Synthesis and characterization of chiral diphosphine platinum(II) VANOL and VAPOL complexes

Article abstract of DOI:10.1021/om0302140

Reaction of (dppe)PtCO₃ with S-VANOL or S-VAPOL yielded (dppe)Pt(S-VANOL) and (dppe)Pt(S-VAPOL), respectively. NMR data indicate that the VANOL ligand in the former complex adopts a C₂-symmetric O,O′-bound form, while the VAPOL ligand binds to the metal in a C,O-binding mode that partially disrupts the ligand aromaticity. When matched complexes of S-VANOL and S-VAPOL were synthesized with (S,S-chiraphos)PtCO ₃, both complexes adopt the symmetric O,O′-mode. Mismatched complexes with (R,.R-chiraphos)PtCO₃ have both ligands adopting the C,O-binding mode; however, the S-VANOL complex could not be isolated. Competition experiments between S-VANOL and S-VAPOL for the (S,S-chiraphos)Pt²⁺ fragment indicate that VANOL is the thermodynamically preferred ligand.

Full text of DOI:10.1021/om0302140

Organometallics 2003, 22, 3245-3249
3245
Syn th esis a n d Ch a r a cter iza tion of Ch ir a l Dip h osp h in e
P la tin u m (II) VANOL a n d VAP OL Com p lexes
J ennifer J . Becker, Peter S. White,‡ and Michel R. Gagne´*
Department of Chemistry, University of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599-3290
Received March 20, 2003
Reaction of (dppe)PtCO3 with S-VANOL or S-VAPOL yielded (dppe)Pt(S-VANOL) and
(dppe)Pt(S-VAPOL), respectively. NMR data indicate that the VANOL ligand in the former
complex adopts a C2-symmetric O,O′-bound form, while the VAPOL ligand binds to the metal
in a C,O-binding mode that partially disrupts the ligand aromaticity. When matched
complexes of S-VANOL and S-VAPOL were synthesized with (S,S-chiraphos)PtCO3, both
complexes adopt the symmetric O,O′-mode. Mismatched complexes with (R,R-chiraphos)-
PtCO3 have both ligands adopting the C,O-binding mode; however, the S-VANOL complex
could not be isolated. Competition experiments between S-VANOL and S-VAPOL for the
(S,S-chiraphos)Pt2+ fragment indicate that VANOL is the thermodynamically preferred
ligand.
Sch em e 1
In tr od u ction
Enantiopure 1,1′-binaphth-2,2′-ol (BINOL) is a widely
used ligand in asymmetric catalysis.1 However since it
does not always perform optimally, Wulff introduced the
vaulted biaryl ligands, VANOL and VAPOL,2 which
were designed to project in an asymmetric fashion high-
definition aromatic rings toward a chelated metal
center. These design principles were validated in a
number of highly enantioselective metal-VANOL and
-VAPOL catalyzed reactions, including the Diels-
Alder,2a,3 aziridination,4 and imino Aldol reactions,5 with
VAPOL generally producing the more selective cata-
lysts. In all cases VANOL and VAPOL were used in
combination with oxophilic early transition or main
group metals. As a prelude to imprinting experiments
with these topologically unique ligand structures, we
wished to examine the coordination chemistry of these
ligands with a more carbophilic late metal complex like
the (dppe)Pt2+ fragment.
and VAPOL required 2 and 4 days, respectively, in
contrast to BINOL, which is typically converted in 4 h.
The 31P NMR spectrum of 1 displays the expected
singlet at 24.7 ppm (J P-Pt ) 3633 Hz) for a C2-symmetric
structure. Suitable yellow crystals of r a c-1 were grown
at room temperature from a saturated CH2Cl2 solution
with slow diffusion of diethyl ether.7 The ORTEP
representation in Figure 1 of r a c-1 confirms the C2-
symmetric structure in the solid state and is the first
reported structure of a VANOL-metal complex.2b The
Pt-O and Pt-P bond lengths and P-Pt-P and O-Pt-O
bond angles, reported in the caption, are similar to
previously reported chelating Pt-biphenolate-type struc-
tures8 and are otherwise unexceptional. The stereo-
chemical projection of this ligand is directly linked to
(2) (a) Bao, J .; Wulff, W. D. J . Am. Chem. Soc. 1993, 115, 3814-
3815. (b) Bao, J .; Wulff, W. D.; Dominy, J . B.; Fumo, M. J .; Grant, E.
B.; Rob, A. C.; Whitcomb, M. C.; Yeung, S.-M.; Ostrander, R. L.;
Rheingold, A. L. J . Am. Chem. Soc. 1996, 118, 3392-3405.
(3) (a) Bao, J .; Wulff, W. D. Tetrahedron Lett. 1995, 36, 3321-3324.
(b) Heller, D. P.; Goldberg, D, R.; Wulff, W. D. J . Am. Chem. Soc. 1997,
119, 10551-10552.
(4) (a) Antilla, J . C.; Wulff, W. D. J . Am. Chem. Soc. 1999, 121,
5099-5100. (b) Antilla, J . C.; Wulff. W. D. Angew. Chem., Int. Ed. 2000,
39, 4518-4521. (c) Loncaric, C.; Wulff, W. D. Org. Lett. 2001, 3, 3675-
3678.
Resu lts
(Dppe)Pt(S-VANOL) (1) and (dppe)Pt(S-VAPOL) (2)
were synthesized from the versatile dppePtCO3 starting
material by the method of Andrews in 70 and 81% yield,
respectively (Scheme 1).6 The reactions with VANOL
(5) Xue, S.; Yu, S.; Deng, Y.; Wulff, W. D. Angew. Chem., Int. Ed.
2001, 40, 2271-2274.
‡ To whom correspondence regarding X-ray crystallography should
be directed.
(1) Seyden-Penne, J . Chiral Auxiliaries and Ligands in Asymmetric
Synthesis; Wiley: New York, 1995.
(6) Andrews, M. A.; Voss, E. J .; Gould, G. L.; Klooster, W. T.; Koetzle,
T. F. J . Am. Chem. Soc. 1994, 116, 5730-5740.
(7) Enantiopure 1 proved too soluble for crystal growth. r a c-1 was
prepared in an identical fashion to 1, except with rac-VANOL.
10.1021/om0302140 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 07/02/2003

3246 Organometallics, Vol. 22, No. 16, 2003
Becker et al.
across the square plane of platinum. On the basis of
spectroscopic similarities (two doublets, J P-Pt ) 3560
and 2510 Hz) with a previously structurally character-
ized (dppe)Pt(3,3′-Me2BINOL) complex,8b we propose a
similar C,O-binding mode for 2 (Scheme 1).10-12 The
relief of steric strain and the carbophilic nature of Pt
are largely responsible for this platinum “keto-enol”
tautomerism. Also consistent with this formulation of
one C2 carbon as a carbonyl is its downfield shift (194.1
ppm) in the 13C NMR, a shift that was also observed in
(dppe)Pt(3,3′-Me2BINOL) (195.5 ppm). Structurally, the
spirocyclic carbon center will project the phenanthrene
ligands orthogonal to one another (90° dihedral), one
in and one out of the Pt-square plane.13
In addition to the doublets, a singlet at 27.2 ppm
(J Pt-P ) 3740 Hz) is also observed, which integrates for
8% of the total at -24 °C, and is assigned to the O,O′-
bound form. The C,O-/O,O′- ratio is temperature de-
pendent and is described by the parameters ∆H ) +1.6
( 0.1 kcal mol-1 and ∆S ) +1.4 ( 0.4 eu for C,O- T
O,O′- over a temperature range of -61 (95.5:4.5) to +19
°C (87.5:12.5) in CD2Cl2.14 Above 20 °C the signal
ascribed to the O,O′-form disappears into the baseline
as the doublets similarly broaden, in both CD2Cl2 and
chlorobenzene.15 Although the O,O′-form presumably
acts to interconvert the inequivalent phosphorus nuclei
in the C,O-form, a fast exchange limit is never reached
in chlorobenzene (up to 90 °C).
F igu r e 1. ORTEP representation of r a c-1. Selected bond
distances (Å) and bond angles (deg): Pt1-P1 ) 2.2299-
(12), Pt1-P2 ) 2.2191(10), Pt1-O3 ) 2.067(3), Pt1-O4 )
2.063(3), P1-Pt1-P2 ) 86.40(4), O3-Pt1-O4 ) 90.37(11),
C29-C38-C54-C45 ) 66.0.
The stereochemical consequences of the diphosphine-
VANOL/VAPOL interaction were further probed by
replacing dppe with the chiral diphosphine, chiraphos.
Incorporation of two chiral, C2-symmetric ligands into
the platinum complex leads to either an efficient gearing
of the ligands (matched) or a steric clashing (mis-
matched). On the basis of previous experiments between
chiraphos and 3,3′-Me2BINOL8b we hoped to overturn
the C,O- propensity of the VAPOL ligand in 2 by making
a matched complex, and the O,O′- propensity of VANOL
in 1 by making a mismatched complex.
Treatment of (S,S-chiraphos)PtCO3 with S-VANOL
and S-VAPOL produced the corresponding (S,S-chira-
phos)Pt(S-VANOL) (3) and (S,S-chiraphos)Pt(S-VAPOL)
(4) complexes in 77 and 72% yield, respectively (Scheme
2). As in the case of dppe, the reaction with VANOL
reached completion in half the time of the VAPOL
reaction. The 31P NMR data for these complexes indicate
a C2-symmetric O,O′-binding mode for both the VANOL
and VAPOL ligands (singlets at 29.1 (J P-Pt ) 3536 Hz)
and 30.7 ppm (J P-Pt ) 3626 Hz), respectively). The
combinations of S,S-chiraphos and S-VANOL or S-
VAPOL are conformationally and configurationally
matched, and no traces of any asymmetric products are
observed in the 31P NMR.
F igu r e 2. Chem3D representations of (dppe)Pt(VANOL)
(left) and (dppe)Pt(BINOL)8a (right); the common biphenyl
portions on the ligands are colored green.
the naphthyl-naphthyl dihedral angle of 66.0°, which
is reinforced by a slipped π-stack between the 3,3′-Ph2
substituents (3.35 Å from plane to plane).9
The coordination geometries of the VANOL and
BINOL ligands on the (dppe)Pt2+ fragment are com-
pared in Figure 2. Both have a similar dihedral angle
relating the naphthyl planes (66° and 63°, respectively),
which skews the rings into a chiral environment capable
of distinguishing the chiral reactive quandrants on the
metal. One obvious difference between the two struc-
tures is the enhanced directionality of VANOL, which
more effectively projects its chirality toward the metal,
consistent with its enhanced performance in several
asymmetric catalysis reactions.2-5
In contrast to the symmetric structure of 1, the -24
°C 31P NMR spectrum of the VAPOL product 2 contains
two doublets with significantly different couplings to
195Pt (δ 33.9, J P-Pt ) 3603 Hz; 40.0 ppm, J P-Pt ) 2620
Hz; J P-P ) 10.4 Hz), consistent with a compound with
inequivalent phosphorus nuclei. The smaller Pt-P
coupling for the downfield resonance suggests a ligand
with a trans influence that is stronger than oxygen
(10) Bergens, S. H.; Leung, P.-H.; Bosnich, B. Organometallics 1990,
9, 2406-2408.
(11) Brunkan, N. M.; Gagne´, M. R. Organometallics 2002, 21, 4711-
4717.
(12) Kyba, E. P.; Gokel, G. W.; de J ong, F.; Koga, K.; Sousa, L. R.;
Siegel, M. G.; Kaplan, L.; Soga, G. D. Y.; Cram, D. J . J . Org. Chem.
1977, 42, 4174-4184.
(8) (a) Brunkan, N. M.; White, P. S.; Gagne´, M. R. Angew. Chem.,
Int. Ed. 1998, 37, 1579-1582. (b) Brunkan, N. M.; White, P. S.; Gagne´,
M. R. J . Am. Chem. Soc. 1998, 120, 11002-11003. (c) Tudor, M. D.;
Becker, J . J .; White, P. S.; Gagne´, M. R. Organometallics 2000, 19,
4376-4384.
(9) (a) J orgensen, W. L.; Severance, D. L. J . Am. Chem. Soc. 1990,
112, 4768-4774. (b) Hunter, C. A.; Sanders, J . K. M. J . Am. Chem.
Soc. 1990, 112, 5525-5534.
(13) Unfortunately, all attempts to obtain X-ray quality crystals of
either racemic or enantiomerically pure 2 were unsuccessful.
(14) Errors were calculated by a nonlinear least-squares method;
computer program kindly provided by Prof. Barry Carpenter of Cornell
University.
(15) A slight solvent dependence is observed. At -24 °C in CD2Cl2
and chlorobenzene the C,O/O,O′ ratio is 92.1:7.9 and 89.8:10.2,
respectively (by 31P NMR).

Platinum(II) VANOL and VAPOL Complexes
Organometallics, Vol. 22, No. 16, 2003 3247
Sch em e 2
Sch em e 4
Ta ble 1. Equ ilibr iu m Ra tio of C,O- a n d
O,O′-Bou n d Str u ctu r es a t Room Tem p er a tu r e in
CD2Cl2
Sch em e 3
(dppe)Pt(O,O′)
(dppe)Pt(C,O)
BINOL
3,3′-Me2BINOL
VANOL
>98
24
>98
12
<2
76
<2
88
Treatment of (R,R-chiraphos)PtCO3 with S-VAPOL
produced a C,O-bound complex (6) in 69% yield (Scheme
3), the 31P NMR signatures being nearly identical to the
dppe analogue 2 (two doublets at 47.7, J P-Pt ) 2594 Hz,
J P-P ) 23.2 Hz, trans to C and 35.6 ppm, J P-Pt ) 3558
Hz, J P-P ) 23.2 Hz, trans to O). Similar reaction of (R,R-
chiraphos)PtCO3 with S-VANOL produced what ap-
peared to be a clean C,O-bound complex (5) by in situ
VAPOL
Discu ssion
To date we have synthesized a number of (dppe)Pt2+
coordinated biphenol-type complexes. The BINOL18 and
VANOL compounds appear to be exclusively of the O,O′-
type, while the seemingly more bulky ligands 3,3′-
Me2BINOL and VAPOL prefer the C,O-form (Table 1).
In both of the C,O-forms the symmetric O,O′-isomer is
present and a dynamic process equilibrates the tau-
tomers. Related to these observations is 10,10′-dihy-
droxy-9,9′-biphenanthol, which was the first crystallo-
graphically characterized biphenol-type ligand to adopt
a C,O-binding mode (A).10 The propensity of this ligand
31P NMR (δ 45.3, J P-Pt ) 2554 Hz, and 33.7, J P-Pt
)
3543 Hz); however attempts to isolate this complex led
to extensive decomposition. The combination of R,R-
chiraphos and S-VANOL or S-VAPOL is stereochemi-
cally mismatched.
The relative binding affinities of VANOL and VAPOL
to platinum were also determined through a variety of
pairwise ligand exchange reactions. Only the (S,S-
chiraphos)Pt fragment was used in this study, as it
promotes an O,O′-binding mode for both ligands. Moni-
toring the ratio of products by 31P NMR to equilibrium
afforded information about the relative binding strengths
of S-VANOL and S-VAPOL to the (S,S-chiraphos)Pt
fragment. When (S,S-chiraphos)Pt(S-VAPOL) and 1.01
equiv of S-VANOL were allowed to equilibrate, the
VANOL complex was the major product (74%) after 55
h (Scheme 4) and was accompanied by an unknown
asymmetric byproduct; the VAPOL complex was no
longer detected.16 Consistent with (S,S-chiraphos)Pt-
(S-VANOL) being favored, reaction of (S,S-chiraphos)-
Pt(S-VANOL) and 1.08 equiv of S-VAPOL showed no
detectable amounts of the VAPOL complex, though the
same byproduct was observed (days). This byproduct
was observed in all reactions where both VANOL and
VAPOL were present; however attempts to isolate and
identify this species were unsuccessful.17
to adopt the C,O-mode only may be related to the
diminished cost of dearomatizing the central ring of the
phenanthrene, at least when compared to an end ring,
as in VAPOL.
Dearomatizing nonsymmetric bonding modes are also
observed in nonbiphenol-type ligands, especially when
the ligand is a natural seven-membered chelator. The
significant ring strain (and subsequent skew conforma-
tions) in these chelates can often be attenuated by
tautomerization to the five-membered chelate. Several
cases have been documented with the MAP and MOP
(16) After 25 h, the ratio of compounds was (S,S-chiraphos)Pt-
(VANOL) 54%; (S,S-chiraphos)Pt(VAPOL) 21%, and asymmetric byprod-
uct 25%.
(17) The asymmetric byproduct was characterized by two doublets
in the 31P NMR at 41.3 (J Pt-P ) 1704 Hz, J P-P ) 12.3 Hz) and 36.8
ppm (J Pt-P ) 4129 Hz, J P-P ) 12.3 Hz).
(18) We have synthesized numerous P2M(BINOL) compounds (M
) Pd, Pt; P2 ) BINAP, MeObiphep, Biphep, dppe; BINOL ) 6,6′,4,4′-
substituted), and each of these remotely substituted cases adopts the
O,O′-binding mode (ref 8 and unpublished results).

3248 Organometallics, Vol. 22, No. 16, 2003
Becker et al.
Sch em e 5
sterically encumbered VANOL complex exists in the
more traditional O,O′-form, but the bulkier VAPOL
prefers the C,O-isomer, despite the partial dearomati-
zation of one ring. The binding preference of each ligand
can be overturned by a suitable matching or mismatch-
ing with chiraphos. For VANOL, the C,O-isomer is
accessible (but unstable) by synthesizing the mis-
matched diastereomer, while the O,O′-bound form of
VAPOL is accessible via the matched diastereomer.
Competition experiments between S-VAPOL and S-
VANOL for the (S,S-chiraphos)Pt2+ fragment indicate
that the S-VANOL ligand is thermodynamically pre-
ferred, presumably for steric reasons.
ligands (MAP, Scheme 5). For example, (MAP)PdCl2
exists as an equilibrium mixture of P-, P,N-, and P,C-
modes,19 the P,C-form being implicated in unique cross-
coupling reactivity.19b
Diphosphine ligands are also well known to partici-
pate in binding modes that permit secondary interac-
tions with backbone unsaturation. Pregosin has exten-
sively characterized20 this η2-olefin binding interaction21
by NMR and noted the significant upfield shifts of the
affected H’s and C’s (e.g., in CpRu(BINAP)+) (B). The
diminished ligating effectiveness of the oxidized phos-
phorus in BINAPO also promotes a partial dearoma-
tizing P,C-binding mode (C).22 Similarly, Buchwald has
noted a Pd-η2-olefin binding interaction in the ground
state structure of complexes used for Suzuki couplings
(D).23 These examples capture the spirit of the argument
Exp er im en ta l Deta ils
Gen er a l Meth od s. Starting materials (dppe)PtCO3, (S,S-
chiraphos)PtCO3, and (R,R-chiraphos)PtCO38a,b were prepared
according to literature procedures. VANOL and VAPOL ligands
were generously donated by Prof. William Wulff. NMR spectra
were recorded on a Bruker Avance400 or Bruker AMX300
spectrometer. Chemical shifts are reported in ppm and refer-
enced to residual solvent peaks (1H and 13C NMR) or to an
external standard (85% H3PO4, 31P NMR). Elemental micro-
analyses were performed by Complete Analysis Laboratories,
Parsippany, NJ .
(d p p e)P t(S-VANOL), 1. To a solution of (dppe)PtCO3
(103.0 mg, 0.158 mmol) in 20 mL of CH2Cl2 was added 69.0
mg (0.158 mmol) of S-VANOL. The reaction was stirred at
room temperature, open to the atmosphere to allow CO2
escape. By 31P NMR, the reaction was complete after 48 h.
The solvent was evaporated in vacuo and the yellow solid
recrystallized from CH2Cl2/Et2O to yield 113.0 mg of (dppe)-
Pt(S-VANOL) (70%). 31P NMR (121.0 MHz, CD2Cl2): δ 24.7
1
(J P-Pt ) 3633 Hz). H NMR (300 MHz, CD2Cl2): δ 8.49 (m, 4
H), 7.76 (m, 4 H), 7.62 (m, 6 H), 7.49 (m, 6 H), 7.28 (t, J ) 6.9
Hz, 4 H), 7.07 (t, J ) 7.3 Hz, 2 H), 6.96 (m, 4 H), 6.83 (t, J )
7.6 Hz, 4 H), 6.55 (d, J ) 7.3 Hz, 4 H), 6.35 (t, J ) 7.4 Hz, 2
H), 2.43 (m, 2 H), 2.05 (br. s, 2 H). 13C{31P, 1H} (75.5 MHz,
CD2Cl2): δ 160.9, 143.1, 142.8, 134.6, 134.3, 133.6, 132.4, 132.3,
130.1, 129.7, 129.4, 128.9, 128.7, 127.36, 127.1, 126.9, 125.6,
125.2, 124.9, 122.3, 118.5, 28.4.24 Anal. Calcd for C58H44P2-
PtO2: C, 67.63; H, 4.31. Found: C, 67.84; H, 4.11.
(d p p e)P t(S-VAP OL), 2. To a solution of (dppe)PtCO3 (99.1
mg, 0.152 mmol) in 20 mL of CH2Cl2 was added 99.0 mg (0.184
mmol) of S-VAPOL. The reaction was stirred at room temper-
ature, open to the atmosphere to allow CO2 escape. By 31P
NMR, the reaction was complete after 96 h. The solvent was
evaporated in vacuo and the orange solid recrystallized from
CH2Cl2/pentane, to yield 136.3 mg of (dppe)Pt(S-VAPOL)
(81%). At room temperature, the NMR spectra were broad and
uninterpretable, and characterization was carried out at -24
°C, which results in sharp spectra. At -24 °C, the O,O′-bound
structure is observed in 8%.25 31P NMR (121.0 MHz, CD2Cl2):
δ 40.0 (J P-Pt ) 2620 Hz, J P-P ) 10.4 Hz, trans to C, 2C,O), 33.9
(J P-Pt ) 3603 Hz, J P-P ) 10.4 Hz, trans to O, 2C,O), 27.2 (J P-Pt
that carbophilic late metals can satisfy steric or elec-
tronic discomfort by tautomerizing (NfC or OfC) or
simply employing secondary chelation interactions to
backbone unsaturation, often at the expense of partial
aromaticity.
Su m m a r y
We report herein the synthesis of several diphosphine
Pt(II) VANOL and VAPOL complexes. For dppe, the less
1
) 3746 Hz, 2O,O′). H NMR (300 MHz, CD2Cl2): δ 10.47 (d, J
) 8.7 Hz, 1 H, 2C,O only), 9.64 (d, J ) 8.7 Hz, 1 H), 8.33 (m, 2
H), 7.82 (m, 4 H), 7.69 (m, 5 H), 7.51 (m, 10 H), 7.29 (m, 1 H),
7.19 (m, 1 H), 7.01 (m, 5 H), 6.68 (m, 2 H), 6.52 (d, J ) 8.4
Hz, 1 H), 6.43 (d, J ) 7.2 Hz, 2 H), 6.31 (dd, J ) 7.5, 11.7 Hz,
2 H), 5.94 (m, 2O,O′ only), 4.46 (s, 1 H, 2C,O only), 2.42 (m, 2
H), 1.89 (br s, 1 H), 1.68 (m, 1 H). 13C{31P,1H} (75.5 MHz,
CD2Cl2): δ 194.1 (2C,O), 176.4 (2C,O), 152.6 (2C,O), 142.2, 141.5,
140.6, 139.4, 135.1, 133.5, 133.4, 133.2, 132.9, 132.6, 132.1,
(19) (a) Kocovsky, P.; Vyskocil, S.; C´ısarova´, I.; Sejbal, J .; Tislerova´,
I.; Smrcina, M.; Lloyd-J one, G. C.; Stephan, S. C.; Butts, C. P.; Murray,
M.; Langer, V. J . Am. Chem. Soc. 1999, 121, 7714-7715. (b) Lloyd-
J ones, G. C.; Stephen, S. C.; Murray, M.; Butts, C. P.; Vyskocil, S.;
Kocovsky, P. Chem. Eur. J . 2000, 6, 4348-4357.
(20) (a) Feiken, N.; Pregosin, P. S.; Trabesinger, G. Organometallics
1997, 16, 537-543. (b) Feiken, N.; Pregosin, P. S.; Trabesinger, G.
Organometallics 1997, 16, 5756-5762. (c) Pregosin, P. S.; Trabesinger,
G. J . Chem. Soc., Dalton Trans. 1998, 727-734.
(21) Pathak, D. D.; Adams, H.; Bailey, N. A.; King, P. J .; White, C.
J . Organomet. Chem. 1994, 479, 237-245.
(22) Grushin, V. V.; Marshall, W. J . Organometallics 2003, 22, 555-
562.
(23) Yin, J .; Rainka, M. P.; Zhang, X.-X.; Buchwald, S. L. J . Am.
Chem. Soc. 2002, 124, 1162-1163.
(24) Not all aromatic 13C NMR resonances were observed.
(25) Most 1H and 13C resonances for 2C,O and 2O,O overlap and are
indistinguishable. Those that could be assigned to a single isomer are
noted.

Platinum(II) VANOL and VAPOL Complexes
Organometallics, Vol. 22, No. 16, 2003 3249
Ta ble 2. Cr ysta llogr a p h ic Da ta a n d Collection
P a r a m eter s for r a c-1
127.4, 126.7, 126.6, 126.5, 125.4, 124.4, 124.1, 123.1, 121.8,
118.0, 39.5, 14.0.24 Anal. Calcd for C68H52P2PtO2: C, 70.52; H,
4.53. Found: C, 70.37; H, 4.52.
(dppe)Pt(rac-VANOL)‚CH2Cl2
(R,R-ch ir a p h os)P t(S-VAP OL), 6. To a solution of (R,R-
chiraphos)PtCO3 (116.5 mg, 0.171 mmol) in 20 mL of CH2Cl2
was added 103.5 mg (0.192 mmol) of S-VAPOL. The reaction
was stirred at room temperature, open to the atmosphere to
allow CO2 escape. By 31P NMR, the reaction was complete after
96 h. The solvent was evaporated in vacuo and the orange
solid recrystallized from CH2Cl2/pentane, to yield 135.9 mg of
(R,R-chiraphos)Pt(S-VAPOL) (69%). 31P NMR (121.0 MHz,
CD2Cl2): δ 47.7 (J P-Pt ) 2594 Hz, J P-P ) 23.2 Hz, trans to C),
formula
fw
space group
a, Å
b, Å
c, Å
PtP2C58H46O2‚CH2Cl2
1114.94
P21/c
18.6328(6)
12.1003(4)
22.1229(7)
104.802(1)
4822.4(3)
4
â, deg
V, Å3
Z
T, °C
-100
1.536
1.5418
1
35.6 (J P-Pt ) 3558 Hz, J P-P ) 23.2 Hz, trans to O). H NMR
Dc, g/cm3
λ,Å
(300 MHz, CD2Cl2): δ 10.12 (d, J ) 8.7 Hz, 1 H), 9.55 (d, J )
8.7 Hz, 1 H), 8.36 (m, 2 H), 7.99 (m, 2 H), 7.67 (m, 8 H), 7.46
(m, 10 H), 7.32 (d, J ) 7.8 Hz, 1 H), 7.25 (t, J ) 7.2 Hz, 2 H),
7.10 (m, 2 H), 6.86 (m, 6 H), 6.66 (m, 6 H), 6.52 (br. s, 2 H),
4.66 (d, J ) 2.1 Hz, 1 H), 2.23 (m, 1 H), 1.47 (m, 1 H), 0.89 (m,
3 H), 0.60 (m, 3 H). 13C{31P,1H} (75.5 MHz, CD2Cl2): δ 193.9
(CdO), 177.4, 151.9, 143.0, 142.4, 141.2, 139.2, 136.4, 135.0,
134.4, 133.9, 133.3, 133.2, 132.5, 132.2, 132.1, 131.0, 130.9,
130.8, 129.6, 129.5, 129.3, 128.5, 127.8, 127.6, 127.5, 127.4,
127.2, 127.1, 126.7, 126.4, 126.2, 125.8, 125.4, 125.0, 124.8,
124.0, 120.9, 120.8, 118.2, 115.5, 88.3, 49.6, 31.7, 14.8, 13.6.24
Anal. Calcd for C68H52P2PtO2: C, 70.52; H, 4.53. Found: C,
70.26; H, 4.32.
Typ ica l Equ ilibr a tion Exp er im en t. To a solution of 4
(28.4 mg, 24.5 µmol) in 0.5 mL of CD2Cl2 was added S-VANOL
(10.8 mg, 24.7 µmol). The NMR tube was sealed and was
allowed to equilibrate at ambient temperature. Monitoring by
31P NMR after 55 h indicated that 74% of 3 and 26% of an
asymmetric byproduct (31P NMR: δ 41.3, J Pt-P ) 1707 Hz, and
36.9, J Pt-P ) 4128 Hz, J P-P ) 12.4 Hz) was present.
Cr ysta llogr a p h y. Crystals of (dppe)Pt(rac-VANOL) suit-
able for X-ray crystallography were grown at room tempera-
ture from a saturated CH2Cl2 solution with slow diffusion of
Et2O. Single crystals were mounted in oil on the end of a fiber.
Intensity data were collected on a Bruker SMART diffracto-
meter using the omega scan mode. The structure was solved
by direct methods and refined by a least-squares technique
on F using structure solution programs from the NRCVAX
System.26 All non-hydrogen atoms were refined anisotropic-
ally. Absorption corrections were performed using SADABS;
hydrogen atoms were included using a riding model. Crystal
data, data collection, and refinement parameters are listed in
Table 2.
µ, mm-1
R indices (all data)
7.22
a
Rf ) 0.042
Rwb ) 0.034
Rfa ) 0.031
Rwb ) 0.034
1.5362
R indices (sig. reflns)
GoFc
a
b
2 1/2
] .
c GoF )
Rf ) ∑(Fo - Fc)/∑Fo. Rw ) [∑w(Fo - Fc)2/∑wFo
[∑w(Fo - Fc)2/(n - p)]1/2, where n ) number of reflections and p )
number of parameters.
131.9, 131.84, 131.81, 131.7, 131.1, 130.9, 130.4, 130.1, 129.4,
129.3, 129.2, 128.8, 128.2, 127.9, 127.4, 127.2, 127.1, 126.7,
126.4, 126.2, 125.7, 125.0, 124.9, 123.9, 123.7, 122.2, 120.4,
118.2, 115.6, 88.3 (2C,O), 35.6, 22.3.24 Anal. Calcd for C58H44P2-
PtO2: C, 70.14; H, 4.28. Found: C, 70.05; H, 4.34.
(S,S-ch ir a p h os)P t (S-VANOL), 3. To a solution of (S,S-
chiraphos)PtCO3 (103.1 mg, 0.151 mmol) in 20 mL of CH2Cl2
was added 68.5 mg (0.156 mmol) of S-VANOL. The reaction
was stirred at room temperature, open to the atmosphere to
allow CO2 escape. By 31P NMR, the reaction was complete after
38 h. The solvent was evaporated in vacuo and the yellow
solid recrystallized from CH2Cl2/pentane, to yield 123.2 mg of
(S,S-chiraphos)Pt(S-VANOL) (77%). 31P NMR (162.0 MHz,
CD2Cl2): δ 29.1 (J P-Pt ) 3536 Hz). 1H NMR (400 MHz,
CD2Cl2): δ 8.28 (m, 4 H), 7.80 (dd, J ) 8.0, 10.4 Hz, 4 H), 7.65
(m, 8 H), 7.52 (d, J ) 8.0 Hz, 2 H), 7.43 (m, 6 H), 7.10 (m, 2
H), 6.93 (m, 4 H), 6.80 (m, 4 H), 6.47 (m, 4 H), 6.38 (m, 2 H),
2.37 (m, 2 H), 0.99 (m, 6 H). 13C{31P,1H} (75.5 MHz, CD2Cl2):
δ 161.4, 142.9, 142.7, 136.4, 134.2, 133.1, 132.7, 132.2, 130.1,
129.9, 129.3, 128.8, 127.1, 127.0, 126.7, 125.5, 125.4, 125.2,
125.1, 124.7, 122.2, 118.2, 36.5, 13.9. Anal. Calcd. for C60H48P2-
PtO2: C, 68.11; H, 4.57. Found: C, 67.98; H, 4.47.
(S,S-ch ir a p h os)P t(S-VAP OL), 4. To a solution of (S,S-
chiraphos)PtCO3 (113.1 mg, 0.166 mmol) in 20 mL of CH2Cl2
was added 104.5 mg (0.194 mmol) of S-VAPOL. The reaction
was stirred at room temperature, open to the atmosphere to
allow CO2 escape. By 31P NMR, the reaction was complete after
132 h. The solvent was evaporated in vacuo and the orange
solid recrystallized from CH2Cl2/pentane, to yield 139.2 mg
of (S,S-chiraphos)Pt(S-VAPOL) (72%). 31P NMR (162.0
Ack n ow led gm en t. We gratefully acknowledge the
generosity of the National Science Foundation (CHE-
0075717). M.R.G. is a Camille-Dreyfus Teacher Scholar.
We thank Professor William Wulff of Michigan State
University for a generous donation of his VANOL and
VAPOL ligands.
1
MHz, CD2Cl2): δ 30.7 (J P-Pt ) 3626 Hz). H NMR (400 MHz,
Su p p or tin g In for m a tion Ava ila ble: van’t Hoff plot for
2 and X-ray crystallographic files for (dppe)Pt(rac-VANOL) are
available free of charge via the Internet at http://pubs.acs.org.
CD2Cl2): δ 9.93 (d, J ) 8.4 Hz, 2 H), 8.28 (dd, J ) 8.4, 11.2
Hz, 4 H), 7.61 (m, 2 H), 7.54 (t, J ) 6.8 Hz, 4 H), 7.49 (m, 2
H), 7.43 (m, 4 H), 7.33 (m, 6 H), 7.10 (m, 6 H), 6.85 (m, 2 H),
6.74 (br. s, 2 H), 6.67 (t, J ) 4.8 Hz, 4 H), 6.42 (d, J ) 7.6 Hz,
4 H), 6.17 (t, J ) 7.6 Hz. 2 H), 1.96 (m, 2 H), 0.74 (m, 6 H).
13C{31P,1H} (75.5 MHz, CD2Cl2): δ 143.0, 134.5, 134.2, 133.8,
132.5, 132.2, 132.1, 132.0, 130.0, 129.9, 129.2, 128.4, 127.7,
OM0302140
(26) Gabe, E. J .; Le Page, Y.; Charland, J . P.; White, P. S. J . Appl.
Crystallogr. 1989, 22, 384-387.