Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) Formation of stable -aryliron(III) complexes from the reaction of chloroiron(III) octaphenyltetraazaporphyrinate with aryl Grignard reagents Pavel A. Stuzhin,*a Ol’ga V. Mal’chugina,a Stanislaw Wolowiec,b Lechoslaw Latos-Grazynskib and Boris D. Berezina a Department of Organic Chemistry, Ivanovo State Academy of Chemical Technology, 153460 Ivanovo, Russian Federation.Fax: +7 0932 37 7743; e-mail: stuzhin@icti.ivanovo.su b Department of Chemistry, University of Wroclaw, 50383 Wroclaw, Poland Chloro(octaphenyltetraazaporphyrinato)iron(III) [(Cl)FeIIIOPTAP] reacts with aryl Grignard reagents (ArMgBr; Ar = phenyl or p-tolyl) forming stable low-spin s-aryliron(III) complexes [(Ar)FeIIIOPTAP]. The inactivation of hemoproteins by arylhydrazines includes formation of aryl–iron s-bonded complexes of heme as intermediates.1 The structure, physico-chemical properties and reactivity of s-aryliron(III) complexes of synthetic porphyrins [(Ar)FeIIIP; P = OEP (octaethylporphine) or TPP (tetraphenylporphine)] which form in the reaction of iron(III) porphyrins with aryl Grignard reagents under strictly anaerobic conditions2,3 have been extensively investigated.4,5 The preparation of s-aryliron(III) phthalocyanines [(Ar)FeIIIPc] has also been demonstrated,6–8 but no full report on their synthesis and characterization has appeared since then.Thus s-phenyliron(III) phthalocyanine (Ph)FeIIIPc was prepared7,8 by oxidation of s-phenyliron(II) complex Li[(Ph)FeIIPc] which in turn forms in the reaction of BrFeIIIPc (or Py2FeIIPc) with phenyllithium.6 Grignard reagents can not be used in the synthesis of (Ar)FeIIIPc because they reduce iron(III) phthalocyanines to the iron(0) complex ([Fe0Pc]2–).6 Unlike s-phenyliron(III) phthalocyanine, which was reported to be a stable compound,7 s-aryliron(III) porphyrins are easily oxidized in the presence of dioxygen forming m-oxodiiron(III) or aryloxoiron(III) complexes [m-O(FeIIIP)2 or (PhO)FeIIIP]9 and give upon addition of acids HX acidoiron(III) complexes [(X)FeIIIP].2 Thus the stability of the Ar–Fe bond depends strongly on the properties of the macrocyclic ligand.In order to throw some more light on the factors determining the stability of the C–Fe bond we have obtained the s-phenyliron(III) complex of octaphenyltetraazaporphine, a macrocyclic ligand having an intermediate structure between common porphyrins and phthalocyanine.s-Phenyl(octaphenyltetraazaporphyrinato)iron(III) [(Ph)FeIIIOPTAP 2] was obtained by addition of phenylmagnesium bromide (PhMgBr) to a solution of chloro(octaphenyltetraazaporphyrinato) iron(III) [(Cl)FeIIIOPTAP 1]10 in dry benzene in aerobic conditions (Scheme 1). The colour of the solution changed immediately from red-brown to dark blue and then to green.Excess PhMgBr was hydrolyzed with water and the benzene layer (after drying with Na2SO4) was chromatographed on neutral Al2O3. s-Phenyliron(III) complex 2 was obtained from the second greenish-blue fraction (yield 14%)† while the first green fraction contained mostly m-oxodiiron(III) complex [m-O(FeIIIOPTAP)2]. In a similar manner using various aryl Grignard reagents other s-aryliron(III) complexes (Ar)FeIIIOPTAP (Ar = p-MePh, p-MeOPh etc.) can be obtained.Complex 2 is air-stable in the solid for several weeks, but in a solution in neutral solvents such as benzene or toluene it converts after several days to m-O(FeIIIOPTAP)2.Addition of † Analysis for 2: 1H NMR (300 MHz, [2H8]toluene, 293 K) d: 1.25 (o-Phb), 7.40 (m-Phb) and 3.53 (p-Phb) (OPTAP); 84.34, 8.00 and –30.85 (o-Phax, m-Phax and p-Phax). UV/VIS [benzene, lmax/nm (log e)]: 344 (4.45), 440sh, 458 (4.17), 489sh, 555sh, 607 (4.45). IR (KBr, n/cm–1): 536m, 608m, 640w, 696vs, 744s, 776m, 832s, 888w, 916w, 992vs, 1064w, 1152s, 1204w, 1296w, 1372s, 1440m, 1460m, 1484s.Found (%): C, 79.5; H, 4.4; N, 10.4. Calc. for C70H45N8Fe (%): C, 79.77; H, 4.30; N, 10.63. FAB-MS m/z: (Ph)FeOPTAP+ (1053, 14%; 1052, 28%; 1051, 35%; 1050, 44%; 1049, 39%; 1048, 29%); FeOPTAP+ (976, 46%; 975, 57%; 974, 100%; 973, 86%; 972, 71%; 971, 38%; 970, 28%). acid HX (X = Cl, CCl3COO) to a solution of 2 results in slow formation of the corresponding acidoiron(III) complex (X)FeIIIOPTAP and dissolution of 2 in pure pyridine leads to (py)2FeIIOPTAP.The CHN elemental analysis data for 2 are in agreement with the formula (Ph)FeIIIOPTAP. The mass spectrum of 2 obtained by a fast atom bombardment method contains mass peaks corresponding to the molecular ion [(Ph)FeOPTAP]+ and to the dephenylated fragment [FeOPTAP]+. In the IR spectrum of (Ph)FeIIIOPTAP the vibrations of the axially coordinated phenyl (Phax) coincide with that of the eight equatorial phenyls (Phb) attached to the b-pyrrole positions of the macrocyclic ligand, but some structural information can be obtained from the skeleton vibrations of the latter.Thus the band at 1296 cm–1 is characteristic of the five-coordinated (X)FeIIIOPTAP complexes10 and the position of the oxidation-state sensitive band at 1152 cm–1 is typical of the iron(III) complexes.11 Conversion of the chloride complex 1 to the s-phenyl complex 2 is accompanied by strong changes in the UV/VIS spectra (Figure 1).This is not unusual because the oxidation and spin states of the iron(III) ion have a large impact on the energies of the p ® p* transitions of the OPTAP macrocycle and on the appearance of the charge-transfer transitions.10,11 The spectrum of (Ph)FeIIIOPTAP [Figure 1(b)] differs greatly from the spectrum of the initial intermediate-spin (IS) FeIII complex (Cl)FeIIIOPTAP10 [Figure 1(a)] and is typical of complexes with low-spin (LS) FeIII.However, all known LS FeIII complexes of OPTAP2– are six-coordinate {e.g. [(CN)2FeIIIOPTAP] –, [(N3)2FeIIIOPTAP]–, [(HIm)(N3)FeIIIOPTAP] or s Figure 1 UV/VIS spectra of (a) (Cl)FeIIIOPTAP, (b) (Ph)FeIIIOPTAP in toluene (2.1×10–5 M) and (c)–(f) spectral changes observed after addition of 1-methylimidazole (2.55×10–4, 8.90×10–4, 3.56×10–3, 2.09×10–2 M, respectively) to a solution of (Ph)FeIIIOPTAP.A 0.8 0.6 0.4 0.2 0.0 400 500 600 700 800 l/nm a b c d e f b b fMendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) [(HIm)2FeIIIOPTAP]+}.11,12 Five-coordinate complexes even with axial ligands possessing a stronger field than the halogenide [e.g. (N3)FeIIIOPTAP or even (CN)FeIIIOPTAP] usually have UV/VIS spectra typical of IS FeIII complexes. Evidently the s-Ar carbanion forming the strong s-bond with the iron atom raises the energy of the dz2 orbital and makes favourable the LS state of FeIII even in the five-coordinate complex.s- Aryliron(III) porphyrins and phthalocyanine are also LS complexes.2,7 Addition of small amounts of N-bases L (L = pyridine, imidazole) to a solution of 2 in neutral solvents results in spectral changes that are indicative of coordination of L in the trans-position to the s-phenyl anion with formation of (L)(Ph)FeIIIOPTAP 3 and under certain conditions an equilibrium between five- and six-coordinate complexes 2 and 3 can be observed [Figure 1, spectra (b)–(f)]. Formation of the six-coordinate complex 3 from 2 is accompanied by a strong bathochromic shift of the B-band [a2u(p) ® eg(p*) transition] from 344 to 397 nm, whereas the position of the Q-band [a1u(p) ® eg(p*) transition] at 607 nm remains practically unchanged.This is well explained by the different symmetry properties of the two highest occupied molecular orbitals. The a2u(p) orbital destabilizes upon coordination of the p-donor ligand in the sixth position, in contrast to the a1u(p) orbital which, having nodes on the coordinating pyrrole N-atoms of the OPTAP macrocycle, is much less sensitive to the changes in the coordination state of the Fe atom.In the 1H NMR spectra of (Ph)FeIIIOPTAP [Figure 2(a)] the paramagnetically-shifted phenyl protons of the macrocycle are observed at 1.25 (o-Phb), 7.40 (m-Phb) and 3.53 ppm (p-Phb) ([2H8]toluene, 293 K). The pattern of three singlets suggests fast rotation of the b-phenyl rings with respect to the Cb–Cphenyl bond.The signals of the axial phenyl protons are located at –84.34, 8.00 and –30.85 ppm for o-Phax, m-Phax and p-Phax, respectively. An identical 1H NMR spectrum has been obtained in the course of titration of (Cl)FeIIIOPTAP with PhMgBr in [2H8]toluene. The strong isotropic shift of the axial phenyl proton resonances is dominated by the contact contribution. The analysis indicates the large p-spin density at the axial ligand as the contact shift decreases in the characteristic order ortho > para > meta and can be accounted for by the spin delocalization from the dp orbitals to the p-type orbitals of the axially-coordinated phenyl ligand (although some contribution of the s-contact mechanism should be considered as well).14,15 In the relevant case of s-phenyliron(III) porphyrins the resonances of the axial phenyl protons were observed in the same region [for (Ph)FeIIITPP at 294 K by –81, 13.6 and –27 ppm for o-Phax, m-Phax and p-Phax, respectively].3 Coordination of a strong p-donor ligand such as 1-methylimidazole (1MeIm) in the trans-position to phenyl [(1MeIm)- (Ph)FeIIIOPTAP] decreases the range of paramagnetic shifts found for the Phax protons (–57.46, 14.30 and –14.42 ppm for o-Phax, m-Phax and p-Phax, respectively) [Figure 2(b)].The effect is comparable with that demonstrated for (1MeIm)(Ph)- FeIIITMP (TMP = meso-tetramesitylporphyrin dianion).13 The 1H NMR data suggest that (Ph)FeIIIOPTAP and (1MeIm)- (Ph)FeIIIOPTAP present the (dxy)2(dp)3(dz2)0(dx2 – y2)0 ground electronic state, as previously shown for the corresponding iron(III) porphyrin species.13,15 Tetraazasubstitution in the meso-positions of the porphyrin ligand endows the macrocyclic ligand with stronger p-acceptor and s-donor properties.These factors determine the strengthening of the Fe � Phax p-bonding and Fe � OPTAP s-bonding which can explain the higher oxidation stability observed for the s-aryliron(III) complexes of tetraazaporphyrins (and phthalocyanine as well).Further study of s-aryliron(III) octaphenyltetraazaporphyrin complexes using Mössbauer, NMR and EPR spectroscopy which are now in progress will reveal the details of their formation mechanism. We thank Professor B. Floris (Università di Roma ‘Tor Vergata’, Italy) for help in obtaining the mass spectra.References 1 K. L. Kunze and P. R. Ortiz de Montellano, J. Am. Chem. Soc., 1983, 105, 1380. 2 H. Ogoshi, H. Sugimoto, Z.-I. Yoshida, H. Kobayashi, H. Sakai and Y. Maeda, J. Organomet. Chem., 1982, 234, 185. 3 P. Cocolios, G. Lagrange and R. Guilard, J. Organomet. Chem., 1983, 253, 65. 4 P. Doppelt, Inorg. Chem., 1984, 23, 4009. 5 R. Guilard and K. M. Kadish, Chem. Rev., 1988, 88, 1121 and references therein. 6 R. Taube and H. Drevs, Z. Anorg. Allg. Chem., 1977, 429, 5. 7 R. Taube, H. Drevs and D. Steinborn, Z. Chem., 1978, 18, 425. 20 10 0 –10 m-Phax m-Phb o-Phb p-Phb m-Phax p-Phax o-Phax (a) (b) 4-H + 2-H 5-H m-Phax + 1-Me o-Phb p-Phax o-Phax 40 20 0 –20 –40 –60 –80 d/ppm Figure 2 300 MHz 1H NMR spectra of (a) (Ph)FeIIIOPTAP (293 K) and (b) (1MeIm)(Ph)FeIIIOPTAP (253 K) in [2H8]toluene. Inset in trace (a) presents details of the –10 to +20 ppm region (spectrum recorded at 180 K).Resonance assignments: o-Ph, m-Ph and p-Ph, resonances of ortho, meta and para phenyl protons (axial and b-phenyl signals are marked by subscripts Phax or Phb, respectively); 2-H, 4-H, 1-Me, 5-H resonances of coordinated 1-MeIm. N N N N N N N N Ph Ph Ph Ph Ph Ph Ph Ph Fe Cl 1 PhMgBr benzene (Cl)FeOPTAP N N N N N N N N Ph Ph Ph Ph Ph Ph Ph Ph Fe 2 (Ph)FeOPTAP Scheme 1Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) 8 E.-Ch. Müller, R. Kraft, G. Etzold, H. Drevs and R. Taube, J. Prakt. Chem., 1978, 320, 49. 9 R. D. Arasasingham, A. L. Balch, R. L. Hart and L. Latos-Grazynski, J. Am. Chem. Soc., 1990, 112, 7566. 10 P. A. Stuzhin, M. Hamdush and U. Ziener, Inorg. Chim. Acta, 1995, 236, 131. 11 P. A. Stuzhin, Koord. Khim., 1995, 21, 125 (Russ. J. Coord. Chem., 1995, 21, 117). 12 P. A. Stuzhin and M. Hamdush, Koord. Khim., 1998, 24, 330 (Russ. J. Coord. Chem., 1998, 24, 309). 13 A. L. Balch and M. W. Renner, Inorg. Chem., 1986, 25, 303. 14 P. J. Chmielewski and L. Latos-Grazynski, Inorg. Chem., 1992, 31, 5231. 15 P. J. Chmielewski, L. Latos-Grazynski and K. Rachlewicz, Magn. Reson. Chem., 1993, 31, 47. Received: Moscow, 28th April 1998 Cambridge, 18th June 1998; Com. 8/03