Haptotropic migration

Moreover, after transfer the free ligand can be recovered by crystallization. The mechanistic proposal for the transfer reaction is based on an initial r 4 to p1 haptotropic migration (Scheme 1.22). 

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]. 

Benzoborepin-Cr(CO)3 complex (9) is readily formed and shows no tendency toward haptotropic migration from the borepin ring to the benzene moiety (Equation (6)) <90OM2944>. 

A proposed mechanism for this transformation includes the dissociation of a pyridine and an imine ligand. Subsequently, the diene is coordinated in an r) -manner. Oxidative addition of the silane gives rise to a hexacoordinated iron complex. The diene is inserted into the Fe-Si bond to form an n -allyl(hydrido)iron complex. Haptotropic migration affords the corresponding Ti -alkyliron complex that subsequently undergoes reductive elimination to release the silylated alkene (Scheme 4—339). ... 

Chromium-Templated Benzannulation and Haptotropic Metal Migration... 

Metal migration is not restricted to a single ring, and there has been considerable interest in inter-ring haptotropic shifts. " Often the barriers are over 125 kj mol so that conventional NMR rather than DNMR studies are used to measure rates in these cases nevertheless, there are a number of cases where DNMR studies have been effective. 

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