New Structural Motifs Resulting from Internal Constraints in Chelating

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New Structural Motifs Resulting from Internal Constraints in Chelating Bis(NHC) Ligands: A Dinuclear Ruthenium(II) Complex Featuring an η2‑Arene Binding Mode and a Remarkable New Tetrameric Silver(I) Halide Form Peter V. Simpson,†,‡ David H. Brown,*,†,‡ Brian W. Skelton,†,# Allan H. White,† and Murray V. Baker*,† †

School of Chemistry and Biochemistry, M310, The University of Western Australia, Crawley, Western Australia 6009, Australia Nanochemistry Research Institute, Department of Chemistry, Curtin University of Technology, GPO Box U1987, Perth, Western Australia 6845, Australia

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S Supporting Information *

ABSTRACT: A novel dinuclear ruthenium(II) complex containing two ortho-xylylene-linked bis(NHC) ligands (NHC = N-heterocyclic carbene) has been synthesized via transmetalation from a silver-NHC complex. Each ruthenium atom in the dinuclear complex is chelated through the two carbene carbon atoms and, unusually, an η2-bound xylylene ring, two separate bis(NHC) units being linked by a Ru(μCl)3Ru core. The same bis(NHC) ligand has yielded a neutral tetranuclear 4:2 AgBr:bis(NHC) complex, where ligand steric constraints seemingly inhibit formation of structures derivative of the more familiar “cubane” or “step” forms, resulting in an interesting new structural type.

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INTRODUCTION Many Ru(II)-NHC complexes of immense catalytic importance have been synthesized,1 and the discovery and use of Grubbs’ second-generation catalyst focused attention on Ru(II)-NHC complexes with a similar structural motif, incorporating a single, monodentate NHC ligand.2−5 By contrast, Ru(II)-NHC complexes bearing two NHC ligands have been studied perfunctorily, and there are relatively few reports of Ru(II) complexes involving chelating bis(NHC) ligands,1,6−11 despite the fact that bis(NHC) chelates of other metals are quite prevalent.12 All of the Ru(II)-NHC complexes bearing chelating NHC or pincer ligands that have been synthesized contain a mononuclear Ru(II) core. We have synthesized many bis(NHC) complexes incorporating ortho-cyclophane ligands such as 1, usually by reaction of the corresponding imidazolium-linked cyclophanes with suitable metal salts in the presence of a mild base.13−17 In all but one of these complexes, the cyclophane binds the metal atom(s) only via the NHCs, adopting a conformation in which the xylylene units are splayed away from the metal center(s). The exception to date is the Ru(II) complex 2+, in which the cyclophane−Ru bonding involves an arene ring (coordinated in η6-fashion) in addition to the two NHC units.11 Like cyclophane 1, non-cyclophane ligands that contain two NHC units linked by an o-xylylene group also typically bind metals via only the two NHC units and adopt a conformation in which the o-xylylene unit is tilted away from the metal center.16,17 For the bis(NHC) ligand 3, however, the preference for the usual mode of coordination is apparently diminished by © XXXX American Chemical Society

unfavorable steric interactions between the butoxy groups and the o-xylylene unit. Consequently, for the PdBr2 adduct of 3, three structural motifs have been characterized: one in which the NHC units are mutually trans, one in which the NHC units are mutually cis and the o-xylylene unit is tilted away from the Pd center, and one in which the NHC units are mutually cis and the o-xylylene unit is tilted toward the Pd center, 4.18 With structures 2+ and 4 in mind, we hypothesized that a similar binding mode to that found in complex 2+ could be possible in a Ru(II)-NHC complex derived from 3. So far, however, our attempts to synthesize an Ru(II) complex of 3 have not led to a complex analogous to 2+ (i.e., containing an η6-arene bound to Ru). Instead, we have obtained a dinuclear complex (5+) of form [LRu(Cl)3RuL]+, in which each organic ligand (L = 3) is bound to an Ru center via both NHC groups and an η2-arene unit. Well-defined ruthenium complexes containing an η2-arene unit are unusual and to our knowledge are unprecedented among NHC complexes. Here we report the synthesis and characterization of this remarkable complex 5+, including structural characterization of its AgCl2− salt, and a novel precursive tetranuclear silver(I) complex. Special Issue: Mike Lappert Memorial Issue Received: November 30, 2014

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DOI: 10.1021/om5012165 Organometallics XXXX, XXX, XXX−XXX

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existed as a dinuclear species of the type [(NHC)2Ag2]X2,22 the benzylic signals would be expected to appear as pairs of doublets due to asymmetry imposed by the rigidity of the coordinated NHC ligands. The consequences of such rigidity are evident for the NHC-Pd(II) complex 6,18 which possesses the NHC ligand 1 in a trans geometry about palladium and which displays two doublets in the 1H NMR spectrum due to the benzylic protons.

RESULTS AND DISCUSSION The bis(NHC)-Ag(I) complexes 3·2AgCl and 3·2AgBr were prepared by the reaction of 3·2HCl or 3·2HBr with Ag2O in refluxing CH3CN for 2 days (Scheme 1). The crude products Scheme 1

precipitated from the reaction mixtures accompanied by small amounts of colloidal silver. After dissolution and filtration sequences, 3·2AgCl and 3·2AgBr were obtained as colorless solids in yields of 76% and 80%, respectively. They displayed excellent solubility in halogenated solvents but were insoluble or only sparingly soluble in DMF, DMSO, CH3CN, MeOH, and acetone. The lack of solubility of 3·2AgCl and 3·2AgBr in polar solvents is consistent with their formulation as neutral species as opposed to ionic complexes of the type [bis(NHC)Ag]+X−, which might be expected to freely dissolve in these solvents. Attempts to prepare a complex of the type [bis(NHC)Ag]+X− by reaction of the 3·2HPF6 and Ag2O in refluxing CH3CN or MeOH were not successful. In both cases, the reaction mixture rapidly darkened, and analysis of the crude residue by 1H NMR indicated multiple unidentified decomposition products. In light of the successful synthesis and isolation of 3·2AgCl and 3·2AgBr, it seems that in the case of [3·Ag]PF6, strain induced by having the NHCs of an oxylylene-based ligand mutually trans about Ag(I) might make this geometry unfavorable. (We note that bis(NHC)-Ag(I) complexes having a trans-spanning bis(NHC) ligand have been reported for cases where the bis(NHC) ligand is a derivative of an m-xylylene unit.19,20) The 1H and 13C NMR spectra of 3·2AgCl and 3·2AgBr in CD2Cl2 are consistent with NHC-Ag(I) complexes in which each carbene carbon is coordinated to one AgX moiety. In the 13 C NMR spectra, signals associated with the carbene carbon occur at 193.3 and 190.3 ppm, respectively, as broad singlets. These signals are in the range expected for carbene carbons of benzimidazolyl-derived NHC-Ag-X complexes,21 whereas those of the carbene carbons of NHC-Ag-NHC complexes appear near 179 ppm for a related m-xylylene-linked complex of the type [bis(NHC)Ag]X19,20 and 178−184 ppm for dinuclear [(NHC)2Ag2](X)2 systems.22,23 The benzylic protons appear as sharp singlets in the 1H NMR spectra, indicating that these protons are equivalent on the NMR time scale. If the NHC units were coordinated to the same Ag(I) atom, or the complex

During an attempt to grow diffraction-quality crystals of 3· 2AgBr by slow evaporation of a CH2Cl2/CH3CN solution of the complex, the isostoichiometric 7 was isolated, having two AgX entities (here AgBr) associated with each bis(NHC) ligand 3. The results of the X-ray study, however, show the complex to be tetranuclear AgBr:3 (4:2) (·MeCN), one formula unit, devoid of crystallographic symmetry, comprising the asymmetric unit of the structure, in association with an uncoordinated disordered acetonitrile molecule. The form of the complex, shown in Figure 1, is novel and remarkable,

Figure 1. Projection of a single molecule of 7. Ellipsoids are displayed at 50% probability; hydrogen atoms have been omitted for clarity. B

DOI: 10.1021/om5012165 Organometallics XXXX, XXX, XXX−XXX

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this reaction (which was conveniently conducted in a thickwalled Schlenk flask sealed with a Young’s tap) due to its ability to dissolve both reagents, its ease of removal, and its relatively poor coordinating ability. After the mixture was concentrated and filtered, addition of hexanes gave (5+)(AgCl2−) as an orange solid in 73% yield (Scheme 2). The compound is airstable in the solid state for at least several hours, but the cation 5+ rapidly decomposes in solutions exposed to air. Treatment of 3·2AgCl with RuCl2(PPh3)3 in CH2Cl2 at 100 °C for 4 days also resulted in the formation of (5+)(AgCl2−), as indicated by 1 H NMR spectroscopy, but the salt could not readily be separated from AgCl(PPh3)3 byproduct.11 Attempts to circumvent this problem by treatment of 3·2HPF6 with RuCl2(PPh3)3 and DBU in CH2Cl2 at 100 °C resulted in the formation of only trace amounts of 5+. Unfortunately, however, the bulk of the material was unidentifiable decomposition products. The salt (5+)(AgCl2−) was easily converted into (5+)(PF6−) by metathesis with KPF6. Crystals of (5+)(AgCl2−) suitable for single-crystal X-ray diffraction studies were grown by slow evaporation of a CH2Cl2/benzene solution of the compound. The results of the single-crystal X-ray study are consistent with the formulation of the complex as [LRu(μ-Cl)3RuL](AgCl2)·3C6H6. A full formula unit, devoid of crystallographic symmetry, constitutes the asymmetric unit of the structure, the core geometry of the binuclear cation exhibiting quasi-2-fold symmetry, with the quasi-2-fold axis passing through the midpoint of the Ru(1)··· Ru(2) line and Cl(3) (Figure 2; Table S2). The organic ligands bind to the ruthenium atoms via the pair of carbene residues (Ru−C 1.967(6)−2.004(6) Å) and the ipso carbon atoms of the o-xylylene groups (Ru−C 2.299(6)−2.331(6); Ru−centroid 2.217, 2.218 Å), and the two ruthenium atoms of the binuclear cation are bridged by a triad of bridging chloride ions, fac in their coordination spheres. The different trans effects of the donor groups of the organic ligand are evident in the Ru−Cl distances, those opposite the aromatic donor (Cl(2) for Ru(1), Cl(1) for Ru(2)) having shorter Ru−Cl distances (2.4215(14), 2.4235(15) Å) than those opposite NHC donors (2.5069(14)− 2.5307(15) Å). The organic ligands are related by the quasi-2fold axis and are rotated by approximately 90° (86.8°) about the Ru(1)···Ru(2) line. The pair of o-xylylene planes are quasiparallel (interplanar dihedral angle: 7.8(3)°). Although ruthenium complexes containing η2-arene and phosphine ligands have previously been reported,27−30 to the best of our knowledge there are no reports of NHC complexes that possess a ruthenium η2-arene linkage. A comparison of other complexes containing Ru(II)−η2arene bonds suggests that the distance between the metal center and the carbon atoms of the arene ring is largely

bearing little relationship to the more usual (and symmetrical) tetrameric “cubane” and “stair” counterparts.24 While the array is tetranuclear, it may also be considered as a (mononuclear plus trinuclear, (1:1) + (3:1)) combination, the trinuclear form itself also being a novel, albeit derivative of the “stair polymer” form found in (for example) AgI:1-(9-anthracenylmethyl)-3ethylimidazol-2-ylidene (1:0)(∞|∞).25 The acetonitrile is not coordinated. About each silver atom, it may be noted that one of the angles between the donor pairs is outstandingly large and associated with those two of the bonds that may be deemed the strongest (Table S1), Br(3)−Ag(0)−Br(4), C(22)−Ag(1)− C(42), Br(2)−Ag(2)−C(62), and Br(1)−Ag(3)−C(82) (144.13(4)°, 149.5(3)°, 143.7(2)°, and 160.1(2)°), suggesting that the aggregate may be regarded as an assemblage of [AgBr2]−, [1]+, and a pair of [(1/2)AgBr] entities, the association of the two “homoleptic” complexes thwarting their integration into one of the more usual aggregates (cube, step, ...), if that is otherwise possible. At its core the array comprises a pair of Ag2Br2 rhombs [Ag(0,3), Br(1,3)], [Ag(0,2), Br(1,2)], hinged along one edge, forming an incipient Ag3Br3 component of a cube or step structure. The two rhombs, however, are not planar; each may be regarded as being appreciably folded along the lines Br(1)··· Br(3) and Ag(0)···Ag(2) with a concomitant interaction between Br(2)···Ag(3) (3.4001(9) Å). The fourth AgBr unit (Ag(1), Br(4)), pendant from Ag(0), cannot close a cube since Ag(0) is bonded to an abundance of bromine atoms and remains pendant, the “naked” Ag(1) binding to the two halves of the first ligand. The latter, notwithstanding the constraint of association and entailing a C−Ag−C angle well bent from linearity (149.5(3)°), nevertheless has the longest (2.9386(9) Å) of the Ag−Br bonds in the array and Ag−C distances (2.092(8), 2.120(7) Å) not notably different from those to the other ligand (2.142(7), 2.121(7) Å), which might be regarded as less constrained. A long Ag(2)···C (aromatic) (C(65,66)) intermolecular interaction (3.389(7), 3.178(8) Å) is found across an inversion center, forming a loose dimer. A higher degree of complexity is noted in the recently described 5AgCl· 2L cluster, obtained with L = bidentate 1-[2-(dimethylamino)ethyl]-3-methylimidazol-2-ylidene;26 in this cluster, however, the carbene carbon atoms have a bridging function. Related studies with mononuclear monodentate 4,7-functionalized benzimidazole NHC complexes with silver(I) halides of 1:1 stoichiometry may be found in a recent publication.18 When 3·2AgCl was allowed to react with [RuCl2(pcymene)]2 in CH2Cl2 at 100 °C for 4 days, the mixture changed from dark red to light orange, and a precipitate, presumably AgCl, formed. CH2Cl2 was used as the solvent for C

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xylylene rings, presumably facilitated by the constraint of the macrocycle closing down the C−Ru−C angle. In 2+, Ru−C(oxylylene)(×2)/Cl are 2.038(2), 2.034(2)/2.4304(5) Å, with Cl−Ru−Cl/C−Ru−C 99.71(6)°, 99.27(6)°/82.56(8)° and Ru−X (centroid (Ar)) 1.666 Å and X−Ru−C(×2)/Cl 122.8°, 120.9°/122.7°. The 1H and 13C NMR spectra (Figure 3) of solutions prepared by dissolving (5+)(AgCl2−) in CD2Cl2 show that the structure seen for the cation 5+ in the solid state persists in solution. The number and splitting patterns of signals in the 1H NMR spectrum are consistent with the two organic ligands being equivalent on the NMR time scale, but individually lacking any symmetry. The 1H NMR spectrum contains four signals that constitute an AMXZ spin pattern (two doublets, two doublets of doublets) for the four nonequivalent proton environments of the o-xylylene rings, as expected for a structure where the organic ligand 3 does not have a plane of symmetry. The spectrum also shows four distinct doublets associated with the four distinct environments for the benzylic protons. Although three of these resonances appear in the range 4.84−5.67 ppm, the fourth is well separated, at 2.70 ppm, suggesting a significantly different chemical environment in solution, possibly due to shielding by the ring current associated with a benzimidazol-2-ylidene moiety. The solidstate structure of (5+)(AgCl2−)·3C6H6 shows one benzylic proton (H2A, H6A) on each organic ligand oriented toward a benzimidazol-2-ylidene moiety in the same ligand, with close contacts to the carbene carbon (H2A···C42 ≈ 2.56 Å, H6A··· C82 ≈ 2.67 Å) and one of the adjacent N atoms (H2A···N43 ≈ 2.55 Å, H6A···N83 ≈ 2.56 Å). The 13C NMR spectrum of (5+)(AgCl2−) shows resonances at 191.2 and 194.4 ppm for the two carbene carbons, which fall in the range of similar Ru(II)NHC complexes.8,32 Interestingly, the signals at 97.0 and 100.8 ppm, attributed to the two Ru-bound quaternary carbons of the o-xylylene rings, appear significantly upfield of the signals for the uncoordinated carbons of the o-xylylene rings (∼130 ppm), but are in a similar region of the spectrum to the carbons of the η6-arene ring of 2+ (∼92−102 ppm). The 1H and 13C NMR spectral data for CD2Cl2 solutions containing (5+)(PF6−) were essentially identical to those for (5+)(AgCl2−). Complex 5+ bears some resemblance to the chloride-bridged dinuclear ruthenium complex 10,33 which possesses an NHC and an η2-ethylene ligand coordinated to one of the ruthenium centers. Complex 10 was shown to effectively promote both ring-opening metathesis polymerization (ROMP) and ringclosing metathesis (RCM) more efficiently than the related complex 11,34 in which the NHC ligand is replaced by a tricyclohexylphosphine ligand. The authors proposed that activation of the catalyst is achieved by dissociation of the relatively weakly bound η2-ethylene ligand followed by coordination of the alkyne cocatalyst to form a ruthenium vinylidene species, well known as initiators in various metathesis reactions. Consistent with that hypothesis, the second-generation ruthenium catalyst 12 was found to possess enhanced metathetical activity and selectivity relative to that of 10.35 Interestingly, the η2-arene linkage in complex 5+ may be thought of as a type of “tethered ethylene” ligand, which could conceivably dissociate from the metal center in the presence of an activator molecule such as phenylacetylene, then re-form to preserve the lifetime of the catalyst. Furthermore, the two η2arene ligands in 5+ have the potential to dissociate from their respective Ru centers simultaneously, thus forming a catalytic species with two coordination sites available for further

Figure 2. (a) Projection of the cation of (5+)(AgCl2−)·3C6H6 (ellipsoids displayed at 30% probability; hydrogen atoms omitted for clarity). (b) Projection of the core of 5+ (ellipsoids displayed at 30% probability; hydrogen atoms and periphery of the NHC ligands removed for clarity). Selected bond lengths (Å) and angles (deg): Ru(1)−C(31) 2.331(6), Ru(1)−C(32) 2.299(6), Ru(2)−C(71) 2.321(6), Ru(2)−C(72) 2.327(6) [Ru−carbene distances]; Ru(1)− C(22) 2.004(6), Ru(1)−C(42) 1.967(6), Ru(2)−C(62) 1.997(6), Ru(2)−C(82) 1.994(6) [Ru−η2-arene distances]; Ru(1)−Cl(1) 2.5069(14), Ru(1)−Cl(2) 2.4235(15), Ru(1)−Cl(3) 2.5289(14), Ru(2)−Cl(1) 2.4215(14), Ru(2)−Cl(2) 2.5307(15), Ru(2)−Cl(3) 2.5278(14); C(22)−Ru(1)−C(42) 88.7(2), C(62)−Ru(2)−C(82) 87.9(2).

governed by the steric hindrance around the metal center. The η2-aryl interaction in complex (8+)(PF6−), with Ru−C distances of 2.3926(6) and 2.386(2) Å, is significantly longer than in (5+)(AgCl2−), presumably due to the bulky phosphoramidite and cymene ligands.31 Conversely, compound 9 has shorter Ru−C distances (2.195(5) and 2.221(5) Å) than (5+)(AgCl2−), concomitant with reduced steric bulk around the metal center, cf. (5+)(AgCl2−) and (8+)(PF6−).30

The present structure (5+)(AgCl2−) begs comparison with our previously reported Ru(II) complex 2+, in which the organic ligand (1), although behaving again as a tridentate, achieves an η6 (rather than η2) interaction with one of the D

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Figure 3. 1H and 13C NMR spectra of a solution of (5+)(AgCl2−) in CD2Cl2. Signals due to solvent and adventitious moisture are marked with asterisks (*).

found that, while substituents on the six-membered ring are somewhat remote from the metal-binding site of the NHC ligand, intramolecular steric constraints that arise due to those substituents nevertheless affect the coordination chemistry of the ligand in interesting ways. When the bis(NHC) ligand 3 binds metals in a chelating fashion, internal steric constraints within the ligand lead to metal complexes having unusual structures. Attempts to grow crystals of 3·2AgBr suitable for Xray diffraction studies instead afforded crystals of the remarkable new tetranuclear complex 7, which has overall stoichiometry AgBr:3 of 4:2, but which can also be viewed as a mononuclear plus trinuclear, (1:1) + (3:1), combination. Treatment of 3·2AgCl with [RuCl2(p-cymene)]2 afforded the dinuclear bis(NHC)-Ru(II) complex 5+, which was characterized as its AgCl2− and PF6− salts. A study of (5+)(AgCl2−)· MeCN by X-ray diffraction showed that in the cation 5+ each organic ligand binds a Ru center via both NHC moieties and also by the xylylene ring in η2-fashion. 1H and 13C NMR studies suggest that the structure of 5+ identified in the solid state is retained in solution. The ruthenium complex 5+ is the first example of an NHC complex involving η2-arene coordination. Complexes containing η2-arene units are rare but are of interest in catalysis due to the potential of the η2-arene to behave as a hemilabile ligand, dissociating from the metal to make coordination sites available for catalysis or binding the metal in the catalyst’s resting state.

transformations. Complex 10 can also activate nitrous oxide; under an atmosphere of N2O, 10 underwent dissociation of ethylene, which led to oxidation of one of the mesityl benzylic C−H bonds and a ruthenium center to give the Ru(II)/Ru(III) mixed-valence complex 13.36 Furthermore, complex 10 could catalyze the oxidation of cyclooctanol by N2O, a process that has much potential, as the byproduct of oxidations by N2O, dinitrogen, is completely environmentally benign. The catalytic activity of complex 5+ and related complexes toward alkynes and nitrous oxide, and in various metathesis reactions, will be reported in due course.

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General Methods. Nuclear magnetic resonance spectra were recorded using Bruker Avance 500 (500.13 MHz for 1H and 125.77 MHz for 13C) or Bruker AV-600 MHz (600.13 MHz for 1H, 150.90 MHz for 13C, and 242.94 MHz for 31P) spectrometers at ambient temperature. 1H and 13C NMR chemical shifts were referenced to solvent resonances. When necessary, assignments were determined by HSQC (one-bond 1H−13C correlation) and HMBC (2/3-bond

CONCLUSIONS We have been interested in transition metal complexes of Nheterocyclic carbenes derived from benzimidazole, in which the six-membered ring of the benzimidazole core has been used as a point of attachment for additional functional groups. We have E

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Organometallics 1

H−13C correlation) 2D NMR experiments. Elemental analyses were executed at the Microanalytical Laboratory at the Research School of Chemistry, Australian National University, Canberra. Benzimidazolium Salt 3·2HCl. A solution of 1-methyl-4,7dibutoxybenzimidazole (0.5 g, 1.81 mmol) and 1,2-bis(chloromethyl)benzene (0.15 g, 0.88 mmol) in THF (20 mL) was heated at reflux for 5 d. The resulting precipitate was collected, washed with hexanes, and air-dried to give 3·2HCl as a white solid (0.21 g, 32%). Crystals suitable for X-ray diffraction were grown by the diffusion of vapors between EtOAc and a solution of the compound in CH3CN. A determination of the crystal structure of this salt (which is isomorphous with that of its structurally characterized bromide analogue, 3·2HBr·H2O)18 was undertaken in the course of this work (see Supporting Information). 1H NMR (500.13 MHz, d6-DMSO): δ 0.86 (6H, t, 3JH,H = 7.4 Hz, −CH2CH3); 1.01 (6H, t, 3JH,H = 7.4 Hz, −CH2CH3); 1.27 (4H, m, −CH2CH3); 1.49−1.60 (8H, m, 2 × −CH2CH3, 2 × −OCH2CH2−); 1.80−1.86 (4H, 2 × m, 2 × −OCH2CH2−); 4.02 (4H, t, 3JH,H = 6.5 Hz, −OCH2−); 4.13 (6H, s, N-CH3); 4.16 (4H, t, 3JH,H = 6.5 Hz, −OCH2−); 5.96 (4H, s, benzylic CH2); 7.01 (2H, d, 3JH,H = 9.0 Hz, H5 or H6); 7.07 (2H, d, 3JH,H = 9.0 Hz, H5 or H6); 7.43 (2H, m, xylyl Ar H); 7.55 (2H, m, xylyl Ar H); 9.40 (2H, s, H2). 13C NMR (75.47 MHz, d6-DMSO): δ 13.6, 13.7 (CH3); 18.5, 18.8 (CH2CH3); 30.3, 30.6 (OCH2CH2); 36.5 (NCH3); 49.5 (benzylic CH2); 68.9, 68.9 (OCH2); 108.7, 108.9 (C5 and C6); 122.3, 123.0 (C8 and C9); 129.7, 129.9 (xylyl Ar CH); 132.5 (xylyl Ar C); 140.7, 141.3 (C4 and C7); 142.7 (C2). Anal. Calcd for C40H56N4O4Cl2·(1.5H2O): C, 63.65; H, 7.88; N, 7.42. Found: C, 63.89; H, 7.64; N, 7.07. Silver Complexes 3·2AgBr and 7. Silver oxide (62 mg, 0.27 mmol) was added to a solution of 3·2HBr (200 mg, 0.25 mmol) in anhydrous CH3CN (15 mL), and the mixture was heated at reflux under N2 in darkness for 4 d. The resulting gray solid was collected and washed with CH3CN. The solid was dissolved in CH2Cl2, and the solution was passed through a 0.2 μm nylon filter and then concentrated under reduced pressure, to afford 3·2AgBr a white solid (193 mg, 76%). 1H NMR (600.13 MHz, CD2Cl2): δ 0.86 (6H, t, 3 JH,H = 7.4 Hz, 2 × CH2CH3), 1.00 (6H, t, 3JH,H = 7.4 Hz, 2 × CH2CH3), 1.32 (4H, m, 2 × CH2CH3), 1.54 (4H, m, 2 × CH2CH3), 1.66 (4H, 2 × m, 2 × OCH2CH2), 1.84 (4H, 2 × m, 2 × OCH2CH2), 4.03 (4H, t, 3JH,H = 6.6 Hz, 2 × OCH2), 4.05 (4H, t, 3JH,H = 6.6 Hz, 2 × OCH2), 4.20 (6H, s, 2 × N-CH3), 6.06 (4H, s, 2 × benzylic CH2), 6.63 (2H, d, 3JH,H = 8.8 Hz, 2 × benzimidazolyl Ar CH), 6.65 (2H, d, 3 JH,H = 8.8 Hz, 2 × benzimidazolyl Ar CH), 6.99 (2H, m, 2 × xylylene Ar CH), 7.19 (2H, m, 2 × xylylene Ar CH). 13C NMR (150.90 MHz, CD2Cl2): δ 13.9, 14.0 (CH2CH3), 19.5, 19.8 (CH2CH3), 31.4, 31.6 (OCH2CH2), 39.9 (NCH3), 50.9 (benzylic CH2), 68.2, 69.3 (OCH2), 106.0, 106.4 (benzimidazolyl Ar CH), 126.2, 126.5 (benzimidazolyl Ar C), 128.6, 128.7 (xylylene Ar CH), 135.7 (xylylene Ar C), 140.8, 141.6 (benzimidazolyl Ar CO), 193.3 (C-Ag). Anal. Calcd for C40H54N4O4Br2Ag2: C, 46.62; H, 5.28; N, 5.44. Found: C, 46.63; H, 5.16; N, 5.29. Attempts to grow crystals of 2 suitable for X-ray studies via the slow evaporation of an CH3CN/CH2CH2 solution of the complex instead gave crystals of the silver complex 7·MeCN. Silver Complex 3·2AgCl. This complex was prepared from silver oxide (35 mg, 0.15 mmol) and 3·2HCl·H2O18 (100 mg, 0.14 mmol) via a procedure analogous to that used for 3·2AgCl with a reaction time of 2 d. Yield: 103 mg, 80%. 1H NMR (500.13 MHz, CD2Cl2): δ 0.83 (6H, t, 3JH,H = 7.4 Hz, 2 × CH2CH3), 1.01 (6H, t, 3JH,H = 7.4 Hz, 2 × CH2CH3), 1.24 (4H, m, 2 × CH2CH3), 1.53 (4H, m, 2 × CH2CH3), 1.59 (4H, 2 × m, 2 × OCH2CH2), 1.84 (4H, 2 × m, 2 × OCH2CH2), 3.99 (4H, t, 3JH,H = 6.6 Hz, 2 × OCH2), 4.06 (4H, t, 3JH,H = 6.6 Hz, 2 × OCH2), 4.21 (6H, s, 2 × N-CH3), 5.95 (4H, s, 2 × benzylic CH2), 6.61 (2H, d, 3JH,H = 8.8 Hz, 2 × benzimidazolyl Ar CH), 6.65 (2H, d, 3JH,H = 8.8 Hz, 2 × benzimidazolyl Ar CH), 6.94 (2H, m, 2 × xylylene Ar CH), 7.24 (2H, m, 2 × xylylene Ar CH). 13C NMR (125.77 MHz, CD2Cl2): δ 13.9, 14.0 (CH2CH3), 19.4, 19.8 (CH2CH3), 31.3, 31.6 (OCH2CH2), 40.1 (NCH3), 51.9 (benzylic CH2), 69.2, 69.3 (OCH2), 106.3, 106.6 (benzimidazolyl Ar CH), 126.2, 126.3 (benzimidazolyl Ar C), 128.4, 128.8 (xylylene Ar CH), 135.0 (xylylene Ar C), 140.8, 141.5 (benzimidazolyl Ar CO), 190.3

(C-Ag). Anal. Calcd for C40H54N4O4Cl2Ag2: C, 51.03; H, 5.78; N, 5.95. Found: C, 50.78; H, 5.88; N, 5.74. Ruthenium Complex (5+)(AgCl2−). A mixture of 3·2AgCl (50 mg, 0.053 mmol) and [(p-cymene)RuCl2]2 (16 mg, 0.027 mmol) in anhydrous CH2Cl2 (10 mL) was heated at 100 °C for 4 d in a sealed flask. The mixture was concentrated to ca. 2 mL, and the flask was transferred to the drybox. The mixture was filtered through a 0.2 μm nylon filter, and crude (5+)(AgCl2−) was precipitated by addition of anhydrous hexanes. The hexanes were decanted, and the resulting residue was triturated with hexanes (3 × 5 mL) and dried in vacuo to afford an orange solid. Yield: 35 mg, 73%. Crystals of (5+)(AgCl2−) suitable for the X-ray study were grown by the slow evaporation of a CH2Cl2/benzene solution of the compound. Anal. Calcd for C80H108N8O8Cl5AgRu2·CH2Cl2: C, 51.69; H, 5.89; N, 5.95. Found: C, 51.93; H, 6.08; N, 6.03. Ruthenium Complex (5+)(PF6−). In the drybox, a solution of KPF6 in anhydrous CH2Cl2 (50 μL, 14 mg/mL, 2.78 μmol) was added to a solution of 6·AgCl2 (5 mg, 2.78 × μmol) in anhydrous CH2Cl2 (1 mL). The solution immediately became cloudy. The mixture was filtered through a 0.2 μm nylon filter, benzene (1 mL) was added, and (5+)(PF6−) was allowed to crystallize by slow evaporation of the solution, affording an orange solid. Yield: 4.5 mg, 92%. 1H NMR (600.13 MHz, CD2Cl2): δ 0.79 (6H, t, 3JH,H = 7.4 Hz, 2 × CH2CH3), 0.90 (6H, t, 3JH,H = 7.4 Hz, 2 × CH2CH3), 1.00 (6H, t, 3JH,H = 7.4 Hz, 2 × CH2CH3), 1.09 (6H, t, 3JH,H = 7.4 Hz, 2 × CH2CH3), 1.25 (4H, m, 2 × CH2CH3), 1.40 (4H, m, 2 × CH2CH3), 1.52 (4H, m, 2 × CH2CH3), 1.60 (4H, m, 2 × OCH2CH2), 1.64 (4H, m, 2 × CH2CH3), 1.66 (4H, m, 2 × OCH2CH2), 1.82 (4H, m, 2 × OCH2CH2), 1.94 (4H, m, 2 × OCH2CH2), 2.70 (2H, d, 2JH,H = 13.0 Hz, 2 × benzylic CHH), 3.72 (6H, s, 2 × N-CH3), 3.80−3.95 (8H, m, 4 × OCH2), 4.04 (4H, t, 3JH,H = 6.4 Hz, 2 × OCH2), 4.13 (4H, t, 3JH,H = 6.4 Hz, 2 × OCH2), 4.45 (6H, s, 2 × N-CH3), 4.84 (2H, d, 2JH,H = 13.0 Hz, 2 × benzylic CHH), 5.17 (2H, d, 2JH,H = 14.5 Hz, 2 × benzylic CHH), 5.67 (2H, d, 2JH,H = 14.5 Hz, 2 × benzylic CHH), 6.46 (2H, d, 3JH,H = 8.8 Hz, 2 × benzimidazolyl Ar CH), 6.52 (2H, d, 3JH,H = 8.8 Hz, 2 × benzimidazolyl Ar CH), 6.54 (2H, d, 3JH,H = 8.8 Hz, 2 × benzimidazolyl Ar CH), 6.58 (2H, d, 3JH,H = 8.8 Hz, 2 × benzimidazolyl Ar CH), 6.79 (2H, dd, J = 8.8, 6.8 Hz, 2 × xylylene Ar CH), 6.92 (2H, d, J = 8.8 Hz, 2 × xylylene Ar CH), 6.97 (2H, dd, J = 8.4, 6.8 Hz, 2 × xylylene Ar CH), 7.71 (2H, d, J = 8.4 Hz, 2 × xylylene Ar CH). 13C NMR (150.90 MHz, CD2Cl2): δ 13.8, 13.9, 14.0, 14.1 (CH2CH3), 19.5, 19.7, 19.8, 19.9 (CH2CH3), 31.3, 31.6, 31.7, 32.5 (OCH2CH2), 36.8, 41.1 (NCH3), 50.8, 54.1 (benzylic CH2), 69.0, 69.1, 69.2, 69.5 (OCH2), 97.0, 100.8 (xylylene Ar C), 105.3, 105.5, 105.57, 105.59 (benzimidazolyl Ar CH), 125.0 (benzimidazolyl Ar C), 125.4 (xylylene Ar CH), 126.0 (benzimidazolyl Ar C), 127.0 (xylylene Ar CH), 127.6, 127.8 (benzimidazolyl Ar C), 138.4 (benzimidazolyl Ar CO), 139.2 (xylylene Ar CH), 139.4 (benzimidazolyl Ar CO), 140.0 (xylylene Ar CH), 140.1, 140.3 (benzimidazolyl Ar CO), 191.2, 194.4 (C-Ru). 31P NMR (242.94 MHz, CD2Cl2): δ −144.05 (sep, 1JP,F = 2.92 Hz, PF6). Anal. Calcd for C80H108N8O8Cl3PF6Ru2·(0.5CH2Cl2): C, 53.55; H, 6.08; N, 6.21. Found: C, 53.81; H, 6.32; N, 6.43. Structure Determinations. Full spheres of CCD/area-detector diffractometer data were measured (monochromatic Cu Kα radiation, λ = 1.54178 Å; ω-scans, 2θmax = 134°; T ≈ 100 K), yielding Nt(otal) reflections, these merging to N unique after “analytical” absorption correction and being used in the full-matrix least-squares refinements on F2, refining anisotropic displacement parameters for the nonhydrogen atoms, hydrogen atom treatment following a riding model (reflection weights: (σ2(Fo2) + (aP)2 + (bP))−1 (P = (Fo2 + 2Fc2)/3)) (No reflections with I > 2σ(I)). Neutral atom complex scattering factors were employed within the SHELXL97 program.37 Pertinent results are given below and in the tables and figures. The figures’ displacement ellipsoids have been drawn at the 30% (Figure 2) and 50% (Figure 1) probability amplitude levels. Crystal/Refinement Data. 7·MeCN, C80H108Ag4Br4N8O8·MeCN, M = 2101.9. Monoclinic, space group P21/c, a = 14.6677(1) Å, b = 35.8151(3) Å, c = 17.1801(2) Å, β = 91.928(1)°, V = 9020.0(1) Å3. Dc (Z = 4) = 1.548 g cm−3. μCu = 9.4 mm−1; specimen: 0.29 × 0.18 × 0.08 mm; Tmin,max = 0.23, 0.54. Nt = 87 468, N = 15 885, No = 13426; R1 = F

DOI: 10.1021/om5012165 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics 0.060, wR2 = 0.16 (a = 0.061, b = 72); S = 1.06. |Δρ|max = 2.70 e Å−3. Variata. Disorder was involved in the extremities of various butyl groups: from C (274, 444, 473, 643, 673) and the acetonitrile, site occupancies being refined in concert after preliminary trial, major components 0.631(7) (isotropic displacement parameter forms for major and minor components). (5+)(AgCl2−)·3C6H6 C80H108N8O8Cl5AgRu2·3C6H6. M = 2031.3. Triclinic, space group P1̅, a = 16.7862(10) Å, b = 19.0439(12) Å, c = 19.1721(14) Å, α = 63.626(7)°, β = 88.450(5)°, γ = 64.963(6)°, V = 4876.2(6) Å3, Dc (Z = 2) = 1.384 g cm−3. μCu = 5.8 mm−1; specimen: 0.34 × 0.17 × 0.06 mm; Tmin,max = 0.50, 0.81. Nt = 50395, N = 17 225, No = 11 706; R1 = 0.071, wR2 = 0.20 (a = 0.14); S = 0.98. |Δρ|max = 3.16 e Å−3. Variata. T was 200(2) K.

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(14) Baker, M. V.; Brown, D. H.; Haque, R. A.; Simpson, P. V.; Skelton, B. W.; White, A. H.; Williams, C. C. Organometallics 2009, 28, 3793. (15) Baker, M. V.; Brown, D. H.; Hesler, V. J.; Skelton, B. W.; White, A. H. Organometallics 2007, 26, 250. (16) Baker, M. V.; Brown, D. H.; Simpson, P. V.; Skelton, B. W.; White, A. H.; Williams, C. C. J. Organomet. Chem. 2006, 691, 5845. (17) Baker, M. V.; Skelton, B. W.; White, A. H.; Williams, C. C. J. Chem. Soc., Dalton Trans. 2001, 111. (18) Baker, M. V.; Brown, D. H.; Simpson, P. V.; Skelton, B. W.; White, A. H. Dalton Trans. 2009, 7294. (19) Baker, M. V.; Brown, D. H.; Haque, R. A.; Skelton, B. W.; White, A. H. J. Inclusion Phenom. Macrocyclic Chem. 2009, 65, 97. (20) Willans, C. E.; Anderson, K. M.; Junk, P. C.; Barbour, L. J.; Steed, J. W. Chem. Commun. 2007, 3634. (21) Han, Y.; Hong, Y.-T.; Huynh, H. V. J. Organomet. Chem. 2008, 693, 3159. (22) Baker, M. V.; Brown, D. H.; Haque, R. A.; Skelton, B. W.; White, A. H. Dalton Trans. 2004, 3756. (23) Garrison, J. C.; Simons, R. S.; Talley, J. M.; Wesdemiotis, C.; Tessier, C. A.; Youngs, W. J. Organometallics 2001, 20, 1276. (24) di Nicola, C.; Effendy; Pettinari, C.; Skelton, B. W.; Somers, N.; White, A. H. Inorg. Chim. Acta 2006, 53, 359 (CCDC: TENRUZ01). (25) Liu, Q.-X.; Xu, F.-B.; Li, Q.-S.; Zeng, X.-S.; Leng, X.-B.; Chou, Y. L.; Zhang, Z.-Z. Organometallics 2003, 22, 309. (26) Topf, C.; Hirtenlehner, C.; Zabel, M.; List, M.; Fleck, M.; Monkowius, U. Organometallics 2011, 30, 2755. (27) Cyr, P. W.; Rettig, S. J.; Patrick, B. O.; James, B. R. Organometallics 2002, 21, 4672. (28) Feiken, N.; Pregosin, P. S.; Trabesinger, G. Organometallics 1997, 16, 537. (29) Huber, D.; Kumar, P. G. A.; Pregosin, P. S.; Mezzetti, A. Organometallics 2005, 24, 5221. (30) Tagge, C. D.; Bergman, R. G. J. Am. Chem. Soc. 1996, 118, 6908. (31) Schubert, U.; Neugebauer, D.; Aly, A. A. M. Z. Anorg. Allg. Chem. 1980, 464, 217. (32) Leitao, E. M.; Dubberley, S. R.; Piers, W. E.; Wu, Q.; McDonald, R. Chem.Eur. J. 2008, 14, 11565. (33) Sauvage, X.; Borguet, Y.; Noels, A. F.; Delaude, L.; Demonceau, A. Adv. Synth. Catal. 2007, 349, 255. (34) Quebatte, L.; Solari, E.; Scopelliti, R.; Severin, K. Organometallics 2005, 24, 1404. (35) Borguet, Y.; Sauvage, X.; Zaragoza, G.; Demonceau, A. Organometallics 2011, 30, 2730. (36) Tskhovrebov, A. G.; Solari, E.; Scopelliti, R.; Severin, K. Organometallics 2012, 2012, 7235. (37) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112.

ASSOCIATED CONTENT

S Supporting Information *

Full cif files (excluding structure factor amplitudes). Structural determination, refinement data, hydrogen bond information, and projection of 3·2HCl·H2O. Molecular core geometries of 7· MeCN. CCDC 1008899 ((3·2HCl)·H2O), 1008898 ((5+)(AgCl2−)·3C6H6), and 1008897 (7·MeCN). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail (D. H. Brown): [email protected]. *E-mail (M. V. Baker): [email protected]. Present Address #

Centre for Microscopy, Characterization and Analysis, M310, The University of Western Australia, Crawley, WA 6009, Australia. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Australian Research Council for a Discovery Grant (to M.V.B. and A.H.W.), the Gledden Trust for a Robert and Maude Gledden Postgraduate Scholarship (to P.V.S.), and Curtin University of Technology for a Research and Teaching Fellowship (to D.H.B.).

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REFERENCES

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DOI: 10.1021/om5012165 Organometallics XXXX, XXX, XXX−XXX