THE UNPREDICTABLE STRUCTURAL FEATURES OF CHROMIUM(II) PYRROLYLS - SYNTHESIS AND X-RAY STRUCTURES OF MONOMERIC SQUARE-PLANAR (ETA-1-2,5-ME2C4H2N)2CR(PY)2, SQUARE-PYRAMIDAL (ETA-1-C4H4N)2CR(PY)3, DIMERIC [(7-AZAINDOLYL)2CR(DMF)]2, AND POLYMERIC [(ETA-1-2,5-ME2C4N2)4CRNA2(THF)2(ET2O)]N - AN ABORTED CR-CR QUADRUPLE BOND FORMATION

Reaction of CrCl2THF2 with 2 equiv of C4H4NM or 2,5-Me2C4H2NM (M = Li, Na) leads to the formation of monomeric (η1-C4H4N)2Cr(L)3 [L = THF (1), py (2)] and (η1-2,5-Me2C4H2N)2 Cr(L)2 [L = THF (4), py (5)], respectively. The crystal structures of 2 and 5 were solved by X-ray diffraction analyses. In spite of the similarity between the ligands, the two monomeric complexes possess remarkably different structures: 2 has an unusual square-pyramidal geometry, while 5 is square-planar with low-and high-spin electronic configurations of the metal, respectively. Crystal data are as follows (T = 130 K, Mo Kᾱ, λ = 0.71073 Å): 2, triclinic, space group [formula omitted], a = 9.153 (4) Å, b= 10.659 (2) Å, c = 13.707 (3) Å, α = 86.01 (1)°, β = 82.93 (3)°, γ = 88.65 (2)°, Z = 2. 5, triclinic, space group [formula omitted], a = 6.986 (2) Å, b = 8.812 (2) Å, c = 9.018 (3) Å, α = 87.09 (2)°, β = 68.95 (2)°, γ = 83.18 (2)β, Z = 1. Dimerization was observed when a donor atom, attached to one of the two a positions of the pyrrolyl ligands, restored the unique geometry of the three-center chelating ligands. The dimeric structure of [(7-azaindolyl)2Cr-(DMF)]2·2DMF (7) (DMF = N,N-dimethylformamide) was demonstrated by X-ray diffraction analysis. Crystal data for 7: monoclinic, space group P21/a, a = 9.458 (1) Å, b = 19.085 (2) Å, c = 11.850 (1) Å, β = 109.92 (1)°, Z = 2 Magnetic properties and structural features [Cr-Cr = 2.604 (2) Å] suggest the absence of a Cr-Cr quadruple bond. Reaction of 1 and 4 with 2 equiv of C4H4NNa and 2,5-Me2C4H2NNa leads respectively to the formation of stable polymeric chromates [(C4H4N)4CrNa2L3]n (3) and [(2,5-Me2C4H2N)4CrNa2L3]n (6). [L = Et2O, dioxane, THF]. The polymeric aggregation, demonstrated in the case of 6 by an X-ray structure determination, is achieved via a π interaction of the pyrrolyl ligands with the Na cations from two different [(η1-pyrrolyl)4Cr]2− fragments. Crystal data for 6 (T = 130 K, Mo Kᾱ γ = 0.71073 Å) are as follows: monoclinic, space group P21, a = 9.045 (1) Å, b = 15.285 (1) Å, c = 13.621 (1) Å, β = 97.42 (1)°, Z = 2. © 1990, American Chemical Society. All rights reserved.