Low-coordinate terphenyl transition metal complexes (M = chromium, cobalt): Synthesis, characterization, and reacitivity.

摘要

This dissertation focuses on the synthesis, characterization, and reactivity studies of low-oxidation state terphenyl species of chromium, manganese, iron, and cobalt. Single crystal X-ray crystallography was utilized initially to determine the solid-state structures of the novel complexes. Due to the steric effect of the monodentate terphenyl ligands, the metal complexes usually have low-coordination numbers (≤ 4). In most cases, these unsaturated species display paramagnetism. Thus superconducting quantum interference device (SQUID) measurements between 2 and 320 K or Evans' method were conducted to study the magnetic properties. For the few diamagnetic examples, multi-nuclear NMR, such as 1H, 13C, 19F, 28Si or 31P, were employed instead. UV-vis spectroscopy was utilized to characterize the absorptions and energies of the metal to ligand charge transfer or d electron transitions. IR spectroscopy was also used to study the stretching absorptions of certain functional groups, such as N-H, N=N, and C≡C bonds.;Metathesis of the aryl metal halides with lithium reagents, such as lithium amides or alkyls, readily afforded a variety of heteroleptic low-coordinate aryl metal complexes with amido or alkyl coligands. These include the quasi two-coordinate M(II) aryl/amido complexes Ar'MN(H)Ar ;Reactivity studies of some of the complexes were also carried out. The reactions of the quintuple-bonded species Ar'CrCrAr' with small molecules (N2O, N3(1-Ad), or I2) led to complete cleavage of the metal-metal quintuple bond. The Mn(I) inverted sandwich complex (eta 6-C7H8){MnAr*-3,5-iPr 2}2 reacted with bulky terphenyl azides and afforded the Mn(II) aryl/amido complexes via C-H activation of a methyl group or a phenyl group. The reactions of eta6-C6H6)FeAr*-3,5- iPr2 with a variety of heterocumulene molecules were conducted similarly and a variety of low-coordinate iron complexes were formed. In particular, the first example of a stable Fe(V) bis(imido) complex 3,5-iPr2-Ar*Fe{N-(1-Ad)}2 was isolated and characterized in the solid state. In addition, an Fe(III) oxo complex {3,5-iPr2-Ar*OFe(mu-O)} 2, which was obtained by reaction of (eta6-C6 H6)FeAr*-3,5-iPr2 with N2O, features an Fe2(mu-O)2 diamond core with the shortest Fe···Fe separation (2.4818(7) A) among all structurally characterized synthetic model complexes with Fe2(mu-O)2 cores. The synthesis and reactivity studies related two-coordinate diaryl Fe(II) species FeAr'2 towards O 2 and CO are also described.;Reduction of the terphenyl metal halide derivatives by KC8 is a general route to synthesize the reduced M(I) species. This synthetic protocol has led to the isolation of the Cr(I) dimers {4-X-Ar'Cr}2 (X = H, SiMe3, OMe, and F), in which the two chromium(I) atoms are linked by a five-fold metal-metal interaction, the Mn(I) inverted-sandwich complex (mu-eta6:eta6C7H 8{MnAr*-3,5-iPr2}2 the Fe(I) half-sandwich complex (eta6-C6H6)FeAr*-3,5- iPr2 and the related phosphine derivative 3,5- iPr2-Ar'Fe(PMe3), and the allyl Co(I) phosphine complexes, which was formed via an unusual remote C-H activation and triple dehydrogenation of an isopropyl group.