Zirconium Hydrazides as Metallanitrene Synthons: Release of

Article pubs.acs.org/Organometallics

Zirconium Hydrazides as Metallanitrene Synthons: Release of Molecular N2 from a Hydrazinediido Complex Induced by Oxidative N−N Bond Cleavage Thorsten Gehrmann,† Julio Lloret-Fillol,‡ Heike Herrmann,† Hubert Wadepohl,† and Lutz H. Gade*,† †

Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany Departament de Quimica, QBIS, Universitat de Girona, Campus de Montilivi, 17071 Girona, Spain

‡

S Supporting Information *

ABSTRACT: The N−N bond in the zirconium hydrazinediido(2−) complex [Zr(N2TBSNpy)(NNPh2)(py)] (1) is readily cleaved by one-electron oxidation. Reacting [Zr(N2TBSNpy)(NNPh2)(py)] (1) with 0.5 molar equiv of iodine led to the release of molecular N2 and yielded the mixed diphenylamido/ iodo complex [Zr(N2TBSNpyNPh2)(I)] (2). Exposure of hydrazinediide 1 to an excess of iodine resulted in further oxidation of the diphenylamido ligand, yielding the diiodo complex 3 and tetraphenylhydrazine. Similar reactivity was observed in the reaction of 1 with diphenyl diselenide and diaryl disulfides, which reacted to give the corresponding diphenylamido/arylchalcogenido complexes [Zr(N2TBSNpyNPh2)(SePh)] (4a) and [Zr(N2TBSNpy)(NPh2)(SAr)] (Ar = Ph (4b), C6F5 (4c)) along with N2. The reactions were also carried out on an NMR scale with a 15Nα-labeled hydrazido complex (1-15N). In all cases a single 15N NMR resonance at 310.16 ppm, assigned to 15N2, indicated the formation of dinitrogen from the Nα atom in the hydrazide. A crossover labeling experiment employing a 1:1 mixture of 1 and 15Nα-labeled 1-15N revealed that the isotope distribution is, as expected, statistical 1:2:1 (14N2: 14/15N2: 15N2), which is consistent with a reaction pathway involving a dinuclear intermediate in the dinitrogen-forming step. Complex 1 reacted with N2O to give a mixture of two compounds, the bis(diphenylamido) complex 6 and the doubly bridged μ-oxo complex 7. In contrast, reaction of 1 with 1 molar equiv of pyridinium N-oxide only gave the doubly bridged μ-oxo complex 7 along with 2,2′-bipyridine and diphenylamine.

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oxidatively coupled to form μ-bridging N2 complexes or release molecular nitrogen.10 Formally such an N−N bond reformation step may be coupled to the N−N bond cleavage in a redox chemical transformation of a metal hydrazinediide (in the process the oxidation state of the metal is reduced from n to n − 1):

INTRODUCTION Early-transition-metal hydrazides are thought to be intermediates in the reductive activation of dinitrogen.1 A key aim has been the development of molecular catalysts for Haber−Bosch type chemistry2 as well as the direct activation of N2 for the synthesis of more complex organic products.3 Proof of principle for the former has been provided by Schrock and co-workers a decade ago,4 and the conversion of metal-coordinated hydrazides to organic nitrogen compounds, in particular Nheterocycles, was pioneered by the Leigh and Hidai groups.5 Group 4 metal hydrazides have only been studied systematically during the past decade6 and have been identified as active species inter alia in catalytic hydrohydrazinations of alkynes.7 These transformations have been further incorporated into metal-catalyzed domino reactions such as indole cyclization8 and other multicomponent reactions leading to N-heterocycles.9 Whereas research on dinitrogen activation has obviously focused on the reductive cleavage of the N−N bond, it has been shown that the nitrido ligands, which may be viewed as fragments resulting from such a process of reductive N−N scission, may in turn be oxidatively coupled to regenerate the N2 unit. In this context, several group 8 metal nitrido complexes in high oxidation states have been prepared and © 2013 American Chemical Society

We recently studied the reactivity of the zirconium hydrazinediido complex [Zr(N2TBSNpy)(NNPh2)(py)] (1)11,12 and found that in many of the transformations this hydrazinediide may be viewed formally as a synthon for a metallanitrene which readily undergoes coupling reactions with unsaturated substrates.12 Such metallanitrenes could emerge from the hydrazinediide A via type C bent structures, as observed on Lewis acid adducts of the hydrazinediido complex, leading to a type D species (Chart 1).13 A computational study has shown that such a metallanitrene D would be a high-energy species, and combined experimental and computational mechanistic studies of the observed reaction Received: April 18, 2013 Published: July 8, 2013 3877

dx.doi.org/10.1021/om400337g | Organometallics 2013, 32, 3877−3889

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Chart 1

Chart 2

Scheme 1. Oxidative N−N Bond Cleavage in the Reaction of 1 with Iodine, Phenyl Disulfide, or Diaryl Diselenide To Give the Complexes 2−5

N−N bond scission of a group 4 metal hydrazinediide with an oxidation step might lead to the coupling of two of the metalbonded nitrogen atoms. We therefore investigated the behavior of the previously reported zirconium hydrazinediido complex 1 toward oxidizing agents.

patterns of complex 1 indicate that such species do not play a role as intermediates in these reactions, despite their formal relationship to the observed products (Chart 2).11a,13 Instead, initial coupling of a substrate with ZrN−NR2 (inter alia as formal 2 + 2 cycloaddition) appears to induce cleavage of the N−N bond and migration of the NR2 unit. Nevertheless, the notion of the hydrazinediido ligand as a synthon for a nitrene species remains a useful heuristic concept. Nitrido and nitrene complexes differ in their metal−nitrogen bonding but otherwise are closely related.14 Combination of the

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RESULTS AND DISCUSSION

Reactions of [Zr(N2TBSNpy)(NNPh2)(py)] (1) with I2 and Ar−E−E−Ar (E = S, Se). Reacting [Zr(N2TBSNpy)(NNPh2)3878


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Figure 1. Molecular structures of complexes 2 (a), 4a (b), and 4b (c; only one of the two independent molecules is shown). Hydrogen atoms are omitted for clarity. Selected bond lengths and angles are given in Table 1.

(py)] (1)11a with 0.5 molar equiv of iodine led to the release of molecular N2 (vide infra) and selectively yielded the mixed diphenylamido/iodo complex [Zr(N2TBSNpyNPh2)(I)] (2). Exposure of hydrazinediide 1 to an excess of iodine resulted in further oxidation of the diphenylamido ligand, giving the diiodo complex 3 and tetraphenylhydrazine. Complex 3 is also obtained on reacting 2 with excess I2. Similar reactivity was observed in the reaction of 1 with diphenyl diselenide and diaryl disulfides, which reacted to give the corresponding diphenylamido/arylchalcogenido complexes [Zr(N2TBSNpyNPh2)(SePh)] (4a) and [Zr(N2TBSNpy)(NPh2)(SAr)] (Ar = Ph (4b), C6F5 (4c)) along with N2. However, oxidation of the diphenylamido ligand was not observed, even with a 10-fold excess of diaryl dichalcogenide. Evolution of N2 was observed in the reaction of 1 with 1 molar equiv of silver(I) fluoride, giving the fluorido complex 5 and silver(0) (Scheme 1). Complex 5 was also obtained by electrolysis (10 min, 1 V) of a thf solution of hydrazinediide 1 in presence of 1 equiv of the conducting salt tetrabutylammonium hexafluorophosphate, (n-Bu)4NPF6. The analytical data as well as the 1H, 13C, 15N, and 29Si NMR spectra are consistent with the molecular structures as displayed in Scheme 1. To satisfy the atom and electron count in these reactions, the extrusion of molecular N2 is required and is consistent with the observation of gas evolution during the course of the transformations. To prove the identity of the evolved gas unambiguously and to establish its origin, the reactions described above were carried out on an NMR scale with an 15Nα-labeled hydrazido complex (1-15N). In all cases a single resonance at 310.1 ppm was observed in the 15N NMR spectra, which is assigned to 15N2, indicating clearly the

formation of dinitrogen from the former Nα in the hydrazide (all 15N chemical shifts relative to 15NH3 as reference). A crossover labeling experiment (see the Experimental Section) employing a 1:1 mixture of 1 and 15Nα-labeled 1-15N revealed that the expected statistical isotope distribution (14N2:14/15N2:15N2 = 1:2:1) is consistent with a reaction pathway involving a dinuclear intermediate in the dinitrogenforming step (vide infra). In order to establish the structural details of the complexes 2 and 4a,b, single-crystal X-ray structure analyses were carried out. Their molecular structures are closely related and depicted in Figure 1; a comparative listing of the principal bond lengths and angles is given in Table 1. The coordination geometries in compounds 2 and 4a,b are best described as distorted trigonal bipyramidal with the diphenylamido ligand in an equatorial position and the pyridyl and ER (E = S, Se) groups in axial sites. This is in contrast to, for instance, the related carbodiimido complexes prepared from the hydrazinediido complex 1 and isocyanides represented in Chart 2 (NR′2 axial).11a The halogenido and aryl chalcogenido ligands are bonded in the second axial position, in trans disposition to the pyridyl nitrogen donor atom with bond lengths in the range found in the literature15 (Zr(1)−I(1) = 2.8889(11) Å (2), Zr(I)−Se(I) = 2.629(9) Å (3), Zr(I)−S(I) = 2.5711(11) Å (4b)). Although it was not characterized by X-ray diffraction, we assume that the fluorido complex 5 possesses the same overall structure. In the 19 F NMR spectrum one singlet is observed at δ 95.0, in the typical range for fluorine nuclei bound terminally to a zirconium(IV) center.16 3879


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Table 1. Selected Bond Lengths and Angles of Complexes 2 and 4a,b bond length (Å) or angle (deg)

2

4a

Zr(1)−N(1)

2.034(2)

2.045(4)

Zr(1)−N(3)

2.374(2)

2.385(4)

Zr(1)−N(4)

2.133(1)

2.138(4)

Zr(1)−I(1) Zr(1)−S(1) Zr(1)−Se(1)

2.889(1)

N(3)−Zr−N(4) N(3)−Zr(1)−I(1) N(3)−Zr(1)−S(1) N(3)−Zr(1)−Se(1)

86.59(6) 174.11(4)

4ba 2.034(4), 2.045(4) 2.365(4), 2.370(4) 2.146(4), 2.143(4)

2.571(1)

Zr(1)−S(1)−C(34) Zr(1)−Se(1)−C(34) a

Scheme 2. Initial One-Electron Oxidation of 1 by Iodine and Displacement of Pyridine, Generating the Radical Hydrazide Intermediate II

86.6(1)

2.683(2), 2.686(2) 86.6(2), 86.5(2)

compound II the Zr(1)−N(1) bond is longer (by 0.13 Å) and the N(1)−N(2) bond shorter (by 0.07 Å) than in 1, indicating that the oxidation primarily involves the {Zr−N−N} fragment. Previous NLMO analysis of the electronic structure of the [Zr(N2TBSNpy)(NNPh2)(py)] starting complex characterized the formally dianionic NNPh2 unit as a six-electron-donor ligand, which bonds to the Zr atom via one σ and two π nitrogen highly polarized molecular orbitals, one of the π orbitals of the {Zr(1)−N(1)−N(2)} fragment being the HOMO.13 Removing one electron from the π-conjugated HOMO therefore reduces the Zr(1)−N(1) bond and increases the N(1)−N(2) bond order, which accounts for the structural changes upon one-electron oxidation (Table 2).

174.83(9) 174.3(1), 173.7(1) 113.4(2) 110.1(2), 110.7(2)

Two independent molecules.

The complexity of the redox reactions involving the N2 reformation resulting from multistep reaction sequences precluded a complete computational analysis of a mechanism. However, given the experimental results described above, it is possible to speculate about a potential mechanistic scheme and to test the viability of key reaction steps with the aid of modeling tools. Therefore, the oxidation of zirconium hydrazinediide [Zr(N2TBSNpy)(NNPh2)(py)] (1) leading to the extrusion N2 molecules derived entirely from the Zr-bound Nα atom of the hydrazinediide was partially modeled using the ONIOM hybrid DFT(uB3PW91)/UFF computational tool.17 For this study we selected the reaction of zirconium complex [Zr(N2TBSNpy)(NNPh2)(py)] with I2 as oxidant, since it appeared to involve the least complex sequence of reaction steps and intermediates, while providing general insight into the fragmentation of the NNR2 unit and the observed formation of N2. First, the thermodynamics of the {ZrN−NPh2} fragment oxidation in [Zr(N2TBSNpy)(NNPh2)(py)] by 0.5 I2 to a [Zr(N2TBSNpy)(NNPh2)(I)] (II) radical species was considered and found to be highly exothermic. Previous experimental and theoretical studies had shown that [Zr(N2TBSNpy)(NNPh2)] is energetically accessible by the displacement of the py.8f,g,13 Therefore, coordination of the oxidant (I2) to the vacant coordination site in [Zr(N2TBSNpy)(NNPh2)] should induce an internal redox process. A similar transformation is thought to occur in the reactions with other one-electron oxidants, such as AgF, or by electrochemical oxidation in the presence of an excess of tetrabutylammonium hexafluorophosphate. We note that we have not been able to identify the radical species by EPR spectroscopy, which indicates that it is a rather short-lived species and rapidly converts to the reaction products. Since formal two-electron oxidations led to reaction pathways with unacceptably high activation barriers, only the one-electron oxidation of the hydrazide is considered: for the oxidation by I2 the transformation to [Zr(N2TBSNpy)(NNPh2)(I)] is favored by −26.1 kcal mol−1 (Scheme 2). The electronic structure of [Zr(N2TBSNpy)(NNPh2)] is changed significantly by the oxidation, which is clearly reflected in the altered Zr(1)−N(1) and N(1)−N(2) distances. In

Table 2. Comparison between Selected Distances (in Å) Calculated for Compounds 1 and II

Zr(1)−N(1) N(1)−N(2) Zr(1)−N(3) Zr(1)−N(4)

[Zr(N2TBSNpy)(NNPh2) (py)] (1)

[Zr(N2TBSNpy)(NNPh2) (I)] (II)

1.871 1.373 2.152 2.120

1.998 1.299 2.086 2.062

The spin density distribution on the oxidized compound II depicted in Figure 2 illustrates the way in which the unpaired

Figure 2. (left) Spin density distribution on compound II. (right) Corresponding line drawing of II. The black part represents the QM description, while the gray part represents the MM.

electron of the {Zr(1)−N(1)−N(2)} fragment is primarily located on the two nitrogen atoms N(1) and N(2) (possessing spin densities of 0.5 and 0.33). The generation of molecular N2 from the metal-bonded N(1) atom (as shown by the 15N labeling) requires the interaction of two complex molecules at some stage of the reaction pathway. Since dimerization of two radicals is usually a favored process, we considered the dimerization by coupling the atoms on which the radical is mainly located: namely, at 3880


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Scheme 3. Electronic Energy Profile Calculated for the Oxidation of 1 (I) with 0.5 I2 and the Following Sequence of Steps To Form 2 (V) and 0.5 N2a

a

Energies (in kcal mol−1) are given from full DFT (uB3PW91) and ONIOM (uB3PW91/UFF, in parentheses).

N(1). Such a coupling may produce dimer IV′ via N−N singlebond formation (Scheme 3). However, the energy of this intermediate is 21 kcal mol−1 higher than that of II, probably due to steric repulsion of the two complex fragments. Alternatively, a type C bent structure (Chart 1) could give rise to an intermediate for this transformation but was found not to correspond to an energy minimum. In fact, the oxidation of the {Zr(1)−N(1)−N(2)} fragment stabilizes the π conjugation and thus disfavors a bent hydrazide. In contrast, a structural arrangement as in intermediate III, in which the pyridyl unit of the ancillary tripod ligand is decoordinated, was found to be energetically accessible. Notably, intermediate III is sterically less encumbered than its immediate precursor II and, consequently, the N(1)−N(1) radical dimerization, to form intermediate IV, is now associated with a considerably lower activation barrier (ΔE(TSIII−IV) = −12.6 kcal mol−1) and is therefore realistic. Intermediate IV and the observed final product V (complex 2) are connected through an energetically low lying transition state (ΔE(TSIV−V) = −11.0 kcal mol−1). In the process, two N−N bonds of the NNPh2 ligands and the two Zr(1)−N(1) are broken, two Zr− NPh2 bonds are formed concomitantly, and a NN molecule is subsequently ejected. The nitrogen atoms of the liberated dinitrogen molecule would thus originate from the Nα atoms of the hydrazido unit, in agreement with the results of the 15N -labeling experiments. We note that the dichalcogenide oxidants PhSSPh and PhSeSePh are closely related to I2 in their potential interaction with 1. In both cases, the initial step of the reaction, the oxidation of [Zr(N2TBSNpy)(NNPh2)(py)] with 0.5 Ph−E−E− Ph to [Zr(N2TBSNpy)(NNPh2)(E−Ph)] (E = S, Se) is slightly exothermic (ΔE = −0.4 and −0.6 kcal mol−1, respectively), giving rise to the radical Zr intermediates IISPh and IISePh (Scheme 4). In addition, the dimerization of two [Zr(N 2 TBS N py )(NNPh 2 )(E−Ph)] radicals (E = S, Se) is thermodynamically feasible under the reaction conditions

Scheme 4. Initial One-Electron Oxidation of 1 by the Diphenyl Dichalcogenides (PhE)2 and Displacement of Pyridine, Generating the Radical Hydrazide Intermediates IISPh and IISePh

(endothermic by ΔE = 7.7 and 8.7 kcal mol−1, respectively). We therefore assume a reaction sequence similar to that detailed above for the reaction with I2. Reactions of [Zr(N2TBSNpy)(NNPh2)(py)] (1) with N2O and C5H5N−O. Reactions of the hydrazinediido complex 1 with the oxygen transfer reagents N2O and pyridine N-oxide gave rise to diverse results: Bubbling N2O for 5 min through a solution of 1 in toluene led to a mixture of two compounds, the bis(diphenylamido) complex 6 and the doubly bridged μ-oxo complex 7 (Scheme 5). In contrast, reaction of [Zr(N2TBSNpy)(NNPh2)(py)] (1) with 1 molar equiv of pyridine N-oxide only gave the doubly bridged μ-oxo complex 7 along with 2,2′bipyridine (Scheme 6). The analytical data as well as the 1H, 13C, 15N, and 29Si NMR spectra are consistent with the molecular structures displayed in Schemes 5 and 6. These results appear to be in contrast to the reactivity of complex 1 with the transfer reagents for the heavier chalcogen atoms sulfur and selenium. As previously reported, the reaction of [Zr(N 2 TBS N py )(NNPh2 )(py)] (1) with propylene sulfide and triphenylphosphine selenide led to element−N coupling and transformation of the α-nitrogen atom in the hydrazide to bridging [μ-EN2]2− units.11 The 3881


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Scheme 5. Reaction of 1 with N2O Leading Initially to a Proposed Transient Singly Bridged Oxo Dimer Which in Turn Redistributes to 6 and 7

Scheme 6. Selective Formation of 7 from the Reaction of 1 with Pyridine N-Oxide under Release of 2,2′-Bipyridine

5). A precedent for this reaction in the literature is the dismutation of the ansa-zirconocene [{(Me2Si)cp2ZrCl}2-μ-O] to the corresponding dichloro complex [(Me2Si)cp2ZrCl2] and oxo derivatives, described by Royo et al.19 The formation of the oxo complex 7 as only metal-containing product in the reaction of 1 with pyridine N-oxide is consistent with O-atom transfer to the metal center and one-electron oxidation of both the Nα and the Nβ atoms. Similar to the formation of the diiodo complex 3, one would expect the generation of tetraphenylhydrazine as the second reaction product; however, this was not observed. We therefore isolated and carefully analyzed the organic byproducts by NMR and high-resolution mass spectroscopy. Comparison with authentic samples proved the formation of diphenylamine and 2,2′bipyridine, which is thought to be formed by oxidative coupling of two pyridine moieties. The latter was further substantiated by the same reaction with the equivalent amount of d5pyridinium N-oxide. Analysis of the reaction products showed that diphenylamine and 2,2′-bipyridine exclusively carried the deuterium label and no dissociated pyridine from reactant 1 is involved. Accordingly, the complex [Zr(N2TBSNpy)(NNPh2)(py-d5)] (1-d5), bearing a d5-py-labeled pyridine ligand in the axial position, reacted with nondeuterated pyridine N-oxide,

different reaction patterns represented in Schemes 5 and 6, on the other hand, reflect the pronounced oxophilicity of zirconium. The molecular structures of compounds 6 and 7 were established by single-crystal X-ray diffraction (Figures 3 and 4). The tripodal diamido pyridyl ligand coordinates facially, occupying one axial and two equatorial sites of a distortedtrigonal-bipyramidal structure in both complexes. In complex 6 the two diphenylamido ligands are bonded in the remaining axial and equatorial positions. As expected for a trigonalbipyramidal coordination geometry we find d(Zr−N(5)ax) > d(Zr−N(4)eq). The oxo complex 7 adopts a dimeric structure. The molecular halves are related by a crystallographic center of symmetry, which results in an exactly planar Zr2O2 ring. The N2TBSNpy ligands on each Zr are arranged in a way which puts the plane of the respective pyridyl substituent at a small angle to the Zr2O2 ring (interplanar angle 9.55(8)°). Its structure is closely related to those of other reported μ2-oxo zirconium complexes.18 The formation of the two products 6 and 7 in the reaction of 1 with N2O is thought to proceed via a common intermediate, a singly μ-O-bridged amido/oxo complex. Its redistribution leads to the isolated product complexes (Scheme 3882


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The different nature of the oxidant in comparison with I2, PhSSPh, and PhSeSePh leads to the formation of a diradical species (Figure 5). Two spin states are expected: a singlet diradical by antiferromagnetic coupling of the unpaired electrons and a triplet ground state. All attempts to model the antiferromagnetically coupled diradical were unsuccessful, and only the structure corresponding to the closed-shell S = 0 state was found to correspond to a local energy minimum. As expected, the spin density in the triplet diradical IIOPy is distributed over the pyridine N-oxide as well as the {Zr(1)− N(1)−N(2)} fragment (Figure 6). As for the radical intermediate II in the oxidation with I2, dimerization of IIOPy may lead to IIIOpy (16.7 kcal mol−1) (Scheme 7). The isomer/ conformer of IIIOpy shown in Scheme 7 only corresponds to one of many local minima which are of similar or even lower energy. Complete modeling would require a full conformational analysis, which was found to be unfeasible for a system of this complexity. In the dimeric intermediate IIIOPy shown in Scheme 7 the two pyridine N-oxide units are in close proximity and therefore a radical coupling between the two ortho carbons of the pyridine rings leads to the intermediate IVOPy, in which the 2,2-bipyridine product is preformed. Ejection of N2 and intramolecular abstraction of the hydrogen atoms at the coupled ortho carbon atoms of the pyridine N-oxide dimer, followed by fragmentation and oxygen transfer of the latter, leads to the observed dinuclear Zr2O2 complex 7 as well as 2,2′bipyridine.

Figure 3. Molecular structure of complex 6 (hydrogen atoms are omitted for clarity). Selected bond lengths (Å) and angles (deg): Zr− N(1) = 2.069(2), Zr−N(2) = 2.077(2), Zr−N(3) = 2.413(3), Zr− N(4) = 2.143(2), Zr−N(5) = 2.160(2); N(1)−Zr−N(2) = 101.86(8), N(1)−Zr−N(3) = 80.90(9), N(1)−Zr−N(4) = 128.93(8), N(1)− Zr−N(5) = 97.98(10), N(2)−Zr−N(3) = 81.88(7), N(2)−Zr−N(4) = 122.94(9), N(2)−Zr−N(5) = 105.22(8), N(3)−Zr−N(4) = 82.42(7), N(3)−Zr−N(5) = 172.87(7), N(4)−Zr−N(5) = 92.97(8).

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CONCLUSION In this work, we reported the first examples of the oxidative cleavage of the N−NR 2 unit in a group 4 metal hydrazinediido(2−) complex. The hydrazido(2−) moiety therefore can be regarded as a one-electron reductant leading to radical species in which the unpaired electron resides primarily on the metal-bonded α nitrogen atom. On going beyond the one-electron-oxidation “trigger”, the N−N scission and N2 re-formation may be coupled with other transformations such as the coupling of two pyridine molecules derived from the pyridine N-oxide to a bipyridine unit reported in this work. Unsurprisingly for the oxophilic zirconium, oxidations with oxygen transfer reagents lead to hydrazide fragmentation and the formation of oxo complexes.

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Figure 4. Molecular structure of complex 7 (hydrogen atoms are omitted for clarity). Selected bond lengths (Å) and angles (deg): Zr(1)−N(1) = 2.0975(9), Zr(1)−N(2) = 2.0750(9), Zr(1)−N(3) = 2.3742(8), Zr(1)−O(1) = 2.0615(7), Zr(1)−O(1A) = 1.9490(7); N(1)−Zr(1)−N(2) = 97.43(3), N(1)−Zr(1)−N(3) = 84.92(3), N(2)−Zr−N(3) = 84.08(3), N(1)−Zr(1)−O(1) = 134.64(3), N(2)−Zr−O(1) = 122.14(3), N(3)−Zr(1)−O(1) = 78.70(3), N(1)−Zr−O(1A) = 105.28(3), N(2)−Zr−O(1A) = 114.16(3), N(3)−Zr−O(1A) = 157.03(3), O(1)−Zr−O(1A) = 79.62(3).

EXPERIMENTAL SECTION

All manipulations of air- and moisture-sensitive materials were performed under an inert atmosphere of dry argon using standard Schlenk techniques or by working in a glovebox. Solvents were dried over sodium (toluene), potassium (hexanes, thf), or sodium/ potassium alloy (pentane), distilled, and degassed prior to use. Deuterated solvents were dried over potassium (C6D6, thf-d8, toluened8), vacuum-distilled, and stored in Teflon valve ampules under argon. Samples for NMR spectroscopy were prepared under argon in 5 mm Wilmad tubes equipped with J. Young Teflon valves. 1H, 13C, 19F, 29Si, and 15N NMR spectra were recorded on Bruker Avance 400 and 600 NMR spectrometers and were referenced internally, using the residual solvent (1H) or solvent (13C) resonances, or externally to SiMe4, CFCl3, and 15NH3. Elemental analyses were recorded by the analytical service of the Heidelberg Chemistry Department. The hydrazinediido complex [Zr(N2TBSNpy)(NNPh2)(py)] (1) was prepared as previously reported.11 All other reagents were obtained from commercial sources and used as received unless explicitly stated. Preparation of [Zr(N2TBSNpy)(NPh2)I] (2). To a stirred solution of [Zr(N2TBSNpy)(NNPh2)(py)] (1; 300 mg, 1.08 mmol) in toluene (20 mL) was added a solution of iodine (136 mg, 0.54 mmol) in toluene (5 mL) with a cannula. The reaction mixture was stirred overnight at

giving the nonlabeled bipyridine as only observable coupling product (Scheme 4). Whereas a detailed and exhaustive theoretical modeling of the reaction sequences is unrealistic in view of the complexity of the systems, we suggest that the C−C coupling reaction as well as hydrogen transfer occur as coupled reactions in the coordination sphere of the metal complex. First, DFT modeling (see above) revealed that the formation of the [Zr(N2TBSNpy)(NNPh2)(ON2)] and [Zr(N2TBSNpy)(NNPh2)(OPy)] adducts by reaction of 1 with N2O and pyO is slightly endothermic. 3883


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Figure 5. Differences between closed-shell and open-shell computed structures of [Zr(N2TBSNpy)(NNPh2)] with N2O and pyridine N-oxide, reflected in the respective ground-state structures. H4py, p-HPh), 7.20 (t, 3JmHo/pH = 8.0 Hz, 4 H, m-HPh), 7.37 (d, 3JoHmH = 8.0 Hz, 4 H, o-HPh), 8.87 (d, 3JH6pyH5py = 5.9 Hz, 1 H, H6py). 13 C{1H} NMR (150 MHz, C6D6, 296 K): δ −3.4, −3.2 (Si(CH3)2), 20.7 (Si−C(CH3)3), 27.7 (C−CH3), 28.2 (Si−C(CH3)3), 48.5 (C− CH3), 63.5 (CH2), 121.3 (C3py), 122.0 (C5py), 123.3 (p-CPh), 125.6 (o-CPh), 129.9 (m-CPh), 137.9 (C4py), 148.0 (C6py), 150.3 (N−CPh), 161.2 (C2py). 29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 5.09 (Si(CH3)2tBu). 15N NMR (60 MHz, C6D6, 296 K): δ 217.7 (N− Si(CH3)2tBu), 221.3 (NPh2), 282.1 (L−Npy), IR (Nujol, NaCl): ν 1603 m, 1463 s, 1377 s, 1257 m, 1089 sh, 1018 m, 904 w, 852 s, 847s, 778 m, 742 w, 695 cm−1. Anal. Calcd for C33H51N4ISi2Zr: C, 50.94; H, 6.61; N, 7.20. Found: C, 50.63; H, 6.44; N, 7.54. Crossover Experiment for the Oxidation with I2 of a 1:1 Mixture of 14Nα and 15Nα Hydrazide 1. A crossover experiment was carried out in an NMR tube (ca. 0.5 mL of C6D6) using 20 mg of 15Nαlabeled 1 and an equal amount of the unlabeled compound, to which 0.5 equiv of I2 was added (from a stock solution in C6D6). Reaction conditions were as stated above. Given the established stoichiometry of the oxidation and the exact 1:1 ratio of 14Nα and 15Nα hydrazide, the establishment of the ratio of the isotopologues was straightforward: two 15N NMR signals of equal intensity at δ 310.16 and 310.10 were observed, which are assigned to 15N15N and 15N14N, respectively (the difference being due to the isotope effect on the chemical shift). The 1:1 intensity ratio of the two resonances implies a 1:2 ratio of 15N15N and 15N14N, which evolve, and the stoichiometry between labeled and nonlabeled starting material as well as the clean and complete

Figure 6. Spin density distribution on the compound IIOPy (S = 1). 60 °C. The reaction mixture was filtered, and the volatiles were removed under reduced pressure. The resulting dark gray solid was washed with pentane (3 × 5 mL) before drying in vacuo to yield 618 mg (74%) of 2 as a gray solid. Single crystals for X-ray diffraction were grown from a saturated toluene solution at 10 °C. 1H NMR (600 MHz, C6D6, 296 K): δ 0.03, 0.29 (s, 6 H, Si(CH3)2), 0.72 (3 H, CH3), 0.78 (s, 18 H, Si−6(CH3)3), 3.44 (d, 2JHH = 12.7 Hz, 2 H, CHH), 4.06 (d, 2JHH = 12.6 Hz, 2 H, CHH), 6.32 (t, 3JH5pyH4pyH6py = 6.3 Hz, 1 H, H5py), 6.77 (d, 3JH3pyH4y = 8.0 Hz, 1 H, H3py), 6.90−6.95 (m, 3 H, 3884


Organometallics

Article

Scheme 7. Selected Intermediates in the Proposed Mechanism for the Reaction of 1 with Pyridine N-Oxidea

a

DFT (uB3PW91) and ONIOM energies (uB3PW91/UFF, in parentheses) are given in kcal mol−1. Calcd for C21H41I2N3Si2Zr: C, 34.23; H, 5.61; N, 5.70. Found: C, 34.20; H, 5.78; N, 5.62. Preparation of [Zr(N2TBSNpy)(NPh2)(SePh)] (4a). To a stirred solution of [Zr(N2TBSNpy)(NNPh2)(py)] (1; 300 mg, 0.40 mmol) in toluene (20 mL) was added a solution of diphenyl diselenide (63 mg, 0.20 mmol) in toluene (10 mL) dropwise. The reaction mixture was stirred for 2 days at 50 °C. The reaction mixture was filtered, and the volatiles were removed under reduced pressure. The resulting solid was washed with pentane (2 × 20 mL) before drying in vacuo to yield 230 mg (71%) of 3 as a greenish gray solid. Single crystals for X-ray diffraction were grown from a saturated toluene solution at 10 °C. 1H NMR (600 MHz, C6D6, 296 K): δ 0.04, 0.23 (s, 6H, Si(CH3)2), 0.64 (s, 18H, Si−C(CH3)3), 1.07 (s, 3H, CH3), 3.55 (d, 2JHH = 12.7 Hz, 2H, CHH), 4.16 (d, 2JHH = 12.6 Hz, 2H, CHH), 6.34 (pt, 3JH5pyH4/6py = 6.4 Hz, 1H, H5py), 6.82 (d, 3JH3pyH5py = 8.2 Hz, 1H, H3py), 6.89− 7.04 (sh, 3H, p-HSe‑Ph, p-HPh, H4py), 7.15 (m, 2H, m-HSe‑Ph), 7.21 (t, 3 JmHo/pH = 7.5 Hz, 4H, m-HPh), 7.36 (d, 3JoHmH = 7.9 Hz, 4H, o-HPh), 7.95 (d, 3JoHmH = 7.5 Hz, 2H, o-HSe‑Ph), 8.86 (d, 3JH6pyH5py = 5.1 Hz, 1H, H6py). 13C{1H} NMR (C6D6, 100.55 MHz, 296 K): δ −3.8, −2.4 (Si(CH3)2), 20.2 (Si−C(CH3)3), 24.8 (C−CH3), 28.1 (Si−C(CH3)3), 48.8 (C−CH3), 64.1 (CH2N), 121.2 (C3py), 122.2 (C5py),123.0, 123.9 (p-CSe‑Ph, p-CPh), 124.9(o-CPh), 128.4 (m-CSe‑Ph), 129.8 (m-CPh), 135.8 (o-CSe‑Ph), 138.2 (Se-CSe‑Ph), 139.7 (C4py), 148.1 (C6py), 151.0 (N− CPh), 161.7 (C2py). 29Si{1H} NMR (C6D6, 80 MHz, 296 K): δ 5.52 (Si(CH3)2tBu). 15N NMR (C6D6, 60 MHz, 296 K): δ 209.6 (N− Si(CH3)2tBu), 221.9 (NPh2), 282.1 (L−Npy). 77Se NMR (C6D6, 76 MHz, 296 K): δ 481.8 (SePh). IR (Nujol, NaCl): ν 1583 m, 1465 s,

conversion to the reaction product implies a corresponding ratio of 2:1 for 15N14N and 14N14N. The assignment of the signal for the mixed-labeled species was established by combustion of the commercially available monolabeled azide N3−, which gives rise to a mixture of 14N14N and 15N14N, only the latter of which is observed by 15N NMR. Preparation of [Zr(N2TBSNpy)I2] (3). To a stirred solution of [Zr(N2TBSNpy)(NNPh2)(py)] (1; 300 mg, 0.40 mmol) in toluene (10 mL) was added a solution of iodine (130 mg, 0.50 mmol) in toluene (5 mL) with a cannula. The reaction mixture was stirred overnight at 60 °C. The reaction mixture was filtered, and the volatiles were removed under reduced pressure. The resulting red solid was washed with pentane (3 × 5 mL) before drying in vacuo to yield 618 mg (74%) of 6 as a pale yellow powder. 1H NMR (600 MHz, C6D6, 296 K): δ 0.26, 0.58 (s, 6 H, Si(CH3)2), 0.72 (3 H, CH3), 0.82 (s, 18 H, Si−6(CH3)3), 3.17 (d, 2JHH = 12.6 Hz, 2 H, CHH), 3.88 (d, 2JHH = 12.6 Hz, 2 H, CHH), 6.42 (t, 3JH5pyH4pyH6py = 6.4 Hz,v1 H, H5py), 6.67 (d, 3JH3pyH4y = 8.0 Hz, 1 H, H3py), 6.91 (t, 3JH4pyH5pyH3py = 7.7 Hz, 4 H, H4py), 9.80 (d, 3JH6pyH5py = 5.5 Hz, 1 H, H6py). 13C{1H} NMR (150 MHz, C6D6, 296 K): δ −3.7, −3.1 (Si(CH3)2), 20.7 (Si−C(CH3)3), 24.0 (C−CH3), 27.7 (Si−C(CH3)3), 49.3 (C−CH3), 63.1 (CH2), 121.1 (C3py), 122.2 (C5py), 139.4 (C4py), 149.9 (C6py), 159.5 (C2py). 29 Si{1H} NMR (80 MHz, C6D6, 296 K): δ 4.52 (Si(CH3)2tBu). 15N NMR (60 MHz, C6D6, 296 K): δ 247.4 (N-Si(CH3)2tBu), 280.1 (L− Npy). IR (Nujol, NaCl): ν 2727w, 1463 s, 1377 s, 1299 w, 1261 m, 1164 m, 1089 w, 1040 m, 908 w, 843 s, 770 w, 722 s 674 cm−1. Anal. 3885


Organometallics

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JH5pyH4pyH6py = 7.0 Hz, 1 H, H5py), 6.84 (d, 3JH3pyH4y = 8.0 Hz, 1 H, H3py), 6.93 (t, 3Jp‑pho‑Hph = Hz, 2 H, p-HPh) 7.09 (t, 3JH4pyH3pyH5py = 8.0 Hz, 1 H, H4py), 7.34 (t, 3JmHo/pH = 7.7 Hz, 4 H, m-HPh), 7.59 (bs, 4 H, o-HPh), 9.08 (d, 3JH6pyH5py = 3.0 Hz, 1 H, H6py). 13C{1H} NMR (150 MHz, C6D6, 296 K): δ −5.8, −5.2 (Si(CH3)2), 19.8 (Si−C(CH3)3), 23.4 (C−CH3), 27.2 (Si−C(CH3)3), 49.0 (C−CH3), 63.4 (CH2), 120.6 (C3py), 121.0 (p-CPh), 121.9 (C5py), 123.8 (o-CPh), 129.2 (mCPh), 138.8 (C4py), 145.4 (2JN−F = 12.6 Hz, C6py), 155.4 (N−CPh), 160.7 (C2py). 29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 0.93 (Si(CH3)2tBu). 15N NMR (60 MHz, C6D6, 296 K): δ 185.7 (N-− i(CH3)2tBu), 193.3 (NPh2), 290.2 (L−Npy). IR (Nujol, NaCl): ν 2361 m, 1602 w, 1492 m, 1464 s, 1377 w, 1260 s, 1089 ssh, 1029 s, 853 s, 820 m, 800 s, 728 s, 694 cm−1. Anal. Calcd for C33H51N4FSi2Zr: C, 59.14; H, 7.67; N, 8.36. Found: C, 58.87; H, 7.57; N, 8.15. Alternative Preparation of [Zr(N2TBSNpy)(NPh2)F] (5) by Electrolysis. In the glovebox 100 mg (0.14 mmol) of [Zr(N2TBSNpy)(NNPh2)(py)] (1) was dissolved in 2 mL of thf-d8 which contained 0.14 mmol of tetrabutylammonium hexafluorophosphate. The solution was placed in a 10 mL round-bottom flask which was equipped with a septum and two platinum electrodes. The reaction mixture was subjected to electrolysis for 10 min at 1 V. After 10 min 0.5 mL of the reaction mixture was removed by syringe and NMR spectra were recorded. The formation of 5 was confirmed by its identical 1H NMR signals in comparison to those of the compound prepared from 1 and AgF. Preparation of [Zr(N2TBSNpy)(NPh2)2] (6). N2O was bubbled for 5 min through a solution of [Zr(N2TBSNpy)(NNPh2)(py)] (1; 400 mg, 0.54 mmol) in toluene (20 mL). The reaction mixture turned orange and was stirred for 2 h at room temperature. Then it was cooled and filtered, and the volatiles were removed under reduced pressure. The resulting pale yellow solid was washed with pentane (3 × 5 mL) before drying in vacuo to yield 204 mg (46%) of 7 as a colorless solid. Single crystals for X-ray diffraction were grown from a saturated toluene solution at room temperature. 1H NMR (600 MHz, C6D6, 296 K): δ −0.10, 0.19 (s, 6 H, Si(CH3)2), 0.71 (s, 18 H, Si−6(CH3)3), 1.13 (3 H, CH3), 3.56 (d, 2JHH = 12.4 Hz, 2 H, CHH), 4.03 (d, 2JHH = 12.4 Hz, 2 H, CHH), 6.28 (t, 3JH5pyH4pyH6py = 6.6 Hz, 1 H, H5py), 6.66 (d, 3Jo‑Hm‑H = 8.0 Hz, 1 H, o-HPh‑A), 6.84−6.90 (m, 3 H, p-HPh‑A, H3py), 6.92 (d, 3 JpH/mH = 7.3 Hz p-HPh), 6.96 (dt, 3JH4pyH5pyH3py = 7.7 Hz, dt, 4JH4pyH6 = 1.8 Hz, 1 H, H4py), 7.16−7.34 (bm, 14 H, m-HPh‑A, o-HPh‑B, m-HPh‑B, p-HPh‑B), 9.03 (dd, 3JH6pyH5py = 5.6 Hz, 4JH6pyH4py = 1.6 Hz, 1H, H6py). 13 C{1H} NMR (150 MHz, C6D6, 296 K): δ −4.08, −2.7 (Si(CH3)2), 20.0 (Si−C(CH3)3), 25.0(C−CH3), 28.6 (Si−C(CH3)3), 48.8 (C− CH3), 64.2 (CH2), 120.7 (C3py), 121.9 (C5py), 122.3 (p-CPh‑A, pCPh‑A), 123.2(o-CPh‑A), 128.9, 129.4 (o-CPh‑B, m-CPh‑B), 129.9 (m-CPh), 139.3 (C4py), 149.2 (C6py), 151.1 (N−CPh‑A), 162.5 (C2py), n.o. (N− CPh‑B). 29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 5.28 (Si(CH3)2tBu). 15 N NMR (60 MHz, C6D6, 296 K): δ 191.6 (N−Si(CH3)2tBu), 200.9 (NPh2-A), 212.3 (NPh2-B), 284.8 (L−Npy). IR (Nujol, NaCl): ν 1594 m, 1482 ssh, 1464 s, 1377 s, 1261 s, 1188 w, 1024 m, 908 w, 850 s, 798 m, 752 w, 697 cm−1. Anal. Calcd for C45H61N5Si2Zr: C, 65.96; H, 7.50; N, 8.55. Found: C, 65.90; H, 7.50; N, 8.55. Preparation of [Zr(N2TBSNpy)(μ-O)]2 (7). To a stirred solution of [Zr(N2TBSNpy)(NNPh2)(py)] (1; 300 mg, 0.40 mmol) in toluene (20 mL) was added pyridine N-oxide (39 mg, 0.40 mmol). The reaction mixture was stirred overnight at at room temperature. The reaction mixture was filtered, and the volatiles were removed under reduced pressure. The resulting brown solid was washed with pentane (3 × 5 mL) before drying in vacuo to yield 96 mg (24%) of 8 as a colorless solid. Single crystals for X-ray diffraction were grown from a saturated toluene solution at room temperature. 1H NMR (600 MHz, C6D6, 296 K): δ 0.28, 0.50 (s, 6 H, Si(CH3)2), 1.14 (s, 18 H, Si−6(CH3)3), 1.15 (3 H, CH3), 3.47 (d, 2JHH = 12.4 Hz, 2 H, CHH), 3.93 (d, 2JHH = 12.6 Hz, 2 H, CHH), 6.09 (t, 3JH5pyH4pyH6py = 6.7 Hz, 1 H, H5py), 7.01 (d, 3 JH3pyH4y = 8.0 Hz, 1 H, H3py), 7.09 (d, 3JH4pyH3/H5py = 7.6 Hz, 1 H, H4py), 9.80 (dd, 3JH6pyH5py = 5.1 Hz, 1 H, H6py). 13C{1H} NMR (150 MHz, C6D6, 296 K): δ −3.5, −1.4 (Si(CH3)2), 20.5 (Si−C(CH3)3), 25.2(C−CH3), 28.3 (Si−C(CH3)3), 50.5 (C−CH3), 61.8 (CH2), 119.1 (C3py), 120.9 (C5py), 139.4 (C4py), 148.0 (C6py), 163.6 (C2py).

1377 m, 1292 w, 1248 m, 1187 m, 1137 w, 1087 w, 1019m, 904 m, 862 m, 847 m, 778 m, 730 w, 694 w, 665 w. Anal. Calcd for C39H56N4SeSi2Zr: C, 58.03; H, 6.99; N, 6.94. Found: C, 57.88; H, 6.99; N, 7.08. Preparation of [Zr(N2TBSNpy)(NPh2)(SPh)] (4b). To a stirred solution of [Zr(N2TBSNpy)(NNPh2)(py)] (1; 500 mg, 0.68 mmol) in toluene (20 mL) was added a solution of diphenyl disulfide (73 mg, 34 mmol) in toluene (5 mL) dropwise. The reaction mixture was stirred overnight at 80 °C. The reaction mixture was filtered, and the volatiles were removed under reduced pressure. The resulting pale yellow solid was washed with pentane (3 × 5 mL) before drying in vacuo to yield 320 mg (62%) of 4a as a colorless solid. Single crystals for X-ray diffraction were grown from a saturated toluene solution at 10 °C. 1H NMR (600 MHz, C6D6, 296 K): δ 0.04, 0.20 (s, 6 H, Si(CH3)2), 0.64 (s, 18 H, Si−6(CH3)3), 1.07 (3 H, CH3), 3.55 (d, 2JHH = 12.6 Hz, 2 H, CHH), 4.15 (d, 2JHH = 12.6 Hz, 2 H, CHH), 6.35 (dt, 3JH5pyH4pyH6py = 6.5 Hz, 4JH5H3 = 1.0 Hz,1 H, H5py), 6.82 (d, 3JH3pyH4y = 8.1 Hz, 1 H, H3py), 6.92 (d, 3JpH/mH = 7.3 Hz p-HPh), 6.95−7.01 (m, 2H, H4py, pHPhS), 7.20 (t, 3JmHo/pH = 7.7 Hz, 2H, m-HPhS), 7.23 (t, 3JmHo/pH = 8.0 Hz, 4 H, m-HPh), 7.39 (dd, 3JoHmH = 8.0 Hz, 4JoHpH = 1.0 Hz, 4 H, oHPh), 7.79 (d, 3JoHmH = 8.7 Hz, 2H, o-HPhS), 8.92 (dd, 3JH6pyH5py = 5.5 Hz, 4JH6pyH4py = 1.0 Hz, 1H, H6py). 13C{1H} NMR (150 MHz, C6D6, 296 K): δ −3.8, −2.8 (Si(CH3)2), 20.2 (Si−C(CH3)3), 24.8(C−CH3), 28.1 (Si−C(CH3)3), 48.3 (C−CH3), 64.0 (CH2), 121.1 (C3py), 122.2 (C5py), 123.0 (p-CPh), 123.3 (p-CS‑Ph), 124.9 (o-CPh), 128.3 (m-CS‑Ph), 129.8 (m-CPh), 133.3 (o-CS‑Ph), 139.8 (C4py), 145.7 (S-CS‑Ph), 148.3 (C6py), 151.1 (N−CPh), 161.8 (C2py). 29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 5.60 (Si(CH3)2tBu). 15N NMR (60 MHz, C6D6, 296 K): δ 206.3 (N−Si(CH3)2tBu), 219.3 (NPh2), 282.7 (L−Npy). IR (Nujol, NaCl): ν 1584 m, 1482 s, 1464 s, 1377 w, 1252 s, 1192 w, 1021 s, 904 w, 852 s, 847 s, 778 m, 742 w, 695 cm−1. Anal. Calcd for C39H56N4SSi2Zr: C, 61.61; H, 7.42; N, 7.37. Found: C, 61.63; H, 7.55; N, 7.43. Preparation of [Zr(N2TBSNpy)(NPh2)(SC6F5)] (4c). To a stirred solution of [Zr(N2TBSNpy)(NNPh2)(py)] (1; 300 mg, 0.40 mmol) in toluene (10 mL) was added a solution of bis(pentafluorophenyl) disulfide (80 mg, 0.20 mmol) in toluene (3 mL) dropwise. The reaction mixture was stirred overnight at 80 °C. The reaction mixture was filtered, and the volatiles were removed under reduced pressure. The resulting brown solid was washed with pentane (3 × 5 mL) before drying in vacuo to yield 270 mg (80%) of 4b as a light brown solid. 1H NMR (600 MHz, C6D6, 296 K): δ −0.04, 0.00 (s, 6 H, Si(CH3)2), 0.62 (s, 18 H, Si−6(CH3)3), 0.98 (3 H, CH3), 3.23 (d, 2JHH = 12.5 Hz, 2 H, CHH), 4.18 (d, 2JHH = 12.5 Hz, 2 H, CHH), 6.33 (t, 3 JH5pyH4pyH6py = 6.5 Hz, 1 H, H5py), 6.79 (d, 3JH3pyH4y = 8.2 Hz, 1 H, H3py), 6.92 (d, 3JpH/mH = 7.0 Hz p-HPh), 6.97 (t, 3JH4pyH3pyH5py,1H, H4py), 7.20 (t, 3JmHo/pH = 7.7 Hz, 4 H, m-HPh), 7.34 (d, 3JoHmH = 7.9 Hz, 4 H, o-HPh), 8.84 (d, 3JH6pyH5py = 5.1 Hz, 1H, H6py). 13C{1H} NMR (150 MHz, C6D6, 296 K): δ −4.2, −3.4 (Si(CH3)2), 20.2 (Si− C(CH3)3), 24.7 (C−CH3), 27.5 (Si−C(CH3)3), 48.3 (C−CH3), 63.6 (CH2), 121.3 (C3py), 122.2 (C5py), 123.4 (p-CPh), 125.2 (o-CPh), 129.8 (m-CPh), 139.9 (C4py), 148.1 (C6py), 150.6 (N−CPh), 161.4 (C2py). 29 Si{1H} NMR (80 MHz, C6D6, 296 K): δ 4.97 (Si(CH3)2tBu). 19F NMR (380 MHz, C6D6, 296 K): −165.4 (t, 3J = 22 Hz, 2 F, m-F), −164.5 (t, 3J = 22 Hz, 1 F, p-F), −133.6 (d, 3J = 22 Hz, 2 F, o-F). 15N NMR (60 MHz, C6D6, 296 K): δ 214.8 (N−Si(CH3)2tBu), 221.4 (NPh2), 282.1 (L−Npy). IR (Nujol, NaCl): ν 1594 w, 1502 m, 1664 s, 1377 s, 1553 m, 1084 w, 1019 w, 972 w, 858 m, 764 w, 742 w cm−1. Anal. Calcd for C39H51F5N4SSi2Zr: C, 55.09; H, 6.05; N, 6.59. Found: C, 55.00; H, 6.25; N, 6.82. Preparation of [Zr(N2TBSNpy)(NPh2)F] (5). To a stirred solution of [Zr(N2TBSNpy)(NNPh2)(py)] (1; 200 mg, 0.27 mmol) in toluene (20 mL) was added solid silver(I) fluoride (34 mg, 0.27 mmol). The reaction mixture was stirred overnight at 60 °C. The reaction mixture was filtered, and the volatiles were removed under reduced pressure. The resulting dark gray solid was washed with hexane (3 × 5 mL) before drying in vacuo to yield 120 mg (73%) of 5 as a brown solid. 1H NMR (600 MHz, C6D6, 296 K): δ −0.23, 0.06 (s, 6 H, Si(CH3)2), 0.67 (s, 18 H, Si−6(CH3)3), 1.02 (3 H, CH3), 3.28 (d, 2JHH = 12.4 Hz, 2 H, CHH), 4.05 (d, 2JHH = 12.4 Hz, 2 H, CHH), 6.52 (t, 3886


Organometallics

Article

Si{1H} NMR (80 MHz, C6D6, 296 K): δ 1.09 (Si(CH3)2tBu). 15N NMR (60 MHz, C6D6, 296 K): δ 149.5 (N−Si(CH3)2tBu), 283.2 (L− Npy). IR (Nujol, NaCl): ν 1594 s, 1495 s, 1458 s, 1377 m, 1311 m, 1090 w, 1040 w, 908 w, 876 w, 753 m, 746 m, 691 w cm−1. Anal. Calcd for C42H82N6O2Si4Zr2: C, 50.25; H, 8.28; N, 8.42. Found: C, 49.84; H, 8.20; N, 8.04. Computational Studies. A two-shell ONIOM Hybrid QM/MM computational tool17 of the GAUSSIAN09 package20 was employed to model all the systems. For all calculations the spin-unrestricted formalism was applied. For the inner shell (QM), the uB3PW9121 hybrid functional with 6-31g(d) basis set for C, N, H, S, and O22 and SDD+f function effective core potential basis set23 for Zr, Se, and I24 were employed, while (MM) UFF force field calculations were applied to the outer shell.25 The quantum mechanically (QM) and the force field (MM) modeled sectors of the molecule in the ONIOM calculations are defined in Figure 7. Stationary points were verified 29

basis set used for the optimization. Additionally, dispersion effects, neglected in uB3PW91, were thought to give significant contributions and therefore have been taken into account by the simple DFT-D2 correction developed by Grimme.26 X-ray Crystal Structure Determinations. Crystal data and details of the structure determinations are given in Table 3. Full shells of intensity data were collected at low temperature (100 K) with a Bruker AXS Smart 1000 CCD diffractometer (Mo Kα radiation, sealed tube, graphite monochromator). Data were corrected for air and detector absorption, Lorentz, and polarization effects;27 absorption by the crystal was treated by a numeric method28 or with a semiempirical multiscan method.28,29 The structures were solved by the heavy-atom method combined with structure expansion by direct methods applied to difference structure factors30 (complexes 4a,b and 7), by direct methods with dual-space recycling31 (complex 2), or by the charge-flip procedure32 (complex 6) and refined by full-matrix least-squares methods based on F2 against all unique reflections.33 All non-hydrogen atoms were given anisotropic displacement parameters. Hydrogen atoms were placed at calculated positions and refined with a riding model. Crystals of 4a were twinned; after detwinning (approximately twin fractions 0.53:0.47) refinement was carried out against all observations involving both domains.28b

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ASSOCIATED CONTENT

* Supporting Information

Figure 7. Black part representing the QM description and the gray part representing the MM.

S

Tables giving Cartesian coordinates for the calculated structures and CIF files giving crystallographic data for compounds 2, 4a,b, 6, and 7. This material is available free of charge via the Internet at http://pubs.acs.org.

by frequency analyses. Energies were refined by single-point calculations with the full DFT(uB3PW91) model with the same

Table 3. Details of the Crystal Structure Determinations of 2, 4a,b, 6, and 7

formula Mr cryst syst space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z F000 dc/Mg m−3 μ/mm−1 max, min transmission factors θ range/deg index ranges (indep set) h,k,l no. of measd rflns no. of unique rflns (Rint) no. of obsd rflns (I ≥ 2σ(I)) no. of params refined GOF on F2 R indices (F > 4σ(F)): R(F), Rw(F2) R indices (all data): R(F), Rw(F2) absolute structure param largest residual peaks/e Å−3

2

4a

C33H51IN4Si2Zr 778.08 triclinic P1̅ 9.783(5) 10.379(5) 19.010(9) 91.185(8) 99.16(1) 102.47(1) 1858(2) 2 796 1.391 1.218 0.9823, 0.6824 2.0−32.2 −14 to +13, −1 to +15, 0−27 45971 12121 (0.0353) 10379 381 1.042 0.0287, 0.0673

C39H56N4SSi2Zr 760.34 triclinic P1̅ 9.582(5) 10.413(5) 20.309(10) 86.117(6) 87.819(6) 77.450(13) 1973(2) 2 804 1.280 0.424 0.7457, 0.6156 2.0−28.5 −1 to +12, −13 to +13, 0−27 58995 17175 (0.0864) 13483 436 1.091 0.0562, 0.1412

4b

7926(8) 8 3360 1.353 1.288 0.7454, 0.6104 2.0−25.7 −24 to 0, 0−11, −49 to +49 134015 15051 (0.1112) 12547 869 1.040 0.0424, 0.0773

4330(6) 4 1736 1.257 0.346 1.0000, 0.8769 1.1−28.3 −25 to +24, 0−15, 0−27 71257 10741 (0.0984) 7745 489 1.005 0.0440, 0.0786

C21H41N3OSi2Zr 498.97 triclinic P1̅ 10.4274(7) 10.7564(7) 13.5613(9) 66.651(1) 82.552(1) 68.117(1) 1295.6(2) 2 528 1.279 0.532 0.7464, 0.6618 2.1−32.2 −14 to +15, −14 to +16, 0−20 27185 8477 (0.0266) 7910 264 1.030 0.0220, 0.0595

0.0378, 0.0713

0.0795, 0.1580

0.0596, 0.0829

0.0787, 0.0891

0.0241, 0.0606

1.473, −0.752

0.798, −0.759

0.072(7) 0.620, −0.504

0.474, −0.870

0.756, −0.414

3887

6

C39H56N4SeSi2Zr 807.24 orthorhombic Pca21 20.184(12) 9.634(6) 40.76(2)

C45H61N5Si2Zr 819.39 monoclinic P21/c 19.48(2) 11.45(1) 20.76(2) 110.73(2)

7


Organometallics

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Article

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AUTHOR INFORMATION

Corresponding Author

*L.H.G.: fax, (+49) 6221-545609; e-mail, [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the University of Heidelberg and the Deutsche Forschungsgemeinschaft for funding (SFB 623, TP A7). REFERENCES

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Zirconium Hydrazides as Metallanitrene Synthons: Release of

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