Porphyrins. 36. Synthesis and optical and electronic properties of...
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Porphyrins. 36. Synthesis and Optical and Electronic Properties of Some Ruthenium and Osmium Octaethylporphyrins Artemis Antipas,2aJohann W. Buchler,zbMartin Gouterman,*2aand Paul D. Smithzb Contribution f r o m the Department of Chemistry, University of Washington, Seattle, Washington 981 95, and the Institut f u r Anorganische Chernie, Technische Hochschule, D-51 Aachen, Federal Republic of Germany. Receioed August 1 , 1977
Abstract: The optical absorption and emission spectra as well as their rationalization in terms of iterative extended Hiickel (IEH) calculations are reported for eight Ru" and 0 s " complexes of octaethylporphyrin (OEP): Ru(OEP)pyz, R u ( 0 E P ) CO(py), Ru(OEP)NO(OMe) (2a-c); Os(OEP)pyl, Os(OEP)CO(py), Os(OEP)NO(OMe), Os(OEP)[P(OMe)3]2, Os(OEP)Nz(THF) (3a-e). (Here py = pyridine and T H F = tetrahydrofuran.) We also report on the OsIv and Osv' complexes Os(OEP)(OMe)z (4) and Os02(OEP) ( 5 ) . Improved syntheses or spectral and analytical characterizations are presented, especially for the complexes 2a-c, 3e, and 5. Comparison is also made to spectra and calculations for Fell porphyrin complexes with bispyridine (la) and carbonylpyridine (Ib). The absorption spectra of the Fell, RuIl, and Os" porphyrins have blue-shifted Q(T,T*) bands, indicating metal d, porphyrin eg(r*) back-bonding. All the species show evidence for extra electronic absorption bands in the visible-near UV region, which are interpreted by the IEH calculations as follows. Forbidden transitions d eg(s*) provide hints of absorption bands for the M" species 2b, 3b, 3d, and 3e. Extra allowed absorption of character a l u ( r ) , a2,,(*) [NO(**) e,(d,)] is apparent in 2c and 3c. I n 4 and 5 the extra allowed absorption bands are of al,(n), aZu(x) e,(d,) character. The extra allowed absorption bands for the bispyridine complexes 2a and 3a are attributed to doubly excited states of form [e,(d,)13 [al,(~),a2,(*)]3[e,(r*)]~. Four species luminesce: Ru(OEP)CO(py) (2b) shows phosphorescence from the ring Tl(n,?r*) level with origin at 653 nm; at 77 K it shows quantum yield @p 0.06 and an exponential decay with lifetime 405 ps. Os(OEP)NO(OMe) (3c) shows a similar emission with origin at 688 nm; at 77 K it has @p 3 X lO-3and a nonexponential decay that can be fit with decay times of 116 and 35 ps. At 77 K, Os(0EP)co)py) (3b) shows an un-
- -
-
+
-
-
-
usual, broad, weak, short-lived emission between 720 and 780 mm with @p 6 X this emission is attributed to a charge transfer triplet T(d,r*) excited state. OsOZ(0EP) ( 5 ) shows emission with origin 729 nm; at 300 K in deoxygenated solution it has @p 5 X
-
Introduction Iron porphyrins are important as prosthetic groups for a variety of hemoproteins. They can bind many small molecules and ions, and in these complexes show a variety of absorption ~ p e c t r a . ~Given - ~ the semiquantitative nature of electronic theory of large molecules, it would be nearly impossible to understand iron complexes alone; and only through the relationship to other metals can a sound understanding be reached. In this context comparisons of otherwise isosteric metalloporphyrins containing group homologues as central metals has revealed important details of the electronic ~ t r u c t u r e . ~ . ~ Table I lists the 12 Fe, Ru, and Os complexes that will be discussed in this paper and the abbreviations to be used for them. Optical absorption and emission data will be given on the ten R u and Os complexes, and iterative extended Huckel (IEH) calculations are reported for all complexes. W e shall compare the calculations on the Fe complexes to absorption spectra reported for iron mesoporphyrin IX dimethyl ester.5 W e shall also report detailed synthetic procedures and analytic characterizations for those species for which characterization has not appeared (2c, 3a) or for which the characterization is much improved (2a,b, 3a, 3e, 5 ) . Experimental Section Materials and Methods. (J.W.B. and P.D.S.) Elemental analyses were performed by Mikroanalytisches Laboratorium A. Bernhardt, D-525 1 Elbach, West Germany. Mass spectral data were taken on a Varian CH5 (70 eV) using a direct insertion probe, temperature ca. 200 OC. All solvents were distilled before use. Benzene and T H F were dried and stored over sodium. The quantitative electronic absorption spectra were taken with spectroscopic quality solvents (Uvasol, Merck). Column chromatography was performed with AI203 (Woelm) or silica gel (Woelm). Preparatory thin layer chromatography was accomplished with silica gel H, type 60, Stahl (Merck), on 20 X 100 cm glass 0002-7863/78/lS00-3015$01 .OO/O
plates (0.5-mm layer thickness). Instead of melting point determination, analytical thin layer chromatography on metal cards of silica gel SI (Riedel de Haen) with CH2C12 or benzene was used as a criterion of purity. R u ~ ( C O )was I ~ purchased from Alpha Inorganics. Carbonyl(octaethylporphinato)pyridineosmium(lI) (3b),8 methoxonitrosonium(octaethylporphinato)osmium(ll) ( 3 ~ ) , oc~ taethylporphinatobis(trimethy1 phosphite)osmium(II) (3d),8 bis(methoxo)(octaethylporphinato)osmium(IV) (4)? dinitrogen(octaethylporphinato)tetrahydrofuranosmium(II) (3e),l I and octaethylporphinatodioxoosmium(V1) (5)'O were prepared from octaethylporphyrin [H,(OEP)] by the literature methods cited. Carbonyl(octaethylporphinato)pyridineruthenium(lI)(2b). Following earlier w0rkers~~.'3 a solution of Hz(0EP) (500 mg, 0.94 mmol) and 1.O g of Ru~(C0)12in 200 mL of benzene was allowed to reflux under nitrogen for 60 h. After the addition of I O mL of pyridine, the solvent was removed by rotary evaporation and the remaining residue was chromatographed on a silica gel column (activity grade I, Woelm) by eluting with CH2C12. After filtration and evaporation, the desired product was crystallized from 40 m L of CHzClz-MeOH-pyridine (49:49:2) giving 66 mg (53%) of Ru(OEP)CO(py) (2b). Anal. Calcd for C ~ ~ H ~ ~ N(740.1 ~ O g/mol): R U C, 68.10; H, 6.62; N , 9.46; 0, 2.16. Found: C, 68.24; H, 6.53; N, 9.54; 0, 2.1 1. Mass spectrum: A = 634 [100%, '02Ru(OEP)+], 317 [42%, R u ( O E P ) ~ + ] ,662 [29%, Ru(OEP)CO+], 331 [ 1 I%, R u ( 0 E P ) C02+]. (Octaethylporphinato)bis(pyridine)ruthenium(ll) (2a). Modifying a procedure of Whitten et aI.,l4 a solution of 100 mg (0.14 mmol) of Ru(OEP)CO(py) (2b) in 70 mL of pyridine was allowed to reflux under Ar for 1 h. After cooling, the solution was irradiated with a 125-W mercury lamp (Pyrex filter) for 20 h, while continually flushing the solution with Ar. The solution was then reduced to a 2-mL volume by boiling off the pyridine. After cooling, 102 mg (95%) of long, reddish-black needles of Ru(0EP)pyz (2a) were recovered by suction filtration and washed several times with cold MeOH. Anal. Calcd for C & ~ ~ N ~ R(791.1 U g/mol): c , 69.78; H, 6.83; N, 10.62; 0 , O . O O . Found: C, 69.94; H, 6.90; N , 10.76; QO.00. Methoxonitrosonium(octaethylporphinato)ruthenium(ll)(2c). A solution of 100 mg (0.14 mmol) of Ru(OEP)CO(py) (2b) in 15 mL
0 1978 American Chemical Society
Journal of the American Chemical Society
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Mass spectrum: A = 724 [loo%, '920s(OEP)+], 362 [90%, 882 [ 12%, Os(OEP)py2+], Os(OEP)'+], 441 [ 19%,O~(OEP)py2~+], 401.5 [6%, Os(OEP)py2+].
Table I. Abbreviation Scheme for the Compounds"
Dinitrogen(octaethylporphinato)tetrahydrofuranosmium(II) (3e).l I
1-5
No.
M
Zb
L
L'
Short formula
la lb 2a 2b 2c 3a 3b 3c 3d 3e
Fe Fe Ru Ru Ru
+2 +2 +2 t 2 +2 $2 +2 +2 $2 +2 +4 +6
py CO py CO NO py CO NO P(OMe)3 Nz OMe 0
PY PY PY PY OMe PY PY OMe P(OMe)3 THF OMe 0
Fe(OEP)pyz Fe(OEP)CO(py) Ru(OEP)py2 Ru(OEP)CO(py) Ru(OEP)NO(OMe) Os(OEP)Pyz Os(OEP)CO(py) Os(OEP)NO(OMe) Os(OEP)[P(OMe)3]2 OS(OEP)N~(THF) Os(OEP)(OMe)z OSO~(OEP)~~
Os
Os Os Os
Os Os Os
4 5
a Abbreviations used: (P)2-, general porphinate dianion; (OEP)*-. octaethylporphyrinate dianion; (Etio-I)*-, etioporphyrinate-I dianion; M, central metal; Me, CH3; py, pyridine; T H F , tetrahydrofuran; 3MP, 3-methylpentane; EPA, diethyl ether-isopentane-ethanol (5:2:2). /I Z: Formal oxidation state of the central metal M. Note: dioxo, not dioxygen.
of CH2Cl2 was flushed with Ar after the addition of I O mL of MeOH, then briefly exposed to N O 9 (2 min), and then allowed to stand for 1 h. After three similar gas exposure cycles, the A1203 thin layer chromatogram showed complete conversion of the starting material. The solution was then flushed with Ar and evaporated to dryness. The residue was chromatographed on a column of A1203(neutral, activity grade 111) by eluting with CH2C12. Crystallization from CH2ClzMeOH (2:l) afforded 48 mg (55%) of Ru(OEP)NO(OMe) (2c). Anal. Calcd for C37H47Nj02Ru (694.1 g/mol): C, 63.97; H, 6.77; N , 10.09; 0 , 4 . 6 1 . Found: C , 63.82; H, 6.69; N , 10.04; 0, 4.69. Mass spectrum: A = 634 [loo%, 102Ru(OEP)+],695 [61%, Ru(OEP)NO(OMe)+], 664 [36%, Ru(OEP)NO+], 332 [ 17%. R u ( O E P ) N 0 2 + ] , 317 [ 12%, Ru(OEP)'+], 347.5 [7%, R u ( 0 E P ) NO(OMe)*+]. (Octaethylporphinato)bis(pyridine)osmium(II)(3a). To a boiling solution of O s 0 2 ( 0 E P ) ( 5 , 60 mg, 0.08 mmol) in 20 m L of T H F contained in a 50-mL beaker under atmospheric conditions 3 drops of hydrazine hydrate (100%) was added. The color of the solution turned from olive green to orange red. At this point, 15 mL of pyridine was added and the volume of the solution was reduced to 5 mL by distilling off the solvent. After cooling, 60 mg (86%) of the desired Os(OEP)py2 (3a) was recovered by suction filtration and washed several times with cold methanol. Anal. Calcd for C46Hj4N60s (880.2 g/mol): C , 62.71; H, 6.13; N, 9.54; 0 , O . O O . Found: C, 62.60; H , 6.54; N , 9.73; 0 , 0 . 2 1 .
Anal. Calcd for C ~ ~ H ~ ~ N ~ O O (841.1 S ( H ~g/mol): O ) C, 57.12; H, 6.47; N , 9.99; 0, 3.80. Found: C, 58.33; H , 6.52; N,9.95; 0, 3.80. Octaethylporphinatodioxoosmium(V1)(5).1° Anal. Calcd for C36H44N4020~(754.2 g/mol): C , 57.27; H , 5.87; N , 7.42; 0, 4.24. Found: C, 58.27; H , 6.34; N , 7.23; 0 , 4 . 2 7 . N M R data are given in Table 11. Measurement of Optical Emission (A.A., M.G., and P.D.S.) Our emission apparatus has been described previousIy.l5 An additional new feature was that the data were fed via an a-d converter into a PDP 8 / e computer, which plotted the uncorrected as well as the corrected spectra on a Calcomp-565. The emission spectra were corrected for the monochromator and photomultiplier tube wavelength sensitivity. Excitation spectra were taken for all emission peaks and all the reported emission peaks belonged to the main absorbing species. Occasional weak emission was observed from species reported as nonemitting, but all such emissions were shown by excitation spectra to belong to impurities. Our solvent of choice for emission studies was 3-methylpentane, which is particularly inert and forms a glass at 77 K. However, because of insolubility, we used EPA (ethyl ether-isopentane-ethanol, 5:5:2) for Os(OEP)(OMe)z; also Os02(0EP) ( 5 ) was insoluble in common glass forming solvents and was studied in acetone. Os(OEP)Nz(THF) was studied in the solution of T H F and hydrazine hydrate in which the compound is generated from 5.Il All ten Ru and Os complexes (Table I) were examined for emission in undegassed solutions at room temperature (300 K) and in liquid nitrogen (77 K). We covered the spectral range between 600 and 850 nm. In no case did we observe emission from undegassed samples at room temperature. Six of the complexes showed no emission at all, and we conclude that any quantum yield is below ca. W e also studied Ru(OEP)CO(py), Os(OEP)NO(OMe), Os(OEP)N2(THF), and O s 0 2 ( 0 E P ) in deoxygenated solutions at room temperature. These solutions were prepared by bubbling argon deep into the solution through the fine capillary ending of a glass dropper for about 15 min. Then the absorption cell (SCC brand) was capped tightly, while bubbling argon close to the surface of the solution. Solutions deoxygenated in this way maintained constant emission over several hours at room temperature. W e observed phosphorescence of R u ( 0 E P ) CO(py) at room temperature in deoxygenated solutions both of 3methylpentane and of EPA: similarly, we sbserved emission of O s 0 2 ( 0 E P ) both in acetone and in benzene; however, similar preparations of Os(OEP)NO(OMe) both in EPA and in acetone and of Os(OEP)N2(THF) in T H F showed no observable emission. Quantum yields for the four complexes that showed emission, 2b, 3b, 3c, and 5, were estimated relative to Zn(Etio-I), whose fluorescence yield is & = 0.04 both at room and low temperature.I5-l7The yield studies of 2b, 3b, and 3c were done vs. Zn(Etio-I), all in EPA at 77 K. The yield of 5 was determined in a degassed solution vs. Zn(Etio-I), both in benzene at room temperature. Yield estimates were based on the following numbers: ( I ) The intensity of the exciting source at the exciting wavelength had been previously determined using a radiometer.'* (2) The optical density (OD) of the standard and the unknown were determined on a Cary 14; dilute solutions with O D in the range 0.1 0-0.16 were used except for one run on 3b, which was studied with O D = 0.46 to enhance its very weak emission. (3) The intensity of emission was estimated by measuring the area of the uncorrected emission spectrum and multiplying by the detector sensitivity at the mean wavelength. Factors ( I ) , (2), and (3) can be
Table 11. IH N M R Data of the Complexes 2a-c and 3ac Solvent No.
Comnlex
2a 2b 2c 3a
Ru(OEP) PY2 Ru(OWCO(py) Ru(OEP)NO(OMe) Os(OEP)pyz
(concn. m p / m l . \
C6D6 C6D6 CDC13 C6D6
(25.0) (25.0) (28.0) (25.0)
t
1.79 1.81 2.01 1.73
Porphyrin protonsa a 3.72 3.81 4.41 3.59
S
Axial ligands*
9.39 9.93 10.22 8.48
2.04 1.20 -2.69 3.10
t, q, triplet and quartet of the ethyl groups; s, singlet of the protons at the methene bridges. Only the upfield multiplet of the pyridine ligand is given since it should be the most sensitive to perturbations of the porphyrin K system. For the nitrosyl compounds, this value represents the singlet arising from the OCH3 group trans to NO. c 6 in parts per million downfield from Me4Si. JEOL JNM-C-60-HL and JNM-PS100.
Gouterman et al.
/ Ruthenium and Osmium Octaethylporphyrins
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Table 111. Iterative Extended Hiickel Parametersa Metal
Ru
Ionization energies, eV
-- ++ - + -- + -+ - + - ++ -- +
-+ - + -- + -+ -- ++
I , = 7.36 d7s d7 (s) d6s2 d6s (s) 7,49 d6sp d6p (s)
I , = 16.76 d6s d6 (s)
d7sp d6sp
d6p djsp
ds
d7p
os
Exponents, au-l
} d7 + (PI ] 4.29 d6s (p)
d7
(d)
d6p
(d)
I , = 8.7 d6s (s) d6p (s)} 9'03
d6s2 d6sp
dSsp
d7
d5p
s: 1.55 (s)
+ (P)
d6
d5s
d6
(p)
} 10.58
p: 1.55
(d) d: 2.80
d6p d5p (d) d6s d5s (d) I P = *?
+ (s)
[
1s-
[
]
[ [
IP' Id-
[ [
1 + (PI
16.19d
s: 1.81
9.76d 20.33d
p: 1.81 d: 3.10
-+
d6sp d6s t (p) 5.82 d7s d6s (d) 8.1
]
+ (d)
Based on energy levels reported in ref 23. Exponents used for iron: 1.38 (s); 1.38 (p); 3.06 (d). Another extrapolation method gave 9.38 for this value; complexes 2a-c were run with this value too with much the same results. Another set of values [ 17.26 (s), 12.1 1 (p), 19.4 (d)] was extrapolated by another method, but gave similar results in several tests. combined to determine quantum yield in the expected rnanner.l5 For 2b and 3c, our precision on several quantum yield determinations was within f 15%; however, the crudeness of our method suggests that the reported yield values should be considered valid only within f30%. For 3b and 5 we had larger precision errors, and these yields should be considered valid only within f 5 0 % . The apparatus for the determination of lifetimes has also been described previously.'5 The lifetime of the strobotac flash sets a lower limit to the lifetime we can measure as 1 6 ~ s . Iterative Extended Hiickel (IEH) Method (A.A. and M.G.). The iterative extended Hiickel method and the program used have been previously reported along with parameters for H , C, N , 0, and P.19-21 The ionization potentials used for iron were also given earlier.I9 However, the basis set exponentials for the metals (Table 111) were obtained by the method of Cusachs et The exponentials for s and p orbitals were taken to be [(n % ) / ( r ) ] and f o r d orbitals [(n '/2)(n l ) / ( r 2 ) ] i /where 2 n is the principal quantum number and ( r ) , ( r ) 2are atomic values obtained from S C F calculations.22 Although these exponents are slightly different from those used in earlier work,19 comparison runs on Fe, Co, and Ni gave no significant differences. The ionization energies for Ru and Os (Table 111) were calculated in the same manner as before,I9 based on the spectroscopic tables of Moore.23 (For details, see McGlynn et al.24) The geometry of the planar porphine ring was the same as that used p r e v i o ~ s l yexcept , ~ ~ for displacement of the N atoms in accord with metal-nitrogen bond distance estimates. Metals were placed in the porphine ring plane. Crystal structures of Fe and Ru porphyrins have been studied.25,26The Os to ring nitrogen distance was taken the same as for Ru, since they both have the same covalent radii.27 Metal to ligand bond lengths and angles involving the fifth and sixth ligands have been approximated from structure studies of similar compounds having the same oxidation state. These various bond lengths and angles are listed in Table IV. The orientation of the porphyrin molecules with respect to coordinate axes was such that the center of the coordinate system coincided with the center of the porphyrin plane and the nitrogens of the ring were on the x, y axes. The orientation of the ligands was chosen so as to maximize the number of symmetry planes for economy in computation time. Pyridine and TH F were taken to be planar rings in the s z plane, keeping the bond distances and angles as close as possible to x-ray values. For the methoxy groups, the M - 0 - C (M = metal) bond angle was taken as 120" with the three atoms located in the xz plane; the hydrogens were in tetrahedral positions around the 0 - C bond; one of the hydrogens was in the xz plane, thus preserving the xz symmetry plane: the hydrogen in the xz plane was located distal from the porphyrin ring. For Os(P)[P(OMe)3]2 the three oxygen atoms were in tetrahedral positions; one O C bond was located in the xz plane; the other two O C bonds were parallel to the porphyrin plane; the methyl groups were tetrahedral and placed so as to avoid close approaches; the entire molecule had two planes of symmetry. It has
+
+
+
Table IV. Key Bond Lengths and Anglesb Metal Length,
A
Ligand Length,
A
(angle)
2.004 Fe-N, 1.95 Fe-N,, 1.75 (linear) Fe-CO 2.049 Ru-NPa 2.10 RU-N~~' 1.77 (linear) Ru-CO' Ru-NOQ 1.78-1.80 (linear) (1200) 2.00 Ru-OMea 2.41 (tetraOs- P( 0Me) 3 hedral) 1.80 os-0 2.00 (linear) 0s-N~ 2.00 Os-WTHF) 1.97 OS-F
C-0 N-0 0-CH3 CH N-N THF
py
1.14-1.16 1.13 1.42-1.44 1.09 1.16 C-C 1.56, 1.49 (2) C - 0 1.42 C-H 1.08 LCOC 1 IO0 LCCC looo C-C 1.40 C-H 1.08 C-N 1.34
Same for Os. N,, porphyrin; Npb.pyridine; T H F , tetrahydrofuran. been shown by various IEH calculations done a t the University of Washington that rotation of the ligands with respect to the porphyrin plane does not affect the energy levels greatly, nor do the small variations in bond length shown in Table IV.
Results and Discussion Constitution of the Compounds. The constitution of most of the compounds under investigation has been corroborated elsewhere.*-[ Additional evidence from elemental analysis, mass spectra, and N M R was reported above. Further support comes from parallel 1R data between homologous Fe, Ru, and Os porphyrins. Thus the IR spectrum of the new RuI1 nitrosonium methoxide, 2c, shows the following bands characteristic for the axial ligands: 2775, 1055 ( U C H , vco of the methoxide ligand), 1780 ( U N O of the nitrosonium ion), and 491 cm-l (UR,,O of the methoxide ligand). The corresponding values of the 0sI1 analogue, 3c, appear at 2780, 1065, 1745, and 497 cm-l ,9 the lower NO-stretching frequency indicating stronger back-bonding in'this compound as compared with 2c. Special care has been devoted to the identification of the bis(pyridine) complexes, 2a and 3a, because of the difficulties encountered in the interpretation of the IEH calculations discussed below. In addition to support from a crystal structure,28 we prepared a large variety of bis(nitrogen base) complexes Os(OEP)L2, where L. = y-picoline, MeCN, NMe3,
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Journal of the American Chemical Society
/
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/ May 10, 1978
NHMe2, NHZMe, or "3. The spectral and electrochemical data on these complexes fully correspond to the electron donor-acceptor balance expected for these ligands.29 The typical IR vibrations for coordinated pyridine are found in 2a a t 1580, 1448, and 1268 cm-I and in 3a at 1590, 1440, and 1270 cm-I. Especially noteworthy are the large upfield shifts of the mesoprotons of the porphyrin ring in the ' H N M R I spectra of 2a and 3a (Table 11); they indicate a high charge !I (d,d) density on the porphyrin ring which is also evidenced by the I IEH calculations (see below). Review of Porphyrin Electronic Spectra. Before presenting the particular results on the absorption and emission spectra of Ru and Os complexes, it is useful to summarize the general classification scheme recently developed by two of the authors for porphyrin ~ p e c t r a ,because ~ . ~ the Ru and Os spectra provide variations on the categories previously described. Optical spectra of porphyrins fall into three absorption types Porphyrin Metal (normal, hypso, and hyper);diamagnetic complexes have three Figure 1. Schematic illustration of important orbitals for the spectra of emission types fluorescent, phosphorescent, and radiationd6 six-coordinate porphyrins: ( 1 ) A, the ligand field gap determining (d,d) less). transitions; (2) charge transfer transitions, (d,r*); ( 3 ) the back-bonding Regular porphyrins are found for metals from groups 1 to parameter, A, determining hypsochromic effect and spin-orbit coupling. 5 in valence I to V, respectively. They have normal absorption; i.e., in the region X > 320 nm they show only bands N(R,T*), B(R,R*), and Q(R,R*). The Q(0,O) (or a ) band occurs a t X > 570 nm30 for normal complexes M(0EP)LL'. These comMoV, and Wv, that have vacancies in the e,(d,) orbitals and plexes are fluorescent, Le., they show fluorescence yields & have low metal redox potentials; in these cases the extra bands > as modified by the heavy atom e f f e ~ tRecent .~ studies are of al,(n),a2,(7r) e,(d,) character (i,e., ring metal report regular complexes with metals from groups 4A,31 charge t r a n ~ f e r ) . ~ 5A,'8,21,32 4B,I5 and 5B.15 The Q(a,x*) and B(R,R*) abOptical Absorption Studies. Table V reports peak optical sorption as well as the fluorescence and phosphorescence are absorption data taken in Aachen including log t ( t the molar qualitatively interpreted in terms of the "four orbital" extinction coefficient). The spectra shown in Figures 2-6 were and the spectra are more quantitatively described by R electron taken in Seattle, Wash., using the solvents in which the emisth e ~ r y . ~ ~ . ~ ~ sions were studied. Hypso porphyrin spectra are like normal spectra but the Ru(OEP)CO(py) (2b) would seem to show a typical h y p o Q(T,R*) bands are blue shifted to X < 570 nm30 for complexes absorption spectrum, showing blue-shifted Q bands and a very M(OEP)LL'.6,7 These spectra are usually found with transiintense, sharp B (Soret) band (Figure 2). [The weak band with tion metals with configurations d6 to d9 having e,(d,) filled. X 595 nm (Figure 2) has been shown to belong to an impurity Such complexes are either phosphorescent or radiationless. by phosphorescence excitation spectra.] However, the promPhosphorescent complexes show very little fluorescence (4,inent tail to the red of the Soret band, verified by phospho< but clear phosphorescence; examples are Pd", Pt11,36 rescence excitation spectra, shows evidence of other than and Rh111.37 Radiationless complexes have emission quantum ( T , T * ) transitions in the visible region. W e therefore classify yields below examples are Co and Ni complexes36and this compound as hypso/hyper. Note also that the spacing iron between Q ( 1,O) and Q(0,O) is 1090 cm-I, substantantially smaller than the customary value of -1250 cm-I. The abThe optical spectra of hypso complexes can be rationalized sorption spectrum of Os(OEP)CO(py) (3b), also shown in qualitatively as shown in Figure 1 for d6. The main factors a t Figure 2, is quite similar to that of 2b; however, the Q bands play are (1) the ligand field splitting A between the filled orare more blue shifted and are anomalously broadened. This bitals (dx,)2(d,)4 and the empty orbitals dZ2,d,+2; (2) the broadening is evidence for weak underlying bands. Thus 3b is energy for charge transfer (CT) transitions from metal to ring; also classified as hypsolhyper. and (3) the mixing of filled e,(d,) and empty eg(r*) orbitals The absorption spectrum of Os(OEP)NO(OMe) (3c), (back-bonding), indicated by X in Figure 1. (1) When the gap shown in Figure 3, would also seem to be typically hypso. A is small, as with first-row transition metals, low-lying (d,d) However, the Soret band is anomalously broadened, and the transitions may intervene between the lowest (x,R*)level and the ground state causing the complexes to be r a d i a t i o r ~ l e s s . ~ ~ratio ~ ~ ~ tmax(B)/tmax(Q)is lower than that of either 26 or 3b shown in Figure 2. There is a somewhat more prominent ab(2) Charge transfer transitions e,(d,) eg(r*) can also be sorption band a t X 345 nm than is shown by 2b and 3b. Thus expected to provide low-energy transitions that can cause the we characterize this spectrum as hypsolhyper. The spectrum compounds to be radiationless. (3) Finally the mixing of es(r*) of Ru(OEP)NO(OMe) (2c) is more clearly hyper, having a and e,(d,) orbitals (i.e., back-bonding) indicated by X in Figure pronounced shoulder to the red of the Soret band and a tail to 1 has two effects: (a) the levels eg(**) are pushed to higher the red of Q(0,O). Since Q(0,O) is blue shifted, it too is energy giving rise to the hypsochromic effect; and (b) the pahypso/hyper. rameter A produces a strong spin-orbit coupling that decreases In Figure 4, the two bispyridine complexes, 2a and 3a, give triplet lifetime. very clear examples of hypsolhyper spectra. The Q bands are Hyper porphyrin spectra, in the region > 320 nm, show other intense absorption ( e >lo00 M-' cm-I) in addition to very prominent as well as very blue shifted. The ratio N ( R , T * ) , B(T,R*), and Q ( R , R * )bands. Two types of hyper tmax(B)/tmax(Q) is anomalously low compared to normal spectra are fairly well u n d e r ~ t o o d :p-type ~ ? ~ hyper spectra are metalloporphyrins, and there are several prominent absorption bands between the Soret and Q bands. Moreover, Ru(OEP)py2 found in Sn", Pb", P1ll,As11',SbII', and Bill1porphyrins, where shows a tail to the red of Q(0,O) and Os(0EP)pyz shows a clear the extra bands are of a2u(npz) eg(r*) character (Le., metal peak at X -597 nm. ring charge t r a n ~ f e r ) ; ' ~ , * d-type ~ , ~ ~ , hyper ~' spectra are found with transition metal complexes, e.g., Fe"', Mn"', Cr"', Figure 5 gives the spectrum of two other Os" species:
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Table V. Electronic Absorption Maxima (nm) with Extinction Coefficients (log
t)O
of the Complexes 2a-c, 3a-e, 4, and 5
IB(O.0) I
P
Other
Other
lQ(1S))l
a lQ(0,O)I
395 (5.01) 389 (5.04) 396 (5.37) 394 (5.48) 392 (5.08) 419 (4.96) 406 (5.25) 393 (5.18) 370 (5.09) 378 (5.09)
450 (4.20) 410 (4.53)
495 (4.17) 482 (4.36) 518 (4.20) 510 (4.1 I ) 539 (4.08) 533 (4.23) 500 (4.10) 498 (4.15) 497 (3.97) 470' (4.18)
521 (4.58) 510 (4.71) 549 (4.39) 540 (4.31) 572 (4.12) 568 (4.44) 522 (4.21) 523 (4.30) 530 (3.90) 57ge (3.95)
Soret
No.
Complex
Solvent
2a
Ru(OEVpy2
C6H6
b
3a
Os(OWpy2
GHsN
C
2b
Ru(OEP)CO(py)
CHzClz
3b
Os(OEP)CO(py)
CHzClz
2c
Ru ( 0EP) NO( OMe)
CH2Clz
3c
Os(OEP)NO(OMe)
3d
Os(OEP) [P(OMe)312
CHK12/ CH30H CH2Cl2
3e
OS(OEP)N~(THF)~
THF
4
Os(OEP)(OMe)?
5
Os02(0EP)
CH2Cl2/ CH30H CH2C12
350 (4.32) 345 (4.48) 342 (4.56) 348 (4.49)
428 (4.26)
Recorded a t room temperature (Unicam S P 800B). Weak near-IR bands observed a t -645 sh, -715 sh nm. Weak near-IR bands observed (in C6H6) at 648 sh, 723 sh, 850 broad, 980 broad nm. See Figure 4. Values measured indirectly by reaction of hydrazine hydrate with 5 in the spectroscopic solution; absorption intensity values of the product were recorded when the bands of the starting material had disappeared. Because of charge transfer transitions, these peaks are not assigned as a and P bands. See text.
hS$Eli'>G:+ ( n m '
Figure 2. Absorption spectra of Ru(OEP)CO(py) (2b) and Os(0EP)CO(py) (3b) a t room temperature in 3-methylpentane. Possible charge transfer bands (d,r*) identified as the tail absorption -440 nm in 2b and underlying the Q(T,T*) bands -540 nm in 3b, causing their broadness.
Figure 3. Absorption spectra of Ru(OEP)NO(OMe) (2c) and Os(0EP)NO(0Me) (3c) at room temperature in 3-methylpentane. Possible charge transfer bands, a l U ( r ) ,a z u ( r ) [NO(**) + e,(d,)] identified as the shoulder -410 nm in 2c and the band -330 nm in 3c.
O s ( O E P ) [ P ( O M e ) 3 ] 2 and O s ( O E P ) N 2 ( T H F ) . Both a r e basically h y p o . T h e Soret bands are sharp, and the ratio of Soret to visible absorbance m a x i m a is relatively normal. However, the Q bands a r e quite broadened and have m a r k e d tails to the red, suggesting possible extra underlying forbidden transitions. T h u s , all t h e R u l ' and 0 s " spectra a r e classified a s hypsql
a broad red band a t X -61 0 nm. T h e spectrum of O s O ? ( O E P ) follows t h a t typical of d-type hyper complexes with three distinct band systems a t -370, -450, and -580 n m . All three bands a r e broad but structured. Both 4 and 5 have holes in the e,(d,) shell, so t h e d-type hyper spectra a r e not unexpected. As to the relations a m o n g these spectra, we might note that X(Q) decreases along t h e series M ( O E P ) N O ( O M e ) > M ( O E P ) C O ( p y ) > M ( 0 E P ) p y z for both M = Ru and Os. For M ( O E P ) L L ' , with L and L' fixed, X(Q) decreases along the series F e > Ru > Os. However, X(B) show no similar systematic shifts. Optical Emission Studies. T h e emission spectra of four
hyper. Figure 6 shows t h e absorption of t h e OsIv a n d Osv1complexes 4 and 5. Both a r e clearly hyper. T h e S u e t bands of both compounds, though quite intense with respect to t h e visible bands, a r e anomalously broad. T h e Q bands for Os(0EP)( 0 M e ) z a r e anomalous in appearance, and the compound has
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I
350
400
450
5W
550
600
CAVELENGTh Inml
Figure 4. Absorption spectra of Ru(0EP)pyz (2a) and Os(OEP)py2 (3a) at room temperature in 3-methylpentane. The many extra bands are attributed to doubly excited states [es(d,)]3[al,02,]3[e~(~*)]2. The near-IR absorption [inset for Os(OEP)pyz] should be multiplied by 0.038 to compare to visible-UV spectrum; arrows show peaks (Table V, footnote c ) , attributed to charge transfer (d,.rr*) excited states.
Figure 5. Absorption spectra of Os(OEP)[P(OMe)3]2 (3d) and Os(OEP)N2(THF) (3e) at room temperature in 3-methylpentane and tetrahydrofuran, respectively. The broadness of the Q(T,T*)bands is attributed to underlying charge transfer (d,r*) transitions.
complexes are shown in Figure 7. In Table V I we have given the principal emission peaks, the quantum yield estimates, and the measured lifetimes. Two compounds, Ru(OEP)CO(py) and O s ( 0 E P ) NO(OMe), show phosphorescence hands with sharp origins, a t 653 and 688 nm, respectively, followed by several substantially weaker vibronic bands. These phosphorescence spectra
O’
350
400
450
500
550
600
WAVELENGTH ( n m l
Figure 6. Absorption spectra of Os(OEP)(OMe)z (4) and OsOz(0EP) (5) at room temperature in EPA and acetone, respectively. The extra bands are attributed to charge transfer (r,d,) transitions.
Figure 7. Luminescence spectra of Ru(OEP)CO(py) (Zb), Os(0EP)CO(py) (3b), and Os(OEP)NO(OMe) (3c) in 3-methylpentane at 7 7 K; luminescence spectrum of OsOl(0EP) ( 5 ) in degassed acetone solution at room temperature. All spectra were corrected for the variation of detector sensitivity with wavelength. Dashed regions indicate uncertainty due to excessive noise; note the nonzero baseline of 3b. The emissions of 2b and 3c are from ring T I( ~ , r * excited ) states. The emission of 3b is attributed to a T(d,r*) excited state and that of 5 to an excited state with substantial T(T,d,) character.
are rather like those shown by etioporphyrin complexes of Pd”, Pt11,36and Rh1” 37 and can be identified as emission from the T ~ ( T , T * )excited state. The emission decay of R u ( 0 E P ) CO(py) is exponential at 77 K with a lifetime of 405 ps. This is comparable to hut shorter than the decay times observed for etioporphyrin complexes of Pd1I (1930 ps)36and Rhl” (730 p.~).~ The ’ emission of Os(OEP)NO(OMe) at 77 K shows a nonexponential decay, that could be fit as a sum of two expo-
Gouterman et al.
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302 1
Table VI. Emission Maxima, Relative Quantum Yields, and Lifetimes No.
Cornpd
2b 3b 3c
Ru(OEP)CO(py) Os(OEP)CO(py) Os(OEP)NO(OMe) OSO~(OEP)
5 a
Solventa 3MP 3MP 3MP Acetone
See footnotes to Table I for abbreviations.
Quantum yield'
Phosphorescence peaks, nm 653b -720 68gb 729b
661 -782 718 781
681
704
746
769
714
725
6 6 3 5
X IOe2 X X X
Lifetime,
Temp,
KS
K
405
