Ligand Site Preference in Iron Tetracarbonyl Complexes Fe(CO)4L (L = CO,CS, N2, NO+, CN–, NC–, η2‐C2H4, η2‐C2H2, CCH2, CH2, CF2, NH3, NF3, PH3, PF3, η2‐H2)

Equilibrium geometries, bond dissociation energies and relative energies of axial and equatorial iron tetracarbonyl complexes of the general type Fe(CO)₄L (L = CO, CS, N2, NO⁺, CN^–, NC^–, η²‐C₂H₄, η²‐C₂H₂, CCH₂, CH₂, CF₂, NH₃, NF₃, PH₃, PF₃, η²‐H₂) are calculated in order to investigate whether or not the ligand site preference of these ligands correlates with the ratio of their σ‐donor/π‐acceptor capabilities. Using density functional theory and effective‐core potentials with a valence basis set of DZP quality for iron and a 6‐31G(d) all‐electron basis set for the other elements gives theoretically predicted structural parameters that are in very good agreement with previous results and available experimental data. Improved estimates for the (CO)₄Fe–L bond dissociation energies (D₀) are obtained using the CCSD(T)/II//B3LYP/II combination of theoretical methods. The strongest Fe–L bonds are found for complexes involving NO⁺, CN^–, CH₂ and CCH₂ with bond dissociation energies of 105.1, 96.5, 87.4 and 83.8 kcal mol^–1, respectively. These values decrease to 78.6, 64.3 and 64.2 kcal mol^–1, respectively, for NC^–, CF₂ and CS. The Fe(CO)₄L complexes with L = CO, η²‐C₂H₄, η²‐C₂H₂, NH₃, PH₃ and PF₃ have even smaller bond dissociation energies ranging from 45.2 to 37.3 kcal mol^–1. Finally, the smallest bond dissociation energies of 23.5, 22.9 and 18.5 kcal mol^–1, respectively are found for the ligands NF₃, N₂ and η²‐H₂. A detailed examination of the (CO)₄Fe–L bond in terms of a semi‐quantitative Dewar‐Chatt‐Duncanson (DCD) model is presented on the basis of the CDA and NBO approach. The comparison of the relative energies between axial and equatorial isomers of the various Fe(CO)₄L complexes with the σ‐donor/π‐acceptor ratio of their respective ligands L thus does not generally support the classical picture of π‐accepting ligands preferring equatorial coordination sites and σ‐donors tending to coordinate in axial positions. In particular, this is shown by iron tetracarbonyl complexes with L = η²‐C₂H₂, η²‐C₂H₄, η²‐H₂. Although these ligands are predicted by the CDA to be stronger σ‐donors than π‐acceptors, the equatorial isomers of these complexes are more stable than their axial pendants.     

Formal aza-Michael additions to tropone: Addition of diverse aryl- and alkylamines to tricarbonyl(tropone)iron and [(C7H7O)Fe(CO)3]BF4

A formal aza-Michael addition to tropone by way of tricarbonyl(tropone)iron and/or the tetrafluoroborate salt formed via protonation of the complex is reported. Tricarbonyl(tropone)iron smoothly undergoes the direct aza-Michael reaction with unhindered aliphatic amines under solvent free conditions in good yields. Meanwhile, the known cationic complex [(C₇H₇O)Fe(CO)₃]BF₄ (whose reaction with a small number of nucleophiles was previously reported) undergoes addition with an even broader array of amine nucleophiles. Finally, it was discovered that protecting the aza-Michael adduct as a carbamate was necessary for oxidative demetallation of the complex.     

Synthese et reactivite d'un complexe diene-fertricarbonyle derive du phenyl-1-dimethyl-3,4-phosphole

The complex (DMPP)Fe₂(CO)₇ in which DMPP (1-phenyl-3,4-dimethylphosphole) is η⁴-coordinated with Fe(CO)₃ through its diene and η¹-coordinated with Fe(CO)₄ through its phosphorus atom is selectively decomplexed at phosphorus to give (DMPP)Fe(CO)₃ by reaction with AlCl₃ followed by NH₄OH. This new η⁴-complex (DMPP)Fe(CO)₃ can be oxidized, sulfurized and quaternized at phosphorus by H₂O₂, S₈, and PhCH₂Br and MeI, respectively, as an ordinary phosphine without decomplexation of the diene. As a free phosphole, this complex also gives a ring-expanded product by reaction with benzoyl chloride, water and Et₃N. In the presence of some metallic salts such as (PhCN)₂PdCl₂, it loses CO to give the bimetallic sandwich [(DMPP)Fe(CO)₂]₂. It can also give some new bimetallic complexes such as [(DMPP)Fe(CO)₃]W(CO)₅ by complexation of the phosphorus lone pair by W(CO)₅(THF).     

Coordination of α,β-unsaturated aldehydes on d Ru and Rh complexes: A DFT study

The coordination modes of various α,β-unsaturated aldehydes on d⁶ ML₄ and ML₅ complexes of rhodium and ruthenium have been compared by means of density functional theory (DFT) calculations. The studied aldehydes were acrolein, crotonaldehyde, prenal and cinnamaldehyde and the metallic fragments RuH₂(PH₃)₂, RuH₂(PH₃)₃ and RhH₂Cl(PH₃)₂. On the d⁶ ML₄ Ru fragment, the best coordination geometry is η⁴, where both double bonds are involved. On the d⁶ ML₅ Ru fragment, the η²CC geometry is preferred to the η¹O and to the η²CO ones. Finally on the d⁶ ML₅ Rh fragment, the η²CO mode is not stable and only η¹O and η²CC exist, the former being favored. In conclusion, the η²CO coordination geometry is never favored even if the energy gap between η²CC and η²CO is reduced by the use of bulky ligands (PPh₃) or alkyl substituents on the CC bond. The Ru and Rh complexes behave differently: in the case of Ru, η²CC and η²CO can be in competition and in the case of Rh, the best form is η¹O. This different behavior can explain the results obtained in the hydrogenation reaction of α,β-unsaturated aldehydes.     

The reactivity of cycloheptadienyl-1-one iron tricarbonyl cation towards nucleophilic attack

Protonated tropone iron tricarbonyl reacts with neutral and anioic nucleophiles to give neutral complexes, some of which contain η-1,3-diene coordinated to the Fe(CO) moiety.     

Binuclear metal carbonyl dab complexes : VII. A 13C NMR investigation of MM′(CO)6(DAB) complexes (M = M ′ = Fe,Ru; M = Mn,Re and M′ = Co; DAB = 1,4-diazabutadiene). Dynamic behaviour of σ2-N, σ2-N′, η2-C=N coordinated dab in MnCo(CO)6(DAB) and local scrambling of the carbonyl groups

The ¹³C NMR spectra of MM′(CO)₆(DAB) complexes (M = M′ = Fe, Ru; M = Mn, Re and M′ = Co; DAB = 1,4-diazabutadiene) show very characteristic features which are directly related with the bonding mode of the DAB ligand to the binuclear metal carbonyl fragment. In these complexes the DAB ligand is σ²-N, μ²-N′, η²-C=N or σ²-N, σ²-N′, η²-C=N coordinated. Chemical shifts of about 175 ppm are observed for the σ-coordinated imine fragments and about 60 or 80 ppm for the η²-C=N coordinated imine fragments.In MnCo(CO)₆[diacetylbis(cyclopropylimine)] the DAB ligand is fluxional, and the changes in the spectra when recorded at various temperatures can be interpreted in terms of an exchange between the σ- and π-coordinated part of the DAB ligand.The homodinuclear M₂(CO)₆(DAB) complexes (M = Fe or Ru) contain M(CO)₃ fragments on which the carbonyl groups are involved in a local scrambling process with very different activation parameters (T_c = ?50°C and +85°C).MCo(CO)₆(DAB) complexes (M = Mn, Re), which contain a semi-bridging carbonyl group according to the crystal structure, show rapid interchange of this carbonyl group with the terminal carbonyl groups on cobalt. The electronic balance is kept in equilibrium by an internal compensation within the DAB ligand.     

RATES OF RING-OPENING OF 2,2,4,7,7-PENTAMETHYL-3,6-DITHIAOCTANE TETRACARBONYL TUNGSTEN (0)

Abstract

Ring displacement from η²-PDOW(CO)₄ (PDO = 2,2,4,7,7-pentamethyl-3.6-dithiaoctane) by L (L = P(0-i-Pr)₃ and P(OEt)₃) produces a mixture of cis- and trans- (L)₂W(CO)₄. Results from kinetics experiments are consistent with the results observed for the structurally-related η²-DTOW(CO)₄ complex (DTO = 2,2,7,7-tetramethyl-3,6-dithiaoc-tane). A smaller value for the rate constant (k₁) for the ring-opening step of η²-PDOW(CO)₄ reflects the shorter W-S bond distances observed in η²-PDOW(CO)₄. This observation is consistent with the trend observed for a series of η²-DTAW(CO)₄ complexes (DTA = Dithiaalkanes) in which the value of k₁ increases with the size of the chelate ring. Since the species η²-PDOW(CO)₄ and η²-DTOW(CO)₄ are five-membered chelate complexes, differences in their molecular and kinetic parameters are being ascribed to the methyl group in the chelate backbone of η²-PDOW(CO)₄. Our observations confirm earlier findings that small differences in the structure of DTA greatly affect the rates of ring-opening in η²-DTAW(CO)₄ complexes.     

Reactions of coordinated molecules: XLIX. Carboncarbond bond formation between the donor atoms of adjacent acyl and alkenyl ligands

When the ferraenolate anion, (η-C₅H₅)(CO)₂FeC(O)CH₂⁻, is treated sequentially with methyllithium/TMEDA and benzoyl chloride, the known η³-allyl complex, (η-C₅H₅)(OC)Fe{η³-CH₂C[OC(O)Ph]C[OC(O)Ph](CH₃}, is isolated in 36% yield. When the neutral alkenyl complexes, (η-C₅H₅)(CO)₂Fe[C(Me)CH₂] and (η-C₅H₅)(OC)₂Fe{C(OMe)CH₂], were treated sequentially with methyllithium and benzoyl chloride, the η³-allyl complexes, (η-C₅H₅)(OC)Fe{η³-CH₂C(Me)C[OC(O)Ph](Me) and (η-C₅H₅)(OC)Fe{η³-CH₂C(OMe)C[OC(O)Ph](Me) are isolated in 8 and 11% yield, respectively. These η³-allyl ligands are presumably formed via CC coupling of the donor atoms of the formal acyl and alkenyl ligands in the intermediate complexes.     

Koordinationsambivalenz und elektronenstruktur ein- und zweikerniger methylcyclopentadienyldicarbonylmangan-komplexe der cyanpyridine und terephthalsäuredinitrile

The ambident cyanopyridine ligands form N(pyridine) and N′(nitrile) coordinated mono- and binuclear complexes with the (C₅H₄CH₃)(CO)₂Mn fragment. All three possible forms for 4-cyanopyridine could be isolated, whereas mononuclear compounds were obtained as most stable species in N¹-coordinated form with 3-cyanopyridine and in CN²-coordinated form with the 2-isomer. IR, NMR, and UV/VIS spectroscopy as well as electrochemistry and ESR spectroscopy of the anion radicals demonstrate superior π back-bonding via the pyridine nitrogen centers, the isolation of nitrile coordinated complexes is attributed to the kinetic stability of the CNMn bond. While terephthalonitrile was found to form exclusively mononuclear neutral complexes, its anion radical prefers to coordinate to a second metal fragment, illustrating the excellent coordination properties of reduced nitriles. A neutral binuclear complex could be isolated with the stronger π-acceptor, tetrafluoroterephthalonitrile.     

SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF CYCLOPENTADIENYLIRON(II) COMPLEXES WITH BIS(DIPHENYLPHOSPHINO)AMINE AS LIGAND

Abstract

The synthesis and properties of new cationic iron(II) complexes of general formula [(η⁵-C₅H₅)FeL(η²-dppa)]A [A=I^?, L = CO(1); A = BF₄, L = CO(2) CH₃CN(4), η¹-dppa(5); dppa = NH(PPh₂)₂] are described. The carbonyl complex [(η⁵-C₅H₅)Fe(CO)(η²-dppa)]BF₄ is deprotonated to give the neutral complex [(η⁵-C₅H₅)Fe(CO){η²-(PPh₂)₂N}](3). All complexes have been characterized by elemental analysis and IR and NMR spectroscopies. Cyclic voltammetry of complexes 1–5 shows a diverse redox chemistry in acetonitrile solution. While the reduction of 1 and 2 leads to the formation of a dinuclear Fe(I) complex, 4 and 5 form mononuclear species of Fe(I); oxidation of metal centers of 1 and 2 is not observed and in complexes 3 and 4 the metal centers are oxidized at potentials < 1. Complex 5 in acetonitrile solution is transformed into complex 4.     

New indenyl phosphinooxazoline complexes of iron and their catalytic activity in the Mukaiyama aldol reaction

New phosphinooxazoline (PHOX) η⁵-indenyl complexes of iron were synthesized and applied as catalysts in the Mukaiyama aldol reaction. Reaction of three different PHOX ligands with [Fe(η⁵-Ind)I(CO)₂] afforded the iodide salts of three complexes of the general formula [Fe(η⁵-Ind)(CO)(PHOX)]⁺ in 73-81% isolated yields. The molecular structure of one of the new complexes was determined, revealing a pseudo octahedral coordination geometry about the iron center. The iron complexes are catalytically active in the Mukaiyama aldol reaction between aldehydes and 1-(tert-butyldimethylsilyloxy)-1-methoxyethene to give the corresponding aldol adducts (3 mol % catalyst, 15 min, room temperature, 48-83% isolated yields). A previously synthesized iron complex of the general formula [Fe(η⁵-Cp)(CO)(PHOX)]⁺ was found to be catalytically active in the title reaction as well, but needed three hours at room temperature to convert the starting materials to the products.     

Synthesis and molecular structure of (η-pentamethyl-cyclopentadienyl) (η-cyclopentadienyl) hexacarbonyl molybdenum tungsten

The metathesis reaction of Cp*(CO)₃MoBr and NaW(CO)₃Cp produced Cp*(CO)₃Mo-W(CO)₃Cp (1), featuring an unsupported Mo-W bond. Exposure of solutions of 1 to light leads to the quantitative formation of the corresponding homometallic dimers. In the solid state, the title complex exhibits an anti-arrangement of the η⁵-cyclopentadienyl and the η⁵-pentamethyl-cyclopentadienyl ligands and six terminal carbonyls. Comparison to corresponding complexes of molybdenum and tungsten reveals that the Mo-W distance is dictated by the presence of a Cp and a Cp* ligand. This is the first time that an unsupported Mo-W single bond distance is reported.     

η2-dithiomethyliron(II) ionic complexes. Evidence for a strong dependence on the nature of the trans-phosphorus ligands bonded to iron

Cationic η²-dithiomethyliron(II) complexes have been made by alkylation of the uncoordinated sulfur atom of Fe(CO)₂[η²-CS₂](L)₂. Surprisingly, only when the phosphorus ligands L are strong donors (PMe₃, PMe₂Ph) does coordination of iodide take place to give the neutral Fe(η²-CS₂CH₃)(I)(CO)(L)₂ derivatives. The ¹³C NMR spectra of the latter at 215 K indicated the presence of both isomers when L was PMe₂Ph. Reaction with iodine under carbon monoxide regenerated the cationic precursor.     

Übergangsmetall-Silyl-Komplexe, 44. Darstellung der zweikernigen Silyl-Komplexe (CO)3(R3Si)Fe(μ-PR′R′′)Pt(PPh3)2 durch oxidative Addition von (CO)3(R′R′′HP)Fe(H)SiR3 an (C2H4)Pt(PPh3)2

Transition Metal Silyl Complexes, 44. — Preparation of the Binuclear Silyl Complexes (CO)₃(R₃Si)Fe(μ-PR′R′′)Pt(PPh₃)₂ by Oxidative Addition of (CO)₃(R′R′′HP)Fe(H)SiR₃ to (C₂H₄)Pt(PPh₃)₂ The complexes (CO)₃(R′R′′HP)Fe(H)SiR₃ ( 1 ) [PHR′R′′ = PHPh₂, PH₂Ph, PH₂Cy; SiR₃ = SiPh₃, SiPh₂Me, SiPhMe₂, Si(OMe)₃] react with Pt(C₂H₄)(PPh₃)₂ to give the dinuclear, silyl-substituted complexes (CO)₃(R₃Si)Fe(μ-PR′R′′)Pt(PPh₃)₂ ( 2 ) in high yields. Upon reaction of 2 (R = R′ R′′ = Ph) with CO, the PPh₃ ligand at Pt being trans to the PPh₂ bridge is exchanged, and (CO)₃(Ph₃Si)Fe(μ-PPh₂)Pt(PPh₃)CO ( 3 ) is formed. Complex 3 is characterized by an X-ray structure analysis. The rather short Fe — Si distance [233.9(2) pm] and the infrared spectrum of 3 indicate that the Fe — Pt bond is quite polar.     

Modeling of the molecular and electronic structures of some mono- and biosmium complexes of fullerene C60

The modeling of the molecular and electronic structures of the following mono- and biosmium complexes of fullerene C₆₀ was performed by quantum chemical methods (MNDO/PM3 and DFT/PBE): (??²-C₆₀)[Os(PPh₃)₂(CO)CNMe], (??²,??²-C₆₀)[Os(PPh₃)₂(CO)(CNMe)]₂, (??²-C₆₀)[Os(PH₃)₂(CO)H], (??²,??²-C₆₀)[Os(PH₃)₂(CO)H]₂, (??²-C₆₀)[Os(PH₃)₂(CO)CNMe], (??²,??²-C₆₀)[Os(PH₃)₂(CO)CNMe]₂, and (5-C₆₀H₅)[Os(C₅H₅)], (5, 5-C₆₀H₁₀)[Os(C₅H₅)]₂.The osmium atoms in the first six complexes are ??²-coordinated by fullerene C₆₀. In the last two complexes, the ??⁵-coordination mode is observed. The structures of the radical anions of these complexes were calculated. The energies of the frontier orbitals were evaluated. The acceptor properties of the complexes are discussed. The electron affinities were estimated in two ways: from the energy of the lowest unoccupied molecular orbital (LUMO) and as the energy difference between the neutral molecule and its radical anion.     

1,3-Bis(alkylimino)isoindolinates of rare earth metals: Synthesis,molecular structure and photoluminescence

The rare earth metal isoindolinates Ln(ⁱPrL)₃ (Ln = Sc (1), Y (2), Eu (3), Dy (4), Yb (5); ⁱPrL = 1,3-bis(isopropylimino)isoindolinate anion) and [(MeL)Ce]₂(μ-MeL)₄ (6) (MeL = 1,3-bis(methylimino)isoindolinate anion) were synthesized by reactions of the amides Ln[N(SiMe₃)₂]₃ with 1,3-bis(isopropylimino)isoindoline (ⁱPrLH) or 1,3-bis(methylimino)isoindoline (MeLH), respectively. The X-ray diffraction study revealed that in monomeric molecules of the isopropyl-substituted compounds 2 and 4 the cations Ln³⁺ are η²-coordinated by three isoindolinate ligands. The methyl-substituted 6 exists in a crystal as a dimer containing two terminal η²-coordinated ligands and four bridging isoindolinate ligands two of which are bonded to Ce atoms in η³ fashion (η:η:η-N,N,N) but two others in η⁴ manner (η:η²:η-N,N,N). All the obtained complexes in solutions exhibited ligand-centered photoluminescence, the spectra of which consist of one broadened band with a maximum at 400–450 nm.     

Chemistry of vinylidene complexes. XX. Intramolecular carbonylation of vinylidene on the MnFe center: Spectroscopic and structural study. X-ray structure of the new trimethylenemethane type MnFe complex

Reactions of Fe₂(CO)₉ with Cp(CO)₂MnCCHPh (1) and Cp(CO)(PPh₃)MnCCHPh (3) gave the heterometallic trimethylenemethane complexes η⁴-{C[Mn(CO)₂Cp](CO)CHPh}Fe(CO)₃ (2) and η⁴-{C[Mn(CO)(PPh₃)Cp](CO)CHPh}Fe(CO)₃ (4), respectively. The formation of the benzylideneketene [PhHCCCO] fragment included in complexes 2 and 4 occurs via intramolecular coupling of the carbonyl and vinylidene ligands. The structures of 3 and 4 were determined by single crystal XRD methods. The influence of the nature of the L ligands at the Mn atom on the structural and spectroscopic characteristics of η⁴-{C[Mn(CO)(L)Cp](CO)CHPh}Fe(CO)₃ (L = CO (2), PPh₃ (4)) is considered. According to the VT ¹H and ¹³C NMR spectra, complex 2 reversibly transforms in solution into μ-η¹:η¹-vinylidene isomer Cp(CO)₂MnFe(μ-CCHPh)(CO)₄ (2a), whereas complex 4 containing the PPh₃ ligand is not able to a similar transformation.     

Bond‐Strengthening Backdonation in Aminoborylene‐Stabilized Aminoborylenes: At the Intersection of Borylenes and Diborenes

Singly NHC‐coordinated (aminoboryl)aminoborenium salts react with Na₂[Fe(CO)₄] to yield stable coordination complexes of aminoborylene‐stabilized aminoborylenes, which exhibit exceptional σ‐donor properties. Upon photolytic CO extrusion from the metal center, the diboron ligand adopts a novel η³‐BBN coordination mode, where bond‐strengthening backdonation from the metal center into the vacant B?B π‐orbital is observed. This bonding situation can be alternatively described as a Fe‐diaminodiborene complex. In a related reduction of CAAC‐stabilized (aminoboryl)aminoborenium with KC₈, the reduced species can be captured with nucleophiles to form three‐coordinate (diaminoboryl)borylenes, where both amino groups have migrated to the distal boron atom. Collectively, these reactions illustrate the isomeric flexibility imparted by amino groups on this reduced diboron system, thus opening multiple avenues of novel reactivity.     

Density functional theory study on structural isomers and bonding of model complexes M(CO)5(BH3 · PH3) (M = Cr, Mo, W) and W(CO)5(BH3 · AH3) (A = N, P, As, Sb)

The influence of group 15 various substituents and effect of metal centers on metal-borane interactions and structural isomers of transition metal-borane complexes W(CO)₅(BH₃ · AH₃) and M(CO)₅(BH₃ · PH₃) (A = N, P, As, and Sb; M = Cr, Mo, and W), were investigated by pure density functional theory at BP86 level. The following results were observed: (a) the ground state is monodentate, η¹, with C₁ point group; (b) in all complexes, the η¹ isomer with C_S symmetry on potential energy surface is the transition state for oscillating borane; (c) the η² isomer is the transition state for the hydrogens interchange mechanism; (d) in W(CO)₅(BH₃ · AH₃), the degree of pyramidalization at boron, interaction energy as well as charge transfer between metal and boron moieties, energy barrier for interchanging hydrogens, and diffuseness of A increase along the series A = Sb < As < P < N; (e) in M(CO)₅(BH₃ · PH₃), interaction energy is ordered as M = W > Cr > Mo, while energy barrier for interchanging hydrogens decreases in the order of M = Cr > W > Mo.     

d6 and d8 Metal Carbonyl Complexes of 7,7-Dimethoxy-5,6-dimethylidenebicyclo[2.2.1]hept-2-ene. Stereoselective Hydroformylation of an [Fe(CO)4(olefin)] Complex

Reaction of 7,7-dimethoxy-5,6-dimethylidenebicyclo[2.2.1]hept-2-ene ( 2 ) with various metal carbonyls and their derivatives gave the η²-M(CO)₄ (M = Fe ( 17 ), Ru ( 18 )), η⁴-M(CO)₃ (M = Fe ( 19x, 19n ), Ru ( 20n )), and η²-M(CO)₅ and η⁶-M(CO)₃ (M = Cr, Mo, W) complexes. The trigonal bipyramidal η²-M(CO)₄ complexes present an exceptional C_3v symmetry at the metal with the C,C-double bond in an axial position. In all the η²-complexes, this double bond is stereospecifically coordinated by its exo-vs. endo-η⁴-Fe(CO)₃ configuration was established by chemical correlation (hydrolysis, hydrogenation) with the corresponding complexes ( 24x, 24n ) of 7,7-dimethoxy-2,3-dimethylidenebicyclo[2.2.1]heptane ( 5 ). The relative rates of hydrolysis (AcOH/H₂O 2:1, 50°C) of ligands 2 and 5 and of complexes 19x, 19n, 24x , and 24n to the corresponding ketones showed an acceleration effect only when the metal is coordinated to the exo-face. This was attributed to an F-strain effect on the leaving group of the substrate. Compound 17 was further metallated by [Fe₂(CO)₉] giving the bimetallic isomers 21xn and 21xx . The endocyclic C,C-double bond of the latter can be stereospecifically hydroformylated (1 atm CO, AcOH/H₂O, 25°C) giving 29x (49%). Hydroformylation of 17 gave the corresponding uncoordinated aldehydes 30x/30n in better yields (76%) but with lower selectivity (3:1). These are the first examples of hydroformylation of an isolated [Fe(CO)₄(olefin)] complex.