O-Alkenyl complexes

Intermolecular hydroalkoxylation of 1,1- and 1,3-di-substituted, tri-substituted and tetra-substituted allenes with a range of primary and secondary alcohols, methanol, phenol and propionic acid was catalysed by the system [AuCl(IPr)]/ AgOTf (1 1, 5 mol% each component) at room temperature in toluene, giving excellent conversions to the allylic ethers. Hydroalkoxylation of monosubstituted or trisubstituted allenes led to the selective addition of the alcohol to the less hindered allene terminus and the formation of allylic ethers. A plausible mechanism involves the reaction of the in situ formed cationic (IPr)Au" with the substituted allene to form the tt-allenyl complex 105, which after nucleophilic attack of the alcohol gives the o-alkenyl complex 106, which, in turn, is converted to the product by protonolysis and concomitant regeneration of the cationic active species (IPr)-Au" (Scheme 2.18) [86]. 

Rosenthal U, Ohff A, Michalik M et al (1993) Transformation of the first zirconocene alkyne complex without an additional phosphane ligand into a dinuclear o-alkenyl complex by hydrogen transfer from ti -C5H5 to the alkyne ligand. Angew Chem Int Ed Engl 32 1193-1195... 

Alkyne (HC=CC02Et) insertion into the Co-H bond of the complex [Co(np2)H] [np2=N(CH2CH2PPh2)3], followed by the addition of NaBPh, affords the o-alkenyl complex, [Co(np3) C(C02Et)=CH2 ] tBPh ]. Oxidation of an aqueous solution of Lco(dacoda)(H2O)] (dacoda=l,5-... 

The carbonyl complexes in Table XIV are of three types, tricarbonylchromium r] -arene complexes, pentacarbonyltungsten o-pyridine complexes, and car-bonylruthenium o-alkenyl complexes, the first two possessing low y values. For the first two types, lengthening the 7i-system or replacing acceptor by donor substituent on the tricarbonylchromium-coordinated arene ring results in... 

As with aryls, the sp2 hybridization of o-alkenyls may contribute to both an increased BDE and also access to decomposition routes homoleptic examples, e.g. Zr(CPh=CMe2)4, are particularly rare. Decomposition of c/s-bis lkenyl) complexes via reductive elimination of buta-1,3-dienes is occasionally observed however, the butadiene may remain coordinated (Figure 4.11). 

Ind-amido titanium complexes with o -alkenyl functions in position 2 of the indenyl ring have been synthesized and characterized. After activation with MAO, these complexes were used as homogeneous and heterogeneous catalysts for the homopolymerization of ethylene and propylene and the co-polymerization of ethylene and 1,7-octadiene.406 A series of alkyl-, u -alkenyl-, and u -phenylalkyl-substituted Cp- and Ind-amido dichloro titanium complexes have been synthesized and characterized. The cj-phenylalkyl-substituted complexes react with LiBu to give metallacycles via a CH activation reaction on the ortho-position of the phenyl group (Scheme 305).741 742 After activation with MAO, these complexes catalyze ethylene polymerizations. The substituents on the aromatic system influence the polymerization activity of the catalysts and the properties of the polyethylene. The u -alkenyl-substituted catalysts show self-immobilization in ethylene polymerization. 

A coordinatively unsaturated 14-electron palladium(0) complex, usually containing two tertiary phosphanes as weakly electron-donating ligands, has been proved to be the catalyUcaUy active species. It is conunonly generated in situ from either from a palla-dium(0) complex or by reduction of relatively inexpensive paUadium(II) acetate or chloride.In the first step of the catalytic cycle ( in Scheme 1), a haloalkene, a haloarene, or a similar substrate is oxidatively added to the coordinatively unsaturated paUadium(O) species to generate a tr-alkenyl- or (r-arylpalladium(II) complex.f t This then coordinates an alkene molecule, and when the latter and the alkenyl (aryl) residue on the palladium are in a cis orientation, the cr-alkenyl- or o--arylpalladium complex can... 

D.ii.c. Termination by Boranes (Heck-Suzuki Cascade). Similarly, boranates and boronates are suitable reagents for the transfer of aryl or alkenyl groups to rr-alkyl-, o--alkenyl-, and o--arylpalladium complexes and hence are ideal for termination of cascade reactions. Tetraphenylboranate is the reagent of choice for the phenylation of organopaUadium intermediates (Scheme 28). ... 

In the first step of the sequence (A in Scheme 8.1), a haloalkene or haloarene is commonly assumed to add oxidatively to the coordinatively unsaturated palla-dium(O) complex, generating a o-alkenyl- or a-arylpalladium(II) complex [15]. As... 

The reaction of 2-norbomenyllithium with Cp2ZrMe(Ph) affords the alkenyl complex 42. This carbonylates exclusively through insertion into the Zr—C(sp ) bond to form the crystallographicaliy characterized T 2-acyl coin lex 43. This species adopts the thermodynamically preferred "O-inside arrangement. Thermolysis of Cp2TiMe(C6H40Me-2) in the presence of... 

Heck reaction, palladium-catalyzed cross-coupling reactions between organohalides or triflates with olefins (72JOC2320), can take place inter- or intra-molecularly. It is a powerful carbon-carbon bond forming reaction for the preparation of alkenyl- and aryl-substituted alkenes in which only a catalytic amount of a palladium(O) complex is required. 

The electrophilic character of the palladium atom in the complexes formed by oxidative addition of aryl halides and alkenyl halides to palladium(o) complexes can be exploited in useful ways. 

The intramolecular addition of the O-H bond to alkynes catalyzed by palladium complexes has been developed by K. Utimoto et al. (Eq. 6.59) [104]. An alkynyl alcohol can be converted to a cyclic alkenyl ether in the presence of a catalytic amount of [PdCl2(PhCN)2 or [PdCl2(MeCN)2] in ether or THE at room temperature. When the reaction was carried out in MeCN-H20 under reflux in the presence of a catalytic amount of PdCl2, hydration of the acetylenic alcohol occurred and the ketoalcohol was obtained in good yield instead. 

The initially proposed mechanism [14], and one that continues to be considered as the likely pathway for most variants, involves the oxidative cyclization of a Ni(0) complex of an aldehyde and alkyne to a metallacycle (Scheme 18). Metallacycle formation could proceed independently of the reducing agent via metallacycle 19, or alternatively, metallacycle 20a or 20b could be formed via promotion of the oxidative cyclization transformation by the reducing agent. Cleavage of the nickel-oxygen bond in a o-bond metathesis process generates an alkenyl nickel intermediate 21. In the variants involv-... 

A typical second step after the insertion of CO into aryl or alkenyl-Pd(II) compounds is the addition to alkenes [148]. However, allenes can also be used (as shown in the following examples) where a it-allyl-r 3-Pd-complex is formed as an intermediate which undergoes a nucleophilic substitution. Thus, Alper and coworkers [148], as well as Grigg and coworkers [149], described a Pd-catalyzed transformation of o-iodophenols and o-iodoanilines with allenes in the presence of CO. Reaction of 6/1-310 or 6/1-311 with 6/1-312 in the presence of Pd° under a CO atmosphere (1 atm) led to the chromanones 6/1-314 and quinolones 6/1-315, respectively, via the Jt-allyl-r 3-Pd-complex 6/1-313 (Scheme 6/1.82). The enones obtained can be transformed by a Michael addition with amines, followed by reduction to give y-amino alcohols. Quinolones and chromanones are of interest due to their pronounced biological activity as antibacterials [150], antifungals [151] and neurotrophic factors [152]. 

Perez-Pietro et al. have introduced the dirhodium complex (105) with a unique o/7/io-metalated arylphosphine ligand. The complex is an efficient catalyst for the cyclization of alkenyl diazo ketones (Scheme 7S).288 289... 

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