P-FUNCTIONALIZED DIFERRIOPHOSPHONIUM SALTS OF THE TYPE [(CPFE(CO)2)2PPHR]+X- AND [(CPFE(CO)2)2PCLR)+X-

Diferriophosphonium salts containing an alkyl-substituent can be synthesised by two different ways. The first is the deprotonation of [(CpFe(CO)2]2PPhH]Cl (1) with KO(t)Bu in THF as a one-pot reaction at -78-degrees-C to give the unstable diferriophosphine complex (CPFe(CO)2)2PPh (2) and its realkylation by RX (R = Me, CH2Ph, CH2COOEt; X = Cl, I), which results in the open diferriophenylalkylphosphonium salts [(CpFe(CO)2 2PPhR]X (3a-c). Photolysis of 3a-c eliminates one CO-group with formation of the closed diferriophosphonium salts 4a-c with one bridging CO ligand and a Fe-Fe bond. Deprotonation of the salts 3a,b by bases gives the unstable neutral diferriophenylphosphorus-ylides or better the mu2-phosphaalkene complexes {CpFe(CO)2}2PPh=CHR' (5a,b), which eliminate the dimer [CpFe(CO)2]2 to finally give the 1,3-diphosphetanes (PhPCHR')2 by dimerisation of the unstable phosphaalkene. The second and much easier method for the preparation of diferrioalkylphosphonium salts is the cleavage reaction of [CpFe(CO)2]2 with RPCl2 in toluene. The phosphine fragment RPCl inserts into the Fe-Fe bond to give the chlorine substituted diferriophosphonium salts [{CpFe(CO)2}2PClR]Cl (R = Ph, Me, (i)Pr, Cl) (6d-g) and [{CpFe(CO)2}2PMesH]Cl (7). The mass, IR and NMR spectra of 3, 4, 6 and 7 and the reactivity of the compounds 3a-c, as well as the results of the X-ray structure analysis of the first mixed alkyl-aryl-diferriophosphonium salt [{CpFe(CO)2}2PPhCH2Ph]BPh4 (3b'), are reported and discussed.