Norbornadiene complexes

When irradiated in the presence of norbornadiene and high-pressure synthesis gas, rhodium chloride is converted to a catalyst which is active for a variety of reactions. /2A/. The salt is probably converted photochemically to the rhodium norbornadiene complex 9. This dimer may undergo a consecutive photoreaction to give the monomeric hydrido complex 10, which is the actual catalyst for polymerisation, hydrogenation, and hydroformylation reactions. 

In 1991, Park reported123 the first synthesis of iron alkynylcarbene complexes (184), involving the nucleophilic attack of a lithium acetylide on pentacarbonyl iron, followed by electrophilic quench. With such compounds in hand, he proceeded to investigate their reactivity123,124 and found that upon addition of cyclopentadiene to the alkynylcarbene complexes 184, the products formed were 774-vinylketene complexes (185). During column chromatography, some of these products (185.a and 185.b) were transformed into the tricarbonyl(norbornadiene)iron derivatives 186. Others (185.C and 185.d, not shown) were hydrolyzed as part of the workup procedure, to afford pure samples of the norbornadiene complexes 186.C and... 

Oeeasionally, very good enantioselectivities were achieved in the (-)-sparteine-mediated carbolithiation of 6-dimethylaminofulvene (470) by ort/zo-substituted aiyllithiums 471 (equation 129) . Here, (—)-sparteine (11) turned out the best chiral additive. The lithium cyclopentadienides 472 were converted to the corresponding Rh(l)-norbornadiene complexes 473. 

RuCl2(arene)]2 complexes (1) react with 1,5-cyclooctadiene and 1,3- or 1,4-cyclohexadiene in the presence of ethanol and Na2C03 or zinc dust to give Ru°(776-arene)(V diene) compounds of type 196-198 in 60% yield [Eq. (20)] thus, this reaction appears to be the reverse of the 198-> 1 reaction [Eq. (19)]. The same reaction with ethylene leads to the bis-ethylene ruthenium(O) complex 205 (37%) (131,10). The norbornadiene complex 207 is prepared similarly from derivative 206 (125). Combination of transformations 206 - 207 [Eq. (21)] or 1 - 198 [Eq. (20)] with trans-... 

Davidson et al.m have also found that mixtures of [WBr2(CO)2(T/4-diene)] (diene = nbd, cod, cot)/AlCl2Et initiate the metathesis of cis-2-pentene to yield 2-butene and 3-hexene. For the norbornadiene complex, the reactions have been found to be catalytic. 

The transient electrophilic terminal phosphinidene 188, which is readily accessible by thermolysis of 7-phospha-norbornadiene complex 187 (Scheme 59), is a powerful precursor to phospholenes. For example, it reacts with ethoxyacetylene to give phosphole 189, which upon hydrolysis affords the 2-phospholene complex 190 (Scheme 59)... 

Upon treatment with 2,2 -bipyridyl (bipy) or 1,10-phenanthroline (phen), the 1,3-cyclohexadiene complex [(C6H8)Co(CO)2]2 dispropor-tionates to produce [CoL3]+[Co(CO)4] (L = bipy or phen) the analogous norbornadiene complex, however, undergoes only ligand displacement to yield [Co(CO)2L]2 (46). 

Cycloheptadiene interacts slowly with Rh(CO)2(acac), simultaneously undergoing isomerization, to give the norbornadiene complex (C7H8)Rh(acac) (74). 

The norbornadiene complexes of AgNOs (577) and AgBF4 (491) are quite analogous in stoichiometry to those of 1,3-butadiene with the same salts. A structural analysis (28) of the 1 2 complex (C7Hg)(AgNOg)2 has shown chains of silver nitrate molecules cross-linked by norbornadiene molecules (Fig. 11). In this complex, each silver ion is coordinated... 

Recently an indication of path A has been shown by investigating solvolysis of the 7-substituted norbornadiene complexes of Cr, Mo, and W 90). It was found that in an 80% acetone-water solution at 25°C,(t7-C7H7C1)Mo (CO)4 gives free 7-norbornadienol instead of the expected (t7-C7H70H)Mo (CO)4- Moreover, the solvolysis rate constant was of the same order of magnitude as that for free 7-chloronorbornadiene. All these data support fast dissociation of the type... 

Ruthenium norbornadiene complexes undergo similar cyciometailation reactions without group V donor atoms ... 

Norbornadiene complexes of platinum and palladium 14 reacted with silver carboxylates to form the carboxymetalation products 15 which, on treatment with triphenylphosphane, underwent intramolecular alkene insertion to form the nortricyclene skeleton 16. Reductive decom-plexation gave the acylated tricyclo[2.2.1.0 ]heptan-ex n-3-ol 17. ... 

The most facile syntheses of diolefin complexes are those in which the diolefin reacts with a coordinatively unsaturated metal complex without ligand displacement. Thus a unidentate norbornadiene complex of iron, [Fe(f -Cp)(CO)2( 7 -NBD)][BF4], can be prepared by treating [Fe( j -Cp)(CO)2]2 with xs Ph3C[BFJ, followed by quenching with cycloheptatriene prior to addition of norbornadiene . Tetracoordinate complexes of Ir(I) undergo diolefin addition ... 

Related complexes have been formed from a norbornadiene complex (Equation (68)) <90PS(47)477>. In neither case has the decomplexed phosphole yet been reported, however. 

Electron Spin Resonance (ESR). ESR has received but limited use to establish metal oxidation states/ It was shown, for example, that norbornadiene complexes of Rh(I) on a phosphinated polystyrene-DVB formed low levels of Rh(II) during the course of the hydrogenation of ketones and olefins. Supported RhCls was assigned a structure -PPh2Rh(II)Cl2 following ESR and ESCA characterization. 

Atactic poly(methallyl)alcohol reacts with PClPha to give a polyphosphite Pn, and on treatment with [Rh2(Cl)2(CO)4] or [RhaCCOaCnorbornadienela] polymer-bound catalysts are obtained which are active in the hydrogenation of a variety of olefins. The species derived from the norbornadiene complex catalyses oct-l-ene hydrogenation at a rate dependent on catalyst concentration with solutions 0.125 mol 1 in olefin and at a rate oc [olefin] / up to a concentration of 0.3 mol 1. No attempt is made to rationalize these results in mechanistic terms. 

Figure 19.2 Comparison of the enantioselectivities obtained with the PPI- and PAMAM-bound pyrphos-Rh(NBD) (NBD, norbornadiene) complexes [16].

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