Alkenes rhenium complexes

When alkenes are treated with certain catalysts (most often tungsten, molybdenum, or rhenium complexes), they are converted to other alkenes in a reaction in which the alkylidene groups (R RX=) have become interchanged by a process schematically illustrated by the equation ... 

Rhenium complex (37) has been used in the ring-opening metathesis polymerization of strained alkenes such as norbornene.37 The alkenes of the polymer backbone are predominantly Z, the polymer exhibiting high molecular weight and poly-dispersity. 

Gladysz has investigated the solution behaviour and configurational stability of these chiral rhenium complexes further, he extensively studied the chiral recognition process that results from the enantioface binding of alkenes, aldehydes and ketones on these rhenium chiral Lewis acids 3.7 and/or 3.8. There is a huge body of papers and reviews on this chemistry, and the reader may consult the referenced review. ... 

The reaction between excess RO2COCCO2R (R = Me, Et) and ReH5(ttp) (Op = PhP(CH2CH2CH2PPh2)2 affords complex 73. Electroidiilic alkynes react with the rhenium complex Re2(CO)9(NCMe) with displacement of the acetonitrile ligand and insertion of the alkyne into the Re— Re bond to form the trans dimetallated alkene complexes 74. Treatment of TcI(=NAt)3 with one equivalent of KCp results in formation of Tc(tii-CpX=NAr)3. Excess of KCp results in the complex Tc(ti -Cp)2(=NAr)3. > The alkyne RCCR (R = C02Me) inserts into a Mn— P bond of (OC)4Mn(Ti2-PPh2PAr) to form the diphosphamanganacyclopentene complexes 75. ... 

Synthesis and characterisation of the first organometallic Tc(VIII) complex [MeTcOs] is described. Its reactions with alkenes and with aromatic amine bases are different to those of the analogous rhenium complex. 25 Terminal alkynes react with [Tc(Cl)(dppe)2] to form vinylidene complexes [Tc(=C=CHR)(Cl)(dppe)2] (R = Ph, Me, Bu ). Treatment of these complexes with acid yields the respective carbyne complexes [Tc( CH2R)(Cl)(dppe)2]. The Tc-C bond lengths in these complexes vary form 1.861(9) to 1.724(7) A, 26... 

The reactions of olefins with non-organometallic Tc(VII) compounds behaved similarly. In a recent study, [Tc03C1(AaA)] (86a) (in which AA stands for aromatic diamine derivatives) was shown to react quantitatively with olefins, and produce the corresponding Tc(V) diolato-complex [TcOC1(OaO)(AaA)] (87a). The process could not be run catalytically, as Tc(V) complexes tend to undergo disproportionation rather than reoxidation in the presence of water [97]. These alkene-glycol interconversions could not be performed with the analog Re(VII) compound. Rhenium displays completely contrary behaviour, in that alkenes can... 

Finally, whilst rhenium hydride complexes have not been reported to hydrogenate alkenes, there are several reports of the dehydrogenation of alkanes in the presence of tBuCH=CH2 as an hydrogen acceptor (Scheme 6.14) [136-142]. For example, cycloalkanes are transformed catalytically into the corresponding cyclic alkene, which shows that, in principle, a Re-based catalyst could be designed. 

Narasaka and coworkers reported radical-polar crossover addition/cyclization reactions of phenacyl bromides 204 and electron-rich alkenes such as (silyl) enol ethers 205, catalyzed by the rhenium(I) complex 206 (Fig. 57) [302], The active catalyst 206A formed after thermal nitrogen elimination from 206 reduced 204 either directly or by oxidative addition/homolysis via rhenium enolate 204A to... 

Several complexes of rhenium(VII) with alkenes have also been studied in detail. Examples include compounds of the stoichiometry LRe03, studied by Rappe125 (L = Cp, Cp, CH3, OH,...) and Frenking126 as well as by Rosch (L = CH3).30,96 Rappe investigated these compounds in order to determine whether dihydroxylation or epoxidation is the preferred pathway while Rosch studied the MTO epoxidation pathways in great detail.96,99,100... 

Acyloxy)alkenyl carbene complexes, synthesis, 223-224 Alkenes, bishydroxylation cycloreversion of rhenium diolates, 148-156... 

Molybdenum, tungsten, and rhenium alkylidyne compounds similar to the complexes involved in alkene metathesis can metathesize alkynes via metallacyclobuta-diene intermediates ... 

Although high-valent rhenium-oxo complexes such as perrhenate, Rc207, and ReOjX (X = F, Cl, Br) are widely known, their use as oxidants is rather rare. The stoichiometric oxidation of alkenes to a mixture of ketone and epoxide by Rc207 has been reported in the patent literature. For example, 2-butene is transformed to 2,3-epoxybutane and 2-butanone by Rc207 at 100 °C. A catalytic oxidation was observed in the presence of excess hydrogen peroxide but precise data on this reaction are lacking. 

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