Reactions of bis(cyclopentadienyl)vanadium derivatives with nitrogen mono-oxide and the crystal structure of an oxo-bridged nitrosyl complex of vanadium
Abstract
The reaction between [V(η-C5H5)2] and NO has been shown to have a 1 : 1 stoicheiometry but the initial product, presumed to be [V(η-C5H5)2(NO)], undergoes disproportionation to give a mixture of final products. The reaction between [V(η-C5H5)2(CO)] and NO occurred with a 2: 1 stoicheiometry and gave a complex containing NCO which could not be separated from a polymeric oxide. The complex [V(η-C5H5)2(NCO)] was obtained independently from [VCl(η-C5H5)2] and NCO– in aqueous solution. The reaction between [V(η-C5H5)2(CO)] and NOCl gave a mixture of products including one or more containing NCO–, and there was no reaction between NO and [V(η-C5H5)2(CO)2]+. The reaction between [VI(η-C5H5)2] and NO gave two products, both analysing as VI(C5H5)2NO. One was a brown insoluble polymer with ionic iodide which is believed to have bridging N2O22– ligands. The second product was green, monomeric [VI(C5H5)2(NO)]. This is a fluxional molecule as shown by e.s.r. and i.r. spectroscopy in tetrahydrofuran (thf) solution. The two forms of the molecule have different ν(NO) frequencies (1 670 and 1 590 cm–1). The form with the lower frequency [which is presumed to be VI(C5H5)2(NO) with either a bent {VNO} group or a linear {VNO} group but a long N–O bond] predominates at low temperature. The form with the higher ν(NO) frequency has a linear {VNO} group with a short N–O distance and is presumed to have at least one C5H5 ring with less than pentahapticity. When a solution of [VI(C5H5)2(NO)] in thf was set aside at room temperature, diamagnetic [{VI(η-C5H5)}2{V(η-C5H5)(NO)}2(µ-O)4] was formed. The structure of this complex, determined by X-ray diffraction, showed that it has an eight-membered ring of alternating V and O atoms with a two-fold axis in the centre of the ring. The V atoms alternately carry I or NO ligands, which are arranged in trans fashion to one another. The O–V–O angles are all similar, averaging 104.7(3)°, but the V–O–V angles are in two sets, two of 179.3(3) and two of 148.1(3)°. The four oxygen atoms lie in a plane with the V atoms carrying the iodo-ligand displaced 0.261 Å out of the plane towards the iodo-ligand and the V atoms carrying the NO ligand displaced 0.157 Å in the opposite direction. The reaction between [VBr(η-C5H5)2] and NO gave a complicated mixture of insoluble nitrosyl products and a soluble green monomer, [VBr(C5H5)2(NO)] which was analogous to [VI(C5H5)2(NO)] but lost NO far more readily. With [VCl(η-C5H5)2] and NO insoluble nitrosyls were again produced, as well as N2O and [V2O2Cl2(η-C5H5)3] which could also be obtained from [VCl(η-C5H5)2] and O2. There was no reaction between [VCl2(η-C5H5)2] and NO, but on addition of BF3 reduction of [VCl2(η-C5H5)2] to [VCl(η-C5H5)2] occurred.
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