A hydroboration route to geminal P/B frustrated Lewis pairs with a bulky secondary phosphane component and their reaction with carbon dioxide

Article abstract of DOI:10.1039/c7dt02315d

The secondary aryl-P(H) phosphanyl substituted tert-butylacetylenes 7a,b (aryl: Mes or Mes?) undergo hydroboration with [HB(C₆F₅)₂] to give the geminal vinylidene-bridged P/B Lewis pairs 8a,b. The treatment of 8a,b with benzonitrile, N-sulfinylaniline, and phenyl isothiocyanate, respectively, gives the addition products 12a,b, 13a,b, and 14 with proton transfer from the phosphorus to the more basic nitrogen site. The reaction of the FLPs 8a,b with carbon dioxide yields a doubly boron bonded addition product. The reaction of 8b with a conjugated ynone formally proceeded by trans-1,2-hydrophosphination of the alkyne at the geminal FLP framework to give the seven-membered heterocycle 21.

Full text of DOI:10.1039/c7dt02315d

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: G. Erker, Z. Jian,
G. Kehr, C. G. Daniliuc and B. Wibbeling, Dalton Trans., 2017, DOI: 10.1039/C7DT02315D.
This is an Accepted Manuscript, which has been through the
Volume 45 Number
1 7 January 2016 Pages 1–398
Royal Society of Chemistry peer review process and has been
accepted for publication.
Dalton
Transactions
Accepted Manuscripts are published online shortly after
An international journal of inorganic chemistry
www.rsc.org/dalton
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
rsc.li/dalton

Please do not adjust margins
Dalton Transactions
Page 1 of 7
View Article Online
DOI: 10.1039/C7DT02315D
Journal Name
ARTICLE
Hydroboration route to geminal P/B frustrated Lewis pairs with a
bulky secondary phosphane component and their reaction with
carbon dioxide
Received 00th January 20xx,
Accepted 00th January 20xx
Zhongbao Jian, Gerald Kehr, Constantin G. Daniliuc, Birgit Wibbeling and Gerhard Erker*
DOI: 10.1039/x0xx00000x
The secondary aryl‐P(H) phosphanyl substituted tert‐butylacetylenes 7a,b (aryl: Mes or Mes*) undergo hydroboration with
[HB(C6F5)2] with a rarely observed regiochemistry to give the geminal vinylidene‐bridged P/B Lewis pairs 8a,b. Treatment of
8a,b with benzonitrile, N‐sulfinylaniline, and phenyl isothiocyanate, respectively, gives the addition products 12a,b, 13a,b,
and 14 with proton transfer from the phosphorus to the more basic nitrogen site. The reaction of the FLPs 8a,b with carbon
dioxide yields a doubly boron bonded addition product. The reaction of 8b with a conjugated ynone formally proceeded by
trans‐1,2‐hydrophosphination of the alkyne at the geminal FLP framework to give the seven‐membered heterocycle 21.
www.rsc.org/
various types of substituents at the heteroatoms, most of which
show typical FLP reactivities.8,9
We have now prepared a pair of geminal alkylidene‐bridged
Ar(H)P/B(C6F5)2 FLPs by means of a simple regioselective
hydroboration route and found them to show some specific
reaction behavior toward CO2 and some related organic
reagents.
Introduction
The combination of Lewis acids and bases with sufficiently bulky
substituents to effectively hinder their neutralizing Lewis
adduct formation has opened ways of cooperative binding of
small molecules, often resulting in their activation.
Intramolecular frustrated Lewis pairs (FLPs) have played a
significant role in this current development.1,2 Most of these
intramolecular systems contain hydrocarbyl bridges that
feature a separation by two or more atoms between the FLP
antagonists. In contrast, geminal FLPs are less frequently
encountered. There is a sizable number of alkylidene‐bridged
Results and discussion
The secondary aryl, alkinyl phosphanes 7a,b were prepared in a
two‐step procedure by treatment of 2,4,6‐tri‐tert‐butylphenyl
(Mes*), respectively mesityl (Mes)PCl2 with in situ generated
lithio tert‐butylacetylene followed by chloride exchange for
hydride at phosphorus with the Li[HBEt3] reagent.4 We had
previously shown that di‐mesityl vinyl‐ or substituted alkynyl
phosphanes added Piers’ borane [HB(C6F5)2]10 with anti‐
Markovnikov orientation, giving the respective vicinal C2‐
bridged P/B systems.2,11 The secondary phosphane 7a (Ar: Mes*)
reacted rapidly with the [HB(C6F5)2] reagent (pentane, r.t., 1 h)
to cleanly give the hydroboration product with the opposite
regioselectivity, namely the geminal P/B system 8a, which we
isolated as an orange solid in 90% yield (Scheme 2). It was
characterized by C,H elemental analysis and by NMR
phosphane/aluminum FLPs (
1 and 2, Scheme 1) that were
mostly reported by Uhl et al.3−5 We had communicated a related
cationic P/Zr+ system 3.6 The related C1‐bridged P/B FLP systems
are rather rare, including our unusual (C6F5)2P/B(C6F5)2 systems
4
and
5
with a much less nucleophilic
spectroscopy [1H:
Hz, PH); 13C: 151.9 (1JPC = 37.8 Hz, C1), 170.1 (2JPC = 22.0 Hz,
C2); 31P: −67.2; 11B: 62.1; 19F: Δδ19Fm,p = 11.7 ppm, for further

6.60 (3JPH = 25.2 Hz, 2‐H), 5.93 (1JPH = 234.8



Scheme 1 Geminal intramolecular frustrated Lewis pairs.
details see the Supporting Information]. Compound 7b reacted
with [HB(C6F5)2] during a period of 12 h at r.t. to give the geminal
P/B product 8b. We isolated it from the reaction mixture in 85%
yield. It shows similar spectroscopic features as 8a (see the
Supporting Information).
phosphane component.7 Lammertsma, Wagner and others
have described a few methylene‐bridged P/B compounds 6 with
Organisch‐Chemisches Institut, Universität Münster, Corrensstr. 40, 48149
Münster, Germany. E‐mail: erker@uni‐muenster.de
Electronic Supplementary Information (ESI) available: Experimental and analytical
details, spectral data and crystallographic data. CCDC 1534139 to 1534147. For ESI
and crystallographic data in CIF or other electronic format see
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 1
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 2 of 7
ARTICLE
Journal Name
group.8a,12 Capture of fluoride and H+ transfer then resulted in
View Article Online
the formation of the 10/
11 product paiDrO(sI:e1e0.1t0h3e9/SCu7DpTp0o2r3t1in5Dg
Information for their characterization). Compound 10 was also
isolated and identified by an X‐ray crystal structure analysis.
Both the compounds 8a and 8b reacted rapidly (5 to 10 min)
with benzonitrile at r.t. in pentane solution to give the products
12a
products were probably formed by a typical P/B FLP addition
reaction to the −C≡N ‐system followed by proton transfer to
the more basic nitrogen site. A similar rapid reaction is observed
upon treatment of 8a
with N‐sulfinylaniline.13 We isolated the
zwitterionic five‐membered heterocycles 13a (Scheme 3).
,b which were isolated in good yield (Scheme 3). The

,
b
,
b
Again, we note that proton transfer from phosphorus to
nitrogen had occurred. Compound 8b reacted rapidly with the
heterocumulene phenyl isothiocyanate to give the similar
compound product 14 (Scheme 3) (isolated in 82% yield, see the
Supporting Information for the characterization of these
Scheme 2 Preparation of secondary PH/B FLPs by regioselective hydroboration.
compounds). The structures of the products 12b, 13b and 14
were also secured by X‐ray diffraction.
Fig. 1 A view of the molecular structure of the geminal P/B FLP dihydrogen splitting
product 9 (thermal ellipsoids are shown with 30 % probability). Selected bond lengths (Å)
and angles (): P1−C1 1.789(1), C1−B1 1.667(2), C1−C2 1.335(2); C1−P1−C11 129.0(1),
P1−C1−B1 102.1(1), B1CCC = 335.2(1).
The mesityl P/B compound 8b did not turn out to be reactive
toward H2 (60 bar). However, the mesityl* P/B compound 8a
showed FLP behavior and heterolytically split dihydrogen under
more forcing conditions (r.t., 60 bar H2, 7 h) to give the PH2 /BH−
+
zwitterion
(Scheme 2) [31P NMR:
(1JBH = 85.9 Hz); 1H:
9, which we isolated as a white solid in 82% yield
1

−41.4 (t, JPH = 486.9 Hz); 11B:
 −18.7

7.46 (d, PH2), 3.32 (BH)]. Compound 9

was characterized by X‐ray diffraction (Fig. 1). The structure has
confirmed the unusual regioselective outcome of the
hydroboration reaction of the bulky secondary alkynyl
phosphane 7a with [HB(C6F5)2] plus the heterolytic dihydrogen
splitting reaction. The central sp2‐hybridized carbon atom (C1)
has the boron and the phosphorus atom attached it. The
phosphorus atom P1 bears a pair of hydrogen atoms attached
and the bulky Mes* substituent, the boron atom B1 has one
hydrogen bonded to it in addition to the pair of C6F5 groups.
Compound 8a was found being a metal‐free catalyst for the
hydrogenation of a bulky imine and an enamine under more
forcing conditions (60 bar H2, r.t.) but it is not overly active (see
the Supporting Information for details).
The geminal P/B FLP 8a is thermally sensitive. Over a period of
5 d in cyclohexane‐d12 solution at r.t., it was converted to a ca.
1 : 1 mixture of the products 10 and 11 (Scheme 3). This is due
to the frequently observed internal nucleophilic aromatic
substitution reaction of the phosphane at an adjacent C6F5
Scheme 3 FLP reactions of the geminal systems 8a,b.
The geminal P/B FLP 8b was exposed to carbon dioxide14,15 (2
bar) in pentane at r.t. for ca. 12 h. During this time a white
precipitate had formed. The product 16b was isolated in 65%
yield (Scheme 4). The X‐ray crystal structure analysis revealed
that CO2 had reacted with 8b in a 1:2 molar ratio (Fig. 2).16
The formation of the unusually structural product 16b can be
rationalized by P/B FLP addition to a C=O bond of carbon dioxide
followed by trapping of the intermediate 15 by a second
equivalent of the bifunctional starting material 8b with the
boron Lewis acid coordinating to the remaining active carbonyl
2 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 7
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
oxygen atom and the phosphorus Lewis base serving as a proton Hz) and 6.40 (1JPH = 486.8 Hz) in CD2Cl2 solution as wVieewllAartsictlehOen1li9nFe
DOI: 10.1039/C7DT02315D
acceptor in the final stabilization step.
NMR signals of a total of four differentiated C6F5 groups at the
pair of boron atoms [11B:

7.2 and 1.9; 31P:
205.2 (br d, 1JPC = 5.6
 −17.7 and −60.3
(td, 1JPH = 482.9 Hz, 3JPH = 70.5 Hz); 13C:

Hz, C7); for details see the Supporting Information].
Compound 8a reacted analogously with CO2. Again the product
formation occurred with a FLP/CO2 stoichiometry of 2:1 and we
isolated the twofold addition product 16a in 60% yield (Scheme
4). Compound 16a was shown by X‐ray diffraction to have an
analogous structure to 16b. It shows similar NMR data [1H:
7.61 (1JPH = 504.8 Hz) and 7.10 (1JPH = 477.9 Hz); 31P:
−4.5 and
−48.3; 11B: 4.2 and 1.8; 13C: 201.0 (C7), 19F: at 233 K




compound 16a shows a total of twenty resonances; we note
that two of the ortho‐F signals show a rather large through
space TSJFF coupling constant of ca. 70 Hz;17 for details see the
Supporting Information].
We were able to trap the alleged intermediate 15 by the
phosphane‐free strong boron Lewis acid B(C6F5)3. For that
reason B(C6F5)3 (1 molar equiv.) was added to a pentane
solution of in situ generated compound 8a and subsequent
exposure to CO2 (2 bar) for 1 h at r.t. produced compound 17 as
a white precipitate. The product was isolated in 71% yield and
characterized by C,H elemental analysis and by spectroscopy [1H
Scheme 4 Reaction of the geminal FLPs 8a,b with carbon dioxide.
NMR:
175.9 (1JPC = 117.6 Hz, [P]‐CO2); 31P:
Hz, 3JPH = 68.6 Hz); 11B:
12.1 and 4.9, for further details see the

8.24 (1JPH = 484.3 Hz, PH), 6.78 (3JPH = 68.6 Hz, =CH); 13C:
−26.8 (dd, 1JPH = 484.3



Supporting Information]. In an in situ NMR experiment we
noticed that the B(C6F5)3/CO2 FLP adduct 17 over 3 days at r.t.
had partially converted to the CO2 addition product 16a
The FLP 8b (Ar: Mes) reacted rapidly with the ‐unsaturated
.
,
ynone 18 in the often observed 1,2‐P/B carbonyl addition mode
(r.t., pentane, 5 min) to give the substituted five‐membered
heterocyclic product 19 (Scheme 5) (isolated in 84% yield as a
mixture of two stereoisomers, see the Supporting Information
for the characterization of the compounds including the X‐ray
crystal structure analysis of one isomer). The P/B FLP 8a reacted
in a remarkably different way with the ynone 18. Stirring the
reaction mixture of 8a and 18 for 12 h in pentane at r.t. gave a
dark purple solution after filtration, from which the product 21
crystallized at −35 C. We isolated the red crystalline product in
76% yield (Scheme 5). It was characterized by C,H elemental
analysis, by NMR spectroscopy and by X‐ray diffraction. The X‐
ray crystal structure analysis revealed the formation of the
seven‐membered heterocycle (Fig. 3). We assume that it was
formed by initial 1,4‐PB FLP addition to the ynone forming the
Fig. 2 Molecular structure of the CO2 addition product 16b (thermal ellipsoids are shown
with 15 % probability). Selected bond lengths (Å) and angles (): P1−C1 1.805(5), C1−B1
1.639(8), C1−C2 1.330(7), B1−O1 1.580(6), O1−C7 1.277(6), C7−O2 1.274(6), O2−B2
1.559(7), B2−C41 1.639(7), C41−P2 1.792(5), C41−C42 1.333(7), C42−C43 1.513(7);
B1−O1−C7 113.6(4), O1−C7−O2 121.7(5), C7−O2−B2 124.1(4), B2−C41−P2 112.0(3),
C41−P2−C51 123.9(2), P1CCC = 307.6(2).
allenic boron enolate intermediate 20 18
This reactive
.
intermediate contains a phosphonium Brønsted acid and an
enolate carbon base. Consequently, proton transfer takes place
to eventually give the observed product 21, formed by
sequential transformation of the acetylic carbon‐carbon triple
bond of the substrate 18 to the Z‐configurated olefinic double
bond in 21. The 1H NMR spectrum shows the olefinic hydrogen
Consequently, the phosphorus atom P2 has a pair of hydrogen
atoms bonded whereas the other phosphorus atom P1 is tri‐
coordinated. Inside the five‐membered core heterocycle we
find almost identical C7−O1/O2 bond lengths indicating a
delocalized structure of this moiety. Due to the chiral trivalent
phosphorus unit P1, compound 16b shows the 1H NMR signals
signal at
63.9 Hz), 116.3 (2JPC = 5.5 Hz); 31P:
NMR carbonyl resonance of the newly formed conjugated
enone, coordinated to the boron Lewis acid, occurs at 199.3

6.07 (3JPH = 30.3 Hz, −C(Ph)=CH−) [13C:

168.4 (1JPC

3.9]. The 13C
=

60.2; 11B:

of a pair of diastereotopic PH2 hydrogens at

6.61 (1JPH = 479.7
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 3
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 4 of 7
ARTICLE
Journal Name
(3JPC = 13.3 Hz); for further details of the characterization of
compound 21 see the Supporting Information.
8
serves as a latent Brønsted acid, which becomes active
View Article Online
DOI: 10.1039/C7DT02315D
through the generation of the respective phosphonium cation
upon cooperative substrate addition. This may lead to new
reactivities toward carbonyl compounds as we have seen it in
the reaction of 8a with the ynone 18. The combination with the
latent [P]H+ Brønsted acid also causes the B(C6F5)2 FLP
component to appear more Lewis acidic in conjunction with the
phosphonium Brønsted acid under equilibrium conditions as we
have seen it in the reaction of the systems
8 with carbon
dioxide. We shall investigate if this H+/B(C6F5)2 cooperation
might direct us toward new applications in frustrated Lewis pair
chemistry.
Experimental section
For general information and the spectroscopic and structural
data of these new compounds see the Supporting Information.
Preparation of compound 8a
After stirring the white suspension of compound 7a (180 mg,
0.5 mmol) and HB(C6F5)2 (173 mg, 0.5 mmol) in pentane (5 mL)
at room temperature for 5 min, the formed yellow solution was
stirred for 1 h at room temperature to finally give a red solution
(with a little bit solid material). The solution was filtered and
then all volatiles of the obtained red filtrate were removed in
vacuo to give an orange solid. Yield: 318 mg, 90%. Anal. calc. for
C36H40PBF10 (704.5 g mol‐1): C, 61.38; H, 5.72. Found: C, 61.62;
H, 5.74.
Scheme 5 Reaction of the FLPs with a conjugated ynone.
Preparation of compound 8b
After stirring the white suspension of compound 7b (116 mg,
0.5 mmol) and HB(C6F5)2 (173 mg, 0.5 mmol) in pentane (5 mL)
at room temperature for 5 min, the formed yellow solution was
stirred for 12 h at room temperature to finally give a yellow
solution (with a little bit solid material). The solution was
filtered and then all volatiles of the obtained yellow filtrate
were removed in vacuo to give a yellow solid. Yield: 246 mg,
85%. Anal. calc. for C27H22PBF10 (578.2 g mol‐1): C, 56.08; H, 3.84.
Found: C, 56.38; H, 3.95.
Fig 3 Molecular structure of the ynone reaction product 21 (thermal ellipsoids are shown
with 30 % probability). Selected bond lengths (Å) and angles (): P1−C1 1.786(3), C1−B1
1.649(4), B1−O1 1.538(3), O1−C53 1.288(3), C53−C52 1.395(4), C52−C51 1.406(4),
C51−P1 1.736(3); P1−C1−B1 111.1(2), C1−B1−O1 108.4(2), B1−O1−C53 132.5(2),
C53−C52−C51 128.7(2), C52−C51−P1 131.0(2), P1CCC = 351.1(1).
Preparation of compound 16a
After stirring a mixture of compound 7a (180 mg, 0.5 mmol) and
HB(C6F5)2 (173 mg, 0.5 mmol) in pentane (3 mL) at room
temperature for 1 h, the resulting red suspension was filtered
to give a clear red solution which was exposed to CO2 gas (2.0
bar). After the reaction mixture was stirred at room
temperature for 12 h a white precipitate was formed. The
resulting suspension was filtered. The collected solid was
washed twice with pentane (25 mL) and dried in vacuo to give
a white solid. Yield: 218 mg, 60%. Anal. calc. for C73H80P2B2O2F20
(1453.0 g mol‐1): C, 60.35; H, 5.55. Found: C, 60.28; H, 5.48.
Conclusions
Alkenyl and alkynyl phosphanes usually undergo hydroboration
with Piers’ borane [HB(C6F5)2] to give the respective vicinal P/B
systems. Many syntheses of C2‐bridged P/B FLPs rely on that
regioselectivity.11 This strong regiocontrol of the hydroboration
reaction on the other hand had so far precluded the easy
synthesis of the missing alkylidene‐bridged geminal P/B FLPs by
the hydroboration pathway. Our new systems 8, therefore,
represent a remarkable exception. Moreover, the system is
characterized by the joint presence of the strong B(C6F5)2 Lewis
acid function plus the strong P(H)Aryl Lewis base in close spacial
proximity. In addition, the secondary phosphane in the systems
Preparation of compound 16b
After stirring a mixture of compound 7b (116 mg, 0.5 mmol) and
HB(C6F5)2 (173 mg, 0.5 mmol) in pentane (5 mL) at room
4 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 7
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
Hepp, J. C. Slootweg, K. Lammertsma and WV.ieUwhAlr,ticDleaOlntloinne
Trans., 2012, 41, 9033‐9045; (d) C. ApDpOelI:t,10J..10C3.9S/lCo7oDtTw0e2g31,5KD.
temperature for 12 h, the resulting yellow suspension was
filtered to give a clear yellow solution which was exposed to CO2
gas (2.0 bar). After the reaction mixture was stirred at room
temperature for 12 h a white precipitate was formed. The
resulting suspension was filtered. The collected solid was
Lammertsma and W. Uhl, Angew. Chem. Int. Ed., 2013, 52
,
4256‐4259; Angew. Chem., 2013, 125, 4350‐4353; (e) W. Uhl
and E.‐U. Würthwein, Top. Curr. Chem., 2013, 334, 101‐119;
(f) W. Uhl, C. Appelt, J. Backs, H. Westenberg, A. Wollschläger
and J. Tannert, Organometallics, 2014, 33, 1212‐1217; (g) M.
Devillard, R. Declercq, E. Nicolas, A. W. Ehlers, J. Backs, N.
Saffon‐Merceron, G. Bouhadir, J. C. Slootweg, W. Uhl and D.
Bourissou, J. Am. Chem. Soc., 2016, 138, 4917‐4926.
For compound 2 see: L. Keweloh, H. Klöcker, E.‐U. Würthwein
and W. Uhl, Angew. Chem. Int. Ed., 2016, 55, 3212‐3215;
Angew. Chem., 2016, 128, 3266‐3269.
washed twice with pentane (25 mL) and dried in vacuo to give
a white solid. Yield: Yield: 195 mg, 65%. Anal. calc. for
C55H44P2B2O2F20 (1200.5 g mol‐1): C, 55.03; H, 3.69. Found: C,
55.48; H, 4.06.
4
5
Preparation of compound 19
For R2P−CH2−AlR 2
 systems see also: (a) J. Boudreau, M. A.
After stirring a mixture of compound 7b (116 mg, 0.5 mmol) and
HB(C6F5)2 (173 mg, 0.5 mmol) in pentane (3 mL) at room
temperature for 10 h, the resulting yellow suspension was
filtered to give a clear yellow solution. Then one equiv. of 4,4‐
dimethyl‐1‐phenylpent‐1‐yn‐3‐one (93 mg, 0.5 mmol) was
added and after stirring for 5 min a white precipitate was
formed. The resulting suspension was filtered. The collected
Courtemanche and F. G. Fontaine, Chem. Commun., 2011, 47
,
11131‐11133; (b) F. Bertini, F. Hoffmann, C. Appelt, W. Uhl, A.
W. Ehlers, J. C. Slootweg and K. Lammertsma,
Organometallics, 2013, 32, 6764‐6769.
6
7
For compound 3 see: (a) X. Xu, R. Fröhlich, C. G. Daniliuc, G.
Kehr and G. Erker, Chem. Commun., 2012, 48, 6109‐6111; (b)
X. Xu, G. Kehr, C. G. Daniliuc and G. Erker, J. Am. Chem. Soc.,
2013, 135, 6465‐6476.
solid was washed twice with pentane (25 mL) and dried in
For compounds
4 and 5 see: (a) A. Stute, G. Kehr, R. Fröhlich
vacuo to give a white solid. Yield: 321 mg, 84%. Anal. calc. for
C40H36PBOF10 (764.5 g mol‐1): C, 62.84; H, 4.75. Found: C, 62.76;
H, 4.49.
and G. Erker, Chem. Commun., 2011, 47, 4288‐4290; (b) C.
Rosorius, G. Kehr, R. Fröhlich, S. Grimme and G. Erker,
Organometallics, 2011, 30, 4211‐4219; (c) A. Stute, G. Kehr, C.
G. Daniliuc, R. Fröhlich and G. Erker, Dalton Trans., 2013, 42
,
4487‐4499; (d) C. Rosorius, C. G. Daniliuc, R. Fröhlich, G. Kehr
and G. Erker, J. Organomet. Chem., 2013, 744, 149‐155.
Preparation of compound 21
After stirring a mixture of compound 7a (180 mg, 0.5 mmol) and
HB(C6F5)2 (173 mg, 0.5 mmol) in pentane (3 mL) at room
temperature for 1 h, the resulting red suspension was filtered
to give a clear red solution. Then one equiv. of 4,4‐dimethyl‐1‐
phenylpent‐1‐yn‐3‐one (93 mg, 0.5 mmol) was added and after
stirring for 12 h a dark purple suspension was formed which was
filtered. The filtrate was stored at −35 °C to give dark red crystal.
Yield: 339 mg, 76%. Anal. calc. for C49H54PBOF10 (0.5 CH2Cl2): C,
63.71; H, 5.94. Found: C, 63.98; H, 5.90.
8
9
For compound 6 see: (a) F. Bertini, V. Lyaskoyskyy, B. J. J.
Timmer, F. J. J. de Kanter, M. Lutz, A. W. Ehlers, J. C. Slootweg
and K. Lammertsma, J. Am. Chem. Soc., 2012, 134, 201‐204;
(b) J. Yu, G. Kehr, C. G. Daniliuc, C. Bannwarth, S. Grimme and
G. Erker, Org. Biomol. Chem., 2015, 13, 5783‐5792; (c) K.
Samigullin, I. Georg, M. Bolte, H.‐W. Lerner and M. Wagner,
Chem. Eur. J., 2016, 22, 3478‐3484.
For other geminal FLP examples see: (a) F. G. Fontaine, J.
Boudreau and M.‐H. Thibault, Eur. J. Inorg. Chem., 2008, 5439‐
5454; (b) F. Lavigne, E. Maerten, G. Alcaraz, N. Saffon‐
Merceron, C. Acosta‐Silva, V. Branchadell and A. Baceiredo, J.
Am. Chem. Soc., 2010, 132, 8864‐8865; S/B: (c) Y. Gloaguen,
G. Alcaraz, A.‐F. Pécharman, E. Clot, L. Vendier and S. Sabo‐
Etienne, Angew. Chem. Int. Ed., 2009, 48, 2964‐2968; Angew.
Chem., 2009, 121, 3008‐3012; (d) C. A. Tanur and D. W.
Stephan, Organometallics, 2011, 30, 3652‐3657; N/B: (e) L.
Zhao, H. Li, G. Lu, F. Huang, C. Zhang and Z.‐X. Wang, Dalton
Trans., 2011, 40, 1929‐1937; (f) E. Theuergarten, J. Schlosser,
D. Schluns, M. Freytag, C. G. Daniliuc, P. G. Jones and M.
Tamm, Dalton Trans., 2012, 41, 9101‐9110; (g) É. Dorkó, E.
Varga, T. Gáti, T. Holczbauer, I. Pápai, H. Mehdi and T. Soós,
Synlett, 2014, 25, 1525‐1528; (h) D. Yepes, P. Jaque and I.
Fernández, Chem. Eur. J., 2016, 22, 18801‐18809; N/Al: (i) W.
Zheng, C. Pi and H. Wu, Organometallics, 2012, 31, 4072‐
4075; P/Si: (j) B. Waerder, M. Pieper, L. A. Korte, T. A. Kinder,
A. Mix, B. Neumann, H.‐G. Stammler and N. W. Mitzel, Angew.
Chem. Int. Ed., 2015, 54, 13416‐13419; Angew. Chem., 2015,
127, 13614‐13617; P/X (X = Ge, Sn, Pb): (k) J. Schneider, K. M.
Krebs, S. M. Freitag, K. Eichele, H. Schubert and L. Wesemann,
Chem. Eur. J., 2016, 22, 9812‐9826; (l) J. Schneider, C. P.
Sindlinger, S. M. Freitag, H. Schubert and L. Wesemann,
Angew. Chem. Int. Ed., 2017, 56, 333‐337; Angew. Chem.,
2017, 129, 339‐343.
Acknowledgements
Financial support from the European Research Council is
gratefully acknowledged.
Notes and references
1
(a) Frustrated Lewis Pair Chemistry I: Uncovering and
Understanding, Top. Curr. Chem., ed. G. Erker and D. W.
Stephan, Heidelberg, 2013, vol. 332; (b) Frustrated Lewis Pair
Chemistry II: Expanding the Scope, Top. Curr. Chem., ed. G.
Erker and D. W. Stephan, Heidelberg, 2013, vol. 334; (c) D. W.
Stephan and G. Erker, Angew. Chem. Int. Ed., 2015, 54, 6400‐
6441; Angew. Chem., 2015, 127, 6498‐6541; (d) D. W.
Stephan, Science, 2016, 354, aaf7229.
2
3
(a) P. Spies, G. Erker, G. Kehr, K. Bergander, R. Fröhlich, S.
Grimme and D. W. Stephan, Chem. Commun., 2007, 5072‐
5074; (b) G. Kehr, S. Schwendemann and G. Erker, Top. Curr.
Chem., 2013, 332, 45‐84.
For selected examples of the geminal compound type
Appelt, H. Westenberg, F. Bertini, A. W. Ehlers, J. C. Slootweg,
K. Lammertsma and W. Uhl, Angew. Chem. Int. Ed., 2011, 50
1: (a) C.
10 (a) D. J. Parks, R. E. von H. Spence and W. E. Piers, Angew.
Chem. Int. Ed. Engl., 1995, 34, 809‐811; Angew. Chem., 1995,
107, 895‐897; (b) D. J. Parks, W. E. Piers and G. P. A. Yap,
Organometallics, 1998, 17, 5492‐5503.
11 For reactions of substituted alkynyl phosphanes with
[HB(C6F5)2] or [B(C6F5)3] giving vicinal P/B FLP systems see e.g.:
,
3925‐3928; Angew. Chem., 2011, 123, 4011‐4014; (b) C.
Appelt, J. C. Slootweg, K. Lammertsma and W. Uhl, Angew.
Chem. Int. Ed., 2012, 51, 5911‐5914; Angew. Chem., 2012,
124, 6013‐6016; (c) S. Roters, C. Appelt, H. Westenberg, A.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 5
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 6 of 7
ARTICLE
(a) P. Spies, S. Schwendemann, S. Lange, G. Kehr, R. Fröhlich
Journal Name
View Article Online
and G. Erker, Angew. Chem. Int. Ed., 2008, 47, 7543‐7546;
Angew. Chem., 2008, 120, 7654‐7657; (b) O. Ekkert, G. Kehr,
R. Fröhlich and G. Erker, J. Am. Chem. Soc., 2011, 133, 4610‐
4616; (c) O. Ekkert, G. G. Miera, T. Wiegand, H. Eckert, B.
Schirmer, J. L. Petersen, C. G. Daniliuc, R. Fröhlich, S. Grimme,
DOI: 10.1039/C7DT02315D
G. Kehr and G. Erker, Chem. Sci., 2013, 4, 2657‐2664.
12 (a) G. C. Welch, R. R. S. Juan, J. D. Masuda and D. W. Stephan,
Science, 2006, 314, 1124‐1126; (b) A. Schnurr, H. Vitze, M.
Bolte, H.‐W. Lerner and M. Wagner, Organometallics, 2010,
29, 6012‐6019; (c) A. Schnurr, M. Bolte, H.‐W. Lerner and M.
Wagner, Eur. J. Inorg. Chem., 2012, 112‐120; (d) J. S. Reddy,
B.‐H. Xu, T. Mahdi, R. Fröhlich, G. Kehr, D. W. Stephan and G.
Erker, Organometallics, 2012, 31, 5638‐5649.
13 (a) X. Xu, G. Kehr, C. G. Daniliuc and G. Erker, J. Am. Chem. Soc.,
2014, 136, 12431‐12443; (b) L. E. Longobardi, V. Wolter and
D. W. Stephan, Angew. Chem., Int. Ed., 2015, 54, 809‐812;
Angew. Chem., 2015, 127, 823‐826.
TOC
14 For examples of CO2 binding by FLPs see: (a) C. M. Mömming,
E. Otten, G. Kehr, R. Fröhlich, S. Grimme, D. W. Stephan and
G. Erker, Angew. Chem. Int. Ed., 2009, 48, 6643‐6646; Angew.
Chem., 2009, 121, 6770‐6773; (b) A. M. Chapman, M. F.
Haddow and D. F. Wass, J. Am. Chem. Soc., 2011, 133, 18463‐
18478; (c) D. Voicu, M. Abolhasani, R. Choueiri, G. Lestari, C.
Seiler, G. Ménard, J. Greener, A. Guenther, D. W. Stephan and
E. Kumacheva, J. Am. Chem. Soc., 2014, 136, 3875‐3880; (d) D.
H
P
tBu
P
H
Mes*
tBu
+
Mes*
B(C6F5)2
HB(C6F5)2
½ CO2
O
O
tBu
P
H
B(C6F5)2
H
P
H
W. Stephan and G. Erker, Chem. Sci., 2014, 5, 2625‐2641; (e)
H
H
S. Bontemps, Coord. Chem. Rev., 2016, 308, 117‐130.
Mes*
B(C6F5)2
Mes*
tBu
15 For FLP mediated CO2 reduction see: (a) A. E. Ashley, A. L.
Mes*: 2,4,6-tri-tert-butylphenyl
Thompson and D. O'Hare, Angew. Chem. Int. Ed., 2009, 48
,
9839‐9843; Angew. Chem., 2009, 121, 10023‐10027; (b) A.
Berkefeld, W. E. Piers and M. Parvez, J. Am. Chem. Soc., 2010,
132, 10660‐10661; (c) G. Ménard and D. W. Stephan, Angew.
Chem. Int. Ed., 2011, 50, 8396‐8399; Angew. Chem., 2011,
123, 8546‐8549; (d) M. J. Sgro and D. W. Stephan, Angew.
Chem. Int. Ed., 2012, 51, 11343‐11345; Angew. Chem., 2012,
124, 11505‐11507; (e) M. A. Courtemanche, M. A. Legare, L.
Maron and F. G. Fontaine, J. Am. Chem. Soc., 2013, 135, 9326‐
9329; (f) A. E. Ashley and D. O'Hare, Top. Curr. Chem., 2013,
334, 191‐217; (g) M. A. Courtemanche, M. A. Légaré, L. Maron
and F. G. Fontaine, J. Am. Chem. Soc., 2014, 136, 10708‐
10717.
Hydroboration of a secondary alkynyl phosphane gives
a geminal P/B frustrated Lewis pair that reacts with
carbon dioxide
16 For rare examples of bis‐borane binding to CO2, see e.g.: (a) X.
Zhao and D. W. Stephan, Chem. Commun., 2011, 47, 1833‐
1835; (b) Y.‐L. Liu, G. Kehr, C. G. Daniliuc and G. Erker, Chem.
Sci., 2017, 8, 1097‐1104.
17 (a) F. B. Mallory, J. Am. Chem. Soc., 1973, 95, 7747‐7752; (b)
F. B. Mallory, C. W. Mallory and M.‐C. Fedarko, J. Am. Chem.
Soc., 1974, 96, 3536‐3542; (c) A. D. Buckingham and J. E.
Cordle, J. Chem. Soc., Faraday Trans. 2, 1974, 70, 994‐1014;
(d) J. Hilton and L. H. Sutcliffe, Prog. Nucl. Magn. Reson.
Spectrosc., 1975, 10, 27‐39; (e) J. W. Emsley, L. Phillips and V.
Wray, Prog. Nucl. Magn. Reson. Spectrosc., 1976, 10, 83‐756;
(f) L. Ernst, K. Ibrom, K. Marat, R. H. Mitchell, G. J. Bodwell and
G. W. Buschnell, Chem. Ber., 1994, 127, 1119‐1124; (g) W. D.
Arnold, J. Mao, H. Sun and E. Oldfield, J. Am. Chem. Soc., 2000,
122, 12164‐12168; (h) T. Tuttle, J. Gräfenstein and D. Cremer,
Chem. Phys. Lett., 2004, 394, 5‐13; (i) P. Espinet, A. C. Albéniz,
. A. Casares and J. M. Martínez‐Ilarduya, Coord. Chem. Rev.,
2008, 252, 2180‐2208; (j) see also: S. Berger, S. Braun, H.‐O.
Kalinowski, NMR‐Spektroskopie von Nichtmetallen, Band 4,
19F‐NMR‐Spektroskopie, Thieme‐Verlag, Stuttgart, 1994.
18 See for a comparison: (a) B.‐H. Xu, G. Kehr, R. Fröhlich, B.
Wibbeling, B. Schirmer, S. Grimme and G. Erker, Angew.
Chem. Int. Ed., 2011, 50, 7183‐7186; Angew. Chem., 2011,
123, 7321‐7324; (b) B.‐H. Xu, R. Yanez, H. Nakatsuka, M.
Kitamura, R. Fröhlich, G. Kehr and G. Erker, Chem. Asian J.,
2012, 7, 1347‐1356.
6 | J. Name., 2012, 00, 1‐3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 7
Dalton Transactions
View Article Online
DOI: 10.1039/C7DT02315D
TOC
Hydroboration of a secondary alkynyl phosphane gives a geminal P/B frustrated Lewis pair that
reacts with carbon dioxide