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Organometallics 2010, 29, 5878–5884 DOI: 10.1021/om1006787
Catalytic Hydroalkylation of Olefins by Stabilized Carbon Nucleophiles Promoted by Dicationic Platinum(II) and Palladium(II) Complexes Maria E. Cucciolito, Angela D’Amora, and Aldo Vitagliano* Dipartimento di Chimica “Paolo Corradini”, Universit a di Napoli “Federico II”, Complesso Universitario di Monte S. Angelo, Via Cintia, I-80126 Napoli, Italy Received July 12, 2010
The coordinated olefin in dicationic platinum(II) and palladium(II) complexes [M(PNP)(olefin)](SbF6)2 (M = Pt, Pd; PNP = 2,6-bis(diphenylphosphinomethyl)pyridine; olefin = ethylene, propylene) reacts with β-dicarbonyl compounds (pentane-2,4-dione and methyl-3-oxobutanoate). If the proton released after the nucleophilic attack is trapped by a base, stable σ-alkyl derivatives [(PNP)M-CH2CH(R)CH(Ac)COR0 ]SbF6 (R = H, Me; R0 = Me, OMe) are formed; otherwise the M-C σ-bond can be cleaved by the proton, in the rate-determining step of a catalytic cycle that leads to the alkylated dicarbonyl compound. The β-diketone is intrinsically more reactive than the β-ketoester, but in the catalytic reaction of the former an inhibition effect is observed in the case of the platinum catalyst.
Introduction The electrophilic activation of unsaturated substrates by coordination to a transition metal ion is a key feature of organometallic chemistry and a fundamental step in a growing number of catalytic processes.1 The latest developments in this field, concerning the chemistry of platinum(II) and palladium(II), have been summarized in a recent review.2 The primary product of a nucleophilic attack is a M-C σ-bonded species, whose successive fate depends on the metal, the coordination environment, and the kind of nucleophile carrying on the attack. The intermediate σ-bonded derivative can undergo either β-H-elimination, as in Wacker-like reactions,2,3 or an intramolecular carbocationic rearrangement (eq 1),2,4,5 or, more frequently, a protolytic cleavage by an acidic proton released by the nucleophile after the attack *To whom correspondence should be addressed. E-mail:alvitagl@ unina.it. (1) Crabtree, R. H. The Organometallic Chemistry of Transition Metals, 4th ed.; John Wiley & Sons: New York, 2005. (2) Chianese, A. R.; Lee, S. J.; Gagne, M. R. Angew. Chem., Int. Ed. 2007, 46, 4042. (3) Wang, X.; Widenhoefer, R. A. Chem. Commun. 2004, 660. (4) (a) Hahn, C.; Cucciolito, M. E.; Vitagliano, A. J. Am. Chem. Soc. 2002, 124, 9038. (b) Cucciolito, M. E.; D'Amora, A.; Vitagliano, A. Organometallics 2005, 24, 3359. (5) Cucciolito, M. E.; Vitagliano, A. Organometallics 2008, 27, 6360. (6) (a) Karshtedt, D.; Bell, A. T.; Tilley, T. D. J. Am. Chem. Soc. 2005, 127, 12640. (b) Wang, X; Widenhoefer, R. A. Organometallics 2004, 23, 1649. (c) Bender, C. F.; Widenhoefer, R. A. J. Am. Chem. Soc. 2005, 127, 1070. (d) Michael, F. E.; Cochran, B. M. J. Am. Chem. Soc. 2006, 128, 4246. (7) Cucciolito, M. E.; D’Amora, A.; Vitagliano, A. Organometallics 2007, 26, 5216. (8) Whether the protonolysis takes place via a concerted three-center mechanism or via a prior oxidative addition to the metal,9 an interaction of the proton with the metal is involved, which is expected to be disfavored by the positive charge on the metal when the complex is cationic. Indeed, while in zwitterionic or neutral alkyl derivatives derived from the nucleophilic attack of amines on platinum-olefin complexes, the M-C bond is easily cleaved by HCl;10a reversal of the attack was observed in cationic derivatives.10b pubs.acs.org/Organometallics
Published on Web 10/25/2010
(eq 2).2,6,7 In the latter case, a problem is that the same factors that favor the nucleophilic attack also disfavor the protolytic cleavage of the M-C σ-bond,2,8-10 so that an appropriate balance of the factors controlling the two crucial steps is needed to drive the overall reaction to completion.
In practice, catalysis could be obtained either by driving the olefin activation through the use of dicationic complexes6a,7,11 or by favoring the protonolysis step through the use of neutral complexes.2,3,6b One relevant example of the latter case, reported by Widenhoefer and co-workers, is the hydroalkylation of olefins by β-dicarbonyl compounds promoted by Zeise’s dimer, in the presence of hydrogen chloride as a cocatalyst.3 Having in mind the above work and following our previous studies4,5,7 on catalytic cross-coupling reactions promoted by highly electrophilic Pt2þ and Pd2þ species, we report here a deeper investigation of the stoichiometric and catalytic coupling of ethylene and propylene with pentane-2,4-dione and methyl-3-oxobutanoate, promoted by the dicationic complexes 1, containing the tridentate pincer ligand 2,6-bis(diphenylphosphinomethyl)pyridine (PNP). Our results should help in getting a better understanding of the details of the nucleophilic addition/protolytic cleavage catalytic sequence promoted by PtII and PdII complexes. (9) Romeo, R.; D’Amico, G. Organometallics 2006, 25, 3435. (10) (a) Panunzi, A.; De Renzi, A.; Palumbo, R.; Paiaro, G. J. Am. Chem. Soc. 1969, 91, 3879. (b) Hahn, C.; Morvillo, P.; Herdtweck, E.; Vitagliano, A. Organometallics 2002, 21, 1807. (11) Karshtedt, D.; Bell, A. T.; Tilley, T. D. Organometallics 2004, 23, 4169. r 2010 American Chemical Society
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Figure 1. Time-dependent 1H NMR spectrum (400 MHz, CD3NO2) of the reaction between 1a (0.01 mol) and pentane-2,4-dione (4 equiv) in a solution saturated with ethylene. The figure illustrates the fast equilibrium formation of the σ-alkyl derivative 2a and its slow protonolysis to the organic product 2. Signals marked with an asterisk belong to the enolic form of the respective products. Refer to Chart 1 for the labeling of compounds.
Results and Discussion Reactions of the Ethylene Complexes [M(PNP)(C2H4)](SbF6)2 (1a, M=Pt; 1b, M=Pd) with Pentane-2,4-dione. In a preliminary experiment, the platinum complex 1a (11 mg, 0.01 mmol, dissolved in CD3NO2) was reacted with 4 equiv of pentane-2,4-dione in an NMR tube filled with ethylene at atmospheric pressure, and the reaction was monitored by 1H NMR. Shortly after the dissolution of the reactants, a multiplet of relatively small intensity appeared in the spectrum at δ = 1.65, indicating the presence of a Pt-CH2-CH2-R fragment. This signal (accounting for ca. 18% of the platinum complex), together with a singlet at δ = 1.69 (also ascribed to the σ-alkyl species [(PNP)PtCH2CH2CHAc2]þ, 2a), did not grow further with time, but after several minutes other signals began to appear and slowly increased, which could be ascribed to the alkylation product 3-ethylpentane-2,4dione (2); see Figure 1. After 48 h, 75% of the starting dione was converted to its ethyl derivative 2, while the starting complex 1a and the σ-alkyl species 2a were still present in solution in about the same ratio. A very similar result was obtained by running the same experiment on the palladium
complex 1b, which displayed a slightly lower reactivity, giving 65% conversion of the starting dione after 48 h. In another couple of experiments, to an NMR sample of 1a or 1b (in CD2Cl2/CD3NO2 (9:1) solution, saturated with ethylene) was added 2 equiv of pentane-2,4-dione, and the mixture was rapidly shaken with 20 μL of water. This caused the quenching of the catalytic reaction at its very beginning, with almost immediate and nearly complete conversion of the starting complexes into the corresponding σ-alkyl derivatives 2a and 2b, respectively. By essentially the same procedure, complexes 2a and 2b were then prepared on a larger scale, to be isolated and characterized. A distinctive 1H NMR feature (see Experimental Section for the data in CD2Cl2 solution) of the σ-alkyl derivatives 2a and 2b is the multiplet at δ 1.65 and 1.7, respectively, due to the four M-CH2CH2-R protons, formerly belonging to the coordinated ethylene molecule (pseudotriplet at δ = 4.62 and 4.80 in 1a and 1b, respectively). Also relevant is the shift of the CH2 pseudotriplet of the PNP ligand from δ = 5.0 in the dicationic olefin complexes to δ = 4.6 in the monocationic σ-alkyl derivatives. In solution complexes 2a and 2b exist as an equilibrium mixture of keto and enol form, the keto form
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being the major one (80% and 84% abundance, respectively, for 2a and 2b in dichloromethane). The above experiments demonstrated the feasibility of the catalytic coupling reaction between ethylene and pentane2,4-dione, using complexes 1a and 1b as catalysts, and at the same time gave important evidence about its mechanism (Scheme 1). The catalytic reaction takes place through the rapid equilibrium formation of the σ-alkyl derivative 2a or 2b and its successive slow cleavage by the acidic proton released by the dione substrate. This is consistent with the mechanism depicted in Scheme 1, in whose first step (i) the electron-rich enolic double bond leads to a nucleophilic attack on the coordinated ethylene molecule, very much like the first step of the hydroarylation reaction7 or that of other attacks by electronrich double bonds (eq 1).4,5 The released proton will then be shared and exchanged between the basic groups present in the system, notably the ubiquitous water molecules12 and the oxygen atoms belonging either to the product or to the excess substrate, until it irreversibly protonates the σ-bonded carbon atom (step ii), most likely via a metal-mediated process.9 Successively, we ran the catalytic reaction on a larger scale under different conditions, and the results (see Table 1) revealed that the coupling can be performed effectively with good yields and selectivity at a catalyst concentration down to 1 mol %, but at the same time disclosed an unexpected effect in the case of the platinum complex 1a. While the palladium catalyst 1b gave a complete and smooth conversion of the substrate to its ethylated products even at high concentrations of the dicarbonyl compound (roughly corresponding to a 1:1 volume ratio to the nitromethane solvent), in the case of platinum the catalyst (1a) was strongly inhibited by increasing the concentration of the nucleophilic substrate. Indeed, doubling the substrate concentration (Table 1, entry 3 vs 1) gave less than one-third of the conversion (as number of moles reacted), and a similar effect was observed also at a higher temperature and substrate/ catalyst ratio (Table 1, entry 7 vs 5). Increasing the ethylene concentration reduced the inhibition effect (Table 1, entry 4 vs 3, 8 vs 7), suggesting the occurrence of a competitive inhibition (12) In this respect we note that the quantitative aspects of the reaction progress, especially the relative amount of the σ-alkyl derivative present in the quasi-stationary state, are dependent on the amount of trace water doping the solvent (estimated to be between 50 and 100 ppm in our experiments), a larger water content increasing, as expected, the concentration of the σ-alkyl derivative. Nevertheless, the main qualitative features remain unaffected.
Table 1. Yield and Product Distribution in the Catalytic Coupling of Ethylene and Pentane-2,4-dionea yield % (% of monoethylated product 2)b
entry
dione/catalyst (mol/mol)
P (bar)
Pt cat. 1a
Pd cat. 1b
1 2 3 4 5 6 7 8
15 15 30 30 50c 50c 100c 100c
1 7 1 7 1 7 1 7
85 (86) 85 (86) 13 (100) 50 (96) >99 (22) >99 (10) 13 (100) 34 (98)
>99 (100) >99 (98) >99 (98) >99 (98) >99 (70) >99 (65) >99 (95) >99 (92)
a Solvent: nitromethane (free from nitriles). Concentration of the catalyst: 0.1 mol/L (before the addition of the substrate). T: 25 °C (70 °C when stated by note c). Reaction time: 24 h. b Yield determined by 1 H NMR and expressed as % of dione reacted. Monoethylated (2) and diethylated (3) products are formed, and the relative abundance (%) of 2 is given in parentheses. c T = 70 °C.
occurring through displacement of ethylene by the dione. Moreover, the inhibition effect appears to increase almost quadratically with the dione concentration, which could be tentatively explained by the formation of an inactive species containing the acac ligand (possibly σ-bonded to Pt via the C atom13), generated by the autoprotolysis of the substrate pentane-2,4dione. The same species might be less stable in the case of palladium and therefore be irrelevant to the reaction. Unfortunately, this remains a speculative suggestion, because our attempts to prepare such a complex were so far unsuccessful. The relative abundance of the monoethylated and diethylated products indicates a higher reactivity of the starting substrate with respect to its ethylated derivative, which appears to be especially relevant for the palladium complex 1b, considering that at room temperature (Table 1, entries 1-4) very little diethylated product 3 was formed even after exhaustion of the starting substrate. Apart from the inhibition effect observed in the case of the platinum complex and from the latter fine detail, there is no substantial difference between the platinum and palladium catalysis of the alkylation reaction. This contrasts with the outcome of the analogous alkylation reported by Widenhoefer,3 in which the palladium complex gave mainly the (13) De Pascali, S. A.; Papadia, P.; Ciccarese, A.; Pacifico, C.; Fanizzi, F. P. Eur. J. Inorg. Chem. 2005, 788.
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Figure 2. 1H NMR monitoring (400 MHz, CD3NO2) of the reaction between 1a (0.01 mol) and methyl-3-oxobutanoate (4 equiv) in a solution saturated with ethylene. The figure illustrates the relatively slow formation of the σ-alkyl derivative 4a and its slower protonolysis to the organic product 4. Refer to Chart 1 for the labeling of compounds. Strong unlabeled signals belong to methyl-3oxobutanoate.
unsaturated product resulting from a β-H-elimination reaction. In our case, the tridentate pincer ligand PNP prevents the occurrence of the β-H-elimination, and only the plain hydroalkylation reaction is observed. Reactions of the Ethylene Complexes [M(PNP)(C2H4)](SbF6)2 (1a, M = Pt; 1b, M = Pd) with Methyl-3-oxobutanoate. As in the case of pentane-2,4-dione, the reaction of the platinum complex 1a was first monitored by 1H NMR under the same conditions reported in the previous section. Signals due to the σ-alkyl species [(PNP)PtCH2CH2CH(Ac)COOMe]þ (4a) appeared shortly after mixing of the reactants, but in this case they were of much smaller intensity, accounting for ca. 3% of the starting platinum complex, and progressively grew with time, reaching a nearly stationary state at about 13% of the starting complex within 2 h. At the same time, signals that could be ascribed to the alkylation product 4 appeared and slowly grew with time (Figure 2), resulting after 48 h in a 40% conversion of the starting substrate. Under the same conditions, the palladium complex 1b behaved similarly, giving approximately the same stationary concentration of the σ-alkyl species [(PNP)PdCH2CH2CH(Ac)COOMe]þ (4b), but a slower protolytic cleavage of the
M-C bond, resulting after 48 h in a 13% conversion of the starting substrate to its ethylated product 4. Another experiment on the platinum complex 1a (CD2Cl2/ CD3NO2, 9:1, solution saturated with ethylene) was run in the presence of 20 μL of water to trap the protons and consequently quench the catalytic cycle. This gave an interesting result, confirming the much slower formation of the σ-alkyl derivative 4a compared to 2a. While 1a reacted immediately with the diketone, quantitatively forming 2a within the time needed to acquire the spectrum (see previous section), in the case of the ketoester the complex reacted first with water, giving the σ-alkyl species [(PNP)Pt-CH2CH2-OH]þ.10b Due to the reversibility of the nucleophilic addition,10b the kinetic β-hydroxyethyl product was slowly but totally converted to the thermodynamic product 4a within 2 h. In the case of the palladium complex 1b the evolution was similar, but complicated by the simultaneous occurrence of the ethylene displacement reaction by water,14 ultimately giving the thermodynamic product 4b within 3 h. Therefore in the case of (14) Hahn, C.; Morvillo, P.; Vitagliano, A. Eur. J. Inorg. Chem. 2001, 419.
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the β-ketoester as a nucleophile, the addition equilibrium (step i in Scheme 1) is much slower and apparently less shifted to the σ-alkyl product than for the β-diketone, most reasonably due to the enolic form of the compound being both less abundant and less electron-rich. By reacting 1a and 1b with the ketoester in presence of water, 4a and 4b were prepared on a larger scale, to be isolated and characterized (see Experimental Section). Differently from 2a and 2b, in this case no appreciable amount of the enolic form was detectable in dichloromethane solution. When the catalytic runs were made on a larger scale, the results (Table 2) matched the general trend observed in the NMR monitoring of the reaction, i.e., a lower reactivity of the β-ketoester compared with the β-diketone and a lower reactivity of the palladium complex compared to platinum. Indeed, from the inspection of Table 2 it is apparent that the reactivity of the platinum catalyst is not at all inhibited by the substrate, as it was in the case of the β-diketone, so that at 70 °C even with a large initial substrate/catalyst ratio, not only was the conversion complete, but also the diethylated product 5 was either dominant (Table 2, entries 5, 6) or quite abundant (Table 2, entry 7). In view of the explanation proposed in the previous section for the inhibition effect, this is consistent with the much lower stability Table 2. Yield and Product Distribution in the Catalytic Coupling of Ethylene and Methyl-3-oxobutanoatea yield % (% of monoethylated product 4)b
entry
substrate/catalyst (mol/mol)
P (bar)
Pt cat. 1a
Pd cat. 1b
1 2 3 4 5 6 7
15 15 30 30 70c 70c 100c
1 7 1 7 1 7 1
87 (82) 87 (85) 87 (88) 90 (88) >99 (13) >99 (8) >99 (58)
46 (100) 40 (100) 33 (94) 33 (97) >99 (87) >99 (87)
a Solvent: nitromethane (free from nitriles). Concentration of the catalyst: 0.1 mol/L (before the addition of the substrate). T: 25 °C (70 °C when stated by note c). Reaction time: 24 h. b Yield determined by 1 H NMR and expressed as % of ketoester reacted. Monoethylated (4) and diethylated (5) products are formed, and the relative abundance (%) of 4 is given in parentheses. c T = 70 °C.
of an anionic species (analogous to acac) in the case of the β-ketoester. It is worth noting that, in spite of the much lower reactivity of the β-ketoester in the nucleophilic addition (step i in Scheme 1) that was outlined above, the overall rate of the catalytic reaction is not that much smaller, indicating that an increase of the rate of the protonolysis (step ii in Scheme 1) does partially compensate the reduction of both the rate of formation of the σ-alkyl derivative and its equilibrium abundance. This is in agreement with the inverse correlation between the factors favoring the nucleophilic addition and those favoring the protolitic cleavage, which was anticipated in the Introduction. Indeed, a lower “basicity” of the β-dicarbonyl compound combined with a lower abundance of its enolic form disfavors the nucleophilic attack, but at the same time makes the released proton more acidic, favoring the protonolysis of the M-C σ-bond. The lower proton affinity of the β-ketoester compared to the β-diketone is also reflected in the different behavior of the isolated σ-alkyl complexes in their reaction with gaseous HCl in dichloromethane. The dione derivatives 2a and 2b gave mainly the reversal of the nucleophilic addition and only a minor amount (15% and 28%, respectively) of the ethylated product 2, while for the ketoester derivatives 4a and 4b the cleavage of the M-C bond was dominant, resulting in 68% and >98% of the ethylated product 4, respectively. Reactions of the Propylene Complexes [M(PNP)(C3H6)](SbF6)2 (6a, M = Pt; 6b, M = Pd). Propylene proved to be much less reactive than ethylene in the coupling reaction. At room temperature, using the same conditions as in the NMR monitoring experiments reported in the previous sections, no reaction was observed. Nevertheless, by reacting complex 6a or 6b (CH2Cl2 solution saturated with propylene) with pentane2,4-dione in presence of water, the σ-alkyl species (7a or 7b, respectively) were formed within 24 h, indicating that the addition equilibrium (analogous to step i in Scheme 1) was still effective in the case of propylene, although at a slower rate. An interesting side reaction also took place, which prevented the isolation of 7a and 7b, which were identified only by 1H NMR as a mixture with a new species (8a or 8b, respectively) in about 30% abundance (Scheme 2). 8a and 8b were identified by comparison of their NMR signals with those of authentic samples obtained in a previous work.5 The formation of 8a and 8b is
Scheme 2
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Chart 1. Metal σ-Alkyl Derivatives and Corresponding β-Dicarbonyl Products
explained by proton loss from a coordinated propylene molecule,15 with formation of a σ-allyl complex, and its successive coupling with another coordinated propylene molecule, a reaction recently reported by two of us.5 The formation of 8a and 8b was also confirmed by treatment of the crude mixture of σ-alkyl complexes with gaseous HCl. This resulted in the protonolysis of the M-C bond for 8a and 8b, giving the propylene dimer 4-methyl-1-pentene, while for 7a and 7b the reversal of the nucleophilic attack and displacement of propylene produced [(PNP)MCl]Cl and pentane-2,4-dione. In spite of the low reactivity of the propylene complexes and the possible occurrence of a side reaction, the catalytic coupling with pentane-2,4-dione could be performed with moderate yield at 70 °C and 2 bar. In 24 h, reacting with 30 equiv of substrate, the platinum catalyst 6a gave a 40% yield of the Markovnikov product 9 (Chart 1).
Conclusions The results presented in this paper give a further example of the reactivity of electron-rich double bonds (in the present case belonging to the enolic form of β-dicarbonyl compounds) with the electron-poor double bond of an olefin coordinated to a very electrophilic site. The reaction can take place catalytically, since the proton released from the intermediate σ-alkyl complex is able to cleave the M-C σ-bond, making the coordination site available to another olefin molecule. The reaction consists first of a reversible nucleophilic addition step (i in Scheme 1) and then an irreversible protonolysis of the metal-carbon bond (ii in Scheme 1). Differently from the analogous catalytic reaction reported by Widenhoefer,3 here a lower relative amount of catalyst was effective, and no cocatalyst was necessary. Indeed, no Wacker-type reaction takes place, because the tridentate pincer ligand PNP prevents a β-H-elimination from the intermediate palladium σ-complex. Moreover, no addition of HCl is necessary,16 because the first reversible step is favored enough by the highly electrophilic metal center to produce a concentration of acidic protons sufficient to cleave the M-C bond.
Experimental Section General Procedures. CD2Cl2 and CD3NO2 were dried with 4 A˚ molecular sieves. The 1,3-dicarbonyl substrates were obtained by Aldrich and were used without further purification. The NMR (15) Bandoli, G.; Dolmella, A.; Fanizzi, F. P.; Di Masi, N. G.; Maresca, L.; Natile, G. Organometallics 2001, 20, 805. (16) Actually in our case, the addition of HCl would kill the whole process, by irreversible coordination of the chloride ion to the single site needed for the coordination of the olefin.
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spectra were recorded on Varian VXR 200, Varian Gemini 300, and Bruker WH 400 instruments. The 1H NMR shifts were referenced to the resonance of the residual protons of the solvents (δ = 5.32, CHDCl2; δ = 4.33, HCD2NO2); the 13C NMR shifts, to the solvent resonance (δ = 53.8, CD2Cl2). Abbreviations used in NMR data: s, singlet; d, doublet; t, triplet; ps t, pseudo triplet; m, multiplet; br, broad. Syntheses. The complexes [Pt(PNP)(CH2dCHR)](SbF6)2 and [Pd(PNP)(CH2dCHR)](SbF6)2 were prepared according to the procedures described in the literature.10b,14,17 Preparation of σ-Derivatives. General Procedure. To a solution of the alkene complex (0.040 mmol) in 2 mL of CH2Cl2 saturated with the alkene were added 1.5 equiv of 1,3-dicarbonyl compound and 20 μL of H2O. The mixture was stirred for 24 h (30 min in the case of pentane-2,4-dione with the complex 1a). The solution was dried over Na2SO4, filtered, and concentrated in vacuo. The product was precipitated by dropwise addition of diethyl ether, filtered off, and dried under vacuum. In the reaction with the propylene complex, a mixture of products was obtained (7a and 8a, 7b and 8b), and no separation was made. In addition, the assigned structures were confirmed by reductive and/or protolytic degradation of the complex mixture and successive identification of the resulting organic products. 2a. Yield: 37.6 mg, 0.0364 mmol, 91%; light gray solid. Anal. Calcd for C38H38F6NO2P2PtSb: C, 44.17; H, 3.71; N, 1.36. Found: C, 43.91; H 3.88; N, 1.27. 1H NMR (200 MHz, CD2Cl2), ketonic form: δ 1.55-1.65 (br, 4 H, PtCH2CH2), 1.69 (s, 6 H, MeCO), 3.11 (t, 1 H, CH(COMe)2), 4.42 (ps t, 4 H, PCH2), 7.50-7.80 (m, 22 H, PPh, py), 8.00 (t, 1 H, py). 1H NMR (200 MHz, CD2Cl2), enolic form: δ 1.30 (s, 6 H, MeCO). 13C NMR (50 MHz, CD2Cl2), ketonic form: δ -2.0 (PtCH2, JPt = 646 Hz), 29.3 (COMe), 33.8 (PtCH2CH2), 46.2 (ps t, 1JP = 35 Hz, PCH2), 72.5 (3JPt = 85 Hz, CH), 123.5 (py-3,5), 127.5 (ps t, 1JP = 52 Hz, PPhj), 130.0 (PPhm), 133.0 (PPhp), 133.6 (PPho), 141.3 (py-4), 159.8 (ps t, 2JPt = 38 Hz, py-2,6), 204.0 (COMe). 13C NMR (50 MHz, CD2Cl2), enolic form: δ 22.0 (COMe), 191.0 (COMe). 2b. Yield: 36.7 mg, 0.0388 mmol, 97%; light gray solid. Anal. Calcd for C38H38F6NO2P2PdSb: C, 48.31; H, 4.05; N, 1.48. Found: C, 48.07; H 4.13; N, 1.42. 1H NMR (300 MHz, CD2Cl2), ketonic form: δ 1.7-1.75 (br, 4 H, PdCH2CH2), 1.72 (s, 6 H, MeCO), 3.20 (br, 1 H, CH(COMe)2), 4.42 (ps t, 4 H, PCH2), 7.50-7.80 (m, 22 H, PPh, py), 8.00 (t, 1 H, py). 1H NMR (300 MHz, CD2Cl2), enolic form: δ 1.36 (s, 6 H, MeCO). 13C NMR (75 MHz, CD2Cl2), ketonic form: δ 12.6 (PdCH2), 29.3 (COMe), 32.0 (PdCH2CH2), 44.9 (ps t, 1JP = 26 Hz, PCH2), 71.7 (CH), 123.3 (py-3,5), 128.2 (ps t, 1JP = 45 Hz, PPhj), 130.0 (PPhm), 132.3 (PPhp), 133.2 (PPho), 141.0 (py-4), 158.4 (ps t, py-2,6), 203.8 (COMe). 13C NMR (75 MHz, CD2Cl2), enolic form: δ 10.8 (PdCH2), 22.2 (COMe), 45.7 (ps t, 1JP = 26 Hz, PCH2), 112.9 (CH2CdC), 190.9 (CO). 4a. Yield: 39.4 mg, 0.0375 mmol, 94%; white solid. Anal. Calcd for C38H38F6NO3P2PtSb: C, 43.49; H, 3.65; N, 1.33. Found: C, 43.28; H, 3.79; N, 1.30. 1H NMR (200 MHz, CD2Cl2): δ 1.5-1.7 (br, 4 H, PtCH2CH2), 1.73 (s, 3 H, COMe), 2.92 (t, 1 H, CH(COMe)(CO2Me)), 3.42 (s, 3 H, CO2Me), 4.40 (ps t, 4 H, PCH2), 7.50-7.80 (m, 22 H, PPh, py), 8.00 (t, 1 H, py). 13C NMR (50 MHz, CD2Cl2): δ -2.5 (PtCH2, JPt = 634 Hz), 28.6 (COMe), 33.5 (PtCH2CH2), 46.3 (ps t, 1JP = 33 Hz, PCH2), 52.0 (CO2Me), 64.0 (3JPt = 103 Hz, CH), 123.3 (py-3,5), 127.3 (ps t, 1JP = 55 Hz, PPhj), 130.0 (PPhm), 132.7 (PPhp), 133.9 (PPho), 140.4 (py-4), 159.9 (ps t, 2 JPt = 33 Hz, py-2,6), 170.1 (CO2Me), 202.9 (COMe). 4b. Yield: 36.9 mg, 0.0384 mmol, 96%; white solid. Anal. Calcd for C38H38F6NO3P2PdSb: C, 47.51; H, 3.99; N, 1.46. Found: C, 47.23; H, 4.14; N, 1.40. 1H NMR (300 MHz, CD2Cl2): δ 1.65-1.85 (br, 4 H, PdCH2CH2), 1.78 (s, 3 H, COMe), 3.02 (t, 1 H, CH(COMe)(CO2Me)), 3.45 (s, 3 H, CO2Me), 4.42 (ps t, 4 H, PCH2), 7.50-7.70 (m, 22 H, PPh, py), 7.90 (t, 1 H, py). 13C NMR (17) Hahn, C.; Vitagliano, A.; Giordano, F.; Taube, R. Organometallics 1998, 17, 2060.
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(50 MHz, CD2Cl2): δ 12.3 (PdCH2), 28.6 (COMe), 31.9 (PdCH2CH2), 44.9 (ps t, 1JP = 26 Hz, PCH2), 52.2 (CO2Me), 63.1 (CH), 123.4 (py-3,5), 128.4 (ps t, 1JP = 45 Hz, PPhj), 130.0 (PPhm), 132.4 (PPhp), 133.4 (PPho), 141.1 (py-4), 158.6 (py-2,6), 169.9 (CO2Me), 202.7 (COMe). 7a (in a mixture with 8a). 1H NMR (300 MHz, CD2Cl2): δ 0.33 (d, 3 H, Me), 1.34 (m, 1 H, PtCHH), 1.63 (s, 3 H, COMe), 1.76 (s, 3 H, COMe), 2.09 (m, 1 H, CHMe), 2.22 (m, 1 H, PtCHH), 3.02 (d, 1 H, CH(COMe)2), 4.42 (ps t, 4 H, PCH2), 7.40-7.80 (m, 22 H, PPh, py), 8.03 (t, 1 H, py). 7b (in a mixture with 8b). 1H NMR (300 MHz, CD2Cl2): δ 0.50 (d, 3 H, Me), 1.55 (m, 1 H, PdCHH), 1.65 (s, 3 H, COMe), 1.84 (s, 3 H, COMe), 2.03 (m, 1 H, PdCHH), 2.21 (m, 1 H, CHMe), 3.10 (d, 1 H, CH(COMe)2), 4.40 (ps t, 4 H, PCH2), 7.40-7.90 (m, 22 H, PPh, py), 8.02 (t, 1 H, py). 8a. See 1H NMR data reported in ref 5 for complex 5d-Pt. 8b. 1H NMR (400 MHz, CD2Cl2): δ 1.57 (d, 3 H, Me), 1.45 (m, 2 H, βCH and γCHH), 1.53 (m, 1 H, γCHH), 1.90 (m, 1 H, PdCHH), 2.07 (m, 1H, Pd CHH), 4.4 (ps t, 4 H, PCH2), 4.64 (d, 1 H, dCHH), 4.72 (d, 1 H, dCHH), 5.26 (m, 1 H, dCH), 7.4-8.0 (m, 23 H, PPh, py). Catalytic Reactions. The catalytic reactions were run in a 10 mL glass autoclave under the conditions reported in Tables 1 and 2. The appropriate metal complex (0.03 mmol) was dissolved in 0.3 mL of CD3NO2, and 15-100 equiv of the appropriate 1,3-dicarbonyl
Cucciolito et al. compound was added. The solution was stirred under ethylene or propylene for 24 h and then was analyzed by 1H NMR to determine its composition and yields. Reductive Degradation with NaBH4. The reduction was performed on all the σ-alkyl derivatives. The complexes resulting from the base-assisted addition reaction (30-50 mg) were dissolved in 1.5 mL of CH2Cl2/MeOH (5:2), and an excess of solid NaBH4 was added. The mixture was stirred for 12 h and then treated with 1.0 mL of a NH4Cl-saturated aqueous solution. The organic phase was separated and evaporated to dryness. The residue was extracted with diethyl ether, the ether extract was evaporated to dryness, and the residue was analyzed by 1H NMR for identifying the organic products. Reaction with HCl. Protolytic degradation was performed on all the σ-alkyl derivatives. The complexes (10 mg) were dissolved in 0.6 mL of CD2Cl2, and gaseous HCl was bubbled through. The solutions containing M(PNP)Cl2 and organic products were characterized by 1H NMR spectroscopy.
Acknowledgment. This work was supported by MIUR (PRIN Grant No. 2007-X2RLL2). We thank the CIMCF, University of Napoli Federico II, for access to the NMR facilities and Miss Nunzia Contiello for experimental assistance.
