η-Allyl-cobalt (II) complexes

(η³-Cyclooctenyl)Co(bisphosphine) compounds react with HBF₄ in the presence of alkenes with oxidation of the metal to give the novel, paramagnetic organocobalt(II) species [(η³-cyclooctenyl)Co(bisphosphine)]⁺BF₄⁻, (η³-2-RC₃H₄)Co(bisphosphine) complexes react similarly. The Co(II) compounds form adducts with CO and NO (the latter being diamagnetic) and undergo facile chemical and electrochemical reduction.     

Second sphere coordination behavior of aquo and amine ligands bound to a η-benzeneruthenium(II) cation

The bis(oxazoline) ligand, 2,2-bis[4(R)-phenyl-1,3-oxazolon-2-yl]propane (bpop), was introduced to the η⁶-benzenemthenium(II) moiety on treatment with [Ru(η⁶-C₆H₆)Cl₂]₂ to give [Ru(η⁶-C₆H₆)(bpop)Cl]⁺. Aquo and amine complexes [Ru(η⁶-C₆H₆)(bpop)(L)]²⁺ (L = H₂O (1), NH₂R; R = H (2) , Me (3) , and n-Bu (4) ) were prepared by treating the chloride complex with AgBF₄ in the presence of L. X-ray structure determinations of 1 and 3 were carried out. Both complexes possessed a three-leg piano stool structure with the N or O donors located at the three comers of a pseudo octahedron. The aquo complex 1 exhibited a dynamic NMR feature in which two magnetically nonequivalent oxazoline parts observed at lower temperatures were interchanged with each other at higher temperatures. This observation was ascribed to the formation of a C₂-symmetric 16-electron intermediate via Ru-OH₂ cleavage, which is slower in acetone than in dichloromethane owing to more effective solvation by acetone around hydrogens of the coordinated water molecule. The two diastereotopic N-hydrogens of 4 underwent deuterium exchange with CD₃OD with greatly different rates from each other owing to different energy of NHO (D) (CD₃) interaction. Carboxylate and sulfonate ions (A⁻) formed second sphere complexes with 4 by means of NHA⁻ hydrogen bonding, as evidenced by continuous shift of NH₂ resonances with increasing amounts of the anions added.     

Bis(η-allyl) (η-pentalene) zirconium: preparation, structure and structural dynamics

The preparation of a novel mononuclear complex of zirconium having an η⁸-bonded pentalene ligand and two η³-allyl groups is described. Its structure has been determined by ¹H and ¹³C NMR spectroscopy. At room temperature some of the NMR signals are broadened, revealing that the compound is structurally dynamic. It is shown that the compound has C₂ symmetry with the enantiomeric forms undergoing racemisation.     

Silyl reagents (Me3Si-X) efficiently transfer X to Ir(H)2F(PBuP2Ph)2

Me₃Si-X reagents react to completion at 25°C in a short time to convert Ir(H)₂FL₂ (L=P^tBu₂Ph) to Ir(H)₂XL₂. This involves formation of Ir-O, Ir-N, Ir-I, Ir-S and Ir-C(sp) bonds. Products include some η²-X ligands such as carboxylate and acetamide, NHC(O)CH₃. The acetamide is shown to be η² in the solid state and in solution, but readily rearranges, by a transition state with Ir-O bond cleavage, to effect site exchange of the two inequivalent hydrides. The same synthetic approach succeeds for the more crowded metallated species and these reactions arc shown to fail when F is replaced by Cl in the iridium reagent. Unsaturation at Ir is suggested to be central to the mechanism of these F/X transposition reactions.     

Chelated alkyl halide manganese complexes (η:η-C5H4CH2CH2X)Mn(CO)2 from photolysis of (η-C5H4CH2CH2X)Mn(CO)3

Manganese tricarbonyl complexes (η⁵-C₅H₄CH₂CH₂Br)Mn(CO)₃ (3) and (η⁵-C₅H₄CH₂CH₂I)Mn(CO)₃ (4), with an alkyl halide side chain attached to the cyclopentadienyl ligand, were synthesized as possible precursors to chelated alkyl halide manganese complexes. Photolysis of 3 or 4 in toluene, hexane or acetone-d₆ resulted in CO dissociation and intramolecular coordination of the alkyl halide to manganese to produce (η⁵:η¹-C₅H₄CH₂CH₂Br)Mn(CO)₂ (5) and (η⁵:η¹-C₅H₄CH₂CH₂I)Mn(CO)₂ (6). Low temperature NMR and IR spectroscopy established the structures of 5 and 6. Photolysis of 3 in a glass matrix at 91 K demonstrated CO release from manganese. Low temperature NMR spectroscopy established that the coordinated alkyl halide complexes are stable to approximately −20°C.     

η and η olefin complexation by S, S-[Ru(Me2edda)]: a structural change to accommodate bidentate dienes

[Ru^II(Me₂edda)(H₂O)₂] (1), Me₂edda²⁻ = N,N′-dimethylethylenediaminediacetate, exhibits a sterically-controlled molecular recognition in forming η² and η⁴ olefin complexes. 1 exists with an N₂O₂ in-plane set of chelate donors and axial H₂O ligands. The two CH₃ functionalities of Me₂edda²⁻ are poised above and below the N₂O₂ plane of the glycinato rings. Studies herein of the 2,2′-bipyridine complex, [Ru^II(Me₂edda)(bpy)], with bidentate bpy chelation as established via ¹H NMR and electrochemical methods show 1 to be ligated in the S,S configuration with the glycinato rings in-plane as a cis-O form. 1 is sterically discriminating in forming η² complexes with smaller olefins (ethylene, 2-propene, cis-2-butene, methyl vinyl ketone and 3-cyclohexene-1-methanol), but rejects larger decorated ring structures and branched olefins (1,2-dimethyluracil, cyclohexene-1-one 2-methyl-2-propene). η² complexes of 1 have characteristic Ru^II/III DPP waves near 0.55 V which vary slightly with olefin structure. Potentially bidendate dienes (1,3-butadiene, 1,3-cyclohexadiene and 2,5-norbornadiene (nbd) form η⁴ complexes as shown by Ru^II/III waves between 0.94 and 1.30 V, indicate of a highly stabilized Ru^II center by π-backboning. An η²η⁴ ‘equilibrium’ with apparent K = 22 at 25 °C is observed for nbd coordinated to 1. (The η² and η⁴ distribution may be a kinetic one and not a thermodynamic one). To allow formation of the cis η⁴ complexes, 1 must undergo a shift of one or both glycinato donors from the N₂O₂ plane into the axial site away from the dimethyl functionalities. η⁴ chelation by 1,3-butadiene has been confirmed by ¹H NMR spectral assignments of two [Ru^II(Me₂edda)] isomers, one in the axial rans-O glycinato configuration, e.g. 1,3-butadiene is bidentate in the original N₂O₂ plane and a second unsymmetrical glycinato arrangement with in-plane and axial glycinato as well as in-plane and axial η⁴-1,3-butadiene coordination. [Ru^II(hedta)(H₂O)]⁻ (2), hedta³⁻ = N-hydrpxyethylenediaminetriacetate, is less discriminating for olefin structures, forming η² complexes with all eleven olefins and dienes mentioned for studies with 1. However, 2 does not undergo displacement of a carboxylate donor by the second olefin unit of a diene [Ru^II(hedta)(diene)]⁻ complexes possess a pendant non-coordinated olefin and on η²-bound olefin in the complex, indicated by a normal Ru^II(pac)(olefin)Ru^II/III wave near 0.55 V.     

Mechanistic details for metathetical exchange between XCO (X = O and RN) and the tin(II) dimer, {Sn[N(SiMe3)2] (μ-OBu)}2

Metathetical exchange between carbon dioxide and the tin(II) dimer, {Sn[N(SiMe₃)₂](μ-OBu¹)}₂ (3) has been observed to cleanly produce the two new heteroleptic tin(II) dimers, Sn[N(SiMe₃)₂](μ-OBu^t)₂Sn(OSiMe₃) (6) and [Sn(OSiMe₃)](μ-OBu^t)]₂ (7]). In addition, reaction of 3 with I equiv, of tert-butylisocyanate (8), at 25°C, quantitatively provides 6, and with 2 equiv., quantitatively provides 7. Likewise 6 reacts with 1 equiv, of 8 to quantitatively provide 7. The mechanism for these latter processes has been investigated by low temperature ¹H NMR spectroscopy which reveals that metathetical exchange does not involve the tri-coordinate tin(II) centers of the dimeric structures, but rather, it occurs, in each case, via the transient monomeric tin(II) species, Sn[N(SiMe₃)₂](μ-OBu^t) (4), that undergoes metathesis to produce, initially the open dimer intermediate, Sn(OCNBu^t)(OSiMe₃)(μ-OBu^t)Sn(OBu^t) (OSiMe₃) (12), that is observed at −10°C. Subsequent redistribution reactions then generate the final products that are observed. Together, these mechanistic details provide additional support for the ‘monomeric tin(II)’ hypothesis proposed earlier for metathetical exchange between XCO and Sn[N (SiMe₃)₂]₂ (1).     

Alkene rotation in [Ru(η-C5H5) (L2) (η-alkene][CF3SO3] with L2 = iPr- or pTol-diazabutadiene. X-ray crystal structure of [Ru(η-C5H5(pTol-DAB) (η-ethene][CF3SO3]

Reaction of RuCl(η⁵-C₅H₅(pTol-DAB) with AgOTf (OTf = CF₃SO₃) in CH₂Cl₂ or THF and subsequent addition of L′ (L′ = ethene (a), dimethyl fumarate (b), fumaronitrile (c) or CO (d) led to the ionic complexes [Ru(η⁵-C₅H₅)(pTol-DAB)(L′)][OTf] 2a, 2b and 2d and [Ru(η⁵-C₅H₅)(pTol-DAB)(fumarontrile-N)][OTf] 5c. With the use of resonance Raman spectroscopy, the intense absorption bands of the complexes have been assigned to MLCT transitions to the iPr-DAB ligand. The X-ray structure determination of [Ru(η⁵-C₅H₅)(pTol-DAB)(η²-ethene)][CF₃SO₃] (2a) has been carried out. Crystal data for 2a: monoclinic, space group P2₁/n with A = 10.840(1), b = 16.639(1), C = 14.463(2) Å, β = 109.6(1)°, V = 2465.6(5) ų, Z = 4. Complex 2a has a piano stool structure, with the Cp ring η⁵-bonded, the pTol-DAB ligand σN, σN′ bonded (Ru-N distances 2.052(4) and 2.055(4) Å), and the ethene η²-bonded to the ruthenium center (Ru-C distances 2.217(9) and 2.206(8) Å). The C = C bond of the ethene is almost coplanar with the plane of the Cp ring, and the angle between the plane of the Cp ring and the double of the ethene is 1.8(0.2)°. The reaction of [RuCl(η⁵-C₅H₅)(PPh)₃ with AgOTf and ligands L′ = a and d led to [Ru(η⁵-C₅H₅)(PPh₃)₂(L′)]OTf] (3a) and (3d), respectively. By variable temperature NMR spectroscopy the rottional barrier of ethene (a), dimethyl fumarate (b and fumaronitrile (c) in complexes [Ru(η⁵-C₅H₅)(L₂)(η²-alkene][OTf] with L₂ = iPr-DAB (a, 1b, 1c), pTol-DAB (2a, 2b) and L = PPh₃ (3a) was determined. For 1a, 1b and 2b the barrier is 41.5±0.5, 62±1 and 59±1 kJ mol⁻¹, respectively. The intermediate exchange could not be reached for 1c, and the ΔG^# was estimated to be at least 61 kJ mol⁻. For 2a and 3a the slow exchange could not be reached. The rotational barrier for 2a was estimated to be 40 kJ mol⁻. The rotational barier for methyl propiolate (HC≡CC(O)OCH₃) (k) in complex [Ru(η⁵-C₅H₅)(iPr-DAB) η²-HC≡CC(O)OCH₃)][OTf] (1k) is 45.3±0.2 kJ mol⁻¹. The collected data show that the barrier of rotational of the alkene in complexes 1a, 2a, 1b, 2b and 1c does not correlate with the strength of the metal-alkene interaction in the ground state.     

Preparation of trimethylsilyl alkyne complexes of bis(pentamethylcyclopentadienyl)zirconium, (η-C5Me5)2Zr(RC≡CSiMe3), and their regioselective reactions with nitrous oxide

Benzene solutions of Cp^*₂ZrCl₂ (1) (Cp^* = η⁵-C₅Me₅) react with the alkynes Me₃SiC≡CPh, Me₃SiC≡C(c-C₅H₉) and Me₃SiC≡CCMe₃ in the presence of Na/Hg amalgam to afford high yields of the respective alkyne complexes Cp^*₂Zr(Me₃SiC≡CPh) (2), Cp^*₂Zr{Me₃SiC≡C(c-C₅H₉)} (3) and Cp^*₂Zr(Me₃SiC≡CCMe₃) (4) as crystalline compounds. Complex 2 crystallizes in the triclinic space group with a = 9.791(6), b = 10.466(6), c = 15.756(12) Å, = 86.09 (5), β = 72.09(5), γ = 72.06(4)° and Z = 2. The least-squares refinement converged to R(F) = 0.0604 and R(wF) = 0.0628 for the 3655 unique data with F_o > 4σ (F_o). Salient metrical parameters of the bound alkyne include the following: C(30)-C(31) = 1.340(9) Å; Zr-C(30) = 2.178(6) Å; Zr-C(31) = 2.219(5) Å; C(30)-C(31)-Si = 141.0(5)°; C(31)-C(30)-C(26) = 135.5(5)°. Nitrous oxide reacts with 2 or 3 to afford ((5) R = Ph; (6) R = c-C₅H₉) and 1 equiv. of N₂ via an intermediate, , which is unstable with respect to loss of dinitrogen to give the oxametallacyclobutene derivatives 5 and 6. The oxygen-atom insertion is regiospecific for the Zr-C bond that is attached to the carbyl (Ph or c-C₅H₉) substituent. Under similar conditions, complex 4, in which the alkyne is particularly labile, gives a myriad of products in its reaction with N₂O.     

Reactivity, variable temperature solution H NMR studies and MO calculations of dimolybdenum allenylidene complexes of the type [(η-C5H5)2Mo2(CO)4(μ,η(4e)-C=C=CR1R2)]

The reactivity, towards nucleophiles and electrophiles, of dimolybdenum allenylidene complexes of the type [Cp₂Mo₂(CO)₄(μ,η²(4e)-C=C=CR1R2)] (Cp=η⁵-C₅H₅) has been investigated. The nucleophilic attacks occur at the C_γ carbon atom, while electrophiles affec the C atom. Variable temperature solution ¹H NMR studies show a dynamic behavior of these complexes consisting of an equilibrium between two enantiomers with a symmetrical [Cp₂Mo₂(CO)₄(μ-σ,σ(2e)-C=C=CR1R2)] transition state. Extended Hückel MO calculations have been carried out on the model [Cp₂Mo₂(CO)₄(μ,η²-C=C=CH₂]. The calculated charges of the allenylidene carbon atoms suggest that the electrophilic attacks are under charge control, while the nucleophilic attacks are rather under orbital control.     

Alkylcobalt chelates with Schiff bases derived from a β-diketone bearing both alkyl and aryl groups

Organocobalt(III) complexes with Schiff bases derived from a β-diketone bearing both an alkyl and an aryl group have been prepared. The template syntheses using benzoylacetone and ethylenediamine as complexing agents provide a route to alkylcobalt chelates with the corresponding tri- and tetradentate Schiff bases. However, if a β-diketone with two aryl groups, e.g. dibenzoylmethane, was employed as the starting ketoenol component, no organometallic products were detected; a new mixed-ligand ‘inorganic’ chelate of cobalt(II), [Co{O=C(Ph)CH=C(Ph)O}₂(en)], was isolated instead. Its structure as well as that of one of the alkylcobalt complexes with a tridentate Schiff base composed of benzoylacetone and ethylenediamine have been established by X-ray techniques. The current scope of the template synthesis of alkylcobalt complexes with Schiff bases is summarized.     

Hetero-polynuclear complexes containing bridging diphenylphosphino-alkenes and -alkynes. The crystal structure of an Rh2{μ−ν:ν−P(Ph2) (CH2)3C≡CR}Co2 complex

The phosphinoalkenes Ph₂P(CH₂)_nCH=CH₂ (n= 1, 2, 3) and phosphinoalkynes Ph₂P(CH₂)_n C≡CR (R = H, N = 2, 3; R = CH₃, N = 1) have been prepared and reacted with the dirhodium complex (η−C₅H₅)₂Rh₂(μ−CO) (μ−η²−CF₃C₂CF₃). Six new complexes of the type (ν−C₅H₅)₂(Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH₃C₅H₄)Mn(CO)₂thf resulted in coordination of the manganese to the alkene function. The Rh₂---Mn complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂P(CH₂)₃CH=CH₂} (η−CH₃C₅H₄)Mn(CO)₂] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co₂(CO)₈ resulted in the coordination of Co₂(CO)₆ to the alkyne function. The Rh₂---Co₂ complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂PCH₂C≡CCH₃}Co₂(CO)₂], C₃₇H₂₅Co₂F₆O₇PRh₂, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group (C_i¹, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on |F| was 0.052 fo observed (I > 3σ(I)) reflections. The Rh₂ and Co₂ parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh₂ and perpendicular for Co₂. Attempts to induce Rh₂Co₂ cluster formation were unsuccessful.     

Selective C-H bond activation of arenes catalyzed by methylrhenium trioxide

Arenes, in glacial acetic acid, are oxidized to para-benzoquinones by hydrogen peroxide when methylrhenium trioxide (CH₃ReO₃ or MTO) is used as a catalyst. In some cases an intermediate hydroquinone was also obtained in lower yield. Oxidation of the methyl side chains of various methylbenzenes did not occur. The active catalyst species are the previously-characterized η²-peroxorhenium complexes, CH₃Re(O)₂(η²-O₂) and CH₃Re(O)(η²-O₂)₂H₂O). Separate tests showed that hydroquinones and phenols are oxidized by H₂O₂-MTO more rapidly than the simple arenes; in the proposed mechanism they are intermediate products. Higher conversions were found for the more highly-substituted arches, consistent with their being the most reactive species toward the electrophillically-active peroxide bound to rhenium. High conversions of the less substituted members of the series were not achieved, reflecting concurrent deactivation of MTO-peroxide, a process of greater import for the more slowly-reacting substrates.     

Preparation of η-1,3-dienyl, η-1,2-dienyl and η-cyclobutenone complexes via reactions of transition-metal carbonyl containing anions with allenic electrophiles

The preparation and reaction chemistry of 1,3- and 1,2-diene and related complexes derived from metal carbonyl containing anions and allenic electrophiles are addressed. The preparation of some CpFe(CO)₂ η¹-diene complexes and their conversion into CpFe(CO) η³-diene complexes is presented followed by reactions of CpMo(CO)₃⁻, CpW(CO)₃⁻ and CpMo(CO)₂PR₃⁻ anions with allenic electrophiles which produce metal complexed cyclobutenones (via CO and alkene insertions from the initially formed product) and 1,2-diene complexes, respectively. Lastly, the reactions of PPh₃(CO)₃Co⁻ anions with allenic electrophiles are outlined which result in several different coordination geometries depending on the reaction conditions used.     

Timing and magnitude of early Aptian extreme warming: Unraveling primary δO variation in indurated pelagic carbonates at Deep Sea Drilling Project Site 463, central Pacific Ocean

In order to elucidate early Aptian marine paleotemperature evolution across the period of enhanced organic carbon (C_org)-burial [Oceanic Anoxic Event (OAE) 1a], stable isotope analyses were performed on pelagic limestones at Deep Sea Drilling Project Site 463, central Pacific Ocean. The δ¹⁸O data exhibit a distinct anomaly by ~ − 2‰ spanning the OAE 1a interval (i.e., a ~ 6 m-thick, phytoplanktonic C_org-rich unit constrained by magneto-, bio- and δ¹³C stratigraphy). Elucidation of paleotemperature significance of the δ¹⁸O shift is made by taking account of recent Sr/Ca evidence at the same section, which revealed that geochemical signals in carbonate-poor lithologies are relatively unaltered against burial diagenesis. By discriminating δ¹⁸O values from carbonate-poor samples (CaCO₃ contents = 5–30 wt.%), it appears that an abrupt rise in sea-surface temperatures (SSTs) by 8 °C (= − 1.7‰ shift in δ¹⁸O) occurred immediately before OAE 1a, whereas a cooling mode likely prevailed during the peak C_org-burial. In terms of its stratigraphic relationship as to the C_org-rich interval and to a pronounced negative δ¹³C excursion, as well as its timescale, the observed SST rise resembles those associated with the Paleocene–Eocene thermal maximum and, more strikingly, Jurassic Toarcian OAE. This observation is consistent with the hypothesis that these paleoenvironmental events were driven by a common causal mechanism, which was likely initiated by the greenhouse effect via massive release of CH₄ or CO₂ from the isotopically-light carbon reservoir and terminated by a negative productivity feedback.     

Thermal and photochemical substitution reactions of CpRe(PPh3)2H2 and CpRe(PPh3)H4. Catalytic insertion of ethylene into the C-H bond of benzene

The thermal and photochemical reactions of CpRe(PPh₃)₂H₄ and CpRe(PPh₃)H₄ (Cp = η⁵-C₅H₅) with PMe₃, P(p-tolyl)₃, PMe₂Ph, DMPE, DPPE, DPPM, CO, 2,6-xylylisocyanide and ethylene have been examined. While CpRe(PPh₃)₂H₂ is thermally inert, it will undergo photochemical substitution of one or two PPh₃ ligands. With ethylene, substitution is followed by insertion of the olefin into the C-H bond of benzene, giving ethylbenzene. CpRe(PPh₃)H₄ undergoes thermal loss of PPh₃, which leads to substituted products of the type CpRe(L) H₄. Photochemically, reductive elimination of dihydrogen occurs preferentially. The complex trans-CpRe(DMPE)H₂ was structurally characterized, crystallizing in the monoclinic space group P2₁/n (No. 14) with a = 6.249(6), b = 16.671(8), c = 13.867(7) Å, β = 92.11(6)°, V = 1443.7(2.9) Å and Z = 4. The complex trans-CpRe(PMe₂Ph)₂H₂ was structurally characterized, crystallizing in the monoclinic space group P2₁/n (No. 14) with a = 7.467(3), b = 23.874(14), c = 11.798(6) Å, β = 100.16(4)°, V = 2070.2(3.4) ų and Z = 4.     

Monovalent copper as a potential catalyst for formation of acetaldehyde via the migration of methyl radicals to the coordinated carbonyl in the complex (CO)Cu-CH3

Cu_aq⁺ forms stable complexes with carbon monoxide in aqueous solutions. Furthermore it reacts very fast with aliphatic radicals. The reaction of Cu(CO)_maq⁺ with methyl radicals, ^•CH₃ was studied using the pulse-radiolysis technique. The results point out that methyl radicals react with Cu(CO)_aq⁺ to form an unstable intermediate with a Cu^II-C σ bond identified as (CO)Cu^II-CH₃⁺, k = (1.1±0.2) × 10⁹ M⁻¹ s⁻¹. This intermediate has a strong LMCT charge transfer band (λ_max = 385 nm, _max = 2500 M⁻¹ cm⁻¹) which is similar to the absorption bands of other transient complexes with Cu^II-alkyl σ bonds. The coordinated carbon monoxide in (CO)Cu^II-CH₃⁺ inserts into the copper—carbon bond (or rather the coordinated methyl migrates to the coordinated carbon monoxide ligand) at a rate of (3.0±0.8) × 10² s⁻¹ to form the copperacetyl complex (CO)_mCu^II-C(CH₃)=O⁺ (λ_max = 480 nm, _max = 2100 M⁻¹ cm⁻¹). The rate of formation of (CO)Cu^II-CH₃⁺ and of the insertion reaction are pH independent. The complex (CO)_mCu^II-C(CH₃)=O⁺ is also unstable and decomposes heterolytically to yield acetaldehyde and Cu_aq²⁺ as the final stable products. This reaction is slightly pH dependent. The same reactivity pattern has been observed for the Cu(CO_naq⁺ complexes (n = 2 or 3). The results clearly point out that CO remains coordinated to transient complexes of the type Cu^II-alkyl.     

Heterobimetallic chloro bridgedcomplexes of (η:η−C10H16)-ruthenium(IV) with palladium(II), platinum(II), rhodium(III), iridium(III), copper(I) and rhodium(I)

Metathesis of [(η³:η³−C₁₀H₁₆)Ru(Cl) (μ−Cl)]₂ (1) with [R₃P) (Cl)M(μ-Cl)]₂ (M = Pd, Pt), [Me₂NCH₂C₆H₄Pd(μ-Cl)]₂ and [(OC)₂Rh(μ-Cl)]₂ affords the heterobimetallic chloro bridged complexes (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂M(PR₃)(Cl) (M = Pd, Pt), (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂PdC₆H₄CH₂NMe₂ and (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂Rh(CO)₂, respectively. Complex 1 reacts with [Cp^*M(Cl) (μ-Cl)]₂ (M = Rh, Ir), [p-cymene Ru(Cl) (μ-Cl]₂ and [(Cy₃P)Cu(μ-Cl)]₂ to give an equilibrium of the heterobimetallic complexes and of educts. The structures of (η³:η³-C₁₀H₁₆)Ru(μ-Cl)₂Pd(PR₃) (Cl) (R = Et, Bu) and of one diastereoisomer of (η³:η³-C₁₀H₁₆)Ru(μ-Cl)₂IrCp^*(Cl) were determined by X-ray diffraction.     

Ligand induced P---H bond formation and a comparison of the reactivity of two isomers of the carbonyl hydride [Pt2(μ-PBu2)2(H)(CO)(PBu2H)]CF3SO3

The Pt₂ ^(II) isomeric terminal hydrides [(CO)(H)Pt(μ-PBu^t ₂)₂Pt(PBu^t ₂H)]CF₃SO₃ (1a), and [(CO)Pt(μ-PBu^t ₂)₂Pt(PBu^t ₂H)(H)]CF₃SO₃ (1b), react rapidly with 1 atm of carbon monoxide to give the same mixture of two isomers of the Pt₂ ^(I) dicarbonyl [Pt₂(μ-PBu^t ₂)(CO)₂(PBu^t ₂H)₂]CF₃SO₃ (3-Pt); the solid state structure of the isomer bearing the carbonyl ligands pseudo-trans to the bridging phosphide was solved by X-ray diffraction. A remarkable difference was instead found between the reactivity of 1a and 1b towards carbon disulfide or isoprene. In both cases 1b reacts slowly to afford [Pt₂(μ-PBu^t ₂)(μ,η²,η²-CS₂)(PBu^t ₂H)₂]CF₃SO₃ (4-Pt), and [Pt₂(μ-PBu^t ₂)(μ,η²,η²-isoprene) (PBu^t ₂H)₂]CF₃SO₃ (6-Pt), respectively. In the same experimental conditions, 1a is totally inert. A common mechanism, proceeding through the preassociation of the incoming ligand followed by the P---H bond formation between one of the bridging P atoms and the hydride ligand, has been suggested for these reactions.     

Olefin versus sulfur coordination of benzo[b]thiophene (BT) in Cp(CO)2Re(η:η-μ2-BT)Cr(CO)3

Reactions of Cr(CO)₃(η⁶-BT), in which the Cr is π-coordinated to the benzene ring of benzo[b]thiophene (BT), with Cp′(CO)₂Re(THF), where Cp′ = η⁵-C₅H₅ or η⁵-C₅Me₅, give the products Cp′(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ in which the Cr remains coordinated to the benzene ring and Re is bound to the C(2)=C(3) double bond. An X-ray diffraction study of Cp(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ (3) provides details of the geometry. This structure contrasts with that of the Cp′(CO)₂Re(BT) complexes that exist as mixtures of isomers in which the BT is coordinated to the Re through either the double bond (2,3-η²) or the sulfur (η¹(S)). Thus, the electron-withdrawing Cr(CO)₃ group in 3 stabilizes the 2,3-η² mode of BT coordination to the Cp′(CO)₂Re fragment. Implications of these results for catalytic hydrodesulfurization of BT are discussed. Crystal data for 3: triclinic, space group

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