Metal atoms cycloheptatriene

The reactions of cycloheptatriene with transition metal atoms are similar to those of cyclopentadiene. In both cases, the reactions can involve extensive migration of hydrogen in the formation of the final product (9, 10, 133, 136) ... 

It is of interest that identical products to those derived from the metal atom technique are produced by the reduction of the metal halide (Co, Fe, Cr, V, and Ti) with PrjMgBr in the presence of cycloheptatriene (27, 85, 137). There are tentative reports of the formation of an unstable complex with chromium, possibly Cr(Tj -C7Hg)2, but these have not yet been confirmed (115, 140). 

Trienes and isonitriles, cyclic trienes (nonaromatic) codeposited with metal atoms yield new complexes. Often hydrogen transfers from one ring to another are observed, e.g., with cycloheptatriene for the metals Ti, Hf Zr Cr Mo, W, Co, Co and Fe... 

Bis[di-/-butylphosphano] tellurium replaces norbornadiene, cycloheptatriene, acetonitrile, and dimethyl(methylene)oxosulfurane in chromium, molybdenum, and tungsten complexes. The P—Te compound acts as a bidentate ligand with the two phosphorus atoms coordinated to the metal atom. The tetracarbonylchromium complex [R = CH(CH3)J can be recrystallized without loss of tellurium. ... 

Cycloheptatriene is a six-electron donor that can form complexes similar to those of benzene but differing in the localization of the tt electrons in The alternation in bond length in the free cycloheptatriene is retained in the complexes (Fig. 15.43). Furthermore, in C7Hx lo(CO), the double bonds are located trans to the carbonyl groups, providing an essentially octahedral environment for the metal atom. 

The structure of cycloheptatriene-molybdenum tricarbonyl (XXX, M = Mo) was subsequently confirmed by x-ray analysis (76). The six olefinic carbon atoms were found to be approximately planar and symmetrically bonded to the metal, with the methylene carbon bent away from the latter. Carbon-carbon ring distances indicated alternate double and single bonds in the planar portion of the molecule, rather than a delocalized TT-electron system, as was originally suggested. The analogous complex (C7H8)W(C0)3 was subsequently described in the literature (62, 164). 

In the complex (ri" -C7Hg)Fe(CO)3, cycloheptatriene acts as a diene, giving the Fe(0) centre its required 18 electrons. Equation 24.130 shows that deprotonation generates a coordinated [ 7117] ligand which bonds in an t] manner, allowing the metal to retain 18 electrons. At room temperature, the [ 7117] ligand is fluxional, and on the NMR time-scale, the Fe(CO)3 unit effectively visits every carbon atom. 

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