Distorted commo

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Distorted commo-Cobaltacarboranes Based on the 5,6-Dicarba-nidodecaborane(12): The First Bimetal Cobalt−Copper ZwitterionContaining Cluster with Four (B−H)4···Cu Bonds Not Showing Fluxional Behavior in Solution Elena V. Balagurova,* Irina V. Pisareva, Alexander F. Smol’yakov, Fedor M. Dolgushin, Ivan A. Godovikov, and Igor T. Chizhevsky A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences, 28 Vavilova Street, 119991 Moscow, Russian Federation S Supporting Information *

ABSTRACT: Treatment of a recently reported complex [Ph4P][closo,nido-CoH(2,4-C2B8H10)(7,8-C2B8H11)] (1) either by H2O2 in acetone or NaH in THF leads to the loss of both the bridging and terminal hydrides yielding the diamagnetic salt of an anionic commo-cobaltacarborane [Ph4P][Co(2,4-isonido-C2B8H10)2] (2) with the {CoC2B8}-cluster units adopting a distorted skeletal geometry of the isonido-type. The anionic commo complex 2 reacts with in situ generated cationic [CuPPh3]+ species to give stable copper−cobalt zwitterion [Ph3PCu][Co(2,4-isonido-C2B8H10)2] (3) with four two-electron, three-center (B−H)4···Cu bonds, and exhibits no fluxional behavior in solution. Complex 3, at the same time, in CH2Cl2 in the presence of 2-fold excess of PPh3 readily converts to a new anionic species [(Ph3P)3Cu][Co(2,4-isonido-C2B8H10)2] (4) which retains initial isonido geometry. All newly obtained diamagnetic commo complexes were characterized by a combination of analytical and multinuclear NMR spectroscopic data and by single-crystal X-ray diffraction studies of complexes 2 and 3.

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INTRODUCTION

characterized examples such as that presented in ref 8 which would seem to be a useful contribution to the area. We have recently reported on the new anionic commohydridocobaltacarborane [closo,nido-CoH(2,4-C2B8H10)(7,8C2B8H11)]1− (1)10 in which a formal Co(III) atom bound to the terminal hydride ligand is sandwiched between two {C2B8}cages exhibiting different hapticity with respect to the metal center. Continuing our studies of this class of commometallacarboranes, we presently report a convenient route to the new anionic commo-cobaltacarborane sandwich [PPh4][Co(2,4-isonido-C2B8H10)2] (2), in which both {CoC2B8}-cluster units, as was found from the crystallographically determined structure, adopt skeletal geometry of isonido-type. We are also reporting the synthesis and single-crystal X-ray diffraction study of the zwitterionic Co−Cu-cluster derived from 2, viz., [CuPPh3][Co(2,4-isonido-C2B8H10)2] (3), as well as the description of its facile transformation into anionic complex

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A large family of sandwich-type commo-shaped metallacarborane complexes of transition group metals based on the [7,8(or 9)-C2B9H11]2− dianions and their derivatives are, at present, recognized as one of the most widely known metallacarborane systems,1 many of which have already been successfully explored in synthetic chemistry and other related areas.2 At the same time, among commo-metallacarboranes derived from the medium-size carboranes such as [5,6-nido-C2B8H12]3−7 or [1,3-arahno-C2B7H13]4 and their derivatives, many fewer representatives have been previously described, and within this family there is only one commo-rhodacarborane species [tmndH][commo-1,1′-Rh(2,4-isonido-C2B8H11)2],8 which possesses a completely symmetrical structure due to both carborane {2,4-C2B8}-ligands being linked to the metal atom by the same distorted isonido coordination mode. Such a distorted isonido geometrical type in commo-metallacarboranes originating from [5,6-nido-C2B8H12] is of interest as they do not fit with the traditional Williams−Wade electron-counting formalism.9 It is therefore important to have further structurally © XXXX American Chemical Society

Received: July 28, 2016

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DOI: 10.1021/acs.inorgchem.6b01823 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 1

isonido-C2B8H10)2], 4, was isolated in 78% yield after recrystallization of the crude material from a CH2Cl2/n-hexane mixture (Scheme 2).

[Cu(PPh3)3][Co(2,4-isonido-C2B8H10)2] (4) in the presence of a 2-fold excess of PPh3.

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RESULTS AND DISCUSSION Synthesis and Characterization of commo-Cobaltacarborane [PPh4][Co(2,4-isonido-C2B8H10)2] (2) and Its Zwitterionic and Anionic Derivatives. It was found that the reaction of the [PPh4]+ salt of [closo,nido-CoH(2,4-C2B8H10)(7,8-C2B8H11)]1− anion 110 with a 10% molar excess of H2O2 in acetone for 24 h, followed by column chromatography, afforded crude solid [PPh4][Co(2,4-isonido-C2B8H10)2], 2. Complex 2 after crystallization from a CH2Cl2/n-hexane mixture was obtained as an air-stable crystalline material in 71% yield. An alternative synthetic route to the abovementioned anionic cluster 2 involves the room-temperature reaction of 1 with an excess of NaH in THF, followed by treatment with Ph4PBr (Scheme 1). The yield of pure complex 2 obtained in this way proved to be relatively higher (84%). Previously, we have studied the structure and fluxional behavior of complex 1 in detail,10 where the existence of the Co−H terminal hydride ligand associated partially with the B(3) atom of the hexahapto coordinated {C2B8H10} ligand was suggested (based on X-ray diffraction and the 1H and 11 B/11B{1H} NMR spectroscopic data). It seems this hydrogen should have some degree of hydride mobility, while bridging hydrogen B−H−B exhibits proton mobility. Very roughly and simplistically, it is possible to give the reaction scheme in such a way: sodium hydride abstracts the bridging hydrogen with evolution of dihydrogen to form a complex with (−2) charged metallacarborane moiety and counterions Na+ and PPh4+. The complex decomposes with evolution of PPh3 and benzene to furnish the sodium analogue of complex 2. This process is facilitated by hydride mobility of the Co−H hydrogen. The formation of the above complex can occur as a single step without generation of the intermediate complex. The sodium salt is transformed to complex 2 by the reaction with PPh4Br. As for hydrogen peroxide, the reaction may occur via another method involving the evolution of two dihydrogen molecules and an oxygen molecule. The reaction of the anionic commo-cobaltacarborane 2 with a source of {Cu(PPh3)}+ was next studied. Thus, treatment of 2 in CH2Cl2 solution with anhydrous CuCl2 in the presence of PPh3, taken as a reducing and coordinating agent, gave the cobalt−copper zwitterionic cluster [Ph3PCu][Co(2,4-isonidoC2B8H10)2], 3 (Scheme 1). Crude product 3 was successfully purified by recrystallization from a CH2Cl2/n-hexane mixture, thus giving rise to air-stable dark brown crystals in 55% yield. When 3 was treated with a 2-fold excess of PPh3 in CH2Cl2 at room temperature, new anionic product [(Ph3P)3Cu][Co(2,4-

Scheme 2

The structure and solution behavior of the diamagnetic commo-cobaltacarborane complexes 2, 3, and 4 were examined by multinuclear NMR spectroscopy. The 11B NMR spectra of all complexes 2, 3, and 4 consist of eight separate doublets of 2B intensity area each with one resonance in the spectra occurring at extremely low field, with the δ(11B) values of 61.6, 44.2, and 60.0 ppm, respectively. These low-field resonances are, apparently, associated with the low-coordinate boron atoms B(3) and B(3)′ and are typically observed in the 11B NMR spectra of 11-vertex isonido-type metallacarborane compounds.11,12 The 1H{11B} NMR spectra of 2, 3, and 4 are in good agreement with such structures as well; each of these displays eight single BH resonances ranging from ca. −1.9 to +6.5 ppm with one proton signal located at the low part of the spectra, at 6.14, 6.50, and 6.22 ppm, respectively. In the midfield region of the 1H NMR spectra, in between 4.76 and 3.81 ppm, there appear two 2H slightly broadened singlet resonances. Because these latter peaks remain unchanged upon 11 B decoupling, they were assigned to the carborane cluster CH protons. The 1H NMR spectra of these complexes also show aromatic signals from the counterions such as [PPh4] (in the case of 2) or [Cu(PPh3)3] (in the case of 4), as well as from the {CuPPh3}-fragment of the zwitterion 3; the ratios of integral intensities of the resonances from the carborane cage CH protons and multiplet resonances from the Ph group in each case of these complexes are different and appear in the spectra of 2, 3, and 4 as 4:20, 4:15, and 4:45, respectively. Other resonances from the cluster BH vertices occur as extremely broad and unresolved peaks in the range ca. −1.25 to +6.55 ppm (see, for example, Figure 3). In the [11B−11B]-COSY spectra of complexes 2−4 there exists a correlation between most of the resonances from the adjacent boron atoms with a short B−B bond (as an example, see Figure 1 for complex 3). B


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Inorganic Chemistry

Figure 1. [11B−11B]-COSY spectrum of complex 3 in CD2Cl2 solution at 20 °C.

Figure 2. [1H{11B}−11B{1H}]-HETCOR spectrum of complex 3 in CD2Cl2 solution at 20 °C.

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Article

Inorganic Chemistry

Figure 3. NMR 1H{11B} spectra of compound 2 (above) and compound 3 (below) in CD2Cl2 solution at 20 °C.

wherein all four cluster (B−H)4···Cu units can be easily observed with the use of the room-temperature 1H{11B} NMR spectroscopy, as displayed in Figure 3 Further support for the commo structure of 2 and 3 and their precise connectivity pattern in the solid state was provided by single-crystal X-ray diffraction studies (Figure 4, Tables 1 and 2). Diffraction-quality single crystals of 2 and 3 were grown from a CH2Cl2/n-hexane mixture. The X-ray diffraction studies of 2 and 3 proved these species to be rare commo-metallacarborane clusters with the distorted isonido geometric features, where in each of the {Co(2,4C 2 B 8 H 10 )} fragments an 18-electron Co(III) atom is pentahapto coordinated by {2,4-C2B8}-cage ligands. Both complexes 2 and 3 are characterized by a well-defined tetragonal open-face within the {Co(2,4-C2B8H10)} fragments with essentially nonbonding Co(1)···C(4)/C′(4) distances and by the presence of three vertices in the cage ligands that have cluster connectivity of four. It has become apparent that the longest metal-to-cage interatomic distances in the {Co(2,4C2B8H10)} moieties of 2 or 3 are those involving C(4)/C(4′) atoms [2.532(3) and 2.594(3) Å in 2, and 2.622(3) and 2.614(3) Å in 3], while the other carbon atoms C(2)/C(2′) as well as the boron atoms B(3)/B(3′), which also reside at lowconnectivity cage positions, showed significantly shorter bonding distances: [Co−C(2)/C(2′), 1.988(3) and 1.989(3) Å in 2], and [2.008(3) and 1.998(3) Å in 3], and [Co−B(3)/ B(3′), 1.972(4) and 1.960(4) Å in 2, and 1.995(3) and 1.999(3) Å in 3]. The shortest cage distances found in 2 and 3 are C(2)−C(4) and C(2′)−C(4′) [both 1.463(5) Å in 2, and 1.482(5) and 1.465(4) Å in 3], confirming the adjacency of carbon atoms in the polyhedral cages.

However, several theoretical cross-peaks were not observed in the spectrum, and in particular, these were not found for those B atoms which are connected to the cluster carbons.11,13 Since the 11B chemical shifts of cluster boron atoms generally correlate with the corresponding {B−H(exo)} protons,14 all proton and boron resonances observed in the 1H{11B} and 11 1 B{ H} NMR spectra of 2, 3, and 4 can be readily assigned, and for complex 3 these assignments have been clearly confirmed by parallel [1H{11B}−11B{1H}]-HETCOR experiments (Figure 2). As expected, the 31P{1H} NMR spectra of 2 and 4 show in each case only one resonance with chemical shifts at 23.3 and 1.25 ppm, these being in typical NMR positions for such counterions: [PPh4]10,15 and [Cu(PPh3)3],15,16 respectively. The 31P{1H} NMR spectrum of 3 revealed one somewhat broadened resonance due to the {Cu(PPh3)}-moiety with a chemical shift at −0.61 ppm. One particularly noteworthy feature of cluster 3 is that it displays no dynamic behavior in solution, and its NMR spectra are static even at room temperature, in contrast to numerous, if not all, of the previously reported M−Cu bimetallacarborane complexes either with one, two, or three cage (B−H)n···Cu bonds. As far as we are aware, bimetallacarborane clusters with such two-electron, three-center (2e, 3c) bonding systems are usually fluxional in solution, even at very low temperature, due to the fast migration of the copper-containing moiety over the surface of the carborane cage ligands.15−17 This fact, therefore, does not allow us to detect diagnostic resonances for (B−H)n··· Cu linkages in these dynamic M−Cu bimetallacarborane species by the 1H NMR spectroscopy. The absence of the fluxionality in solution makes complex 3 a unique species, D


Article

Inorganic Chemistry

Table 1. Selected Bond Lengths (Å) and Angles (deg) in the [Co(2,4-isonido-C2B8H10)2] Fragment in Complexes 2 and 3 anionic complex 2 Co(1)−C(2) Co(1)−B(3) Co(1)−C(4) Co(1)−B(5) Co(1)−B(6) Co(1)−B(7) Co(1)−C(2′) Co(1)−B(3′) Co(1)−C(4′) Co(1)−B(5′) Co(1)−B(6′) Co(1)−B(7′) C(2)−C(4) B(3)−B(6) C(2′)−C(4′) B(3′)−B(6′) B(3)−H(3) B(6)−H(6) B(3′)−H(3′) B(6′)−H(6′) Co(1)−B(3)−H(3) Co(1)−B(6)−H(6) Co(1)−B(3′)−H(3′) Co(1)−B(6′)−H(6′)

1.988(3) 1.972(4) 2.532(3) 2.203(4) 2.244(4) 2.290(4) 1.989(3) 1.960(4) 2.594(3) 2.203(4) 2.242(4) 2.306(4) 1.463(5) 1.723(6) 1.463(5) 1.739(6) 1.12(4) 1.08(3) 1.19(4) 1.17(3) 131.1(19) 129.0(18) 127.0(18) 126.8(16)

zwitterionic cluster 3 Co(1)−C(2) Co(1)−B(3) Co(1)−C(4) Co(1)−B(5) Co(1)−B(6) Co(1)−B(7) Co(1)−C(2′) Co(1)−B(3′) Co(1)−C(4′) Co(1)−B(5′) Co(1)−B(6′) Co(1)−B(7′) C(2)−C(4) B(3)−B(6) C(2′)−C(4′) B(3′)−B(6′) B(3)−H(3) B(6)−H(6) B(3′)−H(3′) B(6′)−H(6′) Co(1)−B(3)−H(3) Co(1)−B(6)−H(6) Co(1)−B(3′)−H(3′) Co(1)−B(6′)−H(6′)

2.008(3) 1.995(3) 2.622(3) 2.236(3) 2.290(3) 2.346(3) 1.998(3) 1.999(3) 2.614(3) 2.231(4) 2.286(3) 2.363(3) 1.482(5) 1.749(5) 1.465(4) 1.757(5) 1.12(4) 1.13(4) 1.11(4) 1.08(4) 126.1(19) 124.0(19) 125.2(19) 125.1(19)

Table 2. Geometrical Parameters of the Coordination Environment of Copper Atom in Complex 3 Co(1)−Cu(1) B(3)−Cu(1) B(6)−Cu(1) B(3′)−Cu(1) B(6′)−Cu(1) Cu(1)−P(1) Cu(1)−H(3) Cu(1)−H(6) Cu(1)−H(3′) Cu(1)−H(6′)

Figure 4. ORTEP projection of the anion of 2 (in the above) and zwitterionic complex 3 (in the bellow). Thermal ellipsoids are drawn at the 50% probability level. The [PPh4]+ counterion of anion 2 has been omitted for clarity.

Zwitterionic complex 3 represents the first structurally characterized commo-metallacarborane cluster where the cage carborane ligands function in a tetradentate manner toward the exopolyhedrally bound Cu(I)-containing moiety via four B− H···Cu bonds. Consequently, the copper atom in complex 3 has a five-coordinate environment, which is a relatively rare example in the coordination chemistry of CuI. Taking into account the four hydrogen atoms of the B−H···Cu bonds and phosphorus atom of the PPh3 group, a distorted tetragonal pyramidal geometry is observed for the copper atom (see angles in Table 2). As can be seen from Figure 4 (on the right), the [CuPPh3]+ fragment interacts with the [Co(2,4-isonidoC2B8H10)2]− anion by involving both β-boron atoms in the carborane upper belts with respect to the cage carbon atoms. This fact suggests that these boron atoms B(3,3′) and B(6,6′) in 3 are able, to a greater extent than others, to transfer electrons to the [Cu(PPh3)]+ cation via the 2e,3c (B−H)4···Cu bond system. Previously, by means of the analysis of the electron density distribution in the [4,8,8′-(exo-{PPh3Cu}4,8,8′-(μ-H) 3-commo-3,3′-Co(1,2-C2B9H 9)(1′,2′-C 2B9H 10)] cluster, we have shown the 2e,3c character of such B−H···Cu bonding interactions.18 Comparing the geometry of complexes

2.7584(5) 2.284(3) 2.238(3) 2.194(3) 2.350(3) 2.2482(8) 2.24(4) 1.95(4) 2.05(4) 2.35(4)

P(1)−Cu(1)−H(6) P(1)−Cu(1)−H(3′) P(1)−Cu(1)−H(3) P(1)−Cu(1)−H(6′) H(6)−Cu(1)−H(3) H(6)−Cu(1)−H(3′) H(6)−Cu(1)−H(6′) H(3′)−Cu(1)−H(6′) H(3′)−Cu(1)−H(3) H(3)−Cu(1)−H(6′)

107(1) 105(1) 118(1) 99(1) 95(2) 80(2) 154(2) 95(2) 136(2) 71(2)

2 and 3, one can observe that the 2e,3c (B−H)4···Cu bonding motif found in 3 noticeably affects not only B−H fragments involved in the interaction with the copper-containing moiety, but some other geometrical parameters of this complex as well. Thus, there is a subtle widening of the of the X1−Co(1)−X2 angle (98.0°) in 3 as compared to the corresponding angle (93.4°) in the commo cluster 2, not coordinated to the coppercontaining moiety (X1 and X2 are the midpoints of the B(3)− B(6) and B(3′)−B(6′) bonds, respectively). All the Co− {C2B4} distances in 3 are systematically longer than the corresponding distances in 2 (see Table 1), which means that carborane ligand tends to become a little bit more loosely bound to the metal center as a result of the involvement of both {C2B8}-ligands in the coordination with the copper-containing moiety. Such angles as Co−B(3)−H(3) and Co−B(6)−H(6) also show some characteristic differences, being on average equal to 129° and 125° in 2 and 3, respectively (see Table 1). In addition, small but regular increases in some of the cluster bond lengths are noteworthy (e.g., increase in the B(3)−B(6) and B(3′)−B(6′) average lengths from 1.73 Å in 2 to 1.75 Å in 3). E


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Inorganic Chemistry

(d, 1B, B(5), 1J(B, H) = 150 Hz) [+2.79]; 0.44 (d, 1B, B(6), 1J(B, H) = 145 Hz) [+2.30]; −13.7 (d, 1B, B(10), 1J(B, H) = 150 Hz) [+1.85]; −19.3 (d, 1B, B(8), 1J(B, H) = 179 Hz) [+1.24]; −25.1 (d, 1B, B(11), 1 J(B, H) = 141.5 Hz) [+0.84]; −36.58 (d, 1B, B(7), 1J(B, H) = 149 Hz) [−1.92]. 31P{1H} NMR (CD2Cl2, 161.97 MHz, 20 °C) +23.3 (s, PPh4). IR (KBr, cm−1): 2543 ν (BH), 3057 ν (CHcarb). Anal. Calcd for C28H40B16PCo: C, 52.60; H, 6.26; B, 27.05; P, 4.85; Co, 9.24. Found: C 52.80; H, 6.35; B, 27.15; P, 4.86; Co, 9.25. Alternative Route to 2 Starting from commo Complex 1 and NaH in THF. To a suspension of NaH (20 mg, 0.44 mmol), taken as 50% suspension in oil, in 15 mL of THF was added anionic complex 1 (70 mg, 0.11 mmol) in the solid state, and the resulting suspension was stirred at room temperature for 5 min. During this time, the color of the reaction mixture turned from a purple to reddish-brown. Solid PPh4Br (46 mg, 0.11 mmol) was then added to the resulting solution, and the mixture was stirred additionally for 10 min. Solvent was evaporated under reduced pressure, and the residue was treated by column chromatography on silica gel. The only band eluted from the column using CH2Cl2 as eluent was found to contain complex 2. The recrystallization of the crude material from CH2Cl2/n-hexane afforded 60 mg (84% yield) of pure deep brown crystalline product, which from analysis of 1H, 31P{1H} and 11B NMR spectra is deduced to be anionic complex 2. Anal. Calcd for C28H40B16PCo: C, 52.60; H, 6.26; B, 27.05; P, 4.85; Co, 9.24. Found: C 52.80; H, 6.35; B, 27.15; P, 4.86; Co, 9.25. Preparation of [Ph3PCu][Co(2,4-isonido-C2B8H10)2] (3) from commo Complex 2 and an Anhydrous CuCl2 in CH2Cl2. To a mixture of 2 (100 mg, 0.18 mmol) and PPh3 (120 mg, 0.20 mmol) in 15 mL of dry CH2Cl2 was added anhydrous CuCl2 (27 mg, 0.20 mmol) in the solid state, and the resulting suspension was stirred at room temperature for 1 h until starting complex 2 disappeared (TLCcontrol; eluent CH2Cl2/n-hexane, 1:3). Solvent was evaporated under reduced pressure, and the residue was treated by column chromatography on silica gel. The brown band was eluted from the column with a CH2Cl2/n-hexane (1:3) mixture to give the crude solid product. The obtained solid material was then recrystallized from a CH2Cl2/n-hexane (1:5) mixture, resulting in the isolation of 60 mg (55% yield) of analytically pure zwitterionic complex 3 as deep brown crystals. 1H NMR (CD2Cl2, 400.13 MHz, 20 °C): 7.60−7.50 (set of three m, 15H, Ph3P); 4.76, 4.19 (s br, 2H each, CH-carb). 11B NMR (128.33 MHz, CD2Cl2, 20 °C) [1H(11B)] 44.2 (d, 1B, B(3), J(11B, 1H) = 157 Hz) [+6.51]; 10.8 (d, 1B, B(9), J(11B, 1H) = 142 Hz) [+3.29]; 3.6 (d, 1B, B(5), J(11B, 1H) = 141 Hz) [+3.25]; −8.4 (d, 1B, B(6), J(11B, 1H) = 127 Hz) [+2.62]; −13.0 (d, 1B, B(10), J(11B, 1H) = 162.7 Hz) [+2.10]; −16.0 (d, 1B, B(8), J(11B,1H) = 118.5 Hz) [+1.53]; −21.8 (d, 1B, B(11), J(11B, 1H) = 151 Hz) [+1.28]; −31.0 (d, 1B, B(7), J(11B, 1H) = 166 Hz) [−1.03]. 31P{1H} NMR (CD2Cl2, 161.97 MHz, 20 °C) −0.61 (s br, Ph3P). IR (KBr, cm−1): 2556 ν (BH), 3053 ν (CHcarb). Anal. Calcd for C22H35B16PCoCu: C, 42.21; H, 5.63; B, 27.63; P, 4.95; Co, 9.24. Found: C 42.19; H, 5.64; B, 27.59; P, 4.92. Preparation of [Cu(PPh3)3][Co(2,4-isonido-C2B8H10)2] (4) from Complex 3 and PPh3. To a stirred brown solution of 3 (80 mg, 0.13 mmol) in 15 mL of CH2Cl2 was added the 2-fold excess of PPh3 (70 mg, 0.27 mmol). After being stirred for 1.5 h at room temperature, the reaction was complete (TLC-control; eluent CH2Cl2/n-hexane, 1:3), and the resulting solution was evaporated to dryness. The residue was then crystallized from n-hexane/CH2Cl2 affording 110 mg (78% yield) of analytically pure complex 4 as brown crystals. 1H NMR (400.13 MHz, CD2Cl2, 20 °C) 7.40−7.05 (set of three m, 45H, Ph3P); 4.03, 3.84 (s br, 2H each, CH-carb). 11B NMR (CD2Cl2, 128.33 MHz, 20 °C) [1H(11B)] 61.0 (d, 1B, B(3), J(11B, 1H) = 152 Hz) [+6.25], 11.6 (d, 1B, B(9), J(11B, 1H) = 140 Hz) [+3.32], 4.3 (d, 1B, B(5), J(11B, 1 H) = 146 Hz) [+2.86], 0.28 (d, 1B, B(6), J(11B, 1H) = 148 Hz) [+2.43], −13.6 (d, 1B, B(10), J(11B, 1H) = 152 Hz) [+1.92], −19.5 (d, 1B, B(8), J(11B, 1H) = 167 Hz) [+1.32], −25.0 (d, 1B, B(11), J(11B, 1 H) = 137 Hz) [+0.94], −36.32 (d, 1B, B(7), J(11B, 1H) = 149 Hz) [−1.82]. 31P{1H} NMR (CD2Cl2, 161.97 MHz, 20 °C) +1.25 (s br, PPh3). IR (KBr, cm−1): 2549 ν (BH), 3051 ν (CHcarb). Anal. Calcd for C58H65B16P3CoCu: C, 60.56; H, 5.66; B, 15.04; P, 8.09; Co, 5.13; Cu, 5.52. Found: C 60.64; H, 5.57; B, 15.09; P, 7.72; Co, 5.10; Cu, 5.70.

The Co···Cu distance in 3 (2.7584(5) Å) is somewhat longer than those bond lengths found in the majority of the Co−Cuclusters which usually do not exceed 2.60 Å according to the data of Cambridge Crystallographic Data Center (version 5.37, November 2015; see column diagram deposited as Supporting Information, Figure SI-1). Although structural information for the Co−Cu bimetallacarboranes is very limited, the Co···Cu separation found in 3 can usefully be compared with the metal−metal bond distances of Co−Cu found in two monocarbon metallacarborane complexes, viz. tetrametallic [6,7,8,9,10-{Co2Cu(μ-CO)(CO)3(PPh3)2}-6-(μ-CO)-7,8,9-(μH)3-6,6-(CO)2-closo-6,1-CoCB8H5] (2.505 Å)19 and bimetallic [2,7,11-{Cu(PPh 3 )}-7,11-(μ -H) 2 -2-NO-2-PPh 3 -closo-2,1CoCB10H9] (2.597 Å)20 studied by Stone and co-workers. The comparison of the Co···Cu separation found in 3 with those in the above-mentioned compounds leads to the conclusion that the metal−metal interaction in 3 does not exist.

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CONCLUSION In this paper, the facile synthesis of a short series of novel diamagnetic commo-cobaltacarboranes based on 5,6-dicarbanido-decaborane(12) has been described. These include the following: two anionic clusters [Ph4 P][Co(2,4-isonidoC2B8H10)2] (2) and [(Ph3P)3Cu][Co(2,4-isonido-C2B8H10)2] (4), and one zwitterion [Ph3PCu][Co(2,4-isonido-C2B8H10)2] (3). X-ray structure determination of two of these complexes, 2 and 3, unambiguously confirmed the future distorted commometallacarborane clusters, where the {CoC2B8}-units adopt skeletal geometry of the isonido-type. Unlike many other currently known Cu−(transition metal) bimetallacarboranes, showing dynamic behavior in solution, complex 3 exhibits no fluxionality in solution, even at room temperature, and can thus be considered as an excellent NMR model for the study of the two-electron, three-center B−H···Cu bond interaction.

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EXPERIMENTAL SECTION

All experiments were carried out under an atmosphere of dry argon using standard Schlenk techniques. All solvents were freshly distilled from appropriate drying agents under an argon atmosphere. All other reagents were reagent grade and used as received. The roomtemperature 1H, 1H{11B} as well as 11B/11B{1H} NMR spectra were obtained with a Bruker AMX-400 (1H, 400.13 MHz; 11B, 128.33 MHz; 31 P, 161.97 MHz,) spectrometer. Proton, phosphorus, and boron chemical shifts were referenced to residual protons in the deuterated solvent used (CD2Cl2, 5.32 ppm vs Me4Si), to external 85% H3PO4 or to external BF3·Et2O, respectively, with downfield shifts taken as positive. Infrared spectra were determined in KBr pellets on a MagnaIR-750 (Nicolet) instrument. Elemental analyses were performed by the Analytical Laboratory of the Institute of Organoelement Compounds of the RAS. Preparation of [PPh4][Co(2,4-isonido-C2B8H10)2] (2) from commo Complex 1 and H2O2 in Acetone. To a stirred solution of 40% H2O2 (2.2 mL) in 10 mL of acetone was added commo complex 1 (200 mg, 0.31 mmol), and the mixture was stirred for another 24 h, while the color of the reaction mixture became reddishbrown. After the solvent acetone in a mixture of H2O−acetone was removed in vacuum, the crude solid was extracted with 2 × 10 mL of CH2Cl2. The resulting solution was partly concentrated, and then treated by column chromatography on silica gel using CH2Cl2 as eluent. After evaporation of the solvent, the resultant powder was dried in vacuum, and then was recrystallized from a CH2Cl2/n-hexane mixture, affording 140 mg (71% yield) of analytically pure deep brown crystals of 2. 1H NMR (CD2Cl2, 400.13 MHz, 20 °C) 7.92−7.62 (set of three m, 20H, Ph4P); 3.99, 3.81 (s br, each 2H, CH-carb). 11B NMR (CD2Cl2, 128.33 MHz, 20 °C) [1H(11B)] 61.6 (d, 1B, B(3), 1J(B, H) = 167 Hz) [+6.14]; 11.6 (d, 1B, B(9), 1J(B, H) = 140 Hz) [+3.22]; 4.3 F


Article

Inorganic Chemistry X-ray Diffraction Study. Single-crystal X-ray diffraction experiments were carried out with a Bruker SMART APEX II diffractometer (graphite-monochromated Mo Ka radiation, λ = 0.71073 Å, ω-scan technique). The APEX II software21 was used for collecting frames of data, indexing reflections, determining lattice constants, integrating intensities of reflections, scaling, and absorption correction while SHELXTL22 was applied for space group and structure determination, refinements, graphics, and structure reporting. The structures were solved by direct methods and refined by the full-matrix least-squares technique against F2 with anisotropic thermal parameters for all nonhydrogen atoms. Hydrogen atoms at the carborane ligands were located from the Fourier synthesis and refined isotropically. The rest of the hydrogen atoms were placed geometrically and included in the structure factors calculation in the riding motion approximation. Crystallographic data for complexes 2 and 3 are presented in the Supporting Information (Table SI-1).

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Iron and Cobalt Bis(tricarbaborane) Complexes. Organometallics 1992, 11, 1672−1680. (g) Barnum, B. A.; Carroll, P. J.; Sneddon, L. G. Sneddon “Syntheses and Structural Characterizations of Metallabis(tricarbadecaboranyl) Sandwiches,(η4-MeC3B7H9)2M (M= Ni, Pd, Pt): Tricarbadecaboranyl Analogs of (η3-C3H5)2M Complexes. Organometallics 1996, 15, 645−654. (h) Ramachandran, B. M.; Trupia, S. M.; Geiger, W. E.; Carroll, P. J.; Sneddon, L. G. Synthetic, Structural, Chemical, and Electrochemical Studies of the Metallatricarbadecaboranyl Analogues of Ferrocene, Ruthenocene, and Osmocene and the Observation of a Reversible η6−η4 Tricarbadecaboranyl Coordination that Is Analogous to the η5−η3 Cyclopentadienyl Ring-Slippage Process. Organometallics 2002, 21, 5078− 5090. (i) Tomlinson, S.; Zheng, C.; Hosmane, N. S.; Yang, J.; Wang, Y.; Zhang, H.; Gray, T. G.; Demissie, T.; Maguire, J. A.; Baumann, F.; Klein, A.; Sarkar, B.; Kaim, W.; Lipscomb, W. N. Chemistry of CTrimethylsilyl-Substituted Heterocarboranes. 31. New Insights into Reaction Pathways of Carborane Ligand Systems: Synthetic, Structural, Spectroscopic, and Electrochemical Studies on Sandwich and Half-Sandwich Metallacarboranes of Iron, Cobalt, and Nickel. Organometallics 2005, 24, 2177−2187. and references therein. (k) Sivaev, I. B.; Bregadze, V. I. Chemistry of Cobalt Bis(dicarbollides). A Review. Collect. Czech. Chem. Commun. 1999, 64, 783−805. (a review). (l) Sivaev, I. B.; Bregadze, V. I. Chemistry of nickel and iron bis(dicarbollides). A review. J. Organomet. Chem. 2000, 614−615, 27−36 (a review).. (2) See, for example: (a) Paxton, R. J.; Beatty, B. G.; Hawthorne, M. F.; Varadarajan, A.; Williams, L. E.; Curtis, F. L.; Knobler, C. B.; Beatty, J. D.; Shively, J. E. A transition metal complex (Venus flytrap cluster) for radioimmunodetection and radioimmunotherapy. Proc. Natl. Acad. Sci. U. S. A. 1991, 88, 3387−3391. (b) Plešek. Potential applications of the boron cluster compounds. Chem. Rev. 1992, 92, 269−278. (c) Viñas, C.; Gomez, S.; Bertran, J.; Barron, J.; Teixidor, F.; Dozol, J.-F; Rouquette, H.; Kivekäs, R.; Sillanpäa, R. C-substituted bis(dicarbollide) metal compounds as sensors and extractants of radionuclides from nuclear wastes. J. Organomet. Chem. 1999, 581, 188−193. (d) Plešek, J. The age of chiral deltahedral borane derivatives. Inorg. Chim. Acta 1999, 289, 45−50. (e) Grű ner, B.; Plešek, J.; Baca, J.; Cisařová, I.; Dozol, J.-F.; Rouquette, H.; Viñas, C.; Selucký, P.; Rais, J. Cobalt bis(dicarbollide) ions with covalently bonded CMPO groups as selective extraction agents for lanthanide and actinide cations from highly acidic nuclear waste solutions. New J. Chem. 2002, 26, 1519−1527. (f) Hawthorne, M. F.; Zink, J. L.; Skelton, J. M.; Bayer, M. J.; Liu, C.; Livshits, E.; Baer, R.; Neuhauser, D. Electrical or Photocontrol of the Rotary Motion of a Metallacarborane. Science 2004, 303, 1849−1851. (g) Cígler, P.; Kožíšek, M.; Ř ezácǒ vá, P.; Brynda, J.; Otwinowski, Z.; Pokorná, J.; Plešek, J.; Grű ner, B.; Dolečová-Márešová, L.; Másǎ , M.; Sedlácě k, J.; Bodem, J.; Kräusslich, H.-G.; Král, V.; Konvalinka, J. From nonpeptide toward noncarbon protease inhibitors: Metallacarboranes as specific and potent inhibitors of HIV protease. Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 15394−15399. (h) Hao, E.; Jensen, T. J.; Courtney, B. H.; Vicente, M. G. H. Synthesis and Cellular Studies of Porphyrin Cobaltacarborane Conjugates. Bioconjugate Chem. 2005, 16, 1495− 1502. (i) Grimes, R. N. Carboranes, 2nd ed.; Elsevier, 2011; pp 1083− 1105 (Chapter 17) and references therein. (3) Evans, W. J.; Hawthorne, M. F. An 11-Atom Polyhedral Metallocarborane Formed from 1,6-closo-B8C2H10 by Polyhedral Expansion. J. Am. Chem. Soc. 1971, 93, 3063−3064. (4) Jones, C. J.; Francis, J. N.; Hawthorne, M. F. New 10- and 11Atom Polyhedral Metallocarboranes Prepared by Polyhedral Contraction. J. Am. Chem. Soc. 1972, 94, 8391−8399. (5) Jones, C. J.; Francis, J. N.; Hawthorne, M. F. Derivative Chemistry of Metallocarboranes. Nido 11-Atom Metallocarboranes and Their Lewis Base Adducts. J. Am. Chem. Soc. 1973, 95, 7633− 7643. (6) (a) Jones, C. J.; Francis, J. N.; Hawthorne, M. F. The chemistry of an 11-atom polyhedral metallocarborane prepared by polyhedral contraction. J. Chem. Soc., Chem. Commun. 1972, 900−901. (b) Churchill, M. R.; Gold, K. Geometry of the (B8C2H10·C5H5N2−)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01823. Crystal data, data collection, and structure refinement parameters for complexes 2 and 3; histogram of all Co− Cu intramolecular distances in range 2.0−3.0 Å (PDF) Crystallographic information for complexes 2 and 3 (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. CIFs have also been deposited at the Cambridge Crystallographic Database Centre and may be obtained from http:// www.ccdc.cam.ac.uk by citing reference numbers CCDC 1496176 and 1496177 for compounds 2 and 3, respectively.

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ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support of the Russian Foundation for Basic Research (Grants 15-03-08415 and 16-33-00957). We thank Dr. I. A. Garbusova for recording IR spectra of all prepared complexes.

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REFERENCES

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Distorted commo

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