1,6-Diene complexes of palladium(0) and platinum(0): Highly reactive sources for the naked metals and [L-M0] fragments

J. Am. Chem. Soc. 1999, 121, 9807-9823

9807

1,6-Diene Complexes of Palladium(0) and Platinum(0): Highly

Reactive Sources for the Naked Metals and [L-M⁰] Fragments

Jochen Krause, Gu1nter Cestaric, Karl-Josef Haack, Klaus Seevogel, Werner Storm, and

Klaus-Richard Po1rschke*

Contribution from the Max-Planck-Institut fu¨r Kohlenforschung, D-45466 Mu¨lheim an der Ruhr, Germany

ReceiVed NoVember 12, 1998

Abstract: The complexes (cod)MCl₂(M ) Pd, Pt; cod ) cis,cis-1,5-cyclooctadiene) react with Li₂(cot) (cot

) cyclooctatetraene) in a 1,6-diene/diethyl ether mixture (1,6-diene ) hepta-1,6-diene, diallyl ether, dvds

(1,3-divinyl-1,1,3,3-tetramethyldisiloxane)) to afford the isolated homoleptic dinuclear Pd⁰and Pt⁰compounds

Pd₂(C₇H₁₂)₃(1), Pd₂(C₆H₁₀O)₃‚C₆H₁₀O (2′; 2: Pd₂(C₆H₁₀O)₃), Pd₂(dvds)₃(3), and Pt₂(C₇H₁₂)₃(4). When 1-4

are treated with additional 1,6-diene the equally homoleptic but mononuclear derivatives of type M(1,6-diene)₂

(5-8) and with ethene the mixed alkene complexes (C₂H₄)M(1,6-diene) (9-12) are obtained in solution.

Complexes 1-12 react with donor ligands such as phosphanes, phosphites, or ^tBuNC to give isolated complexes

of types L-M(1,6-diene) (13-41), which have also been prepared by other routes. In all complexes the metal

centers are TP-3 coordinated: complexes 1-4 contain chelating and bridging 1,6-diene ligands, whereas the

other complexes contain a chelating 1,6-diene ligand and an η²-alkene (5-12) or η¹-donor ligand (13-41). Of

the studied 1,6-diene complexes the hepta-1,6-diene derivatives are most reactive, while the diallyl ether

complexes are often more convenient to handle. The readily isolable dinuclear hepta-1,6-diene and diallyl

ether complexes 1, 2′, and 4, and their mononuclear pure olefin derivatives are among the most reactive sources

for naked Pd⁰and Pt⁰. The corresponding L-M(1,6-diene) complexes are equally reactive precursor compounds

for the generation of [L-M⁰] fragments in solution, which for M ) Pd are available otherwise only with

difficulty. The results are significant for the operation of naked Pd⁰and L-Pd⁰catalysts in homogeneous

catalysis.

Introduction

in the course of the reactions to afford coordinatively unsaturated

complexes such as 16e (Ph₃P)₃Pd,⁵14e (Ph₃P)₂Pd,⁶and the

elusive 12e [(Ph₃P)Pd].⁷Similarly, when mixtures of “Pd(dba)₂”⁸

and PPh₃are applied as catalysts, the dba ligands are gradually

displaced or eliminated to afford (Ph₃P)₂Pd(dba)⁹and eventually

(Ph₃P)₂Pd and [(Ph₃P)Pd]. It appears that for many reactions in

fact the usually nonisolable complex fragments [(R₃P)₂Pd⁰],

[{(RO)₃P}₂Pd⁰], [(R₃P)Pd⁰], and [{(RO)₃P}Pd⁰] (R ) alkyl,

aryl) are the “true catalysts”.

In organopalladium chemistry innumerable coupling reactions

of organic substrates are known which are catalyzed by species

derived from either Pd(PR₃)₄(R, e.g., Ph)¹or “Pd(dba)₂”²(dba

) dibenzylideneacetone) as catalyst precursors.³It is generally

agreed on that complexes such as Pd(PPh₃)₄⁴gradually dissociate

(1) For reviews of representative reactions, see: (a) de Meijere, A.;

Meyer, F. E. Angew. Chem. 1994, 106, 2473; Angew. Chem., Int. Ed. Engl.

1994, 33, 2379. (b) Herrmann, W. A. In Applied Homogeneous Catalysis

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Weinheim: VCH, 1996; Vol. 2, p 712. (c) Friesen, R. W. In Encyclopedia

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U.K., 1995; Vol. 7, p 4788.

(2) (a) Stille, J. R. In Encyclopedia of Reagents for Organic Synthesis;

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Guram, A. S.; Rennels, R. A.; Buchwald, S. L. Angew. Chem. 1995, 107,

1456; Angew. Chem., Int. Ed. Engl. 1995, 34, 1348. Wolfe, J. P.; Wagaw,

S.; Buchwald, S. L. J. Am. Chem. Soc. 1996, 118, 7215.

Additional insight into the importance of coordinative un-

saturation was gained from an investigation by Hartwig on the

function of isolated {(2-MeC₆H₄)₃P}₂Pd as a catalyst precursor

for various coupling reactions. It was demonstrated through

kinetic studies that the reactions were initiated by a loss of a

P(o-tolyl)₃ligand to generate 12e [{(2-MeC₆H₄)₃P}Pd] as a

(3) Catalytic reactions employing Pt(PPh₃)₄as catalyt: (a) Di- and

Silaboration of Alkenes and Alkynes. Ishiyama, T.; Matsuda, N.; Miyaura,

N.; Suzuki, A. J. Am. Chem. Soc. 1993, 115, 11018. Ishiyama, T.; Matsuda,

N.; Murata, M.; Ozawa, F.; Suzuki, A.; Miyaura, N. Organometallics 1996,

15, 713. Suginome, M.; Nakamura, H.; Ito, Y. J. Chem. Soc., Chem.

Commun. 1996, 2777. Ishiyama, T.; Yamamoto, M.; Miyaura, N. J. Chem.

Soc., Chem. Commun. 1997, 689, 2073. (b) Hydrosilylation of Alkenes and

Alkynes. Marciniec, B.; Gulinski, J.; Urbaniak, W.; Nowicka, T.; Mirecki,

J. Appl. Organomet. Chem. 1990, 4, 27. Itoh, M.; Iwata, K.; Takeuchi, R.;

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Borisova, L.; Popelis, J.; Lukevics, E.; Foltynowicz, Z.; Gulinski, J.;

Marciniec, B. J. Organomet. Chem. 1992, 424, 15. Kusumoto, T.; Ando,

K.; Hiyama, T. Bull. Chem. Soc. Jpn. 1992, 65, 1280. (c) Hydrosulfuration

and -selenation of Alkynes. Kuniyasu, H.; Ogawa, A.; Sato, K.-I.; Ryu, I.;

Kambe, N.; Sonoda, N. J. Am. Chem. Soc. 1992, 114, 5902. Kuniyasu, H.;

Ogawa, A.; Sato, K.-I.; Ryu, I.; Kambe, N.; Sonoda, N. Tetrahedron Lett.

1992, 33, 5525. Ogawa, A.; Kawakami, J.; Mihara, M.; Ikeda, T.; Sonoda,

N.; Hirao, T. J. Am. Chem. Soc. 1997, 119, 12380. (d) Thiosilylation of

Alkynes. Han, L.-B.; Tanaka, M. J. Am. Chem. Soc. 1998, 120, 8249.

(4) (a) Malatesta, L.; Angoletta, M. J. Chem. Soc. (London) 1957, 1186.

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R. Inorg. Synth. 1972, 13, 121.

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Kuran, W.; Musco, A. Inorg. Chim. Acta 1975, 12, 187. Mann, B. E.;

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(6) Urata, H.; Suzuki, H.; Moro-oka, Y.; Ikawa, T. J. Organomet. Chem.

1989, 364, 235.

(7) For reactions assumed to involve the [(Ph₃P)Pd] [Registry number

supplied by author: 12628-74-9] intermediate, see: Grushin, V. V.; Alper,

H. Organometallics 1993, 12, 1890. Grushin, V. V.; Bensimon, C.; Alper,

H. Organometallics 1995, 14, 3259.

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G. Inorg. Chem. 1973, 12, 2955 and 1974, 13, 1891.

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Published on Web 10/08/1999

9808 J. Am. Chem. Soc., Vol. 121, No. 42, 1999

Krause et al.

catalytically active intermediate.¹⁰[(R₃P)Pd⁰]-type complexes

are assumed to be also the “true catalysts” for the telomerization

of butadiene.¹¹Similarly, we have shown that (ⁱPr₃P)₂Pd^5bis a

catalyst for various coupling reactions (formation of germa- and

stannacyclopentadienes by (2+2+1) cycloadditions; trimeriza-

tion of terminal alkynes) and that phosphane dissociation is an

essential step on the reaction path.^12,13

Scheme 1^a

Palladium complexes, in which the elusive [(R₃P)Pd⁰] and

[{(RO)₃P}Pd⁰] (R ) alkyl, aryl) fragments are stabilized by

readily displaceable alkene ligands, are scarce. (Cy₃P)Pd-

(C₂H₄)₂^14ais apparently the only ethene complex mentioned in

the literature, although the series of phosphane derivatives

(R₃P)M(C₂H₄)₂, R ) Me, Et, ⁱPr, Ph, Cy, is known for M ) Ni

and Pt. However, some rare reports have appeared in which

1,6-diene ligands are coordinated to L-Pd⁰moieties. Thus, in

the context of the Pd-catalyzed telomerization of butadiene with

methanol, Jolly isolated complexes such as (Me₃P)Pd{C₇H₁₁(CH₂-

OMe)} with a substituted hepta-1,6-diene ligand.¹¹Continuing

a related study on Ni⁰complexes,^15aYamamoto reported that

allyl alcohol undergoes a dehydration reaction with (Cy₃P)₂Pd

to give the diallyl ether complex (Cy₃P)Pd(C₆H₁₀O) (26), and

with 1-methylallyl alcohol a substituted derivative (Cy₃P)Pd(C₆H₈-

Me₂O) was obtained.^15bIt has apparently not been recognized

in these studies that the L-Pd⁰complexes with heptadiene- and

diallyl ether-type ligands are excellent starting materials to

provide 12e [(R₃P)Pd⁰] moieties under mild reaction conditions.

Our own studies on Pd⁰- and Pt⁰-1,6-diene complexes

commenced with the finding that Ni⁰forms the dinuclear

homoleptic hepta-1,6-diene complex rac-/meso-(µ-C₇H₁₂){Ni-

(C₇H₁₂)}₂in which the bridging hepta-1,6-diene ligand is easily

replaced by donor ligands to produce a broad variety of L-Ni-

(C₇H₁₂) complexes.¹⁶Recognizing that 1,6-dienes also provide

a general access to both the “naked” metals and 12e [L-M⁰]

fragments of palladium and platinum, and in view of their

potential for stoichiometric and catalytic reactions under mild

conditions, we set out to synthesize corresponding homoleptic

complexes M₂(1,6-diene)₃and donor ligand adducts L-M(1,6-

diene) (M ) Pd, Pt) and to study their reactivity. The focus of

this work is primarily on palladium for which stable and yet

^aReagents: (i) hepta-1,6-diene; (ii) diallyl ether; (iii) 1,3-divinyl-

1,1,3,3-tetramethyldisiloxane.

highly reactive M⁰complexes are still missing. Part of this

work¹³has already been communicated.¹⁷

Results

I. Homoleptic M₂(1,6-diene)₃(1-4) and M(1,6-diene)₂(5-

8) (M ) Pd, Pt). rac-/meso-Ni₂(C₇H₁₂)₃^16aand rac-/meso-Pt₂-

18a

(dvds)₃

are readily synthesized from Ni(cdt)¹⁹(cdt )

14,20

trans,trans,trans-1,5,9-cyclododecatriene) and Pt(cod)₂

by

displacement of the alkene ligands. In contrast, corresponding

Pd⁰starting complexes to be considered for the synthesis of

1-3 are either thermally labile, i.e., accessible only with great

difficulty (Pd(cod)₂, Pd(C₂H₄)₃),¹⁴or not sufficiently reactive

(“Pd(dba)₂”)⁸to be employed in practice. However, complexes

1-3 can be synthesized²¹from (cod)PdCl₂by a route similar

to Stone’s synthesis of Pd(cod)₂.¹⁴

When the yellow suspension of (cod)PdCl₂in a mixture of

hepta-1,6-diene and diethyl ether is reacted with Li₂(cot)

between -78 and -10 °C, a thick slurry of 1 and LiCl

precipitates. After evaporation of the diethyl ether, complex 1

dissolves in the neat hepta-1,6-diene. LiCl is removed by

filtration, and after addition of an about equal volume of pentane

pure colorless 1 (60%) precipitates between -30 and -78 °C

(Scheme 1). Using diallyl ether as the 1,6-diene component

affords 2′ in a similar reaction. Pure pale yellow 2′ (42%) slowly

crystallizes from the diallyl ether/pentane mixture at e-30 °C.

2′ contains one molecule of cocrystallized diallyl ether (2:

solvent-free Pd₂(C₆H₁₀O)₃). The synthesis of 3 follows that of

1 and 2′ by using dvds (20 °C) as a 1,6-diene. After removal of

LiCl the dvds solution of 3 is evaporated to form a sticky oil,

and addition of some pentane affords (-78 °C) microcrystalline,

almost colorless 3 in 75% yield. Finally, in a synthesis

(10) Paul, F.; Patt, J.; Hartwig, J. F. J. Am. Chem. Soc. 1994, 116, 5969.

Paul, F.; Patt, J.; Hartwig, J. F. Organometallics 1995, 14, 3030. Hartwig,

J. F.; Paul, F. J. Am. Chem. Soc. 1995, 117, 5373. Hartwig, J. F. Angew.

Chem. 1998, 110, 2154; Angew. Chem., Int. Ed. Engl. 1998, 37, 2046.

(11) Do¨hring, A.; Jolly, P. W.; Mynott, R.; Schick, K.-P.; Wilke, G. Z.

Naturforsch., B: Anorg. Chem., Org. Chem. 1981, 36, 1198. Jolly, P. W.

Angew. Chem. 1985, 97, 279; Angew. Chem., Int. Ed. Engl. 1985, 24, 283.

(12) (a) Stannole synthesis: Krause, J.; Pluta, C.; Po¨rschke, K.-R.;

Goddard, R. J. Chem. Soc., Chem. Commun. 1993, 1254. Krause, J.; Haack,

K.-J.; Po¨rschke, K.-R.; Gabor, B.; Goddard, R.; Pluta, C.; Seevogel, K. J.

Am. Chem. Soc. 1996, 118, 804. (b) Linear trimerization of alk-1-ynes:

see ref 52.

(17) Krause, J.; Haack, K.-J.; Cestaric, G.; Goddard, R.; Po¨rschke, K.-

R. J. Chem. Soc., Chem. Commun. 1998, 1291.

(13) (a) Krause, J. Dissertation, Universita¨t Du¨sseldorf, 1993. (b) Haack,

K.-J. Dissertation, Universita¨t Du¨sseldorf, 1994. (c) Cestaric, G. Dissertation,

Universita¨t Du¨sseldorf, 1999.

(14) (a) Green, M.; Howard, J. A. K.; Spencer, J. L.; Stone, F. G. A. J.

Chem. Soc., Chem. Commun. 1975, 449. (b) Green, M.; Howard, J. A. K.;

Spencer, J. L.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1977, 271. (c)

Stone, F. G. A. Acc. Chem. Res. 1981, 14, 318.

(15) (a) Yamamoto, T.; Ishizu, J.; Yamamoto, A. Chem. Lett. 1979, 1385.

Yamamoto, T.; Ishizu, J.; Yamamoto, A. J. Am. Chem. Soc. 1981, 103,

6863. (b) Yamamoto, T.; Akimoto, M.; Yamamoto, A. Chem. Lett. 1983,

1725. Yamamoto, T.; Akimoto, M.; Saito, O.; Yamamoto, A. Organome-

tallics 1986, 5, 1559.

(16) (a) Proft, B.; Po¨rschke, K.-R.; Lutz, F.; Kru¨ger, C. Chem. Ber. 1991,

124, 2667. (b) Pluta, C.; Po¨rschke, K.-R.; Gabor, B.; Mynott, R. Chem.

Ber. 1994, 127, 489. Rosenthal, U.; Pulst, S.; Kempe, R.; Po¨rschke, K.-R.;

Goddard, R.; Proft, B. Tetrahedron 1998, 54, 1277. (c) Proft, B. Dissertation,

Universita¨t Du¨sseldorf, 1993. (d) Trebbe, R. Planned Dissertation.

(18) (a) Hitchcock, P. B.; Lappert, M. F.; Warhurst, N. J. W. Angew.

Chem. 1991, 103, 439; Angew. Chem., Int. Ed. Engl. 1991, 30, 438. (b)

Beuter, G.; Heyke, O.; Lorenz, I.-P. Z. Naturforsch., B: Anorg. Chem.,

Org. Chem. 1991, 46, 1694. (c) Chandra, G.; Lo, P. Y. K. European Patent

Application EP 182611, May 28, 1986; Chem. Abstr. 1986, 105, 153341y.

Chandra, G.; Lo, P. Y.; Hitchcock, P. B.; Lappert, M. F. Organometallics

1987, 6, 191. (d) Bassindale, A. R.; Brown, S. S. D.; Lo, P. Organometallics

1994, 13, 738. Avent, A. G.; Lappert, M. F.; MacBeath, C. J. Organomet.

Chem. 1995, 502, 163.

(19) Bogdanovic, B.; Kro¨ner, M.; Wilke, G. Liebigs Ann. Chem. 1966,

699, 1.

(20) (a) Mu¨ller, J.; Go¨ser, P. Angew. Chem. 1967, 79, 380; Angew. Chem.,

Int. Ed. Engl. 1967, 6, 364. (b) Herberich, G. E.; Hessner, B. Z. Naturforsch.,

B: Anorg. Chem., Org. Chem. 1979, 34, 638.

(21) Thermolysis of Pd(η³-C₃H₅)₂and (tmeda)PdMe₂in neat hepta-1,6-

diene results in deposition of elemental palladium, instead of the formation

of 1.

1,6-Diene Complexes of Pd(0) and Pt(0)

J. Am. Chem. Soc., Vol. 121, No. 42, 1999 9809

corresponding to that of 1, (cod)PtCl₂reacts with Li₂(cot) in

hepta-1,6-diene to yield colorless microcrystalline 4 (40%) (eq

1), which is also obtained from Pt(cod)₂and hepta-1,6-diene

Scheme 2

by the displacement of the cod ligands. Compounds 1-4

supplement and complete the series of homologous d¹⁰M⁰-

1,6-diene complexes M₂(C₇H₁₂)₃(M ) Ni,^16aPd (1), Pt (4)),

M₂(C₆H₁₀O)₃(M ) Ni,^16cPd (2), Pt²²), and M₂(dvds)₃(M )

Ni,^16c,23Pd (3), Pt^18a).

Complex 2′ is also formed by displacing the hepta-1,6-diene

ligands of 1. Similarly, the diallyl ether ligands in 2 are displaced

by dvds to yield 3 (Scheme 1). Thus, there is an increasing

thermodynamic stability (decreasing reactivity) of the complexes

in solution in the series 1 < 2 < 3. The thermal stability of the

solids also increases in the above series 1 (≈0 °C dec) < 2′

(>0 °C dec) < 3 (mp 55 °C dec). The Pt-hepta-1,6-diene

complex 4 is more stable (indefinitely at ambient temperature;

mp 110 °C dec) than any of the Pd complexes.

Scheme 3

The dinuclear hepta-1,6-diene complexes 1 and 4 are only

sparingly soluble in the usual solvents such as diethyl ether,

THF, or toluene, whereas the dvds complex 3 dissolves quite

well. The diallyl ether complex 2′ is moderately soluble; in

solution dinuclear 2 and the diallyl ether contained in the crystal

are in equilibrium with mononuclear 6 (NMR, see below). The

low solubility of 1, 2′, and 4 is advantageous for the isolation

of the compounds but impedes recording of informative NMR

spectra for 1 and 4. In contrast, dinuclear 1-4 dissolve very

well in an excess of the corresponding 1,6-dienes. Such solutions

of 1 and 2′ in hepta-1,6-diene or diallyl ether are more stable

than the isolated complexes and decompose only after several

days, and a dvds solution of 3 appears to be stable at ambient

temperature for months. In these solutions the dinuclear

complexes are in equilibrium with the excess of 1,6-diene to

produce mononuclear derivatives: dinuclear 1, 2, and 4 are

quantitatively converted into mononuclear 5, 6, and 8, respec-

tively (Schemes 2, 3, and 5), whereas the dinuclear dvds

complex 3 forms only little mononuclear 7 (Scheme 4). A

similar equilibrium has been established for Pt₂(dvds)₃and dvds,

giving rise to Pt(dvds)₂.²⁴The mononuclear complexes 5-8 can

be considered to be the primary reaction products when the

synthesis of 1-4 is carried out in 1,6-diene solution according

to Scheme 1 and eq 1.

Scheme 4

1

NMR Spectroscopic Characterization. The 300 MHz H

and 75.5 MHz ¹³C NMR spectra of 1-8 have been recorded in

THF-d₈between -80 and 27 °C. In the following the spectra

of the homoleptic dinuclear M₂(1,6-diene)₃and corresponding

mononuclear M(1,6-diene)₂complexes are described in the order

of the individual 1,6-dienes.

the poor solubility. It can be assumed that in analogy to the

corresponding rac-/meso-Ni₂(C₇H₁₂)₃^16athe Pd and Pt atoms in

dinuclear 1 and 4 are TP-3 coordinated by a chairlike chelating

and a bridging hepta-1,6-diene ligand and that the complexes

represent a mixture of rac/meso diastereomers. However, when

an excess of hepta-1,6-diene is added to 1 and 4, solutions of

the mononuclear derivatives 5 and 8, respectively, are obtained.

Complex 5 exhibits in the -80 °C ¹³C NMR spectrum 14

signals (each 1C) of which two signals are attributed to an

For the homoleptic dinuclear hepta-1,6-diene complexes 1

and 4 no meaningful NMR spectra have been obtained due to

(22) Preliminary experiments have shown that beige microcrystals of

rac-/meso-Pt₂(C₆H₁₀O)₃, C₁₈H₃₀O₃Pt₂(684.6), can be prepared by reaction

of either 4 or Pt(cod)₂with diallyl ether. The identity was determined by

elemental analysis and the ¹³C NMR spectrum (27 °C).

(23) Hitchcock, P. B.; Lappert, M. F.; MacBeath, C.; Scott, F. P. E.;

Warhurst, N. J. W. J. Organomet. Chem. 1997, 528, 185.

(24) Lappert, M. F.; Scott, F. P. A. J. Organomet. Chem. 1995, 492,

C11.

9810 J. Am. Chem. Soc., Vol. 121, No. 42, 1999

Krause et al.

Scheme 5

1

For dinuclear 2 the -80 to -30 °C H NMR spectrum is

very complex. A total of 30 equally intense signals (each 2H)

for six different diallyl ether moieties H_EH_ZCdCH-CH_aH_bO-

is expected, and these signals overlap with 4 signals of

uncoordinated diallyl ether and 20 signals of 6 (see below). In

the -80 to -30 °C ¹³C NMR spectrum 2 exhibits for the diallyl

ether ligands 18 (partially isochronous) signals of equal intensity

(2C). The signals are arranged in three signal groupings of six

signals each in the ranges δ(C) 84-79 (dCH-), 73-70

(CH₂O), and 63-59 (dCH₂). The ¹³C NMR spectrum is

consistent with a diastereomeric mixture of dinuclear complexes

in which the TP-3 Pd atoms are coordinated by both a chelating

and a bridging diallyl ether ligand (Figure 1). There are two

types each of chelating and bridging diallyl ether ligands (four

types altogether). Both halves of the bridging diallyl ether

ligands are equivalent as is also the case for the corresponding

Pd(η²,η²-C₆H₁₀O) moieties, but all carbon atoms of a single Pd-

(η²,η²-C₆H₁₀O) moiety are inequivalent due to the asymmetry

(R or S stereochemistry) of the substituted olefinic C atoms of

the bridging diene ligands. The R,S stereocenter combination

of the central diallyl ether ligand furnishes a C_ssymmetrical

meso isomer, whereas the R,R and S,S combinations give rise

to a rac mixture of spectroscopically equivalent C₂symmetrical

isomers. The interpretation of the NMR spectra of 2 is in

compliance with the detailed discussion of the spectra of the

structurally related hepta-1,6-diene complex rac-/meso-Ni₂-

(C₇H₁₂)₃.^16a

When an excess of diallyl ether is added to a THF-d₈solution

of 2′, dinuclear 2 is almost completely converted into 6. In the

-80 °C ¹³C NMR spectrum, 6 displays 12 discrete signals of

equal intensity (each 1C). There are two pairs of signals for the

vinyl groups (δ(C) 85.6, 85.4 (dCH-), 59.6, 59.4 (H₂Cd)) of

an unsymmetrical, chelating C₆H₁₀O ligand, and another two

sets of signals for the coordinated (δ(C) 77.3 (dCH-), 63.9

(H₂Cd)) and the uncoordinated vinyl groups (δ(C) 136.4 (d

CH-), 115.7 (H₂Cd)) of an η²-coordinated C₆H₁₀O ligand; four

further close signals arise from inequivalent allylic C atoms

(δ(C) 73.4, 70.5, 69.9, 69.6 (CH₂O)). In the ¹H NMR spectrum

(-80 °C) the expected 20 proton multiplets of 6 strongly

overlap. Similar as for 5, in the diallyl ether derivative 6 a TP-3

Pd⁰center is coordinated by both a chairlike chelating and a

singly coordinating C₆H₁₀O ligand, the latter imposing chirality.

On raising the temperature to -30 °C the signals of 6 broaden

significantly and partially coalesce, whereas the resonances of

residual 2 and uncoordinated diallyl ether remain sharply

resolved. At 0 °C the signals of 2 and 6 are coalesced (the

solvent diallyl ether resonances are still very sharp) and at 27

°C are hardly observable any more (the solvent diallyl ether

resonances are now broadened).

uncoordinated vinyl group (δ(C) 139.6 (dCH-) and 115.1

(H₂Cd)), two sets of three signals to three differently coordi-

nated vinyl groups (δ(C) 84.4, 84.2, 84.0 (dCH-) and 62.8,

62.4, 61.6 (H₂Cd)), and further six signals to the inequivalent

allylic and aliphatic methylene groups (δ(C) 35.6-32.4). The

spectrum of the Pt derivative 8 (-30 °C) is analogous, but the

resonances of the coordinated vinyl groups (δ(C) 70.0, 69.8,

65.6 (dCH-) and 48.5, 48.1, 46.8 (H₂Cd)) are at markedly

higher field than for 5. In 8 the J(¹⁹⁵PtC) couplings allow an

assignment of most resonances. The spectra show that in 5 and

8 a TP-3 M⁰center (M ) Pd, Pt) is coordinated by a chairlike^25a

chelating and a η²-bound C₇H₁₂ligand; the latter renders the

complexes chiral.^25bThe ¹H NMR spectra of 5 (-80 °C) and 8

(-30 °C) are very complex because of 24 inequivalent protons,

giving rise to as many partially overlapping multiplets.

When the temperature is raised, the ¹H and ¹³C NMR

resonances of 5 and 8 broaden and partially coalesce but a full

equilibration of the corresponding signals does not occur up to

0 (5) and 27 °C (8). The sharp solvent hepta-1,6-diene

resonances are seemingly unaffected. The spectra show that for

5 at about -30 °C and for 8 at about 27 °C intramolecular

structural dynamics become relevant which are explained by

an exchange of the coordinated and uncoordinated vinyl groups

of the hepta-1,6-diene ligands. Exchange reactions of the hepta-

1,6-diene ligands with uncoordinated hepta-1,6-diene (solvent)

are much slower and become noticeable only at a higher

temperature (for 5 at about 27 °C).

1

The H and ¹³C NMR spectra of a THF-d₈solution of the

diallyl ether complex 2′ display signals for 2, for an equal

amount of uncoordinated diallyl ether (contained in crystalline

2′), and for twice the amount of 6 (formed by partial reaction

of 2 with diallyl ether), corresponding to a balanced equilibrium

according to eq 2.

(25) (a) If the chelating 1,6-diene ligand in complexes 5-8 were of local

C₂symmetry, fewer ¹H and ¹³C NMR signals would be expected as

compared to the chairlike conformation of local C_ssymmetry. In fact, the

spectra prove that the chelating 1,6-diene ligands assume a locally C_s

symmetrical, chairlike conformation in the ground state. (b) Paiaro, G.

Organomet. Chem. ReV., Sect. A 1970, 6, 319.

The ¹³C NMR spectra of 2 and 6 indicate that with respect

to the coordination of the vinyl groups the structure of 2 is static

between -80 and -30 °C and the structure of 6 is static at

-80 but fluxional at -30 °C on the NMR time scale. For 6 a

1,6-Diene Complexes of Pd(0) and Pt(0)

J. Am. Chem. Soc., Vol. 121, No. 42, 1999 9811

favor of 3 (Scheme 4), (b) the equilibrium between 3 and 7

and their ligand exchange with uncoordinated dvds are slow at

-30 °C, (c) in 7 a TP-3 Pd⁰center is coordinated by a chelating

dvds and a η²-dvds ligand and the complex is chiral (similar as

for 5 and 6), and (d) in 7 the intramolecular exchange of the

coordinated and uncoordinated vinyl groups is fast below -30

°C. The rigidity of the structures of the M(1,6-diene)₂complexes

thus follows the order 7 < 6 < 5 < 8.

II. (Ethene)Pd(1,6-Diene) (9-12). When suspensions of

dinuclear 1-4 in a usual solvent are saturated with ethene at

-78 °C and the mixtures are warmed to -60 (1-3) or -20 °C

(4), clear solutions are obtained. In equilibrium reactions the

bridging 1,6-diene ligands are replaced by ethene and the

mononuclear, 1,6-diene ligated M⁰-ethene complexes 9-12 are

formed. As shown by NMR (see below), the reactions of 1 and

4 to afford the hepta-1,6-diene ligated Pd⁰- and Pt⁰-ethene

complexes 9 and 12 are quantitative (Schemes 2 and 5). Thus,

for (C₇H₁₂)M⁰fragments (M ) Ni,^16aPd, Pt) ethene is a much

better coligand than a further C₇H₁₂vinyl group. The diallyl

ether complex 2′ also reacts completely when treated with

ethene, but in addition to the ethene adduct 10 some homoleptic

mononuclear 6 is obtained due to the competing reaction of 2

with the released 1,6-diene (Scheme 3). In contrast, the dvds

complex 3 reacts only partially with an excess of ethene and

such a solution contains residual 3, the ethene adduct 11, and

some additional 7 (Scheme 4). Complexes 9-12 are extremely

soluble, also in pentane at -78 °C, and only 12 has been

isolated. The platinum complex 12 is very volatile and

decomposes at >15 °C. In the EI mass spectrum (15 °C) the

molecular ion (m/e 319, 36%) is observed; cleavage of the

ethene ligand generates the base ion [(C₇H₁₂)Pt)]⁺(291).

Figure 1. Stereoisomers of rac-/meso-Pd₂(C₆H₁₀O)₃(2); the numbering

refers to inequivalent C atoms. The (C₆H₁₀O)Pd moieties rotate about

the Pd-CdC bond axes of the bridging diene ligand. Corresponding

stereoisomers are formed by the hepta-1,6-diene complexes 1 and 4

and the dvds complex 3.

rapid intramolecular exchange of the coordinated and uncoor-

dinated vinyl groups proceeds at -30 °C. Ligand exchange

reactions between 2 and 6 are observable only at g0 °C and

exchange reactions between 2 or 6 and free diallyl ether become

rapid only at 27 °C.

NMR Spectroscopic Characterization. Corresponding to the

synthesis routes, the THF-d₈solutions of 9-11 (-80 to -30

°C) and 12 (27 °C) display sharp ¹H and ¹³C NMR signals for

the chelating 1,6-diene (Table 1) and coordinated ethene of

9-12, and additional signals for 1 half-equiv of displaced 1,6-

diene and the excess of uncoordinated ethene. For a solution of

10 (obtained from 2′) further signals are found for about 10%

of residual 2 (or 6 at -80 °C), and similarly, for a solution of

11 (obtained from 3) additional signals are observed for about

30% of residual 3 and a small amount of 7.

For a solution of the dinuclear dVds complex 3 in THF-d₈

the -80 °C ¹³C NMR spectrum exhibits 12 signals each for

vinyl C atoms and for silicon bound Me groups; all signals have

the same intensity (2C) (some of them are isochronous). In the

¹H NMR spectrum the multiplets of the vinyl protons (18

resonances expected, each 2H) largely overlap, whereas for the

Si-Me groups 12 singlets are observed (each 6H; four signals

are isochronous). The spectra are almost unchanged at -30 °C

but are broad at ambient temperature. The low-temperature

spectra of 3 agree with a mixture of diastereomeric dinuclear

complexes, similar to the homologous complexes rac-/meso-

M₂(dvds)₃(M ) Ni,^16cPt^18a).

The spectra of 9-12 are in agreement with the presence of

a C_ssymmetrical TP-3 coordination of the metals by ethene

and a chelating 1,6-diene ligand in a chairlike conformation.

The ¹H NMR singlets observed for the ethene ligands indicate

that the latter are rapidly rotating even at -80 °C (an AA′BB′

spin system was to be expected for the static structure), whereas

a possible exchange of the ethene ligands with uncoordinated

ethene is slow (for 12 even at 27 °C), as evidenced both by the

sharp separate signals for coordinated and uncoordinated ethene

and, for 12, by the flanking of the ethene ¹H and ¹³C signals by

¹⁹⁵Pt spin-spin coupling satellites.

1

When 3 is dissolved in a THF-d₈/dvds mixture, the H and

¹³C NMR signals of 3 are consistently sharp between -80 and

-30 °C as are the resonances of uncoordinated dvds. At -80

°C additional broad resonances are observed for a minor amount

(20-40%) of mononuclear 7. In the -80 °C ¹³C NMR spectrum

7 displays signals at δ(C) 140 (dCH-) and 133 (H₂Cd) for

an uncoordinated vinyl group, two sets of three signals each at

δ(C) ≈75 (dCH-) and ≈73 (H₂Cd) for three differently

coordinated vinyl groups, and eight resonances (of which 6

signals are resolved) between δ(C) 3.1 and -1.1 for four

inequivalent SiMe_aMe_bgroups. At -30 °C the signals of 7 are

so broad that they can hardly be located any longer.

1

The ethene ligand H and ¹³C NMR resonances (uncoordi-

nated ethene: δ(H) 5.40, δ(C) 123.7) are shifted to high-field

when the 1,6-diene ligands are exchanged in the series 11

(δ(H) 3.79, δ(C) 73.3) f 10 (δ(H) 3.53, δ(C) 63.0) f 9 (δ(H)

3.39, δ(C) 61.9) f 12 (δ(H) 2.95, δ(C) 44.3), indicative of an

increasing M⁰-C₂H₄back-bonding. Thus, the [(dvds)Pd⁰]

moiety is only weakly back-bonding to the ethene ligand, more

so [(C₆H₁₀O)Pd⁰], and the most [(C₇H₁₂)Pd⁰], in agreement with

a decreasing acceptor strength of the 1,6-diene ligands in that

order (Scheme 6). In the (hepta-1,6-diene)M(C₂H₄) complexes

back-bonding to the ethene ligand, as expected, is stronger for

Pt⁰than for Pd⁰. Nevertheless, for all (1,6-diene)M(C₂H₄)

It is concluded from these results that (a) the equilibrium

between dinuclear 3 and mononuclear 7 in dvds solution is in

9812 J. Am. Chem. Soc., Vol. 121, No. 42, 1999

Krause et al.

Table 1. ¹H and ¹³C NMR Data (1,6-diene ligands) and ³¹P NMR Data of L-M(C₇H₁₂) (M ) Pd, Pt), L-Pd(C₆H₁₀O), L-Pd(C₆H₁₀NH), and

L-Pd(dvds) Complexes^a

δ(H)

δ(C)

dCH-

5.80

H_ZHCd

5.01

HH_ECd

-CH_eqH_ax-

2.02

-CH_aH_b-

dCH-

139.0

84.3

74.2

74.0

74.2

H₂Cd

114.9

60.0

52.1

52.4

52.7

dCHCH₂-

-CH₂-

28.5

34.4

34.0

33.6

33.8

δ(P)

C₇H₁₂

9^b

4.94

1.43

33.4

32.4

33.0

33.3

4.03

3.44

3.48

3.52

3.64

3.79

3.78

3.84

3.52

3.63

3.53

3.51

5.87

4.11

3.54

3.60

3.62

3.69

3.92

3.93

3.64

3.56

3.24

2.54

2.62

2.63

2.80

2.70

2.69

2.25

2.53

2.56

2.49

2.65

5.24

3.14

2.50

2.58

2.57

2.71

2.69

2.17

2.48

2.65

5.16

2.63

2.74

5.73

3.86

3.05

3.09

3.44

3.04

3.00

2.82

3.35

2.76

2.73

2.74

2.83

2.85

2.83

2.73

2.59

2.81

2.44

2.78

5.09

3.49

2.82

2.81

2.79

2.87

2.94

2.76

2.67

2.95

5.00

2.75

2.88

5.91

3.82

3.30

3.36

3.39

3.33

2.93

3.07

2.50, 0.66

2.22, 0.49

2.32, 0.57

2.36, 0.63

2.33, 0.66

2.36, 0.77

2.35, 0.76

2.33, 0.70

2.09, 0.16

2.13, 0.22

2.24, 0.60

2.27, 0.59

3.93

1.96^d

1.78^d

1.85^d

13

-22.3

14

53.6

40.3

88.4

30.6

28.2

22.4

150.9

156.1

155.9

44.3

d

15

-

16^c

17

1.84^d

1.94, 1.84

79.2

78.7

79.0

58.7

58.5

59.8

33.2

33.5

33.6

33.2

33.6

33.1

18

1.87^d

19⁵⁰

20^b

21

1.85^d

1.74, 1.68

1.80, 1.70

1.85, 1.76

1.88, 1.84

82.2

83.8

59.0

58.2

32.4

32.6

32.5

33.1

22

23^b

C₆H₁₀O

10^b

24

136.2

84.2

74.3

73.9

76.6

78.9

78.5

116.0

57.1

49.4

49.1

49.3

52.7

55.5

56.9

71.4

70.0

70.3

70.4

70.3

70.6

71.0

4.54, 2.29

4.35, 2.13

4.35, 2.15

4.38, 2.20

4.38, 2.28

4.42, 2.37

4.35, 2.24

4.17, 1.82

4.33, 2.17

3.18

-21.8

55.2

25

26

41.8

27^c

28

89.8

31.3

29

23.7

30

151.4

31^b

74.7

138.6

75.8

81.0

140.3

72.0

63.1

63.8

69.2

68.7

68.9

70.4

50.7

115.7

48.8

56.2

132.0

68.8

63.0

62.6

66.9

69.9

70.8

46.0

70.2

C₆H₁₀NH^f5.86

52.5

32

33

3.53

3.91

6.12

3.50

2.84

2.82

3.11

3.20

3.17

3.53

3.53, 1.63

3.60, 1.84

0.17^e

51.7

54.7

31.2

52.0

dvds

11^b

34

0.48^e

0.24, -0.32^e

0.18, -0.30^e

0.19, -0.26^e

0.18, -0.22^e

0.19, -0.24^e

0.18, -0.16^e

2.57, 0.42

1.5, -1.2^e

1.4, -0.8^e

1.6, -0.7^e

1.8, -0.3^e

1.4, -0.9^e

1.4, -1.1^e

31.3

-19.9

48.6

90.7

30.2

25.2

35

36^c

37

38

12

1.97, 1.95

1.84, 1.69

1.76, 1.73

1.81, 1.78

34.0

²J(PtH) 54 ²J(PtH) 59 ²J(PtH) 61 ³J(PtH) 44, ...

¹J(PtC) 110 ¹J(PtC) 128 ²J(PtC) 29

³J(PtC) 36

35.7

39

40

41

2.77

²J(PtH) 57 ²J(PtH) 58 ²J(PtH) 58 ³J(PtH) 49, 27

2.81 1.85 2.11 2.20, 0.34

²J(PtH) 57 ²J(PtH) 58 ²J(PtH) 58 ³J(PtH) 54, ...

3.17 1.86 2.17 2.28, 0.51

²J(PtH) 62 ... ²J(PtH) 57 ³J(PtH) 57, ...

1.75

2.13

2.17, 0.32

54.7

¹J(PtC) 143 ¹J(PtC) 165 ²J(PtC) 33

54.5 37.9 32.2

¹J(PtC) 139 ¹J(PtC) 173 ²J(PtC) 31

59.7 44.3 32.4

¹J(PtC) 139 ¹J(PtC) 168 ²J(PtC) 34

37.5

32.1

-23.3

³J(PtC) 53 ¹J(PtP) 3305

35.2

³J(PtC) 50 ¹J(PtP) 3393

34.8 25.8

³J(PtC) 56 ¹J(PtP) 3513

46.5

^aSolvent THF-d₈. Temperature 27 °C, if not indicated otherwise. Coupling constants in hertz. ^bTemperature -30 °C. ^cTemperature -80 °C.

^dNot resolved. ^eSiMe₂resonances. ^fδ(H) 1.67 (NH).

Scheme 6. Sequence of Increasing Reactivity and Increasing

Acceptor Strength of the 1,6-Dienes and of Increasing

Stability (decreasing reactivity) of the Corresponding

L-M(1,6-diene) Complexes (M ) Ni, Pd, Pt)

1 in diethyl ether or pentane is first treated with ethene (0 °C)

to produce a solution of 9 that is then reacted further with L

(Scheme 2).

In analogous reactions the dinuclear diallyl ether complex 2′

is solubilized with diallyl ether or ethene to intermediately afford

mononuclear 6 and 10, respectively, which are reacted further

with PR₃(R ) alkyl, aryl), P(OPh)₃, and ^tBuNC to produce the

L-Pd(C₆H₁₀O) derivatives 24-31 (Scheme 3). Reaction of the

dinuclear dvds complex 3 with PR₃affords the L-Pd(dvds)

complexes 34-38 (Scheme 4).

complexes M⁰-C₂H₄back-bonding is considerably weaker as

compared to (R₂PC₂H₄PR₂)M(C₂H₄) complexes.²⁶

Problems arise for sterically Very demanding ligands such as

(2-MeC₆H₄)₃P (cone angle: θ ) 194°)²⁸and ^tBu₃P (θ ) 182°)^28a

for which crystallization of the products is retarded by excess

of alkene. Isolation of the (o-tolyl)₃P derivatives 19, 29, and

38 is so far possible only by evaporating the 1,6-diene solution

to dryness. The isolated complexes readily dissolve again in

the corresponding 1,6-dienes but poorly in other solvents. We

assume that the extraordinary solubility of the complexes is

caused by polarity effects of the 1,6-dienes (the NMR spectra

gave no indication for the formation of solvent adducts).

III. L-Pd(1,6-diene) (13-38) and L-Pt(1,6-diene) (39-

41). In dinuclear 1-4 and in mononuclear 5-12 the non-

chelating alkene ligands are readily displaced by a broad variety

of donors such as phosphanes, phosphites, and isocyanides.²⁷

In a typical reaction aimed at the synthesis of L-Pd(C₇H₁₂) in

homogeneous solution, dinuclear 1 is dissolved in some hepta-

1,6-diene and to the in situ generated 5 the stoichiometric

amount of phosphane PR₃or phosphite P(OR)₃(R ) alkyl, aryl)

is added. When the mixture is cooled to -78 °C colorless

crystals of the phosphane complexes 13-15, 17, and 18 and

the phosphite complexes 20-22 separate in 70-80% yield.

Alternatively, to avoid the excess of 1,6-diene, a suspension of

t

The synthesis of the Bu₃P complexes 16, 27, and 36 is

furthermore complicated by thermal instability and, hence, needs

to be carried out at low temperatures (<-30 °C) as described

in the Experimental Section. At 20 °C solid 16 decomposes

very quickly and 27 in the course of a day, whereas 36 (>100

°C dec) is stable for a long time. In solution, these complexes

(26) (ⁱPr₂PC₂H₄PⁱPr₂)Pd(C₂H₄): δ(H) 2.30, δ(C) 38.4;^26a(ⁱPr₂PC₂H₄P-

ⁱPr₂)Pt(C₂H₄): δ(H) 1.63, δ(C) ≈25.^26bThe coordination of the ethene ligand

in these complexes is static as compared to the NMR time scale. (a) Krause,

J.; Bonrath, W.; Po¨rschke, K.-R. Organometallics 1992, 11, 1158. (b)

Schager, F.; Haack, K.-J.; Mynott, R.; Rufinska, A.; Po¨rschke, K.-R.

Organometallics 1998, 17, 807.

(28) (a) Tolman, C. A. Chem. ReV. 1977, 77, 313. (b) For (2-MeC₆H₄)₃P

the given cone angle of 194° appears to be overestimated, and on the basis

of chemical experience a value of about 170° reflects the steric bulk of this

phosphane more reasonably.

(27) Attempts to react 3 with pyridine to produce (C₅H₅N)Pd(dvds) have

failed.

1,6-Diene Complexes of Pd(0) and Pt(0)

J. Am. Chem. Soc., Vol. 121, No. 42, 1999 9813

undergo ligand redistribution reactions to afford the very stable

Scheme 7

29

Pd(P^tBu₃)₂together with (decomposing) 5 or 6 or (stable) 7

(eq 3). For 16 this ligand redistribution starts already at -30

°C (and is fast at 20 °C), and for 27 and 36 it starts slowly at

about 0 °C. This reaction cannot be completely suppressed in

the synthesis of highly soluble 16 and 27, which therefore

contain about 10% of Pd(P^tBu₃)₂as a byproduct.³⁰

When 1 is reacted with 1 equiv of bidentate dⁱppe (bis-

(diisopropylphosphino)ethane) the bridging hepta-1,6-diene

ligand is replaced by dⁱppe but the chelating 1,6-diene ligands

are maintained to form the equally dinuclear 23 (eq 4). This

dvds it only reluctantly liberates P^tBu₃to form a small amount

of 36 (10%).

Hence, Pd(PR₃)₂as well as (R₃P)₂Pd(alkene) complexes (R

) alkyl, aryl) react with 1,6-dienes to give (R₃P)Pd(1,6-diene)

complexes in an equilibrium reaction (eq 5), and the applicability

reaction shows that the chelate effect of a 1,6-diene ligand can

outdo that of a bidentate phosphane, affording the latter in a

nonchelating binding mode.

as a synthesis route depends on the special PR₃ligand.

Coordinatively saturated complexes such as Pd(PMe₃)₄and Pd-

(PPh₃)₄react with 1,6-dienes to yield (R₃P)Pd(1,6-diene) only

if the displaced PR₃is trapped by a further complex (see below).

Additional synthesis routes for L-Pd(1,6-diene) start from

either (tmeda)PdMe₂, Pd(η³-C₃H₅)₂, Pd(η³-MeC₃H₄)₂, or CpPd-

(η³-C₃H₅) by inducing reductive elimination of the organic

Alternative Routes to L-Pd(1,6-diene) Complexes. L-Pd-

(1,6-diene) complexes can also be prepared by substituting L

in L₂Pd⁰by 1,6-dienes. An early example of such a reaction

was the synthesis of 26 from Pd(PCy₃)₂and diallyl ether,

although no details were given.^15bPd(PCy₃)₂completely dis-

sociates in 1,6-diene solution to give equimolar mixtures of the

corresponding (Cy₃P)Pd(1,6-diene) complexes (15, 26) and

uncoordinated PCy₃as evidenced by the sharp ³¹P NMR signals.

The same holds for the otherwise sparingly soluble Pd{P(o-

tolyl)₃}₂, yielding the {(o-tolyl)₃P}Pd(1,6-diene) complexes 19,

29, and 38 and free P(o-tolyl)₃.

31

ligands. (tmeda)PdMe₂suspended in the corresponding 1,6-

i

diene reacts with trialkylphosphanes PR₃(R, e.g., Pr, Cy) at

20-30 °C and with triarylphosphanes PR₃(R, e.g., Ph) or

phosphites P(OR)₃(R, e.g, C₆H₃-2,6-Me₂, C₆H₃-2,6-ⁱPr₂) at 70-

80 °C with elimination of ethane to yield the corresponding

L-Pd(1,6-diene) (Scheme 7). For the synthesis of the diallyl-

amine complexes 32 and 33 this route (or the displacement of

hepta-1,6-diene from the L-Pd(C₇H₁₂) complexes 14 and 17 by

diallylamine) is the method of choice since a homoleptic Pd⁰-

diallylamine complex Pd(C₆H₁₀NH)_n, related to 1-3, has not

been isolated.

To gain insight into the mechanism of the L-Pd(1,6-diene)

syntheses from (tmeda)PdMe₂, the synthesis of 14 was studied

in detail (eq 6). (tmeda)PdMe₂reacts with two ⁱPr₃P already at

-30 °C by tmeda displacement^31b,cto give a suspension of cis-

Pd(PⁱPr₃)₂in 1,6-diene solution is subjected to a double

equilibrium. It predominantly dissociates to give about equimolar

mixtures of the corresponding (ⁱPr₃P)Pd(1,6-diene) complexes

14, 25, and 35 and uncoordinated PⁱPr₃, but part of it also forms

an adduct with the released PⁱPr₃to give Pd(PⁱPr₃)₃.^5bWith

respect to the formation of 14 and 25 the ³¹P NMR signals of

Pd(PⁱPr₃)₂, PⁱPr₃, and Pd(PⁱPr₃)₃are broad due to an exchange

reaction, whereas for a solution of Pd(PⁱPr₃)₂in neat dvds a

small amount of Pd(PⁱPr₃)₃precipitates. After separation of the

latter, the ³¹P NMR spectrum displays sharp signals of 35 and

some uncoordinated PⁱPr₃. Evaporation of the volatiles (dvds,

PⁱPr₃) or crystallization affords pure 35. The rather stable Pd-

(P^tBu₃)₂dissolves unchanged in hepta-1,6-diene, and even in

(29) (a) Matsumoto, M.; Yoshioka, H.; Nakatsu, K.; Yoshida, T.; Otsuka,

S. J. Am. Chem. Soc. 1974, 96, 3323. Otsuka, S.; Yoshida, T.; Matsumoto,

M.; Nakatsu, K. J. Am. Chem. Soc. 1976, 98, 5850. Yoshida, T.; Otsuka,

S. Inorg. Synth. 1979, 19, 101. Tanaka, M. Acta Crystallogr., Part C 1992,

48, 739. (b) The shift of the ³¹P NMR signal of Pd(P^tBu₃)₂in THF-d₈is

temperature dependent: δ(P) 85.8 (27 °C), 83.6 (-30 °C), 82.0 (-80 °C).

(30) For ^tBu₃P/Pd catalyst systems, see: (a) Nishiyama, M.; Yamamoto,

T.; Koie, Y. Tetrahedron Lett. 1998, 39, 617 and 2367. (b) Littke, A. F.;

Fu, G. C. Angew. Chem. 1998, 110, 3586; Angew. Chem., Int. Ed. Engl.

1998, 37, 3387. (c) Mann, G.; Incarvito, C.; Rheingold, A. L.; Hartwig, J.

F. J. Am. Chem. Soc. 1999, 121, 3224.

9814 J. Am. Chem. Soc., Vol. 121, No. 42, 1999

Krause et al.

(ⁱPr₃P)₂PdMe₂.³²If only one ⁱPr₃P is used, half of the (tmeda)-

PdMe₂remains unreacted. Isolated cis-(ⁱPr₃P)₂PdMe₂, when

heated in an inert solvent to >0 °C, eliminates ethane and

homoleptic Pd(PⁱPr₃)₂is obtained. When the reaction is carried

out in undiluted hepta-1,6-diene,^33aa part of the Pd(PⁱPr₃)₂reacts

further to 14 while the other traps the released PⁱPr₃to form

Pd(PⁱPr₃)₃. The latter is not obtained in the presence of further

(tmeda)PdMe₂which consumes the liberated PⁱPr₃, thereby

affording a total of 2 equiv of 14.^33bThus, the over-all reaction

of (tmeda)PdMe₂with one PⁱPr₃and hepta-1,6-diene to give

14 involves cis-(ⁱPr₃P)₂PdMe₂and Pd(PⁱPr₃)₂as intermediates

and the reaction is formally catalyzed by PⁱPr₃.

alkyl, aryl) in hepta-1,6-diene at 80 °C by elimination of hexa-

1,5-diene, 2,5-dimethylhexa-1,5-diene, or allylcyclopentadiene^36a

to yield the corresponding (R₃P)Pd(C₇H₁₂) complexes (R, e.g.,

Me (13), ⁱPr (14)) in the course of several hours. The mechanism

of these reactions (eq 8) involves the initial formation of (R₃P)-

Reductive ethane elimination from the (R₃P)₂PdMe₂inter-

mediate is rate-determining. For example, cis-(Ph₃P)₂PdMe₂is

readily obtained from (tmeda)PdMe₂and PPh₃(e20 °C).^31bIn

1,6-diene solution (or toluene) it undergoes reductive ethane

elimination to produce (Ph₃P)₂Pd only at 80 °C.³⁴The reaction

of (Ph₃P)₂Pd with (tmeda)PdMe₂and 1,6-dienes to give (Ph₃P)-

Pd(1,6-diene) products (e.g. 28) likewise proceeds readily (e20

°C).

Pd(η³-allyl)(η¹-allyl) or (R₃P)PdCp(η¹-allyl) adducts,^36,37which

partially thermolyze (20 °C) to generate [(R₃P)Pd⁰] intermedi-

ates. The latter are trapped by the so far unreacted Pd^II

complexes to produce rather stable dinuclear Pd^Icomplexes,³⁸

of which the new {(Me₃P)Pd}₂(µ-η⁵-C₅H₅)(µ-η³-C₃H₅)^39aand

The mechanism shown in eq 6 has two consequences. First,

the (tmeda)PdMe₂route is practicable only for phosphane and

phosphite ligands of intermediate bulk, excluding, for example,

PMe₃and P^tBu₃for which the reactions stop at the stages of

39b

{(ⁱPr₃P)Pd}₂(µ-η³-C₃H₅)₂have been isolated. Only the di-

nuclear Pd^Icomplexes, when thermolyzing at 80 °C, react with

hepta-1,6-diene to give the products. Similarly, in diallyl ether

the complexes (R₃P)Pd(C₆H₁₀O) (R, e.g., Me (24), ⁱPr (25), Ph

(28)) are obtained. It is interesting to note that the formation of

24 proceeds rapidly already at ambient temperature. There is

no doubt that phosphite derivatives {(RO)₃P}Pd(1,6-diene) and

dvds ligated complexes L-Pd(dvds) are also accessible from

the Pd^II,I-allyl complexes. Furthermore, the Pd^II-allyl com-

35

the intermediates. With regard to PMe₃, cis-(Me₃P)₂PdMe₂

does not undergo reductive elimination under the given condi-

tions, not even at 80 °C and in the presence of (tmeda)PdMe₂.

Concerning P^tBu₃, the readily formed Pd(P^tBu₃)₂is thermody-

namically too stable to react further. Second, reactions of L₂-

PdMe₂complexes (L ) phosphane (excluding PMe₃), phosphite)

(20-80 °C; eq 7a) as well as L_nPd⁰complexes (n ) 2-4;

t

plexes react with BuNC and diallyl ether already at 20 °C to

give the isocyanide complex 31 (eq 9).⁴⁰

In short, there are now numerous, well-understood synthesis

routes to L-Pd(1,6-diene) complexes.

excluding Pd(P^tBu₃)₂and Pd(PMe₃)₄) (20 °C; eq 7b) with the

stoichiometric quantity of (tmeda)PdMe₂in 1,6-diene solution

also produce L-Pd(1,6-diene) complexes.

General Properties of L-Pd(1,6-Diene). Displacement

reactions, similar to those in Scheme 1, have shown that in

L-Pd(C₇H₁₂) the hepta-1,6-diene ligand is readily replaced by

stoichiometric amounts of diallylamine or diallyl ether to afford

L-Pd(C₆H₁₀NH) and L-Pd(C₆H₁₀O), respectively, and for all

these complexes the 1,6-diene ligands are displaced by dvds to

Pd(η³-C₃H₅)₂, Pd(η³-MeC₃H₄)₂, and CpPd(η³-C₃H₅) are of

similar reactivity and applicability. They react with PR₃(R )

(31) (a) Nakazawa, H.; Ozawa, F.; Yamamoto, A. Organometallics 1983,

2, 241. (b) de Graaf, W.; Boersma, J.; Grove, D.; Spek, A. L.; van Koten,

G. Recl. TraV. Chim. Pays-Bas 1988, 107, 299. de Graaf, W.; Boersma, J.;

Smeets, W. J. J.; Spek, A. L.; van Koten, G. Organometallics 1989, 8,

2907. (c) de Graaf, W.; Boersma, J.; van Koten, G. Organometallics 1990,

9, 1479.

(36) (a) Werner, H. Angew. Chem. 1977, 89, 1; Angew. Chem., Int. Ed.

Engl. 1977, 16, 1. (b) Werner, H.; Ku¨hn, A. Angew. Chem. 1977, 89, 427;

Angew. Chem., Int. Ed. Engl. 1977, 16, 412.

(37) Henc, B.; Jolly, P. W.; Salz, R.; Stobbe, S.; Wilke, G.; Benn, R.;

Mynott, R.; Seevogel, K.; Goddard, R.; Kru¨ger, C. J. Organomet. Chem.

1980, 191, 449.

(38) (a) Werner, H. AdV. Organomet. Chem. 1981, 19, 155 and references

therein. (b) Jolly, P. W.; Kru¨ger, C.; Schick, K.-P.; Wilke, G. Z. Naturforsch.,

B: Anorg. Chem., Org. Chem. 1980, 35, 926. Benn, R.; Jolly, P. W.; Mynott,

R.; Raspel, B.; Schenker, G.; Schick, K.-P.; Schroth, G. Organometallics

1985, 4, 1945.

(39) (a) Bu¨ch, H. M. Dissertation (P. Binger), Universita¨t Kaiserslautern

(Germany), 1982, p 27. (b) {(ⁱPr₃P)Pd}₂(µ-η³-C₃H₅)₂: Yellow columns.

Anal. Calcd for C₂₄H₅₂P₂Pd₂(615.4): C, 46.84; H, 8.52; P, 10.07; Pd, 34.58.

Found: C, 46.96; H, 8.78; P, 10.06; Pd, 34.28. ³¹P NMR: δ 47.3.

(40) For the reaction of CpPd(η³-allyl) complexes with isocyanides RNC,

see: Otsuka, S.; Nakamura, A.; Tatsuno, Y. J. Am. Chem. Soc. 1969, 91,

6994 and ref 4b.

(32) cis-(ⁱPr₃P)₂PdMe₂: C₂₀H₄₈P₂Pd (457.0). ¹H NMR (-30 °C): δ 2.52

(6H, PCH), 1.28 (36H, PCHMe₂), 0.08 (6H, PdMe₂). ³¹P NMR (-30 °C):

δ 33.6.

(33) (a) At the given temperature neither (tmeda)PdMe₂nor Pd(PⁱPr₃)₃

react with neat hepta-1,6-diene. A reaction between Pd(PⁱPr₃)₂and (tmeda)-

PdMe₂does not occur in the absence or in a dilluted hepta-1,6-diene solution,

nor in neat hexa-1,5-diene, cod, or other dienes with a CdC bond sequence

different from 1,6. (b) The reaction of Pd(PⁱPr₃)₂and (tmeda)PdMe₂in neat

diallyl ether and dvds produces the (ⁱPr₃P)Pd(1,6-diene) complexes 25 and

35, respectively.

(34) Reductive ethane elimination from cis-(Ph₃P)₂PdMe₂is solvent

dependent. In THF solution, the typical dark-green solution of (Ph₃P)₂Pd

(δ(P) 23.2) is obtained already at 20 °C.

(35) Tooze, R.; Chiu, K. W.; Wilkinson, G. Polyhedron 1984, 3, 1025.

1,6-Diene Complexes of Pd(0) and Pt(0)

J. Am. Chem. Soc., Vol. 121, No. 42, 1999 9815

give the thermodynamically and thermally most stable L-Pd-

(dvds). The 1,6-diene displacements are equilibrium reactions.

For example, when the C₆H₁₀O complex 25 is dissolved in

hepta-1,6-diene (and some THF-d₈is added), a mixture of equal

amounts of 14 and 25 is formed as shown by ³¹P NMR.

Similarly, the dvds derivative 35 partially reacts in neat C₆H₁₀O

to give a mixture of 25 and 35. Thus, the L-Pd(1,6-diene)

complexes are related to each other by the sequence of

increasing stability (decreasing reactivity) depicted in Scheme

6,⁴¹which reflects also an increasing acceptor strength of the

1,6-diene ligands (see NMR).

of diallyl ether from M⁺proceeds stepwise via [(Me₃P)Pd-

(C₃H₅)]⁺by extruding C₃H₅O. The thermally rather robust

L-Pt(C₇H₁₂) complexes furnish intense M⁺peaks for all L.

While 41⁺(L ) PPh₃) preferentially eliminates hepta-1,6-diene

to give [(Ph₃P)Pt]⁺, degradation of 39⁺(L ) PMe₃) and 40⁺

(L ) PⁱPr₃) is more complex due to a series of hydrogen (C₇H₁₂

ligand) and propene (ⁱPr₃P ligand) elimination steps.

The ¹H and ¹³C NMR data of the 1,6-diene ligands (Table 1)

are very characteristic. For L-M(C₇H₁₂), data of the complete

homologous series M ) Ni,^16aPd, and Pt are now available. In

1

the H NMR spectrum uncoordinated C₇H₁₂gives rise to five

signals, whereas for C_ssymmetrical TP-3 L-M(C₇H₁₂) seven

hepta-1,6-diene signals are expected because of the inequiva-

lence of the geminal methylene protons dCHCH_eqH_ax- and

-CH_aH_b- of the chairlike M(C₇H₁₂) moiety.^42,43

The L-Pd(C₇H₁₂) complexes are most reactive and prefer-

ential starting complexes for [L-Pd] reactions. For many

purposes, however, L-Pd(C₆H₁₀O) complexes are more con-

venient. The latter are more polar and thus easier to isolate from

nonpolar solvents by crystallization and they are thermally more

stable and easier to handle. For example, (Me₃P)Pd(C₇H₁₂) (13)

melts slightly above ambient temperature and needs to be

handled at low temperature, whereas the melting point of

(Me₃P)Pd(C₆H₁₀O) (24) is at 79 °C. Similarly, (^tBu₃P)Pd(C₇H₁₂)

(16) is difficult to isolate but (^tBu₃P)Pd(C₆H₁₀O) (27) crystallizes

nicely at -78 °C. The reactivity of the L-Pd(C₆H₁₀O)

complexes is somewhat lower than that of the L-Pd(C₇H₁₂)

complexes but still very high. In addition, diallyl ether is

inexpensive, whereas hepta-1,6-diene is precious. L-Pd-

(C₆H₁₀O) complexes are preferred over L-Pd(C₆H₁₀NH) de-

rivatives because isolation of the latter is sometimes impeded

by adhering diallylamine.

The compounds have been isolated and characterized by

elemental analyses, mass spectra, and IR and NMR spectra,

including a single-crystal structure determination for 24.¹⁷With

the exception of the (^tBu₃P)Pd(1,6-diene) complexes 16 and 27

and low-melting 13, all solids are at least temporarily stable at

ambient temperature. Although in solution (THF, ether, pentane)

the Pd complexes slowly deposit metallic Pd, such solutions

can generally be stabilized by the addition of 1,6-diene.

Solutions of some L-Pd(C₇H₁₂) complexes in boiling hepta-

1,6-diene (90 °C) did not indicate decomposition over at least

1 h.

L-Pt(1,6-diene). L-Pt(C₇H₁₂) complexes have been pre-

pared according to Scheme 5 by immediate reaction of 4 with

PⁱPr₃(40) and PPh₃(41) or by first dissolving dinuclear 4 in

hepta-1,6-diene (to give 8) and subsequent reaction with PMe₃

(39). As expected, the platinum complexes are sufficiently

stabilized by the hepta-1,6-diene ligand and we found no reason

to prepare other 1,6-diene derivatives.¹⁸

Spectroscopic Characterization of L-M(1,6-diene) (M )

Pd, Pt). The 1,6-diene ligand IR data of the complexes are

compiled and commented in Table 2. The EI mass spectra reflect

the relative stabilities and volatilities of the complexes. The

molecular ion M⁺is found only for the trialkylphosphane

derivatives (R₃P)Pd(1,6-diene). Here, M⁺is observed the better

the smaller the R₃P ligand. For example, M⁺is readily observed

for (Me₃P)Pd(C₇H₁₂) (13; 31%) and (ⁱPr₃P)Pd(C₇H₁₂) (14; 28%)

but less so for (Cy₃P)Pd(C₇H₁₂) (15; 1%). For the (^tBu₃P)Pd-

(1,6-diene) complexes M⁺is observable only for (^tBu₃P)Pd-

(dvds) (36; <1%). A stabilization of M⁺with increasing 1,6-

diene acceptor strength (Scheme 6) is largely offset by the

opposing increase in molecular weight. Fragmentation of the

(R₃P)Pd(1,6-diene) derivatives occurs by loss of the 1,6-diene

to produce [L-Pd]⁺. For (Me₃P)Pd(C₆H₁₀O) (24) elimination

As compared to uncoordinated C₇H₁₂, both signals of the

central aliphatic protons -CH_aH_b- are shifted to lower field

by 0.3-0.5 ppm; the signal splitting is small and usually

resolved only in the 400 MHz spectra. In contrast, for the allylic

protons dCHCH_eqH_ax- the signal of H_eqis shifted to lower

field by 0.1-0.5 ppm and that of H_axto higher field by 1.2-

1.9 ppm, resulting in a signal separation of up to 2 ppm. These

shifts are explained by anisotropic effects of the metal center,^15b

and it is interesting to note that they appear to be independent

of the respective metal Ni,^16aPd, or Pt. The shifts of the

corresponding -CH₂- and dCHCH₂- ¹³C nuclei are almost

unaffected by coordination. The olefinic ¹H and ¹³C resonances

H_ZH_ECdCH- are all shifted to higher field due to M⁰-CdC

back-bonding, and as expected the shifts are smallest for Pd,

intermediate for Ni,^16aand largest for Pt. The assignment of

H_ZH_ECdCH- is based on the vicinal couplings, which are 12-

14 Hz for H_Z(trans to dCH-) and 8-9 Hz for H_E(cis). For

(R₃P)Pd(C₇H₁₂) the hepta-1,6-diene ¹³C nuclei are all spin-

spin coupled to ³¹P, and interestingly, the couplings are largest

for dCH- (²J(PC) ) 10-12 Hz) and the aliphatic -CH₂-

group (⁴J(PC) ) 7-8 Hz) but smallest (and sometimes not

resolved) for H₂Cd (²J(PC) < 5.5 Hz) and dCHCH₂- (³J(PC)

< 4 Hz). For {(RO)₃P}Pd(C₇H₁₂) the hepta-1,6-diene ¹³C,³¹P

spin-spin couplings are about 50% larger. For L-Pt(C₇H₁₂)

complexes, spin-spin couplings with ¹⁹⁵Pt were observed for

most of the hepta-1,6-diene ¹H and all ¹³C nuclei, but unexpect-

edly, not for the allylic H_axprotons which are directed toward

Pt.

The diallyl ether ligand in L-Pd(C₆H₁₀O) and the diallyl-

amine ligand in L-Pd(C₆H₁₀NH) give rise to five (six) proton

signals due to the inequivalence of the allylic protons

dCHCH_eqH_ax-. Of these, H_eqis deshielded by 0.2-0.6 ppm

and H_axis shielded by 1.6-2.1 ppm as compared to uncoordi-

(42) Corresponding to the chairlike conformation of the M(1,6-diene)

moiety,^16aallylic protons are designated equatorial or axial, dCHCH_eqH_ax-.

An equally applicable designation is exo or endo,^15btaking into account

that the equatorial (exo) protons point away from the metal center and the

axial (endo) protons come close to it. The same holds for the Me substituents

dCHSiMe_eqMe_ax- in M(dvds) complexes.

(43) The inequivalence of the aliphatic protons -CH_aH_b- excludes a

C₂symmetrical as well as a dynamic structure of the L-M(C₇H₁₂)

complexes. For the (ⁱPr₃P)M(1,6-diene) complexes 14, 25, 32, 35, and 40

(41) In addition, we have shown that other 1,6-dienes such as diallyl-

silanes serve also as ligands in L-Pd(1,6-diene) complexes, so that the

applicability of 1,6-dienes as a stabilizing coligand for the [L-Pd⁰] moiety

seems to be very general.

i

C_ssymmetry is also indicated by the enantiotopic Me groups of the Pr₃P

ligand (as opposed to diastereotopic Me groups expected for C₂symmetry).

9816 J. Am. Chem. Soc., Vol. 121, No. 42, 1999

Krause et al.

Table 2. Characteristic 1,6-Diene Ligand IR Data (KBr, cm^-1) of the M₂(1,6-diene)₃Complexes 1-4 and of the L-M(1,6-diene) Complexes

13-41 as Well as Frequencies of the Uncoordinated 1,6-Diene for Comparison

dC-H def

ν(dC-H)

in-plane^aout-of-plane

ν(-CH₂-)

2930, 2860

2915, 2851

2915, 2814

ν(CdC)

SiMe₂

COC or SiOSi

1139 sh, 1090

others

C₇H₁₂

3080, 3000, 2980

C₆H₁₀O 3082, 3016, 2984

C₆H₁₀NH 3078, 3010, 2980

992, 912

990, 923

994, 918

1009, 955

1014, 896

946

1643

1648

1644

1596

3285 ν(NH)

dvds

1

2′

3052, 3013

3058, 2991

3064, 3004

2960, 1255, 840, 787 1060

1085/1055

2958, 1249, 830, 785 1055

1240

1237

2918, 2875, 2848, 2820 1523

2905, 2841

1522

(1646)

1496

3

3045, 3013

1235 sh 1015

4

3044, 2979

3040

3050

3049

3062

b

1219

1223

1227

1225

1242

1235

1229

1228

1235

1236

1245

1230

1240

1238

1021

1008

1005

1009

b

1012

b

1009

1008, 922

1010, 930

b

2915, 2880, 2852, 2830 1489

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

30

31

32

34

35

36

37

39

40

41

c

1498

1496

1498

1522

2918, 2878, 2862, 2815 1505

c

d

1503

b

2912, 2880, 2855, 2820 1513

c

1515

1519

1501

1497

1498

1493

1506

1502

3054, 3017

3047

3052

3054, 3013, 2998 1237

3056

b

3060

3051

3028

3032

3055, 3001

b

3031

3033/3025

b

1215,^a1072

1218,^a1070

1215,^a1070

1231,^a1086

1220,^a1068

1218,^a1072

1215,^a1065

1240

1238

1230

1240

1220

1214

1217

b

1220

1195

1194

1202

932

b

934

933

b

2908, 2885, 2835

2940, 2915, 2890, 2842 1510 sh

c

1494

1500

1480

2150 ν(CN)

3266 ν(NH)

2955, 1249, 837, 781 994

b

1481 sh c, 1245, 835, 785

1485 sh 2954, 1245, 835, 783 997

990

997

937

1017

1010 sh

b

1485 sh 2952, 1249, 836, 787 999

c

1466

1470 sh

d

c

2972, 2911, 2870, 2821

^aStrong bands which are typical of the coordinated 1,6-diene. ^bNot assigned because bands of the 1,6-diene and the coligand L are located in

the same range. ^cObscured by absorptions of other aliphatic groups. ^dOverlapped by C-C arene absorptions.

nated diallyl ether. Strong dCHCH_eqH_ax- signal splittings have

been described before for L-M(C₆H₁₀O) (M ) Ni, Pd) (e.g.

Structural Dynamics of L-M(1,6-diene) Complexes. It has

already been shown for (^tBu₃P)Pt(dvds) that the dvds ligand

undergoes slow structural dynamics.^18dIn the ¹H and ¹³C NMR

spectra, recorded at 22 °C, the SiMe_eqMe_axgroups give rise to

broad singlets which coalesce at a higher temperature,⁴⁵indicat-

ing that a stepwise dissociation-reassociation process with a

rotation of the decoordinated CdC bond takes place (cp Scheme

26).¹⁵The ²J(PC) and ³J(PC) couplings of the diallyl ether ¹³

C

nuclei are of the same magnitude as for hepta-1,6-diene ligands.

For the dvds ligand in L-Pd(dvds) separate ¹H and ¹³C NMR

signals are observed for dCHSiMe_eqMe_ax-, in agreement with

other L-M(dvds) complexes (M ) Ni,^16c,23Pt^18b-d). Here, the

vicinal couplings for H_ZH_ECdCH- amount to 15-17 Hz for

H_Zand 12-13 Hz for H_E. The couplings ²J(PC) of dCH- (7-8

Hz) and H₂Cd (2-4.5 Hz) are relatively small.

For the L-M(1,6-diene) complexes of a given 1,6-diene

ligand the ¹³C coordination chemical shift (absolute value)⁴⁴of

the dCH- and H₂Cd vinyl group C atoms increases with an

increasing donor strength of L in the order of eq 10. When for

t

8). The dynamics are due to the exceeding bulk of the Bu₃P

ligand⁴⁶which weakens the coordination of the dvds ligand.

We have previously described a similar process for a Cu^I-1,5-

hexadiene complex.⁴⁷

As compared to Pt⁰, back-bonding is weaker for Pd⁰which

a priori renders the Pd-1,6-diene coordination more labile.

Furthermore, considering that Pd (single-bond radius 1.283 Å)

is somewhat smaller than Pt (1.295 Å),⁴⁸steric strain is expected

to be more severe for L-Pd(1,6-diene) than for the Pt

derivatives. In general, it can be expected for L-M(1,6-diene)

(M ) Ni, Pd, Pt) that dynamic processes of the 1,6-diene ligands

proceed the more facile (i) the smaller M, (ii) the larger L, (iii)

the weaker back-bonding the [L-M⁰] moiety, and (iv) the

weaker electron accepting the 1,6-diene ligand.

C₂H₄< (ArO)₃P < Ar₃P < ^tBuNC < R₃P

(10)

a given R₃P ligand the 1,6-diene ligands of (R₃P)M(1,6-diene)

are changed in the sequence of increasing acceptor strength

according to Scheme 6, the ³¹P NMR resonances are shifted

downfield in agreement with an increased electron withdrawal

from the [L-M] moiety (35 is an unexplained exception from

this rule).

(45) ¹H NMR (89.6 MHz): T_c) 48 °C. ¹³C NMR (22.5 MHz): T_c)

52 °C.^18d

(44) The ¹H and ¹³C coordination chemical shift, i.e., the change in

chemical shift which the alkene experiences upon coordination to a metal

center, is defined by ∆δ ) δ_ligand- δ_{free alkene}. Thus, typical alkene

coordination shifts to higher field are negative. Jolly, P. W.; Mynott, R.

AdV. Organomet. Chem. 1981, 19, 257.

(46) (Cy₃P)Pt(dvds) (Cy₃P: θ ) 170°) is stereochemically rigid.^18d

(47) Nickel, T.; Po¨rschke, K.-R.; Goddard, R.; Kru¨ger, C. Inorg. Chem.

1992, 31, 4428.

(48) Pauling, L. Die Natur der Chemischen Bindung, 3rd ed.; VCH:

Weinheim, Germany, 1976.

1,6-Diene Complexes of Pd(0) and Pt(0)

J. Am. Chem. Soc., Vol. 121, No. 42, 1999 9817

Scheme 8

Scheme 9

Pd(C₆H₁₀O) (28) the ambient temperature 1,6-diene ¹H and ¹³

C

resonances are sharp as long as additional 1,6-diene is absent.

For {(RO)₃P}Pd(C₇H₁₂) (20-22) some broadening of the hepta-

1,6-diene dCHCH_eqH_ax- and -CH_aH_b- resonances is observed

in the ambient temperature ¹H NMR spectra, but the resonances

are sharply resolved when the temperature is lowered to -30

°C. For these compounds in the presence of uncoordinated 1,6-

diene all 1,6-diene resonances are broad at ambient temperature.

Thus, a decreasing donor strength of L (eq 10) destabilizes the

1,6-diene coordination, resulting in structural dynamics accord-

ing to Schemes 8 and/or 9.

There are three potential dynamic processes of the 1,6-diene

ligand which should be considered for L-M(η²,η²-diene)

complexes: (a) Reversible cleavage of one of the M-CdC

coordination bonds of the chelating 1,6-diene ligand gives rise

to a L-2 L-M(η²-diene) intermediate. When the decoordinated

CdC bond is recoordinated by the same face, the original C_s

symmetrical structure is retained (see lower part of Scheme 8).

This process by itself is not detected by NMR unless the

equilibrium is shifted markedly in favor of the L-M(η²-diene)

intermediate. (b) If the cleaved CdC bond of the L-2 L-M(η²-

diene) intermediate is recoordinated by the reVerse face, a C₂

symmetrical L-M(η²,η²-diene) intermediate is formed. Repeat-

ing such a face-exchange for the second CdC bond leads back

to a C_ssymmetrical L-M(η²,η²-diene) complex (Scheme 8).

In the course of this process for the hepta-1,6-diene ligand the

protons dCHCH_eqH_ax- and -CH_aH_b-, for the diallyl ether and

diallylamine ligands the protons dCHCH_eqH_ax-, and for the

dvds ligand the methyl groups dCHSiMe_eqMe_ax- swap posi-

tions and become equivalent. This process is evidenced by

broadening and eventual coalescence of the corresponding NMR

signals while the vinyl resonances remain sharp. (c) The L-2

L-M(η²-diene) intermediate may reversibly coordinate a further

1,6-diene molecule to produce a L-M(η²-diene)₂intermediate.

Dissociation of the initial 1,6-diene ligand results in its

replacement at the L-M(1,6-diene) complex (Scheme 9). This

process is indicated by a broadening of all resonances of the

coordinated and uncoordinated 1,6-dienes. Alternative associa-

tive mechanisms involving the intermediate formation of an 18e

species⁴⁹to explain the fluxionality of L-M(1,6-diene) com-

plexes are discarded because of steric and electronic reasons.

As the experiments show, at ambient temperature sharply

resolved 1,6-diene NMR resonances are observed for those

L-M(1,6-diene) complexes of Table 1 in which the ligands L

are predominantly electron-donating (trialkylphosphanes) and

not exceedingly large. Typical ligands of this type are PMe₃,

PⁱPr₃, and PCy₃. The 1,6-diene resonances of the given

complexes are unaffected by the presence of additional 1,6-

diene. This is also true for (Ph₃P)Pd(dvds) (37) in which dvds

represents the strongest electron-withdrawing 1,6-diene of

Scheme 6. For these (R₃P)M(1,6-diene) complexes the 1,6-diene

coordination appears to be static on the NMR time scale. A

reversible chelate ring cleavage, which would be a prerequisite

for dynamics according to Schemes 8 and 9, is seemingly

insignificant.

Concerning sterically encumbered {(2-MeC₆H₄)₃P}Pd(1,6-

diene) (19, 29, 38),⁵⁰for the hepta-1,6-diene derivative 19 the

¹H NMR signals of dCHCH_eqH_ax- and -CH_aH_b-, for the

diallyl ether derivative 29 the ¹H NMR signals of dCHCH_eqH_ax-,

and for the dvds derivative 38 the ¹H and ¹³C NMR signals of

dCHSiMe_eqMe_ax- are distinct but broad at ambient temperature,

while the vinyl resonances are sharply resolved. In the presence

of uncoordinated 1,6-diene the spectra of the complexes are

unchanged and additional sharp resonances of the free 1,6-diene

are observed. The spectra show that the 1,6-diene ligands in

these complexes undergo slow intramolecular face-exchange

dynamics of the vinyl groups according to (b) (Scheme 8).

These dynamics are even more rapid for (^tBu₃P)Pd(1,6-diene)

(16, 27, 36). The hepta-1,6-diene derivative 16 displays broad

dCHCH_eqH_ax- resonances as low as -80 °C. Unfortunately,

recording of the coalesced signal at higher temperature was

impeded by the thermolability of this complex. In the ¹H NMR

spectra of the diallyl ether complex 27 the dCHCH_eqH_ax-

resonances are sharp at -80 °C but broad at -30 °C, and in

the ¹H and ¹³C NMR spectra of the dvds complex 36 the SiMe_eq-

Me_axresonances are sharply resolved at -80 °C but coalesced

at -30 °C; the vinyl resonances are constantly sharp at these

temperatures. For added 1,6-diene separate sharp signals are

observed, showing that an exchange of coordinated and

uncoordinated 1,6-diene is slow. Thus, the (^tBu₃P)Pd(1,6-diene)

complexes likewise undergo intramolecular vinyl group face-

exchange dynamics according to (b) (Scheme 8), and these

dynamics, detectable for 16 at -80 °C and for 27 and 36 at

-30 °C, are markedly more rapid than for other L-Pd(1,6-

diene) complexes and the platinum derivative (^tBu₃P)Pt(dvds).^18d

At 27 °C all 1,6-diene resonances of 27 and 36 are broad and

so are the resonances of added 1,6-diene, giving evidence of

an exchange of coordinated and uncoordinated 1,6-diene.

Furthermore, increasing the temperature from -80 to 27 °C

shifts the ³¹P NMR signals of 27 and 36 downfield by about 5

(50) In the -80 °C ¹³C NMR (75.5 MHz) spectrum of 19 seven hepta-

1,6-diene resonances are observed (δ(C) 78.0, 77.4 (dCH-), 59.5, 59.0

(H₂Cd), 33.8, 33.4 (dCHCH₂-), 33.0 (-CH₂-)), indicating chirality of

the complex. This is explained by the propeller-like conformation of the

(o-tolyl)₃P ligand with locked handedness.

The situation is different for weaker donors L. For (Ph₃P)-

Pd(C₇H₁₂) (17), {(4-MeC₆H₄)₃P}Pd(C₇H₁₂) (18), and (Ph₃P)-

(49) Dreher, E.; Gabor, B.; Jolly, P. W.; Kopiske, C.; Kru¨ger, C.;

Limberg, A.; Mynott, R. Organometallics 1995, 14, 1893.

9818 J. Am. Chem. Soc., Vol. 121, No. 42, 1999

Krause et al.

Scheme 10

Conclusions

This work describes the development of a general and

efficient access to 1,6-diene stabilized “naked palladium” and

L-Pd⁰complexes as fundamental and highly reactive building

units in palladium chemistry. In the homoleptic olefinic

complexes 1-12 the metal atoms (Pd and Pt) are TP-3

coordinated (in contrast to, e.g., the T-4 geometry predicted for

the elusive Pd(cod)₂). This feature and the properties of the

chelating 1,6-diene moiety, which chelates a TP-3 d¹⁰M⁰center

with little strain, are the clue for the stability of this class of

complexes.

As exemplified by 13-38, there is now a broad range of 16e

TP-3 L-Pd(η²,η²-1,6-diene) complexes available which may

be prepared by numerous routes. For complexes with weakly

electron-donating (P(OR)₃) or sterically demanding (P(o-tolyl)₃,

P^tBu₃) ligands it is anticipated that the chelate ring opens easily

to generate 14e L-2 L-Pd(η²-diene) intermediates from which

the 1,6-diene ligand can be displaced.

Besides for stoichiometric reactions, L-Pd(1,6-diene) com-

plexes may play an important role in the “soft” catalytic Pd⁰

chemistry under nonforcing conditions, in particular when high

selectivities are desired. Moreover, the complexes are readily

formed as intermediates from a Pd⁰source in the presence of a

donor L simply by running reactions in a 1,6-diene solvent (e.g.

diallyl ether). It is to be expected that the complexes find general

application in homogeneous catalysis in those cases where an

unsaturated complex fragment [L-Pd⁰], which is easily devel-

oped from the complexes, acts as the “true catalyst”. This

concept has already been proven for the reactions cited above.

Although our study focused on the 1,6-dienes given in

Scheme 6, the principle of stabilization of “naked palladium”

and [L-Pd⁰] fragments by 1,6-positioned ene functions is

presumingly quite general. Thus, 1,6-heterodienes (CdNR, Cd

O) are also expected to form stable TP-3 L-M(diene) com-

plexes (M ) Ni, Pd, Pt). In contrast, L-M(1,6-diyne) complexes

are significantly less stable and so far confined to M ) Ni,⁵⁷

and L-M(1,6-enyne) complexes seem to be unstable for all

metals of the d¹⁰triad.

ppm, which we attribute to occurrence of Pd-1,6-diene chelate

ring cleavage and an increased population of an L-2 (^tBu₃P)-

Pd(η²-1,6-diene) intermediate.⁵¹These spectral features are

explained by structural dynamics according to (c) (Scheme 9),

becoming relevant at ambient temperature in addition to those

of (b).

IV. Applications of L-Pd(1,6-Diene) Complexes (Scheme

10). L-Pd(1,6-diene) complexes represent versatile building

blocks for the deliberate synthesis of a large variety of Pd⁰,

Pd^I, and Pd^IIcomplexes. Examples include (i, ii) the formation

of L₂Pd-alkene and L₂Pd-alkyne complexes,⁵²(iii) the forma-

tion of dinuclear Pd^Icomplexes,^13a,53and (iv, v) the formation

of [L-Pd(allyl)] moieties from L-Pd(C₆H₁₀O) by oxidative

addition of allyl halides or protonation.^13a,53Apart from these

stoichiometric reactions, L-Pd(1,6-diene) complexes are ef-

fective catalysts for a variety of coupling reactions under mild

conditions. Examples are given by (vi) the linear telomerization

of butadiene with MeOH to give 1-methoxy-octa-2,7-diene¹¹

above -10 °C,⁵⁴(vii) the Stille coupling of organoelectrophiles

and organostannanes^55aat 20 °C,^55band (viii) the regio- and

stereoselective linear trimerization of alk-1-ynes to give 1,4,6-

trisubstituted cis-hexa-1,3-dien-5-ynes between -30 and 20

°C.^13a,c,17,52Promising candidates are furthermore Pd-catalyzed

cross-coupling reactions such as Heck reactions, Suzuki cou-

plings, and aryl halide amination.⁵⁶

Experimental Section

To exclude oxygen and moisture, all operations were conducted

under an atmosphere of argon by standard Schlenk techniques. (cod)-

PdCl₂,^58a(cod)PtCl₂,^58bPd(η³-C₃H₅)₂,^26aPd(η³-2-MeC₃H₄)₂,^26aCpPd-

31a,b

(η³-C₃H₅),⁵⁹and (tmeda)PdMe₂

were prepared by published pro-

cedures. Microanalyses were performed by the Mikroanalytisches Labor

Kolbe, Mu¨lheim, Germany. ¹H NMR spectra (δ relative to internal

TMS) were measured at 200, 300, and 400 MHz, ¹³C NMR spectra (δ

relative to internal TMS) at 50.3, 75.5, and 100.6 MHz, and ³¹P NMR

spectra (δ relative to external 85% aqueous H₃PO₄) at 81, 121.5, and

162 MHz on Bruker AM-200, WM-300, and WH-400 instruments. For

all NMR spectra solutions of the compounds in THF-d₈were used. EI

mass spectra (the data refer to ²⁸Si, ¹⁰⁶Pd, and ¹⁹⁵Pt) were recorded at

70 eV on a Finnigan MAT 8200, and IR spectra on Nicolet FT 7199

and Magna-IR 750 spectrometers.

(µ-η²,η²-C₇H₁₂){Pd(η²,η²-C₇H₁₂)}₂(1). A suspension of (cod)PdCl₂

(8.57 g, 30.0 mmol) in 40 mL of hepta-1,6-diene was treated slowly at

-78 °C with a 0.2 M solution of Li₂(cot) (150 mL, 30.0 mmol) in

diethyl ether. When the temperature was raised to -40 °C a voluminous

(51) The ³¹P NMR downfield shift indicates an enlarged charge

withdrawal from P. Apparently, in a 14e L-2 (^tBu₃P)Pd(η²-alkene) complex

the charge withdrawal from phosphorus by the trans coordinated CdC group

is larger than that in 16e TP-3 27 and 36 by two CdC groups.

(52) (a) Krause, J.; Po¨rschke, K.-R. 5th International Conference on the

Chemistry of the Platinum Group Metals, St. Andrews, U.K., July 11-16,

1993, A199. (b) Krause, J.; Schager, F.; Po¨rschke, K.-R. 32nd International

Conference on Coordination Chemistry (ICCC), Santiago, Chile, Aug 24-

29, 1997, 7O4. Cestaric, G.; Krause, J.; Po¨rschke, K.-R. Manuscript in

preparation.

(53) Krause, J.; Po¨rschke, K.-R. To be submitted for publication.

(54) Vollmu¨ller, F.; Krause, J.; Klein, S.; Ma¨gerlein, W.; Beller, M.

Submitted.

(55) (a) Stille, J. K. Angew. Chem. 1986, 98, 504; Angew. Chem., Int.

Ed. Engl. 1986, 25, 508. Scott, W. J.; Stille, J. K. J. Am. Chem. Soc. 1986,

108, 3033. Mitchell, T. N. Synthesis 1992, 803. (b) The reactions apparently

proceed without an induction period or deposition of palladium. The results

confirm that in the L_nPd⁰catalyzed Stille reaction phosphane dissociation

gives rise to [L-Pd⁰] species as the “true catalyst”. No second phosphane

ligand is necessary to act in the catalytic cycle. Krause, J.; Po¨rschke, K.-R.

Unpublished results.

(57) Proft, B.; Po¨rschke, K.-R.; Lutz, F.; Kru¨ger, C. Chem. Ber. 1994,

127, 653.

(58) (a) Chatt, J.; Vallarino, L. M.; Venanzi, L. M. J. Chem. Soc. 1957,

3413. (b) Chatt, J.; Vallarino, L. M.; Venanzi, L. M. J. Chem. Soc. 1957,

2496. McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem.

Soc. 1976, 98, 6521.

(59) (a) Shaw, B. L. Proc. Chem. Soc., London 1960, 247. (b) Tatsuno,

Y.; Yoshida, T.; Otsuka, S. Inorg. Synth. 1979, 19, 220.

(56) Hartwig, J. F. Synlett 1998, 329.

1,6-Diene Complexes of Pd(0) and Pt(0)

J. Am. Chem. Soc., Vol. 121, No. 42, 1999 9819

precipitate formed, consisting of 1 and LiCl. At -20/-10 °C the

suspension was so dense that it could hardly be stirred. When diethyl

ether was evaporated under vacuum, 1 dissolved again. LiCl was

removed by D4-filtration, and to the light green solution 50 mL of

pentane was added (-30 °C), whereupon pure, colorless 1 precipitated.

The product was isolated by filtration, washed with cold pentane, and

dried under vacuum (-30 °C): yield 4.59 g (61%); ∼0 °C dec. Anal.

Calcd for C₂₁H₃₆Pd₂(501.4): C, 50.31; H, 7.24; Pd, 42.45. Found: C,

50.41; H, 7.35; Pd, 42.45.

32.5, 32.4 (dCHCH₂- and -CH₂-); all signals of equal intensity.

C₁₄H₂₄Pd (298.8).

Pd(η²,η²-C₆H₁₀O)(η²-C₆H₁₀O) (6). Preparation was performed as

for 5 by dissolving 2 (ca 80 mg) in diallyl ether (0.2 mL) and THF-d₈.

¹³C NMR (75.5 MHz, -80 °C): δ 136.4 (dCH-_uncoord), 115.7 (H₂Cd

_uncoord), 85.6, 85.4, 77.3 (dCH-), 73.4, 70.5, 69.9, 69.6 (-CH₂O-),

63.9, 59.6, 59.4 (H₂Cd); all signals were of equal intensity. C₁₂H₂₀O₂-

Pd (302.7).

Pd(η²,η²-dvds)(η²-dvds) (7). Preparation was as for 5 by dissolving

3 (ca 80 mg) in dvds (0.2 mL) and THF-d₈. ¹³C NMR (75.5 MHz,

-80 °C): δ 140 (dCH-_uncoord), 133 (H₂Cd_uncood), 75.6, 75.0, 74.6 (d

CH-), 73.5, 73.2, 73.0 (H₂Cd), each 1C, vinyl; 3.1 (1C), 1.5 (2C),

1.2 (1C), 0.7 (2C), -0.9 (1C), -1.1 (1C), SiMe_aMe_b; all signals are

broad. C₁₆H₃₆O₂PdSi₄(479.2).

(µ-η²,η²-C₆H₁₀O){Pd(η²,η²-C₆H₁₀O)}₂‚C₆H₁₀O (2′). The reaction

was performed as for 1 by treating a suspension of (cod)PdCl₂(2.86 g,

10.0 mmol) in diallyl ether (20 mL) with a 0.2 M ethereal solution of

Li₂(cot) (50 mL, 10.0 mmol) at -78 °C. After warming the mixture to

0 °C the ether was evaporated under vacuum. Pentane (40 mL) was

added at -30 °C to precipitate LiCl, which was removed by an

immediate D4-filtration. The product crystallized between -30 and -78

°C, and the mother liquor was removed by cannulation. The pale yellow

solid was washed twice with cold pentane and dried under vacuum

(-30 °C): yield 1.26 g (42%); >0 °C dec. EI-MS: The complex

decomposed between 30 and 50 °C; no ions containing Pd were

observed. ¹H NMR of 2 (300 MHz, -30 °C): δ 3.26, 3.26, 3.17, 3.13,

3.05, 3.04 (each 2H, H_ZHCd), 3.56, 3.56, 3.47, 3.46, 3.40, 3.40 (each

2H, HH_ECd), 4.43 (4H), 4.13 (8H, unresolved dCH-), 4.52 (8H),

4.28 (4H, unresolved -CH_aHO-), 4.28, 4.28, 2.31, 2.30, 2.30, 2.29

(each 2H, -CHH_bO-). ¹³C NMR of 2 (75.5 MHz, -30 °C): δ 85.7,

85.7, 85.5, 85.5, 79.3, 79.1 (dCH-), 72.8, 72.5, 70.3, 70.3, 70.1, 69.9

(-CH₂O-), 63.4, 63.4, 59.5, 59.5, 59.3, 59.25 (H₂Cd); all signals have

the same intensity (2C). The signals and intensities refer to the

diastereomeric mixture. Additional signals are observed for uncoordi-

nated C₆H₁₀O (see Table 1) and 6. Anal. Calcd for C₁₈H₃₀O₃Pd₂‚C₆H₁₀O

(605.4): C, 47.61; H, 6.66; O, 10.57; Pd, 35.16. Found: C, 47.79; H,

6.62; Pd, 34.94.

{µ-(η²-H₂CdCHSiMe₂)₂O}[Pd{(η²-H₂CdCHSiMe₂)₂O}]₂(3). The

reaction was performed as for 1 by treating a suspension of (cod)-

PdCl₂(2.86 g, 10.0 mmol) in dvds (10 mL) with a 0.2 M ethereal

solution of Li₂(cot) (50 mL, 10.0 mmol) at 20 °C. Ether was evaporated

under vacuum to afford an ocher suspension. After D4-filtration

(removal of LiCl) the light yellow solution was concentrated under

high vacuum to give a sticky oil, to which some pentane (5 mL) was

added. Between -30 and -78 °C an almost colorless mirocrystalline

precipitate was obtained, from which the mother liquor was removed

by filtration. The product was washed with a small portion of cold

pentane and dried under vacumm (-30 °C): yield 2.90 g (75%); mp

55 °C dec. ¹H NMR (300 MHz, -80 °C): δ 4.3-3.4 (18 overlapping

multiplets, each 2H; H_ZH_ECd and dCH-), 0.25, 0.25, 0.23, 0.23, 0.11,

0.10, -0.05, -0.05, -0.22, -0.23, -0.32, -0.32 (each s, 6H, SiMe).

¹³C NMR (75.5 MHz, -80 °C): δ 75.85, 75.8, 75.1, 75.1, 74.4, 74.4,

73.7, 73.7, 73.4, 73.4, 72.8, 72.8 (vinyl), 3.14, 3.14, 1.60, 1.60, 1.52,

1.52, 1.45, 1.41, -0.92, -0.94, -1.17, -1.17 (SiMe); all signals have

the same intensity (2C). The signals and intensities refer to the

diastereomeric mixture of 3. Anal. Calcd for C₂₄H₅₄O₃Pd₂Si₆(772.0):

C, 37.34; H, 7.05; O, 6.22; Pd, 27.57; Si, 21.83. Found: C, 37.26; H,

7.12; Pd, 27.48; Si, 21.89.

Pt(η²,η²-C₇H₁₂)(η²-C₇H₁₂) (8). Preparation was as for 5 by dissolv-

ing 4 (ca 80 mg) in hepta-1,6-diene (0.2 mL) and THF-d₈. ¹³C NMR

(75.5 MHz, -30 °C): δ 139.7 (dCH-_uncoord, C13), 114.8 (H₂Cd_uncoord

,

C14), 70.0, 69.8 (each J(¹⁹⁵PtC) ) 108 Hz, C2 and C6), 65.6 (137 Hz,

C9), 48.5 (137 Hz, C1/7), 48.1 (133 Hz, C1/7), 46.8 (121 Hz, C8),

35.3 (24 Hz, C11), 34.7 (13 Hz, C12), 33.6 (37 Hz, C4), 33.3 (55 Hz,

C10), 31.4, 31.3 (each 28 Hz, C3 and C5); all signals were of equal

intensity. At 27 °C the resonances are broad but still resolved. C₁₄H₂₄-

Pt (387.4).

(C₂H₄)Pd(η²,η²-C₇H₁₂) (9). A colorless suspension of 1 (ca 80 mg)

in 1 mL of THF-d₈was saturated with ethene at -78 °C. When the

mixture was warmed to -30 °C, the solid dissolved (10 min) to give

a yellow solution. ¹H NMR (200 MHz, -30 °C) (for C₇H₁₂see Table

1): δ 3.39 (4H, C₂H₄). ¹³C NMR (75.5 MHz, -30 °C) (for C₇H₁₂see

Table 1): δ 61.9 (2C, C₂H₄). The spectra displayed additional signals

for 1 half-equiv of the displaced 1,6-diene (Table 1) and for uncoor-

dinated ethene (δ(H) 5.39, δ(C) 123.7). C₉H₁₆Pd (230.7).

(C₂H₄)Pd(η²,η²-C₆H₁₀O) (10). The synthesis was performed as for

9 by reacting 2 (ca. 80 mg) with ethene in THF-d₈at -30 °C. ¹H NMR

(300 MHz, -30 °C) (for C₆H₁₀O see Table 1): δ 3.53 (4H, C₂H₄). ¹³

C

NMR (75.5 MHz, -30 °C) (for C₆H₁₀O see Table 1): δ 63.0 (2C,

C₂H₄). C₉H₁₄OPd (244.6).

(C₂H₄)Pd{(η²-H₂CdCHSiMe₂)₂O} (11). The synthesis was per-

formed as for 9 by reacting 3 (ca. 80 mg) with ethene in THF-d₈at

-30 °C. ¹H NMR (300 MHz, -30 °C) (for dvds see Table 1): δ 3.79

(4H, C₂H₄). ¹³C NMR (75.5 MHz, -30 °C) (for dvds see Table 1): δ

73.3 (2C, C₂H₄). C₁₀H₂₂OPdSi₂(320.9).

(C₂H₄)Pt(η²,η²-C₇H₁₂) (12). A suspension of 4 (204 mg, 0.30 mmol)

in pentane (5 mL) was saturated with ethene (-78 °C) and stirred at 0

°C to produce a clear yellow solution. The solvent was evaporated in

a light vacuum to yield a low-melting, semisolid yellow residue of

pure 12: yield 35-40 mg (40%). Although the reaction appears to be

quantitative, the yield of isolated 12 is low due to its high volatility.

For subsequent reactions an in situ preparation is recommended. EI-

MS: see text. ¹H NMR (300 MHz, 27 °C) (for C₇H₁₂see Table 1): δ

2

2.95 (4H, J(PtH) ) 59 Hz, C₂H₄). ¹³C NMR (75.5 MHz, 27 °C) (for

1

C₇H₁₂see Table 1): δ 44.3 (2C, J(PtC) ) 122 Hz, C₂H₄). C₉H₁₆Pt

(319.3).

(µ-η²,η²-C₇H₁₂){Pt(η²,η²-C₇H₁₂)}₂(4). A suspension of (cod)PtCl₂

(1.496 g, 4.00 mmol) in hepta-1,6-diene (12 mL) was combined with

a 0.2 M ethereal solution of Li₂(cot) (20 mL, 4.00 mmol) at -78 °C.

The stirred brown mixture was slowly (2 h) warmed to ambient

temperature, ether was evaporated, and the concentrated suspension

was stirred for a further 15 h. LiCl was removed by D4-filtration and

washed twice with pentane (10 mL). After addition of further pentane

(20 mL) to the brown solution a yellow beige solid precipitated at -78

°C which was separated by filtration, washed with cold pentane, and

dried under vacuum (20 °C): yield 510 mg (38%); mp 110 °C dec.

EI-MS (90 °C): m/e (%) 582 ([Pt₂(C₇H₁₂)₂]⁺, 0.1), 387 ([Pt(C₇H₁₂)₂]⁺,

5), 291 ([Pt(C₇H₁₂)]⁺, 15); M⁺was not detected. Anal. Calcd for C₂₁H₃₆-

Pt₂(678.7): C, 37.17; H, 5.35; Pt, 57.49. Found: C, 37.10; H, 5.37;

Pt, 57.62.

(Me₃P)Pd(η²,η²-C₇H₁₂) (13). (a) From 1. A suspension of complex

1 (501 mg, 1.00 mmol) in 2 mL of hepta-1,6-diene (0 °C) was treated

with a solution of PMe₃(152 mg, 2.00 mmol) in 5 mL of pentane at

-78 °C. The mixture was slowly warmed to 20 °C, and insoluble

impurities were removed by D4-filtration. From the solution colorless

thin needles separated between -30 and -78 °C. After removal of the

mother liquor by cannulation, the product was washed with a small

volume of cold pentane and dried under vacuum at -30 °C: yield 400

mg (72%). (b) From (η⁵-C₅H₅)Pd(η³-C₃H₅). Addition of PMe₃(0.20

mL, 152 mg, 2.00 mmol) to a red suspension of (η⁵-C₅H₅)Pd(η³-C₃H₅)

(425 mg, 2.00 mmol) in 3 mL of hepta-1,6-diene at -30 °C immediately

afforded a light yellow precipitate. Heating the mixture to 80 °C for 5

h resulted in a clear yellow solution from which thin colorless needles

crystallized at -78 °C. Isolation was as described above: yield 290

mg (52%); mp ca. 27 °C. EI-MS (0 °C): m/e (%) 278 (M⁺, 31), 182

Pd(η²,η²-C₇H₁₂)(η²-C₇H₁₂) (5). Complex 1 (ca. 80 mg) was dis-

solved in hepta-1,6-diene (0.2 mL) and THF-d₈(0.7 mL). ¹³C NMR

(75.5 MHz, -80 °C): δ 139.6 (dCH-_uncoord), 115.1 (H₂Cd_uncoord), 84.4,

84.2, 84.0 (dCH-), 62.8, 62.4, 61.6 (H₂Cd), 35.6, 34.7, 32.9, 32.6,

1

([(Me₃P)Pd]⁺, 81). H NMR (200 MHz, 27 °C) (for C₇H₁₂see Table

1): δ 1.22 (d, 9H), PMe₃. ¹³C NMR (50.3 MHz, 27 °C) (for C₇H₁₂see

Table 1): δ 19.2 (3C), PMe₃. ³¹P NMR (81 MHz, 27 °C): see Table

9820 J. Am. Chem. Soc., Vol. 121, No. 42, 1999

Krause et al.

1. Anal. Calcd for C₁₀H₂₁PPd (278.7): C, 43.10; H, 7.60; P, 11.11;

Pd, 38.19. Found: C, 42.95; H, 7.66; P, 11.03; Pd, 38.42.

solution of PPh₃(262 mg, 1.00 mmol) in 5 mL of diethyl ether at -78

°C. The mixture was slowly warmed to 20 °C, and insoluble impurities

were removed by D4-filtration. From the colorless solution pale yellow

intergrown crystals separated at -78 °C, which were isolated as

described for 13: yield 350 mg (75%). (b) From (tmeda)PdMe₂. A

mixture of (tmeda)PdMe₂(758 mg, 3.00 mmol) and PPh₃(786 mg,

3.00 mmol) in hepta-1,6-diene (5 mL) was heated to 80 °C for 15 min.

After cooling all volatiles were evaporated in a vacuum and the residue

was dissolved in a small volume of diethyl ether. The product

crystallized at -78 °C and was isolated as described for route a: yield

1.18 g (85%); mp 87 °C dec. Crystalline 17 is stable at ambient

temperature for at least several days but slowly decomposes in solution.

EI-MS: the compound decomposed and the spectra of C₇H₁₂(m/e 96)

(ⁱPr₃P)Pd(η²,η²-C₇H₁₂) (14). (a) From 1. Synthesis was as for 13,

route a, by using PⁱPr₃(320 mg, 2.00 mmol) in 5 mL of pentane (20

°C). Between -30 and -78 °C colorless crystals separated which were

washed twice with cold pentane and dried under vacuum at 20 °C:

yield 610 mg (84%). (b) From (tmeda)PdMe₂. To (tmeda)PdMe₂

(1.263 g, 5.00 mmol) was added a solution of PⁱPr₃(801 mg, 5.00

mmol) in 5 mL of hepta-1,6-diene at -30 °C. The stirred colorless

suspension was slowly heated to 25-30 °C, whereupon ethane evolved

and an orange solution was formed. Between -30 and -78 °C a

microcrystalline precipitate was obtained which was isolated as

described (route a): yield 1.69 g (93%). (c) From Pd(η³-C₃H₅)₂. PⁱPr₃

(801 mg, 5.00 mmol) was added to a solution of Pd(η³-C₃H₅)₂(943

mg, 5.00 mmol) in 5 mL of hepta-1,6-diene. The yellow mixture was

heated to 80 °C for 2 h, whereupon the solution decolorized. After

evaporation of the excess of hepta-1,6-diene the residue was dissolved

in pentane (20 mL) and some deposited Pd was removed by filtration.

Between -30 and -78 °C colorless crystals separated which were

isolated as described (route a): yield 1.54 g (85%). (d) From {(ⁱPr₃P)-

Pd}₂(µ-C₃H₅)₂. The yellow suspension of {(ⁱPr₃P)Pd}₂(µ-C₃H₅)₂(615

mg, 1.00 mmol) in 5 mL of hepta-1,6-diene was heated to 80 °C for 2

h, whereupon the solution decolorized. After evaporation of the excess

of hepta-1,6-diene and addition of pentane (10 mL) the solution was

treated further as described (routes a and c): yield 630 mg (87%). (e)

From (tmeda)PdMe₂and Pd(PⁱPr₃)₂. A suspension of (tmeda)PdMe₂

(253 mg, 1.00 mmol) in 1 mL of hepta-1,6-diene was combined at

-30 °C with a solution of Pd(PⁱPr₃)₂(427 mg, 1.00 mmol) in 2 mL of

hepta-1,6-diene. When the mixture was heated to 30 °C ethane evolved

and an orange-yellow solution was obtained. After addition of pentane

(10 mL) the colorless product crystallized between -30 and -78 °C

and was isolated as described (route a): yield 545 mg (75%); mp 52

°C. EI-MS (43 °C): m/e (%) 362 (M⁺, 28), 266 ([(ⁱPr₃P)Pd]⁺, 88). ¹H

NMR (200 MHz, 27 °C) (for C₇H₁₂see Table 1): δ 2.18 (m, 3H, PCH),

1.16 (dd, 18H, Me), PⁱPr₃. ¹³C NMR (100.6 MHz, 27 °C) (for C₇H₁₂

see Table 1): δ 26.9 (3C, PCH), 20.9 (6C, Me), PⁱPr₃. ³¹P NMR (81

MHz, 27 °C): see Table 1. Anal. Calcd for C₁₆H₃₃PPd (362.8): C,

52.97; H, 9.17; P, 8.54; Pd, 29.33. Found: C, 52.84; H, 9.25; P, 8.60;

Pd, 29.54.

1

and PPh₃(m/e 262) were observed. H NMR (400 MHz, 27 °C) (for

C₇H₁₂see Table 1): δ 7.40 (3H, Ph), 7.32 (12H, Ph), PPh₃. ¹³C NMR

(50.3 MHz, 27 °C) (for C₇H₁₂see Table 1): δ 138.7 (3C), 134.3 (6C),

129.6 (3C), 128.7 (6C), PPh₃. ³¹P NMR (81 MHz, 27 °C): see Table

1. Anal. Calcd for C₂₅H₂₇PPd (464.9): C, 64.59; H, 5.40; P, 6.66; Pd,

22.89. Found: C, 64.46; H, 5.55; P, 6.77; Pd, 23.08.

{(4-MeC₆H₄)₃P}Pd(η²,η²-C₇H₁₂) (18). The reaction was carried out

similarly as described for 17 by reacting a suspension of 1 (501 mg,

1.00 mmol) in hepta-1,6-diene (2 mL) with a solution of (4-MeC₆H₄)₃P

(609 mg, 2.00 mmol) in 5 mL of diethyl ether. After warming the

mixture from -78 to 20 °C the solvent was evaporated under vacuum

to give a beige residue. Recrystallization from diethyl ether, including

D4-filtration, afforded small red brown cubes (-30 °C) which were

isolated as described: yield 710 mg (70%); mp 114 °C. EI-MS: the

complex decomposed. ¹H NMR (200 MHz, 27 °C) (for C₇H₁₂see Table

1): δ 7.20 (12H, C₆H₄), 2.31 (9H, Me), (4-MeC₆H₄)₃P. ¹³C NMR (50.3

MHz, 27 °C) (for C₇H₁₂see Table 1): δ 139.7 (s, 3C, C_δ), 136.0 (3C,

PC_R), 134.6 (6C, C_â), 129.6 (6C, C_γ), 21.5 (3C, Me), (4-MeC₆H₄)₃P.

³¹P NMR (81 MHz, 27 °C): see Table 1. Anal. Calcd for C₂₈H₃₃PPd

(507.0): C, 66.34; H, 6.56; P, 6.11; Pd, 20.99. Found: C, 66.45; H,

6.49; P, 6.02; Pd, 21.11.

{(2-MeC₆H₄)₃P}Pd(η²,η²-C₇H₁₂) (19). A solution of 1 (251 mg,

0.50 mmol) in hepta-1,6-diene (3 mL) was added to solid P(o-tolyl)₃

(304 mg, 1.00 mol). The solvent was evaporated from the resulting

yellow solution under vacuum to obtain a yellow-greenish residue,

which was washed with ether and dried under vacuum at -30 °C: yield

500 mg. Isolated 19 contained about 10% of Pd{P(o-tolyl)₃}₂(δ(P)

-6.9) as an impurity. The complex slowly decomposed at ambient

(Cy₃P)Pd(η²,η²-C₇H₁₂) (15). The synthesis was carried out as for

14, route b, by reacting (tmeda)PdMe₂(506 mg, 2.00 mmol) with Cy₃P

(561 mg, 2.00 mmol) in 5 mL of hepta-1,6-diene. At 30 °C a green-

yellow solution formed from which a colorless solid precipitated. The

excess of hepta-1,6-diene was siphoned off (20 °C), and the solid was

recrystallized from diethyl ether (50 mL) to yield colorless cubes (-30

°C) which were isolated as described for 14, route a: yield 735 mg

(76%); mp 131 °C. EI-MS (80 °C): m/e 482 (M⁺, 1), 386 ([(Cy₃P)-

Pd]⁺, 4), 304 ([(Cy₂PH)Pd]⁺, 2). ¹H NMR (200 MHz, 27 °C) (for C₇H₁₂

see Table 1): δ 2.1-1.6 (18H), 1.5-1.2 (15H), (c-C₆H₁₁)₃P. ¹³C NMR

(50.3 MHz, 27 °C) (for C₇H₁₂see Table 1): δ 37.4 (3C, ¹J(PC) ) 9.6

Hz, PC_R), 31.8 (6C, PCHC_â), 28.8 (6C, C_γ), 27.8 (3C, C_δ), P(c-C₆H₁₁)₃.

³¹P NMR (81 MHz, 27 °C): see Table 1. Anal. Calcd for C₂₅H₄₅PPd

(483.0): C, 62.17; H, 9.39; Pd, 22.03; P, 6.41. Found: C, 62.34; H,

9.29; Pd, 22.10; P, 6.63.

1

temperature. H NMR (200 MHz, 27 °C) (for C₇H₁₂see Table 1): δ

7.46 (3H), 7.20 (9H), 2.10 (9H), (2-MeC₆H₄)₃P. ¹³C NMR (50.3 MHz,

27 °C) (for C₇H₁₂see Table 1):⁵⁰δ 142.8, 134.9, 134.5, 132.1, 129.9,

126.2, 22.9 (each 3C), (2-MeC₆H₄)₃P. ³¹P NMR (81 MHz, 27 °C): see

Table 1. C₂₈H₃₃PPd (507.0). No elemental analysis was performed.

{(PhO)₃P}Pd(η²,η²-C₇H₁₂) (20). The reaction was carried out as

described for 13 by reacting a suspension of 1 (501 mg, 1.00 mmol) in

hepta-1,6-diene (2 mL) with a solution of P(OPh)₃(620 mg, 2.00 mmol)

in 5 mL of pentane. From the colorless solution obtained by D4-

filtration (20 °C) small intergrown crystals separated at -78 °C.

Isolation was as described: yield 760 mg (74%). Crystalline 20 is stable

at ambient temperature for at least several days but slowly decomposes

(^tBu₃P)Pd(η²,η²-C₇H₁₂) (16). A suspension of complex 1 (501 mg,

1.00 mmol) in 10 mL of pentane is reacted with ethene at -30 °C to

give a yellow solution of 9. After filtration to remove some insoluble

1

in solution. H NMR (200 MHz, -30 °C) (for C₇H₁₂see Table 1): δ

7.30 (12H), 7.12 (3H), P(OC₆H₅)₃. ³¹P NMR (81 MHz, -30 °C): See

Table 1. Anal. Calcd for C₂₅H₂₇O₃PPd (512.9): C, 58.55; H, 5.31; O,

9.36; P, 6.04; Pd, 20.75. Found: C, 58.95; H, 5.45; P, 5.91; Pd, 20.77.

t

impurities the mixture is combined with a solution of Bu₃P (404 mg,

2.00 mmol) in 5 mL of pentane at -78 °C. From such a solution only

small amounts of product crystallized (up to 30%) in the course of

serveral days. Therefore, the solvent was evaporated under high vacuum

(-78 °C) to give a beige residue that was about 90% pure (NMR).

Isolated 16 contained some Pd(P^tBu₃)₂and 5 as impurities (each about

5%). The product was stable only below -30 °C; at this temperature

it slowly converted into Pd(P^tBu₃)₂. EI-MS: the complex decomposed

{(2,6-Me₂C₆H₃O)₃P}Pd(η²,η²-C₇H₁₂) (21). The synthesis was car-

ried out as for 14, route b, by reacting (tmeda)PdMe₂(505 mg, 2.00

mmol) with (2,6-Me₂C₆H₃O)₃P (791 mg, 2.00 mmol) in 5 mL of hepta-

1,6-diene at 80 °C (evolution of ethane starts at about 70 °C). From

the resulting solution small colorless needles crystallized between 0

and -78 °C, which were isolated as described (14): yield 1.09 g (91%);

mp 131 °C dec. EI-MS: the compound decomposed and the spectra

1

and only Pd(P^tBu₃)₂was detected. H NMR (200 MHz, -80 °C) (for

1

C₇H₁₂see Table 1): δ 1.34 (d, 27H, ³J(PH) ) 12 Hz, Me), P^tBu₃. ³¹

P

of C₇H₁₂(m/e 96) and P(OC₆H₃Me₂)₃(m/e 394) were observed. H

NMR (81 MHz, -80 °C): see Table 1. C₁₉H₃₉PPd (404.9). No

elemental analysis was performed.

(Ph₃P)Pd(η²,η²-C₇H₁₂) (17). (a) From 1. A suspension of 1 (250

mg, 0.50 mmol) in 1 mL of hepta-1,6-diene (0 °C) was treated with a

NMR (400 MHz, 27 °C) (for C₇H₁₂see Table 1): δ 6.90 (6H, Ph),

6.80 (3H, Ph), 2.32 (18H, Me), P(OC₆H₃Me₂)₃. ¹³C NMR (50.3 MHz,

27 °C) (for C₇H₁₂see Table 1): δ 151.1 (3C), 131.7 (3C), 129.5 (6C),

124.9 (6C), 19.1 (6C), P(OC₆H₃Me₂)₃. ³¹P NMR (81 MHz, 27 °C):

1,6-Diene Complexes of Pd(0) and Pt(0)

J. Am. Chem. Soc., Vol. 121, No. 42, 1999 9821

see Table 1. Anal. Calcd for C₃₁H₃₉O₃PPd (597.0): C, 62.36; H, 6.58;

O, 8.04; P, 5.19; Pd, 17.82. Found: C, 62.53; H, 6.72; P, 5.28; Pd,

17.69.

(6C, Me), PⁱPr₃. ³¹P NMR (81 MHz, 27 °C): see Table 1. Anal. Calcd

for C₁₅H₃₁OPPd (364.8): C, 49.39; H, 8.57; O, 4.39; P, 8.49; Pd, 29.17.

Found: C, 49.25; H, 8.68; P, 8.60; Pd, 29.31.

{(2,6-ⁱPr₂C₆H₃O)₃P}Pd(η²,η²-C₇H₁₂) (22). (a) From 1. The reaction

was carried out as described for 13 by reacting a suspension of 1 (501

mg, 1.00 mmol) in hepta-1,6-diene (2 mL) with a solution of (2,6-

ⁱPr₂C₆H₃O)₃P (1.12 g, 2.00 mmol) in 10 mL of pentane. Warming the

mixture from -78 to 0 °C gave a clear yellow solution from which a

colorless solid precipitated at 20 °C. The mother liquor was siphoned

off and the product was recrystallized from 5 mL of diethyl ether (-30

°C) to afford colorless intergrown needles which were washed twice

with pentane (20 °C) and dried under vacuum: yield 460 mg (30%).

(b) From (tmeda)PdMe₂. The synthesis was according to that of 14,

route b, and 21 by reacting (tmeda)PdMe₂(758 mg, 3.00 mmol) with

(2,6-ⁱPr₂C₆H₃O)₃P (1.69 g, 3.00 mmol) in 5 mL of hepta-1,6-diene at

80 °C. A colorless solid precipitated (80 °C) from which the mother

liquor was siphoned off (20 °C). The product was recrystallized and

isolated as described above: yield 1.62 g (71%); mp 142 °C. EI-MS:

the complex decomposed and upon fractional vaporization (50-90 °C)

the ions [Pd(C₇H₁₂)]⁺(m/e 222) and [(2,6-ⁱPr₂C₆H₃O)₃P]⁺(m/e 562)

were detected. ¹H NMR (400 MHz, 27 °C) (for C₇H₁₂see Table 1): δ

7.09 (9H, C₆H₃), 3.65 (sept, 6H, CHMe₂), 0.98 (d, 36H, ³J(HH) ) 6.8

Hz, Me), (2,6-ⁱPr₂C₆H₃O)₃P. ¹³C NMR (50.3 MHz, 27 °C) (for C₇H₁₂

see Table 1): δ 148.8 (3C, POC_R), 142.7 (6C, C_â), 126.2 (3C, C_δ),

125.2 (6C, C_γ), 28.8 (6C, CHMe₂), 25.0 (12C, Me), (2,6-ⁱPr₂C₆H₃O)₃P.

³¹P NMR (81 MHz, 27 °C): see Table 1. Anal. Calcd for C₄₃H₆₃O₃-

PPd (765.4): C, 67.48; H, 8.30; O, 6.27; P, 4.05; Pd, 13.90. Found:

C, 67.38; H, 8.25; P, 4.11; Pd, 14.06.

(Cy₃P)Pd(η²,η²-C₆H₁₀O) (26). The synthesis was performed as for

14, route b, by reacting (tmeda)PdMe₂(505 mg, 2.00 mmol) with Cy₃P

(561 mg, 2.00 mmol) in diallyl ether (5 mL). The stirred suspension

was slowly warmed from -30 to 25-30 °C, whereupon ethane evolved

and a colorless solution was formed from which the product precipitated

in the course of 30 min. After cooling to -78 °C the solid was isolated

as described: yield 790 mg (81%); dec 145 °C. EI-MS (115 °C): m/e

(%) 484 (M⁺, 2), 386 ([(Cy₃P)Pd]⁺, 7), 304 ([(Cy₂PH)Pd]⁺, 3), 280

([Cy₃P]⁺, 5). ¹H NMR (300 MHz, 27 °C) (for C₆H₁₀O see Table 1): δ

2.0 (3H), 1.90 (6H), 1.85-1.7 (9H), 1.5-1.2 (15H), P(c-C₆H₁₁)₃. ¹³C

NMR (75.5 MHz, 27 °C) (for C₆H₁₀O see Table 1): δ 37.1 (3C, PC_RH),

31.6 (6C, C_âH₂), 28.5 (6C, C_γH₂), 27.5 (3C, C_δH₂), P(c-C₆H₁₁)₃. ³¹P

NMR (121.5 MHz, 27 °C): see Table 1. Anal. Calcd for C₂₄H₄₃OPPd

(485.0): C, 59.44; H, 8.94; Pd, 21.94; P, 6.39; O, 3.30. Found: C,

59.24; H, 9.00; Pd, 22.10; P, 6.55.

(^tBu₃P)Pd(η²,η²-C₆H₁₀O) (27). A suspension of 2′ (303 mg, 0.50

mmol) in 2 mL of diethyl ether was combined at -30 °C with an

ethereal solution (5 mL) of ^tBu₃P (202 mg, 1.00 mmol). After stirring

the mixture for 1 h (-30 °C), colorless cubes crystallized at -78 °C.

These were freed from the mother liquor and dried under vacuum: yield

220 mg (55%). The product contained about 10% of Pd(P^tBu₃)₂. Solid

27 decomposes at ambient temperature in the course of 1 day. EI-MS:

1

only the spectrum of Pd(P^tBu₃)₂was observed. H NMR (300 MHz,

-80 °C) (for C₆H₁₀O see Table 1): δ 1.65-1.25 (broad, ^tBu); at -30

3

t

°C: 1.43 (d, 27H, J(PH) ) 11 Hz, Bu). ¹³C NMR (75.5 MHz, -80

°C) (for C₆H₁₀O see Table 1): δ 39.3 (s, 3C, PC), 35.3 (6C, Me), 28.2

(3C, Me′), P^tBu₃. ³¹P NMR (121.5 MHz, -80 °C): see Table 1. C₁₈H₃₇-

OPPd (406.9). No elemental analysis was performed.

(µ-ⁱPr₂PC₂H₄PⁱPr₂){Pd(η²,η²-C₇H₁₂)}₂(23). Synthesis was as for

13, route a, by using dⁱppe (262 mg, 1.00 mmol) dissolved in 5 mL of

pentane. After filtration (20 °C) beige needles separated from the light

brown solution at -78 °C. Isolation was as described: yield 535 mg

(Ph₃P)Pd(η²,η²-C₆H₁₀O) (28). (a) From (tmeda)PdMe₂. The

synthesis was performed as for 14, route b, by reacting (tmeda)PdMe₂

(505 mg, 2.00 mmol) with PPh₃(525 mg, 2.00 mmol) in diallyl ether

(5 mL). The stirred suspension was heated to 80 °C (15 min),

whereupon ethane evolved (70 °C), and a light yellow solution was

formed. After filtration, cooling from 0 to -78 °C gave small colorless

needles which were isolated as described: yield 820 mg (88%). (b)

From (tmeda)PdMe₂and (Ph₃P)₂PdMe₂. A stirred suspension of

(Ph₃P)₂PdMe₂(330 mg, 0.50 mmol) and (tmeda)PdMe₂(126 mg, 0.50

mmol) in diallyl ether (5 mL) was heated to 80 °C (15 min) to afford

a colorless solution. After evaporation of all volatiles the pure product

was obtained: yield 450 mg (96%). (c) From (tmeda)PdMe₂and Pd-

(PPh₃)₄. Heating a stirred suspension of Pd(PPh₃)₄(231 mg, 0.20 mmol)

and (tmeda)PdMe₂(151 mg, 0.60 mmol) in diallyl ether (3 mL) to 80

°C (15 min) afforded a yellow solution that was treated further as

described for route a: yield 300 mg (82%). (d) From Pd(η³-C₃H₅)₂.

The synthesis followed that of 14, route c, by heating a yellow solution

of Pd(η³-C₃H₅)₂(377 mg, 2.00 mmol) and PPh₃(525 mg, 2.00 mmol)

in 5 mL of diallyl ether to 90 °C for a few minutes until the yellow

color of the initially precipitated (Ph₃P)₂Pd₂(µ-C₃H₅)₂disappeared (some

metallic Pd deposited thereby). The mixture was cooled to 20 °C and

filtered to afford a colorless solution, from which the product

crystallized below 0 °C; isolation was as described: yield 800 mg

1

(80%); mp 92 °C dec. H NMR (400 MHz, -30 °C) (for C₇H₁₂see

Table 1): δ 2.07 (m, 4H, PCH), 1.87 (“s”, 4H, PCH₂), 1.11, 1.09 (each

q, 12H, diastereotopic Me), dⁱppe. ³¹P NMR (81 MHz, -30 °C): see

Table 1. Anal. Calcd for C₂₈H₅₆P₂Pd₂(667.5): C, 50.38; H, 8.46; P,

9.28; Pd, 31.88. Found: C, 50.42; H, 8.54; P, 9.29; Pd, 31.72.

(Me₃P)Pd(η²,η²-C₆H₁₀O) (24). Addition of PMe₃(0.20 mL, 152

mg, 2.00 mmol) to a red suspension of (η⁵-C₅H₅)Pd(η³-C₃H₅) (425 mg,

2.00 mmol) in 3 mL of diallyl ether at -78 °C afforded a light yellow

precipitate. When the mixture was warmed to 20 °C a clear solution

was obtained from which colorless cuboids crystallized between -30

and -78 °C. The crystals were freed from the mother liquor, washed

twice with cold pentane, and dried under vacuum at 20 °C: yield 505

mg (90%); mp 79 °C dec. EI-MS (20 °C): m/e (%) 280 (M⁺, 27), 223

([(Me₃P)Pd(C₃H₅)]⁺, 64), 182 ([(Me₃P)Pd]⁺, 64). ¹H NMR (200 MHz,

27 °C) (for C₆H₁₀O see Table 1): δ 1.36 (d, 9H, Me), PMe₃. ¹³C NMR

(50.3 MHz, 27 °C) (for C₆H₁₀O see Table 1): δ 19.2 (3C), PMe₃. ³¹P

NMR (81 MHz, 27 °C): see Table 1. Anal. Calcd for C₉H₁₉OPPd

(280.6): C, 38.52; H, 6.82; O, 5.70; P, 11.04; Pd, 37.92. Found: C,

38.28; H, 6.82; P, 11.09; Pd, 38.03.

(ⁱPr₃P)Pd(η²,η²-C₆H₁₀O) (25). (a) From (tmeda)PdMe₂. The

synthesis was performed as for 14, route b, by reacting (tmeda)PdMe₂

(1.263 g, 5.00 mmol) with PⁱPr₃(801 mg, 5.00 mmol) in diallyl ether

(5 mL). The stirred suspension was slowly warmed from -30 to 25-

30 °C, whereupon ethane evolved and an orange solution was formed.

Between -30 and -78 °C a colorless precipitate was obtained that

was isolated as described: yield 1.73 g (93%). (b) From Pd(η³-C₃H₅)₂.

The synthesis followed that of 14, route c, by heating a mixture of

Pd(η³-C₃H₅)₂(943 mg, 5.00 mmol) and PⁱPr₃(801 mg, 5.00 mmol) in

5 mL of diallyl ether to 80 °C for 2 h. Between -30 and -78 °C

colorless crystals were obtained which were isolated as described: yield

1.55 g (85%). (c) From 14. A colorless solution of 14 (363 mg, 1.00

mmol) in diethyl ether (5 mL) was combined with diallyl ether (98

mg, 1.00 mmol) dissolved in ether (2 mL). After standing at ambient

temperature for 1 h the mixture was cooled to -78 °C, whereupon

colorless crystals separated which were isolated as described above:

yield 347 mg (95%); mp 63 °C. EI-MS (70 °C): m/e (%) 364 (M⁺, 1),

1

(86%); mp 112 °C dec. H NMR (200 MHz, 27 °C) (for C₆H₁₀O see

Table 1): δ 7.75 (3H), 7.65 (12H), PPh₃. ¹³C NMR (50.3 MHz, 27

°C) (for C₆H₁₀O see Table 1): δ 138.3 (3C), 134.4 (6C), 129.9 (3C),

128.9 (6C), PPh₃. ³¹P NMR (81 MHz, 27 °C): see Table 1. Anal. Calcd

for C₂₄H₂₅OPPd (466.9): C, 61.75; H, 5.40; O, 3.43; P, 6.63; Pd, 22.80.

Found: C, 61.93; H, 5.32; P, 6.65; Pd, 22.57.

{(2-MeC₆H₄)₃P}Pd(η²,η²-C₆H₁₀O) (29). A solution of (tmeda)-

PdMe₂(126 mg, 0.50 mmol) and P(o-tolyl)₃(152 mg, 0.50 mmol) in

5 mL of diallyl ether was stirred at 20 °C for 48 h. The solvent was

evaporated under vacuum and the product was washed with diethyl

ether to remove small quantities of unreacted reagents: yield 200 mg

(80%). ¹H NMR (300 MHz, 27 °C) (for C₆H₁₀O see Table 1): δ 7.46,

7.31, 7.22, 7.15 (each 3H), 2.10 (9H), (2-MeC₆H₄)₃P. ¹³C NMR (75.5

MHz, 27 °C) (for C₆H₁₀O see Table 1): δ 142.9, 134.9, 134.0, 132.2,

130.3, 126.4, 22.9, each 3C, (2-MeC₆H₄)₃P. ³¹P NMR (121.5 MHz, 27

°C): see Table 1. C₂₇H₃₁OPPd (508.9). No elemental analysis was

performed.

1

266 ([(ⁱPr₃P)Pd]⁺, 4). H NMR (200 MHz, 27 °C) (for C₆H₁₀O see

Table 1): δ 2.18 (m, 3H, PCH), 1.15 (dd, 18H, Me), PⁱPr₃. ¹³C NMR

(50.3 MHz, 27 °C) (for C₆H₁₀O see Table 1): δ 26.9 (3C, PC), 20.8

9822 J. Am. Chem. Soc., Vol. 121, No. 42, 1999

Krause et al.

{(PhO)₃P}Pd(η²,η²-C₆H₁₀O) (30). The synthesis was performed as

for 14, route b, by reacting (tmeda)PdMe₂(505 mg, 2.00 mmol) with

P(OPh)₃(621 mg, 2.00 mmol) in diallyl ether (5 mL). The stirred

colorless suspension was slowly heated to 80 °C, whereupon ethane

evolved (70 °C), and the solid dissolved. Cooling from 0 to -78 °C

gave colorless crystals which were isolated as described: yield 980

(ⁱPr₃P)Pd{(η²-H₂CdCHSiMe₂)₂O} (35). (a) From (tmeda)PdMe₂.

PⁱPr₃(320 mg, 2.00 mmol) was added to a suspension of (tmeda)-

PdMe₂(505 mg, 2.00 mmol) in 5 mL of dvds at -30 °C. When the

mixture was warmed to 20 °C a colorless solution resulted from which

the product crystallized between 0 and -78 °C. The crystals were freed

from the mother liquor, washed twice with cold pentane, and dried

under vacuum (20 °C): yield 810 mg (89%). (b) From Pd(PⁱPr₃)₂.

Pd(PⁱPr₃)₂(223 mg, 0.50 mmol) was dissolved in dvds (3 mL). In the

course of 2 h some Pd(PⁱPr₃)₃precipitated, which was removed by

filtration. Cooling the solution to -78 °C afforded colorless crystals,

which were isolated as described: yield 150 mg (66%); mp 75 °C dec.

EI-MS (55 °C): m/e (%) 452 (M⁺, 16), 266 ([(ⁱPr₃P)Pd]⁺, 24), 171

([C₄H₆Me₃Si₂O]⁺, 100). ¹H NMR (200 MHz, 27 °C) (for dvds see Table

1

mg (95%); mp 92 °C dec. H NMR (200 MHz, 27 °C) (for C₆H₁₀O

see Table 1): δ 7.2 (15H), P(OPh)₃. ³¹P NMR (81 MHz, 27 °C): see

Table 1. Anal. Calcd for C₂₄H₂₅O₄PPd (514.9): C, 55.99; H, 4.89; O,

12.43; P, 6.02; Pd, 20.67. Found: C, 56.14; H, 5.07; P, 6.15; Pd, 20.59.

t

(^tBuNC)Pd(η²,η²-C₆H₁₀O) (31). BuNC (0.56 mL, 415 mg, 5.00

mmol) was added to a suspension of Pd(η³-2-MeC₃H₄)₂(1.083 g, 5.00

mmol) in 3 mL of diallyl ether at -78 °C. When the mixture was

warmed to 20 °C an intensive yellow solution was obtained. In the

course of 12 h the color changed to dark brown and light brown leaflets

precipitated. These were freed from the mother liquor, washed with

cold pentane, and dried under vacuum at -30 °C: yield 1.12 g (78%).

i

1): δ 2.32 (m, 3H, PCH), 1.20 (dd, 18H, Me), Pr₃P. ¹³C NMR (50.3

MHz, 27 °C) (for dvds see Table 1): δ 27.1 (3C, PC), 20.5 (6C, Me),

PⁱPr₃. ³¹P NMR (81 MHz, 27 °C): see Table 1. Anal. Calcd for C₁₇H₃₉-

OPPdSi₂(453.1): C, 45.07; H, 8.68; O, 3.53; P, 6.84; Pd, 23.49; Si,

12.40. Found: C, 45.25; H, 8.75; P, 6.94; Pd, 23.42; Si, 12.28.

1

EI-MS: the compound decomposed. H NMR (200 MHz, -30 °C)

(for C₆H₁₀O see Table 1): δ 1.51 (s, 9H), CN^tBu. ¹³C NMR (50.3 MHz,

-30 °C) (for C₆H₁₀O see Table 1): δ 149.2 (1C, CtN), 57.1 (1C,

CMe₃), 30.6 (3C, Me), CN^tBu. Anal. Calcd for C₁₁H₁₉NOPd (287.7):

C, 45.92; H, 6.66; N, 4.87; O, 5.56; Pd, 36.99. Found: C, 45.82; H,

6.70; N, 4.80; Pd, 36.83. In THF, diethyl ether, or pentane the compound

decomposes above -30 °C.

(^tBu₃P)Pd{(η²-H₂CdCHSiMe₂)₂O} (36). To the yellow suspension

of 3 (772 mg, 1.00 mmol) in 5 mL of dvds was added at -30 °C a

t

solution of Bu₃P (404 mg, 2.00 mmol) in 10 mL of diethyl ether. In

the course of 1 h a colorless suspension was obtained that was left at

-78 °C (12 h) for complete crystallization. The solid was freed from

the mother liquor, washed twice with cold pentane, and dried under

vacuum at -30 °C: yield 650 mg (66%); mp >100 °C dec. EI-MS

(50 °C): m/e (%) 494 (M⁺, <1), 308 ([(^tBu₃P)Pd]⁺, <1), 171 ([C₄H₆-

(ⁱPr₃P)Pd(η²,η²-C₆H₁₀NH) (32). The synthesis was performed as

for 14, route b, by reacting (tmeda)PdMe₂(505 mg, 2.00 mmol) with

ⁱPr₃P (320 mg, 2.00 mmol) in diallylamine (5 mL). When the suspension

was warmed to 20 °C (2 h), ethane evolved and a light green solution

was obtained. The excess of diallylamine was evaporated under vacuum

and the oily residue was dissolved in diethyl ether. After D4-filtration

colorless cubes crystallized at -30 °C which were isolated as

described: yield 520 mg (72%); mp 92 °C. EI-MS (35 °C): m/e (%)

363 (M⁺, 28), 266 ([(ⁱPr₃P)Pd]⁺, 43), 224 ([(ⁱPr₂PH)Pd]⁺, 43). ¹H NMR

(400 MHz, 27 °C) (for allylic groups of C₆H₁₀NH, see Table 1): δ

1.97 (br, 1H, NH), amine; 2.15 (m, 3H, PCH), 1.17 (dd, 18H, Me),

ⁱPr₃P. ¹³C NMR (75.5 MHz, 27 °C) (for C₆H₁₀NH see Table 1): δ

26.9 (3C, PCH), 20.8 (6C, Me), ⁱPr₃P. ³¹P NMR (121.5 MHz, 27 °C):

see Table 1. Anal. Calcd for C₁₅H₃₂NPPd (363.8): C, 49.52; H, 8.87;

N, 3.85; P, 8.51; Pd, 29.25. Found: C, 49.58; H, 8.81; N, 3.78; P,

8.42; Pd, 29.20.

(Ph₃P)Pd(η²,η²-C₆H₁₀NH) (33). (a) From (tmeda)PdMe₂. The

synthesis was performed as for 14, route b, by reacting (tmeda)PdMe₂

(505 mg, 2.00 mmol) with PPh₃(524 mg, 2.00 mmol) in diallylamine

(5 mL). When the suspension was heated to 80 °C (5 min), ethane

evolved and a light green solution resulted. The solution was worked-

up as for 32 to afford an almost colorless microcrystalline precipitate

at -78 °C: yield 720 mg (77%). (b) From 17. The synthesis followed

that of 25, route c, by reacting 17 (233 mg, 0.50 mmol) with

diallylamine (200 mg, excess) in diethyl ether (5 mL) at 20 °C (2 h).

All volatiles were evaporated in a vacuum and the residue was

recrystallized from diethyl ether (-30 °C) to give light ocher cubes:

yield 150 mg (64%); 77 °C dec. EI-MS: the compound decomposed

and the spectra of C₆H₁₀NH (m/e 97) and PPh₃(m/e 262) were observed.

¹H NMR (300 MHz, 27 °C) (for allylic groups of C₆H₁₀NH, see Table

1): δ 2.10 (br, 1H, NH), amine; 7.5-7.3 (15H), PPh₃. ¹³C NMR (50.3

MHz, 27 °C) (for C₆H₁₀NH see Table 1): δ 138.7 (3C, PC_R), 134.5

(6C, C_â), 129.7 (s, 3C, C_δ), 128.8 (6C, C_γ), PPh₃. ³¹P NMR (81 MHz,

27 °C): see Table 1. Anal. Calcd for C₂₄H₂₆NPPd (465.9): C, 61.88;

H, 5.63; N, 3.01; P, 6.65; Pd, 22.84. Found: C, 62.10; H, 5.70; N,

2.90; P, 6.44; Pd, 22.74.

1

Me₃Si₂O]⁺, 100). H NMR (300 MHz, -80 °C) (for dvds see Table

t

1): δ 1.58 (9H), 1.37 (18H), Bu₃P. ¹³C NMR (75.5 MHz, -80 °C)

(for dvds see Table 1): δ 39.7 (3C, PC), 35.4 (6C, Me), 28.7 (3C,

t

Me), Bu₃P. ³¹P NMR (81 MHz, -30 °C): see Table 1. Anal. Calcd

for C₂₀H₄₅OPPdSi₂(495.1): C, 48.52; H, 9.16; O, 3.23; P, 6.26; Pd,

21.49; Si, 11.34. Found: C, 48.78; H, 9.10; P, 6.17; Pd, 21.29; Si,

11.43.

(Ph₃P)Pd{(η²-H₂CdCHSiMe₂)₂O} (37). A solution of 17 (232 mg,

0.50 mmol) in diethyl ether (5 mL) was treated with 0.5 mL of dvds.

After 1 h the volatiles were evaporated in a vacuum and the residue

was recrystallized (-78 °C) from a small volume of ether to give

colorless intergrown cubes: yield 210 mg (80%). EI-MS: the compound

decomposed and the spectra of dvds (m/e 186) and PPh₃(m/e 262)

were observed. ¹H NMR (300 MHz, 27 °C) (for dvds see Table 1): δ

7.43 (3H), 7.37 (12H), PPh₃. ¹³C NMR (75.5 MHz, 27 °C) (for dvds

1

see Table 1): δ 137.6 (3C, J(PC) ) 29 Hz, PC_R), 134.3 (6C, C_â),

130.1 (3C, C_δ), 129.0 (6C, C_γ), PPh₃. ³¹P NMR (121.5 MHz, 27 °C):

see Table 1. C₂₆H₃₃OPPdSi₂(555.1). No elemental analysis was

performed.

{(2-MeC₆H₄)₃P}Pd(dvds) (38). The synthesis followed that of 29

by reacting (tmeda)PdMe₂(126 mg, 0.50 mmol) with P(o-tolyl)₃(152

mg, 0.50 mmol) in 5 mL of dvds (20 °C). The complex was isolated

1

by evaporating the solvent: yield 280 mg. H NMR (300 MHz, 27

°C) (for dvds see Table 1): δ 7.46, 7.25, 7.17, 7.13 (each 3H), 2.00

(9H), (2-MeC₆H₄)₃P. ¹³C NMR (75.5 MHz, 27 °C) (for dvds see Table

1): δ 142.9, 135.0, 133.4, 132.3, 130.4, 126.3, 23.0, each 3C,

(2-MeC₆H₄)₃P. ³¹P NMR (121.5 MHz, 27 °C): see Table 1. C₂₉H₃₉-

OPPdSi₂(597.2). No elemental analysis was performed. In an inert

solvent the compound slowly decomposes at 20 °C.

(Me₃P)Pt(η²,η²-C₇H₁₂) (39). A solution of 12 in pentane (5 mL),

obtained from 4 (204 mg, 0.30 mmol) and ethene at 0 °C, was combined

with a solution of PMe₃(46 mg, 0.60 mmol) in 2 mL of pentane at

-78 °C. In the course of several hours yellow brownish crystals

separated, which were isolated by filtration and dried under high vacuum

at -30 °C: yield 70 mg (32%); mp 42 °C. EI-MS (10 °C): m/e (%)

367 (M⁺, 63), 365 ([M - 2H]⁺, 50), 363 ([M - 4H]⁺, 81), 271

(Me₃P)Pd{(η²-H₂CdCHSiMe₂)₂O} (34). A solution of 24 (281 mg,

1.00 mmol) in 5 mL of diethyl ether was treated with dvds (1 mL) at

20 °C. All volatiles were evaporated in a vacuum and the oily residue

was recrystallized from pentane at -78 °C to give colorless cubes,

which were isolated and dried under vacuum (20 °C): yield 300 mg

(81%); mp 34 °C. EI-MS (15 °C): m/e (%) 368 (M⁺, 19), 182 ([(Me₃P)-

1

([(Me₃P)Pt]⁺, 100). H NMR (300 MHz, 27 °C) (for C₇H₁₂see Table

1

Pd]⁺, 42), 171 ([C₄H₆Me₃Si₂O]⁺, 100). H NMR (200 MHz, 27 °C)

1): δ 1.51 (d, 9H, PMe₃). ¹³C NMR (75.5 MHz, 27 °C) (for C₇H₁₂see

(for dvds see Table 1): δ 1.38 (d, 9H), PMe₃. ¹³C NMR (50.3 MHz,

27 °C) (for dvds see Table 1): δ 18.1 (d, 3C), PMe₃. Anal. Calcd for

C₁₁H₂₇OPPdSi₂(368.9): C, 35.81; H, 7.38; O, 4.34; P, 8.40; Pd, 28.85;

Si, 15.23. Found: C, 35.63; H, 7.43; P, 8.28; Pd, 28.80.

2

Table 1): δ 19.3 (3C, J(¹⁹⁵PtC) ) 52 Hz, PMe₃). ³¹P NMR (121.5

MHz, 27 °C): see Table 1. Anal. Calcd for C₁₀H₂₁PPt (367.3): C,

32.70; H, 5.76; P, 8.43; Pt, 53.11. Found: P, 8.96; Pt, 53.65.

1,6-Diene Complexes of Pd(0) and Pt(0)

J. Am. Chem. Soc., Vol. 121, No. 42, 1999 9823

(ⁱPr₃P)Pt(η²,η²-C₇H₁₂) (40). A suspension of 4 (339 mg, 0.50 mmol)

in diethyl ether (5 mL) was treated with a solution of Pr₃P (262 mg,

(Ph₃P)Pt(η²,η²-C₇H₁₂) (41). The synthesis was carried out as for

40 by starting from 4 (339 mg, 0.50 mmol) and PPh₃(262 mg, 1.00

mmol). Yellow intergrown crystals were obtained: yield 470 mg (85%);

mp 110 °C dec. EI-MS (120 °C): m/e (%) 553 (M⁺, 10), 457 ([(Ph₃P)-

Pt]⁺, 3), 378 ([(C₁₂H₈P)Pt]⁺, 6), 154 (Ph₂, 81), 78 (C₆H₆, 100). ¹H NMR

(400 MHz, 27 °C) (for C₇H₁₂see Table 1): δ 7.40 (6H), 7.30 (9H),

PPh₃. ¹³C NMR (50.3 MHz, 27 °C) (for C₇H₁₂see Table 1): δ 137.8

(3C, PC_R), 134.4 (6C, C_â), 130.2 (3C, C_δ), 128.7 (6C, C_γ), PPh₃. ³¹P

NMR (81 MHz, 27 °C): see Table 1. Anal. Calcd for C₂₅H₂₇PPt

(553.5): C, 54.23; H, 4.92; P, 5.60; Pt, 35.25. Found: C, 54.36; H,

4.97; P, 5.56; Pt, 35.19.

i

1.00 mmol) in diethyl ether (5 mL) at 20 °C. When the mixture was

stirred for 10 min an orange solution was obtained which was filtered

through a D4 glas fritt. At -78 °C orange crystals separated. The mother

liquor was cannulated away from the crystals and the product was

washed with some cold pentane and dried under vacuum at 20 °C:

yield 360 mg (80%); mp 75 °C. EI-MS (43 °C): m/e (%) 451 (M⁺,

55), 408 ([M - C₃H₇]⁺, 69), 355 ([(ⁱPr₃P)Pt]⁺, 11). ¹H NMR (400 MHz,

27 °C) (for C₇H₁₂see Table 1): δ 2.42 (m, 3H, PCH), 1.17 (dd, 18H,

Me), PⁱPr₃. ¹³C NMR (50.3 MHz, 27 °C) (for C₇H₁₂see Table 1): δ

28.0 (3C, PCH), 20.3 (6C, Me), PⁱPr₃. ³¹P NMR (81 MHz, 27 °C): see

Table 1. Anal. Calcd for C₁₆H₃₃PPt (451.5): C, 42.56; H, 7.37; P, 6.86;

Pt, 43.21. Found: C, 42.44; H, 7.38; P, 6.87; Pt, 43.28.

Acknowledgment. We thank the Fonds der Chemischen

Industrie for financial support.

JA983939H

Article Doi

1,6-Diene complexes of palladium(0) and platinum(0): Highly reactive sources for the naked metals and [L-M0] fragments

DOI: 10.1021/ja983939h

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