Syntheses and structures of alkyl and aryl halide complexes of the type [(PiPr3)2PtH(η1-XR)]BAr(f) and analogues with Et2O, THF, and H2 ligands, halide-to-metal π bonding in halocarbon complexes

Article abstract of DOI:10.1021/ja961836y

The reaction of Pt(PiPr₃)₃ with SO₂ led to the formation of (PiPr₃)₂Pt(SO₂) (1), isolated in 93% yield. The addition of [H(OEt₂)₂]⁺BAr(f) (BAr(f) = B(3,5-(CF₃)₂C₆H₃)₄) to 1 in ether at -78°C afforded the solvent complex trans-[(PiPr₃)₂Pt(H)(PEt₂)]BAr(f) (2) in 85% isolated yield. Complex 2 served as a precursor to monodentate halocarbon complexes of the type Pt(η¹-XR). The dichloromethane complex trans-[(PiPr₃)₂Pt(H)(η¹-ClCH₂Cl)]BAr(f) (3) was isolated in 80% yield by the recrystallization of 2 from CH₂Cl₂/hexane. IR spectroscopy suggested the existence of dichloromethane binding which was confirmed by X-ray crystallography. The reaction of 2 or 3 with iodo- or bromobenzene led to the isolation of the haloarene complexes trans-[(PiPr₃)₂Pt(H)(η¹-XPh)]BAr(f), where X = I (4, 87% yield) or Br (5, 60% yield). Both compounds were characterized spectroscopically and by X-ray crystallography. An unexpected steric interaction in 4, suggested by molecular mechanics calculations to be significant, was rationalized in terms of halide-to-metal π bonding. The PhI complex 4 decomposed under harsh conditions to the bridging iodide compound {trans-[(PiPr₃)₂Pt(H)]₂(μ-I)]BAr(f) (6) which was structurally characterized. The THF adduct [(PiPr₃)₂Pt(H)(THF)]BAr(f) (7), isolated in 78% yield and also characterized by X-ray crystallography, was formed when any of the compounds 2, 3, 4, or 5 was dissolved in THF. The CH₂Cl₂ complex 3 reacted with H₂ to form the dihydrogen complex trans-[(PiPr₃)₂Pt(H)(η²-H₂)]BAr(f) which was characterized by NMR spectroscopy.

Full text of DOI:10.1021/ja961836y

J. Am. Chem. Soc. 1996, 118, 11831-11843
11831
Syntheses and Structures of Alkyl and Aryl Halide Complexes
of the Type [(PiPr3)2PtH(η1-XR)]BArf and Analogues with
Et2O, THF, and H2 Ligands. Halide-to-Metal π Bonding in
Halocarbon Complexes
Matthew D. Butts, Brian L. Scott, and Gregory J. Kubas*
Contribution from the Chemical Science and Technology DiVision, MS C346, Los Alamos
National Laboratory, Los Alamos, New Mexico 87545
ReceiVed May 31, 1996X
Abstract: The reaction of Pt(PiPr3)3 with SO2 led to the formation of (PiPr3)2Pt(SO2) (1), isolated in 93% yield.
The addition of [H(OEt2)2]+BArf (BArf ) B(3,5-(CF3)2C6H3)4) to 1 in ether at -78 °C afforded the solvent complex
trans-[(PiPr3)2Pt(H)(OEt2)]BArf (2) in 85% isolated yield. Complex 2 served as a precursor to monodentate halocarbon
complexes of the type Pt(η1-XR). The dichloromethane complex trans-[(PiPr3)2Pt(H)(η1-ClCH2Cl)]BArf (3) was
isolated in 80% yield by the recrystallization of 2 from CH2Cl2/hexane. IR spectroscopy suggested the existence of
dichloromethane binding which was confirmed by X-ray crystallography. The reaction of 2 or 3 with iodo- or
bromobenzene led to the isolation of the haloarene complexes trans-[(PiPr3)2Pt(H)(η1-XPh)]BArf, where X ) I (4,
87% yield) or Br (5, 60% yield). Both compounds were characterized spectroscopically and by X-ray crystallography.
An unexpected steric interaction in 4, suggested by molecular mechanics calculations to be significant, was rationalized
in terms of halide-to-metal π bonding. The PhI complex 4 decomposed under harsh conditions to the bridging
iodide compound {trans-[(PiPr3)2Pt(H)]2(µ-I)}BArf (6) which was structurally characterized. The THF adduct [(PiPr3)2-
Pt(H)(THF)]BArf (7), isolated in 78% yield and also characterized by X-ray crystallography, was formed when any
of the compounds 2, 3, 4, or 5 was dissolved in THF. The CH2Cl2 complex 3 reacted with H2 to form the dihydrogen
complex trans-[(PiPr3)2Pt(H)(η2-H2)]BArf which was characterized by NMR spectroscopy.
Introduction
oxidative addition of halocarbons to metal centers by an electron
transfer mechanism.6
Alkyl and aryl halides are among the least basic of function-
alized hydrocarbon compounds.1 Despite the fact that they are
poor nucleophiles, alkyl and aryl halides have been shown to
coordinate to transition metal centers to form LnM(η1-XR)
complexes.2 The binding of halocarbons to metal centers was
first suggested by Beck and Schloter in 1978.3 These workers
proposed the existence of the dichloromethane complexes [CpM-
(CO)3(CH2Cl2)]PF6 (M ) Mo, W) on the basis of infrared
spectroscopy. The first crystal structure that showed unambigu-
ously that halocarbons can act as ligands was performed on the
chelating diiodo species [Ir(PPh3)2(H)2(o-C6H4I2)]PF6 by Crab-
tree and co-workers.4 The first structurally characterized
monodentate halocarbon compound was the analogous MeI
complex [Ir(PPh3)2(H)2(IMe)2]PF6.5
The relatively small class of M(η1-XR) compounds is of
interest for a number of reasons. Halocarbon ligands tend to
be labile, and the potential exists for equilibrium between the
LnM(η1-XR) species and the coordinatively unsaturated Lewis
acidic metal centers which can coordinate and activate Lewis
bases. Coordinated alkyl halides have also been shown to be
activated toward nucleophilic attack at the R-carbon.2 Further-
more, η1-XR species may be a representation of the arrested
While a relatively small number of complexes of bidentate
or chelating iodides,4,7 bromides,8 chlorides,9-12 and even
fluorides13 have been reported, all isolable monodentate halo-
carbon complexes have been those of iodides5,14 with only two
exceptions.15,16 This paper describes in part the synthesis of
complexes of the type [(PiPr3)2Pt(H)(η1-XR)]BArf, where X )
Cl, Br, and I, that are the first examples of monodentate
halocarbon complexes of a d10 metal. The structures of the aryl
(6) (a) Amatore, C.; Pflu¨ger, F. Organometallics 1990, 9, 2276. (b) Stille,
J. K.; Lau, K. S. Y. Acc. Chem. Res. 1977, 10, 434.
(7) Casas, J. M.; Falvello, L. R.; Fornie´s, J.; Mart´ın, A. Inorg. Chem.
1996, 35, 56.
(8) (a) Burk, M. J.; Crabtree, R. H.; Holt, E. M. Organometallics 1984,
3, 638. (b) Barcelo´, F.; Luhuerta, P.; Ubeda, M. A.; Foces-Foces, C.; Cano,
F. H.; Martinez-Ripoll, M. J. Chem. Soc., Chem. Commun. 1985, 43. (c)
Solans, X.; Font-Altaba, M.; Aguilo´, M.; Miravitlles, C. Acta Crystallogr.
1985, C41, 841. (d) Cotton, F. A.; Lahuerta, P.; Sanau, M.; Schwotzer,
W.; Solana, I. Inorg. Chem. 1986, 25, 3526.
(9) (a) Fornie´s, J.; Menjo´n, B.; Sanz-Carrillo, R. M.; Toma´s, M.;
Connelly, N. G.; Crossley, J. G.; Orpen, A. G. J. Am. Chem. Soc. 1995,
117, 4295. (b) Harrison R.; Arif, A. M.; Wulfsberg, G.; Lang, R.; Ju, T.;
Kiss, G.; Hoff, C. D.; Richmond, T. G. J. Chem. Soc., Chem. Commun.
1992, 1374. (c) Gomes-Carneiro, T. M.; Jackson, R. D.; Downing J. H.;
Orpen A. G.; Pringle, P. G. J. Chem. Soc., Chem. Commun. 1991, 317.
(10) (a) Colsman, M. R.; Newbound, T. D.; Marshall, W.; Noirot, M
D.; Miller, M. M.; Wulfsberg, G. P.; Frye, J. S.; Anderson, O. P.; Strauss,
S. H. J. Am. Chem. Soc. 1990, 112, 2349. (b) Newbound, T. D.; Colsman,
M. R.; Miller, M. M.; Wulfsberg, G. P.; Anderson, O. P.; Strauss, S. H. J.
Am. Chem. Soc. 1989, 111, 3762.
X Abstract published in AdVance ACS Abstracts, November 1, 1996.
(1) (a) McMahon, T. B.; Heinis, T.; Nicol, G.; Hovey, J. K.; Kebarle, P.
J. Am. Chem. Soc. 1988, 110, 7591. (b) Lias, S. G.; Liebman, J. F.; Levin,
R. D. J. Phys. Chem. Ref. Data 1984, 13, 695. (c) Staley, R. H.; Beauchamp,
J. C. J. Am. Chem. Soc. 1975, 97, 5920.
(11) Van Seggen, D. M.; Hurlburt, P. K.; Anderson, O. P.; Strauss, S.
H. J. Am. Chem. Soc. 1992, 114, 10995.
(2) Kulawiec, R. J.; Crabtree, R. H. Coord. Chem. ReV. 1990, 99, 89.
(3) Beck, W.; Schloter, K. Z. Naturforsch. 1978, 33B, 1214.
(4) Crabtree, R. H.; Faller, J. W.; Mellea, M. F.; Quirk, J. M.
Organometallics 1982, 1, 1361.
(5) Burk, M. J.; Segmuller, B.; Crabtree, R. H. Organometallics 1987,
6, 2241.
(12) Bown, M.; Waters, J. M. J. Am. Chem. Soc. 1990, 112, 2442.
(13) (a) Ruwwe, J.; Erker, G.; Fro¨hlich, R. Angew. Chem., Int. Ed. Engl.
1996, 35, 80. (b) Kulawiec R. J.; Holt, E. M.; Lavin, M.; Crabtree, R. H.
Inorg. Chem. 1987, 26, 2559. (c) Catala, R. M.; Cruz-Garritz, D.; Hills,
A.; Hughes, D. L.; Richards, R. L.; Sosa, P.; Torrens, H. J. Chem. Soc.,
Chem. Commun. 1987, 261.
S0002-7863(96)01836-7 CCC: $12.00 © 1996 American Chemical Society

11832 J. Am. Chem. Soc., Vol. 118, No. 47, 1996
Butts et al.
halide compounds offer new insights into the binding of organic
halides to metal centers concerning halide-to-metal π bonding.
The cationic platinum center also binds other weak donors such
as THF and H2, and generally the complexes are highly labile
yet air-stable; i.e. N2 and O2 do not react, even in solution, and
H2O binds only weakly and reversibly. Such stability is very
rare among complexes that bind extremely weak ligands such
as dichloromethane, which coordinates here to [(PiPr3)2PtH]+
via one rather than both of its chlorine atoms.
groups, respectively, of bound Et2O. These were shifted
downfield with respect to free ether in CD2Cl2 at -83 °C (δ
3.34, q; 1.08, t; both with J ) 6.8 Hz as in 2). Similarly, at
-83 °C the resonances for bound ether were found in the 13C-
{1H} NMR spectrum of 2 at δ 70.37 (s) and 14.76 (s) while
the corresponding peaks for free ether appeared at δ 65.82 and
15.06. The ether ligand did not exchange with CD2Cl2 solvent
1
below -60 °C or with free ether at -83 °C on the H NMR
time scale.
Isolation and Spectroscopic Characterization of a Dichlo-
romethane Complex. The ether ligand in 2 was tightly bound
in the solid state and could not be removed by subjecting the
dry powder to a vacuum for several hours, as determined by
NMR spectroscopy.18 It was, however, quite labile in solution
as would be expected, and it readily dissociated in methylene
chloride solvent. Recrystallization of the cationic platinum
species 2 from CH2Cl2/hexane at -30 °C led to the isolation
of the dichloromethane complex 3 in 80% yield (eq 3). As in
Results
Synthesis of a Cationic Platinum Solvent-Bound Species.
The reaction of Pt(PiPr3)3 with a small excess of SO2 (3 equiv)
in ether led to the loss of one equivalent of PiPr3 and the
isolation of (PiPr3)2Pt(SO2) (1) in 93% yield as emerald green
crystals (eq 1). Infrared spectroscopy has been shown to be a
useful diagnostic tool for determining the geometry of SO2
ligands.17 The S-O stretching frequencies in the IR (KBr)
spectrum of 1 were found at 1176 and 1035 cm-1 and indicate
that the SO2 is sulfur-bound in an η1-pyramidal fashion. The
same bonding mode was established some time ago for the
related complex (PCy3)2Pt(SO2) on the basis of IR spectroscopy
and X-ray crystallography.17b While the 3-coordinate Pt(PiPr3)3
was extremely labile in solution, there was no evidence for either
SO2 or phosphine loss from the 3-coordinate 1 in solution by
the case of the Et2O complex 2, the 31P{1H} NMR spectrum of
3 in CD2Cl2 at -60 °C contained only a singlet (δ 54.61). The
hydride resonance appeared at δ -22.82 (t, JHP ) 11.9 Hz, JHPt
1
) 1852 Hz) in the H NMR spectrum. Unfortunately, the
resonance for the bound CH2Cl2 ligand could not be resolved
by 13C{1H} NMR spectroscopy. Even at -90 °C in CH2Cl2,
solvent exchange was rapid on the NMR time scale. When 3
was dissolved in C6D5F together with an additional 6 equiv of
CH2Cl2, the 13C{1H} NMR spectrum at -40 °C contained only
a sharp singlet at 54.0 ppm for free CH2Cl2.
1
31P{1H} or H NMR spectroscopy. No decomposition could
be detected by NMR when solid 1 was subjected to a vacuum
for several hours, indicating that the SO2 ligand is tightly bound
in the solid state as well.
Surprisingly, both 2 and 3 are air stable compounds even in
solution. No decomposition or binding of N2 or O2 was detected
when a solution of 3 in CD2Cl2 was saturated with air and then
analyzed by NMR spectroscopy. Adventitious water did not
coordinate or cause decomposition in this or any other of our
experiments. However, H2O was observed to displace CH2Cl2
from 3 when added in nearly 2-fold excess to a CD2Cl2 solution
The addition of [H(OEt2)2]+BArf (BArf ) B(3,5-(CF3)2C6H3)4),
referred to hereafter as HBArf, to 1 at -78 °C in ether, followed
by addition of hexane to precipitate the product, led to the
isolation of the air stable yellow cationic ether complex [(PiPr3)2-
Pt(H)(OEt2)]BArf (2) in 85% yield (eq 2). The 31P{1H} NMR
in an NMR tube. A new 31P signal appeared at δ 56.69 (JPPt
)
2754 Hz) and a broad hydride resonance was seen at δ -26.90
(JPtH ) 1644 Hz). In a similar experiment in THF-d8, the new
hydride signal was also broad, indicative of chemical exchange
between reversibly-bound ligands. Thus, it is conceivable that
exposure of 2 or 3 (or the other weak ligand complexes below)
to humid air or wet solvents could result in formation of
equilibrium amounts of the presumed H2O complex, which was
not isolated.
The first real evidence that 3 contained a dichloromethane
ligand came from IR spectroscopy, which has been shown to
be a sensitive probe for binding of CH2Cl2 to a metal center.3,10
The ν(CCl)asym and ν(CCl)sym modes for free CH2Cl2 dispersed
in mineral oil were found at 743 and 707 cm-1, respectively.
Upon coordination to the Pt center of 3, these shifted to 751
and 663 cm-1, respectively. To confirm that these stretches
were assigned correctly, the deuterium analog of 3, [(PiPr3)2-
Pt(H)(η1-ClCD2Cl)]BArf, was prepared by recrystallizing 2 from
CD2Cl2/hexane at -30 °C. Both of the stretching modes found
at 751 and 663 cm-1 for 3 were missing from the IR spectrum
of the CD2Cl2 complex in mineral oil. The spectrum did contain
a new band at 643 cm-1 assigned to the ν(CCl)sym stretch, which
spectrum of 2 in CD2Cl2 at -60 °C contained only a singlet at
δ 55.48, indicating that the phosphine ligands are mutually trans.
The hydride resonance appeared as a triplet in the H NMR
spectrum (CD2Cl2, -83 °C) at δ -27.84 with cis coupling to
the two equivalent phosphines (JHP ) 14 Hz). Resonances at
δ 3.74 (br q) and 1.30 (t) were attributed to the CH2 and CH3
1
(14) (a) Igau, A.; Gladysz, J. A. Organometallics 1991, 10, 2327. (b)
Igau, A.; Gladysz, J. A. Polyhedron 1991, 10, 1903. (c) Kulawiec, R. J.;
Faller, J. W.; Crabtree, R. H. Organometallics 1990, 9, 745. (d) Winter, C.
H.; Veal, W. R.; Garner, C. M.; Arif, A. M.; Gladysz, J. A. J. Am. Chem.
Soc. 1989, 111, 4766. (e) Conroy-Lewis, F. M.; Redhouse, A. D.; Simpson,
S. J. J. Organomet. Chem. 1989, 366, 357. (f) Kulawiec, R. J.; Crabtree,
R. H. Organometallics 1988, 7, 1891. (g) Winter, C. H.; Arif, A. M.;
Gladysz, J. A. J. Am. Chem. Soc. 1987, 109, 7560.
(15) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970.
(16) Van Seggen, D. M.; Anderson, O. P.; Strauss, S. H. Inorg. Chem.
1992, 31, 2987.
(17) (a) Kubas, G. J. Inorg. Chem. 1979, 18, 182. (b) Ritchey, J. M.;
Moody, D. C.; Ryan, R. R. Inorg. Chem. 1983, 22, 2276.
(18) Although no loss of Et2O could be detected by NMR spectroscopy
when 2 was subjected to a vacuum, the elemental analysis of 2 dried under
vacuum overnight indicated that partial loss of Et2O had taken place.

Halide-to-Metal π Bonding in Halocarbon Compounds
J. Am. Chem. Soc., Vol. 118, No. 47, 1996 11833
Å. Similar distances were observed for the minor CH2Cl2 site
(C-Cl(bound) ) 1.80(4) Å and C-Cl(unbound) ) 1.69(4) Å).
The Pt-Cl bond length was found to be 2.489(4) Å for the
major site and 2.60(1) Å for the minor site. The Cl-C-Cl
bond angles were determined to be 111.6(13)° (major site) and
103(2)° (minor site).
Synthesis and NMR Spectroscopic Characterization of the
Platinum Haloarene Complexes, 4 and 5. We were surprised
to find that the Pt center of 3 could stabilize a dichloromethane
ligand, and this prompted us to investigate the scope of reactivity
of the unsaturated [(PiPr3)2Pt(H)]BArf toward other halocarbons.
The ether complex 2 reacted with PhI (only 1 equiv is required)
at room temperature in methylene chloride to form the colorless
air stable PhI complex 4 (eq 5), which was isolated in 87%
Figure 1. ORTEP diagram of trans-[(PiPr3)2Pt(H)(η1-ClCH2Cl)]+ (3),
showing the major CH2Cl2 binding site (see text).
presumably shifted down 20 cm-1 on deuteration because
of mode mixing effects. Unfortunately, the ν(CCl)asym stretch
in the CD2Cl2 complex was obscured by the BArf modes.
Alternate Synthesis of 3. Another convenient preparative
route to 3 was found other than that shown in eqs 2 and 3. The
reaction of trans-(PiPr3)2Pt(H)(Cl) with NaBArf in CH2Cl2 at
room temperature led to the isolation of 3 in 63% yield after
recrystallization from CH2Cl2/hexane at -30 °C (eq 4). The
yield by recrystallization from CH2Cl2/hexane at -30 °C. The
31P{1H} NMR spectrum of 4 in CD2Cl2 included only a singlet
at δ 53.03, which broadened slightly upon cooling to -93 °C.
1
The hydride resonance appeared in the room temperature H
NMR spectrum as a broad resonance at δ -17.02 (JHPt ) 1650
Hz) which was resolved as a triplet at -93 °C (δ -15.89, JHP
) 9 Hz, JHPt ) 1654 Hz). Thus, the overall geometry is the
same as that of 2 and 3.
The 1H and 13C{1H} NMR resonances of PhI are diagnostic
1
of binding in 4. For example, the H NMR spectrum of free
PhI in CD2Cl2 contained resonances at δ 7.72 (t, J ) 8.4, ortho),
7.36 (t, J ) 7.6, para), and 7.13 (vt, J ) 7.7, meta) which shifted
upon coordination to δ 7.66 (J ) 8.1), 7.51 (J ) 7.2), and 7.26
(J ) 7.6). Similar small shifts were observed in the 13C{1H}
NMR resonances of PhI. A spectrum of free PhI includes
resonances at δ 138.03, 130.85, 128.09, and 94.80 (ipso). The
resonances attributed to the PhI ligand of 4 were found at δ
137.21, 131.61, and 130.77. The peak for the ipso carbon in 4
was not resolved and may have been obscured by one of the
BArf resonances.
same reaction performed in Et2O solvent affords the ether
complex 2.
The synthesis of cationic Pt(II) compounds with varying
phosphine sizes was also attempted by this method. The
reaction of trans-(PEt3)2Pt(H)(Cl) with NaBArf in Et2O pro-
ceeded slowly at room temperature to a mixture of products,
indicating that analogues with phosphines with relatively small
cone angles are unstable. In contrast, the solvent-free [(P-t-
Bu3)2Pt(H)]BArf (see Discussion) was isolated in 64% yield
from the reaction of trans-(P-t-Bu3)2Pt(H)(Cl) with NaBArf in
Et2O.
Bromobenzene also reacted with the cationic platinum hydride
species to form the η1-aryl halide complex 5, as shown in eq 6,
which was isolated in 60% yield. Whereas only 1 equiv of
X-ray Crystal Structure of [(PiPr3)2Pt(H)(η1-ClCH2Cl)]-
BArf, 3. In order to confirm that methylene chloride was bound
to the Pt center as suggested by IR spectroscopy, a crystal-
lographic study was performed on yellow plate-like crystals of
3. An ORTEP diagram of the cationic portion of the molecule
is shown in Figure 1 which clearly shows that CH2Cl2 is bound
to the Pt center in an η1-monodentate fashion. Crystal and data
collection parameters are given in Table 1, and important bond
distances and bond angles are shown in Tables 2 and 3 (an
ORTEP diagram of the BArf counterion is included in the
Supporting Information).
A disordered region near the Pt center was modeled as two
disordered CH2Cl2 molecules. These two molecules, labeled
Cl(2)-C(45)-Cl(1) and Cl(3)-C(45′)-Cl(1), were positioned
right next to each other with the outer chloride shared. The
two molecules were refined with their site occupancy factors
tied to one. In the final refinement the occupancy factors refined
to 0.677(8) for the Cl(2)-C(45)-Cl(1) molecule and 0.323(8)
for the Cl(3)-C(45′)-Cl(1) molecule. The ORTEP diagram
in Figure 1 shows the major site.
PhI was required to drive the reaction forming 4 to completion,
the addition of a large excess of PhBr (ca. 25 equiv) was
required in order to observe shifts in the resonances of the
dichloromethane complex 3 in CD2Cl2. Presumably due to the
instability of 5, the static complex was not resolved by NMR
spectroscopy when 5 equiv of PhBr were added to a CD2Cl2
solution of 3 even at -90 °C. Rapid ligand exchange also
occurred in fluorobenzene. The resonances of PhBr were
significantly broadened in the 1H NMR spectrum of 5 containing
an additional 4 equiv of PhBr in C6D5F at -40 °C, indicating
that the slow exchange regime was being approached (fluo-
robenzene freezes at -42 °C, preventing further cooling).
As expected, bromobenzene is a weaker ligand than iodo-
benzene. The following competition experiments were per-
formed in order to gauge relative ligand stabilities. To a CD2Cl2
solution of 3 containing 5 equiv of PhBr was added 0.6 equiv
For the major CH2Cl2 site, the C-Cl(bound) distance was
found to be 1.79(2) Å while the C-Cl(unbound) was 1.70(2)

11834 J. Am. Chem. Soc., Vol. 118, No. 47, 1996
Butts et al.
Table 1. Crystal and Data Collection Parameters for 3, 4, 5, 6, and 7
3
4
5
6
7
formula weight
crystal system
space group
temp (K)
a (Å)
b (Å)
c (Å)
1464.71
monoclinic
P21/n
1583.78
triclinic
P1
1536.79
monoclinic
P21/n
2095.34
monoclinic
P21/n
1451.88
monoclinic
P21/c
173
173
183
193
173
11.997(2)
13.067(2)
37.919(3)
90
97.35
90
5895.5(14)
4
1.650
12.320(2)
15.607(1)
16.993(1)
92.2
106.46
91.09
3129.6(6)
2
1.681
21.142(3)
12.717(1)
25.468(2)
90
113.503(8)
90
6279.5(11)
4
1.626
22.180(4)
16.383(4)
25.585(5)
90
112.17(1)
90
8610(3)
4
1.617
11.830(1)
13.695(1)
37.657(5)
90
99.069(9)
90
6025.8(10)
4
1.600
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
d
calc (g cm-3
)
absp coef (mm-1
)
2.635
2.893
3.029
3.770
2.493
crystal size (mm)
θ range (deg)
index ranges
0.12 × 0.37 × 0.54
2.51-22.50
-1 e h e 12
-1 e k e 14
-40 e l e 40
9810
7622
1.064
4.32
0.21 × 0.29 × 0.45
2.561-25.00
-1 e h e 14
-1 e k e 18
-20 e l e 19
6998
6845
0.885
3.85
0.16 × 0.21 × 0.37
2.51-22.53
-1 e h e 22
-1 e k e 13
-27 e l e 25
9866
8134
1.022
6.86
0.08 × 0.08 × 0.37
2.60-20.00
-1 e h e 21
-1 e k e 15
-24 e l e 23
9734
8028
1.026
7.18
0.21 × 0.25 × 0.41
2.58-22.50
-21 e h e 12
-1 e k e 14
-13 e l e 40
9089
7849
1.042
4.73
no. of rflcns collected
no. of indpd reflections
goodness of fit
R(F) (%)
Rw(F) (%)
9.19
8.58
10.11
5.42
13.80
15.47
13.67
14.31
8.69
10.10
R
all (%)
Table 2. Selected Bond Distances (Å) for 3, 4, 5, 6, and 7
Table 3. Selected Bond Angles (deg) for 3, 4, 5, and 6
compd
atom 1
atom 2
distance
compd
atom 1
atom 2
atom 3
angle
3
Pt
Pt
Pt
Pt
Cl(1)
Cl(1)
Cl(2)
Cl(3)
Pt
Pt
Pt
Pt
I
Pt
Pt
Pt
Pt
Br
Pt(1)
Pt(1)
Pt(2)
Pt(2)
Pt(1)
Pt(2)
Pt(1)
Pt(2)
Pt
Pt
Pt
Pt
O
P(1)
P(2)
Cl(2)
H(Pt)
C(45)
C(45′)
C(45)
C(45′)
P(1)
P(2)
I
H(Pt)
C(1)
P(1)
P(2)
Br
H(Pt)
C(1)
P(1)
P(2)
P(3)
P(4)
I
2.307(2)
2.310(2)
2.489(4)
1.68(9)
1.70(2)
1.69(4)
1.79(2)
1.80(4)
2.311(2)
2.314(2)
2.696(1)
1.4(1)
2.082(5)
2.304(5)
2.309(5)
2.583(2)
1.6(1)
1.91(2)
2.302(6)
2.290(6)
2.291(6)
2.300(6)
2.729(2)
2.737(2)
1.6(2)
3
P(1)
P(1)
P(2)
Cl(2)
C(45)
C(45′)
Cl(1)
Cl(1)
P(1)
P(1)
P(2)
I
Pt
Pt
Pt
Pt
Cl(2)
Cl(3)
C(45)
C(45′)
Pt
Pt
Pt
Pt
I
Pt
Pt
Pt
Br
Pt(1)
Pt(2)
I
Pt(1)
Pt(1)
Pt(2)
Pt(2)
Pt(1)
Pt(2)
Pt
P(2)
Cl(2)
Cl(2)
H(Pt)
Pt
165.77(9)
94.03(11)
99.50(12)
178(3)
112.1(8)
115(2)
111.6(13)
103(2)
163.75(11)
100.75(7)
95.37(7)
170(3)
114.56(19)
163.89(15)
102.18(11)
173(5)
116.4(7)
168.3(2)
168.9(2)
170.14(9)
100.8(2)
90.9(2)
Pt
Cl(2)
Cl(3)
P(2)
I
4
5
6
4
I
H(Pt)
C(1)
P(2)
Br
H(Pt)
C(1)
P(2)
P(4)
Pt(2)
I
Pt
5
6
P(1)
P(1)
Br
Pt
P(1)
P(3)
Pt(1)
P(1)
P(2)
P(3)
P(4)
I
I
I
I
98.6(2)
92.1(2)
171(7)
173(8)
166.50(11)
174(4)
99.3(2)
I
H(Pt1)
H(Pt2)
P(1)
P(2)
O
H(Pt)
C(7)
C(10)
H(Pt1)
H(Pt2)
P(2)
H(Pt)
O
1.4(2)
I
7
2.304(3)
2.310(3)
2.224(7)
1.3(1)
1.46(1)
1.47(1)
7
P(1)
O
P(1)
P(2)
Pt
Pt
Pt
O
94.1(2)
O
utilized as a sensitive probe for the ligation of dichloromethane.
There are, however, no reports on the effects of transition metal
binding on the IR spectra of aryl halides.
of Et2O. Only one set of resonances was observed by 31P{1H}
and H NMR spectroscopy at 25 °C. The spectra at -60 °C,
1
The IR (mineral oil) spectrum of the PhI complex 4 was
compared with those of the related compounds 2, 3, and 5
(discussed below), as well as free PhI, in order to determine
which frequencies could be attributed to the iodobenzene ligand.
Each band that could be identified was shifted slightly to lower
energy relative to those found for free PhI dispersed in mineral
oil. For example, bound PhI had peaks at 1569 (Ph), 1011 δ-
(CH), 994 υ(Ph), and 652 (Ph) cm-1 while those in free PhI
appeared at 1573, 1015, 997, and 655 cm-1 (spectrometer
however, contained resonances for the Et2O complex 2 and the
rapidly exchanging PhBr/CD2Cl2 complexes in a ∼5:3 ratio.
Thus, all of the ether was bound even in the presence of excess
PhBr. In contrast, 4 was stable in Et2O for 2 days at 90 °C
before decomposition could be detected by NMR, although PhI
was displaced by THF at room temperature in THF solvent.
Characterization of Haloarene Ligands by Infrared Spec-
troscopy. As mentioned above, IR spectroscopy has been

Halide-to-Metal π Bonding in Halocarbon Compounds
J. Am. Chem. Soc., Vol. 118, No. 47, 1996 11835
Figure 2. ORTEP diagram of trans-[(PiPr3)2Pt(H)(η1-IPh)]+ (4).
resolution 2 cm-1). The other IR bands expected for bound
PhI (and PhBr below), including the C-I stretching vibration,
were obscured by the large number of stretching and bending
modes of the BArf counterion.
The IR (mineral oil) spectrum of 5 contained peaks at 1571
(Ph), 1017 δ(CH), 998 (Ph), and 457 cm-1 (Ph) assigned to
bound bromobenzene which also only shifted slightly from free
PhBr: 1578, 1020, 1000, and 457 cm-1. Although the above
studies represent the first report of the effect of ligation on the
IR frequencies of an aryl halide, it would appear that, as might
be expected, IR is not a sensitive technique for this purpose.
Unfortunately, the IR stretch expected to be most affected by
the bonding to the Pt center, the C-X stretch, was obscured
for both 4 and 5.
Figure 3. ORTEP diagram of trans-[(PiPr3)2Pt(H)(η1-BrPh)]+ (5): two
views of the same molecule.
X-ray Crystal Structures of the Iodobenzene and Bro-
mobenzene Platinum Complexes. In order to confirm that 4
and 5 were, in fact, monodentate haloarene complexes rather
than the oxidative addition products, X-ray crystallographic
studies were performed on both compounds. The ORTEP
diagrams of the cationic portions of the molecules, shown in
Figures 2 (4) and 3 (5), show clearly that these are η1-aryl halide
complexes. Crystal and data collection parameters are given
in Table 1, and important bond distances and bond angles are
shown in Tables 2 and 3.
Both compounds are psuedo-square planar with mutually trans
phosphines. The P-Pt-P bond angles in the two compounds
were identical (163.7(1)° for 4 and 163.8(1)° for 5). The Pt-P
bond lengths in 4 and 5 were likewise indistinguishable (see
Table 2) considering experimental error. The Pt-X bond
lengths were found to be 2.696(1) Å where X ) I and 2.583(2)
Å for X ) Br.
to metal centers, i.e., they may have relevance in reactions which
proceed through an electron transfer mechanism rather than the
common SN2 mechanism.2,4 Oxidative addition by electron
transfer would not be expected for a d8 Pt(II) species. Thus, it
was not surprising that prolonged heating of the PhI complex 4
in CD2Cl2 did not lead to the oxidative addition product
[(PiPr3)2Pt(H)(Ph)(I)]BArf but rather slow decomposition to
many species (approximately 5% decomposed after 3 days at
80 °C). No benzene was detected in the reaction mixture by
NMR spectroscopy. Decomposition was likewise rather slow
in Et2O solvent, requiring 4 days at 100 °C to reach completion.
This reaction also did not lead to the oxidative addition product
but rather to the air stable bridging iodide complex {trans-
[(PiPr3)2Pt(H)]2(µ-I)}BArf (6), depicted in eq 7, which was
Reactivity and Decomposition of Some Halocarbon
Complexes: Formation and Structure of a Bridging Iodide
Complex, 6. As mentioned in the Introduction, alkyl halide
ligands have been shown to be susceptible to nucleophilic attack
at the R-carbon much more readily than the free organic
halide.2,14c The possibility of this reactivity pathway was
investigated for the PhI complex 4 as the only halocarbon
complex in our study which was stable at room temperature in
solution in the sense that it did not exchange with solvent or
free PhI on the NMR time scale. In contrast to earlier studies
on halocarbon complexes,2,14c the PhI ligand of 4 was merely
displaced by added nucleophiles. Thus, the addition of L, where
L ) PPh3, NEt3, or Cl- (added as PPNCl), to 4 at room
temperature in methylene chloride quickly produced the cor-
responding trans-[(PiPr3)2Pt(H)(L)]BArf (or (PiPr3)2Pt(H)(Cl)
in the case of PPNCl) and free PhI. Not surprisingly, the same
observations were made when these nucleophiles were added
to the CH2Cl2 complex 3 in CD2Cl2.
isolated in 39% yield by recrystallization. No other products
were observed in this reaction by NMR spectroscopy. The
equivalent hydrides of 6 appeared at -18.40 ppm in the H
1
NMR spectrum with a Pt-H coupling constant of 1645 Hz.
This is almost identical to the JPtH of 1650 Hz observed in the
PhI complex 4, indicating perhaps that PhI and trans-[(PiPr3)2-
Pt(H)(I)] exhibit similar trans influence. The structure of 6 was
confirmed by X-ray crystallography (see Figure 4 and Tables
1-3). Both of the formally Pt(II) centers are pseudo-square
planar, and the Pt-I-Pt bond angle is almost linear (170.14-
(9)°). The Pt-I bond lengths are 2.729(3) and 2.737(3) Å. The
average Pt-P bond length was found to be 2.296 Å, slightly
shorter than the average Pt-P bond distance in 4 (2.312 Å).
Surprisingly, although MeI compounds are more common
than aryl iodide complexes,14 the MeI species trans-[(PiPr3)2-
It has been suggested that M(η1-XR) complexes might
represent intermediates in the oxidative addition of alkyl halides

11836 J. Am. Chem. Soc., Vol. 118, No. 47, 1996
Butts et al.
Figure 5. ORTEP diagram of trans-[(PiPr3)2Pt(H)(THF)]+ (6).
Figure 4. ORTEP diagram of {trans-[(PiPr3)2Pt(H)]2(µ-I)}+ (6).
above chelate complex as well as unsupported THF complexes
of other transition metals.20
Pt(H)(IMe)]BArf was much less stable than the PhI compound
4. When prepared in an NMR tube experiment (15 mg of
starting material 3), the MeI adduct was stable at 25 °C in the
presence of excess MeI. When prepared on a large scale,
however, the material isolated by recrystallization was a 1:1
mixture of the MeI adduct and 6. Because the MeI adduct could
not be isolated as a pure compound, our evidence that it is a
Pt(η1-IMe) species is circumstantial. Although the halocarbon
Me resonance was obscured in the proton NMR spectrum by
the phosphine signals, the chemical shifts and shapes of the
Pt-H and i-Pr resonances were consistent with what was
typically observed here for other halocarbon complexes.
Reactivity of the CH2Cl2 Complex toward Dihydrogen.
As part of the continued interest in the coordination of H2 to
transition metal complexes,21 we were curious as to whether
H2 would form a stable complex with the unsaturated trans-
[(PiPr3)2Pt(H)]BArf and how it would compete as a ligand with
CH2Cl2. Thus, approximately three atmospheres of H2 were
added to a yellow CD2Cl2 solution of 3. The room temperature
1H NMR spectrum contained no resonances for free H2 or the
Pt-H, indicating that a fluxional process was taking place. At
1
-60 °C, however, the H NMR spectrum contained a sharp
singlet at 4.55 ppm, a broad lump at δ 0.36, and a triplet at
-10.13 (JHP ) 9.9, JHPt ) 1438 Hz). These resonances are
assigned to free H2 and the dihydrogen ligand and hydride,
respectively, of the dihydrogen complex trans-[(PiPr3)2Pt(H)-
(H2)]BArf (8) shown in eq 8. Each of these three resonances
Heating the MeI adduct, prepared in situ in Et2O solvent, for
2.5 h at 65 °C led to the formation of 6 as the only observable
product by NMR spectroscopy. As in the case of 4, the MeI
complex decomposed in CD2Cl2 (18 h at 70 °C) to a mixture
of products, none of which were 6 or the oxidative addition
product. Methane, which might have been formed by decom-
position of an oxidative addition product, was not detected when
the latter reaction was performed in a sealed NMR tube.
Synthesis and Structure of the Pt-THF Adduct, 7. When
any of the complexes 2, 3, 4, or 5 were dissolved in THF, the
result was displacement of the labile ligand and formation of
the air stable THF complex [(PiPr3)2Pt(H)(THF)]BArf (7), which
was recrystallized from THF/hexane at -30 °C in 78% yield.
The 1H and 31P{1H} NMR spectra of 7 in CD2Cl2 were
consistent with the same pseudo-square planar geometry as-
signed to each of the analogous trans-[(PiPr3)2Pt(H)(L)]+
broadened into the baseline upon rewarming between -10 °C
and 0 °C. The 31P{1H} NMR spectrum at -60 °C included
only a singlet at δ 57.58 (JPPt ) 2432 Hz) which was not
observed at this temperature in the absence of H2. The HD
coupling constant for the HD isotopomer of 8 was found to be
33.7 Hz at -80 °C, while that for free HD is 42.6 Hz at this
temperature. In general, JHD values for M(η2-HD) compounds
are found between 9 and 35 Hz depending on the degree of
metal-to-ligand back-bonding.21 The high value here suggests
an H-H distance in the “short” range, 0.8-0.9 Å, typical of
unactivated dihydrogen ligands. As found for [Mn(CO)(Ph2-
PC2H4PPh2)2(H2)]BArf22 and other cationic systems,21 the
positive charge on the metal undoubtedly helps to stabilize sigma
coordination rather than oxidative addition of H2. The position-
ing trans to hydride in 8 also contributes to the high lability of
the H2 ligand because of the trans effect. No exchange between
1
compounds. The H NMR multiplets for bound THF in 7 (δ
3.84 and 1.94) in CD2Cl2 were shifted downfield relative to
those for the free ligand (3.68 and 1.82 ppm). Similarly, at
-10 °C in CD2Cl2, the bound THF gave rise to 13C NMR
resonances at δ 74.38 and 25.60 while those for free THF
appeared at δ 68.11 and 25.91.
Complex 7 was also characterized by X-ray crystallography,
which surprisingly represents the first structural determination
of an unsupported THF complex of platinum (see Figure 5 and
Tables 1-3). The Pt-O distance was found to be 2.224(7) Å.
This is substantially longer than the Pt-O distance of 2.142(4)
Å found in a related Pt(II) complex in which a THF ligand was
stabilized by phosphine chelation.19 The C-O bond distances
of 1.46(1) and 1.47(1) Å in 7 are consistent with those of the
(20) See, for example: (a) Dick, D. G.; Stephan, D. W. Organometallics
1990, 9, 1910. (b) Davies, C. E.; Gardines, I. M.; Green, J. C.; Green, M.
L. H.; Hazel, N. J.; Grebenik, P. D.; Mtetwa, V. S. B.; Prout, K. J. Chem.
Soc., Dalton Trans. 1985, 669. (c) Churchill, M. R.; Wasserman, H. J. Inorg.
Chem. 1982, 21, 223. (d) Cotton, F. A.; Lewis, G. F.; Mott, G. N. Inorg.
Chem. 1982, 21, 3127.
(21) (a) Heinekey, D. M.; Oldham, W. J., Jr. Chem. ReV. 1993, 93, 913.
(b) Jessop, P. G.; Morris, R. H. Coord. Chem. ReV. 1992, 121, 155. (c)
Crabtree, R. H. Acc. Chem. Res. 1990, 23, 95. (d) Kubas, G. J. Acc. Chem.
Res. 1988, 21 , 120.
(19) Alcock, N. W.; Platt, A. W. G.; Pringle, P. G. J. Chem. Soc., Dalton
Trans. 1989, 2069.
(22) King, W. A.; Luo, X.-L.; Scott, B. L.; Kubas, G. J.; Zilm, K. J.
Am. Chem. Soc. 1996, 118, 6782.

Halide-to-Metal π Bonding in Halocarbon Compounds
J. Am. Chem. Soc., Vol. 118, No. 47, 1996 11837
deuterium from HD or D2 and the Pt-hydride took place when
samples under these gases were warmed to room temperature
for 20 min and then reanalyzed by NMR spectroscopy at -80
°C.
Our findings are analogous to those recently reported by
Gusev and Caulton for a closely related compound.23 These
workers treated trans-(P-t-Bu3)2Pt(H)2 with triflic acid to form
the dihydrogen complex trans-[(P-t-Bu3)2Pt(H)(H2)]OTf stable
only at low temperature. This complex had 1H NMR resonances
(δHH 1.12, JHD ) 34.7 Hz) and exhibited temperature dependent
behavior quite similar to that observed for 8.
Interestingly, the ether complex 2 could not be synthesized
by allowing HBArf to react directly with Pt(PiPr3)3 rather than
1, despite the ease with which the tris(phosphine) compound
dissociates phosphine in solution and the obvious steric advan-
tages of replacement of bulky PiPr3 by solvent. This reaction
yielded only the cationic tris(phosphine)-Pt-hydride species
shown in eq 10,26 reiterating the exceptional lability of SO2 on
Pt(II).
Discussion
Synthesis of a Highly Reactive Cationic Platinum Spe-
cies: A Precursor to Alkyl and Aryl Halide Complexes. The
reaction of Pt(PiPr3)3 with SO2 in ether led to the loss of one
PiPr3 and the isolation of (PiPr3)2Pt(SO2) (1) (eq 1), which
reacted with HBArf in ether to give clean formation of the
solvent species trans-[(PiPr3)2Pt(H)(OEt2)]BArf (2, eq 2). A
likely mechanism for the reaction forming 2 is shown in eq 9.
Successful isolation of the cationic Pt ether complex 2
required the utilization of a large, low coordinating anion such
as BArf-. Smaller, more nucleophilic anions functioned as
ligands which were not displaced by halocarbons. For example,
the addition of triflic acid to 1 in ether at -78 °C led only to
trans-(PiPr3)2Pt(H)(OTf).
Synthesis and Solution Behavior of [(PiPr3)2Pt(H)(η1-
ClCH2Cl)]BArf, 3. Recrystallization of [(PiPr3)2Pt(H)(OEt2)]BArf
(2) from CH2Cl2/hexane led to the isolation of the methylene
chloride complex 3 (eq 3). The CH2Cl2 ligand in 3 is so labile
in solution that the static complex was not observed even at
-90 °C in CH2Cl2 by 13C{1H} NMR spectroscopy. Compound
3 was then dissolved in C6D5F together with an additional 6
equiv of CH2Cl2. Only one resonance was observed for CH2-
1
Cl2 in both the H and 13C{1H} NMR spectra at -40 °C, and
The first step in this mechanism is the protonation of the
platinum center to form the four-coordinate SO2 complex. The
facile loss of SO2 from this cationic Pt species followed by the
binding of a solvent molecule affords the observed product. The
reaction might also proceed through a sulfinic acid species,
[(PiPr3)2Pt(SO2H)]+, either from direct protonation at SO2 or
as a tautomer24 of the intermediate in eq 9. If a Pt-sulfinic
acid species were stable at -78 °C, we would expect it to be
deprotonated by added base to reform starting material. To test
this, 1 was treated with 1 equiv of HBArf at -78 °C followed
8 min later by 2 equiv of NEt3 (the delay ensured that all HBArf
was consumed by reaction with 1). Only 2 was observed by
NMR when the reaction mixture was warmed to room temper-
ature, pumped dry, and dissolved in CD2Cl2. Likewise no
starting material was observed when the much stronger base
n-BuLi was substituted for NEt3 (unidentified species resulted).
Regardless of reaction pathway, these and other observations
suggest that SO2 is rapidly and irreversibly lost on acid addition
even at -78 °C.
Although another convenient route to 2 was found (eq 4, in
Et2O solvent), the reaction shown in eq 2 is important in part
because it illustrates the versatility of the SO2 ligand. The SO2
group, which was strongly bound in the neutral starting material
(PiPr3)2Pt(SO2) (1), became exceptionally labile upon protona-
tion of the compound with HBArf, and even a large excess of
SO2 would not replace the weakly bound ether in 2. Just as
for metal-to-carbon back-donation in carbonyl complexes, metal-
to-sulfur back-bonding has been shown to be important in the
stabilization of SO2 ligands.25 We suggest then that the observed
lability of SO2 in the reaction of eq 2 is a result of the drastically
decreased back-bonding ability of cationic Pt(II) vs Pt(0).
these were unshifted from those observed under the same
conditions in the absence of 3. We believe that rapid solvent
exchange on the NMR time scale, even in fluorobenzene, is
consistent with these results. In contrast to the behavior of 3,
the 13C{1H} NMR resonances for the CH2Cl2 ligands in the
compounds [(C5R5)Re(PPh3)(NO)(CH2Cl2)]BF4 (R ) H, Me)
were identified at -85 °C.27,28
While our results may be in agreement with the persistence
of the coordinatively unsaturated [(PiPr3)2Pt(H)]BArf species
in solution, this is highly unlikely. A strong argument against
this is the fact that this unsaturated species can be isolated as
the methylene chloride adduct in the solid state. Furthermore,
the Pt-H coupling constant (1852 Hz at -60 °C) of 3 in CD2-
Cl2 is significantly smaller than what might be expected in the
absence of a ligand trans to the hydride. The more sterically
bulky complex [(P-t-Bu3)2Pt(H)]BArf, prepared in the reaction
of trans-(P-t-Bu3)2Pt(H)(Cl) with NaBArf, did not react with
an excess of either PhI or MeI at 25 °C. This compound is
believed to indeed exist as a 3-coordinate complex in CD2Cl2,
and importantly has a much larger JHPt of 2605 Hz at room
temperature. Consistent with our results, the series of closely
related 3-coordinate compounds [(P-t-Bu3)2Pt(H)]X (where X
) BF4, PF6, ClO4, SO3CF3) previously studied by Goel and
coworkers gave a Pt-H coupling constant of 2570 Hz invariant
to the nature of X.29 The binding of a number of ligands (H2O,
acetone, MeCN, etc., but not CH2Cl2) trans to the hydride led
to a decrease in JPtH on the order of 1000-1100 Hz. Thus, our
(26) This complex was not prepared on a large scale but was readily
identified by NMR spectroscopy: 1H NMR (THF-d8) δ 7.79 (s, 8H, BArf),
7.57 (s, 4H, BArf), 2.61 (m, 6H, CH), 2.54 (m, 3H, CH), 1.42 (dd, J )
13.8 and 7.2, 18H, CH3), 1.33 (vq, J ) 7.2, 36H, CH3), -9.12 (dt, JHP
)
(23) Gusev, D. G.; Notheis, J. U.; Rambo, J. R.; Hauger, B. E.; Eisenstein,
O.; Caulton, K. G. J. Am. Chem. Soc. 1994, 116, 7409.
(24) For known SO2H complexes, see: (a) Kubas, G. J.; Wasserman,
H. J.; Ryan, R. R. Organometallics 1985, 4, 2012. (b) Randall, S. L.; Miller,
C. A.; Janik, T. S.; Churchill, M. R.; Atwood, J. D. Organometallics 1994,
13, 141.
145.0 and 17.1, JHPt ) 634, 1H, PtH); 31P{1H} NMR (THF-d8) δ 41.82 (d,
JPP ) 18.3, JPPt ) 2585), 39.66 (t, JPP ) 18.3, JPPt ) 2391).
(27) (a) Fernandez, J. M.; Gladysz, J. A. Organometallics 1989, 8, 207.
(b) Winter, C. H.; Arif, A. M.; Gladysz, J. A. Organometallics 1989, 8,
219.
(28) Peng, T. -S.; Winter, C. H.; Gladysz, J. A. Inorg. Chem. 1994, 33,
2534.
(29) Goel, R. G.; Srivastava, R. C. Can. J. Chem. 1983, 61, 1352.
(25) Ryan, R. R.; Kubas, G. J.; Moody, D. C.; Eller, P. G. Struct. Bonding
(Berlin) 1981, 46, 47.

11838 J. Am. Chem. Soc., Vol. 118, No. 47, 1996
Butts et al.
compared to those of alkyl iodides. The isolable η1-iodobenzene
complex [CpRe(NO)(PPh3)(IPh)]BF4 has been reported.14d The
complex [H2Ir(PPh3)2(IPh)2]BF4 reportedly existed at -60 °C
but was unstable and could not be isolated.4 The more basic
aryl halides 4-iodoanisole and 4-iodotoluene have formed the
isolable complexes [CpRe(NO)(PPh3)(p-IC6H4OMe)]BF414d and
[CpRu(CO)(PPh3)(p-IC6H4Me)]BF4.14c
Table 4. Platinum-Hydride Coupling Constants for
trans-[(PiPr3)2Pt(H)(L)BArf
L
JPt-H (Hz)
L
JPt-H (Hz)
L
JPt-H (Hz)
CH2Cl2
PhBr
PhI
1852a
1781b
1654
1631
Et2O
THF
H2
1540
1507
1438
1363c
Et3N
Cl-
PPh3
1359
1280c
784c
MeI
I-
a Ligand exchange averaged value in CD2Cl2 solvent at -60 °C.
b Ligand exchange averaged value when 5 equiv of PhBr was added to
a CD2Cl2 solution at -80 °C. c For these compounds the ligand L was
added to a CD2Cl2 solution of 3; they were not isolated.
As expected, the PhBr complex 5 was much less stable than
that of PhI and represents the first example of an isolable
complex containing a monodentate organic bromide ligand.32
The EtBr compound [CpRe(NO)(PPh3)(BrEt)]BF4 was char-
acterized at low temperature by NMR spectroscopy by Gladysz
and co-workers but was unstable.14d
Solid State Structure of [(PiPr3)2Pt(H)(η1-IPh)]BArf, 4.
A crystallographic study confirmed that 4 was a monodentate
haloarene compound (see Figure 2 and Tables 1-3). The Pt-I
bond length of 2.696(1) Å is at the upper end of the range
normally found for terminal Pt-I bond distances in other Pt-
(II) compounds (approximately 2.60-2.70 Å).33 The only other
structurally characterized organic iodide complex of Pt is the
chelating compound cis-(C6F5)2Pt(N-I), where N-I is 2-io-
doaniline, which had a Pt-I distance of 2.620(1) Å.7
The Pt-I-C(1) angle of 114.56(19)° is larger than would
be expected compared to other monodentate halocarbon com-
pounds; M-X-C angles are usually found in the 100-110°
range.5,14c-e These acute angles have been rationalized by
characterizing the donor orbital on the halide as having a
significant amount of p character (little s-p mixing), an
explanation which is consistent with theoretical calculations on
LnM(η1-XR) compounds.34,35 For example, Hoffmann predicted
a Pt-I-C angle of 100° in model compound Pt(Ph)(NH3)2-
(IMe)+.34
The most unusual feature of the structure of the PhI complex
4, and most likely the reason for the larger than expected Pt-
I-C(1) angle, is the orientation of the phenyl group, which is
situated over one of the phosphine isopropyl groups as a result
of a small C(1)-I-Pt-P(1) dihedral angle of -19.8°. This
can be easily seen in the ball and stick drawings shown in Figure
6. The phenyl ring lies essentially flat over the phosphine, with
a C(6)-C(1)-I-Pt dihedral angle of -87.6°. Analysis of a
space filling model of 4 suggested that in consideration of sterics
alone, the phenyl ring should lie above or below the plane of
the molecule, between the two phosphines (i.e., with a much
larger C(1)-I-Pt-P(1) dihedral angle), as observed in the
structure of the related compound (PEt3)2Pt(H)(OPh).36 Sig-
nificantly, there are no close contacts between the iodide and
any hydrogens on the phosphines (the shortest I‚‚‚H distance is
2.986 Å) or between neighboring molecules.
observation of a JHPt of 1852 Hz is consistent with the existence
of a weakly bound ligand, such as CH2Cl2, trans to the hydride.
It is interesting to compare JHPt for a series of complexes of
the type trans-[(PiPr3)2Pt(H)(L)]BArf (Table 4). There seems
to be a rough inverse correlation with ligand binding strengths,
although there are exceptions. For example, PhI is a better
ligand than Et2O in the sense that it does not dissociate from 4
in Et2O solvent, but it has a larger JHPt. Another notable
exception is the H2 complex 8, which had a JHPt of 1438 Hz at
-60 °C. This relatively small coupling would seem to imply
that H2 is a much stronger ligand than demonstrated by our
variable temperature NMR studies (see Results). However,
dihydrogen is the only ligand in the series which can function
as a good π-acceptor (see discussion below regarding π bonding
in 4), and it is possible that Pt f H2 back-bonding has the effect
of lowering the JPtH of the trans-hydride.
X-ray Crystal Structure of [(PiPr3)2Pt(H)(η1-ClCH2Cl)]-
BArf. The geometry about the Pt center is pseudo-square planar,
and the phosphine ligands are trans to one another as expected
from the NMR spectroscopic studies (P-Pt-P ) 165.77(9)°).
Because of the experimental error in the bond lengths and angles
of the coordinated CH2Cl2 molecule, a clear analysis of the
effects of Pt-Cl bonding on these values is prohibited. They
are, in any case, comparable to the values reported for free CH2-
Cl2 in the gas phase (C-Cl ) 1.7724(5) Å and Cl-C-Cl )
111.78(2)°).30 The Pt-Cl distance of 2.489(4) Å found for the
major CH2Cl2 site is longer than that found in the chelating
halocarbon complex [MePt{η2-Ph2P(CH2CH2Cl)}{η1-Ph2P(CH2-
CH2Cl)}]BF4 (2.425(1) Å)9c as well as what is normally
observed for terminal Pt(II)-Cl bonds. For example, the
analogous neutral compound trans-(PiPr3)2Pt(H)(Cl) had a Pt-
Cl distance of 2.395(1) Å.31 The elongation of this bond in 3
is consistent with the observed lability of the methylene chloride
ligand in solution.
While a few complexes containing bidentate CH2Cl2 or 1,2-
C2H4Cl2 ligands have been characterized by X-ray,10,11,12 there
is only one other example of a structurally characterized
monodentate CH2Cl2 complex. Recently, Arndtsen and Berg-
man reported the structure of Cp*Ir(PMe3)(Me)(η1-ClCH2Cl)]-
BArf which had CH2Cl2 bond distances and angles consistent
with those of 3.15 A longer chain RCl-Ag interaction has been
structurally characterized by Strauss and co-workers in [Ag-
(1,2,3-C3H5Cl3)OTeF5]2 which contains a trichloropropane
ligand bound through only one chloride.16
Synthesis and Stability of the Haloarene Complexes
[(PiPr3)2Pt(H)(η1-XPh)]BArf, 4 and 5. The unsaturated frag-
ment [(PiPr3)2Pt(H)]+ could be stabilized by halocarbon ligands
other than methylene chloride. Both the iodo- and bromoben-
zene complexes 4 and 5 were isolated from the reaction of either
the ether complex or the CH2Cl2 complex with PhX in CH2Cl2
(eqs 5 and 6). Aryl iodide complexes such as 4 are quite scarce
Molecular Mechanics Calculations on [(PiPr3)2Pt(H)(η1-
IPh)]+. An important question is, therefore, the following. Does
the geometry adopted by 4 in the solid state as shown in Figure
2 really include a significant steric repulsion between the phenyl
and isopropyl groups, or could these observations simply be
the result of crystal packing forces? In order to probe the sterics
more indepth, molecular modeling calculations were performed
(32) Structures of complexes containing chelating M‚‚‚Br interactions
have, however, been reported. See ref 8.
(33) (a) Boag, N. M.; Rao, K. M.; Terrill, N. J. Acta Crystallogr., C
1991, 47, 1064. (b) Ogawa, H.; Onitsuka, K.; Joh, T.; Takahashi, S.;
Yamamoto, Y.; Yamazaki, H. Organometallics 1988, 7, 2257. (c) Manojlovic-
Muir, L.; Ling, S. S. M.; Puddephatt, R. J. J. Chem. Soc., Dalton Trans.
1986, 151. (d) Hunter, W. N.; Muir, K. W.; Sharp, W. A. Acta Crystallogr.,
C 1986, 42, 1743.
(34) Ortiz, J. V.; Havlas, Z.; Hoffmann, R. HelV. Chim. Acta 1984, 67,
1.
(30) Myers, R. J.; Gwinn, W. D. J. Chem. Phys. 1952, 20, 1420.
(31) Robertson, G. B.; Tucker, P. A.; Wickramasinghe, W. A. Aust. J.
Chem. 1986, 39, 1495.
(35) Czech, P. T.; Gladysz, J. A.; Fenske, R. F. Organometallics 1989,
8, 1806.
(36) Cowan, R. L.; Trogler, W. C. J. Am. Chem. Soc. 1989, 111, 4750.

Halide-to-Metal π Bonding in Halocarbon Compounds
J. Am. Chem. Soc., Vol. 118, No. 47, 1996 11839
Table 5. Molecular Mechanics Calculations on
trans-[(PiPr3)2Pt(H)(η1-IPh)]+: Important Structural Parameters
Initial and Minimized Structuresa
dihedral angle
initial (deg)
minimized (deg)
C(1)-I(1)-Pt(1)-P1
-19.8
31.1
-87.6
-39.1
-57.9
59.0
-58.3
41.6
-47.4
-33.0
-50.3
67.2
Pt(1)-P(1)-C(9)-C(9a)
C(6)-C(1)-I(1)-Pt(1)
Pt(1)-P(1)-C(7)-C(7b)
I(1)-Pt(1)-P(1)-C(7)
I(1)-Pt(1)-P(1)-C(9)
Pt(1)-P(1)-C(7)-H(7)
Pt(1)-P(1)-C(9)-H(9)
74.7
-84.6
82.4
-72.3
bond angle
initial (deg)
minimized (deg)
Pt(1)-I(1)-C(1)
C(7)-P(1)-C(9)
P(2)-Pt(1)-P(1)
I(1)-Pt(1)-P(1)
I(1)-Pt(1)-P(2)
I(1)-Pt(1)-F
114.8
104.3
163.8
100.8
95.4
113.7
105.0
176.4
90.9
91.8
179.9
170.3
bond distance
initial (Å)
minimized (Å)
Pt(1)-I(1)
Pt(1)-P(1)
Pt(1)-P(2)
I(1)-C(1)
Pt(1)-F
2.696
2.311
2.314
2.123
1.623
2.836
2.305
2.301
2.095
1.874
Figure 6. Ball and stick diagrams of trans-[(PiPr3)2Pt(H)(η1-IPh)]+
(4).
a Distances and Angles refer to Figure 7.
difference between structures A and B, we believe that these
calculations serve to show, overall, that (a) 4 in the solid state
does contain a significant steric interaction between the phenyl
and isopropyl groups and (b) this interaction is too energetically
unfavorable to have come about by crystal packing forces.
Halide-to-Metal π Bonding in [(PiPr3)2Pt(H)(η1-IPh)]+. In
light of these results, we next looked for electronic reasons for
the observed solid state geometry of 4. We believe that the
orientation of the iodobenzene ligand of 4 is consistent with
invoking π donation from the iodide to the Pt center. The
interaction between a planar ML3 fragment and the lone pair p
orbitals on iodide is considered in the MO diagram shown in
Figure 8. The Pt-I single bond results from the interaction of
the lone pair in the py orbital of iodide with the empty 2a1 metal-
based orbital. We propose that the lone pair in the iodide pz
orbital overlaps with the metal dyz and pz orbitals to form a π
bond. Π overlap between the iodide lone pair and the Pt dyz
orbital is a filled-filled interaction, and it is mixing with the
empty Pt pz orbital that makes it overall bonding. In this
scenario, the stabilization gained in Pt pz mixing is qualitatively
sufficient to outweigh the steric repulsion between the phenyl
and isopropyl groups.
This type of π bonding would also be allowed by symmetry
if the phenyl ring as shown in Figure 6 was rotated ap-
proximately 90° about the Pt-I bond such that it lay above or
below the plane of the molecule. However, stabilization of the
corresponding pπ-dπ filled-filled interaction could only be
provided by mixing with the Pt px orbital. While the Pt pz orbital
in the ML3 fragment is nonbonding, the Pt px orbital is
antibonding and is most likely too high in energy to stabilize a
Pt-I π interaction.
Figure 7. Molecular mechanics calculations on trans-[(PiPr3)2Pt(H)-
(η1-IPh)]+ (4): (A) stereoview of the starting structure, derived from
the crystal structure coordinates, (B) stereoview of the optimized
geometry of the platinum cation.
on the cationic portion of 4 using the ESFF force field within
Discover 95.0.37
The atomic coordinates of 4, with the hydride ligand replaced
by a fluoride at the default distance of 1.623 Å (see the
Experimental Section), were used to generate the starting
structure shown in Figure 7A. Optimization led to the structure
shown in Figure 7B. The initial and final energies were 61.87
and 51.42 kcal, respectively. The results of bond distance and
angle optimization are summarized in Table 5. As can be seen
in the stereoviews of Figure 7, the steric strain of having the
phenyl ring in close proximity to the isopropyl groups was
relieved in essentially three ways: (1) rotation about the Pt-I
bond thus decreasing the C(1)-I-Pt-P(1) dihedral angle from
-19.8° to -58.3°, (2) rotation about the I-C(1) bond such that
the C(6)-C(1)-I-Pt dihedral angle is increased from -87.6°
to -47.4°, and (3) optimizing the orientation of the phosphine
ligand close to the phenyl group in structure A. While the
substitution of a fluoride ligand for the hydride probably has
some small effect on the determination of a 10.45 kcal energy
The idea of π bonding between terminal halides and transition
metals has been around for a long time,38 and numerous recent
studies by Caulton and Eisenstein have substantiated the
existence of π interactions in organometallic M-X (X ) halide,
alkoxide) compounds.39 The present work shows that such π
bonding may exist even when the halide is bound to an organic
(37) Discover 95.0 is a product of Molecular Simulations Inc., 9685
Scranton Rd., San Diego, CA 92121-3752.
(38) (a) Jolly, W. L. J. Phys. Chem. 1983, 87, 26. (b) Hall, M. B.; Fenske,
R. F. Inorg. Chem. 1972, 11, 1619.

11840 J. Am. Chem. Soc., Vol. 118, No. 47, 1996
Butts et al.
about the Pt-I bond by 90°. This type of back-bonding has
also been found to be insignificant in other systems as well.35
Low Temperature NMR Spectroscopy of [(PiPr3)2Pt(H)-
(η1-IPh)]BArf. As shown in our crystallographic study, in the
solid state the two phosphines of 4 are chemically inequivalent
(Figures 2 and 6). In solution, however, only one resonance
(slightly broadened) was observed for the two phosphines by
31P{1H} NMR spectroscopy even at -80 °C in CD2Cl2,
unshifted from that observed at room temperature. The chemical
inequivalence between the phosphines in the static compound
would be expected to be largely due to the ring current of the
phenyl group over one phosphine and not the other. Because
the temperature at which the two resonances can be resolved
depends, of course, on the chemical shift difference between
them in the slow exchange regime, it seems most likely that
this shift is too small to be resolved at -80 °C.
Interestingly, the resonances for the averaged isopropyl CH
and CH3 groups for the PhI complex 4 (2.30 ppm, CH; 1.24
ppm, CH3) were found downfield of those for the exchange
averaged (see the Experimental Section) isopropyl resonances
for 3 in the presence of seven equivalents of bromobenzene
(2.24 ppm, CH; 1.19 ppm, CH3). It is possible that these
observations are the result of deshielding in the case of 4,
wherein the phenyl ring lies over the isopropyl groups to a
greater extent in solution compared to the PhBr complex 5.
X-ray structure of [(PiPr3)2Pt(H)(η1-BrPh)]BArf, 5. In
order to compare the structure of the bromobenzene complex
with that of iodobenzene, an X-ray crystallographic study of 5
was performed on crystals isolated from a CH2Cl2 solution of
3 containing 25 equiv of PhBr at -30 °C (Figure 3). There
are important structural differences between the PhBr and PhI
compounds. Unlike in 4, the phenyl ring of 5 is not situated
over one of the phosphine isopropyl groups. Rather it adopts
a geometry like the optimized structure of 4 shown in Figure
7B. More specifically, the C(1)-Br-Pt-P(2) dihedral angle
of -56.4° in 5 is much closer to that found for the optimized
structure of 4 (Figure 7B, Table 5, -58.3°) than for 4 itself
(-19.8°). Likewise, the C(6)-C(1)-Br-Pt dihedral angle of
-30.0° compares more favorably with that in the optimized 4
(-47.4°) than with the analogous angle of -87.6° determined
from the crystal structure of 4. The differences between the
structures of 4 and 5 are most likely caused by steric interactions.
The Pt-Br distance in 5 is shorter than the Pt-I distance in 4
(2.583(2) vs 2.696(1) Å) and requires that the phenyl ring be
closer within the coordination sphere of the platinum center in
5 and thus closer to the phosphine isopropyl groups. The
geometry requirement for π bonding as described for 5 in Figure
8 is thus broken, but because it is possible that hybridization at
Br could allow for π bonding in other PhBr orientations, it is
not clear whether or not Pt-Br π bonding exists in 5. The
Pt-Br bond length of 2.583(2) Å is near the upper limit of the
range normally found for Pt-Br bonds (2.43-2.60 Å)43,44 and
is consistent with the characterization of this bond as a relatively
weak one.
Figure 8. Molecular orbital diagram of trans-[(PiPr3)2Pt(H)(η1-IPh)]+
(4).
moiety. More advanced calculations on our Pt system are
clearly called for, but our results thus far would suggest that
the overall stabilization afforded to 4 by the existence of a Pt-I
π bond is at least 10 kcal. Π bonding, as described herein, has
not previously been suggested to exist in halocarbon compounds.
It has been concluded by many workers that π bonding does
not occur to any significant extent in square planar Pt(II)
alkoxide, hydroxide, or amide complexes.36,39c,40 This is because
π interactions in such compounds are repulsive if one does not
consider the participation of the empty Pt pz orbital to be
significant. We do not doubt that this is a reasonable assumption
with OR, OH, and NR2 ligands. However, the lone pairs on
iodide (as RI) exist at higher energy than do those on OR, OH,
and NR2 ligands, and are perhaps better suited for interactions
with Pt(II) p and d orbitals.34 Furthermore, the participation of
the Pt(II) pz orbital in ligand substitution reactions of square
planar compounds has been widely recognized.41
In principle, ligands of the type M(η1-XR) can act as π
acceptors.5,27,42 Because of the small M-X-C bond angles
typically observed in halocarbon compounds, the empty C-X
σ* orbital can overlap with a filled metal d orbital. In the case
of the PhI complex 4, such an interaction is no more favored in
the observed geometry (Figure 6) than it would be in the less
sterically hindered structure in which the phenyl ring is rotated
Formation and Structure of {trans-[(PiPr3)2Pt(H)]2(µ-I)}-
BArf (6). Despite the propensity for organic iodides to
(39) (a) Gusev, D. G.; Kuhlman, R.; Rambo, J. R.; Berke, H.; Eisenstein,
O.; Caulton, K. G. J. Am. Chem. Soc. 1995, 117, 281. (b) Johnson, T. J.;
Folting, K.; Streib, W. E.; Martin, J. D.; Huffman, J. C.; Jackson, S. A.;
Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1995, 34, 488. (c) Caulton, K.
G. New J. Chem. 1994, 18, 25.
(40) Bryndza, H. E.; Tam, W. Chem. ReV. 1988, 88, 1163.
(41) Langford, C. H.; Gray, H. B. Ligand Substitution Processes; W. A.
Benjamin, Inc.: Reading, MA, 1966; Chapter 2.
(43) Rieger, A. L.; Carpenter, G. B.; Rieger, P. H. Organometallics 1993,
12, 842.
(44) (a) Messmer, G. G.; Amma, E. L. Inorg. Chem. 1966, 5, 1775. (b)
Rajaram, J.; Pearson, R. G.; Ibers, J. A. J. Am. Chem. Soc. 1974, 96, 2103.
(c) Huffman, J. C.; Laurent, M. P.; Kochi, J. K. Inorg Chem. 1977, 16,
2639. (d) Carr, S. W.; Shaw, B. L.; Thornton-Pett, M J. Chem. Soc., Dalton
Trans. 1985, 2131. (e) Yamashita, H.; Hayashi, T.; Kobayashi, T.; Tanaka,
M.; Goto, M. J. Am. Chem. Soc. 1988, 110, 4417.
(42) (a) Uehara, Y.; Saito, N.; Yonezawa, T. Chem. Lett. 1973, 495. (b)
Orpen, A. G.; Connelly, N. G. J. Chem. Soc., Chem. Commun. 1985, 1310.

Halide-to-Metal π Bonding in Halocarbon Compounds
J. Am. Chem. Soc., Vol. 118, No. 47, 1996 11841
oxidatively add to transition metal centers,6,45 oxidative addition
is actually not a typical decomposition pathway taken by
halocarbon compounds. A rare example is the complex [Cp*Re-
(NO)(PPh3)(CH2Cl2)]BF4 which decomposed at -35 °C to
[Cp*Re(NO)(PPh3)(Cl)(CH2Cl)]BF4 in methylene chloride.28
Presumably, the reason for the general lack of observed
oxidative addition reactions lies in the fact that almost all known
alkyl and aryl halide complexes are cationic.46 The barrier to
oxidative addition is high enough such that other decomposition
pathways are more energetically favorable.
especially the Pt-H coupling constant, which has been shown
to be very sensitive to the nature of the trans-ligand.
Crystallographic studies revealed that dichloromethane binds
to the cationic Pt center in a monodentate fashion. The
structurally characterized trans-[(PiPr3)2Pt(H)(η1-BrPh)]BArf
represents the first example of an isolable transition metal
complex containing a monodentate organic bromide ligand. An
X-ray crystallographic study performed on trans-[(PiPr3)2Pt-
(H)(η1-IPh)]BArf (4) revealed an unexpected steric interaction
which was suggested by molecular mechanics calculations to
be significant. These observations were rationalized in terms
of halide-to-metal π bonding in the iodobenzene compound.
Interestingly, 4 decomposed on prolonged heating at 100 °C in
Et2O not to the oxidative addition product but rather to the
iodide-bridged species {trans-[(PiPr3)2Pt(H)]2(µ-I)}BArf.
The formation of an unstable dihydrogen sigma complex with
the cationic Pt(II) center is relevant to recent mechanistic studies
by Bercaw and Labinger49 on C-H activation at very similar
centers, e.g., [(tmeda)Pt(CH3)(OEt2)]BArf (tmeda ) N,N,N′,N′-
tetramethylethylenediamine). These studies relate to oxidation
of alkanes by aqueous solutions containing [PtCl4]2- and
[PtCl6]2- originally studied by Shilov and coworkers and bring
into question the existence of σ complexes such as PtII(RH) as
intermediates. Our studies and the initial work by Caulton23
on PtII(H2) complexes indicate by analogy that Pt-alkane
complexes surely can exist (at least as transients), and would
be expected to be particularly stabilized toward oxidative
addition to PtIV(R)(H) on cationic Pt centers.
In light of these facts, we studied the decomposition of the
PhI complex 4 in diethyl ether and dichloromethane. As
mentioned in the Results, 4 decomposed in CD2Cl2 slowly at
elevated temperatures to a number of products, none of which
were the oxidative addition product [(PiPr3)2Pt(H)(Ph)(I)]BArf
or benzene. Similarly, [(PiPr3)2Pt(H)(CD2Cl)(Cl)]BArf was not
an observed in the decomposition of 3 in CD2Cl2. Clean
decompositions of 4 as well as its MeI analogue to {trans-
[(PiPr3)2Pt(H)]2(µ-I)}BArf (6) were observed in Et2O, however,
but 6 was not one of the products to which 4 or the MeI adduct
decomposed in CD2Cl2. The mechanism of the reaction shown
in eq 7 is obviously enigmatic and has not been addressed here.
The structure of 6 was confirmed in a single crystal X-ray
crystallographic study (Figure 4). Although one way to think
of 6 might be as an adduct of trans-[(PiPr3)2Pt(H)]BArf with
trans-(PiPr3)2Pt(H)(I), not surprisingly the system is delocalized
as evidenced by essentially equivalent Pt-I bond lengths (2.729-
(3) and 2.737(3) Å).47 These are longer than the Pt-I bond
distance in 4 (2.696(1) Å), but they are in the range usually
found for platinum compounds with bridging iodides.48 Because
of the ligand environments, 6 represents the first structurally
characterized example of an otherwise unsupported bridging Pt-
I-Pt moeity that does not exist as part of an infinite chain
structure.
Experimental Section
Unless otherwise noted, all reactions and manipulations were
performed in dry glassware under a helium atmosphere in a Vacuum
Atmospheres drybox or using Schlenk techniques. “Glass bomb” refers
to a cylindrical, medium-walled Pyrex vessel joined to a Kontes
K-826510 high-vacuum teflon stopcock. All NMR spectra were
recorded on a commercial 500 MHz Bruker AMX series spectrometer
or a Bruker WM 300 MHz spectrometer. IR spectra were obtained on
a Biorad FTS-40 instrument. Elemental analyses were obtained from
Oneida Research Services, Inc. Toluene, hexane, Et2O, and THF were
distilled from sodium/benzophenone. Dichloromethane was distilled
from calcium hydride. The Pt(PiPr3)3,50 HBArf (BArf ) B(3,5-
(CF3)2C6H3)4),51 and trans-(PR3)2Pt(H)(Cl) (R ) i-Pr, t-Bu)52 were
prepared according to the literature. Iodo- and bromobenzene were
dried over activated 4 Å molecular sieves. All other reagents were
obtained from commercial suppliers and used without further purifica-
tion. As a general rule, the drybox catalyst was turned off prior to
any reaction in which dichloromethane was used inside the box; use
was then followed by purging of the drybox atmosphere.
(PiPr3)2Pt(SO2) (1). Inside the drybox Pt(PiPr3)3 (960 mg, 1.42
mmol) was added to a 100 mL Schlenk flask followed by 30 mL of
Et2O. The flask was fitted with a septum and flushed with argon on a
schlenk line. A slow flow of SO2 was added through a needle over
the top of the orange solution which immediately turned deep green.
The flow was continued for 10 min after which the SO2-saturated
solution was allowed to stand at room temperature for an additional
45 min. The volatiles were then removed under vacuum leaving a
green powder. Inside the drybox this powder was extracted with 30
mL of warm hexane. The deep green solution was filtered and then
reduced to 20 mL under vacuum. Green crystalline product (771 mg,
94% yield) was isolated after allowing the solution to stand in a freezer
(-30 °C) overnight. This reaction was performed using as little as 3
equiv of SO2, added by vacuum transfer, without a decrease in yield:
Summary and Conclusions. Protonation of (PiPr3)2Pt(SO2)
with HBArf in ether resulted in the labilization of the SO2 and
led to the isolation of the solvent complex, trans-[(PiPr3)2Pt-
(H)(OEt2)]BArf (2). The latter was used as a precursor in the
synthesis of often very labile monodentate halocarbon complexes
of the type trans-[(PiPr3)2Pt(H)(η1-XR)]BArf, a key feature of
which is the use of the noncoordinating BArf- counterion. The
ability of the platinum center to bind a variety of very weak
base donors, including H2, to form air-stable complexes is a
rare feature in coordination complexes, especially those contain-
ing alkylphosphines. Such a metal fragment thus might be
potentially valuable for molecular detection or separations
chemistry. NMR spectroscopy is a simple diagnostic tool here,
(45) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987; pp 306-322.
(46) For examples of neutral chelating halocarbon compounds, see: (a)
Reference 7. (b) Lahuerta, P.; Latorre, J.; Martinez-Manez, R.; Sanz, F. J.
Organomet. Chem. 1988, 356, 355. (c) Solans, X.; Font-Albana, M.; Aguilo,
M.; Miravitlles, C.; Besteiro, J. C.; Lahuerta, P. Acta Crystallogr., C 1985,
41, 841.
(47) If 6 were an adduct of these discrete molecules, the significantly
different Pt-I bond distances would be expected as is most often observed
in infinite chains of repeating mixed valent bridging iodide complexes due
to the Peierls effect. The type of disorder in the position of the bridging
iodide that would be expected for random crystallization of a Pt-I‚‚‚Pt
species was not observed. See, for example: (a) Weinrach, J. B.; Ekberg,
S. A.; Conradson, S. D.; Swanson, B. I. Inorg. Chem. 1990, 29, 981. (b)
Matsumoto, N.; Yamashita, M.; Kida, S. Acta Crystallogr. 1979, B35, 1458.
(48) (a) Toronto, D. V.; Balch, A. L. Inorg. Chem. 1994, 33, 6132. (b)
Casas, J. M.; Falvello, L. R.; Fornie´s, J.; Mart´ın, A.; Toma´s, M. J. Chem.
Soc., Dalton Trans. 1993, 1107. (c) Bennett, M. A.; Berry, D. E.; Bhargava,
S. K.; Ditzel, E. J.; Robertson, G. B; Willis, A. C. J. Chem. Soc., Chem.
Commun. 1987, 1613. (d) Ling, S. S. M.; Jobe, I. R.; Galas, A. M. R.;
Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1983, 1583.
(49) (a) Holtcamp, M. W.; Labinger, J. A.; Bercaw, J. E., submitted. (b)
Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1995, 118,
5961.
(50) Yoshida, T.; Matsuda, T.; Otsuka, S. Inorg. Synth. 1979, 19, 108.
(51) Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992,
11, 3920.
(52) Goel, A. B.; Goel, S. Inorg. Chim. Acta 1982, 65, L77.

11842 J. Am. Chem. Soc., Vol. 118, No. 47, 1996
Butts et al.
1H NMR (C6D6) δ 2.20 (m, 6H, CH), 1.19 (vq ) virtual quartet, JHP
)
PhI were found at 1569, 1011, 994, and 652. All other iodobenzene
bands were obscured by those assigned to the BArf counterion. Anal.
Calcd for C56H60BF24IP2Pt: C, 42.47; H, 3.82. Found: C, 42.74; H,
3.70.
7.2, 36H, CH3); 13C{1H} NMR (CD2Cl2) δ 26.33 (vt, JCP ) 12.7, CH),
20.77 (s, CH3); 31P{1H} NMR (C6D6) δ 61.83 (s, JPPt ) 4189.4); IR
(KBr, cm-1) ν(SO) ) 1176, 1035. Anal. Calcd for C18H42O2P2PtS:
C, 37.30; H, 7.30. Found: C, 37.38; H, 7.25.
[(PiPr3)2Pt(H)(η1-BrPh)]BArf (5). Inside the drybox the Et2O
complex 2 (69.0 mg, 5.00 × 10-5 mol) was dissolved in 0.8 mL of
CH2Cl2. Bromobenzene (125 µL, 1.187 mmol, 24 equiv) was then
added by syringe. The yellow solution was layered with 1 mL of
hexane and placed in a -30 °C freezer. Very pale yellow crystals
were isolated after 1 day (46 mg, 60% yield). The static complex 5
was not observed by NMR spectroscopy (see Results). The following
data represent the solvent exchange averaged resonances when seven
equivalents of PhBr were added to 3 in CD2Cl2: 1H NMR (CD2Cl2,
-58 °C) δ 7.48 (d, J ) 8.0, 2H, Ph), 7.32 (m, 1H, Ph), 7.25 (vt, J )
7.6, 2H, Ph), 2.24 (m, 6H, CH), 1.19 (vq, J ) 7.2, 36H, CH3), -20.74
(br, JHPt ) 1781, 1H, PtH); 13C{1H} NMR (CD2Cl2, -10 °C) δ 131.78
(s, Ph), 130.61 (s, Ph), 130.58 (s, Ph), 26.01 (br, CH), 20.04 (br m,
CH3); the signals for BArf were identical to those for 2; 31P{1H} NMR
(CD2Cl2, -58 °C) δ 52.28 (s, JPPt ) 2627); IR (mineral oil, cm-1):
peaks for bound PhBr were found at 1571, 1017, 998, and 457. All
other bromobenzene peaks were obscured by those assigned to the BArf
counterion. The instability of 5 prevented a satisfactory elemental
analysis.
[(PiPr3)2Pt(H)(OEt2)]BArf (2). (PiPr3)2Pt(SO2) (254 mg, 0.438
mmol) was added to a 100 mL Schlenk flask followed by 20 mL of
Et2O in the drybox. A separate 25 mL Schlenk flask was charged with
469 mg of HBArf (0.463 mmol) and 15 mL of Et2O. Hexane (25 mL)
was added to a third flask. The three flasks were fitted with septa and
flushed with argon on a Schlenk line. The green solution containing
the platinum complex was cooled to -78 °C in a dry ice/acetone bath
after which the HBArf solution was added slowly by cannula under
argon. The solution immediately turned yellow and was stirred at -78
°C for 15 min. The hexane was then added under argon by syringe.
The resulting solvent mixture was reduced to 25 mL under vacuum
during which time yellow powder precipitated. After allowing the
mixture to stand at -78 °C for 30 min, the pale yellow solution was
decanted by syringe. The remaining yellow powder was dried under
vacuum (595 mg, 93% yield): 1H NMR (CD2Cl2, -83 °C) δ 7.72 (s,
8H, BArf), 7.53 (s, 4H, BArf), 3.74 (q, J ) 6.8, 4H, ether CH2), 2.24
(br, 6H, CH), 1.30 (t, JHH ) 6.8, 6H, ether CH3), 1.13 (vq, J ) 6.4,
36H, iPr CH3), -27.84 (t, JHP ) 14, JHPt ) 1540, 1H, PtH); 13C{1H}
NMR (CD2Cl2, -83 °C) δ 161.42 (q, J ) 49.0, i-BArf), 134.18 (s,
o-BArf), 128.18 (qm, JCF ) 31.1, m-BArf), 124.0 (d, JCF ) 272.8, CF3),
117.13 (s, p-BArf), 70.37 (s, CH2), 25.38 (vt, JCP ) 15.3, CH), 19.23
(s, i-Pr CH3), 14.76 (s, ether CH3); 31P{1H} NMR (CD2Cl2, -58 °C) δ
55.48 (s, JPPt ) 2748). Satisfactory elemental analysis could not be
obtained.18
{trans-[(PiPr3)2Pt(H)]2(µ-I)}BArf (6). A 25 mL bomb was charged
with 4 (193 mg, 1.22 × 10-4 mol) followed by 10 mL of Et2O in the
drybox. The closed flask was then removed from the drybox and placed
in an oil bath at 100 °C for four days, during which time the pale
yellow solution turned orange. The volatile materials were removed
under vacuum to afford a sticky orange-red solid which was washed
with hexane (2 × 8 mL) and subsequently isolated as a dark orange
powder. The powder was dissolved in 1.5 mL of CH2Cl2, layered with
1.5 mL of hexane, and placed in a -30 °C freezer. Thin yellow
hexagonal plates were isolated (colorless after a second recrystalliza-
tion). The mother liquor was pumped to dryness and a second crop
isolated by recrystallization from Et2O hexane in the same manner.
The total yield was 96 mg (39%): 1H NMR (CD2Cl2) δ 2.47 (m, 12H,
CH), 1.27 (vq, J ) 7.2, 72H, CH3), -18.40 (br, JHPt ) 1645, 2H, PtH);
13C{1H} NMR (CD2Cl2) δ 27.14 (vt, JCP ) 15.3, CH), 20.59 (s, CH3);
the signals for BArf were identical to those for 4; 31P{1H} NMR (CD2-
Cl2) δ 53.06 (s, JPPt ) 2738); FAB MS (NOBA) m/e (relative intensity)
1159 ([M - BArf]+, 40), 516 ([M - (PiPr3)2Pt(H)(I) - BArf]+, 100).
[(PiPr3)2Pt(H)(THF)]BArf (7). Complex 2 (40 mg, 2.75 × 10-5
mol) was dissolved in 0.8 mL of THF in the drybox. The solution
was then layered with 1 mL of hexane. After allowing the solution to
stand overnight in a -30 °C freezer, colorless crystals of 7 were isolated
which were dried under vacuum (31 mg, 78% yield): 1H NMR (CD2-
Cl2) δ 3.84 (m, 4H, CH2), 2.32 (m, 6H, CH), 1.94 (m, 4H, CH2), 1.29
(vq, J ) 7.2, 36H, CH3), -27.88 (-10 °C, br, JHPt ) 1524, 1H, PtH);
13C{1H} NMR (CD2Cl2, -10 °C) δ 74.38 (br s, THF), 26.12 (vt, JCP
) 14.6, CH), 25.60 (s, THF), 20.10 (s, CH3); the signals for BArf were
[(PiPr3)2Pt(H)(η1-ClCH2Cl)]BArf (3). Method A. Complex 3 was
isolated by recrystallizing the Et2O complex 2 from CH2Cl2/hexane.
For example, 3 was isolated as yellow plates (517 mg, 80% yield) when
a CH2Cl2 solution of 2 (642 mg in 4 mL) was layered with 8 mL of
hexane and allowed to stand at -30 °C overnight. The deuterium
analog was prepared by substituting CD2Cl2 for CH2Cl2. The static
complex 3 was not observed by NMR spectroscopy (see Results). The
following data represent the solvent exchange averaged resonances
when 3 was dissolved in CD2Cl2: 1H NMR (CD2Cl2, -58 °C) δ 2.34
(m, 6H, CH), 1.19 (m, 36H, CH3), -22.82 (t, JHP ) 11.9, JHPt ) 1852,
1H, PtH); 13C{1H} NMR (CD2Cl2, -78 °C) δ 24.51 (m, CH), 19.17
1
(s, CH3), the H and 13C resonances attributed to the counterion were
identical to those reported for 2; 31P{1H} NMR (CD2Cl2, -58 °C) δ
54.61 (s, JPPt ) 2637); IR (mineral oil, cm-1) ν(CCl)asym ) 751, ν-
(CCl)sym ) 663. Satisfactory elemental analysis could not be obtained
due to the instability of the compound toward CH2Cl2 loss.
Method B. In the drybox trans-(PiPr3)2Pt(H)(Cl) (754 mg, 1.37
mmol) was dissolved in 25 mL of CH2Cl2 (see note in general section
of the Experimental Section) in a round bottom flask. NaBArf51 (1.26
g, 1.42 mmol) was then added as a solid with stirring. The
homogeneous yellow solution quickly turned cloudy orange and was
allowed to stir at room temperature for 2 h. The mixture was filtered
through Celite to remove the NaCl, reduced in volume under vacuum
to 4 mL, layered with 6 mL of hexane, and placed in a -30 °C freezer.
Yellow crystalline 3 was isolated in 63% yield.
[(PiPr3)2Pt(H)(η1-IPh)]BArf (4). This reaction was performed in
the drybox. The Et2O complex 2 (123 mg, 8.05 × 10-5 mol) was added
to a 50 mL round bottom flask with a stir bar and dissolved in 15 mL
of dichloromethane. A solution of iodobenzene (103 mg, 0.505 mmol,
6.3 equiv) was added slowly with stirring. After standing at room
temperature for 3 h the volume was reduced to 5 mL. This yellow
solution was layered with 5 mL of hexane and placed in a -30 °C
freezer. Over 12 h time, colorless crystals precipitated (122 mg, 87%
yield) which were dried under vacuum: 1H NMR (CD2Cl2) δ 7.72 (s,
8H, BArf), 7.56 (s, 4H, BArf), 7.66 (d, J ) 8.1, 2H, Ph), 7.51 (t, J )
7.2, 1H, Ph), 7.26 (vt, J ) 7.6, 2H, Ph), 2.30 (m, 6H, CH), 1.24 (vq,
J ) 7.2, 36H, CH3), -17.02 (vbr, JHPt ) 1650, 1H, PtH) (at -93 °C,
the hydride appeared as a triplet at -15.89 (JHP ) 9, JHPt ) 1654));
13C{1H} NMR (CD2Cl2) δ 161.99 (q, J ) 49.8, i-BArf), 137.21 (s,
Ph), 135.08 (s, o-BArf), 131.61 (s, Ph), 130.77 (s, Ph), 129.20 (q, JCF
) 31.5, m-BArf), 124.90 (d, JCF ) 271.7, CF3), 117.76 (s, p-BArf),
27.05 (vt, JCP ) 15.0, CH2), 20.38 (s, CH3); 31P{1H} NMR (CD2Cl2)
δ 53.03 (s, JPPt ) 2603.8); IR (mineral oil, cm-1): peaks for bound
identical to those for 4; 31P{1H} NMR (CD2Cl2) δ 57.10 (s, JPPt
)
2755). Anal. Calcd for C54H63BF24OP2Pt: C, 44.67; H, 4.37.
Found: C, 44.89; H, 4.39.
[(P-t-Bu3)2Pt(H)]BArf. In the drybox, trans-(P-t-Bu3)2Pt(H)(Cl)
(639 mg, 1.00 mmol) was added to a round bottom flask with a stir
bar. Diethyl ether (20 mL) was added to form a pale yellow suspension.
To this was added NaBArf57 (901 mg, 1.02 mmol) piecewise as a solid
with stirring during which time the mixture turned yellow-orange. After
stirring at room temperature for two hours, the volatile materials were
removed under vacuum and the resulting yellow powder was extracted
with 25 mL of CH2Cl2. The dark orange mixture was filtered through
Celite to remove the NaCl and concentrated under vacuum to 16 mL.
This solution was layered with 16 mL of hexane and placed in a -30
°C freezer. Pure [(P-t-Bu3)2Pt(H)]BArf was isolated as a yellow powder
in 64% yield (941 mg): 1H NMR (CD2Cl2) δ 1.51 (vt, J ) 6.4, 54H,
t-Bu), -36.53 (t, JHP ) 8.0, JHPt ) 2605, 1H, PtH); 13C{1H} NMR
(CD2Cl2) δ 41.07 (t, JCP ) 8.9, C(CH3)3), 32.75 (s, C(CH3)3); the signals
for BArf were identical to those for 4; 31P{1H} NMR (CD2Cl2) δ 87.14
(s, JPPt ) 2625). Anal. Calcd for C56H67BF24P2Pt: C, 45.95; H, 4.61.
Found: C, 46.11; H, 4.55.
Reaction of 3 with H2. Complex 3 (15 mg, 1.02 × 10-5 mol) was
loaded into an NMR tube followed by 0.5 mL of CD2Cl2 in the drybox.

Halide-to-Metal π Bonding in Halocarbon Compounds
J. Am. Chem. Soc., Vol. 118, No. 47, 1996 11843
The tube was then attached to a Kontes vacuum adaptor via a Cajon
joint. A calculated quantity of dihydrogen was added by transferring
a measured pressure (ideal gas law) of gas into the NMR tube at 77 K
utilizing a MKS baratron gauge attached to a high-vacuum line (485
Torr at 77 K, 2.83 × 10-4 mol, 28 equiv). The tube was then flame
sealed using an oxygen/propane torch, and immediately transferred to
a dewar packed with dry ice for transport to the NMR spectrometer,
with the probe precooled to -80 °C. An identical reaction was set up
in which H2 was replaced with HD in order to determine the ligated
HD coupling constant (33.7 Hz). The NMR resonances are described
in the Results.
refined with the temperature factor fixed at 0.08 Å2. All remaining
hydrogen atoms were fixed in positions of ideal geometry, with a C-H
distance of 0.96 Å for CH3 hydrogens, 0.97 Å for the CH2 hydrogens,
and 0.98 Å for the CH hydrogens and refined using the riding model
in the HFIX facility in SHELXL 93. These idealized hydrogen atoms
had their isotropic temperature factors fixed at 1.2 times (CH) or 1.5
times (CH3) the equivalent isotropic U of the C atoms to which they
were bonded.
For the aryl halide complexes 4 and 5, Patterson techniques were
used to locate the platinum, halide, and phosphorous atoms. All
remaining atoms were found from subsequent difference maps. The
phenyl group was refined as a rigid body, with ring carbon-carbon
distances fixed at 1.39 Å. All hydrogen atoms were fixed in positions
of ideal geometry. The C-H distances were fixed at 0.980 Å (tertiary),
0.970 Å (phenyl), or 0.960 Å (methyl). All hydrogen atoms were
refined using the riding model in the HFIX facility in SHELX-93, and
had their isotropic temperature factors fixed at 1.2 (tertiary and phenyl)
or 1.5 (methyl) times the equivalent isotropic U of the atom they were
bonded to. The final refinement54 for all compounds included aniso-
tropic thermal parameters on all non-hydrogen atoms.
Molecular Mechanics. The molecular structure of trans-[(PiPr3)2-
Pt(H)(η1-IPh)]+ was minimized using the ESFF force field within
Discover 95.0.37 The optimization routine within the Builder module
was used with the charges option turned on. Since ESFF does not
have force field parameters for a hydride ligand, a fluoride ion was
used in its place with the default distance of 1.623 Å. Force field
parameters for Pt(II) in a square planar geometry were used (Pt024
switch). Charges on the platinum and fluoride ions were set at +2
and -1, respectively. All other atoms were left with neutral charges.
The initial starting point for the minimization was the crystal coordinates
of the [(PiPr3)2Pt(H)(η1-IPh)]+ ion with the hydride replaced with a
fluoride ion (Vide supra). Convergence was achieved (maximum
derivative 0.00605) after 34 iterations of steepest descent and 309
iterations of quasi Newton (BFGS). The initial and final energies were
61.869 and 51.419 kcal, respectively. Starting and ending structures
are summarized in Figure 7 and Table 5. A second minimization was
performed using the final structure of the first minimization with the
dihedral angle C(6)-C(1)-I(1)-Pt(1) ) 0°. This minimization led
to a structure with a final energy 1.5 kcal below the structure found in
the first minimization, but was chemically unreasonable due to a Pt
coordination geometry with trans angles of 149.6° and 146.2°.
X-ray crystal structure determinations. A crystal of 3, 4, 5, 6,
or 7 was mounted on a thin glass fiber using silicone grease. The
crystal, which was mounted from a pool of mineral oil bathed in argon,
was then immediately placed under a liquid N2 stream on a Siemens
P4/PC diffractometer. The radiation used was graphite monachroma-
tized MoKR radiation (λ ) 0.710 69 Å). The lattice parameters were
optimized from a least-squares calculation on 25 (32 for 3, 6, and 7)
carefully centered reflections of high Bragg angle. The data was
collected using ω scans over a 0.80-1.18° scan range. Three check
reflections monitored every 97 reflections showed no systematic
variation of intensities. For 6, data were collected only to 2θ ) 40°
due to the small size of the crystal. Lattice determination and data
collection were carried out using XSCANS Version 2.10b software.
All data reduction, including Lorentz and polarization corrections and
structure solution and graphics were performed using SHELXTL PC
Version 4.2/360 software. The structure refinement was performed
using SHELX-93 software.53 The data were corrected for absorption
using the ellipsoid option in the XEMP facility of SHELXTL PC.
The space groups were uniquely determined from the systematic
absenses. In the case of 3, 6, and 7 the Pt, Pt-bound heteroatom, and
P atoms as well as the majority of C atoms were located from the
direct methods solution. The remaining C atoms and the B and F atoms
were located during subsequent Fourier synthesis. For 3, it was at this
time that significant electron density was observed near some F atoms;
these residual peaks were modeled as disordered F at one-half
occupancy and labled as primed F atoms. A disordered region near
the Pt atom was then modeled as two disordered methylene chloride
molecules. These two molecules, labeled Cl(2)-C(45)-Cl(1) and Cl-
(3)-C(45′)-Cl(1), were refined with their site occupancy factors tied
to one. In the final refinement the occupancy factors refined to 0.677-
(8) for the Cl(2)-C(45)-Cl(1) molecule and 0.323(8) for the Cl(3)-
C(45′)-Cl(1) molecule. It was discovered at this time that the disorder
in the methylene chloride was accompanied by disorder in the closest
isopropyl group [C(8)-C(3)-C(9)]. This disorder was modeled as two
half occupancy isopropyl groups, C(8)-C(3)-C(9) and C(8′)-C(3′)-
C(9′). For 3, 6, and 7 the next step was a high angle refinement to
locate the Pt-hydrides. The weighting function w was multipled by
1 -exp[-5(sin θ/λ)2] in order to weight the high angle data prior to
analysis of the difference map. This tactic revealed all hydrogen atoms
in the structure. The positional coordinates of the hydride peak,
approximately 1.7 Å (3), 1.4 Å (6), or 1.5 Å (7) from the Pt and in a
square plane with the two P atoms and the Pt-bound heteroatom, were
Acknowledgment. This work was supported by the Office
of Basic Energy Sciences of the DOE and the Los Alamos
National Laboratory Directed Research and Development Office.
Supporting Information Available: Complete details of the
structural determinations of compounds 3, 4, 5, 6, and 7 and an
ORTEP drawing of the BArf anion in 3 (53 pages). See any
current masthead page for ordering and Internet access
instructions.
JA961836Y
(54) R1 ) σ||Fo| - |Fc||/σ|Fo| and R2w) [Σ[w(Fo2 - Fc2)2]/Σ[w(Fo ) ]]1/2
.
2 2
The parameter w ) 1/[σ2(Fo ) + (0.0397P)2 + 14.2032P] for 3, 1/[σ2(Fo )
2
2
(53) XSCANS and SHELXTL PC are products of Siemens Analytical
X-ray Instruments, Inc., 6300 Enterprise Lane, Madison, WI 53719. SHELX-
93 is a program for crystal structure refinement written by G. M. Sheldrick
University of Go¨ttingen, Germany, 1993.
+ (0.0857P)2 + 5.2066P] for 4, 1/[σ2(Fo ) + (0.0639P)2 + 34.2822P] for
2
5, 1/[σ2(Fo ) + (0.0482P)2 + 97.7170P] for 6, and 1/[σ2(Fo ) + (0.0273P)2
2
2
2
2
+ 18.3466P] for 7, where P ) (Fo + 2Fc )/3.