Novel Five-Membered Pallada- and Platinacycles ... - ACS Publications

224

Organometallics 2004, 23, 224-236

Novel Five-Membered Pallada- and Platinacycles Containing a [C(sp2, ferrocene), N, S]- Terdentate Ligand. Theoretical Interpretation of Their Electrochemical and Electronic Properties Based on Density Functional Calculations Sonia Pe´rez,† Concepcioń Lo´pez,*,† Amparo Caubet,† Ramon Bosque,† Xavier Solans,‡ Merce` Font Bardıá,‡ Anna Roig,§ and Elies Molins§ Departament de Quı´mica Inorga` nica, Facultat de Quı´mica, Universitat de Barcelona, Martı´ i Franque` s 1-11, 08028-Barcelona, Spain, Departament de Cristal‚lografia, Mineralogia i Dipo` sits Minerals, Facultat de Geologia, Universitat de Barcelona, Martı´ i Franque` s s/n, 08028-Barcelona, Spain, and Institut de Cie` ncia de Materials de Barcelona (ICMAB-CSIC), Campus de la Universitat Auto` noma de Barcelona, 08193-Bellaterra, Spain Received July 3, 2003

The synthesis of the novel ferrocenyl Schiff base [(η5-C5H5)Fe{(η5-C5H4)CHdN(C6H4-2SMe)}] (1c) and the study of its reactivity versus palladium(II) or platinum(II) salts are reported. These studies have allowed us to isolate and characterize [M{[(η5-C5H3)CHdN(C6H42-SMe)]Fe(η5-C5H5)}Cl] {with M ) Pd (2c) or Pt (3c)}, which are the first examples of cyclopallada- and cycloplatinated compounds containing a mer-terdentate [C(sp2, ferrocene), N, S]- ligand. Mo¨ssbauer spectroscopic studies and the X-ray crystal structures of 1c-3c are reported. The crystal structures of 2c and 3c confirmed the mode of binding of the ligand and revealed that the molecules are associated in pairs, which interact by C-H‚‚‚π interactions forming a chain that stacks along the [101] plane. Electrochemical studies, based on cyclic voltammetry, reveal that the ease with which the oxidation of the ferrocenyl moiety occurs increases according to the sequence 1c < 2c < 3c. Molecular orbital calculations at a DFT level have also been carried out to rationalize the influence of the nature of the Pd(II) (in 2c) or Pt(II) in (3c) on the electrochemical properties of these compounds, and theoretical studies using time-dependent density functional theory (TD-DFT) calculations have also been carried out in order to assign the bands observed in the electronic spectra of the cyclometalated compounds. Introduction Transition metal complexes derived from polydentate ligands containing two or more donor atoms with different hardness have attracted great interest due to their potential hemilability,1 which may be particularly important in view of their potential applications in different areas, including homogeneous catalysis.2 Besides that, during the past decade the importance and utility of a wide variety of cyclopalladated and cycloplatinated complexes3 in several fields has also increased considerably.4-12 †

Departament de Quı´mica Inorga`nica, Universitat de Barcelona. Departament de Cristal‚lografia, Mineralogia i Dipo`sits Minerals, Universitat de Barcelona. § Institut de Cie ` ncia de Materials de Barcelona. (1) (a) Jeffrey, J. C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18, 2658. (b) Bader, A.; Lindner, E. Coord. Chem. Rev. 1991, 108, 27. (c) Stone, C. S.; Weinberger, D.; Mirkin, C. A. Prog. Inorg. Chem. 1999, 48, 232. (2) (a) Jolly, P. W., Wilke, G., Kermann, W. A., Cornils, B., Eds. Applied Homogeneous Catalysis with Organometallic Compounds; VCH: Weinheim, Germany, 1996. (b) Omae, I. Applications of Organometallic Compounds; John Wiley: Chichester, U.K., 1998; Chapter 20. (3) (a) Newkome, R. G.; Puckett, G. E.; Gupta, V. K.; Kiefer, G. E. Chem. Rev. 1986, 86, 45. (b) Dunina, V. V.; Zalevskaya, O. A.; Potatov, V. M. Russ. Chem. Rev. (Engl. Transl.) 1988, 57, 250. (c) Ryabov, A. D. Chem. Rev. 1990, 90, 403. (d) Omae, I. Coord. Chem. Rev. 1988, 83, 137. ‡

A wide variety of pallada- and platinacycle complexes having monoanionic bidentate [C,N]- or [C,S]- or terdentate [C,N,N′]- or [X,C,X]- (X ) N, S, or P) ligands and a σ[M-C(sp2, aryl)] or to a lesser extent a σ(MCsp3) bond (M ) Pd or Pt) have been described in the literature.8-12 Some applications of compounds of this type as building blocks for the synthesis of macromolecules,5 as precursors for the synthesis of organic as well as organometallic compounds,4a-d,6 or even in homoge(4) For a general overview concerning the applications of cyclopallada- and cycloplatinated complexes, see for instance: (a) Klaus, A. J. In Modern Colorants: Synthesis and Structure; Peters, A. E., Freeman, H. S., Eds.; Blackie Academic: London, U.K., 1995; Vol. 3. (b) Pfeffer, M. Rec. Trav. Pays-Bas 1990, 109, 567, and references therein. (c) Ryabov, A. D. Synthesis 1985, 233, and references therein. (d) Spencer, J.; Pfeffer, M. Adv. Metal-Org. Chem. 1998, 6, 103, and references therein. (e) Torraca, K. E.; Kuwabe, S. I.; Buchwald, S. L. J. Am. Chem. Soc. 2000, 122, 12907. (f) Shelby, Q.; Kataoka, N.; Mann, G.; Hartwig, J. J. Am. Chem. Soc. 2000, 122, 10718. (g) Serrano, J. L., Ed. Metallomesogens. Synthesis, Properties and Applications; VCH: Weinheim, Germany, 1996. (h) Eran, B. B.; Singer, D.; Praefcker, K. Eur. J. Inorg. Chem. 2001, 111. (i) Maestry, M. Coord. Chem. Rev. 1991, 111, 117, and references therein. (j) Hambley, T. Coord. Chem. Rev. 1997, 166, 1181. (k) Lippert, B. Coord. Chem. Rev. 1992, 92, 263. (l) Wild, S. B. Coord. Chem. Rev. 1997, 166, 291, and references therein. (m) Thompson, N. J.; Serrano, J. L.; Baena, M. J.; Espinet, P. Chem. Eur. J. 1996, 2, 214, and references therein. (n) Bergbreiter, D. E.; Osburn, P. L.; Liu, Y. S. J. Am. Chem. Soc. 1999, 121, 9531. (o) Dupont, J.; Pfeffer, M.; Spencer, J. Eur. J. Inorg. Chem. 2001, 1917.

10.1021/om030520d CCC: $27.50 © 2004 American Chemical Society Publication on Web 12/19/2003

Novel Five-Membered Pallada- and Platinacycles

neous catalysis have been reported.4e,h,9b In addition, several examples of cyclopalladated as well as cycloplatinated complexes having interesting photooptical properties have been reported in the last five years,7 and some of them have been used as luminiscent centers in the design of organic light-emiting diodes (OLEDs).8 However, despite the potential interest of the presence of three atoms [C, N, and X] of different hardness13 bound to the metal, and the prochiral nature of the ferrocenyl moiety in the cyclometalation process, compounds containing “M[C(sp2, ferrocene), N, X]” (M ) Pd or Pt and X ) N′ or S) cores are scarce.14-16 Recently a few pallada- and platinacycles having [C,N,N′]- groups derived from [(η5-C5H5)Fe{(η5-C5H4)CHdN(CH2)nNMe2] (n ) 2 or 3) have been reported,14,15 but to the best of (5) (a) Slagt, M. Q.; Dijkstra, H. P.; McDonald, A.; Klein-Gebbink, R. J. M.; Lutz, M.; Ellis, D. D.; Mills, A. M.; Spek, A. L.; van Koten, G. Organometallics 2003, 22, 27. (b) Torres-Lo´pez, M.; Fernańdez, A.; Fernańdez, J. J.; Sua´rez, A.; Castro-Juiz, S.; Vila, J. M. Pereira, M. T. Organometallics 2001, 20, 1350. (6) For recent applications of pallada- and platinacycles in organic or organometallic chemistry see for instance: (a) Johnson, J. J.; Sames, D. J. Am. Chem. Soc. 2000, 122, 6321. (c) Baar, C. R.; Jenkins, H. A.; Jennings, M. C.; Yap, G. P. A.; Puddephatt, R. J. Organometallics 2000, 19, 4870. (e) Baar, C. R.; Carbray, L. P.; Jennings, M. C.; Puddephatt, R. J. J. Am. Chem. Soc. 2000, 122, 176. (f) Baar, C. R.; Jennings, M. C.; Vittal, J. J.; Puddephatt, R. J. Organometallics 2000, 19, 4150. (g) Baar, C. R.; Carbray, L. P.; Jennings, M. C.; Puddephatt, R. J. Organometallics 2000, 19, 2482. (h) Baar, C. R.; Carbray, L. P.; Jennings, M. C.; Puddephatt, R. J. ; Vittal, J. J. Organometallics 2001, 20, 408. (i) Gu¨l, J. H.; Nelson, Willis, A. C.; Ross, A. D. Organometallics 2002, 21, 2041. (j) Vicente, J.; Abad, J. A.; Frankland, A. D.; Lo´pezSerrano, J.; Ramı´rez de Arellano, M. C.; Jones, D. G. Organometallics 2002, 21, 272. (i) Pe´rez, S.; Lo´pez, C.; Caubet, A. Pawlezkyc, A.; Solans, X.; Font-Bardıá, M. Organometallics 2003, 22, 2936. (7) (a) Che, C. M.; Fu, W. F.; Lai, S. W.; Hou, Y. J.; Liu, Y. L. Chem. Commun. 2003, 118. (b) Tao, C. H.; Wong, K. M. C.; Zhu, N.; Yam, V. W. W. New J. Chem. 2003, 27, 150. (c) Fernańdez, S.; Fornie´s, J.; Gil, B.; Go´mez, J.; Lalinde, E. J. Chem. Soc., Dalton Trans. 2003, 822. (d) Brooks, J.; Babayan, Y.; Lamasky, S.; Djurovick, P. I.; Tsyka, I.; Bau, R.; Thompson, M. E. Inorg. Chem. 2002, 41, 3055. (e) Jude, H.; Bauer, J. A.; Connick, W. B. Inorg. Chem. 2002, 41, 900. (f) Yam, V. W. W.; Wong, K. M. C.; Zhu, N. J. Am. Chem. Soc. 2002, 124, 6506. (8) (a) Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.; Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151. (b) Kwong, R. C.; Dovovoy, T.; Baldo, M. A.; Forrest, S. R.; Thompson, M. E. Chem. Mater. 1999, 11, 3709. (c) Adachi, C.; Baldo, M. A.; Forrest, S. R.; Lamansky, S.; Thompson, M. E.; Kwong, R. C. Appl. Phys. Lett. 2001, 78, 1622. (d) Cleave, V.; Yahioglu, G.; Barny, P. L.; Friend, R. H.; Tessler, N. Adv. Mater. 1999, 11, 285. (e) Kunugi, Y.; Mann, K. R.; Miller, L. L.; Extrom, C. L. J. Am. Chem. Soc. 1998, 120, 589. (f) Chan, S. C.; Chan, M. C. W.; Wang, Y.; Che, C. M.; Cheung, K. K.; Zhu, N. Chem. Eur. J. 2001, 7, 4180. (g) Lu, W.; Mi, B. X.; Chan, M. C. W.; Hui, Z.; Zhu, N.; Lee, S. T.; Che, C. M. Chem. Commun. 2002, 206. (9) For recent advances in the chemistry of pallada- and platinacycles having (C,N)- bidentate ligands see for instance: (a) Li, Y.; Selvaratnam, S.; Vittal, J. J.; Leung, P. H. Inorg. Chem. 2003, 42, 3229. (b) Berger, A.; Djukic, J. P.; Pfeffer, M.; de Cian, A.; Kysitsakas-Gruber, N.; Lacour, J.; Vial, L. Chem. Commun. 2003, 658. (c) Stepnicka, P.; Cisarova, I. Organometallics 2002, 22, 1728. (d) Albert, J.; Cadena, J. M.; Gonzalez, A.; Granell, J.; Solans, X.; Font-Bardıá, M. Chem. Commun. 2003, 528. (e) Li, Y.; Ng, K. H.; Selvaratnam, S.; Tan, G. K.; Vittal, J. J.; Leung, P. H. Organometallics 2003, 22, 834. (f) Meijer, M. D.; Kleij, A. W.; Williams, B. S.; Ellis, D.; Lutz, M.; Spek, A. L.; van Klink, G. P. M.; van Koten, G. Organometallics 2002, 21, 264. (g) Zucca, A.; Doppiu, A.; Cinellu, M. A.; Stoccoro, S.; Minghetti, G.; Manassero, M. Organometallics 2002, 21, 783. (h) Bartolome´, C.; Espinet, P.; Vicente, L.; Villafan˜e, F.; Charment, J. P. H.; Orpen, A. G. Organometallics 2002, 21, 3536. (10) Gruber, A. S.; Zim, D.; Ebeling, G.; Monteiro, A. L.; Dupont, J. J. Org. Lett. 2000, 2, 2187. (11) Crespo, M.; Granell, J.; Solans, X.; Font-Bardıá, M. Organometallics 2002, 21, 5140, and references therein. (12) For recent advances in the chemistry of pallada- and platinacycles having (X,C,X)- (with X ) N or S) terdentate ligands see for instance: (a) Diez-Barra, E.; Guerra, J.; Lo´pez-Solera, I.; Merino, S.; Rodrı´guez-Lo´pez, J.; Sanchez-Verdu´, P.; Tejeda, J. Organometallics 2003, 22, 541. (b) Kimmick, B. F.; Bullock, R. M. Organometallics 2002, 21, 1504. (c) Nakai, H.; Ogo, S.; Watanabe, Y. Organometallics 2002, 21, 1674. (d) Fossey, J. S.; Richards, C. J. Organometallics 2002, 21, 5259. (13) Pearson, R. G. J. Am. Chem. Soc. 1963, 85, 3533.

Organometallics, Vol. 23, No. 2, 2004 225 Chart 1

our knowledge, related derivatives containing merterdentate [C(sp2, ferrocene), N, S] ligands are not known. The cyclopalladation of [(η5-C5H5)Fe{(η5C5H4)CHdN[CH(CO2Me)(CH2)2SMe]}] has been previously studied, but in this case the activation of the σ(Csp3-H) bond took place, giving [Pd{(η5-C5H5)Fe[(η5C5H4)CHdN{C(CO2Me)(CH2)2SMe}]}Cl]2 (Chart 1), in which each palladium atom is bound to a chlorine, the imine nitrogen, the stereogenic carbon atom, and the sulfur atom of half of the molecule.16b As a part of a project aimed at the synthesis and study of metallacycles containing [C,N,S]- terdentate groups, in the last two years we have described a few palladaand platinacycles arising from the activation of the ortho σ[C(sp2, phenyl)-H] bond of the thioimines C6H5CHd NCH2CH2SEt (1a) and C6H5CHdN(C6H4-2-SMe) (1b) (Figure 1).17,18 Among these palladium(II) and platinum(II) complexes (2a,2b and 3a,3b in Figure 1), compounds 3a and 3b are particularly interesting due to their luminescence in solution.18b To the best of our knowledge and despite the great proclivity of N-donor ferrocenyl ligands to undergo cyclometalation,19,20 palladium(II) and platinum(II) complexes having mer-terdentate [C(sp2, ferrocene), N, S]- ligands are still unknown. In view of these facts and our previous experience on cyclometalation of N-donor ferrocenyl ligands,14,20 we were prompted to extend our studies to the novel ferrocenyl Schiff base [(η5-C5H5)Fe{(η5-C5H4)CHdN(C6H42-SMe)}] (1c) (Figure 1), which can be visualized as derived from 1b by replacement of the phenyl ring (14) (a) Caubet, A.; Lo´pez, C.; Bosque, R.; Solans, X.; Font-Bardıá, M. J. Organomet. Chem. 1999, 577, 292. (b) Lo´pez, C.; Caubet, A.; Pe´rez, S.; Solans, X.; Font-Bardıá, M. J. Organomet. Chem. 2002, 651, 105. (c) Lo´pez, C.; Pawelczyk, A.; Solans, X.; Font-Bardıá, M. Inorg. Chem. Commun. 2003, 6, 451. (15) Pe´rez, S.; Lo´pez, C.; Caubet, A.; Solans, X.; Font-Bardıá, M. New J. Chem. 2003, 27, 975. (16) (a) Akersmit, H. A.; Witte, P. T.; Kooijman, H.; Labin, M. T.; Spek, A. L.; Goubith, K.; Vrieze, V.; van Koten, G. Inorg. Chem. 1996, 35, 6035. (b) Lo´pez, C.; Caubet, A.; Bosque, R.; Solans, X.; Font- Bardıá, M. J. Organomet. Chem. 2002, 645, 146. (17) (a) Riera, X.; Caubet, A.; Lo´pez, C.; Moreno, V.; Freisinger, E.; Willermann, M.; Lippert, B. J. Organomet. Chem. 2001, 629, 97. (b) Lo´pez, C.; Pe´rez, S.; Solans, X.; Font- Bardıá, M. J. Organomet. Chem. 2002, 650, 258. (18) (a) Riera, X.; Caubet, A.; Lo´pez, C.; Moreno, V.; Solans, X.; FontBardıá, M. Organometallics 2000, 19, 1384. (b) Caubet, A.; Lo´pez, C.; Solans, X.; Font-Bardıá, M. J. Organomet. Chem. 2003, 669, 164. (19) (a) Wu, Y.; Huo, S.; Gong, J.; Cui, X.; Ding, L.; Ding, K.; Du, C.; Liu, Y.; Song, M. J. Organomet. Chem. 2001, 637-639, 27. (b) Headford, C. E.; Mason, R.; Ranatunge-Bandarage, P. R.; Robinson, B. H.; Simpson, J. J. J. Chem. Soc., Chem. Commun. 1990, 601. (20) (a) Lo´pez, C.; Sales, J.; Solans, X.; Zquiak, R. J. Chem. Soc., Dalton Trans. 1992, 2321. (b) Bosque, R.; Lo´pez, C.; Sales, J.; Solans, X.; Font-Bardıá, M. J. Chem. Soc., Dalton Trans. 1994, 483. (c) Lo´pez, C.; Bosque, R.; Solans, X.; Font-Bardıá, M. New J. Chem. 1996, 20, 1285.

226

Organometallics, Vol. 23, No. 2, 2004

Figure 1. Schematic view of the thioimines of general formulas C6H5CHdN-R′ with R′ ) CH2CH2SEt (1a) or C6H4-2-SMe (1b), their cyclopallada- and cycloplatinated complexes (2a,b and 3a,b) reported before, and the novel complexes prepared in this work (1c-3c).

bound to the imine carbon by a ferrocenyl fragment. In this work we describe the synthesis, characterization, molecular structures, and the study of the electrochemical and spectroscopic properties of 1c and the cyclopalladated and cycloplatinated complexes [M{[η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] {with M ) Pd (2c) or Pt (3c)}, shown in Figure 1, which are the first examples of palladium(II) and platinum(II) complexes having a terdentate [C(sp2, ferrocene), N, S]- ligand. Results and Discussion The Ligand. Compound [(η5-C5H5)Fe{(η5-C5H4)CHd N(C6H4-2-SMe)}] (1c) was prepared according to the general procedure described before for the syntheses of ferrocenyl Schiff bases of general formula [(η5-C5H5)Fe{(η5-C5H4)CHdN-R′}], where R′ represents a phenyl, benzyl, or naphthyl group.20 This procedure consists of the reaction of equimolar amounts of ferrocenecarbaldehyde and the corresponding amine in refluxing benzene. The synthesis is usually carried out using a DeanStark apparatus to remove the benzene-water azeotrope formed in the course of the reaction. For the preparation of 1c, 2-mercaptoaniline was used and the reaction yielded deep red crystals suitable for X-ray diffraction (see below). Compound 1c was also characterized by elemental analyses, FAB+ mass spectra, and infrared, visible, and ultraviolet spectroscopy as well as one- and two-dimensional {NOESY, COSY, HSQC, and HMBC} NMR spectroscopy. The most outstanding feature observed in the infrared spectrum is the presence of a

Pe´ rez et al.

Figure 2. ORTEP plot of the two nonequivalent molecules found in the crystal structure of the ligand [(η5-C5H5)Fe{(η5-C5H4)CHdN(C6H4-2-SMe)}] (1c). Hydrogen atoms are not shown. Table 1. Selected Bond Lengths (Å) and Angles (deg) for the Two Nonequivalent Molecules Found in the Crystal Structure of Complex [(η5-C5H5)Fe{(η5-C5H4)CHdN(C6H4-2-SMe)}], 1c (standard deviation parameters are given in parentheses) S(1)-C(17) S(1)-C(18) N(1)-C(11) N(1)-C(12) C(10)-C(11) C(12)-C(13) C(13)-C(14) C(14)-C(15) C(15)-C(16) C(16)-C(17) Fe-C1 C-Ca C(10)-C(11)-N(1) C(11)-N(1)-C(12) N(1)-C(12)-C(17) C(12)-C(17)-S(1) C(17)-S(1)-C(18) a

Bond Lengths 1.765(3) S(1A)-C(17A) 1.800(4) S(1A)-C(18A) 1.268(4) N(1A)-C(11A) 1.415(4) N(1A)-C(12A) 1.454(4) C(10A)-C(11A) 1.385(5) C(12A)-C(13A) 1.387(5) C(13A)-C(14A) 1.371(6) C(14A)-C(15A) 1.392(5) C(15A)-C(16A) 1.390(4) C(16A)-C(17A) 2.03(11) Fe-Ca 1.40(4) C-Ca Bond Angles 122.8(3) C(10A)-C(11A)-N(1A) 117.6(3) C(11A)-N(1A)-C(12A) 118.1(3) N(1A)-C(12A)-C(17A) 116.3(2) C(12A)-C(17A)-S(1A) 104.20(19) C(17A)-S(1A)-C(18A)

1.755(3) 1.774(5) 1.268(4) 1.411(4) 1.452(4) 1.390(5) 1.373(5) 1.381(6) 1.375(6) 1.396(4) 2.04(7) 1.412(9) 122.2(2) 118.9(2) 118.4(3) 116.0(2) 103.3(2)

Average value for the ferrocenyl moiety.

group of three intense bands in the range 1540-1600 cm-1. The band at higher wavenumber is assigned, according to the literature, to the stretching of the >Cd N- group, while the remaining two bands are due to the stretchings of the >CdC< groups of the aromatic ring. One- and two-dimensional NMR experiments suggested that only one isomer [anti-(E) form)] of 1c was present in solution. The two nonequivalent molecules (herein after referred to as A and B) of 1c present in the unit cell together with the atom labeling schemes are depicted in Figure 2, and a selection of bond lengths and angles is presented in Table 1.


The >CdN- bond lengths [1.268(4) Å in the two molecules] are similar to those found for related Schiff bases of general formula [(η5-C5H5)Fe{(η5-C5H4)CHdNR}], with R ) phenyl, benzyl, or naphthyl groups.20 The values of the torsion angles C(10)-C(11)-N(1)-C(12) [177.79°] and C(10A)-C(11A)-N(1A)-C(12A) [179.13°] indicate that in the two molecules the imine adopts the anti-(E) form. Bond lengths and angles of the ferrocenyl moiety agree with those reported for most ferrocene derivatives.21 In the two molecules the pentagonal rings of the ferrocenyl fragments are planar and nearly parallel (tilt angles: 1.41° and 1.22° for the two molecules), and they deviate by ca. 1.47° and 8.66° from the ideal eclipsed conformation. In the crystal the two nonequivalent molecules are packed in such a way that the distance between the sulfur [S(1) or S(1A)] of a given molecule and one of the hydrogen atoms of the methyl groups [H(18A) or H(18)] of a close molecule [2.21(6) and 2.20(5) Å] is indicative of a weak C-H‚‚‚S intermolecular interaction. Besides that, the distances between (a) the C(14)-H(14) bond of one molecule and the ring defined by the set of atoms [C(1A)-C(5A)] [2.917Å] and (b) the C(5)-H(5) bond and the phenyl ring of a close nonequivalent molecule [2.947 Å] suggest the existence of C-H‚‚‚π intermolecular interactions.22 Similar interactions have also been reported for other ferrocene-based heterobimetallic complexes.23 It is generally recognized that although C-H‚‚‚π interactions have energies that are in the range 2-20 kJ/mol,24 they play an important role in the assembly of small molecules to form supramolecular structures.22,25 In the crystals of 1c four discrete molecules [two of each type] are associated through the two types of intermolecular interactions [C-H‚‚‚π and C-H‚‚‚S] mentioned above (Figure 3). Cyclopalladation and Cycloplatination of Ligand 1c. When ligand 1c was treated with equimolar amounts of Na2[PdCl4] and Na(CH3COO)‚3H2O in methanol at room temperature for 24 h, a deep blue solid formed (Scheme 1). Its characterization data (see below) were consistent with those expected for [Pd{[η5-C5H3)CHd N(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] (2c). This compound arises from the coordination of the two heteroatoms of the ligand (N and S) and the activation of the σ[C(sp2, ferrocene)-H] bond, thus indicating that in this case the ligand acts as a [C(sp2, ferrocene), N, S]- terdentate group. The crystal structure of this complex (vide infra) confirms these results. Recently, some authors have demonstrated the advantages of using cis-[PtCl2(dmso)2]26 as metallating (21) Allen, T. H.; Kennard, O. Chem. Des. Automat. News 1993, 8, 128. (22) Nishio, N.; Hirota, M.; Umezakwo, Y. The CH‚‚‚‚π Interaction; Wiley-VCH: New York, 1988. (23) Dong, G.; Yu-jing, L.; Chung-ying, D.; Hong, M.; Qing-jin, M. Inorg. Chem. 2003, 42, 2519. (24) (a) Steiner, T.; Starikov, E. B.; Tamm, M. J. Chem. Soc., Perkin Trans. 2 1996, 67. (b) Steiner, T.; Stariko, E. B.; Amado, A. M.; TexeiraDias, J. J. C. T. J. Chem. Soc., Perkin Trans. 2 1995, 1321. (25) (a) Lehn, J. M. Supramolecular Chemistry; VCH: Weinheim, Germany, 1995. (b) Fabbrizi, L.; Poggi, A. Transition Metals in Supramolecular Chemistry; Kuwer: Dordecht, Germany, 1994; Vol. 448. (c) Eddaouli, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, M.; O’Keefe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319. (26) Price, J. H.; Williamson, A. N.; Schramm, F. R.; Wayland, B. Inorg. Chem. 1972, 11, 1280.

Organometallics, Vol. 23, No. 2, 2004 227

Figure 3. View of the arrangement of the two types of nonequivalent molecules of ligand 1c in the crystal. Scheme 1a

a (i) Equimolar amounts of Na [PdCl ] and sodium acetate 2 4 in methanol at room temperature. (ii) SiO2 column chromatography. (iii) Equimolar amount of cis-[PtCl2(PhCN)2] in refluxing toluene.

agent.19,27 In particular, this was the method used to prepare the first platinacycle having a terdentate [C(sp2, ferrocene), N, N′]- ligand.15 In view of this we decided to study whether the treatment of ligand 1c with cis[PtCl2(dmso)2] in refluxing methanol could lead to the cycloplatinated derivative. When stoichiometric amounts of ligand 1c and cis-[PtCl2(dmso)2] were refluxed in methanol (HPLC-grade) for varying refluxing times (from 30 min to 3 days), the formation of metallic platinum was detected and the 1H NMR spectrum of the crude of the reaction indicated the formation of large amounts of ferrocenecarboxaldehyde, which may form through a hydrolysis process. This is similar to the (27) (a) Ryabov, A. D.; Payanskina, I. M.; Polyakov, V. A.; Fischer, A. Organometallics 2002, 21, 1633. (b) Wu, J. Y. J.; Ding, L.; Wang, H. X.; Liu, Y. H.; Yuan, H. Z.; Mao, X. A. J. Organomet. Chem. 1997, 535, 49.

228


results obtained when equimolar amounts of cis-[PtCl2(dmso)2] and ligand 1b (which can be visualized as derived from 1c by replacement of the ferrocenyl moiety by a phenyl ring) were refluxed.18b Since this strategy failed to achieve the synthesis of the platinacycle, we decided to replace (a) the starting platinum(II) reagent by cis-[PtCl2(PhCN)2] and (b) the methanol by a nonprotic solvent such as toluene. When 1c was treated with the stoichiometric amount of cis-[PtCl2(PhCN)2] in refluxing toluene, the initial red color of the reaction mixture changed gradually to give a deep green solution. After a refluxing period of 5.5 h, the reaction mixture was filtered out and evidence of the formation of a small platinum mirror on the bottom of the reaction flask was detected. The concentration of the filtrate and the workup of an SiO2 column led to small amounts of ferrocenecarboxaldehyde and a deep green solid, whose characterization data were consistent with those expected for [Pt{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5C5H5)}Cl] (3c), which is formally identical to 2c except for the nature of the metal ion. Characterization of Compounds 2c and 3c. Compounds 2c and 3c were characterized by the usual techniques: elemental analyses, FAB+ mass spectrometry, infrared, one-, and two-dimensional NMR spectroscopy, and X-ray diffraction (vide infra). The most relevant feature observed in the infrared spectra of 2c and 3c is the shift of the band due to the asymmetric stretching of the functional >CdN- to lower frequencies than for 1c. This trend, also reported for related cyclopalladated and cycloplatinated complexes14,17-19,28-30 derived from aldimines and ketimines, suggests the binding of the imine nitrogen to the palladium(II) (in 2c) or the platinum(II) (in 3c). Proton and 13C{1H} NMR data for compounds under study are presented in the Experimental Section. Oneand two-dimensional NMR spectra {HSQC and HMBC} of 2c and 3c provided conclusive evidence of the mode of binding of the ligand 1c in the metal complexes. In 1H NMR spectra of 2c and 3c the signals due to the protons of the >CHdN- and the SMe moieties appeared downfield shifted when compared with the free ligand, and for 3c these resonances exhibited the typical satellites due to coupling with the 195Pt-nucleus, thus suggesting the coordination of the imine nitrogen and the sulfur to the M(II) ions. In addition, a group of four signals of relative intensities 5:1:1:1 was also observed in the region 4.0-5.5 ppm, which is consistent with the typical pattern reported for cyclopalladated and cycloplatinated complexes containing a [C(sp2, ferrocene), N]ligand.15,19,27b,30 The most relevant feature observed in the 13C{1H} NMR spectra of 2c and 3c is the downfield shift of the signals due to the metalated carbon, C2 {δ ) 107.4 (for (28) (a) Onue, H.; Moritani, I. J. Organomet. Chem. 1972, 43, 431. (b) Onue, H.; Moritani, K. Bull. Chem. Soc. Jpn. 1970, 43, 3480. (29) (a) Albert, J.; Granell, J.; Sales, J.; Font-Bardıá, M.; Solans, X. Organometallics 1995, 14, 1393. (b) Benito, M.; Lo´pez, C.; Solans, X.; Font-Bardıá, M. Tetrahedron: Asymm. 1998, 9, 4219. (c) Vila, J. M.; Gayoso, E.; Pereira, T.; Marinõs, M.; Martıńez, J.; Fernańdez, J. J.; Fernańdez, A.; Lo´pez-Torres, M. J. Organomet. Chem. 2001, 637-639, 577. (30) (a) Wu, Y. J.; Cui, X.; Du, C. X.; Wang, W. L.; Guo, R. Y.; Chen, R. F. J. Chem. Soc., Dalton Trans. 1998, 3727. (b) Caubet, A.; Lo´pez, C.; Bosque, R.; Solans, X.; Font-Bardıá, M. J. Organomet. Chem. 1999, 577, 292. (c) Wu, Y. J.; Ding, L.; Wang, H. X.; Liu, Y. H.; Yuan, H. Z.; Mao, X. A. J. Organomet. Chem. 1997, 535, 49.

Pe´ rez et al.

Figure 4. Molecular structure and atom-labeling scheme for [Pd{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] (2c). Hydrogen atoms have been omitted for clarity.

Figure 5. ORTEP plot of the molecular structure of [Pt{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] (3c). Hydrogen atoms have been omitted for clarity.

2c) and 91.8 ppm (for 3c)], the imine carbon {δ ) 167.1 (for 2c) and 167.7 ppm (for 3c)}, and the methyl carbon of the thioether group {δ ) 25.4 (for 2c) and 26.8 ppm (for 3c)} when compared to those of the free ligand {δ(C2) ) 69.3 ppm, δ(>CdN-) ) 161.4 ppm and δ(Me) ) 14.7 ppm}, in good agreement with the results reported for related pallada- and platinacyles reported before.14,15,18, 27b,30 The 195Pt{1H} NMR spectrum of 3c showed one signal at δ ) -3488 ppm, which is consistent with the range expected for complexes containing a [(C,N,S,Cl] environment around the platinum(II).18,31,32 According to the literature,31 an upfield shift of the 195Pt{1H} NMR chemical shift is related to a strong donor interaction, since compounds 3b and 3c differ only in the nature of the group bound to the imine nitrogen (a phenyl in 3b or a ferrocenyl fragment in 3c); the differences observed in their 195Pt NMR spectra (δ ) -3716 ppm for 3b18b and δ ) -3488 for 3c) can be ascribed to different donor abilities of the (C,N,S)- terdentate group. Description of the Molecular Structures of [M{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] {with M ) Pd (2c) or Pt (3c)}. The molecular structures of 2c and 3c together with their atomlabeling schemes are shown in Figures 4 and 5, respectively, and a selection of bond lengths and angles as well as other relevant structural parameters are presented in Table 2. (31) Pregosin, P. S. Coord. Chem. Rev. 1982, 44, 247. (32) (a) Riera, X.; Lo´pez, C.; Caubet, A.; Moreno, V.; Solans, X. Eur. J. Inorg. Chem. 2001, 2135. (b) Ding, L.; Wu, Y. J.; Zhou, D. P. Polyhedron 1998, 17, 1725.

Novel Five-Membered Pallada- and Platinacycles Table 2. Selected Bond Lengths (Å), Angles (deg), and Other Relevant Structural Parameters for Compounds [M{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl], M ) Pd (2c) or Pt (3c) 2c M ) Pd M-C(6) M-N(1) M-Cl M-S S-C(17) S-C(18) N(1)-C(11) N(1)-C(12) C(12)-C(17) C(11)-C(10) C(10)-C(6) Fe-Ca C-Ca

Selected Bond Lengths 1.978(5) 2.020(3) 2.2851(14) 2.3653(11) 1.776(4) 1.805(5) 1.296(4) 1.408(4) 1.391(5) 1.417(5) 1.417(7) 2.031(9) 1.409(12)

Selected Bond Angles S-M-N(1) 84.72(8) N(1)-M-C(6) 81.38(16) C(6)-M-Cl 95.52(15) Cl-M-S 98.83(6) C(11)-N-C(12) 124.9(3) Other relevant parameters Twist angle (in deg.) 1.8 Tilt angle (in deg.) 0.92 Fe...M distance (in Å) 3.5350 a

3c M ) Pt 1.985(10) 1.998(7) 2.302(4) 2.328(3) 1.795(9) 1.821(11) 1.326(11) 1.430(11) 1.396(12) 1.408(14) 1.444(15) 2.037(17) 1.417(23) 85.6(2) 80.8(4) 96.3(4) 97.60(13) 122.9(8) 2.2 0.89 3.5761

Average value for the ferrocenyl unit.

In both cases the structures contain molecules of [M{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] {with M ) Pd (2c) or Pt (3c)}, in which the ligand binds to the metal ion through the sulfur, the nitrogen, and the C(6) atom of the ferrocenyl moiety, thus confirming the results obtained by NMR spectroscopy, which suggested a [C(sp2, ferrocene), N, S] mode of binding of the ligand in the metal complexes. The remaining coordination site is occupied by a chlorine. The palladium(II) in 2c or the Pt(II) in 3c are in a sligthly distorted square-planar environment.33 The Pd-S and Pt-S bond lengths [2.3653(11) Å (in 2c) and 2.328(3) Å (in 3c)] are clearly greater than the value usually reported for palladium(II) and platinum(II) thioether derivatives.34,35 This variation can be explained in terms of the strong trans-influence of the metalated carbon.36 In general terms, all the M-ligand (M ) Pd in 2c or Pt in 3c) bond distances and angles are similar to those found in 2a,b, 3a,b,17,18 or [Pd{(4Cl)C6H3)CHdNCH2CH2SEt}Cl].37 (33) The least-squares equation of the plane defined by the atoms N, S, Cl, and C(6) in 2c is (0.3171)XO + (-0.7093)YO + (0.6296)ZO ) -5.8470 (deviations from the plane: Cl, 0.077; S, -0.083; N, 0.112; and C(6), -0.106 Å) and for 3c (0.2899)XO + (-0.7029)YO + (0.6495)ZO ) -1.065 (deviations from the plane: Cl, 0.078; S, -0.087; N, 0.115; and C(6), -0.106 Å). (34) (a) Al-Shami, E. M.; Abru-Surrah, A. S.; Kling, M.; Hobali, H. A. Z. Anorg. Allg. Chem. 2002, 628, 1433. (b) Go´mez, M.; Jansat, S.; Muller, G.; Maestro, M. A.; Mahia, J. Organometallics 2002, 21, 1077. (c) Battaglia, L. P.; Corradi, A. B.; Palmier, C. G.; Nardelli, M.; Tany, M. E. V. Acta Crystallogr. Sect. B 1973, 29, 762. (d) Enders, D.; Peters, R.; Runsink, J.; Bats, J. W. Org. Lett. 1999, 1, 1863. (e) Okoroafor, M. O.; Ward, D. L.; Brubakerjr, C. H. Organometallics 1988, 7, 1504. (35) (a) Wheman, E.; van Koten, G.; Knaap, C. T.; Ossor, H.; Pffefer, M.; Spek, A. L. Inorg. Chem. 1988, 27, 4409. (b) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D. G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1. (36) (a) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev. 1973, 10, 335. (b) Elder, R. C.; Curea, R. D. P.; Morrison, R. F. Inorg. Chem. 1976, 15, 1623.


Each molecule contains a [5,5,5,6] tetracyclic system formed by the metalated pentagonal ring of the ferrocenyl fragment, a five-membered pallada- (in 2c) or platinacycle (in 3c), a chelate ring formed by the coordination of the two heteroatoms (N and S) of the ligand to the metal, and the aryl group. In the two cases, the five-membered metallacycle, which is defined by the atoms C(6), C(10), C(11), N and the metal ion, is nearly planar38 and contains the >Cd N- functional group (endocyclic). In the two structures, the >CdN- bond lengths are larger than the average value for the two nonequivalent molecules of ligand 1c [1.268(4) Å] present in the crystal structure, and the variations observed in the >CdN- bond lengths of 1.296(4) and 1.326(11) Å in 2c and 3c, respectively, may be related to the different effect produced by the binding of the palladium(II) (in 2c) or the platinum(II) (in 3c) to the imine nitrogen. The value of the torsion angles defined by the atoms C(10), C(11), N, and C(12) are 178.99° in 2c and 179.26°in 3c, in good agreement with the anti-(E) conformation of the ligand in these compounds. In the two structures the five-membered chelate rings formed by the binding of the palladium (in 2c) or platinum (in 3c) to the nitrogen and sulfur atoms have an envelope-like conformation. The phenyl rings are planar and form angles of ca. 9.99° (for 2c) and 9.78° (for 3c) and 4.99° (for 2c) and 8.03° (for 3c) with the coordination plane of the metal and with the mean plane of the metalated C5H3 ring, respectively. Bond lengths and angles of the ferrocenyl moiety agree with those reported for most ferrocene derivatives.21 The two pentagonal rings are planar39 and nearly parallel (tilt angles 0.93° and 0.89° for 2c and 3c, respectively), and they deviate by ca. 1.8° in 2c or 2.2° in 3c from the ideal eclipsed conformation. The separation between the Fe and the Pd(II) [3.5350 Å] in 2c or Pt(II) in 3c [3.5761 Å] is greater than the sum of their van der Waals radii,40 thus suggesting that there is no direct interaction between the two metal ions. In the crystals of 2c and 3c the molecules of [M{[(η5C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] {with M ) Pd (2c) or Pt (3c)} are associated in pairs, forming headto-tail dimers (Figure 6). Each molecule of the dimer is related to its partner by a center of inversion. For this arrangement of groups in 2c and 3c the sulfur of one molecule lies over the imine bond of the other molecule of the dimeric unit and vice versa. In 2c the S‚‚‚C and (37) Fernańdez, A.; Va´zquez-Diaz, D.; Fernańdez, J. J.; Lo´pezTorres, M.; Sua´rez, A.; Castro-Juiz, S.; Ortigueira, J. M.; Vila, J. M. New J. Chem. 2002, 26, 105. (38) In 2c and 3c, the least-squares equations of the planes defined by the atoms C(6), C(10), C(11), N, and M are as follows: for 2c (M ) Pd) is (0.2624)XO + (-0.6680)YO + (0.6964)ZO ) -5.6281 (deviations from the plane: Pd, 0.004; C(6), 0.008; C(10), 0.006; C(11), -0.020; and N, -0.020 Å) and for 3c (M ) Pt) (0.2449)XO + (-0.6579)YO + (0.7122)ZO ) -1.0097 (deviations from the plane: Pt, 0.010; C(6), -0.006; C(10), -0.003; C(11), -0.016; and N, -0.017 Å). (39) The least-squares equations of the planes defined by the sets of atoms [C(1)-C(5)] and [C(6)-C(10)] are (0.2699)XO + (-0.7019)YO + (0.6591)ZO ) 2.0374 and (0.2699)XO + (-0.7019)YO + (0.6591)ZO ) 2.0374 for 2c and (0.2591)XO + (-0.7058)YO + (0.6593)ZO ) -3.0460 and (0.2588)XO+ (-0.7112)YO + (0.6537)ZO ) -1.4580 for 3c. (40) (a) Bondi, A. J. Phys. Chem. 1964, 64, 441. (b) Kitaigorodskii, A. I. Molecular Crystals and Molecules; Academic Press: London, U.K., 1973.

230


Pe´ rez et al.

Figure 6. View of the arrangement of the molecules of compound 2c in the crystal. A similar distribution of structural units is also found for 3c.

S‚‚‚N intermolecular separations are 3.415(4) and 3.440(3) Å, respectively, while in 3c, they are equal to 3.458(1) Å. Several authors have postulated that for cycloplatinated and cyclopalladated complexes having terdentate ligands, the planarity of the terdentate group, the π-stacking of the aryl rings of the ligand, and the intermolecular M‚‚‚M separation are particularly important in view of their potential photoluminiscent properties.7,41 In these compounds the M‚‚‚M intradimer separation in 2c is larger than the sum of the van der Waals radii of the palladium(II) atoms,40 while for 3c the distance between the two platinum(II) atoms of the dimeric unit [4.490(4) Å] is clearly larger than the value reported for 2c [4.216(3) Å] and related platinacycles holding [C(sp2,aryl), N, N′] and [C(sp2, aryl), N, S]terdentate ligands for which intramolecular Pt‚‚‚Pt interactions have been proposed.7e,41 Another outstanding feature of the structures of 2c and 3c is the existence of C-H‚‚‚π(ring) interactions22 between one of the hydrogen atoms of the methyl group bound to the sulfur {H(15)} of one of the molecules forming the dimers and the C5H3 ring of a neighboring molecule belonging to a different dimer. This leads to a chain that stacks along the [101] plane. Mo1 ssbauer Spectra. In all cases, 57Fe Mo¨ssbauer spectra of the compounds consist of a single quadrupole (41) (a) Ratilla, E.; Scott, B. K.; Moxness, M. S.; Kostic, N. M. Inorg. Chem. 1990, 29, 918. (b) Bailey, J. A.; Miskovskii, V. M.; Gray, H. B. Inorg. Chem. 1993, 21, 369. (c) Jovanovic, B.; Manojlovic, L. J.; Muir, K. J. Chem. Soc., Dalton Trans. 1972, 1178. (d) Constable, E. C.; Henney, R. P. G.; Leese, T. A.; Tocher, D. A. Chem. Commun. 1990, 513. (e) Lai, S. W.; Lam, H. W.; Lu, W.; Cheung, K. K.; Chen, C. M. Organometallics 2002, 21, 226. (f) Wong, K. H.; Chan, M. C. W.; Che, C. M. Chem. Eur. J. 1999, 5, 2845. (g) Lu, W.; Mi, B. X.; Chan, M. C. W.; Hui, Z.; Zhu, N.; Lee, S. T.; Che, C. M. Chem. Commun. 2002, 206. (h) Lu, W.; Zhu, W.; Che, C. M. Chem. Commun. 2002, 900.

Figure 7. Mo¨ssbauer spectra of the free ligand 1c and compounds 2c and 3c. Table 3. Iron-57 Mo1 ssbauer Hyperfine Parameters (at 80 K): Isomer Shift, δ, Quadrupole Splitting, ∆Eq, and Full-Width at Half-Heigth, Γ (in mm s-1) (standard deviation parameters are given in parentheses) compound

δ

∆Eq

Γ

1c 2c 3c

0.502(2) 0.485(2) 0.495(2)

2.2541(4) 2.087(4) 2.06(2)

0.361(6) 0.33(1) 0.33(3)

doublet (Figure 7), indicating a unique iron site. The isomer shifts, δ, quadrupole splittings, ∆Eq, and line widths, Γ, are summarized in Table 3. It is well known that for substituted ferrocene derivatives electron-donating substituents cause an increase in the quadrupole splittings relative to ferrocene, whereas electron-pulling groups produce a decrease in the ∆Eq


parameter.42 For the free ligand, the quadrupole splitting is smaller than that of ferrocene43 (∆Eq ) 2.37 mm s-1 at room temperature or 2.41 at 80 K) and of the Schiff base [(η5-C5H5)Fe{(η5-C5H4)CHdN(C6H5)}]44 (∆Eq ) 2.28 mm s-1), which can be visualized as derived from 1c by replacement of the SMe group by a hydrogen, thus indicating that the electron-withdrawing character of the substituent increases according to the sequence H , -CHdN(C6H5) < -CHdN(C6H4-2SMe). The ∆Eq values for 2c and 3c are smaller than that of the free ligand, and the extent of this variation seems to be dependent on the “MCl” (M ) Pd or Pt) unit, since the diference observed in the q.s. values when compared with that of the parent ligand [∆ ) ∆Eq(ligand) - ∆Eq(complex)] is greater for 3c than for 2c, thus suggesting a greater electron-pulling contribution of the “PtCl” moiety. As a first approach one could expect that the “MCl” units may pull electronic density through three different pathways: (a) directly from the C5H3 ring, (b) through the imine nitrogen, or (c) a combination of both. The comparison of the structural data of 2c and 3c presented in Table 2 reveals that the differences observed in the M-C(6) bond distance do not clearly exceed 3σ. However, the C(11)-N(11) bond length increases in the order 1c [1.268(4) Å] < 2c [1.296(4) Å] e 3c [1.326(11) Å], thus suggesting that the formation of the cyclometalated complexes reduces the strength of the imine bond. Electrochemical and Spectroscopic Studies. In a first attempt to elucidate the effect produced by the coordination of the Schiff base to the palladium(II) or platinum(II) upon the electronic environment of the iron(II), we decided to carry out electrochemical studies and to register the ultraviolet-visible spectra of 1c3c. Electrochemical data for compounds under study were obtained from cyclic voltammetric studies of freshly prepared solutions (10-3 M) in acetonitrile using (Bu4N)[PF6] as supporting electrolyte. Cyclic voltammograms of 1c-3c are presented in Figure 8, and the most relevant electrochemical data are summarized in Table 4. In all cases, the voltammograms exhibited an anodic peak with a directly associated reduction in the reverse scan. In all cases the Ipa/Ipc molar ratio was close to 1. For the three compounds the experiments were carried out at different scan rates, υ {from 0.05 to 1.0 V s-1}, and a linear relationship between the Ipa and υ1/2 was obtained in all cases. According to the literature, all these findings are consistent with those expected for a simple reversible one-electron-transfer process.45 For the free ligand and complex 2c the ∆E values (Table 4) depart appreciably from the constant value of 59 mV (theoretically expected for an electrochemically (42) (a) Houlton, A.; Miller, J. R.; Silver, J.; Jasim, N.; Ahmet, M. T.; Axon, T. L.; Bloor, D.; Cross, G. H. Inorg. Chim. Acta 1993, 205, 65. (b) Houlton, A.; Miller, J. R.; Roberts, R. G. M.; Silver, J. J. Chem. Soc., Dalton Trans. 1991, 467. (43) Houlton, A.; Bishop, P. T.; Roberts, R. M. G.; Silver, J.; Herberhold, M. J. Organomet. Chem. 1989, 364, 381. (44) Bosque, R.; Font-Bardıá, M.; Lo´pez, C.; Sales, J.; Silver, J.; Solans, X. J. Chem. Soc., Dalton Trans. 1994, 747. (45) Brown, E. R.; Sandifer, J. R. Physical Methods in Chemistry. Electrochemical Methods; Rossiter, B. W., Hamilton, J. H, Eds.; Wiley: New York, 1986; Vol. 4, Chapter 4.


Figure 8. Cyclic voltammograms of the free ligand [(η5C5H5)Fe{(η5-C5H4)CHdN(C6H4-2-SMe)}], 1c, and compounds [M{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] with M ) Pd (2c) or Pt (3c). Table 4. Electrochemical Data: Anodic (Epa) and Cathodic Potentials (Epc), Half-Wave Potentials Referred to Ferrocene E1/2(Fc), and Separation of the Peaks (∆E) for the Samples and for Ferrocene {∆E′} {which was used as standard} (in mV) for the Free Ligand and Compounds [M{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] with M ) Pd (2c) or Pt (3c) at a Scan Speed υ ) 10 mV s-1 1c 2c 3c

Epa

Epc

E1/2(Fc)

∆E

∆E’

250 199 72

191 103 6

184 104 39

132 96 66

83 83 86

reversible one-electron-step oxidation-reduction process45), suggesting that a structural reorganization takes place on oxidation. However, it must be stated that for compounds under study the highest occupied molecular orbital (HOMO) is not solely iron based. We will return to this point later on. The half-wave potentials E1/2 are presented in Table 4. For the free ligand the E1/2 is greater than the values reported for related ferrocenyl Schiff bases of general formula [(η5-C5H5)Fe{(η5-C5H4)CHdN-R}], with R ) phenyl groups,46 thus suggesting that the incorporation of the -SMe group on the ortho site reduces the proclivity of the iron(II) to oxidize. For 2c, the E1/2(Fc) value {104 mV} is smaller than that obtained for the (46) Bosque, R.; Lo´pez, C.; Sales, J. Inorg. Chim. Acta 1996, 244, 141.

232


Pe´ rez et al.

Table 5. Experimental Visible-Ultraviolet Spectroscopic Data: Wavelengths, λi (in nm), Molar Extinction Coefficients, Ei, in Mol-1 dm2 (in parentheses), Together with the Calculated Wavelengths (in nm) and the Transitions That Have the Greater Contribution to the Given Band for Compounds [M{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] with M ) Pd (2c) or Pt (3c) experimental compound 2c

λi 584

calculated i

λi

transition

assignment

3023

586

(HOMO)f(LUMO+3) (HOMO-1)f(LUMO+3) (HOMO-3) f (LUMO) (HOMO-2) f (LUMO) (HOMO-5) f (LUMO) (HOMO-4) f (LUMO) (HOMO) f (LUMO+4) (HOMO-7) f (LUMO+3) (HOMO-5) f (LUMO +1) (HOMO-1) f (LUMO+1) (HOMO-1) f (LUMO +2) (HOMO-6) f (LUMO) (HOMO) f (LUMO+2) (HOMO-1) f (LUMO+2) (HOMO-2) f (LUMO) (HOMO-4) f (LUMO) (HOMO) f (LUMO+3) (HOMO-6) f (LUMO) (HOMO) f (LUMO+1)

4dxz(Pd) f π* 4dyz(Pd) f π* MPILCTb MPILCTb MPILCTb 4dz2(Pd) f π* 4dyz(Pd) f π* MPILCTb MPILCTb MPILCTb MPILCTb MPILCTb 5dxz(Pt) f π* 5dyz(Pt) f π* MPILCTb 5dz2(Pt) f π* 5dyz (Pt) f π* MPILCTb MPILCTb

435a

3c

a

449 428 413 389 369 360 346

394

4753

359

8826

600

3233

343 593

454 412

2935 5993

452 430

344

8466

345 342

Shoulder. b MPILCT ) metal perturbed intraligand charge transfer transition (π f π*).

free ligand {E1/2(Fc) ) 184 mV}. This finding is in good agreement with the results obtained for related palladacycles of general formula [Pd{[(η5-C5H3)C(H)dN-R′]Fe(η5-C5H5)}Cl(L)] (with R′ ) phenyl, benzyl, or naphthyl groups and L ) pyridine or phosphine ligands)46,47 when compared with the corresponding free ligand. Besides that, the half-wave potential for 3c {E1/2(Fc) ) 39 mV} is smaller than that of 2c {E1/2(Fc) ) 94 mV}, thus indicating that the proclivity of the cyclometalated complexes to oxidize is markedly dependent on the nature of the central metal ion Pd(II) (in 2c) or Pt(II) (in 3c). For compounds under study the E1/2(Fc) decreases according to the sequence 1c > 2c > 3c, thus suggesting that the binding of the nitrogen, the sulfur, and the C2 atom of the ferrocenyl ligand to the platinum(II) center (in 3c) produces a greater enhancement of the proclivity of the ferrocenyl moiety to oxidize than for the palladium(II) analogue (in 2c). The ultraviolet-visible spectrum of a 10-5 M solution of 1c in CH2Cl2 at ca. 20 °C showed two intense bands at 364 ( ) 6544) and 464 ( ) 1262) nm. Their positions fall in the range reported for related ferrocenylketimines of general formula [(η5-C5H5)Fe{(η5-C5H4)CHdN-R′}] with R′ ) substituted phenyl ring20c and have been attributed to intraligand transitions (ILT) [3d(Fe) f π* and πfπ*, respectively]. A summary of the results obtained from the spectroscopic studies of 10-4 M solutions of 2c and 3c in CH2Cl2 at ca. 20 °C is presented in Table 5. In these cases four absorption bands were observed in the spectrum, and three of them appeared in the range 300-400 nm. Previous studies focused on cyclopalladated derivatives of general formula [Pd{[(η5-C5H3)C(H)dN-R′]Fe(η5C5H5)}Cl(L)] (with R′ ) phenyl groups and L ) pyridine or phosphine), which contain a bidentate [C(sp2, ferrocene), N]- ligand, have shown that this sort of compound also exhibits bands in this region and that their position is strongly sensitive to changes in the nature of the neutral L group.47 The spectra of 2c and 3c showed an additional and symmetric band at lower energies [λ ) 584 (for 2c) and

600 nm (for 3c)], and its position was dependent on the nature of the M(II) ion. This band was not detected before in the UV-vis spectra of other ferrocenylketimines or their cyclometalated derivatives containing [C(sp2, ferrocene), N]- ligands. Theoretical Approaches to Clarify the Influence of the Palladium(II) and Platinum(II) in the Cyclometalated Complexes upon the Electronic Environment of the Iron(II). As a first attempt to explain why the cycloplatinated complex 3c is more prone to undergo oxidation of the Fe(II) than the palladium(II) analogue, 2c, we decided to undertake DFT calculations of the free ligand as well as of the two cyclometalated compounds (2c and 3c). The first step of the theoretical studies consisted in the optimization of the geometries, taking the experimental ones (determined by X-ray diffraction) as input. For each compound, two geometry optimizations have been performed: the first one has been done in vacuo, using the LANL2DZ basis set,48 while for the second one solvent effects have been included via the polarizable conductor calculation model, CPCM;49 in this case the TZV basis set50 has been used for all the atoms except Pd and Pt, for which LANL2DZ has been employed. Although the inclusion of the solvent, as well as the use of a better basis set, results in a slight improvement of the geometry, some discrepancies between the experimental and calculated geometries remain, mainly in the >CdN- bond length and in the environment (47) (a) Lo´pez, C.; Bosque, R.; Solans, X.; Font-Bardıá, M. New J. Chem. 1998, 22, 977. (b) Riera, X.; Caubet, A.; Lo´pez, C.; Moreno, V. Polyhedron 1999, 19, 2555. (c) Lo´pez, C.; Bosque, R.; Solans, X.; FontBardıá, M.; Tramuns, D.; Fern, G.; Silver, J. J. Chem. Soc., Dalton Trans. 1994, 3039. (48) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (b) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284. (c) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299. (d) For C, H, and N, the D95 basis set is used; Dunning, T. H., Jr.; Hay, P. J. In Modern Theoretical Chemistry; Schaefer, H. F., III, Ed.; Plenum Press, New York, 1976; Vol. 3, p 1. (49) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 1995. (50) (a) Schaefer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571. (b) Schaefer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829.


Figure 9. HOMO and LUMO for [(η5-C5H5)Fe{(η5-C5H4)CHdN(C6H4-2-SMe)}], 1c (A and B), compound [Pd{[(η5C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] (2c) (C and D), and [Pt{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] (3c) (E and F).

around the sulfur atoms; these differences could be ascribed to the existence in the crystal of intermolecular interactions that involve these atoms. No significant improvement of the calculated geometries was achieved by including polarization functions in the basis set. The calculations performed on the free ligand, at the B3LYP/LANL2DZ level, show that the HOMO (Figure 9, A) is mainly formed by the 3dx2-y2 orbital of the iron(II), the pz orbitals of the nitrogen and sulfur, and a π orbital of the aryl ring, while the LUMO (Figure 9, B) consists of a mixture of a π orbital centered on the imine bond and the ipso carbon of the aryl ring and a small contribution of the 3dxy orbital of the iron(II). The HOMO and LUMO of 2c and 3c are shown in Figure 9, C-F. In the two cases, the HOMO (Figure 9, C and E) is mainly formed by the contribution of the 3dxy orbital of the iron, a 3pz orbital of the chloride, and the dyz orbital of the M(II) center (M ) Pd or Pt). These findings confirm that for the compounds under study the HOMO is not only iron based. The replacement of the palladium(II) (in 2c) by a platinum(II) (in 3c) produces an increase of the contribution of the atomic orbitals of the M(II) in the HOMO [from 0.11 (in 2c) to 0.16 (in 3c)] and a decrease of the participation of the atomic orbitals of the Fe(II) [from 0.26 (in 2c) to 0.23 (in 3c)]. In 3c, the HOMO of the platinum(II) derivative is 0.105 eV higher in energy than in the palladium(II) analogue. This trend is consistent with the results obtained from the electrochemical studies which revealed that 3c is more prone to oxidize than 2c.


The LUMO (Figure 9, D and F) of 2c and 3c is mainly a combination of a π orbital of the aryl ring, the dyz orbital of the M(II) atom, and the dxz, dx2-y2 and dxy orbitals of the iron. On the other hand, and in order to elucidate the origin of the band detected in the UV-vis spectra of 2c and 3c in the range 590-600 nm, we decided to undertake a study, based on the time-dependent DFT (TD-DFT) methodology,51 to achieve the assignment of all the bands detected in the UV-vis spectra of the cyclometalated complexes. After the optimization of the geometries at the B3LYP/LANL2DZ level (see above), the excitation energies and the corresponding oscillator strengths were calculated. A summary of the results obtained from these calculations is presented in Table 5. In general all the bands arise from a combination of several transitions, among which those having the greater contributions are presented in Table 5. The study of the molecular orbitals involved in these transitions has been very useful to assign the bands, in particular, to distinguish between those due to intraligand transitions (ILT) and those due to metal to ligand charge transfer transitions (MLCT). The position of the band at λ ) 584 nm (for 2c) shifts to lower energies in the platinum(II) analogue (3c), thus suggesting a significant character of metal to ligand charge transfer. The results obtained from the calculations indicate that these absorption bands are mainly a combination of two electronic transitions [from (HOMO) or (HOMO-1) to the (LUMO+3) for (2c) or to the (LUMO+2) (for 3c)]. Since in the two cases the virtual orbital is mainly π* ferrocene in character with a small contribution of the aryl ring, the observed absorption bands can be attributed predominantly to a dxz(M) or dyz(M)fπ* (ligand) charge transfer transition. The comparison of the UV-vis spectroscopic data for 3c and for [Pt{C6H3CHdN(C6H4-2SMe}Cl] (3b) {λ ) 530 nm} (which can be visualized as derived from 3c by replacement of the metalated ferrocenyl fragment by a 1,2disubstituted phenyl ring) also supports this assignment, since the greater σ-donating ability of the ferrocenyl group in 3c compared with that of the aryl ring52 in 3b is expected to desestabilize the HOMO orbital, giving rise to a lower energy metal to ligand charge transfer transition. The bands centered at λ ) 394 nm (for 2c) or 412 nm (for 3c), with extinction coefficients () between 2000 and 5000, arise mainly from two transitions, one of them being the (HOMO-4) f (LUMO) (for 2c and 3c). Since the (HOMO-4) is mainly a M(II)-centered orbital, these bands (which are not present in the spectrum of the free ligand) are assigned to metal to ligand charge transfer transitions (MLCT). The second component of the observed band is due to the (HOMO) f (LUMO+4) (for 2c) or (LUMO+3) (for 3c) transition. As mentioned above in the two cases the HOMO is mainly centered on the M(II), the iron, and the chlorine atom (Figure 9, (51) (a) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. Chem. Phys. 1998, 109, 8218. (b) Bauernschmitt, R.; Ahlrichs, R. Chem. Phys. Lett. 1996, 256, 454. (c) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R. J. Chem. Phys. 1998, 108, 4439. (52) Hansch, C.; Leo, A.; Koekman, D. Exploring QSAR. Hydrophobic, Electronic and Steric Constants; American Chemical Society: Washington, DC, 1995.

234


C and E). The (LUMO +4) (in 2c) is very similar to the (LUMO+3) (in 3c), and in the two cases they consist of a combination of the 2pz orbital of the imine nitrogen and π* orbitals of the ferrocenyl fragment and the aryl ring, thus suggesting that also in this case the band can be mainly due to a metal to ligand charge transfer transition. This interpretation also explains why the position of this band depends on the nature of the substituents on the imine nitrogen and of the remaining ligands bound to the M(II) ion. The remaining two absorption bands [at λ ) 359 and 435 nm (for 2c) or 344 and 454 nm (for 3c)], also observed for related metal complexes derived from Schiff bases,53 correspond to the metal-perturbed intraligand π f π* transitions. Conclusions The results presented here have allowed the preparation and characterization of the two first examples of cyclopallada- and cycloplatinated complexes (2c and 3c) containing a [C(sp2, ferrocene), N, S]- ligand. The electrochemical studies of the three compounds under study provide a method for fine-tuning the oxidation potential of the ferrocenyl fragment from 184 mV in the free ligand to 104 mV (for 2c) or 39 mV (for 3c) by modifying the nature of the M(II) ion [Pd or Pt] in the cyclometalated complexes. The theoretical studies based on the DFT methodology revealed that for these systems the HOMO is not solely iron(II) based and have explained why the half-wave potentials of compounds 2c and 3c are so sensitive to changes in the nature of the M(II) ion in the two cyclometalated complexes. In particular for the palladium(II) complex (2c), the energy level of the HOMO is smaller than that of 3c, in good agreement with the variations observed in their halfwave potentials. On the other hand, the UV-vis spectra calculated using the TD-DFT methodology show a reasonable agreement with the experiment and have allowed the assignation of the main absorptions. Experimental Section Materials and Methods. All the reagents used for the preparations described in this work were obtained from Aldrich and used as received except for Na2[PdCl4], which was prepared according to the literature.54 The solvents, except benzene, were dried and distilled before use.55 Some of the preparations described below require the use of HIGHLY HAZARDOUS MATERIALS, such as benzene and toluene, which should be handled with CAUTION. Elemental analyses (C, H, N, and S) were carried out at the Serveis Cientifico-Te`cnics (Universitat de Barcelona) and at the Serveis de Recursos Cientifics i Te`cnics (Universitat de Rovira i Virgili, Tarragona). FAB+ mass spectra were performed at the Servei d’Espectrometria de Masses (Universitat de Barcelona) using 3-nitrobenzyl alcohol (NBA) as matrix. Infrared spectra were obtained with a Nicolet 400-FTIR instrument using KBr pellets. Routine 1H NMR spectra and 13C{1H} NMR spectra were obtained with a Gemini-200 MHz and a Bruker 250-DXR or a Mercury-400 instruments, respec(53) Bosque, R.; Caubet, A.; Lo´pez, C.; Espinosa, E.; Molins, E. J. Organomet. Chem. 1997, 544, 233. (54) Brauer, G. Handbook of Preparative Inorganic Chemistry; Academic Press: New York, 1965; Vol. 2, p 1584. (55) Perrin, D. D.; Amarego, W. F. L.; Perrin, D. L. Purification of Laboratory Chemicals, 3rd ed.; Pergamon: London, UK, 1988.

Pe´ rez et al. tively. High-resolution 1H NMR spectra and the two-dimensional [{1H-1H}-NOESY and COSY, {1H-13C}-heteronuclear single quantum coherence (HSQC), and heteronuclear multiple bond coherence (HMBC)] NMR experiments were recorded with either a Varian VRX-500 or a Bruker Advance-DMX 500 instrument at 20 °C. The 195Pt{1H} NMR spectrum of 3c was registered at 20 °C with a Bruker 250-DXR instrument and Na2[PtCl6] [δ195Pt ) 0.00 ppm] as reference. In all cases the solvent used for the NMR experiments was CDCl3 (99.8%), and SiMe4 was used as internal reference for the spectra in CDCl3. To check the stability of 1c-3c in the solvent used for the electrochemical studies, the 1H NMR spectra of these compounds in CD3CN (99.8%) were also recorded. In all cases, the chemical shifts (δ) are given in ppm and the coupling constants (J) in Hz. Visible-ultraviolet spectra of 10-5 M solutions of compounds under study in CH2Cl2 were registered at 20 °C with a Hewlett-Packard 8452A spectrophotometer. Preparation of the Compounds. [(η5-C5H5)Fe{(η5-C5H4)CHdN(C6H4-2-SMe)}], 1c. A suspension formed by ferrocenecarboxaldehyde (1.024 g, 4.78 × 10-3 mol) and 50 mL of benzene was stirred at room temperature (ca. 20 °C) for 20 min and filtered out. Then H2N(C6H4-2-SMe) (0.666 g, 4.78 × 10-3 mol) was added to the filtrate. The reaction flask was connected to a condenser equipped with a Dean-Stark apparatus. The mixture was refluxed until ca. 15 mL of the benzene-water azeotrope had condensed on the Dean-Stark apparatus. The hot solution was then filtered out and concentrated on a rotary evaporator to ca. 10 mL. Slow evaporation of the solvent produced orange prisms of 1c (yield: 1.326 g, 85%). Anal. Calcd: C, 64.50; H, 5.20; N, 4.0; S, 9.6. C18H17NSFe requires: C, 64.49; H, 5.11; N, 4.18; S, 9.56. MS (FAB+): m/z 355 [{M}+]. IR: 1625 cm-1, ν(>CdN-). 1H NMR (in CDCl3): δ 4.27(s, 5H, C5H5), 4.84(t, 2H, H2 and H5, 3J(H-H) ) 2), 4.49(t, 2H, H3 and H4, 3J(H-H) ) 2), 2.46(s, 3H, -SMe), 8.26(s, 1H, -CHdN-), 6.84(t, 1H, H3′, 3J(H-H) ) 2.5), 7.16(d, 1H, H4′, 3J(H-H) ) 2.5), 7.13(d, 1H, H5′, 3J(H-H) ) 2.5), 7.16(t, 1H, H6′, 3J(H-H) ) 2.5); in CD3CN: δ 4.28(s, 5H, C5H5), 4.80(s, 2H, H2 and H5), 4.53(t, 2H, H3 and H4), 2.44(s, 3H, -SMe), 8.30(s, 1H, -CHdN-), 6.94(dd, 1H, H3′, 3J(H-H) ) 7.5, 4J(H-H) ) 1.5), 7.22(td, 1H, H4′, 3J(H-H) ) 7.5, 4J(H-H) ) 1.5), 7.16(td, 1H, H5′, 3J(H-H) ) 7.5, 4J(H-H) ) 1.5), 7.16(d, 1H, H6′, 3J(H-H) ) 7.5,4J(H-H) ) 1.5). 13C{1H} NMR: δ 69.5(C5H5), 80.2(C1), 69.2(C2 and C5), 71.3(C3 and C4), 14.7(Me), 161.4(-CHdN-), 150.2(C1′), 132.6(C2′), 117.6(C3′), 124.1(C4′), 125.1(C5′), 125.4(C6′). [Pd{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl], 2c. Compound 1c (0.507 g, 1.51 × 10-3 mol), Na2[PdCl4] (0.440 g, 1.49 × 10-3 mol), and Na(CH3COO)‚3H2O (0.207 g, 1.51 × 10-3 mol) were dissolved in 20 mL of methanol. The reaction mixture was protected from the light with aluminum foil and stirred at room temperature (ca. 20 °C) for 24 h. The deep blue solid formed was filtered out and washed with small portions of methanol, until the mother liquor became nearly colorless. The resulting solid was air-dried and then dried in a vacuum (yield: 0.520 g, 72%). Anal. Cacld: C, 44.9; H, 3.53, N, 2.8; S, 6.1. C18H17NFeSPdCl 1/2 H2O requires: C, 44.6; H, 3.53; N, 2.9; S, 6.6. MS (FAB+): m/z 477[{M}+], 441[{M - Cl}+]. IR: 1530 cm-1, ν(>CdN-). 1H NMR data (in CDCl3): δ 4.40(s, 5H, C5H5), 4.74(d, 1H, H3, 3J(H-H) ) 2.5), 4.61(t, 1H, H4, 3J(H-H) ) 2.5), 5.36(d, 1H, H5, 3J(H-H) ) 2.5), 2.78(s, 3H, -SMe), 8.82(s, 1H, -CHdN-), 7.62(d, 1H, H3′, 3J(H-H) ) 7.5), 7.32(t, 1H, H4′, 3J 5′ 3 5 (H-H) ) 7.5), 7.39(t, 1H, H , J(H-H) ) 7.5), 7.54(d, 1H, H , 3J 3 (H-H) ) 7.5); in CD3CN: δ 4.38(s, 5H, C5H5), 4.72(s, 1H, H ), 4.72(s, 1H, H4), 5.08(s, 1H, H5), 2.76(s, 3H, -SMe), 9.03(s, 1H, -CHdN-), 7.83(dd, 1H, H3′, 3J(H-H) ) 8, 4J(H-H) ) 1), 7.40(td, 1H, H4′, 3J(H-H) ) 8, 4J(H-H) ) 1), 7.48(td, 1H, H5′, 3J(H-H) ) 8, 4J 5 3 4 13C{1H} (H-H) ) 1), 7.68(dd, 1H, H , J(H-H) ) 8, J(H-H) ) 1). NMR: δ 71.4(C5H5), 90.2(C1), 107.4(C2), 68.6(C3), 72.5(C4), 78.23(C5), 25.4(-SMe), 167.1(>CdN-), 148.4(C1′), 130.8(C2′), 116.3(C3′), 128.0(C4′), 130.7(C5′), 135.3(C6′). [Pt{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl], 3c. cis-[PtCl2(PhCN)2] (0.100 g, 2.12 × 10-4 mol) was suspended



Table 6. Crystal Data and Details of the Refinement of the Crystal Structures of the Free Ligand [(η5-C5H5)Fe{(η5-C5H4)CHdN(C6H4-2-SMe)}], 1c, and Compounds [M{[(η5-C5H3)CHdN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] {with M ) Pd (2c) or Pt (3c)} empirical formula fw temperature/K cryst size/mm× mm × mm cryst syst space group unit cell params

V/Å3 Z Dcalc/Mg m-3 abs coeff/mm-1 F(000) θ range for data collection/deg no. of collected reflns no. of unique reflns [Rint] no. of data no. of params goodness of fit on F2 final R indices [I > 2σ(I)] final R indices (all data) extinction coeff largest diff peak and hole/e Å-3

1c

2c

3c

C18H17FeNS 335.23 293(2) 0.1 × 0.1 × 0.2 triclinic P1 h a ) 10.5900(10) Å b ) 10.7490(10) Å c ) 14.0280(10) Å R ) 94.90° β ) 98.8590(10)° γ ) 94.79° 1564.4 2 1.423 1.089 696 1.96 to 28.87 10 329 6393 [0.0215] 6393 511 1.093 R1 ) 0.0440, wR2 ) 0.1296 R1 ) 0.0649, wR2 ) 0.1508

C18H16ClFeNPdS 476.06 293(2) 0.1 × 0.1 × 0.2 monoclinic P21/n a ) 7.9010(10) Å b ) 13.6820(10) Å c ) 15.8700(10) Å R ) 90.0° β ) 93.5000(10)° γ ) 90° 1712.4(3) 4 1.847 2.172 944 2.97 to 31.60 11 179 5038 [0.0344] 5038 209 1.106 R1 ) 0.0453, wR2 ) 0.118 R1 ) 0.0772, wR2 ) 0.11312 0.0013(9) 0.555 and -0.878

C18H16ClFeNPtS 564.77 293(2) 0.1 × 0.1 × 0.2 monoclinic P21/n a ) 8.033(8) Å b ) 13.710(4) Å c ) 15.753(8) Å R ) 90.0° β ) 92.71(6)° γ ) 90° 1733(2) 4 2.165 9.172 1072 3.17 to 30.02 5184 4993 [0.415] 4993 208 0.949 R1 ) 0.05065, wR2 ) 0.1094 R1 ) 0.1751 wR2 ) 0.397

0.415 and -0.491

in 20 mL of toluene. The reaction mixture was refluxed until complete dissolution of the starting platinum(II) reagent, which was filtered out. Then the filtrate was treated with 0.070 g (2.09 × 10-4 mol) of ligand 1c, and the mixture was refluxed for 5.5 h. The resulting dark solution was concentrated to dryness on a rotary evaporator. The residue was washed with small portions of n-hexane to remove small amounts of ferrocenecarboxaldehyde formed in the course of the process. Finally the resulting solid was dissolved in the minimum amount of CH2Cl2. The addition of n-hexane followed by the slow evaporation of the solvents at room temperature (ca. 20 °C) produced green monocrystals of 3c, which were collected and air-dried (yield: 0.069 g, 59%). Anal. Calcd: C, 38.40; H, 2.90; N, 2.40; S, 6.0. C18H17NFeSPtCl requires: C, 38.28; H, 2.86; N, 2.48; S, 5.68. MS (FAB+): m/z 564[{M}+]. IR: 1531 cm-1, ν(>CdN-). 1H NMR (in CDCl3): δ 4.35(s, 5H, C5H5), 4.72(s, 1H, H3), 4.96(s, 1H, H4), 5.26(s, 1H, H5), 2.98(s, 3H, -SMe, 3J(H-Pt) ) 22), 9.02(s, 1H, -CHdN-, 4J(H-Pt) ) 119), 7.64(d, 1H, H3′, 3J(H-H) ) 7), 7.37(t, 1H, H4′, 3J(H-H) ) 7), 7.39(t, 1H, H5′, 3J(H-H) ) 7), 7.58(d, 1H, H6′, 3J(H-H) ) 7); in CD3CN: δ 4.32(s, 5H, C5H5), 4.79(s, 1H, H3), 4.89(s, 1H, H4), 4.95(s, 1H, H5), 2.90(s, 3H, -SMe, 3J(H-Pt) ) 22), 9.24(s, 1H, -CHdN-, 4J 3′ 3 4 (H-Pt) ) 119), 7.86(td, 1H, H , J(H-H) ) 7.5, J(H-H) ) 1.5), 4′ 3 3 7.41(t, 1H, H , J(H-H) ) 7.5, J(H-H) ) 1.5), 7.46(td, 1H, H5′, 3J(H-H) ) 7.5, 4J(H-H) ) 1.5), 7.73 (dd, 1H, H6′, 3J(H-H) ) 7.5, 4J 13C{1H} NMR: δ 71.1(C H ), 91.8(C2), 69.2(C3), (H-H) ) 1). 5 5 74.5(C4), 77.5(C5), 26.8 (-SMe), 167.7(>CdN-), 149.7(C1′), 132.6(C2′), 116.4(C3′), 128.4(C4′), 130.8(C5′), 134.8(C6′) (the signal due to the C1 carbon atom could not be detected in this case). 195Pt{1H} NMR: δ -3488. Electrochemical Studies. Electrochemical data for compounds under study were obtained by cyclic voltammetry under nitrogen at ca. 20 °C using acetonitrile HPLC-grade as solvent, tetrabutylammonium hexafluorophosphate, {(Bu4N)[PF6]}, (0.1 M) as supporting electrolyte, and a M263A potentiostat from EG&G instruments. The half-wave potentials E1/2 were referred to an Ag-AgNO3 (0.1 M in acetonitrile) electrode separated from the solution by a medium-porosity fritted disk. A platinum wire auxiliary electrode was used in conjunction with a platinum disk working TACUSSEL-EDI rotatory electrode (3.14 mm2). Cyclic voltammograms of ferrocene were

0.517 and -0.382

recorded before and after each sample to ensure the repeatability of the results, in particular to test and monitor the stability of the Ag-AgNO3 electrode. Cyclic voltammograms of freshly prepared solutions (10-3 M) of the samples in acetonitrile were run, and average E1/2 values measured were then referred to ferrocene, E1/2(Fc), which was used as internal reference. In these experimental conditions the standard error of the measured potentials is (5 mV. In all experiments, the cyclic voltammograms were registered using scan speeds varying from υ ) 10 mV s-1 to 100 mV s-1. Mo1 ssbauer Spectra. Mo¨ssbauer spectra were recorded using powdered solid samples. The spectra were collected at 80 K with the sample placed inside an Oxford Instrument cryostat. The samples were placed in liquid N2 quenched to 80 K and transferred to a cryostat. The spectra were obtained using a constant acceleration Mo¨ssbauer spectrometer with a 57Co/Rh source. The source was moved via triangular velocity wave and the γ-counts were collected in a 512 multichannel analyzer. The data were folded, plotted, and fitted by a computer procedure. Velocity calibration was done using a 25 µm thick metallic Fe foil, and the Mo¨ssbauer spectral parameters (presented in Table 3) are given relative to this standard at room temperature. Crystallography. A prismatic crystal of 1c, 2c, or 3c (sizes in Table 6) was selected and mounted on a MAR345 diffractometer (for 1c and 2c) with an image plate detector or on a Enraf-CAD4 four-circle diffractometer (for 3c). Unit cell parameters were determined from automatic centering of 10 329 reflections (in the range 3° < θ < 21°) for 1c or 6787 reflections (3° < θ < 31°) for 2c, while for 3c, unit cell parameters were determined from automatic centring of 25 reflections in the range 12° < θ < 21° and refined by a leastsquares full-matrix method. In the three cases intensities were collected with graphite-monochromatized Mo KR radiation. The number of reflections collected was 10 329 (in the range 1.96° e θ e 28.87°) for 1c, 11 179 (2.97° e θ e 31.60°) for 2c, and 5184 (in the range 3.17° e θ e 30.02°) for 3c; among these reflections 6393 (for 1c), 5038 (for 2c), and 4993 (for 3c) were nonequivalent by symmetry [Rint (on I) ) 0.021, 0.034, and 0.41 for 1c-3c, respectively]. The number of reflections assumed as observed applying the condition I > 2σ(I) was 4870

236


for 1c, 3318 for 2c, and 2462 for 3c. Lorentz-polarization corrections were made in the three cases, and absorption corrections were also performed for 2c and 3c. The structures were solved by direct methods, using the SHELXS computer program,56 and refined by a full-matrix least-squares method with the SHELX97 computer program,57 using 6393 (for 1c), 5038 (for 2c), and 4993 (for 3c) reflections (very negative intensities were not assumed). The function minimized was ∑w ) ||Fo|2 - |Fc|2|2, where w ) [σ2(I) + (0.0912P)2 + 0.5827P]-1 (for 1c), w ) [σ2(I) + (0.0602P)2 + 1.4499P]-1 (for 2c), and w ) [σ2(I) + (0.0618P)2]-1 (for 3c) and P ) (|Fo| + 2|Fc|)/3; f, f ′, and f ′′ were taken from International Tables of X-Ray Crystallography.58 For 1c, 33 hydrogen atoms were located from a difference synthesis and refined with an overall isotropic temperature factor, and one hydrogen was computed and refined using a riding model, with an isotropic temperature equal to the equivalent temperature factor of the atom linked to it, while for 2c and 3c all the hydrogen atoms were computed and refined, using a riding model, with an isotropic temperature factor equal to 1.2 times the equivalent temperature factor of the atom to which it is linked. The final R(on F) factors were 0.044, 0.045, and 0.056 for 1c, 2c, and 3c, respectively. Further details concerning the resolution and refinement of the crystal structures of 1c-3c are presented in Table 6. Computational Details. Calculations were carried out at the B3LYP computational level59 with the Gaussian 98 package,60 using the LANL2DZ basis set.48 Geometry optimizations were performed without symmetry restrictions. To improve the calculated geometry, polarization functions were added to the (56) Sheldrick, G. M. SHELXS. A computer program for determination of crystal structure; University of Go¨ttingen: Germany, 1997. (57) Sheldrick, G. M. SHELX97. A computer program for determination of crystal structure; University of Go¨ttingen: Germany, 1997. (58) International Tables of X-Ray Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV, pp 99-100 and 149. (59) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.

Pe´ rez et al. Dunning-Huzinaga full double basis set48d for H, C, N, and S atoms, while for Pd and Pt the LANL2DZ basis set was used.48a-c Solvent effects have been taken into account using the polarizable conductor calculation model49 also at the B3LYP level; in this case, the basis set was chosen as follows: LANL2DZ for Pd and Pt and TZV50 for the other atoms. Time-dependent DFT calculations have been performed at the B3LYP/LANL2DZ level using the geometries previously optimized in the same conditions.

Acknowledgment. We are grateful to the Ministerio de Ciencia y Tecnologıá of Spain and to the Generalitat de Catalunya for financial support (projects BQU2003-00906 and 2001-SGR-00045). S.P. is also grateful to the Generalitat de Catalunya for a predoctoral fellowship. Supporting Information Available: Tables containing a selection of bond lengths and angles for the optimized geometries (Table S1), crystal data and structure refinement details, atomic coordinates and equivalent isotropic parameters, all bond lengths and angles, hydrogen bond lengths and angles, anisotropic displacement parameters, and hydrogen coordinates for compounds 1c-3c: Tables S2-S16. This material is available free of charge via the Internet at http://pubs.acs.org. OM030520D (60) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewsi, V. G.; Montgomery, J. A., Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Menucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Salvador, P.; Dannenberg, J. J.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; AlLaham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, Revision A.11; Gaussian, Inc.: Pittsburgh, PA, 2001.

Novel Five-Membered Pallada- and Platinacycles ... - ACS Publications

Recommend Documents