The complexes [M(η-C₃H₅)(CO)₃L][M = Mn, L = PPh₃, AsPh₃, P(C₆H₁₁)₃, PBuⁿ₃, or PMePh₂; M = Re, L = PPh₃] and [M(η-C₃H₅)(CO)₂L₂][M = Mn, L = PMePh₂, P(OMe)₃, P(OEt)₃, or ½ Ph₂PCH₂PPh₂; M = Re, L = PPh₃] have been prepared from [M(η-C₃H₅)(CO)₄] using thermal or photolytic methods. Taking the allyl group as bidentate, the complexes are considered to possess pseudo-octahedral structures, the carbonyl ligands being facial in the tricarbonyls and cis in the dicarbonyls. The ¹H n.m.r. spectra are characteristic of η³-allyl species and show strong ¹H–³¹P coupling. The mass spectra of the complexes have also been obtained and fragmentation pathways suggested mainly on the basis of observed metastable peaks. Crystals of [Mn(η-C₃H₅)(CO)₂{P(OMe)₃}₂] are monoclinic with a= 18.618(11), b= 9.218(7), c= 10.607(11), β= 102.1(1)°, Z= 4, and space group P2₁/a. 1 742 Independent reflections above background have been collected on a diffractometer and refined to R 0.059. The metal atom has a distorted octahedral environment, being bonded to two mutually trans phosphorus atoms [Mn–P 2.175(5) and 2.219(5)Å], two cis carbonyls [Mn–C 1.75(2) and 1.83(2)Å], and an allyl group [Mn–C 2.223(17), 2.114(14), and 2.229(13)Å].