMP-enantiomer in the solid crystal, which is therefore optically active. This chirality is induced by a conformation of dppcb, where all four PPh₂ groups are non-equivalent. Variable-temperature ³¹P{¹H} NMR spectroscopy of dppcb confirms this explanation, since the single signal at room temperature is split into two doublets at 183 K. The goal of this article is to demonstrate the facile production of a new tetradentate phosphine from a diphosphine precursor via Pt(II) used as a template.     

Synthesis and structure determination of some platinum (II) complexes with hydrophilic carboxylated tertiary phosphine ligands

[Pt(COD)Cl₂] (1) reacts with PPh₂(C₆H₄COOH) (2a,b,c), PPh₂(C₆H₄COONa) (2d), PPh(C₆H₄COOH)₂ (4b,c) and P(C₆H₄COOH)₃ (6b,c) with formation of the corresponding complexes [Pt(L)₂Cl₂] (3a,b,c,d, 5b,c, 7b,c). Halide abstraction from 3a by Ag⁺ promotes coordination of the ortho-carboxylate function to platinum, yielding [ -2)}{PPh₂(C₆H₄COOH-2)}Cl] (bd8) and [ovbar|{PPh₂(C₆H₄COO-2)}₂] (bd9). Reaction of 1 with CO and 2a or 2b gives [Pt(CO)(L)Cl₂] (10a,b), wherea 1 and 2,3-bis(diphenylphosphino) maleic anhydride yields

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(bd12) and [Pt{Ph₂PC(COOH)=C(COOMe)-PPh₂}Cl₂] (13). The ¹H, ¹³C and ³¹P NMR spectra are reported and discussed. The X-ray structural analysis of 3b showed the compound to be monoclinic, space group P2₁/n, Z=4, with a=1038.5(3), B=1792.6(4), C=2311.5(4) pm, β=91.6(2)° and D_calc=1.353 g cm⁻³. The structure was solved from 4832 observed reflections with F₀ > 4 σ(F₀) and refined to a final R value of 0.0743. The Pt atom is surrounded by two Cl and two P atoms in a square planar arrangement.     

Quantifying the electronic cis effect of phosphine, arsine and stibine ligands by use of rhodium(I) Vaska-type complexes

The cis effects of phosphine, arsine and stibine ligands have been evaluated by measuring the IR stretching frequency in dichloromethane of the carbonyl ligand in a series of Rh(I) Vaska-type complexes, trans-[RhCl(CO)(L)₂]. These data were correlated with those obtained by Tolman for the electronic trans influences in the [Ni(L)(CO)₃] complexes. The electronic contribution, χ_Fc, of ferrocenyl was determined as 0.8 from these plots by evaluating PPh₂Fc as ligand. In order to accommodate arsine and stibine ligands an additional correction term, to compensate for differences in the donor atom, was added to Tolman’s equation for calculation of the Tolman electronic parameter of phosphine ligands. In the resulting equation: ν(CO_Ni)=2056.1+∑_i=1³χ_i+C_L values for C_L of C_P=0, C_As=−1.5 and C_Sb=−3.1 are suggested for phosphine, arsine and stibine ligands, respectively. The crystal and molecular structures of trans-[RhCl(CO)(PPh₂Fc)₂] · 2C₆H₆, trans-[RhCl(CO){P(NMe₂)₃}₂] and trans-[RhCl(CO)(AsPh₃)₂] are reported. The Tolman cone angles for PPh₂Fc and P(NMe₂)₃ were determined as 169° and 166°, while the effective cone angles for PPh₂Fc, P(NMe₂)₃ and AsPh₃ were determined as 171°, 168° and 147°, respectively.     

Synthesis, characterization and reactivity of polypyridyl ruthenium(II) carbonyl complexes with phosphine derivatives: Ruthenium-carbon bond labilization based on steric and electronic effects

Ruthenium phosphine complexes with a CO ligand [Ru(tpy)(PR₃)(CO)Cl]⁺ (tpy = 2,2′:6′,2″-terpyridine, R = Ph or p-tolyl), were prepared by introduction of CO gas to the corresponding dichloro complexes at room temperature. New carbonyl complexes were characterized by various methods including structural analyses. They were shown to release CO following the addition of several N-donors to form the corresponding substituted complexes. The kinetic data and structural results observed in this study indicated that the CO release reactions proceeded in an interchange mechanism. The molecular structures of [Ru(tpy)(PPh₃)(CO)Cl]PF₆, [Ru(tpy)(P(p-tolyl)₃)(CO)Cl]PF₆ and [Ru(tpy)(PPh₃)(CH₃CN)Cl]PF₆ were determined by X-ray crystallography.