Distorted boat-like conformation

Diazadiphosphacyclooctane (51) interacts with only two molecules of borane with participation of the phosphorus atoms [Eq. (50)]. The number of borane molecules added is likely to be determined by the conformation of the eight-membered ring, which exists in a distorted boat-boat form similar to that of the analogous sulfide. 

This different behavior can be explained by the conformation of the radicals and by stereoelectronic effects [6]. Electron spin resonance (ESR) investigations have revealed that the D-glucopyranosyl radical 7 does not adopt the 4C1 conformation 7a, but is distorted into the B2 5 shape 7b (Scheme 5) [7,8], The equatorial-like attack at the boat conformer... 

While 2,2 -bipyridine or phenanthroline adducts are likely to contain an approximately planar, five-membered -M-N-C-C-N moiety, upon coordination of a RR 2C(pz)2 a six-membered cycle is formed for which a boat conformation is predicted. Nevertheless, both the internal and external angles of the formally related M-(N-N)2-E moieties (where E is not carbon), are known to be able to undergo wide variations. Indeed, X-ray studies carried out on several / ,-pyrazolato-/V,/V -derivatives showed that the six-membered ring is not always in the boat conformation. This may undergo a severe folding as in bis(3,5-dimethylpyrazolyl)borato-7V,/V ](//3-cyclohepLatrienyl) (dicarbonyl)molybdenum,195 or may even approximate a chair, or at least, a distorted chair as in dimeric bis(cyclopentadienyltitanium)(//-pyrazolato-/V,7V ) (Scheme 10a).196... 

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