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Preparation and characterisation of some stereochemically rigid 7-coordinate mono-methylcyclopentadienyl zirconium(IV) tris-N, N-dialkyl dithiocarbamate complexes
i~l,,r m . ; Ckem, /978. \ o l 40. pp 239 24~
Pergamon Press
Printed in Great Britain
PREPARATION AND CHARACTERISATION OF SOME STEREOCHEMICALLY RIGID 7-COORDINATE MONOMETHYLCYCLOPENTADIENYL ZIRCONIUM(IV) TRIS-N, N-DIALKYL DITHIOCARBAMATE COMPLEXES V1NOD KUMAR JAIN and B. S. GARG* Department of Chemistry, University of Delhi, DelhM 10 007, India
(Received 13 May 1977) Abstract--Zirconium(IV) N,N-dialkyl dithiocarbamates of the type MeCpZr(S2CNR2) 3 where R = Me, Et have been prepared by reaction of bis-methycyclopentadienyl zirconium(IV) dichloride with sodium salts of substituted dithiocarbamic acids in aqueous and non-aqueous media. They have also been prepared by reaction of monomethycyclopentadienyl zirconium(IV) trichloride with sodium salts of substituted dithiocarbamic acids in nonaqueous medium. Molecular weight, conductance and IR studies point out that these complexes are monomeric non-electrolytes in which all of the dithiocarbamate ligands are bidentate. Therefore. a coordination number "7" may be assigned to zirconium(IV) ion in these compounds. Proton NMR spectra of these complexes in carbon disulfide or deuterated chloroform indicate that ill there is hindered rotation about C--N bonds at ambient temperature, and (ii) metal centered rearrangement is slow on the NMR time-scale at ambient temperature (30°C).
INTRODUCTION Of the many ligands that are known to stabilise the higher coordination states of metals, the dithiocarbamate tigands are particularly welt suited due to (i) their low charge, and (ii) their relatively small "bites" (2.8-2.9 ,~). The different resonating structures of the dithiocarbamate ligands are shown in the following Figs. l(a) to l(c):
R\N__c
\S,~
l(a)
R\
/S ~
~ R/N--C~s
I(b)
R\~ .._c/SG (
~ R/
\S e
l(cl
Fig. I. Resonating structures for dithiocarbamate ligands. Although the literature on metal dithiocarbamates is extensive, there are very few such complexes and still more few, the 7-coordinate complexes of the early transition metals. The present communication deals with the preparation and characterisation of the 7-coordinate meth~lcyclopentadienyl zirconium(IV) N,N-dialkyl dithiocarbamate complexes of the type MeCpZrIS2CNR2b where R = Me. Et. These complexes are closely related to the dithiocarbamade complexes Ti[(S2CNR2)3]CI[I, 2], VO[S?CN(C2Hs)2]3[3], NbO[S:CN(C2H,bb[3], Mo(NO)[S,('NIn-C4H9)2]3[4I and ( r [ C~H,)Zr [S2CN(CH02]3[5}. Other reported 7 coordinate compounds of zirconium(W) include M(acachCl ( M = Zr or Hf; a c a c = C H 3 - C O - C H - C O CH~)[6] and (rr-C~HdZrICF3COCHCOCF~b[7]. All the above 7-coordinate compounds have been shown to possess pentagonal bipyramidal structures in which the monodentate ligand occupies an axial position. A similar structure for (~r-CH3CsH4)Zr(S2CNR2)3 R = Me, Et is suggested by the proton NMR spectrum which exhibit a complex pattern (when R = Me, four methyl resonances of relative intensity 2 : 1 : 2 : 1 are observed at ambient probe temperature (30°C): A more complex pattern is observed for the corresponding ethyl derivative). *Author for correspondence
EXPERIMENTAL Reagents and techniques. Sodium salts of dithiocarbamic acid Na(S2CNR2) were prepared by the method[8] described by Klopping and Kerk. The above sodium salts were dried in vacuum over phospboruspentoxide (first at room temperature and then at 110°). For reactions in aqueous medium, however, the sodium salts were used without any drying. Bis-methylcyclopentadienyt zirconium(IV) dichloride was prepared by reaction of zirconium tetrachloride with sodium salt of methylcyclopentadiene in tetrahydrofuran[9]. Dichloromethane and benzene were dried by refluxing for 24 hr over calcium hydride. Nitrobenzene was purified for conductance measurements by the method described by Fay et al.[10]. Preparation of the complexes. The compounds included in this communication were prepared by the following methods, viz. (a) in aqueous medium, and (b) in non-aqueous medium by reaction of (i) bis-methycyclopentadienyl zirconium(IV) dichloride, and (ii) mono-methylcyclopentadienyl zirconium(IV) trichloride with anhydrous Na(S2CNR2). (MeCp)2ZrC12 + 3Na(S2CNR ~) MeCpZr(S2CNR2) 3 + 2NaCl + NaCp (in aqueous and non-aqueous medium) MeCpZrCI~ + 3Na(S2CNR2) ~ MeCpZr(S,CNR2) ~+ 3NaC1 (in non-aqueous medium). (A) Preparation in aqueous medium. The bis-methylcyctopentadienyl zirconium(IV) dichloride was dissolved in water by refluxing and the solution was filtered to remove insoluble materials, the filtrate was cooled to room temperature. The sodium salt of dithiocarbamate ligand was dissolved in water at room temperature and filtered. The filtrate so obtained was added dropwise to the solution of bis-methylcyclopentadienyl zirconium(IV) dichloride. The precipitate so obtained was repeatedly extracted by shaking with dichloromethane. The above process was continued till the aqueous layer did not give any more precipitate upon addition of sodium dithiocarbamate solution. The dichloromethane containing the dissolved reaction product was dried over calcium chloride. Colourless crystals of the compounds were obtained by adding petroleum ether (6080°C) to the above and allowing the mixture to stand overnight. The above method of preparation is unsuitable because of very low solubility of bis-methytcyclopentadienyl zirconium(IV) dichloride in water.
239
240
VINOD KUMAR JAIN and B. S. GARG
(B) Preparation in non-aqueous medium (i) By refiuxing bis-methylcyclopentadienyl zirconium(IV) dichloride with sodium salts of dithocarbamates in dichloromethane: A solution of bis-methylcyclopentadienyl zirconium(IV) dichloride in dichloromethane was refluxed with calculated amounts of anhydrous sodium salts of the dithiocarbamate ligands for 24 hr. The hot solution was then filtered through a filtration unit fitted with a G-4 sintered glass disc. Colourless crystals of the compounds were obtained by adding petroleum ether (60-80°C) to the filtrate and allowing the mixture to stand overnight. (ii) By refluxing mono-methylcyclopentadienyl zirconium(IV) trichloride with sodium salts of dithiocarbamate ligands in dichloromethane: A solution of mono-methylcyclopentadienyl zirconium(IV) trichloride (prepared by the reaction of quantitative amounts of methylcyclopentadienyl thallium(1) with zirconium tetrachloride in tetrahydrofuran) in dichloromethane was refluxed with stoichiometric amounts of sodium salts of dithiocarbamate ligands for 24 hr. The hot solution was then filtered through a filtration unit fitted with a G-4 sintered glass disc to remove the solid sodium chloride. Colourless crystals of the compounds were obtained as in B(i).
Molecular weight and conductance measurements Molecular weights were determined ebullioscopically in benzene using a Gallen Kamp (U.K.) ebulliometer. Conductance measurements were made in nitrobenzene at 30-+0.05°C with a Beckmann Conductivity Bridge Model No. RC-18A. IR spectra. IR spectra were recorded in solid state (KBr pellets) in the region 4000-250cm ~ with a Perkin-Elmer 621 grating spectrophotometer.
Nuclear magnetic resonance spectra The proton NMR spectra were recorded at ambient temperature (30°C) at sweep width of 100-500Hz with a Varian A-60 spectrometer. Spectra were recorded in triplicate, and the values reported in Table 1 are average values; the magnetic field sweep was calibrated with a standard sample of chloroform and tetramethysilane (1%) in deuterated chloroform.
RESULTS AND DISCUSSION
Mono-methylcyclopentadienyl zirconium(IV) dithiocarbamate complexes of the type MeCpZr(SzCNR2t3 (R = Me, Et) have been prepared by reaction of bis-methylcyclopentadienyl zirconium(IV) dichloride with sodium N,N-dialkyldithiocarbamates in aqueous medium and in non-aqueous medium by refluxing in dichloromethane. They have also been prepared by refluxing mono-
methylcyclopentadienyl zirconium(IV) trichloride with sodium N,N-dialkyldithiocarbamates in dichloromethane. The methods used for preparation and isolation of these compounds (see Experimental section) give materials of good purity as judged by satisfactory elemental analysis and by the proton NMR spectra of carbon disulfide or deuteriochloroform solutions (Table 1). Both the compounds are new. The two compounds are white in colour. They are moderately soluble in carbon disulfide, dichloromethane and chloroform. Dichloromethane was used to crystallise the compounds. The two compounds are thermally stable but decompose near their m.ps. The solids are quite stable in air but their solutions are hydrolysed relatively rapidly. The ethyl compound is more susceptible to hydrolysis. Conductance measurements (Table 2) show that both the complexes are essentially non-electrolytes in nitrobenzene. The subject of chief interest in the preparation of these compounds is the stereochemistry. A coordination number of "7" may be assigned if all three dithiocarbamate ligands are bidentate, as in Mo(NO)(S2CNR2)3 (R = Me[11] or n-Bu [4]) and the methylcyclopentadienyl group occupies one coordination site. Fay et al.[5] have described the X-ray diffraction of (r~5CsHs)Zr[S2CN(CH3)2]3 in which (though zirconium is formally l 1-coordinate but) because of the relatively small size of the cyclopentadienyl group it is considered to occupy single axial coordination site in a pentagonal bipyramidal structure. On this analogy methylcyclopentadienyl group in the compounds included in this communication is assumed to occupy single coordination site; however, the more common coordination number of 6 would result if one of the dithiocarbamate ligands behaves as an s-bonded mondentate ligand, as in Ru(NO)(S2CNRz)3 ( R = Me[ll] or having only bidentate ligands. The most significant of these extra bands are a second C-N stretching band near 1470 cm 1112, 13] and a second C-S stretching band near exhibit additional IR bands not found for complexes Et[12]). These two bonding possibilities can be distinguished by IR spectroscopy since complexes having both monodentate and bidentate-dithiocarbamate ligands 1000 cm -j [14]. The Sn(SzCNEt~.)4 which has been shown by X-ray analysis to be a 6-coordinate complex having two monodentate SzCNEtz groups [15] exhibits two C-N bands (1512 and 147lcm -~) and two C-S bands (1008 and 989cm ~)[16] while the 8-coordinate
Table I. Proton chemical shift (in Hz) and coupling constant data (in Hz) at 30°C Deuteriochloroform solution S2CNR2 portion
Compound MeCpZr(S2CNMe2)3¶ MeCpZr(S2CNEtz)3¶
7r-CH3CsH4 - 359.8t, - 337.6t, - 133.4s - 362.0t, - 339.3t, - 134.3s
J
-CH2-
-CH3
2.5 -- 199.5,- 197.6,- 195.7, - 194.4t 2.6 - 228.1, - 222.9, 221.0~: - 74.6, - 72.9§
J 7.0, 6.9II
tFor the methyl compound, the four peaks observed (the intensity ratio being 2:0.95 : 2.05 : 0.98) are due to four non equivalent methyl groups present in the compound and not due to the coupling of protons on adjacent atoms. :~Position of three most intense peaks. §Position of two most intense peaks. ]lTwo J values; both are J(CH~-CH2-) but the different values are due to different types of ethyl groups. Both are approximate values due to overlapping of the four triplets due to four types of ethyl groups. ¶Me = CH3-; and Et = CH3CH:t, triplet; s, singlet.
Preparation and characterisationof some complexes
241
Ti(S2CnEt2)4[17] displays just one C-N band (1503 cm ~) and one C-S band (1001 cm ')[16, 181. Characteristic IR frequencies for the MeCpZr(S2CNR2)3 complexes are presented in Tabk', 3. In the IR some of the absorption bands due to the dithiocarbamato ligands are masked by methylcyclopentadienyl absorption bands, but several assignments are possible. The "thioureide'" band (C---N) near 1500 cm t is very characteristic of dithiocarbamates. The frequency of this band lies between that for C-N (1250-1350 cm ') and C=N (1640-1690 cm '), which suggests that this bond has some double bond character. Table 3 shows that both the complexes exhibit just one C-N band and one C-S band. It is assumed from this evidence that the C-S bonds are most likely equivaltnt. The spectra, therefore, indicate bidentate dithiocarbamate attachment and therefore coordination number "7" for Zr(IV) ion. On the whole then, the IR data favour a 7-coordinate structure for the above two compounds.
-t:~ z
~,
~
~
, r ¸,
~
Interpretation of NMR spectra Stereochemical non-rigidity. Three kinetic processes + + + ~ ; ~
~ N N N
._=
< ~ < ~
.,..
,x=
>,
"2 --: >
e--!
-
>.. k.s
e<
g=
Z
Z ¢..o
G ca
are known to affect the line shape in NMR spectra of metal dithiocarbamate complexes (1) metal centered rearrangement[19] I21 S2C-'-N bond rotation[201 and (3) hindered rotation about C-N single bonds in the NR2 portion of the S2CNR2 ligand[21]. The expected number and relative intensities of R-group resonances for the MeCpZr(S2CNR~)3 complexes are indicated in Table 4 for the following possibilities: (a) metal centered rearrangement and SeC---N bond rotation are both slow on the NMR time scale: (b) S2C---N bond rotation is fast, but metal centered rearrangement is slow'; and (c) metal centered rearrangemem is fast (S2C---N bond rotation is slow or fast I. The analysis assumes 7-coordinate complexes have pentagonal bipyramidal structure and neglects for the moment, the possibilit} of hindered rotation about N-R bonds. The complexes cis-Mo(NOI2(SeCNM%)~ and Mo(NO) (S2CNMe2)~ which are stereochemically rigid at 30° exemplify the possibility (a): for the former compound, the two methyl resonances are well separated (by 0.23 ppm), and for the latter, the four methyl signals span (/.24 ppm [22]. The protor~ NMR spectra for the compounds (~CH~C~H4)Zr(S2CNMe2)3 and (~'-CH3C~H4)Zr(S2CNEt2)~ are represented in Fig. 2 and Fig. 3 respectively. Two triplets due to protons of C2~ and C3.4 in substituted cyclopentadienyl ring (Fig. 5) and a singlet due to protons of CH~ (the substituent) are observed in both the compounds (Table I1. The two triplets observed are due to the shielding of the protons of C2., and C-,4 by the methyl substiluent, the effect being more pronounced for protons at C,,~. The remaining resonance lines in the two Figs. are due to the methyl and ethyl protons on the dithiocarbamate ligands in the methyl and ethyl compounds respectively. Four distinct methyl resonances are observed (Fig. 2) due to group "Me. ~'Me, ~"Me and *'Me (Fig. 4t with relative intensities 2:1:2:1. The inequivalence of the methyl protons arises from the low symmetry (CO of the complex and the barrier to rotation about the C,-=N bond. Figure 3 shows a complex pattern for the -CH:- and -CH3 lines (of the ethyl groups). Considering the fact that the environment for the R groups is not very much different and that coupling constant is small, the four quartets (for the -CH2- protons) are expected to intermix. Similarly, the four triplets (due to -CH3 protons) are expected to overlap. Thus, a complex pattern is observed
242
VINOD KUMAR JAIN and B. S. GARG
Resonance signals due t o :
-CH~ protons of S ~ N (C H3)2 aI
- C5 H4 protons of "rr- CH3C5 H4
CH 3 protons of "/TCH3C5H 4
ol
2
j
I
6
2(0): At 5 0 0 cps O
(3 ~
_2 2 ( b ) : At 2 5 0 c p s
o
2 ( c ) : At I 0 0 cps
oI
S
Fig. 2. Proton NMR spectrum of MeCpZr[S~CN(CH3)z]3. Position of the peaks (in Hz). 1, -362.4; 2, -359.8: 3, -357.5; 4, -340.3; 5, -337.6; 6, -335.3; a, -199.5; a' -197.6; b, -195.7: b', -194.4; x, -133.4.
Preparation and characterisation of some complexes
Resonance signols due t o
243
- CH3Pro10ns of SzCN(C2Hs)2
- C H 2- protons of S2CN(C2H5)2
- C5 H 4 protons ofTT CN3CsH 4
-CH 3 protons of TT- CH~jCsH 4
b
I
3
4
y-J 3(0]: A~ 5 0 0 cps
t 3(b) AI 2 5 0 c p s
l L_
Fig. 3. Proton NMR spectrum of MeCpZr[S2CN(CzHs)2]~. Position of the peaks (in Hz). I.-364.4; 2,-362.0; 3 -359.4 4, 341.9: ~,. 339.5"6,-336.5;x.-134.3;a, 229.9:b. 228.1:c,-222.9:d,-221.O;e.-216.1:f,-214.2:k,-80.9:i, 79,5: m, -74.6: n. -72.9: o, 67.9: p, 65./): q, -60.9.
244
VINOD KUMAR JAIN and B. S. GARG Table 3. Characteristic IR bands of MeCoZr(S2CNR2)3 (R = Me, Et) complexes Peak position (in cm-1) Due to Due to MeCpZr(S2CNMe2)3 MeCpZr(S2CNEt2)3
S. No.
Assignment
1 2 3 4t (i) (ii)
353 s, b 1490 vs, b 995 s
355 s, b 1485 vs 1000 s, b
u(Zr-S) v(C=N) u(C=S)
2940 sh 1435 sh
3010 m 1425 s
(iii)
1028 m
1032 m
~'(C-H) v(C-C) (asymmetric ring breathing) ~,(C-H) (in plane bending) v(C-H) (out of plane deformation) t,(C-N-C) v(C-H) aliphatic
(iv)
793m, 812sh
5 6
802s
l138vs, b 2905 m
l140s 2965 sh
tlR band characterising ~--CH3CsH4 ring. Table 4. Predicted number (relative intensity) of R group resonances for various rearrangement possibilities Compound
Symmetry
(A)
(B)
(C)
Cs-m Cs-m C:m
4(2 : 2 : 1: l) 4(2: 2:1 : 1)t 8~:(2 : 2 : 1 and 2 : 2 : 1 : 1)§
2(2: 1) 2(2: 1)t 4(2:1 and 2: 1)jr
1 1 2¶
(zr-CH3CsHs)Zr(S2CNR2)3 (~--CH3CsH4)Zr(S2CNMe2)3 (Tr-CH3CsH4)Zr(S2CNEt2)3
tEach resonance line will be observed as a singlet due to the absence of protons on adjacent carbon atoms. :~Four resonance lines due to four different types of -CH2 protons, each singal will be observed as a quartet due to adjacent -CH 3 protons; Another four resonance lines due to four different types of -CH 3 protons, each signal will be observed as a triplet due to adjacent -CH 2- protons. §The overall integrated ratio of resonance signals of -CH 2- protons to resonance lines of -CH 3protons is really 2: 3. ]ITwo resonance signals due to -CH2- protons (each a quartet) and two resonance signals due to -CH3 protons (each a triplet). ¶One resonance signal (a quartet) due to -CH 2- protons and one resonance signal (a triplet) due to -CH 3 protons.
RO' MeCp
\ ~ N
c/
l--s C--
.---'I/ c/
/
',
/
Ro
R°
"-4 \
,/
"_s" / I
Rb
N / R/b ,
MeCp : "/r-CH3CmH4R:CH3-,CeH 5-
Fig. 4. Pentagonal bipyramidal structure of MeCpZr[S2CNR2]3. 3
2
CH3
5
Fig. 5. Methylcyclopentadienyl anion.
as shown in Fig. 3. The intensities were determined by planimetric integration of three spectra. The integrated proton ratios correspond to the formula (CH3CsH4)Zr(S2CNR2)3 (R = CH3-, C H 3 C H 2 - ) for the two complexes. From the above discussion it must be concluded that observed methyl and - C H 2 - proton resonances result from non-equivalent environments for these groups in the (~r-CH3CsH4)Zr(S2CNR2)3 ( R = Me, Et) molecule.
Preparation and characterisation of some complexes l'he resonance lines for the R group in the two compounds conform to the possibility (A) in Table 4. T h u s the above two 7-coordinate complexes have pentagonal bipyramidal structures. The structure is bound to be slightly distorted due to the presence of a methylcyclopentadienyl group in the molecule. 4cknowledgement--The authors are thankful to National Council of Educational Research and Training, New Delhi, India for the Award of National Science Talent Search Fellowship to one of ns IV.K.J.t REFERENCES I \ . N. Bhal. R, ('. Fay, I). F. Lewis, A. F. landmark and S. H Strauss, lnorg. Chim. 13, 886 (1974). 2. D. F. Lewis and R. C. Fay, J. Am. Chem. Soc. 96, 3843 ~1974). J. C. Dewan, D. L. Kepert, C. L. Raston, D, Taylor, A. H. While and E. N. Maslen. J Chem. Soc. (Dalton Trans.) 2082 (1973). 4 T. F. Brennan and I. Bernal, Chem. Commun. 138 (1970); [not~,,. Chim. Acta 7,283 (1973). H. Alan Bruder, R. C. Fay, David F. Lewis and Alice Ann Sayler, J. Am. Chem. Soc. 98, 6932 (1976). 6. R (. Fay and T. J. Pinnavaia, lnorg. Chem. 7, 508 (1968). 7 M. Elder, lnor~,,. Chem. 8, 2103 (1969). 8. H [.. Klopping and G. J. M. Van der Kerk, Recl. Tray. Chim. Pov~-Ba~ 70. 917 (1951).
74 ~
9, E. Samuel, B~dl. Sot. Chim. I Frame) 3548 (1966t. 10. R. C. Fay and R. N. Lowry, lnorg. Chem. 6, 1512 (1967) 11. B. F. G. Johnson, K. H. A10baidi and J, A. McCleverty J. Chem. Soc, (A), 1668 (1969}. 12. A. Domenciano, A. Vaciago, L. Zambonelli, P. I_ l,oader and L. M. Venanzi Chem. Commun. 476 (1966). 13. C. O'Connor. J. D. Gilbert and G. Wilkinson, J. Chem. So(. (A), 84 (1969). 14. F, Bonati and R. Ugo, J. Organometal Chem. 10, 257 (1967L 15. C. S. Harreld and E. O. Schlemper, Acta Crystallovr Sec. B, 27. 1964 (1971). 16. E. C. Alyea, B. S. Ramaswamy, A. N. Bhal and R C. Fay, lnor~,. NucL Chem. Lett. 9, 399 (1973). 17. M. Colapietro, A. Vaciago. D. C. Bradley, M. B. Hursthouse and I. F. Rendall, Chem. Commun. 743 (1970~: J. ("hem. So~. (Dalton Trans.)1052 (1972). 18. D. C. Bradl% and M. H. Gitlitz, Chem. Commun. 289 (1965): J. Chem. Soe (A), 1152 (1969). 19. M. C. Palazzotto, D. T. Duffy, B. L. Edgar. L. Que, Jr. and I,. H. Pignolet, J. Am. Chem. Soc. 45, 4537 (1973): and references therein. 20. B. L. Edgar, D. T. Duffy, M. C. Palazzotto and 1, H. Pignolel, J. Am. Chem. Soc. 95, 1125 (1973): and references therein. 21. R. M. Golding, P. C. Healy, P. W, G. Newman, l!. Sinn ~md A. H. White, lnorg. Chem. 11, 2455 (1972). 22. R. Davis, M. N. S. Hill. C. E. Holloway. B. F. (;, Johnson and K. H. AI Obaidi, J. Chem. Soc. (A), 994 (1971).
Pergamon Press
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PREPARATION AND CHARACTERISATION OF SOME STEREOCHEMICALLY RIGID 7-COORDINATE MONOMETHYLCYCLOPENTADIENYL ZIRCONIUM(IV) TRIS-N, N-DIALKYL DITHIOCARBAMATE COMPLEXES V1NOD KUMAR JAIN and B. S. GARG* Department of Chemistry, University of Delhi, DelhM 10 007, India
(Received 13 May 1977) Abstract--Zirconium(IV) N,N-dialkyl dithiocarbamates of the type MeCpZr(S2CNR2) 3 where R = Me, Et have been prepared by reaction of bis-methycyclopentadienyl zirconium(IV) dichloride with sodium salts of substituted dithiocarbamic acids in aqueous and non-aqueous media. They have also been prepared by reaction of monomethycyclopentadienyl zirconium(IV) trichloride with sodium salts of substituted dithiocarbamic acids in nonaqueous medium. Molecular weight, conductance and IR studies point out that these complexes are monomeric non-electrolytes in which all of the dithiocarbamate ligands are bidentate. Therefore. a coordination number "7" may be assigned to zirconium(IV) ion in these compounds. Proton NMR spectra of these complexes in carbon disulfide or deuterated chloroform indicate that ill there is hindered rotation about C--N bonds at ambient temperature, and (ii) metal centered rearrangement is slow on the NMR time-scale at ambient temperature (30°C).
INTRODUCTION Of the many ligands that are known to stabilise the higher coordination states of metals, the dithiocarbamate tigands are particularly welt suited due to (i) their low charge, and (ii) their relatively small "bites" (2.8-2.9 ,~). The different resonating structures of the dithiocarbamate ligands are shown in the following Figs. l(a) to l(c):
R\N__c
\S,~
l(a)
R\
/S ~
~ R/N--C~s
I(b)
R\~ .._c/SG (
~ R/
\S e
l(cl
Fig. I. Resonating structures for dithiocarbamate ligands. Although the literature on metal dithiocarbamates is extensive, there are very few such complexes and still more few, the 7-coordinate complexes of the early transition metals. The present communication deals with the preparation and characterisation of the 7-coordinate meth~lcyclopentadienyl zirconium(IV) N,N-dialkyl dithiocarbamate complexes of the type MeCpZrIS2CNR2b where R = Me. Et. These complexes are closely related to the dithiocarbamade complexes Ti[(S2CNR2)3]CI[I, 2], VO[S?CN(C2Hs)2]3[3], NbO[S:CN(C2H,bb[3], Mo(NO)[S,('NIn-C4H9)2]3[4I and ( r [ C~H,)Zr [S2CN(CH02]3[5}. Other reported 7 coordinate compounds of zirconium(W) include M(acachCl ( M = Zr or Hf; a c a c = C H 3 - C O - C H - C O CH~)[6] and (rr-C~HdZrICF3COCHCOCF~b[7]. All the above 7-coordinate compounds have been shown to possess pentagonal bipyramidal structures in which the monodentate ligand occupies an axial position. A similar structure for (~r-CH3CsH4)Zr(S2CNR2)3 R = Me, Et is suggested by the proton NMR spectrum which exhibit a complex pattern (when R = Me, four methyl resonances of relative intensity 2 : 1 : 2 : 1 are observed at ambient probe temperature (30°C): A more complex pattern is observed for the corresponding ethyl derivative). *Author for correspondence
EXPERIMENTAL Reagents and techniques. Sodium salts of dithiocarbamic acid Na(S2CNR2) were prepared by the method[8] described by Klopping and Kerk. The above sodium salts were dried in vacuum over phospboruspentoxide (first at room temperature and then at 110°). For reactions in aqueous medium, however, the sodium salts were used without any drying. Bis-methylcyclopentadienyt zirconium(IV) dichloride was prepared by reaction of zirconium tetrachloride with sodium salt of methylcyclopentadiene in tetrahydrofuran[9]. Dichloromethane and benzene were dried by refluxing for 24 hr over calcium hydride. Nitrobenzene was purified for conductance measurements by the method described by Fay et al.[10]. Preparation of the complexes. The compounds included in this communication were prepared by the following methods, viz. (a) in aqueous medium, and (b) in non-aqueous medium by reaction of (i) bis-methycyclopentadienyl zirconium(IV) dichloride, and (ii) mono-methylcyclopentadienyl zirconium(IV) trichloride with anhydrous Na(S2CNR2). (MeCp)2ZrC12 + 3Na(S2CNR ~) MeCpZr(S2CNR2) 3 + 2NaCl + NaCp (in aqueous and non-aqueous medium) MeCpZrCI~ + 3Na(S2CNR2) ~ MeCpZr(S,CNR2) ~+ 3NaC1 (in non-aqueous medium). (A) Preparation in aqueous medium. The bis-methylcyctopentadienyl zirconium(IV) dichloride was dissolved in water by refluxing and the solution was filtered to remove insoluble materials, the filtrate was cooled to room temperature. The sodium salt of dithiocarbamate ligand was dissolved in water at room temperature and filtered. The filtrate so obtained was added dropwise to the solution of bis-methylcyclopentadienyl zirconium(IV) dichloride. The precipitate so obtained was repeatedly extracted by shaking with dichloromethane. The above process was continued till the aqueous layer did not give any more precipitate upon addition of sodium dithiocarbamate solution. The dichloromethane containing the dissolved reaction product was dried over calcium chloride. Colourless crystals of the compounds were obtained by adding petroleum ether (6080°C) to the above and allowing the mixture to stand overnight. The above method of preparation is unsuitable because of very low solubility of bis-methytcyclopentadienyl zirconium(IV) dichloride in water.
239
240
VINOD KUMAR JAIN and B. S. GARG
(B) Preparation in non-aqueous medium (i) By refiuxing bis-methylcyclopentadienyl zirconium(IV) dichloride with sodium salts of dithocarbamates in dichloromethane: A solution of bis-methylcyclopentadienyl zirconium(IV) dichloride in dichloromethane was refluxed with calculated amounts of anhydrous sodium salts of the dithiocarbamate ligands for 24 hr. The hot solution was then filtered through a filtration unit fitted with a G-4 sintered glass disc. Colourless crystals of the compounds were obtained by adding petroleum ether (60-80°C) to the filtrate and allowing the mixture to stand overnight. (ii) By refluxing mono-methylcyclopentadienyl zirconium(IV) trichloride with sodium salts of dithiocarbamate ligands in dichloromethane: A solution of mono-methylcyclopentadienyl zirconium(IV) trichloride (prepared by the reaction of quantitative amounts of methylcyclopentadienyl thallium(1) with zirconium tetrachloride in tetrahydrofuran) in dichloromethane was refluxed with stoichiometric amounts of sodium salts of dithiocarbamate ligands for 24 hr. The hot solution was then filtered through a filtration unit fitted with a G-4 sintered glass disc to remove the solid sodium chloride. Colourless crystals of the compounds were obtained as in B(i).
Molecular weight and conductance measurements Molecular weights were determined ebullioscopically in benzene using a Gallen Kamp (U.K.) ebulliometer. Conductance measurements were made in nitrobenzene at 30-+0.05°C with a Beckmann Conductivity Bridge Model No. RC-18A. IR spectra. IR spectra were recorded in solid state (KBr pellets) in the region 4000-250cm ~ with a Perkin-Elmer 621 grating spectrophotometer.
Nuclear magnetic resonance spectra The proton NMR spectra were recorded at ambient temperature (30°C) at sweep width of 100-500Hz with a Varian A-60 spectrometer. Spectra were recorded in triplicate, and the values reported in Table 1 are average values; the magnetic field sweep was calibrated with a standard sample of chloroform and tetramethysilane (1%) in deuterated chloroform.
RESULTS AND DISCUSSION
Mono-methylcyclopentadienyl zirconium(IV) dithiocarbamate complexes of the type MeCpZr(SzCNR2t3 (R = Me, Et) have been prepared by reaction of bis-methylcyclopentadienyl zirconium(IV) dichloride with sodium N,N-dialkyldithiocarbamates in aqueous medium and in non-aqueous medium by refluxing in dichloromethane. They have also been prepared by refluxing mono-
methylcyclopentadienyl zirconium(IV) trichloride with sodium N,N-dialkyldithiocarbamates in dichloromethane. The methods used for preparation and isolation of these compounds (see Experimental section) give materials of good purity as judged by satisfactory elemental analysis and by the proton NMR spectra of carbon disulfide or deuteriochloroform solutions (Table 1). Both the compounds are new. The two compounds are white in colour. They are moderately soluble in carbon disulfide, dichloromethane and chloroform. Dichloromethane was used to crystallise the compounds. The two compounds are thermally stable but decompose near their m.ps. The solids are quite stable in air but their solutions are hydrolysed relatively rapidly. The ethyl compound is more susceptible to hydrolysis. Conductance measurements (Table 2) show that both the complexes are essentially non-electrolytes in nitrobenzene. The subject of chief interest in the preparation of these compounds is the stereochemistry. A coordination number of "7" may be assigned if all three dithiocarbamate ligands are bidentate, as in Mo(NO)(S2CNR2)3 (R = Me[11] or n-Bu [4]) and the methylcyclopentadienyl group occupies one coordination site. Fay et al.[5] have described the X-ray diffraction of (r~5CsHs)Zr[S2CN(CH3)2]3 in which (though zirconium is formally l 1-coordinate but) because of the relatively small size of the cyclopentadienyl group it is considered to occupy single axial coordination site in a pentagonal bipyramidal structure. On this analogy methylcyclopentadienyl group in the compounds included in this communication is assumed to occupy single coordination site; however, the more common coordination number of 6 would result if one of the dithiocarbamate ligands behaves as an s-bonded mondentate ligand, as in Ru(NO)(S2CNRz)3 ( R = Me[ll] or having only bidentate ligands. The most significant of these extra bands are a second C-N stretching band near 1470 cm 1112, 13] and a second C-S stretching band near exhibit additional IR bands not found for complexes Et[12]). These two bonding possibilities can be distinguished by IR spectroscopy since complexes having both monodentate and bidentate-dithiocarbamate ligands 1000 cm -j [14]. The Sn(SzCNEt~.)4 which has been shown by X-ray analysis to be a 6-coordinate complex having two monodentate SzCNEtz groups [15] exhibits two C-N bands (1512 and 147lcm -~) and two C-S bands (1008 and 989cm ~)[16] while the 8-coordinate
Table I. Proton chemical shift (in Hz) and coupling constant data (in Hz) at 30°C Deuteriochloroform solution S2CNR2 portion
Compound MeCpZr(S2CNMe2)3¶ MeCpZr(S2CNEtz)3¶
7r-CH3CsH4 - 359.8t, - 337.6t, - 133.4s - 362.0t, - 339.3t, - 134.3s
J
-CH2-
-CH3
2.5 -- 199.5,- 197.6,- 195.7, - 194.4t 2.6 - 228.1, - 222.9, 221.0~: - 74.6, - 72.9§
J 7.0, 6.9II
tFor the methyl compound, the four peaks observed (the intensity ratio being 2:0.95 : 2.05 : 0.98) are due to four non equivalent methyl groups present in the compound and not due to the coupling of protons on adjacent atoms. :~Position of three most intense peaks. §Position of two most intense peaks. ]lTwo J values; both are J(CH~-CH2-) but the different values are due to different types of ethyl groups. Both are approximate values due to overlapping of the four triplets due to four types of ethyl groups. ¶Me = CH3-; and Et = CH3CH:t, triplet; s, singlet.
Preparation and characterisationof some complexes
241
Ti(S2CnEt2)4[17] displays just one C-N band (1503 cm ~) and one C-S band (1001 cm ')[16, 181. Characteristic IR frequencies for the MeCpZr(S2CNR2)3 complexes are presented in Tabk', 3. In the IR some of the absorption bands due to the dithiocarbamato ligands are masked by methylcyclopentadienyl absorption bands, but several assignments are possible. The "thioureide'" band (C---N) near 1500 cm t is very characteristic of dithiocarbamates. The frequency of this band lies between that for C-N (1250-1350 cm ') and C=N (1640-1690 cm '), which suggests that this bond has some double bond character. Table 3 shows that both the complexes exhibit just one C-N band and one C-S band. It is assumed from this evidence that the C-S bonds are most likely equivaltnt. The spectra, therefore, indicate bidentate dithiocarbamate attachment and therefore coordination number "7" for Zr(IV) ion. On the whole then, the IR data favour a 7-coordinate structure for the above two compounds.
-t:~ z
~,
~
~
, r ¸,
~
Interpretation of NMR spectra Stereochemical non-rigidity. Three kinetic processes + + + ~ ; ~
~ N N N
._=
< ~ < ~
.,..
,x=
>,
"2 --: >
e--!
-
>.. k.s
e<
g=
Z
Z ¢..o
G ca
are known to affect the line shape in NMR spectra of metal dithiocarbamate complexes (1) metal centered rearrangement[19] I21 S2C-'-N bond rotation[201 and (3) hindered rotation about C-N single bonds in the NR2 portion of the S2CNR2 ligand[21]. The expected number and relative intensities of R-group resonances for the MeCpZr(S2CNR~)3 complexes are indicated in Table 4 for the following possibilities: (a) metal centered rearrangement and SeC---N bond rotation are both slow on the NMR time scale: (b) S2C---N bond rotation is fast, but metal centered rearrangement is slow'; and (c) metal centered rearrangemem is fast (S2C---N bond rotation is slow or fast I. The analysis assumes 7-coordinate complexes have pentagonal bipyramidal structure and neglects for the moment, the possibilit} of hindered rotation about N-R bonds. The complexes cis-Mo(NOI2(SeCNM%)~ and Mo(NO) (S2CNMe2)~ which are stereochemically rigid at 30° exemplify the possibility (a): for the former compound, the two methyl resonances are well separated (by 0.23 ppm), and for the latter, the four methyl signals span (/.24 ppm [22]. The protor~ NMR spectra for the compounds (~CH~C~H4)Zr(S2CNMe2)3 and (~'-CH3C~H4)Zr(S2CNEt2)~ are represented in Fig. 2 and Fig. 3 respectively. Two triplets due to protons of C2~ and C3.4 in substituted cyclopentadienyl ring (Fig. 5) and a singlet due to protons of CH~ (the substituent) are observed in both the compounds (Table I1. The two triplets observed are due to the shielding of the protons of C2., and C-,4 by the methyl substiluent, the effect being more pronounced for protons at C,,~. The remaining resonance lines in the two Figs. are due to the methyl and ethyl protons on the dithiocarbamate ligands in the methyl and ethyl compounds respectively. Four distinct methyl resonances are observed (Fig. 2) due to group "Me. ~'Me, ~"Me and *'Me (Fig. 4t with relative intensities 2:1:2:1. The inequivalence of the methyl protons arises from the low symmetry (CO of the complex and the barrier to rotation about the C,-=N bond. Figure 3 shows a complex pattern for the -CH:- and -CH3 lines (of the ethyl groups). Considering the fact that the environment for the R groups is not very much different and that coupling constant is small, the four quartets (for the -CH2- protons) are expected to intermix. Similarly, the four triplets (due to -CH3 protons) are expected to overlap. Thus, a complex pattern is observed
242
VINOD KUMAR JAIN and B. S. GARG
Resonance signals due t o :
-CH~ protons of S ~ N (C H3)2 aI
- C5 H4 protons of "rr- CH3C5 H4
CH 3 protons of "/TCH3C5H 4
ol
2
j
I
6
2(0): At 5 0 0 cps O
(3 ~
_2 2 ( b ) : At 2 5 0 c p s
o
2 ( c ) : At I 0 0 cps
oI
S
Fig. 2. Proton NMR spectrum of MeCpZr[S~CN(CH3)z]3. Position of the peaks (in Hz). 1, -362.4; 2, -359.8: 3, -357.5; 4, -340.3; 5, -337.6; 6, -335.3; a, -199.5; a' -197.6; b, -195.7: b', -194.4; x, -133.4.
Preparation and characterisation of some complexes
Resonance signols due t o
243
- CH3Pro10ns of SzCN(C2Hs)2
- C H 2- protons of S2CN(C2H5)2
- C5 H 4 protons ofTT CN3CsH 4
-CH 3 protons of TT- CH~jCsH 4
b
I
3
4
y-J 3(0]: A~ 5 0 0 cps
t 3(b) AI 2 5 0 c p s
l L_
Fig. 3. Proton NMR spectrum of MeCpZr[S2CN(CzHs)2]~. Position of the peaks (in Hz). I.-364.4; 2,-362.0; 3 -359.4 4, 341.9: ~,. 339.5"6,-336.5;x.-134.3;a, 229.9:b. 228.1:c,-222.9:d,-221.O;e.-216.1:f,-214.2:k,-80.9:i, 79,5: m, -74.6: n. -72.9: o, 67.9: p, 65./): q, -60.9.
244
VINOD KUMAR JAIN and B. S. GARG Table 3. Characteristic IR bands of MeCoZr(S2CNR2)3 (R = Me, Et) complexes Peak position (in cm-1) Due to Due to MeCpZr(S2CNMe2)3 MeCpZr(S2CNEt2)3
S. No.
Assignment
1 2 3 4t (i) (ii)
353 s, b 1490 vs, b 995 s
355 s, b 1485 vs 1000 s, b
u(Zr-S) v(C=N) u(C=S)
2940 sh 1435 sh
3010 m 1425 s
(iii)
1028 m
1032 m
~'(C-H) v(C-C) (asymmetric ring breathing) ~,(C-H) (in plane bending) v(C-H) (out of plane deformation) t,(C-N-C) v(C-H) aliphatic
(iv)
793m, 812sh
5 6
802s
l138vs, b 2905 m
l140s 2965 sh
tlR band characterising ~--CH3CsH4 ring. Table 4. Predicted number (relative intensity) of R group resonances for various rearrangement possibilities Compound
Symmetry
(A)
(B)
(C)
Cs-m Cs-m C:m
4(2 : 2 : 1: l) 4(2: 2:1 : 1)t 8~:(2 : 2 : 1 and 2 : 2 : 1 : 1)§
2(2: 1) 2(2: 1)t 4(2:1 and 2: 1)jr
1 1 2¶
(zr-CH3CsHs)Zr(S2CNR2)3 (~--CH3CsH4)Zr(S2CNMe2)3 (Tr-CH3CsH4)Zr(S2CNEt2)3
tEach resonance line will be observed as a singlet due to the absence of protons on adjacent carbon atoms. :~Four resonance lines due to four different types of -CH2 protons, each singal will be observed as a quartet due to adjacent -CH 3 protons; Another four resonance lines due to four different types of -CH 3 protons, each signal will be observed as a triplet due to adjacent -CH 2- protons. §The overall integrated ratio of resonance signals of -CH 2- protons to resonance lines of -CH 3protons is really 2: 3. ]ITwo resonance signals due to -CH2- protons (each a quartet) and two resonance signals due to -CH3 protons (each a triplet). ¶One resonance signal (a quartet) due to -CH 2- protons and one resonance signal (a triplet) due to -CH 3 protons.
RO' MeCp
\ ~ N
c/
l--s C--
.---'I/ c/
/
',
/
Ro
R°
"-4 \
,/
"_s" / I
Rb
N / R/b ,
MeCp : "/r-CH3CmH4R:CH3-,CeH 5-
Fig. 4. Pentagonal bipyramidal structure of MeCpZr[S2CNR2]3. 3
2
CH3
5
Fig. 5. Methylcyclopentadienyl anion.
as shown in Fig. 3. The intensities were determined by planimetric integration of three spectra. The integrated proton ratios correspond to the formula (CH3CsH4)Zr(S2CNR2)3 (R = CH3-, C H 3 C H 2 - ) for the two complexes. From the above discussion it must be concluded that observed methyl and - C H 2 - proton resonances result from non-equivalent environments for these groups in the (~r-CH3CsH4)Zr(S2CNR2)3 ( R = Me, Et) molecule.
Preparation and characterisation of some complexes l'he resonance lines for the R group in the two compounds conform to the possibility (A) in Table 4. T h u s the above two 7-coordinate complexes have pentagonal bipyramidal structures. The structure is bound to be slightly distorted due to the presence of a methylcyclopentadienyl group in the molecule. 4cknowledgement--The authors are thankful to National Council of Educational Research and Training, New Delhi, India for the Award of National Science Talent Search Fellowship to one of ns IV.K.J.t REFERENCES I \ . N. Bhal. R, ('. Fay, I). F. Lewis, A. F. landmark and S. H Strauss, lnorg. Chim. 13, 886 (1974). 2. D. F. Lewis and R. C. Fay, J. Am. Chem. Soc. 96, 3843 ~1974). J. C. Dewan, D. L. Kepert, C. L. Raston, D, Taylor, A. H. While and E. N. Maslen. J Chem. Soc. (Dalton Trans.) 2082 (1973). 4 T. F. Brennan and I. Bernal, Chem. Commun. 138 (1970); [not~,,. Chim. Acta 7,283 (1973). H. Alan Bruder, R. C. Fay, David F. Lewis and Alice Ann Sayler, J. Am. Chem. Soc. 98, 6932 (1976). 6. R (. Fay and T. J. Pinnavaia, lnorg. Chem. 7, 508 (1968). 7 M. Elder, lnor~,,. Chem. 8, 2103 (1969). 8. H [.. Klopping and G. J. M. Van der Kerk, Recl. Tray. Chim. Pov~-Ba~ 70. 917 (1951).
74 ~
9, E. Samuel, B~dl. Sot. Chim. I Frame) 3548 (1966t. 10. R. C. Fay and R. N. Lowry, lnorg. Chem. 6, 1512 (1967) 11. B. F. G. Johnson, K. H. A10baidi and J, A. McCleverty J. Chem. Soc, (A), 1668 (1969}. 12. A. Domenciano, A. Vaciago, L. Zambonelli, P. I_ l,oader and L. M. Venanzi Chem. Commun. 476 (1966). 13. C. O'Connor. J. D. Gilbert and G. Wilkinson, J. Chem. So(. (A), 84 (1969). 14. F, Bonati and R. Ugo, J. Organometal Chem. 10, 257 (1967L 15. C. S. Harreld and E. O. Schlemper, Acta Crystallovr Sec. B, 27. 1964 (1971). 16. E. C. Alyea, B. S. Ramaswamy, A. N. Bhal and R C. Fay, lnor~,. NucL Chem. Lett. 9, 399 (1973). 17. M. Colapietro, A. Vaciago. D. C. Bradley, M. B. Hursthouse and I. F. Rendall, Chem. Commun. 743 (1970~: J. ("hem. So~. (Dalton Trans.)1052 (1972). 18. D. C. Bradl% and M. H. Gitlitz, Chem. Commun. 289 (1965): J. Chem. Soe (A), 1152 (1969). 19. M. C. Palazzotto, D. T. Duffy, B. L. Edgar. L. Que, Jr. and I,. H. Pignolet, J. Am. Chem. Soc. 45, 4537 (1973): and references therein. 20. B. L. Edgar, D. T. Duffy, M. C. Palazzotto and 1, H. Pignolel, J. Am. Chem. Soc. 95, 1125 (1973): and references therein. 21. R. M. Golding, P. C. Healy, P. W, G. Newman, l!. Sinn ~md A. H. White, lnorg. Chem. 11, 2455 (1972). 22. R. Davis, M. N. S. Hill. C. E. Holloway. B. F. (;, Johnson and K. H. AI Obaidi, J. Chem. Soc. (A), 994 (1971).