Borabenzene adducts of ylidic lewis bases. Syntheses and structures of 3,5-Me2C5H3BCH2PPh3, 3,5-Me2C5H3BCH(SiMe3)PPh3 , and C5H5BN(Ph)PPh3

Article abstract of DOI:10.1021/om011081q

The methylenephosphorane Ph₃PCH₂ reacts with 1-chloro-3,5-dimethyl-2-(trimethylsilyl)1,2-dihydroborinine (2c) (in a 2/1 ratio) at ambient temperature to produce (triphenylphosphonio)methanide-3,5-dimethylborabenzene, 3,5-Me₂C₅H₃BCH₂PPh₃ (3), with 1 equiv of (Ph₃PCH₂SiMe₃)Cl (4), and (trimethylsilyl)(triphenylphosphonio)methanide-3,5-dimethylborabenzene, 3,5-Me₂C₅H₃BCH(SiMe₃)PPh₃ (5), with 1 equiv of (PMePh₃)Cl (6). Both adducts 3 and 5 are yellow crystalline compounds. Treatment of the iminophosphorane Ph₃PNPh with an isomer mixture of 1-chloro(trimethylsilyl)dihydroborinines (8) produces Af-(triphenylphosphonio)anilide-borabenzene C₅H₅BN(Ph)PPh₃ (9) as brown-yellow crystals. The reaction of PMe₃ with 2c affords the colorless trimethylphosphine adduct 3,5-Me₂C₅H₃BPMe₃ (10). The structures of the new adducts 3, 5, and 9 are reported. They do not show conjugation between the two remote charge centers, even in the case of the iminophosphorane adduct 9.

Full text of DOI:10.1021/om011081q

Organometallics 2002, 21, 1949-1954
1949
Bor a ben zen e Ad d u cts of Ylid ic Lew is Ba ses. Syn th eses
a n d Str u ctu r es of 3,5-Me2C5H3BCH2P P h 3,
1
3,5-Me2C5H3BCH(SiMe3)P P h 3, a n d C5H5BN(P h )P P h 3
Xiaolai Zheng, Bing Wang, and Gerhard E. Herberich*
Institut fu¨r Anorganische Chemie, Technische Hochschule Aachen, D-52056 Aachen, Germany
Received December 20, 2001
The methylenephosphorane Ph3PCH2 reacts with 1-chloro-3,5-dimethyl-2-(trimethylsilyl)-
1,2-dihydroborinine (2c) (in a 2/1 ratio) at ambient temperature to produce (triphenylphos-
phonio)methanide-3,5-dimethylborabenzene, 3,5-Me2C5H3BCH2PPh3 (3), with 1 equiv of
(Ph3PCH2SiMe3)Cl (4), and (trimethylsilyl)(triphenylphosphonio)methanide-3,5-dimeth-
ylborabenzene, 3,5-Me2C5H3BCH(SiMe3)PPh3 (5), with 1 equiv of (PMePh3)Cl (6). Both
adducts 3 and 5 are yellow crystalline compounds. Treatment of the iminophosphorane Ph3-
PNPh with an isomer mixture of 1-chloro(trimethylsilyl)dihydroborinines (8) produces
N-(triphenylphosphonio)anilide-borabenzene C5H5BN(Ph)PPh3 (9) as brown-yellow crystals.
The reaction of PMe3 with 2c affords the colorless trimethylphosphine adduct 3,5-Me2C5H3-
BPMe3 (10). The structures of the new adducts 3, 5, and 9 are reported. They do not show
conjugation between the two remote charge centers, even in the case of the iminophosphorane
adduct 9.
In tr od u ction
compound of types 2a -c should be able to produce the
corresponding Lewis base adducts. Obvious new candi-
dates to be tested are methylenephosphoranes or phos-
phoniomethanides7 (traditionally called phosphonium
ylides) and isoelectronically related iminophosphoranes
or phosphonioamides,7 examples of which are the sub-
ject of this paper. We also describe a further trimeth-
ylphosphine adduct.
The pyridine adduct of borabenzene, C5H5NBC5H5 (1),
was described in 19853 and is the first example of a
Lewis base borabenzene adduct.4 Up to now 10 such
Resu lts a n d Discu ssion
borabenzene derivatives have been described, compris-
ing 7 adducts of nitrogen bases,5 1 adduct of a phos-
phorus Lewis base, Me3PBC5H5,5a 1 of an isocyanide,
ButNCBC5H5,5a and 1 of a carbene.6
The known borabenzene adducts have been synthe-
sized by treating the dihydroborinines 2a -c with a
Lewis base.3,5a,6 In the case of the starting materials
Syn th eses of Meth ylen ep h osp h or a n e Ad d u cts.
Compound 2c6 can readily be synthesized from Li(3,5-
Me2C5H3BNMe2)8 via silylation with Me3SiCl and sub-
sequent chlorodeamination with BCl3. Treatment of the
methylenephosphorane Ph3PCH29 with 2c in a 2/1 ratio
results in the formation of the two pairs of products,
the yellow adduct 3 with 1 equiv of the phosphonium
salt (Ph3PCH2SiMe3)Cl (4), and the yellow adduct 5 with
(5) (a) Hoic, D. A.; Wolf, J . R.; Davis, W. M.; Fu, G. C. Organome-
tallics 1996, 15, 1315-1318. (b) Qiao, S.; Hoic, D. A.; Fu, G. C.
Organometallics 1997, 16, 1501-1502. (c) Maier, G.; Reisenauer, H.
P.; Henkelmann, J .; Kliche, C. Angew. Chem. 1988, 100, 303; Angew.
Chem., Int. Ed. Engl. 1988, 27, 295-296. (d) Tweddell, J .; Hoic, D. A.;
Davis, W. M.; Fu, G. C. J . Org. Chem. 1997, 62, 8286-8287. (e)
Herberich, G. E.; Englert, U.; Ganter, B.; Pons, M.; Wang, R. Orga-
nometallics 1999, 18, 3406-3413.
2a ,c this reaction is presumably initiated by a reversible
addition of the Lewis base at the boron center and
subsequent elimination of Me3SiOMe or Me3SiCl to give
the desired adduct; compound 2b requires an additional
proton shift. This speculation suggests that any un-
charged nucleophile that can form an adduct with a
(6) Zheng, X.; Herberich, G. E. Organometallics 2000, 19, 3751-
3753.
(7) J ohnson, A. W. Ylides and Imines of Phosphorus; Wiley: Chich-
ester, U.K., 1993.
(8) (a) Herberich, G. E.; Englert, U.; Schmidt, M. U.; Standt, R.
Organometallics 1996, 15, 2707-2712. (b) Herberich, G. E.; Englert,
U.; Fischer, A.; Ni, J .; Schmitz, A. Organometallics 1999, 18, 5496-
5501. (c) Standt, R. Doctoral Dissertation, Technische Hochschule
Aachen, Aachen, Germany, 1995.
(1) Borabenzene Derivatives. 39. Part 38: Reference 2.
(2) Herberich, G. E.; Basu Baul, T. S.; Englert, U. Eur. J . Inorg.
Chem. 2002, 43-48.
(3) Boese, R.; Finke, N.; Henkelmann, J .; Maier, G.; Paetzold, P.;
Reisenauer, H. P.; Schmid, G. Chem. Ber. 1985, 118, 1644-1654.
(4) Fu, G. C. Adv. Organomet. Chem. 2001, 47, 101-119.
(9) (a) Bestmann, H. J .; Stransky, W.; Vostrowsky, O. Chem. Ber.
1976, 109, 1694-1700. (b) Albright, T. A.; Freeman, W. J .; Schweizer,
E. E. J . Org. Chem. 1976, 41, 2716-2720. (c) Schmidbaur, H.; J eong,
J .; Schier, A.; Graf, W.; Wilkinson, D. L.; Mu¨ller, G.; Kru¨ger, C. New
J . Chem. 1989, 13, 341-352. (d) Bart, J . C. J . J . Chem. Soc. B 1969,
350-365.
10.1021/om011081q CCC: $22.00 © 2002 American Chemical Society
Publication on Web 04/03/2002

1950 Organometallics, Vol. 21, No. 9, 2002
Zheng et al.
Sch em e 1
chloro compound 8a with a small admixture of the
isomer 8b. The commercially available N-(phosphonio)-
anilide or triphenyl(phenylimino)phosphorane Ph3-
PNPh13 smoothly reacted with the chloro compounds
8a ,b at ambient temperature to form the adduct 9 as
brown-yellow microcrystalline material and, of course,
1 equiv of Me3SiCl.
Syn th esis of a P h osp h in e Ad d u ct. The single
known phosphine adduct Me3PBC5H5 has been synthe-
sized via the 1,4-dihydroborinine 2b.5a Dihydroborinines
derived from 8a or 8b are, of course, equally suitable
sources of the borabenzene ring. Thus, the dimethyl
compound 2c reacts smoothly with trimethylphosphine
to give the 3,5-dimethyl derivative 3,5-Me2C5H3BPMe3
(10) and 1 equiv of Me3SiCl, as expected. We also learn
1 equiv of (PMePh3)Cl (6). The second pair of products,
5 and 6, results from an intervening proton-transfer
reaction (Scheme 1). Both the silylation of methylene-
phosphoranes7,10 and the proton transfer or, in this
context, transylidation reaction11 are well-known trans-
formations.
The preparative outcome of the reaction depends on
the sequence of addition. When a solution of the phos-
phorane is added dropwise to a solution of 2c, the
products are essentially the simple adduct 3 and the
salt 4. With inverse addition, the phosphorane concen-
tration in the reaction mixture is high, favoring the
proton-transfer reaction. The silylated adduct 5 is now
produced in appreciable quantities together with adduct
3 and the corresponding phosphonium chlorides.
Most previously described borabenzene adducts have
adjacent charge centers, as in 1, or at least some
conjugation between the charge centers which will
stabilize the adducts to some extent. In contrast, the
compounds 3 and 5 have only remote charge compensa-
tion and the methylene linker between the boron and
the phosphorus atoms does not allow for any conjuga-
tion. It would therefore be justified to consider 3 and 5
as derivatives of 1-methylboratabenzene, and indeed,
spectroscopic and structural comparisons (see below)
lend support to this interpretation.
that the Lewis basicity of the attacking phosphine is
crucial, since the much less basic phosphaferrocene
CpFe(3,4-Me2C4H2P)14 failed to react. This negative
result suggests that, for instance, a phosphinine-
borabenzene adduct that would be a particularly at-
tractive synthetic goal will not be easily accessible.
Cr ysta l Str u ctu r es. Crystals of 3 and 5 that were
suitable for a single-crystal structural study were
obtained from toluene; in the case of 5, the crystals
1
contained
/ mol of cocrystallized toluene. The mol-
2
ecules of 3 and 5 (Table 1, Figures 1 and 2) consist of a
planar borabenzene ring (maximum vertical deviation
of 0.010(3) Å for 3 and of 0.011(2) Å for 5), a triph-
enylphosphonio group, and a methylene or a (trimeth-
ylsilyl)methylene linker. The dihedral angle between the
borabenzene plane and the plane (B,C1,P) amounts to
63.4(2)° for 3 and to 54.3(1)° for 5. The angle C1-B-
C11 (127.0(4)°) for 3 is larger than the angle C1-B-
C15 (117.0(4)°), reflecting steric crowding and repulsion
between the C11-H11 vertex of the borabenzene ring
and the PPh3 group. This effect is somewhat less
pronounced in the sterically more crowded molecule 5
(with C1-B-C11 ) 124.9(2)° and C1-B-C15 ) 118.7-
(2)°).
Syn th esis of a n Im in op h osp h or a n e Ad d u ct. The
dihydroborinine component 8a ,b was synthesized from
Li(TMEDA)(C5H5BNMe2)12 in the usual two steps.
(10) Seyferth, D.; Grim, S. O. J . Am. Chem. Soc. 1961, 83, 1610-
1613.
(11) Schmidbaur, H. Acc. Chem. Res. 1975, 8, 62-70.
(12) (a) Herberich, G. E.; Schmidt, B.; Englert, U.; Wagner, T.
Organometallics 1993, 12, 2891-2893. (b) Herberich, G. E.; Schmidt,
B.; Englert, U. Organometallics 1995, 14, 471-480. (c) Schmidt, B.
Doctoral Dissertation, Technische Hochschule Aachen, Aachen, Ger-
many, 1994.
(13) (a) Horner, L.; Oediger, H. Liebigs Ann. Chem. 1959, 627, 142-
162. (b) Albright, T. A.; Freeman, W. J .; Schweizer, E. E. J . Am. Chem.
Soc. 1975, 97, 940-942. (c) Bo¨hm, E.; Dehnicke, K.; Beck, J .; Hiller,
W.; Stra¨hle, J .; Maurer, A.; Fenske, D. Z. Naturforsch. 1988, 43B, 138-
142.
(14) (a) Mathey, J . Organomet. Chem. 1978, 154, C13-C15. (b)
Ganter, C.; Brassat, L.; Glinsbo¨ckel, C.; Ganter, B. Organometallics
1997, 16, 2862-2867.
Treatment with Me3SiCl gave a distillable isomer
mixture 7a ,b of variable isomer ratio; after thermal
equilibration (150 °C, 12 h) the isomer ratio amounts
to 3/2.12c Subsequent treatment with BCl3 produced the

Borabenzene Adducts of Ylidic Lewis Bases
Organometallics, Vol. 21, No. 9, 2002 1951
Ta ble 1. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 3, 5‚0.5(tolu en e), a n d
9‚0.5(tolu en e)a
3
5‚0.5(toluene)
9‚0.5(toluene)
(a) Bond Distances (Å)
B-X
1.617(6)
1.796(4)
1.494(4)
1.488(4)
1.372(5)
1.387(5)
1.386(6)
1.386(5)
1.652(3)
1.769(2)
1.495(3)
1.508(3)
1.398(3)
1.403(3)
1.399(3)
1.389(3)
1.533(3)
1.633(2)
1.506(3)
1.504(3)
1.390(3)
1.398(3)
1.396(3)
1.385(3)
P-X
B-C11
B-C15
C11-C12
C12-C13
C13-C14
C14-C15
(b) Bond Angles (deg)
P-X-B
118.5(3)
115.1(1)
124.9(2)
118.7(2)
116.4(2)
119.7(2)
120.2(2)
120.4(2)
123.1(2)
120.1(2)
123.4(2)
119.7(2)
123.9(2)
116.4(2)
118.6(2)
119.1(2)
123.1(2)
119.8(2)
122.9(2)
C11-B-X
127.0(4)
117.0(4)
115.7(4)
119.6(4)
120.4(4)
121.8(5)
121.9(5)
120.5(4)
C15-B-X
C11-B-C15
C12-C11-B
C14-C15-B
C11-C12-C13
C12-C13-C14
C13-C14-C15
F igu r e 2. Platon plot15 of 5 (at the 30% probability level).
a
X represents the exocyclic atom attached to the boron atom:
(1.617(6) Å) is rather long and similar to that in NMe3-
Ph(C5H5BMe) (1.599(3) Å).12b The bonding picture that
emerges from these structural details is that of a
phosphonio-substituted 1-methylboratabenzene. Com-
pound 3 is the first borabenzene adduct with two
nonadjacent charge centers that are not conjugated; the
methylene linker does not allow for resonance interac-
tions between the charge centers. The situation in 5 is
similar. The polarity of the bond Si-C1 increases the
charge at C1 and gives rise to a somewhat shorter bond
P-C1 (1.769(2) Å). The bond C1-B (1.652(3) Å) is
remarkably long, presumably because of increased steric
repulsion and reduced Lewis basicity of the trimethyl-
silyl-substituted methylenephosphorane. The simple
adduct Me3PCH2BH3 (P-CH2 ) 1.756(6) Å and CH2-B
) 1.655(11) Å) may be of interest for comparison and
also shows a rather long C-B bond.17
X ) C1 for 3 and 5‚0.5(toluene), X ) N for 9‚0.5(toluene).
Crystals of 9 were obtained by crystallization from
toluene; as in the case of 5, the crystals of 9 contained
1/2 mol of cocrystallized toluene. The molecule of 9 (Table
1, Figure 3) consists of a planar borabenzene ring
(maximum vertical deviation of 0.019(3) Å at boron), a
triphenylphosphonio group, and a phenylimino linker.
The dihedral angle between the borabenzene plane and
the plane (B,N,P) amounts to 2.4(2)°.
The bond length P-N for 9 (1.633(2) Å) is longer than
for the free (phenylimino)phosphorane Ph3PNPh (1.602-
(3) Å).13c On the other hand, the bond length N-B
(1.533(3) Å) is rather long. It may be compared to the
N-B distances (i) in Li(TMPDA)(C5H5BNMe2) (1.448-
(2) Å),12a where the presence of considerable π interac-
tions has been deduced from the structural data12a and
from the presence of a marked barrier to internal
rotation around the N-B bond (measured for Li(C5H5-
BNMeCH2Ph), ∆Gq ) 10.1 kcal/mol),18 and (ii) in 1
(1.558(3) Å)3 with negligible π interactions.19 This
comparison leads to the conclusion that the nitrogen
lone pair of 9 exerts little π interaction with the pz
F igu r e 1. Platon plot15 of 3 (at the 30% probability level).
The bond lengths of the B-C-P unit are particularly
interesting. The bond length P-C1 for 3 (1.796(4) Å) is
much longer than for the free methylenephosphorane
Ph3PCH2 (1.693 Å (av) at 100 K;9c see also refs 9d and
16) and may be compared to P-C bonds in organophos-
phonium ions (P-C ) 1.79-1.80 Å for P-C(alkyl) and
1.80-1.81 Å for P-C(Ph)).16a Since the coordination of
the borabenzene ring largely removes the negative
charge from the methylene C atom, the electrostatic
attraction of this C atom and the positive P center is
attenuated and similar to the situation in a phospho-
nium salt. On the other hand, the bond length C1-B
(15) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
(16) (a) Gilheany, D. G. Chem. Rev. 1994, 94, 1939-1374; see p 1366.
(b) Gilheany, D. G. The Chemistry of Functional Groups. In The
chemistry of Organophosphorus Compounds; Patai, S., Ed.; Hartley,
F. R., Volume Ed.; Wiley: Chichester, U.K., 1994; Vol. 3, pp 1-44. (c)
Bachrach, S. M.; Nitsche, C. I. The Chemistry of Functional Groups.
In The Chemistry of Organophosphorus Compounds; Patai, S., Ed.;
Hartley, F. R., Volume Ed.; Wiley: Chichester, U.K., 1994; Vol. 3, pp
273-302.
(17) Schmidbaur, H.; Mu¨ller, G.; Milewski-Mahrla, B.; Schubert, U.
Chem. Ber. 1980, 113, 2575-2578.
(18) Ashe, A. J ., III; Kampf, J . W.; Mu¨ller, C.; Schneider, M.
Organometallics 1996, 15, 387-393.
(19) Bock, H.; Nick, S.; Na¨ther, C.; Bensch, W. Chem. Eur. J . 1995,
1, 557-563.

1952 Organometallics, Vol. 21, No. 9, 2002
Zheng et al.
of 3 and 5 do not allow for conjugation. Compound 9
does not display appreciable conjugation either. In this
case the positive charge of the phosphonio group stabi-
lizes the nitrogen lone pair. This not only is the cause
of the planarity around the nitrogen atom but also
suppresses any appreciable shortening of the N-B bond
by π interactions.
Transition-metal complexes of borabenzene adducts
all still quite rare. The known examples contain Cr(CO)3
groups22,23 and, in single examples, also Mo(CO)3,23
W(CO)3,23 and Co(C4Me4)2 groups. The fact that the
borabenzene rings of the new adducts 3, 5, and 9 are
electronically close to boratabenzene ions suggests that
these adducts should be excellent ligands to a wide
range of transition metals.
Exp er im en ta l Section
Gen er a l P r oced u r es. Reactions were carried out under
an atmosphere of nitrogen by means of conventional Schlenk
techniques. Hexane was distilled from sodium/potassium alloy,
toluene from sodium, diethyl ether from sodium/benzophenone,
and methylene dichloride from calcium dihydride. Elemental
analyses were performed by Analystische Laboratorien, D-51779
Lindlar, Germany.
F igu r e 3. Platon plot15 of 9 (at the 30% probability level).
orbital at boron. The atoms B, N, P, and C51 are located
in a perfect plane (angle sum around the N atom 360.0°;
B-N-P ) 123.4(2)°, B-N-C51 ) 118.6(2)°, P-N-C51
) 118.0(2)°). The planarity of such nitrogen centers is
well-known and is caused by the stabilization of the
nitrogen lone pair by the neighboring positive charge
at the phosphorus center.20 It is this same effect which
also suppresses N-B π bonding.
Mass spectra were recorded on a Finnigan MAT-95 at a
nominal electron energy of 70 eV. NMR spectra were recorded
on a Varian Unity 500 (1H, 500 MHz; 13C, 125.7 MHz; 11B,
160.4 MHz) spectrometer. Chemical shifts are referenced to
TMS for 1H and 13C, to BF3‚OEt2 for 11B, and to H3PO4 (84%)
Other properties of the compounds 3, 5, and 9 are
consistent with the interpretation given here. The intra-
ring C-B bond distances (1.491(4) Å (av) for 3, 1.502-
(3) Å (av) for 5, and 1.505(3) Å (av) for 9) are close to
those of NMe3Ph(C5H5BMe)12b (1.501(3) Å (av)), while
adducts with adjacent charge centers display markedly
shorter bonds (1.473(4) Å (av) for 1 and 1.47(1) Å (av)
for Me3PBC5H55a). For monosubstituted benzenes it is
well established that 13C chemical shift data of the para
carbon atoms reflect the resonance contribution to the
electron density distribution within the aromatic ring;
the meta carbon atoms are not much affected at all, and
the data for ortho carbon atoms are influenced both by
resonance and by electrostatic effects. A similar situa-
tion seems to exist for bora- and boratabenzenes.
Comparison of the 13C chemical shifts of the boraben-
zene atoms C-4 (for 3,5-dimethyl compounds δ(13C)
110.1 ppm for Li(3,5-Me2C5H3BMe),21 114.8 ppm for 3,
114.2 ppm for 5, 127.9 ppm for the carbene adduct 3,5-
Me2C5H3BC(NMeCMe)2,6 and 122.3 ppm for 10; 107.9
ppm for Li(C5H5BMe),12b 108.4 ppm for 9, 116.6 ppm
for 1,3,5a and 120.7 ppm for Me3PBC5H55a) show that the
borabenzene rings of the new adducts 3, 5, and 9 are
similar to those of comparable boratabenzene ions but
not to those of borabenzene adducts with adjacent
charge centers.
1
for 31P. Assignments of NMR signals are based on H,1H-COSY
and HMQC techniques.
Syn t h esis of (Tr ip h en ylp h osp h on io)m et h a n id e-3,5-
Dim eth ylbor a ben zen e (3) a n d (Tr im eth ylsilyl)(tr ip h -
e n y lp h o s p h o n io )m e t h a n id e -3,5-D im e t h y lb o r a b e n -
zen e (5). Meth od A. Ad d ition of P h 3P CH2 to 2c. A solution
9
of Ph3PCH2 (0.696 g, 2.52 mmol) in ether (10 mL) was added
dropwise to 1-chloro-3,5-dimethyl-2-(trimethylsilyl)-1,2-dihy-
droborinine6 (2c; 0.268 g, 1.26 mmol) in ether (10 mL). A yellow
precipitate formed immediately. After the reaction mixture
was stirred at ambient temperature for 2 h, the precipitate
was collected by filtration and washed with ether (5 mL). The
yellow solid obtained was suspended in toluene (20 mL), and
the mixture was stirred vigorously at 100 °C for 10 min. A
white solid of phosphonium chlorides was removed by fast
filtration of the hot suspension and was washed with toluene
(2 × 10 mL). The combined yellow filtrate, after being
concentrated to ca. 20 mL, was stored at 4 °C to give 3 (0.290
g, 61%) as yellow needles, which were sensitive to air and
moisture.
Meth od B. In ver se Ad d ition . A solution of 2c (0.198 g,
0.93 mmol) in ether (5 mL) was added slowly to Ph3PCH2
9
(0.542 g, 1.86 mmol) in ether (10 mL). The solution turned
orange, and a yellow precipitate formed almost immediately.
After the reaction mixture was stirred for 2 h, the solid was
collected by filtration and washed with ether (5 mL). (a) The
combined orange filtrate was concentrated to dryness under
vacuum, and the residue was crystallized from toluene to give
the (trimethylsilyl)methanide adduct 5 as the toluene solvate
5‚0.5(toluene) (0.088 g, 19% based on 2c) as air- and moisture-
sensitive yellow platelets. (b) The yellow powder obtained from
the above filtration was extracted with toluene (20 mL) at 100
°C for 10 min. A fast filtration of the hot suspension removed
Con clu d in g Rem a r k s
This paper presents the three new borabenzene
adducts 3, 5, and 9 with remote charge compensation.
The two opposite charge centers, i.e., that in the
borabenzene ring and that of the phosphonio group, are
not conjugated. This is so because the methylene linkers
(22) (a) Tweddell, J .; Hoic, D. A.; Davis, W. M.; Fu, G. C. J . Org.
Chem. 1997, 62, 8286-8287. (b) Amendola, M. C.; Stockman, K. E.;
Hoic, D. A.; Davis, W. M.; Fu, G. C. Angew. Chem. 1997, 109, 278-
281; Angew. Chem., Int. Ed. 1997, 36, 267-269. (c) Qiao, S.; Hoic, D.
A.; Fu, G. C. J . Am. Chem. Soc. 1996, 118, 6329-6330.
(23) Boese, R.; Finke, N.; Keil, T.; Paetzold, P.; Schmid, G. Z.
Naturforsch. 1985, 40b, 1327-1332.
(20) See ref 7, p 413.
(21) Herberich, G. E.; Eckenrath, H. J .; Ni, J . Unpublished work.

Borabenzene Adducts of Ylidic Lewis Bases
Organometallics, Vol. 21, No. 9, 2002 1953
Ta ble 2. Cr ysta l Da ta , Da ta Collection
P a r a m eter s, a n d Con ver gen ce Resu lts for 3,
5‚0.5(tolu en e), a n d 9‚0.5(tolu en e)
a white solid of phosphonium chlorides. The yellow filtrate,
after being concentrated under vacuum, was stored at 4 °C to
give yellow needles of 3 (0.085 g, 24%).
Da ta for 3. Anal. Calcd for C26H26BP: C, 82.12; H, 6.89.
Found: C, 81.58; H, 7.12. H NMR (500 MHz, CDCl3): δ 5.83
(s, 1H, 4-H), 5.57 (s, 2H, 2-/6-H), 2.05 (s, 6H, 3-/5-Me); signals
3
5‚0.5(toluene) 9‚0.5(toluene)
1
empirical formula
C
26H26BP
C29H34BPSi‚ C29H25BNP‚
0.5C7H8
498.53
0.5C7H8
475.38
for Ph3PCH2 moiety δ 7.68-7.75 (m, 9H, 2′-/4′-/6′-H), 7.57 (m,
fw
380.28
monoclinic
space group (No.) P21/n (14)
2
6H, 3′-/5′-H), 2.93 (d, J (31P-1H) ) 17.7 Hz, 2H, PCH2)). 13C-
cryst syst
triclinic
P1h (2)
triclinic
P1h (2)
{1H} NMR (126 MHz, CDCl3): δ 141.5 (d, 4J (31P-13C) ) 1.1
Hz, C-3,5), 125.6 (br, C-2,6), 114.8 (C-4), 25.4 (3-/5-Me); signals
radiation (λ, Å)
Mo KR
(0.710 73)
9.498(2)
12.950(3)
17.303(5)
Cu KR
Cu KR
2
for Ph3PCH2 moiety: 134.1 (d, J (31P-13C) ) 9.3 Hz, C-2′,6′),
(1.541 84)
(1.541 84)
4
3
133.9 (d, J (31P-13C) ) 2.8 Hz, C-4′), 129.6 (d, J (31P-13C) )
12.1 Hz, C-3′,5′), 123.7 (d, 1J (31P-13C) ) 85 Hz, C-1′), 13.7 (br,
PCH2). 11B{1H} NMR (160 MHz, CD2Cl2, external BF3‚OEt2):
δ 28.5. 31P{1H} NMR (202 MHz, CD2Cl2, external H3PO4): δ
24.4. MS (70 eV): m/z (Irel) 380 (11, M+), 365 (4, M+ - Me),
275 (42, Ph3PCH+), 262 (100, PPh3+), 185 (18, PPh2+), 108 (20,
M+ - PPh3).
a, Å
b, Å
c, Å
9.141(2)
10.733(1)
14.701(2)
84.889(8)
82.61(1)
81.40(1)
1410.7(4)
2
9.217(2)
12.037(5)
12.448(3)
81.27(2)
83.57(2)
74.77(2)
1313.3(7)
2
R, deg
â, deg
γ, deg
V, Å3
Z
93.04(3)
2125.2(9)
4
d
calcd, g cm-3
1.19
808
1.33
1.17
1.20
Da ta for 5‚0.5(tolu en e). Anal. Calcd for C32.5H38BPSi: C,
1
F(000)
534
502
78.30; H, 7.68. Found: C, 77.92; H, 7.77. H NMR (500 MHz,
µ, cm-1
13.92
10.56
CD2Cl2): δ 5.81 (s, 1H, 4-H), 5.45 (s, 2H, 2-/6-H), 2.05 (s, 6H,
3-/5-Me); signals for Ph3PCH(SiMe3) moiety δ 7.74 (m, 6H, 2′-/
6′-H), 7.64 (m, 3H, 4′-H), 7.51 (m, 6H, 3′-/5′-H), 2.53 (d, 2J (31P-
1H) ) 21.4 Hz, 1H, PCH), -0.05 (s, 9H, SiMe3); signals for
toluene 7.24 (m), 7.17 (m), 7.14 (m), 2.34 (s). 13C{1H} NMR
(126 MHz, CD2Cl2): δ 141.1 (s, C-3,5), 127.2 (b, C-2,6), 114.2
(s, C-4), 25.5 (s, 3-/5-Me); signals for Ph3PCH(SiMe3) moiety δ
θ range, deg
temp, K
2.4-26.0
4.2-69.9
180
3.6-74.9
150
223
cryst dimens, mm3 0.95 × 0.25 × 0.65 × 0.40 × 0.54 × 0.40 ×
0.20
none
0.35
0.26
abs cor
max/min
transmissn
no. of rflns
no. of indep rflns
no. of indep obsd
rflns
empirical
0.998/0.876
numerical
0.786/0.554
2
4
134.5 (d, J (31P-13C) ) 9.4 Hz, C-2′,6′), 133.3 (d, J (31P-13C)
9050
4165
7731
8346
) 2.8 Hz, C-4′), 129.2 (d, 3J (31P-13C) ) 11.5 Hz, C-3′,5′), 126.0
5321
5412
1
3
1419 (I >
2σ(I))
357
4200 (I >
2σ(I))
489
4109 (I >
2σ(I))
433
(d, J (31P-13C) ) 85 Hz, C-1′), 14.2 (br, PCH), 1.9 (d, J (31P-
13C) ) 2.7 Hz, SiMe3), and signals for toluene. 11B{1H} NMR
(160 MHz, CD2Cl2, external BF3‚OEt2): δ 29.3. 31P{1H} NMR
(202 MHz, CD2Cl2, external H3PO4): δ 25.0. MS (70 eV)): m/z
(Irel) 452 (2, M+), 379 (22, M+ - SiMe3), 262 (100, PPh3+), 185
(18, PPh2+), 73 (12, SiMe3+).
no. of variables
R1,a obsd (all data) 0.062 (0.195) 0.051 (0.067) 0.057 (0.076)
wR2,b obsd (all
data)
GOF
0.086 (0.105) 0.121 (0.128) 0.140 (0.149)
0.704
1.038
0.67
1.060
0.71
max resd density, 0.18
Syn th esis of 1-(Dim eth yla m in o)-2-(tr im eth ylsilyl)-1,2-
d ih yd r obor in in e (7a ) a n d 1-(Dim eth yla m in o)-4-(tr im -
eth ylsilyl)-1,4-d ih yd r obor in in e (7b). Me3SiCl (27.2 g, 250
mmol) in ether (50 mL) was added dropwise to a suspension
of Li(C5H5BNMe2)(TMEDA)12a (38.2 g, 157 mmol) in ether (250
mL) at -40 °C. After the addition was complete, the reaction
mixture was stirred at ambient temperature for 2 h. The excess
Me3SiCl and the solvent were pumped off under vacuum.
Hexane (200 mL) was added to the residue, and a white
precipitate of LiCl was filtered off. The filtrate was concen-
trated under reduced pressure to remove all volatiles. Vacuum
distillation (95-100 °C, 10 mbar) of the residue using a
Vigreux column (10 cm) afforded the isomer mixture 7 (19.1
g, 63%; the isomer ratio a /b was 85/15, and is 3/2 after thermal
equilibration at 150 °C) as an air- and moisture-sensitive pale
yellow oil. Anal. Calcd for C10H20BNSi: C, 62.18; H, 10.44; N,
7.25. Found: C, 62.05; H, 10.37; N, 7.41.
e Å-3
R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑w(Fo2 - Fc2)2/∑w(Fo2)2]1/2
where w ) 1/[σ2(Fo2) + (aP)2] and P ) [max(Fo2,0) + 2Fc2]/3.
,
a
b
warmed to 0 °C, and stirring was continued for 2 h. After all
volatiles were removed under reduced pressure, condensation
(45 °C, 0.01 mbar) of the residue afforded the isomer mixture
8 (14.3 g, 80%, isomer ratio a /b ca. 95/5) as an air- and
moisture-sensitive pale yellow oil. Anal. Calcd for C8H14
BSiCl: C, 52.07; H, 7.65. Found: C, 52.39; H, 7.71.
-
1
Da ta for 8a . H NMR (500 MHz, CDCl3): δ 7.51 (br, 1H,
5-H), 6.86 (br, 1H, 3-H), 6.53 (t, J ) 7.6 Hz, 1H, 4-H), 6.51
(br, 1H, 6-H), 3.64 (br, 1H, 2-H), 0.12 (s, 9H, SiMe3). 13C{1H}
NMR (126 MHz, CDCl3): δ 150.4 (br, C-5), 143.7 (br, C-3),
132.8 (br, C-6), 123.3 (C-4), 54.2 (br, C-2), -0.6 (SiMe3). 11B
NMR (160 MHz, CDCl3, external BF3‚OEt2): δ 57.8.
1
1
Da ta for 7a . H NMR (500 MHz, CDCl3): δ 6.88 (dd, J )
Da ta for 8b. H NMR (500 MHz, CDCl3): δ 7.44 (dd, J )
12.2, 5.5 Hz, 1H, 5-H), 6.30 (dd, J ) 9.0, 6.1 Hz, 1H, 3-H),
6.17 (d, J ) 12.2 Hz, 1H, 6-H), 6.05 (dd, J ) 9.0, 5.5 Hz, 1H,
4-H), 2.83 (s, 3H, NMe), 2.70 (s, 3H, NMe), 2.49 (d, J ) 6.1
Hz, 1H, 2-H), -0.01 (s, 9H, SiMe3). 13C{1H} NMR (126 MHz,
CDCl3): δ 142.9 (C-5), 137.2 (C-3), 127.7 (br, C-6), 121.9 (C-
4), 39.8 (NMe), 38.5 (NMe), 34.4 (br, C-2), -0.8 (SiMe3). 11B
NMR (160 MHz, CDCl3, external BF3‚OEt2): δ 40.5.
11.9, 3.7 Hz, 2H, 3-/5-H), 6.65 (d, J ) 11.9 Hz, 2H, 2-/6-H),
3.85 (t, J ) 3.7 Hz, 1H, 4-H), 0.08 (s, 9H, SiMe3). 13C{1H} NMR
(126 MHz, CDCl3): δ 157.2 (C-3,5), 132.3 (br, C-2,6), 51.7 (C-
4), -2.2 (SiMe3). 11B NMR (160 MHz, CD2Cl2, external BF3‚
OEt2): δ 49.0.
Syn th esis of N-(Tr ip h en ylp h osp h on io)a n ilid e-Bor a -
ben zen e (9). A solution of 8 (0.298 g, 1.61 mmol) in ether (10
mL) was added slowly to N-(triphenylphosphonio)anilide (Al-
drich, 0.522 g, 1.48 mmol) in ether (20 mL). A brown precipi-
tate appeared immediately. After the reaction mixture was
stirred at room temperature for 2 h, the solid was collected by
filtration, washed with hexane (5 mL), and dried under high
vacuum to give 9 (0.52 g, 82%) as shiny air- and moisture-
sensitive brown-yellow microcrystals. Crystallization of 9 from
hot toluene afforded the toluene solvate 9‚0.5(toluene) as
platelets suitable for an X-ray diffraction study.
1
Da ta for 7b. H NMR (500 MHz, CDCl3): δ 6.92 (dd, J )
12.2, 3.8 Hz, 2H, 3-/5-H), 6.27 (d, J ) 12.2 Hz, 2H, 2-/6-H),
3.07 (d, J ) 3.8 Hz, 1H, 4-H), 2.87 (s, 6H, NMe2), 0.01 (s, 9H,
SiMe3). 13C{1H} NMR (126 MHz, CDCl3): δ 148.1 (C-3,5), 127.7
(br, C-2,6), 43.9 (C-4), 38.7 (NMe2), -2.9 (SiMe3). 11B NMR (160
MHz, CDCl3, external BF3‚OEt2): δ 31.8.
Syn th esis of 1-Ch lor o-2-(tr im eth ylsilyl)-1,2-dih ydr obor i-
n in e (8a) an d 1-Ch lor o-4-(tr im eth ylsilyl)-1,4-dih ydr obor i-
n in e (8b). A CH2Cl2 solution of boron trichloride (1.5 M, 78
mL, 117 mmol) was added dropwise to 7 (18.8 g, 97.5 mmol)
in CH2Cl2 (60 mL) at -78 °C. The reaction mixture was slowly
Da ta for 9. Anal. Calcd for C29H25BNP: C, 81.13; H, 5.87;
N, 3.26. Found: C, 80.82; H, 6.08; N, 2.91. 1H NMR (500 MHz,

1954 Organometallics, Vol. 21, No. 9, 2002
Zheng et al.
CD2Cl2): δ 6.87 (dd, J ) 10.4, 7.0 Hz, 2H, 3-/5-H), 5.83 (t, J )
7.0 Hz, 4-H), 5.26 (d, J ) 12.4 Hz, 2H, 2-/6-H); signals for Ph3-
PNPh moiety δ 7.77 (m, 6H, 2′-/6′-H, PPh3), 7.67 (m, 3H, 4′-
H, PPh3), 7.51 (m, 6H, 2′-/6′-H, PPh3), 6.95-7.10 (m, 5H, NPh).
13C{1H} NMR (126 MHz, CD2Cl2): δ 133.5 (C-3,5), 117.5 (br,
C-2,6), 108.4 (C-4); signals for Ph3PNPh moiety δ 143.9 (C-1′′,
gence results are collected in Table 2. The structures were
solved by direct methods and refined on reflection intensities
(F2) with the SHELXL-97 program.24 Before merging over
symmetry-related reflections, absorption corrections25 were
applied to the data sets collected with Cu KR radiation.
In both the structures of 5‚0.5(toluene) and of 9‚0.5(toluene),
the toluene molecules were disordered with respect to crystal-
lographic inversion centers. The structural parameters of this
solvent molecule were refined with the restraint that all six
intra-ring C-C bond distances are taken to be equal within a
standard deviation of 0.02 Å. Except for the disordered atoms,
all non-hydrogen atoms were assigned with anisotropic dis-
placement parameters, whereas the hydrogen atoms were
refined isotropically.26
2
NPh), 133.1 (d, J (31P-13C) ) 9.5 Hz, C-2′,6′, PPh3), 132.5 (C-
4′, PPh3), 129.1 (d, 3J (31P-13C) ) 12.1 Hz, Ph3P, C-3′,5′, PPh3),
129.0 (d, 1J (31P-13C) ≈ 100 Hz, C-1′), 128.9 (C-3′′,5′′, NPh),
123.6 (d, 3J (31P-13C) ) 16.5 Hz, C-2”,6”, NPh), 118.4 (C-4′′,
NPh). 11B{1H} NMR (160 MHz, CD2Cl2, external BF3‚OEt2):
δ 33.5. 31P{1H} NMR (202 MHz, CD2Cl2, external H3PO4): δ
34.5. MS (70 eV): m/z (Irel) 429 (2, M+), 262 (100, PPh3+), 185
(25, PPh2+).
Tr im eth ylp h osp h in e-3,5-Dim eth ylbor a ben zen e (10).
Trimethylphosphine (0.426 g, 5.60 mmol) in hexane (10 mL)
was added to a solution of 1-chloro-3,5-dimethyl-2-(trimeth-
ylsilyl)-1,2-dihydroborinine (2c; 1.18 g, 5.54 mmol) in hexane
(20 mL) at room temperature. The reaction mixture was stirred
for 6 h, and a white precipitate formed during this time. The
solid was collected by filtration, washed with hexane (2 × 10
mL), and dried under high vacuum to give 10 (0.93 g, 93%) as
an air- and moisture-sensitive white powder. Crystallization
of 10 from toluene at 30 °C afforded large colorless prisms.
Da ta for 10. Anal. Calcd for C10H18BP: C, 66.71; H, 10.08.
Found: C, 66.86; H, 9.95. 1H NMR (500 MHz, CD2Cl2): δ 6.50
(dm, 2J (31P-1H) ≈ 9 Hz, 2H, 2-/6-H), 6.38 (s, 1H, 4-H), 2.27 (s,
Ack n ow led gm en t. We thank Dr. Ulli Englert for
helpful advice. This work was generously supported by
the Deutsche Forschungsgemeinschaft and by the Fonds
der Chemischen Industrie.
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystallographic data for the structure determinations of 3,
5‚0.5(toluene), and 9‚0.5(toluene) and files, in CIF format, for
these same compounds.26 This material is available free of
charge via the Internet at http://pubs.acs.org.
OM011081Q
2
6H, 3-/5-Me), 1.61 (d, J (31P-1H) ) 11.6 Hz, 9H, PMe3). 13C-
3
{1H} NMR (126 MHz, CD2Cl2): δ 142.4 (d, J (31P-13C) ) 8.2
(24) (a) Sheldrick, G. M. SHELXS-97, Program for Structure Solu-
tion; University of Go¨ttingen: Go¨ttingen, Germany, 1997. (b) Sheldrick,
G. M. SHELXL-97, Program for Structure Refinement; University of
Go¨ttingen: Go¨ttingen, Germany, 1997.
(25) (a) Coppens, P.; Leiserowitz, L.; Rabinovich, D. Acta Crystallogr.
1965, 18, 1035-1038. (b) North, A. C. T.; Phillips, D. C. Mathews, F.
S. Acta Crystallogr. 1968, A24, 351-359.
(26) Crystallographic data (excluding structure factors) for the
structures reported in this paper are also available free of charge from
the Cambridge Crystallographic Data Centre, on quoting the depository
numbers CCDC-175679 for 3, CCDC-175680 for 5‚0.5(toluene), and
CCDC-175681 for 9‚0.5(toluene).
Hz, C-3,5), 125.7 (br, C-2,6), 122.3 (s, C-4), 25.1 (d, 4J (31P-
13C) ) 1.6 Hz, 3-/5-Me), 11.7 (d, 1J (31P-13C) ) 42.8 Hz, PMe3).
11B{1H} NMR (160 MHz, CD2Cl2, external BF3‚OEt2): δ 21.8
(d, 1J (31P-11B) ) 110 Hz). 31P{1H} NMR (202 MHz, CD2Cl2,
1
external H3PO4): δ -22.3 (q, J (31P-11B) ) 110 Hz).
Cr ysta l Str u ctu r e Deter m in a tion s. The data collections
were performed on ENRAF-Nonius CAD4 diffractometers
equipped with graphite monochromators using the ω-2θ scan
mode. Crystal data, data collection parameters, and conver-