Bis(pyridino- <i>o</i> -carboranyl)phosphenium Cation: A Platform for Dual-Site Reactivity

High Resolution Image Download MS PowerPoint Slide Phosphenium salt, [ L 2 P + ][B(C 6 F 5 ) 4 ], substituted by two pyridino- ortho -carboranyl groups ( L ), was prepared, fully characterized, and its preliminary reactivity with small molecules was studied. Surprisingly, cation [ L 2 P + ][B(C 6 F 5 ) 4 ] reacts differently with O–H and N–H bonds. With RO–H (R = H, Me, Ph), the reaction takes place at P center in [ L 2 P + ][B(C 6 F 5 ) 4 ], via hydrolysis or alcoholysis of the P–C bonds, leading to the carboranopyridinium salt ([ LH 2 + ][B(C 6 F 5 ) 4 ]) and the complementary (RO) 2 P(O)H. In contrast, the reaction of [ L 2 P + ][B(C 6 F 5 ) 4 ] with R 2 N–H (Et 2 NH, Ph(H)NH, i Pr(H)NH) does not proceed at the P center, but takes place at the ortho -carboranyl ( o Cb) moiety by deboronation, producing zwitterionic phosphenium ( L(L nido )P + ), with significant reduction in the reactivity of the P center compared to L 2 P + . Remarkably, [ L 2 P + ][B(C 6 F 5 ) 4 ] reacts with SO 2 in MeCN at both sites, the P and o Cb, stripping both oxygens from sulfur, leading to zwitterionic phosphonium sulfide ( L(L nido )P + ═S ).