Lithium and Dilithium Guanidinates, a Starter Kit for Metal Complexes Containing Various Mono- And Dianionic Ligands

Tomas Chlupaty, Jana Nevoralova, Zdenka Ruzickova, and Ales Ruzicka*

Article

Lithium and Dilithium Guanidinates, a Starter Kit for Metal

Complexes Containing Various Mono- and Dianionic Ligands

Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c01362

Read Online

ACCESS

Metrics & More

Article Recommendations

sı Supporting Information

ABSTRACT: Comparative studies of the synthesis of lithium

guanidinates via nucleophilic addition of lithium amides to

carbodiimides were performed. Four combinations of small or sterically

crowded carbodiimide and sterically crowded lithium amide or lithium

amide containing an adjacent amino donor group give ten diﬀerent

types of complexes. In particular, 2,6-[(CH ) CH] C H NHLi

(

DipNHLi, 1) reacts with (CH ) CHNCNCH(CH ) upon the

3 2

formation of the dissymmetric dimeric complex 2 with four-coordinate

Li atoms. In contrast, 1 with DipNCNDip gives the mononuclear

lithium guanidinate 3 with two-coordinate lithium by κ -guanidinate,

solvent molecule, and additional interaction with a π-electron cloud of

one of the Dip groups. Analogous reactions of 2-[(CH ) NCH ]-

C H NHLi (7) yield complexes 8 and 9, where the adjacent amino

donors are always coordinated. Further deprotonation of 2, 3, 8, and 9

leads to dilithium guanidinates(2−)4, 5, 10, and 11, among which only 5, containing three Dip groups, is monomeric with

contacts to two π-electron systems of Dip groups. The rest of the complexes are tetranuclear with diﬀerent structural patterns. In the

central parts of molecules, toward which the nitrogen atoms of the guanidinates are oriented, lithium atoms are usually

pseudotetrahedral, but trigonal in peripheral parts. Adjacent solvent molecules, chelating amino groups, and π-electron systems of

Dip groups are coordinated in order to complete coordination polyhedra. Complexes 4 and 5 deoligomerize in solution upon the

formation of ﬂuxional monomeric dilithium species. Conversely, 11 is a dimer in solution due to the strong donation of an amino

group. The silylated lithium amide {2-[(CH ) NCH ]C H }[(Si(CH ) ]NLi (12) reacts with both carbodiimides to give dinuclear

3 3

3 obtained from diisopropylcarbodiimide and monomeric 14 from the second carbodiimide. Complexes 13 and 14 structurally

resemble 8 and 9, with the highest degree of the localization of π-electron density within the N C guanidinate system, η -contact to

the Dip ring, and a lack of the solvent molecule in 14.

INTRODUCTION

and nanoparticles prepared from transition metal oxides are

reported to catalyze most of the guanylation reactions.

The deprotonation of amidines and guanidines by one

equivalent of a strong base leads to amidinates and

guanidinates, systems with an electron-rich chelating arrange-

■

Several amidines and guanidines as formal derivatives of

carbonic or carbamic acids have found many applications in

their neutral and neutral-condensed forms (biguanides). For

example, they appeared in organic chemistry as catalysts or

bases, in the production of plastics, biochemistry, natural

ment (Figure 1A,B), frequently used for the complexation

of nearly all metals and metalloids of the Periodic Table of the

Elements. Speciﬁcally N,N′,N″-triscarbyl-substituted guanidi-

nato ligands, which are also the subject of the present study,

exhibit a higher basicity than amidinates, more bonding modes,

and, last but not least, the ability to be also doubly

deprotonated (Figure 1C). Metal complexes containing

products or drugs, and as propellants in car air bags.

Protonated forms (of amidinium or guanidinium type) can

serve as organocatalysts, ionic liquids, drugs, in protein folding,

and nonlinear optics.

The preparation of guanidines mostly proceeds by direct

addition of an amine to cumulated double bonds of

carbodiimides. This atom-economic protocol called guanyla-

tion of an amine requires harsh conditions; in a remarkable

number of cases, it is driven catalytically. The guanylations of

secondary, aromatic, or sterically crowded amines cannot be

achieved satisfactorily without a catalyst, owing to their

Received: May 10, 2020

decreased nucleophilicity. The d- and f-block metal

complexes, as well as the coordination compounds of

electron-deﬁcient main-group metals (Li, Al, Mg, and Al)

XXXX American Chemical Society

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

RESULTS AND DISCUSSION

■

In order to avoid the problems of the separation of the desired

guanidines from the starting material and various catalysts,

attention has been focused on the direct reactions of the

respective lithium amides with carbodiimides, presumably

yielding the desired lithium guanidinates. It is worth

mentioning here that the direct noncatalyzed reactions of

selected anilines with carbodiimides to guanidines gave only

mixtures of starting material with products even when a

prolonged reﬂux in toluene solution was applied. Reliable

candidates for this comparative study are a series of complexes

made by a combination of both sterically demanding lithium

anilide or anilide with the adjacent donor amino group

(

Schemes 1 and 2) and carbodiimides substituted by bulky aryl

Scheme 1. Reaction Pathways to Lithium and Dilithium

N,N′-Disubstituted-{N″-[2,6-di(propan-2-

yl)phenyl]}guanidinates

Figure 1. Examples of the structural motifs of lithium guanidinates. R

H or an organic or silyl group; R = an organic or silyl group; D =

a donor/solvent. Data sources: refs 9e; 15a,d−p; and 16a,b.

various types of guanidinato ligand are habitually tested as

catalysts of various organic reactions, as precursors of new

materials, and for the stabilization of unusual, generally

lower, oxidation states of metals. Very recently, these highly

basic building blocks have been used as stabilizing substituents

for the synthesis of phosphorus dications, which have

superacidic character and are able to activate for example

such strong C−F bonds.

Nevertheless, most of these metal complexes are prepared

from the starting lithium compounds followed by trans-

metalation with metal halides. The number of the studies

dedicated to the preparation, structure, and reactivity of the

mentioned lithium precursors is still limited. Generally, the

chemistry of the monolithium guanidinates(1−) is more

frequent (Figure 1B), and there are only two reports dealing

or alkyl groups. For all complexes, H, C, and Li NMR

with dilithium guanidinates(2−) (Figure 1C). In addition,

spectra were recorded in THF-d or C D . When suﬃcient

solubility in noncoordinating solvents such as C D was

achieved, the measurement was also performed in them in

order to compare the same parameters, which could provide

essential information on the association of complexes in

solution.

related structures of dianionic guanidinates compensated by

6 6

one lithium and another metal atom

or dilithium

boraamidinates/boraguanidinates have also been reported.

Unlike in the related amidinates, the known structures of

lithium guanidinates range from only two monomeric

examples, with an extra donor as an aromatic π-system or

a chelating methoxy group, through several diﬀerent

to the sole example

of a higher aggregate (tetranuclear) or an adduct. Two

examples of lithium bis-guanidinates with a dimeric structure

15e

The reaction of lithium anilide 1, prepared by the lithiation

of 2,6-(diisopropyl)aniline (ArNH , Scheme 1), with one

5a,d,f−j,17a

symmetric or asymmetric dimers,

molar equivalent of iPrNCNiPr, led almost exclusively to

the desired compound 2 in diethyl ether solution at room

temperature. The H NMR spectra of 2 recorded both in C D

and THF-d showed rather unsymmetrical behavior of both

have been found as well.

Syntheses and comparative solution and solid-state studies

of corresponding lithium amidinate complexes containing both

aliphatic and aromatic substituents as well as substituents with

potentially chelating groups have revealed a great diversity of

structures, behavior, and potential use.

The main target of this particular study is the synthetic and

structural investigation of groups of lithium and dilithium

guanidinates substituted by a combination of both aliphatic,

bulky aromatic group, and a potentially chelating group in

order to create a tool for the preparation of guanidinates of

various metals.

isopropyl and Dip groups. Apart from two signals for H-atoms

of aromatic rings, one signal at 3.45 ppm (C D ) or 3.29 ppm

(in THF-d ) was attributed to the NH group; three signals

were found for methine and four doublets of equal intensity for

methyl groups. Three methine signals have the integral

intensity ratio of 2:1:1, where the intense signal resonates at

a higher frequency, which indicates the equivalency of

methines bound to the Dip substituent, while other isopropyls

are inequivalent. On the basis of this, one can predict the

structure with the bidentate bonding mode of the guanidinate

to the lithium atom, to which nitrogen from the former aniline

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

(dimethylamino)methyl]phenyl}guanidinates

Article

Scheme 2. Reaction Pathways to Lithium and Dilithium N,N′-Disubstituted-{N″-[2-

[

Figure 2. Molecular structure of 2 (left) and 2a (right). Selected bond lengths are given along with atom connectors in angstroms. Full ORTEP-

type plots with more bond distances and angles with standard uncertainties are given in the SI .

and the second one from the carbodiimide is bound. The

migration of the hydrogen atom from the former aniline/

lithium anilide to the starting carbodiimide (formal amination

or addition to an unsaturated system) is another consequence

of the presence of this structural motif. Moreover, the

characteristic signals for coordinated diethyl ether, coming

from the synthetic procedure, are also present in the spectrum

measured in deuterated benzene. Only a two- and three-fold

connected to the structural changes in the dimeric one with

only one coordinated diethyl ether molecule in C D , and thus

two distinct lithium atoms, one four-coordinated by two

bidentate guanidinates and the other one three-coordinated by

only one nitrogen atom from both guanidinates and an oxygen

atom from the diethyl ether molecule. Such a structure is most

likely a product of the deﬁciency of the coordinating solvent,

and the explanation of this structural arrangement requires the

presence of a fast equilibrium between both coordination

(

for -OCH CH ) intensity of these signals as compared to the

2 3

integral value of the signal for the N−H group must be

associated with coordination of the diethyl ether molecule per

the dimeric structure of 2, which is not known in the lithium

guanidinate family. The ¹³C NMR spectra of 2 in C D and

motifs, as Li NMR observes only one signal at 2.0 ppm.

Unfortunately, all attempts to perform a low-temperature

measurement in a noncoordinating solvent such as toluene-d₈

have nearly no inﬂuence on the spectral patterns or failed due

to low-solubility issues at the lowest temperature. On the other

hand, similar changes in chemical-shift values connected to the

THF-d resemble each other. The diﬀerence is admittedly seen

in chemical shifts for the middle carbon of the guanidinate unit

and the carbons bound to nitrogen atoms, but these are only

structural ones have been observed for lithium amidinates,

−2 ppm. On the other hand, a major change is observed in

the structure of dissymmetric dinuclear lithium guanidinate

15e

Li NMR spectra, where the distinction in C D and THF-d is

reported by Jones (Figure 1E, δ 2.6 in C D ) and in the

about 2.5 ppm. This particular shift could be virtually

solid state (see below). The second structure of 2 in THF-d₈

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

solution could be monomeric with two THF molecules (see

Figure 1F) coordinated to the lithium center as described for

symmetric lithium guanidinates or amidinates, or dimeric with

one coordinated THF molecule per one lithium atom as also

reported earlier (see Figure 1D). The solid-state structures of

2, determined on the single crystal material obtained from both

solvents, correspond to the structure predicted from solution

NMR spectroscopic investigations. Both are dimers with a

dissymmetrical arrangement of planar ligands, which coor-

dinate two lithium atoms by the nitrogen atoms bearing

smaller substituents (isopropyl), while nitrogen atoms

substituted by Dip groups are prone to coordinate only one

lithium atom. In the centrosymmetric structure of the THF

complex (Figure 2 (right)) with coplanar and nearly

isobidentate ligands (Li−N distances diﬀer by less than 0.15

Å), each lithium atom is four-coordinated in the pseudote-

trahedral environment by three nitrogen donors originating

from both ligands and the THF molecule. In the diethyl ether-

solvated complex (Figure 2 (left)), there are two diﬀerent

lithium atoms, the one that is three-coordinated by two

nitrogens from two ligands, and the other, four-coordinated by

two nitrogen atoms from each mutually twisted and nearly

perpendicularly oriented ligand. Such a structural arrangement

is similar to the solvent-free structures depicted in Figure 1E,

where the coordination polyhedra of the lithium atom are

completed by agostic interactions with the C−H moieties of

the ligands instead of diethyl ether in 2 (see Figure 2).

Although the Li−N and Li−O separations seem to be similar

in both structures of 2, slightly bigger discrepancies are

recognized in the dissymmetric (1.975(3)−2.182(3) Å) and a

more strained structure with diethyl ether (2.054(4)−2.108(3)

Å) (see Figure 2 and Supporting Information (SI) Figures S1

and S2).

Figure 3. Molecular structure of 3. Selected bond lengths are given

along with atom connectors in angstroms. Full ORTEP-type plots

with more bond distances and angles with standard uncertainties are

given in the SI .

connected to the N1 atom, and the lithium coordinated to

nitrogen N3 and O1 atoms from the diethyl ether molecule.

Although the contacts are slightly closer than found for 2, the

lithium-coordination sphere is not saturated enough and

requires extra electron density from the π-system of the

phenyl ring (Li−Cg, 2.444(3) Å). For comparison with other

complexes in this study and some of the literature-reported

separations for other types of lithium−aryl complexes, the

centroid of the phenyl ring is depicted showing the η -type of

coordination, but the η - to η -type would be more appropriate

in the case of 3 (Li−Cg(η ), 2.293(3) Å). Direct literature

comparison is available with the lithium guanidinate of Jones et

15e

al. (Figure 1E), which, however, resembles the dissymmetric

complex 2, but when synthesis was conducted in THF instead

In the case of the DipNC=NDip, the same reaction

pathway that led to 2 provided 3. According to the studies in

solution of both solvents, all NMR spectra are much easier to

read than in the case of 2 (as a result of the presence of the

same substituents at all three nitrogen atoms). One set of

broader signals is found in THF, which makes it possible to

suggest the monomeric structure with a higher degree of

molecular dynamics, probably the exchange of the lithium and

hydrogen atoms between all three possible positions within the

plane of the guanidinato unit. The NH group resonates at a

much higher frequency (4.94 ppm for 3 in benzene vs 3.45

ppm for 2), which is caused by the presence of the hydrogen

on the nitrogen atom connected to the phenyl instead of the

of hexane, a mononuclear complex with η -guanidinato-η -aryl

and coordinated THF molecule has been isolated. All of the

structural parameters of the mononuclear lithium guanidinate

of Jones et al.’s work and 3 seem to be the same including the

separations of the Li−phenyl ring and Li−O of THF or diethyl

ether molecule (Figure 3), respectively. The only exception is

thus the diﬀerence between the chemical shifts in the Li NMR

15e

spectra recorded in C D solution (1.6 vs −1.0 ppm for 3).

According to Scheme 1, monolithiated complex 2 gave

dilithiated guanidinate(2−) 4 by a simple addition of an

appropriate amount of n-butyllithium. Once crystallized after

the synthesis, 4 became only sparingly soluble in coordination

solvents. That is why in this case only the H and Li NMR

isopropyl group. In the H NMR spectrum in deuterated

spectra were recorded in THF-d . The H NMR spectrum

benzene, four diﬀerent signals were assigned to the methyl

groups with the integral ratio 18:6:6:6 due to the less dynamic

process in this solvent. Both ¹³C NMR spectra exhibit a high-

shows one set of broad signals and the disappearance of any

signal attributable to the NH group. In Li NMR spectrum just

one signal at −1.0 ppm was observed. In the solid state, the

associated species of 4 probably deoligomerize in the THF

solution upon the formation of a highly dynamic molecule with

both lithium atoms coordinated by the guanidinato(2−) unit

in a more or less bidentate bonding mode. The coordination

sphere of distorted tetrahedra is completed by additional

molecules of THF. In the solid state, the situation diﬀers

dramatically. Although two diﬀerent structures of 4 have been

obtained from THF and diethyl ether solutions (see Figure 4

ﬁeld shift of the middle guanidinate (N C) atom by ca. 8 ppm

in comparison to 2, which is a sign for the lower delocalization

of π-electrons within the guanidinato system. The chemical

shifts in Li NMR are rather distant (−1.0 in benzene and −2.8

ppm in THF-d ), probably as a result of the structure with one

coordinated diethyl ether molecule, originating from the

synthesis, in deuterated benzene, and very strongly coordi-

nated or easily accessible THF molecules. Unfortunately, the

measured variable temperature NMR spectra did not provide

any additional information on these structures in the range of

for the THF adduct 4; for Et O adduct (4a), see Figure S5 in

the SI), these have an essentially identical pattern and are also

very close in all of the interatomic distances and angles. The

structure from the THF solution displayed in Figure 4 is

composed of two perpendicularly oriented distinct guanidina-

−

80 to 60 °C. The solid-state structure of 3 (Figure 3),

crystallized from diethyl ether, is monomeric with the localized

double bond between the C1 and N2 atoms, hydrogen

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

NMR spectrum in THF-d , indicate once again the monomeric

structure of the species in solution. One can expect a rather

high degree of molecular motion and low hapticity of the

guanidinato ligand toward the lithium atoms, which are

additionally connected to the solvent donor molecules. In

the solid state, the molecule is monomeric−dinuclear (Figure

) with the all-in-plane arrangement of the guanidinate(2−).

Figure 4. Molecular structure of 4. Selected bond lengths are given

along with atom connectors in angstroms. Full ORTEP-type plots

with more bond distances and angles with standard uncertainties are

given in the SI .

to(2−) ligands bridged by three lithium atoms. All of these

central lithium atoms have diﬀerent stereochemistry. The ﬁrst

(

Li1) exists in the neighborhood of a heavily distorted

Figure 5. Molecular structure of 5. Selected bond lengths are given

along with atom connectors in angstroms. Full ORTEP-type plots

with more bond distances and angles with standard uncertainties are

given in the SI .

tetrahedron with out-of-plane isobidentate guanidinate coor-

dination by N2 and N3 atoms, N4 atom from the next

guanidinate, and the oxygen of the THF close to the

polyhedra. The second case is the pyramidal three-coordinated

atom Li2, which is coordinated analogously to Li2 by the N4

and N5 atoms of ﬁrst and the N2 atom of the second

guanidinato unit. Contrary to Li1, the coordination of an

adjacent solvent molecule is missing in the case of Li2. These

two lithium guanidinates form a U-shaped unit instead of the

staircase-like arrangement, the most typical for lithium

The Dip ligands are perpendicularly oriented, thus forming the

paddle-wheel structure of the whole molecule. The lithium

atoms are indeed two-coordinated, but each of them has

additional noncovalent contact with the close π-system of the

Dip group (2.374(3) and 2.479(4) Å), which resembles the

pattern already found in 3 or 4 (∼2.4−2.5 Å). Although the

separations of all coordinated atoms from lithium atoms are

slightly shorter (Li−N, 1.892(3) and 1.907(3) Å; Li−O,

1.925(3) and 1.938(3) Å) than in other more associated

structures, the O−Li−N angles seem to be sharper by ∼5 or

20° than those found in 3 and 4, respectively. Also the C1−N

distances are slightly closer to each other (1.338(3) −

1.378(4) Å) than in 3, which indicates a higher degree of π-

electron conjugation within the central system.

15a,d,f−j,17a

amidinates and guanidinates

and observed for 2.

This unusual composition is probably caused by the presence

of the third lithium atom Li3, which has enforced the closing of

this system by coordination with N3 and N5 atoms. The

vicinity of this ion is trigonal, completed by an O2 atom.

Nevertheless, both guanidinates exhibit, according to the

planar shape and N−C separations, a similar type of

delocalization of the electron densitytwo longer (1.370(3)

and 1.398(2)Å) and one shorter (1.336(3)Å). The order of

the nitrogen-atom substituents is diﬀerent. The guanidinate

with the pivotal atom C1 has smaller substituents on the

nitrogen atoms routed to the center of the structure, and the

Dip substituent of the N1 atom indicates the center. On the

contrary, the C26 and N6 atoms, where the π-electron density

is concentrated, are in an outer location. The N6 atom bears

the isopropyl substituent and the additional lithium atom Li4.

The N4 and N5 atoms conﬁned to the center of the structure

are bound to the Dip and isopropyl groups as in 2 and 3. The

Li4 atom is two-coordinated by the N6 atom and O3 from the

THF molecule with a rather obtuse angle of 146.7(4)°.

Additional contact with the π-system of the Dip ring should be

taken into account as well, approaching the same distance of

the Li4 atom to the centroids (2.492(4)Å) as in 3

The trimethylsilylated compound 6 was selected for further

reactivity studies as the representative lithiated amide prepared

from secondary amine with a Dip substituent in order to

conﬁrm the presumption that the reactivity of lithium amides

is inﬂuenced by the steric demands of the amide. The NMR

spectra of 6 in both solvents of choice along with the molecular

structure (see Figure S7) of the mononuclear complex with

two diethyl ether molecules are given in the SI. The molecular

structure of 6 in the form of the dimer crystallized from a

noncoordinating solvent is reported elsewhere. Reactions of

6 with both carbodiimides in various solvents do not proceed

at room temperature (Scheme 1). Unfortunately, it is not

possible to increase the temperature because amide 6 becomes

unstable in solution at a slightly elevated temperature.

(

2.444(4)Å).

In fact, the list of reaction pathways given in Scheme 2 is a

replica of the above-described reactivity and structures

When another equivalent of nBuLi is added to 3, complex 5

is isolated quantitatively. The same solubility and dynamics

issues are valid for this complex as those for dilithium

guanidinate(2−) (4). The absence of the NH resonance, one

mentioned in Scheme 1 with only one important diﬀer-

enceaniline L H with the adjacent donor group is used

instead of bulky ArNH .

set of broad signals in the H NMR spectrum, together with

Lithium amide 7 (see the SI for its characterization and

dimeric structure with one coordinated diethyl ether molecule

only one broad resonance at −2.6 ppm observed in the Li

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

structure of 9 (Figure 7 ) is mononuclear with the three-

Article

per one lithium atom) reacts smoothly with smaller

(2.027(4)Å) and Li2−N6 (2.056(3)Å). The NH groups are

located at the N4 and N8 atoms at the periphery of the

molecule.

carbodiimide iPrNCNiPr to give complex 8 (Scheme

). The H, Li, and C NMR spectra recorded in both

coordinating and noncoordinating deuterated solvents exhibit

essentially the same traces and patterns. A common feature of

the H NMR spectral patterns of compounds containing a

A moderate yield for complex 9 was achieved by analogous

reactions to 2, 3, and 8. The H NMR spectrum in benzene

solution is characterized by relatively broad sets of signals,

indicating fast exchange processes of Dip substituents as well as

structure with the [N,N-(dimethyl)aminomethyl]phenyl-

group is the existence of an AX-spin system for methylene

and two distinct signals for methyl groups. This is only possible

when the nitrogen atom from this group is intramolecularly

connected rigidly to the metal center, expressing the properties

of the diastereotopic methylene group. Exactly this phenom-

enon occurs in 8, where also two diﬀerent signals for CH

groups and four doublets for the methyl groups of the

guanidinate substituents are visible. The resonance of the NH

the methylene group of the L parttypical of changes in the

coordination modes of the amino pendant group. The NH

group resonates at 5.92 ppm, which is a sign of the migration

of hydrogen from the former amide to the carbodiimide part.

The chemical shift (−1.9 ppm) in the Li NMR spectrum

indicates the monodentate fashion of the guanidinato ligand

plus an extra coordination of another donor such as the

pendant amine and probably also the inﬂuence of the π-system.

group found at a lower frequency (4.00 ppm in H NMR in

The H NMR spectrum in THF-d is diﬀerent to some extent

THF-d , while in C D it is not detected) and the sole signal at

(less dynamic system). The presence of extra donor molecules

caused sharpening of signals, while the NH group seems to be

NMR silent. This is also reﬂected in the Li NMR spectrum

.0 ppm in Li NMR spectra indicate the migration of the

hydrogen atom from amide to the former carbodiimide

nitrogen atom, also observed for complex 2. This allows a

dissymmetric orientation of the guanidinate toward the lithium

atom in an anisobidentate bonding mode and the formation of

a dimer where the lithium atom is four-coordinated with

pendant arm coordination. The structure of this complex has

been conﬁrmed to be similar in solid state (Figure 6 ) to a U-

with the 1.5 ppm resonance as a result of the higher

coordination number of the lithium atom. It is worth

mentioning that the signals for the central carbon atoms of

the guanidinato ligand have not been detected in the C NMR

spectra in either solvent, which is in line with the proposed fast

exchange processes within the whole molecule. The solid-state

Figure 6. Molecular structure of 8. Selected bond lengths are given

along with atom connectors in angstroms. Full ORTEP-type plots

with more bond distances and angles with standard uncertainties are

given in the SI .

Figure 7. Molecular structure of 9. Selected bond lengths are given

along with atom connectors in angstroms. Full ORTEP-type plots

with more bond distances and angles with standard uncertainties are

given in the SI .

shaped lithium guanidinate dimer 4. The presence of two L^N^N

chelating fragments is evident in the lower part of the structure,

coordinated lithium atom in a pyramidal vicinity of tightly

thus completing unusual κ -guanidinato (to the ﬁrst lithium

bound κ -guanidinate (Li−N, 1.936(3) Å), the pendant amino

atom) and κ -guanidinato-κ -amino (to the second lithium

atom) bonding modes. The cumulation of π-electron density

between C10−N3 (1.296(3) Å) and C26−N7 atoms

arm (Li−N, 2.108(3) Å), and the oxygen (Li−O, 1.957(3) Å)

of the diethyl ether molecule. The distance between the amino

nitrogen N1 and Li1 is slightly longer than in 8 (2.028(4) and

(

1.301(3) Å), as reﬂected in their separations, is a common

2.056(3) Å). The contribution of the additional contact of the

feature of a number of anisobidentately bonded guanidinates.

Each of these nitrogen atoms substituted by isopropyl groups is

very strongly coordinated to only one lithium atom in the

upper part of the structure, which is in contrast to the

structures of 2, where nitrogen atoms with smaller substituents

are always bidentate. The remaining nitrogen atoms of

guanidinates (N1 and N5) are bound to both lithium atoms

asymmetrically, with the diﬀerence in the distances being

π-system of the Dip group completing the shape to a virtual

tetrahedron is also signiﬁcant, but much smaller (Li1−Cg1,

.274(4) Å) than in 3−5, where the contact is ∼0.8 Å closer.

Distinct separations of C1 atom and nitrogen atoms of the

guanidinato unit (1.296(3)−1.410(3) Å) imply less π-electron

conjugation within this system.

The second deprotonation of 8 (Scheme 2) led to the fairly

insoluble complex 10 in good yield. This issue was managed to

grow single crystals of suitable quality from a highly diluted

THF solution. The structure of 10 (Figure 8) strongly

∼

0.25 Å. Tighter connection is similar to the surprisingly short

connection of Li atoms to the amino nitrogen atomsLi1−N2

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Figure 9. Molecular structure of 11. Selected bond lengths are given

along with atom connectors in angstroms. Full ORTEP-type plots

with more bond distances and angles with standard uncertainties are

given in the SI .

Figure 8. Molecular structure of 10. Selected bond lengths are given

along with atom connectors in angstroms. Full ORTEP-type plots

with more bond distances and angles with standard uncertainties are

given in the SI .

Li1 from the Cg1. The L^N^Nparts are quite screwed out of the

central plane of the molecule.

resembles 8 with respect to important parameters and shape.

In fact, the same U-shaped core of 8, with two central lithium

atoms pseudotetrahedrally coordinated by three nitrogen

atoms from two guanidinates and the amino pendant arm, is

further deprotonated at peripheral N3 atoms to give virtually

Reactions of potentially more reactive and soluble silylated

lithium amide 12 (Scheme 2) with both studied

carbodiimides were investigated in spite of previous

unsuccessful attempts in the case of the simpler silylated

lithium amide 6 because of low steric protection and, last but

not least, also proposed chelating behavior of the ligand with

an activation potential. Complex 12 seems to be dimeric in

solution as well as in the solid state, where the classical

centrosymmetric structure with bridging amide is observed.

Moreover, the very strong intramolecular connection of the

adjacent amino donor protects the lithium from the necessity

of the further aggregation or accommodation of an additional

donor solvent to the coordination sphere (see Figure S13 in

the SI).

0. Two lithium atoms Li2 bear one nitrogen atom of

guanidinate (Li2−N3, 1.927(3)Å) and two oxygen atoms from

THF molecules in the trigonal neighborhood run out from the

molecular core. The shape of this dilithium guanidinate(2−)

dimer is fairly diﬀerent from the similar type of complex

reported by Reed et al. (Figure 1H), which seems to be the

staircase-like central part with two parallel ends, thus

promoting an S-shaped structure.

16a

The preparation of 11 is much easier in comparison with 10

because the solubility in coordinating solvents is better. The

H NMR spectrum in THF shows one set of relatively sharp

Complex 12 reacts nicely with both carbodiimides upon the

formation of the desired lithium guanidinates substituted by

the trimethylsilyl group, but their structures are greatly

diﬀerent. The complex originating from the smaller carbodii-

mide (Scheme 2; 13) has exactly the same NMR spectral

patterns and chemical shifts as complex 2 in benzene. Of

course, there are diﬀerences in the presence of the

trimethylsilyl group instead of the hydrogen atom and in the

signals with inequivalent signals only for the methyls of the Dip

group. For the ﬁrst time, two diverse signals of equal intensity

have been found in the Li NMR spectrum at −0.2 and −3.0

ppm. Surprisingly enough, the solid-state structure of 11

(

Figure 9) exhibits a nearly planar arrangement of all nitrogen

atoms, and thus also guanidinato units, in the centrosymmetric

16a

dimeric species. As for the structure published by Reed et al.

Figure 1H) and 10, the complex is formed by two lithium

(

presence of the L fragment instead of the DipN one, but it is

guanidinates and two peripheral L −Li fragments distributed

to the opposite sides from the center. On the other hand, for

the steric reasons of four Dip groups in the central part, the

repulsion causes an unusual planar arrangement with both

lithium atoms oscillating above and below this unit. The C−N

distances within the guanidinate(2−) core are decently

equilibrated, signifying a perfectly conjugated system. The

shortest distance (of negligible diﬀerence of 0.015 Å) to the

N4 atom could be associated with the N4-bearing Dip ring,

which provides a noncovalent interaction to the peripheral

lithium atom Li1 (2.172(4) Å). Apparent diﬀerences between

the Li−N distances in the central part are once again caused by

the repulsion of both ligands. The peripheral lithium atoms Li1

are strongly coordinated to the guanidinate and amino group

in a bent fashionthe N1−Li1−N2 angle is 105.85(19)°. The

extra supply of the electron density from the π-electron system

of the Dip group is reﬂected in the very short separation of the

clear that the trimethylsilyl group has migrated (ﬁrst described

by Cole and Junk on 2-aminopyridine) from the L to the

nitrogen atom of the former carbodiimide. The structure of 13

is suggested to be dimeric as the methylene group of the

pendant arm is diastereotopic and the guanidinate ligand is

isobidentate to one of the lithium atoms while monodentate to

the other one, which is based on the increase if the C NMR

chemical-shift value of the central atom of guanidinate to ∼166

ppm from ∼162 ppm for 8. The central core of the complex is

suggested to have a staircase-like arrangement with two lithium

atoms bound between dissymmetrically oriented guanidinato

ligands. The fourth coordination place is occupied by the

amino pendant moiety. The disappearance of the AX spin

pattern and the coalescence of inequivalent signals for

isopropyls in the H NMR spectrum in THF-d determining

compound 13 to be monomeric. The disaggregation of the

dimer with subsequent rearrangement of the guanidinate and

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

the employment of solvent donor to the coordination sphere of

the three-coordinated lithium atom are predicted.

on this problem. For example, (i) the reaction of any lithiated

amide with carbodiimide always proceeds with the subsequent

migration of hydrogen or the trimethylsilyl group to the

nitrogen atom originating from carbodiimide; (ii) the use of

any combination of smaller/aliphatic carbodiimide and an

amide always produces dissymmetric aggregated structures

stable in the solution of a noncoordinating solvent and in the

solid state, which deoligomerize upon the formation of

monomeric species when the coordinating solvent is added;

(iii) in contrast, the use of the combination of all three

aromatic substituents of trisubstituted guanidinate in most

cases yields monomeric species with an extra coordination of

one of the aromatic groups to the lithium atom, which also

occurs in the solid state (while in the coordinating solvents, the

tendency to form monodentately bound guanidinates with an

adjacent donor solvent at the lithium centers is explored); (iv)

when the adjacent donor group capable of an intramolecular

interaction with lithium atoms is used, this is always done in

noncoordinating solvents and in the solid state; (v)

trimethylsilylated lithium guanidinates exhibit diﬀerent struc-

tural behavior from those having an NH group as a

consequence of the higher basicity at the guanidinate core

and the impossibility to form intra- or intermolecular H-

bridges; (vi) it is possible to evaluate and predict the structures

on the basis of the confrontation of the measurements of

multinuclear NMR spectra in the solutions of diﬀerent

solventsamong other things, the higher π-electron con-

jugation of the guanidinate unit is reﬂected in the increase of

The complex 14 in C D solution reveals a monomeric

nature with κ -bonded guanidinate via the nitrogen from the

part and strong contact of the pendant arm (formation of

a diastereotopic methylene group). The spectral patterns in the

THF-d solution indicate the decoordination of the pendant

moiety. The formation of an inverted structure where the

lithium sits between two nitrogen atoms bearing the Dip and

groups (bidentate fashion) and the additional coordina-

tion of solvent molecules most likely conﬁrm this statement.

Paradoxically, the combination of the Dip and trimethylsilyl

groups reserves more place for coordination of four donors

than the i Pr groups in 13 (for proposed structures see SI

Scheme S1 ). In the solid state, the structure of 14 approaches

the C NMR chemical shift of the central carbon atom.

We believe a starter kit for the preparation of structurally

predictable metal guanidinates further usable in catalysis or

material science has been explored. Moreover, the guanidinates

containing an NH group, dilithium guanidinates(2−), or

trimethylsilylated lithium guanidinates could open a new ﬁeld

for the preparation of bimetallic complexes mainly with regard

to the heterobimetallic ones with cooperative behavior or

properties. These are currently being investigated in our group.

Figure 10. Molecular structure of 14. Selected bond lengths are given

along with atom connectors in angstroms. Full ORTEP-type plots

with more bond distances and angles with standard uncertainties are

given in the SI.

addition, the structure has all-in-plane heteroatoms together

with the central C1 atom and only the phenyl rings are

deviated. At ﬁrst sight, that structure resembles 8, but it is

made unique by signiﬁcant diﬀerences: (i) lithium here

interacts with the Dip group settled on the nitrogen group

together with the trimethylsilyl group, while in 8 with the Dip

group at imino nitrogen, (ii) absence of an additional donor

induces the shortest (1.922(4)Å) separation of π-electron

EXPERIMENTAL SECTION

■

In the following paragraphs, only simpliﬁed and general procedures

are presented. A detailed description of the synthesis and the

characterization of all complexes are given in the SI .

All syntheses were performed using the standard Schlenk

techniques under an inert argon atmosphere. All solvents and starting

carbodiimides were purchased from commercial sources (Sigma-

Aldrich and VUOS, a.s., Pardubice-Rybitvı). Solvents were dried by

cloud to lithium (∼1.3 Å shorter than in 8).

the PureSolv MD 7 solvent puriﬁcation system supplied by Innovative

Technology, Inc., degassed, and then stored under argon atmosphere.

Single crystals suitable for X-ray analyses were obtained under argon

from the corresponding saturated solutions of products in organic

solvent(s) cooled to 7 or −30 °C. Melting points were measured in an

inert perﬂuoroalkyl ether and were uncorrected. Deuterated solvents

for NMR spectra were distilled, degassed, and stored over a K or Na

mirror under argon atmosphere.

CONCLUSION

■

To conclude, we have prepared and structurally characterized

ﬁve diﬀerent types of lithium guanidinato complexes by a

combination of the reaction pathways of the following: bulky

lithium anilide and both aliphatic and aromatic carbodiimides;

lithium anilide with an adjacent amino donor group and both

aliphatic and aromatic carbodiimides; and trimethylsilylated

lithium anilide with an adjacent amino donor group and both

aliphatic and aromatic carbodiimides. On the other hand,

reactions of bulky trimethylsilylated lithium anilide with

carbodiimides did not proceed under the desired conditions.

Lithiated guanidinates, which contain an NH group, can

further be easily deprotonated to give dilithium guanidi-

nates(2−). From the structural point of view, the family of

these complexes is very diverse, but some light has been shed

NMR spectra of the starting lithium amides 1, 6, 7, and 12 in THF-

and/or in C

D (see the SI for NMR data) were measured for

6 6

comparison and for the studies of the chemical shifts of target

compounds. The syntheses of 1, 6, 7, and 12 are reported

elsewhere. The NMR spectra were recorded from the solutions of

appropriate compounds in deuterated solvent(s) on a Bruker Avance

00 spectrometer (equipped with a Z-gradient 5 mm probe) at 295 K

at the frequencies of 500.13 MHz for H, 125.76 MHz for C{ H},

and 194.37 MHz for Li{ H}. Solutions were obtained by dissolving

approximately 40 mg of each compound in approximately 0.6 mL of

deuterated solvents. The values of H chemical shifts were calibrated

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

32 10 Pardubice, Czech Republic; orcid.org/0000-0001-

Article

to the internal standardtetramethylsilane (δ( H) = 0.00) or to the

data can be obtained free of charge via www.ccdc.cam.ac.uk/

data_request/cif, or by emailing data_request@ccdc.cam.ac.

uk, or by contacting The Cambridge Crystallographic Data

Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44

residual signals of benzene (δ( H) = 7.16) and THF (δ( H) = 3.58 or

.73), respectively. The values of C chemical shifts were calibrated

to the signals of THF (δ( C) = 67.6) or benzene (δ( C) = 128.4)

and those of Li to the external 1 M LiCl in D O (δ( Li) = 0.0,

recalculated to the frequency ratio Ξ for a 500.13 MHz spectrometer

194.3695079361 MHz). All C NMR spectra were measured using

a standard proton-decoupled experiment, and CH and CH vs C and

CH were diﬀerentiated using the APT method.

1223 336033.

−

AUTHOR INFORMATION

■

Corresponding Author

Ales Ruzicka − Department of General and Inorganic Chemistry,

Faculty of Chemical Technology, University of Pardubice, CZ-

The X-ray data for the colorless crystals of 2−5, 6·[Et O] , [7·

Et O] , 8−11, [12] and 14 (see Table S1 in the SI) were obtained at

50 K using an Oxford Cryostream low-temperature device on a

Nonius KappaCCD diﬀractometer with Mo Kα radiation (λ =

.71073 Å), a graphite monochromator, and the φ and χ scan mode.

191-0273; Email: ales.ruzicka@upce.cz; Fax: +420-

466037068

Data reductions were performed with DENZO-SMN. The

absorption was corrected by integration methods. The structures

were solved by direct methods (Sir92) and reﬁned by full matrix

least-squares method on the basis of F (SHELXL97). Hydrogen

atoms were mostly localized on a diﬀerence Fourier map, but to

ensure the uniformity of crystal treatment, all hydrogens were

recalculated into idealized positions (riding model) and assigned

temperature factors H (H) = 1.2U (pivot atom) or 1.5U_e_q

Authors

Tomas Chlupaty − Department of General and Inorganic

́ ̌

Chemistry, Faculty of Chemical Technology, University of

Pardubice, CZ-532 10 Pardubice, Czech Republic

Jana Nevoralova − Department of General and Inorganic

Chemistry, Faculty of Chemical Technology, University of

Pardubice, CZ-532 10 Pardubice, Czech Republic

iso

(

methyl). H atoms in methyl, methylene, and methane moieties

and hydrogen atoms in aromatic rings were placed with C−H

distances of 0.96, 0.97, 0.98, and 0.93 Å, and 0.86 Å for N−H bonds.

Crystallographic data for structural analysis have been deposited

with the Cambridge Crystallographic Data Centre, CCDC Nos.

Zdenka Ruzickova − Department of General and Inorganic

̌ ́

Chemistry, Faculty of Chemical Technology, University of

Pardubice, CZ-532 10 Pardubice, Czech Republic

997777 −1997791 for all complexes: 2−5, 6·[Et O] , [7·Et O] , 8−

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.inorgchem.0c01362

1, [12] , and 14 and its solvatopolymorphs.

General Procedure of Preparation of Lithium N,N′-Disub-

stituted-{N″-[2,6-di(propan-2-yl)phenyl]}guanidinates

Notes

Dipp‑R

HLi) (2, 3). To a solution of lithium [2,6-di(propan-2-

The authors declare no competing ﬁnancial interest.

yl)phenyl]azanide (1) in Et O cooled to 0 °C, one equivalent of

starting N,N′-disubstituted carbodiimides (a solution in Et O) was

ACKNOWLEDGMENTS

We thank the Czech Science Foundation for continuous

ﬁnancial support.

added. The reaction mixtures were allowed to warm to room

■

temperature and stirred overnight. After that, the Et O was

evaporated in vacuo and crude products were washed with a small

amount of hexane to give white crystalline products of 2 and 3.

General Procedure of Preparation of Lithium N,N′-Disub-

DEDICATION

■

stituted-{N″-[2-[(dimethylamino)methyl]phenyl}guanidinates

NN‑R

Dedicated to Professor Dr. Antonın Lycka on the occasion of

his 70th birthday and enormous contribution to the ﬁeld of

NMR spectroscopy.

HLi) (8, 9). To a solution of lithium 2-[(dimethylamino)-

methyl]phenylazanide (7) in Et O cooled to 0 °C, one equivalent of

starting N,N′-disubstituted carbodiimides (a solution in Et O) was

added. The reaction mixtures were allowed to warm to room

temperature and stirred overnight. After that, the Et O was

REFERENCES

1) (a) For example:Corey, E. J.; Czako

■

evaporated in vacuo and crude products were washed with a small

amount of hexane to give white crystalline products of 8 and 9.

General Procedure of Preparation of Lithium N,N′-Disub-

(

, B.; Ku

rti, L. Molecules and

medicine, 1st ed.; Wiley: Hoboken, NJ, USA, 2007. (b) Mori, A.;

Cohen, B. D.; Lowenthal, A. Guanidines: Historical, biological,

biochemical, and clinical aspects of the naturally occurring guanidino

compounds, 1st ed.; Plenum Press: New York, 1985. (c) Castagnolo,

D.; Schenone, S.; Botta, M. Guanylated Diamines, Triamines, and

Polyamines: Chemistry and Biological Properties. Chem. Rev. 2011,

11, 5247−5300. (d) Superbases for Organic Synthesis: Guanidines,

Amidines, Phosphazenes and Related Organocatalysts ; Ishikawa, T., Ed.;

Wiley: Chichester, U.K., 2009; DOI: 10.1002/9780470740859.

̈ ̈

2) For example: (a) Blondeau, P.; Segura, M.; Perez-Fernandez, R.;

stituted-{N″-trimethylsilyl-[2-[(dimethylamino)methyl]-

NN‑R

phenyl}guanidinates (L

(SiMe )Li) (13, 14). To a solution of

lithium trimethylsilyl-2-[(dimethylamino)methyl]phenylazanide (12)

in Et O cooled to 0 °C, one equivalent of starting N,N′-disubstituted

carbodiimides (a solution in Et O) was added. The reaction mixtures

were allowed to warm to room temperature and stirred overnight.

After that, the Et O was evaporated in vacuo and crude products were

washed with a small amount of hexane to give white crystalline

products of 13 and 14.

(

de Mendoza, J. Molecular recognition of oxoanions based on

guanidinium receptors. Chem. Soc. Rev. 2007 , 36 , 198 −210.

(b) Aakeroy, C. B.; Seddon, K. R. The hydrogen bond and crystal

engineering. Chem. Soc. Rev. 1993, 22, 397−407. (c) Dhavamurthy,

M.; Peramaiyan, G.; Nizam Mohideen, M.; Kalainathan, S.; Mohan, R.

Structural, growth and optical characterizations of an organic third-

order nonlinear crystal: Guanidinium trichloroacetate. J. Nonlinear

Opt. Phys. Mater. 2015, 24, 1550045.

ASSOCIATED CONTENT

sı Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c01362.

■

Full experimental section and all molecular structures of

tilted compounds in ORTEP views with selected

interatomic distances and angles (PDF)

(

3) (a) For example: Ulrich, H. Chemistry and Technology of

Carbodiimides ; Wiley: Chichester, U.K., 2007; DOI: 10.1002/

780470516683 . (b) Maesy, B.; Cossy, J.; Plonac, S. Guanidines as

Accession Codes

CCDC 1997777 −1997780 and 1997782−1997791 contain

the supplementary crystallographic data for this paper. These

Reagents and Catalysts II; Seling, P., Ed.; Topics in Heterocyclic

Chemistry: 51; Springer International: Cham, Switzerland, 2017,

1−203.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

4) Alonso-Moreno, C.; Antin

olo, A.; Carrillo-Hermosilla, F.; Otero,

Containing Iridium Complexes Capable of Efficient Photocatalytic

Water Reduction. Chem. - Eur. J. 2013, 19 , 1303 −1310. (l) Xu, L.;

Wang, Y.-C.; Ma, W.; Zhang, W.-X.; Xi, Z. Mechanistic Insights into

N-N Bond Cleavage in Catalytic Guanylation Reactions between 1,2-

Diarylhydrazines and Carbodiimides. J. Org. Chem. 2014 , 79 , 12004 −

12009. (m) Coles, M. P. Application of neutral amidines and

guanidines in coordination chemistry. Dalton Trans. 2006, 985−1001.

(9) (a) Jones, C.; Furness, L.; Nembenna, S.; Rose, R. P.; Aldridge,

S.; Stasch, A. Bulky guanidinato and amidinato zinc complexes and

their comparative stabilities. Dalton Trans. 2010 , 39 , 8788 −8795.

(b) Edelmann, F. T. Lanthanide amidinates and guanidinates in

catalysis and materials science: a continuing success story. Chem. Soc.

Rev. 2012 , 41 , 7657 −7672. (c) Wang, Y.; Luo, Y.; Chen, J.; Xue, H.;

Liang, H. Synthesis of mono(guanidinate) rare earth metal bis(amide)

complexes and their performance in the ring-opening polymerization

of L-lactide and rac-lactide. New J. Chem. 2012 , 36 , 933 −940.

(d) Zhang, J.; Yi, W.; Chen, Z.; Zhou, X. Room temperature C-N

bond cleavage of anionic guanidinate ligand in rare-earth metal

complexes. Dalton Trans. 2013, 42, 5826−5831. (e) Willcocks, A. M.;

Robinson, T. P.; Roche, Ch; Pugh, T.; Richards, S. P.; Kingsley, A. J.;

Lowe, J. P.; Johnson, A. L. Multinuclear Copper(I) Guanidinate

Complexes. Inorg. Chem. 2012 , 51 , 246 −257. (f) Tin, M. K. T.; Yap,

G. P. A.; Richeson, D. S. Transition Metal Complexes of Guanidinate

Dianions: Reactions between Guanidines and M(NMe2)5 (M = Ta,

Nb). Inorg. Chem. 1998, 37, 6728 −6730. (g) Milanov, A. P.; Thiede,

T. B.; Devi, A.; Fischer, R. A. Homoleptic Gadolinium Guanidinate: A

Single Source Precursor for Metal-Organic Chemical Vapor

Deposition of Gadolinium Nitride Thin Films. J. Am. Chem. Soc.

2009, 131, 17062−17063.

A. Guanidines: from classical approaches to efficient catalytic

syntheses. Chem. Soc. Rev. 2014, 43, 3406 −3425.

5) (a) Xu, L.; Zhang, W.-X.; Xi, Z. Mechanistic Considerations of

the Catalytic Guanylation Reaction of Amines with Carbodiimides for

Guanidine Synthesis. Organometallics 2015 , 34 , 1787 −1801.

b) Zhang, W.-X.; Xu, L.; Xi, Z. Recent development of synthetic

preparation methods for guanidines via transition metal catalysis.

Chem. Commun. 2015 , 51 , 254 −265. (c) Edelmann, F. T. Recent

Progress in the Chemistry of Metal Amidinates and Guanidinates. In

Advances in Organometallic Chemistry, Vol. 61; Hill, A., Fink, M. J.,

Eds.; Academic Press, Elsevier: San Diego, CA, USA, 2013; pp 55−

74, DOI: 10.1016/B978-0-12-407692-1.00002-3 . (d) Pottabathula,

S.; Royo, B. First iron-catalyzed guanylation of amines: a simple and

highly efficient protocol to guanidines. Tetrahedron Lett. 2012, 53,

6) (a) Mannepalli, L. K.; Dupati, V.; Vallabha, S. J.; Sunkara V, M.

156−5158.

Synthesis of substituted guanidines using Zn-Al hydrotalcite catalyst.

J. Chem. Sci. 2013, 125, 1339−1345. (b) Elorriaga, D.; Carrillo-

Hermosilla, F.; Antinolo, A.; Lopez-Solera, I.; Fernandez-Galan, R.;

Serrano, A.; Villasenor, E. Synthesis, Characterization and Reactivity

of New Dinuclear Guanidinate Diimidoniobium Complexes. Eur. J.

Inorg. Chem. 2013, 2013 , 2940 −2946. (c) Li, D.; Guang, J.; Zhang,

W.-X.; Wang, Y.; Xi, Z. Zn(OTf)2-catalyzed addition of amines to

carbodiimides: efficient synthesis of guanidines and unpredicted

formation of Zn-N amido species. Org. Biomol. Chem. 2010, 8, 1816−

(

820.

7) (a) Kantam, M. L.; Priyadarshini, S.; Amal Joseph, P. J.; Srinivas,

P.; Vinu, A.; Klabunde, K. J.; Nishina, Y. Catalytic guanylation of

aliphatic, aromatic, heterocyclic primary and secondary amines using

nanocrystalline zinc (II) oxide. Tetrahedron 2012, 68, 5730−5737.

(10) For example: (a) Gornitzka, H.; Stalke, D. Coordination of the

Bis(pyridyl)methyl Substituent to Group 1 and 13 Metals. Organo-

b) Yavari, I.; Sodagar, E.; Nematpour, M.; Askarian-Amiri, M.

metallics 1994, 13, 4398−4405. (b) Azhakar, R.; Sarish, S. P.; Tavcar,

Nanoparticulate Copper(II) Oxide Catalyzed Synthesis of Guanidine

Derivatives and Their Conversion into Functionalized Iminoguani-

dines. Synlett 2015, 26, 1230−1232.

G.; Roesky, H. W.; Hey, J.; Stalke, D.; Koley, D. Formation of Silicon

Centered Spirocyclic Compounds: Reaction of N-Heterocyclic Stable

Silylene with Benzoylpyridine, Diisopropyl Azodicarboxylate, and 1,2-

Diphenylhydrazine. Inorg. Chem. 2011, 50, 3028 −3036. (c) Xiong, Z.;

(

8) (a) Patai, S., Rappoport, Z., Eds. The Chemistry of Amidines and

Imidates , Vol. 2 , Wiley Interscience: New York, 1991; DOI: 10.1002/

780470772478 . (b) Edelmann, F. T. N-silylated benzamidines:

Yao, S.; Muller, R.; Kaupp, M.; Driess, M. From silicon(II)-based

dioxygen activation to adducts of elusive dioxasiliranes and sila-ureas

stable at room temperature. Nat. Chem. 2010, 2 , 577 −580.

(d) Meltzer, A.; Inoue, S.; Praesang, C.; Driess, M. Steering S-H

and N-H Bond Activation by a Stable N-Heterocyclic Silylene:

Different Addition of H2S, NH3, and Organoamines on a Silicon(II)

Ligand versus Its Si(II)→Ni(CO)3 Complex. J. Am. Chem. Soc. 2010 ,

132 , 3038 −3046. (e) Asay, M.; Jones, C.; Driess, M. N-Heterocyclic

Carbene Analogues with Low-Valent Group 13 and Group 14

Elements: Syntheses, Structures, and Reactivities of a New Generation

of Multitalented Ligands. Chem. Rev. 2011, 111, 354−396.

versatile building blocks in main group and coordination chemistry.

Coord. Chem. Rev. 1994 , 137 , 403 −481. (c) Edelmann, F. T.

Lanthanide amidinates and guanidinates: from laboratory curiosities

to efficient homogeneous catalysts and precursors for rare-earth oxide

thin films. Chem. Soc. Rev. 2009 , 38 , 2253 −2268. (d) Collins, S.

Polymerization catalysis with transition metal amidinate and related

complexes. Coord. Chem. Rev. 2011 , 255 , 118 −138. (e) Edelmann, F.

T. Homogeneous Catalysis Using Lanthanide Amidinates and

Guanidinates. In Molecular Catalysis of Rare-Earth Elements; Roesky,

P., Ed.; Structure and Bonding, Vol. 137 ; Springer: Berlin, Heidelberg,

(11) Maes, B.; Cossy, J.; Plonac, S. In Guanidines as Reagents and

Catalysts II; Seling, P., Ed.; Topics in Heterocyclic Chemistry;

Springer International: Cham, Switzerland, 2017; p 51.

010; pp 109 −163, DOI: 10.1007/430_2010_19 (f) Mohamed, A.

A. Advances in the coordination chemistry of nitrogen ligand

complexes of coinage metals. Coord. Chem. Rev. 2010 , 254 , 1918 −

(12) For example: (a) Krasnopolski, M.; Hrib, C. G.; Seidel, R. W.;

Winter, M.; Becker, H.-W.; Rogalla, D.; Fischer, R. A.; Edelmann, F.

T.; Devi, A. Homoleptic Gadolinium Amidinates as Precursors for

MOCVD of Oriented Gadolinium Nitride (GdN) Thin Films. Inorg.

Chem. 2013, 52, 286−296.

947. (g) Edelmann, F. T. Advances in coordination chemistry of

amidinate and guanidinate ligand. In Advances in Organometallic

Chemistry, Vol. 57; Hill, A., Fink, M. J., Eds.; Academic Press, Elsevier:

Burlington, MA, USA, 2008; pp 183−352, DOI: 10.1016/S0065-

055(08)00003-8. (h) Kratsch, J.; Kuzdrowska, M.; Schmid, M.;

(13) (a) Junold, K.; Baus, J. A.; Burschka, C.; Tacke, R. Bis[N, N ′-

diisopropylbenzamidinato(−)]silicon(II): A Silicon(II) Compound

with Both a Bidentate and a Monodentate Amidinato Ligand. Angew.

Chem., Int. Ed. 2012, 51, 7020−7023. (b) Jones, C.; Bonyhady, S. J.;

Holzmann, N.; Frenking, G.; Stasch, A. Preparation, Characterization,

and Theoretical Analysis of Group 14 Element(I) Dimers: A Case

Study of Magnesium(I) Compounds as Reducing Agents in Inorganic

Synthesis. Inorg. Chem. 2011 , 50 , 12315 −12325. (c) Jones, C. Bulky

guanidinates for the stabilization of low oxidation state metallacycles.

Coord. Chem. Rev. 2010, 254, 1273 −1289. (d) Sen, S. S.; Khan, S.;

Nagendran, S.; Roesky, H. W. Interconnected Bis-Silylenes: A New

Dimension in Organosilicon Chemistry. Acc. Chem. Res. 2012 , 45 ,

578 −587. (e) Inoue, S.; Epping, J. D.; Irran, E.; Driess, M. Formation

of a Donor-Stabilized Tetrasilacyclobutadiene Dication by a Lewis

Kazeminejad, N.; Kaub, C.; Ona-Burgos, P.; Guillaume, S. M.;

Roesky, P. W. Chiral Rare Earth Borohydride Complexes Supported

by Amidinate Ligands: Synthesis, Structure, and Catalytic Activity in

the Ring-Opening Polymerization of rac-Lactide. Organometallics

013, 32, 1230 −1238. (i) Obenauf, J.; Kretschmer, W. P.; Bauer, T.;

Kempe, R. An Efficient Titanium Amidinate Catalyzed Version of

Ziegler ’s Aufbaureaktion. Eur. J. Inorg. Chem. 2013, 2013, 537−544.

(

j) Hamidi, S.; Jende, L. N.; Martin Dietrich, H.; Maichle-Mossmer,

C.; Tornroos, K. W.; Deacon, G. B.; Junk, P. C.; Anwander, R. C-H

Bond Activation and Isoprene Polymerization by Rare-Earth-Metal

Tetramethylaluminate Complexes Bearing Formamidinato N-Ancil-

lary Ligands. Organometallics 2013, 32 , 1209 −1223. (k) Yu, Z.-T.;

Yuan, Y.-J.; Cai, J.-G.; Zou, Z.-G. Charge-Neutral Amidinate-

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

the novel anions [C(NtBu)2(HNtBu)]- and [C(NtBu)3]2-. J.

Article

Acid Assisted Reaction of an N-Heterocyclic Chloro Silylene. J. Am.

Organomet. Chem. 1998, 550, 213−220.

Chem. Soc. 2011, 133, 8514−8517. (f) Chlupaty,

T.; Padelkova, Z.;

̌ ́

Lycka, A.; Brus, J.; Ruzicka, A. Reactivity of lithium n-butyl amidinates

(17) (a) Zhang, X.; Qian, C.; Wang, Ch; Zhang, Y.; Wang, Y.; Yao,

Y.; Shen, Q. Synthesis, Molecular Structures, and Reactivity of

Dianionic Guanidinate Lanthanide/Lithium Derivatives. Eur. J. Inorg.

Chem. 2012, 2012, 847−858. (b) Zheng, P.; Hong, J.; Liu, R.; Zhang,

Z.; Pang, Z.; Weng, L.; Zhou, X. Synthesis and Reactivities of

Guanidinate Dianion Complexes of Heterobimetallic Lanthanide-

Lithium Cp2Ln[(CyN)2CNPh]Li(THF)3. Organometallics 2010 , 29 ,

1284 −1289. (c) Foley, S. R.; Yap, G. P. A.; Richeson, D. S. Synthesis

and Characterization of Iron Complexes with Monoanionic and

Dianionic N, N ′, N “-Trialkylguanidinate Ligands. Inorg. Chem. 2002,

41, 4149−4157.

towards group 14 metal(ii) chlorides providing series of hetero- and

homoleptic tetrylenes. Dalton Trans. 2012, 41, 5010−5019.

14) Mehlmann, P.; Witteler, T.; Wilm, L. F. B.; Dielmann, F.

Isolation, characterization and reactivity of threecoordinate phospho-

rus dications isoelectronic to alanes and silylium cations. Nat. Chem.

(

019, 11, 1139−1143.

15) (a) Fernandez-Galan, R.; Antinolo, A.; Carrillo-Hermosilla, F.;

Lopez-Solera, I.; Otero, A.; Serrano-Laguna, A.; Villasenor, E. New

zirconium and zirconocene guanidinate complexes. J. Organomet.

Chem. 2012, 711, 35 −42. (b) Coles, M. P.; Sozerli, S. E.; Smith, J. D.;

Hitchcock, P. B. Metal Complexes of Guanidine-Substituted Alkyl

Ligands: An Unsolvated Monomeric Two-Coordinate Organolithium.

Organometallics 2007 , 26 , 6691 −6693. (c) Coles, M. P.; Hitchcock, P.

B. Spontaneous assembly of a nine-vertex lithium framework

encapsulating the peroxide dianion. Chem. Commun. 2005 , 3165 −

(18) (a) Chivers, T.; Fedorchuk, C.; Schatte, G.; Brask, J. K.

Syntheses and X-ray structures of boraamidinate complexes of lithium,

phosphorus, and tellurium. Can. J. Chem. 2002 , 80 , 821 −831.

(b) Fedorchuk, C.; Copsey, M.; Chivers, T. The coordination

chemistry of boraamidinate ligands. Coord. Chem. Rev. 2007 , 251 ,

897 −924. (c) Corrente, A. M.; Chivers, T. Boraguanidinates:

Synthesis, X-ray Structures, and Reactions of {Li2[iPr2NB(NDipp)-

2]}2 with p-Block and Group 12 Element Halides. Inorg. Chem. 2008,

167. (d) Rudolf, D.; Kaifer, E.; Himmel, H.-J. Novel Bi- and

Trinuclear Gallium Halides and Hydrides with Acyclic and Bicyclic

Guanidinate Substituents: Synthesis and Reactivity. Eur. J. Inorg.

Chem. 2010, 2010, 4952−4961. (e) Jin, G.; Jones, C.; Junk, P. C.;

Lippert, K.-A.; Rose, R. P.; Stasch, A. Synthesis and characterisation of

bulky guanidines and phosphaguanidines: precursors for low

oxidation state metallacycles. New J. Chem. 2009, 33, 64−75.

47, 10073−10080. (d) Braun, U.; Habereder, T.; Noth, H.;

Piotrowski, H.; Warchhold, M. Triaminoboranes and Their Metal-

lation to N-Lithiotriaminoboranes. Eur. J. Inorg. Chem. 2002 , 2002 ,

1132 −1145. (e) Chivers, T.; Fedorchuk, C.; Parvez, M. Synthetic and

Structural Investigations of Monomeric Dilithium Boraamidinates and

Bidentate NBNCN Ligands with Bulky N-Bonded Groups. Inorg.

Chem. 2004 , 43 , 2643 −2653. (f) Corrente, A. M.; Chivers, T.

Syntheses and structures of new alkali-metal boraamidinates and

ferrocenyl aminoboranes. New J. Chem. 2010 , 34 , 1751 −1759.

(g) Brask, J. K.; Chivers, T.; Schatte, G. A new route to dilithio

boraamidinates: formation and X-ray structures of the dimeric and

trimeric clusters {Li2[RB(NBut)2]}x (R = Bun, x = 2 and R = Me, x

= 3). Chem. Commun. 2000, 1805−1806.

f) Han, H.-F.; Zhang, S.-F.; Guo, Z.-Q.; Tong, H.-B.; Wei, X.-H.

Three asymmetric guanidinato metal complexes: Synthesis, crystal

structures and their use as pre-catalysts in the Meerwein-Ponndorf-

Verley reduction. Polyhedron 2015, 99, 71−76. (g) Melen, R. L.;

Simmonds, H. R.; Wadepohl, H.; Wood, P. T.; Gade, L. H.; Wright,

D. S. Formation of an Unusual Bis(diguanidinate) Ligand via

Nucleophilic Attack of a Guanidinate onto a Carbodiimide. Aust. J.

Chem. 2014, 67, 1030−1036. (h) Tutacz, P.; Syre, R.; Hrib, C. G.;

Hilfert, L.; Frenzel, N.; Burte, E. P.; Kuhling, M.; Edelmann, F. T. The

First Aziridinylguanidinates: New Precursors for Potentially Volatile

Metal Guanidinates. Aust. J. Chem. 2014, 67, 1110−1114. (i) Wong,

G. F.; Yeung, L. F.; Tsoi, H. Y.; Chan, H.-S.; Chiang, M.-H.; Lee, H.

K. A Mononuclear Iron(II) Bis(guanidinate) Complex: Synthesis,

Structure, and Reactivity. Eur. J. Inorg. Chem. 2019, 2019, 98−109.

(19) Chlupaty,

Performance and Safety; Tabares

NY, USA, 2013; Chapter 4.

T.; Olejník, R.; Ru

zicka, A. In Lithium: Technology,

̊ ̌

, F. L., Ed.; Nova Science: Hauppauge,

(20) Ong, T.-G.; O ’Brien, J. S.; Korobkov, I.; Richeson, D. S. Facile

and Atom-Efficient Amidolithium-Catalyzed C-C and C-N Formation

for the Construction of Substituted Guanidines and Propiolamidines.

Organometallics 2006, 25, 4728−4730.

(21) Willcocks, A. M.; Robinson, T. P.; Roche, C.; Pugh, T.;

Richards, S. P.; Kingsley, A. J.; Lowe, J. P.; Johnson, A. L.

Multinuclear copper(I) guanidinate complexes. Inorg. Chem. 2012,

51, 246−247.

(22) Boss, S. R.; Coles, M. P.; Eyre-Brook, V.; Garcia, F.; Haigh, R.;

Hitchcock, P. B.; McPartlin, M.; Morey, J. V.; Naka, H.; Raithby, P.

R.; Sparkes, H. A.; Tate, C. W.; Wheatley, A. E. H. Encapsulation of

hydride by molecular main group metal clusters: manipulating the

source and coordination sphere of the interstitial ion. Dalton Trans.

2006, 5574−5582.

(

j) Liebing, P.; Harmgarth, N.; Lorenz, V.; Zorner, F.; Hilfert, L.;

Busse, S.; Edelmann, F. T. Structural Investigation of New Lithium

Amidinates and Guanidinates. Z. Anorg. Allg. Chem. 2019 , 645 , 440 −

46. (k) Luo, Y.-J.; Zhang, Y.; Shen, Q. Synthesis and Structural

Characterization of Alkali Metal Guanidinates. Chin. J. Chem. 2007 ,

5 , 562 −565. (l) Giesbrecht, R. S.; Shafir, A.; Arnold, J. Alkali-metal

guanidinates: solid-state structural diversity in solvent-free derivatives.

J. Chem. Soc., Dalton Trans. 1999, 3601−3604. (m) Trifonov, A. A.;

Lyubov, D. M.; Fedorova, E. A.; Fukin, G. K.; Schumann, H.; Muhle,

S.; Hummert, M.; Bochkarev, M. N. Chloro, Alkyl and Aryl

Complexes of Rare Earth Metals Supported by Bulky Tetrasubstituted

Guanidinate Ligands. Eur. J. Inorg. Chem. 2006, 2006, 747−756.

(

n) Castillo, M.; Barreda, O.; Maity, A. K.; Barraza, B.; Lu, J.; Metta-

(23) (a) Hu, J.-H.; Tong, H.-B.; Li, J.-F.; Huang, S.-P.; Liu, D.-S.

(1R,2R)-(−)-Bis[μ 4 −1-{[1,1-dimethyl-2-(trimethylsilyl)amidino]-

amino}-2-({1,1-dimethyl-2-[1,1-dimethyl-2-(trimethylsilyl)amidino]-

amidino}amino)cyclohexane]tetralithium(I). Acta Crystallogr., Sect. C:

Cryst. Struct. Commun. 2004, 60, m272−m274. (b) Zhou, M.; Song,

Y.; Gong, T.; Tong, H.; Guo, J.; Weng, L.; Liu, D. Synthesis and

Structures of Selected Triazapentadienate of Li, Mn, Fe, Co, Ni,

Cu(I), and Cu(II) using 2,4-N, N ′-Disubstituted 1,3,5-Triazapenta-

dienate Anions as Ancillary Ligands: [N(Ar)C(NMe2)NC(NMe2)-

N(R)]- (Ar = Ph, 2,6-iPr2-C6H3; R = H, SiMe3). Inorg. Chem. 2008,

47, 6692−6700.

Magana, A. J.; Fortier, S. Advances in guanidine ligand design:

synthesis of a strongly electron-donating, imidazolin-2-iminato

functionalized guanidinate and its properties on iron. J. Coord.

Chem. 2016, 69, 2003−2014. (o) Wong, G. F.; Yeung, L. F.; Tsoi, H.

Y.; Chan, H.-S.; Chiang, M.-H.; Lee, H. K. A Mononuclear Iron(II)

Bis(guanidinate) Complex: Synthesis, Structure, and Reactivity. Eur. J.

Inorg. Chem. 2019, 2019, 98−109. (p) Maity, A. K.; Fortier, S.;

Griego, L.; Metta-Magana, A. J. Synthesis of a Super Bulky.

Guanidinate Possessing an Expandable Coordination Pocket. Inorg.

Chem. 2014, 53, 8155−8164.

16) (a) Bailey, P. J.; Blake, A. J.; Kryszczuk, M.; Parsons, S.; Reed,

(24) (a) Chlupaty,

Structure and properties of lithium n-butyl amidinates. J. Organomet.

Chem. 2011, 696, 2346−2354. (b) Nevoralova, J.; Chlupaty, T.;

Padelkova, Z.; Ruzicka, A. Quest for lithium amidinates containing

T.; Padelkova, Z.; Lycka, A.; Ruzicka, A.

́ ̊ ̌

̌ ́ ̌ ̌

D. The first triazatrimethylenemethane dianion: crystal structure of

dilithio-triphenylguanidine Li2[C(NPh)3] as its tetrahydrofuran

solvate. J. Chem. Soc., Chem. Commun. 1995 , 1647 −1648. (b) Chivers,

T.; Parvez, M.; Schatte, G. Preparation and structures of {Li[C-

adjacent amino donor group at the central carbon atom. J. Organomet.

Chem. 2013, 745−746, 186−189.

NtBu)2(HNtBu)]}2.(THF) and {Li2[C(NtBu)3)]}2, containing

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

(

25) An, Y.; Wheeler, S. E. Cation-π Interactions. In: Hanusa, T. P.,

Ed., The Lightest Metals: Science and Technology from Lithium to

Calcium, Part 2; Wiley: Hoboken, NJ, USA, 2015; pp 173−185.

26) Kennepohl, D. K.; Brooker, S.; Sheldrick, G. M.; Roesky, H. W.

Synthesis and Molecular Structure of the Solvent-Free [LiN(SiMe3)-

2,6iPr2C6H3)]2 Dimer. Chem. Ber. 1991 , 124 , 2223 −2225.

27) Cole, M. P.; Junk, P. C. Pyridyl donor induced 1,3-silyl

migration in metal complexes of the guanidine CyHNC{N(SiMe3)-

Py}NCy, Py = 2-(6-MeC5H3N). Dalton Trans. 2003 , 2109 −2111.

28) Patton, J. T.; Bokota, M. M.; Abboud, K. A. Indium-Bridged

Chelating Diamide Group IV Metal Olefin Polymerization Catalysts.

Organometallics 2002, 21, 2145−2148.

29) Luo, B.; Young, V. G.; Gladfelter, W. L. Si-C bond cleavage in

the reaction of gallium chloride with lithium bis(trimethylsilyl)amide

and thermolysis of base adducts of dichloro(trimethylsilyl)amido

gallium compounds. J. Organomet. Chem. 2002, 649, 268−275.

(

30) Van

kat

ova,

Z.; Ru

H.; Broeckaert, L.; De Proft, F.; Olejník, R.; Turek,

zicka, A. Tetrylenes Chelated by Hybrid Amido-

J.; Padelkova,

Amino Ligand: Derivatives of 2-[(N,N-Dimethylamino)methyl]-

aniline. Inorg. Chem. 2011, 50, 9454 −9464.

34) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.

31) Patt, S.; Shoolery, J. N. Attached proton test for carbon-13

NMR. J. Magn. Reson. 1982, 46, 535 −539.

32) Otwinowski, Z.; Minor, W. Processing of X-ray diffraction data

collected in oscillation mode. Methods Enzymol. 1997, 276, 307−326.

33) Coppens, P. In Crystallographic Computing; Ahmed, F. R., Hall,

S. R., Huber, C. P., Eds.; Munksgaard: Copenhagen, 1970; pp 255−

70.

Early finding of preferred orientation: a new method. J. Appl.

Crystallogr. 1994, 27, 1045−1050.

(

35) Sheldrick, G. M. SHELXL-97; University of Gottingen:

Gottingen, Germany, 2008.