Investigations of benzyl and aryl palladium complexes with pendant hydroxy substituants and their transformation into benzolactones on carbonylation

Organometallics 2005, 24, 1119-1133

1119

Investigations of Benzyl and Aryl Palladium Complexes

with Pendant Hydroxy Substituents and Their

Transformation into Benzolactones on Carbonylation

W. Edward Lindsell,* Daniel D. Palmer, Peter N. Preston,* and

Georgina M. Rosair

Department of Chemistry, School of Engineering and Physical Sciences,

Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, U.K.

Ray V. H. Jones and Alan J. Whitton

Syngenta, Earls Road, Grangemouth, Stirlingshire FK3 8XG, U.K.

Received November 10, 2004

Reactions of 2-hydroxymethylbenzyl halides with Pd(PPh₃)₄afford complexes Pd(CH₂C₆H₄-

2-CH₂OH-κ²C^1R,O)(PPh₃)X (X ) Br, 3; X ) Cl, 4) containing bidentate 2-hydroxymethylbenzyl

ligands. Further reactions of 3 or 4 with NaH produce the binuclear cyclocondensation

product Pd₂(µ-2-OCH₂C₆H₄CH₂)₂(PPh₃)₂, 7, containing a central planar Pd₂O₂unit incorpo-

rated into a system of five fused rings. Compound 7 undergoes phosphine substitution to

form related binuclear products Pd₂(µ-2-OCH₂C₆H₄CH₂)₂(PAr₃)₂{Ar ) p-MeC₆H₄, 8; p-(MeO)-

C₆H₄, 9} but is cleaved by more electron-donating phosphines and by diphosphines to give

mononuclear alkoxides Pd(OCH₂C₆H₄CH₂-κ²C^1R,O)(P-P) (P-P ) dppf, 10; dppe, 11).

Compounds 3, 4, and 7-9 react readily with carbon monoxide to liberate the lactone

3-isochromanone via carbonyl insertion, and the acyl intermediate PdCl(COCH₂C₆H₄-2-CH₂-

OH)(PPh₃), 12b, has been studied spectroscopically. Reactions of 2-halogenobenzenealkanols

with Pd(PPh₃)₄afford simple derivatives with monodentate aryl ligands, trans-Pd(C₆H₄-2-

(CH₂)_nOH)(PPh₃)₂X (n ) 1, X ) Br, 15; n ) 2, X ) I, 17) and the known complex (n ) 1, X

) I, 14), which on reaction with NaH are also converted into binuclear products Pd₂(µ-2-

O(CH₂)_nC₆H₄)₂(PPh₃)₂{n ) 1, 19a (previously reported) and n ) 2, 20}; compound Pd₂(µ-

2-OCH₂C₆H₄)₂{P(C₆H₄-4-OMe)₃}₂, 25, is formed from 19a by phosphine exchange, and

cleavage of 19a or 20 by diphosphines generates new mononuclear complexes 22-24

containing chelating alkoxide ligands. Carbonylations of these arylpalladium derivatives of

2-hydroxyalkylphenyl halides to form the respective benzolactones, phthalide and 3,4-

dihydroisocoumarin, have been investigated. Crystal structures of mononuclear compounds

3, 4, 14, and 17, including intermolecular H-bonding interactions to halogen ligands in the

solid state, and of binuclear compounds 7, 8, and 25 are reported and discussed. The new

complexes are discussed in relation to the mechanism of Pd(0)-catalyzed syntheses of

benzolactones from aromatic halo alcohols; in production of 3-isochromanone, the results

support a process involving coordination of a hydroxyl group prior to reductive elimination

of organic product but with CO insertion into the Pd-C rather than the Pd-O bond.

1. Introduction

3H-2-benzopyran-3-one), 1, of industrial interest as a

precursor for various pharmaceuticals and plant protec-

tion agents, can be prepared from ortho-xylylene deriva-

tives, including 2-hydroxymethylbenzyl halides 2.³Ca-

talysis normally requires the presence of an added base

(or a basic medium⁴) to remove the hydrogen halide

byproduct, and a likely mechanism^1,5for the process is

Palladium-catalyzed carbonylation is a convenient

method for the synthesis of carboxylic acids and esters

from organic halides and related substrates.¹Using this

procedure, lactones can be synthesized from organo-

halogen compounds with adjacent hydroxyl functions.²

Thus, the benzolactone 3-isochromanone (1,4-dihydro-

(2) Mori, M.; Chiba, K.; Inotsume, N.; Ban, Y. Heterocycles 1979,

12, 921. Mori, M.; Washioka, Y.; Urayama, T.; Yoshiura, K.; Chiba,

K.; Ban, Y. J. Org. Chem. 1983, 48, 4058. Martin, L. D.; Stille, J. K. J.

Org. Chem. 1982, 47, 3630. Morin-Phelippeau, B.; Favre-Fafet, A.;

Hugues, F.; Commereuc, D.; Chauvin, Y. J. Mol. Catal. 1989, 51, 145.

Lin, Y.-S.; Yamamoto, A. Tetrahedron Lett. 1997, 38, 3747.

(3) Cowell, A.; Stille. J. K. J. Am. Chem. Soc. 1980, 102, 4193.

(4) Urata, H.; Maekawa, H.; Takahashi, S.; Fuchikami, T. J. Org.

Chem. 1991, 56, 4320.

* To whom correspondence should be addressed. (W.E.L.) E-mail:

w.e.lindsell@hw.ac.uk. Tel: + 44 131 451 8028. Fax: + 44 131 451

3180. (P.N.P.) E-mail: p.n.preston@hw.ac.uk. Tel: + 44 131 451 8035.

(1) For example see: Tsuji, J. Palladium Reagents and Catalysts;

Wiley: New York, 1995. Cornils, B., Hermann, W. A., Eds. Applied

Homogeneous Catalysis with Organometallic Compounds; VCH: Wein-

heim, Part 1, 1996. Colquhoun, H. M.; Thompson, D. J.; Twigg, M. V.

Carbonylation. Direct Synthesis of Carbonyl Compounds; Plenum: New

York, 1991. Heck, R. F. Palladium Reagents in Organic Syntheses;

Academic Press: New York, 1985.

(5) (a) Milstein, D. Acc. Chem. Res. 1988, 21, 428. (b) Lin, Y.-S.;

Yamamoto, A. Organometallics 1998, 17, 3466. See also: Yamamoto,

A. J. Chem. Soc., Dalton Trans. 1999, 1027, and references therein.

Publication on Web 02/09/2005

1120 Organometallics, Vol. 24, No. 6, 2005

Lindsell et al.

Scheme 1

to afford pale yellow cubic crystals. This product was

characterized as bromo[2-(hydroxymethyl-κO)benzyl-

κC^1R]triphenylphosphinepalladium, 3, on the basis of

elemental analysis, spectroscopic studies, and X-ray

diffraction (XRD). NMR spectroscopy supports the 1:1

stoichiometry of triphenylphosphine:hydroxymethylben-

zyl ligands and indicates the presence of a unique

isomeric species with a single ³¹P{¹H} resonance at δ

42.6 ppm in CDCl₃solution (δ 45.7 ppm in solid state);

1

important H resonances include a doublet at δ 2.70

ppm (J_H-P2.5 Hz), assigned to the metal-bound meth-

ylene group, a singlet at δ 4.55 ppm from CH₂O, and a

broad singlet assignable to the OH group at ca. δ 5.2-

5.5 (variable) ppm. The ¹³C{¹H} spectrum is also

consistent with the formulation, with resonances as-

signable to PdCH₂and PdOCH₂groups at 32.5 and 64.2

ppm, respectively, in CDCl₃(33.0 and 65.4 ppm in the

solid state). The ESI+ mass spectrum (120 °C) does not

include a molecular ion but exhibits peaks for binuclear

ions [2M - H_xBr]⁺(x ) 0, 1, 2) and mononuclear

fragments, including [M - H_xBr]⁺. Compound 3 is stable

as a solid on exposure to air over many days at ambient

temperatures and also stable in solution under an

atmosphere of nitrogen, but solutions exposed to air for

extended periods decompose, forming black deposits.

illustrated in Scheme 1, although none of the steps in

an active catalytic system has been directly verified for

this substrate; moreover, coordination of the hydroxyl

group before reductive elimination of the ester link (cf.

refs 5b, 6) and the insertion of CO into the Pd-C rather

than the Pd-O bond (cf. ref 7) have not been proven.

The nature of the active Pd(0) species is also dependent

on the precursor, which may be a Pd(II) compound;

when tetrakis(triphenylphosphine)palladium is em-

ployed, PdL_nis probably Pd(PPh₃)₂.⁸

With the aim of elucidating the steps in the synthesis

of 3-isochromanone and related benzolactones, we have

undertaken a study of reactions of 2-hydroxymethyl-

benzyl and 2-hydroxyalkylphenyl halides with pal-

ladium(0) species to establish the structures and reac-

tivity of intermediates in their cyclocarbonylation.

In a reaction similar to that described above, 2-hy-

droxymethylbenzyl chloride 2b and tetrakis(triphen-

ylphosphine)palladium afford the chlorine analogue

chloro[2-(hydroxymethyl-κO)benzyl-κC^1R]triphenyl-

phosphinepalladium, 4, isolable as pale yellow crystals.

This compound was also characterized by elemental

analysis, ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectra in

solution and solid state, and XRD. NMR spectral

parameters for compound 4 are similar to those of 3,

providing evidence for one principal isomeric form (see

Experimental Section). A broad resonance assignable

1

to the hydroxyl hydrogen is observed in the H NMR

2. Results

spectrum in CDCl₃at variable shifts in the range δ

6-6.7 ppm, and the IR spectrum in Nujol includes a

ν(OH) band at ca. 3200 cm^-1. The ESI+ mass spectrum

shows only a very weak signal for the molecular ion but

significant peaks for binuclear ions [2M - H_xCl]⁺and

mononuclear fragments, including [M - Cl]⁺.

2.1.2. Crystal Structures of Compounds 3 and 4.

Single crystals of nonsolvated 3 and monosolvated 4‚

CH₂Cl₂were obtained by slow diffusion of petroleum

ether into a solution of the respective compound in

dichloromethane, and these were subjected to analysis

by XRD. Figure 1 depicts the derived molecular struc-

tures, which are closely related, and selected bond

lengths and angles are listed in Table 1.

The geometries around the Pd center are approxi-

mately square planar with the rms deviations from the

mean plane of Pd and the four coordinating atoms (C,

O, P, and halogen) being 0.0313 and 0.1125 Å for

compounds 3 and 4, respectively; angles P-Pd-halogen

show the largest deviations from 90° {3: P(1)-Pd(1)-

Br(1) ) 99.44(10)°; 4: P(1)-Pd(1)-Cl(1) ) 100.24(3)°},

with other angles subtended at the metal between cis

coordinating atoms lying in the range 86-88°. The

2-hydroxymethylbenzyl ligands are C-O chelating and

form six-membered palladacycles with boatlike confor-

mations. The isomer obtained, in both cases, contains

phosphine trans to the hydroxyl group: this places the

2.1. Derivatives of 2-Hydroxymethylbenzyl Ha-

lides. The palladium-catalyzed reaction of carbon mon-

oxide (1 atm) with 2-hydroxymethylbenzyl bromide 2a

is a route for the synthesis of 3-isochromanone with a

reported yield of 71%, although in our hands, using

PdCl₂(PPh₃)₂activated by hydrazine as catalyst and K₂-

CO₃as base in tetrahydrofuran according to the pub-

lished procedure,³significantly lower conversions were

obtained. However, with a catalytic system comprising

Pd(PPh₃)₄(2-5 mol %) and NEt(i-Pr)₂as base, at 60 °C

in toluene, we have achieved virtually quantitative

conversion to the lactone within 2 h. To understand this

process more fully, we therefore investigated reactions

of Pd(PPh₃)₄with 2-hydroxymethylbenzyl halides.

2.1.1. Synthesis of Palladium Compounds by

Oxidative Addition. Solutions of equimolar amounts

of 2-hydroxymethylbenzyl bromide 2a and tetrakis-

(triphenylphosphine)palladium in toluene at room tem-

perature produce an off-white precipitate, which can be

recrystallized from dichloromethane-petroleum ether

(6) Van Leeuwen, P. W. N. M.; Zuideveld, M. A.; Swennenhuis, B.

H. G.; Freixa, Z.; Kamer, P. C. J.; Goubitz, K.; Fraanje, J.; Lutz, M.;

Spek, A. L. J. Am. Chem. Soc. 2003, 125, 5523.

(7) (a) Macgregor, S. A.; Neave, G. W Organometallics 2003, 22,

4547. (b) Macgregor, S. A.; Neave, G. W Organometallics 2004, 23,

891, and references therein.

(8) For example see: Amatore, C.; Pflu¨ger, F. Organometallics 1990,

9, 2276.

Benzyl and Aryl Palladium Complexes

Organometallics, Vol. 24, No. 6, 2005 1121

Figure 1. Molecular structures of (a) compound 3; (b) compound 4 (ellipsoids drawn at the 50% probability level).

Table 1. Selected Bond Lengths [Å] and Angles

[deg] of Compounds 3 and 4

3

4

Pd(1)-C(1)

2.067(13)

2.123(9)

2.194(3)

2.5056(18)

1.49(2)

2.057(3)

2.1521(18)

2.2103(7)

2.4082(7)

1.484(4)

1.406(4)

1.505(4)

1.454(3)

86.66(9)

86.95(8)

171.56(6)

169.44(8)

86.86(5)

100.24(3)

108.84(17

121.22(15)

108.0(2)

Pd(1)-O(8)

Pd(1)-P(1)

Pd(1)-Halogen(1)

C(1)-C(2)

C(2)-C(7)

1.41(2)

C(7)-C(8)

1.53(2)

C(8)-O(8)

1.454(19)

86.6(5)

C(1)-Pd(1)-O(8)

C(1)-Pd(1)-P(1)

O(8)-Pd(1)-P(1)

C(1)-Pd(1)-Halogen(1)

O(8)-Pd(1)-Halogen(1)

P(1)-Pd(1)-Halogen(1)

C(2)-C(1)-Pd(1)

C(8)-O(8)-Pd(1)

O(8)-C(8)-C(7)

87.7(4)

174.0(3)

171.7(4)

86.2(3)

99.44(10)

110.5(9)

122.4(8)

107.8(12)

Figure 2. Hydrogen-bonding network in the lattice of

compound 3.

monodentate ligand with the stronger trans-influence

(PPh₃) opposite the weaker O-donor of the chelate; Pd-P

bonds {2.194(3) and 2.2103(7) Å} and Pd-O bonds

(2.123(9) and 2.1521(18) Å) are both slightly shorter in

compound 3 than in compound 4. In contrast, the Pd-C

bond lengths are virtually the same {2.067(13) and

2.057(3) Å}, although the marginally longer bond in 3

may relate to the larger trans-influence of Br compared

to Cl. The ortho-phenylene planes of the chelating

ligands lie at angles of 53.1(4)° and 51.58(8)° to the

palladium coordination planes in compounds 3 and 4,

respectively.

There are intermolecular hydrogen-bonding interac-

tions between the coordinated hydroxyl groups and

halogen ligands in both compounds 3 and 4. In com-

pound 3, the H-bonds to Br have distances H‚‚‚Br ) 2.40

Å and O‚‚‚Br ) 3.232(10) Å and angle O-H‚‚‚Br )

168.9° and generate a linked chain of complexes with

alternating orientations, as illustrated in Figure 2.

In the solvated crystals of compound 4, there are no

significant interactions between the incorporated CH₂-

Cl₂and the palladium complexes, but a discrete cen-

trosymmetric binuclear entity is created by dual hydro-

gen bonds between hydroxyl groups and chlorine ligands

on adjacent complexes; see Figure 3, with distances

H‚‚‚Cl ) 2.20 Å and O‚‚‚Cl ) 3.016(2) Å and angle

O-H‚‚‚Cl ) 164.8°.

Figure 3. Hydrogen bonding between adjacent molecules

of compound 4 in the crystal.

Few examples of palladium alcohol complexes have

been structurally characterized, but it is of interest to

compare the structure of the reported ionic species [Pd-

{(2-HOCH₂CH₂-κO)C₆H₄-κC¹}(tmeda)]NO₃, 5, which con-

tains a six-membered chelate ring formed by an aryl-

alcohol ligand and also a bidentate dinitrogen ligand.⁹

In compound 5 there is hydrogen-bonding between the

(9) Alsters, P. L.; Boersma, J.; Smeets, W. J. J.; Spek, A. L.; van

Koten, G. Organometallics 1993, 12, 1639.

1122 Organometallics, Vol. 24, No. 6, 2005

Lindsell et al.

Scheme 2^a

hydroxyl group of the cation and the nitrate anion but

no intermolecular interactions. Also, the Pd-O distance

of 2.076(4) Å is shorter than those of compounds 3 and

4, reflecting the positive charge on the ionic complex

and the weaker N-donor trans ligand.

2.1.3. Deprotonation of Compounds 3 and 4:

Formation and Reactions of Binuclear Compound

7. The hydroxyl group in the cationic complex 5 is

reported to be weakly acidic, and deprotonation with

potassium methoxide forms the neutral alkoxide [Pd-

{(2-OCH₂CH₂-κO)C₆H₄-κC¹}(tmeda)], 6, which is stable

in the solid state but decomposes slowly in solution.⁹It

was also reported that reaction of 5 with pyridine leads

to displacement of the coordinated alcohol ligand rather

than formation of the alkoxide.⁹

^aReagents and conditions: (i) toluene, RT, 12 h; (ii) NaH,

PPh₃, THF, RT, 12 h; (iii) PAr3, toluene, RT, 12 h; (iv)

diphosphine (P-P), toluene, RT, 3 h.

compounds 3 and 4. A singlet resonance at δ 39.7 ppm

in the ³¹P NMR spectrum indicated the presence of only

one phosphorus environment, and no changes were

observed in the ¹H and ³¹P NMR spectra over the

temperature range 25-60 °C. The ESI+ mass spectrum

includes a significant peak with m/z ) 999, assignable

to binuclear product 7 as an adduct with Na⁺, [M +

Na]⁺. Air-stable solid 7 is insoluble and unreactive to

water, used to remove NaCl byproduct; crystallization

generally produced solvated materials including water

or dichloromethane molecules as shown by elemental

and XRD analyses (vide infra).

Compound 7 did not react with excess triphenylphos-

phine, as evinced from its preparation in the presence

of an excess of this ligand, and, similarly, no reaction

was observed in solutions at ambient temperature with

the sterically demanding ligands trimesitylphosphine

or tris(2-methylphenyl)phosphine. However, tris(4-me-

thylphenyl)phosphine and tris(4-methoxyphenyl)phos-

phine react in toluene with 7, causing substitution of

phosphine ligands to form the new binuclear products

[Pd{(µ-2-OCH₂-κO)C₆H₄CH₂-κC^1R}(PAr₃)]₂, 8, Ar )

4-MeC₆H₄; 9, Ar ) 4-MeOC₆H₄, isolable in good yields.

Compounds 8 and 9 were fully characterized by elemen-

tal analysis and spectroscopic studies and show little

variation in NMR parameters of the bridging organic

ligand from those of the closely related parent compound

7; compound 8 was also subjected to structural analysis

by XRD (vide infra). Neither P(C₆H₄-4-Me)₃nor P(C₆H₄-

4-OMe)₃cleave the alkoxy bridge. The more electron-

rich, monodentate ligands PMe₃and PMe₂Ph react to a

greater extent with compound 7, and, although the final

products were unstable and incompletely characterized,

it appears that cleavage of the binuclear structure does

occur.

By analogy, simple deprotonation of complex 3 or 4

might produce a chelating benzyl-alkoxide ligand in an

anionic complex A or, if accompanied by loss of halide

in the presence of a 2e-ligand L, may lead to a neutral

complex B: however, equimolar mixtures of 3 or 4 with

noncoordinating bases 1,8-diazabicyclo[5.4.0]undec-7-

ene (DBU) or 1,8-bis(dimethylamino)naphthalene (“Pro-

ton sponge”) or with ethyldiisopropylamine (the base

employed in our catalytic system), in the absence or

presence of excess triphenylphosphine, were investi-

gated, but no reaction was observed and only unreacted

substrates could be detected and isolated. On the other

hand, reaction of 3 or 4 with 1 equiv of sodium hydride

occurred readily in the presence of free triphenylphos-

phine to form the new binuclear complex bis[2-(µ-

oxomethyl-κO)benzyl-κC^1R]bis(triphenylphosphine)-

dipalladium, 7, in ca. 77% isolable yield, by deprotona-

tion and displacement of halide by a bridging alkoxy

group (Scheme 2). In the absence of triphenylphosphine,

yields of this compound were lower and variable and,

although not incorporated in the final product, addition

of ca. 1.1 molar equiv of PPh₃was found to be important

for the good yield and reproducibility of this cyclocon-

densation. Compound 7 was characterized by elemental

analysis, spectroscopy, and XRD. The ¹H NMR spectrum

confirms the 1:1 stoichiometry of phosphine:oxometh-

ylbenzyl ligands and includes resonances at δ 2.36 and

3.34 ppm for PdCH₂and µ-OCH₂groups, respectively,

the latter shifted by over 1 ppm to high field from the

hydroxymethyl resonances of the mononuclear precur-

sors (3, 4); also, respective ¹³C resonances for these

methylene groups at δ 25.6 and 68.2 ppm in compound

7 are both significantly shifted from the resonances of

Alkoxy-bridge cleavage was clearly established in the

reactions of compound 7 with the bidentate diphosphine

ligands 1,1′-bis(diphenylphosphino)ferrocene (dppf) and

1,2-bis(diphenylphosphino)ethane (dppe), from which

the mononuclear products Pd{(2-OCH₂-κO)C₆H₄CH₂-

κC^1R}(dppf), 10, and Pd{(2-OCH₂-κO)C₆H₄CH₂-κC^1R}-

(dppe), 11, were isolated; see Scheme 2. These com-

pounds were characterized as solvated crystalline solids

Benzyl and Aryl Palladium Complexes

Organometallics, Vol. 24, No. 6, 2005 1123

Figure 4. Molecular structures of (a) compound 7 (ellipsoids drawn at the 40% probability level); (b) compound 8 (ellipsoids

drawn at the 50% probability level).

Table 2. Selected Bond Lengths [Å] and Angles

[deg] of Compounds 7 and 8

7

8

Pd(1)-C(1)

2.034(6)

2.082(4)

2.128(4)

2.2283(15)

1.472(9)

1.398(9)

1.505(9)

1.402(7)

87.1(2)

164.4(2)

77.30(16)

93.99(18)

178.45(13)

101.58(11)

102.70(16)

104.8(4)

119.4(6)

119.1(5)

111.2(5)

121.4(3)

134.2(4)

2.064(11)

2.044(7)

2.146(7)

2.227(3)

1.457(16)

1.425(16)

1.493(17)

1.420(12)

89.7(4)

Pd(1)-O(8)

Pd(1)-O(8)A

Pd(1)-P(1)

C(1)-C(2)

C(2)-C(7)

C(7)-C(8)

C(8)-O(8)

C(1)-Pd(1)-O(8)

C(1)-Pd(1)-O(8)A

O(8)-Pd(1)-O(8)A

C(1)-Pd(1)-P(1)

O(8)-Pd(1)-P(1)

O(8)A-Pd(1)-P(1)

Pd(1)-O(8)-Pd(1)A

C(2)-C(1)-Pd(1)

C(7)-C(2)-C(1)

C(2)-C(7)-C(8)

O(8)-C(8)-C(7)

C(8)-O(8)-Pd(1)

C(8)-O(8)-Pd(1)A

165.2(4)

75.6(3)

91.0(3)

178.3(2)

103.8(2)

104.4(3)

108.6(7)

122.1(11)

117.9(9)

109.3(9)

121.2(6)

133.5(6)

Figure 5. Structure around the five fused rings at the

center of compound 7.

bond trans to phosphine is longer in compound 7,

containing PPh₃, whereas the other Pd-O bond is

marginally shorter. Each bridging alkoxy arm is part

of a boat-shaped, six-membered ring which chelates a

Pd(II) center with a Pd-C distance of 2.034(6) Å in 7

and 2.064(11) Å in 8. The coordination sphere around

Pd is completed by a phosphine ligand with virtually

identical Pd-P bond lengths in both compounds:

2.2283(15) Å in 7 and 2.227(3) Å in 8. The geometry

around each Pd atom is distorted square-planar with

the four angles varying in the range 75-104°, the

largest being P(1)-Pd-O(8)A {101.58(11)° in 7;

103.8(2)° in 8}, but the sum of the angles around each

Pd is 359.97° in 7 and 360.1° in 8, indicating near

planarity of the coordination sphere; this planarity

essentially extends over the eight central atoms,

Pd₂O₂P₂C₂. The ortho-xylylene units are also planar,

and the angles of these aromatic planes to the coordina-

tion plane are 67.06(15)° and 53.6(4)° in 7 and 8,

respectively. Overall the five fused rings form an

extended chairlike arrangement, shown in Figure 5.

The structures of 7 and 8 are related to that of the

reported¹⁰aryl-alkoxy derivative [Pd{(µ-2-OCH₂-κO)-

C₆H₄-κC¹}(PPh₃)]₂, 17a, which contains five-membered

C-O chelate rings and is discussed below. Diaryloxy-

bridged organopalladium dimers have been reported by

Hartwig and co-workers:¹¹the structurally character-

by elemental analysis, by ESI+ mass spectra, which

gave molecular ions, and by NMR spectra. Two doublets

are present in the ³¹P{¹H} NMR spectra, assignable to

the two, mutually coupled, inequivalent cis P-nuclei of

the chelating diphosphine ligands, and the ¹H NMR

spectra show resonances with appropriate shifts and

relative intensities assignable to the bidentate oxom-

ethylbenzyl and diphosphine entities. Solutions of both

compounds 10 and 11 in chlorinated solvents decompose

over several hours so that crystals suitable for analysis

by XRD could not be grown. Attempts to react compound

7 with the bidentate nitrogen ligands N,N,N′,N′-

tetramethyl-1,2-ethanediamine (tmeda) and 1,10-phen-

athroline (phen) at temperatures between 20 and 50 °C

were unsuccessful, leading only to recovery of starting

materials.

2.1.4. Crystal Structures of Compounds 7 and 8.

Solvated single crystals 7‚CH₂Cl₂and 8‚CH₂Cl₂were

obtained from dichloromethane/petroleum ether and

subjected to analysis by XRD.

Discrete binuclear molecules of 7 and 8 were identi-

fied, as depicted in Figure 4, with negligible interaction

between the complexes and dichloromethane. Selected

geometrical parameters are listed in Table 2. Both

compounds have related centrosymmetric structures,

comprising a central planar rhomboid, PdOPdO, with

Pd-O distances 2.082(4) and 2.128(4) Å in complex 7,

and 2.044(7) and 2.146(7) Å in complex 8; the Pd-O

(10) Ferna´ndez-Rivas, C.; Ca´rdenas, D. J.; Martin-Matute, B.;

Monge, A.; Gutie´rrez-Puebla, E.; Echavarren, A. M. Organometallics

2001, 20, 2998.

(11) Mann, G.; Shelby, Q.; Roy, A. H.; Hartwig, J. F. Organometallics

2003, 22, 2775. Mann, G.; Incarvito, C.; Rheingold, A. L.; Hartwig, J.

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

1124 Organometallics, Vol. 24, No. 6, 2005

Lindsell et al.

Scheme 3^a

ized di-tert-butylferrocenylphosphine derivative [Pd(µ-

OC₆H₄-4-OMe)(C₆H₄-4-Me){PBu^t₂(Fc)}]₂contains two

planar, four-coordinate Pd centers with large P-Pd-O

angles of 102.9°, comparable to those in 7 and 8, but

the central Pd₂O₂ring adopts a nonplanar, puckered

geometry.¹¹

2.1.5. Carbonylation of Palladium Complexes

Derived from 2-Hydroxymethylbenzyl Halides.

Carbon monoxide at atmospheric pressure reacts over

0.5-2 h with mononuclear compounds 3 and 4 or

binuculear 7 in tetrahydrofuran to give intense yellow-

orange colored solutions from which 3-isochromanone

can be isolated in high yields, accompanied by palladium

residues which rapidly turn black in the solid state.

Therefore, the palladacycles in these complexes must

form insertion products with CO (cf. Scheme 1) but, even

under these mild conditions, undergo facile subsequent

reductive elimination of lactone. On the other hand, the

mononuclear diphosphine complexes with the deproto-

nated 2-oxomethylbenzyl ligands, 10 and 11, failed to

react with CO under the same experimental conditions.

The nature of the insertion product in the above

reaction of complex 4 with CO was subjected to further

investigation. After 20 min, the reaction mixture was

rapidly cooled to -78 °C and palladium-containing

products present were collected after precipitation by

addition of petroleum ether. The IR spectrum of the

resulting yellow solid included a strong band at 1707

cm^-1(KBr disk) assignable to a carbonyl function;

reported vibrational frequencies of the acyl group in

phenylacetyl complexes Pd(COCH₂C₆H₅)X(PPh₃)₂are

1670 cm^-1(X ) Cl in CD₂Cl₂)¹²and 1696 cm^-1(X ) Br

in Nujol).¹³Monitoring the IR spectra of solutions of the

yellow product in CH₂Cl₂showed that this band (1709

cm^-1) completely decayed over 20-30 min at ambient

temperature with the concomitant growth of a band at

1750 cm^-1from 3-isochromanone. This instability of the

insertion product in solution prevented the isolation of

analytically pure samples or the growth of crystals

suitable for XRD. However, NMR studies on freshly

prepared solutions were informative: a ³¹P resonance

occurred at δ27.4 ppm, shifted 14 ppm to low frequency

^aReagents and conditions: (i) CO (1 atm), THF, RT, 20 min;

(ii) THF, RT, <26 min.

Scheme 4^a

^aReagents and conditions: (i) Pd(PPh₃)₄, toluene; (a) X ) I,

RT, 12 h; (b) X ) Br, 70 °C, 48 h.

2.2.1. Products of Oxidative Addition to Pd(0).

Echavarren and co-workers¹⁰have reported that 2-io-

dobenzenemethanol 13a reacts with tetrakis(tri-

phenylphosphine)palladium at 40 °C to form trans-[2-

(hydroxymethyl)phenyl]iodobis(triphenylphosphine)-

palladium, 14, in good yield: in addition to 14, we have

also obtained the bromo analogue, PdBr(C₆H₄-2-CH₂-

OH)(PPh₃)₂, 15, by reaction of 2-bromobenzenemethanol

13b and Pd(PPh₃)₄at 70 °C. Similarly (see Scheme 4),

we found that 2-iodobenzeneethanol 16 adds oxidatively

to Pd(PPh₃)₄at ambient temperature to form trans-Pd-

(C₆H₄-2-CH₂CH₂OH)I(PPh₃)₂, 17, but that the corre-

sponding reaction of 2-bromobenzeneethanol with Pd-

(PPh₃)₄requires temperatures > 80 °C and under these

conditions decomposition of the initial product occurs

so that it was not possible to obtain pure samples of

the bromo analogue, trans-PdBr(C₆H₄-2-CH₂CH₂OH)-

(PPh₃)₂. The new compounds have been characterized

by elemental analyses and by NMR and mass spectra,

with 15 showing closely similar NMR parameters to

those reported¹⁰for compound 14. Related products,

described in the literature, include the structurally

characterized PdBr(C₆H₄-2-CH₂CH₂OH)(tmeda), 18, con-

taining a chelating diamine ligand,⁹and a complex with

a longer side-chain alcohol, PdBr(C₆H₄-2-CH₂CH₂CMe₂-

OH)(dppf),¹⁵containing a chelating diphosphine, but

both compounds have a cis arrangement of aryl and

bromide ligands. Products 14, 15, and 17 contain Pd-

aryl bonds and, as confirmed by crystal structure

determinations of 14 and 17, possess uncoordinated

hydroxyl groups; five- or six-membered C-O chelate

systems are not formed by displacement of a phosphine

ligand, in contrast to the facile formation of oxapalla-

dacycles in the benzylpalladium derivatives 3 and 4

under similar or milder reaction conditions.

1

of that in complex 4; the H NMR spectrum included

resonances at δ 4.16 and 4.01 ppm assignable to

hydrogen nuclei of the two ortho-methylene groups, both

significantly shifted from resonances expected for a

PdCH₂system and consistent with the presence of PdO-

(H)CH₂and PdCOCH₂groupings {cf. PdCOCH₂: δ 3.4

ppm in Pd(COCH₂C₆H₅)Cl(PPh₃)₂;¹²δ 3.9 ppm in Pd-

(COCH₂C₆H₅)Cl(PEt₃)₂¹⁴}. This evidence supports the

formation of acyl complex Pd{(2-HOCH₂-κO)C₆H₄CH₂-

CO}Cl(PPh₃), 12b, by insertion of CO into the Pd-C

rather than the Pd-O bond (Scheme 3). The EI mass

spectrum of 12b showed a peak at m/z ) 551, [M - 1]⁺.

2.2. Derivatives of 2-Halogenobenzenealkanols.

For comparison with the studies of benzylpalladium

compounds derived from 2-hydroxymethylbenzyl halides

2, we have investigated the properties of related aryl-

palladium compounds derived from 2-halogenobenzene-

methanol and -ethanol.

(12) Gavin˜o, R.; Pellegrini, S.; Castanet, Y.; Mortreux, A.; Mentre´,

O. Appl. Catal. A 2001, 217, 91.

(13) Kudo, K.; Sato, M.; Hidai, M.; Uchida, Y. Bull. Chem. Soc. Jap.

1973, 46, 2820.

(15) (a) Palucki, M.; Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc.

1996, 118, 10333. (b) Widenhoefer, R. A.; Zhong, H. A.; Buchwald, S.

L. J. Am. Chem. Soc. 1997, 119, 6787.

(14) Becker, Y.; Stille, J. K. J. Am. Chem. Soc. 1978, 100, 838.

Benzyl and Aryl Palladium Complexes

Organometallics, Vol. 24, No. 6, 2005 1125

Figure 6. Molecular structures of (a) compound 14; (b) compound 17 (ellipsoids drawn at the 50% probability level).

Table 3. Selected Bond Lengths [Å] and Angles

[deg] of Compounds 14 and 17

14

17

Pd(1)-C(1)

2.030(11)

2.330(3)

2.336(3)

2.6900(12)

1.385(15)

1.452(14)

1.448(15)

-

2.007(11)

2.3355(19)

2.7067(11)

1.391(16)

1.386(16)

1.518(15)

1.40(2)

Pd(1)-P(2)

Pd(1)-P(1)

Pd(1)-I(1)

C(1)-C(6)

C(1)-C(2)

C(6)-C(7)

C(7)-C(8)

C(7)-O(8)

1.486(13)

-

C(8)-O(1)

1.323(12)

87.61(5)

174.39(11)

167.0(3)

92.66(5)

116.9(9)

124.5(9)

118.9(10)

-

C(1)-Pd(1)-P(2)

C(1)-Pd(1)-P(1)

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

C(1)-Pd(1)-I(1)

P(2)-Pd(1)-I(1)

P(1)-Pd(1)-I(1)

C(2)-C(1)-Pd(1)

C(6)-C(1)-Pd(1)

C(1)-C(6)-C(7)

C(6)-C(7)-O(8)

C(6)-C(7)-C(8)

C(7)-C(8)-O(1)

88.1(3)

87.8(3)

175.84(10)

167.1(3)

90.11(7)

94.03(7)

116.0(8)

124.3(8)

118.3(11)

112.5(9)

-

Figure 7. Hydrogen-bonding network in the lattice of

compound 17.

located from the X-ray data, but there is a close contact

between this oxygen and the C(5)-H(5) unit of the aryl

ligand {O‚‚‚C(5) 2.863(17) Å; O‚‚‚H(5) 2.56 Å; angle

O-H(5)-C(5) 98.7°}; there are no significant interac-

tions between the OH group and atoms on neighboring

molecules, with the separation O‚‚‚I being >5 Å. In

contrast, the terminal hydroxyl group on the longer side-

chain of 17 shows evidence for intermolecular hydrogen

bonding to an iodide ligand on an adjacent molecule

{H‚‚‚I 2.72 Å, O‚‚‚I 3.493(13) Å, angle O-H‚‚‚I 153.3°}

to form a linked chain; see Figure 7: it may be noted

that intramolecular hydrogen bonding has been re-

ported between OH and Br in PdBr(C₆H₄-2-CH₂CH₂-

OH)(tmeda), 18.⁹The crystal structures of complexes

14 and 17 present no clear explanation for the relatively

119.9(12)

128.5(13)

-

2.2.2. Crystal Structures of Compounds 14 and

17. Solvated crystals 14‚CH₂Cl₂and 17‚2CH₂Cl₂, ob-

tained from solutions in dichloromethane/petroleum

ether, were subjected to analysis by XRD. Derived

structures and atomic numbering of individual mol-

ecules are shown in Figure 6, and Table 3 lists impor-

tant geometrical parameters.¹⁶

Molecules 14 and 17 are trans square planar, with

planarity being supported by the sum of the four angles,

360.0° and 360.54°, respectively, but with angles P-Pd-I

> 90° and angles C-Pd-P < 90°. Unlike 14, the

molecular structure of 17 includes a mirror plane,

containing the ortho-phenylene ring, which bisects the

P-Pd-P angle, with the OH group lying just off this

plane, resulting in 50% disorder. Pd-P, Pd-I, and

Pd-C bond lengths are similar in both complexes. The

Pd-C(aryl) bonds are shorter than the Pd-C(benzyl)

bonds of complexes 3 and 4, and the two trans-Pd-P

bonds in 14 and 17 are longer than the Pd-P bonds

trans to OH in the chelated complexes. In 14 or 17,

respectively, the aromatic rings lie approximately {85.8-

(3)°}or precisely perpendicular to the coordination plane;

the hydroxyl groups point away from the palladium

center and do not interact with the metal. In 14, the

hydrogen atom of the hydroxyl group could not be

1

high field H NMR shift (δ ∼0 ppm) of the hydroxyl

groups, but these are surrounded by phenyl rings of the

triphenylphosphine ligands and could be magnetically

shielded by these ligands in solution.

2.2.3. Formation and Reactions of Binuclear

Oxoarylpalladium Complexes. The mononuclear com-

plex 14 has previously been transformed via a silyl

derivative or, reportedly less reliably, by direct depro-

1126 Organometallics, Vol. 24, No. 6, 2005

Lindsell et al.

Scheme 5^a

Figure 8. Molecular structures of compound 25 (ellipsoids

drawn at the 50% probability level).

in solution than compounds 7 and 19; solutions of 20

visibly darkened over 2-3 h, precipitating palladium

residues, so that single crystals suitable for structural

determination by XRD were not obtainable. ¹H, ¹³C{¹H},

and ³¹P{¹H} NMR and ESI+ mass spectra of 20 are in

accord with a dimeric structure containing six-mem-

bered bridging oxapalladacycles, isomeric with 7 but

containing aryl-palladium bonds and two linked me-

thylene units in the rings, which should lead to a

different conformation around the Pd centers.

^aReagents and conditions: (i) NaH, PPh₃, THF, RT, 12 h;

(ii) diphosphine, toluene, RT, 13 h; (iii) P(OC₆H₄OMe-4)₃,

toluene, RT, 12 h.

Scheme 6^a

As reported by Echavarren and co-workers,¹⁰19

reacts with dppf to form the mononuclear oxopallada-

cyclic compound 21, an arylpalladium analogue of the

benzylic derivative 10, and we have also characterized

an analogous derivative, 22, formed by cleavage of 19

with dppe at ambient temperature (Scheme 5). Simi-

larly, 20, containing the larger oxopalladacycles, reacts

with dppf and dppe to form the corresponding mono-

nuclear complexes 23 and 24 (Scheme 6). Complexes

22-24 are stable in the solid state and were character-

1

ized by elemental analysis, H and ³¹P{¹H} NMR, and

mass spectra, but solutions decompose within hours so

that ¹³C{¹H} NMR spectra or crystals suitable for XRD

were not obtained. It should be noted that compounds

of this type are potential intermediates in the pal-

ladium-catalyzed formation of aryl ethers by thermal

reductive elimination of a C-O bond,¹⁸as demonstrated

by the complex Pd[2-{OCMe₂CH₂CH₂-κO}C₆H₄-κC¹]-

(dppf) isolated by Buchwald et al.,¹⁵and this is one

possible decomposition path for compounds 22-24.

Although the monodentate phosphines P(C₆H₄-4-Me)₃

and P(C₆H₄-4-OMe)₃will replace PPh₃in 7 to form new

binuclear compounds 8 and 9, NMR studies indicated

that neither of these phosphines reacted readily at

ambient temperature with 20 and that only P(C₆H₄-4-

OMe)₃reacted with 19 to form the tri(4-methoxyphenyl)-

phosphine product 25, which was isolated and charac-

terized. A solvated crystal, 25‚4CH₂Cl₂, was analyzed

by XRD, and the derived molecular structure is depicted

in Figure 8 with selected geometrical parameters given

in Table 4. The structure of 25 is very similar to that

reported¹⁰for the triphenylphosphine analogue, 19, and

the presence of P(C₆H₄-4-OMe)₃ligands causes negli-

gible changes to the geometry.

^aReagents and conditions: (i) NaH, PPh₃, THF, RT, 12; (ii)

diphosphine, toluene, RT, 4 h.

tonation using NaH, into the binuclear compound 19,¹⁰

which is a precatalyst for some Heck and cross-coupling

reactions;¹⁷we found the synthesis of 19 from 14 using

NaH to be successful in the presence of free triphen-

ylphoshine, as in preparation of 7 (see Scheme 5). The

crystal structure of compound 19 has been reported and

is related to that of the benzyl compound 7 formed from

hydroxymethylbenzyl halides, but contains five- rather

than six-membered C-O chelating ligands.¹⁰

Deprotonation of complex 17 afforded the binuclear

compound 20 (Scheme 6), which was characterized

analytically and spectroscopically, but it is less stable

(16) A nonsolvated crystal of 17 {triclinic, P1h, a ) 10.848(2) Å, b )

14.295(3) Å, c ) 24.476(5) Å, R ) 75.34(2)°, â ) 88.90(2)°, γ ) 89.17-

(2)°} was also analyzed by XRD establishing the presence of molecules

very similar to that of Figure 8: the lattice contained two independent

molecules per unit cell, one with disorder at the hydroxyl group, but

refinement of the data gave high final R factors {indices [I>2σ(I)]: R1

) 0.1129, wR2 ) 0.2677; all indices R1 ) 0.1260, wR2 ) 0.2702}. See

Supporting Information.

2.2.4. Carbonylation of Palladium Complexes

Derived from 2-Halogenobenzenealkanols. The

(17) Mun˜oz, M. P.; Mart´ın-Matute, B.; Ferna´ndez-Rivas, C.; Ca´rde-

nas, D. J.; Echavarren, A. M. Adv. Synth. Catal. 2001, 343, 338.

(18) Muci, A. R.; Buchwald, S. L. Top. Curr. Chem. 2002, 219, 131.

Benzyl and Aryl Palladium Complexes

Organometallics, Vol. 24, No. 6, 2005 1127

Table 4. Selected Bond Lengths [Å] and Angles

[deg] of Compound 25

respectively, the alcoholic function of the ortho-hy-

droxymethyl substituent also coordinates to the pal-

ladium to form a six-membered oxapalladacycle with the

displacement of a phosphine ligand. Also, in accord with

known reactivities of aryl halides,²¹the aromatic iodides

13a and 16 add oxidatively to Pd(PPh₃)₄at ambient

temperature, whereas the bromide 13b reacts at 70 °C

and an even higher temperature is required for complete

reaction of the bromo analogue of 16, preventing isola-

tion of pure product. In the characterized products, 14,

15, and 17, the hydroxy group of the ortho-hydroxy-

methyl or -ethyl substituent is not coordinated so that

five- or six-membered oxapalladacycles are not so

readily formed for these arylpalladium derivatives.

Reactions of carbon monoxide at atmospheric pressure

and room temperature with the benzyl- or aryl-pal-

ladium products of oxidative addition give quantitative

conversion to the corresponding lactone, 1, 26a, or 26b,

and spectroscopic studies indicate that the insertion of

CO occurs into the Pd-C bond to form a labile acyl or

aroyl intermediate. This pathway is to be expected for

the monodentate aryl compounds 14, 15, and 17, but

the alternative insertion into the Pd-O bond of the

coordinated OH group in 3 or 4, to form an alkoxycar-

bonyl intermediate, is possible and this mechanism has

been previously proposed for the formation of lactone

26b from the chelated 2-hydroxyethylphenyl ligand in

[Pd{(2-HOCH₂CH₂-κO)C₆H₄-κC¹}(tmeda)]NO₃, 5.⁹How-

ever, notable differences between 5 and the monophos-

phine complexes 3 and 4 are the positive charge and

the presence of a chelating nitrogen ligand in the former

complex. It is also of interest that a recent theoretical

study of the iron-catalyzed [2+2+1] cycloaddition of

diazabutadiene, ethylene, and carbon monoxide to form

lactam supports preferential insertion of CO into an

Fe-C rather than an Fe-N bond.²²

Pd(1)-C(1)

Pd(1)-O(8)

Pd(1)-O(8)A

Pd(1)-P(1)

[Pd(1)-Pd(1)A]

C(1)-C(6)

1.994(4)

2.051(3)

2.114(3)

O(8)-Pd(1)-O(8)A 78.37(13))

C(1)-Pd(1)-P(1)

O(8)-Pd(1)-P(1)

96.11(12)

178.42(11)

2.2250(11) O(8)A-Pd(1)-P(1) 102.46(8)

[3.2287(7)] Pd(1)-O(8)-Pd(1)A 101.63(13)

1.409(6)

1.511(6)

1.367(6)

C(6)-C(1)-Pd(1)

C(1)-C(6)-C(7)

O(8)-C(7)-C(6)

110.1(3)

117.7(4)

109.9(4)

111.5(3)

C(6)-C(7)

C(7)-O(8)

C(1)-Pd(1)-O(8) 83.00(14) C(7)-O(8)-Pd(1)

C(1)-Pd(1)-O(8)A 161.23(14) C(7)-O(8)-Pd(1)A 138.3(3)

aryl-palladium complexes derived from 2-halogenoben-

zenealkanols 13 and 16 show similar reactivity to the

related benzyl derivatives on exposure to carbon mon-

oxide. At atmospheric pressure and ambient tempera-

ture, CO reacts completely with the simple monodentate

aryl compounds 14, 15, and 17 in tetrahydrofuran

solutions within 0.5-1 h to form the corresponding

lactone, phthalide {1(3H)-isobenzofuranone}, 26a,^3,19or

3,4-dihydroisocoumarin (3,4-dihydro-1H-2-benzopyran-

1-one), 26b,⁹with characteristic IR, NMR, and GC-MS

properties. Carbonylated palladium species, precipitated

from these reactions at -78°C, exhibited IR spectra

containing ν(CO) bands assignable to aroyl species, but

these bands decayed completely within 5-15 min after

redissolving the solids in CH₂Cl₂at ambient tempera-

ture, accompanied by the growth of bands of the

respective lactone 26a or 26b (see Experimental Sec-

tion). It may be concluded that the intermediates in

these processes are simple aroyl compounds, probably

27a,b, or c (or possibly monophosphine complexes 28

with coordinated hydroxy group), which undergo a facile

reductive elimination of lactone by intramolecular al-

coholysis of the aroyl function.

Carbonylations under mild conditions (1 atm, RT) of

binuclear products 7, 19, and 20 readily produce the

corresponding lactones, but in these cases no evidence

for the nature of intermediates has been adduced and

CO insertion into either the Pd-C or Pd-O bond could

take place, although the latter bond is initially part of

a bridging alkoxy system. In contrast to these facile

reactions, the neutral, mononuclear complexes 10, 11,

and 22 containing bidentate alkoxy-benzyl or -aryl and

diphosphine ligands, formed by cleavage of the binuclear

compounds with dppe or dppf, show no reaction with

CO under the same mild conditions. Low or zero

reactivity of palladium catalysts containing dppe ligands

for carbonylation of halo alcohols has previously been

noted by Stille and was explained by assuming that a

necessary fifth coordination site on palladium was

blocked by the hydroxy group;³this is not the case with

the four-coordinate complexes 10, 11, and 22, and there

must be an alternative explanation for the retarding

effect of the diphosphine ligands in these species.

We also found that both binuclear triphenylphosphine

complexes 19 and 20 react readily with CO under

ambient conditions to form lactones 26a and 26b,

respectively. However, the mononuclear complex Pd{(2-

OCH₂-κO)C₆H₄-κC¹}(dppe), 22, containing bidentate

alkoxy-aryl and diphosphine ligands, showed no evi-

dence of reaction with CO at atmospheric pressure

during 1 h.

3. Discussion

In line with reported reactions of benzylic halides,²⁰

both bromo and chloro compounds 2a,b readily undergo

oxidative addition to tetrakis(triphenylphosphine)-

palladium, but, in the isolable products 3 and 4,

Mechanisms for insertion of CO into M-R or M-OR

bonds of group 10 metals have been the subject of

several theoretical and experimental studies,^5-7,23-31

with reaction at an M-OR bond (R ) alkyl) generally

being more favored by the larger metals if both ligands

(19) Brown, H. C.; Kim, S. C.; Krishnamurthy, S. J. Org. Chem.

1980, 45, 1. (Aldrich Handbook of Fine Chemicals, 2003-2004, p 1475,

#P3, 906-5).

(21) Fitton, P.; Rick, E. A. J. Organomet. Chem. 1971, 28, 287.

(22) Imhof, W.; Anders, E.; Go¨bel, A.; Go¨rls, H. Chem. Eur. J. 2003,

9, 11.

(20) Fitton, P.; McKeon, J. E.; Ream, B. C. Chem. Commun. 1969,

370.

1128 Organometallics, Vol. 24, No. 6, 2005

Lindsell et al.

are present,⁷although aryloxide bonds are less reac-

tive.³⁰A possible pathway is an associative process to

form a five-coordinate intermediate within which mi-

gratory insertion occurs, and this appears to apply for

some Ni(II) species.⁷An alternative mechanism involves

displacement of a ligand in the square plane by CO to

form a four-coordinate cis-carbonyl species before mi-

gratory insertion, although the migration step may be

assisted by the displaced ligand remaining in a more

loosely bound state;^7,26studies suggest that a pathway

of this type becomes more favored for Pd(II) and Pt(II)

complexes. Assuming the latter mechanism applies, the

displaced ligand for complexes 3, 4, 14, 15, and 17 could

be halide, to form a more active cationic species {cf.

studies on MRCl(PMe₃)₂^5b,25}, or triphenylphosphine, to

form a neutral species.³¹However, for complexes 3 and

4 displacement of the chelating hydroxy group, trans

to phosphine, seems more likely, possibly with this

group remaining weakly coordinated in an apical site

during reaction; removal of the Pd-O bond from the

square plane will also explain the formation of acyl

rather than alkoxycarbonyl intermediates which might

have been expected from these Pd(II) complexes. It is

also possible that in complexes 14, 15, and 17 the

hydroxyl group on the ortho-substituent of the aromatic

ring assists in the migratory process and could remain

coordinated to the palladium in the aroyl product prior

to reductive elimination of lactone; if this occurs, the

insertion intermediates detected by IR spectroscopy may

not contain two phosphine ligands as depicted in 27 but

include a coordinated alcohol function, as in 28. Con-

sidering the binuclear compounds 7, 19, and 20, the

alkoxy bridges may be cleaved by addition of CO to form

a four-coordinate mononuclear complex, and this would

place CO cis to the alkoxy group so that reaction might

proceed via alkoxycarbonyl prior to rapid elimination

of lactone. However, Pd(II) complexes are prone to ready

isomerization so that formation of an acyl/aroyl ligand

cannot be ruled out.

even simple methylpalladium²⁶complexes containing

N-N or N-O chelating ligands undergo carbonylation

very readily; for the latter compounds, theoretical

studies support the formation of a square pyramidal

carbonyl intermediate with a long apical bond to one

chelate arm.²⁶However, CO insertions into the Pd-C

bond of simple, neutral diphosphine complexes PdMeCl-

(P-P) (P-P ) dppe, dppp, dppb, or dppf) do require

pressures above atmospheric and the acetyl products

decarbonylate in the absence of CO; rates of insertion

decrease with diphosphine in the order dppb g dppp g

dppf . dppe, so that the complex containing dppe, with

the smallest bite angle and poorest backbone flexibility,

is significantly the least reactive.²³If the mechanism

involves displacement of one arm of the bidentate

diphosphine from the square plane before alkyl migra-

tion (cf. ref 7b), this would be least favorable for dppe.

Cationic species [PdMe(P-P)L]⁺, with a readily substi-

tuted, weakly coordinating ligand L, are more reactive

to CO insertion,^23-25but again reaction is slowest when

P-P ) dppe.²³Therefore, the low reactivity of complexes

11 and 22 containing dppe ligands is not inconsistent

with observations on related complexes, although com-

plex 10, containing dppf, might be expected to more

reactive. A theoretical study has indicated that the

preferred pathway for migration of a methoxy ligand

to a coordinated CO involves rotation about the metal-

oxygen bond so that an oxygen lone pair of electrons

can participate in O-C bond formation;⁷the ring

conformations of the alkoxy-benzyl or -aryl chelates in

complexes 10, 11, and 22 are likely to prevent the

optimum orientation of orbitals for migration of the

alkoxy group, and this factor may be deactivating with

respect to Pd-O insertion; additionally, the geometrical

restrictions of these chelates may also hamper the

pathway for Pd-C insertion.

There is good evidence that the final steps in forma-

tion of ester from acylpalladium complexes, and alcohol,

in the presence of base, generally involve the coordina-

tion of alcohol, deprotonation, and subsequent reductive

elimination of alkoxy group with the acyl ligand.^5,6An

inverse reductive elimination of alkyl and alkoxycarbo-

nyl ligands occurs when CO preferentially inserts into

the M-O of an alkoxy(alkyl)complex.^28-30Therefore,

coordination of both oxygen and carbon donor ligands

is normally required before final alcoholysis. The benzyl

and aryl palladium complexes 3, 4, 7, 19, and 20

described in this paper contain a cis-alcohol or -alkoxy

function coordinated to the metal or, in the case of aryl

compounds 14, 15, and 17, an adjacent hydroxyl group

that can readily be coordinated; the presence of these

Pd-O bonds will explain the ready formation of lactone

from the carbonyl inserted intermediates derived from

all these complexes.

The lack of reaction of the diphosphine complexes 10,

11, and 22 with CO under mild conditions is in apparent

contrast with literature reports on reactivity of diphos-

phine palladium and platinum complexes containing

both alkyl and alkoxy ligands. Thus, Pt(OMe)Me(dppe)

reacts with CO at low pressures and temperatures by

insertion into the Pt-O bond,²⁷and facile insertions of

CO into the Pd-O bond of complexes Pd(OCHRR′)Me-

(dppe)²⁸and Pd(OMe)Me{(S,S)-bdpp}²⁹lead to liberation

of methyl esters. Also, methyl(alkoxy)palladium^30aand

(23) Dekker, G. P. C. M.; Elsevier: C.J.; Vrieze, K.; van Leeuwen,

P. W. N. M. Organometallics 1992, 11, 1598.

(24) Toth, I.; Elsevier, C. J. J. Am. Chem. Soc. 1993, 115, 10388.

(25) Kayaki, Y.; Tsukamoto, H.; Kaneko, M.; Shimizu, I.; Yamamoto,

A.; Tachikawa, M.; Nakajima, T. J. Organomet. Chem. 2001, 622, 199.

(26) (a) Frankcombe, K. E.; Cavell, K. J.; Yates, B. F.; Knott, R. B.

Organometallics 1997, 16, 3199. (b) Green, M. J.; Britovsek, G. J. P.;

Cavell, K. J.; Gerhards, F.; Yates, B. F.; Frankcombe, K.; Skelton, B.

W.; White, A. H. J. Chem. Soc., Dalton Trans. 1998, 1137.

(27) Bryndza, H. E. Organometallics 1985, 4, 1686.

The characterization of complexes 3 and 4 containing

the bidentate 2-hydroxymethylbenzyl ligand and spec-

troscopic identification of the acyl compound 12b sup-

port the mechanism shown in Scheme 1 as the primary

pathway for the palladium-catalyzed synthesis of 3-iso-

chromanone from 2-hydroxymethylbenzyl halides. The

facile chelation of the hydroxyl group supports Pd-O

bond formation in the catalytic cycle; as in the isolated

derivatives, this bond probably forms prior to carbonyl

insertion, but under catalytic conditions it is possible

(28) Kim, Y.-J.; Osakada, K.; Sugita, K.; Yamamoto, T.; Yamamoto,

A. Organometallics 1988, 7, 2182.

(29) Toth, I.; Elsevier, C. J. J. Chem. Soc., Chem. Commun. 1993,

529.

(30) (a) Kapteijn, G. M.; Dervisi, A.; Verhoef, M. J.; van den Broek,

M. A. F. H.;. Grove D. M.; van Koten, G. J. Organomet. Chem. 1996,

517, 123. (b) Komiya, S.; Akai, Y.; Tanaka, K.; Yamamoto, T.;

Yamamoto, A. Organometallics 1985, 4, 1130. (c) Kim, Y.-J.; Osakada,

K.; Takenaka, A.; Yamamoto, A. J. Am. Chem. Soc. 1990, 112, 1096.

(31) For example see: (a) Anderson, G. K. Organometallics 1983,

2, 665. (b) Garrou, P. E.; Heck, R. F. J Am Chem. Soc. 1976, 98, 4115.

Benzyl and Aryl Palladium Complexes

Organometallics, Vol. 24, No. 6, 2005 1129

(MgSO₄). After filtration the solution was evaporated to

dryness in vacuo to give the title compound as a white, waxy

solid (3.0 g, 82%). NMR (CDCl₃) δ_H/ppm: 2.08 (br s, 1H, OH),

4.64 (s, 2H, CH₂Br), 4.84 (br s, 2H, CH₂O), 7.35 (m, 4H, C₆H₄).

2-(Hydroxymethyl)benzyl Chloride, 2b. 1,2-Benzene-

dimethanol (6.03 g, 43.6 mmol) was dissolved in toluene (65

cm³). The solution was heated to 70 °C, and concentrated HCl

(6.1 cm³) was added dropwise over 5 min. The mixture was

then stirred at 70 °C for 2 h and cooled to RT. Workup as above

gave the title compound as a white, waxy solid (6.35 g, 93%).

NMR (CDCl₃) δ_H/ppm: 1.83 (t, J ) 5.8 Hz, 1H, OH) 4.73 (br s,

2H, CH₂Cl), 4.84 (br d, J ) 5.8 Hz, 2H, CH₂O), 7.37 (m, 4H,

C₆H₄).

that the interaction occurs during, or even after, migra-

tion of the benzyl group to coordinated CO. Since the

isolated binuclear derivative 7 is formed in appreciable

amounts only in the presence of hydride and not with

amine bases, it is less likely to be involved in the

catalytic cycle in which NEt(i-Pr)₂is the added base.

However, 7 is readily transformed by CO into 3-iso-

chromanone and is itself an active catalyst precursor.

The isolated arylpalladium complexes 14, 15, and 17

are also readily transformed into the corresponding

lactones on reaction with CO, and they are probably the

initial oxidative-addition intermediates in the catalytic

carbonylations of 2-halogenobenzenealkanols by Pd(0)

in the presence of PPh₃; insertion of CO occurs readily

into the aryl-palladium bond in the absence of a Pd-O

bond, although subsequent coordination of the neigh-

boring hydroxyl group is very likely to precede lactone

formation. Binuclear products, 19 and 20, although

unlikely to be involved in the basic catalytic cycle, are

also readily carbonylated to form lactone and can act

as precursors of mononuclear catalysts. However, com-

plexes 10, 11, and 21-24, which contain bidentate

diphosphine and chelating, formally dinegative, alkoxy-

alkyl or -aryl ligands, do not react readily with CO to

form the corresponding lactone and are inactive as

catalysts for lactone formation from the parent halo

alcohols.

Bromo[2-(hydroxymethyl-KO)benzyl-KC^1r](triphen-

ylphosphine)palladium, 3. 2-(Hydroxymethyl)benzyl bro-

mide (2a) (0.25 g, 1.24 mmol) dissolved in toluene (10 cm³)

was added dropwise to a stirred suspension of tetrakis-

(triphenylphosphine)palladium(0) (1.43 g, 1.24 mmol) in tolu-

ene (60 cm³) and the mixture stirred at RT for 12 h. The solid

product was collected by filtration, washed with diethyl ether

(3 × 20 cm³), and dried in vacuo to give the title compound as

an amorphous, off-white solid (605 mg, 86%). Crystallization

from dichloromethane and light petroleum ether gave yellow

cubes, mp 168-171 °C (dec). Found: C, 54.96; H, 4.28; C₂₆H₂₄-

BrOPPd requires C, 54.81; H, 4.25. NMR (CDCl₃) δ_H/ppm: 2.79

(d, J_HP) 2.6 Hz, 2H, PdCH₂), 4.53 (d, J_HP) 2.1 Hz, 2H, CH₂O),

ca. 5.5 (vbr s, 1H, OH) 6.19 (d, J ) 7.6 Hz, 1H, C₆H_4,H-6),

6.96 (t, J ) 7.3 Hz, 1H, C₆H_4,H-5), 7.01-7.11 (m, 2H, C₆H₄,

H-3, 4), 7.37-7.50 (m, 9H, PPh₃, m, p-CH), 7.62-7.70, (m, 6H,

PPh₃, o-CH); δ_C/ppm: 33.0 (PdCH₂), 64.2 (d, J_CP) 5.9 Hz,

CH₂O), 124.9 (C₆H₄, CH-4), 127.7-128.9 (C₆H₄, CH-3,5,6),

128.3 (d, J_CP≈ 11 Hz, PPh₃, m-CH), 130.6 (PPh₃, p-CH), 131.1

(d, J_CP) 53.0 Hz, quat.-C, PPh₃, ipso-C), 134.5 (d, J_CP) 11.6

Hz, PPh₃, o-CH),138.8 (quat.-C, C₆H₄, C-2), 141.0 ((d, J_CP) 4

Hz, quat.-C, C₆H₄, C-1); δ_P/ppm: 42.6 (s). MS (ESI+): m/z

1051-1065 {max. 1056, 50%, (2M - H_xBr)}, 484-494 {max.

488, 60%, (M - H_xBr)}; C₂₆H₂₄BrOPPd requires 568.

4. Experimental Section

4.1. General Procedures. Reactions and operations in-

volving palladium compounds were conducted under an at-

mosphere of dry, oxygen-free nitrogen or argon gas, using

Schlenk techniques. Solvents were dried, using sodium (tolu-

ene), sodium-benzophenone (diethyl ether, tetrahydrofuran,

petroleum ether), calcium hydride (dichloromethane), or so-

dium hydroxide (dimethyl sulfoxide) and freshly distilled

before use. Light petroleum ether had a boiling range of 60-

80 °C. Tetrakis(triphenylphosphine)palladium³²and 2-iodo-

benzeneethanol³³were prepared by literature methods, and

other reagents were obtained commercially (Aldrich Chemicals

or Syngenta, Grangemouth, UK) and used as supplied. NMR

spectra were recorded on a Bruker DPX 400 spectrometer (at

ca. 17 °C) using SiMe₄as internal reference for 400.1 MHz ¹H

and 100.6 MHz ¹³C{¹H} spectra and 85% H₃PO₄as external

reference for 162.0 MHz ³¹P{¹H} spectra; many assignments

of ¹H and ¹³C resonances were aided by HMQC, NOE, and

DEPT measurements. Solid-state NMR spectra were run by

the EPSRC service at the University of Durham, UK. IR

spectra were recorded using a Perkin-Elmer 1600 series FTIR

spectrophotometer. EI/ESI mass spectra were measured on an

upgraded VG MS9 instrument. GC-MS spectra were recorded

on a Hewlett-Packard HP6890 gas chromatograph with a

HP5MS (30 m × 0.25 mm) capillary column coupled to a

Hewlett-Packard HP5973 quadrupole mass filter (EI, high-

energy dynode/electron multiplier detector). Elemental CHN

analyses were carried out at Heriot-Watt University.

Chloro[2-(hydroxymethyl-KO)benzyl-KC^1r](triphen-

ylphosphine)palladium, 4. 2-(Hydroxymethyl)benzyl chlo-

ride (2b) (0.25 g, 1.6 mmol) dissolved in toluene (10 cm³) was

added dropwise to a stirred suspension of tetrakis(triph-

enylphosphine)palladium(0) (1.65 g, 1.43 mmol) in toluene (60

cm³), and the mixture was stirred at RT for 12 h. The solid

product was collected by filtration, washed with diethyl ether

(3 × 20 cm³), and dried in vacuo to give the title compound as

an amorphous, off-white solid (640 mg, 76%). Recrystallization

from dichloromethane and petroleum ether gave pale yellow

cubes, mp 192-197 °C (dec). Found: C, 59.16; H, 4.54. C₂₆H₂₄-

ClOPPd requires C, 59.45; H, 4.60. NMR (CDCl₃) δ_H/ppm: 2.70

(d, J_HP) 2.9 Hz, 2H, PdCH₂), 4.45 (br s, 2H, CH₂O), 6.20 (d,

J ) 7.7 Hz, 1H, C₆H₄, H-6), ca. 6.7 (v br, 1H, OH), 6.93 (dt, J

) 1.6 and 7.4 Hz, 1H, C₆H₄, H-5), 6.98 (m, 1H, C₆H₄, H-3),

7.05 (∼tt, J ) 1.1 and 7.3 Hz, 1H, C₆H₄, H-4), 7.3-7.5 (m, 9H,

PPh₃, m, p-CH), 7.6-7.7 (m, 6H, PPh₃, o-CH); δ_C/ppm: 30.6

(PdCH₂), 63.6 (CH₂O), 124.7 (C₆H₄, CH-4), 127.6 (d, J_CP) 2.0

Hz, C₆H₄, CH-6), 128.3 (d, J_CP) 11.0 Hz, PPh₃, m-CH), 128.8

(br, C₆H₄, CH-3, 5), 130.6 (d, J_CP) 2.5 Hz, PPh₃, p-CH), ∼130.9

(d, J_CP≈ 55 Hz, quat.-C, PPh₃, ipso-C), 134.5 (d, J_CP) 11.7

Hz, PPh₃, o-CH), 139.1 (quat.-C, C₆H₄, C-2), 141.5 (d, J_CP

)

3.0 Hz, quat.-C, C₆H₄, C-1); δ_P/ppm: 41.4 (s). MS (EI+): m/z

525 (M + 1) (6%); (ESI+) m/z 1007-1023 {max. 1013, 100%,

(2M - H_xCl)}; C₂₆H₂₄ClOPPd requires 524.

4.2. Synthesis and Characterization. 2-(Hydroxy-

methyl)benzyl Bromide, 2a. 1,2-Benzenedimethanol (2.5 g,

18.1 mmol) was dissolved in toluene (35 cm³). The solution was

heated to 70 °C, and 48% HBr (2.3 cm³) was added dropwise

over 5 min. The mixture was stirred at 70 °C for 3 h, cooled to

RT, neutralized with sodium carbonate solution, and then

extracted with diethyl ether (3 × 20 cm³). The combined

organic phases were washed with water (40 cm³) and dried

Reaction of Chloro[2-(hydroxymethyl-KO)benzyl-KC^1r]-

(triphenylphosphine)palladium (4) with Carbon Mon-

oxide. Carbon monoxide was bubbled through a solution of

chloro[2-(hydroxymethyl)benzyl](triphenylphosphine)-

palladium (4) (150 mg, 0.286 mmol) in tetrahydrofuran (20

cm³) for 20 min. Petroleum ether (40 cm³) was quickly added,

via syringe, and the reaction mixture was cooled to -78 °C.

The precipitate was collected by filtration and dried in vacuo,

to give an amorphous yellow-orange solid, comprising mainly

(32) Coulson, D. R. Inorg. Synth. 1990, 28, 107.

(33) Ram, V. J.; Haque, N. Indian. J. Chem. Sect. B 1996, 35B, 238.

1130 Organometallics, Vol. 24, No. 6, 2005

Lindsell et al.

chloro[2-(hydroxymethyl-κO)phenylacetyl-κC^1â](triphenylphos-

phine)palladium (12b) (134 mg, 85%). NMR (CD₂Cl₂); δ_H/

ppm: 4.01 (s, 2H, CH₂CO), 4.16 (s, 2H, CH₂O), 6.17 (d, J )

7.6 Hz, C₆H₄, H-6), 6.95-7.25 (complex, 3H, C₆H₄, H-3-5),

7.4-7.8 (complex, 15H, PPh₃); δ_P/ppm: 27.4 (s). MS (EI+): m/z

product was recrystallized from dichloromethane/light petro-

leum. Found: C, 57.13; H, 4.85. C₅₈H₅₈O₈P₂Pd₂‚CH₂Cl₂re-

quires C, 57.02; H, 4.87. NMR (CDCl₃); δ_H/ppm: 2.36 (d, J_HP

) 5.0 Hz, 4H, PdCH₂), 3.39 (d, J_HP) 3.8 Hz, 4H, CH₂O), 3.84

(s, 18H, CH₃), 6.22 (d, J ) 8.2 Hz, 2H, C₆H₄, H-3), 6.38 (d, J

) 7.1 Hz, 2H, C₆H₄, H-6), 6.73 (m, 4H, C₆H₄, H-4, 5), 6.95 (d,

J ) 8.8 Hz, 12H, PC₆H₄O, m-CH), 7.74, (dd, J ) 8.8 and 10.6

Hz, 12H, PC₆H₄O, o-CH); δ_C/ppm: 25.5 (d, J_CP) 3.8 Hz,

PdCH₂), 55.3 (CH₃O), 68.3 (CH₂O), 113.9 (d, J_CP) 11.5 Hz,

PC₆H₄OMe, m-CH), 122.6 (C₆H₄, C-4 or 5), 124.0 (d, J_CP) 51.4

Hz, PC₆H₄OMe, ipso-CP), 126.0 (C₆H₄, C-6), 126.6 (C₆H₄, C-5

or 4), 127.2 (C₆H₄, C-3), 136.2 (d, J_CP) 13.9 Hz, PC₆H₄OMe,

o-CH), 144.4 (quat.-C, C₆H₄, C-1 or 2), 147.0 (quat.-C, C₆H₄,

C-2 or 1), 161.1 (d, J_CP) 2.0 Hz, PC₆H₄OMe, p-COMe); δ_P/

ppm: 35.5, (s). MS (ESI+): m/z 1179 (M + Na) (99%);

C₅₈H₅₈O₈P₂Pd₂requires 1156.

[1,1′-Bis(diphenylphosphino)ferrocene-K²P,P′][(2-

oxomethyl-KO)benzyl-KC^1r]benzyl-KC^1r]palladium, 10. 1,1′-

Bis(diphenylphosphino)ferrocene (1.15 g, 2.07 mmol) in toluene

(20 cm³) was added dropwise to a suspension of bis[2-(µ-

oxomethyl-κO)benzyl-κC^1R]bis(triphenylphosphine)di-

palladium, 7 (509 mg, 0.52 mmol), in toluene (40 cm³). The

mixture, which immediately became a homogeneous orange

solution, was stirred for 3 h to produce a bright yellow-orange

solid precipitate. This solid was collected by filtration, washed

with H₂O (2 × 20 cm³), followed by diethyl ether (3 × 20 cm³),

and dried in vacuo to give the title compound (323 mg, 40%).

A purified sample for analysis was obtained by expeditious

recrystallization from dichloromethane/light petroleum.

Found: C, 61.97; H, 4.45. C₄₂H₃₆FeOP₂Pd.0.5CH₂Cl₂requires

C, 61.99; H, 4.53. NMR (CD₂Cl₂); δ_H/ppm: 2.72 (dd, J_HP) 6.8

and 9.7 Hz, 2H, PdCH₂), 3.69 (br ∼t, 2H, C₅H₄), 4.20 (br ∼t,

2H, C₅H₄), 4.32 (br ∼t, 2H, C₅H₄), 4.35 (br ∼t, 2H, C₅H₄), 4.47

(d, J ) 6.5 Hz, 2H, CH₂O), 6.31 (d, J ) 7.2 Hz, 1H, C₆H₄, H-3

or 6), 6.90 (m, 2H, C₆H₄, H-4, 5), 7.05 (d, J ) 6.9 Hz, 1H, C₆H₄,

H-6 or 3), 7.3-7.5 (m, 12H, PPh₂, m, p-CH), 7.67-7.85 (m,

8H, PPh₂, o-CH); δ_P/ppm: 16.2 (d, J_PP) 38.0 Hz), 34.2 (d, J_PP

) 38.0 Hz). MS (ESI+): m/z 780.5 (M); C₄₂H₃₆FeOP₂Pd

requires 780.

[1,2-Bis(diphenylphosphino)ethane-K²P,P′][2-(oxome-

thyl-KO)benzyl-KC^1r]palladium, 11. 1,2-Bis(diphenylphos-

phino)ethane (1.11 g, 2.79 mmol) in toluene (20 cm³) was added

dropwise to a suspension of bis[2-(µ-oxomethyl-κO)benzyl-κC^1R]-

bis(triphenylphosphine)dipalladium, 7 (678 mg, 0.69 mmol),

in toluene (40 cm³). The mixture was stirred for 3 h at RT to

form a creamy-white suspension. The white solid was collected

by filtration, washed with H₂O (2 × 20 cm³), followed by diethyl

ether (3 × 20 cm³), and dried in vacuo to give the title

compound (749 mg, 86%). Found: C, 64.25; H, 5.01. C₃₄H₃₂-

OP₂Pd‚1/2H₂O requires C, 64.41; H, 5.25. NMR (CDCl₃): δ_H/

ppm: 2.11 (m, 2H, dppe, CH₂), 2.29 (m, 2H, dppe, CH₂), 2.80

(dd, J_HP) 5.3 and 10.3 Hz, 2H, PdCH₂), 4.78 (br s, 2H, CH₂O),

6.14 (d, J ) 7.1 Hz, 1H, C₆H₄, H-3 or 6), 6.88 (m, 2H, C₆H₄,

H-4, 5), 7.17 (m, 1H, C₆H₄, H-6 or 3), 7.29-7.37 and 7.43-

7.61 (complex, 16H, PPh₂, CH), 7.82 (m, 4H, PPh₂, CH); δ_P/

ppm: 33.8 (d, J_PP) 29.4 Hz), 55.7 (d, J_PP) 29.4 Hz). MS

(ESI+): m/z 624 (M) (100%); C₃₄H₃₂OP₂Pd requires 624.

trans-[2-(Hydroxymethyl)phenyl]iodobis(triphenyl-

phosphine)palladium, 14 (cf. ref 10). 2-Iodobenzenemetha-

nol, 13a (0.5 g, 2.14 mmol), dissolved in toluene (20 cm³), was

added dropwise to a stirred suspension of tetrakis(triph-

enylphosphine)palladium (2.47 g, 2.14 mmol) in toluene (80

cm³) and the mixture stirred at room temperature for 12 h.

Approximately one-third of the solvent was removed in vacuo

and replaced with petroleum ether (30 cm³), and the mixture

cooled in a refrigerator. The resultant precipitate was collected,

washed with diethyl ether (3 × 20 cm³), and dried in vacuo to

give the title compound as a yellowish solid (1.13 g, 61%).

Further recrystallization from dichloromethane/light petro-

leum ether afforded yellow crystals. Found: C, 55.32; H, 4.07.

C₄₃H₃₇IOP₂Pd.CH₂Cl₂requires C, 55.63; H, 4.14. NMR

551 (M - 1); C₂₇H₂₄ClO₂PPd requires 552. IR ν_max(CO)/cm^-1

:

1707 (KBr); 1709 (CH₂Cl₂). In dichloromethane, compound 12

decomposes completely within 26 min at RT to form 3-iso-

chromanone (IR: ν_max(CO) 1750 cm^-1).

Bis[2-(µ-oxomethyl-KO)benzyl-KC^1r]bis(triphenylphos-

phine)dipalladium, 7. NaH (60% dispersion in mineral oil;

60 mg, 1.51 mmol) was added to a suspension of chloro[2-

(hydroxymethyl)benzyl-κC^1R,κO](triphenylphosphine)-

palladium (4) (790 mg, 1.50 mmol) and triphenylphosphine

(435 mg, 1.66 mmol) in THF (40 cm³). The suspension was

stirred at RT for 12 h. Liberation of hydrogen gas occurred,

and a pale green precipitate formed. The precipitate was

collected by filtration, washed with H₂O (3 × 30 cm³) to remove

NaCl and with diethyl ether (3 × 10 mL), and then dried in

vacuo to give the title compound as a microcrystalline, pale

green solid (570 mg, 77%). Recrystallization from dichloro-

methane and light petroleum ether afforded pale yellow

crystals. Found: C, 62.64; H, 4.92. C₅₂H₄₆O₂P₂Pd₂‚H₂O re-

quires C, 62.72; H, 4.86. NMR (CDCl₃): δ_H/ppm: 2.36 (d, J_HP

) 5.4 Hz, 4H, PdCH₂), 3.34 (d, J_HP) 4.2 Hz, 4H, CH₂O), 6.18

(m, 2H, C₆H₄, H-3), 6.27 (m, 2H, C₆H₄, H-6), 6.72 (m, 4H, C₆H₄,

H-4, 5), 7.42-7.50 (m, 18H, PPh₃, m, p-CH), 7.85 (m, 12H,

PPh₃, o-CH); δ_C/ppm: 25.6, (d, J_CP) 4.4 Hz, PdCH₂), 68.2

(CH₂O), 122.9 (C₆H₄, CH-4 or 5), 126.0 (C₆H₄, CH-6),126.7

(C₆H₄, CH-5 or 4), 127.1 (C₆H₄, CH-3), 128.4 (d, J_CP) 10.5

Hz, PPh₃, m-CH), 130.3 (d, J_CP) 2.1 Hz, PPh₃, p-CH), 132.1

(d, J_CP) 46.6 Hz, PPh₃, ipso-C), 134.8 (d, J_CP) 12.5 Hz, PPh₃,

o-CH), 143.8 (d, J_CP) 1.3 Hz, quat.-C, C₆H₄, C-1 or 2), 146.9

(quat.-C, C₆H₄, C-2 or 1); δ_P/ppm: 39.6 (s). MS (ESI+): m/z

999 (M + Na) (84%), 476 (55%); C₅₂H₄₆O₂P₂Pd₂requires 976.

Bis[2-(µ-oxomethyl-KO)benzyl-KC^1r]bis[tris(4-meth-

ylphenyl)phosphine)]dipalladium, 8. Tris(4-methylphen-

yl)phosphine (9) (376 mg, 1.24 mmol) in toluene (10 cm³) was

added dropwise to a suspension of bis[2-(µ-oxomethyl-κO)-

benzyl-κC^1R]bis(triphenylphosphine)dipalladium (7) (301 mg,

0.31 mmol) in toluene (10 cm³). The mixture was stirred for

12 h at RT to form a homogeneous, olive-green solution. After

partial removal of solvent at reduced pressure the resulting

precipitate was collected by filtration, washed with H₂O (2 ×

20 cm³), followed by diethyl ether (3 × 20 cm³), and dried in

vacuo to give the title compound (272 mg, 83%) as a pale green

solid. Found: C, 64.31; H, 5.40. C₅₈H₅₈O₂P₂Pd₂‚H₂O requires

C, 64.51; H, 5.60. NMR (CDCl₃); δ_H/ppm: 2.38 (br s, 4H,

PdCH₂), 2.42 (s, 18H, CH₃), 3.40 (d, J_HP) 3.8 Hz, 4H, CH₂O),

6.24 (d, J ) 7 Hz, 2H, C₆H₄, H-3), 6.40 (d, J ) 8.5 Hz, 2H,

C₆H₄, H-6), 6.75 (m, 4H, C₆H₄, H-4, 5), 7.26 (m, 12H, PC₆H₄,

m-CH), 7.80 (m, 12H, PC₆H₄, o-CH); δ_C/ppm: 21.4 (CH₃), 25.4

(d, J_CP) 4.0 Hz, PdCH₂), 68.2 (CH₂O), 122.6 (C₆H₄, CH-4 or

5), 125.9 (C₆H₄, CH-6), 126.5 (C₆H₄, CH-5 or 4), 127.1 (C₆H₄,

CH-3), 129.1 (d, J_CP) 11.3 Hz, PC₆H₄Me, m-CH), 129.2 (d,

J_CP≈ 48 Hz, PC₆H₄Me, ipso-CP),134.7 (d, J_CP) 12.7 Hz,

PC₆H₄Me, o-CH), 140.3 (quat.-C, PC₆H₄Me, p-CMe), 144.3

(quat.-C, C₆H₄, C-1 or 2), 147.0 (quat.-C, C₆H₄, C-2 or 1), δ_P/

ppm: 37.5 (s). MS (ESI+): m/z 529.5 (1/2M) (100%); C₅₈H₅₈O₂P₂-

Pd₂requires 1060.2.

Bis[2-(µ-oxomethyl-KO)benzyl-KC^1r]bis[tris(4-meth-

oxyphenyl)phosphine]dipalladium, 9. Tris(4-methoxy-

phenyl)phosphine (350 mg, 1.0 mmol) in toluene (10 cm³) was

added dropwise to a suspension of bis[2-(µ-oxomethyl-κO)-

benzyl-κC^1R]bis(triphenylphosphine)dipalladium (7) (301 mg,

0.31 mmol) in toluene (10 cm³). The mixture was stirred for

12 h at RT to form a homogeneous, pale green solution. After

partial removal of solvent under reduced pressure the resulting

off-white precipitate was collected by filtration, washed with

H₂O (2 × 20 cm³), followed by diethyl ether (3 × 20 cm³), and

dried in vacuo to give the title compound (219 mg, 61%). The

Benzyl and Aryl Palladium Complexes

Organometallics, Vol. 24, No. 6, 2005 1131

(CDCl₃): δ_H/ppm: 0.01 (t, J ) 6.8 Hz 1H, OH), 4.16 (d, J )

6.8 Hz, 2H, CH₂O), 6.41 (d, J ) 7.6 Hz, 1H, C₆H₄, H-3), 6.46

(t, J ) 7.1 Hz, 1H, C₆H₄, H-5), 6.62 (t, J ) 7.6 Hz, 1H, C₆H₄,

H-4), 7.05 (m, 1H, C₆H₄, H-6), 7.21-7.28 (m, 12H PPh₃), 7.30-

7.37 (m, 6H PPh₃), 7.41-7.48 (m, 12H, PPh₃); δ_C/ppm: 68.2,

(t, J_CP) 3.5 Hz, CH₂O), 123.5 (C₆H₄, CH-4), 125.7 (C₆H₄, CH-

5), 127.9 (t, J_CP) 5.0 Hz, PPh₃, m-CH), 128.4 (C₆H₄, CH-3),

130.0 (PPh₃, p-CH), 131.8 (t, J_CP) 23.2 Hz, PPh₃, ipso-C),

134.0 (t, J_CP) 4.2 Hz, C₆H₄, CH-6), 134.8 (t, J_CP) 6.3 Hz,

PPh₃, o-CH), 144.2 (quat.-C, C₆H₄, C-2), 158.4 (quat.-C, C₆H₄,

PdC-1); δ_P/ppm: 23.8, (s). MS (ESI+): m/z 737 {M - I}; C₄₃H₃₇-

IOP₂Pd requires 864.

trans-[2-(Hydroxymethyl)phenyl]bromobis(triphenyl-

phosphine)palladium, 15. 2-Bromobenzenemethanol, 13b

(0.25 g, 1.34 mmol), was dissolved in toluene (10 cm³) and

added dropwise to a stirred suspension of tetrakis(triphen-

ylphosphine)palladium, 1 (1.54 g, 1.33 mmol), in toluene (60

cm³). The suspension was stirred at 70 °C for 48 h. Ap-

proximately one-third of the solvent was removed in vacuo and

replaced with 40 mL of petroleum ether, and the mixture was

cooled in a refrigerator. The resultant precipitate was collected,

washed with diethyl ether (3 × 20 cm³), and dried in vacuo to

give the title compound as a yellowish solid (627 mg, 58%);

this was recrystallized from dichloromethane/light petroleum

ether to give yellow crystals; mp 265 °C (dec). Found: C, 58.35;

H, 4.27. C₄₃H₃₇BrOP₂Pd.CH₂Cl₂requires C, 58.53; H, 4.35.

NMR (CDCl₃); δ_H/ppm: 0.04 (t, J ) 6.8 Hz 1H, OH), 4.16 (d,

J ) 6.6 Hz, 2H, CH₂O), 6.43 (m, 2H, C₆H₄, H-3, 5), 6.62 (t, J

) 7.3 Hz, 1H, C₆H₄, H-4), 7.03 (m, 1H, C₆H₄, H-6), 7.25 (m,

12H PPh₃, m-CH), 7.34 (m, 6H PPh₃, p-CH), 7.45 (m, 12H,

PPh₃, o-CH); δ_C/ppm: 68.6, (t, J_CP) 3.4, CH₂O), 123.4 (C₆H₄,

CH-4), 125.7 (C₆H₄, CH-5), 127.9 (t, J_CP) 5.1 Hz, PPh₃, m-CH),

128.1 (C₆H₄, CH-3), 130.0 (PPh₃, p-CH), 131.2 (t, J_CP) 22.9

Hz, PPh₃, ipso-C), 134.3 (t, J_CP) 4 Hz, C₆H₄, CH-6), 134.6 (t,

J_CP) 6.3 Hz, PPh₃, o-CH), 144.1 (quat.-C, C₆H₄, C-2), 155.7

(t, J_CP) 3.5 Hz, quat.-C, C₆H₄, PdC-1); δ_P/ppm: 24.8, (s). MS

(ESI+) m/z 732-743 (M - Br) (100%); C₄₃H₃₇BrOP₂Pd requires

816.

yellow solid (186 mg), containing a carbonylated product,

tentatively identified as trans-[2-(hydroxymethyl)benzoyl]-

iodobis(triphenylphosphine)palladium, 27a (or related aroyl

derivative). IR: ν_max(CO)/cm^-11659, 1633 (KBr); 1633 (CH₂-

Cl₂). Further purification or spectroscopic characterization was

prevented by instability in solution. In dichloromethane at RT,

this product decomposes completely within 15 min to form

phthalide (IR: ν_max(CO) 1765 cm^-1).

(b) Under similar reactions conditions, trans-[2-(hydroxy-

methyl)phenyl]bromobis(triphenylphosphine)palladium, 15 (200

mg, 0.24 mmol), with CO gave a yellow solid (171 mg),

assumed to contain trans-[2-(hydroxymethyl)benzoyl]bromobis-

(triphenylphosphine)palladium, 27b. IR: ν_max(CO)/cm^-11636

(KBr); 1636 (CH₂Cl₂). This product similarly decomposes in

dichloromethane to form phthalide.

(c) Similarly, trans-[2-(hydroxyethyl)phenyl]iodobis(triphen-

ylphosphine)palladium, 17 (150 mg, 0.17 mmol), gave a yellow

solid (95 mg), assumed to contain trans-[2-(hydroxyethyl)-

benzoyl]iodobis(triphenylphosphine)palladium, 27c. IR: ν_max

-

(CO)/cm^-11651 (KBr); 1652 (CH₂Cl₂). In dichloromethane at

RT, this product decomposes completely within 5 min to form

3,4-dihydroisocoumarin (IR: ν_max(CO) 1722 cm^-1).

Bis[2-(µ-oxomethyl-KO)phenyl-KC¹]bis(triphenylphos-

phine)dipalladium, 19 (cf. ref 10). NaH (60% dispersion in

mineral oil; 10.0 mg, 0.25 mmol) was added to a suspension

of trans-[2-(hydroxymethyl)phenyl]iodobis(triphenylphosphine)-

palladium, 14 (212 mg, 0.245 mmol), and triphenylphosphine

(71 mg, 0.27 mmol) in tetrahydrofuran (20 cm³), and the

mixture was stirred at RT for 12 h. The liberation of hydrogen

gas occurred, and a pale green precipitate formed. The

precipitate was collected by filtration, washed with H₂O (3 ×

5 cm³), to remove NaCl, followed by diethyl ether (3 × 10 mL),

and finally dried in vacuo to give the title compound as a

microcrystalline, pale green solid (68 mg, 58%). Recrystalli-

zation from dichloromethane/light petroleum ether afforded

pale yellow crystals. Found: C, 61.74; H, 4.34. C₅₀H₄₂O₂P₂-

Pd₂‚H₂O requires C, 62.06; H, 4.58. Spectral data as reported

in ref 10.

[1,2-Bis(diphenylphosphino)ethane-K²P,P′][2-(oxome-

thyl-KO)phenyl-KC¹]palladium, 22. 1,2-bis(diphenylphos-

phino)ethane (840 mg, 2.11 mmol) in toluene (20 cm³) was

added dropwise to a suspension of bis[2-(µ-oxomethyl-kO)-

phenyl-kC¹]bis(triphenylphosphine)dipalladium, 19a (500 mg,

0.53 mmol), in toluene (55 cm³) and the mixture stirred for 13

h at RT. The creamy-white precipitate was collected by

filtration, washed with H₂O (2 × 20 cm³), followed by diethyl

ether (3 × 20 cm³), and dried in vacuo to give the title product

as a white solid (508 mg, 79%). Found: C, 63.14; H, 4.54.

C₃₃H₃₀OP₂Pd‚H₂O requires C, 63.02; H, 5.13. NMR (CDCl₃);

δ_H/ppm: 2.20 (m, 2H, dppe, CH₂), 2.42 (m, 2H, dppe, CH₂),

5.70 (br s, 2H, CH₂O), 6.47 (∼t, J ) 7.4 Hz, 1H, C₆H₄), 6.66

(m, 1H, C₆H₄), 6.86 (t, J ) 7.4 Hz, 1H, C₆H₄), ∼7.2 (m, 1H,

C₆H₄), 7.40 (m, 12H, PPh₂), 7.88 (m, 4H, PPh₂), 8.06 (m, 4H,

PPh₂); δ_P/ppm: 34.0 (d, J_PP) 27.1 Hz), 55.7 (d, J_PP) 27.1

Hz). MS (ESI+): m/z 1209-21 (max. 1216, 100%), 606-616

(max. 610, 86%, M); C₃₃H₃₀OP₂Pd requires 610.

[2-(Hydroxyethyl)phenyl]iodobis(triphenylphosphine)-

palladium, 17. 2-Iodobenzeneethanol, 16 (0.75 g, 3.02 mmol),

in toluene (20 cm³) was added dropwise to a stirred suspension

of tetrakis(triphenylphosphine)palladium (3.50 g, 3.03 mmol)

in toluene (150 cm³). The mixture was stirred at RT for 12 h

and then refrigerated to aid crystallization. The resultant

precipitate was collected by filtration, washed with diethyl

ether (3 × 20 cm³), and dried in vacuo to give the title

compound as a white solid (1.135 g, 43%). Recrystallization

from dichloromethane and light petroleum ether afforded

colorless needles. Found: C, 55.52; H, 4.27. C₄₄H₃₉IOP₂Pd.CH₂-

Cl₂requires C, 56.07; H, 4.29. NMR (CDCl₃); δ_H/ppm: 0.38 (t,

J_HH) 6.0 Hz 1H, OH), 2.56 (t, J_HH) 6.8 Hz, 2H, CH₂CH₂O),

3.29 (∼q (dt), J ) 6.0 and 6.8 Hz, 2H, CH₂CH₂O), 6.28 (br d,

J ) 7.6 Hz, 1H, C₆H₄, H-3), 6.36 (t, J ) 7.5 Hz, 1H, C₆H₄,

H-5), 6.57 (t, J ) 7.2 Hz, 1H, C₆H₄, H-4), 6.92 (m, 1H, C₆H₄,

H-6), 7.24 (m, 12H, PPh₃, m-CH), 7.33 (m, 6H, PPh₃, p-CH),

7.43 (m, 12H, PPh₃, o-CH); δ_C/ppm: 42.2 (CH₂CH₂O), 61.4,

(CH₂O), 123.2 (C₆H₄, CH-4), 124.8 (C₆H₄, CH-5), 127.8 (t, J_CP

) 4.9 Hz, PPh₃, m-CH), 129.4 (C₆H₄, CH-3), 129.9 (PPh₃,

Bis[2-(µ-2-oxoethyl-KO)phenyl-KC¹]bis(triphenylphos-

phine)dipalladium, 20. NaH (60% dispersion in mineral oil;

14.4 mg, 0.360 mmol) was added to a suspension of [2-(hy-

droxyethyl)phenyl]iodobis(triphenylphosphine)palladium, 17

(316 mg, 0.36 mmol), and triphenylphosphine (103.9 mg, 0.40

mmol) in THF (20 cm³), and the mixture was stirred at RT for

12 h. Liberation of hydrogen gas occurred, and a pale green

solid precipitated. The solid was collected by filtration, washed

with H₂O (3 × 5 cm³) to remove NaCl, then with diethyl ether

(3 × 10 mL), and finally dried in vacuo to give the title

compound as a microcrystalline, pale green solid (100 mg,

57%). Recrystallization from dichloromethane and light pe-

troleum ether afforded colorless cubic crystals. Found: C,

63.68; H, 5.28. C₅₂H₄₆O₂P₂Pd₂requires C, 63.88; H, 4.74. NMR

(CDCl₃); δ_H/ppm: 2.72 (br d, 8H, CH₂CH₂), 6.21 (∼dt, J ) 1.8

p-CH), 131.9 (t, J_CP) 22.6 Hz, PPh₃, ipso-CP), 135.0 (t, J_CP

)

6.4 Hz, PPh₃, o-CH), 136.0 (t, J_CP∼ 5 Hz, C₆H₄, CH-6), 141.4

(quat.-C, C₆H₄, C-2), 159.7 (quat.-C, C₆H₄, PdC-1); δ_P/ppm:

23.2, (s); MS (ESI+): m/z 751 (M - I); C₄₄H₃₉IOP₂Pd requires

878.

Reactions of Complexes 14, 15, and 17 with Carbon

Monoxide. (a) trans-[2-(Hydroxymethyl)phenyl]iodobis(tri-

phenylphosphine)palladium, 14 (250 mg, 0.29 mmol), was

dissolved in tetrahydrofuran (20 cm³). Carbon monoxide was

then bubbled though the solution for 30 min. Light petroleum

ether (40 cm³) was quickly added via syringe, and the reaction

mixture was cooled to -78 °C. The resultant precipitate was

collected by filtration and dried in vacuo, to give an amorphous

1132 Organometallics, Vol. 24, No. 6, 2005

Lindsell et al.

Benzyl and Aryl Palladium Complexes

Organometallics, Vol. 24, No. 6, 2005 1133

and 7.35 Hz, 2H, C₆H₄, CH-6), 6.56 (m, 6H, C₆H₄, CH-3, 4, 5),

7.18 (m, 12H, PPh₃, m-CH), 7.31 (m, 6H, PPh₃, p-CH), 7.53

(m, 12H, PPh₃, o-CH); δ_C/ppm: 48.0 (CH₂), 65.2 (CH₂O), 122.7

(C₆H₄, CH), 123.3 (d, J_CP) 4.4. Hz, C₆H₄, CH), 125.3 (C₆H₄,

11.1 Hz, 12H, PC₆H₄O, o-CH); δ_C/ppm: 55.3 (CH₃O), 76.0

(CH₂O), 113.8 (d, J_CP) 11.8 Hz, PC₆H₄OMe, m-CH), 118.8

(C₆H₄, CH-3 or 5), 122.4 (C₆H₄, CH-4), 123.1 (d, J_CP) 5.7 Hz,

C₆H₄, CH-5 or 3), 123.1 (d, J_CP) 52.3 Hz, PC₆H₄OMe, ipso-

CP), 136.9 (d, J_CP) 14.1 Hz, PC₆H₄OMe, o-CH) 137.7 (d, J_CP

) 10.1 Hz, C₆H₄, CH-6), 143.6 (d, J_CP) 6.4 Hz, quat.-C, C₆H₄,

C-2), 160.4 (d, J_CP) 2.8 Hz, quat.-C, C₆H₄, PdC-1), 161.4 (d,

J_CP) 1.7 Hz, quat.-C, PC₆H₄OMe, p-CO); δ_P/ppm: 41.5 (s).

MS (ESI+): m/z 1130.7 (M + 2), 564.6 (0.5M); C₅₆H₅₄O₈P₂Pd₂

requires 1128.

CH), 128.1 (d, J_CP) 10.6 Hz, PPh₃, m-CH), 130.1 (d, J_CP

)

2.2 Hz, PPh₃, p-CH), 131.6 (d, J_CP) 48.0 Hz, PPh₃, ipso-C),

134.6 (d, J_CP) 11.3 Hz, PPh₃, o-CH), 138.2 (d, J_CP) 12.7 Hz,

C₆H₄, CH-6), 141.1 (quat.-C, C₆H₄, C-1 or 2), 146.7 (d, J_CP

)

5.6 Hz, quat.-C, C₆H₄, C-1 or 2); δ_P/ppm: 35.6 (s). MS (ESI+):

m/z 978 (M + 2); C₅₂H₄₆O₂P₂Pd₂requires 976.

[1,1′-Bis(diphenylphosphino)ferrocene-K²P,P′][2-(2-

oxoethyl-KO)phenyl-KC¹]palladium, 23. 1,1′-Bis(diphen-

ylphosphino)ferrocene (358 mg, 0.65 mmol) in toluene (10 cm³)

was added dropwise to a suspension of bis[2-(µ-2-oxoethyl-κO)-

phenyl-κC¹]bis(triphenylphosphine)dipalladium, 20 (158 mg,

0.162 mmol), in toluene (10 cm³), and the mixture was stirred

for 4 h at RT. The resulting yellow-orange solid was collected

by filtration, washed with diethyl ether (3 × 10 cm³), and dried

in vacuo to give the title compound (177 mg, 70%). Found: C,

64.18; H, 5.02. C₄₂H₃₆FeOP₂Pd requires C, 64.59; H, 4.65. NMR

(CDCl₃); δ_H/ppm: 3.11 (vbr s, 2H, CH₂CH₂O), 3.51 (br s, 2H,

C₅H₄), 3.60 (vbr s, 2H, CH₂O), 4.14 (br s, 2H, C₅H₄), 4.47 (br

s, 2H, C₅H₄), 4.73 (br s, 2H, C₅H₄), 6.24 (br m, 1H, C₆H₄), 6.64

(m, 2H, C₆H₄), 6.79 (m, 1H, C₆H₄), 7.10 (m, 4H, PPh₂), 7.26

(m, 4H, PPh₂), 7.45 (br m, 8H, PPh₂), 8.06 (br m, 4H, PPh₂);

δ_P/ppm: 9.0 (d, J_PP) 35.2 Hz), 33.0 (d, J_PP) 35.3 Hz). MS

(ESI+): m/z 780.7 (M); C₄₂H₃₆FeOP₂Pd requires 780.

Typical Catalytic Carbonylation Reaction: Carbony-

lation of 2-(Hydroxymethyl)benzyl Bromide. 2-(Hydroxym-

ethyl)benzyl bromide, 2a (250 mg, 1.24 mmol), was added to

a solution of ethyldiisopropylamine (0.48 mL, 2.74 mmol) and

tetrakis(triphenylphosphine)palladium(0) (72 mg, 0.062 mmol)

in toluene (20 cm³). The vessel was immersed in a water bath

and heated to 60 °C, and CO (1 atm) was passed through the

mixture for 2 h to form a bright yellow homogeneous solution.

The mixture was acidified with dilute HCl and filtered, and

the soluble products were extracted into petroleum ether. The

organic phase was dried with magnesium sulfate and filtered

through a coarse sinter. GC-MS analysis of the sample showed

quantitative conversion to 3-isochromanone 1, which was

identified by comparison with an authentic sample: NMR

(CDCl₃); δ_H/ppm: 3.75 (s, 2H, CH₂CO), 5.35 (s, 2H, CH₂O),

7.15-7.4 (m, 4H, Ar-H). IR (CH₂Cl₂): ν_max(CO)/cm^-11750.

4.3. X-ray Data Collection and Crystal Structure De-

termination. Single crystals of compounds were grown by

slow diffusion of light petroleum into solutions of the complex

in dichloromethane at -15 °C. Crystals were mounted on a

glass fiber and data collected with a Siemens P4 diffractome-

ter. All data sets were collected with Mo KR radiation (0.7107

Å) at 160 K with cooling by an Oxford Cryosystems cryostream.

Absorption was corrected for using psi-scans, and structure

refinement was by full matrix least squares against F².³⁴For

all structures, H atoms were constrained to idealized geom-

etries; the hydroxyl hydrogen atoms were found in the differ-

ence map but drifted to unrealistic distances during refinement

and so were constrained. In 7, the disordered CH₂Cl₂solvent

was treated as 20/80% occupancy of both Cl atoms, each over

two sites. In 8, the anisotropy of C8 was restrained and the

disordered CH₂Cl₂solvent was modeled with one Cl atom over

three sites. In 25, one disordered CH₂Cl₂had one Cl atom over

three sites and the C atom over two sites. A summary of the

data from the crystal structure determinations is given in

Table 5.

[1,2-Bis(diphenylphosphino)ethane-K²P,P′][2-(2-oxo-

ethyl-κO)phenyl-KC¹]palladium, 24. 1,2-Bis(diphenylphos-

phino)ethane (450 mg, 1.13 mmol) in toluene (10 cm³) was

added dropwise to a suspension of bis[2-(µ-2-oxoethyl-κO)-

phenyl-κC¹]bis(triphenylphosphine)dipalladium, 20 (276 mg,

0.282 mmol), in toluene (15 cm³), and the mixture was stirred

for 3 h at RT to form a creamy-white suspension. The white

solid was collected by filtration, washed with diethyl ether (3

× 10 cm³), and dried in vacuo to give the title compound (241

mg, 68%). Found: C, 65.39; H, 5.20. C₃₄H₃₂OP₂Pd requires C,

65.34; H, 5.16. NMR (CDCl₃); δ_H/ppm: 2.05-2.6 (m, 4H, dppe

CH₂), 3.05 (m, 2H, CH₂CH₂O), 3.83 (m, 2H, CH₂O), 6.40 (m,

1H, C₆H₄), 6.54 (m, 1H, C₆H₄), ∼6.77 (m, 1H, C₆H₄), ∼7.15 (m,

1H, C₆H₄), 7.2-7.6 (m, 12H, PPh₂), 7.7-7.9 (m, 4H, PPh₂), 8.0-

8.17, (m, 4H, PPh₂); δ_P/ppm: 31.2 (d, J_PP) 28.0 Hz), 50.5 (d,

J_PP) 28.0 Hz). MS (ESI+): m/z 624.7 (M); C₃₄H₃₂OP₂Pd

requires 624.

Bis[2-(µ-oxomethyl-KO)phenyl-KC¹]bis[tris(4-meth-

oxyphenyl)phosphine]dipalladium, 25. Tris(4-methoxy-

phenyl)phosphine (275 mg, 0.78 mmol) in toluene (15 cm³) was

added dropwise to a suspension of bis[2-(µ-oxomethyl-κO)-

phenyl-κC¹]bis(triphenylphosphine)dipalladium, 19 (185 mg,

0.195 mmol), in toluene (15 cm³), and the mixture was stirred

for 12 h at RT. The resulting homogeneous, pale green solution

was reduced to 67% volume by distillation under reduced

pressure, and light petroleum ether (20 cm³) was added. The

white precipitate produced was collected by filtration, washed

with H₂O (2 × 10 cm³), followed by diethyl ether (3 × 20 cm³),

and dried in vacuo to give the title compound (171 mg, 78%).

Found: C, 58.66; H, 4.89. C₅₆H₅₄O₈P₂Pd₂‚H₂O requires C,

58.60; H, 4.92. NMR (CDCl₃); δ_H/ppm: 3.73 (s, 4H, CH₂O), 3.81

(s, 18H, OCH₃), 6.11 (t, J ) 6.6 Hz, 2H, C₆H₄, H-6), 6.24 (m,

4H, C₆H₄, H-3, 5), 6.61 (t, J ) 7.4 Hz, 2H, C₆H₄, H-4), 6.88

(∼d, J ≈ 8 Hz, 12H, PC₆H₄O, m-CH), 7.77 (dd, J ) 8.6 and

Acknowledgment. We thank Syngenta and Heriot-

Watt University for funding. We also thank Dr. A. S.

F. Boyd for recording the NMR spectra and for helpful

discussions.

Supporting Information Available: Tables of X-ray data

for complexes 3, 4, 7, 8, 14, 17 (solvated and unsolvated

crystals), and 25. This material is available free of charge via

the Internet at http://pubs.acs.org.

OM049131P

(34) Siemens XSCANS, Version 2.2; Siemens Analytical X-ray

Instruments Inc.: Madison, WI, 1996. Sheldrick, G. M. SHELXTL,

Version 5.10; Bruker AXS Inc.: Madison, WI, 1997.

Article Doi

Investigations of benzyl and aryl palladium complexes with pendant hydroxy substituants and their transformation into benzolactones on carbonylation

DOI: 10.1021/om049131p

Source and publish data:

Authors:

Article abstract of DOI:10.1021/om049131p

Full text of DOI:10.1021/om049131p

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