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Organic compounds of niobium
JOURNAL
348
ORGANIC
COMPOUNDS
REACTIONS
(Received
METALS
OF NIOBIUM
OF NIOBIUM
R. C. MEHROTRA Department
OF THE LESS-COMMON
PENTA-ALKOXIDES
WITH
ACYL
HALIDES
AND P. N. KAPOOR
ofChemistry, University qf Rajasthan, Jaipur (India) October
16th, 1965; revised January
rst, 1966)
SUMMARY
Compounds Nb(OEt)dX, and Nb(OEt)zXs.CHsCOOEt Nb(OEt)sXz, Nb(OEt)C14.CH3COOEt, NbOBr3.CH3COOEt (where X is chloride or bromide) have been isolated by the reactions of niobium penta-ethoxide with acetyl chloride and bromide. The reactions of niobium penta-isopropoxide and tert.-butoxide with acyl halides in equimolar ratios yield products of the type Nb(OR)JX; the products with excess of acyl halides corresponds to NbOX3.CH3COOR. However, the reaction in the case of penta-tert.-butoxide and acetyl chloride yielded finally NbO(OAc)o.&l3.25 . CH3COOBut. The reaction of niobium penta-ethoxide with dry hydrogen chloride gas yielded triethoxide dichloride derivative. Only niobium tetra-alkoxide monochloride derivatives could be distilled or sublimed and these were found to be dimeric in boiling benzene.
INTRODUCTION
The synthesis of a number of halide alkoxides of niobium by the niobium penta-alkoxides with acyl halides has been examined. The niobium penta-ethoxide with acetyl chloride in benzene in various molar found to be exothermic and can be represented by the following equations Nb(OEt)s+ Nb(OEt)s
CH3COCl + + zCH3COCl
Nb(OEt)a +3CH3COCl
Nb(OEt)&l+CH3COOEt
+
Nb(OEt)3Cl3 + zCH3COOEt
+
Nb(OEt)zC13.CH3COOEt
+ zCH3COOEt
Nb(OEt)C14.CH3COOEt
+ 3CH3COOEt
Nb(OEt)a + 4CH3COCl + (excess)
reactions of reactions of ratios were :
The compounds, isolated by drying under reduced pressure, were soluble in benzene. Niobium triethoxide dichloride was obtained by passing a slow current of dry hydrogen chloride gas into a benzene solution of niobium penta-ethoxide. A similar product was obtained by FUNK AND NIEDERLANDER~ by the reaction of niobium J. Less-Common
Metals, IO (1966) 348-353
REACTIONS OF NIOBIUM PENTA-ALKOXIDES WITH ACYL HBLIDES
349
pentachloride with ethanol. Similar observations have been reported by MEHROTRA? in the dealcoholation reactions of alkoxides of group IV elements. The reactions of niobium penta-isopropoxide with acetyl chloride in molar ratios of I :I and I : 5 can be represented by the following equations : Nb(OPri)j
+ CHaCOCl + Nb(OPri)&l+
Nb(OPr’):,+CH&OCl (excess)
CHaCOOPri
+ NbOC13 * CH&OOPri
The reaction of niobium penta-tert.-butoxide witn acetyl chloride was complicated. The replacement of the first tert.-butoxide group appears to be straightforward; further replacement becomes slow and does not proceed to completion. The analysis of the final end product when niobium penta-tert.-butoxide was heated with an excess of acetyl chloride corresponds to an empirical formula, ‘NbO(OAc)o.&12.25. CH&OOBut. The niobium oxytrichloride formed initially in the reaction appears to react slowly with tert.-butyl acetate according to the following equation: NbOCla + zCH&OOBut
+
NbO(OAc)Clz.CH&OOBut
+ ButCl
Recently, in a detailed study of the reaction of acetyl chloride with the tert.butoxides of aluminiums, titanium4 and zirconium5, MEHROTRA AND MISRA have reported that final end-products in these reactions also are acetoxy compounds. The reactions of acetyl bromide with niobium penta-ethoxide follow the pattern of the corresponding reactions with acetyl chloride. One salient difference in the products obtained in the reaction of niobium penta-ethoxide and acetyl chloride and bromide is that bromide ethoxide appears to have a greater tendency to change into oxycompounds, and the analyses of the products with reactants in the proportions I : 4 and I : excess, correspond approximately to NbOBra . CH3COOEt. The reactions of acetyl bromide were also studied with niobium penta-isopropoxide and tert.-butoxide. The reactions are straightforward with reactants in equimolar ratio. However, with excess acetyl bromide the products are similar to those obtained in the case of the reaction with niobium penta-ethoxide. This appears to indicate that the niobium oxytribromide formed has a lesser tendency to react with tert.-butyl acetate than has the corresponding oxytrichloride. A perusal of the above results shows that oxygen is abstracted from both excess acetyl chloride and bromide by niobium penta-alkoxides except in the case of niobium penta-ethoxide and acetyl chloride. Recently, FAIRBROTHER and co-workers697 have reported that the reactions of niobium and tantalum pentachlorides with dimethyl and diphenyl sulphoxides and triphenyl phosphine and triphenyl arsine oxides involve the abstraction of oxygen from these ligands. NYHOLM and co-workers8 have shown that prolonged heating of niobium pentachloride and diarsine solution caused complete decomposition and produced two crystalline compounds, NbOCla.diarsine and (NbC14.diarsine)zO. The abstraction of the oxygen in these compounds is another example of the marked avidity of niobium for oxygen as previously reported by MARIGNAC? The easier formation of oxy-niobium ‘compounds is one of the chief chemical differences between niobium and tantalum. Of the new halide alkoxides isolated, the niobium tetra-alkoxide monochloride derivatives alone could be distilled or sublimed without decomposition, J. Less-Common Metals, 10 (1966) 348-353
R. C. MEHROTRA,
350
Y
N
N
N
N
d
N
d
N
*
r.
.E
::
w 8 8 ..
H
Y
CI
c1
B 8
J. Less-Common
Metals,
IO
(1966) 348-353
P. N. KAPOOR
I
6.71
3.25
;; \o S
z z
k’
2.74
Nb(OBut)s
2.57
3 k
m, f E ;
2.13
Nb(OPr*)s
5 p E 8
6.11
0.75
5.72
0.68
1:4
3.28
2.12
2.44
1:3
I.89
I
: excess
I:1
I : excess
I:1
:excess
1:2
1.63
I:1
Molar ratio
PENTA-ALKOXIDES
1.52
(s)
Acetyl bromide
NIOBIUM
I.96
OF
0.88
II
2.28
Nb(OEt)s
Alkoxide (69
REACTIONS
TABLE
Time of refluxing (h)
WITH
BROMIDE
IN
BENZENE
;
NbOBra.CHaCOOBuI brown solid.
Nb(OBut)dBr (2.72 g) light-yellow solid. (3.43 g)
;
NbOBra.CH&OOPri (3.02 g) brown, spongy solid.
Nb(OPrf)4Br (2.27 g) light-yellow solid.
;
;
Nb(OEt)aBrz (2.40 g) ; brown, viscous liquid. Nb(OEt)2Bra.CH&OOEt (2.59 g) ; red-brown, viscous liquid. NbOBrs.CHaCOOEt (3.09 g) ; red-brown, viscous liquid. NbOBrs.CHsCOOEt (3.35 g) ; red-brown, viscous liquid.
Nb(OEt)aBr (2.51 g) ; yellow solid.
Molecular formula, yield and state
ACETYL
Disproportionates on heating yielding Nb(OBut)s at 1oo”C/o.5 -
mm.
Disproportionates on heating, yielding Nb(OPr*)b at 110”C/0.5 mm.
-
Disproportionates on heating yielding Nb(OEt)s at 168”C/2.0 mm. Decomposes at 220°C/o.5 mm. Decomposes
Action of heat
19.8
20.1
21.5
22.9
21.1
19.5
19.0
24.2
27.1
IL’b
Analysis
21.3
51.0
17.0
52.4
20.0
20.0
20.6
19.0 22.7
55.9
21.3
51.6
17.2
53.2
19.5
54.9
54.9
46.9
18.2 46.0 51.5
41.2 23.9
40.0
22.6
Br
26.3
Nb
22.7
Br
R. C. MEHROTRA,
352 whereas niobium tetra-alkoxide bium penta-alkoxides : 5Nb(OR)JBr
+
monobromide
derivatives
decompose
P. N. KAPOOR
to give nio-
4Nb(OR)s+NbBrs
Molecular weights of the niobium tetra-alkoxide monochloride derivatives have been determined ebullioscopically in benzene and are found to be dimeric. These derivatives can therefore be assigned the bridge type of structure : (RO)dNb
/c1
L Nb(OR)d
Vl/ (R is Et, Pr” or But) The final products obtained by the reactions of niobium penta-isopropoxide and tert.-butoxide and acetyl chloride and bromide appear to be polymeric, since niobium oxytrichloride, by itself, forms polymeric chains in which the coordination number of niobium is six10 and since in NbOXs.CHaCOOR, the coordination of one additional molecule of organic ester ; this implies a coordination number seven in these compounds, which is now well establisheds. The different halide alkoxides obtained in the above studies exhibit an increasing tendency to add an additional molecule of organic ester as the alkoxide groups are successively replaced by the halide radical. This is understandable as the replacement of the alkoxide group by the more electronegative halide group would tend to decrease the electron density round the niobium atom and thus increase its capacity for acceptance of donor bonds from organic esters. EXPERIMENTAL
The apparatus earlier publicationsll.
and preparation
of reagents
have already
been described
in
Reaction between niobium penta-eth.oxide and acetyl chloride in molar ratio I:I Acetyl chloride (0.59 g) was added to a solution of niobium penta-ethoxide (2.39 g) in benzene (15 g). No heat was produced. The mixture was refluxed for about I h at 8o-90°C. The excess solvent and the ester were evaporated under reduced pressure at go”C/o.5 mm for 3 h. A white, waxy solid (2.30 g), distilling at 168”C/o.6 ,mm, was obtained. Found: Nb, 30.8%; Cl, 11.5%; ethoxy, 58.2%; Mol.wt., 633. Calc. for Nb(OEt)&l: Nb, 30.1%; Cl, 11.5%; ethoxy, 58.4%; Mol.wt., 309. Reaction between niobium penta-ethoxide and hydrogen chloride gas To the niobium penta-ethoxide (2.01 g), benzene (25 g) was introduced. The hydrogen chloride gas was passed slowly for about 6 h, giving a yellow solution. The reaction was found to be exothermic. After removing the excess solvent under reduced pressure at room temperature, a yellow, viscous liquid (1.91 g) was obtained. On heating under reduced pressure, it decomposes. Found: Nb, 32.0%; Cl, 25.0%; ethoxy, 42.8%. Calc. for Nb(OEt)&: Nb, 31.1%; Cl, 23.7%; ethoxy, 45.2%. J. Less-CommonMetals,
IO (1966) 348-353
KEACTIONS
OF NIOBIUM
PENTA-ALKOXIDES
WITH
ACYL
353
HALIDES
ACKNOWLEDGEMENTS
The authors wish to thank the Chemical Society, London, and P.N.K. thanks the C.S.I.R. New Delhi, for fellowship aid.
for financial
support
REFERENCES I H.
FUNK ANDK. NEIDERLANDER,B~V.,~~B
z R. C. MEHROTRA, .j I<. C. MEHROTRA 4 H. C. MEHROTRA 5 R. C. MEHROTRA 6 1I.R. COPLEY, F. 7 8 9 IO
II
(1929) 1688.
J. Ind. Chem. Sot., 30 (195.3) 731. AND R. A. MISRA, Can. J. Chem., 42 (1964) 717. AND R. A. MISRA, J. Ind. Chem. Sot., communicated. AND R. A. MISRA, J, Chem. SIC., (1965) 43. FAIRBROTHER,K.H.GRUNDY AND A.THOMPSON, J. Less-Common
(‘964) 407. U. B. COPLEY, F. FAIRBROTHER AND A. THOMPSON, J. Less-Common Metals, 8 (1965) R. J. H. CLARK,D. L. KEPERT AND R. S. NYHOLM, J. Chem.Soc., (1965) 2877. J. C. MARIGNAC, Ann. Chim. Phys., 4 (1866) 86. II. I:. SANDS, A. ZALKIN AND R. E. ELSON, Acta Crysl.,12 (1959) 21. 12.C. MBHROTRA AND P. N. KAPOOR, J. Less-Common Metals, 7 (1964) 98. j.
/*es+Common
Metals,
IO (1966)
Metals, 6 ~56.
348-353
348
ORGANIC
COMPOUNDS
REACTIONS
(Received
METALS
OF NIOBIUM
OF NIOBIUM
R. C. MEHROTRA Department
OF THE LESS-COMMON
PENTA-ALKOXIDES
WITH
ACYL
HALIDES
AND P. N. KAPOOR
ofChemistry, University qf Rajasthan, Jaipur (India) October
16th, 1965; revised January
rst, 1966)
SUMMARY
Compounds Nb(OEt)dX, and Nb(OEt)zXs.CHsCOOEt Nb(OEt)sXz, Nb(OEt)C14.CH3COOEt, NbOBr3.CH3COOEt (where X is chloride or bromide) have been isolated by the reactions of niobium penta-ethoxide with acetyl chloride and bromide. The reactions of niobium penta-isopropoxide and tert.-butoxide with acyl halides in equimolar ratios yield products of the type Nb(OR)JX; the products with excess of acyl halides corresponds to NbOX3.CH3COOR. However, the reaction in the case of penta-tert.-butoxide and acetyl chloride yielded finally NbO(OAc)o.&l3.25 . CH3COOBut. The reaction of niobium penta-ethoxide with dry hydrogen chloride gas yielded triethoxide dichloride derivative. Only niobium tetra-alkoxide monochloride derivatives could be distilled or sublimed and these were found to be dimeric in boiling benzene.
INTRODUCTION
The synthesis of a number of halide alkoxides of niobium by the niobium penta-alkoxides with acyl halides has been examined. The niobium penta-ethoxide with acetyl chloride in benzene in various molar found to be exothermic and can be represented by the following equations Nb(OEt)s+ Nb(OEt)s
CH3COCl + + zCH3COCl
Nb(OEt)a +3CH3COCl
Nb(OEt)&l+CH3COOEt
+
Nb(OEt)3Cl3 + zCH3COOEt
+
Nb(OEt)zC13.CH3COOEt
+ zCH3COOEt
Nb(OEt)C14.CH3COOEt
+ 3CH3COOEt
Nb(OEt)a + 4CH3COCl + (excess)
reactions of reactions of ratios were :
The compounds, isolated by drying under reduced pressure, were soluble in benzene. Niobium triethoxide dichloride was obtained by passing a slow current of dry hydrogen chloride gas into a benzene solution of niobium penta-ethoxide. A similar product was obtained by FUNK AND NIEDERLANDER~ by the reaction of niobium J. Less-Common
Metals, IO (1966) 348-353
REACTIONS OF NIOBIUM PENTA-ALKOXIDES WITH ACYL HBLIDES
349
pentachloride with ethanol. Similar observations have been reported by MEHROTRA? in the dealcoholation reactions of alkoxides of group IV elements. The reactions of niobium penta-isopropoxide with acetyl chloride in molar ratios of I :I and I : 5 can be represented by the following equations : Nb(OPri)j
+ CHaCOCl + Nb(OPri)&l+
Nb(OPr’):,+CH&OCl (excess)
CHaCOOPri
+ NbOC13 * CH&OOPri
The reaction of niobium penta-tert.-butoxide witn acetyl chloride was complicated. The replacement of the first tert.-butoxide group appears to be straightforward; further replacement becomes slow and does not proceed to completion. The analysis of the final end product when niobium penta-tert.-butoxide was heated with an excess of acetyl chloride corresponds to an empirical formula, ‘NbO(OAc)o.&12.25. CH&OOBut. The niobium oxytrichloride formed initially in the reaction appears to react slowly with tert.-butyl acetate according to the following equation: NbOCla + zCH&OOBut
+
NbO(OAc)Clz.CH&OOBut
+ ButCl
Recently, in a detailed study of the reaction of acetyl chloride with the tert.butoxides of aluminiums, titanium4 and zirconium5, MEHROTRA AND MISRA have reported that final end-products in these reactions also are acetoxy compounds. The reactions of acetyl bromide with niobium penta-ethoxide follow the pattern of the corresponding reactions with acetyl chloride. One salient difference in the products obtained in the reaction of niobium penta-ethoxide and acetyl chloride and bromide is that bromide ethoxide appears to have a greater tendency to change into oxycompounds, and the analyses of the products with reactants in the proportions I : 4 and I : excess, correspond approximately to NbOBra . CH3COOEt. The reactions of acetyl bromide were also studied with niobium penta-isopropoxide and tert.-butoxide. The reactions are straightforward with reactants in equimolar ratio. However, with excess acetyl bromide the products are similar to those obtained in the case of the reaction with niobium penta-ethoxide. This appears to indicate that the niobium oxytribromide formed has a lesser tendency to react with tert.-butyl acetate than has the corresponding oxytrichloride. A perusal of the above results shows that oxygen is abstracted from both excess acetyl chloride and bromide by niobium penta-alkoxides except in the case of niobium penta-ethoxide and acetyl chloride. Recently, FAIRBROTHER and co-workers697 have reported that the reactions of niobium and tantalum pentachlorides with dimethyl and diphenyl sulphoxides and triphenyl phosphine and triphenyl arsine oxides involve the abstraction of oxygen from these ligands. NYHOLM and co-workers8 have shown that prolonged heating of niobium pentachloride and diarsine solution caused complete decomposition and produced two crystalline compounds, NbOCla.diarsine and (NbC14.diarsine)zO. The abstraction of the oxygen in these compounds is another example of the marked avidity of niobium for oxygen as previously reported by MARIGNAC? The easier formation of oxy-niobium ‘compounds is one of the chief chemical differences between niobium and tantalum. Of the new halide alkoxides isolated, the niobium tetra-alkoxide monochloride derivatives alone could be distilled or sublimed without decomposition, J. Less-Common Metals, 10 (1966) 348-353
R. C. MEHROTRA,
350
Y
N
N
N
N
d
N
d
N
*
r.
.E
::
w 8 8 ..
H
Y
CI
c1
B 8
J. Less-Common
Metals,
IO
(1966) 348-353
P. N. KAPOOR
I
6.71
3.25
;; \o S
z z
k’
2.74
Nb(OBut)s
2.57
3 k
m, f E ;
2.13
Nb(OPr*)s
5 p E 8
6.11
0.75
5.72
0.68
1:4
3.28
2.12
2.44
1:3
I.89
I
: excess
I:1
I : excess
I:1
:excess
1:2
1.63
I:1
Molar ratio
PENTA-ALKOXIDES
1.52
(s)
Acetyl bromide
NIOBIUM
I.96
OF
0.88
II
2.28
Nb(OEt)s
Alkoxide (69
REACTIONS
TABLE
Time of refluxing (h)
WITH
BROMIDE
IN
BENZENE
;
NbOBra.CHaCOOBuI brown solid.
Nb(OBut)dBr (2.72 g) light-yellow solid. (3.43 g)
;
NbOBra.CH&OOPri (3.02 g) brown, spongy solid.
Nb(OPrf)4Br (2.27 g) light-yellow solid.
;
;
Nb(OEt)aBrz (2.40 g) ; brown, viscous liquid. Nb(OEt)2Bra.CH&OOEt (2.59 g) ; red-brown, viscous liquid. NbOBrs.CHaCOOEt (3.09 g) ; red-brown, viscous liquid. NbOBrs.CHsCOOEt (3.35 g) ; red-brown, viscous liquid.
Nb(OEt)aBr (2.51 g) ; yellow solid.
Molecular formula, yield and state
ACETYL
Disproportionates on heating yielding Nb(OBut)s at 1oo”C/o.5 -
mm.
Disproportionates on heating, yielding Nb(OPr*)b at 110”C/0.5 mm.
-
Disproportionates on heating yielding Nb(OEt)s at 168”C/2.0 mm. Decomposes at 220°C/o.5 mm. Decomposes
Action of heat
19.8
20.1
21.5
22.9
21.1
19.5
19.0
24.2
27.1
IL’b
Analysis
21.3
51.0
17.0
52.4
20.0
20.0
20.6
19.0 22.7
55.9
21.3
51.6
17.2
53.2
19.5
54.9
54.9
46.9
18.2 46.0 51.5
41.2 23.9
40.0
22.6
Br
26.3
Nb
22.7
Br
R. C. MEHROTRA,
352 whereas niobium tetra-alkoxide bium penta-alkoxides : 5Nb(OR)JBr
+
monobromide
derivatives
decompose
P. N. KAPOOR
to give nio-
4Nb(OR)s+NbBrs
Molecular weights of the niobium tetra-alkoxide monochloride derivatives have been determined ebullioscopically in benzene and are found to be dimeric. These derivatives can therefore be assigned the bridge type of structure : (RO)dNb
/c1
L Nb(OR)d
Vl/ (R is Et, Pr” or But) The final products obtained by the reactions of niobium penta-isopropoxide and tert.-butoxide and acetyl chloride and bromide appear to be polymeric, since niobium oxytrichloride, by itself, forms polymeric chains in which the coordination number of niobium is six10 and since in NbOXs.CHaCOOR, the coordination of one additional molecule of organic ester ; this implies a coordination number seven in these compounds, which is now well establisheds. The different halide alkoxides obtained in the above studies exhibit an increasing tendency to add an additional molecule of organic ester as the alkoxide groups are successively replaced by the halide radical. This is understandable as the replacement of the alkoxide group by the more electronegative halide group would tend to decrease the electron density round the niobium atom and thus increase its capacity for acceptance of donor bonds from organic esters. EXPERIMENTAL
The apparatus earlier publicationsll.
and preparation
of reagents
have already
been described
in
Reaction between niobium penta-eth.oxide and acetyl chloride in molar ratio I:I Acetyl chloride (0.59 g) was added to a solution of niobium penta-ethoxide (2.39 g) in benzene (15 g). No heat was produced. The mixture was refluxed for about I h at 8o-90°C. The excess solvent and the ester were evaporated under reduced pressure at go”C/o.5 mm for 3 h. A white, waxy solid (2.30 g), distilling at 168”C/o.6 ,mm, was obtained. Found: Nb, 30.8%; Cl, 11.5%; ethoxy, 58.2%; Mol.wt., 633. Calc. for Nb(OEt)&l: Nb, 30.1%; Cl, 11.5%; ethoxy, 58.4%; Mol.wt., 309. Reaction between niobium penta-ethoxide and hydrogen chloride gas To the niobium penta-ethoxide (2.01 g), benzene (25 g) was introduced. The hydrogen chloride gas was passed slowly for about 6 h, giving a yellow solution. The reaction was found to be exothermic. After removing the excess solvent under reduced pressure at room temperature, a yellow, viscous liquid (1.91 g) was obtained. On heating under reduced pressure, it decomposes. Found: Nb, 32.0%; Cl, 25.0%; ethoxy, 42.8%. Calc. for Nb(OEt)&: Nb, 31.1%; Cl, 23.7%; ethoxy, 45.2%. J. Less-CommonMetals,
IO (1966) 348-353
KEACTIONS
OF NIOBIUM
PENTA-ALKOXIDES
WITH
ACYL
353
HALIDES
ACKNOWLEDGEMENTS
The authors wish to thank the Chemical Society, London, and P.N.K. thanks the C.S.I.R. New Delhi, for fellowship aid.
for financial
support
REFERENCES I H.
FUNK ANDK. NEIDERLANDER,B~V.,~~B
z R. C. MEHROTRA, .j I<. C. MEHROTRA 4 H. C. MEHROTRA 5 R. C. MEHROTRA 6 1I.R. COPLEY, F. 7 8 9 IO
II
(1929) 1688.
J. Ind. Chem. Sot., 30 (195.3) 731. AND R. A. MISRA, Can. J. Chem., 42 (1964) 717. AND R. A. MISRA, J. Ind. Chem. Sot., communicated. AND R. A. MISRA, J, Chem. SIC., (1965) 43. FAIRBROTHER,K.H.GRUNDY AND A.THOMPSON, J. Less-Common
(‘964) 407. U. B. COPLEY, F. FAIRBROTHER AND A. THOMPSON, J. Less-Common Metals, 8 (1965) R. J. H. CLARK,D. L. KEPERT AND R. S. NYHOLM, J. Chem.Soc., (1965) 2877. J. C. MARIGNAC, Ann. Chim. Phys., 4 (1866) 86. II. I:. SANDS, A. ZALKIN AND R. E. ELSON, Acta Crysl.,12 (1959) 21. 12.C. MBHROTRA AND P. N. KAPOOR, J. Less-Common Metals, 7 (1964) 98. j.
/*es+Common
Metals,
IO (1966)
Metals, 6 ~56.
348-353