AN INVESTIGATION OF THE FLUXIONALITY OF [FE-3(CO)(11)(CNBU(T))] AND [FE-3(CO)(10)(CNBU(T))(P(OME)(3))], AND THE X-RAY STRUCTURE OF [FE-3(CO)(10)(CNBU(T))(P(OME)(3))]

[Fe-3(CO)(11)(CNBu(t))] and [Fe-3(CO)(10)(CNBu(t)){P(OMe)(3)}] have be en examined by variable temperature C-13 and, in the latter case, P-31 NMR spectroscopy. At low temperatures both compounds are undergoing a rapid concerted bridge-opening bridge-closing carbonyl exchange. This results in a carbonyl C-13 NMR spectrum for [Fe-3(CO)(11)(CNBu(t))] w hich consists of three signals in the ratio 1:5:5. [Fe-3(CO)(10)(CNBu( t)){P(OMe)(3)}] shows two sets of (CO)-C-13 signals at low temperature , each in the ratio 1:2:2:2:2:1. The two major isomers present have be en identified. The X-ray structure of one of the isomers of [Fe-3(CO)( 10)(CNBu(t)){P(OMe)(3)}] has been determined.