Metallacycles thermolysis

Donor-substituted alkynes can insert into the C-M double bond of alkoxycarbene complexes, yielding donor-substituted vinylcarbene complexes [191,192]. In addition to this, photolysis or thermolysis of a-alkoxycyclopropyl carbonyl complexes or a-alkoxycyclobutanoyl complexes can lead to rearrangement to metallacyclic carbene complexes (Table 2.11). This methodology has not been used as extensively for the preparation of carbene complexes as the other methods described above. 

The major product of the reaction of [(rj -CplaTiMea] with dimethylacetylene is the titanacyclopentene 161 (R = Me) <2000POL879>. With diethylacetylene metallacycle, 161 (R = Et) is formed. Thermolysis of bis(methylcy-clohexenyljzirconocene in the presence of trimethylphosphine and further reaction with diphenylacetylene gives 162. Allene complex 163 reacts with 2-butyne or diphenylacetylene to yield the titanacyclopentenes 164 (R = Me, Ph). 

Imido zirconocenes see Imide Complexes) are synthesized from thermolysis of Cp2Zr(Me)NHR. They react with a wide variety of organic substrates (alkynes, imines, azides, carbodiimides, ketones) to yield [2 + 2] cycloaddition products (Scheme 4) see Metallacycle) ... 

Cp2Ti(CH2Ph)2 is thermolyzed in the presence of acetonitrile to give the double insertion product (Scheme 519). The reaction with cyclododecanone leads to olefination. The major product in the thermolysis of Cp(C5H4But)Ti(CH2Ph)2 in toluene is the metallacycle shown in Scheme 520, which results from the C-H activation of one methyl ligand of the Buc group and elimination of toluene.1327... 

Some rare cases of cyclopropane formation from metallacycles other than metallacyclobutanes have been reported. Thus thermolysis of a rhenacyclopentane 3, obtained from CpRe(CO)2H2 (1) and 1,4-diiodobutane (2), yields methylcyclopropane (4) in near quantitative yield. Based... 

Not much is known about such systems and the heterocyclic nature of these metallacycles is questionable. The few reports concerning this area have involved the postulation of 1,3-thia-tungstacycles as intermediates during thermolysis of their 1,2-congeners <84CC964, 86JCS(D)1577>... 

Thermolysis of complexes Vila and VIIc, respectively, gives p-tolylalkylketone and the expected cyclopropane derivative, but no 7t-alkene or metallacycle intermediate is... 

When 0s(02CMe)2(PMe3)4 reacts with PhCH2MgCl, a product formulated as the osmacycle is isolated . A related benzomanganacyclobutene is reportedly the thermolysis product from the remarkable inert (dmpe)Mn(CH2Ph)2 in the presence of xs dmpe. Metallacyclization of this precursor or of (dmpe)Mn(CH2SiMe3)2 cannot be photo- or thermochemically induced in the absence of dmpe . ... 

Perhaps the most remarkable illustration of the ability of metals to activate alkynes comes from reactions in which complete scission of the carbon-carbon triple bond occurs. On the stoichiometric level these include examples in which carbyne complexes are produced from alkyne completes as in the melt-thermolysis of CpCo(PPh3)(RCsCR) [112] or from reactions of alkynes with unsaturated metal species (Scheme 4-34) [113]. The remarkable alkyne metathesis reaction (Scheme 4-35), which involves overall cleavage and regeneration of two o-and four rt-bonds, is conceptually related. A variety of functionalized alkynes can be tolerated as metathesis substrates [114] and especially effective catalysts for these reactions are Mo(VI)-and W(VI)-carbyne complexes. Metallacyclobutadienes 64, formed by the reaction of the alkyne with a metal-carbyne complex, appear to be central intermediates in these reactions and the equilibrium between metallacycle and alkyne/metal-carbyne is observable in some cases [115]. 

Another case of bimetallic cooperative C-S bond activation involves the reaction the triphos-Rh BT-derived metallacycle with W(CO)s to yield the heterobimetallic sulfur-bridged species 47, which upon thermolysis under H2 (30 atm) induced HDS of BT to ethylbenzene, plus [(triphos)RhH(CO)] together with an insoluble W-S material (Equation (9)). This shows that the S-bridged Rh-W couple switches the reactivity from hydrogenolysis... 

Thermolysis of Cp2TiMe2 in the presence of internal alkynes affords the corresponding titanacyclobutenes. The reaction is first order in Cp2TiMe2 and there is a primary kinetic isotope effect. Two equivalents of nitriles RCN react to give the diaza metallacycles... 

Thermolysis of the amides Cp2Zr(THF)(=NBu ) in benzene at 85°C affords the aryl complex Cp2ZrPh(NHBu ) and THF. The reaction between various complexes Cp2ZrL(=NR) (R = Bu , C6H3Mb2-2,6) and alkynes R OCR affords the metallacycles Cp r C(R2)=C(R )-NR). Some alkenes behave in similar fashion to form metallacyclobutanes. The reaction between NCC6H4CN and Cp2Zr(butadiene) is sensitive to conditions. Addition of the nitrile to the zirconium reagent results in complex 36. ... 

Addition of CpMo(CH20Me)(CO)2 P(OPh)3) to PhaC in 01202 results in the carbene [CpMo(CO)2 =C(OMe)H P(OPh)3 ] . On standing in solution at ambient temperature for 24h this converts into the metallacycle 112. The same species is produced through the thermolysis of CpMo(CH2Br)(CO)2 P(OPh)3. The formyl complex CpMo(CHO)(CO)2 P(OPh)3 reacts with... 

The dipolar addition reaction between DMAD or dimethyl maleate and the diimine species [Fe(CNR)3(Pr N=C HCH=NPr>)] (R = Bu , CH2Ph, Cy, 2,6-xylyl etc.) occurs to give complexes of type (4) in the case of [Fe(CO)2(CNR)(Pr N=CHCH=NPri)] there is a competition between CO and CNR insertion into the metallacycle. Compounds containing fused pyrrole rings arc also formed which on heating release substituted 2-vinylpyrroles. -64 similar cycloaddition also occurs between [Fe(C0)3(Bu N=CHCR=0)] (R = Me, Ph) and DMAD. 5 Purther details of the insertion of alkynes into vinylketene iron tricarbonyl complexes have appeared thermolysis of the insertion products gives cyclopentenediones or phenols. -... 

Reduction of ZrCl(CH2PPh2)Cp2 with LiAlH(0Bu >3 provides ZrH(CH2PPh2)Cp2 which upon thermolysis or treatment with BuLi gives metallacycle 7(CH Ph2)Cp2 and ZrHCp2. On the other hand, reaction with phosphines gives ZrH(PR3)Cp2 and the metallated... 

Thermolysis of either methyl compound proceeds by y-hydrogen-atom elimination to produce a metallacycle (21) [74, 75] ... 

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