Novel inorganic heterocycles from dimetalated carboranylamidinates

Article abstract of DOI:10.1039/c3dt52751d

Mono- and dianionic carboranylamidinates are readily available in one-pot reactions directly from o-carborane (1). In situ-monolithiation of 1 followed by treatment with N,N′-diisopropylcarbodiimide, ⁱPrNCN ⁱPr, or N,N′-dicyclohexylcarbodiimide, CyNCNCy, provided the lithium carboranylamidinates (o-C₂B₁₀H ₁₀C(NHⁱPr)(NⁱPr)-κ²C,N)Li(DME) (2a) and (o-C₂B₁₀H₁₀C(NHⁱCy)(N ⁱCy)-κ²C,N)Li(THF)₂ (2b). Controlled hydrolysis of 2a,b afforded the free carboranylamidines o-C₂B ₁₀H₁₁C(NHⁱR)(NⁱR) (3a: R = ⁱPr, 3b: R = Cy). The first dimetalated carboranylamidinates, o-C₂B₁₀H₁₀C(NⁱPr)(N ⁱPr)Li₂(DME)₂ (4a) (DME = 1,2-dimethoxyethane) and o-C₂B₁₀H₁₀C(NⁱPr)(N ⁱPr)Li₂(THF)₄ (4b), were prepared in high yield (83% yield) directly from 1 using a simple one-pot synthetic protocol. Treatment of 4b with 2 equiv. of Me₃SiCl afforded the disilylated derivative o-C₂B₁₀H₁₀-κ²C,N- [C(NⁱPrSiMe₃)(NⁱPr)]SiMe₃ (5). Dianionic 4b also served as an excellent precursor for novel inorganic heterocycles incorporating the closo-1,2-C₂B₁₀H ₁₀ cage, including the unsymmetrical distannene [o-C ₂B₁₀H₁₀C(NⁱPr)(NⁱPr)- κ²C,N]SnSn[(ⁱPrN)₂CⁿBu] ₂ (6) and the azaphosphole derivative [o-C₂B ₁₀H₁₀C(NⁱPr)(NⁱPr)- κ²C,N]PPh (7). Surprisingly, it was found that the synthesis of new inorganic ring systems from dianionic carboranylamidinates can also be achieved by employing only 1 equiv. of n-butyllithium in the generation of the anionic carboranylamidinate intermediates. Using this straightforward one-pot synthetic protocol, the Group 14 metallacycles [o-C₂B ₁₀H₁₀C(NCy)(NCy)-κ²C,N]SiR₂ (R = Cl (8), Me (9), Ph (10)) and [o-C₂B₁₀H ₁₀C(NCy)(NCy)-κ²C,N]GeCl₂ (11) have become accessible. The same synthetic strategy could be successfully adapted to prepare the corresponding Group 4 metallocene derivatives Cp₂Ti[o- C₂B₁₀H₁₀C(NCy)(NCy)-κ²C,N] (12) and Cp₂Zr[o-C₂B₁₀H₁₀C(NCy)(NCy) -κ²C,N] (13). The molecular structures of 2b, 3b, 4b, 5, 6, 7, 10, 12, and 13 were confirmed by single-crystal X-ray diffraction.

Full text of DOI:10.1039/c3dt52751d

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DOI: 10.1039/C3DT52751D
Full Paper submitted to Dalton Transactions
Novel Inorganic Heterocycles from Dimetalated
Carboranylamidinates†
Nicole Harmgarth,‡ Daniel Gräsing,‡ Peter Dröse,‡ Cristian G. Hrib,‡ Peter G.
Jones,§ Volker Lorenz,‡ Liane Hilfert‡, Sabine Busse‡ and Frank T.
Edelmann*‡
‡Chemisches Institut der Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2,
39106 Magdeburg, Germany
§Institut für Anorganische und Analytische Chemie der TU Braunschweig, Hagenring 30,
38106 Braunschweig, Germany
Dedicated to Professor John W. Gilje on the occasion of his 75th birthday
† Electronic supplementary information (ESI) available: Complete IR data, ORTEP
drawings and additional X-ray data. CCDC-963124 - 963132 for compounds 2b, 3b, 4b, 5,
6, 7, 10, 12, and 13. For crystallographic data in CIF or other electronic format see DOI:

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Mono- and dianionic carboranylamidinates are readily available in one pot-reactions
directly from o-carborane (1). In situ-monolithiation of 1 followed by treatment with N,N'-
i
diisopropylcarbodiimide, PrN=C=NiPr, or N,N'-dicyclohexylcarbodiimide, CyN=C=NCy,
provided the lithium carboranylamidinates (o-C2B10H10C(NHiPr)(=NiPr)-κ2C,N)Li(DME)
(2a) and (o-C2B10H10C(NHiCy)(=NiCy)-κ2C,N)Li(THF)2 (2b). Controlled hydrolysis of
2a,b afforded the free carboranylamidines o-C2B10H11C(NHiR)(=NiR) (3a: R = iPr, 3b: R =
Cy). The first dimetalated carboranylamidinates, o-C2B10H10C(NiPr)(=NiPr)Li2(DME)2 (4a)
(DME = 1,2-dimethoxyethane) and o-C2B10H10C(NiPr)(=NiPr)Li2(THF)4 (4b) were
prepared in high yield (83% yield) directly from 1 using a simple one-pot synthetic
protocol. Treatment of 4b with 2 equiv. of Me3SiCl afforded the disilylated derivative o-
C2B10H10-κ2C,N-[C(NiPrSiMe3)(=NiPr)]SiMe3 (5). Dianionic 4b also served as excellent
precursor for novel inorganic heterocycles incorporating the closo-1,2-C2B10H10 cage,
including the unsymmetrical distannene [o-C2B10H10C(NiPr)(=NiPr)-κ2C,N]Sn=Sn-
[(iPrN)2CnBu]2 (6) and the azaphosphole derivative [o-C2B10H10C(NiPr)(=NiPr)-κ2C,N]PPh
(7). Surprisingly, it was found that the synthesis of new inorganic ring systems from
dianionic carboranylamidinates can also be achieved by employing only 1 equiv. of n-
butyllithium in the generation of the anionic carboranylamidinate intermediates. Using this
straightforward one-pot synthetic protocol, the Group 14 metallacycles [o-C2B10H10C-
(NCy)(=NCy)-κ2C,N]SiR2 (R = Cl (8), Me (9), Ph (10)) and [o-C2B10H10C(NCy)(=NCy)-
κ2C,N]GeCl2 (11) have become accessible. The same synthetic strategy could be
successfully adapted to prepare the corresponding Group 4 metallocene derivatives
Cp2Ti[o-C2B10H10C(NCy)(=NCy)-κ2C,N] (12) and Cp2Zr[o-C2B10H10C(NCy)(=NCy)-
κ2C,N] (13). The molecular structures of 2b, 3b, 4b, 5, 6, 7, 10, 12, and 13 were confirmed
by single-crystal X-ray diffraction.
INTRODUCTION
Carboranes (= dicarba-closo-dodecaboranes)1 continue to attract tremendous
interest due to their wide range of applications,2 including the synthesis of polymers,
ceramics, catalysts, complexes with non-linear optical properties or radiopharmaceuticals,
as well as the important BNCT (= Boron Neutron Capture Therapy) technique.1b,c;3 o-
Carboranyl ligands providing C,N-,4 C,P-,5 N,S-,6 N,P-,7 and S,S’-chelating8 coordination
modes have been reported to form a variety of interesting new transition metal complexes.
Carboranylamidinates, which combine the versatile characteristics of both carboranes and
the widely used amidinates9 into one system, were first synthesized in our laboratory in

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2010.10 In situ-monolithiation of o-carborane (1)1a,11,12 followed by treatment with N,N'-
diisopropylcarbodiimide in DME (= 1,2-dimethoxyethane)/n-pentane directly provided the
novel lithium carboranylamidinate (o-C2B10H10C(NHiPr)(=NiPr)-κ2C,N)Li(DME) (2a) as
DME adduct. Even more surprising was the finding that the resulting carboranylamidinate
anion unexpectedly did not act as the normal N,N'-chelating amidinate ligand but rather
adopted an unexpected C,N-chelating coordination mode (Scheme 1).10 The dicyclohexyl
derivative could be prepared in an analogous manner.13
Scheme 1 Formation of the lithium carboranylamidinate (o-C2B10H10C(NHiPr)-
(=NiPr)-κ2C,N)Li(DME) (2a).
In our previous work, besides the formation of 2a, we reported the corresponding
free carboranylamidine as well as one Sn(II) and two Cr(II) carboranylamidinate
complexes.10 More recently, the area has been significantly broadened through very
interesting contributions by Jin et al. These authors not only expanded the range of
transition metal carboranylamidinate complexes to elements like Ru, Co, Rh, Ir, Ni, and Cu;
they also demonstrated that the carboranylamidinate system can be modified by attaching
thiolate or selenolate functional groups or by generating novel nido-carboranylamidinate-
type ligands.13-16 Meanwhile, the chemistry of carboranylamidinate complexes has already
been summarized in two recent review articles.17,18 One of the most surprising initial
findings was that in the products a N-H functionality remained uncoordinated and available
for further chemistry, e.g. deprotonation reactions. Subsequently, we10 as well as Jin et al.13
reported the preparation of the free carboranylamidines o-C2B10H11C(NHiPr)(=NiPr) (3a,
85% yield) and o-C2B10H11C(NHCy)(=NCy) (3b, 78% yield)) using a straightforward
i
synthetic protocol (monolithiation of 1, followed by treatment with R-N=C=N-R (R = Pr,
Cy) and subsequent hydrolysis).10 It was then attempted to force the imine N atom to
coordinate to suitable metal centers by the addition of a base. It was found that the free
carboranylamidines 3a and 3b could be doubly deprotonated upon addition of two

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equivalents of nBuLi as illustrated in Scheme 2. The resulting C,N-
dilithiocarboranylamidinates were used in situ for reactions with [Cp*MCl2]2 (M = Rh, Ir;
Cp* = C5Me5) to give the corresponding 16-electron half-sandwich Rh and Ir
carboranylamidinate complexes [o-C2B10H11C(NHCy)(=NCy)]MCp* (M = Rh, Ir).13
Scheme 2 Formation of dianionic carboranylamidinate intermediates.
Thus far the intermediate C,N-dilithiocarboranylamidinates have not been
structurally authenticated through X-ray diffraction. In this contribution we report the
synthesis and structures of C,N-dilithiocarboranylamidinates and their use as precursors for
novel carboranylamidinate-derived inorganic heterocycles comprising Si, Ge, Sn, P, Ti,
and Zr as heteroatoms.
RESULTS AND DISCUSSION
Starting materials
The key starting materials for studying carboranylamidinates are the easily
accessible lithium derivatives 2a and 2b as well as the free carboranylamidines 3a and 3b.
Thus far, only carboranylamidinates comprising N-isopropyl or N-cyclohexyl substituents
have been prepared. Apparently, this has
a
simple reason in that N,N'-
diisopropylcarbodiimide and N,N'-dicyclohexylcarbodiimide are both available in large
quantities from commercial sources. In the course of the present study we set out with a
more detailed structural characterization of two of these potentially useful starting
materials. The N-cyclohexyl-substituted carboranylamidinate (o-C2B10H10C(NHiCy)-
(=NiCy)-κ2C,N)Li(THF)2 (2b) was prepared in the same manner as shown in Scheme 1 by
reaction of in situ-prepared o-lithiocarborane with N,N'-dicyclohexylcarbodiimide
followed by crystallization from THF. Colorless, block-like, moisture-sensitive crystals of

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2b were isolated in 58% yield. As in 2a, an IR band at 3404 cm-1 clearly showed the
presence of an N-H functionality in the molecule. A very strong band at 2547 cm-1 is
characteristic for B-H vibrations. A 1H NMR signal at δ = 4.63 ppm could be
13
unequivocally assigned to the N-H proton, while the C NMR resonance of the amidinate
carbon (NCN) was observed at δ = 155.5 ppm. The presence of only one resonance at δ =
7
-4.3 ppm in the Li NMR spectrum confirmed the formation of a single Li-containing
species. The 11B NMR spectrum displayed three signals at δ = -3.5, -6.4, and -9.3 ppm in
the intensity ratio of 2:4:4. An EI mass spectrum of 2b showed the molecular ion at m/z
501, albeit with very low intensity (1%). The molecular structure of 2b was also verified
by X-ray diffraction analysis. Suitable single-crystals were obtained directly by cooling the
concentrated reaction mixture in THF to 4 °C. Figure 1 shows the molecular structure of
2a. Crystal data for all crystal structures reported in this contribution are listed in Table 1,
while Table 2 summarizes selected bond lengths and angles.
Figure 1 here
Tables 1 and 2 here
In the solid state, the lithium carboranylamidinate 2b shows the typical C,N-
chelating coordination mode which is by now well established for various
carboranylamidinates10,13-18 and differs from the normal N,N'-coordination mode of other
amidinate anions.9 This results in the formation of a nearly planar five-membered LiNC3
chelate ring. The exocyclic C-NH bond (C3-N2) is slightly longer (0.1 Å) than the C3-N1
bond within the ring. The tetrahedral coordination geometry around Li is completed by
addition of two THF ligands.
The corresponding cyclohexyl-substituted free amidine o-C2B10H11C(NHCy)(=NCy)
(3b) has already been mentioned in the previous literature by Jin et al. and used as a
precursor for preparing various transition metal carboranylamidinates.13-15 These authors
prepared 3b in 78% yield by hydrolysis of in situ-prepared (o-C2B10H10C(NHiCy)(=NiCy)-
κ2C,N)Li in DME solution. We employed careful hydrolysis of isolated 2b in acetonitrile
solution, a method which also gave a high yield (85%) in the case of 3a. However,
following this procedure the cyclohexyl-substituted carboranylamidine 3b could only be
isolated in 36% yield. Apparently, in this case the method using isolated lithium
carboranylamidinate offers no preparative advantages over the original route.
Carboranylamidine 3b was also structurally characterized by X-ray diffraction (Fig. 2;

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Tables 1 and 2). Colorless, needle-like single-crystals were grown from a saturated
solution in MeCN.
Figure 2 here
Figure 2 gives a good impression of the high steric demand of the -C(NHCy)(=NCy)
moiety as compared to the smaller -C(NHiPr)(=NiPr) group in 3a.10 Apart from that, all
important structural features of 3b are very similar to those of the isopropyl derivative 3a.
The N2-C3-N1 angle of the amidine functional group is 131.59(10)°. With a bond length
of 1.3734(14) Å the C-N single bond (C3-N1) is again significantly longer than the formal
C=N double bond C3-N2 with 1.2788(14) Å. In 3a the corresponding distances are
1.3620(15) Å (C-NH) and 1.274(3) Å (C=N)10 and for (E)-N,N'-diisopropyl-3-
phenylpropiolamidine they were reported to be 1.373(4) Å (C-NH) and 1.266(4) Å,
respectively.19
Of central importance for the present study are dianionic carboranylamidinates. As
illustrated in Scheme 2, the formation of C,N-dilithiocarboranylamidinates and their use as
intermediates for the preparation of 16-electron half-sandwich Rh and Ir
carboranylamidinate complexes has already been reported by Jin et al.13 Independently, a
simple one-pot preparation leading to the C,N-dilithiocarboranylamidinates o-
C2B10H10C(NiPr)(=NiPr)Li2(DME)2 (4a) and o-C2B10H10C(NiPr)(=NiPr)Li2(THF)3 (4b) has
been developed in our laboratory. This route involves in situ-preparation of the lithium
carboranylamidinate 2a according to Scheme 1 followed by addition of a second
n
equivalent of BuLi to achieve deprotonation of the uncoordinated N-H group. Using this
synthetic
protocol,
the
solvated
C,N-dilithiocarboranylamidinates
o-
C2B10H10C(NiPr)(=NiPr)Li2(DME)2 (4a) and o-C2B10H10C(NiPr)(=NiPr)Li2(THF)4 (4b)
have become available for the first time as colorless, crystalline materials in high yields of
>80% (Scheme 3).

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Scheme 3 Synthesis of the C,N-dilithiocarboranylamidinates o-C2B10H10C(NiPr)-
(=NiPr)Li2(DME)2 (4a) and o-C2B10H10C(NiPr)(=NiPr)Li2(THF)4 (4b)
The presence of isolable C,N-dilithiocarboranylamidinates was clearly established
by a single-crystal X-ray analysis of 4a (Fig. 3; Tables 1 and 2). The carboranylamidinate
dianion is coordinated to one lithium in the now familiar κ2C,N-coordination mode
resulting in the formation of a nearly planar five-membered chelate ring (Li-N 1.988(3) Å).
This Li+ ion (Li2) is tetrahedrally coordinated through addition of a DME ligands, while
the second lithium is only tricoordinated (trigonal planar) through κ1-bonding to N1 (Li-N
1.948(3) Å) and coordination of a chelating DME. It should be noted that such type of κ1-
bonding between lithium and monodentate amidinate anions is quite rare in amidinate
coordination chemistry. Examples are so far limited to lithium amidinates containing very
bulky terphenyl20 or triptycenyl21 substituents. The bonding environment around Li2 is
distorted trigonal planar with an angle sum around Li2 = 355.9(2)°. The latter value can be
favorable compared to those found in other structurally characterized bulky lithium
amidinates comprising tricoordinate Li, e.g. 357.5° in [Li(THF)2][(triptycenyl)C(NiPr)2],21
358.4(3)° in (dimb)Li(TMEDA) (dimb
=
N,N'-diisopropyl(2,6-dimesityl)benz-
amidinate),20a and 354.4(4)° (LPr)Li(TMEDA)] (LPr = N,N'-diisopropyl[2,6-bis(2,4,6-
triisopropylphenyl)]benzamidinate).20b Interestingly, it has been reported that in the
molecular structure of (dimb)Li(TMEDA) the Li atom appears to have a weak interaction
with one aromatic C-centre of the triptycenyl substituent (Li···C = 2.690(6) Å). In 4a the
tricoordinate Li resides directly above the centre (X1A) of a B-B bond (B4-B5) of the
carborane cage (distance Li···X1A = 2.582 Å).
Figure 3 here

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Colorless, block-like single crystals of the THF adduct 4b could also be obtained by
slow cooling of a concentrated solution in THF to 5 °C. Unfortunately the low crystal
quality did not permit full refinement of the crystal structure. However, the X-ray
diffraction study clearly showed the presence of a molecule analogous to 4a, again with
two differently coordinated Li atoms (one tetrahedral and one trigonal planar) just with
each of the DME ligands in 4a replaced by two THF molecules. Thus the present study
clearly demonstrates that pure, crystalline C,N-dilithiocarboranylamidinates are readily
available in high yields by a simple one-step synthetic route. With these promising
materials in hand we started exploring their use as precursors for the synthesis of novel
carboranylamidinate-based inorganic heterocycles.
Carboranylamidinate-based heterocycles containing Group 4 and 5 elements (Si, Ge, Sn,
and P)
The first experiments in this direction clearly demonstrated that new inorganic ring
systems can be synthesized from dianionic carboranylamidinates. Scheme 4 summarizes
the results obtained with different Group 4 and 5 element halides. In the first step, the C,N-
dilithiocarboranylamidinate 4b was prepared directly from o-carborane (1) using the one-
pot synthetic protocol outlined in Scheme 3. It was found that the use of in situ-prepared
4b gave excellent results in subsequent reactions. The use of isolated 4a or 4b afforded
similar or even lower yields so that this modification does not offer any advantages.

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H
C
CH
1
1. nBuLi
2.iPr
3. nBuLi
i
N
C
N Pr
THF
iPr
N
iPr
N
(THF)2Li
Li(THF)2
C
C
iPr
N
iPr
iPr
N
PhPCl2
- 2 LiCl
iPr
N
2 Me3SiCl
- 2 LiCl
4b
N
Me3Si
P
SnCl2
- 2 LiCl
C
C
SiMe3
C
Ph
C
iPr
iPr iPr
Sn
N
C
N
N
5
7
N
N
iPr
iPr
Sn
N
C
iPr
6
Scheme 4 Synthesis of compounds 5-7 from in situ-prepared 4b.
Silylation of 4b using Me3SiCl afforded the C,N-bis(trimethylsilyl) derivative o-
C2B10H10-κ2C,N-[C(NiPrSiMe3)(=NiPr)]SiMe3 (5) as colorless, block-like crystals. Its
formation can be seen as a chemical proof for the presence of a C,N-
dilithiocarboranylamidinate species in solution. The comparably low isolated yield (32%)
can be explained by the very high solubility of 5 in hydrocarbon solvents including n-
pentane. Compound 5 was fully characterized by spectroscopic methods, elemental
analysis, and single-crystal X-ray diffraction. Single-crystals were obtained by cooling a
concentrated solution in n-pentane to -32 °C. Occasionally the product tends to form an oil
which is difficult to obtain free from n-pentane even under prolonged heating in vacuum.
The X-ray analysis confirmed the presence of the expected bis-silylated product (Figure 4;

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Tables 1 and 2). The carbon-nitrogen bond lengths in the amidine moiety in 5 are N(1)-C(3)
1.425(3) Å and N(2)-C(3) 1.249(3) Å, clearly corresponding to a carbon-nitrogen single
and double bond, respectively. In the free carboranylamidine o-C2B10H11C(NHiPr)(=NiPr)
(3a) the corresponding C-N distances are 1.3620(15) Å (C-N) and 1.274(3) Å (C=N),
respectively.10 Future work will show if the bis(trimethylsilyl) derivative 5 might serve as a
potentially useful starting material for the synthesis of new transition metal
carboranylamidinates through reactions with high-valent transition metal halides. Such
reactions have been explored many years ago by Roesky et al.22 and Dehnicke et al.23 for
the closely related fully silylated benzamidine precursors PhC(=NSiMe3)[N(SiMe3)2. For
example, reaction his compound with the tantalum(V) complex (C5Me5)TaF4 was found to
result in elimination of Me3SiF and clean formation of the mixed-ligand tantalum(V)
amidinate complex [PhC(NSiMe3)2](C5Me5)TaF3.22
Figure 4 here
In marked contrast to the easily foreseeable formation of 5, the reaction of 4b with
tin(II) chloride, which was carried out with the goal of making the carboranylamidinate-
stannylene [o-C2B10H10C(NiPr)(=NiPr)-κ2C,N]Sn, had a surprising result (Scheme 4).
Reaction of 4b with anhydrous SnCl2 in THF solution reproducibly yielded red/blue
dichroitic crystals for which an X-ray diffraction study revealed the presence of the
unsymmetrical distannene [o-C2B10H10C(NiPr)(=NiPr)-κ2C,N]Sn=Sn[(iPrN)2CnBu]2 (6).
Suitable single-crystals of 6 could be grown from concentrated solutions in toluene, while
other methods of crystallization, e.g. diffusion of n-pentane into solutions of 6 in THF,
diethyl ether or toluene, only led to separation of 6 in the form of a purple oil. As shown in
Figure 5, an unexpected structural feature of 6 is the presence of two n-butylamidinate
ligands [(iPrN)2CnBu]- which are attached to one Sn atom, while the second Sn atom forms
the expected metallacycle with the formally dianionic carboranylamidinate ligand (cf.
Tables 1 and 2). The formation of the n-butylamidinate anion [(iPrN)2CnBu]- can be
n
explained by the presence of both N,N'-diisopropylcarbodiimide and BuLi in the reaction
mixture of the in situ-preparation of 4b. The easy formation of such n-butylamidinates
n
from BuLi and carbodiimides has already been reported in the literature.24 This can
explain why n-butylamidinate ligands [(iPrN)2CnBu]- are present in compound 6, but it
remains unclear why this unsymmetrical distannene is the only reaction product instead of
the expected stannylene [o-C2B10H10C(NiPr)(=NiPr)-κ2C,N]Sn or the symmetrical

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distannene [o-C2B10H10C(NiPr)(=NiPr)-κ2C,N]Sn2. Attempts to deliberately prepare the
latter, i.e. by varying the stoichiometric ratios of the reactants, have thus far not been met
with success. The binuclear tin carboranylamidinate 6 belongs to the small group of
unsymmetrical distannenes.25 It is well known that the tin-tin bond distance in distannenes
R4Sn2 can vary in the wide range between ca. 2.67 and 3.64 Å.26 With a distance of
2.9869(8) Å the Sn-Sn bond in 6 is fairly long, which can be seen as an indication for steric
congestion in this molecule. A very similar value (2.961(1) Å) was reported by Lappert et
al. for the unsymmetrically substituted distannene Cl2SnSn[C(H)SiMe3C9H5N]2.25a On the
Sn[(iPrN)2CnBu]2-side of the molecule 6, the Sn2 atom adopts a distorted square-pyramidal
geometry, while the coordination around Sn1 can be described as roughly pyramidal. The
C-N distances in the [(iPrN)2CnBu]- ligands are all very similar (between 1.318(4) and
1.337(5) Å), a situation which is characteristic for N,N'-chelating amidinate ligands.9 The
Sn2-N bond lengths are in the range of 2.139(3) - 2.302(3) Å.
Figure 5 here
So far the isolation of the unsymmetrical distannene 6 is unique among Group 4
element carboranylamidinate derivatives. Several attempts were made to prepare the
analogous germanium and lead compounds. However, reactions of 4a or 4b with
GeCl2(dioxane) in our hands invariably produced unstable red oils, which we could not
characterize, while similar reactions with PbCl2 afforded dark solutions which were very
thermolabile and easily decomposed under precipitation of metallic lead. Thus, until now
carboranylamidinate-based germylenes, digermenes, plumbylenes, or diplumbenes remain
elusive classes of main-group compounds.
The synthetic protocol illustrated in Scheme 4 also allowed the preparation of the
first P-containing carboranylamidinate-based inorganic heterocycle. Treatment of in situ-
prepared 4b with PhPCl2 gave the azaphosphole derivative [o-C2B10H10C(NiPr)(=NiPr)-
κ2C,N]PPh (7) which was isolated in the form of colorless, air-sensitive crystals (33%
yield). A singlet at δ = 50.7 ppm in the 31P NMR spectrum confirmed the formation of a
single reaction product. Compound 7 was also structurally authenticated by X-ray
diffraction. Large, colorless single-crystals could be obtained by recrystallization from
CH2Cl2 at room temperature. The molecular structure of 7 is shown in Figure 6 (cf. Tables
1 and 2). The P-N distance in 7 is 1.7174(14) Å, while the two P-C bond lengths are
1.8475(12) (P-C2) and 1.8249(13) (P-C10), respectively. With 1.2605(17) Å (C3-N2) the

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C=N double bond within the amidinate unit can be clearly distinguished from the single
bond C3-N1 (1.4123(15) Å). The five-membered C3PN ring is nearly planar. Clearly this
potentially useful new phosphine derivative awaits further exploration as a novel ligand for
transition metals.
Figure 6 here
Further in the course of this investigation the important observation was made that
the synthesis of new inorganic ring systems from dianionic carboranylamidinates can also
be achieved by using only one equivalent of n-butyllithium for the generation of the anionic
carboranylamidinates. Obviously the desired ring formation easily takes place under
spontaneous elimination of HCl. This was successfully demonstrated by the
straightforward synthesis of the novel Group 14 element heterocycles [o-C2B10H10C-
(NCy)(=NCy)-κ2C,N]SiR2 (R = Cl (8), Me (9), Ph (10)) and [o-C2B10H10C(NCy)(=NCy)-
κ2C,N]GeCl2 (11) which have become accessible according to Scheme 5. The dichlorosilyl
derivative [o-C2B10H10C(NCy)(=NCy)-κ2C,N]SiCl2 (8) was synthesized following a simple
one-pot synthetic protocol by treatment of in situ-generated 2b (cf. Scheme 3) with 1 equiv.
of SiCl4. In the same manner, the diorganosilyl derivatives [o-C2B10H10C(NCy)(=NCy)-
κ2C,N]SiMe2 (9) and [o-C2B10H10C(NCy)(=NCy)-κ2C,N]SiPh2 (10) were made using
Me2SiCl2 or Ph2SiCl2 as starting materials. These results clearly demonstrate that the easily
accessible monoanionic carboranylamidinates 2a and 2b can be advantageously employed
for the synthesis of new inorganic ring systems formally derived from dianionic
carboranylamidinates.
Scheme 5 Straightforward access to the Group 14 element heterocycles [o-
C2B10H10C(NCy)(=NCy)-κ2C,N]SiR2 (R = Cl (8), Me (9), Ph (10)) and [o-
C2B10H10C(NCy)(=NCy)-κ2C,N]GeCl2 (11).

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All four compounds were isolated as colorless crystals in moderate to good yields
(8: 57%, 9: 46%, 10: 76%, 11: 76%). As expected, the dichloro derivatives 8 and 11 are
highly moisture-sensitive. The products 8-11 were fully characterized by spectroscopic
methods and elemental analyses. In all cases the EI mass spectra showed the molecular ion,
indicating significant volatility under MS conditions. The 29Si NMR spectra of the three
silicon derivatives each show only one singlet at δ -15.3 (8), 8.7 (9), and -15.1 (10) ppm.
As a typical representative of this series of carboranylamidinate-based inorganic ring
systems, the diphenyl derivative 10 has been structurally characterized by X-ray diffraction.
Figure 7 displays the molecular structure of 10 (cf. Tables 1 and 2). Incorporation of the
SiPh2 unit into the carboranylamidinate dianion affords a five-membered 1,2-azasilole ring
system which is anellated to the carborane cage. The five-membered SiNC3 ring is once
again nearly planar. As in the 1,2-azaphosphole derivative 7 the C=N double bond in the
amidinate moiety (C3-N2 1.2619(16) Å) can be clearly distinguished from the C-N single
bond within the five-membered ring (C3-N1 1.4128(15) Å). It may be noted here that an
initial attempt to reduce the dichlorosilane derivative 8 with elemental potassium to give
the corresponding disilene [o-C2B10H10C(NCy)(=NCy)-κ2C,N]2Si2 was unsuccessful under
the chosen reaction conditions. However, the results reported in the present study clearly
demonstrate the high potential of both mono- and dianionic carboranylamidinates as
precursors for novel inorganic ring systems.
Figure 7 here
Early transition metal carboranylamidinates
Previously reported carboranylamidinate complexes of middle and late transition
metals include derivatives of Cr, Ru, Co, Rh, Ir, Ni, and Cu.10,13-18 Among these, only the
16-electron half-sandwich Rh and Ir carboranylamidinate complexes [o-C2B10H11C-
(NHCy)(=NCy)]MCp* (M = Rh, Ir) are formally derived from dianionic carboranyl-
amidinates,13 and complexes of early transition metals have not yet been reported. In the
course of the present study we found that the simple strategy leading to the
carboranylamidinate-based Group 14 element heterocycles 8-11 could be successfully
adapted to prepare the corresponding Group 4 metal metallocene derivatives according to
Scheme 6.

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Scheme 6 Synthesis of the Group 4 element heterocycles [o-C2B10H10C-
(NCy)(=NCy)-κ2C,N]MCp2 (M = Ti (12), Zr (13)).
n
Once again a solution of 2b was prepared from o-carborane (1), BuLi, and N,N'-
dicyclohexylcarbodiimide (molar ratio 1:1:1) in THF and treated directly with 1 equiv. of
either Cp2TiCl2 or Cp2ZrCl2. Work-up was done by evaporation of the reaction mixtures to
dryness, extraction of the product with n-pentane, and recrystallization of the crude product
from
a
minimum amount of hot THF. The titanium complex Cp2Ti[o-
C2B10H10C(NCy)(=NCy)-κ2C,N] (12) was isolated in 69% yield in the form of glistening,
copper-colored needles, while the zirconium derivative Cp2Zr[o-C2B10H10C(NCy)(=NCy)-
κ2C,N] (13) (44% yield) forms orange, needle-like crystals. Both compounds were readily
1
characterized by their spectroscopic and analytical data. In the H NMR spectra the
cyclopentadienyl protons give rise to a singlet at δ 6.30 (12) and 6.39 (13) ppm,
respectively. The EI mass spectrum of 12 shows the molecular ion at m/z 527 with very
low relative intensity (1%), while in the mass spectrum of 13 the molecular ion at m/z 570
is the base peak with 100% intensity. Typical for all complexes formally derived from
dianionic carboranylamidinates is the absence of an N-H band at ca. 3400 cm-1 in the IR
spectra. The molecular structures of both 12 and 13 were determined by X-ray diffraction.
In both cases single-crystals were obtained by slow cooling of concentrated solutions of
the complexes in THF to room temperature. The molecular structures are depicted in
Figures 8 and 9 (cf. Tables 1 and 2).
Figures 8 and 9 here
The Ti and Zr carboranylamidinate metallacycles 12 and 13 are almost identical in
their structural parameters, but their are not isostructural. The formally dianionic
carboranylamidinate forms a nearly planar five-membered ring system incorporating the
metal atom. In both compounds the angle between the metals and the cyclopentadienyl ring

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centroids is 127°. The bond lengths of the M-N σ-bonds are Ti-N 2.012(3) Å for 12 and Zr-
N 2.0782(18) Å for 13. With 1.282(4) Å (12) and 1.271(3) Å (13) the exocyclic C3-N2
bonds have clearly double bond character.
CONCLUSIONS
In summarizing the work reported here, the first dimetalated carboranylamidinates
were prepared in high yield directly from o-carborane (1) using a simple one-pot synthetic
protocol and structurally characterized by X-ray diffraction. The compounds were shown
to be excellent precursors for novel inorganic heterocycles incorporating the closo-1,2-
C2B10H10 cage, including an unsymmetrical distannene and the novel azaphosphole
derivative [o-C2B10H10C(NiPr)(=NiPr)-κ2C,N]PPh (7). For these syntheses the dimetalated
carboranylamidinates are most conveniently generated and employed in situ. The synthetic
route could be simplified even further by employing only 1 equiv. of n-BuLi in the
generation of the anionic carboranylamidinate intermediates. Using this simplified
approach, a series of Group 4 (Ti, Zr) and Group 14 (Si, Ge) metallacycles have been
prepared and fully characterized, including X-ray diffraction studies. These results clearly
demonstrate that the combination of o-carborane and amidinate anions in one ligand
system provides a highly useful platfrom for promising further studies in the field of
inorganic ring systems.
EXPERIMENTAL
General Procedures
All operations were performed with rigorous exclusion of air and water in oven-dried or
flame-dried glassware under an inert atmosphere of dry argon, employing standard Schlenk,
high-vacuum and glove box techniques (MBraun MBLab; <1 ppm O2, <1 ppm H2O). THF
and toluene were dried over sodium/benzophenone and freshly distilled under nitrogen
atmosphere prior to use. Filtrations were done using the cannula technique. All glassware
was oven-dried at 115 °C for at least 24 h, assembled while hot and cooled under high
vacuum prior to use. The starting materials o-carborane (1), N,N'-diisopropylcarbodiimide,
N,N'-dicyclohexylcarbodiimide, n-butyllithium, SiCl4, Me3SiCl, Ph2SiCl2, GeCl4,
anhydrous SnCl2, PhPCl2, Cp2TiCl2 and Cp2ZrCl2 were all obtained from commercial
sources and used as received. Every sample of o-carborane (1) was dried under high
1
7
vacuum prior to use. The H NMR (400 MHz), Li NMR (155.5 MHz), 11B NMR (128.4
MHz), 13C NMR (100 MHz), 29Si NMR (79.5 MHz) and 31P NMR (162 MHz) spectra

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were recorded on a Bruker DPX 400 spectrometer. IR (KBr) spectra were measured using
a Perkin-Elmer FT-IR 2000 spectrometer. Mass spectra (EI, 70 eV) were run on a MAT 95
apparatus.
Single crystal X-ray crystallography
The intensity data of 2b, 4a, 5, 6, and 7 were collected on a Stoe IPDS 2T diffractometer
with MoK radiation. The data were collected with the Stoe XAREA27 program using
ω-
scans. The space groups were determined with the XRED3227 program. The intensity data
of 3b, 10, 12, and 13 were registered on an Oxford Diffraction Nova A diffractometer
using mirror-focussed CuKα radiation. Absorption corrections were applied using the
multi-scan method. The structures were solved by direct methods (SHELXS-97) and
refined by full matrix least-squares methods on F2 using SHELXL-97.28 The hydrogen
atoms were refined as mixed for 2b, 3b, 4a, 5, 6, as free for 7 and as constrained for 10, 12,
13.
Synthesis of carboranylamidinates
(o-C2B10H10C(NHiCy)(=NiCy)-κ2C,N)Li(THF)2 (2b). In a 250 ml Schlenk flask, o-
carborane (1.00 g, 7 mmol) was dissolved in 50 ml of THF and nBuLi (1.6 M in n-hexane,
4.4 ml, 7 mmol) was added to the solution at r.t. while stirring. After stirring for 1 h, neat
N,N´-dicyclohexylcarbodiimide (1.44 g, 7 mmol) was added and stirring at r.t. was
continued for 12 h. The color of the solution changed from colorless to pale yellow. The
solution was concentrated in vacuum to a total volume of ca. 15 ml. Cooling to 4 °C for 72
hours afforded colorless, block-like crystals suitable for X-ray diffraction. Yield: 2.03 g
1
(58%). H NMR (400 MHz, THF-d8, 25 °C):
δ 4.63 (s br, 1 H, (CyN=)C(NHCy)), 3.62
(O(CH2)2(CH2)2), 3.23 (s br, 2 H, NCH(CH2)5), 2.00-3.00 (br, 10 H, B-H), 1.17-1.85 (br,
13
20 H, NCH(CH2)5) 1.77 (O(CH2)2(CH2)2). C{1H} NMR (100.6 MHz, THF-d8, 25 °C):
δ
155.5 ((CyN=)C(NHCy)), 95.9 ([-C-CLi]B10H10), 81.3 ([-C-CLi]B10H10), 68.1
(O(CH2)2(CH2)2), 57.2 (NCH(CH2)5), 54.8 (NCH(CH2)5), 35.7, 34.7, 26.5, 25.8, 25.4, 25.2
(NCH(CH2)5), 26.2 (O(CH2)2(CH2)2). 7Li NMR (155.5 MHz, THF-d8, 25 °C):
δ -4.3 (s br).
11B{1H} NMR (128.4 MHz, THF-d8, 25 °C):
δ
-3.5 (2 B), -6.4 (4 B), -9.3 (4 B). MS (EI):
+
+
m/z (%) 501 (1) [M+], 350 (28) [M - Li(THF)2 ], 269 (100) [M - C6H8, Li(THF)2 ], 187 (73)
+
[M - C12H18, Li(THF)2 ], 168 (13) [NC-C2H10B10+], 143 (13) [C2H11B10+]. Anal. Found: C,
54.82; H, 10.01; N, 5.57. Calc for C23H49B10LiN2O2 (500.68 g/mol): C, 55.17; H, 9.86; N,
5.60.

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o-C2B10H11C(NHiCy)(=NiCy) (3b).13,14 2.0 g (4 mmol) of 2b were dissolved in
acetonitrile (30 ml) and a few drops of distilled water were added. The reaction mixture
was stirred at room temperature overnight and filtered through a P4 glass-frit to separate
the white lithium hydroxide from the solution. After reducing the volume of the solution in
vacuum to 10 ml the product crystallized in the form of colorless, needle-like crystals
1
suitable for X-ray diffraction. Yield: 0.50 g (36%). H NMR (400 MHz, THF-d8, 25°C):
δ
4.81 (s, [-C-CH]B10H10), 4.51 (s br, 1 H, (CyN=)C(NHCy)), 3.17-3.35 (s br, 2 H,
NCH(CH2)5), 1.70-3.00 (br, 10 H, B-H), 1.18-1.68 (br, 20 H, NCH(CH2)5). 13C{1H} NMR
(100.6 MHz, THF-d8, 25°C):
δ 143.1 ((CyN=)C(NHCy)), 77.1 ([-C-CH]B10H10), 60.1 ([-C-
CH]B10H10), 56.1 (NCH(CH2)5), 54.7 (NCH(CH2)5), 34.4, 33.5, 26.4, 25.9, 25.7, 25.1
+
(NCH(CH2)5). MS (EI): m/z (%) 351 (38) [M+], 269 (93) [M -C6H9 ], 188 (72) [M -
C12H18+], 143 (100) [C2H11B10+]. Anal. Found: C, 51.34; H, 9.73; N, 7.91. Calc for
C15H34B10N2 (350.54 g/mol): C, 51.39; H, 9.78; N, 7.99.
o-C2B10H10C(NiPr)(=NiPr)Li2(DME)2 (4a). o-Carborane (1, 2.0 g, 14 mmol) was
dissolved in THF (150 ml) and nBuLi (1.6 M in n-hexane, 8.8 ml, 14 mmol) was added to
the solution at r.t. while stirring. After stirring for 30 min, neat N,N'-
diisopropylcarbodiimide (2.4 ml, 14 mmol) was added. After further stirring for 12 h at r.t.
n
a second equivalent of BuLi (1.6 M, 8.8 ml, 14 mmol) was added. After stirring for
another 30 min, the THF was removed in vacuo and the remaining white solid was
dissolved in 20 mL of DME. Cooling to 5 °C afforded colorless, block-like crystals. Yield:
1
5.3 g (82%). H NMR (400 MHz, C6D6, 25 °C): δ 3.8-2.0 (m, 10 H, BH), 3.94 (m, 2 H,
CH(CH3)2), 3.05 (s, 6 H, CH3 (DME)), 2.83 (s, 4 H, CH2 (DME)), 1.17 (d, 6 H, CH(CH3)2,
3
3J =6.0 Hz), 1.10 (d, 6 H, CH(CH3)2, J = 6.0 Hz). 13C{1H} NMR (100.6 MHz, C6D6,
25°C): δ 161.9 (N=C−N), 88.4 ([C−CLi]B10-H10), 70.1 (CH2 (DME)), 68.5 ([C−Li]B10H10),
59.1 (CH3 (DME)), 45.8 (=N−CH−), 45.7 (−NLi−CH−), 25.3 (CH3), 25.1 (CH3). 7Li NMR
(155.5 MHz, C6D6, 25 °C) δ 1.3 (1 Li), 0.2 (1 Li). 11B{1H} NMR (128.4 MHz, C6D6, 25 °C)
δ -3.82 (2B), -5.96 (4B), -8.88 (4B). MS (EI): m/z (%) 294 (10) [M - Li(DME), NiPr,
+
+
+
CH2 ], 220 (15) [M - Li(DME)2, NC3H5 ], 206 (15) [M - Li(DME)2, NC3H5, CH2 ], 164
(15) [C3H13B10Li+], 142 (10) [C2H10B10+], 90 (100) [DME+]. Anal. Found: C, 49.10; H,
6.36; N, 5.91. Calc. for C17H44B10Li2N2O4 (462.50 g/mol): C, 49.58; H, 6.24; N, 5.87.

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o-C2B10H10C(NiPr)(=NiPr)Li2(THF)4 (4b). o-Carborane (1, 0.5 g, 3.5 mmol) was
n
dissolved in THF (70 ml) and BuLi (1.6 M in n-hexane, 2.2 ml, 3.5 mmol) was added to
the solution at r.t. while stirring. After stirring for 20 min, neat N,N'-
diisopropylcarbodiimide (0.6 ml, 3.5 mmol) was added and stirring at r.t. was continued
for 90 min. nBuLi (1.6 M, 2.2 ml, 3.5 mmol) was added. After stirring for another 20 min,
the solution was concentrated to a total volume of ca. 10 ml. Cooling to 5 °C for 2 d
1
afforded colorless, block-like crystals. Yield: 1.46 g (83%). H NMR (400 MHz, THF-d8,
25 °C): δ 3.63-3.54 (m, 18 H, CH2O and CH(CH3)2), 1.8-1.72 (m, 16 H, CH2), 0.9 (t, 3JHH
= 8 Hz, 12 H, CH(CH3)2). 13C{1H} NMR (100.6 MHz, THF-d8, 25°C): δ 162.6 (iPrN=C-
NiPr), 89.1 ([C–CLi]B10H10), 67.8 (CH2O), 45.9 (NCH(CH3)2), 45.7 (NCH(CH3)2), 28.1
([C–CLi]B10H10), 25.9 (CH2), 24.5 (CH(CH3)2), δ 24.3 (CH(CH3)2). 11B{1H} NMR (128.4
MHz, THF-d8, 25 °C): δ -7.2 (2 B), -9.5 (2 B), -12.2 (br, 6 B). MS (EI): m/z (%) 270 (12)
+
[ M – Li2(THF)4 ], 142 (100) [C2H10B10+]. Anal. Found: C, 55.87; H, 11.23; N, 5.55. Calc.
for C25H56B10Li2N2O4 (570.56 g/mol): C, 56.26; H, 11.14; N, 5.53.
o-C2B10H10-κ2C,N-[C(NiPrSiMe3)(=NiPr)]SiMe3 (5). o-Carborane (1, 0.5 g, 3.5 mmol)
was dissolved in THF (80 ml) and nBuLi (1.6 M in n-hexane, 2.2 ml, 3.5 mmol) was added
to the solution at r.t. while stirring. After stirring for 20 min, neat N,N'-
diisopropylcarbodiimide (0.6 ml, 3.5 mmol) was added and stirring at r.t. was continued
for 90 min. Then Me3SiCl (0.5 ml, 3.5 mmol) was added to the solution at r.t. The THF
was removed in vacuo after stirring for another 12 h. n-Pentane was added to the remaining
white solid giving a white suspension, which was filtered. The resulting colorless solution
was concentrated in vacuo to a total volume of ca. 10 ml. Cooling to -32 °C for 2 d
afforded colorless, block-like crystals suitable for X-ray diffraction. Yield: 0.16 g (32%).
3
1H NMR (400 MHz, C6D6, 21 °C): δ 3.65 (sept, JHH = 6.2 Hz, 1 H, NCH(CH3)2), 3.26
(sept, 1 H, 3JHH = 6.6 Hz, SiNCH(CH3)2), 1.09 (d, 3 H, 3JHH = 8.0 Hz, CH2(CH3)2), 1.00 (d,
3
3
3 H, JHH = 8.0 Hz, CH2(CH3)2), 0.92 (d, 3 H, JHH = 6.2 Hz, CH2(CH3)2), 0.89 (d, 3 H,
3JHH = 6.4 Hz, CH2(CH3)2), 0.24 (s, 9 H, [C–C]B10H10 -Si(CH3)2), 0.09 (s, 9 H, N-Si(CH3)3).
13C{1H} NMR (100.6 MHz, C6D6, 20 °C): δ 153.5 (iPrN=C-NiPr), 85.6 ([C–CLi]B10H10),
74.5 ([C–CSi(CH3)3]B10H10), 51.4 (NCH(CH3)2), 51.0 (SiNCH(CH3)2), 24.5 (CH(CH3)2),
24.5 (CH(CH3)2), 23.9 (CH(CH3)2), 23.4 (CH(CH3)2), 3.7 ([C–C]B10H10 -Si(CH3)3), 2.8 (N-
Si(CH3)3). 11B{1H} NMR (128.4 MHz, C6D6, 25°C): δ -0.3 (2 B), -2.0 (1 B), -7.6 (3 B),
29
-10.1 (4 B). Si NMR (79.5 MHz, C6D6, 23°C): δ 7.8 (1 Si), 8.6 (1 Si). MS (EI): m/z (%)

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+
299 (100) [M – SiC3H9, C3H6 ]. Anal. Found: C, 42.77; H, 10.15; N, 6.80. Calc. for
C15H42B10N2Si2 (414.79 g/mol): C, 43.43; H, 10.21; N, 6.75.
[o-C2B10H10C(NiPr)(=NiPr)-κ2C,N]Sn=Sn[(iPrN)2CnBu]2 (6): The preparation of the
dilithium precursor was carried out as described for 2a. The dilithium precursor was then
treated with anhydrous SnCl2 (2.17 g, 11.4 mmol) at r.t. giving a red solution which was
stirred over night. The THF was removed in vacuo. The remaining purple solid was
washed with 20 ml of pentane, extracted with 15 ml of toluene and filtered, leaving behind
a white solid. The toluene was removed in vacuo at 40 °C to give a purple solid. Single-
crystals suitable for X-ray diffraction where obtained by cooling a concentrated toluene
solution to -32 °C for about 1 week. Yield: 5.24 g (53 %). 1H NMR (400 MHz, toluene-d8,
20 °C): δ 3.72-3.54 (m, 4H, NCH(CH3)2), 3.37 (m, 6 H, CH2-CH3), 3.24 (m, 2 H,
3
NCH(CH3)2), 2.09 (quint, J = 2.2 Hz, β-CH2(nBu)), 1.7 (d, 2 H, α-CH2(nBu)), 1.40-1.11
(br m, 35 H, α-CH2 + β-CH2 + γ-CH2 + NCH(CH3)2), 1.03-0.65 (br m, 12 H, δ-CH2).
13C{1H} NMR (150.9 MHz, THF-d8, 20 °C): δ 173.8 (N=C(nBu)-N), 151.6 (N=C-
(C2B10H10)-N), 80.2 ([C−CSn]B10H10), 65.2 ([C−Sn]B10H10), 51.1 (=NCH(iPr)), 48.4 (CH
(iPr)), 47.5 (CH (iPr)), 47.4 (CH (iPr)), 46.3 (−NCH (iPr)), 30.8 (α-CH2(nBu)), 28.1
(CH3(iPr)), 27.3 (CH3(iPr)), 24.1 (CH3(iPr)), 23.8 (CH3(iPr)), 23.6 (CH3(iPr)), 23.5
(CH3(iPr)), 19.4 (γ -CH2(nBu)), 14.3 (δ-CH2(nBu)), 13.9 (δ-CH2(nBu)). 11B{1H} NMR
(128.4 MHz, THF-d8, 20 °C): δ 2.55 (3 B), -2.55 (br, 7 B). 119Sn-NMR (149.21 MHz,
i
+
THF-d8, 20 °C): δ -45.64. MS (EI): m/z (%) 387 (5) [M - Sn(N2 Pr2Bu)2, C2 ], 344 (5) [M -
i
+
Sn(N2 Pr2Bu)2, C5H7 ], 270 (10) [(iPr)2N2C-C2H11B10+], 227 (36) [iPrN2C-C2H11B10+], 84
+
(50) [C4H8N2 ], 58 (100) [C3H8N+]. Anal. Found: C, 42.42; H, 8.15; N, 9.67. Calc. for
C31H70B10N6Sn2 (872.46 g/mol): C, 42.68; H, 8.09; N, 9.63.
[o-C2B10H10C(NiPr)(=NiPr)-κ2C,N]PPh (7). The preparation of the dilithium precursor
was carried out as described for 2a. The dilithium precursor was then cooled to 0 °C and
treated with PhPCl2 (3.6 ml, 26.6 mmol). The solution heated up and immediately turned
yellow. After stirring for 12 h, the THF was removed in vacuo and a mixture of
pentane/dichloromethane (3:2, 50 ml) was added to the remaining yellow solid. A white
solid, which separated from the golden yellow solution, was removed by filtration. The
solution was concentrated in vacuo to a total volume of ca. 20 ml. After 1 week colorless,
rectangular single-crystals suitable for X-ray diffraction were obtained. Yield: 2.82 g
(33 %). 1H NMR (400 MHz, THF-d8, 25 °C): δ 7.55-7.40 (m, 5 H, P-C6H5), 4.57-4.44 (m,

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3
2 H, =NCH(CH3)2, −NPCH(CH3)2), 1.18 (d, 6 H, CH(CH3)2, J = 6.4 Hz), 1.14 (dd, 7 H,
3
4
−NPCH(CH3)2, JHH= 6.0 Hz, JHP = 3.6 Hz) ppm. 13C{1H} NMR (100.6 MHz, THF-d8,
25 °C): δ 145.5 (d, 2J = 10.1 Hz, iPrN=C-NiPr), 138.7 (d, 1J = 36.2 Hz, P-Cpara(Ph)), 132.1
(d, 2J = 15.1 Hz, Cortho(Ph)), 131.8 (Cpara(Ph)), 129.2 (d, 3J = 7.0 Hz, Cmeta (Ph)), 75.6 ([C–
1
2
CP]B10H10), 73.4 (d, J = 49.3 Hz, ([C–CP]B10H10 ), 49.8 (d, J = 17.1 Hz, NPCH(CH3)2),
3
3
48.8 (NCH(CH3)2), 24.9 (NCH(CH3)2, 22.0 (d, J = 15.1 Hz, (CH3)2CHNP), 20.4 (d, J =
5.0 Hz, (CH3)2CHNP). 31P{1H} NMR (161.98 Hz, THF-d8, 25 °C): δ 50.7 (([C–C]B10H10
P-Ph). 11B{1H} NMR (128.4 Hz, THF-d8, 25 °C): δ -4.9, -8.7, -10.2, -12.2, -15.5. MS (EI):
-
+
+
m/z (%): 376 (30) [M+], 362 (10) [M - CH2 ], 334 (100) [M - C3H7 ], 319 (10) [M -
C4H10+], 292 (49) [M - C6H14+]. Anal. Found: C, 47.57; H, 7.81; N, 7.50. Calc. for
C15H29B10N2P (376.49 g/mol): C, 47.85; H, 7.76; N, 7.44.
[o-C2B10H10C(NCy)(=NCy)-κ2C,N]SiCl2 (8). Compound 2b was prepared as described
above from 1 (1.00 g, 7 mmol) and treated with SiCl4 (0.80 ml, 7 mmol). The solution was
filtered to separate the LiCl after stirring for at least 48 hours at r.t. The resulting yellow
solution was concentrated in vacuum to a total volume of ca. 15 ml. Cooling to 4 °C for 2
d afforded colorless, block-like and needle-like crystals suitable for X-ray diffraction.
Yield: 1.78 g (57%) 1H NMR (600.1 MHz, THF-d8, 25 °C):
1 H, NCH), 2.10-3.20 (br, 10 H, B-H), 1.14-2.00 (m br, 20 H, NCH(CH2)5). 13C{1H} NMR
(100.6 MHz, THF-d8, 25 °C): 139.5 ((CyN=)C(NCy)), 73.8 ((CyN=)C-CCage), 63.6
(CCage-Si), 56.1 (NCH(CH2)5), 55.9 (NCH(CH2)5), 35.0, 32.3, 26.7, 26.5, 26.3, 24.5
(NCH(CH2)5). 11B{1H} NMR (128.4 MHz, THF-d8, 25 °C):
-2.0 (1 B), -3.7 (1 B), -8.0 (3
δ 4.14 (s, 1 H, NCH), 3.95 (s,
δ
δ
B), -11.5 (3 B), -14.1 (2 B). 29Si NMR (79.5 MHz, THF-d8, 25 °C):
δ -15.3. MS (EI): m/z
+
(%) 448 (8) [M+], 366 (90) [M - C6H9 ], 351 (25) [M - SiCl2, +2H+], 284 (30) [M -
+
+
C12H19+], 269 (100) [M - C6H7, SiCl2 ], 187 (77) [M - C12H17, SiCl2 ], 143 (8) [C2H11B10+].
Anal. Found: C, 40.11; H, 7.10; N, 6.34. Calc for C15H32B10Cl2N2Si (447.52 g/mol): C,
40.26; H, 7.21; N, 6.26.
[o-C2B10H10C(NCy)(=NCy)-κ2C,N]SiMe2 (9). Following the procedure given for 8 using
Me2SiCl2 (0.84 ml, 7 mmol) instead of SiCl4 and crystallization of the product from DME
(20 ml) at 4 °C for 48 hours afforded colorless needle-like crystals which were not suitable
1
for X-ray diffraction. Yield: 1.31 g (46%) H NMR (400.1 MHz, THF-d8, 25°C):
δ
δ
3.28-
0.54
3.40 (2 H, NCH), 2.00-3.20 (br, 10 H, B-H), 1.11-2.02 (m br, 20 H, NCH(CH2)5),
(6 H, -Si-(CH3)2). 13C{1H} NMR (100.6 MHz, THF-d8, 25°C):
δ 143.0 ((CyN=)C(NCy)),

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76.9 ((CyN=)C-CCage), 74.6 (CCage-Si), 56.1 (NCH(CH2)5), 54.4 (NCH(CH2)5), 34.8, 33.0,
26.6, 26.1, 25.7, 25.1 (NCH(CH2)5), 0.3 (-Si-(CH3)2). 11B{1H} NMR (128.4 MHz, THF-d8,
25°C):
δ
δ
-5.6 (2 B), -6.6 (1 B), -11.6 (4 B), -15.3 (3 B). 29Si NMR (79.5 MHz, THF-d8,
+
25°C):
8.7. MS (EI): m/z (%) 406 (23) [M+], 352 (100) [M - Si, C2H2 ], 269 (29) [M - Si,
C2H2, C6H11+], 187 (6) [M - Si, C2H2, C12H21+]. Anal. Found: C, 49.73; H, 9.39; N, 6,76.
Calc for C17H38B10N2Si (406.68 g/mol): C, 50.20; H, 9.42; N, 6.89.
[o-C2B10H10C(NCy)(=NCy)-κ2C,N]SiPh2 (10). Following the procedure given for 8 using
Ph2SiCl2 (1.50 ml, 7 mmol) instead of SiCl4 and crystallization of the product from DME
(10 ml) at 4 °C for 48 hours afforded colorless, block-like crystals suitable for X-ray
diffraction. Yield: 2.83 g (76 %). 1H NMR (400.1 MHz, THF-d8, 25 °C):
(10 H, Si-C(C6H5)), 3.26-3.44 (2 H, NCH), 2.00-3.15 (br, 10 H, B-H), 1.09-1.93 (m br, 20
H, NCH(CH2)5). 13C{1H} NMR (100.6 MHz, THF-d8, 25 °C):
143.4 ((CyN=)C(NCy)),
143.1 (Si-C(C6H5)), 137.7, 132.5, 128.9 (Si-C(C6H5)), 77.0 ((CyN=)C-CCage), 74.5 (CCage
Si), 56.4 (NCH(CH2)5), 54.7 (NCH(CH2)5), 35.8, 32.2, 26.9, 25.8, 25.1, 24.8
(NCH(CH2)5). 11B NMR (128.4 MHz, THF-d8, 25 °C):
-5.6 (2 B), -6.6 (1 B), -8.6 (1 B), -
δ 7.81, 7.57, 7.48
δ
-
δ
δ
11.6 (3 B), -15.3 (3 B). 29Si NMR (79.5 MHz, THF-d8, 25°C):
δ -15.1. MS (EI): m/z (%)
+
531 (22) [M+], 449 (7) [M - C6H9 ], 367 (15) [M - C12H19+], 350 (38) [M - C12H9Si+], 269
(100) [M - C6H8, C12H9Si+]. Anal. Found: C, 60.97; H, 7.96; N, 5.33. Calc for
C27H42B10N2Si ( 530.82 g/mol): C, 61.09; H, 7.98; N, 5.28.
[o-C2B10H10C(NCy)(=NCy)-κ2C,N]GeCl2 (11). Following the procedure given for 8 using
GeCl4 (0.80 ml, 7 mmol) instead of SiCl4 and crystallization of the product from THF (15
ml) at r.t. afforded yellow, needle-shaped crystals which were not suitable for X-ray
1
structure analysis. Yield: 2.61 g (76 %) H NMR (400.1 MHz, THF-d8, 25 °C):
δ 4.04
(NCH(CH2)5), 3.27 (NCH(CH2)5), 2.10-3.15 (br, 10 H, B-H), 1.12-2.05 (m br, 20 H,
(NCH(CH2)5). 13C{1H} NMR (100.6 MHz, THF-d8, 25 °C):
138.0 ((CyN=)C(NCy)),
72.1 ((CyN=)C-CCage), 64.3 (CCage-Ge), 56.0 (NCH(CH2)5), 54.1 (NCH(CH2)5), 34.5, 32.9,
26.1, 25.2, 24.6, 24.0 (NCH(CH2)5). 11B{1H} NMR (128.4 MHz, THF-d8, 25 °C):
-1.6 (1
δ
δ
B), -3.8 (1 B), -6.4 (2 B), -9.8 (3 B), -13.4 (3 B). MS (EI): m/z (%) 493 (68) [M+], 411 (9)
+
[M - C6H9 ], 351 (100) [M - GeCl2, + 3H+], 187 (1) [M - GeCl2, C12H17+], 142 (<1)
[C2H10B10+]. Anal. Found: C, 36.59; H, 6.37; N, 5.58. Calc for C15H32B10Cl2GeN2 (492.01
g/mol): C, 36.61; H, 6.56; N, 5.69.

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Cp2Ti[o-C2B10H10C(NCy)(=NCy)-κ2C,N] (12). Following the procedure given for 8 using
titanocene dichloride (1.74 g, 7 mmol) instead of SiCl4 and crystallization of the red
product from hot THF (15 ml) afforded copper-colored, needle-shaped crystals which were
1
suitable for X-ray structure analysis. Yield: 2.53 g (69%). H NMR (400 MHz, THF-d8,
25 °C):
(NCH(CH2)5)), 2.00-3.20 (br m, 10 H, B-H), 1.72 (THF), 1,15-1.89 (m, 20 H, CH(CH2)5).
13C{1H} NMR (100.6 MHz, THF-d8, 25 °C):
143.1 ((CyN=)C(NCy)), 117.5 (Cp), 77.1
δ 6.30 (s, 10 H, Cp), 3.57 (THF), 3.30 (s br, 1 H, (NCH(CH2)5)), 3.26 (s br, 1 H,
δ
((CyN=)C-CCage), 68.1 (THF), 56.4 (NCH(CH2)5), 54.8 (NCH(CH2)5), 52.9 (CCage-Ti), 26.3
(THF), 34.9, 26.7, 26.2, 25.8, 25.6, 25.1 (NCH(CH2)5). 11B{1H} NMR (128.4 MHz, THF-
d8, 25 °C):
δ
-3.9 (2 B), -10.0 (3 B), -13.6 (5 B). MS (EI): m/z (%) 527 (1) [M+], 350 (22)
+
[M - C10H8Ti+], 269 (100) [M - C10H8Ti, C6H9 ], 187 (76) [M - C10H8Ti, C12H19+], 98 (34)
[C6H12N+], 83 (43) [C6H11+]. Anal. Found: C, 56.96; H, 8.13; N, 5.29. Calc for
C25H42B10N2Ti ( 526.58 g/mol): C, 57.02; H, 8.04; N, 5.32.
Cp2Zr[o-C2B10H10C(NCy)(=NCy)-κ2C,N] (13). Starting from o-Carborane (1, 0.75 g, 5.2
mmol), (1.6 M in n-hexane, 3.25 ml, 5.2 mmol) and N,N´-dicyclohexylcarbodiimide (1.07
g, 5.2 mmol) a solution of 2b was prepared and treated with zirconocene dichloride (1.52 g,
5.2 mmol), whereby the color of the pale yellow solution changed to amber. Extraction
with n-pentane followed by recrystallization from hot THF (15 ml) afforded orange,
needle-shaped crystals which were suitable for X-ray structure analysis. Yield: 1.31 g
1
(44%) H NMR (400 MHz, THF-d8, 25 °C):
δ 6.39 (s, 10 H, Cp-H), 3.42 (s, 1 H, NCH),
3.26 (s, 1 H, NCH), 2.00-2.80 (br, 10 H, B-H), 1.16-1.90 (m br, 20 H, NCH(CH2)5).
13C{1H} NMR (100.6 MHz, THF-d8, 25 °C):
150.9 ((CyN=)C(NCy)), 115.5 (Cp), 77.1
((CyN=)C-Ccage), 56.2 (NCH(CH2)5), 54.8 (NCH(CH2)5), 36.0, 34.9, 25.8, 25.6, 25.4, 25.2
(NCH(CH2)5). 11B{1H} NMR (128.4 MHZ, THF-d8, 25 °C):
-2.9 (2 B), -3.8 (1 B), -4.8
δ
δ
(1 B), -9.6 (3 B), -13.5 (3 B). MS (EI): m/z (%) 570 (100) [M+], 487 (34) [M – C6H10+],
405 (25) [M – C12H20+], 186 (11) [M - C12H20, C10H8Zr+]. Anal. Found: C, 52.71; H, 7.38;
N, 4.87. Calc for C25H42B10N2Zr (569.92 g/mol): C, 52.68 ; H, 7.43; N, 4.92.
ACKNOWLEDGEMENTS
Financial support by the Otto-von-Guericke-Universität Magdeburg is gratefully
acknowledged.

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Trans., 1986, 2387; (c) M. Weidenbruch, H. Kilian, K. Peters, H. G. von Schnering
and H. Marsmann, Chem. Ber., 1995, 128, 983; (d) M. Stürmann, W. Saak, K. W.
Klinkhammer and M. Weidenbruch, Z. Anorg. Allg. Chem., 1999, 625, 1955; (e) P.
P. Power, Chem. Rev., 1999, 99, 3463; (f) T. Fukawa, V. Y. Lee, M. Nakamoto and
A. Sekiguchi, J. Am. Chem. Soc., 2004, 126, 11758; (g) V. Y. Lee, T. Fukawa, M.

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DOI: 10.1039/C3DT52751D
26
Nakamoto, A. Sekiguchi, B. L. Tumanskii, M. Karni and Y. Apeloig, J. Am. Chem.
Soc., 2006, 128, 11643.
27
28
Stoe, XAREA Program for Xray Crystal Data collection, (XRED32 included in
XAREA) (Stoe, 2002).
(a) G. M. Sheldrick, SHELXL-97 Program for Crystal Structure Refinement,
Universität Göttingen (Germany) 1997; (b) G. M. Sheldrick, SHELXS-97 Program
for Crystal Structure Solution, Universität Göttingen (Germany) 1997.

Page 27 of 38
Dalton Transactions
Table 1. Crystallographic Data for 2b, 3b, 4a, 5, 6, 7, 10, 12 and 13.
2b
C23H49B10LiN2O2
10.518(2)
11.229(2)
14.087(3)
103.86(3)
108.18(3)
96.24(3)
1504.1(5)
2
3b
C15H34B10N2
6.6180(10)
10.2110(18)
15.859(3)
86.218(15)°
86.380(14)°
77.332(14)
1042.1(3)
2
4a
C17H44B10Li2N2O4
10.182(2)
13.527(3)
20.850(4)
90
5
C15H42B10N2Si2
15.616(3)
9.2632(19)
19.139(4)
90
6
C31H70B10N6Sn2. C6H6
10.334(2)
12.194(2)
19.991(4)
104.60(3)
90.89(3)
108.06(3
2305.5(8)
2
7
C15H29B10N2P
35.600(7)
6.6979(13)
24.238(5)
90
10
C27H42B10N2Si
11.8346(15)
32.995(5)
9.2931(11)
90
12
13
Empirical formula
C29H50B10N2OTi C25H42B10N2Zr
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
12.608(3)
10.454(2)
24.129(5)
90
10.4438(4)
10.7747(4)
13.2968(6)
107.827(4)
96.672(4)
93.456(3)
1407.49(10)
2
90
111.97(3)
90
131.32(3)
90
123.079(17)
90
90.13(3)
90
90
3
2871.8(10)
4
2567.4(9)
4
4341(2)
8
3040.7(7)
4
3180.2(12)
4
V (Å )
Z
formulaweight
spacegroup
T (°C)
500.68
350.54
462.52
P212121
-130
414.79
P21/n
950.52
376.47
C2/c
530.82
Cc
598.68
Pmc21
-173
569.93
P-1
P-1
P-1
P-1
-120
-173
-130
-130
-130
-173
-173
λ (Å)
0.71073
1.105
1.54184
1.117
0.71073
1.070
0.71073
1.073
0.71073
1.257
0.71073
1.152
1.54184
1.160
1.54180
1.250
1.54184
1.345
Dcalcd (g cm-3)
-1
0.062
0.409
0.064
0.144
1.111
0.130
0.814
2.466
3.316
ꢀ (mm
)
F(000)
540
376
992
896
896
1584
1128
1272
592
data/restraints/parameters
7418 / 170 / 404
1.000
4309 / 0 / 252
1.049
7686 / 0 / 364
1.082
5204 / 0 / 312
0.916
11312 / 0 / 482
0.947
5833 / 0 / 369
1.060
6195 / 2 / 361
1.021
6908 / 1 / 424
1.033
5822 / 0 / 343
1.039
2
goodness-of-fit on F
R(Fo or Fo2)
Rw(Fo or Fo2)
0.0475
0.0414
0.0574
0.1099
0.0603
0.0998
0.0453
0.0432
0.0973
0.0275
0.0735
0.0466
0.1257
0.0373
0.1259
0.1094
0.0706
0.0967

Dalton Transactions
Page 28 of 38
28
Table 2. Selected bond lenghts (Å) and angles (°) for compounds 2b, 3b, 4b, 5, 6, 7, 10, 12, and 13.
2b
3b
4a
5
6
7
10
12
13
C23H49B10LiN2O2 C15H34B10N2 C17 H44 B10 Li2 N2 O4 C15H42B10N2Si2 C31 H70 B10 N6 Sn2 . C6 H6 C15 H29 B10 N2 P C27H42B10N2Si C29H49B10N2OTi C25H42B10N2Zr
N1-C3
N2-C3
1.2773(16)
1.3771(17)
1.5269(17)
1.6793(18)
2.102(2)
1.3734(14)
1.2788(14)
1.5279(14)
1.6316(14)
1.317(2)
1.3232(19)
1.549(2)
1.687(2)
2.067(3)
1.988(3)
1.947(3)
1.425(3)
1.249(3)
1.547(3)
1.698(3)
1.924(3)
1.758(2)
1.384(4)
1.268(5)
1.539(5)
1.669(5)
2.216(3)
2.110(3)
1.4123(15)
1.2605(17)
1.5179(17)
1.6322(18)
1.8475(12)
1.7174(14)
1.4128(15)
1.2619(16)
1.5332(16)
1.6616(15)
1.8964(13)
1.7404(10)
1.372(4)
1.280(5)
1.531(5)
1.700(5)
2.339(3)
2.012(3)
1.377(3)
1.271(3)
1.531(3)
1.717(3)
2.433(2)
2.0782(18)
C1-C3
C1-C2
C2-M
N1-M
2.057(3)
N2-Li
Sn1-Sn2
Sn2-N3
Sn2-N4
Sn2-N5
Sn2-N6
N3-C10
N4-C10
N5-C21
N6-C21
Cp-Ti
2.9869(8)
2.139(3)
2.295(3)
2.302(3)
2.150(3)
1.337(5)
1.318(4)
1.323(4)
1.332(4)
2.106/2.103
Cp-Zr
2.243/2.247
121.5(2)
N1-C3-N2
N1-M-C2
C3-C1-C2
Si1-C2-C1
C3-N1-Si2
N3-Sn2-N4
N5-Sn2-N6
N4-Sn2-N5
128.54(11)
86.99(10)
115.33(10)
131.59(10)
115.61(8)
136.18(15)
89.27(12)
116.85(13)
129.8(2)
120.7(3)
78.90(12)
113.8(3)
120.05(11)
90.99(5)
120.32(11)
92.56(5)
122.2(3)
75.13(12)
112.0(3)
71.57(7)
120.6(2)
124.97(15)
124.06(18)
108.80(9)
110.18(9)
112.26(17)
59.60(11)
59.35(11)
143.39(10)

Page 29 of 38
Dalton Transactions
View Article Online
DOI: 10.1039/C3DT52751D
Figures
Fig. 1 Molecular structure of (o-C2B10H10C(NHiCy)(=NiCy)-κ2C,N)Li(THF)2 (2b).
Most of the hydrogen atoms are omitted for clarity.