Homo- and Heteropolynuclear Clusters of Phosphine Triphenolates

Nov 20, 2015 - The synthesis and structural characterization of a series of homo- and heteropolynuclear clusters constructed with a potentially tetrad...
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Homo- and Heteropolynuclear Clusters of Phosphine Triphenolates Lan-Chang Liang,*,†,‡ Kuan-Wei Chou,† Wei-Jia Su,† Han-Sheng Chen,† and Yu-Lin Hsu† †

Department of Chemistry and Center for Nanoscience & Nanotechnology, National Sun Yat-sen University, Kaohsiung 80424, Taiwan ‡ Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 80708, Taiwan S Supporting Information *

ABSTRACT: The synthesis and structural characterization of a series of homo- and heteropolynuclear clusters constructed with a potentially tetradentate phosphine triphenolate ligand are presented. Treatment of tris(3,5-di-tert-butyl-2-hydroxyphenyl)phosphine (H3[O3P]) with 3 equiv of nBuLi in diethyl ether at −35 °C affords hexanuclear Li6[O3P]2(OEt2)2 (1) as colorless crystals. In situ lithiation of H3[O3P] with 3 equiv of nBuLi in THF at −35 °C followed by metathetical reactions with MnCl2 or NiCl2(DME) gives crystals of forest green pentanuclear MnLi 4 [O 3 P] 2 (THF) 3 (2) or dark brown tetranuclear Ni2Li2[O3P]2(THF)2 (3), respectively. Alkane elimination of ZnR2 (R = Me, Et) with H3[O3P] in THF at 25 °C generates high yields of colorless crystalline trinuclear Zn3[O3P]2(THF)2 (4). The cluster structures of 1−4 were all determined by single crystal X-ray diffraction studies. These molecules represent the first examples of metal complexes supported by phosphine triphenolate derivatives. The cluster 2 contains a paramagnetic core of high spin Mn(II) (S = 5/2) as indicated by solution and solid state magnetic susceptibility measurements.

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INTRODUCTION Cluster chemistry, representing one of the actively expanding subareas of contemporary inorganic chemistry, lies essentially at the cutting edge between molecular and surface chemistry.1 With deliberate bridging and blocking ligands incorporated, molecular metal clusters2 have over the last decades shown significant impacts on structural and reaction chemistry, particularly in the pursuits of materials and catalysis applications.3 For instance, preorganized aggregates of lithium phenolates have been investigated for the preparation of metal−organic frameworks.4 Subtle changes on preparation methods and conformations of participating starting materials such as metallic and ligand precursors and coordinating or noncoordinating solvents employed may lead to dramatically distinct cluster structures and different physical properties thereafter. We are interested in structural and reaction chemistry of metal complexes of hybrid chelating ligands.5 In particular, a number of lithium phenolate clusters (Figure 1)6 have been investigated and their structure/constitution relationship examined. For instance, the molecular cluster Li2[O2PPh](DME)2 ([O2PPh]2− = 2,2′-phenylphosphino-bis(4,6-di-tert-butylphenolate))6a differs in conformation and structure from Li4[O2PPh]2(OEt2)36b and Li4[O2PtBu]2(DME)2 ([O2PtBu]2− = 2,2′-tert-butylphosphinobis(4,6-di-tert-butylphenolate))6c upon changes on coordinating solvents employed for cluster preparation or P-substituents incorporated in the chelating phenolate ligands, respectively. Given the profound versatility of these phosphine biphenolates in cluster conformation and structure variations, we envisioned that the development of cluster chemistry employing a © XXXX American Chemical Society

phosphine triphenolate ligand should also be interesting and fruitful. We note that literature reports on metal complexes of phosphine triphenolates are unprecedented, a result that we found surprisingly as ligands of this general type are close analogues of phosphine mono-7 and biphenolates.6,8 The only report on coordination chemistry of phosphine triphenolates that we are aware of concerns their derivatives of phosphinoxide.9 We present in this contribution the synthesis of tris(3,5di-tert-butyl-2-hydroxyphenyl)phosphine (H3[O3P]) and its, upon complete deprotonation, versatile coordination chemistry in molecular cluster formation.

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RESULTS AND DISCUSSION The ligand precursor H3[O3P] was synthesized in a manner similar to those of its biphenolate analogues H2[O2PPh]10 and H2[O2PtBu].6c In situ lithiation of 2-bromo-4,6-di-tert-butylphenol with 2 equiv of nBuLi in diethyl ether at −35 °C followed by reaction with one-third equiv of phosphorus trichloride affords, after standard anaerobic aqueous workup procedures, H3[O3P] as an off-white solid in 72% yield on a multigram scale. Multinuclear NMR studies are indicative of C3v symmetry for this molecule. For instance, the 1H NMR spectrum reveals only 2 singlet resonances for tBu groups. The hydroxyl protons resonate as a doublet signal at 5.95 ppm with JHP = 7 Hz. This coupling constant is similar to that of H2[O2PPh] (8 Hz)10 but Received: September 25, 2015

A

DOI: 10.1021/acs.inorgchem.5b02208 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. Representative examples of lithium phenolate clusters.

somewhat smaller than that of H2[O2PtBu] (12 Hz),6c consistent with what would be expected for P-aryl versus P-alkylsubstituted derivatives from the viewpoint of substituent electronic effects. The phosphorus atom of H3[O3P] gives rise to a singlet resonance at −65 ppm in the 31P{1H} NMR spectrum. In comparison, the phosphorus atom of H2[O2PPh] resonates at −50 ppm10 and that of H2[O2PtBu] at −60 ppm.6c Preparation of lithium complexes of [O3P]3− free of coordinating solvents was attempted. Addition of 3 equiv of nBuLi to H3[O3P] in toluene or pentane at −35 °C led to clean deprotonation as indicated by only one singlet resonance observed at ca. −50 ppm in the 31P{1H} NMR spectra of these reaction solutions. This 31P signal is shifted notably downfield from that of the protio H3[O3P]. Attempts to grow quality crystals without participation of any coordinating solvents gave unfortunately amorphous solids, whose 1H NMR spectra are featureless. Similar reactions were also performed in diethyl ether, THF, and DME, the 31P{1H} NMR spectra of which are also indicative of the clean formation of a trilithium complex as evidenced by the only singlet resonating at ca. −57 ppm. Colorless crystals suitable for X-ray diffraction analysis were successfully obtained in 69% from lithiation reactions in diethyl ether (eq 1). Interestingly, dissolution of the amorphous solid

Li6[O3P]2(OEt2)2 (1). Alternatively, direct isolation of 1 from diethyl ether solutions of ligand synthesis without an aqueous workup also afforded X-ray quality crystals in 64% yield. As depicted in Figure 2, the molecular cluster 1 is a hexanuclear species, containing two coordinated diethyl ether

Figure 2. Molecular structure of 1 with thermal ellipsoids drawn at the 35% probability level for lithium and heteroatoms. All tBu groups in [O3P]3− and ethyl groups in coordinated OEt2 are omitted for clarity.

and two [O3P]3− ligands. This solid state structure is rather complicated and characteristic of having C1 symmetry, due in part to the π-coordination of some phenylene carbons to highly electrophilic lithium atoms.11 Notably, C(71) and C(84) from the same phenylene ring have close contacts with Li(2) while C(1) and C(28) from distinct rings have close contacts with Li(5). The P(1) donor is found to have a weak interaction with Li(3), whereas P(2) shows no interaction at all with any lithium atoms. The P(1)−Li(3) distance of 2.642(6) Å is considerably longer than those of Li4[O2PtBu]2(DME)2 (average 2.430 Å),6c Li4[O2PPh]2(THF)4 (2.499(3) Å),12 Li4[O2PPh]2(OEt2)3 (2.553(2) Å),6b and Li2[O2PPh](DME)2 (2.573(5) Å).6a In general, all lithium atoms are bridged with phenolate oxygen donors. The Li(4) and Li(5) atoms are further end-blocked by diethyl ether. With distinct coordination enrivonments, the Li(1), Li(4), and C(6) atoms are 3-coordinate but the others are 4. Selected bond distances and angles are summarized in Table S1. In contrast to the low symmetry found in the solid state structure, 1 is highly symmetric in solution at room temperature on

that was originally isolated from toluene reactions in diethyl ether shifts the 31P signal from −50 to −57 ppm, implicating the coordination of diethyl ether to the lithium aggregates. Accordingly, recrystallization of this amorphous solid in diethyl ether at −35 °C led indeed to X-ray quality crystals of B

DOI: 10.1021/acs.inorgchem.5b02208 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry the NMR timescale, as evidenced by the appearance of, for instance, only two singlet resonances of the tBu groups in the 1H NMR spectrum and only one signal in the 31P{1H} or 7 Li{1H} NMR spectrum. The solution structure of 1 is thus extrememly fluxional in nature and exhibits a time-averaged C3 or C3v symmetry. A simiar 3-fold symmetric feature was also found for a trilithium salt of the triamidoamine [N(CH2CH2NSiMe3)3]3− in solution.13 No 31P−7Li coupling was observed for 1, implicating no or extremely weak interaction between the soft phosphorus and the hard lithium.14 A variable temperature 31P{1H} NMR spectroscopic study of 1 in toluene-d8 revealed two well-resolved broad singlet resonances at ca. − 48 and −74 ppm at temperatures lower than −70 °C, consistent with the distinct chemical environments of the two phosphorus atoms found in the solid state. The low-temperature 7Li{1H} NMR spectra, however, are featureless. Addition of 2 equiv of diethyl ether to a C6D6 solution of 1 resulted in the observation of only one set of diethyl ether signals in the 1H NMR spectrum, indicating the coordinated diethyl ether is labile and tends to exchange facilely with the exogenous unbound ones.6c,8b−d,15 Synthesis of sodium and potassium congeners of 1 was also attempted in ethereal solutions with the employment of excess NaH and KH, respectively, in the place of nBuLi under conditions similar to those described above. Unfortunately, no conclusive results were derived, due primarily to the lack of X-ray quality crystals of these heavier group 1 complexes. The reactions of H3[O3P] with NaH in THF or DME behave similarly, giving rise to cleanly a singlet resonance at ca. −99 ppm in the 31P{1H} NMR spectra. A colorless crystalline solid could be isolated from reactions conducted in THF. The 1H NMR spectrum of this solid is indicative of a structure having high symmetry similar to what was found in the 1H NMR spectrum of 1. The relative integrals of these diagnostic 1H NMR signals indicate the presence of 3 equiv of coordinated THF per [O3P]3−, thus suggesting a formulation of {Na3[O3P](THF)3}x where x should in principle be equal to or larger than 2 in view of the larger atomic size of Na than Li. In contrast to that in THF solutions, the phosphorus donors of this sodium cluster resonate at −72 ppm in C6D6 as a rather widened singlet with its peak width at half-height of 135 Hz. We suggest that {Na3[O3P](THF)3}x also undergoes rapid fluxional exchange in solution, presumably at a rate much faster than that of 1. The potassium analogue, on the other hand, remains more elusive as reactions that we attempted gave multiple broad signals in the 31P{1H} NMR spectra (e.g., −38 and −54 ppm in DME). The found multiple 31P signals do not necessarily mean the formation of multiple products but instead may be presumably due to the production of an aggregate containing multiple phosphorus donors with distinct chemical environments in view of the higher propensity of potassium to have π-interaction6a,c,11a,b with phenylenes. Exploratory synthesis of low valent transition metal complexes of [O3P]3− was attempted. Having confirmed the clean lithiation of H3[O3P] in THF, we chose to prepare in situ the THF adduct of Li3[O3P] for the subsequent metathetical reactions with transition metal halides, because these halides usually have much better solubility in THF than in diethyl ether. Our interests in transition metal chemistry with this potentially tetradentate phosphine triphenolate ligand were in part inspired by the prosperous structural and reaction chemistry established with known tripodal or 3-fold symmetric ligands,16 particularly those capable of stabilizing metal−ligand multiple bonds.16b

These established studies often begin with the employment of trilithium complexes of trianionic chelates13,17 to react with transition metal chlorides. Addition of one equiv of MnCl2 or NiCl2(DME) to a THF solution of Li3[O3P] generates pentanuclear MnLi 4 [O 3 P] 2 (THF) 3 (2) or tetranuclear Ni2Li2[O3P]2(THF)2 (3), respectively, as confirmed by X-ray diffraction studies (eqs 2 and 3). It is thus apparent that

the mononuclear complexes of the type {M[O3P]}− are not the ground state conformations for these divalent transition metal complexes under the conditions examined. Note that both 2 and 3 are heteronuclear clusters, complementary to the homonuclear 1. In contrast to that of 3, the conformation of 2 is rather surprising in view of the 1:1 stoichiometry of MnCl2 and Li3[O3P] employed. This discrepancy in the cluster conformations of 2 and 3 highlights the sensitivity of these divalent 3d metals and the versatility of [O3P]3− in coordination modes. The reaction of Li3[O3P] with 0.5 equiv of MnCl2 in THF also affords the production of 2 as confirmed by another diffraction study. In another attempt to synthesize {M[O3P]}− (M = Mn(II), Ni(II)), the reactions of MnCl2 or NiCl2(DME) with one equiv of Li3[O3P] were examined in the presence of three C

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Figure 3. Two views of the molecular structure of 2 with thermal ellipsoids drawn at the 35% probability level for manganese, lithium, and heteroatoms. All tBu groups in [O3P]3− are omitted for clarity.

equiv of nBu4NBr in THF, assuming the cationic nBu4N+ would possibly exchange with Li+. These reactions again led to the formation of 2 or 3, respectively. Analytically pure crystals of forest green 2 were grown from a concentrated dichloromethane solution at −35 °C. The crystals, however, were of poor quality but sufficient to construct the connectivity between atoms in this molecular cluster. As depicted in Figure 3, this pentanuclear cluster contains two [O3P]3− ligands to bridge between one divalent manganese and four lithium atoms, with Li(1) and Li(2) being end-blocked by one and two THF, respectively. The coordination geometry of the 6-coordinate Mn(II) is severely distorted from an ideal octahedron, due primarily to the sharp angles of O(1)−Mn− O(4) of 84.1(3)° and O(3)−Mn−O(6) of 78.6(2)° for bridging Li(2) and Li(1), respectively, in two distinct four-membered rings. The two phosphorus donors are thus relatively cis-disposed, though with a rather wide P(1)−Mn−P(2) angle of 115.06(9)°. Constitutionally, this cluster may be regarded as a manganese complex supported by two facially tridentate, monoanionic [OP(OLi)2]− ligands that in practice function as phosphine biinstead of triphenolate chelates to manganese with a dangling third phenolate arm to bind to lithium. Interestingly, one of the lithium atoms in what we formulate as [OP(OLi)2]− also has close contact with one of the phenylene rings [i.e., C(29) and C(42) with Li(3) while C(43) and C(56) with Li(4)]. If the three end-blocked THF moieties are neglected from Li(1) and Li(2), the MnLi4[O3P]2 core is approximately C2 symmetric; the principle axis of this moiety lies on the P−Mn−P plane and bisects the P−Mn−P angle. Table S1 summarizes selected bond distances and angles. The molecular cluster 2 is 31P NMR silent, indicating this is a paramagnetic species. Its effective magnetic moment (μeff) of 5.32(5) μB (average of three independent runs) in benzene solutions was determined at room temperature by Evans’s method,18 indicative of a high spin 3d5 (S = 5/2) electron configuration.19 This high spin state was further confirmed by a SQUID magnetization measurement that revealed μeff to be nearly constant at 5.40 μB (Figure 4). The molecular structure of dark brown 3 is depicted in Figure 5. Selected bond distances and angles are summarized in

Figure 4. Plot of SQUID magnetization data of 2.

Table S1. This cluster is composed of two [O3P]3− ligands to bridge between two divalent nickel and two lithium atoms, with the latter being further end-blocked by THF. This cluster is C2 symmetric; the C2 axis coincides with the vector defined by the two distinct central points of Ni(1)−Ni(2) and Li(1)−Li(2). In view of this, 3 is a dimer, comprised of two NiLi[O3P](THF) units. Constitutionally, the nickel center in the monomeric NiLi[O3P](THF) unit may be regarded to be coordinated with a formally dianionic [O2P(OLi)]2− ligand that acts as a tridentate phosphine biphenolate chelate for one nickel with a pendant Li-bound dative oxygen donor to the other. Interestingly, this “tridentate” moiety is nearly meridional, contrasting with the facially tridentate [OP(OLi)2]− in 2. Each nickel is five-coordinate. Its coordination geometry is best described as square pyramidal with the other nickel being at the apical position. The Ni−Ni bond is 2.614(1) Å. The two mean basal planes are nearly parallel and approximately staggered to each other. In contrast to 1 and 2, 3 does not exhibit close contacts between any phenylene carbons and lithium. D

DOI: 10.1021/acs.inorgchem.5b02208 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 5. Two views of the molecular structure of 3 with thermal ellipsoids drawn at the 35% probability level for nickel, lithium, and heteroatoms. All tBu groups in [O3P]3− are omitted for clarity.

employed. No reaction, however, was found in toluene or diethyl ether solutions under otherwise identical conditions, revealing the significance of THF participation to trigger these alkane elimination reactions. After a standard workup, colorless crystals suitable for X-ray diffraction analysis were grown from a concentrated toluene solution at −25 °C. As depicted in Figure 6, this is a homonuclear cluster containing two [O3P]3− ligands to bridge between three zinc atoms,

Multinuclear NMR spectroscopic data of 3 in solution are consistent with the C2-symmetric, dimeric structure found in the solid state. This cluster is soluble in chloroform and dichloromethane but poorly soluble in benzene or toluene, indicative of its somewhat high polarity in nature. Characteristically, six distinct singlet resonances are observed for tBu groups in the 1H NMR spectrum. The two phosphorus donors resonate as a singlet at −6.2 ppm, a value that is significantly downfield shifted from that of H3[O3P] or Li3[O3P], consistent with the coordination of phosphorus to nickel.14,20 The 7Li{1H} NMR spectrum reveals one singlet resonance at −0.8 ppm. Collectively, this cluster is not fluxional on the NMR timescale as what was found for 1. Alkane elimination of ZnMe2 or ZnEt2 with one equiv of H3[O3P] in THF at 25 °C produces trinuclear Zn3[O3P]2(THF)2 (4) in high yields (eq 4). The empirical conformation

Figure 6. Molecular structure of 4 with thermal ellipsoids drawn at the 35% probability level for zinc and heteroatoms. All tBu groups in [O3P]3− are omitted for clarity.

with Zn(1) being further end-blocked by two THF ligands. Each zinc is four-coordinate, having a distorted tetrahedral geometry. Interestingly, each [O3P]3− ligand acts as an O,P chelate for one zinc, dangling with two phenolates to bind to the other two zinc atoms in this cluster. This molecular cluster is thus C2 symmetric; the C2 axis lies on the O(7)−Zn(1)−O(8) plane and bisects the O(7)−Zn(1)−O(8) angle, making the two [O3P]3− ligands chemically equivalent. Selected bond distances and angles are summarized in Table S1. Solution NMR data of 4 are consistent with the C2 symmetric structure found in the solid state, as evidenced by, for instance,

of this trinuclear cluster is apparently not consistent with the stoichiometry of the starting materials employed, reminiscent of what was found for pentanuclear 2. Accordingly, similar results were also obtained when 1.5 equiv of ZnR2 (R = Me, Et) was E

DOI: 10.1021/acs.inorgchem.5b02208 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Catalytic ROP of ε-CLa entry

initiator

temp (°C)

time (h)

Mn (calc)b

Mn (GPC)c

Mw/Mnc

1 2d 3e

1 Li2[O2PPh](DME)2 Li4[O2PtBu]2(DME)2

25 80 80

16 12 3

11.4 11.4 22.8

4.7 18.7 2.9

1.64 1.59 1.44

Conditions: [initiator] = 1.2 mM, 100 equiv of ε-CL, toluene; reaction parameters were not optimized; Mn values are reported in kg mol−1 unit; conversions are all quantitative as determined by 1H NMR analysis. bCalculated from fw of ε-CL × ([ε-CL]/[initiator]) × conversion, assuming one propagation chain per initiator. cMeasured by GPC in THF, calibrated with polystyrene standards. d[initiator] = 1.4 mM.6a e200 equiv of ε-CL.6c a

the observation of six distinct singlet resonances for tBu groups in the 1H NMR spectrum. The phosphorus donors resonate as a singlet at −70 ppm, which is shifted relatively upfield from that of H3[O3P]. Such an upfield change in 31P chemical shifts is typical for zinc complexes upon phosphine coordination.21 In addition, the 1H NMR spectrum reveals four well-resolved multiplet resonances with equal intensity for the methylene groups of the coordinated THF, reflective of the diastereotopic nature of these OCHAHBCHCHD moieties. The formation of clusters 1, 2, 3, and 4 is unique as they represent hexa-, penta-, tetra-, and trinuclear molecules, respectively. In principle, complete replacement of lithium in 1 with Mn(II) or Ni(II) would give the homonuclear clusters of the type M3[O3P]2. The isolation of heteronuclear clusters 2 and 3 instead of M3[O3P]2 or mononuclear {M[O3P]}− indicates apparently the strong affinity of lithium in these complex formation. As exemplified by 4, homonuclear M3[O3P]2 may be synthesized by alkane elimination routes. Notably, the conformation and structure of these clusters are less sensitive to the stoichiometry of their corresponding starting materials employed. Several lithium phenolates are known to initiate catalytic ringopening polymerization (ROP) of ε-caprolactone (ε-CL).6a,c,15,22 In this regard, the catalytic activity of 1 was examined. As summarized in Table 1, 1 reacts with 100 equiv of ε-CL in toluene at 25 °C to produce quantitatively poly(ε-caprolactone) (PCL) with a molecular weight distribution (Mw/Mn) similar to those corresponding to the phosphine biphenolate initiators Li2[O2PPh](DME)26a and Li4[O2PtBu]2(DME)2.6c The measured number-averaged molecular weight (Mn) of this PCL is a bit larger than that produced from catalytic Li4[O2PtBu]2(DME)26c but significantly lower than that derived from Li2[O2PPh](DME)2.6a These results implicate a significant extent of chain transfer reactions occurring from the propagating chain(s) initiated by 1, presumably via transesterification, from which the new initiators thus produced, however, are sufficiently active so as to consume all monomeric ε-CL.

its versatility in cluster constructions. This particular ligand binds to manganese in a facially O,P,O-tridentate mode but to nickel nearly meridionally, as exemplified in clusters 2 and 3, respectively. In addition, [O3P]3− can also be an O,P-bidentate chelate for one zinc, with two dangling phenolates to bind to the other zinc atoms in cluster 4. The conformation of homonuclear 4 contrasts with those of heteronuclear 2 and 3 that underscore substantially the inherent propensity of lithium incorporation in these cluster constructions. Collectively, these molecules represent the first example of metal complexes derived from a phosphine triphenolate. The manganese core in 2 has a high spin 3d5 electron configuration (S = 5/2) as evidenced by solution and solid state magnetic susceptibility measurements. As demonstrated, the derived lithium cluster is not only a good starting material for metathetical reactions but also an active initiator for catalytic ROP of ε-CL.

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EXPERIMENTAL SECTION

General Procedures. Unless otherwise specified, all experiments were performed under nitrogen using standard Schlenk or glovebox techniques. All solvents were reagent grade or better and purified by standard methods. Compounds 2-bromo-4,6-di-tert-butylphenol10 and NiCl2(DME)23 were prepared according to literature procedures. All other chemicals were obtained from commercial vendors and used as received. All NMR spectra were recorded on Varian Unity or Bruker AV instruments in specified solvents at room temperature unless otherwise noted. Chemical shifts (δ) are listed as parts per million downfield from tetramethylsilane. Coupling constants (J) and peak widths at half-height (Δv1/2) are in hertz. Routine coupling constants are not listed. 1H NMR spectra are referenced using the residual solvent peak at δ 7.16 for C6D6 and δ 7.24 for CDCl3. 13C NMR spectra are referenced using the internal solvent peak at δ 128.39 for C6D6 and δ 77.23 for CDCl3. The assignment of the carbon atoms for all compounds is based on the DEPT 13C NMR spectroscopy. 31P and 7 Li NMR spectra are referenced externally using 85% H3PO4 at δ 0 and LiCl in D2O at δ 0, respectively. Elemental analysis was performed on a Heraeus CHN-O Rapid analyzer. Solid state magnetic susceptibility was measured on a Quantum Design MPMS5 SQUID magnetometer at temperatures ranging from 2 to 300 K. X-ray Crystallography. Data were collected on a diffractometer with graphite monochromated Mo Kα radiation (λ = 0.7107 Å). Structures were solved by direct methods and refined by full matrix least-squares procedures against F2 using SHELXL-97.24 All full-weight nonhydrogen atoms were refined anisotropically. Hydrogen atoms were placed in calculated positions. The structures of 1−4 contain disordered solvent molecules. Attempts to obtain suitable disorder models failed. The SQUEEZE procedure of Platon25 was used to obtain a new set of F2 (hkl) values without the contribution of solvent molecules, leading to the presence of significant voids in this structure. The refinement reduced the R1 value to 0.0806, 0.1397, 0.0965, and 0.0611 for compounds 1, 2, 3, and 4, respectively. Synthesis of Tris(3,5-di-tert-butyl-2-hydroxyphenyl)phosphine (H3[O3P]). To a solution of 2-bromo-4,6-di-tert-butylphenol (10.34 g, 36.2 mmol) in diethyl ether (50 mL) at −35 °C was added dropwise a prechilled diethyl ether solution (40 mL) of nBuLi (29 mL, 2.5 M in hexane, 72.5 mmol, 2 equiv) at −35 °C. The solution was stirred at room temperature for 1 h and cooled to −35 °C again. A prechilled

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CONCLUSIONS We have prepared and structurally characterized a number of molecular clusters based on a phosphine triphenolate ligand. In particular, the synthesis of hexanuclear 1, pentanuclear 2, tetranuclear 3, and trinuclear 4 was achieved by means of either alkane elimination or metathetical reactions. The solid state and solution structures, where appropriate, of these clusters were all confirmed by single crystal X-ray diffraction analysis and multinuclear NMR spectroscopy, respectively. Interestingly, the ground state conformations and structures of these clusters are somewhat irrelevant to stoichiometry of the starting materials employed. With the divalent 3d metals examined, this phosphine triphenolate ligand disfavors to act as a tetradentate chelate in a mononuclear complex of the type {M[O3P]}−. Instead, a variety of coordination modes was realized for [O3P]3−, demonstrating F

DOI: 10.1021/acs.inorgchem.5b02208 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Synthesis of Ni2Li2[O3P]2(THF)2 (3). Solid H3[O3P] (108 mg, 0.167 mmol) was dissolved in THF (3 mL) and cooled to −35 °C. To this was added nBuLi (0.2 mL, 2.5 M in hexane, 0.5 mmol, 3 equiv). The reaction solution was stirred at room temperature for 1 h, and NiCl2(DME) (37 mg, 0.167 mmol) was added. The reaction solution was stirred at room temperature overnight and evaporated to dryness under reduced pressure. Dichloromethane (6 mL) was added. The dichloromethane solution was filtered through a pad of Celite and concentrated under reduced pressure until the volume became ca. 2 mL. Cooling the concentrated solution to −35 °C afforded the product as dark brown crystals suitable for X-ray diffraction analysis; yield = 120 mg (92%). 1H NMR (CDCl3, 500 MHz): δ 7.69 (d, 4, 3 JPH = 9.5, Ar), 7.57 (d, 2, 3JPH = 9.5, Ar), 7.27 (s, 2, Ar), 7.12 (s, 2, Ar), 6.82 (s, 2, Ar), 2.94 (br s, 8, OCH2), 1.48 (br s, 8, OCH2CH2), 1.43 (s, 18, CMe3), 1.33 (s, 18, CMe3), 1.31 (s, 18, CMe3), 1.30 (s, 18, CMe3), 1.28 (s, 18, CMe3), 0.26 (s, 18, CMe3). 31P{1H} NMR (CDCl3, 202.3 MHz): δ −6.24. 7Li{1H} NMR (CDCl3, 194 MHz) δ −0.79 (Δv1/2 = 7). 13C{1H} NMR (CDCl3, 125.7 MHz): δ 174.47 (d, JCP = 18.23, C), 168.68 (d, JCP = 16.47, C), 164.43 (d, JCP = 4.14, C), 140.65 (d, JCP = 7.42, C), 139.73 (d, JCP = 11.8, C), 139.48 (d, JCP = 4.14, C), 137.98 (d, JCP = 9.05, C), 137.50 (d, JCP = 9.18, C), 133.93 (d, JCP = 7.29, C), 130.36 (d, JCP = 52.2, C), 129.02 (s, CH), 128.21 (s, CH), 126.85 (d, JCP = 19.23,CH), 126.58 (s, CH), 125.20 (s, CH), 124.32 (d, JCP = 20.11,CH), 123.70 (d, JCP = 67.00, C), 117.65 (d, JCP = 60.50, C), 67.98 (s, OCH2), 35.52 (s, CMe3), 35.00 (s, CMe3), 34.29 (s, CMe3), 34.05 (s, CMe3), 33.83 (s, CMe3), 33.71 (s, CMe3), 31.94 (s, CMe3), 31.58 (s, CMe3), 31.46 (s, CMe3), 30.80 (s, CMe3), 30.32 (s, CMe3), 28.74 (s, CMe3), 25.44 (s, OCH2CH2). Anal. Calcd for C92H136Li2Ni2O8P2: C, 70.66; H, 8.77. Found: C, 70.29; H, 8.69. Synthesis of Zn3[O3P]2(THF)2 (4). Method 1: To a THF solution (6 mL) of H3[O3P] (213.5 mg, 0.33 mmol) was added ZnEt2 (0.30 mL, 1.1 M in toluene 0.33 mmol) at 25 °C. The reaction mixture was stirred at room temperature for 13 h. All volatiles were removed in vacuo. The solid residue was triturated with pentane (1 mL × 3). Toluene (4 mL) was added. The toluene solution was filtered through a pad of Celite and concentrated under reduced pressure until the volume became ca. 1 mL. Cooling the concentrated toluene solution to −25 °C afforded the product as colorless crystals suitable for X-ray diffraction analysis; yield = 158.9 mg (89%). Method 2: The procedures were identical to those of method 1 except that one equiv of ZnMe2 was used, producing 4 as a crystalline solid in 88% yield. Method 3: The procedures were identical to those of method 1 except that 1.5 equiv of ZnEt2 or ZnMe2 was used, producing 4 quantitatively in 40 min as judged by 31P{1H} NMR spectroscopy. 1 H NMR (C6D6, 500 MHz): δ 8.19 (s, 2, Ar), 8.06 (s, 2, Ar), 7.80 (s, 2, Ar), 7.40 (s, 2, Ar), 7.36 (br m, 2, Ar), 7.17 (s, 2, Ar), 3.73 (m, 4, OCHAHB), 3.29 (m, 4, OCHAHB), 1.89 (s, 18, CMe3), 1.69 (s, 18, CMe3), 1.61 (s, 18, CMe3), 1.37 (s, 18, CMe3), 1.34 (s, 18, CMe3), 1.06 (s, 18, CMe3), 0.95 (m, 4, OCH2CHCHD), 0.84 (m, 4, OCH2CHCHD). 31 1 P{ H} NMR (C6D6, 202.3 MHz): δ −70.30. 13C{1H} NMR (C6D6, 125.7 MHz): δ 169.63 (t, JCP = 9.2, C), 168.57 (t, JCP = 8.2, C), 161.42 (t, JCP = 7.3, C), 143.33 (s, C), 139.40 (s, C), 139.11 (s, C), 136.51 (t, JCP = 6.4, C), 135.54 (s, C), 130.42 (s, CH), 130.00 (s, CH), 128.92 (m, C), 128.68 (s, CH), 126.77 (s, CH), 126.52 (s, CH), 126.16 (s, CH), 124.53 (t, JCP = 22, C), 115.01 (t, JCP = 28, C), 112.46 (t, JCP = 30, C), 73.80 (s, OCH2), 36.61 (s, CMe3), 36.56 (s, CMe3), 35.76 (s, CMe3), 35.12 (s, CMe3), 34.93 (s, CMe3), 32.62 (s, CMe3), 32.57 (s, CMe3), 31.97 (s, CMe3), 30.39 (s, CMe3), 30.19 (s, CMe3), 25.08 (s, OCH2CH2). Anal. Calcd for C92H136O8P2Zn3: C, 67.85; H, 8.42. Found: C, 67.49; H, 8.05. ROP of ε-CL Initiated by 1. ε-CL (67 μL, 0.60 mmol) was added to a toluene solution (5 mL) of 1 (8.9 mg, 6.0 μmol) at room temperature. The solution was stirred at 25 °C for 16 h and quenched with a methanol solution of HCl (1 M). The solution was filtered through a pad of Celite, and all volatiles were removed under dynamic vacuum upon heating until the weights of the resulting viscous residues remained constant.

solution of PCl3 (1.656 g, 12.1 mmol, 0.33 equiv) in diethyl ether (15 mL) at −35 °C was added dropwise. The reaction solution was naturally warmed to room temperature and stirred at room temperature for 12 h. Degassed deionized water (40 mL) was added. The diethyl ether solution was separated from the aqueous solution, from which the product was further extracted with degassed dichloromethane (25 mL). The diethyl ether and dichloromethane solutions were combined, dried over MgSO4, filtered, and evaporated to dryness under reduced pressure. The pale yellow oily residue thus obtained was washed with MeCN (40 mL) to afford the product as an off-white solid which was isolated and dried in vacuo; yield 5.64 g (72%). 1H NMR (C6D6, 500 MHz): δ 7.54 (d, 3, 4JHH = 2.5, ArH4), 7.19 (dd, 3, 3JHP = 7, 4JHH = 2.5, ArH6), 5.95 (d, 3, JHP = 7, OH), 1.50 (s, 27, CMe3), 1.17 (s, 27, CMe3). 31P{1H} NMR (C6D6, 202.3 MHz): δ −65.07. 13C{1H} NMR (C6D6, 125.7 MHz) δ 156.25 (d, JCP = 17.47, C), 143.99 (d, JCP = 3.65, C), 137.03 (s, C), 129.23 (d, JCP = 4.53, CH), 127.20 (s, CH), 117.92 (d, JCP = 5.41, C), 35.75 (d, JCP = 1.76, CMe3), 34.93 (s, CMe3), 31.89 (s, CMe3), 30.24 (s, CMe3). Anal. Calcd for C42H63O3P: C, 77.98; H, 9.82. Found: C, 77.66; H, 9.84. Synthesis of Li6[O3P]2(OEt2)2 (1). Solid H3[O3P] (215.7 mg, 0.33 mmol) was dissolved in diethyl ether (8 mL) and cooled to −35 °C. To this was added nBuLi (0.4 mL, 2.5 M in hexane, 1.0 mmol, 3 equiv) dropwise. The reaction solution was stirred at room temperature for 1 h, filtered through a pad of Celite, and concentrated under reduced pressure until the volume became ca. 2 mL. Pentane (1 mL) was layered on top of this concentrated diethyl ether solution. Cooling the solution to −35 °C afforded the product as colorless crystals suitable for X-ray diffraction analysis; yield 169.5 mg (69%). 1H NMR (C6D6, 500 MHz): δ 7.52 (m, 12, Ar), 3.19 (q, 8, OCH2CH3), 1.45 (s, 54, CMe3), 1.28 (s, 54, CMe3), 1.06 (t, 12, OCH2CH3). 31P{1H} NMR (C6D6, 202.3 MHz): δ −57.25. 7Li{1H} NMR (C6D6, 194.2 MHz): δ 1.52. 13C{1H} NMR (C6D6, 125.7 MHz) δ 166.79 (t, JCP = 10.06, C), 138.64 (s, C), 138.32 (s, C), 128.68 (s, CH), 126.76 (s, CH), 121.20 (t, JCP = 9.18, C), 66.21 (s, OCH2CH3), 35.68 (s, CMe3), 34.80 (s, CMe3), 32.31 (s, CMe3), 30.68 (s, CMe3), 15.75 (s, OCH2CH3). Anal. Calcd for C92H140Li6O8P2: C, 74.78; H, 9.55. Found: C, 74.39; H, 9.25. Synthesis of {Na3[O3P](THF)3}x. THF (6 mL) was added at room temperature to a solid mixture of H3[O3P] (200 mg, 0.307 mmol) and NaH (30 mg, 1.25 mmol, 4 equiv). The reaction mixture was stirred at room temperature overnight and filtered through a pad of Celite. The filtrate was concentrated under reduced pressure and cooled to −35 °C to afford the product as a colorless crystalline solid; yield 85 mg (30%). 1H NMR (C6D6, 500 MHz): δ 7.63 (d, 3, Ar), 7.48 (d, 3, Ar), 3.41 (t, 12, OCH2CH2), 1.44 (s, 27, CMe3), 1.34 (m, 39, CMe3 overlapped with OCH2CH2). 31P{1H} NMR (C6D6, 202.3 MHz): δ −72.07 (Δv1/2 = 135). 13C{1H} NMR (C6D6, 125.70 MHz) δ 169.48 (d, JCP = 21.12, C), 137.74 (s, C), 135.16 (s, C), 129.62 (s, CH), 125.53 (s, CH), 122.45 (d, JCP = 11.94, C), 68.23 (s, OCH2CH2), 35.65 (s, CMe3), 34.74 (s, CMe3), 32.53 (s, CMe3), 30.40 (s, CMe3), 26.00 (s, OCH2CH2). Anal. Calcd for (C54H84Na3O6P)x: C, 69.80; H, 9.11. Found: C, 69.42; H, 8.81. Synthesis of MnLi4[O3P]2(THF)3 (2). Method 1: Solid H3[O3P] (108 mg, 0.167 mmol) was dissolved in THF (3 mL) and cooled to −35 °C. To this was added nBuLi (0.2 mL, 2.5 M in hexane, 0.5 mmol, 3 equiv). The reaction solution was stirred at room temperature for 1 h, and MnCl2 (21 mg, 0.167 mmol) was added. The reaction solution was stirred at room temperature overnight and evaporated to dryness under reduced pressure. Dichloromethane (6 mL) was added. The dichloromethane solution was filtered through a pad of Celite and concentrated under reduced pressure until the volume became ca. 2 mL. Cooling the concentrated solution to −35 °C afforded the product as forest green crystals suitable for X-ray diffraction analysis; yield = 84 mg (63%). Method 2: The procedures were identical to those of method 1 except that 0.5 instead of 1 equiv of MnCl2 was employed, affording forest green crystals suitable for X-ray diffraction analysis; yield = 50%. Anal. Calcd for C96H144Li4MnO9P2: C, 72.63; H, 9.15. Found: C, 72.44; H, 8.89. G

DOI: 10.1021/acs.inorgchem.5b02208 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02208. X-ray crystallographic data for 1−4 (CCDC reference nos. 1423340−1423343) (PDF) Four structures (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Ministry of Science and Technology of Taiwan for financial support (NSC 102-2113-M-110-002-MY3), Mr. Ting-Shen Kuo (NTNU) and Dr. Ming-Tsz Chen for assistance with X-ray crystallography, Professor Hui-Lien Tsai (NCKU) and Mr. Wu-Han Cheng (NTHU) for assistance with magnetization measurements, and the National Center for High-Performance Computing (NCHC) for access to the chemical databases.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.5b02208 Inorg. Chem. XXXX, XXX, XXX−XXX