Heterometallic Derivatives of [Fe2Cp2(μ-PCy)(μ-CO)(CO)2]: Rational Synthesis of Polynuclear Complexes from Neutral Precursors Having Pyramidal–Phosphinidene Bridges

The title complex (Cp = η5-C5H5) reacted with the labile carbonyl complexes [M(CO)5(THF)] (M = Cr, Mo, W) and [MnCp′(CO)2(THF)] (Cp′ = η5-C5H4Me) to give phosphinidene-bridged trimetallic compounds of formula [Fe2MCp23-PCy)(μ-CO)(CO)7] (Cr–P = 2.479(1) Å) and [Fe2MnCp2Cp′(μ3-PCy)(μ-CO)(CO)4], respectively, after formation of a new M–P bond in each case, and related heterometallic complexes [Fe2MClCp23-PCy)(μ-CO)(CO)2] (M = Cu, Au; Au–P = 2.262(1) Å) were cleanly formed upon reaction with CuCl or the labile tetrahydrothiophene (THT) complex [AuCl(THT)]. The reaction with [Fe2(CO)9] proceeded analogously to give the triiron derivative [Fe3Cp23-PCy)(μ-CO)(CO)6] in high yield (new Fe–P bond =2.318(1) Å), along with a small amount of the pentanuclear compound [{Fe(CO)3}{(μ3-PCy)Fe2Cp2(μ-CO)(CO)2}2], the latter displaying a central Fe(CO)3P2 core with a distorted bipyramidal geometry (P–Fe–P = 164.2(1)°). In contrast, the reaction with [Co2(CO)8] resulted in a full disproportionation process to give the salt [{Co(CO)3}{(μ3-PCy)Fe2Cp2(μ-CO)(CO)2}2][Co(CO)4], having a pentanuclear Fe4Co cation comparable to the above Fe5 complex (P–Co–P = 165.3(2)°). The attempted photochemical decarbonylation of the above trinuclear complexes gave results strongly dependent on the added metal fragment. Thus, the irradiation with visible or visible–UV light of the new Fe3 and Fe2Cr species caused no decarbonylation but a tautomerization of the metal framework to give the corresponding isomers [Fe2MCp23-PCy)(μ-CO)(CO)n] now exhibiting a dangling FeCp(CO)2 moiety (M = Cr, n = 7, Cr–Fe = 2.7370(3) Å; M = Fe, n = 6, new Fe–Fe bond = 2.6092(9) Å) as a result of the cleavage of the Fe–Fe bond in the precursor and subsequent formation of a new M–Fe bond. These processes are reversible, since the new isomers gave back the starting complexes under low (Cr) or moderate (Fe) thermal activation. In contrast, the manganese–diiron complex [Fe2MnCp2Cp′(μ3-PCy)(μ-CO)(CO)4] could be decarbonylated stepwise, to give first the tetracarbonyl complex [Fe2MnCp2Cp′(μ3-PCy)(μ-CO)2(CO)2] and then the tricarbonyl cluster [Fe2MnCp2Cp′(μ3-PCy)(μ-CO)3], the latter having a closed triangular metal core (Fe–Fe = 2.568(7) Å; Mn–Fe = 2.684(8) and 2.66(1) Å).