Cycloheptatrienylmolybdenum complexes. Part 2. Synthesis of cationic acetylacetonate derivatives [ Mo(acac)L(η7-C7H7)]+(L = H2O, PEt3, PMe2Ph, PMePh2, P(OMe)3, AsMe2Ph, or py); molecular and crystal structure of [Mo(acac)(H2O)(η7-C7H7)][BF4]

Abstract

The cations [Mo(CO)₃(η⁷-C₇H₇)]⁺ and [Mo(η⁶-C₆H₅Me)(η⁷-C₇H₇)]⁺ react with an excess of acetylacetone in dry tetrahydrofuran to form the seventeen-electron aqua-complex [Mo(acac)(H₂O)(η⁷-C₇H₇)]⁺, from which the water molecule may be displaced affording the species [Mo(acac)L(η⁷-C₇H₇)]⁺(L = PEt₃, PMe₂Ph, PMePh₂, P(OMe)₃, AsMe₂Ph, or py). 1,2-Bis(diphenylphosphino)ethane (dppe) reacts with the aqua-complex to give a dimolybdenum dication [Mo₂(acac)₂(dppe)(η⁷-C₇H₇)₂]²⁺. Crystals of the title compound are monoclinic, space group P2₁/n, with a= 8.664(9), b= 18.997(4), c= 9.625(13)Å, β= 112.39(8)°. The structure has been refined to R 0.059 (R′ 0.071) for 3 226 independent observed reflections to 2θ 65°(Mo-K_αX-radiation) collected at ca. 215 K. All hydrogen atoms present have been located and positionally and thermally refined.

The crystal structure is built up of two pairs of [Mo(acac)(H₂O)(η⁷-C₇H₇)]⁺ cations and [BF₄]^– anions surrounding a symmetry centre and linked via two independent H ⋯ F contacts of 1.84(9) and 2.07(12)Å. The cation features a formally Mo^I metal atom in an approximate octahedral geometry. The tetrafluoroboratecounter ion is essentially tetrehedral.