Organometallics 2011, 30, 653–656 DOI: 10.1021/om1010885
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A Percyanovinylidene-Ruthenium Complex, Ru{dCdC5(CN)3[dC(CN)2]2}(dppe)Cp* )
Michael I. Bruce,*,† Jonathan C. Morris,‡ Brian K. Nicholson,§ Brian W. Skelton, Allan H. White, and Natasha N. Zaitseva† †
School of Chemistry & Physics, University of Adelaide, South Australia 5005, Australia, School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia, § Department of Chemistry, University of Waikato, Hamilton, New Zealand, and Chemistry M313, SBBCS, The University of Western Australia, Crawley, Western Australia 6009, Australia )
‡
Received November 18, 2010 Summary: The reaction between Ru(CtCCtCAg)(dppe)Cp* and tcne affords a novel percyanovinylidene complex by an unusual decyano-dimerization reaction of the cyanocarbon with the diynyl fragment. This complex is also obtained from tcne and Ru{CtCCtC[Au(PPh3)]}(dppe)Cp*, together with Ru{CtCC[dC(CN)2]C[Au(PPh3)]dC(CN)2}(dppe)Cp*, formed by the anticipated [2 þ 2] cycloaddition and subsequent ringopening reactions.
For several years, we have studied the reactions of tetracyanoethene, C2(CN)4 (tcne), with alkynyl- and polyynyltransition-metal complexes.1 Characteristic of these is the [2 þ 2] cycloaddition to the alkynyl complex A to give tetracyanocyclobutenyl derivatives B, which undergo a more or less ready ring opening (retro-cycloaddition) to form the η1-tetracyanobuta-1,3-dienyl complexes C (Scheme 1). A further reaction occurs if weakly bound ligands are present on the metal center, with formation of the analogous η3-tetracyanobutadienyl complexes D. An interesting structural feature of D is the presence of a short Ru-C bond, consistent with some degree of multiple-bonding character. This feature has been examined in more detail using DFT calculations.2 The chemistry of cyanoethynyl complexes has recently attracted some attention, with early studies being dependent upon the reactions of cyanoethyne, a reactive and not easily accessible alkyne. Improved yields were obtained from cyanoethynyltrimethylsilane,3 although this too requires prior synthesis of HCtCCN. More convenient are the sequential reactions of Ru(CtCH)(PPh3 )2 Cp or [Ru(dCdCH2)(dppe)Cp*]þ with LiBu followed by phenyl cyanate, which *To whom correspondence should be addresssed. Fax: þ 61 8 8303 4358. E-mail:
[email protected]. (1) (a) Bruce, M. I.; Rodgers, J. R.; Snow, M. R.; Swincer, A. G. J. Chem. Soc., Chem. Commun. 1981, 271. (b) Bruce, M. I.; Hambley, T. W.; Snow, M. R.; Swincer, A. G. Organometallics 1985, 4, 501. (c) Bruce, M. I.; Cifuentes, M. P.; Snow, M. R.; Tiekink, E. R. T. J. Organomet. Chem. 1989, 359, 379. (d) Bruce, M. I.; Hall, B. C.; Low, P. J.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 1999, 592, 74. (e) Bruce, M. I.; Skelton, B. W.; White, A. H.; Zaitseva, N. N. Dalton Trans. 2001, 3627. (f) Bruce, M. I.; Skelton, B. W.; White, A. H.; Zaitseva, N. N. J. Organomet. Chem. 2002, 650, 141. (g) Bruce, M. I.; Low, P. J.; Hartl, F.; Humphrey, P. A.; de Montigny, F.; Jevric, M.; Lapinte, C.; Perkins, G. J.; Roberts, R. L.; Skelton, B. W.; White, A. H. Organometallics 2005, 24, 5241. (h) Bruce, M. I.; Jevric, M.; Perkins, G. J.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2007, 692, 1757. (2) Bruce, M. I.; Fox, M. A.; Low, P. J.; Skelton, B. W.; Zaitseva, N. N. Dalton Trans. 2010, 39, 3759. (3) Zhou, Y.; Arif, A. M.; Miller, J. S. J. Chem. Soc., Chem. Commun. 1996, 1881. r 2011 American Chemical Society
afford the cyanoethynyl complexes directly with concomitant loss of phenol (or phenoxide).4 Recently, we have described the nucleophilic displacement of CN from tcne by Ru(CtCH)(dppe)Cp* to give Ru{CtCC(CN)dC(CN)2 }(dppe)Cp*, together with some of its chemistry.5 [2 þ 2] cycloaddition of tcne to Ru(CtCCN)(dppe)Cp afforded the pentacyanobutadienyl complex Ru{C[dC(CN)2]C(CN)dC(CN)2}(dppe)Cp.4b Approaches to cyanovinylidene ligands using reactions of the N-cyano(dimethylamino)pyridinium cation, [Me2NC5H4N(CN)]þ, with Ru(CtCH)(dppe)Cp* allow both preparation of the cyanoethynyl complex and also subsequent addition of CN to give the dicyanovinylidene ligand in [Ru{dCdC(CN)2}(dppe)Cp*]BF4.6 This note describes related reactions of group 11 derivatives of Ru(CtCCtCH)(dppe)Cp*.
Results and Discussion Reaction between tcne and Ru(CtCCtCAg)(dppe)Cp*. We recently described the reaction of AgNO3 with Ru(Ct CCtCH)(dppe)Cp* to give a yellow solid with elemental analyses consistent with its formulation as the ligand-free silver(I) derivative Ru(CtCCtCAg)(dppe)Cp* (1).7 The structure of this interesting derivative is presently unknown, neither the electrospray mass spectrum nor X-ray-quality single crystals yet having been obtained. In the course of trying to characterize this material, however, its reaction with tcne was examined. In a one-pot synthesis, during which the silver complex 1 was not separated, two products, blue (2) and red (3), were isolated. The IR spectrum of 2 in MeCN contains ν(CN) at 2208, 2185 cm-1 and ν(CtC) at 1932 cm-1; in CH2Cl2, ν(CN) occurs at 2213, 2184 cm-1 and ν(CtC) at 1934 cm-1. The 1H NMR spectrum contains peaks characteristic of the Ru(dppe)Cp* group, while the 31P NMR spectrum contains only one signal for dppe at δ 80.9. The ES-MS contains Mþ and [M þ Na]þ at m/z 913 (corresponding to M = [Ru{C8(CN)7}(dppe)Cp*]þ) and 936, respectively, although during the measurement, the solution changed color to red, (4) (a) Cordiner, R. L.; Corcoran, D.; Yufit, D. S.; Goeta, A. E.; Howard, J. A. K.; Low, P. J. Dalton Trans. 2003, 3541. (b) Cordiner, R. L.; Smith, M. E.; Batsanov, A. S.; Albesa-Jove, D.; Hartl, F.; Howard, J. A. K.; Low, P. J. Inorg. Chim. Acta 2006, 359, 946. (5) Bruce, M. I.; Burgun, A.; Kramarczuk, K. A.; Nicholson, B. K.; Parker, C. R.; Skelton, B. W.; White, A. H.; Zaitseva, N. N. Dalton Trans. 2009, 33. (6) Brown, N. J.; Eckert, P. K.; Fox, M. A.; Yufit, D. S.; Howard, J. A. K.; Low, P. J. Dalton Trans. 2008, 433. (7) Bruce, M. I.; Low, P. J.; Nicholson, B. K.; Skelton, B. W.; Zaitseva, N. N.; Zhao, X.-L. J. Organomet. Chem. 2010, 695, 1569. Published on Web 01/19/2011
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Scheme 1. [2 þ 2] Cycloaddition of tcne to Alkynyl-Metal Complexes
so that we cannot be certain that these data refer to the initial product 2. Compound 2 is very unstable, solutions in common solvents readily precipitating red crystals of 3 (see below). The red complex 3 also has a composition corresponding to addition of two molecules of tcne with loss of AgCN: i.e., a heptacyano compound. The IR spectrum contains ν(CN) bands between 2227 and 2181 cm-1 but no ν(CtC) absorption. The ES-MS (from a solution containing NaOMe) contains ions at m/z 936 and 952, assigned to [M þ Na]þ and [M þ K]þ, respectively, for the X-ray-determined formulation: i.e., the same as found for 2. The molecular ion is present in only very low concentration, possibly because of the high affinity of Naþ or Kþ (also present in the spectrometer) for the CN groups. Complex 3 has extremely low solubility in all organic solvents, including MeCN and DMSO, so that it has not been possible to record any NMR spectra. However, the decomposition/isomerization of 2 afforded red crystals of 3 as the MeCN solvate, allowing its molecular structure to be established as the unusual cyclic vinylidene by a single-crystal XRD study. Elemental analyses of the former agree with the solid-state formulation. The same product 3, obtained as a different phase, is formed from Ru{CtCCtC[Au(PPh3)]}(dppe)Cp* and tcne, together with the known Ru{CtCC[dC(CN)2]C[Au(PPh3)]d C(CN)2}(dppe)Cp* (4), the product of the anticipated [2 þ 2] cycloaddition of the cyanocarbon to the diynyl-ruthenium complex, followed by a ring-opening reaction.8 However, attempts to obtain 3 from the reaction between 4 and another 1 equiv of tcne (in refluxing thf or benzene for 24 h) were unsuccessful.
(8) Bruce, M. I.; Jevric, M.; Parker, C. R.; Patalinghug, W.; Skelton, B. W.; White, A. H.; Zaitseva, N. N. J. Organomet. Chem. 2008, 693, 2915.
A molecule of 3 3 MeCN is depicted in Figure 1, selected bond parameters being included in the caption; more extensive details, together with those of the different solvate phase, which are slightly less precise but independent and generally in agreement, are given in Table S1 in the Supporting Information. The Ru(dppe)Cp* group is unexceptional with Ru-C(cp) (average 2.305 A˚) and Ru-P(1,2) distances (2.3315, 2.3511(10) A˚) and the near-octahedral geometry for the Ru center (P(1)-Ru-P(2) = 80.72(4)°, P(1,2)-RuC(1) = 84.7, 97.7(1)°) being within the ranges previously observed. The cyanocarbon ligand consists of an Rud C(1)dC(2) vinylidene (Ru-C(1) = 1.825(3) A˚, C(1)-C(2) = 1.330(4) A˚), with atom C(2) being part of the five-membered ring C(2-6). There are two CN groups on C(3) and one on C(4), while C(5) and C(6) are both parts of CdC(CN)2 groups. Around the ring, C(2)-C(3) and C(3)-C(4) are long, at 1.545(5) and 1.539(5) A˚, respectively, with C(4)-C(5) being short at 1.386(5) A˚ but C(2)-C(6) and C(5)-C(6) longer, at 1.469(5) and 1.491(5) A˚, respectively. The C(5)-C(7) and C(6)-C(8) separations (1.392(5) and 1.349(5) A˚, respectively) are CdC double bonds linking the C(CN)2 groups to the C5 ring. Angles within the C5 ring are between 100.3(3) and 111.4(3)°, while Ru-C(1)-C(2) is close to linear (168.7(3)°). These structural data can be accommodated by the unprecedented zwitterionic formulation shown, where the Ru(dppe)Cp* center carries a positive charge, with negative charge being delocalized around C(4)-C(5)-C(6) and the two attached dicyanomethylene groups. The presence of the highly cyanated ligand results in exceptional back-bonding from the metal, and the RudC(1) and C(1)-C(2) bonds are respectively somewhat shorter and longer than normal (cf. e.g., values of 1.848(2) and 1.305(4) A˚ found in [Ru(dCd CH2)(dppm)Cp*]PF69). A plausible route to 3 is shown in Scheme 2 and involves [2 þ 2] cycloaddition of tcne to the outer CtC triple bond of Ru(CtCCtCAg)(dppe)Cp* (1 )followed by ring opening to give the silver derivative of the tetracyanobutadienyl complex A. Reaction of A with a second molecule of tcne would give intermediate B, which then undergoes intramolecular 5-exo-trig cyclization by attack of the dicyanomethylene anion (9) Bruce, M. I.; Ellis, B. G.; Low, P. J.; Skelton, B. W.; White, A. H. Organometallics 2003, 22, 3184.
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Scheme 2. Suggested Mechanism for the Reaction of tcne with Ru(CtCCtCAg)(dppe)Cp*
Figure 1. Projection of a molecule of Ru{dCdC5(CN)3[dC(CN)2]2}(dppe)Cp* (3) in the MeCN solvate; H atoms are omitted for clarity. Selected bond parameters (distances in A˚ and angles in deg): Ru-C(1) = 1.825(3), C(1)-C(2) = 1.330(4), C(2)-C(3,6) = 1.545, 1.469(5), C(3)-C(4) = 1.539(5), C(4)C(5) = 1.386(5), C(5)-C(6,7) = 1.491(5), 1.392(5), C(6)-C(8) = 1.349(5); Ru-C(1)-C(2) = 168.7(3), C(1)-C(2)-C(3,6) = 129.1(3), 126.9(3), C(2)-C(3)-C(4) = 100.3(3), C(3)-C(4)C(5) = 111.4(3), C(4)-C(5)-C(6) = 105.5(3), C(2)-C(6)-C(5) = 105.8(4).
on Cβ to give C. Elimination of AgCN from C then affords 3. While we have not yet characterized the blue compound 2, the presence of ν(CN) and ν(CtC) bands in its IR spectrum, the latter disappearing upon conversion to red 3, suggests that its structure is closely related to those depicted for B and C.
Experimental Section The general reaction conditions and instrumentation used are similar to those described earlier.9 Ru(CtCCtCH)(dppe)Cp* was obtained from RuCl(dppe)Cp* and HCtCCtCSiMe3;10 tcne was a commercial product (Aldrich). Reaction of tcne with Ru(CtCCtCAg)(dppe)Cp*. Solid AgNO3 (12.5 mg, 0.073 mmol) was added to a solution of Ru(Ct CCtCH)(dppe)Cp* (50 mg, 0.073 mmol) in thf (8 mL), and the mixture was stirred in the dark. After 1 h, tcne (18.7 mg, 0.146 mmol) was added, upon which the yellow solution immediately turned blue. After a further 1 h of stirring, most of the solvent was removed and the residue was separated by preparative tlc (silica, 1/2 acetone/hexane). One major band (2, turquoise blue, Rf = 0.50) separated and was collected. A dark blue solid (22.4 mg, 41%) was obtained from a MeCN extract. IR (MeCN, cm-1): ν(CN) 2208 w, 2185 w; ν(CtC) 1932 w (br); other bands at 1597 w (br), 1573 w, 1528 m (br). IR (CH2Cl2, cm-1): ν(CN) 2213 w, 2184 w; ν(CtC) 1934 m (br); other bands at 1593 w, 1524 s. 1H NMR (CDCl3): δ 1.50 (s, 15H, Cp*), 2.54, 3.08 (2 m, 4H, CH2), 7.18-7.52 (m, 20H, Ph). 31P NMR (CDCl3): δ 80.9 (s, dppe). ES-MS (MeCN, MeOH þ NaOMe, m/z): 936, [M þ Na]þ; 913, Mþ. The red baseline was extracted with acetone to give red solid 3 (27.3 mg, 41%), which gave X-ray-quality crystals of the MeCN solvate from CH2Cl2/MeCN/EtOH. The solid material so obtained proved to be resistant to redissolution. Anal. Found: C, 67.20; H, 4.39; N, 10.69. Calcd for C51H39N7P2Ru: C, 67.10; H. 4.31; N, 10.74; M, 914. IR (Nujol, cm-1): ν(CN) 2227 w, 2202 w, (10) Bruce, M. I.; Ellis, B. G.; Gaudio, M.; Lapinte, C.; Merlino, G.; Paul, F.; Skelton, B. W.; Smith, M. E.; Toupet, L.; White, A. H. Dalton Trans. 2004, 1601.
2181 m; other bands at 1595 m, 1571 m, 1526 m. ES-MS (MeOH þ NaOMe, m/z): 936.171 (calcd 936.169), [M þ Na]þ; 952.142 (calcd 952.143), [M þ K]þ; 887, [M - CN]þ. Conversion of blue to red isomers occurs spontaneously, a blue solution of 2 in MeCN slowly depositing red crystals of 3 over a period of several hours. Reaction between tcne and Ru{CtCCtC[Au(PPh3)]}(dppe)Cp*. A solution of Ru{CtCCtC[Au(PPh3)]}(dppe)Cp* (35 mg, 0.031 mmol) and tcne (8 mg, 0.62 mmol) in benzene (6 mL) was stirred overnight at room temperature, after which time it was burgundy red with a red-orange precipitate. The precipitate was filtered off and washed with benzene, and the combined solutions were evaporated. Preparative tlc of a CH2Cl2 extract of the residue (3/7 acetone/ hexane) afforded Ru{CtCC[dC(CN)2]C[Au(PPh3)]dC(CN)2}(dppe)Cp* (4; 15.9 mg, 41%), obtained as red crystals (CH2Cl2/ hexane). The red-orange precipitate was crystallized (CH2Cl2) to give Ru{dCdC5(CN)3[dC(CN)2]2}(dppe)Cp* (3; 6.4 mg, 23%). Structure Determinations. Full spheres of diffraction data were measured using a Bruker AXS CCD area-detector instrument. All data were measured using monochromatic Mo KR radiation (λ = 0.710 73 A˚). Ntotal reflections were merged to Nunique (Rint cited) after “empirical”/multiscan absorption correction (proprietary software) and used in the full-matrix leastsquares refinements on F2, No with F > 4σ(F) being considered “observed”. Anisotropic displacement parameter forms were refined for the non-hydrogen atoms, hydrogen atom treatment following a riding model (weights: (σ2(Fo)2 þ (aP)2 (þ bP))-1, with P = (Fo2 þ 2Fc2)/3). Neutral atom complex scattering factors were used; computation used the SHELXL 97 program.11 Pertinent results are given in Figure 1 (which shows non-hydrogen atoms with 50% probability amplitude displacement ellipsoids; hydrogen atoms have been omitted for clarity) and its caption. Crystal data and refinement details for 3 3 MeCN (=Ru{dCdC5(CN)3[dC(CN)2]2}(dppe)Cp*.MeCN C51H39N7P2Ru 3 C2H3N): M = 953.96, orthorhombic, space group P212121, a = 9.485(2) A˚, b = 20.908(5) A˚, c = 23.495(6) A˚, V = 4659(2) A˚3, Fc = 1.360 g cm-3, Z = 4, μ(Mo KR) = 0.45 mm-1, crystal 0.28 0.20 0.20 mm, Tmin/max = 0.83, 2θmax = 58°, Nt = 30 225, N = 11 517 (Rint = 0.076), No = 9033, R1 = 0.045, wR2 = 0.105 (a = 0.055, b = 0.79), xabs = 0.23(2), T = 150 K. (11) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
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Crystal data and refinement details for 3 3 2.5S (=Ru{dCd C5(CN)3[dC(CN)2]2}(dppe)Cp* 3 2.5S C51H39N7P2Ru 3 2.5S): M = 912.9 (þ 2.5S), monoclinic, space group P21/n, a = 17.2203(6) A˚, b = 12.527(2) A˚, c = 22.520(2) A˚, β = 101.908(5)°, V = 4753.4(9) A˚3, Fc = 1.276 g cm-3, Z = 4. μ(Mo KR) = 0.44 mm-1, crystal 0.19 0.16 0.08 mm, Tmin/max = 0.75, 2θmax = 56°, Nt = 72 949, N = 10 184 (Rint = 0.092), No = 6773, R1 = 0.059, wR2 = 0.149 (a = 0.0815), T = 100 K. Minor difference map residues were insusceptible to sensible modeling and were suppressed using “SQUEEZE”.12 The Cp* was modeled as disordered over two sets of sites, occupancies refining to 0.644(11) and complement. (12) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.
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Acknowledgment. We thank the Australian Research Council for support of this work and Johnson Matthey plc, Reading, U.K., for a generous loan of RuCl3 3 nH2O. Supporting Information Available: Table S1, giving selected bond parameters for both forms of 2, and CIF files giving crystallographic data for 3 3 MeCN and 3 3 2.5S. This material is available free of charge via the Internet at http://pubs.acs.org. Full cif depositions have also been deposited with the Cambridge Crystallographic Data Centre as CCDC 793948 and 793949. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax, þ 44 1223 336 033; e-mail, deposit@ccdc. cam.ac.uk; web, http://www.ccdc.cam.ac.uk).
