Butadiene complex

Complexes of conjugated olefins may react to give complexes containing ligands bound by an essentially delocalized system with either one 

These reactions may be compared with the conversion of mono-ene 2-electron ligands either into 1-electron (alkyl) or 3-electron (w-enyl) systems mentioned above. Understandably, however, unconjugated diene and triene ligands, in which the C=C systems are separated by more than one carbon atom may not react so readily to form delocalized systems. 

The structure of ir-cyclopentadienyl hexatrifluoromethylbenzene rhodium, 7.18, is of some interest. Normally benzenoid aromatic hydrocarbons 

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A carbon-iron bond is also formed by the reaction of the cyclopropenium salt 185 with dicarbonyl(i/5-cyclopentadienyl)(trimethylsilyl)iron [92], (Scheme 69) In the reaction with benzocyclobutenylidene- 5-cyclopentadienyliron(II) hexafluorophosphate 186, CpFe(CO)2R (R=cyelo-C3H5, CH2-cyclo-C3H5) is converted to the allene and butadiene complexes, 187 and 188, respectively [93]. (Scheme 70)... 

In the case of other Group 6 metals, the polymerization of olefins has attracted little attention. Some molybdenum(VI) and tungsten(VI) complexes containing bulky imido- and alkoxo-ligands have been mainly used for metathesis reactions and the ring-opening metathesis polymerization (ROMP) of norbornene or related olefins [266-268]. Tris(butadiene) complexes of molybdenum ) and tungsten(O) are air-stable and sublimable above 100°C [269,270]. At elevated temperature, they showed catalytic activity for the polymerization of ethylene [271]. 

If the unsaturated hydrocarbon is a diene, both double bonds may coordinate to palladium ). (Diene)palladium(II) complexes have been isolated and characterized. For example, 2 and 3 are stable complexes in which both double bonds are coordinated to the metal10. Conjugated dienes constitute a special case and although /j4-diene complexes, e.g. 4, are postulated as intermediates, they have not yet been isolated. The butadiene complex 4 is in equilibrium with the zr-allyl complex 5 in solution, and attempts to isolate the diene complex from this mixture lead to formation of a yellow crystalline complex 511. 

Some [MX]+ ions enter into reactions in which the ligand X and the reacting molecule become chemically bonded. Polymerization processes have been observed involving the [MC4H4]+ ions (147). The butadiene complex ions [MC4H4]+ of Co and Ni are unreactive to ethyne but the Fe, Ru, and Rh ions react to yield benzene and the bare metal ion. The [MC4H4]+ complex ions of Os+, Ir+, and Pt+ react with ethyne to form the MC4I I4 + ions that probably correspond to the benzyne complexes previously observed for platinum (126). 

However, upon thermolysis of 178.d or 178.h, isomeric mixtures of the butadiene complexes 183.a and 183.b were formed. Since intramolecular hydrogen transfer within (3,3-dime thyl-773 r -allylacy iron complexes is well precedented101 (see Section VI,B), it seems likely that this process is responsible for diene complex formation. Note that only the Z-diene complex was isolated from the reaction mixture, a surprisingly stereoselective result. 

Scheme 20. The gas-phase reactions of CoO+ with n-butane. Note that the compound labeled A is a butadiene complex of Co+.

Although bis(phosphite) carbyne complex Cp[P(OMe),]2Mo=C(c-Pr) is incapable of undergoing carbonyl insertion reactions, it adds 1 equivalent of HCl in ether forming the ring-opened -butadiene complex Cp[P(OMe),l(Cl)Mo( 4-butadiene) in 15% yield, and P(OMe)j in equal amounts (equation 108)158. Careful analysis of the reaction using... 

These results suggest the presence of two competing pathways to products, which depend upon the location of protonation at the M=C carbyne bond. Charged controlled protonation at the carbyne carbon followed by nucleophilic attack of the CT leads to the butadiene complex. Frontier control of protonation results in attack at the metal center, leading ultimately to the hydride complex164. This has been verified by reaction of the... 

CpCo(mcp)2, which in turn can be further transformed to the mono-complex CpCo(PPh3)(mcp) by exchange of one methylenecyclopropane ligand with PPhj (equation 312). Although both complexes are isolable crystals, they are thermally less stable than the analogous Feist s ester complexes. CpCo(mcp)2 readily undergoes thermal isomerization at 110 °C, to give cyclopropyl-substituted -butadiene complexes (see below). 

Table 5 Synthetic Routes and Some Structural Data of Metal 1,4-Disubstituted Tetraaza- 1,3-butadiene Complexes... 

Bis(butadiene) complexes, with tantalum, 5, 173 Bis(z-butanethiolato) complexes, with bis-Cp Ti(IV), 4, 601 Bis(calixarene) complexes, as organic molecule hosts, 12, 799 Bis(carbene) complexes with gold(I), 2, 287-288 with manganese, 5, 780, 5, 826 with mercury, 2, 429 with palladium, 8, 230 with silver , 2, 206... 

N-donor ligands, 5, 94 O- and S-donor ligands, 5, 93 P-donor ligands, 5, 94 tj4-butadiene complexes, 5, 88 in carbometallations, 10, 284 carbonyl derivatives, 5, 63 carbonyls, 5, 64... 

Friedel Crafts acetylation of butadiene complex 56 proceeds smoothly to give a mixture of 1-acetyldienes 58 and 59 via the cationic 7r-allyl complex 57 [16]. Intramolecular Friedel-Crafts acylation with the acid chloride of the diene complex 60, promoted by deactivated AICI3 at 0 °C, gave the cyclopentanones. The (Z)-dienone complex 61 was the major product and the ( )-dienone 62 the minor one [17]. Acetylation of the 1,3-cyclohexadiene phosphine complex 63 proceeded easily at —78°C to give the rearranged complex 65 in 85% yield. Without phosphine coordination, poor results were obtained [18,19], In this reaction, the acetyl group at first coordinates to Fe, and attacks at the terminal carbon of the diene from the same... 

Nucleophilic attack occurs at C(2) of the diene. The 1,3-cyclohexadiene complex 66 is converted to the homoallyl anionic complex 67 by nucleophilic attack, and the 3-alkyl-1-cyclohexene 68 is obtained by protonation. Insertion of CO to 67 generates the acyl complex 69, and its protonation and reductive elimination afford the aldehyde 70 [20]. Reaction of the butadiene complex 56 with an anion derived from ester 71 under CO atmosphere generates the homoallyl complex 72 and then the acyl complex 73 by CO insertion. The cyclopentanone complex 74 is formed by intramolecular insertion of alkene, and the 3-substituted cyclopentanone 75 is obtained by reductive elimination. The intramolecular version, when applied to the 1,3-cyclohexadiene complex 76 bearing an ester chain at C(5), offers a good synthetic route to the bicyclo[3.3.1]nonane system 78 via intermediate 77 [21]. 

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