First Row Divalent Transition Metal Complexes of Aryl-Appended Tris((pyridyl)methyl)amine Ligands: Syntheses, Structures, Electrochemistry, and Hydroxamate Binding Properties

Inorg. Chem. 2003, 42, 7472−7488

First Row Divalent Transition Metal Complexes of Aryl-Appended

Tris((pyridyl)methyl)amine Ligands: Syntheses, Structures,

Electrochemistry, and Hydroxamate Binding Properties

Magdalena M. Makowska-Grzyska,^†Ewa Szajna,^†Crystal Shipley,^†Atta M. Arif,^‡Michael H. Mitchell,^§

,†

Jason A. Halfen,^§and Lisa M. Berreau*

Department of Chemistry and Biochemistry, Utah State UniVersity, Logan, Utah 84322-0300,

Department of Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112, and Department of

Chemistry, UniVersity of WisconsinsEau Claire, Eau Claire, Wisconsin 54702

Received July 12, 2003

Divalent manganese, cobalt, nickel, and zinc complexes of 6-Ph₂TPA (N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-

pyridyl)methyl)amine; [(6-Ph₂TPA)Mn(CH OH)₃](ClO ) (1), [(6-Ph₂TPA)Co(CH CN)](ClO ) (2), [(6-Ph₂TPA)Ni(CH -

3

4 2

3

4 2

3

CN)(CH OH)](ClO ) (3), [(6-Ph₂TPA)Zn(CH CN)](ClO ) (4)) and 6-(Me₂Ph)₂TPA (N,N-bis((6-(3,5-dimethyl)phenyl-

3

4 2

3

4 2

2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-(Me₂Ph)₂TPA)Ni(CH CN)₂](ClO ) (5) and [(6-(Me₂Ph)₂TPA)-

3

4 2

Zn(CH CN)](ClO ) (6)) have been prepared and characterized. X-ray crystallographic characterization of 1A‚CH OH

3

4 2

3

and 1B‚2CH OH (differing solvates of 1), 2‚2CH CN, 3‚CH OH, 4‚2CH CN, and 6‚2.5CH CN revealed mononuclear

3

cations with one to three coordinated solvent molecules. In 1A‚CH OH and 1B‚2CH OH, one phenyl-substituted

3

pyridyl arm is not coordinated and forms a secondary hydrogen-bonding interaction with a manganese bound

methanol molecule. In 2‚2CH CN, 3‚CH OH, 4‚2CH CN, and 6‚2.5CH CN, all pyridyl donors of the 6-Ph₂TPA and

3

6-(Me₂Ph)₂TPA ligands are coordinated to the divalent metal center. In the cobalt, nickel, and zinc derivatives,

CH/π interactions are found between a bound acetonitrile molecule and the aryl appendages of the 6-Ph₂TPA and

6-(Me₂Ph)₂TPA ligands. ¹H NMR spectra of 4 and 6 in CD NO solution indicate the presence of CH/π interactions,

3

2

as an upfield-shifted methyl resonance for a bound acetonitrile molecule is present. Examination of the cyclic

voltammetry of 1−3 and 5 revealed no oxidative (M(II)/M(III)) couples. Admixture of equimolar amounts of 6-Ph₂-

TPA, M(ClO ) ‚6H O, and Me₄NOH‚5H O, followed by the addition of an equimolar amount of acetohydroxamic

4 2

2

acid, yielded the acetohydroxamate complexes [((6-Ph₂TPA)Mn)₂(µ-ONHC(O)CH ) ](ClO ) (8), [(6-Ph₂TPA)Co-

3 2

4 2

(ONHC(O)CH )](ClO ) (9), [(6-Ph₂TPA)Ni(ONHC(O)CH )](ClO ) (10), and [(6-Ph₂TPA)Zn(ONHC(O)CH )](ClO )

4 2

3

4 2

3

4 2

3

(11), all of which were characterized by X-ray crystallography. The Mn(II) complex 8‚0.75CH CN‚0.75Et₂O exhibits

3

a dinuclear structure with bridging hydroxamate ligands, whereas the Co(II), Ni(II), and Zn(II) derivatives all exhibit

mononuclear six-coordinate structures with a chelating hydroxamate ligand.

Introduction

include the histidine-rich mononuclear Mn(II) centers in

oxalate oxidase¹and oxalate decarboxylase,^2,3and the

mononuclear Ni(II) center in acireductone dioxygenase.⁴

These enzymes have in common (1) a six-coordinate divalent

metal center situated in a largely hydrophobic active site and

having two water occupied coordination sites, and (2)

proposed mechanistic pathways that involve the oxidation

of a substrate or intermediate that may be coordinated to

The chemical reactivity of catalytically active metal centers

in metalloenzymes is influenced by many factors, including

the number and orientation of coordination sites occupied

by labile ligands (e.g., water) that may be displaced by

substrate or inhibitor binding, and the secondary environment

surrounding the metal center. Interesting biological metal

sites for which no model systems have been reported to date

(1) (a) Woo, E.-J.; Dunwell, J. M.; Goodenough, P. W.; Marvier, A. C.;

Pickersgill, R. W. Nat. Struct. Biol. 2000, 11, 1036-1040. (b) Woo,

E.-J.; Dunwell, J. M.; Goodenough, P. W.; Pickersgill, R. W. FEBS

Lett. 1998, 437, 87-90.

(2) Anand, R.; Dorrestein, P. C.; Kinsland, C.; Begley, T. P.; Ealick, S.

E. Biochemistry 2002, 41, 7659-7669.

* To whom correspondence should be addressed. E-mail:

berreau@cc.usu.edu. Phone: (435) 797-1625. Fax: (435) 797-3390.

^†Utah State University.

^‡University of Utah.

^§University of WisconsinsEau Claire.

7472 Inorganic Chemistry, Vol. 42, No. 23, 2003

Published on Web 10/15/2003

Aryl-Appended TPA Complexes

a 30 m HP-5 (cross-linked 5% PhMe-silicone) column. ¹H and ¹³C-

{¹H} NMR spectra were recorded on a JEOL GSX-270 or Bruker

ARX-400 spectrometer. Chemical shifts (in ppm) are referenced

to the residual solvent peak(s) in CD₃CN (¹H, 1.94 (quintet); ¹³C-

{¹H}, 1.39 (heptet) ppm), CD₃OD (¹H, 3.31 (pentet); ¹³C{¹H}, 49.15

(heptet) ppm), and CDCl₃(¹H, 7.25 (singlet);¹³C{¹H}, 77.23 (triplet)

ppm). Room-temperature magnetic susceptibilities were determined

by the Evans method.¹¹Electrochemical experiments were con-

ducted with a BAS CV50 potentiostat, using a platinum disk

working electrode, a silver wire pseudoreference electrode, and a

platinum wire auxiliary electrode. Cyclic voltammograms were

obtained in freshly distilled CH₃CN (0.1 M n-Bu₄NClO₄) with an

analyte concentration of 1 mM under an atmosphere of N₂. Under

these experimental conditions, the ferrocene/ferrocenium redox

couple was observed at + 363 mV versus Ag wire (∆E_p) 88 mV)

with i_pa/i_pc) 0.97. To obtain the potentials quoted herein (vs SCE),

the measured potentials were scaled on the basis of the Fc/Fc⁺

potential in CH₃CN (0.1 M n-Bu₄NClO₄) versus SCE (+ 380 mV).¹²

EPR spectra were obtained by using a Bruker ESP-300E spectrom-

eter fitted with a liquid helium cooled probe. Mass spectrometry

data for metal complexes were obtained at the Mass Spectrometry

Facility, Department of Chemistry, University of California,

Riverside. Elemental analyses were performed by Atlantic Micro-

labs of Norcross, GA.

the metal center via two oxygen donors to form a five-

membered chelate ring.^3a,4bNotably, five-membered chelate

rings involving a coordinated substrate are also proposed to

form during isomerization reactions mediated by the mono-

nuclear active site metal centers in glyoxalase I (human,

Zn²⁺; E. coli, Ni²⁺; isomerization of a hemithioacetal

substrate).⁵

In the work described herein, we have evaluated the

feasibility of using aryl-substituted tris((pyridyl)methyl)amine

ligand derivatives to form mononuclear metal complexes

that exhibit several key features. These include the follow-

ing: (1) a hydrophobic environment surrounding a divalent

metal center having one or more solvent-occupied coor-

dination sites, (2) stability of the divalent metal oxidation

state with respect to oxidation, and (3) an ability to main-

tain a mononuclear structure in derivative complexes having

a coordinated chelating anion. While aryl-substituted

tris((pyridyl)methyl)amine (TPA) ligands have received

recent attention in the literature for many applications,

including as building blocks for copper-containing molecular

recognition systems,⁶hemilabile ligands for Fe(II/III) deriva-

tives,⁷and ligand systems wherein an internal aromatic

substrate is present for Fe(II)/ROOH reactivity studies,⁸to

our knowledge such ligands have received minimal attention

in regard to their utility for developing chemistry relevant

to several other mononuclear divalent metal sites in metal-

loenzymes.⁹Herein we report the synthesis and comprehen-

sive characterization of two families of complexes supported

by aryl-appended TPA ligands.

Caution! Perchlorate salts of metal complexes with organic

ligands are potentially explosiVe. Only small amounts of material

should be prepared, and these should be handled with great care.¹³

Synthesis of Ligands. N,N-Bis((6-phenyl-2-pyridyl)methyl)-N-

((2-pyridyl)methyl)amine (6-Ph₂TPA) was synthesized following,

in part, reported literature procedures.^6a6-Phenyl-2-pyridinecar-

boxyaldehyde was prepared from 6-bromopicolylaldehyde following

a method reported by Canary and co-workers.^6aModified procedures

are reported for the synthesis of 6-phenyl-2-pyridinemethanol and

2-(chloromethyl)-6-phenylpyridine hydrochloride.

Experimental Section

General Methods. All reagents and solvents were obtained from

commercial sources and were used as received unless otherwise

noted. Solvents were dried according to published procedures and

were distilled under N₂prior to use.¹⁰Air-sensitive reactions were

performed in a MBraun Unilab glovebox under an atmosphere of

purified N₂.

Physical Methods. UV-vis spectra were recorded on a Hewlett-

Packard 8453 diode array spectrophotometer. IR spectra were

recorded on a Shimadzu FTIR-8400 spectrometer as KBr pellets,

neat films between NaCl plates, or solution spectra in CH₃CN

(∼100 mM). Low resolution electron impact mass spectra (LRE-

IMS) were obtained on a Shimadzu QP500 GC/MS equipped with

6-Phenyl-2-pyridinemethanol. To a methanol solution (40 mL)

of 6-phenyl-2-pyridinecarboxyaldehyde (3.37 g, 18.4 mmol) was

added dropwise an aqueous solution (15 mL) of NaBH₄(0.974 g,

25.8 mmol) over a period of 5 min. The resulting solution was

stirred at ambient temperature for ∼30 min. It was then heated at

∼50 °C for 2 h. To the cooled solution was added 6 M HCl to pH

) 1, and this solution was stirred for ∼5 min. To this solution was

added 1 M NaOH to pH ) 12. The resulting solution was extracted

with methylene chloride (3 × 80 mL), and the combined organic

fractions were dried over Na₂SO₄. Filtration and evaporation of

the solvent under reduced pressure yielded a yellow oil (3.39 g,

99%). ¹H NMR (CDCl₃, 400 MHz) δ 8.02-7.98 (m, 2H), 7.73 (t,

J ) 7.7 Hz, 1H), 7.62 (d, J ) 7.7 Hz, 1H), 7.49-7.39 (m, 3H),

7.14 (d, J ) 7.7 Hz, 1H), 4.80 (s, 2H). These ¹H NMR spectroscopic

features matched those previously reported.^6a

(3) (a) Tanner, A.; Bowater, L.; Fairhurst, S. A.; Bornemann, S. J. Biol.

Chem. 2001, 47, 43627-43634. (b) Tanner, A.; Bornemann, S. J.

Bacteriol. 2000, 182, 5271-5273.

(4) (a) Dai, Y.; Pochapsky, T. C.; Abeles, R. H. Biochemistry 2001, 40,

6379-6387. (b) Al-Mjeni, F.; Ju, T.; Pochapsky, T. C.; Maroney, M.

J. Biochemistry 2002, 41, 6761-6769.

2-(Chloromethyl)-6-phenylpyridine hydrochloride. To a 250-

mL round-bottom flask containing 6-phenyl-2-pyridinemethanol

(3.39 g, 18.3 mmol) in an ice bath was added dropwise 20 mL of

freshly distilled thionyl chloride. After an initial vigorous reaction

subsided, the reaction mixture was refluxed for 2 h. It was then

allowed to cool, and unreacted SOCl₂was removed under reduced

pressure. The resulting solid was collected, washed several times

with CH₂Cl₂, and dried, yielding a white powder (3.95 g, 90%).

¹H NMR (CD₃CN, 400 MHz) δ 8.28 (t, J ) 8.0 Hz, 1H), 8.12-

8.09 (m, 2H), 8.00 (d, J ) 8.0 Hz, 1H), 7.81 (d, J ) 8.0 Hz, 1H),

(5) Creighton, D. J.; Hamilton, D. S. Arch. Biochem. Biophys. 2001, 387,

1-10.

(6) (a) Chuang, C.-L.; Lim, K. T.; Chen, Q.; Zubieta, J.; Canary, J. W.

Inorg. Chem. 1995, 34, 2562-2568. (b) Chuang, C.-L.; Lim, K. T.;

Canary, J. W. Supramol. Chem. 1995, 5, 39-43.

(7) (a) Mandon, D.; Machkour, A.; Goetz, S.; Welter, R. Inorg. Chem.

2002, 41, 5364-5372. (b) Mandon, D.; Nopper, A.; Litrol, T.; Goetz,

S. Inorg. Chem. 2001, 40, 4803-4806.

(8) (a) Jensen, M. P.; Lange, S. J.; Mehn, M. P.; Que, E. L.; Que, L., Jr.

J. Am. Chem. Soc. 2003, 125, 2113-2128. (b) Lange, S. J.; Miyake,

H.; Que, L., Jr. J. Am. Chem. Soc. 1999, 121, 6330-6331.

(9) He, Z.; Craig, D. C.; Colbran, S. B. J. Chem. Soc., Dalton Trans.

2002, 4224-4235.

(11) Evans, D. F. J. Chem. Soc. 1959, 2003-2005.

(12) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877-910.

(13) Wolsey, W. C. J. Chem. Educ. 1973, 50, A335-A337.

(10) Armarego, W. L. F.; Perrin, D. D. Purification of Laboratory

Chemicals; 4th Ed.; Butterworth-Heinemann: Boston, MA, 1996.

Inorganic Chemistry, Vol. 42, No. 23, 2003 7473

Makowska-Grzyska et al.

1

7.61-7.56 (m, 3H), 5.28 (s, 2H). These H NMR spectroscopic

Hz, 1H), 8.17 (d, J ) 7.8 Hz, 1H), 7.61 (bs, 2H), 7.36 (s, 1H),

5.20 (s, 2H), 2.46 (s, 6H); ¹³C{¹H} NMR (CD₃OD, 100 MHz) δ

155.7, 153.2, 149.3, 141.1, 135.3, 132.0, 127.6, 127.4, 126.9, 41.2,

21.5 (11 signals expected and observed).

features matched those previously reported.^6a

N,N-Bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)-

amine (6-Ph₂TPA). This ligand has been previously reported.^6b,7a

However, the preparative method we have employed has not been

reported. A 250-mL round-bottom flask was charged with 2-(chlo-

romethyl)-6-phenylpyridine hydrochloride (6.62 g, 27.6 mmol),

2-pyridylmethylamine (1.49 g, 13.8 mmol), sodium carbonate (7.3

g), tetrabutylammonium bromide (∼3 mg), and CH₃CN (300 mL).

After establishing a nitrogen atmosphere, the mixture was refluxed

for 20 h. The reaction mixture was then cooled to room temperature

and poured into 1 M NaOH (∼150 mL). The resulting solution

was extracted with methylene chloride (3 × 150 mL), and the

combined organic fractions were dried over Na₂SO₄. After filtration,

the organic solution was brought to dryness under reduced pressure.

Column chromatography on silica gel (230-400 mesh; 1:2

methanol/ethyl acetate, R_f≈ 0.8), followed by removal of the

solvent under reduced pressure, yielded a white solid material (4.59

g, 75%). Mp: 103-105 °C. ¹H NMR (CD₃CN, 400 MHz) δ 8.49

(d, J ) 4.8 Hz, 1H), 8.06-8.02 (m, 4H), 7.77 (t, J ) 7.7 Hz, 2H),

7.72-7.67 (m, 4H), 7.56 (d, J ) 7.6 Hz, 2H), 7.49-7.40 (m, 6H),

7.20-7.18 (m, 1H), 3.96 (s, 6H); (CD₃OD, 400 MHz) δ 8.42 (d,

J ) 4.4 Hz, 1H), 7.96 (d, J ) 7.2 Hz, 4H), 7.77 (t, J ) 7.1 Hz,

4H), 7.64 (d, J ) 7.6 Hz, 2H), 7.55 (d, J ) 7.6 Hz, 2H), 7.44-

7.36 (m, 6H), 7.24-7.22 (m, 1H), 4.01 (s, 2H), 3.99 (s, 4H); ¹³C-

{¹H} NMR (CD₃OD, 100 MHz) δ 160.8, 160.5, 158.4, 149.6, 140.8,

138.9, 138.8, 130.1, 129.8, 128.3, 125.0, 123.9, 123.1, 120.5, 61.5,

61.4 (16 signals expected and observed). LREI-MS m/z (relative

intensity): 443 ([M + H]⁺, 100%). Anal. Calcd for C₃₀H₂₆N₄: C,

81.41; H, 5.93; N, 12.67. Found: C, 81.18; H, 5.93; N, 12.71.

6-(3,5-Dimethylphenyl)-2-pyridinecarboxyaldehyde. To a stirred

solution of 6-bromopicolylaldehyde¹⁴(3.01 g, 16.2 mmol) and Pd-

(PPh₃)₄(0.561 g, 0.485 mmol) in 30 mL of toluene under nitrogen

were added 17 mL of 2 M Na₂CO₃(aq) and 3,5-dimethylphenyl-

boronic acid (2.91 g, 19.4 mmol) in 15 mL of methanol. The

resulting mixture was refluxed for 12 h. It was then allowed to

cool and was partitioned between 100 mL of methylene chloride

and 60 mL of 2 M Na₂CO₃(aq) containing 6 mL of concentrated

NH₃. The organic layer was dried over Na₂SO₄, filtered, and brought

to dryness under reduced pressure. Column chromatography on

silica gel (230-400 mesh; 4:1 ethyl acetate/hexanes, R_f≈ 0.6)

followed by removal of the solvent under reduced pressure yielded

yellow solid material (3.00 g, 88%). ¹H NMR (CDCl₃, 270 MHz)

δ 10.1 (s, 1H), 8.10-7.60 (m, 2H), 7.85 (d, J ) 7.2 Hz, 1H), 7.76

(s, 2H), 7.15 (s, 1H), 2.40 (s, 6H); ¹³C{¹H} NMR (CDCl₃, 100

MHz) δ 194.1, 158.3, 152.7, 138.6, 138.3, 137.7, 131.4, 124.9,

124.7, 119.7, 21.5 (11 signals expected and observed).

N,N-Bis((6-(3,5-dimethyl)phenyl-2-pyridyl)methyl)-N-((2-py-

ridyl)methyl)amine (6-(Me₂Ph)₂TPA). This was prepared follow-

ing the procedure for 6-Ph₂TPA. Yield 5.00 g, 70%. H NMR

1

(CD₃CN, 400 MHz) δ 8.47 (m, 1H), 7.75-7.55 (m, 10H), 7.50 (d,

J ) 7.6 Hz, 1H), 7.18-7.14 (m, 1H), 7,02 (bs, 2H), 3.90 (s, 6H),

2.30 (s, 6H); ¹³C{¹H} NMR (CD₃CN, 100 MHz) δ 160.7, 160.3,

157.3, 149.9, 140.3, 139.2, 138.2, 137.3, 131.4, 125.6, 123.9, 123.0,

122.3, 119.5, 61.0, 60.9, 21.6 (17 signals expected and observed).

LREI-MS m/z (relative intensity): 499 ([M + H]⁺, 55%). Anal.

Calcd for C₂₈H₂₆N₄‚0.5H₂O: C, 80.43; H, 6.95; N, 11.04. Found:

1

C, 80.30; H, 6.80; N, 10.99. H NMR in dry CD₃CN confirmed

the presence of water in the elemental analysis sample.

General Procedure for Synthesis of Metal Complexes. To a

methanol slurry (2 mL) of the ligand (6-Ph₂TPA or 6-(Me₂Ph)₂TPA)

was added a methanol solution (2 mL) of M(ClO₄)₂‚6H₂O (M )

Mn, Co, Ni, or Zn; <100 mg scale), and the resulting mixture was

stirred at ambient temperature until all of the ligand had dissolved

(∼15 min) and then for an additional 20 min. Each solution was

then added to excess diethyl ether (∼80 mL), and the resulting

cloudy solution was cooled at ∼-20 °C for 12 h. Solid that had

deposited in each reaction mixture was then collected and carefully

dried under vacuum.

[(6-Ph₂TPA)Mn(CH₃OH)₃](ClO₄)₂(1). Recrystallization of a

pale yellow-brown solid from diethyl ether diffusion into a CH₃-

OH solution yielded two types of crystals (light brown, 1A; and

colorless, 1B), both suitable for single crystal X-ray diffraction

(combined yield: 57%). LRFAB-MS (CH₃CN/NBA), m/z (relative

intensity): 596 ([M - ClO₄- 3CH₃OH]⁺, 100%). Anal. Calcd

for C₃₀H₂₆N₄Cl₂O₈Mn(CH₃OH)_1.5: C, 50.87; H, 4.34; N, 7.54.

Found: C, 50.57; H, 3.98; N, 7.72. By X-ray crystallography, three

methanol molecules are coordinated to the Mn(II) center in this

complex. An additional one or two methanol solvate molecules,

respectively, were also found in the two different crystalline forms

of this complex (1A‚CH₃OH and 1B‚2CH₃OH) that were char-

acterized by X-ray crystallography. Drying of the crystals for

elemental analysis indicates that partial loss of methanol will occur

under vacuum.

[(6-Ph₂TPA)Co(CH₃CN)](ClO₄)₂‚CH₃CN (2). The deposited

purple solid was recrystallized by diethyl ether diffusion into a CH₃-

OH/CH₃CN (1:1) solution which yielded brown crystalline prisms

suitable for single crystal X-ray diffraction (80%). LRFAB-MS

(CH₃CN/NBA), m/z (relative intensity): 600 ([M - ClO₄- CH₃-

CN]⁺, 57%). Anal. Calcd for C₃₀H₂₆N₄Cl₂O₈Co(CH₃CN)‚CH₃CN:

C, 52.23; H, 4.13; N, 10.76. Found: C, 51.91; H, 4.24; N, 10.97.

The presence of a noncoordinated acetonitrile solvate in the solid

was confirmed by X-ray crystallography.

[(6-Ph₂TPA)Ni(CH₃CN)(CH₃OH)](ClO₄)₂(3). Recrystallization

of a light green solid from diethyl ether diffusion into a CH₃OH/

CH₃CN (1:1) solution yielded purple crystalline prisms suitable for

single crystal X-ray diffraction (70%). LRFAB-MS (CH₃CN/NBA),

m/z (relative intensity): 599 ([M - ClO₄- CH₃CN - CH₃OH]⁺,

100%). Anal. Calcd for C₃₀H₂₆N₄Cl₂O₈Ni(CH₃CN)(CH₃OH): C,

51.36; H, 4.31; N, 9.08. Found: C, 50.06; H, 4.23; N, 8.86.

Repeated attempts to obtain elemental analysis data for this complex

always yielded low carbon contents.

6-(3,5-Dimethylphenyl)-2-pyridinemethanol. This was prepared

following the procedure for 6-phenyl-2-pyridinemethanol. Yield

2.99 g, 99%. ¹H NMR (CD₃CN, 270 MHz) δ 7.80 (t, J ) 7.7 Hz,

1H), 7.71-7.68 (m, 3H), 7.32 (d, J ) 7.6 Hz, 1H), 7.09 (bs, 1H),

4.69 (d, J ) 5.6 Hz, 2H), 3.76, (t, J ) 5.6 Hz), 2.37 (s, 6H); ¹³C-

{¹H} NMR (CD₃CN, 67.5 MHz) δ 161.5, 157.1, 140.0, 139.3,

138.9, 138.6, 131.5, 125.6, 119.8, 65.4, 21.5 (11 signals expected

and observed). LREI-MS m/z (relative intensity): 212 ([M - H]⁺,

100%).

2-(Chloromethyl)-6-(3,5-dimethylphenyl)pyridine hydrochlo-

ride. This was prepared following the procedure for 2-(chlorom-

ethyl)-6-phenylpyridine hydrochloride. Yield 3.63 g, 97%. ¹H NMR

(CD₃OD, 400 MHz) δ 8.69 (t, J ) 8.0 Hz, 1H), 8.31 (d, J ) 8.0

[(6-Ph₂TPA)Zn(CH₃CN)](ClO₄)₂(4). Recrystallization of a

white powder from diethyl ether diffusion into a CH₃OH/CH₃CN

(1:1) solution yielded colorless crystalline prisms suitable for single

crystal X-ray diffraction (72%). LRFAB-MS (CH₃CN/NBA), m/z

(14) Parks, J. E.; Wagner, B. E.; Holm, R. H. Inorg. Chem. 1971, 10, 2472-

2478.

7474 Inorganic Chemistry, Vol. 42, No. 23, 2003

Aryl-Appended TPA Complexes

(relative intensity): 605 ([M - ClO₄- CH₃CN]⁺, 100%). ¹H NMR

(CD₃CN, 270 MHz): δ 8.34 (d, J ) 4.6 Hz, 1H), 8.25-8.17 (m,

3H), 7.78 (d, J ) 7.6 Hz, 2H), 7.70 (d, J ) 7.9 Hz, 2H), 7.61 (d,

J ) 7.6 Hz, 2H), 7.52 (t, J ) 7.3 Hz, 2H), 7.39 (t, J ) 7.6 Hz,

4H), 7.12 (d, J ) 7.3 Hz, 4H), 4.53 (d, J ) 17 Hz, 2H), 4.45 (s,

2H), 4.40 (d, J ) 17 Hz, 2H), 1.96 (s, CH₃CN, 3H); ¹³C{¹H} NMR

(CD₃CN, 100 MHz) δ 160.7, 157.6, 155.8, 149.1, 143.2, 139.7,

131.4, 130.6, 129.4, 126.9, 126.8, 126.3, 124.5, 57.0, 56.8 (15 of

16 expected signals of the supporting chelate ligand were observed;

1 aromatic resonance was missing, presumably due to overlap with

another aromatic signal). Anal. Calcd for C₃₀H₂₆N₄Cl₂O₈Zn(CH₃-

CN)‚0.5CH₃CN: C, 51.73; H, 4.02; N, 10.06. Found: C, 51.68;

H, 4.07; N, 10.05. The presence of a noncoordinated acetonitrile

solvate in the solid state was confirmed by X-ray crystallography.

Drying of the crystals for elemental analysis leads to partial loss

of CH₃CN. The amount of CH₃CN present in a dried crystalline

through a Celite/glass wool plug. The filtrate solution was then

evaporated to dryness.

[((6-Ph₂TPA)Mn)₂(µ-ONHC(O)CH₃)₂](ClO₄)₂(8). Recrystal-

lization of a pale yellow-brown solid from diethyl ether diffusion

i

into a PrOH/CH₃CN (1:3) solution yielded colorless crystals

suitable for single crystal X-ray diffraction (yield: 80%). Anal.

Calcd for C₃₂H₃₀N₅ClO₆Mn: C, 57.30; H, 4.51; N, 10.45. Found:

C, 56.99; H, 4.67; N, 10.16.

[(6-Ph₂TPA)Co(ONHC(O)CH₃)](ClO₄) (9). The red solid was

recrystallized by diethyl ether diffusion into a ⁱPrOH/CH₃CN (1:2)

solution, which yielded red crystalline prisms suitable for single

crystal X-ray diffraction (yield: 84%). Anal. Calcd for C₃₂H₃₀N₅-

ClO₆Co: C, 56.96; H, 4.49; N, 10.39. Found: C, 57.12; H, 4.63;

N, 10.72.

[(6-Ph₂TPA)Ni(ONHC(O)CH₃)](ClO₄) (10). Recrystallization

of a light green solid from diethyl ether diffusion into a CH₃OH/

CH₃CN (1:1) solution yielded green crystalline prisms suitable for

single crystal X-ray diffraction (yield: 79%). Anal. Calcd for

C₃₂H₃₀N₅ClO₆Ni: C, 57.05; H, 4.49; N, 10.40. Found: C, 56.94;

H, 4.61; N, 10.29.

1

sample (1.5 equiv) was confirmed by H NMR.

[(6-(Me₂Ph)₂TPA)Ni(CH₃CN)₂](ClO₄)₂(5). The deposited light

i

green solid was recrystallized by diethyl ether diffusion into a -

PrOH/CH₃CN (1:2) solution, which yielded purple crystalline

prisms (68%). LRFAB-MS (CH₃CN/NBA), m/z (relative inten-

sity): 655 ([M - ClO₄- 2CH₃CN]⁺, 100%). Anal. Calcd for

C₃₄H₃₄N₄Cl₂O₈Ni(CH₃CN)₂: C, 54.53; H, 4.82; N, 10.05. Found:

C, 54.63; H, 4.96; N, 10.53.

[(6-Ph₂TPA)Zn(ONHC(O)CH₃)](ClO₄) (11). The yellow solid

i

was recrystallized by diethyl ether diffusion into an PrOH/CH₃-

CN (1:2) solution, which yielded colorless crystalline prisms suitable

1

for X-ray crystallographic analysis (yield: 68%). H NMR (CD₃-

[(6-(Me₂Ph)₂TPA)Zn(CH₃CN)](ClO₄)₂(6). The deposited white

powder was recrystallized by diethyl ether diffusion into a CH₃-

OH/CH₃CN (1:1) solution and yielded colorless crystalline plates

suitable for X-ray diffraction (59%). LRFAB-MS (CH₃CN/NBA),

m/z (relative intensity): 661 ([M - ClO₄- CH₃CN]⁺, 100%). ¹H

NMR (CD₃CN, 400 MHz): δ 8.32 (d, J ) 5.1 Hz, 1H), 8.22-

8.16 (m, 3H), 7.70-7.67 (m, 4H), 7.60 (d, J ) 7.7 Hz, 2H), 7.18

(s, 2H), 6.70 (s, 4H), 4.54 (d, 18 Hz, 2H), 4.43 (s; 2H), 4.40 (d, 18

Hz, 2H), 2.19 (s, -CH₃, 6H), 1.96 (s, 3H, CH₃CN); ¹³C{¹H} NMR

(CD₃CN, 100 MHz) δ 161.1, 157.5, 155.9, 149.4, 143.2, 143.0,

140.2, 140.0, 132.8, 127.1, 127.0, 126.8, 126.6, 124.5, 56.8, 56.7,

21.6 (17 signals for the 6-(Me₂Ph)₂TPA ligand were expected and

observed). Anal. Calcd for C₃₄H₃₄N₄Cl₂O₈Zn(CH₃CN): C, 53.92;

H, 4.65; N, 8.74. Found: C, 52.72; H, 4.72; N, 8.58. Repeated

attempts to obtain elemental analysis data for this complex always

led to low carbon contents.

[(TPA)Zn(CH₃CN)](ClO₄)₂(7). The deposited yellow powder

was recrystallized by diethyl ether diffusion into a CH₃CN solution

and yielded a yellow crystalline solid (84%). LRFAB-MS (CH₃-

CN/NBA), m/z (relative intensity): 455 ([M - ClO₄- CH₃CN]⁺,

97%). ¹H NMR (CD₃CN, 270 MHz): δ 8.79 (d, J ) 5.4 Hz, 3H),

8.12 (td, J₁) 7.7 Hz, J₂) 1.6 Hz, 3H), 7.68 (t, J ) 6.4 Hz, 3H),

7.60 (d, J ) 7.9 Hz, 3H), 4.27 (s, 6H); ¹³C{¹H} NMR (CD₃CN, 68

MHz) δ 155.3, 148.5, 142.2, 125.6, 125.1, 57.0 (6 signals for the

TPA ligand were expected and observed). Anal. Calcd for C₁₈H₁₈N₄-

Cl₂O₈Zn(CH₃CN): C, 40.47; H, 3.57; N, 11.81. Found: C, 40.04;

H, 3.60; N, 11.75.

General Procedure for Synthesis of Acetohydroxamate Com-

plexes. To a methanol slurry (2 mL) of the ligand (6-Ph₂TPA) was

added a methanol solution (2 mL) of an equimolar amount of

M(ClO₄)₂‚6H₂O (<100 mg scale), and the resulting mixture was

stirred at ambient temperature until all of the ligand had dissolved

(∼15 min) and then for an additional 20 min. This solution was

then added to a methanol solution (1 mL) of an equimolar amount

of Me₄NOH‚5H₂O. Following 1 h of stirring, this solution was

added to a methanol solution (1 mL) of 1.04-1.07 equiv of

acetohydroxamic acid, and the new solution was stirred for 12 h.

At this time, the solvent was removed under reduced pressure. The

dried solid was then dissolved in CH₂Cl₂(10 mL) and filtered

CN, 400 MHz): δ 9.81 (bs, N-H, 1H), 8.04 (d, J ) 7.6 Hz, 1H),

7.85-7.75 (m, 2H), 7.45-7.20 (m, 16H), 7.18 (d, J ) 7.8 Hz,

1H), 4.55 (d, J ) 15 Hz, 2H), 4.35 (d, J ) 15 Hz, 2H), 4.24 (s,

2H), 1.46 (s, CH₃, 3H); ¹³C{¹H} NMR (CD₃CN, 100 MHz) δ 164.5,

159.6, 156.0, 155.8, 148.5, 141.4, 140.4, 139.5, 130.3, 129.5, 128.8,

125.1, 124.7, 124.2, 123.6, 61.7, 58.2, 17.9 (18 signals expected

and observed). Anal. Calcd for C₃₂H₃₀N₅ClO₆Zn: C, 56.54; H, 4.45;

N, 10.31. Found: C, 56.05; H, 4.53; N, 10.72.

X-ray Crystallography. A crystal of 1A, 1B, 2-4, and 6-11

was mounted on a glass fiber with traces of viscous oil and then

transferred to a Nonius KappaCCD diffractometer with Mo KR

radiation (λ ) 0.71073 Å) for data collection at 150(1) K. For each

compound, an initial set of cell constants was obtained from 10

frames of data that were collected with an oscillation range of 1

deg/frame and an exposure time of 20 s/frame. Final cell constants

for each complex were determined from a set of strong reflections

from the actual data collection. For each data set, these reflections

were indexed, integrated, and corrected for Lorentz, polarization,

and absorption effects using DENZO-SMN and SCALEPAC.¹⁵The

structures were solved by a combination of direct methods and

heavy atom using SIR 97. All of the non-hydrogen atoms were

refined with anisotropic displacement coefficients. Unless otherwise

stated, hydrogen atoms were assigned isotropic displacement

coefficients U(H) ) 1.2U(C) or 1.5U(Cmethyl), and their coordi-

nates were allowed to ride on their respective carbons using

SHELXL97.

Structure Solution and Refinement. Complex 1A‚CH₃OH

crystallized in the space group P2₁/a. One molecule of noncoor-

dinated methanol is present per asymmetric unit. All hydrogen

atoms were located and refined independently using SHELXL97,

except those of the noncoordinated molecule of methanol, which

were assigned isotropic displacement coefficients. Complex 1B‚

2CH₃OH crystallized in the space group P1h. Two noncoordinated

molecules of methanol are present in the asymmetric unit. All

hydrogen atoms were located and refined independently using

SHELXL97, except hydrogen atoms on C(31), C(32), C(33) of the

coordinated molecules of methanol, and on C(34), O(12), and C(35)

(15) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307-326.

Inorganic Chemistry, Vol. 42, No. 23, 2003 7475

Makowska-Grzyska et al.

Scheme 1

of the noncoordinated solvate molecules of methanol, which were

assigned isotropic displacement coefficients. Complex 2‚2CH₃CN

crystallized in the space group P2₁/c. Two noncoordinated aceto-

nitrile molecules are present in the asymmetric unit. All hydrogen

atoms were located and refined independently using SHELXL97,

except those on C(32) of the coordinated molecule of acetonitrile,

and on C(34) and C(36) of the noncoordinated molecules of

acetonitrile, which were assigned isotropic displacement coef-

ficients. In the structure of 2‚2CH₃CN, each perchlorate anion

exhibits disorder. Each disordered atom was split into two fragments

(O(2)/O(2′), O(3)/O(3′), O(4)/O(4′), O(7)/O(7′), O(8)/O(8′)) and

was refined. This refinement led to a 0.88:0.12 ratio in occupancy

over two positions. Complex 3‚CH₃OH crystallized in the space

group Pca2₁. The methanol hydroxyl proton of nickel-bound

methanol was located and refined independently using SHELXL97.

One molecule of noncoordinated methanol is present per asymmetric

unit. One perchlorate anion exhibits disorder. Each oxygen atom

of this perchlorate (O(6)-O(9)) was split into two fragments

(second denoted by a prime) and refined. This refinement led to a

0.50:0.50 ratio in occupancy over two positions for each oxygen

atom. Complex 4‚2CH₃CN crystallized in the space group P2₁/c.

Two molecules of noncoordinated acetonitrile solvate are present

in the asymmetric unit. All hydrogen atoms were located and refined

independently using SHELXL97, except those on C(32) of the

coordinated molecule of acetonitrile, and on C(34) and C(36) of

the noncoordinated solvate molecules of acetonitrile, which were

assigned isotropic displacement coefficients. Each perchlorate anion

exhibits disorder. Each disordered oxygen atom was split into two

fragments (second denoted by a prime) and was refined. This

refinement led to a 0.83:0.17 ratio for O(2), O(3), and O(4) and a

0.92:0.08 ratio for O(7) and O(8). Complex 6‚2.5CH₃CN crystal-

lized in the space group P1h. Two formula units are present per

asymmetric unit, with the second denoted by “A.” Five molecules

of noncoordinated acetonitrile were present in the asymmetric unit.

Three of the four perchlorate anions exhibit disorder. Each

disordered oxygen atom (O(1)-O(4), O(3A), O(4A), O(7), O(8))

was split into two fragments (second denoted by a prime) and

refined. This refinement led to a 0.83:0.17 ratio in occupancy over

two positions for each oxygen atom. Complex 7‚CH₃CN crystal-

lized in the space group P2₁/a. One molecule of noncoordinated

CH₃CN was found in the lattice. All hydrogen atoms were located

and refined independently using SHELXL97. Complex 8‚0.75-

CH₃CN‚0.75Et₂O crystallizes in the space group P1h with two

formula units present per asymmetric unit, with the second denoted

by “A”. One perchlorate anion exhibits disorder in the positions of

the chlorine atom and three oxygen atoms. Each was split into two

fragments and refined. This refinement led to a 0.50:0.50 ratio in

occupancy over two positions for each atom. One full molecule of

acetonitrile solvate was identified. Another half-occupied acetonitrile

molecule, as well as two diethyl ether molecules, one of which is

half-occupied, were also identified. Complex 9 crystallized in the

space group P2₁/c. All hydrogen atoms were located and refined

independently using SHELXL97. Complex 10‚1.5CH₃CN crystal-

lized in the space group I2/a. One and one-half molecules of

acetonitrile, dispersed over three half-occupied orientations, were

present in the asymmetric unit. All hydrogen atoms were located

and refined independently using SHELXL97, except those on C(34),

C(36), and C(38) of the noncoordinated molecules of acetonitrile,

which were assigned isotropic displacement coefficients. Complex

11 crystallized in the space group P2₁/n. All hydrogen atoms were

located and refined independently using SHELXL97. All four

oxygen atoms of one perchlorate anion exhibited disorder. These

disordered oxygen atoms were split into three fragments (second

denoted by “A” and third denoted by “B”) and were refined. This

refinement led to a 0.33:0.33:0.33 ratio in occupancy over three

positions for each oxygen atom.

Results

Synthesis of Ligands. The 6-Ph₂TPA and 6-(Me₂Ph)₂TPA

ligands were synthesized following the pathway outlined in

Scheme 1. Canary and Mandon et al. have previously

reported the synthesis of the 6-Ph₂TPA ligand.^7a,6bIn the

synthetic pathway reported by Canary et al., the final chelate

was produced in 30% yield via a reductive amination reaction

involving 6-phenyl-2-pyridinecarboxyaldehyde and 2-ami-

nomethylpyridine in the presence of NaCNBH₃. Mandon et

al. utilized a Suzuki coupling pathway to prepare 6-Ph₂TPA

starting from N,N-bis(6-bromo-2-pyridylmethyl)-N-(2-py-

ridylmethyl)amine and phenylboronic acid. However, no

yield was reported for this reaction. We have found that a

relatively high yield synthesis (overall yield: 53% starting

from 6-bromopicolylaldehyde) of 6-Ph₂TPA may be achieved

7476 Inorganic Chemistry, Vol. 42, No. 23, 2003

Aryl-Appended TPA Complexes

Scheme 2

Scheme 3

nickel complex (5) was obtained as single crystals upon

recrystallization from 2-propanol/acetonitrile/diethyl ether.

In all cases, yields of analytically pure crystalline materials

exceeded 50% (Schemes 2 and 3).

X-ray Structures. Single crystals of X-ray quality were

obtained for compounds 1-4, and 6. Details of the data

collection and structure refinement are given in Table 1.

Selected bond distances and angles are given in Tables 2

and 3.

[(6-Ph₂TPA)Mn(CH₃OH)₃](ClO₄)₂(1). Crystallization of

the Ph₂TPA-ligated Mn(II) complex from methanol/diethyl

ether repeatedly produced two crystalline forms of the

complex (light brown and colorless crystals) in an ap-

proximately 2:1 ratio. The light brown crystals (1A‚CH₃OH)

belong to the monoclinic space group P2₁/a and were found

to contain one molecule of noncoordinated methanol in the

lattice. The colorless crystalline (1B‚2CH₃OH) material

instead crystallized in the triclinic space group P1h and was

found to contain two noncoordinated methanol molecules

per asymmetric unit. As the overall structural features of the

cationic portions of 1A‚CH₃OH and 1B‚2CH₃OH are very

similar, only a single ORTEP representation of 1B‚2CH₃-

OH is shown in Figure 1. In this structure, the Mn(II) ion

adopts a distorted octahedral geometry, with the 6-Ph₂TPA

ligand binding in a meridional fashion, with only one of the

two available phenyl-substituted pyridyl groups binding to

the divalent manganese center. This type of coordination is

not unexpected as halide-, alkyl-, and aryl-substituted pyridyl

donors have been previously shown to exhibit hemilabile

behavior with a variety of metal ions.^7,9,16,17However,

reported manganese complexes of TPA and substituted alkyl

derivatives have to date shown coordination of all available

nitrogen atoms of the tetradentate chelate donor.¹⁸

using a synthetic route that involves as the final step

alkylation of 2-aminomethylpyridine with 2 equiv of 2-(chlo-

romethyl)-6-phenylpyridine hydrochloride. The crude mate-

rial obtained from this reaction may be purified by column

chromatography on silica gel using methanol as the final

eluent. When purified, the 6-Ph₂TPA and 6-(Me₂Ph)₂TPA

ligands are pale yellow to white solids with moderate to good

solubility in several organic solvents (e.g., methylene

chloride, acetonitrile, methanol), albeit the methyl derivative

6-(Me₂Ph)₂TPA exhibits better solubility, particularly in

acetonitrile solution.

Synthesis and Isolation of Divalent Metal Complexes

Having Solvent-Occupied Coordination Sites. Treatment

of a methanol solution of 6-Ph₂TPA or 6-(Me₂Ph)₂TPA with

a methanol solution of an equimolar amount of a divalent

metal perchlorate salt (M(ClO₄)₂‚6H₂O, M ) Mn, Co, Ni,

Zn) yielded crude solid materials following precipitation

induced by the addition of diethyl ether. Recrystallization

of the 6-Ph₂TPA manganese derivative 1 from methanol/

ethyl ether yielded a clear crystalline solid. 6-Ph₂TPA-ligated

cobalt and nickel perchlorate complexes (2 and 3), and a

6-(Me₂Ph)₂TPA-ligated zinc perchlorate derivative (6), were

obtained as crystalline solids from diethyl ether diffusion

into methanol/acetonitrile solutions. A 6-Ph₂TPA-chelated

The Mn-N distances in 1A‚CH₃OH and 1B‚2CH₃OH

are generally similar. However, while identical M-N_py

(16) 6-Me₃TPA. Fe: (a) Jo, D.-H.; Chiou, Y.-M.; Que, L., Jr. Inorg. Chem.

2001, 40, 3181-3190. Cu(II): (b) Nagao, H.; Komeda, N.; Mukaida,

M.; Suzuki, M.; Tanaka, K. Inorg. Chem. 1996, 35, 6809-6815.

(17) TPA. Cu(I): Tyekla´r, Z.; Jacobson, R. R.; Wei, N.; Murthy, N. N.;

Zubieta, J.; Karlin, K. D. J. Am. Chem. Soc. 1993, 115, 2677-2689.

Inorganic Chemistry, Vol. 42, No. 23, 2003 7477

Makowska-Grzyska et al.

Table 1. Summary of X-ray Data Collection and Refinement^a

1A‚CH₃OH 1B‚2CH₃OH

C₃₄H₄₂N₄Cl₂O₁₂Mn C₃₅H₄₆N₄Cl₂O₁₃Mn C₃₆H₃₅N₇Cl₂O₈Co

2‚2CH₃CN

3‚CH₃OH

4‚2CH₃CN

6‚2.5CH₃CN

empirical formula

fw

C₃₄H₃₇N₅Cl₂O₁₀Ni

805.30

C₃₆H₃₅N₇Cl₂O₈Zn

829.98

C₄₁H_44.5N_7.5Cl₂O₈Zn

906.61

824.56

856.60

823.54

cryst syst

space group

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³)

monoclinic

P2₁/a

13.5366(2)

16.8549(2)

17.4487(3)

triclinic

P1h

monoclinic

P2₁/c

13.6560(3)

19.2024(4)

14.2572(3)

orthorhombic

Pca2₁

20.2150(2)

14.4727(2)

12.3174(4)

monoclinic

P2₁/c

13.6463(2)

19.2789(3)

14.2590(2)

triclinic

P1h

10.8211(2)

14.0027(3)

15.1617(4)

96.8521(8)

107.5620(9)

110.3167(13)

1988.48(8)

2

11.18630(10)

18.4130(2)

21.6868(4)

90.7240(5)

90.3750(5)

106.4669(7)

4283.10(10)

4

104.9156(5)

94.5372(12)

94.5087(5)

3846.92(10)

4

1.424

3726.92(14)

4

1.468

3603.65(13)

4

1.484

3739.73(10)

4

1.474

Z

d

_calcd, Mg m^-3

1.431

1.406

temp (K)

150(1)

cryst size (mm³)

abs coeff (mm^-1

2θ max (deg)

reflns collected

indep reflns

0.33 × 0.25 × 0.23 0.28 × 0.25 × 0.08 0.28 × 0.25 × 0.13 0.35 × 0.28 × 0.20 0.40 × 0.38 × 0.28 0.30 × 0.15 × 0.10

)

0.547

54.94

16616

8738

0.534

55.04

13924

8886

0.665

54.98

14524

8517

0.751

54.96

7953

0.861

55.00

15122

8530

0.759

55.78

29920

19735

variable params

633

0.0565/0.1464

1.030

622

0.0533/0.1330

1.037

616

0.0511/0.1252

1.032

513

0.0613/0.1468

1.119

617

0.0367/0.0890

1.026

1121

0.0532/0.1118

1.014

R1/wR2^b

GOF (F²)

largest diff (e Å^-3

)

0.933/-0.521

1.042/-0.970

0597/-0.434

0.867/-0.586

0.634/-0.575

1.683/-0.851

2

^aRadiation used: Mo KR (λ ) 0.71073 Å). Diffractometer: Nonius KappaCCD. ^bR1 ) ∑||F_o| - |F_c||/∑|F_o|; wR2 ) [∑[w(F_o- F_c)²]/[∑(F_o)²]]^1/2

where w ) 1/[σ²(F_o) + (aP)²+ bP].

2

Table 2. Selected Bond Distances for Solvent-Coordinated Complexes^a

1A‚CH₃OH

1B‚2CH₃OH

2‚2CH₃CN

3‚CH₃OH

4‚2CH₃CN

6A^b

6B^b

M-N(1)

M-N(2)

M-N(3)

M-N(4)

M-N(5)

M-O(1)

M-O(2)

M-O(3)

2.254(3)

2.348(2)

2.298(2)

2.254(2)

2.355(2)

2.258(2)

2.052(2)

2.154(2)

2.082(2)

2.114(2)

2.059(2)

2.065(4)

2.082(4)

2.218(5)

2.200(5)

2.044(4)

2.083(3)

2.053(2)

2.167(2)

2.139(2)

2.075(2)

2.070(2)

2.090(2)

2.177(2)

2.113(2)

2.064(2)

2.073(3)

2.072(2)

2.156(2)

2.144(2)

2.076(2)

2.060(3)

2.170(2)

2.153(2)

2.138(2)

2.199(2)

2.136(2)

2.164(2)

^aEstimated standard deviations in the last significant figure are given in parentheses. ^bTwo independent cations are present in the asymmetric unit of

6‚2.5CH₃CN.

Table 3. Selected Bond Angles for Solvent-Coordinated Complexes^a

1A‚CH₃OH

1B‚2CH₃OH

2‚2CH₃CN

3‚CH₃OH

4‚2CH₃CN

6A^b

6B^b

N(5)-M-N(2)

O(2)-M-N(2)

N(2)-M-N(1)

N(2)-M-N(3)

N(2)-M-N(4)

N(2)-M-O(3)

N(2)-M-O(1)

N(1)-M-N(3)

N(3)-M-O(1)

N(1)-M-O(1)

O(1)-M-N(4)

N(1)-M-N(4)

N(3)-M-O(3)

O(3)-M-N(1)

N(3)-M-N(4)

O(1)-M-O(3)

171.55(8)

175.12(19)

170.41(6)

169.53(9)

171.10(10)

163.34(10)

74.67(10)

74.46(9)

163.82(8)

74.47(7)

74.51(7)

78.54(8)

77.21(8)

76.68(8)

83.53(14)

76.80(18)

82.54(17)

79.92(6)

77.05(6)

78.78(6)

78.37(9)

77.40(9)

79.63(9)

79.15(9)

77.60(9)

79.09(9)

94.14(8)

90.86(9)

148.80(9)

87.62.(9)

88.42(10)

92.78(7)

90.89(7)

148.97(8)

83.69(7)

96.05(8)

92.81(14)

97.71(16)

84.46(17)

175.17(14)

91.06(17)

85.36(15)

110.04(8)

122.88(6)

119.44(9)

121.00(9)

121.28(8)

114.88(8)

111.08(6)

114.45(6)

112.24(9)

116.55(9)

112.04(10)

115.48(9)

93.25(8)

93.36(9)

87.65(7)

94.57(8)

158.59(16)

174.98(9)

169.35(8)

^aEstimated standard deviations in the last significant figure are given in parentheses. ^bTwo independent cations are present in the asymmetric unit of

6‚2.5CH₃CN.

distances are observed in 1B‚2CH₃OH (both 2.254(2) Å),

the Mn(1)-N(3) distance (2.258(2) Å) involving the phenyl-

substituted pyridyl donor is slightly shorter than the Mn-

(1)-N(3) distance (2.298(2) Å) in 1A‚CH₃OH. The Mn-

N_pydistances for both 1A‚CH₃OH and 1B‚2CH₃OH are

comparable to those found for trans pyridyl groups in Mn-

(II) derivatives of the parent TPA ligand, including [Mn-

(TPA)(µ-O₂CCH₃)]₂(TCNQ)₂‚2CH₃CN (2.239(3), 2.227(3)

Å; TCNQ ) tetracyanoquinodimethane), [Mn(TPA)(TCNQ)-

(CH₃OH)](TCNQ)₂‚2CH₃CN (2.253(4), 2.237(4) Å), [Mn-

(TPA)(NCS)₂]‚CH₃CN (2.265(3), 2.252(3) Å), [Mn₂(TPA)₂-

(CA)](ClO₄)₂‚3H₂O (2.231(2), 2.205(2) Å), and [Mn₂(TPA)₂-

(CA)](ClO₄)₂‚2CH₃CN (2.223(4), 2.290(4) Å; CA ) chloro-

anilate).^18a,bNotably, manganese(II) catecholate derivatives

7478 Inorganic Chemistry, Vol. 42, No. 23, 2003

Aryl-Appended TPA Complexes

Figure 2. ORTEP representation of the cationic portion of 3‚CH₃OH.

All ellipsoids are drawn at the 50% probability level. All hydrogens except

the methanol proton were omitted for clarity.

Figure 1. ORTEP representation of the cationic portion of 1B‚2CH₃OH.

All ellipsoids are drawn at the 50% probability level. All hydrogens except

the methanol protons were omitted for clarity.

of 6-Me₃-TPA, in which all the pyridyl donors of the chelate

are coordinated to the manganese(II) center, have generally

longer trans Mn-N_pybond distances ([(6-Me₃TPA)Mn-

(DBCH)]ClO₄, two cations in the asymmetric unit, 2.367-

(4), 2.333(5), 2.294(4), 2.368(4) Å; [(6-Me₃TPA)Mn(4-

NC)]ClO₄, 2.316(2), 2.4064(18) Å). This is due to steric

crowding involving the 6-methyl substituents on the trans

pyridyl rings.^18gOn the basis of this literature precedent, it

might be anticipated that coordination of the 6-Ph₂TPA

ligand to a Mn(II) ion in a meridional fashion, with the

unsubstituted pyridyl ligand positioned trans to a phenyl-

substituted pyridyl donor, might result in Mn-N_pydistances

that are elongated relative to those of Mn(II) complexes of

the parent TPA ligand. However, as already outlined, this is

not the case. This observation, combined with the finding

of several interesting secondary interactions involving the

ligand (vida infra) in 1, provides evidence that the 6-Ph₂-

TPA chelate provides a unique coordination environment on

a Mn(II) center relative to that introduced via TPA or 6-Me₃-

TPA ligation.

In each structure, one of the Mn(II)-bound methanol

ligands participates in a CH/π interaction (Figure S1) with

the phenyl substituent of the bound pyridyl ring. These

interactions are characterized by short C(32)-arene centroid

distances (1A‚CH₃OH, 3.44 Å; 1B‚2CH₃OH, 3.40 Å) and

may be conferred to provide a small amount of stabilization

energy (<2 kcal/mol) to the metal-bound alcohol ligand.¹⁹

A secondary hydrogen-bonding interaction involving the

same Mn(II)-bound methanol molecule (C(32)-O(2)-

H(2A)) and a noncoordinated methanol solvate molecule

(1A‚CH₃OH, O(2)‚‚‚O(12) 2.760(5) Å, O(2)-H(2A)‚‚‚

O(12) 163(4)°; 1B‚2CH₃OH, O(2)‚‚‚O(13) 2.590(4) Å,

O(2)-H(2A)‚‚‚O(13) 156(4)°) is found in the cationic portion

of each complex. Notably, a hydrogen-bonding interaction

is also found between a different Mn(II)-coordinated metha-

nol molecule (C(33)-O(3)-H(3A)) and the noncoordinated

pyridyl nitrogen (1A‚CH₃OH, O(3)‚‚‚N(4) 2.664(3) Å,

O(3)-H(3A)‚‚‚N(4) 169(3)°; 1B‚2CH₃OH, O(3)‚‚‚N(4)

2.715(3) Å, O(3)-H(3A)‚‚‚N(4) 174(4)°).

[(6-Ph₂TPA)Ni(CH₃CN)(CH₃OH)](ClO₄)₂‚CH₃OH (3‚

CH₃OH). An ORTEP representation of the cationic portion

of 3‚CH₃OH is shown in Figure 2. The Ni(II) center exhibits

an octahedral geometry, with the two phenyl-substituted

pyridyl donors bound in a trans orientation. The Ni-N_py

bond lengths for the phenyl-substituted pyridyl donors (Ni-

N_PhPy, 2.200(5), 2.218(5) Å) in 3‚CH₃OH are elongated with

respect to the unsubstituted pyridyl donor (2.065(4) Å) in

the same complex and Ni-N_Pydistances in a variety of Ni-

(II) complexes of the parent TPA ligand (av Ni-N_py∼2.08

Å).²⁰However, the average Ni-N_Pydistance in 6-Me₃-TPA

Ni(II) derivatives (2.215 Å) matches well with the Ni-N_PhPy

distances in 3‚CH₃OH.²¹It is also worth noting that the bond

involving the tertiary amine nitrogen in 3‚CH₃OH (Ni-N_Am

2.082(4) Å) is shorter than that typically found in Ni(II) TPA

complexes (av 2.11 Å)²⁰but is similar to that found in 6-Me₃-

TPA complexes (av 2.08 Å).²¹Thus, these structural

comparisons indicate that while the 6-Ph₂TPA ligand pro-

vides additional steric hindrance and hydrophobicity sur-

rounding the divalent nickel center, the geometric parameters

of its bonding to Ni(II) generally fall in line with those

previously reported for ligands of the tris(pyridylmethyl)-

amine family. The same conclusions generally hold for nickel

coordination to a recently reported monoaryl-substituted TPA

(18) TPA: (a) Xiang, D. F.; Duan, C. Y.; Tan, X. S.; Liu, Y. J.; Tang, W.

X. Polyhedron 1998, 17, 2647-2653. (b) Oshio, H.; Ino, E.; Mogi,

I.; Ito, T. Inorg. Chem. 1993, 32, 5697-5703. (c) Towle, D. K.;

Botsford, C. A.; Hodgson, D. J. Inorg. Chim. Acta 1988, 141, 167-

168. (d) Gultneh, Y.; Farooq, A.; Karlin, K. D.; Liu, S.; Zubieta, J.

Inorg. Chim. Acta 1993, 211, 171-175. 6-Me₂TPA: (e) Goodson, P.

A.; Oki, A. R.; Hodgson, D. J. Inorg. Chim. Acta 1990, 177, 59-64.

(f) Goodson, P. A.; Oki, A. R.; Glerup, J.; Hodgson, D. J. J. Am.

Chem. Soc. 1990, 112, 6248-6254. 6-Me₃TPA: (g) Reynolds, M.

F.; Costas, M.; Ito, M.; Jo, D.-H.; Tipton, A. A.; Whiting, A. K.; Que,

L., Jr. JBIC, J. Biol. Inorg. Chem. 2003, 8, 263-272. (h) Zhang, Z.-

H.; Bu, X.-H.; Ma, Z.-H.; Bu, W.-M.; Tang, Y.; Zhao, Q.-H.

Polyhedron 2000, 19, 1559-1566.

(20) (a) Zhang, Z.-H.; Bu, X.-H.; Zhu, Z.-A.; Jiang, Z.-H.; Chen, Y.-T.

Transition Met. Chem. 1996, 21, 235-237. (b) Ito, M.; Takita, Y.

Chem. Lett. 1996, 929-930. (c) Ito, M.; Sakai, K.; Tsubomura, T.;

Takita, Y.-S. Bull. Chem. Soc. Jpn. 1999, 72, 239-247. (d) Tong, B.;

Norman, R. E.; Chang, S.-C. Acta Crystallogr. 1999, C55, 1236-

1238. (e) Tong, B.; Chang, S.-C.; Carpenter, E. E.; O’Connor, C. J.;

Lay, J. O., Jr.; Norman, R. E. Inorg. Chim. Acta 2000, 300, 855-

861.

(21) (a) Zhang, Z.-H.; Bu, X.-H.; Ma, Z.-H.; Bu, W.-M.; Tang, Y.; Zhao,

Q.-H. Polyhedron 2000, 19, 1559-1566. (b) Shiren, K.; Ogo, S.;

Fujinami, S.; Hayashi, H.; Suzuki, M.; Uehara, A.; Watanabe, Y.;

Moro-oka, Y. J. Am. Chem. Soc. 2000, 122, 254-262.

(19) Nishio, M.; Hirota, M.; Umezawa, Y. The CH/π Interaction: EVidence,

Nature and Consequences; Wiley-VCH: New York, 1998.

Inorganic Chemistry, Vol. 42, No. 23, 2003 7479

Makowska-Grzyska et al.

τ ) 0.79; for a perfect trigonal bipyramid τ ) 1),²²with the

three pyridyl nitrogen donors forming the trigonal plane. For

each, the divalent metal center is displaced from this plane

toward the acetonitrile ligand (2‚2CH₃CN, ∼0.45 Å; 4‚

2CH₃CN, ∼0.41 Å). The M(II)-N_PhPyand M(II)-N_py

distances in 2‚2CH₃CN and 4‚2CH₃CN differ by ∼0.02-

0.08 Å, with the M(II)-N_PhPydistances again being slightly

longer. Complex 2‚2CH₃CN is the third structurally char-

acterized mononuclear five-coordinate cobalt(II) complex of

a TPA-type ligand.^9,23Notably, one example was isolated

using a monoaryl-substituted TPA ligand (N-((6-(2′,5′-

dimethoxy)phenyl)-(2-pyridyl)methyl)-N,N-bis((2-pyridyl)-

methyl)amine).⁹To our knowledge, four mononuclear, five-

coordinate zinc complexes of the parent TPA ligand have

been reported.^23a,24The average Zn-N_pybond lengths in these

complexes ([(TPA)ZnCl]ClO₄,^23a2.069 Å; [(TPA)ZnCl]-

BPh₄‚2CH₃CN,^24b2.073 Å; [(TPA)ZnI]ClO₄,^23a2.090 Å;

[(TPA)Zn(O₂CPh)]BPh₄‚CH₃CN,^24b2.064 Å) are generally

similar to the Zn-N_py(2.053(2) Å), and slightly shorter than

the average Zn-N_PhPy(∼2.11 Å) distances found in 4‚

2CH₃CN. In the course of our work, we also prepared and

characterized [(TPA)Zn(CH₃CN)](ClO₄)₂(7‚CH₃CN). The

geometry of the Zn(II) ion in this complex is more trigonal

bipyramidal (τ ) 0.97; Figure S3)²²than is observed for 4‚

2CH₃CN. Comparison of the bond angles in 4‚2CH₃CN and

7‚CH₃CN reveals a smaller N_amine-Zn- N(CH₃CN) angle

in 4‚2CH₃CN (170.41(6)°) than is found in 7‚CH₃CN

(177.38(7)°). This appears to be a consequence of steric

crowding due to the presence of the phenyl substituents, as

the bound acetonitrile ligand is canted away from the phenyl-

substituted pyridyl donors. The Zn-N distances in 4‚

2CH₃CN and 7‚CH₃CN are generally similar, albeit one

Zn-N_PhPybond is elongated in 4‚2CH₃CN (Zn(1)-N(3)

2.139(2) Å).

Secondary CH/π interactions involving the bound aceton-

trile ligand and the 6-Ph₂TPA phenyl groups are present in

the solid state structures of 2‚2CH₃CN and 4‚2CH₃CN

(Figures S4 and S5).¹⁹The C(32)‚‚‚arene centroid distances

(2‚2CH₃CN, 3.79, 3.80 Å; 4‚2CH₃CN, 3.78, 3.78 Å) are

longer than those observed in 3‚CH₃OH (vida supra).

In order to evaluate the effect of aryl group substitution

on the steric properties of divalent metal complexes, the

6-(Me₂Ph)₂TPA-ligated 6‚2.5CH₃CN (Figure 4) was char-

acterized by X-ray crystallography. Two independent mol-

ecules are present in the asymmetric unit. Both cations exhibit

a distorted trigonal bipyramidal geometry (τ ) 0.83, 0.84),²²

with bond distances, angles, and metrical parameters of

secondary CH/π interactions very similar to those of 4‚

Figure 3. ORTEP representations of the cationic portions of 2‚2CH₃CN

and 4‚2CH₃CN. All ellipsoids are drawn at the 50% probability level. All

hydrogens were omitted for clarity.

ligand (N-((6-(2′,5′-dimethoxy)phenyl)-(2-pyridyl)methyl)-

N,N-bis((2-pyridyl)methyl)amine).⁹

Notably, the Ni(II)-coordinated acetonitrile molecule in

3‚CH₃OH is positioned in a sandwich motif between two

phenyl rings of the 6-Ph₂TPA ligand. This results in CH/π

interactions involving the acetonitrile methyl group and the

phenyl rings (Figure S2; C(33)‚‚‚arene centroid, 3.66, 3.63

Å), as well as in short contacts between the arene carbons

and the nitrile carbon (C(32)) and nitrogen (N(5)) of the

bound solvent molecule. The presence of the hydrophobic

environment has no effect on the Ni-NNCCH₃bond distance

(2.044(2) Å), which is identical to that found in [(TPA)Ni-

(CH₃CH₂CN)(OH₂)](ClO₄)₂(2.043(9) Å).^20c

A series of hydrogen-bonding interactions are present

involving the cationic portion of 3‚CH₃OH in the solid state.

Specifically, the hydroxyl moiety of the coordinate meth-

anol ligand donates a hydrogen bond to a noncoordi-

nated methanol solvate (O(1)‚‚‚O(10) 2.615(6) Å, O(1)-

H(1A)‚‚‚O(10) 143(5)°), which in turn forms a hydrogen-

bonding interaction with a perchlorate anion (O(10)‚‚‚O(3)

2.816(8) Å).

(22) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G.

C. J. Chem. Soc., Dalton Trans. 1984, 1349-1356.

(23) (a) Allen, C. S.; Chuang, C.-L.; Cornebise, M.; Canary, J. W. Inorg.

Chim. Acta 1995, 239, 29-37. (b) Hilt, G.; Jarbawi, T.; Heineman,

W. R.; Steckhan, E. Chem. Eur. J. 1997, 3, 79-88. (c) Nanthakumar,

A.; Fox, S.; Murthy, N. N.; Karlin, K. D. J. Am. Chem. Soc. 1997,

119, 3898-3906.

(24) (a) Canary, J. W.; Allen, C. S.; Castagnetto, J. M.; Chiu, J. M.; Chiu,

Y.-H.; Toscano, P. J.; Wang, Y. Inorg. Chem. 1998, 37, 6255-6262.

(b) Adams, H.; Bailey, N. A.; Fenton, D. E.; He, Q.-Y. J. Chem. Soc.,

Dalton Trans. 1997, 1533-1539. (c) Canary, J. W.; Allen, C. S.;

Castagnetto, J. M.; Wang, Y. J. Am. Chem. Soc. 1995, 117, 8484-

8485.

[(6-Ph₂TPA)Co(CH₃CN)](ClO₄)₂‚2CH₃CN (2‚2CH₃CN)

and[(6-Ph₂TPA)Zn(CH₃CN)](ClO₄)₂‚2CH₃CN(4‚2CH₃CN).

Structurally similar Co(II) and Zn(II) complexes of the 6-Ph₂-

TPA ligand were isolated and characterized (Figure 3). In

each, the metal center adopts a slightly distorted trigonal

bipyramidal geometry (2‚2CH₃CN, τ ) 0.84; 4‚2CH₃CN,

7480 Inorganic Chemistry, Vol. 42, No. 23, 2003

Aryl-Appended TPA Complexes

Table 4. Selected Physical Properties of 1-3 and 5

1

2

3

5

UV-vis, nm

(ꢀ, M^-1cm^-1

477 (105)

570 (90)

678 (24)

558 (10)

1007 (15)

556 (10)

1005 (15)

)

CV,^amV

-1101

-881

-885

µ

_eff,^bµ_B

6.1

4.3

3.2

^aPotentials reported versus SCE. ^bAverage value of two independent

determinations at 298 K.

only values for high-spin Co(II) and Ni(II) (3.9 and 2.8 µ_B,

respectively) due to spin-orbit coupling.²⁵

UV-Vis Spectroscopy. Electronic absorption spectra of

2, 3, and 5 were recorded in dry CH₃CN solution (Table 4).

All spectra show strong ligand-based absorptions at <400

nm. The cobalt complex 2 exhibits three electronic transitions

(477(105), 570(90), and 678(24) nm), with extinction coef-

ficients for these transitions suggesting that the Co(II) center

in 2 remains five coordinate in CH₃CN solution. On this

basis, the transitions corresponding to these absorptions may

be assigned as ⁴A′(F)f⁴E′′(P), ⁴A′(F)f⁴A′(P), and

Figure 4. ORTEP representation of one of two cations present in the

asymmetric unit of 6‚2.5CH₃CN. All ellipsoids are drawn at the 50%

probability level. All hydrogens were omitted for clarity.

2CH₃CN. Hence, 3,5-dimethyl substitution of the phenyl

substituent induces little change in the structural properties

of zinc complexes.

Solution Characterization. Electrochemistry. Cyclic

voltammetric examination of complexes 1-3 and 5 was

performed in freshly distilled CH₃CN under an atmosphere

of N₂. Complexes 2, 3, and 5 exhibit reversible couples

corresponding to reduction of the +2 metal complexes,

presumably to +1 (Figure S6). The observed formal poten-

tials (scaled to the SCE potential) for these couples are shown

in Table 3. The Co(II) complex 2 has a quasireversible Co-

(II)/Co(I) couple at -1101 mV versus SCE measured at a

scan rate of 250 mV/s. The reversibility of this couple

decreased at slower scan rates, indicating that the electro-

chemically generated Co(I) complex can readily react in

solution, either with trace O₂or perhaps with the solvent.

No oxidative couples (Co(II)/Co(III)) were observed. Both

Ni(II) complexes (3 and 5) exhibited very similar electro-

chemical behavior. Complex 3 has a quasireversible Ni(II)/

Ni(I) couple at -881 mV versus SCE, measured at a scan

rate of 100 mV/s. Likewise, complex 5 has a quasireversible

Ni(II)/Ni(I) couple at -885 mV versus SCE, also measured

at a scan rate of 100 mV/s. Thus, while the electrochemically

generated Ni(I) complexes are strongly reducing, they are

readily observed in thoroughly deoxygenated solutions. The

peak-to-peak separations, which are of a similar magnitude

as that of the ferrocene/ferrocenium couple, suggest that only

minor structural reorganizations accompany the Ni(II)/Ni(I)

redox processes. No oxidative couples (Ni(II)/Ni(III)) were

observed. The Mn(II) complex 1 is unique in this series, in

that no oxidative (Mn(III)/Mn(II)) or reductive (Mn(II)/Mn-

(I)) couples were observed over the potential range +1.8 V

to -1.8 V versus SCE. A weak, quasireversible couple was

observed at ∼ -1.25 V. However, the intensity of this feature

did not scale with the amount of complex present in solution.

Therefore, we suspect that this couple is a result of a trace

impurity in the original sample.

2

⁴A′(F)f⁴E′(F), respectively.²⁶For the Ni(II) complex 3,

2

two absorptions are found in the region 400-1100 nm, which

3

correspond to the A_2g

f f

³T_1g(F) and A_2g³T_2g(F)

transitions, respectively, for an octahedral Ni(II) center. The

energy of these absorptions is not affected by methyl

substitution in 5 (Table 4).

1

EPR and H NMR Spectroscopy. Mn(II) complex 1

exhibits an axial EPR signal at g ∼ 2.0, with a six line

hyperfine pattern (Figure S7), and A_|) 97 ( 4 G.

1

The H NMR spectra of the zinc complexes 4 and 6 in

CD₃CN solution at ambient temperature have signals con-

sistent with the X-ray crystallographically determined struc-

tures of these complexes, albeit an upfield shifted resonance

for the bound acetonitrile molecule involved in a CH/π

interaction in each complex is not observed. This is likely

due to exchange of the bound CH₃CN with CD₃CN. To probe

for CH/π interactions in solution, 4 and 6 were dissolved in

1

CD₃NO₂and H NMR spectra were again obtained. In this

case, for 4, two resonances associated with CH₃CN were

found at 2.21 and 1.78 ppm, respectively, each integrating

to approximately three protons. Free CH₃CN in CD₃NO₂is

found at 2.00 ppm. Thus, it appears that one of the

acetonitrile molecules present in CD₃NO₂solutions of 4 is

shifted upfield, consistent with its involvement in a CH/π

interaction. The magnitude of the upfield shift (δ ) 0.22

ppm) is smaller than that observed for acetonitrile in CCl₄

versus benzene solution (δ ) 0.97 ppm).¹⁹This may be due

to an additional inductive effect resulting from zinc coor-

dination of the acetonitrile molecule in 4, which would be

expected to produce a downfield shift of the CH₃CN

1

resonance. The second CH₃CN resonance found in the H

NMR spectrum of 4 in CD₃NO₂is shifted downfield of free

acetonitrile by ∼0.21 ppm. In the X-ray structure of 4, a

noncoordinated CH₃CN molecule is present. We propose that

Magnetic Moment. The solution magnetic moments of

1-3 and 5 (Table 4) were determined at 298 K by the Evans

method.¹¹The experimentally measured magnetic moment

for 1 (6.1 µ_B) is near the spin-only value expected for a high-

spin Mn(II) ion (5.9 µ_B), whereas the values found for 2

(4.3 µ_B), 3 (3.2 µ_B), and 5 (3.2 µ_B) are higher than the spin-

(25) Jolly, W. L. The Synthesis and Characterization of Inorganic

Compounds; Waveland Press: Prospect Heights, IL, 1970.

(26) Lever, A. B. P. Inorganic Electronic Spectoscopy, 2nd ed.; Elsevier:

Amsterdam, 1984.

Inorganic Chemistry, Vol. 42, No. 23, 2003 7481

Makowska-Grzyska et al.

Scheme 4. Synthetic Route for Preparation of Hydroxamate

in CD₃NO₂solution, where the solvent is only a very weak

Lewis base, the previously noncoordinating CH₃CN solvate

molecule may interact with the zinc center in a sixth

coordination position. Formation of a six-coordinate TPA-

ligated zinc center has been previously reported.²⁷In general,

the CD₃NO₂solution properties of 6 are similar to those of

4, with an upfield-shifted peak present at 1.82 ppm. The

assignment of the upfield shifted resonances at ∼1.8 ppm

in both 4 and 6 as a bound CH₃CN molecule participating

in a CH/π interaction is further supported by comparison of

the solution properties of these complexes with those of

[(TPA)Zn(CH₃CN)](ClO₄)₂(7). Unlike the complexes of the

6-Ph₂TPA and 6-(Me₂Ph)₂TPA ligands, 7 does not exhibit

an upfield shifted CH₃CN resonance in CD₃NO₂solution,

consistent with the fact that CH/π interactions are not present.

A resonance at ∼2.12 ppm is observed indicating the

presence of a zinc-bound CH₃CN molecule.²⁸

Complexes 8-11^a

Preparation of Hydroxamate Compounds. To evaluate

whether using the 6-Ph₂TPA ligand will enable the isolation

of mononuclear divalent metal complexes having a chelate

anionic ligand, we have investigated the chemistry of divalent

metal hydroxamate derivatives. Treatment of the 6-Ph₂TPA

ligand with equimolar amounts of M(ClO₄)₂‚6H₂O, Me₄-

NOH‚5H₂O, and acetohydroxamic acid in methanol (Scheme

4) yielded the hydroxamate complexes 8-11 in yields of

68-84% as crystalline solids from either CH₃CN/ⁱPrOH/Et₂O

(8, 9, and 11) or CH₃CN/MeOH/Et₂O (10) solutions.

X-ray Crystallography. Details of the data collection and

structure refinement are given in Table 5. Selected bond

distances and angles are given in Table 6.

[(6-Ph₂TPAMn)₂(µ-ONHC(O)CH₃)₂](ClO₄)₂‚0.75CH₃CN‚

0.75Et₂O (8‚0.75CH₃CN‚0.75Et₂O). To our knowledge, this

complex represents the first structurally characterized man-

ganese(II) hydroxamate complex.²⁹Two chemically similar,

but structurally unique, dimeric cations are found in the

asymmetric unit of this complex. As the metrical parameters

of these two cations are generally similar, for the most part

only one (8A; Figure 5) will be discussed. The two

manganese centers in the cationic portion of 8A are bridged

by two hydroxamate ligands, with each coordinating in a

µ-η¹:η²-ONHC(O)CH₃fashion. This coordination mode has

been previously observed in dimeric Ni(II), Zn(II), and Co-

(II) hydroxamate complexes.^30-32The 6-Ph₂TPA ligand

chelates to each Mn(II) ion in 8A in a facial arrangement,

^aAll reactions involve treatment of 6-Ph₂TPA with equimolar amounts

of M(ClO₄)₂‚6H₂O, Me₄NOH‚5H₂O, and acetohydroxamic acid.

with only one of the two available phenyl-substituted pyridyl

donors for each 6-Ph₂TPA moiety binding to a Mn(II) center.

The facial coordination mode of 6-Ph₂TPA in 8A and 8B

differs from the meridional type ligation found for the same

chelate ligand in 1A‚CH₃OH and 1B‚2CH₃OH. The Mn-N

bond distances in both ligand coordination modes are similar

(∼2.25-2.40 Å), with the Mn-N(amine) distance being the

longest for each Mn(II) center. As in 1A‚CH₃OH, the Mn-

N_pydistances for both the phenyl-substituted and unsubsti-

tuted pyridyl rings are similar. The average Mn(II)-O

distance in 8A is 2.18 Å (8B, 2.18 Å), and the Mn‚‚‚Mn

distance is 3.409 Å (8B, 3.386 Å). In 8A, a relatively weak

hydrogen-bonding interaction is found between a hydrox-

amate N-H and a nitrogen atom of one of the two

noncoordinated pyridyl donors in the dimer (N(10)‚‚‚N(4)

3.009(6) Å, N(10)-H‚‚‚N(4) 139.8°). The other bound

(27) Murthy, N. N.; Karlin, K. D. J. Chem. Soc., Chem. Commun. 1993,

1236-1238.

1

(28) A downfield-shifted resonance for water is also present in H NMR

spectra of bulk samples of 7. Upon heating of the NMR sample at

∼45-50° under vacuum for 12 h, the acetonitrile resonance disappears,

but the water resonance remains. This indicates that water coordination

is also likely in this complex.

(29) Mn(II) complexes of aminohydroxamic acids have been previously

reported to form in water solution but were not structurally character-

ized: Enyedy, E. A.; Cso´ka, H.; Lazar, I.; Micera, G.; Garribba, E.;

Farkas, E. J. Chem. Soc., Dalton Trans. 2002, 2632-2640.

(30) Ni(II): (a) Stemmler, A. J.; Kampf, J. W.; Kirk, M. L.; Pecoraro, V.

L. J. Am. Chem. Soc. 1995, 117, 6368-6369. (b) Arnold, M.; Brown,

D. A.; Deeg, O.; Errington, W.; Haase, W.; Herlihy, K.; Kemp, T. J.;

Nimir, H.; Werner, R. Inorg. Chem. 1998, 37, 2920-2925.

(31) Zn(II): Brown, D. A.; Errington, W.; Fitzpatrick, N. J.; Glass, W.

K.; Kemp, T. J.; Nimir, H.; Ryan, A. T. Chem. Commun. 2002, 1210-

1211.

(32) Co(II): Brown, D. A.; Errington, W.; Glass, W. K.; Haase, W.; Kemp,

T. J.; Nimir, H.; Ostrovsky, S. M.; Werner, R. Inorg. Chem. 2001,

40, 5962-5971.

7482 Inorganic Chemistry, Vol. 42, No. 23, 2003

Aryl-Appended TPA Complexes

Table 5. Summary of X-ray Data Collection and Refinement for Hydroxamate Complexes

8‚0.75CH₃CN‚0.75Et₂O

9

10‚1.5CH₃CN

11

empirical formula

fw

cryst syst

space group

a (Å)

b (Å)

c (Å)

R (deg)

â (deg)

γ (deg)

V (Å³)

C

_68.5H_69.75N_10.75Cl₂O_12.75Mn₂

C₃₂H₃₀N₅ClO₆Co

674.99

monoclinic

P2₁/c

10.9561(4)

18.2711(6)

15.2867(6)

C₃₅H_34.50N_6.50ClO₆Ni

736.35

monoclinic

I2/a

14.5773(3)

19.4711(5)

24.8678(5)

C₃₂H₃₀N₅ClO₆Zn

681.43

monoclinic

P2₁/n

12.1875(4)

17.0501(3)

14.6762(4)

1428.38

triclinic

P1h

12.3182(3)

19.6718(3)

28.9826(7)

77.4760(1)

87.0389(1)

73.3676(1)

6568.7(2)

4

98.5818(18)

103.6499(13)

97.3202(11)

3025.83(19)

4

1.482

6859.0(3)

8

1.426

3024.83(14)

4

1.496

Z

d

_calcd, Mg m^-3

1.444

temp (K)

150(1)

cryst size (mm³)

abs coeff (mm^-1

2θ max (deg)

reflns collected

indep reflns

0.23 × 0.20 × 0.10

0.25 × 0.20 × 0.15

0.30 × 0.30 × 0.20

0.35 × 0.28 × 0.08

)

0.539

0.710

0.699

0.954

55.00

39816

28390

54.96

11782

6890

54.92

13465

7788

55.00

12813

6903

variable params

1781

0.0799/0.1713

1.020

526

0.0413/0.0892

1.057

564

0.0415/0.0922

1.028

541

0.0448/0.1098

1.022

R1/wR2^b

GOF (F²)

largest diff (e Å^-3

)

1.226/-1.277

0.559/-0.478

0.515/-0.437

0.687/-0.636

2

^aRadiation used: Mo KR (λ ) 0.71073 Å). Diffractometer: Nonius KappaCCD. ^bR1 ) ∑||F_o| - |F_c||/∑|F_o|; wR2 ) [∑[w(F_o- F_c)²]/[∑(F_o)²]]^1/2

where w ) 1/[σ²(F_o) + (aP)²+ bP].

2

hydroxamate in 8A donates a hydrogen bond to a noncoor-

dinated perchlorate anion (N(5)‚‚‚O(9) 3.027(7) Å, N(5)-

H(5)‚‚‚O(9) 174.5°).

amate complexes (10‚1.5CH₃CN and 11) were isolated using

the 6-Ph₂TPA ligand. ORTEP representations of the cationic

portions of these complexes are shown in Figure 6b,c. Similar

to the Co(II) derivative 9, the divalent metal centers in 10‚

1.5CH₃CN and 11 have a distorted octahedral geometry, with

the bound hydroxamate positioned between the two phenyl

substitutents of the supporting 6-Ph₂TPA chelate ligand.

However, the orientation of the hydroxamate binding in 10‚

1.5CH₃CN and 11 is reversed with respect to the [(6-Ph₂-

TPA)M(II)]²⁺fragment from what is observed for 9. This

leads to the formation of hydrogen-bonded pairs of cations

in the solid state for 10‚1.5CH₃CN and 11 (Figure 7), where

the two cations are bridged by a six-membered ring involving

two hydrogen-bonding interactions. These secondary interac-

tions are each composed of a hydroxamate N-H moiety

donating a hydrogen bond to a hydroxamate hydroxyl oxygen

bound to the second cation (10‚1.5CH₃CN, N(5)‚‚‚O(2)

2.781(2) Å, N(5)-H(5)‚‚‚O(2) 146(2)°; 11, N(5)‚‚‚O(2)

2.746(3) Å, N(5)-H(5)‚‚‚O(2) 147(3)°).

Complex 10‚1.5CH₃CN is only the second structurally

characterized example of a mononuclear nickel hydroxamate

complex to be reported, with the previous example having a

square pyramidal geometry ([Ni[12]aneN₃-mc2(Ah)]PF₆).³³

In 10‚1.5CH₃CN, the Ni-N_Pyand Ni-N_PhPybond lengths

are very similar to those found for 3‚CH₃OH, indicating that

for nickel little change occurs regarding the bonding of the

chelate ligand as a consequence of replacement of solvent

ligands (CH₃OH and CH₃CN) with an anionic, bidentate

chelate ligand. Akin to [Ni[12]aneN₃-mc2(Ah)]PF₆, very

similar Ni-O bond lengths are found for the bound hydrox-

amate anion in 10‚1.5CH₃CN (Ni(1)-O(1) 1.996(1) Å, Ni-

(1)-O(2) 2.020(2) Å).

[(6-Ph₂TPA)Co(ONHC(O)CH₃)]ClO₄(9). The cobalt

hydroxamate complex 9 has a mononuclear structure in the

solid state, with all available donors of the 6-Ph₂TPA

coordinated to the Co(II) center. A Cambridge Crystal-

lographic Database search (Version 5.24 (Nov 2002))

revealed that only two cobalt hydroxamate complexes, both

having bridging hydroxamate ligands, have been previously

characterized by X-ray crystallography.³²In 9, the Co(II)

center has a pseudo-octahedral geometry (Figure 6a), with

the hydroxamate coordinated in a hydrophobic sandwich

created by the two phenyl substitutents of the 6-Ph₂TPA

ligand. The Co-N distances of the phenyl-substituted pyridyl

donors are >0.1 Å longer than the Co-N distance of the

unsubstituted pyridyl donor. This differentiation in Co-N

bond lengths is smaller than that present in the five-

coordinate complex 2 (<0.065 Å), and presumably arises in

9 due to increased steric interactions between the phenyl

substituents of the two trans pyridyl donors (N(3) and N(4)).

Two distinct Co-O bond distances are found for 9 (Co(1)-

O(1) 2.141(2) Å, Co(1)-O(2) 1.935(2) Å), with the shorter

distance being the Co-O interaction trans to the tertiary

amine nitrogen. The carbonyl-derived oxygen atom (O(1))

of the hydroxamate ligand is positioned trans to the unsub-

stituted pyridyl donor. In this orientation, the hydroxamate

N-H moiety lies within the hydrophobic sandwich and forms

a hydrogen-bonding interaction (N(5)‚‚‚O(3) 2.993(3) Å,

N(5)-H(5)‚‚‚O(3) 152(2)°) with the noncoordinated per-

chlorate anion (Figure S8).

[(6-Ph₂TPA)Ni(ONHC(O)CH₃)]ClO₄‚1.5CH₃CN (10‚

1.5CH₃CN) and [(6-Ph₂TPA)Zn(ONHC(O)CH₃)]ClO₄(11).

Structurally similar mononuclear Ni(II) and Zn(II) hydrox-

(33) Santana, M. D.; Garc´ıa, G.; Pe´rez, J.; Molins, E.; Lo´pez, G. Inorg.

Chem. 2001, 40, 5701-5703.

Inorganic Chemistry, Vol. 42, No. 23, 2003 7483

Makowska-Grzyska et al.

Table 6. Selected Bond Lengths (Å) and Angles (deg) for Hydroxamate Complexes^a

[((6-Ph₂TPA)Mn)₂(µ-ONHC(O)CH₃)₂](ClO₄)₂(8‚0.75CH₃CN‚0.75Et₂O)

Cation 8A

Mn(1)-O(1)

2.143(3)

2.269(4)

2.142(3)

2.308(4)

2.394(4)

146.84(2) O(4)-Mn(1)-O(2)

73.15(1)

83.45(1)

Mn(1)-N(3)

C(31)-N(5)

O(1)-C(31)

N(5)-O(2)

2.277(4)

Mn(2)-O(2)

2.129(3)

2.144(4)

2.252(4)

2.297(4)

2.399(4)

152.01(1) O(4)-Mn(2)-O(2)

73.97(1)

83.26(1)

128.19(2) N(8)-Mn(2)-N(6)

100.17(1) C(63)-O(3)-Mn(2)

151.60(1) O(3)-C(63)-N(10)

71.70(1)

123.07(1) N(10)-O(4)-Mn(2)

Mn(2)-N(8)

2.291(4)

1.307(6)

1.261(6)

1.386(5)

Mn(1)-O(2)

1.313(7)

1.263(6)

1.378(5)

Mn(2)-O(3)

C(63)-N(10)

O(3)-C(63)

N(10)-O(4)

Mn(1)-O(4)

Mn(2)-O(4)

Mn(1)-N(1)

Mn(2)-N(6)

Mn(1)-N(2)

Mn(2)-N(7)

O(1)-Mn(1)-N(2)

O(1)-Mn(1)-O(2)

O(1)-Mn(1)-N(1)

O(1)-Mn(1)-N(3)

O(1)-Mn(1)-O(4)

O(2)-Mn(1)-N(1)

N(1)-Mn(1)-N(2)

N(1)-Mn(1)-O(4)

Mn(1)-O(2)-Mn(2)

77.76(1)

82.93(1)

72.40(2)

O(3)-Mn(2)-N(7)

O(3)-Mn(2)-O(4)

O(3)-Mn(2)-N(6)

78.37(1)

83.88(1)

71.22(2)

102.81(1)

115.8(3)

121.3(5)

119.4(4)

108.4(2)

O(4)-Mn(1)-N(2)

N(3)-Mn(1)-N(2)

O(2)-Mn(2)-N(7)

N(8)-Mn(2)-N(7)

135.80(2) N(3)-Mn(1)-N(1)

100.24(2) O(3)-Mn(2)-N(8)

96.49(1)

145.61(1) O(1)-C(31)-N(5)

72.58(1) O(2)-N(5)-C(31)

C(31)-O(1)-Mn(1)

115.9(3)

120.9(5)

118.9(4)

108.5(3)

101.73(1)

O(3)-Mn(2)-O(2)

O(4)-Mn(2)-N(6)

N(6)-Mn(2)-N(7)

N(6)-Mn(2)-O(2)

O(4)-N(10)-C(63)

130.74(2) N(5)-O(2)-Mn(1)

101.61(1) Mn(1)-O(4)-Mn(2)

Cation 8B

Mn(3)-O(1A)

Mn(3)-O(2A)

Mn(3)-O(4A)

Mn(3)-N(1A)

Mn(3)-N(2A)

2.151(4)

2.233(3)

2.127(3)

2.287(4)

2.422(4)

Mn(3)-N(3A)

C(31A)-N(5A)

O(1A)-C(31A)

N(5A)-O(2A)

2.295(4)

1.310(6)

1.272(6)

1.384(5)

Mn(4)-O(2A)

Mn(4)-O(3A)

Mn(4)-O(4A)

Mn(4)-N(6A)

Mn(4)-N(7A)

2.137(3)

2.149(3)

2.266(3)

2.280(4)

2.394(4)

Mn(4)-N(8A)

C(63A)-N(10A)

O(3A)-C(63A)

N(10A)-O(4A)

2.263(4)

1.306(7)

1.266(6)

1.383(5)

O(1A)-Mn(3)-N(2A) 151.26(1) O(4A)-Mn(3)-O(2A)

79.04(1)

83.36(1)

70.79(1)

O(3A)-Mn(4)-N(7A) 145.40(1) O(4A)-Mn(4)-O(2A)

78.09(1)

81.13(1)

72.81(2)

100.32(1)

116.0(3)

O(1A)-Mn(3)-O(2A) 73.90(1)

O(1A)-Mn(3)-N(1A) 83.17(1)

O(4A)-Mn(3)-N(2A)

N(3A)-Mn(3)-N(2A)

O(3A)-Mn(4)-O(4A) 73.31(1)

O(3A)-Mn(4)-N(6A) 83.45(1)

O(2A)-Mn(4)-N(7A)

N(8A)-Mn(4)-N(7A)

O(1A)-Mn(3)-N(3A) 129.45(1) N(3A)-Mn(3)-N(1A)

103.89(1) O(3A)-Mn(4)-N(8A) 137.75(1) N(8A)-Mn(4)-N(6A)

O(1A)-Mn(3)-O(4A) 99.81(1)

C(31A)-O(1A)-Mn(3) 115.9(3)

O(3A)-Mn(4)-O(2A) 96.28(1)

C(63A)-O(3A)-Mn(4)

O(2A)-Mn(3)-N(1A) 152.65(1) O(1A)-C(31A)-N(5A) 120.3(5)

O(4A)-Mn(4)-N(6A) 145.23(1) O(3A)-C(63A)-N(10A) 120.4(4)

N(1A)-Mn(3)-N(2A) 70.94(1)

O(2A)-N(5A)-C(31A) 119.5(4)

N(6A)-Mn(4)-N(7A) 73.15(1)

O(4A)-N(10A)-C(63A) 119.9(4)

N(1A)-Mn(3)-O(4A) 120.20(1) N(5A)-O(2A)-Mn(3)

Mn(3)-O(2A)-Mn(4) 101.57(1) Mn(3)-O(4A)-Mn(4)

109.2(2)

100.81(1)

N(6A)-Mn(4)-O(2A) 130.93(1) N(10A)-O(4A)-Mn(4)

108.1(3)

[(6-Ph₂TPA)Co(ONHC(O)CH₃)](ClO₄) (9)

[(6-Ph₂TPA)Ni(ONHC(O)CH₃)](ClO₄) (10‚1.5CH₃CN)

Co(1)-O(1)

2.141(2)

1.935(2)

2.103(2)

2.177(2)

2.244(2)

Co(1)-N(4)

O(1)-C(31)

C(31)-N(5)

N(5)-O(2)

2.298(2)

1.268(3)

1.312(3)

1.379(2)

Ni(1)-O(1)

1.996(1)

2.020(2)

2.056(2)

2.082(2)

2.229(2)

Ni(1)-N(4)

O(1)-C(31)

C(31)-N(5)

N(5)-O(2)

2.263(2)

1.272(2)

1.311(3)

1.384(2)

Co(1)-O(2)

Ni(1)-O(2)

Co(1)-N(1)

Ni(1)-N(1)

Co(1)-N(2)

Ni(1)-N(2)

Ni(1)-N(3)

Co(1)-N(3)

O(2)-Co(1)-N(2)

O(2)-Co(1)-O(1)

O(2)-Co(1)-N(1)

O(2)-Co(1)-N(3)

O(2)-Co(1)-N(4)

O(1)-Co(1)-N(1)

N(1)-Co(1)-N(2)

N(1)-Co(1)-N(4)

175.26(7) N(4)-Co(1)-O(1)

78.74(6)

78.55(7)

73.66(6)

99.75(7)

O(1)-Ni(1)-N(2)

O(1)-Ni(1)-O(2)

O(1)-Ni(1)-N(1)

O(1)-Ni(1)-N(3)

173.01(6) N(4)-Ni(1)-O(2)

79.80(6)

81.16(7)

76.37(7)

101.10(7)

110.61(1)

120.43(2)

120.22(2)

105.72(1)

81.17(6)

99.80(7)

N(4)-Co(1)-N(2)

N(3)-Co(1)-N(2)

82.75(6)

94.67(7)

99.85(6)

N(4)-Ni(1)-N(2)

N(3)-Ni(1)-N(2)

N(3)-Ni(1)-N(1)

102.20(6) N(3)-Co(1)-N(1)

106.17(6) C(31)-O(1)-Co(1)

176.72(6) O(1)-C(31)-N(5)

107.26(1) O(1)-Ni(1)-N(4)

104.62(6) C(31)-O(1)-Ni(1)

176.30(7) O(1)-C(31)-N(5)

120.2(2)

O(2)-Ni(1)-N(1)

78.87(7)

97.98(7)

O(2)-N(5)-C(31)

N(5)-O(2)-Co(1)

120.71(2) N(1)-Ni(1)-N(2)

109.79(1) N(1)-Ni(1)-N(4)

80.45(7)

98.37(7)

O(2)-N(5)-C(31)

N(5)-O(2)-Ni(1)

[(6-Ph₂TPA)Zn(ONHC(O)CH₃)](ClO₄) (11)

Zn(1)-O(1)

2.041(2)

1.992(2)

2.083(2)

2.188(2)

2.679(2)

169.27(8) N(4)-Zn(1)-O(2)

82.59(7)

90.92(8)

103.86(7) N(3)-Zn(1)-N(1)

110.60(7) C(31)-O(1)-Zn(1)

164.38(8) O(1)-C(31)-N(5)

79.05(8)

106.45(8) N(5)-O(2)-Zn(1)

Zn(1)-N(4)

O(1)-C(31)

C(31)-N(5)

N(5)-O(2)

2.219(2)

1.269(3)

1.304(3)

1.382(3)

Zn(1)-O(2)

Zn(1)-N(1)

Zn(1)-N(2)

Zn(1)-N(3)

O(1)-Zn(1)-N(2)

O(1)-Zn(1)-O(2)

O(1)-Zn(1)-N(1)

O(1)-Zn(1)-N(3)

O(1)-Zn(1)-N(4)

O(2)-Zn(1)-N(1)

N(1)-Zn(1)-N(2)

N(1)-Zn(1)-N(4)

89.15(7)

76.31(8)

72.97(7)

91.89(8)

109.19(2)

120.80(2)

120.70(2)

106.67(1)

N(4)-Zn(1)-N(2)

N(3)-Zn(1)-N(2)

O(2)-N(5)-C(31)

^aEstimated standard deviations indicated in parentheses.

The isolation of 11 adds to the growing list of mononuclear

zinc hydroxamate complexes to have been discovered.

Previously, Vahrenkamp³⁴and Cohen³⁵have reported mono-

nuclear zinc hydroxamate species, supported by tris(pyra-

zolyl)borate chelate ligands, that exhibit a five-coordinate

zinc center. In 11, the zinc ion is six-coordinate and has a

psuedo-octahedral geometry. While the Zn-N_Pydistance

(Zn(1)-N(1) 2.083(2) Å) is only slightly longer than the

corresponding distance in 4‚2CH₃CN (Zn(1)-N(1) 2.053-

(2) Å), the increase in Zn-N_PhPybond lengths in going from

4‚2CH₃CN to 11 is much greater. Specifically, whereas Zn-

(34) Ruf, M.; Weis, K.; Brasack, I.; Vahrenkamp, H. Inorg. Chim. Acta

1996, 250, 271-281.

(35) (a) Puerta, D. T.; Cohen, S. M. Inorg. Chem. 2002, 41, 5075-5082.

(b) Puerta, D. T.; Cohen, S. M. Inorg. Chem. 2003, 42, 3423-3430.

N_PhPydistances of 2.139(2) and 2.075(2) Å are observed for

4‚2CH₃CN, in 11 these distances elongate to 2.679(2) and

2.219(2) Å, respectively. The longer of these distances, which

7484 Inorganic Chemistry, Vol. 42, No. 23, 2003

Aryl-Appended TPA Complexes

Figure 5. Top: ORTEP representation of one of two dinuclear cations

found in the asymmetric unit of 8‚0.75CH₃CN‚0.75Et₂O. All ellipsoids

are drawn at the 50% probability level. All hydrogens except the

hydroxamate N-H were omitted for clarity. Bottom: ORTEP representation

of the dinuclear Mn(II) core.

is for Zn(1)-N(3), suggests only a weak interaction between

the zinc center and this phenyl-substituted pyridyl donor. The

Zn-O bond lengths in 11 (1.992(2) and 2.041(2) Å) are

similar to those reported for monomeric five coordinate zinc

hydroxamate complexes (range 1.98-2.10 Å).^34,35

The methyl group of the bound hydroxamate anion in 10‚

1.5CH₃CN and 11 is positioned to form CH/π interactions

with the phenyl groups of the 6-Ph₂TPA ligand (Figures S9

and S10). For both complexes, there is a C(methyl)‚‚‚arene

centroid distance of ∼3.7-3.8 Å (10‚1.5CH₃CN, 3.724 Å;

11, 3.783 Å), and a second C(methyl)‚‚‚arene centroid

distance that is greater than 4 Å (10‚1.5CH₃CN, 4.13 Å;

11, 4.46 Å).

Magnetic Moment. The solution magnetic moments of

8-10 were measured in CH₃CN solution at 298 K using the

Evans¹¹method (Table 7). For 8, the µ_effvalue of 5.6 µ_B/

Mn(II) is slightly lower than the spin-only magnetic moment

(5.9 µ_B) for an isolated high-spin Mn(II) ion. For 9 and 10,

the observed magnetic moments, µ_eff) 4.4 and 3.2 µ_B,

respectively, are slightly higher that the spin-only values

calculated for high-spin Co²⁺(3.9 µ_B) and Ni²⁺(2.8 µ_B) due

to spin-orbit coupling.²⁵

Figure 6. ORTEP representations of the cationic portions of 9, 10‚

1.5CH₃CN, and 11. All ellipsoids are drawn at the 50% probability level.

Hydrogen atoms, except the hydroxamate N-H, are not shown for clarity.

(90 M^-1cm^-1) in 2, versus the extinction coefficient found

for a similar transition in the spectrum of 9 (562 nm (30

M^-1cm^-1), Table 7). This is consistent with the increase in

coordination number for the Co(II) center from five to six

upon hydroxamate binding.³⁶The octahedral Ni(II) com-

plexes 3 and 10 show differences in the energy of both the

³A_2gf ³T_1gand ³A_2gf ³T_2gtransitions. The latter, found at

∼1007 nm in 3, is shifted into the near-IR region in 10. The

former transition is also shifted to lower energy upon

hydroxamate coordination.

EPR and ¹H NMR Spectroscopy. The EPR spectrum of

8 was recorded at 70(1) K (Figure S12). The general features

UV-Vis Spectroscopy. Comparison of the UV-vis

spectral features of the solvent-coordinated complex 2 ([(6-

Ph₂TPA)Co(CH₃CN)](ClO₄)₂) with those of 9 in the region

of 500-600 nm (Figure S11) reveals a higher extinction

coefficient for the ligand field transition found at ∼570 nm

(36) McMillin, D. R. Electronic Absorption Spectroscopy. In Physical

Methods in Bioinorganic Chemistry: Spectroscopy and Magnetism;

Que, L., Jr., Ed.; University Science Books: Sausalito, CA, 2000; pp

1-58.

Inorganic Chemistry, Vol. 42, No. 23, 2003 7485

Makowska-Grzyska et al.

structural models for substrate-bound species in copper and

zinc metalloenzymes, with the calixarene ligand serving as

a type of hydrophobic channel to the metal center. Notably,

these functionalized calix[6]arene-type ligands, as well as

trispyrazolylborate derivatives, generally enforce coordination

numbers of four to five, with the latter generally being found

for chelate anions.³⁵In the work described herein, we have

evaluated whether aryl-appended TPA ligands will enable

the isolation of mononuclear divalent metal complexes

having the following: (1) a hydrophobic environment

surrounding a metal center that has one or more solvent-

occupied coordination sites, (2) stability with respect to

oxidation by dioxygen, and (3) an ability to maintain a

mononuclear structure in derivative complexes having a

coordinated chelating anion. Such features are key if aryl-

appended TPA ligands are to be utilized to produce synthetic

models for species relevant to several recently reported

metalloenzymes.

Figure 7. Representation of the hydrogen-bonded cations found in the

solid state structure of 11. Similar hydrogen-bonding interactions are found

in 10‚1.5CH₃CN.

Mechanistic pathways proposed for the mononuclear Mn-

(II) centers in oxalate oxidase and decarboxylase involve

interaction of a N₃(His)O(Glu)-ligated Mn(II) center with

both oxalate and dioxygen through the displacement of two

water ligands, leading to the oxidation of Mn(II) to Mn-

(III).^3a,44During catalytic turnover, it is suggested that the

manganese centers in oxalate oxidase and decarboxylase

likely exhibit a coordination number of five or six.⁴⁵As an

approach toward generating complexes relevant to oxalate

oxidases and decarboxylases, we initiated studies to evaluate

the divalent manganese chemistry of aryl-appended TPA

ligands. In the Mn(II) derivatives 1 and 8, the 6-Ph₂TPA

ligand coordinates only via one of the phenyl-substituted

pyridyl donors, leaving three coordination sites available for

methanol or anion binding. This coordination mode of the

chelate ligand may explain why a dinuclear Mn(II) hydrox-

Table 7. Selected Physical Properties of 8-11

8

9

10

11

UV-vis, nm

(ꢀ, M^-1cm^-1

472 (110)

562 (30)

925(6)

4.4

585 (13)

1004 (5)

a

)

µ_eff^b(µ_B)

5.6/Mn(II)

3.2

FTIR^c(cm^-1

)

ν_CdO

1617

1095

623

1597

1096

623

1598

1097

623

1597

1093

623

_-d

ν_X

^aSpectra collected in dry CH₃CN. ^bAverage value of two independent

determinations at 298 K by the Evans method: Evans, D. F. J. Chem. Soc.

1959, 115, 2003. ^cSpectra collected as dilute KBr pellets. ^dVibrations of

counterion.

of this spectrum are similar to those observed in the solid

state spectrum of [(bpmp)Mn₂(µ-OAc)₂]ClO₄(bpmp ) 2,6-

bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenol).³⁷

1

The H NMR of 11 in CD₃CN at ambient temperature

(38) (a) Blanchard, S.; Le Clainche, L.; Rager, M.-N.; Chansou, B.;

Tuchagues, J. P.; Duprat, A. F.; Le Mest, Y.; Reinaud, O. Angew.

Chem., Int. Ed. 1998, 37, 2732-2735. (b) Rondelez, Y.; Se´ne`que,

O.; Rager, M.-N.; Duprat, A. F.; Reinaud, O. Chem. Eur. J. 2000, 6,

4218-4226. (c) Se´ne`que, O.; Rager, M.-N.; Giorgi, M.; Reinaud, O.

J. Am. Chem. Soc. 2000, 122, 6183-6189. (d) Le Clainche, L.; Giorgo,

M.; Reinaud, O. Eur. J. Inorg. Chem. 2000, 1931-1933. (e) Le

Clainche, L.; Giorgi, M.; Reinaud, O. Inorg. Chem. 2000, 39, 3436-

3437. (f) Se´ne`que, O.; Giorgi, M.; Reinaud, O. Chem. Commun. 2001,

984-985. (g) Se´ne`que, O.; Rager, M.-N.; Giorgi, M.; Reinaud, O. J.

Am. Chem. Soc. 2001, 123, 8442-8443. (h) Se´ne`que, O.; Rondelez,

Y.; Le Clainche, L.; Inisan, C.; Rager, M.-N.; Giorgi, M.; Reinaud,

O. Eur. J. Inorg. Chem. 2001, 2597-2604. (i) Rondelez, Y.; Bertho,

G.; Reinaud, O. Angew. Chem., Int. Ed. 2002, 41, 1044-1046. (j)

Se´ne`que, O.; Campion, M.; Douziech, B.; Giorgi, M.; Rivie`re, E.;

Journaux, Y.; Le Mest, Y.; Reinaud, O. Eur. J. Inorg. Chem. 2002,

2007-2014. (k) Rondelez, Y.; Rager, M.-N.; Duprat, A.; Reinaud,

O. J. Am. Chem. Soc. 2002, 124, 1334-1340.

exhibits a methyl resonance at 1.46 ppm associated with the

bound hydroxamate ligand. This resonance is shifted by 0.34

ppm upfield of that observed for free acetohydroxamic acid

(1.80 ppm) under identical conditions and is consistent with

the presence of CH/π interactions involving this methyl

group and the phenyl rings of the 6-Ph₂TPA ligand. Further

evidence for these secondary interactions was found in the

¹³C{¹H} spectrum of 11, where the methyl carbon of the

acetohydroxamate ligand is found at 17.9 ppm, which is

again upfield of the same resonance found for the free acid

(19.6 ppm) under identical conditions.

Discussion

(39) Kersting, B. Angew. Chem., Int. Ed. 2001, 40, 3988-3990.

(40) Wieser-Jeunesse, C.; Matt, D.; De Cian, A. Angew. Chem., Int. Ed.

1998, 37, 2861-2864.

Several ligand systems have been reported that provide a

hydrophobic coordination environment surrounding one or

more open coordination sites on mononuclear metal

centers.^38-43Particularly interesting are recent examples of

tetrahedral copper and zinc complexes constructed by Re-

inaud and co-workers using functionalized calix[6]arene-type

ligands. Members of this family of complexes include

(41) Ooi, T.; Kondo, Y.; Mauroka, K. Angew. Chem., Int. Ed. 1998, 37,

3039-3041.

(42) Hecht, S.; Fre´chet, J. M. J. Angew. Chem., Int. Ed. 2001, 40, 74-91.

(43) (a) Ruf, M.; Vahrenkamp, H. Inorg. Chem. 1996, 35, 6571-6578.

(b) Kitajima, N.; Tolman, W. B. Prog. Inorg. Chem. 1995, 43, 419-

531. (c) Weis, K.; Vahrenkamp, H. Eur. J. Inorg. Chem. 1998, 271-

274.

(44) Reinhardt, L. A.; Svedruzic, D.; Chang, C. H.; Cleland, W. W.;

Richards, N. G. J. J. Am. Chem. Soc. 2003, 125, 1244-1252.

(45) Whittaker, M. M.; Whittaker, J. W. JBIC, J. Biol. Inorg. Chem. 2002,

7, 136-145.

(37) Blanchard, S.; Blondin, G.; Rivie`re, E.; Nierlich, M.; Girerd, J.-J. Inorg.

Chem. 2003, 42, 4568-4578.

7486 Inorganic Chemistry, Vol. 42, No. 23, 2003

Aryl-Appended TPA Complexes

amate complex having µ-η¹:η²-ONHC(O)CH₃coordination

is isolated, versus mononuclear hydroxamate derivatives for

the other 3d metal ions (Co(II), Ni(II), and Zn(II)), where

all available donors of the 6-Ph₂TPA ligand interact with

the divalent metal center. Tridentate coordination of the

6-Ph₂TPA ligand does not impart a significant degree of

hydrophobic character or steric hindrance around the man-

ganese centers in 1 and 8, and this differs from that found

for 6-Me₃TPA in synthetic Mn(II) complexes having a bound

monoanionic or dianionic catecholate ligand, wherein tet-

radentate N₄coordination is observed.^18gDetermination of

the nuclearity of 8 in solution, as well as further EPR studies

of this complex, is currently in progress.^39,46

study of the redox properties of four copper(II) complexes

that differed in the number of phenyl-appended pyridyl

donors present from zero to three ([(TPA)Cu(CH₃CN)]-

(ClO₄)₂, [(6-PhTPA)Cu(CH₃CN)](ClO₄)₂, [(6-Ph₂TPA)Cu-

(CH₃CN)](ClO₄)₂, and [(6-Ph₃TPA)Cu(CH₃CN)](ClO₄)₂), the

Cu(II)/Cu(I) redox potential in CH₃CN solution was found

to increase by ∼100 mV for each phenyl substituent present.

This behavior was attributed primarily to the fact that the

phenyl appendages reduce the local dielectric by shielding

the metal center from the polar solvent, thus favoring a lower

oxidation state for the metal. Other factors considered by

Canary and co-workers included the effect of steric interac-

tions involving the phenyl substituents, and the difference

in σ-donor properties between pyridyl and phenyl-appended

pyridyl donors. However, comparison of the X-ray crystal-

lographically characterized Cu(II) and Cu(I) complexes [(6-

Ph₃TPA)Cu(CH₃CN)](ClO₄)₂and [(6-Ph₃TPA)Cu]BPh₄re-

vealed only minor structural perturbations resulting from

reduction of the metal center, inconsistent with the increase

in redox potential for [(6-Ph₃TPA)Cu(CH₃CN)](ClO₄)₂(300

mV vs NHE) versus [(TPA)Cu(CH₃CN)](ClO₄)₂(0.00 mV

vs NHE). In addition, literature precedent suggests that the

introduction of a phenyl substituent to a pyridyl donor should

impart only a small inductive effect.⁴⁷It was on the basis of

these combined analyses that Canary et al. concluded that

environmental effects were the primary reason for the more

positive reduction potentials observed for phenyl-appended

tris((pyridyl)methyl)amine copper complexes. In regard to

the metal complexes reported herein, investigation of ad-

ditional derivatives (e.g., TPA and 6-PhTPA analogues) is

necessary to fully evaluate the influence of phenyl substit-

uents on the redox properties of tris((pyridyl)methyl)amine-

ligated Mn(II), Co(II), and Ni(II) complexes.⁴⁸Finally, the

electrochemical properties of the nickel derivatives 3 and 5

are consistent with the observation that nitrogen/oxygen-

ligated Ni(II) centers typically do not undergo oxidation in

a biologically relevant redox range. Notably, X-ray absorp-

tion spectroscopic studies of the nickel-containing acireduc-

tone dioxygenase (ARD), wherein the active site metal center

is ligated by a mixture of nitrogen and oxygen donors, do

not indicate any change in redox level upon substrate binding,

thus suggesting a non-redox role for the metal center in this

enzyme.^4b

The coordination chemistry of the aryl-appended TPA

ligands with Ni(II), Co(II), and Zn(II) differs dramatically

from that observed for Mn(II). In all of the complexes

isolated of these metals, each of the donor atoms available

on the aryl-appended TPA chelate ligand coordinates to the

metal center to produce mononuclear structures. For the

solvent adducts 2-6, while divalent cobalt and zinc com-

plexes (2, 4, and 6) each have a coordination number equal

to five, with only one bound solvent molecule, the divalent

nickel complexes 3 and 5 have six-coordinate structures. For

2, 4, and 6, the aryl appendages of the 6-Ph₂TPA and 6-(Me₂-

Ph)₂TPA ligands form CH/π interactions with the methyl

group of the bound acetontrile ligand. These interactions are

1

detectable by H NMR spectroscopy when zinc complexes

4 and 6 are dissolved in CD₃NO₂solution, as an upfield

shifted acetonitrile methyl resonance, consistent with the

presence of CH/π interactions, is present in spectra of both

complexes. It is important to note that a similar resonance

1

is not found in H NMR spectra of [(TPA)Zn(CH₃CN)]-

(ClO₄)₂(7) collected under identical conditions. This indi-

cates a unique hydrophobic influence on the solvent-occupied

coordination site by the aryl substituents in the 6-Ph₂TPA

and 6-(Me₂Ph)₂TPA ligands found in 2, 3, and 5. Notably,

the six coordinate Ni(II) center in 4 exhibits a sandwich type

motif, wherein a bound acetonitrile molecule is positioned

between the aryl substitutents of the 6-Ph₂TPA ligand. This

results in the formation of two shorter CH/π interactions

(C(33)‚‚‚arene centroid distances of 3.66 and 3.63 Å) than

are found in the Co(II) and Zn(II) analogues.

Examination of the electrochemical properties of the cobalt

and nickel complexes 2, 3, and 5 revealed reversible couples

corresponding to the reduction of the +2 metal complexes,

presumably to +1. No oxidative couples were found for

M(II)/M(III) in this family of complexes. The electrochemical

properties of these complexes are consistent with studies

reported by Canary and co-workers of copper derivatives of

phenyl-appended tris((pyridyl)methyl)amine ligands.^6bIn a

Admixture of the 6-Ph₂TPA ligand, M(ClO₄)₂‚6H₂O, and

Me₄NOH‚5H₂O in methanol solution, followed by the

addition of an equimolar amount of acetohydroxamic acid,

yielded the mononuclear hydroxamate complexes [(6-Ph₂-

TPA)Co(ONHC(O)CH₃)](ClO₄)₂(9), [(6-Ph₂TPA)Ni(ONHC-

(O)CH₃)](ClO₄)₂(10), and [(6-Ph₂TPA)Zn(ONHC(O)CH₃)]-

(ClO₄)₂(11), all of which were characterized by X-ray

crystallography. Isolation of these hydroxamate complexes

indicates that use of the 6-Ph₂TPA ligand system enables

(46) The magnetic and EPR properties of dinuclear Mn(II) complexes are

of interest toward understanding features of the dinuclear manganese

sites found in several enzymes including arginase and catalase: (a)

Dubois, L.; Xiang, D.-F.; Tan, X.-S.; Pe´caut, J.; Jones, P.; Baudron,

S.; Le Pape, L.; Latour, J.-M.; Baffert, C.; Chardon-Noblat, S.;

Collomb, M.-N.; Deronzier, A. Inorg. Chem. 2003, 42, 750-760 and

references therein. (b) Howard, T.; Telser, J.; DeRose, V. J. Inorg.

Chem. 2000, 39, 3379-3385. (c) Hureau, C.; Anxolabehere-Mallart,

E.; Nierlich, M.; Gonnet, F.; Riviere, E.; Blondin, G. Eur. J. Inorg.

Chem. 2002, 10, 2710-2719.

(47) (a) James, B. R.; Williams, R. J. P. J. Chem. Soc. 1961, 2007-2019.

(b) Sorrell, T. N.; Jameson, D. L. Inorg. Chem. 1982, 21, 1014-

1019.

(48) Solvent-coordinated tris((pyridyl)methyl)amine complexes of Ni(II)

and Co(II) akin to 2, 3, and 5 have been structurally characterized;

however, the electrochemical properties of these complexes were not

reported.^20c,23c

Inorganic Chemistry, Vol. 42, No. 23, 2003 7487

Makowska-Grzyska et al.

the generation of novel mononuclear divalent metal com-

plexes of nickel, zinc, and cobalt having a single chelating

anion. These structures are reminiscent of proposed substrate

adducts in Ni²⁺-containing ARD and Zn²⁺- and Ni²⁺-

containing glyoxalase I. Thus, further studies of nickel and

zinc complexes of these aryl-appended TPA ligands with

acidreductone and hemithioacetal model substrates are clearly

warranted.

Acknowledgment. We acknowledge the support of the

Herman Frasch Foundation (501-HF02 to L.M.B.) and the

National Science Foundation (CAREER Award CHE-

0094066 to L.M.B.; CHE-0078746 to J.A.H.).

Supporting Information Available: ORTEP representations

showing CH/π interactions in 1A‚CH₃OH, 1B‚2CH₃OH, 2‚

2CH₃CN, 3‚CH₃OH, 4‚2CH₃CN, 10‚1.5CH₃CN, and 11; Chem3D

space-filling figure of 9; EPR spectra for 1 and 8; cyclic voltam-

mograms for 2, 3, and 5; X-ray crystallographic files (CIF) for

complexes 1A‚CH₃OH, 1B‚2CH₃OH, 2‚2CH₃CN, 3‚CH₃OH, 4‚

2CH₃CN, 6‚2.5CH₃CN, 7‚CH₃CN, 8‚0.75CH₃CN‚0.75Et₂O, 9,

10‚1.5CH₃CN, and 11. This material is available free of charge

via the Internet at http://pubs.acs.org.

Concluding Remarks

The 6-Ph₂TPA and 6-(Me₂Ph)₂TPA ligands employed in

this study are easily prepared in multigram quantities via

straightforward synthetic procedures. As shown by the isola-

tion of novel hydroxamate derivatives, these ligands enable

the isolation of interesting mononuclear complexes with

hydrophobic encapsulation of a metal-bound chelating anion.

IC034810Y

7488 Inorganic Chemistry, Vol. 42, No. 23, 2003

Article Doi

First Row Divalent Transition Metal Complexes of Aryl-Appended Tris((pyridyl)methyl)amine Ligands: Syntheses, Structures, Electrochemistry, and Hydroxamate Binding Properties

DOI: 10.1021/ic034810y

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Article abstract of DOI:10.1021/ic034810y

Full text of DOI:10.1021/ic034810y

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