Stepwise formation of an acetylide-bridged mixed-metal triangular dicobalt–iron cluster from [(OC)4Fe(PPh2CCPh)]

Reaction of [(OC)4Fe((eta)^1-PPh2CCPh)] (1) with [Co2(CO)8] at room temperature affords the heterotrimetallic complex [(OC)4Fe((mu)-(eta) ^1:(eta)^2-PPh2CCPh)Co2(CO)6] (2), in which the alkynic moiety in 1 is bound to a Co2(CO)6 unit. Both the mono- and di-substituted complexes, [(OC)4Fe((mu)-(eta)^1:(eta)^2-PPh2CCPh)Co2(CO)5{P(OMe)3}] (3) and [(OC)4Fe((mu)-(eta)^1:(eta)^2-PPh2CCPh)Co2(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 [FeCo2(CO)6{(mu)3-(eta)^2(perpendicular)-CCPh}{P(OMe)3}((mu)-PPh2)] (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 [FeCo2(CO)5{(mu)3-(eta)^2-(perpendicular)CCPh}{P(OMe)3}(PPh3)((mu)-PPh2)] (6). Single crystal X-ray diffraction studies have been performed on 2 and 6.