Comprehensive Study on Reactions of Group 13 Diyls with Tetraorganodipentelanes

Article abstract of DOI:10.1021/acs.inorgchem.8b01489

L¹Ga {L¹ = HC[C(Me)N(2,6-iPr₂C₆H₃)]₂} reversibly reacts with E₂Ph₄ (E = Sb, Bi) in a temperature-dependent equilibrium reaction with insertion into the E-E bond and formation of L¹Ga(EPh₂)₂ (E = Sb 1, Bi 2). Analogous findings were observed in the reactions of L²Ga {L² = (C₆H₁₁)₂NC[N(2,6-iPr₂C₆H₃)]₂} with E₂R₄ (R = Ph, Et), yielding L²Ga(EPh₂)₂ (E = Sb 3, Bi 4) and L²Ga(EEt₂)₂ (E = Sb 5, Bi 6). 1-3 and 5 were isolated by fractional crystallization at low temperature, whereas 4 and 6 could not be isolated in their pure form even at low temperature. In contrast, reactions of [Cp?Al]₄ (Cp? = C₅Me₅) with Sb₂R₄ (R = Ph, Et) and Bi₂Et₄ did not proceed with insertion into the E-E bonds but with formation of (Cp?Al)₃E₂ (E = Sb, 7; Bi, 8), whereas the reaction with Bi₂Ph₄ yielded metallic bismuth. 8 was also formed in the reaction of [Cp?Al]₄ and BiEt₃ at ambient temperature, whereas the analogous reaction of [Cp?Al]₄ with SbEt₃ did not yield 7 even under drastic reaction conditions (120 °C, 3 days). In contrast, Cp?Ga and Sb₂R₄ (R = Ph, Et) were found to react only at elevated temperature (120 °C) with formation of antimony metal.

Full text of DOI:10.1021/acs.inorgchem.8b01489

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Comprehensive Study on Reactions of Group 13 Diyls with
Tetraorganodipentelanes
†
†
†
†
†
̈
̈
Chelladurai Ganesamoorthy, Julia Kruger, Eduard Glockler, Christoph Helling, Lukas John,
‡
†
,†
̈
Walter Frank, Christoph Wolper, and Stephan Schulz*
†Faculty of Chemistry, Inorganic Chemistry, and Center for Nanointegration Duisburg-Essen (CENIDE), University of
̈
Duisburg-Essen, Universitatsstrasse 7, 45141 Essen, Germany
‡Institute for Inorganic Chemistry and Structural Chemistry, University of Du
sseldorf, 40225 Dusseldorf, Germany
̈ ̈
S
* Supporting Information
ABSTRACT: L1Ga {L1 = HC[C(Me)N(2,6-iPr2C6H3)]2} reversibly reacts with E2Ph4 (E
= Sb, Bi) in a temperature-dependent equilibrium reaction with insertion into the E−E
bond and formation of L1Ga(EPh2)2 (E = Sb 1, Bi 2). Analogous findings were observed
in the reactions of L2Ga {L2 = (C6H11)2NC[N(2,6-iPr2C6H3)]2} with E2R4 (R = Ph, Et),
yielding L2Ga(EPh2)2 (E = Sb 3, Bi 4) and L2Ga(EEt2)2 (E = Sb 5, Bi 6). 1−3 and 5 were
isolated by fractional crystallization at low temperature, whereas 4 and 6 could not be
isolated in their pure form even at low temperature. In contrast, reactions of [Cp*Al]4
(Cp* = C5Me5) with Sb2R4 (R = Ph, Et) and Bi2Et4 did not proceed with insertion into
the E−E bonds but with formation of (Cp*Al)3E2 (E = Sb, 7; Bi, 8), whereas the reaction
with Bi2Ph4 yielded metallic bismuth. 8 was also formed in the reaction of [Cp*Al]4 and
BiEt3 at ambient temperature, whereas the analogous reaction of [Cp*Al]4 with SbEt3 did
not yield 7 even under drastic reaction conditions (120 °C, 3 days). In contrast, Cp*Ga
and Sb2R4 (R = Ph, Et) were found to react only at elevated temperature (120 °C) with
formation of antimony metal.
addition, L1M was also found to activate a variety of main
group element H−X (X = H, B, C, Si, N, P, and O),6 C−F, and
C−O σ-bonds,7 while L1Ga was found to readily insert into
several main group metal−X bonds of heavy elements of
groups 13 (Ga, In), 14 (Ge, Sn, Pb), 15 (Bi), and 16 (Te),
respectively.8 This reactivity results from the presence of a
metal-centered electron lone pair, resulting in nucleophilic
properties (Lewis basic), and due to the presence of a formally
vacant π-orbital, rendering the molecules also electrophilic
(Lewis acidic). Quantum chemical calculations revealed that
the electronic structure of L1Al and L1Ga slightly differs with
respect to their singlet−triplet energy gap (Al: 34.3−45.7 kcal/
mol; Ga: 51.7−55.5 kcal/mol) and HOMO−LUMO separa-
tion (Al: 75.76 kcal/mol; Ga 96.24 kcal/mol),9 and as a
consequence, the reactivity of alanediyl L1Al and gallanediyl
L1Ga was also found to slightly differ. While L1Al shows very
promising applications in bond activation reactions as
mentioned before, L1Ga also showed very promising properties
as stabilizing terminal ligand in main group metal10 and
transition metal chemistry.11 This was also observed for Cp*-
substituted alane- and gallanediyls Cp*M (M = Al, Ga), which
are strong σ-donors and serve as powerful two-electron ligands
in transition metal complexes12 and in Lewis acid−base
reactions, i.e., in reactions with earth alkaline metal complexes
INTRODUCTION
■
The synthesis and reactivity of monovalent group 13 diyls of
the general type RM (M = Al, Ga), in which the metal centers
adopt the oxidation state +I, has been investigated since the
landmarking synthesis of [Cp*Al]4 (Cp* = C5Me5) in 1991.
̈
[Cp*Al]4 was initially prepared by Schnockel et al. by
metathesis reaction of a metastable AlCl solution with
Cp*2Mg, whereas Roesky et al. reported on a more convenient
method by reduction reaction of Cp*AlCl2 with potassium.1
Since then, several alanediyls RAl and gallanediyls RGa have
been synthesized by metathesis reaction or by reduction
reaction of trivalent species RMX2 (M = Al, Ga, X = halide), in
particular compounds containing sterically demanding ter-
phenyl ligands2 and N,N′-chelating ligands such as diimines,
guanidinates, diiminophosphinates, and β-diketiminates,3
respectively. Monovalent group 13 diyls typically adopt
monomeric (RM) or oligomeric ([RM]x) structures with
metal−metal bonds in solution and in the solid state,
depending on the steric demand and coordination properties
of the organic substituent. Aside from their interesting
structures, group 13 diyls received increasing interest due to
their fascinating properties in reactions with organic
compounds and in coordination chemistry. L1M (M = Al,
Ga; L1 = HC[C(Me)N(2,6-iPr2C6H3)]2) containing the
sterically demanding N,N′-chelating β-diketiminate ligand L1
showed very promising properties in the activation of small
molecules including P4, O2, S8, azobenzene, and azides,4
respectively, as was also observed for Cp*M (M = Al, Ga).5 In
Received: May 30, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b01489
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
Cp*2M (M = Ca, Sr, Ba)13 and group 13 trialkyls tBu3M (M =
Found: C, 53.1; H, 5.11; N, 2.24%. H NMR (toluene-d8, −20 °C,
300 MHz): δ 8.18−6.87 (m, 26 H, C6H3(iPr)2, Bi(C6H5)2), 4.90 (s, 1
H, γ-CH), 3.76 (br sept, 2 H, CH(CH3)2), 3.30 (br sept, 2 H,
CH(CH3)2), 1.59 (s, 6 H, CCH3), 1.54 (br d, 6 H, CH(CH3)2), 1.10
(br d, 6 H, CH(CH3)2), 0.76 (br d, 6 H, CH(CH3)2), 0.68 (br d, 6 H,
CH(CH3)2). 13C NMR (C6D6, 25 °C, 75.5 MHz): δ 170.4 (CCH3),
142.7, 130.2, 128.9, 128.4, 127.5, 126.5, (C6H3(iPr)2, C6H5), 99.2 (γ-
CH), 35.0 (CH(CH3)2), 29.7 (br, CH(CH3)2), 27.2 (CH(CH3)2),
25.7 (CH(CH3)2), 25.3 (br, CH(CH3)2), 24.3 (CH(CH3)2), 20.9
(CCH3). IR: ν 3051, 2965, 2922, 2861, 1566, 1511, 1468, 1425, 1376,
1309, 1254, 1162, 1094, 1057, 1014, 934, 855, 794, 714, 695, 622,
524, 438 cm−1.
Al, Ga).14
Our general interest in group 13/15 chemistry prompted us
to investigate reactions of L1M (M = Al, Ga, In) with group 15
compounds such as distibines and dibismuthines E2Et4, which
occurred with insertion into the E−E bonds15 as was
previously observed in reactions of L1Al with diphosphines.16
17
In addition, reactions of L1Ga with BiEt3 and EX3 (E = As,
Sb, Bi; X = NR2, halide)18 proceeded with insertion into Bi−C
bonds and E−X bonds, respectively, and L1Ga was found react
with [Cp*Sb]4 with elimination of decamethylfulvalene
(Cp*2) and subsequent formation of [(L1Ga)2(μ,η2:2-Sb4)],19
whereas stable stibanyl- and bismuthinyl radicals [L1(X)Ga]E·
(E = Sb, Bi; X = Cl, I) were formed in reactions with
Cp*EX2.20 To investigate the role of the organic ligand of
group 13 diyls on the outcome of these reactions, we
systematically reacted L1,2Ga {L2 = (C6H11)2NC[N(2,6-
iPr2C6H3)]2}, Cp*Ga, and [Cp*Al]4 with dipnictines E2R4
(E = Sb, Bi; R = Ph, Et).
Synthesis of L2Ga(SbPh2)2 (3). 3 was synthesized by a procedure
similar to that of 1 using L2Ga (28 mg, 0.046 mmol) and Sb2Ph4 (25
mg, 0.046 mmol). Analytically pure 3 was obtained as pale-yellow
crystals from saturated n-hexane solution after storage at 8 °C for 1
day. Yield: 30 mg (0.026 mmol, 56%). Mp 151−153 °C. Anal. Calcd
for C61H76N3GaSb2: C, 62.91; H, 6.58; N, 3.61. Found: C, 62.77; H,
6.64; N, 3.64%. 1H NMR (toluene-d8, 25 °C, 300 MHz): δ 7.27−6.84
3
(m, 16 H, C6H3(iPr)2, Sb(C6H5)2), 3.99 (sept, JHH = 6.6 Hz, 4 H,
CH(CH3)2), 3.66 (m, 2 H, NCH), 1.50−1.41 (m, 12 H, Cy−CH2),
1.45 (d, 3JHH = 6.9 Hz, 12 H, CH(CH3)2), 1.25 (d, 3JHH = 6.6 Hz, 12
H, CH(CH3)2), 0.97−0.81 (m, 8 H, Cy−CH2). 13C NMR (toluene-
d8, 25 °C, 75.5 MHz): δ 162.2 (CN3), 144.6, 141.1, 139.2, 134.7,
128.6, 127.0, 125.7, 124.7, 124.0, 123.4 (C6H3(iPr)2, C6H5), 59.0
(NCH), 34.8 (Cy−CH2), 28.9 (CH(CH3)2), 28.0 (CH(CH3)2), 27.1
(Cy−CH2), 25.6 (Cy−CH2), 24.3 (CH(CH3)2). IR: ν 3056, 2950,
2919, 2850, 1573, 1454, 1423, 1367, 1324, 1280, 1249, 1193, 1156,
1093, 1056, 1018, 956, 894, 856, 825, 794, 763, 726, 688, 508, 445,
389 cm−1.
EXPERIMENTAL SECTION
■
General Procedures. Argon gas was purified by passing the gas
through preheated Cu2O pellets and molecular sieves columns.
Reactions were carried out using standard Schlenk and glovebox
techniques. Toluene and n-hexane were dried using a mBraun Solvent
Purification System, degassed, and stored in Schlenk flasks under
argon atmosphere. Deuterated solvents were dried over activated
molecular sieves (4 Å) and degassed prior to use. L1Ga,4e L2Ga,21
Cp*M (M = Al, Ga),22 and E2R4 (E = Sb, Bi; R = Et, Ph)23 were
prepared according to literature methods. 1H (300 MHz) and
13C{1H} (75.5 MHz) NMR spectra were recorded using a Bruker
Avance DPX-300 spectrometer and referenced to internal C6D5H
(1H: δ = 7.15; 13C: δ = 128.62) and C6D5CD2H (1H: δ = 2.08; 13C: δ
= 20.43).24 1−6 form temperature-dependent equilibria with the
starting reagents in solution state as was shown by 1H and 13C NMR
spectroscopy. The spectra are rather complex due to the presence of
resonances of the starting reagents, but tentative assignments of the
resonances are given. IR spectra were recorded in a glovebox under
argon atmosphere using an ALPHA-T FT-IR spectrometer equipped
with a single reflection ATR sampling module. Microanalyses were
performed at the Elemental Analysis Laboratory of the University of
Duisburg-Essen. Melting points were determined in sealed glass
capillaries and are not corrected.
Synthesis of L2Ga(SbEt2)2 (5). A 1:2 molar mixture of L2Ga (50
mg, 0.082 mmol) and Sb2Et4 (59 mg, 36 μL, 0.163 mmol) was
suspended in n-hexane (1.5 mL) and heated to 70 °C for 10 min,
yielding a light-yellow solution. The solution was cooled to ambient
temperature and stored at 0 °C. Pale yellow crystals of 5 were formed
after 2 weeks, which were isolated by filtration and dried in vacuo.
Yield: 43 mg (0.044 mmol, 54%). Mp 143−145 °C. Anal. Calcd for
C45H76N3GaSb2: C, 55.59; H, 7.88; N, 4.32. Found: C, 55.80; H,
8.04; N, 4.46%. 1H NMR (toluene-d8, 25 °C, 300 MHz): δ 7.10−7.02
3
(m, 6 H, C6H3(iPr)2), 3.90 (sept, JHH = 6.6 Hz, 4 H, CH(CH3)2),
3.50 (m, 2 H, NCH), 2.02−1.77 (m, 12 H, Cy−CH2, SbCH2CH3),
1.43−1.36 (m, 36 H, CH(CH3)2, SbCH2CH3), 0.97−0.62 (m, 16 H,
Cy−CH2). 13C NMR (toluene-d8, 25 °C, 75.5 MHz): δ 160.9 (CN3),
144.7, 141.1, 125.4, 124.2 (C6H3(iPr)2), 58.8 (NCH), 34.7 (Cy−
CH2), 28.6 (CH(CH3)2), 28.4 (CH(CH3)2), 27.0 (Cy−CH2), 25.7
(Cy−CH2), 23.9 (CH(CH3)2), 16.4 (SbCH2CH3), −0.1
(SbCH2CH3). IR: ν 2963, 2932, 2857, 1454, 1423, 1374, 1324,
1249, 1174, 1093, 1018, 950, 863, 800, 763, 744, 713, 688, 657, 508,
489, 396 cm−1.
Synthesis of L1Ga(SbPh2)2 (1). A solution of L1Ga (53 mg, 0.109
mmol) and Sb2Ph4 (60 mg, 0.109 mmol) in 2 mL of toluene was
stirred at ambient temperature for 1 h. The solvent was removed at
reduced pressure, yielding a yellow residue, which was dissolved in 1
mL of n-hexane and stored at room temperature. Analytically pure
yellow crystals of 1 were obtained after storage for 1 day. Yield: 85 mg
(0.082 mmol, 75%). Mp 168 °C (dec.). Anal. Calcd for
C53H61N2GaSb2: C, 61.25; H, 5.92; N, 2.70. Found: C, 61.17; H,
L2Ga(BiPh2)2 (4) and L2Ga(BiEt2)2 (6). 4 and 6 could not be
isolated in their pure form from the reaction equilibrium. Upon
cooling solutions of 4 and 6 in n-hexane to −30 °C, L2Ga and Bi2Ph4
start to crystallize and therefore shifted the equilibria to the side of the
starting reagents. 1H NMR spectra of the reaction equilibriums as well
as temperature-dependent in situ NMR studies are given in Figures
S18−S21.
1
5.88; N, 2.74%. H NMR (C6D6, 8 °C, 300 MHz): δ 7.83−6.81 (m,
26 H, C6H3(iPr)2, Sb(C6H5)2), 4.96 (s, 1 H, γ-CH), 3.87 (br sept, 2
H, CH(CH3)2), 3.49 (br sept, 2 H, CH(CH3)2), 1.63 (br d, 6 H,
CH(CH3)2), 1.60 (s, 6 H, CCH3), 1.13 (br d, 6 H, CH(CH3)2), 0.80
(br d, 6 H, CH(CH3)2), 0.76 (br d, 6 H, CH(CH3)2). 13C NMR
(C6D6, 25 °C, 75.5 MHz): δ 170.3 (CCH3), 146.3, 143.4, 142.6,
139.5, 138.4, 138.1, 135.5, 132.0, 129.3, 128.7, 127.5, 127.0, 126.0,
124.7 (C6H3(iPr)2, C6H5), 99.0 (γ-CH), 35.0 (CH(CH3)2), 29.7 (br,
CH(CH3)2), 28.6 (br, CH(CH3)2), 25.9 (br, CH(CH3)2), 25.5 (br,
CH(CH3)2), 25.2 (br, CH(CH3)2), 24.3 (CCH3). IR: ν 3051, 2959,
2922, 2861, 1511, 1468, 1431, 1382, 1315, 1254, 1162, 1094, 1016,
930, 850, 801, 721, 691, 629, 525, 445, 396 cm−1.
Synthesis of (Cp*Al)3Sb2 (7). In a J Young NMR tube, a
suspension of [Cp*Al]4 (50 mg, 0.077 mmol) and Sb2R4 (R = Et: 22
mg, 13.4 μL, 0.062 mmol; R = Ph: 34 mg, 0.062 mmol) in toluene-d8
(0.5 mL) was heated to 80 °C, and the reaction progress was
monitored via 1H NMR spectroscopy. A complete consumption of all
starting reagents was observed after 1 day. The resulting solution was
cooled to ambient temperature. Orange crystals of 7 were formed
upon storage at 0 °C for 1 week, which were filtered and washed with
2 mL of n-hexane. The yields in both reactions varied from 64 to 70%,
and a maximum of 32 mg of 7 was obtained from the reaction with
Synthesis of L1Ga(BiPh2)2 (2). 2 was synthesized by a similar
procedure to that of 1 using L1Ga (100 mg, 0.205 mmol) and Bi2Ph4
(149 mg, 0.205 mmol). Yield: 167 mg (0.138 mmol, 67%). Mp 117
°C (dec.). Anal. Calcd for C53H61N2GaBi2: C, 52.45; H, 5.07; N, 2.31.
Sb2Et4. 1H NMR (C6D6, 300 MHz): δ 2.08 (s, 45 H, C5(CH3)5). 13
NMR (C6D6, 75.5 MHz): δ 116.1 (C5Me5), 12.0 (C5Me5).
Synthesis of (Cp*Al)3Bi2 (8). Method A. In a J Young NMR
tube, a suspension of [Cp*Al]4 (50 mg, 0.077 mmol) and Bi2Et4 (33
C
B
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mg, 13.2 μL, 0.062 mmol) in toluene-d8 (0.5 mL) was stirred at
ambient temperature and the reaction was periodically monitored via
1H NMR spectroscopy. The reaction occurred slowly, finally yielding
8 in very small amount within 3 days. During this period, a complete
disproportionation of Bi2Et4 into BiEt3 was observed. Further heating
of this solution to 120 °C yielded considerable amounts of 8 after 3
days. The solution was filtered, and the metallic precipitate was
washed with 2 mL of toluene. The combined filtrate was concentrated
under reduced pressure and kept at −30 °C for 1 day to give red
microcrystals.
Method B. A suspension of [Cp*Al]4 (199 mg, 0.308 mmol) and
BiEt3 (121 mg, 67 μL, 0.409 mmol) in toluene (10 mL) was heated to
120 °C for 4 days. The reaction mixture was filtered to remove traces
of Bi metal, concentrated to 2 mL and kept at −30 °C for 1 day to
give red microcrystals. Yield: 63 mg (0.069 mmol, 34%). Mp 226 °C
(dec.). Anal. Calcd for C30H45Al3Bi2: C, 39.83; H, 5.01. Found: C,
39.40; H, 4.98%. 1H NMR (C6D6, 300 MHz): δ 2.06 (s, 45 H,
C5(CH3)5). 13C NMR (C6D6, 75.5 MHz): δ 116.5 (C5Me5), 13.4
(C5Me5). IR (neat): ν 2904, 2849, 1425, 1370, 800, 591, 432 cm−1.
products) resulting from the reaction of equimolar amounts
of L1Ga and E2Ph4 in toluene-d8 at room temperature are 1:11
(1) and 1:2 (2) (Table S1). Upon cooling, the resonances due
to 1 and 2 increase and the equilibrium is completely shifted to
1 at −20 °C, whereas 2 shows a maximum intensity at −80 °C
1
with a molar ratio of 1:3 (L1Ga vs 2). H NMR spectra of
isolated crystals of 1 and 2 show broad resonances at room
temperature, but the signals became sharper and well-resolved
at lower temperatures. For instances, the 1H NMR spectra of 1
in C6D6 at 8 °C and 2 in toluene-d8 at −20 °C exhibit single
resonances for the γ-CH (1, 4.96; 2, 4.90 ppm) and two
methyl groups (1, 1.60; 2, 1.59 ppm) of the C3N2Ga ring. The
methyl protons of the isopropyl substituents appear as four
doublets (1, 0.76, 0.80, 1.13, 1.63; 2, 0.68, 0.76, 1.10, 1.54
ppm), and the methine proton appears as two septets (1, 3.49,
3.87; 2, 3.30, 3.76 ppm). The aryl protons show several
multiplets between 6.80 and 8.22 ppm, including those of the
−EPh2 groups. The 13C{1H} NMR spectrum of 1 at room
temperature shows sharp single resonances for the γ-CH (99.0
ppm), two C3N2Ga ring carbon atoms (170.3 ppm), the C3N2
methyl groups (24.3 ppm), broad resonances for the methine
(35.0, 29.7 ppm), and methyl carbon atoms of the isopropyl
RESULTS AND DISCUSSION
■
Equimolar amounts of L1Ga and E2Ph4 (E = Sb, Bi) react with
insertion of L1Ga into the E−E bond and formation of
L1Ga(EPh2)2 (E = Sb 1; Bi 2). 1 and 2 form reversible,
temperature-dependent reaction equilibria with the starting
reagents as was previously observed for the analogous Et-
substituted derivatives L1Ga(EEt2)2 (Scheme 1).15 The same is
groups (28.6, 27.2, 25.9, 25.5, and 25.2 ppm), whereas the 13
C
NMR spectrum of 2 is complicated due to presence of a
mixture of L1Ga, Bi2Ph4, and 2.
In order to investigate the role of the organic substituent of
the gallanediyl on the formation and the nature of the
equilibrium in solution, the guanidinate-substituted gallanediyl
L2Ga21 was chosen. The Ga(I) center within the four-
membered metallacycle of L2Ga is sterically less shielded by
the N-substituents than in the five-membered metallacycles
[Ga{N(R)CH}2]− (R = t-Bu, 2,6-iPr2C6H3)25 and the six-
membered metallacycle of L1Ga. This is indicated by the
smaller endocyclic N−Ga−N bond angles, which steadily
increase with increasing ring size (L2Ga, 63.77(7)°;21 [Ga{N-
(R)CH}2]−: R = tBu, 81.8(3)°; 2,6-iPr2C6H3, 83.02(11)°;25
L1Ga, 87.53(5)°).4e Therefore, the Ga(I) center in L2Ga is
expected to interact differently with dipentelanes E2R4 than
L1Ga.
Scheme 1. Synthesis of 1−6 by Insertion Reaction of L1,2Ga
with E2R4 (E = Sb, Bi; R = Et, Ph)
observed when isolated samples of 1 and 2 are dissolved in
In situ 1H NMR spectra of the reaction of equimolar
amounts of L2Ga with E2R4 (E = Sb, Bi; R = Ph, Et) in
1
nonpolar solvents as was shown by H NMR spectroscopy
(Figure 1). The equilibria (starting reagents vs reaction
1
Figure 1. Variable-temperature H{13C} NMR spectra of 1 (a) and 2 (b). Only γ-CH and −CH(CH3)2 signals are shown.
C
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toluene-d8 show the formation of the expected insertion
compounds, L2Ga(ER2)2 (R = Ph: Sb 3, Bi 4; Et: Sb 5, Bi 6),
which form equilibria with the starting reagents. Comparing
the relative ratios of the −CHMe2 resonances addressed to
L1,2Ga and L1,2Ga(ER2)2 (E = Sb, Bi), it becomes clear that the
concentrations of 3−6 in the equilibrium at ambient
temperature are significantly lower than those observed for 1
and 2 as well as previously reported for L1Ga(EEt2)2 (Table
S1).15 However, pure 3 and 5 were isolated from saturated
solutions in n-hexane upon storage at 8 °C. Crystals of 5 were
obtained from a solution of L2Ga and Sb2Et4 in a molar ratio of
1:2, which was applied to shift the equilibrium toward the
1
formation of 5. The H NMR spectra of isolated samples of 3
and 5 show characteristic septets for the −CHMe2 groups at
3.99 and 3.90 ppm, while resonances of the cyclohexyl and
−CH Me2 groups form overlapping multiplets. The 13C{1H}
NMR spectra of 3 and 5 show distinct singlets for the CN3 (3,
162.2 ppm; 5, 160.9 ppm) and cyclohexyl-HCN carbon atoms
(3, 59.0 ppm; 5, 58.8 ppm). A tentative assignment of the
resonances as well as overlayered spectra of 3 and 5 along with
starting reagents is given in the Experimental Section.
Figure 2. van’t Hoff plot of the equilibrium reaction of 1 with L1Ga
and Sb2Ph4.
All attempts to isolate pure L2Ga(BiR2)2 (Ph, 4; Et, 6) from
the reaction mixtures through fractional crystallization failed.
L2Ga and Bi2Ph4 started to crystallize from solutions in n-
hexane and toluene upon cooling below −30 °C. We therefore
Single crystals of 1, 2, and 5 suitable for X-ray diffraction
analyses were grown within 1 day from saturated solutions of
1, 2, and 5 in n-hexane upon storage at ambient temperature
(1, 2) and at 8 °C (5), respectively. 1 and 2 crystallize in the
1
performed variable-temperature (VT) H NMR studies with
̅
triclinic space group P1. 2 includes a highly disordered n-
1:1 molar mixtures of L2Ga and Bi2R4 (R = Ph 4, Et 6). While
the molar ratios of L2Ga to 4/6 in toluene-d8 at ambient
temperature are 6:1 and 2.6:1, respectively, the relative
concentration of 6 in the reaction mixtures was found to
increase upon cooling. The highest molar ratios of L2Ga to 6 of
1:1.6 was observed at −20 °C. The equilibrium ratio remains
constant below −20 °C for 6 and no considerable variation is
seen at lower temperatures for L2Ga(BiPh2)2 4.
hexane solvent molecule, whose electron density was excluded
from the refinement by SQUEEZE (see the Supporting
Information). The full crystal data were as follows: 1:
[C56H64GaN2Sb2], M = 1078.33, yellow crystal, (0.150 ×
0.120 × 0.015 mm3); triclinic, space group P1
̅
; a = 11.5155(8)
Å, b = 12.6896(8) Å, c = 19.0438(11) Å; α = 79.327(5)°, β =
80.734(5)°, γ = 67.987(5)°, V = 2522.5(3) Å3; Z = 2; μ =
1.630 mm−1; ρcalc = 1.420 g·cm−3; 18 888 reflections (θmax
=
To further support the above interpretations, the formation
25.000°), 8783 unique (Rint = 0.0713); 539 parameters; largest
1
of L1,2Ga and E2Ph4 from 1−3 were studied by H NMR
max./min. in the final difference Fourier synthesis 2.263 e·Å−3/
−1.138 e·Å−3; max./min. transmission 0.947/0.808; R1
=
spectroscopy (eq 1). Equilibrium constants (Keq) were
determined by measuring the concentrations of 1−3, L1,2Ga,
and E2Ph4 in the temperature range between 293 and 353 K (
Table S2) and the thermodynamic parameters (ΔH, ΔS, and
ΔG) were extracted from van’t Hoff plots (Table 1, Figures 2,
0.0838 (I > 2σ(I)), wR2 = 0.1461 (all data). 2:
[C59H75Bi2GaN2], M = 1299.89, colorless crystal, (0.159 ×
0.133 × 0.119 mm3); triclinic, space group P1
̅
; a = 11.421(2)
Å, b = 12.599(2) Å, c = 18.841(3) Å; α = 80.002(8)°, β =
81.030(9)°, γ = 68.224(7)°, V = 2466.9(7) Å3; Z = 2; μ =
7.699 mm−1; ρcalc = 1.750 g·cm−3; 99 724 reflections (θmax
=
Table 1. ΔH, ΔS, and ΔG Values (298 K) from van’t Hoff
a
Plots of the Equilibrium Reactions of 1−3
33.571°), 18 970 unique (Rint = 0.0336); 533 parameters;
largest max./min. in the final difference Fourier synthesis 1.251
e·Å−3/−1.159 e·Å−3; max./min. transmission 0.75/0.51; R1 =
0.0197 (I > 2σ(I)), wR2 = 0.0440 (all data). 5:
[C45H76GaN3Sb2], M = 972.30, pale yellow crystal, (0.230 ×
compounds
ΔH (kJ mol−1
)
ΔS (J K−1 mol−1
)
ΔG (kJ mol−1
)
1
2
3
75.9
66.2
55.5
189.9
181.8
150.9
19.2
12
10.5
0.170 × 0.092 mm3); triclinic, space group P1
̅
; a = 9.8989(12)
a
Uncertainties associated with the proton signal integrations and
Å, b = 11.6851(13) Å, c = 20.310(2) Å; α = 85.025(6)°, β =
temperature variations during the H{13C} NMR measurements are
1
85.115(6)°, γ = 75.497(6)°, V = 2260.9(5) Å3; Z = 2; μ =
not shown.
1.810 mm−1; ρcalc = 1.428 g·cm−3; 105 882 reflections (θmax
=
33.251°), 16 357 unique (Rint = 0.0746); 482 parameters;
largest max./min. in the final difference Fourier synthesis 2.951
e·Å−3/−3.505 e·Å−3; max./min. transmission 0.75/0.51; R1 =
0.0814 (I > 2σ(I)), wR2 = 0.1958 (all data). 8: [C30H45Al3Bi2],
M = 904.56, dark red crystal, (0.430 × 0.380 × 0.350 mm3);
hexagonal, space group P63; a = 11.1596(8) Å, b = 11.1596(8)
Å, c = 14.7597(11) Å; α = 90°, β = 90°, γ = 120°, V =
1591.9(3) Å3; Z = 2; μ = 11.139 mm−1; ρcalc = 1.887 g·cm−3;
10 555 reflexes (θmax = 25.242°), 3704 unique (Rint = 0.0805);
84 parameters; Flack parameter x = 0.57(4); largest max./min.
in the final difference Fourier synthesis 3.467 e·Å−3/−2.184 e·
S28, and S29). At lower temperatures 3 has larger Keq values
than those of 1 and 2, suggesting a favorable formation of L2Ga
and Sb2Ph4 from 3. Furthermore, the dissociation enthalpy
(ΔH) is smaller for 3 than those of 1 and 2. ΔG values suggest
that the formation of L 1,2Ga and E2Ph4 from 1−3 are
endergonic processes.
Formation of L1,2Ga and E2Ph4 from L1,2Ga(EPh2)2:
1,2
1,2
L Ga(EPh2)2 F L Ga + E2Ph4
(1)
D
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Inorganic Chemistry
Article
Å−3; max./min. transmission 0.0392/0.1045; R1 = 0.0459 (I >
2σ(I)), wR2 = 0.1328 (all data).
membered NCNGa ring (rms deviation from best plane =
0.0158 Å; Figure 5). The Ga atom in 1, 2, and 5 each adopt a
The structures of 1 and 2 (Figures 3 and 4) are comparable
to those of the Et-substituted derivatives L1Ga(EEt2)2.15 The
Figure 5. Solid-state structure of L2Ga(SbEt2)2 (5). H atoms and
disordered atoms have been omitted for clarity and thermal ellipsoids
are shown with 50% probability level. Selected bond lengths [Å] and
angles [°]: Sb1−Ga1−N1 2.6420(9), Sb2−Ga1 2.6534(8), Ga1−N2
2.006(5), Ga1 N1 2.030(5), N2−Ga1−N1 65.7(2), N2−Ga1−Sb1
113.00(15), N1−Ga1−Sb1 105.11(15), N2−Ga1−Sb2 114.67(15),
N1−Ga1−Sb2 116.05(15), Sb1−Ga1−Sb2 126.21(3).
Figure 3. Solid-state structure of L1Ga(SbPh2)2 (1). H atoms have
been omitted for clarity and thermal ellipsoids are shown with 50%
probability level. Selected bond lengths [Å] and angles [°]: Sb1−Ga1
2.8458(13), Sb2−Ga1 2.6469(11), Ga1−N1 1.993(6), Ga1−N2
2.030(6), N1−Ga1−N2 94.3(2), N1−Ga1−Sb2 109.53(19), N2−
Ga1−Sb2 108.56(17), N1−Ga1−Sb1 107.9(2), N2−Ga1−Sb1
96.32(18), Sb2−Ga1−Sb1 132.71(4).
distorted tetrahedral coordination geometry, whereas the Sb
and Bi metal atoms show pyramidal coordination spheres. The
bite angles of the chelating β-diketiminate ligand L1 in 1
(94.3(2)°) and 2 (94.06(6)°) are considerable larger
compared to that of the guanidinate ligand L2 in 5
(65.7(2)°). The two independent Ga−N distances in 1, 2,
and 5 are virtually identical (1.993(6) and 2.030(6) Å in 1;
1.9955(14) and 2.0312(14) Å in 2; 2.006(5) and 2.030(5) Å
in 5), whereas the two Ga−Sb bond lengths in 1 vary
significantly (2.6469(11) and 2.8458(13) Å 1) and in 2 and 5
vary slightly (2.7310(5) and 2.8036(5) Å in 2; 2.6420(9) and
2.6534(8) Å in 5). The Ga−E bonds in 1 and 2 are elongated
compared to those observed in L1Ga(EEt2)2 (2.6246(3) and
2.6743(5) Å Sb; 2.6961(6) and 2.7303(10) Å Bi),15 but
comparable to the sum of the respective covalent radii (Ga
1.24 Å; Sb 1.40 Å; Bi 1.51 Å)26 and to those reported for
monomeric compounds (dmap)Ga(R2)ER′2 (E = Sb, Bi; R =
alkyl, R′ = alkyl, SiMe3; dmap = 4-dimethylamino pyridine)27
as well as for four- and six-membered heterocyclic compounds
[R2GaE(SiMe3)2]x (E = Sb, 2.65−2.76 Å; E = Bi, 2.74−2.78
Å).27 In contrast, Lewis acid−base adducts R3Ga−ER′3 such as
tBu3GaSbR3 (R = Et, 2.8479(5) Å; iPr, 2.9618(2) Å),27
tBu3GaBiiPr3 (3.135(1) Å),)28 (Et4Bi2)(GatBu3)2 (3.099(2)
and 3.114(2) Å),29 and Et3GaBi(SiMe3)3 (2.966(1) Å)28 show
significantly elongated Ga−E bond lengths. The E−Ga−E
angles of 132.71(4)° (1), 134.76(10)° (2), and 126.21(3)° (5)
are significantly larger than those observed in LGa(EEt2)2 (Sb,
119.155(17)°; Bi, 119.89(7)°).15
Figure 4. Solid-state structure of L1Ga(BiPh2)2 (2). H atoms have
been omitted for clarity and thermal ellipsoids are shown with 50%
probability level. Selected bond lengths [Å] and angles [°]: Ga1−Bi1
2.7310(5), Ga1−Bi2 2.8036(5), Ga1−N2 1.9955(14), Ga1−N1
2.0312(14), N2−Ga1−N1 94.06(6), N2−Ga1−Bi1 108.93(4), N1−
Ga1−Bi1 107.50(4), N2−Ga1−Bi2 107.36(4), N1−Ga1−Bi2
95.86(4), Bi1−Ga1−Bi2 134.756(10).
Reactivity Studies with Cp*M (M = Al, Ga). To further
investigate the specific influence of the organic ligand of the
group 13 diyl, we became interested in the analogous reactions
of Cp*-substituted alanediyl [Cp*Al]4 and gallanediyl Cp*Ga
(Scheme 2). The reactivity of [Cp*Al]4 and Cp*Ga toward
E2R4 (E = Sb, Bi; R = Et, Ph) significantly differs from that
Ga atom in the C3N2Ga heterocycles in 1 and 2 is out of plane
(deviation from best plane of the ligand backbone 0.885(9) Å
1, 0.9074(17) Å 2), whereas 5 has an almost planar four-
E
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Inorganic Chemistry
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Scheme 2. Reactions of Cp*Ga and [Cp*Al]4 with E2R4 (E = Sb, Bi; R = Et, Ph) and Formation of (Cp*Al)3M2 (E = Sb 7, Bi 8)
observed for L1,2M (M = Al, Ga).15 [Cp*Al]4 was found to
slowly react with Sb2R4 (R = Et, Ph) at room temperature with
formation of (Cp*Al)3Sb2 (7) within 3 days. The reaction is
faster at elevated temperatures and (Cp*Al)3Sb2 7 is
quantitatively formed at 80 °C within 1 day. The reaction
mechanism of 1:4 molar amounts of [Cp*Al]4 and Sb2R4 was
studied by in situ 1H NMR studies. According to these studies,
the formation of Cp*Al(SbR2)2 as reaction intermediate via
insertion of Cp*Al into the Sb−Sb bond can be excluded. 7
and the analogous arsenic derivative (Cp*Al)3As2 were
previously obtained in reactions of [Cp*Al]4 with cyclo-
tetraarsine and -stibine (tBuE)4 (E = As, Sb). The reaction of
[Cp*Al]4 and (tBuSb)4 was reported to proceed with
formation of tBu3Sb.30 A similar germyl-bridged
[(C6F5)2Ge]3Bi2 was prepared from the reaction of
(C6F5)2GeH2 with Et3Bi, which proceeded with the elimi-
nation of ethane.31 The reaction of [Cp*Al]4 with Bi2Et4 in
toluene also required high reaction temperatures (>80 °C) and
resulted in the formation of (Cp*Al)3Bi2 (8) in low yield. In
Problems with disorder made the choice of the space group
ambiguous. The best model was found to have space group
P63.
The Cp*Al unit is disordered over two positions by pseudo-
2-fold symmetry, and the major component comprises about
70%. Owing to this disorder, the structural parameters of 8 are
of only limited reliability or insignificant for the vast use of
restraints and constraints. The molecular structure of 8 shows
an Al3Bi2 framework adopting a trigonal-bipyramidal structure.
The two apical Bi atoms are bridged by three Cp*Al moieties
and the Al atoms adopt equatorial positions (Figure 6). The Bi
1
situ H NMR spectroscopy proved that the formation of 8
occurred after disproportionation of Bi2Et4 into Bi metal and
BiEt3, which started at 55 °C, followed by the reaction of
[Cp*Al]4 with BiEt3, which occurred with Bi−C bond
activation and subsequent formation of 8. 8 was also obtained
in moderate yield in an independent study in the reaction of
BiEt3 with [Cp*Al]4 in toluene at 120 °C. In contrast, the
reactions of Cp*Ga and [Cp*Al]4 with Bi2Ph4 proceeded
already at ambient temperature with formation of metallic
bismuth. Although Cp*Ga did not react with Sb2R4 (R = Et,
Ph) and Bi2Et4 at room temperature, it reacted under drastic
conditions (120 °C, 3 days) with formation of metallic
antimony and bismuth, respectively, as was proven by
elemental dispersive X-ray analysis (EDX).
Figure 6. Solid-state structure of (Cp*Al)3Bi2 (8). H atoms and
disordered Cp*Al units have been omitted for clarity and thermal
ellipsoids (C isotropic) are shown with 50% probability level. Parts
depicted in pale colors are generated via 3-fold rotational symmetry.
7 and 8 are air- and moisture-sensitive solids, which are
moderately soluble in benzene, toluene, and fluorobenzene.
The H NMR spectra of 7 and 8 in benzene-d6 are almost
and Al atoms adopt distorted pyramidal and tetrahedral
coordination geometries, respectively. The Bi−Al bond lengths
range from 2.692(13) to 2.867(13) Å, which is close to the
sum of the covalent single bond radii (Al, 1.26 Å; Bi, 1.51 Å).26
Furthermore, the Al−Bi−Al (63.3(4)−68.0(4)°) and Bi−Al−
Bi (102.50(12) and 102.5(3)°) bond angles differ significantly
from the ideal values of a regular trigonal-bipyramidal structure
(90 and 109.5°). The Cp* ligand in 8 likely adopts a η5
coordination mode.
Quantum Chemical Calculations. To investigate the
electronic nature and bonding situation of (Cp*Al)3Bi2 8 and
to compare this with analogous compounds containing the
lighter group 15 elements, DFT calculations on (Cp*Al)3E2 (E
1
identical and show a sharp singlet at 2.06 ppm (7) and 2.08
ppm (8) for the Cp*, whereas the 13C NMR spectra consist of
two singlets (12.0 ppm, 116.1 ppm, 7; 13.4 ppm, 116.5 ppm,
8) for the methyl and cyclopentadienyl carbon atoms. The
molecular structure of 8 was further determined by single-
crystal X-ray diffraction analysis. The structure of 7 could not
be solved but according to its unit cell dimensions, we suggest
it is isostructural to 8.
Single crystals of 8 suitable for X-ray diffraction analysis
were grown from saturated benzene solutions at room
temperature. 8 crystallizes in the hexagonal crystal system.
F
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Inorganic Chemistry
Article
Figure 7. HOMO and LUMO of P′ and Bi′.
= P P′, As As′, Sb Sb′, Bi Bi′) were performed. All quantum
chemical calculations were employed with the ORCA quantum
chemistry package (version 4.0).32 Ground-state geometry
optimizations were calculated with the composite approach
PBEh-3c,33 utilizing the geometrical counterpoise correction
(gCP)34 and the atom-pairwise dispersion correction with
Becke-Johnson damping scheme (D3BJ).35 The RIJK approx-
imation was employed to accelerate the calculations in
conjunction with the appropriate auxiliary basis sets (def2-
SVP/JK).36 Additionally, effective core potentials (ECP) were
employed for the Sb and Bi atoms.37,38 Natural bond orbital
analysis was performed using the NBO 6.0 program.39
The calculated bond lengths (Al−Bi Å) and angles (av.
Al−Bi 2.759(1) Å) and angles (av. Al−Bi−Al 66.6(1)°, av.
Bi−Al−Bi 101.3(1)°) of Bi′ agree very well with the
experimental values of 8 and deviate only by 0.8% (bond
lengths) and 1.5% (bond angles), respectively. The DFT
calculations on P′−Bi′ reveal covalent bonds between Al and
the pnictogen atoms with Mayer bond orders (MBOs) of
0.81−0.85. On the basis of NBO analysis, the Al−E bonding
orbitals show constant p-character of 59% on the Al atom and
an increasing p-character of 82% (P), 84% (As), 87% (Sb), and
90% (Bi) on the pnictogen. As a result, s-character of the
electron lone-pair of the group 15 element E steadily increases
with increasing atomic number of the pnictogen: 47% (P),
54% (As), 63% (Sb), and 72% (Bi).
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01489.
1H and 13C NMR and IR spectra of 1−8 as well as
crystallographic details and quantum chemical calcu-
lations (PDF)
Accession Codes
CCDC 1843322−1843324 and 1846071 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Author
*Fax: +(0)201-1833830. Phone: +(0)201-1833830. E-mail:
stephan.schulz@uni-due.de.
ORCID
Stephan Schulz: 0000-0003-2896-4488
Funding
The atomic charges and Al−E bond polarities steadily
decrease from P′ (Al: 1.3 e, P: −1.0 e, pol.: 26−74%), As′ (Al:
1.2 e, As: −0.9 e, pol.: 29−71%), Sb′ (Al: 1.0 e, Sb: −0.6 e,
pol.: 35−65%), to Bi′ (Al: 1.2 e, As: −0.9 e, pol.: 29−71%) due
to the decreasing difference in electronegativity between Al
and the respective pnictogen atom.
This research was funded by the German Research Foundation
(DFG, project title SCHU 1069/22−1) and the IMPRS
RECHARGE (MPI CEC).
Notes
The authors declare no competing financial interest.
In the case of P′, As′, and Sb′, the HOMO is a
representation of the p-orbitals on the pnictogen atom, facing
the Al3-plane with small contributions from the Cp* π-systems
(Figure 7). In Bi′, the order of orbitals is switched, so a
different set of p-orbitals represents the HOMO, facing one
Cp* ligand, with a stronger contribution from the Cp* π-
systems. The LUMO is expanded over the whole molecule in
all cases.
ACKNOWLEDGMENTS
■
S.S. gratefully acknowledges financial support by the German
Research Foundation (DFG, project SCHU 1069/22-1), and
L.J. is thankful to the International Max-Planck Research
School on Reactive Structure Analysis for Chemical Reactions
(IMPRS-RECHARGE).
DEDICATION
■
CONCLUSIONS
■
Dedicated to Prof. Peter Jutzi on the occasion of his 80th
birthday.
In summary, gallanediyls containing β-diketiminate (L1) and
guanidinate (L2) ligands reversibly react with E2R4 (E = Sb, Bi;
R = Ph, Et) with insertion into the E−E bond and formation of
L1,2Ga(ER2)2. The position of the reaction equilibrium is
significantly affected by the organic substituents (L1,2, Et, Ph),
the E−E bond strengths as well as the molar ratio of the
starting reagents. In contrast, [Cp*Al]4 reacts with Sb2R4 (R =
Ph, Et) and Bi2Et4 with formation of (Cp*Al)3E2 (E = Sb, 7;
Bi, 8). Analogous reactions of Cp*Ga and E2R4 only yielded
metallic antimony and bismuth.
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