Activation of gaseous PH3 with low coordinate diaryltetrylene compounds

Article abstract of DOI:10.1039/c3cc48933g

The reaction of phosphine gas with a low coordinate diaryl germylene or diarylstannylene results in both oxidative addition and arene elimination at the group 14 atom. The products were characterised by ³¹P NMR spectroscopy and X-ray crystallography, and represent the first P-H bond activation by a heavy group 14 element compound.

Full text of DOI:10.1039/c3cc48933g

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Activation of gaseous PH3 with low coordinate
diaryltetrylene compounds†
Cite this: Chem. Commun., 2014,
50, 1944
Jonathan W. Dube,a Zachary D. Brown,b Christine A. Caputo,b Philip P. Powerb and
Paul J. Ragogna*a
Received 22nd November 2013,
Accepted 9th December 2013
DOI: 10.1039/c3cc48933g
www.rsc.org/chemcomm
The reaction of phosphine gas with a low coordinate diaryl germylene or systems also activate ammonia under ambient conditions, a
diarylstannylene results in both oxidative addition and arene elimination feature that is not as common for transition metals.9
at the group 14 atom. The products were characterised by 31P NMR
Bertrand et al. have shown that unique, stable N-heterocyclic
spectroscopy and X-ray crystallography, and represent the first P–H carbenes (i.e. C) can also insert into B–H, Si–H, and P–H bonds.10
bond activation by a heavy group 14 element compound.
While primary and secondary phosphines were used in work
reported previously, reactions involving phosphine (PH3) are
The activation of small molecule substrates by coordinatively rare.11 Driess et al. have recently shown that a Si(II) center (F)12
unsaturated main group molecules is a continuously expanding inserts into the P–H bond of phosphine to produce a ligand
area of research.1 Of particular intrigue is the fact that these stabilized Si(H)(PH2) fragment.13
commodity, and typically unreactive, chemicals can be activated
The primary mode of reactivity for low valent main group
directly without the use of transition metals. The activation of centers is to undergo oxidative addition across the X–H (X = H,
dihydrogen by a main group compound under ambient conditions B, N, Si, P) bond. For the N-heterocyclic carbenes and heavier
was first achieved by using a digermyne (A; Fig. 1).2 Subsequent analogues there are few examples to the contrary. The diaryl-
studies have shown that frustrated Lewis pairs (FLPs, i.e. B),3 stable tetrylenes (D, EAr2; E = Ge, Sn; Ar = C6H3-2,6-Mes2)13 however,
singlet carbenes (e.g. C),4 diaryltetrylenes (D),5 heavier p-block have displayed different reactivity based on the group 14 element.
alkyne analogues,2,6 silylenes,7 and group 13 dimetallenes (E)8 In the reaction with ammonia, germanium exclusively favours the
can also accomplish the same feat. Several of these unique oxidative addition pathway, while tin exclusively favours arene
elimination to remain in the +2 oxidation state (Scheme 1).5
In this context, we report an extension of the reactivity studies
on diaryltetrylenes to PH3, ammonia’s heavier congener.
In contrast to ammonia, both oxidative addition and arene
elimination products are observed for germanium and tin, and
also in different ratios relative to each other.
The reaction of the diarylgermylene (GeAr2; Ar = C6H3-2,6-Mes2)
with an excess of PH3 (80 psi) in a stainless steel pressure reactor for
three hours results in the complete consumption of the purple
starting material to give a colourless solution.‡ Analysis of a fraction
of the concentrated reaction mixture by 31P{1H} NMR spectroscopy
revealed the presence of two signals (dP = À232; À180), which
Fig. 1 Examples of main group compounds that activate small molecules.
Note that Dipp = 2,6-diisopropylphenyl and that Mes = 2,4,6-trimethylphenyl.
a Department of Chemistry and Center for Advanced Materials and Biomaterials
Research (CAMBR), The University of Western Ontario, 1151 Richmond St.,
London, Ontario, Canada N6A 5B7. E-mail: pragogna@uwo.ca
b Department of Chemistry, The University of California, 1 Shields Ave, Davis,
California, 95616, USA
Scheme 1 Reactivity of ammonia with a diarylgermylene (left) and a
diarylstannylene (right) highlighting the oxidative addition and reduction
elimination pathways (Ar = C6H3-2,6(C6H2-2,4,6-Me3)2 = C6H3-2,6-Mes2).
† Electronic supplementary information (ESI) available: Selected NMR spectra
and ORTEP diagrams. CCDC 973191 and 973192. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c3cc48933g
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again revealed two signals (dP = À249, À227), in this case in an
approximate 68 : 32 ratio. The phosphorus–proton coupling con-
stants are comparable to those of the analogous germanium
1
2
species (dP = À249, JP–H = 174 Hz, JP–H = 18.6 Hz; dP = À227,
1JP–H = 174 Hz). Phosphorus–tin coupling is also observed
with the values being consistent with a tin–phosphorus covalent
bond (dP = À249, 1J117Sn–P = 496 Hz, 1J119Sn–P = 518 Hz; dP = À227,
1J
= 597 Hz, 1J
= 621 Hz). The 1H NMR spectrum
117Sn–P
119Sn–P
reveals the characteristic doublet of triplets for the Sn–H (dH
=
2
3
6.15, JP–H = 18.6 Hz, JH–H = 3.6 Hz) while the FT-IR spectrum
displayed resonances consistent the P–H and Sn–H bond vibra-
tions. The solid-state structure of the oxidative addition product,
Ar2Sn(H)(PH2), 3, was obtained as structural confirmation, while
unfortunately structural verification of the arene elimination
product, {ArSn(m-PH2)}2, 4, has proven elusive despite considerable
effort. This is likely a result of the fact that completely separating 3
and 4 was not possible under the conditions employed.
Fig. 2 Plots of 31P{1H} and 31P NMR spectra for the reaction of EAr2 (E = Ge,
Sn) with phosphine. Inset: FT-IR spectrum of 1 focusing on hydride vibrations.
The solid-state structures of the oxidative addition products 1,
and 3 are shown in Fig. 3.§ The structures are nearly identical,
and also similar to the ammonia insertion product, with the
tetrel center in a distorted tetrahedral geometry. The Ge–H and
Sn–H distances are 1.58(4) and 1.90(5) Å. The Ge–C bond lengths
are 1.981(3) and 2.003(3) Å, while the Ge–P bond length is
2.3194(11) Å. The analogous bond lengths for 3 are 2.193(6),
2.181(6), and 2.5997(17) Å, respectively. For both 1 and 3 the
phosphorus–hydrogen bond lengths fall within the range of 1.32
and 1.42 Å with the exception of one very short outlier (1.02(4) Å
in 1).16 The C–E–C bond angle has increased considerably from
the free diaryltetrylene14 for 3 (138.1(2)1 cf. 114.7(2)1 for SnAr2)
while the same angle in 1 is slightly smaller than in GeAr2
Scheme 2 The reaction of phosphine with the diaryltetrylenes (E = Ge,
Sn) to give both the oxidative addition (1 or 3) and arene elimination (2 or 4)
products. Ratios determined by 31P{1H} NMR spectroscopy of the crude
reaction mixture.
integrate to an approximate 80 : 20 ratio (Fig. 2). The 31P NMR (112.5(1) cf. 114.4(2) for GeAr2). The P–E–H bond angles are much
spectrum was particularly informative revealing the signals smaller in comparison, consistent with the use of unhybridized
to be proton coupled as a triplet of doublets and a triplet p-orbitals in the bonding, and also an obvious result of the
1
2
1
(dP = À232, JP–H = 181 Hz, JP–H = 11.2 Hz; dP = À180, JP–H
=
steric pressure of the terphenyl substituents.
183 Hz), consistent with the formation of both the oxidative
In conclusion, a diarylgermylene and a diarylstannylene
addition product, Ar2Ge(H)(PH2) (1), and the arene elimination react with phosphine gas under ambient conditions to produce
1
product, {ArGe(m-PH2)}2 (2) (Scheme 2). The H NMR spectrum both oxidative addition and arene elimination products, the
of a recrystallized sample of 1 revealed a doublet of triplets structures of the oxidative addition products being confirmed
2
3
(dH = 5.33, JP–H = 11.2 Hz, JH–H = 4.3 Hz), consistent with a
germanium hydride adjacent to a PH2 functionality. The phos-
phorus hydrides were also observed as a doublet of doublets in
the 1H NMR spectrum (dH = 1.29, 1JP–H = 181 Hz, 3JH–H = 4.3 Hz)
and agree nicely to the other coupling constants. The FT-IR
spectrum also reveals signals consistent with a P–H (n = 2310 cmÀ1
)
and a Ge–H stretch (n = 2069 cmÀ1). Confirmation of the solid-
state structure of 1 was obtained from an X-ray diffraction study
on single crystals grown from a saturated hexane solution at
À35 1C. There is a significant presence of GeH2Ar2 in the crude
reaction mixture (40–50%), which cannot be efficiently separated
from 1.15 While the origin of this species is not clear, its identity
was unambiguously confirmed by 1H NMR and FT-IR spectro-
scopies as well as by single crystal X-ray diffraction. The analogous
reaction of the diarylstannylene (SnAr2) with PH3 (80 psi) requires
longer reaction times (24 hours) to go to completion, as evi-
denced by the disappearance of the characteristic purple colour.
Fig. 3 The solid-state structure of 1 (left) and 3 (right). Ellipsoids are drawn at
50% probability, hydrogen atoms, with exception to the main group hydrides,
and hexane solvate (1) are removed for clarity. Selected bond lengths (Å) and
angles (1): 1 Ge–H 1.58(4), Ge–P 2.3194(11), P–H 1.34(4), P–H 1.02(4), C–Ge–C
112.5(1), P–Ge–H 102.1(13); 3 Sn–H 1.90(5), Ge–P 2.5997(17), P–H 1.391(10),
The proton decoupled and coupled 31P NMR spectra (Fig. 2) P–H 1.384(10), C–Sn–C 138.1(2), P–Sn–H 96.1(14).
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activation of a P–H bond at a low coordinate main group center,
and the first of the heavier group 14 elements (Ge, Sn).
We thank the Natural Science and Engineering Research
Counsel (NSERC), the Ontario government, The University of
Western Ontario, and the U.S. Department of Energy (DE-FG02-
07ER46475), for their financial support. The phosphine setup
was aided greatly by the support of Cytec industries and the
excellent work of the chemistry department electronics shop
(J. Vanstone and J. Aukema).
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Notes and references
‡ All manipulations were performed in a nitrogen filled MBraun glove-
box with solvents stored over 4 Å molecular sieves or a potassium mirror.
Phosphine (Cytec) was loaded into a stainless steel Parr reactor and
excess gas was swept with N2 and controllably burnt after the desired
reaction time. The product distribution was determined from integration
of the 31P{1H} NMR spectrum of the isolated crude powder in C6D6.
Experimental data: 1: 1H NMR (400 MHz, C6D6, d): 1.29 (dd, 2H,
3
1JP–H = 181 Hz, JH–H = 4.3 Hz), 1.79 (s, 12H), 1.84 (s, 12H), 2.19 (s,
8 Z. Zhu, X. Wang, Y. Peng, H. Lei, J. C. Fettinger, E. Rivard and
P. P. Power, Angew. Chem., Int. Ed., 2009, 48, 2031.
2
3
3
12H), 5.33 (dt, 1H, JP–H = 11.2 Hz, JH–H = 4.3 Hz), 6.71 (d, 2H, JH–H
=
6.4 Hz), 6.75 (s, 4H), 6.83 (s, 4H), 7.02 (t, 1H, JH–H = 7.6 Hz); 31P{1H}
NMR (161.8 MHz, C6D6, d): À232; 31P NMR (161.8 MHz, C6D6, d): À232
3
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(td, JP–H = 181 Hz, JP–H = 11.2 Hz); FT-IR (cmÀ1); 2069 (Ge–H), 2310
1
2
(P–H); 3: 1H NMR (400 MHz, C6D6, d): resonances that could assigned to
3 are listed: 0.84 (dd, 2H, JP–H = 174 Hz, JH–H = 3.6 Hz, 2J117
=
1
3
Sn–H
61.8 Hz, 2J119Sn–H = 68.7 Hz), 6.15 (dt, 1H, 2JP–H = 18.6 Hz, 3JH–H = 3.6 Hz);
31P{1H} NMR (161.8 MHz, C6D6, d): À249 (1J117
= 496 Hz, 1J119
=
=
Sn–P
Sn–P
518 Hz); 31P NMR (161.8 MHz, C6D6, d): À249 (td, JP–H = 174 Hz, JP–H
1
2
18.6 Hz); HRMS: found (calculated) for C48H53NaPSn 803.2687 (803.2800).
§ Crystallographic details: 1: C48H53GeP, C6H14; FW = 819.64 g molÀ1
;
colourless block; size: 0.052 Â 0.061 Â 0.130 mm; monoclinic, P21/c;
unit cell: a = 14.813(3) Å, b = 19.868(4) Å, c = 16.899(3) Å, b = 111.25(3)1,
V = 4635.1(16) Å; Z = 4; r = 1.175; T = 150 K; l = 0.71073 nm (MoKa);
F(000) = 1752; m = 0.729; 2ymax = 55.12; 2ymin = 3.30; 35 818 reflections,
10 616 unique (Rint = 0.0449); parameters = 538; restraints = 5; R1
0.0583; wR2 = 0.1449; R1(all data) = 0.0751; wR2(all data) = 0.1563;
14 R. S. Simons, L. Pu, M. M. Olmstead and P. P. Power, Organometallics,
1997, 16, 1920–1925.
=
15 Both products are hexanes soluble and crystallize from hexanes
solution at À35 1C. Therefore, the products cannot be consistently
isolated free of each other in usable quantities.
16 There is disorder about the germanium and phosphorus atoms,
with the major component refining to 91% occupancy. While the
hydride refines to a logical location by bond angle, the bond
distance is much shorter than one would expect, potentially a result
of this disorder.
GooF
= 1.017; percent complete: 99.3%; 3: C48H53SnP; FW =
779.56 g molÀ1; colourless block; size: 0.040 Â 0.055 Â 0.131 mm;
triclinic, P21/c; unit cell: a = 10.3576(11) Å, b = 22.461(2) Å, c =
17.5165(19) Å, b = 99.453(3)1, V = 4019.8(7) Å; Z = 4; r = 1.288; T =
150 K; l = 0.71073 nm (MoKa); F(000) = 1624; m = 0.707; 2ymax = 55.0;
2ymin = 2.98; 45 865 reflections, 9226 unique (Rint = 0.1763); parameters =
474; restraints = 4; R1 = 0.0661; wR2 = 0.1475; R1(all data) = 0.1692;
wR2(all data) = 0.1888; GooF = 1.007; percent complete: 99.9%.
1946 | Chem. Commun., 2014, 50, 1944--1946
This journal is ©The Royal Society of Chemistry 2014