Tetranuclear phosphinidine, phosphide, arsenide, and oxide anionic clusters of molybdenum and tungsten supported by neopentoxide ligands: Na(18-crown-6)[M(4)(mu(3)-PSiMe(3))(OCH(2)(t)Bu)(11)], K(18-crown-6)[M(4)(mu(3)-E)(OCH(2)(t)Bu)(10)] (E=P, As), K(18-crown-6)(2)[Mo-4(mu(3)-O)(OCH(2)(t)Bu)(11)]

From the reactions between M(2)(OCH(2)(t)Bu)(6) (2 equiv) and NaP(SiMe(3))(2) (1 equiv) in benzene and 18-crown-6 the phosphinidine clusters [M(4)(mu(3)-PSiMe(3))(OCH(2)(t)Bu)(11)](-), compounds 1 (M = Mo) and 2 (M = W) are formed and are reactive intermediates in the formation of [M(4)(mu(3)-P)(OCH(2)(t)Bu)(10)](-) cluster anions, compounds 3 (M = Mo) and 4 (M = W), respectively, which have been isolated and characterized as their Na(18-crown-6)(+) salts. Crystals of Na(18-crown-6)(+)[Mo-4(mu(3)-P)(OCH(2)(t)Bu)(10)](-). C6H6 were examined by single crystal X-ray crystallography at -110 degrees C in the space group Pn with a 13.000(2) Angstrom, b = 17.501(3) Angstrom, c = 18.703(2) Angstrom, and beta = 93.11(1)degrees with Z = 2 and at -173 degrees C in the space group Cc with a = 22.118(4) Angstrom, b = 17.480(3) Angstrom, c = 23.250(4) Angstrom, and beta = 110.82(1)degrees with Z = 4. At the lower temperature, there is higher symmetry and no disorder of the 18-crown-6 molecule. The cluster anion has a Mo-4 butterfly with a mu(3)-P ligand and virtual mirror symmetry. One wing-tip Mo atom is five-coordinate and bonded to the mu(3)-P atom and shows longer Mo-to-Mo distances (2.68(1) and 2.71(1) Angstrom) relative to its counterpart (2.48(1) and 2.50(1) Angstrom); the backbone Mo-Mo distance is 2.53(1) Angstrom. The cluster anion in 3 but not 4 is also accessible from the reaction between Mo-2(OCH(2)(t)Bu)(6) (2 equiv), PH3, and KOCH(2)(t)Bu (1 equiv) in THF/18-crown-6 (THF = tetrahydrofuran). A similar approach involving AsH3, Mo-2(OCH(2)(t)Bu)(6), and KOCH(2)(t)Bu gave the mu(3)-arsenide cluster complex K(18-crown-6)(+)[Mo-4(mu(3)-As)(OCH(2)(t)Bu)(10)](-), compound 5, which by NMR spectroscopy is analogous in structure to 3. The reaction between Mo-2(OCH(2)(t)Bu)(6) (2 equiv) and KOH in THF/18-crown-6 gave K(18-crown-6)(2)(+)[Mo-4(mu(3)-O)(OCH(2)(t)Bu)(11)](-), compound 6, which is proposed to be isostructural with the phosphinidine complexes 1 and 2 on the basis of NMR data. Crystal data for K(eta(6)-C12H24O6)(eta(2)-C12H24O6)(+)[Mo-4(mu(3)-O)(OCH(2)(t)Bu)(11)](-) at -165 degrees C: a 17.595(2) Angstrom, b = 28.044(3) Angstrom, c = 20.443(2) Angstrom, beta = 97.61(1)degrees with Z = 4, and space group P2(1)/n. The cluster anion in 6 contains a 12-electron Mo-4 butterfly with 12 M-M bonding electrons, as in 3, but the shortest Mo-Mo distance 2.42(1) Angstrom involves the backbone metal atoms. The Mo-Mo distances involving the ore-capped triangle (2.61(1) and 2.62(1) Angstrom) are notably longer than those in the other triangle (2.48(1) Angstrom).