Chromium. Molybdenum, and Tungsten

Black and P. S. Braterman, tnorg. Chim. Acta, 1980, 44, L181. 

The nature of the intermediate species formed on photolysis of mixtures of M(CO)g and CCI4, (a useful initiating system for olefin metathesis and acetylene polymerization have been further investigated using spin-trapping reagents. 

Masuda, Y. Kuwane, K. Yamamoto, and T. Higashimura, Polvm. Bull. (Berlin). 1980, 2, 823. R. G. Gasanov and R. Kh. Freidlina, Dokl. Akad. Nauk SSSR. 1980, 254, 113. 

Photoexcitation of W(CO)5 CPh2 appears to yield diphenylcarbene as this has been trapped by diethyl fumarate. In the absence of trapping agents PhjC CPhj is formed, probably by reaction of the carbene with W(CO)5CPh2. 

A full account is given of the structures and properties of [Mo -- (y-CgMe)Cp23 and its protonation product [Mo, (w-CgMeg) (yj j -H)Cp23 which contains a 3-centre C-H-Mo interaction. 

More evidence has been adduced for the formation of 19-electron intermediates in the photochemical disproportionation of [Mo2(C0)g - 

Aryl and alkyl isocyanides readily cleave [MO2(CO)gCp2 giving disproportionation products [Mo(CNR)(C0) Cp][Mo(CO) Cp3 (n = 0/ R = 

There are many further reports of binuclear complexes containing two, metal-metal bonded (M(C0) Cp units, bridged by a range of ligands. Thermal decomposition of Cmo (C =CPh) (CO) Cp3 produces I M02 (P-l,2-n -PhC=C-CS Ph) (C0)4CP23 and a triclinic form [Mo2( -n - 

Cp2 3 will also coordinate through phosphorus to other transition metal centres, as in the structurally characterised adduct with 

Flash-photolysis studies of the hexacarbonyls Cr(CO)g, Mo(CO)g and W(CO)g are, like previous years, still abundant Nayak and Burkey have found that there are low quantum yields for Cr(CO)g substitution in fluorocarbon solvents - which provides yet more evidence that metal-fluorocarbon interactions are very weak There have been estimates made of solvent-metal bond strengths in (Solvent)M(CO)5 complexes (Solvent = Benzene [M = Mo, W] and Tetrachloromethane [M = Cr]) and the photolysis of W(CO)g in the presence of hex-l-ene has been reported Flash-photolysis studies of the photochemical reactions of silanes with Cr(CO)g have been published Using time-resolved infrared spectroscopy RIR), Turner and co-workers have captured the IR spectrum of the MLCT excited state of W(CO)5(4-cyanopyridine) which rapidly decays to W(CO)5. The excited state of W(CO)5(4-cyanopyridine) is relatively long lived, which makes the experiment possible. This reporter will be interested to see how this technique develops. 

Continuing the theme of unstable metal carbonyl species being generated by the irradiation of parent crystals, Hynes et al report the formation of [M(CO)5]2  

Mo(CO)g and W(CO)g carbonyls on X and Y type zeolites has been reported and an EXAFS analysis of W(CO)g on Na5gY (with evidence of photo-oxidation products) has been reported 

The general chemistry of the Group VI hexacarbonyls and closely related species is represented in this report with several new types of complex stemming bom the parmit M(CX))g species 46,47,48 Catalytic uses of the Group VI carbonyls continue to be reported 49,S0,51  

3 Chromium, Molybdenum and Tungsten.- The half sandwich complex 

The addition of cyclopentadienyl ligands to electron rich complexes x2-n) 3 n/2 been studied and products include 

The unusual bistungsten complex (4) results from the coupling of 3,7-decadiyne and W(C Et )(OCMe2CMe20)(OCMe3). 

CH2SiMe3), can be made from the dimers [CpM NO)l2]2-cationic 16-electron intermediate [CpWCCO) ] can be utilised synthetically starting with CpW(CO)3(BF ). 

High valent complexes including Cp WCl. are produced when 

The photochemical disproportionation of [Mo2(C0)gCp2l with PPh3 and the back reaction have been studied.Complexes [M2(n-h in -C5H4SlMe2C5H4)(C0)g] (M = Mo,W) with a linked cyclopentadienyl bridge and their reactions with P2Me4 are described,The structure and reactivity of fulvalene bridged 

Structurally characterised trinuclear complexes include opened triangular species [M03 /i3-o, jjn2-C4 CF3)4) (m3-0)( -C1 )Cp3and closed triangular [Mo3( -i7 -CCHCMeCH) C0)4Cp3]. J -Ray structures of cubane-like sulphides [Cr4(M3-S)2(M3-L)2CP4l (L - are reported. Derivatives 

The use of new ligands is common in this group. For example, Agbossou and co-workers have described free and Cr(CO)3-complexed aminophosphine 

Aubke and co-workers have been producing some interesting carbonyls with metal atoms in higher than normal oxidation states (compare this with the work of Ellis and co-workers who routinely produce new species in highly reduced states). Their contribution in 2000 was the synthesis and the molecular structure of [W(CO)6(FSbF5)][Sb2Fii]. 

Reports of new tungsten complexes include the reaction of the transient species W(CO)5(cyclohexane) with cyclo-C4H 0 (n = 4, 6, 8) studied by time-resolved infrared absorption spectroscopy. Schultz and co-workers have noted an unusual solvent isotope effect in the reaction of W(CO)5(solv) (solv = cyclohexane or cyclohexane-rfu) with TFIF. Some interesting chemistry involving W(CO)5(2,5-dihydrofuran) is noted by the same group. Adducts of cyclotriphosphorus complexes have been reported by Di Vaira and co-workers, leading to the synthesis, solid state structure and solution behaviour of the bis-adducts [ (MeC(CH2PPh2)3)Co (P3)(M(CO)5 2], where M is a Group 6 metal. 

Catalysis using tungsten carbonyl species include the W(CO)6 catalysed oxidative carbonylation of primary amines to A,A -disubstituted ureas.  

Complexes of molybdenum containing cyclopentadienyl and ir-allyl ligands, the latter 

A dynamic NMR study of the behaviour of the complex [(2-propynylbotityl)Mo(GO) Cp] BF4 has highli iied a corrdation between die kmisatioo and the diasteteraneric ratios formed in metal stabilised cationic clusters. Variable temperature NMR spectroscopy has been used to examine the fluxianality of [Gp MofCOURCwCCR R )] comiriexes and the results have been correlated with MO calculation data.  

I yidd [Cp 2Mo2Y4) [Gp MoX4] by electron transfoi the dieniisliyftflCp MoXs], X Br, 

The synthetic chemistry of this group is extended by a number of studies PPh2CH2C(But )sNNR2 (R - H, Me) and PPh2CH2C(But)=NN=CHPh have been prepared and their reactions with the Group 6 hexacarbonyls have been described a series of Mo(CO)4[P(OMe)20J2SiRR complexes (R=Ph R =Ph, Me) have been prepared the synthesis and characterization of Group 6 carbonyl tellurides [M4(CO)jg(u -Te)2l (M = Cr, W), [Cr4(CO)20 1 l Te2)] , and [Cr4(C0) 2o(n -H -Te3 ) ] 2 have 

The earliest estimate of the rate coefficient for the exchange in perchlorate media was obtained by Plane and Taube from data obtained on the catalytic effect of 

Anderson and Bonner made the first detailed kinetic study on the exchange using the isotopic method ( Cr) and a separation method based on the conversion of Cr(II) into Cr(IIl) oxalate and an ion-exchange treatment. To prevent oxidation of Cr(II) during exchange a hydrogen atmosphere was maintained over the reaction mixture. The rate law found to be obeyed for the concentration ratio range Cr(III)/Cr(II) of between 3.3 x 10 and 2.0 in perchlorate media was 

From data obtained at /t 1.0 M with [H ] varying over the range 0.213 to 1.0 M, kobs was found to be given by 

The species CrOH being formed by the hydrolysis Cr -hH20 CrOH +-hH+ 

The effect of chloride ion on the exchange was found by these workers to be very small, whereas Plane and Taube had estimated a rate coefficient about five times larger in the presence of 10 M chloride ion than in perchlorate solution. Van der Straaten and Aten have studied the exchange in media 1 M with respect to HCl and have estimated a rate coefficient 3.0 x 10 l.mole . sec . The isotopic method ( Cr) and a separation procedure based on the precipitation of Cr(II) as the acetate complex was used. 

DFT calculations of vibrational wavenumbers for metal-metal bonded complexes gave excellent agreement with experimental IR and Raman wavenumbers for, e.g. M2(02CR)4, where M = Mo or Rh, R = H or The IR and Raman 

Resonance Raman spectra for (TOEP)MM (TOEP), where TOE = meso-monotolyloctaethylporphyrin, gave the assignments to vMM shown in Table 3. [Mo(Pc) ]2 has vMoMo in the resonance Raman spectrmn at 374 cm . IR data have been reported for the M02 units in Mo2(DTolF)3Cl2, where DTolF = Af Af -di-p-tolylformamidinate.  

The complex MoH(SC6H2 Pr3-2,4,6)(NH3)(PMePh2) shows vMoH as a weak IR band at 1890 cm Mo4(H)3(0 Bu)7(HNMe2) has IR bands at 1609 and 1561 cm which have been assigned tentatively to stretching modes involving bridging hydrides. 

Mo(C5Pli4R)02Br, where R = 2,5-dimethoxyphenyl, shows vMo=0 bands at 926 and 895 cm. In Mo 0(02)(TMP), where TMP = 5,10,15,20-tetramesi-tylporphyrinato, vMo=0 is at 912 cm , with Vs/VasMo-02 at 503 and 574 cm i. 3 Resonance Raman data (vMoO, vMoOMo) were used to probe the catalytic mechanism of molybdenum 0x0transferases. M0O2L complexes, where L Schiff bases prepared by condensation of an aryl hydrazine with ethylaceto-acetate, etc., have two VM0O2 bands due to cis-Mo02 units.  

Thin films of M0O3 and WO3 obtained by pulsed laser irradiation were 

C5H4Bu )2Mo(PhEMe)H] + indicate that the barrier to inversion at the chalcogen increases in the sequence E = S Se Te. The Se and Te NMR spectra 

Perfluoro-(l-methylpropenyl)silver readily displaces chlorine from (rr-C5Hj)Cr(NO) Cl to give (7T-C5H5)Cr(NO)2 C(CF,) CF CF3 (the CF3 groups being trans), and can also be used to procure the previously inaccessible ions [ CFj CF C(CF3) M(CO)5]- (M = Cr, Mo, or W) by the redox reaction  

Mo—C bond (restricted by the sterically demanding side-chain) or a polytopal rearrangement via a quasi-square-planar intermediate, 

Two series of complexes containing the CFs-P or (CFs)aP groups have been prepared from norbomadienetetracarbonylmolybdenum  

Under similar mild conditions, the use of CFg-PIj results in evolution of carbon monoxide and extensive decomposition. In contrast, the reaction of norbomadienetetracarbonylchromium with CFs-PHj requires a somewhat higher temperature for efficient reaction. The pCgA] and [XsA] spin systems (X = F, A = P) give well-resolved spectra V(PP ) decreases in magnitude as the electronegativity of the substituents bonded to CF3-P or (CFj),P is decreased.  

Compound (4c) and the related complex from l,2-bis(dimethylarsino)-fluoroethane are included in a series of l,2-bis(dimethylarsino)ethane complexes of tetracarbonylchromium whose n.nLx. spectra have been studied 

Carbonylation of the chromium carbene complex (CO)5Cr=C(OCH3)Ph at 150bar pressure in the presence of l-vinyl-2-pyrrolidone resulted in Cr(CO)6 and organic products that were rationalized by the intermediate formation of methoxyphenylk-etene [33]. The formation of a free vinylketene and vinylketene chromium complexes were found in the reaction of (CO)5Cr=C(OCH3)Ph and bis(trimethylsilyl)acetylene at 50 °C (reaction 8.19) [34-36]. 

In the presence of ethanol, the reaction of (CO)5Cr=C(OCH3)Ph and ethyl propiolate gives malonate derivatives [37]. 

Diphenylketene was isolated in up to 70% yield from (CO)5Cr=CPli2 under 1 bar carbon monoxide at 50 °C. An intramolecular carbene-carbon monoxide coupling was assumed in the reaction based on the observation that no incorporation of CO 

Ketene Ph3Si(EtO)C=C=0 prepared in situ from the carbene complexes (CO)3M=C(OEt)SiPh3 (M=Cr, Mo, W) with 50bar carbon monoxide was found to react at 80-100 °C, among others, vdth N-methylbenzimine to give the corresponding P-lactam in 90% isolated yield (reaction 8.21) [39]. 

The photolysis of chromium carbene complexes leading to short-lived species with ketenelike reactivity was applied for the synthesis of carboxylic add derivatives. 

Further t-emperature dependence studies of the doublet lifetimes of coordination complexes of Cr(III) have sho%m that the RISC (reverse Intersystem crossing) Is the lifetime limiting process in compounds with a small energy separation.A small reduction of the lifetimes of excited fCr(NH3)g) and (Cr (cyclam) (MH3)2] (eye lam - 1,4,8,11-tetraazacyclotetradecane) with Increased solvent mobility has been observed but which Is absent in the deuterated analogues. This has been interpreted to indicate that increased anharmonicity in accepting modes enhances nonradiative rates. The photoaquation of 

Studies of the kinetics of the photoaquation of [Mo(CN)3) in alkaline media,the light-induced redox reactions of ( M Mo(Vl), W(VI), V(V), Re(Vll)), and of molecular hydrogen formation on photoreduction of Mo(VI) in aqueous-ethanolic solutions have been published. A kinetic Investigation of the mechanism of photodlssoclatlon of WClg and VK1C14 in the gas phase containing H2 has been described.A study of the effect of 

The mass spectra of a considerable number of 77--bonded complexes of the group VIA metals have been reported, but in many cases mass spectrometry has only been used to determine the molecular weight, so that a detailed examination of the fragmentation processes involved has not been attempted, and only the molecular ion and perhaps a few other major peaks are reported. Within this section it is more convenient to discuss the compounds in terms of the attached ligands rather than in terms of the central metal atom. The classifications are (A) cyclopentadienyl compounds (B) arene compounds and (C) olefin, acetylene, and allyl compounds. 

A similar structure has been proposed for the product of the reaction of 9,10-dihydroindene with Mo(CO)6, which was originally believed to be 

The observation of the molecular ion peaks for the mercury derivatives [C5HsM(CO)3]2Hg (M = Mo, W) has been reported (139). The composition of the bis(trifluoromethyl)ethylenedithiolate complex [C5H5W (CO)S2C2(CF3)2]2 was confirmed by observation of the molecular ion and the [M —CO]+ fragment ion (120). 

The strongest ion in the spectra of the dicarbonyl cycloheptatrienyl complexes C5H5M(CO)2C7H7 (M=Mo, W) corresponds to C5H5MC7H7, and no peak is observed for the [M — CO]+ ion 114, 123). Loss of acetylene from the (M —2 CO]+ ion, as observed in the spectra of C5H5MC7H7 complexes 150), gave the bis(cyclopentadienyl) metal ion (C5H5)2M+. 

King 118) has studied the spectra of some indenylmolybdenum carbonyl compounds and has observed that the indenyl ligand fragments by loss of acetylene in a similar manner to the fragmentation of the cyclopentadienyl ligand. The molecular ion of C9H7Mo(CO)3Me (V) exhibits stepwise loss of the CO groups, but after the loss of one CO, loss of methyl competes with loss of CO. 

When trifluoroiodomethane is treated with a solution of chromium(u) ions, the brownish orange [Cr(OH2)s(CF3)] + is obtained. This complex is stable towards aquation compared with the corresponding methylchromium species, slowly giving hydrogen fluoride and carbon monoxide but no detectable fluoroform. With sodium fluoride [Cr(OH2)4F(CFs)]+ is formed. The formation of Cr[C(CFs)2(CN)]2 in good yield from Cr(OAc)2 and (CF3)2CH CN under naild conditions has been reported.  

Chromium hexacarbonyl does not react appreciably at room temperature with l,l-bis trifluoromethyl)methyleneamino(trimethyl)stannane.ii Chlorotiicarbonylcyclopentadienyl-molybdenum and -tungsten react with hexa-fluorobut-2-yne with displacement of all three carbon monoxide ligands to give the 

M(nbdXCO)4 complex has also been reported,together with that of die related ditertiary phosphine complexes (7). Yields vary considerably, and in some reactions the ligands fail to chelate, giving M(CO)6 complexes as mqjor products. The njnj. spectra of the chelated complexes are interpreted in terms of rotamer populations of the ligands and conformational preferences of the chelate rings, and the effects of the systematic variation of donor atoms, metal atom, and solvent are discussed. 

An -ray crystal structure of the diarsine complex (8), prepared by the reaction of iodine in methylene chloride with the corresponding complex (L-L)W(CX 4, shows the seven-co-ordinate tungsten as a distorted capped octahedron , one of the CO ligands forming the cap, and the CsAssW ring being puckered. 

The metal hexacarbonyls all give polymeric material when subjected to unfiltered u.v. irradiation in the presence of bis(trifluoromethyl)disulphide the use of filtered radiation allows preparation of [M(CO)4(SCF3)]2 (M = Mo, W), but the cones- 

The first quantitative measurement of the distribution of excited atomic states produced in the multiphoton dissociation of a metal carbonyl has been made for Cr(CO)6. Photodissociation does not yield spin- or parity-differentiated states, rather the state distribution appears to be statistical. Photofragmentation dynamics of Cr(CO)6 in the gas phase have been measured and two channels of dissociation revealed. One of these is a rapid predissociation (efficiency 36%) and the other a slow process (efficiency 

Evidence has been provided that adsorption of several (t] -arene)tricarbonylchromium(O) complexes on to silica gel can perturb the electronic structure of these complexes and the quantum efficiencies with which they undergo photodecomposition. The steric constraint imposed by the support also seems to influence the photoreactivity of these complexes. M(CO)4(bipym) (where M = Cr or W, bipym = 2,2 -bipyrimidyl) and (W(CO)4]2(bipym) both have a lowest MLCT state, and on irradiation CO is lost. Wavelength-dependent quantum yields have been obtained for this transformation and at 366 nm = 2.4x 10 quanta/min for Cr-bipym, 2.5 x 10 quanta/min for W-bipym, and 1.1 x 10 quanta/min for W-bipym-W. Correlations have been described between the MLCT absorption energies of a series of M(CO)4 diimine complexes and Reichardt s solvent parameters (Et), and Kamlet s and Taft s solvent polarity scale Paramagnetic complexes 

HMn(CO)s has been photolysed in Ar and CH4 matrices and this produces CO and HMn(CO)4, a compound having a C, structure. Narrow band photolysis also leads to small amounts of a second isomer of HMn(CO)4 which has a C4 structure. PhMn(CO)5 has been observed to photoreact with 6,6-dimethyl- and 6,6-diphenylfulvene to give Ph(CO)4Mn(T -fulvene) complexes. Irradiation of RMn(CO)jL2 [10 R = H or Me, L = P(OPh)j] and of MeMn(CO 4L in benzene induces formation of the orthometallated products (11). These arise by formation of a 16-electron intermediate which in-tramolecularly activates a C-H bond of Ph in PCOPha).  

Irradiation of Re2(CO)io in the presence of ethylene gives (13) via a radical pathway which produces a [Re(CO)4(-n -olefin)]2 intermediate. At room temperature, (13) undergoes a rapid fluxional process in which the or- and ir-bonds rapidly interchange between the Re atoms. Re2(CO)io is reported to react with acyclic or cyclic olefins on photolysis. Thus with cyclohexene, (14) is 

Chetwynd-Talbol, P. Grebenik, R. N. Perutz, and M. H. A. Powell tnorg. Chern, 1983, 22, 1675. 

The chemistry of various Group 6 carbonyl species on surfaces or in zeolites continues to be prominent in the literature Ozin and co-workers have continued to explore the chemistry of Mo(CO 5 in NaY zeolites the carbonyl species formed by UV photoreduction of silica-supported Mo(VI) in a carbon monoxide atmosphere have been characterized by their infrared spectra and the kinetics of the thermolysis of Mo(CO)g on a tungsten surface have been released . 

Hydrocarbon ligands receive attention elsewhere in this report, but of relevance here has been the synthesis of W(CO)g(cis-cyclooctene) and W(00)4(cis-cyclooctene)2. Several molybdenum cyclopentadieneone complexes have also been prepared . Hydrocarbon ligands are also in evidence in the reaction between (C7H3)Cr(CO)4 and (C7H8)Mo(CO)4 with P2N2 and 

P2N2H4. Carbonyl scrambling has been noted in the anionic acyl complex [Cr(CO)5(COPh)].  

Continuing a long series of kinetic and mechanistic studies on transition metal complexes, rischer et al have published a detailed account of the reaction between 

Also exploring reaction mechanisms, Rheingold and coworkers have examined the electrophilic reactions between zerovalent tungsten nitrenes and hydrazido complexes and phosphines .  

19-hexazeU3icyclo[6.6.6 eicoseuie) have been prepared, auid emit strongly at 77 Photoselection data for the D, 

An amalysls of the temperature dependence of the emission spectrum amd emission lifetime of frans-(N2)2M(Ph2PCHxCH2PPh2)2 (M-Mo,W) In a homogeneous medium has been carried out in terms of a mamifold of thermally equilibrated emitting levels. A B, (W- P) 

CT term is lowest in energy followed by a LF term lying about 200 cm above. Orbital schemes are proposed for both compounds.The temperature dependence of the luminescence of the hexanuclear Mo(II) chloride cluster [Mo Cl, ] has been investigated over the rauige 1.4-300 K and analysed in terms of the emission from several Boltzmeuin populated triplet sublevels. The lowest triplet state was identified as t, and is due to the tjg to t y orbital excitation.A flash photolysis study of the quenching of [Mo Cl, ] by [IrCl ] shows it to occur by a one electron transfer process from the cluster medium euid pressure effects have been noted.An investigation of the 

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Complexes (191) and (192) are formed from dimethyldiazirine with carbonyls of chromium, molybdenum and tungsten. They show no tendency towards N—N cleavage (80JOM(193)57). Complex (193) is made from a mixed complex by displacement of norbor-nadiene. 

Table 23.2 Oxidation states and stereochemistries of compounds of chromium, molybdenum and tungsten...

The known halides of chromium, molybdenum and tungsten are listed in Table 23.4. The observed trends are as expected. The group... 

Chromium, molybdenum and tungsten thermodynamic properties, chemical equilibria and standard potentials. I. Dellien, F. M. Hall and L. G. Hepler, Chem. Rev., 1976, 76, 283-310 (400). 

Adam and Lohray122 have used thianthrene 5-oxide (88) as a mechanistic probe in oxidations with transition metal peroxides. They oxidized 88 with various diperoxo complexes of chromium, molybdenum and tungsten and formulated a plausible mechanism on the basis of the products formed, 89 and 90. 

Hydrogen reduction has a major advantage in that the reaction generally takes place at lower temperature than the equivalent decomposition reaction. It is used extensively in the deposition of transition metals from their halides, particularly the metals of Groups Va, (vanadium, niobium, and tantalum) and Via (chromium, molybdenum, and tungsten). The halide reduction of Group IVa metals (titanium, zirconium, and hafnium) is more difficult because their halides are more stable. 

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