Bis vinylidene

Oxidation ]PhIO or Cu(OAc)2] of ]Fe(=C=CHMe)(dppe)Cp]" affords bis(vinyli-dene) ] Fe(dppe)Cp 2(p-C4Me2)], possibly via an intermediate radical cation ]222]. Similar oxidative coupling of cyclopropenyl Ru C=CPhCH(CN) (PPh3)2Cp affords bis(vinylidene) ] Cp(Ph3P)2Ru =C=CPhCH(CN)2 2] which, in turn, can be de-protonated to the bis(cydopropenyl) ]223]. Oxidation of ]Ru(N4Meg)(=C=CH2)] with PhNj or ]FeCp2]+ affords ] Ru(N4Meg) 2(p-C=CHCH=C)] ]51]. 

Vinylidene and carbyne complexes also offer a rich chemistry following electron transfer, and a comprehensive review on that topic is available in the literature.As an example, oxidation of vinylidene complexes generates highly reactive radical cations. These may undergo a host of different follow-up reactions and they are summarised in Scheme 6.10. Possible follow reactions include dimerisation by direct Cp—Cp homocoupling to dinuclear butanediyli-dyne complexes M " =C—CRH—CRH—deprotonation to 17 valence-electron alkynyl radicals M —C=CR, which subsequently dimerise to the corresponding bis(vinylidenes) (= 1,3-butadiene-1,4-diylidene derivatives) M = C = CR-CR = C = C Mf and CH-bond homolysis. The latter... 

Scheme 4. Li-mediated radical coupling of a vinylidene phosphine to give a bis(diphos-phinomethanide) complex. Reproduced with permission from W. Clegg et al., Organo-metallics 1998, 17, 5231. Copyright 1998, the American Chemical Society.

A most significant advance in the alkyne hydration area during the past decade has been the development of Ru(n) catalyst systems that have enabled the anti-Markovnikov hydration of terminal alkynes (entries 6 and 7). These reactions involve the addition of water to the a-carbon of a ruthenium vinylidene complex, followed by reductive elimination of the resulting hydridoruthenium acyl intermediate (path C).392-395 While the use of GpRuGl(dppm) in aqueous dioxane (entry 6)393-396 and an indenylruthenium catalyst in an aqueous medium including surfactants has proved to be effective (entry 7),397 an Ru(n)/P,N-ligand system (entry 8) has recently been reported that displays enzyme-like rate acceleration (>2.4 x 1011) (dppm = bis(diphenylphosphino)methane).398... 

Unusual iron-porphyrin vinylidene complexes were obtained from DDT [l,l-bis(4-chlorophenyl)-2,2,2-tricMoroethane] and Fe(tpp) [tpp = meso-tetraphenylporphinato (2-)] in the presence ofa reducing agent [10a, 264]. The derived N,N -vinylene-bridged porphyrin reacts with metal carbonyls [Fe3(CO)i2, Ru3(CO)i2] to break one or both N—C bonds with insertion of the vinylidene into an M—N bond. While the iron complex was formed in 90% yield, the reaction with Ru3(CO)i2 afforded three products, the vinylidene being formed in only 40% yield [265]. 

Although the chemistry of bi- and poly-nuclear vinylidene complexes is beyond the scope of this chapter, several examples of the interaction of metal-vinylidene fragments with a second metal-ligand fragment have been described. This type of reaction usually produces complexes containing bridging vinylidene ligands (Equation 1.21) ... 

Recently, isolable bis (triphenylstannyl)-substituted butatrienylidene complexes of manganese (13) were obtained by photolysis of alkynyl(triphenylstannyl)vinylidene complexes 12 (Scheme 3.9) [4, 5]. Treatment of the resulting bis(stannyl)butatrie-nylidene complexes 13 with tetrabutylammonium fluoride and water afforded the first characterizable butatrienylidene complexes (14) containing an unsubstituted [M=C=C=C=CH2] moiety (Scheme 3.9). In contrast to 13, complexes 14 were unstable above —5 °C and were therefore characterized in solution only by NMR spectroscopy at —40°C. Complexes 14 were also formed instantaneously when solutions of 12 were treated at — 30 °C with one equivalent of tetrabutylammonium fluoride. 

Materials. For holographic information storage, materials are required which alter their index of refraction locally by spotwise illumination with light. Suitable are photorefractive inorganic crystals, eg, LiNb03, BaTi03, LiTa03, and Bi SiO. Also suitable are photorefractive ferroelectric polymers like poly(vinylidene fluoride-co- trifluorethylene) (PVDF/TFE). Preferably transparent polymers are used which contain approximately 10% of monomeric material (so-called photopolymers, photothermoplasts). These polymers additionally contain different initiators, photoinitiators, and photosensitizers. 

The acylate anion from Mn(CO)3(j/-C5H5) and LiMe reacts similarly reaction with l,8-bis(dimethylamino)naphthalene (proton sponge) affords the vinylidene, although in this reaction, it is the binuclear complex which is isolated as the final product (38) ... 

Acetylene-vinylidene rearrangements of silylacetylene-iron carbonyl complexes have been observed,537 while iron-acetylide hydride complexes of the type [Fe(H)(C=CR)(dmpe)2], where dmpe=l,2-bis(dimethylphosphino)ethane, have been found to react with anions to afford substituted alkenyl complexes. It has been proposed538 that a likely reaction course for this latter rearrangement involves initial protonation of the cr-bound acetylide ligand at the carbon (I to the metal centre to form a vinylidene complex. Metal-to-carbon hydride migration in this vinylidene complex with attack by the anion would then lead to the neutral complex (see Scheme 106). A detailed mechanistic investigation has been carried out539 on the novel metathetical... 

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