Synthesis and crystal structure of a novel heterocyclic compound bearing a pentacoordinate germanium atom and a deprotonated HMPA moiety

Article abstract of DOI:10.1021/om0206608

The synthesis and crystal structure of a novel heterocyclic compound, 1,3,2,5-oxazaphosphagermolidin-2-ium-5-uide, was analysed. The compound was synthesized by sequential treatment of hexamethylphosphoric triamide (HMPA) with t-BuLi and a hydrogermane. Crystal structure of the compound was examined by x-ray crystallography. The analysis confirmed the intramolecular coordination of the oxygen atom to the germanium atom in both crystalline and solution states.

Full text of DOI:10.1021/om0206608

1152
Organometallics 2003, 22, 1152-1155
Notes
Syn th esis a n d Cr ysta l Str u ctu r e of a Novel Heter ocyclic
Com p ou n d Bea r in g a P en ta coor d in a te Ger m a n iu m Atom
a n d a Dep r oton a ted HMP A Moiety
Naokazu Kano, Satoshi Goto, and Takayuki Kawashima*
Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-0033, J apan
Received August 15, 2002
Sch em e 1a
Summary: A novel heterocyclic compound, 1,3,2,5-ox-
azaphosphagermolidin-2-ium-5-uide, was synthesized by
sequential treatment of HMPA with t-BuLi and a
hydrogermane, and its crystal structure was established
by X-ray crystallographic analysis.
Hexamethylphosphoric triamide (HMPA) has been
known to be one of the most useful solvents and
additives in organic synthesis because of its high
solvating power and coordination ability as an aprotic
polar molecule.1 The coordination ability of HMPA has
been utilized as a monodentate ligand for the construc-
tion of several main-group-element species with high
coordination states.2 If a heavier main-group element
with high Lewis acidity is introduced in the vicinity of
an HMPA moiety, a new type of heterocycle bearing a
high-coordinate main-group element and an HMPA
moiety could be constructed by the successive intramo-
lecular coordination of the oxygen atom to the main-
group element. Metalation of HMPA is expected to be a
direct and facile method for the synthesis of such a
heterocyclic compound. To the best of our knowledge,
however, metalation of a part of HMPA as a substrate
is limited to one example of the proton abstraction from
the methyl group of HMPA by sec-BuLi at low temper-
ature.3 In our study on the generation of germyllithium
by abstraction of a proton from a hydrogermane bearing
the Martin ligand,4 this method was found to be useful
for the synthesis of a heterocycle including a deproto-
nated HMPA moiety as its component. We report here
the synthesis and structure of a novel heterocyclic
compound bearing both a pentacoordinate germanium
atom and a deprotonated HMPA moiety in the ring. The
Martin ligand was used for stabilization of the penta-
coordinate state of the germanium atom.
a
Legend: (a) CF3SO3H (1.2 equiv), 0 °C to room tempera-
ture, CHCl3; (b) evaporation; (c) LiAlH4 (4.0 equiv), room
temperature, Et2O; (d) aqueous NaHCO3, room temperature;
(e) t-BuLi (1.0 equiv), -30 °C, dimethoxymethane; (f) 2 (1.0
equiv), -30 °C to room temperature; (g) aqueous NH4Cl.
Resu lts a n d Discu ssion
Hydrogermane 2 was prepared in 60% yield by
treatment of diphenylgermane 1 bearing the Martin
ligand with trifluoromethanesulfonic acid (1.2 equiv) in
CHCl3 at 0 °C, followed by reduction of the resulting
germyl triflate with lithium aluminum hydride (4.0
equiv) in Et2O at room temperature after the exchange
of the solvent5 (Scheme 1). t-BuLi (1.0 equiv) and
hydrogermane 2 (1.0 equiv) were sequentially added to
a dimethoxymethane solution of HMPA at -30 °C. The
reaction mixture was gradually warmed to room tem-
perature, quenched with aqueous NH4Cl, and separated
by chromatography to give the compound 3 (57%)
together with tert-butylgermane 4 (35%). The H, 13C,
1
19F, and 31P NMR spectral data show that 3 contains
both the Martin ligand and a deprotonated HMPA
moiety. The structure of 3 was finally determined by
X-ray crystallographic analysis, as shown in Figure 1.
Selected bond lengths and angles are shown in Table
1. The 1,3,2,5-oxazaphosphagermolidine ring exists in
the envelope form close to the planar form; in the
former, the O1 atom is located at the tip slightly above
the least-squares plane defined by the other four atoms,
(1) (a) Fieser, L. F.; Fieser, M. In Reagents for Organic Synthesis;
Wiley: New York, 1967; Vol. 1, p 430. (b) Normant, H. Angew. Chem.,
Int. Ed. Engl. 1967, 6, 1046. (c) Morrison, R. T.; Boyd, R. N. In Organic
Chemistry, 5th ed.; Allyn and Bacon: Boston, MA, 1987; p 230.
(2) For examples, see: (a) Yatsenko, A. V.; Aslanov, L. A.; Schenk,
H. Polyhedron 1995, 14, 2371. (b) Ivor, W.; Simard, M. G. Inorg. Chim.
Acta 1998, 282, 30. (c) Ko, B.-T.; Wu, C.-C.; Lin, C.-C. Organometallics
2000, 19, 1864.
(3) Magnus, P.; Roy, G. Synthesis 1980, 575.
(4) A bidentate ligand, -C6H4C(CF3)2O-, was developed by Martin
for stabilizing hypervalent species. See: Perozzi, E. F.; Michalak, R.
S.; Figuly, G. D.; Stevenson, W. H., III; Dess, D. B.; Ross, M. R.; Martin,
J . C. J . Org. Chem. 1981, 46, 1049.
(5) Kawashima, T.; Nishiwaki, Y.; Okazaki, R. J . Organomet. Chem.
1995, 499, 143.
10.1021/om0206608 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 01/31/2003

Notes
Organometallics, Vol. 22, No. 5, 2003 1153
Sch em e 2
with a polar apical bond. It indicates that 3 has a TBP
structure maintaining the coordination of an oxygen
atom of the phosphoryl group also in the solution state.
The 31P NMR signal of 3 in CDCl3 was observed at lower
field (δ 32.4) than that of free HMPA (δ 25.9). In the
31P CP-MAS solid-state NMR spectra, the signal was
observed in a region (δ 32.5) similar to that in the
solution state. In the IR spectrum of 3, a PdO stretching
band was observed at 1180 and 1187 cm-1 in the KBr
disk and in CCl4 solution, respectively, which are lower
than that of HMPA (1205 cm-1).9 These results are
consistent with the cationic character of the phosphorus
atom in 3 as the result of the coordination of the oxygen
atom to the germanium atom. The betaine structure,
-Ge--O-P+-N-C-, should contribute to the struc-
ture of 3, although the formal negative charge on the
germanium atom seems to be localized on the apical
oxygen atoms. The combination of the electron-with-
drawing property of the Martin ligand and high coor-
dination ability of an HMPA moiety should result in the
maintenance of the Ge-O interaction even in the
solution state.
F igu r e 1. ORTEP drawing of 3 (thermal ellipsoids are at
the 50% probability level for all non-hydrogen atoms).
Ta ble 1. Selected Bon d Dista n ces a n d An gles for 3
(a) Bond Distances (Å)
Ge1-O1
Ge1-O2
Ge1-C1
Ge1-C2
Ge1-C3
2.1746(14)
1.9106(13)
1.9644(18)
1.9421(17)
1.9529(18)
P1-O1
P1-N1
P1-N2
P1-N3
C1-N1
1.5060(13)
1.6309(16)
1.6410(16)
1.6426(16)
1.457(2)
(b) Bond Angles (deg)
The formation mechanism of 3 was reasonably ex-
plained as follows (Scheme 2). Deprotonation of the
HMPA molecule with t-BuLi gives the corresponding
alkyllithium 5 (LiCH2(Me)N(Me2N)2PdO) similarly to
the method reported in the literature,3 and successive
nucleophilic substitution of the alkyllithium 5 at the
germanium atom results in the formation of 3 with
elimination of lithium hydride followed by intramolecu-
lar coordination. Competitive substitution of t-BuLi at
the germanium atom of 2 gave the corresponding tert-
butylgermane 4. We have independently confirmed the
first process: the generation of 5 by the reaction of
HMPA with t-BuLi. Furthermore, treatment of hydro-
germane 2 with t-BuLi and successive addition of
benzophenone gave not the adduct of the corresponding
germyllithium and benzophenone but tert-butylgermane
4 in good yield, as judged by NMR spectra, suggesting
that nucleophilic substitution of alkyllithiums at the
germanium atom of 2 took place instead of deprotona-
tion. Although the coordination of HMPA or 5 to the
germanium atom of 2 to form a pentacoordinated
structure might cooperatively increase the electrophi-
licity of the germanium atom and facilitate the substi-
tution of 2 along with elimination of a hydride, such a
coordination was not confirmed by the low-temperature
31P NMR experiments of a THF solution of 2 and HMPA
(-60 °C).
O1-Ge1-O2
C1-Ge1-C2
C1-Ge1-C3
C2-Ge1-C3
C1-Ge1-O1
171.52(5)
123.34(8)
114.92(8)
121.30(7)
84.85(6)
Ge1-C1-N1
113.01(12)
120.22(12)
105.45(8)
111.86(7)
C1-N1-P1
N1-P1-O1
P1-O1-Ge1
i.e., Ge1, C1, N1, and P1. This five-membered-ring
system is interesting as a novel heterocyclic system
constituted of C, N, O, P, and Ge elements.6 Compound
3 has a slightly distorted trigonal-bipyramidal (TBP)
structure with two oxygen atoms at apical positions and
three carbon atoms at equatorial positions, respectively
(% TBP f SP, 24%).7 The Ge1-O1 bond length (2.1746-
(14) Å) is much shorter than the sum of the correspond-
ing van der Waals radii (3.50 Å). The P1-O1 bond
length (1.5060(13) Å) is longer and the P1-N1 bond
length (1.6309(16) Å) is shorter than those of HMPA
(1.477(1) and 1.652 Å (average)), respectively, suggest-
ing a strong intramolecular interaction between ger-
manium and oxygen atoms as well as a slight pertur-
bation on the bond lengths of 3 compared to those of
HMPA in the solid state.8
1
In the H NMR spectrum, the signal due to the ortho
proton of the Martin ligand was observed at δ 8.26-
8.28 in CDCl3. Such a downfield shift is one of the
typical features of the trigonal-bipyramidal structure
(6) For a 1,5,3,2-oxazaphosphagermolidine, see: Ranaivonjatovo, H.;
Escudie´, J .; Couret, C.; Satge´, J . J . Organomet. Chem. 1991, 415, 327.
(7) Holmes, R. R.; Deiters, J . A. J . Am. Chem. Soc. 1977, 99, 3318.
(8) Mitzel, N. W.; Lustig, C. J . Chem. Soc., Dalton Trans. 1999, 3177.
(9) Bollinger, J . C.; Yvernault, G.; Yvernault, T. Spectrochim. Acta
1985, 41A, 399.

1154 Organometallics, Vol. 22, No. 5, 2003
Notes
1-Phenyl-3,3-bis(trifluoromethyl)-1,3-dihydro-2,1-benzoxager-
mole (2): colorless viscous oil; H NMR (500 MHz, CDCl3) δ
6.95 (s, 1H), 7.43-7.46 (m, 2H), 7.50-7.51 (m, 1H), 7.52-7.56
(m, 2H), 7.59-7.62 (m, 2H), 7.69-7.70 (m, 1H), 7.81-7.82 (m,
The reactivities of 3 with organolithium reagents were
tentatively investigated in anticipation of the substitu-
tion at the pentacoordinate germanium atom of 3.
Treatment of 3 with phenyllithium (1.4 equiv) or tert-
butyllithium (1.3 equiv) at -30 °C in THF followed by
gradual warming to room temperature resulted in the
almost quantitative recovery of 3 without formation of
1 and 4.
In summary, we have shown the formation of the
novel heterocyclic compound 3 using deprotonated
HMPA as a component. Intramolecular coordination of
the oxygen atom to the germanium atom was confirmed
in both crystalline and solution states.
1
2
1H); 13C{1H} NMR (125 MHz, CDCl3) δ 85.19 (sept, J CF
)
1
1
29.9 Hz), 122.99 (q, J CF ) 286.4 Hz), 123.19 (q, J CF ) 286.5
Hz), 126.17 (m), 128.87, 130.67, 130.85, 131.68, 132.00, 132.96
(ipso), 134.18 (ipso), 134.22, 139.90 (ipso); 19F NMR (254 MHz,
CDCl3) δ -76.65 (q, J FF ) 9.1 Hz, 3F), -75.95 (q, J FF ) 9.1
Hz, 3F); HRMS m/z calcd for C15H10F674GeO 393.9848, found
393.9828. Anal. Calcd for C15H10F6GeO‚0.24H2O: C, 45.36; H,
2.66. Found: C, 45.10; H, 3.21.
4
4
Syn th esis of Heter ocycle 3. To a solution of HMPA (71
µL, 0.41 mmol) in dimethoxymethane (2 mL) at -30 °C was
added dropwise a pentane solution of t-BuLi (2.26 M, 0.18 mL,
0.41 mmol). The reaction mixture was stirred for 2 h, treated
with 2 (158 mg, 0.40 mmol), and gradually warmed to room
temperature. The reaction mixture was quenched with aque-
ous NH4Cl, worked up in the usual manner, and separated by
chromatography to give 3 (131 mg, 57%) and 4 (64 mg, 35%).
2′,2′-Bis(dimethylamino)-3′-methyl-1-phenyl-3,3-bis(trifluo-
romethyl)-3H-spiro[2,1-benzoxagermole-1,5′-[1,3,2,5]oxaza-
Exp er im en ta l Section
Gen er a l Meth od s. All experiments were performed under
an argon atmosphere unless otherwise noted. Solvents were
dried by standard methods and freshly distilled prior to use.
1H (500 MHz) and 13C (125 MHz) NMR spectra were recorded
on a Bruker DRX500 spectrometer using tetramethylsilane as
internal standard. 19F (254 MHz) and 31P (109 MHz) NMR
spectra were recorded on a J EOL EXcalibur270 spectrometer
using Freon and 85% H3PO4 as external standards, respec-
tively. CP-MAS solid-state 31P (122 MHz) NMR spectra were
recorded on a Chemagnetics CMX-300 spectrometer using a
zirconia rotor (5 mm diameter) at 6.0 kHz in air with
triphenylphosphine as an external standard. Silica gel column
chromatography was carried out with Wakogel C-200. Pre-
parative gel permeation liquid chromatography (GPLC) was
performed with an LC-908 instrument with J AIGEL 1H and
2H columns (J apan Analytical Industry) and chloroform as
solvent. Melting points were determined on a Yanaco micro
melting point apparatus and were uncorrected. Elemental
analyses were carried out at the Microanalytical Laboratory
of the Department of Chemistry, Faculty of Science, The
University of Tokyo.
phosphagermolidin]-2′-ium-1-uide (3): colorless crystals; mp
3
120-121 °C dec; 1H NMR (500 MHz, CDCl3) δ 2.43 (d, J PH
)
3
10.0 Hz, 6H, N(CH3)2), 2.58 (d, J PH ) 10.0 Hz, 6H, N(CH′3)2)
2.64 (d, J PH ) 9.4 Hz, 3H, CH2NCH3), 3.00 (dd, J PH ) 6.2
3
3
2
3
Hz, J HH ) 11.8 Hz, 1H, GeCHH), 3.26 (dd, J PH ) 13.5 Hz,
2J HH ) 11.8 Hz, 1H, GeCHH), 7.26-7.30 (m, 3H), 7.45-7.51
(m, 2H), 7.70-7.71 (m, 1H), 7.74-7.76 (m, 2H), 8.26-8.28 (m,
1H); 13C{1H} NMR (125 MHz, CDCl3) δ 36.20 (d, J PC ) 4.9
2
2
Hz, CH2N(CH3)), 36.61 (d, J PC ) 4.0 Hz, N(CH3)2), 36.78 (d,
2J PC ) 3.7 Hz, N(C′H3)2), 44.14 (d, J PC ) 8.5 Hz, GeCH2N),
2
2
1
82.62 (sept, J CF ) 29.1 Hz, C(CF3)2), 123.84 (q, J CF ) 287.5
1
Hz, CF3), 124.15 (q, J CF ) 287.5 Hz, C′F3), 125.70 (s), 127.55
(s), 128.67 (s), 129.26 (s), 129.77 (s), 133.46 (s), 134.43 (s),
137.75 (s, ipso), 140.21 (s, ipso), 140.38 (s, ipso); 19F NMR (254
4
4
MHz, CDCl3) δ -76.35 (q, J FF ) 8.6 Hz, 3F), -75.93 (q, J FF
) 8.6 Hz, 3F); 31P NMR (109 MHz, CDCl3) δ 32.4 (s); IR (KBr)
1180 cm-1 (s, νPdO). Anal. Calcd for C21H26F6GeN3O2P: C,
44.25; H, 4.60; N, 7.37. Found: C, 44.51; H, 4.52; N, 7.18.
1-tert-Butyl-1-phenyl-3,3-bis(trifluoromethyl)-1,3-dihydro-2,1-
benzoxagermole (4): colorless crystals; mp 112.1-113.8 °C; 1H
NMR (500 MHz, CDCl3) δ 1.23 (s, 9H), 7.36-7.42 (m, 3H),
7.52-7.58 (m, 4H), 7.73-7.77 (m, 2H); 13C{1H} NMR (125
Syn th esis of Dip h en ylger m a n e 1. According to the
literature,5 to a solution of dibromodiphenylgermane (1.27 g,
3.3 mmol) in THF (10 mL) at -72 °C was added dropwise the
dilithio derivative of 2,2,2,2′,2′,2′-hexafluorocumyl alcohol,
which was prepared from hexafluorocumyl alcohol (0.53 mL,
3.2 mmol), n-BuLi (1.59 M, 4.4 mL, 7 mmol), and TMEDA (0.11
mL, 0.7 mmol) in THF (0.5 mL).4 The reaction mixture was
warmed to room temperature, stirred for 1 h, and quenched
with aqueous NH4Cl. After the usual workup, the crude
material was separated with column chromatography on silica
gel (hexane-CH2Cl2) to give 1 (549 mg, 37%). 1,1-Diphenyl-
3,3-bis(trifluoromethyl)-1,3-dihydro-2,1-benzoxagermole (1): col-
2
MHz, CDCl3) δ 26.87, 28.68, 85.10 (sept, J CF ) 30.4 Hz),
123.10 (q, 1J CF ) 286.5 Hz), 123.29 (q, 1J CF ) 287.5 Hz), 126.21,
128.41, 130.17, 130.25, 130.31, 131.85, 133.31, 134.29, 135.90,
4
140.04; 19F NMR (254 MHz, CDCl3) δ -76.14 (q, J FF ) 9.1
Hz, 3F), -75.11 (q, 4J FF ) 9.1 Hz, 3F). Anal. Calcd for C19H18F6-
GeO: C, 50.83; H, 4.04. Found: C, 50.68; H, 4.06.
Rea ction of 2 w ith t-Bu Li. To a solution of 2 (71.3 mg,
0.18 mmol) in THF (2 mL) at -78 °C was added a pentane
solution of t-BuLi (2.14 M, 0.17 mL, 0.36 mmol). The reaction
mixture was stirred for 2 h, quenched with benzophenone (38.1
mg, 0.21 mmol), and gradually warmed to room temperature.
The usual workup afforded a colorless crude solid which
contains 3 in 90% yield, as judged by NMR spectra.
Attem p ted Rea ction of 3 w ith P h Li. To a solution of 3
(28.9 mg, 0.051 mmol) in THF (3 mL) at -30 °C was added a
cyclohexanes-ether solution of PhLi (1.02 M, 0.07 mL, 0.071
mmol). The reaction mixture was stirred for 2 h and gradually
warmed to room temperature. The usual workup and separa-
tion resulted in the recovery of 3 (21.7 mg, 75%).
Attem p ted Rea ction of 3 w ith t-Bu Li. Similarly to the
reaction with PhLi, the reaction of 3 (29.0 mg, 0.051 mmol)
with a pentane solution of t-BuLi (2.15 M, 0.03 mL, 0.065
mmol) resulted in the recovery of 3 (22.4 mg, 77%).
X-r a y Da ta Collection a n d Str u ctu r e Refin em en t of
3. Colorless single crystals of 3 were grown by the slow
evaporation of its saturated solution in hexane at room
1
orless crystal; mp 104-107 °C; H NMR (500 MHz, CDCl3) δ
7.42-7.45 (m, 4H), 7.48-7.51 (m, 2H), 7.59-7.60 (m, 6H),
7.75-7.77 (m, 1H), 7.82-7.83 (m, 1H); 13C{1H} NMR (125
2
1
MHz, CDCl3) δ 84.84 (sept, J CF ) 30.1 Hz), 123.18 (q, J CF
)
287.8 Hz), 126.23 (m), 128.74, 130.62, 130.73, 131.17, 132.02,
132.63 (ipso), 134.27, 135.02 (ipso), 140.01 (ipso); 19F NMR
(254 MHz, CDCl3) δ -75.84 (s, 6F); HRMS m/z calcd for
C
C
21H14F674GeO 470.0161, found 470.0174. Anal. Calcd for
21H14F6GeO: C, 53.79; H, 3.01. Found: C, 53.91; H, 3.10.
Syn th esis of Hyd r oger m a n e 2. To a solution of 1 (931
mg, 1.99 mmol) in CHCl3 (20 mL) was added trifluoromethane-
sulfonic acid (0.22 mL, 2.5 mmol) at 0 °C. The reaction mixture
was warmed to room temperature and stirred for 5 h. To
change the solvent, the original solvent was evaporated in
vacuo and ether (10 mL) was added to the residue. The
resulting mixture was added to a suspension of lithium
aluminum hydride (309 mg, 8.14 mmol) in ether (20 mL) at
room temperature to give a green-brown solution, which was
stirred for 15 h. The usual workup and separation with HPLC
(CHCl3 as eluent) gave the hydrogermane 2 (561 mg, 60%).
temperature. Crystal data of 3:
C21H26F6GeN3O2P, fw )

Notes
Organometallics, Vol. 22, No. 5, 2003 1155
570.01, monoclinic, space group P21/n, Z ) 8, a ) 16.288(5) Å,
b ) 14.097(4) Å, c ) 21.237(6) Å, â ) 97.358(5)°, V ) 4836(3)
Å3, Dcalcd ) 1.566 g cm-3, µ ) 1.403 mm-1, T ) 120 K. A
colorless crystal of 3 having dimensions of 0.30 × 0.30 × 0.05
mm was mounted within a loop. The data set was collected on
Ack n ow led gm en t. This work was partially sup-
ported by a Grant-in-Aid for Scientific Research from
the Ministry of Education, Culture, Sports, Science and
Technology of J apan. We are grateful to Central Glass
and Tosoh Finechem Corp. for the gifts of organofluorine
compounds and alkyllithiums, respectively.
a
Rigaku MERCURY CCD diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.710 69 Å) to 2θmax
)
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data of 3. This material is available free of charge
via the Internet at http://pubs.acs.org. These data also have
been deposited with the Cambridge Crystallographic Data
Centre as Supplementary Publication No. CCDC-185065.
Copies of the data can be obtained free of charge on application
to the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax,
(+44)1223-336-033; e-mail, deposit@ccdc.cam.ac.uk).
55°. The structure was solved by direct methods with SIR-97
and refined with SHELXL-97. The intensities were corrected
for Lorentz and polarization effects. The non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were placed
using AFIX methods. The final cycle of full-matrix least-
squares refinement was based on 10 761 observed reflections
and 623 variable parameters and converged to R1 ) 0.032
(I > 2.00σ(I)) and wR2 ) 0.073 (all data) with GOF )
1.119.
OM0206608