Terminal CO Research Articles

1,3-Dipolar cycloaddition to the FeSC fragment 20. Preparation and properties of carbonyliron complexes of di-thiooxamide. Reactivity of the mononuclear (di-thiooxamide)Fe(CO) 3 towards dimethyl acetylenedicarboxylate

Reaction of Fe 2(CO) 9 at room temperature in THF with the di-thiooxamides (L), SC{N(R,R′)}C{(R,R′)N}S [R=Me, R′–R′=(CH 2) 2 ( a); R=H, R′= iPr ( b); R=H, R′=iPr ( c), R=H, R′=benzyl ( d); R=H, R′=H ( e)], results for ligands a– d initially in the formation of the mononuclear σ-S, σ-S′ chelate complexes Fe(CO) 3(L) ( 7a– d), which could be isolated in case of 7a and 7d. Under the reaction conditions, complexes 7a– d react further with [Fe(CO) 4] fragments to give three types of Fe 2(CO) 6(L) complexes ( 8a– d) in high yields, depending on the di-thiooxamide ligand used together with traces of the known complex S 2Fe 3(CO) 9 ( 14). The molecular structures of these complexes have been established by the single crystal X-ray diffraction determinations of 8a, 8b and 8d. In the reaction with ligand e the corresponding complex 7e was not detected and the well-known complexes 14 and S 2Fe 3(CO) 9 ( 15) were isolated in low yield. In situ prepared 7a reacts in a slow reaction with 1 equiv. of dimethyl acetylene dicarboxylate in a 1,3-dipolar cycloaddition reaction to give the stable initial ferra [2.2.1] bicyclic complex 10a in 60% yield. In complex 10a an additional Fe(CO) 4 fragment is coordinated to the sulfido sulfur atom of the cycloadded FeSC fragment. When a toluene solution of 10a is heated to 50 °C it loses two terminal CO ligands to give the binuclear FeFe bonded complex 11a in almost quantitative yield. The molecular structures of 10a and 11a have been confirmed by single crystal X-ray diffraction. Reaction of 7d at room temperature with 2 equiv. of dimethyl acetylene dicarboxylate results in the mononuclear complex 12d in 5% yield. The molecular structure of 12b has been established by single crystal X-ray diffraction and comprises a tetra dentate ligand with two ferra-sulpha cyclobutene, and a ferra-disulpha cyclopentene moiety. When the reaction is performed at 60 °C a low yield of 2,3,4,5-thiophene tetramethyl tertracarboxylate is obtained besides complex 12d.

Stereochemical nonrigidity of [Rh6(CO)15L] clusters in solutionElectronic supplementary information (ESI) available; the relationship between the rate of S-type exchange in [Rh6(CO)15(PR3)] and the pKa′ values of the phosphine ligand. See http://www.rsc.org/suppdata/dt/b1/b101962g/

A series of substituted hexarhodium carbonyl clusters [Rh6(CO)15L] (L = PR3 (R = alkyl, aryl), P(OPh)3, NCMe, I−) has been studied by variable temperature and two-dimensional, X-{103Rh}, (X = 13C, 31P) HMQC and 13C EXSY NMR spectroscopy in solution. At low temperatures, the spectra are consistent with retention of the solid state structure. Different localised exchanges of terminal (COt) and face-bridging (COfb) CO's are found to occur over different atoms of the Rh6-octahedron at higher temperatures and the different pathways of the exchanges are discussed. When L = PR3 (R = alkyl, aryl), the lowest energy scrambling surprisingly involves exchange of COt and COfb, associated with the substituted rhodium (text-decoration:underline'S-type), with concomitant exchange of L between the two terminal sites on the substituted rhodium, followed by other localised stereospecific exchanges involving CO's associated with unsubstituted rhodium atoms (text-decoration:underline'U-type). For the other substituted clusters (L = P(OPh)3, NCMe, I−), only text-decoration:underline'U-type exchanges are observed. The kinetics of these exchanges are reported at different temperatures and for the text-decoration:underline'S-type exchange mechanism, the rate is found to vary with the nature of PR3.

Metal–support interactions in cobalt-aluminum co-precipitated catalysts: XPS and CO adsorption studies

Cobalt-aluminum catalysts were prepared using either the precipitation of Co 2+ in the presence of freshly prepared Zn-Al hydrotalcite (the promoted sample) or the co-precipitation of Co 2+ and Al 3+ (the unpromoted samples). The evolution of the initial hydrotalcite-like structure was monitored during its calcination and the reductive treatment by means of XPS. It was shown that at 480°C the reduction of the calcined samples results in the formation of Co 0 species, the further reduction at 650°C results in an increase of the amount of the Co 0 species. The samples reduced at 650°C chemisorb readily carbon monoxide at 77 K, while the sample reduced at 480°C does not chemisorb CO at 77 K. At elevated temperatures, all reduced samples are found to be able to chemisorb CO. Terminal CO moieties as well as monodentate carbonates, formates and carboxyl species were detected at the surface of the reduced samples at their exposure to the CO medium at the elevated temperature. The intensity of the IR absorption bands of chemisorbed CO are found proportional to the surface fraction of the Co 0 species, measured by XPS. The apparent red shift of the IR absorption bands is observed for CO adsorbed on the samples reduced at 480°C. The obtained data correlate with the catalytic properties of the Co-Al samples in hydrogenation reactions. The conclusion on the existence of a strong metal–support interaction in the samples under the study is made.

Spatial electron distribution of CO adsorbed on Ni(100) and Ni(111) surfaces probed by metastable impact electron spectroscopy

Electron emission spectra obtained by thermal collisions of He*(2 3S) metastable atoms with CO on Ni(100) in the c(2×2) structure and on Ni(111) in the c(4×2) structure were measured to probe directly the spatial electron distribution. For a systematic comparison, the metastable spectra of free CO, condensed CO on Ni(111), and gaseous Cr(CO)6 were also measured under the same beam conditions. Our data showed that the relative ionization cross sections for the CO 4σ-, 1π-, and 5σ-derived states depend drastically on the molecular orientation of CO with respect to the metastable beam, reflecting the local electron density of CO in the impact region. Moreover, it was found that the 4σ- and 5σ- derived states of CO at hollow sites on Ni(111) are strongly modified in space by mixing with each other, where considerable charge transfer occurs from the C site to the O site in the 5σ-derived state and in the opposite way in the 4σ-derived state. In contrast, such a strong charge redistribution was not seen in the cases of terminal CO on Ni(100) and Cr(CO)6. These findings were in good accordance with the crystal orbital overlap population obtained by density functional theory through a generalized gradient approximation.

Photochemically Induced Silicon−Carbon Bond Cleavage in a Dimethylsilyl-Bridged Dicyclopentadienyl Diruthenium Complex

The synthesis and X-ray crystal structure of the novel permethylated dimethylsilyl-bridged diruthenium complex Me2Si[(C5Me4)Ru(CO)2]2 (1) is reported. The molecular structure displays a metal−metal bond of 2.7121(4) Å, which is supported by two symmetrical μ-bridging CO groups and, in addition, two terminal carbonyl ligands. In solution, exchange of these carbonyl groups is observed, as shown by 13C NMR EXSY and VT IR-measurements. It is suggested that the exchange process proceeds via the energetically disfavoured intermediate 1a, which displays four terminal CO ligands. This view is supported by density functional calculations, which indicate a C2-symmetrical structure for 1a. Photochemically induced cleavage of the silicon−carbon and Ru−Ru bonds in 1 results in complex 3, which is thermodynamically uphill from 1 according to our DFT calculations. The molecular structure of complex 3 was unambiguously confirmed by X-ray crystallography.

Ship-in-bottle synthesis of anionic Rh carbonyls in faujasites

Direct carbonylation of [Rh(NH 3) 5Cl] 2+ ion exchanged in sodium and potassium faujasites yields carbonyls, the composition of which depends on the extent of dehydration before carbonylation, and on the carbonylation temperature. Polynuclear anionic Rh carbonyls are formed at 25–100°C, if the water amount is sufficient. Greenish color of the species created at 75–100°C in NaX, KX and KY points to the [Rh 6(CO) 15] 2− complex; at 50°C a white carbonyl is formed in NaX which structure seems to differ from the green complex in CO configuration. The anionic character of this species also follows from the lower wavenumber of terminal CO ligands in X zeolites and in KY compared to polynuclear neutral Rh carbonyl formed in less basic NaY. Carbonylation at 70–100°C after dehydration or carbonylation at 160–200°C lead to the formation of [Rh(CO) 2] +. This carbonyl reacts to the polynuclear complexes at 25–100°C after readsorption of water vapors. Individual carbonyl types once formed can be interchanged by varying the temperature and water amount. In addition to the FTIR spectroscopy, UV/VIS measurements and mass spectrometric analysis of ammonia released during the thermal decomposition of carbonyls were also employed.

Ligand effects on the structures of Rh6(CO)15L clusters

The crystal and molecular structures of the hexarhodium carbonyl clusters Rh6(CO)15L (L = P(OPh)3, 1; P(4-XC6H4)3, (X = CF3, 2; Cl, 3; F, 4; OMe, 5); P(nBu)3, 6; Me2SO, 7; MeCN, 8; C8H14, 9) have been determined by single crystal X-ray crystallography. Redetermination of the structure of the parent Rh6(CO)16 cluster, 10, has also been performed and all the results are compared with those for the rather disparate group of monosubstituted derivatives reported earlier. The structures all relate closely to that of the parent which has an octahedral array of Rh atoms with four opposite faces triply bridged by CO ligands. Each Rh atom also has two terminal CO groups attached. The substituents simply replace one of the terminal COs. A group of ligands, comprised of the P-donors and cyclooctene, all show distortions with a high degree of stereoselectivity in the vicinity of the substitution site, and demonstrate the significantly local character of the effect. The effects on the terminal CO groups are mainly limited to the CO attached to the substituted Rh atom for which there is a clear decrease in the Rh–CO distance and a smaller lengthening of the C–O distance. The triangle of Rh atoms that contains the substituted Rh atom, with the substituent projecting above that triangle, shows a pronounced lengthening of the Rh–Rh bonds cis to the heteroligand. There is an equally pronounced shortening of the Rh–Rh bond across the triangle from the substituted Rh atom. A third effect is the displacement of the CO groups in triply bridged Rh3 triangles containing the RhL moiety, so that they almost doubly bridge the two Rh–Rh bonds cis to the substituted Rh atom. Although no clear correlations exist within this group of substituents the localized effects can generally be associated with an increase of electron density on the substituted Rh atom. The other monosubstituted clusters that contain quite different neutral and anionic heteroligands do not display common trends in the structural distortions induced by the substituents, and this is evidently due to the very varied nature of the ligands within this group.

Local Electron Distribution of CO Adsorbed on Ni(100) and Ni(111) Surfaces Studied by Metastable Atom Electron Spectroscopy.

Electron emission spectra caused by thermal collisions of He* (23S) metastable atoms with Ni(100)c(2×2)-CO and Ni(111)c(4×2)-CO were measured to probe the local electron distribution. Our data showed that the 4σ- and 5σ-derived states of CO at hollow sites on Ni(111) are strongly modified in space by mixing with each other, where considerable charge transfer occurs from the C atom to the O atom in the 5σ-derived state and in the opposite way in the 4σ-derived state. In contrast, such a heavy charge redistribution was not seen in the case of terminal CO on Ni(100). These findings were in good accordance with the crystal orbital overlap population obtained by density functional theory within the generalized gradient approximation.

Reaction of Fe2(CO)9with Lithium: Preparation and Structures of Compounds with Strong Ion Pairing

The reduction of Fe2(CO)9 with elemental lithium in THF solution at room temperature generates the dinuclear complex [Li2(THF)6Fe2(CO)8] (1), in which the Li atoms are bonded to the oxygen atoms of bridging CO groups. Dissolution of 1 in toluene leads to loss of two THF molecules to give the polymeric complex [Li2(THF)4Fe2(CO)8]n (2); dimeric units (n = 2) are formed with the help of a planar Li2O2 ring, and these units are further linked by Li−O contacts to terminal carbonyl groups. Alkylation of 1 with MeSO3CF3 yields the known dinuclear compound [(CO)3Fe(μ-C(Me)O)2Fe(CO)3] (4). Treatment of 1 with Me3SnCl leads to splitting of the Fe−Fe bond, resulting in cis-[CO)4Fe(SnMe3)2] (6) as the main product. The X-ray structures of 1, 2, and 4 are presented along with the structure of the sodium salt [Na2(THF)4Fe2(CO)8]n (5), which has only terminal CO groups.

Reduction of a CO Ligand in an Iron Phosphonate Complex with a Neutral Borane Compound. Formation of a Formyl Complex with Intramolecular Coordination to a Boron Atom

Treatment of Cp(CO)2Fe{P(O)(OMe)2} with an electrically neutral hydroborane, 9-borabicyclo-3,3,1-nonane, yielded (1), with a terminal CO ligand reduced. The X-ray structure analysis revealed that 1 includes intramolecular coordination of the formyl oxygen to the boron atom to form a six-membered metallacycle, which would stabilize the complex as a whole.

The reactions of cis-[Fe 2(η-C 5H 5) 2(CO) 2(μ-CNMe 2) 2][SO 3CF 3] 2 and related compounds with nucleophiles

The terminal CO ligands in the cis-[Fe 2(η-C 5H 5) 2(CO) 2(μ-CNMe 2) 2] 2+ cation are both labile and susceptible to nucleophilic attack at carbon depending on the nucleophile and the reaction conditions. The CO substitution is effected by nucleophiles L such as organonitriles, acetone or tertiary phosphines to give [Fe 2(η-C 5H 5) 2(CO)(L)(μ-CNMe 2) 2][SO 3CF 3] 2 and [Fe 2(η-C 5H 5) 2(L) 2(μ-CNMe 2) 2][SO 3CF 3] 2 salts. Coordinated acetone is replaced by organonitriles and these in turn are displaced by phosphines. These reactions may be brought about thermally or more reliably by photolysis. The consequences of varying the UV lamp power and the nature of the phosphine are reported. Similar reactions take place with cis-[Fe 2(η-C 5H 5) 2(CO) 2{μ-CN(H)Me}(μ-CNMe 2)][SO 3CF 3] 2 and cis-[Fe 2(η-C 5H 5) 2(CO) 2(μ-CNH 2)(μ-CNMe 2)][SO 3CF 3] 2 salts, but phosphines deprotonate the μ-CNH 2 ligand and lead to decomposition. Harder nucleophiles Nu − such as OH −, OR − (from NaCN–ROH) or NHR − (from RNH 2) deprotonate the μ-CN(H)Me and μ-CNH 2 ligands but do not de-methylate the μ-CNMe 2 ligand to any great extent. Instead they attack one terminal CO ligand of cis-[Fe 2(η-C 5H 5) 2(CO) 2(μ-CNMe 2) 2][SO 3CF 3] 2 to give cis-[Fe 2(η-C 5H 5) 2(CO){C(O)Nu}(μ-CNMe 2) 2][SO 3CF 3] with no evidence for attack elsewhere in the molecule. When RNH 2C 6H 11NH 2, the reaction work-up may be modified so that [Fe 2(η-C 5H 5) 2(CO)(CNC 6H 11)(μ-CNMe 2) 2][SO 3CF 3] 2 and [Fe 2(η-C 5H 5) 2(CNC 6H 11) 2(μ-CNMe 2) 2][SO 3CF 3] 2 are the products. They result from the dehydration of the first-formed carbamoyl complexes; a reaction which does not take place with the more volatile i PrNH 2. The mechanism of the reactions and the spectra of the products are discussed.

Hexacarbonyldiplatinum(I). Synthesis, Spectroscopy, and Density Functional Calculation of the First Homoleptic, Dinuclear Platinum(I) Carbonyl Cation, [{Pt(CO)3}2]2+, Formed in Concentrated Sulfuric Acid

The dissolution of PtO2 in concentrated H2SO4 under an atmosphere of CO results in the formation of hexacarbonyldiplatinum(I), [{Pt(CO)3}2]2+ (1), the first homoleptic, dinuclear, cationic platinum carbonyl complex, of which a prolonged evacuation leads to reversible disproportionation to give cis-[Pt(CO)2]2+(solv) (2) and Pt(0). 1 has been completely characterized by NMR (13C and 195Pt), IR, Raman, and EXAFS spectroscopy. The structure of 1 is rigid on the NMR time scale at room temperature. NMR: δ(13CA) 166.3, δ(13CB) 158.7, δ(195Pt) −211.0 ppm; 1J(Pt−CA) = 1281.5 Hz, 1J(Pt−CB) = 1595.7 Hz, 1J(Pt−Pt‘) = 550.9 Hz. The strongly polarized, sharp Raman band at 165 cm-1 (ρ = ca. 0.25) indicates the presence of a direct Pt−Pt bond. The IR and Raman spectra in the CO stretching region are entirely consistent with the presence of only terminal CO's on a nonbridged Pt−Pt bond with D2d symmetry. ν(CO)IR: 2174 (E), 2187 (B2), and 2218 cm-1 (B2); ν(CO)Raman: 2173 (E), 2194 (B2), 2219 (B2), 2209 (A1) and 2233 cm-...

Reactions of the dirhenium(II) complexes Re 2X 4(μ-dppm) 2 (X=Cl, Br; dppm =Ph 2PCH 2PPh 2) with isocyanides : Part XX . Oxidation of the complexes Re 2X 4(μ-dppm) 2(L) (X=Cl or Br; dppm=Ph 2PCH 2PPh 2; L= t-BuNC, XylNC or CO) to the edge-sharing bioctahedral dirhenium(III) cations [Re 2(μ-X) 2(μ-dppm) 2X 3(L)] +

The reactions of the halogens X 2 (X=Cl or Br) with the diamagnetic dirhenium(II) complexes Re 2X 4(μ-dppm) 2(L), where dppm=Ph 2PCH 2PPh 2, X=Cl or Br, and L=XylNC (xylyl isocyanide), t-BuNC or CO, and with salts of the edge-sharing bioctahedral species [Re 2X 3(μ-dppm) 2(CO)(NCMe) 2] +, provide convenient routes to the dirhenium(III) species [Re 2X 5(μ-dppm) 2(L)] +. These cations, where L=XylNC, t-BuNC or CO, have been isolated as their halide (Cl − or Br 3 −), [PF 6] − and [O 3SCF 3] − salts. IR spectroscopy shows that terminal RNC and CO ligands are present, and a crystal structure determination of the complex [Re 2Cl 5(μ-dppm) 2(CO)]PF 6 confirms that the cation has the edge-sharing bioctahedral structure [Re 2(μ-Cl) 2(μ-dppm) 2Cl 3(CO)] + with a formal ReRe bond (ReRe distance=2.6607(4) Å). 31P-NMR spectroscopy indicates that these salts are weakly paramagnetic, with their P resonances exhibiting unusually large upfield shifts.

Synthesis and characterization of high-nuclearity iridium–ruthenium and –gold mixed-metal carbonyl clusters, [Ir7Ru3(CO)23]−, [Ir7Ru3(CO)23(AuPPh3)] and [Ir6Ru3(CO)21(AuPPh3)]−, possessing tetrahedrally capped octahedral iridium cores obtained by capping reactions with [Ru3(CO)12] and [AuCl(PPh3)

The new carbonyl cluster [PPh4][Ir7Ru3(CO)23] 1 has been obtained by the high yield reaction of [PPh4]2[Ir6(CO)15] with [Ru3(CO)12] in the presence of p-toluenesulfonic acid. The monoanionic decanuclear cluster 1 has an octahedral arrangement of the iridium atoms with three ruthenium atoms and an iridium atom tetrahedrally capping four triangular faces. Two terminal CO ligands are bound to each iridium atom and three to each ruthenium atom. In this synthesis p-toluenesulfonic acid served as a degradation reagent for [Ir6(CO)15]2− to generate the capping {Ir(CO)2}+ moiety. Reaction of 1 with [AuCl(PPh3)] in the presence of AgOSO2CF3 at ambient temperature yielded the undecanuclear neutral cluster [Ir7Ru3(CO)23(AuPPh3)] 2. The {AuPPh3}+ group co-ordinates to the apical iridium atom of the parent metal carbonyl monoanion 1 maintaining the cluster framework as well as the stereogeometry of the CO ligands. Thermal treatment of 1 with [AuCl(PPh3)] in refluxing 1,2-dichloroethane caused substitution of the capping {Ir(CO)2}+ group in 1 with an isolobal {AuPPh3}+ group, resulting in the formation of decanuclear monoanionic cluster [PPh4][Ir6Ru3(CO)21(AuPPh3)] 3.

Coupling of Carbomethoxy and Vinylidene Ligand in Molybdenum Complexes

Treatment of [Cp(dppe)(CO)MoCC(Ph)CH2CHCH2]I (2) with MeONa caused nucleophilic attack to occur at the terminal CO ligand. This is followed by a coupling reaction of the resulting carbomethoxy group with Cα of the vinylidene ligand accompanied with coordination of the terminal olefin to afford Cp(dppe)MoC(COOMe)C(Ph)CH2CHCH2 (5). Similar coupling was observed when [Cp(dppe)(CO)MoCC(Ph)CH2Ph]I (3) was treated with MeONa, but the reaction afforded the neutral allylic complex Cp(dppe)Mo[CH(COOMe)C(Ph)CHPh] (6). The structures of complexes 5 and 6 have been determined by X-ray diffraction analysis.

Parsec-Scale CO Outflow and H[TINF]2[/TINF] Jets in Barnard 5

New observations of the Barnard 5 IRS 1 molecular outflow, including maps in the 12CO J = 2–1 transition and images and high-resolution spectra in the H2 v = 1–0 S(1) line, are presented. In the 12CO J = 2–1 maps, the outflow has a projected length of over 30' (3 pc) and is highly collimated with a width smaller than 2' (0.2 pc), with one outflow lobe containing clear evidence of a limb-brightened cavity. Like the associated Herbig-Haro flow, the CO lobes exhibit C-shaped symmetry about IRS 1. Bow- or cone-shaped clumps, which are not associated with visible shocks, are located at the ends of the CO outflow. While the presence of Herbig-Haro objects and associated shock excited H2 emission in the outer parts of the CO flow several arcminutes closer to the source indicate that a relatively recent mass-loss episode is still transferring momentum to CO-bearing gas, these terminal CO structures may provide a fossil record of a much older mass-loss episode. The new observations provide support for bow shock entrainment models for the acceleration of CO-bearing gas. Several 15' long 12CO-emitting filaments lie parallel to but displaced by several arcminutes from the IRS 1 outflow. These features may trace perturbations excited by magnetosonic waves triggered by major mass-loss eruption episodes of IRS 1. The terminal H2 emission closely traces the Hα and [S II] emission produced by Herbig-Haro objects located near the ends of the main CO outflow body and is likely to be powered by shocks. However, the H2 emission is systematically displaced downstream from the Herbig-Haro objects. Since the B5 outflow appears to lie within 13° of the plane of the sky, this displacement is not likely to be a geometric projection effect. The specific excitation mechanism may require heating by a magnetic precursor or fluorescence produced by radiation originating in the shocks associated with the Herbig-Haro objects. A compact chain of H2 knots located within 30'' of IRS 1 appears to delineate a bipolar jet originating from this source. This H2 feature and the associated Hα emission bisects the limb-brightened CO cones found within 20'' of IRS 1. The presence of both axial knots and a wide-angle cavity implies that the central source may simultaneously power both a jet and a wide-angle wind that are formed within 2000 AU of IRS 1. A new method that accounts for the velocity dependence of the 12CO optical depth is used to estimate the mass in the outflow lobes. The resulting power-law mass spectra have slopes that are much steeper than those obtained by assuming that the 12CO line is optically thin in the outflow lobes, an assumption that has been frequently used in other studies. The flow orientation, the outflow evolution, and the velocity at which the outflow lobes becomes optically thin also affect the mass spectrum. The source luminosity, outflow dynamic timescale, outflow strength, and embedded nature of IRS 1 imply that it is in an intermediate evolutionary stage between a Class I and Class 0 source. We also present a new optical spectrum of HH 367, which originates from IRS 3, confirming its Herbig-Haro nature and showing evidence for different excitation conditions along the flow and variable mass ejection rates from the source.

Reaction patterns of ‘tetraferrio-azaallenium’, [(OC) 3Cp 2Fe 2(μ 4-CNC)Fe 2Cp 2(CO) 3] +, and its ‘activated cyanide’-precursor (μ-phthalimidocarbyne)tricarbonyldicyclopentadienyldiiron(1+)

(μ-Phthalimidocarbyne)tricarbonyldicyclopentadienyldiiron(1+) ( 2) which, due to the facile cleavage with cis-[Fe 2Cp 2(CN)(μ-CO) 2CO] − ( 1) of its μ-CN bond to give ‘tetraferrio-azaallenium’ [(OC) 3Cp 2Fe 2(μ 4-CNC)Fe 2Cp 2(CO) 3] + ( 3), has been termed ‘activated cyanide’ reacts with pyrrolidine with ring opening to give the μ-acylisocyanide complex 5 carrying a further amido function in the o-position. Butyllithium gives rise to only traces of the corresponding mono deacylation product 6 while the main product is 3. Formation of complex 3 which is presumed to occur via partial bis-deacylation of 2 to give 1 and subsequent recombination with loss of phthalimide also dominates the reactions of 2 with CN − and [W(CN)(CO) 5] −. Here, however, the nucleophile also attacks the μ-carbyne carbon atom to give moderate yields of the desired μ-cyanoalkyliden complexes 7 and 10, the latter with [W]CN↔[W]NC isomerization and C–C bond formation. With [Cr(CN)(CO) 5] −, in contrast, substitution of a terminal CO ligand occurs with formation of the cyano-bridged trinuclear complex 9. The structures of complexes 7, 9 and 10 have been elucidated by X-ray analysis. Action upon ‘tetraferrio-azaallenium’ 3 of the primary amines H 2NCH 2CH 2R (R=Me, OMe, Ph) gives rise in low yields to the respective terminal isocyanides in compounds 11– 13. Here as in the reaction with NaNH 2 to give 14, a terminal carbonyl ligand is converted into an isocyanide or, respectively, cyano ligand by an exchange of oxygen for NR (N −). A second though less efficient approach to 14 is CO substitution in 3 by NaCN. Disubstitution of 3 to give 15 is observed with trimethylphosphite. In the reactions of 3 with diamines (H 2NCH 2CH 2NH 2, H 2NCH 2CH 2CH 2CH 2NH 2), on the other hand, cluster fragmentation occurs with formation of the mononuclear complexes 16 and 17 containing cyclic diaminocarbene ligands. A cyclic μ-aminocarbyne diiron complex 18 is obtained in traces from 3 and pyrrolidine.

Palladium(I) Carbonyl Cation-Catalyzed Carbonylation of Olefins and Alcohols in Concentrated Sulfuric Acid

A new palladium catalyst was found to exhibit high catalytic activity for carbonylation of olefins and alcohols. cyclo-Bis(μ-carbonyl)dipalladium(I) cation (1) with bridging CO ligands is formed by reductive carbonylation of palladium sulfate, PdSO4, in concentrated H2SO4. When an olefin or alcohol is added, complex 1 changes to a new complex (2) with terminal CO ligands, and tertiary carboxylic acids are obtained in high yields at room temperature and atmospheric pressure of CO. IR and 13C NMR studies suggest that complex 2 may be tentatively formulated to be [Pd2(CO)2]2+, in which the terminal CO ligands are chemically equivalent. Complex 1 is a catalyst precursor, and complex 2 functions as an active species for the carbonylation of olefins and alcohols. The catalytic behavior of the palladium carbonyl catalyst supports the recently proposed reaction mechanism involving an olefin−metal−CO complex as an intermediate for the catalytic carbonylation of olefins and alcohols in strongly acidic solution.

Ruthenocenyl ruthenium bimetallic complexes: electrospray mass spectrometric study of [RuX( η5-C 5H 5)( η2-dppr)] n+ (dppr=1,1′-bis(diphenylphosphino)ruthenocene) (X=Cl, n=0; X=CO, CH 3CN, CCHPh, n=1) and the X-ray crystal and molecular structure of [Ru( η5-C 5H 5)(CO)( η2-dppr)]PF 6

[RuCl(Cp)(PPh 3) 2] (Cp= η 5-C 5H 5) reacts with dppr in refluxing benzene to give [RuCl(Cp)(dppr)], 1, {dppr=[Ru( η 5-C 5H 4PPh 2) 2]} in 91% yield. Complex 1 ionizes in boiling acetonitrile in the presence of excess NH 4PF 6 to give [Ru(Cp)(CH 3CN)(dppr)]PF 6, 2, in 76% yield. Under CO at 60°C, 1 converts to [Ru(Cp)(CO)(dppr)]Cl, 3a, whose derivative [Ru(Cp)(CO)(dppr)]PF 6, 3b, can also be obtained from 2 in 86% with CO. With HCCPh, 2 instantaneously gives a vinylidene complex, [Ru(CCHPh)(Cp)(dppr)]PF 6, 4, quantitatively (98%). The kinetic stability of the η 2-coordinated dppr ring is evident in these reactions. The X-ray molecular structure of 3b [space group P2 1/ c, a=9.990(2), b=19.498(4), c=19.113(4) Å and β=96.21(3)°] reveals a pseudo-octahedral Ru(II) structure with a η 5-Cp, a chelated dppr, a terminal CO and an uncoordinated PF 6 − anion. It is the first piano-stool dppr structure characterized by X-ray single-crystal diffractometry. The dppr chelate has a large bite (100.5(1)°) and there is no direct interaction between the two Ru(II) centers (Ru(1)⋯Ru(2) 4.389 Å). The electrospray mass spectra (ESMS) of 2–4 generally give peaks due to the intact cations at low cone voltages. As the cone voltage increases, fragmentation commences which inevitably gives [Ru(Cp)(dppr)] + as the primary fragment ion. In-situ doping of dppr with AgNO 3 gives [Ag(dppr)] + as the major species plus [Ag(dppr) 2] + ( m/z 1307) and other oxidized by-products. Similar treatment of 4 gives an acetylide complex [Ag{Ru(Cp)(CCPh)(dppr)} 2] + ( m/z 1843) at 20 V which ejects one Ru metalloligand to give [Ag{Ru(Cp)(CCPh)(dppr)}] + ( m/z 975) at higher voltages. Complex 4 is hydrogenated with H 2 gas to give ethylbenzene in 55% yield after 4 h in refluxing THF. It also catalyzes the hydrogenation of HCCPh to give 52% of ethylbenzene in 5 h at 5 mol.% catalyst level.

Oxidative-Addition Reactions of Diiodine to Dinuclear Rhodium Pyrazolate Complexes.

The pyrazolato (Pz) rhodium(I) complexes [{Rh(&mgr;-Pz)(CO)(L)}(2)] (L = CNBu(t), P(OMe)(3), PMe(2)Ph, P(OPh)(3), P(p-tolyl)(3)) result from the reaction of [{Rh(&mgr;-Pz)(CO)(2)}(2)] with the appropriate L ligand in a trans:cis ratio ranging from 60:40 (L = CNBu(t)) to 95:5 (L = P(p-tolyl)(3)). The pure trans isomers add 1 molar equiv of diiodine to give the dirhodium(II) complexes [{Rh(&mgr;-Pz)(I)(CO)(L)}(2)] (L = CNBu(t) (6), P(OMe)(3) (7), PMe(2)Ph (8), P(OPh)(3) (9)). These complexes incorporate two iodide ligands trans to the rhodium-rhodium bond, as substantiated by the X-ray structure for 7, while the complex [(P{p-tolyl}(3))(CO)(I)Rh(&mgr;-Pz)(2)(&mgr;-CO)Rh(I)(P{p-tolyl}(3))] (10) contains a bridging ketonic CO ligand, due to the insertion of a terminal CO into the metal-metal bond. The metal-metal bond formation involves a 2e oxidation, since identical compounds (6-9) are obtained by oxidation with [Fe(Cp)(2)](PF(6)) followed by addition of potassium iodide. Further reactions of the dirhodium(II) complexes 6-9 with diiodine leading to the metal-metal rupture are electrophilic additions, as exemplified by the reactions with the positive iodine complex [I(Py)(2)](+). They start at the "endo site" (the metal-metal bond) if it is sterically accessible to the electrophile, to give directly the dirhodium(III) complexes [{Rh(&mgr;-Pz)(I)(CO)(L)}(2)(&mgr;-I)](+) (L = CNBu(t), CO). Otherwise, as for the complexes with P-donor ligands, abstraction of a iodide ligand trans to the metal-metal bond (the "exo site") occurs first, to give the dirhodium(II) cationic complexes [(PR(3))(CO)(I)Rh(&mgr;-Pz)(2)Rh(CO)(PR(3))](+) and triiodide. These react again with diiodine to give dirhodium(III) complexes [{Rh(&mgr;-Pz)(I)(CO)(PR(3))}(2)(&mgr;-I)](+) similar to those described above, but with triiodide or pentaiodide as counterion, as substantiated by the X-ray structure of [{Rh(&mgr;-Pz)(I)(CO)(PMe(2)Ph)}(2)(&mgr;-I)]I(5) (18). The diiridium(II) complexes [{Ir(&mgr;-Pz)(I)(CO)(PR(3))}(2)] (PR(3) = P(OPh)(3), PMe(2)Ph) also react with diiodine to give the cationic diiridium(III) complexes [{Ir(&mgr;-Pz)(I)(CO)(PR(3))}(2)(&mgr;-I)]I(3) through a reaction pathway involving the "exo site", while no reaction is observed for [{Ir(&mgr;-Pz)(I)(CO)(2)}(2)]. Finally, replacement of a carbonyl ligand in [{Rh(&mgr;-Pz)(I)(CO)(L)}(2)(&mgr;-I)](+) (L = CNBu(t), CO) by iodide gives the compounds [(CO)(L)(I)Rh(&mgr;-Pz)(2)(&mgr;-I)Rh(I)(2)(L)].