Synthesis, redox properties, EPR and ENDOR spectroscopy of the 17-electroncycloheptatrienylmolybdenum complexes [MoX(Ph2PCH2CH2PPh2)(eta-C7H7)](z+) (z=1, X = I, Br, Cl, F, NCO, NCS, CN, (CN)-C-13, Me, C=CPh; z=2, X = NCMe, CNMe, (CNMe)-C-13, oxacyclopentylidene)

The synthesis of a series of new 18-electron cycloheptatrienylmolybdenum co mplexes [MoX(dppe)(eta-C7H7)](z+) (dppe=Ph2PCH2CH2PPh2; z=0, X=NCO, NCS, CN , (CN)-C-13; z =1, X=CNMe, (CNMe)-C-13, oxacyclopentylidene) and [Mo(tripho s)(eta-C7H7)](+) (triphos=1,1,1-tris(diphenylphosphinomethyl)ethane) is rep orted. Cyclic voltammetric investigations reveal that each of these complex es undergoes a reversible one-electron oxidation to the corresponding 17-el ectron radicals which have been generated by chemical oxidation, isolated a nd characterised. Additional examples of 17-electron radicals [MoX(dppe)(et a-C7H7)](z+) (z = 1, X=I, Br, Cl, F, Me, C=CPh; z=2, X=NCMe) were either is olated directly or reinvestigated in this work. Fluid solution, X-band EPR studies at 243 K on the 17-electron radicals [MoX(dppe)(eta-C7H7)](z+) (z = 1 or 2) afford well resolved spectra characteristic of molybdenum species s plit by ligand hyperfine interactions with two equivalent phosphorus atoms, seven equivalent protons of the cycloheptatrienyl ring and an additional s plitting from the ligand X (where this contains nuclei with non-zero spin). Calculations to determine contributions to the ground state molecular orbi tal from (i) the ns orbital of the ligand X (based on the EPR work) and (ii ) the dppe phosphorus s and p orbitals (based on ENDOR work) suggest that t he unpaired electron occupies an essentially metal-based molecular orbital.