Synthesis and electrochemical behavior of a new series of macrocyclic complexes of iron produced by oxidative dehydrogenation and tautomerization

Abstract

5502 Figure 1. PhotFelectron spectrum of 1,4-~yclohexadiene, obtained using the 304-A helium line with interpretation according to a SPINDOil calculation. For the ?r orbitals the symmetry is indicated. lo ' l1 carbon. For the carbon atom USs = -48.289 eV and Slater exponent = 1.925. In the resonance integrals H p v = S f i v [ I p A + IvBlf(RAB) the factors f have different values for different types of interaction: for ls/ls, J(R) = 0.13647; for ls/2s, f(R) = 0.17832; for ls/2pu,f(R) = 0.35100; for 2s/2s, f ( R ) = 0.20187 + 0.09500/R2; for 2s/2pu, f ( R ) = 0.27625 + 0.13000/R2; for 2pu/2pu,f(R) = 0.47000 + 0.24000/R2 + 100 exp(-5R); for 2p~/2p7r, f(R) = 0.40375 + 0.19000/R2. The parameters were chosen to give reasonable agreement in the case of benzene (with interpretation according to Jonsson and Lind-h0lm4), methane, ethane, ethylene, and acetylene.To demonstrate the usefulness of the new procedure we will in this communication apply it to two molecules: 1,4-cyclohexadiene and trans-l,3-butadiene.In the SPINDO calculation of cyclohexadiene the "planar" geometry discussed by Oberhammer and Bauers was used (cJ ref 6,7). The SPINDO orbital energies are compared in Figure 1 with the photoelectron spectrum, observed in our photoelectron spectrometer.8 Its low-energy part agrees well with an earlier study.g It can be seen that the distribution of the orbital energies corresponds well to the maxima of the curve. This supports our method and indicates that also the form of the molecular orbitals is obtained approximately correctly from the SPINDO calculation.The most interesting feature of the molecular orbitals of 1,4-cyclohexadiene is that the u orbitals are nearly identical with the corresponding orbitals in benzene. Also the orbital energies are nearly the same as in benzene, although, of course, the degenerate benzene orbitals are split. The introduction of two extra hydrogens in cyclohexadiene does not influence the uorbital system much.The P orbitals of 1,4-cyclohexadiene have no similarity with those of benzene. Owing to the two extra hydrogens the cyclohexadiene has four P orbitals. The two highest are in-phase @ and out-of-phase @ combinations of the ethylene T orbitals and the two lowest are similar combinations of the CH2 orbitals, @ and 0. That the in-phase combination @ is highest depends upon the destabilizing influence of the two CH, orbitals. This result is in good agreement with earlier (4) B. 0. Jonsson and E. Lindholm, Ark. Fys., 39,65 (1969). (5) H. Oberhammer and S . H. Bauer, J . Amer. Chem. SOC., 91, 10 (6) G. Dalinga and L. H. Toneman, 2L 22 20 18 16 1L 12 10 8 CV Figure 2. Photoelectron spectrum of butadiene16 compared with orbital energies from SPINDO/l and from a n ab initio c a l c~l a t i o n .~~ The band at 22.4 eV was observed by Brundle and Robin.21treatments of interaction through bonds10-12 in this molecule.In the SPINDO calculation of butadiene the geometry given by Haugen and Traettebergl3>l4 and Kuchitsu, et a1.,15 was used. The SPINDO orbital energies are compared in Figure 2 w...

Reactions at the azomethine CN bonds in the nickel(ii) and copper(ii) complexes of pyridine-containing Schiff-base macrocyclic ligands

“…Several examples of double-bond migration in Schiffbase metal complexes have been reported in the literature. [58][59][60][61][62][63] These isomerization reactions are similar to transaminations catalyzed by vitamin B6 or other pyridoxal derivatives. 60, 64 The mechanisms of pyridoxal-dependent transaminations involve deprotonation of the C-H bond that yields a resonancestabilized anion, followed by an addition of a proton to another carbon atom (Scheme 4, pathway A).…”

Expanding and quantifying the crystal chemistry of the flexible ligand 15aneN5

“…However, the phenomenon of transition metals oxidizing their complexed macrocyclic amines to imines is well known, as revealed by Busch for nickel and iron complexes. 61–63 Similar Ru complex chemistry is known in bidentate amine chelates, 64,65 and tetraazamacrocycles, 66 dating back at least to the 1970's. Taube invokes the stabilization of Ru 2+ by π-back donation to the imine as the driving force for imine formation.…”

Mono‐ and Bis‐Alkynyl Iron Complexes Supported by a “Softened” Tetraaza Macrocycle

“…The potentials of the Fe + 3/ + 2 couples in Fe(HMTI) species follow a consistent trend, shifting by roughly + 0.6 V from 2 to 3, and from 3 to the previously reported [Fe II (HMTI)(NCCH 3 ) 2 ] 2 + (0.6 V). [23] However, comparison to cyclam-based complexes (vide supra) indicates that the αdiimines participate in B through an electron-withdrawing stabilization. The assignment of D/D' as tetraimine-centered is based on the analysis of TIM complexes by Wieghardt and coworkers, [26,27] consistent with the LUMOs being π*(α-diimine) (Figure 4).…”

“…[22] Seeking to extend the chemistry to Csubstituted cyclam complexes, we recently attempted the synthesis of iron bis-alkynyls supported by meso-HMC (5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). During these investigations, we serendipitously rediscovered [23] the oxidative dehydrogenation of HMC to form HMTI (5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene; Scheme 2 below), and a unique pair of Fe(HMTI) alkynyl complexes, 2 and 3, are reported here.…”