Full text of DOI:10.1021/acs.inorgchem.7b01275

Article
pubs.acs.org/IC
Reactions of Germylenes and Stannylenes with Halo(hydrocarbyl)-
and Chloro(amino)phosphines: Oxidative Addition versus Ligand
Transfer
Joseph K. West† and Lothar Stahl*
Department of Chemistry, University of North Dakota, Grand Forks, North Dakota 58202-9024, United States
ABSTRACT: Oxidative addition (OA) is an important
elementary step in chemistry, but it has been studied mainly
in the context of transition-metal-catalyzed reactions and
mainly with carbon−X substrates (X = halogen, H). Reports of
main-group metal compounds undergoing OA are rare by
comparison, and those involving phosphorus−halogen sub-
strates are rarer still. Acyclic and cyclic diazagermylenes and
-stannylenes react with chloro(hydrocarbyl)phosphines with
the intermediacy of oxidative addition products. Stannylenes
react faster than germylenes, and these reactions are first-order
in both reactants and slowed by steric bulk. Kinetic data and
the structures of intermediates and products had suggested an
adduct/insertion mechanism for these reactions. To gain further insight into these transformations, the work presented herein
was extended to chloro(hydrocarbyl)phosphines with varying organic substituents. These studies confirmed prior conclusions
concerning the rate-diminishing effect of steric bulk, and the rate dependence on leaving groups also seems to suggest adduct/
insertion or SN2 mechanisms. Importantly, these new data now also point to associative decomposition pathways. In the course
of the investigation, it was discovered that aliphatic chloro(amino)phosphines react differently with the carbene analogues, giving
oxidative addition products for germylenes but metathesis reactions for stannylenes.
transformations are consistently used as benchmarks for novel
carbene analogues in these and related reactions, as recent
reports confirm.16−25
1. INTRODUCTION
Oxidative addition (hereafter also OA) is a key elementary step
in many catalytic cycles because it entails the functionalization
of molecules by the controlled breaking of chemical bonds to
set up the subsequent formation of new bonds.1 Although the
reaction can principally occur on any metal with two stable
oxidation states that are two units apart, it is most often
observed for second- and third-row transition metals of Groups
9 and 10, Vaska’s complex and Wilkinson’s catalyst being classic
examples.2,3
Main-group metals also undergo oxidative additions, as the
reaction of magnesium with hydrocarbyl halides shows.4 This s-
block metal, however, does not exhibit the facile two-oxidation
state shuttle seen in transition metals. The p-block elements,
particularly those of Group 14, undergo oxidative additions that
more closely resemble those of the transition metals, as, for
example, demonstrated by the OA of methyl iodide to
stannocene.5 Studies by Lappert et al. on organic halides
adding to tin(II) and germanium(II) carbene analogues
revealed the broader scope of such reactions.6−8 The work
was recently expanded by the group of Banaszak Holl, who
published the most extensive and potentially most useful series
of papers on C−X bond activation by germylenes and
stannylenes.9−13 Of course, silylenes also react with a variety
of organic functional groups, but their even greater reactivity
comes with loss of selectivity and control.14,15 Because of the
long history of carbene analogues in oxidative additions, these
There is considerable current interest in the generation and
manipulation of homo- and heteronuclear bonds between
pnictogens, particularly those involving phosphorus,26−37 for
both fundamental studies and the potential use of such
compounds in new materials. We are investigating homoge-
neous reductions of halophosphines by Group 14 carbene
analogues for generating phosphorus−phosphorus bonded
species. The reductions are usually performed with reactive
bulk metals,38−40 but homogeneous reductions are known.41,42
These latter transformations also proceed with the intermediacy
of OA products, but they are more complex than those of their
carbon analogues. This is partly due to phosphorus’ ability to
exhibit hypervalency in both, intermediates and products, but it
is also due to the weaker phosphorus−metal bonds which rarely
afford isolable metal-containing species. However, because
these reactions are homogeneous, they are amenable to
mechanistic investigations, and we initiated such studies to
gain insight into OA reactions of soluble Group 14 metal
compounds.
Early work by du Mont and Schumann had suggested that
germanium(II) and tin(II) halides insert reversibly into the
Received: May 21, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b01275
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Article
phosphorus−halogen bonds of halo(organo)phosphines.43−50
These authors also produced strong evidence that these
oxidative additions are preceded by adduct formation. Later,
Veith et al. reported that phosphorus trichloride reacts with
homologous cyclic Group 14 carbene analogues to give three
entirely different products, which are depicted in Scheme 1.51
phosphines are primarily the corresponding dichloroger-
manes and -stannanes and phosphorus−phosphorus
coupled products, namely, diphosphines or cyclic
oligophosphines.
2. All reactions seem to proceed with the intermediacy of
oxidative addition products, which are almost always
isolable if M = Ge, but less frequently so when M = Sn.
The isolated tin compounds are often the decomposition
products of the OA intermediates.
3. Conversion times vary greatly and range from seconds to
months. They follow first-order kinetics for both, carbene
analogues and chlorophosphines.
Scheme 1. Homologous Group 14 Carbene Analogues React
Differently with PCl3
4. The reactivities of the carbene analogues follow the
order: cyclic stannylene > cyclic germylene ∼ acyclic
stannylene > acyclic germylene
5. Steric bulk on either the halophosphines or the carbene
analogues hinders the rate of oxidative addition.
Below, we report on the expansion of this work to sterically
smaller chloro(alkyl)phosphines, sterically bulkier chloro(aryl)-
phosphines, and to chloro(amino)phosphines. These studies
not only support earlier mechanistic evidence about the
oxidative additions but also provide key insights into the
decomposition pathway of the ensuing products. The chloro-
(amino)phosphines, which had not been studied previously,
showed an unexpected divergence in reactivity, giving oxidative
addition products with germylenes but amide-ligand transfer
products with stannylenes. These differences, in turn, hint at
the subtle kinetic and thermodynamic factors that underlie
these reactions.
2. EXPERIMENTAL SECTION
All three of the P−Cl bonds of PCl3 added to three
germylenes to furnish a C3-symmetrical trioxidative addition
product. The stannylene, by contrast, underwent a redox
reaction (eq 2) and was transformed to a dichlorostannane.
Cyclic diazaplumbylene reacted by apparent ligand exchange
only, producing PbCl2 and a P-chloro-1,3,2λ3,4-diazaphospha-
siletidine, which had been previously accessible only by a much
more cumbersome route.52 Attempts by these authors to isolate
intermediates using bulkier chlorophosphines were thwarted,
but NMR spectroscopy allowed the identification of a few of
these products in the reaction mixtures.42
Because chloro(organo)phosphines are less reactive than
phosphorus trichloride, we reinvestigated prior work by
incorporating these reagents. In addition to cyclic diazagermy-
lenes and -stannylenes, we also tested their acyclic versions, all
four of which are shown in Chart 1.
2.1. General Procedures. All manipulations and reactions were
done under an atmosphere of argon using standard Schlenk
techniques. Solvents were dried over and distilled from Na/
benzophenone (toluene) and K/benzophenone (THF and hexanes).
PhPCl2 and Ph2PCl were purchased from Aldrich Chemical Co. and
distilled before use. tBu2PCl was synthesized using a published
procedure,54 and tBuPCl2 was synthesized similarly using only 1 equiv
of tBuLi. The chloro(amino)phosphines Me2Si(μ-NtBu)2PCl,51-
56
(Et2N)2PCl,55and Et2NPCl2 were prepared as previously reported.
Cyclic Me2Si(μ-NtBu)2E [E = Ge (A), Sn (B)],57,58 and acyclic
[(Me3Si)2N]2E [E = Ge (C), Sn (D)] were synthesized according to
literature procedures.59 Elemental analyses were conducted by Desert
Analytics, Midwest Microlabs, and Columbia Analytical Services. All
1H, 13C, and 31P NMR spectra were recorded on a Bruker Avance 500
NMR spectrometer in C6D6, THF-d8, and CD2Cl2. 119Sn NMR spectra
were acquired on a JEOL ECX-300 NMR spectrometer. The chemical
shifts, δ, are relative to the residual solvent peak(s) (e.g., C6HD5) for
1H and 13C spectra and the external standard P(OEt)3 for 31P spectra.
Tin spectra are referenced to external SnCl4 at −150.0 ppm. Melting
points were obtained on a Mel-Temp apparatus; they are uncorrected.
2.2. Syntheses. 2.2.1. Halophosphines. (2,6-Me2Ph)2PCl. In a 250
mL, 3-neck flask, fitted with an addition funnel, Et2NPCl2 (1.31 mL,
9.00 mmol) was stirred in hexanes (24 mL) at 0 °C. A 1.0 M THF
solution of 2,6-Me2PhMgBr (18.0 mL, 18.0 mmol) was added
dropwise over 1 h. After 40 min, the flask was allowed to warm to rt.
Volatiles were removed in vacuo, and the solid residue was redissolved
in hexanes and filtered. Dry HCl was bubbled through this solution for
ca. 30 min, and the ammonium salt that formed was removed by
filtration. Colorless crystals formed in the filtrate at room temperature.
Chart 1
These modifications proved to be fortuitous, as numerous
oxidative addition products were isolated and their solid-state
structures were determined.53 The results of our initial study
can be summarized as follows:
1
Yield 1.98 g (80%). Mp: 57−59 °C. H NMR (500.1 MHz, C6D6, 25
°C): δ 7.04 (t, 2 H, JHH = 15 Hz, p-Ph), 6.86 (m, 4 H, m-Ph), 2.35 (s,
12 H, o-MePh). 31P{1H} NMR (202.5 MHz, C6D6, 25 °C): δ 82.2 (s).
tBu(Ph)PI. In a 250 mL, 3-neck flask, Bu(Ph)PCl (4.71 mL, 25.0
t
1. The ultimate products of the reactions between
diazagermylenes and -stannylenes and chloro(organo)-
mmol) and sodium iodide (15.0 g, 100 mmol) were stirred in refluxing
toluene for 8 h, while the reaction mixture changed from colorless to
B
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pale yellow. The solvent was removed in vacuo. This crude product,
which was determined by H NMR spectrometry to be >95% pure,
PNtBu), 0.77 (s, 6 H, SiMe2), 0.24 (s, 3 H, SiMe), 0.17 (s, 3 H, SiMe).
1
13C{1H} NMR (125.8 MHz, C6D6, 25 °C): δ 53.3 (s, NC), 36.8 (d,
1
2
PC, JPC = 37.3 Hz), 36.5 (s, NtBu), 33.7 (d, PtBu2, JPC = 13.5 Hz),
8.52 s, 6 H, SiMe), 7.23 (s, 6 H, SiMe). 31P{1H} NMR (202.5 MHz,
C6D6, 25 °C): δ 85.95 (s) (1J119,117SnP = 2022, 1932 Hz). 119Sn NMR
(112.1 MHz, C6D6, 25 °C): δ 90.34 (d), (1J119SnP = 2023 Hz).
[Me2Si(μ-NtBuSnCl)(μ-NtBu(P(NEt2)2)] (6). To a solution of Me2Si-
(μ-NtBu)2Sn (0.720 g, 2.26 mmol), dissolved in hexanes (35 mL), was
added at 0 °C neat (Et2N)2PCl (0.47 mL) by syringe over 6 min.
Upon addition of the phosphine, the reaction mixture turned from
orange to yellow. After 1 h, the flask was removed from the cold bath
and allowed to stir overnight at rt. Large, clear, colorless crystals,
suitable for X-ray analysis, were obtained after the solution had been
stored at 3 °C for several days. Yield: 0.770 g (64%). Mp: 91−93 °C.
Anal. Calcd for C18H44ClN4PSiSn (529.79): C, 40.81; H, 8.37; N
was found to be of sufficient purity for all studies, Yield 5.23 g (72%).
1H NMR (500.1 MHz, C6D6, 25 °C): δ 7.02−7.81 (m, 5 H, Ph), 1.01
t
3
(d, 9 H, Bu, JPH = 15 Hz). 31P{1H} NMR (202.5 MHz, C6D6, 25
°C): δ 106.1 (s).
2.2.2. Group 14 Derivatives. {{[(Me3Si)2N]2Ge(Cl)P(Cl)}2·C6H14} (1).
A stirred solution of [(Me3Si)2N]2Ge (0.651 g, 1.66 mmol) in hexanes
(20 mL) was treated at 0 °C with a 1.0 M hexanes solution of PCl3
(0.83 mL, 0.83 mmol) all at once. After 1 h, the reaction mixture was
allowed to warm to rt. The initially bright-yellow solution, which
changed to bright pink after 3.5−5 h, deposited pale-pink crystals as a
hexane solvate after standing at 3 °C for several days. Yield: 0.94 g
(57%). Mp: 150−153 °C (dec.). Anal. Calcd for C27H79Cl4Ge2N4P2Si8
(1033.11): C, 31.37; H, 7.70; N, 5.42. Found: C, 30.27; H, 7.33; N,
5.44. 1H NMR (500.1 MHz, C6D6, 25 °C): δ 0.48 (s, SiMe). 13C{1H}
NMR (125.8 MHz, C6D6, 25 °C): δ 1.8 (s). 31P{1H} NMR (202.5
MHz, C6D6, 25 °C): δ 62.6 (s).
1
10.58. Found: C, 40.51; H, 7.99; N, 10.71. H NMR (500.1 MHz,
C6D6, 25 °C): δ 2.83 (m, 8 H, NCH2), 1.53 (s, 9 H, SnNtBu), 1.26 (s,
9 H, PNtBu), 0.93 (t, 12 H, NCH2CH3, JHH = 15 Hz), 0.74 (s, 6 H,
SiMe). 13C{1H} NMR (125.8 MHz, C6D6, 25 °C): δ 56.6 (d,
SnNCCH3, JPC = 11 Hz), 55.2 (d, PNCCH3, JPC = 14 Hz), 39.0 (s,
[(Me3Si)2N)]2SnI2 (2). A solution of [(Me3Si)2N)]2Sn (8.21 mmol)
in hexanes (10 mL) was treated dropwise with a PI3 (2.74 mmol)
solution in hexanes (10 mL) at 0 °C. The dark-red reaction mixture
was stirred overnight, whereupon it took on a bright-orange color,
which deposited a black precipitate. A 1H NMR spectrum taken on an
aliquot showed a complex product mixture. After the solution had
been concentrated in vacuo and kept at 3 °C overnight, 0.94 g of
colorless crystals formed. Yield: 55%. Mp: 92−94 °C. Anal. Calcd for
C12H36I2N2Si4Sn (693.91): C, 20.79; H, 5.23; N, 4.04. Found: C,
20.47; H, 5.33; N, 4.14. 1H NMR (500.1 MHz, C6D6, 25 °C): δ 0.424
(s, SiMe). 13C{1H} NMR (125.8 MHz, C6D6, 25 °C): δ 6.2 (s). 119Sn
NMR (111.9 MHz, C6D6, 25 °C): δ −669.65 (s).
{[(Me3Si)2N]2Ge(Cl)PEt2} (3). A stirred solution of [(Me3Si)2N]2Ge
(0.389 g, 0.989 mmol) in hexanes (10 mL) was treated dropwise at 0
°C with a Et2PCl solution (0.99 mL, 0.99 mmol) in hexanes (10 mL).
After 10 min, the flask was removed from the cold bath and the
reaction mixture was stirred at rt for 7.5 h. All volatiles were removed
in vacuo, leaving a pale orange-yellow solid, which was redissolved in a
minimal amount of hexanes. Crystals formed after the flask had been
stored at rt for several days. Yield: 0. 226 g (43%). Mp: 102−105 °C.
Anal. Calcd for C16H46ClGeN2PSi2 (517.96): C, 37.10; H, 8.95; N,
5.41. Found: C, 37.24; H, 8.77; N, 5.09. 1H NMR (500.1 MHz, C6D6,
25 °C): δ 2.56 (m, 4 H, PCH2), 0.85 (t, 6 H, J = 4.5 Hz PCH2CH3),
0.50 (s, 36 H, SiMe). 13C{1H} NMR (125.8 MHz, C6D6, 25 °C): δ
18.4 (d, JPC = 20 Hz), 7.9 (s), 6.1 (s, SiMe). 31P{1H} NMR (202.5
MHz, C6D6, 25 °C): δ 20.4 (s).
3
NCH2), 37.4 (SnNCCH3, JSnC = 52 Hz), 33.3 (s, PNCCH3), 13.9
(NCH2CH3), 12.1 (s, SiMe). 31P{1H} NMR (202.5 MHz, C6D6, 25
°C): δ 96.1 (s) (1J119,117SnP = 2057, 1966 Hz). 119Sn NMR (112.1
MHz, C6D6, 25 °C): δ 65.85 (d) (1J119SnP = 2057 Hz).
[Me2Si(μ-NtBu)2PNEt2]SnCl2 (7). Me2Si(μ-NtBu)2Sn (150 mg, 0.470
mmol) in hexanes (5 mL) was treated dropwise at −78 °C with a 0.50
M hexanes solution of Et2NPCl (0.94 mL) by syringe. After several
minutes, the flask was removed from the cold bath. Upon warming, a
white precipitate slowly formed in the yellow solution. The solution
was filtered and crystals suitable for X-ray analysis grew after the
filtrate had been stored at 3 °C for several days. Yield: 95 mg (41%).
Mp: 161−163 °C (dec.). Anal. Calcd for C14H34Cl2N3PSiSn (493.12):
1
C, 34.10; H, 6.95; N, 8.52. Found: C, 34.28; H, 7.09; N, 8.79. H
NMR (500.1 MHz, C6D6, 25 °C): δ 2.97 (dq, 4 H, NCH2CH3, JPH
=
165 Hz, JHH = 9 Hz), 1.18 (s, 18 H, NtBu), 0.91 (dt, 6 H, NCH2CH3,
JPH = 60 Hz, JHH = 9 Hz), 0.32 (s, 6 H, SiMe). 13C{1H} NMR (125.8
2
MHz, C6D6, 25 °C): δ 57.6 (d, NCH2CH3, JPC = 10.1 Hz), 53.0 (s,
NC(CH3)3), 35.1 (s, NC(CH3)3), 15.2 (d, NCH2CH3, 3JPC = 5.0 Hz),
7.32 (s, SiMe3), 6.03 (s, SiMe3). 31P{1H} NMR (202.5 MHz, C6D6, 25
°C): δ 105.0 (s), major component. 119Sn NMR (112.1 MHz, C6D6,
25 °C): δ −57.7 (d), (1J119SnP = 2057 Hz), minor component.
[Me2Si(μ-NtBu)2Ge(Cl)]2PNEt2 (8). In a two-neck flask, Me2Si(μ-
NtBu)2Ge (0.622 g, 2.28 mmol) was stirred in ca. 1 mL of hexanes at 0
°C. A sample of neat Et2NPCl2 (1.1 mmol, 0.23 mL) was added all at
once by syringe. Approximately 2 mL of hexanes was added to dissolve
the small amount of precipitate which appeared. X-ray quality crystals
were obtained from this solution at rt after it had been stored for 3
days. Yield: 0.367 g (72%). Mp: 106−107 °C. Anal. Calcd for
C24H58Cl2Ge2N5PSi2 (720.08): C, 40.03; H, 8.12; N, 9.73. Found: C,
Me2Si(μ-NtBu)2Sn(Cl)P(2,6-Me2Ph)2 (4). To a cold (0 °C) benzene
solution (5 mL) of (2,6-Me2C6H3)2PCl (0.13 g, 0.47 mmol) was
added dropwise a 1.0 M Me2Si(μ-NtBu)2Sn solution (0.47 mL). After
30 min, the reaction mixture was allowed to warm to rt and all volatiles
were removed in vacuo. The residue was dissolved in a minimal
amount of toluene, and the ensuing solution was kept at 3 °C until it
deposited block-shaped, orange crystals. Yield: 0.25 g, 89%. Mp: 135−
138 °C. Anal. Calcd for C26H42ClN2PSiSn (596.16): C, 52.41; H, 7.10;
1
40.24; H, 7.89; N, 9.54. H NMR (500.1 MHz, C6D6, 25 °C): δ 3.28
3
3
(dq, 4 H, NCH2CH3, JHH = 14.4 Hz, JPH = 2.3 Hz), 1.41 (s, 36 H,
NtBu), 1.12 (t, 6 H, NCH2CH3, 3JHH = 14.4 Hz), 0.48 (s, 3 H, SiMe3),
0.41 (s, 3 H, SiMe3). 13C{1H} NMR (125.8 MHz, C6D6, 25 °C): δ
1
N, 4.70. Found: C, 52.58; H, 7.22; N, 4.96. H NMR (500.1 MHz,
C6D6, 25 °C): δ 6.94 (t, 2 H, JHH = 15 Hz, p-Ph), 6.84 (m, 4 H, m-Ph),
2.44 (s, 12 H, o-MePh), 1.27 (s, 18 H, NtBu), 0.50 (s, 3 H, SiMe), 0.29
(s, 3 H, SiMe). 13C{1H} NMR (125.8 MHz, C6D6, 25 °C): δ 53.0 (s,
NC(CH3)3), 36.2 (s, NC(CH3)3), 8.41 (s, SiMe3), 7.13 (s, SiMe3),.
2
57.6 (d, NCH2CH3, JPC = 10.1 Hz), 53.0 (s, NC(CH3)3), 35.1 (s,
NC(CH3)3), 15.2 (d, NCH2CH3, 3JPC = 5.0 Hz), 7.32 (s, SiMe3), 6.03
(s, SiMe3). 31P{1H} NMR (202.5 MHz, C6D6, 25 °C): δ 66.3 (s).
2.3. X-ray Crystallography. Suitable single crystals of 1−8 were
coated with Paratone N oil, affixed to Mitegen crystal holders, and
centered on the diffractometer in a stream of cold nitrogen. Reflection
intensities were collected with a Bruker Apex diffractometer, equipped
with an Oxford Cryosystems 700 Series Cryostream cooler, operating
at 173 K. Data were measured with ω scans of 0.3° per frame for 20 s
until complete hemispheres of data had been collected. Data were
retrieved using SMART software and reduced with SAINT-plus,60
which corrects for Lorentz and polarization effects and crystal decay.
Empirical absorption corrections were applied with SADABS.61 The
structures were solved by direct methods with SHELXS-97 and refined
by full-matrix least-squares methods on F2 with SHELXL-97.62
31P{1H} NMR (202.5 MHz, C6D6, 25 °C): δ −26.6 (s) (1J117/119SnP
=
1725/1804 Hz). 119Sn NMR (112.1 MHz, C6D6, 25 °C): δ 114.6 (d),
(1J119SnP = 1802 Hz).
[Me2Si(μ-NtBuSnCl)(μ-NtBu(P(μ-NtBu)2SiMe2))] (5). To a stirred
toluene solution of Me2Si(μ-NtBu)2PCl (7.5 mmol) at 0 °C was added
7.5 mL a solution of Me2Si(μ-NtBu)2Sn (1.0 M in toluene) by syringe.
The reaction mixture was stirred at 60 °C for 15 days, and the product
was collected as transparent, colorless crystals directly from the
reaction mixture by cooling to −15 °C. Several crystal fractions were
collected for an overall yield of 1.49 g (34%). Mp: 159−160 °C. Anal.
Calcd for C20H48ClN4PSi2Sn (585.93): C, 41.00; H, 8.26; N, 9.56.
1
Found: C, 40.74; H, 8.11; N, 9.18. H NMR (500.1 MHz, C6D6, 25
°C): δ 1.55 (s, 9 H, SnNtBu), 1.49 (s, 9 H, PNtBu), 1.33 (s, 18 H,
C
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Scheme 2. Reactions of Acyclic Group 14 Carbene Analogues with Trihalophosphines
3. RESULTS AND DISCUSSION
3.1. Syntheses and Structures. 3.1.1. Trihalophosphine
Substrates. With the extensive set of data gathered in our first
study and aided by our improved ability to identify solution
structures, we reinvestigated the reactions between Me2Si(μ-
NtBu)2M (M = Ge, Sn) and PCl3 to see if any additional
information might be gleaned from these transformations. We
confirmed that, when A reacted with PCl3 in a 3:1 ratio, the
stable trioxidative addition product [Me2Si(μ-NtBu)2Ge(Cl)]3P
was obtained as indicated by a (previously unreported) 31P{1H}
NMR singlet at δ −78.0 ppm. The 3:1 addition of B to PCl3
allowed the observation of an analogous trioxidative addition
product at δ −114.6 ppm with the expected satellites,
1J119/117SnP = 1541/1472 Hz. The formal redox reaction of
stannylene B (eq 2) thus also proceeds via an intermediate
Figure 1. Solid-state structure and partial labeling scheme of inversion-
symmetric 1. Hydrogen atoms and hexane solvent have been omitted,
and all non-hydrogen atoms are drawn as 50% probability thermal
ellipsoids. Selected bond lengths (Å) and angles (deg). Ge1−P1
2.4086(6), P1−P1′ 2.2192(11), Ge1−Cl2 2.1853(5), P1−Cl1
2.0577(8), Ge1−N1 1.8373(16), Ge1−N2 1.8386(16); Ge1−P1−
P1′ 100.57(3), Cl2−Ge1−P1 105.13(2), Ge1−P1−Cl1 96.37(3),
P1′−P1−C11 96.69(4), N1−Ge1−N2 114.36(8), N1−Ge1−Cl2
108.10(6), N2−Ge1−Cl2 105.32(5), N1−Ge1−P1 113.51(5), N2−
Ge1−P1 109.66(5), Cl2−Ge1−P1 105.13(2).
oxidative addition product.
When the bulkier acyclic diazastannylene D was allowed to
react with PCl3 in a 3:1 ratio, the 31P NMR spectrum showed
that only a dioxidative addition product had formed, although it
did so in almost quantitative yield. This intermediate
decomposed only very slowly, but it escaped isolation. The
reaction of the analogous diazagermylene in a 2:1 ratio (eq 4,
Scheme 2), however, afforded an isolable product, namely, 1,
whose solid structure is shown in Figure 1..
The thermal-ellipsoid plot of 1 shows that this compound is
not the actual OA product, but rather a decomposition product
thereof. On the basis of the solution structure of the dioxidative
addition product with acyclic stannylene D, we hypothesize that
a similar product was formed here. We were unable to detect
the remaining product(s) of this reaction by NMR spectros-
copy, which, based on stoichiometry and by analogy, should be
the digermane {[(Me3Si)2N]2(Cl)Ge−Ge(Cl)[N(SiMe3)2]2}.
The reaction mixture was initially orange in color, but it
changed to pink, perhaps suggesting homolysis of the Ge−P
bonds and the presence of radicals in the decomposition
pathway. Compound 1 is a structural analogue of the product
formed when the acyclic stannylene D reacted with PhPCl2, the
main difference being that, in 1, the phosphorus−phosphorus
bond (2.2192(11) Å) is slightly shorter than that of the D/
PPhCl2 product, but it is virtually isometric with those in
similar compounds featuring phosphorus−phosphorus
bonds.63−65 This central linkage is flanked by two Ge−P
bonds (2.4086(6) Å) which are comparatively shorter than the
corresponding bonds in the above-mentioned stannylene
analogue (2.5702(6) Å).
we investigated phosphorus triiodide as an alternative
phosphorus trihalide. The reaction with PI3, shown in eq 5,
was quite complex, however, perhaps due to the weakness of
the phosphorus−iodine bonds and the redox sensitivity of this
compound. Only the reaction of the acyclic diazastannylene D
with phosphorus triiodide yielded an isolable compound,
namely, the oxidation product [(Me3Si)2N]2SnI2 (2). While
eq 5 may suggest a direct interaction between PI3 and cyclic
stannylene B, the transformation itself is likely more complex.
The colorless, crystalline compound obtained showed only one
singlet each in the 1H and 13C NMR spectra, characteristic of a
highly symmetrical structure. A single-crystal X-ray study of 2,
depicted in Figure 2, confirmed this assumption by revealing a
C2-symmetric tin bis(hexamethyldisilylazide)-diiodide.
The tin(IV) derivative 2 is a member of a series of
compounds of the formula [(Me3Si)2N]2ElX2, El = Ge, Sn, X =
amide, acyl, hydrocarbyl, halogen,6a whose dichloride analogue
had been the only dihalide reported previously.6b In the unit
cell, the molecules lie on the two-fold axes of space group C2/c,
the axes bisecting the I−Sn−I angle. The tin atom is in a
pseudo-tetrahedral environment, and both Si2N planes form a
dihedral angle of 86.10°. The Sn−I bonds are expectedly
Thus far, only phosphine chlorides had served as substrates
in these transformations, and to avoid a bias toward this halide,
D
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the stability of the tin(IV) products is primarily due to steric
shielding of the Sn−P bond and not the electronic properties of
the organic substituents.
Acyclic diazagermylene Cthe least reactive of the carbene
analoguesreacted with chloro(diethyl)phosphine (eq 7), to
furnish the expected OA product 3 in a 48% yield after a
comparatively long 8 h reaction time. This product was isolated
as a stable, colorless, crystalline compound and studied by
single-crystal X-ray methods. Its solid-state structure is shown
in Figure 3, while the caption contains selected bond
Figure 2. Solid-state structure and partial labeling scheme of C2-
symmetric 2. Hydrogen atoms have been omitted, and all non-
hydrogen atoms are drawn as 50% probability thermal ellipsoids.
Selected bond lengths (Å) and angles (deg): Sn1−I1 2.6995(3), Sn1−
N1 2.0237(15), N1−Si1 1.7604(16), N1−Si2 1.7654(16); I−Sn−I′
102.125(13), N1−Sn−I1 104.37(4), N1−Sn−N1′ 117.29(9), Sn−
N1−Si1 116.98(8), Sn−N1−Si2 118.54(8), Si1−N1−Si2 122.16(9).
shorter than in the tin(II) derivative Sn(I)(2.6-Trip-C6H3),
Trip = 2,4,6-iPrC6H2,66 where the lone Sn−I bond was found
to be 2.766(2) Å long, but they are also slightly shorter than the
Sn−I bonds in a similar tin(IV) species.67
3.1.2. Chloro(hydrocarbyl)phosphine Substrates. Our
initial study consisted of more than one dozen reactions,
involving both cyclic and acyclic germylenes and stannylenes.
The chlorophosphine substrates, however, were limited to
PhPCl2, Ph2PCl, tBuPCl2, and (tBu)2PCl, the phenylphosphines
reacting orders of magnitude faster than their tert-butyl
counterparts. Phenyl rings are smaller than tert-butyl groups,
but they are also electron-poorer. The greater reactivity of
phenyl-substituted phosphines could thus also be interpreted
electronically, namely, that electron-poorer chlorophosphines
add faster to the carbene analogues. To separate electronic
from steric effects, we compared the compact, electron-richer
Et2PCl with the bulky, electron-poorer (2,6-Me-C6H3)2PCl.
Expectedly, Et2PCl oxidatively added much faster to A−D
than the tert-butyl analogues, with the notable difference that all
tin-containing intermediates were unstable, furnishing only
tetraethyldiphosphine and unidentified tin species, as emblem-
atically shown by eq 6 (Scheme 3). Not only were the
stannylene-derived OA products of Et2PCl unstable but also
these intermediates broke down even faster than those of the
corresponding chloro(phenyl)phosphines. This suggests that
Figure 3. Solid-state structure and partial labeling scheme of 3.
Hydrogen atoms have been omitted, and all non-hydrogen atoms are
drawn as 50% probability thermal ellipsoids. Selected bond lengths (Å)
and angles (deg): Ge1−Cl1 2.2093(5), Ge1−P1 2.3446(5), Ge1−N1
1.8575(13), Ge−N2 1.8473(14), N1−Si1,2 (avg.) 1.7650(14), N2−
Si3,4 (avg.) 1.7646(14); Cl1−Ge1−P1 104.857(19), N2−Ge1−P1
111.51(4), N1−Ge1−N2 114.77(6), N1−Ge1−P1 114.92(5).
parameters. The structure confirms that the phosphorus−
chlorine bond of the compact chloro(diethyl)phosphine
oxidatively added to the bulky diazagermylene, creating an
almost perfectly tetrahedral germanium(IV) center. The
metalloid is surrounded by two isometric and normal-length
Ge−N bonds (1.852(1) Å), which enclose an angle of
114.77(6)°. The Ge−Cl bond length of 2.2093(5) Å is equally
unremarkable, while the germanium−phosphorus bond
(2.3446(5) Å) is similar in length to some of the Ge−P
bonds measured by Izod et al. in low-coordinate germanium
compounds. Although, these latter species contain germanium-
(II) centers whose bond lengths are much more sensitive to
bond conformations.68 Reactions with the sterically small
chloro(diethyl)phosphine thus mirrored the results of our
earlier studies in that the germylene inserted more slowly, but it
produced stable products.
Scheme 3. Reactions of Chloro(hydrocarbyl)phosphines
with Group 14 Carbene Analogues
Ph2PCl had reacted almost instantly with Me2Si(μ-NtBu)2Sn
to produce solely decomposition products, namely, the
distannane [Me2Si(μ-NtBu)2(Cl)Sn−Sn(Cl)(μ-NtBu)2SiMe2]2
and the diphosphine Ph2PPPh2. The structures of these
compounds suggest that the initially generated OA inter-
mediate dissociated at the Sn−P bond and that both moieties
then dimerized with like species. By using the bulkier chloro-
bis(2,6-dimethylphenyl)phosphine, we hoped to ascertain if
added steric bulk slowed the reaction. This was indeed
observed, but even more important was the discovery that
the oxidative addition product of the bulkier chlorophosphine
was stable, despite being more sterically congested. This is a
strong indication that the unstable tin-containing OA products
decompose via an associative, rather than a dissociative,
mechanism.
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The solid-state structure of 4 is shown in Figure 4, while
selected bond parameters are listed in the figure caption. In this
Table 1. Kinetic Data for Selected Oxidative Addition
Reactions
carbene
analogue
time (min.) for 99%
conversion of reactants
halophosphine temp. (°C)
A
A
B
D
A
C
C
(tBu)PhPCl
(tBu)PhPCl
(tBu)PhPCl
(tBu)PhPCl
(tBu)PhPI
(tBu)PhPI
(tBu)PhPI
25
50
25
25
50
50
25
>1288
>690
70−75
93−98
<15
79−94
178−206
intermediates to support the former. Rather than attempting
to confirm our mechanistic hypotheses by isolating such
species, if this were indeed possible, we focused on substrates
that should be able to undergo the adduct/insertion or SN2
mechanisms only with great difficulty, or not at all. The P-
chloro diazasilaphosphetidine produced in eq 3 is a special case
of a monochlorophosphine, but it is a cyclic chlorophosphine
with little or no conformational flexibility. Notably, no
inversion at phosphorus is possible, ruling out an SN2-type
reaction, and even an adduct/insertion mechanism, while
feasible, appears very sterically impeded. One would therefore
expect this substrate to oxidatively add to the carbene analogues
only very slowly, if at all, by these pathways.
Figure 4. Solid-state structure and partial labeling scheme of 4.
Hydrogen atoms have been omitted, and all non-hydrogen atoms are
drawn as 50% probability thermal ellipsoids. Selected bond lengths (Å)
and angles (deg): Sn1−Cl1 2.3758(3), Sn1−P1 2.5218(3), Sn1−N1
2.0349(11), Sn1−N2 2.0370(9), Si1−N1 1.7398(11), Si−N2
1.7405(11); Cl1−Sn1−P1 96.378(12), N1−Sn1−P1 142.44(3),
N1−Sn1−N2 76.50(4), N1−Sn1−Cl1 115.77(12), N1−Si1−N2
82.41(11).
molecule, a normal-length tin−phosphorus bond, 2.5218(3) Å,
connects a pseudo-tetrahedral metal atom to a three-
coordinate, pyramidal phosphorus atom. The plane bisecting
the heterocycle contains one of the dimethylphenyl ligands,
while the second aromatic ring lies perpendicular to that plane.
The tin−nitrogen bonds are isometric at 2.0349(11) and
2.0370(9) Å and of normal length, as is the Sn−Cl bond, which
is 2.3758(3) Å long. Because tin is part of a heterocycle, the
bond angles about this metal differ significantly from
tetrahedral values, ranging from 76.50(4)° to 142.44(3)°.
We hoped to gain further insight into the influence of steric
bulk on these reactions by synthesizing the mixed chloro(alkyl/
Upon combining solutions of B and Me2Si(μ-NtBu)2PCl, no
change was observed in either the appearance of the reaction
mixture nor in the 31P NMR spectra obtained on aliquots taken
from it. Only on heating the solution to 60 °C were the
extremely slow disappearance of the signal for the cyclic
chlorophosphine and the concomitant appearance of a new
signal at δ = 96.1 ppm observed. The slowness of this reaction,
which took 15 days at 60 °C to go to complete conversion,
seemed to support our hypotheses regarding its mechanism. A
free-radical mechanism, similar to the one proposed by West et
al.,14,15 should certainly be feasible for this substrate, but such a
reaction would be expected to proceed much faster than the
transformation we observed.
t
aryl)phosphine Bu(Ph)PCl and allowing it to react with all
four carbene analogues. Although no OA products were
isolated, kinetic 31P NMR data indicated that the reactivity of
this mixed chlorophosphine was intermediate between those of
Clear, colorless crystals of 5 were isolated in moderate yield
from this reaction, and a suitable specimen was subjected to a
single-crystal X-ray diffraction analysis. The result of this study
may be seen in Figure 5, while selected bond parameters appear
in the figure caption. It is apparent from the structure of the
t
Ph2PCl and Bu2PCl, and that the steric effects are essentially
additive. Decomposition rates for the OA products of cyclic and
acyclic stannylenes followed the same relative rates as
t
t
insertions, viz., Ph2PCl > Bu(Ph)PCl ≫ Bu2PCl. Because
steric bulk shields the reactive tin−phosphorus bond, it slows
or prevents an associative decomposition pathway.
To investigate possible leaving group effects, the iodo
t
t
analogue of Bu(Ph)PCl, i.e., Bu(Ph)PI, was also prepared by
halide replacement using a modified literature procedure.69 As
in the case of the mixed chloro(tert-butyl)phenylphosphine
reactions, no products were isolated, but the oxidative addition
reactions were monitored by 31P NMR spectroscopy. The
iodophosphines showed an enormous rate increase in their
reactions with the carbene analogues, as seen in Table 1,
supporting the case for a rate-determining step that is highly
sensitive to the nature of the leaving group and pointing to
either an SN2-type mechanism or an adduct/insertion
mechanism with a rate-determining 1,2 halide shift.
3.1.3. Chloro(amino)phosphine Substrates. Previous work
and that discussed above suggested that reactions of
chlorophosphines with diazagermylenes and -stannylenes likely
proceed via either an adduct/insertion or an SN2-type
mechanism, but we were unable to isolate potential
Figure 5. Solid-state structure and partial labeling scheme of 5.
Hydrogen atoms and toluene solvent have been omitted, and all non-
hydrogen atoms are drawn as 50% probability thermal ellipsoids.
Selected bond lengths (Å) and angles (deg): Sn1−Cl1 2.5109(9),
Sn1−P1 2.6322(7), Sn1−N4 2.105(2), P1−N1 1.6673(12), P1−N2
1.6791(12), P1−N3 1.6769(12), Si1−N1,2 (avg.) 1.749(2), Si2−N3
1.820(3), Si2−N4 1.720(3); Cl1−Sn1−P1 101.873), N3−P1−Sn1
108.02(8), N1−P1−N2 85.75(11), N2−P1−N3 115.77(12), N1−
Si1−N2 82.41(11), N3−Si2−N4 109.09(11).
F
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molecule that the P−Cl bond of the chlorophosphine did not
add to the stannylene in a straightforward fashion. Rather, the
Sn−N3 bond of the stannylene ruptured, and the tert-butyl-
amido group (N3) was transferred to phosphorus, yielding a
spiro-heterocycle, composed of four- and five-membered rings
which share a central phosphorus(III) atom. With the
exception of the P−Cl bond, the four-membered ring remained
presumably unchanged from the cyclic chlorophosphine, but
the five-membered ring was newly formed by the formal
insertion of the phosphorus atom into the Sn−N bond. This
latter ring has an envelope conformation, featuring a slightly
twisted rectangular portion (N3−P1−Sn1−N4) which encloses
an angle of 151.00(7)° with the triangular N3−Si2−N4 flap.
Because no oxidative addition took place in this reaction, the
metal is still a tin(II) ion, and at first glance, this might explain
the very long Sn−Cl bond of 2.5109(9) Å. Closer inspection,
however, reveals that this bond is too long for even a Sn(II)−Cl
bond. It is likely not a conventional covalent bond at all, but it
appears that the chloride ion forms a contact-ion pair with a
cationic spiro-heterocycle.
Figure 6. Solid-state structure and partial labeling scheme of 6.
Hydrogen atoms have been omitted, and all non-hydrogen atoms are
drawn as 50% probability thermal ellipsoids. Selected bond lengths (Å)
and angles (deg): Sn1−Cl1 2.5156(6), Sn1−P1 2.6194(4), Sn1−N4
2.1137(12), P1−N1 1.6673(12), P1−N2 1.6791(12), P1−N3
1.6769(12), Si1−N3 1.8052(12), Si1−N4 1.7279(12); Cl1−Sn1−P1
96.991(15), N3−P1−Sn1 105.36(4), N1−P1−N2 102.19(6), N1−
P1−N3 117.00(6), N2−P1−N3 107.35(6), N3−Si1−N4 106.89(6).
The second chloro(amino)phosphine tested, namely,
chlorobis(diethylamino)phosphine, is also a very bulky
substrate, but one that should be able to undergo an adduct/
insertion reaction, if not an SN2 reaction. This substrate, when
treated with B, as shown in eq 10 (Scheme 4), also reacted
groups, rather than a second ring. This heterocycle, however,
has a more perfectly shaped envelope conformation, presum-
ably because it is not tethered to another ring. Thus, the nearly
planar rectangle, composed of P1, N3, Si1, and N4, encloses an
angle of 144.88(3)° with the flap composed of the P1−Sn1−
N4 plane. The five bonds within the heterocycle have virtually
identical lengths as those in 5, as does the unusually long Sn−
Cl bond, thereby further confirming the close structural relation
ship between 5 and 6.
Scheme 4. Reactions of Amino(chloro)phosphines with
Group 14 Carbene Analogues
The two previously discussed reactions did not proceed with
the expected oxidative additions, but they resulted in ligand
exchange. Both substrates were monochlorophosphines,
however, and only a partial ligand exchange was realized in
each case because [Me2Si(tBuN)2]2− is bidentate and di-
negative. Once it became clear that these reactions proceed via
metathesis rather than OA, we tried to generate a product in
which the chelating diamide ligand of the stannylene was fully
exchanged with the chloride ions. Upon treating Et2NPCl2 with
1 equiv of B, as shown in eq 11, a decidedly faster
transformation took place than those depicted in eqs 9 and
10, and the reaction was judged complete after 1 h of stirring at
rt. The 31P{1H} NMR spectrum displayed only one singlet
peak, with a chemical shift characteristic of a heterocyclic
diaminophosphine. A single-crystal X-ray analysis of the
product showed that the targeted reaction had indeed taken
place. The solid-state structure of 7 is depicted in Figure 7,
while selected bond parameters are listed in the figure caption.
The diethylamino group is still bound to the phosphorus
atom, and this moiety is chelated by a k2-N-dimethylsila-di-tert-
butylamido group, thereby forming a triaminophosphine. The
endocyclic P−N bonds are isometric and 1.690(1) Å long,
while the exocyclic bond is slightly shorter at 1.645(1) Å, as is
usual for these heterocycles. The displaced chloride ions now
ligate the tin(II) ion (mean distance = 2.456(1) Å) and enclose
an angle of 94.42(1)°. Both fragments form a Lewis acid−base
adduct, with the longest phosphorus-to-tin bond (2.7274(4) Å)
of any species structurally analyzed in these studies. Only a
small amount of the adduct 7, shown in Figure 7, is present in
benzene solution, however, the major solution species being
free triaminophosphine. This reaction is reminiscent of that
much slower than chloro(hydrocarbyl)phosphines, but the
reaction was significantly faster than that shown in eq 9, being
complete in 12 h at room temperature. Because the reaction
was also much slower than those of the previously observed
oxidative additions, a nonstandard transformation was again
suggested. This was borne out by the structure of the product,
6, which is shown in Figure 6.
The thermal-ellipsoid plot (Figure 6) confirms 6 to be a
structural analogue of 5, with an identical five-membered
heterocycle, although here it is substituted by two diethylamino
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8, which is shown in Figure 8 and whose bond parameters are
given in the figure caption.
Figure 7. Solid-state structure and partial labeling scheme of 7.
Hydrogen atoms have been omitted, and all non-hydrogen atoms are
drawn as 50% probability thermal ellipsoids. Selected bond lengths (Å)
and angles (deg): Sn1−Cl1 2.4520(6), Sn1−Cl2 2.4591(5), P1−Sn1
2.7274 (4), P1−N1 1.6862(14), P1−N2 1.6930(14), P1−N3
1.6449(14); Cl1−Sn1−Cl2 94.416(18), N3−P1−Sn1 119.73(5),
N1−P1−N2 85.63(7), P1−Sn1−Cl1 95.011(17), P1−Sn1−Cl2
94.282(16), N1−Si−N2 82.11(6).
Figure 8. Solid-state structure and partial labeling scheme of 8.
Hydrogen atoms have been omitted, and all non-hydrogen atoms are
drawn as 50% probability thermal ellipsoids. Selected bond lengths (Å)
and angles (deg): Ge1−P1 2.3526 (7), Ge2−P1 2.3336(7), Ge1−Cl1
2.2103(8), Ge2−Cl2 2.1970(6), Ge1−N (avg.) 1.838(2), Ge2−N
(avg.) 1.833(2), P1−N5 1.671(2); Ge1−P1−Ge2 108.00(3), Cl1−
Ge1−P1 96.53(3), P1−Ge2−Cl2 100.10(3), Ge1−P1−N5 109.29(5),
Ge2−P1−N5 107.11(9).
shown in eq 3, although, there, an adduct was not formed,
perhaps due to the lesser Lewis acidity of PbCl2.
The molecule is composed of a central diethylaminophos-
phine unit, which is flanked by two large chlorogermyl moieties.
It is the third representative in a series of compounds of the
While most of the compounds described in this study feature
conventional covalent bonds between phosphorus and
tetravalent germanium or tin, all products of eqs 9−11, viz. 5,
6, and 7, are triaminophosphines with phosphorus-to-tin(II)
donor bonds. Those in 5 and 6 are comparatively short
intermolecular contacts of ca. 2.62 Å length, which lie at the
short end of such bonds.70−74 The intermolecular bond in 7 is
expectedly ca. 0.1 Å longer and accordingly weaker, as
confirmed by the compound being mainly present in solution
in a dissociated form.
t
formula [Me2Si(μ-NtBu)2Ge(Cl)]2PR, where R is Ph, Bu, or
NEt2, syntheses and structures of the phenyl and tert-butyl
analogues having appeared in our earlier study.53 The slightly
asymmetric P−Ge bonds in 8 are somewhat longer than those
of its analogues, perhaps reflecting the greater steric bulk of the
diethylamino group. Steric repulsion is also the likely reason for
the relatively shallow pyramid which features an angle sum of
324.4° at phosphorus.
Just like the chloro(hydrocarbyl)phosphines had done in our
first study, the three chloro(amino)phosphines described above
also exhibited vastly different rates in their reactions with
stannylene B. For example, the formation of 5 required heating
at 60 °C for 15 days, while that of 7 took only 1 h at rt. None of
these reactions is a formal oxidative addition, however, thereby
preventing additional insight into the mechanism(s). The lack
of OA products for B suggests that such species are
thermodynamically unstable with respect to the amino-
phosphines that were formed. Because identical five-membered
heterocycles are present in both, 5 and 6, it appears that these
compounds went through essentially the same mechanistic
steps. They differ in the rate-determining step, which is
obviously much slower in 5 than in 6. The ligation of tin by
chloride despite an absent OA product may suggest that adduct
formation, followed by a 1,2 chloride shift, is the rate-
determining step, and this step would be expected to be
much slower for the cyclic chlorophosphine.
The previous three reactions demonstrate that chloro-
(amino)phosphines, unlike chloro(hydrocarbyl)phosphines,
do not add oxidatively to the tin(II) center, but are either
partially or fully aminated by the cyclic stannylene B. We
wondered if the germanium analogue, A, would show the same
altered reactivity and allowed it to interact with both acyclic
chloro(amino)phosphines, namely, Et2NPCl2 and (Et2N)2PCl.
The fast rate of the reaction with Et2NPCl2, which is shown in
eq 12, immediately signaled an oxidative addition similar to
those PhPCl2 and tBuPCl2 had undergone with this germylene.
This was confirmed by the solid-state structure of the product,
Unfortunately, the reaction of A with the monochlorophos-
phine, (Et2N)2PCl, was less clear-cut, because the product(s)
did not crystallize and could thus not be isolated in a pure form.
The speed of the transformation and the chemical shift of the
phosphorus-containing product, however, strongly suggested an
insertion reaction.
3.2. Thermodynamic and Mechanistic Considerations.
The thermodynamic driving force in OAs is the breaking of one
bond and concomitant formation of two bonds. In the OA of
the P−Cl bond to both A and B, the same bond is broken, but
the Ge−P and Ge−Cl bonds formed are stronger than the Sn−
P and Sn−Cl bonds, as reflected in the greater stability of the
Ge-containing products. It appears that chloro(amino)-
phosphines yield weaker M−P bonds than the corresponding
chloro(hydrocarbyl)phosphines, and that, for the cyclic
stannylene B, such OA intermediates become unstable. In the
absence of an oxidative addition, B functions as an amine
transfer reagenta not unusual transformation given the
polarity of the Sn−N bond.
Oxidative addition reactions proceed by a variety of
mechanisms, which are determined by both, the substrates
and the molecules, undergoing the additions. Relatively polar
substrates, like P−Cl bonds, usually oxidatively add by an SN2-
type mechanism. The faster reactions of stannylenes versus
germylenes with these chlorophosphines suggest that the OA
reactions discussed above proceed by either SN2 or adduct/
insertion mechanisms, because stannylenes are stronger
nucleophiles and stronger Lewis acids than germylenes. If
these OAs were to proceed via concerted or radical
H
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Notes
mechanisms, one would expect the germylenes to react faster,
because they undergo both, the +2 to +4 and the singlet-to-
triplet transitions, more readily than stannylenes.75 Mechanistic
studies of substitution reactions centered on a third row
element, such as phosphorus, present additional problems
because of the potential hypervalency of the elements. It is
therefore impossible to differentiate between SN2 and adduct/
insertion mechanisms, which are closely related, the latter
mechanism implying the presence of a short-lived intermediate,
viz., a Lewis acid/base adduct.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Science Foundation (Grant No. EPS-
0814442) for financial support of this work.
REFERENCES
■
(1) For modern treatments of oxidative addition reactions, see:
(a) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 6th ed.; Wiley: Hoboken, NJ, 2014; pp 163−185. (b) Hartwig,
J. Organotransition Metal Chemistry; University Science Books:
Sausalito, CA, 2010; Chapters 6 and 7.
4. SUMMARY AND CONCLUSION
The work detailed in the previous pages shows that Group 14
carbene analogues reduce chlorophosphines with the inter-
mediacy of oxidative addition products. These reactions are
faster for stannylenes than for germylenes, and they are always
faster for the cyclic variant of each. Steric bulk on either the
carbene analogue or the chlorophosphine substantially slows
these reactions, but the electronic properties of the organic
substituents appear to play only a minor role. On the basis of
these data and observed leaving group effects, we propose that
the oxidative additions proceed via an associative process
either an adduct/insertion or an SN2 mechanism. The ensuing
OA products are almost always stable for germylenes but,
because of the weaker Sn−P bond, rarely so for stannylenes,
making the isolation of tin-containing products more
challenging. An important finding of this study was the
discovery that the kinetically unstable OA products of a cyclic
stannylene decompose via an associative mechanism.
Our goal to shed more light on the reaction mechanism by
using chloro(amino)phosphines substrates was not fully
realized. While chloro(amino)phosphines add readily to cyclic
germylenes, the OA products of chloro(amino)phosphines to
cyclic stannylene (if these indeed form) are apparently unstable.
In the absence of such a product, the diazastannylene reacts
with ligand transfer to the chlorophosphines. Given the polarity
of the Sn−N bond, this outcome is not unexpected, but it does
show that the energetics of the oxidative additions described
above are delicately balanced. The role of di(tert-butylamino)-
stannylenes or -plumbylenes as selective amination agents for
halophosphines and other nonmetal halides deserves further
study, because these reactions are remarkably selective.
(2) Vaska, L.; Diluzio, J. W. Activation of Hydrogen by a Transition
Metal Complex at Normal Conditions Leading to a Stable Molecular
Dihydride. J. Am. Chem. Soc. 1962, 84, 679−680.
(3) Young, J. F.; Osborn, J. A.; Jardine, F. H.; Wilkinson, G. J.
Hydride intermediates in homogeneous hydrogenation reactions of
olefins and acetylenes using rhodium catalysts. Chem. Commun.
(London) 1965, 0, 131−132.
(4) Smith, M. B. Organic Synthesis, 2nd ed.; McGraw-Hill: New York,
2002; pp 613−614.
(5) Bos, K. D.; Bulten, E. J.; Noltes, J. G. Oxidative additions of some
organotin(II) and organic tin(II) compounds. J. Organomet. Chem.
1974, 67, C13−C15.
(6) (a) Gynane, M. J. S.; Lappert, M. F.; Miles, S. J.; Power, P. P.
Ready Oxidative Addition of an Alkyl or Aryl Halide to a Tin(II) Alkyl
or Amide; Evidence for a Free-radical Pathway. J. Chem. Soc., Chem.
Commun. 1976, 256−257. (b) Lappert, M. F.; Power, P. P. Di-and
Trivalent Trimethylsilyl-Substituted Tin Amides and Related Com-
pounds Such as Sn[(SiMe3)2]2 or 3. Adv. Chem. Ser. 1976, 157, 70−81.
(7) Gynane, M. J. S.; Lappert, M. F.; Miles, S. J.; Carty, A. J.; Taylor,
N. J. Subvalent Group 4B Metal Alkyls and Amides. Part 6. Oxidative
Addition of an Alkyl Halide to Bis[bis(trimethylsilyl)methyl]tin(II);
Hydrogen-1 Nuclear Magnetic Resonance Data on the Tin(IV)
Adducts and a Single-crystal X-Ray Study of Tris[bis(trimethylsilyl)-
methyl]chloro-tin(IV). J. Chem. Soc., Dalton Trans. 1977, 2009−2015.
(8) Lappert, M. F.; Misra, M. C.; Onyszchuk, M.; Rowe, R. S.; Power,
P. P.; Slade, M. J. Subvalent group 14 metal compounds XI. Oxidative
addition reactions of organic halides or acid anhydrides (including
CH4−nCln, PhBr, BrN(SiMe3)2, ButCOCl, or (CF3CO)2O) to some
bivalent group 14 metal amides or alkyls. J. Organomet. Chem. 1987,
330, 31−46.
(9) Kavara, A.; Cousineau, K. D.; Rohr, A. D.; Kampf, J. W.; Banaszak
Holl, M. M. A Stannylene/Aryl Iodide Reagent for Allylic CH
Activation and Double Bond Addition Chemistry. Organometallics
2008, 27, 1041−1043.
(10) Miller, K. A.; Bartolin, J. M.; O’Neill, R. M.; Sweeder, R. D.;
Owens, T. M.; Kampf, J. W.; Banaszak Holl, M. M.; Wells, N. J. C-H
Activation of Ethers and Alkanes by GermyleneAryl Halide
Complexes. J. Am. Chem. Soc. 2003, 125, 8986−8987.
(11) Walker, R. H.; Miller, K. A.; Scott, A. L.; Cygan, Z. T.; Kampf, J.
W.; Banaszak Holl, M. M.; Bartolin, J. M. Silylene- and Germylene-
Mediated C−H Activation: Reaction with Alkanes, Ethers, and
Amines. Organometallics 2009, 28, 2744−2755.
(12) Bartolin, J. M.; Kavara, A.; Kampf, J.; Banaszak Holl, M. M. Tin-
Mediated CH Activation and Cross-Coupling in a Single Flask.
Organometallics 2006, 25, 4738−4740.
(13) Miller, K. A.; Watson, T. W.; Bender, J. E., IV; Banaszak Holl,
M. M.; Kampf, J. W. Intermolecular C−H Insertions and Cyclization
Reactions Involving a Stable Germylene. J. Am. Chem. Soc. 2001, 123,
982−983.
ASSOCIATED CONTENT
■
Accession Codes
CCDC 1544260−1544267 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing 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
*E-mail: lothar.stahl@und.edu. Phone: 1-701-777-2242. Fax: 1-
701-777-2331.
(14) Moser, D. F.; Bosse, T.; Olson, J.; Moser, J. L.; Guzei, I. A.;
West, R. Halophilic Reactions of a Stable Silylene with Chloro and
Bromocarbons. J. Am. Chem. Soc. 2002, 124, 4186−4187.
ORCID
Lothar Stahl: 0000-0003-4482-9673
Present Address
(15) Moser, D. F.; Naka, A.; Guzei, I. A.; Muller, T.; West, R.
̈
†Department of Chemistry, Winona State University, Winona,
MN.
Formation of Disilanes in the Reaction of Stable Silylenes with
Halocarbons. J. Am. Chem. Soc. 2005, 127, 14730−14738.
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DOI: 10.1021/acs.inorgchem.7b01275
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(16) Dickie, D. A.; Lee, P. T. K.; Labeodan, O. A.; Schatte, G.;
Weinberg, N.; Lewis, A. R.; Bernard, G. M.; Wasylishen, R. E.;
Clyburne, J. A. C. Flexible coordination of the carboxylate ligand in
tin(II) amides and a 1,3-diaza-2,4-distannacyclobutanediyl. Dalton
Trans. 2007, 2862−2869.
(17) Wetherby, A. E., Jr.; Samanamu, C. R.; Schrick, A. C.;
DiPasquale, A.; Golen, J. A.; Rheingold, A. L.; Weinert, C. S. Synthesis
and structures of aryloxo- and binaphthoxogermanium(IV) alkyl
iodide complexes. Inorg. Chim. Acta 2010, 364, 89−95.
(18) Wills, C.; Izod, K.; Clegg, W.; Harrington, R. W. Oxidation
reactions of a phosphine-borane-stabilised dialkylstannylene. Dalton
Trans. 2010, 39, 2379−2384.
(19) Sen, S. S.; Hey, J.; Kratzert, D.; Roesky, H. W.; Stalke, D. A
Remarkable End-On Activation of Diazoalkane and Cleavage of Both
C−Cl Bonds of Dichloromethane with a Silylene to a Single Product
with Five-Coordinate Silicon Atoms. Organometallics 2012, 31, 435−
439.
(20) Erickson, J. D.; Vasko, P.; Riparetti, R. D.; Fettinger, J. C.;
Tuononen, H. M.; Power, P. P. Reactions of m-Terphenyl-Stabilized
Germylene and Stannylene with Water and Methanol: Oxidative
Addition versus Arene Elimination And Different Reaction Pathways
for Alkyl- and Aryl-Substituted Species. Organometallics 2015, 34,
5785−5791.
(21) Erickson, J. D.; Riparetti, R. D.; Fettinger, J. C.; Power, P. P.
Molecular Zinc Species with Ge−Zn and Sn−Zn Bonds: A Reversible
Insertion of a Stannylene into a Zinc−Carbon Bond. Organometallics
2016, 35, 2124−2128.
(22) Wang, X.; Zhu, Z.; Peng, Y.; Lei, H.; Fettinger, J. C.; Power, P.
P. Room-Temperature Reaction of Carbon Monoxide with a Stable
Diarylgermylene. J. Am. Chem. Soc. 2009, 131, 6912−6913.
(23) Peng, Y.; Ellis, B. D.; Wang, X.; Power, P. P. Diarylstannylene
Activation of Hydrogen or Ammonia with Arene Elimination. J. Am.
Chem. Soc. 2008, 130, 12268−12269.
(24) Peng, Y.; Ellis, B. D.; Zhu, Z.; Fettinger, J. C.; Nagase, S.; Power,
P. P.; Guo, J.-D. Diarylstannylene Activation of Hydrogen or
Ammonia with Arene Evolution. J. Am. Chem. Soc. 2009, 131,
16272−16282.
(25) Erickson, J. D.; Fettinger, J. C.; Power, P. P. Reaction of a
Germylene, Stannylene, or Plumbylene with Trimethylaluminum and
Trimethylgallium: Insertion into Al−C or Ga−C Bonds, a Reversible
Metal−Carbon Insertion Equilibrium, and a New Route to
Diplumbenes. Inorg. Chem. 2015, 54, 1940−1948.
(26) Burford, N.; Ragogna, P. J.; Sharp, K.; McDonald, R.; Ferguson,
M. J. Arsinophosphonium Cations from Arsenium-phosphine and
-bisphosphine Coordination Chemistry. Inorg. Chem. 2005, 44, 9453−
9460.
(27) Burford, N.; Ragogna, P. J. Coordination Chemistry of
Phosphorus(III) as a Lewis Acceptor. ACS Symp. Ser. 2006, 917,
280−292.
(28) MacDonald, E.; Doyle, L.; Burford, N.; Werner-Zwanziger, U.;
Decken, A. Stannylphosphonium Cations. Angew. Chem., Int. Ed. 2011,
50, 11474−11477.
(29) Chitnis, S. S.; Whalen, J. M.; Burford, N. Influence of Charge
and Coordination Number on Bond Dissociation Energies, Distances,
and Vibrational Frequencies for the Phosphorus−Phosphorus Bond. J.
Am. Chem. Soc. 2014, 136, 12498−12506.
(30) Chitnis, S. S.; Burford, N. Phosphine complexes of lone pair
bearing Lewis acceptors. Dalton Trans. 2015, 44, 17−29.
(31) Bamford, K. L.; Chitnis, S. S.; Stoddard, R. L.; McIndoe, J. S.;
Burford, N. Bond fission in monocationic frameworks: diverse
fragmentation pathways for phosphinophosphonium cations. Chem.
Sci. 2016, 7, 2544−2552.
(34) Shah, S.; Concolino, T.; Rheingold, A. L.; Protasiewicz, J. D.
Sterically Encumbered Systems for Two Low-Coordinate Phosphorus
Centers. Inorg. Chem. 2000, 39, 3860−3867.
(35) Smith, R. C.; Gantzel, P.; Rheingold, A. L.; Protasiewicz, J. D.
Arsa-Wittig Complexes (ArAs = PMe3) as Intermediates to Diarsenes.
Organometallics 2004, 23, 5124−5126.
(36) Dutan, C.; Shah, S.; Smith, R. C.; Choua, S.; Berclaz, T.;
Geoffroy, M.; Protasiewicz, J. D. Sterically Encumbered Diphosphaal-
kenes and a Bis(diphosphene) as Potential Multiredox-Active
Molecular Switches: EPR and DFT Investigations. Inorg. Chem.
2003, 42, 6241−6251.
(37) Smith, R. C.; Urnezius, E.; Lam, K.-C.; Rheingold, A. L.;
Protasiewicz, J. D. Syntheses and Structural Characterizations of the
Unsymmetrical Diphosphene DmpPPMes* (Dmp = 2,6-Mes2C6H3,
Mes* = 2,4,6-tBu3C6H2) and the Cyclotetraphosphane [DmpPPPh]2.
Inorg. Chem. 2002, 41, 5296−5299.
(38) Cowley, A. H.; Kilduff, J. E.; Newman, T. H.; Pakulski, M.
Diphosphenes (RP = PR). Synthesis and NMR Characterization. J.
Am. Chem. Soc. 1982, 104, 5820−5821.
(39) Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotsu, K.; Higuchi, T.
Synthesis and Structure of Bis(2,4,6-tri-tert-butylphenyl)diphosphene:
Isolation of a True “Phosphobenzene. J. Am. Chem. Soc. 1981, 103,
4587−4589.
(40) Smith, R. C.; Shah, S.; Protasiewicz, J. D. A role for free
phosphinidenes in the reaction of magnesium and sterically
encumbered ArPCl2 in solution at room temperature. J. Organomet.
Chem. 2002, 646, 255−261.
(41) Veith, M.; Huch, V.; Majoral, J.-P.; Bertrand, G.; Manuel, G.
Stannylene and germylene as powerful dechlorinating reagents: new
route to diphosphene. Tetrahedron Lett. 1983, 24, 4219−4222.
(42) Veith, M.; Gouygou, M.; Detemple, A. Germa-Phosphines and
Stanna-Phosphines from the Insertion of Germylenes and Stannylenes
into P−Cl Bonds. Phosphorus, Sulfur Silicon Relat. Elem. 1993, 75,
183−186.
(43) du Mont, W.-W.; Schumann, H. Chloro(di-tert-
butylphosphino)germanediyl and -stannanediyl: Stable Germanium-
(II) and Tin(II) Organophosphorus Compounds. Angew. Chem., Int.
Ed. Engl. 1975, 14, 368−369.
(44) du Mont, W.-W.; Schumann, H. α-Elimination Reactions at Di-
t-Butyl(Trichlorogermyl)phosphine: A Route to Phosphinogermy-
lenes and Triorganophosphino-Dichlorogermylene-Complexes. J.
Organomet. Chem. 1975, 85, C45−C47.
(45) du Mont, W.-W.; Neudert, B.; Schumann, H. Novel Redox
Reactions of Tri-tert-butylphosphane with Tetrahalides of Germanium
and Tin. Angew. Chem., Int. Ed. Engl. 1976, 15, 308−309.
(46) Schumann, H.; du Mont, W.-W.; Kroth, H.-J. Organo[chlor-
(methyl)stannyl]phosphines and -amines. Chem. Ber. 1976, 109, 237−
245.
(47) Schumann, H.; du Mont, W.-W.; Wobke, B. Substitution
̈
Reactions at Di-tert-butyl(chlorodimethylstannyl)phosphine and Di-
tert-butyl(chlorodimethylgermyl)phosphine. Chem. Ber. 1976, 109,
1017−1022.
(48) du Mont, W.-W.; Kroth, H.-J.; Schumann, H. Redox Reactions
between Tri-tert-butylphosphin and Element(IVb)-Tetrachlorides:
Tri-tert-butylchlorophosphonium-Salts. Chem. Ber. 1976, 109, 3017−
3024.
(49) du Mont, W.-W.; Neudert, B. Organophosphine-substituted
Halogenogermylenes and − stannylenes. Z. Anorg. Allg. Chem. 1977,
436, 270−276.
(50) du Mont, W.-W.; Neudert, B. Synthesis und Vibrational Spectra
of Pentacarbonyl[chloro-di-tert-butylphosphino)stannio]metal(VI A)
Complexes. Chem. Ber. 1978, 111, 2267−2272.
(51) Veith, M.; Grosser, M.; Huch, V. Cyclic Diazastannylenes. XIX.
Reaction of a Bis(amino)germylene, -stannylene, and -plumbylene
with Phosphorus Trichloride and 2, 3-Dimethyl-1, 3-butadiene. Z.
Anorg. Allg. Chem. 1984, 513, 89−102.
(32) Robertson, A. P. M.; Gray, P. A.; Burford, N. Interpnictogen
Cations: Exploring Vistas in Coordination Chemistry. Angew. Chem.,
Int. Ed. 2014, 53, 6050−6069.
(33) Shah, S.; Protasiewicz, J. D. ‘Phospha-variations’ on the themes
of Staudinger and Wittig: phosphorus analogs of Wittig reagents.
Coord. Chem. Rev. 2000, 210, 181−201.
(52) Scherer, O. J.; Puttmann, M. L.; Kruger, C.; Wolmershauser, G.
̈
̈
̈
Rotamers of Aminophosphanes- and Aminophosphoranes. Chem. Ber.
1982, 115, 2076−2124.
J
DOI: 10.1021/acs.inorgchem.7b01275
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(53) West, J. K.; Stahl, L. Insertions of Cyclic and Acyclic
Germanium and Tin Heterocarbenoids into Phosphorus-Chlorine
Bonds: Syntheses, Structures, and Reactivities. Organometallics 2012,
31, 2042−2052.
(72) Krebs, K. M.; Maudrich, J.-J.; Wesemann, L. Reaction of
stannylene phosphorus Lewis pairs with dichlorides of germanium, tin
and lead − the formation of base stabilized stannyl stannylenes/
germylenes and redox reaction with PbCl2. Dalton Trans. 2016, 45,
8081−8088.
(73) Arras, J.; Eichele, K.; Maryasin, B.; Schubert, H.; Ochsenfeld, C.;
Wesemann, L. Intermolecular 119Sn,31P Through-Space Spin−Spin
Coupling in a Solid Bivalent Tin Phosphido Complex. Inorg. Chem.
2016, 55, 4669−4675.
(74) Barney, A. A.; Heyduk, A. F.; Nocera, D. G. Synthesis of an
anionic tridentate phosphinoborate and its reaction chemistry with
Sn(II). Chem. Commun. 1999, 2379−2380.
(75) Su, M.-D. Theoretical Study of Halophilic Reactions of Stable
Silylenes with Chloro- and Bromocarbons. J. Am. Chem. Soc. 2003,
125, 1714−1715.
(54) Schweizer, S.; Becht, J.-M.; Le Drian, C. Highly Efficient and
Reusable Supported Pd Catalysts for Suzuki−Miyaura Reactions of
Aryl Chlorides. Org. Lett. 2007, 9, 3777−3780.
(55) Pudovik, M. A.; Mikhailov, Y. B.; Pudovik, A. N. Synthesis and
some reactions of cyclic oligomers - derivatives of a 2-coordinate
phosphorus atom. Zh. Obshch. Khim. 1985, 55, 1475−1479.
(56) Amigues, E. J.; Hardacre, C.; Keane, G.; Migaud, M. E. Solvent-
modulated reactivity of PCl3 with Amines. Green Chem. 2008, 10,
660−669.
(57) Veith, M. Cyclic Nitrogen Derivatives of Tetra- and Divalent
Tin. Angew. Chem., Int. Ed. Engl. 1975, 14, 263−264.
(58) (a) Veith, M. Cyclic Diazastannylenes, II. Intermolecular Lewis-
Acid-Based Adducts of 1,3,2,4λ2-Diazasilastannetidines. Z. Naturforsch.,
B: J. Chem. Sci. 1978, 33, 1−6. (b) Veith, M. Cyclic Diazastannylenes,
III. The Crystal and Molecular Structure of the Monoclinic Phase of
1,3-Di-tert-butyl-2,2-dimethyl-1,3,2,4λ2-Diazasilastannetidine. Z. Natur-
forsch., B: J. Chem. Sci. 1978, 33, 7−13.
(59) Gynane, M. J. S.; Harris, D. H.; Lappert, M. F.; Power, P. P.;
Riviere, P.; Riviere-Baudet, M. Subvalent Group 4B Metal Alkyls and
̀ ̀
Amides. Part 5. The Synthesis and Physical Properties of Thermally
Stable Amides of Germanium(II), Tin(II), and Lead(II). J. Chem. Soc.,
Dalton Trans. 1977, 2004−2009.
(60) SMART and SAINT-plus; Siemens Analytical X-ray Systems:
Madison, WI, 1995.
(61) SADABS program for absorption corrections using the Bruker
CCD Detector System. Based on: Blessing, R. H. Acta Crystallogr., Sect.
A: Found. Crystallogr. 1995, 51, 33−38.
(62) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr.,
Sect. A: Found. Crystallogr. 2008, 64, 112−122.
(63) Dyker, A. C.; Burford, N.; Lumsden, M. D.; Decken, A. Acyclic
catena-Diphosphinodiphosphonium Dications [R3P-PR‘-PR‘-PR3]2+ or
Bisphosphine−Diphosphenium Complexes [R3P→PR‘-PR‘←PR3]2+:
Synthesis by Reductive P−P Coupling of [R3P-PR‘Cl]+ and Phosphine
Ligand Exchange. J. Am. Chem. Soc. 2006, 128, 9632−9633.
(64) Geier, J.; Harmer, J.; Grutzmacher, H. Naked” Phosphanediide
̈
Chains and their Fragmentation into Diphosphene Radical Anions.
Angew. Chem., Int. Ed. 2004, 43, 4093−4097.
(65) Stein, D.; Dransfeld, A.; Flock, M.; Ruegger, H.; Grutzmacher,
̈
̈
H. Lithium Oligophosphanediides in the Li/PhPCl System. Eur. J.
Inorg. Chem. 2006, 2006, 4157−4167.
(66) Pu, L.; Olmstead, M. M.; Power, P. P.; Schiemenz, B. Synthesis
and Characterization of the Monomeric Terphenyl-Metal Halides
Ge(Cl){C6H3-2,6-Trip2} (Trip = C6H2-2,4,6-i-Pr3) and Sn(I){C6H3-
2,6-Trip2} and the Terphenyl-Metal Amide Sn{N(SiMe3)2}{C6H3-2,6-
Trip2}. Organometallics 1998, 17, 5602−5606.
(67) Kavara, A.; Kampf, J. W.; Banaszak Holl, M. M. Direct
Formation of Propargyltin Compounds via C−H Activation. Organo-
metallics 2008, 27, 2896−2897.
(68) Izod, K.; Evans, P.; Waddell, P. G.; Probert, M. R. Remote
Substituent Effects on Structures and Stabilities of P=E π-Stabilized
Diphosphatetrylenes (R2P)2 (E = Ge, Sn). Inorg. Chem. 2016, 55,
10510−10522.
́
(69) Humbel, S.; Bertrand, C.; Darcel, C.; Bauduin, C.; Juge, S.
Configurational Stability of Chlorophosphines. Inorg. Chem. 2003, 42,
420−427.
(70) Weicker, S. A.; Dube, J. W.; Ragogna, P. J. Synthesis of
Zwitterionic Group 14 Centered Complexes: Traditional Coordina-
tion and Unusual Insertion Chemistry. Organometallics 2013, 32,
6681−6689.
(71) Karsch, H. H.; Appelt, A.; Muller, G. Functional trimethyl-
̈
phosphine derivatives. Part 24. Main group element phosphine
complexes. 5. Tri- and tetracoordinated, monomeric tin(II) phosphine
complexes and x-ray structure of Sn[C(PMe2)3]2. Organometallics
1986, 5, 1664−1670.
K
DOI: 10.1021/acs.inorgchem.7b01275
Inorg. Chem. XXXX, XXX, XXX−XXX