Indian Journal or Chemi slry Vol. 44A. Deecmher 2005. pp. 2439-2444

Synthesis and characterisation of heterobimetallic N-substituted diethanolaminate-alkoxides of niobium(V) t

Rajendra S Ghadwal & Anirudh Singh *

Deranmelll or Chemislry. Uni ve rsil Y or Rajaslhan . Jaipur 302 004. India Email: anirudhsinghu ni vjpr@yahoo .eo.in

Receil'ed J Mav 2005; accepled 25 OClOber 2005

Helerohimelalli c IV-Subsliluled die lh :lI1olaminale-alkoxide co mplexes or nJobium(V) or the lype: Nh(RDE A)d M(OR I) ". I} (where RDEA == RN(C H2C H10 'h and R == Ph (2), Me(3 ) or Bu (4) (M == AI. n == 3. RI == PI) : Ph( M == Ga. n == 3. R I = Pr)(S): Ph(M == Sb. n == 3. R I == Plj

)(6): Ph(M == Ti. n == 4. R I == Pi')(7): Ph(M == Ge, n == 4. R I == EL)(8): Ph(M == Zr. n == ~ . R: = PIJ ;(9): Ph(M == Ta. n == 5. R' == Pt))( IO)) have heen prepared by the equimolar reacli ons of homolepl ic N-s uhslilu ted dielhano iaillinale complexes (ie .. mewllo li gands) or the formu lali on: Nb(RD EA h( RD EA H)( R == Ph ( Ia ): Me ( I b): Bu ( I e)l \\ ilh di lTereIl l meta l alkoxides. All of lhese he lerohimelallic co mplexes have heen characlcri ~ed hy analYlical. molecul ar weight. and <; peclra l (JR. IH and 27 AI NMR ) dala. On thc basis or lhese resulls. plausible stru clures for the new complexes have heen <; uggesled . The .,ynlhesi s and ci1aracteri sali on or a ncw series o r heterohimelallic co mp lexcs reponcd in lhi s paper greatl y expand, the horizon or hetcromelal alkoxlde chemislry. Funhcrmorc. these fascinaling compounds have Oh viOUS Imporlance' .IS precurso rs In ceramics.

IPC Code: InL CLc

C07F9/00

During the last fe w years, we have been involved in exploring the chemistry of novel heterometalli c alkoxide coordination systems derived from poiyalcohols such as glycols l

, di- and tri-ethanoia mines ~l . React ions in differen t molar ratios of niobium and tantal um aikoxides with dicthanoiamine have bee n investi ga ted.) earl ier to isolate der i va Ii ves of the types Nb(DEA)(ORh

b(DEA)c(OR ) and Nb(DEA)z(DEAH). But. complexes of the type Nb(RDEAH RDEAH) have not been used as ligands"() for the synthesis of novel heterometall ic compounds. Recentl y. an interesting heterobimeta!lic diethanoiaminate deri vative Zr{rr' , ~~-NH(C2 I-LO)2b­lTi(OPI\ d2 with nona-coordina te zirconium has been prepared and cha rac ter ized by X-ray crystall ograph/ . Furthermore. the poly hydroxy alcohols react with metal alkox ides to prod uce derivatives \.,r ith structural diversity and modified chemical reac ti vitl , lO towards protic reagents including water. The modified metal al koxide deri va ti ves are potential precursors II fo r the prepa ration of oxide ceramic materi als via sol-gel process.

' Dedicated lO our menlor Emcrilus Professor R C Mchrolra. lhe emi nen l Inorganic chemisl and renowned cducalionist. who Icft us fo r hi s hcavcnl y ahode on I I July 2004. We always remember him.

Keepi ng tha t In vIew. the synthesis and characterisat ion of novel heterobimetalli c coordin at ion complexes containing both the diethanolaminare and alkoxide group are reported here.

Materials and Methods All reactions and manipulations we re perrormed

under anhydrous conditions us ing oven-dried gl assware fitted with interchangeable quickfit jo ints. Analytical grade (BDH or Merck. India) soivents Ivere made anhydrous by known methods 12.13 N- Phenyldiethanolamine, PhDEAH2 (Aldri ch. 160.2°CII .0 mm); N- methyldiethanolami ne. MeDEAH, (Aldrich, I 46.3°Cl0.3 mm ); and N-butyldiethanolamine, BuDEAH2 (Merck. l20.0°CIl.S mm) were dried by re flu xing over AI(OPrih followed by di stillati on under red uced pressure prior to use.

N· b' !4 I .. 15 II ' 16 . 6 j 10 tum . a umlnlum , ga lum , ant imony.

. . 17 . 18· . 19 d 1 "0 ti talllum , germanium , Zirconium , an tanta um-alkox ides were prepared by the known methods. Amounts of Nb. Ga, Ti, Ge. Zr, and Ta in the complexes were determined as their ox ides21 . Aluminium was estimated grav imetricall y as oxinate21 . Nitrogen was determined by the Kj eldahl' s

2440 INDIAN J CHEM , SEC A. DECEMBER 2005

method 21. Isopropyl alcohol in the azeotrope was

determined by ox idimetric method 22.

IR spectra (4000-400 cnf') were recorded as Nujol mull s or KBr pell ets on a Nicolet Magna 550 spectrophotometer. 'H and 27 AI M R spectra were recorded on a JEOL AUOO FTNMR spectrometer. Carbon. hydroge n. and nitrogen were determined on a Perkin-Elmer CH S/O 2400 analyser. The molec ul ar we ights were determined by freezing point depress ion method in benzene solutions.

Synthesis of homomclaIIic precursor complexes ( I a)-( I c)

Si mil ar procedure was empl oyed for the prepa rati on of homometa II ic comp lexes (1a)-(1 c). However. detail s onl y for a typical complex (1a ) are desc ribed.

Nb(PhDEA )lPhDEA H) (/a)

After addition of N-phenyldiethanolamine, PhD EA H2 (5.12 g, 28 . 15 mmol ) to Nb(OPri)s (3.65 g, 9.40 mmol) in benzene (- 40 mL), the res ulting li ght ye ll ow solution was reflu xed under a fractionating column with continuous removal of the liberated isopropy l alcohol (2.83 g) as an azeot rope with benzene. When the liberation of isopropyl alcohol ceased. re flu xing was stopped and reaction mixture was a Il owed to cool to room temperatu re. Removal of vo la til e co mponents from the solution under reduced ( 10 mm Hg) pressure gave ye ll ow so lid. whi ch was recrys talli sed from 1:3 mi xture of dichl oromethane and II -hexane at _20DC to yie ld ana lyti ca lly pure complex (la) as a ye ll ow so lid. Yi eld: 3.29 g (55%), m.p . I 72 DC. Anal. Cal cd. for CJo H.)1) JOc,Nb(631): C, 57.05: H. 6.38: N. 6.65 ; Nb, 14.7 1 %. Found : C. 56.8 I: H. 6.44; . 6.49; Nb, 14.66%. Mol. WI. , 662. I R (N uj o l. cm' 'l: 33 10 v(O- H); 139 I, 1366, 1240, 11 99 v(C- N) ; 1099. 1040, 1016 v(C-O); 766,7 16, 683 v(CrH ,); 583 v(Nb- O); 450 v( b(-N) . I H NM R (C DCI ,, : 8. ppm): 3.54-3.71 (m, 12H, NCH2); 3.88-4. 24 (m. 13H. CH20 + CH20 H); 6.45- 7.37 (m. ISH. aromat ic-H).

Comp lexes (1 b) and (J c) were prepared by the procedure similar to that used for (1a ). Spectroscopic data for (1 b) and (1 c) are:

l\'b(MeDEA)lMeDEAH) ( Ib)

Colourl ess sti cky so lid . Anal. Ca lcd. for CI5H1.) NJOc, Nb(445): C. 40.45 ; H. 7.70; N, 9.43; Nb. 20.86%. Found: C. 40.39; H, 7.7 1; . 9.28 ; Nb. 20.8W~ . Mol. WI.. 453. fR : 3285 v(O- H): 1249, I 188 v(C-N): 1088 . 1066. 1033 v(C-O); 583 v(Nb-O) ;

450 v(Nb(-N). 'H NMR: 2.39(s. 3H. Me); 2.68(s. 6H, NMe); 3.00(m, 12H, NCH2); 3.68(br. 3H. CH:cO + OH); 4.42(m, IOH, CH20 ).

Nb(BIIDEA)lBIIDJ:'A II) ( I e)

Cream sticky solid . Ana l. Calcd . for C2.)H'2N,0 (,N b (57 I): C, 50.43 ; H. 9.17 ; N. 7.35; Nb. J().25 %. Found : C. 50.45 ; H, 9.09; . 7.16; Nb. I 6. 17(Jr . Mo l. WI.. 602. IR : 3300 v(O- H); 1241. 11 89 v(C- N): 1090. 1043. 1020 v(C - 0 ); 578 v(Nb- O): 4('() v(Nb(-N). I H NMR: 0.93(t. J = 7.32 Hz, 3H. N(C H2HVJc ): 0.97(t. J =7. 14 Hz, 6H. (CH2)J Mc); 1. 27- 1.56(m. 12 H. NCH2(C H2h Me) : 2.65(m. 6H. NCH2(CH 2):cMe): 2.78(m, 12H, NCH 2) ; 3.4I(br, IH, CH20H ); 3.7 1-4.35(m. I 2H. CH 20 ).

SYllthesis of Nb (M eD t.'A)lOPri) ( Id)

A colourless benzene solution (-30 IllL) containing Nb(OPri)s (0.93 g. 2.39 mmol ) and N-methy ldi ethan olami ne. MeDEAH: (0.57 g. 4.78 mmol) was re flu xed with continuou remova l of the liberated isopropyl alcoho l as an azeotrope. After - 4 h. when required amount (0. 57 g) of isopropyl al cohol was di stilled out. re flu xing was stopped and reacti on mi xture was a ll owed to cool to 1'00111 temperature. Volatiles were removed under redu ced pressure to obta in white sticky soli d, whic h on rec rystal li ati on from to luene at _20DC afforded white st icky so lid (l ei )

in 76% (0.70 g) yield . Anal. Calcd . for C 13H2<J :cO:\Nb (386); C, 40.42 ; H. 7.57; N. 7.25; b. 24.05 %. Found : C. 40.31; H, 7.39; N. 7.17; Nb. 23 .76'Yc,. Mol. Wl.. 392. IH NMR: 1.20 (d, J = 6.58 Hz, 6H. OCHMc2) ; 2.68 (s. 6H. NMc); 3.02 (m. 8H. CI-U; 4.40 (m. 8H. CH20 ); 4.78 (m, J = 6.58 Hz, IH. OCHMe2).

Complex (1b) has al so been synthes ized by the equimo lar reac ti on of (JeI ) with MC' DEAH2 under re fluxin g conditions in benze ne.

Sy nthesis of hcterobimctaIIic wmplcxcs (2)-( I 0) fNb(PflD/~'A!.dA I(OP/!:JJ (2)

To a ye ll ow so lution of (1a ) ( 1.44 g. 2.28 mlllol) in benzene (-30 IllL) was added AI(OPr\ , (0.46 g. 2.25 mlllol ) and the res ul ting soluti on wa~ reflu xed with conti nuous relllova l of the liberated isopropyl alcohol. which was esti mated peri odical I y to III 0 II i tor progress and completi on of the reac tion. After 2 h. 'vvhen required amount (0. 13 g) of isopropyl alcohol was di stilled out. reflu xing was stopped and reac ti on mi xture was a ll owed to coo l to room temperature. Removal of vo latiles from the solution under reduced press ure afforded li ght ye ll ow solid. Rec rysta lli sa ti on at-20DC from a 1:2 mixture of dichl ol"Omethane and

GHADWA L & SINGH HET EROBIM ETALLIC A LKOX IDES OF NIOBI UM ( V ) 24-1-1

Table I - Preparali ve and analyli cal dala for hClerobimctallic complexes (2)-( 10)

Producl Yield

Reaclants (empcri ca l formula)

g(%)

(g. 11111101) M .Pl. co lour and Slale (OC)

Nb(Ph DEA),-( Ia ) A I(OPr'), {A I(OPr'J, 1(2) 1.2 1 (68) ( 144.2.2X) (046.225) (C,.H" A IN,NhO, ) (200)

Ydlow solid Nb(McDEAh-

( Ib) A I(OPr'); {A I(OPr'J, 1(3) 446 (96)

n49.7R3) ( 1.60. 7 . 8~) (C" H" A IN,NbO,) Colourless sli cky solid

Nb(l3uDEA),-(l c) A I(OPr'), {A I(O Pr'h l( -t )

1.08 (99) (0 87. 1.52) (03 1. 152) (C,oH",AIN,NbO )

Colourless slicky solid Nb(Ph DEA»)-

(l a ) Ga(OPr'), {Ga(OPr'), I (5) 1.2-t (73) (UI. 2(7) (05 1.206) (C",Hs,Ga 1NbO, ) ( 194)

Wh ile so lid Nb( Ph DEA), -

(l a ) 5b(OPr'), {5b(OPr'), }(6) 2.11 (73) (20').3.31 ) (099.D I ) (C,,, I-I 5J 1NbO.Sb) ( 140)

Ye llow so lid Nb( PhDEA ),-

(l a ) Ti(OPr'), {Ti(Ol'r'h }(7) ~09 (75) (3.04.48 1 ) ( 1.37.482) (C]"H""N]NbO"Ti ) ( 13'»

Ye llow so lid Nh(PhDEAlJ-

( I n ) Gc(OEl), {Ge(OPr')11(S) 235 (')9)

( I n.2X I ) (O.7 1.2XO) (C](, Hs,GeN,NbO,,) Ye llow , li cky solid

Zr(OPr'k Nb(PhDEAlJ-

(l a ) Pr'OH ( 1.03.

{Zr(OPr'h }(9) 1.6 1 (67) ( 1.(,S.267)

2.(,6) (C,»H""N, bO.Zr) (222) Yel low so lid

Nb(PhDEAh-(I n ) Ta(OPr'), {Ta(O l'r'), }( IO ) O.X7 (52) ( 1.00. 1.58) (075 . 1.57) (Cd~ "7N , hO",Ta) ( 182)

Yellow so lid

II-hexa ne afforded analyti call y pure compl ex (2) as a light ye ll ow solid . Yield: 1.2 1 g (68%). Analytical detail s are given in Tabl e I.

The procedure similar to (2) was used for the preparation of complexes (3}-{ lO). Preparative and analytical detail s are summari sed in Table 1.

Results and Discussion Reac ti ons of Nb(OPr')s with N-s ubstituted

di ethanolamines III 1: 3 molar rati o homometa II ic prec ursor complexes metall oli ga nds) (1a )-(1c), Eq. (1):

CGH6

i\b(OPr'), + :l RDEA H2 refl ux, - 4 h

Nb(RDEPd2(R DEAH) + - Pr'OH

afford (i.e.,

... 0 }

Li beraled Analys is (%) Found Mol. \Vl.

Pr'OH (Ca led.) (g)

Found (Cabl )

Found Nb M C H N

(Ca led.)

0.1 ~ 11.90 H9 55(,] 6.54 5.23 7~')

(O . I ~) ( 11.9ll) (3 48) (55.73) (689) (54 1 ) (775 )

0.46 15.69 4.56 42 .60 R. OO 6.92 602 (047) ( 15.76) (458) (42.78) (8 04) (7 12) (5 9)

0.08 12.79 3.60 50 0 1 '1 .06 5.71 720 (0.09) ( 12.98) (3 .77) (5033) (9 .15) (5 .87) (715 )

0. 11 1972 52 4 3 5.99 5.0(, 824 (0 12) ( 19 87) (52.82) (653) (5 13) (RI X)

0.20 10.29 13.58 49.06 5.8 2 4.74 885 (0.20) ( 10.67) ( 13.99) (4966) (6 14) (4.82) (X70)

0.28 16.26 5463 6.92 4.83 ~nJ (0.29) ( 1545) (54 74) (7 07 ) (.t .!) I ) (ll55)

19.44 5 1.53 5.91 4.88 R~()

( 19.74) (5 1 57) 16.49) (S Ol ) (X3 X)

0.31 20.20 52 4 3 6 8 4.59 c)1:l (0.32) (2048) (52 .10) (673) (4.67) (X9'»

0.09 24.94 48.5 1 5.8 1 D9 1 03~ (0.09) (25 .1:1) (4tU .') (6 .44) (4.0 1 ) ( 1047)

R = Ph(1a); Me(1b); Bu(lc)

Equimolar reactions of the meta ll oli gands (1a )­(1 c) with different metal alkox ides yield new heterobi meta II ic N-substituted diethanolami na te alkoxide complexes (2)-( 10), Eg. (2):

Nb(RDEAh(RDEAH) +

re flu x. - 2 h

Nb(RDEA)3 {M(OR \_d + (x + I) RIOH i ... (2)

M = AI (n = 3, x = O. Rl = ph. R = Ph(2). Me(3). Bu(4); Ga(n = 3. x = O. RI = Pr', R = Ph)(S); Sb(n = 3. x = O. RI = PI.i. R = Ph)(6); T i (n = 4. x = O. Rl = Pr'. R = Ph) (7); Ge (n = 4, x = O. RI = Et. R = Ph )(8): Zr

2442 INDIAN J CHEM. SEC A. DECEMBER 2005

(la)-( Ic)

Fig . 1 - Plau si hle stru cture for the deri vat ives (la)-(l c).

I . I (n = 4. X = L R = Pr'. R = Ph)(9); Ta (n = 5, X = 0, R = PI.i. R = Ph)(10).

These (yellow, pale ye ll ow or white) solid compl exes (Table I) are soluble in common organic solvents (e.g., benzene, toluene, tetrahydrofuran, dichloromethane, etc. ) and are monomeric.

Infrared spectral studies

Homometallic niobium(V) complexes (Ia)-(1e) ex hibit absorption bands characteri st ic of metal attac hed N-substituted diethanolaminate groups23 For exa mple. the two absorption bands in the ranges 1249-1240 and 1199-1188 cm· l

, are ass ignable to v(C-N) of the aliphatic amino:!.! group. The fonner is almost in the sa me range as observed for the free li ga nds ( 1250- 1245 cm· I

). whereas the latter shows a lowering of - 55±5 cm·1 with respect to in the parent li ga nd. These observat ions SUppOl1 the involvement of both the bi- and tridentate I iga ting modes of the N­substituted diethanolaminate groups (Fig. J) in the sa me molecule . Further ev idence in favo ur of the structure shown in Fig. I is the appearance of two strong absorptions at 1391 and 1366 cm· 1 in the spectra of (Ia). assignable to v(C-N) of aromatic amin025 group. The latter. whic h shows a lowering of -29 cm·1 with respect to that found in the N­phenyldiethanolamine, supports the formation of intramolecular ~Nb dative bond. The appearance of two absorption bands for aromatic v(C-N) supports the presence of at least one N­phenyldiethanol-aminate moiety in which nitrogen is uncoordinated . Other important absorption bands are observed at 3310-3285 v(O-H). 1099-1083 v(C-O)cu. 583- 578 V(Nb-O)27. and 460-450 cm·1 v(Nbf-N ).

Heterobimetallic complexes (2)-(10 ) ex hibit structurall y important absorption bands at 1374- 1200 v(C-N), 1099-937 v(C-O), 583-564 v(Nb-O). 800-547 v(M-O) (M = AI, Ga, Sb. Ti. Ge. Zr. Ta). and 516-437 cm·1 v(Mf-N) (M i:. Ge) The absorption bands due to v(C-N) in complexes (2)-(10 ). whi ch appear in the ranges 1234- 1200 (a liphatic ) and 13 74-1343 (aromatic) cm·1 ex hibit a lowering of - 30 ± 10 cm· l

. Absorptions due to metal attached isopropoxo groups appear at 11 78 ± 6, I 123 ± 6 veOPri) and 1040 ± 10 cm·1 v(C-O) terminal. The bands due to v(C-O) stretching vibrations of diethanolaminate groups appea r in the 1098- 937 cm l region The va riable intensity bands in the 800-547 cm·1 region are ass ignable to v(M- O)U(M = AI. Ga . Sb. Ti . Ge. Zr. Ta) vibrations .

NMR spectral sludies

IH NMR spectra of homometall ic cOlllpl exes (1 a )­(Ie) ex hibit signals fo r NC H2. CH20. N-R (R = Ph. Me, Bu) along with a signal for hydroxy group as di sc ussed already. Sal ient features of the spect ral data are: (i) the appearance of two sin glets for NCH, protons in (1 b) at 0 2.68 and 2.39: the fonner shows a lowering of 00.3 1 ppm with respect to that observed in the free MeDEAH2 (2.37 ppm), this may be interpreted in terms of the formatio n of N~Nb dat Ive bond. The singlet found at 0 2.39 ppm may be as a result of uncoordinated nitrogen of the amino group (Fig. I). (ii) observation of complex multipl ets due to phenyl and butyl protons respec ti vely for (la) and (Ie). and (iii ) appearance of broad signals or compl ex multiplets fo r NCH 2 and CH20 protons.

The IH NMR spectral data for hc terobimeta llic complexes (2)-(10) are desc ribed in Tab le 2. Complexes (2)-(1 0) show two complex ITIult iplets for eac h NCH2 and CH20 protons in the 8 2.77-3.74 and 3.65-4.42 ppm regions , respect ive ly. Complex (3 )

ex hibits a si nglet for NCH, protons at 8 2.60 ppm. whereas signals for butyl protons in (4) appear at 0 0.94 (N(CH2)3Me). 1.31 - 1.50 (NCH:(C H2h Me). and 2.77 (NCH 2(CH2h Me). Isopropoxy group protons appear as a doublet (OCHMe:) and a multiplet (OCHMe2) in the 0 1.21 - 1.28 and 4.02-4.62 ppm regions. respect ive ly.

It is noteworthy that lIlonomeric Nb(MeDEA )c(OPr') (Jd ) ex hibits ( d e~cr iocd earli er)

GHA DWAL & SI GH: HETEROBIMETA LLIC A LKOX IDES OF NIOBI UM(V) 2.+43

Tab le 2 -IR (cnf ' ) and ' H MR (8. pp m) data for tb e new complexes (2)-(IU )

COl11 po unu IR

(2) 137'+. 1349. 1230 v(C' - N): I 183 . 111 6 v(OPr' ): 1099. 1050.

1033. 950 viC-O J; 800. 750. 700 683 v(C. 1-I 5): 6 16 v

(A I- O ): 583 v(Nlr-O): 500 v( A I N): .+ 50 v(N bf-- N)

(J ) 1234. 1203 v(C-N): 11 76. 1125 v(O I"l'): 109} 103 1. 937 v(C-D): 620 v(AI--O): 578 v(NlrO): 500 v(AIf--N): 468 v(Nbf--N)

(.+ ) 123 1. I 200 v(C-N): 11 78. 1136 v(O I"l'): 1084. 1030. 940 v(C -D): (iIO v(A I-O ):5(>-I v( 'h--D):506v(A If-- ): 460v(r-..'bf--- )

(5 ) 1370. 1353. 1220 v(C-N): I 18'+ . I 130 v(OPr'): 1085 . 1036.

9.+ 2«(,-0 ): 8 11. 7(,0 . 683 v(C"H5): 600 veGa- O J: 578 v( b- O ): 4')0 v(Gaf--N): 4.+7 v( bf-- N)

(6) 13(,5. 1349 . 123 '+.1 200 v(C-N): 1183. 11 40 v(O l'r'): 1083.

1032. 950 v(C- O ): 7')0 . 765 . 683 v(C"H5) : 583 v(Nh- O): 5 16 v( SI}-O ): .+ 39 v(N bf-- N) : 424 v(Sbf-- N)

(7 ) 13(,.+. 1359. 12 18 v(C- N): I 17 1. I 109 v(OPr' ): 1078. 1035.

10 15.937 \'(('-0 ): 7')5 . 766. 680 v(C. H5): 601 yeTi- O J;

578 v( Nlr-O): 5 15 v(T if-- N): 46 1 v(Nbf-- N)

( ll ) 1378. 1343. 1236 v(C-N): 1098. 1067. 1050957 v(C - 0 ):

772.709. 680 v(C.H, ): 800 v(Ge- O ): 578 (Nb- O ): .+60 v(Nb )

( 9 ) 137'+. 13'+3. 12 18 v( C-N): I 172. 111 2 v(O Pr'): 1078. 1030.

1015 . 940 v(C - 0 ): 71)8. 753. 690 v(('. I-I \) : 58 1 v(Zr- O ):

578 v(N h- O ): 507 v(Zr ): 460 v( bf-- N)

( 10) 1370. 1347. 12 10 v(C-N): 11 78 . 11 20 v(OPr'): 109 1. 1045.

950 v(C' -0 ): 795 . 735 . 697 v(C.1-I 5): 572 v(Nlr-O): 547

viTa- O J: 457 v(Nbf-- N): 437 v(Taf-- N)

\~N/ I!~ M. AI( .. oJ, R. Ph!, Md, B, 4)

o I o_~.-o Ga(n = 3. R = Ph 5);

" • / • (OPr').. , Sb(n = 3, R = Ph 6); _ Nb--O

o f~ j Ti (n =4. R=Ph7);

o Zr(n = 4. R = Ph 9); R/N0 T,(,. 5, R. Ph 10)

(2)-(7); (9)-(10)

Fi g.2 - Pl au sihle structu re 1'0 1' the derivati ves (2)-(7) and (9). (1 0 )

onl y one sharp singlet for NCH, at <5 2.68 ppm. which is shifted down field by <5 0.31 ppm with respect to that observed in the free li gand. Thi s observation is supporti ve of seven-coordinate ni obium in (ld), in volving tridentate li gating mode of deprotonated N­methyldiethanolaminate moieties . Keeping thi s fact in mind and the IH NMR data di scussed above, the structure shown in Fig. 2 appears to be more convincing for the deri va ti ves (5)- (7) and (9). (10).

~7A I NMR spectra of (2), (3 ). and (4) show signals at <5 7.43 . 3.60 and 5.62 ppm, respecti vely, consistent with aluminium (n 3) in six-coordinate28

.29

environment. in volving additi onal coordinati on through one of the di ethanolaminate oxygens marked

'H

1.21 (d. J = 6JF1 I-I z. 12H. OCI-IMl'2): 3'('()(br. 12H. CII2): 4 23 (m, 2H. OCIIM~l); 4.37(m. 12H. CillO): 6.62-7.37 (Ill. 151-1 . aromatic-II )

1.21 (d. J = 5.85 Hz. 121-\. OCI-IMCl): 2Hl (s. 91-\. 1\ Ie): 2.80< m. 12H. NClll): 3.72 (Ill. 12H. CII,o): 4.02 (m. J = 5.85 11/_ 21\' OClIMc2)

0 .9 '+ (m. J = 6 .96 I-Iz. ') 1-1 . N<C HJ , 'Ic ): 1.3 1- 1.50 (m. 12H. NCH 2(C II ~)oMc): 2.77 ( Ill . (, I-\. NCII ~ (C H ~)M cJ 3.0(, (m. 12H. NCII ~): 3.65 (111 . 12 1-1 . C II ,O ): .+ .05( 111 . 2H. OCII Me~ )

1.21 (d. J = 586 Hz. 12H. OCHl\k~): 3.('<)(m. 121-1. NCII, ):4,37( 'Tl 12H. (,II! »: .+.54(1Il. J = 5.86 H7_ 2H. OCIIMc~): 6{,2-7J7(m. ISH. ;uu lIl;lIic-11j

1.28(d. J = 6.04 Hz. 12H. OCI-IMl~): 3.63(111. 121-1. NCI I ~): '+.24(111. 12H. ClI,O): 4.44(m. J = 6.04 Hz. 2H. OCllMc, ): 6.6:>--7 ,43(m. 15H. :uIJl11alic- lI )

1.21(d. J = 6.22 I'V_ ISH. OCHMl'2): 3.74 (111. 12H. NCI U: 4.23 (m. 12H. CII ,O ): 4 .36 (m. J = 6 .22 Hz. 3H. OCIIM c~): 6.57-7,42 (m. 15 H. aromatic-II )

1.24 (L J = 5.86 Hz. ,)H. OCH~Mc): 3,(,<) (Ill. 121-\' CII,):.+.II (111. 12H. CII,O): 5.25 (m. J = 5 .86 Hz. 6 H. OCII, Mc): 6.S3-7 ,4 1 (m. ISH. aromatic-II )

1.08(d . J = 6.0'+ Hz. ISH, OCI-IMc~): 3.67 (m. 12H. C II ~ ): '+ .25 (m . 12H. C II ,O ): 4 .37(m. J = 6 .0'+ Hz. 3H. Oe Il Me, ): 6 .65-7 .+ X

(m. 15 11 . aro mati ('- II )

1.2 1 (d. J = 6 .04 Hz. 24 H. OC HMe,): 3. (,5 (m. 12H. NC II ,): .+,47 (m. 12H. C lr,O): 4 .62 (m. J = 6 .04 Hz. 4 H. OC IIMc2): 6.48-7,40

(m, ISH. aro ma ti c-II )

by asteri sk (Fig. 2). The similar six-coordinate structure for the gallium co mpl ex (5) is also poss ible.

Acknowledgement R.S.G. is grateful to the Department of Chemi stry.

University of Rajasthan, Jaipur and State Government of Rajasthan for a Fell owship under Special Assistance Programme. A.S. (Emeritu s Scienti st) is thankful to the Uni versity Grants Commiss ion, New Delhi for financial support. Authors are al so grateful to Mr. Suman Kumar Gupta for recordi ng mi croa nal ytical (c, H. N) and MR spectral data .

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