Diiron Aminoalkylidene Complexes - American Chemical Society

Oct 1, 1995 - Valerio Zanotti,t Silvia Bordoni,t Luigi Busetto,*vt Lucia Carlucci,'. Antonio Palazzi,+ ... Fabio Prestopino,* Franco Laschi,§ and Pie...
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Organometallics 1995, 14, 5232-5241

5232

Diiron Aminoalkylidene Complexes Valerio Zanotti,t Silvia Bordoni,t Luigi Busetto,*vt Lucia Carlucci,' Antonio Palazzi,+Rossella Serra,? Vincenzo G. Albano,*s$Magda Monari,$ Fabio Prestopino,*Franco Laschi,§ and Piero Zanellos Dipartimento di Chimica Fisica ed Inorganica, Universita di Bologna, Viale Risorgimento 4, I-40136 Bologna, Italy, Dipartimento di Chimica "G. Ciamician", Universita di Bologna, Via Selmi 2, I-40126 Bologna, Italy, and Dipartimento di Chimica, Universitci di Siena, Pian dei Mantellini 44, I-53100, Siena, Italy Received May 17, 1995@ The reactions of the sulfonium salts [F~~(CO)~(C~)~+-CO){~-C(X)SM~~}ISO~CF~ [X = CN (la), H ( l b ) ] with a variety of amines are presented. l a yields ammonium cations [Fez( C O ) ~ ( C ~ ) ~ ~ - C O ) { ~ - C ( C N[R) N=RMe ~ } ](2), Dabco (3)(Dabco = 1,4-diazabicycl0[2.2.21octane)], aminoalkylidene [F~~(CO)~(C~)~+-CO)(CL-C(CN)NR~)I (41, isocyanide [FedCO)dcph+CO)+-CNR)] (7), or diaminoakylidene [Fez{CN(HXCH2>2N(H)}(COXcpk(M-COkl (11)complexes by reacting with tertiary amines, secondary amines, primary amines, or ethylenediamine, respectively. l b and secondary amines yield [Fe2(CO){C(H)NR2}(cp)n+-CO)21 (6). The formation of type 4 bridging and 6 terminal aminoalkylidene derivatives also via p-C addition respectively, as well as of CN- or H- to aminoalkylidyne [F~~(CO)~(~~)Z+-CO)+-CNR~)~+, the preparation of the terminal [Fez{C(CN)NPr'z}(CO)(cp)2+-C0)21(5)from la and NHPr'2, allows to clarify the role of electronic and steric effects in determining the position of the aminoalkylidene ligands. The X-ray structure of 5 has been determined. The crystal contains two independent molecules of the trans-isomer. The terminally bonded aminoalkylidene ligand exhibits weaker Fe-C(carbene) (Fe-C 1.915(3)A) and stronger C(carbene)-N(amine) n bonds (C-N 1.320(4)A) with respect to the bridging coordination. Electrochemistry shows that 5 undergoes a chemically reversible one electron oxidation to the corresponding monocation [5]+, which has been characterized by X-band EPR spectroscopy. All the complexes have been spectroscopically characterized, and a variable-temperature NMR on [F~~(CO){C(H)NM~~}(C~)~(~-CO)~] (6a) indicates exchange of the aminoalkylidene ligand between the two Fe atoms. philes, including alcohols and phosphine^.^-^ Moreover, we have preliminarily communicateds that la, like Cationic binuclear p-alkylidyne complexes provide a terminal carbene complexes, reacts with tertiary, secvery effective entry into the synthesis of bridging ondary, or primary amines t o form ammonium cations alkylidene derivatives, simply via nucleophilic addition [F~~(CO)~(C~)~(M-CO){~-C(CN)NR~}], aminoalkylidene at the p-C carb0n.l However this method has been less [F~~(CO)~(C~)~O~-CO)@-C(CN)NR~}I, or isocyanide [Fezsuccessful in the preparation of heteroatom-substituted (CO)z(cp)zCu-CO)Cu-CNR)Icomplexes, respectively. p-alkylidene complexes2 which still represent a relaWe wish t o report here on all the results obtained in tively unexplored class of compound^.^ this field, namely the reactions of la,b with a variety In the last few years we have been developing an of amines including diamines, focusing on the hitherto alternative approach t o the synthesis of diiron p-alkyunexplored synthesis, spectroscopic properties, struclidene complexes, which consists of the SMe2 displaceture, and bonding of the bridging [Fe2(CO)z(cp)2(~-CO)ment from [F~~(CO)~(C~)~~-CO)@-C(X)SM~ZISO~CF~ {p-C(CN)NR2}1(4)and terminal [Fe2(CO){C(H)NRR}(la, X = CN;4 lb, X = H5 ) with a variety of nucleo(cp)Z(p-C0)21(6)aminoalkylidene complexes. In addition an alternative synthesis for these complexes will be Dipartimento di Chimica Fisica ed Inorganica, Universita di described via H- and CN- nucleophilic addition at the Bologna. p-C aminoalkylidyne [ F ~ ~ ( C O ) ~ ( ~ ~ ) ~ ( L L - C O ) @ - C " ) I + , * Dipartimento di Chimica "G. Ciamician", Universita di Bologna. 8 Dipartimento di Chimica, Universita di Siena. and the role of electronic and steric factors in determin@Abstract published in Advance ACS Abstracts, October 1, 1995. ing the bridging, as in type 4, or the terminal, as in type (1)Jemmis, E. D.; Prasad, B. V. Organometallics 1992,11, 2528 and references therein. 6, coordination modes of the aminoalkylidene ligands (2) Significant examples include: (a) Casey, C. P.; Crocker, M.; will be pointed out. Finally for one of the latter Vosejpka, P. C.; Fagan, P. J.; Marder, S. R.; Gohdes, M. A. Organometallics 1988, 7, 670. (b) Kao, S. C.; Lu, P. P. Y.; Pettit, R. complexes, [Fez{C(CN)NPr"2}(CO)(cp)z@-CO)d(51, the

Introduction

+

Organometallics 1982, 1, 911. (c) Schroeder, N. C.; Funchess, R.; Jacobson, R. A,; Angelici, R. J . Organometallics 1989, 8, 521. (d) Howard, J. A. K.; Jeffery, J. C.; Laguna, M.: Navarro, R.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1981,751. (3)Adams, R. D. Chem. Reu. 1989,'89, 1703. (4) Busetto, L.; Zanotti, V.; Bordoni, S.; Carlucci, L.; Albano, V. G.; Braga, D. J . Chem. Soc., Dalton Trans. 1992,1105. (5) Bordoni, S.; Mazza, F.; Zanotti, V. Inorg. Chim. Acta 1994,223, 31.

0276-7333/95/2314-5232$09.00/0

(6) Busetto, L.; Cassani, M. C.; Zanotti, V.; Albano, V. G.; Braga, D. J. Organomet. Chem. 1991,415,395. (7) (a)Busetto, L.; Carlucci, L.; Zanotti, V.; Albano, V. G.; Monari, M. Chem. Ber. 1992,125,1125. (b) Bassi, M.; Carlucci, L.; Zanotti, V. Inorg. Chim. Acta 1993,204,171. (8) (a) Albano, V. G.; Bordoni, S.; Braga, D.; Busetto, L.; Palazzi, A.; Zanotti, V. Angew. Chem., Int. Ed. Engl. 1991,30,847.

0 1995 American Chemical Society

Diiron Aminoalkylidene Complexes

Organometallics, Vol. 14, No. 11, 1995 5233

Scheme 1 l+

NC

A k-A

4

NRR

-

h

la

4a-1

d e t

X-ray molecular structure together with the electrochemical properties are presented and discussed.

Results Reactions with Amines. The addition of a 5-fold excess of tertiary amines like NMe3 or Dabco (Dabco =1,4-diazabicyclo[2.2.2]octane) to a MeCN solution of ZOO0 loo ZOO0 loo zoo0 l o o I) b C [F~Z(CO)Z(C~)~~-CO)(CL-C(CN)SM~Z}ISO~CF~ (la)causes the displacement of MezS t o form the corresponding NC ,NMI)z NC .NEtz ammonium complexes [Fez(CO)z(cp)zOl-CO)(CL-C(CN)\' OC\ /c\ co OC\ /c\ \' co OC\ /c\ A-CN NMe3}lS03CF3 (2) and [Fez(CO)z(cp)zOl-CO){p-C(CN)FOFO/: FO-FO: FOFO: cp/ CP Dabco}]SO&F3 (3),respectively, which, owing to decp/ \c/ cp cp' \c/ CP 0 0 composition, have been characterized only by infrared spectroscopy in the reaction mixture. This result contrasts with the stability shown by the strictly related compound [Fe~(CO)~(cp)~~-CO)(CL-C(H)NMe~}ISO~CF~, 0 VEtr OC, ,c, C-CN which has been analogously obtained by reacting NMe3 FO -FO/: (lb)5 with [F~z(CO)Z(C~)Z~-CO)(CL-C(H)SM~Z}ISO~CF~ cp/ \c/ cp 0 or, alternatively, by simple addition of NMe3 to the cationic methylidyne complex [Fez(CO)z(cp)zOl-CO)OlFigure 1. IR spectra (in CHzClz solution)of the complexes CH)1+.2a (a) 4a, (b) 4b, and (c) 5. Absorptions attributable to the bridging-aminoalkylidene complexes are indicated with a The room-temperature reactions of la, in MeCN A mark, and those due to the terminally bonded carbene solution, with a large excess of anhydrous secondary isomer with a dot. amine (HNRR') readily form the corresponding bridgingaminoalkylidene complexes [Fez(CO)z(cp)z(p-CO){pcomplexes [F~Z(CO)Z(C~)Z~-CO){~-C(CN)X}] bearing a C(CN)NRR')I (4a-f) (Scheme 11, which could be isolated less sterically demanding p-C substituent (X = H,1° in variable yields (20-60%) as red air-stable crystalline CN,1° OMe6). solids. The bulky diphenylamine was found to be unreactive, under the same experimental conditions. In contrast to the IR absorptions of compounds 4aCompounds 4a-e show, in their IR spectra, a weak e, the product of the reaction of l a with diisopropyv(CN) absorption at about 2148 cm-l and a stronglamine shows, in CHzClz, only two v(C0) bands at 1949 weak-medium v(C0) band pattern (e.g. for 4a at 2004, (9) and 1742 (vs) cm-l (Figure IC). This pattern is 1970, and 1799 cm-l) (Figure l a ) common to all the similar to that observed for [Fez{CN(R)CHzCHzNR}analogous p-cyanoalkylidene complexes [Fez(CO)z(cp)z(CO)(cp)z@-CO)zl[R = H (see below), Me, Etll I and in @-CO){p-C(CN)X)l(X = SR? OR,6 P R z , ~N(H)Ph8), agreement with the formulation of the complex as [Fezwhich adopt a cis configuration (cp ligands on the same { C(CN)NP~~}(CO)(C~)Z~-CO)ZI (5) in which the cyside of the Fe-Fe bond). Despite the possible presence anoaminoalkylidene ligand is terminally bonded to one of two cis-isomers, depending on the relative orientation of the iron atoms. Moreover, its 13C NMR spectrum, of the CN and NRR p-C substituents with respect to the CO (or cp) ligands, only one isomer was observed in recorded a t -50 "C, shows two alkylidene carbon solution. In accordance, one single cp resonance in both resonances (indicative of a cis-trans isomeric mixture) the lH and 13CNMR spectra of the 4a-e complexes has at 6 232.7 and 234.0, which are well within the range been found (e.g. for 4d at 6 4.76 and 91.2). Since the expected for terminal aminocarbene ligands12and about structurally c h a r a ~ t e r i z e d ~p-cyanoalkylidene -~ com60 ppm downfield with respect to the corresponding plexes, including the precursor la,4have been demonresonance in the bridging alkylidene complexes (e.g., for strated t o adopt the cis configuration with the CN group 4a at 6 160 ppm). The proton resonances, at room on the cp side, we assume that compounds 4a-e also temperature, appear as broad signals, presumably due adopt this geometry. However, the 13C NMR of 4a to ligand exchange between bridging and terminal shows, in addition to the usual cp resonances, two minor signals of equal intensity (at 6 87.5 and 87.2) which (10)Aime, S.; Cordero, L.; Gobetto, R.; Bordoni, S.; Busetto, L.; account for the presence of small amounts of the trans Zanotti, V.; Albano, V. G.; Braga, D.; Grepioni, F.; J. Chem. Soc., Dalton Trans. 1992,2961. isomer. This is consistent with the fact that trans(11)Lappert, M.F.; &e, P. L. J. Chem. Soc., Dalton Trans. 1977, isomers are observed only among the p-cyanoalkylidene 2172.

4?

-

(9) Busetto, L.; Bordoni, S.; Zanotti, V.; Albano, V. G.; Braga, D. Gazz. Chim. Ital. 1988,118, 667.

(12)Dotz, K.H., Fischer, H., Hoffman, P., Kreissl, F. R., Schubert, U., Weiss, K., Eds. Transition Metal Carbene Chemistry; Verlag Chemie: Weinheim, West Germany, 1983.

Zanotti et al.

5234 Organometallics, Vol. 14,No.11, 1995 Scheme 3 R

NC A-Fr

Q and likewise attributed to the movement of the alkylidene ligand about the Mo-Mo bond.13b We believe that a plausible mechanism of the exchange process involves the bridging alkylidene [Fez(C0)2(cp)zOl-C0)2@-C(H)(NMez)}Icomplex as intermediate. This idea is d supported by the observation that terminal-bridging Figure 2. ORTEP drawing of [Fez(C(CN)NPrz}(CO)(cp)zinterconversion occurs in the related type 4 complexes. @-C0)2l (5) (molecule A). Moreover, whereas the cp protons exhibit a broadening at room temperature, the alkylidene ligand protons Scheme 2 remain sharp indicating that the ligand remain intact while moving from one metal to the other. One more feature in the lH NMR spectra of 6a must be evidenced: the room-temperature, as well as the lowtemperature, spectra show two singlets for the Me groups. Their expected inequivalence is the consequence of the hindered rotation around the C(carbene)-N bond, as usually found in aminocarbene comcoordination positions.13 The nature of compound 5 has plexes.12 The rotational barrier for aminocarbene ranges been ascertained by an X-ray diffraction study, which about 25-30 kcdmol. In fact the spectra of 6a recorded has shown the terminal coordination of the aminoalkyat about 50 "C show a marked broadening of the Me lidene ligand and the trans-configuration of the molecule signals which start to coalesce due to exchange occur(Figure 2). Stereochemicalfeatures are discussed in the ring a t that temperature. structural section. Finally complex 4f, obtained by reacting la with It is worth mentioning that an alternative route to HNEt2, shows in CH2C12 solution IR 4CO) absorptions the synthesis of type 4 and 6 complexes is feasible. This at 2004 s, 1965 sh, 1949 s, 1796 m, and 1743 s cm-l, consists in the room-temperature reaction of the cationic (Figure lb) which do not change with time and are the aminoalkylidyne complexes [Fez(CO)z(cp)201-CO)(,usum of the band patterns of type 4 and 5 complexes, CNRR)I+ l4 with Bu"8CN or NaBH4, respectively. indicating the presence, in solution, of an equilibrium Under these mild conditions, the bridging carbon semixture of the terminal and bridging isomers. lectively adds CN- or H- to give the corresponding cyano-aminoalkylidenecomplexes [Fez(CO)z(cp)2(u-C0)Likewise la, the sulfonium [Fez(CO)z(cp)zOl-C0)2@C(H)(SMe2)}lS03CF3(lb) readily reacts with the sec@-C(CN)(NRR')}l(4a,b,g) and [FedCO)(C(H)(NRR)}ondary amines HNMe2 or HN(Me)Et to form the com(6a-c) (Scheme 3). (cp)2@-CO)~l (Scheme plexes [F~~(CO){C(HXNRR')}(C~)~~-CO)~~(~~,~) Cyanide and hydride nucleophilic addition at the ,u-C 21, whose spectroscopic properties are similar to those C ~= R Fe,15J6 ) I + Ru17 of [ M ~ ( C O ) ~ ( C P ) Z ~ - C O ) ~ - (M found for type 5 complexes. In fact the IR spectra of 6 has been-previously reported. Formation of type 6 consist of two v(C0) absorptions at about 1933 and 1725 complexes also by this method confirms the tendency cm-l. In the lH NMR spectra, at room temperature, of the aminoalkylidene ligands =C(H)NRR to occupy a the cyclopentadienyl ring protons give rise to a single terminal coordination position. Therefore, on substitutvery broad signal (e.g. for 6a at 6 4.57)which becomes ing CN with H, the formation of terminally bonded sharp by increasing the temperature (at about 40 "C) aminocarbene complexes 6 is observed even in the case whereas, at lower temperature (-20"C), two distinct of less sterically demanding amines which give the sharp signals are originated (e.g. for 6a at 6 4.69 and bridging complexes in the cyanide counterparts 4. 4.49). These results are clearly indicative of a temper(14)(a) Cox, G.;Dowling, C.; Manning, A. R.; McArdle, P.; Cunature dependent fluxional process involving the exningham, D. J . Organomet. Chem. 1992, 438, 143. (b) Willis, S.; change of the aminoalkylidene ligand between the two Manning, A. R.; Stephens, F. S. J. Chem. Soc., Dalton Trans. 1980, Fe atoms. A very similar fluxional process has previ186. (15)Busetto, L.; Carlucci, L.; Zanotti, V.; Albano, V. G.; Braga, D. ously been observed in the alkoxy-alkylidene fulvalene J. Chem. Soc., Dalton Trans. 1990, 243. (Fv = fulvalene) complex [F~~MO~(CO)~(=CO(CH~)~CH~)I (16)Albano, V. G.;Busetto, L.; Castellari, C.; Monari, M.; Palazzi, (13)(a) Colborn, R. E.; Dyke A. F.; Knox, S. A. R.; Mead K. A.; Woodward, P. J. Chem. Soc., Dalton Trans. 1983,2099.(b) Drage, J. S.; Vollhardt, K. P. C. Organometallics 1986, 5,280. (c) Fanugia, L. J.; Mustoo, L. Organometallics 1992,11, 2941.

A.; Zanotti, V. J. Chem. Soc., Dalton Trans. 1993,3661. (17)(a) Busetto, L.;Carlucci, L.; Zanotti, V.; Albano, V. G.; Monari, M. J. Organomet. Chem. 1993,447, 271. (b) Albano, V. G.; Busetto, L.; Cassani, M. C.; Monari, M.; Zanotti, V. J. Organomet. Chem. 1995, 488, 133.

Diiron Aminoalkylidene Complexes Scheme 4

Organometallics, Vol. 14, No. 11, 1995 5235 m

{CN(H)(CHZ)~N(H>)(CO)(CP)ZC~-CO)ZI (11)(eq 1). h a l o -

11

Treatment of acetonitrile solutions of l a with a large excess of primary amine (NH2R) causes degradation of the p-C(CN)SMez unit to form the corresponding isocyanide derivatives [Fe2(CO)3(cp)z(CNR)] (7a-e)(Scheme

4).

gous formation of diaminocarbenes has been observed in the reactions of HzNCHzCHzNHz with the dithio- and [(CO)sWCdichlorocarbenes [(cp)(Co)FeC(SMe)~l+,~~~ (SMe)z1,lgdand [ R U C ~ Z ( C C ~ Z ) ( P P ~ ~ ) Z I . ~ ~ Formation of the terminally bonded diaminocarbene complex 11 presumably occurs via the bridging ami-

Complexes 7a-e have been isolated (25-60% yield) by chromatography, purified by crystallization, and identified by comparison of their physical and spectror noalkylidene intermediate [Fez(CO)z(cp)zCu-CO)(CL-CNscopic properties with those reported in the literature.18 I Since formation of the isocyanides occurs very rapidly, (H)(CH2)zN(H)}]. In fact, when the reaction is perpossible intermediates containing the p-C(CN)N(H)R formed a t -40 "C, the infrared spectrum of the crude group are usually not detected. However, when the reaction mixture exhibits absorptions at 2169, 1981, reactions described in Scheme 4 were performed by 1948,and 1791 cm-l which are in accordance with the adding the stoichiometric amount of amines, it has been formation of the mentioned intermediate. possible t o detect by IR spectroscopy (H2NPP)and even The infrared spectrum of 11 is similar to that of [Fezto isolate (H2NPh) the intermediates [Fez(CO)z(cp)&{C(CN)NP~Z~}(CO)(C~)~-CO)ZI (51, displaying two strong CO)(CL-C(CN)(N(H)R)}](R = Ph, 8a; R = PF, 8b). v(C0) absorptions at 1929 and 1716 cm-l. The alkyCompound 8a, which has been structurally characterlidene carbon gives rise to a low-field 13C NMR resoized,' upon standing in CHzClz solution slowly converts nance at 6 222.6which is comparable to the correspondinto the p-phenyl isocyanide derivative 7e. ing values in 5 (at about 6 230). The spectroscopic properties of 8a,b are similar to By analogy with the above described reactions of l a those of the above described cyanoaminoalkylidene with primary amines, the N,N-dimethylethylenediamine complexes 4a-e. A comparison shows that in 8a,b the converts the sulfonium alkylidene ligand into the isoIR v(CN) absorptions are shifted (about 20 cm-l) t o cyanide CN(CH2)zNMeZ affording [Fez(CO)s(cp)z{CNhigher wavenumbers, whereas the v(C0) bands occur (CH2)zNMez)I (12). The latter compound is unstable, a t somewhat lower wavenumbers compared to those of 4a-e. and it has been characterized only by infrared spectroscopy exhibiting the usual v(C0) and v(CN)band pattern. The reaction of l a with NH3 proceeds via the corresponding amino-alkylidene intermediate [Fez(CO)z(cp)zLikewise, the reaction of l a with N,"-dimethylethyl(9) which has been detected in @-CO)(~-C(CN)NHZ}] enediamine affords one unstable product identified, on solution by infrared spectroscopy. However, any atthe basis of its IR spectrum, as [Fez(CO)z(cp)zCu-CO){ptempt to isolate 9 has failed because of decomposition C(CN)N(Me)(CHz)zNHMe)I(13). In fact its v(C0) abwith formation of [Fe(cp)(CO)z(CN)las the only recogsorptions at 2004,1969and 1801 cm-l and dCN) band nizable product. Further evidence on the nature of 9 at 2147 cm-I are similar to the corresponding values of has been obtained by transforming the NHz into a the p-aminoalkylidene complexes 4a-e. presumably more stable NHC(0)Me group. Indeed, Molecular Structure of trans-[Fe2{C(CN)NP&}immediately after being generated, complex 9 reacts in (CO)(cp)g(u-CO)~l(5). The crystals of the title coma few minutes with acetyl chloride, in the presence of pound contain two independent molecules based on the pyridine, to form in about 70% yield the expected planar core Fe&-CO)z to which two cp groups, a CO complex [Fe~(CO)~(cp)z~-CO)~-C(CN)N(H>C(O)Me}1(10) molecule, and the aminocarbene grouping =C(CN)NPFz which has been fully characterized. The presence of the are coordinated in a trans configuration (Figure 2). The amide group NHC(0)Me is well evidenced in the 13C two independent molecules are strictly equivalent in NMR spectra by the occurrence of signals at 6 168.2and terms of the bond distances (Table 1). The orientation 23.4 attributable to the carbonyl and methyl carbons, of the carbene ligand lowers the idealized molecular respectively, whereas the resonance due t o the p-alkysymmetry that, if the substituents at the carbene atom lidene carbon is observed at 6 130.7. Moreover the lH are ignored, is C,. The actual molecular conformation NMR spectra display a resonance at 6 6.79 assigned to is asymmetric, but the crystal is racemic. the amidic proton, and the IR spectrum, in addition to The structural peculiarities of this compound with the usual 4CO) and v(CN) bands, shows an absorption respect to the other carbene derivatives of the same at 1677 cm-l attributable to the v(C=O) of the NHCfamily are the trans configuration of the ligands and, (0)Me group. Reactions with Diamines. The reaction of l a with (19)(a) Werner, H.; Fischer, E. 0.; Heckl, B.; Kreiter, C. G . J . ethylenediamine results in the cleavage of both the C-S Organomet. Chem. 1971,28,367. (b) McCormick, F. B.; Angelici, R. J. and C-C bonds at the p-alkylidene carbon yielding [FezInorg. Chem. 1981,20,1118.(c)McCormick, F. B.;Angelici, R. J. Inorg. (18)(a) Bellerby, J.; Boylan, M. J.; Ennis, M.; Manning, A. R. J . Chem. SOC.,Dalton Trans. 1978,1185.(b)Howell, J. A. S.; Rowan, A. J. J . Chem. SOC.,Dalton Trans. 1980,503.

(d) Steinmetz, A.L.; Hershberger, S. A.; Angelici, Chem. 1979,18,1231. R. J. Organometallics 1984,3,461. (20)Roper, W. R.; Wright, A. H. J . Organomet. Chem. 1982,233, c59.

5236 Organometallics, Vol. 14,No. 11, 1995

Zanotti et al.

Table 1. Selected Bond Lengths (A)and Angles (deg) for [Fen{C(CN)~z}(CO)(Cp)aOl-CO)al

bond in the same molecule and chemical environment. The Fe-C(carbene) value is 0.17 A longer than the Femolecule A molecule B C(carbony1) one. The difference is large and clearly indicates a weaker Fe-Ucarbene) n interaction. That 2.5313 1) 2.538(1) Fe( 1)-Fe(2) Fe( 1)-C(3) 1.909(3) 1.887(4) happens not only because the carbonyl ligand sets up a Fe(2)-C(3) 1.932(3) 1.944(4) double n interaction but also because the unique car1.891(3) 1.915(4) Fe( 1)-C(2) n orbital is in competition with the orbitals of bene Fe(2)-C(2) 1.944(3) 1.918(3) suitable symmetry on the CN and NPr5 substituents. 1.173(4) C(2)-0(2) 1.184(4) 1.181(4) 1.185(4) C(3)-0(3) The experimental evidence tells of substantial double 1.910(3) Fe(1)-C(4) 1.919(3) bond localization between C(carbene1 and N(amine) 1.454(5) C(4)-C(5) 1.450(4) [C(4)-N(2) 1.320(4),, AI. This value is in strict agree1.324(4) C(4)-N(2) 1.317(4) ment with what was found in the just mentioned 1.143(5) C(5)-N(1) 1.159(5) 1.495(4) N(2)-C(9) 1.484(4) aminocarbene~.~ In~spite ? ~ ~ of the above observation 1.539(5) C(9)-C(lO) 1.522(6) the n component of the Fe-C(carbene1 interaction is not C(9)-C(ll) 1.515(6) 1.520(5) canceled, as shown by the significantly longer values Fe(2)-C(1) 1.745(4) 1.738(4) (0.14 8, on average) found for the Fe-C(sp3) distances, 1.158(5) C(1)-0(1) 1.146(4) 1.510(4) N(2)-C(6) 1.504(4) and e.g. 2.060(6) 8, in [F~{C(CF~)~(OH)}(CO)~(C~)I~~ 1.517(5) C(6)-C(7) 1.522(6) 8, in [(OC)(cp)FeC{(CN)(SMe)}SC{Fe(cp)2.045(3) 1.527(6) C(6)-C(8) 1.510(6) (CO)Z}S].~~ A stronger iron-carbon bond is surely 2.160 Fe( 1)-C(cplav 2.169 present when this ligand is in bridging geometry, as in Fe(2)-C(cp),, 2.137 2.122 cis-[Fe~(C0)~(cp)2~-CO)@-C(CN)N(Me)C(O)SMe}l [Fe140.6(3) Fe(l)-C(2)-0(2) 141.3(3) C(carbene) 1.99av, C(carbene)-N(amine) 1.492(4) All5 135.9(3) 136.4(3) Fe(2)-C(2)-0(2) Fe(l)-C(3)-0(3) 140.9(3) 141.5(3) and cis-[Fe~(C0)2(cp)~~-CO)Cu-C(CN)N(H)Ph}l [Fe135.4(3) Fe(2)-C(3)-0(3) 136.5(3) C(carbene)2.016,,, C(carbene)-N(amine) 1.429(3) 178.5(4) 177.2(4) Fe(2)- C(1)-O(1) In fact a C(carbene1-N(amine) double bond is absent Fe(l)-C(4)-C(5) 110.7(2) 111.7(2) in the former species, because the n orbitals on the two 133.5(2) 133.6(2) Fe(l)-C(4)-N(2) C(4)-C(5)-N(1) 173.0(4) 173.1(4) atoms are in orthogonal orientation, and is weak in the 125.5(3) C(4)-N(2)-C(6) 125.7(3) latter, because the implied orbitals are significantly 119.6(3) C(4)-N(2)-C(9) 119.8(3) twisted. Therefore the Fe atoms do not have competi114.9(3) C(6)-N(2)-C(9) 114.5(3) tors for n-donation t o the carbene carbon. 112.9(3) 112.7(3) c(lo)-c(9)-c(ll) 113.5(4) 114.9(4) C(7)-C(6)-C(8) In the light of these considerations the terminal C(5)-C(4)-N(2) 115.3(3) 114.3(3) of the carbene group seems motivated by coordination 110.1(3) C(S)-C(6)-N(2) 113.7(3) steric factors, but one should not forget that the loss in C(7)-C(6)-N(2) 111.0(3) 112.9(3) 110.9(3) C(lO)-C(9)-N(2) 110.5(3) iron-carbene n bond is, a t least in part, compensated C(ll)-C(9)-N(2) 111.0(3) 110.2(3) by a gain in the C(carbene)-N(amine) double bond in the terminal coordination. more importantly, the terminal mode of bonding of the Electrochemistryof [Fe2{C(CN)NPf2}(CO)(cp)2carbene function. @-CO)2](5) and EPR Spectra of [51+. Previously Being that the Fez@-CO)zmoiety is unchanged with reported electrochemical studies on a series of p-cyrespect to the unsubstituted molecules cis- and transanoalkylidene complexes [Fez(CO)z(cp)20L-CO)@-C(CN)[Fez@-C0)2(C0)2(cp)2], the Fe-Fe distance [2.536(1)AI (XI}], including 4d (X = NCH2(CH2)3CH2),have shown is also strictly equivalent [2.531(2),2.534(2) 8,) respecthat these complexes undergo a one-electron reduction t i ~ e l y ] . ~The l chemical nonequivalence of the iron atoms complicated by relatively slow degradation of the corgives rise to some asymmetry of the bridging CO ligands to furtherly electroreducible responding monoanions that exhibit slightly shorter distances from Fe(l), t o by product^.^' The redox behavior of complex 5 is quite which the carbene group is coordinated. The cp ligands ks illustrated in Figure 3, it exhibits an different. show slightly different Fe-C(cp) average distances as irreversible cathodic step at very negative potential well, with longer distances (0.035 8,) from Fe(1). values (E, = -1.64 V) as well as two consecutive anodic The Fe-C(carbene) distance [1.915(3)avAI has to be processes (at E"' = f0.26 V and E , = f1.04 V, compared with what found in other terminal aminocarrespectively), the first of which only shows preliminary bene species, e.g. 1.97(1)8, in [Fe2@-SPh)2(C0)5{C(NMe2)features of chemical reversibility. Ph}],22 1.95(1) A in [Fe(C0)3(PEt3){CN(Me)(CH2)2NControlled potential coulometry in correspondence to and 1.927(4)A in [ F ~ ( C O ) ( C ~ ) C ~ H ~ N ( C ~the H first ~ ) ~ anodic ~ . ~ ~ step (E, = +0.5 V) shows the consumpThese values are a bit longer than the present one but tion of one electrodmolecule. Cyclic voltammetric tests are in line with the observed variations of bond lengths on the resulting solution exhibit a voltammetric profile around a metal center caused by the different nature quite complementary to that shown in Figure 3, thus and stereogeometry of the ligands. The strength of this confirming the chemical reversibility of the 5451+ redox interaction can be assessed if compared to the Fe-CO change also in the long times of macroelectrolysis.

-

(21)Bryan, R. F.;Greene, P. T. J. Chem. SOC.A 1970, 3064. (22)Dillen, J. L. M.; van Dyk, M. M.; Lotz, S. J. Chem. Soc., Dalton Trans. 1989, 2199. (23) Hitchcock, P. B;Lappert, M. F.; Thomas, S. A,; Thorne, A. J.; Carty, A. J.;Taylor N. J. J . Organomet. Chem. 1986, 315, 27. (24)Stenstrcam, Y.;Koziol. A. E.: Palenik, G. J.: Jones. W. M. Organometallics 1987,6 , 2079.

(25)Bruce, M.I.; Duffy, D. N.; Snow, M. R.; Tiekink, E. R. T. J . Organomet. Chem. 1986,310, C33. (26)Busetto, L.; Zanotti, V.; Albano, V. G.; Braga, D.; Monari, M.; J. Chem. Soc., Dalton. Trans. 1988, 1067. (27)Bordoni, S.;Busetto, L.; Calderoni, F.; Carlucci, L.; Laschi, F.; Zanello, P.;Zanotti, V. J . Organomet. Chem. 1995, 488, 133.

Diiron Aminoalkylidene Complexes

Organometallics, Vol. 14, No. 11, 1995 5237

n

6

1

DPPH

A!9o

*1.200

U

E [VOLT 1 A

W

Figure 3. Cyclic voltammograms recorded at a platinum electrode on a THF solution containing 5 (1.7 x mol dm-3) and [NBu41~C1041(0.2mol dm-9 Scan rate = 0.2 V S-1.

Analysis28 of the cyclic voltammograms relevant to this reversible one-electron removal with scan rate varying from 0.02 to 5.12 V s-l shows that: the ipJipa ratio is constantly equal to 1; the i, x v-lD parameter remains substantially constant; the peak-to-peak separation progressively increases from 71 to 410 mV. In view of the fact that, under the same experimental conditions, the ferrocene/ferrocenium oxidation process (E"' = +0.55 V) exhibits a quite similar significant departure from the constant value of 59 mV expected for a reversible one-electron transfer, we attribute it to uncompensated solution resistances of the low conductive THF medium. In this connection the fact that the 5/[51+ anodic oxidation is chemically as well as electrochemically reversible allows to think that [51+maintains a geometric structure substantially similar to that of its neutral parent 5.29 Because of the framework-destroying nature of the most anodic and cathodic steps, respectively, we discarded any further investigation on them. Figure 4 illustrates the X-band EPR spectra of [51+ electrogenerated at 253 K. The line shape recorded at liquid nitrogen temperature (100 K), Figure 4a, can be suitably interpreted in terms of a S = l/2 spin Hamiltonian. It shows a well-recognizable rhombic structure, with a significant line-broadening effect at low field. The relevant anisotropic parameters are consistent with the presence of a paramagnetic metal-centered system:

g, = 2.176 z t 0.005 g, = 2.067 f 0.005 g h = 1.999 f 0.005

+ +

(g) = ('/~)@1 g,

gh)

= 2.081 f 0.005

The second derivative analysis and simulation procedure~ point ~ ~ out the noticeable orbital contribution of the [5]+ monocation paramagnetism reflecting the overall unsymmetrical framework experienced by the f28) Brown, E. R.; Sandifer, J. R. In Physical Methods of Chemistry. Elec&bChemical Methods; Rossiter, B. W., Hamilton, J. F., Eds.;Wiley; New Chanter 4. . Yokk. ~ ,. . 2. ~ -1986: - - -~Vol. -. (29) Zanello, P. Struct. Bonding (Berlin) 1992,79, 101. (30)Lozos, G . P.; Hoffman, B. M.; Franz, C. G . QCPE 1974,11,265. ~

-I

*V

Figure 4. X-Band EPR spectra recorded on a THF solution of [6]+,electrogenerated at 253 K (a) 100 K (b) 200 K. unpaired electron. On the other hand, the line shape does not evidentiate any hyperfine interaction with nuclei external to the diiron core, thus suggesting that a very minor delocalization,if any, of the S = l/2 electron on the ligands occurs. Comparison of the EPR features of [51+with those previously reported for [4dl-, which exhibits an axial absorption pattern,27 makes evident that the unsymmetrical position of the cyanoaminoalkylidenefragment significantly affects the EPR response, allowing us t o assume that in [51+ the unpaired electron should be mainly localized on the carbene-substituted iron atom. At the glassy-fluid transition (200 K) the rhombic line shape evolves toward a single isotropic signal, centered at giso = 2.081 z t 0.005 and with a relatively broad line width ( M i s o = 55 f 5G), Figure 4. When the temperature is increased, the intensity slightly decreases, but the isotropic parameters remain unaltered and wellfitting the glassy ones; upon refreezing, the original rhombic pattern is restored. These data suggest that [SI+ maintains its geometry under very different thermal conditions.

Discussion The results described in the previous sections indicate that the sulfonium complexes la,b undergo the welldocumented aminolysis,12J9transforming the C(X)SMe2 into the C(X)NRR or CNR ligand by reacting with secondary or primary amines, respectively. These reactions share several features with the aminolysis of the dithiocarbene complexes [(cp)(CO)FeC(SMe)zI+lgCor [(CO)gWC(SMe)J19d Similarly, the reactions with secondary amines show a marked dependence on the steric hindrance of the amine. Only small amines (like dimethylamines or heterocyclic amines) react promptly and give satisfactory yields. Further analogies come from the reactions with diamines, but these will be discussed later. These similarities strongly support the idea that the mechanism involved might closely resemble that proposed for the aminolysis of [(OC)sWC(SMe)2]which has been studied in detail.lgd Therefore the reaction of la with amines may proceed via SMe2 displacement to form the ammonium intermediate

5238 Organometallics, Vol. 14, No. 11, 1995

Zanotti et al.

Scheme 5 NC, ,we2

-oc,

-

yC\

la

l+

,co

F0 Cp’ \gNF0*Cp

l+ NC HNRR HNRR

OC

SM*

cp‘

k’

\Fs/-be:

8‘ ’

A

CO Cp

I *+

over the terminal position in polynuclear complexes, may clearly explain the importance of the electronwithdrawing CN substituent in stabilizing the bridging coordination adopted by the carbene ligand in type 4 complexes. Further clues on the pivotal role assumed by the cyano group come from the coordination mode of the C(H)NR2group. A comparison between [Fe2{C(H)(NMez))(CO)(cp)z@-CO)21 ( 6 4 and [Fez(CO)2(cp)2@-CO){p-C(CN)(NMe2)1(4a) is particularly significant. The H for CN substitution dramatically affects the coordination mode: bridging in the cyanoaminoalkylidene 4a and terminal in 6a. Finally as found in the reaction of l a with ethylenediamine, the expected bridging is converted to terminal coordination mode in order to allow stronger n-interaction of the two N-atoms with

(A), which is deprotonated by the excess of amine affording type (B) complexes. Finally, in the case of the carbene carbon of the =CN(H)CH2CH2N(H)ligand. primary amines the aminothiocarbene intermediate is These findings justify the complete absence of polyconverted into the isocyanide product by elimination of and dinuclear complexes bearing the diamino carbene HCN (Scheme 5). in bridging position. Despite the mentioned instability of type A amHaving monium complexes [ F ~ ~ ( C O ) ~ ( C ~ ) ~ @ - C O ) { ~ - C ( N M ~ ~ ) - shown the effects of the electronic factors on the coordination mode, one should also notice the (CN)}lS03CF3(2) and [F~~(CO)~(C~)~@-CO)C~-C(D~~CO)formation of the terminally bonded cyanoaminoalky(CN)}lS03CF3(31, stable type B derivatives (compounds lidene ligand in the trans-[Fe2{C(CN)NPriz)(CO)(cp)z4a-f)are formed upon reaction with secondary amines. The analogous [F~~(CO)~(C~)~@-CO)@-C(NHR)(CN)}] (p-CO)z] complex (5) (see structural section) and the has been isolated in the reaction of l a with aniline. The spectroscopic evidence of an equilibrium between bridg[F~~(CO)~(C~)~@-CO){~-C(CN)N(H)P~)I (8a) complex, ing and terminal coordination in [ F ~ ~ ( C O ) ~ ( C ~ ) ~ @ - C O ) which is the unique type B intermediate isolated in the @-C(CN)NEt2}1(50 (Figure 11, which clearly indicate reaction with primary amines, slowly decomposes to the that steric effects play an important role as well. isocyanide derivative 7e, in CHzClz solution. The 8a The bridging coordination is favored by increasing the 7e transformation is faster in the presence of an n-acid properties of the p-C and lor by decreasing the excess of aniline suggesting that HCN elimination is bulkiness of the NR2 substituent in the cyanoalkylidene probably favored by basic media. It is worth noting that ligand. cyanide elimination from several type 4 cyanoamiThe noalkylidene complexes [ F ~ ~ ( C O ) ~ ( C ~ ) ~ @ - C O ) C ~ - C ( C N ) - reaction of l a with NJV-dimethylethylenediamine offers a chance to compare its reactivity with primary (NRR)}] has also been observed to occur under acidic and tertiary amines, both functional groups being conditions to give the aminoalkylidyne products [Fezpresent in the diamine reagent. Formation of the (CO)~(C~)~@-CO)~-CNRR}].~~ (10) isocyanide product [F~~(CO)~(C~)~{CN(CH~)~NM~~}I In our opinion, the most important result of the shows that the NH2 group is, as expected, more reactive present study is the isolation of type 4a-e derivatives and that the synthetic method via the sulfonium l a can which are among the first stable bridging aminoalky~ J lack ~ J ~of, ~ ~ be of some interest for the preparation of functionalized lidene complexes so far r e p ~ r t e d . ~ ~ JThe isocyanide complexes. this class of complexes is generally believed to be a In light of the reactivity of l a with primary amines, consequence of the destabilization caused by a competition of the nitrogen and iron n-electrons for the occupathe reaction with anhydrous ammonia would be extion of the empty p-orbital on the carbon atom.13,32This pected to give the hydrogen isocyanide (HCN)33complex idea is supported by the observation that, in most of [Fe2(CO)s(cp)z(CNH)].The latter has been previously the p-aminoalkylidene complexes so far reported, the obtained, as an unstable intermediate, in the protonaN atom exhibits n-donor character reduced by the tion reaction of the cyanide complex [Fez(C0)3(cp)2(CN)I-, presence of adjacent electron-withdrawing functional which ultimately gives the aminoalkylidyne [Fez(cp)zgroups. Examples include the complexes [Fe2(CO)&p)2(C0)2@-CO)@-CNH2)1+ and [Fez(C0)3(cp)z(CN)l-,in a (p-CO)@-C(CN)N(Me)C(0)SR}l,15 [Fez(CO)z(cp)z(~-CO)- sort of acidhase disprop~rtionation.~~ None of these b-C(H)(N=CPh2)}l,2a[ C O ~ ( C O ) ~ ~ ~ - C O ) ~ - C ( P ~ ) N ( P ~ ) C - have been detected in the reaction mixture of species (Ph)=N(Ph)}l,31aand [Fe2(CO)~Cu-C(H)NHC(0)Me}l.31cl a with NH3; in contrast, IR data support formation of In other cases, for instance in [WPt(PR3)3(COkCu-C(H)the cyanoalkylidene intermediate [Fez(cp)2(CO)2@-CO)N E t ~ } l ,n-interaction ~l~ between N and the p-alkylidene @-C(CN)(NH2)}1(9).It is worth mentioning that in the carbon is prevented by direct donation from N to the analogous reaction of la with PH3 the phosphonium metal. [Fe~(cp)2(C0)2@-CO){pU-C(CN)(PH3)}1SO~CF~ and the These considerations, together with the observation phosphinoalkylidene[Fez(cp)z(C0)2~-CO)b-C(CNXPH2))1 that strong n-acid ligands preferably adopt the bridging have been obtained, that, on the contrary, are very stable.7b

-

(31) (a) Adams, R. D.; Chodosh, D. F. J. Organomet. Chem. 1977, 139, C39. (b) Davis, J. H., Jr.; Lukehart, C. M.; Sacksteder, L. A.

Organometallics 1987,6,50. (c) Sumner, C. E., Jr.; Collier, J. A,; Petitt, R. Organometallics 1982,1, 1350. (32) Matachek, J. R.; Angelici, R. J. Inorg. Chem. 1986,25, 2877.

(33) Fehlhammer, W. P.; Fritz, M. Chem. Rev. 1993,93, 1243. (34) Fehlhammer, W. P.; Schoder, F.; Beck, G.; Schrolkamp, S. Z. Anorg. Allg. Chem. 1993,619, 1171.

Organometallics, Vol. 14, No. 11, 1995 5239

Diiron Aminoalkylidene Complexes

Experimental Section

Table 2. Crystal Data and Experimental Details

for [F~z{C(CN)NP~'Z}(CO)(CP)Z~-CO)ZI

General Procedures. All reactions were routinely carried chem formula CzlH24FezNz03 out under nitrogen by standard Schlenk techniques. Solvents fw 464.13 monoclinic system were distilled immediately before use under nitrogen from space group P 2 1 / ~(NO.14) appropriate drying agents. Instruments employed: IR, Per15.791(3) a,A kin-Elmer 983-G, NMR, Varian Gemini 200. Elemental 13.741(2) b,A analyses were by Pascher Microanalytical Laboratory (Rema18.937(6) C. A gen, Germany). The compounds tFe2(CO)z(cp)2(p-CO){pc90.75(2) deg C(SMed(CN)}IS03CF3 (la),4[Fez(C0)z(cp)z@-CO){y-C(SMe~)v, A 3 4108.8 (H)}lS03CF3(lb),6and [F~Z(CO)Z(C~)ZO~-CO)C~-CN(M~)R)ISO~2 8 CF3 (R = Me, Et)14 (R = B z ) were ~ ~ prepared according to 1.50 dcalcd, g cm-3 published methods. The syntheses and characterization of the 13.6 p(Mo Ka), cm-l 1920 F(000) complexes [F~~(CO)~(C~)Z(~-CO)~-C(CN)(NM~Z)I} (4aY and 0.15 x 0.25 x 0.40 cryst dimens, mm [ F ~ ~ ( C O ) ~ ( C P ) Z ( ~ - C O ) { ~ - C ( C N ) ( N C H Z ((4dP C H ~ )have ~ ~ H Z ) } I 28 max, deg 54 been previously reported. Materials and apparatus for elecfh,Sk,+l octants of reciprocal space explored scan type w trochemistry and coupled EPR measurements have been de0.9 0.35 tan 8 w scan width, deg scribed elsewhere.36 Unless otherwise specified, all potential 8094 reflcns collcd values refer to the saturated calomel electrode (SCE). 6140 unique obsd reflcns [Fo> 4u(Fo)1 Reaction of l a with NMes. Trimethylamine was bubbled 0.0394, 0.0446 R(F), wR(F) into a MeCN solution (10mL) of l a (75 mg, 0.13 mmol) for 5 GOF 1.84 min. IR inspection of the crude reaction mixture evidenced the absorptions v(C0) 2003 s, 1980 w, 1821 m and v(CN) 2165 1971 mw, 1799 m; v(CN) 2146 w. 'H NMR (CDC13; 6): 4.79 w cm-', which have been attributed to the formation of (s, 10 H, cp), 3.17 (q,2 H, NCHZCH~), ~ F ~ z ~ C ~ ~ ~ ~ C ~ ~ Z ~ ~ - C O(2). ~ {Attempts ~ - C ~ N M(t,~3~H,~NCH2CH3). ~ C N ~ } I S ~ ~ C F ~2.82 (8,3 H, NMe), 1.10 to isolate complex 2 have been unsuccessful. [F~~(CO)~(C~)Z~-CO)C~-C(CN)N(M~)P~}I (44: yield 17%; Reaction of la with Dabco. Addition of a large excess of mp 134-136 "C dec. Anal. Calcd for CzzHl~FezN203:C, 56.17; Dabco to a MeCN solution (10 mL) of l a (75 mg, 0.13 mmol), H, 3.86. Found: C, 56.33; H, 3.90. IR (CH2C12) (cm-l): Yas described above, gave [Fez(CO)~(cp),Ol-CO){p-C(Dabco)(CO) 2000 s, 1963 mw, 1799 m; v(CN) 2146 w. IH NMR (CN)}ISO&F3 (3)as detected from infrared spectra of the (CDCl3; 6): 7.39-6.90 (m, 5 H, Ph), 4.84 (s, 10 H, cp), 3.51 (s, reaction mixture. IR (MeCN) (cm-l): v(C0) 2003 s, 1971 w, 3 H, Me). 1824 m; v(CN) 2165 w. [F~z(CO)Z(C~)ZO~-CO)C~-C(CN)(NCHZ(CHZ)~CHZ)}I (4d): Synthesis of [F~~(CO)Z(~~)Z~-CO)~L-C(CN)(NM~Z))I (4a). yield 56%; mp 140-142 "C dec. Anal. Calcd for C20HzoMethod a. The synthesis of 4a has been previously briefly FezNz03: C, 53.61; H, 4.50. Found: C, 53.35; H, 4.60. IR described:8 gaseous dimethylamine was bubbled into a MeCN (CHzClZ)(cm-'): v(C0) 2005 s, 1971 mw, 1798 m; v(CN) 2147 solution (10 mL) of la (91 mg, 0.16 mmol); the color of the w. lH NMR (CDzC12; 6): 4.76 (9, 10 H, cp), 3.15 (m, 4 H, NCH2solution turned immediately bright red, and the mixture was (CH2)3CH2), 1.52 (m, 6 H, NCHZ(CH~)&HZ). 13C NMR (CDZdried under vacuum. The residue was dissolved in CHzClz and Cl2; 6 ) : 268.9 @-CO), 211.2 (CO), 162.4 01-0, 128.3 (CN), 91.2 filtered on an alumina pad (3 x 5 cm). The red filtered solution (cP), 60.1, 27.2, 25.2 (NC5Hio). was evaporated to dryness under reduced pressure and the residue crystallized from CHzClz layered with n-pentane a t [ F ~ z ( C O ) Z ( ~ ~ ) Z ~ - C O ~ ~ - C ~ C N ~ (4e): ~NCHZ~CHZ~ -20 "C to yield 45 mg (69%) of 4a, mp 132-133 "C dec. Anal. yield 43%. Anal. Calcd for C19H1sFe2Nz03: C, 52.58; H, 4.18. Calcd for C17H&ezNz03: C, 50.04; H, 3.95. Found: C, 50.12; Found: C, 52.60; H, 4.24. IR (CHzC12) (cm-l): v(C0) 2004 s, H, 3.92. IR (CH2Clz)(cm-I): v(C0) 2004 s, 1970 mw, 1799 m; 1965 mw, 1792 m; v(CN) 2147 w. IH NMR (CDCl3; 6): 4.74 Y(CN)2148 W. 'H NMR (CDCl3; 6): 4.79 (s, 10 H, CP), 2.84 (5, (s, 10 H, cp), 3.19 (m, 4 H, NCHZ(CHZ)ZCHZ), 1.88 (m, 4 H, 6 H, Me). 13C NMR (CDzC12; 6): 267.6 @-CO), 211.0 (CO), NCH~(CHZ)~CHZ). 161.6 h-C), 127.5 (CN), 91.0 (Cp), 49.6 (Me). [F~~(CO)~(C~)~~-CO){~U-C(CN)(~~Z)}I (40: yield 52%; Method b. To a stirred solution of [Fe2(CO)z(cp)z@-CO)@mp 98-100 "C dec. Anal. Calcd for C19HzoFe2N203: C, 52.33; CNMe2)]S03CF3(290 mg, 0.55 mmol) in CHzClz (25mL) was H, 4.62. Found: C, 52.31; H, 4.60. IR (CHzC12)(cm-l): v(C0) added Bu"4NCN (150 mg, 0.55 mmol). After 60 min the 2004 s, 1965 sh, 1949 s, 1796 m, 1743 s; v(CN) 2183 w, 2145 mixture was filtered on a n alumina pad. The red solution was w. IR (KBr) (cm-l): v(C0) 1999 s, 1964 mw, 1789 m; v(CN) evaporated to dryness under reduced pressure and the residue 2143 w. lH NMR (CDC13; 6): 4.70 (s, 10 H, cp), 3.6 (m, br, 4 crystallized from CHzCl2 layered with n-pentane a t -20 "C. H, NCHZCH~), 1.25 (t, 6 H, NCH2CH3). Yield: 96 mg (43%). [F~~(CO)~(C~)ZO~-CO)C~-C(CN)N(M~)B~)I (4g). A solu(300 mg, tion of [Fez(CO)~(cp)~(p-CO){p-CN(Me)Bz)lSO~CF~ Synthesis of Compounds 4b-f. The compounds 4b-f 0.52 mmol) was treated with Bu"4NCN (150 mg, 0.55 mmol) were all synthesized according to the procedure for the in CHzClz (25 mL). After 30 min the mixture was filtered on synthesis of 4a (method a) outlined above. The liquid amines a n alumina pad. The red solution was evaporated to dryness were syringed into MeCN solutions of la. A detailed descripunder reduced pressure and the residue crystallized from CH2tion of the preparation of 4d has been previously reported.16 Cl2 layered with n-pentane a t -20 "C. Yield: 182 mg (73%). The complex 4b has been prepared either from l a with Anal. Calcd for C23HzoFezNz03: C, 57.06; H, 4.16. Found: C, NHMeEt (method a, 16% yield) and by reacting [Fe&O)z(cp)[email protected]; H, 4.10. IR (CHzC12) (em-'): v(C0) 2004 s, 1969 mw, CO){p-CN(Me)Et)lS03CF3 with Bu"6NCN (method b, 38% 1800 m; v(CN) 2147 w. IH NMR (CDzC12; 6): 7.25 (m, 5 H, yield). Ph), 4.86 (s, 10 H, CP), 4.32 (9, 2 H, NCHzPh), 2.70 (s, 3 H, [F~Z(CO)Z(C~)ZO~-CO){~-C(CN)N(M~)E~}] (4b):mp 112NMe). 13C NMR (CDC13; 6): 267.1 &-CO); 210.0 ((20); 160.5 113 "C dec. Anal. Calcd for ClsHlsFe2N203: C, 51.23; H, 4.30. @-C); 128.3 (CN); 139.8, 128.8, 127.4 (Ph); 90.9 (cP), 66.4 Found: C, 50.12; H, 3.92. IR (CH2C12) (cm-I): v(C0) 2005 s, (NCHzPh); 46.1 (NMe). Synthesis of [F~z{C(CN)NP~'~}(CO)(C~)Z~-C~)Z~ (5). (35)Busetto, L.; Zanotti, V. Albano, V. G.; Monari, M.; Castellari, The synthesis of 5 has been previously briefly described? C. Gazz. Chim. Ital. 1993, 123, 703. compound l a (108 mg, 0.16 mmol) in MeCN (10 mL) was (36)Barbaro, P.; Bianchini, C.; Laschi, F.; Midollini, S.; Moneti, S.; treated with NHPr'z (40 mg, 0.4 mmol). The reaction mixture Scapacci, G.; Zanello, P. Inorg. Chem. 1994, 33, 1622.

b,

+

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5240 Organometallics, Vol. 14, No. 11, 1995

Zanotti et al.

Table 3. Atomic Coordinates for [F~~(C(CN)NP~'~}(CO)(CP)~~~-CO)~I atom

X

Y

0.44175(3) 0.30262(3) 0.3726(3) 0.3891(2) 0.3464(2) 0.3734(2) 0.3862(2) 0.3949(2) 0.3633(2) 0.3541(2) 0.3990(2) 0.3845(2) 0.3681(2) 0.4403(3) 0.2829(3) 0.3990(2) 0.3151(3) 0.4700(3) 0.5612(3)

0.23439(3) 0.18392(3) 0.4894(2) 0.3386(2) 0.0957(3) 0.0370(2) 0.2816(2) 0.3382(2) 0.1344(2) 0.0709(2) 0.3332(2) 0.4232(2) 0.4292(3) 0.5024(3) 0.4723(4) 0.2499(3) 0.2224(4) 0.2623(3) 0.2731(3)

0.06037(3) 0.20068(3) 0.1451(3) 0.1086(2) 0.1561(3) 0.1280(2) 0.1300(2) 0.1311(2) 0.1252(2) 0.1234(2) 0.1035(2) 0.1270(2) 0.1318(2) 0.2220(2) 0.0644(3) 0.0866(2) 0.0105(2) 0.1639(3) -0.0465(4)

0.66677(4) 0.61221(4) 0.9146(3) 0.7371(2) 0.5328(3) 0.4768(3) 0.5558(3) 0.4855(2) 0.7196(3) 0.7818(2) 0.7472(2) 0.8431(3) 0.8166(3) 0.8524(3) 0.8963(3) 0.6416(3) 0.6521(3) 0.5983(3) 0.5655(2)

z

atom

Molecule A -0.00547(2) C(16A) 0.04901(2) C(17A) 0.0065(2) C(18A) -0.1370(1) C(19A) 0.1048(2) C(20A) 0.1417(2) C(21A) 0.0755(2) C(22A) 0.1222(1) C(23A) -0.0313(2) C(24A) -0.0727(1) C(151) -0.0680(2) C(161) -0.0300(2) (3171) -0.1782(2) C(181) -0.1738(3) C(191) -0.1606(3) C(201) -0.1809(2) (3211) -0.2159(2) C(221) -0.2332(2) C(231) 0.0439(2) C(241) Molecule B C(16B) 0.19322(2) C(17B) 0.24684(3) C(18B) 0.1728(2) C(19B) 0.0504(1) C(20B) 0.3074(2) C(21B) 0.3463(2) C(22B) 0.1746(2) C(23B) 0.1395(1) C(24B) 0.2683(2) C(152) 0.3117(1) C(162) 0.1197(2) C(172) 0.1457(2) C(182) -0.0009(2) C(192) 0.0091(2) C(202) -0.0009(3) C(212) 0.0171(2) C(222) -0.0339(2) C(232) -0.0182(2) C(242) 0.1999(4)

Y

z

0.5446(3) 0.5406(3) 0.5547(3) 0.5675(3) 0.1964(4) 0.1785(4) 0.1836(4) 0.2045(4) 0.2125(4) 0.5468(4) 0.5345(4) 0.5436(4) 0.5616(4) 0.5635(4) 0.1928(4) 0.1773(4) 0.1869(4) 0.2083(4) 0.2119(4)

0.1733(3) 0.1238(3) 0.1929(3) 0.2852(3) 0.2519(5) 0.1534(5) 0.1434(5) 0.2357(5) 0.3027(5) 0.2196(5) 0.1303(5) 0.1485(5) 0.2490(5) 0.2930(5) 0.2170(6) 0.1358(6) 0.1668(6) 0.2672(6) 0.2982(6)

0.0575(2) -0.0082(2) -0.0626(2) -0.0303(2) 0.0998(2) 0.0825(2) 0.0080(2) -0.0206(2) 0.0361(2) 0.0678(2) 0.0313(2) -0.0420(2) -0.0509(2) 0.0170(2) 0.1051(2) 0.0604(2) -0.0105(2) -0.0097(2) 0.0618(2)

-0.0381(4) -0.0475(4) -0.0618(4) -0.0612(4) 0.3141(4) 0.3251(4) 0.3126(4) 0.2938(4) 0.2947(4) -0.0553(4) -0.0380(4) -0.0366(4) -0.0530(4) -0.0646(4) 0.3178(4) 0.3244(4) 0.3106(4) 0.2953(4) 0.2998(4)

0.6179(2) 0.7185(2) 0.7283(2) 0.6337(2) 0.5705(5) 0.5637(5) 0.6578(5) 0.7227(5) 0.6687(5) 0.6055(5) 0.5729(5) 0.6555(5) 0.7392(5) 0.7083(5) 0.5522(3) 0.5899(3) 0.6919(3) 0.7172(3) 0.6309(3)

0.2642(4) 0.2488(4) 0.1750(4) 0.1447(4) 0.1937(4) 0.2681(4) 0.2971(4) 0.2407(4) 0.1768(4) 0.1555(3) 0.2254(3) 0.2704(3) 0.2284(3) 0.1574(3) 0.2166(4) 0.2863(4) 0.2830(4) 0.2112(4) 0.1702(4)

X

br, 1H, CHNMez), 4.69(s, 5 H, cp), 4.49 (s, 5 H, cp), 3.70 (s, 3 was stirred for 15 min and the solvent removed under vacuum. H, Me), 3.09 (s, 3 H, Me). I3C NMR (CDC13, -20 "C, 6): 286.9 After the residue was dissolved in CH2C12, the solution was (p-CO); 260.4 (CHNMez), 212.9 (CO), 86.0 (cp), 53.0, 44.1 chromatographed on an alumina column (15 x 3 cm) by using (NMe). CHZCld petroleum ether (1/2, v/v) as eluent. After elution of the first fraction containing [Fez(cp)z(CO)rl,the second redMethod b. To a stirred solution of [Fez(CO)z(cp)z(pu-C0)01violet fraction was collected and the solvent evaporated to CNMez)]S03CF3 (200 mg, 0.38 mmol) in MeCN (25mL) was dryness. Crystallization from CHzClz layered with n-hexane added NaBH4 (17 mg, 0.45 mmol). After 60 min the mixture at -20 "C afforded 56 mg (64%) of 5, mp 123-125 "C dec. Anal. was filtered on an alumina pad. The green-brownish solution Calcd for CzlH24FezNz03: C, 54.35; H, 5.21. Found: C, 54.45; was evaporated to dryness under reduced pressure and the H, 5.32. IR (CHzC12)(cm-I): v(C0) 1949 s, 1742 s; v(CN) 2177 residue crystallized from CHzClz layered with n-pentane at w. 'H NMR (CDC13;6): 4.4 (s, br, 10 H, cp), 3.9 (m, br, 2 H, -20 "C. Yield: 77 mg (53%). CHMeZ), 1.5 (s, br, 12 H, Me). 13C NMR (CD2C12, -50 "C; cis Syntheses of the complexes 6b,c. The complex 6b was trans isomers; 6): 286.0, 282.0 (p-CO), 232.7, 234.0 (p-C), prepared according to the procedures for the synthesis of 6a; 212.3, 213.0 (CO), 113.3, 113.6 (CN), 88.4, 88.0 (cp), 62.3 both methods (method a, from lb and NHMeEt, 36% yield; (CHMeZ), 21.1, 20.7, 20.1 (CHMe2). method b, from [Fe~(CO)~(cp)~~-CO){p-CN(Me)Et}lS0~CF~ Synthesis of [F~~(CO){C(H)NM~~}(C~)Z~-CO)~I (6a). and NaBH4, 49% yield) have been used. The compound 6c Method a. Through a stirred solution of l b (0.19 g, 0.35 was obtained in 47% yield, reacting [Fe2(CO)z(cp)zOl-C0){pummol) in MeCN (15 mL), HNMez was slowly bubbled for about CN(Me)Bz}]S03CF3 with NaBH4 according to the procedure 10 min. The mixture, which turned green-brown, was stirred described for the synthesis of 6a (method b). for 30 min, and then the volatile material was removed in [Fe2(CO){C(H)N(Me)Et}(cp)~~-CO)21 (6b):Anal. Calcd uucuo. The residue was redissolved in CHzCl2-hexanes (1/2, for Cl7Hl9FezN03:C, 51.43; H, 4.82. Found: C, 51.45; H, 5.00. v/v) and chromatographed on an alumina column, eluting with IR (CH2C12) (cm-'): v(C0) 1934 s, 1723 s. 'H NMR (CDC13; the same solvents mixture. A first yellow fraction containing 6): 9.50 (8,br, 1H, CHNMeEt), 4.53 (s, br, 10 H, cp), 3.65 (s, unidentified mononuclear complexes and a second fraction br, 3 H, Me), 3.20 (m, br, 2 H, CHZCH~), 0.97 (m, br, 3 H, containing some [Fez(CO)4(cp)z]were discharged. A green CH2CH3). fraction was collected and evaporated to dlyness under reduced [F~~(CO){C(H)N(M~)B~}~(~~)Z~-CO)Z~ (6~): Anal. Calcd pressure. The residue was crystallized from CHzCl2 layered for Cz2HzlFe2N03: C, 57.56; H, 4.61. Found: C, 57.45; H, 4.82. with n-pentane at -20 "C. Yield: 56 mg (42%). Anal. Calcd IR (CH2C12) (cm-l): v(C0) 1933 s, 1726 s. 'H NMR (CDC13; for C16H17Fe~N03:C, 50.18; H, 4.47. Found: C, 50.10; H, 4.46. 6): 9.77 (s, br, 1 H, CHNMeBz), 7.43-6.94 (m, 5 H, Ph), 4.60 IR (CH2Clz) (cm-I): v(C0) 1933 s, 1735 s. 'H NMR (CDzClz; (6, br, 10 H, cp), 3.55 (s, br, 3 H, Me), 2.87 (s, br, 2 H, CH2Ph). 6): 9.30 (s, br, 1 H, CHNMeZ), 4.43 (s, br, 10 H, cp), 3.57 (s, 'H NMR (CDC13; 6, -30 "C): 9.54 (s, br, 1 H, CHNMeBz), br, 3 H, Me), 2.95 (s, br, 3 H, Me); (CDC13; -20 "C, 6 ) 9.49 (s,

+

Organometallics, Vol. 14, No. 11, 1995 5241

Diiron Aminoalkylidene Complexes 7.35-6.90 (m, 5 H, Ph), 4.74,4.52 (6, br, 10 H, cp), 3.53 (s, br, 3 H, Me), 2.87 (s, br, 2 H, CH2Ph). Synthesis of [Fe2(CO)s(cp)2(CNMe)](7a). Gaseous NH2Me was bubbled into a stirred MeCN solution (10 mL) of l a (0.15 g, 0.26 mmol), for 10 min, and then the volatile material was removed under reduced pressure and the residue, redissolved in CH2C12, was filtered on an alumina column. Crystallization from a CH2Clz-hexane mixture gave 7a (34 mg, 37%), which was identified by comparison of its spectroscopic properties with those reported in the literature.18 Synthesis of 7b-e. The compounds 7b-e were all synthesized by a procedure similar to that for 7a, adding the corresponding primary amines dropwise, by a syringe, to MeCN solutions of la. The complexes 7b-e were obtained with the following yields: 7b, 41%; 7c, 20%; 7d, 35%; 7e, 46%. They were identified by comparison of their spectroscopic properties with those reported in the literature.18 [F~Z(CO)~(C~)Z~~-CO){~-C(CN)N(H)P~}] (Sa). The synthesis of Sa has been previously briefly described? compound l a (160 mg, 0.28 mmol) in MeCN (10 mL) was treated with aniline (0.54 mmol). After 10 min the mixture was dried under vacuum and the residue, redissolved in CHzC12, was filtered on an alumina pad (3 x 5 cm). The red filtered solution was evaporated t o dryness under reduced pressure and the residue crystallized from CHzClz layered with n-pentane at -20 "C to yield 40 mg (32%)of Sa; mp 147-149 "C dec. Anal. Calcd for C~lH16FezN203:C, 55.31; H, 3.54. Found: C, 55.33; H, 3.90. IR (CH2C12) (cm-l): v(C0) 1992 s, 1954 mw, 1798 m; v(CN) 2166 w. lH NMR (CDCl3; 6): 7.3-6.9 (m, 5 H, Ph), 5.4 (s, 1 H, NH), 4.9 (s, 10 H, CP); 13CNMR (CDzC12; 6): 267.0 (p-CO); 211.8 ((30);147.0, 117.1, 130.3, 121.0, 124.9 (Ph); 91.8 (cp). Synthesis of [Fe2(CO)z(cp)zOl-CO){p-C(CN)N(H)Pr')l (Sb). The reaction of l a with H2NPr' following the same procedure above described for the preparation of Sa has allowed us to detect, but not to isolate, the compound Sb. IR (CH2C12)(cm-l): v(C0) 1977 s, 1943 mw, 1786 m; v(CN) 2167

Found: C, 48.52; H, 4.10. IR (CH2Clz) (cm-'): v(C0) 1929 s, 1716 S. 'H NMR (CDCl3; 6): 4.62, 4.38 (s, 10 H, CP), 3.25 (s, 4 H, NCHz), 6.24 (5, 2 H, NH). 13C NMR (CDzC12; 6): 290.8 h-CO), 215.0 (CO), 222.6 @-C), 86.7, 86.5 (Cp), 45.9 (CH2). Reaction of l a with NJV-Dimethylethylenediamine.A solution of l a (0.11 g, 0.185 mmol) in MeCN (10 mL) was treated with NJV-dimethylethylenediamine (0.3 mL, 2.73 mmol). m e r 10 min the mixture was worked up as described for the preparation of type 7 complexes. Attempts to crystal(12) have lize the product [F~Z(CO)~(C~)~{CN(CH~)~NM~~}] been unsuccessful. IR (CHzC12) (cm-l): v(C0) 1989 w, 1948 s; v(CN) 2138 w, 1748 s. Reaction of l a with N,N-Dimethylethylenediamine. NJV-Dimethylethylenediamine(0.3mL, 2.73 mmol) was added to a solution of l a (98 mg, 0.17 mmol) in MeCN (10 mL) and the mixture was stirred for 10 min. Then the solvent was removed under vacuum yielding the complex [Fe2(COMcp)z@CO){p-C(CN)N(Me)(CH2)2NHMe}l (13) as a red oily residue. IR (CH2C12)(cm-l): v(C0) 2004 s, 1969 w, 1801 m; v(CN) 2147 W.

X-ray Structure Determination of trans-[Fez{C(CN)Nhiz)(CO)(cp)z(u-C0)2](5). Crystal data and details of the data collection for 5 are given in Table 2. The diffraction experiments were carried out at room temperature on a fully automated Enraf-Nonius CAD4 dmactometer using graphitemonochromated Mo Ka radiation. The unit cell parameters were determined by a least-squares fitting procedure using 25 reflections. Data were corrected for Lorentz and polarization effects. No decay correction was necessary. The asymmetric unit was found to contain two independent molecules. The positions of the metal atoms were found by direct methods using the SHELXS 86 program3' and all the non-hydrogen atoms located from difference Fourier syntheses. An empirical absorption was applied by using the azimuthal scan method.38 The cyclopentadienyl rings were treated as rigid groups (C-C 1.42, C-H 0.96 A) and presented positional disorder in both molecule A and B. They were disordered ca. 53 and 47% W. (C(15A)-C(19A) and C(151)-C(191)), 51 and 49% (C(20A)Reaction of l a with NHs. Gaseous ammonia was slowly C(24A) and C(201)-C(241)), 52 and 48% (C(15B)-C(19B) and bubbled into a MeCN solution (10 mL) of l a (0.52 g, 0.90 mmol) C(152)-C(192)), and 50 and 50%(C(20B)-C(24B) and (3202)for 15 min. An IR inspection of the mixture showed v(C0) (3242)). The hydrogen atoms of the diisopropyl amino ligand absorptions at 1983 s, 1949 w, and 1792 m and v(CN) at 2173 were located from difference-Fourier maps, and their positional w cm-l which are in agreement with the formation of [Fezparameters were allowed to refine. The refinement proceeded ( C O ) ~ ( C ~ ) Z ( ~ - C O ) C ~ - C ( C(9). N ) NAny H ~ )effort ~ to isolate the by full-matrix least-squares calculations (SHELX 76)39using compound failed because of extensive decomposition to [Feanisotropic thermal parameters for all the non-hydrogen atoms (CO)z(cp)(C". except the cyclopentadienyl C atoms. The H atoms of the Synthesis of [F~~(CO)~(C~)~O~-CO){~-C(CN)N(H)C(O)amino group were assigned fured isotropic thermal parameters Me}] (10). A solution of l a (0.52 g, 0.90 mmol) was treated 1.3 times U, of the carbon atoms to which they were attached. with NH3 as above described. The mixture was then treated The cyclopentadienyl H atoms were assigned a fured isotropic with CH3COC1 (71 mg, 0.90 mmol) and pyridine (72 mg, 0.90 thermal parameter (0.08&) . The final difference Fourier map mmol) and stirred for 10 min. The solvent was then removed showed peaks not exceeding 0.54 e A-3. The final positional in uacuo, and the residue, redissolved in CHzC12, was chroand equivalent isotropic thermal parameters with their e s d s matographed on an alumina column. A first green fraction are given in Table 3. containing traces of an unidentified product was discharged; a second red fraction was eluted with CHsCN, collected, and evaporated to dryness. Crystallization from CHzCl2 layered Acknowledgment. This work was supported by the with n-pentane at -20 "C afforded 0.28 g (73%)of 10, mp 159MURST (Minister0 dell'Universita e della Ricerca Sci160 "C dec. Anal. Calcd for C17H14Fe2N203: C, 48.39; H, 3.34. entifica) and the CNR (Consiglio Nazionale delle Found: C, 48.42; H, 3.30. IR (CH2C12)(cm-l): v(C0) 1998 s, Ricerche). 1959 w, 1808 m, 1678 mw; v(CN) 2170 w. 'H NMR (CDC13; 6): 6.79 (s, 1H, NH), 4.95 (s, 10 H, cp), 1.92 (s, 3 H, Me). Supporting Information Available: Tables of H coorNMR (CD2C12; 6): 264.9 (p-CO), 211.5 (CO), 168.2 (NCOMe), dinates, anisotropic thermal parameters, and bond lengths and 131.5 (CN), 130.7 ( p - 0 , 91.9 (Cp), 23.4 (Me). angles and ORTEP diagrams (12 pages). Ordering information Synthesis of [Fe~{CN~H)(CH~)~N~H)}(CO)(cp)~~-CO)~l is given on any current masthead page. (11). Ethylenediamine (0.10 mL, 1.50 mmol) was added to a OM950356X solution of l a (0.24 g, 0.42 mmol) in MeCN (10 mL), and the mixture was stirred for 15 min. Then the solvent was removed (37) Sheldrick G. M. SHELXS 86, Program for Crystal Structure under vacuum and the residue, redissolved in CHzC12, was Solution, Gottingen, 1986. filtered on an alumina pad. Evaporation of the solvent t o (38) North, A. C.; Philips, D. C.; Mathews, F. S.Acta Crystallogr. minimum volume and addition of Et20 gave, upon standing 1988, A24,351. at -20 "C, red crystals of 11 (70 mg, 43%), mp 189-190 "C (39) Sheldrick G. M. SHELXS 76, Program for Crystal Structure dec. Anal. Calcd for c1~H16Fe~N203:c, 48.53; H, 4.07. Determination, University of Cambridge, 1976.