Various substituted cyclopentadienyl molybdenum(V) tetrachlorides are reduced on reaction with PH-functionallzed lithium phosphanides to give the corresponding cyclopentadienyl molybdenum(II1) dichloro which can then react with further lithium reagent, yielding terminal phosphanido. diphosphanyl, and diphosphene complexes [5]. We attempted to prevent the reduction of Mo(V) by employing a primary phosphane instead of the highly reducing lithium reagents for the introduction of a P-functionalized ligand.Here we report on the preparation, spectroscopic properties and molecular structures of the first organometallic molybdenum(V) complexes with primary phosphane ligands, [Cp'MoCI4(PH2R)] [Cp' = C5H4Me, R = 2,4,6-Pr!3C6H2 (l), Cy (211.