Syntheses and reactivity of molybdenum complexes containing the
diphenylphosphinodithioformato ligand
Kuang-Hway Yih
a, Ying-Chih Lin
b,*
aDepartment of Applied Cosmetology, Hung Kuang Institute of Technology, Sahlu, Taichung, Taiwan433, Taiwan, ROC bDepartment of Chemistry, National Taiwan Uni6ersity, Taipei, Taiwan106, Taiwan, ROC
Received 3 August 1998; received in revised form 12 October 1998
Abstract
Treatment of [Et4N][Mo(CO)5(PPh2)] (1) with CS2afforded [Et4N][Mo(CO)5(PPh2CS2)] (3) which was also synthesized from the
reaction of Mo(CO)5(CH3CN) with [Et4N][PPh2CS2] (2). In complex 3, the diphenylphosphinodithioformato ligand, PPh2CS2−,
coordinated to the molybdenum through the phosphorus atom. The reactions of 3 with various alkyl halides yielded the neutral complexes Mo(CO)5[PPh2(CS2R)] (R = C2H5, C2H4OH, C3H5, 4 – 6). Acylation of 3 with 1-naphthoyl chloride [C10H7C(O)Cl]
gave the complex Mo(CO)5[PPh2(CS2COC10H7)] (7) with moderate yield. Alkylation and acylation reactions occurred at the sulfur
atom. Complex 3 reacted with CH2I2 to give the dinuclear complex [Mo(CO)5(PPh2CS2)]2(m-CH2) (8) in which the two metal
atoms are bridged by the bidentate phosphorus ligand. Decarbonylation of 3 in CH3CN produced an anionic product which was
identified as [Et4N][Mo(CO)4(PPh2CS2)] (9). The PPh2CS2− ligand of 9 bound to the metal center through both the phosphorus
and one of the sulfur atoms. All of the complexes are identified by spectroscopic methods. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Diphenylphosphinodithioformato ligand; Molybdenum complex; Alkylation, acylation and decarbonylation reactions
1. Introduction
Although the dithiocarbamato ligands [1], R2NCS2−,
have attracted considerable attention, little effort has been directed toward investigating the analogous di-alkylphosphinodithioformato ligands, R2PCS2−. Until
now, only a few well-characterized Ph2PCS2− complexes
of early transition metals such as Zr [2] and W [3] were reported, of which, this ligand coordinates to metal centers through the two S atoms or the P and S atoms by chelation, or the simple P-coordination. We were interested in the Ph2PCS2− and Ph
2PCS2R complexes of
W(0) which brought about some novel chemistry such as unprecedented monodentate P-coordination mode [3a], sulfur-assisted cyclization reaction [3b], phosphine transfer reaction, CS p-coordination in Pd [3c] and
intermolecular cyclization forming 6a-thiathiophthen [3d]. In the context of our previous studies, we extended the research to the syntheses and reactivity of molybde-num complexes with the Ph2PCS2− ligand.
2. Experimental
2.1. Materials
All manipulations were performed under nitrogen using vacuum-line, drybox, and standard Schlenk tech-niques. NMR spectra were recorded on a Bruker
AC-200, or on a Bruker AM-300 WB FT-NMR
spectrometer and are reported in units of d with resid-ual protons in the solvent as an internal standard (CDCl3, d 7.24; CD3CN, d 1.93; C6D6, d 7.15;
C2D6CO, d 2.04). IR spectra were measured on a
* Corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII: S 0 0 2 2 - 3 2 8 X ( 9 8 ) 0 1 0 3 9 - 0
Perkin – Elmer 983 instrument and were referenced to polystyrene standard, using cells equipped with calcium fluoride windows. Mass spectra were recorded on a Jeol SX-102A spectrometer. Solvents were dried and deoxy-genated by refluxing over the appropriate reagents be-fore use. n-Hexane, diethyl ether, THF and benzene were distilled from sodium-benzophenone. Acetonitrile and dichloromethane were distilled from calcium hy-dride, and methanol from magnesium. All other sol-vents and reagents were of reagent grade and were used as received. Mo(CO)6, allyl bromide and KPPh2 were
purchased from Strem, Merck and Aldrich, respec-tively. CS2, n-BuLi, Et4NBr, C2H5I, IC2H4OH, C3H5Br
and CH2I2 were purchased from Janssen. The
com-pound [Et4N][PPh2(CS2)] [3e] and Mo(CO)5(PPh2H) [3f]
were prepared according to the literature method. Ele-mental analyses were carried out at the Regional Center of Analytical Instrument located at the National Tai-wan University.
2.2. Preparation of[Et4N][Mo(CO)5(PPh2)] (1)
To a flask containing Mo(CO)5(PPh2H) (0.633 g, 1.5
mmol) and Et4NBr (0.315 g, 1.5 mmol) in THF, n-BuLi
(1 ml, 1.6 mmol) was added at 0°C. The solution was stirred for 5 min and the solvent was removed under vacuum. MeOH (15 ml) was added to the flask and the solution was stored at − 18°C for 12 h to give yellow precipitates. These precipitates were filtered, washed with diethyl ether (2 × 10 ml) and then dried under vacuum to give 1 (0.77 g) as yellow powder in 93% yield. Spectroscopic data for 1: IR (CH2CI2): nCO 2070(m), 1910(vs) cm− 1; 1H-NMR (CDCl 3):d 1.18 (tt, 12H, CH3, JN – H= 1.87 Hz, JH – H= 7.30 Hz), 3.18 (q, 8H, CH2, JH – H= 7.30 Hz), 7.47 (m, 6H, Ph), 7.67 (m, 4H, Ph); 13C-NMR (CD 3CN): d 7.6 (s, CH3), 52.9 (s, CH2), 128.2 (d, meta-C of Ph, JP – C= 9.0 Hz), 131.5 (s, para-C of Ph), 133.0(d, ortho-C of Ph, JP – C= 9.7 Hz), 134.6 (d, ipso-C of Ph, JP – C= 34.6 Hz), 205.7 (d, cis-CO, JP – C= 9.8 Hz), 210.0 (d, JP – C= 25.8 Hz,
trans-CO); MS (FAB, NBA): m/z 681 (M++ Et
4N); Anal.
Calc. for C25H30NO5PMo (551.41) C: 54.45, H: 5.48, N:
2.54. Found C: 54.35, H: 5.42, N: 2.25.
2.3. Preparation of[Et4N][Mo(CO)5(PPh2CS2)] (3) Method A: a CH2Cl2 solution (5 ml) of Mo(CO)5(CH3CN) (0.277 g, 1.0 mmol) was added slowly at room temperature to a CH2Cl2 solution (20
ml) of [Et4N][PPh2CS2] (2) (0.391 g, 1.0 mmol). The
solution was stirred for 1 h. The reaction was moni-tored by 31P-NMR. After complete disappearance of
the 31P resonance of 2, dichloromethane was removed
under vacuum to give red – brown powder. The crude product was recrystallized from a 1:1 CH2CI2/MeOH
solution to give a microcrystalline complex 3 (0.53 g,
84%). Method B: to a THF solution of 1 (0.551 g, 1.0 mmol), CS2 (0.1 ml, 1.6 mmol) was added at room
temperature. The color changed from bright yellow to red immediately accompanied with the formation of some red precipitates. The solution was filtered and the precipitates were washed with n-hexane (2 × 10 ml) to give a red powder 3 (0.55 g) in 87% yield. Spectroscopic data for 3: IR (KBr): nCO 2065(s), 1979(m), 1949(vs), 1909 (vs) cm− 1, 31P-NMR (CDCl 3): d 69.8; H-NMR (CDCl3):d 1.18 (tt, 12H, CH3, JN – H= 1.87 Hz, JH – H= 7.30 Hz), 3.15 (q, 8H, CH2, JH – H= 7.30 Hz), 7.35 (m, 6H, Ph), 7.66 (m, 4H, Ph); 13C-NMR (CD 3CN): 0 7.6 (s, CH3), 52.9 (s, CH2), 128.3 (d, meta-C of Ph, JP – C= 9.8 Hz), 129.9 (s, para-C of Ph), 134.4 (d, ortho-C of Ph, JP – C= 9.8 Hz), 141.0 (d, ipso-C of Ph, JP – C= 34.2 Hz), 204.8 (d, cis-CO, 2J P – C= 7.5 Hz), 209.7 (d,
trans-CO, JP – C= 25.5 Hz), 235.7 (s, CS2); MS (FAB, NBA):
m/z 759 (M++ Et
4N), 703 (M++ Et4N – 2CO); Anal.
Calc. for C26H30NO5PS2Mo (627.56) C: 49.76, H: 4.82, N: 2.23. Found C: 49.74, H: 4.85, N: 2.22.
2.4. Preparation of Mo(CO)5[PPh2(CS2C2H5)] (4)
C2H5I (0.01 ml, 1.0 mmol) was added to a solution of
3 (0.627 g, 1.0 mmol) in CH2Cl2 (20 ml) and the
mixture was stirred at room temperature for 1 min. The solvent was removed under vacuum and the residue was extracted with n-hexane (2 × 10 ml), and the extracts were filtered through celite. The filtrate was concen-trated to ca. 5 ml and cooled to − 18°C for 12 h to give the red crystalline product Mo(CO)5[PPh2(CS2C2H5)] (4) (0.45 g, 85%). Spectroscopic data for 4: IR (CH2Cl2): nCO 2074(m), 1940(vs) cm− 1; 31P-NMR (CDCl3):d 75.6;1H-NMR (CDCl 3):d 1.32 (t, 3H, CH3, JH – H= 7.50 Hz), 3.29 (q, 2H, CH2 JH – H= 7.50 Hz), 7 47 (m, 6H, Ph), 7.67 (m, 4H, Ph); 13C-NMR (CDCl 3): d 11.8 (s, CH3), 32.0 (s, CH2), 128.4 (d, meta-C of Ph, 3J P – C= 9.6 Hz), 130.8 (s, para-C of Ph), 133.6 (d, ortho-C of Ph,2J P – C= 12.4 Hz), 134.1 (d, ipso-C of Ph, JP – C= 31.9 Hz), 205.4 (d, cis-CO, JP – C= 8.3 Hz), 210.1 (d, trans-CO, JP – C= 26.3 Hz), 238.9 (d, JP – C= 4.8 Hz, CS2); MS (FAB, NBA): m/z 528 (M+), 499 (M+− C2H5), 471 (M+− C2H5− CO), 443 (M+− C2H5− 2CO), 415 (M+− C 2H5− 3CO), 387 (M+− C
2H5− 4CO), 359 (M+− C2H5− 5CO). Anal.
Calc. for C20H15O5PS2Mo (526.37) C: 45.63, H: 2.87. Found C: 45.60, H: 2.85.
2.5. Preparation of Mo(CO)5[PPh2(CS2C2H4OH)] (5)
The synthesis and work-up were similar to those used in the preparation of complex 4. The pure complex Mo(CO)5[PPh2(CS2C2H4OH)] (5) as the red
microcrys-talline solid was isolated in 90% yield. Spectroscopic data for 5: IR (CH2CI2): nCO 2073(m), 1984(m),
1943(vs) cm− 1; 31P-NMR (CDCl
(CDCl3):d 3.30 (t, 2H, SCH2, JH – H= 6.12 Hz), 3.53 (t, 2H, CH2OH, JH – H= 6.12 Hz), 7.46 (m, 6H, Ph), 7.64 (m, 4H, Ph);13C-NMR (CDCl 3):d 39.9 (s, SCH2), 59.8 (s, CH2OH), 128.5 (d, meta-C of Ph, JP – C= 13.5 Hz), 131.1 (s, para-C of Ph), 133.8 (d, ortho-C of Ph, JP – C= 17.3 Hz), 134.3 (d, ipso-C of Ph, JP – C= 38.8 Hz), 205.4 (d, cis-CO, JP – C= 9.1 Hz); 239.7 (s, CS2);
MS (FAB, NBA): m/z 544 (M+), 516 (M+− CO), 460
(M+− 3CO), 432 (M+− 4CO), 404 (M+− 5CO).
Anal. Calc. for C20H15O6PS2Mo (542.37) C: 44.29, H:
2.79. Found C: 44.25, H: 2.85.
2.6. Preparation of Mo(CO)5[PPh2(CS2C3H5)] (6)
The synthesis and work-up were similar to those used in the preparation of complex 4. The pure complex Mo(CO)5[PPh2(CS2C3H5)] (6) as the red microcrys-talline solid was isolated in 85% yield. Spectroscopic data for 6: IR (CH2CI2): nCO 2073(m), 1985(m), 1946(vs) cm− 1; 31P-NMR (CDCl 3): d 76.0; 1H-NMR (CDCl3): d 3.93 (d, 2H, SCH2, JH – H= 6 99 Hz), 5.18, 5.28 (d, 2H, CH2, JH – H= 9 99 Hz), 5.78 (m, 1H, CH), 7.46 (m, 6H, Ph), 7.67 (m, 4H, Ph); 13C-NMR (CDCl3): 0 41.5 (s, SCH2), 120.5 (s, CH), 128.5 (d, meta-C of Ph, JP – C= 9.8 Hz), 129.6 (s, = CH2), 130.8 (s, para-C of Ph), 133.7 (d, ortho-C of Ph, JP – C= 12.4 Hz), 134.9 (d, ipso-C of Ph, JP – C= 38.8 Hz), 205.4 (d, cis-CO, JP – C= 8.4 Hz), 210.0 (d, trans-CO, JP – C= 25.5 Hz), 238.2 (s, CS2); MS (FAB, NBA): m/z 540 (M+),
512 (M+− CO), 456 (M+− 3CO), 428 (M+− 4CO),
400 (M+− SCO), 359 (M+− 5CO − C
3H5). Anal.
Calc. for C21H15O5PS2Mo (538.38) C: 46.85, H: 2.81. Found C: 46.82, H: 2.87.
2.7. Preparation of Mo(CO)5[PPh2(CS2OCC10H7)] (7)
The synthesis and work-up were similar to those used in the preparation of complex 4. The pure complex Mo(CO)5[PPh2(CS2OCC10H7)] (7) as the red
microcrys-talline solid was isolated in 46% yield. Complex 7 is air and moisture sensitive and elemental analysis was not obtained. Spectroscopic data for 7: IR (CH2Cl2): nCO
2073(m), 1976(m), 1943(vs), 1726(vs) cm− 1; 13P-NMR (CDCl3): d 775; 1H-NMR (CDCl3): d 7.46–7.67 (m, 17H, Ph); 13C-NMR (CDCl 3): d 128.5–134.9 (m, C of Ph), 170.0 (s, SCO), 207.4 (d, cis-CO, JP – C= 8.4 Hz), 211.0 (d, trans-CO, JP – C= 25.5 Hz), 238.4 (s, CS2); MS (FAB, NBA): m/z 654 (M+). 2.8. Preparation of[Mo(CO)5(PPh2CS2)]2(m-CH2) (8)
CH2I2 (0.1 ml, 3.0 mmol) was added slowly to a
solution of 3 (0.627 g, 1.0 mmol) in 20 ml of CH2Cl2at
room temperature and the solution was stirred for 5 min. The solvent was removed under vacuum and the residue was extracted with n-hexane (2 × 10 ml), and
the extract was filtered through celite. The filtrate was concentrated to 5 ml and stored at − 18°C for 12 h to give the red – brown crystalline product [Mo(CO)5(PPh2CS2)]2(m-CH2) (8) (0.41 g, 82%). Spec-troscopic data for 8: IR (CH2Cl2): nCO 2074(m), 1985(m), 1945(vs) cm− 1; 31P-NMR (CDCl 3): d 77.0; 1H-NMR (CDCl 3): d 4.99 (s, 2H, CH2), 7.40 – 7.66 (m, 20H, Ph);13C-NMR (CDCl 3):d 42.4 (s, CH2), 128.5 (d, meta-C of Ph, JP – C= 8.3 Hz), 131.3 (s, para-C of Ph), 133.6 (d, ortho-C of Ph, JP – C= 11.8 Hz), 134.3 (d, ipso-C of Ph, JP – C= 46.0 Hz), 205.2 (d, cis-CO, JP – C= 6.5 Hz), 209.2 (d, trans-CO, JP – C= 25.5 Hz), 237.6 (s, CS2); MS (FBA, NBA): m/z 1010 (M+), 786 (M+
−8CO), 758 (M+− 9CO), 730 (M+− 10CO); Anal.
Calc. for C37H22O10P2S4Mo2 (1008 65) C: 44.06, H:
2.20. Found C: 44.00, H 2.27.
2.9. Preparation of [Et4N][Mo(CO)4(PPh2CS2)] (9)
Compound 3 (0.627 g, 1.0 mmol) was dissolved in 10 ml of CH3CN. The solution was stirred at room
tem-perature and the reaction monitored by IR spectra. After stirring for 10 min, and IR spectrum indicated that the starting material was completely consumed. The solution was cooled and the solvent was removed in vacuum. Recrystallization using a cold 1:1 n-hexane/ CH2CI2 to give the red crystalline product 9 (0.42 g,
70%). Spectroscopic data for 9: IR (CH2Cl2): nCO
2009(m), 1893(vs), 1865(sh), 1827(s) cm− 1; 31P-NMR (CDCl3): d 38.9; 1H-NMR (CDCl3): d 1.18 (tt, 12H, CH3, JN – H= 1.87, JH – H= 7.30 Hz), 3.15 (q, 8H, NCH2, JH – H= 7.30 Hz), 7.47 (m, 6H, Ph), 7.69 (m, 4H, Ph);13C-NMR (CDCl 3):d 7.6 (s, CH3), 52.9 (s, NCH2), 129.0 (d, meta-C of Ph, JP – C= 8.3 Hz), 130.9 (s, para-C of Ph), 133.8 (d, ortho-C of Ph, JP – C= 14.6 Hz), 136.5 (d, ipso-C of Ph, JP – C= 21.8 Hz), 211.0, 212.2 (cis-CO), 222.7 (d, trans-CO, JP – C= 28.9 Hz), 238.1 (s, CS2); MS (FAB, NBA): m/z 731 (M++ Et4N), 703 (M++ Et
4N − CO); Anal. Calc. for C25H30NO4PS2Mo
(599.55) C: 50.08, H: 5.04, N: 2.34. Found C: 50.15, H: 5.20, N: 2.14.
3. Results and discussion
3.1. Synthesis of the anionic complex [Et4N][Mo(CO)5(PPh2CS2)] (3)
Abstraction of a proton from the metal coordinated phosphine has been reported for the synthesis of the phosphorus derivatives [4]. Interestingly, up to now, only a few examples are known for dialkylphos-phinodithioformato ligand, R2PCS2−. These R2PCS2−
ligands are probably air-sensitive and oxidized easily to give R2P(X)CS2 (X = O, S).
Scheme 1.
Complex [Et4N][Mo(CO)5(PPh2)] (1) was produced in high yield by the reaction of Mo(CO)5(HPPh2) with
n-BuLi in diethyl ether ( − 78°C) in the presence of
Et4NBr. The slightly air-sensitive yellow compound 1 is soluble in CH2Cl2 and CH3CN and insoluble in
n-hex-ane and diethyl ether. The 13C-NMR of 1 reveals two
resonances atd 205.7 and 210.0 with a 4:1 ratio, which are assigned to the carbon atoms of the cis and trans carbonyl groups, respectively. Complex [Et4
N][Mo-(CO)5(PPh2CS2)] (3) can be obtained by two routes
(Scheme 1). Both treatment of 1 with CS2 and the
reaction of Mo(CO)5(CH3CN) with [Et4N][PPh2CS2] (2)
lead to the formation of 3 in 87 and 84% yield, respec-tively. The red complex 3 is stable in solid-state and undergoes decarbonylation reaction in solution (de-scribed below). The analytical data of 3 are in agree-ment with the formula. FAB mass spectrum of 3 shows a base peak with a typical Mo isotope pattern corre-sponding to the [M++ Et
4N] molecular mass. The IR
spectrum of 3 shows three terminal carbonyl stretchings (2A1+ E) that reveal a typical pattern for a LM(CO)5
unit with an octahedral geometry. Down-field shift of the 31P resonance of 3 (d 69.8) relative to that of 1
indicates formation of the Ph2PCS2− ligand and transfer
of electron density from the phosphorus atom to the CS2 portion. The 13C-NMR of 3 reveals three
reso-nances at d 204.8 (JP – C= 7.5 Hz), 209.3 (JP – C= 25.5
Hz) and 235.7 assignable to the carbon atoms of the cis carbonyl groups and the trans carbonyl group and the carbon disulfide, respectively.
Kunze, Ambrosius and co-workers [5] have synthe-sized the anionic heteroallyl ligands containing phos-phorus such as R2P(X)C(Y)NR− or R2PC(Y)NR−
(X = O or S, Y = O or S). Notably, all of these anionic heteroallyl ligands bound to transition metals through O and S [5a], N and S [5c,d], S and S [5e], P and S [5b,d, f – i] and no mono-dentate phosphorus coordina-tion has been observed. Obviously, 3 is formed via abstraction of a proton by n-BuLi, followed by the addition of the resulting phosphido unit onto the car-bon atom of CS2. In 1987, Hey and co-workers re-ported the insertion reaction of CS2 into a Zr – P [2] bond, forming the dialkylphosphinodithioformato lig-and, R2PCS2−. The bis(trimethylsily)phosphino
zirco-nium complex [Zr(h5-C
5H5)2{h2-S2CP(SiMe3)2}Cl],
obtained from the reaction of [Zr(h5-C
5H5)2(PR2)X]X
(R = SiMe3, X = Cl or Me) with CS2, contains a
R2PCS2− ligand chelating through the two sulfur atoms
of the CS2moiety. No insertion of CS2into the metal –
phosphine bond was observed for our tungsten- and molybdenum complexes. Instead, the dithiocarbamato ligand, R2NCS2− was synthesized by the insertion
reac-tion of CS2into the M – N bond (M = Cr, Mo, W) [6b].
The fact that the formation of 3 was observed in two different synthetic routes clearly indicates that 3 is a thermodynamic product and the P-coordination seems to be more favorable than the S-coordination for the Ph2PCS2− ligand.
3.2. Alkylation and acylation of [Et4N][Mo(CO)5(PPh2CS2)] (3)
To explore the reactivity of complex 3, we carried out the reactions of 3 with several alkyl halides and acyl halide. The reaction of 3 with C2H5I in CH2Cl2gave the
neutral complex Mo(CO)5[PPh2(CS2C2H5)] (4). This red
powder was isolated in 85% yield. Extraction with
n-hexane followed by removal of the solvent gave the
analytically pure product 4. Complex 4 is stable in refluxing CH3CN or C6H6 under N2. The FAB mass spectrum of 4 shows a base peak in agreement with the [M+] ion fragment. The 1H-NMR spectrum of 4
ex-hibits two resonances atd 1.32 and 3.29 with a 3:2 ratio attributed to the ethyl protons and the corresponding resonances in the13C-NMR spectrum appear atd 11.8
and 32.0, respectively. The 31P-NMR spectrum of 4
shows a resonance atd 75.6, close to that of 3. On the basis of these spectroscopic data, it is likely that the alkylation takes place at one of the sulfur atom. This result is consistent with that of the analogue complex W(CO)5[PPh2(CS2Me)] [3c], which was structurally
confirmed by an X-ray diffraction analysis. The other alkylated complexes Mo(CO)5[PPh2(CS2R)] (R = C2H4OH, 5; C3H5; 6) have been prepared in a similar way. In the mass spectra of 5 and 6, the molecular ion along with the [M+− CO] peak are detected. The 13C-NMR spectra of 5 and 6 both reveal singlet
reso-nances at d 39.9 and 59.9 for 5 and d 41.5, 120.5 and 129.6 for 6, which are assigned to the carbon atoms of the SCH2CH2OH and SCH2CHCH2 groups,
respec-tively. By comparing the spectroscopic data of the alkylated molybdenum complexes with that of the cor-responding alkylated tungsten complexes [3e], it is clear that the organic segments have the same chemical envi-ronment, namely, S-alkylation.
In the reaction of 3 with 1-naphthoyl chloride [C10H7C(O)Cl], complex 7 was obtained. The lower yield of this green complex relative to the higher yields of the alkylation products may result from its air- and moisture-sensitive character. The IR absorption of the acyl group of 7 appears at 1726 cm− 1and the13C-NMR
resonance atd 170.0. Interestingly, chemical shifts of the
31P resonances of all the alkylated and acylated
com-plexes all fall within the region ofd 75–78, indicating similar structure for all these complexes. Although the differences are small, 31P chemical shift moves toward
down-field region as the group attached to the phos-phine ligand becoming more electron-withdrawing.
This alkylation reaction was extended for CH2I2 in
order to synthesize dinuclear complex. The reaction of
3 with excess CH2I2 in CH2Cl2 gave the dinuclear complex [Mo(CO)5(PPh2CS2)]2(m-CH2) (8). The pro-posed monomeric complex Mo(CO)5[PPh2(CS2CH2I)] was not detected in the reaction. The 1H-NMR
spec-trum of 8 exhibits a resonance atd 4.99 assignable to the CH2group and the corresponding13C-NMR signal is at
d 42.4. The31P-NMR spectrum of 8 shows a resonance
at d 77.0. The FAB mass spectrum of 8 shows a base peak at m/z 730 corresponding to [Mo(PPh2CS2)]2
(m-CH2), formed by loss of ten CO groups from 8 and this
phenomenon was also observed for the complex [W(Co)5(PPh2CS2)]2(m-CH2) [3e]. On the basis of these
data, it is clear that the two metal centers are connected by the (Ph2PCS2)2CH2 bridge.
3.3. Decarbonylation of [Et4N][Mo(CO)5(PPh2CS2)] (3) When the CH3CN solution of 3 was stirred, decar-bonylation occurred affording a stable compound which can be formulated as [Et4N][Mo(CO)4(PPh2CS2)] (9)
based on its analytical and spectroscopic data (Scheme 1). The IR spectrum of 9 shows a pattern different from that of M(CO)5L. The four IR absorptions at 2009,
1893, 1865, 1827 cm− 1, are typical for a M(CO)
4[6] unit
with a pseudooctahedral geometry. The31P-NMR
spec-trum of 9 shows a resonance atd 38.9. The significant up-field shift of the31P resonance of 9 relative to that of
3 (d 69.8) suggests a distinctively different chemical and
electronic environment for the R2PCS2− ligand which
supports its structure depicted in Scheme 1. Kunze and Cotton have reported complexes with similar coordina-tion via the P and S atoms in the hetero-allylic Ph2PCSNR− ligands [5]. Notably, the decarbonylation
reaction of 3 occurred in acetonitrile instantly but very slowly in dichloromethane. The phenomenon probably caused by better donor ability of CH3CN than CH2Cl2.
The acylation and alkylation reaction of 3 can also be carried out in CH2Cl2and the alkylated products can be
obtained in higher yield.
4. Concluding remarks
This study describes the chemical behavior of the anionic diphenylphosphinodithioformato Mo(0) com-plex [Et4N][Mo(CO)5(PPh2CS2)] (3) toward alkylation, acylation and decarbonylation reactions. By comparing with our previous study of the W analogues, significant differences between the Mo and W complexes in solubil-ity, stability and nucleophilicity are observed. Notably, the decarbonylation reaction is spontaneous for Mo but requires heating for the W complex. The molybdenum complexes with the Ph2PCS2− ligand are more soluble in
tung-sten complexes but the stability of molybdenum com-plexes are lower and with weaker nucleophilicity.
Acknowledgements
We thank the National Science Council of Taiwan, ROC for support.
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