Trinuclear Zirconium Polyhydride ({Cp*Zr(BH3CH3 ... - ACS Publications

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Trinuclear Zirconium Polyhydride ({Cp*Zr(BH3CH3)}(μH)2{Cp*Zr(BH3CH3)}(μ-H){Cp*Zr(BH3CH3)})(μ‑κ2C,H:κ1C:κ2C,H-CHBH3) and Its Derivatives: Compounds Containing a Pentacoordinated Carbon Atom Fu-Chen Liu,*,† Heng-Guang Chen,† and Gene-Hsiang Lee‡ †

Department of Chemistry, National Dong Hwa University, Hualien 974, Taiwan, ROC Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, ROC

‡

S Supporting Information *

ABSTRACT: The reaction of Cp*Zr(BH3CH3)3 with an excess amount of trimethylamine in a toluene solution yields the hypercarbon-containing complex ({Cp*Zr(BH3CH3)}(μH) 2 {Cp*Zr(BH 3 CH 3 )}(μ-H){Cp*Zr(BH 3 CH 3 )})(μκ2C,H:κ1C:κ2C,H-CHBH3), 1. To our knowledge, this is the first example in which a hypercoordinated carbon-containing complex was prepared from the reaction of a hydroborate complex with a Lewis base. The reaction of 1, NaH, and [N(CH3)4]Cl produces the anionic product [N(CH3)4][({Cp*ZrCl}{(μ-H)2{Cp*Zr(BH3CH3)}}2)(μ-κ2C,H:κ1C:κ2C,HCHBH3)], 2, whereas the reaction of 1 with B(C6F5)3 produces the hydride abstraction cationic product [({Cp*Zr(BH3CH3)}{(μ-H){Cp*Zr(BH3CH3)}}2)(μ-κ2C,H:κ1C:κ2C,H-CHBH3)][HB(C6F5)3], 3. The further reaction of 3 with [N(CH3)4]Cl and NaOH produces the neutral complex ({Cp*Zr(BH3CH3)}((μ-H){Cp*Zr(BH3CH3)})2)(μ-κ2C,H:κ1C:κ2C,H-CHBH3)(μ3-X) (X = Cl (4), OH (5)). Single-crystal X-ray structures of 1, 2, 3, 4, and 5 reveal a pentacoordinated carbon atom, which coordinates to a boron atom, a hydrogen atom, and three Zr atoms in each complex. The geometry around the hypercarbon in each complex can be best described as either distorted trigonal bipyramidal or distorted square pyramidal. The μ3-bridging Cl− ligand in 4 and OH− ligand in 5 bond to three Zr atoms on the opposite side of the hypercarbon. These hypercarbon-containing complexes were further characterized by elemental analysis, infrared spectroscopy, and NMR spectroscopy. Formations of 2−5 confirm the robust framework of the hypercarbon when undergoing reactions.

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INTRODUCTION It is generally accepted in organic chemistry1 that carbon obeys the octet rule, according to which no more than four bonds can be formed. This rule is applicable to the vast majority of compounds. Consequently, compounds containing a carbon atom with a coordination number higher than four are termed hypercarbon compounds.2 Due to their unusual bonding situation, hypercarbon compounds show many interesting structural and chemical properties.3 Although stable hypercarbon compounds have been suggested through theoretical calculations,4 only rare examples of organic hypercarbon compounds have been reported.5 In contrast, many metalstabilized hypercarbon complexes, most of which contain a bridging μ-CH3 hypercarbon, have been isolated.6 In general, these hypercarbon complexes were prepared from the reaction of an organometallic precursor with Lewis acids, including electrophilic metal-containing reagents7 and nonmetal Lewis acids.8 In continuing efforts toward the study of the chemistry of hydroborate complexes,9 we found that the pentacoordinated carbon-containing complex ({Cp*Zr(BH3CH3)}(μ-H)2{Cp*Zr(BH3CH3)}(μ-H){Cp*Zr(BH3CH3)})(μκ2C,H:κ1C:κ2C,H-CHBH3), 1, can be prepared from the reaction © XXXX American Chemical Society

of Cp*Zr(BH3CH3)3 with excess trimethylamine. The reactions of hydroborate complexes with amine Lewis bases always result in metal hydride species.9,10 To our knowledge, the formation of a hypercarbon complex though C−H activation initiated by an amine Lewis base is unprecedented. The reactivity of 1 was further investigated, and the results show the robust framework of this hypercarbon.

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RESULTS AND DISCUSSION

Preparation and Characterization of 1. The reaction of Cp*Zr(BH3CH3)311 with an excess amount of N(CH3)3 (eq 1) in a toluene solution produced the pentacoordinated carboncontaining complex ({Cp*Zr(BH 3 CH 3 )}(μ-H) 2 {Cp*Zr(BH 3 CH 3 )}(μ-H){Cp*Zr(BH 3 CH 3 )})(μ-κ 2 C,H :κ 1 C :κ 2 C,H CHBH 3), 1. Received: July 29, 2014

A

dx.doi.org/10.1021/om500773e | Organometallics XXXX, XXX, XXX−XXX

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Figure 1. Molecular structure of 1. Selected bond lengths [Å] and angles [deg]: Zr(1)···Zr(2), 3.1194(3); Zr(2)···Zr(3), 3.2928(4); Zr(1)−C(1), 2.333(2); Zr(2)−C(1), 2.391(2); Zr(3)−C(1), 2.311(2); C(1)−B(1), 1.587(3); C(1)−H(1D), 0.88(3); Zr(1)−B(1), 2.565(2); Zr(3)−B(1), 2.533(2); Zr(1)−B(2), 2.601(3); Zr(2)−B(3), 2.592(3); Zr(3)−B(4), 2.341(3); Zr(3)−C(1)−Zr(1), 115.65(9); Zr(3)−C(1)−Zr(2), 88.88(7); Zr(1)−C(1)−Zr(2), 82.64(6); B(1)−C(1)−Zr(3), 78.63(12); B(1)−C(1)−Zr(1), 79.23(12); B(1)−C(1)−Zr(2), 150.71(15); Zr(1)−Zr(2)− Zr(3), 75.568(7).

Zr(1)−C(1)−H(1D) = 123(2)°; Zr(3)−C(1)−H(1D) = 121(2)°); however, the axial bond angle has a large deviation from linearity (Zr(2)−C(1)−B(1) = 150.7(2)°). The Zr−C(1) bond distances fall into the range 2.311(2)−2.391(2) Å and are within the sum of the Zr−C covalent bond radii.12 The C(1)− B(1) bond distance is 1.587(3) Å, which is comparable to distances found in the three terminal [BH3CH3]− ligands (1.575(4)−1.596(4) Å) and to distances found in other methyltrihydroborate complexes.9,13 The hydrogen atom (H(1D)) attached to C(1) is located and refined isotropically with a C(1)−H(1D) distance of 0.88(3) Å. The three bridging hydrides connect the adjacent Zr atoms in a single and double hydride-bridged fashion with corresponding Zr···Zr distances of 3.2928(4) and 3.1194(3) Å, respectively. For the three “{Cp*Zr(BH3CH3)}” fragments, two terminal [CH3BH3]− ligands bond to zirconium atoms through a bidentate bonding mode (Zr(1)−B(2) = 2.601(3) Å; Zr(2)−B(3) = 2.592(3) Å), and the other bonds to zirconium atoms through a tridentate bonding mode (Zr(3)−B(4) = 2.341(3) Å). Their Zr−B distances are consistent with those reported in the literature.14 The tridentate bonding mode found in the third “{Cp*Zr(BH3CH3)}” fragment is caused by the slightly electrondeficient nature of this fragment, in which the Zr(3) atom is bridged to the internal Zr(2) atom by a single hydride. Two broad signals at 10.44 (3B) and −7.78 ppm (1B) were observed in the 11B NMR spectrum and were assigned to the three terminal [CH 3 BH 3 ] − ligands and the bridging [CHBH3]3− ligand, respectively. The broad nature of the boron signals causes the three terminal [CH3BH3]− ligands to appear at the same chemical shift. In the proton NMR spectrum, two major peaks appeared at 2.18 and 1.99 ppm in a 1:2 ratio. These were attributed to the pentamethylcyclopenta-

3Cp*Zr(BH3CH3)3 + 5N(CH3)3 → (Cp*Zr(BH3CH3))3 (H)3 (CHBH3) + 2H 2 + 5CH3BH 2 ·N(CH3)3

(1)

Pale yellow crystals of 1 were isolated with a yield of 36% from a hexane solution. The formation of 1 may proceed through a tandem process that involves the stepwise removal of the CH3BH2·N(CH3)3 amine adduct, double C−H activations to eliminate hydrogen gas, and the assembly of the resulting metal fragments. The formation of the amine adduct CH3BH2· N(CH3)3 and the liberation of hydrogen gas were confirmed through 11B NMR spectroscopy and GC-MS analysis, respectively. A possible mechanism is included in the Supporting Information. The solid-state structure of 1 was determined by singlecrystal X-ray diffraction analysis. The molecular structure of 1 (Figure 1) is composed of three “{Cp*Zr(BH3CH3)}” fragments joined together by a bridging [μ3-CHBH3]3− ligand and three bridging hydrides. The bridging [μ3-CHBH3]3− ligand bonds to the Zr atoms through two BH3 hydrides and a carbon atom. Two BH3 hydrides bond to two peripheral Zr atoms to form two Zr−H−B single hydride-bridged bonds (Zr(1)−B(1) = 2.565(2) Å; Zr(3)−B(1) = 2.533(2) Å). The carbon atom bonds to all three Zr atoms through a μ3-bonding mode, resulting in the pentacoordination of C(1). The geometry around C(1) can be best described as distorted trigonal bipyramidal, with the Zr(1), Zr(3), and H(1D) atoms in the equatorial plane and the Zr(2) and B(1) atoms in the axial positions. The C(1) atom is displaced by 0.031 Å out of the equatorial plane. The equatorial bond angles are slightly deviated from 120° (Zr(1)−C(1)−Zr(3) = 115.65(9)°; B


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Scheme 1

supposition, we intended to prepare the deuterated complex 1, ({Cp*Zr(BD3CH3)}(μ-D)2{Cp*Zr(BD3CH3)}(μ-D){Cp*Zr(BD3CH3)})(μ-κ2C,H:κ1C:κ2C,H-CHBD3) from the reaction of Cp*Zr(BD3CH3)317 with an excess amount of N(CH3)3. However, this experiment was not successful because the H− D exchange occurred during the reaction. The deuterium signals of this deuterated complex were observed not only in the BH3 and the μ-H region but also in the μ-CH region in the 2 D NMR spectrum.18 Reactivity of 1. Although many hypercarbon complexes have been prepared, many of them are stable only under restricted conditions, and their reactions have always involved the destruction of their hypercoordination.6d,f,7f,8a,19 With complex 1 in hand, we were interested in investigating the stability of its hypercarbon framework when it underwent various reactions. Thus, reactions of 1 with the Lewis base NaH and the Lewis acid B(C6F5)3 were performed. The reaction of 1 with NaH was monitored by 11B NMR spectroscopy, and only signals corresponding to complex 1 and the [CH3BH3]− anion were observed during the reaction. The formation of the [CH3BH3]− anion could suggest the replacement of the [CH3BH3]− ligand by a H− anion to yield a complex such as “({Cp*Zr}{(μ-H)2{Cp*Zr(BH3CH3)}}2)(CHBH3)”, as shown in eq 2; however, no new signal was observed in the 11B NMR study.

dienyl groups bound to the internal and two peripheral Zr atoms, respectively. Methyl signals of the related methyltrihydroborate ligands appeared at 1.02 and 0.73 ppm. The μ-CH hydrogen appeared at 5.62 ppm as a broad singlet, and the corresponding carbon signal appeared at 151.11 ppm, also as a broad peak, as was confirmed by the 1H−13C HMQC experiment. The broad μ-CH signal could be caused by the fluxional behavior of 1; however, the results of the variabletemperature proton NMR study (Supporting Information, Figures S1 and S2) showed the rigid nature of 1 and the broad signal of the μ-CH hydrogen remained in the temperature range −80 to 80 °C. The broad carbon signal could be caused by the quadrupolar effect of the adjacent boron nucleus. Two environments of Zr−H−Zr bridging hydrides, appearing at 4.12 (m, 1H) and 0.67 ppm (d, 2JHH = 5.8 Hz, 2H), were observed. The 1H−1H COSY experiment confirmed the coupling of these two kinds of hydrides, which resulted in the appearance of a doublet at 0.67 ppm. The hydride at 4.12 ppm also coupled with the μ-CH hydrogen and resulted in the appearance of a multiplet. Although the chemical shifts of these two kinds of hydrides appeared within the generally observed range (4.73 to −3.17 ppm),15 their chemical shifts are substantially different. Considering the symmetric NMR data of 1 and the formation of μ3-bridging derivatives in 4 and 5 (see below), we suspect the structure of 1 in solution is slightly different from that in the solid state. In solution, complex 1 may contain two single hydride μ2-bridged Zr−H−Zr bonds, which appeared at 0.67 ppm. The hydride, which appeared at 4.12 ppm, could be flipped around the three Zr atoms or exhibit μ3-bridging to all three Zr atoms. In the infrared spectrum, broad absorption bands that appeared within the range 1260−1540 cm−1 can be assigned to the Zr−H stretching of the Zr−H−Zr bridges.16 The hydrogen on the pentacoordinated carbon atom could originate from the methyl substituent of the methyltrihydroborate ligand of the reactant Cp*Zr(BH3CH3)3. To verify this

1 + NaH → ({Cp*Zr}{μ‐H)2 {Cp*Zr(BH3CH3)}}2 ) (CHBH3) + Na[BH3CH3]

(2)

One possibility is that the product was not stable and decomposed immediately as it was formed. Although this suspected product could not be obtained, in the presence of [N(CH3)4]Cl, the Cl− ligand-stabilized product [N(CH3)4][({Cp*ZrCl}{(μ-H)2{Cp*Zr(BH3CH3)}}2)(μ-κ2C,H:κ1C:κ2C,HCHBH3)], 2, was obtained (Scheme 1). Colorless crystals of 2 C


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Figure 2. Molecular structure of the cation in 2. Selected bond lengths [Å] and angles [deg]: Zr(1)···Zr(2), 3.0954(7); Zr(1)−C(1), 2.326(3); Zr(2)−C(1), 2.335(7); Zr(2)−Cl(1), 2.567(2); C(1)−B(1), 1.584(11); C(1)−H(1D), 0.96(7); Zr(1)−B(1), 2.583(5); Zr(1)−B(2), 2.604(8); Zr(1)−C(1)−Zr(2), 83.22(19); Zr(1)−C(1)−Zr(1)#1, 136.2(3); B(1)−C(1)−Zr(1), 80.2(2); B(1)−C(1)−Zr(2), 134.5(6); Zr(1)−Zr(2)−Zr(1) #1, 88.43(3); Zr(3)···Zr(4), 3.0830(8); Zr(3)−C(19), 2.322(3); Zr(4)−C(19), 2.333(8), Zr(4)−Cl(2), 2.583(2); C(19)−B(3), 1.596(13); C(19)− H(19), 0.96(8); Zr(3)−B(3), 2.594(6); Zr(3)−B(4), 2.618(8); Zr(3)−C(19)−Zr(4), 82.9(2); Zr(3)−C(19)−Zr(3)#2, 136.1(3); B(3)−C(19)− Zr(3), 80.6(2); B(3)−C(19)−Zr(4), 135.0(5); Zr(3)−Zr(4)−Zr(3)#2, 88.62(3).

Figure 3. Molecular structure of the cation in 3. Selected bond lengths [Å] and angles [deg]: Zr(1)···Zr(2), 3.3950(4); Zr(2)···Zr(3), 3.3644(5); Zr(1)−C(1), 2.278(3); Zr(2)−C(1), 2.348(3); Zr(3)−C(1), 2.268(3); C(1)−B(1), 1.598(5); C(1)−H(1D), 1.02(4); Zr(1)−B(1), 2.564(4); Zr(3)−B(1), 2.563(4); Zr(1)−B(2), 2.317(4); Zr(2)−B(3), 2.363(4); Zr(3)−B(4), 2.329(4); Zr(3)−C(1)−Zr(1), 136.06(15); Zr(3)−C(1)− Zr(2), 93.57(11); Zr(1)−C(1)−Zr(2), 94.41(11); B(1)−C(1)−Zr(3), 81.06(17); B(1)−C(1)−Zr(1), 80.77(17); B(1)−C(1)−Zr(2), 165.7(2); Zr(1)−Zr(2)−Zr(3), 77.163(8). D


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Figure 4. Molecular structure of 4. Selected bond lengths [Å] and angles [deg]: Zr(1)···Zr(2), 3.2440(5); Zr(2)···Zr(3), 3.2645(5); Zr(1)−C(1), 2.353(4); Zr(2)−C(1), 2.399(3); Zr(3)−C(1), 2.344(3); C(1)−B(1), 1.588(5); C(1)−H(1D), 0.83(4); Zr(1)−Cl(1), 2.6881(9); Zr(2)−Cl(1), 2.6480(9); Zr(3)−Cl(1), 2.7182(10); Zr(1)−B(1), 2.556(4); Zr(3)−B(1), 2.546(4); Zr(1)−B(2), 2.596(5); Zr(2)−B(3), 2.592(5); Zr(3)−B(4), 2.577(4); Zr(3)−C(1)−Zr(1), 120.62(15); Zr(3)−C(1)−Zr(2), 86.98(12); Zr(1)−C(1)−Zr(2), 86.10(11); Zr(2)−Cl(1)−Zr(1), 74.88(2); Zr(2)−Cl(1)−Zr(3), 74.93(2); Zr(1)−Cl(1)−Zr(3), 98.01(3); B(1)−C(1)−Zr(3), 78.1(2); B(1)−C(1)−Zr(1), 78.2(2); B(1)−C(1)−Zr(2), 148.6(3); Zr(1)−Zr(2)−Zr(3), 77.648(11).

or prohibit this pπ−dπ bonding interaction, thus resulting in the longer Zr−Cl bond distances in 2. In contrast to 1, the geometry about the pentacoordinated carbon in 2 can be best described as distorted square pyramidal with three zirconium atoms and one boron atom defining the basal plane (Zr1, Zr1A, Zr2, and B1 in a; Zr3, Zr3A, Zr4, and B3 in b) and a hydrogen atom in the apical position. These basal atoms are displaced away from the least-squares mean plane by 0.053−0.083 Å in a and 0.056−0.086 Å in b. The hypercarbon is displaced above the basal plane by 0.799 Å in a and 0.798 Å in b, and the bond angles between the adjacent basal atoms fall into the ranges 80.2(2)−83.2(2)° in a and 80.6(2)−82.9(2)° in b. The Zr−C bond distances are comparable and fall into a narrow range; they are 2.326(3) and 2.335(7) Å in a and 2.322(3) and 2.333(8) Å in b. The hydrogen atoms attached to the hypercarbons are also located and refined isotropically, displaying C−H bond distances of 0.96(7) Å in a and 0.96(8) Å in b. As each adjacent Zr atom is double hydridebridged, the two terminal [CH3BH3]− ligands in each molecule bond to the Zr atom in a bidentate mode (Zr−B = 2.604(8) and 2.618(8) Å).14 The cationic structure of 3 is shown in Figure 3. Overall, it is quite similar to that of 1 except that one of the bridging hydrides is removed from the double hydride-bridged bond. The two single hydride-bridged Zr···Zr distances are 3.3644(5) and 3.3950(4) Å and are approximately 0.09 Å longer than that found in 1. The geometry of hypercarbon C(1) can be best described as distorted trigonal bipyramidal, with Zr(1), Zr(3), and H(1D) atoms in the equatorial plane and Zr(2) and B(1) atoms in the apical positions. The C(1) atom is displaced out of the equatorial plane by 0.008 Å. In contrast to 1, the bond angles of the atoms in the equatorial plane have larger

were isolated from a THF/hexane two-layer solution. Complex 1 not only reacted with the Lewis base, NaH, but also reacted with the Lewis acid, B(C6F5)3. The reaction of 1 with 1 equiv of B(C6F5)3 in an ether solution produced a hydride abstraction product, [({Cp*Zr(BH3CH3)}{(μ-H){Cp*Zr(BH3CH3)}}2)(μ-κ2C,H:κ1C:κ2C,H-CHBH3)][HB(C6F5)3], 3 (Scheme 1), in a quantitative yield. The purity of the yellow powder of 3 was confirmed by elemental analysis. Complex 3 decomposed gradually in a THF solution; however, yellow crystals of 3 suitable for single-crystal X-ray diffraction analysis could be isolated from a fast crystallization in the THF/hexane two-layer solution. The molecular structures of 2 and 3 are shown in Figures 2 and 3, respectively. The unit cell of 2 contains two molecules of 2 (a and b) and one THF solvent molecule. The bond distances and angles of the two molecules are slightly different, and only the structure of one of them is shown in Figure 2. The anionic structure of 2 is similar to that of 1 except that the terminal [CH3BH3]− ligand bonding to the internal Zr atom in 1 is replaced by a Cl− ligand and that adjacent Zr atoms are connected by two bridging hydrides. The double hydridebridged Zr···Zr distances are 3.0954(7) Å in a and 3.0830(8) Å in b, and the Zr−Cl bond distances are 2.567(2) Å in a and 2.583(2) Å in b. These double hydride-bridged Zr···Zr distances are slightly shorter than that found in 1, while the Zr−Cl bond distances found in 2 are significantly longer than those reported in the literature. The terminal Zr−Cl bond distances in other monocyclopentadienyl or monopentamethylcyclopentadienyl compounds previously reported fall into the range 2.402(1)−2.419(9) Å,20 and these short Zr−Cl bond distances have been attributed to a pπ−dπ bonding interaction. As an anionic species, the electron-rich nature of 2 could reduce E


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Figure 5. Molecular structure of 5. Selected bond lengths [Å] and angles [deg]: Zr(1)···Zr(2), 3.1580(8); Zr(2)···Zr(3), 3.130(1); Zr(1)−C(1), 2.351(7); Zr(2)−C(1), 2.406(7); Zr(3)−C(1), 2.334(7); C(1)−B(1), 1.615(11); C(1)-H(1D), 0.927(6); Zr(1)−O(1), 2.317(6); Zr(2)−O(1), 2.220(6); Zr(3)−O(1), 2.268(6); O(1)−H(1D), 0.84(8); Zr(1)−B(1), 2.557(8); Zr(3)−B(1), 2.547(9); Zr(1)−B(2), 2.563(11); Zr(2)−B(3), 2.585(8); Zr(3)−B(4), 2.577(9); Zr(3)−C(1)−Zr(1), 110.1(3); Zr(3)−C(1)−Zr(2), 82.6(2); Zr(1)−C(1)−Zr(2), 83.2(2); Zr(2)−O(1)−Zr(1), 88.20(19); Zr(2)−O(1)−Zr(3), 88.4(2); Zr(1)−O(1)−Zr(3), 113.8(2); B(1)−C(1)−Zr(3), 78.0(4); B(1)−C(1)−Zr(1), 77.9(4); B(1)−C(1)− Zr(2), 146.2(5); Zr(1)−Zr(2)−Zr(3), 75.28(2).

terminal [CH3BH3]− ligands, the bridging [CHBH3]3− ligand, and the [HB(C6F5)3]− anion, respectively. The chemical shift of the terminal [CH3BH3]− ligands is almost the same as that found in 1, but due to the cationic nature of 3, the bridging [CHBH3]3− signal had an approximate 2 ppm downfield shift. In the proton NMR spectrum, the μ3-CH proton appeared at 5.22 ppm as a broad signal, and the corresponding carbon signal appeared at 164.02 ppm. Due to the D−H exchange with the deuterated THF solvent, the Zr−H−Zr bridging hydrides were not observed. However, the Zr−H stretching16 was observed in the infrared spectrum within the range 1270−1510 cm−1. The [HB(C6F5)3]− hydride at 3.73 ppm was observed from the 1H{11B} NMR experiment. Reactivity of 3. Further reactions of 3 with [N(CH3)4]Cl and NaOH in a THF solution produced the neutral compounds ({Cp*Zr(BH3CH3)}((μ-H){Cp*Zr(BH 3 CH 3 )}) 2 )(μ-κ 2 C,H :κ 1 C :κ 2 C,H -CHBH 3 )(μ 3 -Cl), 4, and ({Cp*Zr(BH 3 CH 3 )}((μ-H){Cp*Zr(BH 3 CH 3 )}) 2 )(μκ2C,H:κ1C:κ2C,H-CHBH3)(μ3-OH), 5, respectively (Scheme 1). Yellow crystals of 4 and pale yellow crystals of 5 were isolated from ether solutions with yields of 41% and 37%, respectively. The solid-state structures of 4 and 5 were determined by single-crystal X-ray diffraction analysis. Their molecular structures are shown in Figures 4 and 5. The molecular structure of 4 can be described as a Cl− ligand capped to the three Zr atoms of the cation in 3 on the opposite side of the bridging [μ3-CHBH3]3− ligand. The geometry about hypercarbon C(1) can be described as distorted trigonal bipyramidal, with the Zr(1), Zr(3), and H(1D) atoms in the equatorial plane

deviations from 120° (Zr(1)−C(1)−Zr(3) = 136.06(15)°; Zr(1)−C(1)−H(1D) = 109(2)°; Zr(3)−C(1)−H(1D) = 115(2)°), but the axial bond angle has a smaller deviation from linearity (Zr(2)−C(1)−B(1) = 165.7(2)°). The Zr−C(1) bond distances fall into the range 2.278(3)−2.348(3) Å, which are slightly shorter than those found in 1. The C(1)−H(1D) bond distance is 1.02(4) Å. Due to the electron-deficient nature of the cation, all three terminal [CH3BH3]− ligands bond to the Zr atoms through a tridentate bonding mode, in which the Zr− B distances fall into the range 2.317(4)−2.363(4) Å.14 In the 11B NMR spectrum of 2, two broad signals at 6.62 and −12.88 ppm in a ratio of 2:1 were observed and were assigned to the two terminal [CH3BH3]− ligands and the bridging [CHBH3]3− ligand, respectively. Compared to those observed in 1, these chemical shifts reflect the electron-rich nature of anionic complex 2, which causes its boron signals to shift to an upfield region. In contrast, the 1H and 13C NMR spectroscopy are not sensitive to the change of the electronic environment in this series of complexes. In the proton NMR spectrum, the μCH hydrogen appeared at 6.52 ppm as a broad singlet. The corresponding carbon signal appeared at 165.73 ppm, also as a broad signal. Due to the D−H exchange with the deuterated THF solvent, only two Zr−H−Zr bridging hydrides appearing at 3.47 ppm were observed. The Zr−H stretching of these Zr− H−Zr bridges16 appeared as broad absorption bands in the infrared spectrum within the range 1260−1520 cm−1. The 11B NMR spectrum of 3 displayed three signals at 10.46 (br s), −6.13 (br s), and −25.49 ppm (d, 2JHB = 93.6 Hz) in a ratio of 3:1:1 in a THF solution, which correspond to three F


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CHBH3]3− ligand in solution.14,23 The two Zr−H−Zr bridging hydrides appeared at 0.65 ppm as a singlet, and their Zr−H stretching16 appeared in the infrared spectrum within the range 1290−1500 cm−1. Unlike complexes 1−4, two isomers of complex 5 were found in solution. Complex 5 displayed two broad asymmetric signals at 8.78 (3B) and −4.95 (1B) ppm in the 11B NMR spectrum. The signal at 8.78 ppm spanned a range of 10 ppm and became more asymmetric upon proton decoupling, while the signal at −4.95 ppm split into two separate signals at −4.76 and −7.81 ppm. In the proton NMR, the μ3-OH protons of the two isomers appeared at 5.05 (d, 4JHH = 5.8 Hz) and 4.14 (m) ppm, and the μ3-CH protons of the two isomers appeared at 5.80 (br s) and 5.63 (br s) ppm. The 1H−1H COSY NMR spectrum suggested that the doublet appearance at 5.05 ppm was caused by the coupling of the μ3-CH proton at 5.80 ppm, and the multiplet at 4.14 ppm was caused by the coupling of the μ3-CH proton at 5.63 ppm and the Zr−H−Zr bridging hydrides at 0.67 ppm. Both the integrations of the μ3-OH and the μ3-CH protons suggested that the ratio of the two isomers is 5:1. In the 13C NMR spectrum, the μ3-CH carbon resonances of the two isomers appeared at 161.00 and 151.35 ppm, respectively, and were confirmed through the 1H−13C HMQC experiment. The formation of isomers in 5 could be attributed to the coordination of the OH− ligand. Although the OH− ligand is μ3-bridging to all three Zr atoms in the solid state, it is possible that the small size of the OH− ligand could have the tendency to reduce its coordination, and it could perhaps form a μ2-bridging mode in solution. Therefore, two different bonding modes for the OH− ligand, μ3-bridging and μ2bridging, may coexist in solution, which explains the observation of isomers in the NMR spectrum. In the infrared spectrum, the Zr−H stretching of the Zr−H−Zr bridges16 appeared within the range 1280−1540 cm−1, and the O−H stretching appeared at 3467 cm−1.

and the Zr(2) and B(1) atoms in the apical positions. The C(1) atom is displaced out of the equatorial plane by 0.039 Å, where the equatorial bond angles are close to 120° (119(3)°, 120.62(15)°, 120(3)°), but the axial bond angle (Zr(2)− C(1)−B(1) = 148.6(3)°) has a large deviation from linearity. The two single hydride-bridged Zr···Zr distances are 3.2440(5) and 3.2645(5) Å, which are approximately 0.12 Å shorter than those found in 3. This is due to the capping effect of the μ3bridging Cl− ligand, which forces the Zr atoms closer to each other. This capping effect also caused a more acute Zr(1)− C(1)−Zr(3) angle in 4 than in 3 (136.06(15)° in 3; 120.62(15)° in 4) and resulted in slightly longer Zr−C(1) bond distances (2.344(3)−2.399(3) Å). The C(1)−H(1D) bond distance is 0.83(4) Å. The μ3-bridging Zr−Cl bond distances fall into the range 2.6480(9)−2.7182(10) Å, and the Zr−Cl−Zr bond angles fall into the range 74.88(2)−98.01(3)°. These μ3-chloride bridging zirconium complexes are rare, and, to our knowledge, there are only two complexes that have been reported. The Zr−Cl bond distances of these complexes fall into the range 2.7890(16)−2.886(1) Å.21 These longer Zr−Cl bond distances could be caused by their larger Zr···Zr separation (3.278(2)−3.574(2) Å). All three terminal [CH3BH3]− ligands in 4 bond to the Zr atoms through a bidentate bonding mode, and the Zr−B distances fall into the range 2.577(4)−2.596(5) Å.14 The molecular structure of 5 is similar to that of 4 except that the μ3-Cl− ligand was replaced by an OH− ligand. The geometry about hypercarbon C(1) also can be described as distorted trigonal bipyramidal with the Zr(1), Zr(3), and H(1D) atoms in the equatorial plane and the Zr(2) and B(1) atoms in the axial positions. The C(1) atom is displaced out of the equatorial plane by 0.013 Å, in which the equatorial bond angles fall into the range 110.1(3)−138.2(5)°, and the Zr(2)− C(1)−B(1) axial bond angle is 146.2(5)°. Due to the capping effect of the smaller μ3-bridging OH− ligand, the Zr atoms are even closer to each other in 5 compared to 4. The Zr(1)− C(1)−Zr(3) bond angle (110.1(3)°) is 10° less than that found in 4, and the two single hydride-bridged Zr···Zr distances are 3.1580(8) and 3.130(1) Å, which are approximately 0.11 Å shorter than those found in 4. The Zr−C(1) bond distances fall into the range 2.334(7)−2.406(7) Å, and the C(1)−H(1D) bond distance is 0.927(6) Å. Compared to the μ3-Cl− ligand in 4, the small atomic radius of oxygen results in shorter Zr−O bond distances and larger Zr−O−Zr bond angles. The μ3bridging Zr−O bond distances fall into the range 2.220(6)− 2.317(6) Å, and the corresponding Zr−O−Zr bond angles fall into the range 88.2(2)−113.8(2)°. The μ3-bridging Zr−O bond distances have been reported to fall into the range 2.05(1)− 2.375(4) Å.22 All three terminal [CH3BH3]− ligands in 5 bond to the Zr atoms through a bidentate bonding mode, and their Zr−B distances fall into the range 2.563(11)−2.585(8) Å.14 The 11B NMR spectrum of 4 displayed two broad signals at 14.85 (3B) and −3.14 (1B) ppm, which correspond to the three terminal [CH3BH3]− ligands and a bridging [CHBH3]3− ligand. In the proton NMR, the μ3-CH proton appeared at 5.82 ppm as a broad doublet (3JHH = 9.1 Hz), and the corresponding carbon signal appeared at 160.23 ppm. The 1H−1H COSY spectrum revealed this μ3-CH proton coupled with one BH3 hydride (possibly from the bridging [μ3-CHBH3]3− ligand), which is obscured by the Cp* signals at approximately 2.01 ppm. The broad doublet signal of μ3-CH turned into a broad singlet as the temperature was raised above 40 °C, suggesting a fast exchange of the bridging borohydrides of the [μ3-

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CONCLUSIONS We prepared a pentacoordinated carbon-containing complex, 1, from the reaction of an organohydroborate complex Cp*Zr(BH3CH3)3 with an excess amount of the amine Lewis base N(CH3)3. The formation of 1 is unique, as it involves double C−H bond activation initiated by the amine Lewis base. The reactions of 1 with a Lewis base and a Lewis acid produce the anionic complex 2 and the cationic complex 3, respectively. Further reactions of 3 with [N(CH3)4]Cl and NaOH produce the μ3-bridging Cl− ligand-containing complex 4 and the OH− ligand-containing complex 5, respectively. The formation of 2− 5 confirms the robust framework of this hypercarbon, in which the pentacoordinated carbon moiety remains intact during reactions.

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EXPERIMENTAL SECTION

General Procedure. All manipulations were carried out on a standard high-vacuum line or in a glovebox under a nitrogen atmosphere. Trimethylamine and all of the solvents were dried over Na/benzophenone and were freshly distilled prior to use. Cp*Zr(BH3CH3)3 was prepared according to the method found in the literature.11 Elemental analyses were recorded on a Hitachi 270-30 spectrometer. Proton spectra (δ(TMS) 0.00 ppm) were recorded on a Bruker Advance DPX300 spectrometer operating at 300.131 MHz or on a Bruker Avance II spectrometer operating at 400.130 MHz. 11B spectra (externally referenced to BF3·OEt2 (δ 0.00 ppm)) were recorded on a Bruker Advance DPX300 spectrometer operating at 96.294 MHz. Infrared spectra were recorded on a Jasco FT/IR-460 G


Organometallics

Article

Plus spectrometer with 4 cm−1 resolution. GC/MS analyses were carried out on a Finnigan Trace GC, to which a Finnigan Trace mass selective detector was attached. The GC was equipped with an EQUITY-5 fused silica capillary column (30 m × 0.25 mm × 0.25 μm film thickness). Helium was used as the carrier gas, and the following temperature program was employed: initial isothermal period of 1 min at 35 °C, an increase at 1 °C/min to 50 °C, and finally an isothermal period of 15 min at 50 °C. X-ray Structural Determinations. Suitable single crystals were mounted and sealed inside glass fibers under nitrogen. Crystallographic data collections were carried out on a Nonius KappaCCD diffractometer with graphite-monochromatored Mo Kα radiation (λ = 0.710 73 Å) at 150(2) or 200(2) K. Cell parameters were retrieved and refined using the DENZO−SMN24 software on all reflections. Data reduction was performed with the DENZO−SMN24 software. An empirical absorption correction was based on the symmetry-equivalent reflections and was applied to the data using the SORTAV25 program. Structural analysis was made using the SHELXTL program on a personal computer. The structure was solved using the SHELXS-9726 program and refined using the SHELXL-9727 program by a full-matrix least-squares method on F2 values. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms attached to the zirconium, boron, or pentacoordinated carbon atoms were found from the Fourier difference map and were refined isotropically. Hydrogen atoms attached to other carbon atoms were fixed at calculated positions and refined using a riding model. Preparation of ({Cp*Zr(BH3CH3)}(μ-H)2{Cp*Zr(BH3CH3)}(μ-H){Cp*Zr(BH3CH3)})(μ-κ2C,H:κ1C:κ2C,H-CHBH3), 1. A 1.250 g (4.0 mmol) amount of Cp*Zr(BH3CH3)3 was dissolved in 10 mL of toluene solution. After degassing, 1.4 mL (16.0 mmol) of N(CH3)3 was transferred into the flask. The solution was warmed to room temperature and continually stirred for 2 days. The solvent and volatilized species were removed from this dark yellow solution under a dynamic pump for 1 day. The resulting oily species was dissolved in hexane for crystallization. A yield of 379.3 mg (36%) of pale yellow crystals was obtained. 11B NMR (C6D6): δ 10.44 (3B), −7.78 ppm (1B). 11B NMR (THF): δ 10.12 (3B), −8.06 (1B). 1H NMR (C6D6): δ 5.62 (br s, 1H, μ-CH), 4.12 (m, 1H, μ-H), 2.18 (s, 15H, Cp*), 1.99 (s, 30H, Cp*), 1.02 (br s, 3H, CH3), 0.73 (br s, 6H, CH3), 0.67 (d, 2 JHH = 5.8 Hz, 2H, μ-H). 1H{11B} NMR (C6D6): δ 1.18 (br s, 3H, BH3), 0.53 (br s, 6H, BH3), −0.03 (br s, 3H, BH3). 13C NMR (C6D6): δ 151.39 (μ-CH), 121.01 (CCH3), 120.01 (CCH3), 13.58 (CCH3), 12.89 (CCH3), 3.94 (BH3CH3), 2.76 (BH3CH3). IR (KBr): 1260− 1540 cm−1 (μ-H). Anal. Calcd for C34H70B4Zr3: C, 51.31; H, 8.87. Found: C, 51.52; H, 8.48. Preparation of [N(CH 3 ) 4 ][({Cp*ZrCl}{(μ-H) 2 {Cp*Zr(BH3CH3)}}2)(μ-κ2C,H:κ1C:κ2C,H-CHBH3)]·THF, 2·THF. Compound 1 (200.50 mg, 0.25 mmol), NaH (7.0 mg, 0.29 mmol), N(CH3)4Cl (55.4 mg, 0.51 mmol), and approximately 5 mL of THF were placed into a 50 mL flask. After stirring for 4 h, the solution was filtered, and the solvent was removed under a dynamic pump. The resulting solids were washed with ether (2 × 5 mL), dissolved in THF, and layered with hexane for crystallization. A yield of 90.1 mg (43%) of colorless crystals was obtained. 11B NMR (d8-THF): δ 6.62 (2B), −12.88 (1B). 1 H NMR (d8-THF): δ 6.52 (br s, 1H, CH), 3.47 (br s, 2H, μ-H), 3.28 (s, 12H, (CH3)4N), 2.06 (s, 30H, Cp*), 1.95 (s, 15H, Cp*), 0.29 (br s, 6H, CH3). 1H{11B} NMR (d8-THF): δ 0.38 (br s, 6H, BH3), −0.27 (d, 3JHH = 7.0 Hz, 3H, BH3). 13C NMR (d8-THF): δ 165.73 (μ-CH), 118.07 (CCH3), 115.40 (CCH3), 55.01 (2JCN = 3.7 Hz, (CH3)4N), 12.26 (CCH3), 11.77 (CCH3), 4.82 (BH3CH3). IR (KBr): 1260−1520 cm−1 (μ-H). Anal. Calcd for C41H85B3ClNOZr3: C, 51.85; H, 9.02. N, 1.47. Found: C, 51.72; H, 8.74; N, 1.43. Preparation of [({Cp*Zr(BH3CH3)}{(μ-H){Cp*Zr(BH3CH3)}}2)(μκ2C,H:κ1C:κ2C,H-CHBH3)][HB(C6F5)3], 3. Compound 1 (200.0 mg, 0.25 mmol), B(C6F5)3 (130 mg, 0.25 mmol), and 5 mL of ether were put into a flask. The yellow precipitate formed immediately after the solvent was added. After stirring for an additional 3 h, the solution was removed through filtration, the yellow solids were washed with 5 mL of ether three times, and they were dried in vacuo. A quantitative yield was obtained. Yellow crystals suitable for X-ray analysis were obtained

from a THF/hexane layered solution. 11B NMR (d8-THF): δ 10.46 (3B), −6.13 (1B), −25.49 (d, 2JHB = 93.6 Hz, 1B). 1H NMR (d8THF): δ 5.22 (br s, 1H, μ-CH), 2.23 (s, 15H, Cp*), 2.21 (s, 30H, Cp*), 0.43 (br s, 3H, CH3), 0.25 ((br s, 6H, CH3). 1H{11B} NMR (d8THF): δ 3.73 (br s, 1H, HB(C6F5)3), 0.61 (br s, 3H, BH3), 0.03 (d, 3 JHH = 6.3 Hz, 3H, BH3), −0.28 (br s, 6H, BH3). 13C NMR (d8-THF): δ 164.02 (μ-CH), 146.43 (d, 2JC−F = 237.6 Hz, C6F5), 135.6 (d, 2JC−F = 241.7 Hz, C6F5), 134.33 (d, 2JC−F = 236.4 Hz, C6F5), 123.51 (CCH3), 122.52 (CCH3), 11.14 (CCH3), 10.20 (CCH3), −2.48 (BH3CH3), −3.42 (BH3CH3). IR (KBr): 1270−1510 cm−1 (μ-H). Anal. Calcd for C52H70B5F15Zr3: C, 47.76; H, 5.39. Found: C, 47.78; H, 5.28. Preparation of ({Cp*Zr(BH3CH3)}((μ-H){Cp*Zr(BH3CH3)})2)(μκ2C,H:κ1C:κ2C,H-CHBH3)(μ3-Cl), 4. Compound 2 (326.0 mg, 0.25 mmol), N(CH3)4Cl (27.4 mg, 0.25 mmol), and approximately 5 mL of THF were placed into a 50 mL flask. The solution was stirred for 4 h, and the yellow solution changed to a light yellow color. The solvent was removed in vacuo, and the resulting solids were extracted with hexane. The hexane was removed, and the resulting white solids were dissolved in ether for crystallization. A yield of 85.8 mg (41%) of yellow crystals was obtained. 11B NMR (C6D6): δ 14.85 (br, 3B), −3.14 (br, 1B). 1H NMR (C6D6, 400 MHz): δ 5.82 (d, 3JHH = 9.1 Hz, 1H, CH), 2.02 (s, 30H, Cp*), 2.01 (s, 15H, Cp*), 1.03 (br s, 9H, CH3), 0.65 (s, 2H, μ-H). 1H{11B}NMR (C6D6): δ 1.37 (br s, 3H, BH3), 0.97 (br s, 6H, BH3), −1.32 (d, 3JHH = 9.0 Hz, 2H, BH3). 13C NMR (C6D6): δ 160.23 (μ-CH), 122.05 (CCH3), 121.62 (CCH3), 13.18 (CCH3), 13.02 (CCH3), 4.88 (BH3CH3), 3.42 (BH3CH3). IR (KBr): 1290−1500 cm−1 (μ-H). Anal. Calcd for C34H69B4ClZr3: C, 49.18; H, 8.38. Found: C, 49.06; H, 8.00. Preparation of ({Cp*Zr(BH3CH3)}((μ-H){Cp*Zr(BH3CH3)})2)(μκ2C,H:κ1C:κ2C,H-CHBH3)(μ3-OH), 5. Compound 2 (326.2 mg, 0.25 mmol), NaOH (10.4 mg, 0.26 mmol), and approximately 5 mL of THF were placed into a 50 mL flask. The solution was stirred for 5 h, and the solvent was removed from this yellow solution. The resulting pale yellow solids were extracted with ether. The ether was removed under vacuum. The extraction was repeated three times, and the resulting solids were dissolved in an ether solution and kept at RT for crystallization. Pale yellow crystals (74.4 mg, 37% yield) were obtained. 11B NMR (C6D6): δ 8.78 (3B), −4.95 (1B). 1H NMR (C6D6, 400 MHz): major: δ 5.80 (br s, 1H, CH), 5.05 (d, 4JHH = 5.8 Hz, OH), 2.05 (s, 15H, Cp*), 1.99 (s, 30H, Cp*), 1.11 (br s, 3H, CH3), 0.86 (br s, 8 H, μ-H + CH3). 1H{11B} NMR (C6D6): δ 1.38 (br s, 3H, BH3), 0.82 (br s, 6H, BH3), 0.54 (br s, 1H, BH3), −1.46 (br s, 2H, BH3); minor: δ 5.63 (m, 1H, CH), 4.14 (m, 1H, OH), 2.18 (s, 15H, Cp*), 1.99 (s, 30H, Cp*), 1.05 (br s, 3H, CH3), 0.75 (br s, 6H, CH3), 0.67 (br s, 2H, μ-H). 1H{11B} NMR (C6D6): δ 1.18 (br s, 1H, BH3), 0.82 (br s, 9H, BH3), −0.01 (br s, 2H, BH3). 13C NMR (C6D6): major: δ 161.00 (μ-CH), 120.44 (CCH3), 120.08 (CCH3), 12.77 (CCH3), 12.51 (CCH3), 5.35 (BH3CH3), 2.66 (BH3CH3); minor: δ 151.35 (μ-CH), 120.81 (CCH3), 119.80 (CCH3), 13.37 (CCH3), 12.67 (CCH3), 3.64 (BH3CH3), 2.66 (BH3CH3). IR (KBr): 1280− 1540 (μ-H), 3467 cm−1 (O−H). Anal. Calcd for C34H70B4OZr3: C, 50.30; H, 8.69. Found: C, 50.07; H, 8.32.

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ASSOCIATED CONTENT

S Supporting Information *

Experimental details, characterization data, and X-ray crystallographic data for 1−5. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. H


Organometallics

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(9) Liu, F.-C.; Chu, Y.-J.; Yang, C.-C.; Lee, G.-H.; Peng, S.-M. Organometallics 2010, 29, 2685. (10) (a) Wolczanski, P. T.; Bercaw, J. E. Organometallics 1982, 1, 793. (b) Luinstra, G. A.; Rief, U.; Prosenc, M. H. Organometallics 1995, 14, 1551. (11) Liu, F.-C.; Yang, C.-C.; Chen, S.-C.; Lee, G.-H.; Peng, S.-M. Dalton Trans. 2008, 3599. (12) Cordero, B.; Gómez, V.; Platero-Prats, A. E.; Revés, M.; Echeverría, J.; Cremades, E.; Barragán, F.; Alvarez, S. Dalton Trans. 2008, 2832. (13) (a) Kot, W. K.; Edelstein, N. M.; Zalkin, A. Inorg. Chem. 1987, 26, 1339. (b) Shinomoto, R.; Zalkin, A.; Edelstein, N. M.; Zhang, D. Inorg. Chem. 1987, 26, 2868. (14) Marks, T. J.; Kolb, J. R. Chem. Rev. 1977, 77, 163. (15) (a) Visser, C.; van den Hende, R. J. R.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics 2001, 20, 1620. (b) Gozum, J. E.; Girolami, G. S. J. Am. Chem. Soc. 1991, 113, 3829. (16) (a) Wang, Y.; Quillian, B.; Wei, P.; Wannere, C. S.; Schleyer, P. V. R.; Robinson, G. H. Organometallics 2006, 25, 3286. (b) Pez, G. P.; Putnik, C. F.; Suib, S. L.; Stucky, G. D. J. Am. Chem. Soc. 1979, 101, 6933. (17) The preparation of Cp*Zr(BD3CH3)3 was similar to that of Cp*Zr(BH3CH3)3, except the reactant [LiBD3CH3] was isolated from the reaction of CH3B(OH)3 with excess LiAlD4. The NMR spectra of Cp*Zr(BD3CH3)3 are included in the Supporting Information. (18) The NMR spectra of complex 1 and deuterated complex 1 are included in the Supporting Information. (19) (a) Waymouth, R. M.; Santarsiero, B. D.; Coots, R. J.; Bronikowski, M. J.; Grubbs, R. H. J. Am. Chem. Soc. 1986, 108, 1427. (b) Chen, Y.; Metz, M. V.; Li, L.; Stern, C. L.; Marks, T. J. J. Chem. Soc. 1998, 120, 6287. (20) (a) Engelhardt, L. M.; Papasergio, R. L.; Raston, C. L.; White, A. H. Organometallics 1984, 3, 18. (b) Ding, E.; Liu, F.-C.; Liu, S.; Meyers, E. A.; Shore, S. G. Inorg. Chem. 2002, 41, 5329. (c) Martín, A.; Mena, M.; Palacios, F. J. Organomet. Chem. 1994, 480, C10. (21) (a) Kirillov, E.; Roisnel, T.; Carpentier, J.-F. Organometallics 2012, 31, 3228. (b) Evans, W. J.; Ansari, M. A.; Ziller, J. W. Polyhedron 1998, 17, 869. (22) (a) Babcock, L. M.; Day, V. W.; Klemperer, W. G. Inorg. Chem. 1989, 28, 806. (b) Otero, A.; Fernández-Baeza, J.; Antiñolo, A.; Tejeda, J.; Lara-Sánchez, A.; Sánchez-Barba, L.; Fernández-López, M.; López-Solera, I. Inorg. Chem. 2004, 43, 1350. (c) Puchberger, M.; Kogler, F. R.; Jupa, M.; Gross, S.; Fric, H.; Kickelbick, G.; Schubert, U. Eur. J. Inorg. Chem. 2006, 3283. (d) Pan, L.; Heddy, R.; Li, J.; Zheng, C.; Huang, X.-Y.; Tang, X.; Kilpatrick, L. Inorg. Chem. 2008, 47, 5537. (e) Li, J.; Gao, Z.; Han, L.; Gao, L.; Zhang, C.; Tikkanen, W. J. Organomet. Chem. 2009, 694, 3444. (f) Malaestean, I. L.; Speldrich, M.; Ellern, A.; Baca, S. G.; Kögerler, P. Dalton Trans. 2011, 40, 331. (g) Kirillov, E.; Roisnel, T.; Carpentier, J.-F. Organometallics 2012, 31, 3228. (23) (a) Frost, P. W.; Howard, J. A. K.; Spencer, J. L. J. Chem. Soc., Chem. Commun. 1984, 1362. (b) Letts, J. B.; Mazanec, T. J.; Meek, D. W. J. Am. Chem. Soc. 1982, 104, 3898. (24) DENZO-SMN: Otwinowsky, Z.; Minor, W. Processing of X-ray Diffraction Data Collected in Oscillation Mode. In Methods in Enzymology, Vol. 276: Macromolecular Crystllography, Part A; Carter, C. W., Jr., Sweet, R. M., Eds.; Academic Press: New York, 1997; p 307. (25) (a) Blessing, R. H. Acta Crystallogr., Sect. A 1995, A51, 33. (b) Blessing, R. H. J. Appl. Crystallogr. 1997, 30, 421. (26) SHELXS-97: Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467. (27) Sheldrick, G. M. SHELXL-97; University of Gö ttingen: Göttingen, Germany, 1997.

ACKNOWLEDGMENTS This work was supported by the National Science Council of the ROC through Grant NSC 101-2113-M-259-005-MY3.

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