Reaction of equimolar amounts of the ferriophosphaalkene Cp*(CO)2FePC(Ph)NMe2 (1a) and fumarodinitrile in diethyl ether afforded the ferriophosphetane (2a). Analogously, Cp*(CO)2FePC(tBu)NMe2 (1b) was converted into (2b). Evidence for the cyclic structure of 2a,b in the crystal was provided by the X-ray structural analysis of 2a. Whereas the phosphetane ring of 2b is retained in solution, product 2a in CH2Cl2 solution underwent an isomerization to give the acyclic secondary ferriophosphane Cp*(CO)2Fe−P(H)−CH(CN)−C(CN)C(Ph)NMe2 (3a) as a mixture of isomers. The ferriophosphane Cp*(CO)2FeP[CH(CN)−CH2CN][CH(CN)−C(CN)C(tBu)NMe2] (5) was isolated in less than 1% yield from the reaction of 1b and the alkene. The reaction of ferrioarsaalkene Cp*(CO)2FeAsC(Ph)NMe2 (6) and fumaronitrile gave rise to the formation of the ferrioarsetane (7), which unlike 2a resists ring opening in solution.

Reaction of one equivalent of the complexes [FeCp*(CO)2PnCl2] (Pn = P, As, Sb) with tetramethylcyclopentadienyllithium afforded compounds [FeCp*(CO)2[Pn(Cl)(C5Me4H)]]. Dehydrochlorination by means of tert-butyllithium led to decomposition. Only in the case of the phosphorus compound was evidence for the initial formation of a phosphaalkene given by 31P NMR spectroscopy. Similarly treatment of equimolar amounts of [FeCp*(CO)2PnCl2] with 2,7-di-tert-butyl-9-H-fluorenyllithium or 2,7-di-tert-butyl-9-trimethylsilylfluorenyllithium yielded the asymmetrically substituted ferriopnicogenanes [FeCp*(CO)2[Pn(Cl)-9-R-Fl*]] (Pn = P, As, Sb; R = H, Me3Si; Fl* = 2,7-di-tert-butylfluorenylidene). Dehydrohalogenation of [FeCp*(CO)2[Pn(Cl)-9-H-Fl*]] with lithium diisopropylamide resulted in the formation of the anticipated phosphaalkene [FeCp*(CO)2[P = Fl*]], whereas in the case of the arsenic and antimony derivatives the novel ferriopnicogenanes [FeCp*(CO)2[Pn(9-H-Fl*)2]] (Pn = As, Sb) were obtained as products. The new compounds were characterized by elemental analyses and spectra (IR, 1H, 13C, 29Si, 31P NMR). The molecular structures of [FeCp*(CO)2[Pn(Cl)(C5Me4H]]] (Pn = As, Sb), [FeCp*(CO)2[As(Cl)(9-Me3Si-Fl*)]] and [FeCp*(CO)2[Sb(9-H-Fl*]2] were elucidated by single X-ray diffraction analyses.

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