Heterometallic Derivatives of [Fe<sub>2</sub>Cp<sub>2</sub>(μ-PCy)(μ-CO)(CO)<sub>2</sub>]: Rational Synthesis of Polynuclear Complexes from Neutral Precursors Having Pyramidal–Phosphinidene Bridges

The title complex (Cp = η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>) reacted with the labile carbonyl complexes [M(CO)<sub>5</sub>(THF)] (M = Cr, Mo, W) and [MnCp′(CO)<sub>2</sub>(THF)] (Cp′ = η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>Me) to give phosphinidene-bridged trimetallic compounds of formula [Fe<sub>2</sub>MCp<sub>2</sub>(μ<sub>3</sub>-PCy)(μ-CO)(CO)<sub>7</sub>] (Cr–P = 2.479(1) Å) and [Fe<sub>2</sub>MnCp<sub>2</sub>Cp′(μ<sub>3</sub>-PCy)(μ-CO)(CO)<sub>4</sub>], respectively, after formation of a new M–P bond in each case, and related heterometallic complexes [Fe<sub>2</sub>MClCp<sub>2</sub>(μ<sub>3</sub>-PCy)(μ-CO)(CO)<sub>2</sub>] (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 [Fe<sub>2</sub>(CO)<sub>9</sub>] proceeded analogously to give the triiron derivative [Fe<sub>3</sub>Cp<sub>2</sub>(μ<sub>3</sub>-PCy)(μ-CO)(CO)<sub>6</sub>] in high yield (new Fe–P bond =2.318(1) Å), along with a small amount of the pentanuclear compound [{Fe(CO)<sub>3</sub>}{(μ<sub>3</sub>-PCy)Fe<sub>2</sub>Cp<sub>2</sub>(μ-CO)(CO)<sub>2</sub>}<sub>2</sub>], the latter displaying a central Fe(CO)<sub>3</sub>P<sub>2</sub> core with a distorted bipyramidal geometry (P–Fe–P = 164.2(1)°). In contrast, the reaction with [Co<sub>2</sub>(CO)<sub>8</sub>] resulted in a full disproportionation process to give the salt [{Co(CO)<sub>3</sub>}{(μ<sub>3</sub>-PCy)Fe<sub>2</sub>Cp<sub>2</sub>(μ-CO)(CO)<sub>2</sub>}<sub>2</sub>][Co(CO)<sub>4</sub>], having a pentanuclear Fe<sub>4</sub>Co cation comparable to the above Fe<sub>5</sub> 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 Fe<sub>3</sub> and Fe<sub>2</sub>Cr species caused no decarbonylation but a tautomerization of the metal framework to give the corresponding isomers [Fe<sub>2</sub>MCp<sub>2</sub>(μ<sub>3</sub>-PCy)(μ-CO)(CO)<sub><i>n</i></sub>] now exhibiting a dangling FeCp(CO)<sub>2</sub> moiety (M = Cr, <i>n</i> = 7, Cr–Fe = 2.7370(3) Å; M = Fe, <i>n</i> = 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 [Fe<sub>2</sub>MnCp<sub>2</sub>Cp′(μ<sub>3</sub>-PCy)(μ-CO)(CO)<sub>4</sub>] could be decarbonylated stepwise, to give first the tetracarbonyl complex [Fe<sub>2</sub>MnCp<sub>2</sub>Cp′(μ<sub>3</sub>-PCy)(μ-CO)<sub>2</sub>(CO)<sub>2</sub>] and then the tricarbonyl cluster [Fe<sub>2</sub>MnCp<sub>2</sub>Cp′(μ<sub>3</sub>-PCy)(μ-CO)<sub>3</sub>], the latter having a closed triangular metal core (Fe–Fe = 2.568(7) Å; Mn–Fe = 2.684(8) and 2.66(1) Å).