Mechanochemical synthesis and structural analysis of trivalent lanthanide and uranium diphenylphosphinodiboranates. Issue 33 (4th August 2021)

• Record Type: Journal Article
• Authors: Fetrow, Taylor V.; Daly, Scott R.
• Is Part Of: Dalton transactions. Volume 50:Issue 33(2021)
• Page Start: 11472
• Page End: 11484
• Publication Date: 2021-08-04
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d1dt01932e
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Here we report how mechanochemistry was used to overcome limited solution reactivity for the synthesis of homoleptic uranium and lanthanide phosphinodiboranate complexes with weakly-coordinating (H3 BPPh2 BH3 ) 1− . Abstract : Phosphinodiboranates (H3 BPR2 BH3 − ) are a class of borohydrides that have merited a reputation as weakly coordinating anions, which is attributed in part to the dearth of coordination complexes known with transition metals, lanthanides, and actinides. We recently reported how K(H3 BP t Bu2 BH3 ) exhibits sluggish salt elimination reactivity with f-metal halides in organic solvents such as Et2 O and THF. Here we report how this reactivity appears to be further attenuated in solution when the t Bu groups attached to phosphorus are exchanged for R = Ph or H, and we describe how mechanochemistry was used to overcome limited solution reactivity with K(H3 BPPh2 BH3 ). Grinding three equivalents of K(H3 BPPh2 BH3 ) with UI3 (THF)4 or LnI3 (Ln = Ce, Pr, Nd) allowed homoleptic complexes with the empirical formulas U(H3 BPPh2 BH3 )3 (1 ), Ce(H3 BPPh2 BH3 )3 (2 ), Pr(H3 BPPh2 BH3 )3 (3 ), and Nd(H3 BPPh2 BH3 )3 (4 ) to be prepared and subsequently crystallized in good yields (50–80%). Single-crystal XRD studies revealed that all four complexes exist as dimers or coordination polymers in the solid-state, whereas 1 H and 11 B NMR spectra showed that they exist as a mixture of monomers and dimers in solution. Treating 4 with THF breaks up the dimer to yield the monomeric complex Nd(H3 BPPh2 BH3 )3 (THF)3 (4-THF ). XRD studies revealed that 4-THF has one chelating and two dangling H3 BPPh2 BH3 − ligands bound to the metal to accommodate binding of THF. In contrast to the results with K(H3 BPPh2 BH3 ), attempting the same mechanochemical reactions with Na(H3 BPH2 BH3 ) containing the simplest phosphinodiboranate were unsuccessful; only the partial metathesis product U(H3 BPH2 BH3 )I2 (THF)3 (5 ) was isolated in poor yields. Despite these limitations, our results offer new examples showing how mechanochemistry can be used to rapidly synthesize molecular coordination complexes that are otherwise difficult to prepare using more traditional solution methods.