Haptotropic rearrangements

Structural analysis of the reaction products clearly shows that the ligand on silicon undergoes a haptotropic rearrangement from if -C5MC5 in 50 to in1 -C5MC5 in 52 and 53 as in the cases of oxygenation and thionation of 50.36 Apparently, silaneselone 51 is not kinetically stable enough to be isolated under normal conditions. 

Finally, theoretical studies of haptotropic rearrangements of polyene-MLn complexes were reported together with detailed literature surveys144,145. 

A special application of the haptotropic rearrangement is the reaction of diastereopure complex 59a (Section 8.3.4, Scheme 23). Upon warming to 90 °C in di-n-butyl ether, haptotropic migration of the chromium tripod occurs intramolecularly along the same face of the naphthalene system to produce pure diastereomer 59c (Scheme 25) [57d]. 

Scheme 25. Stereoselective haptotropic rearrangement in naphthalene tricarbonylchromium complexes.

Scheme 30. Synthesis and haptotropic rearrangement of meta-benzonaphthohydroquinonophane tricarbonylchromium complexes.

Nickelocene reacts with the tin(II) diamine Me2Si(NBut)2Sn to give the Sn-Ni bonded compound 9-2 in which one cyclopentadienyl group remains r 5-bonded to the nickel, but the other is 71-bonded to two tin atoms and is rapidly haptotropically rearranging both in solution and in the solid state111-112... 

An inter-ring 77 -77 -haptotropic shift of an MnjCOjs fragment in an anionic dibenzopentalene has also been observed in the interconversion of 7 and 8 using line-shape analysis of the methyl resonances (Scheme 6). " Reference to the review of Oprunenko " is recommended for a comprehensive treatment of intra-ring haptotropic rearrangements. 

In 1989 Jutzi and coworkers reported the reaction of decamethylsilicocene 41 with tri- -butylphosphine selenide in benzene at room temperature leading to almost quantitative formation of 1,3,2,4-diselenadisiletane derivative 138, a head-to-tail [2 + 2] cycloaddition reaction product of the initially formed silaneselone 137. The intermediacy of silaneselone 137 was supported by the fact that the reaction in the presence of 2,3-dimethyl-l,3-butadiene resulted in the formation of the corresponding [2-1-4] cycloaddition reaction product 139 (Scheme 41). As in the cases of silanone 44 and silanethione 80, the ligands on silicon undergo a haptotropic rearrangement from jj -CsMes in 41 to ij -CsMes in 138 or 139. Apparently, silaneselone 137 is not kinetically stable enough to be isolated under normal conditions. 

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