Reductions of metal carbonyls by quaternary ammonium borohydrides

Quaternary ammonium borohydrides, used directly or generated in phase transfer reactions, are highly effective reagents for preparing metal carbonyl anions from metal carbonyls [Mo(CO)₆, Mn₂(CO)₁₀, Re₂(CO)₁₀, CO₂(CO)₈, Fe₃(CO)₁₂, Ru₃(CO)₁₂ and (η⁵-C₅H₅)₂Mo₂(CO)₆] and from some metal carbonyl halides [BrMn(CO)₅ and η⁵-C₅H₅Mo(CO)₃Cl]. Where strongly basic anions would be formed from a halide [BrMn(CO)₄PPh₃ and η⁵-C₅H₅Ru(CO)₂Br], the reactions provide efficient syntheses of the corresponding hydrides instead. The anion η⁵-C₅H₅Fe(CO)₂^? is not accessible by these techniques; reaction of η⁵-C₅H₅Fe(CO)₂Br yields the iron dimer (via the highly nucleophilic anion) and the dimer is unreactive toward Q⁺BH₄^?. Reductions of Re₂(CO)₁₀ conducted in CH₂Cl₂ provide Re₂(CO)₉Cl^? in high yield.     

Syntheses of organometallic compounds containing iminoacyl ligands. Reactions of metal carbonyl anions with imidoyl halides

Reactions of metal carbonyl anions with imidoyl halides provide a convenient route for the preparation of organometallic complexes containing both η¹- and η²-iminoacyl ligands. With poorer nucleophiles such as tetracarbonyl cobaltate anion, coupling of imidoyl groupings becomes important. This is illustrated by the molecules Co₂(CO)₅(P(CH₃)₂C₆H₅){(C₆H₅)CN(C₆H₅)}₂ which has been crystallographically analyzed.     

The hapticity of cyclooctatetraene in its first row mononuclear transition metal carbonyl complexes: Several examples of octahapto coordination

The two cyclooctatetraene metal carbonyls that have been synthesized are the tetrahapto derivative (η⁴-C₈H₈)Fe(CO)₃ and the hexahapto derivative (η⁶-C₈H₈)Cr(CO)₃ using the reactions of cyclooctatetraene with Fe(CO)₅ and with fac-(CH₃CN)₃Cr(CO)₃, respectively. Related C₈H₈M(CO)_n (M = Ti, V, Cr, Mn, Fe, Co, Ni; n = 4, 3, 2, 1) species have now been investigated by density functional theory in order to explore the scope of cyclooctatetraene metal carbonyl chemistry. In this connection, the existence of octahapto (η⁸-C₈H₈)M(CO)_n species is predicted as long as the central metal M does not exceed the 18-electron configuration by receiving eight electrons from the η⁸-C₈H₈ ring. Thus the lowest energy structures (η⁸-C₈H₈)Ti(CO)_n (n = 3, 2, 1), (η⁸-C₈H₈)M(CO)_n (M = V, Cr; n = 2, 1), and (η⁸-C₈H₈)Mn(CO) all have octahapto η⁸-C₈H₈ rings. An exception is (η⁶-C₈H₈)Fe(CO), with a hexahapto η⁶-C₈H₈ ring and thus only a 16-electron configuration for the iron atom. Hexahapto (η⁶-C₈H₈)M(CO)_n structures are predicted for the known (η⁶-C₈H₈)Cr(CO)₃ as well as the unknown (η⁶-C₈H₈)Ti(CO)₄, (η⁶-C₈H₈)V(CO)₃, (η⁶-C₈H₈)Mn(CO)₂, and (η⁶-C₈H₈)Fe(CO)₂ with 18, 18, 17, 17, and 18 electron configurations, respectively, for the central metal atoms. There are two types of tetrahapto C₈H₈M(CO)_n complexes. In the 1,2,3,4-tetrahapto (η⁴-C₈H₈)M(CO)_n complexes two adjacent CC double bonds, forming a 1,3-diene unit similar to butadiene, are bonded to the metal atom. In the 1,2,5,6-tetrahapto (η^2,2-C₈H₈)M(CO)₃ derivatives two non-adjacent CC double bonds of the C₈H₈ ring are bonded to the metal atom. The known (η⁴-C₈H₈)Fe(CO)₃ is a 1,2,3,4-tetrahapto complex. The unknown isomeric 1,2,5,6-tetrahapto complex (η^2,2-C₈H₈)Fe(CO)₃ is predicted to lie ∼15 kcal/mol above (η⁴-C₈H₈)Fe(CO)₃. The related 1,2,5,6-tetrahapto complexes (η^2,2-C₈H₈)Cr(CO)₄, (η^2,2-C₈H₈)Mn(CO)₄, [(η^2,2-C₈H₈)Mn(CO)₃]⁻, (η^2,2-C₈H₈)Co(CO)₂, and (η^2,2-C₈H₈)Ni(CO)₂ are all predicted to be low-energy structures.     

Zur kenntnis der cyclopentadienyl-nitrosyl-carbonyl-isonitril-komplexe der VI. Und der cyclopentadienyl-dicarbonyl-isonitril-komplexe der VII. Nebengruppe

The nitrosylcarbonylisonitrile complexes η⁵-C₅H₅M(NO)(CO)CNR (R = Me for Cr, Mo, W; R = Et, SiMe₃, GeMe₃, SnMe₃ for Mo) are formed by treatment of the nitrosylcarbonylcyanometalates Na[η⁵-C₅H₅M(NO)(CO)CN] with [R₃O]BF₄ (R = Me, Et), Me₃SiCl, Me₃GeCl or Me₃SnCl. The isoelectronic dicarbonylisonitrile compounds η⁵-C₅H₅Mn(CO)₂CNR (R = SiMe₃, GeMe₃, SnMe₃, PPh₂, AsMe₂) and η⁵-C₅H₅Re(CO)₂CNAsMe₂ are obtained by analogous reactions of Na[η⁵-C₅H₅M(CO)₂CN] (M = Mn, Re) with Me₃ECl (E = Si, Ge, Sn), Ph₂PCl and Me₂AsBr.With phosgene the anionic complexes Na[η⁵-C₅H₅M(CO)₂CN] (M = Mn, Re) can be transformed into the new carbonyldiisocyanide-bridged dinuclear complexes η⁵-C₅H₅M(CO)₂CN-C(O)-NC(OC)₂M-η⁵-C₅H₅. Finally, the reactions of η⁵-C₅H₅M(NO)(CO)CNMe (M = Cr, Mo, W) with NOPF₆, leading to the cationic dinitrosylisonitrile complexes [η⁵-C₅H₅M(NO)₂CNMe]⁺, are described.     

Double addition du methanol sur des complexes η5-cyclopentadienyl η1-hexadiyne-2,4-yl tricarbonyl molybdene et dicarbonyl fer

The η¹-diacetylenic molybdenum complexes η-C₅H₅(CO)₃MoCH₂CCCCCH₃ (Ia) can add two methanoi molecules successively. The first addition, with CO insertion, gives a usual η³-allyl-alkoxycarbonylated compound, gh⁵-C₅H₅(CO)₂Mo-η₃CH₂C(COOCH₃)CHCCCH₃ (IIa). The second reaction needs propargyl bromide as catalyst. It is a 1,5-methanol addition on the unsaturated η³-allyl ligand to give the new complex η⁵-C₅H₅(CO)₂Mo-η³-CH₃OCH₂C(COOCH₃)CHCCHCH₃ (IIIa). The synthesis of the two unstable cationic intermediates and their reactions with methoxide yielding the same addition products have been achieved and have confirmed the mechanism postulated. With the iron analogue (η⁵-C₅H₅)(CO)₂FeCH₂CCCCCH₃ (Ib), direct addition of methanoi is not possible, but the same reactions are obtained by protonation followed by methoxide addition to give complexes IIb and IIIb. In this case, the more stable cationic intermediates IVb and Vb can be fully characterised.     

Reversal of the bonding mode of μ-C7H7 on an FeRh framework: Synthesis and structure of (μ-C7H7)(μ-CO)Fe(CO)2Rh(dppe)

Phosphine ligands rapidly displace one or two carbonyl groups from (μ-C₇H₇)F$\text{e(CO)}{}_3\text{R}$h(CO)₂ (I). The substitution occurs exclusively at the Rh center and proceeds with reversal of the bonding mode of the μ-C₇H₇ moiety from η⁴-Rh and η³-Fe in I to η³-Rh and η⁴-Fe in μ-C₇H₇)(μ-CO)Fe(CO)₂Rh(dppe).     

On the role of the indenyl effect in controlling intramolecular hydride transfer in iron carbonyl complexes

Density functional theory reveals multiple pathways for intramolecular hydride transfer in the cyclopentadienyl and indenyl species (η⁵-C₅H₅)Fe(CO)₃H and (η⁵-C₉H₇)Fe(CO)₃H. The ability of the indenyl ligand to undergo facile η⁵- to η³-‘ring slippage’ stabilises the isomer where the hydride is bonded directly to the metal, which opens up a low-energy pathway for hydride transfer from CO to metal.     

Use of an optically active germanium species for the resolution of diastereoisomeric transition metal complexes with five different and independent ligands

Reaction of optically active MePh(1-C₁₀H₇)GeLi with (η⁵-C₅H₅)M(CO)₂NO (M = Mo, W) results in replacement of CO and formation of anionic species which can be alkylated with CH₃I to afford mixtures of diastereoisomeric complexes, (η⁵-C₅H₅)M(CO)(NO)(GeR₃)CH₃ (R₃ = MePh(1-C₁₀H₇); M = Mo, W). These complexes are the first in which a transition metal, surrounded by five different ligands shows optical activity. These compounds are not fluxional and show a high optical stability; under forcing conditions decomposition occurs before epimerisation.     

Di- and poly-nuclear transition metal complexes as catalysts for the metal carbonyl substitution reaction. The role of supported metals and metal oxides as catalyst promoters

Various di- and poly-nuclear transition metal complexes have been investigated as catalysts for the metal carbonyl substitution reaction. The complexes [{(η⁵-C₅H₄R)Fe(CO)₂} ₂] (R = H, Me, CO₂Me, OMe, O(CH₂)₄OH) and [{(η⁵-C₅H₅)-Ru(CO)₂} ₂] are active catalysts for a range of substitution reactions including the probe reaction [Fe(CO)₄(CNBu^t)] + Bu^tNC → [Fe(CO)₃(CNBu^t)₂] + CO. [{(η⁵-C₅Me₅)Fe(CO)₂}₂] is catalytically active only on irradiation with visible light. For [{η⁵-C₅H₅)Fe(CO)₂}₂] and a range ofisocyanides RNC ( R = Bu^t, C₆H₅CH₂, 2,6-Me₂C₆H₃), catalyst modification by substitution with isocyanide is a major factor influencing the degree of the catalytic effects observed, e.g. [{(η⁵-C₅H₅)Fe(CO)(CNBu^t)}₂] is approximately 35 times as active as [(η⁵-C₅H₅)₂FE₂(CO)₃(CNBu^t)] for the [Fe(CO)₄(CNBu^t)] → [Fe(CO)₃(CNBu^t)₂] conversion. Mechanistic studies on this system suggest that the catalytic substitution step probably involves a rapid intermolecular attack of isonitrile, possibly on a labile catalyst-substrate radical intermediate such as {[Fe(CO)₄(CNR)][(η⁵-C₅H₅)Fe(CO)₂]}; or on a reactive radical cation such as [Fe(CO)₄(CNR)]⁺ generated via electron transfer between the substrate and the catalyst. Other transition metal complexes which also catalyze the substitution of CO by isocyanide in [Fe(CO)₄(CNR)] (and [M(CO)₆] (M = Cr, Mo, W), [Mn₂(CO)₁₀], [Re₂(CO)₁₀]) include [Ru₃(CO)₁₂], [H₄Ru₄(CO)₁₂], [M₄(CO)₁₂] (M = Co, Ir) and [Co₂(CO)₈]. These reactions conform to the general mechanistic patterns established for [{(η⁵-C₅H₅)Fe(CO)₂}₂], suggesting a similar mechanism. A range of materials, notably PtO₂, PdO and Pd/C, act as promoters for the homogeneous di- and poly-nuclear transition metal catalysts, and can even be used to induce activity in normally inactive dimer and cluster complexes e.g. [Os₃(CO)₁₂]. This promotion is attributed to at least three possible effects: the removal of catalyst inhibitors, a catalyzed substitution of the homogeneous catalyst partner, and a possible homogeneous-heterogeneous interaction which promotes the formation of catalytic intermediates.     

Rules governing asymmetric synthesis with organotransition metal complexes

A set of rules are presented which allow prediction of (1) the conformational properties of organotransition metal complexes of the type (η⁵-C₅H₅)M(Ph₃P)(L)R [M = Fe, Co, Re; L = CO, NO]; and (2) the stereochemical consequences of their reactions.     

Reactions of bis(η4-1,5-cyclooctadiene)nickel(0) with transition metal halides,and the crystal structure of μ-dichloro-bis(tetrahydrofuran)hexacarbonyldimanganese

Bis-(η⁴-1,5-cyclooctadiene)nickel(0) reacted with η⁵-C₅H₅Fe(CO)₂Cl, η³-C₅H₅Fe(CO)₃Cl, Mn(CO)₅Cl and {Mn[P(OMe)₃](CO)₄}₂ to form metal metal bonded coupling products. Partial reduction of Mn(CO)₅Cl gave [MnCl(CO)₃(THF)]₂ shown to have a chlorine-bridged C_2h structure by X-ray diffraction analysis. Ligand transfer also accompanied the reduction of Fe[P(OMe)₃]₂(CO)₂Br₂ and Fe(CO)₄Cl₂ to Fe[P(OMe)₃]₂(CO)₃ and Fe(CO)₅, respectively. Only partial reduction was observed for Ti(acac)₂Cl₂ and (η⁵-C₅H₅)₂TiCl₂ which gave [Ti(acac)₂Cl]₂ and (η⁵-C₅H₅)₂Ti(py)Cl, respectively.     

Theoretical studies on the protonation behavior of tropone and its metal complexes

Density functional theory calculations were carried out to investigate structures and stabilities of tropone and troponeiron complexes, (tropone)Fe(CO)₃, (tropone)Fe(CO)₂(PH₃) and (tropone)Fe(PH₃)₃, and their protonated species. The results show that the oxygen-protonated tropone is more stable than the carbon-protonated tropone. On the contrary, in the troponeiron complexes, the carbon protonated species are more stable than the oxygen protonated species. In the neutral and oxygen-protonated complexes, the tropone and oxygen-protonated tropone ligands are η⁴-coordinated. In the carbon-protonated complexes, the carbon-protonated tropone ligand is η⁵-coordinated. The results also show that the metal shift for complexes containing phosphine ligands is more difficult than that for those containing carbonyl ligands. For the neutral methyl-substituted troponeiron complexes, steric effect was found to play a key role in determining the relative stability of the regioisomers. For their protonated species, the electron-donating properties of the methyl substituent(s) were found to be important in determining the relative stability among the different regioiosmers.     

Effect of methyl substituents on the preferred conformations of Bis(pentadienyl) open metallocenes

Density functional theory (DFT) methods indicated that the preferred geometries, spin states, and energetics of unsubstituted bis(pentadienyl)metal open sandwich complexes (C₅H₇)₂M of the first row transition metals (M = Ti to Ni) are similar to those of the corresponding substituted and more stable (2,4-Me₂C₅H₅)₂M open sandwich complexes with 2,4-dimethylpentadienyl ligands. Structures with two fully bonded pentahapto η⁵-C₅H₇ ligands are energetically preferred for iron and for the transition metals to the left of iron in the Periodic Table. However, for the electron-rich first-row transition metals cobalt and nickel, structures with at least one trihapto η³-C₅H₇ ligand are preferred in order to prevent the electron configuration of the central metal atom from exceeding the favored 18-electrons. For the manganese systems (C₅H₇)₂Mn and (2,4-Me₂C₅H₅)₂Mn the presence of the two methyl substituents is found to have little effect on the complicated potential energy surface with low-energy structures in the doublet, quartet, and sextet spin states.     

Isomere η2-Acyl- und σ-Alkyl(carbonyl)-Komplexe von Molybdän und Wolfram. Eine Studie zum Bildungs-mechanismus,zur Isomerisierungsgeschwindigkeit und zur Steuerung der Gleichgewichtslage

η²-Acyl and σ-Alkyl(carbonyl) Coordination in Molybdenum and Tungsten Complexes: Synthesis and Studies of the Isomerization Equilibria and Kinetics The anionic molybdenum and tungsten complexes [L_RM(CO)₃]^? (L_R^? = [(C₅H₅)Co{P(O)R₂}₃]^?, R = OCH₃, OC₂H₅, O-i-C₃H₇; M = Mo, W) have been alkylated with the iodides R′ I, R′ = CH₃, C₂H₅, i-C₃H₇, and CH₂C₆H₅. The reactivity pattern of the alkylation is in accord with a S_N2 mechanism. Depending on M, R′, reaction temperature, and time the η-alkyl (carbonyl) compounds [L_RM(CO)₃R′] and/or the isomeric η²-acyl compounds [L_RM(CO)₂(η²-COR′)] can be obtained. 8 new σ-alkyl(carbonyl) compounds and 15 new η²-acyl compounds have been isolated and characterized. The ¹H NMR and the IR spectra give conclusive evidence that the σ-alkyl(carbonyl) compounds [L_RM(CO)₃R′] are formed as the primary products of the alkylation and that they isomerize partly or completely to give the η²-acyl compounds [L_RM(CO)₂(η²-COR′)]. The position of the equilibrium σ-alkyl(carbonyl)/η²-acyl is controlled by the steric demands of the groups R′ and the ligands L_R^?. The molybdenum compounds isomerize much more readily than the tungsten compounds. The rate constants of the isomerization processes [L_RMo(CO)₃CH₃] → [L_RMo(CO)₂(η²-COCH₃)], R = OCH₃, OC₂H₅, and O-i-C₃H₇, measured at 305 K in acetone-d₆, are 6–8 x 10^?3 s^?1.     

Adamantylcyclopentadienyldicarbonyliron(II) compounds

Synthesis of 1- and 2-adamantyl derivatives of η⁵-cyclopentadienyldicarbonyliron is reported. The 2-adamantyl is prepared from the metal carbonyl anion but the 1-adamantyl derivative is prepared by decarbonylation of the acyl derivative. 1-adCOFe(CO)₂(η⁵-C₅H₅) is in turn prepared from 1-AdCOCl and NaFe-(CO)₂(η⁵-C₅H₅). Phosphine-substituted acyl derivatives AdCOFe(CO)(PR₃)-(η⁵-C₅H₅) are also reported.     

Carbon-13 NMR spectra of some group VIB and VIIB transition metal chalcocarbonyl complexes

The ¹³C NMR spectra of the five series of chalcocarbonyl complexes, (η⁶-C₆H₆)Cr(CO)₂(CX), (η⁶-C₆H₅CO₂Me)Cr(CO)₂(CX), (η⁵-C₅H₅)Mn(CO)₂(CX), (η⁵-C₅H₄Me)Mn(CO)₂(CX) and (η⁵-C₅H₅)Re(CO)₂(CX) (X = O, S, Se), and some of their derivatives including several ¹³C-enriched species have been investigated at ?30 to ?50°C. The chemical shift variations observed with changes in the CX ligand suggest that the π-acceptor/σ-donor capacity of these ligands increases in the order CO < CS < CSe. Changes in the nuclear charge and in the electronic density at the central metal atom affect δ(¹³CS) and δ(¹³CO) in the same manner. The increased downfield chemical shift for δ(¹³CX) in the chromium and manganese series on changing X from O to S and Se is in the direction expected from considerations of Pople's paramagnetic shielding expression.     

Reactions of coordinated propargyl and allene ligands in cyclopentadienyliron dicarbonyl complexes

Reactions of η⁵-C₅H₅Fe(CO)₂CH₂CCR (R  CH₃, C₆H₅, and CH₂Fe(CO)₂(η⁵-C₅H₅)) with HBF₄ in acetic anhydride yield [η⁵-C₅H₅Fe(CO)₂(η²CH₂CCHR)]⁺BF^?₄. The resultant cationic iron-η²-allene complexes react with a wide range of nucleophiles (Nu) to give the following types of behavior: (a) addition of Nu to carbon-1 of the η²-allene fragment (with NaBH₄, (C₂H₅)₂NH, and P(C₆H₅)₃, inter alia), (b) addition of Nu to carbon-2 of the η²-allene fragment (with NaOCH₃), (c) addition of Nu to the carbonyl carbon (with NaOC₂H₅), (d) deprotonation of the iron-η²-allene cation to the parent propargylic complex (with N(C₂H₅)₃), and (e) nonselective reactions to yield a mixture of products (with CH₃Li). Of these, the most common is behavior (a); together with the protonation of η⁵-C₅H₅Fe(CO)₂CH₂CCR it stimulates the two-step (3 + 2) cycloaddition reactions between electrophilic molecules and these iron-propargyl complexes.     

Säureinduzierte carbin-acylumwandlung

The reaction of dicarbonyl- and carbonyl(trimethylphosphine)(cyclopentadienyl)-carbyne complexes of molybdenum and tungsten η⁵-C₅H₅(CO)_2−n(PMe₃)_nMCR (n = 0, 1; M = Mo, W; R = CH₃, C₆H₅, C₆H₄CH₃, C₃H₅) with protic nucleophiles HX (X = Cl, CF₃COO, CCl₃COO) leads, through a combined protonation/carbon-carbon coupling reaction, to η²-acyl complexes η⁵-C₅H₅(CO)_1−nX₂(PMe₃)_n-M(η²-COCH₂R). The reaction conditions, the results of the spectroscopic measurements and the X-ray structure of η⁵-C₅H₅(CO)(Cl₂)W(η²-COCH₂CH₃) are reported.     

Transition metal nitrosyls as nitrosylation agents : II.Photo-nitrosylation of η5-C5H5V(CO)3L(L = CO,Pz3) by [Co(NO)2Br]2

η⁵-C₅H₅V(NO)₂CO is prepared in 40% yield by the photo-reaction between η⁵-C₅H₅V(CO)₄ and [Co(NO)₂Br]₂.η⁵-C₅H₅V(NO)₂CO reacts by an S_N1 mechanism with various phosphines PZ₃ to yield η⁵-C₅-H₅V(NO)₂PZ₃. The phosphine complexes are also obtained by photo-induced ligand interchange between η⁵-C₅H₅V(CO)₃PZ₃ and [Co(NO)₂Br]₂, or η⁵-C₅H₅V(CO)₄ and Co(NO)₂Br(PZ₃). In all cases, the main cobalt species formed is Co(NO)(CO)₃. While the one-bond vanadiumphosphorus coupling constants of most of the phosphine complexes are virtually the same (ca 410 Hz),the chemical shift values δ(⁵¹V) (?1328 to ?973 ppm rel. VOCl₃) decrease in the order PF₃ > CO > P(OR)₃ > P(alkyl)₃ > PPh₃ > PPh(NEt₂)₂, reflecting the decreasing π-acceptor ability of the ligands. δ(⁵¹V) also decreases in the series of alkylphosphines PR₃ (R = Me, Et, Prⁿ, Buⁱ, Prⁱ, BU^t) as the cone angle of PR₃increases.     

Electron-impact studies of organometallic molecules—X. Some simple transition metal fluorocarbon complexes

The mass spectra of several fluoroalkyl, fluoroalkenyl and fluoroacyl complexes of manganese, rhenium, iron and ruthenium carbonyls are described. After loss of carbonyl groups, fluoroalkyl compounds eliminate an olefin, with formation of metal halide species. A trifluorovinyl complex shows a novel elimination of a carbon atom to give an ion postulated to be a difluorocarbene-metal fluoride; the occurrence of difluorocarbene-metal ions in the spectra of some related complexes is also discussed. The spectra of the acyl complexes show little evidence of elimination of the acyl carbonyl group; the major process is fission of the CO? R_f bond with loss of a fluoroalkyl radical and formation of the cationic metal carbonyl, e.g. π-C₅H₅M(CO)₃⁺ (M ? Fe or Ru). The relevance of thermal or photochemical model reactions to processes occurring in the mass spectrometer is discussed.