Darstellung und Bildungsmechanismus von π‐Cyclopentadienyl‐nickel‐(tert.‐phosphit)‐dialkylphosphonat‐Komplexen – eine metallorganische Variante der Michaelis‐Arbuzov‐Reaktion

Synthetic routes for complexes of the type π‐C5H5Ni[P(OR)3]X have been developed. Nickelocene reacts with tertiary phosphites P(OR)3 in the presence of CX4 to give the complexes for which R = Me, Ph; X = Cl, and R = Ph; X = Br. π‐C5H5Ni(CO)I reacts with P(OR)3 to give the complexes for which R = Me, Et, Ph. [π‐C5H5Ni(P(OMe)3)2]Cl is also formed in the preparation of π‐C5H5Ni[P(OMe)3]Cl from nickelocene; the corresponding [π‐C5H5Ni(P(OEt)3)2]I is obtained from π‐C5H5Ni[P(OEt)3]I and P(OEt)3. π‐C5H5Ni[P(OMe)3]X (X = Cl, I) react with P(OMe)3 to give π‐C3H5Ni[P(OMe)3] [P(O)(OMe)2] in quantitative yields, but with P(OEt)3 and P(OPh)3 π‐C5H5Ni[P(OEt)3] [P(O)(OMe)2] respectively π‐C5H5Ni[P(OPh)3] [P(O)‐(OMe)2] are obtained as the main products. The complex (t‐C4H9C5H4)Ni[P(OMe)3] [P(O) (OMe)2] can be synthesized by the same route. The course of the reactions of π‐C5H5Ni[P(OR)3]X and P(OR′)3 has been investigated in some detail. Intermediate compounds {C5H5Ni[P(OR)3] [P(OR′)3]X} with a π‐bonded cyclo‐ pentadienyl ligand have been detected at low temperatures by 1H‐ and 13C‐NMR.‐spectroscopy. They are stable up to about −10° and react at higher temperatures smoothly to π‐C5H5Ni[P(OR)3] [P(O) (OR′)3] and R′X. The structure proposed for the intermediates suggests that the mechanism of formation of the nickel phosphonate complexes is quite similar to that of the Michaelis‐Arbuzov reaction.