Group 15 complexes
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
As(OtBu)3 does not form adducts with alkali metal tert-butoxides MOtBu (M = Li, Na, K, Rb and Cs), whereas the corresponding Sb(OtBu)3 (2) and Bi(OtBu)3 (3) react with MOtBu (M = K, Rb, Cs) to yield M(OtBu)4Sb (M = K (6), Rb (7), Cs (8)) and M(O-tBu)4Bi (M = 9), respectively. X-ray structure determinations for 6 and 9 show them to be one-dimensional coordination polymers composed of E(OtBu)4 (E = Sb, Bi) units linked through potassium atoms. These E(OtBu)4 units display a ψ-trigonal-bipyramidal coordination around the metal atom (Sb—O = 1.971(2) and 2.181(2) Å, Bi—O = 2.068(8) and 2.275(8) Å). Both the structures exhibit a planar four-coordinate environment of oxygen around the potassium atoms (K—O = 2.650(2)-2.967(2) Å in 6, 2.53(1)-3.15(1) Å in 9). Compound 2 reacts with two equivalents of KOtBu to afford K2Sb(OtBu)5 · dioxane (10), which contains Sb2K2O5 cage units and can be described as an O5 trigonal bipyramid with metal atoms inserted in the equatorial edges. Each metal atom is tetracoordinated by oxygen atoms of the cage (Sb—O = 1.979(3)-2.144(3) Å. K—O = 2.592(3)-2.778(2) Å). The dioxane molecules increase the coordination number at each potassium atom to five by forming bridges between the molecules through K—O bonds. Reaction of 2 and 3 with NaOtBu produce the cluster compounds Na4Sb2O(OtBu)8 (4) and Na4Bi2O-(OtBu)8 (5) in high yields. K4Sb2O-(OtBu)8 (11) is obtained in almost quantitative yield by heating KSb(OtBu)4 in benzene for 24 h. Compounds 4, 5 and 11 crystallise in rhombohedral lattices; the crystal structure analyses show a superposition of molecules. With an isotropic oxygen-centred M6 octahedron. The formation of these oxo-tert-butoxides is accompanied by evolution of isobutene. Addition of four equivalents of THF to 11 gives K4Sb2O(OtBu)8 · 4 THF (12). X-ray diffraction studies reveal a cis arrangement of the Sb atoms in the central OSb2K4 unit. K4Sb2O2(OiPr)12 (13) is obtained as the major product on heating KSb(OtBu)4 and subsequent reaction with isopropyl alcohol. In the crystal structure, two oxygen-centred Sb2K2 tetrahedra (K—O 2.693(4) Å, Sb—O = 1.982(5) Å) linked through iPrO—K bonds (2.726(7)-2.738(7) Å) are observed. In the reactions of KSb(OtBu)4 (6) with the metal halides CaCl2, TlCl and CuI, a halide ion is transferred to potassium; this results in formation of potassium halide, the corresponding alkoxide and Sb(OtBu)3.
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