Bis cycloocta-l,5-diene -nickel

Thermal cyclodimcrization of methylenecyclopropane results in head-to-head cycloaddition (see Section 1.3.1.1.). By contrast the bis(cycloocta-l,5-diene)nickel(0) catalyzed reaction of methylenecyclopropane gives the head-to-tail dimerization product 6 in 9% yield in addition to a [3 + 2] dimer 7.20... 

Amino-3-cyanofurans (307) are obtained by base catalyzed condensation of the acyloins (306) with malonodinitrile, and on acid hydrolysis yield the butenolides (308) (Scheme 80) (66CB1002). Diketene and an isocyanide react to give the lactone (309) in the presence of a tertiary base (73GEP2222405). When diphenylketene is treated with bis(cycloocta-l,5-diene)nickel and pyridine, the complex Ni(py)2(Ph2C=CO)2 is formed which is converted into compound (310) by carbon monoxide (78JOM(l52)C29). 

Bis(cycloocta-l,5-diene)nickel, (C8H,2)2Ni, shows the molecular ion, and fragment ions C8H12Ni+, C4H6Ni+, and Ni+ (149). The platinum analog, (C8H12)2Pt, shows as the principal ions (C8H12)2Pt+, CgH12Pt+,... 

Complexes of nickel constitute a distinct group of homogeneous alkylalumi-nium-free catalysts for olefin polymerisation. An efficient catalyst for ethylene polymerisation is formed in the reaction of bis(cycloocta-l,5-diene)nickel(0) [Ni(Cod)2] with phosphorus-ylid and triphenylphosphine in toluene solvent [181] ... 

Only small amounts of a cyclotrimer 7, the trani-tris-a-homobenzene derivative 3,3,6,6,9,9-hexamethyl-e c/o,ex o-tetracyclo[6.1.0.0. 0 ]nonane, are formed under these conditions. Additionally, two other trimers, 5 and 6, are obtained in low yield. When more basic phosphanes, such as ( -Bu)3 n(i-Pr) P (n = 1,2), are employed, oligomeric mixtures are produced. On the other hand, with a bulky phosphane, such as tricyclohexylphosphane [3 mol-% with 2 mol-% of bis(cycloocta-l,5-diene)nickel], 36% of the cyclodimer 4 is obtained after 3 hours at 35°C in benzene as solvent. Without phosphane coligands, only benzene-soluble oligomers, presumably containing cyclopropane rings, are formed. 

When phosphane-free nickel complexes, such as bis(cycloocta-l,5-diene)nickel(0) or te-tracarbonylnickel, are employed in the codimerization reaction of acrylic esters, the codimer arising from [2-1-1] addition to the electron-deficient double bond is the main product. The exo-isomer is the only product in these cyclopropanation reactions. This is opposite to the carbene and carbenoid addition reactions to alkenes catalyzed by copper complexes (see previous section) where the thermodynamically less favored e Jo-isomers are formed. This finding indicates that the reaction proceeds via organonickel intermediates rather than carbenoids or carbenes. The introduction of alkyl substituents in the /I-position of the electron-deficient alkenes favors isomerization and/or homo-cyclodimerization of the cyclopropenes. Thus, with methyl crotonate and 3,3-diphenylcyclopropene only 16% of the corresponding ethenylcyc-lopropane was obtained. Methyl 3,3-dimethylacrylate does not react at all with 3,3-dimethyl-cyclopropene, so that the methylester of tra 5-chrysanthemic acid cannot be prepared in this way. This reactivity pattern can be rationalized in terms of a different tendency of the alkenes to coordinate to nickel(O). This tendency decreases in the order un-, mono- < di-< tri- < tet-... 

Table 3. Formation of Substituted 2-(Alk-l-enyl)cyclopropanecarboxylates by [2 + 1] Cycloaddition of 3,3-Disubstituted Cyclopropenes and Alkenes with Electron-Withdrawing Substituents in the Presence of Bis( -cycloocta-l,5-diene)nickel(0)...

During 30 min 3,3-dimethylcyclopropene ° (7.5 g, 110 mmol) was added dropwise to a suspension of bis( -cycloocta-l,5-diene)nickel(0) (0.74 g, 2.7 mmol) and dimethyl fumarate (29.1 g, 202 mmol) in benzene (75 mL). External cooling was used to prevent the temperature of the mixture from rising above dO-SO C. After the end of the exothermic reaction (about 1 h), unreacted dimethyl fumarate (7.2 g) was filtered off and washed with benzene (25 mL). From the combined benzene filtrates 72 g of benzene (98% pure by GC) and then 18.8 g of a mixture consisting of dimethyl fumarate and 23a were distilled off at 40 - 70 C/ 0.001 Torr 3.2 g of a dark, viscous residue remained. The distiiiate was taken up in hexane (30 mL), additional dimethyl fumarate was removed by filtration, then evaporation of the filtrate yielded 23a yield 13.5 g (50%) 94% pure [determined by GC remainder consists of benzene (1.8%) and dimethyl fumarate (3.1%)] mp 27-28 C. 

In order to liberate hydrocarbon fragments from metallacycles such as a,a -bipyridyl-5-nickela-3,3,7,7-tetramethyl-cxo-tricyclo[4.1.0.0 ]heptane(l), there have been various attempts to react them with cosubstrates to achieve reductive elimination. When bis(> -cycloocta-l,5-diene)nickel(O) is treated with 2,2 -bipyridyl and 3,3-dimethylcyclopropene, complex 1 is initially formed. Reaction of 1 with dibromomethane results in a 47% yield of 3,3,7,7-tetramethyl-tricyclo[4.1.0.0 ]heptane (2). ... 

A test tube fitted with a three-way stopcock was filled with argon by repeated evacuation and back-filling. To a benzene solution (3 mL) of dibromomethyl phenyl ketone (0.278 g, 1.0 mmol) was added pentacar-bonyliron [Fe(CO)j, 0.234 g, 1.2 mmol], and the solution was heated at 80 C with stirring. The precipitate was separated by filtration through a thin layer of alumina. The concentrated solution was poured into petroleum ether, thus giving rran5-l,2,3-tribenzoylcyclopropane as a colorless product yield 28%. This procedure is representative for those carried out with octacarbonyldicobalt or bis(cycloocta-l, 5-diene)nickel rather than pentacarbonyliron. 

Oxatrimethylenemethanepalladium complexes can also be generated by oxidative addition of palladium(O) to 5-methylene-l,3-dioxolan-2-ones and subsequent decarboxylation. Again, reaction with norbornene, norbornadiene and dicyclopentadiene yields polycyclic cyclopropyl ketones in medium to high yield (Table 19). In this case, tetrakis(triphenylphosphane)pal-ladium(O) was the best catalyst found, whereas tris(dibenzylideneacetone)palladium(0)-chloro-form/triphenylphosphane (see above) and bis(cycloocta-l,5-diene)nickel/triphenylphosphane (used in stoichiometric amounts) proved less efficient. 

When bis(cycloocta-l,5-diene)nickel/tris(2-phenylphenyl)phosphite (1 1) was used as the catalyst a [3 -f 2] cycloaddition with cleavage of the three-membered ring was observed. However, when l-methylene-2-trimethylsilylcyclopropane was reacted with l-phenylpyrrole-2,5-dione, traces of a product (9%) that derived from a [2 -h 2] addition were isolated. 

A suitable approach to the synthesis of spiro[2.3]hexanes is the [2-1-2] cycloaddition of alkenes to the double bond of methylenecyclopropanes. This reaction is often described as a codimerization and usually requires catalysis by a nickel(O) complex such as bis(cycloocta-l,5-diene)nickel. l,l-Dimethyl-2-methylenecyclopropane reacts with alkyl acrylates to give a mixture of alkyl cis- and tranj-l,l-dimethylspiro[2.3]hexane-5-carboxylates 1 (19-40%) and alkyl 3,3-dimethyl-4-methylenecyclopentanecarboxylate 2 (60-81 %). The proportion of spiro [2.3]hexane derivative was highest when rer/-butyl acrylate was used as the activated alkene. 

Using a triphenylphosphane-modified bis(cycloocta-l,5-diene)nickel it is possible to add methylenecyclopropane to one of the double bonds of norbornadiene to give predominantly the endo-addwci 4 together with some of the homo-Diels-Alder product.When a chiral phos-phane, such as (— )-benzylmethylphenylphosphane, was used, an optically active endo-aAAuci was isolated in 48% yield. 

Another way to improve the yield of dimers 1-3 was the addition of derivatives of unsaturated acids, such as alkyl methacrylates and fumarates, to bis(cycloocta-l,5-diene)nickel(0). With maleic anhydride dimers were formed in 68% yield the proportion of 5-methylenespiro[2.4]hep-tane (2) was 95%. 

For the dimerization of 2-methyl-, 2,2-dimethyl- and 2,2,3,3-tetramethylmethylenecyclo-propane the bis(cycloocta-l,5-diene)nickel(0) catalyst was modified with dialkyl fumarate, maleic anhydride, or various trialkylphosphanes. For all of the substituted methylenecy-clopropanes but the tetramethyl derivative, dimers of the spiro[2.4]heptane and dispiro[2.1.2.11-octane type were obtained in good yields. 

Modification of the bis(cycloocta-l,5-diene)nickel(0) catalyst by trialkyl- or triphenylphos-phanes changed the course of the oligomerization of methylenecylopropane from dimerization towards trimeric products. The formation of six different trimers 1-6 was observed in an overall yield of 95% all of them contained one or two cyclopropyl groups, which were part of spirosystems in three cases. 

To a mixture of bis(cycloocta-l,5-diene)nickel (16.3 g, 59.1 mmol) and 2,2 -bipyridyl (9.3 g, 59.6 mmol) was added EtjO (50 mL). The yellow color of the suspension rapidly changed to deep violet. The suspension was stirred for 5 h at 25 °C and the solid was separated, washed with cold EtjO (2 x 20 mL) and dried under vacuum (0.001 Torr) to give a dark violet microcrystalline complex yield 16.8 g (88%). 

Indeed, methyl rw-6,6-dimethyl-2-(triphenylphosphanyl)-2-nickelabicyclo[3.1.0]hexane-3-carboxylate (13) [and the corresponding ethenebis(dimethylphosphane) complex] was isolated in 65% yield from the conversion of (/7 -methylacrylate)bis(triphenylphosphane)nickel and 3,3-dimethylcyclopropene. The former complex catalyzes the cotrimerization of dimethylcyclo-propene with methyl acrylate with almost identical activity as earlier observed with an in situ catalyst obtained by mixing bis(cycloocta-l,5-diene)nickel and triphenylphosphane (1 1). Thus, this metallacyclic system can be regarded as an intermediate in the co-cyclotrimerization reaction. ... 

The following reactions of norbornene and other nonfunctionalized alkenes with substituted methylenecyclopropanes illustrate these points. (1-Methylethylidene)- and (diphenyl-methylene)cyclopropane (1 R = Me, Ph) give rise to the same type of cycloadducts in the presence of either nickel(O) or palladium(O) catalysts. Even at temperatures as low as 40 "C with bis(> -cycloocta-l,5-diene)nickel(0) as catalyst, 2 may be isolated in 70% yield. The reaction can be extended to vinylbenzene and ethene at temperatures of between 40 and 60 °C, where it may be advantageous to use (cyclododeca-l,3,5-triene)nickel(0) ° as a source of the catalytically active nickel(O) species instead of bis(j7" -cycloocta-l,5-diene)nickel(0). ° This is because ligand dissociation from the former complex is more facile, especially at relatively low temperatures. 

The reaction of substituted methyienecyciopropanes, such as (1-methylethylidene)- or (diphenylmethylene)cyclopropane, with compound 2 only leads to the formation of [3 -I- 2] cycloadducts. The best combined yield of three isomeric cyclocodimers (93%) is obtained with (1-methylethylidene)cyclopropane in a bis(> -cycloocta-l,5-diene)nickel(0)/tris(2-phenylphenyl) phosphite (1 1) catalyzed reaction at 120°C after 8 hours. ... 

Dimerization of 2,3-disubstituted cyclopropenones catalyzed by bis(cycloocta-l,5-diene)nickel(O) gave 1,4-benzoquinones 25 via bond cleavage between Cl and C2 of the cyclopropenones. ... 

Recently, the nickel-catalyzed isomerization of geraniol and prenol has been investigated in homogeneous and two-phase systems. The best results with respect to activity and selectivity have been obtained in homogeneous systems with a bis(cycloocta-l,5-diene) nickel(0)/l,4-bis(diphenylphosphanyl)butane/trilluoroacetic acid combination. Catalyst deactivation occurs in the course of the reaction owing to coordination of the aldehyde group formed to the nickel species or as a result of protonolysis of hydrido- or (7t-allyl)nickel complexes [1]. 

Bis(tetramethylbutynediol)nickel(0), 64, the first homoleptic nickel alkyne complex, was prepared according to Eq.(l) by treatment of bis(cycloocta-l,5-diene)-nickel(O) with two equivalents of the ligand [127a]. 

The nickel catalyst is obtained by reduction of a nickel(II) compound such as the acetylacetonate in the presence of butadiene, or simply by exchange of butadiene and bis( -allyl)nickel or bis(cycloocta-l, 5-diene)nickel. In the absence of added ligands, butadiene is rapidly and catalytically converted at low temperatures into 1,5,9-cyclododecatriene, mainly the trans, trans, trans isomer. The trimerization bears the mark of a template process, three butadiene molecules linking very specifically around a naked nickel centre. Detailed studies show that the process is not synchronous but occurs in a stepwise fashion (Fig. 12.5). 

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