Phosphine Boranes in Coordination Chemistry: An Efficient Method for the Synthesis of Chiral and Achiral Organophosphorus Pentacarbonyltungsten Complexes

Article abstract of DOI:10.1021/ic980004t

Organophosphorus boranes 1-6 and amine pentacarbonyltungsten complexes 14-20 react under mild conditions, to afford by ligand exchange the corresponding W(CO)₅(PR₃) 21-26 derivatives in 63-92% yields. The use of piperazine 13 as a diamine tungsten substituent permits a tandem reaction which removes the borane group and leads to the formation of the corresponding organophosphorus tungsten complex. The stereochemistry of the formation of pentacarbonyltungsten complexes from tertiary chiral organophosphorus borane compounds proceeds with a high stereoselectivity and retention of configuration at the chiral P center.

Full text of DOI:10.1021/ic980004t

2438
Inorg. Chem. 1998, 37, 2438-2442
Phosphine Boranes in Coordination Chemistry: An Efficient Method for the Synthesis of
Chiral and Achiral Organophosphorus Pentacarbonyltungsten Complexes
Nancy Brodie and Sylvain Juge´*
University of Cergy Pontoise, EA 1389, 5 Mail Gay Lussac, 95031 Cergy Pontoise Cedex, France
ReceiVed January 2, 1998
Organophosphorus boranes 1-6 and amine pentacarbonyltungsten complexes 14-20 react under mild conditions,
to afford by ligand exchange the corresponding W(CO)5(PR3) 21-26 derivatives in 63-92% yields. The use of
piperazine 13 as a diamine tungsten substituent permits a tandem reaction which removes the borane group and
leads to the formation of the corresponding organophosphorus tungsten complex. The stereochemistry of the
formation of pentacarbonyltungsten complexes from tertiary chiral organophosphorus borane compounds proceeds
with a high stereoselectivity and retention of configuration at the chiral P center.
Introduction
allows nucleophilic or electrophilic attack at the phosphorus
center with recovery of the final compound under a nonrace-
mizing decomplexation step.6 Moreover, borane adducts of
phosphorus compounds are interesting in organophosphorus
ligand synthesis because they possess an excellent reactivity
and do not present any purification or storage problems. As
part of our program concerning phosphine boranes in organo-
phosphorus synthesis, the direct use of borane complexes in
coordination chemistry was investigated.
Previously, we studied the asymmetric synthesis of organo-
phosphorus compounds via an oxazaphospholidine complexed
to a borane1 or a pentacarbonyl tungsten.1b,7 The main purpose
for this synthesis was the regio- and stereoselective ring opening
of the complex via P-O bond cleavage. Unfortunately, it was
not possible at the time to determine the stereochemistry of the
tungsten products, although it had been well established for the
analogous borane series.1d,e
As the stereochemistry of bond formation or cleavage at the
phosphorus center depends on the nucleophile substituents,3 it
is important to know the absolute configuration of phosphorus
compounds bearing sterically hindering groups such as W(CO)5.
On the other hand, new chiral tungsten complexes are of
particular interest for use in applied organometallic chemistry.8
For these reasons, we report here the direct transformation of
organophosphorus borane complexes 1-6 into chiral and achiral
pentacarbonyltungsten derivatives 21-26 (Table 1).
In recent years, significant strides have been achieved in the
asymmetric synthesis of phosphine ligands owing to the use of
the protecting group borane (BH3).1-5 The presence of BH3
(1) (a) U.S. Patent 5 043 465, 1989; Chem. Abstr. 1991, 115, 136399. (b)
Juge´, S.; Stephan, M.; Achi, S.; Geneˆt, J. P. Phosphorus Sulfur 1990,
49/50, 267-270. (c) Juge´, S.; Stephan, M.; Laffitte, J. A.; Geneˆt, J.
P. Tetrahedron Lett. 1990, 31 (44), 6357-6360. (d) Juge´, S.; Stephan,
M.; Geneˆt, J. P.; Halut-Desportes, S.; Jeannin, S. Acta Crystallogr.
1990, C46, 1849-1872. (e) Juge´, S.; Stephan, M.; Merde`s, R.; Geneˆt,
J. P.; Halut-Desportes, S. J.Chem. Soc., Chem. Commun 1993, 531-
533. (f) Juge´, S.; Merde`s, R.; Stephan, M.; Laffitte, J. A.; Geneˆt, J. P.
Phosphorus Sulfur 1993, 77, 199. (g) Kaloun, E. B.; Merde`s, R.; Geneˆt,
J. P.; Uziel J.; Juge´, S. J. Organomet. Chem. 1997, 529, 455-463.
(2) (a) Imamoto, T.; Oshiki, T.; Onozawa, T.; Kusumoto, T.; Sato, K. J.
Am. Chem. Soc. 1990, 112 (2), 5244-5252. (b) Oshiki, T.; Hikosaka,
T.; Imamoto, T. Tetrahedron Lett. 1991, 32 (28), 3371-3374. (c)
Oshiki, T.; Imamoto, T. J. Am. Chem. Soc. 1992, 114, 3975-3977.
(d) Imamoto, T.; Oshiki, T.; Onozawa, T.; Matsuo, M.; Hikosaka, T.;
Yanagawa, M. Heteroatom Chem. 1992, 3 (5.6), 563-575. (e)
Imamoto, T. Pure Appl. Chem. 1993, 65 (4), 655-660. (f) Imamoto,
T.; Matsuo, M.; Nonomura, T.; Kishikawa, K.; Yanagawa, M.
Heteroatom Chem. 1993, 4 (5), 475-486. (g) Imamoto, T.; Tsuruta,
H.; Wada, Y.; Masuda, H.; Yamaguchi, K. Tetrahedron Lett. 1995,
36 (45), 8271-8274.
(3) Uziel, J.; Stephan, M.; Kaloun, E. B.; Geneˆt, J. P.; Juge´, S. Bull. Soc.
Chim. Fr. 1997, 134, 379-389.
(4) (a) Ramsden, J. A., Brown, J. M.; Hursthouse, M. B.; Karalulov, A.
I. Tetrahedron: Asymmetry 1994, 5 (10), 2033-2044. (b) Peper, V.;
Stingl, K.; Thu¨mler, H.; Saak, W.; Haase, D.; Pohl, S.; Juge´, S.;
Martens, J. Liebigs Ann. 1995, 2123-2131. (c) Muci, A. R.; Campos,
K. R.; Evans, D. A. J. Am. Chem. Soc. 1995, 117, 9075-9076. (d)
Zhu, G., Terry, M., Zhang, X.Tetrahedron Lett. 1996, 37 (26), 4475-
4478. (e) Yang, H.; Lugan, N.; Mathieu, R. Organometallics 1997,
16, 2089-2095.
Experimental Section
Solvents (THF, ether, toluene) were dried and freshly distilled over
sodium/benzophenone under an argon atmosphere. Ethyl acetate and
CH2Cl2 were of reagent grade and distilled before use. Flash chro-
matography was realized on silica gel (230-400 mesh; Merck).
(5) (a) Brisset, H.; Gourdel, Y.; Pellon, P.; Le Corre, M. Tetrahedron
Lett. 1993, 34 (28), 4523-4526. (b) Gourdel, B.; Pellon, P.; Toupet,
L.; Le Corre, M. Tetrahedron Lett. 1994, 35 (8), 1197-1200. (c)
McKinstry, L.; Livinghouse, T. Tetrahedron 1995, 51, 7655-7666.
(d) Longeau, A.; Langer, F.; Knochel, P. Tetrahedron Lett. 1996, 37
(13), 2209-2212. (e) Pellon, P.; Le Goaster, C.; Toupet, L. Tetrahe-
dron Lett. 1996, 37 (27), 4713-4714. (f) Longeau, A.; Knochel, P.
Tetrahedron Lett. 1996, 37 (34), 6099-6102. (g) Hamada, Y.; Seto,
N.; Ohmori, H.; Hatano, K. Tetrahedron Lett. 1996, 37 (42), 7565-
7568. (h) Morimoto, T.; Ando, N.; Achiwa, K. Synlett 1996, 1211-
1212. (i) Longmire, J. M.; Zhu, G.; Zhang, X. Tetrahedron Lett. 1997,
38(3), 375-378. (j) Langer, F.; Pu¨ntener, K.; Stu¨rmer, R.; Knochel,
P. Tetrahedron: Asymmetry 1997, 8 (5), 715-738. (k) Longeau, A.;
Durand, S.; Spiegel, A.; Knochel, P. Tetrahedron: Asymmetry 1997,
8 (7), 987-990. (l) Longmire, J. M.; Zhang, X. Tetrahedron Lett.
1997, 38 (10), 1725-1728.
(6) (a) Imamoto, T.; Kusumoto, T.; Suzuki, N.; Sato, K. J. Am. Chem.
Soc. 1985, 107, 5301-5303. (b) Ward, T. R.; Venanzi, L. M.; Albinati,
A.; Lianza, F.; Gerfin, T.; Gramlich, V.; Ramos Tombo, G. M. HelV.
Chim. Acta 1991, 74, 983-988. (c) Brenchley, G.; Merifield, E.; Wills,
M.; Fedouloff, M. Tetrahedron Lett. 1994, 34 (17), 2791-2794.
(7) (a) Fr. Patent 2 603 286, 1986; Chem. Abstr. 1989, 110, 135490. (b)
Achi, S.; Geneˆt, J. P.; Juge´, S.; Potin, Ph. Phosphorus Sulfur 1987,
30, 688.
(8) Kirtley, S. W. In ComprehensiVe Organometallic Chemistry; Wilkin-
son, G., Ed.; Pergamon Press: New York, 1982; Vol. 3, pp 1255-
1384.
S0020-1669(98)00004-4 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/28/1998

Phosphine Boranes in Coordination Chemistry
Inorganic Chemistry, Vol. 37, No. 10, 1998 2439
Table 1. Formation of the Pentacarbonyltungsten Complexes 21-26 by Ligand Exchange with the Organophosphorus Boranes 1-6
All NMR spectral data were obtained on a Bruker DPX 250 (1H,
and piperazine (pipz) 20 were characterized by 1H NMR, IR, and
elemental analyses.
1
13C, 31P) spectrometer with TMS as the internal reference for H and
13C NMR, and 85% phosphoric acid as the external reference for 31P
NMR. Infrared spectra were recorded on a Perkin-Elmer 1600 FT and
a Bruker FT 45. Specific rotation values were determined at 20 °C on
a Perkin-Elmer 241 polarimeter. Mass spectral analyses were performed
on a Nermag R10-10C and a Kratos MS-50 for exact mass, at the
laboratories of mass spectroscopy of ENSCP and University of P. &
M. Curie (Paris), respectively. The major peak m/z is given with the
intensity as the percent of the base peak in brackets. Elemental analyses
were measured with a precision superior to 0.3%, at the Laboratories
of Microanalyse of the University P. & M. Curie (Paris), and at the
CNRS (Vernaison, France).
The diphenylmethyl phosphine borane 1 and triphenylphosphine
borane 2 were prepared from the corresponding phosphine and borane
dimethyl sulfide in THF and then recrystallized in hexane (1, mp )
55 °C; lit.6a mp ) 51 °C; 2, mp ) 189 °C; lit.9 mp ) 189 °C). The
complexes (2S,4R,5S)-(-)-3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphos-
pholidineborane 3, (R)-(+)-[(O-methyl)methylphenylphosphinite]borane
4, (S)-(+)-[(O-methyl) o-anisylphenylphosphinite]borane 5, and (R)-
(+)-o-anisylmethylphenylphosphineborane 6, were prepared from the
(+)-ephedrine according to the published procedure.1c,g
The amine pentacarbonyltungsten complexes 14-20 were prepared
from amines 7-13 and W(CO)5(THF), freshly prepared by irradiation
of W(CO)6 in THF10,11 (Table 2). In the case of the pyrazine 12 and
piperazine 13, an excess of amine (5 equiv) was used to alleviate the
formation of the bimetallic complex.
The pentacarbonyltungsten complexes of pyridine (py) 14,11 piperi-
dine (pip) 15,12 benzo[c]cinnoline (bzc) 16,13 and pyrazine (pyz) 1714
were identified by their IR spectra as previously reported. The
complexes of 4-phenylpyrimidine (4Ph-pm) 18, pyrimidine (pm) 19,14a
4-Phenylpyrimidine Pentacarbonyltungsten Complex: W(CO)5‚
(4Ph-pm) 19. Orange-yellow crystals; mp ) 160-162 °C (3:7 hexane/
CH2Cl2); Rf ) 0.3 (9:1 cyclohexane/AcOEt); IR (THF) νjCO cm-1 2072
1
(w), 1974 (w), 1931 (s), 1902 (sh); H NMR (CDCl3) δ 9.47 (1H, s,
3
H(2) pm), 8.98 (1H, d, JH(6)H(5) ) 6 Hz, H(6) pm), 8.12 (2H, m, Ph),
3
7.71 (1H, d, JH(5)H(6) ) 6 Hz, H(5) pm), 7.57 (3H, m, Ph); 13C NMR
(CDCl3) δ 198.4 (CO(cis)), 163.3, 162.0, 132.7, 129.4, 127.4, 117.3;
anal. calcd for C15H8N2O5W (480), C, 37.50; H, 1.67; N, 5.83; found
C, 37.83; H, 1.76; N, 5.90.
Pyrimidine Pentacarbonyltungsten Complex: W(CO)5‚(pm) 19.14a
Orange-yellow crystals; IR (THF) νjCO cm-1 2071 (w), 1975 (w), 1932
1
(s), 1903 (sh); H NMR (CDCl3) δ 9.5 (1H, s, H(2)), 9.06 (1H, dd,
3JH(6)H(5) ) 4.5 Hz, 4JH(6)H(4) ) 2.2 Hz, H(6)), 8.84 (1H, dd, 3JH(4)H(5)
4.9 Hz, JH(4)H(6) ) 2.3 Hz, H(4)), 7.37 (1H, dd, JH(5)H(4) ) 4.9 Hz,
3JH(5)H(6) ) 2.3 Hz, H(5)); anal. calcd for C9H4N2O5W (404), C, 26.73;
H, 0.99; N, 6.93; found C, 26.91; H, 1.02; N, 7.09.
)
4
3
Piperazine Pentacarbonyltungsten Complex: W(CO)5‚(pipz) 20.
Yellow crystals; mp ) 141 °C (3:7 hexane/CH2Cl2); Rf ) 0.55
(8:2 cyclohexane/AcOEt); IR (THF) νjCO cm-1 2068 (w), 1974 (m),
1
2
1922 (s), 1894 (sh); H NMR (dioxane-d8) δ 2.93 (2H, d, JH
)
H
eq ax
3
12.6 Hz, Heq(1, 1′)), 2.76 (2H, qd, J ) 11.3 Hz, JH
) 3.1 Hz,
) 12.6 Hz, Heq(2, 2′)), 2.46 (2H, qd,
H
ax eq
2
Hax(1, 1′)), 2.60 (2H, d, JH
H
eq ax
3
J ) 11.2 Hz, JH
) 2.8 Hz, Hax(2, 2′)); 13C NMR (dioxane-d8) δ
H
eq ax
60.1 (WNCCN), 49.1 (WNCCN); MS (EI) m/z (relative intensity)
395 (3), 382 (16), 354 (18), 326 (45), 324 (59), 322 (59), 296 (20),
268 (32), 238 (27), 211 (34), 85 (75), 56 (100); anal. calcd for
C9H10N2O5W (410), C, 26.34; H, 2.44; N, 6.83; found C, 26.30; H,
2.67; N, 7.16.
Procedure for Exchange Reactions. The exchange reactions were
carried out in Schlenk tubes under an atmosphere of argon with stirring.
Equivalent quantities of an amine pentacarbonyltungsten complex and
a phosphine borane (1 mmol) were dissolved in dry THF (10 mL) and
heated to the desired temperature (between 60 and 120 °C), and the
progress of the reaction was monitored by IR spectroscopy. Formation
of the phosphine pentacarbonyltungsten complex is indicated by a
characteristic shift of the CO stretching frequency to higher energy in
comparison to the amine adduct. After a 24 h period, the formation of
W(CO)6 became predominant in most cases, so the exchange reactions
were stopped. In contrast, only a very small amount of W(CO)6 was
detected during the reactions with the piperazine complex 20, even
after several days. After solvent removal, the crude product was
purified by flash chromatography using a mixture of cyclohexane/ethyl
acetate as eluent to give the phosphine pentacarbonyltungsten complexes
21-26. The pentacarbonyltungsten complexes W(CO)5PPh2Me 2115
(9) (a) Frisch, M. A.; Heal, H. G.; Mackle, H.; Madden, I. O. J. Chem.
Soc. 1965, 899-907. (b) Nainan, K. C.; Ryschkewitsch, G. E. Inorg.
Chem. 1969, 8, 2671-2674.
(10) Strohmeier, W. Angew. Chem., Int. Ed. Engl. 1964, 3, 730-737.
(11) Angelici, R. J.; Malone, M. D. Inorg. Chem. 1967, 6, 1731-1736.
(12) (a) Ingemanson, C. M.; Angelici, R. J. Inorg. Chem. 1968, 7, 2646-
2648. (b) Dennenberg, R. J.; Darensbourg, D. J. Inorg. Chem. 1972,
11, 72-77.
(13) (a) Kooti, M.; Nixon, J. F. J. Organomet. Chem. 1976, 105, 217-
230. (b) Frazier, C. C., III; Kisch, H. Inorg. Chem. 1978, 17, 2736-
2744. (c) Abel, E. W.; Blackwall, E. S.; Orrell, K. G.; Sik, V. J.
Organomet. Chem. 1994, 464, 163-170.
(14) (a) Pannell, K. H.; Guadalupe de la Paz Saenz Gonzalez, M.; Leano,
H.; Iglesias, R. Inorg. Chem. 1978, 17, 1093-1095. (b) Zulu, M. M.;
Lees, A. J. Inorg. Chem. 1989, 28, 85-89. (c) Zulu, M. M.; Lees, A.
J. Organometallics 1989, 8, 955-960.

2440 Inorganic Chemistry, Vol. 37, No. 10, 1998
Brodie and Juge´
Table 2. Amine Pentacarbonyltungsten Complexes 14-20 Used for Ligand Exchange
Scheme 1
and W(CO)5PPh3 2215,16 were identified by their NMR and IR spectra
as previously described.
(2S,4R,5S)-(+)-3,4-Dimethyl-2,5-diphenyl-1,3,2-oxazaphospholi-
dine Pentacarbonyltungsten 23. Yellow solid; mp ) 68 °C (hexane);
TLC Rf ) 0.4 (95:5 hexane/AcOEt); [R]D ) +32.1 (c 5, CHCl3); IR
1
(THF) νjCO cm-1 2075 (w), 1942 (br, s); H NMR (CDCl3) δ 7.56-
7.31 (10H, m, arom), 5.41 (1H, dd, 3JH(4)H(5) ) 6.6 Hz, 3JPOCH ) 3 Hz,
CHO), 3.36 (1H, m, 3JHH ) 6.4 Hz, CHN), 2.85 (3H, d, 3JPNCH ) 12.5
Hz, NCH3), 0.75 (3H, d, JHH ) 6.5 Hz, CH3); 13C NMR (CDCl3) δ
3
(20); MS (EI) isomass calcd for C19H15O7PW (570) m/z (relative
intensity), 573 (18), 572 (85), 571 (21), 570 (100), 569 (58), 568 (76);
found 573 (20), 572 (76), 571 (27), 570 (100), 569 (55), 568 (70).
2
196.0 (d, JPWCO ) 8.7 Hz, CO(cis)), 137.1, 130.5, 128.4 (d, JPC
)
2
13.3 Hz), 128.3, 127.9 (d, JPC ) 13 Hz), 126.9, 85.0 (d, JPOC ) 8.8
2
3
Hz, CHO), 58.1 (CHN), 30.6 (d, JPNC ) 5 Hz, NCH3), 14 (d, JPNCC
) 14 Hz, CH3); 31P NMR (CDCl3) δ +147.6 (m, 1JPW ) 313 Hz); MS
(EI) m/z (relative intensity) 597 (84), 595 (100), 565 (9), 511 (55),
455 (16); anal. calcd for C21H18NO6PW (595), C, 42.29; H, 3.20; N,
2.46; found C, 42.35; H, 3.02; N, 2.35.
(S)-(-)-o-Anisylmethylphenylphosphine Pentacarbonyltungsten
26. Uncrystallized, yellow; TLC Rf ) 0.51 (9:1 cyclohexane/AcOET);
[R]D ) - 77 (c 2.3, CHCl3); IR (THF) νjCO cm-1 2069 (w), 1933 (br,
vs); 1H NMR (CDCl3) δ 7.6-6.8 (9H, m, arom), 3.66 (3H, s, CH3O),
2
2.14 (3H, d, JPCH ) 6.5 Hz, CH3P); 13C NMR (CDCl3) δ 197.5 (d,
The minor epimer (2R,4R,5S) is detected in a 6:94 ratio, after the
complexes 14 and 3 were heated in refluxing toluene for 24 h. 1H
NMR (CDCl3) δ 5.60 (1H, d, 3JH(4)H(5) ) 5.6 Hz, CHO), 3.77 (1H, m,
2JPWC ) 7 Hz, CO(cis)), 159.7, 135.5, 132.1, 131.5 (d, JPC ) 3 Hz),
130.0, 126.6 (d, JPC ) 41 Hz), 128.5 (d, JPC ) 10 Hz), 120.9 (d, JPC
1
) 8 Hz), 110.9, 54.9 (CH3O), 21.0 (d, JPC ) 29.5 Hz, PCH3); 31P
3
3JHH ) 6.3 Hz, CHN), 3.05 (3H, d, JPNCH ) 10.9 Hz, NCH3), 0.46
NMR (CDCl3) δ -10.4 (1JPW ) 237 Hz); MS (EI) m/z (relative
intensity) 554 (12), 526 (32), 498 (11), 470 (81), 414 (100), 319 (17),
91 (33); HRMS (EI) calcd for C19H15O6PW [M], 554.0115; found
554.0109; anal. calcd for C19H15O6PW (554), C, 41.15; H, 2.70; found
C, 41.94; H, 2.88.
3
(3H, d, JHH ) 6.7 Hz, CH3).
(R)-(+)-[(O-Methyl)methylphenylphosphinite] Pentacarbonyl-
tungsten 24. Uncrystallized; TLC Rf ) 0.6 (9:1 hexane/AcOEt); [R]D
) +4.6 (c 1.1, CH2Cl2); IR (THF) νjCO cm-1 2080 (w), 1970 (br, vs);
1H NMR (CDCl3) δ 7.65 (m, 5H), 3.40 (3H, d, 3JPOCH ) 10 Hz, CH3O),
2.20 (3H, d, 2JPCH ) 4 Hz, CH3P); 31P NMR (CDCl3) δ +114 (1JPW
280 Hz).
)
Results and Discussion
(S)-(+)-[(O-Methyl)-o-anisylphenylphosphinite] Pentacarbonyl-
tungsten 25. Uncrystallized; [R]D ) +64.4 (c 2.3, CH2Cl2); IR (THF)
νjCO cm-1 2071 (w), 1940 (br, vs); 1H NMR (CDCl3) δ 7.70-7.55 (3H,
The reaction of the borane complex 2 or 3 with W(CO)5-
(THF) (or W(CO)6) at room temperature or after heating gave
poor yields of the corresponding phosphine pentacarbonyltung-
sten complexes W(CO)5(PPh3) 22 or W(CO)5(C16H18NOP) 23
(<5%).17
Thus, our strategy toward ligand exchange was modified in
order to favor the rupture of the P-B bond. This was achieved
m), 7.5-7.4 (4H, m), 7.15 (1H, dd), 6.9 (1H, dd), 3.4 (3H, d, 3JPOCH
)
2
13 Hz, OCH3); 13C NMR (CDCl3) δ 196.9 (d, JPWC ) 8.1 Hz, CO-
(cis)), 132.0 (d, JPC ) 30 Hz), 132.0, 131.2, 129.6, 128.2 (d, JPC ) 10
Hz), 121.0 (d, JPC ) 7.2 Hz), 110.8 (d, JPC ) 5 Hz), 53.8, 53.7; MS
(EI) m/z (relative intensity) 572 (18), 570 (25), 542 (39), 514 (9), 486
(59), 430 (63), 383 (13), 247 (100), 183 (55), 107 (34), 91 (23), 77
(15) (a) McFarlane, C. E.; McFarlane, W.; Rycroft, D. S. J. Chem. Soc.,
Dalton Trans. 1976, 1616-1622. (b) Dickson, C. A.; McFarlane, A.
W.; Coville, N. J. Inorg. Chim. Acta 1989, 158, 205-209.
(16) (a) Grim, S. O.; Wheatland, D. A.; McFarlane, W. J. Am. Chem. Soc.
1967, 89, 5573-5577. (b) Bancroft, G. M.; Dignard-Bailey, L.;
Puddephatt, R. J. Inorg. Chem. 1986, 25, 3675-3680.

Phosphine Boranes in Coordination Chemistry
Inorganic Chemistry, Vol. 37, No. 10, 1998 2441
Table 3. Results of Ligand Exchange between the Amine Pentacarbonyltungsten Complexes 14-20 and the Organophosphorus (PIII) Borane
1-3
entry no.
amine (pKa)
W(CO)5(amine)
BH3(PR3)
conditions (solvent; T, °C)
W(CO)5(PR3)
yielda (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
7 (5.2)
7 (5.2)
7 (5.2)
8 (11.1)
8 (11.1)
9 (1.8)
14
14
14
15
15
16
16
17
18
18
19
19
20
20
1
3
3
1
3
1
3
1
1
3
1
3
1
2
toluene; reflux
toluene; reflux
THF; reflux
THF; 60 °C
THF; 60 °C
THF; 60 °C
THF; 60 °C
THF; 60 °C
THF; 60 °C
THF; 60 °C
THF; 60 °C
THF; 60 °C
THF or dioxane; 60 °C
THF or dioxane; 60 °C
21
23b
23c
21
23
21
23
-
21
23
21
23
21
22
40
30
8
50
8
60
0
-
73
5
87
10
92
90
9 (1.8)
10 (0.65)
11 (1.3)
11 (1.3)
12 (1.3)
12 (1.3)
13 (4.19)
13 (4.19)
a Isolated yield. b [R]D ) +11.3 (c 1, CHCl3). c [R]D ) +20.9 (c 1, CHCl3).
by supplying an amine for the dissociating borane group,18
instead of CO or THF which form weaker bonds with borane.
Moreover, the quantitative substitution of an amine substituent
by a phosphine ligand in pentacarbonyltungsten complexes is
a well-known reaction.12,19 In this case, the facility of the
reaction is directly related to the basicity of the coordinated
amine ligand, with a good correlation between the decreasing
rate of substitution and the increasing pKa values of the amine.
The rupture of the amine-metal bond is the rate determining
step for these substitution reactions, and for this reason the
kinetics give an idea of the strength of the W-N bond.12a
Here, the substitution reaction is not quite the same because
the free PIII compound must be generated by a tandem reaction,
involving the complexation of the borane group by the amine
ligand (Scheme 1). We emphasize here that an amine with a
low pKa increases the possibility of its dissociation from the
tungsten complex, while the removal of the borane group should
be favored by an amine with a high pKa. Consequently, in view
of these opposing factors, the ligand exchange was studied with
a variety of amine pentacarbonyltungsten complexes 14-20
(Scheme 1; Table 3). Examination of the results in Table 3
shows that the pyridine pentacarbonyltungsten 14 reacts with
the diphenylmethylphosphineborane 1 in refluxing toluene, to
give the complex 21 with 40% yield (entry 1). This is already
an improvement over the reaction with W(CO)5(THF) men-
tioned above.17 Under the same conditions, W(CO)5(py) 14
also reacts with oxazaphospholidine borane 3 to give complex
23 in a 30% yield (entry 2). The optical activity ([R]D ) +11.3)
and the 1H NMR analysis of the chiral complex 23, obtained in
refluxing toluene (entry 2), indicate partial epimerization of the
oxazaphospholidine ligand.20 This can be explained by the
inversion of configuration at the chiral P center, owing to the
permutation of the phenyl and W(CO)5 groups, bringing the
latter group in opposite position to the substituents of the ring.21
Unfortunately, the yield of 23 decreased to 8% under milder
conditions (refluxing THF), even though a better diastereose-
lectivity was obtained (entry 3). When the piperidine complex
15 was used for the ligand exchange with 1 or 3, the phosphine
pentacarbonyltungsten complexes 21 and 23 were obtained with
yields of 50 and 8%, respectively (entries 4 and 5). Better
results were obtained when the diamine ligands benzo[c]-
cinnoline, phenylpyrimidine, and especially pyrimidine were
used, because the phosphine pentacarbonyltungsten complex 21
was isolated in yields ranging from 60 to 87% (entries 6, 9,
and 11). However, the same efficiency was not observed for
the formation of the chiral complex 23, which was obtained in
very low yields (0-10%) (entries 7, 10, and 12). W(CO)5-
(pyz) 17 undergoes quantitative ligand substitution with free
phosphines at room temperature but does not react with the
phosphine boranes even by heating at 60 °C (entry 8). The
facility of substitution of W(CO)5(pyz) 17 indicates that the
W-N bond is relatively weak, but at the same time the pKa
(0.65) for pyrazine is too low for borane group removal from
the phosphine borane complex. Moreover, this complex is
thermally unstable and decomposes rapidly at 60 °C. Finally,
the use of the complex 20 bearing the piperazine ligand (pKa
) 4.19), permits efficient exchange with the phosphine boranes
1-6 in THF or dioxane at 60 °C (Tables 3 and 4). Under these
conditions, the corresponding phosphine pentacarbonyltungsten
complexes 21 and 22 were obtained from 1 and 2, in yields of
90 and 92%, respectively (Table 3, entries 13 and 14).
Another interesting aspect of the exchange reactions, is the
formation of a white insoluble powder 27 when the amine
complexes 18-20 are used (Scheme 1). These insoluble white
powders do not melt but decompose between 200 and 220 °C,
and their IR spectra exhibit strong bands at 800 and 1300 cm-1
which are characteristic of the presence of B-N bonds.22
The efficiency of ligand exchange with piperazine penta-
carbonyltungsten 20 is demonstrated by the preparation of chiral
complexes 23-26 from the borane adducts 3-6 in yields of
63-90% (Table 4, entries 1-4). It is also of great interest that
1
the optical activity20 and the H NMR analysis of the oxaza-
phospholidine complex 23 indicate no detectable epimerization
(entry 1). These results also prove that the mechanism of ligand
exchange occurs with retention of configuration at the chiral P
(20) A sample of the enantiomer of the complex 23 ([R]D ) -32.1; c 5,
CHCl3) has been prepared according to the procedure decribed in refs
1c and 7, by reaction of W(CO)5(THF) with (2R,4S,5R)-(+)-3,4-
dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine derived from (-)-
ephedrine.
(21) The epimerization of this heterocycle during quaternization has already
been observed; see: Juge´, S.; Wakselman, M.; Stephan, M.; Geneˆt, J.
P. Tetrahedron Lett. 1990, 31, 4443-4444.
(17) The exchange reaction between the complex 2 and W(CO)5(THF) was
mentioned by P. Pellon, Y. Gourdel, and M. Le Corre at the “Journe´es
de Chimie Organique de SFC”, Palaiseau, France in September 1992
and reexamined by us.
(18) (a) Baldwin, R. A., Washburn, R. M. J. Org. Chem. 1961, 26, 3549-
3550. (b) Pelter, A.; Smith, K. Boron-Nitrogen Compounds. In
ComprehensiVe Organic Chemistry; Barton, D., Ollis, W. D., Eds.;
Pergamon Press: New York, 1979; Vol. 3, pp 925-940.
(22) The formation of oligomers and eventually polymers by heating
diborane and piperazine together has been described (Burg, A. B.;
Iachia, B. Inorg. Chem. 1968, 7, 1670-1672) and prepared by reaction
of W(CO)5(THF) with the enantiomerically pure (R)-(+)-o-anisylm-
ethylphenylphosphine derived from (+)-ephedrine.1c
(19) Howell, J. A.; Burkinshaw, P. M. Chem. ReV. 1983, 83, 557-599.

2442 Inorganic Chemistry, Vol. 37, No. 10, 1998
Brodie and Juge´
Table 4. Results of the Ligand Exchange between the Piperazine Pentacarbonyltungsten Complexes 20 and the Chiral Organophosphorus (PIII)
Boranes 3-6
entry no.
BH3(PR3)
abs. conf.
react. timea
W(CO)5(PR3)
yieldb (%)
abs. conf. product
1
2
3
4
3
4
5
6
(-)-(2S,4R,5S)
(+)-(R)
72 h
168 h
48 h
23
24
25
26
63
65
90
80
(+)-(2R,4R,5S)c
(+)-(S)d
(+)-(S)
(+)-(R)e
(-)-(R)
24 h
(-)-(S) f
a All essays were realized in THF (or dioxane) at 60 °C. b Isolated yield. c Reference 20. d [R]D ) +4.6 (c 1.1, CH2Cl2). e [R]D ) +64.4 (c 2.3,
CH2Cl2). f [R]D ) -77 (c 2.3, CHCl3).
center. The high stereoselectivity has been confirmed by the
reaction between the piperazine complex precursor 20, and the
(R)-(+)-o-anisylmethylphenylphosphine borane (PAMP‚BH3) 6,
which gives the first example of an optically pure (S)-PAMP
pentacarbonyltungsten complex 26 (entry 4). On this basis, we
can reasonably believe that the absolute configurations of the
phosphinite pentacarbonyltungsten complexes 24 and 25 (dex-
trogyre) must be S and R, respectively (entries 3 and 4).
It also appears that the reactions with the oxazaphospholi-
dine and the phosphinite borane 3, 4, require longer reaction
times and give the lowest yields of the borane complexes
studied (Tables 3 and 4). The efficiency of the exchange could
be related to the strength of the B-P bond, which depends on
the basicity and on the Tolman cone angle of the phosphorus
compounds.23,24
In conclusion, the first efficient method giving chiral and
achiral phosphine pentacarbonyltungsten complexes has been
achieved from a ligand exchange reaction between amine
W(CO)5 and a phosphine borane. The piperazine pentacarbo-
nyltungsten W(CO)(pipz) 20 was found to be the best precursor,
affording the corresponding chiral and achiral phosphorus
complexes in high yields (63-92% yields). The stereochemistry
of this reaction proceeds with retention of configuration at the
chiral P center and high stereoselectivity, permitting the
preparation of new optically active organophosphorus penta-
carbonyltungsten complexes. It is noteworthy that this method
is of particular interest, because the isolation of the organo-
phosphorus compounds in tricoordinate form is not necessary.
The mechanism of ligand exchange25 and the principle strategy
for the preparation of complexes with other transition metals
are currently under investigation.
(23) Tolman, C. A. Chem. ReV. 1977, 77, 313-348.
Acknowledgment. We thank Ms. S. Baudu and B. Gilles
for partial technical assistance, and the Ministry of Research
for financial support to our team.
(24) For the influence of σ donor character or basicity of P(III) organo-
phosphorus ligands toward borane complex, see: (a) Lines, E. L.;
Centofanti, L. F.; Hafler, D. A. Phosphorus 1974, 5, 5-7. (b) Alford,
K. J.; Bishop, E. O.; Smith, J. D. J. Chem. Soc., Dalton Trans. 1976,
920-922. For empiric rules on the donor-acceptor properties of
phosphorus ligand, see: (c) Tolman, C. A. J. Am. Chem. Soc. 1970,
92, 2953-2956.
IC980004T
(25) Brodie, N.; Dosseh, G. In preparation.