Indian Journal of Chemistry Vol. 41 A, February 2002, pp. 284-289

Synthesis, characterization and structure of Ti(IV) complexes of hydroxy-rich ligands

P Venkateshwara Rao, Erkki Kolehmainent & Chebrolu P Rao*

Bioinorganic Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India Fax: (+9 1-22) 572-3480: E-mail: cprao@chem.iitb.ac.in

Received 4 July 2001,' revised 27 September 2001

Coordination chemistry of two multi-hydroxy rich ligands has been explored with Ti(IV) by isolating the resultant products followed by their characterization. One of the products is also structurally characteri zed by single crystal XRD.

For quite sometime our group was involved in understanding the coordination behaviour of hydroxy­containing molecules towards transition metal ions in the context of the involvement of such groups at the coordination centres in metalloproteins of vanadium l

and molybdenum2• In the process, we have been able

to develop the coordination chemistry of such molecules towards oxo-metal centres3

.4, such as, V02+, V03+, cis-V02+, cis-MoO/+ and trans-UO/+. Recently we have also reported the coordination behaviour of some of these molecules towards Ti(IV) centre5 where our studies included the molecules based on naphthalidene moiety. In continuation with our work regarding the coordination aspects of titanium towards multi-hydroxy molecules, herein we report the results of the reactions of two such molecules with cis-Ti(acachCI2• Therefore, this paper deals with the isolation, characterization and single crystal XRD studies of the reaction products.

Materials and Methods 11-1 and 13C NMR spectra were recorded on Avance

DRX500 working at 500/126Ml-lz for 1H/13C nuclei. The FTIR spectra were recorded in KBr matrix on a Nicolet impact 400 instrument. The FAB mass spectra were recorded on a JEOL SX 102/DA-6000 Mass Spectrometer/Data System · using Argon/Xenon (6kV, IOmA) as the FAB gas. The accelerating voltage was IOkV and the spectra were recorded at room temperature and matrix used was m-nitrobenzyl alcohol (NBA). Ligand labelling and the structures of

+Department of Chemistry, University of Jyvaskyla, Jyvaskyla, Fin 40351 , Finland.

those used in this study are shown in Fig 1. All the operations were carried out under nitrogen/argon atmosphere using standard Schlenk apparatus unless otherwise mentioned. All the solvents were dried and distilled using standard procedures immediately before use. H2Ll, H4L2 and cis-Ti(acachCb, 1 were synthesized and recrystallized before use, as reported earl ier6.3d.

O:::r! &c~:" H3C CH3 ('--

OH

(a) (b)

Fig. l--Schematic representation of the ligands used, [(a) H2LI ; (b) H4L2l

[Ti( sa/amp hi, 2 A solution of 1 (0.158 g, 0.5 mmol) in 15 ml of

CH3CN was added drop wise to a solution of H2L I (0.193 g, 1 mmol) and sodium acetate (0.082 g, 1 mmol) in 15 ml CH3CN under N2 atmosphere. The resulting orange suspension was stirred at room temperature for 6h. The reaction mixture was then cooled to room temperature and filtered through celite. The filterate was evaporated to dryness and the residue was recrystallized from CH3CN by adding hexane to yield yellow coloured single crystals of X­ray quality. Yield (0.283 g) 66%. FrlR (cm· I

): 2969 (VC-H); 1064 (vc-a); 1617 (VC=N). IH NMR (CDCl3, ppm): 8.49 (s, 2H, HC=N) ; 7.45 (dd, 2H, Ar-H); 7.37 (dt, 2H, Ar-H); 6.83 (dt, 2H, Ar-H); 6.71 (d, 2H, Ar­H); 4.34 (d, 2H, CH20 , j=9.2 Hz) ; 4.07 (d, 21-1,

VENKATESHWARA RAO el al.: Ti(IV) COMPLEXES OF HYDROXY -RICH LIGANDS 285

CH20 , J=9 .2 Hz); 1.53 (s, 6H, CH3); 1.48 (s, 6H, CH3) . I3C NMR (COCb, ppm): 163.9 (HC=N); aromatic carbon resonances are: 160.9, 135.0, 133.5, 121.5, 118.1, 117.9; 81.8 (CH 20); 72.1 (C-tert); 27.4 (CH3); 23.6 (CH3) . FAB Mass, mle: 431 (M+Ht (100%).

[Ti( H2naptrishl. 3 To CH3CN (l5 mL) solution, H4Lz (0.275 g,

1 mmol) and sodium acetate (0.082 g, 1 mmol) were added and stirred at room temperature under N2 atmosphere. A solution of cis-TiCI2(acach in CH3CN (10 mL) was added drop wise, yellow solid was formed which was stirred for 6 h at r.t. The reaction mixture was filtered and the precipitate obtained was washed with pet. ether and dried in vacuo. The residue was extracted into OMSO. filtered and to the filtrate, ethanol was layered . Yellow microcrystalline solid was isolated, and thi s was washed with pet. ether and dried. Yield (0.282 g) 57%. FTIR (cm· I

) : 3325

(VOH); 2969 (VC.H); 1049 (vc-o); 1600 (VC=N). 'H NMR (COCl3, ppm): 9.58 (s, 2H, HC=N) ; 8.29 (d, 2H, Ar­H) ; 7.96 (d, 2H, Ar-H) ; 7.86 (d, 2H, Ar-H); 7.64 (t,

Table I-Summary of crystallographic data for 2

2

Mol. formulae C20H'1004N2 Ti

Formu la wI. 420.43

TemperalUre 293(2)

Crysl. Sysl Orthorhombic

Space group P2 12 12 1

Cell conSlants

alAo 10.2 14(2)

b/Ao 12. 11 3(2)

ciAo 17.046(5)

~/deg

V/A o) 2109. 1 (8)

Z 4

Dc/gc m') 1.727

F(OOO) 11 68

Tol. rencs 2209

Uniq ue rencs 2 123

Param 266

Final R 0.0506

Rw" 0.1216

Rw=ILw(IFol-IFiILwIFil"2 w=I/(j~ + 1.00,

where a Chebychev weighting scheme was employed.

2H, Ar-H); 7.39 (t, 2H, Ar-H); 6.84 (d, 2H, Ar-H) ; 5.15 (t, 2H, CH20H); 5.07 (t, 2H, CH20H); 4.39 (d, 2H, CH20, 1=9.6 Hz); 4.19 (d, 2H, CH20, 1=9.6 Hz); 4.06-4.03 (m, 2H, CH20H) ; 3.87-3.82 (m, 4H, CH20H) ; 3.70-3.67 (m, 2H, CH20H). I3C NMR (COCI3, ppm): 164.0 (HC=N); naphthyl carbon resonances are: 158.6, 135.7. 133.5, 128.9, 127.9, 127.0,122.9,120.8,119.9, IlLS ; 79.2 (CH20 ); 74.5 (C-tert); 62.0, (CH20H); 60.9 (CH20H). FAB Mass, mle: 495 (M+Ht(lOO%).

X-ray crystallography

The diffraction data for 2 were collected on an Enraf Nonius CAO-4 diffractometer in the w-28 scan mode using Mo Ka radiation. The structure was solved using SHELXS867 and the model was refined using SHELXL938 program packages. The diagrams were generated using ORTEP-3 and PLATON-98 program9

. The hydrogen atoms were fixed through SHELXL program. Empirical absorption corrections were carried out. Full matrix least-squares refinement with anisotropic thermal parameters for all non­hydrogen atoms was used. The hydrogen atoms were treated as riding atoms with fixed thermal parameters. Other detai ls of data collection and structure refinement are provided in Table I . Atomic coordi­nates and isotropic temperature parameters for all non-hydrogen atoms are given in Table 2.

Results and discussion

Ligands, HzLI and H4Lz were reacted with 1 in 2: I mole ratio in CH3CN to result in the homoleptic complexes of titanium, 2 and 3 respectively, by replacing both the chloro- and acac- groups from 1 completely as shown in Scheme 1. Earlier we have demonstrated the reactions of cis- TiCl2(acach with ligands having one -CH20H which resulted in the formation of mono nuclear mixed ligand as well as homoleptic complexes.s But these ligands were based on naphthalidene moiety. Even the ligand ~Lz hav ing three -CH20H and one Ph-OH groups resulted in the formation of only mono nuclear complex, rather than forming any higher nuclear ones. Such ligands have indeed exhibited dinuclear complexes with V03+ and trans-UO}+ cores3aAa

. The molecular weights of both the titanium complexes. 2 and 3 agrees well with the structures shown in Scheme 1 as obtained from the molecular ion peaks in the corresponding FAB mass spectra, and the crystal structure of 2 further confirms the structure.

286 INDlAN J CHEM, SEC. A, FEBRUARY 2002

Table 2- Atomic coordinates (x 10"4) and equivalent isotropic displacement parameters (A"2 x 10"3) for 2 U(eq) is defined

as one third of the trace of the orthogonalized Uij tensor

Ti ( l)

0(1)

0(2)

0(3)

0(4)

N(I)

N(2)

C(I)

C(2)

C(3)

C(4)

C(5)

C(6)

C(7)

C(8)

C(9)

C( IO)

C(II)

C( 12)

C(l3)

C(14)

C(l5)

C(16)

C(17)

C(18)

C(19)

C(20)

C(21)

C(22)

x

1488(1 )

2151(4)

662(4)

3123(4)

242(4)

148(4)

2282(5)

1578(6)

2170(7)

1587(8)

403(7)

-167(7)

399(6)

-212(6)

-492(6)

-549(7)

453(7)

-1843(6)

4015(5)

4864(6)

5774(7)

5918(7)

5095(6)

4147(6)

3295(6)

1474(6)

122(6)

1997(6)

1470(8)

y

6944(1)

5638(3)

7733(3)

7063(3)

7192(4)

5746(4)

8350(4)

4762(5)

4197(5)

3289(6)

2900(5)

3421(5)

436 1 (5)

4829(4)

6144(5)

7387(5)

5858(6)

5682(5)

7822(5 )

7721 (6)

8515(7)

9428(7)

9531 (6)

8749(5)

8901(4)

8603(5)

8235(5)

7900(7)

9833(5)

z

1328(1 )

824(2)

2 122(3)

1866(2)

564(2)

1835(3)

675(3)

527(3)

-96(4)

-412(4)

-135(4)

494(4)

831(3)

1520(3)

2562(3)

2423(3)

3228(4)

2732(4)

1999(3)

2637(4)

2784(4)

2301(5)

1659(4)

1504(3)

839(3)

-38(3)

195(4)

-706(3)

-268(4)

Molecular and crystal structure of2 ,

U(eq)

36(1 )

44(1)

49(1 )

49(1)

46(1)

33(1)

33( I)

40(1)

52(2)

60(2)

55(2)

53(2)

37( I)

37(1)

39(2)

44(2)

58(2)

55(2)

36(1)

51(2)

66(2)

74(2)

56(2)

38(1)

35(1)

42(1)

42(2)

59(2)

62(2)

Molecule 2 is a neutral, homoleptic and octahedral complex of titanium(IV) possessing two tridentate ligands of LI, Each ligand of LI is bound to the metal centre through an oxygen atom of alkoxo and phenoxo groups and also through an imine nitrogen to result In one five-membered and another six­membered chelate as seen in Fig. 2. The ligands are bound to the titanium centre in a meridional fashion as can be seen from the stereoview of 2 given in Fig. 3. Metric parameters of the coordination sphere around titanium centre is shown in Table 3. The data IS indicative of the distortion in the octahedral geometry. The trans- angles in 2 are in the range from 155.2 to 162.6° and hence exhibits a large distortion. The 5-membered chelate bite angles in 2 are in the

2 3

(a) HzLI, CH}COONa. CH}CN, ReOux. 4h; (b) H4L2, CH}COONa, CH}CN. 11, 6h

Scheme 1

15

Fig. 2-Molecular structure of 2, showing 40% probability ellipsoids using ORTEP

Fig. 3--Seteroview for structure 2

VENKATESHWARA RAO el al.: Ti(lV) COMPLEXES OF HYDROXY-R ICH LIGANDS 287

range 76.6 to 82.2°. Selected bond lengths and bond angles of the ligand portion in the structure are shown in Table 4. No abnormalities were found with this bond length data in the structure.

FTIR studies FTIR spectra of 2 and 3 were compared with the

spectra of the corresponding precursor ligands. Complex 2, did not exhibit any peaks in the VOH

OH OH

a (

region as both the hydroxy Is are involved in binding via deprotonation. However, in the VOH region, 3 exhibits a broad band with high frequency shoulder corresponding to the two free hydroxyl groups present in 3. The binding of the imine function through nitrogen has been revealed from the low frequency shift of 15 and 18 cm-' observed with the VeN peaks in the complexes 2 and 3 respectively .

d r-. a N ..... ~ d c2)-o-, " OHb %b

X r-t

bb cc

v

(A) .'--T- '--- 1 - I ='=

V

~

(B) ~ .- -10-0 8-0 6-0 4-0 2-0 0'0

Fig. 4-{A) Proton NMR spectra of 3, recorded in DMSO [d61 (500 MHz). (8) D20 exchange of 3. Peaks marked with 'X' in (A) were exchanged upon D20 addition.

288 INDIAN J CHEM, SEC. A, FEBRUARY 2002

Tab le 3- Bond lengths (A) and bond angles (deg) connecting the ti tanium centre in the complex, 2

T i( I )-O( I ) 1.923(4) Ti( I )-N( I ) 2. 174(4)

T i( I )-0(2) 1.859( 4) Ti ( I )-N( I ) 2. 191 (5)

Ti( I )-0(3) 1.9 11 (4) Ti ( I )-O(4) 1.846(4)

O( I )-Ti( I )-0 (2) 155.2(2) 0 (2)-Ti ( I )-N(2) 98.0(2)

O( I )-Ti( I )-0 (3) 88.2(2) 0 (3)-Ti ( I )-0 (4) 158.3(2)

O( I )-T i( I )-0(4) 93.5(2) 0 (3)-Ti ( I )-N( I ) 11 4.2(2)

O( I )-Ti ( I )-N( I ) 81.4(2) O(3)-Ti ( I )-N(2) 82. 1(2)

O( I )-Ti( I )-N(2) 106.4(2) 0 (4)-Ti ( I )-N( I ) 87.4(2)

0(2)-Ti ( I )-0(3) 90.5(2) O(4)-Ti ( I )-N(2) 76.7(2)

O(2)-Ti ( I )-0 (4) 96.7(2) N( I )-Ti ( I )-N(2) 162.6(2)

O(2)-Ti ( I )-N( I ) 76.6(2)

I H NMR studies Proton NMR spectra of complexes 2 and 3 showed

di sappearance of signals corresponding to phenolic proton, and an alkoxo-OH proton (in case of 3 only one of the alkoxo proton) and further showed a downfield shift of imine proton in the range of 0.48 to 0.69 ppm respectively upon coordination.

In case of 2, the protons of bound CH20-appears as 'AB ' type quartet where the individual doublets are centered around 4.34 and 4.07 ppm and the methyl protons of L I appeared as two singlets at 1.33 and 1.48 ppm. In complex 3, the bound CH20-appears as 'AB ' type quartet, where individual doublets are centered around 4.39 and 4.19 ppm. The two free CH20H groups (non-coordinated ones) appeared as two sets of multiplets due to the neighbouring hydroxyl groups as shown in Fig. 4a. The free hydroxyl protons (CH20H) also appeared as two sets of triplets at 5 . 15 and 5.07. Upon D20 exchange, the two hydroxyl peaks disappeared and free CH20H peaks appeared as two sets of doublet of doublets as shown in Fig. 4b. Both the FTIR and IH NMR studies clearly indicated that there are two unbound CH20H groups in 3 and further the bound ligand H2L 2 acts as di -anionic through deprotonation of the phenolic-OH and one of the -CH20H groups and thereby binds as tridentate including Imme nitrogen.The results obtained from FTIR, IH NMR and FAB mass in case of 2 and 3, and the crystal structure obtained in case of 2, have clearly supported the structures of 2 and 3 as shown in Scheme 1. In the crystal structure determined for 2, the ligand was based on the salicylidene moiety . While our earlier work demonstrated the formation of mono nuclear complexes with hydroxy rich ligands, the present

Table 4--Selected bond lenglhs and bond ang les or the ligand port ion in the structure 2

C(7)-N( I ) 1.287(7) C( I )-O( I ) 1.313(7)

C( 18)-N(2) 1.262(7) C(9)-0(2) 1.403(7)

N(J )-C(8) 1.487(7) C( 12)-0(3) 1.314(7)

N(2)-C( 19) 1.500(7) C(20)-0 (4) 1.4 16(7)

C(7)-N( I ) 1.287(7) C( I )-O( I ) 1.313(7)

C(6)-C(7)-N( I ) 123.6(5) C( 17)-C( 18)-N(2) 126.9(5)

C(7)-N( I )-C(8) 120.3(5) C( 18)-N(2)-C( 19) 121.5(5)

N( I )-C(8)-C(9) 102. 1 (5) N(2)-C( I tJ)-C(20) 103.4(5)

work al so revealed similar mono nuclear T iOV ) core. inspite of the fact that there were additional -CH20H groups available for binding. However, the coordinat ion behaviour observed with the mono-ox a and di-oxo metal ion species was different and the core structures lead to the dinuclear ones in case of V03+ and trans-U02

2+ when the ligands possess more

than one -CH20H groups. On the other hand, cis­V02+ and cis-MoO/+ showed only mono-nuclear structures immaterial of whether the ligand possess one -CH20H or more groups.

Acknowledgement CPR acknowledges the financial support from the

Board of Research in Nuclear Sciences of Department of Atomic Energy, the CSIR, and the DST, New Delhi. CPR is grateful to DST fo r the National Facility on Single Crystal XRD at lIT, Bombay . We thank RSIC, CDRI Lucknow for mass spectral measurements.

References I (a) Viller, H, Metal ions in biological systems, edited by H

Sigel & A Sigel (Marcel Dekker, Inc. USA), 31 (1995) 325. (b) Kusthart U, Hedman B, Hodgson K 0, Hahn R & Vilter H, FEBS Letls 329 (1993) 5. (c) Arber J M , de Boer E, Garner C 0 , Hasnain S S & Wever R, Biochemistry, 28 (1989) 7968.

2 (a) Hille R, Chem Rev, 96 (1996) 2757. (b) Geroge G. M , Hilton J & Rajagopalan K V, JAm chem Soc, 11 8 (1996) 1113. .

3 (a) Asgedom G, Sreedhara A, Kivikoski J, Valkonen J, Kolehmainen E & Rao C P, lnorg Chem, 35 (1996) 5674. (c) Asgedom G, Sreedhara A, Kivikoski 1, Kolehmainen E & Rao C P, J Chem Soc, Dalton Trans, (1996) 93. (d) Asgedom G, Sreedhara A, Kivikoski 1, Valkonen 1 & Rao C P, J chem Soc, Dalton Trans, (1995) 2459. (e) Asgedom G, Sreedhara A & Rao C P, Polyhedron , 14 (1995) 1873. (e) Asgedom G, Sreedhara A , Ki vikoski J & Rao C P, Polyhedron. 16 (1997) 643.

4 (a) Rao C p, Sreedhara A, Rao P V, Vcrghese B M . Rissanen K, Kolehmainen E, Lokanath N K, Sridhar M A & Prasad J

VEN KATESHWARA RAO et al.: Ti(IV ) COMPLEXES OF HYDROXY- RI CH LI GANDS 289

S. J chelll Soc. Daltoll Trails. ( 1998) 2383. (b) Rao C P, Si'ccdhara A. Rao P V, Lokanath N K, Sridhar M A & Prasad J S, Polyhedroll , 18 ( 1998) 289.

5 Rao P V, Rao C P, Wegilus E K, Kolehmainen E & Ri ssanen K, J chelll Soc, Daltoll Trail s, ( 1999) 4469.

6 Wilkic C A, Lin G & Haworth T 0 , Illorg SYllth , 19 (1979) 146.

7 Program for Crystal Structure solution. Sheldrick G. M., InstitUt fUr Anorganische Chemie der Univers itti t, Tamlllanstrasse 4. 0 -3400 Gbtlingen, Gcrmany, 1986.

8 Program for Crystal Structurc Refinement. Sheldrick G.M .. InstitUt fUr Anorganischc Chemie der Uni versittit. Tammanstrasse 4, 0 -3400 Gbtlingen, Germany , 1993.

9 (a) ORTEP-III -B urnett M N & Johnson C K, Report ORNL-6895. Oak Ridge National Laboratory (Oak Ridge. Tennessee) 1996. (b) Spek A L, Acta Crystallogr A. 46. ( 1990) C34. (c) Spek A L, PLATON , A MUltipurpose Crystallographic Tool (U trecht Un ivers ity, Utrecht. The Netherlands) 1998.