Synthesis and structure of the phosphinophosphide niobocene complex Cp2Nb(PPh2)(PHPh2)

Article abstract of DOI:10.1016/S0277-5387(98)00408-2

The phosphinophosphido niobocene complex Cp₂Nb(PHPh₂)(PPh₂) (2) was prepared by deprotonation of the cationic diphosphino complex [Cp₂Nb(PHPh₂)₂]Cl (3). Complex 2 is thermally unstable and readily dissociates phosphine to give the ortho-metallated complex Cp₂Nb(PHPhC₆H₄-). Crystal structure determination of 2 supported its formulation as the phosphinophosphido compound. The Nb-P(1) (phosphino) bond length is 2.524(2) A and Nb-P(2) (phosphido) bond length is 2.610(2) A.

Full text of DOI:10.1016/S0277-5387(98)00408-2

Polyhedron 18 (1999) 1159–1162
Synthesis and structure of the phosphinophosphide niobocene complex
Cp2Nb(PPh2)(PHPh2)
Georgii I. Nikonova, , Dmitry A. Lemenovskii , Konstantin Yu. Dorogov , Andrei V. Churakov
a
a
b
*
aChemistry Department, Moscow State University, Vorob’evy Gory, 119899 Moscow, Russia
bInstitute of General and Inorganic Chemistry, RAS, Leninsky prosp. 31, 117907 Moscow, Russia
Received 21 July 1998; accepted 10 November 1998
Abstract
The phosphinophosphido niobocene complex Cp2Nb(PHPh2)(PPh2) (2) was prepared by deprotonation of the cationic diphosphino
complex [Cp2Nb(PHPh2)2]Cl (3). Complex 2 is thermally unstable and readily dissociates phosphine to give the ortho-metallated
complex Cp2Nb(PHPhC6H42). Crystal structure determination of 2 supported its formulation as the phosphinophosphido compound. The
˚
˚
Nb–P(1) (phosphino) bond length is 2.524(2) A and Nb–P(2) (phosphido) bond length is 2.610(2) A.
rights reserved.
1999 Elsevier Science Ltd. All
Recently there has been an increased interest in the
chemistry of early transition metal phosphido complexes
[1–49]. Much of this interest has focused on the known
ability of these compounds to form stable phosphido-
bridged bimetallic complexes [19–34], although the high
reactivity of the phosphido moiety in other reactions was
also studied [35–47]. We were interested to prepare
complexes with neighbouring hydrido and phosphido
ligands that could exhibit a richer reactivity. We found that
Cp2Nb(PPh2)(HPPh2) (2), that has more explicit NMR
features.
1. Results and discussion
The easiest route to complex 2 is via deprotonation of
the cationic diphosphino complex [Cp2Nb(PHPh2)2]Cl
(3). Three-step synthesis of the latter compound, using the
insertion/deprotonation technique (Scheme 1), has been
previously reported [48]. Now we report that complex 3
can be conveniently prepared in a one-pot synthesis shown
below (1).
the
cationic
dihydridephosphino
complex
[Cp2NbH2(PHPh2)]1 can be deprotonated to give initially
the dihydridephosphido complex Cp2NbH2(PPh2) that
rapidly rearranges into Cp2NbH(PHPh2), whereas the
analogous tantalocene complex Cp2TaH2(PPh2) was found
to be quite stable towards further transformations [48,49].
The closely related diphosphorus substituted hydride com-
plexes could, in principle, also exist in two isomeric forms,
namely, Cp2NbH(PPh2)2 (A) and Cp2Nb(PPh2)(HPPh2)
(B). For the methyl ring-substituted compound
(1)
9
Cp2Nb(PPh2)(HPPh2) (1) (Cp95C5H4Me) only the form
B was observed. However, the nonequivalence of the
cyclopentadienyl protons in 1 and its little thermal stability
complicated further studies. Therefore, we set out to
prepare the unsubstituted analogue of 1, i.e. complex
Apparently, this reaction proceeds via the same steps
which are shown in Scheme 1. However, the strength of
the base NEt3 is not sufficient to effect significant deproto-
nation of 3 to give 2, i.e. in this case, the equilibrium in (2)
is shifted towards 3. Complete deprotonation of 3 was
achieved using aqueous NaOH. Complex 2 was isolated as
1
*
oily red crystals and is highly air sensitive. The H NMR
Corresponding
author.
Fax:
17-095-932-88-46;
e-mail:
nikonov@org.chem.msu.su
spectrum of 2 obtained
0277-5387/99/$ – see front matter
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1999 Elsevier Science Ltd. All rights reserved.

1160
G.I. Nikonov et al. / Polyhedron 18 (1999) 1159–1162
Scheme 1.
˚
tion. The Nb–P bond distances are 2.524(2) A for the
˚
niobium–phosphino bond and 2.610(2) A for the niobium–
phosphido bond. In the only one previously reported
phosphido
derivative
of
niobocene,
complex
(2)
Cp2Nb(CO)(PPhPri), the Nb–P bond lengths are 2.644(3)
˚
˚
A and 2.622(3) A for two crystallographically independent
molecules [50]. The reported niobium–phosphino bond
˚
lengths lay in the range 2.462–2.579 A [51]. The P(1)–
Nb–P(2) bond angle is 87.70(5)8, close to the value found
for other d2 niobocene derivatives and the calculated value
for the d2 complexes Cp2MXY [52]. The P–H bond
at 400 MHz shows only one signal for the cyclopen-
tadienyl protons that appears as a triplet at 4.42 ppm
(JP–H 51.8 Hz), consistent with the formation of the form
A. However, a hydride signal was not observed. Also, the
31P NMR spectrum of 2 shows the presence of two
nonequivalent phosphorus centres with the resonances at
66.2 and 5.9 ppm, expected for the form B. The latter
formulation was further supported by a X-ray diffraction
study. Therefore, the triplet signal for the cyclopentadienyl
protons is in fact composed of two overlapping doublets
due to coupling to two nonequivalent phosphorus atoms
with similar JP–H and the structure of 2 is analogous to 1.
We expected that the phosphino and phosphido centres in 2
could be in a degenerated exchange, probably, via the
diphosphidohydride form A. This exchange would result in
a coalescence of the phosphorus resonances at higher
temperatures. However, complex 2 was found to be
thermally unstable, like its methyl substituted analogue 1.
Even at room temperatures it releases free HPPh2 to give
the previously described ortho-metallated product
Cp2Nb(PHPh–C6H4 2) [4a].
˚
distance of 1.24(5) A observed in 2 is somewhat shorter
˚
than the sum of covalent radii (1.40 A) and also than the
The formulation of 2 as the phosphidophosphine deriva-
tive B was confirmed by an X-ray structure determination.
The molecular structure of 2 is shown in Fig. 1 and
selected bond lengths and angles are given in Tables 2 and
3. Complex 2 has a disubstituted metallocene geometry,
typical for d2 niobocene complexes of the type Cp2NbXL.
The cyclopentadienyl rings are in an eclipsed conforma-
Fig. 1. Molecular structure of 2. Displacement parameters are shown at
50% probability level. Hydrogen atoms (except H(01)) are omitted for
clarity.

G.I. Nikonov et al. / Polyhedron 18 (1999) 1159–1162
1161
Table 1
spectra were referenced to the residual protiosolvent
(relatively to SiMe4). 31P NMR spectra were referenced to
85% H3PO4 as external standard. Cp2NbH3 was prepared
by the modified procedure as reported earlier [48]. ClPPh2
was purchased from Merck.
Crystal data and details of data collection and structure refinement for 2
Empirical formula
Temperature
Wavelength
Crystal system
Space group
Unit cell dimensions
C34H31NbP2.C7H8.0.5C7H8
183(2)
0.71069 A
˚
monoclinic
P2(1)/n
a512.847(3) A
b514.134(3) A
c520.124(4) A
˚
˚
˚
2.1. Preparation of [Cp2Nb(PHPh2 )2 ]Cl (3)
In a typical experiment 2 equivalents of ClPPh2 are
added to a toluene solution containing 1 equivalent of
Cp2NbH3 and 1.1 equivalent of NEt3 under rapid stirring.
The mixture becomes red and an orange precipitate of
complex 2 deposits. The mixture is stirred overnight to
ensure the completeness of the reaction. The solution is
filtered and the residue is washed by toluene until the
washings are almost colourless. The material thus obtained
is contaminated by ClHNEt3 which can be removed by
washing with THF. Alternatively, it can be used as
obtained to make complexes 2 and [Cp2Nb(PPh2)2]Li by
treatment with NaOH or excess BuLi, respectively. This
procedure was used to make 3 on a 1–3 g scale. Example
experiment: Cp2NbH3 (1.07 g, 4.73 mmol)/NEt3 (0.73 ml,
5.20 mmol)/ClPPh2 (1.70 ml, 9.46 mmol)/toluene (60
ml).
b590.72(3)
3653.8(14) A
4
1.76 to 20.148
212#h#12, 0#k#13, 219#l#0
3
˚
Volume
Z
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
refinement method
Rint
Data/restraines/parameters
Goodness -of-fit on F2
Final R indices (all data 3121)
R indices [2487 with I.2s(I)]
Largest diff. peak and hole
3221
3121
full-matrix-least-squares on F2
.0404
3118/17/425
1.065
R1 50.0506, wR2 50.0949
R1 50.0337, wR2 50.0891
3
˚
0.528 and 20.339 e/A
Table 2
˚
Selected bond lengths (A) for 2
Nb–P(1)
2.524(2)
1.833(5)
1.843(5)
2.342(5)
2.404(5)
2.408(5)
2.370(5)
2.348(6)
1.24(5)
Nb–P(2)
2.610(2)
1.831(5)
1.852(5)
2.402(6)
2.374(5)
2.358(5)
2.387(5)
2.406(6)
P(1)–C(21)
P(1)–C(11)
Nb–C(1)
Nb–C(2)
Nb–C(3)
Nb–C(4)
Nb–C(5)
P1–H(01)
P(2)–C(31)
P(2)–C(41)
Nb–C(6)
Nb–C(7)
Nb–C(8)
Nb–C(9)
Nb–C(10)
2.2. Preparation of [Cp2Nb(PHPh2 )(PPh2 )] (2)
0.848 g (1.34 mmol) of [Cp2Nb(PHPh2)2]Cl suspended
in 30 ml of toluene was treated by 25 ml of 0.2 M aqueous
NaOH. The mixture is intensively stirred with intensive
grinding of the oily material formed until all the oil is
dissolved in organic phase. The toluene solution is then
separated and dried in vacuo. Recrystallization from ether
of the material formed gives red oily crystals of 2. The
yield: 0.347 g (0.584 mmol, 43%). Thermal instability of
this compound prevented obtaining satisfactory combus-
tion analysis data.
Table 3
Selected bond angles for 2
P(1)–Nb–P(2)
87.70(5)
119.2(2)
99.0(2)
C(21)–P(1)–C(11)
C(11)–P(1)–Nb
C(31)–P(2)–Nb
Nb–P1–H01
100.1(2)
119.8(2)
112.3(2)
C(21)–P(1)–Nb
C(31)–P(2)–C(41)
C(41)–P(2)–Nb
1H NMR (toluene-d8): 6.9–7.6 (m, 20, Ph), 6.14 (half of
doublet, 0.5, P–H), 4.42 (t, J(P–H)51.8 Hz, 10, Cp). 31
P
113.2(2)
118(2)
h1Hj NMR (toluene-d8): 5.9 (bs, PHPh2), 66.2 (bs, PPh2).
P–H bond found in the phosphinobromide complex
i
˚
2.3. Crystal structure determination
Cp2NbBr(PHPr2) (1.51 A) [51]. This difference can be
attributed to the influence of the Ph rings. In the cationic
diphosphite complex [Cp2Nb(PH(OR)2)2]Cl the coopera-
tive action of charge and electron-withdrawing alkoxy
Red crystals of 2 were grown from toluene-d8 solution
on keeping at 2268C for three months. The crystal was
covered by oil and mounted on an Enraf–Nonius CAD-4
diffractometer at 2908C. Crystallographic data are given
in Table 1. The unit cell parameters were determined using
25 accurately centered reflections, two reflections were
measured every 2 h for orientation and decay control. The
data were corrected for Lorentz and polarization effects.
The structure was solved by direct methods [53] and
refined by full-matrix least squares procedures [54]. Two
toluene solvate molecules were found, one of them oc-
cupies a special position and is disordered. This molecule
was refined only isotropically without hydrogen atoms. In
˚
groups results in much shorter P–H bonds of 1.0 A [51].
2. Experimental
All manipulations were carried out in vacuo using
conventional Schlenk techniques. Solvents were dried over
sodium or sodium benzophenone ketyl and distilled into
the reaction vessel by high vacuum gas phase transfer.
NMR spectra were recorded on a Varian VXR-400 spec-
1
trometer (1H, 400.0 MHz; 31P 161.9 MHz). H NMR

1162
G.I. Nikonov et al. / Polyhedron 18 (1999) 1159–1162
[22] J. Ho, D.W. Stephan, Organometallics 10 (1991) 3001.
[23] D.G. Dick, D.W. Stephan, Organometallics 10 (1991) 2811.
[24] J. Ho, D.W. Stephan, Organometallics 11 (1992) 1014.
[25] J. Ho, Z. Hou, R.J. Drake, D.W. Stephan, Organometallics 12 (1993)
3145.
[26] S. Xin, H.G. Woo, J.F. Harrod, E. Samuel, A.-M. Lebuis, J. Am.
Chem. Soc. 119 (1997) 5307.
[27] U. Senff, S. Kurz, E. Hey-Hawkins, Z. Anorg. Allg. Chem. 623
(1997) 1255.
[28] R. Payne, J. Hachgenei, G. Fritz, D.Z. Fenske, Naturforsch 41(b)
(1986) 1535.
[29] E. Hey-Hawkins, S. Kurz, J. Sieler, G. Baum, J. Organomet. Chem.
486 (1995) 229.
[30] G.I. Nikonov, L.G. Kuzmina, D.A. Lemenovskii, J. Organomet.
Chem. 496 (1995) 187.
the final cycles of refinement, all other non-hydrogen
atoms were refined with anisotropic displacement parame-
ters. Hydrogen atoms were found from Fourier difference
syntheses and were refined isotropically using a ‘‘riding’’
model. The location and magnitude of the residual electron
density was of no chemical significance.
Full details of crystallographic study including the
atomic coordinates and displacement coefficients, hydro-
gen atom parameters, and a full list of bond lengths and
angles for 2 have been deposited as supplementary data
with the CCDS, deposition number 102173.
[31] G. Bonnet, O. Lavastre, G. Boni, J.C. Leblanc, C. Moise, CR Acad.
Sci. Paris Ser. 319(2) (1994) 1293.
Acknowledgements
[32] G. Bonnet, O. Lavastre, J.-C. Leblanc, C. Moise, New J. Chem. 12
(1988) 551.
[33] C. Barre, M.M. Kubicki, J.-C. Leblanc, C. Moise, Inorg. Chem. 29
(1990) 5244.
The Russian Foundation for Basic Research is acknowl-
edged for financial support of this work.
[34] O. Lavastre, G. Bonnet, G. Boni, M.M. Kubicki, C. Moise, J.
Organomet. Chem. 547 (1997) 141.
[35] D.M. Roddick, B.D. Santarsiero, J.E. Bercaw, J. Am. Chem. Soc.
107 (1985) 4670.
References
[36] G.A. Vaughan, G.L. Hillhouse, A.L. Rheingold, Organometallics 8
(1989) 1760.
[1] R.T. Baker, J.F. Whitney, S.S. Wreford, Organometallics 2 (1989)
1049.
[2] R.T. Baker, P.J. Krusic, T.H. Tulip, J.C. Calabrese, S.S. Wreford, J.
Am. Chem. Soc. 105 (1983) 6763.
[3] R.T. Baker, J.C. Calabrese, R.L. Harlow, I.D. Williams, Or-
ganometallics 12 (1993) 830.
¨
[37] E. Lindner, M. Stangle, W. Hiller, R. Fawzi, Chem. Ber. 122 (1989)
823.
¨
[38] E. Lindner, M. Stangle, W. Hiller, R. Fawzi, Chem. Ber. 121 (1988)
1421.
[39] S.R. Wade, M.G.H. Wallbridge, G.R. Willey, J. Chem. Soc., Dalton
Trans. (1983) 2555.
[4] P.J. Domaille, B.M. Foxman, T.J. McNeese, S.S. Wreford, J. Am.
Chem. Soc. 102 (1980) 4114.
[40] L. Weber, G. Meine, R. Boese, N. Augart, Organometallics 6 (1987)
2484.
¨
[5] H. Kopf, V. Richtering, J. Organomet. Chem. 346 (1988) 355.
[6] Z. Hou, T.L. Breen, D.W. Stephan, Organometallics 12 (1993) 3158.
[41] H.-U. Reisacher, W.F. McNamara, E.N. Duesler, R.T. Painer,
Organometallics 16 (1997) 449.
[7] J.W. Ho, R. Rousseau, D.W. Stephan, Organometallics 14 (1995)
4030.
¨
[42] W.F. McNamara, E.N. Duesler, R.T. Painer, J.V. Ortiz, P. Koller, H.
[8] Z. Hou, T.L. Breen, A. Ozarowski, D.W. Stephan, Inorg. Chem. 14
(1995) 3126.
¨
Noth, Organometallics 5 (1985) 380.
[43] W. Malisch, K. Hindahl, R. Schemm, Chem. Ber. 125 (1992) 2027.
[44] E. Hey-Hawkins, F. Lichtenberg, Z. Naturforsch. 48(b) (1993) 951.
¨
[9] H. Kopf, V.Z. Richtering, Naturforsch 43(b) (1988) 1653.
[10] T.L. Breen, D.W. Stephan, Organometallics 15 (1996) 4223.
[11] T.L. Breen, D.W. Stephan, Organometallics 15 (1996) 4509.
[12] A.H. Cowley, D.M. Giolando, C.M. Nunn, M. Pakulski, D. Wes-
tmoreland, N.C. Norman, J. Chem. Soc., Dalton Trans. (1988) 2127.
[13] J.B. Bonanno, P.T. Wolczanski, E.B. Lobkovsky, J. Am. Chem. Soc.
116 (1994) 11159.
[14] E. Hey-Hawkins, S. Kurz, J. Organomet. Chem. 479 (1994) 125.
[15] E. Hey-Hawkins, M. Lappert, J.A. Awood, S.G. Bott, J. Chem. Soc.,
Dalton Trans. (1988) 939.
¨
[45] E. Hey-Hawkins, U. Muller, Z. Naturforsch. 44(b) (1989) 1538.
[46] E. Hey-Hawkins, F. Lichtenberg, Chem. Ber. 125 (1992) 1815.
[47] E. Hey, M. Lappert, J.A. Awood, S.G. Bott, Polyhedron 7 (1988)
2083.
[48] G.I. Nikonov, D.A. Lemenovskii, J. Lorberth, Organometallics 13
(1994) 3127.
[49] G.I. Nikonov, L.G. Kuzmina, P. Mountford, D.A. Lemenovskii,
Organometallics 14 (1995) 3588.
[50] G. Bonnet, M.M. Kubicki, C. Moise, R. Lazzaroni, P. Salvador, G.
Vitulli, Organometallics 11 (1992) 964.
[16] D. Fenske, A. Grissinger, E. Hey-Hawkins, J. Magull, Z. Anorg.
Allg. Chem. 595 (1991) 57.
[51] G.I. Nikonov, L.G. Kuzmina, Yu.K. Grishin, D.A. Lemenovskii,
J.A.K. Howard, J. Organomet. Chem. 547 (1997) 183.
[52] J.W. Lauher, R. Hoffmann, J. Am. Chem. Soc. 98 (1976) 1729.
[53] G.M. Sheldrick, SHELXS-86, Program for crystal structure de-
[17] E. Hey-Hawkins, S. Kurz, G. Baum, Z. Naturforsch. 50(b) (1995)
239.
[18] Yu.A. Ol’dekop, Knizhnikov VZ Zh. Obshch. Chem. 51 (1981) 723.
[19] M.Y. Chlang, S. Gambarrotta, F. van Bolhuls, Organometallics 7
(1988) 1864.
¨
¨
termination. Universitat Gottingen, 1986.
[20] B.L. Benac, R.A. Jones, Polyhedron 8 (1989) 177.
[21] J. Ho, D.W. Staphan, Inorg. Chem. 33 (1994) 4595.
[54] G.M. Sheldrick, SHELXL-97, Program for crystal structure refine-
¨
¨
ment. Universitat Gottingen, 1997.