Influence of Chain Length on the Structures and Dynamic Behavior of Alkyl-Tethered α,ω-Diphosphide Complexes of Lithium and Their Use in the Synthesis of P-Heterocyclic Stannylenes

Article abstract of DOI:10.1021/acs.inorgchem.8b02510

The alkyl-tethered α,ω-diphosphines (Dipp)PH(CH₂)_nPH(Dipp) (n = 1 (3H), 2 (4H), 3 (5H), 4 (6H), and 5 (7H)) were prepared in good yield and characterized by multinuclear NMR spectroscopy [Dipp = 2,6-iPr₂C₆H₃]. Treatment of 3H with 2 equiv of nBuLi and 2 equiv of TMEDA gives the diphosphide complex [CH₂{P(Dipp)}₂]Li₂(TMEDA)₂ (3Lia), which crystallizes as discrete monomers which do not exhibit temperature-dependent NMR behavior. Treatment of 4H-7H with 2 equiv of nBuLi in THF gives the diphosphides [[CH₂{P(Dipp)}]₂]₂Li₄(THF)₂(OEt₂)₂ (4Li), [CH₂{CH₂P(Dipp)}₂]Li₂(THF)₄ (5Li), [{CH₂CH₂P(Dipp)}₂]Li₂(THF)₆ (6Li), and [CH₂{CH₂CH₂P(Dipp)}₂]₂Li₄(THF)₆·PhMe (7Li) after crystallization. Compounds 4Li-7Li adopt either monomeric or dimeric structures in the solid state, depending on the length of the alkyl tether of the diphosphide ligand. In solution, compounds 4Li-7Li exhibit dynamic behavior: variable-temperature ³¹P{¹H} and ⁷Li NMR spectroscopic studies indicate that this involves equilibria between monomeric and dimeric or higher oligomeric species with the nature of the equilibrium again depending on the length of the alkyl tether of the diphosphide ligand. The reactions between 3Li, 6Li, or 7Li and SnCl₂ in THF give mixtures of products which could not be separated. In contrast, the reactions between 4Li or 5Li and 1 equiv of SnCl₂ give the dimeric P-heterocyclic stannylenes [{CH₂P(Dipp)}₂Sn]₂ (4Sn) and [CH₂{CH₂P(Dipp)}₂Sn]₂.1/2THF (5Sn), respectively. While compound 5Sn is isolated exclusively as the cis isomer, 4Sn is isolated as a mixture of cis and trans isomers in an approximate 5:1 ratio. The solid-state structures of trans-4Sn and cis-5Sn were obtained, and multinuclear NMR spectroscopy indicates that the dimeric structures of these compounds are maintained in solution. Compounds 4Sn and 5Sn represent the first P-heterocyclic stannylene dimers to be structurally characterized.

Full text of DOI:10.1021/acs.inorgchem.8b02510

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Influence of Chain Length on the Structures and Dynamic Behavior
of Alkyl-Tethered α,ω-Diphosphide Complexes of Lithium and Their
Use in the Synthesis of P‑Heterocyclic Stannylenes
Keith Izod,* Peter Evans, Thomas Horsley Downie, William McFarlane, and Paul G. Waddell
Main Group Chemistry Laboratories, School of Chemistry, Newcastle University, Newcastle upon Tyne NE1 7RU, U.K.
S
* Supporting Information
ABSTRACT: The alkyl-tethered α,ω-diphosphines (Dipp)PH-
(CH2)nPH(Dipp) (n = 1 (3H), 2 (4H), 3 (5H), 4 (6H), and 5
(7H)) were prepared in good yield and characterized by
multinuclear NMR spectroscopy [Dipp = 2,6-iPr2C6H3]. Treat-
ment of 3H with 2 equiv of nBuLi and 2 equiv of TMEDA gives
the diphosphide complex [CH2{P(Dipp)}2]Li2(TMEDA)2 (3Lia),
which crystallizes as discrete monomers which do not exhibit
temperature-dependent NMR behavior. Treatment of 4H−7H
with 2 equiv of nBuLi in THF gives the diphosphides
[[CH2{P(Dipp)}]2]2Li4(THF)2(OEt2)2 (4Li), [CH2{CH2P-
(Dipp)}2]Li2(THF)4 (5Li), [{CH2CH2P(Dipp)}2]Li2(THF)6
(6Li), and [CH2{CH2CH2P(Dipp)}2]2Li4(THF)6·PhMe (7Li) after crystallization. Compounds 4Li−7Li adopt either
monomeric or dimeric structures in the solid state, depending on the length of the alkyl tether of the diphosphide ligand. In
7
solution, compounds 4Li−7Li exhibit dynamic behavior: variable-temperature 31P{1H} and Li NMR spectroscopic studies
indicate that this involves equilibria between monomeric and dimeric or higher oligomeric species with the nature of the
equilibrium again depending on the length of the alkyl tether of the diphosphide ligand. The reactions between 3Li, 6Li, or 7Li
and SnCl2 in THF give mixtures of products which could not be separated. In contrast, the reactions between 4Li or 5Li and 1
equiv of SnCl2 give the dimeric P-heterocyclic stannylenes [{CH2P(Dipp)}2Sn]2 (4Sn) and [CH2{CH2P(Dipp)}2Sn]2.1/2THF
(5Sn), respectively. While compound 5Sn is isolated exclusively as the cis isomer, 4Sn is isolated as a mixture of cis and trans
isomers in an approximate 5:1 ratio. The solid-state structures of trans-4Sn and cis-5Sn were obtained, and multinuclear NMR
spectroscopy indicates that the dimeric structures of these compounds are maintained in solution. Compounds 4Sn and 5Sn
represent the first P-heterocyclic stannylene dimers to be structurally characterized.
around the same time, Stelzer and coworkers reported that the
methylene-tethered diphosphines RP(H)CH2PR(H) [R = Me,
iPr, tBu, Ph, Mes; Mes = 2,4,6-trimethylphenyl] underwent
double deprotonation upon treatment with 2 equiv of MeLi to
give the dilithium derivatives [RPCH2PR]Li2, which were
characterized by multinuclear NMR spectroscopy.7 Variable-
temperature 31P{1H} and 7Li NMR spectroscopy of these
compounds suggested a monomer−oligomer equilibrium
operated in solution. Wagner and coworkers also reported
the solid-state structure of a related alkyl-tethered bis-
(phosphido-borane) complex.8 A small number of transition
metal complexes of alkyl-tethered α,ω-diphosphides have also
been reported,9−13 along with a selection of variously
substituted aryl- or alkenyl-bridged diphosphide com-
pounds.14−24
INTRODUCTION
■
Alkyl-tethered α,ω-diphosphines such as bis-
(diphenylphosphino)-methane and -ethane are a mainstay in
transition metal coordination chemistry and catalysis. In
contrast, the corresponding dianionic, alkyl-tethered α,ω-
diphosphides [RP(CH2)nPR]2− have received far less attention
despite their potential utility for the formation of phosphorus-
element or phosphorus−metal σ-bonds and for the synthesis of
novel phosphorus-containing heterocycles.
Compounds of the type [RP(CH2)nPR]M [R = Cy, Ph; M =
Li2, Na2, K2, Mg, Sn, AlX; n = 2−6] were first reported by
Isslieb and coworkers in the 1960s but were not investigated in
detail;1−4 no structural data and only very limited spectro-
scopic data were presented. Subsequently, in the late 1980s,
Lappert and coworkers and Craig and coworkers independ-
ently reported that Ph2PCH2CH2PPh2 underwent Ph−P
cleavage on treatment with elemental lithium under carefully
controlled conditions to give the dilithium derivative
[{PhPCH2CH2PPh}Li2(THF)4]2 (1);5,6 Lappert and cow-
orkers indicated that this compound may be used for the
synthesis of Ge(II) and Sn(II) heterocycles, although these
latter compounds were not well-characterized (see below).6 At
Our interest in alkyl-tethered α,ω-diphosphides stems from
their potential use as precursors to novel cyclic diphosphate-
trylenes (P-heterocyclic tetrylenes), heavier element analogues
of the now ubiquitous N-heterocyclic carbenes.25 We recently
Received: September 4, 2018
© XXXX American Chemical Society
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Scheme 1. Synthesis of α,ω-Diphosphines 3H−7H
reported the synthesis of a series of acyclic diphosphatetrylenes
(Ar2P)2E (2), in which the steric and electronic properties of
the aryl substituents encourage the planarization of one of the
phosphorus centers, enabling stabilization of the electron-
deficient tetrel centers by PE π-interactions [Ar = 2,6-
iPr2C6H3 (Dipp) or 2,4,6-iPr3C6H2 (Trip)].26,27
phosphine (Dipp)(iPr2N)PH as a colorless oil. Treatment of
this phosphine with PhCH2K gave the potassium phosphide
[(Dipp)(iPr2N)P]K, which reacted with 0.5 equiv of
ClCH2CH2Cl to give the diphosphine [CH2{P(Dipp)-
(NiPr2)}]2. Deprotection of [CH2{P(Dipp)(NiPr2)}]2 with 4
equiv of anhydrous ethereal HCl, followed by treatment with 2
equiv of LiAlH4 gave 4H as a colorless crystalline solid in good
yield.
The remaining alkyl-tethered α,ω-diphosphines
CH2{CH2PH(Dipp)}2 (5H), {CH2CH2PH(Dipp)}2 (6H),
and CH2{CH2CH2PH(Dipp)}2 (7H) were prepared by the
reaction of 2 equiv of in situ prepared [(Dipp)PH]K with 1,3-
dibromopropane, 1,4-dibromobutane, or 1,5-dibromopentane,
respectively, and were isolated as either colorless oils (5H, 7H)
or solids (6H) in good yield (Scheme 1c). The use of the
potassium reagent [(Dipp)PH]K in these reactions gives
cleaner products and higher yields than the corresponding
lithium derivative.31 P{1H} and 1H NMR spectroscopy
indicate that compounds 3H, 4H, and 5H are formed as an
essentially 1:1 mixture of rac and meso diastereomers. For
compounds 6H and 7H, only a single signal is observed in the
31P{1H} NMR spectrum due to accidental coincidence of the
signals from the rac and meso diastereomers; however, the PH
signal in each of the 1H NMR spectra of these two compounds
clearly shows the presence of the two possible diastereomers in
each case.
Dilithium α,ω-Diphosphides. Treatment of 3H with 2
equiv of nBuLi in THF gave the corresponding dilithium
complex [CH2{P(Dipp)}2]Li2(THF)n (3Li). We were not able
to isolate this dilithium complex as single crystals, but addition
of 2 equiv of TMEDA yielded the complex [CH2{P(Dipp)}2]-
Li2(TMEDA)2 (3Lia), after crystallization from methylcyclo-
hexane, in a form suitable for X-ray crystallography (Chart 1)
[TMEDA = N,N,N′,N′-tetramethylethylenediamine]. In con-
trast, the reaction between 4H and 2 equiv of nBuLi in THF
gave single crystals of the mixed solvate [[CH2{P-
(Dipp)}]2]2Li4(THF)2(OEt2)2 (4Li) after crystallization
from a mixture of diethyl ether and light petroleum; after
workup, the bulk of this compound was found to have the
a l t e r n a t i v e s t o i c h i o m e t r y [ [ { C H 2 P -
(Dipp)}2]2Li4(THF)2(OEt2)3 (4Lia). The reactions between
5H, 6H, and 7H with 2 equiv of nBuLi in THF gave the
complexes [CH2{CH2P(Dipp)}2]Li2(THF)4 (5Li),
[ { C H 2 C H 2 P ( D i p p ) } 2 ] L i 2 ( T H F ) 6 ( 6 L i ) , a n d
Because planarization of phosphorus is also favored by
incorporation of the phosphorus center into a ring, we were
interested to observe whether alkyl-tethered α,ω-diphosphides
would serve as precursors to P-heterocyclic tetrylenes and
whether these latter species would exhibit PE π-interactions
in spite of the necessarily reduced steric bulk of these ligands in
comparison to those used in the synthesis of 2. Herein, we
present the syntheses of a series of sterically hindered
secondary diphosphines (Dipp)PH(CH2)nPH(Dipp) [n =
1−5] and their dilithium derivatives and the reactions of
these latter species with tin(II) chloride to give dimeric P-
heterocyclic stannylenes.
RESULTS AND DISCUSSION
■
α,ω-Diphosphines. The precursor α,ω-diphosphines
(CH2)n{PH(Dipp)}2 [n = 1−5] were prepared by a variety
of routes, according to the length of the alkyl tether.
Straightforward reactions between lithium phosphides and
dihaloalkanes were unsuccessful for short tether lengths (n = 1
or 2). For example, treatment of either CH2Cl2 or CH2Br2 with
2 equiv of in situ prepared [(Dipp)PH]Li gave mixtures, from
which clean samples of CH2{PH(Dipp)}2 (3H) could not be
isolated, while reactions between 2 equiv of [(Dipp)PH]Li and
either ClCH2CH2Cl or BrCH2CH2Br gave the phosphirane
(Dipp)P(CH2CH2) as the major product. In contrast, the
reaction between Cl2PCH2PCl2 and 2 equiv of (Dipp)Li-
(OEt2) gave the disecondary chlorophosphine CH2{PCl-
(Dipp)}2, which reacted with 2 equiv of LiAlH4 to give the
diphosphine 3H in good yield (Scheme 1a).
The ethylene-bridged diphosphine {CH2PH(Dipp)}2 (4H)
was successfully prepared by a multistep synthesis involving
protection of the phosphine as its amide (Scheme 1b). The
reaction between (iPr2N)PCl2 and (Dipp)Li(OEt2) in diethyl
ether, followed by treatment with 1 equiv of LiAlH4 gave the
B
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Chart 1. Schematic Structures of 3Lia, 4Li, 5Li, 6Li, and 7Li
[CH2{CH2CH2P(Dipp)}2]2Li4(THF)6.PhMe (7Li) after crys-
tallization from diethyl ether, THF, and toluene, respectively.
Compound 7Li rapidly loses solvent upon exposure to
vacuum, yielding the alternative solvate [CH2{CH2CH2P-
(Dipp)}2]2Li4(THF)5 (7Lia).
Compounds 3Lia and 5Li crystallize as discrete monomers
in which the two phosphorus atoms bridge the two lithium
ions (Figure 1); for 3Lia, the coordination of each lithium ion
is completed by two nitrogen atoms from a molecule of
TMEDA, while for 5Li, the coordination of each lithium is
completed by two molecules of THF to give a distorted
tetrahedral geometry at lithium in each case. In contrast, 4Li
crystallizes as dimers (Figure 2), whose structure closely
resembles that of the dilithium complex 1.5,6 Compound 4Li
contains two distinct lithium environments: Li(2) and Li(4)
are coordinated by the two phosphorus atoms of one ligand
each, generating two five-membered chelate rings [P−Li−P
bite angles 96.02(19) and 96.0(2)°], with coordination of each
of these lithium ions completed by a molecule of THF, while
Li(1) and Li(3) are coordinated by two phosphorus atoms
from two different diphosphide ligands and by a molecule of
diethyl ether. Thus, each lithium ion in 4Li is three-coordinate
with an essentially trigonal planar geometry. Compound 6Li
crystallizes as linear monomers in which each lithium ion is
coordinated by a single phosphorus atom and three molecules
of THF in a distorted tetrahedral geometry (Figure 3). In
contrast, 7Li crystallizes as centrosymmetric dimers, in which
each lithium ion is coordinated by one phosphorus atom from
each of the two diphosphide ligands, generating two Li2P2 four-
membered rings (Figure 4). The coordination of Li(1) is
completed by two molecules of THF, to give a distorted
tetrahedral geometry, while the coordination of Li(2) is
completed by a single molecule of THF, to give an essentially
trigonal planar geometry.
Figure 1. Molecular structures of (a) 3Lia and (b) 5Li with 40%
probability ellipsoids and with H atoms omitted for clarity. Selected
bond lengths (Å) and angles (deg): 3Lia P(1)−Li(1) 2.537(4),
P(1)−Li(2) 2.500(4), P(2)−Li(1) 2.559(4), P(2)−Li(2) 2.533(4),
N(1)−Li(1) 2.118(4), N(2)−Li(1) 2.099(5), N(3)−Li(2) 2.071(5),
N(4)−Li(2) 2.082(4), Li(2)−P(2)−Li(1) 93.11(13), P(1)−Li(1)−
P(2) 67.27(10), N(2)−Li(1)−N(1) 87.25(17), P(1)−Li(2)−P(2)
68.23(10), N(3)−Li(2)−N(4) 88.63(16); 5Li P(1)−Li(1) 2.555(3),
P(1)−Li(1A) 2.547(3), Li(1)−O(1) 1.946(3), Li(1)−O(2)
1.967(3), Li(1A)−P(1)−Li(1) 81.05(11), C(13)−P(1)−Li(1A)
107.5(2), P(1A)−Li(1)−P(1) 82.11(8), O(1)−Li(1)−O(2)
98.88(13).
single set of ligand resonances, consistent with the structure
observed in the solid state being retained in solution; these
spectra do not change significantly with temperature. For the
remaining α,ω-diphosphides 4Li−7Li, the room temperature
1H and 13C{1H} NMR spectra are complex, with broad and
overlapping signals, clearly suggesting the operation of
dynamic processes in solution. These spectra become more
complex at lower temperatures, and so it is not possible to
assign them unambiguously. The 31P{1H} and 7Li NMR
spectra of 4Li−7Li are more informative and reveal multiple
dynamic processes to be operating in solution.
In each of 3Li−7Li the P−Li distances are typical of the P−
Li distances reported for other lithium phosphides,28 with
longer distances observed for four-coordinate lithium ions
compared to three-coordinate lithium ions, as expected. For
example, the P−Li distances for the four-coordinate lithium
ions in 5Li are 2.555(3) and 2.547(3) Å, while the P−Li
distances in four-coordinate [(Ph2P)Li(TMEDA)]2 range from
2.574(19) to 2.629(20) Å.29 In contrast, the P−Li distances
for the three-coordinate lithium ions in 4Li range from
2.469(6) to 2.503(5) Å, while the corresponding distances in
three-coordinate [(Ph2P)Li(OEt2)]∞ range from 2.469(10) to
2.492(10) Å.30
At 80 °C, the 31P{1H} NMR spectrum of 4Li consists of a
pair of very broad signals at approximately −113 (A) and −123
ppm (B) (Figure 5a). As the temperature is reduced, peak B
decreases in intensity with respect to peak A, until at 0 °C, a
7
The 31P{1H} and Li NMR spectra of 3Lia consist of a
1:2:3:4:3:2:1 septet and a 1:2:1 triplet (JPLi = 41 Hz),
respectively, while the 1H and 13C{1H} NMR spectra exhibit a
C
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Figure 4. Molecular structure of 7Li with 40% probability ellipsoids;
H atoms, solvent of crystallization, and disorder components omitted
for clarity. Selected bond lengths (Å) and angles (deg): P(1)−Li(1)
2.578(4), P(1)−Li(2A) 2.485(3), P(2)−Li(1A) 2.600(4), P(2)−
Li(2) 2.492(4), Li(1)−O(1) 1.997(7), Li(1)−O(2) 2.004(9), Li(2)−
O(3) 1.915(9), Li(2A)−P(1)−Li(1) 80.32(12), Li(2A)−P(2)−Li(1)
803.32(12), Li(2)−P(2)−Li(1) 79.77(12), P(1)−Li(1)−P(2A)
96.40(12), O(1)−Li(1)−O(2) 112.7(5), O(1A)−P(1)−O(2A)
95.9(5), P(1A)−Li(2)−P(2) 101.74(13).
Figure 2. Molecular structure of 4Li with 40% probability ellipsoids
and with H atoms and disorder component omitted for clarity.
Selected bond lengths (Å) and angles (deg): P(1)−Li(2) 2.496(6),
P(1)−Li(1) 2.503(5), P(2)−Li(2) 2.470(6), P(2)−Li(3) 2.498(5),
P(3)−Li(4) 2.489(6), P(3)−Li(3) 2.486(5), P(4)−Li(4) 2.469(6),
P(4)−Li(1) 2.496(5), Li(1)−O(1) 1.963(7), Li(2)−O(2B)
1.801(10), Li(3)−O(3A) 1.907(10), Li(4)−O(4A) 1.882(11),
Li(2)−P(1)−Li(1) 126.1(2), Li(2)−P(2)−Li(3) 106.0(2), Li(3)−
P(3)−Li(4) 124.0(2), Li(4)−P(4)−Li(1) 107.0(2).
monomeric form is no longer observed. The dimeric structure
of 4Li found in the solid state is chiral at each of the
phosphorus centers, and at 0 °C, there is a rapid dynamic
equilibrium between the possible stereoisomers, leading to a
single, time-averaged peak in the 31P{1H} NMR spectrum.
7
However, at this temperature, the Li NMR spectrum consists
of a binomial quintet (I) with a relatively small 31P−7Li
coupling constant of 33 Hz (cf. JPLi = 41 Hz for 3Li, in which
each phosphorus center bridges two lithium ions), suggesting
that each lithium ion is in contact with four phosphorus
centers. Because a static arrangement of this type would
require each phosphorus center to be six-coordinate, and
because each lithium center would be highly crowded with four
adjacent phosphorus centers, such an arrangement seems
highly unlikely. Instead, we suggest a rapid dynamic
equilibrium within each dimer, such that each lithium can
become associated with each of the four phosphorus centers,
Figure 3. Molecular structure of 6Li with 40% probability ellipsoids
and with H atoms and disorder component omitted for clarity.
Selected bond lengths (Å) and angles (deg): P(1)−Li(1) 2.530(3),
Li(1)−O(1) 1.968(3), Li(1)−O(2) 1.960(3), Li(1)−O(3) 1.941(3),
C(1)−P(1)−C(13) 102.72(7), C(1)−P(1)−Li(1) 114.08(8),
C(13)−P(1)−Li(1) 107.17(8).
7
but not all four simultaneously. This gives a time-averaged Li
signal with a time-averaged 31P−7Li coupling constant which, if
the dimeric solid-state structure or a stereoisomer thereof is
3
maintained in solution, will be given by (1JPLi + JPLi)/2; this
will clearly be significantly smaller than typical one-bond
31P−7Li coupling constants, which usually fall in the range 40−
60 Hz,28 consistent with the observed coupling constant of 33
Hz. Such a dynamic process is unusual, but related processes
have been seen before for a dimeric lithium phosphinometha-
nide complex31 and for dimeric 2-[(dimethylamino)methyl]-
phenyllithium.32 Exchange of the lithium centers could
proceed via a “carousel” mechanism similar to that observed
for the lithium ions in the phosphinidene cluster [Sb-
(PCy)3]2Li6·6HNMe2·2PhMe.33 At low temperatures, the
dynamic equilibrium between stereoisomers of 4Li is frozen
out, and so signals are observed for each of these stereo-
isomers.
single broad singlet (C) is observed at −109.9 ppm. This signal
broadens and decoalesces below this temperature until, at −80
°C, the spectrum consists of four major, broad signals at −99.9
(D), −113.6 (E), −122.4 (F), and −129.3 ppm (G). At 80 °C,
the 7Li NMR spectrum of 4Li consists of a broad singlet (H) at
3.2 ppm, which gradually resolves into a broad quintet (JPLi
=
33 Hz) at 3.2 ppm (I) (Figure 5b). Below this temperature, the
signal broadens and decoalesces until, at −80 °C, the spectrum
consists of a series of overlapping multiplets lying between 1.6
and 4.9 ppm.
7
We suggest that the variable-temperature 31P{1H} and Li
NMR spectra of 4Li may be accounted for by the operation of
both a monomer−dimer equilibrium and a dynamic equili-
brium between stereoisomers of the dimeric species. At high
temperatures both the dimeric and monomeric forms are
observed (peaks A and B, respectively). As the temperature
decreases, the dimeric form is favored and, by 0 °C, the
7
The variable-temperature 31P{1H} and Li NMR spectra of
5Li are somewhat simpler. At 25 °C and above, the 31P{1H}
NMR spectrum consists of a broad singlet at −104.9 ppm (J)
(Figure 6a). As the temperature is reduced, this peak
decoalesces into a major and minor peak at −106.0 (K) and
D
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7
Figure 5. Variable-temperature (a) 31P{1H} and (b) Li NMR spectra of 4Li in d8-toluene.
7
Figure 6. Variable-temperature (a) 31P{1H} and (b) Li NMR spectra of 5Li in d8-toluene.
−99.7 ppm (L), respectively; the former signal is resolved as a
1:2:3:4:3:2:1 septet (JPLi = 52 Hz), while peak L appears to be
a broad, poorly resolved septet. At lower temperatures, peak L
diminishes in intensity, such that, at −80 °C, the spectrum
consists of a single septet (JPLi = 45 Hz) centered at −106.8
ppm. The room temperature 7Li NMR spectrum of 5Li
consists of a broad singlet at 2.7 ppm, which gradually resolves
as the temperature is reduced to −20 °C into a binomial triplet
at 2.2 ppm (M) and a low intensity, broad singlet (N) at
approximately 3 ppm (Figure 6b). Below this temperature,
peak N decreases in intensity, such that at −80 °C the
spectrum consists of a single binomial triplet (JPLi = 47 Hz) at
2.0 ppm.
These data suggest a dynamic equilibrium between two
species, one of which predominates, both involving P2Li2 cores.
With the available data, it is not possible to comment
unambiguously on the nature of these species.
7
The 31P{1H} and Li NMR spectra of 6Li exhibit different
behavior again. At 100 °C, the 31P{1H} NMR spectrum of 6Li
consists of a broad singlet at −102.7 ppm (Figure 7a). This
signal broadens and decoalesces as the temperature is reduced,
such that, at −40 °C, the spectrum consists of three signals: a
E
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Figure 7. Variable-temperature (a) 31P{1H} and (b) Li NMR spectra of 6Li in d8-toluene (*free phosphine 6H).
7
Figure 8. Variable-temperature (a) 31P{1H} and (b) Li NMR spectra of 7Li in d8-toluene (*free phosphine 7H).
septet (O) at −101.7 ppm (JPLi = 57 Hz) and two broad
signals at approximately −105 (P) and −110 ppm (Q) (at −20
°C peak Q is resolved as a septet, JPLi = 55 Hz). As the
temperature is reduced, peaks P and Q decrease in intensity,
while a small broad signal appears at low field, such that, at
−80 °C, the spectrum consists of a major, broad septet at
−100.6 ppm (O), and two very low intensity peaks at −112
(Q) and −92 ppm (R). The 7Li NMR spectrum of 6Li at 100
°C consists of a broad singlet at 3.0 ppm, which gradually
resolves into a quintet (S, JPLi = 32 Hz) at the same chemical
shift at −40 °C (Figure 7b). As the temperature is reduced this
peak broadens and decoalesces until, at −20 °C, the spectrum
consists of two binomial triplets at 2.1 (T, JPLi = 55 Hz) and
3.3 ppm (U, JPLi = 58 Hz). At lower temperatures, peak T
decreases in intensity, eventually disappearing into the
baseline, while a new, low intensity doublet (V, JPLi = 64.8
Hz) emerges at 0.7 ppm.
These spectra clearly suggest the presence of multiple
species in dynamic exchange in solution; at least three of these
(corresponding to peaks O, P, and Q in the 31P{1H} NMR
7
spectra and T and U in the Li NMR spectra) contain P2Li2
7
moieties. The presence of a quintet (S) in the Li NMR
F
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Scheme 2. Synthesis of Diphosphastannylene Dimers
spectrum at −40 °C suggests a situation similar to that
proposed for 4Li, corresponding to an aggregate (possibly a
dimer) containing four lithium and four phosphorus centers, in
which each lithium ion can be in contact with each phosphorus
center but not all four simultaneously. It is notable that the
31P−7Li coupling constant observed for this quintet (32 Hz) is
of a similar magnitude to that observed for 4Li (33 Hz) and
that this coupling constant is significantly smaller than typical
coupling constants observed in P2Li2 units (see above). At low
Lappert and coworkers report that (PhPCH2CH2PPh)Sn is
unstable at temperatures above −78 °C.6
In 2008 Russell, Hahn, and coworkers reported that the N-
heterocyclic stannylenes and plumbylenes [{CH2N(Dipp)}2E]
(E = Sn (9Sn), Pb (9Pb)) and [CH2{CH2N(Dipp)}2E] (E =
Sn (10Sn), Pb (10Pb)) could be isolated from the reaction
between either SnCl2 or PbCl2 and the dilithium derivative of
the corresponding diamide ligand.48 These compounds were
shown by X-ray crystallography to crystallize as monomeric N-
heterocyclic tetrylenes, although both 9Sn and 10Pb exhibit
weak E···arene ring contacts in the solid state.
The foregoing, along with our previous success in synthesiz-
ing acyclic diphosphatetrylenes with Dipp-substituted phos-
phide ligands, prompted us to speculate that the ligands
developed above might be suitable precursors for the synthesis
of P-heterocyclic tetrylenes.
The reactions between SnCl2 and 1 equiv of 3Li, 6Li, or 7Li
in THF resulted in mixtures of products (as judged by 31P{1H}
NMR spectroscopy), which we were unable to separate.
However, the reactions between SnCl2 and 1 equiv of either
4Li or 5Li in THF gave the diphosphastannylene dimers
[{CH2 P(Dipp)}2 Sn]2 (4Sn) and [CH2 {CH2 P-
(Dipp)}2Sn]2·1/2THF (5Sn), respectively, after workup
(Scheme 2). In addition, in one instance a small number of
colorless crystals were isolated from the reaction between 5Li
and SnCl2 in THF; these were shown by X-ray crystallography
to be the heteroleptic compound [([CH2{CH2P-
(Dipp)}2SnX]Sn)2{P(Dipp)CH2}2CH2] (5SnX; X = disor-
dered mixture of Cl and Br in a 60:40 ratio; see Supporting
Information). It is likely that the bromide in 5SnX stems from
a small amount of contamination by KBr arising from the
reaction between 1,3-dibromopropane and (Dipp)PHK during
the synthesis of 5H. This compound clearly arises from a slight
error in the stoichiometric ratios of 5Li and SnCl2 in this
reaction.
Compound 5Sn was isolated exclusively as the cis isomer, in
which the two propylene linkers lie on the same side of the
P2Sn2 ring, while 4Sn was isolated as a mixture of cis and trans
isomers in an approximate 1:5 (or 5:1) ratio, as judged by
31P{1H} NMR spectroscopy of the crystalline material (see
below). In contrast, the previously reported diphosphatetrylene
dimers [(iPr2P)2Ge]2 and [(tBu2P)2Pb]2 were isolated as the
trans isomer, with respect to the configurations of the terminal
phosphide ligands;37,39 however, the diphosphaplumbylene
7
temperatures, the presence of a doublet (V) in the Li NMR
spectrum of 6Li suggests a species in which there is a single P−
Li contact, possibly a monomer with a structure similar to that
observed in the solid state.
7
The variable-temperature 31P{1H} and Li NMR spectra of
7Li again suggest the operation of multiple dynamic equilibria
(Figure 8). At 100 °C, the 31P{1H} NMR spectrum exhibits
broad peaks at approximately −106 and −114 ppm, and these
peaks gradually decoalesce as the temperature is reduced, such
that, at 0 °C, the spectrum has major signals at −100, −109
(W, septet, JPLi = 62 Hz) and −117 ppm, along with minor
broad signals at approximately −103 and −115 ppm. Below
this temperature, all peaks, with the exception of W, decrease
in intensity. The 7Li NMR spectrum of 7Li at 100 °C consists
of a broad singlet at 3.1 ppm, and this gradually decoalesces as
the temperature is decreased until, at −40 °C, the spectrum
consists of several overlapping multiplets, the largest of which
is clearly resolved as a binomial triplet (X, JPLi = 62 Hz). These
spectra indicate that, while numerous species are present in
solution, the dominant species contains a P2Li2 core, consistent
with the solid-state structure.
P-Heterocyclic Stannylenes. While N-heterocyclic tetry-
lenes and their acyclic analogues have been extensively
studied,34 far less is known about the corresponding
phosphorus-substituted species, diphosphatetrylenes, and
their cyclic analogues, P-heterocyclic tetrylenes.35 The first
monomeric diphosphatetrylenes [{(Trip)(tBu)(F)Si}(iPr3Si)-
P]2E (E = Sn, Pb) were reported by Driess in 1995,36 but few
other diphosphatetrylenes have been isolated.26,27,35,37−45 This
is especially true of P-heterocyclic tetrylenes, the heavier
element analogues of NHCs: while Bertrand and coworkers
reported the first P-heterocyclic carbene (8) in 2005,46 there
have been limited reports of their Ge and Sn analogues, and no
such species have been structurally characterized. Indeed, while
the groups of Issleib, Lappert, and Escudie have all
independently reported the synthesis of (PhPCH2CH2PPh)E
(E = Ge, Sn),4,6,47 the data reported for these compounds are
limited to elemental analyses and 31P{1H} and 119Sn{1H}
NMR measurements, which suggest that (PhPCH2CH2PPh)
Ge is isolated as a mixture of rac and meso diastereomers;
G
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dimer [{(Me3Si)2P}2Pb]2 crystallizes as the cis isomer,
although both this latter compound and its tin analogue are
subject to cis−trans isomerization in solution (see below).38
Single crystals of the solvate trans-[{CH2 P-
(Dipp)}2Sn]2.Et2O (4Sna) were grown from cold diethyl
ether, while single crystals of cis-[CH2 {CH2P-
(Dipp)}2Sn]2.2THF (5Sna) were grown from a mixture of
benzene and THF at room temperature. In a separate
crystallization attempt, crystals of the alternative solvate cis-
[CH2{CH2P(Dipp)}2Sn]2.3THF (5Snb) were grown from
cold THF; the structure of 5Snb differs only marginally from
that of 5Sna and, due to the superior quality of the data for this
solvate, only the latter is discussed here. The solvent of
crystallization is only weakly held in 4Sna and 5Sna/5Snb and
is readily lost under vacuum to regenerate 4Sn and 5Sn. In
contrast to previous reports of the less sterically congested
(PhPCH2CH2PPh)Sn, which was observed to decompose
above −78 °C,6 compounds 4Sn and 5Sn are stable at room
temperature in the absence of light for extended periods.
Compound trans-4Sna crystallizes as centrosymmetric
dimers with a planar, rhombus-shaped P2Sn2 core (Figure 9).
Figure 10. Molecular structure of 5Sna with 40% probability
ellipsoids and with H atoms and solvent of crystallization omitted
for clarity. Selected bond lengths (Å) and angles (deg): Sn(1)−P(1)
2.6616(6), Sn(1)−P(2) 2.5986(6), Sn(1)−P(3) 2.6216(6), Sn(2)−
P(1) 2.6322(6), Sn(2)−P(3) 2.6662(6), Sn(2)−P(4) 2.6013(6),
P(1)−Sn(1)−P(2) 83.584(18), P(1)−Sn(1)−P(3) 79.723(18),
P(2)−Sn(1)−P(3) 93.756(18), P(1)−Sn(2)−P(3) 79.451(18),
P(1)−Sn(2)−P(4) 93.856(18), P(3)−Sn(2)−P(4) 83.376(18),
Sn(1)−P(1)−Sn(2) 92.143(19), Sn(1)−P(3)−Sn(2) 92.277(17).
from the second diphosphide ligand. Due to the cis
arrangement of the propylene linker groups, the terminal
phosphide centers adopt a PSPS configuration.
The Sn−P distances within the Sn2P2 core [2.6600(7) and
2.6282(7) Å (4Sna), 2.6216(6)−2.6662(6) Å (5Sna)] are
longer than the Sn−P(terminal) distances [2.5949(7) Å
(4Sna), 2.5986(6) and 2.6013(6) Å], as expected; however,
all of the Sn−P distances lie within the typical range for P−
Sn(II) bonds.35 For example, the Sn−P(terminal) distance in
{2,6-(2,4,6-iPr3C6H2)2C6H3}Sn{P(SiMe3)2} is 2.527(1) Å,49
while the Sn−P(bridging) distances in (tBu2P)Sn(μ-PtBu2)-
Li(THF) are 2.702(3) and 2.671(4) Å.50
The dimeric structures of trans-4Sna and 5Sna contrast with
the monomeric structures adopted by the nitrogen-substituted
homologues 9Sn and 10Sn reported by Russell, Hahn, and
coworkers.48 The ligands in compounds 4Sna, 5Sna, 9Sn, and
10Sn have similar steric properties, and so this difference in
molecularity does not appear to be steric in origin. This may be
quantified using the concept of the percent buried volume of
the ligands (%Vbur), which is defined as the percentage of a
sphere of radius 3.5 Å around the metal center that is occupied
by a given ligand.51 For the ligands in 4Sna, 5Sna, 9Sn, and
10Sn, we calculate relatively similar values for %Vbur of 47.1,
47.7, 48.4, and 54.4%, respectively, indicating rather similar
steric properties.52
The difference in structures may be attributed to the greater
barrier to inversion of phosphorus compared to that of
nitrogen (for comparison, the inversion barriers of NH3 and
PH3 are approximately 25 and 150 kJ mol−1, respectively).53
Whereas the nitrogen atoms in 9Sn and 10Sn may readily
adopt a planar configuration, the combination of steric and
electronic properties of the ligands in 4Sna and 5Sna is
insufficient to overcome the high barrier to inversion of
phosphorus, preventing planarization and, hence, the con-
sequent stabilization of the electron-deficient tin centers
through P−Sn pπ−pπ interactions. This leaves the phosphorus
Figure 9. Molecular structure of trans-4Sna with 40% probability
ellipsoids; H atoms, disorder component, and solvent of crystal-
lization are omitted for clarity. Selected bond lengths (Å) and angles
(deg): Sn(1)−P(1) 2.6600(7), Sn(1)−P(1A) 2.6282(7), Sn(1)−
P(2) 2.5949(7), P(1)−C(1) 1.849(3), P(1)−C(25) 1.866(3), P(2)−
C(13) 1.862(3), P(2)−C(26) 1.86(3), Sn(1)−P(1)−Sn(1A)
99.99(2), P(1)−Sn(1)−P(1A) 80.01(2), P(1)−Sn(1)−P(2)
76.94(2), P(2)−Sn(1)−P(1A) 87.31(2).
Each tin atom is coordinated by the two phosphorus centers of
one diphosphide ligand to give a five-membered chelate ring
(bite angle 76.94(2)°) and by a phosphorus atom of the
second diphosphide ligand; the two tin atoms are strongly
pyramidal (sum of angles at Sn = 257.03°). The trans
arrangement of the ethylene linker groups induces a PSPR
configuration at the terminal phosphorus centers which
minimizes steric clashes between the Dipp groups.
Compound 5Sna also crystallizes as discrete dimers, but
with a cis arrangement of the propylene linker groups and with
a consequently puckered P2Sn2 core (Figure 10). Once again,
each diphosphide ligand chelates one tin center, generating a
six-membered chelate ring (bite angles P(1)−Sn(1)−P(2)
83.548(18), P(3)−Sn(2)−P(4) 83.376(17)°). The coordina-
tion of each tin atom is completed by a phosphorus center
H
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lone pairs available to form Sn−P−Sn bridges, generating
electron-precise tin centers in the dimers.
d i p h o s p h a t e t r y l e n e s [ { ( M e 3 S i ) 2 P } 2 S n ] 2 a n d
[{(Me3Si)2P}2Pb]2, which undergo cis−trans isomerization of
the terminal phosphide ligands in solution.38 However, the
similar dimeric diphosphatetrylenes [(tBu2P)2Sn]2 and
[(tBu2P)2Pb]2, which are isolated as the trans isomers only,
show no evidence for cis−trans isomerism in solution.37
The 31P{1H} and 119Sn{1H} NMR spectra of 5Sn indicate
that the dimeric structure observed in the solid state is
preserved in THF solution. The 31P{1H} NMR spectrum of
5Sn exhibits two multiplets, both exhibiting tin satellites, at
−106.5 and −134.0 ppm, which we assign to the terminal and
bridging phosphide groups, respectively, on the basis of the
intensities of the tin satellites on each signal (see Supporting
Information); the 119Sn{1H} NMR spectrum of 5Sn consists of
a complex multiplet at 262 ppm. These spectra do not change
significantly with temperature. Simulation of the 31P{1H} and
119Sn{1H} signals yields coupling constants for all of the 31P
and 119Sn nuclei, as shown in Table 1 and Chart 2.
CONCLUSIONS
■
The alkyl-tethered α,ω-diphosphines (Dipp)PH(CH2)nPH-
(Dipp) (n = 1 (3H), 2 (4H), 3 (5H), 4 (6H), and 5 (7H))
are readily accessible and are isolated as approximately 1:1
mixtures of their rac and meso diastereomers. Deprotonation of
these α,ω-diphosphines with 2 equiv of nBuLi gives the
corresponding dilithium diphosphides as yellow-to-orange
crystalline solids with either monomeric or dimeric structures
in the solid state. In solution, these compounds are subject to
dynamic equilibria between oligomers, with the exact nature of
the equilibria dependent on the length of the alkyl tether.
While the dilithium complexes may appear to be suitable
precursors for the synthesis of P-heterocyclic stannylenes, only
[[CH2{P(Dipp)}]2]2Li4(THF)2(OEt2)2 (4Li) and
[CH2{CH2P(Dipp)}2]Li2(THF)4 (5Li) react cleanly with
SnCl2 to give the dimeric P-heterocyclic stannylenes [{CH2P-
(Dipp)}2Sn]2 (4Sn) and [CH2{CH2P(Dipp)}2Sn]2·1/2THF
(5Sn), respectively. The dimeric nature of these compounds
may be attributed to the large barrier to planarization of
phosphorus, which prevents the adoption of a planar
configuration at the phosphorus centers, inhibiting any P−Sn
pπ−pπ interactions and enabling the formation of Sn−P−Sn
bridges and consequent electron-precise Sn(II) centers.
Table 1. 31P and 119Sn Chemical Shifts (ppm) and 31P−31P
a
and 31P−119Sn Coupling Constants (Hz) for 4Sn and 5Sn
4Snmaj
4Snmin
5Sn
δ (ppm) P1/P2
−71.9
−109.6
476
−60.3
−80.2
218
−105.9
−133.4
262
P3/P4
Sn5/Sn6
JPP (Hz) P1−P2
3.0 0.5
19.0 0.5
141 0.5
0.0
1.6 0.5
47.0 0.5
159.6 0.5
1
0.0
3.5 0.5
32.6 0.5
108.5 0.5
1
P2−P4/P1−P3
P2−P3/P1−P4
P3−P4
140
1
JPSn (Hz) P1−Sn5/
717.6 0.5
40 0.5
883
8
1
715
10
1
P2−Sn6
P1−Sn6/
4
2
P2−Sn5
P3−Sn5/
P4−Sn6
1075
1143
2
2
1167
1182
3
3
1085
1255
2
2
EXPERIMENTAL SECTION
■
General. All manipulations were carried out using standard
Schlenk and drybox techniques under an atmosphere of dry nitrogen
or argon. THF, diethyl ether, toluene, light petroleum (bp 40−60
°C), methylcyclohexane, and n-hexane were dried prior to use by
distillation under nitrogen from sodium, potassium, or sodium/
potassium alloy, as appropriate. THF was stored over activated 4 Å
molecular sieves; all other solvents were stored over a potassium film.
Deuterated toluene and THF were distilled from potassium, and
CDCl3 was distilled from CaH2 under argon; all NMR solvents were
deoxygenated by three freeze−pump−thaw cycles and stored over
activated 4 Å molecular sieves. DippLi(OEt2),26,54 (iPr2N)PCl2,55
P3−Sn6/
P4−Sn5
a
Coupling constants were derived from simulations of the
experimental 31P{1H} and 119Sn{1H} NMR spectra, see Supporting
Information for further details.
Chart 2. Numbering Scheme for NMR Simulations
57
PhCH2K,26,56 and Cl2PCH2PCl2 were prepared by previously
published procedures; n-butyllithium was purchased from Aldrich as
a 2.5 M solution in hexanes, and its concentration was accurately
determined by titration before use. All other compounds were used as
supplied by the manufacturer.
The 31P{1H} NMR spectrum of 4Sn exhibits two pairs of
signals in an approximate 5:1 ratio (Figure 11). The major pair
of signals are resolved as complex multiplets at −71.9 and
−109.6 ppm exhibiting tin satellites, while the minor signals,
also complex multiplets with tin satellites, occur at −60.3 and
−80.2 ppm. Once again, we assign the high- and low-field
signals in each pair to the bridging and terminal phosphide
groups, respectively, on the basis of the intensities of the tin
satellites in each case. It is not possible to assign the peaks in
the 31P{1H} and 119Sn{1H} NMR spectra to either the cis or
trans isomers of 4Sn on the available data because there is no
direct correlation between either the chemical shifts or
coupling constants and those of cis-5Sn (see Table 1).
Variable-temperature 31P{1H} NMR spectroscopic studies
reveal that the ratio of cis- and trans-4Sn does not change
with temperature, indicating that these two isomers do not
interconvert. This contrasts with the behavior of the dimeric
1H and 13C{1H} NMR spectra were recorded on a Bruker
AvanceIII 500 spectrometer operating at 500.16 and 125.65 MHz,
respectively, or a Bruker AvanceIII 300 spectrometer operating at
300.15 and 75.47 MHz, respectively; chemical shifts are quoted in
7
ppm relative to tetramethylsilane. Li, 31P{1H}, and 119Sn{1H} NMR
spectra were recorded on a Bruker AvanceIII 500 spectrometer
operating at 194.38, 202.35, and 186.59 MHz, respectively; chemical
shifts are quoted in ppm relative to external 0.1 M LiCl, 85% H3PO4
and Me4Sn, respectively. Due to the air-sensitive nature of the
compounds reported, it was not possible to obtain consistent
elemental analyses; however, the bulk purity of the compounds is
confirmed by multinuclear NMR spectroscopy (see below and in the
Supporting Information).
Synthesis of (Dipp)PH2. To a cold (−78 °C) solution of
(EtO)2P(O)Cl (5.0 mL, 34.6 mmol) in Et2O (80 mL) was added,
slowly, a solution of (Dipp)Li(OEt2) (8.46 g, 34.9 mmol) in Et2O (80
mL). This mixture was allowed to warm to room temperature and was
stirred for 2 h. The resulting mixture was cooled to −78 °C, and solid
I
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Figure 11. (a) 31P{1H} and (b) 119Sn{1H} NMR spectra of 4Sn in d8-toluene at 25 °C (insets: simulated 119Sn NMR spectra).
LiAlH4 (2.64 g, 64.8 mmol) and chlorotrimethylsilane (9.0 mL, 70.9
mmol) were added. This mixture was allowed to warm to room
temperature and was stirred for 1 h. The resulting mixture was cooled
to 0 °C, and degassed water (40 mL) was slowly added. The product
was extracted into light petroleum (3 × 20 mL), and the combined
organic phases were dried over 4 Å molecular sieves overnight. The
solution was filtered, and the solvent was removed in vacuo from the
filtrate to give a cloudy, colorless oil. The product was purified by
distillation under reduced pressure (oil bath temperature 100 °C, 0.01
Torr) to give (Dipp)PH2 as a colorless, clear oil. Yield: 5.52 g, 81%.
1H NMR [CDCl3]: δ 1.27 (d, JHH = 6.8 Hz, 12H, CHMe2), 3.37 (m,
2H, CHMe2), 3.89 (d, JPH = 208 Hz, 2H, PH2), 7.15 (dd, JHH = 7.7
Hz, JHH = 2.5 Hz, 2H, ArH), 7.28 (m, 1H, ArH). 13C{1H} NMR
[CDCl3]: δ 23.77 (CHMe2), 33.07 (d, JPC = 11.4 Hz, CHMe2),
122.83 (d, JPC = 2.5 Hz, ArH), 126.06 (d, JPC = 13.1 Hz, ArH), 128.38
(Ar), 151.87 (d, JPC = 9.3 Hz, Ar). 31P NMR [CDCl3]: δ −157.1 (t,
JPH = 208 Hz).
Synthesis of CH2{PH(Dipp)}2 (3H). To a cold (−78 °C) solution
of Cl2PCH2PCl2 (1.87 g, 8.59 mmol) in Et2O (40 mL) was added,
dropwise, a solution of (Dipp)Li(OEt2) (4.16 g, 17.17 mmol) in Et2O
(40 mL). The resulting solution was allowed to warm to room
temperature and was stirred for 2 h. This mixture was cooled to −78
°C, and solid LiAlH4 (0.65 g, 17.15 mmol) was added in portions.
The resulting mixture was allowed to warm to room temperature,
stirred for 2 h, and cooled to 0 °C, and then degassed water (30 mL)
was slowly added. The product was extracted into light petroleum (3
× 15 mL), and the combined organic phases were dried over 4 Å
molecular sieves overnight. The solution was filtered, and the solvent
was removed in vacuo from the filtrate to give 3H as a turbid colorless
oil that slowly crystallized at room temperature. Yield: 3.13 g, 91%.
J
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1H{31P} NMR [CDCl3]: δ 1.14−1.28 (m, 24H, CHMe2), 1.77−2.07
(m, 2H, PCH2), 3.45−3.68 (m, CHMe2), 4.39 (m, 2H, PH), 7.13−
7.16 (m, 4H, ArH), 7.26−7.33 (m, 2H, ArH). 13C{1H} NMR
[CDCl3]: δ 16.83 (t, JPC = 23.8 Hz, PCH2), 24.65 (CHMe2), 32.82 (t,
(30 mL). The resulting mixture was allowed to warm to room
temperature, and the solvent was removed in vacuo to give a sticky
gray solid. The product was extracted into light petroleum (40 mL)
and filtered, and the solvent was removed in vacuo from the filtrate to
give 5H as a turbid colorless oil. Yield: 1.68 g, 92%. 1H NMR
[CDCl3]: δ 1.21 (d, JHH = 6.8 Hz, 12H, CHMeMe), 1.28 (d, JHH = 6.8
Hz, 12H, CHMeMe), 1.67 (br. m, 4H, PCH2CH2), 1.90 (br. m, 2H,
J
PC = 7.1 Hz, CHMe2), 123.28 (t, JPC = 1.6 Hz, ArH), 129.48 (ArH),
132.02 (t, JPC = 6.3 Hz, Ar), 152.76 (t, JPC = 5.6 Hz, Ar). 31P{1H}
NMR [CDCl3]: δ −98.2 (s), 98.8 (s) in a 1.1:1 ratio.
PCH2CH2), 3.61 (m, 4H, CHMeMe), 4.28 (dt, JPH = 215 Hz, JHH
=
Synthesis of (Dipp)(iPr2N)PH. To a cold (−78 °C) solution of
(iPr2N)PCl2 (3.73 g, 18.5 mmol) in Et2O (40 mL) was added,
dropwise, a solution of (Dipp)Li(OEt2) (4.47 g, 18.5 mmol) in Et2O
(20 mL). The mixture was allowed to warm to room temperature and
was stirred for 1 h. The mixture was cooled to 0 °C, and solid LiAlH4
(0.70 g, 18.5 mmol) was added in portions. The resulting mixture was
allowed to warm to room temperature, stirred for 1 h, and then cooled
to 0 °C, and degassed water (50 mL) was slowly added. The product
was extracted into light petroleum (3 × 15 mL), and the combined
organic phases were dried over 4 Å molecular sieves overnight. The
solution was filtered, and the solvent was removed in vacuo from the
filtrate to give (Dipp)(iPr2N)PH as a pale yellow oil. Yield: 4.50 g,
7.2 Hz, 2H, PH), 7.16 (dd, JHH = 7.9 Hz, JHH = 2.2 Hz, 4H, ArH),
7.30 (m, 2H, ArH). 13C{1H} [CDCl3]: δ 24.43 (CHMeMe), 24.95
(CHMeMe), 25.38 (m, PCH2CH2), 27.52 (t, JPC = 11.5 Hz,
PCH2CH2), 32.80 (d, JPC = 13.8 Hz, CHMeMe), 123.27 (d, JPC
=
3.3 Hz, ArH), 129.19 (ArH), 131.25 (d, JPC = 16.2 Hz, Ar), 152.89
(d, JPC = 10.8 Hz). 31P NMR [CDCl3]: δ −95.6 (d, JPH = 215 Hz),
−95.4 (d, JPH = 215 Hz) in a 1:1.2 ratio.
Synthesis of {CH2CH2PH(Dipp)}2 (6H). A solution of PhCH2K
(1.126 g, 8.95 mmol) in THF (15 mL) was added to a solution of
(Dipp)PH2 (1.68 g, 8.65 mmol) in THF (15 mL). The resulting
solution was stirred for 30 min and added, dropwise, to a solution of
1,4-dibromobutane (0.52 mL, 4.35 mmol) in THF (20 mL). The
solvent was removed in vacuo, and the product was extracted into light
petroleum (30 mL) and filtered. The solvent was removed in vacuo
from the filtrate to give 6H as a white powder. Yield: 1.64 g, 86%. 1H
NMR [CDCl3]: δ 1.22 (d, JHH = 6.8 Hz, 12H, CHMeMe), 1.28 (d,
JHH = 6.8 Hz, 12H, CHMeMe), 1.48−1.87 (m, 8H, PCH2CH2), 4.28
(dm, JPH = 215 Hz, PH), 7.14−7.18 (m, 4H, ArH), 7.30 (m, 2H,
ArH). 13C{1H} [CDCl3]: δ 23.70 (dd, JPC = 11.4 Hz, JP’C = 1.4 Hz,
PCH2CH2), 24.42 (CHMeMe), 24.96 (CHMeMe), 30.03 (m,
1
83%. H NMR [CDCl3]: δ 1.10 (d, JHH = 6.7 Hz, 6H, NCHMeMe),
1.15 (d, JHH = 6.7 Hz, 6H, NCHMeMe), 1.19 (d, JHH = 6.8 Hz, 6H,
ArCHMeMe), 1.29 (d, JHH = 6.8 Hz, 6H, ArCHMeMe), 3.18 (m, 2H,
NCHMeMe), 3.83 (m, 2H, ArCHMeMe), 6.00 (d, JPH = 208 Hz, 1H,
PH), 7.17 (d, JHH = 7.8 Hz, 1H, ArH), 7.18 (d, JHH = 7.8 Hz, 1H,
ArH), 7.31 (t, JHH = 7.8 Hz, 1H, ArH). 13C{1H} NMR [CDCl3]: δ
21.63 (d, JPC = 11.6 Hz, NCHMeMe), 22.96 (d, JPC = 2.8 Hz,
NCHMeMe), 24.09 (ArCHMeMe), 25.44 (ArCHMeMe), 31.72 (d,
JPC = 10.3 Hz, ArCHMeMe), 48.39 (d, JPC = 6.9 Hz, NCHMeMe),
123.23 (d, JPC = 2.3 Hz, ArH), 129.24 (ArH), 132.14 (d, JPC = 6.6 Hz,
Ar), 153.33 (d, JPC = 13.0 Hz, Ar). 31P NMR [CDCl3]: δ 36.8 (d, JPH
= 208 Hz).
PCH2CH2), 32.76 (d, JPC = 13.8 Hz, CHMeMe), 123.24 (d, JPC
=
3.2 Hz, ArH), 129.16 (ArH), 131.41 (d, JPC = 16.3 Hz, Ar), 152.90
(d, JPC = 10.8 Hz, Ar). 31P NMR [CDCl3]: δ −94.6 (d, JPH = 215 Hz).
Synthesis of CH2{CH2CH2PH(Dipp)}2 (7H). A solution of
PhCH2K (1.160 g, 8.90 mmol) in THF (20 mL) was added to a
solution of (Dipp)PH2 (1.73 g, 8.90 mmol) in THF (20 mL). The
resulting solution was stirred for 30 min and added, dropwise, to a
solution of 1,5-dibromopentane (0.60 mL, 4.40 mmol) in THF (20
mL). The solvent was removed in vacuo from the resulting mixture,
and the product was extracted into light petroleum (30 mL). The
resulting mixture was filtered, and the solvent was removed from the
Synthesis of {CH2(PHDipp)}2 (4H). To a solution of (Dipp)-
(iPr2N)PH (2.09 g, 7.12 mmol) in THF (25 mL) was added a
solution of PhCH2K (0.930 g, 7.14 mmol) in THF (10 mL). The
resulting solution was stirred for 30 min and then added, dropwise, to
a cold (−78 °C) solution of 1,2-dichloroethane (0.28 g, 3.55 mmol)
in THF (20 mL). The resulting red solution was allowed to warm to
room temperature and was stirred for 1 h. The solvent was removed in
vacuo, and the product was extracted into warm (40 °C) light
petroleum (50 mL). The light petroleum extract was filtered, and the
solvent was removed in vacuo from the filtrate to give [CH2{P-
(Dipp)(NiPr2)}]2 as a pale yellow solid (1.98 g, 3.23 mmol). This
solid was dissolved in light petroleum (60 mL) and cooled to 0 °C,
and a solution of anhydrous HCl in Et2O (2.0 M, 6.5 mL, 13.0 mmol)
was slowly added. A white solid immediately formed, and the resulting
mixture was stirred for 1 h. The mixture was filtered, and the solvent
was removed in vacuo from the filtrate to give {CH2PCl(Dipp)}2 as a
white solid (1.25 g, 2.59 mmol). This solid was dissolved in Et2O (40
mL) and cooled to 0 °C before solid LiAlH4 (0.10 g, 2.66 mmol) was
added in portions. The mixture was allowed to warm to room
temperature, stirred for 1 h, and then cooled to 0 °C, and degassed
water (30 mL) was slowly added. The product was extracted into light
petroleum (2 × 15 mL), and the combined organic phases were dried
over 4 Å molecular sieves overnight. The solution was filtered, and the
solvent was removed in vacuo from the filtrate. Volatile impurities
were removed by vacuum distillation (100 °C, 10−3 Torr) to leave 4H
as a white crystalline solid upon cooling. Yield: 0.90 g, 61%. 1H NMR
[CDCl3]: δ 1.15 (m, 12H, CHMeMe), 1.22 (d, JHH = 6.7 Hz, 12H,
CHMeMe), 1.75 (m, 2H, PCHH), 1.87 (m, 2H, PCHH), 3.55 (m,
4H, CHMeMe), 4.36 (d, JPH = 216, 2H, PH), 7.13 (d, JHH = 7.6 Hz,
ArH), 7.27 (t, JHH = 7.6 Hz, ArH). 13C{1H} NMR [CDCl3]: δ 22.73
(m, PCHH), 24.31 (ACHMeMe), 24.35 (BCHMeMe), 24.86
(CHMeMe), 32.81 (CHMeMe), 123.27, 129.22 (ArH), 132.68 (m,
Ar), 152.85 (m, Ar). 31P NMR [CDCl3]: δ −88.8 (d, JPH = 216 Hz),
−88.2 (d, JPH = 216 Hz) in a 1.1:1 ratio.
1
filtrate in vacuo to give 7H as a colorless oil. Yield: 1.75 g, 87%. H
NMR [CDCl3]: δ 1.21 (d, JHH = 6.8 Hz, 12H, CHMeMe), 1.28 (d,
J
HH = 6.8 Hz, 12H, CHMeMe), 1.38−1.88 (m, 10H, PCH2CH2CH2),
3.63 (m, 4H, CHMeMe), 4.27 (m, JPH = 215 Hz, 2H, PH), 7.14−7.17
(m, 4H, ArH), 7.29 (m, 2H, ArH). 13C{1H} [CDCl3]: δ 23.86 (d, JPC
= 11.1 Hz, PCH2CH2CH2), 24.42 (CHMeMe), 24.95 (CHMeMe),
28.35 (d, JPC = 10.8 Hz, PCH2CH2CH2), 32.56 (PCH2CH2CH2),
32.75 (d, JPC = 13.9 Hz, CHMeMe), 123.21 (d, JPC = 3.3 Hz, ArH),
129.11 (ArH), 131.52 (d, JPC = 16.2 Hz), 152.88 (d, JPC = 10.6 Hz).
31P{1H} NMR [CDCl3]: −94.4 (d, JPH = 215 Hz).
Synthesis of [CH2{P(Dipp)}2]Li2(TMEDA)2 (3Lia). To a solution
of CH2{PH(Dipp)]2 (0.72 g, 1.80 mmol) in Et2O (10 mL) was added
a solution of nBuLi (2.3 M, 1.6 mL, 3.70 mmol) in hexanes and
TMEDA (0.55 mL, 3.70 mmol), and the resulting orange solution was
stirred for 1 h. The solvent was removed in vacuo, and the resulting
sticky orange solid was dissolved in hot (80 °C) methylcyclohexane
(15 mL) and allowed to cool. Storage of this solution at −25 °C
overnight yielded large yellow crystals of 3Lia. These were washed
with cold (−10 °C) light petroleum (2 × 5 mL), and the residual
1
solvent was removed in vacuo. Yield: 0.51 g, 44%. H NMR [d8-
toluene]: δ 1.40 (d, JHH = 6.9 Hz, 24H, CHMe2), 1.88 (s, 8H, Me2N),
2.08 (s, 24H, CH2N), 3.46 (t, JPH = 4.2, 2H, PCH2P), 4.54 (m, 4H,
CHMe2), 7.09−7.13 (m, 6H, ArH). 13C{1H} NMR [d8-toluene]:
21.83 (t, JPC = 34 Hz, PCH2P), 25.37 (CHMe2), 32.04 (t, JPC = 8 Hz,
CHMe2), 46.01 (Me2N), 56.73 (CH2N), 121.61, 121.95 (ArH),
7
149.93 (t, JPC = 3 Hz, Ar), 151.16 (m, Ar). Li NMR [d8-toluene]: δ
Synthesis of CH2{CH2PH(Dipp)}2 (5H). A solution of PhCH2K
(1.116 g, 8.57 mmol) in THF (20 mL) was added to a solution of
(Dipp)PH2 (1.66 g, 8.55 mmol) in THF (20 mL). The resulting red
solution was stirred for 15 min and added, dropwise, to a cold (−78
°C) solution of 1,3-dibromopropane (0.43 mL, 4.24 mmol) in THF
1.75 (t, JPLi = 42 Hz). 31P{1H} NMR [d8-toluene]: δ −111.9 (sept,
JPLi = 42 Hz).
Synthesis of [{CH2P(Dipp)}2]Li2(THF)(OEt2)1.5 (4Lia). To a
solution of 4H (0.48 g, 1.16 mmol) in THF (10 mL) was added a
solution of nBuLi in hexanes (2.47 M, 0.95 mL, 2.34 mmol). The
K
DOI: 10.1021/acs.inorgchem.8b02510
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
resulting red solution was stirred for 30 min and the solvent was
removed in vacuo. The resulting sticky yellow solid was dissolved in
Et2O (5 mL), and this solution was left to stand overnight to give
yellow crystals of [{CH2P(Dipp)}2]2Li2(THF)2(OEt2)2 (4Li).
Further crystalline material was obtained by storage of the mother
liquor at −25 °C overnight. The supernatant solution was removed by
filtration, and the remaining crystalline solid was washed with cold
(−10 °C) light petroleum (5 mL). The residual solvent was removed
in vacuo to give the alternative solvate [{CH2P(Dipp)}2]2Li2(THF)-
(OEt2)1.5 (4Lia) as a yellow powder. Combined yield: 0.28 g, 40%.
1H NMR [d8-toluene, 253 K]: δ 0.96 (t, 9H, Et2O), 1.16 (br. s, 4H,
THF), 1.41 (d, JHH = 6.8 Hz, 24H, CHMe2), 2.68 (br. s, 4H, PCH2),
3.16 (q, 6H, Et2O), 3.34 (br. s, 4H, THF), 4.47 (br. m, 4H, CHMe2),
7.16 (d, JHH = 7.3 Hz, 4H, ArH), 7.21 (m, 2H, ArH). 13C{1H} NMR
[d8-toluene, 253 K]: δ 15.23 (Et2O), 25.27 (THF), 28.92 (PCH2),
33.93 (CHMe2), 65.82 (Et2O), 69.08 (THF), 122.47, 125.33 (ArH),
removed in vacuo to give the alternative solvate [CH2{CH2CH2P-
(Dipp)}2]Li2(THF)2.5 (7Lia). Yield: 0.87 g, 56%. 1H NMR [d8-
toluene, 353 K]: 1.32 (d, JHH = 6.8 Hz, 24H, CHMe2), 1.40 (m, 10H,
THF), 1.76 (br. s, 6H, PCH2CH2CH2), 2.26 (br. s, 4H,
PCH2CH2CH2), 3.47 (m, 10H, THF), 4.37 (br. s, 4H, CHMe2),
7.06 (s, 6H, ArH). 13C{1H} NMR [d8-toluene, 353 K]: 25.36
(CHMe2), 25.76 (THF), 34.08 (CHMe2), 68.80 (THF), 122.67
(ArH), 152.93 (br. s, Ar). 7Li NMR [d8-toluene, 353 K]: 3.10 (br. s)
31P{1H} NMR [d8-toluene, 353 K]: −105.8 (br. s), −114.7 (br. s) in a
1:0.7 ratio respectively.
Synthesis of [{CH2P(Dipp)}2Sn]2 (4Sn). To a solution of 4H
(0.44 g, 1.06 mmol) in THF (15 mL) was added a solution of nBuLi
in hexanes (2.45 M, 0.9 mL, 2.21 mmol). The resulting orange
solution was stirred for 30 min and added, dropwise, to a cold (−78
°C) solution of SnCl2 (0.20 g, 10.5 mmol) in THF (15 mL). The
resulting yellow solution was allowed to warm to room temperature;
the solvent was removed in vacuo, and the product was extracted into
Et2O (30 mL). The mixture was filtered, and the yellow filtrate
spontaneously formed yellow crystals of [{CH2P(Dipp)}2Sn]2·Et2O
(trans-4Sn) on standing. Further material was obtained by storage of
this solution at 4 °C overnight. The supernatant was removed by
filtration and the residual solvent was removed in vacuo from the
remaining solid to give a yellow powder (0.08 g, 14% yield). Further
material was obtained by adding light petroleum (15 mL) to the
filtrate and reducing the solution in volume to 20 mL. Storage of this
solution at −25 °C overnight gave yellow microcrystalline material.
The solid was isolated by filtration, and the residual solvent was
removed in vacuo to give a yellow powder (0.17 g, 30% yield).
7
146.40, 152.34 (Ar). Li NMR [d8-toluene, 253 K]: δ 3.3 (br. m).
31P{1H} NMR [d8-toluene, 253 K]: δ −109 (br. s), −121 (br. s) in a
15:1 ratio.
Synthesis of [CH2{CH2P(Dipp)}2]Li2(THF)4 (5Li). To a solution
of 5H (1.84 g, 4.29 mmol) in THF (20 mL) was added a solution of
nBuLi in hexanes (2.3 M, 3.7 mL, 8.51 mmol). The resulting red
solution was stirred for 1 h, and the solvent was removed in vacuo to
give a sticky yellow solid. The solid was dissolved in Et2O (15 mL),
and this solution was stored at −25 °C overnight to give large yellow
crystals of 5Li. The supernatant solution was removed by filtration;
the crystals were washed with cold (−10 °C) light petroleum (2 × 5
mL), and the residual solvent was removed in vacuo from the
remaining solid to give a yellow powder (1.03 g, 33%). A second crop
of material was obtained by reducing the volume of the combined
filtrate and washings to 10 mL and then storage at −25 °C for 1 week.
The supernatant solution was removed by filtration, and the residual
solvent from the remaining solid was removed in vacuo to give a
further crop of 5Li as a yellow microcrystalline powder (0.67 g, 22%).
Combined yield: 1.70 g, 55%. 1H NMR [d8-toluene, 298 K]: δ 1.38−
1.40 (m, THF + CHMe2, 40H), 2.41 (br. s, PCH2CH2, 2H), 2.53 (br.
s, PCH2CH2, 4H), 3.59 (m, THF, 16H), 4.68 (br. s, CHMe2, 4H),
7.17 (s, ArH, 6H). 13C{1H} NMR [d8-toluene, 298 K]: δ 25.52
(CHMe2), 25.66 (THF), 30.20 (br. s, PCH2CH2), 33.54 (br. s,
PCH2CH2), 68.59 (THF), 122.33, 124.68 (ArH), 148.82, 152.51 (br.
s, Ar). 7Li NMR [d8-toluene, 298 K]: δ −2.7 (s). 31P{1H} NMR [d8-
toluene, 298 K]: δ −105.0 (br. s).
1
Combined yield: 0.25 g, 44%. The H and 13C{1H} NMR spectra of
cis/trans-4Sn exhibit multiple overlapping signals from two stereo-
isomers (A = major stereoisomer, B = minor stereoisomer) and for a
1
small amount of Et2O. H NMR [d8-THF]: δ 0.74 (br. m, 6.3H,
A
ACHMe2), 0.89 (d, JHH = 6.8 Hz, 12.6H, CHMe2), 1.13 (m, 12.4H,
ACHMe2 + Et2O), 1.19 (m, 2.8H, BCHMe2), 1.24 (br. m, 11.7H,
ACHMe2), 1.31−1.33 (m, 4.8H, BCHMe2), 1.35 (d, JHH = 6.6 Hz,
B
A
2.4H, CHMe2), 1.63 (br. m, 5.7H, CHMe2), 2.40−2.60 (m, 3.1H,
APCH2
+
BPCH2), 2.66 (br. m, 2.1H, APCH2), 2.90 (m, 2.6H,
APCH2), 3.08 (br. s, 2.0H, CHMe2), 3.35−3.43 (m, 3.1H, APCH2 +
A
Et2O), 3.52 (m, 4.0H, ACHMe2), 3.76 (br. m, 1.3H, BCHMe2
+
BPCH2), 4.05 (m, 0.9H, BCHMe2), 4.57 (br. s, 2.0H, ACHMe2), 6.96
(m, 3.9H, ArH), 7.04 (br. m, 1.9H, ArH), 7.10 (m, 2.6H, ArH), 7.15
(m, 2.0H, ArH), 7.22−7.30 (m, 4.7H, ArH). 13C{1H} NMR [d8-
THF]: δ 24.74 (ACHMe2), 26.16 (ACHMe2), 26.89 (BCHMe2), 27.45
(ACHMe2), 30.28 (m, APCH2), 30.49 (m, APCH2), 33.26 (br. m,
Synthesis of [{CH2CH2P(Dipp)}2]Li2(THF)6 (6Li). To a solution
of 6H (0.86 g, 1.94 mmol) in THF (15 mL) was added a solution of
nBuLi in hexanes (2.3 M, 1.7 mL, 3.90 mmol), and this solution was
stirred for 1 h. The volume of the resulting solution was reduced to 5
mL, and the solution was heated to dissolve a small amount of yellow
solid that had formed. Storage of this solution at 4 °C overnight
yielded large yellow crystals of 6Li. The supernatant was removed by
filtration, and the remaining solid material was washed with light
petroleum (3 × 5 mL). The residual solvent was removed in vacuo to
APCH2 + PCH2 + ACHMe2), 34.01 (d, JPC = 17.6 Hz, ACHMe2),
B
34.58−34.78 (ACHMe2 + CHMe2), 123.85 (ArH), 124.16 (d, JPC
=
B
2.4 Hz, ArH), 124.41, 125.71, 128.96, 129.51, 130.38, 130.49 (ArH),
135.82 (m, Ar), 136.17 (m, Ar), 153.61 (br. m, Ar), 154.48 (br. m,
Ar), 154.72 (br. m, Ar), 156.08 (d, JPC = 11.5 Hz), 156.26 (d, JPC
=
10.8 Hz). 31P{1H} NMR [d8-THF]: δ −109.6 (m, JPSn = 1085 Hz,
APbridging), −80.2 (m, JPSn = 1150 Hz, BPbridging), −71.9 (m, JPSn = 700
Hz, APterminal), −60.3 (m, JSnP = 870 Hz, BPterminal). The stereoisomers
A and B are in a 5:1 ratio. 119Sn{1H} NMR [d8-THF]: δ 218.17 (m,
1
give a further crop of 6Li as a yellow powder. Yield: 1.11 g, 64%. H
NMR [d8-toluene, 298 K]: δ 1.35 (m, 24H, THF), 1.43 (s, CHMeMe,
12H), 1.45 (s, 12H, CHMeMe), 2.10 (br. s, 4H, PCH2CH2), 2.59 (br.
s, 4H, PCH2CH2), 3.46 (m, 24H, THF), 4.13 (br. s, 4H, CHMeMe),
7.07−7.11 (m, 6H, ArH).13C{1H} NMR [d8-toluene, 298 K]: 25.59
(CHMe2), 25.67 (THF), 27.55 (m, PCH2CH2), 33.50 (CHMe2),
36.34 (PCH2CH2), 68.15 (THF), 122.45, 123.60 (ArH), 149.78 (d,
A
BSn), 476.41 (m, Sn).
Synthesis of [CH2{CH2P(Dipp)}2Sn]2·1/2THF (5Sn). To a
solution of 5H (0.86 g, 2.01 mmol) in THF (20 mL) was added a
solution of nBuLi in hexanes (2.45 M, 1.6 mL, 3.92 mmol). The
resulting orange solution was stirred for 30 min and added, dropwise,
to a cold (−78 °C) solution of SnCl2 (0.38 g, 1.99 mmol) in THF (15
mL). The mixture was allowed to warm to room temperature, and the
solvent was removed in vacuo to give a sticky orange solid. The
product was extracted into Et2O (20 mL) and filtered, and the solvent
was removed in vacuo from the filtrate. n-Hexane (10 mL) was added,
and a yellow solid immediately precipitated. The mixture was stored
at 4 °C for 2 days; the supernatant was removed by filtration, and
residual solvent was removed from the remaining solid in vacuo to give
[CH2{CH2P(Dipp)}2Sn]2·1/2THF (5Sn) as a yellow powder. Yield:
0.33 g, 27%. Single crystals of [CH2{CH2P(Dipp)}2Sn]2.2THF
(5Sna) suitable for characterization by X-ray crystallography were
J
PC = 38 Hz, Ar), 150.88 (Ar). 7Li NMR [d8-toluene, 298 K]: 3.1 (m).
31P NMR [d8-toluene, 298 K]: δ −102.4 (br. s), −111.1 (br. s) in a
11:1 ratio.
Synthesis of [CH2{CH2CH2P(Dipp)}2]Li2(THF)2.5 (7Lia). To a
solution of 7H (1.08 g, 2.38 mmol) in THF (15 mL) was added a
solution of nBuLi (2.3 M, 2.1 mL, 4.80 mmol) in hexanes, and the
resulting red solution was stirred for 1 h. The solvent was removed in
vacuo, and the sticky orange solid was extracted into toluene (10 mL)
and left to stand overnight. The resulting large yellow crystals of
[CH2{CH2CH2P(Dipp)}2]Li2(THF)4(C7H8) (7Li), which were
characterized by X-ray crystallography, were washed with cold (0
°C) light petroleum (2 × 5 mL), and the residual solvent was
L
DOI: 10.1021/acs.inorgchem.8b02510
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
obtained by standing a solution of [CH2{CH2P(Dipp)}2Sn]2 in a
mixture of THF and benzene at room temperature for 1 week. Single
crystals of the alternative solvate [CH2{CH2P(Dipp)}2Sn]2·3THF
(5Snb) were obtained by storage of a solution of [CH2{CH2P-
AUTHOR INFORMATION
Corresponding Author
*E-mail: keith.izod@ncl.ac.uk.
ORCID
Keith Izod: 0000-0003-3882-9343
Notes
The authors declare no competing financial interest.
■
1
(Dipp)}2Sn]2 in THF at −25 °C for 3 days. H NMR [d8-THF, 233
K]: δ 0.40 (d, JHH = 6.4 Hz, 6H, CHMe2), 0.94 (d, JHH = 6.3 Hz, 6H,
CHMe2), 1.24 (d, JHH = 6.1 Hz, 6H, CHMe2), 1.27 (d, JHH = 6.8 Hz,
6H, CHMe2), 1.31 (d, JHH = 6.8 Hz, 6H, CHMe2), 1.35 (d, JHH = 6.1
Hz, 6H, CHMe2), 1.38 (d, JHH = 6.8 Hz, 6H, CHMe2), 1.43 (d, JHH
=
6.8 Hz, 6H, CHMe2), 1.77 (m, 2H, THF), 1.80−1.85 (m, 2H,
PCH2CH2), 2.15 (m, 2H, PCH2CH2), 2.50−2.66 (br. m, 4H, CHMe2
+ PCH2CH2), 2.95 (br. m, 2H, PCH2CH2), 3.35 (br. m, 2H,
PCH2CH2), 3.61 (m, 2H, THF), 3.82 (br. m, PCH2CH2), 4.04 (m,
2H, CHMe2), 4.12 (m, 2H, CHMe2), 4.61 (m, 2H, CHMe2), 7.02 (d,
ACKNOWLEDGMENTS
This work was partially funded by the UK Engineering and
Physical Sciences Research Council (EPSRC; EP/L5048281).
■
J
HH = 7.7 Hz, 2H, ArH), 7.13 (d, JHH = 7.7 Hz, 2H, ArH), 7.18−7.20
REFERENCES
(m, 4H, ArH), 7.25−7.30 (m, 4H, ArH). 13C{1H} NMR [d8-THF,
233 K]: δ 21.37 (br. m, PCH2CH2), 21.61 (br. m, PCH2CH2), 22.24
(CHMe2), 22.40 (br. m, PCH2CH2), 22.68 (br. m, PCH2CH2), 23.84,
24.00, 24.51, 24.71, 24.94, 25.05, 25.25 (CHMe2), 25.31 (PCH2CH2),
25.25 (PCH2CH2), 25.85 (THF), 26.66, 26.88, 27.04 (CHMe2),
27.18 (d, JPC = 4.0 Hz), 33.10 (JPC = 37.8 Hz, CHMe2), 33.72
(CHMe2), 34.56 (2 CHMe2), 67.68 (THF), 122.2 (d, JPC = 5.6 Hz,
ArH), 124.49, 124.59, 125.33, 128.91, 130.31 (ArH), 153.23 (m, Ar),
154.55, 155.70, 157.04, 157.09 (Ar). 31P{1H} NMR [d8-THF, 298
K]: δ −105.89 (m, JPSn = 700 Hz, Pt), −133.4 (m, JPSn = 1140 Hz, Pb).
119Sn{1H} NMR [d8-THF, 298 K]: δ 266.8 (m).
■
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The cleavage of P-C bonds in diphosphines by lithium: the crystal
structure of [Li4{PhPCH2CH2PPh}2(OC4H8)8]. J. Organomet. Chem.
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X-ray Crystallography. Crystal structure data sets for all
compounds were collected on an Xcalibur, Atlas, Gemini ultra
diffractometer (Rigaku Oxford Diffraction) using an Enhance Ultra X-
ray Source (λCuKα = 1.54184 Å) for 3Lia, 4Li, 5Li, 6Li, 7Li, 4Sna, and
5Sna, and a fine-focus sealed X-ray tube (λMoKα = 0.71073 Å) for
5Snb and 5SnX. Using an Oxford Cryosystems CryostreamPlus open-
flow N2 cooling device, data for all structures were collected at 150 K,
with the exception of 5Snb and 7Li which, as crystals of these
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collected at 200 and 210 K, respectively. Cell refinement, data
collection, and data reduction were undertaken using CrysAlisPro.58
For 4Li, 5Li, 6Li, 4Sna, and 5Sna, an analytical numeric absorption
correction was applied using a multifaceted crystal model based on
expressions derived by Clark and Reid.59 For 3Lia, 7Li, 5Snb, and
5SnX, intensities were corrected for absorption empirically using
spherical harmonics.
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The structures were solved by intrinsic phasing using XT60 and
refined on F2 values for all unique data by XL61 through the Olex2
interface.62 Table S1 in the Supporting Information gives further
details. All nonhydrogen atoms were modeled as anisotropic.
Hydrogen atoms were positioned with idealized geometry, and their
displacement parameters were constrained using a riding model.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b02510.
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Details of structure determination, atomic coordinates,
bond lengths and angles, and displacement parameters;
1H, 13C{1H}, and 31P{1H} NMR spectra of all
compounds; and 7Li and 19Sn{1H} NMR spectra
where applicable (PDF)
Accession Codes
CCDC 1865742−1865750 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, 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.
M
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