The X-ray Structures of [Fe(CO)3(η4-6-exo-(PPh2R)cyclohepta-2,4-dien-1-one][BF4] (R = Me or tBu)

The structures of [Fe(CO)₃(η⁴-6-exo-(methyldiphenylphosphine)cyclohepta-2,4-dien-1-one][BF₄] [orthorhombic, a = 12.3269(4), b = 13.5243(5), c = 13.7127(4), space group Pna2₁] and [Fe(CO)₃(η⁴-6-exo-(tert-butyldiphenylphosphine)cyclohepta-2,4-dien-1-one][BF₄] [monoclinic, a = 9.7947(3), b = 12.8766(3), c = 20.2168(5), β = 91.089(3), space group P2₁/c] have been determined. The disordered tetrafluoroborate ion in [Fe(CO)₃(η⁴-6-exo-(methyldiphenylphosphine)cyclohepta-2,4-dien-1-one][BF₄] sits between two of the cations and displays interactions with hydrogen atoms in the ortho- position of the phenyl rings, the methyl group and the 6-position of the seven-membered ring. There is also close contact between the ketone oxygen atom and two protons in another cation, a proton of the methyl group and the proton in the 5-position of the seven-membered ring. The tetrafluoroborate anion in [Fe(CO)₃(η⁴-6-exo-(tert-butyldiphenylphosphine)cyclohepta-2,4-dien-1-one][BF₄] is not disordered and shows close contacts with protons in three cation units. In one cation the interaction is with two protons from separate methyl groups of the tert-butyl substituent. The remaining interactions are with a proton in the ortho- position of a phenyl ring in one cation and the proton in the 2-position of the seven-membered ring. There is also an interaction between the ketone oxygen and a proton from the tert-butyl group in another cationic unit.

Graphical abstract

Addition of PPh₂R (R = Me or ^tBu) to [Fe(CO)₃(η⁵-cyclohepta-2,4-dien-5-yl-1-one)][BF₄] results in exo- attack at the coordinated ring forming the [Fe(CO)₃(η⁴-6-exo-(PPh₂R)cyclohepta-2,4-dien-1-one][BF₄] compounds, both of which were structurally characterized.