DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2155–2161 2155 New SchiV bases derived from trans-pyrazolylcyclohexanol: synthesis, co-ordination chemistry and structural features‡ Michael Barz, Monika U. Rauch and Werner R. Thiel*,† Anorganisch-chemisches Institut der Technischen Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany Transformation of the OH function of trans-2-(pyrazol-1-yl)cyclohexan-1-ol into an amino group was achieved by various methods with inversion of the reaction centre and provided access to new polydentate Schiff bases bearing phenol, pyridine and furan donors.The co-ordination chemistry of these bases was investigated for PdII, ReI and ReV. It was shown by means of NMR spectroscopy that the special stereochemical situation of the 1,2-cisconfigurated cyclohexane backbone allows a flexible adaptation to different co-ordination conditions. On the other hand, the rigid asymmetrically substituted cyclohexane ring is responsible for an asymmetric arrangement of the donor fragments at the metal centre, which is required for applications of these compounds in enantioselective catalysis.During the last 25 years the development of new chiral compounds has led to rapid progress in the area of enantioselective catalysis. Especially the introduction of C2-symmetric phosphanes gave rise to a multitude of new catalytic and enantioselective reactions, like hydrogenations, isomerisations or hydroformylations.2 Besides these new chiral phosphanes, chiral nitrogen-containing compounds play an increasingly important role in enantioselective catalysis.An outstanding example is the enantioselective cis hydroxylation of olefins, catalysed by osmium complexes in the presence of cinchona alkaloids.3 Additionally, compounds bearing nitrogen atoms as donor centres have been applied for enantioselective hydrogenations (Co, Rh), hydrosilylations (Rh), the synthesis of chiral cyclopropanes (Co, Cu, Rh), stereoselective Diels–Alder reactions (Al, Mg, Fe), alkylation of ketones with dialkylzinc compounds, coupling reactions [MgR(X) and Pd], oxidations (Mo, V, Mn) and olefin metathesis (Mo).4 In our group the ring-opening reaction of prochiral, cyclic epoxides with various nucleophiles is used for the synthesis of new cycloalkanol ligands bearing two stereocentres at a rigid cyclic backbone. Pyrazoles and imidazoles, for example, give exclusively the corresponding trans-substituted 2-(diazol-1-yl)- cycloalkan-1-ols.We previously demonstrated for the corresponding phosphanes1 that the cyclic backbone forces the (bulky) substituents at the donor moieties into a pseudo-C2- symmetrical arrangement around the metal centre, as is known for complexes of C2-symmetric diphosphanes.2c Obviously, racemic mixtures are obtained in the ring-opening reaction, which have to be separated. We therefore recently worked out a procedure for the separation of the enantiomers of 2-(pyrazol- 1-yl)cyclohexan-1-ol I by an enzymatic kinetic resolution,5 which gives access to a multitude of enantiomerically pure 1,3- diaminoalcohols.Besides the co-ordination chemistry of these aminoalcohols, which turned out to be ideal ligands for the complexation of first-row transition metals,6 we are interested in these compounds as starting materials for the synthesis of other chiral chelates like Schiff bases, diamines or phosphorus donors.In all these cases the molecular geometry of the resulting transition-metal complexes depends on the absolute configurations of the stereocentres and on the particular conformation † E-Mail: thiel@arthur.anorg.chemie.tu-muenchen.de ‡ Cycloalkanes as ligand backbones. Part 3.1 of the cycloalkane ring. Additionally, if several donor centres can compete for a co-ordination site, fluxional behaviour may be observed. In the present paper we report the synthesis of Schiff bases derived from racemic I and their co-ordination chemistry with high- and low-valent transition-metal fragments with special regard to the conformational behaviour of the cyclohexane ring system.Results and Discussion Ligands For the synthesis of new Schiff bases, compounds known to be excellent donors for transition and main-group elements,7 the OH functionality of I had to be transformed into an amino group. Since the second stereocentre at the cyclohexane ring will not be affected during the synthetic procedure, the stereoselectivity of the appropriate transformations can easily be determined by NMR spectroscopy.The conversion of the alcohol I into the corresponding amine IV was realised by two different routes (Scheme 1): via a classical nucleophilic substitution reaction or a Mitsunobu amination. The tosylate II, accessible in good yields by reaction of I with toluene-psulfonyl chloride,8 is converted in a SN2 type reaction with sodium azide in dmf solution at 160 8C into the cis- Scheme 1 (i) p-MeC6H4SO2Cl (RCl), pyridine, room temperature (r.t.), 48 h; (ii) NaN3, dimethylformamide (dmf), 160 8C, 3 h; (iii) LiAlH4, diethyl ether, reflux, 3 h; (iv) (a) EtO2CN]] NCO2Et, PPh3, tetrahydrofuran (thf), 24 h, r.t.; (b) N2H4, methanol, HCl, reflux, 14 h OH N N OR N N N3 N N NH2 N N I IV ( i ) ( iv ) ( iii ) II III ( ii )2156 J.Chem. Soc., Dalton Trans., 1997, Pages 2155–2161 configurated azide III.9 Irrespective of the high reaction temperatures, III is formed in more than 99% diastereomeric excess (inversion at the reaction centre).It can be used as a chelate for complexation of transition metals, and its stereochemistry (1,2- cis substitution) was demonstrated by a X-ray analysis of the corresponding CuCl2 complex.6 Reduction of III with LiAlH4 in thf solution leads to the desired amine IV.10 In an alternative reaction sequence, the alcohol I is converted into the amine IV by the so-called Mitsunobu reaction, which also proceeds with more than 99% diastereomeric excess under inversion at the reaction centre.11 Starting from diastereomerically pure compound IV, the Schiff bases Va–Vd are obtained in almost quantitative yields (Scheme 2).12 In the case of free Va and Vb, 1H NMR spectroscopy revealed an interaction between the phenolic hydrogen atoms and the imine nitrogen as the resonances of these protons are shifted to lower field (d 13.57 and 14.69).As previously shown by means of NMR spectroscopy and X-ray analysis,5 the 1,2-trans-disubstituted cyclohexane ring of I occupies the energetically favourable chair conformation with both the pyrazolyl and the hydroxy substituent orientated in equatorial positions, minimising axial–axial interactions. The same situation is found for the corresponding tosylate II.During the formation of the amine IV, described above, inversion at the reaction centre takes place. This results in a 1,2-cisconfigurated cyclohexane ring, a common structural feature for III, IV, the imines V and the corresponding transition-metal complexes discussed later on.These compounds can now exist as a mixture of two conformers, which should be in equilibrium in solution. In these conformers the pyrazolyl group either occupies an equatorial or an axial position (opposite orientation of the second substituent X, Scheme 3). Proton NMR spectroscopy allows one to distinguish between these conformers, as in each case only one of the protons in 1 or 2 position will show one strong trans coupling of about 12 Hz, while the other proton–proton couplings are weak (ca. 2–3 Hz) due to dihedral angles (H]C]C]H) of about 608. Molecular mechanics (MM) calculations, using the MM2 force field implemented in CHEM3D,13 showed that the equatorial orientation of the pyrazolyl moiety should be favoured by about 6–8 kJ mol21, depending on the second substituent, and a barrier of about 30 kJ mol21 should hinder the interconversion of the conformers.While the latter value corresponds to reported Scheme 2 NH2 N N N N N R¢ OH OH Cl Cl O N + IV R¢ = d b a c R¢CHO V Scheme 3 The equilibrium between the two conformers of compounds III, IV and Va, Vb H N H H X H H H X H H H H N N N data,14 the calculated energy differences between the conformers should be underestimated by some kJ mol21. In the case of the pure organic compounds III–V, we only observed one conformer (>98%), bearing an equatorial pyrazolyl group, by NMR spectroscopy. Depending on the metal fragment, the imines V can coordinate in a mono- (excluded for reasons of complex stability), bi- or tri-dentate mode.Additionally, the geometry of the cyclohexane backbone of the ligands will be determined by the specific co-ordination pattern, as the barriers to ring interconversion and the energy differences between the conformers described above are low. Metal complexes Substitution of the labile benzonitrile ligands of [PdCl2- (PhCN)2] by compound Va in the presence of NEt3 results in tridentate co-ordination of the ligand.While one chloro ligand is displaced by the deprotonated phenol fragment, the second chloride occupies the fourth co-ordination site of the squareplanar palladium centre (complex 1a, Scheme 4). If palladium acetate is used as the starting material, the corresponding acetato complex 1b is obtained even in the absence of a base by simple elimination of acetic acid.Proton NMR spectroscopy reveals the stereochemistry of the cyclohexane ring in 1a, 1b: in both cases, a large coupling constant is observed for the ring proton geminal to the imine nitrogen, indicating an equatorial orientation of the imine fragment and an axial orientation of the pyrazole moiety, which is opposite to the geometry of the free imine. There is no special influence of the chloro or the acetato ligand on the geometry of the ligand backbone.One single C]] O absorption at 1716 cm21 in the infrared spectrum of 1b is characteristic for a h1-co-ordinated acetato ligand. By slowly cooling a saturated acetonitrile solution of the palladium complex 1a orange plates are obtained. The complex crystallizes in the monoclinic, centric space group P21/c with one additional solvent molecule per formula unit, which does not co-ordinate to the palladium centre. Fig. 1 presents the molecular structure, characteristic bond lengths and angles are given in Table 1, and further crystallographic and experimental details in Table 2.The distances between the square-planar palladium centre and the four ligands are comparable to those of analogous compounds.17 Five different ring systems are responsible for the molecular structure of 1a. Three (pyrazole, cyclohexane, phenol) originate from the chelate Va, while the two new rings are formed by co-ordination of the metal atom by three donor centres of the chelate.The first three ring systems show normal conformations after co-ordination. While the pyrazole and the phenol ring are almost planar, the cyclohexane ring is in the energetically favourable chair conformation. In that conformation the pyrazole moiety is orientated in an axial, and the nitrogen atom of the imine in an equatorial, Scheme 4 (i) [PdCl2(PhCN)2], NEt3; (ii) Pd(O2CMe)2 O N Cl Pd N N O N O Pd O Me N N 1a Va 1b ( i ) ( ii ) – NEt3HCl – MeCO2HJ. Chem.Soc., Dalton Trans., 1997, Pages 2155–2161 2157 position as observed in solution. The pyrazole ring is twisted about 218 around the axis Pd]N(2), which leads to a remarkable asymmetry in the co-ordination sphere of palladium. Owing to the cis arrangement of the substituents at the cyclohexane ring, the six-membered ring formed by co-ordination of N(2) and N(3) to palladium is found in a skewed-boat conformation. The least-squares planes of the cyclohexane ring and the pyrazole are orientated almost perpendicular (ca. 838) to each other. Obviously, cis substitution of cyclohexane ring systems is an ideal tool for generation of asymmetric ligand spheres at catalytically active metal centres. We are now looking for derivatives of our compounds, bearing bulky substituents at C(1) (pyrazole) or C(15) (phenol), which should lead to a further increase in steric demand at the metal atom. Fig. 1 A PLATON plot15 of complex 1a (the additional acetonitrile molecule is omitted).Thermal ellipsoids are at the 50% probability level Table 1 Selected bond lengths (Å) and angles (8) for complex 1a Pd]Cl Pd]O Pd]N(2) Pd]N(3) 2.3181(7) 1.977(2) 2.010(2) 1.988(2) O]C(16) N(3)]C(9) N(3)]C(10) 1.313(3) 1.483(3) 1.298(3) Cl]Pd]O Cl]Pd]N(2) Cl]Pd]N(3) Pd]N(3)]C(9) Pd]O]C(16) 84.32(5) 90.54(6) 177.16(6) 121.9(2) 125.4(2) O]Pd]N(3) N(2)]Pd]N(3) O]Pd]N(2) Pd]N(3)]C(10) C(9)]N(3)]C(10) 93.24(8) 91.92(8) 174.83(8) 123.4(2) 114.7(2) Table 2 Crystallographic data for complex 1a Formula Mr Crystal system Crystal dimensions/mm Space group a/Å b/Å c/Å b/8 U/Å3 Dc/g cm23 ZF (000) m/cm21 q Range/8 T/8C Absorption correction Data measured Unique data Reflections used [I > 2s(I)] No.parameters Residual electron density/e Å23 Ra wR2b Goodness of fit C16H18ClN3OPd?CH3CN 451.224 Monoclinic 0.40 × 0.16 × 0.08 P21/c (no. 14) 9.120(1) 19.626(2) 10.903(1) 108.19(1) 1854.0(3) 1.617 4 912 11.6 2.2–25.06 280 Ref. 16(a) 14 240 3232 2949 310 10.36, 20.63 0.0282 0.0776 1.09 a S Fo| 2 |Fc /S|Fo|.b wR2 = [Sw(Fo 2 2 Fc 2)2/SwFo 2]� �� , w = 1/[s2Fo 2 1 (0.0555P)2 1 0.68P] where P = [max(Fo 2, 0) 1 2Fc 2]/3.16b Reaction of the pyridine-substituted compound Vc with [PdCl2(PhCN)2] leads, by displacement of one chloro ligand, to the square-planar complex 2a (Scheme 5). The cationic nature of this species, bearing a tridentate ligand, is revealed by conductivity measurements (Lm = 62 S cm2 mol21, 25 8C, 0.001 mol dm23 in dmf).Additionally, mass spectrometric investigations [fast atom bombardment (FAB)] only showed the isotope pattern of the cationic species PdL(Cl)1. In the 1H NMR spectrum all resonances are shifted to lower field, with respect to 1a and Vc, which is in accordance with the cationic nature of the palladium complex. At room temperature broad signals are observed, indicating a dynamic process in the ligand sphere. For a detailed investigation of this process we carried out NMR experiments in the temperature range between 120 and 280 8C. At low temperatures (<240 8C) the resonances of two cationic palladium complexes, observed in a 1 : 1 ratio, can be identified.Two-dimensional NMR experiments allowed a complete assignment of the signals and, in combination with data from experiments at various temperatures, the calculation of the energy of activation for this dynamic process (DG‡ = 57 ± 2 kJ mol21). Since NMR spectroscopy clearly demonstrates a tridentate co-ordination for both species, the only explanation possible for the nature of this process is an inversion of the cyclohexane ring, as shown in Scheme 6.Replacing the pyridine fragment of compound Vc by the weaker donating furan group of Vd generates a new system, which could co-ordinate either in a bidentate mode or as a tridentate chelate with a labile donor site.18 The composition of the corresponding dichloropalladium complex 2b, obtained by reaction of Vd with [PdCl2(PhCN)2], is verified by elemental analysis; NMR spectroscopic investigations were impossible as the compound is completely insoluble in most organic solvents, with the exception of hot dimethylformamide and hot dimethyl sulfoxide, wherein decomposition occurs. Refluxing [ReBr(CO)5], synthesized from [Re2(CO)10] and bromine,19 with 1 equivalent of compound Va in thf solution, yields the octahedral rhenium(I) complex 3.Even in its depro- Scheme 5 2a + Cl – [PdCl2(PhCN)2] + Vc N N N Pd N Cl Scheme 6 Fluxional process equilibrating the two isomers of the cation of complex 2a N N N CO Re CO CO Br H O H N N N Cl Pd Cl H O 2b 32158 J.Chem. Soc., Dalton Trans., 1997, Pages 2155–2161 tonated form Va is not able to replace the bromo ligand at the low-valent rhenium centre. From NMR and IR investigations it is clear that the carbonyl ligands are co-ordinated facially, as is known for other complexes of the type [ReBr(CO)3(L]L)] (L]L = bidentate chelate ligand).20 If the donor sites of the chelate ligand are inequivalent, as they are in our case, the metal becomes a centre of chirality.In combination with the racemic ligand Va, the introduction of a new chiral centre should result in the formation of two diastereomeric speciesh are not observed in the NMR spectra of 3. At the moment we do not know why only one of the diastereomers is formed selectively. Since the resonance of the OH proton is observed fairly deshielded at d 10.87, a weak hydrogen interaction of the OH group and the bromo ligand may be the reason for this behaviour.If this is true, the imine fragment must be orientated almost perpendicular to the phenol group. This would minimise p interactions between these fragments and lead to a low-field shift of the resonance of the imine proton, which is indeed observed at d 9.80. For steric reasons, the imine group should be configurated, as shown in Scheme 6, to prevent interaction of the bulky phenol group with the equatorial carbonyl ligand in the cis position, a fact which also may be responsible for the deshielding of the imine proton.Switching to the more Lewis-acidic rhenium(V) precursor [NEt4][ReOCl4] results in a tridentate co-ordination mode of the chelates Vc, Vb with oxygen as well as both nitrogen atoms binding to rhenium. The octahedral complexes 4a, 4b are obtained in high yields. For steric reasons, the three donor centres of the ligand co-ordinate meridionally.This mode allows the formation of three isomers, one (C) with the oxo ligand trans to the imine nitrogen. In the other isomers one chloro ligand is trans to the imine nitrogen and the oxo ligand is in the cis position, which results in the generation of a new chiral centre, the metal atom. As we use racemic mixtures of Va, Vb these isomers are diastereomers (A and B). All three isomers can be observed by NMR spectroscopy.While the resonances of the diastereomeric complexes A and B can be assigned without problems (see Experimental section), the minor (ca. 10% of intensity) product C can be clearly identified by a characteristic resonance for the imine proton at about d 9.27, indicating the strong trans influence of the oxo ligand. In contrast to the square-planar palladium(II) complexes 1a, 1b, the geometry of the cyclohexane backbone in 4a, 4b switches back to that of the free Schiff bases: pyrazole in equatorial, imine in axial orientation. As described in this paper, the 1,2-cis-substituted cycloalkane ring system allows detailed investigations into stereochemical N N N Re O X X Cl Cl O N N N Re O X X Cl O Cl N N N Re O X X O Cl Cl Isomer A and B Isomer C 4a X = H 4b X = Cl features of the ligands and transition-metal complexes.Its conformational flexibility, in combination with the rigidity of the six-membered ring, can readily be compared with the structural characteristics of e.g.C2-symmetric phosphanes like the well known 2,29-bis(diphenylphosphino)-1,19-binaphthyl system.2c We therefore are now looking out for catalytic applications of the enantiomerically pure Schiff bases. Experimental The compounds rac-trans-2-(pyrazol-1-yl)cyclohexan-1-ol I,5 [PdCl2(PhCN)2],21 [ReBr(CO)5] 19 and [NEt4][ReOCl4] 22 were synthesized according to published procedures. All other starting materials were from Aldrich and used without further puri- fication.The NMR (Bruker DPX 400), infrared (Perkin-Elmer 1600 Series FTIR) and mass spectra (Hewlett-Packard HP 5890 gas chromatograph and mass-selective detector HP 5970, Finnigan MAT 90) and all elemental analyses were carried out at the Anorganisch-chemisches Institut der TU München. The assignments of the NMR spectra of the 2-(pyrazol-1-yl)- cyclohexyl moiety were made according to Fig. 1, those of the imine residues according to Scheme 7. Syntheses rac-trans-2-(Pyrazol-1-yl)cyclohexyl toluene-p-sulfonate II.Compound I (20.0 g, 120 mmol) and toluene-p-sulfonyl chloride (22.9 g, 120 mmol) were dissolved in CHCl3 (150 cm3) at 0 8C. Pyridine (40 cm3) was added dropwise and the reaction mixture stirred for 2 d at room temperature. The solution was extracted three times with water (30 cm3), the organic layer separated, dried over MgSO4 and the solvent removed in vacuo. After washing the colourless residue with diethyl ether (50 cm3) and pentane it was recrystallised from ethyl acetate.Colourless crystals, m.p. 154–156 8C, yield 17.1 g (45%) (Found: C, 59.95; H, 6.2; N, 8.75; S, 10.6. C16H20N2O3S requires C, 60.0; H, 6.3; N, 8.75; S, 10.0%); n& max/cm21 (KBr) 1192s, 1177vs (SO2); dH(250.13 MHz, 25 8C, CDCl3) 7.35 [d, 3J(HoHm) 8.0, Ho], 7.23 [d, 3J(H1H2) 1.5, H1], 7.15 [d, 3J(H2H3) 2.5, H3], 7.12 (d, Hm), 5.99 (dd, H2), 4.69 [dt, 3J(H8 eqH9) 5.1, 3J(H4H9) 10.2, 3J(H8 axH9) 10.2, H9], 3.99 [dt, 3J(H4H5 eq) 7.0, 3J(H4H5 ax) 10.2 Hz, H4], 2.36 (3 H, s, CH3) and 2.44–1.34 (8 H, 5m, CH2); dC(100.62 MHz, 25 8C, CDCl3) 144.0 (ipso-C), 139.2 (C1), 133.3 (Cp), 129.5 (Co), 129.2 (C3), 127.5 (Cm), 104.7 (C2), 82.5 (C9), 63.7 (C4), 32.7 (C8), 31.8 (C5), 24.3 (C6), 23.8 (C7) and 21.5 (CH3); m/z (electron impact, EI) 320 (1, M1), 256 (6, M 2 SO2), 228 (6, M 2 C7H8), 171 (53, C7H7O3S), 165 (27, M 2 C7H7O2S), 155 (10, C7H8O2S), 148 (74, M 2 C7H8O3S), 121 (8, C3H3N2]C4H6), 120 (14, C3H3N2]C4H5), 119 (12, C3H3N2]C4H4), 107 (30, C3H3N2]C3H4), 91 (63, C7H7), 81 (37, C3H3N2]CH2), 77 (9, C6H5), 69 (100, C3H5N2), 55 (8, C4H7), 51 (6, C4H3) and 41 (36%, C3H5).rac-cis-1-(2-Azidocyclohexyl)pyrazole III. A mixture of compound II (4.00 g, 12.5 mmol) and sodium azide (6.50 g, 100 mmol) in dry dmf (50 cm3) was heated to reflux for 3 h. After completion of the reaction, water (50 cm3) was added and the Scheme 7 N OH N Cl Cl OH N N 10 14 15 11 12 13 N 11 13 16 12 14 11 O 16 10 15 12 10 14 15 13 11 12 10 14 13J. Chem.Soc., Dalton Trans., 1997, Pages 2155–2161 2159 resulting orange solution extracted three times with diethyl ether (30 cm3). The combined organic layers were extracted three times with water (30 cm3), dried over MgSO4 and the solvent removed in vacuo. The product was obtained as a pale yellow oil, which solidifies at 234 8C. Yield 1.80 g (75%) (Found: C, 56.4; H, 6.8; N, 36.75. C9H13N5 requires C, 56.55; H, 6.85; N, 36.6%); n& max/cm21 (KBr) 2110vs (N3); dH(400.13 MHz, 25 8C, CDCl3) 7.51 [d, 3J(H1H2) 1.5, H1], 7.45 [d, 3J(H2H3) 2.5, H3], 6.25 (dd, H2), 4.32 [dt, 3J(H4H9) 3.4, 3J(H4H5 eq) 3.4, 3J(H4H5 ax) 12.6, H4], 4.20 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3 Hz, H9] and 2.12–1.37 (8 H, 6m, CH2); dC(100.62 MHz, 25 8C, CDCl3) 139.2 (C1), 127.0 (C3), 105.2 (C2), 62.5, 62.2 (C4, C9), 29.3 (C5), 25.5, 24.7 (C8, C6) and 19.5 (C7); m/z (EI) 191 (1, M1), 163 (3, M 2 N2), 149 (1, M 2 N3), 121 (3, C3H3N2]C4H6), 120 (4, C3H3N2]C4H5), 119 (6, C3H3N2]C4H4), 107 (4, C3H3N2] C3H4), 95 (8, C3H3N2]C2H4), 81 (16, C3H3N2]CH2), 69 (24, C3H5N2), 68 (15, C3H4N2), 67 (10, C3H3N2) and 41 (26%, C3H5).rac-cis-1-(2-Aminocyclohexyl)pyrazole IV. Method A, reduction of III. A solution of compound III (6.9 g, 36 mmol) in diethyl ether (50 cm3) was added dropwise to a suspension of LiAlH4 (2.1 g, 55 mmol) in diethyl ether (250 cm3) and the resulting mixture refluxed for 3 h. The reaction was quenched by the addition of water (1 cm3), the resulting precipitate was filtered off, the filtrate dried over Na2SO4 and the solvent removed in vacuo.The product was obtained as a colourless oil. Yield 3.2 g (53%). Method B, from compound I. A solution of compound I (6.7 g, 40 mmol) in dry thf (50 cm3) and EtO2CN2CO2Et (6.3 cm3, 40 mmol) were added dropwise and simultaneously to a solution of phthalimide (5.9 g, 40 mmol) and PPh3 (10.5 g, 40 mmol) in dry thf (200 cm3) under a nitrogen atmosphere.The reaction mixture was stirred at 20 8C for 1 d and the solvent removed in vacuo. After dissolution of the residue in methanol (200 cm3), hydrazine hydrate (80%, 4.9 cm3, 80 mmol) was added and the mixture refluxed for 7 h. Concentrated hydrochloric acid (6 cm3) was added and the mixture refluxed for 7 h. A colourless precipitate formed, which was filtered off and rinsed with dilute hydrochloric acid. The combined aqueous solutions were extracted with CHCl3 (7 × 30 cm3) and Et2O (4 × 30 cm3) and then treated with saturated NaOH until pH > 13.A brownish oil separated, which was extracted with diethyl ether (4 × 30 cm3). The combined organic layers were washed with brine (4 × 30 cm3) and dried over MgSO4. The solvent was removed in vacuo to yield a yellow oil. Kugelrohr distillation gave the pure amine IV as a colourless oil. Yield 3.70 g (56%). n& max/cm21 (CHCl3) 3372m and 3300m (NH2); dH(400.13 MHz, 25 8C, CDCl3) 7.43 [d, 3J(H1H2) 1.5, H1], 7.38 [d, 3J(H2H3) 2.0, H3], 6.15 (dd, H2), 4.17 [ddd, 3J(H4H9) 3.5, 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 12.0, H4], 3.41 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3 Hz, H9] and 2.15–1.24 (10 H, 6m, CH2, NH2); dC(100.62 MHz, 25 8C, CDCl3) 138.6 (C1), 127.2 (C3), 104.4 (C2), 63.4 (C4), 50.1 (C9), 31.5 (C5), 24.7, 24.6 (C8, C6) and 18.9 (C7); m/z (EI) 165 (1, M1), 81 (34, C3H3N2]CH2), 69 (61, C3H5N2), 55 (9, C4H7), 41 (35, C3H5), 30 (33, CH2NH2), 28 (100, N2) and 27 (28%, C2H3). Schiff bases V (general procedure).An equimolar solution of compound IV and of the appropriate aromatic aldehyde in ethanol (200 cm3) was refluxed for 2 h. The solvent was removed and pentane added to the resulting yellow oil. With the exception of Vc, the Schiff bases crystallised after 24 h at 228 8C. Yields 70–90%. rac-cis-2-[2-(Pyrazol-1-yl)cyclohexyliminomethyl]phenol Va. (Found: C, 70.95; H, 7.0; N, 15.55; O, 6.45. C16H19N3O requires C, 71.35; H, 7.1; N, 15.6; O, 5.95%); n& max/cm21 (KBr) 3428vs (OH), 1626vs (C]] N); dH(400.13 MHz, 25 8C, CDCl3) 13.57 (s, OH), 7.66 (s, H10), 7.45 [d, 3J(H1H2) 1.8, H1], 7.26 [ddd, 3J(H14H15) 8.2, 3J(H13H14) 7.4, 4J(H12H14) 1.7, H14], 7.19 [d, 3J(H2H3) 2.4, H3], 7.00 [dd, 3J(H12H13) 7.6, H12], 6.91 [dd, 4J(H13H15) 0.5, H15], 6.78 (dt, H13), 6.03 (dd, H2), 4.54 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 12.9, H4], 3.95 [br, 3J(H8 axH9) = 3J(H8 eqH9) 2–3 Hz, H9] and 2.25–1.50 (8 H, 6m, CH2); dC(100.25 MHz, 25 8C, CDCl3) 165.4 (C10), 161.1 (C16), 139.0 (C1), 132.4 (C12), 131.5 (C14), 127.0 (C3), 118.7, 118.6 (C11, C15), 116.8 (C13), 104.7 (C2), 68.4 (C4), 63.8 (C9), 32.1 (C5), 26.1, 25.5 (C8, C6) and 20.2 (C7); m/z (EI) 269 (3, M1), 201 (3, M 2 C3H4N2), 120 (9, C7H6NO), 81 (11, C3H3N2]CH2), 69 (100, C3H5N2) and 41 (19%, C3H5).rac-2,4-Dichloro-6-[cis-(2-pyrazol-1-yl)cyclohexyliminomethyl] phenol Vb. (Found: C, 56.25; H, 5.15; Cl, 20.8; N, 12.45. C16H17Cl2N3O requires C, 56.8; H, 5.05; Cl, 20.95; N, 12.4%); n& max/cm21 (KBr) 3406 (br) (OH), 1628vs (C]] N); dH(400.13 MHz, 25 8C, CDCl3) 14.69 (s, OH), 7.48 (s, H10), 7.47 [d, 4J(H12H14) 2.5, H12], 7.35 [d, 3J(H1H2) 2.5, H1], 7.19 [d, 3J(H2H3) 2.0, H3], 6.87 (d, H14), 6.06 (dd, H2), 4.53 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 12.6, H4], 4.08 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3 Hz, H9] and 2.25–1.50 (8 H, 6m, CH2); dC(100.25 MHz, 25 8C, CDCl3) 163.9 (C10), 157.3 (C16), 139.4 (C1), 132.4 (C14), 129.0 (C12), 127.0 (C3), 122.9, 122.4 (C11, C15), 119.1 (C13), 104.7 (C2), 67.7 (C4), 63.3 (C9), 31.4 (C5), 25.7, 25.5 (C8, C6) and 20.1 (C7); m/z [chemical ionisation (CI), 35Cl] 338 (100, M 1 H), 337 (50, M1) and 269 (3%, M 2 C3H4N2).rac-cis-2-[2-(Pyrazol-1-yl)cyclohexyliminomethyl]pyridine Vc. n& max/cm21 (KBr) 1647vs (C]] N); dH(400.13 MHz, 25 8C, CDCl3) 8.43 [d, 3J(H14H15) 5.0, H15], 7.88 [d, 3J(H12H13) 7.5, H12], 7.67 (s, H10), 7.66 [d, 3J(H2H3) 2.0, H3], 7.58 [t, 3J(H13H14) 7.5, H13], 7.31 [s, 3J(H1H2) < 1.0, H1], 7.13 (dd, H14), 5.91 (br, H2), 4.45 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 12.5, H4], 3.85 [br, 3J(H8 axH9) = 3J(H8 eqH9) 2–3 Hz, H9] and 2.25–1.30 (8 H, 4m, CH2); dC(100.25 MHz, 25 8C, CDCl3) 161.6 (C10), 154.3 (C11), 148.9 (C15), 138.7 (C1), 136.1 (C12), 126.7 (C3), 124.3, 120.6 (C13, C14), 104.5 (C2), 68.6 (C4), 64.3 (C9), 29.9 (C5), 26.8, 25.6 (C8, C6) and 19.8 (C7); m/z (EI) 254 (3, M1), 186 (42, M 2 C3H4N2), 176 (63, M 2 C5H4N), 157 (9, C5H4N]CHNC4H4), 145 (52, C5H4N]CHNC3H4), 131 (52, C5H4N]CHNC2H2), 119 (32, C5H4N]CHNCH2), 118 (35, C5H4N]CHNCH), 107 (13, C5H4N]CHNH2), 105 (26, C5H4N]CNH), 92 (58, C5H4N] CH2), 81 (30, C3H3N2]CH2), 80 (26, C5H6N), 79 (41, C5H5N), 78 (35, C5H4N), 69 (100, C3H5N2), 68 (30, C3H4N2), 67 (23, C3H3N2), 65 (36, C4H3N) and 41 (44%, C3H5).rac-cis-2-[2-(Pyrazol-1-yl)cyclohexyliminomethyl]furan Vd. (Found: C, 67.65; H, 7.35; N, 16.95. C14H17N3O requires C, 69.1; H, 7.05; N, 17.25%); n& max/cm21 (KBr) 1642vs (C]] N); dH(400.13 MHz, 25 8C, CDCl3) 7.46 [dd, 3J(H13H14) 1.2, 4J(H12H14) 0.6, H14], 7.43 [d, 3J(H1H2) 1.8, H1], 7.41 (s, H10), 7.28 [d, 3J(H2H3) 2.3, H3], 6.55 [dd, 3J(H12H13) 3.4, H12], 6.40 (dd, H13), 6.05 (dd, H2), 4.52 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 12.9, H4], 3.95 [br, 3J(H8 axH9) = 3J(H8 eqH9) 2–3 Hz, H9] and 2.46–1.50 (8 H, 3m, CH2); dC(100.25 MHz, 25 8C, CDCl3) 151.7 (C11), 149.8 (C10), 144.7 (C14), 138.5 (C1), 127.4 (C3), 114.2 (C12), 111.4 (C13), 104.4 (C2), 69.9 (C4), 64.8 (C9), 32.9 (C5), 26.4, 25.9 (C8, C6) and 20.1 (C7); m/z (EI) 243 (4, M1), 175 (10, M 2 C3H4N2), 150 (42, M 2 C4H3O 2 CN), 146 (32, M 2 C3H4N2 2 C2H5), 134 (8, M 2 C3H4N2 2 C3H5), 107 (21, C4H3O]CHNCH), 94 (57, C4H3O]CHN), 81 (49, C5H5O), 80 (32, C4H4N2), 79 (19, C4H3N2), 69 (100, C3H5N2), 68 (34, C3H4N2), 67 (29, C3H3N2) and 52 (56%, C4H4).Chloro{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl]- phenolato}palladium(II) 1a.Bis(benzonitrile)dichloropalladium( II) (1.42 g, 3.70 mmol) and triethylamine (0.50 cm3) were added to a solution of compound Va (1.00 g, 3.70 mmol) in dry CH2Cl2 (30 cm3) and the mixture stirred for 48 h at room temperature. The product, which precipitated as a yellow2160 J. Chem. Soc., Dalton Trans., 1997, Pages 2155–2161 microcrystalline solid, was contaminated with a small amount of triethylammonium chloride and traces of elemental palladium. It can be recrystallised from methanol or concentrated acetonitrile solution at 50 8C, resulting in formation of the acetonitrile adduct 1a?MeCN as deep orange plates (m.p. 288 8C). Yield 1.27 g (76%) (Found: C, 47.75; H, 4.65; Cl, 7.75; N, 12.35; Pd, 24.0. C16H18ClN3OPd?CH3CN requires C, 47.9; H, 4.7; Cl, 7.85; N, 12.4; Pd, 23.6%); n& max/cm21 (KBr) 1611vs (C]] N); dH(400.13 MHz, 25 8C, [2H7]dmf) 8.40 [d, 3J(H1H2) 2.0, H1], 8.38 [d, 3J(H2H3) 3.0, H3], 8.28 (s, H10), 7.42 [dd, 3J(H12H13) 8.0, 4J(H12H14) 1.8, H12], 7.31 [ddd, 3J(H14H15) 8.5, 3J(H13H14) 6.8, H14], 6.83 (d, H15), 6.49 (m, H2, H13), 4.92 [br, 3J(H4H9) = 3J(H4H5 eq) = 3J(H4H5 ax) 2–3, H4], 4.10 [dt, 3J(H4H9) = 3J(H8 eqH9) 2.0, 3J(H8 axH9) 11.6 Hz, H9] and 2.16–1.22 (8 H, 4m, CH2); dC(100.25 MHz, 25 8C, [2H7]dmf) 164.1, 162.0 (C10, C16), 145.4 (C1), 136.0, 135.4, 134.7 (C3, C12, C14), 120.1 (C15), 118.2 (C11), 115.6 (C13), 107.0 (C2), 69.0 (C4), 60.5 (C9), 28.4, 28.4, 24.4 (C5, C6, C8) and 20.0 (C7). Acetato{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl]- phenolato}palladium(II) 1b.Compound Va (0.20 g, 0.74 mmol) in dry CH2Cl2 (5 cm3) was added dropwise via a syringe to a solution of palladium acetate (0.17 g, 0.74 mmol) in dry CH2Cl2 (5 cm3). After 48 h of stirring at room temperature the solvent was removed in vacuo. The residue was washed with diethyl ether (20 cm3) and dried in vacuo. Yield 0.27 g (85%), yellow microcrystalline solid (Found: C, 48.55; H, 5.3; N, 10.05.C18H21N3O3Pd requires C, 49.85; H, 4.85; N, 9.7%); n& max/cm21 (KBr) 1610vs (C]] N); dH(400.13 MHz, 25 8C, CD2Cl2) 7.70 [d, 3J(H1H2) 2.4, H1], 7.69 (s, H10), 7.65 [d, 3J(H2H3) 2.8, H3], 7.31 [ddd, 3J(H14H15) 8.8, 3J(H13H14) 6.8, 4J(H12H14) 1.8, H14], 7.18 [dd, 3J(H12H13) 7.9, H12], 6.93 (d, H15), 6.57 [ddd, 4J(H13H15) 1.0, H13], 6.42 (dd, H2), 4.75 [br, 3J(H4H9) = 3J(H4H5 eq) = 3J(H4H5 ax) 2–3, H4], 3.71 [dt, 3J(H4H9) = 3J(H8 eqH9) 2.6, 3J(H8 axH9) 12.1 Hz, H9], 2.12 (s, O2CCH3) and 2.54–1.26 (8 H, 4m, CH2); dC(100.25 MHz, 25 8C, CD2Cl2) 177.7 (C]] O), 164.8 (C16), 162.2 (C10), 142.4 (C1), 136.0, 134.8 (C12, C14), 132.0 (C3), 120.2 (C15), 119.6 (C11), 115.6 (C13), 107.2 (C2), 70.6 (C4), 60.1 (C9), 30.1 (CH3), 28.7 (C5), 24.7, 24.0 (C6, C8) and 19.3 (C7).Chloro{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl]- pyridine}palladium(II) chloride 2a. The compound [PdCl2- (PhCN)2] (1.11 g, 2.90 mmol) was added to a solution of compound Vc (0.74 g, 2.90 mmol) in dry CH2Cl2 (30 cm3). The mixture was stirred for 5 h at room temperature.The solvent was removed in vacuo and the brown oily residue recrystallised from CH2Cl2–diethyl ether to give bright yellow crystals containing about 2.5 equivalents of CH2Cl2 per molecule of complex 2a. Yield 0.99 g (53%) (Found: C, 32.2; H, 3.4; N, 9.1. C15H18Cl2N4Pd?2.5CH2Cl2 requires C, 32.65; H, 3.6; N, 8.7%); n& max/cm21 (KBr) 1624vs (C]] N); dH(400.13 MHz, 260 8C, CD2Cl2), isomer A, 10.37 (s, H10), 9.11 [d, 3J(H14H15) 4.5, H15], 9.02 [d, 3J(H12H13) 7.5, H12], 8.31 [d, 3J(H1H2) 2.6, H1], 8.24 [dd, 3J(H13H14) 8.0, H13], 7.96 [d, 3J(H2H3) 3.5, H3], 7.70 (m, H14), 6.55 (dd, H2), 4.87 [dt, 3J(H8 axH9) 12.0, 3J(H4H9) = 3J(H8 eqH9) 3.5, H9], 4.74 [br, 3J(H4H5 eq) = 3J(H4H5 ax) 2–3, H4) and 2.55– 1.30 (8 H, m, CH2); isomer B, 10.52 [d, 3J(H9H10) 2.0, H10], 9.10 [d, 3J(H14H15) 4.5, H15], 8.65 [d, 3J(H12H13) 7.0, H12], 8.22 [dd, 3J(H13H14) 8.0, H13], 8.15 [d, 3J(H1H2) 2.0, H1], 7.95 [d, 3J(H2H3) 2.0, H3], 7.70 (m, H14), 6.44 (t, H2), 5.00 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 13.0, H4], 4.45 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3 Hz, H9] and 2.55–1.30 (8 H, m, CH2); isomer ratio A:B 1.00); m/z (FAB, 35Cl, 106Pd) 395 (13, PdLCl) and 359 (2%, C15H17N4Pd). Dichloro{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl]- furan}palladium(II) 2b. The compound [PdCl2(PhCN)2] (1.57 g, 4.1 mmol) was added to a solution of compound Vd (1.0 g, 4.1 mmol) in dry CH2Cl2 (30 cm3).The mixture was stirred for 48 h at room temperature. A brown precipitate formed which was washed three times with CH2Cl2 (10 cm3) and dried in vacuo. Yield 1.66 g (96%), orange-brown microcrystalline powder (Found: C, 39.55; H, 3.9; Cl, 17.05; N, 9.85; O, 3.85; Pd, 25.0. C14H17Cl2N3OPd requires C, 40.0; H, 4.05; Cl, 16.85; N, 10.0; O, 3.8; Pd, 25.3%); n& max/cm21 (KBr) 1608vs (C]] N). Bromotricarbonyl{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl] phenol}rhenium(I) 3.A solution of [ReBr(CO)5] (0.3 g, 0.74 mmol) and compound Va (0.20 g, 0.74 mmol) in thf (20 cm3) was heated under reflux for 48 h, changing from yellow to orange. After evaporation of the solvent in vacuo, the solid residue was washed three times with diethyl ether (10 cm3) and dried in vacuo. Yield: 0.18 g (41%), yellow microcrystalline powder (Found: C, 35.25; H, 3.2; Br, 13.3; N, 6.5; O, 11.25; Re, 31.0. C19H19BrN3O4Re requires C, 36.85; H, 3.1; Br, 12.9; N, 6.8; O, 10.35; Re, 30.05%); n& max/cm21 (KBr) 2019vs, 1902vs (CO), 1609vs (C]] N); (thf) 2020vs, 1914vs, 1888s (CO); dH(400.13 MHz, 25 8C, CD2Cl2) 10.87 (s, OH), 9.80 (s, H10), 7.88 [d, 3J(H1H2) 2.5, H1], 7.64 [d, 3J(H2H3) 2.0, H3], 7.60 [dd, 3J(H12H13) 7.5, 4J(H12H14) 1.5, H12], 7.55 [dd, 3J(H14H15) 8.8, 3J(H13H14) 7.5, H14], 7.04 [ddd, 4J(H13H15) 1.1, H13], 6.98 (dd, H15), 6.45 (dd, H2), 4.62 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.0, 3J(H4H5 ax) 10.0, H4], 3.80 [br, 3J(H8 axH9) = 3J(H8 eqH9) 2–3 Hz, H9) and 2.25–1.80 (8 H, 6m, CH2); dC(100.25 MHz, 25 8C, CD2Cl2) 196.9 (2COeq), 194.8 (COax), not observed (C10, C16), 146.5 (C1), 137.0 (C3), 133.8 (C12), 133.2 (C14), 119.9 (C15), 117.4, 117.4 (C11, C13), 107.8 (C2), 63.0 (C4, C9), 33.1 (C5), 28.7, 23.2 (C8, C6) and 20.0 (C7).Dichlorooxo{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl] phenolato}rhenium(V) 4a and dichloro{rac-cis-2,4-dichloro- 6-[2-(pyrazol-1-yl)cyclohexyliminomethyl]phenolato}oxorhenium( V) 4b.The appropriate compound Va or Vb (1 mmol) was added to a solution of [NBu4][ReOCl4] (293 mg, 0.5 mmol) in ethanol (20 cm3). The resulting brown reaction mixture was heated to reflux for 3 h during which a green precipitate formed, which was filtered off, washed with ethanol and pentane and dried in vacuo. Yield 0.20 (73%) of 4a and 0.20 g (65%) of 4b, green microcrystalline solids, poorly soluble in organic solvents. Complex 4a (Found: C, 35.6; H, 3.65; N, 7.3.C16H18Cl2- N3O2Re requires C, 35.5; H, 3.35; N, 7.75%); n& max/cm21 (KBr) 1614vs (C]] N); dH[400.13 MHz, 25 8C, (CD3)2SO], isomer A, 8.92 (s, H10), 8.91 [d, 3J(H1H2) 2.5, H1], 8.76 [d, 3J(H2H3) 2.5, H3], 7.69 [ddd, 3J(H14H15) 8.5, 3J(H13H14) 7.0, 4J(H12H14) 1.5, H14], 7.63 [dd, 3J(H12H13) 8.0, H12], 7.15 (d, H15), 7.07 (t, H2), 7.00 (dd, H13), 5.20 [br d, 3J(H4H9) = 3J(H4H5 eq) ca. 2–3, 3J(H4H5 ax) 12.5, H4], 5.01 [br, 3J(H4H9) = 3J(H8 eqH9) = 3J(H8 axH9) ca. 2–3, H9] and 2.90–1.35 (8 H, 5m, CH2); isomer B, 9.16 (s, H10), 8.98 [d, 3J(H1H2) 2.5, H1], 8.87 [d, 3J(H2H3) 2.5, H3], 7.79 [td, 3J(H14H15) = 3J(H13H14) 7.8, 4J(H12H14) 1.5, H14], 7.75 [dd, 3J(H12H13) 8.0, H12], 7.25 (d, H15), 7.13 (t, H2), 7.10 (dd, H13), 5.17 [br d, 3J(H4H9) = 3J(H4H5 eq) ca. 2–3, 3J(H4H5 ax) 14.0, H4], 4.77 [br, 3J(H4H9) = 3J(H8 eqH9) = 3J(H8 axH9) ca. 2–3 Hz, H9] and 2.90–1.35 (8 H, 5m, CH2), isomer ratio A:B 1.56; dC[100.15 MHz, 25 8C, (CD3)2SO], isomer A, 174.7, 174.1 (C10, C16), 147.8 (C1), 138.5, 138.0, 137.7 (C3, C12, C14), 121.2, 120.8, 118.8 (C11, C13, C15), 108.7 (C2), 76.8 (C4), 60.8 (C9), 29.7, 28.7, 24.2 (C5, C6, C8), 18.7 (C7); isomer B, 175.8 (C10), 172.0 (C16), 149.2 (C1), 139.7, 139.0, 138.5 (C3, C12, C14), 121.5, 120.6 (C11, C15), 120.6 (C13), 109.5 (C2), 75.4 (C4), 56.2 (C9), 29.0, 28.8, 23.9 (C5, C6, C8) and 18.6 (C7).Complex 4b (Found: C, 31.7; H, 2.7; Cl, 22.6; N, 6.95; O, 5.55; Re, 30.1. C16H16Cl4N3O2Re requires C, 31.5; H, 2.65; Cl, 23.25; N, 6.9; O, 5.25; Re, 30.5%); n& max/cm21 (KBr) 1619vs (C]] N); dH[400.13 MHz, 25 8C, (CD3)2SO], isomer A, 8.93 [d, 3J(H1H2) 2.5, H1], 8.88 (s, H10), 8.81 [d, 3J(H2H3) 2.5, H3], 8.00 [d, 4J(H12H14) 2.5, H12], 7.70 (d, H14), 7.10 (t, H2), 5.15 [br d, 3J(H4H9) = 3J(H4H5 eq) ca. 2–3, 3J(H4H5 ax) 12.0, H4], 5.01 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3, H9] and 2.90–1.35 (8 H, 5m, CH2); isomer B, 9.11 (s, H10), 8.99 [d, 3J(H1H2) 2.5, H1], 8.91 [d,J.Chem. Soc., Dalton Trans., 1997, Pages 2155–2161 2161 3J(H2H3) 2.5, H3], 8.13 [d, 4J(H12H14) 2.5, H12], 7.84 (d, H14), 7.15 (t, H2), 5.12 [br d, 3J(H4H9) = 3J(H4H5 eq) ca. 2–3, 3J(H4H5 ax) 17.6, H4], 4.78 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3 Hz, H9] and 2.90–1.35 (8 H, 5m, CH2); isomer ratio A:B 1.35. Crystallography Intensity data for complex 1a were collected on a STOE-IPDS diffractometer using graphite-monochromated Mo-Ka radiation (l 0.710 73 Å). The structure was solved by the Patterson method with SHELXS 8623 and refined (based on F 2) by fullmatrix least-squares analysis with SHELXL 93.24 All non-H atoms were refined with anisotropic thermal parameters.The positions of all H atoms were obtained from the least-squares refinement and were refined with isotropic thermal parameters. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J.Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC should quote the full literature citation and the reference number 186/496. Acknowledgements The authors thank Professor Dr. W. A. Herrmann, the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie for support of this work and Dr. E. Herdtweck for X-ray data collection. References 1 Part 2, C. Thurner, M. Barz, M. Spiegler and W. R. Thiel, J. Organomet. Chem., in the press. 2 (a) Catalytic Asymmetric Synthesis, ed.E. Ojima, VCH, New York, 1993; (b) H. Brunner and W. Zettlmeier, Handbook of Enantioselective Catalysis with Transition Metal Compounds, VCH, Weinheim, 1993, vols. I and II; (c) R. Noyori, Asymmetric Catalysis in Organic Synthesis, Wiley, New York, 1994. 3 K. B. Sharpless, W. Amberg, M. Beller, H. Chen, J. Hartung, Y. Kawanami, D. Lübben, E. Manoury, Y. Ogino, T. Shibata and T. Ukita, J. Org. Chem., 1991, 56, 4585. 4 L. M. Venanzi and A. Togni, Angew.Chem., 1994, 106, 517; Angew. Chem., Int. Ed. Engl., 1994, 33, 497. 5 M. Barz, E. Herdtweck and W. R. Thiel, Tetrahedron Asymm., 1996, 7, 1717. 6 M. Barz and W. R. Thiel, unpublished work. 7 M. Calligaris and L. Randaccio, in Comprehensive Coordination Chemistry, ed. G. Wilkinson, Pergamon, London, 1987, vol. 2, pp. 715–738. 8 F. Muth, in Methoden der Organischen Chemie (Houben Weyl), ed. E. Müller, Georg Thieme Verlag, Stuttgart, 4th edn., 1955, vol. 9, pp. 663–668. 9 A. Hassner, in Methoden der Organischen Chemie (Houben Weyl), ed. D. Klamann, Georg Thieme Verlag, Stuttgart, 4th edn., 1990, vol. E16a/2, pp. 1255–1265. 10 E. F. V. Scriven and K. Turnbull, Chem. Rev., 1988, 88, 297. 11 O. Mitsunobu, Synthesis, 1981, 1. 12 S. Pawlenko, in Methoden der Organischen Chemie (Houben Weyl), eds. D. Klamann and H. Hagemann, Georg Thieme Verlag, Stuttgart, 4th edn., 1990, vol. E14b/1, pp. 239–243. 13 U. Burkert and N. C. Allinger, American Chemical Society, Washington, DC, 1982; T. Clark, A Handbook of Computational Chemistry, Wiley, New York, 1985; J. W. Ponder and F. M. Richards, J. Comput. Chem., 1987, 8, 1016. 14 J. E. Anderson, in The Chemistry of Alkanes and Cycloalkanes, eds. S. Patai and Z. Rappoport, Wiley, New York, 1992; H.-J. Schneider, R. Price and T. Keller, Angew. Chem., 1971, 83, 759. 15 A. L. Spek, Acta Crystallogr., Sect. A, 1990, 46, C34. 16 (a) STOE IPDS software manual, version 2.80, 1997; (b) E. Prince, Mathematical Techniques in Crystallography, Springer, Berlin, 1982. 17 H. Elias, E. Hilms and H. Paulus, Z. Naturforsch., Teil B, 1982, 37, 1266; P. Bandyopadhyay, D. Bandyopadhyay, A. Chakravorty, F. A. Cotton, L. R. Falvello and S. Han, J. Am. Chem. Soc., 1983, 105, 6327; B. F. Hoskins, C. J. McKenzie and R. Robson, J. Chem. Soc., Dalton Trans., 1992, 3083; M. Kurahashi, Bull. Chem. Soc. Jpn., 1974, 47, 2045. 18 A. Bader and E. Lindner, Coord. Chem. Rev., 1991, 108, 27. 19 W. Hieber, R. Schuh and H. Fuchs, Z. Anorg. Allg. Chem., 1941, 248, 243; S. P. Schmidt, W. C. Trogler and F. Basolo, Inorg. Synth., 1985, 23, 44. 20 R. E. Cobbledick, L. R. J. Dowdell, F. W. B. Einstein, J. K. Hoyano and L. K. Peterson, Can. J. Chem., 1979, 57, 2285; W. Tikkanen, W. C. Kaska, S. Moya, T. Layman, R. Kane and C. Krüger, Inorg. Chim. Acta, 1983, 76, L29; M. C. Couldwell and J. Simpson, J. Chem. Soc., Dalton Trans., 1979, 1101; E. W. Abel, V. S. Dimitrov, N. J. Long, K. G. Orrell, A. G. Osborne, H. M. Pain, V. Sik, M. B. Hursthouse and M. A. Mazid, J. Chem. Soc., Dalton Trans., 1993, 597; S. A. Moya, J. Guerrero, R. Pastene, R. Schmidt, R. Sariego, R. Sartori, J. Sanz-Aparicio, I. Fonseca and M. Martinez-Ripoll, Inorg. Chem., 1994, 33, 2341. 21 G. K. Anderson and M. Lin, Inorg. Synth., 1990, 28, 61. 22 R. Alberto, R. Schibli, A. Egli, P. A. Schubiger, W. A. Herrmann, G. Artus, U. Abram and T. A. Kaden, J. Organomet. Chem., 1995, 492, 217. 23 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467. 24 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure Determination, University of Göttingen, 1993. Received 27th November 1996; Paper 6/08031F