Diene ligand

On carbonylation in methylene chloride it undergoes the substitution of the diene ligands, rearrangement, and cis-trans isomerization to yield 64 (97JOM(530) 259). l,r-(l,2-Ethylene)-3,3 -imidazol-2,2 -diylidene and the dimer [(T -cod)Rh (ir-Cl)] form the dinuclear species 65. 

A comprehensive series of mono- and dinuclear iodoplatinum(II) complexes [Ptl(dien)]+ and [ PtI(dien) 2(/r-CH2) ] (42) (dien = parent or substituted diethylenetriamine n = 2-9), respectively, have been synthesized as potential probes of nucleic acid structure.158 Both chiral and achiral species were prepared. In general, the complexes are synthesized by the reaction of trans-[PtI2(DMSO)2] with the dien ligand in DMF solution. 

The reactions of mercury(II) salts with oligo-amines afford informative examples for the fact that counterions induce the formation of a distinct complex or select a distinct complex in an equilibrium to crystallize with. Thus, Hg11 acetate with dien under exactly the same reaction conditions, in the presence of C104- or PF6-, yields the dinuclear complex [Hg2(dien)3](C104)4 or the mononuclear species [Hg(dien)(H20)](PF6)2, respectively, both characterized by IR, H, and 13C NMR spectrometries, by fast-atom bombardment (FAB) MS, cyclovoltammetry, and X-ray structure analyses.209 In the first compound Pna2, Z = 4), one Hg adopts five-coordination with one tridentate and one bidentate dien ligand, which with the remaining N-donor binds to the... 

Lawrance Curtis, 1975) in this case the trans-diene ligand was isolated, for example, in greater than 80% yield, as its dihydrobromide. 

Recently considerable attention has been given to chiral 72-bonded olefin spectator ligands for the asymmetric conjugate addition.122 Hayashi and Carreira independently reported that new chiral diene ligands 83,123 84,124 and 85125 showed high enantioselectivities in Rh(i)-catalyzed conjugate addition of arylboronic acids to enones (Scheme 41). 

Further proof for the fact that these induction periods are caused by slow hydrogenation of the diene ligand was obtained by NMR-spectroscopic measurements under hydrogenation conditions [10f, 15]. The registration of 31P- and 1H-spectra allows the simultaneous monitoring of changes in the bisphosphine complexes and substrate conversion. The results of the hydrogenation of methyl-... 

The crystal structures of a number of s-trans (diene)metal complexes (3) have been determined10-14. The diene ligand in all s-trans complexes is distinctly non-planar the torsional angle between the two olefin groups is between 114° and 127°. In general, the terminal carbon to metal distance is greater than for the internal carbon to metal distance, and the Cl—C2/C3—C4 bonds are shorter than the C2—C3 bond. 

In solution, certain complexes are observed to undergo an envelope-flip from one face of the diene ligand to the other. The XH NMR spectra of Cp2Zr(s-cis diene) complexes (11 R = R" = H) at ambient temperatures indicate a fluxional process which equilibrates the Cp signals as well as the terminal protons (equation 4). At lower temperature, signals for a... 

A wide variety of s-cis acyclic (43) and cyclic (44) and (diene)Mo(CO)2L+ cations [L = Cp, Cp, indenyl (In), trispyrazolylborohydride (Tp)] have been prepared. Direct complexation may be achieved by reaction of the stable cation [( j5-indenyl)Mo(CO)2 (NCMe)2]+ BF (45) (prepared by the reaction of [( j5-indenyl)Mo(CO)2]2 with AgBF4 in MeCN) with a solution of the diene ligand (Scheme ll)81. It is not necessary to isolate 45, since treatment of [( j5-indenyl)Mo(CO)2]2 or [Cp Mo(CO)2]2 with AgBF4 in the presence of the diene ligand gives the corresponding cation 43 (L = indenyl)82. 

Reduction of the metal dimer [CpMo(NO)l2]2 with Na/Hg in the presence of a variety of acyclic dienes generates the (diene)MoCp(NO) complexes in moderate to low isolated yield (equation 8)12,31,89. For the majority of diene ligands, complexes 60 are formed exclusively as the s-trans isomers as evidenced by NMR spectroscopy and single-crystal X-ray diffraction analysis. In comparison, complexation of the 2,3-dimethyl-l,3-butadiene initially gives a separable mixture of the s-trans (60) and s-d.v-complex (61). The s-cis isomer isomerizes to the more thermodynamically stable s-trans isomer in solution (THF, 1/2 = 5 min C6H6, ti/2 = 24 h). 

For diene ligands which are prochiral, complexation results in the formation of a racemic mixture. Resolution of this racemic mixture has been accomplished via either classical methods102, chromatographic separation on chiral stationary phases103 or kinetic resolution104. For certain acyclic or cyclic dienes possessing a pendent chiral center(s)... 

The reaction of o-halomethylene benzyl halides, l,4-dihalobut-2-enes, cyclo-2-hexenols or 2,5-dihydrothiophene-l,1-dioxides with Na2Fe(CO)4 or Fe2(CO)9 results in the formation of (diene)Fe(CO)3 complexes108. In each case, the precursor is transformed in situ into the free diene ligand, followed by complexation. 

Direct displacement of a diene ligand by CO is rare and the only report of this involves treatment of ( j5-indenyl)(diene)Mo(CO)2+ cations with carbon monoxide (10 atm/50°C) to generate the free diene ligand816. In this case, ligand substitution may be due to... 

The complete shift of a conjugated diene to a new conjugated diene system has also been observed in the -ionone system (33). Such diene rearrangements require a stoichiometric quantity of Fe(C0)5. The rearranged diene ligand is conveniently liberated from the Fe by oxidation of the complex with FeCls-... 

Catalysts lacking phosphorus ligands have also been used as catalysts for allylic substitutions. [lr(COD)Cl]2 itself, which contains a 7i-accepting diolefin ligand, catalyzes the alkylation of allylic acetates, but the formation of branched products was only favored when the substitution reaction was performed with branched allylic esters. Takemoto and coworkers later reported the etherification of branched allylic acetates and carbonates with oximes catalyzed by [lr(COD)Cl]2 without added ligand [47]. Finally, as discussed in Sect. 6, Carreira reported kinetic resolutions of branched allylic carbonates from reactions of phenol catalyzed by the combination of [lr(COE)2Cl]2 and a chiral diene ligand [48]. 

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