Organometallics 1991,10, 2319-2327
2319
Preparation, Properties, and Bonding Analysis of Tantalum( I I ) q6-Arene Complexes Pamela A. Wexler and David E. Wigley' Department of Chemkby, University of Arizona, Tucson, Arizona 85721
John B. Koerner and Thomas A. Albright' Department of Chemisby, University of Houston, Houston, Texas 77204-564 1
Received October 9, 1990
The tantalum(II1) $-arene complexes (V~-CBR~)T~(DIPP)~C~ (DIPP = 2,&diisopropylphenoxide) undergo P),. facile one-electron reductions to afford the paramagnetic Ta(I1) arenes ( T ~ - C ~ ~ ) T ~ ( D I PThus, (&C& )Ta(DIPP)2Cl(l),itself prepared by the cyclotrimerizationof E t C e E t , reacts with excess NaHg to affor the maroon Ta(I1) complex ($-C6Eb)Ta(DIPP)2(3) in high yield. Alternatively, 3 is prepared from the three-electron reduction of Ta(DIPP)2C13(OEtJ in the presence of E t C e E t . Similarly, ($CeMee)Ta(DIPP)2(4) is prepared upon reducing (tle-CeMe6)Ta(DIPP)2C1 (2) with excess NaHg. ($C&tB)Ta(DIPP)2(3) undergoes oneelectron oxidative addition reactions with CH2C12to regenerate 1, with allyl bromide to afford ($-C6Eb)Ta(DIPP)2Br(5), and with CH3CH21to provide (qe-C6EtJI'a(DIPP),I (7). ($-C,E )Ta(DIPP)2(3) crystallizes in the monoclinic space group R 1 / c , with a = 12.396 (4) A, b = 17.344 (6) , c = 18.622 (4) A, and p = 99.11 (2)O, with V = 3953.3 A3 and 2 = 4 for a calculated density of 1.31 g ~ m - The ~ . @-areneligand in 3 is characterized by a folded or boatlike distortion, with two carbons making a close approach to the metal. The arene also displays a C2, "twist-boat" deformation of the other four arene carbons. Molecular orbital calculations at the extended Hiickel and ab initio level on (q6CeHe)Ta(OH), are used to investigate the bonding and geometric distortions for these molecules. It is found that the boatlike deformation of the benzene ligand is primarily due to maximization of the overlap between an s hybridized x 2 - y2 orbital at the metal and ?r* on benzene. The peculiar C2deformation of the remaining four carbon atoms in the benzene ligand is tied to rotation of the ML2 unit about the metal-benzene axis. At the ab initio level, a fully optimized structure was found to lie 19.8 kcal/mol lower in energy than one where the benzene ligand was constrained to be planar.
3
1
(1) (a) Silverthom, W. E. Adu. Organomet. Chem. 197S, 13,47. (b) Muetterties, E. L.; Bleeke, J. R.; Wucherer, E. J.; Albright, T. A. Chem.
Reu. 1982,82,499.
(2) (a) Jonea, W. D.; Feher, F. J. J. Am. Chem. SOC. 1984,106,1650. (b) . . Jones. W. D.: Feher. F. J. Ibid. 1982,104,4240. (3) (a)'Bleeke; J. R.; Muetterties, E. L.J. Am. Chem. SOC.1981,103, 556. (b) Muetterties, E. L.; Bleeke, J. R. Acc. Chem. Res. 1979,12,324 and references therein. (c) Steffey, B. D.; Chesnut, R. W.; Kerschner, J. L.; Pellechia, P. J.; Fanwick, P. E.; Rothwell,I. P. J.Am. Chem. SOC. 1989, 111, 378. (4) (a) Muetterties, E. L.; Bleeke, J. R.; Sievert, A. C. J. Organomet. Chem. 1979,178,197. (b) Sievert, A. C.; Muetbrties, E. L. Inorg. Chem. 1981,20, 489. (5) (a) Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1984,23,539.
(b) Vollhardt, K. P. C. In Strategies and Tactics in Organic Synthesis; Lmdberg, T., Ed.; Academic Press: Orlando, 1984; pp 299-324. (c) McAlister,D. R.; Bercaw, J. E.; Berg", R. G. J. Am. Chem. SOC.1977, 99, 1666 and references therein. (6) [($-Arene)RhL2]+: (a) Albano, P.; Aresta, M.; Manassero, M. Inorg. Chem. 1980,19, 1069. (b) Townsend, J. M.; Blount, J. F. Inorg. Chem. 1981,20,269. (c) Thompson, M. R.; Day, C. S.; Day, V. W.; Mink, R. I.; Meutterties, E. L. J. Am. Chem. SOC.1980,102,2979. (d) Schrock, FL R.; Oebom, J. A. J. Am. Chem. SOC.1971,93,3089. (e) Green, M.; Kuc, T. A. J. Chem. SOC., Dalton Trans. 1972,832. (f) Nolte, M. J.; Gafner, G.; Haines, L. M. J. Chem. SOC.,Chem. Commun. 1969,1406. (8) Nolte, M. J.; Gafner, G. Acta Cryetallogr., Sect. B 1974,830, 738. (7) (qO-Arene)R&: (a) Bennett, M. A,; Matheson, T. W.; Robertson, G. B.; Smith, A. K.; Tucker, P. A. Inorg. Chem. 1980, 19, 1014. (b) Schmid, H.; Ziegler, M. L. Chem. Ber. 1976, 109, 132. (c) Huttner, G.; m e , S.; Fischer, E. 0. Angew. Chem., Int. Ed. Engl. 1971,10,556. (d) Huttner, G.; Lange, S. Acta Crystallogr., Sect. B 1972, B28,2049. (e) Wemer, H.; Werner, R. Angew. Chem., Int. Ed. Engl. 1978, 17, 683.
13 electrons, these molecules represent extremely electron deficient (q6-arene)ML2-typecomplexes. Further interest in these species arises since the arene ligand was assembled at the metal center by alkyne cyclization c h e m i s e " and since they represent rare examples of tantalum(I1) or(8) ($B-Arene)FeL*: (a) Green, M. L. H.; Wong, L. L. J. Chem. SOC., Chem. Commun. 1984, 1442. (b) Radonovich, L. J.; Eyring, M. W.; Groehens,T. J.; Klabunde, K. J. J. Am. Chem. SOC.1982,104,2816. (c) Weber, S. R.; Brintzinger, H. H. J. Organomet.Chem. 1977,127,45. (d) Itbl, S. D.; Tolman, C. A. J. Organomet. Chem. 1979,172, C47. (9) (q6-Arene)N&: (a) Radonovich,L. J.; Koch, F. J.; Albright, T. A. Inorg. Chem. 1980,19,3373. (b) Klabunde, K. J.; Andereon, B. B.; Bader, M.; Radonovich, L. J. J. Am. Chem. SOC.1978,100, 1313. (10) See, for example: (a) Gardner, T. G.; Guolami, G. S. Angew. Chem., Int. Ed. Engl. 1988,27,1693. (b) Cloke, F. G. N.; Courtney, K. A. E.; Sameh, A. A.; Swain, A. C. Polyhedron 1989,8,1641. (c) King,R. B.; Braitach, D. M.; Kapoor, P. N. J. Am. Chem. SOC. 1971,97,60. (d) Cloke, F. G. N.; Dix, A. N.; Green, J. C.; Perutz, R.N.; Seddon, E. A. Organometallics 1983,2, 1150. (e) Solari, E.; Floriani, C.; Chieei-Villa A.; Guastini, C. J. Chem. SOC.,Chem. Commun. 1989,1747. (0 Cloke, F. G. N.; Green, M. L. H. J. Chem. SOC.,Dalton Tram. 1981, 1938. (11) Radonovich,L. J.; Klabunde, K. J.; Behrens, C. B.; McCollor, D. P.; Anderson, B. B. Inorg. Chem. 1980,19,1221. (12) (a) Bruck, M. A.; Copenhaver, A. 5.;Wigley,D. E. J. Am. Chem. SOC.1987,109,6525. (b) Ballard, K. R.; Gardiner, I. M.; Wigley, D. E. Ibid. 1989,111, 2159. (13) Wexler, P. A.; Wigley, D. E.J. Chem. SOC.,Chem. Commun. 1989, 664. (14) Amey, D. J.; Wexler, P. A,; Wigley, D. E. Organometallics 1990, 9, 1282.
0276-7333/91/2310-2319$02.50/0 0 1991 American Chemical Society
Werler et al.
2320 Organometallics, Vol. 10, No. 7, 1991 ganometallics.16 The molecular structure of one of these species, (?f-C6Eh)Ta(DIPP), (where DIPP = 2,6-diisopropyl phenoxide) has been determined and is shown to exhibit some unusual structural properties; thus, molecular orbital calculations at the extended Huckel and ab initio level on (~6-C6H6)Ta(oH), are used to investigate the bonding and geometric distortions for these molecules. A portion of this work has been ~0mmunicated.l~ Experimental Section General Synthetic Details. All syntheses were performed under a nitrogen atmosphere either by standard Schlenk techniques16 or in a Vacuum Atmospheres HE-493 drybox at room temperature (unless otherwise indicated). Solvents were purified under Nz by standard techniques17and transferred to the drybox without exposure to air. Ta(DIPP)2C13(OEt2)14and ($C6Me6)Ta(DIPP)2C1izb (2) (DIPP = 2,6-diisopropyl phenoxide) were prepared as described previously. Allyl bromide, 1,2-dibromoethane, and iodoethane were obtained from Aldrich, and 3-hexyne was purchased from Farchan Laboratories. These reagents were passed down a short (ca. 5-6 cm) column of activated alumina (at ca. -10 "C) prior to use. The "cold" solvents used to wash isolated solids were at ca. -30 "C. Physical Measurements. lH (250 MHz) and 13C (62.9 MHz) NMR spectra were recorded at probe temperature (unless otherwise specified) on a Bruker WM-250spectrometer in C6D6 solvent. Chemical shifts are referenced to protio impurities (6 7.15) or solvent l9C resonances (6 128.0) and are reported downfield of Me,Si. Infrared spectra in the region 1600-180 cm-' were recorded as CsI pellets on a Perkin-Elmer PE-983 spectrometer or from 4000 to 600 cm-' as a Nujol mull (NaC1 plates) on a Perkin-Elmer 1310 instrument and were not assigned. Molecular weight measurements were determined by vapor pressure osmometry, using a device similar to one previously described.18 Cyclic voltammetry experiments were performed under a nitrogen atmosphere with a BioAnalytical Systems CV-27 voltammograph and recorded on a Houston Instruments Model 100 X-Y recorder. Msasurementa were taken at a Pbdisk electrode in THF solutions containing 0.1 M n-Bu4NPF6as supporting electrolyte. voltammograms were recorded at room temperature at a sweep rate of 150 mV/s. Potentials were referenced to Ag/AgCl and are uncorrected for junction potentials. Magnetic moment measurementa were performed by the Evan's method1@ on c& solutions (250 MHz) at probe temperature, and frequency shifts were measured for solvent protio impurity resonances. Diamagnetic corrections (xdi.) were calculated from Pascal's constants.20 X-Band ESR spectra were recorded on toluene solutions by using a Varian E-3 spectrometer. All microanalytical samples were handled under nitrogen and were combusted with WOa (Desert Analytics, Tucson, AZ). Preparations. (q%E&.)Ta(DIPP)@l(l). A solution of 2.00 g (2.79 mmol) of Ta(DIPP)2C13(0Eh)in 50 mL of diethyl ether was prepared and cooled to -40 OC. To this stirred solution were added 1.00 mL (8.80 mmol) of 3-hexvne and 2.00 mL (5.60 "01) of a 0.47% NaHg amalgam. Afte; being stirred at'room temperature for 1 h, the resulting blue solution was filtered through ~
~~
~
(16) (a) Curtis has recently prepared tantalum(I1) or anometallic complexes of the form [(~s-C,Mes~Ta(CO)~Cll~ and [($-CsMes)Ta(PhCICPh)CI]*, similar to hie prevlously reported niobium analogues. We thank Prof. M. D. Curtis (University of Michigan) for informing us of them results. For Curtir' niobium(I1)complexes, see: Curtis, M. D.; Real, J. Organometallics 1986,4,940. (b) A compound of the apparent formulation [TaBr (C6Me,J], hae been reported (ref 1Oc) and the Ta(I1) complex P'a#dC&ef may have been isolated in an impure s t a b , see: Fmher, E. R6 c eid, F. J. Orgonomet. Chem. 1966, 6, 53. (18) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-Send i v e Compounds, 2nd ed.; John Wiley and Sone: New York, 1986. (17) Pemn, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals, 3rd ed.; Pergamon Press: Oxford, U.K. 1988. (18) Burger, B. J.; Bercaw, J. E. In Experimental Organometallic Chemistry, Wayda, A. L., Darensbourg, M. Y., EMS.; ACS Symposium S d e a 367; American Chemical Society: Washington, DC, 1987. (19) Evans, D. F. J. Chem. SOC.1969,2003. (20) Selwood, P. W. Magnetochemistry; Interscience Publishers, Inc.; New York, 1956.
Celite (EhO wash) and the solvent was removed from the filtrate in vacuo. The resulting blue solid was washed with 5-10 mL of cold pentane, filtered off, and dried in vacuo to provide 1.22 g (1.49 mmol, 53% yield) of product. This compound was recrystallized from toluene/pentane solutions to afford analytically pure samples. 'H NMR (C6D6): 6 7.11-6.93 (A2B m, 6 H, H I), 3.23 (spt, 4 H, CHMez), 2.37 (4, 12 H, CH2CH31, 1.19 (d, 2 4 3 , CHMeJ, 1.09 (t,12 H, CH2CH3). '9C NMR ( C a d : 6 156.1 (C , 137.1 (Co), 126.8 (c&), 123.6 (Cm),122.4 (CJ, 25.7 (CHh e2), r) 25.1 (CHMeJ, 23.9 (CH2CH3),17.7 (CH2CH3). IR (Nujol): 1580 (w), 1435 (s), 1320 (m), 1254 (s), 1193 (sh), 1182 (s), 1098 (m), 1091 (m), 1038 (m), 930 (w), 904 (81,885 (w), 861 (m), 820 (w), 788 (m), 742 (s), 700 cm-' (m). Anal. Calcd for C4z&C10zTa: C, 61.72; H, 7.89. Found: C, 62.30; H, 8.21. (qe-C6Et6)Ta(DIPP)2 (3). (i) From (q6-C6Et6)Ta(DIPP)~l. To a room-temperature solution of 1.00 g (1.22 mmol) of (#C&t,JTa(DIPP),Cl(l) in 20 mL of diethyl ether was added exNaHg amalgam (0.80 mL, 2.44 "01, of a 0.46% amalgaam). After being stirred for 24 h, this mixture was filtered through Celite and the solvent removed from the filtrate in vacuo to afford a red solid. When this solid was dissolved in minimal pentane and the solution cooled to -40 "C, dark red cubes (0.63 g, 0.81 mmol, 66%) formed and were filtered off, washed with minimal cold pentane, and dried in vacuo. Samples of compound obtained in this fashion were analytically pure. (ii) From Ta(DIPP)2C13(OEt2).To a -40 "C solution of 1.00 g (1.40 mmol) of Ta(DIF'P)2C13(OEh)in 25 mL of diethyl ether were added 0.50 mL (4.40 mmol) of 3-hexyne and 2.00 mL (5.60 mmol) of 0.50% NaHg amalgam. The reaction was allowed to stir for 24 h at room temperature. The resulting dark red solution was filtered through Celite, and the filtrate was pumped to dryness. The resulting dark red solid was dissolved in pentane and cooled to -40 "C. A 0.35-g (0.45 mmol, 32% yield) sample of maroon crystals was filtered off, washed with a minimal volume of cold pentane, and dried in vacuo. lH NMR (C6D6)[all resonances are broad, featureless signals (peak width at half-maximum (in Hz) in parentheses)]: 6 9.70 (40), 4.73 (135), 4.06 (80), 3.77 (90). IR (CsI): 1588 (m, w), 1453 (sh), 1434 (s), 1380 (m), 1359 (m), 1336 (s), 1326 (s), 1268 (s), 1258 (s), 1206 (e), 1104 (m), 1057 (m), 1044 (m), 904 (s), 875 (m), 823 (m), 791 (m), 748 (s), 707 (m, s), 593 (m, w), 419 (w), 258 cm-' (w). Molecular weight (EbO solution): calcd. for monomer, 781.9; found, 809 80. Magnetic moment (c6D6 solution): pea = 2.14 pg. Anal. Calcd for Cu&O2Ta: C, 64.52; H, 8.25; C1,O.OO. Found: C, 65.01; H, 8.57; C1,
