DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 847–852 847 Reactions of a ditungsten-capped tetrayne with cobalt carbonyls: molecular structures of {W(CO)3Cp}2{Ï-C8[Co2(Ï-dppm)m- (CO)6 2 2m]n} (m 5 0, 1; n 5 1, 2) Michael I. Bruce,a Brian D. Kelly,a Brian W. Skelton b and Allan H. White b a Department of Chemistry, University of Adelaide, Adelaide, South Australia 5005. E-mail: mbruce@chemistry.adelaide.edu.au b Department of Chemistry, University of Western Australia, Nedlands, Western Australia 6907 Received 15th December 1998, Accepted 12th January 1999 The carbon-rich complex {W(CO)3Cp}2(m-C8) reacts with Co2(m-dppm)m(CO)8 2 2m (m = 0, 1) to give several complexes formed by addition of Co2(m-dppm)m(CO)6 2 2m moieties to one or two C]] ] C triple bonds.X-Ray structure determinations on {W(CO)3Cp}2{m-C8[Co2(m-dppm)m(CO)6 2 2m]n} [m = 0, n = 1, 2; m = 1, n = 1, 2 (two isomers)] confirm the presence of the C8 chain linking the two W(CO)3Cp groups.Introduction There is much current interest in molecules containing carbon chains capped by transition metal–ligand groups.1 These materials have potential utility as quasi-one dimensional conductors, 2 poly-yne systems allowing electronic interactions over relatively long distances through p-delocalisation.3–5 Unsaturated carbon chains with up to 20 carbon atoms have been used to link redox-active metal centres.6–8 While p-bonding of MLn groups to complexes of this type is thought to reduce communication along the chain,9,10 recent studies of diyne complexes of cobalt have suggested that both through-bond and through-space interactions may occur.11 Three groups have described compounds containing C8 chains bridging two W(CO)3Cp,12 Re(NO)(PPh3)Cp*,13 or Fe(dppe)Cp* groups.14 However, complexes of this type have proved diYcult to characterise crystallographically, as crystals of suitable size and quality have not been obtained.The use of Co2(CO)6 and Co2(m-dppm)(CO)4 as protecting groups for C]] ] C triple bonds is well-established as these groups can be easily displaced to regenerate the parent alkyne.15 Consequently, the preparation of similar derivatives of metal complexes containing carbon chains would provide independent evidence for the existence of these chains, although distortions in the Cn geometry as a result of complexation do not give any useful structural information about the uncomplexed polyalkynes.In the limit, it is possible to envisage a novel form of carbon consisting of Cn chains which might be stabilised by formation of the dicobalt derivatives.Indeed, just such a material is considered to form the black insoluble polymer obtained from {Co2(CO)6}2(m,m-Me3SiC2C2SiMe3) on standing in methanol.16 In this paper we describe several complexes which we have prepared from the recently described C8 complex {W(CO)3Cp}2- (m-C8) 1 12 and the dicobalt carbonyl complexes. Results and discussion Reactions between 1 and Co2(CO)8 were carried out at room temperature in thf.The black reaction products were purified by preparative TLC, initial separation into two black fractions occurring. Subsequent crystallisation aVorded X-ray quality crystals of mono- and di-adducts, which were shown by the X-ray structural studies to have Co2(CO)6 groups attached to the C(3)–C(4) (2) and C(3)–C(4), C(39)–C(49) triple bonds (3), respectively. Numbering the C]] ] C triple bonds along the chain from one tungsten allows these complexes to be formulated as {W(CO)3Cp}2{m-C8[Co2(CO)6]-2} 2 and {W(CO)3Cp}2{m-C8- [Co2(CO)6]2-2,3} 3, respectively.The IR n(CO) spectra contained only terminal n(CO) bands between 2096 and 1951 cm21. The 1H NMR spectra contained singlet resonances for the Cp protons at d 5.64 and 5.67 (2) and at d 5.59 (3). Similar reactions between 1 and Co2(m-dppm)(CO)6 aVorded a mono-adduct {W(CO)3Cp}2{m-C8[Co2(m-dppm)(CO)4]} 4 and two isomeric products, again characterised by single crystal X-ray studies as the bis-adducts, containing Co2(m-dppm)(CO)4 groups attached to the C(1)–C(2) and C(19)–C(29) or to the C(3)–C(4) and C(39)–C(49) triple bonds, respectively, namely {W(CO)3Cp}2{m-C8[Co2(m-dppm)(CO)4]2-1,4} 5 and {W(CO)3- Cp}2{m-C8[Co2(m-dppm)(CO)4]2-2,3} 6.Complexes 5 and 6 have essentially indistinguishable IR spectra (Table 1) with terminal n(CO) bands between 2038 and 1933 cm21, at lower energies than those in 2 and 3; those for 4 are found some 3–10 cm21 higher.The 1H NMR spectra contained singlet resonances for the Cp protons at d 5.56 and 5.81, respectively, while the CH2 protons of the dppm ligands occurred at d 3.19 and 3.91 (5) and at d 3.30 and 3.82 (6). Molecular structures of 2–6 Representations of the five molecular structures are given in848 J. Chem. Soc., Dalton Trans., 1999, 847–852 Fig. 1–5, while significant structural parameters are summarised in Table 2.Molecules of 3, 5 and 6 are centrosymmetric. Comparison of the W(CO)3Cp groups with that found in Fig. 1 Projection of {W(CO)3Cp}2{m-C8[Co2(CO)6]} 2. For this and subsequent figures, 20% thermal ellipsoids are shown for the nonhydrogen atoms, hydrogen atoms having arbitrary radii of 0.1 Å. Table 1 IR n(CO) spectra Complex 17238456 n(CO)/cm21 2043s, 1959vs 2101m, 2082s, 2062vs, 2037s, 2028s (sh), 1984w (br) 2090w, 2057s, 2038s, 2031m (sh), 1967vs, 1955s 2096w, 2079s, 2057vs, 2038s, 2025s, 1965s, 1951s 2029m, 2002vs, 1968s 2047w, 2038m, 2010m, 1995s, 1967s, 1955s, 1943m 2037m, 2030m, 2004s, 1992vs, 1960m, 1942m, 1933m 2038m, 2034m, 2011vs, 1996m, 1972s (br), 1960s (br), 1940m (sh) W(C]] ] CC]] ] CSiMe3)(CO)3Cp12 show no significant diVerences to result from the coordination of the dicobalt fragments to the C]] ] C triple bonds.Thus the W–C(Cp) distances all fall in the range 2.27–2.37(1) Å, with the W–CO distances being between 1.929(8) and 2.02(1) Å.Fig. 2 Projection of {W(CO)3Cp}2{m-C8[Co2(CO)6]2} 3. Fig. 3 Projection of {W(CO)3Cp}2{m-C8[Co2(m-dppm)(CO)4]} 4. Fig. 4 Projection of {W(CO)3Cp}2{m-C8[Co2(m-dppm)(CO)4]2} (1,4- isomer) 5.J. Chem. Soc., Dalton Trans., 1999, 847–852 849 The C2Co2 tetrahedra are similar to those found in many other related complexes, with Co–Co separations of 2.4595(8)– 2.480(1) Å, Co–C distances of between 1.951(8) and 2.023(5) Å, and C-C bonds now between 1.33(1) and 1.358(6) Å.The uncoordinated C]] ] C triple bond lengths are between 1.20(1) and 1.214(5) Å. These data may be compared with the other similarly characterised pair of derivatives, {Co2(CO)6}2(m,m-PhC2- C2Ph) 7 17 and {Co2(m-dppm)(CO)4}2(m,m-PhC2C2Ph) 8,18 in which the Co–Co and Co–C distances are between 2.438 and 2.469(4) Å, and between 1.94 and 1.98(1) Å, respectively. The separation of the centre-points of the two Co–Co bonds in 3 and 6 are both 4.373 Å, very similar to the values of 4.43 and 4.36 Å found for 7 and 8.As expected, significant distortions of the C8 chains from linearity occur in these complexes. The bend-back angles of the coordinated C]] ] C triple bonds range from 33.8 to 38.2(5)8. Comparison of 2 and 4, in which the Co2 units are attached to the C(3)–C(4) and C(1)–C(2) bonds, respectively, shows that the total bending is greater in the latter (79.3 vs. 70.38), suggesting that steric pressure from the bulky W(CO)3Cp group may play a role here.As a result of the symmetry of the bis-adducts, the C8 chains describe transoid or S-shaped conformations, with the W–C(1) vectors being approximately orthogonal to the central C(4)–C(49) vectors (range 82.6–92.68). Although the dppm ligands are much larger than the CO groups which they replace, comparison of the bending of the C8 chains shows essentially no diVerence, with angles at C(3) and C(4) in 3 and 6 summing to 276.88 and 276.18, respectively. In 3 and 6, the W–C(1)–C(2)–C(3) sequences are approximately linear, with angles at C(1) and C(2) being 176.9(4) and 175.7(5)8 (for 3) and 174.5(4) and 176.1(4)8 (for 6).The central sequence in 5 has angles at C(3) and C(4) of 170.9(4) and 179.3(4)8, respectively. Closer structural comparisons can be made between 5 and the centrosymmetric molecule Me3SiC2{Co2(m-dppm)- (CO)4}(C]] ] C)2C2{Co2(m-dppm)(CO)4}SiMe3 9,19 the only other tetrayne–dicobalt complex to have been structurally characterised. The C–C bond lengths are 1.343(11), 1.386(9), 1.210(10) and 1.372(14) Å for the bonds between atoms C(1)–C(2)–C(3)– C(4)–C(49), all closely similar to those found in 5.In 9, angles at atoms C(1–4) are 147.0(7), 144.4(9), 171.1(11) and 178.8(3)8, respectively, resulting in the two Si–C(1,19) vectors forming angles of 68.68 with the central C(4)–C(49) bond. Again, this suggests that the bulk of the substituent at C(1) has an eVect on Fig. 5 Projection of {W(CO)3Cp}2{m-C8[Co2(m-dppm)(CO)4]2} (2,3- isomer) 6.the bend-back angle, in additon to any electronic influence of the dicobalt fragment. In the case of 6, in spite the bulk of the Co2(m-dppm)(CO)4 moiety, the angles subtended by the CO and diynyl groups at the W atoms are not significantly diVerent from those in 5. As expected, the W–C(1) distance in the latter has lengthened to 2.213(4) Å compared with 2.123(6) Å in 6, consistent with rehybridisation of this carbon towards sp2. The structural results enable a rationalisation of the 1H NMR data to be obtained.Coordination of a Co2 group to the inner C]] ] C triple bonds results in the Cp signal being at lower field than the resonance observed for the complex in which the outer C]] ] C triple bond is coordinated. For 1, the Cp resonance is at d 5.67; in the case of the mono-adduct 2, two Cp signals separated by 0.03 ppm are found. The presence of the dppm ligands results in a shift of ca. 0.3 ppm to low field.Small amounts of other products were also present in the reaction mixtures, as evidenced by several other bands developing on the TLC plate. However, we have not been able to characterise these compounds. Their IR n(CO) spectra contained bands at significantly lower energies, suggesting that monoadducts were present, while their 1H NMR spectra contained multiple Cp resonances, perhaps indicating that there were up to three other, unsymmetrical isomers of the mono-adducts.Finally, the Co2(CO)6 groups may be removed from the complexed diyndiyl complexes by treatment with ammonium cerium(IV) nitrate in acetone, a method which has been used for more conventional alkyne–Co2(CO)6 complexes.15 Thus, treatment of 2 with [NH4]2[Ce(NO3)6] in acetone resulted in lightening of the colour to orange; conventional work-up aVorded 1 in 50% yield. Conclusions We have shown that it is possible to prepare and characterise derivatives of the C8 complex 1 containing dicobalt carbonyl groups attached to one or two C]] ] C triple bonds; in contrast to the parent complex, crystalline samples of four of these complexes were readily obtained, for which single crystal X-ray studies showed that apparent preferential coordination to the inner C]] ] C triple bonds occurred with Co2(CO)8.However, with Co2(m-dppm)(CO)6, two isomeric complexes containing two dicobalt units attached to the two outer (5) or the two inner C]] ] C triple bonds (6) were obtained. It is of interest that we have been able to isolate derivatives containing Co2(CO)6 moieties attached only to the ‘inner’ C]] ] C triple bonds, whereas with the Co2(m-dppm)(CO)4-substituted complexes the ‘outer’ C]] ] C triple bonds can also coordinate.The dicobalt carbonyl moiety may be removed by oxidation with cerium(IV). Experimental General reaction conditions Reactions were carried out under an atmosphere of nitrogen, but no special precautions were taken to exclude oxygen during work-up.Instrumentation IR: Perkin-Elmer 1700X FT IR. NMR: Bruker CXP300 or ACP300 (1H NMR at 300.13 MHz, 13C NMR at 75.47 MHz). ES MS: Finnegan LCQ: solutions were directly infused into the instrument. Chemical aids to ionisation were used as required.20 Reagents Complex 1 12 and Co2(m-dppm)(CO)6 21 were prepared by the literature methods; Co2(CO)8 (Strem) was used as received. Reaction of {W(CO)3Cp}2(Ï-C8) with Co2(CO)8 A mixture of {W(CO)3Cp}2(m-C8) (100 mg, 0.13 mmol) and850 J.Chem. Soc., Dalton Trans., 1999, 847–852 Table 2 Selected bond lengths (Å) and angles (8) W–CO (av.) W–C(Cp) (av.) W–C(1) Co(2)–Co(3) Co–CO (av.) Co(2)–P(1) Co(3)–P(2) Co(2)–C(1/3) Co(2)–C(2/4) Co(3)–C(1/3) Co(3)–C(2/4) P(1)–C(0) P(2)–C(0) C(1)–C(2) C(2)–C(3) C(3)–C(4) C(4)–C(49) C(11)–W–C(12) C(11)–W–C(13) C(12)–W–C(13) C(1)–W–C(11) C(1)–W–C(12) C(1)–W–C(13) C(21)–Co(2)–C(22) C(21)–Co(2)–C(23) C(22)–Co(2)–C(23) C(31)–Co(3)–C(32) C(31)–Co(3)–C(33) C(32)–Co(3)–C(33) Co(2)–C(4)–C(49) Co(3)–C(3)–C(2) W–C(1)–C(2) C(1)–C(2)–C(3) C(2)–C(3)–C(4) C(3)–C(4)–C(49) Co(2)–P(1)–C(0) P(1)–C(0)–P(2) C(0)–P(2)–Co(3) P(1)–Co(2)–C(21) P(1)–Co(2)–C(22) P(2)–Co(3)–C(31) P(2)–Co(3)–C(32) 2 a 1.99–2.02(1) 1.998 2.27–2.37(1) 2.33 2.143(8) [2.118(8)] 2.461(1) 1.802–1.838(9) 1.821 1.951(8) 1.987(7) 1.978(7) 1.963(7) 1.19(1), 1.23(1) 1.43(1), 1.36(1) 1.33(1), 1.21(1) 1.40(1) 111.8(4) [107.5(4)] 77.4(4) [79.6(4)] 79.4(4) [76.6(4)] 72.5(4) [75.6(3)] 76.5(3) [73.6(3)] 130.5(3) [132.8(4)] 105.3(4) 103.8(4) 98.3(4) 108.6(4) 98.6(4) 98.3(4) 131.5(46) 131.3(6) 173.4(7) 171.6(8) 146.2(8) 143.5(7) 3 1.992–2.006(6) 1.998 2.302–2.351(7) 2.329 2.127(4) 2.4794(9) 1.794–1.825(6) 1.812 1.995(4) 1.964(4) 1.978(5) 1.970(5) 1.213(5) 1.398(5) 1.353(5) 1.425(6) 113.0(3) 78.6(2) 77.8(2) 75.2(2) 73.4(2) 128.8(2) 102.3(2) 103.6(2) 97.6(3) 105.2(2) 102.2(2) 99.0(2) 134.2(3) 137.4(3) 176.9(4) 175.7(5) 142.7(5) 133.6(5) 4 1.96–2.02(1) 1.977 2.293(8)–2.370(9) 2.327 2.216(7), 2.108(9) 2.476(1) 1.765(9)–1.79(1) 1.774 2.243(3) 2.232(2) 2.019(7) 1.954(7) 2.023(5) 1.961(6) 1.827(8) 1.834(9) 1.36(1), 1.22(1) 1.40(1), 1.36(1) 1.20(1), 1.20(1) 1.37(1) 76.0(4), 109.7(4) 77.1(3), 77.6(4) 106.9(4), 79.9(4) 132.1(4), 75.4(4) 73.2(3), 74.3(4) 77.9(3), 133.2(3) 101.8(4) 99.7(4) 141.9(4) 138.8(5) 177.6(8) 178.1(8) 107.7(3) 108.7(5) 108.8(2) 97.6(3) 107.8(3) 96.0(3) 112.9(2) 5 1.955–1.997(5) 1.977 2.307–2.368(6) 2.337 2.213(4) 2.4595(8) 1.752–1.787(4) 1.773 2.221(1) 2.244(1) 1.996(4) 1.969(4) 2.022(3) 1.983(3) 1.830(4) 1.842(4) 1.353(5) 1.398(5) 1.214(5) 1.372(5) 78.2(2) 76.7(2) 105.7(2) 132.8(2) 76.0(2) 73.3(2) 99.6(2) 97.7(2) 143.7(3) 143.5(4) 170.9(4) 179.3(4) 108.5(1) 110.5(2) 110.2(1) 104.4(2) 103.7(2) 112.1(2) 96.5(2) 6 1.929–2.002(8) 1.972 2.28–2.35(1) 2.31 2.123(6) 2.480(1) 1.750–1.783(7) 1.767 2.219(1) 2.232(1) 1.975(5) 1.955(5) 1.964(6) 1.973(5) 1.821(5) 1.834(5) 1.219(8) 1.395(8) 1.358(6) 1.424(6) 78.9(3) 78.0(3) 110.7(3) 131.7(3) 77.0(2) 72.5(3) 103.9(3) 101.6(3) 134.1(3) 132.7(4) 174.5(4) 176.1(4) 142.2(5) 141.8(6) 108.6(2) 109.3(2) 108.9(2) 95.9(2) 112.2(2) 97.2(2) 109.8(2) a This molecule has no crystallographic centre of symmetry; second entries correspond to the counterpart atoms in the primed/second ‘half’ of the molecule.Co2(CO)8 (54 mg, 0.16 mmol) in thf (10 mL) was left to stir for 1 h at r.t., then concentrated under reduced pressure. The resulting black residue was extracted with CH2Cl2 and purified by TLC (silica gel; hexane–CH2Cl2 3 : 2).The top two black bands were removed. Band 1 (Rf 0.7) contained {W(CO)3Cp}2{m-C]] ]CC2[Co2- (CO)6]C2[Co2(CO)6]C]] ] C} 3 (10 mg, 6%). Crystals suitable for X-ray study were obtained from CH2Cl2–pentane (Found: C, 31.38; H, 0.59. C36H10Co4O18W2?CH2Cl2 calcd.: C, 31.32; H, 0.85%; M, 1334). IR (cyclohexane) n(CO) 2096w, 2079s, 2057vs, 2038s, 2025s, 1965s, 1951s cm21. 1H NMR (CDCl3): d 5.59 (s, Cp).Band 2 (Rf 0.6) aVorded {W(CO)3Cp}2{m-C]] ] CC2[Co2(CO)6]- (C]] ] C)2} 2 (37 mg, 37%). Crystals suitable for X-ray study were obtained from CH2Cl2–pentane (Found: C, 34.38; H, 0.96. C30H10Co2O12W2 calcd.: C, 34.40; H, 1.16%; M, 1048). IR (cyclohexane) n(CO) 2090w, 2057s, 2038s, 1967vs, 1955s cm21. 1H NMR (CDCl3): d 5.64, 5.67 (2s, Cp). ES MS (with NaOMe in MeOH): m/z 1071, [M 1 Na]1. Reaction of {W(CO)3Cp}2(Ï-C8) with Co2(Ï-dppm)(CO)6 A stirred mixture of {W(CO)3Cp}2(m-C8) (56 mg, 0.07 mmol) and Co2(m-dppm)(CO)6 (100 mg, 0.15 mmol) in benzene (20 mL) was refluxed for 1 h.The mixture was allowed to cool, concentrated under reduced pressure and the resulting black residue extracted with CH2Cl2 and purified by TLC (silica gel; hexane–CH2Cl2 1 : 1). The top three black bands were removed. Band 1 (Rf 0.8) aVorded {W(CO)3Cp}2{m-C]] ] CC2[Co2- (m-dppm)(CO)4]C2[Co2(m-dppm)(CO)4]C]] ] C} 6 (45 mg, 31%). Crystals suitable for X-ray study were obtained from CH2Cl2– pentane (Found: C, 46.13; H, 2.74.C82H54Co4O14P4W2?2CH2- Cl2 calcd.: C, 46.70; H, 2.71%; M, 1991). IR (cyclohexane) n(CO) 2026m, 1997s, 1974s, 1958m, 1941m, 1925s, 1912s cm21. 1H NMR (CDCl3): d 3.30, 3.82 (2m, 4H, CH2P2), 5.81 (s, 10H, Cp), 7.09–7.39 (m, 40H, Ph). Band 2 (Rf 0.7) contained {W(CO)3Cp}2{m-C2[Co2(m-dppm)- (CO)4](C]] ] C)2C2[Co2(m-dppm)(CO)4]} 5 (25 mg, 17%). Crystals suitable for X-ray study were obtained from CH2Cl2–benzene– pentane (Found: C, 48.48; H, 2.42.C82H54Co4O14P4W2 calcd.: C, 47.77; H, 2.64%; M, 1991. IR (cyclohexane) n(CO) 2031m, 1991s, 1956s, 1947m, 1937m, 1922s, 1913s cm21. 1H NMR (CDCl3): d 3.19, 3.91 (2m, 4H, CH2P2), 5.56 (s, 10H, Cp), 6.87– 7.58 (m, 40H, Ph). Band 3 (Rf 0.5) contained {W(CO)3Cp}2{m-C2[Co2(m-dppm)- (CO)4](C]] ] C)3}?C6H6 4 (10 mg, 7%). Crystals of the hemi-J. Chem. Soc., Dalton Trans., 1999, 847–852 851 Table 3 Crystal and refinement data Compound Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 V/Å3 Z DC/g cm23 F(000) Crystal size/mm T (min, max) m cm21 NN r (Rint) No RR w 2 C30H10Co2O12W2 1048.0 Triclinic P1� 6.9570(8) 12.280(1) 18.768(2) 99.267(2) 96.708(2) 94.144(2) 1564.9 2 2.224 976 0.37 × 0.10 × 0.10 0.53, 0.91 84 18066 7621 (0.048) 6299 0.048 0.056 3 C36H10Co4O18W2? CH2Cl2 1418.8 Triclinic P1� 9.753(2) 11.498(1) 12.046(2) 108.760(2) 103.562(2) 111.034(2) 1096.3 1 2.149 668 0.55 × 0.35 × 0.12 0.47, 0.77 69.0 12368 5322 (0.025) 4442 0.026 0.032 4 C53H32Co2O10P2W2? 0.5C6H6 1415.4 Triclinic P1� 13.656(2) 14.520(2) 15.450(2) 100.616(3) 103.489(3) 113.166(3) 2605 2 1.804 1366 0.20 × 0.10 × 0.04 0.65, 0.88 52 30621 12876 (0.029) 7498 0.040 0.039 5 C82H54Co4O14P4W2? 2CH2Cl2 2160.5 Monoclinic C2/c 19.256(2) 14.656(2) 30.588(4) 105.234(2) 8321 4 1.724 4232 0.2 (cuboid) 0.76, 0.89 38.0 44221 10489 (0.023) 7746 0.034 0.041 6 C82H54Co4O14P4W2? 2C6H6 2146.9 Monoclinic P21/c 18.304(1) 14.0866(8) 18.729(1) 115.739(1) 4350 2 1.639 2116 0.20 × 0.18 × 0.14 0.582, 0.773 35.2 44160 10855 (0.045) 6205 0.040 0.041 benzene solvate suitable for the X-ray study were obtained from CH2Cl2–benzene–hexane (Found: C, 47.23; H, 2.70; C53H32Co2- O10P2W2?0.5C6H6 calcd.: C, 47.52; H, 2.49%).IR (cyclohexane) n(CO) 2047w, 2038m, 2010m, 1995s, 1967s, 1955s, 1943m cm21. 1H NMR (CDCl3); d 3.30, 3.65 (2 × m, 2H, CH2P), 5.66, 5.78 (2 × s, 10H, Cp), 6.97–7.36 (m, 20H, Ph). Decomplexation of 2 A mixture of 2 (20 mg, 0.019 mmol) and [NH4]2[Ce(NO3)6] (35 mg, 0.064 mmol) in acetone (10 ml) was stirred at r.t.for 2 h. The initial black solution became orange over this time. Evaporation, extraction of the residue with CH2Cl2 (3 × 50 ml) and washing the extracts with water (2 × 100 ml) and evaporation of the dried (MgSO4) organic phase gave 1 (7 mg, 50%), identi- fied by 1H NMR [d(CDCl3) 5.63 (Cp); lit.,12 d 5.67]. Crystallography Full spheres of data were measured at ca. 300 K to 2qmax = 588 using a Bruker AXS CCD instrument (monochromatic Mo-Ka radiation, l 0.71073 Å); N data were measured and reduced to Nr independent reflections, No with |F| > 4s(F) being considered ‘observed’ and used in the full matrix least squares refinement after ‘absorption correction’ (proprietary software SADABS).22 Anisotropic thermal parameters were refined for the nonhydrogen atoms; (x, y, z, Uiso)H were included constrained at estimated values. Conventional residuals R, R9 on |F| are quoted, statistical weights derivative of s2(I) = s2(Idiff) 1 0.0004s4(Idiff) being used.Computation used the XTAL 3.4 program system23 implemented by S. R. Hall; neutral atom complex scattering factors were employed. Pertinent results are given in the figures and Table 3. Special features 3. DiVerence map residues were modelled in terms of a molecule of dichloromethane, population constrained at unity after trial refinement, but disordered about an inversion centre. 4 DiVerence map residues were modelled in terms of benzene of solvation, disposed about a crystallographic centre of symmetry, site occupancy set at unity after trial refinement. 5 DiVerence map residues were modelled in terms of a molecule of dichloromethane disordered over two sets of sites, total occupancy constrained at unity after trial refinement, occupancies of the individual components being x, 1 2 x, with x = 0.57(1). 6 DiVerence map residues were modelled in terms of benzene of solvation, site occupancy set at unity after trial refinement.CCDC reference number 186/1311. See http://www.rsc.org/suppdata/dt/1999/847/ for crystallographic files in .cif format. Acknowledgements We thank the Australian Research Council for financial support. References 1 U. H. F. Bunz, Angew. Chem., 1996, 108, 1047; Angew. Chem., Int. Ed. Engl., 1996, 35, 969. 2 G. Frapper and M. Kertesz, Inorg. Chem., 1993, 32, 732. 3 W. Beck, B. Niemer and M. Wieser, Angew.Chem., 1993, 105, 969; Angew. Chem., Int. Ed. Engl., 1993, 32, 923. 4 H. Lang, Angew. Chem., 1994, 106, 569; Angew. Chem., Int. Ed. Engl., 1994, 33, 547. 5 J. S. Schumm, D. L. Pearson and J. M. Tour, Angew. Chem., 1994, 106, 1445; Angew. Chem., Int. Ed. Engl., 1994, 33, 1360. 6 N. Le Narvor, L. Toupet and C. Lapinte, J. Am. Chem. Soc., 1995, 117, 7129. 7 M. Brady, W. Weng, Y. Zhigou, J. W. Seyler, A. J. Amoroso, A. M. Arif, M. Böhme, G. Frenking and J. A. Gladysz, J. Am. Chem. Soc., 1997, 119, 775. 8 T. Bartik, B. Bartik, M. Brady, R. Dembinski and J. A. Gladysz, Angew. Chem., 1996, 108, 467; Angew. Chem., Int. Ed. Engl., 1996, 35, 414. 9 D. Osella, L. Milone, C. Nervi and M. Ravera, J. Organomet. Chem., 1995, 488, 1. 10 N. DuVy, J. McAdam, C. Nervi, D. Osella, M. Ravera, B. H. Robinson and J. Simpson, Inorg. Chim. Acta, 1996, 247, 99. 11 D. Osella, L. Milone, C. Nervi and M. Ravera, Eur. J. Inorg. Chem., 1998, 1473. 12 M. I. Bruce, M. Ke, P. J. Low, B. W. Skelton and A. H. White, Organometallics, 1998, 17, 3539. 13 M. Brady, W. Weng and J. A. Gladysz, J. Chem. Soc., Chem. Commun., 1994, 2655. 14 F. Coat and C. Lapinte, Organometallics, 1996, 15, 477. 15 D. Seyferth, M. O. Nestle and A. T. Wehman, J. Am. Chem. Soc., 1975, 97, 7417. 16 P. Magnus and D. P. Becker, J. Chem. Soc., Chem. Commun., 1985, 640. 17 B. F. G. Johnson, J. Lewis, P. R. Raithby and D. A. Wilkinson, J. Organomet. Chem., 1991, 408, C9. 18 C. J. McAdam, N. W. DuVy, B. H. Robinson and J. Simpson, Organometallics, 1996, 15, 3935.852 J. Chem. Soc., Dalton Trans., 1999, 847–852 19 J. Lewis, B. Lin, M. S. Khan, M. R. A. Al-Mandhary and P. R. Raithby, J. Organomet. Chem., 1994, 484, 161. 20 W. Henderson, J. S. McIndoe, B. K. Nicholson and P. J. Dyson, J. Chem. Soc., Dalton Trans., 1998, 519. 21 L. S. Chia and W. R. Cullen, Inorg. Chem., 1975, 14, 482. 22 G. M. Sheldrick, SADABS, University of Göttingen, 1996. 23 S. R. Hall, G. S. D. King and J. M. Stewart (Editor), The XTAL 3.4 Users’ Manual, University of Western Australia, Lamb, Perth, 1994. Paper 8/