Ligand and alkali metal cation control on the molecular complexity of anionic chromium(II) aryloxides. Preparation and crystal structure of dimeric (PhO)10Cr2Li6(THF)6 and (2,6-Me2C6H3O)6Cr2Li2(THF)4 and trimeric (GuO)14Cr3Na9Cl [GuO = (o-CH3O)C6H4O] with an encapsulated chloride ion

Abstract

Two new anionic, dimeric chromium(II) alkoxides, (PhO)10Cr2Li6(THF)6 (3) and (2,6-Me2C6H3O)6Cr2Li2(THF)4 (4), have been prepared and characterized by X-ray structure determination. The two complexes possess similar Cr2(OR)2 cores with a fairly long Cr-Cr distance [Cr...Cr' = 3.149 (2) and 3.091 (1) angstrom for 3 and 4, respectively]. In complex 3, the unit Cr2(OPh)2 is incorporated into two separated (PhO)4Li3(THF)3 polyhedra, while in complex 4 the same core is attached to two (RO)Li(THF)2 units with an overall linear arrangement of the Li-Cr-Cr-Li backbone. Replacement with TMEDA of the four THF molecules attached to lithium cleaved the dimeric structure of 3 and 4, forming the monomeric (RO)4CrLi2(TMEDA)2 [R = Ph (5a), 2,6-Me2C6H3O (5b)]. Reaction of CrCl2(THF)2 with 2 equiv of GuONa [GuO = (omicron-CH3O)C6H4O] led to the formation of the polymer [(GuO)2Cr]n, as an insoluble, pyrophoric solid. Further reaction with an excess of (GuO)Na formed the trinuclear (GuO)14Cr3Na9Cl (6). Treatment of 6 with 18-crown-6 led to the disruption of the trinuclear arrangement and formation of the polymeric [(GuO)2Cr]n species. Crystal data for 3, 4, and 6 are as follows. 3 is triclinic, space group P1BAR, with a = 12.511 (1) angstrom, b = 13.145 (1) angstrom, c = 15.260 (2) angstrom, alpha = 98.77 (1)-degrees, beta = 106.27 (1)-degree, gamma = 117.18 (1)-degrees, V = 2024.2 (3) angstrom-3, and Z = 1; 4 is monoclinic, space group C2/c, with a = 15.318 (4) angstrom, b = 18.245 (4) angstrom, c = 22.113 (6) angstrom, beta = 100.90 (2)-degrees, V = 6069 (3) angstrom-3, and Z = 4; 6 is orthorhombic, space group Pba2, with a = 26.720 (1) angstrom, b = 26.916 (2) angstrom, c = 15.670 (2) angstrom, V = 11269.8 (17) angstrom-3, and Z = 4.