NEW NIOBIUM COMPLEXES WITH ALKYNES .6. 2 COMPOUNDS CONTAINING NB2[PHCC(PH)C(PH)CPH] UNITS JOINED IN UNORTHODOX WAYS

Two new compounds are described that contain the recently discovered Nb2[PhCC(Ph)C(Ph)CPh] moiety. In each of these the manner in which two of these are joined to form a tetranuclear species is unsymmetrical and thus unorthodox in comparison to the very symmetrical linking across one μ4-O and four µ2-Cl bridges previously observed. Compound 1, [Nb4O2Cl4{(PhC)4}2(THF)4]·2THF, contains centrosymmetric tetranuclear molecules in which the equivalent halves, Nb2{(PhC)4}Cl2(THF)2O, are joined solely by having the μ-O atom of each half form a strong donor bond to one of the Nb atoms of the other half. This compound crystallizes in space group P21/c with Z = 2 and has been refined to R = 0.049 and RW = 0.066. The unit cell dimensions are a = 13.409 (2) Å, b = 27.421 (5) Å, c = 10.805 (3) Å, and β = 106.76 (2)°. Compound 2, [Mg2Cl3-(THF)6][Nb4O2Cl7{(PhC)4}2{Mg(THF)3}]·THF, crystallizes in space group P1 with Z = 2 and no rigorous molecular symmetry. The unit cell dimensions are a = 12.614 (2) Å, b = 16.706 (3) Å, c = 27.153 (5) Å, α = 107.45 (1)°, β = 99.11 (1)°, and γ = 90.61 (2)°. The two Nb2(PhC)4 moieties are arranged to form a rectangle with a µ4-O atom at the center and two μ-Cl atoms bridging one long edge, essentially as in the previously described symmetrical [Nb4O{(PhC)4}2Cl8]2- anions. The other long edge is spanned by an oxygen atom and has an Mg(THF)3 unit attached to this oxygen atom and to one terminal pair of the neighboring Cl atoms, to give a distorted octahedron about Mg. © 1990, American Chemical Society. All rights reserved.