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SYNTHESIS AND CHARACTERIZATION OF MOLYBDENUM AND TUNGSTEN COMPLEXES CONTAINING tert-BUTYLCYCLOPENTADIENYL
LIGAND
MohammadEl-khateeb*, Nattier Al-rawashdeh, Qutaiba Abu-salem
Department of Chemistry, Jordan University of Science and Technology,
P.O. Box 3030, Irbid22110, JORDAN
kateebCcfjust. edu.jo
Received 15-02-2001 Abstract
New molybdenum and tungsten complexes containing fert-butylcyclopentadienyl ligand (Cp'= 'Bu-C5H4) have been prepared and characterized. The reaction of M(CO)3(CH3CN)3 with fert-butylcyclopentadiene provide improved route to the metal-metal bond compounds [Cp'M(CO)3]2 (M= Mo (la), W (lb)) in good isolated yields. New examples of mononuclear complexes have also been prepared. The yellow complexes Cp'M(CO)3R (R= CH3, CH2C6H5) (IV) and [Cp'Mo(CO)3S02(p-C6H4X)] (V) (X= CH3, CI) have been prepared from the reaction of the anions, [Cp'M(CO)3]~, with alkyl halides or arylsulfonyl chlorides in THF solvent, respectively. Protonation of the anion [Cp'M(CO)3]~ with glacial acetic acid, which gave the hydride complexes, followed by stirring in CCI4/ THF or refluxing with CH3I in benzene produce the corresponding halides Cp'IVl(CO)3Cl (II) or Cp'M(CO)3I (III), respectively.
Introduction
The synthesis of substituted cyclopentadienyl ligands and their complexes remains an active area of research. " Although cyclopentadienyl metal carbonyl complexes of group VIB have been intensively studied, several examples of the corresponding susbstituted cyclopentadienyl complexes have been reported [20-27]. For example, the dimers [Cp+M(CO)3]2 (Cp+= C5H4COOH, C5Me4(CH(Et)(Ph)), 'BuC5H4, ÌBU2C5H3) have been prepared and some are structurally characterized [20-23]. The mono-nuclear complexes Cp+M(CO)3X (Cp+= 'Bu2C5H3, C5'Pr4H; X= CI, Br; M= Mo and Cp+= C5H4COR, C5H4CH(OH)Me; X= Me; M= Mo, W) were also prepared.20'24"27 We are interested in preparing and characterizing organometallic complexes containing teTt-butyl-substituted cyclopentadienyl ligands. To that end, we prepared the
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iron dimers [Cp+Fe(CO)2]2 and the thiocarboxylate derivetavies Cp+Fe(CO)(L)SCOR (Cp+= 'BuC5H4, 'BU2C5H3, L= CO, PPh3, AsPh3, SbPh3).23' 28 The goal of the work reported here is to prepare and characterize the tungsten and molybdenum dimers [Cp'M(CO)3J2 and some mono-nuclear carbonyl complexes of these metals that contain a teft-butylcyclopentadienyl ligand.
Results and discussion
The dimers, [(tBu-C5H4)M(CO)3]2 (M= Mo (la), W (lb)), were synthesized in good yields by reacting of M(CO)3(CH3CN)3 with ter?-butylcyclopentadiene ligand (Equation 1).
fBu-^CÏD> OC.   CO
I          \/^co
M(CO)3(CH3CN)     ----------?           M------------ivr                        hq- '
Od    CO^^^'Bu
I
These reactions were followed by IR spectroscopy. Progressive disappearance of the CO
stretching bands of M(CO)3(CH3CN)3 is a direct indication for the progress of the reaction. Compounds I are purple crystals, soluble in common organic solvent, and are stable in the solid state and in solution. These complexes were characterized by IR, H-NMR spectroscopy as well as elemental analysis. The IR spectra of these compounds have three bands corresponding to the stretching frequencies of the terminal CO ligands. These were observed in the ranges 1950-1947, 1913-1905 and 1893-1887 cm"1. These bands are indicative of the presence of M(CO)3 moieties which is consistent with the structure shown in Equation 1. Comparison of the IR spectra of I and the unsubstituted analogs [CpM(CO)3]2 (M= Mo, W) shows clearly the electronic effects of the tert-butyi group which results in a shift of vco to lower values. The 'H-NMR spectra of compounds I show a singlet in the range 1.25-1.26 ppm for the tert-butyi group, and two multiplets in the ranges 5.11-5.25 and 5.26-5.34 ppm for the (C5H4) ring protons.
The synthesis of Cp'M(CO)3X (X= CI, I; M= Mo, W) (II, III) started by deprotonation  of 'BU-C5H5 ligand using  sodium metal  to  give  sodium  tert-butyi
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cyclopentadienide that reacted with M(CO)6 (M= Mo, W) to yield Cp'M(CO)3Na. This salt was protonated with glacial acetic acid in THF to give the hydride complex, which was utilized insitu as outlined in Scheme 1.
OCT    / \     s—Ar CH3COOH                                 oc'   co Ä
The progress of these reactions was also followed by withdrawing samples of the solution, and monitoring the disappearance of the bands of Cp'M(CO)3Na. The newly prepared compounds II and III are orange-red crystals, air stable as solids and in solutions. They are soluble in organic solvents such as hexane, CH2CI2 and diethyl ether. The IR spectra (vco region) of II in CCI4 solution exhibited three absorbances in the ranges 2051-2045, 1980-1962 cm"1 and 1952-1946 cm"1 while two bands (2038-2034, 1968-1956 cm"1) are observed for compounds III.30'jl 'H-NMR spectra of compounds II and III exhibit signals which are in good agreement with the proposed structures. All chemical shift values of the protons appear in the expected region. However, they shift to high field compared to those of the unsubstituted cyclopentadienyl carbonyl analogs. For example: the Cp-ring protons of CpMo(CO)sI appear as singlet at 5.57 ppm,   in
9Q
CDCI3 solution   while those of Ilia appear as two multiplet at 5.45 and 5.52 ppm.
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The reaction of Cp'M(CO)3Na (M= Mo, W) with CH3I or C6H5CH2C1 in THF afforded the mononuclear complexes ('Bu-C5H4)M(CO)3R (R= CH3, CH2C6H5; M= Mo (IVa, IVc), M= W (IVb)) in moderate yields as shown in Scheme 1. Complexes IV are yellow powders and stable under N2 for several days. Their solutions in organic solvents are slowly decomposed even under N2 atmosphere and increased upon exposure to air (require several minutes for complete decomposition). This instability, which is a general feature of transition metal alkyl complexes alters the elemental analysis results of complexes IV. Complexes IV are soluble in common organic solvents and insoluble in hexane. Infrared and H-NMR spectroscopic data have confirmed the structures of these compounds/ The IR spectra for IVa and IVb have two bands and in the case of IVc three bands are found in the C-0 stretching region. The assignment of these bands was made on the basis of reported results of similar compounds/ ' For the unsubstituted analogs, where R= Et, 'Pr, two strong bands in the C-0 stretching region have also been reported.
The H-NMR spectra of compounds IV show a singlet in the range 1.15-1.18 ppm for the tert-bvity\ group, a singlet in the range 5.38-5.58 ppm for the (C5H4) ring protons and the protons of the alkyl group with the appropriate multiplicity and integration. The chemical shift values of the protons for the methyl and methylene groups are smaller than those found for methyl and methylene groups attached to carbon atoms.
Although the four protons of ('BU-C5H4) constitute an AA'BB' system. Their splitting pattern is markedly affected by the structural and electronic environment around the metal center. It has been found that the ring protons of this system appear as symmetrical multiplet in Cp'2TiCl2, as an unsymmetrical multiplet in Cp'2Ti(Cl)(NCS),34 as a singlet in Cp'2Ti(NCS)2, as two multiplets in Cp'Fe(CO)2SCOR [23] and as four multiplets in Cp'Fe(CO)(PPh3)SCOR.28 Accordingly, the 'H-NMR spectra of IV, in which the CsH^ring protons appear as singlet, could be possible.
The reaction of Cp'Mo(CO)3Na with sulfonyl chlorides afforded the S-bonded sulfinato (S02Ar) compounds of molybdenum Cp'Mo(CO)3S02Ar (Ar= p-C6H4CH3 (Va), P-C6H4CI (Vb)) as shown in Scheme 1. These reactions were monitored by IR spectroscopy, the production of the sulfinato compounds was evidenced by the shift (to higher values) in the carbonyl stretching frequencies and a change in the color of the
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solution from yellow brown to red. The complexes are yellow powders and stable under N2; however, their solutions in organic solvents slowly decomposed when exposed to air. They are soluble in CH2CI2, CHCI3 and insoluble in hexane. On the basis of the observed positions of the CO and SO2 stretching frequencies and the H-NMR signals and their similarity to the corresponding absorption in the spectrum of CpMo(CO)3S02Ph,3;' these complexes are assigned the S-sulfmato structures. A satisfactory elemental analysis has confirmed the structures of these compounds.
The IR spectra of complexes V have three bands in the ranges 2046-2024, 1986-1967 and 1927 cm" , which are indicative of the presence of the M(CO)3 moieties. The presence of an S-sulfinato ligand (S02Ar) is confirmed by the observation of strong infrared bands in the ranges 1322-1199 and 1146-1035 cm"1 (KBr).35"37 The 'H-NMR spectra of compounds V show that all chemical shift values of the protons appear in the expected region. Comparison of the H-NMR data of Va and Vb shows clearly the electronic effects of the para substituent group (-S02-p-C6H4X, X= CI, CH3). The 'H-NMR spectrum of Va show two multiplets at 5.52 and 5.82 ppm for the (C5H4) ring protons, while those of Vb appear at 5.80 and 6.23 ppm. The method used to prepare complexes V are novel and simple one. The use of this method to prepare the unsubstituted analogs, CpM(CO)3S02Ar, which have been prepared by more difficult methods, may be tested in the future.
Experimental
All reactions were carried out under a dinitrogen atmosphere using standard Schlenk or vacuum line techniques. Diethyl ether, tetrahydrofuran (THF) and hexane were dried by refiuxing over sodium/benzophenone. Dichloromethane and acetonitrile were dried over P2O5. All solvents were distilled just prior to use. The following chemicals were used as received: M(CO)6 (M= Mo, W; Aldrich), tert-butyX chloride and glacial acetic acid (Fluka), methyl iodide, carbon tetrachloride (BDH), 4-chlorobenzenesulfonyl chloride and p-toluenesulfonyl chloride (Acros). The complex M(CO)3(CH3CN)3 and the tert-bxvtyX cyclopentadiene ligand   were prepared as reported in the literature.
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IR specrtra: Nicolet-Impact 410 FT-IR spectrometer; in cm" . H-NMR spectra: Bruker WP80SY spectrometer with TMS as an internal standard; in ppm. Elemental analysis: Laboratoire D'Analyse Élémentaire Université de Montréal, Montréal, Canada. M.p.: Thomas Hoover Capilary melting point apparatus and are uncorrected. [Cp'M(CO)3]2: A solution of 7.00 mmol of M(CO)6 in 60 mL acetonitrile was refluxed for 4 hours when M= Mo and for 6 days when M= W. The resulting bright yellow solution of M(CO)3(CHsCN)3 was evaporated under reduced pressure to give yellow solid residue. To this solid a freshly distilled (5.0 mL, 32.1 mmol) tert-butyX cyclopentadiene was added directly. The mixture was refluxed for 3 hours and the color of the solution turned to dark red. The volatiles were removed under vacuum at room temperature to give a dark red solid. The solid was washed with hexane and collected by filteration as purple crystals of [Cp'M(CO)3J2 and air-dried.
[Cp'Mo(CO)3]2 (la): Yield = 90 %. M.p.= 164-165 °. IR (CH2C12,): vvco: 1950 (vs), 1913 (s, br), 1893 (sh). 'H-NMR (CDC13): 1.25 (s, 9 H, C(CH3)3), 5.1 l(m, 2 H, C5H4 ), 5.26 (m, 2 H, C5H4 ). . Anal. cale, for C24H26M02O6: C 47.85, H, 4.35; found: C 47.45, H 4.33.
[Cp'W(CO)3]2 (lb): Yield = 70 %. M.p.= 210-212 °. IR (CH2C12): vco: 1947 (vs), 1905 (s), 1887 (sh). 'H-NMR (CDCI3): 1.26 (s, 9 H, C(CH3)3), 5.25 (s, 2 H, C5H4), 5.34 (s, 2 H, C5H4). Anal.   cale. For C24H26O6W2: C 37.04, H 3.36; found: C 37.04; H 3.36
Cp'M(CO)ìNa: In a 100 mL schlenk flask fitted with a reflux condenser and a magnetic stirrer, sodium (0.200 g, 8.70 mmol) was finely dispersed by rapid stirring in refiuxing toluene (40 mL). Toluene was replaced by THF (40 mL) and freshly distilled tert-butyl cyclopentadiene (3.0 mL, 19.3 mmol) was added dropwise to the stirred suspension at room temperature. When all sodium was dissolved, a pale pink solution of sodium tert-butyl cyclopentadienide was formed. To the resulting solution, M(CO)6 (8.70 mmol) was added. The solution was refluxed until no unreacted M(CO)6 found in the solution, producing yellow to yellow-brown solution of the salt Cp'M(CO)3Na. The progress of the reaction was followed by withdrawing samples of the solution at various time
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intervals; and monitoring the appearance of the bands of Cp'M(CO)3Na (1897 (s), 1793 (s), 1744 cm"1 (s) where M= Mo and 1891 (s), 1790 (s), 1739 cm"1 (s) where M= W). No attempt has been made to isolate the pure sodium salts, and the products were utilized insitu for further reactions.
Cp'M(CO)3Cl: To the tetrahydrofuran solution of Cp'M(CO)3Na prepared as described above; glacial acetic acid (1.0 mL, 17.5 mmol) was added. The mixture was stirred for one hour and the solvent was removed under reduced pressure. The resulting hydride was dissolved in 2.0 mL (20.8 mmol) of CCI4 and stirred for 25 minutes. The volatiles were evaporated under reduced pressure and the remaining residue was recrystallized from CH^CLVhexane mixture. The solid was collected as orange-red crystals and air-dried.
Cp'Mo(CO)3Cl (Ha): Yield= 50 %. M.p.= 48-50° . IR (CCI4): vvco: 2051 (s), 1980 (vs), 1952 (s). 'H NMR (CDCI3): 1.25 (s, 9 H, C(CH3)3), 5.1 l(m, 2 H, C5H4), 5.25 (m, 2 H, C5H4). Anal. cale, for C12H13CIM0O3: C 42.81, H, 3.89; found: C 43.41, H 4.34.
Cp'W(CO)3Cl (IIb): Yield= 70 %. M.p.= 64-65°. IR (CCI4): vvco: 2045 (s), 1962 (vs), 1946 (w). 'H NMR (CDCI3): 1.31 (s, 9 H, C(CH3)3), 5.41 (m, 2 H, C5H4 ), 5.72 (m, 2 H, C5H4). Anal. cale, for C12H13CIO3W: C 33.95, H 3.08; found: C 34.35, H 3.30.
Cp'M(CO)3l: A similar procedure to that described for Cp'Mo(CO)3Cl was followed. Except that the resulting hydride was refiuxed with (1.0 mL, 16.1 mmol) of methyl iodide in 30 mL of benzene for 24 hours.
Cp'Mo(CO)3I (Ilia): Yield = 45 %. M.p.= 51-53°. IR (CCI4): vvco: 2038 (vs), 1968 (vs). 'H-NMR (CDCI3): 1.25 (s, 9 H, C(CH3)3), 5.45 (m, 2 H, C5H4 ), 5.52 (m, 2 H, C5H4). Anal. cale, for C12H13IM0O3: C 33.67, H 3.06; found: C 33.19, H 2.91. CpW(CO)3I (Hib): Yield= 52 %. M.p.= 71-73°. IR (CCI4): vvco: 2034 (vs), 1956 (vs). 'H NMR (CDCI3): 1.28 (s, 9 H, C(CH3)3), 5.48 (m, 2 H, C5H4 ), 5.64 (m, 2 H, C5H4). Anal. cale, for C12H13IO3W: C 27.93, H 2.53; found: C 27.86, H 2.36. Cp'M(CO)3R (R= CHi, CH2C6H5): To the tetrahydrofuran solution of Cp'M(CO)3Na prepared as above; the alkyl halide (16.0 mmol) was added. A rapid reaction occurred
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with methyl iodide and the mixture was stirred for 2 hours at 40 C to ensure complete reaction. However, the reaction with benzyl chloride was stirred for 16 hours at room temperature. After the removal of tetrahydrofuran under reduced pressure, the residue was extracted with 25 mL of CH2CI2. The solution was filtered, the solvent was removed, and the resultant yellow solid was recrystallized from CEbCb/hexane mixture. Cp'Mo(CO)3CH3 (IVa): Yield= 60 %.   M.p. = 143° (dec). IR (CCI4): vvco: 2017 (vs), 1931 (vs, br). 'H-NMR (DMSO-<4): 0.32 (s, 3 H, CH3), 1.16 (s, 9 H, C(CH3)3), 5.45 (s, 4 H, C5H4). Anal. cale, for Cl3H,6Mo03: C 49.37, H 5.10; found: C 46.47, H 3.48. CpW(CO)3CH3 (IVb): Yield= 55 %. M.p. = 160°. IR (CCI4): veo: 2015 (vs), 1923 (vs, br).   'H-NMR (DMSO-Jö): 0.38 (s, 3 H, CH3), 1.18 (s, 9 H, C(CH3)3 ), 5.58 (m, 4 H, C5H4). Anal.   cale,   for Ci3H,603W: C 38.63, H 3.99; found: C 36.13, H 2.21 Cp'Mo(CO)3CH2C6H5 (IVc): Yield= 65 %. M.p.= 123° (dee). IR (CCI4): veo: 2013 (vs), 1953 (s), 1925 (vs). 'H NMR (DMSO-<4): 1.15 (s, 9 H, C(CH3)3), 2.89 (s, 2 H, CH2) 5.38 (m, 2 H, C5H4), 5.56 (m, 2 H, C5H4 ), 7.15 (m, 5 H, C6H5). Anal,    cale for Ci9H20MoO3: C 58.17, H 5.13; found: C 56.67, H 3.58.
Cp'Mo(CO)3SC>2Ar: To the tetrahydrofuran solution of Cp'Mo(CO)3Na prepared as described above; ArS02Cl (Ar= C6H4CH3 and C6H4C1) (8.00 mmol) was added. The color of the solution changed from yellow brown into red. The mixture was stirred for 4
o
hours at ~ 50 C to ensure complete reaction. The solvent was removed under vacuum. The resultant solid material was extracted with 25 mL of CH2C12. Removal of the solvent from the filtered dichloromethane extracts left yellow solid of crude Cp'Mo(CO)3S02Ar. This solid was recrysatllized from CH2Cl2/hexane mixture. Cp'Mo(CO)3S02C6H4CH3 (Va): Yield= 75 %. M.p. = 120° (dec). IR (CH2C12, cm"1): vco: 2048 (vs), 1965 (vs, br). IR (KBr): vco: 2041 (vs), 1986 (s), 1927 (vs). vso2: 1199 (vs), 1035 (vs). 'H-NMR (CDC13): 1.22 (s, 9 H, C(CH3)3 ), 2.41 (s, 3H, CH3), 5.52 (m, 2 H, C5H4 ), 5.82 (m, 2 H, C5H4), 7.48 (m, 4 H, C6H4). Anal, cale for Ci9H2oMo05S: C 50.0, H 4.41, S 7.02; found: C 49.6, H 4.11, S 6.52.
Cp'Mo(CO)3S02C6H4Cl (Vb): Yield= 72 %. M.p.= 122° (dec). IR (CH2C12): vco: 2051 (s), 2029 (m) 1970 (vs). IR (KBr): vco: 2046 (s), 2024 (w), 1967 (vs). vso2: 1322 (vs), 1146 (vs). 'H-NMR (CDC13): 1.53 (s, 9 H, C(CH3)3), 5.80 (m, 2 H, C5H4), 6.23
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(m, 2 H, C5H4), 7.41 (m, 4 H, C6H4). Anal. cale, for Ci8Hi7Mo05S: C 45.34, H 3.59, S 6.72; found: C 44.89, H 3.34, S 6.27.
Acknowledgements
The  authors  thank  the  Deanship   of Research,   Jordan  University  of Science   & Technology for financial support, Grant No. 57/98.
References and Notes
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Povzetek
Opisana je priprava in karakterizacija novih kompleksov molibdena in volframa, ki vsebujejo terc-butilciklopentadienilni ligand ('Bu-C5H4; Cp'), s sestavo [Cp'M(CO)3]2 in Cp'M(CO)3X (X= halogen, alkil, alkilsulfonil).
M. El-khateeb, N. Al-rawashdeh, Q. Abu-salem: Synthesis and Characterization of Molybdenum...