Barium phosphidoboranes and related calcium complexes

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry
• Coordination Chemistry

Background:

• The direct synthesis of barium phosphide complexes like [{Carb}BaPPh2] (1) is hindered by solution instability.
• Fragility of early transition metal phosphides necessitates alternative synthetic strategies.

Purpose of the Study:

• To develop stable barium and calcium phosphide complexes using phosphinoborane reagents.
• To characterize novel phosphinoborane-supported alkaline earth metal complexes.
• To investigate the structural and electronic properties influencing compound stability.

Main Methods:

• Synthesis of novel barium and calcium phosphide complexes utilizing phosphinoboranes (HPPh2·BH3 and HPPh2·B(C6F5)3).
• Characterization using multinuclear NMR spectroscopy and X-ray diffraction crystallography.
• Density Functional Theory (DFT) analysis to probe electronic properties and bonding.

Main Results:

• Successful synthesis of a series of stable barium and calcium phosphide complexes, including [{Carb}Ae{PPh2·BH3}] (Ae = Ba, Ca), [{Carb}Ca{(H3B)2PPh2}·(thf)], [{Carb}Ba{PPh2·B(C6F5)3}], and others.
• X-ray crystallography revealed stabilizing Ba⋯F interactions in fluorine-containing compounds.
• DFT analysis indicated that the instability of precursor 1·(thf)2 stems from a high-energy HOMO with nucleophilic character, not Ba-P bond weakness.

Conclusions:

• Phosphinoboranes are effective stabilizing moieties for synthesizing fragile alkaline earth metal phosphide complexes.
• The presence of fluorine atoms can lead to significant stabilizing interactions.
• Understanding the electronic properties, particularly HOMO energy and reactivity, is crucial for predicting and controlling the stability of these organometallic compounds.