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Synthesis and Reactivity inInorganic and Metal-OrganicChemistryPublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/lsrt19

Synthesis and Characterisationof a New Class ofHeterotrimetallic Isopropoxidesof Strontium and BariumMalti Sharma a , Anirudh Singh a & Ram C. Mehrotra aa Department of Chemistry , University ofRajasthan , Jaipur, 302004, IndiaPublished online: 23 Apr 2008.

To cite this article: Malti Sharma , Anirudh Singh & Ram C. Mehrotra (2000) Synthesisand Characterisation of a New Class of Heterotrimetallic Isopropoxides of Strontiumand Barium, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 30:7,1331-1345, DOI: 10.1080/00945710009351837

To link to this article: http://dx.doi.org/10.1080/00945710009351837

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SYNTH. REACT. INORG. MET.-ORG. CHEM., 30(7), 1331-1345 (2000)

SYNTHESIS AND CHARACTERISATION OF A NEW CLASS OF HETEROTRIMETALLIC ISOPROPOXIDES OF

STRONTIUM AND BARIUM

Malti Sharmaa, Anirudh Singh* and Ram C. Mehrotra*

Department of Chemistry, University of Rajasthan, Jaipur-302004, India

ABSTRACT

New heterotrimetallic isopropoxides of the types { ~(OPr-i),}M'{M1(OPr-i),) (M= Zr, Sn(rv); M' = Sr, Ba; M I = Ti, Sn(IV)) and { Sq(0Pr-i),} Sr{Al(OPr-i)4} have been synthesised for the first time by the single-pot reactions of metal isopropoxides (e.g., M'(OPr-i)2 (M' =

Sr, Ba), Ti(OPr-i)4, Sn(0Pr-i),.i-PrOH, or Al(OPr-i)3) in the desired molar ratios in refluxing benzene. All of these novel derivatives have been characterised by elemental analyses, molecular weight measurements, and spectroscopic DR, NMR ('H, I3C, 27Al, I19Sn)] studies. Reactions of the derivative {Zr2(0Pr-i),}Ba{ Sn(0Pr-i),} with alcohols (Me,CCH,OH and Me3COH) have been carried out to shed light on its possible structd features.

INTRODUCTION

Recently, there has been an increasing interest in the alkoxo chemistry of heavier alkaline earth metals',* with emphasis on barium, which is one

~~ ~

'Nee Bhagat

1331

Copyright 0 2000 by Marcel Dekker, Inc. www.dekker.com

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1332 SHARMA, SMGH, AND MEHROTRA

of the constituents in mixed metal-oxide superconducting materials3 such as YBa,Cu,O,,. Further, due to the larger size of heavier alkaline earth metals (Srt2, r = 1.13A; Ba+', r = 1.35A) and their higher electropositive nature, the derivatives of these metals may be expected to exhibit greater diversity in the structural, physical, and chemical properties.

Nona(isopropoxo)dizirconate derivatives4 of alkaline earth metals were reported by Mehrotra and Govil in 1975, followed by studies on nona(isopropoxo)distannate derivatives5 in 1995. The fust heterotrimetallic isopropoxides of Group I1 metals of the types [(Pr-iO),A1(~-OPr-i) ,Be(~-OPr-i) ,Be(~-OPr-i)2Zr(OPr-i)3]6 and {~(OPr-i),}M'{A1(OPr-i),} (M' = Mg, Ba; M = Sn(IV)),' (MI = Mg; M =

Zr),7 ( M = Ba; M = Zr)" were reported earlier from our laboratories.

More recently, single crystal X-ray crystallographic studies on the interesting heterotrimetallic complex [ { (Pr-iO),Cd}Ba{Zr,(OPr-i),}],,9 and the bimetallic isopropoxide { Ti(0Pr-i),}Ba{Ti(OPr-i),} have been canied out.

In view of our continued interesP." in heterometallic alkoxides of alkaline earth metals, we now report the synthesis and characterisation of a new class of heterotrimetallic isopropoxides of the types {M,(OPr-i),} M'{M"(OPr-i),} and { S~(0Pr-i)9}Sr{Al(OPr-i)4}.

RESULTS AND DISCUSSION

Heterotrimetallic isopropoxides of the formulae {$(OPr-i),}M'{M"(OPr-i),} (M = Zr, Sn(1V); M' =Sr, Ba; M" = Ti, Sn(1V)) and { S%(OPr-i),} Sr { Al(OPr-i)4} have been synthesised according to the following sequential reactions (eqs. (l), (2) and (3)) in a single-pot reaction.

(1) i-PrOH M' + 2i-PrOH M(0Pr-i), + H, ? - 6 h

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HETEROTRIMETALLIC ISOPROPOXIDES 1333

I"(OPr-i), + 2M(OPr-i),.i-PrOH +[ {~(OP~-~),}M'(~-OP~-Z')] + 2i-PrOH

M = Zr; M' = Sr; M" = Ti; x = 0 (1) M = Zr; I" = Ba; M" = Ti; x = 0 (2)

M = Zr; M' = Sr; M" = Sn; x = 1 (3) M = Zr; M' = Ba; M" = Sn; x = l(4) M = Sn; M' = Sr; M" = Ti; x = 0 (5) M = Sn; M = Ba; M" = Ti; x = 0 (6)

M = Sn; M' = Sr; M" = Sn; x = 1 (7) M = Sn; M' = Ba; M" = Sn; x = 1 (8)

M = Sn; M' = Sr (9)

The general facility' of homo- and hetero-metallic alkoxides to undergo alcoholysis reactions with primary alcohols was confirmed for some of the above derivatives in preliminary experiments even with a long chain normal amyl alcohol. The alcoholysis was, therefore, repeated with neopentyl alcohol, which could be expected to exhibit some steric hindrance due to the presence of a tertiary butyl attached to the CTOH group. The alcoholysis reaction, however, was completed with the stagewise liberation of 7, 5 and 2 isopropoxy groups within -10 h.

{ Zr,(OPr-i),}Ba( Sn(0Pr-i),} + 14 Me,CCH,OH ' ~ 5 ~ 6 , (4) (excess) - 10h

{Zr,(OCH2CMe3),}Ba{Sn(OCH,CMe,),}

+14 i-PrOH? (+ Me,CC$OH) (4) (10)

(excess)

However, when the alcoholysis of (4) was repeated in benzene with the sterically more demanding tertiary butyl alcohol, it was found that the reaction became much slower after removal of seven isopropoxy groups

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1334 SHARMA, SINGH, AND MEHROTRA

during the initial -8 h, after which only another five (out of the remaining 7) additional isopropoxy groups could be replaced even with continuous fractionation for -20 h.

{Zr2(0Pr-i&} Ba{Sn(OPr-i),}+ 12 Me,COH C6H6 , -25h (4) (excess)

{Zr2(OPr-i),(OCMe,),}Ba{ Sn(OCMe,),} + 12 i-PrOH ?' ( 5 ) (11)

The interesting observations in the stagewise alcoholysis'* with tertiary butyl alcohol tend to suggest a structure shown in Fig. 1, which has seven terminal (unbridged), five doubly-bridged (p2) and, two triply- bridged (p,) isopropoxy groups. The results of the alcoholysis experiments are, therefore, fully consistent with the well established (Fig. 1) tendency of replaceability in the order of terminal > p,-bridged >> p,-bridged isopropoxy groups.

The new heterotrimetallic alkoxides (1)-(11) are soluble in common organic solvents, in which they depict monomeric nature. Attempted sublimation under reduced pressure resulted in decomposition to yield metal-oxide systems. For example, on heating the derivative (2)

{Zr,(OPr-i)9}Ba{Ti(OPr-i),} at 210" U O . 1 mm for -1 h, a benzene- insoluble product of composition approximating BaZr,TiO,,, was obtained.

EXPERIMENTAL

All of the preparative reactions were performed under strictly anhydrous conditions. The (BDH) solvents benzene, toluene and n-hexane were dried by refluxing over sodium benzophenone ketyl. Isopropyl alcohol (BDH) was dried by refluxing over sodium isopropoxide and subsequently over AJ(OPr-i),, and distillation prior to use. Neopentyl alcohol and t-butyl alcohol were dried by refluxing over sodium metal

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HETEROTRIMETALLIC ISOPROPOXIDES 1335

followed by distillation prior to use. Freshly cut and dried pieces of barium and strontium metal (Aldrich) were used. Zr(OPr-i),.i-PrOH,I3 and Ti(OPr-i),13 were prepared by literature methd . Sn(0Pr-z),.i-P10H~~ was prepared by the sodium kopropxide m&od.

Barium, strontium, titanium, tin(IV), and zirconium were determined gravimetrically as BaSO,, SrSO,, TiO,, SnO,, and ZrO,, respectively. The isopropoxy determinati~n'~ was carried out oxidimetrically using 1 N K,Cr,O, solution in 12.5% %SO,.

Infrared spectra (4000-200 cm-I) were recorded on a Nicolet Magna 550 spectrophotometer in Nujol mulls. NMR spectra, 'H (in CDCl,), I3C (in CC1,) and II9Sn(in C,H,), were recorded on a JEOL FX 90Q spectrometer. Molecular weights were determined ebullioscopically in benzene using a Gallenkamp ebulliometer with a thermister device.

Preuaration of HeteroaetallicIsouropoxides of Alkaline Earth Metals

Due to the preparative similarity, only one synthetic procedure is described below.

{Zr2(OPr-i)9}Ba(Ti(OPr-i)s}.Freshly cut and dried barium (0.44 g, 0.00 17 mole) in isopropyl alcohol (-20 mL) was refluxed till all the pieces were dissolved. After removal of the volatiles under reduced pressure, the solid was treated with benzene and Zr(0Pr-i),.i-PrOH (1.34 g, 0.0034 mole) were added. The reaction mixture was then refluxed for - 6 h, and after cooling, Ti(0Pr-i), (0.49 g, 0.0017 mole) was added and the mixture refluxed for - 7 h. Removal ofthe volatiles under reduced pressure afforded a white solid, which was recrystallised from a n-hexane and toluene (1 : 3) mixture at -20" C to yield a white solid powder (1.43 g, -70%). Preparative and analytical details for all of the crystallised products are listed in Tables I and 11.

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Tab

le I.

Rea

ctio

ns o

f [ (M

2(O

Pr-i)

,) M

'(p-O

Pr-i)

] with

Sn(

0Pr-

i),.C

PrO

H, T

i(OPr

-i),,

or A

I(0P

r-i),

fi(O

Pr-i)

,.i-P

rOR

M=

ZI

(1.3

9.0.

0036

)

M=

Zr

(1.3

4.0.

0034

)

M =

Zr

(1.3

5,0.

0035

)

M=Z

r (1

.25,

0.00

32)

M=

Sn

(1.4

2,0.

0034

)

M=

Sn

(1.4

2,0.

0034

)

M=

Sn

(1.4

1,0.

0034

)

Rea

ctan

ts (g

, m

ole)

Meh

l is

opro

pond

c

Ti(O

Pr-i)

4 (0

.51,

0.00

18)

Ti(O

Pr-i)

, (0

.49,

0.00

17)

Sn(O

Pr-i)

,.i-P

rOH

(0

.72.

0.00

17)

Sn(O

Pr-i)

,.i-P

rOH

(0

.67,

0.00

16)

Ti(O

Pr-1)

4 (0

.48,

0.00

17)

Ti(O

Pr-i)

, (0

.49,

0.00

17)

Sn(O

Pr-i)

,.&Pr

OH

(2

.08,

0.00

50)

Sn(O

Pr-I)

,.f-P

rOH

(2

.00,

0.00

48)

AI(

OR

-I),

(0.3

5.0.

0017

)

M'(O

P~-I

),

M =

Sr

(0.3

8,0.

0018

)

M=

Ba

(0.4

4,0.

0017

)

M=

Sr

(0.3

5,0.

0018

)

M=

Ba

(0.4

1,0.

0016

)

M =

Sr

(0.3

5.0.

0017

)

M=

Ba

(0.4

3,0.

0017

)

M=

Sr

(0.3

5,0.

0017

)

M =

Ba

(0.4

1,0.

0016

)

M =

Sr

(0.3

5,0.

0016

)

27.7

7 (2

8.02

)

26.7

3 (2

6.96

)

20.3

1 (2

0.13

)

- - 2.38

(2

.28)

I

Product

Yie

ld (g

, %)

Col

our a

nd S

tate

{ZI,(

OPr

-i),}S

r{Ti

(OR

-~),}

(1

.97,

81%

) Y

ello

wis

h so

lid w

wde

r

Yel

low

(lig

ht) s

olid

pow

der

{ Zr,(

0Pr-

1),}

Sr( S

n(O

Pr-z

),}

(2.0

8, 8

6%)

Yel

low

ish

solid

pow

der

{Zr1

(OPr

-1),}

Ba{ S

n(0P

r-I)

,}

(2.0

3, 7

4%)

whi

tc so

lid p

owde

r { S

q(0P

r-1)

~) Sr{ T

i(OPr

-i),}

Yel

low

ish

solid

pow

der

(S%

(OP~

-I),}

Ba(T

i(0Pr

-I),}

Yel

low

ish

solid

now

der

(2.0

0,77

%)

(2.0

9,73

%)

Yel

low

ish

solid

pow

der

{ Sr4

(O~-

I),}B

a(Sn

(OPr

-I),}

(2

.10,

63%

) W

hite

solid

pow

der

(2.0

1,71

%)

Whi

te so

lid p

owde

r

{ Sq(

OR

-i),} Sr{ A

I(O

P~-I

)~}

7.37

(7

.65)

11.2

6 (1

1.49

)

7.10

(7

.21)

10.6

7 (1

0.85

)

7.18

(7

.30)

10.6

1 (1

0.99

: 6.

68

(6.8

9)

10.2

6 (1

0.40

:

7.32

(7

.43)

-

Ana

lysi

s, Fo

und

((

zr/s

a

15.8

1 (1

5.93

)

15.0

9 (1

5.27

)

14.8

1 (1

5.00

)

14.2

2 (1

4.42

)

- lc.

) m

4.12

(4

.18)

3.82

(4

.00)

9.64

(9

.76)

9.19

(9

.38)

0Pr-

i 71

.88

(72.

23)

69.1

1 (6

9.23

)

68.0

0 (6

8.03

)

65.3

3 (6

5.36

)

68.6

5 (6

8.93

:

65.9

8 (6

6.18

: 65

.02

(65.

09:

62.6

4 (6

2.64

70.1

0 (7

0.15

M.w

t. Fo

und

(Cal

c)

1156

(1

145)

1203

(1

195)

1220

(1

216)

1270

( 1

266)

1240

(1

200)

1238

(1

250)

12

88

(127

1)

1356

(1

321)

1185

(1

179)

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Tab

le II. R

eact

ions

of {Zr,(OPr-i),}Bn{Sn(OPr-i)J

witb

Ste

rica

lly H

inde

red

Alc

ohol

s

(10)

M

e,C

CyO

H

12

(2.0

2,0.

0016

) (5

.01,

0.00

57)

(11)

M

e,CO

H

25

(2.0

5.0.

0016

) (2

.02,

0.00

27)

M.W

t Pr

oduc

t Li

bera

ted

Yid

d (g

, Yo

)’ i4

lOH

Faon

d (C

alc)

Fo

und

(Col

our a

nd State)

(Cal

c)

B8

Ana

lysi

i Fou

nd

10.2

5

‘Yiel

d re

fers

to p

rodu

ct re

crystallized fr

om a

n-hexane-toluene (

I :3)

mix

ture

.

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1338 SHARMA, SINGH, AND MEHROTRA

IR Spectra

IR spectra (Table 111) of the derivatives (1)-(11) show characteristic absorptions of metal-attached alkoxo groups2.I6 in the following regions cm-I: 1203 v(OCMe,); 1209 v(OCH,CMe,); 1185-1 161, 1145-1 116 v(OCHMe,); 1031-972 v(C-0). Absorptions due to v(M-0)" (M = Zr, Sn(IV), Ti, Al, Sr, Ba) have been observed in the region 680-400 cm-I.

The IR data have been included mainly as characteristic absorbances observed in different regions, but these do not shed conclusive light on the structural features of the derivatives.

NMR (lH, l3CY 27AIy and lieSn) Spectra

By contrast to IR spectra, 'H NMR spectra are able to distinguish between terminal and bridging alkoxy groups. In addition, and Il9Sn spectra give clear indication of the coordination states of the individual metals (A1 and Sn). As mentioned briefly, all the NMR spectra are in full conformity with plausible structures suggested in Figs. 1 and 2, postulated on the basis of structures of similar derivatives characterised re~ent ly . ' . '~ . '~

The 'H NMR spectra of derivatives (1)-(9) (Table IV) exhibit two doublets in the regions 6 1.26-1.3 1 and 1.38-1.5 1 due to terminal and bridging OCHMe, groups in 1 : 1 integrated ratio. The methine protons also appear in 1 : I integrated ratio as multiplets in the regions 6 3.98-4.23 and 4.29-5.07. The integrated ratios ofthe corresponding peaks for terminal and bridging isopropoxy groups is approximately 6 : 7 in the derivative (9) (Fig. 2).

The derivative (10) shows two singlets at 6 0.92 (CH,CMe,) and 3.30 (CH,CMe,). The derivative (11) shows peaks due to both isopropoxy groups at 6 1.24 (d (J = 6.15 Hz), CHMe,) and 4.26 (septet (J = 6.15 Hz), CHMe,)] and tert-butoxy groups [ 1.33 (s, CMe,)]. The existence of two

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Tab

le I

II. IR

Dat

a'(c

m-')

of S

ome

Het

erot

rim

etal

lic A

lkox

ides

of Strontium

and

Bar

ium

Com

poun

d C.Na

v(C

(ter

min

al)

{Zr2

(0Pr

-z),}

Sr{T

i(OPr

-z],}

{ Z

r,(O

Pr-z

],}Ba

{ Ti

(OPr

-z],]

{Zr2

(OPr

-i)9}

Sr{ S

n(0P

r-z]

,}

(Zr,(

OPr

-z],}

Ba {

Sn(0

Pr-z

], }

{ Sq(

0Pr-

1)~)

Sr{T

i(OPr

-z],}

{ SnJ

OPr

-i],}B

a{

Ti(O

Pr-z

?,}

(Sq(

OPr

-z],}

Sr{S

n(O

Pr-i)

,}

{ S%

(OPr

-z],}

Ba(

Sn(0

Pr-I]

,}

{ Sn&

OPr

-z],}

Sr{

Al(0

Pr-i)

,}

{qq

meA

}h{s

n (q

WJ

{a

2(O

R-t

A (O

B~)

,JW

Sn(O

Bu3

,}

1016 s

1008 s

1023 m

1016 s

1020 s

1031 s

1015 s

1026 s

1014 s

I051 m

1028 m

1) @

ridg

ing)

969

s, 922 m

953

s

969 m

937 m

972 s

970 s

%9

s

969

s

949

s

920 m

949 m

~

1172s

1172 s

1125 s

1187m

1141 rn

1172s

11Wm

1169s

1116s

1173 s

1125 s

1172s

1125 s

1172 s

1125 s

1174 s

1116s

1209 m

1159 m

1116m

1203 m

v(B

a-O

)/(Sr

-O)

453

s 469

s

469 m

439

s

444s

454

s,

469

s

406 s, 453 s

449

s

450 m

449 m

v(Sn

-O)/(

Zr-

O)

563

s 500

s

500 w1578 w

500 ~1547 s

516 m

594

s

560

s,64

0 s

578

s

558

s

515 d

545 m

551

m/

515 m

641

s 563

s

628 s

680 s

614 m

'Abb

revi

atio

ns : s

= st

rong

, m =

med

ium

, w =

wea

k

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Tab

le IV. N

MR

(IH, "C, n

AI,

and "%n)

Dat

a' (

6, p

pm) of

Het

erot

rirn

etal

lic A

lkox

ides

of S

tron

tium

and

Bar

ium

1.27

(d, J

= 6.

15 Hz, 42

H, C

HM

e,(t)

); 1.

52 (d

, J=

6.15

Hz, 4

2H, C

HM

e,(b

)); 3

.98

(br,

7H, C

HM

e,(t))

; 4.

49

(br,

7H. C

me,

(b))

1.

26(d

, J=6

.I5H

z,42

H,C

HM

el(t

));

1.43

(d, J

z6.1

5 Hz, 4

2H, C

HM

e,(b)

); 4.

11 (b

r, 7H

, CH

Me,(

t));

4.50

(br,

7H, C

HM

eJb)

) 1.

31 (d

, J =

6.15

Hz, 42

H, C

HM

e,(t)

); 1.

52 (d

, J=

6.15

Hz,

42

H, C

HM

e,(b)

); 41

20 (b

r, 7H

, CH

Me,(

t));

4.49

1.26

(d, J

=6.

15H

z,42

H,C

HM

e7(t)

); 1.

38(d

,J=6

.15H

z (b

r , 7

H, C

me,

(b))

2oom

ponn

d [Z

r2(O

Pr-r]

9}Sr

[ Ti(0

Pr-

0,)

(Zr,(

OPr

-r],}B

a(

Ti(O

Pr-i)

,)

[Zr2

(OPr

-i]J

Sr(S

n(O

Pr-r

J5)

{Zr,(

OPr

-r),J

Ba

{ Sn(

0Pr-I

],}

{ Sn+

OPr

-i],}

Sr (T

i(0Pr

-i),)

{ Srq

(OPr

-'),}

Ba (

Ti(O

Pr-O

,}

(Srq

(OPr

-i]J

Sr{ S

n(0P

r-i),

}

{ S~(

OPr

-i],)B

a{Sn

(OPr

-i?,)

(SnJ

OPr

-I],)

Sr(A

l(OPr

-r],}

(Zr,(

OC

YC

Me,

),)

Wsn

(qrn

e3

)J

{Zr,(

OPr

-i),(o

CM

c,),)

Ba

(Sn(

oCM

e,),

25.5

2,27

.19

(CH

Me,

); 64

.10.

71.2

4 (C

HM

e,)

25.6

1,27

.43

(CH

Me,)

; 67

.46,

70.

19 (C

HM

e,)

26.3

3,27

.57

(CH

Me,)

; 68

.69,

71.5

6 (

We

,)

26.1

3,27

.08(

CH

Me,

);

1.30

(d, J

-6.1

iK42

H,C

HM

e2(t

));

1.49

(d, J

z6.1

5 Hz, 4

2H,C

HM

e,@

)); 4

.23

(br,

7H, C

HM

e,(t

));

5.07

(b

r, 7K

CH

Me,

(b))

1.29

(d, J

= 6.

15-

42H

, CH

Me,(

t));

1.38

(d, J

= 6

.1 5H

74

42H

, CH

Me,

(b));

4.1

7 (b

r, 7H

, CH

Me,

(t));

4.63

(br

, 7H

, Cm

e,(b

))

1.26

(d, J

=6.I

5Hz,

42H

,CH

Me2

(t))

; 1.5

1 (d

, Jz6

.15

Hz, 4

2H. C

HM

eJb)

); 4.

13 (b

r, 7H

, CW

e,(t

));

4.61

(br,

7H, C

HM

e,(b)

) 1.2

4 (d

, J =

6.15

Hz,

42H

, CH

Me,(

t));

1.43

(d, J

= 6.

15

Hz, 4

2H, C

HM

e,(b)

); 4.

21 (

br, 7

H, C

me,

(t))

; 4.

88 (b

r, 7H

, CH

Me,(

b))

0.92

(s,

126H

, CY

CM

e,);

3.3

0 (s,

28

9 C

A,C

Me,)

1.24

(d, J

=6.

15?l

z, 1

2H, C

HM

e,);

1.33

(s,

108H

, CM

e,)

4.26

(sen

t J =

6.1 5

Hz.

2H. C

HM

e.)

CH

Me,

(b));

4.2

3 (b

r, 7H

, CH

M<(

t)); 4

.29

(br,

7H, C

HM

e.(b)

) I6

7.73

.71.

13 (C

HM

;,)

26.4

6,27

.46(

CH

Me2

);

64.2

3, 6

7.16

(CH

Me2

)

26.1

I, 2

7.46

(CH

Me,

); 66

.47,

67.

88 (C

HM

e,)

25.4

6,27

.09(

CH

Me2

);

67.9

3,71

.02

(CH

Me,)

26:16

,27.43

(C

HM

e,);

67.8

1, 7

0.91

(CH

Me,

)

26.6

1 (C

YC

Me,

);

32.2

1 (q

CM

e,);

73

.13

(CyC

Me,

) 25

.16(

CHM

e2);3

2.13

(CM

eJ

66.1

6(C

HM

e-k6

9.19

(CM

e,

1.26

(d, J

=L6

.15 Hz, 4

2H, C

HM

e,(t)

); 1.

45 (d

, J =

6.1

5Hz,

125

.31,

27.3

2 (C

HM

e,);

42H

, CH

Me,(

b));

4.19

(br,

7H, C

hMe,

(t));

4.79

(b

r, 7

H. C

meA

bN

164.

73.7

1.53

(C

HM

4)

"9sn

-405

.73

-410

.61

-596

.3 I

-593

.73

-590

.3 1,

-395

.00

-593

.76,

-4

06.1

6

-594

.80,

61

13c"

AI)

-403

.16

-396

.00

'Abb

revi

atio

ns:

s =

sing

let,

d =

dou

blet

, sep

t = se

ptet

, (1) =

term

inal

, (b)

=br

idgi

ng, b

r = br

oad

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HETEROTRIMETALLIC ISOPROPOXIDES 1341

differently bonded isopropoxy groups as depicted in Figs. 1 and 2 is further corroborated by the appearance of two I3C peaks for each P-carbon (25.13- 27.73), and a-carbon (64.10-71.53) atom, respectively, for the derivatives (1H9). Tbe 13C spectral data for the derivatives (10) and (11) are also consistent with the type of group(s) attached to the metal centres. (Table IV).

The derivative { S%(OPr-i)9} Sr{ Al(OPr-i)4} (9) exhibits an 27Al NMR signal at 6 67.13, which is characteristic of a tetrahedral environment around a l u m i n i ~ r n ~ . ~ ~ .

The observed Ii9Sn Nh4R signals for the derivatives (5), (6), and (9)

at 6-594.80 to -598.60 are characteristic of an octahedral geometry21,22 for tin(IV), whereas the appearance of a signal in the range 6 -396.00 to -410.61 for the derivatives (3), (4), (lo), and (11) supports a penta- ~oord ina ted~ ' .~~ environment around tin(1V). The derivatives (7) and (8) show two Il9Sn NMR signals in the regions 6-590.31 to -593.76 and -395.00 to -406.16, characteristic ofhexa- and penta-coordinated tin atoms (Table IV), respectively, which is consistent with the proposed structure shown in Fig. 1.

Structural Features In spite of repeated efforts, crystallographically suitable crystals could

not be obtained. Attempts have, therefore, been made to shed light on the structural features of these novel derivatives by NMR spectra and replacement reactions with sterically hindered alcohols (e.g., Me,CCYOH, Me,COH). For example, alcoholysis reactions of derivatives (4) shows three types of isopropoxy groups in the ratios of 7 : 5 : 2, which is fully consistent with the structure (Fig.1) in which there are 7 terminal, 5 p2- bridged and 2 p,-bridged isopropoxy groups. Further, the 'H NMR spectra of (1)-(8) show terminal and bridged isopropoxy groups in the ratio of 7 : 7 (Fig.1) whereas that of (9) shows them to be in 6 : 7 ratio (Fig. 2).

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1342 SHARMA, SINGH, AND MEHROTRA

M M' M" M M' M" (1) Zr Sr Ti (5 ) Sn Sr Ti (2) Zr Ba Ti (6) Sn Ba Ti (3) Zr Sr Sn (7) Sn Sr Sn (4) Zr Ba Sn (8) Sn Ba Sn

1. Proposed Structure ofthe Derivatives~(OPr-i),}l\lf{M'(OPr-i),} (1)-(8)

, Al

Fig. 2. Proposed Structure for the Derivative { Sn.JOPr-i),} Sr { AI(OPr-z&} (9)

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HETEROTRIMETALLIC ISOPROPOXIDES 1343

The coordination state 5 for Sn in (3), (4), (7) and (8) and 4 for A1 in (9) are also confmed by the respective NMR spectra.

The above physico-chemical studies, therefore, support the structures shown in Figs. 1 and 2 for the derivatives (1)-(9) wherein Srq(OPr-i)9- and Zr2(OPr-i)9- function as a tetradentate24.25 and Sn(OPr-i), , Ti(OPr-i)5- and Al(OPr-i);as bidentate ligands, respectively.

The observed ‘H, I3C, 27Al, and I19Sn NMR data for the derivative (9) are consistent with the structure shown in Fig. 2.

It may not be out of place to mention that conclusions arrived at by similar methods for structures of a number of derivatives like {Al(OPr-i)3}4:6 Ln{AI(OPr-i)4}3,27-29 M{M‘2(OPr-i)9} (M = alkali metal, M‘ = Zr, Hf),l3.3O231 M {A12(OPr-i),o} (M = Zr, Hf),”32 have been corroborated later by single crystal X-ray studies.

ACKNOWLEDGEMENTS

We are thankful to the Department of Science and Technology, New Delhi, for financial support of our work.

REFERENCES

1.

2.

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HETEROTRIMETALLIC I SOPROPOXI DES 1345

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Received: 24 February 2000 Referee I: 1. P. Oliver Accepted: 24 April 2000 Referee 11: T. Hughbanks

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