- Email: [email protected]
Chemistry of transition-metal nitrogen complexes
P46
PRELIMINARY
COMMUNICATION
BIBLIOGRAPHIE 1 2 3 4 5 6 7 8 9
R. Dabard et G. Jaouen, Tetruhedron Lett., (1969) 3391. R. Dabard, A. Meyer et G. Jaouen, C.R. Acad. Sci. Paris, s&r. C. 268 (1969) 201. A: Meyer, 2 parae. H. NicholIs et M.C. Whiting, J. Chem Sot., (1959) 551. D.A. Brown et J.R. Raju, J. Chem Sot.. A. (1966) 40. E. Mostardini, F. Calderazzo et R. Ercoli, Chim Ihd. (Milan), 42 (1960) 123 1. K. S&l&I, Topics in Stereochemist?y, 1[1967) 39. . G. Jaouer. et L. Tchissambou, $ para%tre. H. FaIk et K. S&l&l, Monatsh. C?zem. 99 (1968) 578.
J. Organometal
Chem,
21(1970)
P43-P46
Preliminary communication Chemistry of transition-metal nitrogen compIexes III*. Reduction of tris-tertiary phosphine cobalt nitrogen complexes
G. SPEIEk and L. MARK6 Research Group for Petrochemistry
of the Hungarian Academy
of Sciences,
Veszpr&m (Hungaryl
(Received November 13th, 1969)
Co(N2)L3 complexes (L = Ph3P1, n-B&P) react with sodium amalgam or n-butyllithium as indicated by the shift of the strong v(N,N) band of the reaction mixture_ Apparently several new complexes are formed depending on the reaction conditions. The observations are summarized in Table 1. The reaction between n-BuLi and Co(Nz)L3 leads to at least two classes of new nitrogen complexes, characterized by u(N,N) bands around 2016-2006 cm-’ and 1904-1864 cm-’ _ The formation of the compounds with the higher v(N,N) values (2016-2006 cm-‘) required less n-BuLi than that of the complexes with lower v(N,N) values. In the case of the triaIky1 phosphine compIexes the former. compounds could be observed only in hexane as solvent and even then their formation was accompanied by a decomposition to cobalt metal. The compounds with lower frequencies (1904-1864 cm-‘) were formed when an excess of n-BuLi was used along with tetrahydrofuran as solvent. The nature of the reactions taking place in the Co(N,)Le + n-BuLi systems can be inferred from the following observations: (a) When n-heptane was used as solvent with the triethylphosphine complex, n-hexane (identified by GLC) was formed. *For Part II, see ref.4 J. Orgunometa.? Chem,
21 (1970) P46-P48
PRELIMINARY
COMMUNICATION
P47
TABLE 1 Starting nitrogen
Reducing agent
Solvent
-
THF THF
V(N,N) (cm-‘)
complex
Co(N2)(Ph
%$Na/Hg (excess)
or
n-BuLi (1 mole)
Co(NZ)(n-Bu3P)g ’ Co(N2)(QP)3
=
n-BuLi (excess)
THF
n-BuLi N-BuLi (excess) n-BuLi n-BuLi (excess)
hexane THF THF hexane hexane THF THF
2093
I-
2040 (sh)
1
2016 19041 2018 2056 2049 1864
.
2059 2014 2050 1866
“These complexes were prepared in situ from CoBr2 (in THF) or Co(acac)2 (in hexane) and the appropriate phosphine under nitrogen by reduction with n-BuLi (2 moles).
(b) When the triphenylphosphine complex was used the band at 2016 cm” is replaced by that at 1904 cm-’ when an additional quantity of n-BuLi is added. This indicates that the compound with v(N,N) of 2016 cm-’ is an intermediate in the formation of that with Y(N,N) of the 1904 cm-’ . The same shifts of z@,N) were also achieved by treating Co(N,)(PPh3) with Kpph2 ‘dioxane in THF, bands appearing at 2014 and I904 cm-‘, respectively, when one or two moles of the phosphide were used. (c) When iodobenzene was added to the mixture obtained from the triphenylphosphine complex, the infrared spectra showed that the original complex was regenerated. The reactions occurring can probably be represented as follcws: . + n -B u L i --z Li(Et,P)Co(N,
Co(N,)(Et,P),
)(Et,P),
+ n-CsH14
(a)
(b)
Co@4Wh PI3 b
K(PhzPICo(N2 XphsP), 3
T;;‘;-
K,(Ph,P),Co(N2)(Ph3P) 3
L@% Wo(N2 flh3 02 +Phi
-Lil
CoW XPh3P)a
(c)
J. OrgunometaL Chem, 21(1970)
P46-P48
P48
PRELIMINARY
COMMUNICATION
Thus the complexes with v(N,N) of 2016-2006 and 1904-1864 cm-’ are thought to have the formula (M) [(Ks P)Co(N, )(RaP), ] and M2 [(Rs P)z CO& XRs P)] , respectively (M = Li, Na, IQ. N,N stretching frequencies of 1866-64 are the lowest values observed for transition metal nitrogen complexes, and indicate a very large contribution from Co+N back bonding. This can be explained by the accufnulation of negative charge in the complexes. Reduction of nitrogen to metal nitrides through metal-nitrogen complexes’ is probably involved in nitrogen furation by the Volpin-Shur systems3. Our observations suggest that the ligands in a nitrogen complex may play a significant part in this reduction by accepting electrons from the reductant and (partly) transferring them through the transition metal to the N2 entity.
REFERENCES 1 G. Speier and L. Mark6, Inorg. Chfm. Actu, 3 (1969) 126. 2 E.E. van Tamelen, R.B. Fechter, SW. Schneller, G. Boche, R.H. Greeley and B. Akermark, L Amer. Cfzem SW., 91 (1969) 1551. 3 M.E. Volpin and V.B. Shur, Narure, 209 (1966) 1236. 4 G. Speier and L. Mark6, Acta Chim. Acad. Sci. Hung., to be published.
J. OrganometaL
Chem,
21(1970)
P46-P48
PRELIMINARY
COMMUNICATION
BIBLIOGRAPHIE 1 2 3 4 5 6 7 8 9
R. Dabard et G. Jaouen, Tetruhedron Lett., (1969) 3391. R. Dabard, A. Meyer et G. Jaouen, C.R. Acad. Sci. Paris, s&r. C. 268 (1969) 201. A: Meyer, 2 parae. H. NicholIs et M.C. Whiting, J. Chem Sot., (1959) 551. D.A. Brown et J.R. Raju, J. Chem Sot.. A. (1966) 40. E. Mostardini, F. Calderazzo et R. Ercoli, Chim Ihd. (Milan), 42 (1960) 123 1. K. S&l&I, Topics in Stereochemist?y, 1[1967) 39. . G. Jaouer. et L. Tchissambou, $ para%tre. H. FaIk et K. S&l&l, Monatsh. C?zem. 99 (1968) 578.
J. Organometal
Chem,
21(1970)
P43-P46
Preliminary communication Chemistry of transition-metal nitrogen compIexes III*. Reduction of tris-tertiary phosphine cobalt nitrogen complexes
G. SPEIEk and L. MARK6 Research Group for Petrochemistry
of the Hungarian Academy
of Sciences,
Veszpr&m (Hungaryl
(Received November 13th, 1969)
Co(N2)L3 complexes (L = Ph3P1, n-B&P) react with sodium amalgam or n-butyllithium as indicated by the shift of the strong v(N,N) band of the reaction mixture_ Apparently several new complexes are formed depending on the reaction conditions. The observations are summarized in Table 1. The reaction between n-BuLi and Co(Nz)L3 leads to at least two classes of new nitrogen complexes, characterized by u(N,N) bands around 2016-2006 cm-’ and 1904-1864 cm-’ _ The formation of the compounds with the higher v(N,N) values (2016-2006 cm-‘) required less n-BuLi than that of the complexes with lower v(N,N) values. In the case of the triaIky1 phosphine compIexes the former. compounds could be observed only in hexane as solvent and even then their formation was accompanied by a decomposition to cobalt metal. The compounds with lower frequencies (1904-1864 cm-‘) were formed when an excess of n-BuLi was used along with tetrahydrofuran as solvent. The nature of the reactions taking place in the Co(N,)Le + n-BuLi systems can be inferred from the following observations: (a) When n-heptane was used as solvent with the triethylphosphine complex, n-hexane (identified by GLC) was formed. *For Part II, see ref.4 J. Orgunometa.? Chem,
21 (1970) P46-P48
PRELIMINARY
COMMUNICATION
P47
TABLE 1 Starting nitrogen
Reducing agent
Solvent
-
THF THF
V(N,N) (cm-‘)
complex
Co(N2)(Ph
%$Na/Hg (excess)
or
n-BuLi (1 mole)
Co(NZ)(n-Bu3P)g ’ Co(N2)(QP)3
=
n-BuLi (excess)
THF
n-BuLi N-BuLi (excess) n-BuLi n-BuLi (excess)
hexane THF THF hexane hexane THF THF
2093
I-
2040 (sh)
1
2016 19041 2018 2056 2049 1864
.
2059 2014 2050 1866
“These complexes were prepared in situ from CoBr2 (in THF) or Co(acac)2 (in hexane) and the appropriate phosphine under nitrogen by reduction with n-BuLi (2 moles).
(b) When the triphenylphosphine complex was used the band at 2016 cm” is replaced by that at 1904 cm-’ when an additional quantity of n-BuLi is added. This indicates that the compound with v(N,N) of 2016 cm-’ is an intermediate in the formation of that with Y(N,N) of the 1904 cm-’ . The same shifts of z@,N) were also achieved by treating Co(N,)(PPh3) with Kpph2 ‘dioxane in THF, bands appearing at 2014 and I904 cm-‘, respectively, when one or two moles of the phosphide were used. (c) When iodobenzene was added to the mixture obtained from the triphenylphosphine complex, the infrared spectra showed that the original complex was regenerated. The reactions occurring can probably be represented as follcws: . + n -B u L i --z Li(Et,P)Co(N,
Co(N,)(Et,P),
)(Et,P),
+ n-CsH14
(a)
(b)
Co@4Wh PI3 b
K(PhzPICo(N2 XphsP), 3
T;;‘;-
K,(Ph,P),Co(N2)(Ph3P) 3
L@% Wo(N2 flh3 02 +Phi
-Lil
CoW XPh3P)a
(c)
J. OrgunometaL Chem, 21(1970)
P46-P48
P48
PRELIMINARY
COMMUNICATION
Thus the complexes with v(N,N) of 2016-2006 and 1904-1864 cm-’ are thought to have the formula (M) [(Ks P)Co(N, )(RaP), ] and M2 [(Rs P)z CO& XRs P)] , respectively (M = Li, Na, IQ. N,N stretching frequencies of 1866-64 are the lowest values observed for transition metal nitrogen complexes, and indicate a very large contribution from Co+N back bonding. This can be explained by the accufnulation of negative charge in the complexes. Reduction of nitrogen to metal nitrides through metal-nitrogen complexes’ is probably involved in nitrogen furation by the Volpin-Shur systems3. Our observations suggest that the ligands in a nitrogen complex may play a significant part in this reduction by accepting electrons from the reductant and (partly) transferring them through the transition metal to the N2 entity.
REFERENCES 1 G. Speier and L. Mark6, Inorg. Chfm. Actu, 3 (1969) 126. 2 E.E. van Tamelen, R.B. Fechter, SW. Schneller, G. Boche, R.H. Greeley and B. Akermark, L Amer. Cfzem SW., 91 (1969) 1551. 3 M.E. Volpin and V.B. Shur, Narure, 209 (1966) 1236. 4 G. Speier and L. Mark6, Acta Chim. Acad. Sci. Hung., to be published.
J. OrganometaL
Chem,
21(1970)
P46-P48