FORMATION, STRUCTURES, AND REACTIONS OF CALCIUM AND BARIUM MONO(ALKOXIDE) COMPLEXES

Calcium diiodide dissolves in THF to produce the tetrasolvated octahed ral complex CaI2(THF)4 (1). The complex crystallizes in the space grou p P2(1)\c with a = 8.201(7) angstrom, b = 14.262(9) angstrom, c = 10.0 08(6) angstrom, beta = 93.93(6)degrees and D(c) = 1.656 g/cm3 for Z = 2. The iodide ligands are trans to each other with Ca-I bond distances of 3.106(2) A. CaI2 reacts with 1 equiv of K[OC(C6H5)2CH2C6H4-Cl-4](= Kclox) in THF to produce the mono(alkoxide)complex ICa(clox)(THF)4 (2) . The mono(alkoxide) is also produced by the conproportionation of Ca( clox)2(THF)3 and CaI2 in THF. It crystallizes from THF in the space gr oup P1BAR with a = 10.547(3) angstrom, b = 19.537(5) angstrom, c = 10. 343(3) angstrom, alpha = 90.54(2)degrees, beta = 93.93(6)degrees, gamm a = 103.60(2)degrees, and D(c) = 1.387 g/cm3 for Z = 2. The geometry a round the calcium in ICa(clox)(THF)4 is a distorted octahedron, with t he iodide and alkoxide in a cis arrangement: Ca-I = 3.108(3) angstrom and Ca-OR = 2.097(7) angstrom. ICa(clox)(THF)4 can be derivatized in T HF with K(clox) and KN(SiMe3)2 to yield Ca(clox)2(THF)3 and (clox)Ca[N (SiMe3)2](THF)3 (3), respectively. The latter is the first example of a monomeric calcium complex containing both monodentate alkoxide and a mide ligands. It crystallizes in the space group P1BAR with a = 12.298 (4) angstrom, b = 17.025(4) angstrom, c = 10.958(3) angstrom, alpha = 91.04(2)degrees, beta = 114.88(2)degrees, gamma = 89.57(2)degrees, and D(c) = 1.156 g/cm3 for Z = 2. (clox)Ca[N(SiMe3)2](THF)3 has a distort ed trigonal bipyramidal geometry, with THF ligands occupying axial sit es: Ca-N = 2.353(3) angstrom and Ca-OR = 2.087(4) angstrom. BaI2 will react with K[OC6H2-t-Bu2-2,6-Me-4] (=KBHT) in THF to form the mono(ary loxide) complex [IBa(BHT)(THF)3]2 (4). It is also formed from the conp roportionation of BaI2 and Ba(BHT)2(THF)3 in THF. The compound crystal lizes as an iodide-bridged dimer, [Ba(mu-I)(BHT)(THF)3]2.(THF)2, with two lattice THF molecules per dimer. The space group is P2(1)/c, with a = 13.997(4) angstrom, b = 14.164(8) angstrom, c = 18.161(4) angstrom , beta = 104.26(2)degrees, and D(c) = 1.469 g/cm3 for Z = 2 (dimers). The barium atoms have a distorted octahedral coordination geometry, wi th Ba-I (I') = 3.442(2) (3.590(2)) angstrom and Ba-OAr =2.408(8) angst rom. [IBa(BHT)(THF)3]2 will react with KBHT in THF to form the known b is(alkoxide)Ba(BHT)2(THF)3. Both ICa(clox)(THF)4 and [IBa(BHT)(THF)3]2 are stable toward disproportionation in THF. Stirring [IBa(BHT)(THF)3 ]2 in toluene removes the THF ligands and produces the insoluble oligo mer [IBa(BHT)]n (C7H8)x, whereas ICa(clox)(THF)4 Slowly decomposes in aromatics to give primarity the bis(alkoxide) [Ca(mu-clox)(clox)(THF)] 2 and CaI2(THF)x. The metal coordination numbers for the mono(alkoxide s), which are often less than might be expected from steric considerat ions, suggest that the Lewis acidity of the metal center influences th e extent of solvation in alkoxide complexes.