Allenylidene reduction

Quite recently it has also been reported that the neutral Mn(I) allenylidene [MnCp(=C=C=CPh2)(CO)(PPh3)] catalyzes the reduction of protons from HBF4 into dihydrogen via initial formation of the corresponding alkenyl-carbyne [MnCp... 

Other catalytic reactions involving a transition-metal allenylidene complex, as catalyst precursor or intermediate, include (1) the dehydrogenative dimerization of tributyltin hydride [116], (2) the controlled atom-transfer radical polymerization of vinyl monomers [144], (3) the selective transetherification of linear and cyclic vinyl ethers under non acidic conditions [353], (4) the cycloisomerization of (V2V-dia-llyltosylamide into 3-methyl-4-methylene-(V-tosylpyrrolidine [354, 355], and (5) the reduction of protons from HBF4 into dihydrogen [238]. 

Reductive Coupling Reaction via Hydroboration of Allenylidene Intermediates... 

Reductively induced alterations from cumulenic to alkynyl resonance structures have been observed for mononuclear and dinuclear ruthenium allenylidene complexes. The half-wave potentials for the one-electron reduction of allenylidene complexes [ Ru = C = C = C(ER )(R )] ( Ru = trun.s-Cl(L2)2Ru L2 = chelating diphosphine ER = NR2, SR, SeR, aryl, alkyl R = aryl, alkyl) strongly depends on the nature of the ER substituent. Amino- and aryl-substituted congeners with reduction potentials of ca. -2.2 V and -1.0 V, respectively, constitute the two extremes within this series. These sizable potential... 

These studies imply that allenylidene cations [CpRu(=C=CHR)(AZARYPHOS)2] are reaction intermediates their attack by water produces a tautomeric metal acyl species with a hydrogen-bond to the pyridine nitrogen (Scheme 23b), as proven by multidimensional NMR experiments involving markers [133], Current work is addressing the details of reductive elimination of aldehyde from the acyl complex. 

PropargyUc alcohol 124 was fragmented into the alkene 128 and CO in the presence of a ruthenium catalyst (Scheme 7.47) [66]. Oxidative addition of the C-H bond to ruthenium affords alkynylruthenium 125, which is converted into the allenylidene complex 126 with elimination of hydroxide anion. The hydroxide then adds to the allenylidene carbon directly connected to the ruthenium center, leading to the formation of acylruthenium 127 via tautomerization. Subsequent migratory deinsertion of CO followed by reductive elimination gives 128. 

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