Aspects of group 14 element - transition metal cluster chemistry
The synthesis of Sn[Fe₂(CO)₈]₂ from the SnCl₄/[Fe(CO)₄]²⁻ and SnCl₄/[Fe₂(CO)₈]²⁻ systems has been investigated. The reaction of SnCl₄ with the product mixture obtained by Na/amalgam reduction of Fe(CO)₅ provided the optimum yield (64% based on Sn). E[Co₂(CO)₇]₂ (E = Si, Ge), (CO)₄CoECo₃(CO)₉ (E = Si, Ge) and E[Fe₂(CO)₈]₂ (E = Si, Ge, Sn) have been reacted with various transition metal carbonyl anions. The Si[Co₂(CO)₇]₂/[Co(CO)₄]⁻ synthesis of [SiCo₉(CO)₂₁]²⁻, has also yielded [CCo₈(CO)₁₈]²⁻ (characterised by infrared spectroscopy and FABS mass spectroscopy) and [Cl₂SiCo₇(CO)₂₁]⁻ (characterised by X-ray crystallography as the [Et₄N]⁺ salt). A [CCo₁₀(CO)₂₄]ⁿ⁻ species has also been detected by FABS mass spectroscopy. (CO)₄CoGeCo₃(CO)₉ with [Mn(CO)₅]⁻ provided (CO)₅MnGeCo₃(CO)₉ in improved yields (72%). The reaction of the Si analogue gave (CO)₅MnSiCo₃(CO)₉, characterised by infrared spectroscopy and FASS mass spectroscopy. [Co₆(CO)₁₅]= acted as a source of [Co(CO)₄]⁻ and Co₄(CO)₁₂ in reactions with (CO)₄CoECo₃(CO)₉ (E = Si, Ge). [SiCo₉(CO)₂₁]²⁻ and Co₄(CO)₁₂ were isolated as the major products from the Si reaction, and [GeCo₅(CO)₁₆]⁻ from the Ge reaction. [GeCo₅(CO)₁₆]⁻ was also isolated as the major product from the reaction of Ge[Co₂(CO)₇]₂ with [CpNi(CO)]₂. In reactions of Si[Co₂(CO)₇]₂ with [Fe2(CO)₈]²⁻ and [Fe(CO)₃NO]⁻, no Si-containing clusters were detected amongst the products. The first reaction yielded [FeCo₃(CO)₁₂]⁻ (characterised by infrared spectroscopy and preliminary X-ray diffraction), Co₄(CO)₁₂ and Fe(CO)₅; and the latter reaction, [FeCo₃(CO)₁₂]⁻, Co₄(CO)₁₂ and the nitrido cluster, [NCo₆(CO)₁₅]⁻ ( characterised by infrared spectroscopy and X-ray crystallography). Combining E[Fe₂(CO)₈]₂ with [Co(CO)₄]⁻, [Fe₂(CO)₈]²⁻ or [Mn(CO)₅]⁻ also failed to produce clusters containing E atoms. No reaction was detected with [Co(CO)₄]⁻; the second reaction yielded [HFe₃(CO)₁₁]⁻ and [Fe₄(CO)₁₃]²⁻; and the third, Mn₂(CO)₁₀ and the carbido cluster [CFe₆(CO)₁₆]²⁻ (characterised by infrared spectroscopy and FABS mass spectroscopy). Some reactions of [SiCo₉(CO)₂₁]²⁻ and [GeCo₅(CO)₁₆]⁻ have been investigated. With [Ph₃PAu]⁺, [SiCo₉(CO)₂₁]²⁻ yielded a species formulated as [SiCo₉(CO)₂₂]³⁻ (from infrared and FABS mass spectroscopy data). A [CCo₁₀(CO)₂₄]⁻ species was also detected by FABS mass spectroscopy. NO⁺ appeared to add on to [SiCo₉(CO)₂₁]²⁻ but the exact nature of this product is not known. Reactions with Cp₂Co, [BuNCAu]⁺ and H⁺ have also yielded products which have not been fully characterised. Treatment of [SiCo₉(CO)₂₁]²⁻ with [(MeCN)₄Cu]⁺ led to disintegration of the cluster. [GeCo₅(CO)₁₆]⁻ did not react with [Ph₃PAu]⁺ or [CpNi(CO)]₂, but with CpFe(CO)₂I yielded Co₄(CO)₁₂, CpFeCo(CO)₆ and [GeCo₇(CO)₂₀]⁻ (characterised by infrared spectroscopy and FABS mass spectroscopy). The electrochemistry of clusters containing trigonal pyrimidal and spiro μ₄-EM₄ groups has been investigated using cyclic voltammetry. LₙMECo₃(CO)₉ (E = Si, Ge; and MLₙ = Co(CO)₄, Mn(CO)₅) compounds undergo an electrochemically reversible one electron reduction process, conforming with what has been reported for YCCo₃ (CO)₉ compounds. [Ge₂Co₇(CO)₂₁]⁻ and [Ge₂Co₅Fe₂(CO₂₂]⁻ contain two EM₃ redox centres which appear to behave independently. Reduction of spiro- E[Fe₂(CO)₈]₂ clusters occurs via two routes leading to [(CO)₄FeEFe₃(CO)₁₀]⁻ (more important for Si and Ge) or [(CO)₈Fe₂]E[Fe(CO)₄]₂²⁻ (more important for Sn and Pb). The cobaltocene reduction of Si[Fe₂(CO)₈]₂ yielded [(CO)₄FeSiFe₃(CO)₁₀]⁻, characterised using infrared spectroscopy. The vibrational spectra of E[Fe₂(CO)₈]₂ (E = Si, Ge, Sn), E[Co₂(CO)₇]₂ (E = Si, Ge) and (CO)₄CoECo₃(CO)₉ (E = Si, Ge) have been recorded and assigned where possible. For the E[Co₂(CO)₇]₂ systems a ‘double-Bor’ model, based on Bor’s analysis of (μ-E)₂M₂(CO)₆ compounds, provides a consistent assignment for the carbonyl vibrations.
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