Molybdenum silyl complexes

The molybdenum complex [(CF3)2MeCO]2Mo(NAr)(=CHCMe2Ph) has been observed to be a more efficient catalyst for cyclization of vinyl silyl ether dienes than the ruthenium complex Cl2(PCy3)2Ru(=CHPh), probably because this type of alkene is sterically more demanding (than allyl derivatives) and therefore requires a catalyst less sensitive to steric bulkiness near the reaction center. However, some examples of the RCM of substituted vinylsilanes catalyzed by ruthenium complexes have been reported [127, 131] (Eq. 74). For more examples see Ref. [127]. 

Ethene, molybdenum complex, 26 102 rhenium complex, 26 110 Europium, tetrakis[T) -l, 3-bis(trimethyl-silyl)cyclopentadienyl]di-p.-chloro-di-, 27 171... 

Treatment of Cp"Cr(Ti -Cot), Cp" = Cp, Cp with (EtCN)3M(CO)3, M = Mo, W and Fe2(CO)9 affords the complexes [(Cp Cr)(CO)3M][ i-Cot], M = Fe, Cr, W, Cp = Cp and I(Cp Cr)(CO)3Crl/i-Cot, Cot = Cyclooctatetrane, which have been spectroscopically characterised. Bimetallic complexes containing bis(tetramethylcyclopentadienyl) dimethylsilane bridges have been prepared from the reaction of arene tricarbonyl molybdenum complexes with the silyl substituted cyclopentadienyl derivative. The synthesis of pinanylcyclopentadienes followed by metallation and reaction with Mo(CO)s and Mel gives the chiral (-)-[(ii -C5Me4-3-pinanyl)(CO)3Me], which has been structurally characterised. The chiral methallyl complexes CpMo(NO)X(Ti -2-methallyl) X = camphorsulfonate have been resolved and the reactions of the... 

The ruthenium carbene catalysts 1 developed by Grubbs are distinguished by an exceptional tolerance towards polar functional groups [3]. Although generalizations are difficult and further experimental data are necessary in order to obtain a fully comprehensive picture, some trends may be deduced from the literature reports. Thus, many examples indicate that ethers, silyl ethers, acetals, esters, amides, carbamates, sulfonamides, silanes and various heterocyclic entities do not disturb. Moreover, ketones and even aldehyde functions are compatible, in contrast to reactions catalyzed by the molybdenum alkylidene complex 24 which is known to react with these groups under certain conditions [26]. Even unprotected alcohols and free carboxylic acids seem to be tolerated by 1. It should also be emphasized that the sensitivity of 1 toward the substitution pattern of alkenes outlined above usually leaves pre-existing di-, tri- and tetrasubstituted double bonds in the substrates unaffected. A nice example that illustrates many of these features is the clean dimerization of FK-506 45 to compound 46 reported by Schreiber et al. (Scheme 12) [27]. 

Ojima and co-workers first reported the RhCl(PPh2)3-catalyzed hydrosilylation of carbonyl-containing compounds to silyl ethers in 1972.164 Since that time, a number of transition metal complexes have been investigated for activity in the system, and transition metal catalysis is now a well-established route for the reduction of ketones and aldehydes.9 Some of the advances in this area include the development of manganese,165 molybdenum,166 and ruthenium167 complex catalysts, and work by the Buchwald and Cutler groups toward extension of the system to hydrosilylations of ester substrates.168... 

TRICARBONYL-(ii5-CYCLOPENTADIENYL)SILYL COMPLEXES OF CHROMIUM, MOLYBDENUM, AND TUNGSTEN... 

The orange complex is air sensitive in the solid state. It is reasonably soluble and stable in THF but decomposes in nonpolar solvents, such as benzene, to give polymeric halogen-bridged products.9 It is paramagnetic with a magnetic moment of 3.63 BM, and its IR spectrum shows a very intense band at about 820 cm-1 due to coordinated THF. Its reactions with tertiary phosphines in THF give a series of molybdenum (III) tertiary phosphine complexes,9 and with trimethyl-silyl azide Mo(V) nitrido complexes are formed.8... 

OLuSiC,HH24, Lutetium, bis(T] -cyclopenta-dienyl)(tetrahydrofuran)[(trimethyl-silyl)methyl]-, 27 161 O, Oxide, gold complex, 26 326 ON, Nitrosyls, molybdenum and tungsten, 26 132, 133... 

Many metal silyl complexes, especially those with early transition metals, have weak metal-silicon bonds. The molybdocene silyl hydride complexes seem to have molybdenum-silicon bonds of sufficient strength to withstand nucleophilic attack by strong hydride reagents (Eq. 4)... 

We must however keep in mind that some of the above reactions may not be simple reactions at the silicon atom, since transition metal complexes show multicenter reactivity (metal atom, ligands) as exemplified in the chemistry of triphenylgermyl-carbene complexes of cobalt carbonyl (253). Thus, displacements of a silyl ligand may result from a multistep process and a thorough examination of these reactions has to be made. An example can be drawn from molybdenum-germanium chemistry (247). As shown in Scheme 59, germanium is displaced from complex 167 by HO with retention of configuration. Actually,... 

As for the diols, the symmetric compounds have found most uses for nonsymmetric diols, a versatile synthesis via silyl ketones using the SAMP/RAMP methodology has been developedl5. Both enantiomers of the simplest symmetric diol, 2,3-butanediol (11), are often used in asymmetric synthesis, mostly for the formation of acetals and ketals with carbonyl compounds and subsequent reactions with acidic catalysts (Section D. 1.1.2.2.), Grignard reagents (Section D. 1.3.1.4.) and other carbanions (Sections D. 1.5.1., D. 1.5.2.4.), and diastereoselective reductions (Section D.2.3.3.). Precursors of chiral alkenes for cycloprotonations (Section D.1.6.1.5.) and for chiral allenes (Section B.I.), and chiral haloboronic acids (Section D. 1.1.2.1.) are other applications. The free diol has been employed as a chiral ligand in molybdenum peroxo complexes used for enantioselective epoxidation of alkenes (Section D.4.5.2.2.). 

The gas-phase equilibrium between 2-hydroxypyridine and 2-pyridone favours the hydroxy-form, but in the equilibrium between 2-hydroxypyridine iV-oxide and N-hydroxy-2-pyridone, the major tautomer is the hydroxy-pyridone. Bicyclic adducts between 2-pyridones and dimethyl acetylene-dicarboxylate, unobtainable at atmospheric pressure, have been obtained at 10—15 kbar. A novel route to iV-hydroxy-2-pyridone involves the trimethyl-silylation of 2-pyridone followed by oxidation of the resulting 2-(trimethyl-silyloxy)pyridine with the DMF complex of molybdenum pentoxide. p-Nitro-phenols (45) and nitro-acetamides (46) are formed from the reaction of 3,5-dinitro-2-pyridones (43) with the sodium salts of /3-keto-esters (44) (Scheme 20). ... 

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