Organometallics 1983,2, 551-554
sulfide) (PPS), Le., poly@-phenylene selenide)" (PPSe), is readily prepared from either p-dichloro- (4) or p-dibromobenzene (5) and either sodium or potassium selenide in either DMF or N-methylpyrrolidinone (NMF'). Our best results are observed on reaction of 5 with NazSe in DMF at 120-140 "C for 20 h, where we isolate PPSe free of low molecular weight contaminants in 80% yield as a light yellow powder, mp 220 "C. While both 4 and 5 react with NazTe in NMP or DMF to give materials that are at least oligomeric,18our best approach to poly@-phenylene telluride) (PPTe) was obtained via p-diiodobenzene and NazTe in DMF at 110-120 "C to give a partially crystallinelg tan solid, mp 162-170 "C, in 70% yield free of low molecular weight contaminants. The infrared spectra of PPSe and PPTe as prepared herein are superimposable on that of PPS between 4000 and 600 cm-l, while bands at 550 and 475 cm-' in PPS are observed at 500 and 475 cm-' in PPSe and 489 and 465 cm-' in PPTe. The solidstate absorption spectra of PPSe and PPTe exhibit maxima at 300 and 310 nm, respectively, with long tails into the visible. At 140-150 "C, 5 reacts with NazTezin DMF to give in 10% yields bis(pbromopheny1) ditelluride and black amorphous polymer, mp 230-250 "C dec, whose solid-state absorption spectrum shows a maximum at 310 nm tailing into the visible. Although we have not as yet made a detailed mechanistic study of the experiments reported herein, our observation of products derived from reduction of halogen to hydrogen in reactions of 1,5 9-bromoanthracene, and 2-bromonaphthalene (6) suggest involvement of electrontransfer processes. In fact, using electron-transfer initiation with sodium naphthalenide (1.0 M in THF), we have been able to isolate 3 in yields up to 22% from either 6 or 2-chloronaphthalene and Na2Te2in HMPA at temperatures as low as 25 "C. The order of reactivity of C$I& with Na2Teznoted above, the greater reactivity of 4 vs. 5 in reactions with Na2Se,and the depression of PPSe yield from 80% noted above to 15% by addition of benzophenone21 equimolar to 5 in the reaction mixture are consistent with a mechanistic pattern of the SRN121 type. In addition to entry 4 in Table I, another anomalous reaction in molecular compounds has been noted. In HMPA at 170 "C, NazTe2reads with 6 to give an isolated 9% yield of 2 as the only organotellurium product. Fragmentation of an intermediate anion radicaln may be involved in these experiments. Summarizing, we have used new alkali chalcogenide reagents to prepare both new and previously known selenium and tellurium materials. In some cases, it is apparent that the routes described herein are the methods of choice for laboratory synthesis. We expect that further development of this chemistry will result in additional new materials with interesting chemical, physical, and structural properties. (17) The structural and electrical properties of PPSe are separately detailed: Sandman, D. J.; Rubner, M., Samuelson, L. J. Chem. SOC., Chem. Commun. 1982, 1133-1134. (18) Isolated molecular products of reaction 3 at 180-190 OC in NMP include 4,4-dichlorobiphenyland bis(p-chlorophenyl) ditelluride in combined yield of ca.25%, while bis(p-bromophenyl)ditelluride was isolated in 4% yield from reaction of 4 in DMF at 130-140 OC. (19) X-ray diffraction of PPTe reveals the preecence of small amounts of elemental tellurium, also observed in the other organotellurium pol mers we have isolated, and reflections at d = 5.09,4.27,3.57, and 3.04 These reflections indicate that PPTe is not cryatallogra hically similar to PPSe, which was found to be isomorphous to PPSP? PPTe has a flotation density of 2.46 g/cml. (20) Scamehorn, R. G.; Bunnett, J. F. J. Org. Chem. 1977, 42, 1449-1457. (21) Bunnett, J. F. Acc. Chem. Res. 1978, 11, 413-420. (22) Rossi, R. A. Acc. Chem. Res. 1982, 15, 164-170.
f
551
Acknowledgment. We thank L. Samuelson and S. Meyler for technical assistance, M. Downey and J. Mullins for providing X-ray powder diffraction data, Dr. D. Dugger and V. Mastricola for providing mass spectra, and F. Kochanek for providing Fourier transform IR spectra. Registry No. 2,63212-75-9; 3, 1666-12-2;4,106-46-7;5, 10637-6; 5-NazSepolymer, 84170-68-3; 5-NazTezpolymer, 84174-16-3; 6,580-13-2; NazTez, 11089-53-5;NazTe, 12034-41-2;KzSe, 131274-9; PPSe, 52410-66-9;PPTe, 84174-18-5;p-diiodobenzene disodium telluride polymer, 84174-17-4; poly@-phenylene ditelluride), 84174-19-6;9-bromoanthracene, 1564-64-3;2-chloronaphthalene, 91-58-7; iodobenzene, 591-50-4; di-9-anthracenyl ditelluride, 84174-14-1;diphenyl telluride, 1202-36-4;di-2-naphthyl selenide, 84174-15-2; p-diiodobenzene, 624-38-4; bis@-bromophenyl) ditelluride, 28192-35-0;4,4-dichlorobiphenyl,2050-68-2; bis(p-chlorophenyl) ditelluride, 36062-86-9.
Polypyrldyl Hydrldo Complexes of Osmium( I I ) and Ruthenium( I I ) Jonathan V. Caspar,' B. Patrlck Sulllvan,' and Thomas J. Meyer Department of Chemistry, University of North Carolina Chapel Hill, North Carolina 27514 Received July 26, 1982
Summary: A series of polypyridyl hydrido complexes of Os(1I) and Ru(I1) has been prepared, e.g., cis-[M(bpy),(CO)HI2+(bpy is 2,2'-bipyridine; M = Ru, Os)and [Os(phen)(1,2-(Ph2P),C8H,)(PPh3)H]*+ (phen is 1 , l O phenanthroline), utilizing three different synthetic routes. The complexes have been characterized by NMR ('H and 31P)and by infrared spectroscopy. Initial resutts are reported on these photochemical and photophysical properties. The complexes of Os(I1) represent rare examples of luminescent metal hydride complexes in fluid solution at room temperature.
In recent work we have reported on the photophysical properties of two series of polypyridyl complexes of Os(II)-(phen)Os1*L42+ and (bpy)O~"L,~+(phen is 1,lOphenanthroline; bpy is 2,2'-bipyridine; L is py, 0.5bpy, 0.5phen, MeCN, PR3, AsR3, CO).' The complexes are strong visible light absorbers, and their excited state properties are of note because of the following. (1)They are dictated by metal to ligand charge-transfer (MLCT) excited states, e.g., (bpy-.)Os111L,2+*,which are largely triplet in character.2 (2) Emission energies and excitedstate redox potentials can be varied systematically with changes in L. (3) Variations in radiative (k,)and nonradiative (k,) rate constants, which determine excited-state lifetimes ( T = ~ (k,+ kJ1) and emission quantum yields (4, = k,(k, + km)-'), can be accounted for quantitatively on the basis of existing t h e ~ r i e s . (4) ~ The excited states undergo facile oxidation or reduction and have provided the basis for an excited-state photoelectrochemical cell for the production of H20z and Br2.4 The excited-state (1) Kober, E.M.; Sullivan, B. P.; Dressick, W. J.; Caspar, J. V. J.Am. Chem. SOC.1980,102,7383. (2) Kober, E.M.; Meyer, T. J. Znorg. Chem. 1982, 21, 3967 and references therein. (3) Caspar, J. V.; Kober, E. M.; Sullivan, B. P.; Meyer, T. J. J. Am. Chem. SOC.1982,104,630. Caspar, J. V.; Meyer, T. J. J. Phys. Chem., in press. Caspar, J. V., Ph.D. Thesis, University of North Carolina, 1982.
0276-7333/83/2302-0551$01.50 f 0 0 1983 American Chemical Society
552 Organometallics, Vol. 2, No. 4, 1983
Communications
Table I. Spectroscopic and Excited-State Data for Metal Hydride and Related Complexes EP(MInI complex
U C - , , ~ cm-'
U H , cm-' ~
[ Os(Phen)(l,2-(Ph,P),C,H4)(PPh,)Hl(PF, 1
2075 ( w )
[ Os(phen)(cis-Ph,PCH= CHPPh,)(PEt,)H](PF,)
g
cis-[Os(phen),(CO)H](PF,) cis-[Os(bpy)z(CO)Hl(PF,) cis-[Ru(bPY ),(CO)H I(pF,) cis-[Os(bpy),(CO)Cl](PF,)
1913 (s) 1 9 1 1 (s) 1941 (br) 1965 ( s )
cis-[Ru(bpy),(CO)Cl ](PF,) t r a m - [ OS(bpy)( PPh 3 ) 2 ( CO )H I( PF, )
1984 (s) 1 9 3 1 (s)
2006 (m) 2005 ( m ) g
2060 ( w )
'H NMR
6
-14.6 (d o f t ) -1 5.5 (d o f t ) -11.5 (s) -11.4 (s) -11.3 ( s )
-12.2 ( t )
E,,,d cm-'
k,,e
0.83
14300
>1 x 1 0 8
0.74
13700
4.8 x 10'
0.90 0.88 1.14
13700 1 3 500
5.1 x 10, 2.4 x l o 7
g
1.18f
1 4 660
1.50f
g 16580
v
~ 1 1 1 , ~
1.54
s-'
1.09 X l o 7 (2.3 x
a In CH,Cl, solution. Taken in (CD,),CO solution for the hydride resonance with Me4Si as internal standard. s stands for singlet; t stands for triplet; for the first t w o entries in the column, t h e resonance is a doublet of triplets. Peak potential values f o r the irreversible oxidation of M(I1) t o M(II1) in CH,CN solution with 0.1 M [NEt,](ClO,) as supporting electroIn acetolyte vs. the saturated calomel electrode (SCE) using a Pt bead working electrode. The scan rate was 200 mV/s. nitrile solution; corrected for phototube response. e In acetonitrile from lifetime measurements using laser flash photolysis. ,TI,, values for the M(III)/(M(II) couples which are reversible o n the cyclic voltammetry timescale, scan rate = 200 mV/s. g Not observed. h , for the 1,lO-phenanthroline analogue cis-[Os(phen),(CO)Cl](PF,).
properties of related polypyridyl complexes of Ru(I1) are similar but are complicated by the presence of low-lying dd states which can provide an efficient pathway for excited-state decay or even can lead to photochemical decomposition by loss of ligand^.^ We are attempting to develop more sophisticated photochemical systems in which complex photochemical pathways, e.g., multiple-electron-transfer reactions, are induced by initial excitation of polypyridyl-Mn (M = Ru, Os) MLCT chromophores. Of considerable interest to us in this context are the photochemical and photophysical properties of metal hydride complexes, in part because of their possible use as photocatalysts.6 We describe here the preparation of a series of polypyridyl hydrido complexes of Ru(I1) and Os(I1) and some initial observations concerning their photochemical and photophysical properties. Three basic synthetic strategies were used to obtain the hydrido complexes; the first, which is a well-known procedure, involves the reaction between a carbonyl halide precursor in alcoholic base with either PPh3 or 2,6-lutidine as base and ethylene glycol as the alcohol. For example, the reaction shown in eq 1gives the related carbonyl hydride complex in -50% yield. In some cases the use of ~is-[Os(bpy)~(CO)Cl]+ + excess PPh,
HOCHZCHgOH
A reflux
cis-[Os(bpy)2(CO)H]+(1) PPh3 resulted in carbonyl displacement (e.g., eq 2, where dppb is bis(l,2-diphenylphosphino)benzene). A poten[Os(phen)(dppb)(CO)Cl]++ excess PPh3
HOCH,CH,OH
A reflux
[Os(phen)(dppb)(PPh3)Hl+ (2) tially general route to metal hydride complexes, although one that has yet to be exploited extensively for chemical synthesis, is the thermolysis of monodentate formate complexes. The complexes ~is-[M(bpy)~(C0)(O~CH)] (PF,) (4)Neyhart, G . A.; Marshall, J. A.; Dressick, W. J.; Sullivan, B. P.; Watkins, P. A.; Meyer, T. J. J. Chem. Soc., Chem. Commun.1982,915. (5) (a) van Houten, J.; Watts, R. J. Znorg. Chem. 1978,17, 3381. (b) Durham, B.;Caspar, J. V.; Nagle, J. K.; Meyer, T. J. J. Am. Chem. SOC. 1982, 104, 4803. (6) (a) Cole-Hamilton, D. J. J. Chem. Soc., Chem. Commun. 1980, 1213. (b) Chou, M.; Creutz, C.; Mahajon, D.; Sutin, N.; Zipp, A. P. Znorg. Chem. 1982,21, 3989.
(M = Ru, Os) can be heated either in 2-methoxyethanol or ethylene glycol or in the solid state to give the corresponding hydrido carbonyls (eq 3).'r8 Reaction 3 proceeds HOCH2CH20CH3
c~s-[Ru(~~~)~(CO)(OC(=O)H)]+ A
.w
to give 45% isolated yield after purification. A third route that gives exclusively monobipyridyl or phenanthroline complexes involves ligand substitution by the added polypyridine as shown in eq 4. The reaction of eq 4 proceeds in 85% yield as written and appears to be general for many different chelating polypyridyl ligands.
+
mer-0~(PPh,)~(Co)(Cl)Hbpy
HOCHzCH20H ~
10 min
trans-[O~(bpy)(PPh,)~(CO)H]+ + C1- + PPh3 (4) The complexes were purified as hexafluorophosphate salts by chromatography on alumina using toluene-acetonitrile mixtures as eluant in a manner that has been described previo~sly.~J~ The complexes are all water- and air-stable crystalline solids that are extensively soluble in polar solvents like CH2C12,acetone, and CH3CN. Characterization of the complexes was achieved by elemental analysis, 'H NMR spectroscopy, infrared spectroscopy, cyclic voltammetry, and, where appropriate, 31PNMR spectroscopy. Table I shows typical characterization data for the products. As shown in the table the M-H stretch occurs between 2000 and 2100 cm-' for all the osmium complexes and is medium to weak in intensity compared to the carbonyl stretch that occurs below 2000 cm-' in all cases. It is interesting to note that for the complexes cis-[M(b~y)~(CO)X]+ (M = Ru, Os; X = H, C1) lower energy CO stretches occur for the hydrido complexes (Table I) apparently because of enhanced electron density at the metal center relative to C1- as the cis ligand. The structures of the hydride complexes are readily assignable by use of NMR spectroscopy. For example, for (7)See, for example: Darensbourg, D. J.; Rokicki, A.; Darensbourg, M. Y. J.Am. Chem. SOC.1981, 103, 3223. (8)After this paper was submitted, a report appeared concerning the synthesis of cis-Ru(bpy)2(CO)H+. See: Kelley, J. M.; Vos, J. G. Angew. Chem., Int. Ed. Engl. 1982, 21, 628. (9) Sullivan, B. P.; Salmon, D. J.; Meyer, T. J. Inorg. Chem. 1978,17, 3334. (10)Connor, J. A.;Meyer, T. J.; Sullivan, B. P. Inorg. Chem. 1979, 18, 1388.
Organometallics, Vol. 2, No. 4, 1983 553
Communications
A
50
40
Figure 1.
30
20
'0
0
(A) 31P(1HJNMR spectrum of [Os(phen)(l,2-
(PhzP)2C6H,)(PPh3)H](PF6) in CH&N (see text). (B) 'H NMR spectrum of [O~(phen)(1,2-(Php)~C&&PPh3)H](PF,J in acetone in the hydride region. The apparent quartet is a doublet of triplets
that is more easily seen for the analogous salt [Os(phen)(cisPhzPCH=CHPPh2)(PPh3)H](PF6) in Figure 1C. (C) 'H NMR (PFB)in spectrum of [Os(phen)(cis-PhzPCH=CHPPhz)(PPh3)H] acetone solution.
the complexes [O~(phen)~(CO)Hl+, [Os(bpy)&O)H]+, and [R~(bpy)~(C0)H]+ the lack of symmetry in the 'H NMR spectra for the polypyridyl ligand is consistent with the cis geometry. For tr~ns-[Os(bpy)(PPh~)~(CO)H]+ (where the PPh3 groups are trans) the 'H NMR spectrum also shows no symmetry, that is, four doublets and four triplets in first order. The hydride resonance is a triplet centered at -12.2 ppm (Me,Si internal standard in 6 units)with Jp-H = 20.8 Hz. The 31P(1H)NMR spectrum exhibits a single resonance at +19.4 ppm (85% H3P01as external standard, CHBCN solution) that is consistent with magnetically equivalent phosphorus nuclei. Of the three possible isomers for [Os(phen)(l,2(Ph2P)&H4)(PPh3)(CO)H]+the structure shown below is suggested on the basis of the following: (1) T i e lack
of magnetic symmetry for the phen ligand by 'H NMR spectroscopy; (2) the appearance of the hydride ligand resonance as two overlapping triplet patterns (Table I and Figure 1A); (3)the existence of three 31P{1H)NMR resonances in CH3CN solution due to PPh3 appearing as a doublet centered at +51.5 ppm (Jp,+-pl = 247 Hz) while the dppb chelate phosphine resonances are found centered a t +37.8 ppm (d, Jp = 13 Hz) and at +14.8 ppm (d of d, Jp1+p3= 247 I&, Jp+pl = 15 Hz)(Figure 1B). The isomer suggested by the d M R study is the least sterically crowded of the three possible isomers. Cyclic voltammetry studies on the hydrido complexes in CH3CN with tetraethylammonium perchlorate as supporting electrolyte vs. the saturated calomel reference electrode (SCE) show an irreversible oxidative process that is presumably a metal-based Osn Osrn or Ru" Runr oxidation followed by a rapid, irreversible chemical step. There are few examples of well-defined electrochemical studies on metal hydride complexes and the new complexes reported here provide an opportunity for such a study. Although irreversible in nature, the peak potential values (E,) presumably provide at least a rough measure of the relative ability of the hydride ligand to stabilize the M(II1) state over the M(I1) state by enhanced c donation. For
-
-
I
15
10
05
0
-05 -10 -15
VOLTS (ssce)
Figure 2. Cyclic voltammograms of [Ru(bpy),(CO)X]PF,in 0.1 M tetraethylammonium perchlorate/CH&N medium taken at a Pt bead electrode. The potential for oxidation becomes less positive in the order X = C1 (A), X = H (B),and X = CHzPh (C). The cathodic processes are stepwise one-electronreductions of the coordinated bpy ligands. All potentials are reported vs. the saturated calomel electrode at a scan rate of 200 mV/s.
the series [ R ~ ( b p y ) ~ ( C 0 ) Xwhere ] + , X = PhCH2," H, OC(=O)H, or C1, Ep or El values are +0.76, +1.14, 1.44, and 1.50 V,respectively (bigure 2). Apparently the relative stabilization of Rum over Run is more important for the benzyl group than for hydride, but hydride is in turn a better stabilizing ligand for Rum than either formate or chloride. We are just beginning to investigate the thermal reactivity of the hydride ligand in these complexes; however, several interesting points have begun to emerge. For most of the complexes in Table I, addition of HPFGin CH3CN solution at room temperature results in the rapid appearance of the acetonitrile complex by eq 5. For
CH&N
[Os(bpy)2(CO)H]++ H+ [Os(bpy)z(CO)CH3CNI2++ H2 (5)
tram-[Os(bpy)(PPh3),(CO)H]+ the reaction with acid does not occur even with prolonged heating. From the relative magnitudes of the E, and v(C0) values in Table I, the metal center in the latter complex appears to be relatively electron deficient and the metal-H bond less "hydridic" in character. The observation is significant since it suggests that the reactivity of the M-H bond in the ground state of these complexes can be tuned by making systematic variations in the remaining ligands. The results of our initial photochemical and photophysical studies are revealing. The complexes absorb light ~
(11) Sullivan, B. P.; Smythe, R. S.; Kober, E. M.; Meyer, T. J. J. Am. Chem. SOC.1982,104, 1701.
Organometallics 1983,2, 554-555
554
strongly in the visible. For example, in acetonitrile ,A, for the lowest energy visible MLCT band in CH3CNoccurs at 445 nm for [Ru(bpy),(CO)H](PF,) (e 3170) and at 499 nm for [Os(phen),(CO)H](PFs) (t 5320). As can be seen from the data in Table I, the Os complexes represent rare examples of metal hydride complexes which luminesce in fluid solution at room temperature.', However, the complexes are weak emitters, 4, for [0~(bpy)~(Co)H](PF,) is in CH3CN at room temperature, and excited3.8 X state decay is dominated by nonradiative processes, 1/r0 N kn,. In this context the values of k,, in Table I are worthy of note. Especially striking are the values for the non-C0-containing hydrides, [Os(phen)(l,2(PhzP)&H4) (PPh3)H]+ and [Os(phen) (cis-Ph,PCH= CHPPh,)(PES)H]+. Compared to our earlier results based on the series (phen)O~L,~+, values for k, are
