4114 Organometallics, Vol. 23, No. 17, 2004
Kalberer et al.
trend established for other d8 (dfepe)M systems: while
(dfepe)Ru(η6-C6H6) undergoes arene exchange very slowly
at 180 °C,15 and (dfepe)Ir(η6-C6H6)+ exchanges at 80
°C,16 we observe rapid arene exchange for (dfepe)Pt(η6-
C6H6)2+ at 20 °C and favorable arene complex formation
only in the presence of very weakly coordinating anions.
This lability trend correlates with the relative back-
bonding capabilities of these isoelectronic moieties.
Sch em e 3
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were conducted
under N2 using high-vacuum, Schlenk, and glovebox tech-
niques. All reactions were carried out under an ambient
pressure of approximately 590 Torr (elevation ∼2195 m). All
organic solvents were dried over sodium benzophenone ketyl
and stored under vacuum. Deuterated solvents were dried over
activated 3 or 4 Å molecular sieves. Fluorosulfonic acid was
distilled under nitrogen and stored at -30 °C in an inert
atmosphere glovebox prior to use. Elemental analyses were
performed by Desert Analytics. NMR spectra were recorded
with a Bruker Avance DRX-400 instrument. 31P NMR spectra
were referenced to an 85% H3PO4 external standard. (dfepe)-
Pt(OTf)2 and (dfepe)Pt(OSO2F)2 were prepared as described
previously.5 (cod)Pt(Ph)2 was prepared according to a modifica-
tion of Manzer’s procedure:17 after arylation, quenching of the
excess Grignard was carried out with NH4Cl in methanol;
removal of volatiles and extraction with ether afforded high
(>80%) yields of pure diphenyl after crystallization.
of excess benzene to (dfepe)Pt(Me)(OSO2F) in FSO3H
does not result in any spectroscopic changes due to the
formation of (dfepe)Pt(Me)(η2-benzene)+.
At ambient temperatures the resonances due to arene
complex 2 in FSO3H diminish over the course of several
hours concomitant with the growth of resonances due
to (dfepe)Pt(OSO2F)2 and a ∼2:1 mixture of benzene-
sulfonyl fluoride and diphenyl sulfone.12 Subsequent
addition of additional excess benzene to solutions of 1
in FSO3H cleanly regenerated 2. These observations are
consistent with the reversible coordination of benzene
to (dfepe)Pt2+ coupled with the electrophilic aromatic
substitution reaction of free benzene with FSO3H
(Scheme 3).13
Su m m a r y
(cod )P t(P h )O2CCF 3. (cod)Pt(Ph)2 (105 mg, 23 mmol) was
dissolved in 10 mL of CH2Cl2, and 1 equiv of CF3CO2H (17µL)
was added via syringe. The reaction mixture was stirred for 5
h, and all volatiles were removed. Ether was added, and the
solution was filtered, concentrated, and cold filtered at -78
°C, yielding 80 mg of off-white product (71% yield). Anal. Calcd
for C18H9O2F23P2Pt: C, 38.96; H, 3.40. Found: C, 38.61; H,
In all electron-rich mixed aryl/alkyl platinum(II)
systems examined to date, preferential protonolysis of
Pt(II)-alkyl bonds is observed, which is consistent with
an SE(ox) mechanism involving the intermediacy of
Pt(IV) hydrides. These systems all possess donor phos-
phine or diimmine supporting ligands. The (dfepe)-
Pt(II) system has a substantially lower electron density
and is the only class of Pt(II) compounds that we are
aware of which displays a distinct kinetic protonolysis
preference for Pt(II)-aryl bonds. We have previously
noted the inaccessibility of the formal Pt(IV) oxidation
state in (dfepe)Pt systems.5 We believe that this pro-
nounced lowering of electron density is accompanied by
a discrete change to a concerted SE2 protonolysis mech-
anism, a mechanism that is generally operative in main-
group organometallic systems.14 We expect that com-
petitive SE2 and SE(ox) M-C cleavage mechanisms will
be encountered in platinum(II) systems with ancillary
ligands of intermediate donating ability.
(dfepe)Pt2+ is shown to bind readily to benzene under
conditions where the counterions are weakly binding.
Although the single 1H and 13C NMR aromatic reso-
nances observed for (dfepe)Pt(C6H6)2+ at low tempera-
ture could be accommodated by a highly fluxional
(dfepe)Pt(η2-C6H6)(OSO2F)+ coordination geometry, the
inability of (dfepe)Pt(Me)+ to form a (dfepe)Pt(Me)(η2-
arene)+ complex leads us to favor a (dfepe)Pt(η6-C6H6)2+
bonding description. The lowered coordination ability
of arene to the (dfepe)Pt(II) center extends the lability
1
3.58. H NMR (400 MHz, C6D6, 27 °C): δ 1.20 (m, 4H); δ 1.55
2
3
(m, 4H), 3.94 (s, 2H; J PtH ) 40 Hz) 5.31 (s, 2H), 6.95 (t, J HH
3
) 7 Hz, 1H; p-C6H5), 7.07 (t, J HH ) 7 Hz, 2H; m-C6H5), 7.32
(d, J HH ) 7 Hz, J PtH ) 36 Hz, 2H; o-C6H5).
3
3
(d fep e)P t(P h )O2CCF 3 (1). A solution of 0.465 g (1.02
mmol) of (cod)Pt(Ph)2 in 15 mL of CH2Cl2 was cooled to -78
°C, 80 µL CF3CO2H (1.03 equiv) was added via syringe, and
the solution was allowed to warm to ambient temperature over
the course of 15 min with stirring. After 4 h, 0.35 mL of dfepe
(1.24 mmol) was added. Volatiles were removed after 16 h at
ambient temperature, and the residue was redissolved in 10
mL of CH2Cl2 and filtered to remove a small amount of
insoluble white solid. Cooling to -78 °C and filtering afforded
0.74 g of crude product, which NMR indicated was contami-
nated with a small amount of (dfepe)2Pt. Washing this crude
product thoroughly with petroleum ether to remove residual
(dfepe)2Pt gave 0.640 g (66.2%) of (dfepe)Pt(Ph)O2CCF3 as an
analytically pure white solid. Anal. Calcd for C18H9F23P2O2-
Pt: C, 22.85; H, 0.95. Found: C, 22.84; H, 0.91. 1H NMR (400
MHz, acetone-d6, 27 °C): δ 7.33 (m, 2H; Pt(C6H5)), 7.16 (m,
2H; Pt(C6H5)), 7.06 (m, 1H, Pt(C6H5)), 3.38 (m, 2H; PCH2), 3.12
(m, 2H; PCH2). 31P NMR (161.7 MHz, C6D6, 27 °C): δ 68.2 (m,
1
1J PtP ) 1270 Hz; trans to Ph), 49.0 (m, J PtP ) 4735 Hz; trans
to O2CCF3).
[(d fep e)P t(η6-C6H6)]2+ (2). To a solution of 25 mg of (dfepe)-
Pt(OSO2F)2 or (dfepe)Pt(OTf)2 in 0.5 mL of FSO3H or HOTf,
respectively, was added 5 µL (∼3 equiv) of benzene. After 30
1
min, H and 31P NMR indicated the clean generation of 2 as
(12) NMR spectroscopic data for PhSO2F in FSO3H: 1H: δ 7.15 (d,
J ) 8 Hz, 2H; o-C6H5), 7.01 (t, J ) 8 Hz, 1H; p-C6H5), 6.82 (t, J ) 8
Hz, 2H; m-C6H5). 19F: δ 64.52. NMR spectroscopic data for Ph2SO2 in
FSO3H: 1H: δ 7.12 (d, J ) 8 Hz, 2H; o-C6H5), 6.90 (t, J ) 8 Hz, 1H;
p-C6H5), 6.79 (t, J ) 8 Hz, 2H; m-C6H5).
the major solution species, with <10% unreacted starting
material. Spectroscopic data in FSO3H: 1H NMR (400 MHz,
(13) Tanaka, M.; Souma, Y. J . Org. Chem. 1992, 57, 3738.
(15) Koola, J . D.; Roddick, D. M. J . Am. Chem. Soc. 1991, 113, 1450.
(16) (a) Hoerter, J . M.; Roddick. D. M., unpublished results. (b)
Schnabel, R. C.; Roddick, D. M. Organometallics 1996, 15, 3550.
(17) Clark, H. C.; Manzer, L. E. J . Organomet. Chem. 1973, 59, 411.
(14) Protonolysis via
a SE2 mechanism is proposed for Pt(IV)
systems: Kondo, Y.; Ishikawa, M.; Ishihara, K. Inorg. Chim. Acta 1996,
241, 81.
Kalberer, Eric W.
