Reactions of benzylidene pentacarbonyltungsten with alkenes

Abstract

Addition of CF3C02H to a CHzClz solution of N ( C H~C H , )~+ ( C O ) S W C H ( O C H~) C~H~-(5) at -78 OC produces a red solution of ( C O ) S W C H C~H~ (4), which was characterized by low-temperature ' H N M R and by reaction with P(n-Bu3) to give (C0)5WCH [ P (~-B U )~] C~H~ (6). Thermal decomposition of 4 at -56 OC occurs with a half-life of 24 min. The reaction of 4 with alkenes occurs rapidly at -78 " C to give phenylcyclopropanes; no metathesis-like products were observed. The relative reactivity of alkenes toward 4 was in theorder CH>=C(CH3)2 > CH2=CHCH3 >> CHz=CHl, indicating that the reaction involved electrophilic attack of the carbene complex on the alkene. The stereochemistry of cyclopropane formation could not be explained in terms of formation of the most stable intermediate metallacyclobutane. The stereochemistry of cyclopropane formation is explained in terms of transition state 25 which involved formation of a bond from the carbene carbon atom of 4 to the less substituted end of an alkene and interaction of the positively polarized, more substituted end of the alkene with the ipso carbon atom of the phenyl group of 4

Metal-Assisted Cycloaddition Reactions in Organotransition Metal Chemistry

“…Naturally, such interference does not apply to benzylidene transfer reactions which can efficiently and stereoselectively be effected with (CO) 5 WdCH-C 6 H 4 R [17][18][19] or Cp(CO)(L)MdCH(C 6 H 4 R) + (M ) Fe, Ru; L ) CO, PPh 3 ; R ) p-H, p-F, p-Me, p-OMe). [20][21][22] Benzylidene transfer from (CO) 5 WdCHPh to the thiocarbonyl group in thiobenzophenones results in thiirane complexes.…”

Collision-induced dissociation study of stereospecific elimination processes of stereoisomeric phenylcyclohexanols and their derivatives upon electron ionization

“…The resulting yellow solution was warmed to 0 ¡C, stirred for 30 min, cooled to [78 ¡C, a solution of 8.5 g (33 mmol) of iodine in 25 ml of THF was added and the mixture was allowed to warm to room temperature and left overnight with stirring. The THP-ether of ethyl 4-hydroxy-1-phenylcyclohexanecarboxylate (36) Propylphosphonic dichloride (4 g, prepared by the reaction of 1-bromopropane with phosphorus trichloride and aluminum chloride) in diethyl ether was added to a solution of 2.5 g of s-dimethylethylenediamine in 200 ml of anhydrous diethyl ether and 50 ml of triethylamine with stirring at 0 ¡C under a nitrogen atmosphere and the solution was stirred for 3 h at 0 ¡C and overnight at room temperature. Addition of methylene chloride (50 ml) followed by Ðltration and evaporation yielded 3.12 g (73%) of N,N@-dimethyl-2-propyl-1,3,2-diazaphospholidene 2-oxide (37).…”

Towards a better understanding of alkene metathesis: elucidating the properties of the major metal carbene catalyst types

“…Therefore, in the dissociative mechanism, the stable metal carbene acts as a precatalyst and the unsaturated activated species is the catalyst. Certain metal carbenes, especially Fischer-type metal carbenes, however, form cyclopropane as a major side product of the alkene metathesis reaction [6,7]. Dedicated to Prof. Franz Stelzer for his lifelong contribution to metathesis research.…”

“…Four Fischer-(1-4) [6,7,14,15], a Tebbe-(5) [10], five Grubbs-(6-10) [5,8,[16][17][18][19] and a Schrock-type (11) carbene [11] were investigated (Scheme 1). All carbenes are presented in the initiated unsaturated active catalyst form except for 11 for which the dissociation of a ligand is not necessary for activity as catalyst.…”