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

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.