Abstract The stepwise formation of the bifunctional σ 3,λ 4-phosphanediyl complex (2,4,6-Bu t 3C 6H 2O)(Cl)PMoCp(CO) 2 ( 4) (R = 2,4,6-Bu t 3C 6H 2O) is reported. The primary metallo-chlorophosphine (R)(Cl)PMoCp(CO) 3 ( 3) is isolated in almost quantitative yield from the reaction of RPCl 2 ( 1) with Na[MoCp(CO) 3] ( 2). Decarbonylation of 3 affords 4. The reactivity of 4 towards different nucleophiles is discussed. The identities of all new compounds are documented by analytical as well as spectroscopic (IR, MS, 1H, 13C and 31P NMR) data; the X-ray structure of (R)(Cl)PMoCp(CO) 3 ( 3) is reported.