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Syntheses, X-ray structures, and reactions of ruthenium carbonyl
complexes containing 1,1-dithiolates
Kom-Bei Shiu
a,*, Shin-Jay Yu
a, Yu Wang
b, Gene-Hsiang Lee
baDepartment of Chemistry, National Cheng Kung Uni6ersity, Tainan701, Taiwan, ROC bInstrument Center, National Taiwan Uni6ersity, Taipei106, Taiwan, ROC
Received 27 September 2001; received in revised form 15 November 2001; accepted 26 November 2001
Abstract
Treatment of [Ru2(CO)4(MeCN)6][BF4]2or [Ru2(CO)4(m-O2CMe)2(MeCN)2] with uni-negative 1,1-dithiolate anions via potas-sium dimethyldithiocarbamate, sodium diethyldithiocarbamate, potaspotas-sium tert-butylthioxanthate, and ammonium O,O%-diethylth-iophosphate gives both monomeric and dimeric products of cis-[Ru(CO)2(h2-(SS))2] ((SS)−= Me2NCS2− (1), Et2NCS2− (2),
tBuSCS
2
− (3), (EtO)
2PS2− (4)) and [Ru(CO)(h2-(Me2NCS2))(m,h2-Me2NCS2)]2 (5). The lightly stabilized MeCN ligands of [Ru2(CO)4(MeCN)6][BF4]2 are replaced more readily than the bound acetate ligands of [Ru2(CO)4(m-O2CMe)2(MeCN)2] by thiolates to produce cis-[Ru(CO)2(h2-(SS))2] with less selectivity. Structures 1 and 5 were determined by X-ray crystallography. Although the two chelating dithiolates are cis to each other in 1, the dithiolates are trans to each other in each of the {Ru(CO)(h2-Me
2NCS2)2} fragment of 5. The dimeric product 5 can be prepared alternatively from the decarbonylation reaction of 1 with a suitable amount of Me3NO in MeCN. However, the dimer [Ru(CO)(h2-Et2NCS2)(m,h2-Et2NCS2)]2(6), prepared from the reaction of 2 with Me3NO, has a structure different from 5. The spectral data of 6 probably indicate that the two chelating dithiolates are cis to each other in one {Ru(CO)(h2-Et
2NCS2)2}fragment but trans in the other. Both 5 and 6 react readily at ambient temperature with benzyl isocyanide to yield cis-[Ru(CO)(CNCH2Ph)(h2-(SS))2] ((SS) = Me2NCS2−(7) and Et2NCS2−(8)). A dimerization pathway for cis-[Ru(CO)2(h2-(SS))2] via decabonylation and isomerization is proposed. © 2002 Elsevier Science B.V. All rights reserved.
Keywords:Ruthenium; Carbonyl; Dithiocarbamate; Thioxanthate; Dithiophosphate; Alkyl isocyanide
1. Introduction
In the course of a program of synthesis and struc-tural characterization of a series of 1,1-dithiolate com-plexes of the type cis-[Ru(CO)2(h2-(SS))2] ((SS)−=
Me2NCS2− (1), Et2NCS2− (2), tBuSCS2− (3), (EtO)2PS2−
(4)), following a similar procedure reported for cis-[Ru(CO)2(h2-S
2PMe2)2] from [Ru2(CO)4(m-O2CMe)2
-(MeCN)2] [1], we have obtained on one occasion small
amount of another product (5), either from [Ru2(CO)4(m-O2CMe)2(MeCN)2] or a derived complex with lightly stabilized ligands MeCN, [Ru2(CO)4
-(MeCN)6][BF4]2 [2]. The elemental analysis results of 5
appear consistent with the formulation of [Ru(CO)(h2
-(Me2NCS2))(m,h2-Me2NCS2)]·1/2CH2Cl2, but the real
structure cannot be assigned without any ambiguity. It may be a mononuclear product with a half CH2Cl2
molecule as one chloro ligand around Ru [3], or a dinuclear product, as a CH2Cl2 solvate, through sulfur
coordination in a chelating – bridging mode [4]. If it is a dimeric compound, the related structure may adopt one of the three possible configurations: configuration A contains two cis-disposed dithiolates; configuration B contains two trans-disposed dithiolates; and configura-tion C contains one cis- and one trans-dithiolates around each metal atom (Chart 1).
We report here the results of an X-ray study of 5 which definitely settles the question of its solid-state structure to be dimeric with configuration B. This work, along with the results of an X-ray study of 1 and a reactivity study of 1 and 2, has revealed the dimeriza-tion pathway for cis-[Ru(CO)2(h2-(SS))
2] via
decar-bonylation and isomerization.
* Corresponding author. Fax: + 886-6-274-0552.
E-mail address:kbshiu@mail.ncku.edu.tw(K.-B. Shiu).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 1 4 0 - 3
2. Experimental
The compounds [Ru2(CO)4(MeCN)6][BF4]2 [2a] and
[Ru2(CO)4(m-O2CMe)2 (MeCN)2] [5] were prepared
ac-cording to literature methods. All the reactions were performed under prepurified nitrogen using freshly dis-tilled solvents.1H- and31P-NMR spectra were recorded
in a Bruker AMC400 spectrometer (1H, 400 MHz;31P,
162 MHz) calibrated against internal deuterated sol-vents (1H) or external 85% H
3PO4 (31P). IR spectra
were recorded in a Bio-Rad FTS 175 instrument. Mi-croanalyses were carried out by the staff of the Micro-analytical Service of the Department of Chemistry, National Cheng Kung University.
2.1. Preparation of cis-[Ru(CO)2(p2-Me2NCS2)2] (1)
and [Ru(CO)(p2-Me
2NCS2)(v,p2-Me2NCS2)]2 (5)
2.1.1. Method A
Potassium dimethyldithiocarbamate monohydrate (0.830 g, 4.68 mmol) was added directly to a stirred yellow solution of [Ru2(CO)4(m-O2CMe)2(MeCN)2], prepared in situ from catena-[Ru(CO)2(m,h2-O
2CMe)]
(0.190 g, 0.88 mmol), in 36 ml of THF. The color changed immediately to orange – brown. The mixture was stirred for 3.5 h and then taken to dryness under vacuum. Recrystallization using Et2O – MeOH from this
solid residue gave 0.244 g pale-yellow cis-[Ru(CO)2(h2
-Me2NCS2)2] (1) (yield 70%). Then, recrystallization
us-ing CH2Cl2– hexane from the remaining solid gave
orange – brown [Ru(CO)(h2-Me
2NCS2)(m,h2-Me2
-NCS2)]2·CH2Cl2 (5) (31 mg, 9%). 1, Anal. Calc. for
C8H12N2O2RuS4: C, 24.17; H, 3.04; N, 7.05. Found: C, 23.88; H, 3.05; N, 7.03%.1H-NMR (CDCl 3):l 3.26 (s, 6H, Me), 3.28 (s, 6H, Me). IR (CH2Cl2, cm− 1): wCO 2039 (s), 1972 (s). IR (KBr, cm− 1): w CO2024 (s), 1962
(s). 5, Anal. Calc. for C14H24N4O2Ru2S8.CH
2Cl2: C,
21.87; H, 3.18; N, 6.80. Found: C, 21.67; H, 3.19; N, 6.78%. 1H-NMR (CDCl
3): l 3.22 (br, 6H, Me), 3.36
(br, 6H, Me), 3.60 (br, 6H, Me), 3.62 (br, 6H, Me), 5.32 (s, 2H, CH2Cl2). IR (CH2Cl2, cm− 1): wCO1927 (s). IR
(KBr, cm− 1): w
CO, 1921 (s). 2.1.2. Method B
Potassium dimethyldithiocarbamate monohydrate (0.240 g, 1.35 mmol) was added directly to a stirred
orange solution of [Ru2(CO)4(MeCN)6][BF4]2 (0.102 g,
0.139mmol) in 20 ml of CH2Cl2 and 1 ml of MeOH.
The mixture was stirred for 2 h and the solvents were removed under vacuum. A procedure similar to that described above was applied, giving 76 mg of 1 (yield 68%) and 12 mg of 5 (yield 11%).
2.2. Preparation of cis-[Ru(CO)2(p2-Et
2NCS2)2] (2)
The yellow 2 was obtained as the only product from the reaction of [Ru2(CO)4(MeCN)6][BF4]2 with sodium diethyldithiocarbamate trihydrate by method B. Yield: 73%. Anal. Calc. for C12H20N2O2RuS4: C, 31.77; H,
4.44; N, 6.18. Found: C, 31.68; H, 4.45; N, 6.17%. 1H-NMR (acetone-d 6): l 1.25 (t, 6H, CH3CH2, 3J(HH) = 7.2 Hz), 1.26 (t, 6H, CH 3CH2, 3JH,H= 7.2 Hz), 3.76 (q, 4H, CH3CH2, 3JH,H= 7.2 Hz), 3.80 (q, 4H, CH3CH2,3JH,H= 7.2 Hz). IR (CH2Cl2, cm− 1):wCO 2035 (s), 1968 (s). IR (KBr, cm− 1): w CO2030 (s), 1952 (s).
2.3. Preparation of cis-[Ru(CO)2(p2-tBuSCS 2)2] (3)
The orange – brown 3 was obtained as the only product from the reaction of [Ru2(CO)4(MeCN)6][BF4]2
with potassium tert-butylthioxanthate by method B. Yield: 67%. Anal. Calc. for C12H18O2RuS6: C, 29.55; H,
3.72. Found: C, 29.34; H, 3.75%. 1H-NMR (acetone-d6): l 1.71 (s, 18H, (CH3)3C). IR (CH2Cl2, cm− 1):wCO,
2051 (s), 1991 (s). IR (KBr, cm− 1): w
CO2041 (s), 1985
(s).
2.4. Preparation of cis-[Ru(CO)2(p2-(EtO)
2PS2)2] (4)
The orange – yellow 4 was obtained as the only product from the reaction of [Ru2(CO)4(MeCN)6][BF4]2 with ammonium O,O’-diethyldithiophosphate by method B. Yield: 68%. Anal. Calc. for C10H20O6P2RuS4: C, 22.77; H, 3.82. Found: C, 22.64; H, 3.87%. 1H-NMR (acetone-d 6): l 1.33 (t, 6H, CH3CH2, 3JH,H= 7.1 Hz), 1.37 (t, 6H, CH3CH2, 3J H,H= 7.0 Hz), 4.22 (m, 8H, CH3CH2).31P{1H}-NMR (acetone-d6): l 100.8 (s, 2P). IR (CH2Cl2, cm− 1): wCO 2053 (s), 1987 (s). Chart 1.
Table 1
Crystal data and structure refinement parameters for compounds 1 and 5·CH2Cl2 Empirical formula C8H12N2O2Ru2S4 C15H26Cl2N4O2 -Ru2S8 Formula weight 397.51 823.92 Temperature (K) 150(1) 150(1) 0.71073 0.71073 Wavelength (Mo–Ka) (A, )
Space group monoclinic, P21/c monoclinic, C2/c Unit cell dimensions
a (A, ) 6.2803(1) 10.9628(2) 14.8235(1) 17.6427(1) b (A, ) 13.2120(1) c (A, ) 17.0111(1) 94.159(1) i (°) 97.336(1) 2757.14(6) 1451.93(3) V (A,3) 4 Z 4 1.985 1.818 Dcalc(g cm−3) 792 F(000) 1640 0.20×0.10×0.10 0.30×0.20×0.15 Crystal size (mm) 3–55 2q Range (°) 3–55 98, 923, 917 Index ranges (h, k, l) 914, 919, 922 1.919 1.645 v(Mo–Ka) (mm−1) 9266 Reflections collected 8254 3307 (\2|)
No. of observed reflections 3121 (\2|) (No)
Absorption correction Sadabs Sadabs Max/min transmission 0.8015/0.6805 0.8621/0.7325
NRCVAX Refinement program NRCVAX
155 147 No. of reflection parameters (Np) Ra, R wa 0.0255, 0.0634 0.0631, 0.1389 1.120 1.067 Goodness-of-fita [|2(F o) [|2(F o) Weighting scheme + 0.0016Fo2]−1 + 0.00029Fo2]−1 (Dz)max (e A,3) 0.505 2.040 −1.356 (Dz)min(e A,3) −0.502 aR = [ F o − Fc / Fo ]. Rw= [ ( Fo − Fc )2/ Fo 2]1/2. Good-ness-of-fit = [S ( Fo − Fc )2/No−Np]1/2.
mixture was stirred at ambient temperature for 22 h, and the solvent was stripped off, giving a yellow – brown solid. Recrystallization from CH2Cl2– MeOH
gave yellow [Ru(CO) (h2-Et
2NCS2)(m,h2-Et2NCS2)]2(6)
(0.335 g, 88%). Anal. Calc. for C22H40N4O2Ru2S8: C,
31.04; H, 4.74; N, 6.58. Found: C, 30.88; H, 4.73; N, 6.59%. 1H-NMR (CD 2Cl2): l 1.19 (m, 9H, CH3CH2), 1.24 (m, 9H, CH3CH2), 1.37 (m, 6H, CH3CH2), 3.45 (m, 4H, CH3CH2), 3.61 (m, 2H, CH3CH2), 3.78 (m, 6H, CH3CH2), 3.88 (m, 2H, CH3CH2), 4.15 (m, 2H, CH3CH2). IR (CH2Cl2, cm− 1): w CO1925 (s). IR (KBr, cm− 1): w CO1943 (s), 1924 (s). 2.7. Preparation of cis-[Ru(CO)(CNCH2Ph)(p2-Me2NCS2)2] (7)
To a stirred suspension of 5 (0.294 g, 0.357 mmol) in CH2Cl2 (50 ml) 0.2 ml of PhCH2NC (ca. 1.61 mmol)
was added. The mixture was stirred at ambient temper-ature for 3 days, and the volatile was removed under vacuum. Recrystallization from CH2Cl2– MeOH gave
yellow cis-[Ru(CO)(CNCH2Ph)(h2-Me2NCS2)2] (7)
(0.165 g, 95%). Anal. Calc. for C15H19N3ORuS4: C, 37.02; H, 3.93; N, 8.63. Found: C, 36.89; H, 3.94; N, 8.63%.1H-NMR (acetone-d 6):l 3.20 (br, 6H, Me), 3.21 (br, 6H, Me), 7.37 (m, 5H, Ph), 7.51 (d, 1H, CNCH2Ph, 2J H,H= 7.6 Hz), 7.56 (d, 1H, CNCH2Ph, 2JH,H= 7.6 Hz). IR (CH2Cl2, cm− 1):wCN2109 (s);wCO1962 (s). IR (KBr, cm− 1): w CN 2105 (s); wCO1971 (s). 2.8. Preparation of cis-[Ru(CO)(CNCH2Ph)(p2-Et2NCS2)2] (8)
To a stirred solution of 6 (0.136 g, 0.319 mmol) in CH2Cl2 (15 ml) 0.2 ml of PhCH2NC (ca. 1.61 mmol)
was added. The mixture was stirred at ambient temper-ature for 2 h, and the volatile was removed under vacuum. Recrystallization from CH2Cl2– hexane gave yellow cis-[Ru(CO)(CNCH2Ph)(h2-Et
2NCS2)2] (8)
(0.169 g, 97%). Anal. Calc. for C19H27N3ORuS4: C,
42.04; H, 5.01; N, 7.74. Found: C, 41.93; H, 5.05; N, 7.73%.1H-NMR (CD 2Cl2):l 1.52 (m, 12H, CH3CH2), 3.96 (m, 8H, CH3CH2), 7.64 (m, 5H, Ph), 7.73 (d, 1H, CNCH2Ph, 2JH,H= 7.2 Hz), 7.77 (d, 1H, CNCH2Ph, 2J H,H= 7.2 Hz). IR (CH2Cl2, cm− 1):wCN, 2105 (s);wCO, 1958 (s). IR (KBr, cm− 1): w CN, 2089(s); wCO, 1938 (s). 2.9. X-ray data collection, solution and refinement
Data were collected at 150 K in a Siemens SMART-CCD instrument, equipped with a normal focus and 3 kW sealed-tube X-ray source. The structures of 1 and 5 were solved by heavy-atom methods and refined by a full-matrix least-squares procedure using NRCVAX [6].
All the non-hydrogen atoms were refined anisotropi-cally. The other essential details of single-crystal data
2.5. Reaction between cis-[Ru(CO)2(p2-Me2NCS2)2] (1)
and Me3NO
Trimethylamine N-oxide dihydrate (0.072 g, 0.65 mmol) was added directly to a stirred yellow suspension of 1 (0.218 g, 0.55 mmol) in 20 ml of MeCN. The mixture was stirred at ambient temperature for 10 h, and the volume of the solvent was reduced to ca. 1 ml. Twenty milliliters of CH2Cl2 was then added to the suspension. After filtration, the orange – brown solid was washed thoroughly with CH2Cl2 (20 ml) twice and
dried under vacuum to give [Ru(CO)(h2
-Me2NCS2)(m,h2-Me2NCS2)]2·CH2Cl2(5) (0.214 g, 95%). 2.6. Reaction between cis-[Ru(CO)2(p2-Et
2NCS2)2] (2)
and Me3NO
Trimethylamine N-oxide dihydrate (0.119 g, 1.07 mmol) was added directly to a stirred yellow suspension of 2 (0.406 g, 0.90 mmol) in 20 ml of MeCN. The
measurement and refinement are given in Table 1. One chlorine atom of CH2Cl2in the asymmetric unit of the
crystal of 5 is disordered and two chlorine positions with 70 and 30% occupancy were assigned to Cl(1) and Cl(1%), respectively. There is a residual peak with 2.040 e A, − 3 in a distance of 0.09 A, close to the Cl(1) atom
on the last difference Fourier map.
3. Results and discussion
Reactions of [Ru2(CO)4(MeCN)6][BF4]2 or
[Ru2(CO)4(m-O2CMe)2(MeCN)2] with uninegative
1,1-dithiolate anions, (S,S)−, occur as expected [1] to
pro-duce a series of mononuclear products, cis-[Ru(CO)2
-(h2-(SS))
2] ((SS)−= Et2NCS2− (2),
t
BuSCS2− (3), and
(EtO)2PS2− (4)). However, the reaction with potassium
dimethyldithiocarbamate affords a mixture of two products, cis-[Ru(CO)2(h2-Me
2NCS2)2] (1) and
[Ru(CO)(h2-Me
2NCS2)(m,h2-Me2NCS2)]2(5), which are
difficult to separate. Fortunately, after several attempts, satisfactory separation of the two products was finally achieved by the tedious fractional crystallization method. A1H-NMR spectrum of the reaction solution
after complete conversion indicated that the ratio be-tween 1 and 5 is 3.35 and 4.63, respectively, favoring 1. Apparently the lightly stabilized MeCN ligands of [Ru2(CO)4(MeCN)6][BF4]2 are replaced more readily
than the bound acetate ligands of [Ru2(CO)4
(m-O2CMe)2(MeCN)2] by dithiolates to produce
cis-[Ru(CO)2(h2-(SS))
2] with less selectivity.
Compounds 1 [7] and 2 [8] were reported earlier, but the preparation procedures, either via the direct substi-tution of cis-[RuCl2(CO)2(PPh3)2] with NaS2CNMe2· 2H2O or via the oxidative addition of [Ru3(CO)12] with
R2NC(S)SSC(S)NR2(R = Me, Et), gave lower yields of
the complexes, compared with that of ours. Like cis-[Ru(CO)2(h2-S2PMe2)2] [1], compounds 1 – 4 display
two carbonyl stretching bands with almost equal inten-sity in the IR spectra measured either in CH2Cl2 or as
a KBr disc, indicating that the two carbonyls are cis to each other in solution or in the solid state. Indeed, this feature is shown clearly in the solid-state structure of 1 (Fig. 1). The CN distances of 1.328(3) and 1.325(3) A, is indicative of the presence of a partial CN bond [9], which is found compatible with the two methyl signals observed in the 1H-NMR spectrum of 1 or 2. The
coordination environment of the metal with two mutu-ally cis dithiolates is approximately octahedral with the angle, formed by two carbonyls, C(1)O(1) and C(2)O(2), as 91.90(11)°. Two short and two long RuS bonds were found (d(RuS(1))=2.4146(7) and
d(RuS(4))=2.4144(7) versus d(RuS(2))=2.4586(7)
and d(RuS(3))=2.4566(7) A,). Since the two long bonds are trans to carbonyls, the lengthening is under-standable in terms of trans influence of the carbonyl group. However, we cannot exclude the possible in-volvement of the steric repulsive interactions between the dithiolate groups.
The crystal structure of 5 was also determined by X-ray diffraction methods to reveal the dimeric nature with two chelating – bridging dithiolates (Fig. 2). The molecule CH2Cl2 was found as the solvent of
crystal-lization. There is a crystallographically imposed C2axis
through the center of the plane defined by Ru(1),
Fig. 1.ORTEP plot of 1 with 50% thermal ellipsoids. Selected bond lengths: RuC(1)=1.887(3), RuC(2)=1.885(3), RuS(1)= 2.4146(7), RuS(2)=2.4586(7), RuS(3)=2.4566(7), RuS(4)= 2.4144(7), S(1)C(3)=1.726(3), S(2)C(3)=1.724(3), S(3)C(6)= 1.730(3), S(4)C(6)=1.731(3), C(1)-O(1)=1.144(3), C(2)O(2)= 1.151(3), N(1)C(3)=1.328(3), N(2)C(6)=1.325(3) A,. Selected bond angles: C(1)RuC(2)=91.90(11), C(1)RuS(1)=93.44(8), S(1)RuS(2)=72.46(2), S(1)RuS(3)=93.67(2), S(1)RuS(4)= 161.86(2), S(2)RuS(3)=89.03(2), S(2)RuS(4)=95.11(2), S(3)RuS(4)=72.49(2), C(2)RuS(4)=93.17(8)°.
Fig. 2.ORTEP plot of 5 with 50% thermal ellipsoids. Selected bond lengths: Ru(1)C(1)=1.814(7), Ru(1)S(1)=2.395(2), Ru(1)S(2)= 2.412(2), Ru(1)S(3)=2.399(2), Ru(1)S(4)=2.410(2), Ru(1) S(4A) = 2.554(2), S(1)C(2)=1.721(7), S(2)C(2)=1.731(6), S(3) C(5) = 1.701(7), S(4)C(5)=1.772(7), C(1)O(1)=1.165(9), N(1)C(2)=1.319(8), N(2)C(5)=1.324(8) A,. Selected bond angles: C(1)Ru(1)S(1)=90.5(2), S(1)Ru(1)S(2)=72.81(6), S(1)Ru(1) S(3) = 106.75(6), S(3)Ru(1)S(4)=73.30(6), S(2)Ru(1)S(4)= 106.62(6), S(4)Ru(1)S(4A)=83.16(6), Ru(1)S(4)Ru(1A)= 95.41(6)°.
Ru(1A), S(4), and S(4A). Hence, the structure can be described as consisting of two [Ru(CO)(h2-(SS))
2]
frag-ments. It is noteworthy that the relative orientation between the two chelating dithiolates in each fragment of 5 is trans, rather than cis as observed in 1. Hence, the structure of 5 adopts configuration B. This structure is kept in solution as reflected in the IR and 1H-NMR
spectra; only one carbonyl stretching band was ob-served in solution or in the solid state, and four methyl
1H signals were observed in CDCl
3. One sulfur atom,
S(4) or S(4A), of one dithiolate group in each fragment acts as the bridging atom to connect with the metal atom in the other fragment in a position trans to the carbonyl group. The bridging RuS bonding is appar-ently weaker with d(Ru(1)S(4A))=2.554(2) A, in 5, compared with the distances of 2.4586(7) and 2.4566(7) A, for similar bonds found in 1. Two such weak bridg-ing bondbridg-ing interactions in 5 is probably caused by the nonbonded repulsive interactions between the dithiolate groups in different fragment. As a result, the CN distances of 1.319(8) and 1.324(8) A, in 5 are not significantly different from those in 1.
Compound 5 can be prepared alternatively via decar-bonylation of 1, using trimethylamine N-oxide in MeCN. However, the dimer [Ru(CO)(h2
-Et2NCS2)(m,h2-Et2NCS2)]2 (6), prepared from a similar
decarbonylation reaction of 2 with Me3NO, has a
struc-ture different from 5. Rather complicated 1H-NMR
signals were observed with three resolved multiplets in an integration ratio of 9:9:6 at l 1.19, 1.24, and 1.37, respectively. Apparently there are more than four methyl signals observed for 6. Though this compound displays in the IR spectrum one broad and strong carbonyl stretching band at 1925 cm− 1 in CH
2Cl2, it
shows two sharp such bands at 1943 and 1924 cm− 1
with almost equal intensity in the solid state. The broad band at 1925 cm− 1is probably caused by the
overlap-ping of two bands at a close wave number. All these spectral evidences may suggest another configuration for 6, probably configuration C. However, both 5 and 6 reacts readily at ambient temperature with benzyl isocy-anide to yield a product with a similar geometry, cis-[Ru(CO)(CNCH2Ph)(h2-(SS))2] ((SS)−= Me2NCS2− (7)
and Et2NCS2− (8)). The cis assignment is based on one
set of the AB quartet observed in the 1H-NMR
spec-trum assigned to the benzyl hydrogen nuclei for 7 or 8. Various kinds of structure for mono- and dinuclear compounds can be explained in terms of both electronic and steric factors. The steric repulsive interactions are believed to be present between any two cis chelating dithiolates in either mono- or dinulcear complexes. However, two strongp-acceptor ligands in all mononu-clear species (i.e. two COs in 1 – 4 and one CO and one RNC in 7 – 8) prefer to locate at cis positions on an octahedral coordination sphere around the Ru atom to help releasing the accumulated charge density of the Ru
complexes of two strong s-donor ligands, dithiolates, via back donation. The electronic factor, rather than the steric factor, determines the cis-geometry as ob-served in 1 – 4 and 7 – 8. Thus, once the decarbonylation of cis-[Ru(CO)2(h2-(SS))2] (1 and 2) occurred in MeCN
and the resulting intermediate cis-[Ru(CO)(NCMe)(h2
-(SS))2] (9) with only one p-acceptor, CO, formed, this
intermediate isomerizes to relieve the steric congestion between the two cis chelating dithiolates and form
trans-[Ru(CO)(NCMe)(h2-(SS))
2] (10). The subsequent
replacement of MeCN of 10 with a strong donating dithiolate of another species, 10 or 9, forms a dimer [Ru(CO)(h2-(S,S))(m,h2-(S,S))]
2 ((SS)−= Me2NCS2− (5)
or Et2NCS2− (6)) in configuration B or C, respectively
(Scheme 1). The mononuclear intermediate trans-[Ru(CO)(CNCH2Ph)(h2-(SS))2] (11), if produced during
the reaction of 5 and 6 with benzyl isocyanide in CH2Cl2, isomerize into cis-[Ru(CO)(CNCH2Ph)(h2
-(SS))2] ((SS)−= Me2NCS2− (7), Et2NCS2− (8)). It is
apparent that 11 is a kinetic product while 7 and 8 are thermodynamic products. No dinuclear products in configuration A was observed, probably indicating that the steric repulsive interactions between the two mutu-ally cis dithiolates in cis-[Ru(CO)(NCMe)(h2-(SS))
2] are
slightly larger than that in cis-[Ru(CO)2(h2-(SS)) 2].
Such repulsion may be increased appreciably during the dimerization, thus weakening the dimerization of cis-[Ru(CO)(NCMe)(h2-(SS))
2] into [Ru(CO)(h2
-(S,S))(m,h2-(S,S))]
2 in configuration A, a feature
reminiscent of the B (back) strain in influencing the acid – base interaction [10].
4. Conclusion
The reaction of [Ru2(CO)4(MeCN)6][BF4]2 or [Ru2(CO)4(m-O2CMe)2(MeCN)2] with potassium dimethyldithiocarbamate, sodium diethyldithiocarba-mate, potassium tert-butylthioxanthate, and ammo-nium O,O’-diethylthiophosphate gives both mono- and dimeric products of cis-[Ru(CO)2(h2-(SS))2] (1 – 4) and
[Ru(CO)(h2-Me
2NCS2) (m,h2-Me2NCS2)]2 (5) with two
structures 1 and 5 determined (Fig. 1 Fig. 2). The lightly stabilized MeCN ligands of [Ru2(CO)4(MeCN)6][BF4]2 are replaced more readily
than the bound acetate ligands of [Ru2(CO)4
(m-O2CMe)2(MeCN)2] by dithiolates to produce
cis-[Ru(CO)2(h2-(SS))2] with less selectivity. Two dinuclear
products 5 and 6 can also be prepared from the decar-bonylation reaction of cis-[Ru(CO)2(h2-R
2NCS2)]2]
(R = Me (1) and Et (2)) with Me3NO. Although
struc-ture 5 adopts configuration B, strucstruc-ture 6 takes configu-ration C. Both 5 and 6 react readily at ambient temperature with benzyl isocyanide to yield cis-[Ru(CO)(CNCH2Ph)(h2-R2NCS2)2] (R = Me (7) and Et
-Scheme 1.
(SS))2] via decabonylation and isomerization is pro-posed (Scheme 1).
5. Supplementary material
Crystallographic data for structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC nos. 173452 and 173453 for com-pounds 1 and 5, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (Fax: + 44-1223-336033; e-mail: deposit@ccdc. cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
The authors thank the National Science Council of the Republic of China for financial support of this research (Contract No. NSC89-2113-M006-013).
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