Synthesis and characterization of the first Niobocene germyl complexes and reactivity of triphenylsilyl-, triphenylgermyl-, and triphenylstannylniobocene derivatives. X-ray molecular structures of d0 Nb(η5-C5H4SiMe3) 2(H)2(EPh3) (E = Ge, Sn)

Article abstract of DOI:10.1021/om971001b

Thermal treatment of Nb(η⁵-C₅H₄SiMe₃) ₂(H)₃ (1) with the appropriate organogermanium hydrides (HGeR₃) and HSnPh₃ gives the corresponding niobocene germyl hydrides Nb(η⁵-C₅H₄SiMe₃) ₂(H)₂(GeR₃), GeR₃=GePh₃ (2), GePh₂H (3), GeEt₃ (4), Ge(C₆H₁₃)₃ (5), GeⁱAm₃ (ⁱAm = CH₂CH₂CH(CH₃)₂) (6), Ge(C₆H₁₃)₂Cl (7), GeⁱAm₂Cl (8), Ge(C₆H₁₃)₂H (9), GeⁱAm₂H (10), and Nb(η⁵-C₅H₄SiMe₃) ₂(H)₂(SnPh₃) (11) in good yields. Spectroscopic data indicate the presence of only one of the two possible structural isomers in which the germyl or stannyl group is in the equatorial plane with a symmetrical structure. Reactivity studies on the series Nb(η⁵-C₅H₄SiMe₃) ₂(H)₂(ER₃), E = Si (12), Ge (2), Sn (11), were carried out. 12 reacts with H₂ to give 1, but 2 and 11 were unreactive toward this reagent. Furthermore, a similar behavior was observed with CO and CN(2,6-Me₂C₆H₃). Thus, 12 reacts with these reagents to give rise, after elimination of HSiPh₃, to Nb(η⁵-C₅H₄SiMe₃) ₂(H)(CO) and Nb(η⁵-C₅H₄SiMe₃) ₂-(H)(CN(2,6-Me₂C₆H₃)), respectively, while 2 and 11 do not react. Reactions of 12 with HGePh₃ and HSnPh₃ and of 2 with HSnPh₃ gave σ-bond metathesis products, but no reactions were observed between 2 and HSiPh₃ or between 11 and HSiPh₃ or 11 and HGePh₃. The kinetics of these processes have been studied by ¹H NMR spectroscopy and indicated the following reactivity trends Nb-SiPh₃ > Nb-GePh₃ > Nb-SnPh₃ for the different processes considered. The X-ray molecular structures of 2 and 11 were established by diffraction studies The two isostructural complexes show a bent-sandwich coordination with the two hydrides flanking either side of the Nb-Ge and Nb-Sn bonds (2.710(1), 2.830(1) A? in 2 and 11, respectively).

Full text of DOI:10.1021/om971001b

Organometallics 1998, 17, 1523-1529
1523
Syn th esis a n d Ch a r a cter iza tion of th e F ir st Niobocen e
Ger m yl Com p lexes a n d Rea ctivity of Tr ip h en ylsilyl-,
Tr ip h en ylger m yl-, a n d Tr ip h en ylsta n n yln iobocen e
Der iva tives. X-r a y Molecu la r Str u ctu r es of d 0
Nb(η5-C5H4SiMe3)2(H)2(EP h 3) (E ) Ge, Sn )
A. Antin˜olo,† F. Carrillo-Hermosilla,† A. Castel,‡ M. Fajardo,§
J . Ferna´ndez-Baeza,† M. Lanfranchi,| A. Otero,*,† M. A. Pellinghelli,| G. Rima,‡
J . Satge´,‡ and E. Villasen˜or†
Departamento de Quı´mica Inorga´nica, Orga´nica y Bioquı´mica, Universidad de
Castilla-La Mancha, Campus Universitario de Ciudad Real, 13071 Ciudad Real, Spain,
Departamento de Quı´mica Inorga´nica, Universidad de Alcala´, Campus Universitario,
28871 Alcala´ de Henares, Spain, Dipartimento di Chimica Generale ed Inorganica,
Chimica Analitica, Chimica Fisica, Universita` degli Studi di Parma, Centro di Studio per la
Strutturistica Diffractometrica del CNR, Viale delle Scienze 78, 43100 Parma, Italy, and
Laboratoire de Chimie des Organomine´raux-URA 477, Universite´ Paul Sabatier,
Route de Narbonne, 118, 31062 Toulouse Cedex, France
Received November 13, 1997
Thermal treatment of Nb(η5-C5H4SiMe3)2(H)3 (1) with the appropriate organogermanium
hydrides (HGeR3) and HSnPh3 gives the corresponding niobocene germyl hydrides Nb(η5-
C5H4SiMe3)2(H)2(GeR3), GeR3dGePh3 (2), GePh2H (3), GeEt3 (4), Ge(C6H13)3 (5), GeiAm3 (iAm
) CH2CH2CH(CH3)2) (6), Ge(C6H13)2Cl (7), GeiAm2Cl (8), Ge(C6H13)2H (9), GeiAm2H (10),
and Nb(η5-C5H4SiMe3)2(H)2(SnPh3) (11) in good yields. Spectroscopic data indicate the
presence of only one of the two possible structural isomers in which the germyl or stannyl
group is in the equatorial plane with a symmetrical structure. Reactivity studies on the
series Nb(η5-C5H4SiMe3)2(H)2(ER3), E ) Si (12), Ge (2), Sn (11), were carried out. 12 reacts
with H2 to give 1, but 2 and 11 were unreactive toward this reagent. Furthermore, a similar
behavior was observed with CO and CN(2,6-Me2C6H3). Thus, 12 reacts with these reagents
to give rise, after elimination of HSiPh3, to Nb(η5-C5H4SiMe3)2(H)(CO) and Nb(η5-C5H4SiMe3)2-
(H)(CN(2,6-Me2C6H3)), respectively, while 2 and 11 do not react. Reactions of 12 with
HGePh3 and HSnPh3 and of 2 with HSnPh3 gave σ-bond metathesis products, but no reactions
were observed between 2 and HSiPh3 or between 11 and HSiPh3 or 11 and HGePh3. The
1
kinetics of these processes have been studied by H NMR spectroscopy and indicated the
following reactivity trends Nb-SiPh3 > Nb-GePh3 > Nb-SnPh3 for the different processes
considered. The X-ray molecular structures of 2 and 11 were established by diffraction
studies. The two isostructural complexes show a bent-sandwich coordination with the two
hydrides flanking either side of the Nb-Ge and Nb-Sn bonds (2.710(1), 2.830(1) Å in 2 and
11, respectively).
In tr od u ction
we recently prepared4 several niobocene silyl complexes
Nb(η5-C5H4SiMe3)2(H)2(SiR3). We wanted to prepare a
series of metallocene niobium derivatives with silyl,
germyl, and stannyl ligands to compare their chemical
Early transition metal d0 complexes containing bonds
with group 14 elements have received special attention
in the past few years. In particular, research on d0
metal silyl complexes has revealed a number of inter-
esting reactivity patterns, such as migratory insertions
of unsaturated substrates into metal-silicon bonds1 and
σ-bond metathesis processes.2 In recent years, there has
been mounting evidence that the oxidative addition of
organosilicon hydrides to coordinatively unsaturated
hydride group 5 metal complexes is a successful method
for preparing d0 metal complexes.3 Using this method,
(1) Selected references: (a) Campion, B. K.; Falk, J .; Tilley, T. D. J .
Am. Chem. Soc. 1987, 109, 2049. (b) Arnold, J .; Tilley, T. D. J . Am.
Chem. Soc. 1987, 109, 3318. (c) Elsner, F. H.; Tilley, T. D.; Rheingold,
A.L.; Geib, S. J . J . Organomet. Chem. 1988, 358, 169. (d) Arnold, J .;
Tilley, T. D.; Rheingold, A. L.; Geib, S. J .; Arif, A. M. J . Am. Chem.
Soc. 1989, 111, 149. (e) Roddick, D. M.; Heyn, R. H.; Tilley, T. D.
Organometallics 1989, 8, 324. (f) Arnold, J .; Engeler, M. P.; Elsner, F.
H.; Heyn, R. H.; Tilley, T. D. Organometallics 1989, 8, 2284. (g)
Campion, B. K.; Heyn, R. H.; Tilley, T. D. J . Am. Chem. Soc. 1990,
112, 2011. (h) Woo, H.-G.; Tilley, T. D. J . Organomet. Chem. 1990,
393, C6. (i) Campion, B. K.; Heyn, R. H.; Tilley, T. D. Inorg. Chem.
1990, 29, 4355.
† Universidad de Castilla-La Mancha.
‡ Universite´ Paul Sabatier.
(2) Selected references: (a) Tilley, T. D. Inorg. Chem. 1990, 10, 37.
(b) Harrod, J . F.; Mu, Y.; Samuel, E. Polyhedron 1991, 11, 1239. (c)
Corey, J . Advances in Silicon Chemistry; Larson, G., Ed.; J AI Press:
Greenwich, CT, 1991; Vol. 1, p 327.
§ Universidad de Alcala´.
| Universita` degli Studi di Parma.
S0276-7333(97)01001-7 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/15/1998

1524 Organometallics, Vol. 17, No. 8, 1998
Antin˜olo et al.
and physical properties. For the niobocene chemistry,
Green et al.5 prepared the stannyl complexes Nb(η5-
C5H5)2(H)2(SnR3) by reaction of [{Nb(η5-C5H5)2(H)2Lix]
with the appropriate SnR3Cl reagents. To complete the
series of analogous d0 niobocene silyl, germyl, and
stannyl complexes we have started studies focused on
the preparation of the corresponding d0 niobocene
germyl derivatives. Here, we report the results con-
cerning the synthesis and characterization of the first
niobocene germyl complexes Nb(η5-C5H4SiMe3)2(H)2-
(GeR3) as well as the reactivity trends for a series of
analogous Nb(η5-C5H4SiMe3)2(H)2(EPh3) (E ) Si, Ge, Sn)
complexes in hydrogenolysis and σ-bond metathesis
reactions.
drance in its approach to the metal center in the
oxidative addition of the organogermanium hydride
reagent. Similarly, the diorganogermanium hydride
(HGe(mes)2)2 containing a Ge-Ge bond did not react
with 1 in refluxing toluene. As far as we know, this is
the first time that d0 early transition metal germyl
complexes have been prepared by oxidative addition of
organogermanium hydrides to coordinatively unsatur-
ated hydride substrates. Previously, several germyl
derivatives of the group 4 metals, actinides, or scandium
have been described6 by reaction of germyllithium
reagents with the appropriate haloderivatives. Com-
plexes 2-11 were characterized spectroscopically. The
NMR data suggest that only the symmetrical isomer of
these complexes is present in solution. The cyclopen-
tadienyl rings are equivalent, showing two broad reso-
nances (see Experimental Section) for an A2B2 spin
system in the 1H NMR spectra, which indicates a
symmetrical disposition on the niobium center with a
rapid rotation of the ER3 moiety around the Nb-E bond.
In addition, the 13C NMR spectra show the three
expected resonances for the cyclopentadienyl carbon
atoms (see Experimental Section). We conclude that the
thermodynamically more favorable symmetrical isomer
(see eq 1) was obtained for all of the germyl and stannyl
complexes. Similar NMR spectral behavior was found
for the analogous niobocene silyl complexes.4 The IR
spectra of 2-11 show ν(Nb-H) at ca. 1750 cm-1, and
in addition, the spectra of 3, 9, and 10, which contain
hydrogen on the germyl moieties, exhibit ν(Ge-H) as a
medium-sized intensity band at ca. 1900 cm-1 (see
Experimental Section). The 1H NMR spectra show
resonances due to the hydride ligands at ca. -4.0 ppm
as broad signals, and these values are at similar
chemical shifts as those reported for the equivalent
hydride ligands in Nb(η5-C5H4SiMe3)2(H)2(SiR3)4 (SiR3
) SiPh3 (12)). On the basis of the 29Si NMR data, we
established the classical nature of these silyl hydrides.
In the germyl and stannyl complexes, both the NMR
and the structural data support a classical or nonclas-
sical hydrido germyl or stannyl structure. Solid-state
X-ray molecular structure determination of complexes
2 and 11 was carried out. Views of complexes 2 and 11
are shown in Figure 1 together with the atomic-
numbering scheme. Selected bond distances and angles
are listed in Table 1. The coordination around the Nb
atom can be described as a distorted tetrahedron with
the vertexes occupied by the two Cp′ ring centroids and
the two hydrides. The E atom interacts (Nb-Ge )
2.710(1) Å, Nb-Sn ) 2.830(1) Å) with the Nb atom,
roughly bisecting the H1T-Nb-H2T angle (H1T-Nb-
H2T ) 107(3)°, Ge-Nb-H1T ) 56(2)°, and Ge-Nb-
H2T ) 51(2)° in 2 (H1T-Nb-H2T ) 120(3)°, Sn-Nb-
H1T ) 65(2)°, and Sn-Nb-H2T ) 55(2)° in 11). The
coordination environment is of pseudo-C2 symmetry
with the 2-fold axis passing through the Nb-E bond.
This coordination is very similar to that found in the
parent Nb(η5-C5H4SiMe3)2(H)2(SiPh2H),4 with pseudo-
Resu lts a n d Discu ssion
The reaction between Nb(η5-C5H4SiMe3)2(H)3 (1) and
several organogermanium hydrides, HGeR3, and HSn-
Ph3 in toluene at 65 °C gives the corresponding monoger-
myl and -stannyl complexes (eq 1), GeR3dGePh3 (2),
GePh2H (3), GeEt3 (4), Ge(C6H13)3 (5), GeiAm3 (iAm )
CH2CH2CH(CH3)2) (6), Ge(C6H13)2Cl (7), GeiAm2Cl (8),
Ge(C6H13)2H (9), GeiAm2H (10) and SnPh3 (11). The
reaction may proceed via reductive elimination of H2 to
give the 16e coordinatively unsaturated Nb(η5-C5H4-
SiMe3)2H complex and subsequent oxidative addition of
HER3 to give a closed-shell 18e configuration in the
germyl and stannyl dihydride derivatives. This method
was previously employed in the synthesis of several
tantalocene silyl hydride derivatives3b,d,e and some
related niobocene hydride complexes.3b,f,4 Complexes
2-11 were isolated as air-sensitive microcrystalline
materials. No reaction was observed between 1 and
HGe(mes)2H, mes ) 2,4,6-trimethylphenyl, even when
the reaction mixture was refluxed in toluene for several
hours. We propose that the more sterically demanding
germyl moiety should encounter greater steric hin-
(3) (a) Allison, J . S.; Aylett, B. J .; Colquhoun, H. M. J . Organomet.
Chem. 1976, 112, 67. (b) Curtis, M. D.; Bell, L. G.; Buttler, W. M.
Organometallics 1985, 4, 701. (c) Berry, D. H.; J iang, Q. J . Am. Chem.
Soc. 1987, 109, 6211. (d) Aitken, C.; Barry, J . P.; Gauvin, F.; Harrod,
J . F.; Malek, A.; Rousseau, D. Organometallics 1989, 8, 1732. (e) J iang,
Q.; Carroll, P. J .; Berry, D. H. Organometallics 1991, 10, 3648. (f)
Green, M. L. H.; Hughes, A. K. J . Organomet. Chem. 1996, 506, 221.
(4) Antin˜olo, A.; Carrillo, F.; Fajardo, M.; Otero, A.; Lanfranchi, M.;
Pellinghelli, M. A. Organometallics 1995, 14, 1518.
7
C2 symmetry, and in Nb(η5-C5H5)2(H)3 with pseudo-Cs
symmetry. The Nb-CE distances in 2 and 11 compare
well with those reported for the latter two compounds
(6) (a) Kingston, B. M.; Lappert, M. F. J . Chem. Soc., Dalton Trans.
1972, 69. (b) Nolan, S. P.; Porchia, M.; Marks, T. J . Organometallics
1991, 10, 1450. (c) Woo, H.-G.; Freeman, W. P.; Tilley, T. D. Organo-
metallics 1992, 11, 2198.
(5) (a) Green, M. L. H.; Hughes, A. K.; Mountford, P. J . Chem. Soc.,
Dalton Trans. 1991, 1407. (b) Green, M. L. H.; Hughes, A. K.;
Mountford, P. J . Chem. Soc., Dalton Trans. 1991, 1699.

Niobocene Germyl Complexes
Organometallics, Vol. 17, No. 8, 1998 1525
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) (w ith Esd ’s in P a r en th eses) for Com p ou n d s 2
a n d 11a
2
11
Nb-CE1
Nb-CE2
Nb-H1T
Nb-H2T
Nb-E
2.074(7)
2.078(7)
1.58(5)
2.064(9)
2.074(8)
1.62(5)
1.69(6)
1.72(6)
2.710(1)
2.000(8)
2.000(8)
1.976(8)
1.861(8)
1.863(10)
1.856(10)
1.875(8)
1.859(9)
1.852(9)
1.868(9)
1.847(8)
2.24(5)
2.830(1)
2.128(9)
2.192(10)
2.177(10)
1.839(10)
1.836(11)
1.842(11)
1.860(11)
1.849(10)
1.865(11)
1.841(10)
1.812(10)
2.59(5)
E-C17
E-C23
E-C29
Si1-C1
Si1-C6
Si1-C7
Si1-C8
Si2-C9
Si2-C14
Si2-C15
Si2-C16
E‚‚‚H1T
E‚‚‚H2T
2.11(6)
2.31(6)
CE1-Nb-CE2
CE1-Nb-H1T
CE1-Nb-H2T
CE2-Nb-H1T
CE2-Nb-H2T
H1T-Nb-H2T
E-Nb-CE1
E-Nb-CE2
E-Nb-H1T
E-Nb-H2T
Nb-E-C17
138.1(3)
100(2)
104(2)
102(2)
102(2)
139.5(4)
101(2)
106(2)
96(2)
102(2)
107(3)
120(3)
113.1(2)
108.7(2)
56(2)
112.0(3)
108.5(3)
65(2)
51(2)
55(2)
118.9(2)
113.5(2)
115.4(2)
99.7(3)
102.8(3)
104.3(3)
119.3(3)
115.1(2)
115.6(3)
98.7(4)
102.2(4)
103.3(4)
Nb-E-C23
Nb-E-C29
C17-E-C23
C17-E-C29
C23-E-C29
a
E ) Ge (2), Sn (11), and CE1 and CE2 are the centroids of
the C1‚‚‚C5 and C9‚‚‚C13 cyclopentadienyl rings, respectively.
range for the values retrieved from the Cambridge
Structural Database System (CSDS) files,8 are not
considered to be significantly different. To our knowl-
edge, the germyl complex is the first structurally
characterized complex with a Nb-Ge bond. The Nb-
Sn bond length agrees very well with the mean value
retrieved from CSDS (2.833(9) Å). On the basis of the
Nb, Si, Ge, and Sn covalent radii (1.34, 1.11, 1.22, and
1.41 Å, respectively), we can hypothezise that the Nb-E
bond strengths are in following order Nb-Sn > Nb-
Ge > Nb-Si (dobs ) 2.830(1) (11), 2.710(1) (2), 2.616-
(3)4 Å; dcalc ) 2.75, 2.56, and 2.45 Å; ∆(dobs - dcalc) )
0.08, 0.15, and 0.17 Å in 11, 2, and Nb(η5-C5H4SiMe3)2-
(H)2(SiPh2H),4 respectively). The coordination around
the E atoms shows a distorted tetrahedral geometry due
to the steric hindrance between the Ph‚‚‚Ph and the
Ph‚‚‚Cp′ rings.
F igu r e 1. ORTEP drawings of complexes 2 (a, top), and
11 (b, bottom), with the atomic-labeling scheme. The
thermal ellipsoids are at the 30% probability level.
with the 3 esd criteria. The Nb, E, H1T, and H2T atoms
are coplanar (maximum deviation 0.04(5) Å for H2T in
2 and 0.0032(8) Å for Nb in 11), and their weighted
least-squares plane is almost perpendicular to the plane
defined by the Nb atom and the two centroids of the
Cp′ rings (91(1)° (2) and 92(1)° (11)). The two bent Cp′
rings, which are nearly staggered (mean torsion angles
values 28.3(8)° (2) and 27.4(10)° (11)) with the two SiMe3
groups trans to each other, form a dihedral angle of
42.8(3)° (2) and 41.8(4)° (11) and are bound to the Nb
atom in the symmetric conventional η5-fashion (Nb-
CCp′ ranges 2.375(8)-2.411(7), 2.375(8)-2.423(8) Å in
2 and 2.350(10)-2.418(9), 2.366(9)-2.427(9) Å in 11).
The two hydride ligands were clearly located in each
structure, and the Nb-H bond lengths (1.58(5), 1.69(6)
Å in 2 and 1.62(5), 1.72(6) Å in 11), which fall in the
Reactivity of Niobocen e Com plexes with -SiP h 3,
-GeP h 3, a n d -Sn P h 3 Moieties. A toluene solution
of 12 reacts at room temperature with CO (1 atm) over
48 h to give the hydride-carbonyl complex Nb(η5-C5H4-
SiMe3)2(H)(CO)9 and HSiPh3 in 100% yield. No reaction
of 2 and 11 with CO, under similar experimental
(7) Wilson, R. D.; Koetzle, T. F.; Hart, D. W.; Kvick, A.; Tipton, D.
L.; Bau, R. J . Am. Chem. Soc. 1977, 99, 1775.
(8) Allen, F. H.; Bellard, S.; Brice, M. D.; Cartwright, B. A.;
Doubleday, A.; Higgs, H.; Hummelink, T.; Hummelink-Peters, B. G.;
Kennard, O.; Motherwell, W. Acta Crystallogr., Sect. B 1979, 35, 2331.
(9) Antin˜olo, A.; Fajardo, M.; J alo´n, F.; Lo´pez-Mardomingo, C.;
Otero, A.; Sanz-Bernabe´, C. J . Organomet. Chem. 1989, 369, 187.

1526 Organometallics, Vol. 17, No. 8, 1998
Antin˜olo et al.
Sch em e 1
Ta ble 2
Ea
conditions, was observed after 48 h. A similar behavior
was found in the reactions with CN(2,6-Me2C6H3).
Thus, 12 reacts with this isonitrile in toluene to give,
over 48 h at room temperature, the hydride-isonitrile
derivative Nb(η5-C5H4SiMe3)2(H)(CN(2,6-Me2C6H3)10 and
HSiPh3 in 100% yield, while no reaction was observed
with 2 and 11. These results indicate that complex 12
is more reactive toward CO and CN(2,6-Me2C6H3) than
complexes 2 and 11. Furthermore, it is noteworthy that
the reaction of 12 with these π-acid ligands proceeds
with elimination of HSiPh3, without insertion, to give
a silaacyl derivative, as found previously for other d0
M-Si bonds.1c-g,i,6c Hydrogenolysis reactions were also
studied. These reactions provide convenient routes to
the corresponding hydrides from the appropriate d0
transition metal alkyl and silyl derivatives.1a,e,11 Thus,
the silyl complex 12 reacts at room temperature with
hydrogen (3 atm) in toluene over 48 h to afford the
trihydride derivative 1 in 30% yield along with HSiPh3.
In contrast, no reaction was observed for 2 and 11 under
similar experimental conditions. These results indicate
that the Nb-Si bond is more reactive toward hydro-
genolysis than the Nb-Ge and Nb-Sn bonds in these
complexes. Finally, the reactivity of silyl-, germyl-, or
stannyl-containing niobocene complexes toward the
HEPh3, E ) Si, Ge, Sn, reagents in σ-bond metathesis
reactions of d0 Nb-E bonds with E-H σ bonds have
been studied. The reactions were monitored by 1H NMR
spectroscopy. Complex 12 reacts at 40 °C with HGePh3
or HSnPh3 over 1.5 h in toluene-d8 solution to afford
the σ-bond metathesis products 2 or 11 and HSiPh3,
respectively (eq 2 and 3; 100% conversion in both
processes). In addition, a similar σ-bond metathesis
experi- 104kapp
T
∆Hq
∆Sq
ment
(s-1
)
(K) (kcal mol-1) (kcal mol-1) (kcal mol-1 K-1
)
1
5
3
2
333
328
323
23.9
27.6
36.1
23.3
3.10-3
0.1 318
0.5 313
2
3
16
333
328
323
318
313
363
358
26.9
35.3
9.10-3
9
5
2
1
4
2
23.10-3
0.7 353
0.6 351
0.5 348
analogous experimental conditions, between 2 and
HSiPh3 or between 11 and HSiPh3 or HGePh3.
Kinetic studies on these σ-bond metathesis processes
have been carried out by following the reactions as a
1
function of time and temperature by H NMR spectros-
copy. The experiments using 1, 2, and 12 with HEPh3
were carried out under pseudo-first-order conditions,
with respect to the niobocene species, by using a high
initial concentration of HEPh3.12 Values of the apparent
pseudo-first-order rate constants, kapp, at five temper-
ature values were obtained for the different processes.
The kapp values satisfactorily fit the Arrhenius plot, kapp
) A exp(-Ea/RT), and the Ea values for the different
reactions were calculated (Table 2). The Eyring plot,
ln(kapp/T) against 1/T (kapp ) (kT/h)exp(-∆Hq/RT)exp-
(∆Sq/R)), gives the activation parameters ∆Hq and ∆Sq
for the different reactions (Table 2). A possible mech-
anism for these processes is shown in Scheme 1, which
corresponds to a consecutive reaction with a reversible
step.4 This mechanism was previously proposed for the
reactions of 1 with several π-acid ligands and olefins,
i.e., reaction of 1 with styrene to give the corresponding
hydride-styrene species.14 A similar mechanism was
also proposed15 for a ligand-displacement process in
Nb(η5-C5H4SiMe3)2(H)2(SiPh3) + HGePh3 f
Nb(η5-C5H4SiMe3)2(H)2(GePh3) + HSiPh3 (2)
Nb(η5-C5H4SiMe3)2(H)2(SiPh3) + HSnPh3 f
Nb(η5-C5H4SiMe3)2(H)2(SnPh3) + HSiPh3 (3)
(11) (a) J ordan, R. F.; Bajgur, C. S.; Dasher, W. E.; Rheingold, A. L.
Organometallics 1987, 6, 1042. (b) Wochner, F.; Brintzinger, H. H. J .
Organomet. Chem. 1986, 309, 65. (c) Gell, K. I.; Posin, B.; Schwartz,
J .; Williams, G. M. J . Am. Chem. Soc. 1982, 104, 1846. (d) Lin, Z.;
Marks, T. J . J . Am. Chem. Soc. 1987, 109, 7979.
reaction was observed when 2 was heated at 75 °C with
HSnPh3 over 1.5 h in toluene-d8 solution (eq 4; 100%
conversion). However, no reaction was found, under
(12) See, for example: (a) Espenson, J . H. Chemical Kinetics and
Reaction Mechanisms, 1st ed.; McGraw-Hill: New York, 1981; p 76.
(b) Wilkins, R. G. Kinetics and Mechanism of Reactions of Transition
Metal Complexes, 2nd ed.; VCH: Weinheim, 1991; p 11.
(13) See, for example: (a) Kemp, W. NMR in Chemistry. A Multi-
nuclear Introduction; McMillan: London, 1986. (b) Sandstro¨m, J .
Dynamic NMR Spectroscopy; Academic Press: London, 1982.
(14) Antin˜olo, A.; Carrillo, F.; Garc´ıa-Yuste, S.; Otero, A. Organo-
metallics 1994, 13, 2761.
Nb(η5-C5H4SiMe3)2(H)2(GePh3) + HSnPh3 f
Nb(η5-C5H4SiMe3)2(H)2(SnPh3) + HGePh3 (4)
(10) Antin˜olo, A.; Carrillo-Hermosilla, F.; Fajardo, M.; Garc´ıa-Yuste,
S.; Otero, A.; Camanyes, S.; Maseras, F.; Moreno, M.; Lledo´s, A.; Lluch,
J . M. J . Am. Chem. Soc. 1997, 119, 6107.

Niobocene Germyl Complexes
Organometallics, Vol. 17, No. 8, 1998 1527
the following values:18 D(Nb-H) ) 63.8 kcal mol-1
D(Si-H) ) 90 kcal mol-1, and D(Ge-H) ) 82 kcal mol-1
,
.
∆H2q = D(Nb-H) + D(Nb-Si) - D(Si-H) (6)
∆H3q = D(Nb-H) + D(Nb-Ge) - D(Ge-H) (7)
Bond dissociation enthalpies of 53.3 and 53.6 kcal mol-1
are found for Nb-Si and Nb-Ge, respectively, indicat-
ing that a similar bond strength for both Nb-E bonds
in complexes 12 and 2 must be considered.
Because complex 11 (see experiment 3, Scheme 1)
results from an irreversible reaction of 1, 2, or 12 with
HSnPh3, it was not possible to evaluate the value of
D(Nb-Sn) by using the equilibrium method. However,
if we consider the term ∆H as the major contribution
in the equation ∆G ) ∆H - T∆S, because ∆S is lower,
we can evaluate D(Nb-Sn) from eq 8. Thus, ∆H3, the
∆H3 = D(Nb-Ge) + D(Nb-H) + D(Sn-H) -
D(Nb-Sn) - D(Nb-H) - D(Ge-H) (8)
enthalpy for the reaction in eq 4, must be <0 in a
irreversible process. With these considerations, a value
of D(Nb-Sn) > 45 kcal mol-1 was obtained.
F igu r e 2. Energy diagram for the σ-bond metathesis
processes.
Thus, our analysis was focused on bond-dissociation
enthalpies, considering the same D(Nb-H) value for the
different niobocene complexes. Factors such as solva-
tion energies essentially canceled, and a comparison of
solution-phase Nb-E bond strengths with those of gas-
phase E-H bonds have been made.19 Despite these
disadvantages, the qualitative trends are clear. In
conclusion, we have shown that the silyl-, germyl-. and
stannyl-containing niobocene complexes have compa-
rable D(Nb-E) values. However, the experimental
results indicate the reactivity trend Nb-SiPh3 > Nb-
GePh3 > Nb-SnPh3 for the σ-bond metathesis pro-
cesses. This behavior can be rationalized in terms of
differences in reactant and product bond strenghts (see
Scheme 1). Thus, in experiment 1, the energy required
to break two Nb-H bonds is supplied by formation of a
strong H-H bond and a similar driving force is likely
to account for the results of experiments 2 and 3, where
the energy required to break the Nb-H and Nb-Si or
Nb-Ge bonds is compensated by formation of relatively
strong H-Si and H-Ge bonds. This explanation has
been postulated by Tilley et al.6c to rationalize the
reactivity trends of silyl, germyl, and stannyl d0 zir-
conocene complexes in σ-bonds metathesis reactions
which parallel those found in the niobium system. In
an analogous way, the reactivity trend observed for the
complexes in the hydrogenolysis processes can be ra-
tionalized.
cobalt complexes. It is noteworthy that for analogous
metathesis processes of group 4 d0 M-E σ-bonds,6c
concerted four-center transition states have been pro-
posed. However, in the group 5 d0 niobocenes, this is
not possible since an empty orbital is not available on
the niobium center to form the σ-bond metathesis
transition state.
Absolute bond dissociation enthalpies are typically
difficult to determine. One technique for determining
a limit for absolute bond dissociation enthalpies by
kinetic methods involves measuring ∆Hq for a reaction,
such as that proposed in Scheme 1. If the barrier for
the reverse reaction is sufficiently low, perhaps between
2 and 5 kcal mol-1, ∆Hq provides a reasonable estimate
for the bond-dissociation energies.16 This is shown
schematically in the energy diagram of Figure 2.
Since the appropriate X-H bond strengths are known,
we can use ∆Hq to estimate the Nb-X bond dissociation
enthalpies. Thus, from experiment 1 (see Scheme 1),
assuming that ∆Hq corresponds (in accordance with the
proposed mechanism) to the dissociation of two Nb-H
bonds and the consequent formation of an H2 molecule,
eq 5 allows us to estimate the value of mean bond-
dissociation enthalpy of the Nb-H bond, D(Nb-H), as
63.8 kcal mol-1, using a value of 104 kcal mol-1 for the
bond dissociation enthalpy of H2, D(H2).17
∆H1q = 2D(Nb-H) - D(H2)
(5)
Con clu d in g Rem a r k s
Likewise, the bond dissociation enthalpies for the
Nb-Si, D(Nb-Si), and Nb-Ge bonds, D(Nb-Ge), can
be estimated from eqs 6 and 7, which correspond to
experiments 2 and 3, respectively (see Scheme 1), using
This study has revealed that niobocene germyl and
stannyl hydrides Nb(η5-C5H4SiMe3)2(H)2(ER3), E ) Ge,
Sn, can be easily prepared from reaction of the trihy-
(18) Bond dissociation enthalpies D(Si-H) and D(Ge-H) were
estimated in the compounds Me3E-H: J ackson, R. A. J . Organomet.
Chem. 1979, 166, 17.
(19) (a) Martinho Simoes, J . A.; Beauchamp, J . L Chem. Rev. 1990,
90, 629. (b) Schaller, C. P.; Cummins, C. C.; Wolczanski, P. T. J . Am.
Chem. Soc. 1996, 118, 591. (c) J ones, W. D.; Feher, F. J . J . Am. Chem.
Soc. 1984, 106, 1650.
(15) J anowicz, A. H.; Bryndza, H. E.; Bergman, R. G. J . Am. Chem.
Soc. 1981, 103, 1516.
(16) Stoutland, P. O.; Bergman, R. G.; Nolan, S. P.; Hoff, C. D.
Polyhedron 1988, 7, 1429.
(17) Berkowitz, J .; Ellison, G. B.; Gutman, D. J . Phys, Chem. 1994,
98, 2744.

1528 Organometallics, Vol. 17, No. 8, 1998
Antin˜olo et al.
(s, 2H, Nb-H). 13C NMR (300 MHz, C6D6): δ 0.52 (SiMe3),
94.61 (C1), 90.84, 93.27 (C5H4), 22.35, 22.94, 31.14, 32.08, 41.01
(Ge(iAm)3).
dride Nb(η5-C5H4SiMe3)2(H)3 with the appropriate HER3
reagents. Reactivity studies on the Nb(η5-C5H4SiMe3)2-
(H)2(EPh3) species in hydrogenolysis and σ-bond me-
tathesis processes indicate a reactivity trend Nb-SiPh3
> Nb-GePh3 > Nb-SnPh3. On the basis of data
obtained from a 1H NMR study at different tempera-
tures, bond-dissociation enthalpies, D(Nb-E), have been
estimated for these species, and similar values were
found for all complexes. The results indicate that the
differences in product stabilities in the processes are
probably responsible for the reactivity trend found.
7: pale pink crystals, 70% yield. IR (Nujol) ν(Nb-H): 1736
cm-1 1H NMR (200 MHz, C6D6): δ 0.14 (s, 18H, SiMe3), 4.80
.
(m, 4H, C5H4), 5.11 (m, 4H, C5H4), 1.35 (m, 20H, Ge((CH2)5-
CH3)2Cl), 0.38 (t, 6H, Ge((CH2)5CH3)2Cl), -3.89 (s, 2H, Nb-
H). 13C NMR (300 MHz, C6D6): δ 0.95 (SiMe3), 98.64 (C1), 92.9,
95.06 (C5H4), 23.48, 26.71, 32.46, 32.63, 34.07 (Ge((CH2)5CH3)2-
Cl), 14.89 (Ge((CH2)5CH3)2Cl). Anal. Calcd for C28H54NbSi2-
GeCl: C, 54.85; H, 8.98. Found: C, 54.68; H, 8.77.
8: pale pink crystals, 73% yield. IR (Nujol) ν(Nb-H): 1757
cm-1 1H NMR (200 MHz, C6D6): δ 0.14 (s, 18H, SiMe3), 4.49
.
(m, 4H, C5H4), 5.11 (m, 4H, C5H4), 0.60-1.60 (m, 22H,
Ge(iAm)2Cl), -3.89 (s, 2H, Nb-H). 13C NMR (300 MHz,
C6D6): δ 0.90 (SiMe3), 98.63 (C1), 92.88, 95.06 (C5H4), 23.09,
31.74, 29.61, 35.62 (Ge(iAm)2Cl). Anal. Calcd for C26H50NbSi2-
GeCl: C, 53.37; H, 8.72. Found: C, 53.61; H, 8.63.
Exp er im en ta l Section
Gen er a l P r oced u r es. All operations were performed
under an inert atmosphere using standard vacuum-line
(Schlenk) techniques. Solvents were purified by distillation
from the appropriate drying agents before use. NMR spectra
were obtained on a Varian Unity FT-300 and Varian Gemini
FT-200 instruments. IR spectra were recorded as Nujol mulls
9: brown oil, 78% yield. IR (Nujol): ν(Nb-H) 1717 cm-1
,
ν(Ge-H) 1913. 1H NMR (200 MHz, C6D6): δ 0.17 (s, 18H,
SiMe3), 4.26 (m, 4H, C5H4), 4.49 (m, 4H, C5H4), 1.38 (m, 20H,
Ge((CH2)5CH3)2H), 0.82 (t, 6H, Ge((CH2)5CH3)2H), -4.32 (s, 2H,
Nb-H). 13C NMR (300 MHz, C6D6): δ 0.89 (SiMe3), 96.21 (C1),
91.25, 93.72 (C5H4), 23.40, 27.91, 32.29, 33.19, 34.07 (Ge((CH2)5-
CH3)2H), 14.82 (Ge((CH2)5CH3)2H).
between CsI plates (in the region between 4000 and 200 cm-1
)
on a Perkin-Elmer PE 883 IR spectrophotometer. Elemental
analyses were performed on a Perkin-Elmer 2400 microana-
lyzer. Nb(η5-C5H4SiMe3)2(H)3 was prepared as described
earlier.20
10: brown oil, 82% yield. IR (Nujol): ν(Nb-H) 1749 cm-1
,
ν(Ge-H) 1907. 1H NMR (200 MHz, C6D6): δ 0.16 (s, 18H,
SiMe3), 4.26 (m, 4H, C5H4), 4.98 (m, 4H, C5H4), 0.80-1.65 (m,
22H, Ge(iAm)2H), -4.37 (s, 2H, Nb-H). 13C NMR (300 MHz,
C6D6): δ 0.96 (SiMe3), 96.35 (C1), 91.17, 93.25 (C5H4), 23.35,
32.00, 20.79, 36.94 (Ge(iAm)2H).
P r ep a r a tion of Nb(η5-C5H4SiMe3)2(H)2(GeR3) (GeR3
)
GeP h 3 (2), GeP h 2H (3), GeEt3(4), GeHexyl3 (5), GeiAm 3
(6), GeHexyl2Cl (7), GeiAm 2Cl (8), GeHexyl2H (9), GeiAm 2H
(10)). To a solution of Nb(η5-C5H4SiMe3)2(H)3 (1; 300 mg, 0.81
mmol) in 25 mL of toluene was added R3GeH (0.81 mmol) by
syringe. The solution was warmed to 65 °C and stirred for 3
h. The resulting solution was filtered and evaporated to
dryness. The brown oily residue was extracted with 20 mL of
ethanol. After concentration and cooling, white or pale crystals
were obtained for compounds 2, 3, 7, and 8.
Nb(η5-C5H4SiMe3)2(H)2(Sn P h 3) (11). To a solution of
Nb(η5-C5H4SiMe3)2(H)3 (1; 300 mg, 0.81 mmol) in 25 mL of
toluene was added Ph3SnH (0.81 mmol) by syringe. The
solution was warmed to 65 °C and stirred for 3 h. The
resulting solution was filtered and evaporated to dryness. The
oily residue was extracted with 20 mL of ethanol. After
concentration and cooling, white crystals were obtained.
11: white crystals, 88% yield. IR (Nujol) ν(Nb-H): 1756
2: white crystals, 90% yield. IR (Nujol) ν(Nb-H): 1760
cm-1 1H NMR (200 MHz, C6D6): δ 0.04 (s, 18H, SiMe3), 4.28
.
(m, 4H, C5H4), 5.00 (m, 4H, C5H4), 7.50 (m, 15H, GePh3), -3.48
(s, 2H, Nb-H). 13C NMR (300 MHz, C6D6): δ 0.14 (SiMe3),
97.81 (C1), 92.30, 95.51 (C5H4), 126.50, 129.41, 135.98, 150.63
(GePh3). Anal. Calcd for C34H43NbSi2Ge: C, 60.66; H, 6.39.
Found: C, 60.34; H, 6.07.
cm-1 1H NMR (200 MHz, C6D6): δ 0.01 (s, 18H, SiMe3), 4.34
.
(m, 4H, C5H4), 4.96 (m, 4H, C5H4), 7.50 (m, 15H, SnPh3), -4.44
(s, 2H, Nb-H). 13C NMR (300 MHz, C6D6): δ 0.193 (SiMe3),
95.92 (C1), 90.34, 92.75 (C5H4), 127.84, 128.00, 137.46, 149.62
(SnPh3). Anal. Calcd for C34H43NbSi2Sn: C, 56.76; H, 5.98.
Found: C, 56,26; H, 5.90.
3: white crystals, 81% yield. IR (Nujol) ν(Nb-H): 1759
cm-1 1H NMR (200 MHz, C6D6): δ 0.13 (s, 18H, SiMe3), 4.14
.
Kin etics of th e Rea ction of 1 w ith HSiP h 3 (Exp er im en t
(m, 4H, C5H4), 4.94 (m, 4H, C5H4), 7.30 (m, 15H, GePh2H),
5.81 (s, 1H, GePh2H), -3.69 (s, 2H, Nb-H). 13C NMR (300
MHz, C6D6): δ 0.21 (SiMe3), 98.60 (C1), 91.10, 94.47 (C5H4),
127.32, 131.18, 134.6, 148.3 (GePh2H). Anal. Calcd for C28
39NbSi2Ge: C, 56.32; H, 6.54. Found: C, 56.22; H, 6.32.
1). Deter m in a tion of F ir st-Or d er Ra te Con sta n ts.
A
measured amount of 1 (24 mg) was dissolved in toluene-d8 in
a 5-mm-NMR tube, and HSiPh3 (166 mg) was added. The final
volume was 0.8 mL. The concentration of 1 was 0.08 M, and
the molar ratio of 1:HSiPh3 was 1:10. The tube was vigorously
shaken for about 5 s and then placed into the spectrometer.
Each spectrum recorded at 313 K was the result of coadding
16 transients which required nearly 1 min to acquire. Spectra
were automatically recorded every 10 min using the kinetic
analysis software from Varian. Variations of the intensity of
the more intense peak from the pseudodoublet for the hydride
ligands in 1 were measured for three t1/2. A computer analysis
method for intensities gives a straight-line segment in a plot
of ln(intensity) against time. The error is given by the
standard deviation in the regression analysis. Similar experi-
ments were carried out at 318, 323, 328, and 333K.
Kin etics of th e Rea ction of 12 w ith HGeP h 3 (Exp er i-
m en t 2). Deter m in a tion of F ir st-Or d er Ra te Con sta n ts.
A measured amount of 12 (40 mg) was dissolved in toluene-d8
in a 5-mm-NMR tube, and HGePh3 (190 mg) was added. The
final volume was 0.8 mL. The concentration of 12 was 0.08
M, and the molar ratio of 12: HGePh3 was 1:10. The tube
was vigorously shaken for about 5 s and then placed into the
spectrometer. Each spectrum recorded at 313 K was the result
of coadding 16 transients which required nearly 1 min to
-
H
4: brown oil, 85% yield. IR (Nujol) ν(Nb-H): 1740 cm-1
.
1H NMR (200 MHz, C6D6): δ 0.12 (s, 18H, SiMe3), 4.35 (m,
4H, C5H4), 4.95 (m, 4H, C5H4), 0.90 (q, 6H, Ge(CH2CH3)3), 1.30
(t, 9H, Ge(CH2CH3)3), -4.46 (s, 2H, Nb-H). 13C NMR (300
MHz, C6D6): δ 0.43 (SiMe3), 94.82 (C1), 90.69, 93.11 (C5H4),
13.99 (Ge(CH2CH3)3), 10.73 (Ge(CH2CH3)3).
5: brown oil, 81% yield. IR (Nujol) ν(Nb-H): 1731 cm-1
.
1H NMR (200 MHz, C6D6): δ 0.16 (s, 18H, SiMe3), 4.43 (m,
4H, C5H4), 5.02 (m, 4H, C5H4), 1.40 (m, 30H, Ge((CH2)5CH3)3),
0.92 (t, 9H, Ge((CH2)5CH3)3), -4.33 (s, 2H, Nb-H). 13C NMR
(300 MHz, C6D6): δ 0.90 (SiMe3), 95.13 (C1), 91.27, 93.73
(C5H4), 14.90, 23.7, 27.5, 32.81, 34.95 (Ge((CH2)5CH3)3), 13.10
(Ge((CH2)5CH3)3).
6: brown oil, 81% yield. IR (Nujol) ν(Nb-H): 1724 cm-1
.
1H NMR (200 MHz, C6D6): δ 0.15(s, 18H, SiMe3), 4.41 (m, 4H,
C5H4), 5.00 (m, 4H, C5H4), 1.08-1.60 (m, 33H, Ge(iAm)3), -4.34
(20) Antin˜olo, A.; Chaudret, B.; Commenges, G.; Fajardo, M.; J alon,
F.; Morris, R. H.; Otero, A.; Schweitzer, C. T. J . Chem. Soc., Chem.
Commun. 1988, 1210.

Niobocene Germyl Complexes
Organometallics, Vol. 17, No. 8, 1998 1529
Ta ble 3. Su m m a r y of Cr ysta l Da ta for Com p ou n d s
2 a n d 11
by least-squares refinement of the setting angles of 24
randomly distributed and carefully centered reflections with
θ in the range 8-15° (2) and 10-17° (11). The data collections
were performed by the θ/2θ scan mode, at 293 K, with a
variable scan speed of 3-9.6 and 1.2-4.8 deg min-1 for 2 and
11, respectively, and a scan width of 1.20 + 0.34 tan θ for both.
One standard reflection was monitored every 100 measure-
ments; no significant decay was noticed over the course of data
collection. The individual profiles were analyzed following the
method of Lehmann and Larsen.21 Intensities were corrected
for Lorentz and polarization effects and reduced to Fo2. The
structures were solved by direct methods (SIR9222) and refined
by full-matrix least-squares on F2 using SHELXL-93,23 first
with isotropic thermal parameters and then with anisotropic
thermal parameters for all the non-hydrogen atoms. The
niobium hydrides were clearly located in the ∆F maps and
refined isotropically. All of the other hydrogen atoms were
placed at their geometrically default-distance calculated posi-
tions and refined riding on their parent carbon atoms with
2
11
formula
fw
C
34H43GeNbSi2
C34H43NbSi2Sn
673.38
cryst syst
space group
diffractometer
radiation
monochromator
temp, K
a, Å
monoclinic
P21/n
Philips PW 1100
(Mo KR), λ ) 0.710 73 Å
graphite
293
13.336(3)
22.403(5)
11.344(3)
98.47(2)
3352(1)
13.547(4)
22.459(8)
11.448(4)
99.00(2)
b, Å
c, Å
â, deg
V, Å3
3440(2)
Z
D
4
calcd, g cm-3
1.334
1392
1.389
1464
F(000)
cryst dimens, mm
µ(Mo KR), cm-1
2θ range, deg
0.25 × 0.30 × 0.35 0.20 × 0.25 × 0.30
13.30
11.49
6-48
6-44
three common isotropic displacement parameters for the HCp′
,
reflns measd, range h, k, l 0/15,0/25,-12/12
-16/15,0/26,0/13
H
Ph, and HMe atoms, respectively. After the final cycles of
2
total no. of unique data
no. of unique obsd data
(Fo g 4σ(Fo))
4042 (Fo g -σ(Fo2)) 4206 (Fo g -3σ(Fo2))
refinement, no parameters shifted by more than 0.009 Å (for
H2T) in 2 and 0.011 Å for H1T in 11 and the max and mean
shift/esd deviations were 0.105 for y(H2T) and 0.007 in 2 and
-0.204 for z(H1T) and 0.013 in 11, respectively. The final
difference Fourier maps showed no residual density outside
-0.79 and 1.12 and -0.56 and 0.68 e/Å3 in 2 and 11,
respectively. All calculations were carried out on the GOULD
POWERNODE 6040 and ENCORE 91 of the Centro di Studio
per la Strutturistica Diffrattometrica del CNR, Parma. The
Parst24 and ORTEP25 programs were also used. The final
atomic coordinates are provided in the Supporting Information.
2264
1964
data/restraints/params
goodness of fita
R1b
4042/0/354
1.089
0.0352
0.0894
0.0176, 0.0000
4206/0/354
0.785
0.0403
0.0755
0.0131, 0.0000
wR2c
weighting scheme, a, bd
a
2
b
GOOF ) [∑[w(Fo - Fc2)2]/(n - p)]1/2
.
R1 ) ∑||Fo| - |Fc||/
∑|Fo|. c wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
.
w ) 1/[σ2(Fo2) +
2
d
(aP)2 + bP], where P ) [max(Fo2,0) + 2Fc2]/3.
acquire. Spectra were automatically recorded every 10 min
using the kinetic analysis software from Varian. Variations
of the intensity of the singlet peak for the hydride ligands in
12 were measured for three t1/2. A computer analysis method
for intensities gives a straight-line segment in a plot of ln-
(intensity) against time. The error is given by the standard
deviation in the regression analysis. Similar experiments were
carried out at 318, 323, 328, and 333K.
Kin etics of th e Rea ction of 2 w ith HSn P h 3 (Exp er i-
m en t 3). Deter m in a tion of F ir st-Or d er Ra te Con sta n ts.
A measured amount of 2 (43 mg) was dissolved in toluene-d8
in a 5-mm-NMR tube, and HSnPh3 (224 mg) was added. The
final volume was 0.8 mL. The concentration of 2 was 0.08 M,
and the molar ratio of 2:HSnPh3 was 1:10. The tube was
vigorously shaken for about 5 s and then placed into the
spectrometer. Each spectrum recorded at 348 K was the result
of coadding 16 transients which required nearly 1 min to
acquire. Spectra were automatically recorded every 10 min
using the kinetic analysis software from Varian. Variations
of the intensity of the singlet peak for the hydride ligands in
2 were measured for three t1/2. A computer analysis method
for intensities gives a straight-line segment in a plot of ln-
(intensity) against time. The error is given by the standard
deviation in the regression analysis. Similar experiments were
carried out at 351, 353, 358, and 363K.
Ack n ow led gm en t. A.A., F.C.-H., M.F., J .F.-B., A.O.,
and E.V. gratefully acknowledge financial support from
the Direccio´n General de Ensen˜anza Superior (DGES)
(Grant No. PB 95-0023-CO1) of Spain, and M.L. and
M.A.P. gratefully acknowledge financial support from
the Ministero dell′Universita` e della Ricerca Scientifica
e Tecnologica (MURST) and Consiglio Nazionale delle
Ricerche (CNR) (Rome, Italy). We thank also several
commentaries from Prof. R. Andersen, Berkeley Uni-
versity.
Su p p or tin g In for m a tion Ava ila ble: Tables of final
atomic coordinates for the non-hydrogen atoms (Tables SI, SII)
and hydrogen atoms (Tables SIII, SIV), anisotropic thermal
parameters (Tables SV, SVI), complete bond distances and
angles (Tables SVII, SVIII), and complete crystallographic data
(Tables SIX, SX) (14 pages). Ordering information is given
on any current masthead page.
OM971001B
(21) Lehman, M. S.; Larsen, F. K. Acta Crystallogr., Sect. A 1974,
30, 580.
(22) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Gualiardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr. 1994, 27,
580.
(23) Sheldrick, G.M. SHELXL-93. Program for the refinement of
crystal structures; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
(24) Nardelli, M. Comput. Chem. 1983, 7, 95.
(25) J ohnson, C. K. ORTEP. Report ORNL-3794; Oak Ridge Na-
tional Laboratory: Oak Ridge, TN, 1965.
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t of Com p lexes 2 a n d 11. Suitable crystals were
sealed in Lindemann capillaries under dry nitrogen and used
for data collection. The crystallographic data are summarized
in Table 3. Accurate unit-cell parameters were determined