Chromium Hexacarbonyl Research Articles

Stabilization of Binuclear Chromium Carbonyls by Substitution of Thiocarbonyl Groups for Carbonyl Groups: Nearly Linear Structures for Cr2(CS)2(CO)9

The chromium carbonyl thiocarbonyls Cr(CS)(CO)(n) (n = 5, 4, 3) and Cr(2)(CS)(2)(CO)(n) (n = 9, 8, 7, 6) were studied by density functional theory (DFT). The expected octahedral structure was found for the known Cr(CS)(CO)(5). The structures for the unsaturated derivatives Cr(CS)(CO)(n) (n = 4, 3) are derived from the octahedral Cr(CS)(CO)(5) by removal of one or two carbonyl groups, respectively. The lowest energy structures for the binuclear derivatives Cr(2)(CS)(2)(CO)(n) (n = 9, 8, 7, 6) all contain four-electron donor bridging eta(2)-mu-CE (E = O, S) groups. For the formally saturated Cr(2)(CS)(2)(CO)(9), no chromium-chromium bond is then required to give the chromium atoms the favored 18-electron configuration. This leads to a uniquely linear Cr-C-O-->Cr arrangement or bent Cr-C-S-->Cr arrangement (C-S-->Cr angle of approximately 110 degrees ) with a long clearly nonbonding Cr...Cr distance. A similar structural feature is found in the known stable arene-chromium carbonyl thiocarbonyl (eta(6)-MeC(6)H(5))Cr(CO)(2)[CS-->Cr(CO)(5)]. The lowest energy structures for the formally unsaturated Cr(2)(CS)(2)(CO)(n) (n = 8, 7, 6) are predicted to have one (n = 8) or two (n = 7, 6) four-electron donor eta(2)-mu-CS groups with a Cr-Cr single bond (n = 8 and 7) or Cr horizontal lineCr double bond (n = 6) to give both chromium atoms the favored 18-electron configuration. The lowest energy structures for the binuclear Cr(2)(CS)(2)(CO)(n) (n = 9, 8, 7, 6) are all predicted to be stable with respect to fragmentation into mononuclear Cr(CS)(CO)(m) in contrast to the homoleptic Cr(2)(CO)(11). This suggests that there is a reasonable chance that at least some of the binuclear Cr(2)(CS)(2)(CO)(n) (n = 9, 8, 7, 6) derivatives will be synthesized as stable or at least detectable molecules.

Valence ionization spectra of group six metal hexacarbonyls studied by the symmetry-adapted cluster-configuration interaction method

The valence ionization spectra up to 20 eV of group six metal carbonyls, chromium hexacarbonyl, molybdenum hexacarbonyl, and tungsten hexacarbonyl were studied by the symmetry-adapted cluster-configuration interaction (SAC-CI) method. The assignments of the spectra are given based on reliable SAC-CI calculations. The relativistic effects including the spin-orbit effects are important for the ionization spectrum of W(CO)(6). The relation between the metal-CO distance and ionization energies was examined. The lowest ionization energies of the three metal carbonyls are approximately the same because of the energy dependence of the metal-CO length and relativistic effects. In Cr(CO)(6), the Cr-CO interaction significantly increases the lowest ionization energy in comparison with Mo(CO)(6) and W(CO)(6) because of the relatively short metal-CO bond length. The relativistic effect reduces the lowest ionization energy of W(CO)(6) because the effective core potential of 5d electrons is more efficiently screened as a result of the relativistic contraction of the inner electrons.

Phase formation in gas-phase combustion and pyrolysis reactions under spark and radio-frequency discharge conditions

Doped ultrafine silicon dioxide powder with a narrow particle size distribution was obtained by RF discharge-stimulated dichlorosilane (SiH2C) oxidation at a low pressure using isobutylene as the combustion inhibitor and chromium hexacarbonyl (Cr(CO)6) as the dopant. The formation and morphology of the ultrafine particles are governed by the parameters of the RF discharge and by the chemical mechanism of the combustion reaction yielding the aerosol. Submicron-sized filamentous carbon structures can be obtained by isobutylene decomposition under spark discharge conditions in the presence of a molybdenum metal catalyst.

Effect of the vapors of organometallic compounds on the processes of ignition and combustion of hydrogen, propylene, and natural gas

It is established that small additions (∼10−1%) of hexacarbonyls of chromium and molybdenum promote combustion of the stoichiometric 2H2 + O2 mixture, which manifests itself in a decrease in the lower limit of initiated ignition by the pressure and in an increase in the visible propagation rate of the flame. However, inhibition of oxidation of propylene by these additives takes place. This fact means that the role of hydrogen atoms in the development of chains during flame propagation in hydrocarbon-air mixtures is not determining. Therefore, the kinetic mechanism inhibiting combustion of hydrocarbons by carbonyls based on accounting for termination of hydrogen atoms, which is suggested in the literature, should be refined. In the flame of oxidation of hydrogen in the presence of chromium hexacarbonyl, excited chromium atoms are found. Comparison of the inhibiting efficiency of the vapors of ferrocene Fe(C5H5)2, butyrylferrocene C14H16FeO, carbonyls of metals and their mixture with the vapors of sulfur hexafluoride SF6, and a series of halogen-substituted hydrocarbons (CF2Cl2, C4H9J, CCl4, CHCl3) on combustion of mixtures of natural gas with air is performed.

Development of Ultrafast Photochromic Organometallics and Photoinduced Linkage Isomerization of Arene Chromium Carbonyl Derivatives

We review recent studies of processes relevant to photoinduced linkage isomerization of organometallic systems with the goal of preparing organometallics with an efficient and ultrafast photochromic response. The organometallic system thus corresponds to two linkage isomers with different electronic environments that are responsible for different optical properties. Much of this work has focused on examining processes following irradiation of cyclopentadienyl manganese tricarbonyl derivatives (compounds 3-21) including solvent coordination, thermal relaxation, solvent displacement by tethered functional groups (chelation), dissociation of tethered functional groups, and linkage isomerization. A new platform is investigated for obtaining a photochromic response in new experiments with arene chromium dicarbonyl complexes. A photochromic response is observed for arene chromium dicarbonyl complexes with tethered pyridine and olefin functional groups based on light-driven linkage isomerization on the nanosecond time scale. Irradiation at 532 nm of 23 ([Cr{eta(6)-C(6)H(5)CH(2-Py-kappaN)CH(2)CH=CH(2)}(CO)(2)]) (Py = pyridine) results in the isomerization to 22 ([Cr{eta(6)-C(6)H(5)CH(2-Py)CH(2)-eta(2)-CH=CH(2)}(CO)(2)]), and 355 nm irradiation isomerizes 22 to 23. The ultrafast linkage isomerization has been investigated at room temperature in n-heptane solution on the picosecond to microsecond time scale with UV- or visible-pump and IR-probe transient absorption spectroscopy by comparing the dynamics with model compounds containing only a tethered pyridine. Irradiation of 24 ([Cr{eta(6)-C(6)H(5)(CH(2))(3)(2-Py)}(CO)(3)]) and 25 ([Cr{eta(6)-C(6)H(5)(CH(2))(2)(2-Py)}(CO)(3)]) at 289 nm induces CO loss to immediately yield a Cr-heptane solvent coordinated intermediate of the unsaturated Cr fragment, which then converts to the kappaN(1)-pyridine chelate within 200 and 100 ns, respectively. Irradiation of 26 ([Cr{eta(6)-C(6)H(5)CH(2)(2-Py)}(CO)(3)]) also induces CO loss to immediately yield three species: the Cr-heptane solvent coordinated intermediate, a kappaN(1)-Py nitrogen chelate, and an agostic eta(2)-chelate in which the pyridine is coordinated to the metal center via a C-H agostic bond as opposed to the nitrogen lone pair. Both the transient Cr-heptane coordinated intermediate and the agostic pyridine chelate convert to the stable kappaN(1)-pyridine chelate within 50 ns. Similar reaction dynamics and transient species are observed for the chelate 33 ([Cr{eta(6)-C(6)H(5)CH(2)(2-Py)-kappaN}(CO)(2)]) where a Cr-Py bond, not a Cr-CO bond, initially cleaves.

Reactions of Complex Ligands. Part 107 Densely Substituted Hydroquinoid Phenanthrene and Triphenylene Cr(CO)3 Complexes: Chromium‐Templated Synthesis and Molecular Structure

AbstractDensely substituted hydroquinoid phenanthrene (10–18), acephenanthrene (19), and triphenylene chromium tricarbonyl complexes (20–22) have been prepared via benzannulation of naphthalenyl (1–7), acenaphthenyl (8) and phenanthrenyl carbene complexes (9), respectively. The naphthalenyl, acenaphthenyl and phenanthrenyl carbene complexes 1–9 were obtained in 52–88 % yield starting from commercially available bromoarenes by dehalolithiation, addition of hexacarbonyl chromium to the lithioarene and O‐alkylation of the resulting acyl chromates with trimethyloxonium tetrafluoroborate (Fischer route). The benzannulation of the aryl carbene complexes (either with 3‐hexyne / (t‐butyl)dimethylsilyl chloride or with (t‐butyl)dimethylsilylethyne) allowed the regiospecific synthesis of the oligocyclic hydroquinoid arene tricarbonyl chromium complexes 10–22 in 44–94 % yield thus providing a two‐step synthesis with overall yields of 18 ‐ 80 %. Under the kinetic reaction conditions used the metal atom is exclusively coordinated to the persubstituted terminal hydroquinoid ring. The molecular structures of phenanthrene complexes 10, 12–14, and 16, acephenanthrene complex 19, and triphenylene complexes 20 and 21 in the solid state have been determined by X‐ray crystallography. The carbonyl ligands either adopt an eclipsed (10, 12, 14, 16, 19, 20) or staggered (13, 21) exo‐conformation pointing away from the center of the phenanthrene, acephenanthrene and triphenylene ligands, respectively. The coordination of the metal atom to the hydroquinoid ring is unsymmetric with the largest metal‐carbon distances found between the chromium atom and one bridgehead carbon and the ring carbon atom bearing the bulky (t‐butyl)dimethylsilyloxy (TBDMSO) substituent.

Synthesis and reactivity of metal carbene complexes with heterobiaryl spacer substituents

Mono- and binuclear Fischer carbene complexes, [M(CO)5{C(OR)Ar-ArX}], X = H, {C(OR)M'(CO)5}; M, M' = W or Cr; R = Me, Et or (CH2)4OMe; Ar = thiophene, N-methylpyrrole or furan units 1-20, were synthesized. For this purpose, mono-, bi- or stepwise lithiated bithiophene, N,N'-dimethylbipyrrole, thienylfuran and N-methyl(thienyl)pyrrole were reacted with chromium and tungsten hexacarbonyl precursors. Dilithiation in the 2- and 9-positions of N-methyl(thienyl)pyrrole could not be achieved. Alkylation of acyl metallates with triethyloxonium tetrafluoroborate or methyl trifluoromethanesulfonate in THF afforded not only the expected carbene complexes with ethoxy or methoxy substituents, but in the case of bithiophene with methyl trifluoromethanesulfonate, carbene complexes with alkoxy substituents incorporating a ring-opened tetrahydrofuran moiety. X-Ray crystallographic structure determinations were performed on [W(CO)5{C(OMe)(thienylfuran)}] (14), [W(CO)5{C(OMe)(N-methylthienylpyrrole)}] (20) and [{W(CO)5}2{mu-C(OEt)(N,N'-dimethylbipyrrolylC(OEt)}] (12) to assess the role of the heterobiaryl substituent on the structural features of the carbene ligand in the complexes. Complexes [{Cr(CO)5}2{mu-C(OMe)bithienylC(OEt)}] (3), [(CO)5Cr{mu-C(OMe)bithienylC(OMe)}W(CO)5] (5) and [{Cr(CO)5}2 {mu-C(OMe)thienylfuranC-(OMe)}] (15) were reacted with 3-hexyne to study their behaviour in benzannulation reactions. The major products generated by the biscarbene complexes were regio-selectively determined by the nature of the metal site and that of the heteroatom in the arene rings. The monocarbene complexes [Cr(CO)5{C(OMe)thienylfuran] (13) and [Cr(CO)5{C(OEt)(N-methylthienylpyrrole)}] (19) were refluxed in THF for 2 hours in the presence of [Pd(PPh4)4] to afforded the carbene-carbene coupled olefinic products and small amounts of the corresponding 2-ethyl(biheteroaryl)acetate. By contrast, the biscarbene complex of thienylfuran (15), afforded only the 2,9-diester of thienylfuran.

Steric and Electronic Effects of Metal-Containing Substituents in Fischer Carbene Complexes of Chromium

The Fischer carbene complexes of chromium pentacarbonyl with one or two different metal-containing substituents were synthesized and studied in solution and in the solid state. The dimetallic complexes [Cr(CO)5{C(OTiCp2Cl)(2-BT)}] (2) (BT = benzo[b]thienyl) and [Cr(CO)5{C(OEt)((η6-2-BT)Cr(CO)3)}] (3) and trimetallic complexes [Cr(CO)5{C(OTiCp2Cl)((η6-2-BT)Cr(CO)3)}] (4) and [Cr(CO)5{C(OTiCp2Cl)Fc}] (5) (Fc = ferrocenyl) were prepared and systematically studied with respect to the reference complex [Cr(CO)5{C(OEt)(2-BT)}] (1) for the importance of the metal substituents in influencing carbene ligand reactivity. It was clear from the crystal structure determination of 4 that most of the unoccupied space was found around the benzo[b]thienyl substituent. Hence, it was also possible to synthesize the analogous more crowded trimetallic carbene complex 5 containing an electron-donating ferrocenyl instead of the [Cr(η6-2-BT)(CO)3] substituent. Dilithiated ferrocene reacts with 2 equiv of chromium hexacarbonyl, wh...

Plasma enhanced chemical vapor deposition of Cr 2O 3 thin films using chromium hexacarbonyl (Cr(CO) 6) precursor

Chromium oxide (Cr 2O 3) thin films have been deposited by plasma enhanced chemical vapor deposition on c-cut sapphire (Al 2O 3) and oxidized silicon substrates at temperatures between 250 and 400 °C using the precursor chromium hexacarbonyl (Cr(CO) 6). The film growth rate ranges between 5 and 14 Å/min, with the growth rate going through a maximum at 300 °C before decreasing at higher temperature, suggesting the presence of competing deposition and desorption reaction channels. Scanning electron microscope images indicate that the density of grains and film crystallinity increases with increasing substrate temperatures, while atomic force microscopy shows an overall decrease in film roughness with increasing temperature. Normal θ – 2 θ Bragg X-ray diffraction results show that films deposited on SiO 2 are polycrystalline, while those on sapphire have a preferred (0 0 0 l) orientation. The epitaxial nature of the film growth on Al 2O 3 has been confirmed from the symmetry of off-axis X-ray scans.

Synthesis of chromium N-heterocyclic carbene complexes using chromium Fischer carbenes as a source of chromium carbonyls

Chromium Fischer carbene complexes, [Cr{ OMe(R)}(CO) 5] have been utilized as a source of chromium carbonyls in the synthesis of chromium NHC complexes. Using the synthetic method, chromium complexes of various NHC ligands were isolated in reasonable yields. Moreover, the method can be employed for the synthesis of molybdenum and tungsten NHC compounds.

Intensity of d−d Symmetry-Forbidden Electronic Transition in Cr(CO)6

Absolute absorption intensities (oscillator strengths) are calculated for the d-d symmetry-forbidden transition in hexacarbonyl chromium. The vibronic coupling mechanism is taken into account in a way that represents an alternative to the traditional perturbative approach of Herzberg and Teller. In the so-called direct method, the electronic transition moment is directly expanded in a power series of the vibrational normal coordinates of suitable symmetry. In the present case, i.e., d-d ligand field transitions, or more specifically (1)A(1g) --> (1)T(1g) and (1)A(1g) --> (1)T(2g) transitions, the dipole selection rule is broken by vibronic interaction induced by normal modes that transform like T(1u) and T(2u) representations of the O(h) group. An analysis of the relative importance of normal modes in promoting electronic transitions is carried out.

Chromium Carbonyl Nitrosyls: Comparison with Isoelectronic Manganese Carbonyl Derivatives

Density functional methods indicate that the global minimum for Cr2(NO)2(CO)8 is a staggered D4d structure in accord with experiment and analogous to the isoelectronic Mn2(CO)10. For the unsaturated Cr2(NO)2(CO)n derivatives the lowest energy structures are very different from the lowest energy structures for the isoelectronic Mn2(CO)n+2 derivatives. Thus the global minimum for Cr2(NO)2(CO)7 is an unbridged structure with a Cr(NO)(CO)4 fragment linked to a Cr(NO)(CO)3 fragment through a Cr=Cr double bond. For Cr2(NO)2(CO)6 the global minimum is a structure with two bridging CO groups, whereas the global minimum for Mn2(CO)8 is an unbridged structure. For Cr2(NO)2(CO)5 both NO groups are bridging NO groups with one of them having a short enough Cr-O distance to be considered a formal five-electron donor eta2-mu-NO group. Thus the isoelectronic substitution of NO for CO with a necessary adjustment in the central metal atom can lead to significant shifts in the relative energies of various structural types of metal carbonyl nitrosyls, particularly for unsaturated molecules. For the mononuclear Cr(NO)2(CO)3 the theoretical structure differs from that deduced from matrix isolation experiments. Moreover, the nu(CO) and nu(NO) vibrational frequencies predicted here for Cr(NO)2(CO)3 correspond more closely with the unassigned species labeled "Cr(NO)(CO)x" in the experiments rather than the species claimed to be Cr(NO)2(CO)3.

Alternativ-Liganden XXXVIII. [1] Neue Versuche zur Synthese von Pd(0)- und Pt(0)-Komplexen des Tripod-Phosphanliganden FSi(CH2CH2PMe2)3 / Alternative Ligands XXXVIII. [1] Further Attempts to Synthesize Pd(0) and Pt(0) Complexes with the Tripod Phosphane Ligand FSi(CH2CH2PMe2)3

The tripod phosphane ligand FSi(CH2CH2PMe2)3 (1) has been prepared again and attempts to generate F3CSi(CH2CH2PMe2)3 (2) were undertaken for the preparation of transition metal cage compounds of the type A(CCP)3M or A(CCP)3M-L (A = FSi, F3CSi). The photochemical addition of dimethylphosphane to trifluoromethyl-trivinylsilane, however, gave 1 instead of the expected CF3Sitripod ligand 2, obviously due to difluorocarbene elimination. 1 was used to prepare the chromium carbonyl derivative (CO)3Cr[(Me2PCH2CH2)3SiF] (3) from Cr(CO)3CHT, and 3 was characterized by NMR and IR spectroscopy. The novel complex FSi(CH2CH2PMe2)3Pd (4) and its PPh3 derivative [FSi(CH2CH2PMe2)3Pd]PPh3 (5) have been obtained by reacting 1 with Pd(PPh3)4 and were characterized by NMR (4) and X-ray diffraction (5). The data prove the expected Pd→Si interaction by characteristic coordination shifts and a Pd-Si distance of 3.875 Å which is smaller than the Ni-Si distance in the corresponding nickel compound (3.92 Å ). The preparation of the analogous platinum complex from the precursors Pt(PPh3)4, Pt(C7H10)3, or (Ph3P)2Pt(η2-C2H4) failed, whereas the reaction of 1 with Pt(PEt3)4 was successful, but surprisingly led to the trinuclear complex [FSi(CH2CH2PMe2)3Pt]3(PMe2CH2CH2)3SiF (6) with three cages of type 4 and an additional ligand 1 as a bridging unit. Complex 6 was isolated and characterized spectroscopically. Quantum chemical calculations have been used to elucidate the coordination geometry expected for 4, 5 and the corresponding platinum cage 4′ in 6. The calculations support the structure of 5 within the expected limitations of the experimental and theoretical methods and - in spite of the extremely soft coordination sphere of the studied cages - are in accord with the spectroscopic results.

Carbon Dioxide Fixation by an Unprecedented Hydroxo Lead−Chromium Carbonyl Complex: Synthesis, Reactivity, and Theoretical Calculations

The novel hydroxo-bridged dimeric lead-chromium carbonyl complex [Et4N]2[{PbCr2(CO)10}2(mu-OH)2] ([Et4N]2[1]) was synthesized from the reaction of PbCl2 and Cr(CO)6 followed by metathesis with [Et4N]Br in a KOH/MeOH solution. The X-ray crystallographic structure shows that dianion 1 consists of two Pb{Cr(CO)5}2 units bridged by two hydroxo fragments in which the Pb atoms are further coordinated with two Cr(CO)5 groups, resulting in a distorted tetrahedral geometry. A CO2 molecule can insert itself into dianion 1 to form two new carbonate complexes, [Et(4)N]2[{PbCr2(CO)10}(CO3)] ([Et4N]2[2]) and [Et4N]2[{PbCr2(CO)10}2(CO3)] ([Et4N]2[3]), depending on the reaction conditions. In addition, complex 2 can be transformed into 3 in CH2Cl2 solution at an elevated temperature. While the carbonate group in dianion 2 is bonded to one Pb atom, which is coordinated with two Cr(CO)5 fragments, the carbonate group in 3 bridges the two Pb centers in a mu-1kappa2OO':2kappa2OO' fashion in which each Pb atom is further bonded to two Cr(CO)5 moieties. Complexes 2 and 3 can be converted back the hydroxo complex 1 under appropriate conditions. All three unprecedented lead-chromium compounds, 1-3, were fully characterized by spectroscopic methods and single-crystal X-ray diffraction analyses. The nature and formation of complexes 1-3 were also examined by molecular orbital calculations using the B3LYP method of the density functional theory.

A Chromium-Diphosphine System for Catalytic Ethylene Trimerization: Synthetic and Structural Studies of Chromium Complexes with a Nitrogen-Bridged Diphosphine Ligand withortho-Methoxyaryl Substituents

To gain molecular-level insight into the important features of a chromium-diphosphine catalytic system for ethylene trimerization, the coordination chemistry of chromium with “PNP” ligands (PNPOMe = (o-MeOC6H4)2PN(CH3)P(o-MeOC6H4)2, Pt-BuNi-amylPOMe = (2-MeO-4-t-BuC6H3)2PN(i-amyl)P(2-MeO-4-t-BuC6H3)2) has been explored. Chromium(0) carbonyl complexes have been synthesized by CO displacement with diphosphine. Oxidation of Cr(CO)4{κ2-(P,P)-(PNPOMe)} with I2, Br2, and PhICl2 generates the corresponding chromium(III) halide complexes. Chromium(III) complexes CrCl3{(κ3-(P,P,O)-(PNPOMe)}, CrCl3{κ3-(P,P,O)-(Pt-BuNi-amylPOMe)}, and CrCl2(CH3){κ3-(P,P,O)-(PNPOMe)} can be synthesized by metalation with CrCl3(THF)3 or CrCl2(CH3)(THF)3. Reaction of CrCl3{κ3-(P,P,O)-(PNPOMe)} with o,o‘-biphenyldiyl diGrignard affords CrBr(o,o‘-biphenyldiyl){κ3-(P,P,O)-(PNPOMe)}. Single-crystal X-ray diffraction studies show that the Cr−O and Cr−P distances can vary significantly as a function of metal oxidation state and the other lig...

Influence of Cr(CO) 6 and Mo(CO) 6 on the critical conditions for ignition and the velocities of flame propagation for the chain-branching oxidation of hydrogen and propylene

It has been found that small additions (∼0.1 vol%) of chromium hexacarbonyl and molybdenum hexacarbonyl promote the combustion of a stoichiometric mixture of H 2 + O 2 , resulting in a lowering of the lower limit of initiated ignition and an increase of the visible velocity of flame propagation; as this takes place, inhibition of propylene oxidation by the additives is observed indicating that hydrogen atoms do not play a noticeable role in chain branching in the initiated oxidation of hydrocarbons at room temperature; this indicates also that the kinetic mechanism of inhibition by carbonyls based on termination by the recombination of hydrogen atoms reported in the literature must be revised. Excited Cr atoms have been observed in a H 2 + O 2 flame in the presence of chromium hexacarbonyl.

Photochemical reactions of chromium, molybdenum and tungsten hexacarbonyls with dimethylglyoxime

Sunlight irradiation of the reactions of [M(CO) 6], M=Cr, Mo and W with dimethylglyoxime (H 2dmg) in THF were investigated. The reaction of [Cr(CO) 6] with H 2dmg resulted in the formation of the square pyramidal complex [CrO(H 2dmg) 2] (1). The H 2dmg coordinated the metal from the two nitrogen atoms. The corresponding reactions of molybdenum and tungsten carbonyls yielded the binuclear oxo complex [(H 2dmg)O 2M(μ-O) 2MO 2(H 2dmg)] (2, 3). Unusual bonding of H 2dmg was observed with the formation of six membered chelates. All complexes were characterized by elemental analysis, infrared, mass and 1H NMR spectroscopy. The UV–vis spectra of the complexes showed visible bands due to ligand-to-metal charge transfer. Thermal properties of the complexes were investigated by thermogravimetry (TG) technique.

Synthesis of hydrophenanthrenes through a ‘green’ Fischer carbene–alkyne coupling process

Coupling of alkynylbenzoyl systems with γ,δ-unsaturated Fischer carbene complexes leads to the formation of hydrophenanthrene derivatives. This reaction is not affected by aqueous systems, which offer a further advantage such that chromium hexacarbonyl sublimes during the reaction process. Chromium carbene–alkyne coupling processes can thus be performed in environmentally friendly solvents with substoichiometric net consumption of chromium hexacarbonyl.

Gold acyls and imidoyls prepared from anionic Fischer-type carbene complexes

Reaction of [(CO) 5WC(O)Ph]Li or [(CO) 5WC(O)Ph]NBu 4 with Ph 3PAuCl affords acyl complexes of gold. In the latter conversion, both the crystalline products [(CO) 5WCl]NBu 4 ( 2) and Ph 3PAuC(O)Ph ( 3) have been isolated and fully characterised. Similarly, imidoyl gold compounds ( 4– 8) result from deprotonated aminocarbene complexes, [(CO) 5MC(NR 2)R 1]Li (M = Cr, W; R 1 = Ph, Me; R 2 = H, Me) and Ph 3PAuCl. Crystal and molecular structure determinations of dinuclear [Ph 3PAuC(NH)Ph] · Cr(CO) 5 ( 6) show N-coordination of the chromium carbonyl unit that selectively affords a Z-isomer.

Assessment of vapor pressure data of solid metal carbonyls

The vapor pressure data of solid metal carbonyls have been assessed and compiled using the “Oonk arc representation” (OAR), also called the “ln f representation”. A simple modification is proposed to the existing OAR called the “ modified Oonk arc representation” (MOAR), which aids in the visual representation of the vapor pressure data. The solid metal carbonyls chosen for these data assessment do not exhibit any disproportionation: chromium carbonyl (Cr(CO) 6), tungsten carbonyl (W(CO) 6), osmium carbonyl (Os 3(CO) 12), molybdenum carbonyl (Mo(CO) 6), rhenium carbonyl (Re 2(CO) 10), and manganese carbonyl (Mn(CO) 5) have been evaluated. The sublimation properties using the assessed data (Δ sub G ∘, Δ sub H ∘ and Δ sub C p , m ∘ ) of these compounds have been evaluated and a discussion on the mutual consistency of various data sets for each compound over a wide range of temperature is presented.