Synthesis, structure, and reactivity of a tetranuclear amidinato zinc hydride complex

Article abstract of DOI:10.1021/om100966d

The tetranuclear amidinato zinc hydride complex {C[C(Ni-Pr) ₂ZnH]₄} (3) was synthesized by reaction of the Cl-substituted complex {C[C(Ni-Pr)₂ZnCl]₄} with CaH ₂. 3 was found to react with phenylacetyl

Full text of DOI:10.1021/om100966d

Organometallics 2010, 29, 6133–6136 6133
DOI: 10.1021/om100966d
Synthesis, Structure, and Reactivity of a Tetranuclear Amidinato Zinc
Hydride Complex
€
Benjamin Gutschank, Stephan Schulz,* Dieter Blaser, Roland Boese, and
€
Christoph Wolper
Institute of Inorganic Chemistry, University of Duisburg-Essen, 45117 Essen, Germany
Received October 5, 2010
Scheme 1. Synthesis of {C[C(Ni-Pr)2ZnH]4, 3a
Summary: The tetranuclear amidinato zinc hydride complex
{C[C(Ni-Pr)2ZnH ]4} (3) was synthesized by reaction of the
Cl-substituted complex {C[C(Ni-Pr)2ZnCl ]4} with CaH2. 3
was found to react with phenylacetylene and acetylene at
ambient temperature with elimination of H2 and subsequent
formation of C[C(Ni-Pr)2ZnCtCPh]4 (4) and {C[C(Ni-Pr)2-
ZnCtCH ]4 (5), respectively. 3-5 have been characterized by
multinuclear NMR (1H, 13C) and IR spectroscopy, elemental
analyses, and single-crystal X-ray diffraction.
a i-Pr groups bound to the N atoms are omitted for clarity; amidinato
units containing a delocalized π-electron system are accentuated.
expected to show an increased reactivity toward hydrogen
elimination reactions, insertion reactions, or addition reactions.
Herein we report on the synthesis and crystal structure
of {C[C(Ni-Pr)2ZnH]4 (3). Moreover, initial studies on its
reactivity toward C-H acidic organic substrates such as
acetylene, HCtCH, and phenylacetylene, HCtCPh, proved
3 to be a suitable starting reagent for substitution reactions
(hydrogen elimination) under mild reaction conditions.
These reactions were found to proceed with preservation of
the central cluster-like zinc amidinato core and subsequent
formation of {C[C(Ni-Pr)2ZnCtCPh]4 (4) and {C[C(Ni-
Pr)2ZnCtCH]4 (5), respectively. 5 represents the first struc-
turally characterized Zn complex containing covalently
bound, terminal CtCH groups.
Introduction
The reactions of main group and transition metal alkyl
complexes with carbodiimides, C(NR)2, typically proceed with
insertion of the carbodiimide into a metal-carbon bond and
subsequent formation of the corresponding amidinato com-
plexes.1 In remarkable contrast, we found that dimethylzinc
reacts with C(NR)2 (R=i-Pr; Cy) at elevated temperatures with
elimination of methane and unforeseen formation of tetranu-
clear amidinato complexes such as {C[C(NR)2ZnMe]4} (R=
i-Pr, 1a; Cy, 1b).2 Due to the presence of four Zn-Me moieties,
these complexes were expected to be suitable starting reagents
for further substitution reactions. However, reactions of 1a with
H-acidic amines RNH2, alcohols ROH, and even water at
ambient temperature did not occur, whereas at elevated tem-
peratures the complexes completely decomposed due to pro-
tonation of the Lewis basic N centers rather than give the
expected methane elimination products. We therefore syn-
thesized the corresponding halide-substituted complexes
{C[C(Ni-Pr)2ZnX]4} (X=Cl, 2a; Br, 2b; I, 2c) by a methyl/
halide exchange reaction with AlX3 in order to investigate
substitution reactions at the Zn centers via salt elimination
pathways.3 However, a major drawback of salt elimination
reactions using Li organyls and Grignard reagents is the forma-
tion of solid byproducts, necessitating further purification steps.
We therefore became interested in the tetranuclear zinc hydride
complex {C[C(Ni-Pr)2ZnH]4 since the Zn-H groups were
Results and Discussion
The reaction of {C[C(Ni-Pr)2ZnCl]4} (2a) with an excess of
CaH2 in THF at 0 °C gave 3 in high yield after workup.
The 1H NMR spectrum of the bulk reaction mixture shows
the typical resonance pattern due to two nonequivalent i-Pr
groups, as was observed for the halide-substituted complexes
{C[C(Ni-Pr)2ZnX]4}.3 An additional sharp singlet (4.60 C6D6;
4.11 THF-D8), which is in the typical range previously observed
for Zn-H groups,4 proved the formation of the zinc hydride
moiety. The IR spectrum of 3 shows a strong Zn-H valence
vibration band at 1766 cm-1, in accordance with values pre-
viously reported for zinc complexes containing terminal hy-
drides such as [HZnOt-Bu]4 (1821 cm-1)5 and [tris(3-tert-butyl-
pyrazolyl)hydroborat]ZnH (1770 cm-1).6
*To whom correspondence should be addressed. Phone: þ49 0201-
1834635. Fax: þ 49 0201-1833830. E-mail: stephan.schulz@uni-due.de.
(1) For references, see: (a) Edelmann, F. T. Chem. Soc. Rev. 2009, 38,
2253. (b) Edelmann, F. T. Adv. Organomet. Chem. 2008, 57, 133. (c)
Edelmann, F. T.; Coles, M. P. Dalton Trans. 2006, 985. (d) Barker, J.; Kilner,
M. Coord. Chem. Rev. 1994, 133, 219. (e) Cole, M. L. Chem. Commun.
2007, 1579.
(2) (a) Munch, M.; Florke, U.; Bolte, M.; Schulz, S.; Gudat, D.
Angew. Chem. 2008, 120, 1535; Angew. Chem., Int. Ed. 2008, 47, 1512.
€
(b) Schmidt, S.; Gondzik, S.; Schulz, S.; Blaser, D.; Boese, R. Organo-
Colorless crystals of 3 suitable for single-crystal X-ray
diffraction determination were obtained from a solution in
THF at -30 °C. 3 crystallizes in the monoclinic space group
(4) For references, see: Schulz, S.; Eisenmann, T.; Schuchmann, D.;
Bolte, M.; Kirchner, M.; Boese, R.; Spielmann, J.; Harder, S. Z.
Naturforsch. 2009, 64b, 1397.
€
€
(5) Marciniak, W.; Merz, K.; Moreno, M.; Driess, M. Organometal-
metallics 2009, 28, 4371.
(3) Gutschank, B.; Schulz, S.; Westphal, U.; Blaser, D.; Boese, R.
Organometallics 2010, 29, 2093.
lics 2006, 25, 4931.
(6) Looney, A.; Han, R.; Gorrell, I. B.; Cornebise, M.; Yoon, K.;
Parkin, G. Organometallics 1995, 14, 274.
€
r
2010 American Chemical Society
Published on Web 10/22/2010
pubs.acs.org/Organometallics

6134 Organometallics, Vol. 29, No. 22, 2010
Gutschank et al.
Figure 1. Molecular structure of {C[C(Ni-Pr)2ZnH]4, 3 (thermal
ellipsoids are shown at 50% probability levels). H atoms except for
˚
Zn-H ones are omitted for clarity. Selected bond lengths [A]
and angles [deg]: Zn1-H1 1.45(3), Zn2-H2 1.47(3), Zn1-N1
2.1273(17), Zn1-N2 2.1428(16), Zn1-N4 2.1357(16), Zn2-N2
2.1445(17), Zn2-N3 2.1266(16), Zn2-N4 2.1372(17), N1-C14
1.314(2), N2-C14a 1.344(2), C13-C14 1.559(2), C13-C15
1.561(2); N1-C14-N2a 137.27(18), N3a-C15-N4 137.44(18),
C14-C13-C15 100.42(10), C14a-C13-C15 130.06(10), N1-Zn1-
N2 96.19(6), N1-Zn1-N4 97.25(6), N2-Zn1-N4 83.00(6), N2-
Zn2-N3 96.80(6), N2-Zn2-N4 82.92(6), N3-Zn2-N4 97.01(6).
Scheme 2. Synthesis of 4 and 5a
a i-Pr groups bound to the N atoms are omitted for clarity; amidinato
units containing a delocalized π-electron system are accentuated.
Figure 2. Time-dependent 1H NMR monitoring of the reaction
of 3 and HCtCH in THF-D8 (Zn-H indicated by *, Zn-Ct
CH by #).
C2/c. The cluster-like core as was observed in the starting com-
plex 2a is still preserved. The central sp3-hybridized Ccenter atom
is coordinated by four C atoms of adjacent amidinato groups,
and the C-C bond lengths are in the range of typical C-C
{C[C(NR)2ZnCtCH]4 (5) within 24 h.8 In contrast, 1a com-
pletely failed to react with phenyl acetylene even at elevated
temperatures (110 °C) and long reaction periods (7 d). These
findings clearly demonstrate the enhanced reactivity of the
Zn-H group compared to the Zn-Me group in complex 1a,
which most likely results from the replacement of the Me group
by the sterically less demanding hydride group (kinetically
controlled reaction).
˚
single bonds (1.559(0)-1.560(7) A). The N-C bond lengths
within the amidinato groups indicate an almost perfectly delo-
˚
calized π-electron system (average value 1.330 A). Almost anal-
ogous structural parameters were observed in 1a and 2a-c,
respectively. The Zn atoms in 3, which bind to three N atoms of
adjacent amidinato groups and an additional H atom, adopt
tetrahedral coordination spheres. The Zn-N bond lengths in 3
1H NMR monitoring of the reaction of 3 and HCtCH
showed a constantly decreasing Zn-H and an increasing acet-
ylide resonance. The intermediate appearances of four different
acetylide resonances of different intensity around 2.1-2.15 ppm
after 7.5 h (see inset box in Figure 2) indicate a stepwise sub-
stitution of the four hydride centers. The characteristic none-
quivalent i-Pr resonances of the tetraamidinato framework
shifted to lower field with ongoing formation of complex 5.
Colorless crystals of 4 and 5 suitable for a single-crystal
structure determination were obtained from solutions in THF.
4 crystallizes in the orthorhombic space group Pbcn, containing
three disordered THF molecules in the unit cell, whereas 5 crys-
tallizes in the triclinic space group P1. Both complexes again
˚
(2.1266(16)-2.1445(17) A) are almost identical to those of 1a
˚
and 2a-c, and the Zn-H bond length (1.46(3) A) is within the
range previously reported for terminal zinc hydrides.6,7 Zinc
hydrides containing terminal Zn-H groups are still rare, and 3
is only the second example of a complex containing four
terminal Zn-H groups in a single molecule.
In order to evaluate the reactivity of the amidinato zinc
hydride complex in more detail, 3 was reacted with HCtCR
(R=Ph, H) under mild reaction conditions (ambient tem-
perature, acetylene at atmospheric pressure). These reactions
almost quantitatively yielded the corresponding hydrogen
elimination products {C[C(Ni-Pr)2ZnCtCPh]4 (4) and
(7) Spielmann, J.; Piesik, D.; Wittkamp, B.; Jansen, G.; Harder, S.
Chem. Commun. 2009, 3455.
(8) 4 was also synthesized by reaction of {C[C(Ni-Pr)2ZnCl]4} (2a) with
sodium phenylacetylide in THF (see Experimental Section, method A).

Note
Organometallics, Vol. 29, No. 22, 2010 6135
Figure 4. Molecular structure of {C[C(Ni-Pr)2ZnCtCH]4, 5
(thermal ellipsoids are shown at 50% probability levels). H atoms
except for CtCH ones are omitted for clarity. Selected bond lengths
Figure 3. Molecular structure of {C[C(Ni-Pr)2ZnCtCPh]4, 4
(thermal ellipsoids are shown at 50% probability levels). H atoms
˚
[A] and angles [deg]: Zn2-C32 1.926(3), Zn3-C34 1.949(3), C30-
C31 1.171(4), C32-C33 1.183(4), Zn1-N1 2.127(2), Zn1-N2
2.130(2), Zn1-N8 2.116(2), Zn2-N1 2.127(2), Zn2-N2
2.124(2), Zn2-N3 2.095(2), N1-C4 1.352(3), N2-C2 1.354(2),
N3-C3 1.314(2), N4-C2 1.303(3), C1-C3 1.555(3), C1-C2
1.567(3); N1-C4-N7 137.9(2), N3-C3-N5 137.7(2), C2-C1-
C3 99.58(18), C2-C1-C4 130.43(19), C2-C1-C5 99.96(17),
N1-Zn1-N2 83.43(8), N1-Zn1-N8 98.93(8), N2-Zn1-N8
97.54(8), N1-Zn2-N2 83.61(8), N1-Zn2-N3 97.60(8), N2-
Zn2-N3 97.89(8).
˚
are omitted for clarity. Selected bond lengths [A] and angles [deg]:
Zn1-C4 1.9261(13), Zn2-C12 1.9307(13), Zn1-N1 2.1078(10),
Zn1-N3 2.1768(11), Zn1-N4 2.0986(10), Zn2-N2 2.1055(11),
Zn2-N3 2.0996(11), Zn2-N4 2.1524(10), N1-C3a 1.3065(15),
N2-C2a 1.3111(16), N3-C2 1.3545(15), N4-C3 1.3578(15), C1-
C2 1.5576(76), C1-C3 1.5649(15); N2a-C2-N3 137.21(12), N1a-
C3-N4 137.26(11), C2-C1-C3 130.26(6), C2-C1-C2a 98.27(12),
C2-C1-C3a 102.38(6), N1-Zn1-N3 101.34(4), N1-Zn1-N4
95.53(4), N3-Zn1-N4 83.43(4), N2-Zn2-N3 95.19(4), N2-
Zn2-N4 100.62(4), N3-Zn2-N4 84.00(4).
trend. The Zn2-C12-C13 unit (178.8°) shows an almost
perfect linear arrangement, whereas the Zn1-C4-C5 bond
angle (164.4°) significantly differs from linearity. Green et al.
reported on similar structural findings for group 2 metal
acetylides of the type [M([18]crown-6)(CtCSiPh3)2] (M =
Ca, Sr) and explained the bending by packing effects due to
space limitations and a low-energy barrier for the bending.15
Moreover, Clegg et al. recently reported that CtC-Zn bond
angles typically lie in the range 164.2-175.5°.13
show the cluster-like core with the central sp3-hybridized Ccenter
˚
atom. The C-C (4: 1.557(7)-1.564(9), 5: 1.555(1)-1.567(0) A)
˚
˚
and N-C bond lengths (average values: 4 1.332 A, 5 1.330 A)
within this core are almost unchanged compared to 3 and again
indicate delocalized π-electron systems within the amidinato
groups. The Zn atoms in 4 and 5 are tetrahedrally coordinated
by three N atoms of adjacent amidinato groups and the acetylide
moiety. The Zn-N (4: 2.0986(10)-2.1768(11; 5: 2.092(8)-
Zinc acetylide complexes of the general type LZnCtCH
have only been scarcely described in the literature. To the best of
˚
2.137(8) A) and Zn-C bond lengths (4: 1.926(1)-1.930(8); 5:
˚
1.925(6)-1.948(7) A) are very similar. The C-C bond lengths
our knowledge, the ionic zincates K2Zn(CtCH)4 2NH3 and
˚
3
of the ethinyl groups in 4 (1.208(4)-1.210(3) A) are slightly
elongated compared to that in free phenylacetylene (1.183 A),
Rb2Zn(CtCH)416 are the only structurally characterized com-
plexes of this type. 5 therefore represents the first structurally
characterized neutral Zn acetylide complex containing a cova-
lently bound, terminal CtCH moiety.
9
˚
but comparable to values reported for [Zn(CtCSiMe3)-
˚
(NPMe3)]4 (1.20(2) A), [Zn(CtC-CtCSiMe3)(NPEt3)]4
10
11
˚
˚
(1.22(1) A), [(dpp-BIAN)Zn( μ-CtCPh)]2 (1.2099(17) A),
12
and DippNacNacZnCtCPh (1.207(3) A), as well as to
˚
Conclusions
the base-stabilized complex (PhCtC)2Zn(tmeda) (1.211(5),
1.219(5) A),13 respectively. The CtC triple-bond lengths in 5
˚
{C[C(NR)2ZnH]4 (3) is a valuable starting reagent for
further substitution reactions due to its enhanced reactivity
toward organic substrates containing acidic H atoms. Reactions
with acetylenes were found to occur under very mild reaction
condition with stepwise elimination of hydrogen and subsequent
formation of {C[C(Ni-Pr)2ZnCtCPh]4 (4) and {C[C(Ni-
Pr)2ZnCtCH]4 (5), the first structurally characterized neutral
zinc acetylide complex.
˚
(1.170(5)-1.183(3) A) are shorter than in 4 but comparable
to that reported for free acetylene (1.126(8) A at 140 K).
14
˚
The M-C-C angles in 5 are almost linear, with values
around 177.5°, whereas the angles in 4 show a rather unusual
€
(9) Weiss, H.-C.; Blaser, D.; Boese, R.; Doughan, B. M.; Haley,
M. M. Chem. Commun. 1997, 1703.
(10) Krieger, M.; Gould, R. O.; Neumuller, B.; Harms, K.; Dehnicke,
€
Experimental Details
K. Z. Anorg. Allg. Chem. 1998, 624, 1434.
(11) Fedushkin, I. L.; Eremenko, O. V.; Skatova, A. A.; Piskunov,
A. V.; Fukin, G. K.; Ketkov, S. Y. Organometallics 2009, 28, 3863.
(12) Prust, J.; Hohmeister, H.; Stasch, A.; Roesky, H. W.; Magull, J.;
Alexopoulos, E.; Uson, I.; Schmidt, H. G.; Noltemeyer, M. Eur. J. Inorg.
Chem. 2002, 2156.
All manipulations were performed in a glovebox under an Ar
atmosphere or using standard Schlenk line techniques. Solvents
(13) Clegg, W.; Garcia-Alvarez, J.; Garcia-Alvarez, P.; Graham,
D. V.; Harrington, R. W.; Hevia, E.; Kennedy, A. R.; Mulvey, R. E.;
Russo, L. Organometallics 2008, 27, 2654.
(14) McMullan, R. K.; Kvick, A.; Popelier, P. Acta Crystallogr. 1992,
B48, 726.
(15) (a) Green, D. C.; Englich, U.; Ruhlandt-Senge, K. Angew. Chem.
1999, 111, 365; Angew. Chem., Int. Ed. 1999, 38, 354. (b) Root, D. M.;
Landis, C. R.; Cleveland, T. J. Am. Chem. Soc. 1993, 115, 4201.
(16) (a) Cremer, U.; Pantenburg, I.; Ruschewitz, U. Inorg. Chem. 2003,
42, 7716. (b) Cremer, U.; Ruschewitz, U. Z. Anorg. Allg. Chem. 2004, 630, 337.

6136 Organometallics, Vol. 29, No. 22, 2010
Gutschank et al.
Table 1. Crystallographic Details of 3, 4, and 5
Yield: 0.49 g (81%). Melting point: 269 °C (dec). Anal. Found
(calcd) for C61H76N8Zn4 (1182.95 g/mol): H, 6.41 (6.48); C, 61.64
(61.85); N, 8.50 (8.47). 1H NMR (300 MHz, CDCl3, 25 °C): δ 1.42
(d, 24H, 3JHH =6.4Hz, CH(CH3)2), 1.68(d, 24H, 3JHH =6.4Hz,
CH(CH3)2), 4.03(sept, 4H, 3JHH =6.4Hz, CH(CH3)2), 4.43(sept,
4 H, 3JHH = 6.4 Hz, CH(CH3)2), 7.24 (m, 8 H, m-H), 7.27 (m, 4 H,
p-H), 7.43 (m, 8 H, o-H). 13C NMR (200 MHz, CDCl3, 25 °C): δ
24.4 (CH3), 24.8 (CH3), 48.2 (CH), 49.8 (CH), 72.9 (C), 109.1
(ZnCC), 111.8 (ZnCC), 126.4 (ipso-C), 126.8 ( p-C), 128.2 (m-C),
131.5 ( p-C), 169.5 (NCN). ATR-IR: ν 2956, 2922, 2895, 2868,
1554, 1516, 1481, 1392, 1363, 1248, 1206, 1121, 1064, 1026, 938,
3
4
5
empirical
formula
molecular mass
space group
T [K]
C
29H60N8Zn4
C61H76N8Zn4
3[C4H8O]
1399.09
Pbcn
100(2)
0.71073
16.7697(5)
16.1494(5)
25.9714(8)
90
90
90
7033.6(4)
4
4.503
C
37H60N8Zn4
3
782.33 Da
C2/c
878.41
P1
103(1)
100(2)
0.71073
11.1432(14)
18.004(2)
17.722(2)
90
97.395(7)
90
3526.0(7)
4
1.399
˚
˚
λ [A]
0.71073
10.6259(8)
11.0517(8)
18.1353(13)
85.136(4)
89.363(4)
72.877(4)
2027.8(3)
2
2.373
1.439
0.0291
0.0671
a [A]
˚
b [A]
˚
c [A]
896, 865, 830, 788, 761, 727, 693, 666, 651, 555, 532, 463, 444 cm-1
.
R (deg)
β (deg)
γ (deg)
{C[C(Ni-Pr)2ZnCCH]4}, 5. A 0.4 g (0.5 mmol) sample of
3 was dissolved in 15 mL of THF and stirred for 1 day at 35 °C
under an acetylene atmosphere of 4 bar in a sealed Pyrex tube.
Colorless crystals of 5 were formed within 24 h after storage at
-30 °C. Yield: 0.38 g (84%). Melting point: 250 °C (dec). Anal.
Found (calcd) for C37H60N8Zn4 (878.57 g/mol): H, 6.81 (6.88); C,
50.63 (50.58); N, 12.61 (12.75). 1H NMR (300 MHz, C6D6, 25 °C):
3
˚
V [A ]
Z
μ [mm-1
]
Dcalcd [g cm-3
R1
wR2
]
1.474
1.321
0.0275
0.0709
a
0.0246
0.0582
P
b
δ 1.06 (d, 24 H, 3JHH = 6.4 Hz, CH(CH3)2), 1.40 (d, 24 H, 3JHH
=
P
P
a R1
=
( Fo| - |Fc )/ |Fo| (for I > 2σ(I )). b R2 = { [w(Fo
-
2
6.4 Hz, CH(CH3)2), 1.98 (s, 4 H, CCH), 3.47 (sept, 4 H, 3JHH = 6.4
Hz, CH(CH3)2), 3.85 (sept, 4 H, 3JHH = 6.4 Hz, CH(CH3)2). 1H
NMR (300 MHz, THF-D8, 25 °C): δ 1.36 (d, 24 H, 3JHH = 6.4 Hz,
CH(CH3)2), 1.60(d, 24H, 3JHH = 6.4 Hz, CH(CH3)2), 2.15 (s, 4 H,
CCH), 3.98 (sept, 4 H, 3JHH = 6.4 Hz, CH(CH3)2), 4.41 (sept, 4 H,
3JHH = 6.4 Hz, CH(CH3)2).13C NMR (200 MHz, C6D6, 25 °C): δ
24.2 (CH3), 24.8 (CH3), 48.2 (CH), 50.0 (CH), 63.8 (C), 96.7
(ZnCCH), 106.5 (ZnCCH), 169.9 (NCN). ATR-IR: ν 3278 (sym
ZnCC-H), 3259 (asym ZnCC-H), 2959, 2922, 2867, 1564, 1519,
1456, 1386, 1364, 1327, 1304, 1256, 1164, 1123, 1093, 1012, 938, 894,
Fc2)2]/Σ[w(Fo2)2]}1/2 (for all data).
were carefully dried over Na/K and degassed prior to use. 2a3
and sodium phenylacetylene17 were prepared according to
literature methods. 1H and 13C NMR spectra were recorded
on a Bruker DMX 300 spectrometer and are referenced to
internal C6D5H (1H: δ = 7.154; 13C: δ = 128.0), THF-D8
(1H: δ = 3.58, 1.73), or CDCl3 (1H: δ = 7.26; 13C: δ = 77.0). IR
spectra were recorded on an ALPHA-T FT-IR spectrometer
equipped with a single-reflection ATR sampling module. Melt-
ing points were measured in sealed capillaries and were not
corrected. Elemental analyses were performed at the Elementar-
analyse Labor of the University of Essen.
868, 798, 657, 646, 631, 542, 524 472, 431 cm-1
.
Single-Crystal X-ray Analyses. The crystals were mounted in
inert oil on nylon loops. The data were collected on a Bruker D8
Kappa diffractometer with an APEX2 detector using mono-
chromated Mo KR radiation. Crystallographic data for 3, 4, and
5 are summarized in Table 1. Absorption corrections were
performed semiempirically from equivalent reflections on the
basis of multiscans (Bruker AXS APEX2). The structures were
solved by direct methods (Bruker AXS APEX2) and refined
anisotropically against F2 (G. M. Sheldrick SHELXL-9718). Hy-
drogen atoms were refined using a riding model or rigid methyl
groups. In 3 H(1) and H(2) were found in a difference Fourier
synthesis and refined freely. The high anisotropic displacement
parameter of C(51) in 4 indicates a slight disorder, which is too
weak to be refined as two alternative positions. In 5 H(31), H(33),
H(35), and H(37) were found and refined freely with fixed U.
The crystallographic data of the structures (excluding structure
factors) have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication nos. CCDC-790554 (3),
-790555 (4), and -790556 (5). Copies of the data can be obtained
free of charge on application to The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: int.code_(1223)336-033;
e-mail for inquiry: fileserv@ccdc.cam.ac.uk; e-mail for deposition:
deposit@ccdc.cam.ac.uk).
{C[C(Ni-Pr)2ZnH]4}, 3. A 0.4 g (0.4 mmol) amount of 2a and
0.04 g (0.9 mmol) of CaH2 were suspended in 15 mL of THF,
stirred for 3 days at 0 °C, and then filtered. The filtrate was
stored at -30 °C, yielding colorless crystals of 3 after 24 h. Yield:
0.31 g (91%). Melting point: 228 °C (dec). Anal. Found (calcd)
for C29H60N8Zn4 (782.48 g/mol): H, 7.06 (7.13); C, 44.44
(44.51); N, 14.21 (14.32). 1H NMR (300 MHz, C6D6, 25 °C): δ
1.24 (d, 24 H, 3JHH = 6.4 Hz, CH(CH3)2), 1.48 (d, 24 H, 3JHH
=
6.4 Hz, CH(CH3)2), 3.74 (sept, 4 H, 3JHH = 6.4 Hz, CH(CH3)2),
4.14 (sept, 4 H, 3JHH = 6.4 Hz, CH(CH3)2), 4.67 (s, 4 H, ZnH).
1H NMR (300 MHz, THF-D8, 25 °C): δ 1.22 (d, 24 H, 3JHH
=
6.4 Hz, CH(CH3)2), 1.41 (d, 24 H, 3JHH = 6.4 Hz, CH(CH3)2),
3.90 (sept, 4 H, 3JHH = 6.4 Hz, CH(CH3)2), 4.67 (s, 4 H, ZnH),
4.32 (sept, 4 H, 3JHH=6.4 Hz, CH(CH3)2). 13C NMR (200 MHz,
C6D6, 25 °C): δ 24.9 (CH3), 25.6 (CH3), 47.6 (CH), 48.9 (CH),
74.3 (C), 169.7 (NCN). ATR-IR: ν 2958, 2927, 2904, 2864, 1766
(Zn-H), 1560, 1520, 1449, 1386, 1362, 1255, 1079, 1013, 868,
791, 690, 660, 556, 495 cm-1
.
{C[C(Ni-Pr)2ZnCCPh]4}, 4. Method A: A solution of 0.25 g
(0.27 mmol) of 2a in 10 mL of THF was added to a suspension of
0.14 g (1.1 mmol) of NaCCPh in 15 mL of THF. The suspension
was stirred for 2 h at 25 °C and filtrated, and the filtrate was stored
at -30 °C. Colorless crystals of 4 were formed within 24 h. Yield:
0.22 g (68%). Method B: A solution of 0.4 g (1 mmol) of 3 and
0.5 mL (1 mmol) of phenylacetylene in 20 mL of THF was stirred
for 3 h at 60 °C, yielding a yellowish solution, which was stored
at -30 °C. Colorless crystals of 4 were formed within 24 h.
Acknowledgment. S.S. thanks the German Science
Foundation (DFG) for financial support.
Supporting Information Available: CIF file giving X-ray
crystallographic data of 3, 4, and 5. This material is available free
of charge via the Internet at http://pubs.acs.org.
(17) Jimenez, R.; Barral, M. C.; Moreno, V.; Santos, A. J. Organo-
met. Chem. 1979, 182, 353.
(18) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.