Synthesis of NPN-Coordinated Tantalum Alkyl Complexes and Their

Article pubs.acs.org/IC

Synthesis of NPN-Coordinated Tantalum Alkyl Complexes and Their Hydrogenolysis: Isolation of a Terminal Tantalum Hydride Incorporating a Doubly Cyclometalated NPN Scaffold Sonja Batke,† Malte Sietzen,† Hubert Wadepohl, and Joachim Ballmann* Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 276, 69120 Heidelberg, Germany S Supporting Information *

ABSTRACT: The closely related benzylene-linked diaminophosphines PhP(CH2C6H4-o-NHPh)2 (AH2) and PhP(C6H4-oCH2NHXyl)2 (BH2 with Xyl = 3,5-Me2C6H3) were employed for the synthesis of tantalum(V) alkyls, which were then studied with respect to hydrogenolysis. In the case of AH2, the tantalum trimethyl complex [Ta(A)Me3] (1) and the tantalum hydrocarbyl complex [Ta(A)(CH2SiMe3)(η2-EtCCEt)] (2) were prepared from the ligand’s dilithium salt (A)Li2(diox). Upon hydrogenolysis of 1 and 2, the formation of methane and SiMe4, respectively, was observed, but well-defined tantalum hydrides could not be detected. In the case of BH2, the cyclometalated species [Ta(B*)(NMe2)2] (3 with B* = κ4-N,P,N,C-(PhP(C6H4o-CH2NXyl)(C6H4-o-CHNXyl))3−) was isolated and converted to the corresponding diiodo species [Ta(B*)I2] (4). Treatment of 4 with LiCH2SiMe3 resulted in the isolation of the corresponding dialkyl complex [Ta(B*)(CH2SiMe3)2] (5), which was converted to the doubly cyclometalated monoalkyl complexes [Ta(B**)(CH2SiMe3)(PMe3)] (6 with B** = κ5-C,N,P,N,C(PhP(C6H4-o-CHNXyl)2)4−) and [Ta(B**)(CH2SiMe3)(dmpe)] (7) via reaction with PMe3 and dmpe, respectively. In contrast to 5 and 6, 7 was found to react cleanly with dihydrogen to afford the corresponding terminal tantalum(V) hydride [Ta(B**)(H)(dmpe)] (8). Upon reaction of 7 with D2, the deuteride [Ta(d2-B**)(D)(dmpe)] (9) was obtained and found to contain deuterium atoms in the methine positions of both tantalaaziridine subunits. The partially deuterated derivatives [Ta(B**)(D)(dmpe)] (10) and [Ta(d2-B**)(H)(dmpe)] (11) were generated via reaction of 8 and 9 with PhSiD3 and PhSiH3, respectively. Prior to the addition of gaseous D2 or H2, no H/D scrambling was observed in 10 or 11, indicating that the exchange of the methine positions proceeds via addition of D2 or H2 across the tantalaaziridine Ta−C bonds.

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INTRODUCTION Since Wilkinson’s synthesis of [TaCp2H3] in 1961,1 Cp-based tantalum hydrides have attracted considerable attention and have been studied in detail by Bercaw,2−4 Schrock,5−7 Tilley,8 Mountford,9,10 Fryzuk,11,12 and others.13 In 1973, Tebbe demonstrated that the phosphine-stabilized pentahydride [TaH5(dmpe)] can be prepared,14 which sparked an enduring interest in Cp-free tantalum hydrides and their reactivities,15−17 especially toward small molecules.18−21 In the following decades, phosphine-, amide-, siloxide-, and aryloxide-stabilized tantalum hydrides, such as [TaCl2H2(PMe3)4],22 [{TaCl(μH)(NCy2)2}2]23,24 (Cy = cyclohexyl), [Ta(OSitBu3)3H2],25 and [TaCl(OAr) 2 H 2 (PMe 3 ) 2 ] 26,27 (Ar = 2,6- i Pr 2 C 6 H 3 , 2,6Ph2C6H3), have been isolated and studied inter alia by Sattelberger, 22,28,29 Gambarotta/Cotton, 23,24 Wolczanski,25,30−32 and Rothwell.26,27,33−37 The groups of Otero and Kawaguchi have shown that chelating aryloxide ligands are also well-suited for the stabilization of tantalum hydrides.38−41 Coordinatively unsaturated tantalum(III) species, such as [Ta(OSi t Bu 3 ) 3 ], 31 [Ta(XylNCH 2 t Bu) 3 ] 42 (Xyl = 3,5Me2C6H3), and [Ta(Arnacnac)(NtBu)]43 (Arnacnac = ArNC(Me)CHC(Me)NAr with Ar = 2,6-iPr2C6H3), were shown to © 2017 American Chemical Society

undergo C−H activations to afford the corresponding cyclometalated tantalum(V) hydrides. With respect to their reactivity, amidophosphine-coordinated tantalum hydrides44,45 certainly stand out, which is particularly true for Fryzuk’s Si NPN-coordinated tetrahydride [{Ta(SiNPN)}2(μ-H)4] (complex II, SiNPN = (PhP(CH2SiMe2NPh)2)2−; see Scheme 1).46,47 This highly reactive species, which is generated via hydrogenolysis of [Ta(SiNPN)Me3] (I), was shown to react not only with gaseous dinitrogen46,47 but also with several other small molecules, including alkynes,48 CO,49 CO2,50 CS2,51 and N2H4.52 In recent work, Fryzuk and co-workers demonstrated that the closely related 1,2-arylene-linked MesNPN ligand (MesNPN = (PhP(2-(mesitylamido)-5-MeC6H3)2)2−) is also well-suited for the synthesis of tantalum hydrides: starting from III, the dinuclear tetrahydride IV (see Scheme 1) was prepared53,54 but was found to be unreactive toward N2, even under forcing conditions.55 Despite Fryzuk’s detailed studies,56 Received: February 1, 2017 Published: April 20, 2017 5122

DOI: 10.1021/acs.inorgchem.7b00277 Inorg. Chem. 2017, 56, 5122−5134

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Inorganic Chemistry Scheme 1. Hydrogenolytic Synthesis of II and IV Starting from I and III, Respectively

Scheme 2. Synthesis of (A)Li2(diox) and (B)Li2(thf) (Xyl = 3,5-Me2C6H3a

a

Green Arabic numbers are used in the Experimental Section for the NMR signal assignment of symmetric compounds.

the electronic and steric requirements that render the original system, i.e. [{Ta(SiNPN)}2(μ-H)4] (II), so unique still remain obscure.19 The isolation of the 12-fold deuterated system d12-II with all eight o-N-phenyl protons and the four bridging hydrides exchanged for deuterium,49 however, clearly indicated that reversible cyclometalation processes play a role, either during the formation of this complex or during formation of the trivalent intermediate [{Ta(SiNPN)}2(μ-H)2] by loss of H2. Inspired by Fryzuk’s work, we posed the question as to whether tantalum alkyls bearing the benzylene-linked diamidophosphines PhP(CH2C6H4-o-NHPh)2 (AH2)57 and PhP(C6H4o-CH2NHXyl)2 (BH2)57 can be prepared and hydrogenated. Given that benzylic positions are known to undergo cyclometalation chemistry (vide supra),58 we expected to observe this type of reactivity, a priori. To our surprise, we found that a doubly cyclometalated, coordinatively saturated system was actually required to access a tantalum hydride via hydrogenolysis, while noncyclometalated and singly cyclometalated tantalum alkyls failed to hydrogenate cleanly. These findings are discussed in the following and contrasted with Fryzuk’s findings.

Figure 1. ORTEP diagram of the molecular structure of (B)Li2(thf)(Et2O) (hydrogen atoms omitted for clarity, thermal ellipsoids set at 50% probability). Selected bond lengths (Å) and angles (deg) (values in brackets refer to the second independent molecule): Li1···Li2 2.478(9) [2.504(9)], P1−Li1 2.554(6) [2.495(6)], O1−Li1 1.910(7) [1.916(7)], O2−Li2 1.917(7) [1.925(7)], N1−Li1 2.049(7) [2.096(7)], N1−Li2 2.028(7) [1.992(7)]; Li2−N1−Li1 74.9(3) [75.3(3)], Li2−N2−Li1 74.2(3) [74.9(3)], O1−Li1−P1 112.0(3) [107.5(3)], O1−Li1−N1 124.3(3) [127.5(4)], O1−Li1−N2 124.2(3) [125.2(3)], N1−Li1−P1 90.2(2) [92.4(2)], N1−Li1−N2 102.3(3) [102.1(3)], N2−Li1−P1 95.0(2) [89.9(3)], O2−Li2−N1 117.8(3) [124.8(4)], O2−Li2−N2 130.9(4) [127.0(4)], N2−Li2−N1 107.2(3) [106.6(3)].

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RESULTS AND DISCUSSION Preparation of Tantalum Complexes via Salt Metathesis Pathways. Inspired by Fryzuk’s methodology to prepare complexes I and III,45,46,53,54 we explored salt metathesis routes at first. The required dilithium salts were synthesized via treatment of AH2 and BH2 with BuLi or LiN(SiMe3)2 (see Scheme 2) and isolated as yellowish powders either as the dioxane adduct (A)Li2(diox) (68% yield) or as the thf adduct (B)Li2(thf) (75% yield). Upon dissolution in thf-d8, an exchange of the coordinated solvent molecules for thf-d8 was observed in both cases. According to 7Li NMR spectroscopy, equivalent lithium atoms were found to be present in solution, indicating that both structures are dynamic on the NMR time scale. Supposedly, each lithium ion is coordinated by thf-d8 in solution. From a diethyl ether solution of (B)Li2(thf), single crystals of the ether adduct, i.e. (B)Li2(thf)(OEt2), were grown and subjected to X-ray diffraction (see Figure 1). In the synthesis of (B)Li2(thf), the latter ether adduct was observed as well and shown to lose the coordinated Et2O molecule upon prolonged storage under dynamic vacuum. The core of the molecular structure of (B)Li2(thf)(Et2O) consists of a μ2-Li2N2 diamond unit with each lithium ion coordinated by one solvent molecule. Similar to Fryzuk’s (SiNPN)Li2(thf)2,46 one of the

lithium ions in (B)Li2(thf)(Et2O) is only three-coordinate, while the other is bound to the phosphine, forming a slightly distorted tetrahedron. The intermetallic separation of 2.48 Å and the Li1−P1 distance of 2.55 Å are both well within the usual boundaries for phosphine-coordinated μ2-Li2N2 diamond cores.46,59−65 With (A)Li2(diox) and (B)Li2(thf) available in gram quantities, the synthesis of tantalum methyl complexes was pursued via reaction with [TaCl2Me3]. Following Fryzuk’s procedure for the preparation of [Ta(SiNPN)Me3],46 the trimethyl species [Ta(A)Me3] (1) was obtained in 35% yield starting from (A)Li2(diox) (see Scheme 3) and isolated as a light-sensitive yellow powder. In the 1H NMR spectrum of 1 only one set of signals was detected for the equivalent ligand side arms. Similar to Fryzuk’s [Ta(MesNPN)Me3],53 the three tantalum-bound methyl groups 5123


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Inorganic Chemistry Scheme 3. Synthesis of 1 from (A)Li2(diox) and [TaCl2Me3]

Scheme 4. Synthesis of 2 Starting from (A)Li2(diox), [TaCl3(dme)(η2-EtCCEt)], and LiCH2SiMe3

gave rise to only one 1H NMR resonance, although three distinct signals were detected in the corresponding 13C{1H} NMR spectrum of 1 (note that no 13C{1H} signal was found for the tantalum-bound methyls in [Ta(MesNPN)Me3]).53,66 In the 31P{1H} NMR spectrum, the expected singlet was found at 26.5 ppm in C6D6. Since efforts to crystallize 1 were unsuccessful, the N,N′-bis(p-tolyl)-substituted derivative of the ligand and the corresponding trimethyl tantalum complex were synthesized (see the Supporting Information for experimental details). Using this tantalum species, single crystals suitable for X-ray diffraction were grown from diethyl ether at −40 °C. In the corresponding molecular structure, the central tantalum atom is situated in a slightly distorted trigonalprismatic coordination environment (see Figure 2). Interest-

In the proton NMR spectrum of 2, a broad singlet at 1.21 ppm was detected and assigned to the metal-bound methylene group of the trimethylsilylmethyl unit (the signal assignment was corroborated by 1H,31P HMBC and 1H,13C HSQC NMR spectroscopy). Only one set of proton NMR signals was found for the diamidophosphine ligand, which is indicative of a Cssymmetric species in solution. For the ethyl substituents of the coordinated alkyne ligand, two broad signals were detected at approximately 1.2 and 3.3 ppm.67 Interestingly, 1 and 2 exhibit nearly identical 31P{1H} NMR shifts at δ 26.5 ppm, suggesting that both core fragments “[TaVMe3]2+” and “[TaV(CH2SiMe3)(η2-EtCCEt)]2+” are fairly similar with respect to their Lewis acidity. Single crystals of 2 were grown from toluene/pentane mixtures, which allowed for an elucidation of its molecular structure by X-ray diffraction (see Figure 3). Assuming that the

Figure 2. ORTEP diagram of the molecular structure of the N,N′bis(p-tolyl)-substituted derivative of 1 together with a truncated view on the prismatic core of the complex (hydrogen atoms omitted for clarity, thermal ellipsoids set at 50% probability, disorder of one of the p-tolyl substituents not shown). Selected bond lengths (Å) and angles (deg): Ta−P 2.7337(15), Ta−N1 2.067(2), Ta−N2 2.011(2), Ta− C35 2.201(3), Ta−C36 2.216(3), Ta−C37 2.267(3); N1−Ta−P 80.19(6), N1−Ta−C35 139.69(11), N1−Ta−C36 87.63(11), N1− Ta−C37 83.19(9), N2−Ta−P 75.95(7), N2−Ta−N1 126.85(9), C35−Ta−C37 78.65(11), C35−Ta−C36 75.67(13), C37−Ta−P 151.53(7), C36−Ta−P 75.16(8), C35−Ta−P 128.07(9).

Figure 3. ORTEP diagram of the molecular structure of 2 (hydrogen atoms omitted for clarity, thermal ellipsoids set at 50% probability). Selected bond lengths (Å) and angles (deg): Ta−P 2.6880(6), Ta−N1 2.113(2), Ta−N2 2.037(2), Ta−C33 2.071(2), Ta−C34 2.073(3), Ta−C39 2.221(2); N1−Ta−P 78.72(5), N2−Ta−P 77.35(6), N1− Ta−C39 85.88(9), C33−Ta−P 115.95(7), C34−Ta−P 84.49(8), C33−Ta−C34 37.23(11), C33−Ta−C39 91.72(10), C39−Ta−P 152.29(7).

alkyne unit in 2 occupies only one coordination site, the coordination sphere around Ta is best described as a distorted square pyramid with a τ5 value68 of 0.29. The equatorial plane is defined by N1, N2, P, and the trimethylsilylmethyl carbon atom C39, while the η2-EtCCEt moiety is situated in the apical position. In the solid state, the Ta−P and C33−C34 vectors are significantly twisted against each other with a torsion angle Ta− P−C33−C34 of approximately 35°. A similar geometry was found for [Ta(MesNPN)(CH2Ph)(η2-Me3SiCCSiMe3)] (τ5 = 0.48), while [Ta(MesNPN)(CH2Ph)(η2-EtCCEt)] (III, see Scheme 1) was shown to adopt a nearly idealized trigonalbipyramidal structure.53 With the alkyls 1 and 2 in hand, hydrogenolysis reactions under various conditions (25−80 °C, 4−10 bar of H2 or H2/N2 mixtures in C6D6, Et2O, or pentane) were studied carefully,69

ingly, Fryzuk and co-workers found a similar trigonal-prismatic geometry in the case of [Ta(MesNPN)Me3]53 but a distorted octahedral coordination polyhedron in the case of [Ta(SiNPN)Me3] (I).46 Targeting a system similar to [Ta(MesNPN)(CH2Ph)(η2EtCCEt)] (III, see Scheme 1),54 we reacted [TaCl3(dme)(η2-EtCCEt)] with (A)Li2(diox) (see Scheme 4). As the resulting oily chloro complex [Ta(A)(Cl)(η2-EtCCEt)] resisted purification (see the Supporting Information for details and for the molecular structure of the corresponding triflate), it was used directly for the preparation of the desired alkyl derivative [Ta(A)(CH2SiMe3)(η2-EtCCEt)] (2, see Scheme 4). 5124


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In comparison to 3 (δ(31P{1H}) −9.1 ppm), a downfieldshifted 31P{1H} NMR resonance was detected for 4 (δ(31P{1H}) 11.1 ppm), while the benzylic 1H NMR signals were found in a similar range (δ(1H) 3.5−5.5 ppm). The tantalumbound methine carbon was detected at δ(13C{1H}) 67.4 ppm. A crystallographic analysis confirmed the molecular structure of 4 (see Figure 4), which can be described as trigonal-

but no well-defined product could be isolated. In both cases, the expected hydrocarbons (methane or SiMe4) were detected as the only NMR-active products in the respective 1H NMR spectra, but no X-band EPR signals were observed in frozen C6D6.70 Therefore, the nature of the NMR- and EPR-silent tantalum species present in solution remains unclear, although dinuclear tetrahydrides (akin to II and IV, cf. Scheme 1) can be excluded due to their diamagnetism.46,53 As numerous attempts to prepare the closely related B-coordinated complexes [Ta(B)(CH2SiMe3)(η2-EtCCEt)] and [Ta(B)Me3] met with failure, we turned our attention to protonolysis reactions between BH2 and [Ta(NMe2)5]. Preparation of Cyclometalated Tantalum Complexes. At elevated temperatures, BH2 was found to react with [Ta(NMe2)5], as judged by the appearance of a new downfield-shifted 31P{1H} NMR signal at −19.4 ppm. After prolonged heating, complete conversion was reached and the isolated product was identified as the cyclometalated complex [Ta(B*)(NMe2)2] (3 with B* = κ4-N,P,N,C(PhP(C6H4-oCH2NXyl)(C6H4-o-CHNXyl))3−, see Scheme 5). The presence Scheme 5. Synthesis of the Singly Cyclometalated Complexes 1−3 (Xyl = 3,5-Me2C6H3)a

Figure 4. ORTEP diagram of the molecular structure of 4 (only one of the three independent molecules with fairly similar metrical parameters is shown, hydrogen atoms omitted for clarity, thermal ellipsoids set at 50% probability). Selected bond lengths (Å) and angles (deg) (values in brackets refer to the other independent molecules): Ta−I1 2.7432(13) [2.7566(12), 2.7405(13)], Ta−I2 2.7972(15) [2.7822(13), 2.8133(15)], Ta−P 2.615(2) [2.611(2), 2.620(2)], Ta−N1 1.926(5) [1.918(6), 1.923(6)], Ta−N2 1.970(5) [1.977(6), 1.973(6)], Ta−C1 2.190(7) [2.204(7), 2.190(8)]; I1−Ta− I2 92.08(2) [90.67(4), 90.14(2)], P−Ta−I1 175.51(4) [173.77(5), 172.70(4)], P−Ta−I2 85.24(4) [85.81(6), 85.53(4)], N1−Ta−I1 94.99(16) [96.72(17), 96.91(17)], N1−Ta−I2 131.86(15) [132.44(18), 131.52(18)], N1−Ta−N2 91.5(2) [91.8(3), 91.0(2)], N1−Ta−C1 40.2(2) [39.9(2), 39.9(2)].

bipyramidal, if the tantalaaziridine (TaV) is seen as an η2coordinated imine (TaIII), which occupies one equatorial coordination site. In this picture, the principal axis through P, Ta, and I1 is only slightly deviating from linearity (range 172.7−175.5° in the three crystallographically independent molecules in the structure). The trigonal plane is spanned by N2, I2, and the centroid of the N1−C1 bond. The Ta−P distance (approximately 2.61 Å) is well within the usual range,72 which is also the case for the N1−Ta−C1 angle (∼40°).13,41,42,73−77 The corresponding bis(triflate) was prepared similarly and found to be a triflate-bridged dimer in the solid state (see the Supporting Information for experimental details and for an ORTEP plot of the molecular structure of [{Ta(B*)(OTf)}2(μ-OTf)2]). Alkylation of 4 with LiCH2SiMe3 led to the singly cyclometalated bis(trimethylsilylmethyl) complex [Ta(B*)(CH2SiMe3)2] (5) (see Scheme 5). The latter dialkyl was isolated in high yields as a pale yellow powder and found to exhibit a 31P{1H} NMR resonance at −8.6 ppm: i.e., close to that observed for 3 (δ(31P{1H}) −9.1 ppm). In the proton NMR spectrum, inequivalent CH2SiMe3 groups cis and trans to the phosphine were detected at δ(SiMe3) 0.05 and 0.23 ppm. The tantalaaziridine motif was left unchanged, as indicated by a broadened 1H NMR signal for the methine proton at 4.10 ppm and an HSQC-correlated 13C{1H} NMR resonance at 70.0

a Red Arabic numbers are used in the Experimental Section for the NMR signal assignment of asymmetric compounds.

of a cyclometalated benzylic position in 3 was confirmed by one- and two-dimensional NMR techniques. A 13C{1H} NMR signal at 63.8 ppm was identified as the metal-bound methine carbon resonance, which appears as a 31P-coupled doublet (2JC,P = 3.9 Hz). Two well-separated 1H NMR signals were detected for the dimethylamido units, indicating that one of them is situated cis and the other trans to the phosphine (see Scheme 5). Upon reaction of 3 with Me3SiI, an exchange of the two Me2N units for iodides was observed without affecting the tantalaaziridine moiety, which led to the isolation of 4 as an orange powder (see Scheme 5).71 When AH2 was reacted with [Ta(NMe2)5], a related cyclometalated dimethylamido complex, namely [Ta(A*)(NMe2)2] (with A* = κ4-N,P,C,N(PhP(CHC6H4-o-NPh)(CH2C6H4-o-NPh))3−), was isolated, but the dimethylamides could not be exchanged for iodides or triflates in this case (see the Supporting Information for experimental details and an ORTEP plot of the molecular structure of [Ta(A*)(NMe2)2]). 5125


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species present in solution. The 1H NMR signals of the inequivalent tantalaaziridine protons were found as singlets at 3.71 and 4.45 ppm and shown to correspond to methine resonances by HSQC and DEPT NMR experiments. Similarly, two well-separated, mutually coupled signals were found for the CH2 moiety of the trimethylsilylmethyl group. On the basis of the 2JP,P coupling constant noted above,78,79 a trans alignment of both P donors was anticipated and confirmed by singlecrystal X-ray diffraction (see Figure 6). Two independent

Figure 5. ORTEP diagram of the molecular structure of 5 (hydrogen atoms omitted for clarity, thermal ellipsoids set at 50% probability). Selected bond lengths (Å) and angles (deg): Ta−P 2.7687(8), Ta−N1 1.970(3), Ta−N2 1.994(3), Ta−C1 2.214(3), Ta−C37 2.170(3), Ta− C41 2.213(3); N1−Ta−P 75.66(8), N1−Ta−N2 107.78(11), N1− Ta−C1 39.63(11), N1−Ta−C37 100.46(12), N1−Ta−C41 128.85(12), C37−Ta−P 174.26(9), C41−Ta−P 81.47(9).

ppm. Single crystals of 5 were grown from toluene/pentane at −40 °C and subjected to X-ray diffraction (see Figure 5). Akin to the case for 4, the tantalaaziridine in 5 may be seen as an η2bound imine, which is justified by the trigonal-bipyramidal structure resulting from the latter view. In comparison to the former diiodide, a longer tantalum−phosphorus distance (2.77 Å vs 2.61 Å) is evident in 5 and ascribed to the decreased Lewis acidity of the metal center. Doubly Cyclometalated Tantalum Alkyls and Their Hydrogenolysis. As hydrogenolysis of 5 under different conditions (25−80 °C, 1−10 bar of H2, C6D6, Et2O) led to complicated product mixtures, coligands (PMe3, thf, and pyridine) were added to trap or selectively stabilize one of the products. In the case of PMe3, a clean reaction was monitored by 31P{1H} NMR spectroscopy but found to take place in the absence of H2 as well. The resulting product with δ(31P{1H}) 28.7 and 44.3 ppm (2JP,P = 104 Hz) was then isolated and identified as the doubly cyclometalated monoalkyl [Ta(B**)(CH2SiMe3)(PMe3)] (6, B** = κ5-C,N,P,N,C(PhP(C6H4-o-CHNXyl)2)4−, see Scheme 6). In the proton NMR spectrum of 6, two sets of signals were detected for the ligand side arms, indicative of a C1-symmetric

Figure 6. ORTEP diagrams of the molecular structures of 6 (top, only one of the two independent molecules is shown) and 7 (bottom) (hydrogen atoms omitted for clarity, thermal ellipsoids set at 50% probability). Selected metrical parameters are summarized in Table 1.

Scheme 6. Synthesis of the Doubly Cyclometalated Complexes 6 and 7 (Xyl = 3,5-Me2C6H3)

molecules with very similar molecular structures were found to be present in the crystal (cf. Table 1). The tantalaaziridine plane through N1, C7, and Ta is twisted by 75.6(1)° (76.5(1)° in the second independent molecule) with respect to the second tantalaaziridine plane through N2, C22, and Ta, which is in line with the ligand side arms being inequivalent in solution. The metal−carbon distances within these threemembered rings are significantly different as well (Ta−C7 = 2.28 Å vs Ta−C22 = 2.18 Å). When the tantalaaziridines are seen as η2-imines (one contact with the metal), the overall geometry is best described as a distorted trigonal bipyramid with the trigonal plane defined by C37 and by the centroids of N1−C7 and N2−C22. The principal axis through P1, Ta, and P2 is bent away from the upright N-xylyl group and deviates from linearity by about 24°. Interestingly, the Ta−P1 distance 5126


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Inorganic Chemistry Table 1. Selected Metrical Parametersa and 31P NMR Shifts of the Doubly Cyclometalated Complexes 6−8 6 Ta−PB** (Å)

2.5449(5) [2.5465(5)] 2.6624(6) [2.6716(5)]

Ta−Pcoligand (Å)

Ta−Naziridine (Å)

2.0222(16) [2.0192(18)] 1.9670(17) [1.9709(16)] 2.251(2) [2.239(2)] 2.2837(19) [2.282(2)] 2.179(2) [2.181(2)] 157.361(16) [156.430(18)]

Ta−X (Å)d M−Caziridine (Å)

PB**−M−P (deg) PB**−M−X (deg) N−M−N (deg) δ(31PB**) (ppm)g

d

92.61(6) [92.35(6)] 100.27(7) [100.11(7)] 43.3

7

Scheme 7. Synthesis of 8 and 9 via Hydrogenolysis of 7 (Xyl = 3,5-Me2C6H3)

8

2.6351(10)

2.5257(4)

2.6259(11)b

2.6009(4)b

2.7557(10)c 2.138(3)

2.5885(4)c 2.0271(14)

1.977(3)

2.0235(14)

2.278(4)

1.78(2)

2.214(4)

2.2417(16)

2.266(4)

2.2398(17)

90.68(3)e

146.761(14)e

93.80(3)f 165.90(11)

140.497(14)f 75.3(7)

89.58(13)

171.65(6)

36.7

26.0

a

For 6, values in brackets refer to the second independent molecule. b Ta−P2. cTa−P3. dX = trimethylsilylmethyl carbon or hydride. eP1− Ta−P2. fP1−Ta−P3. gRecorded in C6D6 at room temperature.

(2.55 Å) is significantly shorter than the Ta−P2 distance (2.66 Å) and even shorter than the corresponding Ta−P distance in 4 (2.61 Å). When dmpe was reacted with 5, [Ta(B**)(CH2SiMe3)(dmpe)] (7) was obtained in 68% yield (see Scheme 6). In the 1 H NMR spectrum of 7, two sets of signals were detected for the tetraanionic ligand B** and two broadened 31P{1H} NMR signals were found for the dmpe unit in addition to a tripletshaped 31 P{ 1 H} signal for B**. A crystallographically determined molecular structure (see Figure 6) revealed that the phosphorus atoms (P2 and P3) of the dmpe unit were aligned cis to the phosphine of B** (P1) and cis to the CH2SiMe3 unit (C43). Similar to the case for 6, both tantalaaziridine planes are mutually twisted by 83.5(2)°, which renders both halves of the dmpe and both halves of B** inequivalent. Provided that the tantalaaziridines are seen as one contact each, the structure can be regarded as octahedral (see the Supporting Information for an illustration of the corresponding polyhedron). In contrast to 6, 7 was found to react cleanly with dihydrogen (10 bar), although elevated temperatures (85 °C) were required to ensure complete conversion within 24 h. In the 31 1 P{ H} NMR spectrum of the resulting product (8, cf. Scheme 7) three signals at 26.0, 18.3, and 16.3 ppm were detected, with the last two signals coupled to the first signal. In the proton NMR spectrum, both symmetry-equivalent methine protons of the tantalaaziridine subunits were detected at 3.65 ppm, but the hydride signal at 7.01 ppm was not easily identified due to overlapping signals of the aryl protons (vide infra). The molecular structure of 8 (see Scheme 7) was then elucidated by single-crystal X-ray diffraction (see Figure 7), and the terminal hydride was located cis to the ligand’s phosphine. This allowed for an assignment of the 31P{1H} NMR signals on the basis of the 2JP,P coupling constants,78,79 the molecular structure, and the 1H,31P COSY NMR spectrum (26.0 ppm

Figure 7. ORTEP diagram of the molecular structure of 8 (hydrogen atoms omitted for clarity except for the hydride, thermal ellipsoids set at 50% probability). The hydride was located in the difference electron density map and fully refined. Selected metrical parameters are summarized in Table 1.

(P1) with 2JP1,P3 = 24 Hz, 2JP1,P2 = 77 Hz, 18.3 ppm (P3) with JP1,P3 = 24 Hz, 16.3 ppm (P2) 2JP1,P2 = 77 Hz). Interestingly, both C−N vectors of the tantalaaziridines (C22−N2 and C7− N1) in 8 are nearly collinear and span a plane which also includes the central tantalum atom. The three phosphines span a second perpendicular plane (angle between both planes =89.11(2)°), which includes the tantalum atom and the hydride (see the Supporting Information for an illustration of the resulting coordination polyhedron). During hydrogenolysis, the dmpe ligand obviously rearranged within the coordination sphere of the central metal and is no longer cis to the phosphine of B**. Attempts to identify or even isolate the intermediates of this rearrangement process, e.g. by employing lower dihydrogen pressures or by using silanes instead of H2, have not been successful so far (see the Supporting Information for details). In order to unambiguously identify the hydride by NMR spectroscopy, the corresponding deuteride 9 (see Scheme 7) was prepared in analogy to 8 (10 bar of D2, 85 °C, 24 h). In the 2

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P{1H} NMR spectrum, a well-resolved 2JP,D coupling to the deuteride (I = 1) was observed for P1 and P3 (cis to the deuteride) but not detected for the trans-D-positioned phosphine P2 (see Figure 8). In the 2D NMR spectrum

well and that no deuterium scrambling to the methine positions was observed, it is concluded that the H/D scrambling discussed above cannot involve transient tantalum(III) species [TaIII(dx-B*)(dmpe)] (x = 1−3). Instead, it is proposed that the exchange of the methine positions, which is only observed with gaseous D2, proceeds via addition of D2 across one of the Ta−C bonds in 8: i.e., via the hydrido tantalum(V) deuteride [TaV(d1-B*)(D)(H)(dmpe)]. Complementary deuteration experiments, which led to [Ta(d2-B**)(H)(dmpe)] (11), are in line with this proposal (see Scheme 8). As expected, the selectively deuterated complexes 10 and 11 were found to react readily with D2 and H2, affording 9 and 8, respectively. That trivalent species are not readily accessible via cycloreversion processes might explain why 8 was found to be unreactive toward N2, CO (10 bar in both cases), N2O (8 bar), 3-hexyne (excess, 80 °C in C6D6), and isonitriles (tBu-NC or 2,6Me2C6H3NC, 80 °C in C6D6). In preliminary experiments, a productive conversion between 8 and CO2 (1 bar) was observed. Three mutually coupled 31 1 P{ H} NMR resonances at 44.6, 14.1, and −9.9 ppm were detected for the resulting product. The Ta−H moiety of the starting material, however, is still present in the product, as indicated by a 31P-coupled 1H NMR resonance at 9.1 ppm. The ligand side arms were found to be inequivalent. and both tantalum-bound CH groups were left unreacted according to 1 H, 13C{1H}, and HSQC NMR spectroscopy. The inequivalent signals for the ligand side arms suggested that only one molecule of CO2 was added to one side arm. The possibility that CO2 was inserted into one of the Ta−C bonds of the tantalaaziridines was excluded, due to the absence of 1H,13C HMBC cross peaks for the CH protons. In contrast to D2 or PhSiD3, which are assumed to add across the Ta−C bonds or react via σ-bond metathesis with the Ta−H bond, respectively, it is proposed that CO2 is inserted into one of the Ta−N bonds in 8. Using 13C-labeled CO2, the 13C{1H} NMR signal of the carbamate thus formed was identified as a 31P-coupled signal at 166 ppm, but single crystals suitable for X-ray diffraction have not been obtained so far. Further reactivity studies (inter alia with PhNCO, CS2, and allene) and more comprehensive studies on the effect of the coligand in 8 (inter alia by replacing dmpe for bipy, tmeda, or dmpm) are currently ongoing in our laboratory and directed toward a deeper understanding of this new class of doubly cyclometalated terminal tantalum hydrides.

Figure 8. 31P{1H} NMR spectra (243 MHz, C6D6) of 8 (top) and 9 (bottom).

(recorded in thf, see the Supporting Information), the signal corresponding to the deuteride was detected as a doublet of doublets at 7.01 (2JD,P = 11 and 6 Hz) and an additional singlet was found at 3.65 ppm. Both of these signals were absent in the 1 H NMR spectrum, indicating that a high degree of deuteration was reached. In conjunction with the 1H NMR spectrum of 8, the former singlet was unambiguously assigned to the methine positions, revealing that these protons were exchanged for deuterium as well (cf. structural drawing of [Ta(d2-B**)(D)(dmpe)] (9) in Scheme 7). A similar observation was made when 9 was pressurized with H2: i.e., all three D atoms were exchanged for H (see Scheme 7). Upon reaction of 8 with PhSiD3, a selective exchange of only the hydride for a deuteride, i.e. the formation of [Ta(B**)(D)(dmpe)] (10), was observed by NMR spectroscopy (see Scheme 8). Given that this reaction was carried out at 85 °C as Scheme 8. NMR-Scale Reactions of 8 and 9 with PhSiD3 and PhSiH3, Respectively (Xyl = 3,5-Me2C6H3)

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CONCLUSIONS In summary, the two benzylene-linked diamidophosphines AH2 and BH2 were found to be well-suited for the preparation of tantalum alkyl complexes. In the case of A, the noncyclometalated tantalum alkyls 1 and 2 have been isolated, but these species could not be converted into hydrides. In the case of B, the singly cyclometalated complexes 3−5 were prepared in addition to the doubly cyclometalated monoalkyl complexes 6 and 7. Despite the close relationship between [Ta(B**)(CH2SiMe3)(PMe3)] and [Ta(B**)(CH2SiMe3)(dmpe)], only the dmpe derivative was found to react cleanly with H2 or D2. The resulting doubly cyclometalated terminal hydride [Ta(B**)(H)(dmpe)] (8) was isolated and the hydride found cis to the ligand’s phosphine. Upon reaction of 8 with D2, the methine protons of the tantalaaziridine were exchanged reversibly, as indicated by the high degree of deuteration in [Ta(d2-B**)(D)(dmpe)] (9). The selectively deuterated derivatives 10 and 11 were accessed via reaction of 8 5128


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7.12−7.06 (m, 2 H, 5-ArH), 6.96−6.88 (m, 2 H, 6-ArH), 6.22 (sbr, 4 H, o-Xyl), 5.76 (s, 2 H, p-Xyl), 4.20 (d, 2JH,H = 10.5 Hz, 2 H, CH2), 3.84 (d, 2JH,H = 10.5 Hz, 2 H, CH2), 3.65−3.60 (m, 4 H, thf), 2.09 (s, 12 H, Xyl-Me), 1.81−1.75 (m, 4 H, thf). 13C{1H} NMR (151 MHz, thf-d8): δ [ppm] 161.7 (s, ipso-Xyl), 149.5−148.9 (sbr, ipso-PPh), 136.7 (s, 4-ArC), 134.3 (d, 2JC,P = 18.3 Hz, o-PPh), 133.6 (sbr, p-PPh), 132.9 (s, 6-ArC), 130.8 (s, 3-ArC), 128.8 (s, p-Xyl), 128.5 (d, 3JC,P = 7.3 Hz, m-PPh), 126.1 (s, 5-ArC), 112.4−110.7 (sbr, o-Xyl), 67.2 (s, thf), 55.1 (sbr, CH2), 25.4 (s, thf), 21.3 (s, Xyl-Me). 31P{1H} NMR (243 MHz, thf-d8): δ [ppm] −23.0 (s). 7Li{1H} NMR (155 MHz, thf-d8): δ [ppm] 1.4 (s). Anal. Calcd for C40H43Li2N2OP: C, 78.42; H, 7.07; N, 4.57. Found: C, 78.60; H, 7.11; N, 4.24. [Ta(A)Me3] (1). To a stirred solution of (A)Li2(diox) (273 mg, 477 μmol, 1.00 equiv) in Et2O (100 mL) maintained at −78 °C was added a solution of [TaCl2Me3] (179 mg, 603 μmol, 1.26 equiv) in Et2O (30 mL) dropwise over 30 min. The mixture was stirred in the dark for 1 h at −78 °C. The cooling bath was then replaced by an ice bath, and stirring in the dark was continued for 2 h at 0 °C. The solvent was removed under reduced pressure, the residue was extracted with toluene (40 mL), and the extract was filtered over Celite. The filtrate was condensed to dryness and the residue washed with pentane (2 × 5 mL) to afford the product as an orange powder (116 mg, 167 μmol, 35%). 1H NMR (600 MHz, C6D6): δ [ppm] 7.24 (d, J = 7.8 Hz, 2 H, ArH), 7.02 (t, J = 7.9 Hz, 4 H, ArH), 6.98−6.94 (m, 1 H, ArH), 6.91− 6.88 (m, 4 H, ArH), 6.80−6.77 (m, 4 H, ArH), 6.74 (d, J = 8.0 Hz, 4 H, ArH), 6.76−6.65 (m, 4 H, ArH), 3.02−2.94 (m, 2 H, PCH2), 2.76− 2.68 (m, 2 H, PCH2), 1.69 (sbr, 9 H, TaCH3). 13C{1H} NMR (151 MHz, C6D6): δ [ppm] 153.0 (s, ArC), 146.0 (s, ArC), 135.2 (s, ArC), 131.7 (s, ArC), 131.3 (d, J = 4.9 Hz, ArC), 130.9 (d, J = 9.3 Hz, ArC), 129.9 (d, J = 1.6 Hz, ArC), 129.2 (d, J = 1.9 Hz, ArC), 129.0 (s, ArC), 126.9 (s, ArC), 121.6 (s, ArC), 121.0 (s, ArC), 118.1 (s, ArC), 117.3 (s, ArC), 65.9 (s, TaCH3), 42.9 (d, J = 42.6 Hz, TaCH3), 28.7 (d, J = 7.7 Hz, PCH2), 15.6 (s, TaCH3). 31P{1H} NMR (243 MHz, C6D6): δ [ppm] 26.5 (s). Anal. Calcd for C35H36N2PTa: C, 60.35; H, 5.21; N, 4.02. Found: C, 60.31; H, 5.17; N, 3.98. [Ta(A)(CH2SiMe3)(η2-EtCCEt)] (2). A cooled (−40 °C) solution of [TaCl3(dme)(η2-EtCCEt)] (441 mg, 963 μmol, 1.10 equiv) in toluene (10 mL) was slowly added to a stirred solution of (A)Li2(diox) (500 mg, 873 μmol, 1.00 equiv) in toluene (15 mL) at −40 °C. The resulting reaction mixture was warmed to room temperature over the course of 1 h. Subsequently, lithium chloride was separated via filtration over Celite. The clear orange filtrate was evaporated and an oily residue obtained after drying under vacuum. After trituration with pentane, crude [Ta(A)(Cl)(η2-EtCCEt)] was obtained as a solid (443 mg, 576 μmol, 66%) and used without further purification (see the Supporting Information for details). 1H NMR (400 MHz, C6D6): δ [ppm] 7.50 (d, J = 7.6 Hz, 2 H, ArH), 7.03−6.97 (m, 6 H, ArH), 6.94−6.90 (m, 2 H, ArH), 6.85 (t, J = 7.6 Hz, 3 H, ArH), 6.72−6.63 (m, 4 H, ArH), 6.59 (d, J = 7.3 Hz, 2 H, ArH), 6.46 (d, J = 7.9 Hz, 4 H, ArH), 3.58 (sbr, 2 H, CH2CH3), 3.35 (sbr, 2 H, CH2CH3), 3.17 (dd, J = 7.3 Hz, J = 13.7 Hz, 2 H, PCH2), 2.71 (t, J = 13.7 Hz, 2 H, PCH2), 1.30 (sbr, 3 H, CH2CH3), 0.90 (sbr, 3 H, CH2CH3). 31P{1H} NMR (162 MHz, C6D6): δ [ppm] 34.8 (s). A solution of LiCH2TMS (27 mg, 287 μmol, 2.45 equiv) in toluene (10 mL) was added slowly to a stirred solution of crude [Ta(A)(Cl)(η2EtCCEt)] (90 mg, 117 μmol, 1.00 equiv) in toluene (10 mL) at room temperature. The reaction mixture was stirred for 1 h, and the resulting finely suspended LiCl was then separated via filtration over Celite. The Celite pad was washed with toluene (5 mL), and the filtrate was evaporated under vacuum. The residue was washed with pentane (2 × 3 mL) to afford the product as a yellow powder (50 mg, 60.8 μmol, 52%). 1H NMR (600 MHz, C6D6): δ [ppm] 7.29 (d, J = 12.3 Hz, 2 H, ArH), 7.08−6.97 (m, 4 H, m-Ph), 6.95−6.90 (m, 5 H, ArH), 6.88−6.82 (m, 2 H, ArH), 6.70 (q, J = 7.2 Hz, 2 H, ArH), 6.69 (d, J = 7.1 Hz, 2 H, p-Ph) 6.63 (d, J = 7.5 Hz, 2 H, ArH), 6.28 (d, J = 8.0 Hz, 4 H, o-Ph), 3.43−3.22 (m, 4 H, CH2CH3), 3.12 (dd, J = 6.3 Hz, J = 13.5 Hz, PCH2), 2.63 (t, J = 13.1 Hz, 2 H, PCH2), 1.21 (sbr, 8 H, CH2SiMe3 and CH2CH3), 0.42 (s, 9 H, CH2SiMe3). 13C{1H} NMR (151 MHz, C6D6): δ [ppm] 153.9 (s, ArC), 144.3 (d, J = 5.7 Hz, ArC), 137.3 (d, J = 1.8 Hz; ArC), 134.8 (d, J = 10.8 Hz, ArC), 133.4

and 9 with PhSiD3 and PhSiH3, respectively. No H/D scrambling was observed in these species, indicating that trivalent intermediates of the type [TaIII(B*)(dmpe)] are not involved in this process.

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EXPERIMENTAL SECTION

All manipulations were performed under an atmosphere of dry and oxygen-free argon by means of standard Schlenk or glovebox techniques. Toluene, thf, pentane, hexane, and diethyl ether were purified by passing the solvents over activated alumina columns (MBraun Solvent Purification System). Benzene, 1,4-dioxane, toluened8, thf-d8, and benzene-d6 were refluxed over sodium and purified by distillation. CD2Cl2 was dried over CaH2 and distilled prior to use. NMR spectra were recorded on a Bruker Avance II 400 MHz or a Bruker Avance III 600 MHz spectrometer at room temperature. 1H and 13C NMR spectra were referenced to residual proton signals of the lock solvent. 31P NMR spectra were referenced to external P(OMe)3 (141.0 ppm with respect to 85% H3PO4 at 0.0 ppm). Microanalyses (C, H, N) were performed at the Department of Chemistry at the University of Heidelberg. Compounds AH2,57 BH2,57 [TaCl2Me3],80 and [TaCl3(dme)(η2-EtCCEt)]81 were synthesized according to the literature. A purchased solution of ((trimethylsilyl)methyl)lithium (1.0 M solution in pentane) was concentrated to half of its volume, and LiCH2SiMe3 crystallized at −40 °C and was isolated as a white powder. Iodotrimethylsilane and phenylsilane were purified by simple distillation and stored over molecular sieves. Solutions of butyllithium (2.5 M in hexanes), LiN(SiMe3)2, [Ta(NMe2)5], PMe3, dmpe, H2, and D2 were purchased from commercial suppliers and used as received. (A)Li2(diox). To a precooled (−30 °C) solution of AH2 (1.95 g, 4.13 mmol, 1.00 equiv) in Et2O (30 mL) was added a solution of BuLi (2.5 M in hexanes, 3.47 mL, 8.67 mmol, 2.10 equiv) dropwise over 20 min. The solution was stirred for 1 h at −30 °C and for 1 h at 0 °C. Neat 1,4-dioxane (16.5 mmol, 1.41 mL, 4.00 equiv) was added to precipitate the product in the form of its dioxane adduct. The resulting suspension was filtered, and the collected solids were washed with Et2O (2 × 10 mL). After it was dried under vacuum, the product was obtained as a pale yellow powder (1.60 g, 2.80 mmol, 68%). 1H NMR (400 MHz, thf-d8): δ [ppm] 7.42 (t, J = 6.6 Hz, 2 H, o-PPh), 7.08− 7.05 (m, 3 H, m-PPh and p-PPh), 7.03−7.00 (m, 2 H, 6-ArH), 6.86 (d, J = 7.4 Hz, 2 H, 3-ArH), 6.77−6.73 (m, 2 H, 5-ArH), 6.72−6.69 (m, 4 H, m-Ph), 6.46 (d, J = 7.8 Hz, 4 H, o-Ph), 6.26 (t, J = 7.2 Hz, 2 H, 4ArH), 5.94 (t, J = 7.0 Hz, 2 H, p-Ph), 3.55 (s, 8 H, OCH2), 3.32 (dd, J = 4.2 Hz, J = 13.5 Hz, 2 H, PCH2), 2.96 (d, J = 13.5 Hz, 2 H, PCH2). 13 C{1H} NMR (101 MHz, thf-d8): δ [ppm] 160.2 (s, ipso-Ph), 158.3 (d, J = 3.5 Hz. 1-ArC), 133.1 (d, J = 15.3 Hz, o-PPh), 131.6 (d, J = 5.3 Hz, 2-ArC), 130.9 (d, J = 9.5 Hz, 3-ArC), 129.7 (s, ipso-PPh), 129.1 (s, m-Ph), 128.9 (s, m-PPh or p-PPh), 128.5 (d, J = 6.1 Hz, m-PPh or pPPh), 126.6 (s, 5-ArC), 123.8 (s, 6-ArC), 116.5 (s, o-Ph), 115.9 (s, 4ArC), 109.6 (s, p-Ph), 67.9 (s, OCH2), 32.7 (d, J = 8.2 Hz, PCH2). 31 1 P{ H} NMR (162 MHz, thf-d8): δ [ppm] −22.3 (s). 7Li{1H} NMR (155 MHz, thf-d8): δ [ppm] 0.5 (s). Thoroughly dried batches of (A)Li2(diox) containing one molecule of 1,4-dioxane were used for the synthesis of 1 and 2. These batches, however, gave low carbon values (approximately 1% low in C) upon combustion analysis. Samples containing 1.5 molecules of 1,4-dioxane (by 1H NMR integration) gave satisfactory carbon values. The latter samples were obtained by recrystallization from Et2O/dioxane and drying under vacuum for only 20 min. Anal. Calcd for C32H27Li2N2P·1.5C4H8O2: C, 74.02; H, 6.38; N, 4.54. Found: C, 74.15 H 6.25; N, 4.27. (B)Li2(thf). Solid lithium bis(trimethylsilyl)amide (367 mg, 2.20 mmol, 2.20 equiv) was added in small portions to a stirred solution of BH2 (529 mg, 1.00 mmol, 1.00 equiv) in thf (30 mL) over the course of 15 min. The resulting yellow solution was stirred for 1 h at room temperature and evaporated subsequently. The dark yellow solid residue was washed with Et2O (2 × 5 mL) and dried under vacuum overnight to ensure complete removal of the coordinated Et2O molecule. The title compound was obtained as a pale yellow powder (460 mg, 0.75 mmol, 75%). 1H NMR (600 MHz, thf-d8): δ [ppm] 7.56−7.47 (m, 2 H, 3-ArH), 7.43−7.21 (m, 7 H, 4-ArH and PPh), 5129


Article

Inorganic Chemistry

filtered off and washed with cold pentane (5 mL). After it was dried under vacuum, the title compound was obtained as a yellow powder (450 mg, 0.51 mmol, 63%). 1H NMR (600 MHz, C6D6): δ [ppm] 7.70 (sbr, 1 H, 3-ArH), 7.18 (sbr, 3 H, 9-ArH and ArH), 6.90−7.08 (m, 9 H, ArH), 6.84 (s, 2 H, o-Xyl), 6.66−6.74 (m, 2 H, 6-ArH and ArH), 6.64 (s, 1 H, p-Xyl), 6.43 (s, 1 H, p-Xyl), 5.35 (d, J = 14.8 Hz, 1 H, CH2), 5.03 (d, J = 15.2 Hz, 1 H, CH2), 4.10 (s, 1 H, CH), 2.16 (s, 6 H, Xyl-Me), 2.11 (s, 6 H, Xyl-Me), 0.98−1.05 (m, 2 H, TaCH2), 0.44 (d, J = 12.5 Hz, 1 H, TaCH2), 0.23 (s, 9 H, SiMe3), 0.21 (d, J = 12.5 Hz, 1 H, TaCH2), 0.05 (s, 9 H, SiMe3). 13C{1H} NMR (151 MHz, C6D6): δ [ppm] 159.2 (d, J = 31.2 Hz, 2-ArC), 152.2 (d, J = 27.1 Hz, 8-ArC), 149.4 (s, ipso-Xyl), 148.4 (s, ipso-Xyl), 139.9 (s, m-Xyl), 137.7 (s, mXyl), 135.0 (d, J = 27.5 Hz, ArC), 134.3 (s, ArC), 133.6 (s, 9-ArC), 133.0 (d, J = 12.7 Hz, ArC), 132.7 (s, C-3), 132.2 (d, J = 6.8 Hz, ArC), 131.9 (d, J = 7.5 Hz, ArC), 131.5 (d, J = 29.8 Hz, 7-ArC), 131.1 (s, ArC), 130.8 (d, J = 26.0 Hz, 1-ArC), 129.9 (s, ArC), 129.3 (d, J = 3.5 Hz, ArC), 128.9 (d, J = 7.8 Hz, ArC), 128.5 (s, ArC), 126.0 (s, p-Xyl), 125.8 (s, o-Xyl), 124.2 (s, p-Xyl), 118.2 (s, o-Xyl), 74.7 (sbr, TaCH2), 70.0 (s, CH), 63.6 (sbr, CH2), 51.1 (sbr, TaCH2), 22.0 (s, Xyl-Me), 21.4 (s, Xyl-Me), 3.0 (s, SiMe3), 2.9 (s, SiMe3). 31P{1H} NMR (243 MHz, C6D6): δ [ppm] −8.6 (s). Anal. Calcd for C44H56N2PSi2Ta: C, 59.98; H, 6.41; N, 3.18. Found: C, 59.83; H, 6.45; N, 3.36. [Ta(B**)(CH2SiMe3)(PMe3)] (6). To a solution of 5 (100 mg, 0.11 mmol, 1.00 equiv) in toluene (5 mL) was added excess trimethylphosphine (approximately 84 mg, 1.1 mmol, 10 equiv), and the reaction mixture was heated to 65 °C for 2 h. All volatiles were removed under vacuum, and the crude product was washed with cold pentane (2 mL). After it was dried under vacuum, the title compound was obtained as an orange powder (60 mg, 0.07 mmol, 61%). 1H NMR (600 MHz, C6D6): δ [ppm] 7.93 (sbr, 1 H, 3-ArH), 7.83 (sbr, 1 H, 9-ArH), 7.38 (m, 2 H, PPh), 7.25−7.34 (m, 4 H, o-Xyl and PPh), 6.95−7.03 (m, 5 H, 4-ArH and 6-ArH and 10-ArH and 12-ArH and pPPh), 6.78 (m, 1 H, 11-ArH), 6.60−6.63 (m, 2 H, 5-ArH and p-Xyl), 6.42 (s, 2 H, o-Xyl), 6.21 (s, 1 H, p-Xyl), 4.45 (s, 1 H, CH), 3.71 (s, 1 H, CH), 2.32 (s, 6 H, Xyl-Me), 1.89 (s, 6 H, Xyl-Me), 1.07 (d, J = 7.1 Hz, 9 H, PMe3), 0.18−0.24 (m, 1 H, TaCH2), −0.15 (s, 9 H, SiMe3) −0.25 to −0.30 (m, 1 H, TaCH2). 13C{1H} NMR (151 MHz, C6D6): δ [ppm] 166.8 (d, J = 29.8 Hz, 2-ArC), 156.8 (s, ipso-Xyl), 156.3 (d, J = 32.0 Hz, 8-ArC), 152.0 (s, ipso-Xyl), 139.8 (d, J = 29.8 Hz, ipso-PPh) 138.2 (s, m-Xyl), 137.4 (s, m-Xyl), 134.1 (d, J = 36.4 Hz, 1-ArC), 133.9 (d, J = 3.2 Hz, PPh), 133.0 (d, J = 10.0 Hz, PPh), 132.6 (d, J = 10.2 Hz, 3-ArC), 131.7 (s, 4-ArC or 10-ArC), 130.5 (d, J = 31.3 Hz, 7ArC), 130.0 (s, 9-ArC), 129.9 (s, 4-ArC or 10-ArC), 128.6 (d, J = 9.2 Hz, PPh), 128.5 (s, 6-ArC or 12-ArC), 127.6 (s, 6-ArC or 12-ArC), 126.7 (d, J = 6.1 Hz, 5-ArC), 124.3 (s, p-Xyl), 123.6 (s, 11-ArC), 122.3 (s, p-Xyl), 119.3 (s, o-Xyl), 117.5 (s, o-Xyl), 63.7 (sbr, CH), 57.3 (sbr, CH), 42.0 (s, TaCH2), 21.8 (s, Xyl-Me), 21.4 (s, Xyl-Me), 14.3 (d, J = 19.0 Hz, PMe3), 3.9 (s, SiMe3). 31P{1H} NMR (243 MHz, C6D6): δ [ppm] 43.3 (d, J = 104 Hz, PAr3), −28.7 (d, J = 104 Hz, PMe3). Anal. Calcd for C43H53N2P2SiTa: C, 59.44; H, 6.15; N, 3.22. Found: C, 59.31; H, 5.95; N, 3.41. [Ta(B**)(CH2SiMe3)(dmpe)] (7). Neat dmpe (55 mg, 0.37 mmol, 1.50 equiv) was added to a solution of 5 (220 mg, 0.25 mmol, 1.00 equiv) in toluene (20 mL), and the resulting reaction mixture was heated to 75 °C for 2 h. All volatiles were removed under vacuum, and the crude product was triturated with pentane (10 mL). The suspended material was filtered off, washed with pentane (5 mL), and dried under vacuum to afford the title compound as a salmon pink powder (160 mg, 0.17 mmol, 68%). 1H NMR (600 MHz, C6D6): δ [ppm] 8.14 (dd, 3JH,H = 7.4 Hz, 4JH,P = 3.5 Hz, 1 H, 3-ArH), 7.75 (dd, 3 JH,H = 7.4 Hz, 4JH,P = 3.8 Hz, 1 H, 9-ArH), 7.58 (s, 2 H, o-Xyl), 7.51− 7.40 (m, 3 H, o-PPh and 12-ArH), 7.25 (t, 3JH,H = 7.5 Hz, 1 H, 10ArH), 7.13 (t, 3JH,H = 7.6 Hz, 1 H, p-PPh), 7.10−6.97 (m, 3 H, o-Xyl and 4-ArH), 6.93−6.83 (m, 3 H, m-PPh and 11-ArH), 6.69 (dd, 3JH,H = 7.9 Hz, 3JH,P = 7.9 Hz, 1 H, 6-ArH), 6.60 (s, 1 H, p-Xyl), 6.47 (t, 3 JH,H = 7.3 Hz, 1 H, 5-ArH), 6.21 (s, 1 H, p-Xyl), 4.30−4.20 (m, 1 H, CH), 3.90−3.82 (m, 1 H, CH), 2.60 (s, 6 H, Xyl-Me), 1.94 (s, 6 H, Xyl-Me), 1.55 (sbr, 2 H, dmpe-CH2), 1.21−1.11 (m, 1 H, TaCH2), 0.89−0.07 (m, 17 H, dmpe-CH2 and dmpe-Me and SiMe3), −0.37 to −0.48 (m, 1 H, TaCH2). 1H{31P} NMR (600 MHz, C6D6): δ [ppm]

(d, J = 2.3 Hz, ArC), 132.0 (d, J = 5.1 Hz, ArC), 130.6 (d, J = 10.9 Hz, ArC), 129.7 (s, ArC), 129.2 (d, J = 2.2 Hz, ArC), 129.0 (s, m-Ph), 128.7 (d, J = 7.2 Hz, ArC), 128.5 (s, ArC), 119.1 (s, p-Ph), 117.6 (s, oPh), 57.5 (s, CH2SiMe3), 32.3 (s, CH2CH3), 30.9 (d, J = 7.1 Hz, PCH2), 14.3 (d, J = 4.1 Hz, CH2CH3), 4.6 (s, CH2SiMe3). 31P{1H} NMR (243 MHz, C6D6): δ [ppm] 26.5 (s). Anal. Calcd for C42H48N2PSiTa: C, 61.45; H, 5.89; N, 3.41. In numerous attempts, low carbon values were found, e.g.: C, 60.51; H, 5.85; N, 3.64. [Ta(B*)(NMe2)2] (3). A stirred solution of BH2 (3.00 g, 5.67 mmol, 1.00 equiv) and [Ta(NMe2)5] (2.50 g, 6.23 mmol, 1.10 equiv) in toluene (50 mL) was heated to 115 °C for 24 h. All volatiles were removed under vacuum, and the crude product was washed with cold pentane (3 × 5 mL) and dried under vacuum (8 h) to afford the title compound as a bright yellow powder (3.20 g, 4.03 mmol, 71%). 1H NMR (600 MHz, C6D6): δ [ppm] 7.60 (dd, J = 7.5 Hz, J = 4.7 Hz, 1 H, 3-ArH), 7.27 (dd, J = 7.2 Hz, J = 4.6 Hz, 1 H, 9-ArH), 7.18 (m, 3 H, 4-ArH and 10-ArH and p-PPh), 7.05 (s, 2 H, o-Xyl), 6.92−7.02 (m, 5 H, 6-ArH and o-PPh and m-PPh), 6.90 (t, J = 7.8 Hz, 1 H, 11-ArH), 6.81 (t, J = 7.5 Hz, 1 H, 5-ArH), 6.69 (t, J = 7.4 Hz, 1 H, 12-ArH), 6.63 (s, 1 H, p-Xyl), 6.39 (s, 2 H, o-Xyl), 6.36 (s, 1 H, p-Xyl), 5.42 (d, J = 14.2 Hz, 1 H, CH2), 4.66 (dd, J = 14.3 Hz, J = 7.3 Hz, 1 H, CH2), 3.77 (s, 1 H, CH), 3.71 (s, 6 H, NMe2), 2.73 (s, 6 H, NMe2), 2.31 (s, 6 H, Xyl-Me), 2.14 (s, 6 H, Xyl-Me). 13C{1H} NMR (151 MHz, C6D6): δ [ppm] 162.1 (d, J = 27.4 Hz, 2-ArC), 159.0 (d, J = 13.8 Hz, 8-ArC), 151.1 (s, ipso-Xyl), 149.7 (s, ipso-Xyl), 138.6 (s, m-Xyl), 138.1 (s, mXyl), 136.4 (d, J = 32.9 Hz, 1-ArC), 134.8 (d, J = 11.9 Hz, 12-ArC), 132.7 (d, J = 28.1 Hz, 7-ArC), 131.7 (d, J = 12.1 Hz, ipso-PPh), 129.0 (s, 10-ArC), 129.1 (d, J = 1.4 Hz, m-PPh), 129.0 (d, J = 12.7 Hz, 4ArC), 128.6 (d, J = 7.5 Hz, 11-ArC), 128.1 (d, J = 2.0 Hz, o-PPh), 127.4 (d, J = 11.1 Hz, 3-ArC), 127.1 (sbr, 9-ArC), 126.9 (d, J = 4.9 Hz, 6-ArC), 125.9 (s, p-PPh), 123.6 (s, p-Xyl), 122.5 (s, p-Xyl), 120.2 (s, oXyl), 115.0 (sbr, o-Xyl), 66.6 (d, J = 18.6 Hz, CH2), 63.8 (d, J = 3.9 Hz, CH), 48.7 (sbr, NMe2), 44.0 (s, NMe2), 20.6 (s, Xyl-Me), 20.5 (s, XylMe). 31P{1H} NMR (243 MHz, C6D6): δ [ppm] −9.1 (s). Analytically pure samples were only obtained after recrystallization from toluene/ pentane and found to contain half a molecule of toluene by 1H NMR spectroscopy. Anal. Calcd for C40H46N4PTa·0.5C7H8: C, 62.14; H, 5.99; N, 6.66. Found: C, 61.94; H, 6.08; N, 6.69. [Ta(B*)I2] (4). A solution of iodotrimethylsilane (685 mg, 3.42 mmol, 2.10 equiv) in toluene (10 mL) was added dropwise to a stirred solution of 3 (1.30 g, 1.63 mmol, 1.00 equiv) in toluene (50 mL), and the resulting reaction mixture was stirred for 15 min at room temperature. All volatiles were removed under vacuum, and the crude product was washed with pentane/diethyl ether (1/1, 2 × 5 mL). After it was dried under vacuum, the title compound was obtained as an orange powder (1.22 g, 1.27 mmol, 78%). 1H NMR (600 MHz, C6D6): δ [ppm] 7.55 (dd, J = 7.6 Hz, J = 4.0 Hz, 1 H, 3-ArH), 7.23− 7.35 (m, 6 H, 7-ArH and o-Xyl and o-PPh and p-PPh), 7.13 (t, J = 7.6 Hz, 1 H, 4-ArH), 6.97 (sbr, 3 H, H-5 and o-Xyl), 6.80−6.84 (m, 2 H, m-PPh), 6.76 (t, J = 7.2 Hz, 1 H, 8-ArH), 6.72 (t, J = 7.3 Hz, 1 H, 10ArH), 6.60−6.67 (m, 2 H, 9-ArH and p-Xyl), 6.54 (s, 1 H, p-Xyl), 5.42 (d, J = 13.2 Hz, 2 H, CH2), 4.24 (s, 1 H, CH), 2.14 (s, 6 H, Xyl-Me), 2.11 (s, 6 H, Xyl-Me). 13C{1H} NMR (151 MHz, C6D6): δ [ppm] 158.2 (d, J = 22.1 Hz, 2-ArC), 152.9 (d, J = 18.3 Hz, 8-ArC), 149.1 (s, ipso-Xyl), 147.8 (s, ipso-Xyl), 145.8 (sbr, m-Xyl), 144.2 (s, m-Xyl), 139.2 (sbr, ArC), 137.2 (sbr, ArC), 135.0 (s, o-Xyl), 133.6 (d, J = 9.4 Hz, C-4), 132.5−132.7 (m, C-3 and PPh), 131.3 (d, J = 2.0 Hz, 8ArC), 130.8 (d, J = 1.3 Hz, ArC), 130.3 (d, J = 1.8 Hz, ArC), 129.0 (s, ArC), 128.2 (s, o-Xyl), 127.0 (d, J = 5.9 Hz, PPh), 125.3 (s, o-Xyl), 119.8 (sbr, p-Xyl), 68.3 (sbr, CH2), 67.4 (sbr, CH), 66.4 (sbr, CH2), 21.2 (s, Xyl-Me), 20.8 (s, Xyl-Me). 31P{1H} NMR (243 MHz, C6D6): δ [ppm] 11.1 (sbr). Anal. Calcd for C36H34I2N2PTa: C, 45.02; H, 3.57; N, 2.92. Found: C, 45.37; H, 4.11; N, 2.88. [Ta(B*)(CH2SiMe3)2] (5). To a stirred solution of 4 (780 mg, 0.81 mmol, 1.00 equiv) in toluene (50 mL) was added solid ((trimethylsilyl)methyl)lithium (170 mg, 1.81 mmol, 2.20 equiv) at room temperature. The reaction mixture was stirred for 15 min and then filtered over Celite. The filtrate was evaporated to dryness, and the residue was taken up in Et2O (3 mL). Addition of pentane (15 mL) resulted in the formation of a yellow precipitate, which was 5130


Article

Inorganic Chemistry 8.14 (d, 3JH,H = 7.5 Hz, 1 H, 3-ArH), 7.75 (d, 3JH,H = 7.5 Hz, 1 H, 9ArH), 7.58 (s, 2 H, o-Xyl), 7.47 (d, 3JH,H = 6.5 Hz, 2 H, o-PPh), 7.43 (d, 3JH,H = 7.3 Hz, 1 H, 12-ArH), 7.25 (dd, 3JH,H = 7.4 Hz, 3JH,H = 7.6 Hz, 1 H, 10-ArH), 7.13 (t, 3JH,H = 7.7 Hz, 1 H, p-PPh), 7.09 (s, 2 H, oXyl), 6.99 (m, 1 H, 4-ArH), 6.93−6.82 (m, 3 H, m-PPh and 11-ArH), 6.69 (d, 3JH,H = 7.6 Hz, 1 H, 6-ArH), 6.60 (s, 1 H, p-Xyl), 6.46 (dd, 3 JH,H = 7.6 Hz, 3JH,H = 7.4 Hz, 1 H, 5-ArH), 6.21 (s, 1 H, p-Xyl), 4.25 (s, 1 H, CH), 3.86 (s, 1 H, CH), 2.60 (s, 6 H, Xyl-Me), 1.94 (s, 6 H, Xyl-Me), 1.55 (sbr, 2 H, dmpe-CH2), 1.16 (d, 2JH,H = 12.1 Hz, 1 H, TaCH2), 0.81−0.15 (m, 17 H, dmpe-CH2 and dmpe-Me and SiMe3), −0.43 (d, 2JH,H = 12.1 Hz, 1 H, TaCH2). 13C{1H} NMR (151 MHz, C6D6): δ [ppm] 165.2 (d, 2JC,P = 33 Hz, 8-ArC), 159.8−159.2 (m, ipso-Xyl), 157.3 (d, 2JC,P = 29 Hz, 2-ArC), 153.3 (m, ipso-Xyl), 143.9 (d, 1JC,P = 58 Hz, 1-ArC), 137.9 (overlapping d and s, ipso-PPh and mXyl), 135.9 (overlapping d and s, 1JC,P = 25 Hz, 7-ArC and m-Xyl), 133.5 (d, 2JC,P = 10 Hz, o-PPh), 132.2−131.8 (m, 3-ArC and 12-ArC), 130.7 (d, 3JC,P = 13 Hz, 9.ArC), 130.3 (d, 4JC,P = 2 Hz, 10-ArC), 129.2 (d, 3JC,P = 1 Hz, 11-ArC), 129.0 (sbr, 6-ArC), 128.5 (d, 4JC,P = 3 Hz, pPPh), 127.3 (d, 3JC,P = 8 Hz, m-PPh), 125.4 (d, 3JC,P = 7 Hz, 5-ArC), 123.4 (d, 4JC,P = 5 Hz, 4-ArC), 122.9 (s, p-Xyl), 120.1 (sbr, o-Xyl), 117.3 (s, p-Xyl), 115.8 (sbr, o-Xyl), 67.8 (d, 2JC,P = 8 Hz, CH), 59.3− 57.8 (m, CH), 32.9−32.7 (m, TaCH2), 27.5−26.1 (sbr, dmpe-CH2), 22.5 (s, Xyl-Me), 21.7 (s, Xyl-Me), 15.9, 13.6, and 10.6 (overlapping sbr, dmpe-Me), 6.5 (s, SiMe3); 31P{1H} NMR (243 MHz, C6D6): δ [ppm] 36.7 (t, 2JP,P = 114 Hz, 1 P, PAr3), 7.9 (sbr, 1 P, dmpe), −24.4 (sbr, 1 P, dmpe). Anal. Calcd for C46H60N2P3SiTa: C, 58.59; H, 6.41; N, 2.97. Found: C, 58.86; H, 6.59; N, 2.60. [Ta(B**)(H)(dmpe)] (8). A solution of 7 (40 mg, 42 μmol) in toluene (0.7 mL) was transferred to a thick-walled high-pressure NMR tube and pressurized with H2 (9 bar). After the sealed tube was kept at 85 °C for 24 h, the pressure was released and the solvent evaporated under vacuum. A brownish impurity and traces of free dmpe were removed by washing the crude solid with pentane (2 × 1 mL). The product was dried under vacuum and obtained as a pale yellow powder (30 mg, 35 μmol, 83%). 1H NMR (600 MHz, C6D6): δ [ppm] 7.60 (dd, 3JH,H = 7.5 Hz, 4JH,P = 3.9 Hz, 2 H, 3-ArH), 7.42−7.34 (m, 2 H, oPPh), 7.17 (d overlapping with residual protons in C6D6, 3JH,H = 7.4 Hz, 2 H, 6-ArH), 7.08 (s, 4 H, o-Xyl), 7.04−7.00 (m, 3 H, m-PPh and p-PPh), 6.98 (t, 3JH,H = 7.5 Hz, 2 H, 4-ArH), 6.60 (t, 3JH,H = 7.4 Hz, 2 H, 5-ArH), 6.38 (s, 2 H, p-Xyl), 3.71−3.60 (m, 2 H, CH), 2.28 (s, 12 H, Xyl-Me), 1.21 (d, 2JH,P = 8.3 Hz, 6 H, dmpe-Me), 1.03 (d, 2JH,P = 7.8 Hz, 6 H, dmpe-Me), 0.76−0.58 (m, 4 H, dmpe-CH2); the signal for the tantalum-bound hydride (1 H) is buried below the aromatic signals and was not detected unambiguously, but found in the corresponding deuterium derivative 9 (vide infra). 13C{1H} NMR (151 MHz, C6D6): δ [ppm] 160.9 (dd, 2JC,P = 30 Hz, 4JC,P = 3 Hz, 2ArC), 154.6 (s, ipso-Xyl), 139.0 (dd, 1JC,P = 42 Hz, 3JC,P = 4 Hz, 1ArC), 137.1 (s, m-Xyl), 134.5 (d, 1JC,P = 39 Hz, ipso-PPh), 133.2 (d, 2 JC,P = 11 Hz, o-PPh), 132.4 (sbr, 6-ArC), 131.3 (d, 3JC,P = 13 Hz, 3ArC), 129.0 (d, 4JC,P = 2 Hz, p-PPh), 128.9 (d, 4JC,P = 2 Hz, 4-ArC), 127.7 (overlapping with C6D6, but detected in the DEPT NMR, d, 3 JC,P = 9 Hz, m-PPh), 123.9 (d, 3JC,P = 6 Hz, 5-ArC), 121.6 (s, o-Xyl), 121.1 (s, p-Xyl), 51.1−50.2 (m, CH), 27.8 (dd, JC,P = 22 Hz, JC,P = 18 Hz, dmpe-CH2), 27.2 (t, JC,P = 15 Hz, dmpe-CH2), 21.7 (s, Xyl-Me), 16.7 (d, 1JC,P = 24 Hz, dmpe-Me), 11.6 (d, 1JC,P = 18 Hz, dmpe-Me). 31 1 P{ H} NMR (243 MHz, C6D6): δ [ppm] 26.0 (dd, 2JP,P = 77 Hz, 2 JP,P = 24 Hz, PAr3), 18.3 (d, 2JP,P = 24 Hz, dmpe), 16.3 (d, 2JP,P = 77 Hz, dmpe). Anal. Calcd for C42H50N2P3Ta: C, 58.88; H, 5.88; N, 3.27. Found: C, 58.49; H, 5.95; N, 3.16. [Ta(d2-B**)(D)(dmpe)] (9). Following the procedure provided for 8, the title compound was prepared starting from 7 and D2. 2H NMR (92 MHz, thf): δ [ppm] 7.01 ppm (dd, 2JD,P = 11 Hz, 2JD,P = 6.3 Hz, 1 D, TaD), 3.70 (sbr, 2 D, CD). Alternatively, 9 can be prepared by reacting 8 with D2 (10 bar, 85 °C, 24 h, toluene). The reverse reaction of 9 with H2 (10 bar, 85 °C, 24 h, toluene), afforded 8, as shown by in situ 2H and 31P{1H} NMR spectroscopy. NMR Spectroscopic Detection of [Ta(B**)(D)(dmpe)] (10) and [Ta(d2-B**)(H)(dmpe)] (11). A solution of 8 (8.8 mg, 10 μmol) in C6D6 (0.4 mL) was transferred to a thick-walled high-pressure

NMR tube, and 5 drops of PhSiD3 (excess) were added. The tube was sealed and kept at 85 °C for 24 h; 10 was identified by NMR spectroscopy. 1H NMR (600 MHz, C6D6, selected peaks only): δ [ppm] 3.71−3.60 (m, 2 H, CH); 31P{1H} NMR (243 MHz, C6D6): δ [ppm] 26.0 (ddt, 2JP,P = 77 Hz, 2JP,P = 24 Hz, 2JP,D = 6.3 Hz, PAr3), 18.3 (dt, 2JP,P = 24 Hz, 2JP,D = 11 Hz, dmpe), 16.3 (d, 2JP,P = 77 Hz, dmpe). Similarly, 9 was reacted with PhSiH3 to afford 11, as shown by 2 H and 31P{1H} NMR spectroscopy.

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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.7b00277. Additional experimental details, selected NMR spectra, and details of the structure determinations (PDF) Crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Author

*J.B.: tel, (+49) 6221-548596; e-mail, [email protected]. ORCID

Joachim Ballmann: 0000-0001-6431-4197 Author Contributions †

S.B. and M.S. contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Fonds der Chemischen Industrie (FCI, Li 187/02) and the Deutsche Forschungsgemeinschaft (DFG, BA 4859/1-1) for funding of this work. We thank Jan Wenz for a gift of distilled PhSiD3 and Prof. Dr. L. H. Gade for generous support, fruitful discussions, and continued interest in our work. We are grateful to a reviewer who suggested the use of silanes to probe for the mechanism of the H/D exchange reaction that interconnects 8 and 9.

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REFERENCES

(1) Green, M. L. H.; McCleverty, J. A.; Pratt, L.; Wilkinson, G. 955. The Di-π-cyclopentadienyl Hydrides of Tantalum, Molybdenum, and Tungsten. J. Chem. Soc. 1961, 0, 4854−4859. (2) Parkin, G.; Van Asselt, A.; Leahy, D. J.; Whinnery, L.; Hua, N. G.; Quan, R. W.; Henling, L. M.; Schaefer, W. P.; Santarsiero, B. D.; Bercaw, J. E. Oxo-Hydrido and Imido-Hydrido Derivatives of Permethyltantalocene. Structures of (η5-C5Me5)2Ta(:O)H and (η5C5Me5)2Ta(NC6H5)H: Doubly or Triply Bonded Tantalum Oxo and Imido Ligands? Inorg. Chem. 1992, 31, 82−85. (3) Burger, B. J.; Santarsiero, B. D.; Trimmer, M. S.; Bercaw, J. E. Kinetics and Mechanism of the Insertion of Olefins into Niobium- and Tantalum-Hydride Bonds: A Study of the Competition between Steric and Electronic Effects. J. Am. Chem. Soc. 1988, 110, 3134−3146. (4) Mayer, J. M.; Wolczanski, P. T.; Santarsiero, B. D.; Olson, W. A.; Bercaw, J. E. X-ray Crystal Structure Determination of [η5-C5(CH3)5]Ta[P(CH3)3]2H4 and High-Field NMR Studies of Phosphine Derivatives of (Pentamethylcyclopentadienyl)tantalum(V) Hydrides. Inorg. Chem. 1983, 22, 1149−1155. (5) Belmonte, P. A.; Cloke, F. G. N.; Schrock, R. R. Reduction of Carbon Monoxide by Binuclear Tantalum Hydride Complexes. J. Am. Chem. Soc. 1983, 105, 2643−2650. (6) Churchill, M. R.; Wasserman, H. J.; Belmonte, P. A.; Schrock, R. R. Reduction of Nitriles by a Binuclear Tantalum Hydride Complex. 5131


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Inorganic Chemistry Structural Study of [(η5-C5Me4Et)TaCl2](μ-η1-N,η2-C,N-NCHMe)(μCl)(μ-H)[η5-C5Me4Et)TaCl]. Organometallics 1982, 1, 559−561. (7) Belmonte, P. A.; Schrock, R. R.; Day, C. S. Binuclear Tantalum Hydride Complexes. J. Am. Chem. Soc. 1982, 104, 3082−3089. (8) Burckhardt, U.; Casty, G. L.; Tilley, T. D.; Woo, T. K.; Rothlisberger, U. Ditantalum Hydride Complexes with Bridging (2,6-iPr2C6H3)NSiHPh Silanimine Ligands Resulting from PhSiH3− Imido Ligand Coupling. A Combined Spectroscopic and Theoretical Investigation. Organometallics 2000, 19, 3830−3841. (9) McLeod, N. A.; Kuzmina, L. G.; Churakov, A. V.; Mountford, P.; Nikonov, G. I. Group 5 hydride and borohydride complexes supported by cyclopentadienyl-imido ligand sets. Dalton Trans. 2014, 43, 188− 195. (10) Ignatov, S. K.; Rees, N. H.; Merkoulov, A. A.; Dubberley, S. R.; Razuvaev, A. G.; Mountford, P.; Nikonov, G. I. Silyl Hydrides of Tantalum Supported by Cyclopentadienyl-imido Ligand Sets: Syntheses, X-ray, NMR, and DFT Studies. Organometallics 2008, 27, 5968−5977. (11) Ostapowicz, T. G.; Fryzuk, M. D. Anionic Tantalum Dihydride Complexes: Heterobimetallic Coupling Reactions and Reactivity toward Small-Molecule Activation. Inorg. Chem. 2015, 54, 2357−2366. (12) Fryzuk, M. D.; Clentsmith, G. K. B.; Rettig, S. J. Coordination behaviour of LiBEt4 towards (η5-C5H5)2ReH, (η5-C5H5)2WH2 and (η5 -C 5 H 5 ) 2 TaH 3 . Solid state structure of [(η 5 -C 5 H5 ) 2 TaH · AlH2(OCH2CH2CH2CH3)]2. Inorg. Chim. Acta 1997, 259, 51−59. (13) Fandos, R.; Fernández-Gallardo, J.; Otero, A.; Rodríguez, A.; Ruiz, M. J. Tantalum Complexes Containing a Tridentate [NSN]Type Ligand: Unusual Reactivity of a Dihydride Complex with an Isocyanide to Give an Azatantallaziridine Moiety. Organometallics 2011, 30, 1551−1557. (14) Tebbe, F. N. Synthesis of a Tantalum Pentahydride Complex. J. Am. Chem. Soc. 1973, 95, 5823−5824. (15) Fellmann, J. D.; Turner, H. W.; Schrock, R. R. TantalumNeopentylidene Hydride and Tantalum-Neopentylidyne Hydride Complexes. J. Am. Chem. Soc. 1980, 102, 6608−6609. (16) Schrock, R. R. The preparation of NbH5(Me2PCH2CH2PMe2)2 and NbHL2(Me2PCH2CH2PMe2)2 (L = CO or C2H4). J. Organomet. Chem. 1976, 121, 373−379. (17) Hlatky, G. G.; Crabtree, R. H. Transition-metal polyhydride complexes. Coord. Chem. Rev. 1985, 65, 1−48. (18) Hu, Y.; Shaw, A. P.; Estes, D. P.; Norton, J. R. Transition-Metal Hydride Radical Cations. Chem. Rev. 2016, 116, 8427−8462. (19) Ballmann, J.; Munha, R. F.; Fryzuk, M. D. The hydride route to the preparation of dinitrogen complexes. Chem. Commun. 2010, 46, 1013−1025. (20) Hoskin, A. J.; Stephan, D. W. Early transition metal hydride complexes: synthesis and reactivity. Coord. Chem. Rev. 2002, 233−234, 107−129. (21) Antiñolo, A.; Carrillo-Hermosilla, F.; Fajardo, M.; FernándezBaeza, J.; García-Yuste, S.; Otero, A. Advances in the chemistry of biscyclopentadienyl hydride derivatives of niobium and tantalum. Coord. Chem. Rev. 1999, 193−195, 43−72. (22) Luetkens, M. L.; Huffman, J. C.; Sattelberger, A. P. Development of Low-Valent Tantalum Chemistry: Syntheses and Xray Structures of TaCl 2 (PMe 3 ) 4 , TaCl 2 H 2 (PMe 3 ) 4 and TaClH2(PMe3)4. J. Am. Chem. Soc. 1983, 105, 4474−4475. (23) Scoles, L.; Ruppa, K. B. P.; Gambarotta, S. Preparation of the First Ditantalum(III) Complex Containing a Ta−Ta Bond without Bridging Ligands. J. Am. Chem. Soc. 1996, 118, 2529−2530. (24) Cotton, F. A.; Daniels, L. M.; Murillo, C. A.; Wang, X. A Wonderful Bond That Wasn’t There: Reformulation of a Compound “Containing a Ta−Ta Bond without Bridging Ligands” as [(Cy2N)2ClTa(μ-H)]2. J. Am. Chem. Soc. 1996, 118, 12449−12450. (25) Miller, R. L.; Toreki, R.; LaPointe, R. E.; Wolczanski, P. T.; Van Duyne, G. D.; Roe, D. C. Syntheses, Carbonylations, and Dihydrogen Exchange Studies of Monomeric and Dimeric Silox (tBu3SiO−) Hydrides of Tantalum: Structure of [(silox)2TaH2]2. J. Am. Chem. Soc. 1993, 115, 5570−5588.

(26) Parkin, B. C.; Clark, J. R.; Visciglio, V. M.; Fanwick, P. E.; Rothwell, I. P. Synthesis and Characterization of a Series of Mononuclear Tantalum(V) Hydride Compounds Containing Aryloxide Ligation. Organometallics 1995, 14, 3002−3013. (27) Visciglio, V. M.; Fanwick, P. E.; Rothwell, I. P. Crystal and Molecular Structure of [Ta(H)2(OC6H3Pri2-2,6)3(PMe2Ph)]: a Distorted Six-coordinate Tantalum Dihydride. J. Chem. Soc., Chem. Commun. 1992, 1505−1507. (28) Scioly, A. J.; Luetkens, M. L., Jr; Wilson, R. B., Jr; Huffman, J. C.; Sattelberger, A. P. Synthesis and characterization of binuclear tantalum hydride complexes. Polyhedron 1987, 6, 741−757. (29) Luetkens, M. L.; Elcesser, W. L.; Huffman, J. C.; Sattelberger, A. P. Paramagnetic Hydride Complexes of Niobium(IV) and Tantalum(IV). Inorg. Chem. 1984, 23, 1718−1726. (30) Toreki, R.; LaPointe, R. E.; Wolczanski, P. T. CO Hydrogenation, Deoxygenation, and C-C Coupling Promoted by [(silox)2TaH2]2. J. Am. Chem. Soc. 1987, 109, 7558−7560. (31) LaPointe, R. E.; Wolczanski, P. T.; Mitchell, J. F. Carbon Monoxide Cleavage by (silox)3Ta (silox = t-Bu3SiO−). J. Am. Chem. Soc. 1986, 108, 6382−6384. (32) LaPointe, R. E.; Wolczanski, P. T. Silox Hydrides [silox = (Me3C)3SiO−] of Group 5: Do [(Me3C)3SiO]2MH2]2 (M = Nb, Ta) Contain Unbridged M-M Bonds? J. Am. Chem. Soc. 1986, 108, 3535− 3537. (33) Weinert, C. S.; Fanwick, P. E.; Rothwell, I. P. Synthesis of the Tantalum Hydride Complex (R,R)-[Ta(O2C20H10{SiMe3}2-3,3′)2(H)] and Reactivity with Aldehydes, Ketones, Acetylenes, and Related Substrates: A Reagent for the Asymmetric Hydrogenation of Prochiral Carbonyl Species. Organometallics 2005, 24, 5759−5766. (34) Mulford, D. R.; Clark, J. R.; Schweiger, S. W.; Fanwick, P. E.; Rothwell, I. P. Reactions of Alkynes and Olefins with Tantalum Hydrides Containing Aryloxide Ancillary Ligation: Relevance to Catalytic Hydrogenation. Organometallics 1999, 18, 4448−4458. (35) Clark, J. R.; Fanwick, P. E.; Rothwell, I. P. Reactivity of Tantalum Hydride Aryloxide Complexes toward Organic Isocyanide Reagents. Organometallics 1996, 15, 3232−3237. (36) Clark, J. R.; Fanwick, P. E.; Rothwell, I. P. Reaction pathways for the oligomerization of organic isocyanides by tantalum hydride reagents. J. Chem. Soc., Chem. Commun. 1993, 1233−1235. (37) Rothwell, I. P. Cyclometalation Chemistry of Aryl Oxide Ligation. Acc. Chem. Res. 1988, 21, 153−159. (38) Fernández-Gallardo, J.; Bajo, Á .; Fandos, R.; Otero, A.; Rodríguez, A.; Ruiz, M. J. Insertion Reactions in Ta−H and Ta−Me Bonds in Complexes Containing Tridentate κ3O,S,O-Type Ligands. Organometallics 2013, 32, 1752−1758. (39) Watanabe, T.; Ishida, Y.; Matsuo, T.; Kawaguchi, H. Reductive Coupling of Six Carbon Monoxides by a Ditantalum Hydride Complex. J. Am. Chem. Soc. 2009, 131, 3474−3475. (40) Kawaguchi, H.; Matsuo, T. Aryl−Oxygen Bond Cleavage by a Trihydride-Bridging Ditantalum Complex. J. Am. Chem. Soc. 2003, 125, 14254−14255. (41) Watanabe, T.; Kurogi, T.; Ishida, Y.; Kawaguchi, H. Insertion and reduction chemistry of isocyanide with a cyclometalated ditantalum hydride complex. Dalton Trans. 2011, 40, 7701−7703. (42) Rankin, M. A.; Cummins, C. C. Carbon Dioxide Reduction by Terminal Tantalum Hydrides: Formation and Isolation of Bridging Methylene Diolate Complexes. J. Am. Chem. Soc. 2010, 132, 10021− 10023. (43) Kriegel, B. M.; Bergman, R. G.; Arnold, J. Generation of lowvalent tantalum species by reversible C-H activation in a cyclometallated tantalum hydride complex. Dalton Trans. 2014, 43, 10046− 10056. (44) Fryzuk, M. D.; Johnson, S. A.; Rettig, S. J. Reaction of [P2N2]TaCH2(Me) with Ethylene: Synthesis of [P2N2]Ta(C2H4)Et, a Neutral Species with a β-Agostic Ethyl Group in Equilibrium with an α-Agostic Ethyl Group ([P2N2] = PhP(CH2SiMe2NSiMe2CH2)2PPh). J. Am. Chem. Soc. 2001, 123, 1602−1612. (45) Fryzuk, M. D.; Johnson, S. A.; Rettig, S. J. Synthesis and Bonding in the Diamagnetic Dinuclear Tantalum(IV) Hydride Species 5132


Article

Inorganic Chemistry ([P2N2]Ta)2(μ-H)4 and the Paramagnetic Cationic Dinuclear Hydride Species {([P2N2]Ta)2(μ-H)4}+I− ([P2N2] = PhP(CH2SiMe2NSiMe2CH2)2PPh): The Reducing Ability of a Metal− Metal Bond. Organometallics 2000, 19, 3931−3941. (46) Fryzuk, M. D.; Johnson, S. A.; Patrick, B. O.; Albinati, A.; Mason, S. A.; Koetzle, T. F. New Mode of Coordination for the Dinitrogen Ligand: Formation, Bonding, and Reactivity of a Tantalum Complex with a Bridging N2 Unit That Is Both Side-On and End-On. J. Am. Chem. Soc. 2001, 123, 3960−3973. (47) Fryzuk, M. D.; Johnson, S. A.; Rettig, S. J. New Mode of Coordination for the Dinitrogen Ligand: A Dinuclear Tantalum Complex with a Bridging N2 Unit That Is Both Side-On and End-On. J. Am. Chem. Soc. 1998, 120, 11024−11025. (48) Shaver, M. P.; Johnson, S. A.; Fryzuk, M. D. Activation and cleavage of alkynes by the dinuclear tantalum complexes ([NPN]Ta)2(μ-H)4 and ([NPN]Ta)2(μ-η1:η2-N2)(μ-H)2 (where NPN = PhP(CH2SiMe2NPh)2). Can. J. Chem. 2005, 83, 652−660. (49) Ballmann, J.; Pick, F.; Castro, L.; Fryzuk, M. D.; Maron, L. Cleavage of Carbon Monoxide Promoted by a Dinuclear Tantalum Tetrahydride Complex. Organometallics 2012, 31, 8516−8524. (50) Ballmann, J.; Pick, F.; Castro, L.; Fryzuk, M. D.; Maron, L. Reduction of Carbon Dioxide Promoted by a Dinuclear Tantalum Tetrahydride Complex. Inorg. Chem. 2013, 52, 1685−1687. (51) Ballmann, J.; Yeo, A.; MacKay, B. A.; Rijt, S. v.; Patrick, B. O.; Fryzuk, M. D. Complete disassembly of carbon disulfide by a ditantalum complex. Chem. Commun. 2009, 46, 8794−8796. (52) Shaver, M. P.; Fryzuk, M. D. Cleavage of Hydrazine and 1,1Dimethylhydrazine by Dinuclear Tantalum Hydrides: Formation of Imides, Nitrides, and N,N-Dimethylamine. J. Am. Chem. Soc. 2005, 127, 500−501. (53) Parker, K. D. J.; Nied, D.; Fryzuk, M. D. Hydrogenolysis of Tantalum Hydrocarbyl Complexes: Intermediates on the Road to a Dinuclear Tantalum Tetrahydride Derivative. Organometallics 2015, 34, 3546−3558. (54) Parker, K. D. J.; Fryzuk, M. D. Carbon−Carbon Bond Forming Reactions with Tantalum Diamidophosphine Complexes That Incorporate Alkyne Ligands. Organometallics 2014, 33, 6122−6131. (55) Burford, R. J.; Yeo, A.; Fryzuk, M. D. Dinitrogen Activation by Group 4 and Group 5 Metal Complexes Supported by PhosphineAmido Containing Ligand Manifolds. Coord. Chem. Rev. 2017, 334, 84. (56) Carmichael, C. D.; Shaver, M. P.; Fryzuk, M. D. Synthesis and coordination chemistry of the diamido-arsine ligand [NAsN] (NAsN = PhAs(CH2SiMe2NPh)2. Can. J. Chem. 2006, 84, 1667−1678. (57) Batke, S.; Sietzen, M.; Merz, L.; Wadepohl, H.; Ballmann, J. Closely Related Benzylene-Linked Diamidophosphine Scaffolds and Their Zirconium and Hafnium Complexes: How Small Changes of the Ligand Result in Different Complex Stabilities and Reactivities. Organometallics 2016, 35, 2294−2308. (58) Albrecht, M. Cyclometalation Using d-Block Transition Metals: Fundamental Aspects and Recent Trends. Chem. Rev. 2010, 110, 576− 623. (59) Kreye, M.; Freytag, M.; Jones, P. G.; Williard, P. G.; Bernskoetter, W. H.; Walter, M. D. Homolytic H2 cleavage by a mercury-bridged Ni(I) pincer complex [{(PNP)Ni}2{μ-Hg}]. Chem. Commun. 2015, 51, 2946−2949. (60) Meinholz, M. M.; Pandey, S. K.; Deuerlein, S. M.; Stalke, D. Access to new Janus head ligands: linking sulfur diimides and phosphanes for hemilabile tripodal scorpionates. Dalton Trans. 2011, 40, 1662−1671. (61) Peitz, S.; Peulecke, N.; Aluri, B. R.; Müller, B. H.; Spannenberg, A.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F. M.; Wöhl, A.; Müller, W. Metalation and Transmetalation Studies on Ph2PN(iPr)P(Ph)N(iPr)H for Selective Ethene Trimerization to 1-Hexene. Organometallics 2010, 29, 5263−5268. (62) Olbert, D.; Kalisch, A.; Görls, H.; Ondik, I. M.; Reiher, M.; Westerhausen, M. Syntheses, Crystal Structure and Reactivity of Tin(II) Bis[N-(diphenylphosphanyl)(2-pyridylmethyl)amide]. Z. Anorg. Allg. Chem. 2009, 635, 462−470.

(63) Chomitz, W. A.; Mickenberg, S. F.; Arnold, J. First-Row Transition Metal−Halide Complexes Supported by a Monoanionic [N2P2] Ligand. Inorg. Chem. 2008, 47, 373−380. (64) MacLachlan, E. A.; Fryzuk, M. D. A New Arene-Bridged Diamidophosphine Ligand and Its Coordination Chemistry with Zirconium(IV). Organometallics 2005, 24, 1112−1118. (65) Shaver, M. P.; Thomson, R. K.; Patrick, B. O.; Fryzuk, M. D. Vanadium and niobium diamidophosphine complexes and their reactivity. Can. J. Chem. 2003, 81, 1431−1437. (66) In the 1H NMR spectrum of 1, a significantly broadened singlet was detected for the three methyl groups at room temperature and at −80 °C. In view of the molecular structure and the 13C{1H} NMR spectrum of 1, three different 1H NMR signals are to be expected in theory. However, the crystallographically inequivalent methyls are chemically and structurally very similar, which is reflected by the isochromism of their 1H NMR signals within the relatively narrow spectral width of the 1H NMR experiment (compared to the 13C{1H} NMR experiment). (67) At −40 °C, two signals were detected for methylene (3.91 and 2.74 ppm) and the methyl groups (1.76 and 0.86 ppm) of the η2EtCCEt unit. The two methylene protons of the Me3SiCH2 unit appeared as one singlet at −40 °C, indicating that the molecule’s plane of symmetry renders these protons equivalent. (68) Marlin, D. S.; Olmstead, M. M.; Mascharak, P. K. Structure− Spectroscopy Correlation in Distorted Five-Coordinate Cu(II) Complexes: A Case Study with a Set of Closely Related Copper Complexes of Pyridine-2,6-dicarboxamide Ligands. Inorg. Chem. 2001, 40, 7003−7008. (69) Irradiating (low-pressure mercury vapor lamp) samples of 1 in C6D6 at room temperature for 24 h afforded a mixture of products, as judged by the apperance of four 31P{1H} NMR signals at 59.8, 59.0, 52.7, and 37.7 ppm in a 40:30:15:15 ratio. This ratio was not affected when the sample was irradiated for 7 days. For a photochemically generated dinuclear complex with four bridging methyl units, see: Janes, T.; Xu, M.; Song, D. Synthesis and reactivity of Li and TaMe3 complexes supported by N,N′-bis(2,6-diisopropylphenyl)-o-phenylenediamido ligands. Dalton Trans. 2016, 45, 10672−10680. (70) In the case of 2, a maroon powder was isolated after hydrogenolysis in C6D6 and found to display a weak EPR signal at −196 °C. We assume that this signal arrises from an unidentified byproduct, but this assumption remains to be verified. (71) To verify that Me2NSiMe3 was formed as a byproduct, the reaction was carried out in toluene-d8 and inspected by 1H and 13 C{1 H} NMR spectroscopy. An authentic NMR sample of Me2NSiMe3 in toluene-d8 was used for comparison. (72) A CSD search (version 5.36, including update 3 released in May 2016) revealed that tantalum−phosphorus distances in phosphinestabilized tantalum amides are usually within the range of 2.55−2.78 Å. (73) Manßen, M.; Lauterbach, N.; Dörfler, J.; Schmidtmann, M.; Saak, W.; Doye, S.; Beckhaus, R. Efficient Access to Titanaaziridines by C-H Activation of N-Methylanilines at Ambient Temperature. Angew. Chem., Int. Ed. 2015, 54, 4383−4387. (74) Rankin, M. A.; Cummins, C. C. Terminal phosphinidene formation via tantalaaziridine complexes. Dalton Trans. 2012, 41, 9615−9618. (75) Spencer, L. P.; Beddie, C.; Hall, M. B.; Fryzuk, M. D. Synthesis, Reactivity, and DFT Studies of Tantalum Complexes Incorporating Diamido-N-heterocyclic Carbene Ligands. Facile Endocyclic C−H Bond Activation. J. Am. Chem. Soc. 2006, 128, 12531−12543. (76) Lauzon, J. M. P.; Schafer, L. L. Tantallaaziridines: from synthesis to catalytic applications. Dalton Trans. 2012, 41, 11539−11550. (77) Sietzen, M.; Wadepohl, H.; Ballmann, J. Synthesis and Reactivity of Cyclometalated Triamidophosphine Complexes of Niobium and Tantalum. Inorg. Chem. 2015, 54, 4094−4103. (78) Kü hl, O. Phosphorus-31 NMR Spectroscopy: A Concise Introduction for the Synthetic Organic and Organometallic Chemist; Springer: Berlin, Heidelberg, 2008. 5133


Article

Inorganic Chemistry (79) Ogilvie, F. B.; Jenkins, J. M.; Verkade, J. G. 31P-31P Spin-Spin Coupling in Complexes Containing Two Phosphorus Ligands. J. Am. Chem. Soc. 1970, 92, 1916−1923. (80) Schrock, R. R.; Sharp, P. R. Multiple Metal-Carbon Bonds. 7. Preparation and Characterization of Ta(η5-C5H5)2(CH2)(CH3), a Study of its Decomposition, and Some Simple Reactions. J. Am. Chem. Soc. 1978, 100, 2389−2399. (81) Oshiki, T.; Tanaka, K.; Yamada, J.; Ishiyama, T.; Kataoka, Y.; Mashima, K.; Tani, K.; Takai, K. Preparation, Structural Characterization, and Reactions of Tantalum-Alkyne Complexes TaCl3(R1C CR2)L2 (L2 = DME, Bipy, and TMEDA; L = Py). Organometallics 2003, 22, 464−472.

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Synthesis of NPN-Coordinated Tantalum Alkyl Complexes and Their

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