Stepwise formation of an acetylide-bridged mixed-metal triangular dicobalt–iron cluster from [(OC) 4Fe(PPh 2CCPh)

Abstract

Reaction of [(OC) 4Fe(η 1-PPh 2CCPh)] ( 1) with [Co 2(CO) 8] at room temperature affords the heterotrimetallic complex [(OC) 4Fe(μ-η 1:η 2-PPh 2CCPh)Co 2(CO) 6] ( 2), in which the alkynic moiety in 1 is bound to a Co 2(CO) 6 unit. Both the mono- and di-substituted complexes, [(OC) 4Fe(μ-η 1:η 2-PPh 2CCPh)Co 2(CO) 5{P(OMe) 3}] ( 3) and [(OC) 4Fe(μ-η 1:η 2-PPh 2CCPh)Co 2(CO) 4{P(OMe) 3} 2] ( 4), are obtained on reaction of 2 with an excess of trimethylphosphite at elevated temperature; in both cases CO-substitution takes place solely at the cobalt centres. Thermolysis of 3 results in phosphorus-carbon bond cleavage and iron-cobalt bond formation to yield the mixed-metal 48-electron triangular cluster [FeCo 2(CO) 6{μ 3-η 2-(⊥)-CCPh}{P(OMe) 3}(μ-PPh 2)] ( 5), in which a phenylacetylide ligand perpendicularly-bridges one of the iron-cobalt edges and a phosphido group bridges the cobalt-cobalt edge. Substitution of a cobalt carbonyl ligand occurs on reaction of 5 with triphenylphosphine to give [FeCo 2(CO) 5{μ 3-η 2-(⊥)-CCPh}{P(OMe) 3}(PPh 3)(μ-PPh 2)] ( 6). Single crystal X-ray diffraction studies have been performed on 2 and 6.