Addressing the Chemical Sorcery of “GaI”: Benefits of Solid-State Analysis Aiding in the Synthesis of P→Ga Coordination Compounds

The differing structures and reactivities
of “GaI”
samples prepared with different reaction times have been investigated
in detail. Analysis by FT-Raman spectroscopy, powder X-ray diffraction, 71Ga solid-state NMR spectroscopy, and 127I nuclear
quadrupole resonance (NQR) provides concrete evidence for the structure
of each “GaI” sample prepared. These techniques are
widely accessible and can be implemented quickly and easily to identify
the nature of the “GaI” in hand. The “GaI”
prepared from exhaustive reaction times (100 min) is shown to possess
Ga2I3 and an overall formula of [Ga0]2[Ga+]2[Ga2I62–], while the “GaI” prepared with
the shortest reaction time (40 min) contains GaI2 and has
the overall formula [Ga0]2[Ga+]­[GaI4–]. Intermediate “GaI” samples
were consistently shown to be fractionally composed of each of these
two preceding formulations and no other distinguishable phases. These
“GaI” phases were then shown to give unique products
upon reactions with the anionic bis­(phosphino)­borate ligand class.
The reaction of the early-phase “GaI” gives rise to
a unique phosphine Ga­(II) dimeric coordination compound (3), which was isolated reproducibly in 48% yield and convincingly
characterized. A base-stabilized GaI→GaI3 fragment
(4) was also isolated using the late-phase “GaI”
and characterized by multinuclear NMR spectroscopy and X-ray crystallography.
These compounds can be considered unique examples of low-oxidation-state
P→Ga coordination compounds and possess relatively long Ga–P
bond lengths in the solid-state structures. The anionic borate backbone
therefore results in interesting architectures about gallium that
have not been observed with neutral phosphines.