Palladium-, Platin- und Dieisenkomplexe mit Isocyanacetat: Ringschluß, säureinduzierte Ringöffnung, Diprotonierung

Abstract

Palladium, Platinum, and Diiron Complexes with Isocyanoacetate: Ring Closure, Acid-Induced Ring Opening, Diprotonation Substitution by isocyanoacetate (CNCH2CO2−) of one chloro ligand in trans-[MCl2(PPh3)2] (M = Pd, Pt) results in the Δ2-oxazolin-5-on-2-ato complexes 4a, b, i.e. immediate cyclization occurs in contact with these metal(II) species. In contrast, the open-chain form of the functional isocyanide is retained in [K(18-crown-6][Fe2Cp2(CNCH2CO2)(CO)3] (16) in which it occupies a terminal position. Protonation (alkylation) of the platinum complex 4b proceeds with ring cleavage and formation of isocyano acetic acid 11 (ethyl isocyanoacetate 12) stabilized by metal ion coordination. Protonation of 16 requires two equivalents of acid to yield the aminocarbyne-bridged complex [{μ-C=N(H)CH2CO2H}Fe2Cp2(CO)3](BF4) (17) as the only isolable product. Here isocyanoacetate displays a third kind of reactivity pattern in addition to that at PdII/PtII and that at Cr0/W0 where the primary species [M(CO)5CNCH2CO2]− and [M(CO)5CNCH2CO2H] proved to be the most stable. All of the proposed structures are substantiated by analytical and the usual spectroscopic (IR, NMR{1H, 13C, 31P}, FAB-MS) data, that of 4b also by an X-ray structure determination which reveals a practically perpendicular arrangement of the coordination and the ring plane, and a long C2-O bond as the predetermined breaking point of the heterocycle.