Intermolecular cross-coupling between η2-olefin and η1-allyl ligands in cationic platinum(II) and palladium(II) complexes

Article abstract of DOI:10.1021/om8006882

The terminal (γ) carbon atom of the allyl system in η¹-allyl platinum and palladium complexes of the tridentate pincer ligand PNP (PNP = 2,6-bis-diphenylphosphinomethyl-pyridine) attacks the coordinated olefin of dicationic platinum and palladium complexes with the same ligand, producing binuclear species in which the metal formerly π-coordinated becomes σ-bonded, and the metal formerly σ-bonded becomes π-coordinated. The reaction can be run catalytically with respect to the addition of ethylene to a η¹ -allyl complex, using the dicationic ethylene complex as catalyst.

Full text of DOI:10.1021/om8006882

6360
Organometallics 2008, 27, 6360–6363
Notes
Intermolecular Cross-coupling Between η2-Olefin and η1-Allyl
Ligands in Cationic Platinum(II) and Palladium(II) Complexes
Maria E. Cucciolito and Aldo Vitagliano*
Dipartimento di Chimica “Paolo Corradini”, UniVersita` di Napoli Federico II, Complesso UniVersitario di
Monte S. Angelo, Via Cintia, 80126 Napoli, Italy
ReceiVed July 21, 2008
Summary: The terminal (γ) carbon atom of the allyl system in
η1-allyl platinum and palladium complexes of the tridentate
pincer ligand PNP (PNP ) 2,6-bis-diphenylphosphinomethyl-
pyridine) attacks the coordinated olefin of dicationic platinum
and palladium complexes with the same ligand, producing
binuclear species in which the metal formerly π-coordinated
becomes σ-bonded, and the metal formerly σ-bonded becomes
π-coordinated. The reaction can be run catalytically with respect
to the addition of ethylene to a η1-allyl complex, using the
dicationic ethylene complex as catalyst.
Indeed, the electrophilic addition to the terminus of a
σ-allylmetal species is well-known,7 and the above reaction was
reported to take place between neutral CpFe(CO)2(allyl) and
cationic [CpFe(CO)2(olefin)]+ complexes.8 Various allyl-olefin
couplings, including the Oppolzer reaction,9 have been shown
instead to involve the alkene insertion in a σ or π-allyl metal
bond,10 and a recent theoretical investigation examined the
feasibility of the analogous “ene” reaction, in which a free olefin
couples to a σ-allyl moiety in a process taking place on a single
metal center.11
In this note we report about the actual occurrence of the above
allyl-olefin intermolecular coupling (eq 3), taking place
between monocationic allyl complexes 1 and dicationic olefin
complexes 2, in a reaction that appears to be promising further
developments.
The concept that the electrophilic activation of a coordinated
olefin is greatly enhanced when the metal brings a net positive
charge was brought up in the chemical literature more than 20
years ago.1 However, only in recent years has this idea been
pushed further to complexes bearing a double positive charge,2
and finally exploited to the achievement of new catalytic
processes,3 including hydroamination,4 hydrovinylation,5 and
hydroarylation6 reactions. In the latter two cases, the nucleophilic
attack was brought about by the π-electrons of either a
substituted olefin (eq 1) or an activated aromatic ring (eq 2).
Results and Discussion
When the stoichiometric amount of complex 1a was added
to a suspension of 2a (both as fluoroborate salts) in dichlo-
In both cases, an activation of the carbon nucleophile by
electron-donating substituents was necessary to achieve an
acceptable reactivity, through an adequate stabilization of the
intermediate carbonium ion(s). Seeking for other π-electron
nucleophilic systems capable of attacking a coordinated olefin,
we considered that the double bond of a η1-allyl complex is
activated toward electrophilic attack by the presence of the metal
atom in the allylic position, which would favor a concerted
electron displacement as depicted in eq 3.
(2) (a) Hahn, C.; Morvillo, P.; Vitagliano, A. Eur. J. Inorg. Chem. 2001,
419. (b) Hahn, C.; Morvillo, P.; Herdtweck, E.; Vitagliano, A. Organome-
tallics 2002, 21, 1807.
(3) For a recent review see: Chianese, A. R.; Lee, S. J.; Gagne´, M. R.
Angew. Chem., Int. Ed. 2007, 46, 4042.
(4) (a) Wang, X.; Widenhoefer, R. A. Organometallics 2004, 23, 1649.
(b) Karshtedt, D.; Bell, A. T.; Tilley, T. D. J. Am. Chem. Soc. 2005, 127,
12640. (c) Michael, F. E.; Cochran, B. M. J. Am. Chem. Soc. 2006, 128,
4246. (d) Bender, C. F.; Widenhoefer, R. A. J. Am. Chem. Soc. 2005, 127,
1070.
(5) (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. (c) Kerber, W. D.; Koh, J. H.; Gagne´,
M. R. Org. Lett. 2004, 6, 3013.
(6) (a) Cucciolito, M. E.; D’Amora, A.; Tuzi, A.; Vitagliano, A.
Organometallics 2007, 26, 5216. (b) Karshtedt, D.; Bell, A. T.; Tilley, T. D.
Organometallics 2004, 23, 4169.
(7) Crabtree, R. H. The Organometallic Chemistry of Transition Metals,
4th Edition; John Wiley & Sons: New York, 2005, p. 134.
(8) Lennon, P. J.; Rosan, A.; Rosenblum, M.; Tancrede, J.; Waterman,
P. J. Am. Chem. Soc. 1980, 102, 7033.
* To whom correspondence should be sent. E-mail: alvitagl@
unina.it.
(1) (a) Maresca, L.; Natile, G.; Rizzardi, G. Inorg. Chim. Acta 1980,
38, 53. (b) Maresca, L.; Natile, G. J. Chem. Soc., Chem. Commun. 1983,
40. (c) Maresca, L.; Natile, G. Comments Inorg. Chem. 1994, 16, 95, and
references therein. (d) Sasaki, S.; Maruta, K.; Ohkubo, K. Inorg. Chem.
1987, 26, 2499. (e) Stro¨mberg, S.; Svensson, M.; Zetterberg, K. Organo-
metallics 1997, 16, 3165.
10.1021/om8006882 CCC: $40.75
2008 American Chemical Society
Publication on Web 10/29/2008

Notes
Organometallics, Vol. 27, No. 23, 2008 6361
Scheme 1
temperature, yet still producing the corresponding complexes
5b and 5d. Besides their 1H and 13C characterization, in all the
cases the structure of the reaction products 5 was confirmed by
protonolysis of the M-C σ-bond with gaseous HCl in dichlo-
romethane and identification of the resulting hydrocarbons. The
coupling (ii) appears to be highly regioselective but not
stereoselective. Indeed, in all the cases the C-C bond formation
took place between the most substituted carbon atoms of the
olefin and of the allyl group, but the final products 5b were
obtained as equimolar mixtures of diastereomers.
It is important to note that the η1-allyl complexes 1 do not
react with free olefins, and that the ethylene complexes 2a do
not react with η3-allyl complexes such as [(1,5-COD)Pd(cro-
tyl)]+. The presence of a σ-allyl group on one fragment and of
an electrophilically activated olefin on the other fragment are,
thus, essential for the reaction to take place, and the tridentate
pincer ligand PNP appears to be precisely tailored to achieve
both conditions, supporting the mechanistic picture of an
intermolecular “external” attack given in Scheme 1. Because
this mechanism produces a nice σ-π bond and net charge
switching between the two metal ions involved, to get further
evidence for it we reacted the palladium crotyl complex 1b-Pd
with an equimolar amount of the platinum ethylene complex
2a-Pt in dichlorometane, and then bubbled ethylene for 10 min
while mixing. The result was a 6:1 mixture of the alkyl
complexes 5c-Pt and 5c-Pd, containing the Pt-alkyl derivative
as the expected major product.12
In conclusion, we have demonstrated that the intermolecular
“ene” coupling of a σ-allyl species with an electrophilically
activated olefin is a feasible and smooth reaction, when the use
of a suitable pincer ligand prevents other possible routes, such
as π-allyl formation or olefin insertion reactions. Although the
reaction per se is not novel, having been described almost 30
years ago in the case of cyclopentadienyl iron complexes,8 its
extension within platinum and especially palladium chemistry
might prelude to interesting developments.
romethane, both compounds rapidly dissolved, indicating that
a reaction had occurred. The H NMR spectra of the mixture
revealed that, besides the anticipated coupling reaction, dis-
placement equilibria were taking place according to the general
picture given in Scheme 1.
1
The initial displacement reaction (i) led to allyl-bridged
species to whom we tentatively assign the delocalized electronic
structure 3, which accounts for the chemical equivalence of the
two halves of the complex observed in the 13C NMR spectrum
of 3a-Pt. The stabilization due to charge-delocalization also
accounts for the observation that the ethylene displacement (i)
is favored in the case of complex 3a, in spite of the fact that
the stability of dicationic complexes of ethylene (2b) is usually
greater compared to complexes of higher olefins.2 The coupling
reaction (ii), which was particularly fast in the case of ethylene,
produced the binuclear species 4, which contains one σ-bonded
and one π-bonded M(PNP) fragments. Complexes 4 were
1
generally detected in solution by H and 13C NMR without
Experimental Section
isolation, but in the case of 4c-Pt the complex was also obtained
by ligand exchange (with elimination of ethylene) from equimo-
lar amounts of the isolated final product 5c-Pt and 2a-Pt.
Although the equilibrium i does actually inhibit the coupling ii
(especially when R′ ) H), in all the cases the overall reaction
could be driven to completion by an excess of the free olefin,
leading to the mononuclear species 5 and regenerating the
starting alkene complex 2 via the displacement reaction iii. In
the case of ethylene, the overall reaction could be run catalyti-
cally with respect to the addition of free olefin to species 1,
using complex 2a as a catalyst. In a typical experiment, ethylene
was gently bubbled for 10 min at room temperature through a
solution of 180 mg (0.25 mmol) of the palladium crotyl complex
1b-Pd in 2.0 mL of dichloromethane, in the presence of 5 mol%
of complex 2a-Pd. After addition of diethyl ether and freezing
to -20 °C, the coupling product 5c-Pd was obtained essentially
pure as a yellow crystalline solid (172 mg, 92% yield). The
stoichiometric reaction of the propene complexes was substan-
tially slower, a few hours being necessary to complete it at room
General Procedures. CH2Cl2, CD2Cl2, CD3NO2, and MeNO2
(free from nitriles) were dried with 4 Å molecular sieves. The NMR
spectra were recorded on Varian VXR 200, Varian Gemini 300,
and Brucker WH 400 instruments. The 1H NMR shifts were
referenced to the resonance of the residual protons of the solvents,
the 13C NMR shifts to the solvent resonance (δ ) 53.8, CD2Cl2; δ
) 62.8, CD3NO2). Abbreviations used in NMR data: s, singlet; d,
doublet; t, triplet; ps. t, pseudo triplet; m, multiplet; br, broad.
Starting Materials. The palladium allyl complexes 1-Pd13 and
the olefin complexes 2-Pd2a and 2-Pt2b were prepared according
to the procedures described in the literature. The complex
[Pd(CH2CHCHCH2OMe)Cl]2, precursor to the methoxymethylene
substituted allyl 1e-Pd, was prepared as described.14 The platinum
complexes 1a-Pt and 1b-Pt (see below for NMR data) were
obtained by addition of PNP to a dichloromethane solution of the
corresponding bis(pyridine)[(η3-allyl)platinum] salts, using the same
procedure described for phenanthroline η3-allyl complexes.15
(12) The partial scrambling giving 5c-Pd as a minor unexpected product
can be explained by some olefin exchange taking place during the reaction
time. This would produce small amounts of the Pd-ethylene complex 2a-
Pd whose reaction with 1b-Pd gives the minor product.
(13) Barloy, L.; Ramdeehul, S.; Osborn, J. A.; Carlotti, C.; Taulelle,
F.; De Cian, A.; Fisher, J. Eur. J. Inorg. Chem. 2000, 2523.
(14) Åkermark, B.; Ljungqvist, A.; Panunzio, M. Tetrahedron Lett. 1981,
22, 1055.
(9) For a review see: Oppolzer, W.; Flachsmann, F. HelV. Chim. Acta
2001, 84, 416.
(10) (a) Di Renzo, G. M.; White, P. S.; Brookhart, M. J. Am. Chem.
Soc. 1996, 118, 6225. (b) Ca´rdenas, D. J.; Echavarren, A. M. New J. Chem.
2004, 28, 338, and references therein.
(11) Garc´ıa-Iglesias, M.; Bun˜uel, E.; Ca´rdenas, D. J. Organometallics
2006, 25, 3611.
(15) Sjo¨gren, M.; Hansson, S.; Norrby, P.-O.; Åkermark, B.; Cucciolito,
M. E.; Vitagliano, A. Organometallics 1992, 11, 3954.

6362 Organometallics, Vol. 27, No. 23, 2008
Notes
[(PNP)PtCH2CHdCH2](BF4) (1a-Pt). 1H NMR (300 MHz,
CD2Cl2): δ 2.63 (app quartet, 2 H, PtCH2, JPt ) 105 Hz), 4.20 (m,
2 H, dCH2), 4.40 (ps t, 4 H, PCH2), 5.55 (m, 1 H, dCH),
7.40-7.80 (m, 22 H, PPh, py), 8.00 (t, 1 H, py). 13C NMR (75
MHz, CD2Cl2): δ 5.1 (1JPt ) 581 Hz, PtCH2), 46.1 (ps t, 1JP ) 34
Hz, PCH2), 109.4 (3JPt) 58 Hz, dCH2), 123.3 (py-3,5), 127.3 (ps
PdCH2), 4.40 (ps t, 4 H, PCH2), 4.66 (m, 2 H, dCH2), 5.40 (m, 1
H, dCH), 7.40-7.70 (m, 22 H, PPh, py), 7.88 (t, 1 H, py). 13C
NMR (75 MHz, CD2Cl2): δ 17.0 (PdCH2), 33.2 (ꢀCH2), 37.7
(γCH2), 45.0 (ps t, 1JP ) 30 Hz, PCH2), 114.3 (dCH2), 123.4 (py-
1
3,5), 128.8 (ps t, JP d 44 Hz, PPhj), 129.9 (PPhm), 132.3 (PPhp),
133.3 (PPho), 138.6 (dCH), 140.9 (py-4), 158.4 (py-2,6).
[(PNP)PdCH2CH2CH(Me)CHdCH2](BF4) (5c-Pd). Yield 92%.
Anal. Calcd for C37H38BF4NP2Pd: C, 59.11; H, 5.09; N, 1.86.
Found: C, 58.90; H, 5.20; N, 1.80. 1H NMR (300 MHz, CD2Cl2):
δ 0.60 (d, 3 H, Me), 1.25 (m, 2 H, CH2), 1.70 (hept, 1 H, CH),
1.92 (m, 2 H, PdCH2), 4.40 (ps t, 4 H, PCH2), 4.65 (d, 2 H, dCH2),
5.30 (m, 1 H, dCH), 7.40-7.70 (m, 22 H, PPh, py), 7.90 (t, 1 H,
py). 13C NMR (75 MHz, CD2Cl2): δ 14.7 (PdCH2), 19.4 (Me),
39.9 (CH2), 41.3 (CH), 44.9 (ps t, 1JP ) 26 Hz, PCH2), 112.4
(dCH2), 123.4 (py-3,5), 128.8 (ps t, 1JP ) 44 Hz, PPhj), 129.9
(PPhm), 132.3 (PPhp), 133.3 (PPho), 140.9 (py-4), 144.6 (dCH),
158.5 (py-2,6).
1
t, JP ) 56 Hz, PPhj), 129.8 (PPhm), 132.6 (PPhp), 133.6 (PPho),
2
140.4 (py-4), 143.9 (2JPt ) 60 Hz, dCH), 159.6 (ps t, JPt ) 37
Hz, py-2,6).
[(PNP)PtCH CHdCHMe](BF4) (1b-Pt). 1H NMR (200 MHz,
2
CD2Cl2): δ 1.18 (d, 3 H, Me, JPt ) 25 Hz), 2.57 (app quartet, 2 H,
PtCH2, JPt ) 104 Hz), 4.40 (ps t, 4 H, PCH2), 4.60 (m, 1 H,
dCHMe), 5.15 (m, 1 H, dCHCH2Pt), 7.50-7.90 (m, 22 H, PPh,
py), 8.00 (t, 1 H, py). 13C NMR (50 MHz, CD2Cl2): δ 3.6 (1JPt
)
578 Hz, PtCH2), 17.7 (Me), 46.1 (ps t, 1JP ) 33 Hz, PCH2), 120.4
(3JPt ) 58 Hz, dCHMe), 123.3 (py-3,5), 127.5 (ps t, 1JP ) 56 Hz,
PPhj), 129.8 (PPhm), 132.6 (PPhp), 133.7 (PPho), 136.8 (2JPt ) 64
2
Hz, dCHCH2), 140.4 (py-4), 159.6 (ps t, JPt ) 35 Hz, py-2,6).
[(PNP)PdsCH2CH2CH(CH2OMe)CHdCH2](BF4) (5e-Pd).
NMR Identification of the Allyl-bridged Complexes 3a.
Yield 89%. Anal. Calcd for C38H40BF4NOP2Pd: C, 58.37; H, 5.16;
1
1
Species 3a were not isolated, but were identified by their H and
N, 1.79. Found: C, 58.12; H, 5.25; N, 1.68. H NMR (400 MHz,
13C NMR spectra. Although a full characterization of their
suggested structure would be interesting, it is outside the scope of
the present paper. To prepare an NMR sample containing 3a as
the largely dominant species (among those depicted in Scheme 1),
30 mg of 2a were suspended in 2 mL of dichloromethane, and an
equimolar amount of 1a, dissolved in 1 mL of dichloromethane,
was added to the mixture at room temperature. To remove any
displaced ethylene, nitrogen was immediately bubbled through the
solution until the volume was approximately reduced to 1 mL. The
solution was finally evaporated to dryness, and the crude residue
analyzed by 1H and 13C NMR. 3a-Pt. 1H NMR (400 MHz,
CD2Cl2): δ 2.60 (d app q, 2 H, Hanti, JPt ) 73 Hz), 3.00 (m, 2 H,
CD2Cl2): δ 1.25 (m, 1 H, ꢀCHH), 1.47 (m, 1 H, ꢀCHH), 1.90 (m,
2 H, CH and PdCHH), 2.00 (m, 1 H, PdCHH), 2.92 (m, 2 H,
CH2OMe), 3.07 (s, 3 H, OMe), 4.40 (ps t, 4 H, PCH2), 4.72 (d, 1
H, dCHH), 4.78 (d, 1 H, dCHH), 5.22 (ddd, 1 H, dCH),
7.45-7.75 (m, 22 H, PPh, py), 7.90 (t, 1 H, py). 13C NMR (100
1
MHz, CD2Cl2): δ 14.1 (PdCH2), 34.7 (CH2), 44.9 (ps t, JP ) 26
Hz, PCH2), 47.4 (CH), 58.7 (Me), 75.7 (CH2O), 115.2 (dCH2),
123.4 (py-3,5), 128.8 (ps t, 1JP d 44 Hz, PPhj), 130.0 (PPhm), 132.1
(PPhp), 133.4 (PPho), 141.0 (py-4), 142.4 (dCH), 158.5 (py-2,6).
[(PNP)PtCH2CH2CH2CHdCH2](BF4) (5a-Pt). 1H NMR (400
MHz, CD2Cl2): δ 1.30 (m, 2 H, ꢀCH2), 1.65 (app q, 2 H, γCH2),
1.84 (m, 2 H, PtCH2, JPt ) 69 Hz), 4.40 (ps t, 4 H, PCH2), 4.64
(m, 2 H, sCH2), 5.33 (m, 1 H, sCH), 7.40-7.90 (m, 23 H, PPh,
py). 13C NMR (100 MHz, CD2Cl2): δ 0.9 (1JPt ) 632 Hz, PtCH2),
Hsyn, JPt ) 102 Hz), 4.40 (app q, 8 H, PCH2), 6.26 (m, 1 H, CH),
7.4-8.0 (m, 46 H, PPh, py). 13C NMR (50 MHz, CD2Cl2): δ 33.4
1
1
34.3 (ꢀCH2), 38.5 (3JPt ) 84 Hz, γCH2), 46.2 (ps t, JP ) 33 Hz,
(CH2, JPt ) 340 Hz), 45.6 (ps t, JP ) 33 Hz, PCH2), 123.6 (py-
1
1
3,5), 124.2 (ps t, JP ) 58 Hz, PPhj), 130.5 (PPhm), 133.0 (PPhp,
PCH2), 113.9 (dCH2), 123.4 (py-3,5), 128.0 (ps t, JP ) 54 Hz,
1
PPho), 142.3 (py-4), 160.3 (py-2,6). 3a-Pd. H NMR (200 MHz,
PPhj), 130.0 (PPhm), 132.5 (PPhp), 133.5 (PPho), 139.1 (dCH),
140.3 (py-4), 159.6 (py-2,6).
CD2Cl2): δ 2.80 (d app t, 2 H, Hanti), 3.02 (m, 2 H, Hsyn), 4.40
(ps t, 8 H, PCH2), 7.10 (m, 1 H, CH), 7.3-7.9 (m, 46 H, PPh, py).
[(PNP)PtCH2CH2CH(Me)sCHdCH2](BF4) (5c-Pt). Yield 84%.
Anal. Calcd for C37H38BF4NP2Pt: C, 52.87; H, 4.56; N, 1.67. Found:
Binuclear Complex [(PNP)PtCH2CH2CH(Me)CHdCH2{Pt-
(PNP)}](BF4)3 (4c-Pt). 1H NMR (400 MHz, CD2Cl2): δ 0.00 (m, 1
H, CH), 0.46 (d, 3 H, Me), 0.56 (m, 2 H, PtCH2CH2), 1.00 (m, 2
H, PtCH2, JPt ) 80 Hz), 3.98 (d ps t, 1 H, dCHH), 4.16 (d, 1 H,
dCHH JPt ) 70 Hz), 4.36 (ps t, 4 H, PCH2), 4.56 (d ps t, 2 H,
PCHaHb), 4.80 (m, 1 H, dCH), 5.10 (br, 2 H, PCHaHb), 7.30-8.10
1
C, 52.58; H, 4.77; N, 1.49. H NMR (400 MHz, CD2Cl2): δ 0.54
(d, 3 H, Me), 1.10 (m, 2 H, CH2), 1.61 (hept, 1 H, CH), 1.74 (m,
2 H, PtCH2, JPt ) 80 Hz), 4.41 (ps t, 4 H, PCH2), 4.60 (m, 2 H,
dCH2), 5.22 (ddd, 1 H, dCH), 7.40-7.90 (m, 22 H, PPh, py),
7.96 (t, 1 H, py). 13C NMR (100 MHz, CD2Cl2): δ -1.9 (1JPt
)
(m, 46 H, PPh, py). 13C NMR (100 MHz, CD2Cl2): δ -4.4 (1JPt
)
626 Hz, PtCH2), 18.8 (Me), 40.9 (CH2), 41.3 (CH), 45.6 (ps t, 1JP
) 33 Hz, PCH2), 111.5 (dCH2), 122.9 (py-3,5), 126.3 (ps t, 1JP )
57 Hz, PPhj), 129.4 (PPhm), 132.1 (PPhp), 133.1 (PPho), 139.8 (py-
4), 144.4 (dCH), 159.0 (py-2,6).
635 Hz, PtCH2), 17.8 (Me), 42.2 (3JPt ) 35 Hz, CH), 43.2 (CH2),
1
1
43.4 (ps t, JP ) 33 Hz, PCH2), 45.5 (ps t, JP ) 33 Hz, PCH2),
72.8 (1JPt ) 126 Hz, dCH2), 112.4 (1JPt ) 123 Hz, dCH), 122.9
(py-3,5), 124.0 (py-3,5), 126.6 (ps t, 1JP ) 55 Hz, PPhj), 126.9
Reactions of the Propene Complex 2b-Pt. These were con-
siderably slower than the reactions of the corresponding ethylene
complex and were not performed catalytically. A sample of 50 mg
of 2b-Pt was suspended in 2 mL of dichloromethane, and an
equimolar amount of the appropriate allyl complex (1a-Pt or 1b-
Pt) was added. The solution was saturated with propene at room
temperature, and the mixture was kept stirring for 24 h. The
resulting solution was treated with 100 mL of acetonitrile (to remove
any coordinated double bond) and evaporated to dryness. The crude
residue, composed essentially by the acetonitrile complex
1
(ps t, JP ) 55 Hz, PPhj), 129.4 (PPhm), 130.5 (PPhm), 132-135
(PPho,p), 139.9 (py-4), 144.0 (py-4), 159.2 (py-2,6), 161.2 (py-2,6).
General Procedure for the Catalytic Synthesis of Complexes
5. A 150-200 mg portion of the appropriate allyl complex 1 was
dissolved in 2-3 mL of dichloromethane, and 10-15 mg (ca. 5
mol %) of the ethylene complex 2a was added at room temperature.
In the case of palladium complexes, ethylene was slowly bubbled
through the solution for 10-15 min, and then diethyl ether (3-5
mL) was added to the solution under ethylene atmosphere, and the
solution kept at -20 °C for 1-2 h. The obtained product was
essentially pure as a yellow crystalline solid. In the case of platinum
complexes, the solution was stirred for 24 h at room temperature
under a 2 bar pressure of ethylene and then processed as above.
[(PNP)PdsCH2CH2CH2CHdCH2](BF4) (5a-Pd). Yield 90%.
Anal. Calcd for C36H36BF4NP2Pd: C, 58.60; H, 4.92; N, 1.90.
Found: C, 58.83; H, 5.02; N, 1.82. 1H NMR (300 MHz, CD2Cl2):
δ 1.35 (m, 2 H, ꢀCH2), 1.72 (app q, 2 H, γCH2), 1.98 (m, 2 H,
2b
[(PNP)Pt(MeCN)](BF4)2 and by the Pt-alkyl complex (5d-Pt or
1
5b-Pt) was analyzed by H and 13C NMR, without separation of
the components.
[(PNP)PtCH2CH(Me)CH(Me)sCHdCH2](BF4) (5b-Pt). (two
diastereomers A and B in equal abundances). 1H NMR (400 MHz,
CD2Cl2): δ 0.41 (d, 6 H, γMeA,B), 0.52 (d, 3H, δMeA), 0.55 (d,
3H, δMeB), 1.40 (m, 2 H, ꢀCHA,B), 1.68 (m, 2H, PtCHA,B, JPt
82 Hz), 1.70 (m, 2 H, γCHA,B), 2.30 (m, 2H, PtCHA,B, JPt ) 82
)

Notes
Organometallics, Vol. 27, No. 23, 2008 6363
Hz), 4.35-4.60 (m, 8 H, PCH2), 4.64 (d, 2 H, dCHHA,B), 4.69 (d,
1 H, dCHHA), 4.72 (d, 1 H, dCHHB), 5.26 (ddd, 1H, dCHA),
5.32 (ddd, 1H, dCHB), 7.4-8.0 (m, 46 H, PPh, py).
resulting filtrate, containing the hydrocarbon(s) produced by the
M-C σ-bond cleavage (together with trace amounts of the complex
1
[(PNP)MCl](BF4)) was analyzed by H NMR, and the identity of
[(PNP)PtCH2CH(Me)CH2sCHdCH2](BF4) (5d-Pt). 1H NMR
(400 MHz, CD2Cl2): δ 0.52 (d, 3 H, Me), 1.40 (m, 2 H, ꢀCH and
γCHH), 1.80 (m, 2 H, PtCHH and γCHH), 2.12 (m, 1 H, PtCHH,
JPt ) 78 Hz), 4.5 (m, 4 H, PCH2), 4.66 (d, 1 H, dCHH), 4.73 (d,
1 H, dCHH), 5.25 (m, 1 H, dCH), 7.40-8.10 (m, 23 H, PPh, py).
13C NMR (100 MHz, CD2Cl2): δ 12.6 (1JPt ) 650 Hz, PtCH2),
25.4 (3JPt ) 40 Hz, Me), 41.7 (CH), 47.1 (γCH2), 48.0 (ps t, 1JP )
the hydrocarbon was confirmed by comparison with published
spectra. Interestingly, the sample resulting from the protonolysis
of the crude mixture 5b-Pt contained, besides the expected
hydrocarbon 3,4-dimethyl-1-hexene, a minor amount (ca. 7%) of
4-methyl-1-pentene. This minor product can be explained by the
formation and further reaction of a small amount of the allyl
complex 1a-Pt in the reaction mixture of 1b-Pt with 2b-Pt, arising
from deprotonation of the propene complex 2b-Pt.
1
33 Hz, PCH2), 115.2 (dCH2), 124.8 (py-3,5), 129.6 (ps t, JP )
50 Hz, PPhj), 131.4 (PPhm), 134.1 (PPhp), 135.1 (PPho), 139.8
(dCH), 141.8 (py-4), 161.1 (py-2,6).
Acknowledgment. We thank the MIUR (PRIN 2007) for
financial support. We also thank the CIMCF, Universita` di
Napoli Federico II, for the access to NMR facilities and Miss
Luciana Cimino for experimental assistance.
Protonolysis of Complexes 5. A sample of 30-50 mg of the
complex (or crude mixture in the case of complexes 5b and 5d)
was dissolved in 0.6 mL of CD2Cl2, and gaseous HCl was bubbled
through the solution for 1 min. After 10 min the solution was filtered
through a short column of silica gel (for flash chromatography) in
a Pasteur pipet, eluting with an additional 0.6 mL of CD2Cl2. The
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