Electrochemical reduction of arenechromium tricarbonyl complexes

Conclusions A study was made of the electrochemical reduction of some -ArCr(CO)₃ complexes at a mercury dropping electrode in dimethylformamide on a support of 0.1 NEt₄NClO₄ solution.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 471–473, February, 1975.     

Recovery of chromium hexacarbonyl after nucleophilic reactions of arenechromium tricarbonyl complexes

The arenechromium tricarbonyl complexes C₆H₄R₂Cr(CO)₃, (R = H, CHMe₂), obtained from arenes C₆H₄R₂ and Cr(CO)₆, react with nucleophiles (Nu = CH(CH₃)CN, CH(CH₃)CO₂-t-Bu), to form adducts which give, after treatment with CF₃CO₂H under carbon monoxide, the substituted cyclohexadienes C₆H₅R₂Nu (R = H, CHMe₂) and Cr(CO)₆ in good yield.     

Organometallic polymers. VI. Anchoring of arenechromium carbonyl complexes to macroreticular polymers

The phenanthrenechromium dicarbonyl moiety was anchored by a photosubstitution reaction onto commercial resins substituted by diphenylphosphine groups. From scanning electron microscope photographs it was found that, whereas the chloromethylation reaction proceeded homogeneously throughout the polymer beads, the phosphination and photochemical reactions behaved differently, depending on the macrostructure and the morphology of the polymer beads. Large pore size dimensions (1300 Å) allowed the reagents (phosphine and chromium complex) to react throughout the polymer beads, whereas small pore sizes (< 50 Å) permitted penetration of the reagent only to a limited extent.     

High pressure effects on ligand substitution reactions of molybdenum(0) carbonyl complexes

Summary Substitution reactions ofcis-Mo(CO)₄(py)₂, Mo(CO)₅-(4-Mepy) and Mo(CO)₅(py) with biacetylbis(phenylimine), bipyridine and 1,10-phenanthroline in toluene and 1,2-dichloroethane were studied as a function of temperature and pressure. The volumes of activation are +4 cm³ mol^–1 and almost zero for the tetra- and penta-carbonyl systems, respectively, and independent of entering ligand and solvent. Furthermore, these values closely parallel the trend in S^#. The results are discussed in terms of earlier suggested mechanisms and relevant data recently reported in the literature.     

Influence of arenechromium tricarbonyl on the redox behavior of copper in new heteropentanuclear complexes prepared from functionalized phenanthroline tweezer ligands

Novel mixed [Cu(4a–c)₂]CF₃SO₃ pentanuclear copper(I)/chromium(0) complexes containing tweezer ligands that contain, within the same molecule, a 2,9-disubstituted-1,10-phenanthroline and two arene-chromium subunits. The mononuclear copper(I) complexes [Cu(5a–c)₂] CF₃SO₃ have been prepared from the chromium free ligand species 5a–c, obtained by quantitative photochemical decomplexation of the parent species 4a–c. Cyclic voltammetry showed that in these complexes copper(I) can be reversibly oxidized to copper(II) in CH₂Cl₂. The Cu^II/I couples are more positive in the presence of the four surrounding redox-active arenechromium subunits, revealing an electron-withdrawing effect. Complexes [Cu(4c)₂]⁺, [Cu(5c)₂]⁺ form new species (1 : 1 ligand copper stoichiometry) upon addition of excess [Cu(CH₃CN)₄]⁺, which were identified electrochemically and by FAB⁺ mass spectroscopy.     

Facile cleavage of a phenyl group from SbPh3 by dirhenium carbonyl complexes

The complex Re₂(CO)₈[μ-η²-C(H)C(H)Buⁿ](μ-H) (1) reacts with SbPh₃ at 68 °C to yield the new σ-phenyl dirhenium complex Re₂(CO)₈(SbPh₃)(Ph)(μ-SbPh₂) (4) in 72% yield. Compound 4 contains two rhenium atoms held together by a bridging SbPh₂ ligand. One rhenium atom contains a σ-phenyl group. The other rhenium atom contains a SbPh₃ ligand. Compound 4 was also obtained in 34% yield from the reaction of Re₂(CO)₁₀ with SbPh₃ in the presence of UV–Vis irradiation together with some monorhenium products: HRe(CO)₄SbPh₃ (5), Re(Ph)(CO)₄SbPh₃ (6) and fac-Re(Ph)(CO)₃(SbPh₃)₂ (7) in low yields. Complex 4 is split by reaction with an additional quantity of SbPh₃ to yield the monorhenium SbPh₃ complexes 6, 7 and mer-Re(Ph)(CO)₃(SbPh₃)₂ (8) that contain a σ-phenyl ligand. When 4 was treated with hydrogen, the phenyl ligand was eliminated as benzene and the dirhenium complexes Re₂(CO)₈(μ-SbPh₂)(μ-H) (10), and Re₂(CO)₇(SbPh₃)(μ-SbPh₂)(μ-H) (11), were formed that contain a bridging hydrido ligand. The doubly SbPh₂-bridged dirhenium complex Re₂(CO)₇(SbPh₃)(μ-SbPh₂)₂ (9) that has no metal–metal bond was also formed in these two reactions.     

Photoswitching tetranuclear rhenium(I) tricarbonyl diimine complexes with a stilbene-like bridging ligand

Highly efficient photoswitching tetranuclear rhenium(I) tricarbonyl diimine complexes with a stilbene-like bridging ligand are reported. The ability to directly populate excited states localized on the bridging ligand is the key for the observed efficient photoisomerization.     

Photo-induced ligand substitution at a remote site via electron transfer in a porphyrin-appended rhenium carbonyl supermolecule

The photochemical and electrochemical properties of a Zn-porphyrin appended rhenium(I) tricarbonyl bipyridine 3-Me-pyridine complex have been investigated; visible-light sensitisation of electron transfer results in ligand substitution at a site remote from the chromophore.     

Protonation of homotroponeiron tricarbonyl and cyclooctatrienoneiron tricarbonyl complexes

2,3-Homotroponeiron tricarbonyl, 8-methyl- and 8,8-dimethyl-2,3-homotroponeiron tricarbonyl complexes have been shown to undergo O-protonation in trifluoroacetic (TFA) and 96% sulfuric acids. In the latter acid the O-protonated cations rearrange to give the thermodynamically more stable C-protonated isomers. Cyclooctatrienoneiron tricarbonyl undergoes protonation H₂SO₄ to give the same cation as was obtained from the protonation of the homotroponeiron tricarbonyl complex in H₂SO₄. On the basis of reaction in D₂SO₄, it is suggested that the kinetically preferred site of protonation of the cyclooctatrienone complex is at C(2) one of the coordinated carbon atoms.     

An ESR study of ligand exchange in organometallic radical complexes. Substitution of group VA organometals in the quinone—rhenium carbonyl paramagnetic complexes

Stable heterobinuclear and trinuclear metal organic radical complexes containing rhenium carbonyl and group VA organometals are prepared by ligand exchange reactions. ESR observations provide further insights into the dynamics and the possible exchange sites.     

Syntheses of group 7 metal carbonyl complexes with a stable N-heterocyclic chlorosilylene

Two structurally characterized manganese [L(2)Mn(CO)(4)](+)[Mn(CO)(5)](-) (1) and rhenium [L(3)Re(CO)(3)](+)[ReCO)(5)](-) (2) silylene complexes were prepared in one pot syntheses by reacting 1 equivalent of Mn(2)(CO)(10) with 2 equivalents of stable N-heterocyclic chlorosilylene L {L = PhC(NtBu)(2)SiCl} and 1 equivalent of Re(2)(CO)(10) with 3 equivalents of L in toluene at room temperature. Both complexes 1 and 2 were characterized by single-crystal X-ray structural analysis, NMR and IR spectroscopy, EI-MS spectrometry, and elemental analysis.     

Synthesis and structural studies of phosphorus carbonyl manganacycles containing the tetraphenyldiselenoimidodiphosphinato ligand

The [Mn(CO)_4−x(L){Ph₂P(Se)NP(Se)Ph₂-κ²Se}] complexes, where x = 1 for L = PPh₃ and PMePh₂, and x = 2 for L = Ph₂PCH₂CH₂PPh₂ (diphos), were synthesized by two routes. The complexes were characterized by IR, mass spectrometry (FAB+), NMR (¹H, ¹³C, ³¹P, ⁷⁷Se) spectroscopy and/or single crystal X-ray diffraction. The X-ray diffraction analysis for [Mn(CO)₃PMePh₂{Ph₂P(Se)NP(Se)Ph₂-κ²Se}] showed that the unit cell contains two independent mononuclear molecules with different MnSePNPSe rings’ conformations.     

Indenyl effect in dissociative reactions. Nucleophilic substitution in iron carbonyl complexes: a case study

The mechanism of carbonyl substitution in [Fe(Ind)(CO)(2)I] (Ind = C(9)H(7)(-), indenyl) by P(OMe)(3) was investigated by means of DFT calculations. The most favourable path involves a spin crossover of the complex from the ground state singlet to the triplet potential energy surface (S = 1), followed by dissociative loss of CO, and phosphite addition to the coordinatively unsaturated intermediate, [Fe(Ind)(CO)I], with S = 1. In the final step, the system returns to the spin singlet surface, affording the product. This dissociative mechanism is in agreement with the experimental findings. Several pathways occurring exclusively along the singlet surface (S = 0) were explored, namely the expected associative mechanism, which is the most favourable among them, and the "pseudo" associative including the participation of solvent (n-octane). In all cases the corresponding energy barriers were significantly higher than the ones involved in the "spin forbidden" mechanism. The rate enhancement observed comparing the Ind complex with the cyclopentadienyl (Cp = C(5)H(5)(-)) analogue reflects the stability difference between the corresponding S = 0 and S = 1 species in the initial step. The larger number of π orbitals and the lower symmetry of the indenyl ligand, compared with Cp, results in a smaller HOMO-LUMO gap, in a more accessible triplet species, and in a smaller barrier for the spin crossover.