Cyclic organohydroborate complexes of metallocenes. VII. Synthesis, structure, and fluxional behavior of Cp2ZrX{(μ-H)2BC8H14} (X = H, D, Cl)

Article abstract of DOI:10.1021/om0206249

The reaction of K[H₂BC₈H₁₄] with Cp₂ZrCl₂ in a 1:1 molar ratio afforded Cp₂ZrCl{(μ-H)₂BC₈H₁₄}, 1, which when reacted with KH yielded Cp₂ZrH{(μ-H)₂BC₈H₁₄}, 2. These complexes were structurally characterized by single-crystal X-ray analysis. Partially deuterated 1 and 2, complexes Cp₂ZrCl{(μ-D)(μ-H)BC₈H₁₄}, 3, and Cp₂ZrD{(μ-H)₂BC₈H₁₄}, 4, were prepared. ²H NMR spectra revealed that in complex 3, which contains a terminal chloride on zirconium, no exchange of bridge and Cp hydrogens occurred. However, in complex 4, which includes a terminal hydrogen on zirconium, there was facile mixing of terminal, bridge, and Cp-hydrogens. Furthermore, exchange of terminal zirconium-hydrogen with bridge hydrogen was more rapid than exchange with the Cp-hydrogen. Additionally, this fluxional behavior occurred even at room temperature and in the solid state. Variable-temperature ¹H NMR studies are consistent with these results of dynamic hydrogen exchange in complexes 1 and 2. The complexes Cp₂Nb{(μ-H)₂BC₈H₁₄}, 7, and Cp₂Nb{μ-D)(μ-H)-BC₈H₁₄}, 8, have no terminal hydrogen on niobium, and there is no exchange between bridging hydrogens and Cp-hydrogens. The possible participation of the 9-BBN unit ({(μ-H)₂BC₈H₁₄}) hydrogens in dynamic exchange was examined for 2, the 9-BBN dimer ((C₈H₁₄B)(μ-H)₂(BC₈H₁₄ )), and the 9-BBN anion ([H₂BC₈H₁₄]) through the partially deuterated complexes Li[(D)(H)BC₈H₁₄], 5, and (C₈H₁₄B)(μ-D)(μ-H)(BC₈H₁₄), 6.

Full text of DOI:10.1021/om0206249

Organometallics 2003, 22, 275-283
275
Cyclic Or ga n oh yd r obor a te Com p lexes of Meta llocen es.
VII. Syn th esis, Str u ctu r e, a n d F lu xion a l Beh a vior of
Cp 2Zr X{(µ-H)2BC8H14} (X ) H, D, Cl)
Xuenian Chen, Shengming Liu, Christine E. Plecˇnik, Fu-Chen Liu,
Gideon Fraenkel, and Sheldon G. Shore*
Evans Laboratory, Department of Chemistry, The Ohio State University,
Columbus, Ohio 43210
Received August 1, 2002
The reaction of K[H2BC8H14] with Cp2ZrCl2 in a 1:1 molar ratio afforded Cp2ZrCl{(µ-
H)2BC8H14}, 1, which when reacted with KH yielded Cp2ZrH{(µ-H)2BC8H14}, 2. These
complexes were structurally characterized by single-crystal X-ray analysis. Partially
deuterated 1 and 2, complexes Cp2ZrCl{(µ-D)( µ-H)BC8H14}, 3, and Cp2ZrD{(µ-H)2BC8H14},
2
4, were prepared. H NMR spectra revealed that in complex 3, which contains a terminal
chloride on zirconium, no exchange of bridge and Cp hydrogens occurred. However, in complex
4, which includes a terminal hydrogen on zirconium, there was facile mixing of terminal,
bridge, and Cp-hydrogens. Furthermore, exchange of terminal zirconium-hydrogen with
bridge hydrogen was more rapid than exchange with the Cp-hydrogen. Additionally, this
fluxional behavior occurred even at room temperature and in the solid state. Variable-
temperature 1H NMR studies are consistent with these results of dynamic hydrogen exchange
in complexes 1 and 2. The complexes Cp2Nb{(µ-H)2BC8H14}, 7, and Cp2Nb{(µ-D)( µ-H)-
BC8H14}, 8, have no terminal hydrogen on niobium, and there is no exchange between
bridging hydrogens and Cp-hydrogens. The possible participation of the 9-BBN unit ({(µ-
H)2BC8H14}) hydrogens in dynamic exchange was examined for 2, the 9-BBN dimer
((C8H14B)(µ-H)2(BC8H14)), and the 9-BBN anion ([H2BC8H14]-) through the partially deu-
terated complexes Li[(D)(H)BC8H14], 5, and (C8H14B)(µ-D)(µ-H)(BC8H14), 6.
In tr od u ction
hydrogens that bridge metal and boron atoms in metal
tetrahydroborate complexes.6 However, examples of
metallocene complexes in which Cp-hydrogens are also
involved in the exchange process are rare.7,8 Our studies
Although a number of transition metal tetrahydro-
borate complexes have been prepared, characterized,
and studied, relatively little is known concerning related
metal organohydroborate complexes.1,2 Recently, we
have focused on the chemistry of the cyclic organo-
hydroborate anions, [H2B2(µ-H)(µ-C4H8)2]- (a trans-
of the organohydroborates Cp2ZrH{(µ-H)2BR2} (R2
)
(3) (a) Liu, F.-C.; Liu, J .; Meyers, E. A.; Shore, S. G. J . Am. Chem.
Soc. 2000, 122, 6106. (b) Liu, F.-C.; Du, B.; Liu, J .; Meyers, E. A.; Shore,
S. G. Inorg. Chem. 1999, 38, 3228. (c) Liu, F.-C.; Liu, J .; Meyers, E.
A.; Shore, S. G. Inorg. Chem. 1998, 37, 3293. (d) Liu, J .; Meyers, E.
A.; Shore, S. G. Inorg. Chem. 1998, 37, 496. (e) J ordan, G. T., IV; Liu,
F.-C.; Shore, S. G. Inorg. Chem. 1997, 36, 5597. (f) J ordan, G. T., IV;
Shore, S. G. Inorg. Chem. 1996, 35, 1087. (g) Liu, F.-C.; Plecnik, C. E.;
Liu, S.; Liu, J .; Meyers, E. A.; Shore, S. G. J . Organomet. Chem. 2001,
627, 109.
(4) (a) Shore, S. G.; Liu, J .; J ordan, G. T., IV; Liu, F.-C.; Meyers, E.
A.; Gaus, P. L. Cyclic Organohydroborate Anions as Hydride Transfer
Agents in Reactions with Organic and Organometallic Compounds. In
Advances in Boron Chemistry; Siebert, W., Ed.; Royal Society of
Chemistry: London, 1997; pp 84-91. (b) Casey, C. P.; Neumann, S.
M. J . Am. Chem. Soc. 1976, 98, 5395.
(5) (a) Plecnik, C. E.; Liu, F.-C.; Liu, S.; Liu, J .; Meyers, E. A.; Shore,
S. G. Organometallics 2001, 20, 3599. (b) Liu, S.; Liu, F.-C.; Renkes,
G.; Shore, S. G. Organometallics 2001, 20, 5717. (c) Antelmann, B.;
Chisholm, M. H.; Iyer, S. S.; Huffman, J . C.; Navarro-Llobet, D.; Pagel,
M.; Simonsich, W. J .; Zhong, W. Organometallics 2001, 34, 3159. (d)
Ding, E.; Liu, F.-C.; Liu, S.; Meyers, E. A.; Shore, S. G. Inorg. Chem.
2002, 41, 5329.
(6) (a) Demachy, I.; Esteruelas, M. A.; J ean, Y.; Lledo´s, A.; Maseras,
F.; Oro, L. A.; Valero, C.; Volatron, F. J . Am. Chem. Soc. 1996, 118,
8388. (b) Esteruelas, M. A.; J ean, Y.; Lledo´s, A.; Oro, L. A.; Ruiz, N.;
Volatron, F. Inorg. Chem. 1994, 33, 3609. (c) Frost, P. W.; Howard, J .
A. K.; Spencer, J . L. J . Chem. Soc., Chem. Commun. 1984, 1362. (d)
Letts, J . B.; Mazanec, T. J .; Meek, D. W. J . Am. Chem. Soc. 1982, 104,
3898. (e) Gozum, J . E.; Wilson, S. R. J . Am. Chem. Soc. 1992, 114,
9483.
annular hydrogen-bridged 10-membered ring anion),
-
[H2BC5H10]-, and [H2BC8H14
]
(the hydroborate anion
of the 9-BBN dimer, (C8H14B)(µ-H)2(BC8H14)), and their
metallocene derivatives.3-5 A point of continuing inter-
est is the intramolecular dynamic hydrogen interchange
in metallocene derivatives of these hydroborate ligands.
It is well recognized that dynamic intramolecular
exchange occurs between terminal metal hydrides and
(1) (a) Marks, T. J .; Kolb, J . R. Chem. Rev. 1977, 77, 263. (b) Gilbert,
K. B.; Boocock, S. K.; Shore, S. G. Compounds with Bonds Between a
Transition Metal and Boron. In Comprehensive Organometallic Chem-
istry; Wilkinson, G., Stone, F. G. A., Able, E. W., Eds.; Pergamon Press
Inc.: New York, 1982; pp 879-945.
(2) (a) Spence, R. E. v. H.; Piers, W. E.; Sun, Y.; Parvez, M.;
MacGillivray, L. R.; Zaworotko, M. J . Organometallics 1998, 17, 2459.
(b) Sun, Y.; Spence, R. E. v. H.; Piers, W. E.; Parvez, Yap, G. P. A. J .
Am. Chem. Soc. 1997, 119, 5132. (c) Sun, Y.; Piers, W. E.; Rettig, S. J .
Organometallics 1996, 15, 4110. (d) Spence, R. E. v. H.; Parks, D. J .;
Piers, W. E.; MacDonald, M.-A.; Zaworotko, M. J .; Rettig, S. J . Angew.
Chem., Int. Ed. Engl. 1995, 34, 1230. (e) Hartwig, J . F.; De Gala, S. R.
J . Am. Chem. Soc. 1994, 116, 3661. (f) Erker, G.; Noe, R.; Wingber-
muhle, D.; Petersen, J . L. Angew. Chem., Int. Ed. Engl. 1993, 32, 1213.
(g) Baker, R. T.; Ovenall, D. W.; Harlow, R. L.; Westcott, S. A.; Taylor,
N. J .; Marder, T. B. Organometallics 1990, 9, 3028. (h) Paetzold, P.;
Geret, L.; Boese, R. J . Organomet. Chem. 1990, 385, 1.
(7) Marks, T. J .; Kolb, J . R. J . Am. Chem. Soc. 1975, 97, 3397.
10.1021/om0206249 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/19/2002

276 Organometallics, Vol. 22, No. 2, 2003
Chen et al.
Sch em e 1
C4H8,9 C5H103c) indicate that exchange occurs between
Zr-H, Zr-H-B, and Cp-H hydrogens, based on temper-
ature-dependent H NMR spectra. Additionally, activa-
in a 1:1 molar ratio produces Cp2ZrCl{(µ-H)2BC8H14},
1, in an 80% yield (reaction 1). However, the disubsti-
1
tion parameters for the bridge hydrogen exchange and
bridge-terminal hydrogen exchange were determined.9b
Earlier work7 reported dynamic intramolecular hydro-
gen exchange in Cp2ZrH{(µ-H)2BH2}. Although our
results are generally consistent with this earlier work,
there is a significant difference. The earlier study
observed that hydrogen interchange involving Cp-H and
borohydride hydrogens is more facile than interchange
involving Zr-H and borohydride hydrogens.7 [Due to its
1
fluxional character, on the H NMR time scale bridging
and terminal hydrogens of the borohydride ligand in
Cp2ZrH{(µ-H)2BH2} are equivalent.] On the other hand
in the case of the cyclic organohydroborate derivatives,
temperature-dependent proton NMR spectra indicate
that terminal Zr-H and bridge Zr-H-B hydrogens ex-
change more rapidly than terminal Zr-H and Cp-
hydrogens exchange.3c,9
Previously, we proposed that the exchange pathway
for bridging hydrogens with Cp-hydrogens requires the
presence of a terminal Zr-H hydrogen to facilitate the
exchange process.3c In the present study we are inter-
ested in testing this proposition. We pose the following
fundamental question for these metallocene cyclic or-
ganohydroborates: Is a terminal hydride on the metal
necessary for dynamic intramolecular exchange between
bridge and Cp-hydrogen? It is also of interest to deter-
mine if the â and γ C-H hydrogens of the 9-BBN unit,
{(µ-H)2BC8H14}, in 2 exchange with the bridge hydro-
gens since there is precedence for C-H hydrogens
exchanging with bridge hydrogens in the 9-BBN dimer,
(C8H14B)(µ-H)2(BC8H14).
tuted complex Cp2Zr{(µ-H)2BC8H14}2 could not be pre-
pared from either the reaction of K[H2BC8H14] with
Cp2ZrCl2 in a 2:1 molar ratio or the reaction of 1 with
K[H2BC8H14] in a 1:1 molar ratio. Instead mixtures of
1 and Cp2ZrH{(µ-H)2BC8H14}), 2, plus an unidentified
boron-containing complex, which possesses an 11B NMR
resonance at 6.3 ppm, are produced (Scheme 1). On the
other hand, the reaction between K[H2BC5H10] and
Cp2ZrCl2 in a 2:1 molar ratio generates Cp2Zr{(µ-
H)2BC5H10}2.3c This difference in results is attributed
-
to the larger steric bulk of the [H2BC8H14
]
ligand
compared to [H2BC5H10]-. Treatment of complex 1 with
KH in THF at room temperature affords complex 2 in
90% yield (reaction 2).
Resu lts a n d Discu ssion
P r ep a r a t ion a n d NMR Sp ect r a of Com p lexes
1-6. The reaction between K[H2BC8H14] and Cp2ZrCl2
(8) (a) Kot, W. K.; Edelstein, N. M.; Zalkin, A. Inorg. Chem. 1987,
26, 1339. (b) Mancini, M.; Bougeard, P.; Burns, R. C.; Mlekuz, M.;
Sayer, B. G.; Thompson, J . I. A.; McGlinchey, M. J . Inorg. Chem. 1984,
23, 1072. (c) Bercaw, J . E. Adv. Chem. Ser. 1978, 167, 136.
(9) (a) Shore, S. G.; Liu, F.-C. Cationic Metallocenes Derived from
Cyclic Organohydroborate Metallocene Complexes. In Contemporary
Boron Chemistry; Davidson, M. G., Hughes, A. K., Marder, T. B., Wade,
K., Eds.; The Royal Society of Chemistry: London, 2000; pp 28-35.
(b) Chow, A.; Liu, F.-C.; Fraenkel, G.; Shore, S. G. Magn. Reson. Chem.
1998, 36, 145.
Complexes 1 and 2 are colorless. The solids are stable
under a nitrogen atmosphere at room temperature for

Cyclic Organohydroborate Complexes
Organometallics, Vol. 22, No. 2, 2003 277
several weeks. However, decomposition occurs when
their solutions are exposed to air. Interestingly, when
the colorless solution of 2 is stored under nitrogen for
an extended period of time at room temperature, the
color gradually changes to a faint red, possibly indicat-
ing decomposition or the formation of a nitrogen-
coordinated compound.10
cates the presence of two THF molecules that are
probably coordinated to the Li+ cation. This is consistent
with the structure determined by single-crystal X-ray
1
analysis.13 From the H{11B} NMR spectrum of 5, the
signal at 0.77 ppm is assigned to the bridging hydro-
gens.
According to the 13C and 13C GD NMR spectra of 6,
signals at 33.7 ppm (triplet in the 13C-GD NMR spec-
trum) and 24.4 ppm (triplet in the 13C-GD NMR
spectrum) are designated as the â- and γ-carbons,
respectively. The R-carbon, bonded to the boron atom,
produces a broad signal at about 20.2 ppm. On the basis
The 11B NMR spectra of 1 and 2 in toluene consist of
a broad triplet at δ 17.7 and 32.5 ppm, respectively.
These resonances are further downfield from the signal
at -15.9 ppm (1J BH ) 75 Hz) produced by the parent
salt, K[H2BC8H14], but are similar to the signals of
analogous complexes Cp2ZrX{(µ-H)2BR2} (X ) Cl, H; R2
) C4H8, C5H10).3
1
of a proton-detected H-13C correlation (HMQC) spec-
trum, the different types of hydrogens in 6 are assigned.
The â-hydrogens are correlated to two multiplets at 1.85
and 1.67 ppm; the γ-hydrogens correspond to two
multiplets at 1.96 and 1.51 ppm; and the R-hydrogens
appear as a singlet at 1.63 ppm. The bridging hydrogen
1
In the H NMR spectrum of 1, the two inequivalent
bridging hydrogens give rise to two broad signals at 0.55
and -2.40 ppm. Comparable signals of the two bridging
1
hydrogens appear at -3.17 and -4.12 ppm in the H
1
of 6 is detected at 1.46 ppm by comparing the H and
NMR spectrum of 2. The terminal hydrogen of 2
produces a signal at 3.99 ppm that falls within the range
observed for the terminal hydrides of other zirconocene
hydroborate compounds, Cp2ZrH{(µ-H)2BC4H8} (3.95
ppm),3b Cp2ZrH{(µ-H)2BC5H10} (4.06 ppm),3c Cp2ZrH-
{(µ-H)2BHCH3} (4.16 ppm),8a and Cp2ZrH{(µ-H)2BH2}
(4.53 ppm).11 Assignment of the R-, â-, and γ-protons of
the {(µ-H)2BC8H14} units in 1 and 2 is accomplished by
13C NMR, 13C gated decoupled (GD) NMR, and two-
1H{11B} NMR spectra.
In tr a m olecu la r Hyd r ogen Exch a n ge. Th e Effect
of a Ter m in a l Su bst it u en t , X (X ) Cl, H), on
Zir con iu m . Our earlier studies showed that intramo-
lecular hydrogen exchange occurs among the Zr-H-B
bridging hydrogens, Zr-H terminal hydride, and Cp-
hydrogens in Cp2ZrH{(µ-H)2BC5H10}
3c and Cp2ZrH{(µ-
H)2BC4H8}.9 Here our principal goal is to determine if
dynamic hydrogen exchange takes place between bridg-
ing hydrogens and Cp-hydrogens when the terminal H-
on Zr is replaced by Cl.
1
dimensional H-13C correlation NMR spectra (hetero-
nuclear multiple quantum coherence, HMQC). Since the
spectral results are similar for both 1 and 2, only the
data for 2 are discussed below. In the 13C and 13C GD
NMR spectra, the triplets at 33.9 and 25.3 ppm are
attributed to the â- and γ-carbons, respectively. The
R-carbon resonance, δ 29.9 ppm, appears as a broad
signal since it is bonded to the quadrupolar 11B nucleus.
From the HMQC spectrum, the two sets of proton peaks
at 2.11 and 1.73 ppm are assigned to the γ-hydrogens,
the resonances at 1.91 and 1.83 ppm are identified as
the â-hydrogens, and the chemical shift of the R-hydro-
gens is 1.39 ppm. The R-hydrogen resonance is upfield
Complexes 1 (Cp2ZrCl{(µ-H)2BC8H14}) and 2 (Cp2ZrH-
{(µ-H)2BC8H14}) were investigated for dynamic hydro-
gen exchange. Useful 1H NMR spectra of complex 1
could be obtained only below 330 K due to noticeable
decomposition of the complex above that temperature.
In the narrow temperature range studied (300-330 K),
the two bridging hydrogens’ signals broaden with in-
creasing temperature but do not fully average; the
signal from the Cp-hydrogens does not appear to change.
1
Thus H NMR spectra suggest that the only significant
1
relative to the γ-hydrogens in the H NMR spectra of
dynamic hydrogen interchange occurs between the
bridging hydrogens. Above 330 K, signals at 5.86 and
complexes 1 and 2. But for the 9-BBN dimer, (C8H14B)(µ-
H)2(BC8H14), the signal of the R-hydrogens appears at
1.62 ppm between two sets of resonances for the
1
5.58 ppm in the H NMR spectra and at 27.3 ppm in
the 11B spectrum indicate the formation of complex 2,
zirconocene dichloride,14 and 9-BBN dimer,15 respec-
tively, as decomposition products. The 2H NMR spec-
trum of 3 in toluene reveals only two signals for the
bridging deuterium Zr-D-B at room temperature (Figure
1a). After heating 3 at 318 K for 10 h, a new signal is
present at 1.4 ppm (Figure 1b), which indicates that 3
has partially decomposed to 9-BBN dimer. No signal
corresponding to the presence of Cp-deuterium is ob-
served after heating complex 3. This confirms that the
Cp-hydrogens do not exchange with bridging hydrogens
in this complex, and is consistent with what the tem-
1
γ-hydrogens (1.95 and 1.51 ppm, based upon their H-
13C HMQC cross-peak). The Cp-hydrogens of com-
plexes 1 and 2 are visible at 5.75 and 5.58 ppm,
respectively.
The partially deuterated analogues of 1 and 2, Cp2-
ZrCl{(µ-D)(µ-H)BC8H14}, 3, and Cp2ZrD{(µ-H)2BC8H14},
4, are prepared by the following methods. Compound 3
is formed from the reaction of Li[(D)(H)BC8H14], 5, with
Cp2ZrCl2 (analogous to reaction 1), and complex 4 is
prepared by the reaction of LiD with 1 (analogous to
reaction 2). Complex 5 is prepared from the reaction of
LiD with the 9-BBN dimer. Partially deuterated 9-BBN
dimer, (C8H14B)(µ-D)(µ-H)(BC8H14), 6, is obtained by
abstracting hydride ion from 5 with B(C6F5)3.
(12) (a) J ohnson, P. L.; Cohen, S. A.; Marks, T. J .; Williams, J . M.
J . Am. Chem. Soc. 1978, 100, 2709. (b) Marks, T. J .; Shimp, L. A. J .
Am. Chem. Soc. 1972, 94, 1542. (c) J ames, B. D.; Nanda, R. K.;
Wallbridge, M. G. H. Inorg. Chem. 1967, 6, 1979. (d) J ames, B. D.;
Nanda, R. K.; Wallbridge, M. G. H. J . Chem. Soc. A 1966, 182.
(13) (a) Knizek, J .; No¨th, H. J . J . Organomet. Chem. 2000, 614-
615, 168. (b) Douthwaite, R. E. Polyhedron 2000, 19, 1579.
(14) The chemical shift of the Cp-protons appeared at δ 5.87 in the
1H NMR spectrum of Cp2ZrCl2 in toluene-d8.
Complex 5 was characterized by NMR and IR spec-
troscopies. Integration of the proton signals of 5 indi-
(10) Chirik, P. J .; Henling, L. M.; Bercaw, J . E. Organometallics
2001, 20, 534.
(11) J ames, B. D.; Nanda, R. K.; Wallbridge, M. G. H. Inorg. Chem.
1967, 6, 1979.
(15) (a) Ko¨ster, R.; Yalpani, M. Pure Appl. Chem. 1991, 63, 387. (b)
Ko¨ster, R.; Yalpani, M. J . Org. Chem. 1986, 51, 3054.

278 Organometallics, Vol. 22, No. 2, 2003
Chen et al.
F igu r e 1. 2H NMR spectra of 3 in toluene (a) before
heating and (b) after heating at 318 K for 10 h.
F igu r e 3. 2H NMR spectra of 4 in toluene (a) before
heating, (b) after heating at 318 K for 1 h, and (c) after
heating at 358 K for another 1 h.
chemical shift for Cp-deuterium (Figure 3b). These
observations signify that the terminal hydrogen ex-
changes more rapidly with the bridging hydrogens than
with Cp-hydrogens. This result is in accord with pre-
liminary observations of partially deuterated Cp2ZrH-
{(µ-H)2BC4H8}.9a Intramolecular hydrogen exchange
also occurs in the solid state at room temperature. When
an unheated sample of solid 4, which gives no evidence
for Cp-deuterium, is stored in the drybox for several
weeks and then dissolved in toluene at room tempera-
2
ture, its H NMR spectrum displays the Cp-deuterium
resonance in addition to terminal and bridging deute-
rium resonances.
It is also of interest to determine if bridge hydrogen
exchanges with Cp-hydrogen in the absence of a termi-
nal group on the metal. Proton NMR spectra of complex
7, a niobocene cyclic organohydroborate derivative, were
obtained in the temperature range 300-363 K. The
spectra show no evidence for exchange of bridge hydro-
gens with Cp-hydrogens or decomposition. In this
molecule there is only one bridging hydrogen signal, due
to the mirror symmetry of the molecule. This signal
broadens slightly at elevated temperature, but the Cp-
hydrogen signal is essentially unchanged.
1
F igu r e 2. Variable-temperature H NMR spectra of 2 in
toluene-d8.
perature-dependent 1H NMR spectra of the undeuter-
ated chloro complex 1 imply.
Proton NMR spectra of complex 2 as a function of
temperature are shown in Figure 2. As the temperature
rises from ambient, the two bridging hydrogen signals
coalesce and then broaden into the baseline. At the same
time, the signals assigned to the terminal hydrogen on
zirconium and the Cp-hydrogens noticeably broaden.
These spectra are in accord with variable-temperature
1H NMR spectra of Cp2ZrH{(µ-H)2BC4H8}9 and Cp2ZrH-
{(µ-H)2BC5H10}.3c A point of interest here is the fact that
the Cp, Zr-H, and Zr-H-B hydrogens are exchanging at
temperatures at which 1 does not even display full
coalescence of the bridging hydrogen resonances.
The 2H NMR spectrum of 4 in toluene reveals the
presence of Zr-D and Zr-D-B (Figure 3a), thus denoting
that terminal and bridging hydrogen exchange occurs
at room temperature. But there is no evidence for Cp-
deuterium in this sample (Figure 3a).
To confirm the absence of significant interchange
between bridging and Cp-hydrogen, partially deuterated
Cp2Nb{(µ-D)(µ-H)BC8H14}, 8, was prepared by the reac-
tion of Cp2NbCl2 with 5 in THF.3h Complex 8 in toluene
was maintained at 318 K for 10 h. Its H NMR spectra
before and after heating (Figure 4) give no evidence for
Cp-deuterium.
2
Stu d y of th e 9-BBN Un it in 2, 4, a n d 5 a n d th e
9-BBN Dim er w it h R esp ect t o H yd r ogen E x-
1
ch a n ge. In the H NMR spectrum of 2 (Figure 2) there
is a slight broadening of the R-CH hydrogen signal of
the {(µ-H)2BC8H14} unit at elevated temperature (360
K). This peak returns to its original shape when the
temperature is lowered to ambient (300 K). There are
two plausible explanations for these observations. An
intriguing possibility is the involvement of the R-hy-
drogens in the exchange process. But their rate of
exchange would be appreciably slower than the other
hydrogen exchange processes in the molecule. Another
possibility for the temperature dependence of the line
However, upon heating this sample 4 at 318 K for 1
h, the intensities of the terminal and bridging deuterium
resonances decrease and a new signal emerges at the

Cyclic Organohydroborate Complexes
Organometallics, Vol. 22, No. 2, 2003 279
F igu r e 4. 2H NMR spectra of 8 in toluene (a) before
heating and (b) after heating at 318 K for 10 h.
F igu r e 5. Molecular structure of 1, showing 15% prob-
ability thermal ellipsoids. Hydrogens attached to carbon
atoms are shown with arbitrary thermal ellipsoids.
shape is due to 11B nuclear electric quadrupolar induced
relaxation partially averaging long-range 11B-1H cou-
pling. Since the rate of quadrupolar relaxation varies
inversely with temperature,16 its effect on averaging of
long-range 11B-1H coupling decreases with increasing
temperature and results in a broadened resonance.
After heating Cp2ZrD{(µ-H)2BC8H14}, 4, to 318 K for
1 h and then at 358 K for another hour, its 2H NMR
spectrum (Figure 3c) reveals a low-intensity signal, just
visible at 1.4 ppm. This resonance can be assigned to
the bridging deuterium of the 9-BBN dimer, a decom-
position product, or the R-carbon-deuterium in 4. This
signal is not present in the 2H NMR spectrum of 4 before
it is heated (Figure 3a). Two unidentified very weak
signals at 1.56 and -0.56 ppm are consistent with some
decomposition of 4 (Figure 3c). To minimize decomposi-
tion, a sample of 4 in toluene was allowed to stand at
F igu r e 6. Molecular structure of 2, showing 15% prob-
ability thermal ellipsoids. Hydrogens attached to carbon
atoms are shown with arbitrary thermal ellipsoids.
2
room temperature for 50 days. The H NMR spectrum
2
displays bridging, terminal, and Cp-deuteriums with a
weak signal at 1.4 ppm also present. This signal is too
weak to allow a claim for C-H R-hydrogen exchange with
bridging deuterium. Furthermore, there is no evidence
for exchange of the â- and γ-C-H hydrogens with
bridging deuterium.
appeared in the H NMR spectrum, indicating that no
exchange occurred between the boron and carbon hy-
drogens.
Ko¨ster and co-workers account for the exchange of
only â- and γ-CH hydrogens in the 9-BBN dimer by
assuming a dissociation equilibrium to produce some
monomer HBC8H14 at elevated temperature. The mono-
mer is assumed to be the active participant in the
exchange process in which the BH hydrogen exchanges
with the â- and γ-CH hydrogens through a “topotactical
walk mechanism” (Scheme 2). This scheme not only
accounts for â-CH and γ-CH hydrogen exchange with
BH hydrogen but also provides insight into the lack of
exchange in [(D)(H)BC8H14]-, 5, which has an electroni-
cally saturated boron. Thus there is no need to abstract
a C-H hydrogen as illustrated in Scheme 2.
The Ko¨ster mechanism requires some symmetric
dissociation of the 9-BBN dimer. This mechanism might
also account for the absence of â- and γ-hydrogen
exchange with boron hydrogen in 2 and 4. If the Ko¨ster
mechanism is correct, the lack of â- and γ-CH exchange
in these complexes could be attributed to hydrogen
bridge systems of complexes 2 and 4 that are more
resistant to symmetrical dissociation than the 9-BBN
dimer.
It is reported that only the â-CH and γ-CH hydrogens
in (C8H14B)(µ-H)2(BC8H14) exchange with the bridging
hydrogens, but the R-hydrogens do not. In that account
by Ko¨ster et al.15 the evidence for â- and γ-hydrogen
rearrangement is provided by 13C NMR spectra. We
reexamined the possibility of bridging hydrogens ex-
changing with â- and γ-hydrogens by 2H NMR spec-
troscopy. The bridging deuterium signal of complex
(C8H14B)(µ-D)(µ-H)(BC8H14), 6, appears at 1.46 ppm.
After 6 is heated in toluene at 358 K for 1 h, the 2H
NMR spectrum displays two new peaks at 1.88 and 1.67
ppm besides the bridging deuterium signal. These are
the â- and γ-deuterium resonances, respectively, with
no signal representing the R-carbon deuteriums, fully
in accord with the report by Ko¨ster and co-workers.15
Since the neutral 9-BBN diborane undergoes â- and
γ-exchange, it was also of interest to examine the
deuterated lithium salt of the 9-BBN hydroborate anion,
complex Li[(D)(H)BC8H14], 5, for such exchange. The
2H NMR spectrum of 5 at room temperature shows the
presence of terminal deuteriums at 0.67 ppm. After
heating 5 in toluene at 358 K for 1 h, no new signals
Molecu la r St r u ct u r es of Com p lexes 1 a n d 2.
The molecular structures of 1 and 2 were determined
by single-crystal X-ray diffraction analysis. They are
shown in Figures 5 and 6. Crystallographic data and
selected bond distances and bond angles are given in
Tables 1-3.
(16) Kaplin, J . I.; Fraenkel, G. NMR of Chemically Exchanging
Systems; Academic Press: New York, 1980; pp 114-5.

280 Organometallics, Vol. 22, No. 2, 2003
Chen et al.
Sch em e 2
Ta ble 1. Cr ysta llogr a p h ic Da ta for 1 a n d 2a
1
2
formula
mol wt
C
18H26BClZr
C18H27BZr
345.43
379.87
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/ c
18.799(1)
13.836(1)
13.328(1)
92.23(1)
3464.0(4)
8
monoclinic
P21/ n
11.961(1)
10.253(1)
13.904(1)
102.79(1)
1662.8(2)
4
â (deg)
volume (Å3)
Z
Dc (g/cm3)
F(000)
1.457
1568
1.380
720
θ range (deg)
h k l ranges
cryst size (mm)
µ(Mo KR) (mm-1
transmn: max., min.
no. of reflns collected
no. of ind reflns
2.36-25.02
-22 22, -16 15, -15 15
0.42 × 0.08 × 0.08
0.780
0.9402, 0.7353
19 411
2.49-25.01
-13 14, -12 12, -16 16
0.46 × 0.31 × 0.12
0.650
)
0.9261, 0.7543
10 236
2931
6109
Rint
0.02671
0.0299
completeness to θ
no. of data/restraints/params
final R indices [I g 2σ(I)]b
R indices (all)
99.8%
100%
2931/0/193
R1 ) 0.0259; wR2 ) 0.0631
R1 ) 0.0309; wR2 ) 0.0653
1.112
6109/0/395
R1 ) 0.0279; wR2 ) 0.0585
R1 ) 0.0419; wR2 ) 0.0632
1.042
GOF
largest diff peak, e/Å3
0.460/-0.374
0.373/-0.723
Features common to all determinations: λ(Mo KR) ) 0.71073 Å. R1 ) ∑|Fo| - |Fc|/∑|Fo| wR2 ) {∑w(Fo - Fc2)2/∑w(Fo2)2}1/2
.
a
b
2
The coordination geometry of the zirconium atoms in
distances range from 1.96(2) to 2.08(2) Å, while the B-H
1 and 2 can be described as a distorted tetrahedron,
consisting of B, Cl, or H, and the centroids of the two
Cp rings at the corners of the tetrahedron. The struc-
tures of 1 and 2 each consist of a Cp2ZrX fragment
bonded to a BC8H14 group through two bridging hydro-
gens, which were located and their positions refined.
There are two independent molecules in the asymmetric
unit cell of 1. The Zr-B distances of 2.609(3) and
2.593(3) Å in 1 and 2.566(2) Å in 2 are consistent with
other systems with bidentate Zr-H-B bridges.11,17 The
shorter Zr-B distance in 2 results from the reduction
in steric volume by replacement of the Cl atom on
zirconium with a H atom. The steric bulk of the Cl atom
also affects the average Cpcentroid-Zr distances (2.200
distances range from 1.19(2) to 1.27(2) Å. The terminal
hydrogen in 2 was located and refined isotropically. The
Zr-H bond distance of 1.77(2) Å in 2 falls within the
limits observed for other zirconocene hydride complexes,
Cp2ZrH{(µ-H)2BC5H10} (1.7862(4) Å)3c and Cp2ZrH{(µ-
H)2BC4H8} (1.68(5) Å).3b The Zr-Cl distances of 2.5080(6)
and 2.4971(7) Å in 1 are comparable to the previously
reported Zr-Cl distances of 2.4802(5) Å in Cp2ZrCl{(µ-
H)2BC5H10}3d and 2.4974(7) Å in Cp2ZrCl{(µ-H)2BC4H8}.3f
Su m m a r y a n d Con clu sion s
This study provides strong evidence that exchange
between bridging and Cp hydrogens in the zirconocene
chloro complex Cp2ZrCl{(µ-H)2BC8H14} and the niobo-
cene complex Cp2Nb{(µ-H)2BC8H14} does not occur, or
is minimal when there is a nonhydridic terminal sub-
stituent on zirconium (Cl) or no terminal group on
niobium. However, a terminal hydrogen on zirconium
participates in intramolecular exchange with bridg-
ing and Cp-hydrogens in the hydrido-cyclic organo-
and 2.204 Å for 1 and 2.190 Å for 2) and the Cpcentroid
-
Zr-Cpcentroid angles (129.6° for 1; 136.0° for 2). For the
hydrogen-bridge systems of 1 and 2, the metal-H
(17) (a) Makhaev, V. D. Russ. Chem. Rev. 2000, 69, 727. (b) J oseph,
S. C. P.; Cloke, F. G. N.; Cardin, C. J .; Hitchcock, P. B. Organometallics
1995, 14, 3566. (c) Gozum, J . E.; Girolami, G. S. J . Am. Chem. Soc.
1991, 113, 3829. (d) Corazza, F.; Floriani, C.; Chiesi-Villa, A.; Guastini,
C. Inorg. Chem. 1991, 30, 145.

Cyclic Organohydroborate Complexes
Ta ble 2. Selected Bon d Dista n ces a n d An gles for 1a
Bond Lengths (Å)
Organometallics, Vol. 22, No. 2, 2003 281
Zr1-CpCentroid(C11-C15)
Zr1-CpCentroid(C16-C10)
Zr1- -B1
2.198
2.202
Zr2-CpCentroid(C21-C25)
Zr2-CpCentroid(C26-C20)
Zr2- -B2
2.201
2.206
2.609(3)
2.5080(6)
1.96(2)
2.08(2)
1.26(2)
1.19(2)
1.593(4)
1.596(4)
2.593(3)
2.4971(7)
1.96(2)
2.06(2)
1.27(2)
1.19(2)
1.593(4)
1.592(4)
Zr1-Cl1
Zr2-Cl2
Zr1-H1A
Zr2-H2A
Zr1-H1B
Zr2-H2B
B1-H1A
B2-H2A
B1-H1B
B2-H2B
B1-C111
B2-C211
B1-C115
B2-C215
Bond Angles (deg)
CpCentroid(C11-C15)-Zr1-CpCentroid (C16-C10)
CpCentroid(C11-C15)-Zr1-B1
CpCentroid(C16-C10)-Zr1-B1
CpCentroid(C11-C15)-Zr1-Cl1
CpCentroid(C16-C10)-Zr1-Cl1
CpCentroid(C11-C15)-Zr1-H1A
CpCentroid(C16-C10)-Zr1-H1A
CpCentroid(C11-C15)-Zr1-H1B
CpCentroid(C16-C10)-Zr1-H1B
B1-Zr1-Cl1
129.4
106.5
107.2
105.0
104.2
96.5
96.3
111.8
115.3
CpCentroid(C21-C25)-Zr2-CpCentroid (C26-C20)
CpCentroid(C21-C25)-Zr2-B2
CpCentroid(C26-C20)-Zr2-B2
CpCentroid(C21-C25)-Zr2-Cl2
CpCentroid(C26-C20)-Zr2-Cl2
CpCentroid(C21-C25)-Zr2-H2A
CpCentroid(C26-C20)-Zr2-H2A
CpCentroid(C21-C25)-Zr2-H2B
CpCentroid(C26-C20)-Zr2-H2B
B2-Zr2-Cl2
129.7
106.4
107.3
104.0
104.6
95.2
97.3
114.1
112.8
101.14(6)
101.40(6)
B1-Zr1-H1A
27.6(6)
26.5(6)
128.8(6)
74.7(6)
54.1(9)
B2-Zr2-H2A
28.1(7)
26.5(6)
129.5(7)
74.9(6)
54.7(9)
B1-Zr1-H1B
B2-Zr2-H2B
Cl1-Zr1-H1A
Cl2-Zr2-H2A
Cl1-Zr1-H1B
Cl2-Zr2-H2B
H1A-Zr1-H1B
H2A-Zr2-H2B
a
There are two unique molecules in the asymmetric unit cell of 1.
Ta ble 3. Selected Bon d Dista n ces a n d An gles for 2
Bond Lengths (Å)
Zr1-CpCentroid(C11-C15)
Zr1-CpCentroid(C16-C10)
Zr1- -B1
Zr1-H
Zr1-HA
2.192
2.189
2.566(2)
1.77(2)
1.99(2)
Zr1-HB
B1-HA
B1-HB
B1-C1
B1-C5
2.02(2)
1.20(2)
1.26(2)
1.597(3)
1.600(3)
Bond Angles (deg)
CpCentroid(C11-C15)-Zr1-B1
CpCentroid(C16-C10)-Zr1-B1
CpCentroid(C11-C15)-Zr1-H
CpCentroid(C16-C10)-Zr1-H
CpCentroid(C11-C15)-Zr1-HA
CpCentroid(C16-C10)-Zr1-HA
CpCentroid(C11-C15)-Zr1-HB
CpCentroid(C16-C10)-Zr1-HB
109.2
109.6
97.9
CpCentroid(C11-C15)-Zr1-CpCentroid(C16-C10)
B1-Zr1-H
136.0
95.5(8)
27.1(7)
29.0(5)
122.6(11)
66.5(9)
98.1
B1-Zr1-HA
102.4
102.6
112.1
111.8
B1-Zr1-HB
H-Zr1-HA
H-Zr1-HB
HA-Zr1-HB
56.1(8)
hydroborate zirconocene derivatives. The Zr-H hydro-
gen undergoes more facile exchange with bridging
hydrogen than with the Cp-hydrogen. These results
contrast with those observed from Cp2ZrH{(µ-H)2BH2},
in which the hydrogen of the borohydride ligand inter-
changes more rapidly with Cp-hydrogen than with Zr-H
hydrogen.7
Exp er im en ta l Section
Gen er a l Com m en ts. All operations were carried out on a
standard high-vacuum line or in a drybox under an atmo-
sphere of nitrogen. Toluene, tetrahydrofuran, and hexane were
dried over sodium/benzophenone and freshly distilled prior to
use. Cp2ZrCl2, Cp2NbCl2, (C8H14B)(µ-H)2(BC8H14), B(C6F5)3,
KH, and LiD were purchased from Aldrich and used as
received. Cp2Nb{(µ-H)2BC8H14} (7)3h was prepared by the
literature procedure. Cp2Nb{(µ-D)(µ-H)BC8H14} (8) was pre-
pared by the literature procedure using Li(THF)2[(D)(H)-
BC8H14], 5, instead of K[H2BC8H14].3h Elemental analyses were
obtained from Galbraith Laboratories, Knoxville, TN. Com-
plexes 3, 4, 5, and 6 are partially deuterated materials that
are related to the well-characterized undeuterated complexes
Cp2ZrCl{(µ-H)2BC8H14}, Cp2ZrH{(µ-H)2BC8H14}, Li(THF)2[H2-
BC8H14], and (C8H14B)(µ-H)2(BC8H14). Analyses of these com-
plexes were not attempted in view of the presence of mixed
hydrogen isotopes. However, their NMR spectra are clearly
consistent with those of the undeuterated species since the
chemical shifts of 1H and 2H are identical. 1H (250.1 MHz),
13C (62.9 MHz) (δ (TMS) 0.00 ppm), and 11B (128.4 MHz) (δ
(BF3‚OEt2) 0.00 ppm) NMR spectra were recorded on a Bruker
AM-250 NMR spectrometer. 2H NMR (61.4 MHz) spectra were
recorded on a Bruker DPX-400 NMR spectrometer, and the
The structures of the chloro (Figure 5) and hydrido
(Figure 6) complexes of the zirconocene cyclic organo-
hydroborates are similar. The absence of apparent direct
exchange between bridging and Cp-hydrogens, in the
temperature ranges studied, might be due to the fact
that the cyclic organohydroborate ligands are more
massive than the [BH4]- ligand, which is highly flux-
ional in Cp2ZrH{(µ-H)2BH2}.7 The [BH4]- ligand can
more easily move into a position conducive for direct
hydrogen exchange with Cp-hydrogen than the cyclic
organohydroborate ligands.
A possible pathway in which Zr serves as a conduit
of hydrogen passage in the exchange reactions of the
cyclic organohydroborate derivatives with terminal
hydrogen is shown in Scheme 3.

282 Organometallics, Vol. 22, No. 2, 2003
Chen et al.
Sch em e 3
1H (500.1 MHz)-13C (125.8 MHz) HMQC spectra were re-
corded on a Bruker DRX-500 spectrometer. Infrared spectra
were recorded on a Mattson Polaris Fourier Transform spec-
trometer with 2 cm-1 resolution.
2946(w), 2920(sh), 2873(vs), 2828(s), 1992(s), 1930(w), 1906(w),
1854(w), 1829(m), 1795(w), 1765(w), 1718(w), 1685(w), 1656(m),
1551(w), 1485(w), 1440(m), 1387(vs), 1343(s), 1281(w), 1264(m),
1202(m), 1110(w), 1063(sh), 1041(m), 1013(s), 925(m), 856(m),
809(vs), 738(m), 459(s) cm-1. Anal. Calcd for C18H26BClZr: C,
56.91; H, 6.90. Found: C, 56.74; H, 6.94.
X-r a y Str u ctu r e Deter m in a tion . Single-crystal X-ray
diffraction data were collected on an Enraf-Nonius KappaCCD
diffraction system, which employs graphite-monochromated
Mo KR radiation. A single crystal of 1 and 2 was mounted on
the tip of a glass fiber coated with fomblin oil (a perfluoro-
polyether). Crystallographic data were collected at 150 K for
both complexes. Unit cell parameters were obtained by index-
ing the peaks in the first 10 frames and refined employing
the whole data set. All frames were integrated and corrected
for Lorentz and polarization effects using DENZO.18 The
structures were solved by direct methods and refined using
SHELXTL (difference electron density calculations, full least-
squares refinements).19 For both structures, non-hydrogen
atoms were located and refined anisotropically. For 1 and 2
the bridge hydrogens and the terminal hydrogen atom of 2
were located and refined isotropically. All other hydrogen
atoms were calculated and fixed during the refinement.
P r ep a r a tion of Cp 2Zr Cl{(µ-H)2BC8H14}, 1. A solution of
K[H2BC8H14] (4.0 mmol in 20 mL of THF), which was obtained
by filtration of the reaction of 0.488 g (2.0 mmol) of (C8H14B)-
(µ-H)2(BC8H14) with 0.176 g (4.4 mmol) of KH in 20 mL of THF,
was added dropwise to 1.170 g (4.0 mmol) of Cp2ZrCl2 dissolved
in 20 mL of THF. The solution was stirred overnight at room
temperature and then filtered. The solvent was removed under
dynamic vacuum. The resulting white solid was dissolved in
P r ep a r a tion of Cp 2Zr H{(µ-H)2BC8H14}, 2. A 0.380 g (1.0
mmol) amount of 1 and 0.044 g (1.1 mmol) of KH were charged
into a flask in the drybox. The flask was degassed, and about
20 mL of THF was condensed into the flask. The system was
warmed and stirred at room temperature until all of the
starting material was consumed. The reaction was monitored
by 11B NMR spectroscopy. After the reaction, THF was
removed under vacuum, and toluene was introduced to extract
the product. The toluene solution was concentrated at room
temperature, and colorless crystals formed. The crystals were
washed with hexane and dried under vacuum, giving 0.310 g
(0.90 mmol, 90.0% yield). 11B NMR (toluene-d8): δ 32.5 (br t).
1H NMR (toluene-d8): δ 5.58 (s, 10H, Cp), 3.99 (s, 1H, Ht),
2.11 (br m, 2H, γ-H), 1.91 (br m, 4H, â-H), 1.83 (br m, 4H,
â-H), 1.73 (br m, 2H, γ-H), 1.39 (s, 2H, R-H), -3.17 (br d, 1H,
µ-H), -4.12 (br d, 1H, µ-H). 13C NMR (toluene-d8): δ 104.1
(Cp-C), 33.9 (â-C), 29.9 (br, R-C), 25.3 (γ-C). 13C-GD NMR
1
2
(toluene-d8): δ 104.1 (d-quintet, Cp-C, J CH ) 174.2 Hz, J CH
) 6.7 Hz, coupling to bridging and terminal hydrogen), 33.9
1
1
(t, â-C, J CH ) 123.3 Hz), 25.3 (t, γ-C, J CH ) 111.3 Hz). IR
(KBr): 3108(w), 3074(m), 2975(w), 2920(sh), 2873(vs), 2826(s),
1960(w), 1849(s), 1828(sh), 1794(m), 1733(w), 1699(m), 1651(m),
1557(m), 1539(m), 1425(vs), 1401(sh), 1341(s), 1315(sh, w),
1284(m), 1261(m), 1203(m), 1168(w), 1111(m), 1067(m), 1041(m),
1014(vs), 928(m), 888(m), 865(w), 828(sh), 805(vs), 734(m),
463(m) cm-1. Anal. Calcd for C18H27BZr: C, 62.59; H, 7.88.
Found: C, 60.94; H, 7.70.
a
minimum amount of toluene, and colorless needlelike
crystals were formed upon slow evaporation of the solvent at
room temperature. The crystals were washed with hexane and
dried under vacuum, giving 1.210 g (3.18 mmol, 79.5% yield).
1
11B NMR (toluene-d8): δ 17.7 (br t). H NMR (toluene-d8): δ
P r ep a r a t ion of Cp 2Zr Cl{(µ-D)(µ-H )BC8H 14}, 3. The
procedure was similar to the preparation of 1 using 0.275 g
5.75 (s, 10H, Cp), 2.01 (br s, 6H, 4 â-H and 2 γ-H), 1.91-1.72
(m, 6H, 4 â-H and 2 γ-H), 1.51 (s, 2H, R-H), 0.55 (br d, 1H,
µ-H), -2.40 (br d, 1H, µ-H). IR (KBr): 3106(m), 2980(w),
of [Li(THF)2][(D)(H)BC8H14],
5 (1.0 mmol), instead of
K[H2BC8H14] to react with 0.292 g of Cp2ZrCl2 (1.0 mmol).
Complex 3 was isolated as colorless crystals (0.287 g, 75.3%
yield). 11B NMR (toluene-d8): δ 18.1 (br t). 1H NMR (benzene-
d6): δ 5.76 (s, 10H, Cp), 2.01-1.64 (m, 12H, 8â-H and 4γ-H),
(18) Otwinowsky, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Methods in Enzymology, Vol. 276:
Macromolecular Crystallography, Part A; Carter, C. W., J r., Sweet, R.
M., Eds.; Academic Press: New York, 1997; pp 307-326.
(19) SHELXTL (version 5.10); Bruker Analytical X-ray Systems,
1997.
2
1.50 (s, 2H, R-H), 0.66 (br d, µ-H), -2.47 (br d, µ-H). H NMR
(toluene): δ 0.43 (s, µ-D), -2.48 (s, µ-D). 2H NMR (after heating
for 10 h at 318 K in toluene and then cooling to room

Cyclic Organohydroborate Complexes
Organometallics, Vol. 22, No. 2, 2003 283
temperature, toluene): δ 1.41(s, µ-D of 9-BBN dimer), -0.43
(s, µ-D), -2.43 (s, µ-D). IR (KBr): 3107(m), 2979(w), 2944(w),
2918(sh), 2871(vs), 2827(s), 1986(s), 1933(w), 1848(w), 1828(m),
1793(w), 1768(w), 1752(w), 1734(w), 1714(w), 1698(w), 1682(w),
1649(w), 1633(w), 1557(w), 1538(w), 1519(w), 1504(w), 1483(w),
1468(w), 1438(s), 1386(vs), 1337(s), 1281(m), 1254(m), 1240(w),
1202(m), 1109(w), 1069(m), 1014(s), 925(m), 835(m), 808(vs),
extract the product. The hexane solution was concentrated,
and colorless crystals formed. 6 was recrystallized from
toluene, and the crystals were dried under vacuum overnight
to give 0.056 g (0.23 mmol, 46.0% yield). 11B NMR (toluene-
1
d8): δ 27.1 (br m). H NMR (toluene-d8): δ 1.96 (m, 2H, γ-H),
1.85 (br m, 4H, â-H), 1.67 (m, 4H, â-H), 1.63 (s, 2H, R-H), 1.51
1
2
(m, 2H, γ-H). H{11B} NMR (toluene-d8): δ 1.46 (m, µ-H). H
NMR (toluene): δ 1.46 (s, µ-D). 13C NMR (toluene-d8): δ 33.7
(â-C), 24.4 (γ-C), 20.2 (R-C). 13C-GD NMR (toluene-d8): δ 33.7
735(m), 458(s) cm-1
.
P r ep a r a tion of Cp 2Zr D{(µ-H)2BC8H14}, 4. The procedure
was similar to the preparation of 2 using 0.015 g of LiD (1.5
mmol) instead of KH to react with 0.380 g of 1 (1.0 mmol).
Complex 4 was isolated as colorless crystals (0.252 g, 72.8%
1
1
(t, â-C, J CH ) 124.5 Hz), 24.4 (t, γ-C, J CH ) 125.8 Hz). IR
(KBr): 2982(m), 2952(m), 2926(m), 2884(vs), 2836(s), 1648(m),
1563(m), 1512(m), 1467(s), 1398(m), 1318(m), 1260(s), 1213(s),
1156(s), 1068(vs), 968(m), 916(s), 869(w), 839(w), 804(s),
744(m), 479(m) cm-1. Complex 6 was heated in toluene for 1
h at 358 K and was isolated as colorless crystals, which were
characterized by NMR and IR spectroscopies. 11B NMR
1
yield). 11B NMR (toluene-d8): δ 32.2 (br t). H NMR (toluene-
d8): δ 5.59 (s, 10H, Cp), 3.99 (s, 1H, Ht), 2.07 (br m, 2H, γ-H),
1.90 (br m, 4H, â-H), 1.84-1.71 (m, 6H, 4â-H and 2γ-H), 1.38
(s, 2H, R-H), -3.25 (br d, µ-H), -4.24 (br d, µ-H). 2H NMR
(toluene): δ 3.97 (s, Dt), -3.31 (s, µ-D), -4.26 (s, µ-D). 2H NMR
(after heating for 1 h at 85 °C in toluene and then cooling to
room temperature, toluene): δ 5.60 (s, Cp-D), 3.97 (s, Dt), 1.40
(s, R-D), -3.27 (s, µ-D), -4.27 (s, µ-D). 13C NMR (toluene-d8):
δ 104.1 (Cp-C), 33.9 (â-C), 29.9 (br s, R-C), 25.3 (γ-C). 13C-GD
NMR (toluene-d8): δ 104.1 (d-quintet, Cp-C, 1J CH ) 173.7 Hz,
2J CH ) 6.5 Hz, coupling to bridging and terminal hydrogen),
1
(toluene-d8): δ 27.3 (br m). H NMR (toluene-d8): δ 1.96 (m,
2H, γ-H), 1.86 (br m, 4H, â-H), 1.67 (m, 4H, â-H), 1.63 (s, 2H,
R-H), 1.51 (m, 2H, γ-H). 1H{11B} NMR (toluene-d8): δ 1.47 (m,
2
µ-H). H NMR (toluene): δ 1.88 (s), 1.67 (s), 1.47 (s, µ-D). 13C
NMR (toluene-d8): δ 33.7 (â-C), 24.4 (γ-C). 13C-GD NMR
(toluene-d8): δ 33.7 (t, â-C, 1J CH ) 125.8 Hz), 24.4 (t, γ-C, 1J CH
) 124.5 Hz). IR (KBr): 2982(m), 2952(m), 2926(m), 2905(sh),
2885(vs), 2836(s), 1647(w), 1634(w), 1569(vs), 1511(w), 1467-
(sh), 1445(s), 1398(s), 1358(w), 1318(s), 1301(w), 1260(m), 1213-
(s), 1160(s), 1104(m), 1066(s), 968(m), 916(s), 865(w), 806(s),
1
1
34.0 (t, â-C, J CH ) 122.2 Hz), 25.3 (t, γ-C, J CH ) 121.6 Hz).
IR (KBr): 3111(w), 3074(m), 2974(m), 2918(sh), 2875(vs),
2825(s), 1960(sh), 1849(s), 1827(s), 1796(m), 1733(w), 1699(m),
1651(m), 1557(m), 1539(m), 1429(vs), 1398(sh), 1321(s), 1261(m),
1203(m), 1168(w), 1111(m), 1067(m), 1038(m), 1013(vs), 927(m),
743(m), 477(m) cm-1
.
The dimer C8H14B(µ-H)2BC8H14 was characterized by NMR
and IR spectroscopies for comparison with 6. 11B NMR
(toluene-d8): δ 27.7 (br t). 1H NMR (toluene-d8): δ 1.95 (m,
2H, γ-H), 1.86 (br m, 4H, â-H), 1.65 (m, 4H, â-H), 1.62 (s, 2H,
R-H), 1.51 (m, 2H, γ-H). 1H{11B} NMR (toluene-d8): δ 1.47 (m,
µ-H). 13C NMR (toluene-d8): δ 33.6 (â-C), 24.4 (γ-C).13C NMR
(benzene-d6): δ 33.6 (â-C), 24.3 (γ-C), 20.2 (br s, R-C). 13C-GD
829(sh), 807(vs), 733(m), 669(m), 501(m), 457(m) cm-1
.
P r ep a r a tion of [Li(THF )2][(D)(H)BC8H14], 5. A 50 mL
flask was charged with 0.448 g (2.0 mmol) of (C8H14B)(µ-H)2-
(BC8H14) and 0.040 g (4.5 mmol) of LiD. The flask was
evacuated, and ca. 30 mL of THF was condensed at -78 °C.
The system was warmed to room temperature and stirred until
all of the starting material was consumed. The reaction was
monitored by 11B NMR spectroscopy. After the reaction, the
excess LiD was removed by filtration and THF was removed
under vacuum. The white solid was washed with hexane and
dried under vacuum overnight. Complex 5 was isolated as [Li-
(THF)2][(D)(H)BC8H14] (0.816 g, 2.97 mmol, 74.2% yield). 11B
NMR (toluene-d8): δ -17.5 (asymmetric triplet, 1J ) 68.1 Hz).
1
NMR (toluene-d8): δ 33.7 (t, â-C, J CH ) 125.8 Hz), 24.4 (t,
1
γ-C, J CH ) 125.8 Hz). IR (KBr): 2982(m), 2953(m), 2927(m),
2905(sh), 2884(vs), 2836(s), 1569(vs), 1521(w), 1485(w), 1444(s),
1404(w), 1345(w), 1318(m), 1301(w), 1260(m), 1213(m), 1105(s),
1065(s), 1020(s), 916(s), 8690(w), 839(w), 808(s), 744(m),
479(m) cm-1
.
1
11B{H} NMR (toluene-d8): δ -18.4. H NMR (toluene-d8): δ
Ack n ow led gm en t. This work was supported by the
National Science Foundation through Grant CHE99-
01115 to S.G.S. and CHE-0077605 to G.F. We thank
Dr. Karl Vermillion and Dr. Roman Kultyshev for
assistance with the 2H NMR and 1H-13C correlation
experiments.
3.58 (t, 8H, O(CH2CH2)2), 2.42-2.27 (br m, 2H, γ-H), 2.18 (br
m, 8H, â-H), 1.98 (s, 2H, γ-H), 1.42 (t, 8H, O(CH2CH2)2), 1.12
(s, 2H, R-H). 1H{11B} NMR (toluene-d8): δ 0.77 (µ-H). 2H NMR
(toluene): δ 0.67 (s, µ-D). 2H NMR (after heating for 1 h at
358 K and then cooling to room temperature, toluene): δ 0.70
(s, µ-D). IR (KBr): 2979(m), 2914(vs), 2972(vs), 2834(vs),
1469(s), 1447(s), 1415(vs), 1337(m), 1291(m), 1263(w), 1204(m),
1168(w), 1105(m), 1074(m), 1045(vs), 986(sh), 893(m), 822(m),
Su p p or tin g In for m a tion Ava ila ble: Molecular structure
of the second independent molecule for 1; tables of crystal-
lographic data, positional and thermal parameters, and inter-
atomic distances and angles for 1 and 2; relevant additional
800(m), 734(m), 480(m) cm-1
.
P r ep a r a tion of (C8H14B)(µ-D)(µ-H)(BC8H14), 6. A 50 mL
flask was charged with 0.275 g (1.0 mmol) of 5 and 0.512 g
(1.0 mmol) of B(C6F5)3. Approximately 20 mL of THF was
condensed at -78 °C. The solution was warmed to room
temperature and stirred for 1 h. The 11B NMR spectrum of
the reaction solution indicated that 5 was consumed. The THF
was reduced under vacuum, and dry hexane was added to
2
1
1H, H, 11B, 13C, H-13C, and VT-1H NMR spectra for 1, 2, 3,
4, 5, 6, 7, and 8. Two X-ray crystallographic files in CIF format.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM0206249