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

Abstract

The title complex (Cp = η(5)-C(5)H(5)) reacted with the labile carbonyl complexes [M(CO)(5)(THF)] (M = Cr, Mo, W) and [MnCp'(CO)(2)(THF)] (Cp' = η(5)-C(5)H(4)Me) to give phosphinidene-bridged trimetallic compounds of formula [Fe(2)MCp(2)(μ(3)-PCy)(μ-CO)(CO)(7)] (Cr-P = 2.479(1) Å) and [Fe(2)MnCp(2)Cp'(μ(3)-PCy)(μ-CO)(CO)(4)], respectively, after formation of a new M-P bond in each case, and related heterometallic complexes [Fe(2)MClCp(2)(μ(3)-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 [Fe(2)(CO)(9)] proceeded analogously to give the triiron derivative [Fe(3)Cp(2)(μ(3)-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)}{(μ(3)-PCy)Fe(2)Cp(2)(μ-CO)(CO)(2)}(2)], the latter displaying a central Fe(CO)(3)P(2) core with a distorted bipyramidal geometry (P-Fe-P = 164.2(1)°). In contrast, the reaction with [Co(2)(CO)(8)] resulted in a full disproportionation process to give the salt [{Co(CO)(3)}{(μ(3)-PCy)Fe(2)Cp(2)(μ-CO)(CO)(2)}(2)][Co(CO)(4)], having a pentanuclear Fe(4)Co cation comparable to the above Fe(5) 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(3) and Fe(2)Cr species caused no decarbonylation but a tautomerization of the metal framework to give the corresponding isomers [Fe(2)MCp(2)(μ(3)-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 [Fe(2)MnCp(2)Cp'(μ(3)-PCy)(μ-CO)(CO)(4)] could be decarbonylated stepwise, to give first the tetracarbonyl complex [Fe(2)MnCp(2)Cp'(μ(3)-PCy)(μ-CO)(2)(CO)(2)] and then the tricarbonyl cluster [Fe(2)MnCp(2)Cp'(μ(3)-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).