Organometallics 1995, 14,4611-4616
4611
Enthalpies of Reaction of (@-cymene)RuC12)2 with Monodentate Tertiary Phosphine Ligands. Importance of both Steric and Electronic Ligand Factors in a Ruthenium(I1) System Scafford A. Serron and Steven P. Nolan* Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148 Received April 28, 1 9 9 P
The enthalpies of reaction of (@-cymene)RuClz)z@-cymene = ( C H ~ ) Z C H C ~ H & H with ~) a series of tertiary phosphine ligands, leading to the formation of (p-cymene)RuCl~(PR3) complexes (PR3 = tertiary phosphine) have been measured by solution calorimetry in CHzClz at 30 "C. The range of reaction enthalpies spans some 22 kcal/mol. The overall relative order of stability established is as follows (PR3; -AH,kcal/mol): P@-CF3CsH4)3 < PCy3 < PCyzPh < P(p-CIC&)3 < P(OPh)3 < PPr3 < PPh3 < P@-FCsH& < P@-cH&&)3 < PCyPhz < P(p-CH30CsH4)3 < P'Bu3 < PBz3 < PPhzEt < PPhzMe < P(OMe)3 < PEt3 < PPhMez < PMe3. A quantitative analysis of ligand effect of the present data helps clarify the exact steric versus electronic ligand contributions to the enthalpy of reaction in this system. Both steric and electronic factors appear to play a n important role in dictating the magnitude of the enthalpy of reaction.
Introduction understanding of ligand-binding afinitylthermochemical studies. We have most recently focused o u r therThe importance of tertiary phosphine ligands in mochemical research efforts toward quantitatively adorganometallic chemistry and catalysis is undeniable.lI2 dressing the relative importance of stereoelectronic Kinetic, catalytic, and structural studies have been factors as they effect enthalpies of ligand substitution conducted on organometallic complexes bearing this reactions present in organo-group 8 metal centersgJO ancillary ligand type.3 In spite of the vast amount of (see eqs 1-3): information focusing on PR3- transition metal complexes, few thermodynamic data regarding heats of binding of these ligands to metal centers e x i ~ t . ~ - ~ Interesting catalytic developments involving organoruthenium complexes would surely benefit from a better @Abstractpublished in Advance ACS Abstracts, September 1,1995. (1)Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; 2nd ed.; University Science: Mill Valley, CA, 1987. Ed. Homogeneous Catalysis with Metal Phosphine (2)Pignolet, L. H., Complezes; Plenum: New York, 1983. (3)(a)Noyori, R.Asymmetric Catalysis in Organic Synthesis; Wiley and Sons, Inc.: New York, 1994,and references cited therein. (b)Burk, M. J.;Harper, G. P.; Kalberg, C. S. J.Am. Chem. SOC.1995,117,44234424 and references cited. (4)For leading references in this area, see: (a)Nolan, S. P. Bonding Energetics of Organometallic Compounds. In Encyclopedia of Inorganic Chemistry; J. Wiley and Sons: New York, 1994.(b) Hoff, C. D. Prog. Inorg. Chem. 1992,40, 503-561. ( c ) Martinho SimBes, J. A.; Beauchamp, J. L. Chem. Rev. 1990,90,629-688. (d) Marks, T. J., Ed. Bonding Energetics in Organometallic Compounds; ACS Symposium Series 428;American Chemical Society: Washington, DC, 1990.(e) Marks, T.J.,Ed. Metal-Ligand Bonding Energetics in Organotransition Metal Compounds; Polyhedron Symposium-in-Print 7;Pergamon: New York, 1988.(0 Skinner, H. A.; Connor, J. A. In Molecular Structure and Energetics; Liebman, J. F., Greenberg, A., Eds; VCH: New York, 1987;Vol. 2,Chapter 6. (g) Skinner, H.A.; Connor, J. A. Pure Appl. Chem. 1985,57,79-88. (h) Pearson, R. G. Chem. Rev. 1985,85,4159.(i) Mondal, J. U.; Blake, D. M. Coord. Chem. Rev. 1983,47,204(k) Pilcher, 238.(i) Mansson, M. Pure Appl. Chem. 1983,55,417-426. G.;Skinner, H. A. In The Chemistry of the Metal-Carbon Bond; Hartley, F..R., Patai, S., Eds.; Wiley: New York, 1982;pp 43-90. (1) Connor, J. A. Top. Curr. Chem. 1977,71,71-110. ( 5 ) For a recent review of energetics of phosphorus(II1) ligands to transition metal centers, see: Dias, P. B.; Minas de Piedade, M. E.; Martinho SimGes, J. A. Coord. Chem. Rev. 1994,1351136,737-807. (6)Nolan, S. P.; Lopez de la Vega, R.; Hoff, C. D. Organometallics l986,5,2529-2537. (7)(a) Manzer, L. E.; Tolman, C. A. J. Am. Chem. SOC.1975,97, 1955-1986. (b) Tolman, C. A.; Reutter, D. W.; Seidel, W. C. J. Organomet. Chem. 1976,117,C30-C33.
THF
+ 2pR3(so1n) tran~-(PR3)2Fe(C0)3(~~l,) + BD&,,ln) (3)
(BDA)Fe(C0)3(so1n)
Cp = C,H,; Cp* = C,Me,; BDA = PhCH=CHCOMe; PR3 = tertiary phosphine We recently extended this work to emphasize the importance of electronic factors in a series of parasubstituted triphenyl phosphine ligands with this (LhFe(co)~ system.l°C (8)(a) Nolan, S.P.; Hoff, C. D. J. Organomet. Chem. 1985,290,365373.(b) Mukerjee, S. L.; Nolan, S. P.; Hoff, C. D.; de la Vega, R. Inorg. Chem. 1988,27,81-85. (9)For organoruthenium systems, see: (a) Nolan, S. P.; Martin, K. L.; Stevens, E. D.; Fagan, P. J. Organometallics 1992,11,3947-3953. (b) Luo, L.; Fagan, P. J.; Nolan, S. P. Organometallics 1993,12,34053411. (c) Luo, L.;Zhu, N.; Zhu, N.-J.; Stevens, E. D.; Nolan, S. P.; Fagan, P.J. Organometallics 1994,13,669-675. (d) Li, C.; Cucullu, M. E.; McIntyre, R. A,; Stevens, E. D.; Nolan, S. P. Organometallics 1994,13,3621-3627. (e) Luo, L.; Li, C.; Cucullu, M. E.; Nolan, S. P. Organometallics 1995,14,1333-1338. (10)For organoiron systems, see: (a) Luo, L.; Nolan, S. P. Organometallics 1992,11,3483-3486. (b) Luo, L.;Nolan, S. P. h o g . Chem. 1993,32,2410-2415. (c) Li, C.; Nolan, S. P. Organometallics 1995, 14,1327-1332.
0276-733319512314-4611$09.00/00 1995 American Chemical Society
4612 Organometallics, Vol. 14,No. 10, 1995 PR,
PR3 = P(p-XC,H,),; X = H, C1, F, Me. MeO,CF,
In the present contribution, a ruthenium(I1) arene system is investigated by solution calorimetry in order to gauge the relative importance of stereoelectronic phosphine factors on the enthalpy of ligand substitution. These results allow for a comparison with previously investigated thermochemical results of organo-group 8 systems. Experimental Section General Considerations. All manipulations involving organoruthenium complexes were performed under inert atmospheres of argon or nitrogen using standard high-vacuum or Schlenk tube techniques, or in a VacuudAtmospheres glovebox containing less than 1 ppm oxygen and water. Ligands were purchased from Strem Chemicals or Organometallics, Inc., and were used as received. Methylene chloride was distilled from P& into flame-dried glassware prior to use. Only materials of high purity as indicated by NMR spectroscopy were used in the calorimetric experiments. NMR spectra were recorded using a Varian Gemini 300 MHz spectrometer. Calorimetric measurements were performed using a Calvet calorimeter (Setaram C-80) which was periodically calibrated using the TRIS reaction1' or the enthalpy of solution of KC1 in water.12 The experimentally determined enthalpies for these two standard calibration reactions are the same within experimental error t o literature values. This calorimeter has been previously described,13 and typical procedures are described below. Experimental enthalpy data are reported with 95% confidence limits. lH NMR Titrations. Prior to every set of calorimetric experiments involving a new ligand, an accurately weighed amount (f0.1mg) of the organoruthenium complex was placed in a Wilmad screw-capped NMR tube fitted with a septum, and CDzClz was subsequently added. The solution was titrated with a solution of the ligand of interest by injecting the latter in aliquots through the septum with a microsyringe followed by vigorous shaking. The reactions were monitored by 'H NMR spectroscopy, and the reactions were found to be rapid, clean, and quantitative under experimental calorimetric conditions. These conditions are necessary for accurate and meaningful calorimetric results and were satisfied for all organoruthenium reactions investigated. Only reactants and products were observed in the course of the NMR titration. Calorimetric Measurement for Reaction between ((pcymene)RuCl~)z and Trimethylylphosphine. The mixing vessels of the Setaram C-80 were cleaned, dried in an oven maintained at 120 "C, and then taken into the glovebox. A 20-30 mg sample of 1 was accurately weighed into the lower vessel, which was closed and sealed with 1.5 mL of mercury. A 4 mL aliquot of a 25% stock solution of diphos (1g of PMe3 in 25 mL of CH2C12) was added, and the remainder of the cell was assembled, removed from the glovebox, and inserted in the calorimeter. The reference vessel was loaded in an identical faslyon with the exception that no organoruthenium complex was added to the lower vessel. After the calorimeter had reached thermal equilibrium at 30.0 "C (about 2 h), the vessels were removed from the calorimeter, taken into the glovebox, opened, and analyzed using IH NMR spectrocopy. (11) Ojelund, G.;Wadso, I. Acta Chem. Scand. 1968,22,1691-1699. (12)Kilday, M. V. J . Res. Natl. Bur. Stand. (US.)1980,85, 467-
481. (13)Nolan, S.P.; Hoff, C. D. J . Organomet. Chem. 1986,282,357362.
Serron a n d Nolan Conversion to (p-cymene)RuCMPMes) was found to be quantitative under these reaction conditions. The enthalpy of reaction, -50.2 f 0.1 kcal/mol, represents the average of five individual calorimetric determinations. The enthalpy of solution of 1 was then added to this value to obtain a value of -55.3 f 0.2 kcaVmol for all species in solution. Calorimetric Measurement of Enthalpy of Solution of (@-cymene)RuCl2)2in CHZC12. In order to consider all species in solution, the enthalpies of solution of 1 had to be directly measured. This was performed by using a procedure similar to the one described above with the exception that no ligand was added to the reaction cell. This enthalpy of solution represents the average of five individual determinations and is worth 5.1 i 0.1 kcaVmo1. Synthesis. The compound [RuCl2(p-cymene)lz (1) was synthesized according to the literature procedure.14 Other organoruthenium complexes, (p-cymene)RuCl~(PPhd,( p cymene)RuCl~(PCy3),(p-cymene)RuCl2(P(p-MeCsH4)3), ( p cymene)RuCl~(PPh2Me),(p-cymene)RuClz(PPhMez),and 07cymene)RuClz(P(OPh)d, have previously been reported.15 Experimental synthetic procedures, leading to isolation of previously unreported complexes, are described below. @-cymene)RuCl2(PBz3)(2). A 50 mL flask was charged with 60 mg (0.20 mmol) of PBz3 (tribenzyl phosphine), 61 mg (0.10 mmol) of [RuClz(p-cymene)]z,and 15 mL of CH2C12. The clear wine red solution was stirred at room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with 50 mL of hexane, filtered, and dried under vacuum, which afforded 67 mg of the product (yield: 66%). IH-NMR (300 MHz,CDC13): 1.18 (d, 6H, 2CH3), 1.67 (s, 3H, -CH3), 2.65 (m, lH, -CHI, 3.36 (d, 6H, P-CHd, 4.57 (d, 2H, -CsH4), 5.06 (d, 2H, -CsH4), 7.20 (m, 15H, Ph). Calcd for C31H35RuC12P: C, 60.97; H, 5.78. Found: C, 60.77; H, 5.75. @-cymene)RuCl2(PCyPhz) (3). A 50 mL flask was charged with 103 mg (0.38 mmol) of PCyPhz (cyclohexyldiphenylphosphine), 98 mg (0.16 mmol) of [RuClz(p-cymene)l2,and 15 mL of CH2C12. The clear wine red solution was stirred at room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with 50 mL of hexane, filtered, and dried under vacuum, which afforded 116 mg of the product (yield: 63%). lH-NMR (300 MHz,CDC13): 0.5, 0.9 (m, 2H, P-Cs&), 1.00 (d, 6H, 2CH3), 1.23 (m, 2H, P-CGHll), 1.55 (m, 2H, P-C&d, 1.79 (s, 6H, -CH3), 2.15 (m, 2H, P-csH~d,2.65 (m, lH, -CHI, 3.05 (m, lH, P-CsHd, 4.77 (d, 2H, -CsH4), 4.95 (d, 2H, -CsH4), 7.45 (m, 8H, P-Ph), 7.92 (m, 2H, P-Ph). Calcd for C2sH35RuC12P: C, 58.53; H, 6.14. Found: C, 58.38; H, 6.21. (p-cymene)RuC12(PiPr3)(4),. A 50 mL flask was charged with 70 mL (0.36 mmol) of P'Pr3 (triisopropylphosphine), 100 mg (0.16 mmol) of [RuCl2(p-cymene)l2,and 15 mL of CH2C12. The clear wine red solution was stirred at room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with 50 mL of hexane, filtered, and dried under vacuum, which afforded 113 mg of the product (yield: 74%). 'H-NMR (300 MHz,CDC13): 1.30 (d, 6H, 2CH3), 1.33 (d, 18H, CH3), 2.08 (s, 3H, -CH), 2.74 (m, lH, -CHI, 5.57 (9, 4H, -C6H4). Calcd for C19H35RuC12P: C, 48.92; H, 7.57. Found: C, 48.38; H, 7.21. @-cymene)RuClz(PMeS)(5). A 50 mL flask was charged with 45 mL (0.44 mmol) of PMe3 (trimethylphosphine), 115 mg (0.19 mmol) of [RuClz(p-cymene)lz,and 15 mL of CHzC12. The clear wine red solution was stirred a t room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with 50 mL of hexane, filtered, and dried under vacuum, which afforded 98 mg of the (14)Bennett, M. A,; Huang, T.-N.; Matheson, T.W.; Smith, A. K. Inorg. Synth. 1982,21,74-79. (15)(a) Demonceau, A,; Noels, A. F.; Saive, E.; Hubert, A. J. J.Mol. Cat. 1992,76,123-132.(b) Zelonka, R.A,; Baird, M. C. Can. J . Chem. 1972,50,3063-3072.( c ) Petrici, P.; Bertozzi, S.; Lazzaroni, R.; Vitulli, G.; Bennett, M. A. J . Organomet. Chem. 1988,354,117-121.
Enthalpies of Reaction of ((p-cymene)RuCl& product (yield: 68%). 'H-NMR (300 MHz,CDCL): 1.16 (d, 6H, 2CH3), 1.57 (d, 9H, P-CHs), 2.02 (s, 3H, -CH3), 2.80 (m, lH, -CH), 5.38 (s, 4H, -C6H4). Calcd for C13H23RuC12P C, 40.84; H, 6.07. Found: C, 40.75; H, 6.01. (p-cymene)RuCl2(PEt3) (6). A 50 mL flask was charged with 70 mL (0.48 mmol) of PEt3 (triethylphosphine), 110 mg (0.18 mmol) of [RuClz(p-cymene)lz,and 15 mL of CH2C12. The clear wine red solution was stirred at room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with 50 mL of hexane, filtered, and dried under vacuum, which afforded 110 mg of the product (yield: 72%). 'H-NMR (300 MHz, CDC13): 1.11(p, 9H, P-CH2CH31, 1.21 (d, 6H, 2CH3), 2.02 (p, 6H, PCHCH), 2.07 (8, 3H, -CH3), 2.85 (m, lH, -CH), 5.39 (q, 4H, -C&). Calcd for C16Hz&uClzP: C, 45.28; H, 6.89. Found: C, 44.90; H, 6.76. (p-~ymene)RuClz(P(OMe)3) (7). A 50 mL flask was charged with 43 mL (0.35 mmol) of P(OMe)3(trimethylphosphite), 110 mg (0.18 mmol) of [RuClz(p-cymene)lz,and 15 mL of CHzClZ. The clear wine red solution was stirred a t room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with ca. 50 mL of hexane, filtered, and dried under vacuum, which afforded 98 mg of the product (yield: 63%). 'H-NMR (300 MHz,CDCls): 1.20 (d, 6H, 2CH3), 2.14 (5, 3H, -CH3), 2.88 (m, lH, -CH), 3.75 (d, 9H, POCHs), 5.37 (d, 2H, -CsH4), 5.53 (d, 2H, -Ca4). Calcd for C ~ ~ H Z ~ R U C ~C,Z36.28; P O ~ H, : 5.39. Found: C, 36.58; H, 5.10. (p-cymene)RuCl2(PCySh) (8). A 50 mL flask was charged with 120 mg (0.44 mmol) of PCyzPh (dicyclohexylphenylphosphine), 110 mg (0.18 mmol) of [RuClz@-cymene)lz,and 15 mL of CHZC12. The clear wine red solution was stirred at room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with 50 mL of hexane, filtered, and dried under vacuum, which afforded 135 mg of the product (yield: 65%). IH-NMR (300 MHz,CDCls): 1.07 (d, 6H, 2CH31, 1.24 (m, P(CsH11)z), 1.40 (m, P(csH11)2), 1.71 (9, 3H, -CH3), 1.80 (m, P(C~&)Z),2.50 (m, lH, -CH), 2.65 (m, P(C~HII)Z), 2.80 (9, P(C6H11)z),4.95 (dd, 4H, -C6H4), 7.35 (m, 3H, PPh), 7.72 (m, 2H, PPh). Calcd for C28H41RuClZP: C, 57.93; H, 7.12. Found: C, 57.59; H, 7.14. (p-cymene)RuC12(PiBus) (9). A 50 mL flask was charged with 74 mL (0.37 mmol) of P'Bu3 (triisobutylphosphine), 110 mg (0.18 mmol) of [RuClz(p-cymene)l~,and 15 mL of CH2C12. The clear wine red solution was stirred at room temperature for 15 min, after which the solvent was removed under vacuum. The residue was triturated with 50 mL of hexane, filtered, and dried under vacuum, which afforded 125 mg of the product (yield: 68%). 'H-NMR (300 MHz,CDC13): 1.02 (d, 18H, 6CH3), 1.26 (d, 6H, 2CH3), 2.00 (m, 3H, PCH(CH&), 2.08 (s, 3H, -CH3), 2.85 (m, lH, -CH), 5.28 (d, 2H, -C6H4), 5.42 (d, 2H, -C6H4). Calcd for CzzH41RuClzP: C, 51.95; H, 8.13. Found: C, 51.55; H, 8.20. (p-~ymene)RuC12(PEtPh~) (10). A 50 mL flask was charged with 74 mL (0.35 mmol) of PEtPhz (ethyldipheof ERuCl~@-cymene)l~, and nylphosphine), 110 mg (0.18 "91) 15 mL of CHzClZ. The clear wine red solution was stirred at room temperature for 15 min, after which time the solvent was removed under vacuum. The residue was triturated with 50 mL of hexane, filtered, and dried under vacuum, which afforded 131 mg of the product (yield: 70%). lH-NMR (300 MHz,CDC13): 0.67 (q, 3H, CH3), 0.77 (d, 6H, 2CH3), 1.86 (s, 3H, -CH3), 2.55 (m, lH, -CHI, 2.55 (q,2H, P-CHZCH~),5.05 (d, ZH, -CsH4), 5.24 (d, ZH, -CsH4), 7.44 (t, 6 H, PPh), 7.85 (t, 4 H, PPh). Calcd for C24HzgRuClzP: C, 55.38; H, 5.62. Found: C, 54.85; H, 5.26. (p-cymene)RuClz(P(p-ClC~)~) (11). A 50 mL flask was charged with 123 mg (0.34 mmol) of P@-ClCeH4)3 (trisbchlorophenyl)phosphine), 100 mg (0.16 mmol) of [RuClz@cymene)]^, and 15 mL of CHzC12. The clear wine red solution was stirred at room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with 50 mL of hexane, filtered, and dried under vacuum, which
Organometallics, Vol. 14,No.10,1995 4613 afforded 122 mg of the product (yield: 56%). 'H-NMR (300 MHz, CDCl3): 1.10 (d, 6 H, 2CH3), 1.83 (s, 3H, -CH3), 2.85 (m, l H , -CH), 4.94 (d, 2H, -C6H4), 5.23 (d, 2H, -C6H4), 7.32 (d, 6H, PPh), 7.70 (t, 6H, PPh). Calcd for CzsH~6RuC15P:C, 50.15; H, 3.91. Found: C, 49.73; H, 3.73. (p-cymene)RuClz(P@-CHsOCsH4)3)(12). A 50 mL flask was charged with 120 mg (0.34 mmol) of P(p-CH30C6&)3 (tris(p-methoxyphenyl)phosphine), 100 mg (0.16 mmol) of [RuClz(pcymene)lz, and 15 mL of CH2ClZ. The clear wine red solution was stirred at room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with ca. 50 mL of hexane, filtered, and dried under vacuum, which afforded 133 mg of the product (yield: 62%). lH-NMR (300 MHz, CDCl3): 1.10 (d, 6 H, 2 CH3), 1.83 (s,3 H, -CH3), 2.85 (m,l H , -CH), 3.78 (s, 3H, OCH3), 4.91 (d, 2H, -C6H4), 5.21 (d, 2H, -C&), 6.83 (d, 6H, PPh), 7.71 (t,6H, PPh). Calcd for C ~ I H ~ ~ R U C C, ~ ~56.53; P O ~ H, : 5.36. Found: C, 56.34; H, 5.01. (p-cymene)RuClz(P(p-CFsCeH4)s) (13). A 50 mL flask was charged with 152 mg (0.32 mmol) of P(p-CF&6H4)3 [tris(p-trifluoromethylphenyl)phosphinel,99 mg (0.16 mmol) of [RuCl2@-cymene)]z,and 15 mL of CHzC12. The clear wine red solution was stirred at room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with ca. 50 mL of hexane, filtered, and dried under vacuum, which afforded 180 mg of the product (yield: 72%). 'H-NMR (300 MHz,CDClS): 1.05 (d, 6H, 2CH3), 1.87 (9, -CH3), 2.80 (m, lH, -CHI, 5.02 (d, 2H, -C6H4), 5.22 (d, 2H, -C6H4), 7.63 (d, 6H, PPh), 7.95 (t, 6H, PPh). Calcd for C ~ ~ H Z ~ R U C ~ Z PFs: C, 48.19; H, 3.39. Found: C, 47.89; H, 3.24. (p-~ymene)RuCl2(P@-FCsH4)s) (14). A 50 mL flask was charged with 114 mg (0.36 mmol) of P(p-FC6&)3 [tris(pfluorophenyl)phosphine], 110 mg (0.18 mmol) of [RuClz(pcymene)]^, and 15 mL of CHzClZ. The clear wine red solution was stirred at room temperature for 15 min, after which the solvent was removed under vacuum. The residue was washed with ca. 50 mL of hexane, filtered, and dried under vacuum, which afforded 140 mg of the product (yield: 63%). 'H-NMR (300 MHz, CDCl3): 1.11(d, 6H, -CH3), 1.83 (s, 3H, -CH3), 2.85 (m, l H , -CHI, 4.93 (d, 2H, -C6H4), 5.24 (d, 2H, -C6H4), 7.05 (t, 6H, PPh), 7.77 (m, 6H, PPh). Calcd for C&&uC12PF3: C, 54.02; H, 4.21. Found: C, 53.76; H, 4.01.
Results A facile entryway into the thermochemistry of (pcymene)Ru(PR,)Clncomplexes is made possible by the rapid and quantitative reaction of [(p-cymene)RuClzIz (1)with a variety of phosphine ligands (see eq 5). This
PR3= tertiary phosphine
type of phosphine-binding reaction appears general and was found to be rapid and quantitative for all ligands calorimetrically investigated at 30.0 "C in methylene chloride. A compilation of phosphine and phosphite ligands along with their respective enthalpies of reaction where all species are in solution is listed in Table 1. Discussion The complex [(p-cymene)RuClzlz(1) and some of its phosphine derivatives have been demonstrated as efficient catalystkatalyst precursors. Demonceau and coworkers have, for example, shown 1 and some of its phosphine derivatives to be efficient precursors for the
Serron and Nolan
4614 Organometallics,Vol. 14,No. 20, 1995 -
Table 1. Enthalpies of Substitution (kcaYmol) in the Reaction
A
CH,Cl,
[RuCl,(~-c~mene)l~(,o~n~ + "(soln~
A
30"~-
A
A
BR~Cl~(p-cymene)(PR~)~,~~~,
1
I
34.6 f 0.2 RuClz(p-cymene)(P(p-clC6H4)3) 34.8 f 0.2 R u C l & - c b e n e ) ( PC&Ph)
35.5 f 0.3 35.6 f 0.2 36.3 f 0.1 RuCl~(p-cymene)(P(p-FCsH4)3) 36.5 f 0.3 RuCl~(p-cymene)(P(p-MeCsH4)3) 37.6 f 0.3 RuClz(p-cymene)(PCyPhz) 38.8 f 0.4 RuCl~@-cymene)(P(p-MeOCsH4)3)39.0 f 0.5 RuClz(p-cymene)(P'Bua) 39.6 f 0.1 RuClz(p-cymene)(PBza) 40.7 f 0.3 RuClZ@-cymene)(PEtPhz) 45.2 f 0.2 RuClz(p-cymene)(PPhzMe) 45.6 f 0.3 RuClz(p-cymene)(P(OMe)a) 45.9 f 0.4 RuClz@-cymene)(PEt~) 51.3 f 0.3 RuClz(p-cymene)(PPhMez) 52.5 f 0.3 RuClz(p-cymene)(PMe3) 55.3 i 0.2
RuClz@-cymene)(P(OPh)3) RuClz@-cymene)(PiPr3) RuClz(p-cymene)(PPhd
a
Enthalpy values are reported with 95% confidence limits.
ring-opening metathesis polymerization of 01efins.l~ Faller and Chase have recently reported on the utilization of phosphine derivatives of 1 as synthetic precursors leading to the facile isolation of stable rutheniumolefin-hydride complexes (eq 6).16 Grubbs and Nguyen,
l+
Ph
in synthetic studies related t o their investigations on ring-opening and ring-closing metathesis reactions,17 have recently employed 1 as a synthon, leading to the isolation of catalytically active ruthenium-carbene complexes, (PR3)2C12Ru(CH=CH=CPhz) (eq 7).18 On
+ 4PR3 + 2cyclopropene 2Ru(PR3),C12(=CH-CH=CPh,) + cymene
((cymene)RuCl,),
(7)
PR3 = PCy, and P'Pr, the basis of these recent observations concerning the reactivity of (l),thermochemical studies were undertaken in order t o quantify the enthalpic driving forces behind the fragmentation and ligand binding observed for this dimeric complex. Enthalpies of reaction associated with phosphine coordination t o the @-cymene)RuC12 fragment are presented and discussed in this contribution. (16)Faller, J.; Chase, K. J. Organometallics 1996,14,1592-1600. (17)(a) Nguyen, S.T.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W. J . Am. Chem. SOC.1992,114,3974-3975.(b) Fu,G. C.; Nguyen, S. T.; Grubbs, R. H. J . Am. Chem. SOC.1993,115, 9856-9857. ( c ) Nguyen, S.T.; Grubbs, R. H.; Ziller, J. W. J . Am. Chem. SOC.1993,115,98589859. (18)Nguyen, S.T.; Grubbs, R. H. Personnal communication.
-60
-55
-50 -45 -40 Enthalpy of Reaction (kcalhol)
-35
-30
Figure 1. Enthalpy of reaction (kcal/mol) versus the phosphine cone angle (deg); slope = 1.674,R = 0.80.
Relative Importance of SteridElectronic Ligand Factors. The thermodynamic entryway into this system is made possible by the rapid and quantitative nature of reaction 5 with a series of tertiary phosphine ligands. The enthalpy of reaction data found in Table 1 allow for an interpretation of the factors influencing the strength of the Ru-PR3 bond in @-cymene)RuClz(PR3)complexes. The enthalpy values presented in the Table 1 are based on a molar amount of the dimer and span some 22 kcallmol. This represents a variation of the single Ru-PR3 bond disruption enthalpy of some 11 kcdmol as a function of varied tertiary phosphine ligand. It can readily be seen from these reaction enthalpy data that the most sterically demanding phosphines are the weakest binders, this resulting from a possible combination of steric and electronic factors. In order to quantify the relative role of sterics vs. electronics in this phosphine system, a relationship first proposed by Tolmanlg in which enthalpies of reaction are correlated t o steric (0, cone angle) and electronic (Y, A1 carbonyl stretching frequency in Ni(C0)3L, L = tertiary phosphine) factors was used (eq 8). Treatment
- A H = A , + A l e +A,Y (8) of the data in Table 1 according to eq 8 affords the following parameters: A, = -1057.1; A1 = 0.4542; A2 = 0.4600; R = 0.88. These results can be compared t o earlier studies where the A1IA2 ratio was taken as a gauge of the relative importance of the steric vs. electronic factor. In the diaxial (L)2Fe(C0)3,this ratio was found to be 0.008, indicating an overwhelming influence of the electronic component.loa This makes chemical sense since both PR3 ligands occupy mutually trans coordination sites in the iron system. In a more closely related organoruthenium(I1) system, Cp*Ru(L)2C1, the ratio was calculated as 2.31, showing a slightly larger influence of the steric parameter.gb In the present system, there does not appear t o be an obvious dominant factor, and the A1IAz ratio is 1.0. Graphically, this is illustrated in Figure 1, where a single component relationship does not yield a good correlation. It should also be stated that a similar relationship with the electronic parameter does not lead to a linear relationship (R= 0.10). A number of other groups have been interested in discriminating between steric and electronic ligand (19)Tolman, C. A. Chem. Rev. 1977,77, 313-348.
Enthalpies of Reaction of ((p-cymene)RuClJZ
factors.20~21Giering and co-workers have applied a related but more quantitative test of kinetic and thermodynamic data t o this question of stereoelectronic contributions.22 Results of this treatment are presented in eq 9, where AH is the enthalpy of reaction (kcaV
--AH = -0.698 f 0.189x - 0.536 f 0.04080.302 f O.770Ea,
+ 125.55 f 6.34 (9)
mol), x is the electronic parameter associated with a given phosphine ligand, 8 represents the phosphine steric factor, A is a switching function that turns the steric effect when the size of the ligand exceeds the steric threshold (that is, A = 0 when 8 is less than the steric threshold angle and A = 1when 8 is greater than the threshold angle value), and Ear is the phosphine aryl substituent contribution. All phosphine parameter values (with the exception of the enthalpy data) utilized in the treatment have previously been reported by Giering and Prock.22 The correlation coefficient depicts the excellent fit of the data to this model. This treatment was performed for 15 ligandsz3 and yields R2 = 0.960 as a representation of the goodness of the fit. Here, no clear-cut conclusion can be drawn about the relative overwhelming importance of one factor over the other. The steric and electronic factors both appear to contribute in a relatively equal fashion to the enthalpy of reaction in the @-cymene)RuClz(PR3) system. The relatively poor correlation obtained for the electronic vs. enthalpy data might point toward a small enthalpic contribution from the electronic parameter. We tested this hypothesis by considering a series of isosteric tertiary phosphine ligands. Here, as can be seen in Figure 2, a fair correlation is obtained when the electronic contribution is considered. The electronic factor does have a contribution since a lack of such an effect would have been reflected by a poor or nonexistent correlation in the Hammett relationship. The Hammett a factors are considered as a good indication of electron donating contribution of the para phenyl group. This lack of an effect has been observed for enthalpy data of a series of isosteric phosphines in the Cp’Ru(PR3)zCl (Cp’ = C5H5 and C5Me5) system where steric factors have been determined to play a major role and has been
Organometallics, Vol. 14, No. 10, 1995 4615
8
Y
-
0.4 --
0
m
0.2
-:-
k i7j
t:
5
I
0 ._
-0.2- -
1
-0.4.
--?
33
-.-~
34
~
7-
- -7-T-
i
36 37 30 39 Knllialpy (-AH) of Reaction (kcalhnol) 35
40
Figure 2. Enthalpy of reaction (kcaymol) versus para
substituent Hammett a-parameter; slope = -0.14, R = 0.97. E
% $-
z2
-20
-25
-30 v
3
e
1
-35
16 -40
$ -45 -60
-55 -50 -45 -40 -35 Enlhalpy of Reaction for Ihe (pcymcne)RuC12(PR3) Sysleni
-30
Figure 3. Enthalpies of reaction (kcdmol) of @cymene)RuClz(PR3)versus (PR3)zFe(C0)3(kcaYmo1);slope = 0.686, R = 0.89.
identified as the principal contributor to the enthalpy of reaction (see eq Cp’Ru(COD)Cl(,)
+ 2PR3(,,1,)
-, C P ’ R U ( P R ~ ) Z C+~COD(So1,) ~ ~ ~ ~ ~ ) (10)
R = p-XC,H,; X = C1, F, Me, OMe, CF,, and H
~~
(20) (a) Rahman, M. M.; Liu, H.-Y.; Eriks, K.; Prock, A.; Giering, W. P. Organometallics 1989, 8, 1-7. (b) Liu, H.-Y.; Eriks, K.; Prock, A.; Giering, W. P. Inorg. Chem. 1989, 28, 1759-1763. (c) Poe, A. J. Pure Appl. Chem. 1988, 60, 1209-1216 and references cited therein. (d) Gao, Y.-C.; Shi, &.-Z.; Kersher, D. L.; Basolo, F. Inorg. Chem. 1988, 27, 188-191. (e) Baker, R. T.; Calabrese, J. C.; Krusic, P. J.;Therien, M. J.: Troder. W. C. J. Am. Chem. SOC.1988. 110. 8392-8412. (f, Rahman, fi.M.;Liu, H.-Y.; Prock, A.; Giering, W. P. Organometallics 1987, 6, 650-658. (21) (a) Huynh, M. H. V.; Bessel, C. A,; Takeuchi, K. J. Abstracts of Papers, 208th National Meeting of the American Chemical Society, Washineton. DC. Fall 1994: American Chemical Societv: Washineton. DC, 19g4; INOR.165. (b) Perez, W. J.; Bessel, C. A.; &e, R. F.; cake; C. H.; Churchill, M. R.; Takeuchi, K. J. Abstracts of Papers, 208th National Meeting of the American Chemical Society, Washington, DC, Fall 1994; American Chemical Society: Washington, DC, 1994; INOR 166. (c) Ching, S.; Shriver, D. F. J.Am. Chem. SOC.1989, 111, 32383243. (d) Lee, K.-W.; Brown, T. L. Inorg. Chem. 1987,26,1852-1856. (22) (a)Fernandez, A. L.; Prock, A,; Giering, W. P. Organometallics 1994, 13, 2767-2772 and references cited. (b) Liu, H.-Y.; Eriks, K.; Prock, A.; Giering, W. P. Organometallics 1990, 9, 1758-1766. (c) Lorsbach, B. A,; Prock, A,; Giering, W. P. Organometallics 1995, 14, 1694-1699. (23) Four ligands have been omitted in the analysis (P(OPh)s, P(OMe)3,PB23, and PBu3); these characteristically display deviations from this treatment and have for this reason been omitted. The phosphites have been excluded since they are considered to be a different ligand class.
Comparison with Related Organometallic Systems. Most relevant systems are those revolving around group 8 metal centers. We have been involved in mapping out the thermochemical surfaces of iron and ruthenium complexes. The iron system most closely related to the present ruthenium system involves substitution of similar ligand typeslo (eq 11). Direct (BDA)Fe(C0)3
+ 2PR3
THF
50 OC
PRI
OC-$ico I co
cBDA
(11)
PR3
PR, = tertiary phosphine
comparison of relative bond enthalpy terms can be performed and is conveyed in Figure 3. It is quite surprising that, in spite of a different ancillary ligation and oxidation state, the iron thermochemical data (24) Serron, S. A.; Li, C.; Luo, L.; Cucullu, M. E.; Nolan, S. P. Manuscript in preparation.
Serron and Nolan
4616 Organometallics, Vol. 14, No. 10,1995 -20 -25
24
/
-30
; f -35
1
.40
-45
-60
-60
-55
-50
-45
-40
*35
-30
Reaction Fmthalpy of (p-cymene)RuC12(PR,)Complexes
Figure 4. Enthalpies of reaction (kcdmol) of @-cymene)RuClz(PR3)versus Cp*Ru(PR3)&1(kcdmol); slope = 0.621, R = 0.79.
correlates to the present ruthenium enthalpies of reaction. This might be interpreted according to the argument that the ligand steric factor might play a more important role than denoted by the Tolman or Giering relationships, since the principal factor dictating the enthalpy of reaction in the iron system is steric. A good correlation between the two systems might point toward similar effects contributing in a similar fashion to the enthalpy of reaction. The relationship is noted as interesting, yet absolute conclusions concerning the relative importance of steridelectronic ligand effects cannot (we propose) be based on a system with such dissimilar characteristics. There is no doubt that systems most closely related to the @-cymene)RuClz(PR3)and deserving closer scrutiny are the Cp'Ru(PR3)zCl (Cp' = C5H5 (Cp) and C5Me5 (Cp*)) systems. The available thermochemical information for the Cp*Ru(PR3)&1 systemg is graphically presented and compared with the present @cymene)RuClz(PRs) system in Figure 4. In the Cp* system, phosphine steric factors play a more important role than electronic considerations. Since the two systems presented show important similarities (oxidation state, ancillary ligands), one might expect a linear correlation to exist between the two systems, and the straightforward relationship of the related enthalpies of reaction illustrates this point. A better relationship is obtained for the Cp system , ~ factors (Figure 5), since, as previously r e p ~ r t e dsteric appear to play a less important role in the Cp than in the Cp* system. This would be in line with more even steric and electronic contributions in the present (pcymenehthenium system as compared t o the preva-
-55
-50 .45 -40 Rescuon Enthalpy or (p-cymenc)RuC12(PR,)
-35
-30
Figure 5. Enthalpies of reaction (kcaymol)of @-cymene)RuClz(PR3)versus CpRu(PR3)zCl(kcallmoll;slope = 0.782, R = 0.87. lence of one factor over the other in previously examined systems.
Conclusion The labile nature of the chloride b&dge in [@cymene)RuC12]2 (1) was used t o gain entry into the thermochemistry of ligand binding for monodentate phosphine/phosphite ligands. The enthalpy trend can be explained in terms of electronic and steric contribution to the enthalpy of reaction, with the both constituents playing important roles. A quantitative relationship is established between stereoelectronicand thermodynamic parameters and displays linear correlation. Reactions of monodentate ligands with 1 also show this reaction to be of synthetic use for isolation of complexes of formulation @-cymene)Ru(PR3)Cla.Further thermochemical, kinetic, mechanistic, and catalytic investigations focusing on this and related systems are presently underway.25 Acknowledgment. The Board of Regents of the Louisiana Education Quality Support Fund (LEQSF(RF/1993-96)-RD-A-47)and the National Science Foundation (Grant No. CHE-9305492)are gratefuuy acknowledged for support of this research. The authors are indebted to Johnson-Matthey/Aesar for the generous loan of ruthenium salts. The authors are also indebted to Professors Warren P. Giering and Russell Drago for helpful discussions. OM950308C (25) It has been suggested by one reviewer that structural differences might be present in this system when smaller cone angle phosphines are compared with more sterically demanding ones and that this factor might be correlated to the enthalpy data. We are presently exploring this avenue and thank the reviewer for this suggestion.
