Platinabenzenes: Synthesis, properties, and reactivity studies of a rare class of metalla-aromatics

Article abstract of DOI:10.1021/om900439z

Lithium-halogen exchange of (Z)-1,2-diphenyl-3-(2-iodoethenyl)cyclopropene (1) and subsequent addition to (η^-41,5-cod)PtCl₂ yields the platinabenzene (η^-5-C₅H₃Ph ₂)[PtC₅H₃

Full text of DOI:10.1021/om900439z

Organometallics 2009, 28, 5183–5190 5183
DOI: 10.1021/om900439z
Platinabenzenes: Synthesis, Properties, and Reactivity Studies of a Rare
Class of Metalla-aromatics†
Volker Jacob, Christopher W. Landorf, Lev N. Zakharov, Timothy J. R. Weakley, and
Michael M. Haley*
Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1253
Received May 25, 2009
Lithium-halogen exchange of (Z)-1,2-diphenyl-3-(2-iodoethenyl)cyclopropene (1) and subse-
quent addition to (η4-1,5-cod)PtCl2 yields the platinabenzene (η5-C5H3Ph2)[PtC5H3Ph2] (7), in
which the metallacyclic ring and C5H3Ph2 (Cp0) unit are both derived from the cyclopropene
skeleton. Starting instead with (η5-C5Me5)Pt(CO)I, treatment with three nucleophilic (Z)-3-(2-
lithiovinyl)cyclopropenes provides platinabenzenes (η5-C5Me5)[PtC5H3PhR] (R=Ph (8), t-Bu (9),
Me (10)) in low to modest yield. All platinabenzenes have been fully characterized by NMR
spectroscopy and X-ray crystallography. Intermediate σ-vinyl complexes (η5-C5Me5)Pt(σ-
C5H3PhR) (R=Ph (14), t-Bu (15)) are also isolated from the reaction mixtures and convert cleanly
to the corresponding platinabenzenes in near quantitative yield. Reactivity studies of (η5-C5Me5)-
[PtC5H3Ph2] with a variety of reagents/conditions are also reported.
Introduction
Vaska-type metal complexes possessing small and/or elec-
tron-donating phosphines furnished iridabenzvalenes (e.g., 2),
compounds with a σ-bond to the vinyl group of the vinylcy-
clopropene and π-coordination of the cyclopropene CdC
double bond.5-8 Cyclopropene-vinylalkylidene rear-
rangement,9-11 initiated either through gentle heating of the
intermediate benzvalene or by using larger phosphines on the
starting organometallic complexes, led to formation of the
corresponding iridabenzenes (e.g., 3).3,4 Inclusion of large, less
electron-donating phosphines resulted in direct formation of
the iridabenzene. In certain instances, the iridabenzenes
were not thermally stable and underwent a carbene migratory
insertion to yield η5-cyclopentadienyliridium complexes
(e.g., 4),6-8 which is a known decomposition pathway of
metallabenzenes.12
Since the vinylcyclopropene route has successfully gener-
ated a large variety of iridabenzenes and iridabenzvalenes, we
wished to extend our methodology to include other metals.
Moving up to the second-row metals proved to be proble-
matic. Starting with Rh complexes, we could detect rhoda-
benzenes in the crude reaction mixtures; however, these
studies to date have afforded only rhodabenzvalenes such as
5.13 All attempts to isomerize these molecules to the corre-
sponding rhodabenzenes have instead furnished either Cp0Rh
For the past decade we have been examining the synthesis
of metallabenzenes1,2 and their valence isomers starting
from (Z)-3-(2-iodoethenyl)cyclopropenes such as 1.3-8
Treatment of 1 with BuLi and subsequent addition to
† Metallabenzenes and Valence Isomers 10. For part 9, see ref 7.
*Corresponding author. E-mail: haley@uoregon.edu.
(1) (a) Bleeke, J. R. Chem. Rev. 2001, 101, 1205–1227. (b) Landorf, C.
W.; Haley, M. M. Angew. Chem., Int. Ed. 2006, 45, 3914–3936. (c) Wright,
L. J. Dalton Trans. 2006, 1821–1827. (d) Bleeke, J. R. Acc. Chem. Res.
2007, 40, 1035–1047.
(2) Recent examples, inter alia: (a) Liu, B.; Wang, H.; Xie, H.; Zeng,
B.; Chen, J.; Tao, J.; Wen, T. B.; Cao, Z.; Xia, H. Angew. Chem., Int. Ed.
2009, 48, 5430–5434. (b) Liu, B.; Xie, H.; Wang, H.; Wu, L.; Zhao, Q.; Chen,
J.; Wen, T. B.; Cao, Z.; Xia, H. Angew. Chem., Int. Ed. 2009, 48, 5461–5464.
(c) Zhang, H.; Wu, L.; Lin, R.; Zhao, Q.; He, G.; Yang, F.; Wen, T.; Xia, H.
Chem.;Eur. J. 2009, 15, 3546–3559. (d) Clark, G. R.; O'Neale, T. R.;
Roper, W. R.; Tonei, D. M.; Wright, L. J. Organometallics 2009, 28, 567–
572. (e) Clark, G. R.; Johns, P. M.; Roper, W. R.; Wright, L. J. Organome-
ꢀ
tallics 2008, 27, 451–454. (f) Paneque, M.; Poveda, M. L.; Rendon, N.;
Alvarez, E.; Carmona, E. Eur. J. Inorg. Chem. 2007, 2711–2720. (g) Zhang,
H.; Feng, L.; Gong, L.; Wu, L.; He, G.; Wen, T.; Yang, F.; Xia, H.
Organometallics 2007, 26, 2705–2713. (h) Clark, G. R.; Lu, G.-L.; Roper,
W. R.; Wright, L. J. Organometallics 2007, 26, 2167–2177. (i) Paneque, M.;
ꢀ
Posadas, C. M.; Poveda, M. L.; Rendon, N.; Santos, L. L.; Alvarez, E.;
~
Salazar, V.; Mereiter, K.; Onate, E. Organometallics 2007, 26, 3403–3415.
(j) Hung, W.; Zhu, J.; Wen, T.; Yu, K.; Sung, H. H. Y.; Williams, I. D.; Lin, Z.;
Jia, G. J. Am. Chem. Soc. 2006, 128, 13742–13752.
(3) Gilbertson, R. D.; Weakley, T. J. R.; Haley, M. M. J. Am. Chem.
Soc. 1999, 121, 2597–2598.
(4) Gilbertson, R. D.; Lau, T. L.; Lanza, S.; Wu, H.-P.; Weakley, T. J.
R.; Haley, M. M. Organometallics 2003, 22, 3279–3289.
(5) Gilbertson, R. D.; Weakley, T. J. R.; Haley, M. M. Chem.;Eur.
J. 2000, 6, 437–441.
€
(9) Binger, P.; Muller, P.; Benn, R.; Mynott, R. Angew. Chem., Int.
Ed. Engl. 1989, 28, 610–611.
(10) Nguyen, S. T.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W. J. Am.
Chem. Soc. 1992, 114, 3974–3975.
(11) Gagne, M. R.; Grubbs, R. H.; Feldman, J.; Ziller, J. W.
Organometallics 1992, 11, 3933–3935.
(6) Wu, H.-P.; Lanza, S.; Weakley, T. J. R.; Haley, M. M. Organo-
metallics 2002, 21, 2824–2826.
(7) Wu, H.-P.; Weakley, T. J. R.; Haley, M. M. Chem.;Eur. J. 2005,
11, 1191–1200.
(8) Wu, H.-P.; Ess, D. H.; Lanza, S.; Weakley, T. J. R.; Houk, K. N.;
(12) (a) Iron, M. A.; Martin, J. M. L.; van der Boom, M. E. J. Am.
Chem. Soc. 2003, 125, 13020–13021. (b) Iron, M. A.; Lucassen, A. C. B.;
Cohen, H.; van der Boom, M. E.; Martin, J. M. L. J. Am. Chem. Soc. 2004,
126, 11699–11710.
(13) Wu, H.-P.; Weakley, T. J. R.; Haley, M. M. Organometallics
Baldridge, K. K.; Haley, M. M. Organometallics 2007, 26, 3957–3968.
2002, 21, 4320–4322.
r
2009 American Chemical Society
Published on Web 08/20/2009
pubs.acs.org/Organometallics

5184 Organometallics, Vol. 28, No. 17, 2009
Jacob et al.
Scheme 1
complexes or unidentifiable mixtures. Efforts with Ru led
not to ruthenabenzenes but instead to ruthenocenes.1b
Somewhat surprisingly, prior to our initial14 and follow-
up15 communications, there was only a single report in the
literature of a metallabenzene incorporating a group 10
metal, namely, nickelabenzene 6.16 This molecule, however,
most likely required the stabilization afforded by the
η6-bound Cp*Ru unit in order to be isolable. In fact, a large
number of known metallabenzenes are η6-coordinated to a
second transition-metal fragment.1a We therefore sought to
prepare stable, uncoordinated metallabenzenes containing a
group 10 metal. This paper details our successful synthesis
and characterization of metallacycles 7-10, the first exam-
ples of platinabenzenes, and describes attempts in extending
this method to structural analogues 11 and 12. We also
report the isolation and characterization of intermediate σ-
vinyl complexes 14 and 15, which upon heating afford
quantitatively arenes 8 and 9, respectively.
column chromatography, albeit in only 7% yield. Interest-
ingly, both the η5-1,2-diphenylcyclopentadienyl (Cp0) ring
and metalla-aromatic ring in 7 must be derived from 1 in its
reaction with (cod)PtCl2.
Subsequent attempts in our lab utilizing cis-Pt(PEt3)2MeI
as the Pt source failed to yield platinabenzenes and instead
furnished cationic (η3-1,2-diphenylcyclopentadienyl)Pt(II)
complexes.19 Again, the cyclopentadienyl ring in these com-
plexes was derived from 1. The apparent preference for the
formation of the Cp0Pt fragment in this system, a result
corroborated by DFT calculations,12 led us to conclude that
a Pt complex containing a coordinated Cp ring should be a
viable starting material in platinabenzene synthesis.
Second-Generation Arenes From Cp*Pt(CO)I. Interest-
ingly, compounds containing a (cyclopentadienyl)(halogen)-
Pt(II) fragment, the moiety needed to undergo ligand metath-
esis with lithiated 1, are limited to very few examples.20 After a
few unsuccessful trials with these compounds, we elected to
start with previously unknown Cp*Pt(CO)I (13), obtained by
iodine oxidation21 of Boag’s dimer [Cp*Pt(CO)]2 (Scheme 2).22
After the lithium-halogen exchange on 1, the vinyl lithiate was
added into the violet slurry of 13 in dry Et2O at -78 °C, which
resulted in a color change to light orange. After standing
overnight at -30 °C, the reaction was worked up and chroma-
tographed on silica to furnish platinabenzene 8, isolated as a
red-orange solid in 14% yield. A second compound, σ-vinyl
complex 14, which is the immediate precursor to 8, was also
isolated in 24% yield. Arene 8 is presumably formed by CO loss
from the 18-electron complex 14, followed by coordination of
the cyclopropene π-bond and then rearrangement of the
strained three-membered ring to give the aromatic platinacycle.
As shown in Figure 1, 14 could be converted to 8 cleanly in
C6D6 solution at room temperature with no evidence of
intermediate species. Only two signals for the Cp* methyl
Results and Discussion
Initial Studies Using (η4-1,5-cod)PtCl2. Although we in-
vestigated several Pt(II) complexes17 as possible starting
points,18 we found success with one of the simplest, (η4-
1,5-cod)PtCl2. Lithium-halogen exchange of 1 (Scheme 1)
and addition of the resultant vinyl lithiate to an ether
suspension of (cod)PtCl2 produced a dark brown slurry,
from which platinabenzene 7 was isolated as a red solid after
(14) Jacob, V.; Weakley, T. J. R.; Haley, M. M. Angew. Chem., Int.
Ed. 2002, 41, 3470–3473.
(15) Landorf, C. W.; Jacob, V.; Weakley, T. J. R.; Haley, M. M.
Organometallics 2004, 23, 1174–1176.
(16) Bertling, U.; Englert, U.; Salzer, A. Angew. Chem., Int. Ed. Engl.
1994, 33, 1003–1004.
(17) (a) Organometallic Compounds of Nickel, Palladium, Platinum,
Copper, Silver and Gold; Cross, R. J., Mingos, D. M. P., Eds.; Wiley:
Chichester, 1985; pp 163-244. (b) Hartley, F. R. In Comprehensive
Organometallic Chemistry, Vol. 6; Wilkinson, G., Stone, F. G. A., Abel,
E. W., Eds.; Pergamon Press: New York, 1982; pp 471-762.
(18) Inter alia: (a) Kumar, R.; Roy, S.; Rashidi, M.; Puddephatt, R.
J. Polyhedron 1989, 8, 551–553. (b) O'Hare, D. Organometallics 1987, 6,
1766–1772. (c) Boag, N. M.; Goodfellow, R. J.; Green, M.; Hessner, B.;
Howard, J. A. K.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1983, 2585–
2591. (d) Clark, H. C.; Shaver, A. Can. J. Chem. 1976, 54, 2066–2076. (e)
Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411–428.
(19) Jacob, V.; Weakley, T. J. R.; Haley, M. M. Organometallics
2002, 21, 5394–5400.
(20) Boag, N. M.; Quyoum, R.; Rao, K. M. J. Chem. Soc., Chem.
Commun. 1992, 114–115.
(21) Fischer, E. O.; Schuster-Woldan, H.; Bittler, K. Z. Naturforsch.
1963, 18b, 429–431.
(22) Boag, N. M. Organometallics 1988, 7, 1446–1449.

Article
Organometallics, Vol. 28, No. 17, 2009 5185
Figure 1. Conversion of 14 to 8 at room temperature monitored by 1H NMR spectroscopy in C6D6.
Stability of Platinabenzenes. Heating solutions of 7 or 8 at
Scheme 2
100 °C for 48 h resulted in no noticeable decomposition in the
1H NMR spectrum. This finding is in contrast to the
reactivity of many iridabenzenes6-8 (and putative platina-
benzenes similar to C),19 which easily undergo carbene
migratory insertion to afford Cp complexes such as 4. Van
der Boom and Martin performed calculations on the stability
of several platinabenzene complexes toward this deleterious
pathway.12 On the basis of their results, inclusion of the
cyclopentadienyl ligand appears to stabilize the platinaben-
zene by increasing the energy barrier for carbene migratory
insertion. In the case of C5H5Pt(PH3)þ2 , a computational
analogue of C, the transition state to forming (η5-Cp)Pt-
(PH3)þ2 was only 24.0 kcal mol-1, which corroborates our
earlier experimental results.19 For the Cp complex C5H5-
PtCp, the computational analogue of 7-10, the transition
state for forming (η3-Cp)2Pt was considerably higher, calcu-
lated to be 45.9 kcal mol-1. De Proft and Geerlings utilized
the isomerization method to predict the aromatic stabiliza-
tion energy (ASE) of the platinabenzene ring in model
system Pt(C5H3Me2)(η3-C5H3Me2).23 They obtained a
calculated value of 23.4 kcal mol-1, approximately two-
thirds of the reported ASE for benzene (33.8 kcal mol-1).
protons of 14 [δ 1.84 (JPt-H=14 Hz)] and 8 [δ 1.59 (JPt-H
8 Hz)] are observed throughout the whole conversion.
=
On the basis of this successful rational synthesis of plati-
nabenzene 8 and taking into account the results of theoretical
studies on platinabenzenes, we can now postulate a plausible
mechanism of formation for platinabenzene 7 (Scheme 1).
Exchange of one of the chloride ligands by the organolithium
reagent, a commonly used method for the synthesis of Pt-σ-
alkyl compounds,17 would give σ-bonded vinylcyclopropene
complex A. Intramolecular displacement of one of the 1,5-
cyclooctadiene double bonds by the cyclopropene double bond
should afford B. Subsequent ring-opening of the strained
cyclopropene would ideally lead to C. Both computational12
and experimental19 studies have shown that square-planar
platinabenzenes like C are thermally unstable and readily
undergo carbene migratory insertion to give either η3- or η5-
cyclopentadienylplatinum complexes such as D. Repetition of
the first three mechanistic steps with a second equivalent of
vinyl lithiate;as required for the formation of platinabenzene
8;would furnish platinabenzene 7 via intermediate E.
ꢀ
Fernandez and Frenking recently used their energy decom-
position analysis method, which provides a quantitative
measure for the strength of conjugation in cyclic molecules,
to examine a number of metallabenzenes.24 Their computed
ASE value for C5H5PtCp (37.6 kcal mol-1) was higher than
the ASE values of any of the other metallabenzenes studied
and was just slightly lower than their ASE value for benzene
(42.5 kcal mol-1). As a whole, these computational results
clearly corroborate our experimental findings: inclusion of a
cyclopentadienyl moiety as part of the overall platinaben-
zene structure affords a thermodynamically robust, strongly
aromatic metallacycle.
(23) De Proft, F.; Geerlings, P. Phys. Chem. Chem. Phys. 2004, 6,
242–250.
ꢀ
(24) Fernandez, I.; Frenking, G. Chem.;Eur. J. 2007, 13, 5873–5884.

5186 Organometallics, Vol. 28, No. 17, 2009
Jacob et al.
Figure 2. X-ray structure of platinabenzenes 8 (left) and 10 (right); ellipsoids at 30% probability level.
Table 1. 1H NMR Chemical Shifts of the Ring Protons for
Platinabenzenes Derived from Unsymmetrical Precursors.
Platinabenzenes 7-10a
In a manner similar to 8, reaction of 13 with the lithiated
1-tert-butyl-2-phenyl analogue7 of 1 afforded platinaben-
zene 9 and σ-vinyl complex 15 in 14% and 16% yield,
respectively. Although the yields of platinabenzene initially
isolated from the reaction mixtures were low, the relative
ratio of benzene to σ-vinyl complex varied depending upon
the length of time the material was in solution. Shorter
reaction times and faster workups favored 14 and 15. Ana-
logous to 14, near quantitative isomerization of 15 to the
corresponding arene could be accomplished by storing the
σ-vinyl complex in a benzene solution at room temperature
for 2-3 days, giving ca. 30% overall yield of the metalla-
aromatic.
cmpd
H5
H4
H3
7
8
9
10
12.76
12.09
11.83
11.93
7.42
7.63
7.60
7.57
8.20
8.25
8.54
8.10
a Data obtained in C6D6 and given in ppm.
metallabenzene.1a,1b The peak for proton H5 (see Figure 2
for atom labeling) is shifted considerably downfield due
primarily to the multiple (π) bonding between the metal
and carbon (12.09 ppm, JPt-H = 50 Hz). The comparable
resonance on complex 7 appears at 12.76 ppm (JPt-H
=
As exciting as the results were for 8/9 and 14/15, we
encountered problems when attempting to extend this syn-
thetic strategy to the other known 1-alkyl-2-phenyl analo-
gues7 of 1. The major difference between 8/9 and 10-12 is the
presence of hydrogen atoms on the carbon atoms directly
attached to the platinacycle. In the case of the methyl
analogue, only a small amount of platinabenzene 10 (4%
yield) could be isolated. No evidence of the corresponding
σ-vinyl complex was found. In the cases of the ethyl and
isopropyl analogues, only minute amounts of platinaben-
zenes 11 and 12, respectively, could be detected, as shown by
the presence of a small proton resonance around 12 ppm in
the 1H NMR spectrum. All attempts to isolate these arenes
were unsuccessful. The difficulty in synthesizing these com-
plexes appears to be related to the formation of side products
like Boag’s dimer and the regenerated starting vinyl iodides,
which were identified in the reaction mixtures. Control
experiments showed that these latter compounds were in-
deed re-formed during the reaction and did not originate
from incomplete lithium-iodine exchange. While a number
of potential deleterious mechanisms abound, these are be-
yond the context of the current synthetic study and will be the
subject of future work.
65 Hz). Additionally, a pseudotriplet and a doublet show
up at 7.63 and 8.25 ppm, respectively, assignable to protons
H4 and H3, respectively, of 8. The methyl protons on the Cp*
ring resonate at 1.59 ppm. In the 13C NMR spectrum of 8, the
signals for the carbon atoms directly connected to the Pt
center appear at 188.7 (C5) and 200.6 (C1) ppm and are
comparable to those in 7 (194.9 and 204.0 ppm).
1
Comparison of the H NMR signals of the ring protons
reveals some clear trends in the platinabenzene series
(Table 1). Essentially, the more electron-donating substitu-
ents cause proton H5 to shift upfield. The biggest difference
comes from replacing the diphenylcyclopentadiene (Cp0) in 7
with the pentamethylcyclopentadiene (Cp*) in 8. For this
change alone the H5 proton resonance shifts 0.67 ppm
upfield, illustrating how much more electron donating the
Cp* unit is compared to the Cp0 group. Replacement of the
phenyl group in 8 with a tert-butyl group as in 9 again shifts
the H5 resonance upfield from 12.09 ppm to 11.83 ppm. The
less electron-donating methyl substituent on 10 shows an H5
resonance in between at 11.93 ppm.
Interestingly, the opposite trend is observed for the H3
proton signals in 7-9. In this case the more electron-donating
substituents apparently cause the signals for H3 to appear
further downfield. The H3 signal for the most electron-rich
arene, t-Bu-substituted 9, resonates at 8.54 ppm, whereas the
least electron-rich ring, arene 7, shows the analogous proton
resonance at 8.20 ppm. This trend does not hold for 10,
Spectroscopic Data. Unlike most metallabenzenes, arenes
7-10 are air-stable for several days in solution and in the
solid state; thus, their spectroscopic data can be easily
secured. The 1H NMR spectrum for platinabenzene 8 exhi-
bits the characteristic resonances for the ring protons of a

Article
Organometallics, Vol. 28, No. 17, 2009 5187
however, as the H3 signal appears the furthest upfield at
8.10 ppm. A plausible explanation for this trend (10 < 7 <
8 < 9) is due to steric effects of the contiguous, coplanarized
Cp0/Cp*, Ph, and Ph/t-Bu/Me substituents; the most sterically
congested substitution pattern (Cp*, Ph, t-Bu) affords the
furthest downfield H3 proton signal.
Complexes 14 and 15 can be identified by the characteristic
1H NMR shifts of the σ-bound vinyl groups.19 For example,
the proton neighboring the Pt center in 14 resonates at
6.69 ppm as a Pt-coupled doublet (JPt-H=14 Hz). The vinyl
proton next to the cyclopropenyl ring appears as a pseudo-
triplet at 6.20 ppm. The comparable resonances for 15
appear at 6.57 and 6.10 ppm, respectively. The IR spectra
for 14 and 15 exhibit bands for carbonyl stretching at 2001
and 2002 cm-1, respectively.
X-ray Crystal Structures. As a new class of metallaben-
zenes, the solid-state structures of 7-10 are of considerable
interest. Recrystallization of the red solids from hexanes
afforded X-ray quality crystals of all four platinacycles. The
molecular structures of 8 and 10 are shown in Figure 2, and
selected bond lengths and bond angles for 7-10 are given in
Table 2.
Figure 3. X-ray structure of σ-complex 14; ellipsoids at 30%
˚
probability level. Selected bond lengths (A) and angles (deg):
Pt-C(1) 2.049(6), Pt-C(11) 1.813(7), C(1)-C(2) 1.315(8), C-
(2)-C(3) 1.482(8), C(3)-C(4) 1.512(8), C(3)-C(5) 1.525(8),
C(4)-C(5) 1.293(8), C(11)-O 1.142(7), C(1)-Pt-C(11)
87.8(3), Pt-C(1)-C(2) 128.1(5), C(1)-C(2)-C(3) 127.0(6), C-
(4)-C(3)-C(5) 50.4(3).
Comparison of the X-ray data of the four platinabenzenes
(Table 2) illustrates the similarities between them. The sums of
the respective platinacycle bond angles are remarkably close
to the 720° required for a perfectly planar hexagon (deviation
16. While both isomers (syn and anti with respect to the
phenyl groups) were observed, the 1H NMR spectrum of the
crude reaction mixture showed that one isomer is formed
preferentially (>20:1). This major product was isolated and
characterized and is provisionally assigned as the anti isomer
16. It is reasonable to assume that the Ph groups perpendi-
cular to the metallacycle plane direct the anhydride into the
anti orientation. Similar [4 þ 2] reactivity has been observed
for iridabenzenes.1a Interestingly, dimethyl acetylenedicar-
boxylate (DMAD) failed to undergo an analogous cycload-
dition, even when heated to 50 °C. This may be due to steric
hindrance of the large Cp* group on 8, which prevents the
proper orientation of the acetylene required for the [4 þ 2]
addition. Similarly, solutions of 8 in acetone at 50 °C also
failed to react in a [4 þ 2] manner, as metallapyrilliums do
with acetone.1a
Like several other metalla-aromatics, platinabenzene 8
reacted with Mo-arene complexes to produce Mo-coordi-
nated metallabenzenes. A red THF solution of (toluene)-
Mo(CO)3 rapidly turned purple upon addition of 8, yielding
η6-complex 17 (Scheme 3). Reaction with (mesitylene)-
Mo(CO)3 also afforded 17, but required several days to
reach completion. Because the Mo(CO)3 fragment favors
the more electron-rich arene, this result suggests that plati-
nabenzenes are electron-rich species.
˚
from mean plane e0.02 A). Such planarity is common for
about half of the known metallabenzenes.1,12b,25 The largest
angles in the platinacycles are found around the two carbon
atoms next to Pt (129.2-129.8°), while the smallest bond
angles are centered around the Pt metal (89.3-91.0°). The
˚
Pt-C bonds are 1.926-1.937 and 1.951-1.975 A in length,
which compare well with Pt-C bonds in other Pt(II) carbene
complexes. The C-C bonds in the metallacycles have an
˚
average length of 1.382-1.396 A, approximately the same
length as observed in benzene, with no appreciable bond
alternation. The Cp ring in each system is η5-coordinated to
˚
Pt, with Pt-CCp distances in the range 2.257-2.342 A.
Crystals suitable for X-ray analysis were also obtained for
σ-complex 14, and its structure is shown in Figure 3. The
˚
Pt-C(1) distance is 2.049(6) A, which is similar to other
Pt-C single bonds.19,26 The carbonyl Pt-C(11) bond length
˚
is 1.813(7) A. This shortened Pt-C bond is indicative of
efficient back-bonding from the electron-rich metal center to
the carbonyl π* orbital. The cyclopropene double bond,
˚
C(4)-C(5), is 1.293(8) A in length, which is comparable to
other uncoordinated 1,2-diphenylcyclopropenes prepared in
this lab.19
Reactivity Studies. To determine the stability/reactivity of
this new class of metalla-aromatics, platinabenzene 8 was
subjected to a variety of conditions (Scheme 3). Arene 8 is
water stable, with no reaction either on direct exposure to
water or in solutions of methanol and water. Slow decom-
position was observed in solutions exposed to oxygen over
the course of a week, but no specific products were isolable.
Exposure to elemental bromine led to decomposition, but
again, no specific products were isolable. This result con-
trasts those reported for the iridabenzenes, where oxidative
addition to the metal is usually observed.1a
The crystal structure of 17 (Figure 4) reveals modest
change in the Pt-C bond lengths upon coordination to the
Mo(CO)3 unit (Table 2). The larger changes upon coordina-
tion are lengthening of the C(2)-C(3) and C(3)-C(4) bonds
˚
(ca. 0.05-0.06 A) and shortening of the C(1)-C(2) bond
˚
(0.036 A). The C(4)-C(5) bond length is essentially un-
˚
changed. The Mo-Pt bond length is 2.819(2) A, which is
slightly longer than the average Mo-C(ring) distances of
2.377 A.
˚
As is the norm with metal arene complexes, the metalla-
cycle ring 1H NMR signals are shifted upfield significantly.
The proton signal for H5 moves from 12.09 ppm in uncoor-
dinated 8 to 8.45 ppm in coordinated 17. Similarly, the
H4 resonance shifts from 7.63 ppm to 5.11 ppm and the
proton signal for H3 from 8.25 ppm to 6.43 ppm. Two bands
One interesting reaction that did occur was the formal
[4 þ 2] cycloaddition of 8 with maleic anhydride to produce
(25) Zhu, J.; Jia, G.; Lin, Z. Organometallics 2007, 26, 1986–1995.
(26) Howard, W. A.; Bergman, R. G. Polyhedron 1998, 17, 803–810.

5188 Organometallics, Vol. 28, No. 17, 2009
Jacob et al.
Scheme 3
˚
Table 2. Selected Bond Lengths (A) and Bond Angles (deg) for
that the Mo center is more electron rich in the platinabenzene
complex.
Platinabenzenes 7-10 and η6-Mo(CO)3 Platinabenzene Complex
17
7a
8
9b,c
10b
17
Conclusion
Pt-Cpd
1.965(4) 1.959(5) 1.957(5) 1.948(14) 1.958(12)
1.959(3) 1.951(4) 1.975(5) 1.951(13) 1.973(11)
1.929(4) 1.937(5) 1.926(5) 1.932(13) 1.916(11)
1.387(5) 1.401(6) 1.406(7) 1.424(15) 1.365(13)
1.392(5) 1.395(6) 1.389(7) 1.405(15) 1.444(14)
1.381(6) 1.363(7) 1.387(8) 1.374(15) 1.428(14)
1.364(6) 1.387(7) 1.350(8) 1.379(15) 1.388(14)
1.382(6) 1.387(7) 1.383(8) 1.396(15) 1.406(14)
129.2(3) 129.2(3) 129.8(4) 129.7(9) 130.6(9)
Four platinabenzenes have been synthesized and fully
characterized in solution and in the solid state. Compounds
7-10 exhibit downfield shifts of the metallacycle ring pro-
tons and no bond alternation and form arene π-complexes,
factors that are consistent with other known metallaben-
zenes. In this class of metallabenzenes, the Pt center lies in the
plane of the ring, leading to highly planar structures. In
addition to platinabenzenes, σ-vinyl complexes 14 and 15
have been isolated and characterized. Upon standing in
solution, the σ-vinyl species cleanly isomerize to the respec-
tive platinabenzenes. The reactivity of platinabenzene 8 to a
variety of reagents and conditions was examined. While 8
was essentially unreactive to water and acetone, it decom-
posed slowly upon exposure to oxygen or rapidly to bromine.
[4 þ 2]-Cycloaddition occurred with maleic anhydride, but
not with DMAD. Reaction of 8 with (toluene)Mo(CO)3
produced the arene complex 17, which was characterized
by FTIR, 1H NMR, and X-ray crystallography. Our experi-
mental studies and published computational results confirm
that Cp-capped platinabenzenes such as 7-10 are thermo-
dynamically robust, highly aromatic molecules.
Pt-C(1)
Pt-C(5)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
CdC mean
Pt-C(1)-C(2)
C(1)-C(2)-C(3) 122.6(3) 122.3(4) 124.1(5) 120.7(11) 123.2(11)
C(2)-C(3)-C(4) 124.8(4) 125.2(4) 126.9(5) 125.5(12) 123.3(11)
C(3)-C(4)-C(5) 124.1(4) 124.5(5) 119.8(5) 125.2(13) 120.3(12)
C(4)-C(5)-Pt
C(1)-Pt-C(5)
sum of angles
130.0(3) 128.9(4) 129.8(4) 127.8(10) 134.2(9)
89.3(2) 89.7(2) 89.4(2) 91.0(6)
720.0 719.8 719.8 719.9
87.8(5)
719.4
a Ref 14. b Average values for two independent molecules. c Ref 15.
d Distance from the Pt center to the centroid of the Cp ring.
Experimental Section
General Procedures. Reactions were carried out using standard
Schlenk techniques in an inert atmosphere (dry Ar or N2) when
necessary. THF, toluene, and Et2O were distilled from Na/benzo-
phenone under N2 prior to use. Unless stated otherwise solvents
and reagents were purchased commercially and used as received.
(Z)-1,2-Diphenyl-3-(2-iodoethenyl)cyclopropene (1),4 (Z)-1-tert-
butyl-3-(2-iodoethenyl)-2-phenylcyclopropene,7 (Z)-1-ethyl-3-(2-
iodoethenyl)-2-phenylcyclopropene,7 (Z)-1-isopropyl-3-(2-iodo-
ethenyl)-2-phenylcyclopropene,7 (Z)-1-methyl-3-(2-iodoethenyl)-
2-phenylcyclopropene,7 and [(η5-C5Me5)Pt(CO)]222 were prepared
according to literature methods. 1H (299.94 or 500.10 MHz) and
13C (75.43 or 125.76 MHz) NMR spectra were recorded using a
Varian Inova 300 or 500 NMR spectrometer. Chemical shifts are
expressed in ppm downfield from tetramethylsilane (CDCl3,
Figure 4. X-ray structure of η6-complex 17; ellipsoids at 30%
probability level.
1
1H: 7.26 ppm and 13C: 77.0 ppm; C6D6, H: 7.15 ppm and 13C:
for carbonyl stretching vibrations appear at 1959 and
1894 cm-1. The analogous bands for (toluene)Mo(CO)3
(1984 and 1916 cm-1) are higher in energy,27 which suggests
128.0 ppm,). Coupling constants are expressed in Hz. IR spectra
were recorded using a Nicolet Magna-FTIR 550 spectrometer.
Melting points were determined on a Meltemp II apparatus and are
uncorrected. Elemental analyses were performed by Robertson
Microlit Laboratories, Inc.
(27) Wagner, G. W.; Hanson, B. E. Organometallics 1987, 6, 2494–
2498.

Article
Platinabenzene 7. Cyclopropene 1 (688 mg, 2.0 mmol) was
Organometallics, Vol. 28, No. 17, 2009 5189
3JHH=7.8 Hz, 4JHH=1.8 Hz, 1H, H3), 12.09 (dd, 3JHH=7.5 Hz,
2
dissolved in dry Et2O (20 mL) under Ar and cooled to -78 °C.
BuLi (0.8 mL, 2.5 M in hexanes, 2.0 mmol) was added dropwise,
and the resulting yellow solution was stirred at -78 °C for
15 min. This solution was added dropwise to a stirred, ice-cooled
suspension of (cod)PtCl2 (374 mg, 1.0 mmol) in Et2O (5 mL).
The resulting dark brown suspension was allowed to warm to
room temperature and stirred for 12 h before filtration. The
filtrate was evaporated to give a dark brown solid that was
chromatographed twice on silica (30:1 hexanes/EtOAc). Eva-
poration of the red band afforded 7 (45 mg, 7%) as a red solid.
4JHH=1.8 Hz, JPtH=50 Hz, 1H, H5). 13C NMR (125 MHz,
2
C6D6): δ 9.03 (s, JPtC=17 Hz, CH3), 107.5 (s, CCH3), 124.6,
124.9, 125.09, 125.5 (C6H5 and C4), 127.1, 127.7, 131.6 (C6H5),
137.2 (s, 2JPtC=43 Hz), 135.1 (s, 3JPtC=163 Hz, C3), 146.40 (s,
3JPtC=73 Hz), 159.4 (s, 2JPtC=24 Hz, C2), 188.7 (s, 1JPtC=1330
1
Hz, C5), 200.6 (s, JPtC = 1370 Hz, C1). Anal. Calcd for
C27H28Pt: C, 59.22; H, 5.15; Pt, 35.62. Found: C, 59.11; H,
5.10; Pt, 35.74.
Platinabenzene 9 and σ-Vinyl Complex 15. Using the condi-
tions described above, reaction of (Z)-1-tert-butyl-3-(2-
iodoethenyl)-2-phenylcyclopropene (309 mg, 0.95 mmol), BuLi
(0.41 mL, 2.5 M in hexanes, 1.03 mmol), and Cp*Pt(CO)I
(420 mg, 0.86 mmol) afforded a red-brown semisolid, which
was chromatographed on silica beginning with hexanes and
gradually increasing in polarity to 9:1 hexanes/Et2O. Isolation
of a yellow band and evaporation gave 15 (78 mg, 16%) as a
Mp: 168 °C (dec). 1H NMR (500 MHz, C6D6): δ 5.09 (t, 3JHH
=
2.7 Hz, 1H, CpH), 5.36 (d, 3JHH=2.7 Hz, 2H, CpH), 6.74 (br t,
3JHH=7.5 Hz, 1H, C6H5), 6.85-6.94 (m, 3H, C6H5), 6.94-6.98
=
(m, 6H, C6H5), 6.99 (t, 3JHH=7.7 Hz, 2H, C6H5), 7.07 (d, 3JHH
7.3 Hz, 2H, C6H5), 7.13 (d, 3JHH=7.3 Hz, 2H, C6H5), 7.25-7.30
(m, 4H, C6H5), 7.42 (t, 3JHH=7.7 Hz, 3JPtH=150 Hz, 1H, H4),
8.20 (dd, JHH =8.1 Hz, JHH =1.7 Hz, 1H, H3), 12.76 (dd,
3
4
1
viscous yellow oil. H NMR (500 MHz, C6D6): δ 1.32 (s, 9H,
3JHH=7.7 Hz, 4JHH=1.7 Hz, 2JPtH=65 Hz, 1H, H5). 13C NMR
CH3), 1.83 (s, 2JPtH=16 Hz, 15H, CH3), 3.02 (d, 3JHH=8.2 Hz,
1H, CHCpr), 6.10 (pseudo t, 3JHH=8.2 Hz, 2JPtH=167 Hz, 1H,
CHdCH), 6.57 (d, 3JHH=8.3 Hz, 2JPtH=10.4 Hz, 1H, PtCH),
0
(125 MHz, C6D6): δ 96.09 (s, CHCp ), 97.83 (s, CHCp’), 114.97 (s,
0
CPhCp ), 124.51, 125.00, 125.46, 125.72, 126.19, 128.51, 130.54,
130.92, 132.22 (s each; C6H5 and C4), 135.73 (s), 140.99 (s,
3
4
7.04 (tt, JHH = 7.5 Hz, JHH = 1.8 Hz, 1H), 7.22 (pseudo t,
3JHH=7.6 Hz, 2H), 7.77 (dd, 3JHH=8.3 Hz, 4JHH=1.3 Hz, 2H).
13C NMR (75 MHz, C6D6): δ 9.9, 29.0, 29.4, 32.9, 104.1, 104.2,
111.5, 127.9, 129.0, 130.0, 130.9, 145.7, 167.0 (s, JPtC=1190 Hz).
IR (toluene): ν 2002 cm-1. HRMS (MALDI) for C26H32OPt
[M]þ: calcd 555.2101, found 555.2087.
3JPtC ≈ 150 Hz, C3), 144.17 (s), 161.74 (s, C2), 194.96 (s, 1JPtC
=
1330 Hz, C5), 204.01 (s, 1JPtC =1400 Hz, C1) (2 signals obscured
by solvent peaks). Anal. Calcd for C34H26Pt: C, 64.86; H, 4.16.
Found: C, 64.95; H, 4.29.
η5-Cp*Pt(CO)I (13). [(η5-Cp*)Pt(CO)]2 (450 mg, 0.63 mmol)
was dissolved in dry toluene (15 mL) under Ar and cooled to
-30 °C. Solid I2 (168 mg, 0.66 mmol) was added, and the
reaction mixture was allowed to warm slowly to room tempera-
ture. After stirring for 10 min at room temperature, the brown
solution was evaporated to a volume of ca. 5 mL and chroma-
tographed on silica (toluene). The violet band (Rf ≈ 0.6) was
collected and evaporated to give 13 (410 mg, 67%) as a purple
solid. Mp: 118 °C (dec). 1H NMR (300 MHz, C6D6): δ 1.63 (s,
2JPtH=17 Hz, 15H, CH3). 13C NMR (75 MHz, C6D6): δ 10.61 (s,
CH3), 108.98 (s, 2JPtC=28 Hz, CCH3), 166.13 (s, 1JPtC=2440
Hz, CO). IR (toluene): ν 2029 cm-1. Anal. Calcd for
C11H15IOPt: C, 27.23; H, 3.12; Pt, 40.20. Found: C, 27.42; H,
2.93; Pt, 40.09.
A red band (Rf ≈ 0.4 using 9:1 hexanes/Et2O) was collected
next and evaporated to afford arene 9 (72 mg, 14%) as an
orange-red solid. Mp: 150 °C. 1H NMR (500 MHz, C6D6):
δ 1.23 (s, 9H, CH3), 1.56 (s, 3JPtH=9 Hz, 15H, CH3), 6.83 (tt,
4
3JHH = 7.3 Hz, JHH = 1.8 Hz, 1H), 7.01-7.08 (m, 2H),
7.08-7.16 (m, 3H), 7.60 (pseudo t, 3JHH=7.9 Hz, 3JPtH=151
Hz, 1H, H4), 8.54 (dd, 3JHH=8.3 Hz, 4JHH=1.6 Hz, 1H, H3),
11.83 (dd, 3JHH=7.5 Hz, 4JHH=1.6 Hz, 2JPtH=41 Hz, 1H, H5).
13C NMR (125 MHz, C6D6): δ 8.9 (s, CH3), 35.1 (s, C(CH3)3),
38.8 (s, C(CH3)3), 107.9 (s, CCH3), 124.5, 124.7, 126.3,
3
126.8 (C6H5 and C4), 134.1 (s, JPtC =134 Hz, C3), 139.9 (s,
2JPtC=43 Hz, C2), 161.2 (s, 2JPtC=48 Hz), 187.8 (s, 1JPtC=1338
Hz, C5), 203.7 (s, JPtC = 1370 Hz, C1). Anal. Calcd for
1
Platinabenzene 8 and σ-Vinyl Complex 14. (Z)-1,2-Diphenyl-
3-(2-iodoethenyl)cyclopropene (1, 167 mg, 0.485 mmol) was
dissolved in dry Et2O (20 mL) under Ar and cooled to
-78 °C. BuLi (0.20 mL, 2.5 M in hexanes, 0.50 mmol) was
added dropwise, and the resulting yellow solution was stirred at
-78 °C for 15 min. The lithiate solution was transferred into a
-50 °C cooled Schlenk flask containing Cp*Pt(CO)I (13,
195 mg, 0.40 mmol). A clear light red solution formed immedi-
ately. The solution was allowed to warm to -20 °C and stirred
for 12 h at this temperature to give a dark brown suspension.
The mixture was evaporated and chromatographed on silica
(30:1 hexanes/EtOAc). Concentration of a yellow fraction (Rf ≈
0.7 using 9:1 hexanes/EtOAc) furnished 14 (71 mg, 24%) as a
C25H32Pt: C, 56.91; H, 6.11; Pt, 36.97. Found: C, 56.79;
H, 6.35; Pt, 36.54.
Platinabenzene 10. Using the conditions described above,
reaction of (Z)-1-methyl-3-(2-iodoethenyl)-2-phenylcyclopro-
pene (180 mg, 0.64 mmol), BuLi (0.28 mL, 2.5 M in hexanes,
0.70 mmol), and Cp*Pt(CO)I (281 mg, 0.58 mmol) afforded a
red-brown semisolid, which was chromatographed on silica
beginning with hexanes and gradually increasing in polarity to
9:1 hexanes/Et2O. A red band was collected and evaporated to
give platinabenzene 10 (11 mg, 4%). 1H NMR (500 MHz,
C6D6): δ 1.61 (s, 3JPtH=8.3 Hz, 15H, CH3), 2.29 (s, 3H, CH3),
6.97 (d, 3JHH=8.2 Hz, 2H), 7.20 (d, 3JHH=8.2 Hz, 1H), 7.26 (t,
3JHH=8.2 Hz, 2H), 7.57 (pseudo t, 3JHH=7.6 Hz, 3JPtH=147.1
1
yellow solid. Mp: 116 °C (dec). H NMR (500 MHz, C6D6):
Hz, 1H, H4), 8.10 (d, 3JHH=7.6 Hz, 1H, H3), 11.93 (dd, 3JHH
=
δ 1.84 (s, 2JPtH=14 Hz, 15H, CH3), 3.38 (d, 3JHH=8.1 Hz, 1H,
CHCpr), 6.20 (pseudo t, JHH = 8.1 Hz, JPtH = 150 Hz, 1H,
7.6 Hz, 4JHH=1.5 Hz, 2JPtH=48.0 Hz, 1H, H5). MS (APCI): m/z
(%) 486.2 (Mþ þ H, 100). Anal. Calcd for C22H26Pt: C, 54.42;
H, 5.40; Pt, 40.18. Found: C, 54.59; H, 5.35; Pt, 39.97.
Transformation of 14/15 into 8/9. σ-Vinyl complex 14 or 15 (30
mg) was dissolved in C6D6 (0.6 mL) and stored at room
temperature under Ar in an NMR tube. The conversion was
monitored by proton NMR spectroscopy and proved to be
complete after 36-48 h. During the course of this conversion
identifiable side products were not formed, nor was significant
decomposition observed. Platinabenzene 8 or 9 was obtained in
>95% yield.
3
3
3
CHdCH), 6.69 (d, JHH=8.1 Hz, JPtH=14 Hz, 1H, PtCH),
2
3
4
7.07 (tt, JHH = 7.5 Hz, JHH = 1.2 Hz, 2H), 7.25 (pseudo t,
3JHH=7.7 Hz, 4H), 7.88 (dd, 3JHH=8.0 Hz, 4JHH=1.2 Hz, 4H).
13C NMR (75 MHz, C6D6): δ 9.7, 28.9, 103.9, 106.5, 117.3,
128.5, 129.0, 130.0, 137.0, 143.7, 167.1 (s, JPtC=1180 Hz). IR
(toluene): ν 2001 cm-1. Anal. Calcd for C28H28OPt: C, 58.43; H,
4.90; Pt, 33.89. Found: C, 58.73; H, 4.89; Pt, 33.47.
A red band (Rf ≈ 0.4 using 9:1 hexanes/EtOAc) was collected
next and evaporated to afford arene 8 (31 mg, 14%) as an
orange-red solid. Mp: 186 °C (dec). 1H NMR (500 MHz, C6D6):
Cycloadduct 16. Platinabenzene 8 (20 mg, 0.036 mmol) and
maleic anhydride (5.5 mg, 0.056 mmol) were dissolved in dry
Et2O (2 mL). This mixture was stirred overnight at room
temperature and then cooled to -30 °C. The solvent was
removed via cannula, leaving behind 16 (15 mg, 63%) as a light
δ 1.59 (s, 3JPtH=8 Hz, 15 H, CH3), 6.74 (tt, 3JHH=9.0 Hz, 4JHH
=
3
4
1.8 Hz, 1H), 6.86 (tt, JHH = 7.2 Hz, JHH = 1.5 Hz, 1H),
6.95-7.01 (m, 4H), 7.02-7.07 (m, 2H), 7.13-7.17 (m, 2H),
7.63 (pseudo t, 3JHH=7.8 Hz, 3JPtH=143 Hz, 1H, H4), 8.25 (dd,

5190 Organometallics, Vol. 28, No. 17, 2009
Table 3. Crystallographic Data and Summary of Data Collection and Structure Refinement
Jacob et al.
8
10
14
17
formula
fw
C27H28Pt
547.61
C22H26Pt
485.52
C28H28OPt
575.62
C30H28MoO3Pt
727.55
cryst syst
space group
T, K
monoclinic
P21/c
296
0.71073
10.575(3)
16.979(3)
12.445(2)
101.32(2)
2190.8(7)
4,1
monoclinic
P21/n
296
0.71073
12.194(5)
18.709(7)
16.940(6)
104.47(1)
3742(2)
8,2
monoclinic
P21/c
296
0.71073
15.981(3)
8.1257(11)
18.673(6)
98.35(2)
2399.1(8)
4,1
monoclinic
P21/n
296
0.71073
14.384(6)
11.007(4)
18.438(7)
112.62(1)
2695(2)
4,1
˚
λ, A
˚
a, A
˚
b, A
˚
c, A
β, deg
3
˚
V, A
Z,Z0
Dcalc, g cm-3
μ, mm-1
reflns measd
indep reflns
R1
wR2
GOF on F2
largest diff peak and hole, e A
1.660
6.39
5749
5281 [Rint = 0.015]
0.028
0.039
1.724
7.50
22 836
2800 [Rint = 0.134]
0.0395
0.0698
1.594
5.84
5522
3051 [Rint = 0.015]
0.034
0.044
1.793
5.68
13 042
2290 [Rint = 0.118]
0.0547
0.0728
1.48
1.28/-0.80
0.76
1.04/-1.30
1.29
1.29/-0.90
0.93
0.75/-0.64
-3
˚
1
yellow powder. H NMR (300 MHz, C6D6): δ 1.22 (s, 15H,
SMART Apex CCD (10 and 17) diffractometers at room
temperature using Mo KR radiation. The crystallographic data
and some details of the data collections and refinements of the
structures are given in Table 3. Absorption corrections were
applied by psi-scan and SADABS for 8/14 and 10/17, respec-
tively. Structures were solved using direct methods or the
Patterson function, completed by subsequent difference Fourier
syntheses, and refined by full matrix least-squares procedures on
F2. All non-H atoms were refined with anisotropic thermal
parameters. H atoms were refined in calculated positions in a
rigid group model. All calculations for 8/14 and 10/17 were
performed using the SIR9228 and Bruker SHELXTL29
packages, respectively.
3
4
CH3), 2.36 (dd, JHH = 8.9 Hz, JHH = 3.4 Hz, Pt satellites
obscured, 1H), 3.07 (dd, 3JHH=8.9 Hz, 3JPtH=145.8 Hz, 1H),
4.22-4.26 (m, 1H), 6.30-6.36 (m, 1H), 6.44 (t, 3JHH=6.4 Hz,
1H), 6.57 (d, 3JHH=6.0 Hz, 1H), 6.67 (dd, 3JHH=5.1 Hz, 3JHH
=
3.6 Hz, 2H), 6.77 (t, 3JHH=7.4 Hz, 1H), 6.92 (t, 3JHH=7.8 Hz,
2H) 7.08-6.97 (m, 4H). 13C NMR (75 MHz, C6D6): δ 8.1, 15.9,
16.4, 44.4, 58.8, 66.2, 108.2, 125.4, 125.9, 127.6, 129.5, 129.7,
130.2, 133.9, 135.7, 143.6, 148.5, 172.6, 180.4. IR (KBr): ν 1831
(CO), 1766 (CO) cm-1. Anal. Calcd for C31H30O3Pt: C, 57.67;
H, 4.68. Found: C, 57.81; H, 4.53.
Molybdenum Complex 17. Platinabenzene 8 (24 mg, 0.044
mmol) and (toluene)Mo(CO)3 were placed in a flask under N2;
then THF (5 mL) was added. Within 5 min the color of the
solution changed from red-orange to deep violet. After stirring
overnight, the THF was removed under reduced pressure and
hexanes was added. The hexanes was slowly evaporated under a
stream of N2 to precipitate 17 (21 mg, 66%) as violet crystals. 1H
NMR (300 MHz, C6D6): δ 1.46 (s, 15H), 5.11 (tt, JPtH=132.7
Hz, 3JHH=7.3 Hz, 1H, H4), 6.43 (dd, 3JHH=6.7 Hz, 4JHH=1.5
Hz, Pt coupling obscured, 1H, H3), 6.60 (t, 3JHH=7.6 Hz, 1H),
Acknowledgment. We thank the National Science Foun-
dation (CHE-0075246 and 0647252) for support of this
research. V.J. gratefully acknowledges the Alexander von
Humboldt Foundation for a Feodor Lynen Fellowship.
Supporting Information Available: X-ray structure cif files for
compounds 8, 10, 14, and 17. This material is available free of
charge via the Internet at http://pubs.acs.org.
6.57-6.83 (m, 6H), 6.99 (d, 3JHH=6.7 Hz, 2H), 7.08 (t, 3JHH
=
6.4 Hz, 1H), 8.43 (dd, 3JHH=7.6 Hz, 4JHH=1.5 Hz, 3JPtH=48.0
Hz, 1H, H5). IR (CCl4): ν 1959 (CO), 1894 (CO) cm-1. Anal.
Calcd for C30H28MoO3Pt: C, 49.52; H, 3.88. Found: C, 49.21;
H, 3.99.
(28) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J.
Appl. Crystallogr. 1993, 26, 343–350.
(29) SMART, SAINT, SHELXTL 6.10; Bruker AXS Inc.: Madison,
WI, 2000.
X-ray Crystallography. X-ray diffraction intensities were
collected on Enraf-Nonius CAD-4 (8 and 14) and Bruker