Zinc, Cadmium, and mercury metallocenes incorporating l,2-diaza-3,5- diborolyl ligands

Article abstract of DOI:10.1021/om070230n

Sandwich compounds incorporating l,2-diaza-3,5-diborolidine ligands have been prepared by metathesis reactions between zinc, cadmium, and mercury dihalides and M[cyclo-MeC(BR)₂(NiPr)₂] (M = Li, K; R = Me, Ph). The metallocenes M[cycl

Full text of DOI:10.1021/om070230n

3516
Organometallics 2007, 26, 3516-3523
Zinc, Cadmium, and Mercury Metallocenes Incorporating
1,2-Diaza-3,5-diborolyl Ligands
Hanh V. Ly,† Taryn D. Forster,† Masood Parvez,† Robert McDonald,‡ and Roland Roesler*,†
Departments of Chemistry, UniVersity of Calgary, Calgary, Alberta, Canada T2N 1N4, and UniVersity of
Alberta, Edmonton, Alberta, Canada T6G 2G2
ReceiVed March 9, 2007
Sandwich compounds incorporating 1,2-diaza-3,5-diborolidine ligands have been prepared by metathesis
reactions between zinc, cadmium, and mercury dihalides and M[cyclo-MeC(BR)2(NiPr)2] (M ) Li, K;
R ) Me, Ph). The metallocenes M[cyclo-MeC(BR)2(NiPr)2)]2 (M ) Zn, R ) Me (2a), Ph (2b); M )
Cd, R ) Me (3a), Ph (3b); M ) Hg, R ) Me (4a)) have been isolated and characterized by multinuclear
NMR and mass spectrometry. The molecular structures of complexes 2a,b, 3a‚BrLi(THF)3, 3b, and 4a
were determined by single-crystal X-ray diffraction and displayed strong similarities to the structures of
their cyclopentadienyl analogues. All molecules are monomeric in the solid state, containing nearly parallel
ligands featuring an η3 coordination mode in 2a and η1 coordination modes in the remaining complexes.
Spectroscopic evidence indicates that the solid-state structure is maintained in solution and that Lewis
basic solvents have the ability to coordinate reversibly to the metal centers. For comparison, the σ-bonded
analogues [cyclo-MeC(BR)2(NiPr)2]SiCl3 (R ) Me (5a), Ph (5b)) were prepared, and the structure of 5b
was determined using single-crystal X-ray diffractometry.
tures for three cadmium sandwich complexes containing Lewis
bases coordinated to the metal have been reported: Cp2-
CdPy2,6a,b Cp2Cd(TMEDA), and Cp2Cd(PMDETA).6d The
structures of the first two base-free cadmocenes, (tBu3C5H2)2-
Cd and (iPr4C5H)2Cd,6e were recently reported, and also
a dimeric half-sandwich complex of cadmium, [Cp*CdN-
(SiMe3)2]2,6c was structurally characterized. Three sandwich
compounds of mercury have been crystallographically charac-
terized, and they all exhibit η1 coordination modes: Cp2Hg,7b
(tBu3C5H2)2Hg,7d and [(tBuMe2Si)C5Me4]2Hg.7e The structures
of η1-bonded mercury half-sandwiches have also been deter-
mined: (Cl5C5)HgC6H5,7a Cp*HgCl,7c and [(tBuMe2Si)C5Me4]-
HgCl.7e Dizincocenes, [(η5-C5Me4R)2Zn2], were recently iso-
lated, and their structures were subsequently the subject of
theoretical calculations.8 Aside from their fundamental impor-
Introduction
Cyclopentadienyl and its derivatives form a versatile and
extensively investigated class of ligands that has played a key
role in organometallic chemistry.1 Cyclopentadienyl complexes,
known as sandwich compounds or metallocenes, have found
numerous applications as olefin polymerization catalysts2 and
materials with special properties.3 In comparison to the other
metals, only few metallocenes of the electron-rich group 12
elements have been reported. The first structurally characterized
sandwich complex of zinc, Cp2Zn, displays a polymeric structure
with η1- and η2-coordinated ligands.4a Five other base-free
zincocenes featuring asymmetric structures with η1:η5-bonded
cyclopentadienyls are known,4 and also tetrahydrofuran and
N-heterocyclic carbene (NHC) adducts of Cp*2Zn and difluo-
renylzinc, respectively, have been described.5 Even fewer
cyclopentadienyl derivatives of the heavier group 12 metals,
cadmium and mercury, have been reported. The crystal struc-
(5) (a) Fischer, B.; Boersma, J.; van Koten, G.; Smeets, W. J. J.; Spek,
A. L. Organometallics 1989, 8, 667. (b) Arduengo, A. J., III; Davidson,
F.; Krafczyk, R.; Marshall, W. J.; Tamm, M. Organometallics 1998, 17,
3375.
(6) (a) Fischer, B.; van Mier, G. P. M.; Boersma, J.; Smeets, W. J. J.;
Spek, A. L. J. Organomet. Chem. 1987, 322, C37. (b) Smeets, W. J. J.;
Spek, A. L.; Fischer, B.; van Mier, G. P. M.; Boersma, J. Acta Crystallogr.
1987, C43, 893. (c) Cummins, C. C.; Schrock, R. R.; Davis, W. M.
Organometallics 1991, 10, 3781. (d) Barr, D.; Edwards, A. J.; Raithby, P.
R.; Rennie, M.-A.; Verhorevoort, K. L.; Wright, D. S. J. Organomet. Chem.
1995, 493, 175. (e) Bentz, D.; Wolmersha¨user, G.; Sitzmann, H. Organo-
metallics 2006, 25, 3175.
(7) (a) Davies, A. G.; Goddard, J. P.; Hursthouse, M. B.; Walker, N. P.
C. J. Chem. Soc., Dalton Trans. 1985, 471. (b) Fischer, B.; van Mier, G. P.
M.; Boersma, J.; van Koten, G.; Smeets, W. J. J.; Spek, A. L. Recl. TraV.
Chim. Pays-Bas 1988, 107, 259. (c) Lorberth, J.; Berlitz, T. F.; Massa, W.
Angew. Chem., Int. Ed. Engl. 1989, 28, 611. (d) Sitzmann, H.; Wolmer-
sha¨user, G. Z. Anorg. Allg. Chem. 1995, 621, 109. (e) Hitchcock, P. B.;
Keates, J. M.; Lawless, G. A. J. Am. Chem. Soc. 1998, 120, 599.
(8) (a) Resa, I.; Carmona, E.; Gutierrez-Puebla, E.; Monge, A. Science
2004, 305, 1136. (b) del R´ıo, D.; Galindo, A.; Resa, I.; Carmona, E. Angew.
Chem., Int. Ed. 2005, 44, 1244. (c) Xie, Y.; Schaefer, H. F., III; King, R.
B. J. Am. Chem. Soc. 2005, 127, 2818. (d) Grirrane, A.; Resa, I.; Rodriguez,
A.; Carmona, E.; Alvarez, E.; Gutierrez-Puebla, E.; Monge, A.; Galindo,
A.; del R´ıo, D.; Andersen, R. A. J. Am. Chem. Soc. 2007, 129, 693. (e)
Alvarez, E.; Grirrane, A.; Resa, I.; del R´ıo, D.; Rodr´ıguez, A.; Carmona,
E. Angew. Chem., Int. Ed. 2007, 46, 1296.
* To whom correspondence should be addressed. E-mail:
roesler@ucalgary.ca.
† University of Calgary.
‡ University of Alberta.
(1) (a) Togni, A.; Halterman, R. L. Metallocenes; Wiley-VCH: Wein-
heim, Germany, 1998; Vols. I and II. (b) Long, N. J. Metallocenes: An
Introduction to Sandwich Complexes; Blackwell Science: London, 1998.
(c) Jutzi, P.; Burford, N. Chem. ReV. 1999, 99, 969.
(2) (a) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (b)
McKnight, A. L.; Waymouth, R. M. Chem. ReV. 1998, 98, 2587. (c) Patil,
A. O.; Hlatky, G. G. Beyond Metallocenes: Next-Generation Polymerization
Catalysts; American Chemical Society: Washington, DC, 2003.
(3) (a) Rao, C. N. R.; Govindaraj, A. Acc. Chem. Res. 2002, 35, 998.
(b) Wong, X.-S.; Arsenault, A.; Ozin, G. A.; Winnik, M. A.; Manners, I.
J. Am. Chem. Soc. 2003, 125, 12686. (c) Wong, X.-S.; Winnik, M. A.;
Manners, I. Angew. Chem., Int. Ed. 2004, 43, 3703.
(4) (a) Budzelaar, P. H. M.; Boersma, J.; van der Kerk, G. J. M.; Spek,
A. L.; Duisenberg, A. J. M. J. Organomet. Chem. 1985, 281, 123. (b)
Fischer, B.; Wijkens, P.; Boersma, J.; van Koten, G.; Smeets, W. J. J.;
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10.1021/om070230n CCC: $37.00 © 2007 American Chemical Society
Publication on Web 05/31/2007

Zn, Cd, and Hg Metallocenes
Organometallics, Vol. 26, No. 14, 2007 3517
Scheme 1
tance, group 12 metallocenes have shown potential as molecular
precursors for semiconducting films.6c,d To our knowledge, no
sandwich compounds of the group 12 metals incorporating
heterocyclic cyclopentadienyl analogues have been reported.
In the search for new ancillary ligands, a series of boron-
containing five-membered cyclopentadienyl analogues have been
isolated through the formal substitution of cyclopentadienyl ring
carbon atoms with isolobal main-group fragments. The 1,2-oxa-,
thia-, and azaborolidines A were obtained by the replacement
confirms that no ligand dissociation occurs in solution. A broad
signal is observed for the ring carbon in the 13C NMR spectra
of complexes 2-4 between δ 69 and 78 ppm. This represents
a 20 ppm upfield shift with respect to the corresponding alkali-
metal salts, indicating an increased covalent character of the
metal-ligand interaction in the former compounds. All com-
plexes display only one broad signal in the 11B NMR spectrum,
with a chemical shift situated in a narrow δ range of 37-41
ppm, which is typical also for the alkali-metal salts of these
of two adjacent ring carbons with boron and oxygen,9k sulfur,9g
or nitrogen,9a-c,f,h-j,l respectively, and have been coordinated
to transition metals. Complexes containing the 1,3-thiaborolide
ligand B have been described as well.9d,e Some of the transition-
metal complexes containing these heterocyclic ligands have been
investigated as catalysts.9e,l Continuing our investigations of
boron-based heterocyclic cyclopentadienyl analogues of type
C,10 we report herein the synthesis and structural characterization
of zinc, cadmium, and mercury sandwich complexes incorporat-
ing 1,2-diaza-3,5-diborolyl ligands. A detailed structural discus-
sion of a recently communicated zincocene from this family,
2a,10a is also presented.
ligands. There is little difference between the 1H, 13C, and 11
B
NMR spectra recorded in C6D6 and those recorded in THF-d8.
However, the 113Cd{1H} NMR spectra of 3a,b exhibit reso-
nances at δ 256.2 and 286.1 ppm, respectively, when recorded
in C6D6, while the resonance for 3a appears at 397.9 ppm when
recorded in THF-d8. The large difference is likely due to the
formation of 3a‚THF and 3a‚2THF adducts in the coordinating
solvent, similar to adducts containing substituted cyclopenta-
dienyls that have been crystallographically characterized for
zinc5 and cadmium.6a,b,d All metallocenes described herein have
been prepared in a THF solution and isolated free of solvent
after workup, which implies that their THF adducts are weakly
bonded. The 199Hg NMR spectrum of 4a in C6D6 displays a
single resonance at δ -2063.3 ppm. To our knowledge, no Cd
NMR data are available in the literature for cadmium cyclo-
pentadienyl compounds, and only one 199Hg NMR resonance
has been reported for a mercury metallocene, at δ -1112 ppm.7e
The mass spectra of all complexes described here feature signals
that were assigned to the molecular ions [ML2]+, as well as to
the fragments [ML]+ and [L]+. No signals corresponding to
CH3CN adducts of the metallocenes were observed in the
electrospray mass spectra of 2b and 3b, which were recorded
using acetonitrile solutions.
Crystal structures have been determined for 2a10 as well as
2b, 3b, 3a‚BrLi(THF)3, and 4a (Table 1), confirming the
sandwich structures predicted on the basis of the multinuclear
NMR and mass spectra. The metric parameters of the CB2N2
ring display little variation between all structures (Table 2),
showing a minor dependence on the organic substituent on boron
(methyl or phenyl) or the coordinated metal. The planarity of
the rings is slightly better for the phenyl derivatives 2b and 3b
than for the methyl derivatives 2a, 3a‚BrLi(THF)3, and 4a, with
the sum of the intraannular angles ranging between 539.5 and
539.7° for the former and between 538.6 and 539.1° for the
latter. The slight deviation from planarity results in an envelope
conformation, which can be described as either a folding along
the B‚‚‚B axis, with the ring carbon pointing toward the metal,
or a folding along a C‚‚‚N axis, with one boron atom pointing
away from the metal (Figure 1). In all cases, the latter model
offers a slightly better description of the structure, with the
CBN2/CBN folding angle measuring 9.6-11.3° for the methyl
derivatives and 5.1-6.5° for the phenyl derivatives.
Results and Discussion
The syntheses of the ligands and their alkali-metal salts (1,2-
diisopropyl-3,5-dimethyl-1,2-diaza-3,5-diborolyl)lithium (1a)
and (1,2-diisopropyl-3,5-diphenyl-1,2-diaza-3,5-diborolyl)po-
tassium (1b) have been previously described.10 The reactions
of these salts with the appropriate group 12 metal dihalides in
THF produced the sandwich complexes 2-4 (Scheme 1).
Complexes 2-4 were isolated as air- and moisture-sensitive
colorless solids with good solubility in organic solvents. Unlike
1
the case for the alkali-metal salts 1a,b, their H and 13C{1H}
NMR spectra exhibit two resonances corresponding to diaste-
reotopic methyl groups on the isopropyl substituents, indicating
that the two faces of the ligand are not equivalent and, therefore,
the sandwich structure is retained in solution. The presence of
1
113Cd satellites in the H and 13C NMR spectra of 3a,b and
1
199Hg satellites in the H and 13C NMR spectra of 4a for the
singlet resonances corresponding to the methyl substituents on
the ring carbon and boron (3JCdH ) 59 Hz, 4JCdH ) 8 Hz, 2JCdC
3
4
2
) 42 Hz, JHgH ) 143 Hz, JHgH ) 20 Hz, JHgC ) 65 Hz)
(9) (a) Schulze, J.; Schmid, G. Angew. Chem., Int. Ed. Engl. 1980, 19,
54. (b) Schulze, J.; Boese, R.; Schmid, G. Chem. Ber. 1980, 113, 2348. (c)
Schmid, G. Comments Inorg. Chem. 1985, 4, 17. (d) Ashe, A. J., III; Fang,
X.; Kampf, J. W. Organometallics 1998, 17, 2379. (e) Ashe, A. J., III;
Fang, X.; Kampf, J. W. Organometallics 1999, 18, 1821. (f) Ashe, A. J.,
III; Fang, X. Org. Lett. 2000, 2, 2089. (g) Ashe, A. J., III; Kampf, J. W.;
Schiesher, M. Organometallics 2000, 19, 4681. (h) Liu, S.-Y.; Hills, I. D.;
Fu, G. C. Organometallics 2002, 21, 4323. (i) Liu, S.-Y.; Lo, M. M.-C.;
Fu, G. C. Angew. Chem., Int. Ed. 2002, 41, 174. (j) Ashe, A. J., III; Yang,
H.; Fang, X.; Kampf, J. W. Organometallics 2002, 21, 4578. (k) Chen, J.;
Fang, X.; Bajko, Z.; Kampf, J. W.; Ashe, A. J., III. Organometallics 2004,
23, 5088. (l) Liu, S.-Y.; Hills, I. D.; Fu, G. C. J. Am. Chem. Soc. 2005,
127, 15352.
(10) (a) Ly, H. V.; Forster, T. D.; Maley, D.; Parvez, M.; Roesler, R.
Chem. Commun. 2005, 4468. (b) Ly, H. V.; Forster, T. D.; Corrente, A.
M.; Eisler, D. J.; Konu, J.; Parvez, M.; Roesler, R. Organometallics 2007,
26, 1750.

3518 Organometallics, Vol. 26, No. 14, 2007
Table 1. Selected Data and Structure Refinement Details for 2b, 3a‚BrLi(THF)3, 3b, 4a, and 5b‚0.25C5H12
Ly et al.
2b
3a‚BrLi(THF)3
3b
4a
5b‚0.25C5H12
empirical formula
C40H54B4N4Zn
C32H68B4BrCd-
LiN4O3
799.40
monoclinic
P21/n
9.396(2)
21.241(7)
21.107(7)
90
96.85(2)
90
C40H54B4CdN4
C20H46B4HgN4
C20H27B2Cl3N2Si‚
0.25C5H12
469.53
monoclinic
P21/n
6.755(6)
19.491(9)
20.603(10)
90
93.47(4)
90
formula wt
cryst syst
space group
a (Å)
b (Å)
c (Å)
699.48
triclinic
P1h
746.51
triclinic
P1h
586.44
monoclinic
I2/m
16.095(2)
15.295(2)
11.350(1)
90
101.249(1)
90
10.681(3)
12.141(4)
17.176(4)
75.483(14)
80.656(15)
66.124(13)
1967.0(10)
2
10.940(3)
12.001(4)
16.987(5)
76.011(16)
80.947(16)
66.866(16)
1985.2(10)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
4182(2)
4
1.270
2740.6(5)
4
1.421
2708(3)
4
1.152
d
calcd (g cm-3
)
1.181
1.249
2θmax (deg)
55.0
0.657
8921 (Rint ) 0.029)
8921/0/451
50.2
1.511
7345 (Rint ) 0.024)
7345/0/425
55.0
0.582
9039 (Rint ) 0.038)
9039/0/442
52.8
5.629
2918 (Rint ) 0.031)
2918/0/240
50
0.393
4738 (Rint ) 0.049)
4738/0/267
µ(Mo KR) (mm-1
)
no. of indep rflns
no. of data/restraints/
params
GOF on F2
1.02
1.04
1.12
1.08
1.11
R1(F) (I > 2σ(I))
0.042
0.109
0.038
0.097
0.061
0.189
0.020
0.050
0.066
0.189
wR2(F2) (all data)
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Metallocenes 2-5
3a‚BrLi(THF)3
5b‚0.25C5H12
(M ) Si)
2a (M ) Zn)
2b (M ) Zn)
(M ) Cd)
3b (M ) Cd)
4a (M ) Hg)b
M-C
M‚‚‚B
B-Cintra
N-B
2.001(3)-2.004(4)
2.443(4)-2.546(5)
1.507(6)-1.541(7)
1.406(5)-1.442(5)
1.424(4)-1.443(4)
1.527(5)-1.56(3)
1.578(6)-1.59(2)
1.451(8)-1.484(5)
175.2(1), 180.0(3)
103.1(3)-104.1(3)
114.2(11)-137.4(8)
1.999(2), 2.004(2)
2.564(2)-2.626(2)
1.537(3)-1.556(3)
1.424(3)-1.433(3)
1.443(2), 1.446(2)
1.527(3), 1.534(3)
1.574(3)-1.581(3)
1.470(3)-1.479(2)
174.71(8)
2.248(3), 2.255(3)
2.796(4)-2.872(4)
1.519(5)-1.529(6)
1.426(5)-1.442(5)
1.438(5), 1.457(4)
1.531(5), 1.533(5)
1.589(6)-1.591(6)
1.40(1)-1.47(1)
159.27(13)
2.201(5), 2.206(5)
2.706(6)-2.758(6)
1.535(8)-1.555(7)
1.423(7)-1.444(7)
1.445(6), 1.450(6)
1.517(7), 1.535(7)
1.570(7)-1.588(8)
1.472(6)-1.488(6)
175.3(2)
2.168(6), 2.177(6)
2.729(7)-2.780(6)
1.546(10)-1.557(9)
1.390(12)-1.416(11)
1.454(7), 1.486(12)
1.524(9), 1.536(11)
1.573(12)-1.597(11)
1.408(17)-1.549(15)
175.6(3), 176.1(3)
102.2(5), 103.0(6)
123.3(6)-124.8(6)
1.829(5)
2.755(6), 2.774(6)
1.585(7), 1.592(7)
1.382(6), 1.404(6)
1.454(5)
1.568(6)
1.560(7), 1.575(7)
1.473(6), 1.476(6)
a
N-N
Cextra-Cintra
B-Cextra
N-Cextra
C-M-C
B-C-B
102.7, 102.8(2)
122.6(2)-126.7(2)
103.1(3), 103.6(3)
124.4(3)-125.3(3)
102.8(4), 103(5)
122.8(4)-127.8(5)
100.3(4)
117.0(4), 117.3(4)
B-Cintra
Cextra
-
N-B-Cintra
Cintra-B-
Cextra
107.4(3)-108.4(4)
113.8(7)-127.7(4)
108.2(2)-109.0(2)
125.0(2)-128.7(2)
108.2(3)-109.1(3)
125.4(3)-128.6(4)
108.0(4)-109.0(4)
124.4(4)-129.6(5)
107.6(6)-109.3(7)
125.0(6)-127.2(6)
108.9(4), 109.2(4)
125.7(4), 127.5(4)
N-B-Cextra
123.3(4)-138.4(7)
108.8(3)-110.9(3)
122.4(4)-145.7(5)
102.3(4)-124.5(3)
81.1, 82.6, 80.3
12.2, 14.4, 16.2
538.9, 539.1
122.7(2)-126.0(2)
109.4(2)-110.2(2)
124.6(2)-128.1(2)
117.1(2)-120.2(2)
86.9, 87.8
122.3(4)-125.5(4)
108.6(3)-109.3(3)
111.0(5)-141.4(5)
103.2(5)-129.4(4)
85.0, 87.7
121.3(5)-127(4)
109.1(4)-110.2(4)
124.6(4)-128.2(4)
116.3(4)-120.7(4)
87.6, 87.9
124.0(6)-126.5(6)
108.8(7)-110.3(6)
111.1(8)-147.6(10)
100.1(8)-132.4(8)
87.6, 88.9
123.3(4), 125.4(4)
110.4(4), 111.0(4)
125.2(4), 130.2(4)
119.3(4), 123.3(4)
64.1
B-N-N
B-N-Cextra
N-N-Cextra
M-C/CB2N2
C-C/CB2N2
19.7, 20.2
539.5, 539.6
15.6, 19.1
239.0, 538.6
17.6, 18.4
539.7, 539.7
20.2, 21.7
539.0, 539.1
48.1
539.8
∑
pentagn angles
a Cintra and Cextra indicate carbon atoms that are part of the ring (intraannular) and directly connected to the ring (extraannular), respectively. b The structure
of 4a is heavily disordered.
bond lengths observed in borazines (1.42-1.44 Å).11 It is
interesting to note that the intraannular B-C bonds are slightly
longer in the group 12 complexes presented here than in the
alkali-metal salts of the same ligands (1.486(6)-1.514(3) Å),10
while the B-N bonds are shorter than those observed in the
group 1 metallocenes (1.452(3)-1.481(3) Å). A similar behavior
was observed for the corresponding C-C bonds in cyclopen-
tadienyl complexes of the group 12 metals by comparison to
alkali-metal cyclopentadienyls, which was explained by the
Figure 1. Side views illustrating the envelope conformation of
strong involvement of one carbon atom in the binding to the
one of the CB2N2 rings in 3a‚BrLi(THF)3: (left) folding along the
metal and the consequent decrease in the aromaticity of the
B(3)‚‚‚B(4) axis; (right) folding along the C(11)‚‚‚N(3) axis. For
ligand in the former derivatives. The N-N bonds in complexes
clarity, only the metal and the ring atoms are represented. Two
2-4 (1.424(4)-1.486(12) Å) are close in length to the single
pairs of ring atoms are eclipsed in each drawing.
N-N bond in hydrazine (1.45 Å).12 It can therefore be
In all complexes, the intraannular C-B bonds (1.507(6)-
1.557(9) Å) tend to be shorter than the extraannular C-B bonds
(1.570(7)-1.597(11) Å), in agreement with the expected
multiple-bond character. The B-N bond lengths, ranging
between 1.390(12) and 1.444(7) Å, are comparable to the B-N
(11) (a) Boese, R.; Maulitz, A. H.; Stellberg, P. Chem. Ber. 1994, 127,
1887. (b) Jaska, C. A.; Temple, K.; Lough, A. J.; Manners, I. J. Am. Chem.
Soc. 2003, 125, 9424. (c) Ja¨schke, T.; Jansen, M. Z. Anorg. Allg. Chem.
2004, 630, 239.
(12) Kohata, K.; Fukuyama, T.; Kuchitsu, K. J. Phys. Chem. 1982, 86,
602.

Zn, Cd, and Hg Metallocenes
Organometallics, Vol. 26, No. 14, 2007 3519
Figure 3. Molecular structure of 2b with 50% probability level
thermal ellipsoids. Hydrogen atoms have been omitted for clarity.
Figure 2. Structure of one of the two independent molecules in
2a, with thermal ellipsoids drawn at the 50% probability level.
Hydrogen atoms have been omitted for clarity.
although the Zn‚‚‚B distances (2.443(4)-2.546(5) Å) are longer
than the shortest Zn-B bonds observed in sandwich compounds
containing boranes as ligands ([Zn(B10H12)2]2- (2.191(7)-2.209-
(10) Å)13a,b and [(nido-C2B9H11)ZnNMe3]2 (2.160(3)-2.177-
(3) Å)13c), the latter description was chosen, given the small
yet distinct difference with respect to the other structures
reported herein.
concluded that the π electron delocalization over the N-B-
C-B-N skeleton of the ligand is similar to but slightly less
significant than that in the alkali-metal complexes of the same
ligands and, as is the case in the latter complexes, it does not
include the N-N bond. An extensive comparison of the metric
parameters of the ligands in alkali-metal complexes containing
diazadiborolidines to those observed in related complexes
featuring heterocyclic π ligands was recently reported.10b
The orientation of the ring substituents with respect to the
ligand plane is similar in all complexes. The methyl substituent
on the ring carbon is bent noticeably away from the metal, with
the C-C bond forming angles of 12.2-21.7° with the CB2N2
plane. This is common in metallocenes of group 12 metals and
was correlated to the partial sp3 hybridization of the carbon
connected to the metal and to a σ component of the η1
coordination mode. In the methyl derivatives, one of the
extraannular B-C bonds lies closer to the ligand plane (B-C/
CB2N2 ) 1.0-5.3°), while the other is bent away more
pronouncedly from the metal (B-C/CB2N2 ) 7.9-13.8°). In
both 2b and 3b the phenyl substituents on boron are only slightly
bent away from the metal, with angles between the B-C bonds
and the CB2N2 plane of 0.1-4.9°. As observed in the alkali-
metal salts of these ligands,10 the isopropyl substituents on
nitrogen alternate above and below the ligand plane, with one
of the N-C bonds tilted toward the metal (N-C/CB2N2 )
10.5-25.8°) and the other away from the metal (N-C/CB2N2
) 5.8-18.4°). This orientation is in disagreement with the
partial multiple-bond character of the B-N bonds and does not
appear to be sterically induced, since it is not visibly affected
by the replacement of methyl substituents on boron with phenyl
groups.
The structure of 2b (Figure 3) is very similar to that of its
methyl analogue. The main difference is that the Zn-C bond
is nearly perpendicular to the CB2N2 plane (86.9 and 87.8°
in 2b vs 81.1, 82.6, and 80.3° in 2a). The coordination mode is
therefore typical η1 (Figure 7). For the rest of this work, an η1
coordination mode will refer to a monoconnective binding
involving the π cloud of the ligand and a planar geometry of
the sp2-hybridized ring carbon, as described by Jutzi and Burford
for π cyclopentadienyl complexes.1c The classical notation σ
refers to a monoconnective binding of the ligand, involving a
tetrahedral, sp3-hybridized ring carbon. Although these are
idealized situations, most structures resemble one of these
geometries more than the other and can be conveniently assigned
to one of the two categories. The Zn-C bond lengths are very
similar in 2a and 2b (1.999(2)-2.004(4) Å) and quite short in
comparison to those found in cyclopentadienyl complexes
(1.99-2.37 Å for η5 coordination and 1.95-2.22 Å for η1
coordination).4 From all five crystal structures of zincocenes
with η1:η5 coordination that have been determined, only Zn-
[C5Me4(SiMe3)]2 is not disordered and provides a reliable
comparison for the ligand geometry. As opposed to the case
for 2a,b, this compound features a structure with a σ-bonded
cyclopentadienyl and a distorted-tetrahedral ring carbon. The
Zn-C and C-C bonds involving the ring carbon form angles
of 69.0 and 43.0°, respectively, with the ring plane. With C-C/
CB2N2 angles of 12.2-20.2°, the methyl substituent on the ring
carbon is bent much less out of the ring plane in the two
zincocenes incorporating diazadiborolyl ligands. The Zn‚‚‚B
distances in 2b (2.564(2)-2.626(2) Å) are even larger than in
2a.
The structure of 2a contains two independent molecules that
are very similar and will be discussed together (Figure 2).10a
The zinc atom is relatively symmetrically coordinated by the
two parallel ligands, which form angles of 0 and 8.9° with each
other. All previously reported zincocenes are asymmetric,
featuring a η1:η2 or η1:η5 coordination mode of the cyclopen-
tadienyl ligand.4 A symmetric η5 coordination mode has been
observed in dizincocenes.8 The zinc center in 2a lies almost
above the ring carbon, with its projection onto the ligand plane
falling only slightly inside the ligand pentagon (Figure 7). Its
coordination can be described as either η1:η1 or η3:η3, and
The two cadmium complexes 3a‚BrLi(THF)3 (Figure 4) and
3b (Figure 5) feature very similar η1 coordination modes of
(13) (a) Greenwood, N. N.; McGinnety, J. A.; Owen, J. D. J. Chem.
Soc. A 1971, 809. (b) Allmann, R.; Ba¨tzel, V.; Pfeil, R.; Schmid, G. Z.
Naturforsch. 1976, 31B, 1329. (c) Goeta, A. E.; Howard, J. A. K.; Hughes,
A. K.; Johnson, A. L.; Wade, K. Chem. Commun. 1998, 1713.

3520 Organometallics, Vol. 26, No. 14, 2007
Ly et al.
Figure 4. Molecular structure of 3b with 50% probability level
thermal ellipsoids. For clarity, only the R-carbon atoms in the
organic substituents are represented and all hydrogen atoms have
been omitted.
Figure 6. Molecular structure of 4a with 50% probability level
thermal ellipsoids. Hydrogen atoms have been omitted for clarity,
and only two of the ligands disordered around the mercury center
are represented.
mocenes containing Lewis bases coordinated to the metal feature
cyclopentadienyl as a ligand and have two or three nitrogen
atoms completing the coordination sphere of cadmium.6a,b,d The
cyclopentadienyl ligand displays σ, η1, and η2 coordination in
these compounds, and the Cd-C bonds are longer in the
complexes featuring η1 coordination (2.307(5)-2.410(6) Å) than
in 3a‚BrLi(THF)3 (2.248(3), 2.255(3) Å). This is likely due to
the better donor ability of the nitrogen bases and their capacity
to reduce the electrophilicity of cadmium and hence its affinity
for the cyclopentadienyl ligands. The angles formed by the
Cd-C bonds with the planes of the cyclopentadienyl rings
measure ca. 77-81° for the η1 binding mode and ca. 59° for
the σ binding mode, being noticeably more acute than the
corresponding angles in 3a‚BrLi(THF)3. Also, the C-Cd-C
angles are more acute in the cyclopentadienyl derivatives (111.4-
(2) and 129.1(2)°). The Cd‚‚‚B distances in 3a‚BrLi(THF)3 and
3b range from 2.706(6) to 2.872(4) Å and are substantially
longer than the shortest Cd-B bonds observed in the three
compounds available for comparison ([(Et2O)2Cd(B10H12)]2
(2.37(3)-2.46(3) Å),15a [Cd(B9H13)2]2- (2.272(4)-2.302(4)
Å),15b and [Cd(B6H6)2]2- (2.388(10)-2.451(14) Å)15c).
The structure of the mercury metallocene 4a is heavily
disordered, with two equally abundant molecules occupying the
same position in the crystal lattice. The Hg center in the two
molecules having nearly perpendicular C-Hg-C axes occupies
the same crystallographic position. The isopropyl substituents
in each of these molecules are also disordered between two
positions (Figure 6). Careful modeling allowed for a good
refinement of the structure, and the crystallographic and metric
parameters are presented in Tables 1 and 2, respectively. Like
the previous structures presented in this paper, the mercury
complex features η1 coordinating ligands (C-Hg/CB2N2 angles
of 87.6 and 88.9°) and a nearly linear geometry at mercury (C-
Hg-C angles of 175.6(3) and 176.1(3)°). Further indicative of
an η1 binding mode, the angles formed by the Me-C bonds
involving the ring carbons with the planes of the ring skeletons
are relatively acute (20.2 and 21.7°). The C-Hg bonds measure
2.168(6) and 2.177(6) Å and are comparable to the bonds
observed in the three mercurocenes that have been crystallo-
Figure 5. Structure of 3a‚BrLi(THF)3 in the solid state, with
thermal ellipsoids drawn at the 50% probability level. Only the
R-carbon atoms are represented for the ring substituents, and all
hydrogen atoms, as well as the methylene groups in THF, have
been omitted. The disorder involving the bromine atom and the
isopropyl groups (C5 and C8) is not depicted.
the ligands, with the Cd-C bonds forming angles of 85.0-
87.9° with the ring planes (Figure 7). In both compounds, the
angles formed by the C-C bonds involving the ring carbons
with the ring plane fall in a narrow range, between 15.6 and
19.1°. Derivative 3b is isocrystalline with 2b, contains parallel
ligands (dihedral angle 7.5°), and displays an almost linear
geometry at cadmium (C-Cd-C ) 175.3°). Only two base-
free cadmocenes have been crystallographically characterized,
featuring η1:η1 and η1:η2 coordinating cyclopentadienyl ligands,
respectively.6e The latter structure is disordered, and therefore
only the former, (tBu3C5H2)2Cd, provides a basis for a rigorous
comparison of the metric parameters. This structure is quite
similar to that of 3b, with the Cd-C and C-CCd bonds forming
angles of 87.2 and 28.6° with the plane of the ring skeleton.
The lengths of the Cd-C bonds are identical in 3b (2.201(5),
2.206(5) Å) and (tBu3C5H2)2Cd (2.201(2) Å). In the complex
3a‚BrLi(THF)3, the coordination of the BrLi(THF)3 unit through
a long Br-Cd bond (2.731(8) and 2.7916(14) Å vs 2.55-2.59
Å in CdBr4 )
2- 14 imposes a narrower C-Cd-C angle of 159.27-
(13)° and prevents the ligands from adopting a parallel arrange-
ment (dihedral angle 19.6°). The Br atom is disordered between
two positions, and the lithium atom has the expected distorted-
tetrahedral geometry. All three reported structures of cad-
(15) (a) Greenwood, N. N.; McGinnety, J. A.; Owen, J. D. J. Chem.
Soc., Dalton Trans. 1972, 989. (b) Schaper, T.; Preetz, W. Inorg. Chem.
1998, 37, 363. (c) Littger, R.; Englich, U.; Spencer, J. T. Inorg. Chem.
1997, 36, 6434.
(14) Hasselgren, C.; Dean, P. A. W.; Scudder, M. L.; Craig, D. C.; Dance,
I. G. J. Chem. Soc., Dalton Trans. 1997, 2019.

Zn, Cd, and Hg Metallocenes
Organometallics, Vol. 26, No. 14, 2007 3521
Figure 7. Perpendicular projection onto the CB2N2 planes, revealing the hapticity of the ligand. From left to right: 2a (two independent
molecules, η3 coordination), 2b, 3a‚BrLi(THF)3, 3b, and 4a (η1 coordination).
graphically characterized, all featuring monoconnective binding
modes of the ligands (2.09(2)-2.163(3) Å).7b,d,e The bonding
in these latter compounds can also be described as η1; however,
the geometries of these derivatives indicate a significant σ
bonding component. The Hg-C and C-CHg bonds in these
complexes form angles of 68.1-77.3 and 31.9-37.7°, respec-
tively, with the planes of the cyclopentadienyl rings. The Hg‚
‚‚B distances in 4a (2.729(7)-2.780(6) Å) are much longer than
the shortest Hg-B bonds observed in mercury half-sandwich
compounds featuring 7,8-dicarba-nido-undecaboranes as ligands
(2.178(8)-2.208(6) Å).16
In order to gain further information regarding the monocon-
nective coordination mode of the diazadiborolyl ligand, com-
plexes 5a,b, expected to display σ bonding, were synthesized
Figure 8. Structure of 5b, with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms and the pentane molecule
have been omitted for clarity. On lower left is given a perpendicular
projection onto the CB2N2 plane, revealing the hapticity of the
by reacting the alkali-metal salts 1a,b with SiCl4. Recrystalli-
zation from hexane yielded the desired compounds as colorless
crystalline solids. The 1H and 13C NMR spectra of these
ligand.
derivatives featured the expected signals corresponding to a Cs
symmetry, and the identity of 5b was confirmed with a high-
of the CB2N2 ring has a folding angle of only 4.1° along one of
resolution mass spectrum. The broad resonance corresponding
the transannular C‚‚‚N axes, and the deviation of the substituents
to the ring carbon appeared at 35.4 and 35.2 ppm in the two
on boron and nitrogen out of the ring plane is less than 4.3°,
derivatives, ca. 40 ppm upfield from the signals displayed by
which is significantly less pronounced than in the group 12
derivatives 2-4 and only ca. 10 ppm downfield from the signals
complexes. Distinctive for a σ binding mode, the ring carbon
displayed by the protonated ligands.10b This is a clear indication
is distorted tetrahedral, with the Si(1)-C(1) and C(2)-C(1)
bonds forming angles of 64.1 and 48.1° with the CB2N2 plane,
respectively. By comparison, these angles range between 80.3
and 88.9° for the M-C bond and between 12.2 and 21.7° for
the C-C bond in complexes 2-4, where the metal-carbon bond
is nearly perpendicular to the ring plane and the carbon-carbon
bond is situated much closer to this plane. In agreement with
the more pronounced sp3 character of the ring carbon in 5b,
the bonds this atom forms to carbon and boron are slightly but
systematically longer (0.01-0.05 and 0.03-0.09 Å, respec-
tively) than in derivatives 2-4. The B-N bonds are only
marginally shorter in 5b in comparison to those in the group
12 metallocenes described herein (on average 0.03 Å). A very
similar structure was reported for Cp*SiCl3, with a planar ring
skeleton and a Si-C bond length of 1.867(3) Å.18 In this
derivative, the angles formed by the Si-C and C-C(Si) bonds
with the ligand plane measure 64.9 and 45.8°, respectively:
nearly identical with the values observed in 5b. The structural
analysis reveals very different monoconnective coordination
modes of the diazadiborolyl ligand in 5b (σ, nearly tetrahedral
ring carbon) and the group 12 complexes described in this paper
(π, nearly planar ring carbon).
for the pronounced sp3 character of the ring carbon in 5,
expected for the σ bonding, versus sp2 in complexes 2-4
featuring η1 coordination. Because of the electronic influence
of the neighboring boron atoms, a direct comparison to
cyclopentadienyl complexes in this regard is not feasible. As
expected, the 11B and 29Si NMR spectra of 5a (43.9 and 5.7
ppm, respectively) and 5b (41.8 and 7.0 ppm, respectively)
displayed singlet resonances. A crystallographic determination
of 5b (Table 1 and 2) validates the proposed structure containing
a tetrahedral SiCl3 moiety σ bonded to the diazadiborolyl ligand
(Figure 8). The lengths of the Si-C and Si-Cl bonds (1.829-
(5) and 2.038(2)-2.040(2) Å, respectively) are comparable to
those found in other alkyltrichlorosilanes such as 1,2-bis-
(trichlorosilyl)ethane (Si-C ) 1.847(2) Å and Si-Cl ) 2.0225-
(6)-2.0283(6) Å).17 Typical for a distorted-tetrahedral geometry,
the C-Si-Cl and Cl-Si-Cl angles measure 111.44(16)-
113.28(15) and 104.02(8)-107.29(9)°, respectively. The ge-
ometry of the ligand skeleton is similar in 5b and the group 12
complexes described in this paper. The envelope conformation
(16) (a) Colquhoun, H. M.; Greenhough, T. J.; Wallbridge, M. G. H. J.
Chem. Soc., Dalton Trans., 1979, 619. (b) Lewis, Z. G.; Welch, A. J. Acta
Crystallogr. 1993, C49, 715. (c) Teixidor, F.; Ayllo`n, J. A.; Vin˜as, C.;
Kiveka¨s, R.; Sillanpa¨a¨, R.; Casabo`, J. J. Organomet. Chem. 1994, 483, 153.
(17) Mitzel, N. W.; Riede, J.; Schmidbaur, H. Acta Crystallogr. 1997,
C53, 1335.
(18) Cowley, A. H.; Ebsworth, E. A. V.; Mehrotra, S. K.; Rankin, D.
W. H.; Walkinshaw, M. D. J. Chem. Soc., Chem. Commun. 1982, 1099.

3522 Organometallics, Vol. 26, No. 14, 2007
Ly et al.
(20 mL). Subsequent solvent removal left behind the target
compound as a colorless powder. Colorless blocklike crystals of
2b (57 mg, 58%) were obtained by cooling a concentrated pentane
solution to -35 °C. 1H NMR (400 MHz, THF-d8, 25 °C): δ 1.14
Conclusions
Zinc, cadmium, and mercury metallocenes containing 1,2-
diisopropyl-3,5-dimethyl-1,2-diaza-3,5-diborolyl and 1,2-diiso-
propyl-3,5-diphenyl-1,2-diaza-3,5-diborolyl ligands were syn-
thesized and characterized. In all complexes, the ring carbon
plays the essential role in the binding of the ligand to the metal
and the geometry of the complexes is, in contrast to the zinc
cyclopentadienyl analogs, fairly symmetric. Four base-free
complexes were isolated and featured linear environments
around the metal, with C-M-C angles situated between 174
and 180°. Compound 3a crystallized with one unit of BrLi-
(THF)3 coordinated to the cadmium center and featured a
C-Cd-C angle of 159°. Except for the zinc complex 2a, where
the Zn-C bond is noticeably tilted toward the ligand and the
coordination is better described as η3:η3, the coordination mode
of the ligand is typical η1:η1 in all other group 12 complexes.
The M-C bond is nearly perpendicular to the CB2N2 plane in
compounds 2b, 3a‚BrLi(THF)3, 3b, and 4a (85.0-88.9°), while
the C-C bond involving the ring carbon forms angles of 12.2-
21.7° with the same plane. In all group 12 cyclopentadienyl
derivatives available for comparison, the σ character of the
metal-to-ligand bonding is more pronounced than in the
complexes described herein. This suggests that the stabilization
of a planar configuration for the negatively charged carbon
involved in the binding to the metal, through π donation to the
electron-deficient boron atoms in the 1,2-diaza-3,5-diborolyl
group, is more effective than the stabilization through delocal-
ization over the ring in the cyclopentadienyl group. For
comparison, the structure of the trichlorosilyl derivative 5b was
determined and featured a typical σ binding mode of the 1,2-
diaza-3,5-diborolyl ligand to the metal. The metal-carbon bond
lengths in all compounds are comparable to those observed in
the cyclopentadienyl analogues.
3
3
(d, 6H, JHH ) 6.8 Hz, CH(CH3)2), 1.27 (d, 6H, JHH ) 6.8 Hz,
3
CH(CH3)2), 1.53 (s, 3H, CCH3), 4.18 (sep, 2H, JHH ) 6.8 Hz,
CH(CH3)2), 7.22-7.36 (m, 6H, m- + p-C6H5), 7.36-7.38 (m, 4H,
o-C6H5). 13C{1H} NMR (100 MHz, THF-d8, 25 °C): δ 11.7 (s,
CCH3), 23.8 (s, CH(CH3)2), 24.6 (s, CH(CH3)2), 50.6 (s, CH(CH3)2),
69.3 (s, br, B2CCH3), 127.5 (s, p-C6H5), 128.3 (s, m-C6H5), 134.0
(s, o-C6H5), 142.0 (s, br, i-C6H5). 11B{1H} NMR (128 MHz, C6D6,
25 °C): δ ) 39.0 (s, br, LW1/2 ) 876 Hz). ESI-MS (CH3CN; m/z
(%)): 698.2 (5) [ZnL2]+, 381.0 (100) [ZnL]+, 319.1 (50) [L + H]+.
Synthesis of Bis(1,2-diisopropyl-3,5-dimethyl-1,2-diaza-3,5-
diborolyl)cadmium (3a). A solution of 1a (0.100 g, 0.500 mmol)
and anhydrous CdBr2 (0.068 g, 0.250 mmol) in THF (30 mL) was
sonicated for 30 min, forming a fine gray suspension. The solvent
was subsequently removed in vacuo, and the oily residue was
extracted with hexane (20 mL). Solvent removal left behind 3a as
a colorless crystalline solid (138 mg, 94%). Colorless needles of
the target compound were obtained by cooling a concentrated
pentane solution to -35 °C. 1H NMR (400 MHz, C6D6, 25 °C): δ
4
3
0.74 (s, 6H, JCdH ) 8.7 Hz, BCH3), 1.24 (d, 6H, JHH ) 6.9 Hz,
3
CH(CH3)2), 1.26 (d, 6H, JHH ) 6.9 Hz, CH(CH3)2), 1.84 (s, 3H,
3JCdH ) 59.6 Hz, CCH3), 3.85 (sep, 2H, 3JHH ) 6.9 Hz, CH(CH3)2).
1H NMR (400 MHz, THF-d8, 25 °C): δ 0.47 (s, 6H, JCdH ) 7.7
4
3
Hz, BCH3), 1.18 (d, 6H, JHH ) 6.8 Hz, CH(CH3)2), 1.27 (d, 6H,
3JHH ) 6.8 Hz, CH(CH3)2), 1.50 (s, 3H, JCdH ) 46.4 Hz, CCH3),
3
3.77 (sep, 2H, JHH ) 6.8 Hz, CH(CH3)2). 13C{1H} NMR (100
3
MHz, C6D6, 25 °C): δ -0.26 (s, br, BCH3), 13.2 (s, 2JCdC ) 39.7
Hz, CCH3), 23.4 (s, CH(CH3)2), 23.7 (s, CH(CH3)2), 47.8 (s, CH-
(CH3)2), 77.6 (s, br, B2CCH3). 13C{1H} NMR (100 MHz, THF-d8,
D1 ) 10 s, LB ) 3 Hz, 25 °C): δ 1.44 (s, br, BCH3), 14.3 (s,
2JCdC ) 43.1 Hz, CCH3), 23.2 (s, CH(CH3)2), 23.8 (s, CH(CH3)2),
48.3 (s, CH(CH3)2), 70.6 (s, br, B2CCH3). 11B{1H} NMR (128 MHz,
C6D6, 25 °C): δ 37.9 (s, br). 11B{1H} NMR (128 MHz, THF-d8,
25 °C): δ 40.9 (s, br, LW1/2 ) 486 Hz). 113Cd{1H} NMR (88 MHz,
C6D6, 25 °C): δ 256.2 (s). 113Cd{1H} NMR (66 MHz, THF-d8, 25
Multinuclear NMR spectroscopy shows that, unlike the related
alkali-metal derivatives, in solution the ligand does not dissociate
and the structure is preserved for the group 12 metallocenes
presented in this paper. This is in agreement with the higher
covalent character of the metal-ligand interaction in the latter
compounds and is consistent with the behavior of the corre-
sponding cyclopentadienyl complexes.
°C): δ 397.9 (s). MS (EI+, 70 eV; m/z (%)): 498.7 (60) [CdL2]+,
112
305.3 (26) [CdL]+, 192.3 (63) [L]+. HRMS for H46C20N411B4
-
Cd (m/z): calcd, 498.3122; found, 498.3124.
Synthesis of Bis(1,2-diisopropyl-3,5-diphenyl-1,2-diaza-3,5-
diborolyl)cadmium (3b). A mixture of 1b (0.100 g, 0.280 mmol)
and anhydrous CdBr2 (0.038 g, 0.140 mmol) in THF (30 mL) was
sonicated for 30 min, forming a gray suspension. The solvent was
subsequently removed in vacuo, and the residue was extracted with
hexane (20 mL). Solvent removal left behind 3b as a colorless
powder. Pale yellow prismatic crystals (84 mg, 80%) of the target
compound were obtained by cooling a concentrated pentane solution
Experimental Section
General Considerations. All operations were performed under
an argon atmosphere using standard Schlenk and glovebox tech-
niques. Solvents were dried and deoxygenated prior to use.
Tetraphenyltin, potassium bis(trimethylsilyl)amide, zinc(II) chloride,
cadmium(II) bromide, and mercury(II) chloride were purchased
from commercial suppliers and used without further purification.
Triethylamine was distilled over CaH2 prior to use. The lithium
and potassium salts 1a,b, respectively, were prepared according to
reported procedures.10 NMR spectra were recorded on Bruker
Advance DRX-400 and AMX-300 spectrometers and calibrated
with respect to C6D5H (1H, 7.15 ppm), THF-d7 (1H, 3.58 ppm),
C6D6 (13C, 128.39 ppm), THF-d8 (13C, 67.57 ppm), BF3‚Et2O (11B,
0 ppm), CdClO4 in D2O (113Cd, 0 ppm), and HgCl2 in THF-d8
1
to -35 °C. H NMR (400 MHz, C6D6, 25 °C): δ 1.13 (d, 6H,
3JHH ) 6.8 Hz, CH(CH3)2), 1.17 (d, 6H, 3JHH ) 6.8 Hz, CH(CH3)2),
3
3
1.87 (s, 3H, JCdH ) 58.7 Hz, CCH3), 4.06 (sep, 2H, JHH 6.8 Hz,
CH(CH3)2), 7.22 (t, 2H, p-C6H5), 7.31 (t, 4H, m-C6H5), 7.62 (d,
4H, o-C6H5). 1H NMR (400 MHz, THF-d8, 25 °C): δ 1.16 (d, 6H,
3JHH ) 6.8 Hz, CH(CH3)2), 1.24 (d, 6H, 3JHH ) 6.8 Hz, CH(CH3)2),
3
3
1.58 (s, 3H, JCdH ) 58.7 Hz, CCH3), 4.16 (sep, 2H, JHH ) 6.8
Hz, CH(CH3)2), 7.23-7.29 (m, 6H, m- + p-C6H5), 7.40-7.43 (m,
4H, o-C6H5). 13C{1H} NMR (100 MHz, THF-d8, 25 °C): δ 13.2
(s, 2JCdC ) 42.2 Hz, CCH3), 23.9 (s, CH(CH3)2), 24.3 (s, CH(CH3)2),
50.4 (s, CH(CH3)2), 77.4 (s, br, B2CCH3), 127.7 (s, p-C6H5), 128.4
(s, m-C6H5), 134.2 (s, o-C6H5), 142.2 (s, br, i-C6H5). 11B{1H} NMR
(128 MHz, THF-d8, 25 °C): δ 36.6 (s, br, LW1/2 ) 897 Hz). 113Cd
(
199Hg, -1498 ppm). The electron impact (EI), electrospray
ionization (ESI), and high-resolution mass spectrometry (HRMS)
measurements were performed by the Analytical Instrumentation
Laboratory, Department of Chemistry, University of Calgary.
Synthesis of Bis(1,2-diisopropyl-3,5-diphenyl-1,2-diaza-3,5-
diborolyl)zinc (2b). A solution of 1b (0.100 g, 0.280 mmol) and
anhydrous ZnCl2 (0.019 g, 0.140 mmol) in THF (30 mL) was stirred
for 3 h at ambient temperature, forming a fine suspension. Volatiles
were removed in vacuo, and the residue was extracted with hexane
3
NMR (88 MHz, C6D6, 25 °C): δ 286.1 (sep, JCdH ) 60.5 Hz).
ESI-MS (CH3CN; m/z (%)): 745.1 (6) [CdL2-H]+, 430.1 (25)
[CdL]+, 317.1 (100) [L]+.
Synthesis of Bis(1,2-diisopropyl-3,5-dimethyl-1,2-diaza-3,5-
diborolyl)mercury (4a). A solution of 1a (0.100 g, 0.500 mmol)

Zn, Cd, and Hg Metallocenes
Organometallics, Vol. 26, No. 14, 2007 3523
and anhydrous HgCl2 (0.068 g, 0.250 mmol) in THF (30 mL) was
stirred for 3 h at ambient temperature, forming a gray suspension.
The solvent was removed in vacuo, and the residue was extracted
with hexane (30 mL). Removal of the solvent in vacuo left behind
colorless, crystalline 4a (138 mg, 94%). X-ray-quality single crystals
of 4a were obtained by slow evaporation of a pentane solution at
in THF (15 mL). The pale yellow mixture was stirred at ambient
temperature for 2 h, and the volatiles were subsequently removed
under vacuum, leaving behind a thick residue. The product was
extracted with hexane and isolated upon removal of the solvent in
the form of a colorless crystalline solid (0.10 g, 79%). Colorless
crystals of 5b‚0.25C5H12 were obtained by cooling a concentrated
1
4
1
-35 °C. H NMR (400 MHz, C6D6, 25 °C): δ 0.71 (s, 6H, JHgH
pentane solution of 5b at -35 °C. H NMR (400 MHz, THF-d8,
3
) 20.2 Hz, BCH3), 1.26 (d, 6H, JHH ) 6.9 Hz, CH(CH3)2), 1.29
25 °C): δ 1.20 (d, br, 6H, 3JHH ) 6.3 Hz, CH(CH3)2), 1.31 (d, 6H,
(d, 6H, 3JHH ) 6.9 Hz, CH(CH3)2), 1.84 (s, 3H, 3JHgH ) 142.5 Hz,
3JHH ) 6.9 Hz, CH(CH3)2), 1.43 (s, 3H, JSiH ) 12.9 Hz, CCH3),
3
3
1
3
CCH3), 3.82 (sep, 2H, JHH ) 6.9 Hz, CH(CH3)2). H NMR (400
4.19 (sep, 2H, JHH ) 6.9 Hz, CH(CH3)2), 7.25-7.31 (m, 6H, m-
4
MHz, THF-d8, 25 °C): δ 0.45 (s, 6H, JHgH ) 19.8 Hz, BCH3),
+ p-C6H5), 7.35 (d, 4H, o-C6H5). 13C{1H} NMR (100 MHz, THF-
d8, 25 °C): δ 10.2 (s, CCH3), 23.7 (s, CH(CH3)2), 24.3 (s, CH-
(CH3)2), 36.2 (s, br, B2CCH3), 49.9 (s, CH(CH3)2), 128.0 (s,
m-C6H5), 128.3 (s, p-C6H5), 132.7 (s, o-C6H5), 140.0 (s, br, i-C6H5).
3
3
1.29 (d, 6H, JHH ) 6.9 Hz, CH(CH3)2), 1.32 (d, 6H, JHH ) 6.9
Hz, CH(CH3)2), 1.59 (s, 3H, 3JHgH ) 143.4 Hz, CCH3), 3.96 (sep,
2H, JHH ) 6.9 Hz, CH(CH3)2). 13C{1H} NMR (100 MHz, C6D6,
3
2
25 °C): δ -0.13 (s, br, BCH3), 13.6 (s, JHgC ) 64.5 Hz, CCH3),
11B{1H} NMR (128 MHz, THF-d8, 25 °C): δ 41.8 (s, br, LW1/2
)
23.4 (s, CH(CH3)2), 23.8 (s, CH(CH3)2), 47.9 (s, CH(CH3)2), 77.8
(s, br, B2CCH3). 13C{1H} NMR (100 MHz, THF-d8, -20 °C): δ
-0.35 (s, br, BCH3), 13.5 (s, CCH3), 23.4 (s, CH(CH3)2), 23.8 (s,
CH(CH3)2), 48.2 (s, br, CH(CH3)2), 77.3 (s, br, B2CCH3). 11B{1H}
NMR (128 MHz, C6D6, 25 °C): δ 39.0 (s, br). 11B{1H} NMR (128
MHz, THF-d8, 25 °C): δ 38.9 (s, br, LW1/2 ) 523 Hz). 199Hg{1H}
NMR (71 MHz, C6D6, 25 °C): δ -2063.3 (s). MS (EI+, 70 eV;
m/z (%)): 586.5 (21) [HgL2]+, 393.3 (1) [HgL]+, 193.3 (20) [L]+.
428 Hz). 29Si{1H} NMR (79 MHz, THF-d8, 25 °C): δ 7.0 (s). MS
(EI+, 70 eV; m/z (%)): 450 (100) [M]+, 435 (96) [M- Me]+, 407
(10) [M- iPr]+, 393 (20) [M - Me - iPr + H]+. HRMS for
H27C20N211B235Cl3Si (m/z): calcd, 450.1195; found, 450.1199.
HRMS for H27C20N211B235Cl237ClSi (m/z): calcd, 452.1166; found,
452.1157.
X-ray Crystallography. Single crystals of 2b, 3b, 3a‚BrLi-
(THF)3, and 5b‚0.25C5H12 were coated with Paratone 8277 oil
(Exxon) and mounted on a glass fiber. All measurements were made
on a Nonius KappaCCD diffractometer with graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å). The crystal data and
data collection and refinement parameters for the complexes are
given in Table 1. The data were collected19 at a temperature of
173(2) K using ω and æ scans and corrected for Lorentz and
polarization effects and for absorption using multiscan methods.20
Since the crystals did not show any sign of decay during data
collection, a decay correction was deemed unnecessary. Data for
the crystal of 4a were measured at 193(2) K on a Bruker SMART
1000 CCD/PLATFORM diffractometer with graphite-monochro-
mated Mo KR radiation using ω scans.21
Synthesis of (1,2-Diisopropyl-3,5-dimethyl-1,2-diaza-3,5-di-
borolyl)trichlorosilane (5a). Silicon tetrachloride (97 µL, 0.85
mmol) was added to a colorless solution of 1a (0.17 g, 0.85 mmol)
in THF (15 mL). The clear mixture was stirred at ambient
temperature for 2 h, and the volatiles were subsequently removed
under vacuum, leaving behind a thick residue. The product was
extracted with hexane and isolated upon removal of the solvent in
1
the form of a colorless crystalline solid (0.21 g, 75%). H NMR
(400 MHz, C6D6, 25 °C): δ 0.64 (s, 6H, BCH3), 1.08 (d, 6H, 3JHH
3
) 6.9 Hz, CH(CH3)2), 1.13 (d, 6H, JHH ) 6.9 Hz, CH(CH3)2),
3
3
1.29 (s, 3H, CCH3, JSiH ) 13.0 Hz), 3.68 (sep, 2H, JHH ) 6.9
1
Hz, CH(CH3)2). H NMR (400 MHz, THF-d8, 25 °C): δ 0.55 (s,
The structures were solved by direct methods22 and expanded
using Fourier techniques.23 The non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were included at geometrically
idealized positions and were not refined. The final cycle of full-
matrix least-squares refinement using SHELXL9724 converged with
unweighted and weighted agreement factors, R and Rw (all data),
respectively, and goodness of fit, F2. The weighting scheme was
based on counting statistics, and the final difference map was
essentially featureless. The figures were plotted with the aid of
Diamond.25
6H, BCH3), 1.26 (s, 3H, CCH3), 1.34 (d, 6H, 3JHH ) 6.9 Hz, CH-
3
(CH3)2), 1.37 (d, 6H, JHH ) 6.9 Hz, CH(CH3)2), 4.07 (sep, 2H,
3JHH ) 6.9 Hz, CH(CH3)2). 13C{1H} NMR (100 MHz, THF-d8, 25
°C): δ 0.6 (s, br, BCH3), 10.7 (s, CCH3), 22.3 (s, CH(CH3)2), 22.9
(s, CH(CH3)2), 35.4 (s, br, B2CCH3), 47.6 (s, CH(CH3)2). 11B{1H}
NMR (128 MHz, C6D6, 25 °C): δ 43.9 (s, br, LW1/2 ) 321 Hz).
29Si{1H} NMR (79 MHz, THF-d8, 25 °C): δ 5.7 (s). MS (EI+, 70
eV; m/z (%)): 327 (13) [M]+, 312 (40) [M - Me]+, 269 (14) [M
- Me - iPr]+.
Synthesis of (1,2-Diisopropyl-3,5-diphenyl-1,2-diaza-3,5-di-
borolyl)trichlorosilane (5b). Silicon tetrachloride (32 µL, 0.28
mmol) was added to a colorless solution of 1b (0.10 g, 0.28 mmol)
Acknowledgment. This work was supported by the Natural
Sciences and Engineering Research Council of Canada, the
Canada Foundation for Innovation, and the Alberta Science and
Research Investments Program.
(19) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(20) Hooft, R. COLLECT; Nonius BV, Delft, The Netherlands, 1998.
(21) Programs for diffractometer operation, data collection, data reduc-
tion, and absorption correction were those supplied by Bruker.
(22) Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1993, 26, 343.
(23) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-94 Program System;
Technical Report of the Crystallography Laboratory; University of Nijmegen,
Nijmegen, The Netherlands, 1994.
(24) Sheldrick, G. M. SHELXL97; University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
(25) DIAMOND-Visual Crystal Structure Information System; CRYS-
TAL IMPACT, Postfach 1251, D-53002 Bonn, Germany.
Supporting Information Available: CIF files giving complete
crystallographic data of the complexes 2b, 3a‚BrLi(THF)3, 3b, 4a,
and 5b and figures giving NMR spectra of all new compounds as
evidence of purity, in the absence of satisfactory elemental analyses.
This material is available free of charge via the Internet at http:/
pubs.acs.org. CIF files are also available online from the Cambridge
Crystallographic Data Centre (CCDC Nos. 635572 (2b), 635573
(3a‚BrLi(THF)3), 635574 (3b), 635575 (4a), and 635576 (5b)).
OM070230N