Lanthanide borohydrido complexes supported by ansa-bis(amidinato) ligands with a rigid o-phenylene linker: Effect of ligand tailoring on catalytic lactide polymerization

Article abstract of DOI:10.1002/ejic.201300931

A series of lanthanide monoborohydrido complexes {C₆H ₄-1,2-[NC(R)NR′]₂}Ln(BH₄)(L)_n (Ln = Y, Nd, Sm; R = tBu, Ph; R′ = 2,6-Me₂C₆H ₃, SiMe₃; L = dme = dimeth

Full text of DOI:10.1002/ejic.201300931

FULL PAPER
DOI:10.1002/ejic.201300931
Lanthanide Borohydrido Complexes Supported by ansa-
Bis(amidinato) Ligands with a Rigid o-Phenylene Linker:
Effect of Ligand Tailoring on Catalytic Lactide
Polymerization
Aleksei O. Tolpygin,[a] Grigorii G. Skvortsov,[a]
Anton V. Cherkasov,[a] Georgy K. Fukin,[a] Tatyana A. Glukhova,[a]
and Alexander A. Trifonov*[a]
Keywords: Lanthanides / Ligand design / Polymerization
A series of lanthanide monoborohydrido complexes {C6H4-
1,2-[NC(R)NRЈ]2}Ln(BH4)(L)n (Ln = Y, Nd, Sm; R = tBu, Ph; RЈ
= 2,6-Me2C6H3, SiMe3; L = dme = dimethoxyethane, n = 1; L
= thf, n = 2), in which lanthanides are coordinated by bulky
ansa-bis(amidinato) ligand systems with a conformationally
rigid o-phenylene linker ({C6H4-1,2-[NC(R)NRЈ]2}2–), were
synthesized by the salt metathesis reactions of equimolar
amounts of Ln(BH4)3(thf)3 and {C6H4-1,2-[NC(R)NRЈ]2}X2-
(thf)n (X = Li, Na) in thf. X-ray diffraction studies revealed
that the complexes are monomeric. Depending on the dentic-
ity of the donor ligand (L = dme or thf), the terminal borohyd-
rido ligand coordinated to the metal ion can be located in
either an equatorial (L = thf) or an apical (L = dme) position.
All complexes are efficient catalysts for the ring-opening po-
lymerization of rac-lactide, which allows to convert up to
1000 equiv. of monomer into a polymer at room temperature
within 10–150 min and affords atactic polylactides with high
molecular weights and moderate molecular-weight distribu-
tions (1.28–2.16). Yttrium–borohydrido complexes coordi-
nated by the {C6H4-1,2-[NC(tBu)N(2,6-Me2C6H3)]2}2– ligand
system showed enhanced catalytic activity compared to that
of the analogue complexes containing the {C6H4-1,2-[NC-
(Ph)NSiMe3]2}2– ligand. The obtained borohydrido com-
plexes catalyze the hydrophosphonylation of benzaldehyde
at room temperature with good reaction rates.
ato ligands provide a good coordination environment, stabi-
lizing lanthanide centers and facilitating immortal ring-
opening polymerization (iROP) of lactide by the introduc-
tion of large amounts of isopropanol as a chain transfer
agent.[6] At present, we aim at designing new ligand frame-
works that provide a rigid geometry of the coordination
sphere of the active metal center and thus allow to better
control catalytic reactions. As monoanionic NCN ligands
proved to be a suitable coordination platform,[7] we focused
on ansa-bis(amidinato) ligand frameworks that contain
conformationally rigid linkers. New bis(amidinato) ligand
systems with 1,8-disubstituted naphthalene[8] and o-phenyl-
ene[9] linkers were prepared and successfully employed for
the synthesis of lanthanide complexes. Herein, we report on
the synthesis and characterization of new lanthanide
borohydrides coordinated by o-phenylene linked bis(amidin-
ato) ligands of different steric demand {C6H4-1,2-[NC(R)-
NRЈ]2}2– (R = tBu, Ph; RЈ = 2,6-Me2C6H3, SiMe3) and on
their application in the catalysis of the polymerization of
racemic lactide. When our study was in progress, a paper of
Shen and co-workers on the synthesis of related lanthanide
borohydrides supported by bis(amidinato) ligand systems
with a flexible (CH2)3 linker, {CH2[CH2NC(Ph)NSiMe3]2}-
Ln(BH4)(dme) (dme = dimethoxyethane), and their cata-
Introduction
To control metal-mediated reactions it is important to
“tailor” new ligand systems, which are suitable for the syn-
thesis of isolable and structurally defined species, that is,
prospective one-site catalysts. Their large ionic radii[1] make
this issue especially significant for lanthanides, the stability
and reactivity of which are known to be highly influenced
by the coordinative and steric saturation of the metal cen-
ter.[2] Lanthanide borohydrides[3] are efficient initiators for
the ring-opening polymerization (ROP) of cyclic esters,[4]
which allows for the synthesis of biodegradable and bio-
compatible thermoplastics.[3,5] In earlier studies, we have
demonstrated that lanthanide–borohydrido complexes sup-
ported by guanidinato[6] ligands initiate the room tempera-
ture ROP of racemic lactide and β-butyrolactone, which
provides atactic polymers with controlled molecular weights
and relatively narrow polydispersities. Moreover, guanidin-
[a] G. A. Razuvaev Institute of Organometallic Chemistry of
Russian Academy of Sciences,
Tropinina 49, 603950 Nizhny Novgorod, GSP-445, Russia
E-mail: trif@iomc.ras.ru
http://www.iomc.ras.ru
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300931.
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FULL PAPER
lytic activity in the ring-opening polymerization of cyclic The disodium derivative of 1 was used in situ for reactions
esters was published.[10] This essentially enriched the base with Ln(BH4)3(thf)3 (Ln = Y, Nd, Sm; 1:1 molar ratio) in
for a comparative analysis of a structure–reactivity relation- thf at ambient temperature (Scheme 1). The evaporation of
ship.
thf, the extraction of the solid residue with toluene, and the
subsequent recrystallization of the reaction product from
dme/hexane mixtures allowed for isolation of the bis(amidi-
nato)–borohydrido–lanthanide complexes 2–4 in 52, 43,
Results and Discussion
Two efficient synthetic approaches to mixed-ligand lan- and 39% yield, respectively. Complexes 2–4 were obtained
thanide borohydrides are generally applied. The first path- as air- and moisture-sensitive, pale-yellow, crystalline solids,
way consists in the reactions of the corresponding halido which are well soluble in thf and toluene but poorly soluble
(Hal) derivatives LnLnHal3–n with XBH4 (X = Li, Na, K) in in hexane.
donor solvents.[11] However, this synthetic method is often
The related bis(benzamidinato) ligand system {C6H4-1,2-
hampered by side reactions, for example, ligand redistri- [NC(Ph)NSiMe3]2}2– was prepared according to the pre-
bution.[3k] Another convenient procedure for the synthesis viously published procedure based on the insertion of
of both bis(borohydrido) and mono(borohydrido) com- PhCN into lithium silylarylamide.[9b] Lithium benzamidin-
plexes is based on the reactions of lanthanide tris(borohyd- ate 5 was treated with an equimolar amount of Y(BH4)3-
rides) Ln(BH4)3(thf)3[12] with alkali-metal salts LX (X = Li, (thf)3 in thf at 65 °C (Scheme 2). The extraction of the reac-
Na, K) of the corresponding ligands.[3a,6,10,13] For the prep- tion product with toluene and a subsequent recrystalli-
aration of lanthanide–borohydrido species coordinated by zation from a thf/hexane mixture afforded complex 6 as yel-
ansa-bis(amidinato) ligand systems, the second synthetic low crystals in 67% yield. It should be mentioned that un-
pathway was employed. In this work, two o-phenylene like other ligands,[3i,6] the employment of {C6H4-1,2-
linked bis(amidinato) ligand systems of different steric de- [NC(Ph)NSiMe3]2}Li2(thf)n allowed for the synthesis and
[9a]
mand, {C6H4-1,2-[NC(tBu)N(2,6-Me2C6H3)]2}2–
and isolation of a salt-free borohydrido complex. Treatment of
{C6H4-1,2-[NC(Ph)NSiMe3]2}2– [9b], were used.
6 with dme leads to the substitution of thf by dme in the
Bis(amidine) 1 can be easily deprotonated by a treatment metal coordination sphere and to the formation of the dme
with two equivalents of NaN(SiMe3)2 in thf at 20 °C.[9a] adduct 7.
Scheme 1. Synthesis of complexes 2–4.
Scheme 2. Synthesis of complexes 6 and 7.
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The IR spectra of complexes 2–4, 6, and 7 show strong Table 1. Selected bond lengths and angles in complexes 2–4, 6, and
absorptions in the region 2150–2500 cm–1, which are diag-
7.
nostic of η3-coordinated bridging and terminal borohyd-
Complex
2
3
4
6
7
1
rido ligands.[14] In the H NMR spectra of the diamagnetic
Ln–N [Å] 2.436(1) 2.521(2) 2.498(2) 2.534(3) 2.525(1)
2.293(1) 2.368(2) 2.347(2) 2.330(3) 2.312(1)
2.294(1) 2.400(2) 2.371(2) 2.329(3) 2.302(1)
2.423(1) 2.478(2) 2.450(1) 2.533(3) 2.532(1)
yttrium complexes 2, 6, and 7, the borohydrido ligands give
broad singlets at δ = 1.17, 1.72, and 1.48 ppm, respectively.
Transparent crystals of complexes 2–4 suitable for X-ray
diffraction analyses were obtained by slow condensation of
hexane into dme solutions of the complexes at ambient tem-
perature. Complex 2 crystallizes in the triclinic space group
C–N [Å]
1.319(2) 1.329(2) 1.335(3) 1.321(4) 1.320(2)
1.360(2) 1.347(2) 1.343(3) 1.335(4) 1.336(2)
1.360(2) 1.358(3) 1.351(3) 1.337(4) 2.331(2)
1.329(2) 1.329(3) 1.334(3) 1.315(4) 2.325(2)
¯
P1, whereas 3 and 4 crystallize in the monoclinic space
group P2(1). The molecular structures of complexes 2–4
were determined by X-ray diffraction studies, which re-
vealed that they have similar structures. Moreover, 3 and 4
N–C–N [°] 109.9(1) 109.6(2) 109.9(2) 113.9(3) 115.0(1)
109.8(1) 110.0(2) 109.6(2) 113.8(3) 114.2(1)
are isostructural. The structure of complex 2 is depicted in Ln–B [Å] 2.559(2) 2.678(3) 2.647(3) 2.646(4) 2.531(2)
Figure 1 (for the structures of complexes 3 and 4 see Fig-
Ln–H [Å] 2.32(2)
2.29(2)
2.50(2)
2.52(2)
2.44(2)
2.47(3)
2.50(3)
2.42(4)
2.48(5)
2.34(5)
2.51(7)
2.27(2)
2.29(2)
2.27(2)
ures S16 and S17). The crystallographic and structure-re-
finement data are given in Table 3. Selected bond lengths
and angles are given in Table 1.
2.41(2)
B–H [Å]
1.14(2)
1.17(2)
1.09(2)
1.10(2)
1.11(2)
1.14(2)
1.16(2)
1.17(2)
1.12(2)
1.16(2)
1.15(2)
1.16(2)
1.11(5)
1.18(6)
1.20(8)
1.11(5)
1.07(2)
1.07(2)
1.07(2)
1.04(2)
Ln–O [Å] 2.457(2) 2.596(2) 2.560(2) 2.335(2) 2.436(1)
2.398(2) 2.530(2) 2.500(1) 2.350(2) 2.428(1)
in complexes 2–4 are noticeably different. The two amidin-
ato 1,2-C6H4N nitrogen atoms are situated much closer to
the metal center [2.293(1) and 2.294(1) Å for 2; 2.369(3) and
2.399(3) Å for 3; 2.348(2), 2.371(2) Å for 4], than the two
nitrogen atoms of the 2,6-Me2C6H3N groups [2.436(1) and
2.424(1) Å for 2; 2.521(4) and 2.475(2) Å for 3; 2.498(2) and
2.448(1) Å for 4]. Similar bonding situations are realized in
the related lanthanide–ansa-bis(amidinato) complexes with
a flexible (CH2)3 linker {CH2[CH2NC(Ph)NSiMe3]2}Ln-
(BH4)(dme).[10] The average Ln–N bond lengths in com-
Figure 1. ORTEP diagram (thermal ellipsoids drawn at the 30%
probability level) of 2, showing the atom numbering scheme. Hy-
drogen atoms of the amidinato ligand and the dme molecule are
omitted for clarity.
In complexes 2–4, the metal atoms are coordinated by plexes 2, 3, and 4 [2.362(1), 2.442(2), and 2.417(2) Å,
four nitrogen atoms of two chelating ligands, one η3-coordi- respectively] are slightly shorter than the values found in
nated terminal borohydrido anion, and two oxygen atoms compounds {CH2[CH2NC(Ph)NSiMe3]2}Ln(BH4)(dme)[10]
of a dme molecule. The nitrogen atoms and one oxygen [2.392(5) Å for Y, 2.470(8) Å for Nd, and 2.444(5) Å for
atom are in the equatorial plane [the maximum deviation Sm].[10] At the same time, for the Ln–B distances, an inverse
of the atoms from the plane is 0.07(2) Å in 2, 0.14(2) Å in tendency was detected: in complexes 2–4 [2.559(2), 2.682(4),
3, and 0.15(2) Å in 4], whereas the borohydrido group and and 2.651(3) Å, respectively], these bonds are slightly longer
the second oxygen atom occupy the apical positions. The than in the related complexes {CH2[CH2NC(Ph)NSiMe3]2}-
B–Ln–O bond angles in complexes 2–4 are 171.17(6), Ln(BH4)(dme) [2.503(8) Å for Y, 2.636(11) Å for Nd, and
172.4(1), and 171.55(7)°, respectively. The dihedral angles 2.630(4) Å for Sm].[10] The lengths of the amidinato N–C
between the two N–Ln–N planes in complexes 2–4 have bonds in complexes 2–4 have similar values, which indicates
values of 159.8(2), 162.6(2), and 163.7(2)°, respectively. The the negative charge delocalization within the N–C–N frag-
Ln–N–C–N fragments in complexes 2–4 are close to planar. ments.
Nevertheless, the values of dihedral angles between the N–
Transparent crystals of complex 6 suitable for an X-ray
Ln–N and N–C–N planes [ 168.1 and 167.6° for 2; 144.8 diffraction study were obtained by slow condensation of
and 177.4° for 3; 145.9(2) and 177.1(2)° for 4] indicate no- hexane into a thf solution of the complex at ambient tem-
ticeable differences between the geometry of 2 and that of perature. Complex 6 crystallizes in the space group
3 and 4. The average Y–N bond length in 2 [2.362(1) Å] is P2(1)2(1)2(1). The molecular structure of complex 6 was
similar to the values found for the related seven-coordinate established by an X-ray diffraction study. The structure of
chlorido–yttrium complexes with ansa-bis(amidinato) li- complex 6 is depicted in Figure 2. The crystallographic and
gands [2.394(4) Å[9a] and 2.392(5) Å[10]]. The Ln–N bonds structure-refinement data are given in Table 3. Selected
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bond lengths and angles are given in Table 1. Similarly to corresponding distance in 6 [2.646(4) Å] and comparable to
complexes 2–4, the metal atom in 6 is coordinated by four that in 2 [2.559(2) Å] and {CH2[CH2NC(Ph)NSiMe3]2}-
nitrogen atoms of two amidinato ligands, one η3-coordi- Y(BH4)(dme) [2.503(8) Å].[10]
nated terminal borohydrido anion, and two oxygen atoms
of two thf molecules. However, unlike in complexes 2–4,
the borohydrido group in 6 is in the equatorial plane [the
maximum deviation of atoms from the plane is 0.10(2) Å]
together with four nitrogen atoms, whereas the oxygen
atoms occupy the apical positions. The distances from Y to
“internal” nitrogen atoms are significantly shorter [2.329(3)
and 2.330(3) Å] than those to “external” nitrogen atoms
[2.533(3) and 2.534(3) Å]. The average Y–N bond in 6
[2.432(3) Å] is noticeably longer than that of 2 [2.362(1) Å]
and that of {CH2[CH2NC(Ph)NSiMe3]2}Y(BH4)(dme)
[2.392(5) Å].[10] The Y–B distance in 6 [2.644(5) Å] is also
Figure 3. ORTEP diagram (thermal ellipsoids drawn at the 30%
probability level) of 7, showing the atom numbering scheme. Hy-
drogen atoms of the amidinato ligand and the dme molecule are
omitted for clarity.
longer than the corresponding bonds in 2 [2.559(2) Å] and
{CH2[CH2NC(Ph)NSiMe3]2}Y(BH4)(dme) [2.503(8) Å].[10]
It is noteworthy that the coordination of the ligand systems
{C6H4-1,2-[NC(tBu)N(2,6-Me2C6H3)]2}2– and {C6H4-1,2-
[NC(Ph)NSiMe3]2}2– to yttrium results in a different mut-
It is worthy to note that the positional change of the
ual disposition of the amidinato fragments in complexes 2 borohydrido group in the coordination sphere of yttrium is
and 6. Thus, in 6 the dihedral angle between the N–Ln–N reflected in the IR spectra of complexes 6 and 7. Thus, in
fragments [172.8(2)°] is much larger than that in 2 the IR spectrum of 6, the borohydrido ligand shows a set
[159.8(2)°].
of four strong well resolved absorptions (2401, 2338, 2280,
2228 cm–1), whereas in that of 7, three badly resolved strong
absorptions are observed (2447, 2216, 2168 cm–1).
rac-Lactide Polymerization Initiated by Complexes 2–4, 6,
and 7
The prepared complexes 2–4, 6, and 7, having a poten-
tially initiating BH4 group, have been evaluated in the ROP
of rac-lactide (LA) (Scheme 3). Representative results are
summarized in Table 2. All complexes proved to be efficient
catalysts under mild conditions, allowing for the total con-
version of 100–1000 equiv. of lactide (toluene, 20 °C,
[LA] = 1.0 mol/L) in 30–150 min and affording atactic
PLAs (polylactides), as determined by NMR analyses.
Figure 2. ORTEP diagram (thermal ellipsoids drawn at the 30%
probability level) of 6, showing the atom numbering scheme. Hy-
drogen atoms of the amidinato ligand and CH2 groups of thf mo-
lecules are omitted for clarity.
Transparent crystals of complex 7 suitable for an X-ray However, catalytic tests revealed that the activities of the
diffraction study were obtained by the slow cooling of its complexes are affected by the nature of the metal center.
toluene solution to –20 °C. Complex 7 crystallizes as a solv- Thus, in the case of 3, a total conversion of 100 equiv. of
ate, 7·C7H8. The X-ray structure determination revealed monomer was achieved within 30 min, whereas within the
that the ligand arrangement in complex 7 is similar to those same time, 4 and 2 only achieved conversions of 86 and
in 2–4 (Figure 3). Despite the same coordination number of 65%, respectively. The observed decrease of polymerization
the yttrium atoms in 6 and 7, the replacement of two thf activity in the order NdϾ SmϾ Y correlates with the ionic
molecules by one chelating dme molecule results in a dra- radii of the lanthanide centers (1.11, 1.02, and 0.96 Å,
matic structure change consisting of a migration of a respectively).[15] For PLA obtained with complex 2, showed
borohydrido ligand from an equatorial position in 6 to an the lowest polymerization rate, a slightly larger polydisper-
apical one in 7. The dihedral angle between the N–Ln–N sity was measured (1.59 for 2; 1.37 for 3; 1.44 for 4). An
fragments in 7 [163.1(2)°] is larger than that in 2 [159.8(2)°] increase of the ratio [M]0/[I]0 to 1000 results in an increase
but smaller than that in 6 [172. 8(2)°]. Similarly to 2–4 and of the reaction time necessary for full conversion to 150 min
6, the distances from the metal center to “internal” nitrogen for 2, 90 min for 3, and 90 min for 4. At [M]0/[I]0 = 1000,
atoms in 7 are significantly shorter than those to “external” the conversion after 60 min reached 25% for 2, 63% for 3,
nitrogen atoms [compare: Y(1)–N(2) 2.301(1) and Y(1)– and 54% for 4. The polymerizations mediated by the com-
N(1) 2.312(1), to Y(1)–N(3) 2.527(1) and Y(1)–N(4) plexes 2 and 7 proceeded much faster in an apolar, non-
2.533(1) Å]. The average Y–N bond length in 7 [2.418(1) Å] coordinating solvent such as toluene than in thf (Table 2,
is somewhat shorter than that in 6 [2.432(3) Å]. The Y– entries 5, 8 and 26, 28). Because of its high affinity for oxo-
B distance in 7 [2.531(2) Å] is noticeably shorter than the philic metals such as lanthanides, we assume that thf com-
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Scheme 3. Catalytic ring-opening polymerization of rac-lactide.
Table 2. Polymerization of rac-lactide with complexes 2–4, 6, and 7.[a]
Entry
Complex
[M]0/[I]0
t [min][b]
Conversion [%][c]
M
nexp ϫ10–3[d]
M
ncalc ϫ10–3[e]
Mw/Mn
Pr
1
2
3
4
5
6
7
8
2
100
100
100
250
500
1000
1000
500
250
100
100
120
250
500
1000
1000
100
100
250
500
1000
1000
100
200
500
200
500
200
10
30
60
60
60
60
150
60
60
10
30
60
30
60
60
90
10
30
30
60
60
90
60
60
60
60
60
60
17
65
96
96
95
25
92
43
65
34
100
100
100
100
63
98
20
96
94
85
54
96
72
40
25
94
71
82
10.92
14.66
8.76
48.18
69.62
37.27
65.41
9.60
2.44
9.36
1.48
1.49
1.59
1.46
1.68
1.49
1.65
1.59
1.86
1.52
1.89
1.37
1.50
1.47
1.60
1.93
1.28
1.38
1.42
1.42
1.44
2.16
1.79
1.63
1.45
1.70
1.65
1.70
0.54
0.55
0.55
0.55
0.53
0.55
0.56
0.63
0.63
0.56
0.55
0.56
0.53
0.56
0.54
0.52
0.52
0.50
0.50
0.56
0.54
0.55
0.55
0.59
0.55
0.55
0.55
0.62
2
2
13.82
34.56
72.00
36.00
132.48
28.80
23.40
4.89
12.96
17.28
36.00
72.00
90.72
141.12
2.88
13.82
33.84
61.20
77.76
138.24
10.37
7.20
28.80
27.07
51.12
23.62
2
2
2
2
2[f]
2[f]
3
9
7.61
8.69
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
3
19.79
20.54
56.05
70.90
59.47
100.77
13.11
34.00
46.93
67.24
49.09
88.01
14.28
0.962
11.95
14.51
37.33
12.85
3
3
3
3
3
4
4
4
4
4
4
6
6
6
7
7
7[f]
[a] General conditions: toluene, [LA] = 1.0 mol/L, T = 20 °C. [b] Reaction time was not necessarily optimized. [c] Conversion of monomer
1
M, as determined by H NMR spectroscopy. [d] Experimental (corrected; see Experimental Section) Mn and Mw/Mn values determined
by GPC in thf vs. polystyrene standards. [e] Mn value calculated by assuming one polymer chain per metal center with the relationship:
144ϫ conversionϫ [M]/[Ln]. [f] Catalytic tests carried out in thf.
petes with the lactide monomer in coordination to the metal borohydrido group acts as both an initiating group and as
center, which would account for the longer times needed for a reducing agent, yielding α,ω-dihydroxy telechelic PLAs.[18]
completion of the ROP. A similar detrimental effect of thf Moreover, additional resonances at δ = 5.50 ppm and at δ
on the rate of ROP reactions promoted by group-3 metal = 4.18 and 4.45 ppm, which could correspond to CH2OH
1
complexes is often observed.[16] The H NMR spectra in end groups, are present in the spectra. However, their lower-
CDCl3 of relatively low-molecular-weight samples of PLA than-expected intensity and diversity point to incomplete
(e.g., entry 25 of Table 2) display besides the main polymer- or multiple processes.
chain signals [a multiplet at δ = 1.56 ppm corresponding to
A comparison of the results of the catalytic performance
–C(O)CH(Me)O and a multiplet at δ = 5.16 ppm corre- of complexes 2 and 7 indicates enhanced activity of yt-
sponding to –C(O)CH(CH3)O] a quartet characteristic for trium–borohydrido complexes coordinated by the {C6H4-
the terminal CH(Me)OH group at δ = 4.35 ppm (Fig- 1,2-[NC(tBu)N(2,6-Me2C6H3)]2}2– ligand system compared
ure S15). The latter group is formed after hydrolysis of the to the complex containing {C6H4-1,2-[NC(Ph)NSiMe3]2}2–
metal–alkoxido bond, an observation that is indicative of a (entries 5 and 28, Table 2). Thus, in the presence of complex
classical coordination–insertion mechanism with an initial 2, at [M]0/[I]0 ratio of 500, monomer was converted into
ring opening through acyl–oxygen bond cleavage.[17] The polymer completely within 60 min, whereas for complex 7,
signals at δ = 3.74 ppm and δ = 2.71 ppm correspond to after the same interval of time, the conversion was notice-
the second chain-end group –CH(Me)CH2OH. It has been ably lower: 71%. The PLAs obtained with complexes 2 and
recently reported that in the ROP of lactide initiated by 7 had similar polydispersities (compare: 1.68 for 2; 1.65 for
lanthanide–borohydrido complexes Ln(BH4)3(thf)3 the 7).
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Lactide polymerization reactions initiated by yttrium
complexes coordinated by the same ligand system turned
out to be strongly influenced by the nature of the Lewis
base coordinated to the metal center. Thus, the activity of
complex 7, which contains a dme molecule, is significantly
higher than that of the thf adduct 6. In the polymerization
initiated by 7 at ratio [M]0/[I]0 = 200, the conversion reaches
94% within 60 min, whereas 6 afforded only 40% conver-
sion in the same time interval. At a ratio [M]0/[I]0 = 500, 7
converted 71% of the monomer into polymer within
60 min, and in the case of 6, the yield of polylactide was
25%. Taking into account the stronger binding of chelating
ligands to a metal center (compared to that of monodentate
ones), it would be reasonable to expect an inverse trend of
activities for complexes 6 and 7. Probably, this difference of
catalytic performance between 6 and 7 is related to their
structural peculiarities.
Figure 4. Mn vs [M]0/[I]0 for ROP initiated by 2. Conditions: tolu-
ene, 20 °C, [M]0 = 1.0 mol/L.
When our studies were in progress, a report of Shen and
co-workers on the synthesis and catalytic behavior in lactide
polymerization of related borohydrido complexes supported
by an ansa-bis(amidinato) ligand system with a nonrigid
(CH2)3 linker {CH2[CH2NC(Ph)NSiMe3]2}Ln(BH4)(dme)
(Ln = Y, Nd, Sm, Yb) was published.[10] A comparison of
the results of catalytic tests obtained with complexes
{CH2[CH2NC(Ph)NSiMe3]2}Y(BH4)(dme) and 7, which
have similar structures but different linkers between the
amidinato ligands, would allow for a deeper insight into the
effect of the linker on the catalytic activity and the control
of metal-promoted reactions. Complex {CH2[CH2NC(Ph)-
NSiMe3]2}Y(BH4)(dme) demonstrated higher activity com-
pared to that of 7. At a ratio [M]0/[I]0 = 1000, the rac-
lactide polymerization promoted by {CH2[CH2NC(Ph)-
NSiMe3]2}Y(BH4)(dme) (toluene, 20 °C) reached 86% con-
version within 8 min, whereas in the case of an initiation
with 7, at a ratio [M]0/[I]0 = 500, the conversion was 95%
after 60 min. Unlike {CH2[CH2NC(Ph)NSiMe3]2}Y-
(BH4)(dme), which showed similar activities in both thf and
toluene, the activity of 7 ([M]0/[I]0 = 500, 60 min) in thf
dropped to 43% compared to 95% in toluene.
Figure 5. Mn vs [M]0/[I]0 for ROP initiated by 3. Conditions: tolu-
ene, 20 °C, [M]0 = 1.0 mol/L.
Experiments aimed at investigating the degree of control
of the polymerizations were carried out. The PLAs pro-
duced with complexes 2–4, 6, and 7 showed monomodal
GPC traces with molecular-weight distributions in the
range Mw/Mn = 1.28–2.17. For all initiators, the number-
average molecular mass (Mn) values increase monoto-
nously, though not linearly, with the monomer-to-metal ra-
tio (see Figures 4, 5, and 6).
Figure 6. Mn vs [M]0/[I]0 for ROP initiated by 4. Conditions: tolu-
ene, 20 °C, [M]0 = 1.0 mol/L.
Relatively narrow molecular-weight distributions (Mw/
Mn = 1.37–1.50) were observed for polymerizations carried (Mnexp) values noticeably exceed the calculated ones
out with monomer-to-metal ratios in the range 100–500. (Mncalc) (entries 1, 10, 17), which is probably due to a slow
However, when higher monomer loadings (1000 equiv.) initiation stage. At [M]0/[I]0 = 500, all initiators showed a
were used for complexes 2–4, a slight increase of the PDI good agreement of Mnexp and Mncalc (entries 5, 14, 20). At
(polydispersity index) was observed (1.65–2.16). A match- [M]0/[I]0 = 1000, Mnexp became significantly lower than
ing of corrected experimental number-average molecular Mncalc, which indicates that a transesterification reaction
mass (Mn) values of PLAs with calculated values was ob- occurs. Shen and co-workers reported that the complexes
served in a few cases (entries 6, 14, 20).
{CH2[CH2NC(Ph)NSiMe3]2}Ln(BH4)(dme) allow to per-
Interestingly, for complexes 2–4, at low [M]0/[I]0 ratios form the polymerization of rac-lactide in a living fashion.[10]
(100–250) and low conversions, the experimental Mn The results obtained in the catalytic tests indicate that com-
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plexes 2–4, 6, and 7, coordinated by bis(amidinato) ligand Ph; RЈ = 2,6-Me2C6H3, SiMe3) in thf in a 1:1 molar ratio
systems with a rigid linker, surprisingly provide a lower de- afforded a series of lanthanide monoborohydrido com-
gree of control compared to the derivatives of the ligand plexes {C6H4-1,2-[NC(R)NRЈ]2}Ln(BH4)(L) (Ln = Y, Nd,
with a nonrigid bridge. The authors of the paper[10] re- Sm; L = dme, thf) coordinated by bulky ansa-bis(amidin-
ported that the solvent plays a crucial role for the stereo- ato) ligand systems with a conformationally rigid o-phenyl-
selectivity of the rac-lactide polymerization initiated by ene linker. Complexes are monomeric and contain a ter-
complexes {CH2[CH2NC(Ph)NSiMe3]2}Ln(BH4)(dme).
minal borohydrido ligand. By the example of the yttrium
Thus, the reactions in toluene afforded atactic PLAs, complexes {C6H4-1,2-[NC(Ph)NSiMe3]2}Y(BH4)(L)n (L =
whereas in thf under the similar conditions heterotactic-en- dme, n = 1; L = thf, n = 2), it was demonstrated that the
riched polymers with Pr values up to 85% were obtained. replacement of two molecules of monodentate thf by one
In contrast, for complexes 2 and 7, only a slight enhance- bidentate dme in the coordination sphere of yttrium results
ment of Pr (up to 63 and 62%, respectively) was detected in the migration of the borohydrido ligand from an equato-
when the polymerizations were run in thf.
rial position to an apical one. All complexes are efficient
catalysts for the ring-opening polymerization of rac-lactide.
They allow to convert up to 1000 equiv. of monomer into
polymer at room temperature within 10–150 min and to ob-
tain atactic polylactides with high molecular weights and
moderate molecular-weight distributions (1.28–2.16). A
comparison of the results of the catalytic tests obtained
with complexes coordinated by linked bis(amidinato) sys-
tems {C6H4-1,2-[NC(tBu)N(2,6-Me2C6H3)]2}2–, {C6H4-1,2-
[NC(Ph)NSiMe3]2}2– and {CH2[CH2NC(Ph)NSiMe3]2}2–
clearly demonstrates that both the bulkiness of the substitu-
ents at the “external” nitrogen atoms and the rigidity of the
linker between the amidinato fragments deeply affect the
catalytic activity of the derived complexes and the degree
of control of the rac-lactide polymerization. The activity of
lanthanide–borohydrido complexes in the catalysis of the
hydrophosphonylation of aldehydes was demonstrated.
Hydrophosphonylation of Benzaldehyde Catalyzed by
Complexes 2–4, 6 and 7
The catalytic hydrophosphonylation of aldehydes and
imines (Abramov and Pudovik reactions)[19] is a straightfor-
ward and atom-economic method for the formation of P–
C bonds, which allows for the synthesis of α-amino and α-
hydroxy phosphonic acids possessing important biological
activities. Various types of lanthanide compounds have
demonstrated high potential in the catalysis of these reac-
tions,[20] but to the best of our knowledge, no reports on
the activity of borohydrido complexes have been published
so far. The borohydrido complexes 2–4, 6, and 7 were tested
as catalysts for the hydrophosphonylation of benzaldehyde.
The reactions of equimolar amounts of benzaldehyde and
diethyl phosphite (Scheme 4) were carried out in toluene at
20 °C in the presence of 1mol-% of catalyst.
Experimental Section
General: All reactions were performed with rigorous exclusion of
air and traces of water by using Schlenk techniques and a vacuum
line. All solvents were distilled from sodium/benzophenone and
thoroughly degassed. C6D6 and C7D8 were dried with sodium prior
to use and condensed under vacuum into NMR tubes. CDCl3 was
used without additional purification. {C6H4-1,2-[NC(tBu)NH(2,6-
Me2C6H3)]2},[9a]{C6H4-1,2-[NC(Ph)NSiMe3]2}Li2(thf),[9b](Me3Si)2-
Scheme 4. Hydrophosphonylation of benzaldehyde catalyzed by
complexes 2–4, 6, and 7.
The borohydrido complexes 2–4, 6, and 7 catalyze the
addition of diethyl phosphite to benzaldehyde under very
mild conditions. In the series of complexes 2–4, a corre-
lation of catalytic activity and ionic radius was observed.
Thus, in the presence of yttrium compound 2, 44% conver-
sion was achieved within 24 h, whereas the complexes of
neodymium and samarium achieved quantitative yields of
diethyl hydroxy(phenyl)methylphosphonate within the same
period of time. Among the yttrium complexes, 2, 6, and 7,
complexes coordinated by the ligand {C6H4-1,2-[NC(Ph)-
NSiMe3]2}2– showed a higher catalytic activity compared to
those with the ligand derivative {C6H4-1,2-[NC(tBu)N(2,6-
Me2C6H3)]2}2–. Complexes 6 and 7 provide 87 and 92%
yield of diethyl hydroxy(phenyl)methylphosphonate, respec-
tively, compared to 44% yield obtained with 2.
NNa,[21] and Ln(BH4)3(thf)3 were prepared according to litera-
[12]
ture procedures. NMR spectra were recorded with Bruker Avance
DRX-400 and Bruker DRX-200 spectrometers in C6D6, C7D8, or
CDCl3 at 25 °C, unless otherwise stated. Chemical shifts for 1H
and 13C NMR spectra were referenced internally to the residual
solvent resonances and are reported relative to TMS. IR spectra
were recorded on Nujol mulls with a Bruker-Vertex 70 spectropho-
tometer. Lanthanide metal analyses were carried out by complexo-
metric titration.[22] The C, H, N elemental analyses were performed
in the microanalytical laboratory of the G. A. Razuvaev Institute
of Organometallic Chemistry. GPC was carried out by using a
chromatograph “Knauer Smartline” with Phenogel Phenomenex
∧
∧
Columns 5u (300ϫ7.8 mm) 10 4, 10 5 and a Security Guard Phe-
nogel Column with RI and UV detectors (254 nm). The mobile
phase was thf and the flow rate was 2 mL/min. The columns were
calibrated by Phenomenex Medium- and High-Molecular-Weight
Polystyrene Standard Kits with peak molecular weights from 2700
to 2570000 Da. The number-average molecular masses (Mn) and
polydispersity indexes (Mw/Mn) of the polymers were calculated
with reference to a universal calibration vs. polystyrene standards.
Conclusions
The salt metathesis reactions of Ln(BH4)3(thf)2 and
{C6H4-1,2-[NC(R)NRЈ]2}X2(thf)n (X = Li, Na; R = tBu, Mn values of PLAs were corrected with a Mark–Houwink factor
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of 0.58 to account for the difference in hydrodynamic volumes be-
tween polystyrene and polylactide.[23] The microstructures of the
PLAs were measured by homo-decoupling H NMR spectroscopy
at 25 °C in CDCl3 with a Bruker Avance DRX-400 spectroscopy
instrument.
(400 MHz, C6D6, 25 °C): δ = 0.20 [s, 5 H, Si(CH3)3], 0.24 [s, 9 H,
Si(CH3)3], 0.50 [s, 4 H, Si(CH3)3], 1.35 (br. s, 8 H, β-CH2, thf), 1.72
1
3
(br. s, 4 H, BH4), 3.65 (br. s, 8 H, α-CH2, thf), 5.71 (dd, JH,H
=
3
7.9 Hz, JH,H = 1.4 Hz, 1 H, C6H4), 6.18–7.31 (m, together 12 H,
C6H4, C6H5), 7.92 (d, JH,H = 7.1 Hz, 1 H, C6H5) ppm. 13C NMR
3
(100 MHz, C6D6, 25 °C): δ = 2.5, 2.9, 3.5 [Si(CH3)3], 25.2 (β-CH2,
thf), 68.2 (α-CH2, thf), 116.2, 120.5, 123.0, 125.9, 128.4, 129.7,
130.5, 137.5, 138.4, 140.1, 142.4 (C6H4, C6H5), 174.7, 185.2 (NCN)
ppm. 11B NMR (128.4 MHz, C6D6, 25 °C): δ = –26.6 ppm. IR
Synthesis of {C6H4-1,2-[NC(tBu)N(2,6-Me2C6H3)]2}Y(BH4)(dme)
(2): To a solution of 1 (0.44 g, 0.91 mmol) in thf (20 mL) was added
a solution of Na(NSiMe3)2 (0.33 g, 1.80 mmol) in thf (20 mL). The
resulting yellow solution was stirred at ambient temperature for
30 min, and the volatiles were removed under vacuum. The solid
residue was redissolved in thf (40 mL) and added to a solution
of Y(BH4)3(thf)3 (0.32 g, 0.91 mmol) in thf (20 mL). The reaction
mixture was stirred for 3 days. After removal of thf, the yellow
solid was extracted with toluene (60 mL). The extract was filtered,
and the solvent was removed under vacuum. The recrystallization
of the solid residue from a dme/hexane mixture afforded yellow,
(KBr): ν = 2401 (s), 2338 (s), 2280 (s), 2228 (s), 1608 (s), 1587 (s),
˜
1566 (s), 1489 (s), 1289 (s), 1252 (s), 1236 (s), 1127 (s), 1074 (s),
1023 (s), 964 (s), 914 (s), 845 (s), 802 (s), 791 (s), 757 (s), 735 (s),
703 (s), 674 (s), 629 (s), 568 (s), 530 (s), 464 (s) cm–1.
Synthesis of [C6H4-1,2-{NC(Ph)NSiMe3}2]Y(BH4)(dme) (7): To a
solution of Y(BH4)3(thf)3 (0.18 g, 0.52 mmol) in thf (20 mL) a solu-
tion of 5 (0.28 g, 0.258 mmol) in thf (20 mL) was added, and the
reaction mixture was stirred for 5 h at 65 °C. The solvent was re-
transparent
crystals
(0.32 g,
0.47 mmol).
Yield
52%.
C36H54BN4O2Y (674.56): calcd. C 64.10, H 8.07, N 8.31, Y 13.18; moved under vacuum, and the remaining solid was extracted with
found C 63.97, H 8.12, N 8.25, Y 13.22. 1H NMR (400 MHz,
C6D6, 25 °C): δ = 1.17 (br. s, 4 H, BH4), 1.37 [s, 18 H, C(CH3)3],
2.38 [s, 12 H, C6H3(CH3)3], 2.83 (s, 6 H, CH3O, dme), 3.09 (s, 4 H,
CH2O, dme), 6.8 [t, 3JH,H = 7.5 Hz, 3 H, C6H4, C6H3(CH3)2], 6.92–
toluene (35 mL), and the extract was filtered. Toluene was evapo-
rated under vacuum, and the solid residue was dissolved in a dme/
toluene mixture (1:1, 20 mL). Cooling the concentrated solution
at –20 °C afforded 0.23 g of pale-yellow crystals of 7. Yield 60%.
6.98 [m, 5 H, C6H4, C6H3(CH3)2], 7.38 (dd, 3JH,H = 6.1 and 3.6 Hz, C37H54BN4O2Si2Y (742.74): calcd. C 59.83, H 7.33, N 7.54, Y
2 H, C6H4) ppm. 13C NMR (100 MHz, C6D6, 25 °C): δ = 20.7 11.97; found C 59.67, H 7.28, N 7.61, Y 12.01. 1H NMR
[C6H3(CH3)2], 29.3 [C(CH3)3], 41.3 [3JY,C = 2.02 Hz, C(CH3)3], 61.6 (400 MHz, C7D8, 25 °C): δ = 0.04–0.5 [m, together 18 H, Si-
(CH3O, dme), 71.5 (CH2O, dme) 119.6, 121.0, 122.1, 123.5, 127.9, (CH3)3], 1.48 (br. s, 4 H, BH4), 3.18 (br. s, 6 H, CH3O, dme), 3.28
128.2, 130.5, 132.5 141.6, 149.3, [C6H4, C6H3(CH3)2], 177.2 (2JY,C
= 1.6 Hz, NCN) ppm. 11B NMR (128 MHz, C6D6, 25 °C): δ =
(br. s, 4 H, CH2O, dme), 5.60–7.45 (m, together 13 H, C6H4, C6H5),
3
7.90 (d, JH,H = 7.0 Hz, 1 H, C6H5) ppm. 13C NMR (100 MHz,
–23.6 ppm. IR (KBr): ν = 2423 (s), 2350 (s), 2233 (s), 1653 (s), 1590
C7D8, 25 °C): δ = 2.5, 2.7, 3.4 [Si(CH3)3], 58.4 (CH3O, dme), 71.7
(CH2O, dme), 116.9, 120.6, 122.8, 126.6, 129.6, 129.9, 130.4, 140.0,
140.4, 141.4, 142.3 (C6H4, C6H5), 174.3, 185.0 (NCN) ppm. 11B
˜
(s), 1568 (s), 1275 (s), 1248 (s), 1097 (s), 1049 (s), 1004 (s), 976 (s),
958 (s), 922 (s), 862 (s), 816 (s), 765 (s), 747 (s), 695 (s), 596 (s)
cm–1.
NMR (128.4 MHz, C D , 25 °C): δ = –29.1 ppm. IR (KBr): ν =
˜
6
6
2438 (s), 2377 (s), 2251 (s), 1608 (s), 1566 (s), 1510 (s), 1489 (s),
1289 (s), 1241 (s), 1215 (s), 1191 (s), 1124 (s), 1079 (s), 1044 (s),
964 (s), 919 (s), 842 (s), 799 (s), 743 (s), 703 (s), 679 (s), 629 (s),
570 (s), 528 (s), 469 (s) cm–1.
Synthesis of {C6H4-1,2-[NC(tBu)N(2,6-Me2C6H3)]2}Nd(BH4)(dme)
(3): An analogous synthetic procedure was used by reacting 1
(0.37 g, 0.76 mmol), Na(NSiMe3)2 (0.28 g, 1.52 mmol), and
Nd(BH4)3(thf)3 (0.31 g, 0.76 mmol). Green crystals of 3 were iso-
lated in 43% yield (0.24 g, 0.33 mmol). C36H54BN4NdO2 (729.89): General Procedure for the rac-Lactide Polymerization: To a solution
calcd. C 59.24, H 7.46, N 7.68, Nd 19.76; found C 59.38, H 7.52,
of the complex (10 mmol) in toluene (per 1 m solution of lactide)
lactide was added. The mixture was immediately stirred with a
magnetic stirring bar at 20 °C. The reaction was quenched by add-
ing a solution 10% H2O in thf (1 mL), and the polymer was pre-
cipitated from a CH2Cl2/pentane mixture (ca. 2 mL:100 mL) five
times. The polymer was dried under vacuum to a constant weight.
N 7.59, Nd 19.80. IR (KBr): ν = 2451 (s), 2426 (s), 2215 (s), 2152
˜
(s), 1656 (s), 1587 (s), 1581 (s), 1535 (s), 1275 (s), 1245 (s), 1179 (s),
1142 (s), 1094 (s), 1028 (s), 952 (s), 910 (s), 765 (s), 744 (s), 695 (s)
cm–1.
Synthesis of [C6H4-1,2-{NC(tBu)N(2,6-Me2C6H3)}2]Sm(BH4)(dme)
(4): An analogous synthetic procedure was used by reacting 1
General Procedure for the Synthesis of Diethyl Hydroxy(phenyl)-
(0.38 g, 0.80 mmol), Na(NSiMe3)2 (0.29 g, 1.60 mmol), and methylphosphonate [C6H5CH(OH)P(O)(OEt)2]: HP(O)(OEt)2
Sm(BH4)3(thf)3 (0.33 g, 0.80 mmol). Yellow crystals of 4 were iso-
lated in 39% yield (0.23 g, 0.31 mmol) yield. C36H54BN4O2Sm
(736.01): calcd. C 58.75, H 7.40, N 7.61, Sm 20.43; found C 58.53,
(1 mmol, 0.138 g, 0.127 mL) was added to a solution of benzalde-
hyde (1 mmol, 0.106 g, 0.101 mL) and catalyst (1ϫ10–5 mol) in tol-
uene (2 mL). The reaction mixture was stirred at room temperature
for 24 h and was subsequently hydrolyzed with water (1.0 mL), ex-
tracted with ethyl acetate (3ϫ10.0 mL), dried with anhydrous
Na2SO4 and filtered. After the solvent was removed under vacuum,
the final product was recrystallized from a thf/hexane mixture. The
yield of diethyl hydroxy(phenyl)methylphosphonate was deter-
mined by weighing. 1H NMR (400 MHz, CDCl3, 25 °C): δ = 1.18–
1.26 (m, 6 H, CH3CH2O), 3.91–4.08 (m, 4 H, CH3CH2O), 4.51 (br.
H 7.46, N 7.55, Sm 20.45. IR (KBr): ν = 2454 (s), 2215 (s), 2154
˜
(s), 1656 (s), 1581 (s), 1535 (s), 1272 (s), 1245 (s), 1212 (s), 1188 (s),
1170 (s), 1142 (s), 1097 (s), 1031 (s), 956 (s), 910 (s), 765 (s) cm–1.
Synthesis of [C6H4-1,2-{NC(Ph)NSiMe3}2]Y(BH4)(thf)2 (6): To a
solution of Y(BH4)3(thf)3 (0.22 g, 0.61 mmol) in thf (20 mL) a solu-
tion of 5 (0.31 g, 0.286 mmol) in thf (20 mL) was added, and the
reaction mixture was stirred for 5 h at 65 °C. The solvent was re-
moved under vacuum, and the remaining solid was extracted with
toluene (35 mL), and the extract was filtered. Toluene was evapo-
rated under vacuum, and the remaining solid residue was recrys-
tallized by slow condensation of hexane into a concentrated thf
3
s, 1 H, CH), 5.00 (d, JH,H = 11 Hz, 1 H, OH), 7.26–7.48 (m, 5 H,
C6H5) ppm. 31P NMR (162 MHz, CDCl3, 25 °C): δ = 21.5 ppm.
X-ray Crystallography: The X-ray data for 2–7 were collected with
a Smart Apex diffractometer [graphite-monochromated Mo-Kα ra-
solution. Pale-yellow crystals of 6 were isolated in 67% yield diation, ω-scan technique, λ = 0.71073 Å, T = 100(2) K]. The struc-
(0.27 g). C34H52BN4O2Si2Y (704.70): calcd. C 57.95, H 7.44, N
7.95, Y 12.62; found C 57.70, H 7.42, N 7.89, Y 12.67. H NMR
tures were solved by direct methods and were refined on F2 by
1
using the SHELXTL[24] package. All non-hydrogen atoms and B-
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Table 3. Crystallographic data and structure refinement details for 2–7.
Complex
2
3
4
6
7
Empirical formula
Formula weight
T, [K]
C
672.54
100(2)
36H52BN4O2Y
C36H54BN4NdO2
729.88
100(2)
C36H54BN4O2Sm
735.99
100(2)
C34H52BN4O2Si2Y C37H54BN4O2Si2Y
704.70
100(2)
742.74
100(2)
Wavelength [Å]
Crystal system
Space group
0.71073
triclinic
P1
monoclinic
P2(1)
8.9309(3)
15.5558(6)
13.2200(5)
90
monoclinic
P2(1)
8.9043(5)
15.5691(8)
13.2033(7)
90
orthorhombic
P2(1)2(1)2(1)
11.8602(14)
12.3233(15)
24.839(3)
90
triclinic
P1
¯
¯
a [Å]
b [Å]
c [Å]
α [°]
12.0009(10)
12.6793(10)
12.9740(10)
83.473(2)
87.144(2)
63.643(1)
1757.5(2)
2
8.3192(2)
14.0383(4)
18.0087(5)
81.446(1)
85.643(1)
73.17
β [°]
100.161(1)
90
99.968(1)
90
90
90
γ [°]
Volume [Å3]
1807.8(1)
2
1802.8(2)
2
3630.4(8)
4
1989.54(9)
2
Z
ρcalcd. [g/cm3]
1.271
1.695
712
1.341
1.356
1.289
1.240
Absorption coefficient, [mm–1
F(000)
]
1.471
1.664
1.707
1.561
758
762
1488
784
Crystal size [mm]
θ range for data collection [°]
Index ranges
0.68ϫ 0.16ϫ 0.14
1.89 to 27.00
–15Յ hՅ 15
–15Յ kՅ 16
–16Յ lՅ 16
16097
0.40ϫ 0.30ϫ 0.15
2.04 to 26.00
–11Յ hՅ 11
–19Յ kՅ 19
–16Յ lՅ 16
15675
0.40ϫ 0.30ϫ 0.15
2.32 to 26.00
–10Յ hՅ 10
–19Յ kՅ 19
–16Յ lՅ 16
15615
0.40ϫ 0.35ϫ 0.23 0.35ϫ 0.28ϫ 0.25
2.33 to 25.99
–14Յ hՅ 14
–15Յ kՅ 15
–30Յ lՅ 30
28842
1.82 to 26.00
–10Յ hՅ 10
–17Յ kՅ 17
–22Յ lՅ 22
17160
Reflections collected
Independent reflections
Rint
7559
0.0280
7027
0.0173
7014
0.0190
6946
7727
0.0464
0.0165
Completeness to θ [%]
Absolute structure parameter
Goodness-of-fit on F2
Final R indices [IϾ2σ(I)]
98.4
99.5
–0.017(8)
1.087
R1 = 0.0202
wR2 = 0.04623
R1 = 0.0219
wR2 = 0.0470
1.368/–0.431
99.5
–0.027(8)
1.064
R1 = 0.0206
wR2 = 0.0501
R1 = 0.0217
wR2 = 0.0507
1.406/–0.424
98.2
–0.004(5)
1.033
R1 = 0.0384
wR2 = 0.0863
R1 = 0.0475
wR2 = 0.0891
1.034/–0.525
98.7
1.010
1.046
R1 = 0.0398
wR2 = 0.0945
R1 = 0.0547
wR2 = 0.0992
R1 = 0.0285
wR2 = 0.0715
R1 = 0.0336
wR2 = 0.0732
0.517/–0.401
R indices (all data)
Largest diff. peak and hole [e/Å3] 0.960/–0.662
slie, Coord. Chem. Rev. 2002, 233, 131–155; c) A. A. Trifonov,
Russ. Chem. Rev. 2007, 76, 1051–1072.
bonded hydrogen atoms were found from Fourier syntheses of elec-
tron density. All non-hydrogen atoms were refined anisotropically,
whereas B-bonded hydrogen atoms were refined isotropically, and
other H atoms were refined isotropically in the riding model. SAD-
ABS[25] were used to perform area-detector scaling and absorption
corrections. Crystallographic data and collection and refinement
details are shown in Table 3, and the corresponding CIF files are
available in the Supporting Information. CCDC-940266 (for 2),
-940267 (for 3), -940268 (for 4), -940269 (for 6), and -940270 (for
7) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[3]
For examples of Ln borohydrides see: a) F. Bonnet, A. R.
Cowley, P. Mountford, Inorg. Chem. 2005, 44, 9046–9055; b) I.
Palard, A. Soum, S. M. Guillaume, Chem. Eur. J. 2004, 10,
4054–4062; c) J. Huang, J. F. Yu, G. M. Wu, W. L. Sun, Z. Q.
Shen, Chin. Chem. Lett. 2009, 20, 1357–1360; d) J. Jenter, P. W.
Roesky, N. Ajellal, S. M. Guillaume, N. Susperregui, L. Maron,
Chem. Eur. J. 2010, 16, 4629–4638; e) D. Robert, M. Kond-
racka, J. Okuda, Dalton Trans. 2008, 2667–2669; f) S. M. Guil-
laume, M. Schappacher, A. Soum, Macromolecules 2003, 36,
54–60; g) H. E. Dyer, S. Huijser, N. Susperregui, F. Bonnet,
A. D. Schwarz, R. Duchateau, L. Maron, P. Mountford, Orga-
nometallics 2010, 29, 3602–3621; h) M. A. Sinenkov, G. K. Fu-
kin, A. V. Cherkasov, N. Ajellal, Th. Roisnel, F. M. Kerton, J.-
F. Carpentier, A. A. Trifonov, New J. Chem. 2011, 35, 204–212;
i) T. V. Mahrova, G. K. Fukin, A. V. Cherkasov, A. A. Tri-
fonov, N. Ajellal, J.-F. Carpentier, Inorg. Chem. 2009, 48, 4258–
4266; j) A. A. Trifonov, G. G. Skvortsov, D. M. Lyubov, G. K.
Fukin, E. A. Fedorova, M. N. Bochkarev, Russ. Chem. Bull.
Int. Ed. 2005, 54, 2511–2518; k) M. Vissaux, F. Bonnet, Coord.
Chem. Rev. 2011, 255, 374–420.
Supporting Information (see footnote on the first page of this arti-
1
cle): The H and 13C NMR spectra of complexes 2, 6, 7, and IR
spectra of 2–4, 6, 7 are presented.
Acknowledgments
[4]
a) P. Dubois, O. Coulembier, J.-M. Raquez (Eds.), Handbook
of Ring-Opening Polymerization, Wiley-VCH Verlag GmbH &
Co. KGaA: Weinheim, Germany 2009; b) O. Dechy-Cabaret,
B. Martin-Vaca, D. Bourissou, Chem. Rev. 2004, 104, 6147–
6176; c) M. J. Stanford, A. P. Dove, Chem. Soc. Rev. 2010, 39,
486–494; d) C. M. Thomas, Chem. Soc. Rev. 2010, 39, 165–173;
e) J. Kratsch, M. Kuzdrowska, M. Schmid, N. Kazeminejad,
C. Kaub, P. Oña-Burgos, S. M. Guillaume, P. Roesky, Organo-
metallics 2013, 32, 1230–1238.
This work was financially supported by the Russian Foundation
for Basic Research (Grants 11-03-00555, 12-03-93109-HжHШЫ_a,
12-03-31865 mol_a).
[1] R. D. Schannon, Acta Crystallogr., Sect. A: Found. Crystallogr.
1976, 32, 751–767.
[2] a) F. T. Edelmann, D. M. M. Freckmann, H. Schumann,
Chem. Rev. 2002, 102, 1851–1896; b) W. E. Piers, D. J. H. Em-
Eur. J. Inorg. Chem. 2013, 6009–6018
6017
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[5]
[14] a) D. A. Laske, R. Duchateau, J. H. Teuben, A. L. Spek, J.
Organomet. Chem. 1993, 462, 149–153; b) T. J. Marks, G. W.
Grynkewich, Inorg. Chem. 1976, 15, 1302–1307; c) D. Deng, X.
Zheng, C. Qian, J. Sun, L. Zhang, J. Organomet. Chem. 1994,
466, 95–100.
[15] R. D. Schannon, Acta Crystallogr., Sect. A: Found. Crystallogr.
1976, 32, 751–767.
[16] See for example: A. Amgoune, C. M. Thomas, S. Ilinca, T. Ro-
isnel, J.-F. Carpentier, Angew. Chem. 2006, 118, 2848; Angew.
Chem. Int. Ed. 2006, 45, 2782–2784 and references cited
therein.
[17] a) H. R. Kricheldorf, M. Berl, N. Scharnagi, Macromolecules
1988, 21, 286–293; b) P. Dubois, C. Jacobs, R. Jérôme, P. Te-
yssié, Macromolecules 1991, 24, 2266–2270; c) M. Lahcini,
P. M. Castro, M. Kalmi, M. Leskelä, T. Repo, Organometallics
2004, 23, 4547–4549; d) M. Kalmi, M. Lahcini, P. M. Castro,
O. Lehtonen, A. Belfkira, M. Leskelä, T. Repo, J. Polym. Sci.,
Part A: Polym. Chem. 2004, 42, 1901–1911.
a) A.-Ch. Albertson, I. K. Varma, Biomacromolecules 2003, 4,
1466–1486; b) A. P. Gupta, V. Kumar, Eur. Polym. J. 2007, 43,
4053–4074; c) R. H. Platel, L. M. Hodgson, C. K. Williams,
Polym. Rev. 2008, 48, 1163.
G. G. Skvortsov, M. V. Yakovenko, P. M. Castro, G. K. Fukin,
A. V. Cherkasov, J.-F. Carpentier, A. A. Trifonov, Eur. J. Inorg.
Chem. 2007, 3260–3267.
a) F. T. Edelmann, Coord. Chem. Rev. 1994, 137, 403–481; b)
J. Barker, M. Kilner, Coord. Chem. Rev. 1994, 133, 219–300; c)
M. P. Coles, Dalton Trans. 2006, 985–1001; d) F. T. Edelmann,
Adv. Organomet. Chem. 2008, 57, 183–352; e) P. J. Bailey, S.
Pace, Coord. Chem. Rev. 2001, 214, 91–141.
a) M. V. Yakovenko, A. V. Cherkasov, G. K. Fukin, D. Cui,
A. A. Trifonov, Eur. J. Inorg. Chem. 2010, 3290–3298; b) M. V.
Yakovenko, A. A. Trifonov, E. N. Kirillov, T. Roisnel, J.-F.
Carpentier, Inorg. Chim. Acta 2012, 383, 137–142.
[6]
[7]
[8]
[9] a) A. O. Tolpygin, A. S. Shavyrin, A. V. Cherkasov, G. K. Fu-
kin, A. A. Trifonov, Organometallics 2012, 31, 5405–5413; b)
G. G. Skvortsov, G. K. Fukin, S. Yu. Ketkov, A. V. Cherkasov,
K. A. Lyssenko, A. A. Trifonov, Eur. J. Inorg. Chem. 2013,
4173–4183.
[18] Y. Nakayama, S. Okuda, H. Yasuda, T. Shiono, React. Funct.
Polym. 2007, 67, 798–806.
[19] A. N. Pudovik, I. V. Konovalova, Synthesis 1979, 81–96.
[20] a) P. Merino, E. Marqués-Lopés, R. P. Herrera, Adv. Synth.
Catal. 2008, 350, 1195–1208; b) S. Zhou, Z. Wu, J. Rong, S.
Wang, G. Yang, X. Zhu, L. Zhang, Chem. Eur. J. 2012, 18,
2653–2659; c) S. Zhou, H. Wang, J. Ping, S. Wang, L. Zhang,
X. Zhu, Y. Wei, F. Wang, Z. Feng, X. Gu, S. Yang, H. Miao,
Organometallics 2012, 31, 1696–1702.
[21] L. E. Manzer, Inorg. Chem. 1978, 17, 1552–1558.
[22] S. J. Lyle, M. M. Rahman, Talanta 1953, 10, 1177–1182.
[23] I. Barakat, P. Dubois, R. Jerome, P. Teyssié, J. Polym. Sci. A:
Polym. Chem. 1993, 31, 505–514.
[24] G. M. Sheldrick, SHELXTL v6.12, Structure Determination
Software Suite; Bruker AXS, Madison, WI, 2000.
[25] G. M. Sheldrick, SADABS v2.01, Bruker/Siemens Area Detec-
tor Absoption Correction Program; Bruker AXS, Madison,
WI, 1998.
[10] W. Li, M. Xue, J. Tu, Y. Zhang, Q. Shen, Dalton Trans. 2012,
41, 7258–7265.
[11] M. Ephritikhine, Chem. Rev. 1997, 97, 2193–2242.
[12] a) U. Mirsaidov, I. Shaimuradov, M. Hikmatov, Zh. Neorg.
Khim. (Rus. J. Inorg. Chem.) 1986, 31, 1321–1326; b) B. G.
Segal, S. J. Lippord, Inorg. Chem. 1978, 17, 844–850.
[13] a) M. Visseaux, T. Chenal, P. Roussel, A. Mortreux, J. Or-
ganomet. Chem. 2006, 691, 86–92; b) M. Visseaux, M. Mainil,
M. Terrier, A. Mortreux, P. Roussel, T. Mathievet, M. Desta-
rac, Dalton Trans. 2008, 4558–4561; c) P. Zinck, M. Visseaux,
A. Mortreux, Z. Anorg. Allg. Chem. 2006, 632, 1943–1944; d)
D. Barbier-Baudry, O. Blacque, A. Hafid, A. Nyassi, H. Sitz-
mann, M. Visseaux, Eur. J. Inorg. Chem. 2000, 2333–2336; e)
S. M. Cendrowski-Guillaume, M. Nierlich, M. Lance, M.
Ephritikhine, Organometallics 1998, 17, 786–788; f) F. Yuan, J.
Yang, L. Xiong, J. Organomet. Chem. 2006, 691, 2534–2539.
Received: July 21, 2013
Published Online: November 4, 2013
Eur. J. Inorg. Chem. 2013, 6009–6018
6018
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim