Pt(Me-Duphos)-catalyzed asymmetric hydrophosphination of activated olefins: Enantioselective synthesis of chiral phosphines

Article abstract of DOI:10.1021/om990882e

Platinum-catalyzed asymmetric hydrophosphination of activated olefins using the catalyst precursor Pt(R,R-Me-Duphos)(trans-stilbene) (1) gives chiral phosphines with control of stereochemistry at phosphorus or carbon centers. Stoichiometric reactions of 1

Full text of DOI:10.1021/om990882e

950
Organometallics 2000, 19, 950-953
P t(Me-Du p h os)-Ca ta lyzed Asym m etr ic
Hyd r op h osp h in a tion of Activa ted Olefin s:
En a n tioselective Syn th esis of Ch ir a l P h osp h in es
Ivan Kovacik, Denyce K. Wicht, Navrose S. Grewal, and David S. Glueck*
Department of Chemistry, 6128 Burke Laboratory, Dartmouth College,
Hanover, New Hampshire 03755
Christopher D. Incarvito, Ilia A. Guzei, and Arnold L. Rheingold
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Received November 2, 1999
Sch em e 1. P r op osed Mech a n ism for P t-Ca ta lyzed
Hyd r op h osp h in a tion a
Summary: Platinum-catalyzed asymmetric hydrophos-
phination of activated olefins using the catalyst precur-
sor Pt(R,R-Me-Duphos)(trans-stilbene) (1) gives chiral
phosphines with control of stereochemistry at phosphorus
or carbon centers. Stoichiometric reactions of 1 allow
observation of P-H oxidative addition, diastereoselective
olefin insertion, and reductive elimination steps, which
make up the proposed catalytic cycle.
Chiral phosphines, valuable ligands for metal-cata-
lyzed asymmetric reactions,1 are usually prepared either
by resolution or by using a stoichiometric amount of a
chiral auxiliary.2 Surprisingly little work has been
reported on metal-catalyzed asymmetric syntheses.3 We
report here that Pt-catalyzed asymmetric hydrophos-
phination of activated olefins4 can be used to prepare
chiral phosphines with control of stereochemistry at
phosphorus or carbon. Although the enantiomeric ex-
cesses (ee’s) available thus far are low, mechanistic
understanding may allow further development of these
new reactions.
a
[Pt] ) Pt(diphosphine), X ) CN, CO2R, or other electron-
withdrawing group.
Sch em e 2. P r op osed Mech a n ism for P t-Ca ta lyzed
Asym m etr ic Hyd r op h osp h in a tion of Disu bstitu ted
Alk en esa
Scheme 1 shows a mechanism for Pt-catalyzed hy-
drophosphination, proposed on the basis of our previous
studies.5 After P-H oxidative addition, P-C bond
* Author for correspondence. E-mail: David.Glueck@Dartmouth.Edu.
(1) (a) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis: the
Applications and Chemistry of Catalysis by Soluble Transition Metal
Complexes, 2nd ed.; Wiley: New York, 1992. (b) Noyori, R. Asymmetric
Catalysis in Organic Synthesis; Wiley-Interscience: New York, 1994.
(2) (a) Pietrusiewicz, K. M.; Zablocka, M. Chem. Rev. 1994, 94,
1375-1411. (b) Kagan, H. B.; Sasaki, M. In The Chemistry of
Organophosphorus Compounds; Hartley, F. R., Ed.; J ohn Wiley and
Sons: Chichester, England, 1990; Vol. 1; pp 51-102.
(3) An important recent exception is Burk’s synthesis of Duphos
ligands, which relies on Ru-Binap-catalyzed asymmetric hydrogenation
of â-keto esters (Burk, M. J .; Feaster, J . E.; Nugent, W. A.; Harlow, R.
L. J . Am. Chem. Soc. 1993, 115, 10125-10138).
a
[Pt] ) Pt(chiral diphosphine), X ) CN, CO2R, or other
electron-withdrawing group.
(4) Pringle and co-workers have shown that Pt-catalyzed hydro-
phosphination can be used to prepare functionalized phosphines. (a)
Costa, E.; Pringle, P. G.; Worboys, K. Chem. Commun. 1998, 49-50.
(b) Costa, E.; Pringle, P. G.; Smith, M. B.; Worboys, K. J . Chem. Soc.,
Dalton Trans. 1997, 4277-4282. (c) Pringle, P. G.; Brewin, D.; Smith,
M. B.; Worboys, K. In Aqueous Organometallic Chemistry and Cataly-
sis; Horvath, I. T., J oo, F., Eds.; Kluwer: Dordrecht, 1995; Vol. 5; pp
111-122. (d) Hoye, P. A. T.; Pringle, P. G.; Smith, M. B.; Worboys, K.
J . Chem. Soc., Dalton Trans. 1993, 74, 269-274. (e) Pringle, P. G.;
Smith, M. B. J . Chem. Soc., Chem. Commun. 1990, 1701-1702. (f)
Harrison, K. N.; Hoye, P. A. T.; Orpen, A. G.; Pringle, P. G.; Smith, M.
B. J . Chem. Soc., Chem. Commun. 1989, 1096-1097. See also: (g)
Nagel, U.; Rieger, B.; Bublewitz, A. J . Organomet. Chem. 1989, 370,
223-239. (h) Giardello, M. A.; King, W. A.; Nolan, S. P.; Porchia, M.;
Sishta, C.; Marks, T. J . In Energetics of Organometallic Species;
Martinho Simoes, J . A., Ed.; Kluwer: Dordrecht, 1992; pp 35-51.
formation occurs by selective insertion of the olefin into
the Pt-P bond. Reductive elimination forms the product
and regenerates Pt(0). Since the insertion step can be
diastereoselective,5,6 use of a chiral Pt catalyst could
lead to enantio-enriched product. For example, a disub-
stituted olefin could give a phosphine (Scheme 2) with
controlled stereochemistry at either of the alkene car-
(5) (a) Wicht, D. K.; Kourkine, I. V.; Lew, B. M.; Nthenge, J . M.;
Glueck, D. S. J . Am. Chem. Soc. 1997, 119, 5039-5040. (b) Wicht, D.
K.; Kourkine, I. V.; Kovacik, I.; Glueck, D. S.; Concolino, T. E.; Yap,
G. P. A.; Incarvito, C. D.; Rheingold, A. L. Organometallics 1999, 18,
5381-5394.
10.1021/om990882e CCC: $19.00 © 2000 American Chemical Society
Publication on Web 02/24/2000

Communications
Organometallics, Vol. 19, No. 6, 2000 951
Sch em e 3. P r op osed Mech a n ism for P t-Ca ta lyzed
Asym m etr ic Hyd r op h osp h in a tion Usin g Ra cem ic
Secon d a r y P h osp h in esa
Sch em e 4
a
[Pt] ) Pt(chiral diphosphine), X ) CN, CO2R, or other
electron-withdrawing group.
temperature, consistent with rapid P inversion on the
NMR time scale.6 A crystal of 2 whose structure was
solved by X-ray crystallography was found to be a single
diastereomer (Figure 2).10
Treatment of 2 with acrylonitrile, observed by NMR
at -20 °C, led to diastereoselective insertion into the
Pt-P bond and formation of four alkyl hydrides Pt(Me-
Duphos)[CH(CN)CH2P(Ph)(Is)](H) (3a -d , Scheme 4, see
Table 1 for selected NMR data) whose relative abun-
dance in solution depended on temperature and reaction
time. For example, after 30 min at -20 °C, the ratio of
these isomers was 1:7:9:20.11 On warming to room
temperature, complexes 3a -d formed the P-chiral
tertiary phosphine PPh(Is)(CH2CH2CN) (4, 63-71%
ee)12 and the acrylonitrile complex Pt(Me-Duphos)(CH2-
CHCN) (5);13 some PH(Ph)(Is) was also produced.14
F igu r e 1. ORTEP diagram of Pt(Me-Duphos)(trans-stil-
bene) (1) with 30% thermal ellipsoids, and hydrogen atoms
omitted for clarity. Selected bond lengths (Å) and angles
(deg): Pt-P(1) ) 2.235(4), Pt-P(2) ) 2.240(3), Pt-C(19)
) 2.102(12), Pt-C(20) ) 2.113(12), C(19)-C(20) ) 1.436-
(18), P(1)-Pt-P(2) ) 88.49(13), C(19)-Pt-C(20) ) 39.8-
(5), P(1)-Pt-C(19) ) 155.3(4), P(1)-Pt-C(20) ) 115.5(4),
P(2)-Pt-C(19) ) 116.2(4), P(2)-Pt-C(20) ) 155.9(4), (P-
Pt-P) - (C-Pt-C) ) 3.9.
(7) (a) Me-Duphos ) (R,R)-Me-Duphos as shown in Figures 1 and 2
and Scheme 4; see: Wicht, D. K.; Zhuravel, M. A.; Gregush, R. V.;
Glueck, D. S.; Guzei, I. A.; Liable-Sands, L. M.; Rheingold, A. L.
Organometallics 1998, 17, 1412-1419, for this and other stilbene
complexes. (b) Crystal data for 1: P21, orange block, a ) 10.4240(4)
Å, b ) 13.6432(5) Å, c ) 11.3386(4) Å, â ) 114.682(2)°, V ) 1465.22(9)
Å3, Z ) 2, µ(Mo KR) ) 49.16 cm-1, temp ) 173(2) K, R(F) ) 3.93%,
R(wF2) ) 9.28%. (c) Pt-P distances (Å) for other chiral Pt(diphos)-
(trans-stilbene) complexes: for Tol-Binap, 2.2806(9), 2.2840(8); for
Chiraphos, 2.272(2), 2.277(2), 2.271(2), 2.274(2); for Diop, 2.284(2),
2.290(2).
bons. In a more complicated case (Scheme 3), racemic
secondary phosphines PH(R)(R′) would give a mixture
of diastereomeric phosphido hydride complexes which
are expected to interconvert readily by phosphorus
inversion.6 Depending on the relative rates of P inver-
sion and olefin insertion, this scheme could lead to
P-chiral phosphines with controlled stereochemistry at
phosphorus.
Successful asymmetric hydrophosphination requires
a tightly binding chiral ligand which will not be dis-
placed by the substrates or products.5 In comparison to
related Pt(0) stilbene complexes of chiral diphosphines,
Pt(Me-Duphos)(trans-stilbene) (1, Figure 1) has shorter
Pt-P bond distances, consistent with tight binding, and
the rigid structure of Me-Duphos should help prevent
its displacement by monodentate phosphines.7 Treat-
ment of 1 with the secondary phosphine PH(Ph)(Is) (Is
) 2,4,6-(i-Pr)3C6H2)8 gave the phosphido hydride Pt(Me-
Duphos)[P(Ph)(Is)](H) (2, Scheme 4).9 As expected from
previous studies of diastereomeric phosphido complexes
Pt(chiral diphosphine)(Me)[P(R)(R′)], the NMR spectra
of 2 show only a single set of resonances even at low
(8) Brauer, D. J .; Bitterer, F.; Dorrenbach, F.; Hessler, G.; Stelzer,
O.; Kruger, C.; Lutz, F. Z. Naturforsch. B 1996, 51, 1183-1196.
(9) P t(R,R-Me-Du p h os)[P (P h )(Is)](H) (2). To Pt(R,R-Me-Duphos)-
(trans-stilbene) (1, 95 mg, 0.14 mmol) in THF (5 mL) was added PH-
(Ph)(Is) (50 mg, 0.15 mmol) in THF (5 mL). The reaction mixture
immediately turned bright orange and was allowed to stir at room
temperature for 10 min. The solvent was removed under vacuum, and
the orange residue was dissolved in petroleum ether (10 mL) and
filtered. The orange solution was concentrated slightly under vacuum
and cooled to -25 °C to give 106 mg (94%) of orange-yellow solid in
three crops. Recrystallization from petroleum ether at room temper-
ature gave crystals suitable for X-ray diffraction. This material was
spectroscopically pure, but we were unable to get satisfactory elemental
analyses for it. 1H NMR (C6D6): δ 7.84-7.80 (m, 2H, Ar), 7.17-6.70
3
(m, 9H, Ar), 4.78-4.67 (m, 2H, o-CHMe2), 2.75 (septet, J HH ) 7, 1H,
p-CHMe2), 2.70-2.60 (m, 1H, CH), 2.13-2.02 (m, 2H, CH), 1.94-1.85
(m, 1H, CH), 1.67-1.54 (m, 4H, CH2), 1.42-1.28 (m, 2H, CH2), 1.29
(d, 3J HH ) 7, 6H, CHMe2), 1.23 (d, 3J HH ) 7, 6H, CHMe2), 1.15 (d, 3J HH
3
3
3
) 7, CHMe2), 1.13 (dd, J HH ) 7, J PH ) 14, 3H, Me), 1.07 (dd, J HH
)
3
3
7, J PH ) 14, 3H, Me), 1.10-0.95 (m, 2H, CH2), 0.45 (dd, J HH ) 7,
3J PH ) 14, 3H, Me), 0.35 (dd, J HH ) 7, J PH ) 14, 3H, Me), -1.58
3
3
(ddd, J PH ) 178, 11, 10, J Pt-H ) 1048, 1H, Pt-H). 31P{1H} NMR
2
1
2
1
2
(C6D6): δ 75.9 (dd, J PP ) 154, 10, J Pt-P ) 1852), 68.6 (d, J PP ) 10,
1J Pt-P ) 1903), -28.0 (d, J PP ) 154, J Pt-P ) 1153). IR: 2952, 2868,
1991 (Pt-H), 1447, 1381, 1243, 1160, 1118, 1052, 1016, 753. Anal.
Calcd for C39H57P3Pt: C, 57.54; H, 7.07. Found: C, 65.62; H, 7.75; an
additional sample also gave poor results: C, 51.65; H, 7.00.
2
1
(6) (a) Wicht, D. K.; Glueck, D. S.; Liable-Sands, L. M.; Rheingold,
A. L. Organometallics 1999, 18, 5130-5140. (b) Wicht, D. K.; Kovacik,
I.; Glueck, D. S.; Liable-Sands, L. M.; Incarvito, C. D.; Rheingold, A.
L. Organometallics 1999, 18, 5141-5151.
(10) Crystal data for 2: P212121, orange block, a ) 14.071(14) (Å), b
) 14.841(3) Å, c ) 19.0769(4) Å, V ) 3775(3) Å3, Z ) 4, µ(Mo KR) )
38.69 cm-1, temp ) 238(2) K, R(F) ) 4.24%, R(wF2) ) 12.05%.

952 Organometallics, Vol. 19, No. 6, 2000
Communications
Ta ble 2. P t(Me-Du p h os)-Ca ta lyzed Asym m etr ic
Hyd r op h osp h in a tion a
F igu r e 2. ORTEP diagram of Pt(Me-Duphos)[P(Ph)(Is)]-
(H) (2) with 30% thermal ellipsoids, and hydrogen atoms
omitted for clarity. The Pt hydride could not be located.
Selected bond lengths (Å) and angles (deg): Pt-P(1) )
2.298(5), Pt-P(2) ) 2.226(4), Pt-P(3) ) 2.335(5), P(3)-
C(34) ) 1.853(9), P(3)-C(19) ) 1.899(9), P(2)-Pt-P(1) )
86.83(18), P(1)-Pt-P(3) ) 100.89(16), C(34)-P(3)-Pt )
112.5(4), C(19)-P(3)-Pt ) 111.9(4), C(34)-P(3)-C(19) )
102.2(5).
Ta ble 1. Selected NMR Da ta for
P t(Me-Du p h os)[CH(CN)CH2P (P h )(Is)](H) (3a -d )
(tolu en e-d 8, -20 °C)a
complex δ (31P)b
4J PP
3J Pt-P δ (1H)c
2J PH
1J Pt-H
a
General procedure for catalytic hydrophosphination: Complex
3a
3b
3c
3d
-20.8
-22.0
-23.4
-25.7
20, 4
8
21
257
169
259
255
-0.60
-0.33
-0.53
-0.13
195, 17
195, 16
200, 16
199, 17
1153
1150
1172
1172
1 (8.2 mg, 0.012 mmol) was used as the catalyst precursor (5 mol
%), and the amounts of phosphine and alkene varied accordingly.
An NMR tube fitted with a rubber septum was charged with a
solution of 1 and the phosphine (0.24 mmol) in THF (0.5 mL). The
olefin (0.25 mmol) was added via microliter syringe, and the
reaction was monitored by 31P{1H} NMR spectroscopy at room
temperature. (In some cases when acrylonitrile was used, the
formation of byproducts required addition of extra acrylonitrile
for complete conversion of the starting phosphine.) After comple-
tion of the reaction, the mixture was treated with an excess (80
mg, 0.14 mmol) of (R)-{Pd[Me2NCH(Me)C6H4](µ-Cl)}2 to determine
the ee of the generated tertiary phosphine (see ref 12 in the text).
24
31P NMR chemical shift reference 85% H3PO4, coupling
a
constants in Hz. CH(CN)CH2P(Ph)(Is). c Pt-H.
b
These steps comprise a catalytic cycle, if 5 can
undergo P-H oxidative addition. Indeed, complex 1 is
a catalyst precursor for addition of PH(Ph)(Is) to acry-
lonitrile at room temperature. However, the catalytic
reaction is very slow, and at this temperature, the ee of
phosphine 4 produced is lower than in the stoichiometric
system (Table 2, entry 1). Related catalytic reactions
with less bulky secondary phosphines are faster, but
proceed with even lower ee’s and with the formation of
several byproducts (Table 2, entries 2-6).15 In contrast,
the very bulky phosphines PH(Me)(Mes*)16 (Mes* )
2,4,6-(t-Bu)3C6H2) and PH(Ph)(Mes-F9) (Mes-F9 ) 2,4,6-
b
Abbreviations: Is ) 2,4,6-(i-Pr)3C6H2, Mes ) 2,4,6-(Me)3C6H2,
o-An ) o-MeOC6H4, Cy ) cyclo-C6H11.
c TOF ) turnover frequency
) equiv of secondary phosphine converted per equiv of catalyst
per unit time (from 31P{1H} NMR integration). For some sub-
strates, reactions were also carried out with 2.5 or 1.25 mol %
catalyst (Supporting Information). Hydrophosphination also occurs
(more slowly, or, in some cases, not at all) in the absence of catalyst
d
(Supporting Information). Selectivity ) percentage of the il-
lustrated phosphine product in the mixture of P-containing organic
products (from 31P{1H} NMR integration). e ee of the product
phosphine, from 31P{1H} NMR integration of the signals of the
chiral Pd-L complexes (see ref 12). The error in ee values depends
on the table entry and is estimated to range from ca. 5 to 10%;
thus only entries 1, 2, 8, 9, 10, and 13 reflect a significant ee. f Not
determined due to overlap of 31P{1H} NMR signals for the two
Pd-L diastereomers.
(11) Rea ction of P t(Me-Du p h os)[P (P h )(Is)](H) (2) w ith Acr ylo-
n itr ile. For m ation of P t(Me-Du ph os)[CH(CN)CH2P P h Is](H) (3a -
d ). A solution of 2 (30 mg, 0.037 mmol) in toluene-d8 (0.5 mL) was
transferred to an NMR tube, which was fitted with a rubber septum.
The solution was cooled to -78 °C in a dry ice/acetone bath, and
acrylonitrile (10 µL, 0.15 mmol) was injected by microsyringe. The tube
was immediately placed in the probe of the 500 MHz NMR spectrom-
eter, which had been precooled to -20 °C, and the reaction was
monitored by 31P{1H} and 1H NMR spectroscopy. The composition of
the mixture depended on temperature and reaction time. In addition
to starting material 2, four diastereomers (3a -d ) of the product,
phosphine 4, PH(Ph)(Is), acrylonitrile complex 5, and a minor, uni-
dentified byproduct (31P{1H} NMR: δ -31.6 at room temperature) were
observed. Their relative amounts were quantified by integration of the
31P NMR signals due to the PPhIs groups and by integration of the 1H
NMR hydride signals.
(12) The ee of 4 (which depended on reaction temperature and time)
and of the other chiral phosphines (see below) was determined by
integration of 31P{1H} NMR spectra after complexation to the chiral
Pd(II) dimer derived from nonracemic R-methylbenzylamine, [Pd(Me2-
NCH(Me)C6H4)(µ-Cl)]2, to give monomeric phosphine complexes [Pd-
(Me2NCH(Me)C6H4)(Cl)(L)]. See: (a) Otsuka, S.; Nakamura, A.; Kano,
T.; Tani, K. J . Am. Chem. Soc. 1971, 93, 4301-4303. (b) Roberts, N.
K.; Wild, S. B. J . Am. Chem. Soc. 1979, 101, 6254-6260. (c) For a
review, see: Wild, S. B. Coord. Chem. Rev. 1997, 166, 291-311.
(CF3)3C6H2)6a did not form hydrophosphination products
under these conditions.
The results of the stoichiometric reactions suggested
that the slow step in catalysis was P-H oxidative
addition, since acrylonitrile binds Pt more tightly than
does trans-stilbene. The formation of PH(Ph)(Is) from
2 also suggests that this step can be reversible. To
promote oxidative addition, we used olefins bulkier than
acrylonitrile, which resulted in faster rates, higher
selectivity, and somewhat higher, but still modest,
enantioselectivity at phosphorus (Table 2, entries 7-9).
Achiral phosphines and disubstituted olefins (entries

Communications
Organometallics, Vol. 19, No. 6, 2000 953
10-13) gave tertiary phosphines with similarly poor
stereocontrol at carbon.
The data of Table 2 show that smaller and more
nucleophilic phosphines give faster reactions, but usu-
ally give more byproducts. More highly substituted
olefins give reduced rates, and 1-cyanocyclopentene and
1-cyanocyclohexene did not react with PHPh2 under
these conditions. The relationship between the nature
and substitution pattern of the olefin, the bulk of the P
substituents, and the enantioselectivity is not yet clear.
However, we anticipate that phosphines PH(R)(R′)
having R and R′ groups with large differences in size
will lead to increased enantioselectivity at P, while
variations in the acrylate and acrylonitrile substrates
may enable better control of stereochemistry at C. These
ideas and additional mechanistic information, including
studies of possible catalyst decomposition, should be
useful in further development of Pt-catalyzed asym-
metric hydrophosphination and analogous reactions.
(13) P t(R,R-Me-Du p h os)(CH2CHCN) (5). A white suspension of
300 mg (0.52 mmol) of Pt(R,R-Me-Duphos)Cl2 in 10 mL of THF was
treated with a solution of 300 mg (2.34 mmol) of NaBH(OMe)3 in 5
mL of THF. The resulting orange suspension was stirred at room
temperature for 3 h, then treated with acrylonitrile (700 µL, 10.6
mmol), which caused a color change to pale yellow and evolution of
gas. The suspension was stirred for 2 h at room temperature. Removal
of the solvent in vacuo gave a pale yellow solid, which was extracted
with ca. 20 mL of toluene. The toluene extract was filtered through
Celite, and the filtrate was passed down a column of silica gel (ca. 0.5
cm diameter, 1 cm height). More toluene (10 mL) was used to elute
the product from the column. Evaporation of toluene from the resulting
solution gave a viscous residue, which became sticky after addition of
petroleum ether. The solvent was removed under vacuum, and the
residue was redissolved in ether. Removal of this solvent under vacuum
gave a white powder (as a mixture of diastereomers a and b in ratio
1.3:1), which was then dried in vacuo (yield: 180 mg (62%)). For
elemental analysis, the solid was recrystallized from petroleum ether.
Anal. Calcd for C21H31NP2Pt: C, 45.48; H, 5.65; N, 2.53. Found: C,
Ack n ow led gm en t. We thank the NSF Career Pro-
gram, the donors of the Petroleum Research Fund,
administered by the American Chemical Society, Du-
Pont, and Union Carbide (Innovation Recognition Award)
for support, Dartmouth College for Presidential and
Zabriskie Fellowships for N.S.G., and Cytec Canada for
gifts of phosphines. The University of Delaware ac-
knowledges the NSF (Grant CHE-9628768) for their
support of the purchase of the CCD-based diffractome-
ter.
2
45.75; H, 5.61; N, 2.45. 31P{1H} NMR (C6D6, a ): δ 76.8 (d, J PP ) 40,
2
1
1J Pt-P ) 3390), 75.6 (d, J PP ) 40, J Pt-P ) 2851).31P{1H} NMR (C6D6,
2
1
2
1
b): δ 76.7 (d, J PP ) 40, J Pt-P ) 3342), 72.9 (d, J PP ) 40, J Pt-P
)
2889). For more spectroscopic data, see the Supporting Information.
(14) The relative amounts of these products depended on temper-
ature and reaction time; phosphine 4 was the major organic product,
and more PH(Ph)(Is) was formed at higher temperature. See the
Supporting Information for additional details.
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails and characterization data for all new compounds, and
details of the crystal structure determinations for 1 and 2. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(15) Some of the tertiary phosphine products in Table 2 were
reported previously. For entry 2, see ref 5b; for entries 4-6, see:
Wolfsberger, W. Chem. Ztg. 1990, 114, 353-354. For entry 10, see:
Habib, M.; Trujillo, H.; Alexander, C. A.; Storhoff, B. N. Inorg. Chem.
1985, 24, 2344-2349. For the other phosphines, see the Supporting
Information.
(16) Yoshifuji, M.; Shibayama, K.; Inamoto, N. Chem. Lett. 1984,
115-118.
OM990882E