Fluxional hydrocarbons

The molecular structure of the bicyclic framework in 108 is best described as a dithiatriazine bridged by an -N=S=N- group. The aryl-substituted derivatives 108 (R=aryl) form 2 1 inclusion complexes with aromatic fluorocarbons or hydrocarbons.266 In solution, the phenyl derivative 108 (R=Ph) is fluxional.258... 

Simmons-Smith cyclopropanation of triene 423 delivers a triscyclopropyl hydrocarbon which exhibits chiral fluxional properties On epoxidation, a mixture of two triepoxides results these rearrange rapidly under a variety of conditions to 424, the first topologically nonplanar molecule The reaction path for this iso-... 

The zinc compound 1 begins to decompose at 10°C to zinc and hydrocarbons, but the magnesium and beryllium complexes are more stable. Crystalline adducts 2 can be isolated on addition of TMEDA. The 1H-NMR spectra of 2 (M = Mg, Zn) show averaged AB2X patterns on account of rapid fluxional processes. The spectra can be frozen out at low temperatures, indicating terminally bonded r l-pentadienyl groups (85-87). 

M. R. Churchill 24. Hydrocarbon rr-complexes- Progr. Inorg. Chem. 11, 53 (1970) —fluxional molecules Transition metal complexes of azulene and related ligands 46 (113) ... 

Fluxional processes involving acyclic unsaturated hydrocarbon ligands, such as allyls and allenes, are also common. For the -n-complex formed between tetramethyl-allene and tetracarbonyliron (Fig. 15.53), the proton magnetic resonance spectrum below -60 C shows three peaks in the ratio 1 1 2. representing the three cis hydrogen atoms, three Irans hydrogen atoms, and six hydrogen atoms in a plane perpendicular to the carbon-iron bond. With an increase in temperature, the spectrum collapses to a... 

These systems are very stable thermally, although some are catalytically active. The hydrocarbon fragment adopts various eonfigurations between the metals, occasionally leading to fluxionality equilibrating the environment around the two metal fragments. 

How far carbocation chemistry has evolved from the old solvolysis days is demonstrated by two recent stmcture determinations the IR spectrum of the nonclassical CHs cation has been measured by solvating this unusual species with molecular hydrogen in the gas phase. This slows down the ultrafast fluxional process which so far prevented the recording of vibrational spectra. The cluster ions CH5" (H2)n (n = 1, 2, 3), after mass selection by an ion trap, were then subjected to IR laser spectroscopy/quadrupol mass spectrometry which ultimately yielded the IR absorption. [40] And the benzene cation, formed by removal of one electron from the parent hydrocarbon was shown to possess Deh symmetry by rotation resolved ZEKE-photoelec-tron spectroscopy (Zero Tinetic Energy-PES). [41]... 

Since 1970 or before, chemists have relied on classical, detailed temperature-dependent line-shape analyses.Indeed, fundamental contributions to our understanding of the dynamics of fluxional metal complexes with vr-hydrocarbon ligands,tertiary phosphorus donors, as well as TT-allyl anions,all stem from these types of measurement. Their contributions to metal carbonyl dynamics and rearrangements in cluster compounds is even more pronounced, and we cite selected studies in this very large area of organometallic chemistry.For slow exchange... 

Non-fluxional vinylic boranes do not react with carbonyl compounds. Nevertheless, the vinylic borane 29 reacts with acetone (2 h under reflux) yielding the Z-isomer of the homoallylic borinic ester 30b. The cw-configuration of the reaction product 30b corresponds to the following sequence of transformations (Scheme 2.11). The [1,7]-H shift in the vinylic borane 29 gives the allylic Z, Z-isomer 28d which immediately reacts with acetone before the equilibrium among the allylic isomers is established. On the other hand, cyclopentanone reacts directly with 29 under mild conditions yielding Z, Z-1,3,5-heptatriene 31 and borinic ester 32 (Scheme 2.12). Apparently 29 reacts with the enol form of cyclopentanone, and a direct splitting of the B-Q ,2 bond takes place. Similar reaction of 29 with acetic acid was used for the preparative synthesis of previously unknown hydrocarbon 31 (Scheme 2.12) [35]. 

The format of this chapter has been altered slightly from that of previous years in response to changes in the research activity in various areas of work, e.g. a section on (T-bonded hydrocarbon ligands has now been included. The decision to continue to include some papers concerned with inter- and intra-molecular rearrangements is somewhat arbitrary since they could equally well have been discussed in Chapter 6. However, it seems more appropriate to bias the coverage in that chapter towards studies involving fluxional molecules although some overlap may be noticed occasionally. 

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