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674 J . Am . Chem. Soc.1983, 05, 674-676

grating the group a nti to the departing sulfonate group in eitheran endocyclicor a n exocyclic m ode to the so-formed ring, we referto them as endo(B) and exo(B) rearrangements, respectively.Further, when the breaking double bondis endocyclic to theso-formed ring, we refer to th em a s suffix endo and exo corre-spondingly. Thus , four possible cyclization modes are endo-(B)-endo, endo(B)-exo, exo(B)-endo, and exo(B)-exo as depictedin Scheme I-IV each of which also illustrates the representativeexamples. Another exa mple of the endo(B)-exo cyclization byuse of an oxime-P205 system was previously reported by G a ~ l e y . ~

Th e following features ofou r new process are noteworthy: (1)

The reaction proceeds at low temperature in aprotic solvent(CH2C 12) with only 1 equiv of Lewis acid.(2 ) Aliphatic andarom atic ketones with acyclic and cyclic structures a re equallyemployable. (3 ) The produ cts are easily predictable, since ourmild reaction conditions are free from the complicated syn/antiequilibrium of oximes. (4) Both carbocyclic and heterocyclicstructures are prepared efficiently via exo(B) and endo(B) cy-clizations, respectively.

Two unusually short syntheses illustrated in Schem eV heavilydepend onou r new process. Thus , solenopsin B was prepared intwo steps froma simple acyclic precursor.13 The similar endo(B)cyclizations provided a direct entry to a variety of heterophanesfrom macrocyclic ketones a s illustrated in the facile synthesis ofmuscopyridine. Th e requisite oxime16 was readily available from2-allylcyclododecanone in four steps.14 Reaction of16 with MsCl(1.1 equiv)-NEt, (1.5 equiv) in CH2C 12at -20 O C fo r 30 minproduced the corresponding oxime mesylate quantitatively, whichwas converted cleanly to muscopyridine (80% yield) as the soleproduct by treatm ent w ith Me,SiOTf (1.1 equiv)I5 in CHC1, a t25 "C for 1.5 h followed by exposure with active MnOz (20equiv)I6 in the presence of N Et ,( 5 equiv) at 50 'C for 1.5 h.17

U p to this point the cyclization was terminated by the depro-tonation, yielding a,@ -unsaturated imines. Th e intermediarycations, however, may also be captured by carbon nucleophilesto afford satura ted imines. Initial efforts are given in eq 1 and2. Tre atme nt of a solution of the oxime mesylate8 ( n = 2) in

q- 1)((2 -) DlBAH1) Me,AI

M s O / ~ 63 N H P h

?!

CH2C12 with Me3A1(4 quiv) at 25 OCfor 1 h followed byreduction with DIBA H(3 equiv) produced the methylated product17 n 63% yield.'* Similarly, the amine19 was obtained in59%yield from the oxime mesylate18.19 It should be noted that

(13) Solenopsin B possesses the trans structure. Th e ratio of &/t ransisomers was determined by G C assay (silicone OV-101, 185 "C) to be 46:54:t, of the cis isomer= 14.55 min; t , of the trans isomer= 16.55 min. See:Matsumura, Y.; M aruoka, K.; Yamamoto,H. Tetrahedron Lert. 1982, 23 ,1929.

(14) The syn oxime was produced in 33% yield. Th e stereochemical as-signments for16 and its sy n isomer are tentative and based in parton 'HN M R analysis according to ref 7c.

(1 5) A number of Lewis acids were screened for a new pyridine synthesisby using 2-allylcyclododecanone oxime mesylate as a sub strate and activeM n 02 as an oxidant. The yields of [10](2,6)pyridinophane thus obtainedfollow: Et2A1CI (39%) ; SnCI, (65%); Me3SiI (68%); Me3SiOTf(80%).

(16) It should be worthy of note that active M n 0 2 was the reagent ofchoice and other oxidizing agents(DDQ, 0 2 , 2O2-FeCI3,Br2. etc.) gave lesssatisfactory results.

(17) The spectra of the synthetic muscopyridine were identical in allre-spects with those of the authe ntic specim en, which ar e kindly provided fromDr . K. Utimoto.

(18) In addition to the methylated amine17, the deprotonated amine10was produced in 8% yield.

0002-7863/83/1505-0674$01.50/0

neither 17 or 19 may be synthesized in a single operation by a nalternative method.2

Acknowledgment. This work was supported by the Ministryof Education, Japanese Government (Grant-In-Aids57 102008and 57118006).

Registry No. (E) -1 , 84099-04-7;2, 84099-05-8;3, 84099-06-9;(E) -4(R = R' = H) , 84099-07-0;( E X ) - 4 (R = H ; R' = prenyl) , 84099-08-1;( E ) - 4 ( R = Me; R ' = H) , 84099-09-2;5, 5194-85-4;6 , 84099-10-5;7 ,84099-11-6;( E ) - 8 ( n = I ) , 84099-12-7;( E ) - 8 n = 2), 84099-13-8;9 ,

(4a, lO-didehydro), 84099-18-3;(E) -13 , 84099-19-4;14 , 84099-20-7;14(1,2-didehydro), 84099-21-8;( f ) - 1 5 , 84099-22-9; 16 , 84099-23-0;16(mesylate), 84099-24-1;17 , 84099-25-2;18 , 84099-26-3;19 , 84099-27-4;19 (1,16-didehydro), 84099-28-5; (Z)-3- (phenylim ino)- -methylcyclo-pentene, 84099- 29-6; (Z)-3-(pheny limino)- 1 methylcyclohexene, 84099-30-9; (f)-2-allylcyclododecanone, 84099-31-0; 2-al lyl- 12-(phe nyl-selenyl)cyclododecanone, 84099-32-1; 2-allyl-11-methylcyclododecanone,84099-33-2;1,16-dihydromuscopyridine, 4099-34-3; (f)-muscopyridine,56912-83-5; solenopsinB, 32778-77- 1;cis-2-methyl-6-tridecylpiperidine,35285-26-8;( Z ) - -isopropylidene-4-methyl-2-(phenylimino)cyclohexane,

Supplementary Material Available: Spectroscopic data for newcompounds described in this paper (1 page). Ordering informationis given on any current masthead page.

84099-14-9; 10 , 84099-15-0; ( E ) - l l , 84099-16-1; 12 , 84099-17-2; 12

84099-35-4.

(19) The yield of the deprotonated product was 19%.

A New Approach to Construction of ArtificialMonolayer Assemblies

Lucy Netzer and J acob Sagiv*

Department of Isotope ResearchThe Weizmann Institute of Science, Rehovot, Israel

Received August 12 , 1982

Preparation of artificial supermolecular organizates representsan important new goal of modern chemistry. Within thisframework, th e study of monolayer assemblies and their appli-

cations has expanded tremendously in recent years, encompassingnow a wide variety of subjects ranging from biological mem bran esto solid-state electronic devices.] Modern film-building techniqueshave evolved; however, the basic approach common to all of themis still that devised by Langmuir and Blodgett (LB) some 50 yearsago.2 Although the LB procedure is powerful as a tool forhandling molecular entitites, it suffers from some inherentdrawbacks, mainly du e to the extensive use of mechanical m a-nipulation in the formation and tra nsfer of the monolayerf ib"

W e are hereby describing a different approacht o assemblingof artificial layered structures based on self-association andself-organization of molecules occ urring spontaneously a t solid-fluid interfaces. Our approach takes adv antage of th e possibilityof obtaining oriented compact monolayers by adsorptionof am -phiphiles from a fluid (solution, melt,or vapor) onto a polar solidsurface contacting the fluid phase.4 W e have recently shown thatunder suitable conditions adsorption may be used to prepareorganized mixed monolayers of several components (including dyes

( I ) See for example: Kuhn,H.; Mobius, D. ; Biicher,H . In 'Techniquesof Chemistry"; Weissberger, A,, Rossiter, B. W., Eds.; Wiley: New Y ork,1972; Vol. I , Par t IIIB, pp 577-702. Vincett,P. S.; Roberts,G. G . Thin SolidFilms 1980, 68 , 135.

(2 ) Blodgett,K. B. J . A m . Chem. S O C . 935, 57 , 1007. Blodgett, K. B.;Langmuir, I . Phys. Reo. 1937, 51 , 964.

(3) Gaines, G .L., Jr. Thin Solid Films 1980, 68 , I . Honig, E. P. J .Colloid Interface Sci. 1973, 43 , 66. Kopp, F.; Fringeli, U.P.; Miihlethaler,K.; Giinthard,Hs. H. Biophys. Strucr. Mech. 1975, 1 , 75 .

(4 ) Bigelow, W . C. ; Pickett,D. L.; Zisman, W. A.J . Colloid Sci . 1946,1 , 513. Levine,0 .; isman, W. A.J . Phys. Chem. 1957,6 1 , 1068. Bigelow,W. C .; Brockway, L.0 . J . Colloid Sci . 1956, 1 1 , 60. Bartell, L.S.; Ruch,R. J. J . Phys. Chem. 1956, 60 , 1231; 1959, 63 , 1045.

0 1983 American Chemical Society

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Communications to the Editor J . Am . Chem. Soc .. Vol. 105, N o . 3, 1983 675

S c h e m e I. Multi layer I o r m a t i o n b y A d s o r p t i o n . U s in gBifunc t iona l S i lane Su r fac tan t s as Monolayer Bui ld ingU n i t s

M o n o l a y e r A c ti v at e d M o n o la y er

i j .h e m c a l activation

I B * H e / T H F I I M )

2 H Z 0 ~ 1 3 0 % I / N a O H i 0 1 M I-

SOSO

-s,o,s,o

l m i n , r o o m t e m p / /Chemisorption 3i

Zmin. room temp

z7AS o l i d s u b s t r a t e

Ta b l e 1. Advanc ing Con tac t Angles (deg) on I ilms Bui lto n aSi l i con ATR Pr i sm

tz-

f i lm hexad ecane uater f igure

H T S / S i 4 0 1 0 5HTS/S i ac t iva ted 0 50H T S / H T S / S i 3 4 9 8 l aH T S / H T S / S i a c t i v at e d 0 5 0 l bO T S / H T S / H T S / S i 44 1 0 5 I dH T S / S i 4 5 1 0 7 I f

or other nonamphipathic components) ona variety of solidsur-f a c e ~ . ~oreover, covalent monolayer-surface binding (chemi-sorption) and intralayer cross-linking were used to obtain mon-olayers of unusual mechanical, chemical, and electrical ~ ta b il it y .~ .~

So far, only one-monolayer films could be obtained by ad-sorption. Surf ace s covered by monolayers exposing nonpolarmoieties (like methyl groups, for instance) become inert to furtherbinding of molecules from the fluid phase, which provides the

means for controlling the adsorption process and preventing de-position of material as a poorly defined thickfib" However,this prevents formation of ordered multilayers as well. It is thepurpose of the present communication to propose a multilayerassembling procedure aime d a t circumventing this difficulty.Ou rstrategy is based on a two-step sequence involving monolayeradsorption followed by chem ical activation of the exposed surface ,in order to provide polar adsorption sites for the a nchoring of thenext monolayer. This is accomplishe d by mea ns of a bifunctionalsurfa ctan t possessing in addition to th e usual polar head alsoan a polar term inal function convertible intoa suitable polar groupafte r completion of the adsorption step.8 To demonstrate thefeasibility of this new monolayer deposition method, we synthesizeda surfactant having the molecular s tructure CH2= CH(C H2), , -SiCI, (HTS,15-hexadecenyltrichlorosilane).9 The SiC1, functionenables covalent attac hme nt of the molecules to surfaces rich inhydroxyl g r o ~ p s , ~ ~ ~hile the terminal ethylenic double bondprovides a convenient path for the activation of the monolayerouter surface via hydroboration andH202 xidation to terminalhydroxylsi0 (see SchemeI) .

(5) Sagiv,J. J . Am. Chem.Soc. 1980, 102,92. Sagiv,J. Is . J . Cbem.1979,

(6) Polymeropoulos,E. E.: Sagiv, J. J . Chem. Phys. 1978, 69, 1836.(7) Such surfaces are usually hydrophobic, oleophobic, and autophobic.(8) A bifunctional surfactant containing two polar end groups would not

adopt the required perpendicular o rientation, thus preventing formation of anordered molecular array.

(9) The synthesisas well as other experimenta l details of the me thod willbe described in a forthcoming publication.

(IO) Brown, A.C. Orga nic Synthesis via Boranes; Wiley: New Yor k,1975.

18, 339, 346.

0 8--

0 0 8 - I

0 -

-1-_ .0-

4 0 0 0 3 6 0 0 3 2 0 0 2 8 0 0 2 4 0 0

WAV E N U M B E R S

Figure 1. In f ra red ATR spec t raon Si prism (45, 17 reflections) mea-sured with a NicoletMX l Fourier t ransform spectrophotometer:(a )H T S / H T S / S i bi la ye r ; ( b )HTS/HTS/Si activated bilayer; (c) Sub-t rac t ion b-a ; (d ) OT S/ HT S/ H TS /S i t r il ayer ; (e )OTS third mono-layer, subtract ion d-b; ( f ) OTS/Si monolayer.

Th e growing process of multila yer films of the type describedin SchemeI was followed by wettability and infrared multipleinternal reflection (AT R) measurements. Contact angles forn-hexadecane and water measured on films ofHTS and OTS(octadecyltrichlorosilane,CH 3(C H, ) 17SiC13) rown on a siliconA T R crystal are given in Table I. Th e IR spectra correspondingto the films in TableI ar e depicted in Figure1 . 1 2

The expected periodicity in th e wetting properties of the growingmultilayer film alternating between a hydroxyl-rich (polar) orvinyl/methyl-rich (nonpolar) outer surface could indeed be ob-served. As theHTS films are perfectly stable under the conditionsof the activation reaction (Figure1, curves a-c), the observedalternation in the contact angles cannot be attributed to a trivialfilm deposition-film removal cycle, thus furnishin g evidence forthe two-step film growing process proposed in Scheme1 . l 2

Under the conditions of present A TR measurementsi t is a goodapproximation to consider the absorbance intensities of themethylene bands arou nd 2900 cm- as proportionalto the amountof material in the film.9s13.i4 Th e I R curves in Figure1 provide,therefore, direct evidence of the step by step growing in thicknessof the film.1211s Adsorption ofa third layer of OT S on topofthe activatedHTS bilayer is confirmed by both the increase inthe absorbance of the -CH,- bands as well as the appea rance of

the weak-CH3 band a t 2958 cm-I, which is obviously abse nt inthe HTS spectrum (Figure1, compare curves e , f , and a) .However, theHTS bilayer and the third O T S monolayer are lesscompact than the firstOTS monolayer, as indicated by their lowercontact angles and lower intensities of their -CH2- IR ba nds, byca . 30% an d 20%, respectively. This reflects the inability of H T S

( I 1) Additional confirming evidence was obtained from external reflection

(12) The weakC= C stretching band at 1641.5 cm-I was not detectable

(13) Harrick,N . J. Int erna l Reflection Spectroscopy: Interscience: New

(14) Takenaka, T.; Nogami, K.; Gotoh,H.; Gotoh, R.J . Colloid Interface

(15 ) The broad O H bands around 3300 cm-l will be discussed in ref 9.

IR measurements and ellipsometryon metal mirror^.^

in the ATR mode.

York, 1967.

Sci. 1971, 35, 395.

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67 6 J . Am . Chem. SOC. 983, 105, 676-677

to form perfect monolayer str uctures , most probably because ofinsufficient length of its hydrocarbon chain.

In conclusion, experimental evidence has been provided de m-onstrat ing the feasibility of the multilayer assembling procedureoutlined in SchemeI. Though not perfect, the present multilayerfilms are first examples of artificial plann ed structu res of this typerealized exclusively by chemic al means. Besides its theore ticalsignificance, this chemical a pproac h might offer, if optimized,important practical advantages over the classical LB method.

Bridging Ligand Effects in Quadruply BondedDichromium(I1) Compounds

Randall A. Kok and MichaelB. Hall*

Department of Chemistry, Texas A & M UniversityCollege Station, Texas 77843

Received October 4, 1982

Most quadruply bonded dichromium(I1) compounds can bedivided into two different groups. The first group is characterizedby the presence of four carboxyla to ligands, some interac tion inthe axial position, an d aCr-Cr bond length ranging from 2.283to 2.541 A , while the second group is characterized by ligandsderived from weaker acids, infrequent axial interactions, andCr-Cr bond lengths of less than1.90 A . The w ide range ofCr-Crbond lengths has been attributed to two facto m2 Of these twofactors, the effect of the axial interaction has been investigatedexperimentally.-* Th e inductive effect of the bridging ligand,however, has not been investigated as thoroughly, although ex-periments are presently ~ n d e r w a y . ~ e have used general izedmolecular orbital (GMO) and configuration interaction(CI)calculations ontetrakis(formato)dichromiumand tetrakis(foi-m-amidat0)dichromium+o nvestigate this problem.Our calculationspredict that the latter has a much strongerCr-Cr bond.

The G M O method consists of a multiconfiguration self-consistent field calculation followed by aCI calculation. All ofthe orbitals are kept doubly occupied except for those involved

in the quadruple bond.Fo r the eight electrons in the quadruplebond, the G M O wave function consists of the dominant singledeterminant (a2, r x 2 , y 2 , 2) plus all paired double excitations,from these bonding orbitals to their antibonding counterparts(a*,r x * , y* , *), weighted Application of the variatio nprinciple yields a set of primary orbitals( n , r x , y , , u* , r x * , y * ,6*) in which the weakly occupied ones( n * , r x * , y * , *) a reoptimized to correlate the strongly occupied ones(a, x , y , ).Th e determinatioii of the GM O orbitals is then followed by a fullCI calculation in this restricted orbital space.

Because of the size of the dichromium systems, some additionalapproximations have been m ade. We have limited the study totwo simple ligand systems, thetetrakis(formato)dichromiuman dth e tetrakis(formamidato)dichromium. The bond distances andangles for the two systems are shown in Figure1 and a re basedon average values compiled from a number of known carboxylato

(1 ) Cotton,F. A,; Ilsley, W. H.; Kaim,W. J. Am . Chem.SOC. 980, 102,

(2 ) Cotton, F. A ; Extine, M. W. ; Rice, G. W .Inorg. Chem. 1978, 17 , 176.(3) Cotton, F. A.; Rice, C. E.; Rice, G. W.J . A m . Chem.S OC. 977, 99 ,

(4 ) Cotton, F. A.; Rice, G. W. Inorg. Chem. 1978, 17 , 2004.( 5 ) Bino,A.; Cotton, F. A.; Kaim,W . J . Am . Chem.SOC. 979, 101, 2506.(6) Bino, A.; Cotton, F. A.; Kaim, W. Inorg. Chem. 1979, 18 , 3030.(7) Cotton,F. A.; Ilsley, W. H.; Kaim,W. J . Am . Chem.SOC.1980, 102,

(8) Cotton, F. A.; Thompson, J. L. Inorg. Chem. 1981, 20, 1292.P ) Cotton, F. A. , private communication.(10) a) Hall,M . . Chem. Phys. Lett. 1979, 61 , 467. (b) Hall, M. . Int.

J . Quantum Chem. 1978, 14 , 613. (c) Hall, M. . In t . J . Quantum Chem.Symp. 1979, 13 , 195.

3464 and references therein.

4704.

3475.

HHI 4.m I

ICrr Cr ~

cJ 00 I I1.10

Figure 1. Struct ure of dichromium model compounds.Th e bond dis-tances and angles given for the tetrakis(format0) species apply for thetetrakis(formamidat0) species, as well.

Table I

Orbi tal O ccupa t ions0 1. 6TI 2 .86 1 . 36 * 0 .77r* 1 . 2LJ* 0 .4

Impor tan t Conf igura t ionsao2n462 0 . 2 2.27T46** 0.08U Z n 2 6 R * 0 . 1 6. 4 6 2 0 * 2 0 . 0 2

GVB Orbital OverlapValuesa 0 . 3 2TT 0.206 0 . 1 3

1 . 73. 51. 50.50.50. 3

0 .370.080 . 1 30 . 0 2

0 . 4 20.450 . 2 6

Rat io o f d Orbital Coefficients(5 0 . 1 8 4 0 . 2 2 7TI 0 . 1 9 6 0 . 3 1 36 0 .211 0 . 2 7 2

* The values represen t the sum of the squareof the coefficientscor responding to d i ffe ren t sp in com ponen ts o f the same conf igura -t ion .

a nd c a rb ox ya mi da to s p e ~ i e s . ~ - ~ J l * ~he symm etry of the tet-rakis(format0) speciesis D4,,while the sym metry of the tetra-kis(formamidat0) species isD2dsince the nitrogens a re tra ns toeach othe r. Even with this reduction in the size of the system,we have not been able to employ a very large basis set. The basisset consists of fully contracted fu nctions on the ligands and th echromium core. The outer d functionon the chromium has beensplit to give a double (repre sentation in order that we might havea better description of the chromiums. Additionals and p functionshave been added to represent the4s and 4p orbitals with exponentsof 0.10 an d 0.15, respectively.

The results are shown in TableI . In the first part, we havelisted the orbital occupation numbers for the two systems. Ascan be seen, the number of electrons in the bonding orbitalsincreasesupon going from the formato species to the formamidatospecies, especially in ther orbital. In the second part, we havelisted the coefficients of the configurations that m ake up theground- state wave function. As shown, the coefficient for thequadru ple bond is much larger for the form amidato species thanfor the formato species. In the third part, we have listed the

general valence bond(GVB) orbital overlap values.13 The se valueswere calculated fromou r natural orbital occupation numbers.14Again, the formamidato species has higher overlap values thanthe formato species for each orbital.

All three metho ds of analyzing the CI wave function indicatethat the fo rmamidato species has a stronger quadruple bond. Oneexplanation for this effect can be found by exa mining the radialextent of the d functions on theCr atoms. At the bottom of Table

(1 1) Cotton, F. A , ; DeBoer, B. G.; LaPr ade, M . D.; Pipal,J. R.; Ucko, D.

(12) Cotton, F. A.; ice, G. W. Inorg. Chem. 1978, 17 , 688.(13) Goddard,W . ., 111; Dunning, R. H.,Jr.; Hunt , W. J .; Hay, P. .

(14) Chinn, J. W., r.; Hall, M . B. Inorg. Chem., in press.

A. Acta. Crystallogr., Sect . B 1971, 827 , 1664.

Acc. Chem. Res. 1973, 6 , 368.

0002-7863/83/ 1505-0676$01.50/0 0 1983 American C hemical Society