Syntheses and crystal structures of group 6 metal complexes containing allyl and cyanotrihydroborate groups

Compounds M(η3-C3H5)(CO)2(NCCH3)2(NCBH3) and [N(CH3)4]2[M(η3-C3H5)(CO)2(NCBH3)3] (M = Mo, W) were prepared and structurally characterized. In the solid state, the allyl group orients its open face to the two carbonyl groups producing an endo form in the above compounds. In solution, an exo form coexists with an endo form in compound Mo(η3-C3H5)(CO)2(NCCH3)2(NCBH3). The cyanotrihydroborate ligand bonds to the metal through a nitrogen atom. Both of the IR and the 11B NMR spectroscopic data suggest the negative charge of the cyanotrihydroborate ligand on the complex is almost localized on the BH3 and this negative charge only has small effect on the metal–nitrogen interaction.