Complexes of Cr, Mo, and

Carbonyl Complexes of Cr, Mo, and W.—Many new ligand substituted carbonyls of the Group VI metals have been reported during 1980, almost all having been prepared from conventional starting materials such as [M(CO)e], [M(C0)5(THF)], [M(C0)6X]- (X=C1 or I), [M(CO) (NCMe) ] (n=l—3), [M(CO)4(nbd)], or [M(CO)3(chpt)]. Most are listed in Table 1, the remainder being discussed below. 

The complexes (6) result from the irradiation of the platinum(ii) pyrazolyl complexes in the presence of [M(CO)e].  

The cis.trans [W(CO)4(PR3)2] product ratio from reactions of PR3 with [W(CO)4 Me2N(CHa)3NMe2 ] depends on phosphine size, smaller phosphines favouring the cis form. For cis- and /ra/w-[W(CO)4(PR3)(ER 3)] [PR3, ER 3= various phosphines, phosphites, AsPhg, or SbPhg] an isomeric equilibrium is attained between 20 and 80 °C with the trans isomer being thermodynamically favoured for nearly every complex. The photochemistry of several of the trans isomers has also been examined.  

Reaction of [CpMo(CO)3Cl] with Bu SH in the presence of NEta produces [CpMo(CO)2( U-SBu )]2, the p-tolS-analogue being obtained by u.v. irradiation of [CpMo(CO)3]a with p-tolgSa. Decarbonylation affords [CpMo(CO)( -SR)]a species. The molecular structures of [CpMo(CO)2(/ -SPh)]2 co-crystallized with 

In the free state 2-azidopyridine exists mainly in its tetrazole form as tetrazolo-[l,5-a]pyridine. Reaction of this ligand with [M(CO)5(THF)] (M=Cr or W) gives [M(CO)sL] with the ligand in the tetrazole form. The anions of N- 

The reaction of the carbyne [Cr(CO)5(CNEt2)][BF4] with [Bu 4N][N3] yields the nitrile complex [Cr(CO)5(NCNEt2)] in which the CrNCN skeleton is linear. The first phosphazide and monosubstituted triazenide complexes, 

Mo(CO)a is decarbonylated on reaction with picolinic acid (picH) to give eight-co-ordinate [Mo(pic)4], and reaction of a mixture of Mo(CO)e, W(CO)8, and 2-hydroxy-6-methylpyridine (Hmhp) affords [MoW(mhp)4] containing a heteronuclear metal-metal quadruple bond.  

The first complexes (11) containing a Tt-bonded heterocyclic ring in which the heteroatom is also cr-bonded to a second metal atom have been isolated by reaction of M(CO)e with the phosphorin.  

CNEt2)2] and [W aO -S)2(OMe)4(S2CNEt2)2] result from the reaction of [W(CO)3-(NCMe)s] with Et2NC(S)SSC(S)NEt2 in MeOH. The W-W bond lengths of 2.53 A and 2.79 A suggest the presence of double and single metal-metal bonds, respectively. 

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Table 8-6. Bond lengths for neutral hexacarbonyl complexes of Cr, Mo, and W in Oh symmetry [A],...

Table 1. Activation barriers (in kcal/mol) calculated for various mechanisms of ethene epoxidation by model peroxo complexes of Cr, Mo and W (see Fig. 1).

It is, however, for the transition metals themselves that DFT has proven to be a tremendous improvement over HF and post-HF methods, particularly for cases where tlie metal atom is coordinatively unsaturated. The narrow separation between filled and empty d-block orbitals typically leads to enormous non-dynamical correlation problems with an HF treatment, and DFT is much less prone to analogous problems. Even in cases of a saturated coordination sphere, DFT methods typically significantly ouqierform HF or MP2. Jonas and Thiel (1995) used the BP86 functional to compute geometries for the neutral hexacarbonyl complexes of Cr, Mo, and W, the pentacarbonyl complexes of Fe, Ru, and Os, and the tetracarbonyl... 

The cation can be reduced to dibenzenechromium with sodium dilhionile, Na-jS-.Oj. The dibenzene complexes of Cr, Mo. and W are all air sensitive and those of Mo and W are especially so. Dibenzenechromium is a black solid that melts at 280 °C. 

Mononuclear cis-biscarbene complexes of Cr, Mo and W were obtained from M(CO)metallates with [EtjO][BF4]. Binuclear biscarbene complexes with a bridging carbene ligand are synthesized from (CO)jM (M = Cr, W) and Li2[p-C H4]-[Et30][BF4]. ... 

Recently an indication of path A has been shown by investigating solvolysis of the 7-substituted norbornadiene complexes of Cr, Mo, and W 90). It was found that in an 80% acetone-water solution at 25°C,(t7-C7H7C1)Mo (CO)4 gives free 7-norbornadienol instead of the expected (t7-C7H70H)Mo (CO)4- Moreover, the solvolysis rate constant was of the same order of magnitude as that for free 7-chloronorbornadiene. All these data support fast dissociation of the type... 

Several modifications of the aluminum method are known. The cation [(MeCeHg)2Cr] has been prepared by the reduction of Cr(acac)3 with R3AI (R = Et, i-Bu) or (i-Bu)2A1H in toluene 333). Bisarene cation complexes of Cr, Mo, and W have been prepared directly by the reaction of aromatic hydrocarbon, AICI3, HCl, and the metal powder 70). 

The step considered to lead to first-order dependence in both (CgH0)Cr-(CO)3 and benzene is depicted in Eq. (19b). Similar conclusions were arrived at for substituted benzene complexes of Cr, Mo, and W 400). The rate of exchange for a given arene was found to increase in the order Mo > W > Cr 400). 

Phosphine and phosphite ligands react with arene tricarbonyl complexes of Cr, Mo, and W yielding complexes of the type /ac-(PRg)3M-(CO)3 32, 261, 341-343, 466). Kinetic studies reveal that the reaction proceeds by an 8 2 mechanism 341-343, 466) which is thought to involve the stepwise displacement of the arene via tetrahapto- and dihapto-coordinated arene intermediates 466) ... 

The reactivity of carbonyls of Cr, Mo, and W with alkyl lithium is somewhat lower than that of nickel and iron carbonyls. The most interesting reaction of these metal carbonyls, found and studied extensively by Fischer and his coworkers, is the formation of carbene complexes 98-"). Phenyl or methyl lithium adds readily to W(CO)6 at room temperature to form carbonylate complexes. The tetramethyl ammonium salt of the complex is treated with acid and then with diazomethane to give a neutral complex whose structure was found to be that of a carbene complex. In this way a series of carbene complexes of Cr, Mo, and Mn were synthesized. 

Only a few cyanate complexes have been reported for Cr and Mo. Both in these complexes and in related thiocyanate complexes of Cr, Mo and the NCX ligands are terminal N-bonded. 

The NMR spectra of mesitylene and durene complexes of Cr, Mo, and W have been obtained by Mann (147). In this study the author demonstrated that changes in C-C bond length in the n ligand could be correlated with the shift of the ligand carbons on complexation. 

An alternative to the construction of multiplet states is the use of time-dependent DFT (TDDFT, see Chapter 2.40). TDDFT not only offers the potential for computing accurate transition energies but also provides the transition moments so that the intensity of the transition can be assessed. For example, hexacarbonyl complexes of Cr, Mo, and W have been analyzed using relativistic TDDFT. In contradiction of the original interpretation of the lowest... 

Following our interest on the redox properties of transition metal isocyanide and carbene complexes [1], we report the investigation of the electrochemical behaviour of new phosphonium-fiinctionalized isocyanide (A), and derived carbene (B), indole (C) and protonated indole (D) complexes of Cr, Mo and W pentacarbonyls. These studies appear to have been undertaken for the Erst time for complexes with such types of ligands. It was also our object to correlate the redox properties of these compounds with the electron donor/acceptor ability of these ligands. Moreover, this study would also extend to novel carbene complexes the rather limited electrochemical investigation reported [2] for compounds with multiple metal-carbon bonds. 

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