Regiospecificity in reactions of alkynes and phosphines with the phosphido-bridged iron-cobalt complex [(OC)(4)Fe(mu-PPh2)Co(CO)(3)]

The iron-cobalt phosphido-bridged complex [(OC)(4)Fe(mu-PPh2)Co(CO)(3)] (1) can be prepared conveniently and in good yield from the reaction of [Co-2( mu-PPh2)(2)(CO)(6)] with [Fe(CO)(5)]. A study of the reactivity of 1 toward s symmetrical and unsymmetrical alkynes, (RC)-C-1=CR2 (R-1 = R-2 = CO2Me, P h; R-1 = H, R-2 = Ph), has been undertaken. In all cases, five-membered fer racycle-containing products of the type [(OC)(3)Fe{mu-PPh2C(O)(CRCR2)-C-1}C o(CO)(3)] (R-1 = R-2 = CO2Me (2a), Ph (2c); R-1 = H, R-2 = Ph (2b)), are in itially obtained in which a molecule of CO and a molecule of (RC)-C-1=CR2 h ave been inserted regiospecifically into a Co-P bond in 1. Decarbonylation of 2a occurs during its preparation or in low yield on its thermolysis to g ive the four-membered ferracyclic species [(OC)(3)Fe{mu-PPh2C(CO2Me)C(CO2Me )}Co(CO)(3)] (3a). Similar thermolysis of 2b results not only in the relate d decarbonylation product [(OC)(3)Fe(mu-PPh2CHCPh)Co(CO)(3)] (3b), but addi tionally in three other products all in low yield, namely the regioisomer o f 3b, [(OC)(3)Fe(mu-PPh2CPhCH)Co(CO)(3)] (4b), the aldehyde-substituted com plex [(OC)(3)Fe{mu-PPh2C(CHO)CPb}Co(CO)(3)] (5b) and the five-membered ferr acycle-containing species [(OC)(3)Fe{mu-PPh2CHCPhC(O)}Co(CO)(3)] (6b). Trea tment of 2a and 2b with PPhMe2 and P(OMe)(3) results in substitution of an iron-bound carbonyl group to give, respectively, [(PhMe2P)(OC)(2)Fe{mu-PPh2 C(O)C(CO2Me)C(CO2Me)}(mu-CO(CO)(2)] (7a) and [{(MeO)(3)P}(OC)(2)Fe{mu-PPh2C (O)CHCPh}(mu-CO)Co(CO)(2)] (7b) in high yield. In contrast, substitution of a cobalt-bound carbonyl is achieved on reaction of 3a with PPhMe2 or PPh2H to give [(OC)(3)Fe{mu-PPh2C(CO2Me)C(CO2Me)}Co(CO)(2)(L)] (L = PPhMe2 (8a), PPh2H (9a)). Thermolysis of the secondary phosphine-substituted complex 9a results in phosphorus-hydrogen bond cleavage to give [(OC)(3)Fe{mu- PPh2C( CO2Me)CH(Co2Me)}(mu-PPh2)Co(CO)(2)] (10a). Single-crystal X-ray diffraction studies have been performed on complexes 7b, 8a and 10a. (C) 2000 Elsevier Science S.A. All rights reserved.