Heavier alkaline earth metal borohydride complexes stabilized by β-diketiminate ligand

Article abstract of DOI:10.1021/ic902338r

The reaction of KB[sec-Bu]₃H with calcium iodide [LCa(μ-I) thf]₂] (1) and strontium iodide [LSr(μ-I) thf]₂ (2) yields calcium trisec-butylborohydride LCaB(sec-Bu)₃H thf (3) and strontium trisec-butylborohydride LSrB(sec-Bu)₃H thf (4) (L = CH(CMe2,6-iPr₂C₆H₃N)₂), respectively. Compounds 2, 3, and 4 were characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and single crystal X-ray analysis, whereas 1 was characterized without X-ray structural analysis. Compounds 3 and 4 are monomeric in the solid state with a hydride ligation between the metal and boron centers.

Full text of DOI:10.1021/ic902338r

3816 Inorg. Chem. 2010, 49, 3816–3820
DOI: 10.1021/ic902338r
Heavier Alkaline Earth Metal Borohydride Complexes Stabilized by β-Diketiminate
Ligand
Sankaranarayana Pillai Sarish, Anukul Jana, Herbert W. Roesky,* Thomas Schulz, Michael John, and Dietmar Stalke
€
€
€
Institut fu€r Anorganische Chemie, Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany
Received November 26, 2009
The reaction of KB[sec-Bu]3H with calcium iodide [LCa( μ-I) thf ]2] (1) and strontium iodide [LSr( μ-I) thf ]2 (2) yields
calcium trisec-butylborohydride LCaB(sec-Bu)3H thf (3) and strontium trisec-butylborohydride LSrB(sec-Bu)3H thf
3
3
3
3
(4) (L=CH(CMe2,6-iPr2C6H3N)2), respectively. Compounds 2, 3, and 4 were characterized by multinuclear NMR
spectroscopy, mass spectrometry, elemental analysis, and single crystal X-ray analysis, whereas 1 was characterized
without X-ray structural analysis. Compounds 3 and 4 are monomeric in the solid state with a hydride ligation between
the metal and boron centers.
Introduction
by our group.5 A well-defined heavier alkaline earth metal,
calcium hydride [LCaH thf ]2 was reported by Harder and co-
3
Metal hydrides are important because their complexes are
considered as valuable synthons in chemistry1 and also as
potential targets for hydrogen storage. Metal hydrides can
act as catalysts in a number of reactions, especially in the case
of transition-metal complexes.2 The main group and the
d-block elements form many metal hydrides especially with
β-diketiminate ligands.3 The unique properties of the β-dike-
timinate ligand provide suitable electronic and steric require-
ments to materialize a number of novel complexes, including
hydrides. Works related to β-diketiminate hydride complexes
of Group 2 metals have been preferentially examined. A
scorpionate ligand stabilized beryllium hydride was reported
in 1992.4 An attempt to prepare magnesium hydride from
workers and showed a startling reactivity.6 The extension of
lanthanide hydride synthetic methods to alkaline earth metals
resulted in the successful synthesis of this complex by using
PhSiH3 as a hydride transfer agent. Recently Jones and co-
workers were successful in isolating [LMgH thf ]2.7 Moreover,
3
Hill and co-workers reported a magnesium hydride cluster
compound with N-heterocyclic carbene coordination.8 Never-
theless, such hydride derivatives are, so far, not reported as
stable species for heavy alkaline earth metals, like strontium
and barium. So we embarked upon an extension of our
successful preparation of well-defined Group 14 hydride
complexes to alkaline earth metals by employing alkaline-
[R3BH] complexes.9 The anion [R3BH]- has found extensive
use as a hydride source and as a reducing agent. Moreover, the
exploration of heavier alkaline earth metals gained a momen-
tum nowadays that has striking similarity to lanthanides.10 We
magnesium iodide, LMgI OEt2 with NaBH4 resulted in a
3
hydrogen-bridged magnesium complex, LMg( μ-H)3BH OEt2
3
*Corresponding author. E-mail: hroesky@gwdg.de.
(1) (a) Zhao, J.; Goldman, A. S.; Hartwig, J. F. Science 2005, 307, 1080–
1082. (b) Himmel, H.-J. Z. Anorg. Allg. Chem. 2005, 631, 1551–1564. (c)
McGrady, G. S.; Guilera, G. Chem. Soc. Rev. 2003, 32, 383–392. (d) Himmel,
H.-J. Dalton. Trans. 2003, 3639–3649. (e) Mitzel, N. W. Angew. Chem. 2003,
115, 3984–3986; Angew. Chem., Int. Ed. 2003, 42, 3856-3858. (f ) Lefebvre, F.;
Basset, J.-M. Main Group Met. Chem. 2002, 25, 15–32. (g) Aldridge, S.; Downs,
A. J. Chem. Rev. 2001, 101, 3305–3365. (h) Kaesz, H. D.; Saillant, R. B. Chem.
Rev. 1972, 72, 231–281. (i) Mueller, W. M.; Blackledge, J. P.; Libowitz, G. G. Metal
Hydrides; Academic Press: London, 1968; pp 1-21.
€
ꢀ
(5) Prust, J.; Most, K.; Muller, I.; Alexopoulos, E.; Stasch, A.; Uson, I.;
Roesky, H. W. Z. Anorg. Allg. Chem. 2001, 627, 2032–20377.
(6) (a) Spielmann, J.; Harder, S. Chem. Eur. J. 2007, 13, 8928–8938. (b)
Harder, S.; Brettar, J. Angew. Chem. 2006, 118, 3554–3558; Angew. Chem., Int.
Ed. 2006, 45, 3474-3478.
(7) Green, S. P.; Jones, C.; Stasch, A. Angew. Chem. 2008, 120, 9219–9223;
Angew. Chem., Int. Ed. 2008, 47, 9079-9083.
(8) Arrowsmith, M.; Hill, M. S.; MacDougall, D. J.; Mahon, M. F. Angew.
Chem. 2009, 121, 4073–4076; Angew. Chem., Int. Ed. 2009, 48, 4013-4016.
(9) (a) Jana, A.; Ghoshal, D.; Roesky, H. W.; Objartel, I.; Schwab, G.;
Stalke, D. J. Am. Chem. Soc. 2009, 131, 1288–1293. (b) Jana, A.; Roesky,
(2) Hoskin, A. J.; Stephan, D. W. Coord. Chem. Rev. 2002, 233-234, 107–129.
€
(3) (a) Pfirrmann, S.; Limberg, C.; Herwig, C.; Stosser, R.; Ziemer, B.
€
Angew. Chem. 2009, 121, 3407–3411; Angew Chem., Int. Ed. 2009, 48, 3357-
3361. (b) Yu, Y.; Sadique, A. R.; Smith, J. M.; Dugan, T. R.; Cowley, R. E.;
Brennessel, W. W.; Flaschenriem, C. J.; Bill, E.; Cundari, T. R.; Holland, P. L.
J. Am. Chem. Soc. 2008, 130, 6624–6638. (c) Singh, S.; Ahn, H.-J.; Stasch, A.;
Jancik, V.; Roesky, H. W.; Pal, A.; Biadene, M.; Herbst-Irmer, R.; Noltemeyer, M.;
Schmidt, H.-G. Inorg. Chem. 2006, 45, 1853–1860. (d) Pineda, L. W.; Jancik, V.;
Starke, K.; Oswald, R. B.; Roesky, H. W. Angew. Chem. 2006, 118, 2664–2667;
Angew. Chem., Int. Ed. 2006, 45, 2602-2605.
H. W.; Schulzke, C.; Doring, A. Angew. Chem. 2009, 121, 4310–4312; Angew.
Chem., Int. Ed. 2009, 48, 1106-1109. (c) Richards, A. F.; Phillips, A. D.;
Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2003, 125, 3204–3205.
(10) (a) Harder, S. Angew. Chem. 2003, 115, 3553–3556; Angew. Chem.,
Int. Ed. 2003, 42, 3430-3434. (b) Feil, F.; M€uller, C.; Harder, S. J. Organomet.
Chem. 2003, 683, 56–63. (c) Harder, S.; Feil, F.; Weeber, A. Organometallics
2001, 20, 1044–1046. (d) Harder, S.; Feil, F.; Knoll, K. Angew. Chem. 2001, 113,
4391–4394; Angew. Chem., Int. Ed. 2001, 40, 4261-4264. (e) Hanusa, T. P.
Chem. Rev. 1993, 93, 1023–1036.
(4) Han, R.; Parkin, G. Inorg. Chem. 1992, 31, 983–988.
r
pubs.acs.org/IC
Published on Web 03/16/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 8, 2010 3817
also assumed that ligation of the alkaline earth metal11,6b with
[R3BH]- is also possible and can stabilize the complex without
decomposition or ligand exchange. The latter properties are
more pronounced in the heavier alkaline earth metal com-
plexes.12 Herein, we report the hydrocarbon soluble β-diketi-
minate ligand supported alkaline earth metal boron hydride
complexes prepared from the corresponding alkaline earth
metal iodides and potassium trisec-butylborohydride.
Results and Discussion
The reaction of LH (L=CH(CMe2,6-iPr2C6H3N)2) and
one equiv of KN(SiMe3)2 with CaI2 or SrI2 at room tem-
Figure 1. Crystal structure of 2. The substituents on the nitrogen atoms
are depicted transparent, while one noncoordinaten-hexane molecule and
all hydrogen atoms have been omitted for clarity. For selected bond
distances (A) and angles (°) see Table 1.
perature led to the formation of calcium iodide [LCa( μ-I)
3
thf ]2 (1) and strontium iodide [LSr( μ-I) thf ]2 (2) as colorless
3
˚
compounds in good yields. Compounds 1 and 2 are soluble in
organic solvents, like benzene, toluene, and THF. Compounds
1 and 2 have been characterized by mass spectrometry, nuclear
magnetic resonance (NMR) spectroscopy (1H, 13C), X-ray
single crystal structure (for 2), and elemental analysis. The 1H
NMR spectra of compounds 1 and 2 show a singlet each [4.80
ppm (1), 4.84 ppm (2)] for the methine CH protons and a
second singlet [1.66 ppm (1), 1.69 ppm (2)] for the ligand
backbone methyl protons, respectively. The molecular ion
peak corresponding to the nonsolvated monomer 2 (704.3
(100) [Mþ/2-2THF ]) was observed in the electron impact (EI)
mass spectrum, while for 1, only fragment ions were detected.
Crystals of 2 suitable for X-ray structural analysis were
obtained from a saturated solution of n-hexane at room
temperature. The structure of 2 crystallizes as a dimer in the
space group P21/c with one molecule in the asymmetric unit
(Figure 1). The structure reveals the presence of two six-
membered C3N2Sr rings. These six-membered rings are
connected to each other by means of two μ-I atoms, which
results in the formation of a four-membered Sr2I2 ring.
Unlike its chloride and fluoride counterparts,13 the coordina-
tion geometries around both metal atoms of 2 are the same.
Thus, both of the strontium atoms are penta-coordinate and
have distorted trigonal bipyramidal geometry with two
nitrogen atoms of the β-diketiminate ligand, two bridging
iodine atoms, and one oxygen atom of the THF donor mole-
cule. The binding mode of the metal atoms is different when
compared to a similar iodide complex [Sr(η5-LtBu)( μ-I)-
(thf )]2 [LtBu=CH(CMetBuN)2].14 In the latter, each stron-
tium is coordinated to one η5-LtBu and one THF molecule in
Unfortunately, we were not able to obtain single crystals of
compound 1.
KB[sec-Bu]3H has proven to be a versatile hydride source
for the conversion of Group 14 chlorides to the correspond-
ing hydrides.9a,b As shown in Scheme 1, potassium trisec-
butylborohydride reacts readily with 2, leading to LSrB-
(sec-Bu)3H thf (4) in excellent yield, instead of giving the
3
corresponding hydride complex with two μ-hydrogen (H)
bonds bridging the alkaline earth metals. Monodentate
ligation of [HBR3]- to alkaline earth metal centers is rare,
although it contributes to the stability of the hydride com-
plexes. We expected the same type of compound when the
β-diketiminate stabilized calcium iodide 1 was used as a
precursor. Indeed, compound 3 (Scheme 1) was formed
accordingly.
Compounds 3 and 4 are yellow solids soluble in toluene,
THF, and benzene. Spectroscopic characterization indicates
the formation of both compounds 3 and 4. The 1H and 11
B
NMR spectra of 3 and 4 show a singlet each [4.76 (3) and
4.74 ppm (4)] for the methine CH protons of the ligand
backbone and a doublet (-4.4 (3) and -4.7 ppm (4)) for the
boron atoms, respectively. The 11B nucleus of 3 resonates
downfield in the NMR spectrum when compared to those
of other calcium borohydride complexes (-12.0 and -13.3
ppm).6b,11c The secBu-methyl groups attached to boron in 3
and 4 are nonequivalent and exhibit three doublets and three
triplets. The carbon atoms alpha to boron are asymmetric
centers, so that RRR, RRS, RSS, and SSS isomers are
possible. The RRR/SSS and RRS/RSS combinations each
are pairwise enantiomeric and will give the same NMR
spectrum. In the RRR/SSS pair, the three sec-Bu groups
are equivalent, whereas in the RRS/RSS pair, they are all
inequivalent by symmetry. X-ray crystallographic analysis,
where the RRS or RSS isomers are observed is also consistent
with the NMR spectrum. The resonance corresponding to
the (M-μH-B) hydride appears very broad in the 1H NMR
spectrum of both complexes. A 11B-1H correlation clearly
indicates the presence of this hydride in the complexes.
Molecular ions corresponding to 3 and 4 in the EI mass
spectra were not observed, and only fragment ions were seen.
For the B-H-M unit of 3 and 4, two absorption bands for 3
(1924 and 1903 cm-1) and one weak absorption band
at 1932.06 cm-1 for 4 are observed in the IR spectrum. The
former are comparable to those of the hydrogen-bridged com-
˚
addition to two bridging iodine atoms. Sr1 is 0.75 A out of the
˚
(N1/N2) plane, and Sr2 is located 1.41 A out of the (N3/N4)
˚
ligand plane. The Sr-I bond distances (3.257av A) are in
accordance with those reported (3.282av A).14 The Sr-I-Sr
˚
bond angles in 2(96.472(6)°av) are more acute than those of Sr-
Cl-Sr (101.27°av) reported in [LSr(thf)( μ-Cl)2Sr(thf )2L].13
(11) (a) Izod, K.; Wills, C.; Clegg, W.; Harrington, R. W. Inorg. Chem.
2007, 46, 4320–4325. (b) Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.;
Hitchcock, P. B.; Procopiou, P. A. Organometallics 2007, 26, 4076–4079. (c)
Harvey, M. J.; Hanusa, T. P.; Pink, M. Chem. Commun. 2000, 489–490.
(12) (a) Hanusa, T. P. Polyhedron 1990, 9, 1345–1362. (b) Hanusa, T. P.
Coord. Chem. Rev. 2000, 210, 329–367. (c) Westerhausen, M. Angew. Chem.
2001, 113, 3063–3065. Angew. Chem., Int. Ed. 2001, 40, 2975-2977.
(d) Alexander, J. S.; Ruhlandt-Senge, K. Eur. J. Inorg. Chem. 2002, 2761–
2774.
(13) Sarish, S. P.; Roesky, H. W.; John, M.; Ringe, A.; Magull, J. Chem.
Commun. 2009, 2390–2392.
(14) El-Kaderi, H. M.; Heeg, M. J.; Winter, C. H. Polyhedron 2006, 25,
224–234.
plex [Ca(HBEt3){1,2,4-C5(SiMe3)3H2}(thf )2] (1935 cm-1 11c
and to the KB[sec-Bu]3H (1904 cm-1). Therefore, we assume
)

3818 Inorganic Chemistry, Vol. 49, No. 8, 2010
Sarish et al.
Scheme 1. Preparation of β-Diketiminate Supported Calcium and Strontium Borohydride Complexes
˚
Table 1. Selected Bond Distances (A) and Angles (°) for 2, 3, and 4
Compound 2
bond distances
bond angles
Sr1-N1 2.5068(15)
Sr2-N3 2.4768(15)
Sr1-O1 2.5291(13)
Sr2-O2 2.5118(14)
Sr1-I1 3.2404(4)
Sr2-I1 3.2284(4)
Sr1-I1 3.2481(4)
Sr2-I2 3.3100(4)
Sr1 Sr2 3.7811(15)
N1-Sr1-N2 74.69(5)
N3-Sr2-N4 77.45(5)
3 3 3
I1-Sr1-I2 83.892(6)
I1-Sr2-I2 83.099(6)
Sr1-I1-Sr2 97.354(6)
Sr1-I2-Sr2 95.590(6)
Compound 3
bond distances
bond angles
Ca1-N1 2.337(3)
Ca1-H100 2.16(3)
B1-H100 1.24(3)
N1-Ca1-N2 78.97(9)
O1-Ca1-B1 102.03(11)
Ca1-N2 2.371(3)
B1-C30 1.643(6)
Ca1-O1 2.337(3)
B-C38 1.655(6)
Ca1-B1 2.861(4)
B-C34 1.673(5)
N1-Ca1-B1 130.00(11)
B1-Ca1-H100 23.8(8)
N2-Ca1-B1 143.02(11)
O1-Ca1-N2 96.19(9)
Compound 4
bond distances
bond angles
Sr1-N1 2.486(2)
Sr1-N2 2.509(2)
B1-C34 1.645(4)
Sr1-O1 2.501(2)
B-C38 1.661(5)
Sr1-B1 3.003(3)
B-C42 1.672(4)
Sr1-H100 2.325(8)
B1-H100 1.246(3)
N1-Sr1-N2 73.00(7)
O1-Sr1-B1 100.31(8)
N1-Sr1-B1 134.97(8)
B1-Sr1-H100 22.8(3)
N2-Sr1-B1 146.01(9)
O1-Sr1-N2 94.28(7)
Figure 2. Crystal structure of 3. The substituents on the nitrogen atoms
are depicted transparent, and all hydrogen atoms have been omitted for
clarity except the hydrogen atom involved in bonding to Ca2þ. For
selected bond distances (A) and angles (°) see Table 1.
Figure 3. Crystal structure of 4. The substituents on the nitrogen atoms
are depicted transparent, and all hydrogen atoms, except the hydrogen
atom involved in bonding to Sr2þ, have been omitted for clarity. For
selected bond distances (A) and angles (°) see Table 1.
˚
˚
that in the solid state for 3 two forms of hydro-
gen bonds might be present. The one that binds more to
the alkaline earth metal and the other more to the
boron.
X-ray quality crystals of 3 and 4 were grown from a
mixture of toluene and THF. Both isomorphic molecules
crystallize in the monoclinic space group P21/c with one
molecule in the asymmetric unit. The boron atoms in 3 and 4
exhibit a distorted tetrahedral coordination environment
with bond angles of 104.3(13)-114.9(2)° (Figures 2 and 3).
Because of the bulky sec-butyl groups, the angles between the
hydrogen atom and the carbon atoms are smaller than the
ideal tetrahedral angle, whereas the angles between the
carbon atoms are larger. As a result of the large metal-boron
distance, the metal has only small to no steric influence on the
geometry around the boron atom. The metal atoms in 3 and 4
display each a distorted trigonal pyramidal environment with
the two nitrogen atoms of the ligand, the boron atom at the
base, and the oxygen atom from the THF at the apex. The
space at the base of the pyramid is occupied by the bulky
substituents of the nitrogen atoms and the boron atom. The
hydride bridge seems to have no influence on the geometry in
comparison to the bulky sec-butyl and iso-propyl groups.
The bridging μH was observed in the X-ray structural

Article
Inorganic Chemistry, Vol. 49, No. 8, 2010 3819
analysis for 3 as well as for 4. In both compounds, the
C66H98I2N4O2Sr2 (1408.56): C, 56.28; H, 7.01; N, 3.98. Found:
C, 56.48; H, 7.29; N, 3.66.
borohydride anion coordinates to the M2þ ion through the
(M-μH-B) bond. The B-H Ca2þ(2.16(3) A) contact
˚
Synthesis of 3. A solution of compound 1 (1.31 g, 1 mmol) in
THF (25 mL) was cooled to -40 °C, and 2 equiv of potassium
trisec-butylborohydride (1 M solution in THF) (2.00 mmol) was
added. The mixture was allowed to warm to room temperature
and stirred for 2 h. From the solution all volatiles were removed
in vacuum, and the residue was extracted with toluene (30 mL).
All volatiles were again removed, and single crystals of 3 were
obtained from a solution of toluene-THF mixture (1:0.25) (8
mL) stored at -32 °C in a freezer. Yield (1.09 g, 1.53 mmol,
76.8%); mp 175-177 °C. 1H NMR (500.13 MHz, C6D6): δ 7.14
(m, 6 H, m-, p-Ar-H), 4.76 (s, 1 H, γ-CH), 3.84 (m, 4 H,
O-CH2-CH2), 3.10 (br, sept, 4H, CH(CH3)2), 1.72-1.06,
1.66-1.34, 1.67-0.73 (m, 6 H, B-CH(CH2-CH3)(CH3)),
1.62 (s, 6 H, CH3), 1.34 (m, (4 H, O-CH2-CH2), 1.33 (d, 12
H, CH(CH3)2), 1.17 (d, 12 H, CH(CH3)2), 1.08 (t, 3 H, B-CH-
(CH2-CH3)(CH3)), 1.05 (d, 3 H, B-CH(CH2-CH3)(CH3)),
0.92 (t, 3 H, B-CH(CH2-CH3)(CH3)), 0.83 (t, 3 H, B-CH-
(CH2-CH3)(CH3)), 0.76 (d, 3H, B-CH(CH2-CH3)(CH3)),
0.73 (d, 3 H, B-CH(CH2-CH3)(CH3)), 0.41 (m, 1 H, B-CH-
(CH2-CH3)(CH3)), 0.07 (m br, 2 H, B-CH(CH2-CH3)(CH3)),
and -0.05 (br, H, Ca-H-B) ppm. 13C{1H}NMR(125.77 MHz,
C6D6): δ 166.6, 146.6, 141.6, 125.2, 124.3, 94.6, 70.3, 31.1, 30.1,
29.7, 28.6, 25.2, 25.1, 25.0, 25.0, 24.9, 24.7, 20.5, 20.2, 19.9, 15.4,
14.9, and 14.7 ppm (B-C is not visible). 11B NMR (128.38 MHz,
C7D8): δ -4.4 ppm (d, 1JBH=50 Hz B, BR). IR (Nujol, cm-1):
ν~ 2649, 2601, 1924, 1903, 1771, 1696, 1625, 1540, 1514, 1458,
1377, 1313, 1262, 1225, 1167, 1098, 1054, 1018, 926, 871,
834, 788, 759, 747, 694, 668, 622, and 597. MS (70 eV):
m/z (%): 403.3 (100) [Lþ-Me]. Anal. calcd for C45H77BCaN2O
(712.99): C, 75.80; H, 10.89; N, 3.93 Found: C, 73.41;
H, 10.86; N, 4.01. (The low value for carbon probably due to
the high air sensitivity of the compound, partial loss of coordi-
nate THF molecule, and/or metal carbide formation, see also
ref 11c).
3 3 3
11c
compares well to those observed in [Ca(HBEt3){1,2,4-
˚
(Me3Si)3Cp}(thf )2] (2.21(4) A) and [ LCa(H2 BC8 H 14 )-
(thf)] (2.25(2) A).6a As expected, the B-H Sr2þ(2.325(8) A)
˚
˚
3 3 3
bond length is longer compared to its lighter counterpart 3
and is shorter to those in the strontium complex, [(Me3Si)2-
11a
˚
{Me2-(H3B)P}C]2Sr(thf )5 (2.735av A).
A reaction was carried out on a NMR scale to check
whetherthe bridging hydride can be released from compound
4. LSrB(sec-Bu)3H thf converts LGeCl f LGeH at room
3
temperature, and the chemical shift of the product was in
agreement with the reported value.3c Moreover, 3 and 4 on
heating yield mainly homoleptic calcium, L2Ca, and stron-
tium, L2Sr, compounds.15
Experimental Section
General Procedures. All manipulations were performed in a
dry and oxygen-free atmosphere (N2 or Ar) using Schlenk-line
and glovebox techniques. Solvents were purified with the
M-Braun solvent drying system. CaI2, SrI2, KN(SiMe3)2
(95%), and KB[sec-Bu]3H (1 M solution in THF) were pur-
chased from Aldrich and used as such. 1H (500.13 MHz) and 13
C
(125.77 MHz) NMR spectra were recorded on a Bruker Avance
500 NMR spectrometer. Chemical shifts are reported in ppm
with reference to SiMe4 (external). IR spectra were recorded on
a Bio-Rad Digilab FTS7 spectrometer in the range of 4000-350
cm-1 as nujol mulls. Mass spectra were obtained with a Finni-
gan MAT 8230 or a Varian MAT CH5 instrument (70 eV) by EI-
MS method. Melting points were measured in sealed glass tubes
€
on a Buchi B-540 melting point apparatus. Elemental analyses
were performed by the Analytisches Labor des Instituts fur
€
€
€
Anorganische Chemie der Universitat Gottingen.
Synthesis of 1. LH (3.349 g, 8.00 mmol) and KN(SiMe3)2
(1.676 g, 8.40 mmol) were dissolved in THF (60 mL) and stirred
for 5 h at room temperature. The clear solution was added to a
suspension of CaI2 (2.351 g, 8 mmol) in THF (60 mL) at room
temperature and stirred for another 12 h. The solvent was
removed from the solution in vacuum, and the residue was
extracted with toluene (90 mL). Removal of the solvent from the
filtrate in vacuum gave compound 1 as off-white solid. Yield
(3.82 g, 2.91 mmol, 72.8%); mp 360-368 °C (decomp).
1H NMR (500.13 MHz, C6D6): δ 7.17-7.10 (m, 12 H, m-,
p-Ar-H), 4.80 (s, 2 H, γ-CH), 3.65 (m, 8 H, O-CH2-CH2),
3.22 (sept, 8H, CH(CH3)2), 1.66 (s, 12 H, CH3), 1.36 (d, 24 H,
CH(CH3)2), 1.32 (m, 8H, O-CH2-CH2), and 1.23 (d, 24 H,
CH(CH3)2) ppm. 13C{1H} NMR (125.77 MHz, C6D6): δ 165.9,
147.1, 141.8, 124.59, 123.8, 94.8, 69.5, 28.5, 25.6, 25.3, 24.8, and
24.5 ppm. MS (70 eV): m/z (%): 704.3 (100) [Lþ-Me]. Anal.
calcd for C66H98Ca2I2N4O2 (1313.47): C, 60.35; H, 7.52; N, 4.27.
Found: C, 60.08; H, 7.92; N, 4.31.
Synthesis of 4. Compound 4 was prepared by the same
method as described for compound 3 with [LSr( μ-I) thf ]2
3
(1.409 g, 1.00 mmol) and potassium trisec-butylborohydride (1
M solution in THF) (2.00 mmol). Analytically pure compound 4
was obtained when a solution of 4 in toluene-THF (1:0.25) (8
mL) was stored at -5 °C in a freezer. Yield of 4 (1.15 g, 1.51
1
mmol, 75.7%); mp 195 °C. H NMR (500.13 MHz, C7D8): δ
7.11-7.06 (m, 6 H, m-, p-Ar-H), 4.74 (s, 1 H, γ-CH), 3.80 (m, 4
H, O-CH2-CH2), 3.09 (br sept, 4 H, CH(CH3)2), 1.69-1.53
(m, 3 H, B-CH(CH2-CH3)(CH3), 1.65 (s, 6 H, CH3), 1.40 (m, 4
H, O-CH2-CH2), 1.29 (br d, 12 H, CH(CH3)2), 1.23 (m, 1 H,
B-CH(CH2-CH3)(CH3), 1.18 (d, 12 H, CH(CH3)2), 1.02 (t, 3
H, B-CH(CH2-CH3)(CH3)), 1.02 (m,
1 H, B-CH-
(CH2-CH3)(CH3), 0.93 (d, 3 H, B-CH(CH2-CH3)(CH3)),
0.92 (t, 3 H, B-CH(CH2-CH3)(CH3)), 0.89 (d, 3 H, B-CH-
(CH2-CH3)(CH3)), 0.82 (t, 3 H, B-CH(CH2-CH3)(CH3)),
0.68 (d, 3 H, B-CH(CH2-CH3)(CH3)), 0.62 (d, 3 H, B-CH-
(CH2-CH3)(CH3)), 0.58 (m, 1 H, B-CH(CH2-CH3)(CH3),
0.24-0.16, and 0.09 to -0.08 (m, 3 H, B-CH(CH2-CH3)-
(CH3)) ppm. 13C{1H} NMR(125.77 MHz, C7D8): δ 165.4,
145.9, 141.5, 125.0, 124.4, 94.2, 69.8, 31.0, 30.8, 30.4, 28.5,
25.2, 25.0, 24.8, 24.7, 20.5, 20.3, 19.9, 15.41, 15.22, and 15.11
ppm. 11B NMR (128.38 MHz, C7D8): δ -4.7 ppm (d, 1JBH=55
Hz, B, BR). IR (Nujol, cm-1): ν~ 2377.21, 2346.89, 1932.06,
1624.06, 1551.52, 1511.58, 1404.65, 1311.02, 1261.36, 1222.12,
1164.31, 1097.60, 1054.10, 1020.09, 925.73, 868.55, 785.96,
757.73, 741.99, 722.78, 664.57, and 619.22. MS (70 eV): m/z
(%): 403.3 (100) [Lþ-Me]. Anal. calcd for C45H77BN2OSr
(760.54): C, 71.07; H, 10.20; N, 3.68 Found: C, 70.42; H, 9.90;
N, 3.70.
Synthesis of 2. Compound 2 was prepared by the same
method as compound 1 with LH (3.349 g, 8.00 mmol), KN-
(SiMe3)2 (1.676 g, 8.40 mmol), and SrI2 (2.731 g, 8.00 mmol).
The solid upon crystallization from a saturated solution of n-
hexane at -5 °C gave analytically pure sample of 2. Yield (4.247
g, 3.02 mmol, 75.4%); mp 188-190 °C. 1H NMR (500.13 MHz,
C6D6): δ 7.20-7.15 (m, 12 H, m-, p-Ar-H), 4.84 (s, 2 H, γ-CH),
3.56 (m, 8 H, O-CH2-CH2), 3.29 (sept, 8 H, CH(CH3)2), 1.69
(s, 12 H, CH3), 1.36 (d, 24 H, CH(CH3)2), 1.25 (d, 24 H,
CH(CH3)2), and 1.19 (m, 8 H, O-CH2-CH2) ppm. 13C-
{1H}NMR (125.77 MHz, C6D6): δ 164.6, 146.6, 141.6, 124.4,
124.0, 94.0, 69.5, 28.4, 26.2, 25.0, 24.7, and 24.6 ppm. MS (70
eV): m/z (%): 704.3 (100) [Mþ/2-2THF]. Anal. calcd for
Crystallographic Details for Compounds 2, 3, and 4. The data
for 2, 3, and 4 were collected from shock-cooled crystals at
100 K. The data for 2 were collected on a Bruker TXS-Mo
(15) Harder, S. Organometallics 2002, 21, 3782–3787.

3820 Inorganic Chemistry, Vol. 49, No. 8, 2010
Table 2. Crystallographic and Structure Refinement Data
param
Sarish et al.
2 0.5C6H14
3
3
4
empirical formula
Fw
T(K)
C69H105I2N4O2Sr2
1451.61
100.0(5)
C45H77BCaN2O
712.98
100.0(5)
C45H77BN2OSr
760.52
100.0(5)
cryst system
space group
monoclinic
P21/c
21.500(6)
15.4867(18)
23.025(3)
112.0880(10)
7014.1(14)
4
1.357
2980
2.413
monoclinic
P21/c
monoclinic
P21/c
˚
a (A)
20.749(5)
13.176(3)
16.106(4)
99.155(5)
4350(1)
4
1.089
1576
0.178
20.721(4)
13.395(2)
16.093(3)
100.014(3)
4398.7(13)
4
1.148
1648
1.259
˚
b (A)
˚
c (A)
β (°)
V (A )
3
˚
Z
F
calcd (Mg/m3)
F(000)
μ (Mo KR)
θ range for data collcn (°)
no. of reflcns collcd/unique
obsd reflcns[ I > 2σ(I)]
data/restraints/params
Gof on F2
1.62-26.77
137550/15123
(Rint = 0.0286)
15 123/16/733
1.061
0.99-25.51
31406/7992
(Rint = 0.1110)
7992/0/471
1.001
1.82-25.11
66750/7808
(Rint = 0.0654)
7808/21/471
1.077
R1, wR2[ I > 2σ(I)]
R1, wR2 (all data)
largest diff peak/hole (e A )
0.0224, 0.0528
0.0283, 0.0545
0.698 and -0.439
0.0645, 0.1480
0.1346, 0.1797
0.381 and -0.602
0.0426, 0.1022
0.0624, 0.1087
0.659 and -0.488
3
˚
rotating anode instrument. For the data collections of 3 and 4 an
Incoatec microfocus source was employed.16 Both diffracto-
meters were equipped with a low-temperature device17 and used
model with their Uiso values constrained to 1.5 times the Ueq of
their pivot atoms for terminal sp3 carbon atoms and 1.2 times
for all other carbon atoms. Disordered moieties were refined
using bond lengths and isotropic displacement parameter
restraints.22 Crystal data and experimental details for the
X-ray measurements are listed in Table 2. The crystals of
compound 3 for X-ray structural analysis were not of good
quality.
˚
monochromated Mo KR radiation, λ = 0.71073 A. Both
machines used mirror optics as radiation monochromator.
The data of 2, 3, and 4 were integrated with SAINT,18 and an
empirical absorption correction (SADABS) was applied.19 All
structures were solved by direct methods (SHELXS-97)20 and
refined by full-matrix least-squares methods against F2
(SHELXL-97).21 All nonhydrogen atoms were refined with
anisotropic displacement parameters. The hydrogen atoms
were refined isotropically on calculated positions using a riding
Acknowledgment. Support of the Deutsche Forschungsge-
meinschaft is highly acknowledged.
Supporting Information Available: X-ray data for 2, 3, and 4
(CIf ). This material is available free of charge via the Internet at
http://pubs.acs.org.
(16) Schulz, T.; Meindl, K.; Leusser, D.; Stern, D.; Graf, J.; Michaelsen, C.;
Ruf, M.; Sheldeick, G. M.; Stalke, D. J. Appl. Cystallogr. 2009, 42, 885–891.
(17) Kottke, T.; Lagow, R. J.; Stalke, D. J. Appl. Crystallogr. 1996, 29,
465–468.
€
(22) Muller, P.; Herbst-Irmer, R.; Spek, A. L.; Schneider, T. R.; Sawaya,
(18) SAINT v7.34A Bruker : Madison, WI , 2005.
M. R. Crystal Structure Refinement - A Crystallographer’s Guide to
SHELXL. In IUCr Texts on Crystallography, 1st ed., M€uller, P., Ed.; Oxford
University Press: Oxford, England, 2006; Vol. 8.
€
(19) Sheldrick, G. M. SADABS 2008/2, Gottingen, 2008.
(20) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467–473.
(21) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.