Organometallics 1995, 14, 1507-1509
1507
Notes ~~~~
~
~
Expansion of Three-Membered Rings by the Insertion of Methyl(methy1idene)borane MeB=C(SiMe& Ulli Englert, Rudi Finger, Peter Paetzold," and Burkhard Redenz-Stormanns Institut fur Anorganische Chemie, Technische Hochschule Aachen, 0-52056 Aachen, Germany
Zbigniew Pawelec and Wieslaw Wojnowski* Instytut Chemii i Technologii Nieorganiczej, Politechnika Gdahka, U1.G. Narutowicza 11, PL-80-952 Gdansk, Poland Received October 18, 1994@ Summary: The methyl(methy1idene)borane MeB=C(SiMedz (1) and dimethylsilylene react in a 2:l ratio to give the 1-sila-3,4-diboracyclopentane [-B(Me)-B(Me)C(SiMed2-Si(Me)z -C(SiMe&-l(2), which crystallizes in the triclinic space group PI, with lattice constants a = 16.648(5) A, b = 17.073(4) A, c = 11.490(3) A, a = 102.79(2)",,6 = 104.80(2)",y = 62.76(2)",and V = 2786(2) A3; Z = 4. It is assumed that 2 is formed via the cyclic 1:l adduct of 1 and SiMez, [-B(Me)-C(SiMedzSi(Me)z-l(3), the B-Si bond of which is subsequently added to the B-C double bond of a second molecule of 1. The azadiboriridine [-B(t-Bu)-B(t-Bu)-N(t-B~)-1(4) u'ndergoes a similar addition to 1 to give the 1 -aza-2,3,5triboracyclopentane [-B(Me)-C(SiMed2-B(t-Bu) -N(tBu)-B(t-Bu)-] (5). Silylenes SiRz are readily added to iminoboranes RBsNR". The primary reaction product, a threemembered ring with a -B-N-Si- skeleton, can be isolated in the case of the reaction of the bulky dimesitylsilylene and the iminoborane t-BuB=Nt-Bu.l In order to complete our investigations on the reactions of two-coordinate boron species with silylenes, we added SiMe2 to the methylideneborane MeB=C(SiMe& (1h2 The silylene SiMe2 was generated photolytically from its cyclohexamer SisMe12~'~ in pentane a t -60 "C in the presence of 1. A 77% yield of the crystalline 1:2 adduct 2 from SiMe2 and 1 was isolated. Three lH NMR signals in an intensity ratio of 6:l:l correspond to three l3C NMR signals, two of which are quartets, indicating SiMe groups, and the third of which may be identified as a BMe group by its typical large half-width. Apparently, two molecules of 1 remain equivalent in the product 2 in an equivalent way, and the two methyl groups of the SiMe2 moiety are incorporated as well. The llB NMR signal (94.8 ppm) is somewhat high-fieldshifted from the range which is typical for tetraalkyldiboranes(4), R2B-BR2 (103-106 ~ p m ) such ; ~ a shift could be caused by a-SiMes groups in the alkyl ligands of R2B-BR2. The NMR data of 2 are in accord with a siladiboracyclopentane structure, formed according to eq 1. The proposed structure of 2 is confirmed by an X-ray structural analysis. There are two symmetrically independent molecules 2a and 2b in the asymmetric unit of the triclinic cell. The structure of 2a is shown in @
Abstract published in Advance ACS Abstracts, February 1, 1995.
c21
c141
Figure 1. Molecular structure of 2a,showing 30% probability ellipsoids and the atomic numbering scheme, which is analogously valid for 2b. Me Me ,si, ,SiMe,
\I
Me,Si,
+
2 Me-B=C(SiMe,),
SiMe,
Me,Si-C
Me 1
C-SiMe,
\-€!
'
(1 1
'Me 2
Figure 1. Atomic coordinates and selected bond lengths and angles of 2a and 2b appear in Tables 1and 2. The differences between the molecular parameters of 2a and 2b turn out to be small. The central structural unit is a five-membered, nonplanar ring. The eight ring ligands are arranged in a way that allows optimal space for the four bulky SiMe3 groups. Bond lengths and angles do not deviate remarkably from well-documented standard values. The three bond angles at each of the B atoms sum up to 360°, thus providing planarly coordinated boron atoms. The C1 point group symmetry of 2a and 2b in the crystal is close to C2 point group symmetry, with the assumed C2 axis passing through Si1 and the center of the Bl-B2 bond. Real C2 point group symmetry may describe the structure of 2 in solution, leaving neighboring SiMes groups nonequivalent. The observed equivalence of all four SiMe3 groups, according to NMR data, can then be ascribed to a dynamic process that transforms the two enantiomers of 2 into each other. Actually, the SiMes groups give rise of a 13C NMR signal in THF-ds, the half-width of which is increased from less than 6 Hz a t room temperature t o
0276-733319512314-15Q7$Q9.OQlQ0 1995 American Chemical Society
1508 Organometallics, Vol. 14,No. 3, 1995
Notes Table 2. Selected Bond Lengths (A) and Bond and Torsional Angles (deg) for [-B(M~)B(M~)C(S~M~~)ZS~~ZC (Isomers ( S I M ~2d2b) ~)Z-]
Table 1. Atomic Coordinates ( x 104) and Equivalent Isotropic Displacement Parameters (A, x 103) for 2a and 2W atom Si1 Si2 Si3 Si4 Si5 B3 B4 c2 c5 C6 c7 C8 c9 c 21 c22 C23 C3 1 C32 c33 C41 C42 c43 C5 1 C52 c53
X
Y
Z
7619.4(8) 1727.8(7) 6267.3(8) 1822.5(9) 8226.7(8) 3077.3(9) 8850.9(8) 2491.7(9) 6739.4(9) 2322.1(9) 7031(3) 3277(3) 7711(3) 3463(3) 7223(3) 2455(3) 7802(3) 2524(3) 8674(3) 1293(3) 6793(3) 596(3) 6324(3) 3875(3) 8203(3) 4453(3) 6 lOO(3) 2469(4) 5117(3) 708(4) 6486(4) 1533(4) 8574(3) 3571(4) 9289(3) 2315(4) 7967(4) 4 107(4) 8905(3) 3141(4) 8949(3) 1284(3) 9955(3) 3028(4) 67 16(4) 206 l(4) 5605(3) 1368(4) 6674(4) 3374(4)
8148.4(7) 7619.4(7) 8364.3(9) 8903.9(8) 6835.2(8) 6885.1(8) 7169.3(8) 6248.4(8) 7806.7(8) 8 163.7(8) 6879(3) 7831(3) 6573(3) 71 14(3) 7586(3) 7856(3) 7383(3) 7223(3) 8304(3) 6801(3) 9330(3) 8590(3) 6483(3) 8367(3) 5570(3) 6423(3) 7839(4) 9010(3) 8829(4) 896l(4) 9331(3) 9964(3) 7568(3) 5776(3) 6127(3) 6818(4) 5994(3) 6936(4) 6552(4) 600l(4) 8219(3) 6438(3) 6462(3) 5175(3) 8670(3) 9268(3) 8286(4) 8351(3) 689l(3) 7930(4)
595(1) 4313(1) 2362(1) 2707(1) 2548(1) 2404(1) -1517(1) 6295(1) -2169( 1) 7133(1) 4435) 4580(5) -636(5) 5551(5) 1463(4) 3525(4) -911(4) 5806(4) 1439(4) 3368(5) 404(4) 4539(4) 360(5) 477 l(5) -1202(5) 6089(5) 3493(5) 1681(5) 1385(5) 1710(6) 3267(5) 3763(5) 3970(4) 2949(5) 1886(5) 918(5) 2974(5 ) 2100(5) -3091(4) 7871(5) - 1563(5) 6277(5) -606(5) 5342(5) -2951(5) 6694(5) -1648(5) 7878(5) 3365(5) 8346(5)
ue,
a Values of crystallographically different molecules 2a and 2b one below the other. Atoms refined using anisotropic dispacement parameters are given in the form of their equivalent isotropic parameters, defined as one-third of the trace of the orthogonalized U tensor. Numbers in parentheses here and in Table 2 are estimated standard deviations in the least significant digit.
50 Hz at -80 "C, thus indicating a slowing down of the fluctuation process with respect to the NMR time scale. The product 2 will certainly not be formed from three components by a one-step mechanism. The head-tail cyclodimerization of 1, well known to occur above ambient temperature,2 is not likely to be possible at -60 "C and would not give the B-B bond found in 2. We therefore assume the formation of a three-membered ring 3 in a first step, analogous t o the cited reaction of (1)Paetzold, P.; Hahnfeld, D.; Englert, U.; Wojnoswki, W.; Dreczewski, B.; Pawelec, 2.; Walz, L. Chem. Ber. 1992, 125, 1073. (2) Boese, R.; Paetzold, P.; Tapper, A.; Ziembinski, R. Chem. Ber. 1989,122, 1057. (3)Ishikawa, M.;Kumuda, M. J. Organomet. Chem. 1972,42,325. (4)Fink, M. J.;Michalczyk, M. J.; Haller, K. J.; West, R.; Michl, J. Organometallics 1984,3, 793. (5) NBth, H.; Pommerening, H. Chem. Ber. 1981, 114, 3044.
B3-B4 B3-C2 B4-C5 C2-Si1 C5-Si1 B3-C3 B4-C4
1.729(8)/1.709(9) 1.570(6)/1.566(6) 1.563(8)/1.582(8) 1.922(6)/1.913(6) 1.923(4)/1.921(4) 1.578(9)/1.566(6) 1.588(6)/1.582(8)
C2-B3-B4 C5-B4-B3 B3-C2-Sil B4-C5-Sil C2-Sil-C5 B4-B3-C8
C2-Si2 C2-Si3 C5-Si5 C5-Si4 Si1-C5 Si1-C6
110.3(5)/110.4(5) 111.8(3)/111.1(5) 101.7(3)/101.2(3) 101.2(3)/100.3(3) 103.4(2)/103.7(2) 122.6(4)/122.7(4)
1.913(4)/1.911(4) 1.916(4)/1.918(4) 1.930(4)/1.924(4) 1.896(5)/1.879(5) 1.880(5)/1.874(5) 1.874(4)/1.888(4)
C2-B3-C8 B3-B4-C9 C5-B4-C9 Si2-C2-Si3 Si4-C5-Si5 C6-Sil-C7
C2-B3-B4-C5 Sil-C2-B3-B4 Sil-C5-B4-B3 C8-B3-B4-C9 B3-C2-Sil-C5 B4-C5-Sil-C2
127.1(5)/126.9(5) 121.8(5)/123.4(5) 126.3(5)/125.5(5) 108.0(2)/108.1(2) 108.3(2)/108.3(2) 100.1(2)/99.3(2)
-39.1 1(52)/-42.02(49) 27.52(39)/29.57(40) 26.75(44)/28.74(38) -42.25(68)/-43.43(66) -1 1.42(33)/-11.83(30) -9.62(34)/- 10.49(20)
t-BuBENt-Bu and SiMesz. The product 2 is then formed by the addition of a second molecule of 1 t o the B-Si bond of 3,eq 2. The formation of a B-B bond during a kind of redox process is made possible by the higher electronegativity of boron as compared to that of silicon. This second step is related to the opening of the B-B bond of the three-membered ring 4 by the B-N triple bond of EtB=Nt-Bu,6 eq 3. Me$ 1
-
SiMe,
t
SiMe,
\I
tl
/"\
,~-si-Me Me
2
(2)
M 'e 3 tB u
I
fBu
I B , -8
mu
\;/
t
EtBBNfBu
'mu
Q
-
N
tBu.B//
\B.fBu
\ Et
I
(3)
/B=N\rBu
The assumed addition of 1 to 3 and the known addition of an iminoborane to 4 prompted us to try the addition of 1 to 4. The 1:l adduct 5 is isolated in a 81% yield as described in eq 4, and its structure is concluded from NMR spectra, which indicate three different B atoms, three nonequivalent t-Bu groups, but two equivalent SiMe3 groups. It should be noted that the 3-methyl
N
f BBu . Q
+
1
\
-
Me
tBu
I
/'-C\\S
(4)
i Me,
SiMe,
5
derivative 5 cannot be distinguished by our NMR data from an isomeric 5-methyl derivative 5', which would be the product of the addition of 1 to one of the B-N bonds of 4. The addition of EtCWEt,6 C0,7 BuNQ,~ (6)Paetzold, P.; Redenz-Stormanns, B.; Boese, R. Chem. Ber. 1991,
124., 2435. ~~
~
(7) Paetzold, P.; Redenz-Stormanns, B.; Boese, R. Angew. Chem., Znt. Ed. Engl. 1990,29, 900. (8) Paetzold, P.; Redenz-Stromanns, B.; Boese, R.; Btihl, M.; Schleyer, P. v. R. Angew. Chem., Znt. Ed. Engl. 1990,29, 1059.
Notes
Organometallics, Vol. 14, No. 3, 1995 1509 Table 3. Crystallographic Data for 2 formula fw space group a, A b, 8, C,
A
a, deg
A deg
Y deg 9
v,A3
ecalc, dcm3
2 F(O@-J) 2, A ~ ( C Ka), U cm-I cryst dimens, mm T, K scan mode scan range, deg total data unique obs dat ( I > 3u(I)) no. of variables R, R , [ w - I = u(F,)*] max resid dens, e A-3
C18H48BzSi5 426.6 P1 (No. 2) 16.648(5) 17.073(4) 11.490(3) 102.79(2) 104.80(2) 62.76(2) 2786(2) 1.017 4 944 1.5418 24.20 0.6 x 0.3 x 0.3 233 omega 5
