The non-heteroatom-substituted alkynyl carbene Cp′(CO) 2 MndC(Tol)CtCPh (1, Cp′ ≡ (η 5 -MeC 5 H 4 )) is first shown to react at low temperature with lithium diorganophosphide LiPR 2 (R ) Ph, Cy) to form an anionic species. Subsequent treatment with CF 3 SO 3 H affords the η 4 -vinylketene complex Cp′(CO) 2 Mn[η 4 -{R 2 P(Ph)CdCHC(Tol)dCdO}] (2; 2a: R ) Ph (70% yield), 2b: R ) Cy (55% yield)) as the major compound, along with trace amounts of the η 2 -allene complex syn-Cp′(CO) 2 Mn[η 2 -{Ph 2 P(Tol)-CdCdC(Ph)H}] (syn-3a) for R ) Ph, or along with the η 2 -allene complex Cp′(CO) 2 Mn[η 2 -{H(Tol)-CdCdC(Ph)PCy 2 }] (4b, 26% yield, 1:2 mixture of syn/anti isomers) for R ) Cy. On the other hand, subsequent treatment with NH 4 Cl aq affords only η 2 -allene complexes, obtained either as a ca. 1:9 mixture of syn-3a and Cp′(CO) 2 Mn[η 2 -{H(Tol)CdCdC(Ph)PPh 2 }] (4a) (75% yield) for R ) Ph or as a 1:2 mixture of syn-and anti-4b for R ) Cy (74% yield). Combined NMR and single-crystal X-ray diffraction studies (for 2a, anti-4b, and syn-4b) revealed that both type 2 and type 4 species result from a nucleophilic attack of the diorganophosphide onto the remote alkynyl carbon atom in 1 (C γ ), whereas type 3 species results from a nucleophilic attack of the carbene carbon atom (C R ). Complexes 3a and 4a,b are prone to undergo a thermal rearrangement to give the η 1 -phosphinoallene complexes Cp′(CO) 2 Mn[η 1 -{Ph 2 P(Tol)CdCdC(Ph)H}] (5a) and Cp′(CO) 2 Mn[η 1 -{R 2 P(Ph)CdCdC(Tol)H}] (6; 6a: R ) Ph, 6b: R ) Cy), respectively. Reaction of 1 with p-toluenethiol in the presence of NEt 3 (20%) affords a 1.8:1 mixture of Cp′(CO) 2 Mn[η 2 -{TolS(Tol)CdCdC(Ph)H}] (syn-11), resulting from a nucleophilic attack at C R in 1, and Cp′(CO) 2 Mn[η 2 -{H(Tol)CdCdC(Ph)STol}] (12), resulting from a nucleophilic attack at C γ , whereas treatment of 1 with lithium p-toluenethiolate at -80 °C followed by protonation with NH 4 Cl aq gave the same syn-11 and 12 complexes now in a 1:2.3 ratio. Finally, 1 was found to react with cyclohexanone lithium enolate to afford, upon protonation, the η 2 -allene complex Cp′(CO) 2 Mn[η 2 -{H(Tol)CdCdC(Ph)CH(CH 2 ) 4 C(O)}] (syn-13), resulting from a nucleophilic attack at C γ in 1. The solidstate structures of syn-11 and syn-13 are also reported.