University of Groningen

Formazanate as redox-active, structurally versatile ligand platformChang, Mu-Chieh

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Chapter 4

(Formazanate)Boron Difluoride Formation

via Zinc to Boron Transmetallation

A high-yield synthetic route to obtain mono(formazanate)boron difluoride complexes (LBF2;

compounds 6) via an uncommon zinc to boron transmetallation reaction is presented. Two

six-coordinated zinc complexes (compounds 7), which are key intermediates in the

transmetallation reaction, were isolated and characterized by multi-nuclear NMR

spectroscopy and X-ray crystallography. A mechanism was proposed that utilizes the flexible

coordination ability of formazanate ligands, involving interconversion between 6- and 5-

membered chelate binding modes. The observed transmetallation demonstrates that the ability

of these ligands to rearrange to a 5-membered chelate ring leads to decreased steric hindrance

around the central metal atom, which can open up new pathways for reactivity.

Parts of this chapter have been published:

M.-C. Chang and E. Otten* “Synthesis and ligand-based reduction chemistry of boron difluoride

complexes with redox-active formazanate ligands” Chem. Commun., 2014, 50, 7431-7433.

Chapter 4  

 76  

Chapter 4 (Formazanate)Boron Difluoride Formation via Zinc to

Boron Transmetallation

4.1 Introduction

Transmetallation is a key elementary reaction in many important (catalytic) reactions, such as

Suzuki coupling1 and Negishi coupling2 (Scheme 4.1), both of which are powerful tools to

make C-C bonds.3 Both of these reactions form a R-Pd-X intermediate (X = halide) resulting

from oxidative addiction (OA) of an organic halide (R-X). In a subsequent step,

transmetallation (TM) takes place, transferring a second organic fragment from organoboron

(Suzuki coupling) or organozinc (Negishi coupling) reagents to the palladium center to give a

palladium diorganyl intermediate. The catalytic cycle is closed by a reductive elimination (RE)

resulting in regeneration of active catalyst and product dissociation. In addition to these well-

known coupling reactions, transmetallation also plays an important role in preparing a wide

range of organozinc reagents, most of which are not commercially available or expensive, via

boron-to-zinc transmetallation (Scheme 4.1).4 Organozinc reagents and chiral ligands are a

very useful combination for asymmetric arylation of aldehydes resulting in enantiopure diaryl

methanols5, which are valuable compounds in the pharmaceutical field as active ingredients

or as synthetic intermediates.6 Besides applications in organic synthesis, organozinc reagents

are also frequently used to transfer aryl or alkyl groups to transition metal centers, such as Ru,

Nb, and Ta.7 The use of organozinc reagents is often advantageous because these are milder

alkylating agents and less prone to give side products resulting from 1e-reduction than the

corresponding organolithium or Grignard reagents.

In all of the examples mentioned above the transferable groups from either organoboron or

organozinc reagents are usually reactive anionic monodentate ligands, more specifically aryl

and alkyl groups. In the field of inorganic/organometallic chemistry, transmetallation

reactions also are frequently used to transfer multidentate ancillary ('spectator') ligands from

alkali metal salts to the target metal centers. Examples of commonly used reagents in this area

are the alkali metal salts MCp8 and M(nacnac)9 (M = Li, Na, K), which are able to transfer the

anionic organic moiety to less electropositive (transition) metal halides. These ionic reagents

show high ligand exchange rates (lability), which results in kinetically facile transmetallation

(metathesis) reactions.

        (Formazanate)Boron Difluoride Formation via Zinc to Boron Transmetallation  

 

77  

 

Scheme 4.1 General mechanism of Suzuki coupling (top left), Negishi coupling (top right), and preparation of organozinc reagents via boron-to-zinc transmetallation (bottom).

A key feature of transmetallation reaction is that the two metal centers (B and Pd;10 Zn and

Pd;2b,11 B and Zn;4b or alkali metal and metal halide) should be able to access a

(hetero)bimetallic dimeric intermediate from which ligand exchange takes place.12 Therefore,

it is relatively uncommon to observe a transmetallation reaction occurring at a four-

coordinated zinc center bearing two bidentate ligands due to the steric hindrance around the

metal center. Here we present an unusual zinc to boron transmetallation between

bis(formazanate)zinc complexes (L2Zn, 5) and boron trifluoride (BF3) resulting in formation

of (formazanate)boron difluoride compounds (LBF2, 6).

4.2 Formazanate Transfer from Zinc to Boron

4.2.1 Formation of (Formazanate)Boron Difluoride via Transmetallation

In Chapter 3, we showed that bis(formazanate) zinc complexes such as

[PhNNC(R)NNPh]2Zn (5a: R = p-tolyl; 5b:R = tBu) are capable of storing one or two

electrons in the ligand frameworks to form stable 1- and 2-electron reduced complexes (5a–

/5b– and 5a–2/5b–2). The crystal structures of the reduced complexes show (weak)

Chapter 4  

 78  

interactions between the internal nitrogen atoms of the formazanate ligands and sodium

counter cations (Chart 4.1, also see Figure 3.14 and Figure 3.15 in Chapter 3).

Chart 4.1

Based on this observation we anticipated that the reduction potential of bis(formazanate) zinc

compounds could be altered by coordination to neutral Lewis acids. In the course of testing a

range of Lewis acids for binding to 5a, we found that BF3 reacts cleanly via salt metathesis,

opening a high-yield synthetic route to obtain mono(formazanate)boron difluoride complexes

(LBF2; compound 6) (Scheme 4.2). The chemical and physical properties of complexes 6 will

be discussed in Chapter 5. In the following parts of this chapter, the unexpected products and

intermediates isolated from the reaction of compounds 5 with BF3·Et2O will be described.

Scheme 4.2 Synthesis of mono(formazanate)boron difluoride complexes (LBF2: 6) from bis(formazanate)zinc complexes (L2Zn: 5).

4.2.2 Isolation of a Six-Coordinated Zinc Complex as a Key Intermediate

Compound 6a can be easily prepared by reacting the bis(formazanate) zinc compound 5a with

3 equivalents of BF3·Et2O at 70°C overnight. During the reaction, the color of the reaction

mixture changes from deep blue to red and a white precipitate, which could be ZnF2, can be

observed in the reaction flask. In contrast, in the case of (PhNNC(C6F5)NNMes)2Zn (5g) the

color of the reaction mixture fades from deep to light orange upon heating 5g in the presence

of 3 eq BF3·Et2O at 70°C overnight, but precipitation of ZnF2 was not observed. From this

reaction mixture, orange crystals of the product 7g were obtained by slow diffusion of hexane

into a toluene solution at -30°C in 85% yield (Figure 4.1, metrical parameters in Table 4.1).

        (Formazanate)Boron Difluoride Formation via Zinc to Boron Transmetallation  

 

79  

The crystal structure of 7g shows a distorted octahedral zinc center, with two BF3 units

incorporated in the compound. In the crystal structure, there are two tridentate

(PhNNC(C6F5)NNMes(BF3)) units coordinated to the Zn center in a meridional fashion via

two nitrogens and a fluorine atom to give a [NNF]2Zn compound. This unusual binding motif

results from the interaction of BF3 with the terminal nitrogen of the formazanate fragment (the

NMes group), which gives rise to 2 five-membered chelate rings upon coordination to the Zn

center. To the best of our knowledge, the structural characterization of this BF3 binding mode

has no precedent in the literature, although the ‘frustrated Lewis pair’ (tmp)MgCl/BF3 has

been postulated to contain a B-F fragment appended to a Mg-N(tmp) bond.13 The formation

of compound 7g suggests that the formazanate ligand has the ability to isomerize from a

binding mode that involves the two terminal nitrogen atoms of the ligand (6-membered

chelate) to a five-membered chelating ring, in which the Zn center binds both a terminal and

an internal N atom. This ligand rearrangement opens sufficient space around the Zn center to

allow the BF3 substrate to bind.

Figure 4.1 Molecular structure of 7g showing 50% probability ellipsoids. One of the two independent molecules in 7g is shown; hydrogen atoms are omitted for clarity.

The metrical parameters of 7g (Table 4.1) show that the bond lengths of N1-N2 and N5-N6

are shorter than N3-N4 and N7-N8 (1.272(3)/1.266(3) Å vs. 1.319(3)/1.327(3) Å); in addition,

the bond lengths of N2-C7 and N6-C29 are longer than C7-N3 and C29-N7 (1.397(3)/1.407(3)

Å vs. 1.317(3)/1.311(3) Å). These bond length distributions suggest that the negative charge

Zn1_1

N1_1 N2_1

N3_1

N4_1

N5_1

N6_1

N7_1

N8_1

B1_1

F11_1

F14_1 B2_1

C7_1

C29_1

Chapter 4  

 80  

of the formazanate ligand [1g]- is partially localized at the terminal nitrogen atoms

coordinated to boron centers due to the strong electron-withdrawing ability of the BF3 units.

In compound 7g there is a face-centered interaction of an electron-poor C6F5 ring with an

electron-rich mesityl group (interplanar angle = 19.00° and 25.08°, centroid-centroid distance

= 3.375 Å and 3.575 Å), indicative of an aromatic donor-acceptor interaction that is

commonly observed for combinations of electron-rich/poor rings.14

Table 4.1 Selected bond length (Å) and bond angles (o) of 7ga N1-N2 1.272(3) N5-N6 1.266(3) N2-C7 1.397(3) N6-C29 1.407(3) C7-N3 1.317(3) C29-N7 1.311(3) N3-N4 1.327(3) N7-N8 1.319(3) N4-B1 1.584(5) N8-B2 1.584(4) B1-F11 1.349(4) B2-F14 1.415(4) Zn1-N1 2.066(2) Zn1-N5 2.067(2) Zn1-N3 2.088(2) Zn1-N7 2.109(2) Zn1-F11 2.203(2) Zn1-F14 2.156(2)

N1-Zn1-N3 77.26(9) N5-Zn1-N7 76.66(8) N3-Zn1-F11 75.76(8) N7-Zn1-F14 76.54(8)

C6F5(C7)-Mes(N4)b 3.375 C6F5(C29)-Mes(N8)b 3.575 NNCNNZn1/NNCNNZn1c 85.24

a the _1 labels on atoms are omitted; b the centroid to centroid distance of C6F5 ring and Mes ring; c the angle between the planes defined by the central Zn atom and the N atoms of the formazanate backbone.

The 19F NMR of 7g shows six distinct resonances with integration ratio of 1:1:3:1:1:1 (Figure

4.2). Five resonances with the same integration (1F) suggest that all F substituents of the C6F5

ring are inequivalent due to hindered rotation around the C-C6F5 bond. The resonance

integrating as 3F shows 11B and 10B coupling features and can be assigned to the BF3 unit.

The appearance of the BF3 group in the 19F NMR does not change upon cooling to -55 °C,

which suggests that the barrier to rotation around the N-BF3 bond is low. Conversely, heating

an NMR sample of 7g to moderate temperature (65 °C for 24 h) does not result in changes in

the spectroscopy, confirming that the octahedral [NNF]2Zn complex is quite stable. Upon

heating the NMR tube to 130 °C overnight, full conversion to the corresponding LBF2

complex 6g is obtained.

        (Formazanate)Boron Difluoride Formation via Zinc to Boron Transmetallation  

 

81  

Figure 4.2 19F NMR spectrum of compound 7g (C6D6, 375 MHz)

4.2.3 Proposed Mechanism of Transmetallation Reaction

The sequential transformation 5g→7g→6g suggests that a six-coordinate species related to 7g

is likely also involved in the formation of 7g. Based on these observations, we propose the

following mechanism for the transmetallation leading to compound 7g (Scheme 4.3): (i)

formazanate rearrangement from a 6- to a 5-membered chelate ring liberates the terminal N-

atom, (ii) BF3 binds to this terminal N-atom and brings a B-F group in proximity of the Zn

centre, and (iii) the F atom binds to the Lewis acidic Zn(II) centre to from a tridentate [NNF]

ligand with two 5-membered chelate rings. Repeating this sequence for the second

formazanate ligand results in the formation of the [NNF]2Zn complex 7g. Elimination of ZnF2

from this complex either occurs rapidly (in case of 5a→6a) or requires heating to proceed so

that the intermediate can be isolated (5g→7g→6g). A reason for the increased stability of 7g

vs that of putative intermediate in the case of 5a could be the favorable -interactions between

the electron-rich N-Mes and the electron-poor C-C6F5 substituents14 which are present only

when the formazanate ligands adopt a 5-membered chelate ring.

Chapter 4  

 82  

Scheme 4.3 Proposed mechanism of transmetallation from bis(formazanate) zinc complex to mono(formazanate) boron difluoride complex.

4.2.4 Reaction of Heteroleptic Complex 5aj with BF3·Et2O

When the heteroleptic complex 5aj ([1a][1j]Zn) was reacted with BF3·Et2O (1 or 3 eq) at

room temperature, there was no indication of formation of boron difluoride complexes (6a

and 6j). Instead, 1H NMR spectroscopy allows identification of the homoleptic

bis(formazanate) complex 5a as one of the major species as a result of ligand redistribution

(Scheme 4.4). The resonances in the aliphatic region indicate that the two mesityl groups of

the remaining formazanate ligand [1j]- become inequivalent. Based on the formation of 5a, it

is likely that this product is a homoleptic zinc complex containing [1j]-. From the reaction

mixture, two types of crystals with different shapes can be isolated. One of these shows a

similar shape as 5a; the other crystals are black diamonds, which were shown by X-ray

crystallography to be compound [MesNNC(CN)NNMes(BF3)]2Zn (7j, Figure 4.3, metrical

parameters in Table 4.2). The data indicate that 7j has very similar structure as 7g; both of

them have an octahedral zinc center bearing two formazanate(BF3) units, which in the case of

7j is a MesNNC(CN)NNMes(BF3) unit. All the metrical parameters of 7j are very similar

with 7g. In the solid state structure of complex 7j the N-Mes rings are oriented nearly parallel

(interplanar angle = 2.45° and distance between centroids = 3.641 Å) and stack in an off-

center fashion as is usually observed for electron-rich aromatic rings.14 The formation of 5a

and 7j from compound 5aj by treatment with BF3·Et2O indicates that formazanate ligands (in

this case [1a]- and [1j]-) are capable of intermolecular ligand exchange.

        (Formazanate)Boron Difluoride Formation via Zinc to Boron Transmetallation  

 

83  

 

Figure 4.3 Molecular structure of 7j showing 50% probability ellipsoids.

Table 4.2 Selected bond length (Å) and bond angles (o) of 7j N1-N2 1.277(2) N6-N7 1.274(3) N2-C10 1.397(2) N7-C30 1.397(3) C10-N3 1.322(2) C30-N8 1.325(2) N3-N4 1.305(2) N8-N9 1.307(2) N4-B1 1.599(3) N9-B2 1.595(3) B1-F1 1.418(3) B2-F4 1.416(3)

Zn1-N1 2.082(2) Zn1-N6 2.078(2) Zn1-N3 2.108(2) Zn1-N8 2.098(2) Zn1-F1 2.203(1) Zn1-F4 2.234(1)

N1-Zn1-N3 76.59(6) N6-Zn1-N8 77.35(6) N3-Zn1-F1 74.47(5) N8-Zn1-F4 73.90(5)

Mes(N1)-Mes(N6)a 3.641 NNCNNZn1/NNCNNZn1b 73.06

a the centroid to centroid distance of Mes rings b the angle between the planes defined by the central Zn atom and the N atoms of the formazanate backbone.

Even though the isolation of 7j as a pure compound proved to be difficult, the 1H and 19F

NMR characterization data (as a mixture with 5a and some unidentified side products) can be

collected by treatment of 5aj with 1.5 eq of BF3·Et2O in C6D6 (Figure 4.4). The 1H NMR

spectrum of 7j shows two sets of resonances for the mesityl groups. In the aliphatic region,

five distinct resonances with integration ratio 3:3:3:3:6 indicate that the free rotation of one of

the mesityl substituents was blocked, similar to what was observed for 7g.

Chapter 4  

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Scheme 4.4 Summary of reaction of compound 5aj with BF3

Figure 4.4 Reaction of compound 5aj with 1.5 eq of BF3·Et2O in C6D6 on NMR scale

        (Formazanate)Boron Difluoride Formation via Zinc to Boron Transmetallation  

 

85  

4.2.5 1,2,3-Triazole Formation

In the course of optimizing the conditions for generating 6j from 5aj, we obtained an

unexpected side product 9 (Scheme 4.4). After comfirming the formation of 5a and 7j by 1H

NMR spectroscopy, the NMR solution was treated with a few drops of d8-THF and the

mixture was allowed to stand at room temperature for overnight. Subsequent 1H NMR

analysis did not show the resonances of 5a or 7j. Workup of the reaction mixture by

crystallization from toluene/hexane afforded single crystals of the new compound 8-toluene,

which contains a toluene molecule in the lattice. The solvomorph 8-THF (Figure 4.5, metrical

parameters in Table 4.3), which has a THF molecule in the lattice, was obtained from another

independent reaction followed by recrystallization from THF/hexane mixture.

Figure 4.5 Molecular structure of 8-THF showing 50% probability ellipsoids. The THF solvent molecule and all hydrogen atoms are omitted; the formazanate ligands [1a]- are shown as wireframe for clarity.

Table 4.3 Selected bond length (Å) and bond angles (o) of 8-THF N1-N2 1.302(2) N6-C30 1.408(2) N3-C7 1.352(2) N3-N4 1.304(2) C30-N7 1.347(2) Zn1-N1 2.016(2) N5-N6 1.263(3) C30-C31 1.409(3) Zn1-N4 2.012(1) N7-N8 1.318(2) C31-N9 1.351(2) Zn1-N9 2.081(2) N8-N9 1.362(2) N2-C7 1.345(2) Zn1-C31 1.998(2)

N4-Zn1-N1 90.25(6) N9-Zn1-C31 105.28(7) C31-N9-N8 106.3(1) N8-N7-C30 103.3(1) N9-C31-C30 104.6(2) C31-N9-N9 111.7(2) N9-N8-N7 114.1(1) Zn1-C31-N9 129.3(1) Zn1-N9-C31 124.6(1)

A crystal structure determination shows that 8 contains two mono(formazanate)zinc units

([1a]Zn) and two anionic triazole units, which are bridging between two zinc centers by using

Chapter 4  

 86  

N9 and C31 as donor atoms (Figure 4.5). The triazole has one mesityl substituent at the 2-

position and one mesityldiazenyl group at the 4-position. The composition of the triazole unit

is exactly the same as [1j]-; in addition, all atom connections are retained. The only additional

connection is between the N atom in the cyano group and one of the terminal N atoms in the

formazanate backbone. The formation of this triazole unit is unlikely to follow a traditional

1,3-dipolar cycloaddition pathway directly.15 We propose that the formation of the triazole

unit in 8 is initiated by Lewis acid (BF3) activation of [1j]-, followed by dissociation of the

[NC-BF3]- unit from activated [1j]- to generate the neutral carbene fragment X (Scheme 4.5).

Fragment X is a resonance structure of the nitrile imine 1,3-dipole Y, which is able to undergo

a dipolar cycloaddition with [NC-BF3]- to generate the final 1,2,3-triazole unit. The 1,2,3-

triazole is a useful building block for more complex chemical compounds and usually

synthesized form azide-alkyne Huisgen cycloaddition. The Reaction we presented here could

be a potential route for 1,2,3-triazole synthesis.

Scheme 4.5 Proposed mechanism of [1j]- cyclization

4.3 Conclusion

In this chapter, a high-yield synthetic route to obtain mono(formazanate)boron difluoride

complexes (LBF2; compounds 6) via an uncommon zinc to boron transmetallation reaction is

developed. The isolation of the six-coordinated zinc complex ([L(BF3)]2Zn, 7) from the

reaction of 5 and BF3 proved the concept mentioned at the end of Chapter 3 that when

substrates were introduced, the formazanate ligand can isomerize to form five-membered

chelates and open space around the metal center to accommodate incoming substrates. The

reaction of heteroleptic complex 5aj with BF3·Et2O not only show a intermolecular ligand

exchange but also open a potential route for 1,2,3-triazole synthesis.

        (Formazanate)Boron Difluoride Formation via Zinc to Boron Transmetallation  

 

87  

4.4 Experimental section

General Considerations. All manipulations were carried out under nitrogen atmosphere

using standard glovebox, Schlenk, and vacuum-line techniques. Toluene, hexane, and pentane

(Aldrich, anhydrous, 99.8%) were passed over columns of Al2O3 (Fluka), BASF R3-11-

supported Cu oxygen scavenger, and molecular sieves (Aldrich, 4 Å). Diethyl ether and THF

(Aldrich, anhydrous, 99.8%) were dried by percolation over columns of Al2O3 (Fluka).

Deuterated solvents were vacuum transferred from Na/K alloy (C6D6, toluene-d8, Aldrich)

and stored under nitrogen.

BF3(ether) was used as received from Aldrich. NMR spectra were recorded on Varian Gemini

200, VXR 300, Mercury 400 or Varian 500 spectrometers. The 1H and 13C NMR spectra were

referenced internally using the residual solvent resonances and reported in ppm relative to

TMS (0 ppm); J is reported in Hz. Assignment of NMR resonances was aided by gradient-

selected COSY, NOESY, HSQC and/or HMBC experiments using standard pulse sequences.

Elemental analyses were performed at the Microanalytical Department of the University of

Groningen.

Synthesis and Characterization

[PhNNC(C6F5)NN(BF3)Mes]2Zn 7g. A mixture of 5g (100.0 mg, 0.108 mmol), BF3·Et2O

(0.04 mL, 0.32 mmol) and 10 mL of toluene was prepared. The reaction mixture was stirred at

70°C for 2 hours after which the color had changed to orange. Slow diffusion of 5 mL of

hexane into the toluene solution at -30 °C for 4 days resulted in precipitation of 98 mg orange

crystals of 7g (0.092 mmol, 85%). 1H NMR (400 MHz, C6D6, 25 °C) δ 7.76 (d, 2H, J = 8.1,

Ph o-H), 7.01 (t, 2H, J = 7.7, Ph m-H), 6.89 (t, 1H, J = 7.4, Ph p-H), 6.35 (s, 1H, Mes m-H),

6.14 (s, 1H, Mes m-H), 2.48 (s, 3H, Mes o-CH3), 2.29 (s, 3H, Mes o-CH3), 1.79 (s, 3H, Mes

p-CH3), 11B NMR (376.4 MHz, C6D6, 25 °C) δ 0.78 (s, 1B, BF3).

19F NMR (128.3 MHz, C6D6,

25 °C) δ -130.3 (d, 1F, J = 23.9, C6F5 m-F), -136.7 (d, 1F, J = 23.9, C6F5 m-F), -148.4 (s, 3F,

BF3), -152.7 (t, 1F, J = 21.8, C6F5 p-F), -161.6 (td, 1F, J = 22.6, 7.3, C6F5 o-F), -163.0 (td, 1F,

J = 22.7, 7.7, C6F5 o-F). 13C NMR (100.6 MHz, C6D6, 25 °C) δ 148.6 (Ph i-C), 146.0-145.0

(m, C6F5), 143.5-142.6 (m, C6F5), 140.8-140.1 (m, C6F5), 139.2 (Mes i-C), 138.6-137.6 (m,

C6F5), 136.3 (Mes o-C), 136.0 (Mes o-C), 135.9-135.2 (m, C6F5), 134.5 (Ph p-C), 132.4 (Mes

p-C), 130.5 (NNCNN), 129.7 (Ph m-C), 129.1 (Mes m-C), ~128.5 (overlapped, Mes m-C),

122.4 (Ph o-C), 108.9 (td, J = 19.4, 4.0, C6F5 i-C), 19.9 (Mes p-CH3), 17.9 (Mes o-CH3). Anal.

Calcd for C44H32B2F16N8Zn: C, 49.68; H, 3.03; N, 10.53. Found: C, 50.18; H, 3.15; N, 10.18.

Chapter 4  

 88  

NMR data of [MesNNC(CN)NN(BF3)Mes]2Zn 7j. 1H NMR (400 MHz, C6D6, 25 °C): δ

6.77 (s, 1H, Mes m-CH, overlapped with compound 5a), 6.70 (s, 1H, Mes m-CH), 6.15 6.70

(s, 2H, Mes m-CH), 2.54 (s, 3H, Mes CH3), 2.43 (s, 3H, Mes CH3), 1.99 (s, 3H, Mes CH3),

1.82 (s, 3H, Mes CH3), 1.72 (s, 6H, Mes o-CH3). 19F NMR (128.3 MHz, C6D6, 25 °C): δ -

149.1 ppm.

Crystal structure determination

Suitable crystals reported in this chapter were mounted on a cryo-loop in a drybox and

transferred, using inert-atmosphere handling techniques, into the cold nitrogen stream of a

Bruker D8 Venture diffractometer. The final unit cell was obtained from the xyz centroids of

9950 (7g), 9328 (7j), and 9677 (8-THF) reflections after integration. Intensity data were

corrected for Lorentz and polarisation effects, scale variation, for decay and absorption: a

multiscan absorption correction was applied, based on the intensities of symmetry-related

reflections measured at different angular settings (SADABS).16 The structures were solved by

direct methods using the program SHELXS.17 The hydrogen atoms were generated by

geometrical considerations and constrained to idealised geometries and allowed to ride on

their carrier atoms with an isotropic displacement parameter related to the equivalent

displacement parameter of their carrier atoms. Structure refinement was performed with the

program package SHELXL.17 Crystal data and details on data collection and refinement are

presented in the following tables.

Crystallographic data 7g 7j 8-THF chem formula C44H32B2F16N8Zn C40H44B2F6N10Zn C88H94N18O2Zn2 Mr 1063.76 865.84 1566.55 cryst syst monoclinic triclinic monoclinic color, habit orange, platelet black, block red, block size (mm) 0.20 x 0.16 x 0.03 0.16 x 0.12 x 0.07 0.22 x 0.19 x 0.06 space group P21/c P-1 P21/c a (Å) 28.1225(14) 11.6518(8) 14.5130(5) b (Å) 20.6482(10) 13.2253(8) 19.2848(7) c (Å) 15.3728(7) 14.0756(9) 14.5017(4) (°) 85.167(2) β (°) 93.868(2) 85.244(2) 107.0814(11) (°) 74.634(2) V (Å3) 8906.3(7) 2079.9(2) 3879.7(2) Z 8 2 2 calc, g.cm-3 1.587 1.383 1.341 Radiation [Å] Mo Kα 0.71073 Mo Kα 0.71073 Mo Kα 0.71073 µ(Mo K), mm-1 0.663 0.66 0.681 µ(Cu K), mm-1 F(000) 4288 896 1648 temp (K) 100(2) 100(2) 100(2) range (°) 5.878-52.737 2.91-27.19 2.94-27.14

        (Formazanate)Boron Difluoride Formation via Zinc to Boron Transmetallation  

 

89  

data collected (h,k,l) -36:36, -26:26, -20:19 -14:14; -16:16: -18:18 -18:18; -24:24; -18:18 min, max transm 0.6950, 0.7456 0.6773, 0.7455 0.5155, 0.7455 rflns collected 285779 70841 132574 indpndt reflns 20514 9196 8585 observed reflns Fo 2.0 σ (Fo) 15776 7344 7295 R(F) (%) 5.26 3.53 3.56 wR(F2) (%) 11.07 6.93 8.39 GooF 1.083 0.983 1.051 weighting a,b 0.0422, 16.6302 0.0211, 2.1321 0.0355, 4.2240 params refined 1353 544 503 min, max resid dens -0.914, 2.757 -0.394, 0.419 -0.561, 0.668

 

4.5 Reference

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Chapter 4  

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