Cycloheptatri-ene and -enyl derivatives of niobium
作者:Malcolm L. H. Green、Andrew K. Hughes、Patrick C. McGowan、Philip Mountford、Peter Scott、Stephen J. Simpson
DOI:10.1039/dt9920001591
日期:——
The new compounds [Nb(eta-6-C7H8)(PMe3)2Cl2] 1, [Nb(eta-C7H7)(eta-4-C7H8)(PMe3)] 2 and [Nb(eta-C7H7)(CO)3] 4 have been prepared. The 17-electron compound 1 has been crystallographically characterised and contains mutually trans tertiary phosphine and chloro ligands. Compound 2 contains the first crystallographically characterised eta-4-cycloheptatriene ligand, the structure of which is discussed in relation to its C-13 NMR spectrum and the use of inverse-mode (H-1-observed) C-13-H-1 shift correlation NMR spectroscopy. Treatment of 1 with magnesium butadiene reagent gives [Nb(eta-C7H7)(eta-4-C4H6)(PMe3)] 3 and photolysis of 4 in the presence of cycloheptatriene gives [Nb(eta-C7H7)(eta-4-C7H8)(CO)] 5. Compound 2 is protonated readily to yield [Nb(eta-C7H7)(eta-5-C7H9)(PMe3)][PF6] 6, and reacts with iodomethane to yield paramagnetic [Nb(eta-C7H7)(PMe3)2l] 7 which is isomorphous with the analogous 16-electron compound [Zr(eta-C7H7)(PMe3)2l], but has an unusually long Nb-l bond. Compound 4 reacts with Me2PCH2CH2PMe2 (dmpe) to give the monomeric [Nb(eta-C7H7)(dmpe)(CO)] 9. The analogous compound [Nb(eta-C7H7)(PMe3)2(CO)] 10 is prepared by reaction of 4 with PMe3. The paramagnetic sandwich complexes [Nb(eta-C5H5)(eta-C7H7)] 11 and [Nb(eta-C5H4Me)(eta-C7H7)] 12 react with 1 equivalent of allyl bromide to yield the diamagnetic bent-sandwich species [Nb(eta-C5H5)(eta-C7H7)Br] 13 and [Nb(eta-C5H4Me)(eta-C7H7)Br] 14 respectively.