Metallkomplexe mit anionischen Liganden von Elementen der 4. Hauptgruppe. IX. Zum komplexchemischen Verhalten von Trichlorstannid-und Trichlorgermid-Ionen gegenüber Komplexen von Übergangsmetallen in niedrigen Oxydationsstufen

Metal Complexes with Anionic Ligands of the Main Group IV Elements. IX. Reactions of Trichlorostannide and Trichlorogermide Ions with Complexes of Transition Metals in Low Oxidation States Carhonyl trichlorostannido- and carbonyl trichlorogermido-metalate complexes have been synthesized both by photochemical and thermical substitution reactions of [ECl₃]^? ions (E = Sn, Ge) with M(CO)₆, (M = Cr, Mo, W), Fe(CO)₅ Fe₃(CO)₁₂, Co₂(CO)₈, as well as with the metalcarbonyl derivatives (π-arene)M(CO)₃, (M = Cr, Mo), (h⁵-C₅,H₅,)V(CO)₄, Mn(CO)₅,Cl, Co(NO)(CO)₃, and Fe(NO)₂,(CO)₂. Mainly the bonding properties of the [ECl₃]^? ligands are discussed by means of i.r. spectroscopic investigations. The progress of the reactions and the necessary reaction conditions show that the nucleophilic properties oft both anions [ECl₃]^? are unexpectedly small. The slightly weaker hasicity of [SnCl₃]^? compared with [GeC1₃]^? arreared, when both anions were reacted with Co₂,(CO)₈, forming the substitution product. [Co₂,(CO)₇,SnCl₃]^? and the products of a “base reaction” Cl₃GcCo(CO)₄, and [Co(CO)₄]^?.     

The chemistry of metal carbonyl anions : III. Sodium-potassium alloy: An efficient reagent for the production of metal carbonyl anions

Reduction of several metal carbonyl dimers including Mn₂](CO)₁₀, [C₅H₅Fe(C0)₂]₂, Co₂(CO)₈, and [C₅H₅M(CO)₃]₂ (M = Cr, Mo and W) by sodium—potassium alloy (NaK) in tetrahydrofuran at room temperature provides a rapid and clean method for the production of the corresponding metal carbonyl anions in high yield. Isolation and characterization of [n-Bu₄N] [Fe(CO)₂C₅H₅] from the iron dimer reduction is described. Reductions of other carbonyls including M(CO)₆ (M = Cr, Mo and W) and Re₂(CO)₁₀ proceed more slowly than previously established methods and provide principally M₂(CO)₁₀^2? and Re(CO)₅₅^?. Methods for the preparation of Re(CO)₅^? are critically considered. The reaction of NaK with [C₅H₅NiCO]₂ is discussed in relation to previously reported results. Infrared solution spectra of a number of carbonyl anions in THF, obtained in a special infrared solution cell, are reported.     

Bildung siliciumorganischer Verbindungen. 88. Zur SiH-Addition von 1,3,5-Trisilacyclohexanen an silylierte Alkine

Formation of Organosilicon Compounds. 88. SiH-Addition of 1,3,5-Trisilacyclohexanes to Silylalkynes Catalyzed by means of H₂PtCl₆ the SiH addition of 1,1,3,3,5-pentamethyl-1,3,5-trisilacyclohexane to HC?C? Sime₂CH₂Cl, and of 1,1,3,3,5-pentaphenyl-1,3,5-trisilacyclohexane to HC?C? Sime₂CH₂Br yields a and b , or c and d , resp. (Formulae see Inhaltsübersicht), whereas 1,3,5-trisilacyclohexanes with more SiH groups preferrably yield polymers. The c/d ratio is strongly governed by the solvent: 38% c in n-hexane, 72% c in CCl₄/cyclohexane. Treatment of c and d with HCl/AlCl₃ under cleavage of all of the phenyl groups, addition of HCl to the vinyl group and subsequent β-elimination leads to (Cl₂Si? CH₂)₃ ClSime₂? CH₂Br and compound e , whereas HBr at ?78°C only cleaves one phenyl group per Si atom.     

POSSIBLE HYDRIDE AND METHIDE TRANSFER REACTIONS: REACTIONS OF Fe(CO)4R−(R = H,CH3) AND W(CO)5R− (R = H,CH3, Cl,Br, I) WITH METAL CARBONYL CATIONS

Abstract

Reactions of metal carbonyl cations (M(CO)₆ ⁺, M = Mn, Re) with hydride-, methide- or halide-containing metal carbonyl anions (Fe(CO)₄R^?, R = H, Me; W(CO)₅R^?, R = H, Me, Cl, Br, I) produce products that indicate several mechanisms are operative. Reactions of the halo-tungsten complexes produce neutral, solvated tungsten complexes, W(CO)₅(CH₃CN) and W(CO)₄(CH₃CN)₂ and M(CO)₅X in a reaction that appears to be initiated by decomposition of W(CO)₅X^?. In contrast, the tungsten hydride and methide complexes react, predominantly, by transfer of the hydride or methide to a carbonyl of the cation at a much faster rate. The iron hydride and methide complexes react by iron-based nucleophilicity involving a two-electron process.     

Übergangsmetall-substituierte vb elementsysteme : VIII. Darstellung und komplexchemisches verhalten von cyclopentadienyl(tricarbonyl)viametall-dimethylstibinen

Starting with the cyclopentadienyl(carbonyl)metal anions [π-C₅H₅(CO)₃M]^? (M = Cr, Mo, W) and (CH₃)₂SbBr, transition metal-substituted stibines of the form π-C₅H₅(CO)₃MSb(CH₃)₂ are obtained. The nucleophilic character of the VB element primarily determines the reactivity of these species, and shows itself in alkyl halide quarternization (a) or ligand exchange on activated metal carbonyl complexes (b). (a) yields the trialkylstibine-substituted metal cations [π-C₅H₅-(CO)₃MSb(CH₃)₂R]X (R = CH₃, CH₂CH=CH₂, CH₂C₆H₅; X = Br, J), (b) leads to the formation of the metal carbonyl derivatives LM(CO)₅, L₂M(CO)₄ (M = Cr, Mo, W), LNi(CO)₃ and LFe(CO)₄ [L = (CH₃)₂SbM(CO)₃-π-C₅H₅] which are the first (CH₃)₂Sb-bridged polynuclear complexes. Phosphorus ylides cause heterolytic cleavage of the antimonytransition metal bond. Transfer of the (CH₃)₂Sb-group to the ylidic carbanion occurs via substitution/transylidation. All new compounds have been fully characterized by means of ¹H NMR, IR and mass spectroscopy     

Formation and reactivity of metal carbonyl anions in the gas phase

The reactions of metal carbonyl anions (M(CO)_n^?; M = Cr, Mn and Fe; n = 1–3) with n-heptane, water and methanol were studied with use of a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer equipped with an external ion source. The M(CO)_n^? ions were formed in the FT-ICR cell by collision-induced dissociation of the most abundant primary ion generated by electron impact of the appropriate metal carbonyl compound present in the external ion source. The M(CO)_n^? ions were allowed subsequently to undergo non-reactive collisions with argon in order to remove possible excess internal/translational energy prior to the ion/molecule reaction. Only the Cr(CO)₃^?, Mn(CO)₃^? and Fe(CO)₂^? ions react with n-heptane. This reaction proceeds by loss of H₂ from the collision complex and the Cr(CO)₃^? and Fe(CO)₂^? ions react about three times more efficiently than the Mn(CO)₃^? ion. With water, Mn(CO)^? and Fe(CO)₃^? are unreactive, whereas the other ions react by loss of one or two CO molecules from the collision complex. The rate of the reaction with water decreases in the order Cr(CO)₃^?, Fe(CO)₂^?, Cr(CO)₂^?, Fe(CO)^?, Mn(CO)₃^? and Mn(CO)₂^?. With methanol, the Cr(CO)₂^? ion reacts by loss of two CO molecules from the collision complex, whereas loss of one CO molecule and elimination of CO + H₂ occur in the reaction with Cr(CO)₃^?. Competing loss of CO and one or two H₂ molecules occurs in the reactions of Mn(CO)₃^? and Fe(CO)₂^? with methanol. The rate of the reaction with methanol decreases in the order Cr(CO)₃^?, Fe(CO)₂^?, Cr(CO)₂^? and Mn(CO)₃^?.     

Insertion reactions of metal carbonyl anions with methyl formate in the gas phase as revealed by 13C- and D-labeling

School of Chemistry, University of New South Wales, Kensington, Australia Institute of Mass Spectrometry, University of Amsterdam, Nieuwe Achtergracht The gas-phase reactions of coordinatively unsaturated metal carbonyl anions (M(CO) _n ^? , M=Cr, Mn, Fe, Co; n=0-3 and Co(CO)_nNO^?, n=0-2) with unlabeled and D- and ¹³C-labeled methyl formate have been studied with Fourier transform ion cyclotron resonance mass spectrometry. The reactions proceed in most instances by loss of one or more CO molecules from the collision complex. In the reactions of the dicarbonyl and tricarbonyl anions with H¹³COOCH₃, part of the eliminated carbon monoxide molecules contain the label revealing the occurrence of initial insertion of the metal center into the bonds adjacent to the carbonyl function of the substrate with formation of five- or six-coordinate intermediates, respectively. In addition, the MnCCO) ₃ ^? , Fe(CO) ₂ ^? , and CoCCO) ₂ ^? ions react by the loss of methanol and a [C,H₂,O] neutral species. The D- and ¹³C-labeling show that methanol is expelled in a reductive elimination from a five- or six-coordinate species, whereas the [C,H₂,O] loss is a more complex process possibly involving the competing losses of formaldehyde and CO + H₂. In the reaction of Fe(CO) ₃ ^? with H ₁₃ ¹³ COOCH₃, a facile consecutive exchange of all three CO ligands of the reactant ion for ¹³CO is observed. This novel reaction appears to involve initial insertion into the H¹³CO—OCH₃-bond followed by facile hydrogen shifts from the formyl ligand to a CO Hgand prior to the loss of unlabeled methyl formate.     

New tetrahedral cluster compounds of iridium. Synthesis of the anions [Ir4(CO)11X]− (X = Cl,Br, I,CN, SCN) and x-ray structure of [PPh4] [Ir4(CO)11Br]

[Ir₄(CO)₁₁X]^? anions are obtained by reaction of halide and pseudo-halide ions with Ir₄(CO)₁₂. X-ray determination of the structure of [Ir₄(CO)₁₁Br]^? shows that the carbonyl arrangement differs from that of the parent Ir₄(CO)₁₂, and is similar to that known for Co₄(CO)₁₂; one terminal CO group in the basal M₃(CO)₉ moiety is replaced by the bromide ligand, and two of the bridging CO groups become markedly asymmetric.     

Homoleptic Metal Carbonyl Cations of the Electron-Rich Metals: Their Generation in Superacid Media Together with Their Spectroscopic and Structural Characterization

Homoleptic carbonyl cations of the electron-rich metals in Groups 8 through 12 are the newest members of the large family of transition metal carbonyls. They can be distinguished from typical metal carbonyl complexes in several respects. Their synthesis entails carbonylation of metal salts in such superacids as fluorosulfuric acid and “magic acid” HSO₃F? SbF₅. Thermally stable salts with [Sb₂F₁₁]^? as counterion are obtained with antimony pentafluoride as reaction medium. Both the [Sb₂F₁₁]^? anion and superacid reaction media have previously found little application in the organometallic chemistry of d-block elements. Also unprecedented in metal carbonyl chemistry are the coordination geometries with coordination numbers 4 (square-planar coordination) and 2 (linear coordination) for the cation. Formal oxidation states of the metals, and the charges of the complex cations, extend from + 1 to +3: thus CO is largely σ-bonded to the metal, and the CO bond is strongly polarized. Minimal metal → CO π-backbonding and a positive partial charge on carbon are manifested in long M? C bonds, short C? O bonds, high frequencies for C? O stretching vibrations (up to 2300 cm^?1), and small ¹³C NMR chemical shifts (up to δ_c, = 121). Prominent examples of these unusual homoleptic carbonyl cations, which were recently the subject of a Highlight in this journal, include the first carbonyl cation of a p-block metal [Hg(CO)₂]²⁺, the first trivalent carbonyl cation [Ir(CO)₆]³⁺, and the first multiply charged carbonyl cation of a 3d metal [Fe(CO)₆]²⁺. In this overview we propose to (a) outline the historical origins of cationic metal carbonyls and their methods of synthesis; (b) present a summary of the general field of carbonyl cations, which has developed over a yery short period of time; (c) discuss the structural and spectroscopic characteritics of metal–CO bonding; (d) discuss the special significance associated with reaction media and the [Sb₂F₁₁]^? anion; and (e) point to the most recent results and anticipated future developments.     

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.     

Reactions of carbon dioxide with metal carbonyl anions

The reactivity of a series of metal carbonyl anions with CO₂ has been found to parallel their relative nucleophilicities. The highly nucleophilic species, C₅H₅Fe(CO)^?₂, reacts readily to give the dimer, (C₅H₅Fe(CO)₂)₂, and carbonate while Co(CO)^?₄ is unreactive. The reaction of ¹³CO₂ with C₅H₅Fe(CO)^?₂ results in the formation of the ¹³CO enriched dimer.     

Structural characterization of the anions [Rh6(CO)15X]− [X = COEt and CO(OMe)]

The anions [Rh₆(CO)₁₅X]^?, with X = COEt and CO(OMe), have been studied by single-crystal X-ray diffraction. They contain octahedral rhodium clusters, with mean metalmetal distances of 2.779 and 2.765 », respectively. The carbonyl stereochemistry in the two anions is similar to that of Rh₆(CO)₁₆, with one terminal CO group replaced by the X ligand. The RhC(carbomethoxy) bond distance (1.96(2) ») is significantly shorter than the RhC(acyl) distance (2.06(2) »).     

Access to Stable Metalloradical Cations with Unsupported and Isomeric Metal–Metal Hemi‐Bonds

Metalloradical species [Co₂Fv(CO)₄]^.+ ( 1 ^.+, Fv=fulvalenediyl) and [Co₂Cp₂(CO)₄]^.+ ( 2 ^.+, Cp=η⁵‐C₅H₅), formed by one‐electron oxidations of piano‐stool cobalt carbonyl complexes, can be stabilized with weakly coordinating polyfluoroaluminate anions in the solid state. They feature a supported and an unsupported (i.e. unbridged) cobalt–cobalt three‐electron σ bond, respectively, each with a formal bond order of 0.5 (hemi‐bond). When Cp is replaced by bulkier Cp* (Cp*=η⁵‐C₅Me₅), an interchange between an unsupported radical [Co₂Cp*₂(CO)₄]^.+ (anti‐ 3 ^.+) and a supported radical [Co₂Cp*₂(μ‐CO)₂(CO)₂]^.+ (trans‐ 3 ^.+) is observed in solution, which cocrystallize and exist in the crystal phase. 2 ^.+ and anti‐ 3 ^.+ are the first stable thus isolable examples that feature an unsupported metal–metal hemi‐bond, and the coexistence of anti‐ 3 ^.+ and trans‐ 3 ^.+ in one crystal is unprecedented in the field of dinuclear metalloradical chemistry. The work suggests that more stable metalloradicals of metal–metal hemi‐bonds may be accessible by using metal carbonyls together with large and weakly coordinating polyfluoroaluminate anions.     

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.     

Salts of Anionic Metal Carbonyl Clusters with Cryptand[2.2.2](Na+), DB‐18‐crown‐6(Na+), and Paramagnetic Cp*2Cr+ Cations Obtained by Reduction

Reduction of neutral metal clusters (Co₄(CO)₁₂, Ru₃(CO)₁₂, Fe₃(CO)₁₂, Ir₄(CO)₁₂, Rh₆(CO)₁₆, {CpMo(CO)₃}₂, {Mn(CO)₅}₂) by decamethylchromocene (Cp*₂Cr) or sodium fluorenone ketyl in the presence of cryptand[2.2.2] and DB‐18‐crown‐6 was studied. Nine new salts with paramagnetic Cp*₂Cr⁺, cryptand[2.2.2](Na⁺), and DB‐18‐crown‐6(Na⁺) cations and [Co₆(CO)₁₅]^2– ( 1 , 2 ), [Ru₆(CO)₁₈]^2– ( 3 – 4 ) dianions, [Rh₁₁(CO)₂₃]^3– ( 6 ) trianions, and new [Ir₈(CO)₁₈]^2– ( 5 ) dianions were obtained and structurally characterized. The increase of nuclearity of clusters under reduction was shown. Fe₃(CO)₁₂ preserves the Fe₃ core under reduction forming the [Fe₃(CO)₁₁]^2– dianions in 7 . The [CpMo(CO)₃]₂ and [Mn(CO)₅]₂ dimers dissociate under reduction forming mononuclear [CpMo(CO)₃]^– ( 8 ) and [Mn(CO)₅]^– ( 9 ) anions. In all anions the increase of negative charge on metal atoms shifts the bands attributed to carbonyl C–O stretching vibrations to smaller wavenumbers in agreement with the elongation of the C–O bonds in 1 – 9 . In contrast, the M–C(CO) bonds are noticeably shortened at the reduction. Magnetic susceptibility of the salts with Cp*₂Cr⁺ is defined by high spin Cp*₂Cr⁺ (S = 3/2) species, whereas all obtained anionic metal clusters and mononuclear anions are diamagnetic. Rather weak magnetic coupling between S = 3/2 spins is observed with Weiss temperature from –1 to –11 K. That is explained by rather long distances between Cp*₂Cr⁺ and the absence of effective π–π interaction between them except compound 7 showing the largest Weiss temperature of –11 K. The {DB‐18‐crown‐6(Na⁺)}₂[Co₆(CO)₁₅]^2– units in 2 are organized in infinite 1D chains through the coordination of carbonyl groups of the Co₆ clusters to the Na⁺ ions and π–π stacking between benzo groups of the DB‐18‐crown‐6(Na⁺) cations.     

The reaction of Ir4(CO)12 with bases

The reaction of Ir₄(CO)₁₂ with potassium hydroxide in methanol and/or with sodium in tetrahydrofuran leads to the carbonyliridate anions [HIr₄(CO)₁₁]^?, [Ir₆(CO)₂₂]^2?, [Ir₈(CO)₂₀]^2?, [Ir₆(CO)₁₅]^2? and [Ir(CO)₄]^? obtained as salts with bulky cations. From these, the tetranuclear carbonyl hydride H₂Ir₄(CO)₁₁ and the hexanuclear carbonyl compound Ir₆(CO)₁₆ are also obtained.     

Bond strengths in cyclopentadienyl metal carbonyl anions

Energy-resolved collision-induced dissociation of metal cyclopentadienyl carbonyl anions CpM(CO)_x⁻(Cpc-C₅H₅, MV, Cr, Mn, Fe, Co) is used to determine metal–carbonyl bond energies in these systems. These bond energies are, in general, slightly stronger than those for the corresponding homoleptic metal carbonyl anions. The bond strength in CpCo(CO)₂⁻, a 19-electron complex, is notably weaker than most of the others. D[CpMn⁻-CO] is also weak; this is attributed to a mismatch in the electronic ground states of CpMn⁻ and CpMnCO⁻. D[CpCo⁻-CO], on the other hand, is substantially larger than the others, and is comparable to the bond energy measured in solution for CpMn(CO)₃.     

A Systematic Investigation of Coinage Metal Carbonyl Complexes Stabilized by Fluorinated Alkoxy Aluminates

The reaction of Cu^I, Ag^I, and Au^I salts with carbon monoxide in the presence of weakly coordinating anions led to known and structurally unknown non‐classical coinage metal carbonyl complexes [M(CO)_n][A] (A=fluorinated alkoxy aluminates). The coinage metal carbonyl complexes [Cu(CO)_n(CH₂Cl₂)_m]⁺[A]^? (n=1, 3; m=4?n), [Au₂(CO)₂Cl]⁺[A]^?, [(OC)_nM(A)] (M=Cu: n=2; Ag: n=1, 2) as well as [(OC)₃Cu???ClAl(OR^F)₃] and [(OC)Au???ClAl(OR^F)₃] were analyzed with X‐ray diffraction and partially IR and Raman spectroscopy. In addition to these structures, crystallographic and spectroscopic evidence for the existence of the tetracarbonyl complex [Cu(CO)₄]⁺[Al(OR^F)₄]^? (R^F=C(CF₃)₃) is presented; its formation was analyzed with the help of theoretical investigations and Born–Fajans–Haber cycles. We discuss the limits of structure determinations by routine X‐ray diffraction methods with respect to the C? O bond lengths and apply the experimental CO stretching frequencies for the prediction of bond lengths within the carbonyl ligand based on a correlation with calculated data. Moreover, we provide a simple explanation for the reported, partly confusing and scattered CO stretching frequencies of [Cu^I(CO)_n] units.     

Some observations on the systems Co2(CO)8/sodium amalgam and Hg[Co(CO)4]2/sodium amalgam,and the effect of added LiBr

Co₂(CO)₈ and Hg[Co(CO)₄]₂ react sodium amalgam and/or mercury in ethereal solvents to give a variety of products. On treatment with aqueous M(o-phen)₃Cl₂(M  Fe, Ni), the anions [Co(CO)₄^?, [Co₃(CO)₁₀]^?, {Hg[Co(CO)₄]₃}^? and {Hg[Co(CO)₄]₂Cl}^? could be isolated as their [M(o-phen)₃]²⁺ salts. The effect of LiBr on the reacting systems was also investigated and the anion {Hg[Co(CO)₄]₂Br}^? isolated.     

Electrochemical studies on organometallic compounds: VIII. Ligand exchange reaction in carbonyl cobalt complexes

The reaction of Co(CO)₃DMPP^? with Co₂(CO)₆(DMPP)₂ (DMPP = dimethylphenylphosphine) yields CoCO₄^? and Co₂(CO)₅(DMPP)₃. The DMPP ligand of Co(CO)₃DMPP^? can be replaced by CO or triphenylphosphite.