Butadiene complexes reactions

A Diels-Alder type [4+2] cycloadditions of 4,5-dihydropyridazine, prepared in situ from its trimer, with 2-methyl- and 2,3-dimethyl-1,3-butadienes (65, R = H, Me R = Me) afforded a complex reaction mixture, from which 6-methyl- and 6,7-dimethyl-3,4,4n,5-tetrahydro-8//-pyrido[l,2-ftjpyridazines (66, R = H, Me R =Me) could be isolated (97CEJ1588). With 1,3-butadiene (65, R = R =H) only a mixture of endo and exo isomers 67 and 68 (R = R =H) was obtained. 

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]. 

Thus it becomes unlikely that 7 can exist long enough to allow extensive dimerization or oligomerization of butadiene. It has also been speculated (7, 9) that the presence of coordinated chlorides on the Rh complex prevents the occurrence of butadiene polymerization reaction. 

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. 

The primary decompositions occurring by parallel first-order processes yield cyclohexene, butadiene plus ethylene, and four cyclopropyl-propenes. The cyclopropylpropenes formed initially decompose to yield various Ce dienes at rates comparable with those of the primary reactions, and this leads to a complex reaction mixture that contains at least seventeen products. 

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... 

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]. 

The method of preparation of the copper (I) chloride-1,4-butadiene complex has been described by Gilliland and coworkers.3 The following procedure uses liquid 1,4-butadiene in contrast with the previous gas phase reactions. 

Similarly, a-acetoxyrhenacyclobutadiene complexes, generated in situ by the reaction of acetyl chloride with rhenacyclobutanone 14, undergo substitution upon reaction with alcohols (Equation 3), giving a-alkoxyrhenacyclo-butadiene complexes 15 <2004JOM2000>. 

Compound 74, which results from a phospha-Wittig reaction via the 1-phospha-1,3-butadiene complex 73, according to Scheme 19, is even more reactive toward alkynes than 26 or 25, respectively. The complex smoothly reacts with alkynes to afford the 1,4-dihydrophosphinine complexes 75a-d. In the case of unsymmetrical alkynes, the cycloaddition is regioselec-tive and seems to be controlled by steric rather than by electronic factors. Less electron-rich 1,2-dihydrophosphete complexes with alkyl or phenyl substituents in the 3- and 4-positions are not sufficiently reactive toward alkynes.44... 

Although bis(phosphite) carbyne complex Cp[P(OMe)3]2Mo=C(c-Pr) is incapable of undergoing carbonyl insertion reactions, it adds 1 equivalent of HCl in ether forming the ring-opened f/ -butadiene complex Cp[P(OMe)3](Cl)Mo( / -butadiene) in 15% yield, and P(OMe)3 in equal amounts (equation 108) . Careful analysis of the reaction using two equivalents of HCl reveals the presence of the metal hydride complex Cp[P(OMe)3]2Cl2MoH as the main products (70%), and free butadiene. It was furthermore shown that the two molybdenum complexes are not interconvertible under the reaction conditions and both the yields and products ratio are invariant with temperature in the range of -40 °C to room temperature and the amount of added HCl (1 or 2 equivalents). 

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