Palladium complexes with a new hemilabile bis(oxazoline)phenylphosphonite ligand. Characterization of an unprecedented chloro palladium(II)-(η1-allyl) complex

2966

Organometallics 2001, 20, 2966-2981

P a lla d iu m Com p lexes w ith a New Hem ila bile

Bis(oxa zolin e)p h en ylp h osp h on ite Liga n d .

Ch a r a cter iza tion of a n Un p r eced en ted Ch lor o

P a lla d iu m (II)-(η¹-Allyl) Com p lex^|

Pierre Braunstein,*^,†Fre´de´ric Naud,^†Alain Dedieu,^‡Marie-Madeleine Rohmer,^‡

Andre´ DeCian,^§and Steven J . Rettig

Laboratoire de Chimie de Coordination (UMR 7513 CNRS), Institut Le Bel, Universite´ Louis

Pasteur, 4 Rue Blaise Pascal, 67070 Strasbourg, France, Laboratoire de Chimie Quantique

(UMR 7551 CNRS), Institut Le Bel, Universite´ Louis Pasteur, 4 Rue Blaise Pascal, 67070

Strasbourg, France, Service de Cristallochimie, Institut Le Bel, Universite´ Louis Pasteur, 4

Rue Blaise Pascal, 67070 Strasbourg, France, and University of British Columbia, 2036 Main

Mall, Vancouver, British Columbia, V6T 1Z1 Vancouver, Canada

Received February 28, 2001

The coordination chemistry of the new, structurally characterized ligand bis(oxazoline)-

phenylphosphonite (I, abbreviated NOPON^Me), shows its flexibility which is due to the

2

possible formation of six-membered chelate rings. In the Pd(II) complexes [Pd(NCMe)-

(NOPON^Me-N,P,N)](BF₄)₂, 1 (characterized by X-ray diffraction in 1‚0.5Et₂O‚0.33MeCN),

2

and [PdCl(NOPON^Me-N,P,N)](PF₆), 2, this ligand behaves in a static tridentate manner,

2

Me₂

whereas in [Pd(Me)Cl(NOPON^Me-N,P)], 3, [PdI₂(NOPON -N,P)], 4, [PdCl₂(NOPON -N,P)],

2

5, and the allyl complex [Pd(η³-C₃H₅)(NOPON^Me-N,P)](PF₆), 6, it displays fluxional bidentate

2

behavior, as shown by variable-temperature NMR studies. In 3, only the isomer in which

the methyl ligand is trans to nitrogen is formed. In the related complex [Pd(η³-C₃H₅)-

(NOPON^Me-N,P)]Cl, 7, an equilibrium has been evidenced between 7a and 7b, which involves

2

coordination of the chloride and isomerization of the allyl ligand from η³to η¹. The latter

isomer is quantitatively formed in toluene at 259 K and in the solid state. This was

established using NMR spectroscopy by combined variable-temperature solution and solid-

state studies. Isomer 7b was also characterized by X-ray diffraction, a rare example of a

fully characterized allyl η¹-bonding mode for Pd complexes and the first in transition metal

chemistry for a mutual cis arrangement of η¹-allyl and chloride ligands, a situation relevant

to intermediates involved in catalytic transformations. The tridentate coordination mode of

I found in complexes 1 or 2 never occurred in the related alkyl or allyl complexes. This is

consistent with the antisymbiotic effect between carbon and phosphorus donors, and this

finding was confirmed by theoretical calculations. To understand whether the mutually cis

disposition in 3 and 7b of the chloride ligand (trans to P) and of a σ-donor ligand such as

the methyl or the η¹-allyl ligand (trans to N) is intrinsic to the nature of these ligands or

related in one way or another to the P,N heterobidentate nature and resulting asymmetry

of the NOPON^Meligand, DFT-B3LYP calculations were carried out on a series of isomeric

2

structures of four- and three-coordinate chloro, methyl, and η¹-allyl Pd(II) complexes. The

existence of an energetic barrier against the formation of a compound where the phosphorus

atom of tridentate NOPON^Meis trans to an alkyl or η¹-allyl ligand was established.

2

In tr od u ction

often control the reactivity at the metal site. This is

nicely illustrated in, for example, the asymmetric allylic

alkylation reaction catalyzed by palladium complexes^5,6

where high enantioselectivities are achieved with the

P,N chelating (phosphinoaryl)oxazoline ligand.^7-9Fur-

thermore, hemilability by reversible decoordination of

The design of heterotopic ligands bearing phosphorus

and nitrogen or oxygen donor atoms is a field of constant

ongoing research owing to the often unique properties

that such ligands confer to their metal complexes in

stoichiometric or catalytic reactions.^1-4The different

(stereo)electronic characteristics of the donor groups

(2) Lindner, E.; Pautz, S.; Haustein, M. Coord. Chem. Rev. 1996,

155, 145.

(3) Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem.

1999, 48, 233.

^|Dedicated to Prof. K. Vrieze for his numerous and outstanding

contributions to chemistry.

* Corresponding author. E-mail: braunst@chimie.u-strasbg.fr. Fax.

+33 390 241 322.

(4) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680.

(5) Trost, B. M.; van Vranken, D. L. Chem. Rev. 1996, 96, 395.

(6) J unker, J .; Reif, B.; J unker, B.; Felli, I. C.; Reggelin, M.;

Griesinger, C. Chem. Eur. J . 2000, 6, 3281.

(7) Pfaltz, A. Synlett 1999, S1, 835.

^†Laboratoire de Chimie de Coordination.

^‡Laboratoire de Chimie Quantique.

^§Service de Cristallochimie.

University of British Columbia. Deceased, October 27, 1998.

(1) Bader, A.; Lindner, E. Coord. Chem. Rev. 1991, 108, 27.

(8) Helmchen, G. J . Organomet. Chem. 1999, 576, 203.

(9) Williams, J . M. J . Synlett 1996, 705.

Publication on Web 06/08/2001

Chloro Palladium(II)-(η¹-Allyl) Complex

Organometallics, Vol. 20, No. 14, 2001 2967

Sch em e 1

one arm of the ligand has been very successfully applied

to the selective activation of small molecules.^3,4,10,11

Among the nitrogen-based ligands, oxazolines have

aroused considerable interest owing to the remarkable

catalytic properties of their metal complexes.^12,13In the

past decade, several groups have been interested in the

study of stoichiometric and catalytic reactions promoted

by complexes with P,O-type ligands.^1-4,10,14-21We have

recently prepared new ligands bearing phosphine and

oxazoline moieties such as (oxazolinylmethyl)diphenyl-

phosphine^22-24and bis(oxazolinylmethyl)phenylphos-

phine²⁵(the latter is abbreviated NPN in the following),

which combine the phosphorus donor atom as a soft

Lewis base with the harder nitrogen atom of the

oxazoline ring (coordination of an oxazoline through the

oxygen has never been observed). (Pseudo)octahedral

ruthenium complexes have been characterized where

the NPN ligand coordinates either as a static bidentate

N,P chelate or as a facial (fac) N,P,N tridentate ligand,

and very high catalytic activity in transfer hydrogena-

tion of ketones was observed.²⁵We now wish to report

the synthesis and properties of the new heterotopic

ligand bis[1-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-1-me-

thylethyl]phenyl phosphonite, referred to as bis(oxazo-

Pd(II) complexes (see A and B, Scheme 1), the latter

illustrating its potentially hemilabile character. The

coordination behavior of NOPON^Mewill be compared

2

line)phenylphosphonite and abbreviated NOPON^Mein

2

to that of other multifunctional N,N,N-, P,N,N-, P,N,P-,

or P,P,P-type ligands.^27-30Differences in bonding mode

and reactivity of the complexes were observed especially

in structures of type C, where chemically different

groups X and Y are in trans position to the phosphorus

and nitrogen atoms, respectively (Scheme 1).

the following.

Transition metal allyl complexes present a rich chem-

istry.^5,27The allyl ligand can coordinate to a transition

metal in three limiting ways: as a η¹-bound ligand, as

a η¹-η³ligand, or as a fully η³ligand. The latter bonding

mode is the most general, while η¹-allyl complexes have

been isolated mainly with platinum,^28-30very recently

with iridium,³¹or with early transition metals.^32-34The

manner in which an allyl fragment coordinates to a

transition metal center and the versatility of its coor-

dination geometries will influence the stereochemistry

of reactions proceeding via allyl intermediates.^5,27For

instance, it is well known in Pd-allyl chemistry that an

η³-η¹-η³mechanism may be operative and that it can

be either detrimental or obligatory for enantioselection.

Therefore it appears important to recognize the bonding

mode of the allyl in a system in order to understand or

rationalize its reactivity. Whereas numerous Pd com-

plexes with an η³-allyl ligand have been isolated, only

few Pd complexes containing η¹-allyl ligands have been

reported despite their considerable interest as either

reactive species or proposed intermediates in C-C

coupling reactions.^28,35-37Recent studies have reported

the isolation of either static or dynamic η¹-allyl Pd

complexes formed upon mer coordination of strong

The increased flexibility offered by the ligand NOPO-

N^Mecompared to NPN, due to the larger chelate size,

2

has led us to isolate Ru(II) complexes where the triden-

tate ligand adopts either a fac or a mer coordination

mode.²⁶We will see in this paper that NOPON^Mecan

2

exhibit tridentate or fluxional bidentate behavior in

(10) Wegman, R. W.; Abatjoglou, A. G.; Harrison, A. M. J . Chem.

Soc. Chem. Commun. 1987, 1891.

(11) Lindner, E.; Schneller, T.; Auer, F.; Mayer, H. A. Angew. Chem.,

Int. Ed. 1999, 38, 2154.

(12) Ghosh, A. K.; Mathivanan, P.; Cappiello, J . Tetrahedron:

Asymmetry 1998, 9, 1.

(13) Helmchen, G.; Pfalz, A. Acc. Chem. Res. 2000, 33, 336.

(14) Keim, W.; Maas, H.; Mecking, S. Z. Naturforsch. 1995, 50b, 430.

(15) Le Gall, I.; Laurent, P.; Toupet, L.; Salau¨n, J .-Y.; des Abbayes,

H. Organometallics 1997, 16, 3579.

(16) Bischoff, S.; Weigt, A.; Miessner, H.; Lu¨cke, B. J . Mol. Catal.

1996, A, 339.

(17) Werner, H.; Stark, A.; Schulz, M.; Wolf, J . Organometallics

1992, 11, 1126.

(18) Andrieu, J .; Braunstein, P.; Naud, F. J . Chem. Soc., Dalton

Trans. 1996, 2903.

(19) Braunstein, P.; Chauvin, Y.; Na¨hring, J .; DeCian, A.; Fischer,

J .; Tiripicchio, A.; Ugozzoli, F. Organometallics 1996, 15, 5551.

(20) Allgeier, A. M.; Mirkin, C. A. Angew. Chem., Int. Ed. 1998, 37,

894.

(27) Consiglio, G.; Waymouth, R. M. Chem. Rev. 1989, 89, 257.

(28) Numata, S.; Okawara, R.; Kurosawa, H. Inorg. Chem. 1977,

16, 1737.

(21) Andrieu, J .; Braunstein, P.; Naud, F.; Adams, R. D. J . Orga-

nomet. Chem. 2000, 601, 43.

(22) Braunstein, P.; Fryzuk, M. D.; Le Dall, M.; Naud, F.; Rettig, S.

J .; Speiser, F. J . Chem. Soc., Dalton Trans. 2000, 1067.

(23) Braunstein, P.; Graiff, C.; Naud, F.; Pfaltz, A.; Tiripicchio, A.

Inorg. Chem. 2000, 39, 4468.

(24) Braunstein, P.; Naud, F.; Rettig, S. J . New J . Chem. 2001, 25,

32.

(25) Braunstein, P.; Fryzuk, M. D.; Naud, F.; Rettig, S. J . J . Chem.

Soc., Dalton Trans. 1999, 589.

(26) Braunstein, P.; Naud, F.; Pfaltz, A.; Rettig, S. J . Organometal-

lics 2000, 19, 2676.

(29) Kaduk, J . A.; Ibers, J . A. J . Organomet. Chem. 1977, 139, 199.

(30) J enkins, H. A.; Yap, G. P. A.; Puddephatt, R. J . Organometallics

1997, 16, 1946.

(31) J ohn, K. D.; Salazar, K. V.; Scott, B. L.; Baker, T.; Sattelberger,

A. P. Chem. Commun. 2000, 581.

(32) Erker, G.; Berg, K.; Angermund, K.; Kru¨ger, C. Organometallics

1987, 2620.

(33) Gambarotta, S. J . Organomet. Chem. 1991, 418, 183.

(34) Antonelli, D. M.; Leins, A.; Stryker, J . M. Organometallics 1997,

16, 2500.

2968 Organometallics, Vol. 20, No. 14, 2001

Braunstein et al.

tridentate ligands.^35,36,38,39Although NOPON^Medid not

display a tridentate coordination in Pd-allyl complexes,

we will see that it led to the isolation and full charac-

terization of an unprecedented η¹-allyl chloro Pd com-

plex in which the Pd-bound carbon atom is always trans

to nitrogen.

2

Resu lts

Liga n d Syn th esis. The synthesis of bis(2-oxazoline-

4,4-dimethyl-2-hydroxydimethyl)phenylphosphonite (I),

abbreviated NOPON^Mein the following, was performed

2

in THF at -78 °C via a one-pot reaction between PPhCl₂

and a mixture of 4,4-dimethyl-2-(1-hydroxy-1-methyl-

ethyl)-4,5-dihydrooxazole and triethylamine (3-fold ex-

cess) (eq 1). This synthetic route differs slightly from

that reported by Pfaltz et al. for the synthesis of a

phosphite-oxazoline ligand.⁴⁰It is straightforward and

allows ligand synthesis in gram-scale quantities.

F igu r e 1. ORTEP view of the structure of the ligand

NOPON^Me(I).

2

Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for th e Liga n d NOP ON^Me(I)

2

P(1)-O(1)

P(1)-O(2)

P(1)-C(17)

1.650(1)

1.644(2)

1.834(2)

C(4)-O(3)

C(4)-N(1)

C(4)-C(1)

O(1)-C(1)

1.375(2)

1.260(3)

1.513(3)

1.460(2)

The ¹H NMR spectrum of NOPON^Mein CDCl₃reveals

2

a set of four singlets for the methyl protons and an AB

spin system for the methylenic protons of the oxazoline.

The only symmetry element in the molecule is a mirror

plane which includes the phenyl ring and the phospho-

rus atom. The NMR spectrum is in agreement with each

arm of the ligand holding enantiotopic pairs of diaste-

reotopic methyl protons and methylene protons. The IR

spectrum in a KBr pellet exhibits a strong band at 1661

cm^-1assigned to the ν(CdN) vibrations of the oxazoline.

A single-crystal X-ray diffraction study confirmed the

O(1)-P(1)-C(17)

O(2)-P(1)-C(17)

O(1)-P(1)-O(2)

C(5)-N(1)-C(4)

N(1)-C(4)-C(1)

94.24(8)

C(4)-C(1)-O(1)

P(1)-O(1)-C(1)

O(3)-C(4)-N(1)

O(3)-C(4)-C(1)

110.0(2)

121.3(1)

119.1(2)

114.1(2)

96.76(9)

101.26(7)

106.3(2)

126.9(2)

both oxazolines to Pd. Phosphorus coordination leads

to a ³¹P{¹H} NMR upfield shift of 44 ppm. The ¹H NMR

spectrum of complex 1 shows an AB spin system for the

methylenic protons of the oxazoline rings. This indicates

the existence of a mirror plane in the molecule which

exchanges both arms of the ligand. Four resonances,

three singlets and one doublet, correspond to the eight

methyl groups of the molecule. The doublet arises from

structure of NOPON^Me(Figure 1).

2

Selected bond distances and angles are given in Table

1 and will be used below for comparison with values

found for this ligand in palladium complexes. The

characterization of complexes with bidentate N,P- or

4

tridentate N,P,N-NOPON^Mewas of particular interest.

a J _PCof 2.0 Hz between the protons of one methyl goup

2

P d Com p lexes w ith NOP ON^Mea s a Tr id en ta te

of the OC(CH₃)₂fragment and the phosphorus atom, as

shown by ¹H{³¹P} NMR experiments. There are four

well-separated ¹³C{¹H} NMR resonances for the methyl

groups, two of which correspond to the two nonequiva-

lent OC(CH₃)₂methyls and exhibit a doublet at δ 25.0

2

N,P ,N Liga n d . Reaction of ligand I with [Pd(NCMe)₄]-

(BF₄)₂in acetonitrile yielded [Pd(NCMe)(NOPON^Me

-

2

N,P,N)](BF₄)₂, 1, in 90% yield (eq 2).

3

and 30.0, with J _PC) 7.8 and J _PC) 2.9 Hz, respec-

tively. The CdN carbon appears as a doublet at 174.2

ppm (³J _PC) 8.7 Hz), which is downfield shifted by 8

ppm compared to uncoordinated I (see Table 2 for

comparative purposes). From these data we conclude

that the ligand coordinates in a tridentate fashion.

An X-ray diffraction study on single crystals of

1‚0.5Et₂O‚0.33MeCN confirmed the geometry of the

molecule (Figure 2, Table 3). There is no symmetry

Its IR spectrum in acetonitrile shows only one ν(CdN)

(37) Byers, P. K.; Canty, A. J . J . Chem. Soc., Chem. Commun. 1988,

639.

band at 1622 cm^-1, consistent with the coordination of

(38) Ru¨lke, R. E.; Kliphuis, D.; Elsevier, C. J .; Fraanje, J .; Goubitz,

K.; van Leeuwen, P. W. N. M.; Vrieze, K. J . Chem. Soc., Chem.

Commun. 1994, 1817.

(39) Barloy, L.; Ramdeehul, S.; Osborn, J . A.; Carlotti, C.; Taulelle,

F.; DeCian, A.; Fischer, J . Eur. J . Inorg. Chem. 2000, 2523.

(40) Pre´toˆt, R.; Pfaltz, A. Angew. Chem., Int. Ed. 1998, 37, 323.

(35) Ramdeehul, S.; Barloy, L.; Osborn, J . A. Organometallics 1996,

15, 5442.

(36) Ru¨lke, R. E.; Kaasjager, V. E.; Wehman, P.; Elsevier, C. J .; van

Leeuwen, P. W. N. M.; Vrieze, K.; Fraanje, J .; Goubitz, K.; Spek, A. L.

Organometallics 1996, 15, 3022.

Chloro Palladium(II)-(η¹-Allyl) Complex

Ta ble 2. Selected ¹³C{¹H} a n d IR Da ta for Liga n d I a n d Com p lexes 1-7^a

Organometallics, Vol. 20, No. 14, 2001 2969

compound

OC(CH₃)₂OC(CH₃₎₂

CdN

OCH₂

79.1

83.8

84.1

NC(CH₃)₂

ν(CdN)

NOPON^Me^b,f(I)

75.6 27.2/28.15 167.2

67.3

72.7

73.0

27.2, 28.15 1661

27.0, 28.5

27.1, 28.5

2

c,g

[Pd(NCMe)(NOPON^Me-N,P,N)](BF₄)₂(1) 86.5

25.0/30.0

25.3/29.6

174.2

172.5

1622

1618

1660, 1634

2

[PdCl(NOPON^Me-N,P,N)](PF₆)^d,f(2)

83.7

2

[Pd(Me)Cl(NOPON^Me-N,P)]^b,f(3)

79.8, 77.4 26.7-29.9 169.5, 166.0 82.4, 79.8 71.4, 67.8 26.7-29.9

2

[PdI₂(NOPON^Me-N,P)] (4)

2

293 K^d,g

172 K^d,h

83.2 83.2 71.2

29.0-29.8 169.7

29.0-29.8

1662, 1631

1662, 1630

84.6, 80.9 28.7-30.4 172.6, 166.6 84.9, 81.5 73.3, 69.4 28.7-30.4

80.0-84.0 27.4-27.8 168.0-170.0 80.0-84.0 70.0-71.0 27.4-27.8

[PdCl₂(NOPON^Me-N,P)]^b,f(5)

2

[Pd(C₃H₅)(NOPON^Me-N,P)](PF₆) (6)

2

293 K^d,f

81.15

27.8-28.5 168.5

80.3

68.9

27.8-28.5

solid state^h

77.0-82.0 27.5-32.1 171.9, 164.0 77.0-82.0 69.5, 67.8 27.5-32.1

[Pd(C₃H₅)Cl(NOPON^Me-N,P)] (7)

2

293 K^b,g(7a h 7b)

177 K^d,h(7a )

78.7 27.1/27.15 167.0 79.5 67.9 26.6/26.9

1659, 1637

78.4, 78.0 26.5-28.5 170.5, 164.2 80.8, 79.8 69.1, 66.7 26.5-28.5

77.8 27.0-28.8 167.5 80.2 69.3 27.0-28.8

78.2, 74.2 24.3-29.6 169.7, 163.2 81.0, 76.0 69.9, 66.8 24.3-29.6

259 K^e,h(7b)

solid state^h(7b)

a

b

d

h

Chemical shifts in ppm, and IR absorptions in cm^-1

.

CDCl₃. ^cAcetonitrile-d₃. CD₂Cl₂. ^eToluene-d₈. ^f50.3 MHz. ^g75.4 MHz. 125.7

MHz.

be compared to that in other Pd complexes containing

a tridentate triphosphine ligand.^41,42The nonideal ge-

ometry is reflected by the different structural features

of the two six-membered ring chelates. The N(2)-Pd-

(1)-P(1) and N(1)-Pd(1)-P(1) bite angles are 90.40-

(9)° and 83.28(9)°, respectively; this decrease is accom-

panied by a pinch of the Pd(1)-P(1)-O(1) angle of 5°.

The planes Pd, N(1), C(1), C(4), C(5), and O(2) and Pd,

N(2), C(9), C(12), C(13), and O(4) form an angle of 23.4°,

which causes the methyl substituents of the oxazolines

to be eclipsed. This could explain the displacement of

the Pd-N(3) vector out of the plane defined by Pd(1),

P(1), N(1), and N(2), such that N(3) is ca. 0.40 Å above

this plane, as well as the remarkably small Pd(1)-N(3)-

C(23) angle of 159.3(3)°, far from the expected 180°.

To further establish the characteristic spectroscopic

features associated with a tridentate behavior of I,

[PdCl(NOPON^Me-N,P,N)](PF₆) (2) was synthesized, in

2

a one-pot procedure, by reacting I with [PdCl₂(COD)]

followed by the addition of 1 equiv of (NH₄)PF₆(eq 3).

F igu r e 2. ORTEP view of the structure of [Pd(NCMe)-

(NOPON^Me-N,P,N)](BF₄)₂in 1‚0.5Et₂O‚0.33MeCN.

2

Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) for [P d (NCMe)(NOP ON^Me-N,P ,N)](BF ₄)₂(1)

2

Pd(1)-N(1)

Pd(1)-N(2)

Pd(1)-N(3)

Pd(1)-P(1)

2.038(3)

2.039(3)

2.104(3)

2.174(1)

C(4)-N(1)

C(4)-C(1)

C(1)-O(1)

O(1)-P(1)

C(4)-O(2)

1.278(4)

1.496(6)

1.484(4)

1.579(2)

1.345(4)

P(1)-Pd(1)-N(1)

P(1)-Pd(1)-N(2)

N(1)-Pd(1)-N(3)

N(3)-Pd(1)-N(2)

N(1)-Pd(1)-N(2)

P(1)-Pd(1)-N(3)

83.28(9) N(1)-C(4)-O(2)

90.40(9) O(2)-C(4)-C(1)

117.1(4)

116.9(4)

125.9(4)

107.3(3)

126.1(2)

The spectroscopic data are similar to those for 1 (see

Table 2). The oxazoline methylenic protons form an

enantiotopic pair of diastereotopic protons revealed by

the corresponding AB spin system at δ 4.30 and 4.45.

The four diastereotopic methyl groups appear in the ¹H

NMR spectrum as three singlet peaks and one doublet.

91.1(1)

96.0(1)

N(1)-C(4)-C(1)

C(4)-C(1)-O(1)

C(1)-O(1)-P(1)

172.1(1)

167.6(1)

O(1)-P(1)-Pd(1) 109.20(9)

Pd(1)-N(3)-C(23) 159.3(3)

O(3)-P(1)-Pd(1) 114.18(9)

element in the molecule. The coordination around the

metal center approximates a square-planar geometry

(41) Barbaro, P.; Togni, A. Organometallics 1995, 14, 3570.

(42) Wander, S. A.; Miedaner, A.; Noll, B. C.; Barkley, R. M.; DuBois,

D. L. Organometallics 1996, 15, 3360.

in which NOPON^Meforms a tridentate ligand. It can

2

2970 Organometallics, Vol. 20, No. 14, 2001

Braunstein et al.

The latter, at δ 1.80, was shown by ¹H{³¹P} NMR

experiments to be coupled to the phosphorus atom by a

⁴J _PHof 2.0 Hz.

We then attempted to isolate and characterize com-

plexes exhibiting a somewhat restricted bidentate co-

ordination mode for ligand I.

There are two bands at 1662 and 1631 cm^-1in the IR

spectrum of 4 in THF, for the ν(CdN) vibrations of the

uncoordinated and coordinated oxazolines, respectively.

In contrast to the case of 3, the ¹H NMR spectrum

exhibits only one AB spin system at δ 4.02 and 4.06

ppm, which accounts for the four methylenic protons.

Consistently, the methyl protons are observed as four

singlets. Each type of carbon atom gives rise to a singlet

in the ¹³C{¹H} NMR spectrum. These NMR data indi-

cate the equivalence of the two oxazoline arms, although

they are not consistent with the static tridentate

coordination mode established for 1 and 2. This led us

P d (II) Com p lexes w ith Bid en ta te a n d F lu xion a l

Bid en ta te NOP ON^Me. The reaction of [Pd(Me)Cl-

2

(COD)] (COD ) 1,5-cyclooctadiene) with NOPON^Me

2

afforded [Pd(Me)Cl(NOPON^Me-N,P)], 3 (eq 4), in 57%

2

isolated yield.

to envisage a rapid fluxional behavior for the NOPON^Me

2

1

ligand, and we therefore performed low-temperature H

and ¹³C{¹H} NMR experiments. At 172 K two species

were indeed found to coexist (eq 6).

Its two IR bands (KBr pellet) at 1660 and 1634 cm^-1

are assigned to the CdN vibrations of the uncoordinated

and coordinated oxazoline, respectively (Table 2). The

1

Pd-CH₃protons appear in the H NMR spectrum as a

3

doublet at δ 0.75 ppm with a J _PH) 2.9 Hz indicative

of a cis relationship between the phosphorus atom and

the Pd-CH₃group. As expected for a different behavior

of the two oxazoline moieties, their methylenic protons

appear at room temperature as two separate AB spin

systems integrating for two protons each. Six singlets

are observed in the methyl region, four integrate for

three protons each and two account for six protons each.

The ¹H NMR spectrum of 3 at 223 K shows eight

singlets for the methyl protons, integrating for three

protons each. The fact that at room temperature only

six rather than eight singlets are observed results from

accidental coincidence. The ¹³C{¹H} NMR spectrum at

room temperature shows two resonances for the oxazo-

line CdN at δ 169.5 and 166.0 ppm, the latter being

identical with the chemical shift of the imine carbon in

the free ligand. Similarly, the other oxazoline carbon

atoms appear as two sets of resonances, with one being

identical to those for the free ligand. The methyl carbons

give rise to overlapping singlets and doublets from δ

26.7 to 29.9 ppm. These data are consistent with an

The major compound at 172 K shows a ¹H NMR

spectrum very similar to that of complex 3 at 223 K,

with two AB spin systems integrating for two protons

each and eight lines in the methyl region. The ¹³C{¹H}

NMR spectrum exhibits resonances corresponding to

coordinated and uncoordinated oxazolines. When the

temperature was raised to 227 K, the two NC(CH₃)₂

singlets coalesced into one resonance. The same obser-

vation was made with all the other carbon atoms and

was particularly clear for the CdN resonance. The

activation barrier calculated for this oxazoline exchange

is ∆G^q) ca. 42 kJ ‚mol^{-1 43}

The minor isomer 4′ in eq 6

.

(10%) shows ¹H and ¹³C{¹H} resonances very similar

to those of compounds 1 or 2. Its ³¹P{¹H} NMR spectrum

exhibits a singlet at δ 102.5 (to be compared with δ 116.0

for 4), a chemical shift almost identical to that of the

complex formed upon addition of 1 equiv of (NH₄)PF₆

to a CD₂Cl₂solution of 4. Thus, compound 4′ would

2

correspond to the cationic complex [PdI(NOPON^Me

-

asymmetric coordination mode of NOPON^Meand ac-

2

N,P,N)]I. Upon warming, the intensity of its resonances

decreases and eventually vanishes at 273 K. These

experiments show that the room-temperature NMR

data, eventhough they first seem to correspond to a

compound with a certain degree of symmetry, relate in

fact to an asymmetric structure in which fast exhange

of the coordinated and dangling oxazolines occurs on the

NMR time scale. Such a mechanism does not allow the

exchange of the methyl and methylenic protons below

and above the plane of the molecule; thus the OCH₂

protons appear as an AB spin system at room temper-

ature. The different time scales of the IR and NMR

experiments account for the observation of two different

oxazoline rings in the IR spectrum.

count for the existence of a coordinated and a dangling

oxazoline arm.

We felt it interesting to compare the behavior of 3

with that of the more symmetrical complex [PdI₂-

(NOPON^Me-N,P)], 4. The latter was prepared by reac-

2

tion of 1 with excess NaI in acetone (eq 5).

(43) Sandstro¨m, J . In Dynamic NMR Spectroscopy; Academic

Press: New York, 1982.

Chloro Palladium(II)-(η¹-Allyl) Complex

Organometallics, Vol. 20, No. 14, 2001 2971

Ta ble 4. ¹³C{¹H} NMR Da ta (J in Hz in

For comparative purposes, we prepared [PdCl₂-

p a r en th eses) for th e Allyl P r oton s in 6 a n d 7a /b^a

(NOPON^Me)] (5) according to (eq 7).

2

compound

C¹

C²

C³

[Pd(C₃H₅)(NOPON^Me-N,P)]-

(PF₆) (6)

2

solid state (η³-allyl)

50-60

123.0

75-85

b

298 K, CD₂Cl₂

54.7 (6.4) 121.5 (8.8) 78.8 (40.1)

[Pd(C₃H₅)Cl(NOPON^Me

-

2

N,P)] (7)

solid state (η¹-allyl) (7b)

22.0

143.4

110.3

298 K, CD₂Cl₂^b(7a h 7b) 37.5 (br) 132.2 (6.7) 96.0 (br)

b

177 K, CD₂Cl₂(7a )

52.5

27.8

121.9 (br) 78.2

143.0 108.5

b

259 K, toluene-d₈(7b)

a

b

Chemical shifts given in ppm. At 125.7 MHz.

Its spectroscopic data are very similar to those of 4.

Thus, the ¹H NMR spectrum at room temperature

shows only one AB spin system assigned to the four

methylenic protons of the oxazolines. The methyl region

exhibits four lines including a broad singlet for the

diastereotopic NC(CH₃)₂methyls. This is due to the fact

that the two methyls each coalesce at a different

temperature and thus appear with a different line shape

of the P donor compared to N⁴⁴and with literature data

for complexes of the type [Pd(η³-C₃H₅)(P,N)]⁺.^45,46The

five protons of the allyl ligand appear as four resonances

1

in the H NMR spectrum. Two protons exhibit two dd

(with appearance of triplet) at δ 4.95 and 3.75 due to

³J _HHwith the central allylic proton of 7.5 and 13.8 Hz,

3

respectively, and to a J _PHcoupling of 8.0 and 14.0 Hz,

1

at a given temperature. This H NMR spectrum at room

respectively, as shown by homonuclear decoupling and

1

¹H{³¹P} NMR experiments. While the H COSY NMR

temperature is comparable to that of 4 at 249 K. In the

room-temperature ¹³C{¹H} NMR spectrum, all reso-

nances except the aryl carbons are broad, being close

to coalescence, and slightly downfield shifted when

compared to the free ligand. Again, this spectrum is

similar to that of 4 at 249 K. The IR and NMR data of

5 indicate that the ligand behaves as a fluxional N,P

chelate, as in 4. Upon cooling to 177 K two species were

found to coexist, the minor one corresponds to a static

spectrum shows that these two protons are not coupled

1

to each other, the H-¹³C HMQC experiments indicate

they are held by the same carbon that is trans to

phosphorus and resonates at δ 78.8. These data allow

us to assign them to the allylic protons H^3sand H^3a

respectively (see 6 for labeling). The H^1sand H^1aprotons

appear as a broad single resonance integrating for two

1

protons in the 500.13 MHz H NMR spectrum at room

[PdCl₂(NOPON^Me-N,P)], while the major exhibits ¹H

3

1

2

temperature but exhibit a broad doublet with a J _{H H}

NMR features identical to those of [PdCl(NOPON^Me

-

2

of 6.8 Hz in the 300.16 MHz spectrum. This coupling to

the central allylic proton H²was determined by homo-

N,P,N)](PF₆), 2.

1

We then felt it interesting to investigate the behavior

nuclear decoupling H experiments. That the syn and

of NOPON^Mecomplexes in which an additional ligand

2

anti protons appear as a broad resonance is consistent

with an η³-η¹allyl isomerization through selective

opening of the Pd-C(3) bond trans to the phosphorus

atom, followed by rotation about the C(1)-C(2) bond.^5,47

We next examined the situation where the chloride

could also display changes in hapticity and examine

their mutual influence. The allyl ligand was a candidate

of choice. Complex [Pd(η³-C₃H₅)(NOPON^Me-N,P)](PF₆),

2

6, was isolated in 71% yield in two steps from the

reaction of 2 equiv of NOPON^Mewith 1 equiv of [Pd-

-

2

ligand has not been replaced by PF₆and could there-

(η³-C₃H₅)(µ-Cl)]₂followed by the addition of 2 equiv of

fore influence the dynamic behavior of the ligands by

coordination to the palladium. Mixing [Pd(η³-C₃H₅)(µ-

NH₄PF₆(eq 8).

Cl)]₂with 2 equiv of NOPON^Meyielded complex 7 in

2

93% yield (eq 9, Scheme 2). The IR spectrum in CH₂Cl₂

exhibits two bands at 1659 and 1637 cm^-1assigned to

the CdN vibrations of uncoordinated and coordinated

1

oxazolines, respectively. We will first examine H and

¹³C{¹H} NMR experiments performed at low tempera-

ture in order to slow any fluxional process additional

to that of NOPON^Meitself (see 4 above). At 177 K, the

2

¹H NMR resonances of the NOPON^Meligand in 7

2

correspond to two broad AB spin systems for two

inequivalent sets of OCH₂protons and eight singlets in

the methyl region. This is similar to the low-tempera-

ture NMR data for 3 or 4 except that, in contrast with

the latter, no additional species exhibiting a tridentate

The two IR bands at 1662 and 1630 cm^-1correspond to

the CdN vibrations of the uncoordinated and coordi-

nated oxazoline, respectively. The ¹H and ¹³C{¹H} NMR

spectra of 6 exhibit sharp resonances for the NOPON^Me

2

coordination mode of NOPON^Mecould be detected in

2

ligand with features similar to those in 4. The three allyl

carbons appear at three different chemical shifts (Table

4).

The terminal CH₂carbons show doublets at δ 54.7

(²J _PC) 6.4 Hz) and 78.8 ppm (²J _PC) 40.1 Hz) for the

carbon cis and trans to phosphorus, respectively. This

assignment is consistent with the larger trans influence

(44) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.

1973, 10, 335.

(45) A° kermark, B.; Krakenberger, B.; Hansson, S.; Vitagliano, A.

Organometallics 1987, 6, 620.

(46) Park, J .; Quan, Z.; Lee, S.; Ahn, H.; Cho, C.-W. J . Organomet.

Chem. 1999, 584, 140.

(47) Breutel, C.; Pregosin, P. S.; Salzmann, R.; Togni, A. J . Am.

Chem. Soc. 1994, 116, 4067.

2972 Organometallics, Vol. 20, No. 14, 2001

Braunstein et al.

F igu r e 3. Variable-temperature ¹³C{¹H} NMR spectrum of 7 in the oxazoline region.

Sch em e 2

singlets at δ 69.1 and 66.7 ppm for the two OCH₂

carbons from coordinated and uncoordinated oxazoline,

respectively, coalesce at 205 K to give an averaged broad

singlet, which sharpens upon further increase of the

temperature (see Figure 5). A similar feature is observed

for the two singlets of the CdN carbons from coordi-

nated and uncoordinated oxazolines (see Figure 3).

The eight methyl singlets in the variable-temperature

¹H NMR spectra at 177 K give rise to four singlets above

220 K. Two coalescence temperatures can be observed:

at 200 K for the NC(CH₃)₂protons at δ 1.35 and 0.92

ppm and 195 K for the OC(CH₃)₂protons at δ 1.50 and

1.80 ppm. The four singlets observed at 220 K sharpen

upon further increase of the temperature (see Figure

1

4). These variable-temperature H NMR and ¹³C{¹H}

NMR data establish the fast exchange between coordi-

nated and dangling oxazolines and provide an estimate

of the activation barrier ∆G^qfor the oxazoline exchange

of ca. 38 kJ ‚mol^{-1 43}

This situation is similar to that

.

described with 4. Looking now at the allyl ligand, we

also find that the ¹H and ¹³C{¹H} NMR spectra are

temperature dependent. Upon raising the temperature

from 177 to 295 K, the resonances of the terminal

carbons shift in opposite direction from 52.5 to 37.5 ppm

for the carbon cis to P and from 78.2 to 96 ppm for the

C trans to P, and they are broad at room temperature

(see Figure 5).

7. At 177 K the allyl protons and carbons of 7 exhibit

the same pattern and chemical shifts as those of 6 at

room temperature (see Table 4).

Similarly, the central carbon resonance is downfield

shifted from 121.9 to 132.2 ppm, but in contrast to C¹

Therefore, at low temperature the allyl fragment

adopts an η³bonding mode, while NOPON^Mebehaves

2

3

and C³it sharpens upon warming (d, J _PC) 6.7 Hz).

as a bidentate N,P chelate as depicted in 7a . For clarity,

we shall describe first the fluxional behavior of NOPO-

The chemical shifts of the η³-allyl carbons progressively

move with increasing temperature toward those of a

static η¹-allyl structure (see below for characterizing

data of the η¹-allyl form). In the variable-temperature

¹H NMR spectra the broad signal for the syn and anti

1

N^Meand then that of the allyl ligand. The H and ¹³C-

2

{¹H} NMR spectra of NOPON^Mein 7a change on raising

2

the solution temperature (see Figures 3-5). In the

variable-temperature ¹³C{¹H} NMR spectra the two

Chloro Palladium(II)-(η¹-Allyl) Complex

Organometallics, Vol. 20, No. 14, 2001 2973

1

F igu r e 4. Variable-temperature H NMR spectrum of 7 in the oxazoline region.

H¹protons sharpens upon warming to form at 230 K a

well-resolved doublet integrating for two protons. At

higher temperature, the doublet broadens to become

very broad at room temperature. The well-resolved

apparent triplets for the allylic H³protons at 177 K

broaden above 250 K. The central allylic proton, which

exhibits a complex multiplet due to couplings to the H^1s,

H^1a, H³, and P atoms, appears above 270 K as a doublet

of quintuplets with a J _HHof 10.6 Hz and a J _PCof 1.7

Hz. This pattern is consistent with an AB₄X (A ) B )

H, X ) P) spin system where the four terminal protons

have become equivalent. Fast equilibrium between η³-

and η¹-allyl is known to occur in Pd-allyl complexes and

could account for the equivalence of the allyl protons in

compound 7 at room temperature. Due to decomposition

of the complex in CD₂Cl₄solution above 333 K, we could

not observe the end of the coalescence phenomenon for

the terminal allylic protons and carbons.

respond to a static η¹-allyl ligand. At room temperature

the H NMR spectrum exhibit broad resonances for the

allylic resonances. Again raising the temperature in

order to observe the end of the coalescence phenomena

resulted in the decomposition of the complex at tem-

peratures above 333 K.

1

Variable-temperature ³¹P{¹H} NMR spectroscopy did

not provide additional information about the coordina-

tion mode of the allyl ligand since the chemical shifts

of 7 in toluene at 203 K (δ 137.7) and at 258 K (δ 136.7)

are not very different from the values at room temper-

ature (δ 135.7) or in CH₂Cl₂, either at 203 K (δ 135.8),

258 K (δ 134.7), or room temperature (δ 133.0).

An X-ray diffraction study showed the complex to

adopt structure 7b in the solid state, a rare example of

a fully characterized allyl η¹-bonding mode for Pd

complexes³⁹and the first in transition metal chemistry

for a mutual cis arrangement of η¹-allyl and chloride

ligands (see below).

3

Replacing the NMR solvent CD₂Cl₂with toluene-d₈

allowed the observation at 259 K of the allyl fragment

in a static η¹-bonding mode, as shown by the charac-

teristic ¹³C{¹H} NMR chemical shifts at 27.8, 108.5, and

143.0 for the Pd-CH₂, dCH₂, and HCd carbons,

respectively (see for example, Mo-CH₂-CHdCH₂, 32.8,

144.9, 106.1 ppm; Pt-CH₂-CHdCH₂, 12.8, 143.0, 111.0

ppm).^30,36,48The allyl protons were assigned unambigu-

The far-IR spectrum of crystals of [Pd(η¹-C₃H₅)Cl-

(NOPON^Me-N,P)] is identical to that of the powder

2

obtained after workup, confirming that the complex

isolated in the solid has the same structure as in the

single crystals. By comparison with the far-IR spectra

of [Pd(η³-C₃H₅)(NOPON^Me-N,P)](PF₆) and [Pd(Me)Cl-

2

-1

(NOPON^Me-N,P)], the strong band at 287 cm in 7b

2

1

ously by HETCOR H/¹³C NMR experiments and cor-

is assigned to the ν(Pd-Cl) vibration.⁴⁴Furthermore,

we recorded a solid state ¹³C{¹H} NMR CP-MAS spec-

(48) Bailey, N. A.; Kita, W. G.; McCleverty, J . A.; Murray, A. J .;

Mann, B. E.; Walker, N. W. J . J . Chem. Soc., Chem. Commun. 1974,

592.

trum of [Pd(η¹-C₃H₅)Cl(NOPON^Me-N,P)]. The allyl ligand

2

exhibits three resonances at δ 143.4, 110.3, and 21.0

2974 Organometallics, Vol. 20, No. 14, 2001

Braunstein et al.

F igu r e 5. Variable-temperature ¹³C{¹H} NMR spectrum of 7 in the allyl region.

ppm assigned to the CH, olefinic CH₂, and Pd-CH₂

carbons, respectively. These data are in agreement with

the solution ¹³C{¹H} NMR data on toluene-d₈at 259 K

for complexes that show a static η¹-C₃H₅ligand. For

comparison, we performed a solid state ¹³C CP-MAS

NMR study of [Pd(η³-C₃H₅)(NOPON^Me-N,P)](PF₆) and

2

found that the allylic carbons appear indeed in the

expected range for an η³-bonding mode at chemical

shifts similar to those found in the solution NMR

spectrum. Furthermore, the carbon chemical shifts of

the NOPON^Meligand in 7b in the solid state NMR

2

spectra are similar to those observed at 177 K in

solution, thus confirming the occurrence of a frozen

bidentate behavior for the NOPON ligand.

The structure of complex 7b was determined by X-ray

diffraction. It approximates square-planar geometry, the

F igu r e 6. ORTEP view of the structure of [Pd(η¹-C₃H₅)Cl

distortion arising from the angles P-Pd-C(23) and

N(1)-Pd-Cl of 85.99(6)° and 95.83(4)°, respectively

(Figure 6, Table 5).

(NOPON^Me-N,P)], 7b.

2

It confirms the cis arrangement of the η¹-allyl frag-

ment and the phosphorus atom. The N(1)-Pd-P angle

in the six-membered ring of 91.95(4)° is similar to the

Discu ssion

While the preparation of palladium complexes with

the new NOPON^Meligand I is straightforward and can

2

larger of the two P-Pd-N angles of NOPON^Mein

2

be performed in good to high yields, their characteriza-

tion requires special attention, owing to the possible

occurrence of a fluxional bidentate coordination mode.

compound 1. The Pd-C(23) and Pd-Cl bond distances

and P-Pd-N(1) angle are similar to those in [Pd(Me)-

Cl(P,N)], where P,N is a six-membered ring phosphino-

amine ligand.⁴⁹The C-C bond distances and angles

within the allyl ligand are consistent with other ex-

amples of transition metal η¹-allyl complexes described

in the literature.^{29-32,35,39,50}

(49) Dekker, G. P. C. M.; Buijs, A.; Elsevier, C. J .; Vrieze, K.; van

Leeuwen, P. W. N. M.; Smeets, W. J . J .; Spek, A.; Wang, Y. F.; Stam,

C. H. Organometallics 1992, 11, 1937.

(50) Huffman, J . C.; Laurent, M. P.; Kochi, J . K. Inorg. Chem. 1977,

16, 2639.

Chloro Palladium(II)-(η¹-Allyl) Complex

Organometallics, Vol. 20, No. 14, 2001 2975

Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles

Sch em e 3. P ossible Mech a n ism s for th e Dyn a m ic

(d eg) for [P d (η¹-C₃H₅)Cl(NOP ON^Me-N,P )], 7b

Beh a vior of th e NOP ON^MeLiga n d

2

Pd-Cl

2.3944(5)

2.071(2)

2.1782(5)

2.183(2)

1.469(3)

1.341(1)

1.621(1)

1.467(2)

C(6)-C(5)

C(5)-N(1)

C(5)-O(1)

P-O(3)

O(3)-C(15)

C(15)-C(18)

C(18)-N(2)

C(18)-O(4)

1.518(3)

1.279(3)

1.334(2)

1.606(1)

1.459(2)

1.516(3)

1.264(3)

1.316(2)

Pd-C(23)

Pd-P

Pd-N(1)

C(23)-C(24)

C(24)-C(25)

P-O(2)

O(2)-C(6)

Cl-Pd-N(1)

N(1)-Pd-P

P-Pd-C(23)

C(23)-Pd-Cl

P-Pd-Cl

95.83(4)

91.95(4)

85.99(6)

87.08(6)

170.88(2)

170.67(7)

Pd-P-O(2)

113.62(2)

125.8(1)

108.9(1)

125.8(2)

123.93(7)

115.7(2)

118.5(2)

P-O(2)-C(6)

O(2)-C(6)-C(5)

C(6)-C(5)-N(1)

C(5)-N(1)-Pd

C(6)-C(5)-O(1)

N(1)-C(5)-O(1)

N(1)-Pd-C(23)

Tr id en ta te vs Bid en ta te Beh a vior . One of the key

tools to distinguish between bi- and tridentate coordina-

tion of the NOPON^Meligand is IR spectroscopy in

2

solution. Complexes of the type A in Scheme 1 exhibit

two ν(CdN) bands, one in the range 1662-1659 cm^-1

for the uncoordinated oxazoline and the other in the

range (1637-1630 cm^-1) for the coordinated oxazoline.

In contrast, compounds with a tridentate NOPON^Me

2

(structure type B) show only one band in the region

1622-1618 cm^-1. A clear differentiation between rigid

structures A and B is also provided by NMR spectros-

copy with resonances for both coordinated and uncoor-

dinated oxazolines, as in complex 3. When NOPON^Me

2

adopts a fluxional bidentate N,P coordination mode, the

fast exchange between the coordinated and dangling

arms of the ligand renders the two oxazolines equiva-

lent. Since in complexes bearing tridentate NOPON^Me

2

that the ligand adopts a pseudo-tridentate bonding

mode in a planar transition state (Scheme 3 (ii)), and a

mechanism through pentacoordination with a trigonal

bipyramidal transition state (Scheme 3 (iii)).

both oxazolines are equivalent owing to the presence of

a mirror plane in the molecule, a dynamic structure of

type A or a structure B gives rise to four resonances

for the four diastereotopic methyls and one AB spin

system for the four OCH₂protons. The OCH₂protons

in fluxional A appear at values (4.00-4.15 ppm) that

correspond to the average between their chemical shift

when ligand I is tridentate (4.30-4.60 ppm) and un-

coordinated (3.80-3.85 ppm). An additional difference

between a fluxional structure A and B is the existence

In the case of a “rotation” mechanism the fluxional

process should be favored in 3 compared to 5 since the

higher trans effect of CH₃^-compared to Cl^-in square-

planar complexes should facilitate dissociation of the

trans-coordinated oxazoline.^44,51This is not the case

since 3 is the only complex that clearly exhibits a static

bidentate coordination mode of NOPON^Meat room

4

2

in the latter case of a small J _PHcoupling of 2 Hz

between one of the two diastereotopic OC(CH₃)₂methyl

protons and the phosphorus atom.

temperature. Furthermore, the isolation of square-

planar complexes containing a tridentate NOPON^Me

2

and the observation in the case of 4 and 5 of a species

with a tridentate NOPON at low temperature are more

in favor of a “tick-tock twist” mechanism. We have no

experimental data to support mechanism (iii), although

it has been invoked in the case of a tridentate N,N,N-

type ligand.⁵²Further studies would be needed to

confirm this, and the use of a chiral version of NOPO-

This hemilabile behavior of the ligand with reversible

opening and closing of the P,N chelate allows intramo-

lecular exchange of the two oxazoline moieties.^1,3,4Such

a fluxional process with a potentially tridentate ligand

has been encountered when the ligand is placed in a

somewhat restricted bidentate coordination mode, as

recently investigated with terpyridine or bis(oxazolinyl)-

pyridine (Pybox) ligands.^53-55On the basis of these

findings, we can consider at least three possible mech-

anisms for the dynamic process: a “rotation” mechanism

(Scheme 3 (i)) that does not lead to an exchange of the

equatorial environment, a “tick-tock twist” that requires

N^Mewould be of interest since a chiral center usually

2

provides an excellent spectroscopic handle for the

elucidation of fluxional mechanistic pathways, although

this is accentuated in octahedral complexes.⁵³

Com p et it ion for Coor d in a t ion of Tr id en t a t e

NOP ON^Mevs η¹-Allyl/Cl^-vs η³-Allyl. Having estab-

2

lished the bonding behavior of the NOPON^Meligand

(51) Hartley, F. R. Chem. Soc. Rev. 1973, 2, 163.

2

(52) Ru¨lke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van

Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.

(53) Heard, P. J .; J ones, C. J . Chem. Soc., Dalton Trans. 1997, 1083.

(54) Zhu, G.; Terry, M.; Zhang, X. Tetrahedron Lett. 1996, 37, 4475.

(55) Wehman, P.; Ru¨lke, R. E.; Kaasjager, V. E.; Kamer, P. C. J .;

Kooijman, H.; Spek, A. L.; Elsevier, C. J .; Vrieze, K.; van Leeuwen, P.

W. N. M. J . Chem. Soc., Chem. Commun. 1995, 331.

as a static or dynamic chelate, it became possible to

study complexes containing an additional, potentially

dynamic ligand. This would allow the investigation of

their mutual influence, which in the case of the allyl

ligand would be of relevance to key intermediates in

2976 Organometallics, Vol. 20, No. 14, 2001

Braunstein et al.

Sch em e 4

process, complexes 3 and 7b have to go through an

intermediate where the phosphorus and the Pd-CH₃

group are in mutually trans position. Such an arrange-

ment of these two ligands of high trans influence has a

destabilizing effect and leads to isomerization into a

more stable situation where the σ-carbon and the

nitrogen atom are mutually trans. This isomerization

is not needed in the case of 5 and 6 and therefore

facilitates the fluxional process. Similar observations

have been made with Pd complexes in which a sym-

metrical P,P or N,N chelate enhances the dynamic

process in trans position, in contrast to P,N chelates.⁴⁹

A third ligand to be considered in the coordination

sphere of 7 is the chloride. Introducing this anion into

the coordination sphere of 7 induces a change of the allyl

bonding mode from η³to η¹, and this, in turn, has an

effect on the fluxional process of the NOPON^Meligand.

2

This clearly shows the mutual influence of the three

ligands on their bonding behavior.

In contrast to the numerous examples of palladium

allyl complexes with bidentate ligands, only few pal-

ladium complexes have been described that possess a

potentially tridentate ligand.^30,35-38,54In the latter

group, complexes obtained with terpy (terpy ) 2,2′:6′,2′′-

terpyridine) or PNN (PNN ) N-(2-(diphenylphosphino)-

benzylidene)-(2-(2-pyridyl)ethyl)amine)) are of particu-

lar relevance. The compound [Pd(C₃H₅)(terpy)]⁺is

fluxional and the terpy bidentate coordination mode is

associated with an η³-allyl bonding [Pd(η³-C₃H₅)(terpy-

N,N)]⁺, while the terpy tridentate coordination mode

induces a dynamic η¹-allyl bonding mode [Pd(η¹-C₃H₅)-

(terpy-N,N,N)]⁺at room temperature.³⁵The complex

[Pd(η¹-C₃H₅)(PNN-P,N,N)]Cl is easily prepared upon

heating a solution of 0.5 equiv of PNN with [Pd(η³-

C₃H₅)(µ-Cl)]₂at 338 K or can be obtained as a triflate

salt in the presence of [Ag(O₃SCF₃)] at room tempera-

ture. In these latter experiments, no intermediates

containing a bidentate PNN and an η³-allyl were

observed.^36,55These two examples contrast with ours

since we never observed a tridentate coordination mode

catalytic reactions. In the solid state the compounds [Pd-

1

(η³-C₃H₅)(NOPON^Me-N,P)](PF₆), 6, and [Pd(η -C₃H₅)-

2

Cl(NOPON^Me-N,P)], 7b, show two different ¹³C-CP/

2

MAS spectra for the allylic carbons, while they show

identical patterns for the carbons of ligand I, charac-

teristic of a bidentate mode of coordination (see Table

2). As expected, the CH₂carbons of 6 appear broader in

the ¹³C-CP/MAS solid state spectrum than in solution.

The chemical shifts of the allylic carbons are similar in

the solid state and in solution, thus confirming the η³

coordination mode of the allyl ligand of [[Pd(η³-C₃H₅)-

(NOPON^Me-N,P)](PF₆) in both phases. We established

2

by ¹³C NMR that the allyl and NOPON ligands of 7a

are respectively locked in an η³and a static bidentate

coordination mode and that upon warming to room

temperature, I remains a bidentate N,P chelate but

exhibits hemilabile behavior. The allylic CH₂resonances

appear broader and move toward the chemical shifts of

an η¹-allyl. A similar behavior is observed for the central

allylic carbon except that it is broad at low temperature

and sharpens upon warming.

of NOPON^Mein Pd-allyl complexes. It is interesting to

2

compare the palladium complexes of PNN and NOPO-

N^Mesince both ligands can form two six-membered

2

chelates. The reactivity of NOPON^Mecompared to PNN

2

toward Pd-allyl and Pd-alkyl complexes is different. The

strong tendency of the PNN ligand to coordinate in a

tridentate fashion is exemplified by its reaction with

[Pd(Me)Cl(COD)], which leads at room temperature to

the complex [Pd(Me)(PNN-P,N,N)]Cl, or to [Pd(Me)-

(PNN-P,N,N)](O₃SCF₃) when an equivalent of [Ag(O₃-

The complexes 5/6 and 3/7b depicted in Scheme 4

share structural similarities. The former pair exhibits

a more symmetrical environment for the P,N chelate

than the latter since the phosphorus and the nitrogen

atoms are trans to two identical atoms.

SCF₃)] is added. With NOPON^Mewe isolated at room

2

This is not the case for 3/7b, which contain a σ-bonded

carbon cis to phosphorus and a chloride atom cis to

nitrogen. This change in the ligand environment of the

P,N chelate manifests itself in a more fluxional behavior

temperature the complex [Pd(Me)Cl(NOPON-N,P)] (3),

where the chloride ligand is not labile, since attempts

to exchange the counteranion by addition of (NH₄)PF₆

led to no reaction. Note that in the case of [PdCl₂-

of NOPON^Mein 6 compared to 7b and in 5 compared

2

(NOPON^Me-N,P)] a similar procedure led to the forma-

to 3. This was established by ¹H NMR spectroscopy

2

tion of [PdCl(NOPON^Me-N,P,N)](PF₆) in 84% yield (eq

since the spectrum of [Pd(η³-C₃H₅)(NOPON^Me-N,P)]PF₆

2

3). Nevertheless we succeeded in abstracting the chlo-

at 177 K does not indicate a static bidentate bonding of

3

Me₂

NOPON^Me, as in the case of [Pd(η -C₃H₅)(NOPON

-

2

ride of 3 by reaction with [Ag(O₃SCF₃)] in CH₂Cl₂and

obtained a complex of formula [Pd(Me)(NOPON^Me)]-

2

N,P)]Cl. Similarly, while NOPON in 5 exhibits fluxional

behavior at room temperature, it behaves as a static N,P

bidentate chelate in 3. These observations are best

explained if one considers that the oxazoline exchange

follows a “tick-tock twist” mechanism. During this

(O₃SCF₃). This complex is highly fluxional, as shown

1

by the H NMR spectrum in the range 298-177 K. The

chemical shift of the singlet in the ³¹P{¹H} NMR

spectrum at δ 132.8 is almost identical to that of its

Chloro Palladium(II)-(η¹-Allyl) Complex

Organometallics, Vol. 20, No. 14, 2001 2977

methyl, and η¹-allyl Pd(II) complexes bearing the (HN-

CHCH₂OPH₂) model ligand 8.

Sch em e 5. Sch em a tic Dr a w in g a n d Rela tive

En er gy, in k ca l m ol-¹, of th e Tw o P ossible Isom er s

for Ea ch of th e System s

[P d Cl(CH₃)(HN-CHCH₂OP H₂)] 9a /9b,

[P d Cl(η¹-C₃H₅)(HN-CHCH₂OP H₂)] 10a /10b,

[P d (CH₃)(HN-CHCH₂OP H₂)] 11a /11b,

[P d (η¹-C₃H₅)(HN-CHCH₂OP H₂)] 12a /12b, a n d

[P d Cl(HN-CHCH₂OP H₂)] 13a /13b

These structures, sketched in Scheme 5, comprise the

four-coordinate systems [PdCl(CH₃)(HN-CHCH₂OPH₂)]

9a ,b, [PdCl(η¹-C₃H₅)(HN-CHCH₂OPH₂)] 10a ,b, and

their three-coordinate derivatives obtained by dissocia-

tion of either Cl, CH₃, or C₃H₅; see 11a ,b, 12a ,b, and

13a ,b. The fully optimized geometries can be found in

the Supporting Information. The relative energies for

each a /b pair are given in Scheme 5.

In the four-coordinate systems, and in agreement with

the above experimental results, the structures with Cl

trans to P and either η¹-C₃H₅or CH₃trans to N are the

most stable ones. For the three-coordinate, T-shaped

fragment the most stable structure corresponds to

having the nonchelating ligandseither CH₃, η¹-C₃H₅,

or Clstrans to nitrogen, whatever its nature is. Thus

the structural preference in the four-coordinate systems

for Cl trans to P, and CH₃or η¹-C₃H₅trans to N, does

not result from the dissymmetry of the P-N ligand only.

As will now be explained, it also results from the

association in the coordination sphere of the P-N ligand

with the Cl ligand.

That in the three-coordinate system the third ligand

sits always trans to N can be related to the fact that in

[(η³-allyl)Pd(phosphine)(imine)] complexes the Pd-C

bond trans to N is stronger (or has a greater covalent

character) than the Pd-C bond trans to the phospho-

rus.⁵⁶In addition to valence-bond type arguments,⁵⁶MO

theory arguments have been provided to rationalize this

feature:⁵⁷the LUMO of the Pd(phosphine)(imine) frag-

ment is polarized away from the imine ligand; that is,

its lobe trans to the imine is greater than the lobe trans

to the phosphorus atom.⁵⁸The orbital plot of the LUMO

of the Pd(HN-CHCH₂OPH₂), Figure 7, shows clearly

this polarization. Hence the interaction of palladium

with either CH₃, η¹-C₃H₅, or Cl in the three-coordinate

system, which takes place via this orbital, will be

stronger when these entities are trans to N. This is best

exemplified by the relative energies of 11a vs 11b, 12a

vs 12b, and 13a vs 13b (see Scheme 5), which are 10-

16 kcal mol^-1in favor of the trans-N structure.

precursor 3 (133.5 ppm). The IR spectrum indicates the

existence of both coordinated and uncoordinated oxazo-

lines. Further studies are needed to determine the exact

geometry of the complex, although we can already

conclude at this stage that this reaction does not lead

to the formation of a mononuclear complex containing

2

As a consequence of this stronger Pd-Cl interaction

in 13b compared to 13a , the LUMO of 13b is more

destabilized than the LUMO of 13a ; see the schematic

drawing in the middle of the Figure 8. In turn, it will

interact more weakly with the σ orbital of an R ligand

(R ) CH₃or η¹-C₃H₅) when R is trans to P, as in 9a or

10a , than when R is trans to N as in 9b or 10b; see

Figure 8. Since this interaction is a two-electron stabi-

lizing one, this results in having 9a and 10a less stable

than 9b and 10b, respectively.

a tridentate NOPON^Me

.

At this stage one may ask whether the mutually cis

disposition in 3 and 7b of the chloride ligand trans to

P, and of a σ-donor ligand such as the methyl or the

η¹-allyl ligand trans to N, is intrinsic to the nature of

these ligands or whether it is related in one way or

another to the P,N heterobidentate nature and resulting

asymmetry of the NOPON^Meligand.

2

Th eor etica l Stu d ies. To unravel this problem, DFT-

B3LYP calculations were carried out on a series of

isomeric structures of four- and three-coordinate chloro,

(56) Szabo, K. J . Organometallics 1996, 15, 1128.

(57) Dedieu, A. Chem. Rev. 2000, 100, 543.

(58) Ward, T. R. Organometallics 1996, 15, 2836.

2978 Organometallics, Vol. 20, No. 14, 2001

Braunstein et al.

ligand and a chloride are in mutually cis position. It is

interesting to note first that in a recent study A° kermark

and Vitagliano have proposed a mechanism for dynamic

processes of η³-allyl palladium complexes accelerated by

the addition of chloride.⁵⁹Second, a four-coordinated Pd

complex containing a bidentate N,N chelate, an η¹-allyl,

and a chloride ligand in mutually cis position was

postulated as an intermediate. Our results support the

possible existence of such compounds, which are also

of relevance to species involved in the transition metal-

catalyzed allylic alkylation.⁵

We have observed and characterized the changes in

the coordination sphere of the palladium allyl complex

when varying the solvent or the nature of the counter-

anion. Surprisingly, while we would have expected the

NOPON^Meto be affected in its coordination mode by

2

the nucleophilic chloride anion, this is actually the allyl

ligand which was perturbed. These findings are relevant

to the various steps known to occur in, for example, the

enantioselective Pd allylic alkylation, and we therefore

believe that our basic understanding of the behavior of

-

both NOPON^Meand the C₃H₅ligands should find

2

F igu r e 7. Orbital plot of the LUMO of the [Pd(HN-

CHCH₂OPH₂)]⁺fragment showing the polarization away

from the imine ligand. Full lines correspond to positive

contours and dotted lines to negative contours. The zero

contour has been omitted for the sake of clarity.

useful extensions when moving on to more complex

systems containing chiral analogues of the new bis-

(oxazoline)phenylphosphonite ligands reported here.

Exp er im en ta l Section

All reactions were performed under purified nitrogen.

Solvents were purified and dried under nitrogen by conven-

1

tional methods. The H NMR spectra were recorded at 300.13

MHz, ³¹P{¹H} NMR spectra at 81.0 or 121.5 MHz, ¹³C{¹H}

NMR spectra at 75.4 MHz on a FT Bruker AC200 or AC300

instrument, IR spectra in the 4000-400 cm^-1range on a

Bruker IFS66 FT spectrometer, and far-IR spectra in the 500-

90 cm^-1range on

a Bruker ATS 83 spectrometer. The

compounds 4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-di-

hydrooxazole,⁶⁰[Pd(NCMe)₄](BF₄)₂,⁶¹[PdCl₂(COD)],⁶²[PdMe-

(Cl)(COD)],⁶²and [Pd(η³-C₃H₅)(µ-Cl)]₂were prepared accord-

63

ing to the literature.

Syn th eses. NOP ON^Me(I). In a 100 mL Schlenk tube

2

containing 4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihy-

drooxazole (3.000 g, 19.1 mmol) in THF (40 mL) was added

triethylamine (7.99 mL, 57.3 mmol). To the colorless solution

cooled to -78 °C was added quickly dichlorophenylphosphine

(0.615 mL, 9.55 mmol). This afforded immediately a white

precipitate. The reaction mixture was allowed to slowly reach

room temperature and was stirred for 16 h. The THF was

evaporated under vacuum, and toluene (80 mL) was added to

the white solid thus obtained. The white suspension was

filtered over Celite, and the filtrate solution was evaporated.

The white powder was washed using 3 × 10 mL of pentane

and dried in vacuo for 1 night. Yield: 2.750 g (69%). Mp: 99

F igu r e 8. Relative destabilization of the lowest unoc-

cupied molecular orbital in the d⁸[PdCl(HN-CHCH₂-

OPH₂)]⁺system upon addition of Cl to [Pd(HN-CHCH₂-

OPH₂)]⁺, either trans to the phosphorus (see 13a ) or trans

to the imine (see 13b) and its subsequent interaction with

the σ orbital of an alkyl or allyl anion to yield 9b, 10b or

9a , 10a , respectively.

1

°C Selected IR data (KBr): ν_CN1661 s cm^-1. H NMR (300.13

MHz, CDCl₃): δ 1.24 (s, 6 H, NC(CH₃)(CH₃)), 1.25 (s, 6 H, NC-

(CH₃)(CH₃)), 1.60 (s, 6 H, OC(CH₃)(CH₃)), 1.70 (s, 6 H, OC-

2

(CH₃)(CH₃)), AB spin system δ_A3.85 (d, 2 H, J _HH) 8.0 Hz,

Con clu sion

OCHH), δ_B3.90 (d, 2 H, OCHH), 7.30-7.40 (m, 3 H, m and p

aryl), 7.60-7.70 ppm (m, 2 H, o aryl). ¹³C{¹H} NMR (50.3 MHz,

CDCl₃): δ 27.2-28.15 (overlapping s and d, OC(CH₃)₂and NC-

(CH₃)₂), 67.3 (s, NC(CH₃)₂), 75.6 (d, ²J _PC) 12.7 Hz, OC(CH₃)₂),

These studies with allyl- and alkyl-palladium com-

plexes indicate the existence of an energetic barrier

against the formation of a compound where the phos-

2

3

79.1 (s, OCH₂), 127.8 (d, J _PC) 5.0 Hz, m-aryl), 129.4 (d, J _PC

phorus atom of a tridentate NOPON^Meis trans to an

2

alkyl or η¹-allyl ligand. This does not happen with the

P,N,N ligand since when it adopts a tridentate coordi-

nation mode, the phosphorus atom is always cis to the

alkyl or η¹-allyl. The X-ray structure of 7b is the first

one for a transition metal complex where an η¹-allyl

(59) Hansson, S.; Norrby, P.-O.; Sjo¨gren, M. P. T.; A° kermark, B.

Organometallics 1993, 12, 4940.

(60) Pridgen, L. N.; Miller, G. J . Heterocycl. Chem. 1983, 20, 1223.

(61) Sen, A.; Lai, T.-W. Inorg. Chem. 1984, 23, 3257.

(62) Lapido, F. T.; Anderson, G. K. Organometallics 1994, 13, 303.

(63) Tatsuno, Y.; Yoshida, T.; Otsuka, S. Inorg. Synth. 1979, 29, 220.

Chloro Palladium(II)-(η¹-Allyl) Complex

Organometallics, Vol. 20, No. 14, 2001 2979

1

) 6.0 Hz, o-aryl), 129.9 (s, p-aryl), 144.1 (d, J _PC) 10.0 Hz,

ipso-aryl), 167.2 ppm (s, CdN). ³¹P{¹H} NMR (121.5 MHz,

CDCl₃): δ 150.5 ppm (s). Anal. Calcd for C₂₂H₃₃N₂O₄P: C,

62.84; H, 7.91; N, 6.66. Found: C, 63.14; H, 8.26; N, 6.85.

OCHH from coordinated oxazoline), 7.40-7.50 (m, 3 H, aryl),

7.80-7.90 ppm (m, 2 H, aryl). ¹³C{¹H} NMR (50.3 MHz,

CDCl₃): δ 2.8 (s, PdCH₃), 26.7-29.9 (overlapping s and m, OC-

(CH₃)₂and NC(CH₃)₂), 67.8 (s, NC(CH₃)₂from uncoordinated

oxazoline), 71.4 (s, NC(CH₃)₂from coordinated oxazoline), 77.4

(s, OC(CH₃)₂from uncoordinated oxazoline), 79.8 (overlapping

s, OC(CH₃)₂from coordinated oxazoline and OCH₂from

uncoordinated oxazoline), 82.4 (s, OCH₂from coordinated

[P d (NCMe)(NOP ON^Me-N,P ,N)](BF ₄)₂(1). In a 50 mL

2

Schlenk tube [Pd(NCMe)₄](BF₄)₂(0.202 g, 0.45 mmol) was

dissolved in acetonitrile (15 mL), and the NOPON^Meligand

2

(0.192 g, 0.45 mmol) was added. The yellow solution was

stirred for 30 min, and the solvent was removed under vacuum.

The pale yellow solid was washed with 2 × 10 mL of diethyl

ether and dried in vacuo overnight to afford a pale yellow

powder. Yield: 0.305 g (90%). X-ray quality crystals were

obtained by slow diffusion in 1:3 acetonitrile/diethyl ether.

3

2

oxazoline), 128.5 (d, J _PC) 13.5 Hz, m-aryl), 131.5 (d, J _PC

)

17.5 Hz, o-aryl), 132.1 (s, p-aryl), 137.1 (d, ¹J _PC) 81.5 Hz, ipso-

aryl), 166.0 ppm (s, CdN from uncoordinated oxazoline), 169.5

(s, CdN from coordinated oxazoline). ³¹P{¹H} NMR (121.5

MHz, CDCl₃): δ 133.5 ppm (s). Anal. Calcd for C₂₃H₃₆ClN₂O₄-

PPd: C, 47.85; H, 6.28; N, 4.85. Found: C, 47.75; H, 6.21; N,

4.79.

Selected IR data (MeCN): ν_CN1622 cm^{-1 1}H NMR (300.13

.

MHz, acetonitrile-d₃): δ 1.25 (s, 6 H, NC(CH₃)(CH₃)), 1.55 (s,

6 H, NC(CH₃)(CH₃)), 1.80 (d, 6 H, J _PH) 2.0 Hz, OC(CH₃)-

4

[P d I₂(NOP ON^Me-N,P )] (4). Compound 1 (0.155 g, 0.209

2

(CH₃)), 2.35 (s, 6 H, OC(CH₃)(CH₃)), AB spin system δ_A4.50

(d, 2 H, ²J _HH) 9.1 Hz, OCHH), 4.60 δ_B(d, 2 H, OCHH), 7.55-

7.75 (m, 4 H, aryl), 7.80-7.90 ppm (m, 1 H, aryl). ¹³C{¹H} NMR

(75.5 MHz, acetonitrile-d₃): δ 25.0 (d, ³J _PC) 7.8 Hz, OC(CH₃)-

(CH₃)), 27.0 (s, NC(CH₃)(CH₃)), 28.5 (s, NC(CH₃)(CH₃)), 30.0

mmol) was dissolved in acetone (20 mL), and solid NaI (0.125

g, 0.840 mmol) was added to the pale yellow solution. It

immediatly turned deep red and was stirred for 20 min. The

solvent was removed under reduced pressure, and the red solid

thus obtained was extracted with toluene (5 × 20 mL).

Evaporation of the solvent under vacuum afforded a brown-

red powder, which was further washed with pentane (2 × 10

mL) and dried in vacuo; yield 0.075 g (45%). Selected IR data

(THF): ν_CN1662 s cm^-1(uncoordinated oxazoline), ν_CN1631 s

cm^-1(coordinated oxazoline); (polyethylene): 490 s, 471 vs,

3

(d, J _PC) 2.9 Hz, OC(CH₃)(CH₃)), 72.7 (s, NC(CH₃)₂), 83.8 (s,

2

OCH₂), 86.5 (d, J _PC) 7.4 Hz, OC(CH₃)₂), 128.0-138.2 (m,

aryl), 174.2 (d, ³J _PC) 8.7 Hz, CdN). ³¹P{¹H} NMR (121.5 MHz,

acetonitrile-d₃): δ 106.5 (s). Anal. Calcd for C₂₄H₃₆B₂F₈N₃O₄-

PPd: C, 38.87; H, 4.89; N, 5.67. Found: C, 38.78; H, 4.95; N,

5.80.

1

414 m, 399 w, 378 sh, 372 m, 337 w, 322 m, 232 m, 220 w. H

[P d Cl(NOP ON^Me-N,P ,N)](P F ₆) (2). In a Schlenk tube

2

NMR (300.13 MHz, CD₂Cl₂, 298 K): δ 1.25 (s, 6 H, NC(CH₃)-

(CH₃)), 1.45 (s, 6 H, NC(CH₃)(CH₃)), 1.80 (s, 6 H, OC(CH₃)-

(CH₃)), 1.90 (s, 6 H, OC(CH₃)(CH₃)), AB spin system δ_A4.02

(d, 2 H, ²J _HH) 8.3 Hz, OCHH), δ_B4.06 (d, 2 H, OCHH), 7.40-

were placed together [PdCl₂(NOPON^Me)] (0.105 g, 0.175 mmol)

2

and NH₄PF₆(0.028 g, 0.175 mmol) in CH₂Cl₂(15 mL). The

reaction mixture was stirred for 2 h, and the deep yellow

solution turned pale yellow. The white precipitate formed was

filtered off through Celite, and the filtrate was taken to

dryness under reduced pressure. The pale yellow solid was

washed with a mixture of 1:4 toluene/pentane (2 × 20 mL).

The solid was dried under vacuum overnight; yield 0.104 g

(84%). Selected IR data (CH₂Cl₂): ν_CN1618 cm^-1; (polyethyl-

ene): 471 s, 426 s, 408 m, 378 w, 326 vs, 295 vs. ¹H NMR

(300.13 MHz, CD₂Cl₂): δ 1.50 (s, 6 H, NC(CH₃)(CH₃)), 1.75 (s,

1

7.60 (m, 3 H, aryl), 7.90-8.00 (m, 2 H, aryl). H NMR (300.13

MHz, CD₂Cl₂, 172 K): major species [PdI₂(NOPON-N,P)] δ

1.05 (s, 3 H, NC(CH₃)(CH₃) from uncoordinated oxazoline), 1.15

(s, 3 H, NC(CH₃)(CH₃) from uncoordinated oxazoline), 1.25 (s,

3 H, NC(CH₃)(CH₃) from coordinated oxazoline), 1.55 (s, 3 H,

NC(CH₃)(CH₃) from coordinated oxazoline), 1.67 (s, 3 H, OC-

(CH₃)(CH₃) from uncoordinated oxazoline), 1.70 (s, 3 H, OC-

(CH₃)(CH₃) from uncoordinated oxazoline), 1.85 (s, 3 H,

OC(CH₃)(CH₃) from coordinated oxazoline), 1.90 (s, 3 H, OC-

(CH₃)(CH₃) from coordinated oxazoline), AB spin system δ_A

4

6 H, NC(CH₃)(CH₃)), 1.80 (d, 6 H, J _PH) 2.0 Hz, OC(CH₃)-

(CH₃)), 2.35 (s, 6 H, OC(CH₃)(CH₃)), AB spin system δ_A4.30

(d, 2, ²J _HH) 9.0 Hz, OCHH), δ_B4.45 (d, 2, OCHH), 7.40-7.80

(m, 5 H, aryl). ¹³C{¹H} NMR (50.3 MHz, CD₂Cl₂): δ 25.3 (d,

³J _PC) 7.3 Hz, OC(CH₃)(CH₃)), 27.1 (s, NC(CH₃)(CH₃)), 28.5

(s, NC(CH₃)(CH₃)₂), 29.6 (d, ³J _PC) 2.0 Hz, OC(CH₃)(CH₃)), 73.0

(s, NC(CH₃)₂), 83.7 (d, ²J _PC) 5.1 Hz, OC(CH₃)₂), 84.1 (s, OCH₂),

2

3.75 (d, 2 H, J _HH) 7.5 Hz, OCHH from uncoordinated

oxazoline), δ_B4.00 (d, 2 H, OCHH from uncoordinated oxazo-

2

line), AB spin system δ_A4.10 (d, 2 H, J _HH) 8.0 Hz, OCHH

from coordinated oxazoline), δ_B4.20 (d, 2 H, OCHH from

coordinated oxazoline), 7.40-7.60 (m, 3 H, aryl), 7.75-7.85 (m,

2 H, aryl); minor species δ 1.20 (s, 3 H, NC(CH₃)(CH₃)), 1.70

3

128.0-135.5 (m, aryl), 172.5 (d, J _PC) 10.0 Hz, CdN). ³¹P-

{¹H} NMR (202.5 MHz, CD₂Cl₂): δ 115.7 (s). Anal. Calcd for

(s, 3 H, NC(CH₃)(CH₃)), 1.77 (s, 3 H, OC(CH₃)(CH₃)), 2.35 (s,

2

3 H, OC(CH₃)(CH₃)), AB spin system δ_A4.35 (d, 2 H, J _HH

)

C

₂₂H₃₃ClF₆N₂O₄P₂Pd‚0.5 CH₂Cl₂: C, 36.01; H, 4.53; N, 3.73.

8.5 Hz, OCHH), δ_B4.65 (d, 2 H, OCHH), 7.40-7.60 (m, aryl),

Found: C, 36.04; H, 4.93; N, 3.83.

7.70-7.80 (m, aryl). ¹³C{¹H} NMR (75.5 MHz, CD₂Cl₂):

δ

[P d (Me)Cl(NOP ON^Me-N,P )] (3). In a Schlenk tube were

2

placed together the NOPON^Meligand (0.320 g, 0.76 mmol) and

29.0-29.8 (m, OC(CH₃)₂and NC(CH₃)₂), 71.2 (s, NC(CH₃)₂),

83.2 (two overlapping s, OC(CH₃)₂and OCH₂), 130.0-138.9

(m, aryl), 169.7 (s, CdN). For the low-temperature ¹³C{¹H}

NMR spectrum of [PdI₂(NOPON-N,P)] at 293 K see Table 2.

¹³C{¹H} NMR (75.5 MHz, CD₂Cl₂,172 K): minor species δ 26.8

2

[PdMe(Cl)(COD)] (0.202 g, 0.76 mmol) in 20 mL of CH₂Cl₂.

The pale yellow solution was stirred overnight, and the solvent

was removed under vacuum. The pale yellow oil thus obtained

was washed with 2 × 15 mL of Et₂O to afford a white powder.

The solid was dried in vacuo overnight; yield 0.250 g (57%).

Selected IR data (KBr): ν_CN1660 cm^-1(uncoordinated oxazo-

line), ν_CN1634 cm^-1(coordinated oxazoline); (polyethylene):

479 vs, 406 s, 375 s, 287 vs, 239 s. ¹H NMR (300.13 MHz,

(d, ³J _PC) 5.6 Hz, OC(CH₃)(CH₃)), 28.8-32.5 (m, OC(CH₃)₂and

2

NC(CH₃)₂), 73.3 (s, NC(CH₃)₂), 83.4 (s, OCH₂), 86.7 (d, J _PC

)

3

5.3 Hz, OC(CH₃)₂), 130.2-138.5 (m, aryl), 172.3 (d, J _PC) 8.6

Hz, CdN). ³¹P{¹H} NMR (121.5 MHz, CD₂Cl₂): δ 116.0 ppm

(s). Anal. Calcd for C₂₂H₃₃I₂N₂O₄PPd: C, 33.85; H, 4.26; N,

3.59. Found: C, 34.46; H, 4.20; N, 3.49.

3

CDCl₃): δ 0.75 (d, 3 H, J _PH) 2.9 Hz, Pd-CH₃), 1.25 (s, 3 H,

NC(CH₃)(CH₃)₂from coordinated oxazoline), 1.35 (s, 3 H, NC-

(CH₃)(CH₃) from coordinated oxazoline), 1.55 (s, 6, NC(CH₃)-

(CH₃) from uncoordinated oxazoline), 1.65 (s, 3 H, OC(CH₃)-

(CH₃) from coordinated oxazoline), 1.80 (s, 6 H, OC(CH₃)₂from

uncoordinated oxazoline), 1.90 (s, 3 H, OC(CH₃)(CH₃) from

[P d Cl₂(NOP ON^Me-N,P )] (5). In

a Schlenk tube were

2

placed together the NOPON ligand (0.277 g, 0.66 mmol) and

[PdCl₂(COD)] (0.188 g, 0.66 mmol) in 20 mL of CH₂Cl₂. The

yellow solution was stirred overnight, and the solvent was

removed under vacuum. The yellow powder thus obtained was

washed (2 × 20 mL) with a mixture 1:3 Et₂O/pentane. The

solid was dried in vacuo overnight; yield 0.350 g (89%).

Selected IR data (CH₂Cl₂): ν_CN1662 s cm^-1(uncoordinated

oxazoline), ν_CN1631 s cm^-1(coordinated oxazoline); (polyeth-

2

coordinated oxazoline), AB spin system δ_A3.95 (d, 1 H, J _HH

) 8.0 Hz, OCHH from uncoordinated oxazoline), 4.02 (br, 2 H

overlapping signal for δ_Bpart of the AB for OCHH from

uncooordinated oxazoline and δ_Apart for the AB for OCHH

2

from coordinated oxazoline), δ_B4.15 (d, 1, J _HH) 8.2 Hz,

2980 Organometallics, Vol. 20, No. 14, 2001

Braunstein et al.

ylene): 490 vs, 485 s, 403 m, 379 s, 340 vs, 325 s, 316 m, 289

vs. ¹H NMR (300.13 MHz, CDCl₃): δ 1.50 (br s, 6 H, NC(CH₃)-

(CH₃)), 1.60 (br s, 6 H, NC(CH₃)(CH₃)), 1.80 (s, 6 H, OC(CH₃)-

(CH₃)) 1.85 (s, 6 H, OC(CH₃)(CH₃)), AB spin system δ_A4.15

(d, 2 H, ²J _HH) 7.5 Hz, OCHH), δ_B4.20 (d, 2 H, OCHH), 7.40-

7.60 (m, 3 H, aryl), 8.00-8.10 (m, 2 H, aryl). ¹³C{¹H} NMR

(50.3 MHz, CDCl₃): δ 27.4-27.8 (m, OC(CH₃)₂and NC(CH₃)₂),

70.0-71.0 (br, NC(CH₃)₂), 80.0-84.0 (br, OC(CH₃)₂and OCH₂),

128.0-134.0 (m, aryl), 168.0-170.0 (br, CdN). ³¹P{¹H} NMR

oxazoline), 1.30 (s, 3 H, NC(CH₃)(CH₃) from coordinated

oxazoline), 1.45 (s, 3 H, OC(CH₃)(CH₃) from uncoordinated

oxazoline), 1.58 (s, 3 H, OC(CH₃)(CH₃) from uncoordinated

oxazoline), 1.62 (s, 3 H, OC(CH₃)(CH₃) from coordinated

oxazoline), 1.80 (s, 3 H, OC(CH₃)(CH₃) from coordinated

oxazoline), 3.40 (br s, 2 H, allylic CH₂cis to P), AB spin system

δ_A3.70 (br, 2 H, OCHH from uncoordinated oxazoline), 3.75

(dd, J _HH) 9.5, J _PH) 9.7 Hz, allylic CH₂trans to P), δ_B3.90

(br, 2 H, OCHH from uncoordinated oxazoline), AB spin system

δ_A4.25 (br, 2 H, OCHH from coordinated oxazoline), δ_B4.35

3

(121.5 MHz, CDCl₃): δ 106.5 ppm (s). Anal. Calcd for C₂₂H₃₃

-

3

Cl₂N₂O₄PPd‚0.25CH₂Cl₂: C, 43.13; H, 5.60; N, 4.68. Found:

(d, 2 H, OCHH from coordinated oxazoline), 4.80 (dd, J _HH

)

C, 43.19; H, 5.52; N, 4.54.

[P d (η³-C₃H₅)(NOP ON^Me-N,P )](P F ₆) (6). The NOPON

4.0, ³J _PH) 4.0 Hz, allylic CH₂trans to P), 5.75 (m, 1 H, allylic

CH), 7.50-7.75 (m, 5 H, aryl). ¹H NMR (500.13 MHz, toluene-

d₈, 298 K): δ 1.40 (s, 12 H, NC(CH₃)₂), 1.50 (s, 6 H, OC(CH₃)₂),

Me

2

ligand (0.155 g, 0.37 mmol) and [Pd(η³-C₃H₅)(µ-Cl)]₂(0.067 g,

0.18 mmol) were dissolved in CH₂Cl₂(20 mL). The pale yellow

solution was stirred for 20 min, and solid NH₄PF₆(0.66 g, 0.41

mmol) was added. The reaction mixture was stirred for 3 h,

and the fine white precipitate formed was filtered off by means

of a cannula fitted with a glass fiber filter paper. The filtrate

was taken to dryness to give a pale yellow oil. Trituration with

pentane afforded an off-white solid, which was further washed

with 2 × 10 mL of pentane. The solid was dried under vacuum

overnight; yield 0.185 g (71%). Selected IR data: (CH₂Cl₂), ν_CN

1662 s cm^-1(uncoordinated oxazoline), ν_CN1630 s cm^-1

(coordinated oxazoline); (polyethylene): 490 s, 476 vs, 419 s,

2

3

1.60 (s, 6 H, OC(CH₃)₂), 3.05 (2 H, J _HH) 6.0, J _PH) 6.5 Hz,

Pd-CH₂), AB spin system δ_A3.45 (2 H, ²J _HH) 8.1 Hz, OCHH),

2

3

δ_B3.60 (2 H, J _HH) 8.1 Hz, OCHH), 4.65 (1 H, J _HH) 17.0

Hz, CdCHH), 4.85 (1 H, J _HH) 9.8 Hz, CdCHH), 6.80-7.20

3

(overlapping m for toluene-d₈, CHdCH₂and aryl), 7.90-8.00

(2 H, m, aryl). For the ¹³C{¹H} NMR spectra in CD₂Cl₂and

toluene-d₈see Tables 2 and 4. ¹³C{¹H} NMR (125.7 MHz, CD₂-

Cl₂, 298 K): δ 26.6 (s, NC(CH₃)(CH₃)), 26.9 (s, NC(CH₃)(CH₃)),

3

27.1 (d, J _PC) 2.3 Hz, OC(CH₃)(CH₃)), 27.15 (s, OC(CH₃)-

(CH₃)), 37.5 (br, allylic CH₂cis to P), 67.9 (s, NC(CH₃)₂), 78.7

3

(d, J _PC) 7.4 Hz, OC(CH₃)₂), 79.5 (s, OCH₂), 96.0 (br, allylic

3

1

CH₂trans to P), 127.7 (d, J _PC) 11.5 Hz, m-aryl), 130.2 (d,

344 m, 313 w, 294 m. H NMR (500.13 MHz, CD₂Cl₂, 293 K):

3

²J _PC) 17.2 Hz, o-aryl), 131.1 (s, p-aryl), 132.2 (d, J _PC) 6.7

δ 1.20 (s, 6 H, NC(CH₃)(CH₃)), 1.25 (s, 6 H, NC(CH₃)(CH₃)),

1.65 (s, 6 H, OC(CH₃)(CH₃)), 1.75 (s, 6 H, OC(CH₃)(CH₃)), 3.45

(br s, 2 H, allylic CH₂cis to P), 3.75 (dd, 1 H, ³J _HH) 13.8, ³J _PH

) 14.0 Hz, allylic CH₂trans to P), AB spin system δ_A4.10 (d,

2 H, ²J _HH) 8.5 Hz, OCHH), δ_B4.15 (d, 2 H, OCHH), 4.95 (dd,

Hz, allylic CH), 136.0 (d, J _PC) 63.2 Hz, ipso-aryl), 167.0 (d,

⁴J _PC) 3.0 Hz, CdN). For the low-temperature spectrum, see

Tables 2 and 4. ³¹P{¹H} NMR (121.5 MHz, CDCl₃): δ 138.1

(s). Anal. Calcd for C₂₅H₃₈ClN₂O₄PPd: C, 49.75; H, 6.35; N,

4.65. Found: C, 50.15; H, 6.50; N, 4.60.

3

1 H, J _HH) 7.5, J _PH) 8.0 Hz, allylic CH₂trans to P), 5.75

3

(m, 1 H, J _HH) 13.8, J _HH) 7.5, J _HH) 0.9 Hz, allylic CH),

7.50-7.60 (m, 3H, aryl), 7.65-7.70 (m, 2H, aryl). ¹³C{¹H} NMR

(125.7 MHz, CD₂Cl₂, 298 K): δ 27.8 (s, NC(CH₃)(CH₃)), 28.0

(s, NC(CH₃)(CH₃)), 28.1 (d, ³J _PC) 4.3 Hz, OC(CH₃)(CH₃)), 28.5

(d, ³J _PC) 6.4 Hz, OC(CH₃)(CH₃)), 54.7 (d, ³J _PC) 6.4 Hz, allylic

CH₂cis to P), 68.9 (s, NC(CH₃)₂), 78.8 (d, ³J _PC) 40.1 Hz, allylic

Com p u ta tion a l Deta ils. The calculations were carried out

at the DFT-B3LYP level with the Gaussian 98 program

package.⁶⁴The B3LYP exchange-correlation functional is

made of the Becke’s three-parameter hybrid exchange func-

tional⁶⁵and the Lee, Yang, and Parr correlation functional.⁶⁶

The geometries were fully optimized at that level by the

gradient technique, using the standard LANL2DZ basis set

to which d polarization functions were added to the carbon,

nitrogen, oxygen, phosphorus, and chlorine atoms. In this basis

the innermost core electrons of the palladium atom (up to 3d)

are described by the relativistic pseudo potential of Hay and

Wadt⁶⁷and the remaining outer core and valence electrons

by a (341/541/31) basis set where the two outermost 5p

functions of the standard LANL2DZ basis set have been

replaced by a (41) split of the optimized 5p function from Couty

and Hall.⁶⁸The exponents of the d polarization functions are

0.75, 0.80, 0.85, 0.34, and 0.514 for carbon, nitrogen oxygen,

phosphorus,⁶⁹and chlorine,⁶⁹respectively. The Cartesian

coordinates of the optimized geometries of the systems 9a -

13b are given in the Supporting Information together with

the corresponding total energies.

3

CH₂trans to P), 80.3 (s, OCH₂), 81.15 (d, J _PC) 8.8 Hz,

3

OC(CH₃)₂), 121.5 (d, J _PC) 8.8 Hz, allylic CH), 129.4 (d, J _PC

2

) 12.5 Hz, m-aryl), 130.5 (d, J _PC) 18.1 Hz, o-aryl), 133.1 (s,

1

p-aryl), 136.4 (d, J _PC) 57.3 Hz, ipso-aryl), 168.5 (s, CdN).

³¹P{¹H} NMR (121.5 MHz, CDCl₃): 136.5 (s), -144.0 (sept, J _PF

) 710 Hz, PF₆^-). Anal. Calcd for C₂₅H₃₈F₆N₂O₄P₂Pd: C, 42.42;

H, 4.70; N, 3.96. Found: C, 42.35; H, 4.92; N, 3.95.

[P d (η³-C₃H₅)Cl(NOP ON^Me-N,P )] (7). The NOPON ligand

2

(0.164 g, 0.39 mmol) and [Pd(η³-C₃H₅)(µ-Cl)]₂(0.071 g, 0.19

mmol) were dissolved in CH₂Cl₂(20 mL). The pale yellow

solution was stirred for 20 min, and the solvent was removed

under vacuum. To the pale yellow oil thus obtained were added

2 mL of CH₂Cl₂and 20 mL of pentane to allow precipitation

of a yellow impurity. The suspension was filtered through a

cannula fitted with glass fiber filter paper. The filtrate was

taken to dryness, and the off-white powder thus obtained

washed with 2 × 5 mL of pentane. The solid was dried

overnight under vacuum; yield 0.079 g (93%). Single crystals

of 7b were obtained by slow evaporation of a 1:4 CH₂Cl₂/

pentane solution. Selected IR data: (CH₂Cl₂), ν_CN1659 s cm^-1

(uncoordinated oxazoline), ν_CN1637 s cm^-1(coordinated ox-

azoline); (polyethylene): 495 m, 476 vs, 439 m, 407 s, 371 vs,

X-r a y Str u ctu r a l An a lyses. The diffraction intensities

were collected using Mo KR graphite-monochromated radiation

(64) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;

Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,

J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;

Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;

Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,

C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;

Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;

Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.;

Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;

Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;

Gonzales, C.; Challacombe, M.; Gill, P. M. W.; J ohnson, B.; Chen, W.;

Wong, M. W.; Andres, J . L.; Gonzales, C.; Head-Gordon, M.; Reploge,

E. S.; Pople, J . A. In Gaussian 98, Revision A.5; Pittsburgh PA, 1998.

(65) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.

1

342 m, 287 s. H NMR (500.13 MHz, CD₂Cl₂, 298 K): δ 1.30

(s, 6 H, NC(CH₃)(CH₃)), 1.35 (s, 6 H, NC(CH₃)(CH₃)), 1.70 (s,

6 H, OC(CH₃)(CH₃)), 1.75 (s, 6 H, OC(CH₃)(CH₃)), 3.00 (very

2

br, 2 H, allylic CH₂), AB spin system δ_A4.00 (d, 2 H, J _HH

)

8.5 Hz, OCHH), δ_B4.05 (d, 2 H, OCHH), 4.30 (very br, 1 H,

allylic CH₂), 4.70 (very br, 1 H, allylic CH₂), 6.00 (d quint, 1

3

4

H, J _HH) 10.6, J _PH) 1.7 Hz, allylic CH), 7.40-7.60 (m, 3 H,

aryl), 7.75-7.85 (m, 2 H, aryl). ¹H NMR (500.13 MHz, CD₂-

Cl₂, 177 K): δ 0.90 (s, 3 H, NC(CH₃)(CH₃) from uncoordinated

oxazoline), 1.05 (s, 3 H, NC(CH₃)(CH₃) from uncoordinated

oxazoline), 1.15 (s, 3 H, NC(CH₃)(CH₃) from coordinated

(66) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.

(67) Hay, P. J .; Wadt, W. R. J . Chem. Phys. 1985, 82, 299.

(68) Couty, M.; Hall, M. B. J . Comput. Chem. 1996, 17, 1359.

(69) Szabo, K. J . J . Am. Chem. Soc. 1996, 118, 7818.

Chloro Palladium(II)-(η¹-Allyl) Complex

Organometallics, Vol. 20, No. 14, 2001 2981

Ta ble 6. Selected Cr ysta llogr a p h ic Da ta for Liga n d I a n d Com p lexes 1‚0.5Et₂O‚0.33MeCN a n d 7b

I

1‚0.5Et₂O‚0.33MeCN

7b

formula

C

₂₂H₃₃N₂O₄P

C₂₄H₃₆B₂F₈N₃O₄PPd‚0.5Et₂O‚0.33MeCN

C₂₅H₃₈ClN₂O₄PPd

603.42

monoclinic

P2₁/c

15.6689(5)

10.0997(4)

17.5458(3)

fw (g mol^-1

cryst syst

)

420.49

790.64

triclinic

P1h (#2)

8.3531(13)

10.006(3)

15.030(3)

74.452(7)

76.372(3)

73.973(3)

1145.3(4)

2

1.219

1.49

180

Rigaku/ADSC CCD

10 754

2251

262

0.090; 0.072

1.07

monoclinic

P2₁/c (#14)

10.7713(8)

18.049(3)

17.5134(6)

space group

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³⁾

91.9285(6)

100.359(2)

1407.6(3)

4

1.543

6.75

2731.4(3)

4

1.47

8.68

173

Kappa CCD

14 307

6187

307

0.037; 0.057

1.16

Z

D(calcd) (g‚cm^-3

)

µ (cm^-1

)

temperature (K)

diffractometer

180

Rigaku/ADSC CCD

31 430

3730

424

0.041; 0.035

1.03

no. of reflns total

no. of obsd reflns (I>3σ(I))

no. of variables

residuals (R; R_w)^a

GOF^a

max. peak in final diff map (e/Å³)

0.48

1.91

0.66

a

2

R ) ∑_hkl(||F_obs| - |F_calc|)/∑_hkl|F_obs|; R_w) [∑_hklw(|F_obs| - |F_calc|)²/∑_hklwF_obs

]

^1/2, w ) 1/σ²(F_obs); GOF ) [∑_hklw(|F_obs| - |F_calc|)²/(n_data

-

n

_vari)]^1/2

.

(λ ) 0.71069 Å). The structures were solved by heavy-atom

Patterson methods and expanded Fourier techniques. The non-

hydrogen atoms were refined anisotropically. Hydrogen atoms

were fixed in calculated positions with C-H ) 0.98 Å. Details

of the data collection and refinement procedures are given in

Table 6.

Su p p or tin g In for m a tion Ava ila ble: Computational de-

tails and tables containing X-ray crystal data, atomic coordi-

nates, bond lengths and angles, and thermal displacement

parameters for compounds I, 1‚0.5Et₂O‚0.33MeCN, and 7b.

This material has been deposited with the Cambridge Crystal-

lographic Data Centre as Supplementary publication no.

CCDC-157514, CCDC-157515, and CCDC-157516. Copies of

the data can be obtained free of charge on application to CCDC,

12 Union Road, Cambridge CB2 1EZ, UK (fax: (44) 1223-336-

033; e-mail: deposit@ccdc.cam.ac.uk) and via the Internet at

http://pubs.acs.org.

Ack n ow led gm en t. We are grateful to the Centre

National de la Recherche Scientifique (Paris) and the

Ministe`re de la Recherche (Paris) for financial support

and a Ph.D. grant to F.N. We thank R. Graff and J .

Raya for numerous NMR experiments.

OM010165W

Article Doi

Palladium complexes with a new hemilabile bis(oxazoline)phenylphosphonite ligand. Characterization of an unprecedented chloro palladium(II)-(η1-allyl) complex

DOI: 10.1021/om010165w

Source and publish data:

Authors:

Article abstract of DOI:10.1021/om010165w

Full text of DOI:10.1021/om010165w

Products guided by the article

R&D Labs maybe for 353797-47-4

Relevant to this article

Hot Product