CSIRO PUBLISHING Full Paper

www.publish.csiro.au/journals/ajc Aust. J. Chem. 2010, 63, 47–55

Oxazoles XXII.∗ The Cobalt(II) Coordination Chemistryof 2-(ortho-Anilinyl)-4,4-dimethyl-2-oxazoline: Syntheses,Properties, and Solid-State Structural Characterization

Felix J. Baerlocher,A Robert Bucur,B Andreas Decken,C Charles R. Eisnor,D,E

Robert A. Gossage,B,F Sarah M. Jackson,D Leslie Jolly,B Susan L. Wheaton,A

and R. Stephen WylieB

ADepartment of Biology, Mount Allison University, 63B York Street,Sackville NB E4 L 1G7, Canada.

BDepartment of Chemistry and Biology, Ryerson University, 350 Victoria Street,Toronto ON M5B 2K3, Canada.

CDepartment of Chemistry, University of New Brunswick, Fredericton NB E3B 6E2, Canada.Corresponding author for the crystallographic work. Email: adecken@unb.ca

DDepartment of Chemistry, Acadia University, Wolfville NS B4P 2R6, Canada.EDeceased 10 September 2006.FCorresponding author. Email: gossage@ryerson.ca

Ethanol solutions of the cobalt(ii) halides react with an excess of 2-(ortho-anilinyl)-4,4-dimethyl-2-oxazoline (1: i.e. 2-(2′-anilinyl)-4,4-dimethyl-4,5-dihydro-1,3-oxazole) to give isolable κ2-N,N′-bonded species of 1 in good to excellent yields.The complexes CoX2(1-κ2-N,N′)·(H2O)n have been isolated for X = Cl (2: n = 1/2), X = Br and I (3 and 4, respectively;n = 0); the solid-state structures (X-ray) are in accordance with those suggested by UV-visible spectroscopy and conductiv-ity measurements (i.e. non-ionic complexes with a pseudo-tetrahedral coordination motif around Co). In contrast, reactionof excess 1 with Co(NCS)2 forms the octahedral (UV-visible, X-ray) bis-isothiocyanato complex Co(NCS-κ1-N′)2(1-κ2-N,N′)2 (5) with cis-oriented NCS groups and trans-disposed oxazolines. Calculations at the PM3(tm) level of theorysuggest that this isomer is close in energy to the four other possible (gas-phase) isomers. Treatment of ethanol solutions ofhydrated cobaltous nitrate with excess 1 yields a material analyzed as [Co(NO3)(1)(H2O)2](NO3) (6a) and a small amount(less than 1%) of a second complex (6b); the latter has been characterized (X-ray) as the hydrated octahedral complex[Co(NO3-κ1-O)(1-κ2-N,N′)2(OH2)](NO3). In this case, the nitrato and aqua groupings are located cis to one another andtrans to the coordinated −NH2 groups. Complex 6a is surmised to have a [Co(NO3-κ2-O,O′)2(1-κ2-N,N′)(OH2)2]NO3structure. Cobalt compounds 2–5 and 1 have also been screened for their antifungal properties against Aspergillus niger,Aspergillus flavus, Candida albicans, and Saccharomyces cerevisiae but were found to be inactive in this regard.

Manuscript received: 30 April 2009.Manuscript accepted: 13 June 2009.

Introduction

2-Oxazolines (i.e. 4,5-dihydro-1,3-oxazoles) are a class of lig-ands used extensively in coordination chemistry and Lewis acidcatalysis.[1–21] The oxazoline ring system is also employed as aprotecting group for carboxylic acids and as a directing group inregio- and enantioselective organic transformations.[22–29] Theheterocycle is likewise found in several natural products, manyof which have been the targets for total syntheses.[30–35] Despitethe widespread interest and advances in the use of oxazolinesin transition metal chemistry,[1–21] there is still a need for thesystematic investigation of the metal bonding modes[12,16,19] ofthese oxazoles and an elucidation of the trends that govern thestructural aspects within related oxazoline complexes.

∗Part XXI: R. A. Gossage, H. A. Jenkins, J. W. Quail, J. Chem. Crystallogr., accepted pending minor revisions.

The aniline derivative 1 (Fig. 1[36]) and its structuralrelatives[9,14,15,37–40] are potentially bidentate mono-oxazolines.Ligands of this type have been previously used as reagents forthe synthesis of larger ligand frameworks,[9,41–43] as supportmolecules[44] and as coordination fragments in themselves.[14,15]

Compound 1 can be readily produced in large quantitiesfrom inexpensive isatoic anhydride[36,45–47] but its coordi-nation chemistry has not been explored in any detail.[14,15]

Our long-term interests are centred within coordinationchemistry,[11–21,41,48] catalysis[14,15,18,49] and also in the designof novel oxazole ligands for several diverse applications.[44] Asthe chemistry of the first-row transition metals is one of the cor-nerstones of our understanding of metal–ligand interactions[50]

© CSIRO 2010 10.1071/CH09259 0004-9425/10/010047

48 F. J. Baerlocher et al.

NH2

O1

N

Fig. 1. The molecular structure of 1.

and coordination chemistry in general,[51] we chose to explorethe bonding ability of 1 with five common CoII metal saltsand to further evaluate the properties of these complexes asbiologically active agents. This work is part of a larger pro-grammed investigation into the medicinal and coordinationchemistry of oxazoles.[11–21,49]

Results and DiscussionSyntheses and Spectroscopic CharacterizationThe treatment of alcoholic solutions of hydrated cobaltous chlo-ride, cobalt(ii) bromide or anhydrous CoI2 with an excess or sto-ichiometric quantity of 2-(o-anilinyl)-4,4-dimethyl-2-oxazoline1 leads to the formation of isolable metal adducts (i.e. complexes2, 3, and 4, respectively) of the title ligand (see Experimental). Inthese cases, elemental analysis measurements suggest that onlyone equivalent of ligand 1 is bound to the metal centre. This is incontrast to a similar reaction protocol involving ethanolic solu-tions of anhydrous Co(NCS)2 to yield compound 5, in whichthe coordination of two equivalents of 1 (i.e. Co(NCS)2(1)2) issuggested (by elemental analysis). Not surprisingly, pronouncedcolour changes were noted when solutions of the above cobaltsalts were treated with 1. Solid complexes [CoX2(1)]·(H2O)n (2:n = 0.5; 3: n = 0) of the lighter two halogens are both deep bluein colour, whereas the iodo analogue 4 (n = 0) is a shade of emer-ald green. In contrast, complex 5 is found to be purple in colour.Crystals of anhydrous complex 2 can be obtained by recrystal-lization of the material from a saturated boiling acetone solution,a procedure that gives crystals of the compound that are suitablefor analysis via X-ray diffraction (see below). Crystalline sam-ples of 3, 4, and 5 were likewise obtained by recrystallizationand slow evaporation from mixtures of CH2Cl2/Et2O or 95%EtOH solutions of the complexes (see Experimental).

The reactions of 1 with hydrated cobaltous nitrate is lessstraightforward than those described above. Treatment of solu-tions of [Co(OH2)6](NO3)2 with excess 1 leads to the formationof two products 6a and 6b, the latter in very low yield (lessthan 1%). Bulk samples of the 6a and 6b mixture provide cleananalyses (elemental analysis, conductivity) as containing a sin-gle complex of general formula Co(NO3)2(1)(H2O)2. Thus, weassume that 6b is a minor product. Although analytically pureand crystalline samples of 6a could be obtained from saturatedEtOH solutions of the complex, on no occasion were the crys-tals found to be suitable for X-ray diffraction work. A suitablesingle crystal was obtained by repeated attempts to induce ade-quate crystal formation from solutions of bulk 6a; however, thismaterial was later identified crystallographically as a complexof different molecular composition to that anticipated from thecombustion analysis (6b: see below). Attempts to maximize theproduction of 6b by adjusting reaction stoichiometry invariablyled to the formation of unseparable mixtures of materials fromwhich no pure complexes could be obtained.

Table 1. Spectroscopic properties of complexes 2–5 and 6a

Complex UV-visible (ε)A ConductivityB µeffC IRD

2 262 (2265) 2 4.65 1621sE

329 (2405)641 (124)

3 258 (975) 2 3.98 1616sE

304 (1015)665 (80)

4 258 (22650) 40 3.85 1613sE

330 (sh)375 (sh)665 (1240)

5 263 (22650) 15 4.68 1626sE

326 (24060) 2083vsF

560 (115) 2095sF

645 (270)6a 247 (1630) 1.3 × 102 –G 1628sE

321 (1685)350 (sh)

AWavelength values reported in nm (±1 nm), extinction coefficients (ε) inunits of L mol−1 cm−1, sh = shoulder; B�−1 mol−1 cm2 (acetone); CBohrmagnetons (see: G.A. Bain, J. F. Berry, J. Chem. Ed. 2008, 85, 532 andAcces-sory Publication) measured at 295 K; D±2 cm−1, v = very strong, s = strong;Eassigned to ν[C=N]; Fassigned to ν[C=S]; Gnot measured.

NH2

I II

IV V

III

NH2 NH2

NCS

NCS SCN

NCS NCSN

NH2 NH2

NH2

N

N

SCNN N

N

H2N

H2N NCS

Co

Co Co

Co Co

NCS

NCS

NCS

H2N

H2N

NH2

N N

N

Fig. 2. The five possible structural isomers of complex 5; bidentate ligand1 is represented as H2N∩N.

The paramagnetic nature of the formal CoII d7 ion obvi-ously precludes the use of NMR spectroscopy for the structuralcharacterization of any of the complexes reported herein.[50,51]

Therefore, IR spectroscopy, magnetic moment measurements,UV-visible spectroscopy, and X-ray crystallographic techniqueswere employed to assist in the elucidation of their structuralproperties (see below). Table 1 gives the spectroscopic data ofcomplexes 2–5 and 6a. Magnetic moment measurements andUV-visible spectral data are in accord with molecular monomericCoII complexes; complexes 2–4 are indicated as containing a(pseudo-) tetrahedral coordination environment around the metalatom, in contrast to 5, which provides strong evidence for anoctahedral coordination of the metal centre. Note that UV-visibleabsorption bands due to coordinated 1[52] are also present (seeTable 1).

The IR and elemental analysis data of complex 5 are in accor-dance with the presence of N-bonded NCS ligands (i.e. isothio-cyanato groups: Table 1)[53,54] and two equivalents of 1. Thesedata, coupled with the non-ionic nature of 5, strongly suggesta general formula of Co(NCS-κ1-N)2(1-κ2-N,N′)2. However,several structural isomers are possible with this coordination

Oxazoles XXII. The Cobalt(ii) Coordination Chemistry of 2-(ortho-Anilinyl)-4,4-dimethyl-2-oxazoline 49

geometry (Fig. 2: I–V). To try to assist in an initial structuralassignment, PM3(tm) calculations of the five possible (gas-phase) structural forms, three with cis-NCS and two with trans-NCS groupings, were carried out.[55] These results suggestedthat all five isomers are quite close in energy (±2%; see Acces-sory Publication) and hence this level of theory was not able tostrictly assign the most likely thermodynamic form (see below).

The nature of complex 6a is likewise difficult to ascertainfrom the available IR and conductivity data. IR absorptions inthe N–O region[56–60] are masked by bands of ligand 1, althoughabsorbances located at 1384 and 827 cm−1 suggest the presenceof a free NO−

3 anion. The measured conductivity of complex 6ais consistent with a 1:1 electrolyte. As we have been unable toobtain suitable crystalline material of 6a, a tentative assignmentof the structure formula as [Co(NO3)(1-κ2-N,N′)(OH2)2]NO3(elemental analysis, conductivity, IR), with an uncertain relativeorientation of ligated groups, is put forward. Assuming distortedoctahedral coordination around Co (UV-visible), this empiricalformula implies the presence of a κ2-O,O′-NO3 unit.

Crystallographic InvestigationsThe characterization of complexes 2–4 via single-crystal X-raydiffraction studies (Tables 2 and 3) reveals the expected dis-torted tetrahedral coordination motif around the Co metal centre(Figs 3–5) as suggested from the UV-visible data.

All three of these complexes contain typical Co–N and Co–X(X = Cl, Br or I) bond lengths when compared with related com-plexes containing N,N′-chelates, aniline ligands, or the halidesin question.[61–76] There is a clear trend in increasing Co–X bondlength in the series Cl < Br < I although the Co–N bond lengthsremain essentially uniform (Table 2). As a quantitative tool, theτ4 parameter has been presented by Houser and coworkers as ameasure of the distortion of a four-coordinate complex from theidealized tetrahedral geometry towards one that is truly squareplanar in nature. This measurement is defined as unity for tetra-hedral and zero for idealized square planar.[77] The τ4 value isobtained by Eqn 1 (below), in which α and β represent the largestand second-largest bond angles, respectively, that are formedbetween the metal and any two of the appended ligands. Thisparameter is based on the earlier τ value presented by Addisonet al.[78] that is used to assign the degree of variation in five-coordinate systems (recently suggested[77] to be referred to asτ5). For complexes 2–4, α and β are found to be an X–Co–Noxand the X′–Co–NH2 angles, with the latter invariably being thewidest angle (i.e. α; see Table 3 and the Accessory Publication).

τ4 = (360◦ − (α + β))/(141◦) (1)

Calculations of τ4 reveal that all three halido complexes areperhaps best described as containing a slightly distorted tetra-hedral coordination motif around the metal sites (τ4 = 0.877, 2;0.893, 3, and 0.880, 4).

Complex 5 has been shown to be a non-electrolyte (by con-ductivity) and suggested to contain a six-coordinate metal cen-tre (UV-visible). The crystallographic characterization (Fig. 6;Tables 2 and 3) supports these earlier hypotheses and showsthe presence of two κ2-N,N′-bonded units of 1 and that thetwo oxazoline rings are oriented in a trans fashion aroundthe metal centre. The structural data also confirm (IR) thepresence of isothiocyanato groups, which are shown to becisoidal and mutually trans to the coordinated –NH2 groupsof 1. This stereoisomer is one of the forms predicted abovevia the PM3(tm) calculations (see above)[55] (Accessory Pub-lication). A further inherent property of this structural isomer

is that by definition this complex is chiral at Co. Not sur-prisingly, both of the � and � enantiomers of 5 are foundwithin the unit cell of this material (see Accessory Publication)and hence the crystalline material does not represent a sponta-neous resolution of the racemate. Complexes that are structurallyrelated to 5 that have appeared in the literature include the cis-isomers of Co(NCS)2(2,2′-bipyrimidine)2,[53] Co(NCS)2(1,10-phenanthroline)2,[79] Co(NCS)2(4,5-diazafluoren-9-one)2,[54]

and several Co2+ materials containing substituted imino-pyridine donor ligands.[80] Both the metal–ligand bond lengthsand angles of complex 5 are similar to these examples above andare typical of this class of Co materials. It has been established[80]

that an analysis of the Co–N bond lengths can serve to distinguishbetween a high- and low-spin situation in CoII complexes with anN6 ligand donor atom set. The average of the six metal–nitrogenbond lengths (i.e. Co–Nav) can vary significantly for Co2+ com-plexes but these average lengths typically lie at ∼1.98 Å inthe low-spin case, whereas high-spin complexes are on averagelonger and centred at ∼2.14 Å. Complex 5 fits this hypothesis asCo–Nav = 2.17 Å and µeff is measured as 4.68 Bohr magnetons;hence, both datasets strongly suggest the high-spin situation.

A single-crystal X-ray diffraction study of the minorproduct 6b revealed a salt-like complex of formula [Co(NO3-κ1-O)(1-κ2-N,N′)2(OH2)](NO3)(H2O). An ORTEP representa-tion of the formally cationic component of 6b appears inFig. 7. One lattice water molecule (not shown) per Co unitis also contained in the unit cell (see Accessory Publica-tion), which is H-bonded to the free nitrate (formal) anion(H44a· · · O42 = ∼2.24 Å). In relation to this material, thereare two structurally analogous CoII complexes in the litera-ture that possess the same general formula. The complexes[Co(NO3)(tbz)2(OH2)]NO3 (7: tbz = thiabendazole)[57] and[Co(NO3)(PyTT)2(OH2)]NO3 (8: PyTT = 2-(2-pyridyl)imino-N-(2-thiazolin-2-yl)thiazolidine)[56] both contain cis-aquo andO-bonded nitrato groups in addition to a pair of bidentate N,N-chelating ligands within the metal coordination sphere. Whencompared with these latter two complexes, the bond lengths andangles around the metal atom within 6b (Table 3) are similar andunsurprising. For example, the O–Co–O′ angle of 6b (Table 3)can be compared with that of 8 (i.e. 85.29(9)◦). Complex 6b alsohas similar Co–OH2 and Co–ONO2 bond lengths (Table 3) com-pared with both those of 7 and 8 (7: 2.100(4) and 2.112(4) Å,respectively; 8: 2.105(2) and 2.249(2) Å, respectively).

Biological ScreeningPart of our research efforts involves biological investigations ofoxazoles and their transition metal derivatives. In this regard,compound 1 and cobalt compounds 2–5 were screened fortheir antifungal properties against Aspergillus niger, Aspergillusflavus, Candida albicans, and Saccharomyces cerevisiae (seeExperimental and the Accessory Publication; Appendix A).Complex 6a was not investigated owing to our uncertainty asto its structural make-up. The low yield of 6b, coupled with thepreviously measured biological inertness of its structural rela-tive 7,[57] also eliminated this material from our biological study.Unfortunately, the compounds that were tested (1–5) were foundto be completely inactive in inhibiting the growth cycle of anyof these four organisms (Accessory Publication).

Conclusions

The coordination chemistry of the title oxazole 1 with sev-eral divalent Co metal salts has been investigated. In all of

50 F. J. Baerlocher et al.

Tab

le2.

Cry

stal

logr

aphi

cda

tafo

rco

mpl

exes

2–5

and

6b

Com

plex

:2

34

56b

Form

ula

C11

H14

N2O

Cl 2

Co

C11

H14

N2O

CoB

r 2C

11H

14N

2O

CoI

2C

24H

28N

6O

2S

2C

oC

22H

32N

6O

10C

oFo

rmul

aw

eigh

t32

0.07

408.

9950

2.97

555.

5759

9.47

Cry

stal

size

[mm

]0.

15×

0.3

×0.

40.

1×

0.25

×0.

550.

075

×0.

375

×0.

10.

4×

0.4

×0.

450.

25×

0.3

×0.

35a

[Å]

6.42

43(6

)11

.834

1(6)

12.1

746(

11)

15.0

376(

9)9.

9619

(11)

b[Å

]20

.016

(2)

20.8

395(

13)

21.3

76(3

)10

.590

8(6)

10.7

311(

12)

c[Å

]10

.138

3(9)

11.9

541(

6)12

.276

6(12

)16

.310

6(9)

25.4

07(3

)α

[◦]

9090

9090

90β

[◦]

92.9

29(1

)11

0.64

10(1

0)11

0.20

1(2)

102.

655(

1)90

γ[◦

]90

9090

9090

V[Å

3]

1302

.0(2

)27

58.8

(3)

2998

.4(5

)25

34.5

(3)

2716

.0(5

)D

calc

[gcm

−3]

1.63

31.

969

1.62

91.

456

1.46

6C

ryst

alsy

stem

,spa

cegr

oup

Mon

ocli

nic,

P2 1

/nM

onoc

lini

c,C

2/c

Mon

ocli

nic,

C2/

cM

onoc

lini

c,P

2 1/c

Ort

horh

ombi

c,P

2 12 1

2 1Z

48

84

4F

(000

)65

215

9218

8011

5612

52T

[K]

198(

1)19

8(1)

198(

1)19

8(1)

198(

1)A

bsor

ptio

nco

effi

cien

t[m

m−1

]1.

712

7.02

21.

607

0.87

60.

696

2θra

nge

[◦]

2.03

–24.

991.

95–2

7.49

1.91

–27.

502.

31–2

7.50

1.60

–24.

99L

imit

ing

indi

ces

−7≤h

≤7−1

5≤h

≤14

−15

≤h≤1

3−1

9≤h

≤19

−11

≤h≤1

1−2

3≤k

≤23

−27

≤k≤2

5−2

7≤k

≤27

−13

≤k≤1

2−1

2≤k

≤12

−11

≤l≤1

2−1

5≤l

≤14

−15

≤l≤1

5−2

0≤l

≤20

−29

≤l≤3

0R

efle

ctio

nsco

llec

ted

6492

9474

1039

317

205

1370

2R

efle

ctio

nsI>

2σ(I

)22

0931

1033

7557

0045

67Pa

ram

eter

s21

015

521

042

848

0G

oodn

ess

offi

ton

F2

1.07

51.

074

1.07

01.

076

1.00

6Fi

nalR

indi

ces

I>2σ

(I)

R1

0.02

160.

0256

0.02

340.

0262

0.02

64w

R2

0.05

880.

0661

0.05

220.

0700

0.05

26R

indi

ces

(all

data

)R

10.

0256

0.03

030.

0310

0.03

170.

0355

wR

20.

0615

0.06

760.

0550

0.07

290.

0554

ρm

in,m

ax[e

Å3]

0.39

5,−0

.202

0.64

8,−0

.725

0.83

0,−0

.537

0.35

8,−0

.223

0.25

1,−0

.148

Oxazoles XXII. The Cobalt(ii) Coordination Chemistry of 2-(ortho-Anilinyl)-4,4-dimethyl-2-oxazoline 51

Table 3. Selected bond lengths and angles for complexes 2–5 and 6bBond lengths are given in units of Å and angles in degrees, standard deviations are given in parentheses

Complex Co–X Co–NoxA Co–NH2 N–Co–N′ X–Co–X

2 2.2186(5)B 2.006(1) 2.061(2) 88.66(6) 111.67(2)2.2492(6)B

3 2.3790(3)C 2.012(2) 2.057(2) 89.35(8) 112.52(1)2.3813(4)C

4 2.5736(5)D 2.003(3) 2.046(3) 89.7(1) 111.65(2)2.5666(4)D

5 2.087(1)E 2.183(1) 2.232(1) 162.77(4)F 92.83(5)G

2.061(1)E 2.227(1) 2.209(1) 96.39(4)H

6b 2.149(2)I 2.158(2) 2.171(2) 173.28(7)F 84.73(7)J

2.076(2)K 2.178(2) 2.149(2) 96.40(8)H

ANox = N-atom of the oxazoline(s); BX = Cl; CX = Br; DX = I; EX = –NCS; FNox–Co–Nox angle; GSCN–Co–NCS angle; HN′NH2–Co–NNH2 angle;

IX = –ONO2; JO–Co–O′ angle; KX = –OH2.

C12

N2 C9

C8 C10

C11C12

C7C1

N1

C4

C3 O1

C5

C6

C11

Co

Fig. 3. ORTEP representation of a molecule of complex 2.

C3C6

C4

C5Br1

Co

N2

N1

C1

C12

C7

C8

C9

C10

C11O1

Br2

Fig. 4. ORTEP representation of a molecule of complex 3.

the examples reported herein that were characterized by X-raydiffraction, the ligand is found to bind in a κ2-N,N′ bonding motifregardless of the Co metal salt. Depending on the nature of themetal counterion, one or two equivalents of 1 coordinate to themetal centre; the result is not affected by the metal-to-ligandreaction stoichiometry. The complexes have been characterized

C6

C4

C5

Co

N1

N2

C1

C3

C7

C8

C9

C10

C11

C12O1

I1

I2

Fig. 5. ORTEP representation of a molecule of complex 4.

C6

S1

C23

N5

N6

N2 C8

C9C10

C11

C12C7

C1

O1

C3

N1

C4

C24

C16

C14

C15

C13O2

C17

C22C21

C20

C19C18

N4N3

Co

C2

S2

C5

Fig. 6. ORTEP representation of a molecule of complex 5. Hydrogen atomshave been removed for clarity.

in solution by UV-visible spectroscopy and in the solid phase byelemental analysis, IR spectroscopy, and by single-crystal X-raydiffraction for five examples. Within the range of concentrationsinvestigated, cobalt compounds 2–5 and 1 have been shown tobe biologically inactive against A. niger, A. flavus, C. albicans,and S. cerevisiae.

52 F. J. Baerlocher et al.

C24

C25

C27C22

C33C32

C28

C29

C31

C30

C10

C11

C12

C13

C8

C9

C26N21

N34O39

O35

O38N36

O37

C7

C6

C5

C4O3

C2

N1

N14Co

O23

Fig. 7. ORTEP representation of the cationic component of complex 6b.Hydrogen atoms have been removed for clarity.

The ease of synthesis, air-stability, and facile complexationbehaviour of 1 make the ligand a good candidate for furtherstudies in coordination chemistry and catalysis. These areas ofinvestigation are current topics of our research endeavours.

ExperimentalGeneral ProceduresAll reactions were carried out using commercially availablereagent-grade solvents in open air. Cobalt halides and pseudo-halides were purchased commercially and used as received.Compound 1 (2-(o-anilinyl)-4,4-dimethyl-2-oxazoline) wassynthesized as previously described[36,46] and its purity deter-mined by a combination of 1H NMR spectroscopy andmp measurements.[36] NMR spectra (CDCl3 solution) wererecorded at room temperature (RT) using a Bruker Avance300 MHz NMR spectrometer operating at 300 MHz (1H). IRspectra were recorded as Nujol mulls or KBr or CsCl diskson a Perkin–Elmer 683 IR or 283B IR spectrometer. Melt-ing points were recorded in air on a Mel-Temp II apparatusand are uncorrected. Elemental analyses measurements wereperformed at the Lakehead University Centre for Analyti-cal Services (LUCAS) located in Thunder Bay, Canada, theanalytical services of the University of Windsor and the Uni-versity of Toronto Environmental Sciences Analytical Unit(ANALEST). UV-visible spectra were recorded at RT usingan LKB Biochrom Ultraspec Plus Model 4045 UV-visiblespectrophotometer from CHCl3 solutions of complexes 2, 4,and 5 and abs. EtOH solutions for compounds 3 and 6a(Table 1; [complex] in M: 2 = 1.082 × 10−3; 3 = 2.685 × 10−3;4 = 1.082 × 10−4; 5 = 6.552 × 10−4; 6a = 1.515 × 10−3). Mag-netic moment measurements were taken with a Johnson Mattheymagnetic susceptibility balance; calculations of χD for com-pound 1 are detailed in the Accessory Publication (Appendix B).Conductivity measurements were carried out using a VWRdigital conductivity meter.[81]

SynthesesCoCl2(C11H14N2O-κ2-N,N′)·1/2(H2O) 2Cobalt(ii) chloride hexahydrate (0.39 g, 1.6 mmol) was dis-

solved in abs. EtOH (25 mL). Compound 1 (0.94 g, 4.9 mmol)was added to this solution and an additional portion of EtOH(10 mL). The mixture was stirred for 3 h and the air-stablePrussian-blue precipitate thus formed was collected by fil-tration. The mother liquor was then evaporated to drynessand the solid blue residue obtained was washed with Et2O(2 × 25 mL), yielding blue-coloured 2 (0.52 g, 99%). Mp 260–266◦C (dec.) (Found: C 40.15, H 4.59, N 8.51. Calc. forC11H14N2OCl2Co·0.5(H2O): C 39.80, H 4.45, N 8.37%.)

CoBr2(C11H14N2O-κ2-N,N′) 3A sample of CoBr2·6H2O (0.39 g, 1.2 mmol) was dissolved

in abs. EtOH (25 mL). To the resulting blue-coloured solutionwas added solid 1 (0.68 g, 3.6 mmol) and an additional 10 mLof abs. EtOH. The solution was stirred for 4 h, over which timea bright blue precipitate had formed. This was collected by fil-tration, washed with EtOH (5 mL) and Et2O (2 × 15 mL) anddried in air (yield 0.32 g). The EtOH mother liquor was allowedto evaporate slowly at RT, a procedure that yielded 0.03 g ofadditional compound (total yield of 0.35 g: 97%). Repetition ofthis reaction using stoichiometric equivalent of cobalt precursor(0.62 g, 1.9 mmol) and 1 (0.36 g, 1.9 mmol) gave a 72% yield(0.56 g) of air-stable 3 following filtration of the precipitatedproduct. Mp 170◦C (dec.) (Found: C 32.30, H 3.45, N 6.85.Calc. for C11H14N2OCoBr2: C 32.14, H 3.25, N 6.05%.)

CoI2(C11H14N2O-κ2-N,N′) 4A sample of anhydrous CoI2 (2.3 g, 7.5 mmol) was added

to a solution of 1 (1.4 g, 7.4 mmol) in acetone (50 mL). Thesolution immediately turned emerald green in colour. This mix-ture was then stirred at RT for 15 min and then filtered to givea clear, emerald-green solution, which was allowed to slowlyevaporate (ambient temperature and pressure) to a volume of∼10 mL. Solid product was obtained by triturating this residuewith Et2O. The yield of this air-stable material was 2.54 g (65%).Mp 164–168◦C (dec.) (Found: C 27.82, H 3.84, N 5.68. Calc.for C11H14N2OCoI2·0.5(C3H6O): C 28.22, H 3.22, N 5.27%.)

Co(NCS-κ1-N)2(C11H14N2O-κ2-N,N′)2 5Anhydrous Co(NCS)2 (1.0 g, 5.7 mmol) was added to abs.

EtOH (60 mL) and stirred for 20 min. This resulted in the forma-tion of a deep blue solution to which solid 1 (3.3 g, 17 mmol) wasadded. Following this procedure, the mixture was stirred at RTfor 4 h. During this time period, a purple precipitate had formed,which was subsequently collected by filtration (yield: 2.82 g)and washed with EtOH (2 × 50 mL), forming a green-colouredsolution that was separated. The above isolated precipitate wasthen further washed with Et2O (2 × 50 mL), forming a blue Et2Owash. Evaporation of the green-coloured EtOH portion (Roto-vap) gave a pink-green oily solid that was heated to the boilingpoint with further EtOH (10 mL) and the less-soluble purpleprecipitate collected by filtration from the green mixture (yield:0.215 g). The blue Et2O wash was allowed to slowly evaporateat RT over several days and this yielded an additional small crop(approx. 0.05 g) of 5 in the form of dark purple crystals. Thecombined yield of air-stable purple product was 3.14 g (99%).Mp 181–185◦C (dec.) (Found: C 51.89, H 5.08, N 15.13. Calc.for C24H28N6O2S2Co: C 51.49, H 4.89, N 15.07%.)

Oxazoles XXII. The Cobalt(ii) Coordination Chemistry of 2-(ortho-Anilinyl)-4,4-dimethyl-2-oxazoline 53

Co(NO3)2(C11H14N2O)(H2O)2 6a and[Co(NO3-κ1-O)(C11H14N2O-κ2-N,N′)2(OH2)](NO3)monohydrate 6bAn abs. EtOH (40 mL) solution of [Co(OH2)6](NO3)2

(1.01 g, 3.47 mmol) was stirred at RT using a magnetic stir-bar. To this solution was added 1.98 g of 1 (10.4 mmol) as asolid and the sides of the reaction flask were washed with abs.EtOH (10 mL). The mixture was stirred for a further 3 h, dur-ing which time the solution changed colour from orange-red todeep pink. The solution was then evaporated under reduced pres-sure (rotary evaporation) and Et2O (150 mL) was added. Thisprocess resulted in the precipitation of an off-red powder of air-stable complex 6a (1.38 g: 97%) that was thereafter collected byfiltration and washed with further Et2O (2 × 20 mL). The pink-coloured Et2O washings were then allowed to slowly evaporateat RT over several days to a volume of ∼20 mL. A small amountof precipitate thus formed was also collected by filtration andfrom this mixture a single small crystal (yield: <1%) of 6b wasisolated.

Preparation of 6a. Method BA MeOH (10 mL) solution of [Co(H2O)6](NO3)2 (2.76 g,9.48 mmol) was stirred at RT using a magnetic stir-bar. To thissolution was added solid 1 (1.80 g, 9.47 mmol); the sides of thereaction flask were then washed with further MeOH (5 mL). Themixture was stirred at RT for a period of 12 h, over which timethe colour of the solution changed from red to a deep red-purple.The mixture was then filtered and evaporated at ambient pres-sure; a procedure which yielded an oil that was dark purple incolour. This material was then triturated with Et2O (3 × 50 mL)and the crude red-purple powder (3.31 g: 85%) was subsequentlyisolated by filtration. An analytical sample of this material wasobtained by redissolving the powder obtained above in boilingacetone and reprecipitating it by the addition of excess Et2O.Thisprocedure yielded the deep-red-coloured solid product. (Found:C 32.25, H 4.03, N 13.74. Calc. for C11H18N4O9Co: C 32.29,H 4.43, N 13.69%.)

X-ray CrystallographySingle crystals were coated with Paratone-N oil, mounted usinga glass fibre and frozen in the cold nitrogen stream of thegoniometer. A hemisphere of data was collected on a BrukerAXS P4/SMART 1000 diffractometer using ω and θ scans witha scan width of 0.3◦ and 10-s exposure times. The detectordistance was 5 cm. The data were reduced (SAINT )[82] and cor-rected for absorption (SADABS).[83] The structure was solvedby direct methods and refined by full-matrix least-squares on F2

(SHELXTL).[84] All non-hydrogen atoms were refined anisotrop-ically. Hydrogen atoms were found in Fourier difference mapsand refined isotropically.[82–87] Figs 3–7 were drawn usingORTEP-III for Windows.[88]

Biological TestingCompounds 1–5 were tested for antifungal activity against purecultures of A. niger, A. flavus, C. albicans, and S. cerevisiaesupplied by Ward’s Natural Science Ltd (St Catharines, ON).All cultures were maintained on Sabouraud dextrose agar. For A.niger or A. flavus, six agar plugs (10 mm diameter) of A. niger orA. flavus were cut from a 5–8-day-old colony and homogenizedin distilled, sterilized water (3 mL). From this suspension, 0.5 mLwas transferred aseptically to a Petri plate with Sabouraud dex-trose agar (25 mL) and spread evenly over the entire surface. In

the case of C. albicans or S. cerevisiae, a 0.5-mL sample of a21-day-old liquid culture medium of C. albicans or S. cerevisiaewas transferred, spread aseptically and allowed to dry. Each platewas provided with four evenly spaced paper disks (6 mm Fisher-brand P8 filter paper) containing the compound (200 µg) to betested. Each compound was applied to the disks as a solution(5 mg compound per 0.5 mL of acetone) whereas the controldisks were treated with neat acetone (20 µL). Amphotericin B(AmB: dissolved in acetone) acted as a standard (100 µg). Testplates with fungal homogenates were incubated at 20◦C for 48 h.Four replicate plates were used for each test. Antifungal activ-ity was measured as the diameter of the clear zone surroundingthe disk.[89] Results of these investigations can be found in theAccessory Publication.

CalculationsCalculations at the PM3(tm) level of theory[55,90] were carriedout using Spartan 8.0[91] (also see Accessory Publication).

Accessory Publication

The Accessory Publication contains details of the biologi-cal screening data, calculations of diamagnetic corrections,PM3(tm) energy calculations for the isomers of compound 5and the cif files of the crystallographic characterizations reportedherein. The Accessory Publication is available on the Journal’swebsite.

AcknowledgementsThe authors are indebted for the support of Ryerson University, Acadia Uni-versity and the Natural Sciences and Engineering Research Council (NSERCCanada). Mr. K. E. Kershaw and Mr. M. J. Hughes (Acadia University) arethanked for their syntheses of samples of 1 that were used in this study. DrJenny Field (Cambridge Crystallographic Data Centre) is also thanked forher contributions to this research. R.A.G. is further indebted to the RoyalSociety of Chemistry for provision of a J. W. T. Jones Travelling Fellow-ship that allowed the author to complete sections of this manuscript duringsabbatical leave at the University of Tasmania.

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