Mixed-Valence Dirhenium Alkylidyne Complexes of the Type [Re2(.mu

Aug 22, 1994 - PFe, SO3CF3) have been formed via the ring-opening reactionsof the ... Conversion to Dirhenium. Alkylidyne Complexes (Anions X = PFe or...
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Organometallics 1995, 14, 448-455

448

Mixed-Valence Dirhenium Alkylidyne Complexes of the Type [Re2@-Cl)@-CO)(=CCH2R)C12(L)@-dppm)21n+(R = n-Pr, n-Bu; L = CO, xylNC; n = 0 , l ) Possessing Very Unsymmetrical Structures David A. Kort, Keng-Yu Shih, Wengan Wu, Phillip E. Fanwick, and Richard A. Walton" Department of Chemistry, Purdue University, 1393 Brown Building, West Lafayette, Indiana 47907-1393 Received August 22, 1994@

A series of mixed-valence, unsymmetrical, dirhenium alkylidyne complexes of the type

[(L)C!lRe(p-Cl)(p-CO)(p-dppm)2Re(cCCH2R)Cl]X (dppm = Ph2PCH2PPh2; L = CO, xylNC; R = n-Pr, n-Bu; X = PFs, S03CF3) have been formed via the ring-opening reactions of the These paramagnetic 3-metallafuran complexes [Re2OL-Cl)(p-COC(R)CH)C12(L)~-dppm)21X. complexes (one unpaired electron) can be reduced to their diamagnetic congeners (L)ClRe&-Cl)(p-CO)(p-dppm)2Re(=CCH2R)Cl, which show well-defined lH and 31PNMR spectra. X-ray crystallographic structure determinations have been carried out on representative members of the ionic and neutral sets of complexes, uzz., [Re2(p-Cl)(p-CO)(=CCHz-nBu)Cl2(CNxyl)(p-dppm)2lSO&F3~.5CH2C12(7d)and Re2Cu-Cl)(p-COX=CCH2-n-~)Cl2(CNxyl)(pdppm)2*2CHzCl2(8a). The structures of the dirhenium units in these two compounds are essential1 the same; the principal difference is the Re-Re distance, which increases from 2.817(2) in 7d to 3.039(1) 8, in 8a. The Re=C distances involving the alkylidyne ligands are typical for this type of unit (1.74(3) in 7d;1.70(1) in 8a). Both complexes have a semibridgin CO ligand, the Re-C distances being 1.93(3) and 2.57(4) in 7d and 1.87(1) and 2.62(1) in 8a. Crystal data for 7d: space group Pnma (No. 62) with a = 24.482(5) b = 15.377(3) c = 17.904(4) V = 6740(4) A3,and 2 = 4. The structure was refined to R = 0.056 (R, = 0.069) for 2650 data with I > 3.OdI). Crystal data for 8a: space group Pnma (No. 62) with a = 24.383(4) b = 15.420(3) c = 17.614(3) A, V = 6622(4) A3,and 2 = 4. The structure was refined to R = 0.034 (R,= 0.042) for 3569 data with 1 > 3.0 40.

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Introduction

We have recently described1s2 novel cases of COalkyne coupling in which the edge-sharing bioctahedral dicarbonyl complex Re2(D-Cl)(D-CO)Cl3(CO)(D-dppm)2 (1) and the analogous mixed carbonyl-isocyanide complex Re2(Li-Cl)(D-CO)Cl3(CNxyl)Ol-dppm)2 (2) react with terminal alkynes R C W H t o generate 3-metallafuran complexes (Scheme 1,step A). These reductively coupled products (L= CO (3);L = xylNC (4)) can be reduced to their paramagnetic, neutral congeners Re2(D-Cl)(D-COC(R)CH)C12(L)(Li-dppm)2 by cobaltocene. Studies of the reactivities of these interesting 3-metallafuran complexes are currently being pursued, and we now describe in full detail their conversion to a new class of mixedvalence dirhenium alkylidyne c~mplexes.~

A,

Scheme 1. Formation of 3-Metallafuran Complexes and Their Conversion to Dirhenium Alkylidyne Complexes (Anions X = PF6 or O S S C F ~) ~

reflux (L 24 h),

polar solvent

r

t

1

Experimental Section Starting Materials. The compounds Re2(p-Cl)(p-C0)CldCO&-dppm)z (l),Re2Cu-C1)Cu-13CO)C13(13CO)(p-dppm)z, Re2Cu-Cl)(p-CO)C4(CN~l)(p-dppm)z (21, [Re&-Cl)Cu-COC(R)CH)-

L = CO (6)or MNC (8)

L = CO(5) or M N C (7)

The p-dppm ligands are omitted for clarity. Abstract published in Advance ACS Abstracts, December 1,1994. (1) Shih, K.-Y.; Fanwick, P. E.; Walton, R. A. J . Am. Chem. SOC. 1993,115,9319. Fanwick, P. E.; Walton, R.A. Organometallics 1994, (2)Shih, IC-Y.; 13, 1235. (3) For a preliminary report of some of these results, see: Shih, K.Y.; Fanwick, P. E.; Walton, R. A. J. Chem. Soc., Chem. Commun. 1994, 861. @

Cl2(CO)(p-dppm)#F6 (R = n-Pr, sa; R = n-Bu, 3b),[Re&Cl)(p-COC(R)CH)Cl2(CNxyl)(p-dppm)z]PF6 (R= n-Pr, 4a;R = n-Bu, 4b)and Tl(S03CF3)were prepared according t o literature procedures.2-6 Alkynes were purchased from Aldrich Chemical Co. and were used without further purification. Solvents were obtained from commercial sources and deoxy-

Q276-7333/95/2314-Q448$09.QQ/Q 0 1995 American Chemical Society

Mixed-Valence Dirhenium Alkylidyne Complexes

Organometallics, Vol. 14, No. 1, 1995 449

genated prior to use. Syntheses were performed using stanProcedure b. A mixture of 1 (0.100 g, 0.075 mmol) and dard Schlenk techniques under an atmosphere of dry nitrogen. TlPF6 (0.040 g, 0.057 mmol) in acetone (15 mL) and CHzClz (5 mL) was treated with 1-pentyne(0.08mL) and heated at reflux A. Synthesis of [R~~~-CI)~-CO)(ICCH~R)C~~(CO)~for 24 h. The white precipitate (TlC1)was filtered off and the dppm)zlX (i) R = n-Pr, X = PF6 (Sa). Procedure a. A green filtrate treated with (v5-C5H&Co(0.015 g, 0.079 mmol). mixture of 1 (0.050 g, 0.037 mmol) and TlPF6 (0.02 g, 0.057 This mixture was then stirred at room temperature for 2 h mmol) in acetone (10 mL) was treated with 1-pentyne (0.07 and the green solid filtered off and washed with diethyl ether mL) and heated at reflux for 24 h. The white precipitate of (3 x 5 mL). This crude product was extracted into a minimum TlCl was filtered off and the green filtrate evaporated to volume of CHzClz (ca. 10 mL), and an excess of n-pentane (ca. dryness. The gray-green solid was extracted into ca. 2 mL of 50 mL) was added. This mixture was chilled to 0 "C to induce CHzClz, and the extract treated with diethyl ether (100 mL) crystallization; yield 0.049 g (48%). Anal. Calcd for C57H53t o induce precipitation. The green product was filtered off, C1308fiez: C, 49.87; H, 3.90. Found: C, 49.23; H, 3.82. washed with diethyl ether (3 x 5 mL), and dried in vacuo; yield 0.021 g (37%). (ii) R = n-Bu (6b). Procedure a. The use of [Rez@-Cl)@-CO)(=CCHZ-~-B~)C~~(CO)@-~~~~)Z]PF~ (5c;0.04 g, 0.026 Procedure b. A quantity of [Rez@-Cl)@-COC(n-Pr)CH)mmol) and a procedure analogous to that described in section Clz(CO)@-dppm)~]PF6 (3a;0.040 g, 0.026 mmol) in acetone (4 B(i), procedure a, produced the title complex; yield 0.027 g mL) was heated at reflux for 12 h. The green solution was (75%). then evaporated t o dryness. The addition of ca. 1mL of CH2Clz to this green residue, followed by 40 mL of diethyl ether, Procedure b. The use of 1-hexyne (0.08 mL) and a precipitated the title compound Sa. The solid was filtered off procedure and workup similar to that described in section B(i), and washed with diethyl ether (3 x 5 mL); yield 0.020 g (50%). procedure b, gave the title complex; yield 0.05 g (49%). Anal. This same reaction may also be carried out with either Calcd for C6oHsgC170zP4Rez (Le., RezC13(iCCHz-n-Bu)(C0)2acetonitrile or methanol as the reaction solvent. @-dppm)2*2CHzC12):C, 46.29; H, 3.82. Found: C, 46.83; H, 3.75. The presence of lattice CHzClz was confirmed by lH (ii) R = n-Pr, X = SOsCFs (Sb). A mixture of 1(0.112 g, NMR spectroscopy. 0.084 mmol) and Tl(S03CF3) (0.033 g, 0.093 mmol) in dichloromethane (10mL) was treated with 1-pentyne (0.1 mL) and C. Synthesis of the W-Labeled Complex Re&-Cl)(lrthen with concentrated HC1 (0.1 mL) and finally heated at 13CO)(~CCH2-n-Pr)C12(13CO)~-dppm)2. This labeled comreflux for 24 h. The white precipitate (TlC1) was filtered off plex was obtained starting from R ~ z @ - C I ) @ - ~ ~ C O ) C ~ ~ ( ~ ~ C O ) @ and the dark green filtrate evaporated to dryness. The green dppm)~(0.050 g, 0.037 mmol) by the use of the method in residue was extracted into ca. 2 mL of CHzClz and the extract section B(i), procedure a, via the intermediacy of [Rez@-Cl)@then layered with 40 mL of diethyl ether t o induce precipita13COX~CH~-n-Pr)C1~(13CO)Cu-dppm)~]PF6; yield 0.018 g (35%). tion of the title compound. The dark green solid was filtered D. Synthesis of CRe201-Cl)(lr-CO)(~CCHaR)Cl2(CNxyl)off, washed with diethyl ether (3 x 5 mL), and dried in vacuo; @-dppm)2lX(i) R = n-Pr, X = PF6 (7a). Procedure a. A yield 0.059 g (46%). Anal. Calcd for C5gH&l5F3O~P&zS (i.e., mixture of 2 (0.100 g, 0.069 mmol) and TlPF6 (0.04 g, 0.114 [ R ~ z C ~ ~ ( ~ C H Z - ~ - P ~ ) ( C O ) ~ @ - ~ ~ ~ ~C,) 44.10; ~ ~ S O ~ C mmol) F ~ C HinZacetone C ~ Z ) :(20 mL) was treated with 1-pentyne (0.08 H, 3.45. Found: C, 43.48; H, 3.36. The presence of lattice mL) and heated at reflux for 24 h. The white precipitate (TlCl) CHzClz was confirmed by 'H NMR spectroscopy. was filtered off and the green filtrate evaporated to dryness. (iii) R = n-Bu, X = PF6 (Sc). Procedure a. The use of The residue was extracted into CHzClz (ca. 2 mL) and excess 1-hexyne (0.07 mL) and a procedure and workup similar to diethyl ether (40 mL) added to induce precipitation. The green that described in section A(i), procedure a, produced the title solid was filtered off, washed with diethyl ether (10 mL), and compound; yield 0.018 g (30%). dried in vacuo; yield 0.050 g (45%). Anal. Calcd for C66H64Procedure b. The use of [Rez@-Cl)@-COC(n-Bu)CH)ClZCW&OP& (i.e., [RezC~(~CHz-n-PrXCO)(CNxylXu-dppm)zl(CO)@-dppm)z]PF6(3b;0.040 g, 0.026 mmol) and a procedure PF&H2C12: C, 46.47; H, 3.79. Found: C, 46.89; H, 3.83. The similar to that described in section A(i), procedure b, gave the presence of a small amount of lattice CHzClz was confirmed title complex; yield 0.018 g (45%). by lH NMR spectroscopy. (iv) R = n-Bu,X = SOsCF3 (Sd). A mixture of 1 (0.128 g, Procedure b. A solution of [Re&-Cl)@-COC(n-Pr)CH)ClZ0.095 mmol) and Tl(S03CF3) (0.035 g, 0.099 mmol) in dichlo(CNxyl)@-dppm)z]PF6(4a;0.040 g, 0.025 mmol) in CH3CN (5 romethane (10 mL) was treated with 1-hexyne (0.1 mL), mL) was heated at reflux for 24 h. The resulting green followed by concentrated HC1 (0.1 mL), and then heated at solution was reduced to ca. 2 mL by evaporation and diethyl reflux for 24 h. The title complex was isolated from the ether (40 mL) added to induce precipitation of the product. reaction mixture with the use of a procedure similar to that The green precipitate was filtered off, washed with diethyl described in section A(ii); yield 0.106 g (73%). Anal. Calcd ether (10 mL), and dried in vacuo; yield 0.012 g (30%). for C59 &&14F305P4Re~S (Le., [ R ~ Z C ~ ~ ( I C C H Z - ~ - B U ) ( C O ) ~ - (ii) R = n-Pr,X = SOsCFs (7b). A mixture of 2 (0.177 g, @-dppm)zlS03CF3.0.5CHzC12):C, 45.28; H, 3.58. Found: C, 0.123 mmol) and Tl(S03CF3) (0.045 g, 0.127 mmol) in dichlo45.54; H, 3.56. The presence of a small amount of lattice CHzromethane (10 mL) was treated with 1-pentyne (0.10 mL), Clz was confirmed by 'H NMR spectroscopy. followed by concentrated HCl (0.1 mL), and then heated at B. Synthesis of Re201-C1)01-CO)(~CCH2R)C12(CO)01- reflux for 24 h. The white precipitate (TlCl) was filtered off dppm)~.(i) R = n-Pr (6a). Procedure a. A mixture of [Rezand the dark green filtrate evaporated to dryness. The green @ - ~ ~ ) @ - C O ) ( ~ C C H Z - ~ - P ~ ) C ~ Z ( C (Sa) O ) Oand ~-~ (v5~ ~ ~ ) Zsolid ] P Fwas ~ extracted into ca. 2 mL of CHzClz and the extract C5H5)zCo (0.007 g, 0.037 mmol) in acetone (5 mL) was stirred then layered with 40 mL of diethyl ether to induce precipitaat room temperature for 2 h. The resulting green precipitate tion of the title compound. The dark green solid was then was filtered off and washed with diethyl ether (3 x 5 mL). filtered off, washed with diethyl ether (3 x 5 mL), and dried The crude product was extracted into CHzClz (ca. 5 mL) and in vacuo; yield 0.141 g (70%). Anal. Calcd for C66.5H63C14F3filtered through a glass frit. A n excess of n-pentane (30 mL) N04P4RezS (i.e., [RezC13(1CCHz-n-Pr)(CO)(CNxyl)@-dppm)~lwas added to the filtrate, which was then chilled to 0 "C for 1 S03CF3.0.5CHzCl~):C, 47.90; H, 3.81. Found: C, 47.74; H, h to yield the green title compound (ea);yield 0.025 g (70%). 3.94. The presence of lattice CHzClz was confirmed by lH NMR spectroscopy. (iii) R = n-Bu, X = PF6 (7c). Procedure a. The use of (4)Cotton, F. A.; Daniels, L. M.; Dunbar, K. R.; Falvello, L. R.; Tetrick, S. M.; Walton, R. A. J.Am. Chem. SOC.1985,107,3524. 1-hexyne (0.08 mL) and a procedure similar to that described (5)Cotton, F. A.; Dunbar, K. R.; Price, A. C.; Schwotzer, W.; Walton, in section D(i), procedure a, gave the title complex; yield 0.052 R.A. J . Am. Chem. SOC.1988,108,4843. g (46%). And. Calcd for C ~ & & ~ ~ F ~ N O P (i.e., & ~ Z[RezCls(6) Woodhouse, M. E.; Lewis, F. D.; Marks, T. J. J . Am. Chem. SOC. 1982,104,5586. ( I C C H Z - ~ - B ~ X C O ) ( C N ~ ~ ) @ - ~ ~ ~ ~ ) ZC,~46.79; PF~H H,Z C ~ Z ) :

450 Organometallics,

Vol. 14,No.1, 1995

Kort et al.

Table 1. Crystallographic Data for [Re&-Cl)@-C0)3.88. Found: C, 46.85; H, 3.90. The presence of a small (=CCH2-n-Bu)Clz(CNxyl)~-dppmh]SO~CF~.0.5CH~Cl~ (7d) amount of lattice CHzClz was confirmed by 'H NMR spectrosand Re201-Cl)@-CO)(~CCH2-n-h.)Cl2(CNxyl)COPY. @-dppm)z*2CHzCb(8a) Procedure b. A quantity of [Rez@-Cl)@-COC(n-Bu)CH)Clz(CNxyl)@-dppm)z]PF6(4b 0.040 g, 0.025 mmol) in metha7d 8a nol (5 mL) was heated at reflux for 24 h. The resulting green chem formula RezCbSP830flC67.5H6s RezCbP40NC67H66 solution was reduced to ca. 2 mL by evaporation and diethyl 1645.75 fw 1681.44 ether added (40 mL) to induce precipitation of the title space group Pnma (No. 62) Pnma (No. 62) compound. The green precipitate was filtered off, washed with 24.383(4) a, A 24.482(5) 15.420(3) b, 8, 15.377(3) diethyl ether (10 mL), and dried in vacuo; yield 0.018 g (45%). 17.614(3) C, A 17.904(4) Procedure c. A solution of [Rez@-Cl)@-COC(n-Bu)CH)6622(4) v, A 3 6740(4) (CNxyl)@-dppm)z]PF6(4b;0.030 g, 0.019 mmol) in acetone (4 Z 4 4 mL) was treated with 60% aqueous HPF6 (0.10 mL) and heated T,K 293 293 at reflux for 24 h. The resulting solution was reduced to ca. 2 0.710 73 0.710 73 A, 8, (Mo Ka) mL by evaporation and diethyl ether added (50 mL) to induce 1.650 ecnlcd,g c w 3 1.657 precipitation. Mer a period of ca. 20 min, the gray-greensolid 41.24 ~ ( M Ka), o cm-' 39.61 1.00-0.74 transmissn coeff 1.00-0.87 was filtered off, washed with diethyl ether (10 mL), and dried 0.034 Ra 0.056 in vacuo; yield 0.013 g (43%). 0.042 RWb 0.069 The analogous [BF4]- salt [Rez@-Cl)@-CO)(~CCHz-n-Bu)1.228 GOF 1.649 Clz(CNxyl)@-dppm)z]BF4can be prepared by the use of a procedure similar to that described above, except that the 60% a R = CIIFoI - lFcllEl~ol. Rw = {Cw(lF0l - IFol)~EwlFo12}'~; w= l/~Z(IFol). aqueous HPF6 is replaced by 0.10 mL of 85% HBF4.EtzO. (iv) R = n-Bu,X = SOsCFs (7d). A mixture of 2 (0.093 g, by the diffusion of n-heptane into a dichloromethane solution 0.064 mmol) and Tl(S03CF3) (0.025 g, 0.071 mmol) in dichloof this complex. romethane (10 mL) was treated with 1-hexyne(0.05 mL) and X-ray Crystallography. The structures of 7d and 8a were concentrated HCl(O.1mL) and then heated at reflux for 24 h. determined at mom temperature by the application of standard The title complex was isolated from this reaction mixture procedures. Each crystalused for data collection was mounted through the use of a procedure analogous to that given in on a glass fiber in a random orientation. The basic crystalsection D(ii); yield 0.071 g (67%). Anal. Calcd for C67.5H65' lographic for these two crystals are listed in Table N ~ ~ ~ )parameters C14F3N04PaezS (i.e., [ R ~ ~ C ~ ~ ( ~ C C H Z - ~ - B U ) ( C O ) ( C 1. The cell constants were based on 25 reflections in the range @-dppm)zlS03CFsG,5CHzCl~):C, 48.22; H, 3.90. Found: C, 9 < f3 c 19" for 7d and 20 c 0 < 23" for 8a, measured by the 48.22; H, 4.01. The presence of lattice CHzClz was confirmed computer-controlled diagonal slip method of centering. Three by 'H NMR spectroscopy. standard reflections were measured after every 5000 s of beam E. Synthesis of RenCu-Cl)(lr-CO)('CCHnR)Clz(CNxyl)time during data collection, and there were no systematic @-dppm)a. (i) R = n-Pr (8a). Procedure a. A mixture of variations in intensity. The data processing was performed [Re~@-Cl)@-CO)(rCCH~-n-Pr)Cl2(CNxyl)Cu-dppm)~lPF6 (0.04 on a microVAX I1 computer using the Enraf-Nonius MolEN g, 0.025 mmol) and (q5-C5H&Co (0.006 g, 0.032 mmol) in structure determination package. Lorentz and polarization acetone (6 mL) was stirred at room temperature for 2 h. The corrections were applied to both data sets, and an empirical resulting green precipitate was filtered off and washed with absorption correction was applied in each case; for 7d the diethyl ether (3 x 5 mL). This crude product was extracted method based on a series of scans was used, while for 8a into ca. 4 mL of CHzClz, and then filtered through a glass frit. the method used was that of Walker and Stuart.' Addition of diethyl ether (25 mL) to the solution and cooling 7d crystallized in the orthorhombic crystal system. The it to 0 "C for 1h yielded the green title compound; yield 0.026 systematic absences in the data set were consistent with both g (71%). Anal. Calcd for C66H64ClsNOP.&ez (i.e., Re&the Pna21 and the &ma space groups. Efforts to solve the (rCCHz-n-PrXCO)(CNxyl)@-dppm)zCHzClz): C, 49.80; H, 4.06. structure in the space group Pna21 were unsuccessful. The Found: C , 49.46; H, 4.16. The presence of a small amount of centric space group was therefore assumed and subsequently lattice CHzClz was confirmed by 'H NMR spectroscopy. confirmed by the successful solution and refinement of the Procedure b. A mixture of 2 (0.100 g, 0.069 mmol) and structure. The structure was solved by a combination of direct T1PF6 (0.040 g, 0.057 mmol) in acetone (20 mL) was treated methods (SHELX-86) and difference Fourier syntheses. The with 1-pentyne (0.08 mL) and heated at reflux for 24 h. The lattice was found t o contain four formula units of the complex white precipitate (TlCl) was filtered off and the green filtrate in the unit cell, and the cation and anion are thus required to treated with (q5-C&15)zCo(0.014 g, 0.074 mmol). This solution contain crystallographic planes of symmetry. Due to an was stirred at room temperature for 2 h. The green title obscure disorder at the end of the six-member alkylidyne compound was filtered off and washed with diethyl ether (3 x carbon chain, C(l)-C(6), the last carbon atom in this chain, 5 mL). This crude product was recrystallized from CHzClz and C(6), could not be refined to convergence. It was thus refined diethyl ether; yield 0.041 g (40%). with fixed parameters, and as a result, one of the carbon(ii) R = n-Bu (8b). Procedure a. This complex was carbon bond distances in this chain was extremely long (C(4)prepared from [Re2@-Cl)@-CO)(rCCHz-n-Bu)Clz(CNxyl)@C(5) = 1.74(9)&. The carbon atoms in this alkylidyne chain dppm)zlPFs (7c; 0.04 g, 0.025 mmol) following a procedure and in the isocyanide ligand were refined isotropically, while analogous to that described in section E(i), procedure a; yield the remaining non-hydrogen atoms were refined with aniso0.025 g (67%). Anal. Calcd for C66H&13NOP&z: c , 53.27; tropic thermal parameters. For the triflate anion, atoms H, 4.21. Found C, 53.02; H, 4.38. F(101), C(lOO), S, and O(1) were located on a mirror plane; Procedure b. The use of 1-hexyne (0.08 mL) and a the uniformly large anisotropic thermal parameters associated procedure analogous to that described in section E(i), procewith the atoms of this anion reflect its rather high thermal dure b, produced the title complex; yield 0.047 g (46%). motion, which may be a consequence of its relatively loose Preparation of Single Crystals. Crystals of [ReZ@-Cl)packing in the crystal. In the final stage of the structure @-CO)(=CCH~-n-Bu)Clz(CNxyl)@-dppm)zlSO~CF~G.5 CHzClz analysis, half a dichloromethane molecule from the crystal(7d) were obtained as dark brown plates by the diffusion of lization solvent was located; the solvent molecule was posidiisopropyl ether into a solution of 7d in dichloromethane while suitable dark cubic crystals of composition ReZ@-Cl)@(7) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A: Found CrysC0)(~CCH~-n-Pr)Cl~(CNxyl&-dppmh.2CH~Clz (8a)were grown tallogr. 1983,A39, 158.

Organometallics, Vol. 14,No.1, 1995 451

Mixed-Valence Dirhenium Alkylidyne Complexes tioned about a crystallographic mirror plane. It was included in the analysis and was satisfactorily refined anisotropically for its chlorine atoms (Cl(501)and Cl(502))and isotropically for its carbon atom (C(500)). Corrections for anomalous scattering were applied to all anisotropically refined atomsea Hydrogen atoms were not included in the calculations. The structure was refined in full-matrix least squares where the function minimized was Cw = (IFol - IFc/)2,where w is the weighting factor defined as w = 1/& lFol). The final residuals for 7d were R = 0.056 (R,= 0.069) and GOF = 1.649. The highest peak in the final difference Fourier was 1.55 e/A3. The structure of a crystal of 8a was determined as described for 7d. The structure was again solved satisfactorily in the centric space group Pnma with Z = 4;the neutral dirhenium unit was required to possess a crystallographic plane of symmetry. All carbon atoms of the alkylidyne ligand refined satisfactorily with anisotropic thermal parameters. Two independent CHzClz solvent molecules were found to be present in the crystal lattice. Both are located about mirror planes, one having its CClz unit in the plane while the other has the CClz angle bisected by the plane. These molecules were refined with full occupancy factors, and all six nonhydrogen atoms were refined with anisotropic thermal parameters. Corrections for anomalous scattering were applied to all anisotropically refined atomsSa All hydrogen atoms, except those of the CHzClz molecules, were introduced at calculated positions (C-H = 0.95 A, B = 1.3BC),not refined but constrained to ride on their C atoms. The structure was refined in full-matrix least squares where the function minimized was Cw = (IF,I - IF#, where w is the weighting factor The final residuals for 8a were R = defined as w = l/uz(~Fo~). 0.034 (R,= 0.042) and GOF = 1.228. The highest peak in the final difference Fourier was 0.83 e/A3. Physical Measurements. A Perkin-Elmer 1800 FTIR spectrometer was used to record the IR spectra of the compounds as mineral oil (Nujol) mulls. Electrochemical measurements were carried out on dichloromethanesolutions that contained 0.1 M tetra-n-butylammoniumhexafluorophosphate (TBAH) as supporting electrolyte. Eli2 values, determined as (Ep+ EPJ2, were referenced t o the silvedsilver chloride (Ag/ AgC1) electrode at room temperature and are uncorrected for junction potentials. Under our experimental conditions El12 = +0.47 vs Ag/AgCl for the ferroceniudferrocene couple. Voltammetric experiments were performed with a BAS Inc. Model CV-27 instrument in conjunction with a BAS Model RXY recorder. The 31P{1H}NMR spectra were obtained with use of a Varian XL-2OOA spectrometer operated at 80.98 MHz or a GE QE-300 spectrometer equipped with a multinuclear Quad probe operated at 121.5 MHz with 85% as an external standard. lH and l3C{lH) NMR spectra were obtained on a GE QE-300 spectrometeroperated at 300 and 75.61 MHz, respectively. Proton resonances were referenced internally t o the residual protons in the incompletely deuteriated solvent. The 2H{1H}NMR spectra were recorded (in CHZClz) with the use of a Varian XL-2OOA spectrometer. Magnetic susceptibility measurements were carried out by the Evans m e t h ~ d .X-Band ~ ESR spectra were recorded at ca. -160 “C with the use of a Varian E-109 spectrometer. Elemental microanalyses were performed by Dr. H. D. Lee of the Purdue University Microanalytical Laboratory. Microanalyses of representative samples of the dirhenium alkylidyne complexes of types 5-8 were obtained.

+

Results When solutions of the 3-metallafuran complexes 3 a n d 4 (R = n-Pr or n-Bu) a r e refluxed i n polar solvents (8) (a)Cromer, D. T. International Tables for X-ray Crystallography; Kynoch Birmingham, England, 1974; Vol. N, Table 2.3.1. (b) For the scattering factors used in the structure solution, see: Cromer, D. T.; Waber, J. T. in ref 8a, Table 2.2B. (9) Evans, D. F. J . Chem. SOC.1969,2003.

Table 2. Positional Parameters and Equivalent Isotropic Displacement Parameters (A2)for the Non-Phenyl Group Atoms of the Dirhenium Cation of 7d and Their Estimated Standard Deviation9 0.15790(5) 0.26294(5) 0.0632(3) 0.3119(3) 0.1777(3) 0.1530(2) 0.2667(2) 0.2716(8) 0.3841(8) 0.157( 1) 0.162(2) 0.1 15(2) 0.129(3) 0.060(3) 0.06443 0.258(1) 0.2216(7) 0.343(1) 0.443(1) 0.453(2) 0.514(2) 0.54 l(2) 0.534(2) 0.474(2) 0.414(2) 0.460(2)

114 114 114 114 114 0.088 l(3) 0.0907(3) 114 1I4 114 114 114 114 1I4 1I4 114 0.043(1) 114 114 1I4 114 114 1I4 114 114 114

0.91397(6) 0.84973(6) 0.8877(5) 0.73lO(4) 0.7760(4) 0.9141(3) 0.8478(2) 1.018(1) 0.905(1) 1.011(2) 1.090(2) 1.143(3) 1.233(4) 1.257(4) 1.34728 0.957(1) 0.921(1) 0.888(2) 0.921(2) l.Ooo(2) 1.018(3) 0.945(3) 0.876(3) 0.854(3) 1.055(2) 0.775(2)

3.40(2) 3.02(2) 5.4(2) 5.1(2) 4.4(2) 3.6(1) 3.10(9) 5.2(5) 3.6(5) 4.7(6)* 7.8(9)* 14(2)* 19(2)* 16(2)* 20* 4.2(6) 4.0(4) 4.9(7) 5.8(7)* 9(u* 12(1)* 12(1)* 12(1)* 11(1)* 9(1)* 8(1)*

Anisotropically refined atoms are given in the form of the isotropic equivalent thermal parameter defined as (41~)[a2~(l,l) bzp(2,2) $B(3,3) &(cos y)B(1,2) ac(cos B)p(1,3) bc(cos a)B(2,3)]. Data for the phenyl group atoms of the dppm ligands, the atoms of the triflate anion, and the atoms of the lattice dichloromethane molecule are available as supplementary material. An asterisk denotes a value for an isotropically refined atom.

+

+

+

+

+

(acetone, methanol, a n d acetonitrile were used) for periods of u p to 24 h, t h e dirhenium alkylidyne complexes of types 5 a n d 7 can be isolated in yields of 3050% upon t h e addition of diethyl ether to the green reaction solutions (Scheme 1, step B). An alternative a n d more convenient procedure is to heat t h e reaction mixtures that a r e known to produce2 t h e 3-metallafuran complexes 3 a n d 4 from the precursors 1 a n d 2 for periods in excess of 24 h (Scheme 1, step C). This strategy avoids the necessity of isolating the “intermediate” complexes 3 and 4 and gives 5 and 7 in isolated yields of 30-70%. The complexes 5 a n d 7 display terminal v(CN)t or v(C0)t modes in their IR spectra at ca. 2150 a n d ca. 2035 cm-l, respectively, as well as a bridging Y(C0)b mode close to 1800 cm-l (Table 6). The v(P-F) mode of t h e [PF& anion is found at ca. 840 cm-l in t h e spectra of 5a,5c, 7a, a n d 7c, while for t h e [SO&FJ- salts 5b, 5d,7b, a n d 7d,there is a characteristic anion mode at ca. 1260 cm-l. The cyclic voltammetric properties of solutions of all six complexes of types 5 a n d 7 i n 0.1 M TBAH/CH&12 a r e very similar to one another (see Table 6). Each shows a reversible one-electron oxidation a n d a reversible one-electron reduction with ip,a= iP+a n d AE (i.e., Ep,a- Ep,J= 60-70 mV at a sweep rate of 200 mVfs. The carbonyl-containing complexes 5a-5d also show an irreversible reduction at of ca. -1.8 V. T h e two reversible processes are s h f t e d to more negative potentials by between 360 and 240 mV on changing from L = CO (5) to L = xylNC ( 7 ) ;this reflects t h e greater n-acceptor properties of CO (compared to xylNC), which

452 Organometallics, Vol. 14, No. 1, 1995

Kort et al.

Table 3. Positional Parameters and Equivalent Isotropic Displacement Parameters (Az)for the Non-Phenyl Group Atoms of the Dirhenium Molecule of 8a and Their Estimated Standard Deviatiow atom

X

Y

0.23541(2) 0.34833(2) 0.1938(1) 0.4457( 1) 0.3249( 1) 0.23353(8) 0.34841(8) 0.2291(3) 0.1128(4) 0.2789(3) 0.2433(5) 0.3485(5) 0.3427(6) 0.3930(7) 0.3921(9) 0.439( 1) 0.1582(4) 0.0569(5) 0.0412(6) -0.0165(8) -0.0514(7) -0.0353(6) 0.0215(6) 0.0810(8) 0.0398(7)

114 114 114 114 114 0.0938(1) 0.0933(1) 114 114 0.0490(5) 114 114 114 114 114 114 114 114 114 114 114 114 114 114 114

Z

B

0.2785(2) 0.1030(2) 0.2179(1) 0.1466(1) 0.0766(1) -0.0215(4) 0.1030(5) 0.0729(4) 0.0449(6) -0.0195(6) -0.1033(7) -0.1478(8) -0.230( 1) -0.273( 1) 0.1205(6) 0.0868(8) O.Oll(1) -0.002( 1) 0.058(2) 0.130(1) 0.149(1) -0.0527(9) 0.227(1)

2.162(8) 2.322(8j 3.66(6) 3.74(6) 2.99(5) 2.56(4) 2.61(4) 4.1(2) 3.9(2) 2.7(2) 3.2(2) 333) 5.4(4) 7.1(4) 12.9(9) 16(1) 2.8(2) 5.0(3) 7.2(4) 11.3(7) 14.9(9) 10.2(7) 6.5(4) 8.4(5) 8.4(5)

Anisotropically refined atoms are given in the form of the isotropic equivalent thermal parameter defined as (413)[a2,!?(l,l) b2/?(2,2) &?(3,3) &(cos y)/3(1,2) ac(cos ,!?),!?(1,3) bc(cos a),8(2,3)]. Data for the phenyl group atoms of the dppm ligands and the atoms of the lattice dichloromethane molecules are available as supplementary material.

+

+

+

+

+

Table 4. Selected Bond Distances (A) and Bond Angles (dee) for the Dirhenium Cation of 7da Re( 1)-Re(2) Re( 1)-C1( 1) Re( l)-Cl(B) Re( l)-P(l) Re( 1)-C( 1) Re(1)-C(10) Re(2)-C1(2) Re(2)-Cl(B) Re(2)-P(2) Re(2)-C( 10) Re(2)-Re(l)-C1(1) Re(2)-Re(l)-Cl(B) Re(2)-Re(l)-P(1) Re(2)-Re(l)-C(l) Cl(1)-Re(1)-Cl(B) Cl(1)-Re(1)-P(1) Cl(1)-Re(1)-C(1) Cl(B)-Re(1)-P(1) Cl(B)-Re(1)-C(1) P( 1)-Re( 1)-C(l) Re(l)-Re(2)-C1(2) Re( 1)-Re(2)-Cl(B) Re(l)-Re(2)-P(2) Re(l)-Re(Z)-C(lO) Re(l)-Re(2)-C(20) C1(2)-Re(2)-Cl(B) C1(2)-Re(2)-P(2)

Distances 2.8 17(2) Re(2)-C(20) 2.366(8) O(10)-C( 10) 2.518(7) N-C(20) 2.492(5) N-C(601) 1.74(3) C(l)-C(2) 2.57(4) C(WC(3) 2.439(7) C(3)-C(4) 2.469(8) C(4)-C(5) 2.451(5) C(5)-C(6) 1.93(3) Angles 144.4(2) C1(2)-Re(2)-C(10) 54.8(2) C1(2)-Re(2)-C(20) 92.5(1) Cl(B)-Re(2)-P(2) 115(1) Cl(B)-Re(2)-C(lO) 89.6(3) Cl(B)-Re(2)-C(20) 87.3(1) P(2)-Re(2)-C(10) lOl(1) P(2)-Re(2)-C(20) 90.6(1) C(lO)-Re(2)-C(20) 170(1) Re(1)-Cl(B)-Re(2) 89.9(1) C(20)-N-C(601) 143.5(2) Re(l)-C(l)-C(2) 56.4(2) C( l)-C(2)-C(3) 92.3(1) C(2)-C(3)-C(4) 62(1) C(3)-C(4)-C(5) 136.8(9) C(4)-C(5)-C(6) 87.1(3) Re(2)-C(10)-0(10) 88.2(1) Re(2)-C(20)-N

2.08(4) 1.13(3) 1.04(3) 1.47(4) 1.41(5) 1.49(6) 1.64(8) 1.74(9) 1.60(7)

154(1) 79.7(9) 91.4(1) 119(1) 166.8(9) 90.9(1) 88.2(1) 74(1) 68.8(2) 175(3) 174(3) 125(4) 117(6) 93w lOl(5) 160(3) 178(3)

Numbers in parentheses are estimated standard deviations in the least significant digits.

results in a higher positive charge a t the dirhenium core in the case of L = CO. The accessibility of the reduction (E1dred) in Table 6) has been shown by the reduction of 5 and 7 to their neutral congeners 6 and 8 through the use of cobaltocene as the reducing agent (Scheme

Table 5. Selected Bond Distances (A) and Bond Angles (deg) for 8@ Distances 3.0391(6) Re(2)-C(21) 2.475(3) Re(2)-C(ll) 2.485(3) 0(12)-C(ll) 2.409(2) N(30)-C(30) 1.87(1) N(30)-C(31) 1.95(1) C(21)-C(22) 2.417(3) C(22)-C(23) 2.542(3) C(23)-C(24) 2.417(2) C(24)-C(25)

Re(1)-Re(2) Re(1)-Cl(1) Re(1)-Cl(B) Re( 1)-P(l) Re(1)-C(11) Re(l)-C(30) Re(2)-C1(2) Re(2)-Cl(B) Re(2)-P(2) Re(2)-Re(l)-Cl( 1) Re(2)-Re(l)-Cl(B) Re(2)-Re(l)-P( 1) Re(2)-Re(l)-C(ll) Re(2)-Re(l)-C(30) Cl(l)-Re( 1)-Cl(B) Cl( 1)-Re( 1)-P(l) Cl(1)-Re(1)-C(l1) Cl(1)-Re( 1)-C(30) Cl(B)-Re( 1)-P( 1) Cl(B)-Re(1)-C(l1) Cl(B)-Re( 1)-C(30) P( 1)-Re(1)-P(1) P(1)-Re(1)-C(l1) P( 1)-Re( 1)-C(30) C( 11)-Re( 1)-C(30) Re( l)-Re(2)-C1(2)

Angles 139.23(7) Re(l)-Re(2)-Cl(B) 53.67(6) Re(l)-Re(2)-P(2) 90.34(5) Re(l)-Re(2)-C(21) 59.0(4) C1(2)-Re(2)-Cl(B) 139.4(3) C1(2)-Re(2)-P(2) 85.6(1) C1(2)-Re(2)-C(21) 90.95(5) Cl(B)-Re(2)-P(2) 161.7(4) Cl(B)-Re(2)-C(21) 8 1.4(3) P(2)-Re(2)-P(2) 91.69(5) P(2)-Re(2)-C(21) 112.7(4) Re(1)-Cl(B)-Re(2) 166.9(3) Re(l)-C(ll)-O(l2) 176.2(1) Re(2)-C(21)-C(22) 88.59(5) C(21)-C(22)-C(23) 88.54(5) C(22)-C(23)-C(24) 80.3(5) C(23)-C(24)-C(25) 144.12(8) Re(l)-C(30)-N(30)

1.70(1) 2.62(1) 1.22(1) 1.15(1) 1.39(2) 1.48(2) 1.46(2) 1.45(2) 1.37(3) 5 1.94(6) 90.16(5) 115.2(4) 92.2(1) 90.01(5) 100.7(4) 90.29(5) 167.1(4) 179.4(1) 89.7 l(5) 74.39(7) 158(1) 174(1) 117(1) 122(2) 122(2) 180.0(9)

a Numbers in parentheses are estimated standard deviations in the least significant digits.

1, step D). This can be accomplished either by the treatment of samples of 5 and 7 with an acetone solution of (g5-C5H&Co or by the addition of cobaltocene to solutions of 5 and 7 that had been generated directly from 1 and 2, respectively, via 3 and 4. The complexes of types 6 and 8 , Rez@-Cl)@-CO)(WCHzR)Clz(L)@-dppm)z(L = CO or xylNC), have v(C0) and Y(CN)bands in their IR spectra (recorded as Nujol mulls) that are a t frequencies lower than the corresponding modes in the spectra of 5 and 7 (Table 6). This reflects the increase in the extent of Re CO(n*) and Re CNxyl(n*) back-bonding in the more electron-rich neutral complexes 6 and 8. The 13Clabeled complex R~z@-C~)@-~~CO)(=CCHZ-~-P~)C~Z(13C0)@-dppm)~ shows the expected shift of the two v ( C 0 )bands to lower frequencies (1944(8)and 1762 (m) cm-l) compared to what is observed with the 12C-labeled derivative 6a (1987(s) and 1804 (m) cm-l). The very close relationship between the pairs of 5, 6 and 7, 8 is further demonstrated by the cyclic voltammetric properties of these sets of complexes (Table 6). The only difference within each pair is that the reduced complexes (6 and 8 ) have processes at +0.29 and f0.03 V, respectively, that correspond t o oxidations of the bulk complexes, whereas they are reductions in the case of 5 and 7 (Table 6). The ionic species 5 and 7 are paramagneticlOJl and display only very broad peaks in their IH NMR spectra. In contrast, their neutral congeners of types 6 and 8 are diamagnetic and exhibit well-defined IH and 31PPH} NMR spectra, the latter having the appearance of AA'BB' patterns (Table 7). The room-temperature

-

-

~

~~~~~~

(10)A magnetic moment determination on a chloroform solution of 7d a t room temperature by the Evans methode gave a value of p e r = 1.8(+0.1)p ~ . (11)A dichloromethane solution of 7c (at -160 "C) gave a broad anisotropic signal centered at g = 2.17 showing Re hyperfine.

Mixed-ValenceDirhenium Alkylidyne Complexes

Organometallics, Vol. 14, No. 1, 1995 453

Table 6. Electrochemical and Infrared Spectral Data for Alkylidyne Complexes of the Types

[Re2@-Cl)@-CO)(sCCH2R)C12(L)@-dppm)2]X and Rez0r-Cl)@-CO)(~CCH2R)Cl,(L)@-dppm)z(R = n-Pr, n-Bu; L = CO, VlNC; X = PFa, SO3CF3) CV half-wave potentials,' V complex 5a

5b 5C

5d 6a

6b 7a

7b 7c

7d 8a

8b

R n-Pr n-Pr n-Bu n-Bu n-Pr n-Bu n-Pr n-Pr n-Bu n-Bu n-Pr n-Bu

L CO CO CO CO CO CO xylNC xylNC xylNC xylNC xylNC xylNC

X PFs SO3CF3 pF6 S03CF3 PF6 SO3CF3 PF6 SO3CF3

EI~OX) +1.17(70) +1.18(60) 1.18(70) +1.19(60) +1.19(70) +1.19(60) +0.86(60) +0.86(60) +0.82(60) +0.85(70) +0.86(60) +0.86(60)

+

Eldred) +0.27(60) +0.27(60) +0.28(70) +0.26(70) +0.29(60)c +0.29(60)c +0.03(60) +0.01(60) +0.02(60) +0.00(70) +0.03(60)c +0.03(60)c

Ew -1.80 -1.85 -1.85 -1.80 - 1.84 -1.85

IR spectra: cm-' v(CN)t

2152 (s) 2150 (s) 2155 (s) 2150 (s) 2078 (s) 2078 (s)

v(CO)r 2036 (s) 2038 (s) 2032 (s) 2036 (s) 1987 (s), 1963 (m, sh) 1990 (s)

V(c0)b

1816 (m) 1820 (m) 1831 (m, br) 1814 (m) 1804 (m) 1804 (m) 1826 (m, sh), 1802 (m) 1794 (m) 1820 (m, br) 1798 (m) 1785 (m) 1785 (m)

-

a Measured on 0.1 M TBAWCHCL solutions and referenced to the Ag/AgCl electrode with a scan rate (Y)of 200 mV/s at a Pt-bead electrode. Under our experimental conditions, E112 = +0.47 V vs Ag/AgCl for the ferroceniudferrocene couple. In all cases, ip.8% ip,c. The Ep,%- Ep,cvalues (in mV) are given in parentheses. IR spectra recorded as Nujol mulls. E ~ / ~ ( ovalue. x)

complex

Table 7. 'H and 31P{1H}NMR Spectral Data for the Diamagnetic Alkylidyne Complexes of the Type Re2gl-Cl)gl-CO)(=CCH2R)C12(L)glIdppm)2 (R = n-Pr, n-Bu; L = CO, xylNC) R L 'H NMR,"6 3 1

6a

n-Pr

6b

n-Bu

co co

8a

n-Pr

xylNC

8b

n-Bu

xylNC

~ NMR: ~ ~

0.03 (m, 2 H), 0.40 (t. 3 HLC0.47 (m, 4 HhC3.39 (m, 2 H),d 4.19 (m, 2 H).d -6.6, 6.90-7.90 (m, 40 H)' 0.05 (m,2H),0.42(p,2H),0.64(t,3H),C0.77(m,4H),'3.40(m,2H),d4.20 -6.6, (m, 2 Hhd 6.90-7.90 (m, 40 H)' 0.07 (m, 2 H), 0.35 (t, 3 H), 0.42 (m, 4 H), -2.15 (vbr, 6 H), 3.40 (m, 2 H)$ -6.7; 4.19 (m, 2 H),d 6.50-8.00 (m, 43 H)e -0.02 (m, 2 H), 0.43 (m, 2 H), 0.64 (t, 3 H),C -0.69 (vbr, 2 H),C0.77 (m, 2 H), -4.6; 1.79 (s, 6 H), 3.43 (m, 2 H),d4.22 (m, 2 H)$6.50-7.90 (m, 43 H)'

61

-12.8 -13.0 -13.0 -13.2

' Spectra were recorded in CD2C12. The appearance of the spectra and the relative intensities are indicated in parentheses: s, singlet; d, doublet; t, triplet; p, pentet; m, multiplet; vbr, very broad. Spectra were recorded in CDzClz and have the appearance of AA'BB' patterns; the chemical shifts quoted are those of the center components of the two multiplets. Overlapping multiplets. Resonances of the CH2 units of the dppm ligands. e Resonances of the phenyl ring protons.

13C{IH}spectrum of Re2@-C1)@-13CO)(=CCH2-n-Pr)C12(13CO)@-dppm)2 (recorded in CD2C12) shows broad resonances at d = +183 and d = +193 that are assiened12 to the terminal and bridging CO ligands, respectively, which are bound to a dirhenium unit. However, we did not observe the natural-abundance carbyne-carbon resonance even with the use of very long data acquisition times. The structural identities of representative members of the two sets of complexes of types 5 , 7 and 6 , s were established by single-crystal X-ray structure analyses. An ORTEP representation of the structure of the Figure 1. ORTEP representation of the structure of the [Re~(u-Cl)@-CO)(~CCH~-n-Bu)C12(CNxyl)(u-dppm)~l+ catdirhenium cation [R~~@-C~)@-CO)(ECCH~-~-BU)C~~ion as present in complex 7d with the phenyl group atoms (CNxyl)@-dppm)21+,present in the triflate salt 7d,is of the dppm ligands omitted. The thermal ellipsoids are shown in Figure 1. The structure is that of a distorted drawn at the 50%probability level. edge-shared bioctahedron. Although two different batches of good-quality single crystals of the neutral Re-Re distance found t o be ca. 3.0 A. After a number dicarbonyl complex 6a were obtained from CHClJnof attempts, a suitable crystal of composition Rea@-Cl)pentane and CHzCIdn-heptane, and two data sets were (p-CO)(=CCH2-n-Pr)C12(CNxyl)@-dppm)2*2CH2Cl2 (Sa) collected a t +20 "C, a complete and satisfactory refinewas obtained and the structure was successfully solved. ment of this complex was thwarted by a twofold disorder The ORTEP drawing of the structure of this dirhenium problem involving the terminal CO and alkylidyne complex is shown in Figure 2. The important structural ligands that is of a type we have encountered previously parameters for 7d and 8a are given in Tables 2-5. Full with other edge-shared bioctahedral dirhenium species details of these structures are available as supplementhat contain the trans Rez@-dppm)zunitS2J3However, tary material. a trans disposition of dppm ligands and the all-cis arrangement of chloride ligands within the [Re2@-Cl)Discussion Clz@-dppm)~Iunit were shown to be present and the The conversion of the 3-metallafuran complexes of (12)Cotton, F. A.; Daniels, L. M.; Dunbar, K. R.; Falvello, L. R.; types 3 and 4 to the dirhenium alkylidyne complexes 5 Tetrick, S. M.; Walton, R. A. J . Am. Chem. SOC.1985,107,3524. and 7 as outlined in the reaction scheme (step B) (13)Esjornson, D.;Derringer, D. R.; Fanwick, P. E.; Walton, R. A. represents a novel entry into rhenium alkylidyne chemInorg. Chem. 1989,28,2821.

454

Kort et al.

Organometallics, Vol. 14, No. 1, 1995

Figure 2. ORTEP representation of the Re&-Cl)@-CO)(=CCHz-n-Pr)C12(CNxyl)@-dppm)z molecule (8a)with the phenyl group atoms of the dppm ligands omitted. The thermal ellipsoids are drawn at the 50% probability level.

istry. This route contrasts, for example, with strategies used in the synthesis of the important mononuclear Re(VII) alkylidyne Schrock complexes, in which ancillary imido, alkoxide, andor alkylidene ligands are also present,14 the mononuclear hydrido-alkylidyne complexes of Re(VI1) we have recently reported,15and the formally Re(V) alkylidyne complexes described by Pombeiro and co-workers.16 While dirhenium alkylidyne complexes of other types are this is the first alkylidyne chemistry to be developed using the electron-rich triple bond ( ~ ~ ~ ~ configuration). 4 3 ~ 6 " ~ Although the paramagnetism of the complexes of types 5 and 7 precluded their characterization by NMR spectroscopy,the accessibility of their neutral, diamagnetic congeners 6 and 8 (Scheme 1,step D)enabled the IH and 31PNMR spectra of this set of complexes to be obtained (Table 7). In all cases, the integrity of the alkyl chain of the alkylidyne ligands was confirmed, thereby establishing that the carbon chain of the parent alkyne (l-pentyne or l-hexyne) was intact. The 31P{1H) spectra, which have the appearance of M B B ' patterns, are in accord with unsymmetrical dirhenium structures, as confirmed by X-ray structure determinations on crystals of the representative complexes 7d and 8a (Figures 1 and 2). The structures of the dirhenium units in these two complexes are very similar to one another; this is to be expected based upon the reversibility of the [53/[61 and [71/[81redox couples as seen in the cyclic voltammograms of these complexes (Table 6). Both are edgesharing bioctahedra in which one of the bridging ligands is an unsymmetrically bound CO ligand displaying quite disparate Re-C distances (1.93(3)and 2.57(4)A for 7d; 1.87(1) and 2.62(1) A for 8a). In each case, the longer of the two distances involves the formally higher valent Re center, i.e., the one bound to the alkylidyne ligand. The R e W distances (1.74(3)A for 7d;1.70(1)A for 8a) are a t the short end of the range encountered for this (14) (a) Edwards, D. S.; Biondi, L. V.; Ziller, J. W.; Churchill, M. R.; Schrock, R. R. Organometallics 1983, 2, 1505. (b) Toreki, R.; Schrock, R. R. J . Am. Chem. SOC.1990,112,2448. (c) Weinstock, I. A,; Schrock, R. R.; Davis, W. M. J . Am. Chem. SOC.1991, 113, 135. (d) Toreki, R.;Schrock, R. R.; Vale, M. G. J . Am. Chem. SOC.1991, 113, 3650. (e) Toreki, R.;Schrock, R. R.; Davis, W. M. J . Am. Chem. SOC. 1992, 114, 3367. (0 Toreki, R.; Vaughn, G . A.; Schrock, R. R.; Davis, W. M. J . Am. Chem. SOC.1993,115, 127. (15)Leeaphon, M.;Fanwick, P. E.; Walton, R. A. J . Am. Chem. SOC. 1992,114, 1890. (16)(a) Almeido, S. S. P. R.; Frau'sto Da Silva, J. J. R.; Pombeiro, A. J. L. J. Organomet. Chem. 1993,450, C7. (b) Carvalho,M. F. N. N.; Henderson, R. A.; Pombeiro, A. J. L.; Richards, R. L. J . Chem. Soc., Chem. Commun. 1989, 1796. (c) Pombeiro, A.J. L.; Hills, A,; Hughes, D. L.; Richards, R. L. J . Organomet. Chem. 1988, 352, C5. (17) For example, see: Casey, C. P.; Ha, Y.; Powell, D. R. J. Am. Chem. SOC.1994,116,3424. This chemistry is accessed via the doubly bonded dirhenium complex [Cp*Re(CO)& and the enyne HCrCC(CH3)=CH2.

structural ~ n i t . ~ The ~ J Re-CUbridging) ~ J ~ ~ bond that is trans to the R e W unit is, as expected, the longest of the two Re-Clb distances (2.518(7)vs 2.46903) 8, in 7d; 2.542(3) vs 2.485(3) A in 8a); this accords with the presence of a structural trans effect. The most significant difference between the structures of 7d and 8a is the difference in the Re-Re distances (2.817(2)8, in 7d;3.039(1) 8,in 8a). While the shorter of the two Re-Re distances clearly signals the presence of a significant %-Re interaction, the distance of 3.039(1)8, in 8a is at the limit of what is normally considered the Re-Re bonding range. A comparison of the changes in the Re-CUB) and Re-CO distances between 7d and 8a is not profitable because of the relatively low precision of these parameters in the structure of 7d. In the case of the cationic dirhenium species that are present in complexes of types 5 and 7,we can consider them to represent formally mixed-valence Re(II1)-Re(N)species. Their one-electron reduction to the neutral complexes 6 and 8 then gives rise to formally Re(I1)Re(ZV) species. While the unsymmetrical nature of these complexes, in which the two Re centers are in such disparate ligand environments, complicates any detailed appraisal of the Re-Re bonding in these complexes, it is clear that the bonding scheme that has been derived for a more symmetrical edge-sharing bioctahedral species, in which there is no metal-ligand multiple bonding,18 will not apply here. Specifically, in the present cases, two of the three d orbitals that would normally be available for Re-Re bonding are involved in forming the ReSC bond at the more highly "oxidized" Re center. This will leave two essentially nonbonding filled d orbitals at the "reduced" Re center for n-back-bonding to the cis xylNC and CO ligands. Accordingly, it seems reasonable to conclude, based on these arguments and the Re-Re bond distance data, that the 5, 6 and 7,8 sets correspond to species in which the metal-metal bond orders are 0.510, rather than 1.511 and that the reductions 5 6 and 7 8 involve the addition of an electron to an antibonding metal-based orbital that is already partially filled in the dirhenium cations of 5 and

-

-

7. The decoupling reactions of the 2-metalated-3-metallafuran units Re@-COC(R)CH)Reof 3 and 4 involve the net addition of a single hydrogen atom and are accompanied by a formal redox change from a Re2(8+) core in 3 and 4 to a Re2(7+) core in 5 and 7 (see Scheme 1). Since the products of types 5 and 7 are paramagnetic, we have not been able to follow the course of these reactions by NMR spectroscopy. However we did monitor these reactions using IR spectroscopy but found no evidence for the formation of intermediates. A plausible mechanism could involve attack of H+at the 5-position of the metallafuran ring (the carbon atom that has the R substituent) or a t the oxygen atom, with concomitant ring opening and the formation of the dirhenium alkylidyne dicationic species [Re2@-Cl)@CO)(~CCH2R)C12(L)@-dppm)212f.Such dicationic species are potent one-electron oxidants (Table 6) and will therefore easily be reduced to the monocationic species 5 and 7 in the reaction medium. The involvement of H+is supported by the observation that the addition of (18)Cotton, F. A.; Walton, R. A. Multiple Bonds Between Metal Atoms, 2nd ed.; Oxford University Press; Oxford, U.K., 1993; pp 593600.

Organometallics, Vol. 14, No. 1, 1995 455

Mixed-ValenceDirhenium Alkylidyne Complexes bases such as DBU and NEts to methanol or dichloromethane solutions of [ReZ(p-Cl)(u-COC(n-Pr)CH)Clz(CNxyl)(p-dppm)zl+prevented the formation of [Re&-

occurred to give significant levels of SCCDZ-n-Bu;this D for H exchange must presumably occur during the formation of an unstable (and undetected) intermediate. We note that small amounts of water might be impliC~)(M-CO)(~CCHZ-~-P~)C~Z(CN~~~)(~-~~~~)ZI+. cated as the source of hydrogen in the other solvent The source of the additional hydrogen atom that is systems in which the 3-metallafuran to alkylidyne incorporated into the alkylidyne product can be the transformations can occur. solvent, as shown by the reaction of [ReZ(u-Cl)(p-COC(n-Bu)CH)Cl2(CNxyl)@-dppm)2lPF6 (4b)with CD30D or Acknowledgment. Support from the National SciCH30D, which leads to the incorporation of deuterium ence Foundation, through Grants CHE91-07578 and t o give [Re~(M-Cl)(~CCHD-n-Bu)C12(CNxyl)(u-dppm)21CHE94-09932to R.A.W. is gratefully acknowledged. We PF6 (7c). The 2H{'H} NMR spectrum (recorded in CHzalso thank the National Science Foundation for Grant Cl2) of its analogous NMR-active reduced congener 8b CHE86-15556 for the purchase of the microVAX I1 shows a single resonance a t 6 +0.69. A comparison of computer and diffractometer. the 'H NMR (Table 7) and 2H{1H}NMR spectra of this productlgshows that the deuterium label is incorporated Supplementary Material Available: Tables giving full exclusively at the 0-carbon of the alkylidyne unit. details of the crystal data and data collection parameters However, integration of this signal in the lH NMR (Tables S1 and ,361, atomic positional parameters (Tables S2, spectrum shows that additional D incorporation has S7,and 581, anisotropic thermal parameters (Tables S3 and SS), bond distances (Tables 54 and SlO), and bond angles (19)Decoupling experiments show conclusively that the assignmenta (Tables S5 and S11) for 7d and 8a (26 pages). Ordering of the 'H NMR spectrum of the =CCHzCHzCH&HzCHs unit in the diamagnetic, reduced complex 8b (see Table 7) are 88 follows (6 values are given in the same order as the atoms are in the alkyl chain): 6 +0.69,-0.02, +0.43, +0.77, and +0.64.

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