1759
Communications to the Editor (IO) A. (1 1) (12) (13) (14)
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J. Kirby and R. J. Martin, J. Chem. Soc., Chem. Commun., 803 (1978). W. J. Hehre, W. A. Lathan, R. Ditchfield, M. D. Newton, and H. A. Pople, Quantum Chemistry Exchange Program, No. 236. S . David, 0. Eisenstein, W. J. Hehre, L. Salem, and R. Hoffman, J. Am. Chem. Soc., 95, 3806 (1973), and references cited therein. (a)E. A. C. Lucken, J. Chem. Soc., 2954(1959). (b)C. Romers, C. Altona. H. R. Buys, and E. Havinga, Top. Stereochem., 4, 39 (1969). The amidophosphorane intermediate 3a is only 2.4-kcai/mol higher energy than 3b and 1.67-kcal/mol higher energy than 3b'. Fellow of the Alfred P. Sloan Foundation, 1975-1979.
David G . Gorenstein,*'5 Bruce A. Luxon, Evelyn M. Goldfield Department of Chemistry University of Illinois at Chicago Circle Chicago, Illinois 60680 Received October 15, 1979
Table 1. Yield of N-tert-Butylaniline and Biphenyl from Reaction of 1 mmol of (Me3Si0)2Cr(NrBu)2 with Diphenylzinc
PhzZn, mmol temp, O 2.0 2.0 2.0 2.0 2.0 1 .o
2.0
80 25 80 80 -78 80 80
C
addition" normal normal inverse normal inverse normal normal
additive
PhNHrBub Ph-Phc
pyridined Moe
0.704 0.334 0.258 0.174 0.038 0.699 0.015
0.293 0.377 0.638 0.660 0.687 0.096 0.352
I n normal addition the PhzZn in 10 mL of toluene was added to the Cr complex in I O mL of toluene. Yield of N-terr-butylaniline i n millimole (by GLC). Yield of biphenyl in millimole (by GLC). The Cr complex was dissolved in 9 mL of toluene and 1 m L of pyridine. e Compound Ib was Substituted for the Cr complex.
Reaction of Group 6 Organoimido Complexes with Organozinc. Reductive Elimination across a Metal-Nitrogen Multiple Bond Sir:
Sharpless and co-workers have suggested that the addition of bis(alky1imido)osmium complexes to olefins proceeds via migration of a n organic ligand to a n electron deficient imido nitrogen atom.' T h e industrially important ammoxidation of propylene to acrylonitrile may similarly involve transfer of an allyl moiety to " ' M F N H . ~ Unfortunately appropriate model compounds for studying this type of process3 have not been available: no complex containing both imido and hydrocarbyl ligands [nor any organomolybdenum(V1) species whatsoever] has been reported. W e now report that such complexes have been prepared and present preliminary evidence that the proposed rearrangements d o occur. Treatment of ( 'BuN)2W(OtBu)2 or ('BuN)2Mo(OSiMe3)z4 with dimethylzinc in hexane, followed by cooling to -40 O C in the latter case,5 follows eq 1. Red-orange crystals of Ia (60%) or violet crystals of Ib (52% after recrystallization) were collected by filtration.6 T h e color of solutions of compounds 1 discharged to pale yellow upon addition of potential donor ligands (PMe3, pyridine, AIMe3, Or) with a concomitant upfield shift of the methyl N M R resonances.'
-
2 ( ' B u N ) ? M ( O R ) 2 + 4Me2Zn [('BuN)?M(CH3)2]2
+ 4MeZnOR
(1)
la, M = W b, M = M o T h e X-ray crystal s t r ~ c t u r e of * ~Ib ~ (Figure 1) shows it to contain the first examplei0 of a n unsymmetrically bridging imido ligand. The dimer is situated on a crystallographic center of symmetry and each molybdenum exhibits distorted trigonal bipyramidal coordination. The three Mo-N bond lengths i n Ib [Mo-N ( I ) = 1.730(2), Mo-N ( 2 ) = 1.819 (2), Mo'-N(2) = 2.322 (2) A] roughly correspond to those expectedI0 for triple-, double-, and single-bonded nitrogen, respectively. However, Mo-N(1) is -0.02 A longerI0 than is anticipated for a Mo-N triple bond and the Mo-N-C bond angle also deviates somewhat from linearity [ M o - N ( I)-C( 1 1 ) = 167.4 When diphenylzinc was added to a solution of ('BUN)*Cr(OSiMe3)2 in hexane, PhZnOSiMe3 precipitated as expected but no complex analogous to Ib could be isolated. Instead, upon hydrolysis, organic products' ] including biphenyl and N-tert-butylaniline were identified by GLC as summarized in Table I. Thus, under conditions where diphenylzinc is added dropwise to the chromium complex at 80 OC, up to 70% tert-butylaniline is observed. It is noteworthy that the 0002-7863/80/1502- I7S9$0l .OO/O
Figure 1. Structure of bis(~-'2'-r~rr-butylimido)-(.v-rerr-butylimido)tetramethyldimolybdenum.
ratio of tert-butylaniline to biphenyl in the product decreases when (1) the reagents a r e added in inverse order, (2) the reaction is carried out a t reduced temperature, (3) the reaction is carried out in the presence of added pyridine, or (4) complex Ib is substituted for the chromium complex in this reaction. The observation of different products depending on the order of addition of the reactants requires formation of at least one intermediate. I n light of the facile substitution of compounds I, a reasonable intermediate is a monophenyl substituted derivative such as II.I2 Intermediate I1 may then undergo phenyl migration to the electron-deficient imido nitrogen affording a chromium(1V) amide (eq 3a). Alternatively, I I can react with a second equivalent of zinc reagent to afford a diphenyl derivative which subsequently reductively eliminates biphenyl (eq 3b). I n accord with this model, factors 1-4 noted above can be expected in each case to increase the likelihood that I1 will survive to undergo reaction 3b.I3 ('BuN),Cr( OSiMe, ), + Ph,Zn -+
(tBuN),Cr(OSiMe,)Ph + PhZnOSiMe, ( 2 )
+ZnPh,
-PhZnOSiMe
\
Ph
-
Ph-Ph
(3b)
Supplementary Material Alailable: Final positional parameters (as fractional coordinates), table of thermal parameters, and structure factor amplitudes (observed and calculated) of CloHjxMozNj ( 2 I pages). Ordering information is given on any current masthead page.
G 1980 American Chemical Society
I760
Journal of the American Chemical Society
References and Notes Chong, A. 0.; Oshima, K.; Sharpless, K. B. J. Am. Chem. SOC. 1977, 99, 3420-3426. Sharpless, K . 6.; Teranishi, A. Y.; Backvall. J.-E. /bid. 1977, 99,3120-3128. Burrington. J. D.; Grasselli, R . K., J. Catal. 1979, 59,79-99. Evidence for a related process involving migration of a phenyl group to electron-deficient oxygen has been reported: Reichle, W. T.; Carrick, W. L. J. Orgaflomet. Chem. 1970, 24, 419-426. See also the reaction of didecylmercury with chromyl chloride in ref 1, For the preparation of starting materials see: Nugent, W. A,; Harlow, R. L., lflorg. Chem., in press. Additional la could be obtained by cooling the solution but was contaminated with white needles of 'BuOZnMe. la: mp 131 'C dec; 'H NMR (C7D8)b 0.98 (s. 12 H, Me), 1.40 (s, 36 H, 'Bu) [meth I resonance exhibited characteristic satellites due to 14.4% lB3W (S = l/2), J = 7 Hz]. Anal. Calcd for C ~ O H ~ ~ C. N 33.72; ~ W ~H,: 6.79; N, 7.86. Found: C, 33.89; H. 6.78; N, 7.83. Ib: mp 102 OC dec; 'H NMR (C7Ds)b 1.02 (s, 12 H, Me), 1.39 (s, 36 H, 'Bu). Anal. Calcd for C20H48N4M02:C, 44.78; H, 9.02; N, 10.44. Found: C, 45.16; H, 8.81; N, 10.93. For instance, on adding 1 equiv of pyridine to Ib, the methyl resonance was shifted to 6 0.59 and the tert-butyl resonance to 1.48; cf. previous note. Crystal Data: C ~ O H ~ ~ MMO536.52: ~ N ~ ; monoclinic; space group P21/n; at -95 OC. a = 12.941 (4), b = 9.487 (2), c = 11.226 (2) A: = 103.36 (2)'; Z = 2: Dc = 1.329 g ~ m - Mo ~ ; K a radiation (h = 0.71069 H ; cm-'). Data were collected on a Syntex P3 diffractometer (4' < 2dl 2.00(4 yielded a conventional R index of 0.024. The largest peak in the final difference Fourier 10.37 eA-3) was close to the Mo atom. (a) Additional important bond'lengths are Mo-C(1), 2.177 (2); Mo-C(2) 2.181 (2); N(l)-C(ll), 1.457(3); N(2)-C(21), 1.487(2); C(l1)-C(av), 1.518 (4); C(21)-C(av). 1.526 (3) A. Additional important bond angles are N(1)MO-N(2), 108.61 (7); N(l)-MO-N(2)', 166.90 (6); N(l)-Mo-C(I), 92.17 (9): N( I)-Mo-C(2), 92.37 (8);N(2)-Mo-N(2)', 84.48 (6);N(2)-Mo-C(1), 110.44 (9); N(2)-Mo-C(2), 110. I 1 (8);N(2)'-Mo-C(1). 82.47 (8);N(2)'-Mo-C(2) 83.24 (8);C(I)-Mo-C(2), 135.21 (IO);Mo-N(2)-Mo', 95.52 (6); Mo-N(2)C(21), 134.7 (I); Mof-N(2)-C(21), 129.8 (1); N(I)-C(Il)-C(av), 108.7 (2); C-C(ll)-C(av), 110.2 (3); N-C(21)-C(av), 109.5 (2); C-C(21)-C(av), 109.5 (2)'. (b) A referee has inquired about the relatively large thermal ellipsoid of C(14). This effect possibly reflects the absence of any close intermolecular contacts with C(14). In contrast, C(13) has a C-H contact of 3.07 A and C(12) has two contacts of 3.17 A each. However, the C ( l I)-C(methy1) distances are all in the range 1.513 (4)-1.526 (4) A with identical esd's. Nugent, W. A,; Haymore, B. L. Coord. Chem. Rev. 1980, 31, 123-175. Thwemaining organic products after hydrolysis in each case were benzene, tert-butylamine, trimethylsilanol, and hexamethyldisiloxane. These were identified, as were biphenyl and N-tert-butylaniline, by GC-mass spectroscopy. Authentic N-tert-butylaniline was purified by spinning-band distillation (119 OC, 45 Torr) after preparation according to Hickenbottom, W. J. J. Chem. SOC. 1933, 946-951. I1 represents the simplest formulation for a species in which a trimethylsiloxo ligand has been replaced by a phenyl group. We cannot at this time exclude other formulations such as "ate" complexes or binuclear (Cr, Cr, or Cr, Zn) species. We are continuing our investigation into the mechanism of this reaction. Brominolysis studies appear to confirm the greater stability of the phenyimolybdenum species derived from Ib. Thus 1 mmol of Ib in hexane was treated with 2 mmol of diphenylzinc. After the resultant PhZnOSiMea was filtered off (0.78 mmol recovered), addition of excess bromine afforded 1.5 mmoi of bromobenzene, determined by GLC.
13
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1 102.5 1 February 27, 1980
or its enantiomer, 1,2,10,1l-(R,R,R,R)-(+)-tetracarbo(N,N)dimethylamide-3,6,9,12,15,18-hexaoxocyclooctadeca n e (D-crown-amide, l ~ ) ,were ~ ' used as starting materials for the synthesis of optically active fluorescent crown ethers. 1~and ID were converted into their acids, 2~ and 2 D . The acids provided the acid chlorides, 3~ and 3 D , which, in turn, allowed the preparation of L-crown-D-Trp (4LD), L-crown-L-Trp ( ~ L L ) , D-crown-D-Trp ( 4 D D ) , D-crown-L-Trp ( 4 D L ) , ' * L-crown-pyr (SL), and D-crown-pyr ( 5 D ) . I 3
1 ~ X, = CON(CH,), 2 ~ X, = CO,H 3L, x = COCl 4 L D , X = D-CONHCHCH2(3-indo1e)
I
~ L LX , =
C0,Me L-CONHCHCH2(3-indole) LO,Me
5 ~X, = CONH-1-pyrene
l", X = CON( CH,), 2D, X = CO,H 3D, = COCl 4DD, X = D-CONHCHCHJ 3-indole)
x
C0,Me I
4DL, X = ~-C0NHCHCH,(3-indole)
I
C0,Me 5 ~ X, = CONH-1-pyrene
Absorption spectra of all isomeric crown ether tryptophans were identical in methan01.I~Small, but noticeable, differences were observed, however, between the emission intensities of the diastereomers: a d D L = 0.200 f 0.008,adLL = 0.180 f William A. Nugent,* Richard L. Harlow 0.008.15Addition of TbC13 decreased the fluorescence yields. Contribution No. 2739 M D-crown-L-Trp and Stern-Volmer plots for 5.0 X Central Research & Decelopment Department M L-crown-L-Trp in M e O H were linear up to -5.0 X E . I . dii Pont de Nemours and Cotnpany TbCl3, after which they leveled off. This data implies the Experiniental Station, Wilmington, Delaware 19898 quenching of the excited states by Tb3+ ions bound in the Receiced December 17, 1979 cavities of the crown ethers. Treatment of fluorescence intensities in the absence and in the presence of different amounts of TbC13I6 leads to binding constants of K ( T b 3 + / ~ - c r o w n L-Trp) = (2.90 f 0.21) X lo4 M-I and K ( T b 3 + l ~ - c r o w n - ~ Trp) = (2.76f 0.12)X lo4 M-I. These values are of the same Photophysical Investigations of Chiral magnitude as determined for metal ion-crown ether comRecognition in Crown Ethers plexes." Complexing an achiral guest into crown ethers is seen to be unaffected by the chirality of the host. Cavity diameters Sir: a r e apparently the same for D-crown-L-Trp and L-crown-LThe present communication reports the first use of photoTrp. Only modest chiral recognitions have been observed using physical techniques for the elucidation of chiral recognition glycine-L-phenylalanine (Gly-L-Phe) and glycine-D-phenylin crown ethers."O Fluorescence quenching, energy transfer, alanine (Gly-D-Phe). Treatment of fluorescence intensities of and excimer formation have provided information on the D-crown-L-Trp (5.0X M in M e O H ) in the absence and complexation of achiral and chiral guests, on the conformation in the presence of different amounts of chiral guestst6 leads to of functionalized crown'ethers and on the effects of solvents K(Gly-L-Phe/D-crown-L-Trp) = (1.3 X 0.1) X 1 O4 M-' and and guests on given conformations. K(G1y-D-Phe/D-crown-L-Trp) = (1.9 f 0. I ) X IO4 M-'. 1.2,10,11-(S,S,.S,S)-(-)-Tetracarbo(N,N)dimethylamidoSubstantial chiral discriminations are seen, however, in the 3,6,9,12,15,18-hexaoxocyclooctadecane (L-crown-amide, 1 ~ ) efficiencies of energy transfer from the tryptophan side arms 0002-7863 /80/ 1502- I760s01 .00/0
0 1980 American Chemical Society
