C-H Activation Induced by Water. Monocyclometalated to Dicyclometalated: C∧N∧C Tridentate Platinum Complexes

Article abstract of DOI:10.1021/om9910423

Metalation of 2,6-diphenylpyridine (1) by potassium tetrachloroplatinate in acetic acid gives a monocyclometalated chloride-bridged dimer 4. This dimer is split with CO to give a kinetic product 9t with the incoming CO trans to the orthometalated carbon.

Full text of DOI:10.1021/om9910423

Organometallics 2000, 19, 1355-1364
1355
C-H Activa tion In d u ced by Wa ter . Mon ocyclom eta la ted
to Dicyclom eta la ted : C∧N∧C Tr id en ta te P la tin u m
Com p lexes
Gareth W. V. Cave,† Francesco P. Fanizzi,‡ Robert J . Deeth,†
William Errington,† and J onathan P. Rourke*,†
Department of Chemistry, Warwick University, Coventry, U.K. CV4 7AL, and Dipartimento
Farmaco-Chimico, Universita di Bari, Via E. Orabona, 4 70125 Bari, Italy
Received December 30, 1999
Metalation of 2,6-diphenylpyridine (1) by potassium tetrachloroplatinate in acetic acid
gives a monocyclometalated chloride-bridged dimer 4. This dimer is split with CO to give a
kinetic product 9t with the incoming CO trans to the orthometalated carbon. The kinetic
product of cleavage is shown to be 16 kJ mol-1 higher in energy than the thermodynamic
product 9c, which has the CO trans to the pyridine nitrogen. The isomerization of 9t to 9c
is shown not to take place via an associative mechanism and, with analogue 11, is effectively
suppressed when excess chloride is added, implying that it takes place via a chloride
dissociation. The monocyclometalated 9 undergoes a second cyclometalation to give the
C∧N∧C dicyclometalated complex 15 in high yield. This second cyclometalation is brought
about by the simple expedient of adding water to the monocyclometalated precursor. The
addition of water is rationalized on the basis of needing to ionize the HCl byproduct of the
reaction. Using a substituted pyridine (5) analogous chemistry is observed. Single-crystal
X-ray structures of one of the intermediates (6) and one of the final products (15) have been
solved. Density functional theory calculations are used to rationalize the isomerizations of
the monocyclometalated intermediates and the need to ionize HCl in the second cyclometa-
lation.
In tr od u ction
as pioneered by Trofimenko15,16 more than a quarter of
a century ago. Another area of research has been the
synthesis of tridentate cyclometalated species where two
coordinating groups hold a C-H bond close to the metal
and this bond is activated. These are relatively common;
thus N∧C∧N17 donor sets,18,19 P∧C∧P donor sets,20-23
or S∧C∧S donor sets24 are well-known. Indeed, some
groups have used two ligating groups to induce a C-C25
or C-Si activation.26 In addition, the use of a chelating
N∧N donor set to yield N∧N∧C tridentate cyclometa-
lated species has been reported.27
Cyclometalation, a recent paper begins, “has been so
well refined that a new but standard report in this area
seems rather ordinary”.1 Cyclometalation might well
have been both widely studied2,3 and widely used,4,5 but
it is still generating much interest. Our own use of the
reaction has been to generate novel cyclopalladated
metallomesogens6-8 and some unusual platinum com-
plexes.9 Some researchers have returned to the area of
double cyclometalation of the same aromatic ring,7,10-14
* E-mail: j.rourke@warwick.ac.uk.
† Warwick University.
(15) Trofimenko, S. J . Am. Chem. Soc. 1971, 93, 1808.
(16) Trofimenko, S. Inorg. Chem. 1973, 12, 1215.
(17) The abbreviation N∧C∧N refers to a tridentate ligand bonding
through two N donors and one C donor, with the ligand connectivity
being N linked to C linked to N. Thus N∧N∧C also represents a
tridentate ligand bonding through two N donors and one C donor, but
this time the ligand connectivity is N linked to N linked to C.
(18) Terheijden, J .; van Koten, G.; Muller, F.; Grove, D. M.; Vrieze,
K.; Nielsen, E.; Stam, C. H. J . Organomet. Chem. 1986, 315, 401.
(19) Gossage, R. A.; Ryabov, A. D.; Spek, A. L.; Stufkens, D. J .; van
Beek, J . A. M.; van Eldik, R.; van Koten, G. J . Am. Chem. Soc. 1999,
121, 2488.
‡ Universita di Bari.
(1) Ryabov, A. D.; Panyashkina, I. M.; Polyakov, V. A.; Howard, J .
A. K.; Kuz’mina, L. G.; Datt, M. S.; Sacht, C. Organometallics 1998,
17, 3615.
(2) Ryabov, A. D. Chem. Rev. 1990, 90, 403.
(3) Steenwinkel, P.; Gossage, R. A.; van Koten, G. Chem. Eur. J .
1998, 4, 759.
(4) Ryabov, A. D. Synthesis 1985, 233.
(5) Pfeffer, M. Pure Appl. Chem. 1992, 64, 335.
(6) Lydon, D. P.; Cave, G. W. V.; Rourke, J . P. J . Mater. Chem. 1997,
7, 403.
(7) Lydon, D. P.; Rourke, J . P. Chem. Commun. 1997, 1741.
(8) Cave, G. W. V.; Lydon, D. P.; Rourke, J . P. J . Organomet. Chem.
1998, 555, 81.
(9) Cave, G. W. V.; Hallett, A. J .; Errington, W.; Rourke, J . P. Angew.
Chem., Int. Ed. 1998, 37, 3270.
(20) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1976,
1020.
(21) Rimml, H.; Venanzi, L. M. J . Organomet. Chem. 1983, 259, C6.
(22) Bennett, M. A.; J in, H.; Willis, A. C. J . Organomet. Chem. 1993,
451, 249.
(10) Chakladar, S.; Paul, P.; Venkatsubramanian, K.; Nag, K. J .
Chem. Soc., Dalton Trans. 1991, 2669.
(23) Weisman, A.; Gozin, M.; Kraatz, H.-B.; Milstein, D. Inorg.
Chem. 1996, 35, 1792.
(24) Dupont, J .; Beydon, N.; Pfeffer, M. J . Chem. Soc., Dalton Trans.
1989, 1715.
(25) Rybtchinski, R.; Vigalok, A.; Ben-David, Y.; Milstein, D. J . Am.
Chem. Soc. 1996, 118, 12406.
(26) Steenwinkel, P.; Gossage, R. A.; Maunula, T.; Grove, D. M.; van
Koten, G. Chem. Eur. J . 1998, 4, 763.
(11) Chakladar, S.; Paul, P.; Mukherjee, A. K.; Dutta, S. K.; Nanda,
K. K.; Podder, D.; Nag, K. J . Chem. Soc., Dalton Trans. 1992, 3119.
(12) Steenwinkel, P.; J ames, S. L.; Grove, D. M.; Kooijman, H.; Spek,
A. L.; van Koten, G. Organometallics 1997, 16, 513.
(13) O’Keefe, B. J .; Steel, P. J . Organometallics 1998, 17, 3621.
(14) Hartshorn, C. M.; Steel, P. J . Organometallics 1998, 17, 3487.
10.1021/om9910423 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 03/03/2000

1356 Organometallics, Vol. 19, No. 7, 2000
Cave et al.
Sch em e 1
Sch em e 2
Sch em e 3
Relatively uncommon are double cyclometalations to
give complexes with tridentate C∧N∧C or C∧P∧C donor
sets, which arise when two cyclometalated rings have
been formed via two C-H activations by the same
metal. In a recent paper28 we reported the first high-
yield synthesis of such tridentate C∧N∧C compounds
of platinum. Here we present mechanistic details on the
crucial second cyclometalation, theoretical studies on
the intermediates, and suggestions as to how to gener-
alize the reaction.
Resu lts a n d Discu ssion
Mon ocyclom et a la t ed Sp ecies: Cis a n d Tr a n s
In ter m ed ia tes. In our earlier paper28 we reported that
the reaction of potassium tetrachloroplatinate with
diphenylpyridine in acetic acid gave a complex we
tentatively formulated as 2 in essentially quantitative
yield (Scheme 1). While we could get no solution data
on 2, solid-state characterization was consistent with
this formulation. On dissolution in hot dimethyl sulfox-
ide (dmso), followed by precipitation with water, 2 gave
dmso complex 3, which was fully characterized (NMR,
elemental analysis, single-crystal X-ray diffraction). Our
new data conclusively proves that 2 is not the correct
formulation, that the intermediate we isolate is actually
only the monocyclometalated chloride bridged dimer 4,
and that the dissolution in dmso followed by precipita-
tion with water is inducing the second cyclometalation
to give complex 3 (Scheme 2).
Monometalated halide bridged dimers of type 4 are
well-known, and with suitable pyridines, they may be
fully characterized. Thus we have used the 4-substituted
pyridine 5 and reacted this to form chloride-bridged
dimer 6 via a literature route (Scheme 3).29 Compound
6 is soluble in common organic solvents, unlike 4, and
has been well characterized, including the solving of the
single-crystal X-ray structure (Figure 1). Using the same
conditions as we used in the isolation of doubly cyclo-
metalated 3 (dissolution in hot dmso, precipitation with
water) we can bring about a second cyclometalation to
give analogue 7 (Scheme 3), which we use as a conve-
nient source of the C∧N∧C tridentate Pt moiety (dmso
can be readily displaced).
In addition to this indirect evidence for the formula-
tion of 4 as a chloride-bridged dimer, we now have
definitive solution NMR data on 4. By using deuterated
dmf we can clearly see 10 different signals, with
appropriate couplings, corresponding to the 12 protons
expected for a compound such as 4 (Figure 2). Our
earlier assignment of the structure as 2 had been on
the basis of elemental analysis, MALDI mass spectrom-
etry, and proton NMR. However, the elemental analysis
fits either formulation 2 or 4, and the peak in MALDI
mass spectrum at m/z ) 39 (which we assigned to K+)
could just as well have come from contamination such
as a fingerprint. Our previous attempts to run the NMR
(27) Constable, E. C.; Henney, R. P. G.; Leese, R. A.; Tocher, D. A.
J . Chem. Soc., Chem. Commun. 1990, 513.
(28) Cave, G. W. V.; Alcock, N. W.; Rourke, J . P. Organometallics
1999, 18, 1801.
(29) Ceder, R. M.; Sales, J . J . Organomet. Chem. 1985, 294, 389.

C-H Activation Induced by Water
Organometallics, Vol. 19, No. 7, 2000 1357
Sch em e 4
Sch em e 5
F igu r e 1. Crystal structure of 6 (50% thermal ellipsoids).
F igu r e 2. 1H NMR spectrum of 4 in dmf.
of 4 in dmso were hampered by the reaction of 4 with
the dmso to give 3. We have now ascertained that, by
using dry dmso and a minimum of heat to assist
dissolution, an NMR spectrum, relatively uncontami-
nated by 3, can be obtained in dmso. One crucial
difference between this spectrum and that of 4 in dmf
is the presence of a dmso coordinated to platinum (Pt
satellites on the signal), implying that the dmso has
split the dimer to give the dmso complex 8 (Scheme 4).
Similar behavior is observed when dimer 6 is dissolved
in CDCl3 and dmso is added (Scheme 5). The cleavage
of 6 to give dmso complex 10 is relatively slow at room
temperature (taking about an hour to go to completion).
The coordinated dmso molecules in 8 and 10 have
similar spectroscopic properties: the chemical shift of
the dmso protons in CDCl3 are 3.44 and 3.43 ppm,
respectively (both with 3J (Pt-H) ) 23 Hz). These are
comparable with the 26 Hz couplings observed in the
C∧N∧C compounds 3 and 7, implying that the dmso is
trans to the pyridine: we would expect these values to
be on the order of 15 Hz if the dmso were cis to the N
(and therefore trans to a C).30,31 On this basis, together
with the modeling studies and the information we can
(30) Eaborn, C.; Kundu, K.; Pidcock, A. J . Chem. Soc., Dalton Trans.
1981, 933.

1358 Organometallics, Vol. 19, No. 7, 2000
Cave et al.
infer from carbonyl complexes 9 and 11 we have
assigned the geometry as that with the dmso trans to
the pyridine N (thus the chloride is cis to the N). No
spectroscopic evidence for the formation of more than
one isomer of either of the dmso complexes 8 or 10 was
observed by NMR or IR, even when the cleavage was
performed at -40 °C.
Conventional arguments based on trans effects would
suggest that each of the compounds 8, 9, 10, or 11,
formed by dimer cleavage, should form with the ligand
coming in trans to the C and cis to the N (indeed, in
the crystal structure of 6 it is very clear that this Pt-
Cl bond is significantly longer than the other one).36
This is what we believe we observe when we use the
mild conditions of a CO atmosphere with a room-
temperature solution of the chloride-bridged dimers 4
and 6 to form 9t and 11t. (Quite how large this trans
effect is in cyclometalated complexes has been the
subject of some debate recently,32,37-39 and we do not
propose to discuss it further here.) However, it is
apparent from our modeling studies (see later) that
these isomers (the kinetic products) with the CO cis to
the N are unfavorable with respect to those with the
chloride cis to the N (the thermodynamic products).
Thus we would expect 9t and 11t to isomerize to 9c and
11c, respectively. When we use dmso as the ligand, we
might expect the energy difference between the isomers
of 8 and 10 to be even greater than in the analogous
CO complexes. Thus the fact that we do not observe the
isomer with the dmso cis to the N could be due to the
very unfavorable nature of this isomer with respect to
the other: as soon as any formed, it could be expected
to isomerize and therefore would not be observed by
NMR. (Additionally, since the dmso would be less
strongly bound than the CO, it would also find it easier
to isomerize via a dissociative mechanism.) Alterna-
tively, the steric constraints posed by the noncyclo-
metalated phenyl ring could render bridge cleavage
trans to the C so energetically unfavorable that none is
ever formed. In any event, once the geometry in 8 and
10 is established with the chloride cis to the N,
displacement of dmso with CO gas gives compounds 9c
and 11c exclusively.
Similar compounds have been reported: thus when
the cyclometalated phenyl pyridine compound 12 is
reacted with either more phenyl pyridine or CO, the
only complexes isolated have the new ligand trans to
the N (Scheme 6), evidence being in the form of crystal
structures of 13 and 14.40
Dicyclom eta la tion . The reactions of dmso complex
8 to give doubly cyclometalated 3 and of 10 to give 7
are quantitative. The reactions progress slowly in dry
dmso at room temperature, but can be brought to
completion in less than 5 min by adding water or base
(solid Na2CO3) to a hot dmso solution of the appropriate
starting material (Scheme 7). The reactions of carbonyl
compounds 9 to form 15 and of 11 to form 16 also
proceed in high yield, in either dmf or dmso solution
(Scheme 7). Doubly cyclometalated compound 15 has
been fully characterized: the 1H NMR spectrum is
shown (Figure 3), as is the single-crystal X-ray structure
(Figure 4). It should be noted that the reactions of 9
and 11 to form 15 and 16 do not need a CO atmosphere.
Different behavior is observed when CO is used as a
ligand. If a dmf solution of chloride-bridged dimer 4 is
exposed to CO gas, the color of the solution changes
rapidly (<5 s) to a much paler yellow, the NMR
spectrum changes significantly (but maintains the same
number of signals, with the same coupling patterns),
and an IR stretching band appears at 2088 cm-1
,
indicating the formation of a compound consistent with
the formulation 9t (Scheme 4). Compound 9t isomerizes
to another compound, consistent with the formulation
9c (Scheme 4). This isomerization is very clear by NMR,
where signals move by up to 0.8 ppm, but less obvious
by IR, where a difference of only 6 cm-1 is observed.
The isomerization of 9t to 9c is apparent after 30 min
at room temperature, halfway after 2.5 h, and complete
after 15 h. Addition of CO gas to a solution of 8 results
in the rapid formation of 9c: as soon as the spectrum
could be run (less than 2 min later), only peaks corre-
sponding to 9c were seen in the NMR.
Similar behavior is seen when we start with dimer 6:
the reaction of 6 to give 11t in CDCl3 is very fast, being
complete as soon it was possible to obtain an NMR, and
the isomerization of 11t to 11c in chloroform is obvious
by NMR (halfway by about 3 h and complete in less than
16 h) (Scheme 5). The isomerization of 11t to 11c, and
that of 9t to 9c, occurs with solutions that have been
purged with nitrogen. Together with the independence
of the isomerization rate upon concentration, and the
observation of isomerization in CD2Cl2 (no HCl present)
at a rate similar to that observed in CDCl3 (potential
contamination with traces of HCl), we can rule out the
associative ligand exchange type of reaction that can
occur with platinum being responsible for the isomer-
ization.32,33 This leaves a dissociative mechanism as the
likely route.34,35 Addition of 4 equivalents of tetrabutyl-
ammonim chloride to a chloroform solution of 11t ef-
fectively suppressed the isomerization to 11c, implying
that chloride dissociation is responsible for the isomer-
ization process. Dissolution of dimer 6 in CDCl3, fol-
lowed by addition of dmso, indicates that the cleavage
of 6 to give 10 is relatively slow (taking about an hour
to go to completion at room temperature), but the
reaction of 10 to give 11c is very fast, being complete
as soon as it was possible to obtain an NMR (less than
2 min later). The slow rate of cleavage by dmso could
be due to the sterically larger dmso molecule finding it
more difficult to approach the platinum, or it could be
due to the dmso complex being less thermodynamically
stable than the CO complex, or indeed a combination
of both factors.
(36) Ryabov, A. D.; Kuz’mina, L. G.; Polyakov, V. A.; Kazankov, G.
M.; Ryabova, E. S.; Pfeffer, M.; van Eldik, R. J . Chem. Soc., Dalton
Trans. 1995, 999.
(37) Elding, L. I.; Romeo, R. J . Chem. Soc., Dalton Trans. 1996,
1471.
(38) Schmu¨lling, M.; Ryabov, A. D.; van Eldik, R. J . Chem. Soc.,
Dalton Trans. 1996, 1472.
(39) Wendt, O. F.; Oskarsson, Å.; Leipoldt, J . G.; Elding, L. I. Inorg.
Chem. 1997, 36, 4514.
(31) Romeo, R.; Scolaro, L. M.; Nastasi, N.; Mann, B. E.; Bruno, G.;
Nicolo`, F. Inorg. Chem. 1996, 35, 7691.
(32) Schmu¨lling, M.; Ryabov, A. D.; van Eldik, R. J . Chem. Soc.,
Dalton Trans. 1994, 1257.
(33) Schmu¨lling, M.; Grove, D. M.; van Koten, G.; van Eldik, R.;
Veldman, N.; Spek, A. L. Organometallics 1996, 15, 1384.
(34) Romeo, R. Comments Inorg. Chem. 1990, 11, 21.
(35) Alibrandi, G.; Scolaro, L. M.; Romeo, R. Inorg. Chem. 1991, 30,
4007.
(40) Mdleleni, M. M.; Bridgewater, J . S.; Watts, R. J .; Ford, P. C.
Inorg. Chem. 1995, 34, 2334.

C-H Activation Induced by Water
Organometallics, Vol. 19, No. 7, 2000 1359
Sch em e 6
F igu r e 3. 1H NMR spectrum of 15 in dmso.
Sch em e 7
F igu r e 4. Crystal structure of 15 (50% thermal ellipsoids).
all these solvents an increase in the reaction rate is
observed with the addition of water and/or base. A
dependence of the rate of cycloplatination on solvent has
been observed before: when cis-PtCl2(dmso)2 is reacted
with tertiary ferrocenylamines in chloroform or acetone,
a simple ligand substitution reaction is observed, whereas
heating in methanol or water results in high yields of
the cycloplatinated product.41 In this instance a possible
reaction route involving the dissociation of chloride was
invoked, in contrast to reactions where a formal oxida-
tive addition takes place.42 Our modeling studies (see
later) indicate that a possible driving force for the
cycloplatination is the elimination of HCl, which, cru-
cially in our case, must subsequently be ionized. This
need for the HCl to be ionized fits with our experimen-
tally observed reaction rates and in particular the
dependence on the presence of water.
The rate of reaction of dmso complex 8 to 3 is
significantly slower than the rate of reaction of carbonyl
9 to 15 under identical conditions (including using the
same batch of dmso as solvent): the first reaction took
5 days to go to completion, whereas the second one took
14 h. Such a variation provides evidence to suggest that
the second cyclometalation takes place via an electro-
philic attack by the platinum: we would expect the CO
ligand to be acting as a much better acceptor than dmso,
giving rise to a reduced electron density on the Pt. The
dissociation of chloride prior to an electrophilic type
mechanism has been postulated41,43 and would seem to
be likely in our case, given our analogous dependence
Indeed a CO atmosphere results in reduction of some
of the species; hence these reactions are purged of CO
with either nitrogen or argon.
The question of which isomer of 9 and 11 is reacting
arises. The reaction of 9c to give doubly cyclometalated
15 in dmso is complete in about 3 h at room tempera-
ture, but is speeded up dramatically by the addition of
base (if solid Na2CO3 is added, the reaction is complete
in less than 15 min) or by the application of heat
(reaction is complete after 20 min at 100 °C). The
reaction of 9t in dmf gives 15 on a similar time scale;
again heating and the addition of base increase the rate
of reaction. However, since 9t is isomerising to 9c, it is
impossible to definitively say whether it is 9t or 9c that
is reacting to form 15. We know that the isomerization
reaction of 11t to 11c in CDCl3 is much faster than the
reaction of 11c to give 16 in CDCl3, which appears to
be very slow (no observable reaction after one week).
Since we can then react pure 11c to give 16 (by adding
base) at a rate comparable to that of mixed isomers of
11, we would suggest that it is indeed the isomers 9c
and 11c that react to give 15 and 16.
The rate of the second cyclometalation is clearly
dependent on solvent and the presence of water and
base. There is no observable reaction of 11c to give
C∧N∧C 16 in the nonpolar chloroform, but a relatively
fast reaction in the polar solvents dmf and dmso. With
(41) Ranatunge-Bandarage, P. R. R.; Robinson, B. H.; Simpson, J .
Organometallics 1994, 13, 500.
(42) Harper, T. G. P.; Desrosiers, P. J .; Flood, T. C. Organometallics
1990, 9, 2523.
(43) Bednarski, P. J .; Ehrensperger, E.; Scho¨nenberger, H.; Burge-
meister, T. Inorg. Chem. 1991, 30, 3015.

1360 Organometallics, Vol. 19, No. 7, 2000
Cave et al.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in th e Cr ysta l Str u ctu r e of 6
Sch em e 8
Pt(1)-C(1)
Pt(1)-N(1)
Pt(1)-Cl(2)
Pt(1)-Cl(1)
Pt(2)-C(36)
Pt(2)-N(2)
Pt(2)-Cl(1)
1.98(3)
Pt(2)-Cl(2)
N(1)-C(7)
N(2)-C(42)
C(1)-C(6)
2.468(8)
1.26(3)
1.32(3)
1.38(3)
1.53(3)
1.42(3)
1.50(3)
2.078(18)
2.339(7)
2.460(7)
1.96(2)
2.07(2)
2.312(6)
C(6)-C(7)
C(36)-C(41)
C(41)-C(42)
C(1)-Pt(1)-N(1)
C(1)-Pt(1)-Cl(2)
80.7(10)
93.5(9)
Pt(2)-Cl(1)-Pt(1)
C(7)-N(1)-C(11)
C(7)-N(1)-Pt(1)
C(11)-N(1)-Pt(1)
99.1(2)
119(2)
113.2(17)
127.3(15)
of reaction rate on solvent. Addition of AgBF4 to a
solution of 11c in acetone under conditions that have
been used to induce cyclometalations44 results in the
rapid formation of C∧N∧C 16 in good yield, providing
further evidence for the elimination of HCl being a
driving force for the reaction.
N(1)-Pt(1)-Cl(2) 173.5(6)
C(1)-Pt(1)-Cl(1) 171.0(9)
N(1)-Pt(1)-Cl(1) 104.4(5)
C(42)-N(2)-C(46) 121(2)
Cl(2)-Pt(1)-Cl(1)
C(36)-Pt(2)-N(2)
80.9(2)
78.9(9)
C(42)-N(2)-Pt(2)
C(46)-N(2)-Pt(2)
C(6)-C(1)-Pt(1)
C(1)-C(6)-C(7)
N(1)-C(7)-C(6)
C(41)-C(36)-Pt(2) 119.0(17)
C(36)-C(41)-C(42) 108(2)
N(2)-C(42)-C(41) 118(2)
111.9(16)
126.1(17)
116(2)
111(3)
117(2)
C(36)-Pt(2)-Cl(1) 97.0(7)
N(2)-Pt(2)-Cl(1) 174.8(7)
C(36)-Pt(2)-Cl(2) 175.4(8)
N(2)-Pt(2)-Cl(2) 102.6(6)
That our second cyclometalation requires different
conditions from the first is evident, unlike other ex-
amples.45 Whether our second cyclometalation takes
place via a mechanistically different reaction route is
less clear. Our first cyclometalation occurs in high yields
in acetic acid under conditions that parallel those
reported in the synthesis of chloride-bridged dimer 12
(Scheme 2).40 Prolonged reaction times under these
conditions do not result in a second cyclometalation,
even when we use 2 equiv of 2-phenylpyridine, where
we might have expected to make 18.46 The only reported
conditions for the synthesis of compounds such as 18
entail the use of 2 equiv of lithiated phenyl pyridine
(Scheme 8),47 and while this method has been used
successfully with a variety of pyridine derivatives,48-51
it resulted in only very poor yields of 3 from 1 (due to
the nonregiospecific nature of the second lithiation).52
Thus it appears that the different reaction conditions
that we need for the first and second cyclometalations
in the synthesis of compounds such as 3 cannot be
attributed to steric crowding or unfavorable distortions
within the C∧N∧C platinum moiety: they must be due
to either the changed properties of the metal affecting
the rate of reaction substantially or the changed nature
of the metal, requiring a mechanistically different
reaction route. Since we also know that a first cyclo-
metalation will not occur under the conditions required
for the second one, this would suggest that the two
cyclometalations have different mechanisms. Even
though we are presenting evidence here that our second
cyclometalation arises through electrophilic attack by
platinum, the mechanism of our first cyclometalation
is unknown,2,53 and thus we cannot say for certain that
the two metalations take place via mechanistically
different routes.
Cl(1)-Pt(2)-Cl(2)
Pt(1)-Cl(2)-Pt(2)
81.2(2)
98.2(2)
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in th e Cr ysta l Str u ctu r e of 15
n ) 1
n ) 2
Pt(n)-C(n)18
Pt(n)-N(n)1
1.864(11)
2.027(7)
2.057(9)
1.837(10)
2.003(7)
2.084(9)
Pt(n)-C(n)01
Pt(n)-C(n)17
N(n)1-C(n)07
N(n)1-C(n)11
C(n)01-C(n)06
C(n)06-C(n)07
C(n)07-C(n)08
C(n)08-C(n)09
C(n)09-C(n)10
C(n)10-C(n)11
C(n)11-C(n)12
C(n)12-C(n)17
2.083(8)
2.084(10)
1.370(10)
1.361(11)
1.401(13)
1.446(13)
1.419(13)
1.383(13)
1.359(12)
1.398(12)
1.453(11)
1.395(12)
1.329(10)
1.352(10)
1.409(12)
1.491(11)
1.407(13)
1.384(12)
1.381(13)
1.375(13)
1.459(13)
1.421(12)
C(n)18-Pt(n)-N(n)1
C(n)18-Pt(n)-C(n)01
N(n)1-Pt(n)-C(n)01
C(n)18-Pt(n)-C(n)17
N(n)1-Pt(n)-C(n)17
C(n)01-Pt(n)-C(n)17
C(n)07-N(n)1-C(n)11
C(n)07-N(n)1-Pt(n)
C(n)11-N(n)1-Pt(n)
C(n)06-C(n)01-Pt(n)
C(n)01-C(n)06-C(n)07
N(n)1-C(n)07-C(n)06
N(n)1-C(n)11-C(n)12
C(n)17-C(n)12-C(n)11
C(n)12-C(n)17-Pt(n)
179.4(4)
100.4(4)
80.2(3)
99.4(4)
80.0(3)
160.2(4)
124.0(8)
117.6(6)
118.3(6)
113.0(6)
114.9(8)
114.2(8)
112.9(8)
117.6(7)
111.1(6)
179.5(4)
99.7(4)
80.0(3)
100.2(4)
80.1(3)
160.0(4)
123.5(8)
118.5(5)
117.9(6)
111.6(7)
116.7(8)
113.6(8)
112.1(8)
118.2(8)
111.0(6)
9t, and 15, to arrive at relative ground-state energies.
A series of unconstrained geometry optimizations were
carried out for the C∧N∧C complex 15 to determine the
optimal combination of Pt frozen core size and func-
tional. Both Pt[4f] and Pt[5p] were considered in con-
junction with the Becke/Perdew (BP) gradient-corrected
functional or the local density approximation (LDA).
Scalar relativistic corrections were included throughout.
The optimized Pt-L distances are shown in Table 3.
The effect of the frozen core and functional on the Pt-
CO distance is minimal, but there are significant
variations in the calculated Pt-C and Pt-N distances.
With the ADF program, the best combination is the
simple LDA and the larger Pt frozen core. This result
parallels our previous findings54 inasmuch as the LDA-
optimized metal-ligand distances are in better agree-
ment with experiment than those obtained from a
Th eor etica l Stu d ies. We have performed density
functional theory (DFT) calculations on compounds 9c,
(44) Avshu, A.; O’Sullivan, R. D.; Parkins, A. W.; Alcock, N. W.;
Countryman, R. M. J . Chem. Soc., Dalton Trans. 1983, 1619.
(45) van der Boom, M. E.; Liou, S.-Y.; Shimon, L. J .; Ben-David, Y.;
Milstein, D. Organometallics 1996, 15, 2562.
(46) Cave, G. W. V.; Rourke, J . P. Unpublished results.
(47) Chassot, L.; Muller, E.; von Zelewsky, A. Inorg. Chem. 1984,
23, 4249.
(48) Chassot, L.; von Zelewsky, A. Inorg. Chem. 1987, 26, 2814.
(49) Deuschel-Cornioley, C.; Stoeckli-Evans, H.; von Zelewsky, A.
J . Chem. Soc., Chem. Commun. 1990, 121.
(50) J olliet, P.; Gianini, M.; von Zelewsky, A.; Bernardinelli, G.;
Stoeckli-Evans, H. Inorg. Chem. 1996, 35, 4883.
(51) Gianini, M.; Forster, A.; Haag, P.; von Zelewsky, A.; Stoeckli-
Evans, H. Inorg. Chem. 1996, 35, 4889.
(52) Cornioley-Deuschel, C.; Ward, T.; von Zelewsky, A. Helv. Chim.
Acta 1988, 71, 130.
(53) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879.

C-H Activation Induced by Water
Organometallics, Vol. 19, No. 7, 2000 1361
Ta ble 3. Selected Bon d Len gth s (Å) in th e
Str u ctu r e of 15
method
Pt-CO
Pt-C
Pt-N
Pt[4f]/BP
1.85
1.88
1.86
1.864
2.00
2.12
2.09
2.070
1.95
2.07
2.04
2.027
Pt[5p]/BP
Pt[5p]/LDA
experiment
gradient-corrected functional. However, we have also
demonstrated that the LDA gives poorer energies.55
Thus, the optimal theoretical methodology for the
present systems is to optimize the structure at the LDA/
Pt[5p] level and to compute the total binding energy at
this geometry using the BP functional.
The optimized structures of 9c and 9t are shown in
Figure 5. In both cases, the uncoordinated phenyl ring
is not perpendicular to the coordination plane. The steric
interactions between this group and the ligand directed
toward it cause the phenyl ring to rotate and the Pt
coordination geometry to distort away from strict pla-
narity. The calculated binding energies show that 9c is
16 kJ mol-1 lower in energy than 9t. This energy
difference allows us to rationalize 9t as the kinetic
product and 9c as the thermodynamic product in
Scheme 4 and is in agreement with the experimentally
observed isomerization of 9t to 9c. We expect the energy
difference between 11c and 11t to be similar in mag-
nitude and, hence, would expect that 11t is the kinetic
product and 11c the thermodynamic product in Scheme
5.
F igu r e 5. Optimized structures of 9t and 9c.
rable to those observed in the crystal structure of 13.40
There are no significant intermolecular interactions in
the structure of 6, and all other bond lengths and angles
are normal: selected bond lengths and angles are listed
in Table 1.
The same calculations indicate that 15 is 68 kJ mol-1
higher in energy than 9c, implying that the reactions
in Scheme 7 are endothermic. However, it must be noted
that the calculations assume that the other product of
the reaction (HCl) is free and not solvated or ionized.
The ionization of HCl in water is known to be exother-
mic by 74.8 kJ mol-1, with the neutralization of the
The structure of 15 has two essentially identical
molecules in the asymmetric unit. These molecules are
flat, with an rms deviation from the plane of 0.0368 and
0.0499 Å, and are inclined at 1.87(8)° to each other with
no significant interactions between them. Selected bond
lengths and angles are listed in Table 2. The two five-
membered cyclometalated rings, fused along the Pt-N
bond, have bond lengths similar to those observed in
the monocyclometalated compounds 6 and 13. A sig-
nificant difference is observed in the angles at the
pyridine nitrogen: these are 117.6(6)°, 118.5(5)°, 118.3-
(6)°, and 117.9(6)° inside the cyclometalated rings and
124.0(8)° and 123.5(8)° inside the pyridine. Thus, whereas
in the monocyclometalated compounds 6 and 13 the
pyridine ring has been distorted by the cyclometalation
with the pyridine being “pulled over” by the five-
membered ring, in the dicyclometalated compound 15
the ring has been “pulled” back to a more symmetrical
arrangement. All the bond lengths and angles observed
in the structure of 15 are similar to those seen in the
X-ray structure of 3.28 It is salient to note that in both
cases it is the more flexible six-membered pyridine ring,
rather than the five-membered metalated ring, that is
distorted the most. This type of distortion has been
noted previously in N∧N∧C complexes of Pd and
Pt.27,57,58
liberated proton generating a further 55.8 kJ mol-1 56
.
These quantities of energy are more than sufficient to
drive the reaction. This result ties in with our experi-
mentally observed dependence of the rate of reaction
on solvent polarity: 11c does not react to form 16 in
CDCl3 unless water and/or base is present, and the
reactions of 9c to 15 in either dmf or dmso are speeded
up dramatically by the addition of water or base.
Cr ysta l Str u ctu r es. The single-crystal X-ray struc-
ture of dimer 6 and C∧N∧C 15 were solved (Figures 1
and 4). The structure of 6 has a central core consisting
of a Pt2Cl2 rectangle, with Cl-Pt-Cl angles of 81.2(2)°
and 80.9(2)° and Pt-Cl-Pt angles of 99.1(2)° and 98.2-
(2)°. Within this rectangle the Pt-Cl bonds are 2.460-
(7) and 2.468(8) Å for the chlorines trans to the
cyclometalated carbon and 2.312(6) and 2.339(7) Å for
the chlorines trans to the pyridine N. This difference is
to be expected on the basis of the relative trans effects
of C and N. Of particular interest is the five-membered
cyclometalated ring: here there are Pt-N distances of
2.078(18) and 2.07(2) Å, Pt-C distances of 1.96(2) and
1.98(3) Å, and an N-Pt-C angle of 80.7(10)° and 78.9-
(9)°. Bond lengths and angles of this order are compa-
Con clu sion s
We have shown that the monocycloplatinated chloride-
bridged dimers of diphenylpyridines can be reacted to
(54) Bray, M. R.; Deeth, R. J .; Paget, V. J .; Sheen, P. D. Int. J .
Quantum Chem. 1997, 61, 85.
(55) Deeth, R. J .; J enkins, H. D. B. J . Phys. Chem. 1997, 101, 4793.
(56) Handbook of Chemistry and Physics, 59th ed.; CRC Press: Boca
Raton, FL, 1978.
(57) Neve, F.; Ghedini, M.; Crispini, A. Chem. Commun. 1996, 2463.
(58) Neve, F.; Crispini, A.; Campagna, S. Inorg. Chem. 1997, 36,
6150.

1362 Organometallics, Vol. 19, No. 7, 2000
Cave et al.
3
3
4
t, J ) 7.6 Hz, central pyridine), 8.10 (2H, dd, J ) 7.6, J )
1.1 Hz, pyridine, metalated side), 7.95 (4H, m, unmetalated
phenyl ring), 7.86 (2H, dd, 3J ) 7.8, 4J ) 1.2 Hz, phenyl, ortho
to Pt), 7.71 (2H, dd, 3J ) 7.8, 4J ) 1.2 Hz, phenyl ortho to
pyridine), 7.56 (6H, m, unmetalated phenyl ring), 7.54 (2H,
dd, 3J ) 7.6, 4J ) 1.1 Hz, pyridine, unmetalated side), 7.11
form dicycloplatinated C∧N∧C complexes if they are
first cleaved by ligands to give monomeric species. When
CO is used as a ligand, the monomeric species formed
is a kinetic product with the incoming CO cis to the
pyridine N, and this then isomerizes so that the CO is
trans to the N. Modeling studies show that the isomer
with the CO cis to the N is 16 kJ mol-1 less stable than
the isomer with the CO trans to the N, fitting in with
our observed isomerization. We have ruled out an
associative mechanism for this isomerization and have
evidence that suggests chloride dissociation is impli-
cated in the isomerization process. When dmso is used
to split the dimers, the only product observed is the
thermodynamic product with the dmso trans to the N.
The reaction of monocycloplatinated complexes to
form the dicycloplatinated complexes is very dependent
on solvent and the presence of water and base. Our
modeling studies indicate that with the simple 2,6-
diphenylpyridine the reaction is endothermic unless the
HCl byproduct is ionized. This leads to the situation
whereby the second cyclometalation can be induced by
the simple expedient of adding water. The dependence
of the rate of reaction of the second cyclometalation on
solvent and ligand also indicates that it is taking place
via an electrophilic attack by platinum on the aromatic
ring, in contrast to the first cyclometalation, where the
mechanism is unclear. However, we are confident the
very different conditions required for the two cyclo-
metalations indicate two mechanistically different steps.
Thus we would suggest that other workers trying to
synthesize analogous complexes should treat the two
cyclometalation steps separately and adjust their condi-
tions accordingly.
3
4
(2H, dd, J ) 7.3, J ) 1.2 Hz, phenyl para to Pt), 7.05 (2H,
dd, J ) 7.3, J ) 1.2 Hz, phenyl meta to Pt).
3
4
Syn th esis of [(4-(4-Octyloxyp h en yl)-2,6-d ip h p yP tCl)2]
(6). Potassium tetrachloroplatinate (187 mg, 0.450 mmol) was
added to a solution of 4-(4-octyloxyphenyl)-2,6-diphenylpyri-
dine (218 mg, 0.500 mmol) in glacial acetic acid (250 mL). The
reaction was stirred at 80 °C until the red platinum salt was
no longer visible (3 days). The reaction mixture was filtered,
yielding the product as a yellow powder, which was washed
with water, acetone, and ether. Yield: 289 mg (97%, 0.217
mmol). Anal. Found (expected): C 55.6 (56.0), H 5.2 (4.85), N
2.0 (2.1). NMR δH (400 MHz, CDCl3): 7.85 (4H, m, unmeta-
lated phenyl), 7.72 (2H, d, 4J ) 2.4 Hz, pyridine, metalated
side), 7.65 (4H, AA′XX′, phenyl, meta to OC8H17 chain), 7.51
3
4
(6H, m, unmetalated phenyl), 7.41 (2H, dd, J ) 7.6, J ) 1.2
Hz, phenyl meta to Pt, ortho to pyridine), 7.35 (2H, d, 4J )
2.4 Hz, pyridine, unmetalated side), 7.06 (2H, dt, 3J ) 7.6,
4J ) 1.2 Hz, phenyl para to Pt), 7.0 (6H, m, phenyl meta to
Pt, para to pyridine and phenyl ortho to OC8H17 chain), 6.93
(2H, dd, 3J ) 7.6, 4J ) 1.2, 3J (Pt-H) ) 35.3 Hz, phenyl, ortho
to Pt), 4.03 (4H, t, 3J ) 6.4 Hz, OCH2), 1.80 (4H, m, OCH2CH2),
3
1.51 (20H, m, chain), 0.91 (6H, t, J ) 7.0 Hz, CH3). NMR δC
(75.4 MHz, CDCl3): 178.1, 162.1, 161.3, 150.0, 145.0, 139.9,
132.4, 130.2, 130.0, 129.2, 128.9, 128.7, 124.2, 124.0, 121.3,
115.7, 113.9, 68.7, 32.2, 32.0, 29.8, 29.6, 26.4, 23.1, 14.5.
X-r a y Cr ysta llogr a p h ic Stu d y of 6. Crystals suitable for
structural analysis were grown from chloroform. A yellow
prism (dimensions 0.26 × 0.04 × 0.04 mm) was mounted with
oil on a thin quartz fiber. Data were collected at 180(2) K using
a Siemens SMART CCD area detector diffractometer. Crystal
data for 6: C62H64N2O2Pt2, M ) 1330.23, orthorhombic, space
group P2(1)2(1)2, a ) 20.8902(15) Å, b ) 34.532(2) Å, c )
7.5473(6) Å, U ) 5444.5(7) Å3, Z ) 4, D(calcd) ) 1.623 Mg/m3.
Refinement was by full-matrix least-squares on F2 for 7562
reflections using SHELXL-97.60 Hydrogen atoms were added
at calculated positions and refined using a riding model with
freely rotating methyl groups. Anisotropic displacement pa-
rameters were used for all non-H atoms; H atoms were given
isotropic displacement parameters equal to 1.2 (or 1.5 for
methyl hydrogen atoms) times the equivalent isotropic dis-
placement parameter of the atom to which the H atom is
attached. The weighting scheme was calculated using w )
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All chemicals were used as
supplied, unless noted otherwise. All NMR spectra were
obtained on either a Bruker Avance 300 or Avance 400 and
are referenced to external TMS, assignments being made with
the use of decoupling and the DEPT, COSY, and GOESY pulse
sequences. All elemental analyses were performed by Warwick
Analytical Service. 2,6-Diphenylpyridine was used as supplied
(Lancaster), and 4-(4-octyloxyphenyl)-2,6-diphenylpyridine syn-
thesized via a standard Kro¨hnke route.59
Syn th esis of [(2,6-d ip h p y)P t(d m so)] (3). The yellow (2,6-
diphpyPtCl)2 produced below (407 mg, 0.441 mol) was dis-
solved in hot dmso (1 mL), allowed to cool, and precipitated
with water (1 mL) to give a yellow crystalline product. Yield:
441 mg (99%, 0.880 mmol). Anal. Found (expected): C 45.0
(45.4), H 3.4 (3.4), N 2.8 (2.8). NMR δH (400 MHz, CDCl3): 7.80
1/[σ2(Fo2) + (0.0962P)2], where P ) (Fo + 2Fc2)/3. Goodness-
2
of-fit on F2 was 1.004, R1[I > 2σ(I)] ) 0.0823, wR2 ) 0.2016.
Data/restraints/parameters 7562/8/532. Largest difference
Fourier peak and hole 2.768 and -2.620 e Å-3; the only large
peaks are near the Pt atoms. The Flack parameter was
determined as 0.49(2); thus the absolute structure could not
be determined reliably. Selected bond lengths and angles are
listed in Table 1.
3
4
3
(2H, dd, J ) 7.6, J ) 1.2, J (Pt-H) 24 Hz, phenyl ortho to
3
Pt), 7.62 (1H, t, J ) 7.3 Hz, central pyridine), 7.47 (2H, dd,
3J ) 7.6, J ) 1.2 Hz, phenyl ortho to pyridine, meta to Pt),
4
Syn th esis of [4-(4-Octyloxyp h en yl)-2,6-d ip h p yP t(d m -
so)] (7). (4-(4-Octyloxyphenyl)-2,6-diphpyPtCl)2 (120 mg, 0.0902
mol) was dissolved in hot dmso (1 mL), allowed to cool, and
precipitated with water (1 mL) to give a yellow crystalline
product. Yield: 121 mg (95%, 0.171 mmol). Anal. Found
(expected): C 56.3 (56.1), H 5.5 (5.3), N 2.3 (2.0). NMR δH (300
MHz, CDCl3): 7.84 (2H, dd, 3J ) 7.8, 4J ) 1.7, 3J (Pt-H) )
34.8 Hz, phenyl ortho to Pt), 7.68 (2H, AA′XX′, phenyl, meta
to OC8H17 chain), 7.58 (2H, dd, J ) 7.8, J ) 1.7 Hz, phenyl
ortho to pyridine, meta to Pt), 7.48 (2H, s, pyridine), 7.31 (2H,
dt, 3J ) 7.8, 4J ) 1.7 Hz, phenyl meta to Pt), 7.15 (2H, dt,
3J ) 7.8, 4J ) 1.7 Hz, phenyl para to Pt), 7.05 (2H, AA′XX′,
7.30 (2H, d, 3J ) 7.3 Hz, pyridine), 7.28 (2H, td, 3J ) 7.6,
4J ) 1.2 Hz, phenyl), 7.21 (2H, td, 3J ) 7.6, 4J ) 1.2 Hz,
3
phenyl), 3.68 (6H, s, J (Pt-H) ) 26.8 Hz, dmso).
Syn th esis of [(2,6-d ip h p yP tCl)2] (4). Potassium tetra-
chloroplatinate (374 mg, 0.900 mmol) was added to a solution
of 2,6-diphenylpyridine (233 mg, 1.00 mmol) in glacial acetic
acid (250 mL). The reaction was stirred at 80 °C until the red
platinum salt was no longer visible (3 days). The reaction
mixture was filtered, yielding the product as a yellow powder,
which was washed with water, acetone, and ether. Yield: 407
mg (98%, 0.441 mmol). Anal. Found (expected): C 43.7 (44.2),
H 2.6 (2.6), N 3.0 (3.0). NMR δH (400 MHz, d7-dmf) 8.22 (2H,
3
4
(60) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; University of Go¨ttingen: Germany, 1997.
(59) Kro¨hnke, F. Synthesis 1976, 1.

C-H Activation Induced by Water
Organometallics, Vol. 19, No. 7, 2000 1363
3
phenyl, ortho to OC8H17 chain), 4.05 (2H, t, 3J ) 7.5 Hz, OCH2),
3.61 (6H, s, 3J (Pt-H) ) 26.3 Hz, dmso), 1.84 (2H, m,
OCH2CH2), 1.32 (10H, m, (CH2)5), 0.89 (3H, t, 3J ) 7.2 Hz,
CH3). NMR δC (75.4 MHz, CDCl3): 165.6, 165.1, 159.9, 152.1,
148.8, 135.2, 129.6, 128.6, 127.4, 123.8, 123.3, 114.0, 111.6,
67.2, 47.3, 30.8, 28.6, 28.3, 28.2, 25.0, 21.6, 13.1.
t, J ) 6.4 Hz, OCH2), 1.80 (2H, m, OCH2CH2), 1.51 (10H, m,
chain), 0.91 (3H, t, 3J ) 7.0 Hz, CH3). FT-IR: ν(CtO) 2097
cm-1 (CDCl3).
Cis Isom er 11c. Carbon monoxide gas was bubbled through
a solution of [(4-(4-octyloxyphenyl)-2,6-diphpy)PtCl(dmso)] (10)
in either dmso or chloroform. The compound was not isolated.
NMR δH (400 MHz, CDCl3): 7.97 (1H, d, 4J ) 2.4 Hz, pyridine),
7.78 (2H, m, unmetalated phenyl), 7.75 (1H, dd, 3J ) 8.0,
4J ) 1.4, phenyl, metalated ring), 7.74 (2H, AA′XX′, phenyl,
meta to OC8H17 chain), 7.60 (1H, d, 4J ) 2.4 Hz, pyridine),7.56
Syn th esis of [(2,6-d ip h p y)P t(Cl)(d m so)] (8). [((2,6-diph-
py)PtCl)2] (4) was dissolved in dmso. The compound was not
isolated. NMR δH (400 MHz, d6-dmso): 8.20 (3H, m, central
pyridine, pyridine on metalated side, phenyl ortho to Pt), 7.96
3
4
3
4
(2H, m, unmetalated phenyl), 7.84 (1H, dd, J ) 9.0, J ) 1.4
(1H, dd, J ) 8.0, J ) 1.4 Hz, phenyl, metalated ring), 7.53
3 4
3
Hz, phenyl meta to Pt, ortho to pyridine), 7.72 (1H, dd, J )
(3H, m, unmetalated phenyl), 7.28 (1H, dt, J ) 8.0, J ) 1.4
Hz, phenyl, metalated ring), 7.17 (1H, dt, 3J ) 8.0, 4J ) 1.4
Hz, phenyl, metalated ring), 7.06 (2H, AA′XX′, phenyl ortho
6.2, 4J ) 2.8 Hz, pyridine, unmetalated side), 7.48 (3H, m,
unmetalated phenyl), 7.23 (1H, dt, 3J ) 9.0, 4J ) 1.4 Hz,
3
4
3
phenyl para to Pt), 7.14 (1H, dt, J ) 9.0, J ) 1.4 Hz, phenyl
meta to Pt, para to pyridine). NMR δH (CDCl3): 3.38 (6H, s,
3J (Pt-H) ) 24 Hz, dmso, note: from a DMF solution spec-
trum).
to OC8H17 chain), 4.04 (2H, t, J ) 6.4 Hz, OCH2), 1.80 (2H,
3
m, OCH2CH2), 1.51 (10H, m, chain), 0.91 (3H, t, J ) 7.0 Hz,
CH3). FT-IR: ν(CtO) 2103 cm-1 (CDCl3).
Syn th esis of [(2,6-d ip h p y)P t(CO)] (15). Carbon monoxide
gas was bubbled through a solution of [(2,6-diphpy)Pt(dmso)]
(3) (56 mg, 0.108 mmol) in chloroform (1 mL). All solvents were
removed in vacuo to give a red product. Yield: 50 mg (99%,
0.107 mmol). Or, a solution of 9 in either dmf or dmso was
left for 6 h at room temperature. Anal. Found (expected): C
47.5 (47.8), H 2.5 (2.4), N 3.3 (3.1). NMR δH (400 MHz, d6-
dmso) 7.89 (1H, t, 3J ) 7.8 Hz, central pyridine), 7.68 (2H, dd,
Syn th esis of [(2,6-d ip h p y)P t(Cl)(CO)] (9). Tr a n s Iso-
m er 9t. Carbon monoxide gas was bubbled through a solution
of [((2,6-diphpy)PtCl)2] (4) in dmf. The compound was not
isolated.
ΝΜR δH (400 MHz, d7-dmf): 8.38 (1H, t, 3J ) 7.4 Hz, central
3
4
pyridine), 8.33 (1H, dd, J ) 7.4, J ) 2.0 Hz, pyridine), 8.02
3
4
(1H, dd, J ) 8.2, J ) 1.3 Hz, phenyl ortho to Pt), 7.96 (1H,
4
3J ) 7.6, J ) 1.1 Hz, phenyl ortho to pyridine), 7.65 (2H, d,
3
4
dd, J ) 8.2, J ) 1.3 Hz, phenyl, ortho to pyridine, meta to
Pt), 7.85 (2H, m, unmetalated phenyl), 7.72 (4H, m, pyridine,
unmetalated phenyl), 7.38 (1H, dt, 3J ) 8.2, 4J ) 1.3 Hz,
phenyl meta to Pt, para to pyridine), 7.32 (1H, dt, 3J ) 8.2,
4J ) 1.3 Hz, phenyl para to Pt). FT-IR: ν(CtO) 2087 cm-1
(dmf).
3J ) 7.8 Hz, pyridine), 7.52 (2H, dd, 3J ) 7.3, 4J ) 1.2, 3J (Pt-
H) ) 33.1 Hz, phenyl ortho to Pt), 7.22 (2H, dd, 3J ) 7.3, 4J )
1.2 Hz, phenyl meta to Pt), 7.16 (2H, dd, 3J ) 7.3, 4J ) 1.2
Hz, phenyl para to Pt). NMR δH (400 MHz, d7-dmf) 7.99 (1H,
3
3
4
t, J ) 7.8 Hz, central pyridine), 7.75 (2H, dd, J ) 7.6, J )
1.1 Hz, phenyl ortho to pyridine), 7.74 (2H, d, 3J ) 7.8 Hz,
pyridine), 7.61 (2H, dd, 3J ) 7.3, 4J ) 1.2, 3J (Pt-H) ) 33.1
Hz, phenyl ortho to Pt), 7.28 (2H, dd, 3J ) 7.3, 4J ) 1.2 Hz,
phenyl meta to Pt), 7.20 (2H, dd, 3J ) 7.3, 4J ) 1.2 Hz, phenyl
para to Pt). FAB MS (NBA): m/z 452 (M+). FT-IR: ν(CtO)
2044 cm-1 (KBr), 2056 cm-1 (dmso), 2055 cm-1 (dmf).
Cis Isom er 9c. Carbon monoxide gas was bubbled through
a solution of [(2,6-diphpy)PtCl(dmso)] (8) in dmso. The com-
pound was not isolated. NMR δH (400 MHz, d6-dmso) 8.20 (3H,
m, central pyridine, pyridine on metalated side, phenyl ortho
3
to Pt), 7.95 (2H, m, unmetalated phenyl), 7.84 (1H, dd, J )
9.0, 4J ) 1.4 Hz, phenyl meta to Pt, ortho to pyridine), 7.72
(1H, dd, 3J ) 6.2, 4J ) 2.8 Hz, pyridine, unmetalated side),
7.48 (3H, m, unmetalated phenyl), 7.22 (1H, dt, 3J ) 9.0, 4J )
X-r a y Cr ysta llogr a p h ic Stu d y of 15. Crystals suitable
for structural analysis were grown from chloroform. An orange-
red prism (dimensions 0.3 × 0.12 × 0.10 mm) was mounted
with oil on a thin quartz fiber. Data were collected at 180(2)
K using a Siemens SMART CCD area detector diffractometer.
Crystal data for 10: C18H11NOPt, M ) 452.37, orthorhombic,
space group P2(1)2(1)2(1) a ) 7.3337(6) Å, b ) 19.1794(12) Å,
c ) 18.9464(12) Å, U ) 2664.9(3) Å3, Z ) 8, D(calcd) ) 2.55
Mg/m3. Refinement was by full-matrix least-squares on F2 for
6260 reflections using SHELXL-97.60 Hydrogen atoms were
added at calculated positions. Anisotropic displacement pa-
rameters were used for all non-H atoms; H atoms were given
isotropic displacement parameters equal to 1.2 times the
equivalent isotropic displacement parameter of the atom to
which the H atom is attached. The weighting scheme was
calculated using w ) 1/[σ2(Fo2) + (0.0272P)2 + 11.62P], where
P ) (Fo2 + 2Fc2)/3. Goodness-of-fit on F2 was 1.105, R1[I > 2σ-
(I)] ) 0.0351, wR2 ) 0.0836. Data/parameters 6260/379.
Largest difference Fourier peak and hole 1.393 and -1.360 e
Å-3; the only large peaks are near the Pt atoms. The Flack
parameter was 0.020(14) and confirms that the correct abso-
lute structure has been determined. The asymmetric unit
contains two essentially identical molecules. Selected bond
lengths and angles are listed in Table 2.
Syn t h esis of [(4-(4-Oct yloxyp h en yl)-2,6-d ip h p y)P t -
(CO)] (16). [(4-(4-Octyloxyphenyl)2,6-diphpy)Pt(dmso)] (7) (60
mg, 0.085 mmol) was dissolved in chloroform and CO gas
bubbled through it. The solvent was removed to yield the
orange product. Yield: 55 mg (99%, 0.084 mmol). Anal. Found
(expected): C 58.0 (58.5), H 4.4 (4.8), N 2.6 (2.1).
NMR δH (400 MHz, CDCl3): 7.57 (2H, AA′XX′, phenyl, meta
to OC8H17 chain), 7.50 (2H, dd, 3J ) 7.5, 4J ) 1.5, 3J (Pt-H) )
38 Hz, phenyl, ortho to Pt), 7.39 (2H, dd, 3J ) 7.5, 4J ) 1.5
Hz, phenyl meta to Pt, ortho to pyridine), 7.23 (2H, s, pyridine)
3
4
1.4 Hz, phenyl para to Pt), 7.14 (1H, dt, J ) 9.0, J ) 1.4 Hz,
phenyl meta to Pt, para to pyridine). FT-IR: ν(CtO) 2098 cm-1
(dmso).
Syn th esis of [(4-(4-Octyloxyp h en yl)-2,6-d ip h p y)P t(Cl)-
(d m so)] (10). [((4-(4-Octyloxyphenyl)2,6-diphpy)PtCl)2] (6) was
dissolved in chloroform and an excess of dmso added. The
mixture was shaken for 1 h. The compound was not isolated.
3
4
NMR δH (400 MHz, CDCl3): 8.31 (1H, dd, J ) 7.6, J ) 1.2,
3J (Pt-H) ) 38 Hz, phenyl, ortho to Pt), 7.98 (2H, m, unmeta-
lated phenyl), 7.89 (1H, d, 4J ) 2.4 Hz, pyridine, metalated
side), 7.72 (2H, AA′XX′, phenyl, meta to OC8H17 chain), 7.66
(1H, dd, 3J ) 9.0, 4J ) 1.4 Hz, phenyl meta to Pt, ortho to
pyridine), 7.59 (1H, d, 4J ) 2.4 Hz, pyridine, unmetalated side),
7.50 (3H, m, unmetalated phenyl), 7.23 (1H, dt, 3J ) 9.0, 4J )
3
4
1.4 Hz, phenyl para to Pt), 7.20 (1H, dt, J ) 9.0, J ) 1.4 Hz,
phenyl meta to Pt, para to pyridine), 7.05 (2H, AA′XX′, phenyl
3
ortho to OC8H17 chain), 4.03 (2H, t, J ) 6.4 Hz, OCH2), 3.43
(6H, s, 3J (Pt-H) ) 23 Hz, dmso), 1.80 (2H, m, OCH2CH2), 1.51
3
(10H, m, chain), 0.91 (3H, t, J ) 7.0 Hz, CH3).
Syn th esis of [(4-(4-Octyloxyp h en yl)-2,6-d ip h p y)P t(Cl)-
(CO)] (11). Tr a n s Isom er 11t. Carbon monoxide gas was
bubbled through a solution of [((4-(4-octyloxyphenyl)2,6-diph-
py)PtCl)2] (6) in chloroform. The compound was not isolated.
3
4
NMR δH (400 MHz, CDCl3): 8.06 (1H, dd, J ) 7.6, J ) 1.2,
3J (Pt-H) ) 34 Hz, phenyl, ortho to Pt), 7.93 (1H, d, J ) 2.0
4
Hz, pyridine), 7.72 (2H, AA′XX′, phenyl, meta to OC8H17 chain),
7.68 (2H, m, unmetalated phenyl), 7.60 (1H, dd, 3J ) 7.6,
4J ) 1.4 Hz, phenyl meta to Pt, ortho to pyridine), 7.55 (3H,
4
m, unmetalated phenyl), 7.48 (1H, d, J ) 2.0 Hz, pyridine),
3
4
7.26 (1H, dt, J ) 7.6, J ) 1.4 Hz, phenyl meta to Pt, para to
3
4
pyridine), 7.19 (1H, dt, J ) 9.0, J ) 1.4 Hz, phenyl para to
Pt), 7.03 (2H, AA′XX′, phenyl ortho to OC8H17 chain), 4.01 (2H,

1364 Organometallics, Vol. 19, No. 7, 2000
Cave et al.
Ta ble 4. Rela tive Bin d in g En er gies (k J m ol-1
)
formulations of Becke65 and Perdew,66,67 respectively. Unless
otherwise stated, the GC functionals were applied after
geometry optimization at the LDA level. The lower core shells
on the atoms (1s on O, 1s to 2p on Cl, 1s to 5p or 4f on Pt)
were treated by the frozen core approximation.68 The total
molecular electron density was fitted in each SCF cycle by
auxiliary s, p, d, f, and g STO functions.69 Scalar relativistic
corrections70,71 were applied throughout. Table 3 lists selected
bond lengths in the structure of 15 and Table 4 the relative
binding energies of 9c, 9t, and 15. Coordinates of the optimized
structures are available as Supporting Information.
compound
relative binding energy
9c
9t
0
16
68
15 + HCl
3
4
7.14 (2H, dt, J ) 7.5, J ) 1.5 Hz, phenyl meta to Pt, para to
3
4
pyridine), 7.06 (2H, dt, J ) 7.5, J ) 1.5 Hz, phenyl para to
Pt), 6.99 (2H, AA′XX′, phenyl ortho to OC8H17 chain), 4.01 (2H,
3
t, J ) 7.0 Hz, OCH2), 1.80 (2H, m, OCH2CH2), 1.51 (10H, m,
chain), 0.89 (3H, t, 3J ) 7.0 Hz, CH3). FT-IR: ν(CtO) 2061
cm-1 (CDCl3).
Ack n ow led gm en t. We thank the EPSRC for a
studentship (G.W.V.C.) and J ohnson-Matthey for loan
of precious metal salts.
Th eor etica l Stu d ies. The DFT calculations were based on
the numerical Amsterdam Density Functional (ADF) program
system version 2.3.0.61 The supplied basis sets IV were used
which comprise uncontracted triple-ú Slater-type-orbital (STO)
expansions for the valence orbitals with an additional function
(2p for H, 3d for C, N, O, and Cl, and 6p for Pt). Geometry
optimizations were generally carried out using the uniform
electron gas local density approximation62 (LDA) and analyti-
cal energy gradients.63 The LDA correlation energy was
computed according to Vosko, Wilk, and Nusair’s64 parametri-
zation of electron gas data. Gradient-corrected (GC) functionals
for the LDA exchange and correlation terms employed the
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
parameters, bond distances, bond angles, and anisotropic
parameters for the structural analysis of 6 and 15 are available
free of charge via the Internet at http://pubs.acs.org, as are
the coordinates for the optimized structures of 9c, 9t, and 15.
OM9910423
(65) Becke, A. J . Chem. Phys. 1986, 84, 4524.
(66) Perdew, J . P. Phys. Rev. 1986, B33, 8822.
(67) Perdew, J . P. Phys. Rev. 1987, B34, 7406.
(68) Baerends, E. J .; Ellis, D. E.; Ros, P. Theor. Chim. Acta 1972,
27, 339.
(69) Krijn, J .; Baerends, E. J . Fit Functions for the HFS Method.
Free University of Amsterdam Internal Report, 1984.
(70) Snijders, J . G.; Baerends, E. J . Mol. Phys. 1978, 36, 1789.
(71) Snijders, J . G.; Baerends, E. J . Mol. Phys. 1979, 38, 1909.
(61) ADF 2.3.0, Theoretical Chemistry, Vrije Universitet, Amster-
dam, 1997; Baerends, E. J .; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2,
41.
(62) Slater, J . C. Adv. Quantum Chem. 1972, 6, 1.
(63) Versluis, L.; Ziegler, T. J . Chem. Phys. 1988, 88, 322.
(64) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J . Phys. 1980, 58, 1200.