Coordination Chemistry of N-Alkylbenzamide-2,3-dithiolates as an Approach to Poly(dithiolate) Ligands: 1,4-Bis[(2,3-dimercaptobenzamido)methyl]benzene and Its Chelate Complex with the (C5H5)Ti Fragment

Article abstract of DOI:10.1021/ic9706616

The bidentate dithiolate ligands N,N-diethyl-2,3-dimercaptobenzamide (H₂-1), bis(N,N-diethyl-2,3-dimercaptoterephthalamide (H₂-2), and 1,4-bis(hydroxymethyl)-2,3-dimercaptobenzene (H₄-3) were synthesized from 2,3-dimercaptobenzoic acid or 2,3-dimercaptoterephthalic acid. The air-sensitive ligands form metallocene complexes of the type [η⁵-C₅H₅)₂Ti(1)] (13), [η⁵-C₅H₅)₂Mo(1)] (15), [(η⁵-C₅H₅)₂Ti(3)] (16), and [(η⁵-C₅H₅)₂Ti(2)] (17). Complexes 15 and 16 were characterized by X-ray diffraction. Selected crystallographic details for 15 are as follows: formula C₂₁H₂₃MoNOS₂; M = 465.49; Pbca; a = 12.536(3), b = 14.313(3), c = 22.463(3) A?; V = 4031(2) A?³; Z = 8; R = 3.56 and R_w = 4.49 for 2111 structure factors (F_o² ≥ 3σ(F_o²)) and 254 refined parameters. The molybdenum complex 15 shows an almost planar Mo(μ-S)₂C₂ chelate ring. Selected crystallographic details for 16 are as follows: formula C₁₈H₁₈O₂S₂Ti; M = 378.35; P1?; a = 10.1778(11), b = 11.5806(14), c = 22.967-(3) A?; α = 96.42(1), β = 101.74(1), α = 108.82(1)°; V = 2462.3(5) A?³; Z = 6; R = 4.79 and R_w = 13.27 for 5426 structure factors (I ≥ 2σ(I)) and 766 refined parameters. All titanocene derivatives assume the envelope conformation. The free activation energy for the flip around the S-S axis was determined for 13 to be 69 kJ/mol. The bis(dithiolate) ligand 1.4-bis[(2,3-dimercaptobenzamido)methyl]benzene (H₄-4) was prepared from 2,3-dimercaptobenzoic acid and converted into the dinuclear air-stable titanocene complex [{(η⁵-C₅H₅)₂Ti}₂(4)] (19). Complex 19 reacts with HCl/CHCl₃ with liberation of free H₄-4 while reaction with NMe₄Cl results in an intramolecular dithiolate shift under formal liberation of [(C₅H₅)₃TiCl] and formation of the square-pyramidal chelate complex (NMe₄)[(η⁵-C₅H₅)Ti(4)], (NMe₄)[20]._ Crystallographic details for (NMe₄)[20]·CH₂Cl₂ are as follows: formula C₃₂H₃₅Cl₂N₃O₂S ₄Ti: M = 740.67; P1?; a = 11.579(4), b = 12.210(4), c = 14.016(4) A?; α = 112.28(2), β = 94.46(3), γ = 104.22(3)?; V = 1744.9(10) A?³; Z = 2; R = 5.35 and R_w = 12.84 for 2870 structure factors (I ≥ 2σ(I)) and 397 refined parameters. The chelate rings in [20]^- assume an endo/exo conformation.

Full text of DOI:10.1021/ic9706616

Inorg. Chem. 1998, 37, 6587-6596
6587
Coordination Chemistry of N-Alkylbenzamide-2,3-dithiolates as an Approach to
Poly(dithiolate) Ligands: 1,4-Bis[(2,3-dimercaptobenzamido)methyl]benzene and Its Chelate
Complex with the (C5H5)Ti Fragment†
Wolfram W. Seidel, F. Ekkehardt Hahn,* and Thomas Lu1gger
Institut fu¨r Anorganische und Analytische Chemie der Freien Universita¨t Berlin, Fabeckstrasse 34-36,
D-14195 Berlin, Germany
ReceiVed May 30, 1997
The bidentate dithiolate ligands N,N-diethyl-2,3-dimercaptobenzamide (H2-1), bis(N,N-diethyl-2,3-dimercaptot-
erephthalamide (H2-2), and 1,4-bis(hydroxymethyl)-2,3-dimercaptobenzene (H4-3) were synthesized from 2,3-
dimercaptobenzoic acid or 2,3-dimercaptoterephthalic acid. The air-sensitive ligands form metallocene complexes
of the type [(η5-C5H5)2Ti(1)] (13), [(η5-C5H5)2Mo(1)] (15), [(η5-C5H5)2Ti(3)] (16), and [(η5-C5H5)2Ti(2)] (17).
Complexes 15 and 16 were characterized by X-ray diffraction. Selected crystallographic details for 15 are as
follows: formula C21H23MoNOS2; M ) 465.49; Pbca; a ) 12.536(3), b ) 14.313(3), c ) 22.463(3) Å; V )
4031(2) Å3; Z ) 8; R ) 3.56 and Rw ) 4.49 for 2111 structure factors (Fo2 g 3σ(Fo )) and 254 refined parameters.
2
The molybdenum complex 15 shows an almost planar Mo(µ-S)2C2 chelate ring. Selected crystallographic details
for 16 are as follows: formula C18H18O2S2Ti; M ) 378.35; P1h; a ) 10.1778(11), b ) 11.5806(14), c ) 22.967-
(3) Å; R ) 96.42(1), â ) 101.74(1), γ ) 108.82(1)°; V ) 2462.3(5) Å3; Z ) 6; R ) 4.79 and Rw ) 13.27 for
5426 structure factors (I g 2σ(I)) and 766 refined parameters. All titanocene derivatives assume the envelope
conformation. The free activation energy for the flip around the S-S axis was determined for 13 to be 69 kJ/
mol. The bis(dithiolate) ligand 1,4-bis[(2,3-dimercaptobenzamido)methyl]benzene (H4-4) was prepared from 2,3-
dimercaptobenzoic acid and converted into the dinuclear air-stable titanocene complex [{(η5-C5H5)2Ti}2(4)] (19).
Complex 19 reacts with HCl/CHCl3 with liberation of free H4-4 while reaction with NMe4Cl results in an
intramolecular dithiolate shift under formal liberation of [(C5H5)3TiCl] and formation of the square-pyramidal
chelate complex (NMe4)[(η5-C5H5)Ti(4)], (NMe4)[20]. Crystallographic details for (NMe4)[20]‚CH2Cl2 are as
follows: formula C32H35Cl2N3O2S4Ti; M ) 740.67; P1h; a ) 11.579(4), b ) 12.210(4), c ) 14.016(4) Å; R )
112.28(2), â ) 94.46(3), γ ) 104.22(3)°; V ) 1744.9(10) Å3; Z ) 2; R ) 5.35 and Rw ) 12.84 for 2870 structure
factors (I g 2σ(I)) and 397 refined parameters. The chelate rings in [20]- assume an endo/exo conformation.
Introduction
olate ligands remained comparatively rare5 and poly(1,2-
dithiolate) chelate ligands were unknown until recently. A first
report on the synthesis and coordination chemistry of a tripodal
tris(dithiolate) ligand appeared in 1995.6 Multidentate, sulfur-
rich ligands of type A (Figure 1), based on benzene-1,2-dithiol,
have been used successfully in the preparation of model
The coordination chemistry of unsaturated 1,2-dithiolate
ligands has been investigated thoroughly during the past decades
and has been reviewed regularly.1 Particularly dithiolenes have
attracted academic interest owing to the “non innocent” behavior
of the dithiolate ligands in these complexes.1,2 On the other
hand, much effort has been dedicated toward practical applica-
tions for dithiolene complexes.3
(4) For example, see the following. (a) Maleonitrile-1,2-dithiolate (mnt2-):
Gray, H. B.; Williams, R.; Bernal, I.; Billig, E. J. Am. Chem. Soc.
1962, 84, 3596 and Eisenberg, R.; Ibers, J. A.; Clark, R. J. H.; Gray,
H. B. J. Am. Chem. Soc. 1964, 86, 113. (b) Bis(trifluormethyl)ethylene-
1,2-dithiolate (tfd2-): Enemark, J. H.; Lipscomb, W. N. Inorg. Chem.
1965, 4, 1729. Schulz, A. J.; Eisenberg, R. Inorg. Chem. 1973, 12,
518. (c) Stilbene-1,2-dithiolate: Schrauzer, G. N.; Mayweg, V.; Finck,
H. W.; Mu¨ller-Westerhoff, U.; Heinrich W. Angew. Chem. 1964, 76,
345. Mahadevan, C.; Seshasayee, M.; Kuppusamy, P.; Manoharan,
P. T. J. Crystallogr. Spectrosc. Res. 1984, 14, 179. (d) Isot-
rithionedithiolate (itd2-): Lindqvist, O.; Sjo¨lin, L.; Sieler, J.; Ste-
imecke, G.; Hoyer, E. Acta Chem. Scand. 1979, A33, 445. (e) 1,2-
Dicarbomethoxyethylene-1,2-dithiolate: Bolinger, C. M.; Rauchfuss,
T. B. Inorg. Chem. 1982, 21, 3947. Coucouvanis, D.; Hadjikyriacou,
A.; Toupadakis, A.; Koo, S.-M.; Ileperuma, O.; Draganjac, M.;
Salifoglou, A. Inorg. Chem. 1991, 30, 754. (f) Two of the few
unsymmetrically substituted dithiolate ligands are the following. (4-
Phenyloctyl)ethylene-1,2-dithiolate: Cotrait, M.; Gaultier, J.; Poly-
carpe, C.; Giroud, A. M.; Mueller-Westerhoff, U. T. Acta Crystallogr.
1983, C39, 833. Trithionedithiolate (ttd-2): Lindqvist, O.; Sjo¨lin, L.;
Sieler, J.; Steimecke, G.; Hoyer, E. Acta Chem. Scand. 1982, A36,
853.
Whereas numerous symmetrically substituted 1,2-dithiolate
ligands are known,4 unsymmetrically functionalized 1,2-dithi-
† Dedicated to Professor Bernt Krebs on the occasion of his 60th birthday.
(1) (a) McCleverty, J. A. Prog. Inorg. Chem. 1968, 10, 49. (b) Schrauzer,
G. N. Acc. Chem. Res. 1969, 2, 72. (c) Eisenberg, R. Prog. Inorg.
Chem. 1970, 12, 295. (d) Burns, R. P.; McAuliffe, C. A. AdV. Inorg.
Chem. Radiochem. 1979, 22, 303. (e) Mahadevan, C. J. Crystallogr.
Spectrosc. Res. 1986, 16, 347.
(2) (a) Stiefel, E. I.; Eisenberg, R.; Rosenberg, R. C.; Gray, H. B. J. Am.
Chem. Soc. 1966, 88, 2956. (b) Davison, A.; Edelstein, N.; Holm, R.
H.; Maki, A. H. Inorg. Chem. 1963, 2, 1227. (c) For EPR studies see:
Maki A. H.; Edelstein, N.; Davison, A.; Holm, R. H. J. Am. Chem.
Soc. 1964, 86, 4580. Kirmse, R.; Stach, J.; Dietzsch, W.; Steimecke,
G.; Hoyer, E. Inorg. Chem. 1980, 19, 2679.
(3) (a) For a review see: Mueller-Westerhoff, U. T.; Vance, B. Compre-
hensiVe Coordination Chemistry; Pergamon Press: Oxford, U.K.,
1987; Vol 2, p 595. (b) Dithiolene dyes with strong near-IR
absorption: Mueller-Westerhoff, U. T.; Vance, B.; Yoon, D. I.
Tetrahedron 1991, 47, 909. Oliver, S.; Winter, C. AdV. Mater. 1992,
4, 119. (c) Building blocks in conducting and superconducting salts:
Cassoux, P.; Valade, L.; Kobayashi, H.; Kobayashi, A.; Clark, R. A.;
Underhill, A. E. Coord. Chem. ReV. 1991, 110, 115.
(5) Pilato, R. S.; Eriksen, K. A.; Greaney, M. A.; Stiefel, E. I.; Goswami,
S.; Kilpatrick, L.; Spiro, T. G.; Taylor, E. C.; Rheingold, A. L. J. Am.
Chem. Soc. 1991, 113, 9372.
10.1021/ic9706616 CCC: $15.00 © 1998 American Chemical Society
Published on Web 12/01/1998

6588 Inorganic Chemistry, Vol. 37, No. 26, 1998
Seidel et al.
Figure 1. Topology of bis(thioether-thiol) (A) and bis(dithiol) ligands
(B).
compounds for the active sites in nitrogenase7 and for certain
nickel enzymes.8 In the ligands of type A, two aromatic
dithiolate units are bridged via a thioether link which leads to
a tetradentate ligand with two thiolate and two thioether sulfur
donor atoms. The formation of the thioether links leads, in spite
of the superb properties of ligands of type A, to a loss of the
dithiolene character in the bidentate binding unit.
Our approach to sulfur-rich multidentate ligands was directed
at the utilization of the dithiolene-like metal-binding capacity
of benzene-1,2-dithiolates, which differs from the benzene-
thiolate-thioether ligation in A. We aimed to prepare tetraden-
tate ligands with two benzene-1,2-dithiolate donors of type B
(Figure 1) in which the bidentate binding unit might retain some
dithiolene character upon coordination.
For the preparation of ligands of type B a suitably ortho-
functionalized benzene-1,2-dithiol was needed. We decided to
base our ligand design on 2,3-dimercaptobenzoic acid6 and to
bridge two such molecules by suitable diamines under formation
of stable amide bonds. A similar approach was used previously
by Raymond et al. for the preparation and evaluation of a
multitude of poly(catechoylamide) ligands.9
Ligands of type B not only offer the opportunity for the
preparation of new model complexes for the active sites in
sulfur-containing metalloenzymes but might also allow an
investigation of how geometric constraints originating com-
paratively far from the metal center in the organic backbone of
the ligand affect the properties of the coordinated metal center.
This might lead to interesting dithiolene complexes for metals
known to change their coordination geometry during redox
reactions.10
In this contribution, we describe the synthesis of the new
ortho-functionalized dithiolate ligands H2-1, H2-2, and H4-3
(Figure 2) from 2,3-dimercaptobenzoic acid or 2,3-dimercap-
toterephthalic acid, respectively, as well as their coordination
chemistry with metallocene fragments. In addition, we present
the synthesis and the purification of the bridged bis(dithiolate)
ligand H4-4 and the crystal structure of the chelate complex
(NMe4)[(η5-C5H5)Ti(4)].
Figure 2. Novel bridged and unbridged dithiolate ligands.
analyses (C, H, N, S) were performed at the Freie Universita¨t Berlin
on a Perkin-Elmer 240 C elemental analyzer. Mass spectra (FAB, EI)
were recorded on Varian MAT 311A and Varian MAT 711 instruments,
respectively. Benzene-1,2-dithiol was prepared from thiophenol.11 1,4-
Bis(aminomethyl)benzene was obtained from Aldrich.
The preparation of 2,3-dimercaptobenzoic acid, C (Scheme 1), has
been reported.6,12 Our preparation from benzene-1,2-dithiol followed
the reported synthesis of mercaptobenzoic acid from thiophenol.13 We
observed the formation of C together with the terephthalic acid
derivative D (Scheme 1). Alkylation of the thiol functions leads to
more stable compounds which can be purified chromatographically.
The isolation of the benzoic acid 5a has been described earlier.6 The
benzoic acid 5b was synthesized similarly to 5a from a mixture of C
and D by using benzyl bromide as the alkylating agent. The 2,3-bis-
(alkylthio)terephthalic acids (R ) isopropyl, 6a; R ) benzyl, 6b) are
formed as byproducts (5-20%) during the preparation of 5a and 5b.6
The purification of 5a, 5b, 6a and 6b was achieved by column
chromatography on SiO2 using diethyl ether/petroleum ether (bp 40-
60 °C) as the eluent.
Synthesis of N,N-Diethyl-2,3-bis(benzylthio)benzamide (7b). The
conversion of 5a,b and 6a,b into the benzamides 7a,b and 8a,b was
achieved by routine procedures (Scheme 2). The preparation of 7b is
described as an example. A mixture of 500 mg of 5b (1.37 mmol) in
10 mL of CHCl3, 0.2 mL of SOCl2, and a few drops of DMF (DMF )
dimethylformamide) was heated under reflux for 2 h. The oily benzoic
acid chloride obtained after removal of the solvent was dissolved in
10 mL of THF (THF ) tetrahydrofuran), and this solution was added
to a solution of diethylamine (0.3 mL, 2.9 mmol) in 20 mL of THF.
After being stirred at ambient temperature for 12 h, the solution was
reduced to dryness. The residue was redissolved in Et2O (Et2O )
diethyl ether), and the solution was filtered through SiO2. After removal
of the solvent, 496 mg (86%) of 7b was obtained as a colorless oil. 1H
NMR (CDCl3, 250 MHz): δ 7.40-7.18 (m, 12 H, Ar H), 7.02 (dd, 1
H, Ar H), 4.24 (d, 1 H, SCH2), 4.14 (s, 2 H, SCH2), 4.12 (d, 1 H,
SCH2), 3.84 (dq, 1 H, NCH2), 3.34 (dq, 1 H, NCH2), 3.00 (m, 2 H,
NCH2), 1.32 (dd, 3 H, CH2CH3), 1.00 (dd, 3H, CH2CH3). 13C{1H}
NMR (CDCl3, 62.90 MHz): δ 168.7 (CON), 145.9, 144.5, 136.9, 125.7
(Ar C), 129.4-126.7 (total of eight signals, Ar C), 124.8, 122.0 (Ar
C), 42.4 (NCH2), 40.3 (SCH2), 38.8 (NCH2), 36.8 (SCH2), 13.5, 12.2
(NCH2CH3).
Experimental Section
Materials and Methods. If not noted otherwise, all manipulations
were performed in an atmosphere of dry argon by using standard
Schlenk techniques. Solvents were dried by standard methods and
freshly distilled prior to use. 1H and 13C NMR spectra were recorded
on Bruker AM 250 and AM 270 spectrometers, respectively. Elemental
(6) Hahn, F. E.; Seidel, W. W. Angew. Chem., Int. Ed. Engl. 1995, 34,
2700.
(7) (a) Sellmann, D.; Soglowek, W.; Knoch, F.; Moll, M. Angew. Chem.,
Int. Ed. Engl. 1989, 28, 1271. (b) Sellmann, D.; Soglowek, W.; Knoch,
F.; Ritter, G.; Dengler, J. Inorg. Chem. 1992, 31, 3711.
(8) Sellmann, D.; Fu¨nfgelder, S.; Po¨hlmann, G.; Knoch, F.; Moll, M. Inorg.
Chem. 1990, 29, 4772.
(9) Garrett, T. M.; McMurry, T. J.; Hossaini, M. W.; Reyes, Z. E.; Hahn,
F. E.; Raymond, K. N. J. Am. Chem. Soc. 1991, 113, 2965.
(10) Henkel, G.; Greiwe, K.; Krebs, B. Angew. Chem., Int. Ed. Engl. 1985,
24, 117.
N,N-Diethyl-2,3-bis(isopropylthio)benzamide (7a). Yield: 80%;
colorless oil. IR (KBr, cm-1): ν ) 1633 (vs, CdO). 1H NMR (CDCl3,
(11) Giolando, D. M.; Kirschbaum, K. Synthesis 1992, 451.
(12) Sellmann, D.; Becker, T.; Knoch, F. Chem. Ber. 1996, 129, 509.
(13) (a) Figuly, G. D.; Loop, C. K.; Martin, J. C. J. Am. Chem. Soc. 1989,
111, 654. (b) Block, E.; Eswarakrishnan, V.; Gernon, M.; Ofori-Okai,
G.; Saha, C.; Tang, K.: Zubieta, J. J. Am. Chem. Soc. 1989, 111,
658. (c) Smith, K.; Lindsay, C. M.; Pritchard, G. J. J. Am. Chem.
Soc. 1989, 111, 665.

Poly(dithiolate) Complexes
Inorganic Chemistry, Vol. 37, No. 26, 1998 6589
Scheme 1. Functionalization of Benzene-1,2-dithiol
Scheme 2. Synthesis of Ortho-Functionalized Dithiols H2-1, H2-2, H4-3, and H2-11
250 MHz): δ 7.28 (m, 2 H, Ar H), 7.04 (dd, 1 H, Ar H), 4.80 (dq, 1
H, NCHHCH3), 3.55 (m, 2 H, SCH(CH3)2), 3.20 (dq, 1 H, NCHHCH3),
3.08 (m, 2 H, NCH2CH3), 1.44 (m, 6 H, CH(CH3)2), 1.25 (m, 9 H,
NCH2CH3 and CH(CH3)2), 1.04 (t, 3 H, NCH2CH3). 13C{1H} NMR
(CDCl3, 62.90 MHz): δ 168.9 (CON), 145.5, 144.6, 128.9, 128.0,
125.8, 122.4 (Ar C), 42.8 (NCH2), 38.5 (NCH2), 40.1 (SCH), 35.5
(SCH), 23.2, 22.9, 22.4, 22.2 (SCH(CH3)2), 13.6, 12.1 (NCH2CH3).
N,N,N′,N′-Tetraethyl-2,3-bis(isopropylthio)terephthalamide (8a).
Pure 8a and 8b were obtained after column chromatography (SiO2,
eluent Et2O). Yield: 8% based on C6H4(SH)2; colorless crystals (mp
67 °C). Anal. Calcd (found) for C22H36N2O2S2 (fw ) 424.66): C,
62.22 (62.07); H, 8.54 (8.49); N, 6.60 (6.53). 1H NMR (CDCl3, 250
MHz): δ 7.25 (s, 2 H, Ar H), 3.90 (dq, 2 H, NCHHCH3), 3.65 (sept,
2 H, SCH), 3.30 (dq, 2 H, NCHHCH3), 3.05 (m, 4 H, 2 × NCHHCH3),
1.30 (t, 6 H, NCH2CH3), 1.25 (m, 12 H, CH(CH3)2), 1.05 (t, 6 H,
NCH2CH3). 13C{1H} NMR (CDCl3, 62.90 MHz): δ 168.4 (CON),
144.6, 137.8, 126.7 (Ar C), 42.4, 41.1 (NCH2), 38.5 (SCH), 23.0 22.6
(CH(CH3)2), 13.6, 11.9 (NCCH3).

6590 Inorganic Chemistry, Vol. 37, No. 26, 1998
Seidel et al.
N,N,N′,N′-Tetraethyl-2,3-bis(benzylthio)terephthalamide (8b).
Yield: 5% based on C6H4(SH)2. Recrystallization from Et2O/hexane
yielded colorless crystals (mp 135 °C) of 8b. Anal. Calcd (found)
for C30H36N2O2S2 (fw ) 520.75): C, 69.19 (69.66); H, 6.97 (6.71); N,
5.38 (5.48). 1H NMR (CDCl3, 250 MHz): δ 7.32-7.12 (m, 12 H, Ar
H), 4.20 (d, 2 H, SCHHPh), 4.00 (d, 2 H, SCHHPh), 3.80 (dq, 2 H,
NCHHCH3), 3.26 (dq, 2 H, NCHHCH3), 2.84 (dq, 2 H, NCHHCH3),
2.74 (dq, 2 H, NCHHCH3), 1.24 (dd, 6 H, CH3), 0.94 (dd, 6 H, CH3).
13C{1H} NMR (CDCl3, 62.90 MHz): δ 168.4 (CON), 144.7, 137.3,
137.0, 129.3, 128.0, 126.9, 126.8 (Ar C), 42.5, 41.3 (NCH2), 38.7
(SCH2Ph), 13.6, 12.1 (NCCH3).
Synthesis of 1,4-Bis(hydroxymethyl)-2,3-bis(isopropylthio)ben-
zene (10). The crude acid 6a (3.0 g) was treated with SOCl2 as
described above. The reaction product was dissolved in 5 mL of
pyridine, and methanol (10 mL) was added. After being stirred
overnight, the mixture was poured into water (50 mL) and extracted
with Et2O (3 time 30 mL). The diester 9 could be isolated after
stripping of the solvent by column chromatography (SiO2, eluent
petroleum ether (bp 40-60 °C)/Et2O, 5:1). Yield: 1.91 g (10% based
on C6H4(SH)2). A 500 mg (1.46 mmol) sample of 9 was dissolved in
20 mL of diethyl ether, and this solution was added dropwise to a
suspension of 89 mg (2.34 mmol) LiAlH4 in 10 mL of diethyl ether.
The reaction mixture was stirred at room temperature for 16 h.
Hydrolysis with water and sulfuric acid resulted in the formation of
two phases. The organic layer was isolated, washed with NaHCO3/
H2O and water, and dried over MgSO4. Removal of the solvent and
column chromatography (SiO2, eluent Et2O/petroleum ether (bp 40-
60 °C), 2:1) yielded 330 mg (78% relative to 9) of 10 as an analytically
pure white powder. Anal. Calcd (found) for C14H22O2S2 (fw )
286.45): C, 58.70 (58.21); H, 7.74 (7.65). 1H NMR (CDCl3, 250
MHz): δ 7.34 (s, 2 H, Ar H), 4.80 (s, 4 H, CH2OH), 3.56 (sept, 2 H,
CH(CH3)2), 3.18 (s, 2 H, OH), 1.20 (d, 12 H, CH(CH3)2). 13C{1H}
NMR (CDCl3, 62.90 MHz): δ 145.4, 138.7, 127.7 (Ar C), 63.8 (CH2-
OH), 40.6 (SCH(CH3)2), 22.8 (CH(CH3)2).
(CH3)2). 13C{1H} NMR (CDCl3, 62.90 MHz): δ 203.0 (CO), 149.2,
145.5, 128.8, 127.8, 126.8, 122.6 (S2Ar C), 133.9, 129.4, 128.3, 127.4
(Bz-Ar C), 50.9 (CH2Ph), 40.7, 35.9 (SCH(CH3)2), 22.9, 22.6 (SCH-
(CH3)2).
Titanocene Complexes 13, 14, 16, and 17. The preparation of 13
is described as an example. A sample of 249 mg (1.0 mmol) of [(η5-
C5H5)2TiCl2] was mixed with crude H2-1 (the reaction product of
method A dealkylation of 1 mmol of 7b) in 30 mL of THF. The
resulting red solution was treated with 0.28 mL (2 mmol) of NEt3,
causing the solution to turn green. After 2 h of stirring, the solvent
was removed and the air-stable green residue was purified chromato-
graphically (SiO2, eluents CH2Cl2/diethyl ether, 1:1, for 13 and 14, CH2-
Cl2/MeOH, 7:1, for 16, CH2Cl2/MeOH, 20:1, for 17).
Bis(η5-cyclopentadienyl)(N,N-diethylbenzamide-2,3-dithiolato)-
titanium(IV) (13). Yield: 241 mg (58% relative to crude H2-1). Anal.
Calcd (found) for C21H23NOS2Ti (fw ) 417.42): C, 60.43 (60.68); H,
5.55 (5.69); N, 3.36 (3.23). 1H NMR (CDCl3, 250 MHz): δ 7.44 (dd,
1 H, Ar H), 7.12 (t, 1 H, Ar H), 7.00 (dd, 1 H, Ar H), 6.24 (s, br, 5 H,
C5H5), 5.80 (s, br, 5 H, C5H5), 3.64 (m, 1 H, NCHHCH3), 3.48 (m, 1
H, NCHHCH3), 3.20 (m, 2 H, NCH2CH3), 1.20 (dd, 3 H, CH2CH3),
1.04 (dd, 3 H, CH2CH3). 13C{1H} NMR (CDCl3, 62.90 MHz): δ 170.2
(CON), 158.4, 151.7, 138.0, 129.6, 124.6, 121.4 (Ar C), 113.5, 112.2
(C5H5), 42.7 (NCH2), 38.5 (NCH2), 14.2 (NCH2CH3), 12.8 (NCH2CH3).
Bis(η5-cyclopentadienyl)[(2-phenyl-1-oxoethyl)benzene-2,3-dithi-
olato]titanium(IV) (14). Complex 14 was a side product in the reaction
of crude H2-1 (containing some H2-11) with titanocene dichloride. The
yield of 14 was especially high if crude H2-1 obtained via method B
was used, while method A yielded H2-1 with little or no H2-11 and
therefore almost no 14. Yield: 131 mg of 14 (30% based on method
B dealkylation of 1 mmol of 7b). Compound 14 crystallized from a
toluene/hexane solution as dark green needles. Anal. Calcd (found)
1
for C24H20OS2Ti (fw ) 436.42): C, 66.05 (66.41); H, 4.62 (4.45). H
NMR (CDCl3, 250 MHz): δ 7.55 (dd, 1 H, Ar H), 7.32-7.12 (m, 7
H, Ar H), 5.96 (s, br, 10 H, C5H5), 4.28 (s, 2 H, CH2).
Bis(η5-cyclopentadienyl)[1,4-bis(hydroxymethyl)benzene-2,3-dithi-
olato]titanium(IV) (16). Yield: 60% (based on crude H4-3). Deep
green crystals (mp 163 °C dec) were grown by slow cooling of a
solution of 16 in toluene/dioxane from 80 °C to ambient temperature.
Anal. Calcd (found) for C18H18O2S2Ti (fw ) 378.34): C, 57.14 (57.17);
H, 4.80 (4.83); S, 16.95 (16.78). 1H NMR (CDCl3, 250 MHz): δ 7.24
(s, 2 H, Ar H), 6.10 (s, br, 10 H, C5H5), 4.85 (d, 4 H, CH2), 2.80 (t, 2
H, OH). MS (EI, 70 eV), m/e (relative intensity, assignment): 378 (1,
M+), 295 (1, M+ - C5H5 - H2O), 183 (3, M+ - (C5H5)2Ti - OH), 66
(100, C5H6+).
Bis(η5-cyclopentadienyl)(N,N,N′,N′-tetraethylterephthalamide-
2,3-dithiolato)titanium(IV) (17). Diffusion of pentane into a solution
of crude 17 in toluene yielded thin green needles that were collected
to yield pure 17 (53% based on crude H2-2). Anal. Calcd (found) for
C26H32N2O2S2Ti (fw ) 516.55): C, 60.46 (60.74); H, 6.24 (6.36); N,
5.42 (5.28). 1H NMR (CDCl3, 250 MHz): δ 7.28 (s, 2 H, Ar H),
7.06, 6.34, 6.10, 5.92 (s, br, 10 H, C5H5), 3.68 (m, 2 H, NCH2), 3.54
(m, 2 H, NCH2), 3.28 (m, 4 H, NCH2), 1.30 (t, 6 H, CH2CH3), 1.12 (t,
6 H, CH2CH3).
Bis(η5-cyclopentadienyl)(N,N-diethylbenzamide-2,3-dithiolato)-
molybdenum(IV) (15). The disodium salt Na2-1 was used for the
preparation of 15. This salt was obtained from 7b by method A without
acidification of the reaction product. A solution of Na2-1 (obtained
from 497 mg of 7b, 1.18 mmol) in 15 mL of water was added to a
suspension of 350 mg (1.18 mmol) of [(η5-C5H5)2MoCl2] in 30 mL of
benzene. After 1 h of stirring, the reddish brown benzene phase was
isolated and reduced to 10 mL. Column chromatography (Florisil,
eluent benzene/MeOH, 10:1) gave 208 mg (38% relative to 7b) of 15.
Crystals were obtained by cooling a CH3CN solution of 15 to -30 °C.
Anal. Calcd (found) for C21H23NOS2Mo (fw ) 465.48): C, 54.19
(54.46); H, 4.98 (5.13); N, 3.01 (2.89); S, 13.78 (13.03). IR (KBr,
cm-1): ν ) 1617 (vs, CdO). 1H NMR (CD3CN, 250 MHz): δ 7.23
(d, 1 H, Ar H), 6.65 (t, 1 H, Ar H), 6.45 (d, 1 H, Ar H), 5.30 (s, 10 H,
C5H5), 3.45 (m, 2 H, NCH2CH3), 3.17 (m, 2 H, NCH2CH3), 1.21 (t, 3
H, NCH2CH3), 1.00 (t, 3 H, NCH2CH3). MS (EI, 80 eV), m/e (relative
intensity, assignment): 467 (100, M+), 395 (13, M+ - NEt2), 367 (9,
M+ - CONEt2), 302 (13, [367 - C5H5]+), 228 (41, [(C5H5)2Mo]+).
Removal of the Protection Groups at Sulfur in 7b, 8b, and 10.
The dealkylation of 7b is described as an example.
Method A. A solution of 421 mg (1 mmol) of 7b in 10 mL of
THF was added to a solution of 92 mg (4 mmol) of sodium in 30 mL
of liquid ammonia. After 15 min, the reaction was quenched with 107
mg (2 mmol) of NH4Cl. Upon quenching, the mixture became clear
and the color turned from blue to orange. The solvents were removed,
and the residue was redissolved in 20 mL of water saturated with argon.
The resulting orange solution was washed with 20 mL of diethyl ether.
Acidification with hydrochloric acid (2 mL of a 36% solution) led to
a white precipitate which was extracted with diethyl ether (3 times, 10
mL each). The combined organic phases were dried over MgSO4, and
after removal of the solvent, crude H2-1 was obtained as an off-white
solid.
The dealkylation of the diol 10 required the previous deprotonation
of the hydroxy functions with 2 equiv of n-BuLi in THF at -78 °C in
order to avoid Birch reductions of the aromatic ring during S-C(iso-
propyl) bond cleavage. For completion of the reaction of deprotonated
10 with sodium in NH3, a distinctly prolonged reaction time of 90 min
was necessary. The workup was carried out as described for 7b.
Method B. A solution of 200 mg (0.47 mmol) of 7b and 270 mg
(2.11 mmol) of naphthalene in 20 mL of THF was treated with 44 mg
(1.92 mmol) of sodium (pieces), and the mixture was stirred for 12 h
at ambient temperature. The reaction in the reddish brown mixture
was quenched with 2 mL of MeOH, and the resulting mixture was
acidified with 10 mL of HCl (1 M solution in diethyl ether), causing
the formation of a white precipitate. After removal of the solvents,
crude H2-1 was obtained as an off-white solid. Dealkylation of 7b
yielded as a side product the ketone H2-11. H2-11 was characterized
as the titanocene complex 14. Reaction of the H2-1/H2-11 mixture with
isopropyl bromide led to re-formation of 7a and of the S-alkylated
ketone 12. 12 could be separated chromatographically from 7a.
2,3-Bis(isopropylthio)phenyl Benzyl Ketone (12). Yield: 12%
(based on 7b); colorless oil. IR (KBr, cm-1): ν ) 1702 (vs, CdO).
1H NMR (CDCl3, 250 MHz): δ 7.25 (m, 7 H, Ar H), 6.80 (dd, 1 H,
Ar H), 4.20 (s, 2 H, C(O)CH2Ph), 3.52 (sept, 1 H, SCH(CH3)2), 3.44
(sept, 1 H, SCH(CH3)2), 1.41 (d, 6 H, CH(CH3)2), 1.16 (d, 6 H, CH-

Poly(dithiolate) Complexes
Inorganic Chemistry, Vol. 37, No. 26, 1998 6591
Table 1. Summary of Crystallographic Data for 15, 16, and (NMe4)[20]‚CH2Cl2
parameter
15
16
(NMe4)[20]‚CH2Cl2
cryst size, mm
formula
mol wt
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
0.40 × 0.25 × 0.15
C21H23MoNOS2
465.49
12.536(3)
14.313(3)
22.463(3)
90.0
90.0
90.0
4031(2)
8
0.50 × 0.13 × 0.08
C18H18O2S2Ti
378.35
0.6 × 0.4 × 0.02
C32H35Cl2N3O2S4Ti
740.67
10.1778(11)
11.5806(14)
22.967(3)
96.42(1)
101.74(1)
108.82(1)
2462.3(5)
6
11.579(4)
12.210(4)
14.016(4)
112.28(2)
94.46(3)
104.22(3)
1744.9(10)
2
Z
space group
Pbca (No. 61)
1.56
1.534
P1h (No. 2)
not measd
1.531
P1h (No. 2)
not measd
1.410
F
exp, g/cm3
calc, g/cm3
F
µ, cm-1
8.43
7.81
6.71
radiation; λ, Å
data collcn temp, K
2θ range, deg
no. of unique data
no. of obsd data
R, %a
Mo KR; 0.710 73
293(2)
Mo KR; 0.710 73
293(2)
3 e 2θ e 45
6419
5426 (I g 2σ(I))
4.79
13.27
1.122
Mo KR; 0.710 73
193(2)
5 e 2θ e 45
4539
2870 (I g 2σ(I))
5.35
12.84
1.149
2 e 2θ e 45
3535
2111 (Fo2 g 3σ(Fo ))
2
3.56
4.49
1.207
254
Rw, %a
GOF
no. of variables
766
397
2
2
a R ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) [∑w||Fo| - |Fc|| /∑w|Fo| ]1/2. 15 was refined with MolEN against F; 16 and (NMe4)[20]‚CH2Cl2 were refined
against F2 with SHELXL-93. All refinement parameters were calculated for observed data only.
1,4-Bis{[2,3-bis(isopropylthio)benzamido]methyl}benzene (18). A
solution of the acid chloride of 5a (7.22 mmol, synthesized from 1.95
g of 5a as described above) in 10 mL of THF was added to a solution
of 465 mg (3.42 mmol) of 1,4-bis(aminomethyl)benzene and 1 mL of
NEt3 (7.2 mmol) in 40 mL of THF. The suspension obtained was stirred
for 24 h at ambient temperature. Subsequently, the solvent was
removed and the product was purified chromatographically (SiO2, eluent
CH3C(O)OC2H5/CH2Cl2, 1:3). Yield: 1.77 g (81%, relative to 1,4-
bis(aminomethyl)benzene); off-white powder (mp 164 °C). Anal. Calcd
(found) for C34H44N2O2S4 (fw ) 640.98): C, 63.71 (63.55); H, 6.92
(6.50); N, 4.37 (4.21); S, 20.01 (19.16). IR (KBr, cm-1): ν ) 1643
(vs, CdO). 1H NMR (CDCl3, 250 MHz): δ 7.44 (m, 2 H, S2Ar H),
7.40 (s, 4 H, Ar H), 7.30 (m, 4 H, S2Ar H), 7.04 (t, 2 H, NH), 4.62 (d,
4 H, NCH2Ar), 3.48 (m, 4 H, (SCH(CH3)2), 1.36 (d, 12 H, CH(CH3)2),
1.18 (d, 12 H, CH(CH3)2). 13C{1H} NMR (CDCl3, 62.90 MHz): δ
168.2 (CO), 145.6, 142.6, 137.2, 128.8, 128.3, 127.7, 125.3 (Ar C),
43.7 (NCH2), 40.5, 35.9 (SCH(CH3)2), 22.8, 22.5 (CH(CH3)2).
Crude H4-4 and {1,4-Phenylenebis[[(methylamino)carbonyl]-
benzene-2,3-dithiolato]}bis[bis(η5-cyclopentadienyl)titanium(IV)] (19).
A solution of 200 mg (0.31 mmol) of 18 and 416 mg (3.25 mmol) of
naphthalene in 30 mL of THF was treated with 71 mg (3.09 mmol) of
sodium (pieces), and the mixture was then stirred for 12 h at ambient
temperature (method B). The reaction in the resulting brownish mixture
was quenched with 2 mL of MeOH and 10 mL of a 1 M solution of
HCl in Et2O. A white precipitate formed upon quenching. All solvents
were removed, and 154 mg (0.62 mmol) of solid [(η5-C5H5)2TiCl2]
was added to the residue. To this mixture were added 30 mL of THF
and 0.28 mL (2 mmol) of NEt3. A green solution was obtained. After
2 h of stirring, the solvent was almost completely removed and the
residue was put on a chromatographic column (SiO2). The dinuclear
complex 19 was eluted with CH2Cl2/MeOH (25:1). Yield: 166 mg
(65% based on 18); dark green powder. Anal. Calcd (found) for
C42H36N2O2S4Ti2 (fw ) 824.76): C, 61.16 (60.55); H, 4.40 (4.55); N,
3.40 (3.30); S, 15.55 (14.87). IR (KBr, cm-1): ν ) 3291 (m, NH),
1655 (s, CdO). 1H NMR (CDCl3, 250 MHz): δ 7.90 (t, 2 H, NH),
7.65 (d, 2 H, Ar H), 7.53 (d, 2 H, Ar H), 7.35 (s, 4 H, Ar H), 7.17 (t,
2 H, Ar H), 6.00 (s, br, 20 H, C5H5), 4.55 (d, 4 H, NCH2Ar). 13C{1H}
NMR (CDCl3, 62.90 MHz): δ 168.2 (CON), 158.9, 152.5, 134.8, 131.5,
125.5, 124.1 (S2Ar C), 137.3, 127.5 (Ar C), 112.9 (C5H5), 43.3 (NCH2-
Ar).
HCl/CHCl3 solution. Immediately, the green color caused by 19
disappeared and the solution turned red (formation of [(η5-C5H5)2TiCl2])
with formation of a white precipitate (pure, chloroform-insoluble H4-
4). The volume was reduced to 10 mL, and the white precipitate was
collected by filtration, after which it was washed twice with HCl/CHCl3
(5 mL each) and dried in vacuo. Yield: 67 mg (94%); white powder.
Anal. Calcd (found) for C22H20N2O2S4 (fw ) 472.65): C, 55.91
(55.23); H, 4.27 (4.39); N, 5.93 (5.64). 1H NMR ((CD3)2SO, 270
MHz): δ 9.15 (s, br, 2 H, NH), 7.51 (d, 2 H, Ar H), 7.28 (m, 6 H, Ar
H), 7.12 (t, 2 H, Ar H), 4.42 (s, 4 H, NCH2Ar), 4.5-3.5 (s, br, 4 H,
SH).
Tetramethylammonium {1,4-Phenylenebis[[(methylamino)car-
bonyl]benzene-2,3-dithiolato]}(η5-cyclopentadienyl)titanate(IV)
((NMe4)[20]). A 70 mg (0.085 mmol) sample of 19 and 19 mg (0.17
mmol) of NMe4Cl were dissolved in 20 mL of acetonitrile. The
intensely green reaction mixture was heated under reflux for 36 h.
During this time, the color of the solution turned purple. The solvent
was removed, the residue was redissolved in 15 mL of CH2Cl2, and
the solution was filtered. Vapor diffusion of Et2O into the filtrate
yielded after 2 days a crystalline sample of purple (NMe4)[20] (10 mg,
18%). Anal. Calcd (found) for C31H33N3O2S4Ti (fw ) 655.74): C,
56.78 (57.06); H, 5.07 (5.48); N, 6.41 (6.14). 1H NMR (CD2Cl2, 250
MHz): δ 9.28 (s, br, 1 H, NH), 8.72 (s, br, 1 H, NH), 7.80 (d, 1 H, Ar
H), 7.70 (d, 1 H, Ar H), 7.60-7.00 (m, 6 H, Ar H), 6.88 (m, 2 H, Ar
H), 6.25 (s, 5 H, C5H5), 4.76-4.56 (m, 3 H, NHCH2Ar), 4.40 (dd, 1
H, NHCH2Ar), 2.48 (s, 12 H, N(CH3)4+). MS (FAB, negative ions,
3-nitrobenzyl alcohol/dimethyl sulfoxide), m/e (relative intensity,
assignment): 581 (1, [20]-).
Crystal Structure Analyses. Air-stable dark green crystals of 16
were obtained by cooling a toluene/dioxane solution from 80 °C to
room temperature. Red crystals of 15 formed upon cooling an
acetonitrile solution to -30 °C. Diffusion of diethyl ether into to a
dichloromethane solution of (NMe4)[20] at room temperature yielded
air-sensitive (loss of dichloromethane) purple crystals of (NMe4)[20]‚CH2-
Cl2. Suitable specimens were mounted at room temperature (15 and
16) or at 193 K ((NMe4)[20]‚CH2Cl2) on an Enraf-Nonius CAD-4
diffractometer. Routine search and autoindexing procedures yielded
the dimensions of the unit cells for all three compounds. Important
crystal and data collection details are listed in Table 1. Diffraction
data were collected at 293(2) K for 15 and 16 and at 193 K for
(NMe4)[20]‚CH2Cl2 using ω-2Θ scans. Raw data were reduced to
structure factors14 (and their esd’s) by correcting for scan speed and
for Lorentz and polarization effects. No decay or absorption corrections
1,4-Bis[(2,3-dimercaptobenzamido)methyl]benzene (H4-4). Dry
CHCl3 was saturated with dry, gaseous HCl. A solution of 124 mg
(0.15 mmol) of 19 in 10 mL of CHCl3 was treated with 20 mL of the

6592 Inorganic Chemistry, Vol. 37, No. 26, 1998
Seidel et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 15a
Results and Discussion
Distances
Synthetic Strategy and Preparation of the Ligands. The
goal of our study was the preparation of chelate complexes with
bridged bis(dithiolate) ligands of type B (Figure 1). The
investigation of the coordination chemistry of such ligands (for
example, H4-4) was hindered by their poor solubility in most
organic solvents (exceptions DMF and DMSO), their sensibility
to air oxidation, and their pronounced tendency to form
polynuclear complexes when completely deprotonated and
reacted with metal halides. To overcome these problems, we
decided to start with an investigation of simple 2,3-dimercap-
tobenzamides which exhibit all features of H4-4 and to study
their preparation and coordination chemistry. In the course of
this study, we found efficient procedures for the preparation
and purification of bis(dithiolate) ligands such as H4-4 and a
versatile reaction for the preparation of their metal complexes.
Our strategy for the preparation of 2,3-dimercaptobenzamides
involves the protection of the thiolate functions in 2,3-
dimercaptobenzoic acid, C,6,12 with isopropyl groups, the
conversion of the carboxylic acid into an amide, and finally
the removal of the protection groups at the sulfur atoms. As
we showed in a preliminary report6 this strategy turned out to
be successful for the synthesis of the secondary amide H2-E
(Scheme 1) and a tris(dithiolate) ligand, respectively. Here we
report extended investigations that resulted in the preparation
of the new dithiolate ligands H2-1, H2-2, H4-3, and H4-4. The
study comprises the use of tertiary amide functions instead of
secondary ones forcing the replacement of the S-protection
groups in C and D and the isolation of different derivatives of
2,3-dimercaptoterephthalic acid, D, which has been found to
be a byproduct in the synthesis of C.
Mo-S1
Mo-S2
Mo-Cp1
2.431(1)
2.424(2)
2.000(7)
Mo-Cp2
S1-C1
S2-C2
2.000(7)
1.743(5)
1.746(5)
Angles
S1-Mo-S2
S1-Mo-Cp1
S1-Mo-Cp2
81.99(4)
106.4(2)
108.2(2)
S2-Mo-Cp1
S2-Mo-Cp2
Cp1-Mo-Cp2
106.5(2)
108.6(2)
133.2(3)
a Cp denotes the centroids of the cyclopentadienyl rings.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 16a
Distances
TiA-S1A
TiA-S2A
TiA-Cp1A
2.4151(13)
2.4037(14)
2.071(5)
TiA-Cp2A
S1A-C1A
S2A-C6A
2.043(5)
1.756(4)
1.757(4)
Angles
S1A-TiA-S2A
S1A-TiA-Cp1A
S1A-TiA-Cp2A
81.72(4)
109.9(2)
105.9(2)
S2A-TiA-Cp1A
S2A-TiA-Cp2A
Cp1A-TiA-Cp2A
107.8(2)
106.6(2)
132.9(3)
a Cp denotes the centroids of the cyclopentadienyl rings. Molecular
parameters for molecule A are listed. They do not differ significantly
from those of the other two independent molecules in the asymmetric
unit.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for the
Anion in (NMe4)[20]‚CH2Cl2
Distances
Ti-S1
Ti-S2
Ti-S3
Ti-S4
2.390(2)
2.406(2)
2.423(2)
2.409(2)
S1-C1
S2-C2
S3-C19
1.753(6)
1.759(6)
1.764(6)
Angles
The isopropyl- and benzyl-protected compounds 5a/6a and
5b/6b were obtained from a mixture of C/D by reactions with
isopropyl bromide/NaOMe and benzyl bromide/NaOMe, re-
spectively (Scheme 1). In contrast to C and D, the alkylated
derivatives 5a/6a and 5b/6b can be isolated by column
chromatography. Standard procedures via the acid chlorides
led to the tertiary amides 7a,b/8a,b. The terephthalic acid 6a
can be converted into the terephthalic diester 9, which can be
reduced to yield the diol 10 (Scheme 2).
For the subsequent reductive cleavage of the S-alkyl bonds,
we used two methods: (i) sodium in liquid ammonia (method
A)19 and (ii) naphthalene/sodium in THF (method B). The latter
in combination with a water-free workup has been proved to
be more convenient because the use of ammonia is avoided.
We found that the isopropyl groups in 7a and 8a could not be
removed using either method A or method B. Apparently the
presence of tertiary amides prevents the S-C(isopropyl) bond
cleavage. When tertiary benzamides or terephthalamides are
employed, the S-protecting group cannot be isopropyl but must
be benzyl instead. The S-C(benzyl) bonds in 7b and 8b are
readily cleaved by either method A or method B, leading to
the crude dithiols H2-1 and H2-2. While the removal of the
benzyl groups proceeds satisfactorily, these protecting groups
pose another problem. In the debenzylation reaction of 7b, we
noted a side product, which was identified as H2-11 after
realkylation of the H2-1/H2-11 mixture with isopropyl bromide
and chromatographic isolation of 12 (Scheme 2). The formation
of H2-11 is surprising, and we think that benzyl radicals attack
the amide function under ketone formation.
S1-Ti-S2
S1-Ti-S3
S1-Ti-S4
82.58(7)
134.80(7)
79.11(7)
S2-Ti-S3
S2-Ti-S4
S3-Ti-S4
83.42(7)
133.38(7)
80.02(6)
were necessary. The space groups were found to be Pbca for 15 and
P1h for 16 and (NMe4)[20]‚CH2Cl2. The structures were solved by
standard Patterson methods. The positional parameters for all non-
hydrogen atoms were refined with anisotropic thermal parameters.
Difference Fourier maps calculated at this stage showed the positional
parameters of the hydrogen atoms. However, hydrogen atoms were
added to the structure models on calculated positions [d(C-H) ) 0.95
Å, d(N-H) ) 0.87 Å]15 and are unrefined. No hydrogen positions
were calculated for the hydroxyl functions in 16. The isotropic
temperature factors for hydrogen atoms were fixed to be 1.3 times the
U
eq or Beq, respectively, of the parent atom. Calculations were carried
out with the MolEN package16 (refinement on F) for 15 and with
SHELXL-9317 (refinement on F2) for 16 and (NMe4)[20]‚CH2Cl2.
ORTEP18 was used for all molecular drawings. One of the ethyl groups
of the amide in 15 is disordered. The asymmetric unit for 16 contains
three independent molecules. These are held together by a network of
hydrogen bonds (O-H‚‚‚O) in the asymmetric unit. Tables 2-4 list
selected bond distances and angles for 15, 16, and (NMe4)[20]‚CH2-
Cl2, respectively. ORTEP drawings of 15 and 16 and of the anion
[20]- are presented in Figures 3 and 5, respectively.
(14) Neutral-atom scattering factors were used: International Tables for
X-Ray Crystallography; Kynoch Press: Birmingham, England, 1974;
Vol. IV, Table 2.2B. Terms of anomalous dispersion were taken
from: International Tables for X-Ray Crystallography; Kynoch
Press: Birmingham, England, 1974; Vol. IV, Table 2.3.1.
(15) Churchill, M. R. Inorg. Chem. 1973, 12, 1213.
(16) MolEN: Molecular Structure Solution Procedures. Program Descrip-
tions; Enraf-Nonius: Delft, The Netherlands, 1990.
(17) Sheldrick, G. M. SHELX-93: Program for the Solution of Crystal
Structures; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1993.
(18) Johnson, C. K. ORTEP II; Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1971.
(19) (a) Block, E. In The chemistry of ethers, crown ethers, hydroxyl groups
and their sulfur analogues; Patai, S., Ed.; John Wiley: New York,
1980; Supplement E, p 587 ff. (b) Ferretti, A. Org. Synth. 1962, 42,
54.

Poly(dithiolate) Complexes
Inorganic Chemistry, Vol. 37, No. 26, 1998 6593
Scheme 3. Preparation of Mononuclear Dithiolate Metal
Complexes
Figure 3. ORTEP plots of complexes 15 (top) and 16 (bottom). Only
one of the three molecules on the asymmetric unit of 16 is shown.
measures 4.5(6)° and is only slightly smaller than that in [(η5-
C5H5)2Mo(bdt)] (9°).20 As expected for a tertiary amide, the
amide plane is strongly twisted against the benzene plane
(torsion angle C1-C6-C7-O ) 91.8(6)°). Steric rather than
electronic effects must be made responsible for this observa-
tion.22
The corresponding torsion angle in the complex [(η5-C5H5)2-
Ti(E)] with a nonplanar TiS2C2 ring and the sterically less
demanding secondary benzamide is only half as large (45.9-
(15)°)6 as that in 15. From this it appears that least substituted
benzamides are particularly useful for the preparation of
chelating bis(dithiolates).
The S-C(aryl) bond distances in 15 (1.743(5) and 1.746(5)
Å) are slightly shorter than those in the corresponding 2,3-bis-
(alkylthio)benzoic acid.6 They fall, however, in the range
observed for benzene-1,2-dithiolate complexes and are signifi-
cantly longer than those measured for dithiolenes with thio-
keto character, where S-C distances of around 1.70 Å are
typical.1e
The molecular structure of 16 (Figure 3, bottom) resembles
that of the prototype complex [(η5-C5H5)2Ti(S2C6H4)]23 and of
some other 1,2-enedithiolates of (η5-C5H5)2Ti, which have been
characterized crystallographically.4e,24 The asymmetric unit of
16 contains three independent molecules, which do not differ
significantly in their molecular parameters. Surprisingly for the
oxophilic titanium, the hydroxy groups are turned away from
the titanium center and are connected together by hydrogen
bridges (shortest oxygen-oxygen contacts are 2.779-2.903 Å).
In light of these results we decided (i) to prepare only
secondary amides during the synthesis of bis(dithiolate) ligands
and (ii) to use exclusively isopropyl protecting groups in order
to avoid radical side reactions on the bridge. However, H2-1,
H2-2, H4-3, and H4-4 could not be obtained analytically pure
and were used in further coordination attempts as crude products.
Synthesis of Metallocene-Dithiolate Complexes (Metal )
Ti, Mo). Seeking purification procedures for our ligands, we
chose the formation of neutral complexes with metallocene
fragments. These complexes proved to be advantageous because
they allow chromatographic purification. The crude ligands H2-
1, H2-2, and H4-3 react with 1 equivalent of [(η5-C5H5)2TiCl2]
in THF in the presence of triethylamine to yield the intensly
green complexes 13, 14, 16, and 17 (Scheme 3). In contrast to
the free ligands, these complexes are air-stable and are readily
purified by chromatography. Complex formation allowed also
for the separation of H2-1 and H2-11 via formation and
purification of the titanocene complexes 13 and 14. Reaction
of the titanium complexes 13, 14, 16, and 17 with dry HCl in
CHCl3 yielded [(η5-C5H5)2TiCl2] together with the free ligands
as monitored by 1H NMR spectroscopy. This complex degra-
dation turned out to be crucial for the purification of H4-4 (vide
infra).
(20) Kutoglu, A.; Ko¨pf, H. J. Organomet. Chem. 1970, 25, 455.
(21) (a) Knox, J. R.; Prout, C. K. J. Chem. Soc., Chem. Commun. 1967,
1277. (b) Knox, J. R.; Prout, C. K. Acta Crystallogr. 1969, B25, 2013.
(22) Chakrabarti, P.; Dunitz, J. D. HelV. Chim. Acta 1982, 65, 1555.
(23) (a) Kutoglu, A. Z. Anorg. Allg. Chem. 1972, 390, 195. (b) Kutoglu,
A. Acta Crystallogr. 1973, B29, 2891.
(24) (a) Chiesi Villa, A.; Gaetani Manfredotti, A.; Guastini, C. Acta
Crystallogr. 1976, B32, 909. (b) Guyon, F.; Lenoir, C.; Formigue,
M.; Larsen, J.; Amaudrut, J. Bull. Soc. Chim. Fr. 1994, 131, 217.
Description of the Molecular Structures of 15 and 16. The
molecular structure of 15 is depicted in Figure 3 (top). The
bond distances and angles for 15 fall in the range observed
previously for [(η5-C5H5)2Mo(bdt)] (bdt2- ) benzene-1,2-
dithiolate)20 and [(η5-C5H5)2Mo(tdt)] (tdt2- ) toluene-3,4-
dithiolate).21 The angle between the MoS2 and the C6S2 planes

6594 Inorganic Chemistry, Vol. 37, No. 26, 1998
Seidel et al.
Table 5. 1H NMR Data and Calculated Activation Enthalpies for
Dithiolate Complexesa
Tc, ∆νCp
, ∆Gc*,
complex
[(Cp)2Ti(E)]6
13
solvent
CDCl3
°C Hz kJ/mol
ref
10 165
55
69
53
54
57
51
6
Figure 4. Schematic representation of the combined amide/chelate ring
motion during the flip around the S‚‚‚S axis.
toluene-d8 55 22.5
toluene-d8 -20 25.0
this work
26a
26a
26b
26c
[(Cp)2Ti(S2C6H4)]
[(Cp)2Ti(S2C6H3-4-Me)] toluene-d8 -15 25.0
(compare [(η5-C5H5)2Ti(S2C6H4)] to [(η5-C5H5)2Ti(X2C6H4)] (X
) Se, Te)).
[(Cp)2Ti(Se2C6H4)]
[(Cp)2Ti(Te2C6H4)]
toluene-d8 -9 13.5
toluene-d8 -38 10.0
Figure 4 illustrates how the flipping process around the S‚‚
‚S axis is likely combined with a rotation of the amide function
around the C(aryl)-C(amide) bond in order to avoid interaction
of the substituents at nitrogen with the (η5-C5H5)2Ti moiety.
This complex motion is probably rendered more difficult in
complexes such as 13 with a tertiary amide function. This
explanation is corroborated by the observation that the NHR
unit in the envelope structure of [(η5-C5H5)2Ti(E)] points away
from the (η5-C5H5)2Ti moiety while the torsion angle C1-C6-
C7-O measures about 90° in the essentially planar complex
15.
Further evidence for an interaction of the amide substituents
with the cyclopentadienyl rings can be drawn from the 1H NMR
data of complex 17 with two bulky diethylamide substituents.
If the ligand assumes the trans geometry as depicted in Scheme
3, one cyclopentadienyl ring will most likely interact with one
of the diethylamide functions, which explains the observation
of four cyclopentadienyl proton signals in the 1H NMR spectrum
of 17 at room temperature. Thus it appears very likely that, in
complexes with envelope geometry and only one amide ligand,
the amide switches over to the other side of the aromatic ring
during the flip around the S‚‚‚S axis.
a Frequencies: [(Cp)2Ti(E)], 300 MHz; 13, 89.55 MHz. Cp ) η5-
C5H5.
The angle between the planes containing TiS2 and S2C6
measures 45.3° (for the depicted molecule A). Thus the chelate
ring of 16 shows about the same folding as those in [(η5-C5H5)2-
Ti(E)] (48.5(3)°),6 [(η5-C5H5)2Ti(S2C6H4)] (46.4 and 45.5° for
the two independent molecules in the asymmetric unit),23 and
[(η5-CH3C5H4)2Ti(S2C2(CO2CH3)2)] (44°).4e The S-C(aryl)
bond distances in 16 (1.756(4) and 1.757(4) Å) compare well
with equivalent distances in the molybdenum complex 15 and
show that the ligand is coordinated as a dithiolate.
Variable-Temperature 1H NMR Studies. Titanocene dithi-
olate complexes assume the so-called envelope conformation
with the chelate ring folded along the S‚‚‚S axis (Figure 3). As
a consequence of the chelate ring folding, the cyclopentadienyl
ligands do not have the same environment. As shown by
Ko¨pf,25 Rauchfuss,4e and others24b the free activation enthalpy
for the flip around the S‚‚‚S axis falls in the range that can be
1
estimated by variable-temperature H NMR spectroscopy. To
evaluate the relevance of the amide function for the flipping
1
process, we carried out variable-temperature H NMR studies
Synthesis and Purification of the Bis(dithiolate) Ligand
H4-4. By utilizing the reactivity of the bis(titanocene) complex
19, a simple purification procedure for the bis(dithiolate) ligand
H4-4 was developed (Scheme 4). Compared with the case of
H4-4, not only is the dinuclear complex 19 air-stable but its
solubility in organic solvents such as CH2Cl2 is extremely
improved over that of the free ligand. After chromatography,
19 can be subjected to acidic degradation with HCl/CHCl3 to
give within seconds a deep red chloroform solution of [(η5-
C5H5)2TiCl2] and the analytically pure H4-4, which precipitates
and can be isolated by filtration. The overall yield of 60% for
the reaction sequence from crude H4-4 via 19 to analytically
pure H4-4 confirms the necessity of this purification step.
The driving force for the complex degradation is apparently
the high stability of [(η5-C5H5)2TiCl2]. The halophilicity of the
(η5-C5H5)2Ti moiety has been exploited previously in trans-
metalation reactions between titanocene-dithiolate complexes
and late transition metal halides to give dithiolate complexes
of the late transition metals and [(η5-C5H5)2TiCl2].4e,27 This type
of transfer has been demonstrated with non-metal halides, which
allowed for the preparation of cyclic sulfur derivatives from
[(η5-C5H5)2TiS5] and SxCl2,28 and the corresponding transfer of
selenates has also been reported.29
with 13.
At ambient temperature, only one slightly broadened signal
for the cyclopentadienyl protons was found in the H NMR
1
spectrum of the complex [(η5-C5H5)2Ti(E)] with a secondary
amide function.6 Both conformational isomers were observed
at low temperature, which is illustrated by two signals for the
cyclopentadienyl protons together with two signals for the
diastereotypical benzyl protons.6 In contrast to that observation,
two signals for the cyclopentadienyl protons were already found
at ambient temperature for complex 13 with the bulkier tertiary
amide substituent. Only at elevated temperature (55 °C, in
toluene-d8) did coalescence occur.
The free activation enthalpy for the flip around the S‚‚‚S axis
in 13 was estimated from the difference in the chemical shift
of the cyclopentadienyl protons and from the coalescence
temperature. In Table 5 the value obtained is compared to the
free activation enthalpy for the flip in the known complexes
[(η5-C5H5)2Ti(E)]6 and [(η5-C5H5)2Ti(X2C6H4)] (X ) S,26a Se,26b
Te26c). While the barriers for [(η5-C5H5)2Ti(E)] and [(η5-C5H5)2-
Ti(Se2C6H4)] are only slightly raised compared with that for
[(η5C5H5)2Ti(S2C6H4)], the activation enthalpy for 13 lies more
than 10 kJ/mol higher.
It appears that the activation enthalpy for the flip depends
strongly on the nature of substitution at the amide nitrogen atom.
The transition from a secondary amide in [(η5-C5H5)2Ti(E)]6
to a tertiary amide in 13 has a stronger influence on the
activation enthalpy than the substitution of the dithiolate in
general (compare [(η5-C5H5)2Ti(S2C6H4)] to [(η5-C5H5)2Ti(E)])
or the substitution of sulfur against other group 16 elements
Synthesis and Molecular Structure of the (Cyclopentadi-
enyl)bis(dithiolato)titanate(IV) Complex Anion [20]-. One
(27) (a) Osakada, K.; Kawaguchi, Y.; Yamamoto, T. Organometallics 1995,
14, 4542. (b) Wark, T. A.; Stephan, D. W. Can. J. Chem. 1990, 68,
565.
(28) (a) Schmidt, M.; Block, B.; Block, H. D.; Ko¨pf, H.; Wilhelm, E.
Angew. Chem., Int. Ed. Engl. 1968, 7, 632. (b) Roesky, H. W.;
Zamankhan, H.; Bats, J. W.; Fuess, H. Angew. Chem., Int. Ed. Engl.
1980, 19, 125.
(25) Ko¨pf, H. Angew. Chem., Int. Ed. Engl. 1971, 10, 134.
(26) (a) Ko¨pf, H.; Klapo¨tke, T. Z. Naturforsch. 1986, 41B, 667. (b) Ko¨pf,
H.; Klapo¨tke, T. J. Organomet. Chem. 1986, 310, 303. (c) Ko¨pf, H.;
Klapo¨tke, T. J. Chem. Soc., Chem. Commun. 1986, 1192.
(29) Giolando, D. M.; Papavassiliou, M.; Pickardt, J.; Rauchfuss, T. B.;
Steudel, R. Inorg. Chem. 1988, 27, 2596.

Poly(dithiolate) Complexes
Inorganic Chemistry, Vol. 37, No. 26, 1998 6595
Scheme 4. Preparation of the Bis(dithiolate) Ligand H4-4
and Its Titanium(IV) Chelate Complex (NMe4)[20]
Figure 5. ORTEP plot of the anion [20]-.
yielded the purple bis(dithiolate) complex (NMe4)[20] (Scheme
4). The solvate (NMe4)[20]‚CH2Cl2 was crystallized by vapor
diffusion of diethyl ether into a dichloromethane solution of
(NMe4)[20]. The reactivity of 19 with chloride ions is readily
explained by the halophilic character of the titanocene fragment.
The substitution of at least one thiolate function at one titanium
center of 19 by a chloride ion probably initiates the reaction.
Several reaction pathways are conceivable for the following
substitution of a cyclopentadienyl ring at the other titanium
center by the released dithiolate donor and the formal elimination
of unstable [(C5H5)3TiCl].
The 1H NMR spectrum of (NMe4)[20] in CD2Cl2 reveals that
the N-H protons and all four benzyl protons are inequivalent,
and the complex is consequently rigid. This result can be
explained with the bend of the dithiolate chelate rings about
the S‚‚‚S axis in an exo/endo conformation. This exo/endo
structure was also found for the prototypical complex (Ph4P)-
[(η5-C5H5)Ti(S2C6H4)2]30 and leads in [20]- to the formation
of enantiomers, which crystallize together in a centrosymmetric
space group.
The determination of the molecular structure by X-ray
diffraction proves the identity of (NMe4)[20]‚CH2Cl2 as a chelate
complex (Figure 5). The titanium center is coordinated in a
distorted tetragonal-pyramidal fashion. The four thiolate donors
take the basal positions, whereas the cyclopentadienyl ligand
assumes the apical position. The bond lengths and bond angles
in the organic backbone are found to be normal within
experimental error. However, the coordination geometry around
the titanium center in the anion [20]- is distorted compared
with that in [(η5-C5H5)Ti(S2C6H4)2]-, with unbridged benzene-
1,2-dithiolate ligands.30
possibility for the synthesis of the anion [(η5-C5H5)Ti(4)]-,
[20]-, involves the metathesis reaction of [(η5-C5H5)TiCl3] with
Li4-4. This strategy was used in the preparation of (Ph4P)[(η5-
C5H5)Ti(S2C6H4)2] from [(η5-C5H5)TiCl3] and 2 equiv of 1,2-
(LiS)2C6H4 by Ko¨pf et al.30 The application of this method to
the bis(dithiolate) ligand 44- has been proved unsuccessful, at
least in our hands, apparently because the reaction suffers from
the high charge at the ligand and its tendency to form
polynuclear species. However, titanocene dithiolate complexes
are known to react with an excess of dithiolate ligand under
displacement of one C5H5 ring to yield the corresponding
(cyclopentadienyl)bis(dithiolato)titanate anions.31
The Ti-S bond lengths (Table 4) ortho to the amide groups
(S1 and S4) are slightly shorter than the meta Ti-S bonds for
each dithiolate unit. Combined with the very small S-Ti-S
angle involving the ortho sulfur atoms (S1-Ti-S4 ) 79.11-
(7)°), this leads to a distinctly shorter inter-dithiolate separation
on one side of the bridge (S1‚‚‚S4 ) 3.057 Å, S2‚‚‚S3 ) 3.213
Å).
In our preparation of (NMe4)[20] from 19, we utilized the
halophilicity of the titanocene moiety together with the attack
of an enedithiolate on a titanocene dithiolate under substitution
of a C5H5 ligand, avoiding the highly charged intermediate 44-
.
Regarding the exo/endo bend of the chelate rings around the
S...S axis, the anion [20]- resembles the complex anion [(η5-
C5H5)Ti(S2C6H4)2]-.30 However, the angles describing this
folding are larger in [20]- (27.5° exo and 44° endo, relative to
the C5H5 ligand) than in [(η5-C5H5)Ti(S2C6H4)2]- (36.3° exo
and 23.3° endo, relative to the C5H5 ligand). Owing to the
requirements of the bridge in [20]-, the endo bend is larger
The reaction of the bis(titanocene) complex 19 with tetram-
ethylammonium chloride in acetonitrile under reflux conditions
(30) Ko¨pf, H.; Lange, K.; Pickardt, J. J. Organomet. Chem. 1991, 420,
345.
(31) (a) Locke, J.; McCleverty, J. A. Inorg. Chem. 1966, 5, 1157. (b) James,
T. A.; McCleverty, J. A. J. Chem. Soc. A 1970, 3318.

6596 Inorganic Chemistry, Vol. 37, No. 26, 1998
Seidel et al.
than the exo bend, which is the inverse of the situation found
in the anion [(η5-C5H5)Ti(S2C6H4)2]-.
complexes in a fast reaction like metal halogenide sodium
thiolate metathesis owing to the necessary rearrangement of the
ligand during complex formation. In contrast to the fast
metathesis reaction, the release of a benzene-1,2-dithiolate in
19 by reaction with NMe4Cl and the subsequent dithiolate
transfer reaction described for the preparation of [20]- proceeds
under reflux conditions in the course of hours. The compara-
tively low reaction rate reveals a high activation enthalpy, which
turns out to be advantageous for the formation of the chelate
complex (NMe4)[20], because the rearrangement barriers for
the ligand become negligible under these conditions.
The steric constraints of the xylylene bridge probably account
both for the distortion and for the magnitude and direction of
the folding. The exo/endo bend of the chelate rings in [20]- is
essential as it reduces the mutual distance of the amide groups
to be bridged and allows the amide functions to assume the
favored twist out of the aromatic planes.
Concluding Remarks. We have shown that benzene-1,2-
dithiol can be ortho-functionalized and that this allows bridging
of two benzene-1,2-dithiol units. The problems during purifica-
tion of such air-sensitive and poorly soluble ligands were
overcome by preparation of the titanocene complexes which
are soluble in most common solvents and which are air-stable
enough for chromatographic purification. Protonolysis of such
complexes with HCl/CHCl3 utilizes the well-established halo-
philicity of the titanocene moiety and leads to the free ligands
H2-1, H2-2, H4-3, and H4-4. These ligands coordinate as
dithiolates in their metal complexes.
Acknowledgment. We thank the Deutsche Forschungsge-
meinschaft and the Fonds der Chemischen Industrie for financial
support. We thank reviewers A and C for useful comments on
an earlier draft of this paper.
Supporting Information Available: X-ray crystallographic files,
in CIF format, for the structures of 15, 16, and (NMe4)[20]‚CH2Cl2
are available on the Internet only. Access information is given on any
current masthead page.
Our experiments indicate that large multidentate ligands with
many degrees of freedom do not favor the formation of chelate
IC9706616