Synthesis of [Co2(µ-PPh2C3H4)(µ-PPh2)(CO)4]; its reactions with P(OMe)3 and with alkynes

Abstract

The bis(phosphido)-bridged complex [Co₂(µ-PPh₂)₂(CO)₆]1 undergoes an insertion reaction of allene into one of the phosphido bridges, to give the new ligand-bridged dinuclear cobalt complex [Co₂(µ-PPh₂C₃H₄)(µ-PPh₂(CO)₄]2 in high yield. Complex 2 reacts with P(OMe)₃ to give the monosubstituted derivative [Co₂(µ-PPh₂C₃H₄)(µ-PPh₂)(CO)₃{P(OMe)₃}]3 in which substitution has occurred at the allyl-co-ordinated cobalt atom. Complex 2 also reacts with alkynes, RCCH (RCH₂OH, Me or H), which insert into the remaining phosphido bridge along with a molecule of CO to give [CO₂(µ-PPh₂C₃H₄){µ-PPh₂C(O)CHCR}(CO)₃](R = CH₂OH 4a, Me 4b or H 4c). In the case of MeCCH which gives 4b, a second isomer, [Co₂(µ-PPh₂C₃H₄){µ-PPh₂C(O)CMeCH}(CO)₃]5, which differs in the mode of insertion of the alkyne, is also obtained. The isomeric complexes [Co₂{µ-PPh₂C(O)CHCR}(µ-PPh₂)(CO)₄](R = CH₂OH 6a or Me 6b) and [Co₂{µ-PPh₂C(O)CRCH}(µ-PPh₂)(CO)₄](R CH₂OH 7a or Me 7b), which may be regarded respectively as analogues of 4 and 5 but with a phosphido bridge and an additional terminal CO group in place of the µ-PPh₂C₃H₄ ligand, have been prepared from [Co₂(µ-RCCH)(CO)₆](R CH₂OH or Me) and P₂Ph₄. The complexes [Co₂{µ-PPh₂CHCRC(O)}(µ-PPh₂)(CO)₄](R CH₂OH 8a or Me 8b), which are also isomers of complexes 6a, 7a and 6b, 7b respectively, have also been obtained in these latter reactions. The complexes 8 contain a bridging ligand which differs from that present in 6 and 7 in that the ordering of the PPh₂, alkene and CO components of the bridging ligand is not the same. The crystal structures of the complexes 3 and 4c have been determined by X-ray diffraction studies.