5492
Inorg. Chem. 2000, 39, 5492-5495
(Schiff Base) Divalent Group 14 Element Species: Manganese and Iron Complexes (Salen)MdMn(CO)2(η5-C5H5) (M14 ) Ge, Sn, Pb) and (Salen)SndFe(CO)4 Dominique Agustin, Ghassoub Rima, Heinz Gornitzka, and Jacques Barrau* He´te´rochimie Fondamentale et Applique´e, UMR 5069 du CNRS, Universite´ Paul-Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 4, France ReceiVed December 30, 1999
Syntheses of the (divalent group 14 species)dicarbonyl(cyclopentadienyl)manganese (Salen)MdMn(CO)2(η5C5H5) [M ) Ge (1), Sn (2), Pb (3)] and [(Salen)tin(II)]tetracarbonyliron (Salen)SndFe(CO)4 (4) are reported. The structures of 2 and 4 were determined by X-ray crystallography. The observed Sn-Mn bond length, 2.4428(7) Å, is the shortest distance observed for this type of bond and corresponds to considerable multiple bonding between these atoms. In complex 4, the iron atom has a slightly distorted trigonal-bipyramidal coordination sphere; the (Salen)tin(II) ligand occupies an axial site, indicating that it functions in this complex as a strong σ-donor and weak π-acceptor ligand. Crystal data for 2: orthorhombic, P212121, a ) 6.972(1) Å, b ) 15.678(2) Å, c ) 19.032(2) Å, R ) β ) γ ) 90°, V ) 2080.3(5) Å3, T ) 173(2) K, Z ) 4. Crystal data for 4: triclinic, P1, a ) 8.465(2) Å, b ) 9.795(3) Å, c ) 13.213(4) Å, R ) 105.55(3)°, β ) 105.15(3)°, γ ) 100.84(3)°, V ) 978.7(5) Å3, T ) 173(2) K, Z ) 2.
Introduction Although numerous transition-metal divalent species of elements of group 14 have been described,1,2 the number of complexes where the main-group metal is bound to manganese is still very small.3-13 Only seven compounds postulated as * To whom correspondence should be addressed. Fax: 33-5-61-55-8204. E-mail:
[email protected]. (1) (a) Brooks, E. H.; Cros, R. J. Organomet. Chem. ReV., Sect. A 1970, 6, 227. (b) Veith, M.; Recktenwald, O. Top. Curr. Chem. 1982, 104, 1. (c) Petz, W. Chem. ReV. 1986, 86, 1019. (d) Lappert, M. F.; Rowe, R. S. Coord. Chem. ReV. 1990, 100, 267. (e) Jastrebski, J. T. B. H.; Van Koten, G. AdV. Organomet. Chem. 1993, 35, 241. (2) For recent investigations, see: (a) Handwerker, H.; Leis, C.; Probst, R.; Bissinger, P.; Grohmann, A.; Kiprof, P.; Herdtweck, E.; Blu¨mel, J.; Auner, N.; Zybill, C. Organometallics 1993, 12, 2162. (b) Ellis, S. L.; Hitchcock, P. B.; Holmes, S. A.; Lappert, M. F.; Slade, M. J. J. Organomet. Chem. 1993, 444, 95. (c) Atwood, D. A.; Atwood, V. O.; Cowley, A. H.; Gobran, H. R. Inorg. Chem. 1993, 32, 4671. (d) Tokitoh, N.; Manmaru, K.; Okazaki, R. Organometallics 1994, 13, 167. (e) Weidenbruch, M.; Stilter, A.; Schlaefke, J.; Peters, K.; von Schnering, H. G. J. Organomet. Chem. 1995, 501, 67. (f) Weidenbruch, M.; Stilter, A.; Peters, K.; von Schnering, H. G. Z. Anorg. Allg. Chem. 1996, 622, 534. (g) Weidenbruch, M.; Stilter, A.; Peters, K.; von Schnering, H. G. Chem. Ber. 1996, 129, 1565. (h) Lang, H.; Weinmann, M.; Fresch, W.; Bu¨chner, M.; Schiemenz, B. J. Chem. Soc., Chem. Commun. 1996, 1299. (i) Weidenbruch, M.; Stilter, A.; Saak, W.; Peters, K.; von Schnering, H. G. J. Organomet. Chem. 1998, 560, 125. (j) Barrau, J.; Rima, G.; El Amraoui, T. J. Organomet. Chem. 1998, 570, 163. (3) Cornwell, A. B.; Harrisson, P. G. J. Chem. Soc., Dalton Trans. 1976, 1054. (4) Magomedov, G. K.-I.; Molasova, G. V.; Druzkhova, G. V. Koord. Khim. 1980, 4 (11), 1687. (5) (a) Gade, W.; Weiss, E. J. Organomet. Chem. 1981, 213, 451. (b) Melzer, D.; Weiss, E. J. Organomet. Chem. 1984, 263, 67. (6) Korp, J. D.; Beranl, I.; Ho¨rlein, R.; Serrano, R.; Herrmann, W. A. Chem. Ber. 1985, 118, 340. (7) Herrmann, W. A.; Kneuper, H.-J.; Herdtweck, E. Angew. Chem., Int. Ed. Engl. 1985, 24, 1062. (8) Onaka, S.; Kondo, Y.; Yamashita, M.; Tatematsu, Y.; Kato, Y.; Goto, M.; Ito, T. J. Am. Chem. Soc. 1985, 107, 1070. (9) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1986, 25, 56. (10) Kneuper, H.-J.; Herdtweck, E.; Hermann, W. A. J. Am. Chem. Soc. 1987, 109, 2508.
having MdMn double bonds have been characterized by X-ray diffraction;5,7,8,10,11,13 they present linear or trigonal-planar arrangements of type I, II, or III. It is noteworthy that the group 14 element M is substituent-free in complexes of types I and III.
Thus, after our studies of the mono- and disubstituted transition-metal complexes of (Schiff base) divalent group 14 metal species [(Salen)M]nM′(CO)6-n (n ) 1, 2; M ) Ge, Sn, Pb; M′ ) Cr, W) characterized by short M′-M bond lengths, indicating that in these complexes the divalent species (Salen)M14a,b,d behave as σ donors with π-acceptor properties,14c we have investigated in this work syntheses and spectroscopic and X-ray analyses of the new monosubstituted divalent group 14 metal dicarbonyl(cyclopentadienyl)manganese (Salen)MdMn(CO)2(η5-C5H5) [M ) Ge (1), Sn (2), Pb (3)] and [(Salen)tin(II)]tetracarbonyliron (Salen)SndFe(CO)4 complexes. Experimental Section General Procedures. All manipulations were performed under an inert atmosphere of nitrogen or argon using standard Schlenk and highvacuum-line techniques. Dry, oxygen-free solvents were employed throughout. Solvents were distilled from sodium benzophenone or P2O5 (11) Herrmann, W. A.; Kneuper, H.-J.; Herdtweck, E. Chem. Ber. 1989, 122, 433, 437, and 445. (12) Schiemenz, B.; Huttner, G.; Zsolnai, Z.; Kircher, P.; Diercks, T. Chem. Ber. 1995, 128, 187. (13) Weidenbruch, M.; Stilter, A.; Saak, W.; Peters, K.; von Schnering, H. G. J. Organomet. Chem. 1998, 560, 125. (14) (a) Agustin, D.; Rima, G.; Barrau, J. Main Group Met. Chem. 1997, 20, 791. (b) Agustin, D.; Rima, G.; Gornitska, H.; Barrau, J. J. Organomet. Chem. 1999, 592, 1. (c) Agustin, D.; Rima, G.; Gornitska, H.; Barrau, J. Eur. J. Inorg. Chem. 2000, 693. (d) Agustin, D.; Rima, G.; Gornitska, H.; Barrau, J. Main Group Met. Chem. 1999, 22, 703.
10.1021/ic9915045 CCC: $19.00 © 2000 American Chemical Society Published on Web 11/01/2000
(Schiff Base) Divalent Group 14 Element Species before use. 1H NMR spectra were recorded on a Bruker AC 80 spectrometer operating at 80 MHz (chemical shifts are reported in ppm relative to internal Me4Si) and 13C NMR spectra on an AC 200 MHz spectrometer; the multiplicity of the 13C NMR signals was determined by the APT technique. 119Sn{1H} NMR spectra were recorded on a Bruker AC 200 or 400 MHz spectrometer (chemical shifts are reported in ppm relative to external Me4Sn). Mass spectra under electron impact (EI) or chemical ionization (CH4) conditions at 70 and 30 eV were obtained on Hewlett-Packard 5989 and Nermag R10-10H spectrometers. IR spectra were recorded on Perkin-Elmer 1600 FT-IR and Lambda17 spectrophotometers. Melting points were taken uncorrected on a Leitz Biomed hot-plate microscope apparatus. Elemental analyses (C, H, N) were performed at the Microanalysis Laboratory of the Ecole Nationale Supe´rieure de Chimie de Toulouse. (Salen)GedMn(CO)2(η5-C5H5) (1). Method 1. A mixture of (Salen)Ge(II)14a,b (0.31 g, 0.91 mmol) and Mn(CO)3(η5-C5H5) (0.18 g, 0.91 mmol) in 50 mL of THF was irradiated for 2 h, during which time the solution became brown. The solvent was removed under reduced pressure. After washing with pentane, filtering, and drying in vacuo, 1 was obtained as a pale orange-brown powder (0.37 g, 80%). Method 2. A solution of Mn(CO)3(η5-C5H5) (0.33 g, 1.62 mmol) in 30 mL of THF was irradiated for 1.5 h. CO was eliminated by bubbling nitrogen gas into the reaction mixture for 15 min. Then a THF (20 mL) suspension of (Salen)Ge(II) (0.55 g, 1.62 mmol) was added. Complex 1 (0.69 g, 83%) was obtained after removing the solvent, washing with pentane, and drying in vacuo. Mp: 280-285 °C (dec). 1H NMR (DMSO-d ): δ 4.66 (m, 9H, C H and CH ), 6.20-7.50 (m, 6 5 5 2 8H, Ar), 8.17 (s, 2H, CHdN). IR (Nujol, KBr, cm-1): νCdN 1620; νCO 1842 s, 1914 s, 2016 w. MS m/z: 516 [M]•+, 460 [M - 2CO]+, 395 [M - (CO)2(η5-C5H5)]+, 340 [M - Mn(CO)2(η5-C5H5)]+. Elem anal. Calcd for C23H19N2O4GeMn: C, 53.49; H, 3.71; N, 5.43. Found: C, 53.60; H, 3.82; N, 5.30. (Salen)SndMn(CO)2(η5-C5H5) (2). Method 1. A mixture of (Salen)Sn(II)14a,b (0.33 g, 0.86 mmol) and Mn(CO)3(η5-C5H5) (0.18 g, 0.86 mmol) in THF (50 mL) was irradiated for 2 h, during which the reaction mixture turned brown. After removal of the solvent, the addition of pentane (ca. 20 mL) gave 2 as a orange-brown powder (0.38 g, 79%). Method 2. Using the same procedure as that described in section 2 of 1, compound 2 was obtained from (Salen)Sn(II) (0.24 g, 0.62 mmol) and Mn(CO)2(η5-C5H5)‚THF (0.15 g, 0.62 mmol). Yield: 0.29 g, 85%. Mp: 270-280 °C (dec). 1H NMR (DMSO-d6): δ 4.25 (m, 9H, C5H5 and CH2), 6.30-7.70 (m, 8H, Ar), 8.25 (s, 2H, CHdN). IR (Nujol, KBr, cm-1): νCdN 1628; νCO 1836 s, 1902 s, 2009 w. MS m/z: 562 [M]•+, 506 [M - 2CO]+, 440 [M - (CO)2(η5-C5H5)]+, 386 [M - Mn(η5-C5H5)(CO)2]+. Elem anal. Calcd for C23H19N2O4SnMn: C, 49.11; H, 3.41; N, 4.98. Found: C, 49.20; H, 3.52; N, 4.90. (Salen)PbdMn(CO)2(η5-C5H5) (3). Method 1. A mixture of (Salen)Pb(II)14a,b (0.31 g, 0.65 mmol) and Mn(CO)3(η5-C5H5) (0.13 g, 0.65 mmol) in 50 mL of THF was irradiated for 2 h. The color of the reaction mixture turned brown. After removal of the solvent, the addition of pentane (ca. 20 mL) and filtration gave 3 as a brown powder (0.25 g, 60%). Method 2. Using the same procedure as that described in section 2 of 1, compound 3 was obtained from (Salen)Pb(II) (0.24 g, 0.51 mmol) and Mn(CO)2(η5-C5H5)‚THF (0.12 g, 0.51 mmol). Yield: 0.27 g, 83%. Mp: >300 °C (dec). 1H NMR (DMSO-d6): δ 4.33 (m, 9H, C5H5 and CH2), 6.40-7.60 (m, 8H, Ar), 8.25 (s, 2H, CHdN). IR (Nujol, KBr, cm-1): νCdN 1626; νCO 1835 s, 1905 s, 2015 w. Elem anal. Calcd for C23H19N2O4PbMn: C, 42.46; H, 2.95; N, 4.31. Found: C, 42.62; H, 3.15; N, 4.20. (Salen)SndFe(CO)4 (4). A suspension of (Salen)Sn(II)14a,b (0.28 g, 0.73 mmol) in 30 mL of toluene was added dropwise to a toluene solution of Fe2(CO)9 (0.27 g, 0.73 mmol). The reaction mixture was stirred for 48 h. The color of the solution turned orange, and a paleyellow precipitate appeared. The precipitate was separated by filtration, washed with pentane, and purified by crystallization from DMSO to give 4 as red-yellow crystals (0.37 g, 92%). Mp: 280-285 °C (dec). 1H NMR (DMSO-d ): δ 4.04 (m, 4H, CH ), 6.50-7.80 (m, 8H, Ar), 6 2 8.81 (s, 2H, CHdN). 13C NMR (DMSO-d6): δ 57.79 (CH2), 123.74 (CHAr), 124.17 (Cq), 127.82 (CHAr), 140.27 (CHAr), 141.60 (CHAr), 135.83 (CHAr), 170.99 (Cq-O), 177.69 (CHdN), 219.29 (CdO). 119Sn{1H} NMR (DMSO-d6): δ -195.8 (1JSn-Fe ) 1909 Hz). IR (Nujol,
Inorganic Chemistry, Vol. 39, No. 24, 2000 5493 Table 1. Selected Bond Lengths [Å] and Angles [deg] for 2 Sn(1)-O(1) Sn(1)-O(2) Sn(1)-N(1) Sn(1)-N(2) Sn(1)-Mn(1) Mn(1)-C(17) Mn(1)-C(18)
Distances 2.064(3) Mn(1)-C(21) 2.082(3) Mn(1)-C(22) 2.244(4) Mn(1)-C(23) 2.294(4) Mn(1)-C(20) 2.4428(7) Mn(1)-C(19) 1.766(5) C(17)-O(3) 1.773(5) C(18)-O(4)
Angles O(1)-Sn(1)-O(2) 81.29(11) N(1)-Sn(1)-N(2) O(1)-Sn(1)-N(1) 81.58(13) O(1)-Sn(1)-Mn(1) O(2)-Sn(1)-N(1) 122.29(12) O(2)-Sn(1)-Mn(1) O(1)-Sn(1)-N(2) 127.67(13) N(1)-Sn(1)-Mn(1) O(2)-Sn(1)-N(2) 77.52(14) N(2)-Sn(1)-Mn(1)
2.117(4) 2.118(4) 2.137(6) 2.139(5) 2.150(5) 1.167(7) 1.162(6) 70.94(15) 117.16(10) 116.38(9) 120.52(10) 115.14(9)
Table 2. Selected Bond Lengths [Å] and Angles [deg] for 4 Sn(1)-O(1) Sn(1)-O(2) Sn(1)-N(1) Sn(1)-N(2) Sn(1)-Fe(1) O(2)-Sn(1)-O(1) O(2)-Sn(1)-N(2) O(1)-Sn(1)-N(2) O(2)-Sn(1)-N(1) O(1)-Sn(1)-N(1) N(2)-Sn(1)-N(1) O(2)-Sn(1)-Fe(1) O(1)-Sn(1)-Fe(1) N(2)-Sn(1)-Fe(1) N(1)-Sn(1)-Fe(1)
Distances 2.063(5) Fe(1)-C(17) 2.044(5) Fe(1)-C(18) 2.226(6) Fe(1)-C(19) 2.224(7) Fe(1)-C(20) 2.4846(14) Angles 83.2(2) C(18)-Fe(1)-C(17) 82.4(2) C(18)-Fe(1)-C(19) 135.2(2) C(17)-Fe(1)-C(19) 124.6(2) C(18)-Fe(1)-C(20) 81.4(2) C(17)-Fe(1)-C(20) 72.6(3) C(19)-Fe(1)-C(20) 116.19(16) C(18)-Fe(1)-Sn(1) 114.02(16) C(17)-Fe(1)-Sn(1) 110.44(18) C(19)-Fe(1)-Sn(1) 118.77(16) C(20)-Fe(1)-Sn(1)
1.770(9) 1.769(8) 1.774(9) 1.782(9)
114.6(4) 89.9(4) 96.7(4) 125.4(4) 119.5(4) 90.9(4) 84.7(3) 89.3(3) 173.2(3) 88.9(3)
KBr, cm-1): νCdN 1627; νCO 1897, 1927, 1944, 2029. MS m/z: 554 [M]•+, 498 [M - CO]+, 470 [M - 2CO]+, 442 [M - 3CO]+, 386 [M - Fe(CO)4]+. Elem anal. Calcd for C20H14N2O6SnFe: C, 43.33; H, 2.55; N, 5.06. Found: C, 43.60; H, 2.70; N, 4.86. X-ray Diffraction Analyses of 2 and 4. All crystals were obtained from concentrated CHCl3 (2) or DMSO (4) solutions. All data were collected at T ) 173 K from an oil-coated shock-cooled crystal21 on a Stoe-IPDS with Mo KR (λ ) 0.710 73 Å) radiation. The structures were solved by direct methods by means of SHELXS-9722 and refined with all data on F2 by means of SHELXL-97.23 All non-hydrogen atoms were refined anisotropically. The hydrogen atoms of the molecules were geometrically idealized and refined using a riding model. Selected bond lengths and angles for 2 and 4 can be found in Tables 1 and 2. A summary of crystal- and structure-refinement data is presented in Table 3. Refinement of an inversion twin parameter24 [x ) 0.01(3) where x ) 0 for the correct absolute structure and +1 for the inverted structure] confirmed the absolute structure of 2.
Results and Discussion The manganese compounds 1-3 were readily obtained by the addition of the divalent (Salen)M14a,b species to the (15) (a) Rossi, A. R.; Hoffmann, R. Inorg. Chem. 1975, 14, 365. (b) Burdett, J. K. Inorg. Chem. 1976, 15, 212. (16) Barbe, J. M.; Guilard, R.; Lecomte, C.; Gerardin, R. Polyhedron 1984, 3, 889. (17) Hitchcock, P. B.; Lappert, M. F.; McGeary, M. J. Organometallics 1990, 9, 884. (18) Weidenbruch, M.; Stilter, A.; Peters, K.; von Schnering, H. G. Chem. Ber. 1996, 129, 1565. (19) Hitchcock, P. B.; Lappert, M. F.; Thomas, S. A.; Thorne, A. J.; Carty, A. J.; Taylor, N. T. J. Organomet. Chem. 1986, 315, 27. (20) Jacobsen, H.; Ziegler, T. Inorg. Chem. 1996, 35, 775. (21) Stalke, D. Chem. Soc. ReV. 1998, 27, 171. (22) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467. (23) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement; Universita¨t of Go¨ttingen: Go¨ttingen, Germany, 1997. (24) (a) Flack, H. D. Acta Crystallogr., Sect. A 1983, 39, 879. (b) Flack, H. D.; Bernardinelli, G. Acta Crystallogr., Sect. A 1999, 55, 908.
5494 Inorganic Chemistry, Vol. 39, No. 24, 2000
Agustin et al.
Table 3. Summary of Crystal Data and Structure Refinement for 2 and 4 formula MT T [K] crystal system space group a [Å] b [Å] c [Å] R [deg] β [deg] γ [deg] V [Å3] Z Fcalcd [mg/m3] cryst size [mm] µ [mm-1] R (I > 2σ(I)) wR2a (all data) a
2
4
C23H19MnN2O4Sn 561.03 173(2) orthorhombic P212121 6.972(1) 15.678(2) 19.032(2) 90 90 90 2080.3(5) 4 1.791 0.7 × 0.2 × 0.1 1.841 0.0288 0.0738
C20H14FeN2O6Sn 552.87 173(2) triclinic P1 8.465(2) 9.795(3) 13.213(4) 105.55(3) 105.15(3) 100.84(3) 978.7(5) 2 1.876 0.6 × 0.5 × 0.3 2.058 0.0552 0.1457
wR2 ) {[∑w(Fc2 - Fo2)2]/[∑w(Fo2)2}1/2.
Scheme 1
photochemically produced Mn(CO)2(η5-C5H5)‚THF intermediate in THF (Scheme 1). Direct irradiation of a mixture of the divalent compounds (Salen)M14a,b and the tricarbonyl complex Mn(η5-C5H5)(CO)3 resulted also in the formation of the complexes in good yields (Scheme 1). The latter method gave pure 1 and 2 in 80% yield, but 3 was contaminated with up to 20% of a second unidentified lead compound and lead metal. All of these newly synthesized complexes (1-3) gave satisfactory elemental analyses and were characterized by 1H, IR, and EI mass spectroscopies. The complexes 1 and 2 are moderately soluble in polar solvents, but compound 3 is almost insoluble in all common organic solvents, except DMSO. All compounds are air- and moisture-sensitive in solution, and compound 3 is also lightsensitive. The 1H NMR spectra showed broad signals at various temperatures, appearing in the expected regions; δ values of the methine proton are between 8.17 and 8.25 ppm, and these signals are shifted slightly downfield compared to those of the parent divalent species. In all cases the chemical shifts and splitting patterns of the CH2N protons are consistent with the presence of N f M intermolecular coordinations in these complexes. The 13C NMR data could not be recorded. The carbonyl region of the IR spectra (Nujol mulls) of samples of compounds 1-3 showed three bands (1, 1842 s, 1914 s, 2016 w cm-1; 2, 1836 s, 1902 s, 2009 w cm-1; 3, 1835 s, 1905 s, 2015 vw cm-1). Only two of these stretching bands are due to compounds 1-3, with Cs symmetry at manganese. The relative position and the very weak intensity (1, 2016 w; 2, 2009 w; 3, 2015 vw cm-1) of the third band observed lead us to attribute it to a solid-state effect3 or to a second compound which is not the structurally characterized one. We were unable
Figure 1. Drawing of (Salen)SndMn(CO)2(η5-C5H5) (2).
to obtain IR spectra of 1-3 in the absence of this band. The CO stretching bands for the germanium compound (1) are at slightly higher frequencies than those for the tin and lead analogues; these differences may indicate a poorer electron transfer from the group 14 metal toward Mn in 1 compared with those in 2 and 3. Because of the N f M intramolecular coordination, the absorptions attributed to the νCdN stretching frequency (1, 1620; 2, 1628; 3, 1626 cm-1) are shifted toward higher frequencies by 5-15 cm-1 in comparison to those for the free ligands; these bands are at lower frequencies than those for the (Salen)M compounds14b but not significantly. The molecular structure of 2 was established by X-ray crystal studies. The molecular structure and atomic numbering scheme are shown in Figure 1. Selected bond lengths and angles are given in Table 1. Crystal data for 2 are given in Table 3. The structure shows that the tin atom is pentacoordinated and lies in a distorted square array, with the salen ligand occupying the base plane at a Sn-N2O2 plane distance of 1.011 Å; this distance is, as expected, shorter than that found for the free stannylene (Salen)Sn (1.11 Å).14d The observed σ(Sn-O) distances (2.064(3) and 2.082(3) Å) are slightly longer than the classical σ(Sn-O) bonds (1.94-2.03 Å);25 the distances 2.244(4) and 2.294(4) Å, shorter than those observed in various Sn(IV) systems with donor-acceptor Sn r N bonds (>2.37 Å),1e are within the normal range for these species. The Sn-Mn bond length, 2.4428(7) Å, is the shortest observed for a compound of the type X2SndMnLn, and this value is almost identical with the SndMn bond length of 2.445(1) Å determined in (µ3-Sn)[(η5-C5H4Me)Mn(CO)2]3, in which the tin atom is substituentfree (type III complex).11 The range for interatomic Mn-Sn single bonds is 2.60-2.70 Å.26 All of these data (NMR, IR, X-ray) seem to indicate that the (Salen)tin(II) ligand behaves as a σ donor with a π-acceptor capacity toward Mn in contrast with numerous X2Sn tin(II) compounds which function as strong σ-donor but very weak π-acceptor ligands. This noteworthy character of (Salen)Sn(II) is most likely due to (i) the peculiar geometry and electronic properties of the Salen group and (ii) the presence on manganese of the cyclopentadienyl ligand, which enhances the π-donor ability of this transition metal. The EIMS spectra of 2 and 3 at 70 eV gave the molecular peaks and the fragments corresponding to successive losses of two carbonyls, cyclopentadienyl, and the transition-metal moiety Mn(CO)2(η5-C5H5). (25) Holloway, C. E.; Melnik, M. Main Group Met. Chem. 1998, 21, 371. (26) Baenziger, N. C. Characterization Organometallic Compounds; Tsutsui, M., Ed.; Interscience Publishers: New York, 1969; Vol. 26, part 1, p 213.
(Schiff Base) Divalent Group 14 Element Species
Figure 2. Drawing of (Salen)SndFe(CO)4 (4).
Scheme 2
Theoretical studies have shown that the axial or equatorial site’s preference of a neutral ligand in trigonal-bipyramidal d8 metal (0) carbonyl complexes depends on the σ-donor and π-acceptor characters of this ligand, with poor σ-donor and good π-acceptor ligands favoring the equatorial sites.15 Thus, to appreciate the relative σ-donor and π-acceptor capacities of the (Salen)M(II) species, complex 4 was synthesized by reaction of nonacarbonyldiiron with the tin(II) compound in toluene at room temperature, as illustrated in Scheme 2, and its structure was elucidated. The molecular structure of 4 is shown in Figure 2. Selected bond lengths and angles of 4 are listed in Table 2. Crystal data are given in Table 3. The local geometries around tin and iron are respectively distorted square-pyramidal (the tin atom lying
Inorganic Chemistry, Vol. 39, No. 24, 2000 5495 1.009 Å above the N2O2 plane) and slightly distorted trigonalbipyramidal. (Salen)Sn occupies an axial position in this trigonal bipyramid, thus indicating that (Salen)tin(II) is a better σ-donor than π-acceptor ligand toward iron. The Sn-Fe distance (2.485(1) Å) is close to those found in three16-18 of the only four X-ray-characterized complexes containing >SndFe bonds but larger than that observed for [2,6-t-Bu2-4-MeC6H2O]2SndFe(CO)4 (2.408(1) Å);19 this may also be indicative of the weak π-acceptor nature of Sn(Salen) toward iron. The lengths of the Sn-O (2.065(5) and 2.044(5) Å) and Sn r N (2.226(6) and 2.224(7) Å) bonds appear to be normal for such a structure. Additionally, the Fe-C trans to tin (1.774(9) Å) bond and the Fe-C equatorial (1.770(9), 1.782(9), and 1.769(8) Å) bond lengths are almost similar. The 1H, 13C, and 119Sn NMR and IR data are consistent with this structure. The 119Sn NMR spectrum consists of a singlet at -195.8 ppm flanked with a satellite doublet produced by coupling with the 57Fe nucleus with 1J(57Fe-119Sn) ) 1909 Hz. The IR spectrum that showed four carbonyl bonds (1897, 1927, 1944, and 2029 cm-1) and the 13C NMR data (219.29 ppm) are also indicative of a C3V symmetry at the iron with the Sn(Salen) ligand in the axial site. The apparent discrepancy between the behavior of the (Salen)tin(II) ligand in 2 and 4 respectively has to be connected with the σ-acceptor and π-donor capacities of the transition-metal moiety [subject to (i) the nature of the transition-metal center and (ii) the number and nature of its ligands]. These results underline the importance of the electronic ground state of the M′Ln fragment in the character of the SndM′ bond.20 To answer the question of the influence of the (Salen)Sn group (in particular of its square-pyramidal geometry) on the π interaction between the tin atom and the transition-metal center, density-functional theory calculations are now in progress. Supporting Information Available: X-ray crystallographic files in CIF format for the structure determinations of compounds 2 and 4. This material is available free of charge via the Internet at http://pubs.acs.org. IC9915045
