Protonolyses of (dfepe)Pt(Me)X (dfepe = (C2F5)2PCH2CH2P(C2F5)2; X = O2CCF3, OSO2H, OSO2CF3, OSO2F) complexes in their respective neat acid solutions cleanly yield (dfepe)Pt(X)2 products with rates ...dependent on relative acid strengths. No (dfepe)Pt(Me)(X)2(H)+ intermediates were observed by variable-temperature NMR in dichloromethane. The (perfluoroaryl)phosphine analogue (dfppe)Pt(Me)2 (dfppe = (C6F5)2PCH2CH2P(C6F5)2) is much less resistant to protonolysis and rapidly converts to (dfppe)Pt(OTf)2 in HOTf at 20 °C. Kinetic studies for protonolysis in CF3CO2H(D) and CF3SO3H(D) solvents were carried out. Examination of ionic strength and chloride anion effects in trifluoroacetic acid indicate that prior association of anion to (dfepe)Pt(Me)X systems is not kinetically important. k H/k D values were obtained from competitive protonolysis studies (CF3CO2H, 9 ± 2 (20 °C); H2SO4, 7 ± 2 (100 °C); CF3SO3H, 2.7 ± 0.7 (100 °C)). In the case of CF3CO2H, separate kinetic runs in protio and deuterio acids gave a lower k H/k D value of 3.6(4). The data obtained in these studies do not differentiate between limiting SE2 and SE(oxidative) protonolysis mechanisms.
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Catalytic ethylene dimerization by (dfepe)Pt(Me)X complexes in aprotic and trifluoroacetic acid solvents is described. In CH2Cl2, catalyst deactivation due to acid loss and generation of ...(dfepe)Pt(η2-C2H4) is observed. In contrast, long-term ethylene dimerization activity takes place in trifluoroacetic acid at 80 °C and produces 2-(trifluoroacetato)butane as the sole organic product. Under these reaction conditions, the catalyst resting state is (dfepe)Pt(Et)(O2CCF3). At 20 °C, reversible acid elimination from (dfepe)Pt(Et)(O2CCF3) and ethylene ligand exchange results in catalytic vinylic H+/D+ exchange with CF3CO2D (t 1/2 ≈ 40 min). Analogous palladium systems exhibit enhanced dimerization activity at 25 °C (340 turnovers/h, 100 psi C2H4) and form (dfepe)2Pd as a catalyst resting state. Inhibition of catalytic activity in the presence of added dfepe was noted. Comparisons between catalytic runs in CF3CO2H and CF3CO2D gave an apparent solvent kinetic effect of 3.5(2), based on an initial second-order rate dependence on ethylene. In CF3CO2D, regioselective acid addition to give only CH3CH(O2CCF3)CH(D)CH3 indicates that isomerization to 2-butene has occurred prior to 1,2-acid addition. A general olefin dimerization mechanism incorporating protonation preequilibria is presented.
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A series of new acceptor pincer Ru(
ii
) complexes are reported. The carbonyl complex (
CF
3
PCP)Ru(CO)Cl
2
−
Et
3
NH
+
is obtained from the reaction of
CF
3
PCPH with (cod)Ru(μ-Cl)
2
n
. Chloride ...displacement with
CF
3
PCPH, CO, PPh
3
, or C
2
H
4
gave complexes of the type (
CF
3
PCP)Ru(CO)(L)Cl, or in the case of
CF
3
PCPH, the bridged dimeric complex (
CF
3
PCP)Ru(CO)Cl
2
(μ-
CF
3
PCPH). Chloride abstraction from (
CF
3
PCP)Ru(CO)(L)Cl, L = CO or PPh
3
by (Et
3
Si)
2
(μ-H)
+
B(C
6
F
5
)
4
−
followed by Et
3
N addition produced (
CF
3
PCP)Ru(CO)(L)(H) products. Reaction of
cis
-(
CF
3
PCP)Ru(CO)
2
Cl with (Et
3
Si)
2
(μ-H)
+
B(C
6
F
5
)
4
−
in the presence of excess CO afforded (
CF
3
PCP)Ru(CO)
3
+
. The reaction of
CF
3
PCPH with (PPh
3
)
3
Ru(H)(O
2
CR) (R = Me or Ph) produced the corresponding carboxylate complexes (
CF
3
PCP)Ru(PPh
3
)(O
2
CR).
(
CF
3
PCP)Ru(CO)Cl
2
−
Et
3
NH
+
serves as a convenient precursor for Cl
−
displacement products (
CF
3
PCP)Ru(CO)(L)Cl (L = 1/2
CF
3
PCPH, CO, PPh
3
, or C
2
H
4
), (
CF
3
PCP)Ru(CO)(L)(H) products (L = CO, Ph
3
P), and (
CF
3
PCP)Ru(CO)
3
+
. The reaction of
CF
3
PCPH with (PPh
3
)
3
Ru(H)(O
2
CR) (R = Me or Ph) produces the corresponding carboxylate complexes (
CF
3
PCP)Ru(PPh
3
)(O
2
CR).
An extension of prior protonolysis studies of platinum−carbon bonds to Pt−aryl bonds is reported. The protolytic stability of (dfepe)Pt(Ph)(O2CCF3) (dfepe = (C2F5)2PCH2CH2P(C2F5)2) in trifluoroacetic ...acid is found to be much less than (dfepe)Pt(Me)(O2CCF3), indicating that a concerted SE2 protonolysis mechanism is most likely operative in these electron-poor platinum systems. VT NMR experiments show that benzene coordination to the (dfepe)Pt2+ center in neat fluorosulfonic acid to form (dfepe)Pt(η6-C6H6)2+ at −80 °C is competitive with benzene dissociation in this weakly coordinating medium.
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Thermolysis of (dfepe)Pt(Et)(O2CCF3) (dfepe = (C2F5)2PCH2CH2P(C2F5)2) in benzene at 80 °C results in the formation of (dfepe)Pt(η2-C2H4). However, at 120 °C in CF3CO2H a bridging ethylidene platinum ...dimer, (dfepe)2Pt2(μ-CHMe)(μ-H)O2CCF3, is produced instead. Product isolation by precipitation with diethyl ether afforded the neutral dimer (dfepe)2Pt2(μ-CHMe3). Alternatively, (dfepe)2Pt2(μ-CHMe) may be prepared at 20 °C by treatment of (dfepe)Pt(μ-H)2(H)+ with 1 atm of ethylene. Complete characterization of this species was accomplished by 1H, 13C, and 31P NMR spectroscopy, as well as X-ray diffraction. Investigations probing the mechanism of formation for this μ-alkylidene product are presented. The synthesis of the benzyl complex (dfepe)Pt(CH2Ph)(O2CCF3) and its reversible rearrangement to the η3-benzyl complex (dfepe)Pt(η3-CH2Ph)+ upon labilization of trifluoroacetate anion is also reported.
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Addition of excess HOSO2CF3 (HOTf) to CpRu(L)H (1) (L = dfepe = PR2CH2CH2PR2, R = C2F5) in CD2Cl2 under N2 produces a mixture of CpRu(L)(H)2+ (2a), CpRu(L)(H2)+ (2b), and CpRu(L)(OTf) (3) in a ratio ...of 1:5:2. Salts of the acid HOEt2+ are not strong enough to protonate 1. Complexes 2 slowly eliminate H2 to give 3; this reaction is slowed by adding excess HOTf. Of all such complexes CpRu(PR2CH2CH2PR2)(H2)+, R = alkyl and aryl, the dihydrogen complex 2b has the greatest acidity (similar to that of HOTf) and the related HD complex has the greatest J HD (29.1 Hz) because of the electron-withdrawing substituents R = C2F5. The reaction of 3 with 1 atm H2(g) proceeds much faster in the presence than in the absence of 1 equiv of HOTf to produce 1 and HOTf. This is a rare example of the production of a strong acid from H2(g) where the intermediate dihydrogen complex has been characterized. Reaction of Cp*Ru(L)Cl (4), Cp* = C5Me5, in dry CH2Cl2 at −78 °C with AgX salts under H2(g) (1 atm) gives mixtures of Cp*Ru(L)H (5) and Cp*Ru(L)(H)2+ (6), which have been identified by 1H NMR. 6 is deprotonated by traces of water or by PPh3 to give Cp*Ru(L)H (5). The addition of excess HOTf to mixtures of 5 and 6 under H2(g) produces 6. Complexes 3, 4, and 5 have been characterized by single-crystal X-ray diffraction. Complexes CpRu(L)Cl, 1, 4, and 5 have very positive redox potentials that indicate that the dfepe ligand has the electron-withdrawing power close to that of two carbonyl ligands.
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New electrophilic dimeric iridium(I) complexes (dfepe)Ir(μ-X)2 (dfepe = (C2F5)2PCH2CH2P(C2F5)2; X = O2CCF3, OTf) have been prepared and their reactions with H2 and cyclopentane examined. Treatment of ...(cod)Ir(O2CCF3)2 with dfepe produced an ionic product (dfepe)Ir(cod)+(dfepe)Ir(O2CCF3)2- (1), which in refluxing benzene rearranged with loss of cyclooctadiene to form (dfepe)Ir(μ-O2CCF3)2 (2). The corresponding reaction of (cod)Rh(O2CCF3)2 with dfepe yielded (dfepe)Rh(μ-O2CCF3)2 (3) directly. X-ray diffraction analysis of 2 revealed a hinged dimeric geometry with an unusually large interplanar angle of 82.7° defined by the two 4-coordinate metal centers (Ir(1)−Ir(2) = 4.307 Å). The triflate-bridged analogue of 2 was prepared via an indirect route: addition of 1 equiv of triflic acid to (dfepe)Ir(η3-C3H5) yielded the allyl hydride complex (dfepe)Ir(η3-C3H5)(H)(OTf) (4), which eliminated propylene in refluxing heptane to quantitatively afford (dfepe)Ir(μ-O3SCF3)2 (5). The structure of 4 was confirmed by X-ray diffraction. In contrast to (dfepe)Ir(μ-Cl)2, the acetate- and triflate-bridged analogues 2 and 5 are reactive toward both H2 and alkane C−H bonds. Treatment of 2 with H2 (20 °C) or cyclopentane (150 °C) cleanly afforded (dfepe)2Ir2(μ-H)2(H)(μ-O2CCF3) (6) and CpIr(dfepe), respectively. Surprisingly, the corresponding reactions of 5 are significantly slower, suggesting that the concomitant release of the stronger acid CF3SO3H may inhibit these heterolysis reactions.
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