Chromium carbonyl complexes with aryl mono- and oligogermanes: Ability for haptotropic rearrangement

Article abstract of DOI:10.1016/j.jorganchem.2019.07.012

The intra- and intermolecular inter-ring η⁶ ? η⁶-haptotropic rearrangements (IRHR), occurring by involving interactions to Ge atoms in arylgermanes, were investigated theoretically and experimentally. The new methods for the synthesis of non-symmetrical polyaromatic Ge compounds were elaborated. Digermane Ph₃GeGeMe₂Cl (2) was obtained from Ph₃GeGeMe₂NMe₂ (1) under action of Me₃SiCl. Aryl digermane Ph₃GeGeMe₂(η⁶-C₆H₅)Cr(CO)₃ (4) was obtained after lithiation of (η⁶-C₆H₆)Cr(CO)₃ (3) with subsequent interaction with 2. It was established that thermally induced intramolecular IRHR in 4 is not observed experimentally; at similar reaction conditions in the presence of tetralin C₁₀H₁₂ (7) the bimolecular intermolecular IRHR occurs giving (η⁶-C₁₀H₁₂)Cr(CO)₃ (8). DFT analysis of the intramolecular IRHRs for model germane (p-Tol)₂Ge(H)(η⁶-Tol-p)Cr(CO)₃ (MC1) and digermane Ph₃GeGeH₂(η⁶-C₆H₅)Cr(CO)₃ (MC2) indicates a plausible effect of 3c-2e (agostic) Ge–H···Cr interaction on success of such rearrangement. The theoretical activation barrier is determined to be in the range of 35–37 kcal/mol. The model compound (η⁶-C₆H₃(GeHPh₂)Me₂-p)Cr(CO)₃ (12) was obtained from (η⁶-C₆H₄Me₂-p)Cr(CO)₃ (11). The decomposition of 12 was observed under conditions of thermally induced IRHR. Molecular structures of 8, 11 and 12 in a crystal were investigated by XRD.

Full text of DOI:10.1016/j.jorganchem.2019.07.012

Journal of Organometallic Chemistry 897 (2019) 217e227
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Chromium carbonyl complexes with aryl mono- and oligogermanes:
Ability for haptotropic rearrangement
,
Kirill V. Zaitsev a *, Igor P. Gloriozov a, Yuri F. Oprunenko a, Elmira Kh Lermontova b,
Andrei V. Churakov b
a Department of Chemistry, Moscow State University, Leninskye Gory 1, 3, Moscow, 119991, Russia
b N.S. Kurnakov General and Inorganic Chemistry Institute, Russian Academy of Sciences, Leninskii pr., 31, Moscow, Russia
a r t i c l e i n f o
a b s t r a c t
The intra- and intermolecular inter-ring h6
# h
6-haptotropic rearrangements (IRHR), occurring by
Article history:
Received 30 April 2019
Received in revised form
15 June 2019
Accepted 9 July 2019
Available online 12 July 2019
involving interactions to Ge atoms in arylgermanes, were investigated theoretically and experimentally.
The new methods for the synthesis of non-symmetrical polyaromatic Ge compounds were elaborated.
Digermane Ph3GeGeMe2Cl (2) was obtained from Ph3GeGeMe2NMe2 (1) under action of Me3SiCl. Aryl
digermane Ph3GeGeMe2(h h
6-C6H5)Cr(CO)3 (4) was obtained after lithiation of ( 6-C6H6)Cr(CO)3 (3) with
subsequent interaction with 2. It was established that thermally induced intramolecular IRHR in 4 is not
observed experimentally; at similar reaction conditions in the presence of tetralin C10H12 (7) the
Keywords:
bimolecular intermolecular IRHR occurs giving (
h
6-C10H12)Cr(CO)3 (8). DFT analysis of the intramolecular
Organogermanium compounds
Arene chromium carbonyl complex
Inter- and intramolecular inter-ring
haptotropic rearrangement (IRHR)
DFT calculations
IRHRs for model germane (p-Tol)2Ge(H)( h
h
6-Tol-p)Cr(CO)3 (MC1) and digermane Ph3GeGeH2( 6-C6H5)
Cr(CO)3 (MC2) indicates a plausible effect of 3c-2e (agostic) GeeH$$$Cr interaction on success of such
rearrangement. The theoretical activation barrier is determined to be in the range of 35e37 kcal/mol. The
model compound (h h
6-C6H3(GeHPh2)Me2-p)Cr(CO)3 (12) was obtained from ( 6-C6H4Me2-p)Cr(CO)3 (11).
3c-2e agostic interaction
XRD analysis
The decomposition of 12 was observed under conditions of thermally induced IRHR. Molecular structures
of 8, 11 and 12 in a crystal were investigated by XRD.
© 2019 Elsevier B.V. All rights reserved.
1. Introduction
time for the polyaromatic (ArPA) (
h
6-ArPA)Cr(CO)3 complexes,
6-rearrangements
thermally induced inter-ring haptotropic h6
#
h
The development of modern organogermanium chemistry
suggests the synthesis and investigation of properties of various
novel derivatives (for example, compounds in unusual valent states
[1] or molecular catenated species [2e4]); all these species are
interesting as fundamental objects and as potentially useful ligands
for metal complexes in catalysis [5] or in material chemistry as
precursors for the optic [6], semiconducting [7] and other [8] de-
vices. In this context the establishment of “structure e property”
relationships may be regarded also as an actual and important goal,
and therefore the synthesis of substituted germanium compounds
is highly desirable.
(IRHR) (Scheme 1) is a typical phenomenon [10]; it is observed in
naphthalenes [11], biphenyls [12] and other polyaromatics (PAH)
[13]. This reaction is valuable in science and applied fields (catalysis
[14], synthesis of new materials [15] etc.). In this case IRHR includes
the change of
h
n-coordination for the Cr atom (usually from n ¼ 6
through n ¼ 4 to n’ ¼ 6) [16].
In continuation of our work on germanium chemistry, here we
extend the number of organogermanium complexes with Cr(CO)3
groups, focusing on investigation of intra- and intermolecular IRHR
in a series of aryl substituted mono- and digermanes (Scheme 2); to
the best of our knowledge, studies of IRHR through Ge atom in
polyaromatic germanes (as opposed to diarylmethane and 1,2-
diarylethane [17]) has not been performed before.
It is well known that introduction of functional groups con-
taining transition metals into organogermanium compounds
changes the properties of them in a high extent [9]. At the same
During IRHR the difference in structure of two Ar groups at Ge is
necessary to delete degeneracy and to distinguish the initial and
final complexes; therefore the synthesis of non-symmetrical Cr
carbonyl polyaromatic di- and monogermanes (Scheme 2, types A
and B, respectively) is performed in this work. This is also desirable
* Corresponding author.
E-mail address: zaitsev@org.chem.msu.ru (K.V. Zaitsev).
https://doi.org/10.1016/j.jorganchem.2019.07.012
0022-328X/© 2019 Elsevier B.V. All rights reserved.

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K.V. Zaitsev et al. / Journal of Organometallic Chemistry 897 (2019) 217e227
including interaction of generated in situ Ph3GeLi with Me2GeCl2
(1.0 eq., reversed addition) resulted in a mixture of compounds,
that were difficult to separate; this mixture includes 2, and
Ph3GeGeMe2GePh3. Interaction of 2 with 3-Li generated in situ gave
target 4 in satisfactory yield (Scheme 4).
The possibility of IRHR in 4 was studied by NMR monitoring in
the course of heating in high-boiling solvents (up to 40 h) or
heating in neat melt (at 140 ꢀC, up to 5 h) (Scheme 5).
It was established that attempts to initiate the thermal intra-
molecular metallotropic rearrangements in 4 (migration of Cr(CO)3
group from the Ph ring “a” to “b”) were unsuccessful; under heating
the partial decomposition of the complex 4 with formation of the
digermane PhMe2GeGePh3 (6) [20] is observed. Increasing the
temperature or time of reaction resulted also in an increase of ratio
of decomposition products. Interesting that thermodynamically
Scheme 1. Typical examples of intramolecular inter-ring haptotropic h6
rangements (IRHR) for Cr(CO)3 complexes with polyaromatics.
# h
6-rear-
rearrangement of 4 into 5 is favorable (
whereas the activation energy is very high (
D
G ¼ ꢁ0.5 kcal/mol),
due to the low rate of rearrangement, which is not suitable for
DNMR. It includes the synthesis of unsymmetrical digermane
Ph3GeGeMe2Cl (2), which was used for the synthesis of Ph3GeGe-
DG ¼ 41.5 kcal/mol for
TS(4e5), Supporting Information, Fig. S14; this value is higher than
for modified model compounds MC1 and MC2, containing GeeH
bonds; see below). These kinetic data for possible mechanism of
IRHR make whole process on rearrangement as highly unfavorable.
At the same time, the intermolecular metallotropic rearrange-
ment is observed by heating 4 with excess tetralin (7), where the
Cr(CO)3 group migrates intermolecularly to the aromatic ring of
Me2(h
6-C6H5)Cr(CO)3 (4). Compounds 8 and 12 were also obtained
and investigated in detail; compounds MC1 and MC2 were used as
models for DFT calculations.
2. Results and discussion
C10H12 (Scheme 5). Apparently, in this case the occurrence of
An effective universal method for the synthesis of non-
symmetrical Cr carbonyl polyaromatic complex (A) (Scheme 2) as
an initial compound for investigation of IRHR is highly desirable.
Due to the presence of two types of aryl groups in A (“a” and “b”),
applying the direct method (interaction of free digermane with
Cr(CO)6 or (MeCN)3Cr(CO)3 under reflux in high boiling solvents) is
not chemically selective, therefore in this work new strategy for
obtaining A was developed (Scheme 3).
The new strategy includes the exploitation of high CeH proton
acidity in chromium tricarbonyl complexes in general [18] and in 3
in particular [19] which allows us to synthesize 3-Li. Due to the
instability of ClGeAr-GeAr bond under the action of strong nucleo-
philes, like organolithium compounds (e.g. 3-Li), R0 should be Me;
R’’ ¼ Ph and R ¼ H (Scheme 3) for the case of the synthesis
simplification. It is possible to assume that such synthetic strategy
is sufficiently convenient and should be effective.
intermolecular IRHR is explained by the severe reaction conditions
prompting a bimolecular rather than dissociative mechanism,
observed in diluted non-polar solvents (decalin, decane, C6F6) [17c].
Absence of by-product, complex 5, in this case may be explained by
both thermal instability of the oligogermane complexes and by the
excess of 7 used in reaction.
The molecular structure of complex 8 was studied by X-ray
diffraction analysis (Fig. 1; Table S1, Supporting Information).
It is interesting that the Cr-CAr bond lengths vary within the
wide range (2.211(1)-2.256(1) Ǻ), where the longest are observed
for alicyclic C(15) and C(20) atoms. Apparently, in this case the
slippage from
electronic (donating effect of condensed saturated six-membered
ring) or steric reasons. This effect is common for related
6-Ar
h h
6- to 4-coordination may be observed due to
h
compounds [21], complexes based on o-xylene or bicyclo[4.2.0]
octa-1,3,5-triene [22], in naphthalene [23] or related heterocycle
[24] complexes. The CO groups are in a staggered anti-conforma-
tion in relation to the arene ring (torsions Csubst-Ccentroid-Cr-CO are
For the synthesis of chlorooligogermane 2 a new method was
used, including substitution of amide on chloride; compound 2 is
easily accessible in high yield from 1. The alternative way to 2
Scheme 2. Model reactions of intra- and intermolecular inter-ring haptotropic h6
# h
6-rearrangements (IRHR) for Cr(CO)3 complexes with germanium polyaromatics.

K.V. Zaitsev et al. / Journal of Organometallic Chemistry 897 (2019) 217e227
219
Scheme 3. Retrosynthetic analysis of compounds of type A (non-symmetrical Cr carbonyl polyaromatic digermane complex).
Scheme 4. Synthesis of catenated germanium compounds Ph3GeGeMe2Cl (2) and Ph3GeGeMe2(h
6-C6H5)Cr(CO)3 (4).
Scheme 5. Intra- and intermolecular haptotropic rearrangements (IRHR) in complex 4.
152.7, 87.8 and ꢁ29.2ꢀ for C(15) and 148.0, 28.5, ꢁ88.5ꢀ for C(20);
Supporting Information).
Scheme 6). The aromatic ring is almost planar (with the largest
deviation of 0.008(1) Ǻ for C(11)) and all substituents at Ar are also
in the same plane (there is a small bending 0.021(2) Å for C(16)
towards Cr atom, and 0.014(2) Å from Cr atom for C(19)). The
saturated six-membered cycle is in a distorted half-chair confor-
mation with C(17) and C(18) as the flaps.
It was established by DFT that the IRHR with a relatively low
activation barrier may be observed only in the case of the presence
of 3c-2e bonding (agostic interaction) [25] Ge‒H$$$Cr; this is crit-
ical for rearrangement. The analysis of related Ge derivatives,
where germanium atoms are fully alkylated or arylated (as for
rearrangement 4 into 5; see above), gave significantly higher values
(41.5 vs. 36.0 kcal/mol).
According to our DFT data the IRHR corresponds to the following
pathway for Cr coordination in MC1: 1a / TS1 / IM1 / TS2 /
IM2 / TS3 / IM3 / TS4 / 1a’. So, here there are four transition
To clarify the possibility of haptotropic rearrangement (IRHR)
for aryl substituted germanes the model reaction was investigated
by DFT for complex (p-Tol)2Ge(H)(
functional PBE and two basis sets, L1 and L2 (Fig. 2; Fig. S15,
h
6-Tol-p)Cr(CO)3 (MC1), using

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K.V. Zaitsev et al. / Journal of Organometallic Chemistry 897 (2019) 217e227
In general, the principal possibility for intramolecular IRHR in
the case of germanium compounds with a dramatic role of
2-Ge-H
h
coordination to Cr is significantly different than for the related
carbon analogs Ar2CH2. In the last case the neighboring effect of an
uncoordinated Ar group has been established (anchimeric assis-
tance) [17a].
To clarify the experimental possibility of intramolecular IRHR in
aryl germanes, facilitated by the existence of agostic GeeH$$$Cr
bonds, the synthesis of non-symmetrical Cr carbonyl polyaromatic
germane (R s H; see B, Scheme 2) was done. In this context, the
retrosynthetic analysis of such species was performed (Scheme 7).
For the simplicity of the synthesis, compound 10 was selected as
an initial reagent (Scheme 7). It was obtained using a known pro-
cedure [27] by action of chlorinated agent (anhydrous CuCl2) on
diphenylgermane 9, but in our hands the full conversion of the
initial 9 was achieved only after addition of catalytic amounts of CuI
(Scheme 8). Compound 11 was synthesized using a typical pro-
cedure [28], including prolonged reflux of Cr(CO)6 and p-xylene in
(n-Bu)2O/THF (10:1). The choice of p-xylene as a ligand in 11 was
explained by a single way of its subsequent metallation. Further-
more, it is possible to assume that IRHR from more substituted ring
to Ph (“a” to “b” or “b0“, Scheme 9) is preferable [13]. It is interesting
that complex 11 is mainly lithiated by n-BuLi into aryl ring yielding
11-Li (kinetically controlled conditions; hard base, low tempera-
ture, below ꢁ40 ꢀC), which in subsequent interaction with
Ph2Ge(H)Cl (10) gave complex 12. The result of such metallation is
correlated with Trahanovsky's works [29]; the possible product of
Fig. 1. Molecular structure of compound (h
6-C10H12)Cr(CO)3 (8). Displacement ellip-
soids are shown at 50% probability level. Selected bond lengths (Å) and bond angles
(deg): Cr(1)-Cav(arene) 2.2277(14), Cr(1)-Cav(centroid) 1.7250(14), Cr(1)-COav
1.8388(16), C-Oav 1.155(2); CeCr(1)-Cav(CO) 89.34 (6).
a
-proton abstraction of Me groups (thermodynamically controlled
states (TS); in intermediate molecules IM1 and IM3 the agostic
bonding is observed, whereas the Cr atom is connected with only
ipso-carbon of the p-Tol group; similar coordination is observed in
TS3, but with the neighboring p-Tol. Related coordination is
observed in IM2. In TS2 the agostic bond is also present, but a direct
CreGe bond is observed; formation of this species has the biggest
activation barrier (36.0 kcal/mol). Activation energy of this level is
relatively high, but comparable also to those in related biphenylene
and biphenyl complexes (33 and 35 kcal/mol, respectively; see
Scheme 1) [12,26].
products) was not identified in our case.
According to NMR, phenyl groups in 12 are nonequivalent due to
the presence of germyl and methyl groups in the
(Scheme 9).
h
6-Ar ring
All chromium complexes 4, 8, 11 and 12 were isolated as
yellowish powders, soluble in common organic solvents (THF,
toluene), stable as solids under inert atmosphere, but decomposed
rapidly (up to days) in solution; also rapid decomposition is
observed in chloroform. The band n
(GeeH) for 12 (2062 cmꢁ1, ATR)
is shifted to somewhat longer wavenumbers in comparison with
typical values of arylgermanes (compare with 2028e2057 cmꢁ1 for
Ar3GeH in non-polar solvents) [30], which is explained by the
presence of the electron withdrawing Cr carbonyl fragment. The
stretching bands for carbonyl groups (nCO symmetric A1 and
asymmetric E bands) appeared in the typical region (1980e1942
and 1905e1846 cmꢁ1, respectively). In NMR spectra of Cr com-
plexes 4, 8, 11 and 12 (for details, see Supporting Information) the
signals of coordinated aryl groups are shifted significantly upfield
For the model digermane Ph3GeGeH2(h
6-C6H5)Cr(CO)3 (MC2)
the rearrangement path is presented below (Fig. 3; basis L1); these
DFT calculations are more complicated and the activation barrier
(
D
E ¼ 34.7 kcal/mol;
D
G ¼ 35.3 kcal/mol) is approximately the
same as for monogermane MC1. In general, the nucleophilicity of
GeeC bonds is smaller than GeeH bonds, and therefore the IRHR is
absent for the full arylated oligogermanes like 4 (see above).
It was established that for MC2 a pathway for IRHR very similar
to MC1 is observed. It includes the next stages: I / TS1 / IM1 /
TS2 / IM2 / TS3 / IM3 / TS4 / II.
(to
d d
5.18e4.25 ppm in 1H and to 109.18e92.55 ppm in 13C NMR)
Scheme 6. Conformations of carbonyl groups in Cr complexes in relation to h
6-Ar ligand.

K.V. Zaitsev et al. / Journal of Organometallic Chemistry 897 (2019) 217e227
221
Fig. 2. Stationary states on PES and mechanism for IRHR in model germane (p-Tol)2Ge(H)(h
6-Tol-p)Cr(CO)3 (MC1) according to DFT (basis L1) (energy total in atomic units, a.u.;
relative energy in kcal/mol).
due to back donation from Cr(CO)3; the signals in 1H NMR spectra
in d(GeeC) is observed (compare GeeC(13) vs. GeeC(7)). The ge-
ometry of Ge atom may be described as a slightly distorted tetra-
hedron. Conformation of Cr(CO)3 group is syn-staggered (torsions
C(18)-Ccentroid-Cr-CO are ꢁ94.3, 146.2 and 24.8ꢀ; C(15)-Ccentroid-Cr-
CO are ꢁ34.7, ꢁ156.1 and 84.7ꢀ; C(13)-Ccentroid-Cr-CO
are ꢁ35.8, ꢁ155.0 and 85.5ꢀ; Scheme 6). Apparently, in di- or tri-
substituted arenes [32] (like 8, 11 and 12 with weak electron-
donating groups) the predominance of staggered conformation is
explained by steric reasons due to diminishing of geometrical in-
are well resolved (3JH-H 6.3e6.8 Hz) giving classical multiplets. The
chemical shifts of GeH (
5.93 (C6D6) ppm in 12) are typical.
Molecular structures of the complexes 11 and 12 were investi-
d 5.15 ppm (CDCl3) in 9, d 6.54 (CDCl3) in 10,
d
gated by X-ray diffraction (XRD) analysis (Figs. 4 and 5; Table S1,
Supporting Information).
In 11 the conformation of carbonyl groups is staggered (torsions
C(3)-Ccentroid-Cr-CO are ꢁ163.2, ꢁ41.5 and 77.4ꢀ; C(6)-Ccentroid-Cr-CO
are 138.8, ꢁ102.3 and 17.1ꢀ; Scheme 6). Both methyl groups, C(7)
teractions between CO groups and substituents in h
6-Ar ring. This is
and C(8), are displaced from the plane of
h
6-aryl rings in the di-
different from mono-substituted derivatives, where electronic ef-
fects (electron donating, D, is usually eclipsed with CO and with-
drawing, W, groups are staggered) [33] may impact on the
conformation (Scheme 6). All substituents, C(19), C(20) and Ge(1),
in 12 are displaced from the plane of aryl group in the direction
rection opposite to the Cr atom (by 0.043(3) and 0.099(3) Å,
respectively), which is typical for electron donor substituents [31].
Introduction of Cr carbonyl fragment in 12 has insignificant ef-
fect on structural parameters of the Ge atom; only a small increase

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K.V. Zaitsev et al. / Journal of Organometallic Chemistry 897 (2019) 217e227
Fig. 3. Stationary states on PES and mechanism for IRHR in model digermane Ph3GeGeH2(
h
6-C6H5)Cr(CO)3 (MC2) according to DFT (PBE functional, basis L1) (energy total in atomic
units, a.u.; relative energy in kcal/mol).
opposite to the Cr atom (by 0.047(6), 0.012(5) and 0.054(4) Å,
respectively), what is typical for electron-donating substituents.
Ring, coordinated to Cr atom, is almost planar (maximal deviation is
0.009(2) for C(15)).
derivatives of another class (1.48(3) Å in Ph3GeH [42], and 1.33(3) Å
in (C6F5)3GeH [43], 2.05 Å in Mes3GeH [44], 1.48 Å in (p-
F3CC6H4)3GeH [4b]). In all of these structures d(GeeH) varies in
1.33e2.06 Å range. The close similarity in geometry parameters for
12 and unsubstituted Ph3GeH indicates the weak effect of para-
substitution in arene on structure; the impact of Cr(CO)3 group is
also small, apparently due to the high degree of conjugation be-
Due to geometrical reasons in a crystal of 12 there is no
GeeH$$$Cr agostic interaction (d(CreH) 4.12 Å, d(GeeH) 1.51(4) Å,
Ge-H-Cr 67.54ꢀ); it should be noted that known
h
2-Ge-H in-
teractions are in a range of 1.65e2.10 Å [34].
tween h
6-Ph and Cr(CO)3 and back-donation [9b].
It should be noted that the majority of triarylgermanes inves-
tigated to date by XRD includes ortho-substituted aryls (where
Under comparison of the crystal structures of 8, 11 and 12 it is
evident that the direct Cr-Caryl bond distance is increased for
substituted C atom (compare 2.256/2.247 vs. 2.211e2.220 for 8;
2.245/2.262 vs. 2.214e2.226 for 11; 2.225/2.233/2.240 vs.
2.195e2.215 Å for 12). In this work this fact may be explained by the
donor properties of the substituents (alicyclic, methyl or germyl
d(GeeH) 1.71 Å in [o-MeC6H4]3GeH [35], 1.58 Å in [o-Me2NC6H4]3
-
GeH [36], 1.42(3) Å in [o-Me2NC6H4]3GeH [37], 1.605 Å in [o-
EtOC6H4]3GeH [38], 1.37(2) Å in [o-(t-Bu)C6H4]3GeH [39], 1.39 [40]
or 1.44 [41] Å in [o-Ph2PC6H4]3GeH) and there are only four

K.V. Zaitsev et al. / Journal of Organometallic Chemistry 897 (2019) 217e227
223
Scheme 7. Retrosynthetic analysis of compounds of type
B (non-symmetrical Cr
carbonyl polyaromatic monogermane complexes).
groups), which in some extent weakened interaction between Ge
and the aryl cycle. The experimental crystallographic main struc-
tural parameters for 8, 11 and 12 (bond lengths, angles) were
compared with those calculated according to DFT (PBE functional,
basis L1, L2) (Table S2, Supporting Information), indicating the good
level of correlation and reliability of the calculated models.
Under investigation of IRHR for 12 according to NMR analysis,
applying even hard conditions (130 ꢀC in n-octane for 40 h; 130 ꢀC
in n-decane for 5 h; 130 ꢀC in neat for 2 h) indicated the absence of
intramolecular IRHR (Scheme 10); the initial 12 was identified as a
single compound together with traces of thermal decomposition
(turbidity, opacity, broadening of the NMR resonances).
Such a result in the case of 12 may be explained by the suffi-
ciently high activation barrier of rearrangement; further modifi-
cation of electron properties of Ar groups both in coordinated and
non-coordinated rings should be performed to diminish the acti-
vation energy of IRHR. Other possibilities to significantly decrease
(by about 5 kcal/mol) the activation barrier of the IRHR consist in
changing the metal from Cr to Mo (the second metal of the triad)
[45] or changing the CO ligand to PR3 [46].
Fig. 4. Molecular structure of compound (
h
6-C6H4Me2-p)Cr(CO)3 (11). Displacement
ellipsoids are shown at 50% probability level. Selected bond lengths (Å) and bond
angles (deg): Cr(1)-Cav(arene) 2.230(2), Cr(1)-Cav(centroid) 1.729(2), Cr(1)-COav
1.839(2), C-Oav 1.157(3); CeCr(1)-Cav(CO) 88.48(1).
arylgermanes was obtained and investigated by a number of
methods. By DFT calculations the possibility of intramolecular IRHR
was shown for mono- and polygermanes, where the presence of 3c-
2e Cr$$$HeGe interaction is crucial. Future improvements should
be directed to decrease the thermal barrier of this rearrangement
by changing the nature of the substituents, metal or ligand. Ther-
mally induced intermolecular IRHR was observed for the Cr
carbonyl complexes based on arylgermanes.
4. Experimental part
4.1. Experimental details
All manipulations were performed under a dry, oxygen-free
argon atmosphere using standard Schlenk techniques. 1H NMR
(400.130 MHz) and 13C NMR (100.613 MHz) spectra were recorded
with Bruker 400 or Agilent 400 MR spectrometers at 298 K.
Chemical shifts are given in ppm relative to internal Me4Si (1H and
3. Conclusions
A
series of new chromium carbonyl complexes with
Scheme 8. Synthesis of compound 12.
Scheme 9. Fischer projections for (h
6-C6H3(GeHPh2)Me2-p)Cr(CO)3 (12).

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K.V. Zaitsev et al. / Journal of Organometallic Chemistry 897 (2019) 217e227
prepared by refluxing copper dichloride in SOCl2 (40 g/50 mL) for
4 h, then filtered off and dried in vacuum over KOH.
4.2. Computational details
The geometries of molecules, transition states, and in-
termediates were fully optimized by means of density functional
theory (DFT) calculations. The GGA PBE functional [48] and the full
electron basis sets L1 and L2 were used, where L1 stands for double
set size and L2 e for triple set size. The numbers of contracted and
primitive functions used in L1 are respectively {2,1}/{6,2} for H,
{3,2,1}/{10,7,3} for C and O, {5,4,2}/{19,15,11} for Ge and {6,5,3,1}/
{19,15,11,5} for Cr. The numbers of contracted and primitive func-
tions used in L2 are respectively {3,2,1}/{8,4,2} for H, {4,3,2,1}/
{12,8,4,2} for C and O, {6,5,3,1}/{23,18,13,2} for Ge, {8,7,5,3,1}/
{23,18,13,8,4} for Cr [49]. Stationary points on the potential energy
surface (PES) were identified by analyzing Hessians. The thermo-
dynamic functions (Gibbs activation energies, G) at 298.15 K were
calculated using an approximation of restricted rotator and har-
monic oscillator. Reaction paths were found by the intrinsic reac-
tion coordinate (IRC) method [50]. All calculations were performed
using the MBC100k cluster at the Joint Supercomputer Centre
(JSCC) (Moscow, Russia) with the use of the PRIRODA04 program
written by Laikov [51].
Fig. 5. Molecular structure of compound
(h
6-C6H3(GeHPh2)Me2-p)Cr(CO)3 (12).
Displacement ellipsoids are shown at 50% probability level. Selected bond lengths (Å)
and bond angles (deg): Ge(1)-H 1.51(4), Ge(1)eC(7) 1.940(3), Ge(1)eC(1) 1.944(4),
Ge(1)eC(13) 1.952(3), Cr(1)-Cav(arene) 2.220(4), Cr(1)-Cav(centroid) 1.720(4), Cr(1)-
COav 1.841(4), C-Oav 1.153(4); CeCr(1)-Cav(CO) 89.51(16), CeGe(1)-Cav 109.50(15),
CeGe(1)-Hav 109.4(14).
4.3. X-ray crystallography
Crystal data, data collection, structure solution and refinement
parameters for 8, 11 and 12 are given in Table S1 (Supporting In-
formation). Experimental intensities were measured on a Bruker
13C NMR spectra). Mass spectra (EI-MS, 70 eV) were recorded on a
quadrupole mass spectrometer FINNIGAN MAT INCOS 50 with
direct insertion; all assignments were made with reference to the
most abundant isotopes. UV/visible spectra were obtained using
two ray spectrophotometer Evolution 300 «Thermo Scientific» with
cuvette of 1.00 cm length. The IR spectra were recorded by using a
200 Thermo Nicolet apparatus. High resolution mass spectra
(HRMS) were measured on a Bruker micrOTOF II instrument using
electrospray ionization (ESI). Flash chromatography was performed
using SiO2 (0.015e0.040 mm) with UV/vis detection.
Solvents were dried by standard methods and distilled prior to
use. Tetrahydrofuran and diethyl ether were stored under solid
KOH and then distilled over sodium/benzophenone. Toluene, n-
hexane, n-decane, tetralin (7), para-xylene were refluxed and
distilled over sodium. Decalin was treated with concentrated
H2SO4, washed with water, dried over anhydrous MgSO4, and then
refluxed and distilled over sodium. CDCl3 was distilled over CaH2;
C6D6 was distilled over sodium under argon.
SMART APEX II diffractometer (graphite monochromatized Mo-K
a
radiation, scan mode. The structures were
l
¼ 0.71073 Å) using
u
solved by direct methods and refined by full matrix least-squares
on F2 (SHELXTL) with anisotropic thermal parameters for all non-
hydrogen atoms. In 8, all hydrogen atoms were found from differ-
ence Fourier synthesis and refined isotropically. As for 11 and 12, all
H atoms were placed in calculated positions and refined using a
riding model. X-ray diffraction studies were performed at the
Centre of Shared Equipment of IGIC RAS. Crystallographic data have
been deposited with the Cambridge Crystallographic Data Centre as
supplementary publications no. CCDC 1907694, 1907696 and
1907695 for 8, 11 and 12 respectively. They can be obtained free of
charge from the Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
4.4. Synthesis
4.4.1. Ph3GeGeMe2Cl (2)
Starting materials, Ph3GeGeMe2(NMe2) (1) [47], Me2GeCl2 [4b],
Me3SiCl (0.60 g, 5.50 mmol, 1.05 eq.) was added dropwise to the
solution of the Ph3GeGeMe2NMe2 (2.32 g, 5.24 mmol) in CH2Cl2
(20 mL). After stirring overnight all volatile materials were
removed under reduced pressure giving target compound (2.29 g,
>99%) as colorless liquid. 1H NMR (400.130 MHz, CDCl3):
Ph3GeH [47], (h
6-C6H6)Cr(CO)3 (3) [28], Ph2GeCl2 [4b] were ob-
tained using known procedures. Trimethylchlorosilane was
distilled over Al powder; n-BuLi (2.5 M in n-hexane) and other re-
agents were used as supplied (Aldrich). Anhydrous CuCl2 was
Scheme 10. Possibility for haptotropic rearrangement (IRHR) in complex 12.

K.V. Zaitsev et al. / Journal of Organometallic Chemistry 897 (2019) 217e227
225
d
¼ 7.57e7.52 (m, 6H), 7.42e7.39 (m, 9H) (aromatic protons), 0.93
mL is equal to the mass of LAH in g), water (0.96 mL, amount is
equal to the mass of LAH), with time intervals of 10e15 min be-
tween additions. This procedure allows to obtain well separated
alumina precipitate, easily removed by filtration or decantation.
The inorganic solid was washed with ether (4 ꢂ 20 mL), organic
phase was dried over anhydrous MgSO4, and then all volatile ma-
terials were removed under reduced pressure; the residue was
distilled, giving the target 9 (2.53 g, 88%) as colorless oil, b.p.
115e118 ꢀC (2 mm Hg), b.p. 95 ꢀC (1 mm Hg) [52]. 1H NMR
(s, 6H, GeMe2) ppm. 13C NMR (100.613 MHz, CDCl3):
d
¼ 135.36
(ipso-C6H5), 135.17 and 128.58 (ortho- and meta-C6H5), 129.28
(para-C6H5), 5.99 (GeMe2) ppm. 1H NMR (400.130 MHz, C6D6):
d
¼ 7.62e7.57 (m, 6H), 7.16e7.12 (m, 9H) (aromatic protons), 0.70 (s,
6H, GeMe2) ppm. 13C NMR (100.613 MHz, C6D6):
d
¼ 135.80 (ipso-
C6H5), 135.57 and 128.96 (ortho- and meta-C6H5), 129.56 (para-
C6H5), 5.74 (GeMe2) ppm. HRMS (ESI), m/z [M ꢁ H]þ, calcd.
441.1058, found 441.1053.
(400.130 MHz, CDCl3):
d
¼ 7.61e7.56 (m, 4H), 7.43e7.39 (m, 6H)
4.4.2. Ph3GeGeMe2(h
6-C6H5)Cr(CO)3 (4)
(aromatic protons), 5.15 (s, 2H, GeH2) ppm. 13C NMR (100.613 MHz,
A) Generation of (h6-C6H5Li)Cr(CO)3 (3-Li). At ꢁ78 ꢀC a solution of
CDCl3):
d
¼ 135.15 and 128.34 (ortho- and meta-C6H5), 133.99 (ipso-
n-BuLi in n-hexane (2.5 M, 0.32 mL, 0.79 mmol) was added drop-
C6H5), 129.07 (para-C6H5) ppm. HRMS (ESI), m/z [M ꢁ H]þ, calcd.
wise to the solution of (
h
6-C6H6)Cr(CO)3 (3) (0.17 g, 0.79 mmol) in
227.8557, found 227.8552.
THF (20 mL), then the solution obtained was stirred at the same
temperature for 3 h. The solution of 3-Li prepared in situ was used
further without additional workup. B) Synthesis of complex 4.
At ꢁ78 ꢀC neat Ph3GeGeMe2Cl (0.35 g, 0.79 mmol) was added to the
solution of 3-Li prepared as stated above. The mixture was slowly
warmed to room temperature and stirred overnight, then saturated
solution of NH4Cl aq. (20 mL) was added, organic phase was sepa-
rated, water phase was extracted with ether (3 ꢂ 20 mL), combined
organic phases were dried over Na2SO4, all volatile materials were
removed under reduced pressure. The residue was purified by
chromatography (SiO2, Rf 0.3, petroleum ether/ether 10:1). The
target complex was isolated as yellow powder (0.27 g, 56%). 1H
4.4.5. Phenylchlorogermane, Ph2Ge(H)Cl (10)
Anhydrous CuCl2 (5.10 g, 37.93 mmol, 2.00 eq.) and CuI (0.10 g,
0.57 mmol, 0.03 eq.) were added to the solution of Ph2GeH2 (9)
(4.34 g, 18.96 mmol) in toluene (190 mL). Reaction mixture was
refluxed for 16 h, then filtered after cooling, all volatile materials
were removed under reduced pressure, and the residue was
distilled on oil bath (temperature in bath is 250 ꢀC) giving com-
pound 10 (3.79 g, 76%) as colorless oil, b.p. 98e101 ꢀC (0.1 mm Hg).
1H NMR (400.130 MHz, CDCl3):
(m, 6H) (aromatic protons), 6.54 (s, 1H, GeH) ppm. 13C NMR
d
¼ 7.67e7.61 (m, 4H), 7.49e7.44
(100.613 MHz, CDCl3):
d
¼ 134.08 (ipso-C6H5), 133.65 and 128.72
NMR (400.130 MHz, C6D6):
d
¼ 7.44e7.40 (m, 6H), 7.15e7.11 (m, 9H)
(ortho- and meta-C6H5), 130.69 (para-C6H5) ppm. 13C NMR spec-
trum corresponds to known data [53]. HRMS (ESI), m/z [M ꢁ H]þ,
calcd. 262.3008, found 262.3012.
(aromatic protons), 4.77 (d, 3JH-H ¼ 6.4 Hz, 2H, 2ortho-
3
C6H5*Cr(CO)3), 4.49 (t, JH-H ¼ 6.4 Hz, 1H, para-C6H5*Cr(CO)3), 4.25
3
(pt, JH-H ¼ 6.4 Hz, 2H, 2meta-C6H5*Cr(CO)3), 0.62 (s, 6H, GeMe2)
ppm. 13C NMR (100.613 MHz, C6D6):
d
¼ 233.62 (Cr(CO)3), 137.01
4.4.6. (h
6-C6H4Me2-p)Cr(CO)3 (11)
(ipso-C6H5Ge), 135.51 and 128.79 (ortho- and meta-C6H5Ge), 129.23
(para-C6H5Ge), 102.42 (ipso-C6H5*Cr(CO)3), 98.87 and 91.32 (ortho-
and meta-C6H5*Cr(CO)3), 94.24 (para-C6H5*Cr(CO)3), ꢁ2.16 (GeMe2)
ppm. MS (EI) m/z (%) 620 ([M]þ, 12), 536 ([M ꢁ 3CO]þ, 100), 484
([M ꢁ Cr(CO)3]þ, 13), 304 ([Ph3Ge]þ, 81), 227 ([Ph2Ge]þ, 18), 180
([PhGeMe2]þ, 33), 151 ([PhGe þ H]þ, 39), 77 ([C6H5]þ, 6), 52 ([Cr]þ,
7). UV/vis (CH2Cl2): 241 (sh) (2.17 ꢂ 104), 318 (0.48 ꢂ 104). IR (nujol)
2960 (s), 1980 (s) (A1 band), 1905 (s) (E band), 1786 (s), 1473 (m).
HRMS (ESI), m/z [M ꢁ H]þ, calcd. 618.7815, found 618.7818.
A mixture of para-xylene (22.39 g, 210.90 mmol, 10.0 eq.),
Cr(CO)6 (4.64 g, 21.09 mmol), THF (20 mL) in (n-Bu)2O (200 mL) was
refluxed (vapor cooling is carried out using two coolers, a Liebig
cooler is used at the bottom to flush out a sublimed Cr(CO)6, and a
Dimrot cooler is used at the top to condensate the solvents) for
26 h. After cooling mixture was filtered through a pad of SiO2, all
volatiles were removed under reduced pressure (below 50 ꢀC), then
the residue was treated with n-hexane and after storage at ꢁ30 ꢀC
was filtered off, giving 11 (3.78 g, 74%) as yellow powder. 1H NMR
(400.130 MHz, C6D6):
2Me) ppm. 1H NMR spectrum corresponds to known data [54]. 13
NMR (100.613 MHz, C6D6):
94.16 (ortho-C6H4*Cr(CO)3), 19.74 (Me) ppm. IR (ATR) 2924 (w),
1942 (s) (A1 band), 1846 (s) (E band), 1478 (m), 1379 (m), 1107 (m),
1032 (m). MS (EI) m/z (%) 242 ([M]þ, 21), 158 ([M ꢁ 3CO]þ, 100), 106
([M ꢁ Cr(CO)3]þ, 32), 52 ([Cr]þ, 4). HRMS (ESI), m/z [M ꢁ H]þ, calcd.
241.1818, found 241.1812.
d
¼ 4.44 (s, 4H, p-C6H4*Cr(CO)3), 1.52 (s, 6H,
4.4.3. (C10H12)Cr(CO)3 (8)
C
It is known compound [22b]. Tetralin (7) (0.92 g, 6.90 mmol, 5.0
d
¼ 234.17 (Cr(CO)3), 106.35 (ipso-C6H4),
eq.) was added to the complex Ph3GeGeMe2(
h
6-C6H5)Cr(CO)3 (4)
(0.86 g, 1.38 mmol) in decalin (30 mL), the reaction mixture was
heated at 120e130 ꢀC for 8 h. Then all volatile materials were
removed under reduced pressure and the residue was purified by
chromatography (SiO2, Rf 0.5, petroleum ether) giving 8 (0.08 g,
22%) as yellowish powder. 1H NMR (400.130 MHz, C6D6):
d
¼ 5.18,
3
5.03 (2d, JH-H ¼ 6.8 Hz, each 2H, C6H4*Cr(CO)3), 2.25e2.18,
4.4.7. (h
6-C6H3(GeHPh2)Me2-1,2,5)Cr(CO)3 (12)
1.92e1.85,1.39e1.32,1.17e1.10 (4 m, each 2H, alkyl C10H12) ppm. 13
NMR (100.613 MHz, C6D6):
C
A) Generation of (h6-C6H3(Li)Me2-1,2,5)Cr(CO)3 (12-Li). At ꢁ78 ꢀC
a solution of n-BuLi in n-hexane (2.37 M, 3.58 mL, 8.49 mmol, 1.07
d
¼ 234.15 (Cr(CO)3), 109.18 (aryl ipso-
C
C
10H12*Cr(CO)3), 93.65, 91.55 (aryl ortho- and meta-
eq.) was added dropwise to the solution of (h
6-C6H4Me2-p)Cr(CO)3
10H12*Cr(CO)3), 27.93, 21.96 (alkyl C10H12) ppm. IR (nujol) 1976 (s)
(11) (1.92 g, 7.93 mmol) in THF (40 mL), then the solution obtained
was stirred at ꢁ60 to ꢁ40 ꢀC for 2 h, giving yellowish solution of 12-
Li, which was used without additional workup. B) Synthesis of 12.
The solution of 12-Li obtained as stated above was cooled to ꢁ78 ꢀC
and Ph2Ge(H)Cl (2.13 g, 8.09 mmol, 1.02 eq.) was added. The
mixture was slowly warmed to room temperature and stirred
overnight, then water (20 mL) was added, organic phase was
separated, water phase was extracted with ethyl acetate (4 ꢂ 20
mL), combined organic phases were dried over Na2SO4, all volatile
materials were removed under reduced pressure. The residue was
purified by chromatography (SiO2, Rf 0.2, petroleum ether) and
after recrystallization from n-hexane giving 12 as yellow powder
(A1 band), 1905 (s) (E band). HRMS (ESI), m/z [M ꢁ H]þ, calcd.
267.2191, found 267.2183.
4.4.4. Diphenylgermane, Ph2GeH2 (9)
Solid LiAlH4 (LAH) (0.96 g, 25.2 mmol, 2.0 eq.) was added por-
tionwise to the solution of diphenyldichlorogermane, Ph2GeCl2
(3.75 g, 12.59 mmol), in ether (40 mL). Then reaction mixture was
refluxed for 6 h. For the workup the improved procedure for
dissolution of products of LAH reduction was applied, including the
sequential dropwise addition of water (0.96 mL, amount in mL is
equal to the mass of LAH in g), 15% aq. NaOH (0.96 mL, amount in

226
K.V. Zaitsev et al. / Journal of Organometallic Chemistry 897 (2019) 217e227
24 (2005) 3219e3228.
(3.09 g, 83%). 1H NMR (400.130 MHz, C6D6):
7.41e7.37 (m, 2H), 7.14e7.05 (m, 6H) (aromatic protons), 5.93 (s, 1H,
GeH), 4.96 (s, 1H, C6H3*Cr(CO)3), 4.59, 4.36 (2d, 3JH-H ¼ 6.3 Hz, each
1H, C6H3*Cr(CO)3), 1.72, 1.32 (2s, each 3H, 2Me) ppm. 13C NMR
d
¼ 7.65e7.61 (m, 2H),
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d
¼ 234.00 (Cr(CO)3), 135.74, 135.11, 129.00,
128.94 (2ortho- and 2meta-C6H5Ge), 134.94, 132.96 (2ipso-C6H5Ge),
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16), 52 ([Cr]þ, 9). HRMS (ESI), m/z [M ꢁ H]þ, calcd. 468.0296, found
468.0296.
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Appendix A. Supplementary data
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