Bonding analysis of transition metal NNR end-on complexes and comparison with isoelectronic NNR2 species

Kahlal, Samia; Saillard, Jean‐Yves; Hamon, Jean‐René; Manzur, Carolina; Carrillo, David

doi:10.1039/b005916l

Cited by 27 publications

(12 citation statements)

References 76 publications

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“…Figure a shows schematically the four highest occupied MOs of a planar, dianionic [NNR 2 ] 2− ligand based on previous EHMO and DFT calculations. ,,, The 1a 1 MO is suitable for M−N α σ bonding, and the 1b 2 MO is N α −N β π bonding and would not be expected to interact to any significant extent with a metal center. , The 1b 1 MO (which we abbreviate as π h ) is essentially N α −N β nonbonding and would form one of the M−N α π bonds. The 2b 2 MO (abbreviated π v ) is the HOMO of [NNR 2 ] 2− and lies significantly higher in energy (≥1 eV , ) than the 1b 1 MO because of its N α −N β π*-antibonding nature.…”

Section: Resultsmentioning

confidence: 99%

Titanium Hydrazides Supported by Diamide-Amine and Related Ligands: A Combined Experimental and DFT Study

et al. 2008

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This paper reports a general method for the synthesis of new terminal titanium diphenyl hydrazido(2−) complexes containing dianionic N3- and N4-donor ligands, along with new hydrazido synthons. Reaction of Ti(NtBu)Cl2(py)3 or Ti(NtBu)Cl2(py′)3 (py′ = 4-NC5H4 tBu) with Ph2NNH2 gave excellent yields of the corresponding monomeric hydrazides Ti(NNPh2)Cl2(L)3 (L = py (7) or py′), which have been structurally characterized. Application of a dynamic vacuum to 7 formed [Ti(NNPh2)Cl2(py)2]2 (4). Both 4 and 7 are entry points to new titanium hydradizo complexes on reaction with metalated reagents. In this way, four new five-coordinate diamide-amine complexes Ti(NNPh2)(“N2N”)(py) were made (“N2N” = MeN(CH2CH2NSiMe3)2, Me3SiN(CH2CH2NSiMe3)2, MeN(CH2CH2CH2NSiMe3)2, (2-NC5H4)C(Me)(CH2NSiMe3)2) and structurally characterized. Five- and six-coordinate terminal titanium hydrazides containing dianionic N4- or O2N2-donor ligands were also synthesized from 4 by an analogous method. The identity of the “N2N” ligand affects the TiNα and Nα−Nβ distances of the TiN−NPh2 functional group. A detailed DFT analysis of the bonding in these and a range of model complexes is presented using molecular orbital and natural bond orbital methods. The competition between N(amide) and N(hydrazide) Ti(3dπ)−N(2pπ) interactions has an indirect and significant effect on the Nα−Nβ bond.

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Section: Resultsmentioning

confidence: 99%

Titanium Hydrazides Supported by Diamide-Amine and Related Ligands: A Combined Experimental and DFT Study

et al. 2008

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“…Density Functional Theory Analysis of Ti(NNPh 2 )Cl 2 {HC(pz) 3 } (I) and a Comparison with Imido Compounds Ti(NMe)Cl 2 {HC(pz) 3 } (II) and Ti(NPh)Cl 2 {HC(pz) 3 } (III). Computational studies of the bonding in transition metal hydrazido complexes are rare in comparison to those of the related imido systems. , Previous computational studies of metal−hydrazido(2−) bonding were based on extended Hückel calculations for hypothetical mono- and bis-hydrazido complexes, along with some ab initio calculations exploring the structure of [Li(NNH 2 )] q ( q = +1, 0, or −1). In particular, these studies examined the bonding of the terminal hydrazido ligand in the model compound [MoH 5 (NNH 2 )] 3- and compared the bonding between NNR end-on complexes with η 1 -bound NNR 2 species.…”

Section: Resultsmentioning

confidence: 99%

Synthesis, Structures, and DFT Bonding Analysis of New Titanium Hydrazido(2−) Complexes

et al. 2005

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The reaction of 1,1-diphenylhydrazine with Ti(NMe2)2Cl2 produced the monomeric terminal titanium hydrazido(2-) species Ti(NNPh2)Cl2(HNMe2)2 (1) in near-quantitative yield. The reaction of Ti(NMe2)2Cl2 with the less sterically demanding ligand precursors 1,1-dimethylhydrazine or N-aminopiperidine gave the dimeric mu-eta2,eta1-bridged compounds Ti2(mu-eta2,eta1-NNMe2)2Cl4(HNMe2)2 (2) and Ti2[mu-eta2,eta1-NN(CH2)5]2Cl4(HNMe2)3 (3). The X-ray structures of 2 and 3 showed the formation of N-H...Cl hydrogen bonded dimers or chains, respectively. The reaction of 1 with an excess of pyridine formed [Ti(NNPh2)Cl2(py)2]n (4, n = 1 or 2). The reaction of the tert-butyl imido complex Ti(N(t)Bu)Cl2(py)3 with either 1,1-dimethylhydrazine or N-aminopiperidine again resulted in the formation of hydrazido-bridged dimeric complexes, namely Ti2(mu-eta2,eta1-NNMe2)2Cl4(py)2 (5, structurally characterized) and Ti2[mu-eta2,eta1-NN(CH2)5]2Cl4(py)2 (6). Compounds 1 and 4 are potential new entry points into terminal hydrazido(2-) chemistry of titanium. Compound 1 reacted with neutral fac-N3 donor ligands to form Ti(NNPh2)Cl2(Me3[9]aneN3) (7), Ti(NNPh2)Cl2(Me3[6]aneN3) (8), Ti(NNPh2)Cl2[HC(Me2pz)3] (9, structurally characterized), and Ti(NNPh2)Cl2[HC(n)Bupz)3] (10) in good yields (Me3[9]aneN3 = trimethyl-1,4,7-triazacyclononane, Me3[6]aneN3 = trimethyl-1,3,5-triazacyclohexane, HC(Me2pz)3 = tris(3,5-dimethylpyrazolyl)methane, and HC((n)Bupz)3 = tris(4-(n)butylpyrazolyl)methane). DFT calculations were performed on both the model terminal hydrazido compound Ti(NNPh2)Cl2[HC(pz)3] (I) and the corresponding imido compounds Ti(NMe)Cl2[HC(pz)3] (II) and Ti(NPh)Cl2[HC(pz)3] (III). The NNPh2 ligand binds to the metal center in an analogous manner to that of terminal imido ligands (metalligand triple bond), but with one of the Ti=N(alpha) pi components significantly destabilized by a pi interaction with the lone pair of the N(beta) atom. The NR ligand sigma donor ability was found to be NMe > NPh > NNPh2, whereas the overall (sigma + pi) donor ability is NMe > NNPh2 > NPh, as judged by fragment orbital populations, Ti-N atom-atom overlap populations, and fragment-charge analysis. DFT calculations on the hydrazido ligand in a mu-eta2,eta1-bridging mode showed involvement of the N=N pi electrons in donation to one of the Ti centers. This TiN2 interaction is best represented as a metallocycle.

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“…Given this behavior, we were curious whether the electronic structures of [(P 3 E )Fe(NNR 2 )] n complexes might feature a significant weight of the intermediate, open-shell hydrazyl radical anion configuration ([NNR 2 ] •– ) of this redox-active ligand. Although this redox state has not, to our knowledge, been explored experimentally, such a proposal is reasonable given the low-energy π* orbital of both parent and N , N -dialkylisodiazenes, which thus bear a resemblance to the classically redox-noninnocent nitrosyl ligand (NO) . Indeed, both neutral and cationic hydrazyl radicals ([HNNR 2 ] • /[H 2 NNR 2 ] •+ ; R = H, alkyl) have been characterized in their free forms .…”

Section: Introductionmentioning

confidence: 93%

Electronic Structures of an [Fe(NNR₂)]^+/0/– Redox Series: Ligand Noninnocence and Implications for Catalytic Nitrogen Fixation

et al. 2019

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The intermediacy of metal–NNH2 complexes has been implicated in the catalytic cycles of several examples of transition-metal-mediated nitrogen (N2) fixation. In this context, we have shown that triphosphine-supported Fe(N2) complexes can be reduced and protonated at the distal N atom to yield Fe(NNH2) complexes over an array of charge and oxidation states. Upon exposure to further H+/e– equivalents, these species either continue down a distal-type Chatt pathway to yield a terminal iron(IV) nitride or instead follow a distal-to-alternating pathway resulting in N–H bond formation at the proximal N atom. To understand the origin of this divergent selectivity, herein we synthesize and elucidate the electronic structures of a redox series of Fe(NNMe2) complexes, which serve as spectroscopic models for their reactive protonated congeners. Using a combination of spectroscopies, in concert with density functional theory and correlated ab initio calculations, we evidence one-electron redox noninnocence of the “NNMe2” moiety. Specifically, although two closed-shell configurations of the “NNR2” ligand have been commonly considered in the literatureisodiazene and hydrazido(2−)we provide evidence suggesting that, in their reduced forms, the present iron complexes are best viewed in terms of an open-shell [NNR2]•– ligand coupled antiferromagnetically to the Fe center. This one-electron redox noninnocence resembles that of the classically noninnocent ligand NO and may have mechanistic implications for selectivity in N2 fixation activity.

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Bonding analysis of transition metal NNR end-on complexes and comparison with isoelectronic NNR2 species

Cited by 27 publications

References 76 publications

Titanium Hydrazides Supported by Diamide-Amine and Related Ligands: A Combined Experimental and DFT Study

Titanium Hydrazides Supported by Diamide-Amine and Related Ligands: A Combined Experimental and DFT Study

Synthesis, Structures, and DFT Bonding Analysis of New Titanium Hydrazido(2−) Complexes

Electronic Structures of an [Fe(NNR₂)]^+/0/– Redox Series: Ligand Noninnocence and Implications for Catalytic Nitrogen Fixation

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Bonding analysis of transition metal NNR end-on complexes and comparison with isoelectronic NNR2 species

Cited by 27 publications

References 76 publications

Titanium Hydrazides Supported by Diamide-Amine and Related Ligands: A Combined Experimental and DFT Study

Titanium Hydrazides Supported by Diamide-Amine and Related Ligands: A Combined Experimental and DFT Study

Synthesis, Structures, and DFT Bonding Analysis of New Titanium Hydrazido(2−) Complexes

Electronic Structures of an [Fe(NNR2)]+/0/– Redox Series: Ligand Noninnocence and Implications for Catalytic Nitrogen Fixation

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Electronic Structures of an [Fe(NNR₂)]^+/0/– Redox Series: Ligand Noninnocence and Implications for Catalytic Nitrogen Fixation