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

Abstract

The synthesis of a series of new 18-electron cycloheptatrienylmolybdenum complexes [MoX(dppe)(η-C₇H₇)]^z+ (dppe = Ph₂PCH₂CH₂PPh₂; z = 0, X = NCO, NCS, CN, ¹³CN; z = 1, X = CNMe, ¹³CNMe, oxacyclopentylidene) and [Mo(triphos)(η-C₇H₇)]⁺ (triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane) is reported. Cyclic voltammetric investigations reveal that each of these complexes undergoes a reversible one-electron oxidation to the corresponding 17-electron radicals which have been generated by chemical oxidation, isolated and characterised. Additional examples of 17-electron radicals [MoX(dppe)(η-C₇H₇)]^z+ (z = 1, X = I, Br, Cl, F, Me, CCPh; z = 2, X = NCMe) were either isolated directly or reinvestigated in this work. Fluid solution, X-band EPR studies at 243 K on the 17-electron radicals [MoX(dppe)(η-C₇H₇)]^z+ (z = 1 or 2) afford well resolved spectra characteristic of molybdenum species split by ligand hyperfine interactions with two equivalent phosphorus atoms, seven equivalent protons of the cycloheptatrienyl ring and an additional splitting from the ligand X (where this contains nuclei with non-zero spin). Calculations to determine contributions to the ground state molecular orbital 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 the unpaired electron occupies an essentially metal-based molecular orbital.