Stereochemically non-rigid transition metal complexes of 2,6-bis[1-(phenylimino)ethyl]pyridine (BIP). Part 3. Dynamic NMR studies of fac-[PtXMe3(BIP)] (X=C1, Br, or I). Crystal structure of fac-[PtIMe3(BIP)]

Article abstract of DOI:10.1016/S0022-328X(97)00690-6

The complexes fac-[PtXMe₃(BIP)] (X=Cl,Br or I;BIP=2,6-bis[1-(phenylimino)ethyl]pyridine) have been synthesised and characterised as involving BIP as a bidentate chelate ligand. In solution the metal-bound ligand exists in four conformational forms, namely distal and proximal E,E and E,Z-isomers. 2D-EXSY NMR has been used to measure 1,4-metallotropic shifts of the PtXMe₃ moiety between equivalent distal E,E forms, E,Z isomerisation of the pendant imine function and restricted C-C rotation of the pendant arm of the BIP ligand. Activation energies, ΔG^≠ (298.15 K), for all these processes are in the range 67-96 kJ mol^-1 and are essentially halogen independent. A crystal structure of fac-[PtIMe₃(BIP)] shows that the pendant imine function is in the E-conformation and is rotated at an angle of 80.1° to the plane of the pyridine.

Full text of DOI:10.1016/S0022-328X(97)00690-6

Journal of Organometallic Chemistry 555 (1998) 35–47
Stereochemically non-rigid transition metal complexes of
2,6-bis[1-(phenylimino)ethyl]pyridine (BIP). Part 3. Dynamic NMR
studies of fac-[PtXMe3(BIP)] (X=C1, Br, or I). Crystal structure of
fac-[PtIMe3(BIP)]
a,
a
a
a
&
Keith G. Orrell *, Anthony G. Osborne , Vladimir Sik , Mateus Webba da Silva ,
Michael B. Hursthouse b, David E. Hibbs b, K.M. Abdul Malik b, Nikolay G. Vassilev c
a Department of Chemistry, Uni6ersity of Exeter, Exeter EX4 4QD, UK
b Department of Chemistry, Uni6ersity of Wales Cardiff, PO Box 912, Park Place, Cardiff CF1 3TB, UK
c Institute of Organic Chemistry, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria
Received 5 September 1997
Abstract
The complexes fac-[PtXMe3(BIP)] (X=Cl,Br or I;BIP=2,6-bis[1-(phenylimino)ethyl]pyridine) have been synthesised and
characterised as involving BIP as a bidentate chelate ligand. In solution the metal-bound ligand exists in four conformational
forms, namely distal and proximal E,E and E,Z-isomers. 2D-EXSY NMR has been used to measure 1,4-metallotropic shifts of
the PtXMe3 moiety between equivalent distal E,E forms, E,Z isomerisation of the pendant imine function and restricted CꢀC
rotation of the pendant arm of the BIP ligand. Activation energies, DG" (298.15 K), for all these processes are in the range 67–96
kJ mol−1 and are essentially halogen independent. A crystal structure of fac-[PtIMe3(BIP)] shows that the pendant imine function
is in the E-conformation and is rotated at an angle of 80.1° to the plane of the pyridine. © 1998 Elsevier Science S.A. All rights
reserved.
Keywords: Platinum; Bis-imine ligand; Fluxionality; 2D-EXSY NMR
carbonyl groups of the rhenium tricarbonyl halide moi-
ety and hence may offer greater impediment to some
1. Introduction
ligand motions. The NMR characteristics of the
As part of a comprehensive investigation [1,2] on the
trimethylplatinum(IV) moiety provide an excellent
fluxional motions of complexes involving 2,6-bis[1-
medium for the study of fluxional motions and the
(phenylimino)ethyl]pyridine (BIP), the series of com-
plexes fac-[PtXMe3(BIP)] (X=Cl, Br, I) was
synthesised. There are strong analogies between the
scalar couplings of 195Pt with surrounding nuclei (as far
as four bonds away) are useful structural probes.
trimethylplatinum(IV) moiety and the rhenium tricar-
bonyl halide moiety discussed previously [2] as both are
isoelectronic, form octahedral complexes with the ancil-
lary ligands in a facial arrangement and are very stable
2. Results
moieties. The methyl groups in the trimethylplatinu-
m(IV) moiety have a greater steric requirement than the
The complexes fac-[PtXMe3(BIP)] (X=Cl, Br, I)
were all prepared in a similar manner from the reaction
of the ligand with the appropriate trimethylplatinum
halide in benzene under conditions of light exclusion.
* Corresponding author.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00690-6

36
K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47
Table 1
Analytical data for the complexes fac-[PtXMe3(BIP)] (X=Cl, Br, or I)
Complex
M.p. (°C)
Yielda (%)
Infraredb (cm−1
)
Analysisc (%)
C
w(CꢀH)
w(PtꢀC)
w(PtꢀX)
H
N
[PtClMe3(BIP)]
[PtBrMe3(BIP)]
[PtIMe3(BIP)]
203/6 (dec)
216/9 (dec)
224/7 (dec)
84.3
82.7
89.0
2966
2901
2815
2975
2910
2816
2975
2910
2816
567
523
513
571
527
516
568
526
505
248
48.94
(48.50)
4.79
(4.67)
7.13
(7.04)
—
—
45.50
(45.28)
4.46
(4.46)
6.63
(6.21)
42.36
(42.30)
4.15
(4.04)
6.17
(5.63)
a Yield quoted relative to monomeric metal containing reactant.
b Recorded as CsI discs.
c Calculated values in parentheses.
The reaction afforded high yields of air-stable, bright-
yellow microcrystalline solids that melt with decompo-
sition between 203 and 227°C when using capillaries
exposed to the air. Synthetic and analytical details for
the complexes are shown in Table 1 and mass spectral
data in Table 2. For all three complexes the ion of
highest mass number corresponds to the molecular ion
of the compound, [M]+. The most abundant fragment
for the chloride and bromide complexes corresponds to
conformation. The PtꢀN distances are unequal, with
the bond to the pyridyl nitrogen being longer than that
to the imine nitrogen [PtꢀN(1) 2.243(5) vs. PtꢀN(2)
˚
2.152(5) A]. This is in sharp contrast to the situation
where a BIP ligand is bonded to a metal in a terdentate
manner; in such cases the shortest metal–nitrogen dis-
tance is to the pyridyl nitrogen [6–8]. The changeover
in relative metal–nitrogen bond lengths between biden-
tate and terdentate forms of a ligand is also found in
a
loss of halide plus all three methyl groups,
the
metal
complexes
of
terpyridine,
e.g.
[MꢀXMe3]+. However the most stable fragment for the
iodide corresponds to a loss of halide alone, [MꢀI]+.
For all cases the observed and calculated isotope pat-
terns are consistent. The IR spectra contain three bands
assigned to CꢀH stretching modes and three due to
PtꢀC stretching modes. The latter set of absorptions is
characteristic of the fac-[PtXMe3] moiety [3–5]. There
is no general trend for these absorptions in the halide
series. The PtꢀCl stretch is only observed for terminal-
bound chloride. Other PtꢀX (terminal) stretches are
[Pd(C6F5)2(terpy)] [9], and may be explained in terms of
steric interactions. These values may be compared with
the PtꢀN distances 2.178(5), 2.190(4) and 2.217(14) A
˚
observed in monomeric [PtClMe3(pydz)] [10] and
dimeric [(PtIMe3)2(v-pydz)] [11], respectively. The
PtꢀMe distances in the present compound vary from
˚
2.039(6) to 2.067(7) A, which are comparable with the
˚
values 2.038(6)–2.077(7) A observed in [PtClMe3(pydz)]
[10] and only slightly smaller than those 2.051(14)–2.11
˚
(2) A in [(PtIMe3)2(v-pydz)] [11], these values also
expected to occur below 200 cm−1
.
follow the trend that the equatorial bonds are some-
what shorter than the axial bond. The PtꢀI distance at
˚
˚
2.7970(5) A is only slightly longer than the value
2.1. X-ray crystallography
2.7648(12) A found in [(PtIMe3)2(v-pydz)] [11].
The crystal structure of the iodine derivative, fac-
[PtIMe3(BIP)], was determined to confirm the proposed
stereochemistry. It was found that the compound con-
sists of discrete molecules of fac-[PtIMe3(BIP)] held
together in the crystal by van der Waals forces only.
The structure of a single molecule together with the
atom numbering scheme is shown in Fig. 1. Molecular
geometry parameters are listed in Table 3. The study
confirms the octahedral coordination for the Pt atom
with the facial disposition of the three methyl groups.
Although the BIP ligand is potentially terdentate, in the
present compound it is bonded to Pt in a bidentate
manner. The pendant imine function is placed outside
the coordination sphere and appears to adopt the E-
Table 2
Mass spectral dataa for fac-[PtXMe3(BIP)] (X=Cl, Br or I) com-
plexes
Complex
m/z
[PtClMe3(BIP)]
[PtBrMe3(BIP)]
[PtIMe3(BIP)]
588 [M]+, 553 [MꢀCl]+, 523 [MꢀClMe2]+
508b [MꢀClMe3]+
,
633 [M]+, 553 [MꢀBr]+, 523 [MꢀBrMe2]+
508b [MꢀBrMe3]+
,
680 [M]+, 553b [MꢀI]+, 523 [MꢀIMe2]+, 508
[MꢀIMe3]+
a Acquired using the LSIMS technique. The values quoted represent
the most abundant ions amongst clusters of isotopic species.
b Most abundant of the ions quoted.

K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47
37
NOE difference experiments were performed on fac-
[PtBrMe3(BIP)] in CDCl3 at 30°C. By irradiating the
equatorial signal MeP a positive NOE built up in the
signals of the isochronous nuclei of HO and HK. This
indicates that the nitrogen in the pendant part of the
ligand is in a cisoidal orientation in respect to the
pyridyl nitrogen, and furthermore, that the relevant
phenyl ring is rapidly rotating around the NꢀCipso
bond. On irradiating signal MeF a positive NOE built
up due to signal HG but no NOE build up was appar-
ent for signals HE and HA. This suggests that the latter
protons are almost orthogonal to the chelate plane as
the X-ray crystal structure shows (Fig. 1). On irradiat-
ing the signal MeJ a positive NOE built up due to
signals HO and HK. However in contrast to fac-
Table 3
˚
Bond lengths (A) and angles (°) for fac-[PtIMe3(BIP)]
Fig. 1. A view of the crystal structure of fac-[PtIMe3(BIP)] showing
the atom labelling. Thermal ellipsoids are drawn at 50% probability
level.
Pt(1)ꢀC(15)
Pt(1)ꢀC(14)
Pt(1)ꢀN(1)
N(1)ꢀC(1)
N(2)ꢀC(6)
N(3)ꢀC(17)
C(1)ꢀC(2)
C(2)ꢀC(3)
C(4)ꢀC(5)
C(6)ꢀC(7)
C(8)ꢀC(13)
C(10)ꢀC(11)
C(12)ꢀC(13)
C(19)ꢀC(24)
C(20)ꢀC(21)
C(22)ꢀC(23)
2.039(6)
2.067(7)
2.243(5)
1.357(8)
1.277(8)
1.291(9)
1.394(9)
1.377(10)
1.389(8)
1.496(9)
1.397(9)
1.358(10)
1.388(10)
1.370(10)
1.389(10)
1.363(10)
Pt(1)ꢀC(16)
Pt(1)ꢀN(2)
Pt(1)ꢀI(1)
N(1)ꢀC(5)
N(2)ꢀC(8)
N(3)ꢀC(19)
C(1)ꢀC(17)
C(3)ꢀC(4)
2.051(6)
2.152(5)
2.7970(6)
1.361(8)
1.461(8)
1.437(9)
1.511(9)
1.387(10)
1.496(9)
1.360(9)
1.395(10)
1.404(11)
1.483(10)
1.400(9)
1.379(11)
1.408(10)
The octahedron around Pt is as expected somewhat
distorted, the main distortion being due to the small
BIP ‘bite angle’ of 74.9(2)°. The IꢀPtꢀMe(eq) angles are
obtuse 92.8(2), 94.7(2)°, and IꢀPtꢀN angles are acute
87.56(14), 87.05(13)° which may be explained by the
steric requirement of the I and Me ligands. The largest
distortion is associated with the N(1)ꢀPtꢀC(16) angle,
105.8(2)° which is clearly due to the C(16)· · ·C(18)
C(5)ꢀC(6)
C(8)ꢀC(9)
C(9)ꢀC(10)
C(11)ꢀC(12)
C(17)ꢀC(18)
C(19)ꢀC(20)
C(21)ꢀC(22)
C(23)ꢀC(24)
˚
interaction 3.267(11) A. The trans angles are 171.3(2),
177.5(2) and 178.2(2)°. The pyridine ring is nearly
coplanar with the Pt(1)N(1)C(5)C(6)N(2) plane but the
phenyl ring C(8)–C(13) is 83.2(2)° rotated out of the
latter plane. The imine moiety N(3)C(1)C(17)C(18)
makes an angle of 80.1(3)° with the pyridine plane and
an angle of 69.1(2)° with the phenyl ring C(19)–C(24).
This indicates considerable flexibility of the BIP ligand.
C(15)ꢀPt(1)ꢀC(16) 82.9(3)
C(16)ꢀPt(1)ꢀC(14) 86.5(3)
C(15)ꢀPt(1)ꢀC(14) 89.5(3)
C(15)ꢀPt(1)ꢀN(2)
C(14)ꢀPt(1)ꢀN(2)
C(16)ꢀPt(1)ꢀN(1)
N(2)ꢀPt(1)ꢀN(1)
C(16)ꢀPt(1)ꢀI(1)
N(2)ꢀPt(1)ꢀI(1)
C(1)ꢀN(1)ꢀC(5)
C(5)ꢀN(1)ꢀPt(1)
C(6)ꢀN(2)ꢀPt(1)
96.4(3)
91.8(3)
105.8(2)
74.9(2)
94.7(2)
87.05(13)
116.1(5)
112.9(4)
119.0(4)
C(16)ꢀPt(1)ꢀN(2)
C(15)ꢀPt(1)ꢀN(1)
C(14)ꢀPt(1)ꢀN(1)
C(15)ꢀPt(1)ꢀI(1)
C(14)ꢀPt(1)ꢀI(1)
N(1)ꢀPt(1)ꢀI(1)
C(1)ꢀN(1)ꢀPt(1)
C(6)ꢀN(2)ꢀC(8)
C(8)ꢀN(2)ꢀPt(1)
N(1)ꢀC(1)ꢀC(2)
C(2)ꢀC(1)ꢀC(17)
C(2)ꢀC(3)ꢀC(4)
N(1)ꢀC(5)ꢀC(4)
C(4)ꢀC(5)ꢀC(6)
N(2)ꢀC(6)ꢀC(5)
C(9)ꢀC(8)ꢀC(13)
C(13)ꢀC(8)ꢀN(2)
C(11)ꢀC(10)ꢀC(9)
178.2(2)
171.3(2)
90.0(2)
92.8(2)
177.5(2)
87.56(14)
130.9(4)
118.8(5)
122.2(4)
123.5(6)
116.9(6)
118.6(6)
123.3(6)
120.4(6)
116.7(6)
121.3(6)
118.2(6)
121.8(7)
1
2.2. H-NMR studies
C(17)ꢀN(3)ꢀC(19) 120.9(6)
N(1)ꢀC(1)ꢀC(17)
C(3)ꢀC(2)ꢀC(1)
C(3)ꢀC(4)ꢀC(5)
N(1)ꢀC(5)ꢀC(6)
N(2)ꢀC(6)ꢀC(7)
C(7)ꢀC(6)ꢀC(5)
C(9)ꢀC(8)ꢀN(2)
C(8)ꢀC(9)ꢀC(10)
C(10)ꢀC(11)ꢀC(12) 119.3(7)
C(12)ꢀC(13)ꢀC(8)
N(3)ꢀC(17)ꢀC(1)
C(24)ꢀC(19)ꢀC(20) 120.5(7)
C(20)ꢀC(19)ꢀN(3) 118.0(7)
C(22)ꢀC(21)ꢀC(20) 120.9(7)
C(22)ꢀC(23)ꢀC(24) 120.0(7)
119.5(5)
119.2(6)
119.3(6)
116.3(5)
124.7(6)
118.7(6)
120.5(6)
118.7(6)
1H-NMR spectra for fac-[PtXMe3(BIP)] complexes
1
were taken at −10°C in CDCl3. H chemical shifts (l)
and coordination shifts (Dl) are recorded in Table 4.
Most coordination shifts are positive but significant low
frequency coordination shifts occur for the meta signals
of the pyridyl unit (HG and HI). These low frequency
shifts are the result of the preferred conformation of the
terminal CꢁN imine bonds relative to the pyridyl ring
changing on metal coordination. Opposing trends in
the para (HH) versus the meta (HI and HG) proton
signals are characteristic of the distribution of charge in
the six-membered heterocycles. With increased elec-
trophilicity of the metal centre the para proton is more
deshielded and the meta protons more shielded.
C(13)ꢀC(12)ꢀC(11) 119.7(7)
N(3)ꢀC(17)ꢀC(18) 127.6(6)
C(18)ꢀC(17)ꢀC(1)
C(24)ꢀC(19)ꢀN(3) 121.3(6)
C(21)ꢀC(20)ꢀC(19) 118.6(7)
C(23)ꢀC(22)ꢀC(21) 120.2(7)
C(19)ꢀC(24)ꢀC(23) 119.8(7)
119.1(7)
113.5(6)
118.6(6)

38
K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47

K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47
39
1
Fig. 2. 400 MHz H-NMR spectrum (methyl region) of fac-[PtIMe3(BIP)] in CDCl3 at 10°C. See Table 5 for labels. * Other non-fluxional species.
abundance of the major species in these samples in-
creases with an increase in the halide radius (Table 5).
However within the minor species the proportions are
roughly the same in the series of halides.
[ReX(CO)3(BIP)] [2] there is no NOE build up due to
the meta signal HI of the pyridyl. This suggests that in
the structure of fac-[PtBrMe3(BIP)] the methyl group
MeJ is at a greater average distance from the meta
proton of the pyridyl ring than in the rhenium com-
plexes [2].
2.3. 13C-NMR spectra
In contrast to the phenyl group of the pendant imine
function, the one attached to the metal-bound nitrogen
is rotating slowly around the NꢀCipso bond and its ortho
protons show anisochronous signals. The coordination
shifts become greater with increased electrophilicity of
the metal centre. Signal HA shows a large positive
coordination shift in contrast to signal HE which shows
a small low frequency coordination shift that might be
a consequence of HE falling in the shielding region of
the CꢁN double bond. In the spectra of each of these
complexes there is evidence for at least three other
species (Fig. 2). Chromatographic separation was tried
without success. The elemental analyses were reliable
for all three complexes (Table 1). In each coordination
complex all minor species were involved in exchange
processes with the major species and were assumed to
be isomerisation products. The major species was as-
sumed to contain the imine function of the pendant
part of the ligand in a distal E-conformation (Fig. 3).
This was confirmed by the X-ray study on fac-
[PtIMe3(BIP)]. Steric interactions between the pendant
imine function and the metal moiety are likely to be
greater than those in the complexes fac-
[ReX(CO)3(BIP)]. Hence the trimethylplatinum (IV)
produces more isomeric species in solution than the
rheniumtricarbonyl moiety. These are depicted in Fig. 3
where the labelling follows that used in ref. [2]. The
The 13C-NMR spectrum of fac-[PtIMe3(BIP)] was
measured in CDCl3 at 30°C (Table 6). Correlations of
the 13C and 1H nuclei were derived from a 2D het-
eronuclear correlation spectrum. The assignments of
the quaternary carbon nuclei are only tentative. The
Fig. 3. The proposed solution isomers of the complexes fac-
[PtXMe3(BIP)] (X=Cl,Br or I).

40
K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47
Table 5
1H-NMR dataa,b of methyl region for fac-[PtXMe3(BIP)] (X=Cl, Br or I) complexes in CDCl3 at 30°C (400.13 MHz)
Compound
Fh
Jh
Fi
Ji
Fk
Jk
Fl
Jl
Abundance (%)
Abundance (%)
Abundance (%)
Abundance (%)
JPtꢀH/Hz
[PtClMe3(BIP)]
[PtBrMe3(BIP)]
[PtIMe3(BIP)]
s 2.43
88.19
3.4
s 2.59
s 2.59
s 2.58
2.36
7.69
2.97
3.00
2.01
2.35
3.57
2.53
2.52
2.51
2.26
0.55
2.77
2.77
2.74
s 2.44
89.59
3.6
2.38
6.74
2.36
3.14
2.26
0.52
s 2.43
90.96
4.0
2.36
5.69
2.35
2.84
2.26
0.51
a Chemical shifts (l) relative to TMS, l=0.
b FhJh/distal E,E; FiJi/distal E,Z; FkJk/proximal E,Z; FlJl/proximal E,E (see Fig. 3).
Table 6
13C-NMR dataa for fac-[PtIMe3(BIP)] in CDCl3 at 30°C (100.62 MHz)
1b
2
3
4
5
6
7b
8
9b
10
11
12
JPtꢀC
JPtꢀC
145.88
12.6
123.29
129.60
127.03
128.90
120.32
162.61
12.7
20.47
7.3
155.62
9.0
127.25
139.39
128.25
13b
JPtꢀC
14b
15
16b
17
18
19
20
21
22
JPtꢀC
23
JPtꢀC
PtꢀMeax
JPtꢀC
148.75
5.4
171.99
22.27
168.16
119.98
129.04
124.65
129.04
119.98
−7.62
650.3
−0.61
687.8
7.76
685.4
a
Chemical shifts (l) relative to TMS, l=0. Scalar couplings in Hertz.
b Tentative assignments.

K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47
41
Fig. 4. 400 MHz 1H-NMR 2D-EXSY spectrum of fac-[PtIMe3(BIP)] in CDCl3 at 30°C. Mixing time ~m=1.5 s.
signals C1, C7, C9, and C13 were assigned according to
the magnitude of the scalar coupling JPtꢀC and the
probable effect of the electrophilicity of the metal cen-
tre. The distinctions between C1/C7 and C14/C16 are
rather speculative. The coupling associated with signal
Me22 is much smaller than for other equatorial and
axial signals, reflecting the magnitude of the trans influ-
ence of the pyridyl unit.
fac-[PtIMe3(BIP)] was measured at 30°C (Fig. 4). The
most abundant species (distal E,E) is represented by its
methyl signals FhJh. Of the minor species, the most
populous (distal E,Z) is represented by its methyl sig-
nals FiJi, the next most populous, attributed to the
proximal E,Z, is represented by signals FkJk and the
least populous species (proximal E,E) by signals FlJl.
All the exchange processes identified are summarised
in Fig. 5. Cross-peak signals identified the exchanges
Fh X Jh, Fh X Fi (and Jh X Ji), Fk X Fl (and Jk X Jl),
Fh X Fl (and Jh X Jl), and Fi X Fk (and Ji X Jk). The
exchange Fh X Jh represents the 1,4-metallotropic shift
in the distal E,E species. There is no metallotropic shift
for any other species. The exchanges Fh X Fi and
Fk X Jl correspond to the imine E,Z isomerisation
process of the pendant part of the BIP ligand. Finally,
the exchanges Fh X Fl and Fi X Fk correspond to the
restricted rotation of the CꢀC bond of the pendant part
of the BIP ligand.
2.4. Dynamic NMR studies
1
A H-NMR 1D variable temperature study was car-
ried out to establish the fluxional nature of the various
isomers. For all three complexes the spectra showed
that the major and the minor species underwent ex-
change to produce, at the higher temperatures, a spec-
trum representative of a single rapidly exchanging
species. In order to identify the different fluxional mo-
tions the 2D-EXSY spectrum of the methyl region of

42
K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47
Fig. 5. General exchange scheme for fluxional motions in the complexes fac-[PtXMe3(BIP)] (X=Cl,Br or I) showing the nine exchange pathways
(four distinct types).
2.5. Kinetic studies
each peak. The method of handling data for the inten-
sity matrix followed the treatment previously described
[2]. The rate constants may be read directly from the
off-diagonal elements of the calculated matrix L.
Choice of ~m values and treatment of errors followed
the literature [12].
The total spin problem for the exchange processes
involves an eight site exchange (Fig. 5). Intensity data
of 2D-EXSY signals taken in the temperature range
20–50°C were used to calculate rate data. However the
results were not reliable for the CꢀC restricted rotation
processes between the proximal E,Z and distal E,Z
forms, since in this temperature range the diagonal and
cross peak signals for the exchange Fi X Fk were too
broad for accurate measurements. Therefore, 2D-
EXSY spectra were measured at a lower temperature
range (see later) to derive rate constants for this latter
process.
2.5.2. Temperature range −10 to 20°C
2D-EXSY spectra were performed in CDCl3 in the
temperature range −10 to 20°C for these complexes.
The aim was to measure the rates of CꢀC restricted
rotation of the pendant arm of the ligand in the minor
species, i.e. the exchange distal E,Z X proximal E,Z
(Fi X Fk, Ji X Jk), Fig. 5.
The D2DNMR program [12] was applied to this
two-site exchange problem using the diagonal and
cross-peaks of the Ji X Jk exchange. The 2D-EXSY
spectrum of fac-[PtBrMe3(BIP)] measured at 10°C with
mixing time 1.0 s is shown in Fig. 6.
2.5.1. Temperature range 20–50°C
2D-EXSY spectra were measured for the temperature
range 20–50°C for complexes fac-[PtXMe3(BIP)]. Be-
cause the exchange Fi X Fk (the CꢀC restricted rota-
tion processes between proximal E,Z and distal E,Z)
was separated from the total spin problem the latter
was formulated as a six-site exchange for this tempera-
ture range. The 2D-EXSY signals were converted into a
6×6 intensity matrix I by integrating the area under
2.5.3. The mechanisms of fluxional processes
Three different fluxional motions were observed for
complexes fac-[PtXMe3(BIP)], namely (i) the 1,4-metal-
lotropic shift, (ii) the E,Z-diastereoisomerisation of the

K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47
43
Fig. 6. 400 MHz 1H-NMR 2D-EXSY spectrum of fac-[PtBrMe3(BIP)] in CDCl3 at 10°C. Mixing time ~m=1.0 s.
about the CꢁN double bond, or through an inversion of
the nitrogen. In the case of fac-[PtXMe3(BIP)] it is not
possible to exclude either mechanism. However, on the
basis of previous studies [1,14] the favoured mechanism
is a nitrogen inversion process.
pendant imine function, and (iii) the CꢀC restricted
rotation of the pendant part of the BIP ligand. Metal
commutation was only observed for the distal E,E-iso-
mer.1H-NMR spectra of the PtꢀMe region of fac-
[PtIMe3(BIP)] in (CDCl2)2 in the temperature range
30–130°C were recorded. In the temperature range
30–80°C the equatorial signals broadened while the
axial signal remained sharp (Fig. 7). The exchange of
the equatorial methyl groups, with no axial group
exchange, is a sign that the mechanism proceeds via the
‘tick-tock’ twist resulting from the ligand trying but
failing to adopt terdentate bonding. The tick-tock twist
involves a seven coordinate platinum(IV) intermediate
(Fig. 8). On further warming, the two equatorial PtꢀMe
signals and the axial PtꢀMe signal start exchanging.
Such an exchange or scrambling of PtꢀMe environ-
ments is a well known feature of fac-[PtXMe3(LꢀL)]
compounds [13]. E,Z-diastereoisomerisation in the pen-
dant imine bond can proceed through a 180° rotation
3. Discussion
Activation energy data were calculated from the
derived rate constants from a least-squares fit of the
Eyring plots, Table 7. The entropies of activation have
magnitudes which cluster around zero, as expected for
purely intramolecular rearrangements, but have rather
large associated uncertainties. The free energy of activa-
tion for all fluxional motions seems to be independent
of the electrophilicity of the metal centre. In general the
DG" values for the three processes, metal commuta-
tion, distal E,Z X distal E,E isomerisation and CꢀC

44
K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47
techniques for studying the complex internal dynamics
of metal complexes of BIP ligands. Rates and activa-
tion energies of 1,4-metallotropic shifts, CꢀC restricted
rotation processes and imine isomerisation processes
were independently measured despite their similarity in
magnitudes.
A fourth process, namely restricted rotation of the
phenyl ring on the coordinated imine function was also
examined in the present Pt(IV) complexes by a variable
temperature 13C-NMR study of the ortho carbons of
the ring. Spectra recorded in the range 303–403 K
revealed a band coalescence effect.
4. Experimental
4.1. Physical measurements
Elemental analyses were carried out by Butterworth
Laboratories (Teddington, Middlesex, London). Melt-
ing points were recorded open to air on a Gallenkamp
melting point apparatus and are uncorrected. Mass
spectra were recorded on a Kratos Profile HV-3 spec-
trometer operating in liquid secondary ion mass spec-
trometry (LSIMS) mode using a 3-nitro-benzyl alcohol
matrix. Infrared spectra were recorded in CHCl3 solu-
tions using matched CaF2 solution cells on a Perkin-
Elmer 881 spectrometer. NMR spectra were recorded
1
on a Bruker DRX400 instrument with H recorded at
1
400.13 and 13C at 100.61 MHz. H and 13C{1H} chem-
ical shifts are quoted relative to Me4Si (TMS). A stan-
dard B-VT 2000 variable temperature unit was used to
control the probe temperature, the calibration of this
unit being checked periodically against a Comark digi-
tal thermometer. The temperatures are considered to be
accurate to 91°C. 1H–13C correlation spectra and
COSY spectra were obtained with the Bruker automa-
tion programs INVBTP and COSY45. 2D-EXSY spec-
tra were obtained with the Bruker automation program
NOESYTP. The initial delay time was typically 2.00 s,
the evolution time was initially 3×10−6 s and the
mixing time was varied according to the experimental
temperature.
Fig. 7. 300 MHz 1H-NMR spectra (platinum methyl region) of
fac-[PtIMe3(BIP)] in (CDCl2)2 in the temperature range 30–130°C,
showing the 1,4-metallotropic shift and platinum–methyl scrambling.
* An impurity.
restricted rotation proximal E,E X distal E,E do not
differ greatly in magnitude. However, these values are
ca. 10 kJ mol−1 greater than the magnitude of DG"
for the CꢀC restricted rotation of the E,Z rotamers.
This work, together with other parts of this series
[1,2], has demonstrated the power of 1D and 2D-NMR
Kinetic data were derived either from band shape
analysis of 1H-NMR spectra using the iterative
DNMR5 program [15] for the simulation of band
Fig. 8. Proposed mechanism of the 1,4-metallotropic shift.

K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47
45
Table 7
Activation parameters for fluxional processes in complexes fac-[PtXMe3(BIP)] (X=Cl, Br, I)
Compound
Process
k
DH" (kJ mol−1
)
DS" (J mol−1 K−1
)
DG" (kJ mol−1 e
)
a
[PtClMe3(BIP)]
79.6890.35
73.4492.23
73.4592.23
84.3491.82
91.3894.87
85.8996.72
87.8991.77
81.8890.69
64.4892.31
62.0792.62
87.2492.42
86.9298.32
74.8897.20
88.4792.27
83.6490.29
67.4090.48
67.4090.48
83.8090.88
120.7599.97
78.9899.10
84.4290.65
1.891.1
79.1490.02
69.3290.19
67.2290.19
81.1990.10
93.7390.34
80.7990.36
87.3090.10
79.6990.03
70.0890.17
68.4990.19
80.9090.11
93.8490.58
80.3190.31
87.3190.11
79.8890.01
70.0190.03
68.4890.03
79.9390.03
96.1790.62
80.7690.33
86.7790.02
b
f
r
f
r
f
r
13.898.1
20.998.1
10.695.8
−7.9915.2
17.1921.3
2.095.6
c
d
a
[PtBrMe3(BIP)]
[PtIMe3(BIP)]
7.392.2
b
f
r
f
r
f
r
−18.898.3
−21.599.4
21.397.7
−23.2926.0
−18.2923.1
3.997.3
12.690.9
−8.791.7
−3.691.7
13.092.9
82.4931.4
−6.0929.4
−7.992.1
c
d
a
b
f
r
f
r
f
r
c
d
f, forward and r, reverse processes.
a 1,4-Metallotropic shift; b CꢀC restricted rotation distal E,Z X proximal E,Z; c distal E,Z X distal E,E isomerisation; d CꢀC restricted rotation
proximal E,E X distal E,E; e Measured at 298.15 K.
shapes, or from 2D-EXSY spectra using the standard
D2DNMR [12] program. Activation parameters were
calculated from a least-squares fit of the Eyring plots.
Quoted errors are standard deviations based on the
uncertainties in the rate constants only.
diethylether (2×20 cm3). It was then dried at ca. 50°C
for 5 h. Yield 0.165 g, 89.0%.
4.2.2. Crystal structure determination of
fac-[PtIMe3(BIP)]
Yellow crystals of fac-[PtIMe3(BIP)] suitable for X-
ray work were obtained by recrystallisation of the crude
material from a benzene/hexane mixture.
4.2. Materials
Previously described methods were used to prepare
the complexes [PtXMe4] (X=Cl [16], Br and I [17]).
The ligand BIP was prepared by condensation of 2,6-di-
acetylpyridine with aniline in benzene [18].
All preparations were performed by standard
Schlenk techniques [19] under purified nitrogen using
freshly distilled dried and degassed solvents. The com-
plexes fac-[PtXMe3(BIP)] were all prepared in an
analogous manner. The preparation of fac-
[PtIMe3(BIP)] is given as a representative example.
The unit cell parameters and intensity data were
measured at 150 K using a Delft Instruments FAST TV
area detector diffractometer positioned at the window
of a rotating anode generator using Mo–Kh radiation
˚
(u=0.71069 A) by following procedures described else-
where [20]. The data were corrected for Lorentz and
polarisation factors and also for absorption effects [21].
The structure was solved by Patterson methods
(SHELXS-86) [22] and difference synthesis and refined
on F2 by full matrix least squares (SHELXL-93) [23]
using all unique data. All non hydrogen atoms were
anisotropic. The hydrogen atoms were included in cal-
culated positions (riding model) with U(iso)=n×
U(eq) of the parent atom (n=1.2 for CH and CH2, 1.5
for CH3). Final R (on F) and wR (on F2) values were
0.0423 and 0.0954, respectively, for all 2622 data and
267 parameters. The corresponding R values for 3334
4.2.1. fac-[PtIMe3(BIP)]
The complex [PtIMe3]4 (0.10 g, 0.27 mmol, based on
monomeric unit) and BIP (0.094 g, 0.3 mmol) were
heated under reflux in benzene (25 cm3) for 7 h. The
solvent was subsequently evaporated under reduced
pressure and the bright yellow powder was washed with

46
K.G. Orrell et al. / Journal of Organometallic Chemistry 555 (1998) 35–47
Table 9
data with I\2|(I) were 0.0393 and 0.0946, respec-
tively. The residual electron density in the final differ-
ence map did not indicate any feature of
stereochemical significance. Molecular geometry
parameters are given in Table 3. The crystal data,
details of data collection and structure refinement
parameters, and atom coordinates are given in Tables 8
and 9. Anisotropic displacement coefficients, hydrogen
atom parameters and structure factor tables have been
deposited at the Cambridge Crystallographic Data
Centre. Calculations were performed on a Pentium 200
MHz personal computer. Sources of scattering factors
were as in ref. [23].
Atomic coordinates (×104) and equivalent isotropic displacement
2
3
˚
parameters (A ×10 ) for fac-[PtIMe3(BIP)]
Atom
x
y
z
U(eq)a
Pt(1)
I(1)
N(1)
N(2)
N(3)
C(1)
C(2)
C(3)
C(4)
C(5)
2327.8(2)
4309.7(4)
3106(4)
2879(4)
1832(4)
3173(5)
3680(6)
4143(6)
4075(5)
3550(5)
3418(5)
3900(5)
2676(5)
3309(5)
3104(6)
2288(6)
1628(6)
1819(5)
895(6)
1663(6)
1754(6)
2714(5)
3347(5)
1331(5)
366(5)
−150(6)
272(6)
1193(6)
1733(6)
1267.1(2)
1749.6(5)
1365(5)
−640(5)
3859(5)
2333(6)
2224(7)
1081(7)
69(7)
929.8(1)
720.1(2)
2225(3)
1263(3)
2597(4)
2742(3)
3542(4)
3833(4)
3319(4)
2530(3)
1970(4)
2270(4)
703(4)
18(1)
27(1)
16(1)
17(1)
24(1)
19(1)
31(2)
30(2)
25(2)
17(1)
17(1)
26(2)
19(1)
23(2)
31(2)
29(2)
28(2)
25(2)
32(2)
31(2)
31(2)
19(2)
28(2)
26(2)
31(2)
33(2)
35(2)
37(2)
28(2)
238(6)
C(6)
C(7)
C(8)
C(9)
−854(6)
−2113(6)
−1694(6)
−1883(6)
−2919(7)
−3730(6)
−3520(7)
−2494(7)
896(8)
Acknowledgements
231(4)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
−282(4)
−326(4)
154(4)
We are most grateful to the Ministry of Petroleum
(Angola) for financial support (to Mateus Webba da
Silva).
668(4)
1136(4)
−230(4)
605(4)
888(7)
3065(6)
3623(6)
4502(7)
5083(7)
5146(7)
6313(7)
7388(8)
7312(8)
6141(7)
2450(4)
2112(4)
2422(4)
1835(4)
1684(5)
2104(4)
2692(4)
2856(4)
Table 8
Crystal data, details of data collection and structure refinement
parameters for fac-[PtIMe3(BIP)]
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C24H28IN3Pt
680.48
150(2)
0.71069
Monoclinic
P21/c
˚
a
U(eq) is defined as one third of the trace of the orthogonalised Uij
tensor.
Unit cell dimensions
˚
a (A)
13.223(2)
10.4810(10)
17.812(2)
106.620(9)
2365.4(5)
4
1.911
7.251
1296
˚
b (A)
˚
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c (A)
i (°)
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