Synthesis of Cage Compounds Containing Boron, Germanium, and Phosphorus Atoms

Article abstract of DOI:10.1021/ic961026n

The 1:1 reactions of [(ⁱPr₂N)BP(H)B(NⁱPr₂)PLi·DME] and [(tmp)BP(H)B(tmp)PLi·DME] (tmp = 2,2,6,6-tetramethylpiperidino) with organylhalogermanes have been surveyed, and germyl-substituted diphosphadiboretanes of the type R₂NBP(H)B(NR₂)PGe(Cl)R'₂ (R₂N = ⁱPr₂N, tmp; Ge(Cl)R'₂ = Ge(Cl)Me₂ and Ge(Cl)Ph₂) have been isolated and characterized. Subsequent dehydrohalogenation of these compounds with BuLi gave the new bicyclic cage compounds P₂(BNR₂)₂(GeR'₂) (R₂N = tmp, R'=Ph; R₂N = tmp, R' = Me) and/or oligomers [-(R₂N)BP(H)B(NR₂)PGeR'₂-]_n (R₂N = ⁱPr₂N, R' = Me; R₂N = tmp, R' = Me). In addition, the 2:1 reactions of [(R₂N)BP(H)B(NR₂)PLi·DME] with R'₂GeCl₂ have been examined. In one case, the cage compound P₂(BNR₂)₂GeR'₂ (R₂N = tmp, R' = Ph) was obtained while a smaller alkyl group on Ge allowed formation of the bis(diphosphadiboretanyl)germanes [R₂NBP(H)B(NR₂)P]₂GeR'₂ (R₂N = ⁱPr₂N, tmp; R' = Me). Two P₂(BNR₂)₂(GeR'₂)·Cr(CO) ₅ (complexes R₂N = tmp, R' = Ph, Me) were isolated and characterized. The molecular structures of the cage compound P₂(Btmp)₂GePh₂ and the complexes P₂(Btmp)₂GeR'₂·Cr(CO)₅ (R' = Ph, Me) were determined with single-crystal X-ray diffraction techniques. The structural and spectroscopic features are discussed in relation to those of other P₂(BNR₂)₂(ER₂) species.

Full text of DOI:10.1021/ic961026n

802
Inorg. Chem. 1997, 36, 802-808
Synthesis of Cage Compounds Containing Boron, Germanium, and Phosphorus Atoms
Tuqiang Chen,† Eileen N. Duesler,† Robert T. Paine,*,† and H. No1th*,‡
Department of Chemistry, University of New Mexico, Albuquerque, New Mexico 87131, and Institut fu¨r
Anorganische Chemie, Universita¨t Mu¨nchen, 80333 Mu¨nchen, Germany
ReceiVed August 22, 1996X
The 1:1 reactions of [(iPr2N)BP(H)B(NiPr2)PLi‚DME] and [(tmp)BP(H)B(tmp)PLi‚DME] (tmp ) 2,2,6,6-
tetramethylpiperidino) with organylhalogermanes have been surveyed, and germyl-substituted diphosphadiboretanes
of the type R2NBP(H)B(NR2)PGe(Cl)R′2 (R2N ) iPr2N, tmp; Ge(Cl)R′2 ) Ge(Cl)Me2 and Ge(Cl)Ph2) have been
isolated and characterized. Subsequent dehydrohalogenation of these compounds with tBuLi gave the new bicyclic
cage compounds P2(BNR2)2(GeR′2) (R2N ) tmp, R′)Ph; R2N ) tmp, R′ ) Me) and/or oligomers
[-(R2N)BP(H)B(NR2)PGeR′2-]n (R2N ) iPr2N, R′ ) Me; R2N ) tmp, R′ ) Me). In addition, the 2:1 reactions
of [(R2N)BP(H)B(NR2)PLi‚DME] with R′2GeCl2 have been examined. In one case, the cage compound
P2(BNR2)2GeR′2 (R2N ) tmp, R′ ) Ph) was obtained while a smaller alkyl group on Ge allowed formation of
i
the bis(diphosphadiboretanyl)germanes [R2NBP(H)B(NR2)P]2GeR′2 (R2N ) Pr2N, tmp; R′ ) Me). Two
P2(BNR2)2(GeR′2)‚Cr(CO)5 (complexes R2N ) tmp, R′ ) Ph, Me) were isolated and characterized. The molecular
structures of the cage compound P2(Btmp)2GePh2 and the complexes P2(Btmp)2GeR′2‚Cr(CO)5 (R′ ) Ph, Me)
were determined with single-crystal X-ray diffraction techniques. The structural and spectroscopic features are
discussed in relation to those of other P2(BNR2)2(ER2) species.
1. Introduction
(Cl)P(SiMe3)2 gives a trigonal-bipyramidal cage P2(iPr2NB)3;5
however, this approach was not generally useful with other
substituent groups. It was observed that a more useful approach
to P2(R2NB)2(E) cages (E ) BNR2) is available through the
sequential substitution and elimination chemistry summarized
in Scheme 1.6 This approach should be relatively general for
compounds with a variety of other heteroatoms and heteroatom
groups. We recently reported the synthesis and structural
characterization of analogs containing E (E ) SiR2, R2Si-
SiR2),7 and we report here the extension of this chemistry to
include cages containing GeR2 groups as constituents.
Main group element cage compounds continue to attract
attention due to their fundamentally interesting structural and
electronic features,1,2 as well as their potential utility as solid
state materials precursors. However, in order to find use in
practical applications, systematic preparative approaches for the
required building blocks must be developed. For example,
phosphinoborane ring compounds should provide useful starting
materials for the systematic construction of BxPy cage species
if appropriate substitution and elimination chemistry can be
developed, and these species may serve as precursors to solid
state boron phosphides. For example, No¨th and co-workers3
found that boron-phosphorus tetrahedrane analogs (R2NBP)2
are obtained in good yield from the photolysis of selected
diphosphadiboretane rings, (R2NBPCEt3)2 (R2N ) tmp,4 tBu2N),
and efforts are still in progress to generalize this approach.
Several thermally driven reactions have been examined for
formation of boron phosphorus cage species. In particular,
thermolysis of a 1:2 mixture of (iPr2N)BCl2 and (iPr2N)B-
Experimental Section
General Information. Standard inert-atmosphere techniques were
used for the manipulations of all reagents and reaction products.
Infrared spectra were recorded on a Matteson 2020 FT-infrared
spectrometer from solution cells or from KBr pellets. Mass spectra
were obtained from a Finnegan mass spectrometer by using a heated
solids inlet probe. NMR spectra were recorded on Bruker WP-250
and JEOL GSX-400 spectrometers. The NMR samples were contained
in sealed 5 mm tubes with deuterated lock solvent, and spectra were
referenced with Me4Si (1H, 13C), 85% H3PO4 (31P), and F3B‚OEt2 (11B).
Elemental analysis data were determined in the UNM microanalytical
services laboratory.
† University of New Mexico.
‡ Universita¨t Mu¨nchen.
X Abstract published in AdVance ACS Abstracts, February 1, 1997.
(1) Grimes, R. N. Carboranes; Academic Press: New York, 1970. Beall,
H. In Boron Hydride Chemistry; Muetterties, E. L., Ed.; Academic
Press: New York, 1975; Chapter 9. Onak, T. Ibid.; Chapter 10. Dunks,
G. B.; Hawthorne, M. F. Ibid.; Chapter 11. Callahan, K. P.; Hawthorne,
M. F. AdV. Organomet. Chem. 1976, 14, 145. Grimes, R. N. Pure
Appl. Chem. 1974, 39, 455. Callahan, K. P.; Hawthorne, M. F. Ibid.
1974, 39, 475.
Materials. Reagents iPr2NBCl2,8 (tmp)BCl2,9 LiPH2‚DME,10
iPr2NBP(H)(iPr2NB)PLi‚DME7,11 (3), (tmp)BP(H)((tmp)B)PLi‚DME11
(5) Wood, G. L.; Duesler, E. N.; Narula, C. K.; Paine, R. T.; No¨th, H. J.
Chem. Soc., Chem. Commun. 1987, 496.
(6) Dou, D.; Wood, G. L.; Duesler, E. N.; Paine, R. T.; No¨th, H. Inorg.
Chem. 1992, 31, 3756.
(7) Dou, D.; Kaufmann, B.; Duesler, E. N.; Chen, T.; Paine, R. T.; No¨th,
H. Inorg. Chem. 1993, 32, 3056.
(2) Sowerby, D. B. In The Chemistry of Inorganic Homo- and Hetero-
cycles; Haiduc, I., Sowerby, D. B., Eds.; Academic Press: New York,
1987.
(3) Ko¨lle, P.; Linti, G.; No¨th, H.; Polborn, K. J. Organomet. Chem. 1988,
355, 7.
(4) Abbreviations used in the text include tmp ) 2,2,6,6-tetramethylpi-
peridino, Me ) Methyl, tms ) trimethylsilyl, THF ) tetrahydrofuran,
iPr ) isopropyl, and DME ) ethylene glycol dimethyl ether, and tBu
) tert-butyl.
(8) Gerrard, W.; Hudson, H. R.; Mooney, E. R. J. Chem. Soc. 1960, 5168.
(9) No¨th, H.; Weber, S. Z. Naturforsch., B 1983, 37, 1460.
(10) Scha¨fer, H.; Fritz, G.; Ho¨lderich, W. Z. Anorg. Allg. Chem. 1977,
428, 222.
(11) Dou, D.; Westerhausen, M.; Wood, G. L.; Linti, G.; Duesler, E. N.;
No¨th, H.; Paine, R. T. Chem. Ber., 1993, 126, 379.
S0020-1669(96)01026-9 CCC: $14.00 © 1997 American Chemical Society

Synthesis of Cage Compounds
Inorganic Chemistry, Vol. 36, No. 5, 1997 803
Scheme 1
(4), and (CO)5Cr‚NMe312 were prepared as described in the literature.
The samples of Me2GeCl2 and Ph2GeCl2 were purchased from Strem
Chemical Co., and tBuLi solutions were obtained from Aldrich
Chemical Co. Solvents were rigorously dried and degassed by standard
methods. Solvent transfers were accomplished by vacuum distillation,
and all product work-ups were performed in Schlenkware under dry
nitrogen.
Synthesis and Characterization of Compounds. 2,4-Bis(dialkyl-
amino)-1-(diorganochlorogermyl)-1,3,2,4-diphosphadiboretanes (5,
6, 7, and 8). Each of these compounds was prepared in a related
fashion illustrated by the specific synthesis for 5. A sample of
733 (m), 696 (m), 575 (w), 472 (m). Anal. Calcd for C30H47B2N2P2ClGe
(627.30): C, 57.44; H, 7.55; N, 4.47. Found: C, 57.91; H, 7.81; N,
4.41.
2,4-Bis(2,2,6,6-tetramethylpiperidino)-5-dimethyl-1,3-diphospha-
2,4-dibora-5-germabicyclo[1.1.1]pentane (9). A solution containing
7 (1.40 g, 2.8 mmol) in hexane (30 mL) was cooled to -78 °C, and
tBuLi (1.6 mL, 2.7 mmol, 1.7 M in pentane) solution was dripped into
the stirred solution through an airtight syringe. The resulting cloudy
yellow mixture was stirred at -78 °C (2 h), slowly warmed to 23 °C,
and stirred (16 h), and then filtered and the solvent removed from the
filtrate. A yellow crystalline solid and yellow oil remained. This
mixture was crystallized from cold hexane (-10 °C, ∼5 mL) providing
pale yellow crystals: yield 0.25 g (19%); mp 101-104 °C dec. Mass
spectrum (30 eV) [m/e (%)]: 471-463 (M+, 467 most intense, 47%).
Anal. Calcd for C20H42B2N2P2Ge (466.71): C, 51.47; H, 9.07; N, 6.00.
Found: C, 51.11; H, 10.17; N, 5.88.
2,4-Bis(2,2,6,6-tetramethylpiperidino)-5-diphenyl-1,3-diphospha-
2,4-dibora-5-germabicyclo[1.1.1]pentane (10). A suspension of 8
(0.95 g, 1.5 mmol) in hexane (30 mL) was cooled to -78 °C and a
tBuLi (0.90 mL, 1.5 mmol, 1.7 M in pentane) solution was dripped
into the stirred suspension through an airtight syringe. The resulting
yellow reaction mixture was warmed slowly (2 h) to 23 °C and stirred
(15 h). The suspension was then filtered and the solvent removed from
the filtrate by vacuum evaporation. The yellow residue was recrystal-
lized from cold hexane (-10 °C, 10 mL). Pale yellow crystals were
obtained: yield 0.39 g (44%); mp 196-198 °C. Mass spectrum (30
eV) [m/e (%)]: 596-587 (M+, 592 most intense, 100%). Infrared
spectrum (KBr, cm-1): 3061 (w), 2961 (s), 2936 (s), 2864 (m), 1582
(w), 1465 (m), 1431 (m), 1364 (s), 1331 (s), 1287 (m), 1252 (m), 1171
(m), 1128 (m), 1086 (w), 993 (m), 976 (m), 735 (s), 698 (m), 571 (w),
471 (m). Anal. Calcd for C30H46B2N2P2Ge (590.84): C, 60.98; H,
7.85; N, 4.74. Found: C, 61.11; H, 7.97; N, 4.84.
Dimethylbis[2,4-bis(diisopropylamino)-1,3,2,4-diphosphadibo-
retanyl]germane (11). A solid sample of 3 (1.40 g, 3.6 mmol) was
added to a cold (-78 °C) hexane solution (40 mL) containing Me2GeCl2
(0.30 g, 1.7 mmol). The mixture was stirred at -78 °C (2 h) and then
at 23 °C (15 h) and then filtered. The filtrate was vacuum evaporated
leaving a pale yellow oil which solidified on standing at 23 °C for
several days. No further purification was required. Yield: 1.20 g
(100%). Mp: 114-118 °C. Mass spectrum (30 eV) [m/e (%)]: 386
(87%), 285 (9%). Infrared spectrum (KBr, cm-1): 2967 (s), 2928 (s),
2868 (m), 2247 (m), 2232 (m), 2221 (m), 1468 (s), 1443 (s), 1366 (s),
1310 (s), 1221 (w), 1184 (m), 1145 (s), 1005 (m), 872 (w), 829 (w),
783 (m), 723 (w), 577 (m), 542 (w). Anal. Calcd for C26H62B2N2P2Ge
(670.51): C, 46.57; H, 9.32; N, 8.36. Found: C, 47.04; H, 9.67; N,
8.44.
iPr2NBP(H)(iPr2NB)PLi‚DME (3) (2.11 g, 5.50 mmol) was added with
stirring to a cold (-78 °C) hexane (40 mL) solution of Me2GeCl2 (0.96
g, 5.5 mmol). The cloudy mixture was stirred at -78 °C (2 h) and at
23 °C (15 h). The resulting mixture was filtered and the filtrate
collected. Further work-up details and characterization data are
individually described.
Compound 5 was recovered as a yellow oil from the filtrate by
vacuum evaporation. After several days at 23 °C, the oil fully
crystallized as a pale yellow solid and no further purification was
required: yield 2.3 g (100%); mp 101-104 °C. Mass spectrum (30
eV) [m/e (%)]: 428-419 (M+, 424 most intense, 44%), 389-383 (388
most intense, 10%), 285 (100%). Infrared spectrum (KBr, cm-1): 2971
(s), 2928 (s), 2870 (s), 2253 (s), 1465 (s), 1445 (s), 1366 (s), 1312 (s),
1231 (m), 1182 (s), 1142 (s), 1001 (m), 870 (m), 841 (m), 806 (s), 716
(m), 606 (m), 574 (m), 546 (m), 530 (w). Anal. Calcd for
C14H35B2N2P2ClGe (423.04): C, 39.75; H, 8.34; N, 6.62. Found: C,
40.18; H, 9.09; N, 6.49.
Compound 6 was not isolated and it was only characterized by 31P
NMR spectroscopy.
Compound 7 was obtained as pale yellow crystals by concentrating
the final filtrate to a few milliliters and cooling to -10 °C: yield 0.90
g, (81%); mp 158-160 °C dec. Mass spectrum (30 eV) [m/e (%)]:
506-500 (M+, 504 most intense, 35%) 469-464 (468 most intense,
28%), 366-363 (M - tmp+, 365 most intense, 100%). Infrared
spectrum (KBr, cm-1): 2963 (s), 2938 (s), 2868 (m), 2249 (m), 1464
(m), 1381 (s), 1369 (s), 1330 (s), 1300 (m), 1300 (m), 1240 (m), 1231
(m), 1190 (w), 1163 (m), 1128 (m), 1088 (w), 1042 (w), 988 (m), 904
(w), 858 (w), 839 (w), 808 (m), 704 (w), 611 (w), 575 (w), 498 (w).
Anal. Calcd for C20H43 B2N2P2ClGe (503.16): C, 47.74; H, 8.61; N,
5.57. Found: C, 47.64; H, 8.64; N, 5.48.
Compound 8 was isolated by evaporating the hexane suspension,
redissolving it in Et2O (20 mL), filtering, and evaporating the Et2O
from the filtrate. The resulting pale yellow powder was washed with
cold hexane and the product recovered as a colorless powder: yield
1.70 g (85.0%); mp 55-57 °C. Mass spectrum (30 eV) [m/e (%)]:
366-363 (M - Ph2GeCl+, 365 most intense, 14%), 333 (4%). Infrared
spectrum (KBr, cm-1): 3052 (w), 2967 (s), 2934 (s), 2870 (m), 2240
(m), 1464 (m), 1431 (m), 1370 (vs), 1333 (s), 1302 (m), 1240 (w),
1165 (m), 1127 (m), 1084 (w), 1044 (w), 988 (m), 862 (w), 816 (w),
Dimethylbis[2,4-bis(2,2,6,6-tetramethylpiperidino)-1,3,2,4-diphos-
phadiboretanyl]germane (12). A solid sample of (tmp)BP(H)-
((tmp)B)PLi‚DME, 4 (1.07 g, 2.3 mmol), was added to a cold (-78
°C) hexane solution (40 mL) containing Me2GeCl2 (0.20 g, 1.2 mmol).
The mixture was stirred at -78 °C (2 h) and then at 23 °C (15 h) and
then filtered. The filtrate was vacuum evaporated, leaving a pale yellow
(12) Wasserman, H. J.; Workulich, M. J.; Atwood, J. D.; Churchill, M. R.
Inorg. Chem. 1980, 19, 2831.

804 Inorganic Chemistry, Vol. 36, No. 5, 1997
Chen et al.
Table 1. Crystallographic Data for P2(tmpB)2(GePh2) (10), P2(tmpB)2(GePh2)‚Cr(CO)5 (13) and P2(tmpB)2(GeMe2)‚Cr(CO)5 (14)
10
13
14
chem formula
a, Å
b, Å
C30H46B2N2GeP2
8.586(2)
16.809(3)
22.240(4)
90
90
90
3209.7(11)
4
1.223
C35H46B2N2O5GeP2Cr
12.040(2)
19.862(4)
16.680(3)
90
104.06(3)
90
3869.4(12)
4
1.344
C25H42B2N2O5P2GeCr
14.969(1)
12.011(1)
18.185(2)
90
97.95(1)
90
3237.9(5)
4
1.397
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
Fcalcd, g cm
fw
-3
590.8
782.9
658.8
cryst dimens, mm
cryst syst
space group
T, °C
0.25 × 0.25 × 0.92
orthorhombic
P212121
20
10.75
3-50
(h, (k, (l
6464
0.21 × 0.58 × 0.69
monoclinic
P21/c
20
11.81
3-47
(h, (k, (l
11 367
0.23 × 0.46 × 0.67
monoclinic
P21/c
20
13.97
2-52
(h, (k, (l
13 488
µ, cm-1
)
2θ range, deg
no. of reflcns measd
no. of collcd reflcns
no. of unique reflcns
no. of obsd reflcns
trans coeff (min/max)
5651
5689
6360
3434 (F > 2σ(F))
0.8069/0.8957
0.0625, 0.0600
0.0007
5231 (F > 1.4σ(F))
0.6664/1.0000
0.0540, 0.0248
0.00001
3534 (F > 2σ(F))
0.7398/1.0000
0.0424, 0.0332
0.0001
a
RF, RwF
g
2
a R ) ∑||Fo| - |Fc||/∑|Fo|, RwF ) [∑w(|Fo| - |Fc|)2/∑wFo ], w-1 ) σ2(F) + gF2.
powder that was recrystallized from cold hexane (-10 °C, ∼5 mL):
yield 0.75 g (78%). The product was contaminated with less than 5%
of 8, ((tmp)BPH)2, and ((tmp)BP)2 as indicated by characteristic 31P
NMR resonances. Due to these small impurities, the samples did not
provide satisfactory elemental analyses. Infrared spectrum (KBr, cm-1):
2965 (s), 2932 (s), 2868 (s), 2268 (m), 2224 (s), 1464 (m), 1369 (s),
1361 (s), 1325 (s), 1300 (s), 1242 (w), 1229 (w), 1194 (w), 1169 (s),
1128 (m), 1090 (w), 1067 (w), 1044 (w), 990 (m), 907 (m), 862 (w),
797 (m), 746 (w), 700 (w), 573 (w).
matrix and unit cell dimensions were performed in a standard manner.
Selected crystallographic data are summarized in Table 1. Data were
collected in the ω scan mode with Mo KR (λ ) 0.710 73 Å) radiation,
a scintillation counter, and a pulse height analyzer. In all cases
inspection of a small data set led to assignment of the space groups.13
Empirical adsorption corrections were applied, based on ψ scans.14 No
signs of crystal decay were noted for 10 and 13; however, 14 displayed
a 6.5% decline in standard intensities, and the intensity data were scaled
accordingly.
(2,4-Bis(2,2,6,6-tetramethylpiperidino)-5-diphenyl-1,3-diphospha-
2,4-dibora-5-germabicyclo[1.1.1]pentane)chromium Pentacarbonyl
(13). Equimolar amounts (1.0 mmol) of Cr(CO)5‚NMe3 and 10 were
combined in 50 mL of hexane at 23 °C, stirred (7 d), and filtered. The
filtrate was concentrated (15 mL) and cooled (-10 °C) and yellow
crystals deposited: yield 0.45 g (57%); mp 89-91 °C dec. Mass
spectrum (30 eV) [m/e (%)]: 784-781 (M+, 2%), 591 (M - Cr(CO5+);
8%). Infrared spectrum (KBr, cm-1): 3065 (w), 2965 (m), 2938 (m),
2054 (m), 1985 (m), 1921 (s), 1466 (w), 1431 (w), 1373 (m), 1343
(m), 1285 (w), 1251 (w), 1171 (w), 1127 (w), 1084 (w), 970 (w), 733
(w), 696 (w), 654 (m), 555 (w), 461 (m). Anal. Calcd for
C35H46B2N2P2Ge (782.85): C, 53.69; H, 5.94; N,3.58. Found: C, 53.67;
H, 5.80; N, 3.62.
All calculations were performed on a Siemens SHELXTL PLUS
structure determination system.15 Solutions for the data sets were by
direct methods (10 and 13) and by heavy atom methods (14), and full-
matrix refinements were employed.16 Neutral atom scattering factors
and anomalous dispersion terms were used for all non-hydrogen atoms
during the refinements. The function minimized was ∑w(|Fo| - |Fc|)2.
Refinements for 10 and 13 gave no unusual features. Compound 14,
however, showed large thermal motions in the tmp group containing
N(2). Disorder models were evaluated, but only one discrete peak per
C atom was found. The second tmp group is well behaved. In each
molecule the nonhydrogen atoms were refined anisotropically and H
atoms were placed in idealized positions (riding model) with Uiso
1.25Uequiv
)
.
2,4-Bis(2,2,6,6-tetramethylpiperidino)-5-dimethyl-1,3-diphospha-
2,4-dibora-5-germabicyclo[1.1.1]pentane)chromium Pentacarbonyl
(14). Equimolar amounts (1.0 mmol) of Cr(CO)5‚NMe3 and 7 were
combined in 30 mL of hexane at 23 °C. The yellow mixture was stirred
(3 d) and then filtered to remove the white solid that formed
[Me3NH]Cl. The filtrate was concentrated to 10 mL and cooled (-10
°C). Yellow crystals of 14 deposited and were collected by filtration:
yield 0.25 g (38%); mp 158-160 °C dec. Infrared spectrum (KBr,
cm-1): 2963 (w), 2051 (m), 1989 (w), 1925 (s), 1910 (s), 1466 (w),
1366 (w), 1337 (w), 1292 (w), 1252 (w), 1227 (w), 1169 (w), 1127
(w), 988 (m), 669 (m), 656 (m), 425 (w). Anal. Calcd for C29H42-
B2N2O5P2GeCr: C, 45.58; H, 6.43; N, 4.25. Found: C, 45.21; H, 6.64;
N, 4.27.
Results and Discussion
The generality of the chemistry summarized in Scheme 1 has
been further tested by exploring the reactions of the lithium
salts iPr2NBP(H)(iPr2NB)PLi‚DME7,11 3 and (tmp)BP(H)-
((tmp)B)PLi‚DME11 4 with Me2GeCl2 and Ph2GeCl2 as sum-
marized in eq 1. The P-germylated diphosphadiboretanes 5, 7,
(13) Space group notation is given in: International Tables for X-Ray
Crystallography; Reidel: Dordrecht, The Netherlands, 1983; Vol. I,
pp 73-346.
(14) The empirical absorption corrections use an ellipsoidal model fitted
to azimuthal scan data that are then applied to the intensity data:
SHELXTL Manual, ReVision 4; Nicolet XRD Corp.: Madison, WI,
1983.
t
Reaction of 5 with BuLi. A solution of 5 (1.49 g, 3.0 mmol) in
t
hexane (30 mL) was cooled (-78 °C) and BuLi (1.7 mL, 2.9 mmol,
1.7 M in pentane) was added through an airtight syringe. The pale
yellow suspension was stirred at -78 °C (2 h) and then at 23 °C (16
h). The resulting mixture was filtered and the filtrate evaporated, and
1.36 g of a glassy pale yellow solid 15 was obtained. Cryscopic
molecular weight analysis in benzene gave MW(av) ) 1180 (n ) 4.6).
Crystallographic Measurements and Structure Solutions. Crys-
tals of 10, 13, and 14 were placed in glass capillaries under a dry
nitrogen atmosphere. The crystals were centered on a Syntex P3/F
automated diffractometer and determinations of crystal class, orientation
(15) Sheldrick, G. M. Nicolet SHELXTL Operations Manual; Nicolet XRD
Corp.: Cupertino, CA, 1981. SHELXTL uses absorption, anomalous
dispersion, and scattering data compiled in International Tables for
X-Ray Crystallography; Knyoch: Birmingham, England, 1974; Vol.
IV, pp 55-60, 99-101, 149-150. Anomalous dispersion terms were
included for all atoms with atomic numbers greater than 2.
(16) A general description of the least-squares algebra is found in
Crystallographic Computing; Ahmed, F. R., Hall, S. R., Huber, C.
P., Eds.; Munksgaard: Copenhagen, 1970; p 187. The least-squares
refinement minimizes ∑w(|Fo| - |Fc|)2.

Synthesis of Cage Compounds
Inorganic Chemistry, Vol. 36, No. 5, 1997 805
and 8 are isolated in high yields as crystalline solids, and they
have been fully characterized. Compound 6 is obtained as a
viscous oil that could not be purified, and it is characterized
here only by 31P NMR spectroscopy. Compounds 5, 7, and 8
give satisfactory elemental analyses, and 5 and 7 display a strong
parent ion in their electron impact mass spectra. Compound 8,
however, does not display a parent ion under the conditions
employed, and the highest mass ion corresponds to [M -
(GeClPh2)+]. It is interesting that, of the P-silylated 1,3,2,4-
diphosphadiboretanes reported previously,7 only the closely
Full assignment of the 13C NMR spectra through nuclear
correlations was not attempted in this study.
Dehydrohalogenation of 5, 7, and 8 promoted with tBuLi was
examined, and the results are summarized in eq 2. Compound
related compound (tmp)BP(H)B(tmp)PSi(Cl)Ph2 failed to pro-
duce a parent ion, suggesting that the P-E(Cl)Ph2 bond in these
compounds may be particularly weak. Each of 5, 7, and 8
shows an infrared band in the region 2253-2240 cm-1 that is
assigned to the terminal P-H stretching vibration, and these
compare favorably with values (2281-2226 cm-1) for related
silyl derivatives.17
(2)
5 produces a glassy yellow solid that is soluble in benzene.
Cryoscopic molecular weight measurements in benzene give
an average value for the molecular weight of 1180 which
corresponds to n ) 4.6. The 31P{1H} NMR spectrum for
samples of this product show 10 resonances in the range δ -110
to -150, with the two dominant peaks centered at δ -138 and
-149. There are no resonances detected in the shift range
associated with cage species, δ +50 to -20. These data are
consistent with intermolecular dehydrohalogenation and sub-
sequent formation of a mixture of low molecular weight
oligomers with relatively complex structures.
(1)
Compound 7, upon dehydrohalogenation, provides a mixture
of a yellow crystalline solid 9 (∼25-30% by 31P NMR) and a
yellow oil 16. Following recrystallization from hexane, 9 was
isolated in 19% yield. The mass spectrum of 9 displays an
intense parent ion envelope of ions (m/e 471-463) which is
consistent with formation of a cage species P2(Btmp)2GeMe2.
An IR spectrum gives no evidence for a P-H stretching vibration.
The 11B{1H} NMR spectrum and the 31P{1H} NMR spectrum
each contain a singlet centered at δ 48.1 and 42.7, respectively.
These compare well with values for the Si analog P2((tmp)B)2-
SiMe2: δ 49.2 (11B) and δ 31.3 (31P). The 1H NMR spectrum
of 9 displays three resonances for the tmp group and a singlet
for the GeMe2 methyl protons. The 31P NMR spectrum for the
oligomer 16 shows resonances at δ -28 and -79 with no P-H
coupling. The mixture also contains a resonance for the known
P2(Btmp)2, δ -290. Unlike the previously reported cage
species, 9 is relatively unstable in solution and the solid state,
decomposing ∼2% in 30 days to unidentified products.
The NMR spectra for 5-8 are summarized in Table 2. Each
compound displays a single 11B{1H} NMR resonance in the
region δ 49.3-47.1 with the resonance for the (tmp)B deriva-
tives appearing at slightly lower field than the resonance for
i
the Pr2NB derivative. A similar trend was observed for the
P-silyl derivatives.7 The 31P{1H} NMR spectra of 5 - 8 reveal
two peaks of equal intensity. The peak corresponding to the
diborylphosphane fragment B2PH is easily assigned since it
splits into a widely spaced (∼200 Hz) doublet with restoration
of P-H coupling. In the iPr2NB derivatives, 5 and 6, the B2PH
resonance appears at higher field while in the (tmp)B derivatives,
7 and 8, the B2PH resonance is the lower field resonance of the
pair. It is also found that both 31P resonances in 7 and 8 are
split into doublets (2JPP ) 48-52 Hz) due to the inequivalency
of the phosphorus environments in the ring. This coupling is
not resolved for 5 and 6. The 1H NMR spectra for 5, 7, and 8
are easily assigned based upon peak intensities, and they are
t
Dehydrohalogenation of 8 with BuLi gives a pale yellow
solid residue which was recrystallized from hexane providing
pale yellow crystals, 10. The compound is isolated in only 44%
yield due to its high solubility in both hexane and benzene. The
mass spectrum of 10 displays an intense parent ion envelope
(m/e 596-587), consistent with the expected molecular weight
of the cage compound. The infrared spectrum shows no
evidence for P-H stretching vibrations consistent with an
intramolecular cage closure reaction of the type already reported
for P-borylated6 and P-silylated7 diphosphadiboretane species.
The 11B{1H} and 31P{1H} NMR spectra each show a single
peak in the shift regions expected for a (tmp)B fragment and
i
consistent with the proposed structures. As expected, the Pr
groups show inequivalent CH and CH3 environments as a result
of hindered rotation about the B-N bond and the asymmetry
in the phosphorus substituents. The Me2Ge resonance in 5 and
3
7 is split into a single doublet, JPH ) 1.9 and 0.9 Hz,
respectively, by the neighboring phosphorus atom. Coupling
to the second, inequivalent phosphorus atom is not resolved.

806 Inorganic Chemistry, Vol. 36, No. 5, 1997
Table 2 NMR Spectral Data for Compounds
Chen et al.
δ(11B{1H})
δ(31P{1H})a
δ(1H)a
δ(13C{1H})a
51.6 (CH)
1
2
3
47.1
-162.8
3.9 (PH)
1.1 (CH3)
23.2 (CH3)
3.5 (CH)
50.8
50.0
-127.2
4.7 (PH)
1.52 (tmp)
58.2 (2), 40.9 (3)
33.4 (7), 30.2 (8)
16.5 (4)
70.7 (DME), 59.4 (DME)
50.6 (CH), 49.3 (CH′)
24.8 (CH3), 23.5 (CH3)
-174.9
-91.2
4.1 (PH)
4.12 (CH), 3.78 (CH′)
3.39 (DME), 3.2 (DME′)
1.45 (CH3), 1.38 (CH3′)
5.62 (PH)
3.38, 3.13 (DME)
1.93, 1.65 (tmp)
4.94 (PH)
4.11 (CH), 3.20 (CH′)
1.16 (CH3), 1.01 (CH3)
0.97 (GeMe3)
4
5
53.6
47.1
-138.3
-15.5
71.8 (DME), 58.8 (DME)
57.0 (2), 44.5 (3)
33.3 (7,8), 17.5 (4)
54.6 (CH), 48.1 (CH′)
24.3 (CH3), 23.3 (CH3)
8.6 (GeMe2)
-146.8
-140.8
6
7
-144.3
-134.6
-111.7
-105.3
49.0
49.3
5.74 (tmp)
58.3, 41.7
32.9, 16.3
8.0 (GeMe2)
140.9, 134.7
129.8, 128.2 (Ph)
58.3, 41.3
1.65, 1.40, 1.30 (tmp)
1.12 (GeMe2)
8.14-8.10,
7.20-7.10 (Ph)
5.8 (PH)
8
-118.1
-102.1
1.47, 1.23 (tmp)
34.1, 32.8
16.2 (tmp)
9
48.1
47.3
42.7
49.8
1.77, 1.73
1.54 (tmp)
1.15 (GeMe2)
7.87-7.90,
7.12-7.18 (Ph)
1.68, 1.66
10
139.5, 135.7
129.1, 127.6 (Ph)
57.8, 37.8
33.9, 15.2 (tmp)
1.50, 1.49
1.48 (tmp)
5.06 (PH)
4.29, 3.28 (CH)
1.27, 1.16 (CH3)
1.08 (GeMe2)
11
48.7
-142.1
-149.09
54.5, 47.7 (CH)
24.6, 22.5 (CH3)
5.7 (GeMe2)
12
13
50.9
44.3
-110.9
-100.5
25.4
7.90-7.87,
7.20-7.08 (Ph)
1.63-1.28 (tmp)
222.3 (COtrans
217.2 (COcis)
136.7, 136.0,
130.0, 128.5 (Ph)
58.0, 35.5,
)
14.0
34.4, 33.2
14.5 (tmp)
14
7.3
6.4
1.58
1.42-1.25 (tmp)
0.81 (GeMe2)
222.9 (COtrans
217.6 (COcis)
57.9, 36.6,
)
35.8, 32.2,
14.6 (tmp)
2.25 (GeMe2)
a Coupling constants (Hz): 5, 1JPH ) 197, 3JPH ) 4.0, 3JHH ) 6.8 (C1), 3JHH ) 6.8 (C1′), 3JHH ) 6.7 (C2), 3JHH ) 6.7 (C2′), 3JPH ) 1.9 (GeMe2),
4JPC ) 1.5 (C2); 6, 1JPH ) 199; 7, 1JPH ) 195, 2JPP ) 48, 3JPH ) 4.9, 3JPH ) 0.9 (GeMe2); 8, 1JPH ) 192, 2JPP ) 52, 3JPH ) 6.3, 2JCP ) 12; 11, 1JPH
3
3
3
3
1
2
1
2
2
) 191, JHH ) 6.7 (CH), JHH ) 6.8 (CH), JHH ) 6.8 (CH3), JPH ) 2.5 (GeMe2); 12, JPH ) 180, JPP ) 45; 13, JPP ) 44, JPC ) 7.2, JPC
cis
trans
2
3
2
) 3.2; 14, JPP ) 57, JPH ) 2.0 (GeMe2), JPC ) 7.0
cis
the pyramidal phosphorus atoms in the trigonal bipyramidal
cage. The corresponding shifts for P2((tmp)B)2SiPh2 17 are δ
48.2 (11B) and δ 32.2 (31P). The 1H and 13C{1H} spectra show
a single environment for the Ph and tmp rings.
The molecular structure of 10 was determined by single-
crystal X-ray diffraction analysis. A view of the molecule is
shown in Figure 1, and selected bond lengths and angles are
summarized in Table 3. The molecule has a trigonal bypyra-
midal structure, similar to that displayed by 17, with the
phosphorus atoms in the apical positions and the (tmp)B and
Ph2Ge fragments in the trigonal plane. The average P-B bond
length, 1.973 Å (range 1.983-1.958 Å), is similar to the average

Synthesis of Cage Compounds
Inorganic Chemistry, Vol. 36, No. 5, 1997 807
Figure 2. Molecular structure and atom labeling scheme for
P2(tmpB)2GePh2‚Cr(CO)5 (13) (30% thermal ellipsoids).
Figure 1. Molecular structure and atom labeling scheme for
P2(tmpB)2GePh2 (10) (30% thermal ellipsoids).
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
P2(tmpB)2(GePh2) (10), P2(tmpB)2(GePh2)‚Cr(CO)5 (13), and
P2(tmpB)2(GeMe2)‚Cr(CO)5 (14)
10
13
14
Bond Lengths
B(1)-P(1)
B(1)-P(2)
B(2)-P(1)
B(2)-P(2)
Ge-P(1)
1.966(10)
1.985(11)
1.958(12)
1.983(12)
2.326(3)
2.322(3)
1.969(9)
2.020(4) 1.990(5)
1.949(4) 2.008(6)
1.995(4) 1.965(5)
1.980(5) 1.982(5)
2.331(1) 2.324(1)
2.310(1) 2.308(1)
1.944(4) 1.951(4)
Ge-P(2)
Ge-C(1)
Ge-C(7)
B(1)-N(1)
B(2)-N(2)
Cr-P(1)
Cr-C(5)
Cr-C(cis)av
Ge-C(6)
1.968(10) Ge-C(12) 1.953(3) 1.931(5)
1.415(13)
1.426(14)
1.392(5) 1.389(6)
1.391(5) 1.374(7)
2.521(1) 2.503(1)
1.843(4) 1.827(6)
1.898(5) 1.889(5)
Figure 3. Molecular structure and atom labeling scheme for
P2(tmpB)2GeMe2‚Cr(CO)5 (14) (30% thermal ellipsoids).
spectra show a characteristic three band pattern in the νCO
region: 13, 2054, 1985, and 1921 cm-1; 14, 2051, 1989, and
1925 cm-1. These values are comparable with the frequencies
Bond Angles
P(1)-Ge-P(2)
Ge-P(1)-B(1)
Ge-P(1)-B(2)
Ge-P(2)-B(1)
Ge-P(2)-B(2)
80.7(1)
74.4(3)
75.1(3)
74.1(3)
74.7(4)
78.9(1)
77.3(1)
77.1(1)
79.2(1)
77.8(1)
69.7(2)
71.5(2)
96.0(2)
95.8(2)
78.0(1)
78.5(1)
76.3(1)
79.3(1)
77.1(2)
73.0(2)
74.0(2)
94.9(2)
93.8(2)
for P2(iPr2NB)2((tmp)B)‚Cr(CO)5:6 2053, 1954, and 1934 cm-1
.
The 11B{1H} NMR spectrum of 13 shows a single resonance at
δ 44.3 shifted slightly upfield from the free ligand 10. The 31
P
B(1)-P(1)-B(2) 70.4(5)
B(1)-P(2)-B(2) 69.5(4)
NMR spectra contain two resonances, each split into a doublet
by P-P′ coupling: 13, δ 25.4, and 14.0, 2JPP′ ) 44 Hz, and 14,
δ 7.3 and 6.4, JPP′ ) 57 Hz. Each of these is shifted
significantly upfield from the resonances of 9 and 10, and the
2JPP′ values are at the upper end of the range so far observed
from other P2(R2NB)2(EX)‚(metal carbonyl) complexes, 45-
24 Hz. The lower field doublet has slightly larger line widths,
and is assigned to the metal-coordinated phosphorus atom. The
13C{1H} NMR spectra show two resonances in the metal
carbonyl shift range: 13, δ 222.3 and 217.2, and 14, δ 222.9
and 217.6. In each case, the latter is assigned to the cis CO
P(1)-B(1)-P(2)
P(1)-B(2)-P(2)
99.3(5)
99.5(5)
value in 17, 1.992 Å, as well as the bond lengths in related
6
cages species P2(R2NB)2BNR′2 and P2(R2NB)2SiR′2.7 The
average P-Ge bond length, 2.324 Å, is, as expected, larger than
the average P-Si bond length, 2.243 Å, in 17 due to the larger
covalent radius of Ge. The P-Ge distance is slightly longer
than the distance in (H3Ge)3P, 2.308(3) Å,18 but identical to
the distance in the cage species (Me2Ge)6P4, 2.322(8) Å.19 The
average P-B-P bond angle in 10, 99.4°, is similar to the
average value in 17, 98.8°, but the P-Ge-P angle, 80.7(1)°, is
slightly smaller than the P-Si-P angle, 84.8(1)°, in 17. The
sums of the internal angles at the phosphorus atoms in 10 are
219.9° (P1) and 218.3 (P2).
The coordination behaviors of 9 and 10 have been examined
with equimolar and excess amounts of Cr(CO)5‚NMe3. In all
cases, the 1:1 complexes P2((tmp)B)2(GePh2)‚Cr(CO)5 13 and
P2((tmp)B)2(GeMe2)‚(Cr(CO)5 14 are obtained as yellow crys-
talline solids. No evidence is found for coordination of two
Cr(CO)5 fragments. Compound 13 provides a weak parent ion
envelope in the mass spectrum (m/e 784-781). The infrared
2
due to its relative intensity and larger JPC coupling constant:
13, cis 7.2 Hz, trans 3.2 Hz, and 14, cis 7.0 Hz, trans
unresolved. These data are comparable to values reported for
Me3P‚Cr(CO)5,20 Cl3P‚Cr(CO)5,20 and Br3P‚Cr(CO)5.20
The molecular structures of 13 and 14 were determined by
single-crystal X-ray diffraction analysis and views of the
molecules are shown in Figures 2 and 3. In both cases the
structure shows a single Cr(CO)5 fragment bonded to one of
the apical phosphorus atoms of the cage. The coordinated cage
fragment in 13 is compressed slightly along the nonbonding
P‚‚‚P′ vector compared to the free ligand: P‚‚‚P′ distances, 13
2.949 Å, 10 3.010 Å. The compression is also reflected by the
internal cage angles. The angles at P(1) and P(2) are generally
larger for 13 relative to 10 and smaller at B(1), B(2) and Ge in
(17) Chen, T.; Duesler, E. N.; Paine, R. T.; No¨th, H. Phosphorus, Sulfur
Silicon 1994, 93-94, 73.
(18) Rankin, D. W. H.; Robiette, A. G.; Shelderick, G. M.; Beagley, B.;
Hewitt, T. G.J. Inorg. Nucl. Chem. 1969, 31, 2351.
(20) Davies, M. S.; Pierens, R. K.; Aroney, M. J. J. Organomet. Chem.
1993, 458, 141.
(19) Baudler, M.; Suchomel, H. Z. Anorg. Allg. Chem. 1983, 503, 7.

808 Inorganic Chemistry, Vol. 36, No. 5, 1997
Chen et al.
13. Similar trends are observed for 14. The Cr-P(1) bond
lengths, 13 2.531(1) Å and 14 2.503(1) Å, are slightly longer
Indeed, the 2:1 combination of 4 with Ph2GeCl2 gives the cage
molecule 10 and 2 exclusively, and that chemistry is summarized
in eq 4.
6
than the distances in P2(iPr2NB)2((tmp)B)‚Cr(CO)5 2.422(1),
Ph3P‚Cr(CO)5 2.486(4) Å21 and ((tmp)BPH)2‚Cr(CO)5 2.458(2)
Å.11 The Cr-CO (trans) distances, for 13, 1.843(4) Å, and for
14, 1.827(6) Å, are significantly shorter than the average Cr-
CO (cis) distance, for 13, 1.898(5) Å, and for 14, 1.889(5) Å,
which is consistent with 9 and 10 acting as moderately good σ
donors and poor π-accepting ligands. The Cr-CO (trans)
distances, for example, are shorter than the Cr-CO distance in
Cr(CO)6 1.909(3) Å.22 Similar trans Cr-CO bond shortening
was observed in P2(iPr2NB)2((tmp)B)‚Cr(CO)5.6
With regard to gaining a greater understanding of the
dehydrohalogenation processes, it is noteworthy that combina-
tion of 8 with the lithium salt 4 was examined. Two reaction
pathways might be anticipated. In one, the lithium salt 4 might
act like tBuLi initiating dehydrohalogenation of 8 with formation
of 10, LiCl, and the diphosphadiboretane 2. Alternatively, the
phosphide salt might substitute for a chloride on Ge, giving
[((tmp)B)2P(H)P]2GePh2 and LiCl. In fact, the dehydrohalo-
genation path is favored, and 10 is formed exclusively over the
substitution product. The generality of this reaction has not
been tested, although related reactions with P-silyl-1,3,2,4-
diphosphadiboretanes have been observed.23 In the present
chemical system, the P-germyl-1,3,2,4-diphosphadiboretane 7
was combined with Cr(CO)5‚NMe3 in an effort to prepare a
Cr(CO)5 complex of 7. Instead, a Cr(CO)5 complex, P2((tmp)B)2-
GeMe2‚Cr(CO)5, 14, of the cage species 9 was obtained in
moderate yield. The mechanism for the formation of 14 has
not yet been elucidated, although Me3N is likely behaving as
the base which promotes the dehydrohalogenation of 7. Whether
Cr(CO)5 addition precedes dehydrohalogenation by complex-
ation of a phosphane center in 7 or coordination follows
dehydrohalogenation and cage closure remains uncertain.
The 2:1 reactions of 3 and 4 with Me2GeCl2 and Ph2GeCl2
were also examined and found to give interesting and different
results. The 2:1 combination of 3 with Me2GeCl2 gives the
double chloride substitution product Me2Ge[P(iPr2NB)2PH]2 11
as shown in eq 3. Similarly, the 2:1 combination of 4 with
(4)
Neither 11 nor 12 displays a parent ion in the mass spectra,
and it is expected that both are susceptible to thermally promoted
P-Ge bond cleavage. Both compounds display P-H stretching
vibrations in the range 2270-2220 cm-1 in infrared spectra.
The compounds show a single resonance in the 11B{1H} NMR
spectra, but two resonances in the 31P{1H} NMR spectra. For
11, the proton coupled 31P NMR spectrum shows a singlet at δ
-142.1 and a doublet δ -149.09, 1JPH ) 191 Hz. Compound
12 gives a similar spectrum with resonances centered at δ
-100.5 and -110.9, but in this case the more downfield member
1
is split into a doublet by P-H coupling, JPH ) 180 Hz, and
both resonances are also split into a doublet by P-P coupling,
2JPP′ ) 45 Hz.
Conclusion
During our previous studies of the dehydrohalogenation
reactions of P-borylated-1,3,2,4-diphosphadiboretanes6 and P-si-
lylated-1,3,2,4-diphosphadiboretanes7 only intramolecular cage
closure products were observed from the chemistry outlined in
Scheme 1. In the present study, however, a condition is revealed
that appears to favor a competing intermolecular HCl elimination
pathway that produces oligomers. That condition is at least large
E element (Ge) with small substituents (Me). When the Ge
substituent is larger (Ph) with the large amino group tmp present
on the B atoms, intramolecular cage closure is favored. More
extensive steric influence studies will be required to elucidate
all the factors competing in this chemistry, and such work is in
progress at this time.
Acknowledgment is made to the National Science Founda-
tion (Grant CHE-9508668) and to the donors of The Petroleum
Research Fund, administered by the American Chemical Society,
for the support of this research (R.T.P.). A NATO grant initiated
the initial collaboration between the research groups in Albu-
querque and Munich.
(3)
Supporting Information Available: Tables containing details of
the X-ray data collection and refinement, heavy atom coordinates,
hydrogen atom coordinates, thermal parameters, and complete bond
lengths and angles (41 pages). Ordering information is given on any
current masthead page.
Me2GeCl2 gives a double substitution product Ph2Ge[P((tmp)B)-
PH]2 12. Compound 11 is obtained pure as a yellow solid while
12 typically is contaminated with small amounts of 4 and the
cage 9. The appearance of 9 suggests that dehydrohalogenation
of the intermediate 7 competes with the substitution process.
IC961026N
(21) Plastas, H. J.; Stewart, J. M.; Grim, S. O. Inorg. Chem. 1973, 12,
265.
(22) Whitaker, A.; Jeffery, J. W. Acta Crystallogr. 1967, 23, 1977.
(23) Chen, T.; Paine, R. T. Unpublished results.