88
M.N. Ackermann et al. / Journal of Organometallic Chemistry 667 (2003) 81ꢁ89
/
The molybdenum chemical shift also shows some
correlation to the 13C shift of the carbonyls of IV.
Because L in cis-M(CO)4L2 affects the carbonyls cis and
trans to it differently, these COs are treated separately in
looking for correlations [24]. Also, because the nitrogen
donor atoms in IV are not equivalent, we use the
average of the chemical shifts for the trans- or cis-
COs. A very good correlation (rꢀ
/
0.987, nꢀ7) exists
/
between d(95Mo) and d(13CO) for the trans-carbonyls
provided that IVh is omitted. The ligand IIh is unique in
having a substituent on the phenyl ring and so may have
different steric effects. There is no correlation between
d(95Mo) and the average cis-13C CO shift or to the
average of all 13C CO shifts. The cis-Mo(CO)4(py-R)2
complexes gave good correlations with d(95Mo) for both
the cis- and trans-13C CO shifts, although the correla-
tion with the cis-carbonyls was not as good as for the
trans [23].The reason for the difference in the two cases
is not clear but may be due to the non-planar ligands in
IV affecting the cis-COs differently than the trans-COs.
Given the correlation of d(13CO) for the trans-carbonyls
to d(95Mo), it is not unexpected that d(13CO) also
The 2-hydrazinopyridine complex cis-Mo(CO)4-
(H2NHNC5H4N) (V) is readily obtained in the same
manner as the 2-PHP complexes (IV) and has similar
physical and spectroscopic properties (Tables 3, 5 and
7). Addition of activated MnO2 to a solution of V in
CH2Cl2 results in an immediate color change from
yellow to deep blue from which a dark blue solid was
isolated. Unfortunately, slow decomposition of this
solid, even at ꢃ25 8C, precluded obtaining a satisfac-
/
tory elemental analysis. However, spectroscopic data are
consistent with the formation of the (2-pyridyl)diazene
complex cis-Mo(CO)4(HNÄ/NC5H4N) (VI). The in-
creased IR carbonyl-stretching frequencies in hexane
of 2035m, 1959s, 1949m, and 1902m cmꢃ1 are similar to
those of the 2-PAP complexes (II) [5]. In the proton
NMR in CDCl3, the only signals present are ones
attributable to the pyridyl protons plus a singlet at
correlates well to the Hammett sigma parameter (rꢀ
/
0.960, nꢀ5).
/
Since the Hammett sigma parameter correlates well
with both the sum of the carbonyl-stretching frequencies
and the molybdenum chemical shift, these two measures
should correlate well with each other. Indeed, complexes
14.69 ppm, which lies within the range found for the NÄ
/
NH proton in known (2-pyridyl)diazene complexes
[26,27,29,30].
IVaꢁ
defined, give an excellent correlation (rꢀ
The correlation is still good if complex IVh is added (rꢀ
0.949, nꢀ6) but is poor if IVg and IVi, whose ligands
/
IVe, for which a Hammett sigma parameter is
/
0.990, nꢀ5).
/
/
References
/
have a 6-methyl group, are included. A similar pattern
was noted in the 2-PAP complexes (II), although the
adverse effect on the correlation is much greater for IV.
[1] G.K. Rauth, S. Pal, D. Das, C. Sinha, A.M.Z. Slawin, J.D.
Woollins, Polyhedron 20 (2001) 363.
[2] R.A. Krause, K. Krause, Inorg. Chem. 19 (1980) 2600.
[3] R.A. Krause, K. Krause, Inorg. Chem. 21 (1982) 1714.
[4] S. Goswami, A.R. Chakravarty, A. Chakravorty, Inorg. Chem.
20 (1981) 2246.
Finally, there is a strong correlation (rꢀ
/
0.978, nꢀ7)
/
between d(95Mo) for IV and d(95Mo) for II if complexes
IIh and IVh are omitted. These are the only complexes in
which the ligand has a substituent on the phenyl ring
and so may create different steric effects. This would be
consistent with the suggestion from the 13C-NMR that
there may be a difference in the ability of the phenyl
group to undergo free rotation in IIh and IVh.
[5] M.N. Ackermann, W.G. Fairbrother, N.S. Amin, C.J. Deodene,
C.M. Lamborg, P.T. Martin, J. Organomet. Chem. 523 (1996)
145.
[6] D.F. Shriver, M.A. Drezdzon, The Manipulation of Air-sensitive
Compounds, 2nd ed., Wiley, New York, 1986.
[7] N. Campbell, A.W. Henderson, D. Taylor, J. Chem. Soc. (1953)
1281.
[8] M.N. Ackermann, J.W. Naylor, E.J. Smith, G.A. Mines, N.S.
Amin, M.L. Kerns, C. Woods, Organometallics 11 (1992) 1919.
[9] H. Beyer, H.-J. Haase, W. Wildgrube, Chem. Ber. 91 (1958) 247.
[10] R.B. King, in: J.J. Eisch, R.B. King (Eds.), Transition Metal
Compounds: Organometallic Syntheses, vol. 1, Academic Press,
New York, 1965.
3.4. Complexes derived from 2-hydrazinopyridine
Synthesis of the 2-PHP complexes (IV) and their facile
oxidation to the 2-PAP complexes stimulated us to
undertake the synthesis of the analogous complexes of
2-hydrazinopyridine and 2-diazenopyridine. Complexes
of 2-diazenopyridine have only recently been reported
but none are known in which the metal center has a zero
[11] M.N. Ackermann, S.R. Kiihne, P.A. Saunders, C.E. Barnes, S.C.
Stallings, H. Kim, C. Woods, M. Lagunoff, Inorg. Chim. Acta
334 (2002) 193.
[12] M.N. Ackermann, L.C. Hardy, Y.Z. Xiao, D.J. Dobmeyer, J.A.
Dunal, K. Felz, S.A. Sedman, K.F. Alperovitz, Organometallics 5
(1986) 966.
[13] N.B. Chapman, J. Shorter, Correlation Analysis in Chemistry,
Plenum Press, New York, 1978.
oxidation state [25ꢁ30].
/