Stereoselectivity in organometallic reactions: Oxidative addition of alkyl halides to platinum(II)

Article abstract of DOI:10.1021/om980065z

The ligands cis- and trans- 1,2-(N=CHC₆H₅)₂C₆H₁₀ (trans, 1; cis, 2) underwent cyclometalation of one phenyl substituent on reaction with [Pt₂Me₄(μ-SMe₂)₂] (3) to give CH₄ and chiral platinum(II) complexes [PtMe{1-(N=CHC₆H₄)-2-(N=CHC₆H ₅)C₆H₁₀}], containing new N,N,C-donor tridentate ligands (trans, 4; cis, 5); complex 4 was structurally characterized. Reaction of racemic 4 and 5 with primary alkyl halides (iodomethane, iodoethane, 1-iodopropane, and benzyl bromide) gave platinum(IV) products by oxidative addition, often with a high degree of stereoselectivity. The absolute configuration of the major stereoisomer was determined for the following representative platinum(IV) products by X-ray crystal structure analyses: [PtIMe₂{cis-1-(N=CHC₆H₄)-2-(N=CHC ₆H₅)C₆H₁₀}] (7a), [PtIMeEt{trans-1-(N=CH-C₆H₄)-2-(N=CHC₆H ₅)C₆H₁₀}] (8a), and [PtBrMeBz{trans-1-(N=CHC₆H₄)-2-(N=CHC₆H ₅)-C₆H₁₀}] (13a; Bz = benzyl). In other cases, structural assignment was made by NMR (including NOE effects in selected cases) and supported by molecular mechanics calculations. The first step of the oxidative addition occurs primarily at the face syn and anti to the cyclohexyl group in 4 and 5, respectively, and the initial oxidative addition is trans. In the case of methyl iodide addition, but in no others, subsequent isomerization can occur to give products which appear to arise from cis oxidative addition, and the basis for this trend is elucidated. Hydrolysis of [PtIMeEt{cis-1-(N=CHC₆H₄)-2-(N=CHPh)C₆H ₁₀}] (9b) gives PhCH=O and [PtIMeEt{cis-1-(N=CHC₆H₄)-2-(NH₂)C ₆H₁₀}], with a change in stereochemistry at platinum.

Full text of DOI:10.1021/om980065z

Organometallics 1998, 17, 2805-2818
2805
Ster eoselectivity in Or ga n om eta llic Rea ction s: Oxid a tive
Ad d ition of Alk yl Ha lid es to P la tin u m (II)
Cliff R. Baar, Hilary A. J enkins, J agadese J . Vittal, Glenn P. A. Yap, and
Richard J . Puddephatt*
Department of Chemistry, The University of Western Ontario,
London, Ontario, Canada N6A 5B7
Received February 2, 1998
The ligands cis- and trans-1,2-(NdCHC6H5)2C6H10 (trans, 1; cis, 2) underwent cyclometa-
lation of one phenyl substituent on reaction with [Pt2Me4(µ-SMe2)2] (3) to give CH4 and chiral
platinum(II) complexes [PtMe{1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}], containing new N,N,C-
donor tridentate ligands (trans, 4; cis, 5); complex 4 was structurally characterized. Reaction
of racemic 4 and 5 with primary alkyl halides (iodomethane, iodoethane, 1-iodopropane,
and benzyl bromide) gave platinum(IV) products by oxidative addition, often with a high
degree of stereoselectivity. The absolute configuration of the major stereoisomer was deter-
mined for the following representative platinum(IV) products by X-ray crystal structure
analyses: [PtIMe2{cis-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (7a ), [PtIMeEt{trans-1-(NdCH-
C6H4)-2-(NdCHC6H5)C6H10}] (8a ), and [PtBrMeBz{trans-1-(NdCHC6H4)-2-(NdCHC6H5)-
C6H10}] (13a ; Bz ) benzyl). In other cases, structural assignment was made by NMR (in-
cluding NOE effects in selected cases) and supported by molecular mechanics calculations.
The first step of the oxidative addition occurs primarily at the face syn and anti to the
cyclohexyl group in 4 and 5, respectively, and the initial oxidative addition is trans. In
the case of methyl iodide addition, but in no others, subsequent isomerization can occur to
give products which appear to arise from cis oxidative addition, and the basis for this trend
is elucidated. Hydrolysis of [PtIMeEt{cis-1-(NdCHC6H4)-2-(NdCHPh)C6H10}] (9b) gives
PhCHdO and [PtIMeEt{cis-1-(NdCHC6H4)-2-(NH2)C6H10}], with a change in stereochemistry
at platinum.
In tr od u ction
lated diimine ligands derived from cis- or trans-diami-
nocyclohexane, which naturally give chiral products.7
It will be shown that the oxidative-addition reactions
occur with high stereoselectivity, and that the presence
of asymmetry can lead to a more complex sequence of
steps in the oxidative addition than is normally ob-
served. It has previously been shown that similar
diimine ligands containing 2-halogenoaryl substituents
give highly stereoselective intramolecular oxidative
additions of the aryl-halogen bonds to platinum(II)8
and that similar ligands are useful in chiral catalysis.9
Since the oxidative addition of alkyl halides to transi-
tion-metal complexes is a key step in several important
catalytic reactions,1 there have been many studies to
determine the scope of the reaction and to study reac-
tivity and mechanism.1-5 In most cases, the oxidative
addition of primary alkyl halides to dimethylplatinum-
(II) complexes occurs by the polar SN2 mechanism and
gives trans stereochemistry,1,3-5 though subsequent
isomerization can give products which appear to arise
from cis oxidative addition, as illustrated in eq 1.6
Resu lts
Syn th esis a n d Ch a r a cter iza tion of Liga n d s. The
Schiff base ligand trans-1,2-(NdCHC6H5)2C6H10 (1) was
(3) (a) J awad, J . K.; Puddephatt, R. J . J . Organomet. Chem. 1976,
117, 297. (b) J awad, J . K.; Puddephatt, R. J . J . Chem. Soc., Dalton
Trans. 1977, 1466. (c) Monaghan, P. K.; Puddephatt, R. J . Organo-
metallics 1986, 5, 439. (d) Crespo, M.; Puddephatt, R. J . Organome-
tallics 1987, 6, 2548. (e) Monaghan, P. K.; Puddephatt, R. J . J . Chem.
Soc., Dalton Trans. 1988, 595.
(4) Brown, M. P.; Puddephatt, R. J .; Upton, C. E. E. J . Chem. Soc.,
Dalton Trans. 1974, 2457.
(5) (a) Monaghan, P. K.; Puddephatt, R. J . Organometallics 1985,
4, 1406. (b) Scott, J . D.; Puddephatt, R. J . Organometallics 1986, 5,
1538.
(6) (a) von Zelewsky, A.; Suckling, A. P.; Stoeckli-Evans, H. Inorg.
Chem. 1993, 32, 4585. (b) Achar, S.; Scott, J . D.; Puddephatt, R. J .
Polyhedron 1996, 15, 2363.
(7) For chirality descriptors see: Block, B. P.; Powell, W. H.;
Fernelius, W. C. Inorganic Chemical Nomenclature: Principles and
Practice; American Chemical Society: Washington, DC, 1990; Chapter
16.
Surprisingly little attention has been placed on the
potential stereoselectivity of oxidative addition of alkyl
halides to square-planar complexes having no plane of
symmetry in the molecular plane.2 This paper reports
such a study, using platinum(II) complexes with meta-
(1) Stille, J . K. The Chemistry of the Metal-Carbon Bond; Hartley,
F. R., Patai, S., Eds.; Wiley: New York, 1985; Vol. 2, Chapter 9.
(2) (a) Gianini, M.; Forster, A.; Haag, P.; Stoeckli-Evans, H. Inorg.
Chem. 1996, 35, 4889. (b) Wehman-Ooyevaar, I.; Drenth, W.; Grove,
D. M.; van Koten, G. Inorg. Chem. 1993, 32, 3347.
S0276-7333(98)00065-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 05/23/1998

2806 Organometallics, Vol. 17, No. 13, 1998
Baar et al.
Sch em e 1
Sch em e 2
prepared by the condensation of racemic (R,R,S,S)-
trans-1,2-diaminocyclohexane with benzaldehyde in the
presence of MgSO4. The meso (R,S) ligand cis-1,2-
(NdCHC6H5)2C6H10 (2) was prepared similarly. The
ligands were formed as single isomers, and anti stereo-
chemistry is assumed about each imine NdCH bond and
has been confirmed in several complexes derived from
them. The complexes were fully characterized using 1H
NMR spectroscopy and either microanalysis or high-
resolution mass spectroscopy.
final products 4 and 5 were characterized. Though
stereoselectivity is expected in the oxidative-addition
step, no useful information is obtained.
Ra cem ic [P tMe{tr a n s-1-(NdCHC6H4)-2-(NdCH-
C6H5)C6H10}] (4) a n d Ra cem ic [P tMe{cis-1-(NdCH-
C6H4)-2-(NdCHC6H5)C6H10}], (5). The ligands trans-
and cis-1,2-(NdCHC6H5)2C6H10 (1 and 2) each reacted
with [Pt2Me4(µ-SMe2)2] (3) to give, not the simple
diimine complexes expected to arise from ligand sub-
stitution, but the products of cycloplatination [PtMe{1-
(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (trans, 4; cis, 5),
with corresponding loss of CH4 (Schemes 1 and 2).10
These reactions are expected to proceed by ligand substi-
tution to give the corresponding dimethyl(diimine)plati-
num(II) complex (Schemes 1 and 2) followed by in-
tramolecular oxidative addition of an aryl C-H bond
to give a platinum(IV) intermediate which undergoes
reductive elimination of methane.10,11 However, these
proposed intermediates are not detectable and only the
Scheme 1 shows only the reaction derived from (R,R-
1, and metalation of either phenyl substituent gives the
same product R,R-4; racemic 1 thus gives racemic 4. The
case of the meso ligand 2 is somewhat more complex,
but the two phenyl groups are chemically identical and
reaction naturally gives equal amounts of the enantio-
meric products S,R-5 and R,S-5 (the nomenclature used
places the descriptor for the higher priority chiral carbon
atom, the one connected to the metalated aryl group,
first). Thus, the meso ligand 1 gives the racemic prod-
uct 5. The spectroscopic properties of the complexes are
fully consistent with these predictions. Thus, the 1H
NMR spectra of complexes 4 and 5 (Table 1) each con-
tained a single methylplatinum resonance with coupling
constant 2J (PtH) ) 83 Hz for 4 and 84 Hz for 5, ty-
pical of platinum(II) methyl groups trans to N-do-
1
nors.10,12 The H NMR spectra of 4 and 5 also show the
(8) Baar, C. R.; Hill, G. S.; Vittal, J . J .; Puddephatt, R. J . Organo-
metallics 1998, 17, 32.
(9) (a) Omae, I. Chem. Rev. 1979, 79, 287. (b) Constable, E. C.
Polyhedron 1984, 3, 1037. (c) Ryabov, A. D. Synthesis 1985, 233. (d)
Newkome, G. R.; Puckett, W. E.; Gupta, C. K.; Kiefer, G. E. Chem.
Rev. 1986, 86, 451.
(10) (a) Anderson, C. M.; Ferguson, G.; Lough, A. J .; Puddephatt,
R. J . J . Chem. Soc., Chem. Commun. 1989, 18, 1297. (b) Anderson, C.
M.; Crespo, M.; J ennings, M. C.; Lough, A. J .; Ferguson, G.; Pud-
dephatt, R. J . Organometallics 1991, 10, 2672. (c) Perera, S. D.; Shaw,
B. L. J . Chem. Soc., Dalton Trans. 1995, 641. (d) Crespo, M. Polyhedron
1996, 15, 1981. (e) Crespo, M.; Solans, X.; Font-Bardia, M. J . Orga-
nomet. Chem. 1996, 518, 105.
(11) (a) Poss, M. J .; Arif, A. M.; Richmond, T. G. Organometallics
1988, 7, 1669. (b) Richmond, T. Coord. Chem. Rev. 1990, 105, 221. (c)
Crespo, M.; Martinez, M.; Sales, J . J . Chem. Soc., Chem. Commun.
1992, 882. (d) Anderson, C. M.; Crespo, M.; Ferguson, G.; Lough, A.
J .; Puddephatt, R. J . Organometallics 1992, 11, 1177. (e) Kiplinger, J .
L.; King, M. A.; Fechtenkotter, A.; Arif, A. M.; Richmond, T. G.
Organometallics 1996, 15, 5292.
characteristic 195Pt satellites on the imine proton reso-
nances (Table 1).
Complex 4 was also characterized by an X-ray struc-
ture determination; selected bond distances and angles
are given in Table 2, and a view of the structure of the
S,S isomer is shown in Figure 1. The structure estab-
lishes the presence of the tridentate N,N,C-donor ligand
formed by metalation of one of the phenyl substituents
of the ligand 1 and shows that the platinum(II) center
has square-planar geometry. The angles at platinum
are distorted due to the constraints of the tridentate
(12) (a) Scott, J . D.; Puddephatt, R. J . Organometallics 1983, 2, 1645.
(b) Kuyper, J . Inorg. Chem. 1977, 16, 2171.

Oxidative Addition of Alkyl Halides to Pt(II)
Organometallics, Vol. 17, No. 13, 1998 2807
Ta ble 1. 1H NMR Da ta (300 MHz in CD2Cl2
Solu tion ) for MeP t a n d NdCH Gr ou p s in
Com p lexes 4-14
N-Pt-Me
2J (PtH)/Hz
X-Pt-Me
2J (PtH)/Hz
NdCH
complex
δ
δ
δ
3J (PtH)/Hz
4
0.51
83
84
67
66
66
67
67
67
8.64
8.98
8.69
9.02
8.51
8.82
8.49
8.96
8.55
8.84
8.51
8.83
8.53
8.88
8.51
8.85
8.37
8.47
8.83
8.51
8.85
8.43
8.71
8.08
9.06
8.40
8.76
61
47
63
45
50
36
49
36
49
34
5
0.61
0.78
0.95
0.87
0.87
0.74
0.87
6a
6b
7a a
7ba
8a
9b
0.67
0.66
0.82
0.65
b
71
72
72
71
52
39
52
38
44
49.5
39
51
38
51
38
53
37
51
37
b
F igu r e 1. View of the structure of the S,S enantiomer of
complex 4.
10
11a
b
0.79
0.93
c
72
66
67
66
66
66
Ch a r t 1. Oxid a tive Ad d ition to 4
12b
13a
13b
14b
0.89
0.77
1.01
0.86
c
d
d
d
a
b
d
Solvent CDCl3. Et group here. c Pr group here. Bz group
here.
Ta ble 2. Selected Bon d Dista n ces a n d An gles for
Com p lex 4
(a) Bond Distances (Å)
Pt(1)-C(2)
Pt(1)-C(1)
N(1)-C(8)
N(2)-C(15)
C(2)-C(7)
C(9)-C(14)
2.01(1)
2.08(1)
1.28(1)
1.29(1)
1.39(1)
1.55(1)
Pt(1)-N(1)
Pt(1)-N(2)
N(1)-C(9)
N(2)-C(14)
C(7)-C(8)
C(15)-C(16)
2.06(1)
2.12(1)
1.46(1)
1.48(1)
1.44(1)
1.49(1)
(b) Bond Angles (deg)
C(2)-Pt(1)-N(1)
N(1)-Pt(1)-C(1)
N(1)-Pt(1)-N(2)
C(8)-N(1)-Pt(1)
C(14)-N(2)-Pt(1)
C(2)-C(7)-C(8)
N(1)-C(9)-C(14)
80.9(4)
171.7(4)
80.8(3)
113.6(7)
104.5(6)
116.5(9)
105.9(8)
C(2)-Pt(1)-C(1)
96.5(4)
C(2)-Pt(1)-N(2)
C(1)-Pt(1)-N(2)
C(9)-N(1)-Pt(1)
C(7)-C(2)-Pt(1)
N(1)-C(8)-C(7)
N(2)-C(14)-C(9)
161.7(4)
101.5(4)
115.0(7)
111.5(8)
117.1(9)
109.1(8)
meridional coordination and the platinum(IV) center
having a strong preference for the facial coordination
of the three carbon donor ligands.3-6,8,10 The possible
isomers are then shown as a -d in Charts 1 and 2. The
R-X groups may add trans to give a and b or cis to
give c and d . For each stereochemistry of R-X addition
to 4, there are two possible diastereomers defined in
Chart 1 as R,R-C and R,R-A (also S,S-C and S,S-A for
the racemic ligand, with C and A defining the chirality
at platinum(IV)) since the methyl group of MeI can
approach and add to either of the two distinct faces of
the chiral square-planar complex during the oxidative
addition, thus giving the isomers a ,b or c,d . Oxidative
addition to 5 gives similar results except that the
diastereomeric pairs have the chirality descriptors
S,R-A and S,R-C (and R,S-C and R,S-A since 5 is
racemic) as shown in Chart 2. Reactions have been
studied with R-X ) MeI, CD3I, EtI, PrI, and BzBr (Bz
) PhCH2), and these are described sequentially below.
Oxid a t ive Ad d it ion of Met h yl Iod id e. Racemic
[PtMe{trans-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (4)
reacted quickly with iodomethane in THF at room
ligand, with N(1)-Pt-N(2) and N(1)-Pt-C(2) less than
90° and C(1)-Pt-N(2) and C(1)-Pt-C(2) greater than
90° (Table 2). The stereochemistry at both imine groups
is anti, and the cyclohexane ring has the chair confor-
mation, as expected. All the bond distances are in the
expected ranges, once allowance is made for the strong
trans influence of the carbon donors.13
The complexes 4 and 5 are stable but electron-rich
chiral platinum(II) complexes and so are clearly suitable
substrates for the study of stereoselectivity in oxidative
addition. The oxidative addition of the reagent R-X to
4 or 5 could give many isomeric platinum(IV) products.
However, the number will be limited to four for a given
enantiomer of 4 or 5, given the constraints imposed by
the tridentate ligand having a strong preference for
(13) For example, see: (a) Clegg, D. E.; Hall, J . R.; Swile, G. A. J .
Organomet. Chem. 1972, 38, 403. (b) Hill, G. S.; Vittal, J . J .;
Puddephatt, R. J . Organometallics 1997, 16, 1209.

2808 Organometallics, Vol. 17, No. 13, 1998
Baar et al.
Ch a r t 2. Oxid a tive Ad d ition to 5
F igu r e 2. View of the structure of the S,R-A enantiomer
of complex 7a .
stereoselectivity during the intermolecular oxidative
addition of iodomethane to complex 4. The absolute
configuration of the major stereoisomer 6a ,c was as-
signed as R,R-C (S,S-A) on the basis of X-ray structural
data obtained from the analogous products from reac-
tion of 4 with iodoethane and benzyl bromide (see below)
and the similarity of 1H NMR data between these
complexes (Table 1). The absolute configuration of the
minor diastereomer, 6b,d could then be assigned as
R,R-A (S,S-C).
temperature to give a mixture of two diastereomers of
the platinum(IV) complex [PtIMe2{trans-1-(NdCHC6H4)-
2-(NdCHC6H5)C6H10}] (6). Note that, in this case with
R ) Me, the isomers 6a ,c and 6b,d are structurally
equivalent; therefore, only two isomers are possible and
two are observed.
Racemic [PtMe{cis-1-(NdCHC6H4)-2-(NdCHC6H5)-
C6H10}] (5) reacted similarly with iodomethane to give
largely one diastereomer of [PtIMe2{cis-1-(NdCHC6H4)-
2-(NdCHC6H5)C6H10}] (7), shown to have structure 7a
(or 7c). Minor resonances were observed due to one or
more minor species, but the low abundance of about 5%,
coupled with partial overlap of key resonances with the
much stronger resonances of 7a , did not allow structural
assignment. NMR data for 7a are given in Table 1 and
are fully consistent with the proposed structure. The
stereochemistry of the major isomer 7a was established
as S,R-A (R,S-C) by an X-ray structure determination.
A view of the structure of the S,R-A enantiomer is
shown in Figure 2, and selected bond lengths and angles
are provided in Table 3. The structure confirms the
presence of an octahedrally coordinated platinum(IV)
center, with a fac-PtC3 geometry for the carbon donor
ligands, with the absolute configuration of the complex
being S,R-A (R,S-C). The tridentate N,N,C ligand
adopts the expected meridional coordination, and the
geometry around platinum(IV) is distorted from octa-
hedral due to the constraints of this ligand. The Pt-C
bond lengths are normal, and the Pt(1)-I(1) bond length
of 2.7844(9) Å is also within the expected range.15 With
respect to the platinum-imine bonds, the distance
N(2)-Pt of 2.216(8) Å is significantly longer than the
N(1)-Pt distance of 2.075(7) Å, though both are trans
to carbon donors; this could be due to steric interactions
between the nonmetalated phenylimine fragment and
the crowded equatorial site occupied by the C2 methyl
ligand. Figure 2 shows that, for the major isomer 7a ,
the iodide ligand is anti to the cyclohexane ring, which
lies above the plane containing the N,N,C tridentate
ligand, while the methyl group is in a position syn to
the cyclohexyl group. This stereochemistry is perhaps
expected for the product of thermodynamic control, since
The presence of two diastereomers was established
1
from the H NMR spectra of the complexes (Table 1),
obtained as soon as possible after isolation so as to
minimize possible complications due to isomerization
after the initial oxidative addition. The major diaste-
reomer, subsequently assigned the structure 6a (or 6c),
2
gave resonances at δ 0.67, J (PtH) ) 71 Hz and δ 0.78,
2J (PtH) ) 67 Hz, assigned to the methylplatinum
groups trans to iodide and the imine group, respectively.
This is consistent with previous work involving similar
platinum(IV) complexes, in which it was shown that
methylplatinum resonances trans to an iodide ligand
occurred at lower frequency than those trans to a
nitrogen donor and have a somewhat higher value of
2J (PtH) due to the low trans influence of iodide.3d,5a,14
The magnitude of the 2J (PtH) coupling constants are
diagnostic of a platinum(IV) species and are consistent
with the expected fac-PtC3 geometry, and the criterion
2
that a MePt group trans to halide gives J (PtH) > 70
2
Hz whereas a MePt group trans to imine gives J (PtH)
< 70 Hz is most useful in structure assignments.3,5,10,11
The iminic proton resonances were present at δ 8.51
3
3
with J (PtH) ) 50 Hz and at δ 8.82 with J (PtH) ) 36
Hz, thus establishing that both imine groups remain
coordinated to the platinum(II) center. A second set of
methylplatinum and imine resonances indicated the
presence of a second, minor stereoisomer, which was
1
assigned structure 6b (or 6d ) (Chart 1). The H NMR
data are similar to those for 6a (Table 1), and so a
similar fac-PtC3 structure is established. Integration
of the methylplatinum and imine 1H NMR signals of
the mixture gave the diastereomeric ratio (6a + 6c):
(6b + 6d ) ) 2.3, establishing a significant degree of
(15) Levy, C. J .; Vittal, J . J .; Puddephatt, R. J . Organometallics
1996, 15, 2108 and references therein.
(14) Crespo, M. Polyhedron 1996, 15, 1981.

Oxidative Addition of Alkyl Halides to Pt(II)
Organometallics, Vol. 17, No. 13, 1998 2809
Ta ble 3. Selected Bon d Dista n ces a n d An gles for
Com p lex 7a a
Thus, the major MePt resonance occurred at δ 0.66 with
2J (PtH) ) 72 Hz, placing the CH3 ligand in an axial
position trans to iodide, with only a minor MePt
resonance at δ 0.95 with 2J (PtH) ) 66 Hz due to the
MePt group trans to imine in 6b* (Figure 3b). The ratio
6d *:6b* ) 2.8. In addition, the ratios 6a *:6d * ) 6c*:
6b* ) 2.3.
(a) Bond Lengths (Å)
Pt(1)-C(3)
Pt(1)-C(2)
Pt(1)-N(2)
N(1)-C(9)
N(2)-C(16)
C(3)-C(8)
C(10)-C(15)
2.00(1)
2.07(1)
2.216(8)
1.28(1)
1.28(1)
1.43(1)
1.51(1)
Pt(1)-C(1)
Pt(1)-N(1)
Pt(1)-I(1)
N(1)-C(10)
N(2)-C(15)
C(8)-C(9)
C(16)-C(17)
2.07(1)
2.075(7)
2.7844(9)
1.48(1)
1.53(1)
1.43(2)
1.46(1)
The stereochemical assignments discussed above were
unexpected, and so it was considered necessary to con-
firm the 1H NMR assignments on which they are based.
This was accomplished by use of nuclear Overhauser
effect (NOE) difference spectroscopy (Chart 3).16 The
NOE difference spectra for the platinum(II) complex
[PtMe{cis-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (5)
demonstrated a significant enhancement between the
ortho Ha protons of the phenylimine group and the
methylplatinum Hb protons (1.9% enhancement), con-
sistent with the close proximity of the Ha and Hb protons
(Chart 3) expected by analogy with the X-ray structure
of the related complex 4 shown in Figure 1. The X-ray
structure of 7a (Figure 2) shows that a corresponding
ortho hydrogen atom of the phenylimino group lies
closer to the equatorial (Hb) than to the axial (Hc)
methylplatinum group and so the NOE difference
spectra should give an independent assignment for
these two resonances. The results are shown in Chart
3 (in which the positions of Hb and Hc are based on the
original assignments discussed earlier), and they con-
firm the original assignments since there is a larger
NOE associated with the methylplatinum resonance
assigned to be in the equatorial position. Similarly,
there was a greater NOE effect between the phenyl
proton Ha of the imine group and the equatorial over
the axial methyl group in 6a (Chart 3). The conclusions
reached on the stereochemistry of the oxidative addition
of CD3I are therefore validated.
Rea ction of [P tMe{cis-1-(NdCHC6H4)-2-(NdCH-
C6H5)C6H10}] (5) w ith CD3I a t Low Tem p er a tu r e.
Since the primary step in the SN2 mechanism of
oxidative addition of alkyl halides must place the alkyl
group in an axial position,3 it was surprising that the
major product of oxidative addition of CD3I to 5, namely
7c*, contained the CD3 group in the equatorial position.
Low-temperature NMR studies of the oxidative addition
of MeI and CD3I with 5 were therefore carried out to
determine if 7c* was really the first-formed product.
MeI or CD3I was added to a solution of complex 5 in
CD2Cl2 at -78 °C, and the progress of the reaction was
followed by 1H NMR spectroscopy; spectra for the
reaction with CD3I are shown in Figure 4. Reaction
began to occur at -60 °C, and the first-formed product
with MeI was determined to be 7b (7d ). The experi-
ment with CD3I distinguishes between these complexes
and showed that 7b* was the kinetic product. As the
solution was warmed, peaks due to 7b* decayed and
those due to 7c* grew. The apparent isomerization
reaction of 7b* to 7c* was only slightly slower than the
oxidative addition and both appeared to be complete at
-20 °C, an equilibrium between 7b* and 7c* being
present at room temperature.
(b) Bond Angles (deg)
C(3)-Pt(1)-C(1)
C(1)-Pt(1)-C(2)
C(1)-Pt(1)-N(1)
C(3)-Pt(1)-N(2)
C(2)-Pt(1)-N(2)
C(3)-Pt(1)-I(1)
C(2)-Pt(1)-I(1)
N(2)-Pt(1)-I(1)
C(9)-N(1)-Pt(1)
C(16)-N(2)-C(15)
C(3)-C(8)-C(9)
N(2)-C(16)-C(17)
84.9(4)
83.8(5)
92.6(4)
160.2(3)
104.9(4)
90.6(3)
94.8(3)
92.6(2)
114.0(7)
113.7(8)
116.9(9)
127.1(9)
C(3)-Pt(1)-C(2)
94.3(4)
81.6(4)
174.8(4)
92.2(4)
78.9(3)
175.2(3)
88.5(2)
129.0(8)
116.6(6)
110.6(7)
116.7(9)
C(3)-Pt(1)-N(1)
C(2)-Pt(1)-N(1)
C(1)-Pt(1)-N(2)
N(1)-Pt(1)-N(2)
C(1)-Pt(1)-I(1)
N(1)-Pt(1)-I(1)
C(9)-N(1)-C(10)
C(10)-N(1)-Pt(1)
C(8)-C(3)-Pt(1)
N(1)-C(9)-C(8)
a
Symmetry transformations used to generate equivalent at-
oms: #1 -x, -y + 1, -z.
it may minimize steric effects. However, it is not easily
explained if the structure represents the product of
kinetic control since, in an SN2 mechanism leading to
trans oxidative addition, the methyl group should ap-
proach the least hindered face, leading ultimately to 7b.
Of course, at this stage it was not possible to determine
if trans or cis oxidative addition had occurred since
structures 7a ,c and 7b,d are equivalent. To gain
further insight into the puzzling observations, it was
1
decided to monitor the reaction of 5 with CD3I by H
NMR spectroscopy.
Rea ction s w ith CD3I. The reaction of racemic
[PtMe{cis-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (5) with
CD3I was followed by 1H NMR spectroscopy at ambient
temperature in CD2Cl2 solution (Figure 3a). The reac-
tion product gave a major methylplatinum(IV) reso-
nance at δ 0.82 with 2J (PtH) ) 72 Hz, identical with
the MePt resonance trans to iodide in 7a (or 7c) (Table
1), which is therefore assigned to 7c*. There was also
a minor resonance at δ 0.87 with 2J (PtH) ) 66 Hz,
which could be due to the MePt group trans to N in
either 7a * or 7b* (the resonances are accidentally
degenerate) but will be shown to be due to 7b*. Hence,
the product is identified as largely 7c*, which is formed
by overall cis oxidative addition of CD3I to platinum-
(II), a process for which there are few precedents and
which is not understood in mechanistic terms.2 The
product 7b*, formed by trans oxidative addition, was
also present, but in low abundance. The ratio 7c*:7b*
) 9.
When the analogous reaction with CD3I was carried
out with racemic [PtMe{trans-1-(NdCHC6H4)-2-(NdCH-
C6H5)C6H10}] (4), the major product could be identified
by 1H NMR as 6a * (Chart 1, Figure 3b) which is formed
largely by trans oxidative addition of CD3I. Thus, the
2
most intense resonance appeared at δ 0.78 with J (PtH)
) 67 Hz, indicating that the CH3 group is trans to imine
in an equatorial position in 6a *, while there was only a
In a similar low-temperature study of the reaction of
CD3I with 4, the initial products at -60 °C were mostly
2
minor resonance at δ 0.67 with J (PtH) ) 71 Hz due to
the axial methyl group in 6c*. The ratio 6a *:6c* ) 2.8.
However, the minor diastereomer is identified as largely
6d *, which is formed by cis oxidative addition of CD3I.
(16) Derome, A. E. Modern NMR Techniques for Chemistry Research;
Pergamon Press: New York, 1987; Chapter 5.

2810 Organometallics, Vol. 17, No. 13, 1998
Baar et al.
F igu r e 3. 1H NMR spectra (200 MHz) in the MePt region of the products of reaction of CD3I with (a) complex 5 (the
major resonance is due to 7c* and the minor one to 7b*) and (b) complex 4 (peaks centered at δ 0.95, 0.78, 0.67, and 0.66
are due to 6b*, 6a *, 6c*, and 6d *, respectively).
Ch a r t 3
6a * and 6b*, with 6a */6b* ) ca. 4, only minor amounts
of 6c* and 6d * being present at the stage when no
starting complex 4 remained. As the reaction mixture
was warmed, the products 6c* and 6d * grew in and the
final product ratio was close to that observed in the
room-temperature reaction. Thus, it seems that 6a *
and 6b* are the primary products and that 6c* and 6d *
are formed subsequently by isomerization of the pri-
mary products.
PtC3 geometry and trans oxidative addition of the Et-I
bond, fixing the methyl group in an equatorial position
trans to an imine ligand and the ethylplatinum group
in an axial position trans to iodide. However, the NMR
data cannot distinguish between the possible structures
8a and 8b. The progress of the reaction in CD2Cl2 solu-
1
tion at room temperature was monitored by H NMR
spectroscopy, and it was shown that there were no long-
lived intermediates en route to the observed product and
that no subsequent isomerization occurred over several
days.
The complex was fully characterized as 8a by an X-ray
structure determination. A view of the structure of the
enantiomer (R,R-C)-[PtIMeEt{trans-1-(NdCHC6H4)-2-
(NdCHC6H5)C6H10}] is shown in Figure 5, and selected
bond lengths and angles are provided in Table 4. The
structure confirms the structural deductions based on
Oxid a tive Ad d ition of Eth yl Iod id e. Reaction of
4 with iodoethane in THF was slower than with io-
domethane, requiring approximately 4 h at ambient
temperature to reach completion. The product was
1
shown by H NMR spectroscopy to be a single stereo-
isomer of [PtIMeEt{trans-1-(NdCHC6H4)-2-(NdCH-
C6H5)C6H10}] (8a , ca.100% diastereoselectivity; Chart
1
1). The H NMR data (Table 1) are consistent with fac-

Oxidative Addition of Alkyl Halides to Pt(II)
Organometallics, Vol. 17, No. 13, 1998 2811
drance at this site than in complex 7a , in which the
ligand is based on cis-diaminocyclohexane. As in 7a ,
meridional coordination is adopted by the N,N,C tri-
dentate ligand. The Pt-N(1) distance of 2.22(1) Å is
long, and this may indicate steric effects between the
uncyclometalated phenylimine fragment and the adja-
cent iodide and C(3)H3 groups; the greater bond distor-
tion from the ideal 90° is N(1)-Pt-C(3) ) 105.3(4)°,
indicating that the greatest steric congestion may be in
the equatorial plane. Clearly then, a structure with the
ethyl group in the equatorial plane would not be favored.
If this analysis is correct, then it is not surprising that
the ethyl iodide attacks the face syn to the cyclohexyl
group and that it remains in the axial site; that is, 8a
is favored by both kinetic and thermodynamic factors.
The reaction of [PtMe{cis-1-(NdCHC6H4)-2-(NdCH-
C6H5)C6H10}] (5) with iodoethane in THF gave [PtIMeEt-
{cis-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (9b) with
essentially complete stereoselectivity (Chart 2). Moni-
toring by NMR again indicated that no long-lived inter-
mediates were formed, and 9b could be isolated in ana-
lytically pure form. However, during the attempted
growth of single crystals of 9b, subsequent slow hydroly-
sis of the nonmetalated imine group occurred to give
[PtIMeEt{cis-1-(NdCHC6H4)-2-(NH2)C6H10}] (10) (eq 2).
F igu r e 4. 1H NMR spectra (300 MHz) of the products of
reaction of CD3I with complex 5: (a) at -50 °C, 5 and 7b*
present; (b) at -30 °C, 5 (trace), 7b*, and 7c* present; (c)
at 20 °C, 7b* (minor) and 7c* (major) present.
1
In the H NMR spectrum of 9b (Table 1), the meth-
ylplatinum resonance occurred at δ 0.87 with 3J (PtH)
) 67 Hz, indicating that the methyl group remains in
the equatorial site in the platinum(IV) product and
hence that trans oxidative addition occurs selectively.
The two imine proton resonances at δ 8.51 and 8.85 each
showed well-resolved 195Pt satellites, confirming that
both imine groups were still present and were coordi-
nated to platinum. The data do not define the chirality
at platinum and so do not distinguish between struc-
tures 9a and 9b, and so the assignment as 9b is based
on other evidence discussed below.
F igu r e 5. View of the structure of the R,R-C enantiomer
of complex 8a .
Ta ble 4. Selected Bon d Dista n ces a n d An gles for
Com p lex 8a
(a) Bond Lengths (Å)
Pt-C(23)
2.00(1)
2.05(1)
2.217(9)
1.27(1)
1.29(1)
1.48(2)
1.52(2)
1.42(1)
Pt-N(2)
2.057(8)
2.120(9)
2.8042(7)
1.52(1)
1.45(1)
1.47(2)
Pt-C(3)
Pt-C(1)
Pt-N(1)
Pt-I
N(1)-C(10)
N(2)-C(17)
C(1)-C(2)
C(11)-C(16)
C(18)-C(23)
N(1)-C(11)
N(2)-C(16)
C(9)-C(10)
C(17)-C(18)
The hydrolysis of 9b to give 10 (along with unidenti-
fied complexes which could be isomers of 10) could be
monitored by 1H NMR in CD2Cl2 on the basis of the
growth of the aldehyde resonance of PhCHO at δ 10.0.
1.45(1)
(b) Bond Angles (deg)
C(23)-Pt-N(2)
N(2)-Pt-C(3)
N(2)-Pt-C(1)
C(23)-Pt-N(1)
C(3)-Pt-N(1)
C(23)-Pt-I
82.0(4)
175.3(4)
91.9(4)
160.8(4)
105.3(4)
88.8(3)
95.5(4)
92.2(2)
135.2(8)
C(23)-Pt-C(3)
93.6(5)
86.1(4)
86.3(5)
79.0(4)
92.0(3)
86.0(2)
174.8(3)
1
In contrast to 9b, the H NMR spectrum of 10 (Table 1)
C(23)-Pt-C(1)
C(3)-Pt-C(1)
N(2)-Pt-N(1)
C(1)-Pt-N(1)
N(2)-Pt-I
contained a methylplatinum resonance at δ 0.93 with
2J (PtH) ) 72 Hz, indicating that the methyl group was
trans to iodide in 10. Hence, complex 10 was also
characterized by an X-ray structure determination. A
view of the structure of the S,R-A enantiomer is shown
in Figure 6, and selected bond lengths and angles are
in Table 5. The complex contains an octahedral plati-
num(IV) center with a meridional tridentate cis-1-
(NdCHC6H4)-2-(NH2)C6H10 ligand. As deduced by NMR,
the methyl group is trans to iodide and the ethyl group
lies in the equatorial plane, corresponding to a product
of overall cis oxidative addition of ethyl iodide. As in
7a , the other platinum(IV) complex with a tridentate
ligand derived from cis-diaminocyclohexane, the rela-
C(3)-Pt-I
C(1)-Pt-I
C(10)-N(1)-C(11) 118.0(9)
C(11)-N(1)-Pt
C(17)-N(2)-Pt
C(2)-C(1)-Pt
N(1)-Pt-I
C(10)-N(1)-Pt
106.4(6)
113.7(7)
116.3(7)
C(17)-N(2)-C(16) 128.9(9)
C(16)-N(2)-Pt
117.2(7)
N(1)-C(10)-C(9)
129.0(11) N(2)-C(16)-C(11) 107.6(9)
N(2)-C(17)-C(18) 117.6(9)
C(18)-C(23)-Pt 111.5(8)
NMR evidence and also defines the chirality at plati-
num, in particular that the ethyl group is syn to the
cyclohexyl group which, in the ligand based on trans-
diaminocyclohexane, appears to create less steric hin-

2812 Organometallics, Vol. 17, No. 13, 1998
Baar et al.
F igu r e 6. View of the structure of the S,R-A enantiomer
of complex 10.
F igu r e 7. View of the structure of the S,S-A enantiomer
of complex 13a .
Ta ble 5. Selected Bon d Dista n ces a n d An gles for
Com p lex 10
selectivities achieved in these reactions closely re-
sembled those observed for the similarly rapid reactions
with methyl iodide. Thus, complex 4 gave two diaster-
eomers of [PtBrMeBz{trans-1-(NdCHC6H4)-2-(NdCH-
C6H5)C6H10}] (13) on reaction with benzyl bromide, as
(a) Bond Lengths (Å)
Pt(1)-C(4)
Pt(1)-N(1)
Pt(1)-N(2)
N(1)-C(10)
N(2)-C(16)
C(4)-C(9)
2.009(8)
2.069(7)
2.193(6)
1.27(1)
1.51(1)
1.39(1)
1.52(1)
Pt(1)-C(1)
Pt(1)-C(2)
Pt(1)-I(1)
N(1)-C(11)
C(2)-C(3)
C(9)-C(10)
2.067(7)
2.076(8)
2.7865(7)
1.46(1)
1.44(1)
1.47(1)
1
1
shown by the H NMR spectra. The H NMR spectra
(Table 1) define the structures as 13a and 13b, and the
major isomer was characterized as 13a by an X-ray
structure determination. The methylplatinum protons
were represented by signals at δ 0.86 with 3J (PtH) )
C(11)-C(16)
(b) Bond Angles (deg)
C(4)-Pt(1)-C(1)
C(1)-Pt(1)-N(1)
C(1)-Pt(1)-C(2)
C(4)-Pt(1)-N(2)
N(1)-Pt(1)-N(2)
C(4)-Pt(1)-I(1)
N(1)-Pt(1)-I(1)
N(2)-Pt(1)-I(1)
C(10)-N(1)-Pt(1)
C(16)-N(2)-Pt(1)
C(9)-C(4)-Pt(1)
N(1)-C(10)-C(9)
N(2)-C(16)-C(11)
86.6(3)
92.5(3)
86.4(4)
159.1(3)
78.5(2)
92.7(2)
91.5(2)
90.8(2)
115.2(6)
107.8(5)
111.7(6)
115.6(8)
110.4(6)
C(4)-Pt(1)-N(1)
80.8(3)
97.0(4)
177.6(3)
91.4(3)
103.6(3)
175.7(3)
89.6(3)
126.2(7)
118.6(5)
116.7(7)
116.7(7)
107.5(7)
C(4)-Pt(1)-C(2)
N(1)-Pt(1)-C(2)
C(1)-Pt(1)-N(2)
C(2)-Pt(1)-N(2)
C(1)-Pt(1)-I(1)
C(2)-Pt(1)-I(1)
C(10)-N(1)-C(11)
C(11)-N(1)-Pt(1)
C(3)-C(2)-Pt(1)
C(4)-C(9)-C(10)
N(1)-C(11)-C(16)
3
66 Hz for 13a and δ 1.01 with J (PtH) ) 66 Hz for 13b,
and the coupling constants confirm that the MePt
groups are trans to imine in both cases. The ratio of
isomers 13a :13b ) 6:1 was determined by integration
of methylplatinum and imine resonances. The benzylic
protons in 13a and 13b are expected to be diaste-
reotopic; the resonances for these protons were well-
resolved for the major isomer only and appeared as two
doublets at δ 2.66 and 2.87 with coupling constants
2J (PtH) ) 93 and 102 Hz, respectively. These large
2J (PtH) coupling constants are typical of benzylplati-
num(IV) complexes.17 The imine resonances for both
stereoisomers showed well-resolved platinum satellites,
which confirms the N,N,C tridentate ligand coordina-
tion.
tively smaller methyl and larger iodide groups lie syn
and anti to the bulky cyclohexyl group, respectively. The
absence of a free PhCHdN group in 10 leads to lower
steric hindrance in the equatorial site where the ethyl
group is found. Thus, 10 is expected to be the most
thermodynamically stable of the possible isomers.
Oxid a tive Ad d ition of n -P r op yl Iod id e. The oxi-
dative addition of propyl iodide to [PtMe{trans-1-
(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (4) required sev-
eral hours to reach completion at ambient temperature,
and some product decomposition occurred during this
period. Nevertheless, it was clear that a single diaste-
reomer of [PtIMe(n-Pr){trans-1-(NdCHC6H4)-2-(NdCH-
C6H5)C6H10}] (11) was formed and the structure was
readily assigned as 11a (Chart 1), based on the similar-
ity of the 1H NMR data (Table 1) to those of the
structurally characterized complex 8a .
Single crystals of isomer 13a grew preferentially from
a mixture of diastereomers 13a and 13b (confirmed by
NMR of the single crystals). A view of the structure of
the S,S-A enantiomer of 13a is provided in Figure 7,
and selected bond lengths and angles are given in Table
6. The platinum atom is octahedrally coordinated by
the N,N,C tridentate ligand and monodentate bromide,
methyl, and benzyl ligands. The usual fac-PtC3 geom-
etry, with mer-N,N,C coordination of the tridentate
ligand, is present. The nonmetalated phenylimine is
syn to the bromide ligand and anti to the benzyl
fragment. The N(2)-Pt distance of 2.24(1) Å is long
and, as for related complexes, this may be partly
attributed to steric hindrance between the phenyl
substituent and equatorial methyl and axial bromide
groups. The benzyl ligand bends under and toward the
cyclometalated ring to minimize steric effects, but there
is no evidence for significant π-stacking effects between
the aromatic groups.
The reaction of propyl iodide with 5 was also slow
and gave a single diastereomer of [PtIMe(n-Pr){cis-1-
(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (12), which was
easily separated from minor decomposition products by
1
recrystallization. A comparison of the H NMR data of
complex 12 with those of 9 indicates that these com-
pounds are isostructural and the S,R-C (or R,S-A)
structure 12b is tentatively proposed.
Oxid a tive Ad d ition of Ben zyl Br om id e. Com-
plexes 4 and 5 each reacted rapidly with benzyl bromide
in THF solution at room temperature, and the stereo-
Complex 5 gave a single stereoisomer of [PtIMe(Bz)-
{cis-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (14, ca. 100%
(17) Rendina, L. M.; Vittal, J . J .; Puddephatt, R. J . Organometallics
1995, 14, 2188.

Oxidative Addition of Alkyl Halides to Pt(II)
Organometallics, Vol. 17, No. 13, 1998 2813
Ta ble 6. Selected Bon d Dista n ces a n d An gles for
Com p lex 13a
(a) Bond Lengths (Å)
Pt(1)-C(28)
Pt(1)-C(1)
Pt(1)-N(2)
N(1)-C(22)
N(2)-C(15)
C(2)-C(3)
2.01(1)
2.09(1)
2.24(1)
1.26(2)
1.25(2)
1.47(2)
1.53(2)
1.44(2)
Pt(1)-N(1)
Pt(1)-C(2)
Pt(1)-Br(1)
N(1)-C(21)
N(2)-C(16)
C(14)-C(15)
C(22)-C(23)
2.06(1)
2.117(8)
2.605(1)
1.47(2)
1.49(2)
1.47(2)
1.47(2)
C(16)-C(21)
C(23)-C(28)
(b) Bond Angles (deg)
C(28)-Pt(1)-N(1)
N(1)-Pt(1)-C(1)
N(1)-Pt(1)-C(2)
C(28)-Pt(1)-N(2)
C(1)-Pt(1)-N(2)
C(28)-Pt(1)-Br(1)
C(1)-Pt(1)-Br(1)
N(2)-Pt(1)-Br(1)
C(21)-N(1)-Pt(1)
C(3)-C(2)-Pt(1)
N(2)-C(16)-C(21)
N(1)-C(22)-C(23)
82.3(5) C(28)-Pt(1)-C(1)
175.1(4) C(28)-Pt(1)-C(2)
90.4(4) C(1)-Pt(1)-C(2)
162.8(4) N(1)-Pt(1)-N(2)
103.1(4) C(2)-Pt(1)-N(2)
86.9(3) N(1)-Pt(1)-Br(1)
96.1(3) C(2)-Pt(1)-Br(1)
93.0(2) C(22)-N(1)-Pt(1)
115.1(7) C(16)-N(2)-Pt(1)
121.1(9) N(2)-C(15)-C(14)
94.0(5)
91.7(7)
86.5(4)
80.5(4)
87.6(6)
86.9(3)
177.0(4)
117(1)
104.4(8)
130(1)
108.4(9)
110(1)
113(2)
N(1)-C(21)-C(16)
C(28)-C(23)-C(22) 120(1)
F igu r e 8. Space-filling models of complexes (a) 9b and
(b) 9c in orientations similar to those in Chart 2. Complex
9c is not favored, due to steric congestion at the ethyl group
in the equatorial position.
C(23)-C(28)-Pt(1) 108(1)
Ta ble 7. Molecu la r Mech a n ics Ca lcu la tion s of
Rela tive En er gies (k ca l/m ol) of Isom er s a -d a
differences of 1.4-5.0 kcal/mol would not preclude
formation of compounds with equatorial groups R as
transient intermediates or transition states in potential
isomerization processes.
complex, R, X
a
b
c
d
trans Isomers
6, Me, I
8, Et, I
11, Pr, I
13, Bz, Br
32.92
34.76
34.09
24.98
32.91
34.78
34.10
24.81
32.92
36.53
35.51
30.70
32.91
36.83
35.98
31.38
The calculations predict much smaller energy differ-
ences between the isomers a and b, in most cases
probably within the error limits of the calculations.
Thus, for compounds based on trans-diaminocyclohex-
ane, isomer b is favored for 6 and 13 but isomer a for 8
and 11. For compounds based on cis-diaminocyclohex-
ane, isomer a is preferred in all cases. This similarity
is not surprising, since the groups R and X are expected
to have similar steric bulk (rotation about the Pt-C bond
allows R to adopt a favored conformation). Clearly then,
the stereoselectivity in oxidative addition cannot be
understood in terms of the thermodynamic stability of
the products but must be addressed in terms of the
transition state for the first step in the oxidative
addition reaction, that is in terms of the relative steric
hindrance to approach of R-X to either face of the
platinum(II) reagent, coupled with consideration of
possible isomerization processes.
For complex 10, in which the nonmetalated phenyl
group is no longer present, the structures with an
equatorial ethyl group are calculated to be more stable
than those with an axial ethyl group by 1.9 kcal/mol,
the opposite trend from that for 9. Hence, the isomer-
ization from axial to equatorial ethyl on hydrolysis of 9
to 10 is favored thermodynamically. Since the structure
of 10 is established, this isomerization provides strong
support for the suggestion that 9 is formed in the
isomeric form 9b, even though the molecular mechanics
calculations indicate that 9a should be preferred slightly
on thermodynamic grounds.
cis Isomers
30.29
7, Me, I
9, Et, I
12, Pr, I
14, Bz, Br
29.92
31.93
31.09
22.01
29.92
33.95
32.86
27.88
30.29
33.94
32.97
27.16
32.26
31.58
22.17
a
For structures of isomers, see Charts 1 and 2.
stereoselectivity) on reaction with benzyl bromide. The
1H NMR data show that the methyl group is equatorial
and so define the structure as 14a or 14b; the structure
14b is tentatively proposed on the basis of the data
discussed below.
Molecu la r Mech a n ics Ca lcu la tion s.18 To provide
additional insight into the thermodynamic and kinetic
factors involved in the stereoselectivity of the oxidative-
addition reactions, molecular mechanics calculations
were carried out for each of the complexes in Charts 1
and 2 and the calculated energies are listed in Table 7.
For the cases with R ) Et, Pr, or Bz, energies were
calculated for several conformations formed by rotation
about the Pt-C bond and the lowest energy found is
reported.
Note that when R ) Et, Pr, or Bz, the energies of
isomers c and d (R equatorial) are always significantly
higher than those of isomers a and b (R axial), and this
is clearly due to strong steric effects between the alkyl
group R in the equatorial site and the phenyl substitu-
ent of the nonmetalated imine. Figure 8 shows space-
filling diagrams for isomers of 9 with the ethyl group
axial or equatorial to illustrate this effect. As found
experimentally, this site is expected to be occupied by
the smallest alkyl group, namely the methyl group in
the thermodynamically favored isomers. The energy
Discu ssion
Dia ster eoselective Oxid a tive Ad d ition of MeI
a n d CD3I. The reaction of complex 5 with MeI or CD3I
to give 7 occurs with >90% stereoselectivity, and the
mechanism shown in Scheme 3 can be deduced from
(18) CACHE Scientific Inc., Version 3.7, 1992.

2814 Organometallics, Vol. 17, No. 13, 1998
Baar et al.
Sch em e 3
Sch em e 4
low-temperature NMR studies. In complex 5 steric
hindrance by the cyclohexyl group above the plane (as
drawn in Scheme 3) is greater than steric hindrance
below the plane arising from the free phenyl substituent
of the imine, therefore, attack of methyl iodide occurs
below the plane only, as shown in Scheme 3. The
primary product observed at low temperature is thus
7b or 7b*. The ionic intermediates cannot be detected,
since they are short-lived in CD2Cl2 solvent.3 As
expected in an SN2 mechanism,3 and proved in the case
of 7b*, the kinetic product is formed by trans oxidative
addition. When the temperature is raised, resonances
due to 7b or 7b* decay and those due to 7c or 7c* grow
and equilibrium between 7b and 7c is reached below
room temperature. Complex 7c* appears to be formed
by cis oxidative addition, but this is clearly deceptive.
The platinum(IV) complexes are stable to reductive
elimination, and 7c* arises by isomerization of 7b*
within the platinum(IV) system. Thus, loss of iodide
gives the cationic intermediate, which can undergo
methyl migration between filled and empty sites, but
only in the meridional plane not occupied by the triden-
tate ligand. A concerted migration of both methyl
groups is likely to avoid the unfavorable situation in
which two methyl groups are mutually trans. There are
two chief differences between the chemistry of 5 and
that of the simpler complexes such as [PtMe2(2,2′-bi-
pyridine)]. First, the present system gives much easier
equilibration between isomers; this is attributed to
much easier iodide dissociation leading to the five-
coordinate intermediate with the bulkier ligand in 5.
Second, the presence of the mer-tridentate ligand in 5
restricts the migration to a linear process in the other
meridional plane and does not allow a turnstile rotation
process which would lead to scrambling between all
possible isomers. It is this feature that leads to a
particularly clear picture of the oxidative-addition and
isomerization mechanisms as depicted in Scheme 3.
The oxidative addition of CD3I to 4 gives all four
possible isomers of the product of oxidative addition 6*,
therefore, the interpretation is somewhat complex
(Scheme 4). The major product of oxidative addition of
MeI to 4 is assigned structure 6a ,c on the basis of the
similarity of its NMR data (Table 1) to those of the
structurally characterized complex 8a and 13a , the
minor product being 6b,d (Chart 1). Use of CD3I in
place of MeI then distinguishes between equivalent
pairs of complexes, and the major product is shown to
be 6a *, formed by trans oxidative addition, rather than
6c*. Similarly, the minor isomer is shown to be 6d *,
formed by overall cis oxidative addition, rather than
6b*. These data are fully consistent with the mecha-
nism of Scheme 4. Thus, the ratio of products (6a * +
6d *)/(6b* + 6c*) ) 2.8 is determined by the stereose-
lectivity of the primary step in the oxidative addition,
whereas the ratio K ) 6a */6d * ) 6c*/6b* ) 2.3 is
determined by the equilibrium constant between these
pairs of complexes. The primary reaction at -60 °C
gives 6a * and 6b*, and the initial ratio 6a */6b* is also

Oxidative Addition of Alkyl Halides to Pt(II)
Organometallics, Vol. 17, No. 13, 1998 2815
Sch em e 5
expected to be 2.8. The observed value of 6a */6b* ) 4
is higher, but this is attributed to partial isomerization
of 6b* even at -60 °C; the ratio 6a */6b* increased with
time to a final value of 5.7, very similar to the value
obtained in the room-temperature reaction. Since there
is rather little difference in steric effects above and
below the plane, the energy differences between the
isomers of complex 6 are low and all of them can be
formed.
Dia ster eoselective Oxid a tive Ad d ition of EtI,
P r I, a n d BzBr . The reactions of EtI and PrI with 4
are similar and are discussed together (Scheme 4).
There are two chief differences from the case of MeI.
First, the reactions are much slower and exhibit greater
stereoselectivity, as might be expected; only one isomer
is observed in each case. Thus, in the case of oxidative
addition to 4, only 8a or 11a is formed, indicating es-
sentially exclusive attack above the plane syn to the
cyclohexyl group. Second, no isomerization is observed
to give an isomer with the ethyl or propyl group in the
equatorial plane. This feature is readily interpreted in
terms of steric effects. Thus, the equatorial site is the
most sterically congested, due to interference with the
free phenyl substituent of the imine, and there is a high
selectivity to place the smallest alkyl group, the methyl
group, in this position. This is probably a thermody-
namic effect in the present case, though it is also likely
that there would be a higher kinetic barrier to isomer-
ization also. The overall result is that the kinetic
product forms with the ethyl or propyl group in the axial
position and that no subsequent isomerization occurs.
the small methyl group syn to the bulky cyclohexyl
group. Assuming that the isomerization, like those dis-
cussed above, must occur by migration within the meri-
dional plane, the observed structure of 10 then strongly
supports the proposed structure of 9b (Scheme 5).
In conclusion, all of the oxidative additions to 4 and
5 can be understood in terms of the mechanisms shown
in Schemes 4 and 3, respectively. The primary oxida-
tive-addition step appears to take place with essentially
complete stereoselectivity in all reactions of 5 and in
reactions of 4 with ethyl and propyl iodides, though
subsequent isomerization can occur easily when R ) Me
or CD3 in Schemes 3 and 4. Only in reactions of 4 with
MeI, CD3I, and PhCH2Br is there evidence for attack
at either face of the platinum(II) complex. The combi-
nation of asymmetry of the two faces of the platinum-
(II) complexes, coupled with limitation on the pathways
of isomerization due to the presence of the tridentate
ligands, has allowed a particularly clear picture of these
oxidative-addition reactions to be obtained.
The case of benzyl bromide oxidative addition to 4 can
be understood in similar terms (Scheme 4). This reac-
tion is similar in rate to that with MeI and gives simi-
lar stereoselectivity in the oxidative addition step,
attack occurring mostly syn to the cyclohexyl group to
give 13a but with a minor component of attack below
the plane to 13b. No subsequent isomerization occurs,
since structures with the benzyl group (as with the ethyl
and propyl groups) in the equatorial position are not
favored.
The oxidative addition of EtI, PrI, and BzBr to 5 all
occur with essentially complete stereoselectivity to give
complexes characterized as 9b, 12b, and 14b, respec-
tively (Scheme 3). Since these are thought to have the
opposite chirality at platinum compared to the major
isomer obtained from MeI and attempts to grow suitable
crystals have been unsuccessful, some explanation for
the structural assignment is needed. The NMR data
show that the methyl group is equatorial but do not
distinguish between the isomers a and b, and the
arguments in favor of b are as follows. First, it has been
established above that CD3I attacks 5 on the face anti
to the cyclohexyl group so it is almost certain that this
will also be the case with the bulkier alkyl halides.
Similarly, it will not be favorable for the bulkier alkyl
group to migrate to the sterically congested site in the
equatorial plane; therefore no subsequent isomerization
is expected to occur. Confirmation is obtained indirectly
in the case of EtI addition. Thus, slow hydrolysis of the
primary product 9 occurs to give 10, which has been
structurally characterized. Once the bulky free imine
group is removed from 9b, isomerization is possible and
the ethyl group migrates to the equatorial site, placing
Exp er im en ta l Section
1H NMR spectra were recorded using a Varian Gemini 300
MHz spectrometer. Chemical shifts are reported relative to
TMS. When NOE difference spectra were collected, the
percent NOE values were calculated using the equation %
NOE ) [(I - Io)/I], where I - Io is the peak integral in the
difference spectrum and Io is the integral in the spectrum
collected with the decoupler frequency set off-resonance. In
the NOE difference studies the temperature was controlled
at 21 °C, while in the low-temperature studies the sample
was cooled using cold nitrogen gas. The molecular mechan-
ics calculations were carried out by using the CAChe soft-
ware package.18 The complex [Pt2Me4(µ-SMe2)2] (3) was
prepared as described previously.19 All operations were
performed under standard Schlenk conditions unless otherwise
stated.
Syn th esis of Liga n d s 1 a n d 2. To a solution of racemic
trans-1,2-diaminocyclohexane (4 mmol) in diethyl ether (20
mL) was added 2 equiv of benzaldehyde (8 mmol). Excess
(19) Scott, J . D.; Puddephatt, R. J . Organometallics 1983, 2, 1643.

2816 Organometallics, Vol. 17, No. 13, 1998
Baar et al.
3
MgSO4 was added directly to the reaction mixture to remove
product water. The solution was stirred for 2 h at room
temperature and then filtered. The solvent was removed
under vacuum, leaving an off-white residue which was recrys-
tallized from CH2Cl2/pentane to give r a cem ic tr a n s-1,2-
(NdCH C6H 5)2C6H 10 (1). Yield: 80%. Anal. Calcd for
NdCH], 8.84 [d, 1H, J (PtH) ) 34 Hz, NdCH]; minor isomer
7b, δ 0.65 [s, 3H, 2J (PtH) ) 71 Hz, MePt], 0.87 [s, 3H, 2J (PtH)
) 67 Hz, MePt], 8.51 [d, 1H, NdCH], 8.83 [d, 1H, NdCH].
[P t IMeE t {tr a n s-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}]
(8). To an orange solution of 4 (0.078 mmol) in THF (10 mL)
was added excess EtI (3.88 mmol). The reaction mixture was
stirred for 4 h at ambient temperature, during which time the
solution changed to yellow. The solvent was evaporated under
reduced pressure and the product purified by recrystallization
C
20H22N2: C, 82.7; H, 7.6; N, 9.65. Found: C, 82.1; H, 7.8; N,
9.5%. 1H NMR (CDCl3): δ 1.48 [br m, 2H, Cy(H)], 1.82 [br m,
6H, Cy(H)], 3.39 [br m, 2H, Cy(H)], 7.29 [m, 6H], 7.56 [m, 4H],
8.18 [s, 2H, NdCH].
from CH2Cl2/pentane. Yield: 96%. Anal. Calcd for C23H29
-
The ligand cis-1,2-(NdCHC6H5)2C6H10 (2) was similarly
prepared. Yield: 75%. MS: calcd m/e for (C20H22N2 + H+)
291.1861, found 291.1864. 1H NMR (acetone-d6): δ 1.63 [br
m, 6H, Cy(H)], 2.02 [br m, 2H, Cy(H)], 3.56 [br m, 2H, Cy(H)],
7.38 [m, 6H], 7.72 [m, 4H], 8.29 [s, 2H, NdCH].
IN2Pt: C, 42.1; H, 4.5; N, 4.3. Found: C, 42.2; H, 4.4; N, 4.1.
3
3
1H NMR (CD2Cl2): δ 0.27 [t, 3H, J (HH) ) 7.8 Hz, J (PtH) )
73.5 Hz, EtPt], 0.74 [s, 3H, 2J (PtH) ) 67.5 Hz, MePt], 1.25
2
[m, 2H, J (PtH) ) 75 Hz, EtPt], 1.40-1.80 [br m, 4H, Cy(H)],
2.0 [m, 2H, Cy(H)], 2.60 [br d, 1H, Cy(H)], 2.75 [br d, 1H, Cy-
(H)], 3.72 [br t, 1H, Cy(H)], 4.45 [br t, 1H, Cy(H)], 7.07 [m,
1H], 7.23 [m, 2H], 7.50 [m, 4H], 8.11[br d, 2H], 8.53 [d, 1H,
4J (HH) ) 2 Hz, 3J (PtH) ) 52 Hz, NdCH], 8.88 [d, 1H, 4J (HH)
Ra cem ic [P tMe{tr a n s-1-(NdCHC6H4)-2-(NdCHC6H5)-
C6H10}] (4). Ligand 1 (0.38 mmol) was reacted with complex
3 (0.19 mmol) in diethyl ether (10 mL). The solution im-
mediately turned orange-yellow which intensified toward
orange with time. Within minutes a bright orange solid pre-
cipitated. The reaction mixture was stirred overnight (ca. 15
h), and the precipitate was filtered off and then washed with
diethyl ether (10 mL) and pentane (10 mL). It was then dried
under reduced pressure. Yield: 56%. Anal. Calcd for
C21H24N2Pt: C, 50.5; H, 4.85; N, 5.6. Found: C, 50.2; H, 4.8;
3
) 2 Hz, J (PtH) ) 39 Hz, NdCH].
[P tIMeEt{cis-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (9)
was similarly prepared from complex 5. Yield: 83%. Anal.
Calcd for C23H29IN2Pt: C, 42.1; H, 4.5; N, 4.3. Found: C, 42.4;
3
H, 4.3; N, 4.0. 1H NMR (CD2Cl2): δ 0.25 [t, 3H, J (HH) ) 7.5
Hz, 3J (PtH) ) 73 Hz, EtPt], 0.87 [s, 3H, 2J (PtH) ) 67 Hz,
2
MePt], 1.27 [m, 2H, J (PtH) ) 75 Hz, EtPt], 1.40-1.64 [br m,
2
N, 5.45. 1H NMR (CD2Cl2): δ 0.51 [s, 3H, J (PtH) ) 83 Hz,
6H, Cy(H)], 1.84 [br m, 2H, Cy(H)], 2.95 [m, 1H, Cy(H)], 4.32
[m, 1H, Cy(H)], 7.06 [m, 1H], 7.21 [m, 2H], 7.42 [m, 1H], 7.53
[m, 3H], 8.14 [br d, 2H], 8.51 [s, 1H, 3J (PtH) ) 52 Hz, NdCH],
Pt-Me], 1.47 [br m, 4H, Cy(H)], 1.95 [br t, 2H, Cy(H)], 2.42
[br d, 1H, Cy(H)], 2.56 [br d, 1H, Cy(H)], 3.7 [br t, 1H, Cy(H)],
4.18 [br t, 1H, Cy(H)], 6.98 [t, 1H], 7.18 [t, 1H], 7.42 [m, 4H],
3
8.85 [s, 1H, J (PtH) ) 38 Hz, NdCH].
4
3
[P tIMeEt{cis-1-(NdCHC6H4)-2-(NH2)C6H10}] (10). 1H
NMR (CD2Cl2): δ 0.41 [t, 3H, 3J (HH) ) 7 Hz, 3J (PtH) ) 75
Hz, EtPt], 0.93 [s, 3H, 2J (PtH) ) 72 Hz, MePt], 8.37 [s, 1H,
3J (PtH) ) 44 Hz, NdCH].
7.56 [t, 1H], 8.27 [d, 2H], 8.64 [d, 1H, J (HH) ) 2 Hz, J (PtH)
4
3
) 61 Hz, NdCH], 8.98 [d, 1H, J (HH) ) 2 Hz, J (PtH) ) 47
Hz, NdCH].
[P tMe{cis-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (5) was
similarly prepared using the ligand cis-1,2-(NdCHC6H5)2C6H10
(2). Yield: 55%. Anal. Calcd for C21H24N2Pt: C, 50.5; H, 4.85;
N, 5.6. Found: C, 50.1; 4.9; 5.4. 1H NMR (CD2Cl2): δ 0.61 [s,
3H, 2J (PtH) ) 84 Hz, Pt-Me], 1.45 [br m, 3H, Cy(H)], 1.90
[br m, 3H, Cy(H)], 2.50 [br d, 1H, Cy(H)], 2.65 [br m, 1H, Cy-
(H)], 4.12 [m, 1H, Cy(H)], 4.45 [br s, 1H, Cy(H)], 6.99 [t, 1H],
7.2 [t, 1H], 7.42 [m, 4H], 7.55 [m, 1H], 8.19 [d, 2H], 8.69 [d,
1H, 4J (HH) ) 2 Hz, 3J (PtH) ) 63 Hz, NdCH], 9.02 [s, 1H,
3J (PtH) ) 45 Hz, NdCH].
[P t IMe (n -P r ){t r a n s-1-(NdCH C6H 4)-2-(NdCH C6H 5)-
C6H10}] (11). To an orange solution of 4 (0.04 mmol) in THF
(10 mL) was added excess 1-iodopropane (4.0 mmol). The
reaction mixture was stirred for 4 h at ambient temperature.
The solvent was evaporated under reduced pressure, yielding
a pale yellow residue, which was recrystallized from CH2Cl2/
pentane to give the product. Yield: 57%. Anal. Calcd for
C
24H31IN2Pt: C, 43.1; H, 4.7; N, 4.2. Found: C, 43.1; H, 4.6;
N, 4.1%. 1H NMR (CD2Cl2): δ 0.66 [br m, 3H, Me of PrPt],
2
0.79 [s, 3H, J (PtH) ) 66 Hz, Pt-Me], 1.38-2.75 [br m, 12H,
[P tIMe2{tr a n s-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (6).
To an orange solution of complex 4 (0.063 mmol) in THF (10
mL) was added 10 equiv of MeI (0.63 mmol). Within minutes
the solution had changed to pale yellow. The reaction mixture
was stirred for a total of 90 min, and then the solvent was
evaporated under reduced pressure to give a pale yellow solid
residue. The residue was recrystallized from a CH2Cl2/pentane
mixture to give a lustrous yellow powder, which was filtered
off and washed with pentane (15 mL). Yield: 78%. Anal.
Calcd for C22H27IN2Pt: C, 41.2; H, 4.2; N, 4.4. Found: C, 40.9;
H, 4.2; N, 4.3. 1H NMR (CD2Cl2): major isomer 6a , δ 0.67 [s,
3H, 2J (PtH) ) 71 Hz, MePt], 0.78 [s, 3H, 2J (PtH) ) 67 Hz,
MePt], 1.40-1.78 [br m, 4H, Cy(H)], 2.05 [m, 2H, Cy(H)], 2.60
[br d, 1H, Cy(H)], 2.75 [br d, 1H, Cy(H)], 3.72 [br t, 1H, Cy-
(H)], 4.45 [br t, 1H, Cy(H)], 7.07 [m, 1H], 7.22 [m, 2H], 7.51
[m, 4H], 8.16 [d d, 2H], 8.51 [d, 1H, 4J (HH) ) 2 Hz, 3J (PtH) )
Cy and Pr], 3.65 [br t, 1H, Cy(H)], 4.48 [br t, 1H, Cy(H)], 7.02
[m, 1H], 7.18-7.50 [br m, 6H], 8.08 [m, 2H], 8.47 [s, 1H,
3J (PtH) ) 50 Hz, NdCH], 8.83 [s, 1H, 3J (PtH) ) 39 Hz,
NdCH].
[P t I M e (n -P r ){c i s -1-(N dC H C 6 H 4 )-2-(N dC H C 6 H 5 )-
C6H10}] (12) was similarly prepared from complex 5. Yield:
55%. Anal. Calcd for C24H31IN2Pt: C, 43.1; H, 4.7; N, 4.2.
Found: C, 43.0; H, 4.6; N, 4.1. 1H NMR (CD2Cl2): δ 0.65 [br
m, 3H, Me of PrPt], 0.89 [s, 3H, 2J (PtH) ) 67 Hz, Pt-Me],
1.44-1.82 [br m, 12H, Cy and Pr], 2.85 [br m, 1H, Cy(H)], 4.60
[br s, 1H, Cy(H)], 7.06 [m, 1H], 7.22-7.58 [br m, 6H], 8.15 [br
d, 2H], 8.51 [s, 1H, 3J (PtH) ) 51 Hz, NdCH], 8.85 [s, 1H,
3J (PtH) ) 38 Hz, NdCH].
[P t B r M e B z{t r a n s-1-(N dC H C 6 H 4 )-2-(N dC H C 6 H 5 )-
C6H10}] (13). To a solution of 4 (0.04 mmol) in THF (10 mL)
was added excess benzyl bromide (4.0 mmol). After 30 min
the solution had become pale yellow, and the solvent was
evaporated under reduced pressure, giving a yellow oil. The
product was crystallized from a CH2Cl2/pentane mixture and
washed with pentane (15 mL). Yield: 80%. Anal. Calcd for
4
3
50 Hz, NdCH], 8.82 [d, 1H, J (HH) ) 2 Hz, J (PtH) ) 36 Hz,
NdCH]; minor isomer 6b, δ 0.66 [s, 3H, 2J (PtH) ) 72 Hz,
MePt], 0.95 [s, 3H, 2J (PtH) ) 66 Hz, MePt], 8.49 [d, 1H, 4J (HH)
) 2 Hz, 3J (PtH) ) 49 Hz, NdCH], 8.96 [d, 1H, 4J (HH) ) 2
3
Hz, J (PtH) ) 36 Hz, NdCH].
[P tIMe2{cis-1-(NdCHC6H4)-2-(NdCHC6H5)C6H10}] (7) was
similarly prepared from complex 5. Yield: 71%. Anal. Calcd
for C22H27IN2Pt: C, 41.2; H, 4.2; N, 4.4. Found: C, 40.7; H,
4.0; N, 4.2. 1H NMR (CD2Cl2): major isomer 7a , δ 0.82 [s,
3H, 2J (PtH) ) 72 Hz, MePt], 0.87 [s, 3H, 2J (PtH) ) 66 Hz,
MePt], 1.38-2.10 [br m, 8H, Cy(H)], 2.50 [m, 1H, Cy(H)], 4.45
[m, 1H, Cy(H)], 7.08 [m, 1H], 7.22 [m, 2H], 7.50 [m, 4H], 7.86
[d d, 2H], 8.55 [d, 1H, 4J (HH) ) 2.8 Hz, 3J (PtH) ) 49.5 Hz,
C28H31BrN2Pt‚0.5CH2Cl2: C, 48.0; H, 4.5; N, 3.9. Found: C,
48.4; H, 4.5; N, 4.1. 1H NMR (CD2Cl2): major isomer 13a , δ
0.77 [s, 3H, 2J (PtH) ) 66 Hz, MePt], 1.20-1.60 [br m, 4H, Cy-
(H)], 1.92 [m, 2H, Cy(H)], 2.36 [br d, 1H, Cy(H)], 2.60 [br d,
2
2
1H, Cy(H)], 2.66 [d, 1H, J (HaHb) ) 9.7 Hz, J (PtH) ) 93 Hz,
CH2Bz], 2.87 [d, 1H, 2J (HaHb) ) 9.7 Hz, 2J (PtH) ) 102 Hz,
CH2Bz], 3.56 [br t, 2H, Cy(H)], 4.17 [br t, 2H, Cy(H)], 6.59 [m,
2H], 6.94 [m, 2H], 7.02-7.26 [m, 4H], 7.42-7.56 [m, 4H], 7.99

Oxidative Addition of Alkyl Halides to Pt(II)
Organometallics, Vol. 17, No. 13, 1998 2817
Ta ble 8. Cr ysta llogr a p h ic Deta ils
complex
4
7a
8a
13a
10
empirical formula
fw
temp, K
C
21H24N2Pt
C22H27IN2O1.5Pt
665.45
294
C23H29IN2Pt
655.47
298
C28H31BrN2Pt
670.55
297
C16H25IN2Pt
567.37
294
499.51
298
wavelength, Å
cryst syst
space group
unit cell dimens
a, Å
0.710 73
orthorhombic
Pbca
0.710 73
monoclinic
P21/c
0.710 73
orthorhombic
Pbca
0.710 73
orthorhombic
Pca21
0.710 73
triclinic
P1h
12.629(2)
16.374(2)
17.998(2)
10.457(2)
13.409(2)
17.048(3)
15.1691(3)
15.3153(2)
19.4482(4)
15.715(2)
11.416(3)
13.603(2)
9.1339(11)
9.801(2)
10.5801(14)
81.558(14)
84.081(10)
70.715(11)
882.8(2)
2
b, Å
c, Å
R, deg
â, deg
104.80 (2)
γ, deg
V, Å3
3721.7(8)
8
2311.1(7)
4
4528.2(1)
8
2440.4(7)
4
Z
calcd density,
1.783
1.913
1.927
1.825
2.134
g cm-3
abs coeff, mm-1
no. of indep rflns
7.544
2563 (R(int) )
0.0354)
7.423
3391 (R(int) )
0.0365)
7.587
2915 (R(int) )
0.0342)
7.405
2430 (R(int) )
0.0458)
9.689
3108 (R(int) )
0.0283)
no. of data/restraints/
params
GOF on F
1417/0/218
3279/0/248
2911/0/244
2400/1/290
2945/0/182
2
1.025
1.073
1.032
1.04
1.014
final R indices
R1 ) 0.0329
wR2 ) 0.0717
R1 ) 0.0821
wR2 ) 0.0944
R1 ) 0.0395
wR2 ) 0.1049
R1 ) 0.0484
wR2 ) 0.1211
R1 ) 0.0462
wR2 ) 0.1013
R1 ) 0.0622
wR2 ) 0.1106
R1 ) 0.0330
wR2 ) 0.0674
R1 ) 0.0504
wR2 ) 0.0739
R1 ) 0.0350
wR2 ) 0.0720
R1 ) 0.0538
wR2 ) 0.0793
(I > 2σ(I))b
R indices (all data)
GOF ) [ ∑w(Fo - Fc2)2/(n - p)]1/2, where n is the number of reflections and p is the number of parameters refined. R1 ) ∑(||Fo| -
a
2
b
|Fc ||)/∑|Fo|; wR2 ) [∑w(Fo - Fc2)2/∑wFo
]
.
2
4 1/2
[m, 2H], 8.43 [d, 1H, 4J (HH) ) 3 Hz, 3J (PtH) ) 51 Hz, NdCH],
-0.501 e Å-3 and the top two peaks were associated with the
Pt atom. The maximum shift in the final cycles was 0.001.
The experimental details are listed in Table 8, and all
positional and thermal parameters, bond distances and angles,
anisotropic thermal parameters, and hydrogen atom coordi-
nates and selected torsion angles have been included in the
Supporting Information.
4
3
8.71 [d, 1H, J (HH) ) 2 Hz, J (PtH) ) 38 Hz, NdCH]; minor
isomer 13b, δ 1.01 [s, 3H, 2J (PtH) ) 66 Hz, MePt], 8.08 [d,
1H, 4J (HH) ) 2 Hz, 3J (PtH) ) 53 Hz, NdCH], 9.06 [d, 1H,
3
4J (HH) ) 2 Hz, J (PtH) ) 37 Hz, NdCH].
[P t Br MeBz{cis-1-(NdCH C6H 4)-2-(NdCH C6H 5)C6H 10}]
(14) was similarly prepared from complex 5. Yield: 63%. Anal.
Calcd for C28H31BrN2Pt‚0.5CH2Cl2: C, 48.0; H, 4.5; N, 3.9.
Found: C, 47.4; H, 4.5; N, 4.1. 1H NMR (CD2Cl2): δ 0.86 [s,
3H, 2J (PtH) ) 66 Hz, MePt], 1.38-1.82 [br m, 6H, Cy(H)], 2.60
[d, 1H, 2J (HaHb) ) 9 Hz, 2J (PtH) ) 96 Hz, CH2Bz], 2.62 [m,
X-r a y Str u ctu r e Deter m in a tion of Com p lex 7a . Crys-
tals of 7a were grown from a saturated solution of CH2Cl2
layered with pentane. A single crystal suitable for X-ray
analysis was mounted inside a glass capillary tube. Data were
collected as above. Crystal data and refinement parameters
for 7a are listed in Table 8. The positional and thermal
parameters, all bond distances and angles, anisotropic thermal
parameters, hydrogen atom coordinates, and selected torsion
angles have been included in the Supporting Information. Unit
cell parameters were calculated from 25 centered high-angle
reflections in the range 15 < 2θ < 25°. Systematic absences
were consistent with the monoclinic space group P21/c. Semiem-
pirical absorption corrections based on ψ-scan data were
applied, and full-matrix least-squares refinement on F2 was
performed with anisotropic thermal parameters for all non-
hydrogen atoms of the platinum complex. Disordered water
molecules (1.5) were modeled in the lattice and refined
isotropically with site occupancy factors of 0.65, 0.50, and 0.35.
The largest residual electron density peak (1.618 e Å-3) was
located between the platinum and iodine atoms.
2
1H, Cy(H)], 2.76 [d, 1H, J (HaHb) ) 9 Hz, J (PtH) ) 102 Hz,
CH2Bz], 3.05 [m, 1H, Cy(H)], 3.95 [m, 1H, Cy(H)], 4.30 [m,
1H, Cy(H)], 6.52 [m, 2H], 6.88 [m, 2H], 6.96-7.24 [br m, 4H],
4
7.34-7.60 [br m, 4H], 7.86 [m, 2H], 8.40 [d, 1H, J (HH) ) 2
3
3
Hz, J (PtH) ) 51 Hz, NdCH], 8.76 [s, 1H, J (PtH) ) 37 Hz,
NdCH].
X-r a y Str u ctu r e Deter m in a tion of Com p lex 4. Red
“cube-like” crystals were grown from a mixture of CD2Cl2 and
pentane, and a crystal of size 0.29 × 0.28 × 0.23 mm was
mounted on a glass fiber. The diffraction experiments were
carried out using a Siemens P4 diffractometer with the
XSCANS software package.20 The cell constants were obtained
by centering 26 high-angle reflections (22.72° e 2θ e 24.93°).
A total of 3250 reflections were collected in the θ range 2.26-
23.0° (-1 e h e 13, -1 e k e 18, -1 e l e 19) in ω-2θ scan
mode at variable scan speeds (2-30 deg/min). An empirical
absorption was applied to the data based on the ψ-scan
method. SHELXTL programs were used for data processing
and the least-squares refinements on F2.21 The space group
Pbca was determined from the systematic absences. All of the
non-hydrogen atoms were refined anisotropically. No attempt
was made to locate the hydrogen atoms, and they were placed
in calculated ideal positions for the purpose of structure factor
calculations only. In the final difference Fourier synthesis,
the electron density fluctuated in the range from 0.597 to
X-r a y Str u ctu r e Deter m in a tion of Com p lex 10. Crys-
tals of 10 were grown from a saturated solution of methylene
chloride layered with pentane. A crystal suitable for X-ray
analysis was selected and mounted in a glass capillary tube,
and data were collected as above. Crystal data and refinement
parameters for 10 are listed in Table 8; the positional and
thermal parameters, all bond distances and angles, anisotropic
thermal parameters, hydrogen atom coordinates, and selected
torsion angles have been included in the Supporting Informa-
tion. A statistical analysis of intensity data indicated the space
group P1h. Data were processed, semiempirical absorption
corrections based on ψ-scan data were applied, and full-matrix
least-squares refinement on F2 was performed using direct
(20) XSCANS version 2.1; Siemens Analytical X-ray Instruments
Inc., Madison, WI, 1994.
(21) SHELXTL Software version 5.0; Siemens Analytical X-ray
Instruments Inc., Madison, WI, 1994.

2818 Organometallics, Vol. 17, No. 13, 1998
Baar et al.
methods and the SHELXTL program package (version 5.03).
All non-hydrogen atoms were refined with anisotropic thermal
parameters. The largest residual electron density peak (0.741
e Å-3) was associated with the Pt atom.
and refined successfully. Semiempirical absorption corrections
based on ψ-scan data were applied, and full-matrix least-
squares refinement on F2 was performed with anisotropic
thermal parameters for all non-hydrogen atoms.
X-r a y Str u ctu r e Deter m in a tion of Com p lex 13a . Crys-
tals of 13a were grown by slow diffusion from a saturated
solution of CH2Cl2 layered with pentane. A crystal suitable
for X-ray analysis was selected and cut to appropriate size and
mounted on a glass fiber. Crystal data and refinement param-
eters for 13a are listed in Table 8; the positional and thermal
parameters, all bond distances and angles, anisotropic thermal
parameters, hydrogen atom coordinates, and selected torsion
angles have been included in the Supporting Information.
Systematic absences were consistent with the orthorhombic
space group Pbcm or Pca21, and the acentric option was chosen
Ack n ow led gm en t. We thank the NSERC of Canada
for financial support and for a Postgraduate Scholarship
to C.R.B.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray data
for complexes 4, 7a , 8a , 10, and 13a (32 pages). Ordering
information is given on any masthead page.
OM980065Z