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

Calcium diiodide dissolves in THF to produce the tetrasolvated octahedral complex CaI2(THF)4 (1). The complex crystallizes in the space group P2(1)\c with a = 8.201(7) angstrom, b = 14.262(9) angstrom, c = 10.008(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 group 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, gamma = 103.60(2)degrees, and D(c) = 1.387 g/cm3 for Z = 2. The geometry around the calcium in ICa(clox)(THF)4 is a distorted octahedron, with the 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 THF 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 amide 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 distorted trigonal bipyramidal geometry, with THF ligands occupying axial sites: 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(aryloxide) complex [IBa(BHT)(THF)3]2 (4). It is also formed from the conproportionation of BaI2 and Ba(BHT)2(THF)3 in THF. The compound crystallizes 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, with Ba-I (I') = 3.442(2) (3.590(2)) angstrom and Ba-OAr =2.408(8) angstrom. [IBa(BHT)(THF)3]2 will react with KBHT in THF to form the known bis(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 oligomer [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(alkoxides), which are often less than might be expected from steric considerations, suggest that the Lewis acidity of the metal center influences the extent of solvation in alkoxide complexes.