Synthesis and alkylation of [Fe(CN)2(C5H5)(CO)]−, [Mo(CN)2(C5H5)(CO)2]−, [W(CN)2(C2H5)(CO)2]− and [W(CN)(C5H5)(CO)3]−

Chem., 1963, Vol. 25, pp. 179 CO 185. Pergamon

J. Inorg. Nucl.

SYNTHESIS

AND

Press

ALKYLATION

Ltd. Printedin NorthernIreland

OF

[Fe(CN),(C,H,)(CO)]-,

W(CN),GH,)(CO),land [W(CN)(GH,)(CO)31-

[Mo(CN),(C,H,)(CO),l-,

C. EUGENE COFFEY Explosives Dept., E. I. du Pont de Nemours & Co., Wilmington, Delaware Abstract-[Fe(CN),(C,H,)(CO)]was best prepared by reacting [FeBr(C,H,)(CO),] with potassium cyanide in aqueous ethanol. Two other syntheses were also found. Alkylation of the anion with and alkyl halides gave two series of isocyanide complexes: neutral [Fe(CN)(C,H,)(CO)(CNR)] cationic [Fe(C,H,)(CO)(CNR)]+. The reaction of potassium cyanide with [WCl(C,H,)(CO),] gave [W(CN)(C,H,)(CO),I and K[W(CN),(C,H,)(CO),I; ~~oClGH6)(COM gave only Kb400% (C,H,)(CO),]. Alkylation of the tungsten monocyanide complex with methyl iodide gave the isocyanide complex [W(C,H,)(CO),(CNCH,)]I and alkylation of the molybdenum dicyanide complex gave [Mo(C,H,)(CO),(CNCH,)& Attempts to form other cyclopentadienyl-carbonyl-cyanide complexes were unsuccessful. THE union of mixed

of metal

ligand

complexes

carbonyl

chemistry.

in which

with

arene-metal

(l) However,

chemistry

little attention

one or more carbonyl

ligands

are replaced

In particular,

no arene-carbonyl-isocyanide complexes in the literature. complex t2) have appeared

cyanide

This paper plexes

of iron,

isocyanide

reports

the synthesis

molybdenum

complexes

and

of four tungsten

has produced

a fertile

area

has been given to arene-carbonyl by carbonyl-like

ligands.

and only one arene-carbonyl-

cyclopentadienyl-carbonyl-cyanide and the alkylation

of these

comcomplexes

to

of two kinds. RESULTS

Cyano-cyclopentadienyl-carbonyl complexes. Potassium dicyanocyclopentadienylcarbonyliron (II) was best obtained through the reaction of potassium cyanide with bromocyclopentadienyldicarbonyliron(II)~3) in aqueous ethanol according to (1). The [FeBr(C,H,)(CO),]

f- 2KCN ---f K[Fe(CN),(C,H,)(CO)]

_t CO $ KBr

(1)

complex also resulted from the oxidation of K2[Fe(CN)e(C5H,)(CO)](4) with bromine. A third route was afforded by the reaction of potassium cyanide with cyclopentadienyldicarbonylironchloromercurate(II)(5) as shown in (2). HgCl[Fe(C,H,)(CO),]

f 2KCN 2~ K[Fe(CN),(C,H,)(CO)]

+ Hg + CO i- KC1

(2)

The potassium salt of the complex is stable in air, very soluble in water and sparingly soluble in polar organic solvents. Aqueous solutions of the complex gave insoluble precipitates with silver nitrate, mercuric chloride and dimethyltin dichloride. (Ii TWO recent reviews discuss arene-metal complexes:

(a) G. WILKINSON and F. A. COLON in Progress in Zno
180

C. EUGENE COFFEY

Acidification of aqueous solutions of the complex precipitated the somewhat airsensitive parent acid: H[Fe(CN)2(CsHs)(CO)]. The ammonium salt of the complex was prepared by passing anhydrous ammonia into a solution of the complex in ethanol. Potassium cyanide reacted with an equimolar quantity of [WCI(CsHs)(CO)a] in aqueous methanol to produce the monocyanide complex as shown in (3). The [WCI(CsHs)(CO)s] + KCN-~- [W(CN)(CsH~)(CO)s] -1- KC1

(3)

corresponding molybdenum monocyanide complex could not be isolated from the products of the reaction of [MoCI(CsHs)(CO)~]Iz) with potassium cyanide. However, with two moles of potassium cyanide the chloro complexes of both tungsten and molybdenum reacted as shown in (4). [MCI(CsH~)(CO)3] + 2KCN -~. K[M(CN)2(CsHs)(CO)2] + KC1 + CO

(4)

The tungsten monocyanide complex was photo-sensitive but stable to air and water. It was shown to be monomeric in benzene and a non-electrolyte in nitrobenzene. Both the molybdenum and tungsten dicyanide complexes were obtained as very hygroscopic yellow powders which were difficult to free of solvent. Their identification rests on the infrared spectra and the conversion of the molybdenum complex to an isocyanide derivative (below) which was easily characterized. Although [Co(C~Hs)(CO)2] (6)was readily attacked by potassium cyanide, apparently producing K[Co(CN)(CsHs)(CO)], we were unable to isolate the product in a pure state. Surprisingly, the complexes [Mn(CH3CsH4)(CO)a ] and [Cr(CO)8 (mesitylene)] (~) were not attacked by potassium cyanide in refluxing aqueous ethanol. Alkylation reactions. Alkylation of K[Fe(CN)2(CsH~)(CO)] was carried out with a variety of alkyl bromides and iodides. Alkyl chlorides reacted too slowly to make the reaction practical and aromatic halides did not react at all. Alkylation of the tungsten and molybdenum complexes was attempted only with methyl iodide. Refluxing the complex iron salt for several hours in acetronitrile with an equimolar quantity of alkyl halide gave monoisocyanide complexes according to (5). This K[Fe(CN)2(CsHs)(CO)] + RX--+ [Fe(CN)(CsHs)(CO)(CNR)] .q- KX

(5)

reaction was carried out with R -- allyl, benzyl, p-chlorobenzyl, p-carbethoxybenzyl and triphenyl-methyl. These isocyanide complexes were insoluble in water but soluble in organic solvents. Air oxidation of the complexes occurred over a period of days but the complexes were immediately decomposed in solution by base, and cyanide ion in particular, with liberation of free isocyanide. Alkylation of the iron complex in acetonitrile with excess alkyl halide gave cationic diisocyanide complexes as shown in (6). Complexes were obtained with R = methyl, K[Fe(CNh(C~Hs)(CO)] + 2RX ~ [Fe(CsHs)(CO)(CNRh]X + KX

(6)

allyl and benzyl. These ionic complexes were soluble in water and polar organic ~) T. S. PIPER, F. A. COTTON and G. WILKINSON,J. Inorg. Nucl. Chem. 1, 165 (1955). tT) B. NICHOLLS and M. C. WHITING, Proe. Chem. Soc. 152 (1958).

Synthesis and alkylation

181

solvents and had about the same stability to air and bases as the monoisocyanide complexes. The methyl and benzyl complexes had conductivities in water and nitrobenzene which were consistent with the proposed ionic structure. The tungsten complex [W(CN)(CsHd(CO)3] was methylated by methyl iodide in acetonitrile to give [W(CNCHa)(CsHs)(CO)3]+I - as a water soluble, photosensitive solid. Attempts to alkylate K [W(CN)e(CsHs)(CO)2] were unsuccessful but K[Mo(CN)2 (CaHs)(CO)2] was easily methylated to [Mo(CsHs)(CO)2(CNCHa)2]I. The molybdenum and tungsten isocyanide complexes were stable to air but rapidly decomposed in solution by bases. DISCUSSION Two cyclopentadienyl-cyanide complexes were known prior to this work. PIPER and WILKINSON(2) made [Fe(CN)(CsHs)(CO)2] by treating [FeBr(CsH6)(CO)2] with potassium cyanide in ethanol and THOMAS(4) prepared the monovalent iron complex, K2[Fe(CN)2(CsH~)(CO)], by the reaction of potassium cyanide with [Fe(CsHs)(CO)2] z. No cyclopentadienyl-isocyanide complexes have been reported in the literature. The attack of cyanide ion on [FeBr(CsH~)(CO),,] displayed an interesting specificity. In ethanol cyanide ion displaced the bromide ion exclusively and the resulting uncharged complex was inert to (or reacted very slowly with) cyanide ion. In 50 per cent aqueous ethanol, however, both the bromide and one carbon monoxide were displaced, giving a negatively charged dicyano complex. The latter complex was only slightly decomposed (to ferricyanide) by treatment with aqueous potassium cyanide at 200 ° for 2 hr. This extreme resistance to attack by cyanide ion can only be partially explained as a consequence of electrostatic repulsion between the two negatively charged reactants; the reaction of CN with [Cu(CN),,] , for example, proceeds rapidly. Possibly the explanation lies in the relative rr-acceptor capabilities of CO and CN . The cyanide ligand is a less effective 7r-acceptor than CO and thus will tend to increase the negative charge on iron and increase the amount of ,-r-bonding from iron to CO. Both effects would oppose displacement of the last CO by C N . The alkyJation of cyanide complexes by alkyl halides is a well-known route to isocyanide complexes (s) and has been of recent interest in this larobatory.(9,1°) Alkylation of [Fe(CN)2(CsHs)(CO)]- proceeded readily and gave two series of complexes, neutral [Fe(CN)(CsHs)(CO)(CNR) ] and cationic [Fe(C~Hs)(CO)(CNR)2] ~. Methylation of [W(CN)(C~Hs)(CO) ~] and [Mo(CN).~(CsHs)(CO)2]- was carried out without difficulty. Surprisingly, we were unable to methylate [W(CN)z(CsHs)(CO)2]-. (The reaction mixture contained [W(CsHs)(CO)z(CNCHz)]I, starting material and decomposition products.) The isocyanide complexes prepared in this work are unique in having both cyclopentadienyl and isocyanide ligands attached to the central metal ion and the isocyanide complexes of tungsten and molybdenum appear to be the first divalent isocyanide complexes of these metals. The complexes [Fe(CN)(C.~Hs)(CO)(CNR) ] are interesting in that all four ligands attached to iron are different. It follows that these complexes must exist as enantiomorphic pairs unless all of the metal-ligand bonds are coplanar. No attempt was ~s)A comprehensivereview of metal isocyanidecomplexes is given by L. MALAXESTAin Progress in Inorganic Chemistry, (Edited by F. A. COTXON). pp. 283-379. Interscience,New York (1959). ~9~W. Z. HELDT,In press. Presented in part at the sixth International Conferenceon Co-ordination Chemistry, held at Wayne State University, Detroit, Michigan, August, 1961. ~9~j. A. C. ALHSON. Unpublished work.

C. EUGENE COFFEY

182

m a d e to separate optical isomers in this work, b u t one of the complexes described below, [Fe(CN)(CsHs)(CO)(CNCH2C6H4COOH)] , should be capable of resolution t h r o u g h salt f o r m a t i o n with a n optically active base. Infra-red spectra of the iron complexes provided a clear delineation between the three types of complex: anionic, n e u t r a l m o n o a l k y l a t e d a n d cationic dialkylated. Bands observed in the 2000 cm -1 region are given in Table 1. The characteristic b a n d s of t e r m i n a l metal carbonyl, cyanide a n d isocyanide ligands fell in rather n a r r o w a n d n o n - o v e r l a p p i n g regions of the spectrum. (The splitting of the metal c a r b o n y l b a n d in K[Fe(CN)2(CsHs)(CO)] m u s t arise from crystal effects.) Infra-red spectra of the m o l y b d e n u m a n d t u n g s t e n complexes are described in the E x p e r i m e n t a l section. TABLE 1.*--INFRA-REDBANDS(cm-1) IN 2000 cm-1 REGION Complex

CO

CN

1950,1970 1990

2080 2100, 2135

1970 1980 2000 1975 1990 1990

2090 2100 2115 2105 2110 2090

CNR

Anionic K[Fe(CN)2(CsHs)(CO)] H[Fe(CN),(CsHs)(CO)] Neutral [Fe(CN)(C~Hs)(CO)(CNCH2CH--CH~)lt [Fe(CN)(C~Hs)(CO(CNCH2C6Hs)]t [Fe(CN)(CsHs)(CO(CNCH2C6H,C1)] [Fe(CN)(C~Hs)(CO)(CNCH2CsH4COOC~Hs)] [Fe(CN)(CsHs)(CO)(CNCH2CeH,COOH)] [Fe(CN)(C~Hs)(CO)(CNC(C6Hs)s)]

2170 2185 2205 2200 2180 2140

Cationic [Fe(CsHs)(CO)(CNCH3)2]I [Fe(CsHs)(CO)(CNCH2CH=CH2)2]Br [Fe(CsHs)(CO)(CNCH2CsHs)2]Br

2000 2010 2010

2200 2200 2200

* Spectra were taken in KBr disc except where noted t Spectrum of thin film of oil between KBr plates EXPERIMENTAL All materials were commercially available unless otherwise noted. Infra-red spectra were recorded on a Perkin-Elmer "lnfracord". Potassium Dicyanocyclopentadienylcarbonylferrate (II). A cooled mixture of 35.4 g (0.100 molz) of [Fe(CsHs)(CO)z]2c11~ in 250 ml of methanol was treated dropwise with 16"0g (0.100 mole) of bromine. The resulting solution of [FeBr(CsH6)(CO)2] was warmed to room temperature, a solution of 50 g (0-77 mole) of potassium cyanide in 250 ml of water was added and the mixture was heated at reflux for 0-5 hr. The cooled mixture was filtered and the filtrate evaporated to dryness at reduced pressure. Extraction of the residue with 300 ml of hot ethanol and addition of a large excess of ether to the solution gave 30-50 g of brown-yellow powder which still contained some potassium cyanide. Recrystallization of a sample of the powder from ethanol gave golden brown crystals soluble in water and insoluble in chloroform. The solid complex was stable in air for weeks, but in hot solution it was noticeably oxidized in a few minutes. (Found: C, 40.6; H, 2"12; N, 11-85. Calcd. for CsHsNa. OFeK" C, 40.0; H. 2-10; N, 11"68~). This complex was also made by the following method. A mixture of 14.2 (0"040 mole) of [Fe(CsH~). (CO)z]~ and 20"8 g (0-32 mole, 100 per cent excess) of potassium cyanide in 300 ml of methanol was refluxed for 15 min and then cooled and a solution of 6.4 g (0"040 mole) of bromine in 50 ml of methanol was added dropwise. The mixture was stirred for 15 min and then filtered and the filtrate evaporated at reduced pressure. Extraction of the residue with hot ethanol and addition of excess ether gave a 45 per cent yield of the crude complex. {11)

W. E. CATLINand J. C. THOMAS,U.S. Pat. 2810736.

Synthesis and alkylation

183

The complex also resulted from reaction (2). A mixture of 11.55 g (0.028 mole) of HgCI[Fe(CsH~) (CO)s] and 8 g of potassium cyanide in 150 ml of 1:1 ethanol-water solvent was refluxed for 0"5 hr. During the reflux period, the complex slowly dissolved and gave a red-brown solution. The cooled solution was filtered to remove 5.40 g (94 per cent of theory) of mercury. Isolation of the complex as in the preceding examples gave a 65 ~ yield of crude complex. Hydrogen dicyanocyclopentadienylcarbonylferrate (II). Addition of concentrated hydrochloric acid to a cooled, filtered, aqueous solution of K[Fe(CN)2(CsHD(CO)] precipitated the complex acid as a yellow microcrystalline powder. Recrystallization from ethanol-ether gave dark yellow needles which darkened somewhat but did not melt at 250 °. (Found: C, 47-64; H, 3.33; N, 13'41. Calcd. for CsH6N~OFe: C, 47"56; H, 3-00; N, 13'88~). Ammonium dicyanocyclopentadienylcarbonv(ferrate (II). Addition of excess ether to a filtered, ammonia saturated, ethanolic solution of H[Fe(CN)2(C~H~)(CO)] precipitated the ammonium salt as a yellow, microcrystalline powder. Recrystallization from ethanol-ether gave yellow crystals soluble in water, alcohol and polar organic solvents but insoluble in ether and benzene. This salt is more airsensitive than the potassium salt, but it is also more convenient to use since it is easier to purify and is much more soluble in organic solvents. (Found: C, 44.05; H, 4"14; N, 19.34; Fe, 25'53. Calcd. for CsHgNaOFe: C, 43-87; H, 4.14; N, 19-19; Fe, 25.48~). Potassium chlorocyclopentadienyltricarbonyltungstate (II). Following FISCHER112~, a mixture of lithium cyclopentadienide (0.11 mole) and tungsten hexacarbonyl (0.10 mole) in 300 ml of dimethylformamide (dried by passing over Linde "Molecular Sieve" 5A) was slowly heated to 100 ° and held there for 2 hr. To the resulting cooled solution of Li[W(CsHs)(CO)3], under nitrogen, there was added 300 ml of water, 500 ml of ether and 7 ml of acetic acid, precipitating light yellow air sensitive H[W(C~H~)(CO)~]. Addition of 30 ml of carbon tetrachloride to the stirred mixture caused the yellow precipitate to disappear within 5 min and the red colour which developed was extracted largely into the ether phase. The phases were separated and the water layer washed twice with 100 ml portions of ether and then the combined ether phases were dried over sodium sulphate. EvaporatiOn of solvent gave a brown residue which was taken up in 150 ml of acetone and stirred with activated charcoal for 0.5 hr at room temperature. Addition of water to the filtered solution until a solid appeared on the surface, followed by cooling overnight at 0 °, gave deep red crystals, m.p. 160 ° (dec.). A second crop of crystals from the mother liquor gave a total yield fo 28-8 g (78 per cent). (Found: C, 26.07; H, 1.38. Calcd. for CsHsOzClW: C, 26.08; H, 1.36~). This procedure which is an adaptation of FISCHERS'SIlz~ preparation of Li[Mo(CsH~)(CO)3] and WILKINSON'S~13~oxidation of the lithium salt to the chloride, also gave [MoCI(CsHs)(CO)8] in 80 per cent yield. Attempts to prepare [CrCI(CsHs)(CO)3] by this method were unsuccessful. Potassium dicyanocylopentadienyldicarbonylmolybdate (II). A solution of 7 g (0.025 mole) of [MoCI(CsHs)(CO)3] and 3"30 g (0'051 mole) of potassium cyanide in 180 ml of methanol was warmed to reflux and held there (0.5 hr) until no more gas was evolved. About one mole of carbon monoxide was evolved per mole of complex. The cooled solution was filtered and the residue washed with methanol. Evaporation of solvent from the combined filtrates left an oily mixture of white and yellow solids. Extraction of this residue with 200 ml of ethanol and evaporation of the solvent gave 6-0 g (80 per cent) of yellow powder after washing with ether and drying in vacuo. The powder was very hygroscopic and good analytical data were not obtained. An infra-red spectrum showed broad metal carbonyl peaks at 1875 cm t and 1960 cm ~ and cyanide peaks at 2060 cm -~ and 2090 cm a, in agreement with the proposed structure. Potassium dicyanocyclopentadienyldicarbonyltungstate (11). Application of the preceding procedure to [WCI(CsHs)(CO)3] gave a yellow solid. Chromatography of an ethanol solution of the mixture on alumina gave two bands, one eluted by ethanol and the other eluted by water. The ethanol band contained the monocyanide described below. Evaporation of solvent from the water band gave a yellow residue which was taken up in ethanol. The solution was filtered and then evaporated to a yellow powder which was washed with methylene chloride and dried in vacuo. This material was also very hygroscopic. An infra-red spectrum showed metal carbonyl bands at 1860 and 1950 cm- t and an incompletely resolved cyanide doublet at 2085, 2100 cm -1. Except for the smaller splitting of the cyanide bands, the spectrum (from 2.5 to 15 ~) was very similar to that of the analogous molybdenum complex. Cyanocyclopentadienyltricarbonyltungsten (II). A stirred solution of 37 g (0.10 mole) of [WCI (C5H.0(CO)3] in 200 ml of ethanol was brought to reflux in a flask shielded from light and then a solution of 7 g (0-11 mole) of potassium cyanide in 25 ml of water was added dropwise during 0-5 hr. About 0.016 mole of carbon monoxide was evolved during 1.3 hr at reflux. The cooled solution was evaporated to near dryness and extracted with chloroform. Chromatographing this solution on alumina gave a yellow band eluted by ethanol. Evaporation of solvent and crystallization of the f121 E. O. FISCHER, W. HAFNER and H. O. STAHL, Z. Anorg. Chem. 287, 47 (1955). i131 T. S. PIPER and G. WILKINSON,Naturwisserchaften 42, 625 (1955).

184

C. EUGENE COFFEY

residue from chloroform-petroleum ether and then from benzene gave orange, light senstive crystals, m.p. 201-5-202 °. An infra-red spectrum showed metal carbonyl bands at 1970 cm x (vs) and 2060 cm -1 (s) and a cyanide band at 2120 cm -1 (m). The complex was a non-electrolyte in nitrobenzene. (Found: C, 30"!8; H, 1.40; N, 4-11 ; W, 51.10; mol. wt., 377 in benzene. Calcd. for CgHsNO~W: C, 30-11 ; H, 1'40; N, 3-90; W, 51'23~; mol. wt. 359). Cyclopentadienylcarbonyl-bis-(methyl isocyanide)iron (II) iodide. A mixture of 4.8 g (0"020 mole) of K[Fe(CN)2(C~H~)(CO)] and 30 ml of methyl iodide in 150 ml of acetonitrile was reftuxed for 20 hr. The resulting solution was filtered and evaporated to dryness under reduced pressure. After taking the residue up in methylene chloride, the solution was filtered and excess petroleum ether was added to precipitate 5"4 g (75 per cent yield) of yellow powder. Recrystallization from chloroform-hexane gave small yellow crystals, m.p. 220-1 ° (dec.), soluble in water and all but least polar organic solvents. The complex had a molar conductance of 91 in water (23 °, 1-00 × 10 -a molar) but the odour of isocyanide over the solution showed that some decomposition had occurred. In nitrobenzene the molar conductance was 28.1 (23 °, 1"99 × 10-a molar). (Found: C, 33.25; H, 3'16; N, 8.11. Calcd. for C10HllN2OFeI: C, 33.45; H, 3"09; N, 7-81~). Cyclopentadienylcarbonyl-bis-(allyl isocyanide)iron (II) bromide. A mixture of 7.2 g (0.030 mole) of K[Fe(CN)~(CsHs)(CO)] and 8.5 ml (about 0"1 mole) of allyl bromide in 175 ml of acetonitrile was refluxed for 18 hr. The solution was filtered and evaporated to dryness and the residual thick oil was taken up in acetonitrile. This solution was filtered, excess ether was added and the solution was allowed to stand about 4 hr until the oil crystallized. Recrystallization from acetonitrile-ether gave a 35 per cent yield of yellow-brown crystals, m.p. 110-13 °, with a powerful isocyanide odour. (Found: C, 46.38; H, 4"26; N, 7.62. Calcd. for C14H1~NzOBrFe: C, 46"31; H, 4'16; N, 7-71 ~). Cyclopentadienylcarbonyl-bis-(benzyl isocyanide)iron (II) bromide. A mixture of 80 g (0.33 mole) of K[Fe(CN)2(CsHs)(CO)] and 100 ml (about 20 per cent excess) of benzyl bromide in 300 ml of acetonitrile was refluxed for 12 hr and then cooled, filtered and evaporated to dryness. Crystallization from acetonitrile-:ether gave an oil which crystallized on standing. Recrystallization from the same solvent gave 112 g (72 per cent yield) of golden-yellow crystals, m.p. 132-5-133"5 °, soluble in polar solvents. The complex had molar conductances of 89.7 (0"995 × 10 a molar), 122 (0-199 x 10-3 molar) and 121 (0.398 × 10 4 molar) in water at 23 °. In nitrobenzene the conductance was 24.6 (23 °, 0-199 × 10 -3 molar). (Found: C, 57.05; H, 4.10; N, 5"91; Fe, 12.0. Calcd. for Cz2H~aN2OBrFe: C, 57.06; H, 4.14; N, 6.06; Fe, 12.1%). Cyanocyclopentadienylcarbonyl(p-carbethoxybenzyl isocyanide)iron (II). A mixture of 2-4 g (0'010 mole) of K[Fe(CN)z(C~H~)(CO)] and 2-45 g (0.010 mole) ofp-carbethoxybenzyl bromide in 100 ml of acetonitrile was refluxed overnight and then the solvent was evaporated at reduced pressure. Addition of petroleum ether to a methylene chloride solution of the residue precipitated oily yellow crystals which were recrystallized from methanol-water as a mustard-yellow powder (50 per cent yield), m.p. 166-166.5 °. The complex showed the expected phenyl and carboxylic ester peaks in the infra-red and was soluble in most organic solvents. (Found: C, 59'49; H, 4-63 ; N, 7"42. Calcd. for ClsH~N~O3Fe: C, 59"36; H, 4-43; N, 7"69 ~). Cyanocyclopentadienylcarbonyl(p-carboxybenzyl isocyanide)iron (II). Hydrolysis of the ester group in the preceeding complex was accomplished by heating at 100 ° in 0.4 molar hydrochloric acid for 6 hr. After this treatment, two-thirds of the complex had dissolved. Isolation of the acid and recrystallization from ethanol-water gave a 52 per cent yield of yellow crystals, m.p. 167'5-168-5 °. An infra-red spectrum showed a carboxylic acid. (Found: C, 56.52; H, 4-04; N, 7.76; Fe, 16'70. Calcd. for C,6H~N~O~Fe: C, 57-17; H, 3.60; N, 8-34; Fe, 16.62~). Cyanocyclopentadienylcarbonyl(p-ehlorobenzyl isocyanide)iron (II). Reaction of equimolar quantities of K[Fe(CN)z(C~Hs)(CO)] and p-chlorobenzyl bromide in acetonitrile for 16 hr followed by the usual work-up gave yellow crystals contaminated with a tarry impurity. Purification by chromatography of a benzene solution of the product on alumina and recrystallization of the major component gave yellow crystals, m.p. 113-15 °. (Found: C, 55.10; H, 3.58; N, 8-60; Fe, 16-92. Calcd. for C15H~lN~OCIFe: C, 55.16; H, 3-40; N, 8'58; Fe, 17'10~o). Cyanocyclopentadienylcarbonyl(triphenylmethyl isocyanide)iron (II). A mixture of 2.4 g (0-010 mole) of K[Fe(CN)~(CsHs)(CO)] and 3.3 g (0.010 mole) of triphenylmethyl bromide in 75 ml of acetonitrile was refluxed for 16 hr. Evaporation of solvent left a glass which was extracted with methylene chloride and precipitated with petroleum ether. Recrystallization from methyl ethyl ketone-petroleum ether gave a 50per cent yield ofyellow brown crystals, m.p. 181-3 ° (dec.). (Found: C, 73.33; H, 4-79; N, 6.11. Calcd. for C~TH2oN2OFe: C, 72-98; H, 4-54; N, 6"31~o). Cyanocyclopentadienylcarbonyl(benzyl isocyanide)iron (II). This complex was obtained as a brown oil by the reaction of equimolar quantities of K[Fe(CN)2(CsHs)(CO)] and benzyl bromide in acetonitrile followed by the usual work-up. The identity of this and the following complex rests on the infra-red spectra (see Table 1 for the 2000 cm -x region) since they could not be purified by recrystallization or distillation.

Synthesis and alkylation

185

C),anocyclopentadienylcarbonvl(allyl isoc),anide)iron (II). This complex was obtained as a viscous brown oil from the reaction of equimolar quantities of allyl bromide and K[Fe(CN)2(C~Hs)(CO)] followed by the usual work-up. CyclopentadienylearbonyLbis-(meth),l isoe),anide)molybdenum (II) iodide. A mixture of 3-1 g (0.01 mole) of K[Mo(CN)2(CsHs)(CO)~] and 10 ml of methyl iodide in 100 ml of acetonitrile was refluxed overnight. The resulting solution was evaporated to dryness and the residue was extracted with hot methylene chloride. Addition of petroleum ether precipitated a yellow powder which was reprecipitated from acetonitrile by addition of ether to produce a mustard yellow, microcrystalline powder, m.p. 180-2 °. An infra-red spectrum showed metal carbonyl bands at 1945 and 2000 cm 1 and an incompletely resolved isocyanide doublet at 2185, 2200 cm ~. (Found: C, 30.94; H, 2.80; N, 6-57. Calcd. for Cl~HllN20~IMo: C, 31"00; H, 2.61; N, 6-57~/o). Attempts to alkylate K[W(CN)2(CsHs)(CO)2] by this procedure gave only small yields of the monoisocyanide complex described below. Cyelopentadienyltricarbon),l(meth),l isoeyanide)tungsten (II) iodide. A solution of 5 g of [W(CN) (C5H5)(CO)3] and 50 ml of methyl iodide in 100 ml of acetonitrile was refluxed for 14 hr in darkness. The cloudy solution was then filtered and evaporated to 5.2 g of residue which was taken up in chloroform and chromatographed on alumina. Ethanol eluted a band containing 4.25 g of starting complex. A second band remained on the column and was removed manually. Extraction of the second band with acetonitrile and precipitation with ether gave 0.41 g of light sensitive, yellow powder which melted at 153.0 153.2 ° with gas evolution, resolidified at 158 ° and remelted at 191-5 ° (dec.). The yield, based on 0.75 g (0.002l mole) of starting material, was 39 per cent. An infra-red spectrum showed metal carbonyl bands at 1985 cm 1 (vs) and 2080 cm -1 (s) and an isocyanide band at 2230 cm ~ (m). (Found: C, 23.76; H, 1.72; N, 3.24; W, 36.42. Calcd. for C~0HsNO31W: C, 23.97; H, 1.61; N. 2-80: W, 36-70 og). Acknowledgements--The

author is grateful to Dr. H. M. HUBBARD for reviewing the manuscript and to Dr. J. A. C. ALLISON and Dr. W. Z. HELm for valuable discussions.