Reactions of M2Cl4(PR3)4 (M  Mo and W) with carbon monoxide

The reactions of M₂Cl₄(PR₃)₄ derivatives (M  Mo, W and PR₃  PEt₃, PBu₃ⁿ) with CO at atmospheric pressure in toluene at 70°C to afford M(CO)₃(PR₃)₂Cl₂ and trans-M(CO)₄(PR₃)₂ are reported.     

Gehinderte Ligandenbewegungen in Übergangsmetallkomplexen : VII. Rotation der olefinliganden L = malein- und furmarsäuredimethylester in komplexen des typs C5H5Mn(CO)2L und C5H5Cr(CO)(NO)L

The restricted rotation of the olefin ligands L = dimethyl maleate and dimethyl fumarate in complexes of the type C₅H₅Mn(CO)₂L and C₅H₅Cr(CO)-(NO)L, respectively, has been investigated on the basis of their temperature-dependent ¹H NMR spectra. The olefinic ligand is arranged preferably in a position where the CC double bond is parallel to the plane of the cyclopentadienyl ring. The possible stereoisomers are discussed using this model. The ¹H NMR spectra of C₅H₅Cr(CO)(NO)(trans-CH₃OOCCHCHCOOCH₃) provide direct evidence that the configuration (R or S) at the metal is stable up to 120°C, and that the restricted motion of the olefin is exclusively rotation around the metal—olefin bond. The activation barriers of the olefin rotation are found to be appreciably lower in the C₅H₅Mn(CO)₂L complexes (ΔG^≠(T_C) 11–12 kcal mol^?1) than in the isoelectric C₅H₅Cr(CO)(NO)L compounds (ΔG^≠(T_C) 15–20 kcal mol^?1).     

Elektronenreiche übergangsmetallkomplexe : V. Phosphinsubstituierte wolframdicarbonyle

Chloride-bridged tungsten tricarbonylmetalates [(OC)₃W(Cl)₃W(CO)₃]^3?, obtainable in high yields from tungsten hexacarbonyl and tetraalkylammonium chlorides, with allyl halides give π-allylhalogenotungsten dicarbonyls. With phosphines reductive elimination of allylhalide yields bis- or tris-(phosphine)-tungsten-dicarbonyls L₂W(PR₃)₂(CO)₂, LW(PR₃)P₃(CO)₂ (L = CH₃CN). Substitution reactions of L with various ligands under mild conditions are described. IR and electronic spectra of more than twenty new compouonds are discussed and compared with corresponding compounds of molybdenum.     

A study of the photochemistry and thermal chemistry of Ru3(CO)9(PR3)3{R = Ph,OMe} with two-electron donor ligands

The photochemistry of the tris-substituted clusters Ru₃(CO)₉(PR₃)₃ (R=Ph or OMe) with no added ligands, with CO, C₂H₄, alkynes and H₂ is compared and contrasted with results obtained for analogous thermal reactions. Photolysis of a CH₂Cl₂ solution of Ru₃(CO)₉(PPh₃)₃ leads to the metallated complex HRu₃(CO)₈(PPh₃)₂(PPh₂C₆H₄). In CCl₄, Ru(CO)₃(PR₃)Cl₂ is formed on photolysis of Ru₃(CO)₉(PR₃)₃. Photolysis of CO saturated solutions of Ru₃(CO)₉(PR₃)₃ leads to Ru(CO)₄(PR₃). C₂H₄ saturated solutions of Ru₃(CO)₉(PR₃)₃ generate the novel Ru(CO)₃(PR₃)(²-C₂H₄) complexes upon photolysis. With C₂H₂, photolysis of solutions of Ru₃(CO)₉(PR₃)₃ leads to the novel complexes Ru(CO)₃(PR₃)(²-C₂H₂). Substituted alkyne complexes have been prepared. Thermolysis of Ru₃(CO)₉(PR₃)₃ with HCCPh leads to the novel acetylide clusters HRu₃(CO)₆(PR₃)₃(₃-²-C₂Ph). With PhC CPh, only Ru₃(CO)₉{P(OMe)₃}₃ reacts, yielding the novel alkyne cluster Ru₃(CO)₆{P(OMe)₃}₃(₃-²-C₂Ph₂). With H₂, photolysis of CH₂Cl₂ solutions of Ru₃(CO)₉(PR₃)₃ leads to H₂Ru(CO)₂(PR₃)₂. Irradiating a 4:1 CH₂Cl₂ to EtOAc solution of Ru₃(CO)₉(PR₃)₃ under an atmosphere of H₂ leads to the novel dihydrido species H₂Ru₃(CO)₇(PR₃)₃. Thermolysis of H₂ saturated solutions of Ru₃(CO)₉(PR₃)₃ leads to H₄Ru₄(CO)₈(PR₃)₄.     

Synthesis and X-ray Molecular Structure Analysis of Some Au-Co,Au-Mn,and Hg-Co Bonded Compounds

The reaction of NaCo(CO)_4-x (PR₃) _x (x = 0, 1) with Au(PR₃)Cl was examined in THF. The products were characterized by single crystal X-ray analysis and/or XPS spectroscopy. When the THF solution of NaCo(CO)_4-x (PR₃) _x which was in situ prepared by the reduction of the corresponding cobalt carbonyl dimer with Na amalgam was filtered, the main product was (R₃P)Au-Co(CO)₄ and (R₃P)Au-Co(CO)_4-x (PR₃) _x (x = 1,2); phosphine migration from the Au to the Co site was observed for bulky phosphines during the recrystallization process. When the THF solution of NaCo(CO)_4-x (PR₃) _x was not filtered, the main product had the composition of M[Co(CO)₃(PR₃)]₂. The element M was clearly determined to be Hg by XPS spectroscopy. The reaction of NaMn(CO)₅ with Au(PR₃)Cl, however, afforded R₃PAu-Mn(CO)₅. The bonding parameters such as Au-M and Hg-Co bond-lengths were interpreted in terms of the electronic nature of the R group of the monodentate PR₃ ligand.     

Anionic and neutral rhodium(I) complexes containing trichlorostannato ligands

The complexes Et₄N[Rh(SnCl₃)₂(diolefin)(PR₃)] (diolefin = COD or NBD) have been isolated and their reactions studied. Reaction with arylic tertiary phosphines led to SnCl₃⁻ displacement and isolation of neutral pentacoordinated Rh(SnCl₃)(diolefin)(PR₃)₂ complexes. Reaction with carbon monoxide involved diolefin displacement when the diolefin was COD, thus giving Et₄N[Rh(SnCl₃)₂(CO)₂(PR₃)] compounds, but SnCl₃⁻ displacement when it was NBD, thus yielding Rh(SnCl₃)(CO)(NBD)(PR₃) complexes. The complexes [Rh(diolefin)Cl]₂ were found to react with triarylphosphines in the presence of SnCl₂ and with CO bubbling through the solution to give Rh(SnCl₃)(CO)(NBD)(PR₃) when the diolefin was NBD but Rh(Cl)(CO)(PR₃)₂ when the diolefin was COD.     

Terminal Phosphanido Rhodium Complexes Mediating Catalytic PP and PC Bond Formation

Complexes with terminal phosphanido (M? PR₂) functionalities are believed to be crucial intermediates in new catalytic processes involving the formation of P? P and P? C bonds. We showcase here the isolation and characterization of mononuclear phosphanide rhodium complexes ([RhTp(H)(PR₂)L]) that result from the oxidative addition of secondary phosphanes, a reaction that was also explored computationally. These compounds are active catalysts for the dehydrocoupling of PHPh₂ to Ph₂P? PPh₂. The hydrophosphination of dimethyl maleate and the unactivated olefin ethylene is also reported. Reliable evidence for the prominent role of mononuclear phosphanido rhodium species in these reactions is also provided.     

IR,Multinuclear-NMR,and Structural Studies on [WH(CO)2(NO)(PR3)2]: cis-Influence of Phosphorus Ligands on Hydride Character

A thorough IR and ¹H-, ¹³C-, ³¹P-, ¹⁸³W-NMR spectroscopic, and X-ray structural study was carried out on complexes of the type trans, trans-[WH(CO)₂(NO)(PR₃)₂], (R = Et, Me, Ph, i-PrO, MeO, and PhO). Linear correlations could be found between Tolman's parameter X and v(CO), v(WH), v(NO), δ(¹³C) (CO), as well as 1n(k), k being the H/D exchange rate constant for the hydride in CD₃OD. The ¹J(¹⁸³W,³¹P), ²J(³¹P,¹H), and ²J(³¹P,¹³C) as well as the ¹J(¹⁸³W,¹H) values are related to the electronegativity of the R groups on the phosphorus ligands. This is also indicated by EHT calculations of s-orbital populations of appropiate W model complexes. The X-ray structures of [WH(CO)₂(NO)(PR₃)₂] (R = Me, Ph, and MeO) were determined. Minor differences were observed in the W? P bond lenghts and in the P? W? P and C? W? C angles. No obvious relationship between X-ray data and spectroscopic parameters could be found. All three structures reveal a bending of both the CO and PR₃ ligands towards the hydride atom. The total octahedral distortion is remarkably constant (25.6, 29.4, and 27.0° tilt, respectively), although the ligands individually are very different. This is attributed to redistribution of π-electron density between CO and PR₃ groups toward the central W-atom in the three complexes.     

Preparation and characterization of mono-cyclopentadienylvanadium dihalide bis-phosphine complexes; crystal structure of (η5-C5H5)VCL2(PMe3)2

Mono-cyclopentadienyl complexes CpVX₂(PR₃)₂ and Cp′VX₂ (PR₃)₂ (Cp = η⁵- C₅H₅; Cp′ = η⁵-C₅H₄Me; R = Me, Et; X = Cl, Br) have been prepared by reaction of VX₃(PR₃)₂ with CpM (M = Na, T1, SnBuⁿ3, 1/2 Mg) or Cp′Na. Attempts to prepare analogous complexes with other phosphine ligands, PPh₃, PPh₂ Me, PPhMe₂, Pcy₃, DMPE and DPPE failed. Reduction of CpVCl₂(PEt₃)₂ with zinc or aluminium under CO (1 bar) offers a simple method for the preparation of CpV(CO)₃(PEt₃). The crystal structure of the trimethylphosphine complex CpVCl₂(PMe₃)₂ is reported.     

Carbonylcobalt(I) complexes. The crystal and molecular structure of [Co(CO)(dppm)2]ClO4

New anionic carbonylcobalt(I) complexes [X₂Co(CO)₂(PPh₃)](PR₄) (X=Cl, PR₄ = PBzPh₃ (I); X = Br, PR₄ = PEtPh₃ (II)) have been prepared by reduction of the cobalt(II) halides with NaBH₄ in the presence of PPh₃ and the phosphonium salt PR₄X. Cleavage of halide bridges in dimeric or polymeric [XCo(PPh₃)₂]_n and [XCo(PPh₃)]_n gives the neutral dicarbonyl derivatives XCo(CO)₂PPh₃)₂. Treatment of ClCo(CO)₂(PPh₃)₂ with alkylating agents gives the known σ- and η- organocobalt(I) derivatives, and reactions with TIClO₄ in the presence of various amounts of different mono- and bi-dentate phosphines give the cationic tricarbonyl [Co(CO)₃(PPh₃)₂]⁺, dicarbonyl [Co(CO)₂(PMePh₂)₃]⁺ and monocarbonyl [Co(CO)L₄]⁺ complexes (L₄ = 4P(OMe)₃, 2 dppe and 2dppm). The dppm complex crystallizes in the monoclinic space group P2₁/c with a 17.895(6), b 10.751(2), c 24.687(4) Å, β 98.92(1)°, and D_calc 1.35 g cm⁻³ for Z = 4. A final R value of 0.077 ( R_w = 0.061), based on 2656 observed reflections, was obtained. The cobalt atom exhibits a distorted trigonal bipyramidal geometry. The perchlorate anion is severely disordered or freely rotating.     

Chemistry of Palladium and Platinum with Selenium and Tellurium Ligands

Reactions of NaER (E = Se, Te; R = Ph, substituted Ph or 2-pyridyl) with a number of mono- and bi-nuclear palladium and platinum complexes have been investigated. Complexes of the type [M(Sepy)₂], [M(ER)₂(PR₃)₂], [M₂Cl₂(μ-ER)₂(PR₃)₂] and [M₂Cl₂(μ-Cl)(μ-ER)(PR₃)₂] (M = Pd, Pt) were isolated. They were characterized by elemental analysis, NMR (¹H, ¹³C, ³¹P, ⁷⁷Se, ¹²⁵Te, ¹⁹⁵Pt) data and in a few cases by X-ray diffraction studies. The [M(Sepy)₂(PPh₃)₂] dissociates into PPh₃ and [M(Sepy)(η²-Sepy)(PPh₃)] in solution. 2-Selenopyridine in its complexes acts in a monodentate (bonding through selenium) as well as in chelating (Se?N) or bridging fashion. The mononuclear complexes [M(ER)₂(PR₃)₂] are useful precursors for stepwise synthesis of cationic bi- and tri-nuclear derivatives.     

Kinetische Untersuchungen über Substitutionsreaktionen an Metallkomplexen. 7. Mitteilung [1]. Kinetik und Mechanismus der Reaktion von Methoxyorganylcarbenpentacarbonyl-chrom-Verbindungen mit tertiären Phosphinen

The kinetics of the reactions of methoxyorganylcarbenechromium complexes Cr(CO)₅C(OCH₃)R′ (R′ = CH₃, C₆H₅) with tertiary phosphines PR₃ have been studied by means of spectrophotometric methods. The reaction products of general composition cis-Cr(CO)₄(PR₃)C(OCH₃)R′, Cr(CO)₅PR₃ and trans-Cr(CO)₄(PR₃)₂ are formed by cleavage of both the Cr-CO and the Cr-C(carbene) bonds. The two-term rate law indicates two parallel, dissociative and associative, mechanisms. The kinetic data will be discussed in connection with the concept of labilising and non-labilising ligands.     

Phosphaalkynes as ligands in organometallic chemistry. Syntheses and 31p NMR spectra of platinum(II), palladium(II) and rhodium(I) complexes of dη5-cyclopentadienyltetracarbonyl-μ-(3,3-dimethyl-1-phosphabutyne)dimolybdenum, [Mo2(CO)4(η-c5H5)2tBuCP)]

Syntheses of the complexes trans-[PtCl₂(PR₃)Mo₂(CO)₄(η⁵-C₅H₅)₂(^tBuCP)], (PR₃=PEt₃, PPr₃, PBu₃, PPh₂Me, PPhMe₂) trans-[PdCl₂(PBu₃)Mo₂(CO)₄(η⁵-C₅H₅)₂(^tBuCP)], and trans[RhCl{(PF₂NMe)₂CO}Mo₂(CO)₄(η⁵-C₅H₅)₂(^tBuCP)] are described and their ³¹P NMR spectra presented and discussed.     

Regioselektive Ringöffnungen von einfach ungesättigten triangularen Clusterkomplexen [M2Rh(μ‐PR2)(μ‐CO)2(CO)8] (M2 = Re2, Mn2; R = Cy,Ph; M2 = MnRe,R = Ph) mit Diphosphanen

Regioselective Ring Opening Reactions of Unifold Unsaturated Triangular Cluster Complexes [M₂Rh(μ‐PR₂)(μ‐CO)₂(CO)₈] (M₂ = Re₂, Mn₂; R = Cy, Ph; M₂ = MnRe, R = Ph) with Diphosphanes Equimolar amounts of the triangular title compounds and chelates of the type (Ph₂P)₂Z (Z = CH₂, DPPM ; C=CH₂, EPP ) react in thf solution at –40 to –20 °C under release of the labile terminal carbonyl ligand attached to the rhodium atom in good yields (70–90%) to ring‐opened unifold unsaturated complexes [MRh(μ‐PR₂)(CO)₄M(DPPM bzw. EPP)(μ‐CO)₂(CO)₃] (DPPM: M₂ = Re₂, R = Cy 1 , Ph 2 ; Mn₂, Cy 5 , Ph 6 ; MnRe, Cy 7 . EPP: M₂ = Re₂, R = Cy 8 ; Mn₂, Cy 10 ). Complexes 1 , 2 and 8 react subsequently under minor uptake of carbon monoxide and formation of the valence saturated complexes [ReRh(μ‐PR₂)(CO)₄M(DPPM bzw. EPP) (CO)₆] (DPPM: R = Cy 3 , Ph 4 . EPP: R = Cy 9 ). Separate experiments ascertained that the regioselective ring opening at the M–M‐edge of the title compounds is limited to reactions with diphosphanes chelates with only one chain member and that the preparation of the unsaturated complexes demands relatively good donor ability of both P atoms. As examples for both types of compounds the molecular structures of 8 and 3 have been determined from single crystal X‐ray structure analysis. Additionally all new compounds are identified by means of ν(CO)IR, ¹H‐ and ³¹P‐NMR data. This includes complexes with a modified chain member in 1 and 5 which, after deprotonation reaction to carbanionic intermediates, could be trapped with [PPh₃Au]⁺ cations as rac‐[MRh(μ‐PR₂)(CO)₄M((Ph₂P)₂CHAuPPh₃)(μ‐CO)₂(CO)₃] (M₂ = Re 17 , Mn 18 ) and products rac‐[MRh(μ‐PR₂)(CO)₄M((Ph₂P)₂CHCH₂R)(μ‐CO)₂(CO)₃] (M₂ = Re, R = Ph 19 , n‐Bu 21 , Me 23 ; Mn, Ph 20 , n‐Bu 22 , Me 24 ) which result from Michael‐type addition reactions of 8 or 10 with strong nucleophiles LiR.     

Metallkomplexe mit 1,2-Dithion-Liganden. III. Dithiooxamide als starke Donatoren oder Akzeptoren in Molybdäncarbonylkomplexen

Metal Complexes with 1,2-Dithione Ligands. III. Dithiooxamides as Strong Donors or Acceptors in Molybdenum Carbonyl Complexes. Starting from substitution labile molybdenum carbonyl complexes L₂Mo(CO)₄, L₃Mo(CO)₃ and L₂L₂′Mo(CO)₂ several new complex types with the C? C-twisted tetraalkyldithiooxamides (R₄dto) and the planar N,N′-dialkyldithiooxamides (R₂H₂dto) such as (R₄dto)Mo(CO)₄ ( 8 – 11 ), (R₂H₂dto)Mo(CO)₄ ( 12 – 18 ), (R₂R₂′dto)Mo(CO)₃(P(C₆H₅)₃) ( 27 – 31 ), (R₂R₂′dto)Mo(CO)₂(PR₃)₂ ( 36 – 51 ) are described and compared with complexes of a cyclic dithiooxamide ( 62 – 64 ) and analogous complexes with thioamides R₂NC(S)R′ ( 19 – 25 , 52 – 55 , 57 – 60 ). In Mo(CO)₄ complexes, dithiooxamides display a rather strong donor character and are thus similar to simple thioamides, but the blue colour of the R₂H₂dto complexes indicates already low-lying acceptor levels. When passing from the Mo(CO)₄ complexes via Mo(CO)₃(PR₃) complexes to the very electron rich Mo(CO)₂(PR₃)₂ complexes, the i.r. and eletronic spectra indicate an unexpected and drastic change in ligand character. Dto ligands in the latter complex type turn out to be very strong acceptors, independent of the degree of N-alkylation. A conformational change, with twisted R₂N? C bonds and a planar S? C? C? S skeleton (as in the dithiolene complexes), can account for all the peculiarities of the (dto)-dicarbonylbis(phosphine) complexes as compared to the “normal” thioamide complexes. Dithiooxamides can thus control the oxidation state of metals by a remote conformational change and possibly act as an electron reservoir in chemical reactions at the metal center.     

Complexes dinucleaires pontes des metaux d8: VII. Reactions d'addition oxydante d'halogenures d'alkyle et d'acycle aux complexes μ-halogenes du rhodium(i) [RhX(CO)(PR3)]2. Structure cristalline de [RhCl(CO)(PMe2Ph)(Me)(Br)]2

The halogen bridged binuclear complexes of rhodium(I) [RhCl(CO)(PR₃)]₂ undergo oxidative addition with methyl halides to yield the complexes [RhCl(CO)(PR₃)(Me)(X)]₂ (X = Cl, Br). The crystal and molecular structures of [RhCl(CO)(PMe₂Ph)(Me)(Br)]₂ have been determined from a single crystal by use of X-ray crystallographic methods. The space group is Pca2₁ or Pacm with a 19.501(5), b 10.381(4), c 13.641(5) e? Z = 4. Parameters of 30 nonhydrogen atoms in the space group Pca2₁ were refined by the full-matrix least squares technique to a conventional R factor of 0.073. In a binuclear unit, each rhodium atom is in an octahedral environment being bonded to a carbonyl group, a methyl group and a tertiary phosphine ligand and three halogen atoms for which, due to a disorder phenomenon, the diffusion factors have been determined as the average between those of chlorine and bromine atoms. In solution the cis-migration of the methyl groups occurs, leading to the acetyl complexes. In the case of CH₃I, it is shown that an equilibrium is present in solution: [RhCl(CO)(PR₃(Me)(I)]₂ ? [RhCl(COMe)(PR₃)(I)(solvant)]₂] Carbonylation reactions shift this equilibrium to give the complexes [RhCl(CO)(COMe)(PR₃(I)]₂. Such complexes are readily prepared by direct oxidative addition of acyl halides to the compounds [RhCl(CO)(PR₃)]₂.     

Zur kenntnis der chemie der metallcarbonyle und der cyanokomplexe in flüssigem ammoniak : XXXIII. Über die darstellung neuer carbamoylcarbonyl-komplexe aus bekannten und neuen kationischen carbonylverbindungen des mangans und rheniums

The covalent carbamoyl carbonyl compounds Re(CO)₅COHN₂, cis-M(CO)₄(L)CONH₂, M(CO)₃(L)₂CONH₂ and M(CO)₃(D)CONH₂ (M = Mn, Re; L = PPh₃, PEt₃; D = bipy, phen) are formed by reactions of the cationic complexes [Re(CO)₆]⁺, [M(CO)₅L]⁺, [M(CO)₄L₂]⁺ and [M(CO)₄D]⁺ (M = Mn, Re; L = PPh₃, PEt₃; D = bipy, phen) with liquid NH₃ with concomitant deprotonation: [M(CO)_6?nL_n]⁺ + 2 NH₃ → M(CO)_5?nL_nCONH₂ + NH₄⁺ (n = 0, 1, 2) and [M(CO)₄D]⁺ + 2 NH₃ → M(CO)₃(D)CONH₂ + NH₄⁺ The stability of the above-mentioned carbamoyl carbonyl complexes increases from the penta- to the tetra- to the tri-carbonyl derivatives. In all cases the rhenium compounds are much more stable than the corresponding manganese complexes. Whereas the carbamoyl compound Re(CO)₄(PEt₃)CONH₂ can be isolated by reaction of [Re(CO)₅PEt₃]⁺ with NH₃, the corresponding manganese complex undergoes Hofmann degradation of amides even at ?70°C to form HMn(CO)₄PEt₃ and NH₄NCO. The IR and some mass and ¹H NMR spectra of the new hexacoordinated carbamoyl carbonyl complexes are discussed and the reactions of these compounds with liquid NH₃, HCl and CH₃OH are described.     

SnCl2 als Brückenligand in [{(CO)5M}2Sn(Cl)2]2− (M = Cr,Mo, W) — Synthese,Struktur und Reaktivität

SnCl₂ as a Bridging Ligand in [{(CO)₅M}₂Sn(Cl)₂]^2? (M = Cr, Mo, W) — Synthesis, Structure, and Reactivity [{(CO)₅Cr}₂Sn(Cl)₂]^2?, 1 , may be obtained from [(CO)₅Cr]^2? or [(CO)₅CrSnCl₂ · THF] in fair yields. Alternatively, 1 is accessible by the reaction of [Cr₂(CO)₁₀]^2? with SnCl₂. This procedure may be extended to the synthesis of [{(CO)₅M}₂Sn(Cl)₂]^2? (M = Mo, 2 ; M = W, 3 ). The compounds 1–3 are crystallized as their alkalimetal (12-crown-4)₂ or [2,2,2]cryptand salts. X-ray analyses demonstrate bridging SnCl₂-moieties with M? Sn? M-angles close to 130° in each case. The relation of the bonding situation in 1–3 to the ones observed for stannylene or ?inidene”? complexes, respectively, is discussed. The transformation of 1 into the rhombododecahedral (X-ray analysis) Sn? O-cage compound [{(CO)₅CrSn}₆(μ₃-O)₄(μ₃-OH)₄], 4 , demonstrates the reactivity of the dianions 1–3 .     

Metallorganische Lewis-Basen : XXXIX. Monomere Carbonylcobalt-Dimethylarsenide

The monomers R₃P(CO)₃Co-AsMe₂ (R = Me,MeO) decompose at ?10°C, the monomers (R₃P)₂(CO)₂Co-AsMe₂ (R = Me, MeO) are stable at room temperature. They are prepared from the very unstable (CO)₄Co-AsMe₂ by phosphine substitution at low temperatures or from KCo(CO)₃PR₃ and Me₂AsCl. They are organometallic Lewis bases forming dinuclear and trinuclear arsenic bridged complexes with metal carbonyls.     

Electron‐Rich Diferrous–Phosphane–Thiolates Relevant to Fe‐only Hydrogenase: Is Cyanide “Nature's Trimethylphosphane”?

The two‐step one‐pot oxidative decarbonylation of [Fe₂(S₂C₂H₄)(CO)₄(PMe₃)₂] ( 1 ) with [FeCp₂]PF₆, followed by addition of phosphane ligands, led to a series of diferrous dithiolato carbonyls 2 – 6 , containing three or four phosphane ligands. In situ measurements indicate efficient formation of 1 ²⁺ as the initial intermediate of the oxidation of 1 , even when a deficiency of the oxidant was employed. Subsequent addition of PR₃ gave rise to [Fe₂(S₂C₂H₄)(μ‐CO)(CO)₃(PMe₃)₃]²⁺ ( 2 ) and [Fe₂(S₂C₂H₄)(μ‐CO)(CO)₂(PMe₃)₂(PR₃)₂]²⁺ (R=Me 3 , OMe 4 ) as principal products. One terminal CO ligand in these complexes was readily substituted by MeCN, and [Fe₂(S₂C₂H₄)(μ‐CO)(CO)₂(PMe₃)₃(MeCN)]²⁺ ( 5 ) and [Fe₂(S₂C₂H₄)(μ‐CO)(CO)(PMe₃)₄(MeCN)]²⁺ ( 6 ) were fully characterized. Relevant to the H_red state of the active site of Fe‐only hydrogenases, the unsymmetrical derivatives 5 and 6 feature a semibridging CO ligand trans to a labile coordination site.