A five-coordinate, sixteen-electron manganese(I) complex [Mn(CO)3(S,S–C6H4)]– stabilized by S,Sπ-donation from chelating [S,S–C6H4]2–

DAL

TON

FULL P

APER

A

five-coordinate, sixteen-electron manganese(

I

) complex

[Mn(CO)

(S,S–C

H

)]

stabilized by S,S ð-donation from

chelating [S,S–C

H

]

Chien-Ming Lee,

Ging-Yi Lin,

Chung-Hung Hsieh,

Ching-Han Hu,*

Gene-Hsiang Lee,

Shie-Ming Peng

and Wen-Feng Liaw *

a

_{Department of Chemistry, National Changhua University of Education, Changhua 50058,}

Taiwan. E-mail: chfeng@cc.ncue.edu.tw

b

Department of Chemistry and Instrumentation Center, National Taiwan University,

Taipei 10074, Taiwan

Received 26th April 1999, Accepted 13th May 1999

The five-coordinate, sixteen-electron manganese() complex [N(PPh3)2][Mn(CO)3(S,S–C6H4)] 1 was prepared from reaction of [N(PPh3)2][Mn(CO)3(NH,S–C6H4)] and 1,2-benzenedithiol via the hexacoordinate intermediate fac-[Mn(CO)3(S–C6H4SH)(NH2,S–C6H4)]2. Alternatively, oxidative addition of 1,2-benzenedithiol to [Mn(CO)5]2, followed by a Lewis acid–base reaction, with evolution of H2 gas (identified by gas chromatography), led to formation of the coordinatively-unsaturated complex 1. In contrast, reaction of bis(2-pyridyl) disulfide and

[N(PPh3)2][Mn(CO)5] afforded hexacoordinate fac-[N(PPh3)2][Mn(CO)3(S–C5H4–N)(S–C5H4N)] 2, with one anionic

[S–C5H4N]2 ligand bound to MnI in a monodentate (S-bonded) manner and the other [S–C5H4–N]2 ligand bound in a bidentate manner (S,N-bonded). Complexes 1 and 2 have been characterized in solution by infrared spectroscopy and in the solid state by X-ray crystallography. The strong π-donating ability of the bidentate [S,S–C6H4]22 ligand stabilizes the unsaturated complex 1 which has short MnI_{–S bond lengths of 2.230(1) Å (average) as a result. The} existence of one π and two σ bonds between the [Mn(CO)3]1 and [S,S–C6H4]22 fragments, based on qualitative frontier molecular orbital analysis, also indicates that the lone-pair electrons are delocalized around the sulfur-manganese-sulfur system stabilizing the five-coordinate complex 1. The IR carbonyl stretching frequencies and the MnI_{–S bond distances of complexes 1 and [N(PPh}

3)2][Mn(CO)3(NH,S–C6H4)] suggest that the relative π-donating ability of the bidentate ligands is [NH,S–C6H4]22>[S,S–C6H4]22. The Mulliken atomic charges derived from Hartree–Fock calculations roughly quantify the charge distribution in the complex [Mn(CO)3(NH,S–C6H4)]2 (δ(N) = –1.14; δ(S) = 20.43; δ(Mn) = 1.14), and supports the premise that the reactions of [Mn(CO)3(NH,S–C6H4)]2 with electrophiles (1,2-benzenedithiol, thiophene-2-thiol, 1,2-ethanedithiol) occur at the more electron-rich amide site, yielding charge-controlled, collision complexes.

Introduction

Anionic metal carbonyls are known to function as nucleophiles and show a range of reactivity that depends on the metal, its oxidation state, its substituents and the ligand environment.1

Recently, application of the anionic metallic fragment

[Mn(CO)5]2 to the preparation of manganese chalcogenolates proved a successful approach in this direction, i.e. oxidative addition of diorganyl dichalcogenides to the low-valent manganese carbonyl fragment [Mn(CO)5]2 led to formation of cis-[Mn(CO)4(ER)2]2 (E= Te, Se, S; R = phenyl) [Scheme 1(a)].2

In addition, [Mn(CO)5]2 may also serve as a lone-pair-electron donor. Coordinative addition of [Mn(CO)5]2 to TeCl4 led to formation of a discrete chlorotellurate, [Cl4Te–Mn(CO)5]2

[Scheme 1(b)].3 _{Very recently, the five-coordinate,} sixteen-electron MnI _{complex [Mn(CO)3(NH,S–C6H4)]}2 _{was prepared}

Scheme 1

by combining the dichalcogen synthetic methodology with the potential for intramolecular H-bonding, via the reaction of

[Mn(CO)5]2 with 1 equiv. of 2-aminophenyl disulfide [Scheme 1(c)].4 _{By way of contrast, the six-coordinate Mn}I _complex fac-[Mn(CO)3(S–C5H4–N)(S–C5H4N)]2 2 was isolated and structurally characterized from the reaction of [Mn(CO)5]2 and bis(2-pyridyl) disulfide [Scheme 1(d)]. In an effort to examine the reaction chemistry of the coordinatively-unsaturated complex [Mn(CO)3(NH,S–C6H4)]2, we report herein a study of the conversion of [Mn(CO)3(NH,S–C6H4)]2 to five-coordinate, sixteen-electron [Mn(CO)3(S,S–C6H4)]2 1, stabilized by the bidentate S,S π-donation of the [S,S–C6H4]

22 _ligand.

Unsatur-ated [Mn(CO)3(S,S–C6H4)]2 was also obtained from the reaction of 2 equiv. of 1,2-benzenedithiol with [Mn(CO)5]2. To our knowledge, only a few examples of d6 _{transition metal} carbonyl complexes containing five-coordinate sixteen-electron metal cores have been reported,5,6 _{e.g. [Mn(CO)3(DBCat)]}2

pre-pared by oxidative substitution of two CO ligands of [ Mn-(CO)5]2 by 3,5-di-tert-butyl-1,2-benzoquinone,5a and [W(CO)3 -(NHC6H4NH)]

22 _{prepared from W(CO)}

5(thf) and 2 equiv. of the monodeprotonated ligand [NHC6H4NH2]2 by inter-molecular deprotonation.6c

Results and discussion

Synthesis

As illustrated in Scheme 2(a,b), treatment of 1 equiv. of

thf led to the formation of the five-coordinate sixteen-electron manganese() complex [N(PPh3)2][Mn(CO)3(S,S–C6H4)] 1 stabilized by incorporation of the π-donating chelate [S,S– C6H4]22 and ejection of HS-C6H4-NH2, identified by NMR. Alternatively, complex 1 was also obtained when 2 equiv. of 1,2-benzenedithiol was added to [N(PPh3)2][Mn(CO)5] and the solution was stirred overnight in thf at ambient temperature

[Scheme 2(c)]. The dark red-purple complex 1 is soluble in common organic solvents, such as thf, MeCN and CH2Cl2, and can be crystallized by vapor diffusion of diethyl ether–hexane into a concentrated thf solution at 215 8C under nitrogen. No decomposition was observed on stirring complex 1 in thf solution at ambient temperature for 2 days. In contrast, proton-ation of complex 1 by 2-aminothiophenol was not successful in synthesising [Mn(CO)3(NH,S–C6H4)]2. The coordinatively-unsaturated complex 1 is completely unreactive toward CO:

1 remains unchanged when treated with 1 atm (101 325 Pa) CO

in thf at room temperature. This is in contrast to the observ-ation that catecholate tungsten(0) tricarbonyl and catecholate

tungsten(0) tetracarbonyl are readily interconvertible.6g _The six-coordinate MnI _{complex fac-[N(PPh}

3)2][Mn(CO)3(S–C5H4– N)(S–C5H4N)] 2, with one anionic [S–C5H4N]2 ligand bound to MnI _{in a monodentate (S-bonded) manner and the second}

[S–C5H4–N]2 bound in a bidentate manner (S,N-bonded), was obtained from the reaction of [Mn(CO)5]2 and 1 equiv. of bis(2-pyridyl) disulfide [Scheme 2(d)]. The air-stable complex 2 was isolated as an orange–yellow semi-solid from thf–diethyl ether, and is soluble in thf, MeCN and CH2Cl2.

Characterization in solution

The IR spectrum of complex 1 shows two strong CO stretching bands, 1986vs and 1887s cm21 (thf), which suggests facial orien-tation of the three CO ligands.4 _The 1_{H and} 13_{C NMR spectra} show the expected signals for the [S,S–C6H4]22 _{ligand in a}

diamagnetic d6 _MnI _{species. The electronic spectrum of} com-plex 1 is dominated by ligand-to-metal charge-transfer bands at approximately 349, 400, 502 and 552 nm. Complex 2 exhibits a three-band pattern in the ν(CO) region of its IR spectrum, at 1994vs, 1901s and 1882s cm21 (thf), which is consistent with a tricarbonyl derivative of pseudo C3v symmetry.7 The 1H and 13_{C NMR spectra are consistent with the presence of low-spin} octahedrally coordinated d6 _MnI_.

Scheme 2

Structures

A definitive assignment of the structure of complex 1 was obtained by X-ray crystallography; the structure of the

[Mn(CO)3(S,S–C6H4)]2 unit in the [N(PPh3)2]1 salt is shown in Fig. 1. The geometry about manganese is intermediate between square pyramidal and trigonal bipyramidal, with the bite angle of the chelating [S–C6H4–S]22 ligand being 87.81(4)8. The five-membered chelate ring MnS2C2 is almost planar, with a deviation from planarity of 0.02 Å. The interesting feature of complex 1 is the asymmetry in the MnI_{–S bond lengths} (2.211(1) and 2.248(1) Å), which shows a difference of 0.036 Å. The significantly shorter MnI_{–S bonds [2.230(1) Å (average)]} in complex 1, as compared to the reported 2.398(1) Å for the MnI_{–SPh bond in cis-[Mn(CO)}

4(SPh)2]2,8 were attributed to the strong π-donating ability of the bidentate [S,S–C6H4]22 ligand which stabilizes the unsaturated complex 1.6,9 _{The Mn}I_–S distances [2.230(1) Å (average)] in complex 1 are shorter than the reported 2.268(1) Å MnI_{–S bond in the analogue}

[Mn(CO)3(NH,S–C6H4)]2.4 The MnI–CO bonds, which aver-age 1.767(4) Å, in compound 1 are comparable to the MnI_{–CO distances [1.763(4) Å (average)] in [Mn(CO)3(NH,S–} C6H4)]2.4

The X-ray crystal structure of complex 2 is shown in Fig. 2. The MnI_{–S distances of 2.380(1) and 2.445(1) Å in complex}

2 are significantly longer than those in five-coordinate,

coordinatively-unsaturated complex 1 [average 2.230(1) Å]. The MnI_{–N(1) bond distance is 2.028(3) Å, which is also} significantly longer than that in [Mn(CO)3(NH,S–C6H4)]2

[1.889(3) Å].4 _{The bond angles at the Mn}I _{center are} consider-ably distorted from the idealized octahedral limits due to the presence of the four-membered N,S-chelate ring, a character-istic apparent in the internal chelate angle, S–Mn–N of 68.30(8)8.10

Fig. 1 ORTEP drawing and labeling scheme for anionic [Mn(CO)3

-(S,S–C6H4)]2 with thermal ellipsoids drawn at the 30% probability level.

Fig. 2 ORTEP drawing and labeling scheme for anionic fac-[ Mn-(CO)3(S–C5H4–N)(S–C5H4N)]2 with thermal ellipsoids drawn at the

Discussion

A reasonable reaction sequence accounting for the formation of complex 1 is shown in Scheme 2(a,b). Protonation of

[Mn(CO)3(NH,S–C6H4)]2 with 1,2-benzenedithiol in thf under N2 at ambient temperature led to formation of the unstable six-coordinate intermediate fac-[Mn(CO)3(S–C6H4SH)(NH2,S– C6H4)]2. Attempts to detect this extremely unstable intermedi-ate by FTIR were unsuccessful. Presumably, the intramolecular S–H? ? ? S interaction (cis arrangement of thiolate and SH groups in the intermediate),11 _{and the subsequent elimination} of 2-aminothiophenol yielded the stable five-coordinate, sixteen-electron complex 1. Apparently, protonation of the amide site of [Mn(CO)3(NH,S–C6H4)]2 labilizes the chelating ligand [NH,S–C6H4)]22 _{and results in the formation of complex} 1. Alternatively, complex 1 was also obtained when 2 equiv. of

1,2-benzenedithiol were added to [N(PPh3)2][Mn(CO)5] and the solution was stirred overnight in thf at ambient temperature

[Scheme 2(c)]. Presumably, oxidative addition of H–SC6H4SH to [Mn(CO)5]2, leading to the intermediate [Mn(CO)4 (H)-(S–C6H4SH)]2, is followed by a Lewis acid–base reaction (the second equiv. of 1,2-benzenedithiol reacts with [ Mn-(CO)4(H)(S–C6H4SH)]2) with evolution of H2 gas, identified by

gas chromatography. Further intermolecular deprotonation of the [S–C6H4SH]2 ligand bound to the MnI center by free anionic [S–C6H4SH]2,6d _{and subsequent dissociation of} a carbonyl ligand as a result of chelation led to formation of complex 1.6d,8 _{However, the presumed intermediate [} Mn-(CO)4(H)S–C6H4(SH)]2 was not observed spectroscopically, even at 220 8C.

In contrast, protonation of [Mn(CO)3(NH,S–C6H4)]2 by 1,2-ethanedithiol in thf under N2 at ambient temperature led to the formation of an orange–yellow solution immediately. A three-band pattern in the ν(CO) region of the IR spectrum at 1980vs, 1899s and 1885s cm21 (thf) was assigned to the formation of six-coordinate fac-[Mn(CO)3(S–(CH2)2SH)(NH2,S–C6H4)]2, isolated as a semi-solid. In order to add further credibility to the formation of the six-coordinate intemediate

fac-[Mn(CO)3(S,NH2–C6H4)(S–C6H4SH)]2 in the proposed mech-anism [Scheme 2(a)] and of six-coordinate fac-[Mn(CO)3(S– (CH2)2SH)(NH2,S–C6H4)]2 in the protonation reaction, the analogous six-coordinate MnI _{complex 2 was isolated and} structually characterized from the reaction of [Mn(CO)5]2 and 1 equiv. of bis(2-pyridyl) disulfide [Scheme 2(d)]. The proposed mechanism, shown in Scheme 2(d), involves oxidative addition of bis(2-pyridyl) disulfide to [Mn(CO)5]2, possibly via the intermediate cis-[Mn(CO)4(S–C5H4N)2]2.2,8

Ab initio calculations

In order to investigate the conversion of [Mn(CO)3(NH,S– C6H4)]2 to complex 1 [Scheme 2(a,b)], ab initio quantum chemistry computations were also performed. The Gaussian 94 suite of programs were used.12 _{The geometries of the four} species, [Mn(CO)3(NH,S–C6H4)]2, [SH–C6H4–SH], complex 1 and [NH2–C6H4–SH] were fully optimized, firstly at the Hartree–Fock level where a 6-311G basis set for Mn and a 6-31G basis set (set 1) for other atoms were used. The frequency analyses on the optimized structures were performed at this level of theory. All four molecules were identified as genuine minima, the vibrational frequencies (scaled by 0.89) were later used in calculating thermal corrections to the reaction ener-getics (298 K). The structures were then further optimized at the MP2 level of theory. Selected geometrical parameters of complex 1 are compared with those obtained from X-ray diffraction data (Table 1). The bond distances and bond angles predicted at the MP2 level of theory compare reasonably well with the experimental results. One exception is the predicted bond angle S(1)–Mn–C(1), which differs from the experimental value by more than 108. A possible explanation for such a deviation is that the prediction is based on gas-phase molecules,

while the experimental structures were determined using crystals. Computations revealed that the energy surface is relatively insensitive to the orientation of the S,S–C6H4 ring. Basis set truncation and correlated level of theory applied could also affect the prediction.

Energetics were evaluated using the MP2 method with extra polarization functions on each atom (311G* on Mn, and 6-31G* on other atoms, named set 2). The theoretical predictions for the energetics of reaction are summarized in Table 2. Sig-nificant electron correlation effects have been observed for the reaction enthalpy: the magnitude of the reaction energy and enthalpy (∆E and ∆H) is reduced by more than 20 kcal mol21 at the correlated MP2 level. Introducing zero-point vibrational energy corrections (from the HF method) reduces the energy difference by another 2.6 kcal mol21, while adding the temper-ature correction raises this difference by about 0.5 kcal mol21. The effect of adding an extra set of polarization functions to the heavy atoms is minor. The reaction enthalpy (∆H) for the conversion of [Mn(CO)3(NH,S–C6H4)]2 to complex 1 [Scheme 2(a,b)] is 212.1 kcal mol21 at 298 K. This result is supportive of the observation that the chemical conversion is not reversible experimentally.

The calculated Mulliken charge distributions on the N, S and Mn atoms of [Mn(CO)3(NH,S–C6H4)]2 are 21.14, 20.43 and 1.14 respectively. The charge distribution on Mn of complex 1 Table 1 Selected bond distances (Å) and angles (8) for (a) 1a _{and (b) 2}

determined via X-ray di_ffraction (a) Complex 1 Mn–S(1) Mn–C(1) Mn–C(3) C(2)–O(2) S(1)–Mn–S(2) S(1)–Mn–C(2) S(2)–Mn–C(1) S(2)–Mn–C(3) C(1)–Mn–C(3) Mn–S(1)–C(4) 2.211(1) [2.217] 1.750(4) [1.670] 1.770(3) [1.670] 1.154(4) [1.221] 87.81(4) [89.2] 149.67(11) [144.6] 98.57(12) [92.5] 170.02(12) [177.1] 91.31(16) [89.7] 107.01(8) [107.5] Mn–S(2) Mn–C(2) C(1)–O(1) C(3)–O(3) S(1)–Mn–C(1) S(1)–Mn–C(3) S(2)–Mn–C(2) C(1)–Mn–C(2) C(2)–Mn–C(3) Mn–S(2)–C(9) 2.248(1) [2.260] 1.781(3) [1.688] 1.157(4) [1.220] 1.159(4) [1.234] 117.96(11) [130.4] 86.34(11) [87.9] 88.76(10) [94.2] 92.35 (15) [84.8] 92.21(15) [88.0] 106.28(11) [106.6] (b) Complex 2 Mn–S(1) Mn–C(1) Mn–C(3) C(2)–O(2) Mn–N(1) S(1)–Mn–S(2) S(1)–Mn–C(2) S(1)–Mn–N(1) S(2)–Mn–C(2) S(2)–Mn–N(1) N(1)–Mn–C(2) Mn–S(1)–C(4) 2.445(1) 1.790(4) 1.775(4) 1.165(4) 2.028(3) 84.84(4) 87.06(11) 68.30(8) 170.76(12) 87.62(7) 93.51(13) 77.74(11) Mn–S(2) Mn–C(2) C(1)–O(1) C(3)–O(3) S(1)–Mn–C(1) S(1)–Mn–C(3) S(2)–Mn–C(1) S(2)–Mn–C(3) N(1)–Mn–C(1) N(1)–Mn–C(3) Mn–S(2)–C(9) 2.380(1) 1.773(4) 1.152(4) 1.160(4) 163.17(12) 103.47(13) 97.86(11) 86.07(12) 95.13(14) 170.08(14) 113.74(12)

a_{Numbers in brackets are geometrical parameters predicted at the}

MP2/set 1 level of theory.

Table 2 Predicted reaction enthalpy for the conversion of [Mn(CO)3

-(NH,S–C6H4)]2 to complex 1 Methoda _{∆E ∆H(0 K) ∆H(298 K)} HF/set 1// HF/set 1 MP2/set 1// MP2/set 1 MP2/set 2// MP2/set 1 238.2 214.5 214.2 235.6 211.9 211.6 236.1 212.3 212.1 a_{Set 1: 6-311G on Mn, 6-31G on H, C, N, O, S; set 2: 6-311G* on Mn,} 6-31G* on C, N, O, S.

is 1.02. Thus both [Mn(CO)3(NH,S–C6H4)]2 and complex 1 can be accurately described as MnI _complexes.

Attempts to compute the energies of the species using density functional theory (DFT) were made. However, serious convergence difficulties were encountered while trying to evaluate these energies. All attempts to overcome these were unsuccessful.

A qualitative analysis using the frontier molecular orbitals (MOs) of complex 1 is illustrated in Fig. 3. The [Mn(CO)3]1 fragment was kept within the C3v point group, while the [S,S– C6H4]22 anionic precursor has C2v symmetry. The model com-plex has Cs symmetry despite the optimized structure being slightly distorted from Cs. Three unoccupied MOs (a1 and e) of the [Mn(CO)3]1 fragment interact with the three highest occupied [S,S–C6H4]22 MOs having proper symmetry (a1, b2 and a2). Two of these interactions form σ bonds, and one interaction results in a π bond. The b1 MO in [S,S–C6H4]

22 _is

nonbonding. The stability of complex 1 is attributed to these three MO interactions.

Summary

Protonation of [Mn(CO)3(NH,S–C6H4)]2 by 1,2-benzenedithiol and 1,2-ethanedithiol yielded complex 1 and fac-[ Mn(CO)3-(S–(CH2)2SH)(NH2,S–C6H4)]2 respectively. The calculated Mulliken atomic charge distribution in the complex

[Mn(CO)3(NH,S–C6H4)]2 supports the hypothesis that the reactions of [Mn(CO)3(NH,S–C6H4)]2 with electrophiles (1,2-benzenedithiol, 1,2-ethanedithiol) occur at the more electron-rich amide site to yield charge-controlled, collision complexes. In contrast, reaction of bis(2-pyridyl) disulfide and [N(PPh3)2]

-[Mn(CO)5] afforded the hexacoordinate complex 2. The

MnI_{–S bond angles, and carbonyl stretching frequencies (ν(CO)} 1986vs and 1887s cm21 (thf) for complex 1 vs. 1973vs and 1870s cm21 (thf) for [Mn(CO)3(NH,S–C6H4)]2) of complexes 1 and

[Mn(CO)3(NH,S–C6H4)]2 unequivocally indicate that the relative π-donating ability of the bidentate ligands investigated here is [NH,S–C6H4]

22_>[S,S–C

6H4]

22_.13 _{The existence of two} σ and one π bond between the [Mn(CO)3]1 and [S,S–C6H4]22

fragments, based on qualitative frontier molecular orbital analysis, also indicates that one lone-pair of electrons is delocal-ized around the sulfur–manganese–sulfur chelate stabilizing the five-coordinate complex 1, i.e. the additional donation of Fig. 3 Frontier molecular orbital (MO) analysis for [N(PPh3)2][

Mn-(CO)3(S,S–C6H4)].

charge from [S,S–C6H4]

22 _{effectively means that there are more}

than 16 electrons around MnI _{(the total electron count around} MnI _{amounts to 18 electrons instead of 16 electrons), and this} explains the unusual stability of complex 1. The hexacoordinate metal centre as well as the long MnI_{–S and Mn}I_{–N bond} distances of complex 2, compared to the five-coordinate complexes 1 and [Mn(CO)3(NH,S–C6H4)]2, reflect the fact that bidentate [S–C5H4N]2 may not serve as a strong π-donating ligand.

Experimental

Manipulations, reactions and transfers of samples were con-ducted under nitrogen according to standard Schlenk tech-niques or in a glove-box (argon gas). Solvents were distilled under nitrogen from appropriate drying agents (diethyl ether from CaH2; acetonitrile from CaH2–P2O5; methylene chloride from P2O5; hexane and tetrahydrofuran (thf) from sodium– benzophenone) and stored in dried, N2-filled flasks over 4 Å molecular sieves. A nitrogen purge was used on these solvents before use and transfers to reaction vessels were via stainless steel cannula under N2 at a positive pressure. The reagents dimanganese decacarbonyl, 2-aminophenyl disulfide, 1,2-benzenedithiol, bis(2-pyridyl) disulfide, bis(triphenylphosphor-anylidene)ammonium chloride, 1,2-ethanedithiol (Lancaster/ Aldrich) were used as received. Infrared spectra were recorded on a Bio-Rad FTS-185 spectrometer with sealed solution cells (0.1 mm) and KBr windows. NMR spectra were recorded on a Bruker AC 200 spectrometer; 1_{H and} 13_{C chemical shifts being} relative to tetramethylsilane. UV/VIS spectra were taken on a GBC 918 spectrophotometer. Gas chromatography was carried out on a Shimadzu GC-3BT with a Shimadzu R-11 recorder. Analyses made use of the thermal conductivity detector (TCD); nitrogen was the carrier gas, the column was OV-17 (5%) on Chromosorb W, 80/100 mesh, 6 ft × 1/8 in stainless steel tubing. Analyses of carbon, hydrogen and nitrogen contents were obtained with a Heraeus CHN analyzer.

Preparations

Reaction of 1,2-benzenedithiol and [N(PPh3)2][Mn(CO)

3-(NH,S–C6H4)]. Initially, 1,2-benzenedithiol (0.2 mmol, 24 µL) was added dropwise to a solution containing 0.16 g (0.2 mmol) of [N(PPh3)2][Mn(CO)3(NH,S–C6H4)] in thf (5 cm3_).4 _After stirring the reaction solution for 30 min at room temperature, diethyl ether was added to precipitate the dark red-purple solid

[N(PPh3)2][Mn(CO)3(S,S–C6H4)] 1. The stable product 1 was washed twice with thf–diethyl ether and dried under vacuum. Crystals suitable for X-ray crystallography were grown by vapor diffusion of diethyl ether into a concentrated thf solution of

1 at 215 8C. Yield 0.151 g (92%). IR (thf): ν(CO) 1986vs, 1887s

cm21. 1_{H NMR (CD3CN): δ 6.99, 7.89 (br, S,S–C6H4).} 13_C NMR (CD3CN): δ 134.49, 133.27, 133.15, 133.03, 130.40, 130.23 and 130.14. UV/VIS (thf): λmax/nm (ε/M21 cm21) 349(2079), 400(4569), 502(2109) and 552(1556). Found: N, 1.83; C, 66.17; H, 4.27. Calc. for C45H34O3P2NS2Mn: N, 1.75; C, 66.13; H, 4.16%).

Reaction of 1,2-benzenedithiol and [N(PPh3)2][Mn(CO)5].

[N(PPh3)2][Mn(CO)5]14 (0.2 mmol, 0.147 g) dissolved in thf (3 cm3_{) was stirred under N2 and 1,2-benzenedithiol (0.4 mmol,} 48 µL) added dropwise at room temperature. After stirring overnight, the volume of the solution was reduced to 2 cm3 _and the dark red-purple product precipitated by addition of diethyl ether (15 cm3_{). The thermally stable product was isolated by} removing the solvent. Yield of [N(PPh3)2][Mn(CO)3(S,S–C6H4)]

(1) 0.130 g (80%). IR (thf): ν(CO) 1986vs, 1887s cm21, consist-ent with the formation of [N(PPh3)2][Mn(CO)3(S,S–C6H4)].

fac-[N(PPh3)2][Mn(CO)3(S–(CH2)2SH)(NH2,S–C6H4)]. 1,2-Ethanedithiol (0.2 mmol, 18 µL) was added dropwise to a

solution containing 0.16 g (0.2 mmol) of [N(PPh3)2]

-[Mn(CO)3(NH,S–C6H4)] in thf (3 cm3_{). The reaction mixture} was stirred for 10 min at ambient temperature and hexane added to precipitate the yellow-brown semi-solid (76% yield). The product was washed with hexane twice and dried under vacuum. IR (thf): ν(CO) 1980vs, 1899s, 1885s cm21. 1_{H NMR} (C4D8O): δ 4.78 (br, NH2), 3.03–2.75 (m, SCH2CH2), 2.25 (s, SH), 6.68, 6.45 (m, C6H4).

fac-[N(PPh3)2][Mn(CO)3(S–C5H4–N)(S–C5H4N)] 2. Bis(2-pyridyl) disulfide (0.4 mmol, 0.088 g) was added to a solution containing 0.308 g (0.4 mmol) of [N(PPh3)2][Mn(CO)5] in tetrahydrofuran (5 cm3_{). After stirring the reaction mixture} overnight at room temperature, diethyl ether was added to precipitate the orange-yellow semi-solid fac-[N(PPh3)2]

-[Mn(CO)3(S–C5H4–N)(S–C5H4N)]2. The stable product 2 was washed twice with thf–diethyl ether and dried under vacuum. Crystals suitable for X-ray crystallography were grown by vapor diffusion of diethyl ether into a concentrated thf solution of 2 at 215 8C. Yield 0.320 g (89%). IR (thf): ν(CO) 1994vs, 1901s, 1882s cm21. 1_{H NMR (CD} 3COCD3): δ 8.05, 7.88, 7.29, 7.11 (d, SC5H4N), 7.01, 6.55, 6.49 (t, SC5H4N) and 7.72–7.58 (m, Ph). 13_{C NMR (CD} 3COCD3): δ 114.68, 115.55, 127.13, 129.27, 130.25, 130.39, 130.52, 133.12, 133.23, 133.35, 133.90, 134.59, 148.22 and 151.21. UV/VIS (thf): λmax/nm (ε/M21 cm21) 384(4599). Found: N, 4.76; C, 65.39; H, 4.20. Calc. for C49H38O3P2N3S2Mn: N, 4.68; C, 65.55; H, 4.27%).

Ab initio calculations

The Gaussian 94 suite of programs12 _{was used in the study of} several complexes. The geometries of these species were fully optimized using analytic gradients at the Hartree–Fock (HF) and MP2 levels of theory. At the stationary points, vibrational frequency analysis was performed. The computed vibrational frequencies were used to verify whether these structures are genuine minima on the potential energy surfaces. These fre-quencies were also used in calculating thermal corrections to enthalpies (up to 298 K). The 6-311G basis set on Mn, and the 6-31G basis sets on other atoms were used in geometry optimizations (set 1). An extra set of polarization functions were added to atoms other than hydrogen (6-311G* on Mn and 6-31G* on C, N, O, and S, named set 2) for the most elaborate energy calculations using MP2.

Crystallography

Crystallographic data for complexes 1 and 2 are collected in Table 3. The crystals of 1 and 2 chosen for the X-ray diffraction studies measured 0.55 × 0.50 × 0.45 mm and 0.23 × 0.20 × 0.15 mm, respectively. Each crystal was mounted on a glass fiber and quickly coated in epoxy resin. Unit-cell parameters for complex

1 were obtained by least-squares refinement from 25 reflections

with 2θ between 19.00 and 28.828. Least-squares refinement of the positional and anisotropic thermal parameters for all non-hydrogen and fixed non-hydrogen atom contributions was based on F. Diffraction measurements were carried out on a Nonius CAD 4 diffractometer with graphite-monochromated Mo-Kα radiation employing the θ/2θ scan mode.15 _{A φ scan absorption} correction was made. The NRCC-SDP-VAX package of struc-ture solution programs was employed16 _{and atomic scattering} factors were obtained from ref. 17. Diffraction measurements for complex 2 were carried out at 228C on a Siemens SMART CCD diffractometer with graphite-monochromated Mo-Kα radiation (λ 0.7107 Å) and θ between 1.38 and 25.008. Least-squares refinement of the positional and anisotropic thermal parameters for all non-hydrogen and fixed hydrogen atom contributions was based on F2_{. A SADABS}18 _absorption correction was made. The SHELXTL19 _{structure refinement} program was employed. Selected bond distances and angles are listed in Table 1.

CCDC reference number 186/1463.

See http://www.rsc.org/suppdata/dt/1999/2393/ for crystallo-graphic files in .cif format.

Acknowledgements

The support of the National Science Council (Taiwan) is gratefully acknowledged. The authors thank Professor Donald J. Darensbourg for helpful suggestions.

References

1 (a) M. S. Corraine and J. D. Atwood, Organometallics, 1991, 10, 2315; (b) M. Tilset and V. D. Parker, J. Am. Chem. Soc., 1989, 111, 6711; (c) C.-K. Lai, M. S. Corraine and J. D. Atwood,

Organometallics, 1992, 11, 582; (d ) R. G. Pearson and P. E. Figdore, J. Am. Chem. Soc., 1980, 102, 1541.

2 (a) W.-F. Liaw, D.-S. Ou, Y.-S. Li, W.-Z. Lee, C.-Y. Chuang, Y.-P. Lee, G.-H. Lee and S.-M. Peng, Inorg. Chem., 1995, 34, 3747; (b) W.-F. Liaw, C.-Y. Chuang, W.-Z. Lee, C.-K. Lee, G.-H. Lee and S.-M. Peng, Inorg. Chem., 1996, 35, 2530; (c) W.-F. Liaw, W.-Z. Lee, C.-Y. Wang, G.-H. Lee and S.-M. Peng, Inorg. Chem., 1997, 36, 1253.

3 W.-F. Liaw, S.-J. Chiou, G.-H. Lee and S.-M. Peng, Inorg. Chem., 1998, 37, 1131.

4 W.-F. Liaw, C.-M. Lee, G.-H. Lee and S.-M. Peng, Inorg. Chem., 1998, 37, 6396.

5 (a) F. Hartl, A. Vlcek, Jr., L. A. deLearie and C. G. Pierpont, Inorg.

Chem., 1990, 29, 1073; (b) P. Jaitner, W. Huber, G. Huttner and

O. Scheidsteger, J. Organomet. Chem., 1983, 259, C1; (c) F. Hartl, D. J. Stufkens and A. Vlcek, Jr., Inorg. Chem., 1992, 31, 1687. 6 (a) D. J. Darensbourg, K. K. Klausmeyer, B. L. Mueller and J. H.

Reibenspies, Angew. Chem., Int. Ed. Engl., 1992, 31, 1503; (b) D. J. Darensbourg, J. D. Draper and J. H. Reibenspies, Inorg. Chem., 1997, 36, 3648; (c) D. J. Darensbourg, K. K. Klausmeyer and J. H. Reibenspies, Inorg. Chem., 1996, 35, 1535; (d ) D. J. Darensbourg, K. K. Klausmeyer and J. H. Reibenspies, Inorg. Chem., 1996, 35, 1529; (e) D. Sellmann, M. Wille and F. Knoch, Inorg. Chem., 1993,

32, 2534; ( f ) D. Sellmann and J. Schwarz, J. Organomet. Chem.,

1983, 241, 343; (g) D. Sellmann, W. Ludwig, G. Huttner and L. Zsolnai, J. Organomet. Chem., 1985, 294, 199; (h) D. J. Darensbourg, K. K. Klausmeyer and J. H. Reibenspies, Inorg.

Chem., 1995, 34. 4676.

7 W.-F. Liaw, C.-H. Chen, G.-H. Lee and S.-M. Peng,

Organometallics, 1998, 17, 2370.

8 W.-F. Liaw, C.-Y. Ching, C.-K. Lee, G.-H. Lee and S.-M. Peng,

J. Chin. Chem. Soc. (Taipei), 1996, 43, 427.

9 (a) M. T. Ashby, Comments Inorg. Chem., 1990, 10, 297; (b) K. W. Penfield, R. R. Gay, R. S. Himmelwright, N. C. Eickman, V. A. Norris, H. C. Freeman and E. I. Solomon, J. Am. Chem. Soc., 1981,

103, 4382; (c) D. Sellmann, M. Geck, F. Knoch, G. Ritter and Table 3 Crystallographic data for complexes 1 and 2

1 2 Formula M Crystal system Space group a/Å b/Å c/Å α/8 β/8 γ/8 V/Å3 Z dcalc/g cm23 µ/cm21 T/8C R Rw RWF2 GOF C45H34NO3P2S2Mn 817.77 Triclinic P1¯ 10.030(3) 14.259(2) 14.396(3) 88.62(2) 80.50(2) 89.76(2) 2030.1(8) 2 1.338 5.273 25 0.036a 0.034b 1.56 C49H38N3O3P2S2Mn 897.82 Monoclinic P21/c 14.7936(2) 10.2732(2) 29.6377(2) 92.567(1) 4499.75(11) 4 1.325 5.02 22 0.051 0.095c 1.044 a_{R= Σ|(F} o2 Fc)|/ΣFo; bRw=[Σω(Fo2 Fc)2/ΣωFo2]¹²; cRWF2= {Σω(F_o22 Fc 2₎2_/Σ[ω(F o 2₎2_]}¹².

J. Dengler, J. Am. Chem. Soc., 1991, 113, 3819; (d ) F. Hartl, D. J. Stufkens and A. Vlcek, Jr., Inorg. Chem., 1992, 31, 1687.

10 (a) S. G. Rosenfield, S. A. Swedberg, S. K. Arora and P. K. Mascharak, Inorg. Chem., 1986, 25, 2109; (b) P. Mura, B. G. Olby and S. D. Robinson, J. Chem. Soc., Dalton Trans., 1985, 2101; (c) B. K. Santra, M. Menon, C. K. Pal and G. K. Lahiri, J. Chem. Soc.,

Dalton Trans., 1997, 1387; (d ) I. P. Evans and G. Wilkinson, J. Chem. Soc., Dalton Trans., 1974, 946; (e) A. J. Deeming,

M. Karim and N. Powell, J. Chem. Soc., Dalton Trans., 1990, 2321; ( f ) D. J. Rose, Y.-D. Chang, Q. Chen and J. Zubieta, Inorg. Chem., 1994, 33, 5167; ( g) S. Kitagawa, M. Munakata, H. Shimono, S. Matsuyama and H. Masuda, J. Chem. Soc., Dalton Trans., 1990, 2105; (h) R. Castro, M. L. Durán, J. A. Garcia-Vázquez, J. Romero, A. Sousa, A. Castiñeiras, W. Hiller and J. Strähle, J. Chem. Soc.,

Dalton Trans., 1990, 531.

11 (a) M. A. Walters, J. C. Dewan, C. Min and S. Pinto, Inorg. Chem., 1991, 30, 2656; (b) D. Sellmann, W. Soglowek, F. Knoch and M. Moll, Angew. Chem., Int. Ed. Engl., 1989, 28, 1271; (c) T.-A. Okamura, N. Ueyama, A. Nakamura, E. W. Ainscough, A. M. Brodie and J. M. Waters, J. Chem. Soc., Chem. Commun., 1993, 1658; (d ) N. Ueyama, N. Nishikawa, Y. Yamada, T. Okamura, S. Oka, H. Sakurai and A. Nakamura, Inorg. Chem., 1998, 37, 2415. 12 M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G.

Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B. Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez and J. A. Pople, Gaussian 94 Revision E.3, Gaussian, Inc., Pittsburgh PA, 1995.

13 D. J. Darensbourg, J. D. Draper and J. H. Reibenspies, Inorg. Chem., 1997, 36, 3648.

14 K. Inkrott, G. Goetze and S. G. Shore, J. Organomet. Chem., 1978,

154, 337.

15 A. C. T. North, D. C. Philips and F. S. Mathews, Acta Crystallogr.,

Sect. A, 1968, 24, 351.

16 E. J. Gabe, Y. LePage, J. P. Chrarland, F. L. Lee and P. S. White,

J. Appl. Crystallogr., 1989, 22, 384.

17 International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4, Table 2.2B.

18 G. M. Sheldrick, SADABS, Siemens Area Detector Absorption Correction Program, University of Göttingen, 1996.

19 G. M. Sheldrick, SHELXTL, Program for Crystal Structure Determination, Siemens Analytical X-Ray Instruments Inc., Madison, WI, 1994.