A structural characterization of polypyrazolylborato and tetraphenyl compounds

Abstract

A series of polypyrazolylborato and tetraphenyl compounds have been studied by x-ray crystallography. The structure of (diphenyldipyrazolylborato) (2-methylallyl) (dicarbonylmolybdenum) has been determined. The molybdenum atom is coordinated by the n³-allyl ligand, two CO ligands and the nitrogen atoms of the two pyrazolyl rings. In the analogous compounds, where the dipyrazolylborato ligand is H₂Bpz₂ or (C₂H₅)₂Bpz₂ (pz=1-pyrazolyl) the dipyrazolylborato ligand interacts further with the molybdenum atom through a B-H group or a methylene C-H group giving a formal eighteen electron valence shell around the molybdenum atom. However, in the (diphenyldipyrazolylcorato)(2-methylallyl) dicarbonylmolybdenum no further litigation of the Mo atom is observed and, thus, the metal atom has only a formal sixteen electron valence shell. Interaction with an ortho C-H bond of one of the phenyl groups does not occur, as might have been expected. The same situation was observed when the structure of bis (diphenyldipyrazolylborato) nickel(II) was determined. The reason for this appears to be that the orientation of the phenyl groups which would be required for such an interaction is inconsistent with the attainment of a satisfactory conformation of the entire set of rings 2C₆H₅ and 2 C₃N₂H₃) about the boron atom. In phenyltrispyrazolylborato) (alyl) dicarbonylmolybdenum, where the configuration around the boron atom is somewhat similar to that in the diphenylbispyrazolylborato compounds, an 18-electron valence shell is attained by the molybdenum atom through the formation of a strong Mo-N bond with the third pyrazolyl group attached to the boron atom. Tetrakis (diethyldipyrazolylborato) dimolybdenum, diacetate-(diethyldipyrazolylborato)dimolybdate, and diacetate (trispyrazolylborato) dimolybdate have been prepared. The structures of the last two have been determined by x-ray crystallography..