Metal Pentacarbonyl Complexes Research Articles

Group 6 metal pentacarbonyl complexes of air-stable primary, secondary, and tertiary ferrocenylethylphosphines.

The synthesis and characterization of a series of Group 6 metal pentacarbonyl complexes of air stable primary, secondary, and tertiary phosphines containing ferrocenylethyl substituents are reported [M(CO)5L: M = Cr, Mo, W; L = PH2(CH2CH2Fc), PH(CH2CH2Fc)2, P(CH2CH2Fc)3]. The structure and composition of the complexes were confirmed by multinuclear NMR spectroscopy, IR and UV-Vis absorption spectroscopy, mass spectrometry, X-ray crystallography, and elemental analysis. The solid-state structural data reported revealed trends in M-C and M-P bond lengths that mirrored those of the atomic radii of the Group 6 metals involved. UV-Vis absorption spectroscopy and cyclic voltammetry highlighted characteristics consistent with electronically isolated ferrocene units including wavelengths of maximum absorption between 435 and 441 nm and reversible one-electron (per ferrocene unit) oxidation waves between 10 and -5 mV relative to the ferrocene/ferrocenium redox couple. IR spectroscopy confirmed that the σ donating ability of the phosphines increased as ferrocenylethyl substituents were introduced and that the tertiary phosphine ligand described is a stronger σ donor than PPh3 and a weaker σ donor than PEt3, respectively.

Photochemical (E)–(Z) Isomerization of the P=C Double Bond in Triphospha[3]radialene–[M(CO)5] (M = W, Cr) Complexes

Abstract Thermal reactions of Mes*-substituted triphospha[3]radialene (Mes*: 2,4,6-tri-t-butylphenyl) with [M(CO)5·(thf)] (M = Cr, W) resulted in the formation of the corresponding group 6 metal–pentacarbonyl complexes bearing the triphospha[3]radialene ligand, where one of the P=C bond moiety of the triphospha[3]radialene was σ-coordinating to the metal moiety in η1-fashion. The noncoordinating P=C bonds in the obtained complexes were found to undergo photochemical (E)–(Z) isomerization.

ChemInform Abstract: 2-Seleno- and 2-Telluroimidazolines: Syntheses, Structures and Properties

2,3-dihydro-2-selenoimidazoles and their tellurium analogues (2) are formed through the reaction of the corresponding 2,3-dihydro-imidazol-2-ylidenes (1) with the chalcogenes. 2 exhibit nucleophilic properties demonstrated by the formation and properties of their iodine derivatives 3 – 7 and their pentacarbonyl metal complexes 8.

First examples of dipyrido[1,2-c:2′,1′-e]imidazolin-7-ylidenes serving as NHC-ligands: Synthesis, properties and structural features of their chromium and tungsten pentacarbonyl complexes

The first use of dipyridocarbenes as Arduengo–Wanzlick type carbene ligands for transition metal complexes is reported. The complexes M(CO) 5L (L = dipyridoimidazolinylidene, di- tert-butyldipyridoimidazolinylidene, M = Cr, W) were synthesized and their spectroscopic and structural properties compared with the literature known N-heterocyclic carbene (NHC) group 6 metal pentacarbonyl complexes. This reveals that the 13C NMR carbene signals of theses complexes with dipyrido carbene ligands show the strongest high-field shift ever observed for M(CO) 5(NHC) (M = Cr, W) complexes. The structural characterization shows alternating single and double bonds in the conjugated dipyrido moiety of the ligand.

Thermal reactions of an overcrowded germacyclopropabenzene with group 6 metal hexacarbonyl complexes [M(CO)6](M = Cr, Mo, and W): a novel mode of CO insertion leading to the formation of cyclic germoxycarbene metal complexes.

Thermal reactions of an overcrowded germacyclopropabenzene with hexacarbonyl complexes of group 6 metals resulted in the formation of the corresponding cyclic germoxycarbene complexes, i.e., 1,2-oxagermolan-5-ylidene pentacarbonyl metal complexes, via a novel mode of CO insertion reaction toward cyclopropabenzene derivatives.

Synthesis of (η 6-arene)tricarbonylmetal and (σ-nitrogen)pentacarbonylmetal complexes of 1,2,3,4-tetrahydroquinoline and 1,2,3,4-tetrahydroisoquinoline with chromium, molybdenum and tungsten

Thermal reactions of [M(CO) 6] with 1,2,3,4-tetrahydroquinoline ( 1) afford the corresponding (η 6-arene)tricarbonylmetal complex (M=Cr, 3; M=Mo, 4; and M=W, 5). In contrast, thermolysis of the same hexacarbonyl complexes with 1,2,3,4-tetrahydroisoquinoline ( 2) affords the (σ-nitrogen)pentacarbonylmetal derivatives (M=Cr, 7; M=Mo, 8; and M=W, 9). For chromium the (η 6-arene)tricarbonylmetal complex ( 6) was also isolated. X-ray crystal structures are reported for 3, 4, 7 and 9.

First structural characterisation of 1,2,4-selenadiphosphole and 1,2,4-telluradiphosphole ring systems. Crystal and molecular structures of the η 1-complexes [M(CO) 5(P 2SeC 2Bu t2)] (M=Cr, W) and [W(CO) 5(P 2TeC 2Bu t2)

The molecular geometries of the 1,2,4-selenadiphosphole and the 1,2,4-telluradiphosphole aromatic ring systems, established by single crystal X-ray diffraction studies on their metal pentacarbonyl complexes, are presented and discussed together with theoretical data.

Thermal Ring-Closure Reactions of Pentacarbonylchromium Complexes with Bidentate N−N Ligands Revisited. Elimination of Side Reactions and Elucidation of the Intimate Chelation Mechanism

Thermal ring-closure reactions of pentacarbonylmetal complexes with bidentate N−N ligands were studied in detail in the past using photochemical techniques to produce these species in solution prior to the actual reaction. Some of the monodentate pentacarbonylchromium complexes have now been isolated and enable a detailed reinvestigation of the thermal chelation reaction of Cr(CO)5(N−N) (N−N = 1,4-diisopropyl-1,4-diazabutadiene, 4,4‘-dimethyl-2,2‘-bipyridine). The reactions were studied as a function of [N−N], temperature, and pressure. The unexpected ligand concentration dependence, viz. a decrease in observed rate constant with increasing [N−N], can be accounted for in terms of competitive reactions leading to the formation of Cr(CO)6 and chelated Cr(CO)4(N−N). At high [N−N] the limiting rate constant represents only the chelation reaction, for which the observed activation volumes are between +13 and +18 cm3 mol-1. These strongly support the operation of a dissociatively activated chelation mechanism.

2-Seleno- and 2-Telluroimidazolines: Syntheses, Structures and Properties

2,3-dihydro-2-selenoimidazoles and their tellurium analogues (2) are formed through the reaction of the corresponding 2,3-dihydro-imidazol-2-ylidenes (1) with the chalcogenes. 2 exhibit nucleophilic properties demonstrated by the formation and properties of their iodine derivatives 3 – 7 and their pentacarbonyl metal complexes 8.

Structure and Bonding of the Noble Gas−Metal Carbonyl Complexes M(CO)5−Ng (M = Cr, Mo, W and Ng = Ar, Kr, Xe)

Quantum mechanical ab initio calculations at the MP2 and CCSD(T) level of theory using effective core potentials for the heavy atoms as well as density functional calculations using various gradient corrections are reported for the noble gas−transition metal pentacarbonyl complexes M(CO)5−Ng (M = Cr, Mo, W and Ng = Ar, Kr, Xe). The optimized geometries show increasing metal−noble gas distances in the order Ar < Kr < Xe and Cr < W < Mo. The theoretically predicted M−Ng bond energies are very close to experimentally observed data. The nature of the interactions between the unsatured 16 e- fragments M(CO)5 and the noble gases is investigated using the topological analysis of the electron density distribution and by a detailed analysis of the bond energies. Excitation energies are predicted using time-dependent density functional theory in good agreement with experimental measurements.

Physical Organic Chemistry of Transition Metal Carbene Complexes. 8.1 Kinetic and Thermodynamic Acidities of Alkoxyalkylcarbene Pentacarbonyl Complexes of Cr, Mo, and W in Aqueous Acetonitrile. Dependence on Metal, Alkyl Group, and Alkoxy Group

A study of the acidity of various Fischer-type (alkoxyalkylcarbene)pentacarbonylmetal complexes and of their rates of deprotonation by OH- and amines in 50% acetonitrile−50% water at 25 °C is reported. The pKa values of (CO)5MC(OMe)CH3 for M = W (12.36) and M = Mo (12.81) are quite comparable to that for M = Cr (12.50) determined previously, and the pKa of (CO)5WC(OMe)CH2Ph (10.18) is similar to that of the chromium analog (10.40) reported earlier. These results indicate that the stabilization of the negative charge of the anion by the (CO)5M moiety depends little on the metal. The pKa of (CO)5CrC(OEt)CH3 (12.98) is 0.48 units higher than that of the methoxy analog; this increase probably reflects an enhanced stabilization of the zwitterionic resonance structure of the carbene complex, (CO)5Cr-C(O+Et)CH3, by the stronger electron-donating effect of the ethyl group. Intrinsic rate constants for the deprotonation of the carbene complexes by OH- (koOH) were estimated based on the Marcus equation, and intrins...

Advances in 2H-Azaphosphirene Complex Chemistry

: Synthesis of a wide variety of 2H-azaphosphirene pentacarbonyl metal complexes is reported. The overall reaction of this heterocyclic synthesis was determined to be stereospecific, but no asymmetric induction has been observed. Generation, decomposition and trapping reactions of nitrilium phosphane ylide complexes, a zwilterionic acyclic isomer of 2H-azaphosphirene complexes possessing a novel 1,3-dipole system, are presented.

Mechanism of thermal ring closure of metal pentacarbonyl complexes, M(CO)5L (L = bidentate ligand), produced during photolysis of Group 6 hexacarbonyl complexes

The kinetics of the thermal ring-closure reactions of M(CO){sub 5}L, produced during the photolysis of M(CO){sub 6}/L for L = ethylenediamine (en) and 1,4-diisopropyl-1,4-diazabutadiene (dab), were studied as a function of (L), temperature, and pressure. The values of {Delta}S{double dagger} and {Delta}V{double dagger} are significantly negative, {minus}40 to {minus}170 J K{sup {minus}1} mol{sup {minus}1} and {minus}5.4 to {minus}13.7 cm{sup 3} mol{sup {minus}1}, respectively, for M = Cr (L = en) and M = Mo, W (L = en, dab) and support an associative ring-closure mechanism. The results demonstrate the crucial role played by the size of the metal center and the steric hindrance on L.

An NMR study of the fluxionality of group VI metal pentacarbonyl complexes of 1,3-dithiolanes

The complexes [M(CO) 5( SC 2H 4SC RR′)] (M = Cr, Mo or W, R = R′= H; M = Cr or W, R = R′= Me, R = H, R′= Me, Bu t or Ph) have been synthesized and characterized. Their solution stereodynamics were examined by 1H NMR spectroscopy. Pyramidal inversion of the metal-coordinated sulphur atoms occurs rapidly at ambient temperatures (Δ G‡ (298 K) = 40–44 kJ mol −1). An appreciably slower 1,3-metal—sulphur shift is also evident at temperatures where sulphur inversion is rapid on the proton NMR timescale. For the ligand complexes (R = R′ = H, Me) this shift is purely intramolecular in nature (Δ G† (298 K) values ∼ 78 kJ mol −1), in contrast to the 2-mono-substituted ligand complexes (R = H, R′ = Me, Bu t, Ph) where it is accompanied by a dissociation process.

Beiträge zur Chemie des Bors, 184 Pentacarbonylmetall‐Komplexe des (tert‐Butylimino)‐ (2,2,6,6‐tetramethylpiperidino)borans

(tert‐Butylimino)(2,2,6,6‐tetramethylpiperidino)borane (1) reacts with Cr(CO)6 under photolytic conditions producing pentacarbonylmetal complexes 2. The M(CO)5 fragment coordinates to the tert‐butylimino group. The X‐ray structure analysis of 2a shows an allene type structure with two distinctly different BN bonds (1.29, 1.36 Å) and a long CrN bond (2.22 Å).

Chemie polyfunktioneller Molek�le, 94 Chrom- und Wolfram-pentacarbonylderivate des 4-Methyl-1,2,6-triphosphatricyclo[2.2.1.02,6]heptans (P3-Nortricyclans)

The P3-nortricyclane 4-methyl-1,2,6-triphosphatricyclo[2.2.1.02,6]heptane, CH3C(CH2P)3, (1), is synthesized in a better yield than earlier described from P4, a Na/K alloy, and CH3C(CH2Br)3 in boiling 1,2-dimethoxyethane. It reacts withM(CO)5thf (M=Cr, W) in the molar ratios of 1:1, 1:2, and 1:3 to form the pentacarbonylmetal complexes CH3C(CH2P)3[M(CO)5] n [n=1, 2, 3;M=Cr (a), W (b)], (2 a, b–4 a, b).1 gives with Mo(CO)5thf only mixtures of CH3C(CH2P)3[Mo(CO)5] n andcis-Mo(CO)4 derivatives, which were identified by their infrared active A1 v(CO) modes at 2075 and 2025 cm−1.

ChemInform Abstract: Novel Basic Ligands for the Homogeneous Catalytic Methanol Carbonylation.

AbstractThe ligands (I) react with the metal Compounds (II) to give the pentacarbonylmetal complexes (IIIb)‐(IIId).

Dynamic nuclear magnetic resonance study of Group 6 metal pentacarbonyl complexes. Pyramidal inversion and 1,2-metal shifts in the complexes [M(CO)5(Me2CCH2EECH2)](M = Cr, Mo, or W; E = S or Se)

Mononuclear complexes of the type [M(CO)5(Me2[graphic omitted]H2)], where M = Cr, Mo, or W and E = S or Se, have been prepared. Detailed variable-temperature n.m.r. studies have established the existence of pyramidal inversion about the co-ordinated sulphur or selenium ligand atom and an intramolecular 1,2-metal shift between adjacent chalcogen ligand atoms. The energy barriers associated with both rate processes have been evaluated by dynamic n.m.r. methods. The metal pentacarbonyl complexes of naphtho[l,8-cd]-dithiole and -thiaselenole, [M (CO)5(C10H6EE′)](M = W, E = E′= S; M = Cr, E = S, E′= Se) have also been prepared but no fluxionality was evident.

Das Reduktionsverhalten von Pentacarbonylpyridin-Komplexen des Chroms, Molybdäns und Wolframs / The Reduction Behaviour of Pentacarbonylpyridinechromium, -molybdenum and -tungsten Complexes

Abstract The reduction of group VIB metal pentacarbonyl complexes and of iodomethylates of 4- trimethylsilyl-, 4-acetyl- and 4-cyanopyridine has been investigated. Informations on the dissociation of the complexes and on the potential and reversibility of the one-electron reduction were obtained by cyclic voltammetry in DMF, whereas electron spin resonance (ESR) studies of the primary reduction products in the 4-acetylpyridine series revealed the distribution of the unpaired electron. The results suggest that the lowest unoccupied molecular orbital (LUMO) is a ligand centered π*-orbital in the 4-acetyl- and 4-cyanopyridine complexes, thus confirming assignments from photochemistry. The results allow an assessment of both N-coordination and substituent effects at the heterocyclic ligand.

Electronic structure of transition metal compounds: XXIII. Theoretical and spectroscopic investigations of heteroligand pentacarbonyl complexes of group via transition metals

The electronic structures of a series of 18 transition metal pentacarbonyl complexes of the general formula M(CO) 5L (M  Cr, Mo, W; L  Me 2XYMe, Me 2XXMe 2; X  P, As; Y  S, Se; Me  CH 3) have been investigated by semiempirical calculations of the CNDO and INDO type and by various spectroscopic studies. Information concerning the ground state of the pentacarbonyl derivatives has been derived from 1H NMR, 31P NMR and IR data; He(I) photoelectron spectra in the outer valence region have been measured in order to study the nature of the cationic hole-states. Theoretical and experimental data are combined to give a detailed description of the electronic structure of the M(CO) 5L complexes.