Defying Stereotypes with Nanodiamonds: Stable Primary Diamondoid Phosphines

Article abstract of DOI:10.1021/acs.joc.6b01219

Direct unequal C-H bond difunctionalization of phosphorylated diamantane was achieved in high yield from the corresponding phosphonates. Reduction of the functionalized phosphonates provides access to novel primary and secondary alkyl/aryl diamantane phos

Full text of DOI:10.1021/acs.joc.6b01219

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Article
Defying stereotypes with nanodiamonds:
stable primary diamondoid phosphines
Oana Moncea, Maria A. Gunawan, Didier Poinsot, Helene Cattey, Jonathan
Becker, Raisa I Yurchenko, Ekaterina D. Butova, Heike Hausmann, Marina
Sekutor, Andrey A Fokin, Jean-Cyrille Hierso, and Peter R. Schreiner
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b01219 • Publication Date (Web): 25 Aug 2016
Downloaded from http://pubs.acs.org on August 27, 2016
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Defying stereotypes with nanodiamonds: stable primary
diamondoid phosphines
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Oana Moncea,a,b$ Maria A. Gunawan,a,b$ Didier Poinsot,a Hélène Cattey,a Jonathan Becker,c
Raisa I. Yurchenko,d Ekaterina D. Butova,d Heike Hausmann,b Marina Šekutor,b Andrey A.
Fokin,*b,d JeanꢀCyrille Hierso,*a,e and Peter R. Schreiner*b
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aInstitut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB), UMR-CNRS 6302,
Université de Bourgogne Franche-Comté, 9 avenue Alain Savary, 21078 Dijon, France
bInstitut für Organische Chemie, Justus-Liebig-Universität, Heinrich-Buff-Ring 17, 35392
Giessen, Germany, prs@org.chemie.uni-giessen.de
cInstitut für Anorganische und Analytische Chemie, Justus-Liebig-Universität, Heinrich-Buff-
Ring 17, 35392 Giessen, Germany
dDepartment of Organic Chemistry, Kiev Polytechnic Institute, Pr. Pobedy 37, 03056 Kiev,
Ukraine, aaf@xtf.kpi.ua
eInstitut Universitaire de France (IUF), 103 Bd. Saint Michel, 75005 Paris Cedex 5, France,
jean-cyrille.hierso@u-bourgogne.fr
$ These authors contributed equally
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Table of Contents /Abstract Graphic
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Abstract
The direct unequal C–Hꢀbond difunctionalization of phosphorylated diamantane is achieved
in high yield from the corresponding phosphonates. The reduction of the functionalized
phosphonates provides access to novel primary and secondary alkylꢀaryl diamantane
phosphines. The prepared primary diamantyl phosphines are quite air stable as compared to
their adamantyl and especially alkyl or aryl analogues. This finding is corroborated by
comparing the SOMO energy levels of the corresponding phosphine radical cations obtained
by density functional theory (DFT) computations.
Introduction
Naturally occurring diamondoids1 are nanometerꢀsized hydrocarbons (i.e., nanodiamonds)
with structures resembling the diamond crystal lattice.2 Higher diamondoids bridge the gap
between simple organic molecules and diamond, possessing some properties of bulk
diamond. Further progress in materials applications of diamondoids requires the synthesis of
functionalized derivatives by introducing strategically placed substituents into their skeleton.3
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For instance, selfꢀassembled monolayers (SAMs) of [121]tetramantaneꢀ6ꢀthiol deposited on
Ag and Au surfaces display unusually high negative electron affinities (NEAs).4 However,
the metalꢀsulfur bond breaks at elevated temperatures,5 and the thiol moiety is therefore not
ideal as a surface attachment group. One of the ways to solve this problem is to create
additional attachment points on the diamondoid (e.g., adamantane tripods bearing several
anchoring thiol groups).6ꢀ8 Alternatively, the thiol group may be replaced with a phosphonate
moiety providing thermally stable multivalent surface bonding.9
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Phosphonic acid dichlorides are also ideal starting materials for the preparation of phosphines
that are viable building blocks for new materials,3,10 and as ligands in catalysis.11,12
Phosphines bearing bulky alkyl moieties such as adamantyl (Figure 1) have shown excellent
ligand properties and have provided many advances in terms of scope and efficiency for C–C
and C–N bond formation reactions.13ꢀ23
Figure 1. a) Adamantane (1), diamantane (2), adamantylphosphine (3), diamondoid
phosphines (4a and 4b) and phosphonium salt 5a; b) commercially available diꢀadamantyl
phosphines (4c and 6–9) and phosphonium salt 5b.
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The preparation of diꢀadamantyl phosphines (e.g., CataCXium® (7), Mor-DalPhos (8),
Figure 1b) was achieved by reacting halophosphorus compounds with organometallic
reagents.14,24ꢀ28 The synthesis of higher diamondoid phosphines was accomplished after
reduction of diꢀ4ꢀdiamantyl and diꢀ9ꢀtriamantyl phosphonic acid chlorides using HSiCl3 with
a Lewis acid. The corresponding secondary phosphines 4a and 4b as well as salt 5a were
obtained in good yields.29 Preliminary studies using phosphonium salt 5a as ligand in C–C
bond formation reactions showed promising results.29 Recently, triadamantyl phosphine
metal complexes were synthesized and their application in cross coupling reactions involving
aryl chlorides and boronic acids was reported. 30
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Although primary phosphines have been used as starting materials in asymmetric catalysis,
31,32 their applications are limited due to their air sensitivity.33 Low molecular weight, lack of
steric hindrance and the absence of a heteroatom in the backbone can even result in
pyrophoricity of such compounds.33 The air stability of some primary phosphines (e.g.,
binaphthyl MOP phosphines) that are neither hindered nor do they include a heteroatom in
their structures,34ꢀ36 is due to a high degree of πꢀconjugation. Bulky substituents also inhibit
the reaction with dioxygen, thereby making primary phosphines more “user friendly”.33 The
primary adamantane phosphine 3 (Figure 1), prepared through the reduction of the
corresponding phosphonic dichloride 16,37 is very airꢀsensitive making its application as
ligand in catalysis challenging. We envisioned that larger diamondoid groups (e.g.,
diamantane) would substantially increase the airꢀstability of the corresponding primary
phosphines.
As diamondoid cage substitution changes the electronic properties
significantly,38 we also studied the influence of additional functional groups on the stability
of primary diamondoid phosphines. This requires the preparation of novel phosphorylated
diamondoid derivatives via the C–H bond substitution, which is described in the present
work.
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Results and Discussion
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Diamondoid phosphorylations
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In contrast to adamantane (1),39,40 diamantane (2) displays two types of tertiary carbons,
apical and medial, thus making its selective functionalization by cationic activation
challenging.2,3,10 Therefore the use of protection/deprotection sequences41ꢀ43 is necessary in
order to obtain unequally difunctionalized diamantyl derivatives. Diamondoid phosphonic
dichloride derivatives are typically obtained via Lewis acid catalysis,37,44 but the direct
monophosphorylation of diamantane in the AlCl3/PCl3/CH2Cl2 system45 results in mixtures29
and low yields compared to that of adamantane. We found that employing a Brønsted acid46ꢀ
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gives rise to higher yields and, most importantly, that it is applicable to cages larger than
adamantane.49 However, this procedure does not allow for the preparation of unequally
disubstituted diamondoids, and in trifluoroacetic acid the reaction of 10 resulted only in
product 13 (Scheme 1).49 This can be understood readily because 10 and all monosubstituted
intermediates are soluble in TFA, while 13 precipitates from this media. As 10 is only poorly
soluble in H2SO4, a variety of products can form. We first tested the phosphorylation of 10
with PCl3 in conc. H2SO4 which gave monoꢀphosphorylated derivative 14 in up to 60% yield
(with method a), Scheme 1) depending on the reaction conditions.
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POCl2
OH
Cl
POCl2
POCl2
POCl2
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PCl3
PCl3
+
+
+
7
TFA
H2SO4
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[ ref. 49 ]
POCl2
13 (87%)
OH
Cl
Cl
POCl2
OH
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a)
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65%
50%
5%
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9%
12%
60%
19%
b) 27%
c) 10%
-
-
d)
-
13
Scheme 1. Phosphorylation of diamantane diol 10 with yields depending on the reaction
conditions: a) 1 eq. PCl3, H2SO4 98% at –15 °C for 1 h, 3.5 h at r.t.; b) 1 eq. PCl3, H2SO4
98% at 0 °C for 1 h, 6 h at r.t.; c) 2.5 eq. PCl3, H2SO4 98% at –15 °C for 1 h, 3.5 h at r.t.; d)
10 eq. PCl3, H2SO4 98% at –15 °C for 1 h, 3.5 h at r.t.; inset: Xꢀray crystal structure of 13
(color code: C, gray; H, white; P, orange; O, red; Cl, green). The Xꢀray crystal structure of 13
was also obtained and we found somewhat bond lengths shorter than typical for C‒P and O‒P
bonds (Capical‒P = 1.813(3) Å and O‒P = 1.463(2) Å).
It has been shown that PCl3 decomposes rapidly in H2SO4.47 Since the reaction proceeds
slowly in sulphuric acid due to the low solubility of the substrate, the carbocation can be
attacked by either nucleophile, resulting in chlorination and phosphorylation products.
Therefore, we chose a different approach based on C–Hꢀbond functionalization (Scheme 2).
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OH
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PCl3, H2SO4
1. HNO3, H2SO4
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OH
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OH
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PCl3, H2SO4
1. HNO3, H2SO4
2. H2O
OH
18
19 (68%)
14 (69%)
HNO3
POCl2
POCl2
POCl2
+
O2NO
15% HNO3
HO
ONO2
20
21 (60%)
22 (not characterized)
POCl2
POCl2
+
OH
23 (not characterized)
24 (35%)
Scheme 2. C–HꢀBond functionalization of diamondoid phosphonic acid dichlorides.
We showed previously that oxidation of diamondoids with 100% nitric acid affects only
tertiary positions and can be performed in a kinetically controlled way.50 While the question
of regioselectivity does not arise for 16, diamantane derivative 19 displays three different
tertiary C–H positions. Moreover, the electron withdrawing group (EWG) deactivates the
medial positions and only the remaining apical position reacts. Consequently, with HNO3 C–
Hꢀbond functionalization of 19 occurs regioselectively in position 9 (apical) of the
diamantane cage. For the medially substituted diamantane phosphonic dichloride 20 the C–
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Hꢀbond functionalization occurs at the position farthest from the POCl2 group, resulting in a
mixture of 1,6ꢀ and 1,4ꢀ derivatives (24 and 23, respectively).
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We also attempted the Brønsted acid catalyzed phosphorylation with two different
substituents (alkyl and aryl) present on phosphorus.46 We chose trifluoroacetic acid to avoid
the formation of chlorinated products. The phosphorylation of 4ꢀhydroxydiamantane 18 with
PhPCl2 gave the corresponding phenylꢀ4ꢀdiamantylphosphonic acid chloride (25) in high
yield (Scheme 3). Although medially substituted diamantane derivatives are sterically
hindered,50 the phosphorylation of 1ꢀhydroxydiamantane (26) also proceeded smoothly to
give phenylꢀ1ꢀdiamantylphosphonic acid chloride (27). The phosphonic dichlorides and
chlorides described above were used as precursors for primary and secondary diamondoid
phosphines.
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Scheme 3. Synthesis of diamantyl phosphonic chlorides.
Primary diamondoid phosphines
Commonly used metal catalyzed hydrogenation methods or reducing agents cannot be
applied to the reduction of diamandoid phosphonic dichlorides; conversely the use of LiAlH4
has been reported.51 Starting from diamantane phosphonic dichlorides 19 and 20, the
corresponding primary phosphines 29 and 31 were obtained. They have different topologies,
29 being less hindered than 31 as the medial position is known to be much more crowded
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than the apical one.10 The two primary phosphines 29 and 31 were only characterized by
NMR and show the following characteristic signals in the 31P NMR: δP(29)= –85.2 ppm,
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1JPH(29)= 145 Hz and δP(31)= –97.4 ppm, JPH(31)= 194 Hz, respectively. They were fully
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characterized via the corresponding Staudinger iminophosphorane derivatives 30 and 32
(Scheme 4). The 1H and 31P NMR spectra of primary phosphines 29 and 31 show broadening
of the signals at room temperature in chloroformꢀd. In order to clarify this observation, we
undertook further NMR investigation using 31 in various solvents, with different additives
and at various temperatures (SI, pages S101ꢀS105). When THFꢀd8 was used as the solvent,
the broadening phenomenon was not observed, but upon addition of acid broadening
occurred again. Therefore, we concluded that the observed behavior was solely caused by
proton exchange at the phosphine.
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NO2
POCl2
PH2
P N
1. LiAlH4
CH3I
2.15% HCl
p-N3PhNO2
19
29 (80%)
30 (73%)
NO2
1. LiAlH4
CH3I
POCl2
PH2
P
N
2.15% HCl
p-N3PhNO2
20
31 (56%)
POCl2
32 (96%)
PH2
1. LiAlH4
2.15% HCl
POCl2
13
PH2
33 (85%)
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Scheme 4. Synthesis of primary diamantyl phosphines.
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The primary diphosphine 33 prepared by reduction of diphosphorylated derivative 13 could
be fully characterized as it appears to be stable for several minutes in air, unlike
monophosphine 29. In compound 29 the donor effect of the cage is proposed to influence
only one phosphorus atom, thus making it more electronꢀrich, which is not the case for 33.
Therefore, the monosubstituted phosphine should react with oxygen more readily. Primary
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diphosphine 33 also showed the same signal broadening in H and 31P NMR spectra like
monophosphines 29 and 31, a consequence of phosphine proton exchange.
The reduction of unequally substituted diamondoids 12, 14, and 17 with LiAlH4 readily led to
primary phosphines 37, 36, and 34, respectively (Scheme 5), similar to the reduction of
monophosphorylated and diphosphorylated compounds 19, 20, and 13. Compound 34 is air
sensitive and quantitatively converts to oxide 35. This result is consistent with the reported
high air sensitivity of other 1ꢀadamantyl phosphines substituted in position 3.52
POCl2
PH2
H2PO
1. LiAlH4
2. H2O
air
5 min
OH
OH
34 (92%)
OH
35 (99%)
17
POCl2
PH2
1. LiAlH4
2. HCl 5%
R
R
14 R=OH
12 R=Cl
36 R=OH (76%)
37 R=Cl (79%)
Scheme 5. Synthesis of unequally substituted primary diamondoid phosphines.
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An increase in the JPH coupling constant is noticeable when comparing compounds 29 and
36 (∆J = 45 Hz). Despite the large spatial separation along the cage framework between the
hydroxy group and the phosphorus, the electronꢀwithdrawing effect is enhanced by
hyperconjugation.53ꢀ56 It is know that primary phosphines attached to a backbone containing
a heteroatom are more likely to be air stable compared to their homologues without
heteroatoms.33 This is also the case for compounds 36 and 37 since we found that in solution
they were stable for at least one hour in air. Such stability was not observed for the
adamantane homologues despite the presence of an EWG. Two EWGs (OH or Cl) seem to
provide additional air stability (e.g., compare compounds 3 and 29 with 34 and 36,
respectively). The mechanism of phosphine oxidation by O2 has not been fully elucidated,
but the formation of the radical cation of primary phosphine is a postulated pathway.34ꢀ36
Primary phosphines with extended πꢀelectron structural motifs (such as naphthyl, binaphthyl,
and triptycenyl) do not have a significant phosphorus contribution to their HOMO and are
stable to air oxidation.35 Even though in our case there is no such conjugated motif, we
propose that an increase of bulkiness by the diamantane cage surrounding the phosphorus
atom can induce a significant resistance towards air oxidation (compare 34 with 36).
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It was suggested that the SOMO level and geometry of the corresponding phosphine radical
cation is a key for understanding the air stability of the related primary phosphine.35 An
empirically derived value of –10.0 eV was proposed to be a threshold and phosphines with
radical cation SOMO energies below this value are expected to be easily oxidized in air.35
This agrees in part with our computed SOMO energies of the radical cations derived from
phosphines 3, 29, 33, 34, 36 and 49 (Figure 2), where these values for relatively air stable
33•+ (–9.9 eV) and 36•+ (–10.3 eV) approach the above threshold. Note that the SOMO of
36•+ is located predominantly on the oxygen atom of the hydroxy group, which is a
complementary explanation for the stability of 36 towards oxidation. As experimentally
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observed, primary diphosphine 33 also is more stable than primary monophosphine 29. This
finding is in agreement with the computed SOMO energies of the radical cations derived
from 33 and 29 (–9.9 eV and –11.0 eV, respectively). We also performed an NBO analysis
of spin densities for radical cations derived from primary diamondoid phosphines and found
that the spin density on phosphorus is generally smaller for more air stable derivatives (SI,
Table S1). These findings are in agreement with the proposed radical mechanism of
phosphine oxidation since radical cations of stable diamondoid phosphines have spin
densities distributed in other parts of the molecule, implying that the spin is not solely
localized on the phosphorus atom, resulting in higher resistance to oxidation.
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PH2
PH2
PH2
OH
PH2
34
11.3
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10.8
3
11.7
PH2
PH2
PH2
OH
PH2
29
36
10.3
33
9.9
11.0
Figure 2. The shapes and energies (in eV) of the SOMOs for the B3LYP/6ꢀ311+G(d,p)
optimized structures of the radical cations derived from primary phosphines 3, 29, 33, 34, 36,
and 49.
Secondary diamondoid phosphines
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Secondary diamantane phosphines were also prepared using a LiAlH4/ethereal system
(Scheme 6). In contrast to primary phosphines 29 and 31, only the apical secondary
phosphine 38 forms a phosphazo derivative. The medial phosphine 39 is unreactive probably
due to steric hindrance caused by the cage in the medial position.57 The 31P NMR
characterization of 38 at room temperature in CDCl3 was surprising since no signal was
observed. At around 240 K the expected doublet appears at –9.5 ppm (1JPH(38) = 178 Hz) as
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1
well as the corresponding doublet at 3.82 ppm in the H NMR. Fluxional behavior was also
observed in the 31P and 1H NMR spectra of 1ꢀdiamantylphenylphosphine (39), which is only
slightly different from secondary phosphine 38 since at 273 K the spectrum of 39 indicates a
broad singlet at –23.1 ppm. Upon cooling, decoalescence occurs at around 255 K and at 240
K the expected doublet is observed at –23.9 ppm (1JPH(39)= 178 Hz). As was the case for
primary diamantyl phosphines, proton exchange is responsible for the observed NMR
behavior of secondary diamantyl phosphines. For further understanding of secondary
diamantyl phosphines 38 and 39, we performed computational studies and identified their
stationary structures for the rotation around the C–P bonds (for details see SI, pages S111ꢀ
S112 and Figures S1 and S2). The results indicate that a planar inversion around phosphorus
is not an energetically favorable pathway and that the conformers interconvert through a
rotation of the diamantane cage or the phenyl group.
POClPh
PHPh
1. LiAlH4
2. HCl 15%
25 (88%)
38 (85%)
1. LiAlH4
2. HCl 15%
POClPh
PHPh
27 (67%)
39 (75%)
Scheme 6. Synthesis of unequally substituted secondary diamantyl phosphines.
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Diamondoid phosphine post-functionalization
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The conversion of primary diamantane phosphines was explored as a direct synthetic
pathway towards functionalized higher analogues. We aimed at exploring whether the direct
functionalization of primary diamondoid phosphines would be a feasible method. By
refluxing hydroxyphosphine 36 with benzyl bromide, the expected alkylation reaction
occurred, but we mainly isolated the phosphonium salt 40 in modest yield (16%, Scheme 7).
A characteristic 31P NMR signal at 27.5 ppm was observed for 40 and its Xꢀray structure
indicates a weak hydrogen bond between the hydroxy group and the bromide O–H…Br
(d(O–Br) = 3.4239(15); angle O–H–Br = 162.6°). The observed bond length values for C4‒P
= 1.835(2) Å and C9‒O = 1.429(2) Å were expected and correspond to typical C‒P and C‒O
bonds.
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Br
PH2
P
BnBr
toluene,
OH
36
OH
40 (16%)
40
Scheme 7. Benzylation of unequally substituted primary diamantane phosphine 36 and the Xꢀ
ray single crystal diffraction structure of phosphonium salt 40 (color code: C, gray; H, white;
P, orange; O, red; Br, dark red).
As the direct approach for phosphine functionalization was low yielding, an indirect strategy
was envisioned that would lead to pentacoordinated phosphorus derivatives that could further
be reduced.58,59 We first arylated diamondoid phosphonic dichlorides in order to obtain the
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mixed phosphorylated oxides 41–44 (Scheme 8). In the obtained Xꢀray crystal structures of
41–44 average C‒P and O‒P bond lengths were observed (e.g., Capical‒P = 1.833(2) Å and
O‒P = 1.500(2) Å for 43). Their reduction was expected to give access to mixed arylꢀalkyl
diamondoid phosphines.
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Scheme 8. Arylation of diamondoid phosphonic acid dichlorides and the Xꢀray single crystal
diffraction structures of 42, 43 and 44 (color code: C, gray; H, white; P, orange; O, red).
Unfortunately, adamantyl derivative 41 (δP= 34.3 ppm, in agreement with the literature60)
could not be reduced with LiAlH4 in THF or dioxane51 to the corresponding phosphine, and
we did not pursue this line of investigation further with the diamantyl homologues. Instead,
we prepared the parent sulfide 46 and selenide 47 that could be readily reduced to the target
phosphine 48 with 60% yield (Scheme 9). In the Xꢀray crystal structure of sulfide 46 we
found somewhat longer bond lengths, for Cmedial‒P = 1.859(2) Å and P‒S = 1.9717(7) Å.
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Scheme 9. Reduction of adamantyl phosphine sulfide or selenide to 1ꢀadamantyl diphenyl
phosphine (48) and the Xꢀray single crystal diffraction structure of 46 (color code: C, gray;
H, white; P, orange; S, yellow).
1
The JP=Se(47) = 712 Hz coupling constant is lower than the value for triphenylphosphine
selenide (1JP=Se= 730 Hz), which is consistent with an electron donating effect of the
adamantyl group towards phosphorus. Thus, we expect a higher basicity of 48 compared to
PPh3, rendering this phosphine potentially useful in the catalytic steps of crossꢀcoupling
reactions.61ꢀ63 The pathway to 48 using sulfide 46 is the synthetically most efficient (Scheme
9) with an overall yield from bromide 45 of 27%. Compound 48 has previously been
reported as a sideꢀproduct formed in the photochemical reaction of 1,3ꢀdichloroadamantane
with the [Ph2P–] anion in liquid ammonia, but had not been isolated (since oxide 41 forms
instead).59
Conclusions
Direct unequal difunctionalization of phosphorylated diamondoid derivatives avoiding
protection/deprotection sequences is now made possible by C–Hꢀbond functionalization
without affecting an existing POCl2 group. Using Brønsted acid catalysis we prepared
unequally substituted diamantyl phosphonic chlorides, which are excellent precursors for the
corresponding phosphines. The reduction of phosphonic chlorides described herein provided
access to novel primary and alkylꢀaryl secondary diamantane phosphines. Primary diamantyl
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phosphines were found to be surprisingly air stable as compared to their adamantyl
homologues. We computed diamantyl and adamantyl phosphine radical cation energies and
found that the corresponding SOMO levels were close to the air stability threshold of –10 eV.
These functionalized diamondoid phosphines are currently explored in material science and
catalytic applications.
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Experimental Section
General Information. The synthesis of sensitive products was done using Schlenk
techniques. Glassware was dried in an oven at 110 °C before use. Tetrahydrofuran (THF)
and diethyl ether were prepared by distillation under argon using sodium (Na) and
benzophenone; dichloromethane (DCM) was purified by distillation under argon using CaH2;
1,4ꢀdioxane was purified by stirring with LiAlH4 under argon overnight and distilled under
argon (b.p. = 101 °C); CDCl3 was dried over activated 4 Å molecular sieves under argon.
The other solvents were obtained directly from the manufacturer or distilled from technical
grade. Commercially available reagents were used without further purification. TLC was
done on 0.2 mm silica gel with fluorescent indicator (preꢀcoated polyester sheets UV254 or
TLC silica gel 60 F254 on aluminum sheets). Column chromatography was done on silica gel
(70–230/100–160/230–400mesh ASTM). NMR spectra were recorded at 300, 400, 500, and
600 MHz spectrometers in chloroform (CDCl3) unless stated otherwise, with/without TMS as
internal standard. 1H and 13C NMR assignments were confirmed by DEPTꢀ135/JMOD and
1
sometimes with twoꢀdimensional Hꢀ13C NMR experiments. Highꢀresolution mass spectra
(HRMS) were recorded using electron impact ionization on a focusing sector fieldꢀtype mass
spectrometer.
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Phosphorylation of 4,9-dihydroxydiamantane (10) in sulphuric acid to prepare
compounds 11, 12, 13 and 14. Concentrated sulphuric acid 98% (8.5 mL, freshly prepared
from oleum 20% and H2SO4 94%) was cooled to 0 °C or –15 °C. At the respective
temperature, 4,9ꢀdihydroxydiamantane (10) (0.880 g, 4 mmol) is added followed by PCl3
(PCl3 was varied according to Scheme 1). The reaction mixture was stirred for 1 h at the
corresponding temperature and 3.5 h or 6 h at r.t. The reaction mixture was slowly poured
onto crushed ice. The white precipitate formed was filtered with a Büchner funnel and rinsed
with distilled water until neutral pH; the remaining solid was dried in air. Purification by
column chromatography on silica gel with pentane:diethyl ether (3:1) afforded 4,9ꢀ
dichlorodiamantane (11) (Rf: 0.88) and (9ꢀchloroꢀdiamantꢀ4ꢀyl)phosphonic dichloride (12)
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(Rf: 0.28).
Changing the eluent to DCM:diethyl ether (3:1) gave (4,9ꢀ
diamantyl)diphosphonic dichloride (13) (Rf: 0.76). Changing the ratio of the same eluent to
1:1 afforded (9ꢀhydroxydiamantꢀ4ꢀyl)phosphonic dichloride (14) (Rf: 0.22) as a white solid.
Yields are specified in Scheme 1 as a function of the reaction conditions.
4,9-Dichlorodiamantane (11). Spectral data were identical to reported.64
(9-Chlorodiamant-4-yl)phosphonic dichloride (12). Xꢀray structure is available in SI, page
S124. 1H NMR (600 MHz, 291 K, CDCl3): δ=2.17 (d, J=3.4 Hz, 6H), 2.11–2.06 (m, 6H),
2.06–2.01 (m, 3H), 2.01–1.06 (m, 3H) ppm. 13C NMR (150 MHz, 291 K, CDCl3): δ=65.7 (s,
Cq), 47.1 (d, J(C,P)=3.1 Hz, CH2), 46.5 (d, J(C,P)=92.8 Hz, Cq), 39.1 (d, J(C,P)=2.6 Hz,
CH), 35.2 (d, J(C,P)=16.7 Hz, CH), 35.0 (d, J(C,P)=3.3 Hz, CH2) ppm. 31P{1H} NMR (243
MHz, 291 K, CDCl3): δ=64.85 ppm.
(4,9-Diamantyl)diphosphonic dichloride (13) was identical to the material previously
obtained through the phosphorylation of 10 in trifluoroacetic acid.49 The Xꢀray structure is
available in the SI, page S128.
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(9-Hydroxydiamant-4-yl)phosphonic dichloride (14). m.p. 204–205 °C. 1H NMR (600
MHz, 298 K, CDCl3): δ=2.14–2.02 (m, 6H), 1.98 (br s, 6H), 1.82–1.68 (m, 6H; CH2), 1.51
(br s, 1H, OH) ppm. 13C NMR (151 MHz, 298 K, CDCl3): δ=66.8 (s, Cq), 46.8 (d,
J(C,P)=91.6 Hz, Cq), 44.8 (d, J(C,P)=3.2 Hz, CH2), 38.5 (d, J(C,P)=2.3 Hz, CH), 35.6 (d,
J(C,P)=16.6 Hz, CH), 35.0 (d, J(C,P)=3.1 Hz, CH2) ppm. 31P{1H} NMR (243 MHz, 300 K,
CDCl3): δ=65.29 ppm. HRMS (EI) m/z: [M]+ Calcd for C14H19Cl2O2P 320.0500; Found
320.0468.
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(4-Diamantyl)phosphonic dichloride (19) was identical to the material previously obtained
through the phosphorylation of 18 in sulphuric acid.49 The Xꢀray structure is available in the
SI, page S139.
Another method for preparing (9-Hydroxydiamant-4-yl)phosphonic dichloride (14)
from 19. Concentrated sulphuric acid 96% (2.5 mL) was placed in a 5 mL round bottom
flask and was cooled to –15 oC with an iceꢀsalt bath. 4ꢀDiamantylphosphonic acid dichloride
(19) (0.332 g, 1.1 mmol) was added and followed by HNO3 100% (0.4 mL, 9.8 mmol, 9
equiv). The reaction mixture was stirred for 1 h at –15 oC and for 7 h at 18 oC. The reaction
mixture was poured slowly onto 40 g of crushed ice. DCM (40 mL) was added and followed
by solid NaHCO3 in portions until a neutral pH was reached and the aqueous phase turned
clear yellow. It was extracted with DCM (3x30 mL) and dried over MgSO4. The solvent
was evaporated to yield 0.325 g of crude product. It was purified by column chromatography
on silica gel using DCM:diethylether (1:1) to afford (9ꢀhydroxydiamantꢀ4ꢀyl)phosphonic
dichloride (14) (0.242 g, 69% yield) as a white solid.
(3-Hydroxyadamant-1-yl)phosphonic dichloride (17). In a 10 mL round bottom flask, 3
o
mL of H2SO4 94% was cooled with an iceꢀsalt bath to –13 C. 1ꢀAdamantylphosphonic
dichloride (16) (1.66 g, 6.6 mmol) was added and stirred until it completely dissolved. Then
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HNO3 100% (3 mL, 72 mmol, 11 equiv) was slowly added. The solution was stirred for 1 h
at –13 oC and for 22 h at r.t. The colorless solution was slowly poured onto 15 g of crushed
ice. 100 mL of DCM were added and the mixture was stirred at r.t. Solid NaHCO3 was
added in small portions until no more gas evolution was observed. The aqueous phase was
extracted with DCM (3x30 mL DCM) and diethyl ether (4x40 mL). The combined organic
layers were dried over MgSO4 and the solvent was evaporated and gave a yellow sticky
compound. Purification by column chromatography on silica gel in diethyl ether 100% (Rf:
0.3) gave pure (3ꢀhydroxyadamantꢀ1ꢀyl)phosphonic dichloride (17) (1.42 g, 80%). The Xꢀ
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ray structure is available in the SI, page S132. H NMR (400 MHz, 300 K, CDCl3): δ=2.50–
2.36 (m, 2H), 2.04–1.94 (m, 6H), 1.78–1.69 (m, 5H), 1.69–1.57 (m, 2H) ppm. 13C NMR
(100 MHz, 300 K, CDCl3): δ=68.1 (d, J(C,P)=19.4 Hz, Cq), 51.0 (d, J(C,P)= 91.3 Hz, Cq),
43.9 (d, J(C,P)=2.5 Hz, CH2), 42.6 (d, J(C,P)=4.6 Hz, CH2), 34.5 (d, J(C,P)=2.8 Hz, CH2),
34.0 (d, J(C,P)=3.8 Hz, CH2), 30.1 (d, J(C,P)=17.6 Hz, CH) ppm. 31P{1H} NMR (162 MHz,
300 K, CDCl3, H3PO4 external standard): δ=62.21 ppm. HRMS (EI) m/z: [M]+ Calcd for
C10H15Cl2O2P: 268.0187; Found: 268.0169. Anal. Calcd for C10H15Cl2O2P: C, 44.63; H,
5.62, Found: C, 44.15; H, 5.59.
4-Nitroxydiamantyl-1-dichlorophosphonate (21). Diamantylꢀ1ꢀdichlorophosphonate (20)
(1.22 g, 4 mmol) was added to 20 mL of 100% HNO3 under intense stirring at 10 °C. The
reaction mixture was stirred for 20 h at 20 °C, poured onto ice (200 g), and extracted with
CHCl3 (3x20 mL). The combined organic extracts were washed with water, saturated aq.
NaHCO3, brine, and dried over Na2SO4 to give 1.45 g of a mixture of 4ꢀnitroxydiamantylꢀ1ꢀ
dichlorophosphonate (21) and of 6ꢀnitroxydiamantꢀ1ꢀyldichlorophosphonate (22) after
solvent removal. The mixture (0.725 g) was separated by column chromatography on silica
gel (hexane:ether= 9:1) to give 4ꢀnitroxydiamantylꢀ1ꢀdichlorophosphonate (21) as a colorless
solid (0.439 g, 60%), m.p. 120–121 °C. The Xꢀray structure is available in the SI, page S144.
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1H NMR (400 MHz, CDCl3): δ=2.97 (d, 2H, J=12 Hz), 2.55–2.43 (bs, 2H), 2.21–2.15 (bs,
2H), 2.06–1.95 (m, 8H), 1.80–1.62 (bs, 4H) ppm. 13С NMR (100 MHz, CDCl3): δ=87.0 (C),
54.0 (C, d, J=78 Hz), 38.8 (CH2, d, J=9.5 Hz), 39.1 (CH, d, J=3 Hz), 38.7 (CH, d, J=3 Hz),
37.5 (CH, d, J=15 Hz), 37.45 (d, CH2, J=1.3 Hz), 36.4 (CH2), 35.5 (CH2, d, J=3 Hz), 25.4 (d,
CH, J=15 Hz) ppm. 31P{1H} NMR (162 MHz, CDCl3, H3PO4): δ=63.1 ppm.
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6-Hydroxydiamantyl-1-dichlorophosphonate (24). The above described mixture (0.725 g)
was refluxed with 3 mL of 15% HNO3 under intense stirring, cooled and extracted with
CHCl3. The combined organic extracts were washed with water, saturated aq. NaHCO3,
brine, and dried over Na2SO4. After concentration under reduced pressure, the mixture was
separated by column chromatography on silica gel (hexane:ether=4:1). 6ꢀHydroxydiamantꢀ1ꢀ
yldichlorophosphonate (24) was obtained (0.225 g, 35%) as a colorless solid, m.p. 168–
1
170°C. The Xꢀray structure is available in the SI, page S129. H NMR (400 MHz, CDCl3):
δ=2.65 (AB, 2H, JAB=8 Hz), 2.42 (d, 2H, J=1.5 Hz), 2.21 (m, 2H), 2.17 (bs, 1H), 1.98–1.88
(m, 3H), 1.77 (d, 2H, J=1.5 Hz), 1.65 (s, 2H), 1.48 (m, 3H), 1.40 (AB, 2H, JAB=8 Hz) ppm.
13С NMR (100 MHz, CDCl3): δ=69.6 (C), 55.0 (d, C, J=75 Hz), 46.7 (CH2), 44.1 (d, CH,
J=17.5 Hz), 38.4 (d, CH2, J=2 Hz), 39.2 (CH), 33.4 (CH2), 30.9 (d, CH2, J=2.6 Hz), 29.2
(CH), 25.3 (d, CH, J=15 Hz) ppm. 31P{1H} NMR (162 MHz, CDCl3, H3PO4): δ=65.4 ppm.
HRMS (EI) m/z: [M]+ Calcd for C14H19Cl2O2P: 320.0500; Found: 320.0503.
4-Diamantylphenylchlorophosphonate (25). To a mixture of 3.00 g (14.7 mmol) of 4ꢀ
hydroxydiamantane (18) and 50 mL of trifluoroacetic acid, 7 mL (80 mmol) of
dichlorophenyl phosphine was added, and the reaction mixture was refluxed for 3.5 h, cooled,
and then poured onto ice. The reaction mixture was filtered and the precipitate was washed
with water, and dried. The crude product was purified by column chromatography on silica
(hexane:ether = 3:1) to give 4ꢀdiamantylphenylchlorophosphonate (25) as colorless crystals
(4.49 g, 88%), m.p. 190−192 °C (hexane). 1H NMR (400 MHz, CDCl3): δ=7.85–7.70 (m,
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2H), 7.65–7.59 (m, 1H), 7.58–7.44 (m, 2H), 2.01–1.83 (m, 9H), 1.79 (bs, 1H), 1.75–1.61 (m,
9H) ppm. 13С NMR (100 MHz, CDCl3): δ=132.8 (d, CH, J=3 Hz), 132.7 (d, CH, J=10 Hz),
129.0 (d, C, J=103 Hz), 128.3 (d, CH, J=14 Hz), 39.8 (d, C, J=80 Hz), 37.5 (d, CH2, J=2 Hz),
36.4 (d, CH, J=13 Hz), 36.1 (d, CH, J=1.3 Hz), 35.7 (d, CH2, J=6.3 Hz), 25.3 (CH) ppm.
31P{1H} NMR (162 MHz, CDCl3, H3PO4): δ=68.8 ppm. HRMS (EI) m/z: [M]+ Calcd for
C20H24ClOP: 346.1253; Found: 346.1249.
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1-Diamantylphenylchlorophosphonate (27) was prepared from 1ꢀhydroxydiamantane (26)
as described above with 67% yield (3.42 g) as a colorless solid, m.p. 257–259 °C (hexane).
1H NMR (400 MHz, CDCl3): δ=7.82–7.70 (m, 2H), 7.58–7.51 (m, 1H), 7.50–7.39 (m, 2H),
3.05–2.90 (m, 2H), 1.95–1.89 (m, 3H), 2.41–2.30 (m, 1H), 1.88–1.86 (m, 1H), 1.85–1.62 (m,
8H), 1.61–1.45 (m, 2H), 1.40–1.25 (m, 2H) ppm. 13С NMR (100 MHz, CDCl3): δ=132.6 (d,
CH, J=10 Hz), 131.0 (d, C, J=100 Hz) 132.5 (d, CH, J=3 Hz), 128.2 (d, CH, J=12 Hz), 47.9
(d, C, J=70 Hz), 38.8 (CH2), 38.7 (CH), 38.5 (d, CH, J=5 Hz), 38.2 (CH2), 37.3 (d, CH,
J=2.5Hz), 37.06 (d, CH2, J=3 Hz), 37.03 (d, CH2, J=3 Hz), 36.7 (CH), 36.5 (d, CH, J=4 Hz),
34.3 (CH2), 33.9 (CH2), 25.6 (d, CH, J=13 Hz), 25.1 (CH) ppm. 31P{1H} NMR (162 MHz,
CDCl3, H3PO4): δ=71.3 ppm. HRMS (EI) m/z: [M]+ Calcd for C20H24ClOP: 346.1253;
Found: 346.1248.
General procedure for the preparations of diamondoid phosphines in benzene/ether.
A solution of the respective diamantylphosphonic acid chloride (1.64 mmol) in dry benzene
(8 mL) was added to a mixture of LiAlH4 (16.4 mmol, 10 equiv) in dry ether (3.5 mL). The
reaction mixture was refluxed for 1–2 h, cooled to 0 ºC, and 15 mL of 15% HCl was added
dropwise. The aqueous phase was extracted with benzene (3x15 mL). Combined organic
phases were washed with water (10 mL) and dried over Na2SO4. Evaporation of solvents in
vacuo yielded respective phosphine in 70–96% yield.
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4-Diamantylphosphine (29) was isolated after 2 h of reflux in 80% (0.288 g) yield as
colorless airꢀsensitive solid. 1H NMR (600 MHz, CDCl3): δ=2.83 (bs, 1H), 2.51 (bs, 1H),
1.79–1.73 (m, 10H), 1.72–1.70 (bs, 6H), 1.69–1.64 (bs, 3H) ppm. 13С NMR (150 MHz,
CDCl3): δ=45.6 (d, CH2, J=21 Hz), 38.2 (d, CH, J=22 Hz), 37.8 (CH2), 36.3 (CH), 26.9 (d, C,
J=8 Hz), 25.6 (CH) ppm. 31P NMR (243 MHz, CDCl3, H3PO4): δ= –85.2 (t, J=145 Hz) ppm.
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4-Diamantyldimethylphosphazo-p-nitrobenzene (30). To a solution of phosphine 29 (0.34
g, 1.54 mmol) in dry benzene (3 mL) 1 mL of methyl iodide was added and the mixture was
stirred for 3 h under reflux. After cooling to r.t. and filtration, the precipitate (0.25 g) was
dissolved in ethanol (6 mL) and NaOH (0.4 g, 10 mmol) was added. The mixture was stirred
for 1 h at r.t., solvent was removed by distillation and 3 mL of water were added. The
residue was extracted with benzene (2x10 mL), combined organic extracts were washed with
water and dried over Na2SO4. Solvent evaporation gave 0.242 g of white solid, which was
dissolved in dry benzene (10 mL), 0.254 g (1.55 mmol) of pꢀnitrobenzene azide were added
and heated at 36 ºC for 5 min. After completion of the gas evolution (N2) and cooling, the
yellow precipitate was filtered and washed with benzene to give 4ꢀ
diamantyldimethylphenylphosphazoꢀpꢀnitrobenzene (30) as yellow solid (0.320 g, 73%), m.p.
1
285–287 °C (ethyl acetate). H NMR (400 MHz, CDCl3): δ=8.0–7.8 (m, 2H), 7.70–7.48 (m,
5H), 6.45 (bs, 2H), 2.00–1.80 (m, 9H), 1.83 (s, 3H), 1.75–1.70 (bs, 10H) ppm. 13С NMR
(100 MHz, CDCl3): δ=161.5 (C), 137.2 (CH), 132.2 (d, CH, J=9.0 Hz), 128.9 (d, CH, J=10
Hz), 125.7 (CH), 121.8 (bd, CH, J=23 Hz), 37.5 (CH2), 36.5 (d, CH, J=14 Hz), 36.3 (CH),
35.2 (CH2), 31.3 (d, C, J=90 Hz), 25.3 (CH), 5.30 (d, CH3, J=55 Hz), ppm. 31P{1H} NMR
(162 MHz, CDCl3, H3PO4): δ=21.2 ppm. HRMS (EI) m/z: [M]+ Calcd for C22H29N2O2P:
384.1967; Found: 384.1957.
1-Diamantylphosphine (31) was prepared after 1 h of reflux in 56% yield as colorless airꢀ
sensitive solid. 1H NMR (600 MHz, CDCl3, TMS): 2.80–2.24 (bs, 2H), 2.24 (AB, 2H,
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JAB=16 Hz), 1.86–1.78 (m, 4H), 1.74–1.66 (m, 11H), δ=1.56 (AB, 2H, JAB=16 Hz) ppm. 13С
NMR (150 MHz, CDCl3): δ=48.5 (d, CH2, J=6 Hz), 42.2 (d, CH, J=7 Hz), 38.7 (d, CH2, J=1
Hz), 38.5 (d, CH, J=5 Hz), 38.3 (CH2), 38.2 (CH2), 37.6 (CH), 37.0 (d, C, J=8 Hz), 34.7 (d,
CH, J=6 Hz), 27.9 (d, CH, J=6 Hz) ppm. 31P{1H} NMR (243 MHz, CDCl3, H3PO4): δ= –
97.4 (t, J=194 Hz) ppm.
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1-Diamantyldimethylphosphazo-p-nitrobenzene (32) was prepared as described above
(procedure for 30) from 31 in 96% yield (0.357 g) as yellow solid, m.p. 162–164 °C
(cyclohexane). 1H NMR (400 MHz, CDCl3): δ=8.0 (d, 2H, J=8 Hz), 6.52 (d, 2H, J=8 Hz),
2.63 (AB, 2H, JAB=16 Hz), 2.15 (bs, 2H), 2.0 (bs, 1H), 1.9 (bs, 2H), 1.81–1.62 (m, 16H), 1.50
(AB, 2H, JAB=16 Hz) ppm. 13С NMR (100 MHz, CDCl3): δ=160.2 (C), 128.3 (CH), 125.9 (d,
CH, J=1 Hz), 121.1 (d, CH, J=18 Hz), 43.4 (d, C, J=63 Hz), 39.0 (CH2), 38.6 (d, CH, J=9
Hz), 38.5 (CH2), 37.5 (d, CH, J=11 Hz), 37.3 (d, CH2, J=13 Hz), 37.0 (d, CH, J=2 Hz), 33.8
(CH2), 26.1 (d, CH, J=10 Hz), 24.9 (CH), 12.1 (d, CH3, J=61 Hz) ppm. 31P{1H} NMR (162
MHz, CDCl3, H3PO4): δ=26.0 ppm. HRMS (EI) m/z: [M]+ Calcd for C22H29N2O2P:
384.1967; Found: 384.1957.
4,9-Diamantyldiphosphine (33). 4,9ꢀBis(dichlorophosphoryl)diamantane (13) (0.051 g,
0.12 mmol) was placed in a 5 mL flask under argon and dissolved in 0.5 mL dry THF. The
obtained solution was cooled to –60 °C and 0.30 mL LiAlH4 (1 M in THF, 2.5 equiv) were
added dropwise for 15 minutes. The mixture was stirred at –20 °C for 1 h and at –10 °C for 4
h. The reaction was quenched with HCl 15% (0.1 mL) followed by extraction with cold
dichloromethane (3x3 mL) and drying over MgSO4 under argon. The solvent was removed
in vacuo affording 4,9ꢀdiphosphinodiamantan (0.029 g, 85%) as a white powder. 1H NMR
(500 MHz, CDCl3): δ=2.72 (d, 2H, JPꢀH=195 Hz), 1.77 (s, 12H), 1.72 (s, 6H) ppm. 13С NMR
(125 MHz, CDCl3): δ=45.2 (s, CH2), 37.0 (s, CH), 26.9 (s, C) ppm. 31P{1H} NMR (202
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MHz, CDCl3): δ= –85.4 ppm. HRMS (EI) m/z: [M+H]+ Calcd for C14H23P2 253.1270;
Found: 253.1259.
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3-Phosphinoadamantan-1-ol (34) and (3-hydroxyadamant-1-yl)phosphine oxide (35).
(3ꢀHydroxyadamantꢀ1ꢀyl)phosphonic dichloride (17) (0.054 g, 0.2 mmol) was placed in a 5
mL flask under argon. Thereafter, dry THF (1 mL) was added. The solution was cooled to –
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78 C and LiAlH4 solution (1 mL, 1 M in THF, 1 mmol, 5 equiv) was slowly added at –78
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oC. The colorless solution was stirred for 4 h at –78 C and for 1 h at r.t. Distilled water (1
mL) was added followed by extraction with DCM (total 10 mL) and drying over MgSO4.
The solvent was evaporated to yield a white air sensitive solid compound 34 (0.034 g, 92%)
that was stored under argon. When put in contact with air for 5 min, the product was
quantitatively oxidized into (3ꢀhydroxyadamantꢀ1ꢀyl)phosphine oxide 35.
3-Phosphinoadamantan-1-ol (34). 1H NMR (600 MHz, 300 K, C6D6): δ=2.70 (d,
J(H,P)=188 Hz, 2H), 1.91–1.83 (m, 2H), 1.59 (d, J=4.2 Hz, 2H), 1.53–1.4 (m, 8H), 1.32–1.23
(m, 2H), 1.16 (s, 1H, OH) ppm. 13C NMR (150 MHz, 300 K, C6D6): δ=67.8 (d, J(C,P)=8.7
Hz, Cq), 52.8 (d, J(C,P)=7.8 Hz, CH2), 44.3 (s, CH2), 43.6 (d, J(C,P)=8.8 Hz, CH2), 35.0 (s,
CH2), 31.6 (d, J(C,P)=8.4 Hz, CH), 31.5 (d, J(C,P)=4.8 Hz, Cq) ppm. 31P NMR (243 MHz,
300 K, C6D6): δ= –85.97 (t, 1J(P,H)=188.5 Hz) ppm.
(3-Hydroxyadamant-1-yl)phosphine oxide (35). 1H NMR (600 MHz, 300 K, CDCl3):
δ=7.15 (d, J(H,P)=452.8 Hz, 2H), 2.40–2.34 (m, 2H), 1.95–1.67 (m, 13H) ppm. 13C NMR
(150 MHz, 303 K, CDCl3): δ=67.7 (d, J(C,P)=15.7 Hz, Cq), 44.5 (s, CH2), 42.1 (s, CH2), 36.8
(d, J(C,P)=72.7 Hz, Cq), 35.1 (d, J(C,P)=2.2 Hz, CH2), 33.6 (s, CH2), 30.0 (d, J(C,P)=13.4
Hz, CH) ppm. 31P NMR (243 MHz, 303 K, CDCl3): δ=25.71 (t, 1J(P,H)=452.8 Hz) ppm.
9-Phosphinodiamantan-4-ol (36). 9ꢀHydroxydiamantꢀ4ꢀyl phosphonic dichloride (14)
(0.050 g, 0.16 mmol) was placed in a 5 mL two neck flask under argon and cooled to a
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temperature between –78 °C and –60 °C while 0.5 mL dry THF were added. The LiAlH4
solution (0.19 mL, 1 M in THF, 0.2 mmol, 1.3 equiv) was added dropwise for 10 minutes.
The mixture was stirred at –10 °C during 5 h. Reaction was quenched with HCl 5% (0.5 mL)
followed by extraction with cold dichloromethane (3x3 mL) and drying over MgSO4. The
solvent was removed in vacuo affording 9ꢀphosphinodiamantanꢀ4ꢀol (36) (0.028 g, 76%) as a
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white powder. H NMR (500 MHz, CDCl3): δ=2.68 (d, 2H, JPꢀH=192.85 Hz), 1.93–1.86 (m,
3H), 1.82–1.78 (m, 6H), 1.77–1.71 (m, 3H), 1.71–1.67 (m, 6H), 1.52 (br, 1H, OH) ppm. 13С
NMR (125 MHz, CDCl3): δ=67.3 (s, C), 45.3 (s, CH2), 44.6 (d, CH2, J=8.75 Hz), 38.7 (s,
CH), 37.1 (d, CH, J=8.75 Hz), 26.9 (d, C, J=2.5 Hz) ppm. 31P{1H} NMR (202 MHz,
CDCl3): δ= –85.7 ppm. HRMS (EI) m/z: [M]+ Calcd for C14H21OP 236.1330; Found:
236.1340.
(9-Chlorodiamant-4-yl)phosphine (37). (9ꢀChlorodiamantꢀ4ꢀyl)phosphonic dichloride (12)
(0.051 g, 0.15 mmol) was placed in a 5 mL flask under argon and dissolved in 0.5 mL of dry
THF. The obtained clear solution was cooled to –40 °C and 0.15 mL LiAlH4 (1 M in THF,
1.2 equiv) were added dropwise for 10 minutes. The mixture was stirred at –10 °C during
4.5 h. The reaction was quenched with HCl 5% (0.5 mL) followed by extraction with cold
dichloromethane (3x3 mL) and drying over MgSO4. The solvent was removed in vacuo
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affording (9ꢀchlorodiamantꢀ4ꢀyl)phosphine (37) (0.030 g, 79%) as a white powder. H NMR
(600 MHz, CDCl3): δ=2.70 (d, 2H, JPꢀH=192 Hz), 2.12–2.11 (m, 6H), 1.89 (br s, 3H), 1.82 (br
s, 3H), 1.80–1.78 (m, 6H) ppm. 13С NMR (150 MHz, CDCl3): δ=67.3 (s, C), 47.7 (s, CH2),
44.4 (d, CH2, J=9 Hz), 39.5 (s, CH), 36.6 (d, CH, J=7.5 Hz), 26.6 (s, C) ppm. 31P{1H} NMR
(243 MHz, CDCl3): –85.9 ppm. HRMS (EI) m/z: [M+O+Na]+ Calcd for C14H20ClNaOP
293.0833; Found: 293.0832.
4-Diamantylphenylphosphine (38) was isolated in 85% yield as a white solid using the
general procedure for the preparations of diamondoid phosphines in benzene/ether, m.p. 96–
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98 °C. H NMR (600 MHz, 223 K, CDCl3): δ=7.50–7.40 (m, 2H), 7.30–7.23 (bs, 3H), 3.87
(d, 1H, JPꢀH=218 Hz), 1.80–1.71 (bs, 5H), 1.70–1.56 (m, 14H) ppm. 13С NMR (150 MHz,
248 K, CDCl3): δ=135.5 (d, CH, J=14 Hz), 132.2 (d, C, J=12 Hz), 128.1 (CH), 127.8 (d, CH,
J=6 Hz), 42.2 (d, CH2, J=9 Hz), 38.2 (d, CH, J=8 Hz), 37.7 (CH2), 36.2 (CH), 25.4 (CH)
ppm. 31P NMR (243 MHz, CDCl3, H3PO4): δ= –8.6 (bs, 293 K, d, J=216.6 Hz, 243 K) ppm.
HRMS (EI) m/z: [M]+ Calcd for C20H25P: 296.1694; Found: 296.1692.
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1-Diamantylphenylphosphine (39) was isolated in 75% yield as a colorless solid using the
general procedure for the preparations of diamondoid phosphines in benzene/ether, m.p. 147–
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148 °C. H NMR (400 MHz, 253 K, CDCl3): δ=7.42 (m, 2H), 7.31 (m, 3H), 4.10 (d, 1H, JPꢀ
H=144 Hz), 2.62 (AB, 2H, JAB=12 Hz), 1.82–1.71 (m, 4H), 1.70–1.43 (m 17H), ppm. 13С
NMR (100 MHz, 253 K, CDCl3): δ=135.8 (d, CH, J=10 Hz), 133.1 (d, C, J=11.5 Hz), 128.1
(CH), 127.9 (d, CH, J=4.8 Hz), 43.8 (d, CH2, J=1.8 Hz), 39.7 (d, CH, J=3 Hz), 39.3 (d, C,
J=9 Hz), 38.9 (d, CH2, J=1.8 Hz), 38.8 (d, CH, J=9 Hz), 38.6 (d, CH, J=2 Hz), 38.3 (CH2),
38.2 (d, CH, J=5 Hz), 37.9 (CH2), 37.7 (CH2), 37.2 (d, CH, J=4 Hz), 33.9 (d, CH2, J=5.5 Hz),
33.6 (d, CH2, J=5.5 Hz), 27.3 (d, CH, J=3 Hz), 26.3 (CH) ppm. 31P NMR (162 MHz, 253 K,
CDCl3, H3PO4, 235 K): δ= –24.0 (d, J=144 Hz) ppm. HRMS (EI) m/z: [M]+ Calcd for
C20H25P: 296.1694; Found: 296.1702.
Tribenzyl(9-hydroxydiamantan-4-yl)phosphonium
bromide
(40).
9ꢀ
Phosphinodiamantanꢀ4ꢀol (36) (0.050 g, 0.21 mmol) and dry toluene (2 mL) were placed
under argon in a 5 mL flask equipped with a reflux system. Benzyl bromide (0.06 mL, 0.50
mmol, 2.4 equiv) was slowly added at r.t. The resulting colorless solution was heated at 100
oC for 16 h; a white precipitate formed which was filtered and rinsed with toluene, diethyl
ether and dried in air. Purification by column chromatography on silica gel with eluent
diethyl ether:methanol (3:1) gave tribenzyl(9ꢀhydroxydiamantanꢀ4ꢀyl)phosphonium bromide
(40). The crystals were grown in ethanol (0.020 g, 16%); the Xꢀray structure is available in
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the SI, page S165. H NMR (600 MHz, 300 K, CD3OD) δ=7.43–7.37 (m, 9H), 7.22–7.17 (m,
6H), 3.84 (d, J=13.3 Hz, 6H), 1.99–1.94 (m, 6H), 1.94–1.90 (m, 3H), 1.88–1.83 (m, 3H),
1.69 (d, J=2.7 Hz, 6H) ppm. 13C NMR (150 MHz, 300 K, CD3OD): δ=132.1 (d, J(C,P)=4.8
Hz, CH), 130.7 (d, J(C,P)=2.3 Hz, CH), 129.8 (d, J(C,P)=3.1 Hz, CH), 129.7 (d, J(C,P)=8.2
Hz, Cq), 66.9 (s, Cq), 45.3 (s, CH2), 39.4 (s, CH), 36.8 (d, J(C,P)=10.3 Hz, CH), 35.5 (s,
CH2), 25.1 (d, J(C,P)=41.3 Hz, CH2) ppm. 31P{1H} NMR (243 MHz, 300 K, CD3OD):
δ=27.51 ppm.
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1-Adamantyldiphenylphosphine oxide (41). 1ꢀAdamantylphophonic dichloride (16) (1.01
g, 4 mmol) and 15 mL of freshly distilled dry THF were placed under argon in a 50 mL flask
equipped with a reflux system. It was cooled to –78 oC and phenyllithium (5.0 mL, 1.8 M in
dibutyl ether, 9 mmol, 2.25 equiv) was slowly added with a syringe and stirred for 30 minutes
at the same temperature, for 40 minutes at r.t., and for 24 h at 60 °C. Distilled water (10 mL)
was added and water phase was extracted with diethyl ether (3x20 mL) and DCM (3x20 mL).
The combined organic phases were dried over MgSO4 and the solvent was evaporated to
yield the crude product. Purification by column chromatography on silica gel was performed
first with pentane as the eluent, then with diethyl ether:ethanol (9:1). A second column
chromatography on silica gel was done with diethylether:methanol (9:1) but failed to remove
all the impurities. The fractions containing the product were then recrystallized from warm
methanol (60 °C) to give pure 1ꢀadamantyldiphenylphosphine oxide (41) (0.772 g, 57%).
The Xꢀray structure is available in the SI, page S170. 1H NMR (400 MHz, 296 K, CDCl3):
δ=8.06–7.91 (m, 4H), 7.63–7.43 (m, 6H), 2.03–1.88 (m, 9H), 1.80–1.60 (m, 6H) ppm. 13C
NMR (100 MHz, 300 K, CDCl3): δ=132.4 (d, J(C,P)=7.9 Hz, CH), 131.5 (d, J(C,P)=2.6 Hz,
CH), 130.8 (d, J(C,P)=90.0 Hz, Cq), 128.4 (d, J(C,P)=10.9 Hz, CH), 37.2 (d, J(C,P)=72.5 Hz,
Cq), 36.6 (d, J(C,P)=1.3 Hz, CH2), 35.5 (d, J(C,P)=1.8 Hz, CH2), 27.7 (d, J(C,P)=10.3 Hz,
CH) ppm. 31P{1H} NMR (162 MHz, 296 K, CDCl3, H3PO4 external standard): δ=34.30 ppm.
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HRMS (EI) m/z: [M]+ Calcd for C22H25PO: 336.1643; Found: 336.1640. Anal. Calcd for
C22H25PO: C, 78.55; H, 7.49, Found: C, 78.44; H, 7.58.
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(3-Hydroxyadamant-1-yl)diphenylphosphine oxide (42).
(3ꢀHydroxyadamantꢀ1ꢀyl)
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phosphonic dichloride (17) (0.269 g, 1 mmol) and fresh distilled dry THF (9 mL) were placed
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under argon in a two neck 25 mL flask cooled to –78 C. Phenyllithium (1.8 mL, 1.8 M in
dibutylether, 3.3 mmol, 3.25 equiv) was slowly added with a syringe. The mixture was
stirred for 1 h at –78 °C, and further 18 h at r.t. Distilled water (4.5 mL) was added and water
phase was extracted with diethyl ether (30 mL) and DCM (30 mL). The combined organic
phases were dried over MgSO4 the solvent was evaporated and the crude compound (0.302 g)
was obtained. It was recrystallized from DCM/hexane to get crystals of 42 (0.269 g, 76%).
The Xꢀray structure is available in the SI, page S174. 1H NMR (600 MHz, 294 K, CDCl3):
δ=7.98–7.93 (m, 4H), 7.56–7.51 (m, 2H), 7.51–7.45 (m, 4H), 2.28–2.21 (m, 2H), 1.96 (s, 1H,
OH), 1.89 (d, J=5.4 Hz, 2H), 1.87–1.75 (m, 4H), 1.66 (ABq, ꢁδAB=0.03, JAB=12 Hz, 4H),
1.55 (s, 2H) ppm. 13C NMR (150 MHz, 294 K, CDCl3): δ=132.4 (d, J(C,P)=8.4 Hz, CH),
131.7 (d, J(C,P)=2.9 Hz, CH), 130.3 (d, J(C,P)=91.1 Hz, Cq), 128.5 (d, J(C,P)=11.1 Hz, CH),
68.1 (d, J(C,P)=12.5 Hz, Cq), 44.4 (s, CH2), 43.1 (s, CH2), 40.4 (d, J(C,P)=72.0 Hz, Cq), 35.1
(s, CH2), 34.3 (s, CH2), 30.3 (d, J(C,P)=11.3 Hz, CH) ppm. 31P{1H} NMR (243 MHz,294 K,
CDCl3): δ=32.38 ppm.
4-Diamantyldiphenylphosphine oxide (43). 4ꢀDiamantylphophonic dichloride (19) (0.122
g, 0.4 mmol) and 1.5 mL of fresh distilled dry THF were placed under argon in a 5 mL flask.
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It was cooled to –78 C and phenyllithium (0.5 mL, 1.8 M in dibutyl ether, 0.9 mmol, 2.25
equiv) was slowly added with a syringe. The mixture was stirred for 4 h at the same
temperature, and for 42 h at r.t. Distilled water (1 mL) was added followed by saturated
NH4Cl (3 mL) and diethyl ether (10 mL). The water phase was extracted with diethyl ether
(2x10 mL) and dichloromethane (3x10 mL). The combined organic phases were dried over
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