A new synthesis of charge-neutral tris-pyrazolyl and -methimazolyl borate ligands.
The dimethylamine in the adducts [(HNMe(2))B(azolyl)(3)] (azolyl=methimazolyl, pyrazolyl), obtained by reaction of the azole with B(NMe(2))(3), can readily be substituted with a range of nitrogen donors to provide new charge-neutral, tripodal ligands in high yield. This observation has led to a revision of an earlier interpretation of the mechanism of the formation of these species. The donor properties of the ligands [(nmi)B(azolyl)(3)] (nmi=N-methylimidazole) have been compared with their anionic analogues [HB(azolyl)(3)](-) by synthesis of their manganese(I)-tricarbonyl complexes and comparison of their infrared nu(CO) energies. This comparison indicates that the new neutral ligands are only marginally weaker donors than the corresponding anionic hydrotris(azolyl)borate ligands. This may be explained by the ability of the attached nmi ring to stabilize a positive charge remotely from the coordinated metal, which may also account for the fact that the [(nmi)B(pyrazolyl)(3)] ligand is a substantially stronger donor than the similarly neutral tris(pyrazolyl)methane ligand.
Bailey
Philip J
PJ
School of Chemistry, The University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh, EH9 3JJ, UK. Philip.Bailey@ed.ac.uk
Budd
Laura
L
Cavaco
Filipa A
FA
Parsons
Simon
S
Rudolphi
Felix
F
Sanchez-Perucha
Alejandro
A
White
Fraser J
FJ