Organometallics 1995, 14, 2387-2394
2387
Synthesis, Redox Reactivity, and X-ray Diffraction Structures of the Rhenium Carbonyl Complexes fuc -ReBr(C0)3(bma) and [fuc-ReBr(C0)3 (bma)][Cp& 01. Structural Consequences of Electron Accession in fuc-ReBr(C0)3(bma) Kaiyuan Yang, Simon G. Bott,* and Michael G. Richmond* Center for Organometallic Research and Education, Department of Chemistry, University of North Texas, Denton, Texas 76203 Received December 29, 1994@ Solvent displacement in the rhenium complex ReBr(C0)3(THF)2(2) by the redox-active diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma) affords the corresponding bma-substituted complex fuc-ReBr(CO)s(bma)(3) in near quantitative yield. The same product is also obtained, albeit in lower yield, from BrRe(C0)S (1)and bma in refluxing 1,2-dichloroethane. fac-ReBr(CO)s(bma)has been isolated and characterized in solution by IR and NMR (31Pand 13C) spectroscopies. The oxidatiodreduction chemistry of fac-ReBr(CO)s(bma)was explored by cyclic and rotating disk electrode voltammetric techniques. Two diffusion-controlled one-electron reduction processes at E1/2 = -0.33 V and E112 = -1.23 V and an irreversible oxidation a t E,, = 1.58 V are observed in CH2ClDBAF' at a platinum electrode. The reductive electrochemistry is discussed in the context of a scheme involving the formal reduction of the bma ligand, a property that is common with other known 18 6 paramagnetic compounds containing an ancillary bma ligand. Reductive bulk electrolyses have been carried out on 3,and the product of one-electron reduction, [fac-ReBr(CO)s(bma)l'(4), has been characterized by IR and W-vis spectroscopies. Large infrared frequency shifts in the carbonyl stretching bands of the bma ligand in [fac-ReBr(CO)s(bma)l'-are observed, as expected for a reduction process confined to the electron-accepting bma ligand. The unequivocal identity of [fm-ReBr(CO)3(bma)Y-was independently established by the isolation and structural characterization of the product formed from the cobaltocene reduction of facReBr(CO)s(bma). The molecular structures of compounds 3 and 4 have been determined by single-cqstal X-ray diffraction analysis. fuc-ReBr(CO)s(bma)crystallizes in the triclinic space b = 12.1153(4) c = 13.7751(8) A, a = 85.322(4)",p = group P1: a = 9.855(1) 73.828(6)",y = 75.812(6)",V = 1531.3(2)As, 2 = 2,dcalc= 1.771 g - ~ m - R ~ ;= 0.0552,R, = 0.0771 for 3342 observed reflections. The radical anion [fac-ReBr(C0)3(bma)l[Cp2Col, as the CHzClz solvate, crystallizes in the monoclinic space group C2k: a = 39.600(3) b = 10.2625(2) c = 23.253(2) p = 120.278(7)",V = 8161(1)A3, 2 = 8,dcalc= 1.793 g - ~ m - ~ ; R = 0.0511, R, = 0.0598 for 3811 observed reflections. These two structures permit a direct comparison regarding the consequences of electron accession in fac-ReBr(CO)s(bma). Extended Huckel calculations have been performed on the model compound fuc-ReBr(CO)s(Hdbma),the results of which are used to support the electrochemical data and the proposed reduction pathway involving electron addition to the bma ligand.
+
A,
A,
A,
A,
A,
Introduction The photochemical and photophysical study of compounds based on XRe(CO)s(N-N) (where X = halide; N-N = diimine ligand) has played a prominent role in the elucidation of the mechanistic details related t o intramolecular energy-transfer processes' and in the catalytic reduction of carbon dioxide.2 Such diiminesubstituted complexes are attractive as starting com@Abstractpublished in Advance ACS Abstracts, April 15, 1995. (1)(a)Geoffroy, G. L.; Wrighton, M. S. Organometallic Photochemistry; Academic Press: New York, 1979.(b) Wrighton, M. S.; Morse, D. L. J. Am. Chem. SOC.1974,96,998. (c) Worl, L. A,; Duesing, R.; Chen, P.; Ciana, L. D.; Meyer, T. J. J . Chem. SOC.,Dalton Trans. 1991, 849 and references therein.
pounds in these studies because of the fact that the lowest unoccupied molecular orbital belongs to the n* system of the diimine ligand.3 The use of mono- and (2)(a) Hawecker, J.; Lehn, J.-M.; Ziessel, R. J. Chem. SOC.,Chem. Commun. 1983,536;1984,328.(b) Kutal, C.;Weber, M. A.; Ferraudi, G.; Geiger, D. Organometallics 1985,4,2161.( c ) Hawecker, J.; Lehn, J.-M.; Ziessel, R. Helu. Chim. Acta 1986,69,1990. (3)For reports dealing with diimine ligand reduction, see: (a) van Outersterp, J. W. M.; Hartl, F.; Stufkens, D. J. Inorg. Chem. 1994,33, 2711.(b) Duesing, R.;Tapolsky, G.; Meyers, T. J . J . Am. Chem. SOC. 1990, 112, 5378. ( c ) Sahai, R.; Rillema, D. P.; Shaver, R.; Van Wallendale, S.; Jackman, D. C.; Boldaji, M. Inorg. Chem. 1989,28, 1022.(d) Baiano, J . A,; Carlson, D. L.; Wolosh, G. M.; DeJesus, D. E.; Knowles, C. F.; Szabo, E. G.; Murphy, W. R., Jr. Inorg. Chem. 1990, 29,2327.(e) Tapolsky, G.;Duesing, R.; Meyer, T. J. Inorg. Chem. 1990, 29,2285.(0 Glyn, P.; George, M. W.; Hodges, P. M.; Turner, J. J. J . Chem. SOC.,Chem. Commun. 1989,1655.
0276-7333/95/2314-2387$09.00/00 1995 American Chemical Society
2388 Organometallics, Vol. 14,No. 5, 1995
Yang et al.
bidentate phosphine-substituted compounds derived from the fuc-ReX(CO)sfragment would not function as suitable probe compounds for such studies since the LUMO is not predicted to be a ligand-based orbital but rather a much higher lying Re-CO antibonding ~ r b i t a l . ~ Given the dearth of fuc-XRe(C0)3(PR3)~ compounds possessing an accessible n* phosphine-based 0rbita1,~ we set out to prepare such a compound using the redoxactive ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma). This ligand displays unique electronic properties in comparison to the common diphosphine ligands such as dppm, dppe, and (Z)-PhzPCH=CHPPhz because it possesses a low-lying n* orbital that is delocalized over the maleic anhydride ring. An organometallic compound with this type of LUMO is expected to serve as an efficient electron reservoir by stabilizing electron counts in excess of 18-electrons. In the case of a one-electron reduction, the resulting radical is expected to exhibit significant unpaired spin density on the bma ligand, which leads to the preferred 18 6 description for this genre of compound.6 Elegant spectroscopic and structural studies that demonstrate this principle have been presented by the groups of Fenske7p8 and TylergJofor a variety of mononuclear compounds bearing a bma ligand. Recently, we have presented data showing this same trend in the binuclear complex COZ(COk+-PhC=CPh)(bma) (chelating and bridging isomers).l1JZ Electrochemical reduction of either isomer affords the corresponding radical anion Coz(C0)d+-PhC=CPh)(bma)’-, which was shown to contain a reduced bma ligand. We are currently investigating bma-substituted polynuclear complexes with the goal of obtaining a compound whose LUMO is formed from bmdcluster framework orbitals. It is hoped that this type of composite LUMO would yield compounds possessing superior electron reservoir properties. Herein we report our results on the synthesis, characterization, and redox properties of fac-ReBr(CO)s-
+
(4) Albright, T. A.; Burdett, J. K.; Whangbo, M. H. Orbital Interactions i n Chemistry; Wiley-Interscience: New York, 1985. (5) (a) Reimann, R. H.; Singleton, E. J. Organomet. Chem. 1973, 59, 309. (b) Singleton, E.; Moelwyn-Hughes, J. T.; Garner, A. W. B. J . Organomet. Chem. 1970,21,449. (c) Freni, M.; Valenti, V.; Giusto, D. J . Inorg. Nucl. Chem. 1965,27,2635. (d) Freni, M.; Giusto, D.; Romiti, P. J . Inorg. Nucl. Chem. 1971, 33, 4093. (e) Zingales, F.; Sartorelli, U.; Trovati, A. Inorg. Chem. 1967, 6, 1246. (0 Chatt, J.; Dilworth, J. R.; Gunz, H. P.; Leigh, G. J. J . Organomet. Chem. 1974, 64, 245. (g) Miller, T. M.; Ahmed, K. J.; Wrighton, M. S. Inorg. Chem. 1989, 28, 2347. (h) Lorkovic, I. M.; Wrighton, M. S.; Davis, W. M. J. Am. Chem. SOC.1994, 116, 6220. (6)Brown, T. L. In Organometallic Radical Processes; Trogler, W. C., Ed.; Elsevier: New York, 1990; Chapter 3 (see also references therein). (7) (a) Fenske, D. Chem. Ber. 1979,112,363. (b) Fenske, D. Angew. Chem., Int. Ed. Engl. 1976, 15, 381. (c) Bensmann, W.; Fenske, D. Angew. Chem., Int. Ed. Engl. 1978,17,462; 1979,18,677. (d) Fenske, D.; Christidis, A. Angew. Chem., Int. Ed. Engl. 1981,20, 129. (8)See also: (a) Fenske, D.; Becher, H. J. Chem. Ber. 1974, 107, 117; 1975, 108, 2115. (b) Becher, H. J.; Bensmann, W.; Fenske, D. Chem. Ber. 1977,110, 315. (9) (a) Mao, F.; Tyler, D. R.; Keszler, D. J. Am. Chem. SOC. 1989, 111, 130. (b) Mao, F.; Philbin, C. E.; Weakley, T. J. R.; Tyler, D. R. Organometallics 1990,9, 1510. (c) Mao, F.; Tyler, D. R.; Rieger, A. L.; Rieger, P. H. J . Chem. SOC.,Dalton Trans. 1991,87,3113. (d) Fei, M.; Sur, S. K.; Tyler, D. R. Organometallics 1991, 10, 419. (e) Mao, F.; Tyler, D. R.; Bruce, M. R. M.; Bruce, A. E.; Rieger, A. L.; Rieger, P. H. J . Am. Chem. SOC.1992,114,6418. (10) For review articles, see: (a) Tyler, D. R.; Mao, F. Coord. Chem. Rev. 1990, 97, 119. (b) Tyler, D. R. Acc. Chem. Res. 1991, 24, 325. (11)(a) Yang, K.; Bott, S. G.; Richmond, M. G. Organometallics 1994, 13, 3788. (b) See also ref 12. (12)(a) Yang, K.; Smith, J. M.; Bott, S. G.; Richmond, M. G. Organometallics 1993, 12, 4779. (b) Yang, K.; Bott, S. G.; Richmond, M. G. Organometallics 1994, 13, 3767.
(bma). A study on the effects of electron accession in fu~-ReBr(CO)3(bma)~’~is facilitated by the isolation and structural characterization of the correspondingneutral and paramagnetic compounds. The bond length alterations observed in going from 3 to 4 are consistent with the known properties of the bma ligand and are validated by extended Hiickel MO calculations. Results and Discussion
I. Synthesis and Spectroscopic Data for facReBr(C0)dbma). fuc-ReBr(CO)s(bma)was initially prepared from the direct thermolysis reaction between BrRe(C0)513(1)and bma8 in 1,2-dichloroethanesolvent. The reaction proceeded easily and gave a good yield of the desired product, as determined by IR spectroscopy. Extensive decomposition of fuc-ReBr(CO)s(bma) was observed when chromatographic purification over silica gel was attempted. Performing the chromatography a t a low temperature (-78 “C) did not significantly improve the isolated yields of 3,which stands in contrast to the other bma-substituted compounds worked with by our g r o u p ~ . ~Silica ~ J ~gel promoted hydrolysis of the anhydride ring is presumed to be responsible for the decomposition of 3 during workup. Alternatively, the quantitative formation of fuc-ReBr(CO)s(bma) was observed in the reaction between the bis(so1vent) compound ReBr(C0)dTHF)z (2) and an equimolar amount of bma at room temperature.14 Compound 2, with its exceptionally labile THF ligands, has been employed in the preparation of a variety of substituted-rhenium compounds under mild reaction conditions. Here the isolated product was pure enough for our purposes and eliminated the need for a purification step. Scheme 1 illustrates the two methods that we employed in the preparation of 3. 3 exhibits three terminal carbonyl bands at 2045 (vs), 1975 (vs), and 1920 (vs) cm-l in CHzC12 consistent with the proposed facial stereochemistry about the rhenium center. The latter two v(C0) bands derive from a splitting of the e mode in a fac-M(CO)sLs (where L = symmetrical ligand) complex.l5 The vibrationally coupled carbonyl bands belonging to the bma ligand are found a t 1848 (w) and 1778 (9) cm-’ and are assigned to the asymmetric and symmetric carbonyl stretches, respectively.16 The 31P{1H) NMR spectrum of 3 in CDCl3 at room temperature displays a single, sharp 31Presonance a t 6 19.2. The high-field frequency associated with the chelating bma ligand is comparable t o the chelating diphosphine ligands in other third-row metal complexes.17J8 Two terminal carbonyl resonances were recorded for 3 in the 13C{lH) NMR spectrum. The slightly overlapping doublet of doublets centered at 6 188.5 (2cb, Jp,,,-c = 11.9 Hz,Jpt,,,,-c = 67.1 Hz) and the triplet a t 6 187.6 Oca,Jp-c = 6.2 Hz) support the facial orientation of the rhenium carbonyl groups shown (13)Schmidt, S. P.; Trogler, W. C.; Basolo, F. Inorg. Synth. 1990, 28, 160. (14) (a) Vitali, D.; Calderazzo, F. Gazz. Chim. Ital. 1972, 102, 587. (b) Calderazzo, F.; Mavani, I. P.; Vitali, D.; Bernal, I.; Korp, J. D.; Atwood, J. L. J. Organomet. Chem. 1978,160, 207. (15) Lukehart, C. M. Fundamental Transition Metal Organometallic Chemistry; Brooks/Cole Publishing Co.: Monterey, CA, 1985. (16)Dolphin, D.; Wick, A. Tabulation of Infrared Spectral Data; Wiley-Interscience: New York, 1977. (17) Garrou, P. E. Chem. Rev.1981,81,229 and references therein. (18)Simpson, R. D.; Bergman, R. G. Organometallics 1993,12,781 and references therein.
Organometallics, Vol. 14,No.5, 1995 2389
fac-ReBr(C0)dbma) and [fa~-ReBr(CO)dbma)l[Cp2CoI Scheme 1 Br
CO l:L=CO 2: L = THF
Go 0
Ph2P Ph2
bma below. Our 13CNMR data are similar to those reported by Bergman for a large variety of fac-ReX(CO)a(L-L) compounds.ls
I
11. Electrochemical Studies. Cyclic voltammetric data were collected at a platinum electrode in solutions containing 0.2 M tetra-n-butylammonium perchlorate (TBAP) as the supporting electrolyte. 3 was examined in the solvents CH2C12, THF, and MeCN. Aside from minor potential shifts observed in the redox couples, the nature of the solvent did not affect the redox process, and we report only the data obtained in CH2C12. Compound 3 displays two well-defined, diffusioncontrolled reductions a t E112= -0.33 and E112 = -1.23 V, assignable to the 011- and 1-12- redox couples, as shown by the cyclic voltammogram (CV) in Figure la. Both couples are chemically reversible on the basis of and the linear plots the near unity current ratios (IpalIpc) of the current function (I,) vs the square root of the scan rate ( v ) observed over the scan rates investigated (0.051.0 VIs).l9 The peak-to-peak separation of each couple at 0.1 VIS was calculated to be 68 and 86 mV and, when compared with the value of 84 mV found for internally added ferrocene, supports a fast electron transfer for each redox couple. The assumed one-electron stoichi(19) (a)Ftieger, P. H. EZectrochemistry;Chapman & Hall: New York, 1994. (b)Bard, A.J.; Faulkner, L. R. Electrochemical Methods; Wiley: New York, 1980.
0.2
I
0.6
I
1.4
Potential (Volts) Figure 1. (A) Cathodic scan cyclic voltammogram of facReBr(CO)s(bma)(ca. M) in CHzClz containing 0.2 M TBAP at 0.1 V/s and (B) RDE voltammogram of fac-ReBr(CO)a(bma)(ca. M) in CHzClz at 273 K containing 0.2 M TBAP at 50 mV1s. ometry of each redox couple of the CV was verified by application of Walden’s rule using added ferrocene. Not shown in the CV of Figure 1 is the irreversible multielectron oxidation at E,, = 1.58 V recorded for 3, an observation that has been reported by ~ t h e r s . ~ g The rotating disk electrode (RDE) voltammogram of the two reductions in 3 (Figure 1B) was also recorded in the same solvent as the CV, as an independent check of the electron stoichiometry for these two couples and the assumption concerning rapid heterogeneous electron transfer (khet) in 3. The RDE voltammogram yields halfwave potentials of E112 = -0.34 V and E112 = -1.29 V in close agreement with the CV data. Since both reduction waves give identical limiting currents ( l i d l ) it may be concluded that the number of electrons transferred in each step is the same. The Nernstian nature of the 011- redox couple is revealed by a plot of E vs
2390 Organometallics, Vol. 14, No. 5, 1995 log[(& - i)/iI, which gave a slope close to the theoretically predicted value of 54.2 mV for a reversible oneelectron transfer, while data analysis using Tomes' criterion for reversibility (IE3/4 - E1/41)affords values of 60 and 80 mV for the 0/1- and 1 4 2 - redox couples, respectively.20 No kinetic complications were observed with these redox couples when the RDE data were analyzed by the relationship developed by Levicha21 Here plots of i d vs w1I2 all displayed intercepts of zero within experimental error. This rules out the possibility of a rate-limiting heterogeneous electron transfer (khet) in each of the reduction steps reported for 3. Finally, using the Levich data we have determined the diffusion of 3 to be 4.9 x cm2/s,which appears coefficient (Do) reasonable given the overall size of 3 with its large ancillary bma ligand (vide We next examined 3 by constant-potential coulometry in an effort to more fully characterize [fac-ReBr(CO)s(bma)l'- (41, the product of one-electron reduction. The reduction of 3 was carried out at -0.60 V in CH2C12 containing 0.1 M TBAP a t 273 K, and the total charge passed upon completion of the reduction was calculated to be Q = 1.05 C/mol of 3. IR analysis of the catholyte allowed us to assess the effect of electron accession on the carbonyl stretching bands of 4. Compound 4 exhibits v(C0) bands at 2026 (vs), 1943 (vs), 1905 (vs), 1730 (s), and 1649 (vs) cm-l, the first three bands represent the Re-CO groups that have shifted from 15 to 32 cm-' to lower energy. The magnitude of these frequency shifts indicates that little of the odd-electron density is associated with these carbonyl groups. The existence of a reduced bma ligand in 4 is readily seen by the large frequency shifts in the latter two bma bands of 118 and 129 cm-l relative t o neutral 3. The IR data for 4 are in total agreement with the 18 6 nature of this and related compounds, as originally put forth by Tyler.gJo Further proof regarding the nature of 4 was obtained from the chemical reduction of 3 using the oneelectron reducing agent cobaltocene. In this experiment, we isolated [41[Cp~Col and were able t o characterize the radical anion by IR and X-ray diffraction analysis (vide infra). The IR spectrum of [4l[Cp~Colin CH2C12 was identical t o that recorded from the bulk electrolysis experiment, removing any doubt as t o the identity of 4. 111. X-ray Diffraction Structures of fuc-ReBr(CO)~(bma) and Vhc-ReBr(CO)a(bma)l[CpzCol. The structural consequences resulting from electron transfer in the redox pair of 3 and 4 were established by X-ray crystallography. Both complexes exist as discrete molecules in the unit cell with no unusually short inter- or intramolecular contacts. The X-ray data collection and processing parameters may be found in Table 1, while Tables 2 and 3 give the listings of the final fractional coordinates and selected bond lengths and angles, respectively. The ORTEP diagrams are depicted in Figure 2. The six-coordinate rhenium center in 3 and 4 confirms the idealized octahedral geometry for each of these compounds, and the presence of three cis carbonyl groups is in agreement with the proposed facial stereo-
+
(20) Tomes, J. Collect. Czech. Chem. Commun. 1937,9, 12, 81, 150. (21) Levich, V. G. Physicochemical Hydrodynamics; Prentice Hall: Englewood Cliffs, NJ, 1962. (22) Cf.: The calculated D ovalue of 7.1 x cmVs obtained from
the X-ray data on fac-ReBr(CO)a(bma) and application of the StokesEinstein relationship.
Yang et al. Table 1. X-ray Crystallographic Data and Processing Parameters for fuc-ReBr(CO)3(bma)(3) and [fuc-ReBr(C0)3(bma)l[Cp&ol (4) 3
space group a,A b, A c,
A
a, deg 0. dep. Y , de;
v, A3
C2/c, monoclinic
9.855(1) 12.1153(4) 13.7751(8) 85.322(4) 73.828(6) 75.812(6) 1531.3(2)
39.600(3) 10.2625(2) 23.253(2)
mol formula
C31HzoBrO6PzRe
fw formula units per cell (2) e, g.cm+ abs coeff @I, cm-l i(Mo Ka), A collecn range, deg max scan time, s scan speed range, degmin-I tot. no. of data collcd no. of ind data, I > 341) R
816.56 2 1.771 54.56 0.710 73 2.0 5 28 5 44.0 120 0.87-8.0 3750 3342 0.0552 0.0771 [O.O4F (uF)2]-1
RW
weights
4
Pi, triclinic
+
120.278(7) 8161(1)
C42H32BrCl~C006PzRe 1101.70
8 1.793 46.36 0.710 73 2.U 4 28 4 44.0 120 0.67-8.0 5399 3811 0.0511 0.0598
[O.OW
+ (uF)2]-1
chemistry. The Re-Br, Re-CO, and Re-P distances found for both structures are unexceptional in comparison with other structurally characterized rhenium complexes.23 The cobaltocenium cation in 4 exhibits no unusual structural perturbations requiring any comment.24 Important differences are observed in the bond lengths of the C-C and C-P bonds of the coordinated bma ligand in each compound. Here bond length decreases of 0.07, 0.06, 0.04, and 0.04 A in the C(ll)-C(l2), C(14)-C(15), P(1)-C(ll), and P(2)-C(15) bonds, respectively, and the C(ll)-C(15) bond length increase of 0.07 A in going from 3 t o 4 reveal the principal site of electron localization in the latter complex. Analogous bond alterations in other 18- and 19-electroncomplexes have been discussed by Tyler in terms of the bma-based canonical resonance contributors (Scheme 2),9band fully support the contention that the vast amount of oddelectron density in 4 occurs on the bma ligand. 3 and 4 represent the first neutraVanionic redox state isomers of a bma-substituted compound. Structural alterations in the core of the reduced bma ligand are reminiscent of the M-M bond length elongations reported for polynuclear cluster compounds during reduction, where the geometrical changes demonstrate the antibonding M-M character of the LUM0.25 IV. Extended Hiickel Calculations. The model compound fuc-ReBr(CO)s(H4bma) was examined by extended Huckel molecular orbital calculations in order t o establish the composition of the HOMO and LUMO in fuc-ReBr(CO)3(bma). Here the phenyl groups have been replaced by hydrogens. Figure 3 shows the three(23) (a) Nunn, C. M.; Cowley, A. H.; Lee, s. W.; Richmond, M. G. Inorg. Chem. 1990,29,2105. (b) Stack, J. G.; Simpson, R. D.; Hollander, F. J.; Bergman, R. G.; Heathcock, C. H. J . Am. Chem. Soc. 1990,112, 2716. (c) Drew, M. G. B.; Brisdon, B. J.;Watts, A. M. Polyhedron 1984, 3,1059. (d) Carriedo, G. A,; Rodriguez, M. L.; Garcia-Granda, S. Inorg. Chim. Acta 1990, 178, 101. (24) Riley, P. E.; Davis, R. E. J . Organomet. Chem. 1978,152, 209. (25)(a) Beurich, H.; Madach, T.; Richter, F.; Vahrenkamp, H. Angew. Chem., Int. Ed. Engl. 1979, 18, 690. (b) Kubat-Martin, K. A.; Barr, M. E.; Spencer, B.; Dahl, L. F. Organometallics 1987, 6, 2570. (c) Bedard, R. L.; Dahl, L. F. J . Am. Chem. Soc. 1986, 108, 5942. (d) Kubat-Martin, K. A.; Spencer, B.; Dahl, L. F. Organometallics 1987, 6, 2580.
Organometallics, Vol.14,No.5, 1995 2391
fac-ReBr(C0)dbma) and [fac-ReBr(CO)dbma)l[Cp~Col
Table 2. Positional Parameters for the Non-Hydrogen Atoms in fac-ReBr(CO)s(bma)(3) and V;ac-ReBr(CO)s(bma)][CpzCol (4) with Estimated Standard Deviations in Parentheses= atom
X
Y
z
0.73911(7) 0.9853(2) 0.6323(5) 0.6989(5) 0.890(2) 0.829(2) 0.45 1( 1) 0.597(2) 0.647(1) 0.697(1) 0.832(2) 0.797(2) 0.561(2) 0.654(2) 0.628(2) 0.681(2) 0.686(2) 0.696(2) 0.829(2) 0.876(2) 0.788(2)
0.08869(6) 0.0567(2) 0.2142(4) -0.0608(4) -0.091(1) 0.272(1) 0.136( 1) 0.238(1) 0.045(1) -0.139(1) -0.025(2) 0.205(2) 0.115(1) 0.120(1) 0.148(2) -0.043(1) 0.006(1) 0.341(1) 0.352(2) 0.452(2) 0.537(2)
0.82953(5) 0.6855(2) 0.7089(3) 0.7378(3) 0.961(1) 0.926(1) 0.991(1) 0.4642(9) 0.4572(8) 0.5014(9) 0.912(1) 0.888(1) 0.930(1) 0.606(1) 0.503(1) 0.523(1) 0.616(1) 0.653(1) 0.660(1) 0.623(2) 0.581(2)
0.08743(1) 0.14396(6) 0.31600(5) 0.12120(8) 0.12628(8) 0.0431(3) 0.0422(3) 0.0267(2) 0.1906(3) 0.1930(2) 0.1840(2) 0.0602(4) 0.0587(4) 0.0491(3) 0.3369(5) 0.3505(5) 0.3716(5) 0.3705(5) 0.3499(5) 0.2588(5) 0.2730(6) 0.2916(4) 0.2874(5) 0.2687(5) 0.1520(3) 0.1789(4) 0.1758(3) 0.1513(3)
0.09612(6) 0.2238(2) 0.0330(2) -0.1031(4) 0.0657(3) 0.330(1) 0.141(1) -0.0763(6) -0.339(1) -0.2588(9) -0.144( 1) 0.241(2) 0.119(2) -0.013(1) 0.076(2) 0.166(2) 0.097(2) -0.032(2) -0.046(2) 0.054(3) 0.122(2) 0.043(2) -0.076(2) -0.071(3) -0.151(1) -0.258(1) -0.156(1) -0.086(1)
0.2828$2) 0.38305(9) 0.44090(9) 0.3444(1) 0.2280(1) 0.1936(5) 0.3576(5) 0.1768(3) 0.3742(4) 0.2864(4) 0.1974(4) 0.2280(6) 0.3294(6) 0.2157(5) 0.3811(7) 0.4329(8) 0.4919(8) 0.4782(8) 0.4093(8) 0.3885(8) 0.448(1) 0.4975(8) 0.4742(9) 0.4097(8) 0.3122(5) 0.3308(6) 0.2408(6) 0.2582(5)
B,&
X
Y
2
B, Az
0.659(2) 0.610(2) 0.437(2) 0.387(2) 0.239(3) 0.140(2) 0.189(2) 0.336(2) 0.847(2) 0.955(2) 1.071(2) 1.078(2) 0.973(2) 0.855(2) 0.532(2) 0.534(2) 0.406(2) 0.277(2) 0.275(2) 0.401(2)
0.526(2) 0.428(1) 0.270(1) 0.347(2) 0.384(2) 0.347(2) 0.273(2) 0.233(2) -0.188(1) -0.208(2) -0.301(2) -0.372(2) -0.353(2) -0.260(2) -0.113(1) -0.221(2) -0.257(2) -0.183(2) -0.072(2) -0.041(2)
0.574(2) 0.611(1) 0.751(1) 0.830(2) 0.873(2) 0.837(2) 0.759(2) 0.717(2) 0.714(1) 0.624(1) 0.617(2) 0.699(2) 0.790(2) 0.797(1) 0.771(1) 0.747(2) 0.767(2) 0.809(2) 0.832(1) 0.815(1)
4.9(6) 3.96) 3.0(4) 5.0(5) 6.5(7) 6.3(7) 6.1(6) 4.4(5) 3.2(4) 3.5(4) 4.1(5) 5.2(6) 4.8(5) 4.0(5) 2.7(4) 4.2(5) 4.9(5) 5.3(5) 4.3(5) 3.6(4)
-0.086(1) -0.068(1) -0.047(2) -0.039(2) -0.056(2) -0.081(2) -0.241(1) -0.370(1) -0.471(2) -0.448(2) -0.322(2) -0.219(2) 0.056(1) 0.169(2) 0.163(2) 0.051(2) -0.062(2) -0.061(2) 0.184(1) 0.305(2) 0.395(2) 0.361(2) 0.244(2) 0.156(1) 0.0755(8) 0.087(2) 0.122(3)
0.4346(5) 0.4641(6) 0.5311(7) 0.5705(7) 0.5424(7) 0.4744(6) 0.3378(5) 0.3377(6) 0.3378(7) 0.3352(8) 0.3363(8) 0.3339(7) 0.1380(6) 0.1020(7) 0.0317(8) 0.0011(8) 0.0338(8) 0.1050(7) 0.2405(6) 0.2670(7) 0.2792(7) 0.2636(7) 0.2337(6) 0.2222(6) 0.3158(3) 0.4208(6) 0.349(1)
2.9(3)* 3.3(3)* 4.8(4)* 5.0(4)* 5.0(4)* 4.0(3)* 2.5(2)* 3.7(3)* 4.7(4)* 5.8(4)* 6.4(5)* 4.9(4)* 3.0(3)* 5.2(4)* 6.2(4)* 6.2(5)* 6.1(4)* 4.6(4)* 2.8(3)* 4.1(3)* 5.1(4)* 4.7(4)* 3.9(3)* 3.3(3)* 9.4(2)* 8.7(3)* 10.3(8)*
atom
fac-ReBr(CO)s(bma) (3) 2.50(1) C(115) 3.88(4) C(116) 2.6(1) C(117) 2.7(1) C(118) 5.7(4) C(119) 6.2(4) C(120) 4.4(3) C(121) 4.9(3) C(122) 3.7(3) C(211) 4.3(3) C(212) 3.8(5) C(213) 3.5(4) C(214) 3.0(4) C(215) 2.7(4) C(216) 3.8(4) C(217) 3.2(4) C(218) 2.6(4) C(219) 3.1(4) C(220) 4.0(5) C(221) 5.2(5) C(222) 5.2(6)
~fuc-ReBr(CO)dbma)l[Cp~Col (4) 2.45iij 7.00(6) 3.996) 2.44(7) 2.44(8) 5.8(3) 7.0(3) 5.7(1)* 4.3(3) 3.4(2) 4.2(2) 4.0(4) 4.2(4) 5.5(2)* 6.2(5) 6.6(5) 6.1(5) 5.6(5) 6.6(5) 15.4(9) 13.4(8) 8.7(5) 7.4(5) 9.4(7) 2.5(3) 3.5(3) 3.2(3) 2.3(3)
C(111) C(112) C(113) C(114) C(115) C(116) C(117) C(118) C(119) C(120) C(121) C(122) C(211) C(212) C(213) C(214) C(215) C(216) C(217) C(218) C(219) C(220) C(221) C(222) Cl(1S) Cl(2s) C(1S)
0.1524(3) 0.1922(3) 0.2146(4) 0.1977(4) 0.1590(4) 0.1358(4) 0.0905(3) 0.1011(4) 0.0795(4) 0.0445(5) 0.0332(5) 0.0554(4) 0.0974(3) 0.0827(4) 0.0579(5) 0.0483(5) 0.0623(5) 0.0880(4) 0.1639(3) 0.1657(4) 0.1953(4) 0.2230(4) 0.2205(4) 0.1913(4) 0.3969(2) 0.4720(4) 0.4418(7)
a Starred values refer to atoms t h a t were refined isotropically. Anisotropically refined atoms are given in the form of the isotropic equivalent displacement parameter defined as (4/3)[a2B(l,l) b2B(2,2) c2B(3,3) ab(cos y)B(1,2) uc(cos p)B(1,3) bc(cos a)B(2,3)].
+
+
+
+
+
dimensional CACAO drawings of these orbitals along with the calculated energy for each orbital.26 The HOMO in fa~-ReBr(CO)a(H4bma)is best described as a Re-Br n bond formed from an out-of-phase overlap of rhenium dyz (29%) and bromine py (52%) orbitals, with minor in-phase contributions t o the rhenium dyzorbital from the facial carbonyl groups being observed. The energy level of the HOMO occurs at -12.38 eV and is only slightly lower in energy than the corresponding symmetry-related orbital derived from overlap of the rhenium dxz(32%)and bromine px (55%) orbitals, which is found at ca. -12.41 eV. Given the large bromine (p,) contribution to the HOMO it is not surprising that an irreversible oxidation a t E,, = 1.58 V was observed in the CV of 3. Typically, a metal-based
HOMO should yield a relatively stable radical cation upon oxidation. The nodal pattern of the LUMO, which occurs exclusively on the bma ligand and at ca. -10.74 eV bears resemblance to Y4 of maleic anhydride and other sixn-electron systems.27 This low-energy n* orbital results from an overlap of pz orbitals and nicely accounts for the above canonical resonance structures for [fac-ReBr(CO)s(bma)?-. Our calculations o n fac-ReBr(CO)s(H4bma) a t the extended Huckel level are in good agreement with analogous SCF-Xa-SW calculations performed on the neutral compound Co(CO)s(bma) by Tyler.ge Finally, we examined the HOMO and LUMO in the phosphine complex fac-ReBr(CO)dPH3)2. Here the two PH3 ligands are not expected to afford a low-
(26) Mealli, C.; Proserpio, D. M. J. Chem. Educ. 1990,67,399.
(27)Hayakawa, K.; Mibu, N.; Osawa, E.; Kanematsu, K. J. Am. Chem. SOC.1982,104,7136.
Yang et al.
2392 Organometallics, Vol. 14,No.5, 1995 Table 3. Selected Bond Distances (A) and Angles (deg) in fuc-ReBr(CO)s(bma)(3)and [fac-ReBr(CO)~(bma)l[CpzCo3(4)a fuc-ReBr(CO)a(bma)(3) Bond Distances 2.638(2) Re-P(1) 2.457(5) Re-C(l) 1.95(2) Re-C(3) 1.83(2) P(2)-C(15) 1.15(2) 0(2)-C(2) 1.16(2) 0(12)-C(12) 1.40(2) 0(13)-C(14) 1.50(3) C(ll)-C(15) 1.48(3) 0(14)-C(14)
Re-Br Re-P(2) Re-C(2) P(l)-C(11) 0(1)-C(1) 0(3)-C(3) 0(13)-C(12) C(ll)-C(12) C(14)-C(15) Br-Re-P(l) Br- Re -C( 1) Br -Re -C (3) P(l)-Re-C(l) P(1)-Re-C(3) P(2)-Re-C(2) C(l)-Re-C(2) C(2)-Re-C(3) Re-P(2)-C(15) . Re-C(2)-0(2) C(12)-0(13)-C(14) P(l)-C(ll)-C(l5) 0(12)-C(12)-0(13) 0(13)-C(l2)-C(ll) 0(13)-C(14)-C(15) P(2)-C(l5)-C(ll) C(ll)-C(l5)-C(l4)
Bond Angles 86.2(1) Br-Re-P(2) 89.5(5) Br-Re-C(2) 178.5(5) P(l)-Re-P(2) 172.9(6) P(l)-Re-C(2) 92.3(5) P(2)-Re-C(1) 172.0(5) P(2)-Re-C(3) 89.0(8) C(l)-Re-C(3) 89.8(7) Re-P(l)-C(ll) 103.7(6) Re-C(l)-O(l) 177(2) Re-C(3)-0(3) 109(1) P(l)-C(ll)-C(l2) 122(1) C(l2)-C(ll)-C(l5) 124(2) 0(12)-C(l2)-C(ll) 107(1) 0(13)-C(14)-0(14) 109(1) 0(14)-C(14)-C(15) 121(1) P(2)-C(15)-C(14) 108(1)
[fac-ReBr(CO)~(bma)l[CpzCol (4) Bond Distances Re-Br 2.626(2) Re-P(l) Re-P(2) 2.463(4) Re-C(l) Re-C(2) 1.94(2) Re-C(3) P(l)-C(ll) 1.79(2) P(2)-C(15) O(1)- C( 1) 1.18(2) 0(2)-C(2) 0(3)-C(3) 1.10(1) 0(12)-C(12) 0(13)-C(12) 1.40(2) 0(13)-C(14) C(ll)-C(12) 1.43(2) C(ll)-C(15) C(14)-C(15) 1.42(2) 0(14)-C(14)
Bond Angles Br-Re-P( 1) 85.89(8) Br-Re-P(2) Br-Re-C(l) 98.4(4) Br-Re-C(2) Br-Re-C(3) 173.8(3) P(1)-Re-P(2) P(l)-Re-C(l) 174.7(4) P(l)-Re-C(2) P(l)-Re-C(3) 87.9(3) P(2)-Re-C(1) P(2)-Re-C(2) 177.7(3) P(2)-Re-C(3) C(l)-Re-C(2) 89.2(6) C(l)-Re-C(3) C(2)-Re-C(3) 94.5(5) Re-P(l)-C(ll) Re-P(2)-C(15) 106.0(5) Re-C(l)-O(l) Re-C(2)-0(2) 175(1) Re-C(3)-0(3) C(12)-0(13)-C(14) 109(1) P(l)-C(ll)-C(l2) P(l)-C(ll)-C(l5) 121.8(9) C(l2)-C(ll)-C(l5) 0(12)-C(12)-0(13) 119(1) 0(12)-C(l2)-C(ll) 0(13)-C(l2)-C(ll) 107(1) 0(13)-C(14)-0(14) 0(13)-C(14)-C(15) 108(1) 0(14)-C(14)-C(15) P(2)-C(E)-C(ll) 121(1) P(2)-C(15)-C(14) C(ll)-C(l5)-C(l4) 107(1) a Numbers in parentheses are estimated standard in the least significant digits.
2.441(4) 1.93(2) 1.88(1)
1.82(2) 1.15(3) 1.19(2) 1.38(2) 1.34(2) 1."
82.0(1) 90.0(5) 83.1(2) 96.7(5) 90.7(7) 98.2(6) 92.0(7) 103.9(5) 178(2) 177(1)
130(1) 108(2) 129(2) 121(2) 130(2) 130(1)
2.467(3) 1.90(1) 1.899(9) 1.78(1) 1.16(2) 1.20(2) 1.41(2) 1.41(2) 1.21(2) 92.69(9) 85.6(4) 84.2(1) 94.3(4) 92.5(5) 87.1(3) 87.8(5) 105.6(4) 179(1) 180(1) 130(1) 108(1) 134(2) 118(1) 134(1) 131(1) deviations
lying acceptor LUMO, as was observed with the bma ligand in 3. While the HOMO in this compound mimics that in 3,the LUMO was found at much higher energy (ca. -8.73 eV), consisting of primarily carbonyl n* interactions. Experimental Section General Procedures. Rez(C0)lowas prepared from [Reo& [NHd] according to the method df Heinekey,28and BrRe(CO)s
was obtained from the published bromination procedure using R ~ ~ ( C O )Cobaltocene ~ O . ~ ~ was prepared by the known method.29 The solvent complex ReBr(C0)3(THF)214 and bmagb were synthesized by using published methods. THF was distilled from Na/benzophenone, while CH2C12, CDC13, and 1,2-CzH4Clz were all distilled from Pz0~.The MeCN solvent used in the electrochemical studies was distilled from CaHz. All purified solvents were transferred t o storage vessels equipped with Teflon stopcocks using Schlenk technique^.^^ TBAP (caution: strong oxidant) was purchased from Johnson Matthey Electronics and recrystallized from ethyl acetate/petroleum ether, after which it dried under vacuum for at least 48 h. Microanalyses were performed by Atlantic Microlab, Atlanta, GA. All infrared spectra were recorded on a Nicolet 20SXB FTIR in 0.1-mm NaCl cells. The 13C and 31PNMR spectra were recorded on a Varian 300-VXR spectrometer at 75 and 121 MHz, respectively. The 31P NMR data were referenced to external (85%),taken to have 6 = 0. The reported positive chemical shift for 3 signifies a resonance that is low field to the external standard. A Hewlett-Packard 8425A diode array spectrometer was used to record the quoted W-visible data on compounds 3 and 4. All W-visible data were obtained in specially designed 1.0-cm quartz cells that were equipped with a Teflon stopcock. Synthesis of fuc-ReBr(CO)s(bma).To a Schlenk tube containing 0.10 g (0.20 mmol) of ReBr(C0)3(THF)z in 20 mL of THF was added 0.10 g (0.23 mmol) of bma, after which the reaction was stirred at room temperature for 2 h. IR analysis at this point revealed only the presence of the desired product fuc-ReBr(CO)3(bma). The solvent was removed and the crude material was extracted with petroleum ether in order to remove the excess bma. The analytical sample and crystals of 3 suitable for X-ray diffraction analysis were obtained from a CHzClz solution of 3 that had been layered with heptane. Yield: 0.15 g (92%). IR (CHZC12): v(C0) 2045 (vs), 1975 (vs), and 1920 (vs), 1848 (w, a s y " bma C=O), 1778 (s, s y " bma C=O) cm-'. W - v i s (CHZC12): I,,, 306 ( E = 73451, 338 (E = 3563). I3C{IH} NMR (CDC13, room temperature): d 188.5 (2C, equatorial, JpCm-c = 11.9 Hz, Jpea,,-c = 67.1 Hz), 187.6 (lC, axial, Jp-c = 6.2 Hz). 31P{1H}NMR (CDC13, room temperature): 6 19.2. Anal. Calcd (found) for C3lHzoBrOePzRe: C, 45.60 (45.08); H, 2.47 (2.42). Synthesisof Vhc-ReBr(CO)s(bma)][CpzCo]. To a Schlenk tube containing 0.1 g (0.12 mmol) of fuc-ReBr(CO)3(bma)in 20 mL of CHzClz at -20 "C was added 25.0 mg (0.13 mmol) of CpzCo. Stirring was continued for 20 min, and then the solution was examined by IR spectroscopy, which revealed only the product of electron transfer, [fu~-ReBr(C0)3(bma)l[CpzCoI. The solvent was concentrated under vacuum t o ca. 5 mL, and excess petroleum ether was added to precipitate the product. The analytical sample and single crystals of 4 suitable for X-ray diffraction analysis were obtained from a CHzClz solution of 4 that was layered with heptane. Yield: 0.11 g (92%). IR (CHzClz): v(C0) 2026 (vs), 1943 (vs), 1905 (vs), 1730 (s, asymm bma C=O), 1649 (s, symm bma C=O) cm-l. W-vis (CH2Clz): I,, 310 ( E = 89431, 340 ( E = 73171, 364 ( 6 = 6498). Anal. Calcd (found) for C41H30BrCo06P2Re3/3CH2C12: C, 47.05 (47.02); H, 3.08 (3.18). X-ray Crystal Structure of fuc-ReBr(CO)s(bma).A yellow crystal, of dimensions 0.2 x 0.3 x 0.5 mm3, was sealed inside a Lindemann capillary and then mounted on an EnrafNonius CAD-4 diffractometer. Cell constants were obtained from a least-squares refinement of 25 reflections with 28 > 34". Intensity data in the range 2.0 5 28 5 44" were collected at 298 K using the W28-scan technique in the variable scan (28)Crocker, L. S.; Gould, G. L.; Heinekey, D. M. J . Organomet. Chem. 1988,342, 243. (29) King, R. B. Organometallic Syntheses; Academic Press: New York, 1965;Vol. 1. (30)Shriver, D. F. The Manipulation of Air-Sensitiue Compounds; McGraw-Hill: New York, 1969.
Organometallics, Vol. 14,No. 5, 1995 2393
fac-ReBdC0)dbma) a n d [fac-ReBr(CO)~(bma)][Cp,Co]
02
013
013
Figure 2. ORTEP diagrams of the non-hydrogen atoms of (A) fac-ReBr(CO)s(bma) (3)and (B) [fa~-ReBr(C0)3(bma)][CpzCo] (4) showing the thermal ellipsoids at the 50% probability level. The gegencation has been omitted from the latter ORTEP diagram for clarity.
Clz. A suitable black crystal, of dimensions 0.08 x 0.22 x 0.34 speed mode and were corrected for Lorentz, polarization, and mm3, was sealed inside a Lindemann capillary and then absorption (DIFABS). Three reflections (600, 060, 007) were mounted on an Enraf-Nonius CAD-4 diffractometer. Cell measured after every 3600 s of exposure time in order to constants were obtained from a least-squares refinement of monitor crystal decay (12%). The structure was solved by 25 reflections with 20 > 25". Intensity data in the range 2.0 using standard Patterson techniques, which revealed the 5 20 5 44"were collected at 298 K using the w-scan technique position of the rhenium atom. All remaining non-hydrogen in the variable scan speed mode and were corrected for atoms were located with difference Fourier maps and fullLorentz, polarization, and absorption (DIFABS). Three reflecmatrix least-squares refinement and were refined anisotropitions (-5,-5,0, 20,0,-10, 0,0,12) were measured after every cally. Refinement converged at R = 0.0552 and R, = 0.0771 3600 s of exposure time in order to monitor crystal decay for 3342 unique reflections with Z > 3u(Z). X-rayStructure of ~m-ReBr(CO)~(bma)l[Cp&ol*CH~- (
