Organometallics 1986, 5 , 602-603
602
An Unexpected Carbon-Carbon Bond Formation in the Reactlon between Mo2(ONp),( p-NCNEt,) and MeCECMe
Malcolm H. Chlsholm, Kirsten Folting, John C. Huffman, and Nancy S. Marchant Department of Chemistry and Molecular Structure Center Indiana University, Bloomington, Indiana 4 7405 Received December 13, 1985
Summary: MO,(ON~)~(~-NCNE~,) (I) and M e C s M e react in hydrocarbon solution at room temperature and below to give Mo,(ON~)~(~-C,M~,)(NCNE~,)(I I) which at +60 OC reacts further to give a novel compound, Mo,(ONp),(p-C,Me,CH,C(NH)NEt,) (I I I), containing two connected five-membered rings bonded to the Mo, centers.
C(3G
Figure 1. A view of the Mo2(ONp)~(p-C4Me,)(NCNEt) molecule. Pertinent distance (A) are Mo-Mo = 2.639 (l), Mo(l)-0(3) = 1.959 (4), M0(1)-0(9) = 1.918 ( 5 ) ,M0(1)-0(22) = 2.073 (4), Mo(l)-N(15) = 2.168 (61, Mo(l)-C(29) = 2.158 ( 7 ) , Mo(l)-C(32) = 2.131 (6), M0(2)-0(22) = 2.150 (4), M0(2)-0(36) = 1.922 (5), M0(2)-0(42) = 2.015 (4), M0(2)-0(48) = 1.941 (4), M0(2)-C(29) = 2.295 ( 7 ) , Mo(2)-C(3@) = 2.432 (6), Mo(2)-C(31) = 2.407 ( 7 ) ,and Mo(2)C(32) = 2.369 (6).
Following the discovery that W2(OR)6(py)n(p-C2R'2) compounds and nitriles reacted under mild conditions to give W2-containing compounds with bridging ligands formed by the coupling of the p-C,R', and R"CN groups, e.g., W,(O-t-Bu),(p-CHCHCPhN) and W,(ONp),(p-N(CMe)4N),' we examined the reactivity of Mo2(ONp),(pNCNEt,) (I) toward alkynes. Compound I has a cyanamide unit which bridges parallel to the dimetal center,, and one would anticipate that similar C-C bond-forming reactions might result. Contrary to this expectation hydrocarbon solutions of I react with MeCGCMe a t ambient temperatures and below (ca. -30 "C)to give MO,(ON~)~(~-C~M~~)(NCNE~~) (11) in which the p-NCNEt, ligand becomes terminally bound (Figure l).3 Compound I1 is closely related to the previously characterized pyridine adduct Mo,(ONp),(pC4H4)py,4and addition of pyridine to I1 leads to the formation of M o ~ ( O N ~ ) ~ ( ~ - C ~ ~ ~ ) ( ~ on ~ )the . 11M is fluxional NMR time scale in toluene-d8 at room temperature. Upon raising the temperature to +60 "C, I1 reacts to give compound I11 which is stereochemically rigid and lacking any elements of symmetry (by NMR spectroscopy). Of particular note in the lH NMR spectrum of 111 was the presence of seven AB quartets of equal intensity and Figure 2. A view of the Mo,(ON )s(C4Me,CH2(NEtz)NH) only three Me signals derived from the p-C4Me4ligand of molecule. Pertinent bond distances are Mo-Mo = 2.711 ( 2 ) , 11. Reactions employing N13CNEt2 revealed that the M0(1)-0(18) = 1.938 (5), M0(1)-0(24) = 1.944 (5), MO (1)-0(3@) high-field AB quartet showed coupling to I3C, ,JC-H = 6.1 = 2.135 ( 5 ) , Mo(l)-N(3) = 2.167 ( 7 ) , Mo(l)-C(ll) = 2.335 (8), M0(l)-C(12) = 2.319 (8), Mo(l)-C(14) = 2.264 (8),Mo(l)-C(16) Hz, suggestive of C-C bond formation involving the
(1)
(1) Chisholm, M. H.; Hoffman, D. M.; Huffman, J. C. J . Am. Chem.
SOC. 1984,106, 6815.
= 2.299 (81, Mo(2)-0(3@)= 2.127 ( 5 ) , M0(2)-0(36) = 1.950 (5), M0(2)-0(42) = 1.890 (6), M0(2)-0(48) = 1.920 (6), M0(2)-C(12) = 2.118 (8), and Mo(2)-C(16) = 2.164 (8).
(2) MoZ(ONp),(EhNCN) was characterized spectroscopicly and found N13CNEt2carbon. A broad singlet at 6 5.07, together with to be structurally analogous to other M O ~ ( O R ) ~ R ' ~ Ncompounds. CN (a) Chisholm, M. H.; Kelly, R. L. Znorg. Chem. 1979,18,2321. (b) Chisholm, a band at 3358 cm-l in the infrared spectrum was also M. H.; Huffman, J. C.; Marchant, N. S. J. Am. Chem. SOC. 1983, 105, indicative of the formation of a CH,C(NH)NEt, unit. 6162. Coordination of the NH function to a Mo atom was (3) Summary of crystal data. (i) M O ~ ( O N ~ ) ~ ( ~ - C , M ~ ~at )(NCNE~ ~) -159 "C: a = 11.892 (5) A,b = 32.487 (18) A,c = 13.919 (6) A,0 = 111.38 anticipated but to which molybdenum atom was uncertain. (2)O, dcdcd= 1.21 g ~ m - and ~ , space group P2,/a. Of 7199 reflections Furthermore which methyl group of the k-C4Me4ligand collected (Mo Ka,6" < 28 < 45'), 6560 reflections were unique and the ( a or p) had reacted could not be ascertained. The mo4486 reflections having F > 30(F) were used in the full-matrix leastsquares refinement. Hydrogen atoms were refined by using fixed lecular structure of I11 was accordingly determined3 and idealized positions. Final residuals are R(F)= 0.049 and RJF) = 0.049. is shown in Figure 2. To our knowledge the two connected (ii) Moz(0Np),(C4Me3CHzC(NEtz)NH) a t -153 OC: a = 11.101 (4) A,b five-membered rings coordinated to the dimetal center is = 17.177 (9) A, c = 25.766 (14) A, dcalcd = 1.24 g ~ m - and ~ , space group P2,2,2,. Of the 3716 reflections collected (MoK a , 6' < 28 < 45'), 3631 without precedent. reflections were unique and 3200 reflections having F > 3dF) were used A possible reaction pathway leading to the formation in the full-matrix least-squares refinement. Hydrogen atoms were inof I11 may be based on the "tuck-in" chemistry established cluded in fixed calculated positions. Final residuals are RcF) = 0.042 and for (C,Me5)2ZrH, c h e m i ~ t r y .In ~ the present instance loss R J F ) = 0.043. (4) Chisholm, M. H.; Folting, K.; Huffman, J. C.; Rothwell, I. P. J . Am. of Et2NCN from I1 would lead to an unsaturated interChem. SOC. 1982,104, 4389. mediate which could undergo H abstraction from the (5).Bercaw, J. E. Adc. Chem. Ser. 1978,No. 167, 135 (Transition Metal C,Me4 ring. The cyanamide would then insert into either Hydrides, Bau, Ed.).
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B 1986 American Chemical Society
Organometallics 1986, 5, 603-604
the M-H bond or the "tucked-in" position of the C4Me4 ligand. Evidence in support of this mechanism is that (1) the cyanamide ligand in I1 is easily replaced by py and (2) that Moz(ONp),(p-C4Me4) (py) in the presence of EtzNCN will also form I11 at slightly higher temperatures. Further kinetic studies are in progress in order to gain a better understanding of this unusual reaction.6
603
synthetic applications of these organometallics reported to date result in mixtures of allenic and propargylic products (eq 1). Our recent discovery of a convenient new
RC=CCH2M
-
-
t
M
I
R~=C=CH~
( I )
X
I
Supplementary Material Available: Tables of fractional coordinates and isotropic thermal parameters, anisotropic thermal parameters, bond distances, bond angles, and structure factor amplitudes for compounds I and I1 (52 pages). Ordering information is given on any current masthead page.
RC=C=CHz
route to allenic and propargylic organomercurichalides (eq 2 and 3)l appeared to offer possible solutions to both of I
I
(6) We thank the Department of Energy, Office of Basic Sciences, Chemical Division for support of this work.
R C H C E C H f Hg
RCECCHJ Mercury in Organic Chemistry. 32. Bromination and Iodination of Allenic and Propargylic Organomercurials: A Convenient Synthesis of 3-Halo-l,2-aikadienes Richard C. Larock" and Mln-Shine Chow Department of Chemistry, Iowa State University Ames, Iowa 50011 Received November 12, 1985
Summary: The bromination (pyridinium hydrobromide perbromide) and iodination (iodine) of allenic and propargylic organomercuric halides in pyridine proceeds with rearrangement to afford the corresponding propargylic and allenic halides, respectively. This procedure provides a convenient, new route to 3-bromo- and 3-iodo-1,2-alkadienes useful in organic synthesis.
While there has been considerable recent interest in the application of allenic and propargylic organometallics in organic synthesis, two major problems in this area remain. Few of the organometallics so far studied accommodate many important functional groups, and the majority of the
RC?CCHzX
-
+ Hg
hv
RCH=C=CHHgI
(2)
RCECCHZHgI
(3)
hv
these problems, since these organometallics do not appear to equilibrate and their method of synthesis readily accommodates functionality. At this time we wish to report our preliminary results on the bromination and iodination of these organometallics. Our results to date are summarized in Table I. All halogenation reactions were carried out by using the following general procedure. The halogenating agent (0.5 mmol) dissolved in 5 mL of pyridine was added to a solution of the organomercurial (0.5 mmol) in 5 mL of pyridine at the appropriate temperature. After 5-min reaction time, methylene chloride was added and the organic layer was washed successively with 3 M NazSz03,water, 1 N HC1, and water. After the solution was dried over MgS04, the solvent was removed affording essentially pure organic halide. The purity and ratio of organic halides was established by 'H NMR spectroscopy. The structure of the products was confirmed by IR spectroscopy, high-resolution mass spectrometry, and comparison with literature data. The reaction of both the allenic and propargylic organomercurials with iodine proceeds readily at room temperature to -40 "C in pyridine to afford the corresponding rearranged propargylic or allenic iodides respectively. No more than minor amounts of the products of retention were observed. The use of solvents other than pyridine
Table I. Halogenation of Allenic and Propargylic Organomercurials
entry
organomercurial CH,
1
\
I
Hi
4 5
I
\
H HgI CH,C=CCH,HgI
6 7
C,H,C=CCH,HgI
8 9
C, H ,C&CH 2HgBr CH,O,C(CH,),C-CCH,HgI
10
< 2/98
I2
-40
CH,CHIC=CH
85
C,H,NHBr,
- 40
CH,CHXC=CH (X: B r / I = 93/7)
82
I2
- 40
CH,CHIC-CC,H,
95
I2 C,H,NHBr,
25 - 40
CH,CI=C=CH2 CH,CX=C=CH, (X: Br/I= 92/8) C,H,CI=C=CH, C,H,CX=C=CH, (X: Br/I = 99/1) C,H ,CBr= C= CH, CH, 0 2 C (CH, ),CI=C=CH , CH,O,C(CH,),CX=C=CH, (X: B r / I = 44/56)
77 71
-1OO/O
100 94
-1oo/o
0/100
C,H,
c=c=c
I
%
yield, product(s)
HgI
2 CH,,
reactn temp, "C
H
c=c=c \
3
halogenating agent
ratio of allenic to propargylic halide
C,H,NHBr,
25 25
C,H,NHBr, 1, C,H ,NHBr,
25 25 -40
I 2
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0 1986 American Chemical Society
94 97 82
< 2/98 98/2 92/8
99/1
1oo/o 1oo/o
