Synthesis of group 4 organometallic complexes that contain the bis(borylamide) ligand [MeS2BNCH2CH2NBMeS2]2-

Article abstract of DOI:10.1021/om950646d

Titanium and zirconium derivatives of the new chelating bis(borylamido) ligand [MeS₂BNCH₂CH₂NBMeS₂]^2- ([Ben]^2-) are prepared by treating MCl₄(THF)₂ (M = Ti, Zr) with (Ben)Mg(THF)₂. Nitrogen-boron π-interactions in (Ben)TiCl₂ and (Ben)ZrCl₂(THF) result in one mesityl group in each BMes₂ unit occupying space roughly above and below the MCl₂ plane. (Ben)TiCl₂ is smoothly alkylated by Grignard reagents in dichloromethane to give (Ben)Ti(R)Cl (R = CH₂Ph, CH₂CMe₃) and (Ben)TiR₂ (R = Me, CH₂Ph), while unstable (Ben)-ZrMe₂ can be prepared from (Ben)ZrCl₂(THF) and methyllithium in toluene. An X-ray study of (Ben)Ti(CH₂Ph)Cl confirms the proposed ligand conformation and features a highly distorted "η²" benzyl ligand with a Ti-C_α-C_ipSO angle of only 87.0(5)°. (Ben)MMe₂ complexes cleanly decompose by metalation of the ortho methyl groups from mesityl rings on different borons at room temperature (for Zr) or upon heating (for Ti). An X-ray crystal structure of (TwistBen)Zr shows it to be a dimer in which the two zirconium centers are bridged by two mesityl o-methylene groups. B(C₆F₅)₃ binds to a methyl group in (Ben)MMe₂ complexes in dichloromethane, but such compounds show little polymerization activity toward ethylene at 25 °C and 1-2 atm as a consequence of strong anion binding.

Full text of DOI:10.1021/om950646d

562
Organometallics 1996, 15, 562-569
Syn th esis of Gr ou p 4 Or ga n om eta llic Com p lexes Th a t
Con ta in th e Bis(bor yla m id e) Liga n d
[Mes2BNCH2CH2NBMes2]2-
Timothy H. Warren, Richard R. Schrock,* and William M. Davis
Department of Chemistry 6-331, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
Received August 16, 1996X
Titanium and zirconium derivatives of the new chelating bis(borylamido) ligand
[Mes2BNCH2CH2NBMes2]2- ([Ben]2-) are prepared by treating MCl4(THF)2 (M ) Ti, Zr) with
(Ben)Mg(THF)2. Nitrogen-boron π-interactions in (Ben)TiCl2 and (Ben)ZrCl2(THF) result
in one mesityl group in each BMes2 unit occupying space roughly above and below the MCl2
plane. (Ben)TiCl2 is smoothly alkylated by Grignard reagents in dichloromethane to give
(Ben)Ti(R)Cl (R ) CH2Ph, CH2CMe3) and (Ben)TiR2 (R ) Me, CH2Ph), while unstable (Ben)-
ZrMe2 can be prepared from (Ben)ZrCl2(THF) and methyllithium in toluene. An X-ray study
of (Ben)Ti(CH2Ph)Cl confirms the proposed ligand conformation and features a highly
distorted “η2” benzyl ligand with a Ti-CR-Cipso angle of only 87.0(5)°. (Ben)MMe2 complexes
cleanly decompose by metalation of the ortho methyl groups from mesityl rings on different
borons at room temperature (for Zr) or upon heating (for Ti). An X-ray crystal structure of
(TwistBen)Zr shows it to be a dimer in which the two zirconium centers are bridged by two
mesityl o-methylene groups. B(C6F5)3 binds to a methyl group in (Ben)MMe2 complexes in
dichloromethane, but such compounds show little polymerization activity toward ethylene
at 25 °C and 1-2 atm as a consequence of strong anion binding.
In tr od u ction
A relatively small number of borylamide complexes
have been reported. For example, hydrozirconation of
(tert-butylimino)(2,2,6,6-tetramethylpiperidino)borane
resulted in zirconium-nitrogen bond formation as well
as a â-agostic B-H-Zr interaction.20 Addition of
t-Bu(Me3Si)NBtN-t-Bu across one MsC bond of the
group 4 benzyne complexes Cp2M(C6H4) (M ) Ti, Zr)
gave five-membered metalacycles containing the MsNsB
unit,21 while a related four-membered metalacycle
resulted from the 2 + 2 cycloaddition of i-BuNtB-i-Bu
with the TadC double bond of CpTaCl2(CHCMe3).22 For
later first-row metals a series of two-coordinate com-
plexes of the type M(NArBMes2)2 (Ar ) Ph, Mes; M )
Cr-Ni) could be prepared.23-25 The π-acceptor ability
The bent metallocene is one of the most important
types of early-transition-metal complexes in which
reactive sites are structurally defined and sterically
protected.1 Consequently, complexes that contain only
one cyclopentadienyl group or even no cyclopentadi-
enyl groups that support a variety of “metallocene-
like” chemistry at the remaining coordination sites are
receiving increasing attention. In the former category
are amido/cyclopentadienyl ligands,2-6 and in the
latter category are some recently reported tridentate
diamido ligands.7 The chelating bis(borylamido) ligand
[Mes2BNCH2CH2NBMes2]2- would be a structurally and
electronically unusual bidentate diamido ligand, since
two mesityl groups should define and sterically protect
two or three coordination sites in a plane roughly
perpendicular to the NCCN ligand backbone as a
consequence of N-B π-bonding. Furthermore, the
strongly π-accepting boryl groups should attenuate the
ability of the nitrogen atoms to donate π-electron density
to the metal center and therefore should yield complexes
in which the metal is more electrophilic than in more
traditional alkyl and arylamide complexes.3,5,8-19
(8) Airoldi, C.; Bradley, D. C.; Chudzynska, H.; Hursthouse, M. B.;
Malik, K. M. A.; Raithby, P. R. J . Chem. Soc., Dalton Trans. 1980,
2010.
(9) Alcock, N. M.; Pierce-Butler, M.; Willey, G. R. J . Chem. Soc.,
Chem. Commun. 1974, 627.
(10) Andersen, R. A. Inorg. Chem. 1979, 18, 2928.
(11) Andersen, R. A. J . Organomet. Chem. 1980, 192, 189.
(12) Bai, Y.; Roesky, H. W.; Noltemeyer, M.; Witt, M. Chem. Ber.
1992, 125, 825.
(13) Brauer, D. J .; Bu¨rger, H.; Wiegel, K. J . Organomet. Chem. 1978,
150, 215.
(14) Bu¨rger, H.; Neese, H.-J . J . Organomet. Chem. 1969, 20, 129.
(15) Bu¨rger, H.; Neese, H.-J . J . Organomet. Chem. 1970, 21, 381.
(16) Cummins, C. C.; Duyne, G. D. V.; Schaller, C. P.; Wolczanski,
P. T. Organometallics 1991, 10, 164.
(17) J ohnson, A. R.; Wanandi, P. W.; Cummins, C. C.; Davis, W. M.
Organometallics 1994, 13, 2907.
X Abstract published in Advance ACS Abstracts, December 15, 1995.
(1) Comprehensive Organometallic Chemistry; Wilkinson, G., Stone,
F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, U.K., 1982; Vol.
3.
(2) Shapiro, P. J .; Cotter, W. D.; Schaefer, W. P.; Labinger, J . A.;
Bercaw, J . E. J . Am. Chem. Soc. 1994, 116, 4623.
(3) Okuda, J .; Schattenmann, F. J .; Wocadlo, S.; Massa, W. Orga-
nometallics 1995, 14, 789.
(4) Okuda, J . Comments Inorg. Chem. 1994, 16, 185.
(5) Hughes, A. K.; Meetsma, A.; Teuben, J . H. Organometallics 1993,
12, 1936.
(18) Planalp, R. P.; Andersen, R. A.; Zalkin, A. Organometallics
1983, 2, 16.
(19) Woo, T. K.; Fan, L.; Ziegler, T. Organometallics 1994, 13, 2252.
(20) Ma¨nnig, D.; No¨th, H.; Schwartz, M.; Weber, S.; Wietelmann,
U. Angew. Chem., Int. Ed. Engl. 1985, 24, 998.
(21) Hebner, B.; Manners, I.; Paetzold, P. Chem. Ber. 1987, 120,
1065.
(6) Devore, D. D.; Timmers, F. J .; Hasha, D. L.; Rosen, R. K.; Marks,
T. J .; Deck, P. A.; Stern, C. L. J . Am. Chem. Soc. 1995, 14, 3132.
(7) Gue´rin, F.; McConville, D. H.; Vittal, J . J . Organometallics 1995,
14, 3154.
(22) Braunschweig, H.; Paetzold, P.; Boese, R. Chem. Ber. 1990, 123,
485.
(23) Chen, H.; Bartlett, R. A.; Olmstead, M. M.; Power, P. P.; Shoner,
S. C. J . Am. Chem. Soc. 1990, 112, 1048.
0276-7333/96/2315-0562$12.00/0 © 1996 American Chemical Society

Group 4 Bis(borylamide) Complexes
Organometallics, Vol. 15, No. 2, 1996 563
of the boryl substituent is probably an important fac-
tor in stabilizing monomeric, low-coordinate struc-
tures, since analogous complexes containing other bulky
amides such as N(SiMe3)2 are dimeric.26-28 Therefore,
a combination of NsB π-bonding and the steric bulk
of the BMes2 group should play a significant role in
the chemistry of group 4 complexes containing the
[Mes2BNCH2CH2NBMes2]2- ligand. In this paper we
describe the synthesis of the [Mes2BNCH2CH2NBMes2]2-
([Ben]2-) ligand and several titanium and zirconium
derivatives.
F igu r e 1. Proposed geometry of (Ben)MCl2 complexes.
1
observed by H NMR spectroscopy in C6D5Br at 150 °C
allowed us to estimate a lower limit of 23 kcal/mol for
the barrier to N-B bond rotation in H2(Ben).) The
decreased barrier to N-B bond rotation observed in 1
may be ascribed to competition between empty metal d
orbitals and boron p orbitals for nitrogen lone pair
electron density. (The d0 borylamides Ti(NHBMes2)3-
Cl, Zr(NHBMes2)4, and Cp2Zr(NHBMes2)Cl also exhibit
substantially reduced barriers to N-B bond rotation
Resu lts
The bis(borylamine) Mes2BNHCH2CH2NHBMes2 (H2-
(Ben)) was prepared from lithium ethylenediamide
(generated in situ) and 2 equiv of dimesitylboron
fluoride (eq 1). Deprotonation of H2(Ben) with butyl-
lithium in the presence of MgBr2(ether) affords (Ben)-
Mg(THF)2 (eq 2). Both H2(Ben) and (Ben)Mg(THF)2 are
white crystalline solids that were prepared in 80-90%
yield on a scale of typically 30 and 10 g, respectively.
(∆Gq ) 15.3(2), 15.2(2), and 16.2(2) kcal/mol, respec-
rot
tively) relative to other (dimesitylboryl)amines, whereas
Sn(NHBMes2)3Cl does not (∆Gq > 22 kcal/mol).32 ) The
rot
H2NCH2CH2NH2 (1) 2LiBu/THF8
fact that 2 binds THF, while 1 does not, is consistent
with the larger size of Zr and its often higher coordina-
tion number in otherwise analogous Ti and Zr com-
plexes. On the basis of X-ray structures of Ben deriva-
tives to be described later, we assume that the THF in
2 is bound to the metal in the ZrCl2 plane between the
two chlorides.
(2) 2Mes2BF
Mes2BNHCH2CH2NHBMes2 (1)
H2Ben 2LiBu, MgBr (ether)8 (Ben)Mg(THF)2
(2)
2
THF
Monoalkyl- and dialkyltitanium derivatives can be
prepared by treating (Ben)TiCl2 in dichloromethane at
-40 °C with Grignard reagents (eqs 4 and 5). Proton
Addition of MCl4(THF)2 (M ) Ti, Zr) to a dichlo-
romethane solution of (Ben)Mg(THF)2 produces yellow-
orange (Ben)TiCl2 (1) or colorless (Ben)ZrCl2(THF) (2)
(eq 3) in 81% and 71% yields, respectively. Room-temp-
CH2Cl2
(Ben)TiCl2 + RMgCl
8
(Ben)Ti(R)Cl
3a : R ) CH2Ph
3b: R ) CH2CMe3
(4)
CH2Cl2
(Ben)Mg(THF)2 + MCl4(THF)2
8
(Ben)MCl2(THF)x (3)
1: M ) Ti, x ) 0
2: M ) Zr, x ) 1
CH2Cl2
(Ben)TiCl2 + 2RMgCl
8
(Ben)TiR2
4a : R ) CH2Ph
4b: R ) Me
(5)
erature proton NMR spectra of both 1 and 2 exhibit a
single sharp resonance for the methylene protons in the
backbone as well as two sets of resonances due to
inequivalent mesityl groups. Inequivalent mesityl groups
within each BMes2 unit are to be expected, since N-B
π-bonding29,30 should favor a structure in which one
mesityl ring of each dimesitylboron unit lies above or
below the MCl2 plane and the other flanks the NCCN
backbone (Figure 1). When a sample of (Ben)TiCl2 is
warmed to 90 °C, the six mesityl proton resonances (m-
H, o-Me, p-Me) coalesce to give three signals as a
consequence of rotation about the N-B bond. The value
NMR spectra of unsymmetrically substituted 3a ,b show
four meta and six mesityl methyl resonances, consistent
with mirror symmetry and no rotation about B-N or
mesityl B-Cipso bonds on the NMR time scale. The
AA′BB′ pattern ascribed to the ethylene backbone
protons is also consistent with the low symmetry of
3a ,b. NMR spectra of 4a ,b, on the other hand, are
consistent with C2v symmetry. The ortho proton reso-
nances of the benzyl ligands in both 3a and 4a are
shifted upfield (to 5.756 and 6.101 ppm, respectively,
in C6D6), which suggests that the phenyl π-systems may
be interacting with the titanium center.33,34 (The o-Ph
1H resonances of the benzyl ligands in 3a and 4a could
be shifted upfield also as a consequence of the ring
current of the mesityl rings flanking the coordination
wedge.) Rotation of the N-dimesitylboryl units in 4a ,b
is qualitatively slower than in 1, presumably as a
of ∆Gq (17.4(2) kcal/mol) in 1 is significantly lower
rot
than the value of ∼25 kcal/mol found for other (dimesi-
tylboryl)amines such as MeNHBMes2, PhNHBMes2,31
and H2(Ben). (The fact that no coalescence of the closely
spaced m-H, o-Me, and p-Me resonances of H2(Ben) was
(24) Bartlett, R. A.; Chen, H.; Power, P. P. Angew. Chem., Int. Ed.
Engl. 1989, 28, 316.
(25) Bartlett, R. A.; Feng, X.; Olmstead, M. M.; Power, P. P.; Weese,
K. J . J . Am. Chem. Soc. 1987, 109, 4851.
(26) Bu¨rger, H.; Wannagat, U. Monatsh. Chem. 1963, 94, 1007.
(27) Bu¨rger, H.; Wannagat, U. Monatsh. Chem. 1964, 95, 1099.
(28) Olmstead, M. M.; Power, P. P.; Shoner, S. C. Inorg. Chem. 1991,
30, 2547.
(31) Brown, N. M. D.; Davidson, F.; Wilson, J . W. J . Organomet.
Chem. 1981, 210, 1.
(32) Warren, T. H.; Schrock, R. R. Unpublished results.
(33) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell, I.
P.; Huffman, J . C. Organometallics 1985, 4, 902.
(34) J ordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echols, S. F.;
Willett, R. J . Am. Chem. Soc. 1987, 109, 4111.
(29) Bartell, L. S.; Clippard, F. B. Inorg. Chem. 1970, 9, 2439.
(30) Zettler, F.; Hess, H. Chem. Ber. 1975, 108, 2269.

564 Organometallics, Vol. 15, No. 2, 1996
Warren et al.
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta ,
Collection P a r a m eter s, a n d Refin em en t
P a r a m eter s
(Ben)Ti(CH2Ph)Cl [(TwistBen)Zr]2‚3C6H6
empirical formula
fw
C43H51B2N2ClTi
700.86
C76H92B4N4Zr2‚3C6H6
1521.60
cryst color, habit
red, plate
pale yellow,
parallelepiped
cryst dimens (mm) 0.25 × 0.12 × 0.50 0.32 × 0.38 × 0.21
cryst syst
triclinic
monoclinic
no. of rflns used for 20 (15.0-30.0)
unit cell determn
25 (15.0-23.0)
(2θ range (deg))
a (Å)
13.949(6)
16.633(7)
9.136(4)
106.00(3)
96.84(3)
88.38(3)
2023(3)
P1h
30.775(2)
11.935(1)
27.435(3)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
125.34(3)
8220(5)
C2/c
4
1.229
-86 ( 1
6416
2.94
space group
Z
2
ρ(calc) (g/cm3)
collecn temp (°C)
F000
1.150
-80 ( 1
744
3.04
ω-2θ
7132
µ(Mo KR) (cm-1
scan mode
)
ω
7601
total no. of unique
rflns
no. of observs with
I > 3.00σ(I)
no. of variable
params
R
Rw
3589
460
4130
470
F igu r e 2. Chem 3D drawing of the molecular structure
of 3a .
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 3a
0.079
0.086
2.48
0.076
0.069
1.62
goodness of fit
indicator
Distances
Ti-N(1)
Ti-C(27)
Ti-Cl
1.894(6)
2.106(8)
2.325(3)
1.43(1)
Ti-N(2)
1.912(6)
2.500(8)
1.46(1)
Ti-C(28)
C(27)-C(28)
N(2)-B(1)
consequence of both the increased steric demands of
alkyl ligands in the coordination wedge and the less
electrophilic nature of the metal in 4a or 4b and
consequently reduced competition for the nitrogen’s
electron pairs.
N(1)-B(2)
1.419(9)
Angles
N(1)-Ti-N(2)
C(27)-Ti-C(28)
N(1)-Ti-C(27)
N(1)-Ti-Cl
N(1)-C(2)-C(1)
Ti-N(1)-B(2)
Ti-N(1)-C(2)
B(2)-N(1)-C(2)
N(2)-B(1)-C(9)
N(2)-B(1)-C(3)
C(9)-B(1)-C(3)
89.2(2)
35.8(3)
Ti-C(27)-C(28)
87.0(5)
125.5(2)
113.9(3)
100.9(2)
107.8(6)
137.6(5)
100.2(4)
121.0(6)
118.7(7)
118.4(7)
122.9(7)
C(27)-Ti-Cl
110.7(3)
110.3(2)
109.2(6)
127.4(5)
108.8(2)
122.3(6)
121.0(7)
117.7(6)
121.3(6)
N(2)-Ti-C(27)
N(2)-Ti-Cl
The structure of 3a was determined in an X-ray study
(Table 1). A drawing can be found in Figure 2 and
relevant distances and angles in Table 2. The Ben
ligand nearly symmetrically chelates the titanium cen-
ter (Ti-N distances 1.894(6) and 1.912(6) Å) to form a
puckered five-membered ring with a “bite” angle (N-
Ti-N) of 89.2(2)°. The Ti-N distances are comparable
to those found in other four-coordinate amido com-
plexes,8,9,13,17,21 which are in the 1.882-1.940 Å range.
The coordination geometry at both B and N is trigonal
planar, and the dihedral angle between the planes con-
taining B and N is small (e.g., the dihedral angle C(2)-
N(1)-B(2)-C(21) is 13°), consistent with substantial
B-N π-bonding. A significant degree of N-B π-bonding
is also suggested by N-B distances of 1.419(9) and
1.43(1) Å. Note, however, that these N-B distances are
longer than N-B distances (1.36-1.41 Å) generally
found in structurally characterized monoborylamines
and metalloborylamides,20,21,23-25,29,30,35,36 perhaps as a
consequence of titanium’s competing with the boryl
groups for the nitrogen lone pairs. Puckering of the
ethylene backbone and maintenance of the N-B π-in-
teractions causes the mesityl rings to be not sym-
metrically oriented directly above and below the re-
maining two coordination sites but rather “off-center”.
N(2)-C(1)-C(2)
Ti-N(2)-B(1)
Ti-N(2)-C(1)
B(1)-N(2)-C(1)
N(1)-B(2)-C(21)
N(1)-B(2)-C(15)
C(21)-B(2)-C(15)
The chloride and benzyl ligands complete the pseudo-
tetrahedral coordination geometry in 3a . It is clear from
the acute Ti-C(27)-C(28) angle (87.0(5)°) as well as the
short Ti-C(28) distance (2.500(8) Å) that the π-system
of the benzyl ligand is interacting in a symmetrical
manner with the titanium center. For comparison, the
most distorted benzyl ligand in Ti(CH2Ph)4 has a
Ti-CR-Cipso angle of 88(2)° and a Ti-Cipso distance of
2.61(3) Å.37,38
Close examination of proton NMR spectra of 3a
suggests that a second isomer is present in small
amounts (<10%) in solution. Two sets of benzyl o-Ph
resonances at δ 5.756 and 5.363 ppm and two sets of
backbone resonances centered at δ 4.063 and 4.086 ppm
are observed in C6D6 for the major and minor isomers,
respectively. In view of the solid-state structure of 3a
we speculate that the minor isomer may be one in which
(37) Davies, G. R.; J arvis, J . A.; Kilbourn, B. T. J . Chem. Soc. D
1971, 1511.
(38) Bassi, I. W.; Allegra, G.; Scordamaglia, R.; Chioccela, G. J . Am.
Chem. Soc. 1971, 93, 3787.
(35) Bartlett, R. A.; Chen, H.; Dias, H. V. R.; Olmstead, M. M.;
Power, P. P. J . Am. Chem. Soc. 1988, 110, 446.
(36) Paetzold, P. Adv. Inorg. Chem. 1987, 31, 123.

Group 4 Bis(borylamide) Complexes
Organometallics, Vol. 15, No. 2, 1996 565
the benzyl group is rotated by 180°; i.e., the Ti-CH2
bond is now in the “central” coordination position, and
the phenyl ring is bound to the metal in an “outside”
position. In this orientation the phenyl group of the
benzyl ligand would interact to a greater degree steri-
cally with the mesityl groups flanking the coordination
wedge, and this isomer therefore should be significantly
less favored than the one found in the solid state.
Thermolysis of (Ben)TiMe2 (4b) in benzene follows
first-order kinetics (kobs ) 1.8(2) × 10-4 s-1 at 79 °C)
and yields deep red, C2-symmetric (TwistBen)Ti (5) and
methane (eq 6). We believe two pathways for this
F igu r e 3. Chem 3D drawing of the molecular structure
of 6 viewed almost down the crystallographic C2 axis.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 6
Distances
Zr-N(1)
2.106(6)
3.251(2)
2.464(8)
2.252(8)
1.38(1)
Zr-N(2)
2.088(6)
2.449(8)
2.549(8)
2.703(8)
1.43(1)
Zr-Zr*
Zr-C(121*)
Zr-C(12)
Zr-C(22)
N(2)-B(2)
Zr-C(121)
Zr-C(221)
N(1)-B(1)
Angles
reaction to be most plausible. The first is a stepwise
σ-bond metathesis18,39-43 involving opposing o-Me C-H
bonds and Ti-Me groups. The second is initial loss of
methane via R-abstraction followed by 1,2-addition of a
CsH bond in one ortho methyl group across the TidCH2
bond; a second R-abstraction followed by CsH addition
to the resulting TidC bond would yield 5.44,45 Ther-
molysis of (Ben)Ti(CD3)2 (4b-d6) yields only CD3H,
according to 2H NMR, consistent with the σ-bond
metathesis pathway. (R-Abstraction requires that both
CD4 and CD2CH2 are formed.) A small inverse second-
ary isotope effect (kH/kD ) 0.84(3)) is found at 79 °C.
(Ben)ZrMe2 may be prepared from 2 and 2 equiv of
methyllithium in toluene at -78 °C. However, it is
much less stable thermally than (Ben)TiMe2 and con-
verts readily to the yellow dicyclometalated (TwistBen)-
Zr (6) and methane. Under conditions where (Ben)-
ZrMe2 is synthesized, only mixtures of (Ben)ZrMe2 and
6 can be obtained; significant conversion of (Ben)ZrMe2
to 6 occurs even during crystallization of (Ben)ZrMe2
at -40 °C. A rate constant could be obtained for
conversion of (Ben)ZrMe2 to 6 in mixtures of the two
(kobs ) 8.4(2) × 10-4 s-1 at 43 °C). Derivatives that
contain
N(1)-Zr-N(2)
73.3(2) C(121)-Zr-C(121*)
69.7(4) Zr-C(221)-C(22)
108.0(3) N(2)-Zr-C(221)
109.3(5) Zr-N(2)-B(2)
119.6(5) Zr-N(2)-C(2)
128.8(7) B(2)-N(2)-C(2)
111.4(7) N(2)-B(2)-C(21)
124.8(8) N(2)-B(2)-C(41)
82.8(2)
90.6(5)
96.1(3)
107.4(5)
123.0(5)
122.9(7)
115.0(7)
123.1(8)
121.9(8)
Zr-C(121)-C(12)
N(1)-Zr-C(221)
Zr-N(1)-B(1)
Zr-N(1)-C(1)
B(1)-N(1)-C(1)
N(1)-B(1)-C(11)
N(1)-B(1)-C(31)
C(11)-B(1)-C(31) 123.8(7) C(21)-B(2)-C(41)
more sterically demanding alkyl derivatives are even
less stable. For example, the reaction between (Ben)-
ZrCl2(THF) and 2 equiv of LiCH2SiMe3 yields only 6
(62% yield) and tetramethylsilane (eq 7).
toluene
BenZrCl2(THF) + 2LiCH2SiMe3
8 6 (7)
-2SiMe4
1H and 13C NMR spectroscopy demonstrate that the
solution structures of 5 and 6 are significantly different.
The titanium complex is C2-symmetric, while the zir-
conium analog appears to lack any symmetry on the
NMR time scale, even at 100 °C. Furthermore, the four
Zr-CH2 J CH coupling constants range from 112 to 145
Hz, suggesting there are significant differences between
the bonding modes of each methylene.
An X-ray diffraction study shows that 6 is dimeric and
possesses crystallographically imposed C2 symmetry
(Figure 3; Table 3). Two methylene groups nearly
symmetrically bridge the two zirconium centers (Zr-
C(121) ) 2.464(8) Å, Zr-C(121*) ) 2.449(8) Å), Zr‚‚‚Zr
) 3.251(2) Å). The ipso carbon from one mesityl group
(e.g., C(12)) also strongly interacts with the zirconium
center from which it originates (Zr-C(12) ) 2.549(8) Å).
These structural parameters should be compared with
the nonbridging mesityl methylene group in which the
1
(39) Rothwell, I. P. Polyhedron 1985, 4, 177.
(40) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J .;
Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J . Am.
Chem. Soc. 1987, 109, 203.
(41) Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Huffman, J .
C. J . Am. Chem. Soc. 1985, 107, 5981.
(42) Chamberlain, L. R.; Rothwell, I. P. J . Am. Chem. Soc. 1983,
105, 1665.
(43) Chamberlain, L. R.; Rothwell, I. P.; Huffman, J . C. J . Am. Chem.
Soc. 1986, 108, 1502.
(44) McDade, C.; Green, J . C.; Bercaw, J . E. Organometallics 1982,
1, 1629.
(45) Heijden, H. v. d.; Hessen, B. J . Chem. Soc., Chem. Commun.
1995, 145.

566 Organometallics, Vol. 15, No. 2, 1996
Warren et al.
Zr-C(221) distance is 2.252(8) Å. However, the Zr-
C(22) distance of 2.703(8) Å and the Zr-C(221)-C(22)
angle of 90.6(5)° demonstrate that the ipso carbon of
even the nonbridging mesityl ring also weakly interacts
with the zirconium center. The N(1)-Zr-N(2) angle
(73.3(2)°) for the five-membered ring is more acute than
that (89.2(2)°) found in the structure of 3a . The con-
traction is due in part to the larger size of zirconium
relative to titanium as well as perhaps to the decreased
steric demands of the mesityl rings upon metalation.
The Zr-N distances (2.088(6) and 2.106(6) Å) are
comparable to those found in other four- and psuedo-
four-coordinate zirconium-amido complexes.3,5,8,9,12,16,18-20
Borylamide N-B π-interactions are maintained in the
metalated structure according to N-B distances (1.38-
(1) and 1.43(1) Å) and the small dihedral angles C(2)-
N(2)-B(2)-C(41) (9°) and C(1)-N(1)-B(1)-C(31) (3°).
The (Ben)MMe2 complexes react with the strong
Lewis acid B(C6F5)3 in dichloromethane to give what we
presume on the basis of analogous studies in metal-
locene chemistry46-49 to be the “zwitterionic” complexes
[(Ben)MMe][MeB(C6F5)3], in which a methyl group is
partially abstracted by the triarylborane (eq 8). The
complexes. The short M-Cipso contacts and acute
M-CR-Cipso angles seen in the solid-state structures of
3a and 6 are of the magnitude commonly seen in
actinide50 and cationic group 4 complexes.33,34,51 The
electrophilic nature of the metal is also evidenced by
facile conversion of (Ben)MMe2 complexes to (Twist-
Ben)M complexes, one that is consistent with attack by
a coordinatively unsaturated, electrophilic metal center
on a CH bond with concerted abstraction of a proton by
the leaving methyl group.39,40 The fact that 7 and 8 do
not react with ethylene is also consistent with the
relatively high electrophilicity of the metal center and
strong binding of the [MeB(C6F5)3]- ion to the metal.46
A disadvantage of the present Ben ligand, however,
is the lack of sufficient steric protection to prevent
dimerization via bridging methylenes (to give 6) or to
expel the [MeB(C6F5)3] anion in 7 and 8 in the presence
of ethylene. Some flexibility in the ethylene bridge
between the two amido nitrogens may exacerbate to
some degree what we perceive to be insufficient “lateral”
steric protection. Nevertheless, the similarity between
the basic coordination geometry of the Ti and Zr Ben
complexes and typical metallocene coordination geom-
etries, in particular the presence of three coordination
sites in a plane perpendicular to the MN2 plane, is
unmistakable. Future efforts will be aimed at a further
exploration of these similarities and differences and the
construction of a more crowded Ben ligand that would
not only resist metalation but would provide a more
crowded environment in which a boron-based anion
would be bound more weakly than observed here.
CD2Cl2
(Ben)MMe2 + B(C6F5)3
M ) Ti, Zr
8
[(Ben)MMe][MeB(C6F5)3] (8)
7: M ) Ti
8: M ) Zr
symmetry of 7 and 8, according to NMR spectra, is the
same as the symmetry of 3a ,b. All of these data, along
with the demonstrated strong B-N π-bonding, would
seem to eliminate the possibility that B(C6F5)3 binds to
a lone pair on nitrogen. We have also eliminated the
possibility that (Ben)MMeCl complexes form (along with
free [MeB(C6F5)3]- ion) by chloride abstraction from
dichloromethane by showing that characteristic reso-
nances for (Ben)MMeCl can be observed by NMR in the
presence of [MeB(C6F5)3]- (as a tetraalkylammonium
salt). Therefore, it would appear that the interaction
between “[MeB(C6F5)3]-” and the metal is relatively
strong. Unfortunately, we have not been able to isolate
either of these adducts and so have not been able to
confirm their identity via X-ray studies. Strong binding
of [MeB(C6F5)3]- to the metal would help explain why
dichloromethane solutions of 7 and 8 do not polymerize
ethylene readily at 25 °C and 1-2 atm.
Exp er im en ta l Section
Gen er a l P r oced u r es. All experiments were performed
under nitrogen in a Vacuum Atmospheres drybox or under
argon using standard Schlenk techniques. All solvents were
purified by standard techniques, while deuterated NMR
solvents were dried and stored over 4-Å molecular sieves before
use.
Magnesium bromide etherate, butyllithium, methyllithium,
methyllithium-d3, methylmagnesium chloride, and benzyl-
magnesium chloride were used as received. Ethylenediamine
containing 0.6% water was stored over 4-Å molecular sieves
before use. MCl4(THF)2 (M ) Ti, Zr),52 Mes2BF,23 B(C6F5)3,53
and neopentylmagnesium chloride in ether54 were prepared
according to literature proceedures.
1H, 13C, 19F, and 11B NMR spectra usually were recorded at
300, 75.4, 282, and 96.2 MHz, respectively. Proton spectra
were referenced internally by the residual solvent proton
signal relative to tetramethylsilane. Carbon spectra were
referenced internally relative to the 13C signal of the NMR
solvent relative to tetramethylsilane. Fluorine and boron
spectra were referenced externally to neat CFCl3 and BF3
etherate, respectively. All J values are given in Hz. IR spectra
were recorded as Nujol mulls between KBr plates on a Perkin-
Elmer 1600 FT-IR spectrometer. Elemental analyses were
performed on a Perkin-Elmer PE2400 microanalyzer in our
laboratories.
Discu ssion a n d Con clu sion
On the basis of the results presented here, we believe
that the concept of using N-B π-bonding to enforce a
desirable orientation of the mesityl groups in complexes
that contain the Ben ligand is a valid one and that Ben
complexes have some characteristics that are reminis-
cent of metallocenes. The N-B π-interaction also is
likely to be responsible for what appears to be a
relatively electron-deficient nature of the metal in Ben
Mes2BNHCH2CH2NHBMes2 (H2(Ben )). Butyllithium (52
mL, 131 mmol, 2.5 M in hexane) was added to a solution of
ethylenediamine (3.74 g, 62.1 mmol) in THF (500 mL) at -40
(46) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1991,
113, 3623.
(47) Gillis, D. J .; Tudoret, M.-J .; Baird, M. C. J . Am. Chem. Soc.
1993, 115, 2543.
(48) Pellecchia, C.; Pappalardo, D.; Oliva, L.; Zambelli, A. J . Am.
Chem. Soc. 1995, 117, 6593.
(49) Quyoum, R.; Wang, Q.; Tudoret, M.-J .; Baird, M. C. J . Am.
Chem. Soc. 1994, 116, 6435.
(50) Edwards, P. G.; Andersen, R. A.; Zalkin, A. Organometallics
1984, 3, 293.
(51) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325.
(52) Manzer, L. E. Inorg. Synth. 1982, 21, 135.
(53) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2, 245.
(54) Schrock, R. R.; Sancho, J .; Pedersen, S. F. Inorg. Synth. 1989,
26, 44.

Group 4 Bis(borylamide) Complexes
Organometallics, Vol. 15, No. 2, 1996 567
°C. A white flocculent precipitate formed almost immediately,
and the color of the solution changed to dark purple. After 5
h the purple had faded and the slurry was chilled to -40 °C.
Solid dimesitylboron fluoride (35.0 g, 131 mmol) was added to
the chilled solution over 10 min. The flocculent white pre-
cipitate dissolved almost immediately to yield a light yellow
solution with suspended LiF. After the solution was stirred
overnight, the solvents were removed in vacuo and the residue
was extracted with warm dichloromethane (800 mL). The
extract was filtered through Celite, concentrated, and cooled
to -40 °C. Fluffy white needles were collected by filtration,
washed liberally with pentane, and dried in vacuo for 12 h to
afford 30.50 g (84% yield) of the product as a dichloromethane
solvate (1 part dichloromethane to 3 parts H2(Ben)). An
analytical sample of H2(Ben) (as a solvate containing 0.5 equiv
of benzene) was obtained by recrystallization from warm ben-
zene: 1H NMR (CDCl3) δ 6.756 (s, 4, m-H), 6.735 (s, 4, m-H),
4.478 (br s, 2, NH), 3.092 (pseudo t, 4, NCH2), 2.267 (s, 6,
p-Me), 2.236 (s, 6, p-Me), 2.205 (s, 12, o-Me), 2.109 (s, 12, o-Me);
13C{1H} NMR δ 140.8, 140.1 (Co), 137.3, 136.9 (Cp), 128.3, 127.6
(Cm), 46.4 (NCH2), 22.8, 22.1 (o-Me), 21.1, 21.0 (p-Me); 11B NMR
Layering with pentane followed by cooling the solution over-
night afforded white crystals, which were collected by filtra-
tion, washed with pentane, and dried in vacuo to give 4.84 g
(71%) of the product. An analytical sample of (Ben)ZrCl2(THF)‚
CH2Cl2 was obtained by recrystallization from dichlorometh-
ane/pentane: 1H NMR (C6D6) δ 6.816 (s, 4, m-H), 6.618 (s, 4,
m-H), 4.129 (s, 4, NCH2), 3.197 (m, 4, THF), 2.694 (s, 12, o-Me),
2.513 (s, 12, o-Me) 2.189 (s, 6, p-Me), 1.945 (s, 6, p-Me), 1.058
(m, 4, THF); 13C{1H} NMR δ 147.2, 140.8, 140.0, 137.3 (Co and
Cp), 129.6, 128.6 (Cm), 73.4 (THF), 55.8 (NCH2), 25.4, 25.3, 23.5,
21.1 (Ar-Me). Anal. Calcd for C43H58N2B2Cl4OZr: C, 59.12;
H, 6.69; N, 3.21. Found: C, 58.84; H, 6.83; N, 2.92.
(Ben )Ti(CH2P h )Cl (3a ). Benzylmagnesium chloride (0.256
mL, 0.446 mmol, 1.74 M in THF) was added to a solution of
(Ben)TiCl2 (0.300 g, 0.446 mmol) in dichloromethane (10 mL)
at -40 °C. The solution immediately turned deep red, and a
fine precipitate formed. The solution was kept at -40 °C for
3 h and was filtered through Celite. The solvents were
removed from the filtrate in vacuo, and the residue was
recrystallized from a mixture of toluene and pentane to afford
0.144 g (32%) of red plates in three crops. 1H NMR(C6D6): δ
6.915-6.70 (m, Ar), major isomer: 5.756 (dd, 2, o-Ph), 4.160
(AA′BB′, 2, NCH2), 3.965 (AA′BB′, 2, NCH2), 3.208 (s, 2, CH2-
Ph), 2.545 (br s, 6, Ar-Me), 2.511 (s, 6, Ar-Me), 2.483 (br s,
6, Ar-Me), 2.320 (s, 6, Ar-Me), 2.172 (s, 6, Ar-Me), 2.122 (s,
6, Ar-Me); minor isomer, δ 5.363 (br d, 2, o-Ph), 4.086 (br m,
4, NCH2), 3.279 (s, 2, CH2Ph), 2.584 (s, Ar-Me), 2.496 (s, Ar-
Me), 2.390 (s, Ar-Me); corresponding integrals and remaining
Ar-Me resonances are obscured by the methyl resonances of
the major isomer. 13C NMR (major isomer): δ 144.2, 142.5,
140.8, 139.9, 139.6, 138.3, 137.8, 130.7, 129.6, 129.5, 129.3,
128.9, 128.5, 126.8 (Caryl), 100.9 (1J CH ) 134, CH2Ph), 54.5 (1J CH
) 142, NCH2), 24.1, 23.3, 23.1, 21.2, 21.1 (Ar-Me). Anal. Calcd
for C45H55N2B2ClTi: C, 74.15; H, 7.61; N, 3.84. Found: C,
73.91; H, 7.83; N, 3.64.
δ 45.3 (width 1170 Hz); IR (Nujol/KBr) 3367, 3356 ν(NH) cm-1
.
Anal. Calcd for C41H53N2B2: C, 82.70; H, 8.96; N, 4.71.
Found: C, 83.03; H, 9.02; N, 4.70.
(Ben )Mg(THF )2. Butyllithium (22.5 mL, 56.2 mmol, 2.5
M in hexane) was added to a solution of H2(Ben) (8.93 g, 16.1
mmol) and MgBr2 (ether) (4.75 g, 18.4 mmol) in THF (250 mL)
at -40 °C. The solution was warmed to room temperature
and stirred overnight. Dichloromethane (100 mL) was added,
and the mixture was stirred for 6 h, after which the solvents
were removed in vacuo to give a yellow oil. The oil was
extracted with CH2Cl2/pentane (150 mL, 50/50). The extract
was filtered and concentrated to an oil. When the residue was
stirred with a mixture of pentane (100 mL) and THF (10 mL),
a white solid formed and was collected by filtration. The white
solid was redissolved in dichloromethane (100 mL), and the
mixture was filtered and concentrated again to an oil. The
oil was triturated with pentane (100 mL) to give white crystals.
The mixture was chilled to -40 °C for 2 h, and the crystals
were collected by filtration, washed liberally with pentane, and
thoroughly dried in vacuo to afford 9.51 g (77%) of the product
as a 2/3 pentane clathrate which contained ∼5% H2(Ben).
Repeated recrystallization failed to remove the H2(Ben) im-
purity: 1H NMR (pyridine-d5) δ 6.897 (s, 4, m-H), 6.551 (s, 4,
m-H), 3.782 (s, 4, NCH2), 3.647 (m, 8, THF), 2.592 (s, 12, o-Me),
2.375 (s, 12, o-Me), 2.262 (s, 6, p-Me), 2.123 (s, 6, p-Me), 1.609
(m, 8, THF); 13C{1H} NMR δ 141.0, 140.5 (Co), 134.6 (Cp), 128.3,
127.9 (Cm), 67.9 (THF), 54.8 (NCH2), 34.2 (CH2), 23.6, 23.4 (o-
Me), 22.5 (CH2), 21.2, 20.9 (p-Me), 14.2 (THF).
(Ben )TiCl2 (1). TiCl4(THF)2 (3.40 g, 10.2 mmol) was added
slowly to a solution of (Ben)Mg(THF)2(pentane)2/3 (7.84 g, 10.2
mmol) in dichloromethane (100 mL) at -40 °C. The solution
quickly turned orange. A copious amount of white precipitate
had formed after 1 h. After 3 h the solution was filtered and
the extracts were concentrated to dryness. The residue was
crystallized from dichloromethane/ether at -40 °C to yield 5.52
g (81%) of fluffy orange solid. An analytical sample was
obtained by double recrystallization from dichloromethane/
pentane: 1H NMR (CDCl3) δ 6.802 (s, 4, m-H), 6.745 (s, 4,
m-H), 4.409 (s, 4, NCH2), 2.402 (s, 12, o-Me), 2.333 (s, 12, o-Me),
2.251 (s, 6, p-Me), 2.193 (s, 6, p-Me); 13C{1H} NMR δ 145.7
(Co), 140.9 (Co), 140.4 (Cp), 138.3 (Cp), 128.9, 128.3 (Cm), 59.5
(CH2), 23.6, 22.8 (o-Me), 21.3, 21.0 (p-Me). Anal. Calcd for
(Ben )Ti(CH2CMe3)Cl (3b). Neopentylmagnesium chloride
(0.495 mL, 1.34 mmol, 2.7 M in ether) was added to a solution
of (Ben)TiCl2 (0.750 g, 1.11 mmol) in dichloromethane (20 mL)
at -40 °C. The mixture was warmed to room temperature,
allowed to stand overnight at room temperature, and filtered
through Celite. The solvents were removed from the filtrate
in vacuo, and the residue was recrystallized from pentane at
-40 °C to afford 0.586 g (74%) of orange crystals in two crops.
An analytical sample was obtained by double-recrystallization
from dichloromethane/pentane: 1H NMR (C6D6) δ 6.834 (s, 2,
m-H), 6.808 (s, 2, m-H), 6.756 (s, 2, m-H), 6.741 (s, 2, m-H),
3.963 (AA′BB′, 2, NCH2), 3.674 (AA′BB′, 2, NCH2), 2.628 (s,
6, Ar-Me), 2.574 (s, 6, Ar-Me), 2.487 (s, 6, Ar-Me), 2.432 (s,
2, CH2CMe3), 2.357 (s, 6, Ar-Me), 2.169 (s, 6, Ar-Me), 2.116
(s, 6, Ar-Me), 0.586 (s, 9, CH2CMe3); 13C{1H} NMR δ 143.24,
141.84, 140.67, 139.89, 139.22, 137.74, 129.63, 129.30, 128.82,
128.56 (Caryl), 53.79 (NCH2), 39.08 (Ti-CH2), 31.65 (CMe3),
31.52 (CMe3), 24.08, 23.36, 23.17, 23.04, 21.12 (Ar-Me). Anal.
Calcd for C43H59N2B2ClTi: C, 72.85; H, 8.39; N, 3.95. Found:
C, 72.31; H, 8.55; N, 3.81.
(Ben )Ti(CH2P h )2 (4a ). Benzylmagnesium chloride (1.11
mL, 1.93 mmol, 1.74 M in THF) was added to a solution of
(Ben)TiCl2 (0.620 g, 0.921 mmol) in dichloromethane (20 mL)
at -40 °C. The solution immediately turned deep red, and a
fine precipitate formed. After the solution stood at -40 °C
for 1.5 h, 1,4-dioxane (0.100 g, 1.12 mmol) was added and the
solution was filtered through Celite. The solvents were
removed in vacuo, and the residue was recrystallized from
pentane at -40 °C to afford 0.382 g (53%) of red crystals: 1H
NMR (C6D6) δ 7.003 (t, 4, m-Ph), 6.836 (t, 2, p-Ph), 6.839 (s, 4,
m-Mes), 6.788 (s, 4, m-Mes), 6.101 (d, 4, o-Ph), 3.776 (s, 4,
NCH2), 2.790 (s, 4, CH2Ph), 2.516 (s, 12, o-Me), 2.249 (s, 12,
o-Me), 2.194 (s, 6, p-Me), 2.184 (s, 6, p-Me); 13C{1H} NMR δ
146.2 (Phi), 142.4, 140.6 (Meso), 138.9, 137.5 (Mesp), 129.3
(Phm), 128.74, 128.65 (Cm), 127.0 (Pho), 124.0 (Phm), 99.7 (CH2-
Ph), 52.1 (NCH2), 23.9, 23.3 (o-Me), 21.13, 21.07 (p-Me). Anal.
C
38H48N2B2Cl2Ti: C, 67.80; H, 7.18; N, 4.16. Found: C, 67.55;
H, 7.13; N, 3.95.
(Ben )Zr Cl2(THF ) (2). ZrCl4(THF)2 (3.25 g, 8.61 mmol) was
added slowly to a stirred solution of (Ben)Mg(THF)2(pentane)0.22
(6.05 g, 8.61 mmol) in dichloromethane (100 mL) at -40 °C.
The solution was warmed to room temperature. After it stood
overnight, the solution was filtered and the extracts were
concentrated to dryness in vacuo. The residue was extracted
with toluene (75 mL) and the extract concentrated to ∼20 mL.

568 Organometallics, Vol. 15, No. 2, 1996
Warren et al.
Calcd for C52H62N2B2Ti: C, 79.61; H, 7.96; N, 3.57. Found:
C, 79.30; H, 8.14; N, 3.38.
6.771 (s, 1, m-H), 6.712 (s, 2, m-H), 6.683 (s, 1, m-H), 6.251 (s,
1, m-H), 6.154 (s, 1, m-H), 4.288 (m, 1, NCH2), 3.941 (m, 1,
NCH2), 3.657 (m, 1, NCH2), 3.451 (m, 1, NCH2), 2.527 (d, 2J HH
(Ben )TiMe2 (4b). Methylmagnesium chloride (1.50 mL,
4.51 mmol, 3.0 M in THF) was added to a solution of (Ben)-
TiCl2 (1.38 g, 2.05 mmol) in dichloromethane (75 mL) at -40
°C. The solution immediately turned yellow, and a fine
precipitate formed. After the mixture stood at -40 °C for 1.5
h, 1,4-dioxane (0.400 g, 4.51 mmol) was added and the solution
was filtered through Celite. The solvents were removed in
vacuo, and the residue was recrystallized from dichloromethane/
ether at -40 °C to afford 0.876 g (67%) of fluffy yellow needles
in two crops. An analytical sample was obtained by recrys-
tallization from dichloromethane/pentane: 1H NMR (C6D6) δ
6.822 (s, 4, m-H), 6.744 (s, 4, m-H), 3.860 (s, 4, NCH2), 2.527
(s, 12, o-Me), 2.427 (s, 12, o-Me), 2.193 (s, 6, p-Me), 2.084 (s, 6,
p-Me), 0.858 (s, 6, Ti-CH3); 13C NMR δ 144.2, 140.3 (Co), 139.5,
2
) 9.2, 1, Zr-CH2), 2.481 (d, J HH ) 7.0, 1, Zr-CH2), 2.410 (s,
3, Ar-Me), 2.353 (s, 3, Ar-Me), 2.242 (s, 3, Ar-Me), 2.226 (s,
3, Ar-Me), 2.149 (s, 3, Ar-Me), 2.101 (s, 3, Ar-Me), 2.083 (s,
3, Ar-Me), 1.900 (s, 3, Ar-Me), 1.881 (s, 3, Ar-Me), 1.866 (s,
2
2
3, Ar-Me), 1.041 (d, J HH ) 9.2, 1, Zr-CH2), -0.121 (d, J HH
) 7.0, 1, Zr-CH2); 13C NMR δ 151.96, 145.50, 145.23, 143.25,
142.73, 142.06, 140.58, 140.31, 139.53, 137.26, 136.85, 130.71,
130.42, 128.23, 127.77, 127.65, 127.24 (Caryl), 71.78 (1J CH ) 145
and 133, Zr-CH2), 58.92 (1J CH ) 135 and 112, Zr-CH2), 57.61
(1J CH ) 134, NCH2), 52.54 (1J CH ) 136, NCH2), 23.67, 23.52,
23.03, 22.56, 22.44, 22.36, 21.48, 21.25, 21.19, 21.16 (Ar-Me).
Anal. Calcd for C38H46N2B2Zr: C, 70.92; H, 7.20; N, 4.35.
Found: C, 71.18; H, 7.57; N, 3.99.
137.5 (Cp), 137.0, 136.2 (Ci), 129.3, 128.6 (Cm), 67.3 (1J CH
)
(Ben )TiMe[MeB(C6F 5)3] (7) was generated in solution by
dissolving (Ben)TiMe2 (0.060 g, 0.094 mmol) and B(C6F5)3
(0.060 g, 0.117 mmol) in CD2Cl2. The orange solution was
analyzed by 1H NMR. No solid product could be recovered
from these solutions: 1H NMR (CD2Cl2) δ 7.286 (s, 2, m-H),
7.254 (s, 2, m-H), 6.940 (s, 4, m-H), 4.507 (AA′BB′, 4, NCH2),
2.471 (s, 6, Ar-Me), 2.443 (s, 6, Ar-Me), 2.308 (s, 6, Ar-Me),
2.275 (br, 12, Ar-Me), 2.229 (s, 6, Ar-Me), 0.710 (s, 3, Ti-
CH3), 0.497 (br, 3, Ti-CH3-B(C6F5)3); 13C{1H} NMR δ 156.6,
121.5, Ti-CH3), 53.8 (NCH2), 23.8, 22.9 (o-Me), 21.2 (p-Me).
Anal. Calcd for C40H54N2B2Ti: C, 75.98; H, 8.60; N, 4.43.
Found: C, 75.71; H, 8.55; N, 4.16.
(Ben)Ti(CD3)2 (4b-d6) was prepared analogously, employing
2 equiv of LiCD3‚LiI in toluene: 2H NMR (C6H6) δ 0.738.
(Ben )Zr Me2. Methyllithium (1.10 mL, 1.64 mmol, 1.5 M
in ether) was added to a solution of (Ben)ZrCl2(THF) (0.707 g,
0.821 mmol) in toluene at -78 °C. After 1 h, the solution
became cloudy as it was warmed to -40 °C. The solution was
further warmed to 0 °C, and the volatile components were re-
moved in vacuo. The oily, yellow residue was extracted with
pentane, and the extract was concentrated and cooled to -40
°C to give 0.212 g (56%) of white crystals after 1 day. Sub-
sequent crops consisted largely of (TwistBen)Zr. Recrystalli-
zation and elemental analysis of (Ben)ZrMe2 were not attemp-
ted due to its thermal instability. 1H NMR (C6D6): δ 6.844
(s, 4, m-H), 6.703 (s, 4, m-H), 3.911 (s, 4, NCH2), 2.461 (s, 12,
o-Me), 2.407 (s, 12, o-Me), 2.213 (s, 6, p-Me), 2.020 (s, 6, p-Me),
-0.015 (s, 6, Zr-CH3). 13C{1H} NMR (CD2Cl2, -40 °C): δ
146.48, 141.15, 140.00, 136.88, 129.78, 127.72 (Caromatic), 54.51
(NCH2), 47.57 (Zr-Me), 23.90, 22.34, 21.19, 20.95 (Ar-Me).
(Tw istBen )Ti (5). (Ben)TiMe2 (0.200 g, 0.316 mmol) in
toluene (4 mL) was heated to 70 °C in a Teflon-sealed tube for
36 h. The solution was filtered, and the volatile components
were removed in vacuo. The resulting red solid was triturated
with dichloromethane to give 0.148 g (79%) of the product. An
analytical sample was crystallized from toluene at -40 °C: 1H
NMR (C6D6) δ 6.951 (br s, 2, m-H), 6.702 (br s, 2, m-H), 6.628
(s, 2, m-H), 6.568 (s, 2, m-H), 4.344 (AA′BB′, 2, NCH2), 4.175
1
148.8 (Co or Cp), 148.8 (m, J CF ) 234, o-C6F5), 142.4, 141.5,
1
140.8 (Co and Cp), 137.9 (m, J CF ) 241, p-C6F5), 137.3 (Cm),
136.8 (m, 1J CF ) 241, m-C6F5), 136.7 (Cm), 129.3 (Cm), 72.0 (Ti-
CH3), 64.6 (NCH2), 26.2, 23.1, 22.9, 22.0, 21.3 (Ar-Me and Me-
B(C6F5)); 19F NMR δ -131.21 (d, 3J FF ) 19.8, o-C6F5), -163.37
3
3
(t, J FF ) 17.8, p-C6F5), -165.94 (m, J FF(av) ) 22.5, m-C6F5).
(Ben )Zr Me[MeB(C6F 5)3] (8) was generated by dissolving
(Ben)ZrMe2 (0.066 g, 0.098 mmol) and B(C6F5)3 (0.050 g, 0.098
mmol) in CD2Cl2: 1H NMR (CD2Cl2) δ 7.281 (s, 4, m-H), 6.903
(s, 4, m-H), 4.095 (AA′BB′, 2, NCH2), 3.968 (AA′BB′, 2, NCH2),
2.535 (s, 6, Ar-Me), 2.310 (s, 6, Ar-Me), 2.288 (s, 12, Ar-
Me), 2.274 (s, 6, Ar-Me), 2.234 (s, 6, Ar-Me), 0.493 (br, 3,
Zr-Me-B(C6F5)3), 0.096 (s, 6, Zr-CH3); partial 13C{1H} NMR
δ 153.76, 148.10 (m, 1J CF ) 236, o-C6F5), 146.88, 143.18, 141.38
(br), 140.70 (br), 139.68, 137.40 (m, 1J CF ) 245, p-C6F5), 136.24
1
(m, J CF ) 246, m-C6F5), 135.08, 132.84, 128.53, 131.58; 19F
3
3
NMR δ -131.63 (d, J FF ) 18.6, o-C6F5), -163.80 (t, J FF
)
3
21.2, p-C6F5), -166.37 (m, J FF(av) ) 21.3, m-C6F5).
Kin etic Mea su r em en ts of In tr a m olecu la r C-H Activa -
tion . Teflon-sealed NMR tubes containing 30-90 mg of the
dimethyl derivatives in 0.60 mL of toluene-d8 (for 4b and 4b-
d6) or benzene-d6 (for mixtures of (Ben)ZrMe2 and 6) were
placed in a heated NMR probe. The probe temperature was
calibrated before and after the measurements using ethylene
glycol (for 4b and 4b-d6) or methanol (for (Ben)ZrMe2) and
remained constant within (0.5 °C. The reactions were
monitored by 1H NMR spectroscopy by integrating the N-CH2
resonances of 4b and 4b-d6 or the Zr-Me resonance in (Ben)-
ZrMe2 relative to an internal benzene standard. In all cases
the kinetics followed first-order behavior over 3 half-lives and
the rate constants obtained were insensitive to the initial
concentration of metal complex.
1
(AA′BB′, 2, NCH2), 2.811 (d, J HH ) 5.7, 2, Ti-CH2), 2.530 (s,
6, Ar-Me), 2.257 (s, 6, Ar-Me), 2.195 (s, 6, Ar-Me), 2.136 (s,
1
6, Ar-Me), 2.071 (s, 6, Ar-Me), 2.247 (d, J HH ) 5.7, 2, Ti-
CH2); 13C{1H} NMR 149.18, 148.34, 140.94, 140.78 (br), 137.80,
131.82, 128.60 (br), 128.32 (Caryl), 75.97 (Ti-CH2), 60.00
(NCH2), 23.15, 22.45 (br), 21.18, 21.11 (Ar-Me). Anal. Calcd
for C38H46N2B2Ti: C, 76.03; H, 7.72; N, 4.67. Found: C, 76.17;
H, 8.04; N, 4.31.
(Tw istBen )Zr (6). (a ) F r om (Ben )Zr Me2. A sample of
(Ben)ZrMe2 was allowed to stand in benzene-d6 overnight. 6
1
was formed quantitatively, according to H NMR, along with
methane.
X-r a y Str u ctu r e of (Ben )Ti(CH2P h )Cl. Suitable deep red
crystals of 3a were grown from a concentrated benzene/
pentane solution at room temperature. A crystal having
approximate dimensions of 0.25 × 0.12 × 0.50 mm was
mounted on a glass fiber. Data were collected at -80 ( 1 °C
on a Rigaku AFC6S diffractometer with graphite-monochro-
mated Mo KR radiation (λ ) 0.710 69 Å). Cell constants and
an orientation matrix for data collection, obtained from a least-
squares refinement using the setting angles of 20 carefully
centered reflections in the range 15.00 < 2θ < 30.00°, cor-
responded to a triclinic cell with parameters a ) 13.949(6) Å,
b ) 16.633(7) Å, c ) 9.136(4) Å, R ) 106.00(3)°, â ) 96.84(3)°,
γ ) 88.38(3)°, V ) 2023(3) Å3, Z ) 2, fw ) 700.86, and F(calc)
) 1.150 g/cm3. On the basis of packing considerations, a
statistical analysis of intensity distribution, and the successful
(b ) F r om R ea ct ion of (Ben )Zr Cl2(TH F ) w it h LiCH2-
SiMe3. A solution of LiCH2SiMe3 (0.056 g, 0.608 mmol) in
toluene (2 mL) at -40 °C was added to a solution of (Ben)-
ZrCl2(THF) (0.240 g, 0.304 mmol) in toluene (10 mL). After
15 min the cloudy, light yellow solution solution was filtered
through Celite and the solvents were removed in vacuo to give
a yellow oil. The oil was extracted with pentane (10 mL) and
immediately filtered through Celite. Yellow needles formed
from the filtrate upon standing. The mother liquor was
removed after 1 day, and the needles were washed with
pentane. Concentrating and cooling the mother liquor to -40
°C afforded a second crop; yield 0.122 g (62%). An analytical
sample was obtained by recrystallization from benzene/pen-
tane: 1H NMR (CD2Cl2) δ 6.982 (s, 1, m-H), 6.807 (s, 1, m-H),

Group 4 Bis(borylamide) Complexes
Organometallics, Vol. 15, No. 2, 1996 569
solution and refinement of the structure, the space group was
determined to be P1h.
as well as the successful solution and refinement of the
structure, the space group was determined to be C2/c.
A total of 7758 reflections were collected in the range 2θ <
49.9°, with 7601 being unique. An empirical absorption
correction was applied, using the program DIFABS, which
resulted in transmission factors ranging from 0.80 to 1.28. The
A total of 7458 reflections were collected in the range 2θ <
50.3°, with 7132 being unique. An empirical absorption
correction was applied, using the program DIFABS,55 which
resulted in transmission factors ranging from 0.84 to 1.18. The
data were corrected for Lorentz and polarization effects. The
structure was solved by direct methods. The non-hydrogen
atoms were refined anisotropically. The final cycle of full-
matrix least-squares refinement was based on 3589 observed
reflections (I > 3.00σ(I)) and 460 variable parameters and
converged with R ) 0.079 and Rw ) 0.086. The maximum
and minimum peaks on the final difference Fourier map
corresponded to 0.47 and -0.68 e/Å3, respectively. All calcula-
tions were performed using the TEXSAN crystallographic
software package of Molecular Structure Corp.
X-r a y Str u ctu r e of [(Tw istBen )Zr ]2‚3C6H6. Suitable
light yellow crystals of 6 containing 3 equiv of benzene were
grown by allowing (Ben)ZrMe2 to decompose in benzene
solution at room temperature. A crystal having approximate
dimensions of 0.32 × 0.38 × 0.21 mm was mounted on a glass
fiber. Data were collected at -86 ( 1 °C on an Enraf-Nonius
CAD-4 diffractometer with graphite-monochromated Mo KR
radiation (λ ) 0.710 69 Å). Cell constants and an orientation
matrix for data collection, obtained from a least-squares
refinement using the setting angles of 25 carefully centered
reflections in the range 15.00 < 2θ < 23.00°, corresponded to
a monoclinic cell with parameters a ) 30.775(2) Å, b ) 11.935-
(1) Å, c ) 27.435(3) Å, â ) 96.84(3)°, V ) 8220(5) Å3, Z ) 4, fw
1521.60, and F(calc) ) 1.229 g/cm3. On the basis of the
systematic absences of hkl (h + k * 2n) and h0l (h, l * 2n)
data were corrected for Lorentz and polarization effects.
A
correction for secondary extinction was applied (coefficient
0.57539 × 10-7). The structure was solved by direct methods.
The non-hydrogen atoms were refined anisotropically. The
final cycle of full-matrix least-squares refinement was based
on 4130 observed reflections (I > 3.00σ(I)) and 470 variable
parameters and converged with R ) 0.076 and Rw ) 0.069.
The maximum and minimum peaks on the final difference
Fourier map corresponded to 0.71 and -0.88 e/Å3, respectively.
All calculations were performed using the TEXSAN crystal-
lographic software package of Molecular Structure Corp.
Ack n ow led gm en t s. R.R.S. thanks the National
Sci.ence Foundation for research support (Grant No.
CHE 91 22827), and T.H.W. thanks Andreas Detig for
technical assistance.
Su p p or tin g In for m a tion Ava ila ble: Tables giving ex-
perimental details of the X-ray data collection and refine-
ment, final positional parameters, and final thermal param-
eters and labeled ORTEP diagrams for (Ben)Ti(CH2Ph)Cl and
[(TwistBen)Zr]2‚3C6H6 (18 pages). This material is contained
in many libraries on microfiche, immediately follows this
article in the microfilm edition of this journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
(55) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
OM950646D