Synthesis, Reactivity, and Structural Transformation of Mono- and

Article pubs.acs.org/Organometallics

Synthesis, Reactivity, and Structural Transformation of Mono- and Binuclear Carboranylamidinate-Based 3d Metal Complexes and Metallacarborane Derivatives Zi-Jian Yao† and Guo-Xin Jin*,†,‡ †

Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Fudan University, Shanghai 200433, People's Republic of China ‡ State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People's Republic of China S Supporting Information *

ABSTRACT: A series of carboranylamidinate-based 3d metal complexes are reported. Treatments of 3d metal dichlorides (CoCl2, NiCl2(DME), CuCl2) with the lithium salts of carboranylamidines (CabNH) generate the mononuclear C,N-coordinated complexes [(RNC(closo-1,2-C2B10H10)(NHR)]2M (1−6; M  Co, Ni, Cu; R = iPr, Cy) in moderate yields, respectively. These complexes have similar structures in the solid state, in which the metal atom is coordinated to two nitrogen atoms and bonded to two cage carbon atoms in a distorted-tetrahedral geometry. As a noninnocent ligand, CabNH can be modified to produce carboranylamidinate thiol (CabNSH) and nido derivatives DcabNH (9, 10), respectively. Reaction of cupric acetate with 1 equiv of CabNSH gave the binuclear complexes {[RNC(closo-1,2-C2B10H10)(NHR)]SCu}2 (R = iPr (7), Cy (8)) in 66 and 63% yields, respectively. The structure of 7 shows the formation of a Cu−Cu bond, and the geometry of the Cu2S2 core is planar. The zwitterionic nickel dicarbollide complexes (DcabN)Ni(PPh3)Cl (11, 12) were prepared by reactions of the lithium salts of DcabNH (9, 10) with NiCl2(PPh3)2 in THF. All complexes were characterized by elemental analysis and IR and NMR spectroscopy. The structures of 1, 3−5, 7, and 9−11 were further confirmed by single-crystal X-ray diffraction.

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were synthesized by Edelmann’s group recently.11 This unique ligand could afford an unexpected C,N-chelating coordination mode, which is different from the normal N,N-coordination mode of amidinate ligands. However, the reactivity of carboranylamidinates has been rarely reported so far, although one Sn and two Cr carboranylamidinate complexes have been structurally characterized.11 Moreover, in the search for new types of ligand systems as alternatives to the ubiquitous cyclopentadienyl (Cp) ligand for stabilization of the metal center, the dicarbollyl moiety appears to be a suitable candidate as a π-bonding group instead of the Cp.12 It is worthwhile to investigate the synthesis and reactivity of dicarbollylamidinate. Our previous work exhibited the versatile reactivity of carboranylamidinates toward half-sandwich iridium and rhodium complexes.13 As an ongoing project, we are interested in the effects of ligands and the nature of transition metals on the formation, structure, and stability of metal carboranylamidinate complexes. We herein report the synthesis and structure characterization of 3d metal carboranylamidinate and dicarbol-

INTRODUCTION Carborane derivatives have been widely used1 in the fields of catalysis,2a−g polymers,2h nonlinear optical materials,2i and BNCT (boron−neutron capture therapy) techniques,2j because of their versatile properties and the exceptionally stable carborane backbone.3 Recent reports on unusually stable C,N-,4 C,P-,5 C,S-,6 N,P-,7 N,S-,8 P,P-9 and S,S-chelating10 ocarboranyl metal complexes imply that the o-carboranyl ligand backbone could largely stabilize metal intermediates in organometallic reactions. Therefore, the study of carboranylbased transition-metal complexes with ligands containing dissimilar donor atoms has been of considerable interest, especially a ligand system containing one functional group strongly bound to the metal center and another group that is coordinatively labile.4c These types of metal complexes often exhibit good catalytic activity in polymerization processes, because the coordinatively labile group in such ligands may dissociate from the metal center to produce a necessary vacancy for substrate complexation during the homogeneous catalytic cycle. Carboranylamidinates, which combine the versatile characteristics of both carboranes and amidinates into one system, © 2012 American Chemical Society

Received: November 16, 2011 Published: February 21, 2012 1767

dx.doi.org/10.1021/om2011358 | Organometallics 2012, 31, 1767−1774

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Scheme 1. Synthesis of C,N-Chelating Coordination Mode Complexes 1−6a

Reaction conditions: (i) 1 equiv of n-BuLi, THF, −78 °C; (ii) 0.5 equiv of metal sources (CoCl2, NiCl2(DME), and CuCl2, respectively), THF, room temperature. a

highly soluble in THF and CH2Cl2 and slightly soluble in ether and toluene. All complexes were fully characterized by various spectroscopic techniques and elemental analysis. The IR spectra of these complexes all display a typical strong and broad characteristic B−H absorption at approximately 2565 cm−1, and the absorption at approximately 3425 cm−1 is ascribed to N−H bond vibrations. The 1H and 13C NMR spectra of these complexes were not informative because of the strong paramagnetism of the metal ions. The 11B NMR spectrum of nickel complex 3 exhibits signals at −3.4, −4.2, and −8.4 ppm in a ratio of 1:1:8. The elemental analysis of these complexes indicates that their structures are similar to each other. To unambiguously elucidate their structures, single crystals suitable for X-ray diffraction analyses were obtained by the slow diffusion of hexane into their saturated CH2Cl2 solutions. The crystallographic data of 1 and 3−5 are summarized in Table 1. Figure 1 shows their molecular structures together with selected bond lengths and angles. These complexes have similar solid-state structures, in which the metal atom is bonded to two cage carbon atoms and coordinated to two nitrogen atoms of imine groups in a distorted-tetrahedral geometry. The C−C bond distances of the carborane cage in these complexes were found to increase on complexation. Complex 3 shows the largest increase (1.702(4) Å), that is, 0.065 Å relative to the free ligand (1.637(3) Å). The reason for the increase of the C−C distances can be attributed to the formation of the carbon− metal bond and the coordination interaction of the N atom. The X-ray diffraction study of these complexes further reveals the C,N-coordination mode of the carboranylamidinate ligand with a nearly planar MNC3 (M  Co, Ni, Cu) ring. Similar to the case for half-sandwich complexes,13 all of the structures suggested that the imine group has a preferential coordination ability because no amine-coordinated products were obtained under the previous reaction conditions. Generally, in the presence of methylaluminoxane (MAO), the labile imine group may dissociate from the metal center to produce a necessary vacancy for olefin insertion. Therefore, we tried to investigate the catalytic activity of the nickel complexes for norbornene polymerization on the basis of our previous work. 17 Unfortunately, both of them exhibited poor catalytic activities. The reason may be ascribed to the nonplanar geometry of the metal center, which indicates that the d orbital of the metal was occupied by a single electron. This also explains why the Ni2+ complex is paramagnetic. The dihedral angles between the two M−C−N rings are 88.8° (1), 34.6° (3), 35.7° (4), and 57.7° (5), respectively. For complex 3, the angles of C(2)−C(1)− Ni(1) (108.7(18)°) and C(2)−C(1)−Ni(1) (108.2(18)°)

lyamidinate complexes. On the basis of the systematic research on 1,2-dicarba-closo-dodecarborane-1,2-dichalcogenolates,14 the reactivity of carboranylamidinate thiol was also studied in the present work. All complexes were fully characterized by elemental analysis and IR and NMR spectroscopy.

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RESULTS AND DISCUSSION Recently, we have prepared a series of 18-electron and 16electron half-sandwich carboranylamidinate-based transitionmetal complexes of the type [Cp*MClCabC,N](18e) and [Cp*MCabC,N′](16e) (M  Ir, Rh).13 We observed that these complexes all show an unexpected C,N-chelating coordination mode. Moreover, the 18-electron iridium complex exhibited a good catalytic activity for norbornene polymerization in the presence of cocatalyst (MAO). It is a natural extension for us to do a stepwise study on the reactivity of carboranylamidinate with 3d metals (Fe, Co, Ni, Cu), because of the wide utilization of these metal complexes as catalysts in organic synthesis15 such as cross-couplings,15a−c Diels−Alder reactions,15d and cycloadditions,15e as well as polymerization processes.15f Reactivity of Carboranylamidinate with 3d Metals (Co, Ni, Cu). Treatments of the carboranylamidine CabNH (CabNH = RNC(closo-1,2-C2B10H11)(NHR), R = iPr, Cy) with 1 equiv of n-BuLi in THF at −78 °C, followed by the addition of 0.5 equiv of anhydrous CoCl2 at room temperature, afforded mononuclear complexes 1 and 2 ([(RNC(closo-1,2C2B10H10)(NHR)]2Co, R = iPr (1), Cy (2)) as purple solids in 48% and 51% isolated yields, respectively (Scheme 1). It is noteworthy that the yields were greatly decreased when cobaltous chloride hexahydrate was used as the starting material. Under the same reaction conditions, purple nickel complexes 3 and 4 and blue copper complexes 5 and 6 were obtained, in moderate isolated yields after column chromatography on silica gel, respectively. Complexes 1−4 are very stable in air for months, but copper complexes 5 and 6 are moderately stable in air and show slow decomposition when they contact with moisture. They are also very thermally stable, and no decomposition is observed even after prolonged heating in THF. The unusual thermal stability of these complexes is related to the formation of a five-membered ring and the advantageous properties of the bulky o-carborane unit, including both its electronic and steric effects.16 Different nickel salts such as NiCl2(PPh3)2, NiBr2(PPh3)2, and (Ph3P)Ni(Ph)Cl2 were used as starting materials, respectively. However, the products (3 and 4) were all obtained in yields more or less the same. These mononuclear complexes 1−6 are 1768


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a

0.0499 0.0997 0.392/−0.246

0.0463 0.1194 0.374/−0.278

C18H50B20NiN4 597.53 296(2) 0.710 73 monoclinic P21/c 14.738(15) 13.098(13) 19.264(2) 90 108.9(2) 90 3517.6(6) 4 0.571 1256 8022/0/404 0.834

C18H50B20CoN4 597.75 293(2) 0.710 73 triclinic P1̅ 10.758(4) 16.535(5) 21.784(7) 68.1(5) 82.9(5) 76.4(4) 3493(2) 4 0.511 1252 12069/2/847 0.805 0.0594 0.1461 0.624/−0.259

C30H66B20NiN4 757.78 293(2) 0.710 73 orthorhombic Pca21 21.703(7) 12.238(4) 19.483(7) 90 90 90 5174(3) 4 0.399 1608 11004/4/525 0.882

4

0.0763 0.1709 3.411/−0.285

C18H50B20CuN4 602.36 293(2) 0.710 73 monoclinic P2/n 13.682(9) 8.324(5) 15.107(10) 90 101.5(9) 90 1685.7(19) 2 0.668 630 3635/0/213 0.912

5

0.0417 0.0638 0.411/−0.403

C9H25B10CuN2S 365.01 293(2) 0.710 73 monoclinic P21/c 10.419(4) 17.301(7) 10.917(4) 90 109.0(5) 90 1860.3(12) 2 1.276 752 3660/2/229 0.745

7

0.0622 0.1597 0.246/−0.193

C9H27B9N2 260.62 293(2) 0.710 73 orthorhombic P212121 9.190(4) 12.995(5) 13.616(5) 90 90 90 1626.1(11) 4 0.054 560 3486/1/219 1.026

9

0.0583 0.1254 0.217/−0.184

C15H35B9N2 340.74 293(2) 0.710 73 monoclinic P21/n 9.343(5) 11.937(6) 19.679(10) 90 101.3(7) 90 2151.7(19) 4 0.054 736 4220/0/269 0.856

10

11

0.0489 0.1093 0.511/−0.438

C27H41B9ClN2NiP 616.04 293(2) 0.710 73 monoclinic P21/c 9.531(3) 18.238(6) 19.183(7) 90 103.2(4) 90 3245.3(19) 4 0.751 1288 6967/3/404 0.876

R1 = ∑||Fo| − |Fc|| (based on reflections with Fo2 > 2σF2). wR2 = [∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]]1/2; w = 1/[σ2(Fo2) + (0.095P)2]; P = [max(Fo2, 0) + 2Fc2]/3 (also with Fo2 > 2σF2).

chem formula fw T/K λ/Å cryst syst space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z μ/mm−1 F(000) no. of data/restraints/params goodness of fit on F2 final R indices (I > 2σ(I)a) R1 wR2 largest diff peak/hole (e Å−3)

3

1

Table 1. Crystallographic Data and Structure Refinement Parameters for 1, 3−5, 7, and 9−11

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Figure 1. Molecular structures of 1 and 3−5 with thermal ellipsoids drawn at the 30% level. All hydrogen atoms are omitted for clarity. Selected lengths (Å) and angles (deg) are as follows. 1: C(1)−C(2), 1.682(5); C(10)−C(11), 1.670(5); Co(1)−C(1), 2.041(3); Co(1)−C(10), 2.031(4); Co(1)−N(1), 2.040(3); Co(1)−N(3), 2.072(3); C(1)−Co(1)−N(1), 85.4(13), N(1)−Co(1)−N(3), 127.8(12). 3: C(1)−C(2), 1.700(4); C(10)− C(11), 1.702(4); Ni(1)−C(1), 1.902(3); Ni(1)−C(10), 1.903(3); Ni(1)−N(1), 1.947(2); Ni(1)−N(3), 1.951(2); C(1)−Ni(1)−N(1), 85.9(10), N(1)−Ni(1)−N(3), 97.9(10). 4: C(1)−C(2), 1.691(5); C(16)−C(17), 1.671(6); Ni(1)−C(1), 1.905(4); Ni(1)−C(16), 1.904(4); Ni(1)−N(1), 1.967(4); Ni(1)−N(3), 1.959(3); C(1)−Ni(1)−N(1), 85.9(16), N(1)−Ni(1)−N(3), 98.6(16). 5: C(1)−C(2), 1.651(6); Cu(1)−C(1), 2.036(4); Cu(1)−N(1), 2.010(4); C(1)−Cu(1)−N(1), 85.4(15); N(1)−Cu(1)−N(1A), 152.6(2); C(1)−Cu(1)−C(1A), 132.8(3).

CH3OH at room temperature afforded the sulfur-bridged binuclear copper complexes {[RNC(closo-1,2-C2B10H10)(NHR)]SCu}2 (R  iPr (7), Cy (8)) in 66 and 63% yields, respectively (Scheme 2). To our surprise, this reaction occurred

within the two five-membered rings are almost the same as the expected 108°. The Ni(1)−C bond lengths (1.902(3) and 1.903(3) Å) are similar to those observed in other crystallographically characterized nickel(II) complexes.17 Reactivity of Carboranylamidinate Thiol. The synthesis of multinuclear complexes containing metal−metal bonds has attracted considerable attention over the past few decades, and this great interest was stimulated by the numerous applications of these complexes.18 On the basis of our systematic study, we found that 1,2-dicarba-closo-dodecarborane-1,2-dichalcogenolates were useful ligands in facilitating the formation of multinuclear complexes containing metal−metal bonds. The sulfur atom can readily be used as a good bridging or chelating donor by an incoming low-oxidation-state metal fragment to form multinuclear complexes,14b owing to their filled pz orbitals. In view of another untouched C−H bond in the carborane cage of carboranylamidinate, we then focused on the stepwise modification of CabNH after successful preparation of 1−6. Therefore, the reactivity of carboranylamidinate thiol CabNSH (CabNSH = RNC(closo-1,2-C2B10H10-SH)(NHR), R  iPr, Cy) was studied as an extension of ligand variation. The reaction of CabNSH with 1 equiv of cupric acetate in

Scheme 2. Synthesis of Binuclear Copper Complexes 7 and 8

very rapidly and the products precipitated from the solution in 5 min. The complexes are air and moisture stable. Their solubility is poor: they are slightly soluble in DMSO and CH2Cl2 and almost insoluble in toluene, THF, and CHCl3. The 1 H NMR data do not offer any structural information on 1770


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solvents made it impossible for us to get useful information from the 11B NMR spectra. Synthesis and Reactivity of Nido Derivatives. Upon heating in neat methanol, CabNH underwent facile degradation to selectively remove the boron atom and generate the new nido ligands DcabNH (DcabNH = nido-7-[C(NHR)2]+(7,8C2B9H11)−, R = iPr (9), Cy (10)), respectively (Scheme 3). The products were recrystallized in a CH2Cl2/hexane mixture as colorless crystals in yields of 82% and 80%, respectively. This type of ligand is often used in the synthesis of zwitterionic metallacarboranes.22 The solubility of DcabNH is much less than that of CabNH because of the destruction of a symmetric structure. The characteristic asymmetric pattern in the 11B NMR spectrum in the range of −7.3 to −36.3 ppm and the presence of an absorption at approximately −3.3 ppm in the 1H NMR spectrum both imply a B−H−B interaction on the C2B3 open face.23 Single-crystal X-ray diffraction analysis of DcabNH ligands further supports the spectral data. The crystallographic data of them are summarized in Table 1. As shown in Figure 3, compound 9 is clearly a zwitterionic structure. Interestingly, the C(1)−N(1) distance of 1.317(3) Å is almost the same as that of the C(1)−N(2) bond, suggesting the charge is delocalized over the N(1)−C(1)−N(2) unit. The structure of 10 is similar to that of 9 (see the Supporting Information). The B−B and C−B distances in 9 and 10 are normal and very comparable to those in their parent compounds. The investigation of the reactivity of DcabNH is desired due to the rich coordination sites (a η5-C2B3 face and two N atoms) in this ligand. The reactions of the lithium salts of DcabNH with the NiCl2(PPh3)2 in THF gave, after workup, the zwitterionic nickel dicarbollide complexes (DcabN)Ni(PPh3)Cl ((DcabN)Ni(PPh3)Cl = nido-7-[C(NHR)2]+[(η5-7,8-C2B9H10)Ni(PPh3)Cl]−, R = iPr (11), 67%; Cy (12), 61%) rather than the Ncoordinated CGC-type complexes (Scheme 3). The reason can possibly be ascribed to the steric effects of the isopropyl or cyclohexyl group. To our knowledge, nido-carboranylamidinatebased transition-metal complexes are unknown so far. These complexes were obtained as purple red powders after chromatographic purification column on silica gel. They are highly soluble in THF and CH2Cl2 and slightly soluble in CHCl3 and toluene. In the 1H NMR spectrum of 11, several groups of signals in the range of δ 7.85−7.33 ppm for aromatic protons of PPh3, a multiplet at 4.13−4.05 ppm for NCH protons, and two doublets at 1.51 and 1.32 ppm for CH(CH3)2 protons were observed. The 1H NMR spectrum of 12 is similar to that of 11 except for several groups of signals for Cy in the range δ 1.93−0.90 ppm, instead of the signals of iPr in 11. The incorporation of the phosphine ligand was verified by the 31P NMR chemical shift, which appeared at δ 34.3 ppm for the triphenylphosphine of 11.

whether 7 is a monomeric or dimeric species. The molecular structure of 7 was characterized by single-crystal X-ray analysis. Figure 2 shows the molecular structure of 7 together with selected bond lengths and angles. The structure is centrosym-

Figure 2. Molecular structure of 7 with thermal ellipsoids drawn at the 30% level. Some hydrogen atoms are omitted for clarity. Selected lengths (Å) and angles (deg) are as follows: C(1)−C(2), 1.755(4); S(1)−C(2), 1.775(3); Cu(1)−N(1), 1.968(3); Cu(1)−S(1), 2.481(12); Cu(1)−Cu(1A), 2.549(11); N(1)−Cu(1)−S(1), 98.7(9); S(1)−Cu(1)−S(1A), 114.5(3); Cu(1)−S(1)−Cu(1A), 65.4(3).

metric with the symmetry center located between the two copper atoms. Thus, the planar four-membered ring of Cu2S2 is a parallelogram, in which the lengths of the sides are 2.215(13) and 2.481(12) Å, respectively. In the solid structure of 7, Cu(II) was reduced to Cu(I), and each copper atom was ligated by two sulfur bridges and a nitrogen donor. No doubt there is a tendency for the Cu(I) centers to cluster together.19 The intromolecular distance between the two Cu atoms is 2.549(11) Å, suggesting the formation of the metal−metal bond. The Cu−N bond lengths (1.968(3) Å) are identical and comparable to other similar complexes. The Cu···H(B(3)) distance of 2.23 Å is much shorter than that of complex 5 (3.0− 3.5 Å), which may indicate some weak interaction between the two atoms. In addition to the typical strong characteristic B−H absorption at approximately 2570 cm−1 in the IR spectrum of 7, a new B−H band at lower frequency (∼2360 cm−1) is shown in the spectrum, also indicating that a specific B−H···Cu interaction and lower overall symmetry of the cage.20 Similar splittings of the B−H absorption were observed in 8. Such interaction would be further confirmed by the significantly reduced JBH values in the 11B NMR spectrum;21 however, the poor solubility of the binuclear copper complexes in organic

Scheme 3. Synthesis and Reactivity of Dicarbollylamidinate Ligands

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Figure 3. Molecular structures of 9 and 11 with thermal ellipsoids drawn at the 30% level. All hydrogen atoms of 11 are omitted for clarity. Selected lengths (Å) and angles (deg) are as follows. 9: C(7)−C(8), 1.563(3); C(1)−C(8), 1.479(3); N(1)−C(1), 1.317(3); N(2)−C(1), 1.313(3). 11: C(7)−C(8), 1.628(4); Ni(1)−C(7), 2.250(3); Ni(1)−C(8), 2.105(3); Ni(1)−B(9), 2.154(3); Ni(1)−B(10), 2.089(4); Ni(1)−B(11), 2.086(3); Ni(1)−P(1), 2.1764(11); Ni(1)−Cl(1), 2.2250(10); Ni−C2B3(centroid), 1.56; P(1)−Ni(1)−Cl(1), 91.5(4).

the production of a zwitterionic metallacarborane complex rather than a CGC-type complex indicated that steric effects played an important role in this reaction. Further studies on the synthesis of half-sandwich metallacarboranes incorporating nido-carboranylamidinate ligands are currently underway in our laboratory.

Single crystals suitable for X-ray diffraction analyses were obtained by the slow diffusion of hexane into a saturated solution of 11 in CH2Cl2. Complex 11 crystallized in the monoclinic space group P21/c. The crystallographic data of 11 are summarized in Table 1. Figure 3 shows the molecular structure of 11 together with selected bond lengths and angles. In comparison with DcabNH 9 (1.563(3) Å), the C−C bond length of the carborane cage in 11 (1.628(4) Å) was also found to increase on complexation. The structure shows that the nickel atom is η5 coordinated to the dicarbollide ligand, and the geometry at the metal atom is that of a two-legged piano stool with the nickel atom coordinated by the η5-C2B3, Cl, and P atoms. The molecule is comprised of a nickel(II) phosphine unit which is bonded to a C2B3 face of a dicarbollylamidinate ligand. This is further confirmed by the IR spectrum of the absorption at approximately 1095 cm−1, which is ascribed to the C−P bond vibration. The Ni−P bond length of 2.176(11) Å is within the range of known values for the bond,24 and the plane of P(1)−Ni(1)−Cl(1) is almost perpendicular to the C2B3 face (the dihedral angle is 89.9(65)°). The Ni−C(cage) bond length (2.18 Å (av)) is longer than that of the Ni−B bond (2.11 Å (av)), which indicates that the nickel atom is closer to boron atoms and is not centered over the ring. The Ni− C2B3(certroid) distance of 1.56 Å is similar to reported values.24a

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EXPERIMENTAL SECTION

General Data. All manipulations were performed under an atmosphere of nitrogen using standard Schlenk techniques. CH2Cl2 was dried over CaH2, and THF, diethyl ether, hexane, and toluene were dried over Na and then distilled under a nitrogen atmosphere immediately prior to use. n-Butyllithium (1.6 M in n-hexane, Acros), ocarborane, and other chemicals were used as commercial products without further purification. CabNH and CabNSH were synthesized according to the literature.11,13 1H NMR (400 MHz) and 31P NMR (162 MHz) spectra were measured with a VAVCE DMX-400 spectrometer. 11B NMR (160 MHz) spectra were recorded with a Bruker DMX-500 spectrometer. Elemental analysis was performed on an Elementar vario EL III analyzer. IR (KBr) spectra were measured with the Nicolet FT-IR spectrophotometer. Synthesis of Mononuclear Metal Complexes 1−6. Complex 1. n-BuLi (1.6 M in n-hexane, 0.25 mL, 0.4 mmol) was added to a solution of iPr-CabNH (108 mg, 0.4 mmol) in THF (10 mL) at −78 °C; the mixture was stirred at −78 °C for 1 h and at room temperature for another 2 h. Then anhydrous CoCl2 (26 mg, 0.2 mmol) was added as solid to the above mixture and stirred for 8 h at room temperature. After removal of the solvent under vacuum, the residue was purified by column chromatography on silica gel. Elution with petroleum ether/ CH2Cl2 (1/1) gave 1 (58 mg, 48%) as purple solid. A suitable single crystal of 1 was obtained by slow diffusion of n-hexane into its concentrated dichloromethane solution. IR (KBr, disk): ν 3430 (N−H), 2601, 2548 (B−H) cm−1. Anal. Calcd for C18H50B20CoN4: C, 36.17; H, 8.43; N, 9.37. Found: C, 36.33; H, 8.49; N, 9.56. Complex 2. A procedure analogous to that used to prepare 1 was used, but starting from Cy-CabNH (140 mg, 0.4 mmol). Yield: 77 mg, 51%. IR (KBr, disk): ν 3423 (N−H), 2606, 2545 (B−H) cm−1. Anal. Calcd for C30H66B20CoN4: C, 47.53; H, 8.78; N, 7.39; Found: C, 47.67; H, 8.80; N, 7.44.

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CONCLUSIONS In summary, a series of novel carboranylamidinate-based metal complexes were obtained through the reactions of 3d metal compounds with carboranylamidinates and their derivatives. Mononuclear complexes 1−6 all showed an unexpected C,Nchelating coordination mode rather than a normal N,Nchelating mode. Interestingly, a binuclear Cu(I) complex, which is comprised of a Cu−Cu bond and two sulfur bridges, was obtained through the reaction of cupric acetate with carboranylamidinate thiol. We speculated that Cu(II) was reduced by the lone pair electrons of sulfur. This further confirmed that the sulfur atom can be used as a good bridging or chelating donor owing to their filled pz orbitals. In addition, 1772


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Complex 3. A procedure analogous to that used to prepare 1 was used, but starting from NiCl2(DME) (44 mg, 0.2 mmol). Yield: 66 mg, 55%. 11B NMR (160 MHz, CDCl3, 25 °C): −3.4 (2B), −4.2 (2B), −8.4 (16B) ppm. IR (KBr, disk): ν 3425 (N−H), 2611, 2536 (B−H) cm−1. Anal. Calcd for C18H50B20NiN4: C, 36.18; H, 8.43; N, 9.38; Found: C, 36.25; H, 8.44; N, 9.42. Complex 4. A procedure analogous to that used to prepare 1 was used, but starting from Cy-CabNH (140 mg, 0.4 mmol) and NiCl2(DME) (44 mg, 0.2 mmol). Yield: 82 mg, 54%. IR (KBr, disk): ν 3430 (N−H), 2610, 2530 (B−H) cm−1. Anal. Calcd for C30H66B20NiN4: C, 47.55; H, 8.78; N, 7.39; Found: C, 47.68; H, 8.88; N, 7.39. Complex 5. A procedure analogous to that used to prepare 1 was used, but starting from anhydrous CuCl2 (68 mg, 0.2 mmol). Yield: 43 mg, 36%. IR (KBr, disk): ν 3425 (N−H), 2611, 2536 (B−H) cm−1. Anal. Calcd for C18H50B20CuN4: C, 35.89; H, 8.37; N, 9.30; Found: C, 35.86; H, 8.37; N, 9.44. Complex 6. A procedure analogous to that used to prepare 1 was used, but starting from Cy-CabNH (140 mg, 0.4 mmol) and anhydrous CuCl2 (68 mg, 0.2 mmol). Yield: 60 mg, 39%. IR (KBr, disk): ν 3430 (N−H), 2606, 2530 (B−H) cm−1. Anal. Calcd for C30H66B20CuN4: C, 47.25; H, 8.72; N, 7.35. Found: C, 47.38; H, 8.78; N, 7.39. Synthesis of Carboranylamidinate Thiolate Binuclear Complexes 7 and 8. Complex 7. iPr-CabNSH (156 mg, 0.5 mmol) was dissolved in 20 mL of MeOH, to which was added Cu(OAc)2·H2O (100 mg, 0.5 mmol). A yellow precipitate soon appeared. The resulting solid was obtained by filtration after the reaction mixture was stirred for another 2 h. The product was washed with Et2O several times and dried under vacuum. Yield: 120 mg, 66%. A suitable single crystal of 7 was obtained by slow diffusion of n-hexane into its concentrated dichloromethane solution. 1H NMR (400 MHz, CD2Cl2, 25 °C): δ 3.97 (br s, 4H, NCH), 1.43−1.30 (m, 24H, CH(CH3)2) ppm. IR (KBr, disk): ν 3430 (N−H), 2570 (B−H), 2360 (B−H···Cu) cm−1. Anal. Calcd for C18H50B20Cu2N4S2: C, 29.61; H, 6.90; N, 7.67. Found: C, 29.63; H, 6.91; N, 7.77. Complex 8. A procedure analogous to that used to prepare 7 was used, but starting from Cy-CabNSH (191 mg, 0.5 mmol). Yield: 140 mg, 63%. IR (KBr, disk): ν 3425 (N−H), 2610 (B−H), 2353 (B− H···Cu) cm−1. Anal. Calcd for C30H66B20Cu2N4S2: C, 40.47; H, 7.47; N, 6.29. Found: C, 40.52; H, 7.48; N, 6.36. Synthesis of Ligands 9 and 10. Ligand 9. iPr-CabNH (540 mg, 2 mmol) was dissolved in degassed MeOH (20 mL), and the reaction mixture was stirred at 65 °C for 6 h. After removal of the solvent under vacuum, the residue was purified by column chromatography on silica gel. Elution with petroleum ether/CH2Cl2 (1/3) gave 7 (425 mg, 82%) as a white solid. 1H NMR (400 MHz, DMSO-d6, 25 °C): δ 3.80−3.73 (m, 1H, NCH), 3.53−3.44 (m, 1H, NCH), 1.33 (d, J = 6.4 Hz, 6H, CH(CH3)2), 1.29 (d, J = 6.4 Hz, 6H, CH(CH3)2) ppm. 11B NMR (160 MHz, CDCl3, 25 °C): −7.3 (2B), −11.7 (3B), −18.9 (2B), −31.7(1B), −36.3 (1B) ppm. IR (KBr, disk): ν 3379 (N−H), 2583, 2538 (B−H), 1622 (CN) cm−1. Anal. Calcd for C9H27B9N2: C, 41.48; H, 10.44; N, 10.75. Found: C, 41.50; H, 10.44; N, 10.82. Ligand 10. A procedure analogous to that used to prepare 9 was used, but starting from Cy-CabNH (700 mg, 2 mmol). Yield: 542 mg, 80%. 1H NMR (400 MHz, DMSO-d6, 25 °C): δ 3.48−3.45 (m, 1H, NCH), 3.07−3.05 (m, 1H, NCH), 1.96−1.07 (m, 20H, CH(CH2)5) ppm. IR (KBr, disk): ν 3429 (N−H), 2615, 2536 (B−H) cm−1. Anal. Calcd for C15H35B9N2: C, 52.87; H, 10.35; N, 8.22. Found: C, 52.83; H, 10.35; N, 8.40. Synthesis of Nickel Dicarbollide Complexes 11 and 12. Complex 11. n-BuLi (1.6 M in n-hexane, 0.25 mL, 0.4 mmol) was added to a solution of iPr-DcabNH (104 mg, 0.4 mmol) in THF (10 mL) at −78 °C; the mixture was stirred at −78 °C for 1 h and at room temperature for another 2 h. Then NiCl2(PPh3)2 (262 mg, 0.4 mmol) was added as a solid to the above mixture, and this mixture was stirred for 8 h at room temperature. The mixture turned dark red immediately. After

removal of the solvent under vacuum, the residue was purified by column chromatography on silica gel. Elution with petroleum ether/CH2Cl2 (2/1) gave 11 (165 mg, 67%) as a purple-red solid. A suitable single crystal of 11 was obtained by slow diffusion of n-hexane into its concentrated dichloromethane solution. 1H NMR (400 MHz, CD2Cl2, 25 °C): δ 7.85−7.80 (m, 6H, Ph), 7.53−7.33 (m, 9H, Ph), 4.13−4.05 (m, 2H, NCH), 1.51 (d, J = 8.0 Hz, 6H, CH(CH3)2), 1.32 (d, J = 8.0 Hz, 6H, CH(CH3)2) ppm. 11B NMR (160 MHz, CDCl3, 25 °C): −8.4 (3B), −16.3 (2B), −21.7 (1B), −25.5 (1B), −31.2 (1B), −36.3 (1B) ppm. 31P NMR (162 MHz, CD2Cl2, 25 °C): δ 34.4 (s, PPh3) ppm. IR (KBr, disk): ν 3430 (N−H), 2601, 2548 (B−H), 1095 (C−P) cm − 1 . Anal. Calcd for C27H41B9ClN2NiP: C, 52.64; H, 6.71; N, 4.55. Found: C, 52.66; H, 6.71; N, 4.56. Complex 12. A procedure analogous to that used to prepare 11 was used, but starting from Cy-DcabNH (136 mg, 0.4 mmol). Yield: 542 mg, 80%. 1H NMR (400 MHz, CD2Cl2, 25 °C): δ 7.84−7.79 (m, 6H, Ph), 7.53−7.41 (m, 9H, Ph), 3.72−3.66 (m, 2H, NCH), 1.93−0.90 (m, 20H, CH(CH2)5) ppm. IR (KBr, disk): ν 3429 (N−H), 2615, 2536 (B−H), 1094 (C−P) cm−1. Anal. Calcd for C33H49B9ClN2NiP: C, 56.93; H, 7.09; N, 4.02. Found: C, 56.86; H, 7.08; N, 4.11. X-ray Crystallography. Diffraction data of were collected on a Bruker Smart APEX CCD diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å). All the data were collected at room temperature, and the structures were solved by direct methods and subsequently refined on F2 by using full-matrix least-squares techniques (SHELXL).25 SADABS26 absorption corrections were applied to the data, all non-hydrogen atoms were refined anisotropically, and hydrogen atoms were located at calculated positions. All calculations were performed using the Bruker program Smart. A summary of the crystallographic data and selected experimental information are given in Table 1.

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ASSOCIATED CONTENT

S Supporting Information *

CIF files giving crystallographic data for 1, 3−5, 7, and 9−11. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel: (+86)-21-65643776. Fax: (+86)-21-65641740. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Shanghai Science and Technology Committee (Nos. 08DZ2270500, 08J1400103), the Shanghai Leading Academic Discipline Project (No. B108), and the National Basic Research Program of China (Nos. 2009CB825300 and 2010DFA41160).

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Synthesis, Reactivity, and Structural Transformation of Mono- and

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