Synthesis and Structural Characterization of Homoleptic 1,2,4

Oct 13, 2014 - The alkaline earth metal complexes [(η2-3,5-tBu2dp)(μ-Mg)(η1:η1-3,5-tBu2dp)]2 (2), {[(η2-3,5-tBu2dp)(μ-η2:η5-3,5-tBu2dp)(μ-η2...
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Synthesis and Structural Characterization of Homoleptic 1,2,4Diazaphospholide Alkaline Earth Metal Complexes Dongling Liu,†,‡ Yongli Wang,†,‡ Chengfu Pi,*,§ and Wenjun Zheng*,†,‡,⊥ †

Institute of Organic Chemistry and ‡College of Chemical and Materials Science, Shanxi Normal Univeristy, Gongyuan Street 1, Linfen, Shanxi 041004, China § School of Chemistry and Chemical Engineering, Qianjiang College, Hangzhou Normal University, Xuelin Street 16, Hangzhou, Zhejiang 310036, China ⊥ Key Laboratory of Magnetic Molecules and Magnetic Information Material, Ministry of Education, Linfen, Shanxi 041004, China S Supporting Information *

ABSTRACT: The alkaline earth metal complexes [(η2-3,5-tBu2dp)(μ-Mg)(η1:η1-3,5-tBu2dp)]2 (2), {[(η2-3,5-tBu2dp)(μ-η2:η53,5-tBu2dp)(μ-η2:η1-3,5-tBu2dp)Ca]2(μ-Ca)} (3), [Sr(3,5-tBu2dp)2]m (4), [Ba(3,5-tBu2dp)2)]n (5), and [η1-{H(3,5tBu2dp)}2Ca(η2-3,5-tBu2dp)2] (6), bearing bulky 1,2,4-diazaphospholide ligands [3,5-tBu2dp]− ([3,5-tBu2dp]− = 3,5-di-tertbutyl-1,2,4-diazaphospholide), were prepared. The structures of magnesium and calcium 1,2,4-diazaphospholide complexes represent homoleptic 1,2,4-diazaphospholide alkaline earth metal oligomers with a novel array of metal−ligand binding modes.

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metal 1,2,4-diazaphospholide complexes, free of any coligands, [(η2-3,5-tBu2dp)(μ-Mg)(η1:η1-3,5-tBu2dp)]2 (2), {[(η2-3,5tBu2dp)(μ-η2:η5-3,5-tBu2dp)(μ-η2:η1-3,5-tBu2dp)Ca]2(μ-Ca)} (3), [Sr(3,5-tBu2dp)2]m (4), [Ba(3,5-tBu2dp)2)]n (5), and [η1H(3,5-tBu2dp)2Ca(η2-3,5-tBu2dp)2] (6) (H[3,5-tBu2dp] = 1H3,5-di-tert-butyl-1,2,4-diazaphosphole (1)10), the first examples of homoleptic 1,2,4-diazaphospholide alkaline earth metal complexes.9d

he alkaline earth metal complexes have been employed in various applications such as in organic synthesis, anionic styrene polymerization, and thin films for solid-state devices.1,2 Although the low solubility in common organic solvents and marginal thermal stability of many magnesium, calcium, strontium, and barium organometallic complexes have hindered their investigation, the use of sterically demanding ligands or multidentate Lewis bases for steric shielding of the metals is expected to promote encapsulation of the metal centers, resulting in stable, soluble compounds.3,4 The application of the bulky stabilized calcium amide, benzylcalcium complexes to the catalytic heterofunctionalization or polymerization of substrates containing unsaturated carbon−carbon bonds has further verified the synthetic approach.5−8 Recently, we reported a series of the sterically hindered 1,2,4diazaphospholide (dp−)-based metal complexes in which dp− ligands have presented novel molecular structure characters with varied coordination of the types η1(N), η1(N1):η1(N2), and η2(N1,N2) via the nitrogen atom(s), of the η5 type via the π-electron system.9 A few of such complexes have presented excellent catalytic behavior in the organic transformations9h and/or have an unusual redox activity toward a persistent dianionic radical species.9f Because of the unique electrochemical and coordinating properties endowed by the lowcoordinated P(σ2λ3) atom, it seemed interesting to assess the potential of the corresponding heavy alkaline earth metal complexes bearing bulky 1,2,4-diazaphospholide ligands.9 Herein, we report the preparation of several alkaline earth © 2014 American Chemical Society

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RESULTS AND DISCUSSION The reaction of 1 with Mg(nBu)2 (2:1) in n-hexane at reflux gave dimeric complex [(η2-3,5-tBu2dp)(μ-Mg)(η1:η1-3,5tBu2dp)]2 (2) as white crystals in 75% yield, while the treatment of 1 with the appropriate metal (fine-cut small piece of calcium, strontium, and barium) at 210 °C in a sealed combustion tube in the presence of 1,2,4,5-tetramethylbenzene (TMB) for 3 days readily afforded, after workup, air- and moisture-sensitive complexes {[(η2-3,5-tBu2dp)(μ-η2:η5-3,5tBu 2 dp)(μ-η 2 :η 1 -3,5-tBu 2 dp)Ca] 2 (μ-Ca)} (3), [Sr(3,5tBu2dp)2)]m (4), and [Ba(3,5-tBu2dp)2)]n (5) as pure white solids in high yields (80% (3), 90% (4), and 86% (5) based on M(3,5-tBu2dp)2, M = Ca, Sr, Ba) (Scheme 1). Complexes 2−5 are soluble in n-hexane (for 2, 3), toluene (for 4), or hot toluene (for 5) and can be obtained by recrystallization from a nondonating solvent such as n-hexane (for 2 and 3) or toluene/ Received: June 11, 2014 Published: October 13, 2014 6013

dx.doi.org/10.1021/om500621s | Organometallics 2014, 33, 6013−6017

Organometallics

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Scheme 1. Preparation of 1,2,4-Diazaphospholide Complexes 2−6

(solv)4]+[(3,5-tBu2dp)]−}, while the broad resonance is tentatively assigned to the [(3,5-tBu2dp)]− ligands and the cationic ion [η2(N,N)-3,5-tBu2dp)M(solv)4]+, between which a dynamic process is probably involved (M = Mg, Ca, Sr, Ba).9d The X-ray diffraction analysis of 2, 3, and 6 was carried out to establish their solid-state structures.12 Complex 2 displays a dinuclear complex with two slightly slipped [η2-3,5-tBu2dp]− and two bridging [η1,η1-3,5-tBu2dp]− ligands (Figure 1). The terminal [η2-3,5-tBu2dp]− ligands are characterized by Mg−N bond lengths of 2.005(3) and 2.104(3) Å, while the corresponding values for the bridging [η1,η1-3,5-

hot toluene (for 4/5) at room temperature or by sublimation at 170 °C for 2 (230 °C for 3, 240 °C for 4 and 5) under reduced pressure (0.01 mmHg) as white crystals (2 and 3) or white crystalline solids (4 and 5). The further treatment of 3 with 2 equiv of 1 affords [η1-{(3,5-tBu2dp)H}2Ca(η2-3,5-tBu2dp)2] (6) as white crystals in 77% yield (Scheme 1). 6 is very soluble in n-hexane and can be sublimed at 220 °C in high vacuum. The 1H NMR (DMSO-d6, 600 MHz, 23 °C) spectrum of 2 (3, 4, or 5) exhibits only one sharp resonance at δ 1.25 ppm (1.31, 1.32, or 1.33 ppm) (36 H), assigned to the −CH3 units of a symmetric molecule in the solution, indicating that complex 2 (3, 4, or 5) dissociates into the DMSO-d6-solvated adduct.9c,d,11 Similarly, the 1H NMR (C6D6, 600 MHz, 23 °C) spectrum of 2 (or 3) shows one sharp signal at δ 1.49 ppm (or slightly broad signal at δ 1.41 ppm), suggesting that the oligomeric conformation of 2 (or 3) in the solid state was not retained in solution due to the dynamic process. As expected, the 1H NMR (CDCl3, 600 MHz, 23 °C) spectrum of 6 shows two sharp resonances at δ 1.29 ppm (54H) and 1.07 ppm (18H) ppm for −CH3 units and one broad resonance at δ 10.5 ppm for a −NH group (2H) in a ratio of 54:18:2, respectively, suggesting two sets of coordinating ligands in the system. On the basis of the integration, the resonance for two tert-butyl groups of H[3,5-tBu2dp] ligands seems overlapped with that of [3,5-tBu2dp]− at δ 1.29 ppm. In the 13C{1H} NMR spectrum (DMSO-d6, 150 MHz, 23 °C), three doublets were exclusively observed for 2−6 (in CDCl3 for 6), suggesting the P−C coupling. The 31P{1H} NMR spectrum (DMSO-d6, 243 MHz, 23 °C) shows one very broad resonance at δ 60.3 ppm for 3 (60.9 for 4 and 62.1 for 5) or two sets of broad resonances at δ 62.8, 45.5 ppm for 2 (74.7, 76.4 for 6). The two observed sets of resonances in the 31P{1H} NMR spectrum probably suggested a dissociation of the related complex in the solution into an ion-associated complex {[η2(N,N)-3,5-tBu2dp)M-

Figure 1. X-ray crystal structure of 2. The hydrogen atoms were omitted for clarity. Selected bond distances (Å) and angles (deg): Mg(1)−N(3) 2.005(3), Mg(1)−N(4) 2.104(3), Mg(1)−N(1) 2.051(2), Mg(1)−N(2A) 2.058(3); N(2A)−Mg(1)−N(4) 126.72(11), N(3)−Mg(1)−N(4) 39.32(10), N(1)−Mg(1)−N(2A) 107.75(10), N(3)−Mg(1)−N(2A) 111.63(11), N(3)−Mg(1)−N(1) 116.00(11). 6014

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Organometallics

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tBu2dp]− ligands are 2.051(3) and 2.058(3) Å. The bond lengths, angles, and coordination mode observed in 2 (N(3)− Mg(1)−N(4) 39.32(10)°, N(2A)−Mg(1)−N(3) 111.63(11)°, N(1)−Mg(1)−N(4) 124.79(11)°, N(2A)−Mg(1)−N(4) 126.72(11)°, N(1)−Mg(1)−N(3) 116.00(11)°) are comparable to those found in the dimeric pyrazolato magnesium complex [(η2-3,5-tBu2dp)(μ-Mg)(η1:η1-3,5-tBu2dp)]2 (3,5tBu2pz = 3,5-di-tert-butyl-pyrazolato; Mg−N 1.987(4)− 2.050(4) Å; N−Mg−N 40.47(11)−124.04(13)°),13a but the framework is in sharp contrast to that found in π-coordination magnesium chloride (2,3,4,5-tetraethylphospholide) (Mg−P 2.6224(4) Å).13b Complex 3 exhibits a trimeric configuration with an almost linear arrangement of calcium atoms, connected by two types of bridging 1,2,4-diazaphospholides and two terminally bonded symmetrical η2-1,2,4-diazaphospholides (Figure 2). Two classes

[{(η2:η5-3,5-tBu2dp)K(THF)}{η2(N,N)-η3(O,P,O)-3,5-tBu2dp(O,O)-O2K}]n,9b in samrium complex [(μ2-η2(N,N):η5-3,5Ph2dp)(η2(N,N)-3,5-Ph2dp)2Sm]2,9c and in dianionic radical species [K(η6-[18]crown-6)]+[(η5,η5-3,5-Ph2dp)•]2− [K(η6[18]crown-6)]+.9f Although the several terminal η2-1,2,4-diazaphospholide barium complexes solvated by donor THF, DMSO, or 18crown-6 ligands were previously reported,9d attempts to get the structures of 4 and 5 under coligand-free condition were not successful. This is probably because they may present a higher aggregation compared to those found in 2 and 3 due to the increased metal covalent radius upon going from the lighter to the heavier congeners. For its potential tendency to join metal ions through its nitrogen atom, 1H-3,5-di-tert-butyl-1,2,4diazaphosphole was then used as a donor to react with 3. As expected, the transformation occurred to afford 6 at room temperature. Compound 6 exists as a monomeric complex bearing two η21,2,4-diazaphospholides and two neutral η1-1H-1,2,4-diazaphospholes with a pseudotetrahedral geometry around the calcium atom (94.578(8)−113.962(8)°) if the center of the η21,2,4-diazaphospholide is considered to be a monodentate donor (Figure 3). The calcium atom is capped by two [η2-3,5-

Figure 2. X-ray crystal structure of 3. The tert-butyl groups were omitted for clarity. Selected bond distances (Å) and angles (deg): Ca(1)−N(12) 2.415(3), Ca(1)−N(11) 2.499(3), Ca(1)−N(4) 2.509(3), Ca(2)−N(1) 2.299(4), Ca(2)−N(2) 2.304(3), Ca(2)− N(3) 2.350(3), Ca(2)−N(12) 2.535(3), Ca(2)−N(11) 2.578(3), Ca(2)−C(56) 2.827(4), Ca(2)−C(51) 2.907(4), Ca(2)−N(4) 2.951(4), Ca(2)−P(6) 3.2707(17); N(12)−Ca(1)−N(10) 82.26(10), N(12)−Ca(1)−N(11) 32.78(9), N(12)−Ca(1)−N(4) 86.84(11), N(11)−Ca(1)−N(4) 89.33(11), N(1)−Ca(2)−N(2) 34.94(10), N(1)−Ca(2)−N(12) 126.74(11).

of bridging 1,2,4-diazaphospholides display μ-η1:η2 coordination with ligand planes almost vertical to the Ca(2)−Ca(1)− Ca(3) axis and exhibit μ-η2:η5 coordination with ligand planes that are inclined toward the two side calcium atoms, respectively. Both bonding modes are in contrast to the bridging μ-η1:η1- and terminal η2-coordination observed in 2 and reminiscent of those in the structures of [(μ2-η2(N,N):η53,5-Ph 2 dp)(η 2 (N,N)-3,5-Ph 2 dp) 2 Sm] 2 9c and [Ca 3 (3,5tBu 2 pz) 6 ]. 14 However, the framework with the μ-η 2 :η 5 coordination ligands locating on the same side is significantly different from those observed in [(μ2-η2(N,N):η5-3,5-Ph2dp)(η2(N,N)-3,5-Ph2dp)2Sm]29c and [Ca3(3,5-tBu2pz)6].14 The distances of calcium to the carbon, nitrogen, and phosphorus atoms of the five-membered ring (Ca(2)−N(11) 2.578(3) Å, Ca(2)−C(56) 2.827(4) Å, Ca(2)−P(6) 3.2707(17) Å) are comparable to and/or slightly longer than those found in a chloride calcium (2,3,4,5-tetraethylphospholide) complex (Ca− C 2.840(7), Ca−P 2.971(2) Å),13b suggesting the slipped η5ligation of calcium due to both a larger phosphorus covalent radius and the electron deficiency relative to that of the nitrogen atom. The η5-coordination of 1,2,4-diazaphospholides to metals is rare to date and only observed in pseudoruthenocene [CpMe5Ru(η5-tBu2dp)],9a in potassium complex

Figure 3. X-ray crystal structure of 6. The hydrogen atoms were omitted for clarity. Selected bond distances (Å) and angles (deg): Ca(1)−N(3) 2.363(2), Ca(1)−N(4) 2.416(2), Ca(1)−N(1) 2.521(2); N(3)−Ca(1)−N(3A) 92.89(12), N(3)−Ca(1)−N(4A), 102.92(8), N(3A)−Ca(1)−N(4A) 33.57(7), N(4A)−Ca(1)−N(4) 127.49(11), N(3)−Ca(1)−N(1) 84.00(8), N(3A)−Ca(1)−N(1) 148.82(8), N(4A)−Ca(1)−N(1) 117.10(8), N(4)−Ca(1)−N(1) 91.52(8), N(1)−Ca(1)−N(1A) 113.96(11).

tBu2dp]−/[η1-H(3,5-tBu2dp)] pairs, between which no expected hydrogen bonding was observed (N(2)−H(1)···N(3) 148(4)°, H(1)···N(3) 2.26(3) Å). This is in contrast to that found in the dinuclear pyrazolato calcium complex [{Ca(iPr2pz)2(iPr2pzH)2}2].15 The Ca−N bond lengths (N(3)− Ca(1) 2.363(2) Å) involved in the ionic terminal η2-1,2,4diazaphospholides are shorter than those (N(1)−Ca(1) 2.521(2) Å) found in the neutral bridging η1-1,2,4-diazaphosphole ligands but comparable to those found in 3 (Ca(2)−N(2) 2.304(3) Å), probably the former being a stronger donor. The observed motif with 1H-1,2,4-diazaphosphole coordination is rare, and only one transition metal carbonyl complex, 6015

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[(η1(N):η1(P)Hdp){Cr(CO)5}2], was structurally characterized (Hdp = 1H-1,2,4-diazaphosphole) to date.16 To elucidate the structure information on 4 and 5 preliminarily, 31P MAS and 13C CP/MAS NMR experiments were carried out on a Bruker AVANCE III 500WB spectrometer (see Supporting Information). The 31P MAS NMR spectrum of 4 (5) exhibits two sharp single resonances at 71.6 and 98.1 ppm (75.3 and 101.3 ppm), respectively, suggesting the two 1,2,4-diazaphospholide coordination modes in the solid state. The 13C CP/MAS NMR spectrum of 4 (5) shows two sets of resonances at 33.6, 34.8 (br, overlapped, CH3), 37.8, 38.2 (2s, CCH3), 186.8, 190.3 (d, 1JP−C = 400.0 Hz, PC), 205.3, 207.9 (d, 1JP−C = 326.8 Hz, PC) for 4 and 33.8, 36.2 (br, overlapped, CH3), 37.2, 38.0 (2s, CCH3), 184.8, 188.7 (d, 1 JP−C = 490.2 Hz, PC), 198.0, 200.6 (d, 1JP−C = 326.8 Hz, PC) for 5, indicative of 1,2,4-diazaphospholide ligands coordinating to metal Sr or Ba with two coordination modes in the solid state as well. The results of the 31P MAS NMR data, consistent with those observed in the 13C CP/MAS NMR spectra, suggested that the structures of 4 and 5 may be somewhat similar, but different from that observed for 3. In summary, several coligand-free, heavy alkaline earth metal 1,2,4-diazaphospholides (2−6) were prepared by a metathesis reaction of Mg(nBu)2 and 1 or by the treatment of an alkaline earth metal with 1 in a sealed combustion tube in the presence of TMB, which are expected to be potentially useful catalysts and precursors in materials science,1−4 due to the extraodinary nature of the ligands.17 The structures of 2, 3, and 6 represent the first examples of homoleptic 1,2,4-diazaphospholide alkaline earth metal oligomers with a novel array of metal−ligand binding modes and may also provide the experimental examples to understand the structural preferences for the widespread metal ion (Mg2+, Ca2+) interactions with various nitrogen- and phosphorus-containing aromatic molecules in biological systems.18

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slowly added Mg(nBu)2 (1.30 mL, 1.0 M in n-hexane) by syringe. The solution was stirred for 2 h at room temperature and then refluxed for 5 h. After the volatile components were removed, the residue was dissolved in n-hexane to give 2 as white crystals at −20 °C (0.41 g, 75%). Mp: 194−195 °C. 1H NMR (400 MHz, DMSO-d6, 23 °C): δ 1.25 (s, 72H, CCH3) ppm. 13C{1H} NMR (100 MHz, DMSO-d6, 23 °C): δ 128.01, 127.76 (d, 1JC−P = 37.5 Hz, PC), 127.76, 127.52 (d, 1 JC−P = 36.0 Hz, PC), 35.23, 35.03 (d, 2JC−P = 20.0 Hz, CCH3), 33.17, 33.11 (s, 3JC−P = 6.0 Hz, CH3) ppm. 31P{1H} NMR (162 MHz, DMSO-d6, 23 °C): δ 62.8 (br), 45.5 (br). IR (KBr, Nujol mull): 1600(m), 1361(s), 1277(m), 1217(m), 1093(s), 1018(m), 920(w), 813(m), 968(m), 669(s), 608(m). Preparation of {[(η2-3,5-tBu2dp)(μ-η2:η5-3,5-tBu2dp)(μ-η2:η13,5-tBu2dp)Ca]2(μ-Ca)} (3), [Sr(3,5-tBu2dp)2]n (4), and [Ba(3,5tBu2dp)2)]m (5). After a mixture of a fine-cut small piece of metal (1.2 mmol), 1 (0.39 g, 2.0 mmol), and TMB (1.0 g, 7.5 mmol) was heated at 210 °C in a sealed combustion tube for 3 days, the resultant mixed solid was sublimed at 80 °C in a Büchi glass oven to remove volatile components under reduced pressure. The remaining solid was dissolved in toluene (10 mL) (or hot toluene for 5), and the solution was then filtered through Celite. The solvent was removed under reduced pressure to give 3−5 as a pure white solid. 3: 0.34 g, 80%. Mp: 271−273 °C. 1H NMR (600 MHz, DMSO-d6, 23 °C): δ 1.31 (s, 36H, CCH3) ppm. 13C{1H} NMR (150 MHz, DMSO-d6, 23 °C): δ 187.57, 187.91 (d, 1JC−P = 51 Hz, PC), 35.58, 35.70 (d, 2JC−P = 18 Hz, CCH3), 33.51, 33.47 (d, 3JC−P = 6.0 Hz, CH3) ppm. 31P{1H} NMR (243 MHz, DMSO-d6, 23 °C): δ 60.3 (br). IR (KBr, Nujol mull): 1620(m), 1461(m), 1377(w), 1261(s), 1094(s), 1020(s), 865(w), 799(s). 4: 0.43 g, 90%. Mp: 275−278 °C. 1H NMR (600 MHz, DMSO-d6, 23 °C): δ 1.32 (s, 36H, CCH3) ppm. 13C{1H} NMR (150 MHz, DMSOd6, 23 °C): δ 188.30, 187.95 (d, 1JC−P = 52.5 Hz, PC), 35.65, 35.52 (d, 2 JC−P = 19.5 Hz, CCH3), 33.38, 33.42 (d, 3JC−P = 6.0 Hz, CH3) ppm. 31 1 P{ H} NMR (243 MHz, DMSO-d6, 23 °C): δ 60.9 (br). 31P MAS NMR (202.3 MHz): δ 71.6 (s), 98.1 (s) ppm. 13C CP/MAS NMR (125.7 MHz): δ 33.6, 34.8 (br, overlapped, CH3), 37.8, 38.2 (br, overlapped, CCH3), 186.8, 190.3 (d, 1JP−C = 400.0 Hz, PC), 205.3, 207.9 (d, 1JP−C = 326.8 Hz, PC). IR (KBr, Nujol mull): 1618(m), 1460(s), 1377(m), 1261(s), 1094(s), 1019(s), 799(s). 5: 0.46 g, 86%. Mp > 300 °C dec. 1H NMR (600 MHz, DMSO-d6, 23 °C): δ 1.29 (s, 36H, CCH3) ppm. 13C{1H} NMR (150 MHz, DMSO-d6, 23 °C): δ 187.83, 187.51 (d, 1JC−P = 48 Hz, PC), 35.72, 35.59 (d, 2JC−P = 19.5 Hz, CCH3), 33.57 (s, CH3) ppm. 31P{1H} NMR (243 MHz, DMSOd6, 23 °C): 59.9 (br). 31P MAS NMR (202.3 MHz): δ 75.3 (s), 101.3 (s) ppm. 13C CP/MAS NMR (125.7 MHz): δ 33.8, 36.2 (2s, CH3), 37.2, 38.0 (2s, CCH3), 184.8, 188.7 (d, 1JP−C = 490.2 Hz, PC), 198.0, 200.6 (d, 1JP−C = 326.8 Hz, PC). IR (KBr, Nujol mull): 1981(w), 1461(s), 1376(s), 1274(m), 1217(w), 1096(s), 1018(m), 800(m), 722(m), 673(m), 606(w). Preparation of [H(3,5-tBu2dp)2(Ca(3,5-tBu2dp)2] (6). To a mixture of 3 (0.65 g, 1.0 mmol) and 1 (0.40g, 2.0 mmol) was added nhexane (30 mL) via syringe. After stirring for 18 h at room temperature, the solution was concentrated to give 6 as white crystals at −20 °C (0.64 g, 77%). Mp: >280 °C dec. 1H NMR (600 MHz, DMSO-d6, 23 °C): δ 10.5, (br, 2H, HN), 1.29 (2s, 54H, overlapped, CCH3 groups of two [tBu2dp]− ligands (36H) and two CCH3 groups of H[tBu2dp] ligands (18H)), 1.07 (s, 18H, CCH3, two CCH3 groups of H[tBu2dp] ligands (18 H)) ppm. 13C{1H} NMR (150 MHz, DMSO-d6, 23 °C): δ 199.10, 198.73 (d, 1JC−P = 55.5 Hz, PC for [tBu2dp]− ligand), 193.32 (br, PC for H[tBu2dp] ligand), 35.92, 35.80 (d, 2JC−P = 12 Hz, CCH3), 35.65, 35.56 (d, 2JC−P = 13.5 Hz, CCH3), 32.47, 32.42 (d, 3JC−P = 7.5 Hz, CCH3), 32.4 (s, CH3), 31.6 (s, CH3) ppm. 31P{1H} NMR (243 MHz, DMSO-d6, 23 °C): δ 76.4 (br, for [tBu2dp]−), 74.7 (s, for H[tBu2dp] ligand). IR (KBr, Nujol mull): 3291(w), 1461(s), 1377(m), 1261(s), 1095(s), 1020(s), 800(s), 680(m). X-ray Crystallography. Suitable single crystals were sealed under N2 in thin-walled glass capillaries. X-ray diffraction data were collected on a SMART APEX CCD diffractometer (graphite-monochromated Mo Kα radiation, φ−ω scan technique, λ = 0.710 73 Å). The intensity data were integrated by means of the SAINT program. SADABS was

EXPERIMENTAL SECTION

General Procedures. All manipulations were carried out in a nitrogen atmosphere under anaerobic conditions using standard Schlenk, vacuum line, and glovebox techniques. The solvents were thoroughly dried, deoxygenated, and distilled in a nitrogen atmosphere prior to use. CDCl3 was degassed and dried with CaH2 for 24 h before use. DMSO-d6 was degassed and dried over molecular sieves for several days before use. The 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded with Bruker DRX-400 and Bruker AV-600 spectrometeres, respectively. 31P MAS NMR experiments were performed on a Bruker AVANCE III 500WB spectrometer at a resonance frequency of 202.3 MHz using a 4 mm double-resonance MAS probe at a sample spinning rate of 12 kHz. The chemical shift of 31 P was referenced to (NH4)2HPO4. 31P MAS NMR spectra were recorded by using a recycle delay of 30 s. 13C CP/MAS NMR experiments were performed on a Bruker AVANCE III 500WB spectrometer at a resonance frequency of 125.7 MHz using a 4 mm double-resonance MAS probe at a sample spinning rate of 7 kHz. The chemical shift of 13C was determined using a solid external reference to adamantanamine. 13C CP/MAS NMR spectra were recorded by using a recycle delay of 5 s and a contact time of 2 ms. IR measurements were carried out on a Nicolet 360 FT-IR spectrometer from Nujol mulls prepared in a drybox. Melting points were measured in sealed nitrogen-filled capillaries without temperature correction with a Reichert-Jung apparatus Type 302102. The analysis is limited to NMR and IR spectroscopic investigations, supplemented by singlecrystal X-ray diffraction studies in the case of 2, 3, and 6. Preparation of [(η2-3,5-tBu2dp)(μ-Mg)(η1:η1-3,5-tBu2dp)]2 (2). To a solution of 1 (0.51 g, 2.6 mmol)10 in n-hexane (30 mL) was 6016

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Organometallics

Article

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used to perform area-detector scaling and absorption corrections. The structures were solved by direct methods and were refined against F2 using all reflections with the aid of the SHELXTL package.12 Crystal data for 2: C40H72Mg2N8P4, Mr = 837.56, monoclinic, space group P2(1)/c, a = 10.208(5) Å, b = 12.886(6) Å, c = 19.110(10) Å, α = 90°, β = 93.840(7)°, γ = 90°, V = 2508(2) Å3, Z = 2, ρcalcd = 1.109 Mg m−3, crystal size 0.20 × 0.15 × 0.15 mm3, F(000) = 904, μ(Mo Kα) = 0.210 mm−1, Gof = 0.965, 4913 independent reflections (Rint = 0.0629). Final R indices were R1 = 0.0636 [I > 2σ(I)] and wR2 = 0.1852 (all data). Crystal data for 3: C60H108Ca3N12P6, Mr = 1303.64, monoclinic, space group P2(1)/c, a = 16.638(6) Å, b = 22.436(9) Å, c = 21.756(8) Å, α = 90°, β = 104.926(6)°, γ = 90°, V = 7847(5) Å3, Z = 8, ρcalcd = 1.103 Mg m−3, crystal size 0.25 × 0.20 × 0.20 mm3, F(000) = 2808, μ(Mo Kα) = 0.373 mm−1, Gof = 0.904, 15 319 independent reflections (Rint = 0.0668). Final R indices were R1 = 0.0613 [I > 2σ(I)] and wR2 = 0.1741 (all data). Crystal data for 6: C40H74CaN8P4, Mr = 831.03, monoclinic, space group C2/c, a = 13.7274(12) Å, b = 19.7191(15) Å, c = 20.0531(18) Å, α = 90°, β = 106.717(9)°, γ = 90°, V = 5198.8(8) Å3, Z = 4, ρcalcd = 1.062 Mg m−3, crystal size 0.211 × 0.167 × 0.121 mm3, F(000) = 1800, μ(Mo Kα) = 0.276 mm−1, Gof = 1.020, 5104 independent reflections (Rint = 0.0338). Final R indices were R1 = 0.0570 [I > 2σ(I)] and wR2 = 0.1675 (all data).

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ASSOCIATED CONTENT

S Supporting Information *

Spectroscopic data for 2−6; crystallographic data for 2, 3, and 6. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the Program for the Top Young and Middle-aged Innovative Talents of Higher Learning Institutions of Shanxi (TYMIT 2011), the Doctoral Foundation of Chinese Education Ministry (Grant No. 20111404110001), National Natural Science Foundation of China (NSFC; Grant Nos. 21272143, 21271057), and Program for Changjiang Scholar and Innovative Research Team in University (IRT1156).

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REFERENCES

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dx.doi.org/10.1021/om500621s | Organometallics 2014, 33, 6013−6017