Group 6 Cr, Mo, and W

A number of reviews contain relevant material such as those on dimolybdenum and ditungsten complexes, substitution reactions of chromium complexes, the reactivity of complexes containing multiple bonds between metal atoms, model reactions of coupling ieactions2 5, and in a review principally on ruthenium chemistry.216 

The reaction between oiganochromium macrocycle complexes of the type [CrR(OH2)(L ] and I2 gives [CrR(OH2)L] aiul F. The kinetic data are consistent with a chain mechanism iititiated by election transfer. The aliphatic free radical CHMeCH(OH)Me reacts with Cr (aq) to form a 

Various Tl -arene complexes W(CO)3(ti -C6R5) react with KBH(Bu )3 to form the anions [W(CO)3(Ti5.C5RgH)] . These react with Mel to form WMe(CX))3(Ti5-C6R6H). The reaction between LiMe and W CO)3(ll -C6H5) results in the anion [W(CO)3( n3-CgH5Me)] , which also reacts with Mel, this time to give WMe(n5-C6H6Me).237 

Treatment of the cations [CpMo(CO)(C2H4)(L2)]+ [L2 = dppe, (MeO)2P(CH2)2P(OMe)2] with carbanions [CH(C02)2] at -80°C results in the alkyl complex CpMo CH2CH2CH(C02Et)2KCD)L2. The corresponding reaction with [CpMo(CO)3(C2H4)]+ results in 

The dioxo complex cis- HB(Me2pz)3 W(C1)C 2 reacts with the Grignard reagents RMgX (R = 

CH(0H)2 radical proceeds via a transient species to the hydrated formyl [ Cr (CH ( OH) 2 ) (OH2 ) 5 ] which decomposes to the formyl [Cr (CHO) (OH2 ) 5 This formyl reacts with H2C=0 with formation of 

The kinetics of CO2 insertion into anionic alkyl and aryl complexes cis,-[ WR( CO) P (OMe ) 3 ] to give primarily [W(C02Me)(CO)4 P(OMe)3 ] are comparable with those of the 

A rare endo addition compound (18), or its deuteride, is formed 

The sulphur ylide Cr[CH2S(0)Me21(CO)5 reacts with (Ph2P)2C=CH2 to form the electrophilic CrTcH pTPhT cT=CH TpPh2](CO)4.In related reactions with (R2P)(RnE)C=PR3 the analogous complexes CrTcH PPh HI=PRj7pPh2 ] (CO) 4 arise (ERjj = PR2 SPh R various 

Addition of MeCaCMe to W2(Bz)2(OPr )4 gives a complex W2(Bz)2(OPr )4(n -MeCCMe)2 that eliminates toluene on warming to form the M-al)cylidyne (23). 

Reviews with relevance material include those on organochromium complexes 3 and cyclopentadienyl molybdenum and tungsten dihalides. 1  

Guided ion beam mass spectrometry studies give values for Z) (Cr-Me) = 37.9 2.0 kcal moH and )o(Cr+-Me) = 30.3+1.7 kcal mol. 2 Results also indicate that excited quartet states of Cr+ react very differently with alkanes than ground state Cr+( S). Calculations suggest that the metallacycles formed by insertion of transiticm metal atoms including Cr, Mo, and W into the C—O bond of ethene oxide are more stable than [metal + epoxide].  

The alkyl CrBut4 is sufficiently stable and volatile to be used as a source for chemical vapour deposition. Vapour deposition of Cr(CH2Bu04 at 250-350 C under a hydrogen atmosphere gave a mixture of cubic CtCi.x phase, amorphous Cr metal, Cr oxides, and free carbon in proportions depending upon on the deposition conditions.  

Addition of KTp [Tp = hydridotris(l-pyrazolyl)borate] W(OTf)2 =CH(Chfc2J ))(NAr)(DME) results in TpW(OTf) =CH(CMe2Ph) (NAr), which in the presence of AICI3 catalyzes the ringopening metathetical polymerizatirm of cyclooctraie. Addition of KTp Up = hydridotris(3,5-dimethyl-l-pyrazolyl)borate] to W(OTf)2 =CH(CMe2Fh) (NAr)(DME) results in the cationic 

Treatment of the chlorides CpMCl(NO)2 (M = Cr, Mo, but not W) with Cd(CF3)2(DME) affords CpM(CF3)(NO)2.208 Decarbonylation of CpMo CH2C(COMe)=CHMe CO)3 promoted by MeaNO results in the tt-allyl CpMo(CO)2 Ti3-CH2C(COMe)CHMe  

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Zr, Hf), group 6 (Cr, Mo, W), and group 10 (Ni, Pd, Pt). (Note that CrH6 was optimized with MoH -like angular geometry to prevent formation of the Cr(H2)3 dihydrogen complex.)... 

Like the corresponding hexacarbonyls the Group V1B triad M(PF3)6, M = Cr, Mo, and W (169, 227), exhibits only one UPS band below 12 eV that is attributable to the production of the 2 T2g ionic state by way of electron ejection from the occupied metal-centered t2g MO (Fig. 27). [However, in constrast to W(CO)6 no spin-orbit coupling effects are discernible in the UPS of W(PF3)6.] Group theoretical considerations indicate that in Oh symmetry the six metal-phosphorus a bonds span the irreducible representations a lg, eg, and tiu. In the case of Cr(PF3)6 these ionizations are apparently degenerate, possibly implying that metal-phosphorus bonding is weaker in the Cr complex... 

Interaction of metals with cyclopropenylidene to form stable complexes has been widely studied340 in the last two decades since the first reported synthesis of pentacarbonyl(2,3-diphenylcyclopropenylidene)chromium (see belowy4. Two groups of cyclopropenylidene metal derivatives may be distinguished neutral cyclopropenylidene complexes represented by two resonance forms, and the cationic cyclopropenylium transition metal complexes of groups 6 (Cr, Mo, W), 7 (Mn), 8 (Fe) and 10 (Pd, Pt), whereas the latter cationic cr-complexes are derived from both main group metals (Li, Mg) and group 10 (Pd, Pt) transition metals. 

A characteristic feature of d-group elements is their ability to form complexes with Tt-acceptor type ligands such as CO. All group-6 elements Cr, Mo, and W form very volatile and stable hexacarbonyls and constitute the only complete family of carbonyls. However, direct production of carbonyls from the elements and CO is only — if at all — accomplished at high pressures and temperatures. 

The synthesis of cyclopropyl carbyne complexes follows the general Fischer synthesis of carbyne complexes from alkoxycarbene complexes typical of transition metals of group 6 (Cr, Mo, W). Thus, addition of cyclopropyllithium to chromium and tungsten hexacar-bonyl followed by alkylation of the acylmetallate intermediate with triethyloxonium fluo-roborate gave cyclopropyl ethoxycarbene complexes which, upon subsequent reaction with boron tribromide at -25 °C, afforded the corresponding /ra 5 -bromotetracarbonyl cyclopropylcarbyne complexes (equation 91). However, whereas the monotungsten... 

The cocondensation of Nb atoms with toluene has yielded bis( -toluene)niobium, which serves as a useful intermediate for the preparation of a wide series of mono- and bis-arene derivatives. While Ti, V, Nb, Cr, Mo, and W form (Ar)2M sandwich complexes, Mn, Tc, and Re appear less promising, because Mn-arene complexes have already been shown to be unstable, Tc is radioactive, and Re remains to be investigated. As already mentioned, Ti forms fairly labile bis(arene)Ti complexes. The unstable 16-electron sandwich complexes from elements of group 4 can be stabilized with phosphine ancillary ligands, yielding bis-arene derivatives as in Table 6. 

The half-sandwich compounds of the trivalent group 6 metals (Cr, Mo, and W) demonstrate how the stmcture... 

Similar structural characteristics of the quadruply bridged dinuclear complexes of Pt(II), Pd(II), and Ni(II) indicate that the mixed-metal dinuclear complexes of these metal ions should be stable. However, probably because of the synthetic difficulties, only a few mixed-metal complexes of group 10 elements with such a structure have been prepared so far, although there are a number of examples having a doubly bridged structure (98, 99). For other metals, quadruply bridged mixed-metal complexes are known with the group 6 metal ions Cr, Mo, and W (1, 100, 101). 

Pulse radiolysis of solutions of the hexacarbonyl complexes M(CO)6 of the Group-6 metals M = Cr, Mo, and W has been shown to produce the corresponding penta-carbonyls, and the following mechanism was proposed [32] ... 

As mentioned in Section 7-1, second-row complexes tend to react faster than first- or third-row complexes in simple ligand substitutions that occur by a dissociative mechanism.35 This trend has been well studied for Group 6 complexes and is often observed with d9 and d10 metals. For the series of metal carbonyls M(CO)6 where M = Cr, Mo, and W, the observed order of reactivity does not mirror the order of M-C bond energies, which are W > Mo > Cr. The order does seem to correspond to the calculated values for the force constants of M-C bonds in Group 6 metal carbonyls.36... 

The most prominent systems studied thus far are the Fischer carbene complexes of the Group 6 metals, i.e., Cr, Mo and W, e.g., 4. One important process that will be discussed at some length in this chapter is nucleophilic substitution, e.g., the replacement of the MeO group by a group with a different heteroatom such as an amino or thioalkyl group. This reaction proceeds via a tetrahedral intermediate (equation 1) and is similar to nucleophilic substitutions on carboxylic esters. 

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