Synthesis and characterization of palladium(II) complexes with chiral aminophosphine ligands: Catalytic behaviour in asymmetric hydrovinylation. Crystal structure of cis-[PdCl2(PPh((R)-NHCHCH3Ph)2)2]

doi:10.1016/j.jorganchem.2007.02.020

Journal of Organometallic Chemistry

Volume 692, Issue 19, 1 September 2007, Pages 4005-4019

https://doi.org/10.1016/j.jorganchem.2007.02.020 Get rights and content

Abstract

Optically active ligands of type Ph₂PNHR (R = (R)-CHCH₃Ph, (a); (R)-CHCH₃Cy, (b); (R)-CHCH₃Naph, (c)) and PhP(NHR)₂ (R = (R)-CHCH₃Ph, (d); (R)-CHCH₃Cy, (e)) with a stereogenic carbon atom in the R substituent were synthesized. Reaction with [PdCl₂(COD)₂] produced [PdCl₂P₂] (1) (P = PhP(NHCHCH₃Ph)₂), whose molecular structure determined by X-ray diffraction showed cis disposition for the ligands. All nitrogen atoms of amino groups adopted S configuration. The new ligands reacted with allylic dimeric palladium compound [Pd(η³-2-methylallyl)Cl]₂ to gave neutral aminophosphine complexes [Pd(η³-2-methylallyl)ClP] (2a–2e) or cationic aminophosphine complexes [Pd(η³-2-methylallyl)P₂]BF₄ (3a–3e) in the presence of the stoichiometric amount of AgBF₄. Cationic complexes [Pd(η⁴3-2-methylallyl)(NCCH₃)P]BF₄ (4a–4e) were prepared in solution to be used as precursors in the catalytic hydrovinylation of styrene. ³¹P NMR spectroscopy showed the existence of an equilibrium between the expected cationic mixed complexes 4, the symmetrical cationic complexes [Pd(η³-2-methylallyl)P₂]BF₄ (3) and [Pd(η³-2-methylallyl)(NCCH₃)₂]BF₄ (5) coming from the symmetrization reaction. The extension of the process was studied with the aminophosphines (a–e) as well as with nonchiral monodentate phosphines (PCy₃ (f), PBn₃ (g), PPh₃ (h), PMe₂Ph (i)) showing a good match between the extension of the symmetrization and the size of the phosphine ligand. We studied the influence of such equilibria in the hydrovinylation of styrene because the behaviour of catalytic precursors can be modified substantially when prepared ‘in situ’. While compounds 3 and bisacetonitrile complex 5 were not active as catalysts, the [Pd(η³-2-methylallyl)(η²-styrene)₂]⁺ species formed in the absence of acetonitrile showed some activity in the formation of codimers and dimers. Hydrovinylation reaction between styrene and ethylene was tested using catalytic precursors solutions of [Pd(η³-2-methylallyl)LP]BF₄ ionic species (L = CH₃CN or styrene) showing moderate activity and good selectivity. Better activities but lower selectivities were found when L = styrene. Only in the case of the precursor containing Ph₂PNHCHCH₃Ph (a) ligand was some enantiodiscrimination (10%) found.

Graphical abstract

Cationic Pd(II) complexes of type [Pd(η³-2-CH₃C₃H₄)(NCCH₃)P]BF₄ with chiral monodentate monoaminophosphines, Ph₂P(NHR), and bisaminophosphines, PhP(NHR)₂, undergo a symmetrization reaction. The behaviour of each of the three species involved has been tested in the hydrovinylation catalytic reaction of styrene.

Introduction

The catalytic asymmetric hydrovinylation of olefins is an important stereoselective carbon–carbon bond-forming reaction in organic synthesis [1]. The reaction is catalyzed by a variety of transition metal compounds being nickel and palladium the most frequently used. The scope of the reaction is limited by the nature of the olefin since excellent stereoselectivity is achieved only with conjugated dienes, strained olefins or intramolecular reactions [2]. The catalytic cycle proposed on nickel and palladium systems shows that the active catalyst is most likely an unsaturated phosphine-stabilized metal-hydride. Allylic precursors stabilized with one monodentate phosphine proved to be very useful since cleavage of the allyl substituent leads to the actual catalyst that initiates the heterodimerization. The model reaction of the process involves codimerization between styrene or vinylnaphtalene and ethylene (Eq. (1)). When these types of vinylarenes are used as prochiral olefins, the excellent regioselectivities obtained originate in the allylic nature of the intermediate.However the control of the enantioselectivity of the reaction is more difficult. Very good enantioselectivities were initially obtained by Wilke [3] and more recently by the groups of Vogt [4], Gibson [5], Rajanbabu [6], [7], Leitner [8] and Zhou [9] using phosphines, planar chromium phosphines, phosphinites, or phosphoramidites as stabilizing ligands with nickel and palladium systems. We investigated the model reaction using nickel and palladium precursors. The initial work provided evidence of the blocking effect of inert bidentate ligands [10]. Further research with allylic palladium precursors containing P-stereogenic phosphines enabled the enantioselective version of the process to be studied [11], [12].

Synthesis of ligands with specific electronic and steric requirements is an essential part of an asymmetric catalysis program that relies on ligand tuning to bring about optimum results. Although there now exists a huge body of work on the chemistry of both phosphines and phosphites, aminophosphines containing P–N bonds instead of P–C or P–O bonds have received a lower level of attention. One potential reason for the underdevelopment of this chemistry is that the P–N bond is envisaged as being susceptible to relatively easily cleavage [13] but several new classes of P–O and P–N bond containing phosphorous ligands of high stability have been demonstrated to be capable of the acceleration and asymmetric catalysis of a number of synthetic organic reactions [14]. Moreover, these ligands may be constructed in large quantities through the use of relatively simple condensation processes, and from commercial starting materials. Woolins and coworkers have reported a number of examples of aminophosphines including these derived from 1,2-diaminobenzene [15], aminopyridine [16] and several diamines [17]. Burrows has reported the synthesis of ether functionalized aminophosphines [18] and aminophosphines derived from methyl benzyl amine are also well documented [19]. There are indications of the potential utility of transition metal complexes with aminophosphines. For example rhodium (I) [20] and platinum (II) [21] complexes of chiral aminophosphines have proved to be efficient catalysts for asymmetric hydrogenation and hydroformylation reactions respectively, and nickel complexes have been employed in the cyclodimerization of buta-1,3-diene [22]. Some preliminary studies on the use of bidentate aminophosphine ligands in palladium catalysed allylic alkylation reactions are reported [23].

We decided to focus the work on the synthesis of cationic allylic palladium(II) complexes with chiral monoamino and bisaminoarylphosphines containing one stereogenic carbon atom in the amino substituent, and use them as catalytic precursors for hydrovinylation asymmetric reaction. It is well known that the factors determining the discrimination ability of the ligands in this process remain poorly defined. The final efficiency of the reaction is determined by the delicate competition between the olefins present as well as all the species contained in the reaction medium. The fully characterization of the precursors solutions indicate that the cationic allylic palladium(II) complexes undergo symmetrization leading to mixtures of three different species $\begin{matrix} 2 [Pd (η^{3} - 2 - {CH}_{3} C_{3} H_{5}) PL]^{+} \\ ⥮ \\ [Pd (η^{3} - 2 - {CH}_{3} C_{3} H_{5}) P_{2}]^{+} + [Pd (η^{3} - 2 - {CH}_{3} C_{3} H_{5}) L_{2}]^{+} \end{matrix}$ The relative amount of each one, using different tertiary phosphines and aminophosphines, seems related to the steric parametres of the phosphine ligands. We evaluated the behaviour of each one in the catalytic hydrovinylation process.

Section snippets

Synthesis and characterization of the aminophosphines (a–e)

The monoaminophosphines Ph₂P(NHR) were conveniently prepared as reported in the literature [19], [24] through the reaction of chlorodiphenylphospine with the chiral primary amines NH₂R (R = (R)-CHCH₃Ph (a), (R)-CHCH₃Cy (b), (R)-CHCH₃Naph (c)) in the presence of triethylamine. Bisaminophosphines PhP(NHR)₂ (R = (R)-CHCH₃Ph (d), (R)-CHCH₃Cy (e)) were prepared by the same way but starting from the dichlorophenylphosphine and the stoichiometric amount of the primary amine [25] (Scheme 1).

Aminophosphines

Hydrovinylation reaction

The solution of mixed allylic cationic complexes (4a–4h) were tested as catalytic precursors in the hydrovinylation reaction of styrene with ethylene and the results are shown in Table 6.

The hydrovinylation reaction was always carried out using a [Pd]/styrene ratio of 1/1000, CH₂Cl₂ as solvent, 15 bar of pressure and at 25 °C temperature. The products of the catalytic process were analyzed after 60 or 360 min reaction. Actually, only in the case of 4f complex was possible to introduce a

Conclusions

The susceptibiliy of aminophosphines and bis(aminophosphine) ligands to air, moisture and protic solvents was not a limitation for the preparation of stable allylic neutral and cationic palladium complexes [Pd(η³-2-methylallyl)ClP] and [Pd(η³-2-methylallyl)P₂]BF₄. The results described here in relation to the symmetrization equilibrium experienced by cationic complexes [Pd(η³-2-methylallyl)(NCCH₃)P]BF₄ may be considered as a warning in the study of a catalytic reaction where the catalyst is

General methods

All compounds were prepared under a purified nitrogen atmosphere using standard Schlenk and vacuum-line techniques. The solvents were purified by standard procedures and distilled under nitrogen. (R)-α-methylbenzylamine, (R)-1-(1-Naphthyl)ethylamine and (R)-1-cyclohexylethylamine (Aldrich) and PPh₃, PMe₂Ph, PCy₃ (Strem) were used as supplied. PBn₃ [40], [Pd(η³-2-CH₃C₃H₄)(μ-Cl)]₂ [41], [PdCl(η³-2-CH₃C₃H₄)(PPh₃)] [31], [PdCl(η³-2-CH₃C₃H₄)(PMe₂Ph)] [30], [Pd(η³-2-CH₃C₃H₄)(PPh₃)₂]BF₄ [34] and [Pd(η³

Acknowledgements

This work was supported by the Spanish Ministerio de Ciencia y Tecnología (CTQ2004-01546). Financial support from MEC (AP2000-2866) is gratefully acknowledged by A.G.

References (45)

G. Francio et al.
J. Am. Chem. Soc.
(2002)
J. Albert et al.
Organometallics
(1999)
J. Albert et al.
Chem. Eur. J.
(2002)
M.R.I. Zubiri et al.
Polyhedron
(2004)
M.R.I. Zubiri et al.
Inorg. Chim. Acta
(2004)
A.D. Burrows et al.
J. Chem. Soc., Dalton Trans.
(2000)
A.D. Burrows et al.
J. Chem. Soc., Dalton Trans.
(2000)
C.A. Tolman
Chem. Rev.
(1977)
J. Powell et al.
J. Chem. Soc. (A)
(1967)
M.D.K. Boele et al.
Chem. Eur. J.
(2004)
G.M. DiRenzo et al.
J. Am. Chem. Soc.
(1996)
P. Dotta et al.
Helv. Chim. Acta
(2004)
S. Filipuzzi et al.
Organometallics
(2006)
C. Amatore et al.
Eur. J. Inorg. Chem.
(2001)

D.J. Mabbott et al.

J. Chem. Soc., Dalton Trans.

(1977)

G. Carturan et al.

Inorg. Chim. Acta

(1986)

A. Sen et al.

Organometallics

(1983)

T.V. Rajanbabu

Chem. Rev.

(2003)

P.W. Jolly et al.L.J. Goosen

Angew. Chem., Int. Ed.

(2002)

U. Boothe et al.

J. Chem. Soc., Perkin Trans. 1

(2001)

G. Dieno Buono et al.

J. Org. Chem.

(1985)

G. Hilt et al.

Angew. Chem., Int. Ed.

(2001)

R. Kumareswaran et al.

Org. Lett.

(2003)

G. Muller et al.

J. Mol. Catal.

(1997)

G. Wilke

Angew. Chem., Int. Ed. Engl.

(1988)

K. Angerlunnd et al.

Z. Naturfosch

(1995)

R. Bayersdörfer et al.

J. Organomet. Chem.

(1998)

S.E. Gibson et al.

Chem. Commun.

(2002)

H. Park et al.

J. Am. Chem. Soc.

(2002)

A. Zhang et al.

Org. Lett.

(2004)

A. Zhang et al.

J. Am. Chem. Soc.

(2006)

W.J. Shi et al.

Tetrahedron: Asymmetry

(2005)

R.M. Ceder et al.

J. Mol. Catal.

(1994)

A. Grabulosa et al.

Organometallics

(2005)

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Synthesis and characterization of palladium(II) complexes with chiral aminophosphine ligands: Catalytic behaviour in asymmetric hydrovinylation. Crystal structure of cis-[PdCl2(PPh((R)-NHCHCH3Ph)2)2]

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis and characterization of the aminophosphines (a–e)

Hydrovinylation reaction

Conclusions

General methods

Acknowledgements

J. Am. Chem. Soc.

Organometallics

Chem. Eur. J.

Polyhedron

Inorg. Chim. Acta

J. Chem. Soc., Dalton Trans.

J. Chem. Soc., Dalton Trans.

Chem. Rev.

J. Chem. Soc. (A)

Chem. Eur. J.

J. Am. Chem. Soc.

Helv. Chim. Acta

Organometallics

Eur. J. Inorg. Chem.

J. Chem. Soc., Dalton Trans.

Inorg. Chim. Acta

Organometallics

Chem. Rev.

Angew. Chem., Int. Ed.

J. Chem. Soc., Perkin Trans. 1

J. Org. Chem.

Angew. Chem., Int. Ed.

Org. Lett.

J. Mol. Catal.

Angew. Chem., Int. Ed. Engl.

Z. Naturfosch

J. Organomet. Chem.

Chem. Commun.

J. Am. Chem. Soc.

Org. Lett.

J. Am. Chem. Soc.

Tetrahedron: Asymmetry

J. Mol. Catal.

Organometallics

Synthesis and characterization of palladium(II) complexes with chiral aminophosphine ligands: Catalytic behaviour in asymmetric hydrovinylation. Crystal structure of cis-[PdCl₂(PPh((R)-NHCHCH₃Ph)₂)₂]