Interaction of Multiple Bonds with NacNacGa: Oxidative Cleavage vs Coupling and Cyclization

Article abstract of DOI:10.1021/acs.inorgchem.9b01005

The reactivity of the gallium(I) compound NacNacGa (4) to a variety of unsaturated compounds has been studied. Whereas 4 proved surprisingly unreactive toward olefins, ketones, guanidines, and thioureas, it reacts with isocyanates and carbodiimides to fur

Full text of DOI:10.1021/acs.inorgchem.9b01005

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Interaction of Multiple Bonds with NacNacGa: Oxidative Cleavage vs
Coupling and Cyclization
Aishabibi Kassymbek,† James F. Britten,‡ Denis Spasyuk,§ Bulat Gabidullin,# and Georgii I. Nikonov*,†
†Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada
‡Department of Chemistry, McMaster University, Hamilton, Ontario, 1280 Main Street West, Hamilton, Ontario L8S 4M1, Canada
§SM and MX Crystallography, Canadian Light Source Inc., 44 Innovation Boulevard, Saskatoon, Saskatchewan S7N 2 V3, Canada
#X-ray Core Facility, Faculty of Science, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario K1N 6N5, Canada
S
* Supporting Information
ABSTRACT: The reactivity of the gallium(I) compound
NacNacGa (4) to a variety of unsaturated compounds has
been studied. Whereas 4 proved surprisingly unreactive toward
olefins, ketones, guanidines, and thioureas, it reacts with
isocyanates and carbodiimides to furnish the products of
coupling of two heterocumulenes. With isothiocyanate, the
CS cleavage occurs, leading to the dimer (NacNacGa)2(μ-S)(μ-CNPh) and the cyclization product NacNacGa(S2CNPh).
These compounds were characterized by multinuclear NMR spectroscopy and X-ray crystal structure analyses. Oxidative
addition of SPPh3 occurs at elevated temperatures and results in the known dimer [NacNacGa(μ-S)]2.
sulfides to give terminal aluminum sulfide derivatives, such as 3
in Scheme 1,17 and also oxidatively adds the CN bond of
INTRODUCTION
■
Oxidative cleavage of σ bonds on reduced main group centers1
has received significant attention in the context of developing
main group analogues of the common catalysts based on
transition metal complexes.2 Much less is known about the
reactivity of main group compounds toward multiple bonds,
although examples of coordination, cyclization, and oxidative
cleavage have been documented.3 In particular, the groups of
Power and Baceiredo demonstrated reversible addition of
ethylene to distannyne,4 silylene,5,6 and stannylene.7 Rieger et
al. further documented the instance of ethylene coordination
to silylene and insertion into the silyl−silylene bond, as well as
butadiene cyclization with a silylamidosilylene.8 The groups of
Roesky and Driess reported that alkynes form π-complexes
with the Al(I) compound NacNacAl (1, NacNac = [ArNC-
(Me)CHC(Me)NAr]− and Ar = 2,6-iPr2C6H3)9 and with
silylene NacNac′Si (2, NacNac′ = [ArNC(Me)CHC(
CH2)NAr]2−).10 Likewise, compound 1 has been recently
shown to reversibly coordinate norbornene.11 On the other
hand, cyclization products were observed in reactions of 1 and
2 with azides.12 Related addition and cyclization reactions of
diimine supported digallene and dialumene compounds with
olefins and alkynes have been described by the groups of
Fedushkin13 and Yang.14 Power et al. reported reactions of
monomeric Ar*Ga (Ar* = C6H3-2,6-(C6H2-2,4,6-iPr3)2) and
dimeric Ga(I) species Ar′GaGaAr′ (Ar′ = C6H3-2,6-(C6H3-
2,6-iPr2)2) with two alkene molecules resulting in cyclization
into digalocycles.15 Reactions of digallene with azides and
diimines leading to monomeric and dimeric gallium imides and
[2 + 2] addition products also were described.16
Scheme 1. Reactivity of 1 toward Unsaturated Bonds
guanidine.18 The cleavage of the OP bond of phosphine
oxides was accomplished as well and was accompanied by
deprotonation of a Me group of the NacNac backbone to give
an aluminum hydroxyl compound.19 In contrast, a reaction of
1 with urea resulted in isomerization to the urea-complexed
hydride NacNac′Al(H)(OC(NMeCH2)2) having the OC
bond intact. How this reactivity pattern changes down group
13 remains to be unveiled. For example, the propensity of
NacNacGa (4) to cleave single bonds is well documented,20
We have previously shown that compound 1 cleaves the
CS bond of thioureas and the PS bond of phosphine
Received: April 8, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.9b01005
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Inorganic Chemistry
Article
whereas its reactivity toward multiple bonds has been probed
only in reactions with azides.21 Here we disclose our efforts to
study this problem.
to the bond with oxygen, in agreement with the relative
electronegativity of these two groups.
Unexpectedly, there was no reaction between 4 and
diphenylketone, which also stands in contrast to the easy
addition of this ketone to the silylene 2.23 This difference in
reactivity between 2 and 4 likely stems from the greater
stabilization of the lone pair of gallium vs the lone pair of
silicon, which results in a larger singlet-to-triplet gap in 4.24
We then looked at the possibility of multiple bond cleavage
at gallium. Oxidative addition of a multiple bond XY to a
group 13 NacNac compound NacNacM is possible if one of
the partners, X or Y, is stable in the subvalent state. The
possible candidates are, therefore, CO2, CS2, isocyanates,
isothiocyanates, and diimines, to name just some.
RESULTS AND DISCUSSION
■
Unlike the aluminum congener 1,11 the gallium compound 4
does not show any sign of olefin coordination in reactions with
cyclohexene and ethylene, even at low temperature (−20 °C).
Neither is there a [1 + 4] cycloaddition with butadiene, which
is in contrast to the reactivity of the isolobal silylene 2.22 On
the other hand, the α,β-unsaturated aldehyde, methacrolein,
easily cyclizes with 4 to give the gallium enolate 5 (Scheme 2).
Scheme 2. Reactions of 4 with Methacrolein
Unlike the reactions of the aluminum analogue 1 shown in
Scheme 1, compound 4 does not react with cyclic urea,
thiourea, guanidine, and phosphine oxides (Ph3PO and
Et3PO). Neither was there any cleavage of the PS bond of
Et3PS, even upon heating to 80 °C. With Ph3PS, however,
a slow reaction (2 days) happens upon heating to 80 °C to
furnish the known sulfide (NacNacGa-S)2 (6 in Scheme 3).25
The identity of this product was established by NMR
spectroscopy and confirmed by X-ray analysis (Figure 1). In
Scheme 3. Reactions of 4 with Phosphine Sulfides
Nevertheless, 4 readily reacts with 2 equiv of isothiocyanate
PhNCS to give the product of CS cleavage and cyclization 7
and the dimer (NacNacGa)2(μ-S)(μ-CNPh) (8) in the ratio
5:1 (Scheme 4). Dropwise addition of only 1 equiv of this
reagent to a toluene solution of 4 produced a mixture
containing products 7 and 8 in the ratio 1:1. The reaction
likely proceeds via intermediate formation of the sulfide
cyanide complex (NacNacGa)(S)(CNPh) that either reacts
with another equivalent of PhNCS to give 7 or is intercepted
by the starting complex 4 to furnish 8. The first reaction is thus
analogous to the reaction of aluminum compound 3 with
isothiocyanate to give NacNacAl(κ2-S2CNPh) (9).17
Figure 1. Molecular structure of 5 (thermal ellipsoids are shown at
30%; hydrogen atoms, except those on C32 and C30, are omitted for
clarity). Selected bond lengths (Å) and angles (deg): Ga(1)−N(1)
1.942(3), Ga(1)−N(2) 1.943(3), Ga(1)−O(1) 1.884(2), Ga(1)−
C(30) 1.979(3), C(31)−C(32) 1.339(5), C(30)−C(31) 1.516(5);
N(1)−Ga(1)−N(2) 96.3(1), O(1)−Ga(1)−C(30) 93.0(1), Ga(1)−
O(1)−C(32) 105.4(2), Ga(1)−C(30)−C(31) 100.3(2).
1
In the H NMR spectrum, compound 7 gives rise to a Cs
symmetric pattern featuring the backbone signals at 4.79 and
1.51 ppm, two septets (at 3.17 and 3.10 ppm) for the methine
i
particular, the olefinic proton gives rise to a resonance at 6.88
ppm and the backbone methine of NacNac is seen at 4.86
ppm. The methyl signal of the enolate part was observed at
1.45 ppm. X-ray study revealed a spiro structure formed as a
result of [1 + 4] cycloaddition. The Ga−O bond of 1.884(2) Å
and the Ga−C bond of 1.979(3) Å are normal for the
respective single bonds. The C(31)−C(30) distance, corre-
sponding to the CC bond in the parent methacrolein, is
elongated to 1.516 (5) Å, whereas the C(31)−C(32) distance
is contracted to 1.339 (5) Å, indicating the formation of an
enolate moiety. Interestingly, the spiro structure is distorted in
such away that the C(30)−Ga(1)−N(1)−N(2) fragment is
close to planarity (the sum of bond angles around Ga of
345.37°), whereas the oxygen atom forms rather acute angles
with the GaN2 fragment, 109.7(1)° and 107.7(1)°. The
C(32)−Ga(1)−O(1) angle is almost right, 93.0(1)°. This
feature indicates that a significant s character of Ga is spent on
the bond to the carbon atom, whereas more p-character goes
part of Pr groups, and four doublets for their methyl groups.
Crystals suitable for X-ray diffraction analysis were grown from
a 1:2 mixture of toluene and hexanes, and the molecular
structure is shown in Figure 2. The gallium atom has a
distorted tetrahedral environment comprised of the chelating
NacNac ligand and the κ2(S,S)-coordinated dithioazacarbon-
ate. The Ga−S bonds have slightly differing distances
2.2639(7) and 2.2561(7) Å and are comparable to the Ga−S
distances (2.2511(7) and 2.2736(7) Å) in the sulfide dimer 6
produced from the reaction of 4 with elemental sulfur. The S−
C−S bond angle of 112.5(1)° is significantly wider than angles
at sulfur (82.54(9)°) or gallium (81.78(3)°) making the
GaS2C ring kite-shaped. Similar metrics, e.g., the S−C−S bond
angle of 112.21(14)° and the S−Al−S bond angle of
82.91(4)°, were found in the aluminum congener 9.
The chemistry of Scheme 3 is reminiscent of the CS bond
cleavage and cyclization observed by Jutzi et al. in the reaction
of silylene Cp*2Si with MeNCS to give Cp*2Si(S2CNMe),26
B
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Scheme 4. Cleavage of the SC Bonds of Isothiocyanate by 4
Figure 3. Molecular structure of 8 (thermal ellipsoids for the core
elements are shown at 30%; hydrogen atoms are omitted for clarity).
Selected bond lengths (Å) and angles (deg): Ga1−N2 1.9988(18),
Ga1−N3 1.9890(19), Ga2−N4 2.0225(18), Ga2−N5 2.0099(19),
Ga1−C1 2.045(2), Ga2−C1 2.086(2), Ga1−S1 2.2844(6), Ga2−S1
2.2648(6), N1−C1 1.276(3), N3−Ga1−N2 93.86(7), N5−Ga2−N4
92.95(8), C1−Ga1−S1 90.73(6), C1−Ga2−S1 90.24(6), Ga2−S1−
Ga1 84.04(2), Ga1−C1−Ga2 94.98(9).
Figure 2. Molecular structure of 7 (thermal ellipsoids are shown at
30%; hydrogen atoms are omitted for clarity). Selected bond lengths
(Å) and angles (deg): Ga(1)−N(1) 1.912(3), Ga(1)−N(2) 1.909(2),
Ga(1)−S(1) 2.2639(7), Ga(1)−S(2) 2.2561(7), S(1)−C(30)
1.787(2), S(2)−C(30) 1.772(2); N(1)−Ga(1)−N(2) 99.28(8),
S(1)−Ga(1)−S(2) 81.78(3), S(1)−C(30)−S(2) 112.5(1), Ga(1)−
S(1)−C(30) 82.54(8), Ga(1)−S(2)−C(30) 83.09(8).
NacNacGa. Red crystals of 8, grown from ether, were manually
isolated from the yellow crystals of 7.
The molecular structure of 8 is shown in Figure 3. The
structure is to a great degree symmetric except that the C(1)
N(1) imine moiety has the bent geometry, so that the N-
bound phenyl group is oriented to Ga(2). Apart from this, the
metrics associated with the bridging atoms as well as the
coordination of NacNac ligands are very similar for both parts
of the dimer. Thus, the Ga−N distances fall in the narrow
range 1.989−2.023(2), albeit the bonds to Ga(2) appear to be
slightly longer, likely in order to accommodate the phenyl
group located in the pocket comprised by two bulky Ar groups
attached to N(4) and N(5). The gallium−sulfide bonds are
very similar at 2.2844(6) and 2.2648(6) Å for Ga(1) and
Ga(2), respectively; as are the gallium−cyanide distances to
the bridging carbon atom, 2.045(2) and 2.086(2) Å,
respectively. The somewhat longer distance from C(1) to
Ga(2) again may reflect the need to accommodate the phenyl
substituent of the bridging isocyanide. The central Ga2SC cycle
is almost planar, with the dihedral of 0.29(6)°. The Ga(1)−
C(1)−Ga(2) bond angle of 94.98(9) is quite acute for a
expected sp2-hybridized carbon, whereas the C(1)−N(1)−
C(2) angle is normal (122.2(2)°) for an imine, as is the N(1)−
C(1) bond length of 1.276(3) Å. On the other had, the
similarly acute bond angle at the sulfur atom, Ga(2)−S(1)−
Ga(1) of 84.04(2)°, is normal for a heavy main group element
and indicative of a high degree of 3p character in the bonds to
gallium atoms. The Ga . . .Ga separation of 3.0452(4) Å is
similar to other known gallium sulfide dimers25,28 and is
significantly larger than the doubled covalent radius of Ga (2 ×
and to the reaction of Kira’s dialkylsilylene, 2,2,5,5-tetrakis-
(trimethylsilyl)-silacyclopentane-1,1-diyl, with isothiocya-
nate.27 These authors suggested initial [2 + 1] cycloaddition
of the CS bond to the silicon center to form a highly
strained three-membered ring. Subsequent extrusion of
isocyanide generates an intermediate silanthione, which then
undergoes cycloaddition reaction with isothiocyanate. In the
course of our of studies, the groups of Fedushkin and Yang
reported on the first instance of the cleavage of the CS bond
of isothiocyanates on a subvalent digallane supported by a
noninnocent diimine ligand.28 It is also noteworthy that the
Ga(II) dimer [(Me3Si)2HC)2Ga−]2 (10) does not react with
isothiocyanates, whereas its aluminum analogue cleaves the
CS bond quite readily.29 Uhl et al. however showed that the
digallane 10 reacts with phosphorus chalcogenides R3PX (X
= S, Se, Te) to give the chalcogen-bridged species
[(Me3Si)2HC)2Ga]2(μ-X).30
The formation of dimeric species 8, having the sulfide and
cyanide bridges (Figure 3), in the reaction mixture of 4 and
SCNPh serves as indirect evidence that the reaction proceeds
via the oxidative addition of the SC bond of isothiocyanate.
Compound 8 then can be considered as the result of a reaction
between the immediate product of CS oxidative addition,
the sulfide NacNacGa(S)(CNPh), and the starting
C
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1.22 Å = 2.44 Å),31 suggesting that there is no interaction
between two gallium centers.
Encouraged by this result, we then studied the possibility of
CO cleavage in isocyanates. (3,5-Me2C6H3)NCO and
PhNCO readily react with 4 giving the coupling products
shown in Scheme 5. The preservation of the CO bond
gallium atom in the bridgehead position. The newly formed
OGaCNC ring is almost planar, with the dihedral angle C(4)−
Ga(1)−O(1)−C(16) being 0.5(2)°. The Ga−O distance of
1.886(2) and Ga−C distance of 1.997(3) are very close to the
respective values in the enolate 5. The OGaC bond angle at
87.4(1)° is considerably smaller than other bond angles within
the OGaCNC cycle.
The regioselectivity of cyclization is such that the CN
bond of one isocyanate adds to the CO bond of another
isocyanate to form a new C−N bond and a cyclic alkoxy alkyl
gallium fragment. While we have no mechanistic data of this
reaction, the reaction may start by coordination of the CO
end of isocyanate to the ambiphilic gallium center,32 acting as a
Lewis acid (Scheme 6). Such a coordination enhances the
nucleophilicity of the gallium-centered lone pair and polarizes
the carbonyl fragment of isocyanate. The regioselectivity of
subsequent [3 + 2] addition of the second molecule of the
substrate is dictated by this polarity and not by the strengths of
Ga-X bonds (i.e., Ga−O + Ga−N vs Ga−O + Ga−C), so that
the more nucleophilic nitrogen atom adds to the first carbonyl
center activated by gallium, whereas the gallium atom adds to
the second carbonyl.
Scheme 5. Addition of Isocyanates to 3
agrees well with its strength (799 kJ/mol) and the lack of C
O oxidative addition in the related aluminum chemistry
(Scheme 1). The xylyl derivative, complex 11, was fully
characterized by multinuclear NMR spectroscopy and X-ray
1
analysis. The H NMR spectrum displays a Cs symmetric
pattern, with two sets of methine signals at 3.44 and 3.22 ppm
i
and four sets of methyl signals for the Pr groups (1.50, 1.36,
1.15, and 1.04 ppm). The molecular structure is shown in
Figure 4, which reveals a bicyclic spiro structure with the
Given the ability of the aluminum compound 1 to cleave the
CN in guanidines but the lack of the corresponding
reactivity for the gallium compound 4, we reckoned that the
more accessible linear carbodiimides RNCNR could be
better candidates for oxidative addition of CN. There has
i
been no reaction between 4 and bulky PrNCNPri or (o-
Tol)NCN(o-Tol), but (p-Tol)NCN(p-Tol) reacted
at room temperature in the course of 5 h to give the coupling
product 13, similar to compound 11 (Scheme 7). The product
Scheme 7. Addition of Carbodiimide (p-Tol)NCN(p-
Tol) to 4
Figure 4. Molecular structure of 11 (thermal ellipsoids for the core
elements are shown at 30%; hydrogen atoms are omitted for clarity).
Selected bond lengths (Å) and angles (deg): Ga(1)−N(1) 1.909(2),
Ga(1)−N(2) 1.899(2), Ga(1)−O(1) 1.886(2), Ga(1)−C(4)
1.997(3); N(1)−Ga(1)−N(2) 99.8(1), O(1)−Ga(1)−C(4)
87.4(1), Ga(1)−O(1)−C(16) 112.8(2), Ga(1)−C(4)−N(3)
104.7(2), O(1)−C(16)−N(3) 115.9(3), C(4)−N(3)−C(16)
119.1(2).
was characterized by NMR and by X-ray diffraction analysis
(Figure 5). As expected, the Ga(1)−N(3) bond of 1.893(2) Å
is slightly longer than the Ga(1)−O(1) distance in 11. The
Ga(1)−C(52) bond is also slightly longer (2.004(2) Å), likely
because of the need to accommodate more sterically
encumbered iminyl-guanidide ligand.
Scheme 6. Possible Mechanism of Addition of Isocyanate to 4
D
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3JH−H = 6.8 Hz), 1.56 (s, 6H, NCCH3), 1.45 (s, 3H, OCHC(CH3)-
3
CH2), 1.43 (d, 6H, CH(CH3)2, JH−H = 6.7 Hz), 1.29 (d, 6H,
3
3
CH(CH3)2, JH−H = 6.8 Hz), 1.16 (d, 6H, CH(CH3)2, JH−H = 6.7
3
Hz), 1.11 (d, 6H, CH(CH3)2, JH−H = 6.8 Hz), 0.66 (s, 2H,
OCHC(CH3)CH2). 13C{1H} NMR (151 MHz, C6D6): δ 169.6
(NCCH3), 148.4 (OCHC(CH3)CH2), 145.7, 142.6, 140.38, 127.8,
125.3, 123.7 (C6H3), 105.5 (OCHC(CH3)CH2), 96.3 (CH), 29.0,
28.1 (CH(CH3)2), 25.8, 24.6, 24.6, 24.2 (CH(CH3)2), 23.4
(NCCH3), 19.4 (OCHC(CH3)CH2), 7.1 (OCHC(CH3)CH2).
Anal. Calcd for C33H47GaN2O: C, 71.10; H, 8.50; N, 5.03. Found:
C, 70.87; H, 8.51; N, 4.93.
Preparation of NacNacGa(S2CNPh) (7). To a solution of phenyl
isothiocyanate (0.046 mL, 0.38 mmol) in toluene was slowly added a
toluene solution of NacNacGa(0.093 g, 0.19 mmol). The reaction was
stirred for 10 min at room temperature. Volatiles were removed under
vacuo. A pale orange solid produced was washed with cold hexanes to
yield 7 (0.114 g, 0.16 mmol, 84%) as light-yellow powder. The
product was recrystallized from a 1:2 mixture of toluene and hexanes
at −30 °C to give light yellow crystals of 7.
1H NMR (600 MHz, C6D6): δ 7.18−7.14 (m, 2H, C6H3), 7.13−
7.08 (m, 4H, C6H3), 6.99 (t, 2H, C6H5, 3JH−H = 7.6 Hz), 6.80 (d, 2H,
Figure 5. Molecular structure of 13 (thermal ellipsoids are shown at
30%; hydrogen atoms are omitted for clarity). Selected bond lengths
(Å) and angles (deg): Ga(1)−N(1) 1.930(2), Ga(1)−N(2) 1.936(2),
Ga(1)−N(3) 1.893(2), Ga(1)−C(52) 2.004(2); N(1)−Ga(1)−N(2)
96.72(7), N(3)−Ga(1)−C(52) 86.81(8), Ga(1)−N(3)−C(37)
114.2(1), Ga(1)−C(52)−N(5) 105.9(1), N(3)−C(37)−N(5)
113.0(2), C(37)−N(5)−C(52) 120.1(2).
3
3
C6H5, JH−H= 7.3 Hz), 6.74 (t, 1H, C6H5, JH−H= 7.3 Hz), 4.79 (s,
3
1H, CH), 3.17 (hept, 2H, CH(CH3)2 JH−H = 6.7 Hz), 3.10 (hept, 2H,
3
CH(CH3)2 JH−H = 6.7 Hz), 1.51 (s, 6H, NCCH3), 1.46 (d, 6H,
3
3
CH(CH3)2, JH−H = 6.7 Hz), 1.36 (d, 6H, CH(CH3)2, JH−H = 6.7
3
Hz), 1.07 (d, 6H, CH(CH3)2, JH−H = 6.7 Hz),1.04 (d, 6H,
3
CH(CH3)2, JH−H = 6.7 Hz). 13C{1H} NMR (151 MHz, C6D6): δ
171.9 (NCCH3), 155.6 (NCS), 144.3, 144.3, 138.7, 128.6, 128.4,
125.0, 125.0 (C6H3), 152.5, 128.7, 123.3, 121.3 (C6H5), 97.1 (CH),
29.3, 29.0 (CH(CH3)2), 25.3, 25.1, 25.0, 25.0 (CH(CH3)2), 23.9
(NCCH3). Anal. Calcd for C36H46GaN3S2·0.6 toluene: C, 68.01; H,
7.21; N, 6,03. Found: C, 67.94; H, 7.15; N, 5.69.
CONCLUSION
■
In comparison to its aluminum analogue 1, the Ga(I)
compound 4 shows much reduced reactivity, which reflects
the greater stabilization of the oxidation state +1 for gallium
relative to aluminum. It does not react with olefins, urea,
thiourea and phosphine oxides, and reacts only sluggishly with
Ph3PS with the P−S bond cleavage. On the other hand, it
easily reacts with a conjugated unsaturated aldehyde to afford
the product of [4 + 1] cycloaddition. 4 also easily affects
oxidative addition of the CS bond of phenyl isothiocyanate
to give the cycloaddition product [NacNacGa(κ2-S2CNPh)]
(7) or the sulfur/isocyanide-bridged dimer 8. Related reactions
with isocyanates and carbodiimides result in [1 + 2+3]
cycloaddition products.
Preparation of (NacNacGa)2(μ-S)(μ-PhNC) (8). A toluene solution
of phenyl isothiocyanate (0.023 mL, 0.19 mmol) was slowly added to
a solution of NacNacGa (0.095 g, 0.19 mmol). The reaction mixture
was stirred for 10 min at room temperature. A 1:1 mixture of
compound 7 and 8 was observed by NMR. The resulting orange
solution was concentrated to the state of a viscous oil, which was then
dissolved in diethyl ether. Red crystals of 8 (0.030 g, 0.025 mmol,
26%) were produced by slow concentration of the solution by
evaporation of solvent in the glovebox and manually separated from
compound 7. 1H NMR (400 MHz, C6D6): δ 7.78 (d, 2H, C6H5,3JH−H
= 8.1 Hz), 7.27 (t, 2H, C6H5, 3JH−H = 8.1 Hz), 7.10 (m, 6H, C6H3 and
C6H5), 7.04 (m, 3H, C6H3), 6.91 (dd, 2H, C6H3, J = 7.8 Hz, J = 1.5
3
Hz), 6.80 (t, 2H, C6H3, JH−H = 4.5 Hz), 4.85 (s, 1H, CH), 4.79 (s,
3
1H, CH), 3.73 (hept, 2H, CH(CH3)2, JH−H = 6.7 Hz), 3.68 (hept,
2H, CH(CH3)2, 3JH−H = 6.8 Hz), 3.22 (hept, 2H, CH(CH3)2, 3JH−H
=
EXPERIMENTAL SECTION
■
3
General Information. All manipulations were performed using
standard inert atmosphere (N2 gas) glovebox and Schlenk techniques.
Toluene, hexanes, and diethyl ether were dried using a Grubbs-type
solvent purification system. d6-Benzene was predried and distilled
from K/Na alloy and stored in a glass vessel in the glovebox. NMR
spectra were obtained with a Bruker AVANCE III HD 400 and 600
MHz spectrometer (1H, 400 and 600 MHz; 13C, 101 and 151 MHz;
31P, 162 MHz) at room temperature, unless stated otherwise, then
processed and analyzed with MestReNova software (v10.0.2−15465).
Elemental analyses were obtained by the analytical laboratories of
Universite de Montreal and University of Toronto. Reagents were
purchased from Sigma-Aldrich. Compound 4 was prepared according
to a literature procedure.33
6.7 Hz), 2.30 (hept, 2H, CH(CH3)2, JH−H = 6.8 Hz), 1.71 (d, 6H,
3
3
CH(CH3)2, JH−H = 6.8 Hz), 1.62 (d, 6H, CH(CH3)2, JH−H = 6.7
Hz) 1.34 (s, 6H, NCCH3), 1.22 (s, 6H, NCCH3), 1.15 (d, 6H,
3
3
CH(CH3)2, JH−H = 6.8 Hz), 1.11 (d, 6H, CH(CH3)2, JH−H = 6.7
3
Hz), 1.07 (d, 6H, CH(CH3)2, JH−H = 6.7 Hz), 0.74 (d, 6H,
3
3
CH(CH3)2, JH−H = 6.8 Hz), 0.57 (d, 6H, CH(CH3)2, JH−H = 6.7
Hz), −0.04 (d, 6H, CH(CH3)2, JH−H = 6.8 Hz). 13C NMR (101
3
MHz, C6D6): δ 169.7 (NCCH3), 169.0 (NCCH3), 151.5 (CN),
146.10, 145.01, 143.84, 143.79, 143.45, 127.38, 127.29, 124.80,
124.70, 124.20, 123.89 (C6H3), 143.90, 128.99, 126.40, 120.30
(C6H5), 97.50 (CH), 97.32 (CH), 29.40, 29.16, 27.86, 27.67
(CH(CH3)2), 27.14, 25.40, 25.30, 24.46, 24.31, 24.26, 23.37
(CH(CH3)2), 24.92, 24.82 (NCCH3). Anal. Calcd for
C65H87Ga2N5S·toluene: C, 71.94; H, 7.97; N, 5.83. Found: C,
72.72; H, 7.34; N, 5.85.
Preparation of NacNacGa(OCHCHMeCH2) (5). To a solution of
NacNacGa (0.099 g, 0.20 mmol) in Et2O was added methacrolein
(0.017 mL, 0.20 mmol). The reaction mixture was stirred for 10 min
at room temperature. Volatiles were removed. The resulting yellow
solid was washed with hexanes to give NacNacGa(−OCH
C(CH3)−CH2−) (0.084 g, 0.15 mmol, 74%). The product was
dissolved in minimum amount of Et2O and recrystallized at −30 °C
Preparation of NacNacGa[(3,5-CH3)2C6H3NCO]2(11). To a sol-
ution of NacNacGa(0.094 g, 0.19 mmol) in diethyl ether (5 mL) was
added 3,5-dimethylphenyl isocyanate (0.054 mL, 0.39 mmol), and the
mixture was left overnight at room temperature. The resulting yellow
solution was concentrated to give yellow crystals of NacNacGa[(3,5-
CH3)2C6H3NCO]2 (0.012 g, 0.015 mmol). The remaining solution
was placed in a −30 °C freezer to give a yellow precipitate that was
1
to give white crystals. H NMR (600 MHz, C6D6): δ 7.10−7.01 (m,
6H, C6H3), 6.88 (s, 1H, OCHC(CH3)CH2), 4.86 (s, 1H, CH), 3.69
3
1
(hept, 2H, CH(CH3)2, JH−H = 6.7 Hz), 3.18 (hept, 2H, CH(CH3)2,
filtered to yield the product (0.115 g, 0.15 mmol, 76%). H NMR
E
DOI: 10.1021/acs.inorgchem.9b01005
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(400 MHz, C6D6): δ 7.14 (s, 1H, C6H3), 7.11 (m, 5H, C6H3(CH3)2
and C6H3), 7.06 (dd, 2H, C6H3, J = 6.6, 2.6 Hz), 6.63 (s, 1H,
C6H3(CH3)2), 6.62 (s, 2H, C6H3(CH3)2), 6.59 (s, 1H, C6H3(CH3)2),
program library, with the latest version used being v.6.12.39 Crystal
and structure refinement data are given in Table S1.
3
4.75 (s, 1H, CH), 3.44 (hept, 2H, CH(CH3)2 JH−H = 6.8 Hz), 3.22
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b01005.
■
3
(hept, 2H, CH(CH3)2 JH−H = 6.8 Hz), 2.21 (s, 6H, C6H3(CH3)2),
S
1.90 (s, 6H, C6H3(CH3)2), 1.50 (d, 6H, CH(CH3)2, 3JH−H = 6.7 Hz),
1.48 (s, 6H, NCCH3)3, 1.36 (d, 6H, CH(CH3)2, 3JH−H = 6.8 Hz), 1.15
3
(d, 6H, CH(CH3)2, JH−H = 6.8 Hz), 1.04 (d, 6H, CH(CH3)2, JH−H
= 6.8 Hz). 13C{1H} NMR (101 MHz, C6D6): δ 171.8 (NCCH3),
153.1 (NCO), 148.8 (NCO), 145.0, 143.5, 138.7, 125.1, 124.8
(C6H3), 138.4, 137.4, 136.8, 128.7, 128.7, 123.7, 123.3
(C6H3(CH3)2), 97.8 (CH), 29.4, 28.5 (CH(CH3)2), 25.6, 24.7,
24.6, 24.4 (CH(CH3)2), 23.3 (NCCH3), 21.7, 21.1 (C6H3(CH3)2).
Anal. Calcd for C47H59GaN4O2:C, 72.21; H, 7.61; N, 7.17; found: C,
72.03; H, 7.54; N, 7.09.
Additional NMR spectra and crystal and structure
refinement data (PDF)
Accession Codes
CCDC 1908463−1908467 contain the supplementary crys-
tallographic 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.
Preparation of NacNacGa[4-CH3C6H4NCN(4-CH3C6H4)]2(13). To
a solution of NacNacGa (0.094 g, 0.19 mmol) in Et2O (5 mL) was
added 1,3-di-p-tolylcarbodiimide (0.054 mL, 0.39 mmol). The
reaction mixture was left overnight at room temperature, after
which time yellow crystals of NacNacGa[(TolNCNTol]2 started to
form. After collecting crystals (0.015 g, 0.016 mmol) volatiles were
removed, and the product was washed with cold hexanes to give 0.126
AUTHOR INFORMATION
Corresponding Author
*(G.I.N.) E-mail: gnikonov@brocku.ca.
■
1
g (0.13 mmol, 70%) of product. H NMR (400 MHz, C6D6): δ 7.71
(d, 2H, C6H4CH3, 3JH−H = 8.3 Hz), 7.21 (m, 2H, C6H3), 6.10 (d, 2H,
3
C6H4CH3, JH−H = 8.3 Hz), 6.99, (m, 2H, C6H3) 6.96 (d, 2H,
ORCID
C6H4CH3, 3JH−H = 8.2 Hz), 6.91 (d, 2H, C6H4CH3, 3JH−H = 8.2 Hz),
Georgii I. Nikonov: 0000-0001-6489-4160
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
3
6.41 (d, 2H, C6H4CH3, JH−H = 8.0 Hz), 6.30 (d, 2H, C6H4CH3,
3
3JH−H = 8.0 Hz), 6.26 (d, 2H, C6H4CH3, JH−H = 8.1 Hz), 5.92 (d,
3
2H, C6H4CH3, JH−H = 8.1 Hz), 4.25 (s, 1H, CH), 3.69 (hept, 2H,
CH(CH3)2, 3JH−H = 6.7 Hz), 2.69 (hept, 2H, CH(CH3)2, 3JH−H = 6.7
Hz), 2.17 (s, 3H, C6H4CH3), 2.08 (s, 3H, C6H4CH3), 1.95 (s, 3H,
C6H4CH3), 1.89 (s, 3H, C6H4CH3), 1.78 (d, 6H, CH(CH3)2, 3JH−H
=
Notes
6.7 Hz), 1.36 (s, 6H, NCCH3), 1.28 (d, 6H, CH(CH3)2, 3JH−H = 6.7
The authors declare no competing financial interest.
3
Hz), 0.91 (d, 6H, CH(CH3)2, JH−H = 6.7 Hz), 0.79 (d, 6H,
3
CH(CH3)2, JH−H = 6.7 Hz). 13C{1H} NMR (101 MHz, C6D6): δ
ACKNOWLEDGMENTS
G.I.N. acknowledges financial support from NSERC (DG
2017-05231)
■
172.2 (NCCH3), 153.8, 150.3 (NCN), 145.6, 143.6, 140.4, 125.2,
124.6 (C6H3), 147.2, 142.6, 138.7, 134.8, 132.6, 130.5, 129.4, 128.7,
126.8, 121.7, 121.5 (C6H4CH3), 100.9 (CH), 28.9, 28.8 (CH(CH3)2),
26.3, 25.6, 24.8, 24.4 (CH(CH3)2), 23.9 (NCCH3), 21.1, 20.8, 20.7,
20.7 (C6H4CH3). Anal. Calcd for C59H69GaN6: C, 76.04; H, 7.46; N,
9.02. Found: C, 76.29; H, 6.09; N, 8.63.
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DOI: 10.1021/acs.inorgchem.9b01005
Inorg. Chem. XXXX, XXX, XXX−XXX