8357 Table I. 4-Lithioenamines. Synthesis and Reactions Conditions of Br-Li exchange using n-BuLi p-Bromoenamines 1
Temp, "C
h
EtCBr=CHNC,H,O (1a)b t-BuCBr=CHNC,H,O (1b)d
-70 -70
1.5 1.5
t-BuCBr=CHNEt, (1c)d t-BuC(NC,H,O)=CHBr (1d)b
-20 -70
PhC(NMe,)=CHBr
-70
0.5
-70
-70
(1e)i
Enamines 3
E (reagent)
% yield=
Bp, "C (mmHg)
Me (MeI) H (H,O) D (D,O) Me (MeI) Et (EtI) Me (MeI) Me (MeI) H-BU(~I-BuI) I(I,) MeCHOH- (MeCHO) Me (MeI) Et (EtI) M-BU(n-BuI)
45c 70e 70e 64 e 45e 45e 75 g 508 50grh 50g 6ocJ 40C 45c
78 87 87 96 68 65 62 92
1
Me (MeI)
55c
96 (0.7)
1.5
Me (MeI) n-Bu (E-BuI)
65C 55c
90 (0.6) 105 (0.7)
2.5 10 minf
(20) (15) (15) (15) (15) (23) (0.75) (0.7) h 95 (0.7) 92 (i5)j 80 (0.65) 88 (0.8)
I
Me
=Yields of distilled products are given except where noted. The IR, NMR, and mass spectral data are fully compatible with the structures shown; purity was established by gas chromatography. bPrepared from the parent enamine according to the procedure of ref 2; the crude bromoenamine was used after filtration and removal of the solvents. Bromoenamine l g and its parent enamine have already been reported: L. Duhamel and J. M. Poirier, Tetrahedron Lett., 2437 (1976). CBased on parent nonhalogenated enamine. dPrepared from the bromoaldehyde according t o the procedure cited in ref 1. e Based on distilled bromoenamine. fThe quantitative bromine-lithium exchange was also observed with t-BuLi after 30 mn at -70 "C. gBased o n crude bromoenamine. hThe p-iodoenamine was decomposed by distillation. iBromine (1.6 g, 10 mmol) in 10 mL of THF was added at -60 "C under nitrogen to dimethylamino 1-phenyl-1-ethylene (1.47 g, 10 mmol) in 25 mL of THF. The reaction mixture was allowed to warm up to 0 "C, and then 1 8 mL (23 mmol) of n-BuLi (1.3 M in ether solution) was added at -70 "C, I Based on 1-phenyl-1-propanone obtained by hydrolysis
P-Bromoenamines are readily available either by reaction of secondary amines with a-halocarbonyl compounds,' or by bromination of the parent enamines and subsequent addition of 1 equiv of base to the intermediate a-bromoiminium salt.2 If the base was a tertiary amine, such as triethylamine, the crude bromoenamine was used without distillation after filtering the triethylamine hydrobromide and removing the solvent under reduced pressure. When the base used was n-butyllithium, the 8-lithioenamine was prepared in a one-pot reaction directly from the parent enamine, as indicated by the following equation. PhC( NMe2)=CH2
1.1 equiv of Br2, THF, -60
2.2 equiv of n-BuLi, -70'
OC
*
PhC(NMez)=CHLi Bromine-lithium exchange reactions have been observed with various P-bromoenamines: open-chain aldo- and ketoenamines, la-d, and cyclic and heterocyclic enamines, If and lg. The ease of exchange decreases with ~ r o w d i n g thus, ; ~ at -70 OC, the halogen-metal exchange was complete with bromoenamine Id after a reaction period of only 10 min, whereas, with the more crowded isomeric P-bromoenamine lb, it was only 60% complete after 10 min. With the very crowded enamine lc, reaction was only 30% complete after 4.5h at -70 OC; in this last case, the reaction rate was greatly accelerated by adding small amounts of H M P A (9:l THF:HMPA, 70% after 4.5 h at -70 "C), or when the temperature was raised (100% after 2.5 h at - 20 "C). Thus we have in hand 0-lithioenamines which can serve in synthesis as equivalents of delocalized anions -CC=Z C=CZ- ( Z = 0,4NR,5-7N-NMe28). Several characteristic advantages of these reagents should be mentioned: (1) their formation is quantitative and rapid even from quite hindered bromoenamines; (2) their reactions with electrophiles are rapid even at very low temperature; (3)
-
alkylation takes place without competitive N-alkylation or polysubstitution; (4) the resulting products are enamines which can be isolated or easily transformed into the corresponding carbonyl compounds.
References and Notes (1)L. Duhamel, P. Duhamel, and J. M. Poirier, Bull. SOC.Chim. Fr., 221 (1972). (2)L. Duhamel, P. Duhamel, and J. M. Poirier, Tetrahedron Lett., 4237 (1973). (3)The yields of exchange were determined by alkylation with CHsI. followed by VPC and NMR analysis.
(4)H. 0. House, "Modern Synthetic Reactions", 2nd ed, W. A. Benjamin, Menio Park, Calif., 1972,pp 546-5170, (5) G.Stork and S. Dowd, J. Am. Chem. SOC., 85, 2178 (1963). (6)(a) G.Wittig, H. Frommeld, and P. Suchanek. Angew. Chem., lnf. Ed. fngl., 2,683 (1963);(b) G.Wittig and H.Reiff, ibid., 7, 7 (1968). (7)(a) T. Cuvigny and H. Normant, C. R. Hebd. Seances Acad. Sci., Ser. C,268, 1380 (1969);(b) T . Cuvigny and H. Normant, Bull. SOC.Chim. Fr., 3976 (1970). (8)E. J. Corey and D. Enders, Tetrahedron Lett., 3 (1976).
Lucette Duhamel,* Jean-Marie Poirier Laboratoire de Chimie Organique de la Facultt? des Sciences et des Techniques de Rouen 76130 Mont Saint Aignan, France Received June 16. 1977
Reactions of Coordinated Molecules. 15. Preparation and Coordination of the Metallo Analogue of the Triacetylmethanide Anion, ~~c-(OC)~R~(CH~CO)~~Sir: We recently reported the preparation of the metallo acetylacetonate anion, 1, and its coordination to aluminum(II1) ion affording the neutral, tris-chelate complex analogous to Communications t o the Editor
8358 Al(acac)3.' The rhenium analogue to the anion, 1, was formed similarly. This anion also coordinates to metal ions, and it can be protonated at -78 "C using HCI/Et20 affording the first example of a metallo acetylacetone molecule, 2.2,3 Several examples of these coordination complexes and metallo P-diketone molecules have been reported.*x4The anion, 1, and the enol tautomer, 2, are metallo analogues of the corresponding 0-diketone species where the M(CO)4 moiety replaces formally the methine group of the organic analogue.
3.55; N , 1.03; Re, 27.29; AI, 1.98. Found: C, 46.47; H , 3.56; N. 0.80; Re, 27.03; AI, 2.06. The tetramethylammonium salt of the above aluminum complex, (Me4N)( Ifac-(OC)3Re(CH3CO)3]zAl), was isolated in 20% yield using the above procedure and substituting (Me4N)BF4 for (PPN)BF4: mp >205 "C dec; IR (CH2C12, in cm-I) v(C0) 1990 (s), 1900 (vs), u(C-0) 1485 (m); ' H N M R (acetoned6 vs. TMS) T 7.49 (s, 18, CCH3), 6.82 (s, 12, NCH3). Anal. Calcd for C22H30012NRe2Al: C , 29.36; H, 3.36; N , 1.56. Found: C, 29.22; H , 3.45; N , 1.15. When acetylpentacarbonylrhenium is treated with 2 molar equiv of methyllithium in T H F solution, the dianion, 3, is formed as shown. This stoichiometric reaction is followed easily by IR. During the slow addition of the methyllithium solution, CH,C(O)RI$CO)~+ 2CH,Li
1
THF 0"~3
pa
2
C'H 3
4 >M = H f ; x = 4;n = 0 5 , M = A1 x = 3 ; 11 = -1 ~
We wish to report the preparation of the fac-triacetyltricarbonylrhenate dianion, 3, and the coordination of this dianion the carbonyl and acyl C - 0 stretching vibrations of the acetyl to the aluminum(II1) and hafnium(1V) ions affording octacomplex disappear with the concomitant appearance of the hedral coordination complexes. bands expected for the monoanionic rhenium analogue of l? To a stirred solution of 0.51 g (1.38 mmol) of acetylpentaThe reaction solution is yellow at this point, but the continued carbonylrhenium2 in 50 mL of T H F at 0 "C under argon was addition of another molar equivalent of methyllithium proadded dropwise 2.05 mL (3.49 mmol) of a 1.7 M solution of duces a reddish orange color change and the appearance of a methyllithium in ether. The resulting reddish orange reaction two-band u(C0) pattern at 1957 and 1857 cm-' having a solution was stirred for 90 min and then was treated with a relative intensity of 1:2, respectively. This is the spectrum of solution of 0.22 g (0.69 mmol) of HfC14 in 13 mL of THF. The the terminal carbonyl ligands of the dianion, 3.xThe acyl C - 0 reaction solution was stirred for an additional 1 h at 0 "C and stretching vibration of 3 appears at 1532 cm-l. The correthen for 1 h at 25 "C. During this period the solution changed sponding acyl band of the rhenium analogue of the monoanion gradually to an amber color. The solvent was removed at re1 appears at 1585 cm-l. The lower frequencies for the carbonyl duced pressure, and the residue was extracted with 80 mL of and acyl bands of dianion 3 are consistent with the increased benzene. The mixture was filtered, and the solvent was renegative charge of the complex.1° moved from the filtrate at reduced pressure. Repeating the The dianion 3 coordinates to hafnium(1V) and aluminumextraction procedure with 130 mL of toluene, followed by (111) ions affording the bis-chelate neutral complex, 4, and the washing the filtrate residue with 3-8-mL portions of pentane, anionic complex 5. Both 4 and 5 exhibit the two-band v(C0) afforded 0.29 g (43%) of the product, Ifac-(OC)3Respectrum expected for afac-(OC)3M group. These bands all (CH3C0)3]2Hf, as a pale yellow solid: mp 120-200 "C dec; occur at frequencies higher than the analogous bands of the IR (CH2C12, in cm-I) v(C0) 2020 (s), 1925 (vs), v(Ci.iO) dianion 3, and the bands of the neutral hafnium complex, 4, 1465 (m); IH N M R (acetoned6 vs. TMS) T 7.54 (s, CH3).5 appear at higher energy than the bands of the anionic alumiAnal. Calcd for ClsH18012Re2Hf C, 22.12; H, 1.86; Re, num complex, 5. However, the frequency of the acyl ligands 38.1 1. Found: C , 22.02; H , 2.16; Re, 37.05.6 drops from 1532 cm-l in 3 to 1465 and 1485 cm-l in the To a solution of the dianion 3 which was prepared by the complexes 4 and 5, respectively. A similar change is observed above procedure using 0.1 5 g (0.41 mmol) of acetylpentacarwhen the monoanions of type 1 are complexed to aluminumbonylrhenium in 20 mL of T H F and 0.94 mmol of the ( I I I ) or g a l I i ~ m ( I I I ) . ~ , ~ methyllithium solution and stirring for 45 min at 0 " C was The single ' H N M R resonance for the methyl substituents added a solution of 0.03 g (0.22 mmol) of anhydrous AIC13 in of 4 and 5 indicates that the six methyl groups of each complex 1 mL of THF. The reaction solution was stirred for 2 h a t 0 "C are equivalent. This is consistent with the dianion, 3, acting as and then was treated with 0.1 3 g (0.21 mmol) of bis(triphena tridentate, chelating ligand which forms bis-chelate, octay1phosphine)iminium (PPN) tetraflu~roborate.~ After the hedral coordination complexes having idealized D 3 d symmetry. mixture was stirred for 20 min, the solvent was removed at The methyl resonances of 4 and 5 occur at -0.32 ppm to higher reduced pressure. The residue was extracted with 40 mL of field than the methyl resonance of the tris-chelate aluminum methylene chloride and was crystallized from a methylene complex of the rhenium metallo acac ligand. [cis-(oc)4chloride-heptane ( 4 : l ) solution at -20 OC affording 0.06 g Re(CH3C0)2I3AI. This shift may reflect an increase in the (21%) of the product, (PPN)(I~U~-(OC)~R~(CH~CO)~]~AI), electron density located on the acyl ligands in going from a as a pale yellow solid: mp 240-265 "C dec; I R (CH2C12, in four-carbonyl to a three-carbonyl metallo fragment. cm-l) v(C0) 1990 (s), 1900 (vs), v(C-0) 1485 (m); ' H Anion 3 represents formally the metallo analogue of the N M R (CD2C12 vs. T M S ) T 7.49 (s, 18, CH3), 2.41 (m, 30, triacetylmethanide anion, (CH3C0)3C-, where the carbanion C6H5). Anal. Calcd for C ~ ! , H ~ ~ O I ~ N P ~CR, 47.54; ~ ~ A IH:, is replaced by the isoelectronic f ~ c - ( O C ) 3 R e -moiety. ~ When Journal of the American Chemical Society
/
99.25
/ December 7 , I977
8359 a THF solution of 3 is treated with 2 equiv of HCl/ether a t -78 OC, the product obtained by ether extraction shows a two-line v(C0) pattern a t 1990 and 1895 cm-I. This species may be the dienol analogue of complex 2, although further characterization is needed. Such a complex would not possess a direct, formal carbon analogue. The preparation and complexation of the dianion 3 and its derivatives and the synthesis of the neutral, dienol complexes are being pursued actively.
I
Potentiometric formation curves of 1 : 1, DPA.3HCI to cobalt(II), solutions have an inflection at a = 3, moles of base per mole of ligand, indicating the formation of [Co(DPA)(H20)32+].6At p H 8.5, a second buffer zone with slow equiAcknowledgment, W e thank the University Research librium times (up to 15 min/titration point) is found, indicating Council of Vanderbilt University and the National Science that a reaction other than that of a simple deprotonation Foundation (Grant No. CHE-76-14304) for support of this (usually quite fast) is occurring. The color of the solution turns research. from pink to deep blue as the deprotonation reaction occurs, indicating a change in cobalt(I1) s t e r e o ~ h e m i s t r y . ~Com-l~ References and Notes puter treatment of the titration data indicate that there are two (1) C. M. Lukehart, G. P. Torrence, and J. V.Zeile, J. Am. Chem. Soc., 97,6903 proton ionizations in the second buffer region.” Infrared (1975). The preparation of a similar anion, cis~OC),Mn(CH3CO)(C~H&O)-, spectra (KBr disk) of the isolated blue compound,was reported earlier: see C. P. Casey and C. A. Bunnell, J. Chem. Soc., Chem.’Commun., 733 (1974). [ C O ( H - I D P A ) O H ] . ~ H ~ Oindicated I~ the lack of a N - H (2) C. M. Lukehart, G. P. Torrence, and J. V.Zeile, Inorg. Chem., 15, 2393 band. Upon recrystallization from MeOH, the infrared spec(1976). trum (KBr disk) of [Co(H-lDPA)OH] (111) contained no (3) C. M. Lukehart and J. V . Zeile, J. Am. Chem. SOC., 98, 2365 (1976). (4) C. M. Lukehart and J. V.Zeile, J. Am. Chem. SOC., 99, 4368 (1977). N-H band and a sharp strong band a t 3640 cm-I, indicating (5) infrared and ’H NMR spectra were recorded on Perkin-Elmer 727 and JOEL a nonhydrogen-bonded OH g r o ~ p . ’The ~ , conductivity ~~ of 111 MH-100 spectrometers, respectively. Microanalyses were performed by Galbraith Laboratories, Inc. Knoxville, Tenn. (9.7 X M ) in C H 3 N 0 2 was measured to be 5.4 R cm2/ (6) Hafnium could not be analyzed in the presence of rhenium. m o l l 5 and the molecular weight of 111 obtained by vapor (7) (PPN)BF4was prepared by the metathesis reaction of (PPN)CI and AgBFd pressure osmometry in MeOH was determined as 265 f 5. The in acetone solution in 95% yield. (8) This dianion IS very similar to the dianion [ ~ ~ C ~ P ~ C H ~ C O ) ~ M ~ ( Cabove O ) ~ ]indicate -~ that 111 is a nonionic monomeric metal complex. prepared by M. Y. Darensbourg et ai.’ However, this manganese dianion This together with infrared and visible spectral data supports was prepared quantitatively using a 20-fold excess of PhCH2MgCI. Presumably such an excess of the alkylating reagent would inhibit the sucthe formulation of 111 as [Co(H-,DPA)OH]. DPA was found cessful coordination or protonation of this dianion. not to undergo amine proton ionization in the presence of Zn2+, (9) D. Drew, M. Y. Darensbourg, and D. J. Darensbourg, J. Organomet. Chem., NiZ+,or Cu2+. 85, 73 (1975). (10) The rapid addition of the methyllithium produces 3 directly. If unreacted Potentiometric formation curves of 1 : 1 and 2: I , N-methacetyl complex is present, the dianion 3 will react with it producing the ylbis(2,2’-pyridylmethyl)amine (MeDPA) to cobalt(II), sorhenium monoanion analogous to 1. lutions have an inflection a t u = 3, indicating the formation David T. Hobbs, C. M. Lukehart* of [Co(MeDPA) ( H 2 0 ) 3 2 + ] and [Co(MeDPA)22+], respecDepartment of Chemistry, Vanderbilt University tively.I6 In both systems, the color of the solutions remained Nashville, Tennessee 37235 pink above p H IO, the equilibria times above p H 8 were fast, and there was no near basic buffer zone as in the Co:DPA Received July 26, 1977 formation curves. The above indicates that the replacement of the amino hydrogen in D P A by a methyl group drastically alters the solution chemistry of Co2+; Le., there is no proton Cobalt(I1) Induced Amine Deprotonation in Aqueous ionization in the near basic p H range and there appears to be Solution in the Near Basic pH Range no change in the stereochemistry of Co2+. The above further supports the ionization of the amino proton in [Co(DPA)Sir: (H20)32+l. There are three major types of N - H bonds generally found Potentiometric formation curves of 2: 1, AMPe2HCI to coin proteins: amide (i), imidazole (ii), and amino (-NH2). Metal balt(II), solutions had an inflection a t a = 2, indicating the formation of [Co(AMP)2(H20)2*+], followed by a second O H buffer zone similar in nature (long equilibrium times) to that II of the 1:1, Co2+-DPA,system.” Again two protons were lib-C-Nerated in the second buffer zone as the solution turned deep i 11 blue, indicating the formation of [ C O ( H - I A M P ) ~ ]It. ~is ~interesting to note that C O ( D P A ) ~ with + two pyridyl donors per ions have been reported to induce both amide’ and imidazole2 amine undergoes deprotonation at a lower pH value (0.3 unit) proton ionizations which are often accompanied by concomithan does C O ( A M P ) ~ with ~ + only one pyridyl residue/amine tant stereochemical changes about the metal ion; e.g., the nitrogen. This suggests that the aromatic ring possibly acts as nickel(I1) complex of the triglycine undergoes a change from an electron density sink for the deprotonated amine, where octahedral to square-planar geometry upon amide proton charge is dispersed through the “d” orbitals of the metal into ionizationIc and the bis(histidinato)cobaIt(II) chelate is rethe r*-antibonding orbitals of the pyridine rings. This would ported to undergo transformation from an octahedral to tetalso explain why similar amine deprotonation reactions have rahedral environment upon imidazole proton ionization. W e not been reported in diethylenetriamine or other polyalknow wish to report the first case of stereochemical changes ylenepolyamine complexes of Co2+. induced in cobalt( 11) chelates upon amino proton ionization The biological consequences of the above are possibly great. in aqueous solution near the physiological p H range. W e chose Deprotonation reactions observed in the metal ion binding of to study the colbalt(1I) complexes of tridentate bis(2,2’-pyripeptides and proteins, often thought to be due to the ionization dy1methyl)amine (DPA) (I)3 and bidentate 2-aminomethylof peptide protons, could in some cases be due to amino proton pyridine (AMP) (11)4 because of possible charge stabilization ionization. [ C O ( D P A ) ( H ~ O ) ~begins ~ + ] to deprotonate at pH due to dispersal from the ionized amino group through the 8.5, a p H value similar to that at which bis(glycylglycinato)metal ion into the pyridine rings via “d”-r* orbital interaccobalt(I1) starts to undergo amide proton i o n i ~ a t i o n .The ’~ tions.5
I
Communications t o the Editor
