Iridium complexes butadiene

The X-ray structure of 170 has been reported (56). Generally only unsubstituted sp -hybridized carbon atoms of butadiene ligands are attacked by HFA (133). Different behavior has been found in the reactions of iridium complexes with HFA. With tris(triphenylphosphane)nitrosyliridium the geometry is retained [Eq. (139)] (63). However, the Vaska complexes lead to... 

Representative products are XLII and XLIV . With butadiene in benzene the rhodium complex XLIIIa reacts fast at RT, whereas the iridium complex XLIIIb requires 2 h at reflux. Other dienes give complex products with XLIIIa. The complex XLIIIb reacts with isoprene (12 h at reflux) but fails to react with cyclic dienes. 

Desulfurization of thiophene by iridium complexes has been further investigated by Jones and coworkers using the diiridium complex [Cp IrH3]2(45). Thermal reaction of this bimetallic compound with thiophene in the presence of tert-butyl-ethylene leads directly to a product (46) in which both of the C-S bonds have been broken, leaving sulfide and butadiene ligands bridging the two iridium centers (Scheme 14). When d4-thiophene is used in this reaction, a d4-butadiene ligand is... 

Hofmann used a triptycene type backbone for preparing diphosphite 145, in overall 40% yield from three steps, starting from a conveniently substituted anthracene. Reaction of the substituted anthracene with dimethyl fumarate under microwave irradiation considerably reduced reaction time to prepare the triptycene derivative. After deprotection, the corresponding diol was then treated with chlorophosphite to give 145. The ligand was used in theoretical studies on rhodium(i)-catalysed hydroformylation of butadiene. The same authors also prepared iridium complex 146, from the already known diphosphite, which was used for the same purpose. 

Third, n-allyl complexes are formed by palladium and cobalt analogous complexes of nickel and platinum are less stable, while ruthenium, rhodium, and iridium are not yet known to form them. In catalytic reactions the deuteration of cyclic paraffins over palladium has provided definite evidence for the existence of rr-bonded multiply unsaturated intermediates, while 7r-allylic species probably participate in the hydrogenation of 1,3-butadiene over palladium and cobalt, and of 1,2-cyclo-decadiene and 1,2-cyclononadiene over palladium. Here negative evidence is valuable platinum, for example does not form 7T-allylic complexes readily and the hydrogenation of 1,3-butadiene using platinum does not require the postulate that 7r-allylic intermediates are involved. Since both fields here are fairly well studied it is unlikely that this use of negative evidence will lead to contradiction in the light of future work. 

Like complex XXXVII, the phosphine complex XXXIX reacts with 2,3-dimethyl-l,3-butadiene to give the expected complex XL. Hydridodiene complexes are intermediates. Using an unreactive diene, 2,3-dimethylbutadiene and (Ph3P)2Co(N2)H, one such complex can be isolated, XLI. Rhodium and iridium hydrides also react with dienes. 

Simpler iridium(I) complexes have also been observed to activate aldehydes. For instance [Tp Tr( " -C4H6)] (234) activates 4-anisaldehyde to ultimately afford the iridium(III) carbonyl complex 455 (Scheme 37). Intermediates in this process were observed spectroscopically and identified as the g g butadiene complexes 456 and 458 by performing an analogous reaction with 4-dimethylaminobenzaldehyde, for which rearrangement is less facile thus enabling the isolation of 457 and 459. It was also determined, by monitoring ( H-NMR) the reaction of 234 with 4-Me2NC6H4C( = 0)H, that the simple aldehyde adducts are intermediates in formation of the Fischer-type carbene complexes 458 and 459. 

Natta et al. (1964a) and Teyssie and Dauby (1964) concluded that the activated complex involved a tt allylic-type structure. The isolation of dodecatriene complexes from the reactions of butadiene with iridium, rhodium, and ruthenium salts (Lydon... 

Cobalt, Rhodium, and Iridium. —Cations of structure [Co(diene)(PRs)3]+ have been prepared (diene = butadiene or isoprene) they are fluxional in solution, but low temperature n.m.r. spectra indicate a square pyramidal structure with diene in the basal plane. The benzoquinone complex (87) has been prepared and undergoes successive mono- and di-protonation at oxygen methylation with Mel also occurs at oxygen to yield (88). Cobaltacyclopentadiene complexes Cp(PPh3)Co(CRi=CR CR =CR ) (RSR =Me, Ph, or CO Me) react with... 

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