Alkaline-Earth Derivatives of Diphenylphosphine-Borane

Treatment of beta-diketiminato (BDI = HC{C(CH3)Ndipp)}(2) where dipp = 2,6-iPr(2)C(6)H(3)) magnesium butyl [(BDI)MgBu] (I) and calcium hexamethyldisilazide [(BDI)Ca{N(SiMe3)(2)}] (H) complexes with equimolar quantities of diphenylphosphineborane, Ph2PH center dot BH3 , results in the formation of the respective alkaline earth (Ae) phosphidoborane derivatives [(BDI)Mg(Ph2PBH3)](2) (6a) and [(BDI)Ca(Ph2PBH3)] (7a). Although satisfactory single crystals of 7a could not be obtained, 6a was crystallographically characterized and both compounds display similar NMR spectra. The dimeric Ae-hydride complexes [(BDI)AeFI], (IIIa, Ae = Mg; IIIb, Ae = Ca) react with substoichiometric quantities of Ph2PH center dot BH3, allowing the crystallization of the dimeric Mg and trimeric Ca phosphidoborane species [(BDI)Mg(H)(H3BPPh2)Mg(BDI)] (8) and [{(BDI)Ca}(3) (H)(H3BPPh2)(2)] (9). In the absence of coordinating Lewis bases, compounds 6a, 7a, 8, and 9 display dynamic solution-state behavior (in benzene and toluene), while addition of THF furnishes the monomeric adducts [(BDI)Mg(H3BPPh2)center dot THF] (6b) and [(BDI)Ca(H3BPPh2)center dot THF] (7b). Addition of Ph2PH center dot BH3 to compound 6a results in BH3 transfer to eliminate Ph-2 PH and generate the phosphinodiboronate complex [(BDI)Mg{(H3B)(2)PPh2}](2) (10) in preference to dehydrocoupling of the phosphidoborane and phosphine-borane reagents.