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Five-coordinate isomers of pentakis(aromatic isocyanide)cobalt(I)
,1 inor~, ntwl Chem.. 197~, Vol. q7 pp. 703-707. Pergamon Press. Printed in Great Britain
FIVE-COORDINATE ISOMERS OF PENTAKIS(AROMATIC ISOCYANIDE)COBALT(I) C. A. L. BECKER Department of Chemistry, Kentucky State University, Frankfort, Ky 40601 (First received 4 June 1974; in final form 8 July 1974) Abstraet--Pentakis (phenyl- and para-substituted phenylisocyanide)cobalt(I) has been re-crystallized from various solvent types to study further the five-coordinate conformational isomerism observed for [Co(CNC6H~)~]CIO4 re-crystallized from chlorohydrocarbons. Characterization is primarily through the -N-=C i.r. pattern and proton-NMR. Perchtorate and tetrafluoroborate salts are used. The aromatic isocyanides include C~H,NC, p-FC~H,NC, p-CIC6H4NC,p-BrC6H4NC, p-IC6H4NC, and p-CH3C6H4NC.Three isomeric structures are maintained with phenylisocyanide but only one geometry is observed with para-substituted phenylisocyanides. INTRODUCTION FIVE-COORDINATE cobalt(I) complexes of isocyanides are well established[l-6]. Pentakis(methylisocyanide)cobalt(I) perchlorate was predicted[7], and later established[8], to be trigonal bipyramidal. For pentakis(phenylisocyanide)cobalt(I) perchlorate, however, recrystallization procedure apparently determines stereochemistry. Re-crystallization from chlorohydrocarbons, in which solubilities appear abnormally high, leads to two series of solvent-adducted complexes (types I and II) Characterized by distinctly different -N-=C i.r. patterns [9, 10]. Rapid re-crystallization of [Co(CNC6Hs)qC104. HCC13 from methanol/water or methanol/vacuum affords the non-adducted [Co(CNC6H~)5]C10~ (type III), with a third distinct -N=C i.r. pattern, while slow precipitation from methanol/water or ethanol/water results in a type I hydrogen chloride adduct, [Co(CNC6H0~]CIO4. HCI[9(b), 10]. Distinctly different Co ~ NQR signals have also been observed for types I and Ill complexes, but no signals have been observed for type II [11]. Square pyramidal coordination was initially suggested for type I complexes[9a], with trigonal bipyramidal and intermediate structures postulated for types II and III, respectively[9b]. The [Co(CNC6H~)~]CIO4. HCCI3, the prototype type I complex, has been shown to be square pyramidal with crystallographic C4-axis[12], and representative types II and III, [Co(CNC6H~CI-p)5]BF4 (from propionitrile/ether) and [Co(CNC6Hs)~IC10~ (from methanol/vacuum), respectively, both are somewhat distorted trigonal bipyramids [13]. Significant structural differences in these Co(I) complexes have been identified, therefore, via the -N=C i.r. This present work extends re-crystallization studies of [Co(CNC~Hs)5]CIO4 to solvents other than chlorohydrocarbons and establishes analogous or dissimilar re-crystallization behavior for [Co(CNC6Hs)5]BF4 and [Co(CNC6H4X-p)5]C104, BF4. Type III [Co(CNC6H~).dC104,BF4 is used to avoid possible formation of the hydrogen chloride.
EXPERIMENTAL
Solvent purity was routinely checked by NMR; when necessary, distillation was over CaC12or Mg(CIO4)2. Anhydrous diethyl ether was filtered through an alumina column immediately before use. Commercial Nujol was dried over CaC12. Proton-NMR spectra were recorded on a Varian A-60 or HA-100 at ambient temperature using 99.8% deuterated cloroform or 99.5% deuterated dimethylsulfoxide with cyclohexane (61.42) or dichIoromethane (85.28) as secondary internal reference. I.r. spectra were recorded on a Beckman IR-7 as Nujol mulls. Elemental analyses were performed commercially. Aniline and para-substituted anilines were commercially available, except p-IC,HaNH2 which was prepared from aniline, NaHCO3, and iodine in aqueous solution[14] and re-crystallized several times from hot pentane. The N-aromaticformamides were prepared by refluxingthe appropriate aniline with formic acid and toluene[I5], and re-crystallizing from hot toluene. Preparation of aromatic isocyanides Aromatic isocyanides were prepared from the corresponding formamides by modification of the synthesis by Hertter and Corey[16, 17], using p-CH3C6H4SO2CIand (C.,H,)3N, and according to Appel et al.[18], using (C6Hs)3P, CCI,, (C2H~)3Nand HCCI~. The former synthesis gives better yields, while the latter is an overall cleaner reaction. In both syntheses the aromatic isocyanide is purified by vacuum distillation or sublimation. C6HsNC: colorless liquid rapidly discoloring dark green upon standing; distilled 19--22°C (uncorr), -0.1 Torr: -N=-C i.r., 2133cm-1; 'H-NMR, unsplit signal, 67.25 (neat, TMS). pFC~H,NC: yellow-green liquid; distilled 28-30°C (uncorr), --0.I Torr;-N=-C i.r., 2142cm '. p-CIC~H4NC: colorless crystals; sublimed 80-90°C (oil-bath temperature), -0.1 Torr: m.p., 71-73°C (uncorr) decomposition: -N-=C i.r.. 2127 cm ': 'H-NMR, unsplit signal, 87.40 (DCCI3, C~H~2), 87.10 ({CD3}2SO, CH~CI:). pBrC6H4NC: colorless crystals; sublimed 80-90°C, -(I. 1Torr; re.p., 98-99°C (uncorr) decomposition;-N-C i.r., 2127 cm ': 'H-NMR, approximate AB quartet, 6,7.56, 827.28 (DCCI3, C,,H,2), 8,7.25, 827.07 ({CD3}zSO, CHzC12). p-IC6H4NC: colorless crystals; sublimed 100-120°C, -0.1 Torr; m.p., 130-131°C (uncorr) decomposition:-N=-C i.r., 2127cm '; IH-NMR, approximate AB quartet, 8,7.74, 827.10 (DCC13,C6Ht2), 8,7.41, ,~z6.89({CD~}2SO,CH2CI2). p-CH3C~H,NC: colorless liquid: distilled 28-30°C (uncorrL ~0.1 Torr. 703
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C.A.L. BECKER
Preparation of Pentakis(aromatic isocyanide)cobalt(I) The complexes [Co(CNC~Hs)~](CIO~)~. 1.0 H20 (blue), [Co(CNC6H~)~](BF,)2.1.0H20 (blue), [Co(CNC~H4CH3-p)5] (ClO,)2(green), [Co(CNC6H4CH3-p),] (BF,)2.1.0H20 (blue), and [Co(CNC~H_,F-p)5](C104)2(yellow)were prepared by reaction of five moles aromatic isocyanide with C0(C10,,BF4)2.6H20 in 95% ethanol [10, 19-21]; but the BF4- salt with p-FC,H,NC, pC1C~H,NC and p-BrC,H,NC; and the CIO,- salt with pC1C6H,NC, p-BrC~H,NC and p-IC~H4NC; were mixtures of Co(II) and Co(I). Reduction to Co(I) followed several procedures. Anhydrous Co(II) complexes could be reduced in CH2C12/C:H~OH solution[10]. The Co(II)-Co(I) mixtures were reduced by digestion in methanol or ethanol under mild heating[17] or by solution in pyfidine (1.0 gm/10.0nil, exothermic) followed by precipitation with distilled water (2.0 ml). Crude product was re-crystallized from HCCI3/(C2H~)20;phenylisocyanidecomplexes were further
re-crystallized f r o m CH3OH/vacuum (type III) [10]. [CO(CNCd-Is)5]CIO,,BF4: m.p., 144--147°, 109-112°C (uncorr); IH-NMR, unsplit signal, 87.50 fDCCI3, TMS), 87.48 (DCCI3, Cd-I12), multiplet, 87.21 ({CD~}2SO,CH2C12). [Co(CNC,H,CH3p)5]CIO,: m.p., 134-137°C (uncorr); IH-NMR: approximate AB quartet, 817'15, 826'93, and 81.94 ({CD3}2SO, CH~CI2). [Co(CNC6FLF-p)~]CIO,,BF,:m.p., 138-141°, 143-146°C(uncorr), decomposition; IH-NMR, approximate AB quartet split into triplet and quartet, 817'56, 827.13 (DCC13,C6Hn), 817.87, 827"46 ({CD3}2SO,C6Hn). [Co(CNCd-I,CI-p)5]CIO,,BF,:m.p., 183-186°, 191-193°C (uncorr), decomposition; 1H-NMR, approximate AB quartet, 817.53,827.43 (DCCI3,CH2C12),817.32, 827.19({CD3}2SO, CH2C12). [Co(CNC6H,Br-p)5]CIO,: m.p., 158--163°C (uncorr); IH-NMR, unsplit signal, 87.53 (DCCI3,C,Hn), 87.28 ({CD3}:SO, CH2C12). [Co(CNC~q4I-p)5]CIO,: m.p., 189-194°C (uncorr), decomposition; 1H-NMR, approximate AB quartet, 817.75, 827.31 (DCCI3, C6H~2), 817.48, 827.07 ({CD3}280,CH2C12).
Table 1. Recrystallizationof [Co(CNC6Hs)5]CIO4 Solvents methanol/vacuum methanol/water ethanol/vacuum ethanol/water 1-propanol/water 2-propanol/water trimethylorthoformate/ether dimethylsulfoxide/water pyridine/water acetone/water acetone/ether methyl ethyl ketone/ether methyl i-butyl ketone/ether acetophenone/ether acetonitrile/ether propionitrile/ether benzylnitrile/ether nitromethane/ether nitroethane/ether 1-nitropropane/ether 2-nitropropane/ether 2-nitropropane/ether 1-nitrobutane/ether
Reaction concentration
Isocyanide i.r.
Type
45 mg/ml 45 mg/ml 12.5 mg/ml 12.5 mg/ml 6 mg/ml 4 mg/ml 75 mg/ml 200 mg/ml 400 mg/ml 200 mg/ml 200 mg/ml 200 mg/ml 100 mg/ml 300 mg/ml 200 mg/ml 200 mg/ml 300 mg/ml 300 mg/ml 300 mg/ml 200 mg/ml 200 mg/ml 200 mg/ml 200 mg/ml
2100, 2118,2143,2163,2208 2102,2118,2140,2162, 2208 2104, 2120,2144,2164,2210 2105,2120,2164,2210 2101, 2119,2142,2162,2208 2101, 2120,2143,2164,2208 2100, 2117,2142,2163,2208 2100, 2119,2142,2164,2208 2100, 2116,2142,2163,2209 2132 2134 2124 2103,2115,2142,2161,2208 2100, 2118,2143,2163,2208 2099,2115,2145,2160,2210 2124,2158,2208 2100, 2117,2142,2162,2208 2102, 2120,2144,2164,2209 2122, 2158,2212 2120, 2155,2207 2128 2099, 2118,2143,2162,2208 2098, 2117,2143,2163,2209
III III III II ~ IIIt III III III III III I I I III III III II III III II I--, IIt I III III
n*
0.84 0.84,0.67 0.51
[0.00] [0.00] [0.00] 0.34
*Adduct composition, [Co(CNC6_Hs)s]CIO4• nS, as determined from 1H-NMRin DCC13. tConsistently indistinct -N-=Ci.r. pattern. Table 2. Selected chemicalanalyses Composition(calcd/found) Solvent methanol/vacuum methanol/water acetone/ether methyl ethyl ketone/ether trimethylorthoformate/ether acetonitrile/ether propionitrile/ether nitromethane/ether chloroform/ether
Formula
C%
[Co(CNC~Hs)5]CIO, 62'37 [Co(CNC6Hs)5]CIO4 62"37 [Co(CNC,H,)5]C104' ~CH3C(O)CH362'35 [Co(CNC~H,)5]CIO4 • ½CH3C(O)CH2CH3 62.59 [Co(CNCd'Is)5]CIO, 62"37 [Co(CNCffls)s]C10, 62'37 [Co(CNC~H,)5]CIO, 62'37 [Co(CNC~I-Is)5]CIO, 62'37 [Co(CNC,H,)5]BF,.HCC13 55.38
H%
N%
C1%
C%
H%
N%
3"74 10'39 5'26 62'31 3'68 10"20 3"74 10"39 5"26 62'16 3"68 10.44 4'14 9'76 4'94 62'29 3'97 9"71 4.12 9.86 3'74 3'74 3.74 3'74 3.36
4.99 5'26 5'26 5"26 5"26 13.62
62.59 62"33 62"17 62"10 62'16 55.78
4.24 3'76 3,57 3.71 3"67 3.38
9.78
C1% 5"38 5'32 4'79 5.06 5"20 5.21 5.35 5'18 12.49
Aromatic isocyanide complexes of Co(I) RESULTS AND DISCUSSION
The significant results of this study are summarized in Tables 1, 3, and 4: the re-crystallizations of [Co(CNC~Hs)5]CIO4, [Co(CNC6Hs),]BF4, and
705
[Co(CNC6H4X-p)5]C104,BF4, respectively, from various type solvents. The chemical analyses of selected complexes are summarized in Table 2; otherwise, composition was established by proton-NMR. Characteristic -N=C i.r.
Table 3. Recrystallization of [Co(CNC6Hs)~]BF,
Solvents
Formula
[Co(CNC6H,),]BF4.½ H:CC12 dichloromethane/ether [Co(CNC6Hs)s]BF4 • 3 H2CCICH:C1 1.2-dichloroethane/ether [Co(CNC6Hs)s]BF, ' HCCIzCHs 1,l-dichloroethane/ether [Co(CNC6Hs)~]BF,. HCCI3 chloroform/ether [Co(CNC~H~)s]BF, • DCCI3 chloroform-d/ether [Co(CNC6Hs)s]BF, chloroform/ether [aged] [Co(CNC6Hs]BF4 ' HCCI:CHzCI 1,1,2-trichloroethane/ether I,l,l-trichloroethane/ether [Co(CNC~Hs)~]BF, • CI~CCH~ 1,1,2,2-tetrachloroethane/ether [Co(CNC6H3)~]BF4• HCCI2CHCI: methanol/vacuum [Co(CNC6H~)5]BF, dimethylsulfoxide/water [Co(CNC6Hs)5]BF4 pyridine/water [Co(CNC6Hs)5]BF4 acetone/water [Co(CNC6Hs)5]BF, • ] CH3C(O)CHs methyl ethyl ketone/ether [Co(CNC~H~)~]BF,. CH3C(O)CH2CH3 propionitrile/ether [Co(CNC6Hs)5]BF, 1-nitrobutane/ether [Co(CNC~Hs)5]BF4
Isocyanide i.r.
Type
n*
2128 2130 2133, 2205 2135, 2208 2130, 2206 2100, 2118, 2144, 2164, 2208 2135, 2207 2110, 2t60 2117, 2160 2100, 2119, 2143, 2162, 2208 2101,2119,2146,2163,2210 2101,2119, 2144, 2165, 2209 2135.2210 2130 2102, 2120, 2145, 2165, 2210 2101,2120, 2145, 2165, 2210
1 1 1 1 1 III l II II lII Ill III 1 1 III 1II
0.51 0.76 0.96 (0.90)+
*Adduct composition, [Co(CNC6Hs)5]BF4. nS, as determined from the 'H-NMR in DCCI3. ~Adduct composition as determined from the chlorine elemental analysis. Table 4. Recrystallization of substituted-phenylisocyanide complexes of cobalt(I) Formula
Solvents
[Co(CNC6H4F-4)5]BF4 re-cryst, from: CH3OH/vacuum CHCl3/ether CH2C1,_/ether CH3NO2/ether acetone/ether acetophenone/ether propionitrile/ether [Co(CNC6H4CI-4)~]BF, re-cryst, from: CH2Clz/ether CH3CH2CN/ether acetone/ether acetophenone/ether CH3CH2CH2NO2/ether [Co(CNC~H.Br-4)5]CIO4 re-cryst, from: CHC13/ether acetone/ether [Co(CNC6H4Br-4)5]BF4 recryst, from: acetophenone/ether CH3CH2CH2CH2NOJether [Co(CNC6H4I-4)5]CIO4 re-cryst, from: CH2Cl2/ether acetone/ether CH3CH2CH2CH2NOJether [Co(CNC6H4CH3-4),]C104 re-cryst, from: CHC13/ether CH2CIJether CH3OH/water dimethylsulfoxide/water CH3CH:CN/ether CH3CH2CH2CH2NO2/ether
lsocyanide i.r.
Type
2108,2155,2207 2112, 2160, 2210 2110, 2162, 2210 2110, 2160, 2210 2105, 2160, 2209 2112, 2162, 2207 2110, 2160, 2211
II II I1 II 11 II I1
21 t2, 2158 2110, 2158 2116, 2160 2115, 2150, 2208 2120, 2152
II 11 I1 II I1
2110, 2158, 2210 2116, 2159
I1 11
2111, 2156 2112, 2142
II I1
2114, 2150. 2196 2110, 2150 2108, 2158
II II II
(2035), 2110, 2157, 2205 (2035), 2110, 2157 (20401, 2110, 2156 (2040), 2108, 2153 (20401, 2110, 2156 (2040), 2110, 2157
II 1I II tl 11 II
10-00] 1.03 0.98 0.98 [0.001 [0.00] [0.00] 0.75 1.05 [0.00] [0.00]
706
C.A.L. BECKER
FREQUENCY
( CM-1 ) i
i
I.--
Z
A Fig, 1. Characteristici.r. spectrafor the isocyanidefunctionin the region 2000-2250cm-~. (A) type I, [Co(CNC6H~)~] BF~.HCC12CH2CI (from HCCI2CH2C1/(C2H~hO);(B) type II, [Co(CNC6H,CI-4)s]BF4 (from CH2C1JC2HshO); (C) type III, [Co(CNC6H~)~]BF4(fromCsHsN/H20). patterns for the three types of complexes (i.e. I, II, III) are pictured in Fig. 1. Recrystallization of [Co(CNC6Hs)5]C104 For [Co(CNC6Hs)5]CIO4, and [Co(CNC6Hs)5]BF4 as well, extremely high solubilities (i.e. Reaction concentration in Table 1) were observed in nitroalkanes, cyanohydrocarbons, and pyridine, as had been observed in chlorohydrocarbons [10], but considerably lower solubility was observed in alcohols. Polar aromatics (e.g., C6HsNO2, C6HsC(O)CH3) were also very good solvents, but recovery with ether was difficult. The type III structure is clearly predominant for solvents other than chlorohydrocarbons, and was the only form seen for re-crystallizations from alcohols, trimethylorthoformate, and dimethylsulfoxide. Type III was also observed using pyridine, the only amine tested in which these complexes were appreciably soluble. Methyl ketones yielded type I complexes, characteristically solvent-adducted, for acetone and methyl ethyl Ketone, but characteristicallynon-adductedtype IIIfrommethyli-butyl ketone and acetophenone. Partial decomposition was observed in methyl i-propyl ketone. Type III was maintained from aceto- and benzylnitriles, but the first non-adducted type II was crystallized from propionitrile/ether. Nitroalkanes were the solvent type, however, which showed greatest versatility. Type III was prepared from nitromethane or 1-nitrobutane; a non-adducted type II, from nitroethane; a consistently indistinct, non-adducted type II, from 1-nitropropane; and both adducted type I and non-adducted type III, from 2-nitropropane/ether under apparently identical re-crystallization procedure. The 2-nitropropane appears to be a unique solvent for [Co(CNC6Hs)s]C104. One pattern clearly evident from re-crystallization studies of [Co(CNC6Hs)s]C104, however, is that type I complexes are solvent-adducted, type III are not solvent-adducted and type II may or may not be solvent-adducted. Recrystallization of [Co(CNC6Hs)5]BF4 The same type complex of [Co(CNC6Hs)5]BF4 was
obtained from various solvent systems as had been obtained with [Co(CNC6Hs)5]C104,with the one exception propionitrile/ether. Recovery from cyanohydrocarbons is in general difficult, however, so duplication of reaction conditions may not have been achieved. Adductcomposition for type I and II complexes of the BF4 and C104 salts differed in only two instances: for 1,2dichloroethane (3/4 vs 1/2) and methyl ethyl ketone (1 vs 1/2). In all other instances [Co(CNC6Hs)5]BF4 behaved analogously to [Co(CNC6Hs]C104. Recrystallization of [Co(CNC6H4X-p)5]C104,BF4 Recrystallization of [Co(CNC6H4F-p )5]BF4, [Co(CNC6H4CI-p)5] BF4,
[Co(CNC6H4Br-p )5]C104,
[Co(CNC6H4Br-p)dBF4, [Co(CNCTHA-p)5]C104 and [Co(CNC6H4CH3-p)5]CIO4 from a selection of solvent types (i.e. Table 4) produced only type II complexes. In general complexes with p-CIC6H4NC and p-BrC6H4NC re-crystallized best; the p-FC6H4NC complexes gave very broad -N-C i.r. patterns, which were nevertheless clearly type II, and p-IC6H4NC and p-CH3C6H4NC complexes had limited stability in solution. In particular the p-IC6H4NC ligand itself partially decomposed in many solvents, while the (yellow) [Co(CNC6H4CH3-p)s]C104 complex produced slight amounts of (unidentified) green material in solvent/ether re-crystallization. Green color vanished upon addition of water in solvent/water recrystallizations. The very weak i.r. band (shoulder) -2035-2040cm -l (not observed in other aromatic isocyanide complexes) may be related to this problem. The -N=C i.r. pattern for [Co(CNC6I-LCH3-p)5]C104, however, is still clearly type II. CONCLUSION Recrystallization studies of pentakis(aromatic isocyanide)cobalt ((I) seem to establish that the three-fold five-coordinate conformational isomerism (i.e. structural types I, II, and lid is unique to the phenylisocyanide ligand, and that only the (distorted) trigonal bipyramidal structure is observed with para-substituted phenylisocyanide ligands. No significant differences are observed for the perchlorate or tetrafluoroborate salts. Adducting of solvent may be crucial for square pyramidal structure (type I), but appears irregular in type II and absent in type III. The [Co(CNC6H4CH3-p)5]CIO4shows unanticipated instability in solution. Acknowledgements--The Robert A. Welch Foundationof Houston, Texas,is mostgratefullyacknowledgedfor financialsupportof this research and for scholarshipsto the undergraduatelaboratory assistants contributingto this work:J. W. Mullins,M. D. Lasleyand W. G. Reed. REFERENCES
1. L. Malatesta and A. Sacco, Z. anorg, allg. Chem. 273, 247 (1953). 2. A. Sacco and M. Freni, Angew. Chem. 70, 599 (1957). 3. L. Malatesta, Prog. Inorg. Chem. 1, 283 (1959). 4. J. M. Pratt and P. R. Silverman,J. chem. Soc. (A), 1286(1967). 5. L. Malatesta and F. Bonati, Isocyanide Complexes of Metals, Chapter 7. Wiley, New York (1969). 6. R. B. King and M. S. Saran, Inorg. Chem. 11, 2112 (1972).
Aromatic isocyanide complexes of Co(I) 7. F. A. Cotton and R. V. Parish, J. chem. Soc. 1440 (1960). 8. F. A. Cotton, T. G. Dunne, and J. S. Wood, Inorg. Chem. 4, 318 (1965). 9. C. A. L. Becket, Data reported in part (a) 161st ACS National Meeting, March 1971, Abstract No. 85 (Inorg. Div.); (b) 163rd ACS National Meeting, April 1972, Abstract No. 5 (Inorg. Div.). 10. C. A. L. Becker, J. inorg, nucl. Chem. 35, 1875 (1973). 11. C. A. L. Becket. Data reported in part I66th ACS National Meeting, August 1973, Abstract No. 74 (Inorg. Div.). 12. K.N. Raymond, personal communication, data reported in part 165th ACS National Meeting, March 1973, Abstract No. 67 (Inorg. Div.). 13. S. H. Simonsen, personal communication, data reported in part 29th ACS Southwest Regional Meeting, December 1973, Abstract No. 184 (Inorg. Div.). 14. R. Q Brewster, Org+ Synth. 2, 347 (1943).
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15. (a) B. C. McKusick and O. W. Webster, Org. Synth. 41. 102 (1961); (b) A. Ladenburg, Ber. 10, 1123 (1877). 16. W. R. Heftier and E. J. Corey, J. org. Chem. 23, 1221 (1958). 17. C. A. L. Becket, Synth. Syn. React. lnorg. Metal-org. Chem. 4. 213 (1974). 18. R. Appel, R. Kleinsttick and K. D. Ziehn, Angew. Chem. 10. 132 (1971). 19. C. A. L. Becket, Data reported in part (a) 25th ACS Southwest Regional Meeting, December 1%9, Abstract No. IN-7; (b) 162nd ACS National Meeting, September 1971, Abstract No. 106 CInorg. Div.). 20. C. G. Johnson, M. A. Thesis, University of Texas at Austin, June 1973. 21. C. G. Johnson and C. A. L. Becket, Data reported in part 28th ACS Southwest Regional Meeting, December 1972+ Abstract No. 138 (lnorg. Div.).
FIVE-COORDINATE ISOMERS OF PENTAKIS(AROMATIC ISOCYANIDE)COBALT(I) C. A. L. BECKER Department of Chemistry, Kentucky State University, Frankfort, Ky 40601 (First received 4 June 1974; in final form 8 July 1974) Abstraet--Pentakis (phenyl- and para-substituted phenylisocyanide)cobalt(I) has been re-crystallized from various solvent types to study further the five-coordinate conformational isomerism observed for [Co(CNC6H~)~]CIO4 re-crystallized from chlorohydrocarbons. Characterization is primarily through the -N-=C i.r. pattern and proton-NMR. Perchtorate and tetrafluoroborate salts are used. The aromatic isocyanides include C~H,NC, p-FC~H,NC, p-CIC6H4NC,p-BrC6H4NC, p-IC6H4NC, and p-CH3C6H4NC.Three isomeric structures are maintained with phenylisocyanide but only one geometry is observed with para-substituted phenylisocyanides. INTRODUCTION FIVE-COORDINATE cobalt(I) complexes of isocyanides are well established[l-6]. Pentakis(methylisocyanide)cobalt(I) perchlorate was predicted[7], and later established[8], to be trigonal bipyramidal. For pentakis(phenylisocyanide)cobalt(I) perchlorate, however, recrystallization procedure apparently determines stereochemistry. Re-crystallization from chlorohydrocarbons, in which solubilities appear abnormally high, leads to two series of solvent-adducted complexes (types I and II) Characterized by distinctly different -N-=C i.r. patterns [9, 10]. Rapid re-crystallization of [Co(CNC6Hs)qC104. HCC13 from methanol/water or methanol/vacuum affords the non-adducted [Co(CNC6H~)5]C10~ (type III), with a third distinct -N=C i.r. pattern, while slow precipitation from methanol/water or ethanol/water results in a type I hydrogen chloride adduct, [Co(CNC6H0~]CIO4. HCI[9(b), 10]. Distinctly different Co ~ NQR signals have also been observed for types I and Ill complexes, but no signals have been observed for type II [11]. Square pyramidal coordination was initially suggested for type I complexes[9a], with trigonal bipyramidal and intermediate structures postulated for types II and III, respectively[9b]. The [Co(CNC6H~)~]CIO4. HCCI3, the prototype type I complex, has been shown to be square pyramidal with crystallographic C4-axis[12], and representative types II and III, [Co(CNC6H~CI-p)5]BF4 (from propionitrile/ether) and [Co(CNC6Hs)~IC10~ (from methanol/vacuum), respectively, both are somewhat distorted trigonal bipyramids [13]. Significant structural differences in these Co(I) complexes have been identified, therefore, via the -N=C i.r. This present work extends re-crystallization studies of [Co(CNC~Hs)5]CIO4 to solvents other than chlorohydrocarbons and establishes analogous or dissimilar re-crystallization behavior for [Co(CNC6Hs)5]BF4 and [Co(CNC6H4X-p)5]C104, BF4. Type III [Co(CNC6H~).dC104,BF4 is used to avoid possible formation of the hydrogen chloride.
EXPERIMENTAL
Solvent purity was routinely checked by NMR; when necessary, distillation was over CaC12or Mg(CIO4)2. Anhydrous diethyl ether was filtered through an alumina column immediately before use. Commercial Nujol was dried over CaC12. Proton-NMR spectra were recorded on a Varian A-60 or HA-100 at ambient temperature using 99.8% deuterated cloroform or 99.5% deuterated dimethylsulfoxide with cyclohexane (61.42) or dichIoromethane (85.28) as secondary internal reference. I.r. spectra were recorded on a Beckman IR-7 as Nujol mulls. Elemental analyses were performed commercially. Aniline and para-substituted anilines were commercially available, except p-IC,HaNH2 which was prepared from aniline, NaHCO3, and iodine in aqueous solution[14] and re-crystallized several times from hot pentane. The N-aromaticformamides were prepared by refluxingthe appropriate aniline with formic acid and toluene[I5], and re-crystallizing from hot toluene. Preparation of aromatic isocyanides Aromatic isocyanides were prepared from the corresponding formamides by modification of the synthesis by Hertter and Corey[16, 17], using p-CH3C6H4SO2CIand (C.,H,)3N, and according to Appel et al.[18], using (C6Hs)3P, CCI,, (C2H~)3Nand HCCI~. The former synthesis gives better yields, while the latter is an overall cleaner reaction. In both syntheses the aromatic isocyanide is purified by vacuum distillation or sublimation. C6HsNC: colorless liquid rapidly discoloring dark green upon standing; distilled 19--22°C (uncorr), -0.1 Torr: -N=-C i.r., 2133cm-1; 'H-NMR, unsplit signal, 67.25 (neat, TMS). pFC~H,NC: yellow-green liquid; distilled 28-30°C (uncorr), --0.I Torr;-N=-C i.r., 2142cm '. p-CIC~H4NC: colorless crystals; sublimed 80-90°C (oil-bath temperature), -0.1 Torr: m.p., 71-73°C (uncorr) decomposition: -N-=C i.r.. 2127 cm ': 'H-NMR, unsplit signal, 87.40 (DCCI3, C~H~2), 87.10 ({CD3}2SO, CH~CI:). pBrC6H4NC: colorless crystals; sublimed 80-90°C, -(I. 1Torr; re.p., 98-99°C (uncorr) decomposition;-N-C i.r., 2127 cm ': 'H-NMR, approximate AB quartet, 6,7.56, 827.28 (DCCI3, C,,H,2), 8,7.25, 827.07 ({CD3}zSO, CHzC12). p-IC6H4NC: colorless crystals; sublimed 100-120°C, -0.1 Torr; m.p., 130-131°C (uncorr) decomposition:-N=-C i.r., 2127cm '; IH-NMR, approximate AB quartet, 8,7.74, 827.10 (DCC13,C6Ht2), 8,7.41, ,~z6.89({CD~}2SO,CH2CI2). p-CH3C~H,NC: colorless liquid: distilled 28-30°C (uncorrL ~0.1 Torr. 703
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C.A.L. BECKER
Preparation of Pentakis(aromatic isocyanide)cobalt(I) The complexes [Co(CNC~Hs)~](CIO~)~. 1.0 H20 (blue), [Co(CNC6H~)~](BF,)2.1.0H20 (blue), [Co(CNC~H4CH3-p)5] (ClO,)2(green), [Co(CNC6H4CH3-p),] (BF,)2.1.0H20 (blue), and [Co(CNC~H_,F-p)5](C104)2(yellow)were prepared by reaction of five moles aromatic isocyanide with C0(C10,,BF4)2.6H20 in 95% ethanol [10, 19-21]; but the BF4- salt with p-FC,H,NC, pC1C~H,NC and p-BrC,H,NC; and the CIO,- salt with pC1C6H,NC, p-BrC~H,NC and p-IC~H4NC; were mixtures of Co(II) and Co(I). Reduction to Co(I) followed several procedures. Anhydrous Co(II) complexes could be reduced in CH2C12/C:H~OH solution[10]. The Co(II)-Co(I) mixtures were reduced by digestion in methanol or ethanol under mild heating[17] or by solution in pyfidine (1.0 gm/10.0nil, exothermic) followed by precipitation with distilled water (2.0 ml). Crude product was re-crystallized from HCCI3/(C2H~)20;phenylisocyanidecomplexes were further
re-crystallized f r o m CH3OH/vacuum (type III) [10]. [CO(CNCd-Is)5]CIO,,BF4: m.p., 144--147°, 109-112°C (uncorr); IH-NMR, unsplit signal, 87.50 fDCCI3, TMS), 87.48 (DCCI3, Cd-I12), multiplet, 87.21 ({CD~}2SO,CH2C12). [Co(CNC,H,CH3p)5]CIO,: m.p., 134-137°C (uncorr); IH-NMR: approximate AB quartet, 817'15, 826'93, and 81.94 ({CD3}2SO, CH~CI2). [Co(CNC6FLF-p)~]CIO,,BF,:m.p., 138-141°, 143-146°C(uncorr), decomposition; IH-NMR, approximate AB quartet split into triplet and quartet, 817'56, 827.13 (DCC13,C6Hn), 817.87, 827"46 ({CD3}2SO,C6Hn). [Co(CNCd-I,CI-p)5]CIO,,BF,:m.p., 183-186°, 191-193°C (uncorr), decomposition; 1H-NMR, approximate AB quartet, 817.53,827.43 (DCCI3,CH2C12),817.32, 827.19({CD3}2SO, CH2C12). [Co(CNC6H,Br-p)5]CIO,: m.p., 158--163°C (uncorr); IH-NMR, unsplit signal, 87.53 (DCCI3,C,Hn), 87.28 ({CD3}:SO, CH2C12). [Co(CNC~q4I-p)5]CIO,: m.p., 189-194°C (uncorr), decomposition; 1H-NMR, approximate AB quartet, 817.75, 827.31 (DCCI3, C6H~2), 817.48, 827.07 ({CD3}280,CH2C12).
Table 1. Recrystallizationof [Co(CNC6Hs)5]CIO4 Solvents methanol/vacuum methanol/water ethanol/vacuum ethanol/water 1-propanol/water 2-propanol/water trimethylorthoformate/ether dimethylsulfoxide/water pyridine/water acetone/water acetone/ether methyl ethyl ketone/ether methyl i-butyl ketone/ether acetophenone/ether acetonitrile/ether propionitrile/ether benzylnitrile/ether nitromethane/ether nitroethane/ether 1-nitropropane/ether 2-nitropropane/ether 2-nitropropane/ether 1-nitrobutane/ether
Reaction concentration
Isocyanide i.r.
Type
45 mg/ml 45 mg/ml 12.5 mg/ml 12.5 mg/ml 6 mg/ml 4 mg/ml 75 mg/ml 200 mg/ml 400 mg/ml 200 mg/ml 200 mg/ml 200 mg/ml 100 mg/ml 300 mg/ml 200 mg/ml 200 mg/ml 300 mg/ml 300 mg/ml 300 mg/ml 200 mg/ml 200 mg/ml 200 mg/ml 200 mg/ml
2100, 2118,2143,2163,2208 2102,2118,2140,2162, 2208 2104, 2120,2144,2164,2210 2105,2120,2164,2210 2101, 2119,2142,2162,2208 2101, 2120,2143,2164,2208 2100, 2117,2142,2163,2208 2100, 2119,2142,2164,2208 2100, 2116,2142,2163,2209 2132 2134 2124 2103,2115,2142,2161,2208 2100, 2118,2143,2163,2208 2099,2115,2145,2160,2210 2124,2158,2208 2100, 2117,2142,2162,2208 2102, 2120,2144,2164,2209 2122, 2158,2212 2120, 2155,2207 2128 2099, 2118,2143,2162,2208 2098, 2117,2143,2163,2209
III III III II ~ IIIt III III III III III I I I III III III II III III II I--, IIt I III III
n*
0.84 0.84,0.67 0.51
[0.00] [0.00] [0.00] 0.34
*Adduct composition, [Co(CNC6_Hs)s]CIO4• nS, as determined from 1H-NMRin DCC13. tConsistently indistinct -N-=Ci.r. pattern. Table 2. Selected chemicalanalyses Composition(calcd/found) Solvent methanol/vacuum methanol/water acetone/ether methyl ethyl ketone/ether trimethylorthoformate/ether acetonitrile/ether propionitrile/ether nitromethane/ether chloroform/ether
Formula
C%
[Co(CNC~Hs)5]CIO, 62'37 [Co(CNC6Hs)5]CIO4 62"37 [Co(CNC,H,)5]C104' ~CH3C(O)CH362'35 [Co(CNC~H,)5]CIO4 • ½CH3C(O)CH2CH3 62.59 [Co(CNCd'Is)5]CIO, 62"37 [Co(CNCffls)s]C10, 62'37 [Co(CNC~H,)5]CIO, 62'37 [Co(CNC~I-Is)5]CIO, 62'37 [Co(CNC,H,)5]BF,.HCC13 55.38
H%
N%
C1%
C%
H%
N%
3"74 10'39 5'26 62'31 3'68 10"20 3"74 10"39 5"26 62'16 3"68 10.44 4'14 9'76 4'94 62'29 3'97 9"71 4.12 9.86 3'74 3'74 3.74 3'74 3.36
4.99 5'26 5'26 5"26 5"26 13.62
62.59 62"33 62"17 62"10 62'16 55.78
4.24 3'76 3,57 3.71 3"67 3.38
9.78
C1% 5"38 5'32 4'79 5.06 5"20 5.21 5.35 5'18 12.49
Aromatic isocyanide complexes of Co(I) RESULTS AND DISCUSSION
The significant results of this study are summarized in Tables 1, 3, and 4: the re-crystallizations of [Co(CNC~Hs)5]CIO4, [Co(CNC6Hs),]BF4, and
705
[Co(CNC6H4X-p)5]C104,BF4, respectively, from various type solvents. The chemical analyses of selected complexes are summarized in Table 2; otherwise, composition was established by proton-NMR. Characteristic -N=C i.r.
Table 3. Recrystallization of [Co(CNC6Hs)~]BF,
Solvents
Formula
[Co(CNC6H,),]BF4.½ H:CC12 dichloromethane/ether [Co(CNC6Hs)s]BF4 • 3 H2CCICH:C1 1.2-dichloroethane/ether [Co(CNC6Hs)s]BF, ' HCCIzCHs 1,l-dichloroethane/ether [Co(CNC6Hs)~]BF,. HCCI3 chloroform/ether [Co(CNC~H~)s]BF, • DCCI3 chloroform-d/ether [Co(CNC6Hs)s]BF, chloroform/ether [aged] [Co(CNC6Hs]BF4 ' HCCI:CHzCI 1,1,2-trichloroethane/ether I,l,l-trichloroethane/ether [Co(CNC~Hs)~]BF, • CI~CCH~ 1,1,2,2-tetrachloroethane/ether [Co(CNC6H3)~]BF4• HCCI2CHCI: methanol/vacuum [Co(CNC6H~)5]BF, dimethylsulfoxide/water [Co(CNC6Hs)5]BF4 pyridine/water [Co(CNC6Hs)5]BF4 acetone/water [Co(CNC6Hs)5]BF, • ] CH3C(O)CHs methyl ethyl ketone/ether [Co(CNC~H~)~]BF,. CH3C(O)CH2CH3 propionitrile/ether [Co(CNC6Hs)5]BF, 1-nitrobutane/ether [Co(CNC~Hs)5]BF4
Isocyanide i.r.
Type
n*
2128 2130 2133, 2205 2135, 2208 2130, 2206 2100, 2118, 2144, 2164, 2208 2135, 2207 2110, 2t60 2117, 2160 2100, 2119, 2143, 2162, 2208 2101,2119,2146,2163,2210 2101,2119, 2144, 2165, 2209 2135.2210 2130 2102, 2120, 2145, 2165, 2210 2101,2120, 2145, 2165, 2210
1 1 1 1 1 III l II II lII Ill III 1 1 III 1II
0.51 0.76 0.96 (0.90)+
*Adduct composition, [Co(CNC6Hs)5]BF4. nS, as determined from the 'H-NMR in DCCI3. ~Adduct composition as determined from the chlorine elemental analysis. Table 4. Recrystallization of substituted-phenylisocyanide complexes of cobalt(I) Formula
Solvents
[Co(CNC6H4F-4)5]BF4 re-cryst, from: CH3OH/vacuum CHCl3/ether CH2C1,_/ether CH3NO2/ether acetone/ether acetophenone/ether propionitrile/ether [Co(CNC6H4CI-4)~]BF, re-cryst, from: CH2Clz/ether CH3CH2CN/ether acetone/ether acetophenone/ether CH3CH2CH2NO2/ether [Co(CNC~H.Br-4)5]CIO4 re-cryst, from: CHC13/ether acetone/ether [Co(CNC6H4Br-4)5]BF4 recryst, from: acetophenone/ether CH3CH2CH2CH2NOJether [Co(CNC6H4I-4)5]CIO4 re-cryst, from: CH2Cl2/ether acetone/ether CH3CH2CH2CH2NOJether [Co(CNC6H4CH3-4),]C104 re-cryst, from: CHC13/ether CH2CIJether CH3OH/water dimethylsulfoxide/water CH3CH:CN/ether CH3CH2CH2CH2NO2/ether
lsocyanide i.r.
Type
2108,2155,2207 2112, 2160, 2210 2110, 2162, 2210 2110, 2160, 2210 2105, 2160, 2209 2112, 2162, 2207 2110, 2160, 2211
II II I1 II 11 II I1
21 t2, 2158 2110, 2158 2116, 2160 2115, 2150, 2208 2120, 2152
II 11 I1 II I1
2110, 2158, 2210 2116, 2159
I1 11
2111, 2156 2112, 2142
II I1
2114, 2150. 2196 2110, 2150 2108, 2158
II II II
(2035), 2110, 2157, 2205 (2035), 2110, 2157 (20401, 2110, 2156 (2040), 2108, 2153 (20401, 2110, 2156 (2040), 2110, 2157
II 1I II tl 11 II
10-00] 1.03 0.98 0.98 [0.001 [0.00] [0.00] 0.75 1.05 [0.00] [0.00]
706
C.A.L. BECKER
FREQUENCY
( CM-1 ) i
i
I.--
Z
A Fig, 1. Characteristici.r. spectrafor the isocyanidefunctionin the region 2000-2250cm-~. (A) type I, [Co(CNC6H~)~] BF~.HCC12CH2CI (from HCCI2CH2C1/(C2H~hO);(B) type II, [Co(CNC6H,CI-4)s]BF4 (from CH2C1JC2HshO); (C) type III, [Co(CNC6H~)~]BF4(fromCsHsN/H20). patterns for the three types of complexes (i.e. I, II, III) are pictured in Fig. 1. Recrystallization of [Co(CNC6Hs)5]C104 For [Co(CNC6Hs)5]CIO4, and [Co(CNC6Hs)5]BF4 as well, extremely high solubilities (i.e. Reaction concentration in Table 1) were observed in nitroalkanes, cyanohydrocarbons, and pyridine, as had been observed in chlorohydrocarbons [10], but considerably lower solubility was observed in alcohols. Polar aromatics (e.g., C6HsNO2, C6HsC(O)CH3) were also very good solvents, but recovery with ether was difficult. The type III structure is clearly predominant for solvents other than chlorohydrocarbons, and was the only form seen for re-crystallizations from alcohols, trimethylorthoformate, and dimethylsulfoxide. Type III was also observed using pyridine, the only amine tested in which these complexes were appreciably soluble. Methyl ketones yielded type I complexes, characteristically solvent-adducted, for acetone and methyl ethyl Ketone, but characteristicallynon-adductedtype IIIfrommethyli-butyl ketone and acetophenone. Partial decomposition was observed in methyl i-propyl ketone. Type III was maintained from aceto- and benzylnitriles, but the first non-adducted type II was crystallized from propionitrile/ether. Nitroalkanes were the solvent type, however, which showed greatest versatility. Type III was prepared from nitromethane or 1-nitrobutane; a non-adducted type II, from nitroethane; a consistently indistinct, non-adducted type II, from 1-nitropropane; and both adducted type I and non-adducted type III, from 2-nitropropane/ether under apparently identical re-crystallization procedure. The 2-nitropropane appears to be a unique solvent for [Co(CNC6Hs)s]C104. One pattern clearly evident from re-crystallization studies of [Co(CNC6Hs)s]C104, however, is that type I complexes are solvent-adducted, type III are not solvent-adducted and type II may or may not be solvent-adducted. Recrystallization of [Co(CNC6Hs)5]BF4 The same type complex of [Co(CNC6Hs)5]BF4 was
obtained from various solvent systems as had been obtained with [Co(CNC6Hs)5]C104,with the one exception propionitrile/ether. Recovery from cyanohydrocarbons is in general difficult, however, so duplication of reaction conditions may not have been achieved. Adductcomposition for type I and II complexes of the BF4 and C104 salts differed in only two instances: for 1,2dichloroethane (3/4 vs 1/2) and methyl ethyl ketone (1 vs 1/2). In all other instances [Co(CNC6Hs)5]BF4 behaved analogously to [Co(CNC6Hs]C104. Recrystallization of [Co(CNC6H4X-p)5]C104,BF4 Recrystallization of [Co(CNC6H4F-p )5]BF4, [Co(CNC6H4CI-p)5] BF4,
[Co(CNC6H4Br-p )5]C104,
[Co(CNC6H4Br-p)dBF4, [Co(CNCTHA-p)5]C104 and [Co(CNC6H4CH3-p)5]CIO4 from a selection of solvent types (i.e. Table 4) produced only type II complexes. In general complexes with p-CIC6H4NC and p-BrC6H4NC re-crystallized best; the p-FC6H4NC complexes gave very broad -N-C i.r. patterns, which were nevertheless clearly type II, and p-IC6H4NC and p-CH3C6H4NC complexes had limited stability in solution. In particular the p-IC6H4NC ligand itself partially decomposed in many solvents, while the (yellow) [Co(CNC6H4CH3-p)s]C104 complex produced slight amounts of (unidentified) green material in solvent/ether re-crystallization. Green color vanished upon addition of water in solvent/water recrystallizations. The very weak i.r. band (shoulder) -2035-2040cm -l (not observed in other aromatic isocyanide complexes) may be related to this problem. The -N=C i.r. pattern for [Co(CNC6I-LCH3-p)5]C104, however, is still clearly type II. CONCLUSION Recrystallization studies of pentakis(aromatic isocyanide)cobalt ((I) seem to establish that the three-fold five-coordinate conformational isomerism (i.e. structural types I, II, and lid is unique to the phenylisocyanide ligand, and that only the (distorted) trigonal bipyramidal structure is observed with para-substituted phenylisocyanide ligands. No significant differences are observed for the perchlorate or tetrafluoroborate salts. Adducting of solvent may be crucial for square pyramidal structure (type I), but appears irregular in type II and absent in type III. The [Co(CNC6H4CH3-p)5]CIO4shows unanticipated instability in solution. Acknowledgements--The Robert A. Welch Foundationof Houston, Texas,is mostgratefullyacknowledgedfor financialsupportof this research and for scholarshipsto the undergraduatelaboratory assistants contributingto this work:J. W. Mullins,M. D. Lasleyand W. G. Reed. REFERENCES
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Aromatic isocyanide complexes of Co(I) 7. F. A. Cotton and R. V. Parish, J. chem. Soc. 1440 (1960). 8. F. A. Cotton, T. G. Dunne, and J. S. Wood, Inorg. Chem. 4, 318 (1965). 9. C. A. L. Becket, Data reported in part (a) 161st ACS National Meeting, March 1971, Abstract No. 85 (Inorg. Div.); (b) 163rd ACS National Meeting, April 1972, Abstract No. 5 (Inorg. Div.). 10. C. A. L. Becker, J. inorg, nucl. Chem. 35, 1875 (1973). 11. C. A. L. Becket. Data reported in part I66th ACS National Meeting, August 1973, Abstract No. 74 (Inorg. Div.). 12. K.N. Raymond, personal communication, data reported in part 165th ACS National Meeting, March 1973, Abstract No. 67 (Inorg. Div.). 13. S. H. Simonsen, personal communication, data reported in part 29th ACS Southwest Regional Meeting, December 1973, Abstract No. 184 (Inorg. Div.). 14. R. Q Brewster, Org+ Synth. 2, 347 (1943).
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15. (a) B. C. McKusick and O. W. Webster, Org. Synth. 41. 102 (1961); (b) A. Ladenburg, Ber. 10, 1123 (1877). 16. W. R. Heftier and E. J. Corey, J. org. Chem. 23, 1221 (1958). 17. C. A. L. Becket, Synth. Syn. React. lnorg. Metal-org. Chem. 4. 213 (1974). 18. R. Appel, R. Kleinsttick and K. D. Ziehn, Angew. Chem. 10. 132 (1971). 19. C. A. L. Becket, Data reported in part (a) 25th ACS Southwest Regional Meeting, December 1%9, Abstract No. IN-7; (b) 162nd ACS National Meeting, September 1971, Abstract No. 106 CInorg. Div.). 20. C. G. Johnson, M. A. Thesis, University of Texas at Austin, June 1973. 21. C. G. Johnson and C. A. L. Becket, Data reported in part 28th ACS Southwest Regional Meeting, December 1972+ Abstract No. 138 (lnorg. Div.).