PHOSPHATOVANADIUM CHEMISTRY - NEW COMPOUNDS, INCLUDING AN EXAMPLE OF TENNES PROSPECT, AND OXIDATION OF CYCLOHEXADIENE

Reactions of various vanadyl (V-v) compounds with silyl phosphato, pho sphonato, or alkyl phosphato compounds have provided the cluster compo unds (VO)(6)(O(3)POSiMe(3))(8)Cl (1), [Et(4)P](+)[(V2O3)(2)(O(3)PPh)(4 )F](-) (2), and the methylphosphonato and butyl phosphato analogues of compound 2. Both compounds 1 and 2 oxidize 1,4-cyclohexadiene to benz ene, and the reduction product of the methylphosphonato analogue of co mpound 2 has been characterized as [Et(4)P](+)(1.5) pyridine)(2)H](+)( 0.5)[(V2O3)(2)(MePo(3))(4)F](2-) (3). In the mixed-valence compounds 1 and 3 the odd electron is determined by EPR spectroscopy to be locali zed on a single VO unit in compound 1 and delocalized in compound 3. C ompound 1 crystallizes in the tetragonal space group I4/m with cell co nstants (at -100 degrees C) a = b = 13.788(2) Angstrom A, c = 19.126(3 ) Angstrom A, V = 3636(1) Angstrom A(3), Z = 2; compound 2 crystallize s in the triclinic space group P ($) over bar 1 with cell constants (a t -70 degrees C) a = 12.541(5) Angstrom A, b = 13.177(4) Angstrom A, c = 14.761(5) Angstrom A, alpha = 83.26(4)degrees, beta = 68.91(4)degre es, gamma = 72.23(3)degrees, V = 2167(1) Angstrom A(3), Z = 2; compoun d 3 crystallizes in the orthorhombic space group Iba2 with cell consta nts (at -100 degrees C) a = 17.462(3) Angstrom A, b = 33.787(6) Angstr om A, c 14.623(2) Angstrom A, V = 8627(2) Angstrom A(3), Z = 8. Featur es common to all compounds are the encapsulated halide ion and the rol e played by the phosph(on)ato moieties: by allowing only three oxygen atoms per phosphorus to participate in cluster bonding, the phosphorus centers become sites of positive Gaussian curvature and support closu re into polyhedral structures. Compound 1 realizes ''Tenne's prospect' ' of expressing a layered structure, in this case alpha-VOPO4, in clos ed polyhedral form.