Organometallics 1995, 14, 2754-2759
2754
Synthesis, Structure, and Fluxional Behavior of a Dihydrosilane Bearing an Aryldiamine Pincer Ligand Francis Carre, Claude Chuit, Robert J. P. Corriu," Ahmad Mehdi, and Catherine Reye Laboratoire "Hitirochimie et Aminoacides" CNRS, URA 1097, Universiti Montpellier II, Sciences et Techniques d u Languedoc, Place E. Bataillon, 34095 Montpellier Cedex 5,France Received February 2, 1995@ 1,4-Bis({2,6-bis[(dimethylamino)methyllphenyl}d~ydrosilyl~benzene (1)was prepared by treatment of the 1,4-bis(trihydrosilyl)benzene with 2 mol equiv of { 2,6-bis[(dimethylamino)methyl1phenyl)lithium. The X-ray crystal structure of 1 shows the hexacoordination of the silicon atom, with a geometry corresponding to a bicapped tetrahedron. Furthermore, the two chelating amino groups are in cis disposition to each other. Dynamic solution NMR studies have been carried out. Of the two interpretations considered, only one is consistent with the solid state structure. Table 1. Summary of Crystal Data, Intensity Measurements, and Refinement
Introduction
Molecular structures of dihydrosilanes in which penformula cryst syst tacoordination is achieved by intramolecular ring clospace group sure of a chelating group are kn0wn.l In all of these a, A structures the geometry around the silicon atom is that b, A c, A of a somewhat distorted trigonal bipyramid in which the A deg donor atom occupies an axial site and the hydrogen v, A3 atoms the equatorial sites. When two chelating ligands mol wt z are coordinated to the silicon center, a [4 21 type coordination is observed around the silicon a t ~ m . ~ , ~ dealed, g cm-3 dmeasd, g ~ m - ~ Interestingly, the geometry of these compound^^,^ is not cryst size, mm3 cryst color octahedral but corresponds to a bicapped tetrahedron, recryst solvent the two nitrogen atoms being cis to each other. Another mp, "C possibility of bis chelation on a silicon center could method of data collectn originate from using the aryldiamine pincer ligand A radiation (graphite-monochromated)
+
fNMe2
p , cm-' 28 limits, deg no. of unique reflns no. of obsd reflns final no. of variables
R RW residual electron density
A
introduced by van K ~ t e n .To ~ illustrate this purpose, we have prepared the bis(dihydrosily1)benzene 1 with two identical silicon centers, from which crystals available for an X-ray structure analysis have been obtained. we report in this paper the synthesis, structural characterization, and dynamic NMR behavior of this compound. @Abstractpublished in Advance ACS Abstracts, May 1, 1995. (1)(a) Blake, A. J.; Ebsworth, E. A. V.; Welch, A. J. Acta. Cystallogr., Sect. C 1984,40,895. (b) BreliBre, C.; Carre, F.; Corriu, R. J. P.; Poirier, M.; Royo, G. Organometallics 1986,5,388. ( c ) Boyer, J.; Breliere, C.; Carre, F.; Corriu, R. J. P.; Kpoton, A,; Poirier, M.; Royo, G.; Young, J . C. J . Chem. Sac., Dalton Trans. 1989,43. (2) Breliere, C.; Carre, F.; Corriu, R. J. P.; Poirier, M.; Royo, G.; Zwecker, J. Organometallics 1989,8 , 1831. (3)Carre, F.;Cerveau, G.; Chuit, C.; Corriu, R. J. P.; Reye, C. New J . Chem. 1992,16,63. (4) van Koten, G. Pure Appl. Chem. 1989,61,1681; 1990,62,1155. Jastrzebski, J. T.B. H.; van Koten, G. Adv. Organomet. Chem. 1993, 35,241.
a
C3oH46N4Siz monoclinic P21lc 9.655(2) 12.630(2) 12.550(3) 99.29(2) 1510.2" 518.9 2 1.141Q 1.10(2)b 0.24 x 0.35 x 0.70 colorless CHzClz 131-33 WIB
Mo Ka 1.366 4-48 2258 1726 95 0.038 0.045 0.25
Measured a t -100 "C. Measured a t 27 "C.
Results and Discussion Synthesis and Solid State Structure of 1. Reduction of 1,4-bis(trimethoxysilyl)benzene5by LNH4 results in the formation of the corresponding 1,4-bis(trihydrosily1)benzene 2. The 1:2 molar reaction of 2 with (2,6-bis[(dimethyla~no)methyllphenyl)lithium affords 1 in 60% yield (see Scheme 1). Translucent crystals were grown from a CHzCl2 solution cooled to -10 "C. The ORTEP drawing is displayed in Figure 1, and selected bond distances and angles are listed in Table 3. Figure 1 showed that the molecule is centrosymmetric. On each silicon atom the lone pairs of both NMe2 groups were directed toward the silicon center, but the bis chelation is not symmetrical, the N(2)Mez group being opposite to the SiH(2) bonds [N(2)-Si-H(2) = 169.4'3 while the N(1)Mez group is (5) Corriu, R. J. P.; Moreau, J. J. E.; Thepot, P.; Wong Chi Man, M. Chem. Mater. 1992, 4 , 1217.
0276-733319512314-2754$09.0010 0 1995 American Chemical Society
A Dihydrosilane Bearing a n Aryldiamine Ligand
Organometallics, Vol. 14,No.6,1995 2755
Figure 1. ORTEP drawing of the molecular structure of silicate 1 showing the numbering scheme. The thermal ellipsoids and spheres are at the 30% probability level. Scheme 1
2
Me2
H
1
Table 2. Fractional Atomic Coordinates ( x lo4) atom
Si
c11 c12 C13 C14 C15 C16 C17 N1 Me1 Me2 C18 N2 Me3 Me4 c21 c22 C26 H1 H2
xla
vlb
zlc
3106.3(6) 3098(2) 1978(2) 1968(2) 3070(2) 4214(2) 4234(2) 5514(2) 5809(2) 6768(2) 6344(3) 786(2) 1296(2) 2140(3) 106(2) 1308(2) 775(2) 492(2) 3620(18) 3762(18)
41.5(4) 833(1) 827(1) 1511(2) 2213(2) 2191(2) 1508(2) 1463(2) 369(1) 305(2) -239(2) 40(2) -1016(1) - 1448(2) - 1714(2) 6(1) -916(1) 918(1) -1025(16) 684(15)
1567.1(4) 2839(2) 3435(1) 4290(2) 4594(2) 4062(2) 3199(2) 2646(2) 2397(1) 1608(2) 3364(2) 3183(2) 2993(2) 3966(2) 2616(2) 722(2) 185(2) 512(2) 1715(15) ,862(15)
trans to the Si-C(21) bond [N(l)-Si-C(21) angle = 166.8'1. Furthermore, the Si N(2) distance (3.008 A) is 12% longer than the Si ...N(l) bond (2.681 A),both distances being below the sum of the van der Waals radii (3.5 AI6 of silicon and nitrogen atoms. The same observation has been previously made for compound 3,2
-
Table 3. Interatomic Distances (A)and Main Bond Angles (deg) Si-C11 Si-C21 Si-H1 Si-H2 Si. * *N1 Si- .N2 Nl-Cl7 N1-Me1 N1-Me2 N2-Cl8 N2-Me3 N2-Me4 C11-Si-C21 C11-Si-H1 C11-Si-H2 C21-Si-H1 C21-Si-H2 H1-Si-H2 Nl..-Si-C21 N2- .Si-H2 N1. .Si* *N2 Si-C11-C12 Si-C11-Cl6 C12-Cll-Cl6
-
1.884(2) 1.883(2) 1.44(2) 1.42(2) 2.681(2) 3.008(2) 1.456(3) 1.464(3) 1.459(3) 1.455(3) 1.460(3) 1.465(3) 111.1(1) 115.9(7) 106.7(8) 108.5(7) 97.2(7) 116(1) 166.8(1) 169.4(7) 117.4(1) 123.7(1) 119.0(1) 117.2(2)
Cll-c12 C12-Cl3 C13-Cl4 C14-Cl5 C15-Cl6 C16-Cll C12-Cl8 C16-Cl7 c21-c22 C21-C26 C26-C22 Cll-Cl2-Cl8 C13-Cl2-Cl8 Cll-Cl6-Cl7 C15-Cl6-Cl7 C16-Cl7-Nl C12-C18-N2 C17-Nl- .Si C18-N2..*Si Si-C21-C22 Si-C21-C26 C22-C21-C26
-
1.411(3) 1.379(3) 1.390(3) 1.380(3) 1.388(3) 1.405(3) 1.514(3) 1.512(3) 1.401(3) 1.397(3) 1.384(3) 120.9(2) 118.3(2) 118.9(2) 119.8(2) 109.7(2) 111.7(2) 91.0(1) 86.3(1) 121.7(1) 121.8(1) 116.2(2)
in which the Si N distance opposite to the Si-H bond is also longer (2.80 A) than that trans to the Si-C bond (2.61 A), in spite of the rigidity of the 8-(dimethylamino)-
2756 Organometallics, Vol. 14, No. 6, 1995
Carre et al.
296 K
173 K
3
naphthyl group. Furthermore, it is noteworthy that the tetrahedral geometry of the silicon atom is maintained (Table 3). Two faces of the tetrahedron are capped by 21 two NMez groups so that compound 1 is [4 coordinated. Another interesting aspect of this structure is the cis disposition of the two nitrogen donor atoms of the ligand [the N(l)-Si-N(2) angle being 117.4'1. This situation was previously observed for the [4 41 coordinate silicon compound 4,7 in which the
+
163 K
T
CH,N
SiH
I
7
~ , ' " ' , " " , , ' " , ' ' " , " " ~ " " ~ ' " 5.0 4.0 3.0 2.0
PPM
Figure 2. lH NMR spectra (250 MHz) of 1from CD2Cld Freon.
+
($$ij-J
Me2 Me2
N N Me2 Me2 4
N(l)-Si-N(B) angle is 116.7". It is noteworthy that in most octahedral organometallic complexes of the late transition metals the ligand A adopts meridional coordination with N-M-N angles of typically 161-163°,8 with the exception of the tantalum compound 6,9in
@YfC1
~
"
'
4.5
I
"
"
I
4.0
"
"
/
"
"
I
"
3.0
3.5
'
'
I
"
2.5
~
2.0
PPM
Figure 3. 'H NMR spectrum (360 MHz) of 1 at 180 K from CD2C12.
Ta = "'C1CH'Bu
Me2 5
which the N(l)-Ta-N(2) angle is 118.63 (1)'. NMR Spectroscopy of 1 in Solution and in the Solid State. The 29SiNMR chemical shift of 1 is -51.3 ppm in solution and -49.6 ppm in the solid state. Since these resonances are upfield of those for PhzSiHzlO (6 -33.8 ppm) and for the pentacoordinated silicon compound 6lC(6 -47.25 ppm), it can be concluded that the silicon atom is at least pentacoordinated. Furthermore the 29SiNMR shift of 1 is not temperature-dependent throughout the temperature range studied (293-173 K (6) Bondi, A. J . Phys. Chem. 1964, 68, 441.
(7) Carre, F.; Chuit, C.; Corriu, R. J . P.; Mehdi, A.; Rey6, C. Angew. Chem. 1994,106, 1152;Angew. Chem., Int. Ed. Engl. 1994,33, 1097. ( 8 )Abbenhuis, H. C. L.; Feiken, N.; Grove, D. M.; Jastrzebski, J . T. B. H.; Kooijman, H.; van der Slius, P.; Smeets, W. J. J.; Speck, A. L.; van Koten, G. J . A m . Chem. SOC.1992, 114, 9773. (9) (a)Therheijden, J.; van Koten, G.; De Booys, J. L.; Ubbels, H. J . C.; Stam, C. H. Organometallics 1983,2, 1882. (b) Grove, D. M.; van Koten, G.; Mul, W. P.; van der Zeijden, A. A. H.; Terheijden, J . Organometallics 1986,5,322. ( c ) van der Zeijden, A. A. H.; van Koten, G.; Luijk, R.; Vrieze, K.; Slob, C.; Krabbendam, H.; Speck, A. L. Inorg. Chem. 1988,27, 1014. (10)Kintzinger, J. P.; Marsmann, H. In NMR Basic Principles and Progress; Diehl, P., Fluck, E., Kosfeld, R., Eds.; Springer-Verlag: New York, 1981.
aNP 6
from CDzC12). The lH NMR spectrum of 1 in solution (250 MHz, CDCM displays at room temperature a single resonance for all the methyl groups and a single resonance for all the methylene protons. A singlet is also observed for the SiH2 protons. Lowering the temperature of the NMR sample resulted in broadening and decoalescence of the NMez and methylene signals (Figure 2). At 180 K (360 MHz, CDzC12) the lH NMR spectrum of 1 exhibited two single resonances for the dimethylamino groups and an AX pattern for the benzylic protons (Figure 31, the SiH2 protons being a singlet. We assume that the 'H NMR spectrum of 1 at 180 K indicates the hexacoordination of the silicon atom. Indeed, if only one NMez group were coordinated at the silicon atom (on the NMR time scale), we would observe two singlets for the benzylic protons and two singlets for the methyl groups (if we consider that the two SiH bonds are in equatorial positions as is always observed1). Hexacoordination of the silicon atom has also been revealed by the X-ray structure analysis of 1. Nevertheless, the lH NMR spectrum of 1 at 180 K cannot be explained by the static arrangement (on the NMR time scale) around the Si atom found in the solid
A Dihydrosilane Bearing a n Aryldiamine Ligand
Organometallics, Vol. 14,No. 6,1995 2757 Scheme 2 Hh
/ \
Ph
Scheme 3
la
lb
IC
state. Indeed, with such a dissymetric geometry a t silicon, the lH NMR spectrum should display four signals for the two NMe2 units, two AB (or AX) systems for the benzylic protons, and one AB system for the SiHz protons, which is not the case. To explain the lH NMR spectrum of 1,we propose two interpretations. The first is that in solution the molecule adopts the same dissymmetric geometry as in the solid state, but at this temperature it undergoes a nondissociative limited isomerization process such as a Bailar twist (Scheme 2) with a AG* too weak to be measured under the experimental conditions employed (360 MHz). This limited process would explain the presence of an AI3 system for the benzylic protons instead of the two expected in the fured geometry. The second interpretation that can be put forward is that the molecule adopts
in solution a geometry in which the two CHzNMe2 units are magnetically equivalent, this being a situation different from that found in the solid state. We have represented in Scheme 3 the three possible arrangements of this type. The low-temperature 'H NMR spectrum of 1 is not consistent with the molecular geometry la,in which all the benzylic protons and all the methyl groups are equivalent. The geometry ICin which the SiH2 protons are different can also be ruled out. The 'H NMR data of 1 can only be explained by the geometry lb,the two CHzNMez units being equivalent as is also the case for the SiHz protons. In each CH2NMez unit, the benzylic protons are different as are the Me groups, which is consistent with the low-temperature NMR spectrum of 1. When the temperature is
Carre et al.
2758 Organometallics, Vol. 14, No. 6, 1995
Me
II
S iH
Me
TT
I CHZN
I
I
1
1
1
1
Me
CH2N
4.5 4.0 3.5 3.0 2.5 2.0 PPM Figure 4. lH NMR spectrum (360 MHz) of 1at 250 K from CD2C12. raised, t h e resonances of t h e NMe2 groups and of the methylene protons coalesce at different rates. The coalescence of NMe2 groups is shown i n Figure 2 (173 K, 250 MHz), and that of methylene protons is shown in Figure 4 (250 K, 360 MHz). This indicates that t h e respective protons become isochronous as a result of two different processes: t h e magnetic equivalence of Me groups at room temperature is interpreted i n terms of a dynamic coordination process involving t h e two NMe2 units whereby fast exchange (on the NMR time scale) of one unit by t h e other occurs. The AG* for this process (173 K, 250 MHz) was estimated to be 35 kJ mol-l from t h e coalescence temperature of t h e methyl protons. To explain t h e equivalence of t h e benzylic protons at room temperature, we have to assume that, during this dissociative process, there is concomitant rotation of t h e chelating ligand around t h e Si-C bond. A similar explanation has been proposed by v a n Koten e t al. to explain t h e lH NMR behavior of compound 7.l' An estimation of t h e AG* of this second process was calculated from the coalescence temperature (250 K, 360 MHz) for t h e benzylic protons (AG* = 48 kJ mold1).
Br
L 7
The 13C NMR spectrum of 1 at room temperature shows i n solution (Figure 5a) a single resonance for t h e benzylic carbons and a single resonance for t h e methyl groups. These are consistent with t h e 'H NMR spect r u m of 1 at the same temperature. The solid state 13C NMR spectrum shows two resonances for the benzylic carbons (Figure 5b) and a broad resonance for the methyl groups. If we consider that the broad signal corresponds to the juxtaposition of several signals, this spectrum is consistent with t h e solid state structure for which four Me signals and two benzyl signals a r e expected. In conclusion, the hexacoordination of the silicon atom has been shown for compound 1 both in t h e solid state as well as in solution. Two hypotheses have been p u t (11)van Koten, G.; Jastrzebski, J. T. B. H.; Noltes, J. G.; Speck, A. L.; Schoone, J. C. J . Organomet. Chem. 1978,148, 233.
u1
1
70
60
(a>
1
1
50 40 PPM
70
60
50
40 PPM
(b)
Figure 5. I3C NMR spectra of 1in solution (a) and in the solid state (b). forward to explain t h e low temperature NMR spectra. One supposes that t h e geometry of 1 in solution is different from that in t h e solid state, but this is not consistent with t h e concept of Dunitz e t al.13 The other explanation, which is consistent with t h e latter concept, supposes that t h e geometry i n solution is t h e same as i n t h e solid state and t h a t t h e compound undergoes at this temperature an easy, nondissociative limited isomerization process.
Experimental Section All of the reactions were performed under a dry argon atmosphere using standard Schlenk techniques. 'H, I3C, and 29SiNMR spectra were obtained using Bruker WP-2OO-SY, Bruker 250 AC, or Bruker WM-360-WB spectrometers. Solid state NMR spectra were recorded on a Bruker AM-300 spectrometer. 'H, I3C, and 29Sichemical shifts were reported relative to Me4Si. Elementary analysis were performed by the Centre de Microanalyse du CNRS. 1,4-Bis(trihydrosilyl)benzene(2). A 7.15 g amount (2.25 x mol) of 1,4-bis(trimethoxysi1yl)ben~ene~ in 30 mL of EtzOwas added dropwise at room temperature t o a suspension of 2.56 g (6.74 x mol) of LiA1H4 in 80 mL of Et2O. The mixture was stirred at room temperature overnight. Ether and the reaction product were removed under vacuum and trapped in liquid nitrogen. After distillation of ether at atmospheric pressure, 2.16 g of a colorless oil was obtained (68%yield). Caution! The 1,4-bis(trihydrosilyl)benzenewas not distilled i n order to avoid a possible explosion. 'H NMR (6 in cc4):4.18 (s, 6H, SiHd, 7.55 (s, 4H, Ar). 29SiNMR (CDC13): -61.5. 1,4-Bis({2,6-bis[ (dimethylamino)methyI]phenyl}dihydrosily1)benzene(1). A 30.5 mmol amount of the {2,6bis[(dimethylamino)methyllphenyl)lithium derivative in 50 mL of Et20 was added dropwise at 0 "C t o 2.1 g (15.2 mmol) of 1,4-bis(trihydrosilyl)benzenein 50 mL of EtzO. The reaction mixture was stirred at room temperature overnight. Then 0.27 mL of HzO was added to hydrolyze LiH; after removal of the solvent, the residue was taken up again in 25 mL of CH2C12. The precipitate of LiOH was filtered through Celite, and then the solvent was removed under vacuum to give 4.7 g (9.12 mmol, 60% yield) of 1 as transparent crystals: mp 131-133 "C. 29SiNMR: (39.76 MHz, CDC13, 25 "C) -51.4 (t, ' J ( s ~ ,= H) 194 Hz); (59.63 MHz, solid state, {H}) -49.6 (s); (49.69 MHz, , H194 ) Hz). 'H CD2C12, Freon, -110 "C) -52.3 (t, ' J < S ~= NMR: (360 MHz, CDzC12, 25 "C) 2.24 (s, 24H, NCHs), 3.48 (s, 8H, CH2N), 4.60 (s, 4H, SiHd, 7.04-7.27 (2m, 6H, Ar), 7.57 (12) Boyer, J.;Corriu, R. J. P.; Kpoton, A,; Mazhar, M.; Poirier, M.; Royo, G. J . Organomet. Chem. 1986,301, 131. (13) Britton, D.;Dunitz, J. D. J . Am. Chem. SOC.1981,103, 2971.
A Dihydrosilane Bearing an Aryldiamine Ligand (s,4H, Ar); (360 MHz, CD2C12, -93 "C) 1.99 (9, 12H, NCHs), 2.34 (s, 12H, NCH3), 2.90 (d, 4H, 2 J ( ~=, ~12.9 ) Hz, CHzN), 3.89 (d, 4H, 2 J ( = ~ 12.9 , ~ ,Hz, CH2N), 4.55 (9, 4H, SiHd, 7.11 (d, 4H, 3 J ( = ~ 6.8 , ~Hz, , Ar), 7.24 (t, 2H, 3 J ( ~=, 6.8 ~ ) Hz, h), 7.57 (s, 4H, Ar). NMR: (62.90 MHz, CDC13, {H}) 43.95 (NCHs), 64.13 (CHzN), 127.27, 128.80,132.50, 132.65, 135.87, 147.88 (Ar);(75.47 MHz, solid state, {H}) 45.65 (broad signal, NCHs), 64.53, 66.21 (CHzN), 126.85, 128.25, 129.94, 132.80, 133.73, 141.22, 143.04, 144.87, 147.64, 149.21 (Ar). IR(KBr): 2114.1, 2156.6 (SiH). MS (IE, 70 eV): mlz = 517 (MI+, 37); 501 ((M - Me 2H)+, 72); 58 ((CH2=NMe2)+, 100). Anal. Calcd for C30H46N4Si2: C, 69.49; H, 8.88;N, 10.81. Found: C, 69.49; H, 8.88; N, 10.73. Crystal Structure of Compound 1. Crystal Preparation. Crystals of compound 1 were grown by slowly cooling to -10 "C a dichloromethane solution in a nitrogen atmosphere. Colorless elongated prisms were obtained. A small block of dimensions 0.24 x 0.40 x 0.60 mm3was sealed inside a capillary and mounted on a Nonius CAD 4 automated diffractometer at 173 K. X-rayData Collection. Data were collected with graphitemonochromated Mo K a radiation (A = 0.710 69 A). Lattice constants (Table 1)come from a least-squares refinement of 21 reflections obtained in the range 27 < 28 < 72. The intensities of three standard reflections were monitored at intervals of 60 min; no significant change in these intensities occurred during data collection. The systematic absences were uniquely defining the space group P ~ ~ Iwith c , z = 2. The structure amplitudes were obtained after the usual Lorentz and polarization reduction. Only the reflections having dm/F < 0.23 were considered to be observed. The absorption corrections were neglected. Structure Determinationand Refinement. Direct meth-
+
Organometallics, Vol. 14,No. 6, 1995 2759 ods (SHELXS-86 program14)succeeded in locating the whole set of non-hydrogen atoms through a single calculation. After four cycles of least-squares refinement with isotropic thermal parameters for all atoms, the hydrogen atoms were positioned by calculation (SHELX-76 program15). The hydrogen atoms on silicon were located in a difference Fourier synthesis and refined with isotropic thermal parameters, while all nonhydrogen atoms were refined anisotropically. Since convergence was difficult to obtain, the thermal parameters of the carbon atoms were kept fixed in the last stages of the refinement. Refinement converged t o the final R value of 0.038. The final atomic coordinates are listed in Table 2. The labeling scheme is given in Figure 1;a stereoview is provided with Figure 2. Individual bond lengths and main bond angles are listed in Table 3. Full lists of the bond angles (Table 41, the anisotropic thermal parameters (Table 5), and the calculated hydrogen atom coordinates (Table 6) are available as supplementary material.
Supplementary Material Available: A full list of the bond angles for compound 1 (Table 41, along with a list of anisotropic parameters for all non-hydrogen atoms (Table 5), and a list of calculated hydrogen atom coordinates (Table 6) (3 pages). Ordering information is given on any current masthead page. OM9500861 (14)Sheldrick, G. M. SHELXS-86, A Program for Cystal Structure Solution; Institiit fur Anorganische Chemie der Universitlt: Gottingen, Germany, 1986. (15) Sheldrick, G. M. SHELX-76, A Program for Crystal Structure Determination; University of Cambridge: Cambridge, England, 1976.
