SERIES OF 2-COORDINATE AND QUASI-2-COORDINATE TRANSITION-METAL COMPLEXES - SYNTHESIS, STRUCTURAL, AND SPECTROSCOPIC STUDIES OF STERICALLY DEMANDING BORYLAMIDE LIGANDS-NRBR'2 (R = PH, R' = MES, XYL - R = R' = MES), THEIR LITHIUM-SALTS LI(ET2O)2NRBR'2, AND THEIR TRANSITION-METAL DERIVATIVES M(NPHBMES2)2 (M = CR, CO, NI), CO(NPHBXYL2)2, AND M(NMESBMES2)2 (M = CR-]NI)

Amide ligands, modified by the presence of the diarylboryl substituents-BMes2 or-BXyl2 (Mes = 2,4,6-Me3C6H2, Xyl = 2,6-Me2C6H3), have been used to effect the synthesis and characterization of several low-coordinate metal complexes of unusual structure. The synthesis of the aminoboranes HNRBMes2 (R = Ph, 1; R = Mes, 2) and HNPhBXyl2 (1a), the lithium borylamide salts Li(Et2O)2NRBMes2 (R = Ph, 3; R = Mes, 4), and 10 transition-metal derivatives, M(NPhBMes2)2 (M = Cr, 5; Co, 6; Ni, 7), Co(NPhBXyl2)2 (6a), Co[N(C6D5)BMes2]2 (6b), and M(NMesBMes2)2 (M = Cr, 8; Mn, 9; Fe, 10; Co, 11; Ni, 12), are reported. The X-ray crystal structures of 2, 4-7,10, and 11 are described and discussed in the context of structures 1, 3, 8, 9, and 12 reported in preliminary publications. The transition-metal complexes were further characterized by UV/vis and EPR spectroscopy and magnetic data. Variable-temperature 1H NMR spectroscopy of 6, 6a, 6b, 7, 11, and 12 is also reported. The transition-metal complexes 5-12 are all high spin with nominally two-coordinate geometries. However, they all display some deviation from linearity. The distortion is most severe for the chromium complexes 5 and 8 (N-Cr-N = 110.8 (1)° and 112.3 (3)°) whereas in Fe, Co, and Ni derivatives of-NMesBMes2 deviation of the NMN angle from 180° is only about 13°. The BN bonds within the ligands are short, and the nitrogen and boron centers are invariably planar. The ligands are, in effect, boron-nitrogen analogues of alkenyls. Instead of association through bridging at the nitrogen centers, moderate (in 5-8) or very weak (in 9-12) intramolecular interactions are observed between the ipso carbons of the-BMes2 groups and the metal centers that may cause the observed structural distortions. Variable-temperature 1H NMR data on 6, 6a, 6b, and 11 indicate that the M-C ligand interactions are not greater than about 10 kcal mol-1 for 6, 6a, 6b, and presumably for 5 and 7, whereas in the NMes compounds 11 and 12 no M-C interactions could be detected at temperatures as low as 192 K. Crystal data with Mo Kα(λ = 0.71069 Å) radiation at 130 K: 2, HNMesBMes2, C27H34BN, a = 8.200 (1) Å, b = 10.370 (3) Å, c = 15.134 (3) Å,α = 109.38 (2)°, ß = 80.96 (2)°, γ = 108.71 (2)°, Z = 2, triclinic, space group Pi, R = 0.063; 4, Li(Et2O)2NMesBMes2, a = 10.927 (4) Å, b = 19.626 (5) Å, c = 31.07 (1) Å, Z = 8, orthorhombic, space group Pbca, R = 0.085; 5, Cr(NPhBMes2)2, C48H54B2CrN2, a = 11.344 (2) Å, b = 22.531 (8) Å, c = 16.285 (3) Å, ß = 94.95 (1)°, Z = 4, monoclinic, space group P21/c, R = 0.046; 6, Co(NPhBMes2)2, C48H54B2CoN2, a = 13.454 (3) Å, b = 15.466 (4) Å, c = 23.191 (7) Å, ß = 99.82 (2)°, Z = 4, monoclinic, space group P21/n, R = 0.080; 7, Ni(NPhBMes2)2, C48H54B2NiN2, a = 10.616 (4)_Å, b = 12.108 (4) Å, c = 17.578 (4) Å, α = 109.27 (2)°, ß = 91.89 (3)°, γ = 103.05 (3)°, Z = 2, triclinic, space group P1, R = 0.057; 10, Fe(NMesBMes2)2, C56H66B2FeN2, a = 11.462 (5) ÅL6 = 13.784 (6) Å, c = 15.797 (6) Å, α = 103.35 (3)°, ß = 101.51 (3)°, γ = 99.87 (4)°, Z = 2, triclinic, space group P1, R = 0.045; 11, Co(NMesBMes2)2, C54H66B2CoN2, a = 11.399 (5)_Å, b = 13.746 (7) Å, c = 15.852 (7) Å, α = 103.13 (4)°, ß = 101.76 (4)°, γ = 99.71 (4)°, Z = 2, triclinic, space group PI, R = 0.057. © 1990, American Chemical Society. All rights reserved.