DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2163–2168 2163 Transition metal complexes containing the 1,2-dicarba-closododecaborane- 1,2-dithiolate ligand: crystal structures of [4-MeC5H4NMe]2[Pd(S2C2B10H10)I2], [NEt3H][Mo(Á5-C5H5)- (NO)(S2C2B10H10)I], [NBu4][Re(] O)(S2C2B10H10)2] and [4-MeC5H4NMe]2[{Mo(] O)(Ï-O)(S2C2B10H10)}2] James D. McKinney, Hongli Chen, Thomas A. Hamor, Keith Paxton and Christopher J.Jones*,† School of Chemistry, The University of Birmingham, Edgbaston, Birmingham, UK B15 2TT The dithiol ligand 1,2-dicarbaborane-1,2-dithiol, 1,2-(HS)2-1,2-C2B10H10 (H2cbdt), reacted with anhydrous PdI2 to form [Pd(cbdt)I2]22, isolated as its [4-MeC5H4NMe]1 salt 1 and with [{Mo(h5-C5H5)(NO)I2}2] in the presence of NEt3 to aVord the mononuclear complex [NEt3H][Mo(h5-C5H5)(NO)(cbdt)I] 2.Complete halide substitution occurred with [NBu4][Re(]] O)Cl4] to give [NBu4][Re(]] O)(cbdt)2] 3 and the reaction with MoCl5 in tetrahydrofuran aVorded the oxo-bridged molybdenum(V) dimer [4-MeC5H4NMe]2[Mo(]] O)(m-O)(cbdt)}2] 4 which is diamagnetic. The salts 1–4 have been characterised by single crystal X-ray diVraction studies. In all cases only very limited conjugation appears to occur between the sulfur atoms and the carbon atoms of the carbaborane cage, C]S bond lengths averaging 1.785 Å, slightly shorter than the pure single bond value.The electrochemical properties of the new complexes were investigated but no simple reversible electron transfer processes were observed. Complexes containing dithiolene ligands have played a well established role in modern co-ordination chemistry.1 Initially such complexes were of interest because of their novel electronic and magnetic properties and the extended redox series which were found for some dithiolene complexes.2 More recently this type of compound has become important in the study of new molecular materials.3 In particular dithiolene complexes, and related materials such as salts of [Ni(dmit)2]22, have been used to produce metal–organic materials which exhibit electrical conductivity 4 or third order non-linear optical properties.5 Another type of dithiolate ligand which may be of interest in the synthesis of new molecular materials is represented by 1,2-dicarbadodecaborane-1,2-dithiol 6 (H2cbdt).The chemistry of H2cbdt has been little studied, although complexes with Co21, Ni21 and Zn21 have been described previously7 and, more recently, a series of gold complexes has been reported.8 In order further to develop the known chemistry of H2cbdt, and assess its ability to form redox active transition metal complexes, we have examined its reactions with a selection of diVerent transition metal compounds.Results and Discussion Synthetic studies The synthetic approach adopted involved the direct reaction of S S S– S– pfdt2–, R = CF3 mnt2–, R = CN dmit2– tdt2– cbdt2– = C = BH R S– R S– S– S– S S– S– † E-Mail: c.j.jones@bham.ac.uk H2cbdt with the appropriate transition metal reagent followed, where necessary, by treatment with a suitable cation. The reaction products were characterised by IR and 11B NMR spectroscopy, positive and negative ion fast atom bombardment mass spectrometry (FABMS), elemental analyses and solution conductivity measurements.The reaction of H2cbdt with PdI2 followed by the addition of 4-MeC5H4NMe1 ions aVorded a product (1) which exhibits bands attributable to nmax(BH) in its IR spectrum and for which the 11B NMR spectrum indicates the presence of the ligand cbdt.The negative-ion FAB mass spectrum of 1 contains an ion at m/z = 674 attributable to {[4-MeC5H4NMe][Pd(cbdt)I2]}2 along with ions at m/z = 566 and 439 which correspond to {H- [Pd(cbdt)I2]}2 and [HPd(cbdt)I]2 respectively. The positive ion FAB mass spectrum contains an ion at m/z = 890 attributable to {[4-MeC5H4NMe]3[Pd(cbdt)I2]}1. These results indicate that substitution of the iodide ligands has not occurred and the elemental analyses are in accord with the formulation of 1 as [4-MeC5H4NMe]2[Pd(cbdt)I2] which has been confirmed by a single crystal X-ray diVraction study described below.The reactions between the binuclear complex [{Mo(h-C5H5)- (NO)I2}2] and thiols or dithiols are of interest since any of a variety of products may form depending on the nature of the thiolate ligand.9 The co-ordinatively unsaturated 16-electron complex [Mo(h5-C5H5)(NO)(SPh)2] may be obtained with PhSH9a but with mnt22 the seven-co-ordinate 18-electron complex [Mo(h5-C5H5)(NO)(mnt)I]2 is formed and with H2tdt or pfdt22 the binuclear complexes [{Mo(h5-C5H5)(NO)(L]L)}2] (L]L22 = tdt22 or pfdt22) are obtained.9b The reaction of H2cbdt with [{Mo(h5-C5H5)(NO)I2}2], in the presence of triethylamine, produced the salt [NEt3H][Mo(h5-C5H5)(NO)(cbdt)I] 2.The positive-ion FAB mass spectrum of 2 contains an ion at m/z = 102 which corresponds to the cation [NEt3H]1 and the highest mass ion appears at m/z = 729 which corresponds with the formula {[NEt3H]2[Mo(h5-C5H5)(NO)(cbdt)I]}1. The negative-ion FAB mass spectrum contains a highest mass ion cluster at m/z = 527 which corresponds to the formally sevenco- ordinate molybdenum complex [Mo(h5-C5H5)(NO)(cbdt)I]2. The solution conductivity and elemental analyses are consistent with the formulation of 2 as [NEt3H][Mo(h5-C5H5)(NO)(cbdt)I] which was confirmed by a single crystal X-ray diVraction study2164 J.Chem. Soc., Dalton Trans., 1998, Pages 2163–2168 described below.In this reaction it appears that H2cbdt behaves more like mnt22 than H2tdt since a mononuclear iodo complex is obtained rather than a dimer in which both iodides have been replaced. In contrast to its cyclopentadienyl containing counterpart, the mononuclear co-ordinatively unsaturated complex [Mo(NO){HB(dmpz)3}I2] (dmpz = 3,5-dimethylpyrazolyl) reacts with PhSH or H2tdt to produce the mononuclear six-co-ordinate, formally 16-electron complexes [Mo(NO){HB(dmpz)3}(SPh)2] and [Mo(NO){HB(dmpz)3}- (tdt)] respectively.9c,10 However, under similar reaction conditions neither [Mo(NO){HB(dmpz)3}(cbdt)] nor [Mo(NO){HB- (dmpz)3(cbdt)I]2 could be obtained from H2cbdt and [Mo(NO){HB(dmpz)3}I2].This finding may result from the steric bulk of the HB(dmpz)3 ligand, which favours six-coordination, precluding the formation of a stable seven-coordinate complex.It is further likely that a pyrazolyl 3-methyl substituent or the HB(dmpz)3 ligand blocks binding of the bulky cbdt22 in the first instance, although the less sterically demanding chelate ligand tdt22 can be accommodated. The value of nmax(NO) for [NEt3H][Mo(h5-C5H5)(NO)(cbdt)I] was found to be 1639 cm21 which is comparable with respective values of 1640, 1630 and 1634 cm21 for [{Mo(h5-C5H5)- (NO)(tdt)}2], [Mo(h5-C5H5)(NO)(mnt)I]2 and [Mo(NO){HB- (dmpz)3}(tdt)].The reactions of H2cbdt with two higher oxidation state metal centres were also investigated. The complexes [NBu4]- [ReOCl4] 11 and MoCl5 were used as respective sources of ReV and MoV.The positive-ion FAB mass spectrum of the product from the reaction of H2cbdt with [NBu4][ReOCl4] contains an ion at m/z = 242 which corresponds to the cation [NBu4]1 and the negative-ion FAB mass spectrum contains a highest mass ion cluster at m/z = 615 which corresponds to [ReO(cbdt)2]2. The solution conductivity and elemental analyses of this salt are consistent with the formulation [NBu4][ReO(cbdt)2] 3 which was confirmed by a single crystal X-ray diVraction study described below.The formation of this product is in keeping with the general tendency of [ReOCl4]2 to form stable complexes with thiolate ligands.12 The IR spectrum of the 4- MeC5H5NMe1 salt of the product of the reaction between H2cbdt and MoCl5 in tetrahydrofuran contained strong bands attributable to nmax(BH).The negative-ion FAB mass spectrum contains a highest mass ion at m/z = 777 which corresponds to {[4-MeC5H4NMe][{MoO2(cbdt)}2]}2. An ion is also observed at m/z = 669 which corresponds to {H[{MoO2(cbdt)}2]}2. The positive-ion FAB mass spectrum contains a highest mass ion at m/z = 994 which corresponds to {[4-MeC5H4NMe]3[{MoO2- (cbdt)}2]}1.The solution conductivity of this salt is consistent with its formulation as a 2 : 1 electrolyte and the elemental analyses are consistent with the formulation [4-MeC5H4- NMe]2[{Mo(]] O)(m-O)(cbdt)}2] 4 which was confirmed by the single crystal X-ray diVraction study described below. It is possible that the formation of this complex results from hydrolysis during the purification process which is carried out in air.However, oxygen abstraction from the thf solvent is also possible as has been observed previously in the formation of [MoO{HB- (pz)3}Cl2] from MoCl5 and K[HB(pz)3] in thf.13 Structural studies All four complexes whose crystal structures have been determined contain as a common feature a metallo-1,2-dicarbadodecaborane- 1,2-dithiolate moiety.The B]B, B]C, C]C and C]S bond lengths agree closely, irrespective of the nature of the metal (Table 1). The overall mean values, 1.767, 1.720, 1.644 and 1.785 Å, respectively, are similar to the mean lengths of the corresponding bonds 1.778, 1.727, 1.632 and 1.781 Å measured 14 in C2B10S2C]] S and 1.775 and 1.716 Å given by Allen et al.15 for B]B and B]C bonds in comparable cage structures.The C]S bonds are only slightly shorter than the standard single bond value, indicating an only relatively small degree of p-electron delocalisation between the sulfur and the carborane cage (see Table 1). For comparison, C]S bond lengths in M(SC]] CS) (M = Pd, Mo or Re) moieties, which might be expected to show some electron delocalisation, average 16 1.709 [M = Pd (21 structures)], 1.733 [M = Mo (20 structures)] and 1.721 Å [M = Re (five structures)], some 0.05–0.08 Å smaller than our mean values, whereas in the saturated systems M(SC]CS) the C]S bond lengths average 16 1.828 Å for M = Pd (one structure), 1.816 for M = Mo (13 structures) and 1.826 Å for M = Re (five structures), approximately 0.04 Å greater than our mean values.This eVect can also be gauged by comparing the lengths of the C]S bonds in the bis(1,2-dithiooxalato)- oxorhenium(V) 17 and the bis(ethane-1,2-dithiolato)oxorhenium( V) 18 anions. In the former, which allows conjugation in the S]C]] O system, C]S bonds are in the range 1.730–1.766 Å, mean 1.742(8) Å, whereas in the latter, saturated system, C]S bonds are 1.795–1.849, mean 1.809 Å.Thus, for all three metals our C]S lengths are intermediate, but rather closer to the pure single bond value. Metal–sulfur lengths, however, do not show any systematic trend.In the palladium complex [4-MeC5H4NMe]2[PdII(cbdt)I2] 1, shown in Fig. 1, crystallographic mirror symmetry imposes a planar geometry on the metal co-ordination but deviations from a square planar geometry of up to 5.38 occur (see Table 2).The large I(2)]Pd]I(1) angle of 95.28(3)8 is presumably due to repulsion between the large iodide ligands. Similarly, in the crystal structure of [1,2-bis(phenylsulfanyl)benzene] diiodo palladium–diiodine,19 the I]Pd]I angle is 92.38 and the Pd]I and Pd]S bond lengths are 2.606 and 2.292 Å, respectively (cf. our values in Table 2). The structure of the anion [Mo(h5-C5H5)(NO)(cbdt)I]2 2 is shown in Fig. 2. If the cyclopentadienyl ligand is represented by its centroid (denoted Cn), the co-ordination geometry can be considered as very roughly approximating to trigonal bipyramidal. The axial angle I(1)]Mo]S(1) is 143.3(1)8 and the basal angles, involving Cn, N(1) and S(2), are in the range 117.4–124.98. In the somewhat analogous structures of (h5- cyclopentadienyl)[2-(1-dimethylamino)ethylphenyl-C,N]iodonitrosylmolybdenum20 and the closely related [Mo(h5-C5H5)- {C6H2(OCH2O)-2,3-CH2NMe2-6}(NO)I] 20 the geometry at molybdenum approximates to square pyramidal with the centroid of the cyclopentadienyl ring axial. The Mo]I bond Fig. 1 View of the dianion in compound 1 Table 1 Bond lengths (Å) for the carbaborane cage B]B B]C C]C S]C 1 1.765(3) a 1.713(9) d 1.638(10) 1.788(16) f 2 1.769(3) b 1.726(6) e 1.659(9) 1.783(3) f 3 1.770(2) c 1.717(5) a 1.636(7) f 1.790(2) d 4 1.765(3) b 1.723(4) e 1.652(7) 1.773(2) f a Mean of 16 values.b Mean of 21 values. c Mean of 42 values. d Mean of 4 values. e Mean of eight values. f Mean of two values.J. Chem. Soc., Dalton Trans., 1998, Pages 2163–2168 2165 lengths in these structures at 2.857 and 2.870 Å are slightly longer than the corresponding length in 2 [2.844(1) Å], but the Mo]N(O) bonds, 1.770 and 1.775 Å, agree well with our value Fig. 2 View of the anion in compound 2 Table 2 Selected bond lengths (Å) and angles (8) involving the metal centres of the anions 1–4 [Pd(C2B10H10S2)I2]22 1 Pd]S(1) Pd]S(2) I(1)]Pd]I(2) I(1)]Pd]S(1) I(1)]Pd]S(2) I(2)]Pd]S(1) 2.268(2) 2.265(2) 95.28(3) 179.90(4) 85.95(5) 84.82(6) Pd]I(1) Pd]I(2) I(2)]Pd]S(2) S(1)]Pd]S(2) Pd]S(1)]C(1) Pd]S(2)]C(2) 2.625(1) 2.643(1) 178.77(5) 93.95(7) 104.7(3) 105.4(2) [Mo(h5-C5H5)(NO)(C2B10H10S2)I]2 2 a Mo]S(1) Mo]S(2) Mo]N Mo]I Mo]Cn N(1)]O I]Mo]S(1) I]Mo]S(2) I]Mo]N I]Mo]Cn S(1)]Mo]S(2) S(1)]Mo]N S(1)]Mo]Cn 2.477(2) 2.514(2) 1.768(6) 2.844(1) 2.050 1.200(7) 143.3(1) 73.9(1) 85.0(2) 107.8 81.4(1) 82.8(2) 108.6 Mo]C(3) Mo]C(4) Mo]C(5) Mo]C(6) Mo]C(7) S(2)]Mo]N S(2)]Mo]Cn N]Mo]Cn Mo]S(1)]C(1) Mo]S(2)]C(2) Mo]N]O 2.443(8) 2.394(8) 2.305(8) 2.313(7) 2.398(7) 117.6(2) 124.9 117.4 109.6(2) 108.4(2) 169.4(6) [Re(]] O)(C2B10H10S2)2]2 3 Re]S(1) Re]S(2) Re]S(19) S(1)]Re]S(2) S(1)]Re]S(19) S(1)]Re]S(29) S(1)]Re]O S(2)]Re]S(19) S(2)]Re]S(29) S(2)]Re]O 2.310(2) 2.314(2) 2.306(2) 87.9(1) 141.3(1) 79.9(1) 109.8(2) 81.1(1) 145.5(1) 107.4(2) Re]S(29) Re]O S(19)]Re]S(29) S(19)]Re]O S(29)]Re]O Re]S(1)]C(1) Re]S(2)]C(2) Re]S(19)]C(19) Re]S(29)]C(29) 2.323(2) 1.678(5) 88.5(1) 108.8(2) 107.1(2) 107.3(2) 107.8(2) 108.0(2) 107.7(2) [{Mo(]] O)(m-O)(C2B10H10S1)}2]22 4 b Mo]S(1) Mo]S(2) Mo]O(1) S(1)]Mo]S(2) S(1)]Mo]O(1) S(1)]Mo]O(2) S(1)]Mo]O(2*) S(2)]Mo]O(1) S(2)]Mo]O(2) S(2)]Mo]O(2*) 2.423(2) 2.424(1) 1.673(4) 85.3(1) 107.2(2) 139.4(1) 79.3(1) 104.5(1) 79.5(1) 144.1(1) Mo]O(2) Mo]O(2*) Mo]Mo* O(1)]Mo]O(2) O(1)]Mo]O(2*) O(2)]Mo]O(2*) Mo]S(1)]C(1) Mo]S(2)]C(2) Mo]O(2)]Mo* 1.933(4) 1.943(3) 2.565(1) 113.0(2) 110.9(2) 91.4(1) 105.2(2) 105.7(2) 82.9(1) a Cn denotes the centroid of the cyclopentadienyl ring. b Starred atoms are related to the corresponding unstarred ones by a crystallographic two-fold axis.of 1.768(6) Å. The Mo]S bonds in 2, mean 2.495(19) Å, are significantly longer than the mean length of 2.418 Å found for this bond in 13 structures containing the Mo(SCH2CH2S) fragment extracted from the CSD.16 The very long Mo]S(2) bond of 2.514(2) Å in 2 may be aVected by the translengthening influence of the cyclopentadienyl ring, angles C(5)]Mo]S(2) and C(6)]Mo]S(2), 146.6(2) and 145.9(3)8 respectively, involving the two shortest Mo]C distances (see Table 2).The flexibility of Mo]S bonds is however demonstrated by the range of lengths found,16 2.339–2.497 Å. The metal centres of both the anions 3 and 4 show approximate square pyramidal co-ordination. In [Re(]] O)(cbdt)2]2 3 (see Fig. 3) the rhenium atom lies 0.726(1) Å from the best plane of the four sulfur atoms, with the apical oxygen atom 2.404(6) Å from this plane on the same side as the rhenium. The Re]S bond lengths average 2.313(4) Å (see Table 2), in good agreement with those measured in two comparable square pyramidal Re(]] O)(SCHRCHRS)2 anions, mean 2.310 Å for both R = H18 and CO2H.21 The Re]O bonds are 1.742,18a 1.673 18b (two independent determinations) and 1.699 Å,21 compared to 1.678(5) Å in 3.The dimeric anion [{Mo(]] O)(m-O)(cbdt)}2]22 4 (Fig. 4) has crystallographic two-fold (C2) symmetry. Excluding the 2.565(1) Å Mo]Mo interaction, the square pyramidal coordination at molybdenum has the two sulfur atoms and the bridging oxygen atoms forming the basal plane (coplanar to within 0.045 Å), the Mo atom being displaced by 0.699(3) Å from this plane and the apical oxygen atom by 2.372(5) Å.The two edge-sharing, symmetry related pyramids are tilted by 25.4(1)8 with respect to one another. The Mo]S, Mo]O (bridging) and Mo]O (terminal) lengths are 2.424(1) (mean of two values), 1.938(5) (mean of two values) and 1.673(4) Å, respectively.In the di-m-oxo-bis[di(benzenethiolato)oxomolybdate(V)] dianion,22 which is based on the same central atomic configuration, mean bond lengths are Mo]S 2.447 Å, Mo]O (bridging) 1.937 Å and Mo]O (terminal) 1.677 Å, with a 278 angle between the basal planes of the molybdenum co-ordinating square pyramids, very similar to the situation in our structure (4). Five-co-ordinated rhenium in Re(]] O)S4 moieties and five-coordinated molybdenum in Mo(]] O)S2O2 moieties, whose structures are presently known,16 adopt, without exception, an essentially square pyramidal co-ordination geometry, with the doubly bonded oxygen ligand axial.The metal atom is displaced from the basal plane in the same direction as the apical Fig. 3 View of the anion in compound 3 Fig. 4 View of the dianion in compound 4 along the crystallographic two-fold symmetry axis.Starred atoms are related to the corresponding unstarred ones by the symmetry axis2166 J. Chem. Soc., Dalton Trans., 1998, Pages 2163–2168 oxygen atom by 0.66–0.76 Å in the rhenium complexes 17,18,21,23 and by 0.66–0.73 Å in the molybdenum complexes,22,24 comfortably spanning our measured metal atom displacements from their respective basal planes.No abnormally close intermolecular contact distances are observed in any of the four structures. However, a significant intermolecular interaction occurs in compound 2 where there is a hydrogen bond between the triethylammonium ion and an iodine atom of the anionic complex, N ? ? ? I 3.795, H ? ? ? I 2.92 Å, and angle N]H? ? ? I 1638.Electrochemical studies Metal–1,2-dithiolene complexes often undergo sequential electron transfer reactions which are usually reversible.2 Electrochemical studies were carried out on the new carbaboranedithiolate complexes to establish whether they too would exhibit well defined electron transfer processes. The complexes [4-Me5H4NMe]2[Pd(cbdt)I2] and [NBu4][ReO(cbdt)2] did not undergo any well defined reduction or oxidation processes in the potential range 21.4 to 11.4 V vs.SCE. However, [NEt3H]- [Mo(h5-C5H5)(NO)(cbdt)I] oxidised at 10.61 V, although the process is electrochemically and chemically irreversible. These findings suggest that the carbaboranedithiolate ligand does not support the range of electron transfer processes found for complexes of dithiolene ligands.Conclusion The dithiol proligand H2cbdt has been found to react with several transition metal complexes. The heteroleptic complex [Pd(cbdt)I2]22 can be obtained from PdI2 but single crystal X-ray crystallography studies reveal no close intermolecular contacts or stacking of the {PdS2I2} moieties. The reaction of H2cbdt with [{Mo(h5-C5H5)(NO)I2}2] aVords the mononuclear complex [Mo(h5-C5H5)(NO)(cbdt)I]2 and, in this respect, cbdt22 behaves more like mnt22 than tdt22 which forms the dimer [{Mo(h5-C5H5)(NO)(tdt)}2]. The reaction with [ReOCl4]2 proceeds according to expectation aVording the five-co-ordinate rhenium(V) complex [ReO(cbdt)2]2.In the case of MoCl5 the reaction in thf involves oxygen abstraction, either from thf during the reaction or water during the purification procedure, and formation of the diamagnetic binuclear molybdenum(V) complex [{MoO(cbdt)(m-O)}2].The structural results suggest that cbdt22 behaves primarily as a dithiolate ligand with little delocalisation of charge between the cababorane cage, the sulfur donor atoms and the metal. The electrochemical behaviour of the new complexes suggests that the cbdt22 ligand is unable to support the rich electron transfer chemistry associated with dithiolene complexes.Experimental Reaction solvents were purified by distillation under nitrogen from standard drying agents before use. The reagents H2cbdt,6 [NBu4][ReVOCl4] 25 and [{Mo(h5-C5H5)(NO)I2}2] 26 were prepared by previously reported methods. All commercial reagents were pre-dried before use but were otherwise used as received.Reactions were carried out under an atmosphere of dry nitrogen but purification procedures were carried out in air. Column chromatography was carried out using silica gel (Merck; Kiesel gel 60, 70–230 mesh) or alumina (Merck, 70–230 mesh) with the eluents stated. The IR spectra were recorded from KBr discs using a Perkin-Elmer 1600 series FT-IR spectrophotometer, 11B NMR spectra at 86 MHz from dichloromethane or acetonitrile solutions using a JEOL GX270 spectrometer, 1H NMR 300 MHz spectra using a Bruker AC300 spectrometer and mass spectra using a Kratos MS80 instrument with positive or negative ion fast atom bombardment of a 3-nitrobenzyl alcohol matrix.Conductivity measurements were recorded from 1024 mol dm23 solutions of the new compounds in acetonitrile using a PTI 58 digital conductivity meter.Elemental analyses were performed by the Microanalytical Service, School of Chemistry, University of Birmingham or the Microanalytical Service, School of Chemistry, University of SheYeld. Preparations [4-MeC5H4NMe]2[Pd(cbdt)I2] 1. Palladium(II) iodide (0.36 g, 1.00 mmol) was dissolved in acetonitrile (10 cm3), the solution added dropwise to a solution of H2cbdt (0.21 g, 1.00 mmol) in acetonitrile (15 cm3) and the mixture stirred for 30 min at room temperature then heated under reflux for 16 h.The salt [4- MeC5H4NMe]I (0.47 g, 2.00 mmol) in acetonitrile (10 cm3) was added dropwise and the solution heated under reflux for 2 h. The solvent was removed in vacuo and the residue dissolved in dichloromethane (10 cm3), filtered, the solution warmed to 35 8C and hexane added until the product just started to precipitate.On standing a red crystalline solid was formed (0.65 g, 83%) (Found: C, 25.1; H, 3.95; N, 3.58. C16H30B10I2N2- PdS2 requires C, 24.6; H, 3.86; N, 3.58%), nmax(BH) 2566s cm21. 11B-{1H} NMR (CH2Cl2): d 219.82, 225.05, 227.64 and 230.17. 1H NMR (CD3CN): d 8.54 and 7.84 (2 H, d, J = 8; 2 H, d, J = 8 Hz, C5H4N), 4.24 (3 H, s, C5H4NCH3) and 2.63 (3 H, d, CH3C5H4N). Mass spectrum [m/z, I(%)]: positive-ion FAB, 890 (42) {[4-MeC5H4NMe]3[Pd(cbdt)I2]}1; 783 (100), {H[4- MeC5H4NMe]2[Pd(cbdt)I2]}1, negative-ion FAB, 674 (6), {[4-MeC5H4NMe][Pd(cbdt)I2]}2; 566 (10), {H[Pd(cbdt)I2]}2; 439 (55), {H[Pd(cbdt)I]}2.Lm 277 W cm2 mol21. [NEt3H][Mo(Á5-C5H5)(NO)(cbdt)I] 2. Triethylamine (0.061 g, 0.60 mmol) was added dropwise to a solution of H2cbdt (0.063 g, 0.30 mmol) in toluene (15 cm3) with stirring. A solution of [{Mo(h5-C5H5)(NO)I2}2] (0.164 g, 0.30 mmol) in toluene (10 cm3) was then added dropwise and the mixture heated under reflux for 16 h, the solvent evaporated in vacuo and the residue redissolved in dichloromethane (10 cm3).The solution was filtered, warmed to 35 8C and hexane added until the product just started to precipitate. On standing dark red crystals of the product were deposited (0.113 g, 60%) (Found: C, 25.3; H, 5.00; N, 4.35. C13H31B10IMoN2OS2 requires C, 24.9; H, 4.99; N, 4.47%). 1H NMR (CDCl3): d 5.94 (5 H, s, h-C5H5), 3.22 (6 H, q, J = 6, HNCH2CH3) and 2.45 (9 H, t, J = 6 Hz, HNCH2CH3).nmax(BH) 2568s, nmax(NO) 1639s cm21. Mass spectrum [m/z, I(%)]: positive-ion FAB, 729 (10), {H[Et3NH][Mo(h5-C5H5)- (NO)(cbdt)I]}1; negative-ion FAB, 524 (100), [Mo(h5-C5H5)- (NO)(cbdt)I]2; 494 (65), [Mo(h5-C5H5)(cbdt)I]2. Lm 143 W cm2 mol21. [NBu4][ReO(cbdt)2] 3. The salt [NBu4][ReOCl4] (0.07 g, 0.12 mmol) was dissolved in thf (10 cm3) and the solution added dropwise to a solution of H2cbdt (0.10 g, 0.48 mmol) in thf (15 cm3).The mixture was stirred vigorously for 30 min at room temperature during which time it changed from yellow to green. The mixture was then heated under reflux for 2 h. During this time it changed from green to bright yellow. The solvent was evaporated in vacuo and the residue recrystallised twice from dichloromethane–hexane to yield bright yellow crystals (0.087 g, 85%) (Found: C, 28.1; H, 6.75; N, 1.56.C20H56B20NOReS4 requires C, 28.0; H, 6.58; N, 1.56%); nmax(BH) 2583s, 2614, nmax (Re]] O) 980s cm21. 11B-{1H) NMR (CH2Cl2): d 219.86 (1B), 225.78 (4B), 226.99 (3B) and 229.07 (1B). Mass spectrum [m/z, I(%)]: positive-ion FAB 242 (100), [Bu4N]1; negative-ion FAB, 615 (100), [ReO(cbdt)2]2.Lm 160 W cm2 mol21. [4-MeC5H4NMe]2[{Mo(O)(Ï-O)(cbdt)}2] 4. A solution of H2cbdt (0.21 g, 1.00 mmol) in thf (20 cm3) was added dropwise to a suspension of MoCl5 (0.082 g, 0.30 mmol) in thf (15 cm3). The mixture was stirred vigorously for 30 min at room temperature then heated under reflux for 4 h to give a yellow solution.J. Chem. Soc., Dalton Trans., 1998, Pages 2163–2168 2167 Table 3 Crystallographic and experimental data for compounds 1–4 Formula M Crystal system Space group a/Å b/Å c/Å b/8 U/Å3 Z Dc/g cm23 m(Mo-Ka)/mm21 Crystal size/mm q Range/8 Reflections measured (unique) Rint Variables Dr/e Å23 D/smax R, wR2 a w(a,b) b Observed reflections [I > 2s(I)] R[I > 2s(I)] 1 C2H10B10I2PdS2?2C7H10N 782.9 Orthorhomic Pbam 18.706(5) 20.764(5) 7.505(2) — 2915(1) 4 1.784 2.908 0.4 × 0.35 × 0.25 1.5–25.2 13 515 (2531) 0.1040 175 0.49, 20.79 0.001 0.0580, 0.1148 0.050, 0.82 2222 0.0415 2 C7H15B10IMoNOS2?C6H16N 626.5 Orthorhombic P212121 14.222(3) 16.514(3) 10.959(3) — 2574(1) 4 1.617 1.881 0.2 × 0.15 × 0.15 1.9–25.2 15 230 (4464) 0.0448 271 0.54, 20.50 0.002 0.0533, 0.0869 0.015, 7.40 4300 0.0494 3 C4H20B20OReS4?C16H36N 857.3 Monoclinic P21/n 10.989(2) 24.156(5) 16.069(4) 105.99(2) 4100(2) 4 1.389 3.188 0.2 × 0.2 × 0.15 1.6–25.2 15 875 (6259) 0.0430 424 0.47, 20.90 0.001 0.0623, 0.1058 0.024, 13.78 5649 0.0518 4 C4H20B20Mo2O4S4?2C7H10N 884.8 Orthorhombic P21212 12.226(4) 22.511(5) 7.215(4) — 1986(1) 2 1.480 0.872 0.35 × 0.3 × 0.3 3.3–25.3 4748 (2887) 0.0280 226 0.40, 20.64 0.001 0.0355, 0.0869 0.033, 3.18 2843 0.0345 a wR2 = [Sw(Fo 2 2 Fc 2)2/Sw(Fo 2)2]� �� .b w = 1/[s2(Fo 2) 1 (aP)2 1 bP] where P = (Fo 2 1 2Fc 2)/3. This was allowed to cool to room temperature before adding [4- MeC5H4NMe]I (0.24 g, 1.00 mmol) over a 10 min period and stirring the mixture for a further hour. The solvent was removed in vacuo and the residue dissolved in dichloromethane (10 cm3), filtered, the solution was warmed to 35 8C and hexane added until the product just started to precipitate.On standing a yellow crystalline solid deposited (0.144 g, 54%) (Found: C, 24.4; H, 4.42; N, 3.06. C9H20B10MoNO2S2 requires C, 24.4; H, 4.56; N, 3.17%); nmax(BH) 2575s, nmax(Mo]] O) 964s cm21. 11B-{1H} NMR (CH2Cl2): d 216.36, 223.38, 225.16 and 229.04. 1H NMR [(CD3)2CO]: d 8.85 and 8.01 (2 H, d, J = 3.9; 2 H, d, J = 3.9 Hz, C5H4N), 4.49 (3 H, s, C5H4NCH3) and 2.86 (3 H, d, CH3C5H4N).Mass spectrum [m/z, I(%)]: positive-ion FAB, 994 (17), {[4-MeC5H4NMe]3[{MoO(m-O)(cbdt)}2]}1; 850 (7), {[4-MeC5H4NMe]3[MoO(cbdt)2]}1; negative-ion FAB, 777 (32), {[4-MeC5H4NMe][{MoO(m-O)(cbdt)}2]}2, 669 (100), {H[{MoO(m-O)(cbdt)}2]}2; 525 (37), {H[MoO(cbdt)2]}2. Lm 260 W cm2 mol21.Crystallography Data for all four structures 1–4 were collected on a Rigaku Raxis II imaging plate area-detector diVractometer at 293(2) K using graphite-monochromated Mo-Ka radiation. The structures were determined by direct methods 27 and refined28 on F2 by full-matrix least squares with anisotropic displacement parameters for the non-hydrogen atoms. Hydrogen atoms were placed in calculated positions with isotropic displacement parameters.Specific absorption corrections were not applied since the crystals used were nearly equidimensional (see Table 3) and averaging of the symmetry-equivalent reflections largely compensates for any absorption eVects. Figures depicting the structures were prepared using ORTEP,29 the thermal ellipsoids being drawn at the 30% probability level.In compound 1 of the two dimethylpyridinium counter ions, one is disordered, so that the NMe and CMe moieties could not be distinguished; in the refinement the relevant ring atoms were treated as (��� N 1 ��� C). In 4 the dimethylpyridinium cation is similarly disordered, and was treated in the same way. The atoms of the triethylammonium counter ion in 2 exhibit high anisotropic displacement parameters and may also be aVected by disorder.CCDC reference number 186/1010. See http://www.rsc.org/suppdata/dt/1998/2163/ for crystallographic files in .cif format. Acknowledgements We are grateful to EPSRC for supporting this work through a studentship (J. D. McK.) and through research grant GR/ G44390. We also thank the EPSRC and the University of Birmingham for funds to purchase the R-Axis II diVractometer, and the British Council for a Sino-British Friendship Scholarship (to H. C.).References 1 U. T. Mueller-WesterhoV and B. Vance, in Comprehensive Coordination Chemistry, eds. R. D. Gillard, J. A. McCleverty and G. Wilkinson, Pergamon, Oxford, 1987, vol. 2, ch. 16.5, pp. 595–631. 2 J. A. McCleverty, Prog. Inorg.Chem., 1968, 10, 49; G. N. Schrauzer, Acc. Chem. Res., 1969, 2, 72. 3 T. Jørgensen, T. K. Hansen and J. Becher, Chem. Soc. Rev., 1994, 23, 41; T. K. Hansen and J. Becher, Adv. Mater., 1993, 5, 288; S. R. Marder, in Inorganic Materials, eds. D. W. Bruce and D. O’Hare, Wiley, New York, 1992, ch. 3; A. Kreif, Tetrahedron, 1986, 42, 1209; A. F. Garito and A. J. Heeger, Acc.Chem. Res., 1974, 7, 232. 4 (a) P. Cassoux and L. 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