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Extensive N-deprotonation of coordinated amines by organolithium reagents
INORG.
NUCL
CHEM.
LETTERS
Vol.
10,
pp. 405-407,
1974.
Pergamon
Press.
Printed in Great Britain.
EXTENSIVE N-DEPROTONATION OF COORDINATED AMINES BY ORGANOLITHIUM IKEAGF/~TS
W. K. Musket z and Mary J. Lukes Department of Chemistry, University of California., Davis, California, 95616 ( R e c e i v e d 14 J ~ u a ~
1974)
Transition metal complexes of chelated primary and secondary amines, such as Co(en)33+ and Ni(daco)22+ (daco = 1,5-diazacyclooctane), can be highly N-deprotona.ted with organolithium reagents (CH3Li or C4HgLi) in non-aqueous solvents (Et20 or THF) without decomposition. Although there is great interest in reactions of coordinated ligands,(2) and numerous
deprotonation reactions have been carried out,(3,4) in cases
previously reported the conjugate base of a protonic solvent is used as the base (OH-, in H20~ NH 2- in NH3).
Under previous reaction conditions when excess KNH 2
is added to Co(en)33+ in liquid ammonia,(5) a maximum of two protons can be removed to give [Co(en)(en-H)2] +.
By comparison, using CH3Li in THF, up to six protons
can be removed to give [Co(en-2H)3] 3- and subsequently the starting material can be regenerated in > 90% yield by treatment with excess acid.
Actually more than
six protons can be removed from Co(en)33+ with CH3Li , but subsequent treatment with acid does not regenerate the starting material in high yield and some decomposition occurs.
When Ni(daco)22+ is treated with CH3Li in THF~ exhaustive
N-deprotonation is achieved with the removal of all four N-H protons to ~ive Ni(daco-2H)22-. Ni(dach)22+ (dach = 1,4-diazacycloheptane) behaves in a similar manner. Based on the isolation of methane and the almost quantitative reconversion back to the original complex, deprotonation at the N-H groups must o c c u r
405
That
406
ORGANOLITHIUM REAGENTS
Vol. 10, No. 5
the amines are still coordinated after this trea£ment is clear, since regeneration with excess aqueous HCI would have protonated any free ligand and prevented reformation of the complex.
Regeneration of the original complex was confirmed by
comparing the visible absorption spectrum of the complex before and after reaction The shape of the curve was identical and only a slight reduction in the intensity of the band was observed. Co(en)sX s + 6CHsLi
T
THF etheror )
C°(en-2H)sS- + 6CH4 + 6Li+ + 30(-
P
I-IX( aqueous )
X = Cl-, Br-, INi(daco)eY 2 + 4CHsLi
THF or ether
Ni(daco-2H) e- + 4CH 4 + 4Li + + 2YI HX(aqueous)
Ni( daco)2X2
Y = CI04-,BF 4-
The reactions were carried out on a vacuum line by adding the solid complex to a frozen ether solution of the organolithium reagent and then allowing the mixture to warm to room temperature.
Even though the complex is insoluble in
the ether solvent, the deprotonation reaction proceeds smoothly, beginning slowly as the solution liquefies and continuing as the temperature is allowed to increase The course of the reaction is followed by measuring the amount of methane evolved with a Toepler pump.
The reaction can be interrupted at say time either by re-
freezing (-196°C) or by adding aqueous acid. Since Watt and coworkers were able to alkylate [Co(en)(en-H)2] + with methyl iodide,(5) we attempted to carry out similar alkylation reactions.
However, as
yet we are unable to isolate any alkylation products even when we begin with a species corresponding to [Co(en)(en-H)e] +.
It is possible that our complexes
differ from those prepared by Watt(5) in that lithium may replace the hydrogen removed thereby changing the reactivity of the amide group.
In that event a
Vol. 10, No. 5
ORGANOLITHIUM REAGENTS
407
more accurate formulation of this deprotonated species may be the polylithiated species [Co(en(enLi)2] s+ . Although Ni(en)3Cl2,
Cu(en)2Cl 2 and Cu(daco)2(Cl04) 2 react with organo-
lithium reagents, the original starting material could not be recovered in high yield on treatment with acid and decomposition occurs. We wish to thank the NSF for support of this research and Mr. L. Fade, Mr. M. Breckenridge,
and Mr. J. Watkins for carrying out some of the preliminary
deprotonation reactions. REFERENCES
i.
ALEXANDER VON HUMBOLDT FELLOW, (1970-1971).
2.
D. H. BUSCH, Science, 171, 241 (1971).
3-
G.W.
4.
Y. YAMANO, I. MASUDA and K. SHINRA, ibid., 33, 521 (1971); and in preceeding papers.
5.
G. W. WATT, P. W. ALEXANDER, 6483 (1967).
Watt and R. L. HOOD, J. Inor~. and Nuc. Chem., 32, 3359 (1970).
and B. S. MANHAS, J. Amer. Chem. Soc., ~9,
NUCL
CHEM.
LETTERS
Vol.
10,
pp. 405-407,
1974.
Pergamon
Press.
Printed in Great Britain.
EXTENSIVE N-DEPROTONATION OF COORDINATED AMINES BY ORGANOLITHIUM IKEAGF/~TS
W. K. Musket z and Mary J. Lukes Department of Chemistry, University of California., Davis, California, 95616 ( R e c e i v e d 14 J ~ u a ~
1974)
Transition metal complexes of chelated primary and secondary amines, such as Co(en)33+ and Ni(daco)22+ (daco = 1,5-diazacyclooctane), can be highly N-deprotona.ted with organolithium reagents (CH3Li or C4HgLi) in non-aqueous solvents (Et20 or THF) without decomposition. Although there is great interest in reactions of coordinated ligands,(2) and numerous
deprotonation reactions have been carried out,(3,4) in cases
previously reported the conjugate base of a protonic solvent is used as the base (OH-, in H20~ NH 2- in NH3).
Under previous reaction conditions when excess KNH 2
is added to Co(en)33+ in liquid ammonia,(5) a maximum of two protons can be removed to give [Co(en)(en-H)2] +.
By comparison, using CH3Li in THF, up to six protons
can be removed to give [Co(en-2H)3] 3- and subsequently the starting material can be regenerated in > 90% yield by treatment with excess acid.
Actually more than
six protons can be removed from Co(en)33+ with CH3Li , but subsequent treatment with acid does not regenerate the starting material in high yield and some decomposition occurs.
When Ni(daco)22+ is treated with CH3Li in THF~ exhaustive
N-deprotonation is achieved with the removal of all four N-H protons to ~ive Ni(daco-2H)22-. Ni(dach)22+ (dach = 1,4-diazacycloheptane) behaves in a similar manner. Based on the isolation of methane and the almost quantitative reconversion back to the original complex, deprotonation at the N-H groups must o c c u r
405
That
406
ORGANOLITHIUM REAGENTS
Vol. 10, No. 5
the amines are still coordinated after this trea£ment is clear, since regeneration with excess aqueous HCI would have protonated any free ligand and prevented reformation of the complex.
Regeneration of the original complex was confirmed by
comparing the visible absorption spectrum of the complex before and after reaction The shape of the curve was identical and only a slight reduction in the intensity of the band was observed. Co(en)sX s + 6CHsLi
T
THF etheror )
C°(en-2H)sS- + 6CH4 + 6Li+ + 30(-
P
I-IX( aqueous )
X = Cl-, Br-, INi(daco)eY 2 + 4CHsLi
THF or ether
Ni(daco-2H) e- + 4CH 4 + 4Li + + 2YI HX(aqueous)
Ni( daco)2X2
Y = CI04-,BF 4-
The reactions were carried out on a vacuum line by adding the solid complex to a frozen ether solution of the organolithium reagent and then allowing the mixture to warm to room temperature.
Even though the complex is insoluble in
the ether solvent, the deprotonation reaction proceeds smoothly, beginning slowly as the solution liquefies and continuing as the temperature is allowed to increase The course of the reaction is followed by measuring the amount of methane evolved with a Toepler pump.
The reaction can be interrupted at say time either by re-
freezing (-196°C) or by adding aqueous acid. Since Watt and coworkers were able to alkylate [Co(en)(en-H)2] + with methyl iodide,(5) we attempted to carry out similar alkylation reactions.
However, as
yet we are unable to isolate any alkylation products even when we begin with a species corresponding to [Co(en)(en-H)e] +.
It is possible that our complexes
differ from those prepared by Watt(5) in that lithium may replace the hydrogen removed thereby changing the reactivity of the amide group.
In that event a
Vol. 10, No. 5
ORGANOLITHIUM REAGENTS
407
more accurate formulation of this deprotonated species may be the polylithiated species [Co(en(enLi)2] s+ . Although Ni(en)3Cl2,
Cu(en)2Cl 2 and Cu(daco)2(Cl04) 2 react with organo-
lithium reagents, the original starting material could not be recovered in high yield on treatment with acid and decomposition occurs. We wish to thank the NSF for support of this research and Mr. L. Fade, Mr. M. Breckenridge,
and Mr. J. Watkins for carrying out some of the preliminary
deprotonation reactions. REFERENCES
i.
ALEXANDER VON HUMBOLDT FELLOW, (1970-1971).
2.
D. H. BUSCH, Science, 171, 241 (1971).
3-
G.W.
4.
Y. YAMANO, I. MASUDA and K. SHINRA, ibid., 33, 521 (1971); and in preceeding papers.
5.
G. W. WATT, P. W. ALEXANDER, 6483 (1967).
Watt and R. L. HOOD, J. Inor~. and Nuc. Chem., 32, 3359 (1970).
and B. S. MANHAS, J. Amer. Chem. Soc., ~9,