Cyclic hydroborate complexes of metallocenes. IV. Weak Unsupported single hydrogen bridges in Cp2Zr{μ-HB(X)CH2Ph}{(μ-H)2BX} (X = C5H10, C4H8)

Article abstract of DOI:10.1021/ic981347u

The compounds Cp₂Zr{(μ-H)(BC₅H₁₀)CH ₂Ph}{(μ-H)₂BC₅H₁₀}, 1, and Cp₂Zr{(μ-H)(BC₄H₈)CH ₂Ph}{(μ-H)₂BC₄H₈}, 2, were prepared in yields of 59percent and 51percent, respectively, from the the unsupported Zr-H-B bridge in complexes 1 and 2. However, NMR spectra at room temperature indicate that the hydrogen bridge is dissociated into Cp₂ZrH{(μ-H)₂BC₅H₁₀} and B(C₅H₁₀)CH₂Ph in the case of complex 1, and Cp₂ZrH{(μ-H)₂BC₄H₈} and B(C₄H₈)CH₂Ph in the case of complex 2. It is possible to pump away the B(C₄H₈)CH₂Ph from solid 2 at room temperature, leaving behind Cp₂ZrH{(μ-H)₂BC₄H₈}. These results suggest that the Zr-H bond acts as an electron pair donor to trivalent boron in the formation of 1 and 2. Crystal data for Cp₂Zr{(μ-H)(BC₅H₁₀)CH ₂Ph}{(μ-H)₂BC₅H₁₀}: monoclinic, P2₁/m (No. 11), a = 9.392(5) A?, b = 13.250(4) A?, c = 9.841(6) A?, β = 95.70(4)°, Z = 2. Crystal data for Cp₂Zr{(μ-H)(BC₄H₈)CH ₂Ph}{(μ-H)₂BC₄H₈}: orthorhombic, Pbca (No. 61), a = 18.1630(10) A?, b = 19.0497(10) A?, c = 13.0393(10) A?, Z = 8.

Full text of DOI:10.1021/ic981347u

Inorg. Chem. 1999, 38, 2169-2173
2169
Cyclic Hydroborate Complexes of Metallocenes. IV. Weak Unsupported Single Hydrogen
Bridges in Cp2Zr{(µ-H)B(X)CH2Ph}{(µ-H)2BX} (X ) C5H10, C4H8)
Fu-Chen Liu, Jianping Liu, Edward A. Meyers, and Sheldon G. Shore*
Department of Chemistry, The Ohio State University, Columbus, Ohio 43210
ReceiVed NoVember 24, 1998
The compounds Cp2Zr{(µ-H)(BC5H10)CH2Ph}{(µ-H)2BC5H10}, 1, and Cp2Zr{(µ-H)(BC4H8)CH2Ph}{(µ-
H)2BC4H8}, 2, were prepared in yields of 59% and 51%, respectively, from the reactions of Cp2ZrCl{(µ-H)2BX}
(X ) C5H10, C4H8) with PhCH2MgCl. Single-crystal X-ray diffraction analyses indicate the presence of an
1
unsupported Zr-H-B bond in these complexes. In solution at low temperature H NMR spectra are consistent
with the presence of the unsupported Zr-H-B bridge in complexes 1 and 2. However, NMR spectra at room
temperature indicate that the hydrogen bridge is dissociated into Cp2ZrH{(µ-H)2BC5H10} and B(C5H10)CH2Ph in
the case of complex 1, and Cp2ZrH{(µ-H)2BC4H8} and B(C4H8)CH2Ph in the case of complex 2. It is possible
to pump away the B(C4H8)CH2Ph from solid 2 at room temperature, leaving behind Cp2ZrH{(µ-H)2BC4H8}.
These results suggest that the Zr-H bond acts as an electron pair donor to trivalent boron in the formation of 1
and 2. Crystal data for Cp2Zr{(µ-H)(BC5H10)CH2Ph}{(µ-H)2BC5H10}: monoclinic, P21/m (No. 11), a ) 9.392-
(5) Å, b ) 13.250(4) Å, c ) 9.841(6) Å, â ) 95.70(4)°, Z ) 2. Crystal data for Cp2Zr{(µ-H)(BC4H8)CH2Ph}-
{(µ-H)2BC4H8}: orthorhombic, Pbca (No. 61), a ) 18.1630(10) Å, b ) 19.0497(10) Å, c ) 13.0393(10) Å, Z
) 8.
Introduction
Chart 1
The M-H-B three-center, two-electron bond is present in
covalent hydroborate metal complexes in which the hydroborate
serves as a monodentate, bidentate, or tridentate ligand (Chart
1). Tridentate and bidentate linkages between metal and boron
atoms are more common than monodentate linkages.1 IR
spectroscopy has been applied as the principal technique for
the identification of monodentate interaction of a hydroborate
anion with a metal for most of the complexes that have been
reported to contain an unsupported M-H-B bond.1a,2 However,
there are some monodentate complexes that have been structur-
ally characterized by single-crystal X-ray or neutron diffraction
analyses. These are [Cu{(µ-H)BH3}(PMePh2)3],3 [Cu{(µ-H)-
BH3}{(PPh2CH2)3CMe}],4 [FeH{(µ-H)BH3}(dmpe)2] (dmpe )
bis(dimethylphosphino)ethane),5 [Hf2{N(SiMe2CH2PMe2)2}2H3-
(BH4)3],6 [V{(µ-H)BH3}2{dmpe}2],7 {Cr(Py)4{(µ-H)BH3}2} (Py
) pyridine),8 {Cr3(TMEDA)2(Py)4((µ-H)2BH2)4}{(µ-H)BH3}2}
(TMEDA ) N,N,N′,N′-tetramethylethylenediamine),8 and {RuH-
{(µ-H)BH3}(Me8[16]aneS4).9 Monodentate, unsupported M-H-B
bridges have also been observed in the following compounds:
{M(CO)5((µ-H)B2H3‚2PMe3)} (M ) Cr, W),10 and {Cp2Ta-
(PMe3){(µ-H)BH2(Si(t-Bu)2H)}.11
Described here is recent work that led to the preparation and
isolation of the following complexes with unsupported single
hydrogen bridges: Cp2Zr{(µ-H)B(X)CH2Ph}{(µ-H)2BX} (X )
C5H10 (1), C4H8 (2)). To our knowledge these are the first
demonstrated examples of the formation of a single M-H-B
bond in which the M-H bond acts as an electron pair donor to
a trivalent boron to form the hydrogen-bridged bond.12 In
previous examples3-11 the B-H bond serves as the electron
pair donor to the unsaturated metal center.
(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
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.;
Pergamon Press Inc.: New York, 1982; pp 879-945.
(2) Marks, T. J.; Kennelly, W. J.; Kolb, J. R.; Shimp, L. A. Inorg. Chem.
1972, 11, 2540.
(3) (a) Takusagawa, F.; Fumagalli, A.; Koetzle, T. F.; Shore, S. G.;
Schmitkons, T.; Fratini, A. V.; Morse, K. W.; Wei, C.-Y.; Bau, R. J.
Am. Chem. Soc. 1981, 103, 5165. (b) Bommer, J. C.; Morse, K. W.
Inorg. Chem. 1980, 19, 587. (c) Kutal, C.; Grutsch, P.; Atwood, J. L.;
Rogers, R. D. Inorg. Chem. 1978, 17, 3558.
(4) (a) Ghilardi, C. A.; Midollini, S.; Orlandini, A. Inorg. Chem. 1982,
21, 4096. (b) Dapporto, P.; Midollini, S.; Orlandini, A.; Sacconi, L.
Inorg. Chem. 1976, 15, 2768.
(5) (a) Bau, R.; Yuan, H. S. H.; Baker, M. V.; Field, L. D. Inorg. Chim.
Acta 1986, 114, L27. (b) Baker, M. V.; Field, L. D. J. Chem. Soc.,
Chem. Commun. 1984, 996.
Results and Discussion
Formation of Cp2Zr{(µ-H)B(X)CH2Ph}{(µ-H)2BX} (X )
2
C5H10,1 C4H8 ). In an attempt to prepare the benzyl-substituted
cyclic hydroborate complex Cp2Zr(CH2Ph){(µ-H)2BC5H10}
from the reaction of Cp2ZrCl{(µ-H)2BC5H10}13 with PhCH2-
(8) Dionne, M.; Hao, S.; Gambarotta, S. Can. J. Chem. 1995, 73, 1126.
(9) Yoshida, T.; Adachi, T.; Ueda, T.; Akao, H.; Tanaka, T.; Goto, F.
Inorg. Chim. Acta 1995, 231, 95.
(10) Katoh, K.; Shimoi, M.; Ogino, H. Inorg. Chem. 1992, 31, 670.
(11) Jiang, Q.; Carroll, P. J.; Berry, D. H. Organometallics 1993, 12, 177.
(12) Ir-H‚‚‚B interaction in fac-[IrH(PMe3)3(η2-CH2BHC8H14)] has been
suggested. Baker, R. T.; Ovenall, D. W.; Calabrese, J. C.; Westcott,
S. A.; Taylor, N. J.; Williams, I. D.; Marder, T. B. J. Am. Chem. Soc.
1990, 112, 9399.
(6) Fryzuk, M. D.; Rettig, S. J.; Westerhaus, A.; Williams, H. D. Inorg.
Chem. 1985, 24, 4316.
(7) Jensen, J. A.; Girolami, G. S. Inorg. Chem. 1989, 28, 2107.
(13) Liu, J.; Meyers, E. A.; Shore, S. G. Inorg. Chem. 1998, 37, 496.
10.1021/ic981347u CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/14/1999

2170 Inorganic Chemistry, Vol. 38, No. 9, 1999
Liu et al.
Figure 2. Molecular structure of Cp2Zr{(µ-H)BC4H8(CH2Ph)}{(µ-
H)2BC4H8} showing 25% probability ellipsoids.
Figure 1. Molecular structure of Cp2Zr{(µ-H)BC5H10(CH2Ph)}{(µ-
H)2BC5H10} showing 50% probability ellipsoids.
Table 1. Crystallographic Data for
Cp2Zr{(µ-H)BC5H10(CH2Ph)}{(µ-H)2BC5H10}, 1, and
MgCl, a complicated sequence of reactions occurred that resulted
in the isolation of Cp2Zr{(µ-H)B(C5H10)CH2Ph}{(µ-H)2BC5H10},
1, a compound that contains an unsupported single hydrogen
bridge in the solid state. The reaction produces a mixture of
several organoborate species. Boron-11 NMR spectra at room
temperature indicate that the initial major products are Cp2ZrH-
{(µ-H)2BC5H10}14 and an organoborate anion (δ ) -15.2 ppm)
that is believed to be [B(C5H10)(CH2Ph)2]MgCl,15 an intermedi-
ate that decreases in concentration with time. Minor initial
components Cp2Zr(CH2Ph){(µ-H)2BC5H10}16 and B(C5H10)CH2-
Ph increase in concentration as the concentration of the
intermediate species decreases. Similar competing reactions
resulting in complicated products are also observed in the direct
alkylation of the cyclic hydroborate complexes Cp2ZrCl{(µ-
H)2X} (X ) BC4H8, BC5H10).13,17 Crystallization from the
reaction mixture yielded two types of crystals that were manually
separated: Cp2Zr{(µ-H)B(C5H10)CH2Ph}{(µ-H)2BC5H10}, 1
(59% yield), colorless crystals identified from a single-crystal
X-ray diffraction analysis, and the previously reported com-
pound Cp2Zr(CH2Ph)218 (10% yield), orange crystals that were
Cp2Zr{(µ-H)BC4H8(CH2Ph)}{(µ-H)2BC4H8}, 2
empirical formula
fm, amu
C27H40B2Zr
477.44
C25H36B2Zr
449.38
space group
a, Å
b, Å
P21/m
Pbca
9.392(5)
13.250(4)
9.841(6)
95.70(4)
1218.7(11)
2c
18.1630(10)
19.0497(10)
13.0393(10)
c, Å
â, deg
vol, Å3
4511.6(5)
8
1.323
Z
F(calcd), g cm-3
cryst size, mm
T, °C
1.301
0.35 × 0.45 × 0.34
0.25 × 0.20 × 0.28
-60
-60
radiation (λ, Å)
Mo KR (0.710 73)
0.463
Mo KR (0.710 73)
0.495
µ, mm-1
scan mode
2θ limits, deg
(h
ω-2θ
4-45
-10, 10
0, 14
-10, 10
3430
1675
1336
ω-2θ
4-50
-21, 21
0, 22
0, 15
7926
3965
2558
(k
(l
no. of rflns measd
no. of unique rflns
no. of unique rflns
[I > 2.0σ(I)]
no. of variables
R1a [I > 2.0σ(I)]
wR2b (all data)
Rint
1
identified by H NMR spectroscopy and confirmed by single-
151
265
crystal X-ray diffraction analysis.19
0.0378
0.0894
0.0466
1.041
0.0341
0.0894
0.0298
1.015
The reaction of Cp2ZrCl{(µ-H)2BC4H8} with PhCH2MgCl
forms the complex Cp2Zr{(µ-H)B(C4H8)CH2Ph}{(µ-H)2BC4H8},
2 (51% yield, colorless crystals), in a sequence of steps, followed
by NMR spectroscopy, with intermediate species similar to those
in the formation of 1.
Molecular Structures of 1 and 2. The molecular structures
of 1 and 2 are shown in Figures 1 and 2. Crystallographic data
and selected positional parameters, bond distances, and bond
GOF
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑w(Fo2 - Fc2)2/∑w(Fo )2}1/2
.
2
c The asymmetric unit for 1 is one half of a molecule. Therefore, there
are 4 asymmetric units in the unit cell.
angles are given in Tables 1-5. The X-ray analyses show that
the structures of complexes 1 and 2 are closely related. In the
solid state, each complex contains an unsupported single
hydrogen Zr-H-B bridge that connects the Cp2Zr{(µ-
H)2BC5H10} and BC5H10(CH2Ph) units in 1 and the Cp2Zr{(µ-
H)2BC4H8} and BC4H8(CH2Ph) units in 2. The Zr-H bond of
the parent zirconocene hydride organohydroborate acts as an
electron pair donor to the boron of the alkyl borane.
(14) Liu, F.-C.; Liu, J.; Meyers, E. A.; Shore, S. G. Inorg. Chem. 1998,
37, 3293.
(15) This chemical shift is consistent with chemical shifts reported for
tetraalkyl borate anions. No¨th, H.; Wrackmeyer, B. Nuclear Magnetic
Resonance Spectroscopy of Boron Compounds; Diehl, P., Fluck, E.,
Kosfeld, R., Eds.; Springer-Verlag: Berlin, 1978; p 384.
(16) Liu, F.-C. Ph.D. Dissertation, The Ohio State University, 1998.
(17) (a) Jordan, G. T., IV; Liu, F.-C.; Shore, S. G. Inorg. Chem. 1997, 36,
5597. (b) Jordan, G. T., IV; Shore, S. G. Inorg. Chem. 1996, 35, 1087.
(18) Fachinetti, G.; Floriani, C. J. Chem. Soc., Chem. Commun. 1972, 11,
654.
(19) The molecular structure, crystallographic data, positional parameters,
bond distances, and bond angles of Cp2Zr(CH2Ph)2 are provided in
the Supporting Information.

Cyclic Hydroborate Complexes of Metallocenes
Inorganic Chemistry, Vol. 38, No. 9, 1999 2171
Table 2. Atomic coordinates (×104) and Equivalent Isotropic
Displacement Parameters (Å2 × 103) for
Table 4. Atomic Coordinates (×104) and Equivalent Isotropic
Displacement Parameters (Å2 × 103) for
Cp2Zr{(µ-H)BC5H10(CH2Ph)}{(µ-H)2BC5H10}, 1
Cp2Zr{(µ-H)BC4H8(CH2Ph)}{(µ-H)2BC4H8}, 2
atom
x
y
z
U(eq)a,b
atom
x
y
z
U(eq)a,b
Zr
C(1)
C(2)
C(3)
C(4)
C(5)
B(1)
C(11)
C(12)
C(13)
B(2)
C(21)
C(22)
C(23)
C
C(1C)
C(2C)
C(3C)
C(4C)
C(5C)
C(6C)
H(1A)
H(1B)
H(2A)
9797(1)
9862(5)
11025(5)
10508(6)
9016(6)
8614(5)
8124(7)
7556(4)
7733(5)
7056(6)
12548(7)
12194(4)
12943(4)
12550(6)
14105(6)
14453(7)
14344(8)
14546(9)
14939(17)
15036(9)
14832(9)
9415(51)
8069(54)
11385(51)
2500
7909(1)
7705(4)
8607(5)
9775(4)
9567(5)
8282(5)
5665(6)
4894(4)
3364(4)
2729(6)
6179(6)
5284(4)
3973(4)
3174(6)
7058(6)
8106(7)
9495(8)
10435(9)
10102(16)
8647(9)
7725(8)
5863(48)
6965(54)
7302(51)
23(1)
40(1)
43(1)
52(1)
52(1)
44(1)
27(1)
39(1)
46(1)
38(2)
31(2)
33(1)
41(1)
46(2)
33(1)
30(2)
37(2)
42(2)
39(2)
40(2)
35(2)
26(13)
35(15)
33(15)
Zr
1256(1)
2025(2)
812(2)
1167(2)
1911(2)
1088(4)
1741(3)
1643(5)
913(7)
6302(1)
6409(2)
6656(2)
7241(2)
7079(2)
6277(2)
6563(3)
7170(4)
7276(4)
6707(5)
5126(2)
4678(2)
4088(2)
3945(2)
4669(2)
5489(2)
4956(2)
4229(2)
4262(2)
4973(2)
6564(2)
7771(2)
7579(2)
6882(2)
6380(2)
5708(17)
5284(16)
5941(16)
2617(1)
732(2)
892(3)
23(1)
42(1)
48(1)
49(1)
42(1)
77(2)
73(2)
114(3)
157(5)
115(3)
31(1)
39(1)
44(1)
41(1)
36(1)
31(1)
40(1)
49(1)
51(1)
42(1)
35(1)
56(1)
56(1)
54(1)
45(1)
44(9)
32(8)
31(9)
4369(3)
4114(3)
3705(3)
3725(3)
4137(3)
2500
3501(3)
3440(3)
2500
C(1)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
B(1)
C(11)
C(12)
C(13)
C(14)
B(2)
C(15)
C(16)
C(17)
C(18)
C(20)
C(21)
C(23)
C(24)
C(25)
HA
1314(3)
1417(3)
4487(3)
4342(3)
3880(4)
3755(5)
4135(5)
2762(3)
3781(3)
3429(3)
2324(3)
1838(2)
2487(3)
3465(3)
3001(3)
1953(3)
1503(3)
1699(3)
1144(4)
152(3)
579(2)
2500
1916(2)
2089(2)
2602(2)
2391(2)
2259(2)
-323(2)
-264(2)
-380(2)
-12(2)
-234(1)
-1098(2)
-1061(2)
-1213(2)
-1299(2)
-1244(2)
2145(18)
1258(16)
259(17)
1491(3)
1541(3)
2500
2500
1651(6)
1816(6)
1053(7)
110(11)
-92(7)
695(6)
2500
2500
2500
-72(3)
687(3)
2809(24)
2651(22)
2451(21)
a U(eq) is defined as one-third of the trace of the orthogonalized Uij
tensor. b Hydrogen atoms from H(1A) to H(2A) were located and
refined isotropically.
HB
HC
a U(eq) is defined as one-third of the trace of the orthogonalized Uij
tensor. b Hydrogen atoms from H(A) to H(C) were located and refined
isotropically.
Table 3. Selected Interatomic Distances (Å) and Bond Angles
(deg) for Cp2Zr{(µ-H)BC5H10(CH2Ph)}{(µ-H)2BC5H10}, 1a
Bond Lengths
av Zr-C(1-5)b
Zr-centroid(C1-C5)
Zr-B(1)
2.480[5]
2.179
B(2)-H(2A)
B(1)-C(11)
C(11)-C(12)
C(12)-C(13)
B(2)-C
1.63(5)
Zr-H-B bond. We believe that the Zr-H and H-B distances
in this bond in complex 2 are more accurate than those in 1. In
complex 2 the Zr-H distance of the Zr-H-B bond is 1.95(3)
Å, longer than that for the terminal Zr-H bond 1.68(5) Å in
Cp2ZrH{(µ-H)2BC4H8}. Upon forming a Zr-H-B bridge,
lengthening of the Zr-H distance is to be expected. Recent ab
initio DFT calculations for the hypothetical compound Cp2NbH2-
(µ-H)BH3 showed a “strong interaction” between BH3 and the
central hydride of Cp2NbH3,20 that lengthens the Nb-H distance
by 0.08 Å with respect to uncomplexed Cp2NbH3. In the case
of 1 the Zr-H distance is apparently shortened to 1.66(5) Å
from 1.79(5) Å in Cp2ZrH{(µ-H)2BC5H10}, an observation we
consider to be unrealistic due to the disordered nature of the
structure. The B-H distance in the unsupported B-H-B bond
of 2 is 1.36(3) Å, a reasonable value for a B-H distance in a
three-center bond.1 In the case of 1 the corresponding B-H
component appears to be unreasonably long, 1.63(5) Å.
1.593(5)
1.534(6)
1.506(5)
1.624(8)
1.618(5)
1.532(5)
1.521(5)
1.539(8)
2.580(6)
3.232(6)
2.01(5)
1.79(5)
1.66(5)
1.21(5)
1.29(5)
Zr-B(2)
Zr-H(1A)
Zr-H(1B)
B(2)-C(21)
C(21)-C(22)
C(22)-C(23)
C-C(1C)
Zr-H(2A)
B(1)-H(1A)
B(1)-H(1B)
Bond Angles
133.3 C(11)#1-B(1)-C(11) 112.7(4)
111.1(4)
centroid-Zr-centroid
centroid(C1-C5)-Zr-B(1) 108.5
centroid(C1-C5)-Zr-H(1A) 113.0
centroid(C1-C5)-Zr-H(1B) 100.0
centroid(C1-C5)-Zr-H(2A) 100.1
C(12)-C(11)-B(1)
C(13)-C(12)-C(11) 111.6(4)
C(12)-C(13)-C(12)#1 111.6(5)
C-B(2)-C(21)
27.1(14) C-B(2)-C(21)#1
114.6(3)
114.6(3)
C(21)-B(2)-C(21)#1 111.5(5)
B(1)-Zr-H(1A)
B(1)-Zr-H(2A)
101(2)
54(2)
74(2)
128(2)
89(3)
H(1A)-Zr-H(1B)
H(1A)-Zr-H(2A)
H(1B)-Zr-H(2A)
H(1A)-B(1)-H(1B)
C(11)#1-B(1)-H(1A)
C(11)-B(1)-H(1A)
C(11)#1-B(1)-H(1B)
C(11)-B(1)-H(1B)
C(22)-C(21)-B(2) 109.6(4)
C(23)-C(22)-C(21) 111.3(4)
C(22)#1-C(23)-C(22) 113.4(5)
C(1C)-C-B(2)
118.5(4)
158.5(33)
105.5(18)
104.7(9)
NMR Studies of 1 and 2. NMR spectra21 of 1 and 2 indicate
the formation of the unsupported Zr-H-B bridge at low
temperature. In d8-toluene, the single-bridge Zr-H-B hydrogen
exibits a high-field shift at -60 °C. It appears at -2.32 ppm in
1 and -0.16 ppm in 2, which are 6.36 and 4.07 ppm upfield
from the chemical shift of the Zr-H hydrogen in the uncom-
plexed zirconocene hydrides, Cp2ZrH{(µ-H)2BC5H10} and Cp2-
ZrH{(µ-H)2BC4H8}, at the same temperature. However, NMR
spectra21 in solution at room temperature (11B and 1H) indicate
that 1 and 2 are dissociated in diethyl ether and in benzene.
111.1(11) Zr-H(2A)-B(2)
111.1(10) H(2A)-B(2)-C
115.4(9) H(2A)-B(2)-C(21)
115.4(9)
a Symmetry transformations used to generate equivalent atoms: #1
x, -y + 1/2, z. b The standard deviation (σl) for the average bond length
of Zr-C is calculated according to the equations25 l ) ∑mlm/m and σl
) [∑m(lm - l )2/m(m - 1)]1/2, where l is the mean length, lm is the
length of the mth bond, and m is the number of bonds.
In general, bond distances involving Zr, H, and B are
comparable for equivalent components of complexes 1 and 2.
However, because complex 1 is disordered in the solid state,
uncertainties in its bond distances are larger than in 2 and
significant differences occur in the “observed” Zr-H and H-B
distances of 1 and 2 and their H-B distances in the unsupported
(20) Camanyer, S.; Maseras, F.; Moreno, M.; Lledo´s, A.; Lluch, J. M.;
Bertra`n, J. Angew Chem., Int. Ed. Engl. 1997, 36, 265.
(21) Proton spectra of Cp2ZrH{(µ-H)2BC5H10}, Cp2ZrH{(µ-H)2BC4H8},
Cp2Zr{(µ-H)BC5H10(CH2Ph)}{(µ-H)2BC5H10}, and Cp2Zr{(µ-H)-
BC4H8(CH2Ph)}{(µ-H)2BC4H8} are provided in the Supporting In-
formation.

2172 Inorganic Chemistry, Vol. 38, No. 9, 1999
Liu et al.
Table 5. Selected Interatomic Distances (Å) and Bond Angles
(deg) for Cp2Zr{(µ-H)BC4H8(CH2Ph)}{(µ-H)2BC4H8}, 2
proton decoupling, the signal at 30.70 ppm collapses to a singlet
and the signal at 90.50 ppm is unchanged. The proton NMR
resonances of component Cp2ZrH{(µ-H)2BC4H8} of 2 is almost
identical to that of the free molecule of Cp2ZrH{(µ-H)2BC4H8},
except for a 0.04 ppm upfield shift.
If any association occurs in solution at room temperature, it
is undoubtedly very weak. When solvent Et2O was pumped from
solution of 2 to a dynamic vacuum of 10-5 Torr at room
temperature for 24 h, 70% of the alkyl borane, BC4H8(CH2Ph),
was removed. A similar result has been observed for Cp3Zr(µ-
H)Al(C2H5)3,23 which crystallizes as an unsupported single
hydrogen bridged compound, but is also apparently dissociated
in solution.
Bond Lengths
av Zr-C(1-5)a
av Zr-C(6-10)a
Zr-centroid(C1-C5)
Zr-centroid(C6-C10)
Zr-B(1)
2.479[6]
2.455[5]
2.175
B(1)-C(11)
B(1)-C(14)
C(11)-C(12)
C(12)-C(13)
C(13)-C(14)
B(2)-C(19)
B(2)-C(18)
B(2)-C(15)
C(15)-C(16)
C(16)-C(17)
C(17)-C(18)
1.610(5)
1.613(5)
1.530(5)
1.516(5)
1.536(5)
1.621(5)
1.625(5)
1.633(5)
1.524(5)
1.523(5)
1.530(5)
2.179
2.548(4)
3.263(4)
1.99(3)
1.94(3)
1.95(3)
1.18(3)
1.24(3)
1.36(3)
Zr-B(2)
Zr-HA
Zr-HB
Zr-HC
B(1)-HA
B(1)-HB
B(2)-HC
Bond Angles
133.2
Experimental Section
centroid-Zr-centroid
C(11)-B(1)-HB
C(14)-B(1)-HB
C(19)-B(2)-HC
C(18)-B(2)-HC
C(15)-B(2)-HC
114.3(14)
114.5(14)
102.8(13)
106.2(12)
111.6(12)
centroid(C1-C5)-Zr-B(1) 107.5
General Procedures. All manipulations were carried out on a
standard high-vacuum line or in a drybox under an atmosphere of
nitrogen. Diethyl ether was dried over Na/benzophenone and freshly
distilled prior to use. Hexane was dried over CaH2 and freshly distilled
prior to use. Cp2ZrCl2, KH, BH3‚THF (1 M solution in THF), and
benzylmagnesium chloride (1.0 M in Et2O) were purchased from
Aldrich and used as received. Cp2ZrCl{(µ-H)2BC5H10}13 and Cp2ZrCl-
{(µ-H)2BC4H8}17 were prepared by literature procedures. Elemental
analyses were obtained by Galbraith Laboratories, Knoxville, TN. Room
temperature 1H (δ(TMS) ) 0.00 ppm) and 11B NMR spectra were
recorded on a Bruker AM-250 NMR spectrometer operating at 250.11
and 80.253 MHz at 303 K. 1H{11B} (δ(TMS) ) 0.00 ppm) NMR
spectra at 213 K were recorded on a Bruker AM-500 NMR spectrometer
operating at 500.13 MHz. Boron-11 spectra were externally referenced
to BF3‚OEt2 (δ ) 0.00 ppm). Infrared spectra were recorded on a
Mattson Polaris Fourier transform spectrometer with 2 cm-1 resolution.
X-ray Crystal Structure Determination. Crystallographic data were
collected at -60 °C on an Enraf-Nonius CAD4 diffractometer with
graphite-monochromated Mo KR radiation. Crystallographic computa-
tions were carried out using the SHELXTL software package.24
Structure solution involved a DIRECT method. Unit cell parameters
were obtained by a least-squares refinement of the angular settings from
25 reflections, well distributed in reciprocal space and lying in a 2θ
range of 24-30°. All reflection data were corrected for Lorentz and
polarization effects. An empirical absorption correction was applied
based on measured ψ scans. All of the non-hydrogen atoms in the
complexes Cp2Zr{(µ-H)BC5H10(CH2Ph)}{(µ-H)2BC5H10}, 1, and Cp2-
Zr{(µ-H)BC4H8(CH2Ph)}{(µ-H)2BC4H8}, 2, were located and refined
anisotropically. All of the bridge hydrogen atoms were located and
refined isotropically. The C-H hydrogens were placed in calculated
positions, riding on the atoms to which they are bonded.
centroid(C6-C10)-Zr-B(1) 109.8
centroid(C1-C5)-Zr-HA
100.6
centroid(C6-C10)-Zr-HA 100.1
centroid(C1-C5)-Zr-HB 111.9
centroid(C6-C10)-Zr-HB 114.4
centroid(C1-C5)-Zr-HC 100.0
centroid(C6-C10)-Zr-HC 101.8
C(11)-B(1)-C(14) 104.8(3)
C(12)-C(11)-B(1) 105.1(3)
C(13)-C(12)-C(11) 105.2(3)
C(12)-C(13)-C(14) 105.7(3)
B(1)-Zr-HA
B(1)-Zr-HB
B(1)-Zr-HC
HA-Zr-HB
HA-Zr-HC
HB-Zr-HC
HA-B(1)-HB
C(11)-B(1)-HA
C(14)-B(1)-HA
Zr-HC-B(2)
26.8(9) C(13)-C(14)-B(1) 103.7(3)
28.1(8) C(19)-B(2)-C(18) 118.0(3)
97.8(9) C(19)-B(2)-C(15) 114.6(3)
55.0(12) C(18)-B(2)-C(15) 103.5(3)
124.6(14) C(16)-C(15)-B(2) 104.2(3)
69.6(12) C(17)-C(16)-C(15) 105.0(3)
97(2)
113(2)
114(2)
159.9(20
C(16)-C(17)-C(18) 105.3(3)
C(17)-C(18)-B(2) 105.0(3)
C(20)-C(19)-B(2) 119.0(3)
a The standard deviation (σl) for the average bond length of Zr-C
is calculated according to the equations25 l ) ∑mlm/m and σl ) [∑m(lm
- l )2/m(m - 1)]1/2, where l is the mean length, lm is the length of
the mth bond, and m is the number of bonds.
The 11B NMR spectrum of 1 in ether solution consists of two
signals. One signal (δ 28.22 ppm, JB-H ) 54.9 Hz) very closely
corresponds to that produced by free Cp2ZrH{(µ-H)2BC5H10}.
The second signal (δ 83.58 (s)) is consistent with signals
produced by alkyl boranes.22 The two signals occur in a 1:1
ratio. Upon proton decoupling, the signal assigned to Cp2ZrH-
{(µ-H)2BC5H10} collapses to a singlet while the singlet assigned
to the alkyl borane at 83.58 ppm does not sharpen. The boron-
11 NMR spectrum is consistent with complete dissociation of
1 in solution as shown in eq 1. By the same token the 1H NMR
The structure of complex 1 was refined in space groups P21 and
P21/m. Solution in P21 was unsatisfactory due to negative thermal
parameters of several atoms and wide variation in C-C distances. X-ray
analysis in P21/m was successful. Complex 1 resides on a crystallo-
graphically imposed mirror plane. The asymmetric unit is one half of
a molecule, and the mirror operation generates the other half of the
molecule. The benzyl group is disordered; it appears on both sides of
the mirror plane. The mirror plane passes through Zr, H(1A), H(1B),
H(2A), B1, B2, C(13), C(23), and C. However, because the structure
is disordered, it is possible that these atoms are also disordered and
are positioned with partial occupancies just off either side of the mirror
plane, with the averaged positions on the mirror plane. Such a situation
spectrum of 1 in d6-benzene consists of signals that closely
match the spectrum of Cp2ZrH{(µ-H)2BC5H10} and a set of
signals that can be assigned to BC5H10(CH2Ph). The H NMR
1
spectrum of the Zr-H hydrogen has a chemical shift of 4.00
ppm, which is only slightly higher (but within experimental
error) than that observed (3.94 ppm) for solutions containing
only Cp2ZrH{(µ-H)2BC5H10} as the solute. Furthermore, the
chemical shifts of the Zr(µ-H)2B hydrogens (-3.26 and -4.16
ppm) are in excellent agreement with those observed for the
free Cp2ZrH{(µ-H)2BC5H10} molecule (-3.26 and -4.16 ppm).
Boron-11 NMR resonances of 2 appear at δ ) 90.50 (s) and
30.70 ppm (t, JB-H ) 61.0 Hz) and are assigned to the two
components BC4H8(CH2Ph) and Cp2ZrH{(µ-H)2BC4H8}.15 Upon
(22) (a) Saturnino, D. J.; Yamauchi, M,; Clayton, W. R.; Nelson, R. W.;
Shore, S. G. J. Am. Chem. Soc. 1975, 97, 6063. (b) Good, C. D.;
Ritter, D. M. J. Am. Chem. Soc. 1962, 84, 1162. (c) No¨th, H.;
Wrackmeyer, B. In Nuclear Magnetic Resonance Spectroscopy of
Boron Compounds; Springer-Verlag: Berlin, 1978; pp 115-124.
(23) Kopf, J.; Vollmer, H.-J.; Kaminsky, W. Cryst. Struct. Commun. 1980,
9, 985.
(24) SHELXTL (version 5), solution and refinement of molecular structures.
Siemens Energy & Automation, Inc., 1994.
(25) Stout, G. H.; Jensen, L. H. X-ray Structure Determination, 2nd ed.;
Wiley: New York, 1989; pp 406-408.

Cyclic Hydroborate Complexes of Metallocenes
Inorganic Chemistry, Vol. 38, No. 9, 1999 2173
could contribute to the “short” Zr-H and “long” B-H distances
observed in the unsupported Zr-H-B bond.
0.95 mmol of Cp2ZrCl{(µ-H)2BC4H8} and 0.98 mL of benzylmagne-
sium chloride were used. After reaction, 108.7 mg (50.9% yield) of
colorless 2 and 32 mg (15.9% yield) of orange Cp2Zr(CH2Ph)2 were
isolated from Et2O at -40 °C. Crystals of 2 suitable for X-ray diffraction
were also obtained from this solution.
Preparation of Cp2Zr{(µ-H)BC5H10(CH2Ph)}{(µ-H)2BC5H10}, 1.
Cp2ZrCl{(µ-H)2BC5H10} (330 mg, 0.97 mmol) was placed in 15 mL
of Et2O in a two-necked flask and cooled to -40 °C. Benzylmagnesium
chloride (1 mmol, 1 mL, 1.0 M in Et2O) was injected into the system
by syringe under nitrogen. The system was warmed to room temperature
over a 3 h period and stirred for an additional 3 h. Initially the mixture
was yellow-green in color, but it turned yellow upon warming. After
stirring at room temperature, the color further changed to orange. The
Et2O was removed under vacuum, and the resulting solid was extracted
with hexane. Removal of the hexane from the filtrate resulted in a pale
yellow solid, which was dissolved in Et2O and crystallized at -40 °C.
Orange crystals of Cp2Zr(CH2Ph)2 (21 mg, 10% yield) and colorless
crystals of 1 (137 mg, 59.1% yield) were obtained.
Data for 2. 11B NMR (Et2O): δ 90.50 (s) and 30.70 ppm (t, JB-H
1
) 61.0 Hz). H NMR (d6-benzene): δ 7.20-6.96 (m, Ph), 5.60 (s,
Cp), 3.91 (br, 1H), 2.63 (s, CH2), 1.80 (br, 4H), 1.57 (br, m, 4H), 1.01
(br, m, 8H), -3.10 (br, µ-H), and -4.25 ppm (br, µ-H). 1H NMR (d8-
toluene): δ 7.17-6.93 (m, Ph), 5.59 (s, Cp), 3.83 (br, 1H), 2.63 (s,
CH2), 1.74 (br, m, 4H), 1.59 (br, m, 4H), 1.05 (br, m, 8H), -3.30 (br,
µ-H), and -4.40 ppm (br, µ-H). IR (KBr): 3123 (vw), 3105 (w), 3095
(vw), 3077 (vw), 3058 (vw), 3019 (vw, br), 2918 (s, br), 2861 (m, sh),
2849 (s), 2806 (vw, sh), 2649 (vw, br), 2059 (vw), 2008 (vw), 1912
(m, br), 1892 (w, sh), 1825 (w), 1597 (w), 1491 (w), 1462 (m, sh),
1444 (s), 1430 (s), 1399 (s), 1368 (s), 1343 (s), 1289 (m, sh), 1238 (m,
sh), 1217 (w, sh), 1180 (w), 1123 (vw, br), 1066 (m), 1014 (m), 957
(vw), 931 (vw), 906 (w), 885 (vw), 870 (vw), 801 (vs), 754 (m), 729
(m, br), 701 (s), 658 (vw), 607 (vw), 538 (vw), 528 (vw), 473 (vw)
cm-1. Anal. Calcd for C25H36B2Zr: C, 66.82; H, 8.08. Found: C, 65.23;
H, 7.90.
Data for 1. 11B NMR (Et2O): δ 83.58 (s) and 28.22 ppm (t, JB-H
)54.9 Hz). 1H NMR (d6-benzene): δ 7.17-6.91 (m, Ph), 5.58 (s, Cp),
4.00 (br, 1H), 2.45 (s, CH2), 1.74 (br, 7H), 1.50 (br, m, 5H), 1.11 (br,
m, 8H), -3.26 (br, µ-H), and -4.16 ppm (br, µ-H). 1H NMR (d8-
toluene): δ 7.16-6.87 (m, Ph), 5.58 (s, Cp), 3.89 (br, 1H), 2.43 (s,
CH2), 1.69 (br, 6H), 1.52 (br, m, 4H), 1.41 (br, m, 2H), 1.09 (br, m,
4H), 1.00 (br, 4H), -3.00 (br, µ-H), and -4.10 ppm (br, µ-H). IR
(KBr): 3117 (w), 3111 (w), 3095 (vw, sh), 3073 (vw), 3050 (vw),
3020 (vw, sh), 3011 (w), 2988 (vw), 2925 (s, sh), 2901 (vs), 2889 (s),
2841 (s), 2827 (s), 2814 (m, sh), 2646 (vw), 1936 (s), 1898 (s), 1882
(s, sh), 1834 (m), 1788 (m, br), 1744 (m, br), 1594 (m), 1490 (m),
1458 (m, sh), 1426 (s), 1409 (vs), 1370 (w, sh), 1341 (m), 1292 (w),
1280 (w), 1275 (w), 1263 (vw, sh), 1226 (w, sh), 1212 (s), 1201 (m,
sh), 1180 (w), 1175 (vw), 1153 (vw), 1129 (vw), 1111 (vw), 1092
(m), 1074 (m), 1067 (m), 1015 (s), 958 (s), 927 (vw), 903 (w), 887
(w), 881 (w), 822 (s), 814 (s), 800 (s), 764 (s), 744 (vw, sh), 705 (s),
662 (w), 582 (w), 551 (m), 491 (m), 458 (vw) cm-1. Anal. Calcd for
C27H40B2Zr: C, 67.92; H, 8.44. Found: C, 66.88; H, 8.23.
Acknowledgment. This work was supported by the National
Science Foundation through Grant CHE 97-00394. NMR spectra
were obtained at the Ohio State University Campus Chemical
Instrument Center.
Supporting Information Available: Tables of crystallographic
data, positional and thermal parameters, and interatomic distances and
angles for 1, 2, and Cp2Zr(CH2Ph)2 and proton spectra of Cp2ZrH{(µ-
H)2BC5H10}, Cp2ZrH{(µ-H)2 BC5H10}, 1, and 2. This material is
available free of charge via the Internet at http://pubs.acs.org.
Preparation of Cp2Zr{(µ-H)BC4H8(CH2Ph)}{(µ-H)2BC4H8}, 2.
The preparation method of 2 is similar to that described above except
IC981347U