Reaction of Me₂NC₆H₄SiH₃ with Co₂(CO)₈ gave Me₂NC₆H₄Si[Co(CO)₄][OCCo₃(CO)₉]₂ which was shown to have one –Co(CO)₄ group and two –OCCo₃(CO)₉ cluster units bonded to the silicon atom

Harfoot, Gwion J.

Nicholson, Brian K.

English

Research Commons@Waikato

1Correspondence to: Professor B K Nicholson  Chemistry Department  University of Waikato  Private Bag 3105  Hamilton  New Zealand  Email: b.nicholson@waikato.ac.nzFax: 64 7 838 4219  Anomalous reaction of an aryl silane with Co2(CO)8; characterisation of Me2NC6H4Si[Co(CO)4][OCCo3(CO)9]2.Gwion J. Harfoot, and Brian K Nicholson*.  Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand.Synopsis Reaction of Me2NC6H4SiH3 with  Co2(CO)8 gives  Me2NC6H4Si[Co(CO)4][OCCo3(CO)9]2 with a mixture of Si-Co and Si-O bonds.  Abstract.Reaction of Me2NC6H4SiH3 with  Co2(CO)8 gave Me2NC6H4Si[Co(CO)4][OCCo3(CO)9]2which was shown to have one -Co(CO)4 group and two -OCCo3(CO)9 cluster units bonded to the silicon atom. 21. Introduction.The reaction of organosilanes with Co2(CO)8 has long been known to give products with Si-Co bonds [1]. Thus Cl3SiH gives Cl3SiCo(CO)4 [2], SiH4 gives Si[Co2(CO)7]2[3], and PhSiH3 results in PhSi[Co(CO)4][Co2(CO)7] which decarbonylates to the closo-cluster PhSiCo3(CO)9 [4]. Reaction of silicon hydrides to give Si-Co bonds is involved in the hydrosilation of alkenes, catalysed by Co2(CO)8 [5].  We have recently examined the reactions of primary silanes RSiH3 with Co4(CO)12,which for R =  Me, Ph, p-MeOC6H4 or MeO(CH2)3- give the pseudo-octahedral clusters Co4(µ4-SiR)2(CO)11 [6,7]  However when R = p-Me2NC6H4 the yields of the Si2Co4cluster were low, giving by-products that from their intense purple colour and infrared spectra appeared to be of the type X-ECo3(CO)9 (E = Si or C), but which could not be further identified [7]. To see if there was a more specific route to these by-products we reacted p-Me2NC6H4SiH3 with Co2(CO)8 and now report that a completely different reaction takes place.  2. Experimental Section 2.1 General  Reactions were carried out under nitrogen, using standard Schlenk techniques. p-Me2NC6H4SiCl3 was prepared by combining the Grignard reagent from p-Me2NC6H4Br with excess SiCl4, and reducing the chloride with LiAlH4 gave the silane [8]. Electrospray mass spectra were recorded on a VG Platform II spectrometer, operated as detailed elsewhere [9] and IR on a Digilab FTS-40 instrument.  32.2 Reaction of p-Me2NC6H4C6H4SiH3 with Co2(CO)8.p-Me2NC6H4SiH3 ( 0.25 g, 1.67 mmol) and Co2(CO)8 (0.93 g, 2.71 mmol) were dissolved in toluene (20 mL) in a Schlenk flask. The mixture was stirred at 45-55°C for 4 hours, by which time it was a deep purple-red. Solvent was removed in vacuo, and the residue chromatographed on a silica column, eluting with petroleum spirits: CH2Cl2 (4:1). Four bands were collected: (i) unreacted Co2(CO)8; (ii) brown Co4(CO)12; (iii) a purple band characterised below; and (iv) orange Co4(µ4-SiC6H4NMe2)2(CO)11 identified by IR spectra [7]. Total recovery of material was low because significant decomposition accompanied the chromatography. The purple band was evaporated to give 0.050 g of microcrystalline solid, CO (petroleum spirit, cm-1) 2109m, 2100m, 2071w,sh, 2060s, 2053s, 2041m, 2033s, 2020m, 2011m, 2005m, 1866m. This could not be further separated but ESI-MS indicated strongly that there were two components in this band:  ESI-MS (MeOH) m/z 1234 [MA+H]+, 1206[MA+H-CO]+, and 1368 [MB+H]+, 1340 [MB+H-CO]+. Recrystallisation from CH2Cl2:petroleum spirits yielded a few black crystals of the Mr =1233 component which was fully characterised by an X-ray structure determination. The Mr = 1367 component has not yet been identified, since insufficient pure material could be obtained for elemental analysis or NMR studies. 2.4 X-ray crystallography 2.4.1 Structure of Me2NC6H4Si[Co(CO)4][OCCo3(CO)9]2Intensely purple-black crystals of 1 were obtained as described above. Data were collected on a Bruker CCD diffractometer. 4Crystal data: C32H10Co7NO24Si, M = 1233.02, orthorhombic, a = 23.454(7), b = 9.672(3), c = 18.810(5) Å, U 4267(2) Å3, T 163 K, space group Pca21, Z = 4, µ(Mo-K) = 2.77 mm-1, 52177 reflections collected, 7295 unique (Rint 0.035) used after correction for absorption (Tmax, min 1.000, 0.864). Crystal dimensions 0.86 x 0.36 x 0.20 mm3.Refinement on F2 gave R1 0.0208 [6876 data with I > 2 (I)] and wR2 0.0487 (all data). The hydrogen atoms were included in calculated positions. The structure of 1 is illustrated in Figure 1, with selected bond parameters included in the caption to the figure.  Crystallography was carried out with the SHELX programs [10]. 3 Results and discussion  The reaction between Me2NC6H4SiH3 and Co2(CO)8 in toluene is clearly different from that of other RSiH3 since the solution turns distinctly purple, in contrast to  the more usual orange-brown. Work-up required chromatographic separation, which led to extensive decomposition on the column so material recovery was relatively low. A small amount of orange Co4(µ4-SiC6H4NMe2)2(CO)11 was identified by comparison with an authentic sample, possibly formed from reaction of the silane with the Co4(CO)12 generated in the reaction mixture [7]. There was no indication of Me2NC6H4Si[Co(CO)4][Co2(CO)7] which might have been expected by analogy with the reaction of  PhSiH3 [4].  The only new material that could be isolated by chromatography was an intense-purple material.  The complexity of the carbonyl-region infrared spectrum indicated there was a mixture of at least two components but these could not be further separated.  ESI-MS gave two sets of clean signals representing two parent ions with daughter ions arising 5from CO loss. The major ions can be assigned as [M+H]+ species under the conditions used, so the two compounds correspond to molecular masses of 1233 and 1367 respectively.  This was confirmed for the lighter species by an X-ray structure determination. No further information could be gathered for the second component which remains unidentified, since a pure sample could not be obtained by crystallisation.  The X-ray structure determination of 1 is shown in the Figure.  The Me2NC6H4Si group is attached to a Co(CO)4 moiety by a Si-Co bond, and to two -OCCo3(CO)9clusters via the oxygen atoms.  This generates a very crowded molecule as shown by an intramolecular O(19)...O(32) distance of 2.86 Å, significantly less that the usual ca 3 Åfor non-bonded O...O contacts in metal carbonyls. Surprisingly, the O(10)-Si-O(20) angle is 97.7(1)°, much more acute than the idealised 109°, despite it being between the two largest groups. However interactions between the two -OCCo3(CO)9 cluster units are accommodated by the high flexibility of the C-O-Si linkages.  In other molecules of the type XOCCo3(CO)9, the X-O-C angle varies between 118° (X = a small group such as Me or Et [11]), to over 170° when X is large as in Cp2Zr[OCCo3(CO)9]2 [12].  In the silicon complex 1 these angles are 153°.The Co(CO)4 group has a Co-Si bond length of 2.284(8) Å, in the middle of the range from 2.226(5) Å for F3SiCo(CO)4 [13] to 2.381(7) Å for H3SiCo(CO)4 [14].  There is an interesting parallel between Me2NC6H4Si[Co(CO)4][OCCo3(CO)9]2 and CpTi[Co(CO)4][OCCo3(CO)9]2 [12], with similar overall structures. The larger size of the organic group in the titanium example is accommodated by the larger metal atom and longer distances to the other substituents, compared with those in the silicon example. However these are not uniformly changed.  If the Ti-O vs Si-O distances ( 1.829 vs 1.6566Å) are used to calculate the difference in radii between the two metals, the resulting figure of 0.17 Å is much smaller than the difference of 0.33 Å between the Ti-Co and Si-Co bonds (2.613 and 2.284 Å respectively). This suggests the Co(CO)4 group is much less strongly bonded to Ti than to Si.  The infrared spectrum for 1 can be assigned on the basis of characteristic patterns for the -Co(CO)4 and -OCCo3(CO)9 groups [15], the bands at 2010, 2011, and 2005 cm-1 arising from the former and those at 2109, 2053, 2041 and 2033 cm-1 from the latter. This leaves distinctive bands at 2060, 2020 and 1866 cm-1 for the second component of the crude reaction product with Mr 1367, but further characterisation was not achieved.  There have been several reports of compounds formed which incorporate OCCo3(CO)9 groups generated from Co2(CO)8. The usual requirements for this are a Lewis-acidic, oxophilic centre which ends up attaches to the oxygen atom (e.g. Li+,Et3NBCl2, Cp2(Cl)Hf, (acac)3Zr or Cl3Si [16]). In some cases where a basic solvent is used, a route involving base-induced disproportionation of Co2(CO)8 to give Co(II) and Co(CO)4-, and subsequent reaction of Co(CO)4- with Co2(CO)8 to give [OCCo3(CO)9]-,which then acts as a nucleophile, provides a rationale for cluster formation. However there are cases where OCCo3(CO)9 groups are formed where this process is unlikely, such as the isolation of N(CH2CH2O)3SiOCCo3(CO)9 from the reaction of the parent silatrane with Co2(CO)8 [17], and of Ph2Si[Co(CO)4][OCCo3(CO)9] from Ph2SiH2 in non-polar solvents [15]. It is therefore not clear which factors divert the reaction of silanes with Co2(CO)8 from the normal H2 elimination reaction leading to Si-Co bonds. For Me2NC6H4SiH3, the amine functional group may be sufficiently basic to induce the disproportionation of Co2(CO)8, initiating that pathway to 1 with OCCo3(CO)9 groups 7attached to the oxophilic Si atom, but other factors are also possible. Despite over thirty years of study, these apparently simple reactions are not yet fully understood. 84. Supplementary material. Crystallographic data for the structural analysis of 1 have been deposited with the Cambridge Crystallographic Data Centre, CCDC no 198997. Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Rd., Cambridge CB2 1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).  Acknowledgements We thank Dr Jan Wikaira and Professor Ward Robinson, University of Canterbury, for collection of X-ray intensity data. The William Georgetti Trust is thanked for a scholarship for GJH.  References. 1 H. G. Ang and P. T. Lau, Organometal. Chem. Rev. (a), 8 (1972) 235; F. Hofler, Top. Curr. Chem., 50 (1974) 129; K. M. Mackay and B. K. Nicholson, Ch 43 in G. Wilkinson, F. G. A. Stone and E. W. Abel (Eds) Comprehensive Organometallic Chemistry, Pergamon, Oxford, 1982. 2. A. J. Chalk and J. F. Harrod, J. Amer. Chem. Soc., 87 (1965) 1133; A. J. Chalk and J. F. Harrod, J. Amer. Chem. Soc., 89 (1967) 1640. 3. K. M. Mackay and C. C. Ngo, J. Chem. Res., (1992) S229, M2301. 4.  R. Ball, M. J. Bennett, E. H. Brooks, W. A. G. Graham, J. Hoyano and S. M. Illingworth, Chem. Commun., (1970) 592. 95 Ojima, I in S. Patai and S. Rappoport (Eds) The Chemistry of Organic Silicon Compounds, Wiley, New York, 1989; A. M. LaPointe, F. C. Rix and M. Brookhart, J. Amer. Chem. Soc., 119 (1997) 906. 6 S. G. Anema, S. K. Lee, K. M. Mackay and B. K. Nicholson, J. Organometal. Chem., 444 (1993) 211. 7. C. Evans, G. J. Harfoot, J. S. McIndoe, C. J. McAdam, K. M. Mackay, B. K. Nicholson, B. H. Robinson and M. L. Van Tiel, Dalton Trans., in press. 8. Y. Nagai, M. A. Ohtsuki, T. Nakano and H. Watanabe, J. Organometal. Chem., 35 (1972) 81. 9. W. Henderson, J. S. McIndoe, B. K. Nicholson and P. J. Dyson, J. Chem. Soc., Dalton Trans., (1998) 519. 10. G. M. Sheldrick, SHELX-97, Programs for the solution and refinement of crystal structures, University of Gottingen, 1997. 11. E. O. Fischer, J. Schneider and D. Neugebauer, Monatsche Chem., 114 (1983) 851; A. A. Aitchison and L. J. Farrugia, Organometallics, 6 (1987) 819. 12. B. Stutte, V. Batzel, R. Boese and G. Schmid, Chem. Ber., 111 (1978) 1603. 13. K. Emerson, P. R. Ireland and W. T. Robinson, Inorg. Chem., 9 (1970) 436. 14. A. G. Robiette, G. M. Sheldrick, R. N. F. Simpson, B. J. Aylett and J. A. Cambell, J. Organometal. Chem., 14 (1968) 279. 15. S. A. Fieldhouse, A. J. Cleland, B. H. Freeland, C. D. M. Mann and R. J. O'Brien, J. Chem. Soc., A (1971) 2536. 16. H. N. Adams, G. Fachinetti and J. Strahle, Angew. Chemie Int. Ed. Eng., 19 (1980) 404; V. Batzel, U. Muller and R. Allman, J. Organometal. Chem., 102 10(1975) 109; K. Kluwe, K. H. Thiele, A. Sorkau, A. Sisak and B. Neumuller, J. Organometal. Chem., 604 (2000) 68; B. K. Nicholson and J. Simpson, J. Organometal. Chem., 155 (1978) 237. 17. M. W. Kim, D. S. Uh, S. Kim and Y. Do, Inorg. Chem., 32 (1993) 5883.  11Caption to figure.  Figure 1.  The structure of the Me2NC6H4Si[Co(CO)4][OCCo3(CO)9]2 (1). Parameters include bond lengths (Å): Si(1)-Co(30) 2.2841(8), Si(1)-O(10) 1.652(2), Si(1)-O(20) 1.660(2), Si(1)-C(1) 1.827(3), C(10)-O(10) 1.316(3), C(20)-O(20) 1.321(3), Co-Co bonds 2.469 (av);  bond angles (degrees) O(10)-Si(1)-O(20) 97.7(1), C(1)-Si(1)-Co(30) 116.9(1), C(10)-O(10)-Si(1) 153.9(2), C(20)-O(20)-Si(1) 151.8(2).  

Anomalous reaction of an aryl silane with Co₂ (CO)₂; characterisation of Me ₂NC₆H₄Si[Co(CO)₄][OCCo₃(CO)₉]₂

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Anomalous reaction of an aryl silane with Co₂ (CO)₂; characterisation of Me ₂NC₆H₄Si[Co(CO)₄][OCCo₃(CO)₉]₂

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