Insignificance of P-H...P hydrogen bonding: Structural chemistry of neutral and protonated 1,8-di(phosphinyl)naphthalene

Article abstract of DOI:10.1021/ja045460x

While there is extensive information on 1,8-di(amino)naphthalene (i.e., the parent compound of the proton sponge series), the corresponding phosphorus compound has not been described. A high-yield synthesis of 1,8-di(phosphinyl)naphthalene (9) and the 1-naphthylphosphine reference compound (4) is now reported. Thermal decomposition of 9 leads to intramolecular dehydrogenative P-P coupling to afford 1,2-dihydro-1,2-diphosphaacenaphthene (10). Protonation of 9 and 4 with CF₃SO₃H gives quantitative yields of the monophosphonium salts 11 and 5, respectively. With excess acid and traces of moisture, the hydronium salt [C₁₀H ₆(PH₂)(PH₃)]⁺[H₃O] ⁺2[CF₃SO₃]^- (13) is obtained. The structures of 9, 11, and 13 have been determined. Molecules of 9 have a planar naphthalene skeleton, C₁₀H₆P₂, with the two -PH₂ groups in a transoid conformation. The molecules form loose dimers in the crystal, the individual chiral enantiomers of which are related by a center of inversion. In contrast to the situation for the amino analogue, and despite the proximity of the two -PH₂ functions, there is no intra- or intermolecular hydrogen bonding. Solutions of 9 (in CD₂Cl ₂) show equivalent P-bound hydrogen atoms due to conformational fluctionality. By analysis of the ABCD₂XX′D′ ₂C′B′A′ spin system, it was shown that, in 9, there are strong through-space pericouplings [ⁿJ(P_XP _X′) = 221.6 Hz, ⁿJ(P_XH _D′) = 31.7 Hz, ⁿJ(H_DH_D′) = 3.9 Hz]. In the cations of 11, the C₁₀H₆P₂ skeleton is also planar (by C_s symmetry), with the -PH₂ and -PH₃⁺ groups in a conformation which rules out any P-H...P hydrogen bonding. The hydronium cation and the two triflate anions in 13 are associated into an anionic network through extensive hydrogen bonding surrounding stacks of the phosphonium cations. In solution, the cations of 11 and 13 show separate ³¹P resonances for the two phosphorus atoms with fully resolved ¹J(PH) couplings, which indicate that there is no intra- or intercationic proton exchange. By contrast, the NMR spectra of solutions of [C₁₀H₆(NH₂)(NH₃)] ⁺X^- salts show proton scrambling equilibrating all five N-bound hydrogen atoms, and in the crystal, the conformations of the cations feature intramolecular N-H...N hydrogen bonding.

Full text of DOI:10.1021/ja045460x

Published on Web 11/10/2004
Insignificance of P-H‚‚‚P Hydrogen Bonding: Structural
Chemistry of Neutral and Protonated
1
,8-Di(phosphinyl)naphthalene
†
†
‡
Stephan A. Reiter, Stefan D. Nogai, Konstantin Karaghiosoff, and
,
†
Hubert Schmidbaur*
Contribution from the Department Chemie, Technische UniVersit a¨ t M u¨ nchen, Lichtenbergstrasse
, 85747 Garching, Germany, and Department Chemie und Biochemie,
4
Ludwig-Maximilians-UniVersit a¨ t M u¨ nchen, Butenandtstrasse 5-13 (D), 81377 M u¨ nchen,
Germany
Received July 28, 2004; E-mail: H.Schmidbaur@lrz.tum.de
Abstract: While there is extensive information on 1,8-di(amino)naphthalene (i.e., the parent compound of
the “proton sponge” series), the corresponding phosphorus compound has not been described. A high-
yield synthesis of 1,8-di(phosphinyl)naphthalene (9) and the 1-naphthylphosphine reference compound
(
4) is now reported. Thermal decomposition of 9 leads to intramolecular dehydrogenative P-P coupling to
afford 1,2-dihydro-1,2-diphosphaacenaphthene (10). Protonation of 9 and 4 with CF SO H gives quantitative
yields of the monophosphonium salts 11 and 5, respectively. With excess acid and traces of moisture, the
3
3
+
+
-
hydronium salt [C10
H
6
(PH
2
)(PH
3
)] [H
3
O] 2[CF
3
SO
3
] (13) is obtained. The structures of 9, 11, and 13 have
, with the two -PH groups
been determined. Molecules of 9 have a planar naphthalene skeleton, C10
6
H P
2
2
in a transoid conformation. The molecules form loose dimers in the crystal, the individual chiral enantiomers
of which are related by a center of inversion. In contrast to the situation for the amino analogue, and despite
the proximity of the two -PH
of 9 (in CD Cl ) show equivalent P-bound hydrogen atoms due to conformational fluctionality. By analysis
XX′D′ C′B′A′ spin system, it was shown that, in 9, there are strong through-space pericouplings
2
functions, there is no intra- or intermolecular hydrogen bonding. Solutions
2
2
of the ABCD
2
2
n
n
n
[
J(P
X
P
X′) ) 221.6 Hz, J(P
X
H
D′) ) 31.7 Hz, J(H
D
H
D′) ) 3.9 Hz]. In the cations of 11, the C10
H
6
P
2
skeleton
+
is also planar (by C
s
symmetry), with the -PH
2
and -PH
3
groups in a conformation which rules out any
P-H‚‚‚P hydrogen bonding. The hydronium cation and the two triflate anions in 13 are associated into an
anionic network through extensive hydrogen bonding surrounding stacks of the phosphonium cations. In
31
solution, the cations of 11 and 13 show separate P resonances for the two phosphorus atoms with fully
1
resolved J(PH) couplings, which indicate that there is no intra- or intercationic proton exchange. By contrast,
+
-
the NMR spectra of solutions of [C10
6 2 3
H (NH )(NH )] X salts show proton scrambling equilibrating all five
N-bound hydrogen atoms, and in the crystal, the conformations of the cations feature intramolecular N-H‚
‚‚N hydrogen bonding.
Introduction
strain as their size is increased beyond that of hydrogen (in
naphthalene itself). The consequences are readily discernible
from peculiar structural details of the molecular geometries, from
spectroscopic properties, and from the striking differences in
reactivity of peridisubstituted as compared to 1-monosubstituted
naphthalenes.
1
For almost half of a century, peridisubstituted naphthalenes
have received unabating interest. Their unique stereochemistry
gives rise to many unusual properties, of which the behavior as
1
2
-4
“
proton sponges”
or the action as “anion pincers” are most
Functional groups in the 1,8-positions of naph-
5-7
prominent.
The extensive literature on 1,8-disubstituted naphthalenes has
detailed information on all prototypes of formulas A and B.
The directly bonded element in functions X can be taken from
almost any group of the s- and p-block elements. In the first
octet period, with substituents for type A ranging from X ) F
thalene are held in proximity and experience significant steric
†
Technische Universit a¨ t M u¨ nchen.
Ludwig-Maximilians-Universit a¨ t M u¨ nchen.
‡
(
(
(
1) (a) Schiemenz, G. P. Z. Anorg. Allg. Chem. 2002, 628, 2597. (b)
Balasubramaniyan, V. Chem. ReV. 1966, 66, 567.
2) Staab, H. A.; Saupe, T. Angew. Chem. 1988, 100, 895; Angew. Chem., Int.
Ed. Engl. 1988, 27, 865.
3) Alder, R. W.; Bowman, P. S.; Steele, W. R. S.; Winterman, D. R. Chem.
Commun. 1968, 723.
8
to X ) Li, the classes of compounds include simple diols and
9
2
10-13
ethers (X ) OR), diamines (X ) NR2), dialkyls (X ) R),
(
4) Hibbert, F. J. Chem. Soc., Perkin Trans. 2 1974, 1862.
5) Hoefelmeyer, J. D.; Schulte, M.; Tschinkl, M.; Gabba ¨ı , F. P. Coord. Chem.
ReV. 2002, 235, 93.
(
(8) Katz, H. E. J. Org. Chem. 1985, 50, 5027.
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(b) Foti, M. C.; Barclay, L. R. C.; Ingold, K. U. J. Am. Chem. Soc. 2002,
124, 12881. (c) Foti, M. C.; Johnson, E. R.; Vinqvist, M. R.; Wright, J. S.;
Barclay, L. R. C.; Ingold, K. U. J. Org. Chem. 2002, 67, 5190.
(6) Gabba ¨ı , F. P. Angew. Chem. 2003, 115, 2318; Angew. Chem., Int. Ed. 2003,
4
2, 2218.
(7) Schmidbaur, H.; O¨ ller, H. J.; Wilkinson, D. L.; Huber, B.; M u¨ ller, G. Chem.
Ber. 1989, 122, 31.
(10) Letsinger, R. L.; Gilpin, J. A.; Vullo, W. J. J. Org. Chem. 1962, 27, 672.
10.1021/ja045460x CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 15833-15843
9
15833

A R T I C L E S
Reiter et al.
5
diboryls (X ) BR2), and their derivatives. (There is only a
grown enormously, and there is a vast literature dealing mainly
with the elusive periinteractions between two phosphorus atoms
in various oxidation states and with a variety of substitution
blank for beryllium, and generally for X representing a group
element, but a few magnesium14 and mercury compounds
7
2
1
9,20
have been described.)
patterns.
Yet, the simple prototype, 1,8-di(phosphinyl)-
naphthalene C1, has not been prepared. We therefore recently
resumed our studies in this field and are now able to present
some results which provide information on the fundamental
structural characteristics of this molecule. The protonation of
C1 with trifluoromethanesulfonic acid has been studied, and
the structure of the corresponding phosphonium salt has been
determined.
The work presented in this account also complements earlier
studies on the related 1,8-di(silyl)naphthalenes, which included
determination of the molecular structure of 1,8-(H3Si)2C10H6
For a long time, research has focused mainly on the diamines,
for which drastic changes of the Br o¨ nsted basicity were observed
as the substitution pattern was gradually changed from the free
2
1
diamine to the tetraalkylated species.2
-4,15
(A, X ) SiH3). There is extensive literature on derivatives
While 1,8-diami-
22
with triorganosilicon, -germanium, and -tin substituents. The
nonaphthalene (A1) exhibits about the same basicity as 1-ami-
nonaphthalene (or aniline), the pK of 1,8-bis(dimethylamino)-
naphthalene (A2) is increased by 7 orders of magnitude as
compared to 1-(dimethylamino)naphthalene. This strongly en-
hanced proton affinity (proton sponge behavior) of A2 as
compared to that of A1 is caused by the introduction of the
four substituents, but clearly not only through the standard
inductive effect of alkyl groups, which is also operative in
new results thus fill the gap between this disilane and the dithiole
1
,8-(HS)2C10H6 (A, X ) SH). Similar to this dithiol,23 the new
diprimary phosphine C1 is an interesting, and yet unexplored,
chelating ligand of extreme rigidity which can be transformed
into many other disecondary and ditertiary phosphine derivatives
with diverse stereochemistry.
Preparative and Analytical Results
1-(dimethylamino)naphthalene. It is rather the steric congestion
As a test run for the preparation of the target molecule (C1),
in the tetraalkylated compounds which forces the lone pairs of
electrons at the two nitrogen atoms into the “bay region” of the
molecule. Relief of the strongly repulsive interactions in this
1
-naphthylphosphine D1 has been obtained as a suitable
reference compound (4, Scheme 1). For its synthesis, 1-naph-
thyllithium (1) was treated with bis(diethylamino)chlorophos-
phine in tetrahydrofuran to give bis(diethylamino)(1-naphthyl)-
1
region (the “peristress”) by protonation is the main reason for
the extreme proton affinity of perinaphthalene proton sponges.
2
4
phosphine (2). This product was readily converted into
For highly strained A2, the incoming proton is accommodated
2
4,25
dichloro(1-naphthyl)phosphine (3)
upon treatment of its
2
in a central position between the two nitrogen atoms, while
solution in hexane with dry hydrogen chloride (83% yield) and
finally into 1-naphthylphosphine in the reaction with lithium
aluminum hydride in diethyl ether (90% yield). 4 was prepared
previously by dearylation of tri(1-naphthyl)phosphine, but no
for the less-strained unsubstituted prototype A1, the proton is
attached to one of the two nitrogen atoms and forms a hydrogen
bond with the neighboring -NH2 group.1
6,17
Phosphines are much poorer Br o¨ nsted bases than amines, and
strong acid (HZ ) HI or HClO4) is required to convert PH3 or
primary phosphines, RPH2, into the corresponding phosphonium
2
6
details were given. It is a colorless, distillable liquid (bp0.9 87
1
°
C), which crystallizes upon cooling at -26 °C. Its H-coupled
3
1
P NMR spectrum (in CD2Cl2) shows a sharp triplet of doublets
for the -PH2 group at δ -133.5 ppm [ J(PH) ) 203.5 Hz,
J(PH) ) 8.0 Hz]. Other details are given in the Experimental
+
-
+ -
salts PH4 Z and RPH3 Z , respectively. Because of this low
proton affinity of phosphines, the protonation equilibria of these
compounds have received only limited interest, and the proton
sponge effect in polyphosphines has not yet been a major issue.
In an earlier investigation carried out in our laboratory, bis-
1
3
Section.
(
19) Kara c¸ ar, A.; Freytag, M.; Th o¨ nnessen, H.; Jones, P. G.; Bartsch, R.;
Schmutzler, R. J. Organomet. Chem. 2002, 643-644, 68 and references
therein.
(dimethylphosphinyl)naphthalene (C2) and 1-(dimethylphos-
phinyl)naphthalene (D2) were prepared, and some of their
fundamental reactions were studied;1 however, the simple
primary phosphines C1 and D1 were not available, and no direct
comparison could be made.
(20) Kilian, P.; Philp, D.; Slawin, A. M. Z.; Woollins, J. D. Eur. J. Inorg. Chem.
2003, 249 and references therein.
8
(
21) (a) Schr o¨ ck, R.; Angermaier, K.; Sladek, A.; Schmidbaur, H. Organome-
tallics 1994, 13, 3399. (b) Schr o¨ ck, R.; Angermaier, K.; Schmidbaur, H.
Z. Naturforsch., B 1995, 50, 613. (c) Schr o¨ ck, R.; Dreih a¨ upl, K.-H.; Sladek,
A.; Angermaier, K.; Schmidbaur, H. Chem. Ber. 1996, 129, 495.
In the period since 1980, the chemistry of 1,8-disubstituted
naphthalenes of type C, with two phosphorus substituents, has
(22) (a) Seyferth, D.; Vick, S. C. J. Organomet. Chem. 1977, 141, 173. (b)
Wroczynski, R. J.; Baum, M. W.; Kost, D.; Mislow, K.; Vick, S. C.;
Seyferth, D. J. Organomet. Chem. 1979, 170, C29. (c) Sooriyakumaran,
R.; Boudjouk, P. Organometallics 1982, 1, 218. (d) Cozzi, F.; Sj o¨ strand,
U.; Mislow, K. J. Organomet. Chem. 1979, 174, C1. (e) Chuit, C.; Corriu,
R. J. P.; Reye, C.; Young, J. C. Chem. ReV. 1993, 93, 1371. (f) Jastrzebski,
J. T. B. H.; van Koten, G. AdV. Organomet. Chem. 1993, 35, 241.
(
11) (a) Handal, J.; White, J. G.; Franck, R. W.; Yuh, Y. H.; Allinger, N. L. J.
Am. Chem. Soc. 1977, 99, 3345. (b) Franck, R. W.; Leser, E. G. J. Am.
Chem. Soc. 1969, 91, 1577.
(
(
(
12) Bright, D.; Maxwell, I. E.; de Boer, J. J. Chem. Soc., Perkin Trans. 2 1973,
2 10 6
(23) For 1,8-(HS) C H , see: (a) Burns, J. A.; Whitesides, G. M. J. Am. Chem.
2
101.
Soc. 1990, 112, 6296. (b) Nakanishi, W.; Hayashi, S.; Uehara, T. J. Phys.
Chem. A 1999, 103, 9906. For a theoretical treatment of the diselenol 1,8-
13) Robert, J. B.; Sherfinski, J. S.; Marsh, R. E.; Roberts, J. D. J. Org. Chem.
1
974, 39, 1152.
2 10 6
(HSe) C H ), see: (c) Glass, R. S.; Andruski, S. W.; Broeker, J. L. ReV.
14) Tinga, M. A. G. M.; Schat, G.; Akkerman, O. S.; Bickelhaupt, F.; Horn,
Heteroat. Chem. 1988, 1, 31. (d) Fujihara, H.; Ishitani, H.; Takaguchi, Y.;
Furukawa, N. Chem. Lett. 1995, 571.
E.; Kooijman, H.; Smeets, W. J. J.; Spek, A. L. J. Am. Chem. Soc. 1993,
1
15, 2808.
(24) Duff, J. M.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1972, 2219.
(25) (a) Weinberg, K. G. J. Org. Chem. 1975, 40, 3586. (b) Green, M.; Hudson,
R. F. J. Chem. Soc. 1958, 3129. (c) Weil, T.; Prijs, B.; Erlenmeyer, H.
HelV. Chim. Acta 1953, 36, 1314.
(15) Staab, H. A.; Krieger, C.; Hieber, G.; Oberdorf, K. Angew. Chem. 1997,
1
09, 1946; Angew. Chem., Int. Ed. Engl. 1997, 36, 1884.
(
16) Basaran, R.; Dou, S.; Weiss, A. Struct. Chem. 1993, 4, 219.
17) Bartoszak, E.; Dega-Szafran, Z.; Jask o´ lski, M.; Szafran, M. J. Chem. Soc.,
Faraday Trans. 1995, 91, 87.
(
(26) (a) Budzelaar, P. H. M.; van Doorn, J. A.; Meijboom, N. Recl. TraV. Chim.
Pays-Bas 1991, 110, 420. (b) Berens, U. PCT Int. Appl. WO 9924444,
1999.
(
18) Costa, T.; Schmidbaur, H. Chem. Ber. 1982, 115, 1374.
15834 J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004

Insignificance of P−H‚‚‚P Hydrogen Bonding
A R T I C L E S
Scheme 1. Preparation of 1-Naphthylphosphines (D)
Scheme 2. Preparation of 1,8-Di(phosphinyl)naphthalenes (C)
Figure 1. 31P NMR spectrum of compound 9. (a) Experimental spectrum
(in CD2Cl2 at 25 °C) and (b) calculated spectrum. (For details, see Table
1.)
Table 1. 1H NMR Data (δ [ppm], J [Hz]) of Compound 9
simulated as an [ABCD2X]2 spin system, δX ) δP)
(
δA
7.83; ∆1/2 ) 0.6 Hz
7.31; ∆1/2 ) 0.8 Hz
7.77; ∆1/2 ) 1.0 Hz
4.58; ∆1/2 ) 1.1 Hz
7.0(1)
JAX′ ) JA′X
JBC
JBX
JCX
JDD′
-0.4(1)
8.2(1)
0.7(1)
-1.2(1)
3.8(1)
δB
δC
δD
JAB
JAC
JAD
JAD′ ) JA′D
JAX
1.4(1)
1.0(1)
0.2(1)
-6.1(1)
JDX
JDX′ ) JD′X
JXX′
207.7(1)
31.7(1)
-221.6(1)
of 1,8-(Cl2P)2C10H6 in diethyl ether gave a 78% isolated yield
of 9 as a crystalline solid (mp 82 °C, from dichloromethane
solution). Solutions of 9 in CD2Cl2 at 25 °C show a singlet
1
31
resonance in the H-decoupled P NMR spectrum at δ -104.9
1
ppm. In the H-coupled form, the spectrum is exceedingly
complex (Figure 1), as expected for the X-part (P) of an ABCD2-
XX′D′2C′B′A′ spin system, where A/A′, B/B′, and C/C′ denote
the (magnetically nonequivalent) protons of the hydrogen atoms
in the 2,7-, 3,6-, and 4,5-positions of the naphthalene, respec-
tively, and D/D′ the hydrogen atoms bound to the phosphorus
1
13
1
atoms. The H and C{ H} NMR spectra which yield ad-
ditional, very significant information have also been recorded
and analyzed and are discussed in some detail below.
The NMR spectra of the crude reaction product (prior to
recrystallization of 9) indicated that a byproduct was present in
the reaction mixture, which was identified as trans-1,2-dihydro-
Treatment of 4 with equimolar quantities of trifluoromethane-
sulfonic acid in dichloromethane gave almost quantitative yields
+
of the corresponding phosphonium triflate [(1-C10H7)PH3] [CF3-
-
31
1
SO3] (5). Its P resonance in the H-coupled spectrum in CD2-
Cl2 is a quartet shifted downfield quite drastically to δ -53.4
1
ppm, with the coupling constant, J(PH), rising from 203.5 Hz
1
,2-diphosphaacenaphthene, 10 [δP -103.7 ppm, in CD2Cl2].
in 4 to no less than 546.9 Hz, indicating the significant increase
It is the product of dehydrogenative P-P coupling, which may
occur upon successive substitution of the chloride by hydride
substituents. It was noted that 10 is also formed during the GC-
3
in the s-character of the phosphorus orbitals to sp .
A similar reaction sequence (Scheme 2), starting with 1,8-
dilithionaphthalene (6), affords 1,8-bis[bis(diethylamino)phos-
phinyl] (7) and bis(dichlorophosphinyl)naphthalene (8, 82%
(
27) (a) Kara c¸ ar, A.; Th o¨ nnessen, H.; Jones, P. G.; Bartsch, R.; Schmutzler, R.
Chem. Ber. Recueil 1997, 130, 1485. (b) Kilian, P.; Slawin, A. M. Z.;
Woollins, J. D. Chem.sEur. J. 2003, 9, 215.
2
7
yield). While previous attempts to obtain C1 by LiAlH4
reduction of bis(dimethoxyphosphinyl)- or bis(dimethoxyphos-
phoryl)naphthalene were not successful,28 the same reduction
(28) Kara c¸ ar, A.; Freytag, M.; Jones, P. G.; Bartsch, R.; Schmutzler, R. Z. Anorg.
Allg. Chem. 2001, 627, 1571.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004 15835

A R T I C L E S
Reiter et al.
Figure 3. Molecular structure of compound 9 with atomic numbering
(ORTEP, 50% probability ellipsoids). Hydrogen atoms H12 and H22 are
disordered over two positions each.
nium cation (i.e., only one of the two phosphinyl groups has
been protonated). The extra proton is not in a symmetrical
position between the two P atoms, and any quite conceivable
proton exchange between the two P atoms is slow on the NMR
time scale (at -80 °C). Line broadening observed at higher
temperatures is evidence that such an exchange is becoming
more rapid, which leads to coalescence at room temperature.
An estimation of the activation energy for the exchange process
was not made because of limited reproducibility of the experi-
ments, which is due to the extreme sensitivity of the system to
any traces of moisture.
Attempts to prepare the 1,8-diphosphonium salt by using 2
equiv of rigorously dried triflic acid in dichloromethane at room
temperature did not afford a well-defined product (12). However,
if residual water was present in the triflic acid, or water was
added deliberately, high yields (89%) of a product could be
crystallized, which was shown to have the stoichiometry of a
monohydrate of the expected bis(phosphonium) bistriflate (13).
Even though the NMR spectra of its solutions (in CD2Cl2 at
Figure 2. 31P NMR spectrum of 11 (in CD2Cl2 at -80 °C). (a) PH3+ signal
and (b) PH2 signal. (For details, see Experimental Section.)
MS analysis of pure 9, owing to pyrolysis in the hot GC
columns. The P,P′-diphenylated 1,2-dihydro-1,2-diphospha-
-
80 °C) showed severe line broadening, the overall pattern
2
9
acenaphthene derivative has recently been described, and the
suggested that the compound contains the same cation as
monotriflate 11. This result was confirmed by the single-crystal
X-ray diffraction analysis which revealed the presence of a
1
,2-dihydro-1,2-disilaacenaphthene is also known.30
Equimolar quantities of the diprimary phosphine 9 and triflic
acid in dichloromethane were shown to form high yields (86%)
of the corresponding monophosphonium monotriflate 11. The
+
hydronium cation, [H3O] , and two triflate anions along with
the 1-(8-phosphinylnaphthyl)phosphonium cation already identi-
1
31
H-decoupled P NMR spectrum of this product (in CD2Cl2 at
80 °C) shows two separate doublet resonances of equal
fied as a constituent of 11 (vide infra). The stoichiometry is
-
+
therefore best represented by the formula [1-(8-H2PC10H6)PH3] -
4
intensity at δ -119.3 and -35.5 ppm [ J(PP) ) 107.0 Hz],
+
-
[
H3O] 2[CF3SO3] (13); it appears that the diprimary phosphine
+
which are readily assigned to the -PH2 and -PH3 groups,
9
can only be monoprotonated, and the incoming proton is
respectively, as suggested by the data of the reference com-
strictly localized at one of the phosphorus atoms.
1
pounds 4 and 5. In the H-coupled spectrum (under similar
Crystal and Molecular Structure of 1,8-Di(phosphinyl)-
naphthalene. Crystals of 1,8-di(phosphinyl)naphthalene (9) are
monoclinic, with space group P21/n and Z ) 4 formula units in
the unit cell (at 143 K). The molecules have no crystallographi-
cally imposed symmetry, but they approach quite closely to a
point group C2 geometry. While one hydrogen atom of each
phosphinyl group is readily localized in the reference plane of
the hydrocarbon unit, the second one is disordered over two
positions above and below this reference plane (Figure 3). The
molecule has the conformation designated as “all-eclipsed” in
previous studies of substituted analogues, referring to the relative
orientation of the hydrogen atoms at C2/C7 and one of the
conditions), the two resonances have the first-order tdq and qdd
multiplicities, as expected for the X,Y-part of an AD2XYE3F
spin system, with X and Y denoting the two phosphorus nuclei,
D and E the P-bound hydrogen nuclei, and F and A the nuclei
of the hydrogen atoms in the 2,7-positions of the naphthalene
(Figure 2; note that this labeling is not identical with that used
for 9 because of the lower symmetry).
This result clearly indicates that in CD2Cl2 solution, salt 11
features a 1-(8-phosphinylnaphthyl)-substituted monophospho-
(
29) Mizuta, T.; Nakazono, T.; Miyoshi, K. Angew. Chem. 2002, 114, 4053;
Angew. Chem., Int. Ed. 2002, 41, 3897.
(30) S o¨ ldner, M.; Sandor, M.; Schier, A.; Schmidbaur, H. Chem. Ber. Recueil
2
7a,31
1
997, 130, 1671.
hydrogen atoms at P1/P2.
Strictly speaking, the disorder
15836 J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004

Insignificance of P−H‚‚‚P Hydrogen Bonding
A R T I C L E S
Figure 4. Projection of the structure of molecule 9 along the C9-C10
axis (arbitrary radii, atomic numbering as in Figure 1), showing a
superposition of the two enantiomeric transoid conformations (which are
disordered in the crystal).
Figure 6. Structure of the cation of compound 11 (mirror symmetry,
ORTEP, 50% probability ellipsoids) with atomic numbering.
Figure 7. Projection of the structure of the cation in compound 11 along
the C9-C10 bond (arbitrary radii, atomic numbering as in Figure 6).
angles P1-C1-C2 ) 116.9(1)° and P2-C8-C7 ) 116.6(1)°.
Thus, the P-C bonds are tilted by ∼3° in opposite directions
in order to minimize steric repulsion between the two -PH2
groups (“perispace crowding”).
Figure 5. Pairs of enantiomeric molecules 9 in the crystal (arbitrary radii).
Hydrogen atoms H22A are in a “phenyl-embraced” orientation. (Note the
disorder of hydrogen atoms H12 and H22.)
The packing of the molecules of 9 in the crystal is not
governed by intermolecular hydrogen bonds. It rather features
pairs of enantiomers with the molecular planes parallel (the two
molecules being related by a center of inversion). The two
components of these dimeric units show no π-π stacking (the
naphthalene parts are not facing each other) but have each
H22-P bond pointing toward a center of a benzene ring of a
neighboring naphthalene unit (Figure 5). The H22 centroid
distance of 2.534 Å may indicate very weak hydrogen bonding
of a pair of hydrogen atoms (H12 and H22) over four positions,
with about equal probability, precludes the decision about a
cisoid (point group Cs) or transoid arrangement (point group
C2) of these hydrogen atoms. The latter has tentatively been
chosen for the presentation in Figure 4, referring to the geometry
of several P,P′-disubstituted derivatives (C, R ) Cl, Ph, NMe2,
3
4
of the “phenyl embrace”-type.
19,27b,32,33
and so forth),
for which the transoid structure has been
There is still a paucity of structural data for the supra-
molecular chemistry of primary arylphosphines. In a previous
structural study of primary phenylphosphines, we have shown
that there is no evidence for significant hydrogen bonding in
the crystals of 1,3,5-chlorophosphinylbenzene molecules,
confirmed by single-crystal X-ray diffraction studies.
Quantum chemical calculations have also shown unambigu-
ously that the transoid conformation (C2) is lower in energy
than the cisoid conformation (Cs), while the C2V conformation
(with overlapping lone pairs of electrons at the two P atoms) is
[
C6H3Clx(PH2)3-x], and the present results support the conclu-
a high-energy transition state for the rotation of the -PH2 groups
about their P-C axes.31 With H12 and H22 in transoid positions,
the molecules are chiral, and the crystals of 9 contain both
enantiomers.
The naphthalene unit shows only very minor deviations from
planarity [the maximum C-C-C-C torsional angle is -1.2-
3
5
sions drawn from these earlier findings.
Crystal and Molecular Structures of the 1-(8-Phosphi-
nylnaphthyl)phosphonium Trifluoromethanesulfonates (11
and 13). Crystals of triflate salt 11 are orthorhombic, with a
space group Pbcm and Z ) 4 formula units in the unit cell, and
+
-
contain [C10H6(PH2)(PH3)] cations and [CF3SO3] anions,
which have no unusually short interionic contacts. The naph-
thalene unit and the P atoms (C10H6P2) are coplanar by
symmetry, with the crystallographically imposed mirror plane
relating the two hydrogen atoms at P2 and two of the three
hydrogen atoms at P1 (Figure 6). Referring to the conformation
of the di(phosphinyl)naphthalene precursor, molecule 9, in the
crystal, we notice that one -PH2 group has been protonated,
resulting in a quasi-tetrahedral coordination of this P atom (P1)
(1)° for C1-C9-C10-C5], and the two phosphorus atoms
reside almost exactly in the plane of the hydrocarbon unit as
indicated by the small torsional angles P1-C1-C9-C8 [-0.2-
(2)°] and P2-C8-C9-C1 [1.7(2)°] (Figures 3 and 4). However,
there is considerable distortion of the bay area geometry within
the reference plane, which is best demonstrated by the bond
(
31) Nakanishi, W.; Hayashi, S. Phosphorus, Sulfur Silicon Relat. Elem. 2002,
77, 1833.
1
(
32) (a) Jackson, R. D.; James, S.; Orpen, A. G.; Pringle, P. G. J. Organomet.
Chem. 1993, 458, C3. (b) James, S. L.; Orpen, A. G.; Pringle, P. G. J.
Organomet. Chem. 1996, 525, 299.
(34) Dance, I.; Scudder, M. J. Chem. Soc., Chem. Commun. 1995, 1039.
(35) Reiter, S. A.; Assmann, B.; Nogai, S. D.; Mitzel, N. W.; Schmidbaur, H.
HelV. Chim. Acta 2002, 85, 1140.
(
33) Kara c¸ ar, A.; Freytag, M.; Th o¨ nnessen, H.; Omelanczuk, J.; Jones, P. G.;
Bartsch, R.; Schmutzler, R. Z. Anorg. Allg. Chem. 2000, 626, 2361.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004 15837

A R T I C L E S
Reiter et al.
Figure 9. (a) Stacking of the cations in crystals of compound 11. (b) A
pair of adjacent cations showing the weak “phenyl-embrace” type interac-
tions with hydrogen atoms H21 (no π-π stacking).
the two sets are very similar, and no separate treatment is
+
necessary. The [C10H6(PH2)(PH3)] cations have no crystallo-
graphically imposed symmetry, but their conformation ap-
proaches quite closely to that described for 11 (Figure 8). With
an entirely different environment of these cations in 11 and 13,
this result suggests that the conformation represents the true,
intrinsic ground state, which is not greatly influenced by crystal
packing or other external directional forces. This is particularly
obvious from the small angles, P11-C1-C2 ) 111.5(2)° and
+
P21-C21-C22 ) 111.6(2)° that are observed for the -PH3
groups, and the “upright” orientation of the -PH2 groups, with
angles of P12-C18-C17 ) 120.0(2)° and P22-C28-C27 )
1
19.0(2)°. It is obvious that this orientation rules out any
Figure 8. (a and b) Structures of the two independent phosphonium cations
in compound 13 (ORTEP, 50% probability ellipsoids) with atomic number-
ing. In the lower parts, the projections along the bonds C19-C10 and C29-
C20 are shown, respectively.
conventional hydrogen bonding between the two phosphorus
atoms in the cations of 11 and 13.
In the unit cells of 11 and 13, the phosphonium cations show
a different stacking pattern. In the former, along the column of
(
equivalent) cations, no arene π-π stacking is observed since
in 11, and this group is in an eclipsed conformation as related
to the hydrogen atom at C2 (Figure 7). Consequently, the
nonprotonated -PH2 group has rotated into a staggered con-
formation as related to the hydrogen atom at C8, which places
the vector of the lone pair at P2 in the molecular plane bisecting
the angle H11-P1-H11′. In this reorganization, the distortion
of the angle P1-C1-C2 [112.0(2)°] has increased very
significantly (from an average of 116.5° in 9), while the angle
P2-C8-C7 has increased from 116.5 to 119.1(2)°, indicating
an almost strain-free “upright” position of the -PH2 group.
Crystals of bistriflate 13 are monoclinic, with the space group
P21/n and Z ) 8 formula units in the unit cell. The asymmetric
unit contains two sets of crystallographically independent
components, including the cations also present in 11, hydronium
the nonpolar C6H3PH2 groups lie on top of each other in a head-
to-tail arrangement (i.e., with the -PH2 group on top of a
benzene ring) (11, Figure 9). In the latter, there is alternating
π-π stacking of the C6H3PH2 parts of the two nonequivalent
cations (13, Figure 10). In both types of columns (11 and 13),
+
the cationic functions of -PH3 are located in the periphery,
where they are close to the anions.
+
The hydronium cations, [H3O] , and the triflate anions,
-
[CF3SO3] (in a 1:2 ratio), in crystals of 13 are associated
through strong hydrogen bonds to give an anionic network
around the columns of the phosphonium cations. Two of the
triflate anions are in bridging positions between two hydronium
cations, while of the other two, each one is attached to only
+
+
+
cations [H3O] , and triflate anions. The geometrical details of
one of the two [H3O] cations. Each [H3O] cation is attached
15838 J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004

Insignificance of P−H‚‚‚P Hydrogen Bonding
A R T I C L E S
Scheme 3. Representation of the Dimerization of
1
,8-Di(amino)naphthalene (A1) through Intra- and Intermolecular
16,37
Hydrogen Bonding
+
+
affinity, for example, between [C10H6(PH2)(PH3)] and [H3O] ,
which would indicate hydrogen bonding.
Discussion
The present study has shown that 1,8-di(phosphinyl)naph-
thalene 9 can be readily prepared in high yield as a crystalline
solid, which is soluble in many common organic solvents. This
simple prototype thus allows an investigation of the ground-
state structure, molecular dynamics, and reactivity of 1,8-di-
(phosphinyl)naphthalenes C, with the smallest possible and least-
polarizing substituents at the phosphorus atoms (R ) H) in the
solid state and in solution.
In the crystal, the compound is present as pairs of enantio-
meric molecules with individual C2 symmetry, related by a
center of inversion. There is no intermolecular hydrogen
bonding, and the aggregation into dimers is based on parallel
head-to-tail stacking with only very weak centroid phenyl
embrace interactions between P-H functions and benzene rings
Figure 10. (a) Stacking of the cations in crystals of compound 13. (b)
Projection along the stacking axis showing the position of the -PH3 groups
in the periphery where these functions are exposed to the anion substructure.
+
(Figure 5). This mode of aggregation is entirely different from
that found for 1,8-di(amino)naphthalene (A1), where pairs of
molecules are formed via intermolecular hydrogen bonding.
Together with two intramolecular hydrogen bonds, the four
amino groups share hydrogen atoms to give an eight-membered
1
6,37
ring (NH)4 (Scheme 3).
The C2 symmetry of the individual molecule 9 in the crystal
arises from a conformation of the -PH2 groups, which is
referred to in the literature as the transoid or biseclipsed
19
arrangement (Figure 4). This conformation places one hydro-
gen atom of each -PH2 group in the molecular plane, while
the other two are positioned perpendicular to this plane, above
and below. The same structure was also found for C (R ) Cl,
Ph, NMe2, and so forth) and therefore appears to be the intrinsic
ground state of this family of molecules, as confirmed by
quantum chemical calculations for 9 and a (PH3)2 model
Figure 11. Hydrogen bonding network of hydronium cations [H3O]+ and
triflate anions [CF3SO3] (1:2 ratio) in crystals of compound 13.
-
3
1
system. In the transoid conformation of 9, any intramolecular
hydrogen bonding (P-H‚‚‚P′) is excluded for geometrical
reasons. The same conclusion was drawn from the structural
Table 2. Hydrogen Bonding in the [H3O] 2[CF3SO3]-
+
Substructure of Compound 13
d(O
−
H)
d(H‚‚‚O)
[Å]
d(O‚‚‚
[Å]
O
<(OHO)
[deg]
+
-
data of [C10H6(PPh2)(PPh2H)] [CF3SO3] , in which the cation
O
−H‚‚‚
O
[Å]
3
8
has an analogous conformation. By contrast, as already noted,
O(1)-H(2)‚‚‚O(11)
O(1)-H(3)‚‚‚O(23)
O(1)-H(1)‚‚‚O(32)′
O(2)-H(4)‚‚‚O(43)
O(2)-H(6)‚‚‚O(33)
O(2)-H(5)‚‚‚O(12)′
0.86(4)
1.05(5)
0.88(4)
0.99(5)
1.30(7)
0.80(5)
1.79(4)
1.47(5)
1.70(4)
1.52(5)
1.30(7)
1.83(5)
2.633(3)
2.502(2)
2.577(3)
2.497(3)
2.587(3)
2.606(3)
169(4)
168(4)
169(4)
169(4)
170(5)
164(4)
the conformation of the 1,8-di(amino)naphthalene molecule (A1)
in the crystal allows for intramolecular hydrogen bonding
16,37
(Scheme 3).
With the small substituents of -PH2 in 9, there is no major
distortion of the naphthalene scaffold, and the phosphorus atoms
are found in the molecular plane and are only tilted slightly in
opposite directions (by ∼3°) to minimize the peristress in the
bay region of the molecule. In the nitrogen analogue with its
smaller -NH2 groups, this distortion leads to N-C-C angles
to three triflate anions (Figure 11). A list of the data for the six
hydrogen bonds is presented in Table 2. A similar connectivity
pattern has been reported for the monohydrate of sulfuric acid,
+
- 36
H2SO4(H2O), which is to be formulated as [H3O] [SO4H] ,
and there are many more examples of structurally characterized
(36) Kemnitz, E.; Werner, C.; Trojanov, S. Acta Crystallogr. 1996, C52, 2665.
(
37) Llamas-Saiz, A. L.; Foces-Foces, C.; Molina, P.; Alajarin, M.; Vidal, A.;
Claramunt, R. M.; Elguero, J. J. Chem. Soc., Perkin Trans. 2 1991, 1025.
+
-
(38) Kara c¸ ar, A.; Klaukien, V.; Freytag, M.; Th o¨ nnessen, H.; Omelanczuk, J.;
Jones, P. G.; Bartsch, R.; Schmutzler, R. Z. Anorg. Allg. Chem. 2001, 627,
2589.
hydronium salts, [H3O] X . It therefore appears that compound
3 is a true hydronium salt. The structure shows no intercation
1
J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004 15839

A R T I C L E S
Reiter et al.
of only 1.5° away from the ideal 120°.16,37 Conversely, with
the more bulky -SiH3 groups in di(silyl)naphthalene (A, X )
SiH3), the distortions are much larger, as shown by symmetrical
in-plane Si-C tilts of as much as 10°.2
1
The structure of 9, as it is found in the crystal, must be
fluctional in solution. The hydrogen atoms of the -PH2 groups
are equivalent on the NMR time scale, both at room temperature
and at -80 °C (in CD2Cl2). The equivalence is determined by
3
1
1
1
31
both the P-coupled H and the H-coupled P NMR spectra.
This result implies that there must be rapid rotational movement
of the -PH2 groups about the P-C bonds with ∼90° amplitude.
[
Dissociative-associative mechanisms for proton exchange can
be excluded at low temperature since, even in the protonated
forms (11 and 13), there is no rapid proton exchange and the
two phosphorus atoms are inequivalent in solution. Note also
1
that the P-H couplings with large J(PH) constants are retained
in 9, 11, and 13.] The rotational movement of the -PH2 groups
can be random or concerted (dis- or conrotatory, of the cog-
wheel-type), possibly involving the conformer of maximum
3
1
symmetry (point group C2V) as a transition state.
The fully coupled H and 31P NMR spectra of compound 9
1
(in CD2Cl2 at 25 °C) show complex multiplets for the ABCD2-
XX′D′2C′B′A′ spin system. The experimental and calculated
spectra are presented in Figures 1 and 12.
The most intriguing feature of the NMR spectra of compound
n
9
is the large coupling constant, J(PP′) ) 221.6 Hz [corre-
n
sponding to J(XX′) in the above spin system; n denotes the
unknown number of bonds, if any, between the coupling nuclei].
This coupling has previously been reported for only one other
symmetrical compound (C, R ) Ph, nJ(PP′) ) 199 Hz,
determined in the solid state by MAS experiments). Data are
known for several asymmetrically P -P -substituted com-
32
III
III
pounds, including the results of very recent measurements on
1
-bis(dimethylamino)phosphinyl-8-[(dimethylamino)(methoxy)-
n
39
phosphinyl]naphthalene [ J(PXPY) ) 246 Hz].
n
It appears to be generally accepted that this coupling, J(PP′),
should be assigned to a through-space spin-spin interaction
transmitted via the lone pairs of electrons at the phosphorus
atoms. These lone pairs are forced into (repulsive) overlap in
the periregion, and the extent of overlap depends strongly on
the conformations and their intramolecular dynamics. The P-P′
coupling obviously is very efficient, as illustrated by a com-
III
III
III
parison with coupling constants for true P -P and P -H
Figure 12. 1H NMR spectrum (phosphinyl and aryl region) of compound
9. (a/a′) experimental (in CD2Cl2 at 25 °C), (b/b′) calculated spectrum. (For
details see Table 1.)
single bonds, which are in the same order of magnitude. An
internal reference parameter of 9 is J(PH) ) 207.7 Hz [ J(XD)
in the above spin system].
1
1
In 9, there are even large 1+nJ(HDPX′) couplings (31.7 Hz)
and significant 2 J(HDHD′) couplings (3.8 Hz) “across the bay”,
which were both measured here for the first time. By contrast,
the “regular” J(HAPX), J(HBPX), and J(HAPX′) couplings,
following the “bond tracks”, are all very small at 6.1, 0.7, and
H21-P2-H22A ) 92(3)°]. [Note also that in PH3, the H-P-H
angles are close to 90° (gas phase and matrix experiments).]40
+n
1
Interestingly, the H NMR spectrum of compound 9 shows
a small but significant temperature dependence in the range from
3
4
5
2
0 to -90 °C. Apart from the common minor shift in the δ
0
.4 Hz, respectively.
value, the line spacings in the multiplet of the -PH2 hydrogen
atoms (which reflect sums and differences of coupling constants,
J) follow major trends. The spacing of the two most-intense
lines (Figure 12) increases steadily from 239.9 (at 20 °C) to
These strong coupling effects are probably associated with
III
the high s-character of lone-pair electrons at P centers, which
is evident from the small bond angles at these centers, even
though these data are of limited accuracy [e.g., C1-P1-H11
2
49.5 Hz (at the experimental limit of -90 °C). This effect
)
95(1)°, H11-P1-H12A ) 90(3)°, C1-P1-H12A ) 105-
may indicate a slowing down of the rotational movement of
the -PH2 groups, but the low-energy barriers probably associ-
(3)°, C8-P2-H21 ) 95(1)°, C8-P2-H22A ) 103(3)°, and
(
39) Kilian, P.; Slawin, A. M. Z.; Woollins, J. D. Phosphorus, Sulfur Silicon
Relat. Elem. 2004, 179, 999.
(40) Bartell, L. S.; Hirst, R. C. J. Chem. Phys. 1959, 31, 449.
15840 J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004

Insignificance of P−H‚‚‚P Hydrogen Bonding
A R T I C L E S
ated with these movements preclude any detailed analysis of
the data for the accessible temperature region.
hydrogen bonding of the type P-H‚‚‚P is insignificant regarding
its effects in structural chemistry of phosphines and phospho-
nium salts, even if the functions are held in proximity, thus
minimizing entropy losses. The inherent low polarity of P-H
bonds, which is comparable to that of most C-H bonds, reduces
their affinity for potential electron donor centers (D) to a degree
that this type of contact, P-H‚‚‚D, is associated with only very
minor gains in energy.
Upon protonation of 9 with triflic acid, monocations are
formed, which could be crystallized as triflate 11 or hydronium
bis(triflate) salt 13. The structure of the cations, including their
conformation, is the same in both salts. (Moreover, in 13, two
almost identical crystallographically independent cations are
present.) The most important structural result is the absence of
any intra- or intermolecular P-H‚‚‚P hydrogen bonding. The
Experimental Section
+
mutual, rotational orientation of the -PH2 and -PH3 groups
places the remaining lone pair of electrons of the former in a
staggered position between two H atoms of the latter (Figure
General. All of the chemicals used as starting materials were
commercially available, except bis(diethylamino)chlorophosphine,
4
1
7
).
It should be noted that, by contrast, in the structure of the
cation resulting from the monoprotonation of the corresponding
,8-di(amino)naphthalene A1 (determined for the hydrogen-
which was prepared according to the literature. All of the reactions
were carried out routinely in an atmosphere of dry and pure nitrogen.
All of the solvents were distilled from an appropriate drying agent and
stored over molecular sieves (4 Å) and under nitrogen. Glassware was
oven dried and filled with nitrogen. Mass spectra were recorded on an
HP 5971A (Hewlett-Packard) spectrometer using EI at 70 eV as an
ionization method. NMR spectra were obtained at room temperature
and at -80 °C on JEOL JNM-GX-400 or JEOL 400 Eclipse
spectrometers. Chemical shifts are reported in δ values relative to the
1
maleate salt), the incoming proton occupies an asymmetric
position between the two nitrogen atoms, which still indicates
1
7
significant intracationic N-H‚‚‚N hydrogen bonding. In
crystals of the di- and trichloroacetate salts, the hydrogen
bonding pattern is more complex due to stronger interactions
between cations and anions.16 The cations, [C10H6(NH2)(NH3)] ,
therefore do not feature Cs or C2V symmetry, attainable for
asymmetrical or symmetrical hydrogen bonding, respectively,
but are significantly distorted because of these N-H‚‚‚O
hydrogen bonds.
1
13
31
19
residual solvent resonance of CD
spectra are referenced to external aqueous H
respectively. Assignments were supported by 2D NMR experiments
HH COSY, HC HMQC, and HC HMBC). Simulation of spin systems
2
Cl
2
( H and C). P and F NMR
+
3
PO (85%) and CFCl
4
3
,
(
42
was carried out using the PERCH program package. Signs of coupling
constants were chosen following reference data.43 GC-MS analyses
of the reaction mixtures were carried out on an HP 5890 Series II
The absence of hydrogen bonding in the cations of 11 and
(
Hewlett-Packard) gas chromatograph with an HP 5971A mass-selective
detector.
Bis(diethylamino)(1-naphthyl)phosphine, 2. The preparation of
1
3 is corroborated by the NMR spectra of solutions of the
31
1
compounds (in CD2Cl2 at -80 °C). Separate P and H signals
are observed for -PH2 and -PH3 groups, which rules out any
rapid proton exchange mediated by hydrogen bonding. (The
and H chemical shifts and the J(PH) coupling constants for
the -PH2 and -PH3 groups are very similar to those of the
reference compounds, 4 and 5.)
+
44
1
-naphthyllithium 1 was based on a modified literature procedure. A
31
P
solution of n-BuLi (75 mL, 120 mmol, 1.6 M in hexane) was diluted
with diethyl ether (80 mL) at -20 °C, and subsequently, 1-bromonaph-
thalene (20.70 g, 100 mmol) was added at the same temperature. The
reaction mixture was allowed to warm to 10 °C and stirred continuously
at this temperature for 15 min. The white suspension was cooled to
1
1
+
This observation is again in notable contrast to the behavior
-20 °C, and after letting the mixture stand for about 10 min, the clear
of the nitrogen analogues. In three different solvents, the [C10H6-
supernatant solution was removed via cannula. Hexane (250 mL) was
added, and after the mixture was swirled, the suspension was recooled
to -20 °C. After the mixture was left to stand for about 10 min, the
clear solution was removed via cannula. These operations were repeated
twice, and 1 was then suspended in THF (150 mL). Bis(diethylamino)-
chlorophosphine (24.05 g, 114 mmol) was slowly added at -78 °C,
and the reaction mixture was allowed to warm to room temperature
and stirred for 12 h. The residue remaining upon evaporation of the
solvent in vacuo was extracted with hexane (150 and 50 mL).
Evaporation of the combined hexane extracts in vacuo yielded a yellow
oily liquid, which contained only small amounts of bis(diethylamino)-
chlorophosphine, tris(diethylamino)phosphine, and (diethylamino)(1-
+
(NH2)(NH3)] cations show only one proton signal for the five
16,17
N-bound hydrogen atoms, suggesting rapid proton exchange.
Conclusions
The present work is a contribution to the discussion of the
significance of hydrogen bonding between the phosphorus atoms
of primary arylphosphines and the corresponding arylphospho-
nium salts. It has been demonstrated, by studies of the crystal
and the solution state, that even in cases where -PH2 and
-
of naphthalene in 9, 11, and 13), there is no evidence for
hydrogen bonding between phosphorus atoms (-PH2 and -PH2
or -PH2 and -PH3 ) or for proton exchange between the two
functions. This is also true for the packing of molecules (9) or
cations (11 and 13) in the crystal, which is clearly not governed
by such intermolecular interactions. It thus appears that hydrogen
bonding between primary (RPH2) or secondary arylphosphines
+
PH3 functions are held in proximity (as in the peripositions
31
1
naphthyl)chlorophosphine: P{ H} NMR (CD Cl , 25 °C) δ 94.7 (s);
MS (EI) m/z 302 [M] .
2
2
+
+
Dichloro(1-naphthyl)phosphine, 3. A solution of the product
(above) in hexane (500 mL) was cooled to 0 °C and saturated with
gaseous HCl. The reaction mixture was stirred for 1 h, again saturated
with gaseous HCl, and stirred for 1 h. This procedure was repeated
until the supernatant solution remained clear upon further addition of
HCl. The reaction mixture was then allowed to warm to room
(R2PH) and their phosphonium salts plays no significant role
in the molecular or supramolecular chemistry of these mol-
ecules.3 Literature data for arylamines and arylammonium salts
show that hydrogen bonding in these N-analogues may be weak,
but it is still discernible from molecular structures in the
condensed phase and from molecular dynamics in solution. The
present account leads to the very general conclusion that
(
41) Albers, W.; Kr u¨ ger, W.; Storzer, W.; Schmutzler, R. Synth. React. Inorg.
Met.-Org. Chem. 1985, 15, 187.
5
(
42) Laatikainen, R.; Niemitz, M.; Weber, U.; Sundelin, J.; Hassinen, T.;
Veps a¨ l a¨ inen, J. J. Magn. Reson., Ser. A 1996, 120, 1.
(43) Karaghiosoff, K. In Encyclopedia of Nuclear Magnetic Resonance; Grant,
2
D. M., Harris, R. K., Eds.; Wiley: Chichester, U.K., 1996; Vol. 6, p 3612.
(
44) Brandsma, L.; Verkruijsse, H. D. In PreparatiVe Polar Organometallic
Chemistry; Springer-Verlag: Berlin, 1987; Vol. 1, p 195.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004 15841

A R T I C L E S
Reiter et al.
temperature and stirred for 12 h. The diethylammonium chloride
precipitate was separated and extracted with hexane (2 × 100 mL).
Evaporation of the combined organic phases in vacuo afforded a white
solid, which was recrystallized from hexane at -30 °C, and yielded
colorless, plate-shaped crystals: 18.94 g, 82.7% (based on 1-bro-
Table 3. Crystal Data, Data Collection, and Structure Refinement
for Compounds 9, 11, and 13
9
11
13
empirical formula
M
crystal system
space group
a (Å)
C10H10P2
192.12
monoclinic
C11H11F3O3P2S C12H14F6O7P2S2
342.20
orthorhombic
Pbcm
510.29
monoclinic
P2 /n
1
3
1
1
2 2
monaphthalene); mp 55 °C; P{ H} NMR (CD Cl , 25 °C) δ 164.2
1
3
1
1
(
s); C{ H} NMR (CD
2
Cl
2
, 25 °C) δ 135.7 (d, J(CP) ) 61.5 Hz,
P2 /n
1
3
2
C1), 134.3 (s), 134.1 (d, J(CP) ) 2.3 Hz, C10), 132.7 (d, J(CP) )
9.2 Hz, C9), 131.2 (d, J(CP) ) 32.3 Hz), 129.7 (s), 127.8 (d, J(CP)
2.3 Hz), 127.2 (s), 125.5 (d, J(CP) ) 9.2 Hz), 124.8 (d, J(CP) )
3.8 Hz); H NMR (CD
H, H2), 8.28 (ddd, J(HP) ) 11.4 Hz, J(HH) ) 7.2 Hz, J(HH) )
8.4840(1)
12.8058(2)
9.7203(2)
115.0878(7)
956.43(3)
1.334
10.5319(2)
18.0050(5)
7.3227(1)
90
1388.58(5)
1.637
14.1998(2)
13.4147(1)
21.2356(3)
98.0005(5)
4005.73(9)
1.692
b (Å)
c (Å)
1
)
2
1
1
1
3
â (deg)
2
Cl
2
, 25 °C) δ 8.63 (dm, J(HH) ) 8.2 Hz,
3
V (Å )
4
3
4
Fcalc (g cm-3)
Z
3
3
.2 Hz, 1H, H8), 8.09 (d, J(HH) ) 8.2 Hz, 1H, H4/5), 7.98 (dm, J(HH)
7.9 Hz, 1H, H5/4), 7.65 (m, 3H, H3/6/7); MS (EI) m/z 228 [M] .
4
4
8
+
)
F(000)
400
696
2064
Anal. Calcd for C10
Found: C, 52.42; H, 3.19; P, 13.28. Bp 139-149 °C (1 Torr), bp
H
7
Cl
2
P (229.04): C, 52.44; H, 3.08; P, 13.52.
T (K)
reflns measured
reflns unique
143
25895
1736
143
32396
1345
144/0
0.0374
0.0947
a ) 0.0476
b ) 1.4323
143
91685
7259
635/0
0.0389
0.0950
a ) 0.0366
b ) 5.0076
0.643/-0.468
24
2
5c
1
5
35-137 °C (0.5 Torr), mp 55 °C; bp 118-120 °C (0.5 Torr), mp
2
5b
25a
parameters/restraints 153/6
4 °C; bp 130-131 °C (0.8 Torr), mp 51-54 °C.
-Naphthylphosphine, 4. A solution of 3 (18.00 g, 78.6 mmol) in
diethyl ether (100 mL) was added slowly to a stirred suspension of
LiAlH (12.00 g, 316.2 mmol) in diethyl ether (400 mL) at -78 °C.
R1 [I g 2σ(I)]
0.0391
0.0990
a ) 0.0480
b ) 0.7188
1
wR2a
weighting scheme
4
The reaction mixture was then allowed to warm to room temperature
and stirred for 12 h. For workup, degassed water (70 mL) was added
dropwise at 0 °C, and the mixture stirred at room temperature for 1 h.
The precipitate was separated and extracted with diethyl ether (2 ×
σfin(max/min) (e Å-3) 0.354/-0.514 0.316/-0.364
a
2
2 2
2 2 1/2
2
2
2
wR2 ) {∑[w(Fo - Fc ) ]/∑[w(Fo ) ]} ; w ) 1/[σ (Fo ) + (ap) +
bp]; p ) (Fo2 + 2Fc )/3.
2
1
4
00 mL), and the combined organic phases were dried over MgSO .
Evaporation of the solvent and distillation of the residue in vacuo
yielded a colorless liquid: 11.35 g, 90.2%; bp 87 °C (0.9 mbar), mp
of LiAlH (5.50 g, 144.9 mmol) in diethyl ether (200 mL) at -78 °C.
4
The reaction mixture was then allowed to warm to room temperature
and stirred for 12 h. For workup, degassed water (30 mL) was added
dropwise at 0 °C, and the mixture was stirred at room temperature for
3
1
1
31
-
26 °C; P{ H} NMR (CD
2
Cl
2
, 25 °C) δ -133.5 (s); P NMR (CD
2
-
1
3
Cl
2
, 25 °C) δ -133.5 (td, J(PH) ) 203.5 Hz, J(PH) ) 8.0 Hz); 13C-
H} NMR (CD
d, J(CP) ) 16.9 Hz, C2), 133.8 (d, J(CP) ) 2.3 Hz, C10), 129.9 (s,
C4/5), 129.1 (s, C5/4), 127.4 (d, J(CP) ) 11.5 Hz, C1), 126.9 (d,
J(CP) ) 10.8 Hz, C8), 126.8 (s, C6/7), 126.4 (s, C7/6), 125.8 (d, J(CP)
6.1 Hz, C3); H (CD
J(HH) ) 0.7 Hz, 1H, H8), 7.92 (d, J(HH) ) 7.2 Hz, 1H, H4/5), 7.89
d, J(HH) ) 8.2 Hz, 1H, H5/4), 7.82 (m, 1H, H2), 7.61 (m, 2H, H6/
), 7.44 (m, 1H, H3), 4.26 (d, J(HP) ) 203.4 Hz, 2H, PH
m/z 160 [M] . Anal. Calcd for C10
3
9.34. Found: C, 74.86; H, 5.72; P, 19.22. [ P NMR (CDCl ) δ -134.0
t, J(PH) ) 200 Hz).]
-Naphthylphosphonium Trifluoromethanesulfonate, 5. Trifluo-
romethanesulfonic acid (0.78 mL, 8.78 mmol) was added to a stirred
solution of 4 (1.40 g, 8.74 mmol) in CH Cl (80 mL) at room
1
2
{
2
Cl
2
, 25 °C) δ 135.8 (d, J(CP) ) 8.5 Hz, C9), 134.9
1
h. The precipitate was separated and extracted with diethyl ether (2
4
50 mL), and the combined organic phases were dried over MgSO .
2
3
(
×
1
Evaporation of the solvent in vacuo yielded a white solid. Repeated
3
3
recrystallization from CH
2 2
Cl at -30 °C gave colorless, block-shaped
1
3
)
2
Cl
2
, 25 °C) δ 8.21 (dd, J(HH) ) 8.2 Hz,
31
1
crystals: 2.71 g, 77.6%; mp 82 °C; P{ H} NMR (CD
2
Cl
2
, 25 °C) δ
4
3
31
-
104.9 (s); P NMR (CD Cl , 25 °C) δ -104.9 (X-part of an
2 2
3
(
7
13
1
[
ABCD
2
X]
2 2 2
spin system); C{ H} NMR (CD Cl , 25 °C) δ 139.0 (t,
1
2
); MS (EI)
2
3
J(CP) ) 17.3 Hz, C9), 138.2 (s, C2/7), 135.1 (t, J(CP) ) 4.6 Hz,
+
H
9
P (160.15): C, 75.00; H, 5.66; P,
C10), 130.6 (t, A-part of an AXX′ spin system, N ) JAX + JAX′ ) 1.8
31
1
(
Hz, C4/5), 128.7 (t, A-part of an AXX′ spin system, N ) JAX + JAX′
1
26a
1
)
20.2 Hz, C1/8), 125.3 (s, C3/6); H NMR (CD
2
Cl
2
, 25 °C), ABCD
2
-
1
part of the [ABCD
2 2
X] spin system, δ 7.83 (A, 2H, H2/7), 7.31 (B,
2
H, H3/6), 7.77 (C, 2H, H4/5), 4.58 (D, 4H, PH
2
). For coupling
2
2
constants, see Table 1. MS (EI) m/z 192 [M] , 191 (100) [M - H] ,
1
1
+
+
temperature. After the mixture was stirred for 0.5 h, the solution was
+
+
+
+
90 [M - 2H] , 189 [M - 3H] , 188 [M - 4H] , 159 [M - PH ] ,
2
concentrated in vacuo and stored at -30 °C and yielded colorless,
+ +
+
6
28 [C10H ] , 127 [C10H ] , 126 [C10H ] . Anal. Calcd for C10H P
8
7
1
0
2
31
1
2
needle-shaped crystals: 2.54 g, 93.7%; mp 91 °C; P{ H} NMR (CD -
(192.13): C, 62.51; H, 5.25; P, 32.24. Found: C, 62.49; H, 5.21; P,
3
1
Cl
2
, -80 °C) δ -53.4 (s); P NMR (CD
2
Cl
Cl
PS (310.23): C, 42.59; H, 3.25; P, 9.98.
Found: C, 42.71; H, 3.24; P, 10.12.
,8-Bis(dichlorophosphinyl)naphthalene, 8. Compound 8 was
prepared by a modification of the procedure reported by Schmutzler et
2
, -80 °C) δ -53.4 (q,
, -80 °C) δ -79.1 (s).
3
1.98.
1
1
19
1
J(PH) ) 546.9 Hz); F{ H} NMR (CD
Anal. Calcd for C11
2
2
,2-Dihydro-1,2-diphosphaacenaphthene, 10. 31P{ H} NMR (CD
1
2
-
H F
10 3
O
3
+
Cl
2
+
, 25 °C): δ -103.7 (s). MS (EI) m/z 190 (100) [M] , 189 [M -
+
H] , 188 [M - 2H] .
1
1-(8-Phosphinylnaphthyl)phosphonium Trifluoromethanesulfonate,
11. Trifluoromethanesulfonic acid (0.13 mL, 1.46 mmol) was added
to a stirred solution of 9 (280.0 mg, 1.46 mmol) in CH Cl (30 mL) at
2
7a
al. A solution of 7 (11.34 g, 23.8 mmol) in diethyl ether (250 mL)
was cooled to 0 °C and saturated with gaseous HCl. The reaction
mixture was stirred for 1 h, and was again saturated with gaseous HCl
and stirred for 1 h. This procedure was repeated until the supernatant
solution remained clear upon further addition of HCl. The reaction
mixture was then allowed to warm to room temperature and stirred for
2
2
room temperature. After the mixture was stirred for 0.5 h, the solution
was concentrated in vacuo, stored at -30 °C, and yielded colorless,
31
1
needle-shaped crystals: 429.7 mg, 86.2%; mp 135 °C; P{ H} NMR
4
+
(CD Cl , -80 °C) δ -35.5 (d, J(PP) ) 107.0 Hz, PH ), -119.3 (d,
2
2
3
4
1
31
J(PP) ) 107.0 Hz, PH ); P NMR (CD Cl , -80 °C) δ -35.5 (qdd,
J(PH) ) 546.9 Hz, J(PP) ) 107.0 Hz, J(PH) ) 23.8 Hz, PH ),
2
2
2
4
3
+
3
1
2 h. The diethylammonium chloride precipitate was separated and
1
4
5
extracted with diethyl ether (2 × 50 mL). Evaporation of the combined
-119.3 (tdq, J(PH) ) 245.7 Hz, J(PP) ) 107.0 Hz, J(PH) ) 39.6
Hz, PH2); 19F{ H} NMR (CD Cl , -80 °C) δ -79.2 (s). Anal. Calcd
1
organic phases in vacuo left a residue, which was recrystallized from
2
2
CH
g, 81.7%. For analytical data, see refs 27a and 27b.
,8-Di(phosphinyl)naphthalene, 9. A solution of 8 (6.00 g, 18.2
mmol) in diethyl ether (50 mL) was added slowly to a stirred suspension
Cl
2 2
at -30 °C, and yielded pale yellow, block-shaped crystals: 6.41
11 11 3 3 2
for C H F O P S (342.21): C, 38.61; H, 3.24; P, 18.10. Found: C,
38.52; H, 3.31; P, 17.94.
1-(8-Phosphinylnaphthyl)phosphonium Hydronium Bis(trifluo-
romethanesulfonate), 13. Trifluoromethanesulfonic acid (0.25 mL, 2.82
1
1
5842 J. AM. CHEM. SOC. VOL. 126, NO. 48, 2004
9

Insignificance of P−H‚‚‚P Hydrogen Bonding
A R T I C L E S
mmol) and degassed water (25.3 µL, 1.40 mmol) were added to a stirred
solution of 9 (270.0 mg, 1.41 mmol) in CH Cl (30 mL) at room
2
The “in plane” P-H hydrogen atom of each -PH group in the
structure of 9 and all hydrogen atoms in 11 and 13 were localized and
2
2
temperature. After the mixture was stirred for 0.5 h, the solution was
concentrated in vacuo, stored at -30 °C, and yielded colorless, block-
shaped crystals: 635.4 mg, 88.6%; mp 74 °C. Anal. Calcd for
refined with isotropic displacement parameters. The disordered P-H
hydrogen atoms of both -PH units in 9 were assigned to peaks of the
2
residual electron density of similar height and orientation (above and
below the reference plane of the hydrocarbon unit), with a site
occupation factor of 0.5 for each position. The corresponding P-H
distances were refined with a similarity restraint placed on the four
bond lengths.
C
11
H
11
F
3
O
3
P
2
S‚CF
Found: C, 28.19; H, 2.86; P, 12.03. The NMR parameters (in CD
at -80 °C) are similar to those of 11, but feature broader signals.
3
SO
3
H‚H
2
O (510.31): C, 28.24; H, 2.77; P, 12.14.
2
Cl
2
Determination of the Crystal Structures. Specimens of suitable
quality and size of 9, 11, and 13 were mounted on the ends of quartz
fibers in inert perfluoropolyalkyl ether and used for intensity data
collection on a Nonius DIP2020 diffractometer, employing graphite
monochromated Mo KR radiation. The structures were solved by a
combination of direct methods (SHELXS-97) and difference Fourier
syntheses and were refined by full-matrix least-squares calculations on
Further information on crystal data, data collection, and structure
refinement is summarized in Table 3.
Acknowledgment. This work was supported by Fonds der
Chemischen Industrie (Frankfurt) and by DAAD (Bonn).
Supporting Information Available: X-ray crystallographic
files for 9, 11, and 13. Crystal data, data collection, structure
refinement, thermal parameters, and complete tables of inter-
atomic distances and angles for 9, 11, and 13. This material is
available free of charge via the Internet at http://pubs.acs.org.
2
45
F (SHELXL-97). The thermal motion was treated anisotropically
for all non-hydrogen atoms.
(
45) Sheldrick, G. M. SHELX-97; University of G o¨ ttingen: G o¨ ttingen, Germany,
1
997.
JA045460X
J. AM. CHEM. SOC.
9
VOL. 126, NO. 48, 2004 15843