Transformation of a Phosphorus-Bound Cp* Moiety in the Coordination Sphere of Manganese Carbonyl Complexes

Abstract

The reaction of Cp*PCl2 with K[Mn(CO)5] yields two novel anionic products, [Mn2(CO)8(μ-PC11H14O)]− (1–) and [Mn2(CO)8(μ-PHCp*)]− (2–), instead of the expected phosphinidene complexes with a delocalized Mn–P–Mn bond system. By treating these anionic complexes with [Ph3PAuCl], they are converted into corresponding neutral derivatives [Mn2(CO)8(μ-PC11H14O)(μ-AuPPh3)] (3) and [Mn2(CO)8(μ-PHCp*)(μ-AuPPh3)] (4). NMR investigations and X-ray structural analyses for 1–, 3, and 4 show that the compounds 1– and 3 as well as 2– and 4 reveal similar molecular structures in which the neutral complexes 3 and 4 contain AuPPh3 units bridging Mn–Mn bonds. In comparison to 1 and 3, complexes 2 and 4 possess one additional H atom bound at the P atom. The structures of 1 and 3 include a novel bicyclic unit consisting of a C5 ring of the former Cp* moiety conjugated to a CCC(O)P four-membered ring. The latter is built by a CO group of a former Mn carbonyl fragment connecting a P and a C atom of the cycle. One of the methyl groups of the Cp* ligand became a CH2 unit, resulting in two isomers containing an exocyclic CH2 moiety in the positions three or five of the C5 ring. Both isomers were found in the reaction mixture, with one as the major isomer. The proposed reaction pathway is based on XRD, NMR, and MS data and includes the reduction of a transient [Cp*P(Mn(CO)5)2] complex by [Mn(CO)5]−, a proton transfer from the neutral to the reduced complex, and a successive reduction of the protonated species. The neutral bicyclic compound 3, containing a 2-phosphacyclobutanone ring, is light sensitive and decomposes to tetramethylfulvene, possibly by a radical decarbonylation mechanism via a transient phosphacyclobutane derivative, [C5(CH3)4(CH2)P(Mn(CO)4)2AuPPh3] (5), detected by NMR spectroscopy.