Surprisingly Different Reaction Behavior of Alkali and Alkaline Earth Metal Bis(trimethylsilyl)amides toward Bulky N-(2-Pyridylethyl)-N′-(2,6-diisopropylphenyl)pivalamidine

DOI: 10.1002/chem.201602074

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&

Coordination Chemistry

Surprisingly Different Reaction Behavior of Alkali and Alkaline

Earth Metal Bis(trimethylsilyl)amides toward Bulky N-(2-

Pyridylethyl)-N’-(2,6-diisopropylphenyl)pivalamidine

Diana Kalden, Ansgar Oberheide, Claas Loh, Helmar Gçrls, Sven Krieck, and

Matthias Westerhausen*^[a]

Dedicated to Professor Wolfgang Seidel on the occasion of his 85th birthday

Abstract: N-(2,6-Diisopropylphenyl)-N’-(2-pyridylethyl)pival-

amidine (Dipp-N=C(tBu)-N(H)-C₂H₄-Py) (1), reacts with metal-

ation reagents of lithium, magnesium, calcium, and stronti-

um to give the corresponding pivalamidinates [(tmeda)Li-

{Dipp-N=C(tBu)-N-C₂H₄-Py}] (6), [Mg{Dipp-N=C(tBu)-N-C₂H₄-

Py}₂] (3), and heteroleptic [{(Me₃Si)₂N}Ae{Dipp-N=C(tBu)-N-

C₂H₄-Py}], with Ae being Ca (2a) and Sr (2b). In contrast to

this straightforward deprotonation of the amidine units, the

reaction of 1 with the bis(trimethylsilyl)amides of sodium or

potassium unexpectedly leads to a b-metalation and an im-

tionship in the periodic table. Protonation of 4a or the

metathesis reaction of 4b with CaI₂in tetrahydrofuran yields

N-(2,6-diisopropylphenyl)pivalamidine (Dipp-N=C(tBu)-NH₂)

(5), or [(thf)₄Ca{Dipp-N=C(tBu)-N(H)}₂] (7), respectively. The

reaction of AN(SiMe₃)₂(A=Na, K) with less bulky formami-

dine Dipp-N=C(H)-N(H)-C₂H₄-Py (8) leads to deprotonation of

the amidine functionality, and [(thf)Na{Dipp-N=C(H)-N-C₂H₄-

Py}]₂(9a) or [(thf)K{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9b), respec-

tively, are isolated as dinuclear complexes. From these ex-

periments it is obvious, that b-metalation/deamidation of N-

mediate deamidation reaction yielding [(thf)₂Na{Dipp-N= (2-pyridylethyl)amidines requires bases with soft metal ions

C(tBu)-N(H)}] (4a) or [(thf)₂K{Dipp-N=C(tBu)-N(H)}] (4b), re-

spectively, as well as 2-vinylpyridine in both cases. The lithi-

um derivative shows a similar reaction behavior to the alka-

line earth metal congeners, underlining the diagonal rela-

and also steric pressure. The isomeric forms of all com-

pounds are verified by single-crystal X-ray structure analysis

and are maintained in solution.

Introduction

merism are possible leading to four major alignments

(Scheme 1). The coordination chemistry of these ligands is de-

termined by whether the metal ions prefer p-interactions with

aryl groups or the coordination of hard Lewis bases such as

ethers. Lewis basic donor sites in the N-bound sidearm also

strongly influence the coordination mode of this ligand.

Multidentate nitrogen donors represent widely used Lewis

bases because they commonly form very stable complexes

with electropositive (s-block) metals and transition metals.^[1]

Therefore, these ligands can often facially shield a metal ion

and direct the attack of substrate molecules. Bulky b-diketimi-

nates,^[2]triazenides,^[3]di- and tri(pyrazolyl)methanes and -meth-

anides,^[4]amidinates, and related anions such as guanidinates^[5]

represent prominent bi- and tridentate ligands that form very

stable complexes with s-block metal ions. Spectacular exam-

ples include magnesium(I) complexes with MgÀMg bonds of

surprisingly high stability,^[6]and an arylcalcium derivative with

a pentafluorophenyl moiety.^[7]The coordination behavior of

amidinate and guanidinate anions with metal ions shows sig-

nificant diversity due to the fact that both anti/syn and E/Z-iso-

The N,N’-bis(2,6-diisopropylphenyl)benz-^[8,9]and -pivalamidi-

nates^[9,10](R=Ph and tBu, respectively) of potassium

(Scheme 2, A) and calcium (Scheme 2, B₁and B₂) bind through

the nitrogen atoms and the negative charge is widely delocal-

ized throughout the syn-E-isomeric 1,3-diazaallyl moiety in

each case (the prefix syn or anti refer to the N-bound organic

groups neglecting the metal atoms). The ytterbium (not

shown) and samarium complexes (C) bind to the anti-Z-isomer-

ic N,N’-bis(2,6-diisopropylphenyl)pivalamidinate resulting in

strong metal p-interactions to one 2,6-diisopropylphenyl

group (Dipp).^[10]In contrast to this binding mode, the lantha-

noids ytterbium, europium, and samarium bind only to the N

atoms of the diazaallyl system of bulky syn-E-isomeric N,N’-

bis(2,6-diisopropylphenyl)guanidinate (B₂).^[11]Substitution of

one N-bound Dipp group by another substituent with a Lewis

basic donor site offers the opportunity to locate the metal ion

on a predetermined definite position with respect to the allyl

system. Thus anti-Z-isomeric N-(2-pyridylmethyl)-^[12](D) and N-

[a] D. Kalden, A. Oberheide, Dr. C. Loh, Dr. H. Gçrls, Dr. S. Krieck,

Prof. Dr. M. Westerhausen

Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University

Humboldstrasse 8, 07743 Jena (Germany)

htt p ://www.lsac1.uni-jena.de

E-mail: m.we@uni-jena.de

Supporting information for this article is available on the WWW under

htt p ://dx.doi.org/10.1002/chem.201602074.

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Generally, two established pathways allow for the synthesis

of calcium complexes, namely (i) the metalation of the ami-

dines with, for example, [(thf)₂Ca{N(SiMe₃)₂}₂], and (ii) the meta-

thetical approach of potassium amidinate with [(thf)₄CaI₂] uti-

lizing the insolubility of KI in ethereal solvents. Therefore, initial

studies investigated the synthesis of the calcium derivative of

the amidine 1 through the straightforward metalation route.

The metalation reaction of N-(2-pyridylethyl)-N’-(2,6-diisopro-

pylphenyl)pivalamidine (1) with [(thf)₂Ae{N(SiMe₃)₂}₂] (Ae=Ca,

Sr) in tetrahydrofuran (THF) yielded the ether-free heteroleptic

complexes [(Me₃Si)₂NAe{tBuC(=NDipp)(-NCH₂CH₂Py)}] [Ae=Ca

(2a), Sr (2b)] according to reaction 2.

Scheme 1. General coordination modes of N-(2,6-diisopropylphenyl)amidi-

nates (R=H, alkyl, aryl) and guanidinates (R=amino) in metal complexes.

Anti-isomers are shown in the top row, syn-isomers in the bottom; Z-isomer-

ism is depicted in the left column, E-isomerism in the right column. The

colors signify different coordination modes.

(8-quinolyl)-N’-2,6-diisopropylphenylamidinate^[13](E) enforce

calcium p-interactions with the 2,6-diisopropylphenyl group,

whereas anti-E-isomeric N-(2-pyridyl)-N’-2,6-diisopropylphenyl-

amidinate^[13](F) binds to calcium exclusively through the nitro-

gen bases. A longer alkyl bridge between the 1,3-diazaallyl

system and the 2-pyridyl moiety leads to the N-(2-pyridyleth-

yl)-N’-2,6-diisopropylphenylamidinate ion. A comparable bind-

ing motif to E and F was observed for the co-ligand-free mag-

nesium complex with a hexa-coordinate alkaline earth metal

atom bound to two N-(2-pyridylethyl)-N’-(3,5-dimethylphenyl)-

4-methylbenzamidinate anions (not shown); all nitrogen bases

were bound to the metal center leading to a distorted octahe-

dral environment.^[14]

The harder magnesium ion prefers hard Lewis bases and

metal p-interactions are disadvantageous in comparison to

MgÀN bonds. To also study the coordination behavior of pival-

amidine 1 toward Mg²⁺ions, this amidine was metalated with

dibutylmagnesium in aliphatic hydrocarbons (reaction 3).

To elucidate the alternative metathetical route, N-(2-pyridyl-

ethyl)-N’-(2,6-diisopropylphenyl)pivalamidine (1) was reacted

Based on our earlier observation that a third Lewis base in

a side arm of the amidinate ligand is able to stabilize calcium

p-interactions with aryl groups,^[12,13]we investigated com-

pounds with an even longer alkyl spacer between the amidi-

nate and the 2-pyridyl moieties.

Results and Discussion

Synthesis

The bulky tridentate Lewis base N-(2-pyridylethyl)-N’-(2,6-diiso-

propylphenyl)pivalamidine (1) was prepared by the reaction of

N-(2,6-diisopropylphenyl)pivalimidoyl chloride^[9,12,15]with an

equimolar amount of 2-(aminoethyl)pyridine in boiling toluene

(reaction 1). Recrystallization from toluene yielded the syn-Z-

isomer of 1 in the crystalline state.

with KH in THF or AN(SiMe₃)₂(A=Na, K) in toluene. In either

case the cleavage of a CÀN bond occurred with the loss of 2-

vinylpyridine, which was identified by gas chromatography

and NMR spectroscopy. Furthermore, the alkali metal-mediated

cleavage of the CÀN bond was also supported by a hydrolysis

experiment that yielded Dipp-N=C(tBu)-NH₂. Finally, the com-

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Scheme 2. N-(2,6-Diisopropylphenyl)amidinate complexes of the s-block metals and related divalent lanthanoids prepared by salt metathesis or metalation

(bottom) reactions from the potassium derivative. The diverse coordination modes are clarified with different colors in accordance with Scheme 1.

plexes [(thf)_nA{HN-C(tBu)=NDipp}] [A/n=Na/2 (4a), K/1 (4b)]

tallic Li/Zn- and Li/Al-based superbases show comparable reac-

tion patterns, and bridging dimethylamide ions between lithi-

um and zinc as well as lithium and aluminium have been ob-

served (reaction 4).^[17]

1

were isolated after filtration, evaporation of the solvent from

the filtrate, and recrystallization from a THF solution. Crystal

structure determinations of the sodium and potassium deriva-

tives 4a and 4b (vide infra) finally verified the liberation of 2-

vinylpyridine. In contrast to the reactivity of the alkaline earth

metal-based metalation reagents, a b-deprotonation occurred,

immediately followed by a deamidation process with release

of 2-vinylpyridine. The lifetime of the b-deprotonation inter-

mediate was too short for detection by NMR spectroscopy, but

the final products form without any other side products (see

Figure S13 in the Supporting Information). Although this two-

step process of b-metalation and deamidation is unique in

amidinate chemistry of the s-block metals, there are some

precedents in the literature employing heterobimetallic super-

bases. Phenylethyldimethylamine has been quantitatively de-

protonated by BuLi/tBuOK reagents (Lochmann–Schlosser

bases) at the b-position of the N atom leading to a coordina-

tion polymer of the thf adduct of 2-dimethylamino-1-phenyl-

ethylpotassium at low temperatures that degraded at RT to

styrene and dimethylamide ions.^[16]Other strong heterobime-

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The strikingly different reaction behavior of complexes with

the isoelectronic ion pairs Na⁺/Mg²⁺and K⁺/Ca²⁺initiated us

to also include the lithium derivative in our investigations. The

reaction of LiN(SiMe₃)₂with N-(2-pyridylethyl)-N’-(2,6-diisopro-

pylphenyl)pivalamidine (1) in a mixture of toluene and TMEDA

(N,N,N’,N’-tetramethylethylenediamine) yielded the metalation

product (reaction 5), as also observed for the alkaline earth

metal derivatives. Crystal structure determination (vide infra)

verified the constitution of the lithium-derived bis(dimethyl-

amino)ethane-(tmeda) adduct 6 . The chemistry of the lithium

derivative represents another example of the diagonal relation-

ship in the periodic table because lithiation follows the same

reaction pathway as metalation with alkaline earth metal re-

agents, whereas the heavier alkali metals exhibit a strikingly

different reactivity.

0.5210^À3, Mg²⁺1.8510^À3, Ca²⁺1.4010^À3, and Sr²⁺1.21

10^À3epm^À2) represents the major factor for this deviating be-

havior of metalation and dehydroamination. Furthermore, in-

tramolecular steric strain in combination with soft alkali metals

was also suspected to be responsible for this exceptional reac-

tion behavior. Due to this consideration, we prepared the ap-

propriate N-(2-pyridylethyl)-N’-(2,6-diisopropylphenyl)formami-

dine (8) from Dipp-NH₂, HC(OEt)₃, and 2-PyCH₂CH₂NH₂without

solvent at 1408C according to reaction 7; isolation and purifica-

tion of intermediately formed Dipp-N=CH-OEt^[20,21]gave no sig-

nificant improvement of the yields. Metalation of formamidine

8 with AN(SiMe₃)₂in toluene yielded the corresponding metal-

ation products [(thf)A{HC(=NDipp)(-NCH₂CH₂Py)}]₂[A=Na

(9a), K (9b)] after recrystallization from THF solution as depict-

ed in reaction 7. Cleavage of the CÀN bond and liberation of

2-vinylpyridine were not observed here, verifying the addition-

al relevance of steric pressure induced by the bulky tert-butyl

group in 1 and the contact to soft alkali metal ions.

The salt-metathesis reaction of intermediately prepared 4b

with [(thf)₄CaI₂] in tetrahydrofuran yielded complex

[(thf)₄Ca{HN-C(tBu)=NDipp}₂] (7) according to reaction 6. The

insolubility of KI in ethereal solutions avoids the formation of

mixed-metal species such as ligated potassium calciates of the

type K[CaR₃] or K₂[CaR₄] (as have been observed and structural-

ly identified previously).^[18,19]The large number of four bound

thf ligands in the isolated and crystalline 7 already indicated

that the amidinate anions act as monodentate bases, which

was verified by an X-ray structure determination (vide infra).

The unique and unexpected dehydroamination reaction of

the heavy alkali metal reagents shown in reaction 4 contrasts

NMR spectroscopy

Selected NMR parameters are summarized in Table 1. Two sets

of resonances are observed for magnesium complex 3 and

amidine 8. This finding suggests the presence of two isomeric

forms in solution. The carbon atoms C_NCNof the amidine and

amidinate units in 3 show low-field-shifted resonances; depro-

tonation enhances these shifts toward even lower field by ap-

proximately 15 ppm. Substitution of the 2-pyridylethyl sub-

stituent by a hydrogen atom shifts this resonance to a higher

field by approximately 10 ppm. Similar effects are also found

for the ipso-carbon atoms iC_Dippof the 2,6-diisopropylphenyl

groups. Small dependencies on the chemical ¹³C{¹H} NMR shifts

are also observed for the 2-pyridylethyl groups with respect to

the coordination of the pyridyl base to the metal ions.

with the reaction of the heavy alkaline earth metal derivatives

and of LiN(SiMe₃)₂. This deviating behavior seems to be inde-

pendent of the metalating reagent [KH and KN(SiMe₃)₂] and

the solvent (THF and toluene), and only a consequence of the

softness of the alkali metal ions. Therefore, the value of the

surface charge (simply calculated as the quotient of charge

and surface of the ion, Li⁺0.8810^À3, Na⁺0.6910^À3, K⁺

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Table 1. Selected ¹H and ¹³C{¹H} NMR data (in ppm) of Dipp-N=C(tBu)-N(H)-C₂H₄-Py (1), [{(Me₃Si)₂N}Ca{Dipp-N=C(tBu)-N-C₂H₄-Py}] (2a), [{(Me₃Si)₂N}Sr{Dipp-

N=C(tBu)-N-C₂H₄-Py}] (2b), [Mg{Dipp-N=C(tBu)-N-C₂H₄-Py}₂] (3), [(thf)₂Na{Dipp-N=C(tBu)-N(H)}] (4a), [(thf)₂K{Dipp-N=C(tBu)-N(H)}] (4b), Dipp-N=C(tBu)-NH₂

(5), [(thf)₄Ca{Dipp-N=C(tBu)-N(H)}₂] (7), Dipp-N=C(H)-N(H)-C₂H₄-Py (8), [(thf)Na{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9a), and [(thf)K{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9b)

(Allred–Rochow electronegativity (EN) of hydrogen and the corresponding s-block metals).

Compound

EN

Solvent

d(C_NCN

)

d(iC_Dipp

)

d(C_CMe3

)

d(C_NCH2

)

d(C_CH2Py

)

d(iC_Py)

1

2a

2b

3

4a

4b

5

7

8

9a

9b

2.20 (H)

1.04 (Ca)

0.99 (Sr)

1.23 (Mg)

1.01 (Na)

0.91 (K)

2.20 (H)

1.04 (Ca)

2.20 (H)

1.01 (Na)

0.91 (K)

C₆D₆

CDCl₃

C₆D₆

CDCl₃

C₆D₆

157.2

172.7

172.2

176.7, 164.5

161.1

162.2

161.2

159.8, 158.3

170.0

147.7

156.4

159.0

151.8, 146.9

145.5

144.5

145.6

147.7

39.1

40.1

39.6

40.3

37.0

37.1

37.0

–

43.1

49.2

49.7

49.2, 46.7

–

37.1

39.0

39.2

40.0, 38.1

–

160.6

162.4

162.5

165.0, 162.8

–

43.9, 39.7

55.9

58.1

40.8, 37.7

42.4

44.3

148.8

163.1

164.1

151.4

150.3

–

[D₈]THF

166.5

Molecular structures

bis[bis(trimethylsilyl)amides].^[23,24]Large Si1ÀN4ÀSi2 bond

angles and short SiÀN4 bonds are characteristic for terminal

bis(trimethylsilyl)amido ligands at electropositive metals and

are a consequence of intramolecular strain and electrostatic re-

pulsion.^[25]

To elucidate the steric pressure within these compounds, we

also performed X-ray diffraction analysis. The resulting molecu-

lar structures and atom number schemes of the amidines

1 and 8 are depicted in Figure 1. Due to poor crystal quality

and disorder of part of the molecule, we were only able to

obtain a structural motif of 8; recrystallization efforts from vari-

ous solvents remained unsuccessful. Despite the fact that dis-

cussion of structural parameters is limited, the isomeric struc-

ture of 8 was verified. Intramolecular steric strain enforces

a syn-Z-configuration of 1 stabilized by a N2ÀH···N3 hydrogen

bridge between the amidine and the pyridyl group. In contrast

to this intramolecular hydrogen bridge, 8 forms a strand struc-

ture through intermolecular N2ÀH···N1’ bridges (intermolecular

N1’···N2 distance: 303.2(5) pm). This kind of aggregation re-

quires an anti-Z-isomeric 8 and also explains the flexibility of

the 2-pyridylethyl sidearm leading to rather free motion and

disordering of this substituent and, thus, to a poor quality of

the crystal structure determination.

The magnesium cation is significantly harder than the heavi-

er homologous alkaline earth metal ions and, hence, avoids in-

teractions to the soft p-systems of aryl groups. Due to this

Molecular structure and atom number scheme of

[{(Me₃Si)₂N}Ca{tBuC(=NDipp)(-NCH₂CH₂Py)}] (2a) are shown in

Figure 2; the strontium derivative 2b crystallized isotypic to

2a and is not represented for simplicity. These complexes ex-

hibit remarkable structural features. The side-on orientation of

the Dipp groups allows an effective alkaline earth metal p-in-

teraction with rather small CaÀC (275.0(3)–304.8(3) pm) and

SrÀC bond lengths (288.5(3)–309.8(3) pm) leading to distances

between the aryl centroid and calcium or strontium atoms of

255.4 and 268.0 pm, respectively. These values are larger than

those observed for calciocenes and strontiocenes due to an

enhanced electrostatic attraction in such sandwich com-

plexes.^[22]The rather low shielding degree of the alkaline earth

metal atoms in 2a and 2b leads to agostic interactions with

methyl groups of the bis(trimethylsilyl)amido ligands

(Ca1···C30, 315.7(3) pm and Sr1···C30, 308.4(3) pm) causing sig-

nificantly different distal and proximal Ae1ÀN4ÀSi1 and Ae1À

N4ÀSi2 bond angles. The Ae1ÀN4 bond lengths lie in charac-

teristic ranges as those also observed for terminally bound

N(SiMe₃)₂groups of the corresponding calcium and strontium

Figure 1. Molecular structures and atom number schemes of the amidines

Dipp-N=C(tBu)-N(H)-C₂H₄-Py (1, top) and Dipp-N=C(H)-N(H)-C₂H₄-Py (8,

bottom). The ellipsoids of 1 represent a probability of 30%; the carbon-

bound H atoms are neglected for clarity. The atoms of 8 are shown with ar-

bitrary radii due to sub-standard structure determination (see text).

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Figure 2. Molecular structure and atom number scheme of heteroleptic

[{(Me₃Si)₂N}Ca{Dipp-N=C(tBu)-N-C₂H₄-Py}] (2a); the strontium congener (2b)

crystallized isotypic to 2a and is depicted in Figure S1 in the Supporting In-

formation. The ellipsoids represent a probability of 30%; H atoms are omit-

ted for clarity.

fact, the magnesium atom exclusively binds to the aza-Lewis

bases. The molecular structure and atom number scheme of 3

are represented in Figure 3. One ligand acts as a tridentate

anion, whereas only two Lewis donors of the other anion bind

to the metal atom. Due to this fact and steric requirements,

these anions adopt different isomeric forms. The tridentate

base binds as a syn-E isomer, whereas the bidentate ligand co-

ordinates as a syn-Z-isomeric anion. This strikingly different co-

ordination behavior also leads to rather similar C1ÀN1 and C1À

N2 bond lengths, whereas in the other ligand the C25ÀN5

bond length is significantly smaller than the C25ÀN4 distance.

The molecular structures and atom number schemes of the

alkali metal derivatives 4a and 4b are depicted in Figures 4

and 5. The amidinate ligands show different isomeric forms for

the sodium (syn-Z) and potassium (anti-Z) complexes. The pref-

erence for the anti-Z-isomeric amidinate of the potassium com-

plex 4b is caused by strong interactions of the alkali metal to

the p-systems of the amidinate ligands. In contrast, the

sodium ion prefers coordination to hard bases such as tetrahy-

drofuran or amidinate nitrogen atoms. Both compounds crys-

Figure 4. Molecular structure and atom number scheme of the asymmetric

unit of [(thf)₂Na{Dipp-N=C(tBu)-N(H)}] (4a) (top). At the bottom, a part of the

strand structure is shown.

Figure 5. Molecular structure and atom number scheme of the asymmetric

unit of [(thf)₂K{Dipp-N=C(tBu)-N(H)}] (4b) (top). At the bottom, the strand

structure is represented; please note that this structure is very different from

the chain of the sodium derivative 4a.

tallize with strand structures of different shapes. In the sodium

derivative 4a, the tetra-coordinate metal atoms are in distorted

tetrahedral environments with rather similar NaÀO and NaÀN

bond lengths and all sodium atoms are in identical crystallo-

Figure 3. Molecular structure and atom number scheme of [Mg{Dipp-N=

C(tBu)-N-C₂H₄-Py}₂] (3). The ellipsoids represent a probability of 30%; H

atoms are omitted.

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graphic positions. In the strand structure 4b, two kinds of po-

tassium atoms are present. The atom K1 binds side-on to two

aryl groups and two nitrogen bases N1. The other alkali metal

atom K2 binds to two crystallographically identical tetrahydro-

furan molecules and to the nitrogen bases N2 of two amidi-

nate ions; here the K2ÀO1 bond length is significantly shorter

than the K2ÀN2 distance.

cule A, Li1AÀC3A, 264.2(4) pm) or to a methylene fragment of

the 2-pyridylethyl group (molecule B, Li1BÀC19B, 275.6(5) pm).

The molecular structure and atom number scheme of the

calcium complex 7 is shown in Figure 8. The hexa-coordinate

calcium atom is in a distorted octahedral coordination sphere

with the anionic ligands in a cis arrangement; due to the bulki-

ness of the monodentate amidinate ions, a large N1ÀCa1ÀN3

bond angle of 115.46(7)8 is observed. The stronger electrostatic

attraction here leads to Ca1ÀN distances that are smaller than

the Ca1ÀO bond lengths.

The molecular structure and atom number scheme of Z-iso-

meric N-(2,6-diisopropylphenyl)pivalamidine 5 are represented

in Figure 6. The asymmetric unit also contains one ethanol

molecule. In the crystalline state, a strand structure is formed

through intermolecular N2ÀH···O_EtOHand O_EtOHÀH···N1 hydrogen

bridges. The ethyl group of the ethanol molecule shows a two-

site disordering. Both nitrogen atoms of the amidine show sp²-

hybridization and the bond angles lie rather close to 1208. This

structure allows a slight p-interaction within the 1,3-diazaallyl

fragment, whereas extension of this delocalization into the aryl

group seems to be impossible because the aryl group is twist-

ed for steric reasons. Therefore, the N1ÀC6 single bond of

142.9(2) pm is 8 pm longer than the N2ÀC1 single bond of the

1,3-diazaallyl moiety.

The lithium derivative 6 crystallizes with two forms in the

asymmetric unit (molecules A and B), which are both shown in

Figure 7. In both molecules, the lithium atoms bind to the pyr-

idyl moieties and the proximal nitrogen bases of the amidinate

units. Furthermore, the coordination spheres are terminated by

bidentate tmeda base groups. However, the Lewis acidic metal

ions show agostic interactions to the tert-butyl group (mole-

Figure 7. Molecular structures and atom number schemes of the two differ-

ent molecules of [(tmeda)Li{Dipp-N=C(tBu)-N-C₂H₄-Py}] (6). These molecules

differ by the agostic interactions to the tert-butyl group (top, molecule A)

and to the methylene unit of the 2-pyridylethyl group (bottom, molecule B).

The ellipsoids represent a probability of 30%; H atoms are only shown for

alkyl fragments involved in agostic bondings (dashed lines).

The molecular structures and atom number schemes of the

alkali metal complexes 9a and 9b are shown in Figure 9. The

presence of another Lewis base in the sidearm leads to dis-

crete dinuclear complexes with central four-membered A₂N₂

[A=Na (9a), K (9b)] rings. These small rings enforce short non-

bonding trans-annular A···A contacts of 300.8(1) and

340.86(8) pm for the sodium and potassium derivatives, re-

spectively. Ligated thf molecules complete the coordination

spheres of the alkali metals. In both complexes, the penta-co-

ordinate alkali metal atoms prefer the coordination to hard

Lewis donors rather than to the soft p-systems of the aryl moi-

eties, which now act as protecting groups at the periphery of

the molecules. A sixth coordination site is blocked by the iso-

propyl group of the Dipp substituent with the smallest Na···Ci_Pr

Figure 6. Molecular structure and atom number scheme of Dipp-N=C(tBu)-

NH₂(5). The ellipsoids represent a probability of 30%; carbon-bound H

atoms are neglected for clarity.

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Figure 8. Molecular structure and atom number scheme of [(thf)₄Ca{Dipp-N=

C(tBu)-N(H)}₂] (7). The ellipsoids represent a probability of 30%; all carbon-

bound H atoms are neglected for clarity.

and K···Ci_Prdistances being 357.9(2) and 336.9(3) pm, respec-

tively. The even shorter K···Ci_Prcontact clearly suggests agostic

bonding and lies on the order of magnitude for K···C p-interac-

tions as observed for the strand structure of 4b.

To discuss the structural peculiarities of the amidinates

(charge delocalization and isomerism) in dependency of the

metal (size and hardness) and the substitution pattern, select-

ed bond lengths and angles are listed in Table 2. For compari-

son reasons, the free amidines 1, 5, and 8 are also included.

The 1,3-diazaallyl fragments show negligible charge transfer to

the attached groups and undisturbed single bonds between

sp²-hybridized carbon and nitrogen atoms (average N_Dipp

_Dipp=140.5 pm) and between sp³-hybridized carbon and ni-

trogen atoms (average N_CH2ÀC_CH2=145.9 pm) are observed.

À

Figure 9. Molecular structures and atom number schemes of the dinuclear

complexes [(thf)Na{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9a, top) and [(thf)K{Dipp-N=

C(H)-N-C₂H₄-Py}]₂(9b, bottom). The ellipsoids represent a probability of

90%; H atoms are neglected for clarity reasons.

C

Table 2. Selected bond lengths and angles of Dipp-N=C(tBu)-N(H)-C₂H₄-Py (1), [{(Me₃Si)₂N}Ca{Dipp-N=C(tBu)-N-C₂H₄-Py}] (2a), [{(Me₃Si)₂N}Sr{Dipp-N=C(tBu)-

N-C₂H₄-Py}] (2b), [Mg{Dipp-N=C(tBu)-N-C₂H₄-Py}₂] (3), [(thf)₂Na{Dipp-N=C(tBu)-N(H)}] (4a), [(thf)₂K{Dipp-N=C(tBu)-N(H)}] (4b), Dipp-N=C(tBu)-NH₂(5),

[(tmeda)Li{Dipp-N=C(tBu)-N-C₂H₄-Py}] (6), [(thf)₄Ca{Dipp-N=C(tBu)-N(H)}₂] (7), Dipp-N=C(H)-N(H)-C₂H₄-Py (8), [(thf)Na{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9a), and

[(thf)K{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9b).

Compound

M

H

Isomer C_DippÀN_Dipp

C_NCNÀN_Dipp

C_NCNÀN_CH2

C_NCNÀC_tBu

N_CH2ÀC_CH2

C_Dipp-N_Dipp-C_NCNN_Dipp-C_NCN-N_CH2C_NCN-N_CH2-C_CH2[8]

[pm]

[8]

1

syn-Z 141.1(2)

syn-Z 141.0(2)

127.8(2)

128.0(2)

132.4(4)

131.7(4)

134.0(2)

131.1(2)

133.8(2)

132.2(3)

129.1(2)

131.6(3)

131.8(3)

131.6(3)

131.9(3)

129.0(5)

132.8(2)

133.4(2)

132.9(3)

135.9(2)

135.8(2)

135.4(4)

134.9(4)

132.9(2)

135.1(2)

131.8(2)

132.5(3)

134.9(2)

133.9(3)

133.5(3)

134.2(3)

134.4(5)

131.2(2)

130.3(2)

131.0(2)

153.9(2)

154.1(2)

155.0(4)

155.3(4)

155.5(2)

155.8(2)

153.6(3)

154.6(4)

153.0(2)

155.0(3)

155.1(3)

154.0(3)

–

145.4(2)

145.2(2)

147.0(4)

146.2(4)

145.0(2)

147.5(2)

90(2) (H)

85(3) (H)

86(2) (H)

146.4(3)

83(3) (H)

88(3) (H)

146.2(5)

145.1(2)

144.7(2)

145.1(2)

126.7(1)

126.1(1)

116.4(3)

117.7(3)

127.4(1)

131.9(1)

115.8(2)

116.5(2)

117.8(1)

128.7(2)

129.8(2)

118.9(2)

118.5(2)

119.9(3)

118.6(1)

119.7(2)

117.4(2)

128.6(1)

120.9(3)

121.7(3)

110.3(1)

130.3(1)

128.3(2)

123.8(2)

123.4(1)

132.8(2)

132.4(2)

128.5(2)

127.7(2)

129.0(4)

122.4(1)

121.8(2)

122.2(2)

128.7(1)

130.0(1)

121.2(3)

121.0(3)

129.4(1)

112.7(1)

110(2) (H)

108(2) (H)

119(2), 123(1) (H)

117.2(2)

2a

2b

3

Ca syn-Z 139.6(4)

Sr syn-Z 139.8(4)

Mg syn-E 141.5(2)

syn-Z 139.6(2)

Na syn-Z 142.0(2)

K

4a

4b

5

anti-Z 140.7(3)

Z 142.9(2)

H

6

Li syn-Z 138.4(3)

syn-Z 138.8(3)

Ca syn-Z 140.6(3)

syn-Z 140.0(3)

H^[a]anti-Z 143.0(5)

Na syn-E 140.2(2)

117.1(2)

7

106(2) (H)

107(2) (H)

122.3(4)

116.2(1)

116.8(2)

8

9a

9b

–

K

syn-E 139.1(2)

syn-E 140.1(2)

116.5(2)

[a] H atom was localized in the difference Fourier synthesis but an isotropic refinement of the parameters was impossible due to poor crystal quality.

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Compared with these bond lengths, the 1,3-diazaallyl units

show far-reaching charge delocalization and even for the pro-

tonated derivatives 1, 5, and 8, the C_NCNÀN_CH2bonds are signifi-

cantly shorter than a characteristic single bond. As expected,

the C_NCNÀC_tBubonds between the 1,3-diazaallyl fragments and

the tert-butyl groups are also long.

between 110.3(1)8 for 3 and 132.8(2)8 for 6. Similar observa-

tions are also true for the angles at the nitrogen atoms of the

amidinate ions.

Summary and Conclusions

The bond lengths between the metal (or hydrogen) and the

nitrogen bases are listed in Table 3. From the column with the

coordination numbers of the s-block metal atoms, it is obvious

that these amidinate ligands can adopt diverse coordination

modes. The coordination behavior is dominated by intramolec-

ular steric repulsion between the ligands and the tendency of

the metal to also form p-interactions with the bulky aryl

group. The hard metal ions lithium, sodium, and magnesium

avoid such side-on coordination to the Dipp substituents,

whereas the softer potassium, calcium, and strontium ions are

able to coordinate to the p-systems of the aryl group. In all

complexes [including the protonated forms (amidines)], the

N_CH2bases of the amidinates are part of the coordination

spheres of the metals and usually form the smallest MÀN dis-

tances; only the bis(trimethylsilyl)amido ligands in complexes

2a and 2b show shorter AeÀN bonds. This fact together with

the observation that the C_NCNÀN_Dippbond is usually shorter

than the C_NCNÀN_CH2bond verifies that the negative charge of

the amidinate ion is more expressed on the N_CH2base leading

to a stronger electrostatic attraction. The bulkiness of the Dipp

group often hinders a coordination of the attached nitrogen

atom and this group is often turned to the outside of the com-

plex.

We have demonstrated that the softness of the s-block metals

play a peculiar role when pivalamidine (1) is reacted with s-

block metal bases. The soft sodium and potassium bis(trime-

thylsilyl)amides lead to a b-deprotonation reaction immediately

followed by a deamidation process yielding the complexes

[(thf)₂Na{Dipp-N=C(tBu)-N(H)}] (4a) and [(thf)₂K{Dipp-N=C(tBu)-

N(H)}] (4b) as well as 2-vinylpyridine, whereas the lighter (and

harder) lithium bis(trimethylsilyl)amide deprotonates this ami-

dine and [(tmeda)Li{Dipp-N=C(tBu)-N-C₂H₄-Py}] (6) is formed

after addition of TMEDA. This strikingly different reaction be-

havior also initiated the investigation of this reaction with alka-

line earth metal-based metalation reagents. According to the

diagonal relationship in the periodic table, only deprotonation

is observed, yielding the pivalamidinates of magnesium,

[Mg{Dipp-N=C(tBu)-N-C₂H₄-Py}₂] (3), calcium, and strontium,

[{(Me₃Si)₂N}Ae{Dipp-N=C(tBu)-N-C₂H₄-Py}] with Ae being Ca (2a)

and Sr (2b), as also found for the lithiation reaction. Neverthe-

less, the metathetical approach of 4b with calcium diiodide

also allows the synthesis of the calcium derivative

[(thf)₄Ca{Dipp-N=C(tBu)-N(H)}₂] (7) with the dehydroaminated

ligand. The protonated form, Dipp-N=C(tBu)-NH₂(5), contains

an amino group, suggesting that the Dipp-bound nitrogen

atom is less basic than the other one. This is in agreement

with those derivatives with a 2-pyridylethyl group attached to

this nitrogen atom [derivatives Dipp-N=C(tBu)-N(H)-C₂H₄-Py (1)

and Dipp-N=C(H)-N(H)-C₂H₄-Py (8)]. Less strained formamidine

Steric requirements as discussed above also lead to distor-

tion of the amidinate backbone (Table 2). The bond angles

seem to be quite flexible and the N_DippÀC_NCNÀN_CH2values vary

Table 3. Selected bond lengths (pm) of Dipp-N=C(tBu)-N(H)-C₂H₄-Py (1), [{(Me₃Si)₂N}Ca{Dipp-N=C(tBu)-N-C₂H₄-Py}] (2a), [{(Me₃Si)₂N}Sr{Dipp-N=C(tBu)-N-C₂H₄-

Py}] (2b), [Mg{Dipp-N=C(tBu)-N-C₂H₄-Py}₂] (3), [(thf)₂Na{Dipp-N=C(tBu)-N(H)}] (4a), [(thf)₂K{Dipp-N=C(tBu)-N(H)}] (4b), Dipp-N=C(tBu)-NH₂(5), [(tmeda)Li-

{Dipp-N=C(tBu)-N-C₂H₄-Py}] (6), [(thf)₄Ca{Dipp-N=C(tBu)-N(H)}₂] (7), Dipp-N=C(H)-N(H)-C₂H₄-Py (8), [(thf)Na{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9a) and of

[(thf)K{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9b) (C.N.(M) coordination number of the metal).

Compound

M

H

Isomer

C.N.(M)

MÀN_Dipp

–

MÀN_CH2

87 (2) (H)

238.5(3)

254.0(3)

205.2(1)

211.4(1)

233.5(2)

275.0(2)

87 (2) (H)

204.5(4)

203.1(4)

236.5(2)

88 (H)^[e]

245.5(1), 251.6(1)

282.8(2), 283.4(2)

282.3(2), 282.5(2)

MÀN_Py

–

MÀN_NSi2

–

[a]

1

syn-Z

syn-E

syn-Z

anti-Z

Z

syn-Z

anti-Z

syn-E

–

[a]

–

2a

2b

3

Ca

Sr

Mg

3+6^[b]

245.5(3)

259.6(3)

230.7(1)

216.5(1)

–

230.4(3)

244.5(3)

–

5

4

221.0(1)

–

237.8(2)

274.4(2)

–

4a

4b

5

Na

K

H

4/2+12^[c]

–

[d]

–

6

Li

4

6

212.5(4)

213.9(5)

–

247.2(1)

284.6(2)

293.1(2)

7

Ca

–

[d]

8

9a

9b

H

Na

K

–

5

246.9(1)

280.0(2)

289.5(2)

[a] Intramolecular N_CH2ÀH···N_Pyhydrogen bridge. [b] The Ae metals bind to three nitrogen bases and six carbon atoms of the aryl group; the agostic interac-

tions are neglected. [c] Two K atoms in different coordination spheres with one K binding to two N bases and side-on to two aryl groups. [d] Intermolecu-

lar hydrogen bridge. [e] H atom was localized in the difference Fourier synthesis but an isotropic refinement of the parameters was impossible due to

poor crystal quality.

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Dipp-N=C(H)-N(H)-C₂H₄-Py (8) can be metalated at the form-

amidine functionality by sodium or potassium bis(trimethyl-

silyl)amide, yielding the corresponding dinuclear complexes

[(thf)Na{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9a) or [(thf)K{Dipp-N=C(H)-

N-C₂H₄-Py}]₂(9b), respectively. This finding verifies that the de-

hydroamination reaction requires steric pressure and that lack

of strain leads to the expected metalation reaction of the ami-

dine unit and finally to the complexes 9a and 9b. This reaction

pattern is presented in Scheme 3.

form either intra- or intermolecular hydrogen bridges. The

metal additionally coordinates to the pyridyl group or to N_Dipp

and the soft metal ions K⁺, Ca²⁺, and Sr²⁺also tend to show

p-interactions with the side-on bound aryl groups. In summary,

these bulky ligands show a diverse coordination chemistry to

s-block metals and even a surprising reactivity with metalation

reagents depending on the softness of the metal and the bulk-

iness of the ligand.

In all of these compounds, the charge delocalization is limit-

ed to the 1,3-diazaallyl unit. The bulky Dipp group is turned

out of the allyl plane hindering effective p-interaction with this

aromatic substituent. The Dipp-bound nitrogen atom N_Dippis

sterically shielded and less negative than the other allyl nitro-

gen base N_CH2and therefore, the hydrogen atoms in amidines

and the s-block metal ions in their amidinates always bind to

this aza-base. In addition, the hydrogen atoms in amidines

Experimental Section

General considerations: All manipulations were carried out under

a nitrogen atmosphere using standard Schlenk techniques. The sol-

vents THF and toluene were dried over KOH and subsequently dis-

tilled over sodium/benzophenone under a nitrogen atmosphere

prior to use. Deuterated solvents were dried over sodium, de-

gassed, and saturated with nitrogen. The yields given are not opti-

Scheme 3. Bases with soft metal ions and overcrowded amidines enforce dehydroamination of the amidines (red arrows at the bottom), whereas bases with

harder metal ions or lack of steric pressure lead to the expected metalating reactions (black arrows), yielding the corresponding amidinates.

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mized. ¹H and ¹³C{¹H} NMR spectra were recorded on Bruker

Avance200, Avance400, and Avance600 spectrometers. For multi-

plets the chemical shifts refer to the centers of the signals, ranges

are only given for overlapping resonances. All NMR spectra are

shown in the Supporting Information. Chemical shifts are reported

in parts per million. In some cases ¹H-¹³C{¹H} HSQC, ¹H-

¹³C{¹H} HMBC, and H-H COSY NMR experiments were performed for

the assignment of the resonances. For mass spectrometric investi-

gations, the spectrometers ThermoFinnigan MAT95XL and Finnigan

SSQ710 were at our disposal. IR spectra were recorded with

a Bruker ALPHA FT-IR spectrometer. Starting [(thf)₂Ca{N(SiMe₃)₂}₂]

and [(thf)₂Sr{N(SiMe₃)₂}₂] were prepared according to literature pro-

tocols.^[23c,26]

toluene (8 mL) at RT and the reaction mixture was stirred at RT for

3.5 h. Thereafter, all volatiles were removed in vacuo and 117 mg

of 2a (59%) were isolated as orange crystals after recrystallization

from toluene. Physical data show

a 6% contamination by

[(thf)₂Ca{N(SiMe₃)₂}₂]. M.p. 156–1588C (dec.); ¹H NMR (400.13 MHz,

C₆D₆, 297.0 K): d 7.87 (m, 1H, Py N-CH), 7.17 (m, 2H, Dipp m-CH),

6.95–6.87 (m, 2H, Py m-CH, Dipp p-CH), 6.48–6.43 (m, 2H, Py p-CH,

Py o-CH), 3.74 (m, 2H, N-CH₂-), 3.59 (m, 2H, thf O-CH₂-), 3.17 (sept,

³J_HH=6.8 Hz, 2H, CH(CH₃)₂), 2.84 (m, 2H, Py-CH₂-), 1.44 (s, 9H,

3

C(CH₃)₃), 1.30 (d, J_HH=6.8 Hz, 7H, CH(CH₃)₂), 1.07 (d, J_HH=6.8 Hz,

5H, CH(CH₃)₂), 0.36 (s, 2H, [(thf)₂Ca{N(SiMe₃)₂}₂], Si(CH₃)₃), 0.31 (s,

18H, Si(CH₃)₃), 0,10 ppm (s, 4H, HN{Si(CH₃)₃}₂); ¹³C NMR

(100.63 MHz, C₆D₆, 300.0 K): d 172.7 (^qC), 162.4 (Py i-C), 156.4 (Dipp

i-C), 147.3 (Py N-CH), 143.2 (Dipp o-C), 138.7 (Py m-C), 124.9 (Py o-

C), 124.1 (Dipp m-C), 121.3 (Py p-C), 120.4 (Dipp p-C), 69.3 (thf, O-

CH₂-), 49.2 (N-CH₂-), 40.1 (C(CH₃)₃), 39.0 (Py-CH₂-), 30.6 (C(CH₃)₃),

28.7 (CH(CH₃)₂), 25.2 (thf, -CH₂-), 23.5/21.9 (CH(CH₃)₂), 5.9 (Si(CH₃)₃),

2.7 ppm (HN{Si(CH₃)₃}₂); MS (DEI): m/z (%) 564 (2, [M]⁺), 521 (10,

[MÀC₃H₇]⁺), 365 (40, [L]⁺), 322 (45, [C₂₁H₂₈N₃]⁺), 308 (20,

[C₂₀H₂₆N₃]⁺), 260 (10, [C₁₇H₂₈N₂]⁺) 244 (25, [C₁₆H₂₃N₂]⁺; [C₁₇H₂₇N]⁺),

229 (90, [C₁₆H₂₃N]⁺; [C₁₅H₂₁N₂]⁺), 203 (45, [C₁₃H₁₉N₂]⁺), 186 (35,

[C₁₂H₁₄N₂]⁺; [C₁₃H₁₆N]⁺), 162 (40, [C₁₀H₁₄N₂]⁺; [C₁₁H₁₆N]⁺), 146 (100,

[C₁₁H₁₄]⁺; [C₁₀H₁₂N]⁺), 130 (35, [C₉H₈N]⁺), 106 (95, [C₇H₈N]⁺), 57 (10,

[C₃H₇N]⁺); MS (Micro-ESI pos. in THF and MeOH): m/z (%) 366 (<1,

[L+H]⁺), 261 (3, [C₇H₁₁N]⁺), 244 (100, [C₁₆H₂₄N₂]⁺; [C₁₇H₂₇N]⁺), 188

(18, [C₁₂H₁₆N₂]⁺; [C₁₃H₁₈N]⁺), 146 (5, [C₁₁H₁₄]⁺; [C₁₀H₁₂N]⁺); IR (pure):

v˜ =3325 (vw), 3055 (vw), 2955 (w), 2863 (w), 1655 (m), 1586 (w),

1534 (w), 1469 (w), 1437 (w), 1381 (w), 1360 (w), 1341 (w), 1312

(w), 1289 (w), 1257 (w), 1231 (w), 1104 (w), 1071 (w), 1032 (w),

1011 (w), 933 (w), 879 (w), 813 (w), 784 (m), 747 (m), 681 (w),

657 cm^À1(w); elemental analysis (%) calcd for (C₃₀H₅₂CaN₄Si₂,

565.01 gmol^À1): C 63.77, H 9.28, N 9.92; found: C 63.55, H 9.24, N

9.74.

Synthesis of N-(2,6-diisopropylphenyl)-N’-(2-pyridylethyl)pival-

amidine (Dipp-N=C(tBu)-N(H)-C₂H₄-Py) (1): Dipp-NH₂(9.4 mL,

50.0 mmol) in 40 mL of anhydrous pyridine and pivaloyl chloride

(6.2 mL, 50.0 mmol) gave 12.34 g (47.2 mmol, 94%) of Dipp-

N(H)CO(tBu). The purity of the product was monitored by use of

NMR spectroscopy. The reaction of Dipp-N(H)CO(tBu) (12.0 g,

45.9 mmol) with SOCl₂(11.0 mL, 151.6 mmol) yielded 11.63 g

(41.6 mmol, 91%) of pure Dipp-N=C(tBu)Cl. To a toluene (15 mL)

solution of NH₂C₂H₄-Py (1.18 g, 10.6 mmol) was added dropwise

Dipp-N=C(tBu)Cl (2.99 g, 10.6 mmol) at room temperature (RT). The

reaction mixture was stirred at 1508C for 24 h to give a clear pale

brown solution. Subsequently, all volatiles were removed in vacuo.

The remaining solid was dissolved in 100 mL of dichloromethane

and washed two times with aqueous Na₂CO₃solution (50 mL, 2%).

After removal of the solvent, the precipitate was recrystallized

1

from n-pentane yielding 2.47 g of 1 (64%). M.p. 58–608C; H NMR

(400.13 MHz, CDCl₃, 298.0 K): d 8.48 (m, 1H, Py N-CH), 7.56 (td,

³J_HH=7.7 Hz, ⁴J_HH=1.8 Hz, 1H, Py m-CH), 7.12 (m, 1H, Py p-CH),

6.98 (m, 2H, Dipp m-CH), 6.94 (m, 1H, Py o-CH), 6.89 (m, 1H, Dipp

p-CH), 5.61 (broad, 1H, NH), 3.01–2.93 (m, 4H, CH(CH₃)₂, N-CH₂-),

2.67 (m, 2H, Py-CH₂-), 1.27 (s, 9H, C(CH₃)₃), 1.16–1.15 ppm (m, 12H,

CH(CH₃)₂); ¹³C NMR (100.62 MHz, CDCl₃, 298.0 K): d 159.9 (Py i-C),

157.4 (^qC), 149.1 (Py N-CH), 147.0 (Dipp i-C), 137.6 (Dipp o-C), 136.8

(Py m-C), 123.1 (Py o-C), 122.0 (Dipp m-C), 121.7 (Py p-C), 120.8

(Dipp p-C), 42.7 (N-CH₂-), 38.8 (C(CH₃)₃), 37.6 (Py-CH₂-), 29.2

(C(CH₃)₃), 28.4 (CH(CH₃)₂), 23.2/22.6 ppm (CH(CH₃)₂); ¹H NMR

(600.15 MHz, C₆D₆, 297.0 K): d 8.23 (m, 1H, Py N-CH), 7.18 (m, 2H,

Synthesis of [{(Me₃Si)₂N}Sr{Dipp-N=C(tBu)-N-C₂H₄-Py}] (2b): A so-

lution of amidine 1 (62 mg, 0.17 mmol) in toluene (2 mL) was

added to a solution of [(thf)₂Sr{N(SiMe₃)₂}₂] (94 mg, 0.17 mmol) in

toluene (3 mL) at RT and the reaction mixture was stirred at RT for

4 h. Thereafter, all volatiles were removed in vacuo and 67 mg of

2b (64%) were isolated as yellow crystals after recrystallization

from toluene. The same procedure using amidine 1 (146 mg,

0.4 mmol) and [(thf)₂Sr{N(SiMe₃)₂}₂] (440 mg, 0.8 mmol) in toluene

(20 mL) also led to the formation of 2b (110 mg, 18%). M.p. 149–

3

4

Dipp m-CH), 7.10 (m, 1H, Dipp p-CH), 6.91 (td, J_HH=7.7 Hz, J_HH

=

3

1.7 Hz, 1H, Py m-CH), 6.51 (m, 1H, Py p-CH), 6.40 (d, J_HH=7.7 Hz,

1H, Py o-CH), 6.11 (broad, 1H, NH), 3.29 (sept, ³J_HH=6.6 Hz, 2H,

CH(CH₃)₂), 3.04 (m, 2H, N-CH₂-), 2.30 (t, J_HH=6.0 Hz, 2H, Py-CH₂-),

1

1538C (dec.); H NMR (400.13 MHz, C₆D₆, 297.0 K): d 7.75 (m, 1H, Py

3

N-CH), 7.08 (m, 2H, Dipp m-CH), 6.87–6.83 (m, 2H, Py m-CH, Dipp

p-CH), 6.44–6.42 (m, 2H, Py p-CH, Py o-CH), 3.80 (m, 2H, N-CH₂-),

1.39 (s, 9H, C(CH₃)₃), 1.32 ppm (m, 12H, CH(CH₃)₂); ¹³C NMR

(150.91 MHz, C₆D₆, 297.0 K): d 160.6 (Py i-C), 157.2 (^qC), 149.0 (Py N-

CH), 147.7 (Dipp i-C), 137.7 (Dipp o-C), 136.4 (Py m-C), 128.4 (Dipp

m-C), 123.0 (Dipp p-C), 122.4 (Py, o-C), 121.4 (Py p-C), 43.1 (N-CH₂-),

39.1 (C(CH₃)₃), 37.1 (Py-CH₂-), 29.4 (C(CH₃)₃), 28.9 (CH(CH₃)₂), 23.6/

22.6 ppm (CH(CH₃)₂); MS (DEI): m/z (%) 365 (20, [M]⁺), 322 (20,

[C₂₁H₂₈N₃]⁺), 308 (10, [C₂₀H₂₆N₃]⁺), 244 (10, [C₁₆H₂₄N₂]⁺; [C₁₇H₂₇N]⁺),

229 (30, [C₁₅H₂₁N₂]⁺; [C₁₆H₂₃N]⁺), 186 (20, [C₁₃H₁₆N]⁺; [C₁₃H₁₆N]⁺), 146

(20, [C₁₁H₁₄]⁺; [C₁₀H₁₂N]⁺), 121 (20, [C₇H₉N₂]⁺), 106 (100, [C₇H₈N]⁺),

93 (60, [C₆H₇N]⁺), 78 (20, [C₅H₄N]⁺), 57 (60, [C₃H₇N]⁺), 43 (20,

[C₃H₇]⁺), 41 (30, [C₂H₃N]⁺). IR (pure): v˜ =3498 (w), 3395 (w), 3324

(w), 3055 (w), 2957 (w), 2924 (w), 2863 (w), 1650 (w), 1586 (w),

1532 (w), 1469 (w), 1429 (w), 1258 (w), 1229 (w), 1095 (w), 1009

(w), 770 (w), 724 (w), 550 (vw), 502 cm^À1(vw); elemental analysis

(%) calcd for C₂₄H₃₅N₃(365.55 gmol^À1): C, 78.85; H 9.65; N 11.49;

found: C, 78.20; H, 9.87; N, 11.14.

3

3.18 (sept, J_HH=6.8 Hz, 2H, CH(CH₃)₂), 2.69 (m, 2H, Py-CH₂-), 1.54

3

(s, 9H, C(CH₃)₃), 1.25 (d, J_HH=6.8 Hz, 6H, CH(CH₃)₂), 1.00 (d, J_HH

=

6.8 Hz, 6H, CH(CH₃)₂), 0.32 (s, 18H, Si(CH₃)₃), 0.10 ppm (s, 3H,

HN{Si(CH₃)₃}₂); ¹³C NMR (100.61 MHz, C₆D₆, 297.0 K): d 172.2 (^qC),

162.5 (Py i-C), 159.0 (Dipp i-C), 146.9 (Py N-CH), 144.3 (Dipp o-C),

138.5 (Py m-C), 124.8 (Py o-C), 124.3 (Dipp m-C), 121.5 (Py p-C),

119.7 (Dipp p-C), 49.7 (N-CH₂-), 39.6 (C(CH₃)₃), 39.2 (Py-CH₂-), 30.8

(C(CH₃)₃), 28.7 (CH(CH₃)₂), 23.3/21.9 (CH(CH₃)₂), 5.8 (Si(CH₃)₃),

2.7 ppm (HN{Si(CH₃)₃}₂); MS (DEI): m/z (%) 365 (75, [L]⁺), 322 (70,

[C₂₁H₂₈N₃]⁺), 308 (20, [C₂₀H₂₆N₃]⁺), 259 (5, [C₁₇H₂₇N₂]⁺) 244 (20,

[C₁₆H₂₃N₂]⁺; [C₁₇H₂₇N]⁺), 229 (100, [C₁₆H₂₃N]⁺; [C₁₅H₂₁N₂]⁺), 186 (20,

[C₁₂H₁₄N₂]⁺; [C₁₃H₁₆N]⁺), 146 (15, [C₁₁H₁₄]⁺; [C₁₀H₁₂N]⁺), 106 (10,

[C₇H₈N]⁺), 58 (2, [C₃H₆N]⁺); MS (Micro-ESI pos. in THF+MeOH): m/z

(%) 366 (60, [L+H]⁺), 261 (3, [C₇H₁₁N]⁺), 244 (100, [C₁₆H₂₄N₂]⁺;

[C₁₇H₂₇N]⁺); IR (pure): v˜ =3366 (vw), 3053 (vw), 2950 (w), 2866 (w),

1651 (w), 1599 (w), 1529 (w), 1477 (w), 1435 (w), 1392 (w), 1355

(w), 1341 (w), 1311 (w), 1246 (w), 1234 (w), 1102 (w), 1063 (m),

1010 (w), 932 (w), 878 (w), 813 (m), 791 (m), 748 (m), 659 (w),

Synthesis of [{(Me₃Si)₂N}Ca{Dipp-N=C(tBu)-N-C₂H₄-Py}] (2a): A so-

lution of amidine 1 (130 mg, 0.35 mmol) in toluene (8 mL) was

added to a solution of [(thf)₂Ca{N(SiMe₃)₂}₂] (270 mg, 0.53 mmol) in

Chem. Eur. J. 2016, 22, 10944 – 10959

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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper

638 cm^À1(w); elemental analysis (%) calcd for C₃₀H₅₂SrN₄Si₂

(612.55 gmol^À1): C, 58.82; H 8.56; N 9.15; found: C, 59.03; H, 8.41;

N, 9.05.

handling and weighing, no reliable CHN elemental analysis data

were obtained.

Synthesis of [(thf)₂K{Dipp-N=C(tBu)-N(H)}] (4b): method 1: A so-

lution of 1 (295 mg, 0.8 mmol) in THF (5 mL) was added to a sus-

pension of KH (53 mg, 1.3 mmol) in THF (10 mL) at RT, and the re-

action mixture was stirred at RT for 24 h. Thereafter, the mixture

was filtered and all volatiles were removed in vacuo. 110 mg of 4b

(31%) were isolated pale as yellow crystals after recrystallization

from THF and dried in vacuo (which removes ligated ether).

method 2: A solution of 1 (366 mg, 1.0 mmol) in toluene (7.5 mL)

was added to a solution of KN(SiMe₃)₂(199 mg, 1.0 mmol) in tolu-

ene (7.5 mL) at RT and the reaction mixture was stirred at RT for

72 h. During this time, formation of a pale orange solid was ob-

served. This precipitate was collected by filtration, consisting of the

solvent-free potassium salt (176 mg, 0.59 mmol, 59%). Recrystalli-

zation of the solid from 0.3 mL THF and storage at 58C gave 4b as

pale yellow crystals. M.p. 122–1278C (dec.); ¹H NMR (400.13 MHz,

C₆D₆, 297.1 K): d 7.14 (m, 1H, Dipp p-CH), 7.06 (m, 2H, Dipp m-CH),

Synthesis of [Mg{Dipp-N=C(tBu)-N-C₂H₄-Py}₂] (3): To a solution of

amidine 1 (366 mg, 1.0 mmol) in n-pentane (10 mL) was added

1.1 mL of a 1m Mg(nBu)₂solution in n-heptane at 08C and this re-

action mixture was stirred at RT for 24 h. During this time, forma-

tion of a pale yellow solid was observed. Toluene was added suc-

cessively to get a clear solution, and after several days, 234 mg of

3 (31%) were isolated. M.p.>3508C; ¹H NMR (400.13 MHz, C₆D₆,

3

297.3 K): d 8.30 (d, J_HH=4.6 Hz, 1H, Py N-CH), 7.76 (m, 1H, Py N-

3

CH), 7.05 (t, J_HH=7.5 Hz, 1H, Dipp p-CH), 7.01 (t, J_HH=7.5 Hz, 1H,

Dipp p-CH), 6.90–7.27 (m, 4H, Dipp m-CH), 6.87 (m, 1H, Py m-CH),

6.66 (m, 1H, Py p-CH), 6.63 (td, ³J_HH=7.7 Hz, J_HH=1.7 Hz, 1H, Py

m-CH), 6.55 (d, J_HH=7.7 Hz, 1H, Py o-CH), 6.18 (m, 1H, Py p-CH),

4

3

6.07 (d, J_HH=7.8 Hz, 1H, Py o-CH), 4.21 (m, 1H, CH(CH₃)₂), 3.87 (m,

2H, N-CH₂-), 3.76 (m, 1H, CH(CH₃)₂), 3.62 (m, 2H, N-CH₂-), 3.47 (m,

1H, CH(CH₃)₂), 3.05 (m, 1H, CH(CH₃)₂), 2.75 (m, 2H, Py-CH₂-), 2.54

(m, 2H, Py-CH₂-), 1.49 (s, 9H, C(CH₃)₃), 1.25 (s, 9H, C(CH₃)₃), 0.04–

1.65 ppm (m, 42H, C(CH₃)₃, CH(CH₃)₂); ¹³C NMR (100.61 MHz, C₆D₆,

297.3 K): d 176.7 (^qC), 165.0 (Py i-C), 164.5 (^qC), 162.8 (Py i-C), 151.8

(Dipp i-C), 149.9 (Py N-CH), 146.9 (Dipp i-C), 146.7 (Py N-CH), 142.2/

142.0 (Dipp o-C), 138.4/138.2 (Py, m-C), 125.4/124.7 (Py, o-C), 123.6

(Dipp m-C), 122.3 (Dipp p-C), 121.6 (Py p-C), 121.6 (Dipp m-C),

121.1 (Py p-C), 118.0 (Dipp p-C), 49.2/46.7 (N-CH₂-), 40.3 (C(CH₃)₃),

40.0/38.1 (Py-CH₂-), 30.2/30.0 (C(CH₃)₃), 29.3 (CH(CH₃)₂), 28.9

(CH(CH₃)₂), 25.2 (CH(CH₃)₂), 24.2/14.0 ppm (CH(CH₃)₂); MS (DEI): m/z

(%) 753 (1, [M]⁺), 739 (1, [C₄₇H₆₆MgN₆]⁺), 722 (1, [C₄₆H₆₂MgN₆]⁺), 710

(2, [C₄₅H₆₁MgN₆]⁺), 648 (10, [C₄₁H₆₂MgN₅]⁺), 365 (100, [L]⁺), 322 (50,

[C₂₁H₂₈N₃]⁺), 308 (17, [C₂₀H₂₆N₃]⁺), 260 (44, [C₁₇H₂₈N₂]⁺) 244 (27,

[C₁₆H₂₄N₂]⁺; [C₁₇H₂₇N]⁺), 203 (68, [C₁₃H₁₉N₂]⁺), 106 (43, [C₇H₈N]⁺), 93

(30, [C₆H₇N]⁺), 57 (21, [C₃H₇N]⁺), 41 (30, [C₂H₃N]⁺); IR (pure): v˜ =

2957 (w), 2927 (w), 2866 (w), 1650 (w), 1588 (w), 1530 (w), 1462

(w), 1432 (w), 1380 (w), 1359 (w), 1329 (w), 1259 (w), 1230 (w),

1095 (w), 1011 (w), 935 (w), 786 (w), 769 (w), 747 (w), 674 cm^À1(w).

Due to the sensitivity of this compound during handling and

weighing, no reliable CHN elemental analysis data were obtained.

3

3.42 (broad, 1H, NH), 3.05 (sept, J_HH=6.8 Hz, 2H, CH(CH₃)₂), 1.20–

1.18 (m, 12H, CH(CH₃)₂), 1.06 ppm (s, 9H, C(CH₃)₃). ¹³C NMR

(100.61 MHz, C₆D₆, 297.1 K): d 161.1 (^qC), 145.5 (Dipp i-C), 138.9

(Dipp o-C), 123.6 (Dipp m-C), 123.2 (Dipp p-C), 37.0 (C(CH₃)₃), 28.5

1

(C(CH₃)_3,CH(CH₃)₂), 23.7/23.6 ppm (CH(CH₃)₂); H NMR (250.13 MHz,

[D₈]THF, 300.0 K): d 7.02 (m, 2H, Dipp m-CH), 6.85 (m, 1H, Dipp p-

CH), 4.88 (broad, 1H, NH), 2.98 (sept, ³J_HH=6.9 Hz, 2H, CH(CH₃)₂),

1.31 (s, 9H, C(CH₃)₃), 1.14 ppm (m, 12H, CH(CH₃)₂); ¹³C NMR

(62.90 MHz, [D₈]THF, 300.0 K): 162.6 (^qC), 146.7 (Dipp i-C), 139.3

(Dipp o-C), 123.5 (Dipp m-C), 122.7 (Dipp p-C), 37.8 (C(CH₃)₃), 28.9

(C(CH₃)₃), 28.8 CH(CH₃)₂), 23.8/23.7 ppm (CH(CH₃)₂); MS (DEI): m/z

(%) 260 (52, [C₁₇H₂₈N₂]⁺), 245 (31, [C₁₆H₂₄N₂]⁺; [C₁₇H₂₈N]⁺), 217 (36,

[C₁₄H₂₁N₂]⁺), 203 (27, [C₁₃H₁₉N₂]⁺), 186 (20, [C₁₃H₁₆N]⁺; [C₁₃H₁₆N]⁺), 41

(35, [C₂H₃N]⁺, 39 (100). IR (pure): v˜ =3499 (vw), 3394 (vw), 2957 (w),

2867 (w) 1647 (w), 1624 (w), 1588 (w), 1473 (w), 1458 (w), 1379 (w),

1325 (w), 1250 (w), 1012 (m), 980 (m), 943 (m), 847 (m), 769 (m),

684 (m), 645 cm^À1(m). Due to the sensitivity of this compound

during handling and weighing, no reliable CHN elemental analysis

data were obtained.

Synthesis of Dipp-N=C(tBu)-NH₂(5): In order to obtain the hydro-

lysis product, 8 mL of the reaction mixture of 2a including amidine

1 (200 mg, 0.5 mmol) and NaN(SiMe₃)₂(100 mg, 0.5 mmol) in THF

was treated with water (4 mL) and extracted with toluene (4 mL).

The organic layer was collected and after removal of the solvent,

the precipitate was recrystallized from n-pentane yielding 100 mg

Synthesis of [(thf)₂Na{Dipp-N=C(tBu)-N(H)}] (4a): A solution of

1 (291 mg, 0.8 mmol) in THF (4 mL) was added to a solution of

NaN(SiMe₃)₂(160 mg, 0.9 mmol) in THF (5 mL) at RT and the reac-

tion mixture was stirred at RT for 24 h. Thereafter, all volatiles were

removed in vacuo and 107 mg of 4a (31%) were isolated as yellow

crystals after recrystallization from THF and dried in vacuo (which

removes ligated ether). M.p. 145–1478C (dec.); ¹H NMR

(300.19 MHz, C₆D₆, 299.1 K): d 7.14 (m, 1H, Dipp p-CH), 7.07 (m, 2H,

Dipp m-CH), 3.49–3.42 (broad, 2H, NH), 3.42 (broad, 2H, NH), 3.04

(sept, ³J_HH=6.6 Hz, 2H, CH(CH₃)₂), 1.19 (m, 12H, CH(CH₃)₂),

1.06 ppm (s, 9H, C(CH₃)₃); ¹³C NMR (100.61 MHz, C₆D₆, 297.0 K): d

161.1 (^qC), 145.5 (Dipp i-C), 138.9 (Dipp o-C), 123.6 (Dipp m-C),

123.2 (Dipp p-C), 37.0 (C(CH₃)₃), 28.5 (C(CH₃)_3,CH(CH₃)₂), 23.7

(CH(CH₃)₂), 23.6 ppm (CH(CH₃)₂); MS (DEI): m/z (%) 427 (5, [M]⁺),

413 (5, [M - CH₃]⁺), 260 (20, [C₁₇H₂₈N₂]⁺), 244 (20, [C₁₆H₂₄N₂]⁺;

[C₁₇H₂₇N]⁺), 229 (10, [C₁₅H₂₁N₂]⁺; [C₁₆H₂₃N]⁺), 217 (30, [C₁₄H₂₁N₂]⁺),

203 (100, [C₁₃H₁₉N₂]⁺), 186 (30, [C₁₃H₁₆N]⁺; [C₁₃H₁₆N]⁺), 146 (20,

[C₁₁H₁₄]⁺; [C₁₀H₁₂N]⁺), 118 (20, [C₉H₁₀]⁺), 106 (65, [C₇H₈N]⁺), 93 (35,

[C₆H₇N]⁺), 77 (20, [C₅H₃N]⁺), 57 (90, [C₃H₇N]⁺), 41 (65, [C₂H₃N]⁺); MS

(Micro-ESI pos. in THF+MeOH): m/z (%) 261 (100, [C₁₇H₂₉N₂]⁺), 244

(30, [C₁₆H₂₄N₂]⁺; [C₁₇H₂₇N]⁺); IR (pure): v˜ =3497 (vw), 3394 (vw),

2956 (w), 2867 (w), 1647 (w), 1624 (w), 1588 (w), 1523 (w), 1459

(w), 1433 (w), 1395 (w), 1360 (w), 1325 (w), 1252 (m), 1212 (w),

1056 (w), 997 (m), 853 (w), 794 (m), 768 (m), 704 (w), 659 (m),

542 cm^À1(w). Due to the sensitivity of this compound during

1

of 5 (77%). M.p. 140–1438C; H NMR (400.13 MHz, CDCl₃, 297.0 K):

d 7.10 (m, 2H, Dipp m-CH), 6.98 (m, 1H, Dipp p-CH), 4.21 (broad,

3

2H, NH₂), 2.96 (sept, J_HH=6.8 Hz, 2H, CH(CH₃)₂), 2.67 (m, 2H, Py-

CH₂-), 1.35 (s, 9H, C(CH₃)₃), 1.16 ppm (m, 12H, CH(CH₃)₂); ¹³C NMR

(100.62 MHz, CDCl₃, 298.0 K): d 162.2 (^qC), 144.5 (Dipp i-C), 139.2

(Dipp o-C), 123.3 (Dipp m-C), 122.9 (Dipp p-C), 37.1 (C(CH₃)₃), 28.7

(C(CH₃)₃), 28.0 (CH(CH₃)₂), 23.8/23.4 ppm (CH(CH₃)₂); MS (DEI): m/z

(%) 308 (1, [M+EtOH]⁺), 260 (80, [M]⁺), 245 (50, [C₁₇H₂₇N]⁺;

[C₁₆H₂₅N₂]⁺), 229 (10, [C₁₆H₂₃N]⁺; [C₁₅H₂₁N₂]⁺), 217 (70, [C₁₄H₂₁N₂]⁺),

203 (100, [C₁₃H₁₉N₂]⁺), 186 (40, [C₁₂H₁₄N₂]⁺; [C₁₃H₁₆N]⁺), 175 (15,

[C₁₁H₁₅N₂]⁺), 160 (10, [C₁₀H₁₂N₂]⁺), 144 (15, [C₁₀H₁₀N]⁺), 130 (10,

[C₉H₈N]⁺), 115 (10, [C₈H₅N]⁺), 91 (10, [C₇H₇]⁺), 77 (5, [C₆H₅]⁺), 57 (15,

[C₄H₉]⁺; [C₃H₇N]⁺), 43 (5, [C₃H₇]⁺), 41 (15, [CHN₂]⁺), 29 (5, [C₂H₅]⁺); IR

(pure): v˜ =3498 (w), 3395 (w), 3057 (vw), 2958 (m), 2866 (m), 1646

(s), 1624 (m), 1587 (s), 1521 (m), 1473 (m), 1460 (m), 1433 (m), 1394

(m), 1378 (m), 1360 (m), 1346 (m), 1325 (m), 1254 (m), 1212 (m),

1177 (w), 1148 (w), 1102 (m), 1056 (m), 1038 (m), 935 (m), 866 (m),

832 (m), 797 (m), 768 (s), 747 (m), 724 (m), 684 cm^À1(w); elemental

analysis (%) calcd for C₁₇H₂₈N (260.42 gmol^À1): C, 78.41; H 10.84; N

10.76; found: C, 77.33; H, 10.28; N, 10.39.

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Synthesis of [(tmeda)Li{Dipp-N=C(tBu)-N-C₂H₄-Py}] (6): To a sus-

pension of [(Et₂O)LiN(SiMe₃)₂] (160 mg, 0.66 mmol) in a mixture of

TMEDA (0.6 mL) and toluene (3 mL) was added a solution of

1 (215 mg, 0.6 mmol) in toluene (5 mL) at RT. The reaction mixture

was stirred at RT for 24 h and thereafter, concentrated to a volume

of approximately 2 mL. Storage at À208C for several days led to

formation of pale yellow crystals of 6, which were collected by fil-

tration and washed with n-pentane (113 mg, 23%). Physical data of

the residue show that a mixture of 6 and 1 in a ratio of 5:1 was

to the sensitivity of this compound during handling and weighing,

no reliable CHN elemental analysis data were obtained.

Synthesis of N-(2,6-diisopropylphenyl)-N’-(2-pyridyl)ethyl form-

amidine (Dipp-N=C(H)-N(H)-C₂H₄-Py) (8): Dipp-NH₂(10.6 mL,

56.4 mmol), triethylorthoformate (11.2 mL, 56.4 mmol), and 10 mL

of a 12m aqueous HCl (0.02 equiv) were mixed and stirred at

1408C for 4 h. After distillation (0.085 mbar, 1058C), 12.81 g of

Dipp-N(H)=C(H)OEt (54.9 mmol, 97%) were isolated. The purity of

the product was monitored by use of NMR spectroscopy. The reac-

tion mixture of Dipp-N(H)=C(H)OEt (3.17 g, 13.6 mmol), NH₂C₂H₄-

1

present. M.p. 111–1138C (dec.); H NMR (400.13 MHz, C₆D₆, 297.0 K):

d 7.79 (broad, 1H, Py N-CH), 7.30 (m, 2H, Dipp m-CH), 7.08 (m, 1H,

Dipp p-CH), 7.01 (m, 1H, Py m-CH), 6.61 (m, 1H, Py o-CH), 6.51 (m,

1H, Py p-CH), 3.65 (m, 2H, CH(CH₃)₂), 3.28 (m, 2H, N-CH₂-), 2.36

(broad, 2H, Py-CH₂-), 2.00–1.98 (m, 16H, tmeda N-CH₂-, tmeda

N(CH₃)₂), 1.49 (broad, 2H, C(CH₃)₃), 1.49–1.45 (m, 17H, C(CH₃)₃,

CH(CH₃)₂), 0.97 ppm (broad, 2H, CH(CH₃)₂); ¹³C NMR (100.61 MHz,

C₆D₆, 297.0 K): d 163.1 (^qC), 153.6 (Dipp i-C), 146.6 (Py N-CH), 137.6

(Dipp o-C), 137.0 (Py m-C), 123.7 (Py o-C), 121.3 (Dipp m-C), 120.7

(Py p-C), 116.6 (Dipp p-C), 57.6 (tmeda, N-CH₂-), 49.5 (N-CH₂-), 46.1

(tmeda, N(CH₃)₂), 40.3 (Py-CH₂-), 39.9 (Py-CH₂-), 31.5 (C(CH₃)₃), 28.6

(CH(CH₃)₂), 24.3/22.6 ppm (CH(CH₃)₂); ⁷Li{¹H} NMR (155.51 MHz,

C₆D₆, 297.0 K): d 1.11 (broad, major), À1.47 ppm (broad, minor); MS

(DEI): m/z (%) 379 (2, [Li₂L]⁺), 366 (25, [L+H]⁺), 365 (95, [L]⁺), 322

(85, [C₂₁H₂₈N₃]⁺), 308 (35, [C₂₀H₂₆N₃]⁺), 260 (20, [C₁₇H₂₈N₂]⁺) 244 (30,

[C₁₆H₂₃N₂]⁺; [C₁₇H₂₇N]⁺), 229 (100, [C₁₆H₂₃N]⁺; [C₁₅H₂₁N₂]⁺), 203 (50,

[C₁₃H₁₉N₂]⁺), 186 (40, [C₁₂H₁₄N₂]⁺; [C₁₃H₁₆N]⁺), 172 (10, [C₁₁H₁₂N₂]⁺;

[C₁₂H₁₄N]⁺), 146 (20, [C₁₁H₁₄]⁺; [C₁₀H₁₂N]⁺), 116 (10, [C₉H₈]⁺;

[C₈H₆N]⁺), 106 (75, [C₇H₈N]⁺), 91 (10, [C₇H₇]⁺), 58 (50, [C₃H₈N]⁺), 41

(8, [C₂H₃N]⁺); IR (pure): v˜ =3325 (b), 2952 (m), 2863 (m), 2831 (m),

2792 (m), 1656 (m), 1587 (m), 1567 (w), 1532 (s), 1465 (m), 1438 (s),

1420 (m), 1381 (m), 1362 (m), 1343 (m), 1312 (m), 1288 (m), 1260

(m), 1229 (m), 1211 (m), 1173 (m), 1152 (m), 1096 (w), 1045 (m),

1032 (m), 1017 (m), 944 (m), 935 (m), 913 (m), 823 (w), 781 (m),

768 (m), 744 (s), 726 (m), 680 (w), 635 cm^À1(w). Due to the sensitiv-

ity of this compound during handling and weighing, no reliable

CHN elemental analysis data were obtained.

Py (1.61 mL, 13.6 mmol), and 10 mL of

a 12m aqueous HCl

(0.01 equiv) was stirred at 1208C for 24 h. The crude product was

precipitated with n-pentane and recrystallized from a mixture of

ethyl acetate and petroleum ether (3:7) yielding 1.23 g of 8 (29%).

The same procedure as

a one-pot-synthesis using Dipp-NH₂

(4.2 mL, 22.6 mmol), triethyl orthoformate (3.7 mL, 22.6 mmol),

0.1 mL glacial acetic acid, and NH₂C₂H₄-Py (2.68 mL, 22.6 mmol)

also led to the formation of 8 (2.48 g, 36%). Physical data show

a coexistence of two isomeric structures of 8 in solution at RT in

1

a ratio of 4:1. M.p. 758C. In the H NMR spectra the intensity has

been adjusted so that both isomers together give integers; the

ratio of the major to the minor component is 4:1; ¹H NMR

(400.13 MHz, CDCl₃, 298.0 K): d 8.55 (m, 0.8H, Py N-CH major), 8.43

3

4

(m, 0.2H, Py N-CH minor), 7.63 (td, J_HH=7.7 Hz, J_HH=1.7 Hz, 0.8H,

Py m-CH major), 7.56 (m, 0.2H, Py m-CH minor), 7.22–7.20 (m, 2H,

Dipp p-CH, NC(H)N), 7.16 (m, 1H, Py p-CH), 7.08 (m, 2H, Dipp m-

CH), 7.00 (m, 1H, Py o-CH), 5.21 (broad, 1H, NH), 4.63 (broad, 1H,

NH), 3.85 (m, 1.6H, N-CH₂- major) 3.55 (m, 0.4H, N-CH₂- minor),

3.14–3.08 (m, 3.2H, CH(CH₃)₂major, Py-CH₂- major), 2.98–2.87 (m,

0.8H, CH(CH₃)₂minor, Py-CH₂- minor), 1.15 (d, ³J_HH=6.8 Hz, 9H,

CH(CH₃)₂major), 1.10 ppm (m, 3H, CH(CH₃)₂minor); ¹³C NMR

(100.61 MHz, CDCl₃, 298.0 K): d 159.8/158.3 (Py i-C), 149.5/149.5 (Py

N-CH), 148.8 (NC(H)N), 147.7/143.5 (Dipp i-C), 140.5/139.3 (Dipp o-

C), 136.7/136.5 (Py, m-C), 123.7/123.6 (Py, o-C), 123.4/123.3 (Dipp p-

C), 122.8 (Dipp m-C), 121.7/121.7 (Py p-C), 43.9/39.7 (N-CH₂-), 40.8/

37.7 (Py-CH₂-), 27.9/27.9 (CH(CH₃)₂), 23.8/23.6 ppm (CH(CH₃)₂); MS

(DEI): m/z (%) 309 (40, [M]⁺), 266 (10, [C₁₇H₂₀N₃]⁺), 203 (10,

[C₁₃H₁₉N₂]⁺), 186 (15, [C₁₂H₁₄N₂]⁺; [C₁₃H₁₆N]⁺), 172 (15, [C₁₁H₁₀N₂]⁺;

[C₁₃H₁₆]⁺), 158 (15, [C₁₀H₁₀N₂]⁺; [C₁₁H₁₂N]⁺), 146 (25, [C₁₁H₁₄]⁺;

[C₁₀H₁₂N]⁺), 130 (20, [C₁₀H₁₀]⁺; [C₉H₈N]⁺), 106 (80, [C₇H₈N]⁺), 93 (100,

[C₆H₇N]⁺), 78 (20, [C₅H₄N]⁺), 65 (15, [C₅H₅]⁺), 43 (20, [C₃H₇]⁺); IR

(pure): v˜ =3025 (b), 3050 (w), 2960 (w), 2929 (w), 2867 (w), 1659

(s), 1628 (m), 1584 (m), 1566 (m), 1460 (m), 1430 (m), 1394 (w),

1380 (w), 1361 (w), 1316 (w), 1257 (m), 1186 (w), 1157 (m), 1107

(w), 1096 (w), 1076 (w), 1051 (w), 986 (m), 845 (w), 795 (w), 783

(m), 770 (s), 748 (m), 701 (w), 604 cm^À1(w); elemental analysis (%)

calcd for C₂₀H₂₇N₃(309.45 gmol^À1): C, 77.63; H 8.79; N 13.58;

found: C, 77.63; H, 8.79; N, 13.78.

Synthesis of [(thf)₄Ca{Dipp-N=C(tBu)-N(H)}₂] (7): The reaction mix-

ture of 1 (360 mg, 1.0 mmol) and KN(SiMe₃)₂(390 mg, 2.0 mmol) in

THF (6 mL) was stirred at RT for 4 h. Thereafter, the mixture was

added to a suspension of CaI₂(550 mg, 2.2 mmol) in THF (15 mL)

and stirred for a further 72 h at RT. All volatiles were removed in

vacuo. The remainder was suspended in toluene (18 mL), filtered

and the resulting filtrate was concentrated. Adding THF (4 mL) and

storage for several days at À208C led to the formation of 240 mg

of 7 (29% yield) as colorless crystals. Drying in vacuo caused partial

1

loss of ligated ether. M.p. 112 8C (dec.); H NMR (400.20 MHz, C₆D₆,

300.0 K): d 7.23 (m, 4H, Dipp m-CH), 7.12 (m, 2H, Dipp p-CH), 3.58

3

(broad, 6H, thf O-CH₂-) 3.52 (broad, 2H, NH), 3.13 (sept, J_HH

=

Synthesis of [(thf)Na{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9a); A solution of

8 (340 mg, 1.1 mmol) in toluene (7 mL) was added to a solution of

NaN(SiMe₃)₂(260 mg, 1.4 mmol) in toluene (7 mL) at RT, and the re-

action mixture was stirred at RT for 24 h. Thereafter, the reaction

mixture was concentrated to a volume of about 2 mL and re-

stocked with THF (10 mL). The mixture was stirred at 608C for

30 min and the resulting solution was concentrated to a volume of

approximately 1 mL. Addition of toluene (2 mL) and storage at 58C

for several days led to the formation of 170 mg of 9a (38%).

M.p. 1698C (dec.); ¹H NMR (400.13 MHz, C₆D₆, 297.0 K): d 8.22

(broad, 1H, Py N-CH), 7.63 (broad, 1H, NC(H)N) 7.18 (m, 2H, Dipp

m-CH), 7.08–7.02 (m, 2H, Py m-CH, Dipp p-CH), 6.70 (m, 1H, Py o-

CH), 6.57 (m, 1H, Py p-CH), 3.64–3.50 (m, 8H, N-CH₂-, thf O-CH₂-,

CH(CH₃)₂), 2.90 (m, 2H, Py-CH₂-), 1.45 (m, 4H, thf, -CH₂-), 1.20 ppm

(d, ³J_HH=6.8 Hz, 12H, CH(CH₃)₂); ¹³C NMR (100.61 MHz, C₆D₆,

6.8 Hz, 4H, CH(CH₃)₂), 1.42 (broad, 6H, thf, -CH₂-), 1.27 (m, 24H,

CH(CH₃)₂), 1.15 ppm (s, 18H, C(CH₃)₃); ¹³C NMR (100.63 MHz, C₆D₆,

300.0 K): d 161.2 (^qC), 145.6 (Dipp i-C), 138.9 (Dipp o-C), 123.6 (Dipp

m-C), 123.2 (Dipp p-C), 67.9 (thf, O-CH₂-), 37.0 (C(CH₃)₃), 28.5

(C(CH₃)_3,CH(CH₃)₂), 25.8 (thf, -CH₂-), 23.7 (CH(CH₃)₂), 23.6 ppm

(CH(CH₃)₂); MS (DEI): m/z (%) 260 (100, [C₁₇H₂₈N₂]⁺), 245 (83,

[C₁₆H₂₄N₂]⁺[C₁₇H₂₈N]⁺), 217 (93, [C₁₄H₂₁N₂]⁺), 203 (35, [C₁₃H₁₉N₂]⁺),

;

186 (65, [C₁₃H₁₆N]⁺; [C₁₃H₁₆N]⁺), 146 (15, [C₁₁H₁₄]⁺; [C₁₀H₁₂N]⁺), 106

(20, [C₇H₈N]⁺), 91 (20, [C₆H₅N]⁺), 77 (10, [C₅H₃N]⁺), 57 (30, [C₃H₇N]⁺),

41 (20, [C₂H₃N]⁺); IR (pure): v˜ =3499 (vw), 3395 (w), 2960 (w), 2868

(w), 1647 (w), 1624 (w), 1587 (m), 1529 (w), 1477 (w), 1461 (w),

1434 (w), 1394 (w), 1378 (w), 1359 (w), 1347 (w), 1326 (w), 1254

(w), 1212 (w), 1178 (w), 1157 (w), 1104 (w), 1057 (w), 1036 (w), 936

(m), 867 (w), 833 (w), 798 (w), 769 (m), 742 (w), 725 cm^À1(w). Due

Chem. Eur. J. 2016, 22, 10944 – 10959

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Full Paper

297.0 K): d 170.0 (NC(H)N), 163.1 (Py i-C), 151.4 (Dipp i-C), 148.8 (Py

N-CH), 142.4 (Dipp o-C), 137.1 (Py, m-C), 124.1 (Py, o-C), 123.2 (Dipp

m-C), 121.4 (Dipp p-C), 121.2 (Py p-C), 67.9 (thf O-CH₂-), 55.9 (N-

CH₂-), 42.4 (Py-CH₂-), 28.1 (CH(CH₃)₂), 25.8 (thf -CH₂-), 24.6 ppm

(CH(CH₃)₂); MS (DEI): m/z (%) 309 (100, [L]⁺), 266 (25, [C₁₇H₂₀N₃]⁺),

203 (25, [C₁₃H₁₉N₂]⁺), 186 (20, [C₁₂H₁₄N₂]⁺; [C₁₃H₁₆N]⁺), 172 (30,

[C₁₁H₁₀N₂]⁺; [C₁₃H₁₆]⁺), 159 (15, [C₁₀H₁₁N₂]⁺; [C₁₁H₁₃N]⁺), 146 (20,

[C₁₁H₁₄]⁺; [C₁₀H₁₂N]⁺), 106 (20, [C₇H₈N]⁺), 93 (15, [C₆H₇N]⁺), 29 (15,

[C₂H₅]⁺); (Micro-ESI pos. in THF+MeOH): m/z (%) 310 (100, [L+H]⁺),

291 (8, [C₁₉H₂₁N₃]⁺), 205 (85, [C₁₃H₂₁N₂]⁺), 106 (10, [C₇H₈N]⁺). IR

(pure): v˜ =3205 (vw), 3050 (vw), 3014 (w), 2957 (w), 2934 (w), 2867

(w), 2804 (vw), 1661 (w), 1642 (w), 1629 (w), 1594 (w), 1585 (w),

1564 (w), 1552 (m), 1461 (w), 1431 (m), 1380 (w), 1343 (w), 1331

(w), 1256 (w), 1214 (w), 1187 (w), 1159 (w), 1108 (w), 1097 (w), 1055

(w), 1000 (m), 986 (w), 845 (w), 796 (w), 782 (w), 772 (w), 760 (m),

701 (w), 608 cm^À1(w). Due to the sensitivity of this compound

during handling and weighing no reliable, CHN elemental analysis

data were obtained.

24.3 ppm (CH(CH₃)₂); MS (DEI): m/z (%) 309 (100, [L]⁺), 266 (35,

[C₁₇H₂₀N₃]⁺); MS (DEI): m/z (%) 839 (2, [M₂]⁺), 765 (1, [M₂- THF]⁺),

355 (20), 341 (15), 309 (100, [L]⁺), 281 (60, C₁₈H₂₃N₃]⁺), 266 (35,

[C₁₇H₂₀N₃]⁺), 230 (30, [C₁₅H₂₂N₂]⁺; [C₁₆H₂₄N]⁺), 203 (83, [C₁₃H₁₉N₂]⁺),

172 (90, [C₁₁H₁₀N₂]⁺; [C₁₃H₁₆]⁺), 146 (80, [C₁₁H₁₄]⁺; [C₁₀H₁₂N]⁺), 106

(90, [C₇H₈N]⁺), 93 (75, [C₆H₇N]⁺), 43 (10, [C₃H₇]⁺); IR (pure): v˜ =3499

(vw), 3054 (vw), 2958 (w), 2865 (w), 2810 (vw), 1658 (m), 1643 (m),

1631 (m), 1585 (m), 1566 (w), 1549 (m), 1460 (m), 1431 (w), 1381

(w), 1359 (w), 1331 (w), 1255 (w), 1203 (w), 1161 (w), 1109 (w),

1076 (w), 1054 (m), 986 (w), 844 (w), 796 (w), 782 (m), 761 (m), 746

(w), 630 (w), 606 cm^À1(w). Due to the sensitivity of this compound

during handling and weighing, no reliable CHN elemental analysis

data were obtained.

Crystal structure determinations: The intensity data for the com-

pounds were collected on a Nonius KappaCCD diffractometer

using graphite-monochromated Mo_Karadiation. Data was corrected

for Lorentz and polarization effects; absorption was taken into ac-

count on a semi-empirical basis using multiple-scans.^[27–29]The

structures were solved by direct methods (SHELXS)^[29]and refined

Synthesis of [(thf)K{Dipp-N=C(H)-N-C₂H₄-Py}]₂(9b): A solution of

8 (320 mg, 1.0 mmol) in toluene (7.5 mL) was added to a solution

of KN(SiMe₃)₂(250 mg, 1.2 mmol) in toluene (7.5 mL) at RT, and the

reaction mixture was stirred at RT for 24 h. The resulting precipi-

tate was collected by filtration and recrystallized from THF (2 mL)

yielding 200 mg of 9b after storage at À208C for several hours

(47% yield). Drying in vacuo partly removes ligated ether.

M.p. 1578C (dec.); ¹H NMR (400.13 MHz, [D₈]THF, 297.1 K): d 8.43

(broad, 1H, Py N-CH), 7.55–6.60 (m, 7H, NC(H)N, H_Aryl), 3.81/3.53 (m,

2H, N-CH₂-), 3.23–2.89 (m, 4H, Py-CH₂-, CH(CH₃)₂), 1.11–1.06 ppm

(m, 12H, CH(CH₃)₂); ¹³C NMR (100.61 MHz, [D₈]THF, 297.0 K): d 166.5

(NC(H)N), 164.1 (Py i-C), 150.3 (Dipp i-C), 149.5 (Py N-CH), 141.9

(Dipp o-C), 136.9 (CH_Aryl), 124.3 (CH_Aryl), 122.9 (CH_Aryl), 121.6 (CH_Aryl),

119.4 (CH_Aryl), 58.1 (N-CH₂-), 44.3 (Py-CH₂-), 28.7 (CH(CH₃)₂),

2

by full-matrix least squares techniques against F_o(SHELXL-97).^[30]

All hydrogen atoms bound to the compounds 1, 3, 4b, 7 (both

with exception of the disordered thf-molecules), and 9a as well as

the hydrogen atoms of the amine groups of 4a and 5 and those

of the methylene groups C3A and C19B of 6 were located by dif-

ference Fourier synthesis and refined isotropically. All other hydro-

gen atoms were included at calculated positions with fixed thermal

parameters. All non-disordered and non-hydrogen atoms were re-

fined anisotropically.^[30]The crystal of 9b contains large voids, filled

3

with disordered solvent molecules. The size of the voids are 215

per unit cell. Their contribution to the structure factors was se-

cured by back-Fourier transformation using the SQUEEZE routine

of the program PLATON^[31]resulting in 56 electrons/unit cell. The

Table 4. Crystal data and refinement details for the X-ray structure determinations of the compounds 1–4.

Compound

formula

1

2a

2b

3

4a

4b

C₂₄H₃₅N₃

365.55

À140(2)

monoclinic

P 2₁/n

14.6120(2)

19.6459(2)

16.6619(2)

90

C₃₀H₅₂CaN₄Si₂

565.02

À140(2)

Monoclinic

P 2₁/n

12.3412(5)

15.7404(6)

18.1095(7)

90

C₃₀H₅₂N₄Si₂Sr

612.56

À140(2)

monoclinic

P 2₁/n

12.4750(3)

15.8620(4)

17.9909(4)

90

C₄₈H₆₈MgN₆

753.39

À140(2)

monoclinic

P 2₁/c

12.7330(2)

20.4882(4)

18.3784(3)

90.00

C₂₅H₄₃N₂NaO₂

426.60

À140(2)

tetragonal

I 4₁c d

21.4723(3)

22.5062(3)

90

C₂₁H₃₂KN₂O

367.59

À140(2)

monoclinic

C 2/c

12.6807(4)

19.3139(5)

18.4522(6)

90

M_r[gmol^À1

T [8C]

]

crystal system

space group

a []

b []

c []

a [8]

b [8]

110.987(1)

90

4465.76(9)

8

1.087

0.64

105.762(2)

90

3385.6(2)

4

1.109

2.8

106.659(2)

90

3410.59(14)

4

1.193

16.74

107.575(1)

90.00

4570.69(14)

4

1.095

0.77

90

100.080(1)

90

4449.4(2)

8

1.097

2.49

g [8]

V [³]

10376.7(2)

16

1.092

Z

1 [gcm^À3

]

m [cm^À1

]

0.82

measured data

35159

20736

19616

32520

11137

12606

data with I>2s(I)

8178

5723

5914

8614

5089

4074

unique data (R_int

)

10216/0.0411

0.1123

0.0477

7505/0.0853

0.1437

0.0742

7750/0.0663

0.1097

0.0547

10402/0.0364

0.1169

0.0492

5904/0.0293

0.1055

0.0471

5074/0.0377

0.1902

0.0686

wR₂(all data, on F²)^[a]

R₁(I>2s(I))^[a]

s^[b]

1.084

1.167

1.131

1.063

1.090

1.096

À3

res. dens. [e·

]

0.236/À0.172

0.347/À0.319

0.521/À0.311

0.284/À0.258

0.177/À0.142

0.829/À0.382

Flack parameter

absorpt method

absorpt corr T_min

CCDC

–

0.2(3)

–

multi-scan

0.7136/0.7456

1462997

multi-scan

0.5326/0.7456

1462998

multi-scan

0.5092/0.7456

1462999

multi-scan

0.7167/0.7456

1463000

multi-scan

0.7099/0.7418

1463001

multi-scan

0.6428/0.7456

1463002

/

max

[a] Definition of the R indices: R₁=(SjjF_ojÀjF_cjj)/SjF_oj ; wR₂={S[w(F_oÀF_c²)²]/S[w(F_o²)²]}^1/2with w^À1=s²(F_o²)+(aP)²+bP; P=[2F_c²+Max(F_o²]/3. [b] s=

2

{S[w(F_oÀF_c²)²]/(N_oÀN_p)}^1/2

.

Chem. Eur. J. 2016, 22, 10944 – 10959

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10957

ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper

Table 5. Crystal data and refinement details for the X-ray structure determinations of the compounds 5–9.

Compound

formula

5

6

7

8

9a

9b

[c]

C₁₉H₃₄N₂O

306.48

À140(2)

monoclinic

P 2₁/n

11.2274(3)

16.5606(4)

11.8370(2)

90

115.632(1)

90

C₃₀H₅₀LiN₅

487.69

À140(2)

monoclinic

P 2₁/c

21.9283(3)

15.4886(3)

18.1164(3)

90

103.499(1)

90

C₅₀H₈₃CaN₄O₄

844.28

À140(2)

monoclinic

P 2₁/n

10.0022(2)

21.2034(4)

24.2187(3)

90

93.124(1)

90

C₂₀H₂₇N₃

309.45

À140(2)

tetragonal

P 4₁

9.0286(1)

44.6099(8)

90

C₂₄H₃₄N₃NaO

403.53

À140(2)

orthorhombic

P b c a

14.1180(3)

15.8834(3)

20.9616(5)

90

C₂₅H₃₆KN₃O_1.25

437.67^[c]

M_r[gmol^À1

T [8C]

]

À140(2)

crystal system

space group

a []

b []

c []

triclinic

P ı

¯

10.1600(2)

14.6984(2)

18.3533(3)

85.666(1)

77.389(1)

84.115(1)

2656.59(8)

4

a [8]

b [8]

90

g [8]

V [³]

1984.30(8)

4

1.026

5983.04(17)

8

1.083

5128.69(15)

4

1.093

3636.40(9)

8

1.130

4700.47(17)

8

1.140

Z

1 [gcm^À3

]

1.094^[c]

2.2^[c]

m [cm^À1

]

0.63

0.64

1.66

0.67

0.86

measured data

data with I>2s(I)

11468

3539

33595

8988

37345

8747

25501

2621

32853

4354

18174

9831

unique data (R_int

)

4530/0.0288

0.1437

0.0605

13176/0.0539

0.1573

0.0763

11690/0.0575

0.1592

0.0669

3634/0.0321

–

5174/0.0478

0.1112

0.0485

11519/0.0221

0.1336

0.0556

wR₂(all data, on F²)^[a]

R₁(I>2s(I))^[a]

s^[b]

1.087

1.114

1.075

–

1.097

1.026

À3

res. dens. [e·

]

0.240/À0.210

multi-scan

0.6894/0.7456

1463003

0.262/À0.229

multi-scan

0.6673/0.7456

1463004

0.535/À0.362

multi-scan

0.7014/0.7456

1463005

0.533/À0.274

multi-scan

0.7062/0.7456

motif

0.391/À0.324

multi-scan

0.6518/0.7456

1463006

0.921/À0.954

absorpt method

absorpt corr T_min

CCDC

multi-scan

/

0.7027/0.7456

1463007

max

2

[a] Definition of the R indices: R₁=(SjjF_ojÀjF_cjj)/SjF_oj ; wR₂={S[w(F_oÀF_c²)²]/S[w(F_o²)²]}^1/2with w^À1=s²(F_o²)+(aP)²+bP; P=[2F_c²+Max(F_o²]/3. [b] s=

2

{S[w(F_oÀF_c²)²]/(N_oÀN_p)}^1/2. [c] Derived parameters do not contain the contribution of the disordered solvent.

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462999 (2b),

1463000 (3),

1463001 (4a),

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Acknowledgements

We appreciate the financial support by the Fonds der Chemi-

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also supported by a Ph.D. fellowship from the Graduate Acade-

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Keywords: 1,3-diazaallyl anions · alkali metals · alkaline earth

metals · formamidinates · pivalamidinates

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Published online on June 29, 2016

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Article Doi

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DOI: 10.1002/chem.201602074

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