Coordination of Pnictogenylboranes Towards Tl(I) Salts and a Tl‐ Mediated P−P Coupling

The coordination chemistry of only Lewis‐base (LB)‐stabilized pnictogenylboranes EH(2)BH(2)⋅NMe( 3 ) (E=P, As) towards Tl(I) salts has been studied. The reaction of Tl[BAr(Cl)] (BAr(Cl)=[B(3,5‐C(6)H(3)Cl(2))(4)](−)) with the corresponding pnictogenylborane results in the formation of [Tl(EH(2)BH(2)⋅NMe(3))][BAr(Cl)] (1 a: E=P; 1 b: E=As). Whereas the Tl ion in 1 a/b is monocoordinated, the exchange of the weakly coordinating anion (WCA) in the Tl(I) salt leads to the formation of a trigonal pyramidal coordination mode at the Tl atom by coordination of three equivalents of EH(2)BH(2) ⋅ NMe(3) in [Tl(EH(2)BH(2) ⋅ NMe(3))(3)][WCA] (2 a: E=P, WCA=TEF(Cl); 2 b: E=As, WCA=TEF) (TEF=[Al{OC(CF(3))(3)}(4)](−), TEF(Cl)=[Al{(OC(CF(3))(2)(CCl(3))}(4)](−)). Furthermore, by using two equivalents of PH(2)BH(2)⋅NMe( 3 ), a Tl(I)‐mediated P−P coupling takes place in CH(2)Cl(2) as solvent resulting in [Me(3)N⋅BH(2)PH(2)PHBH(2)⋅NMe(3)][WCA] (WCA=TEF, 3 a; BAr(Cl), 3 b; TEF(Cl), 3 c). In contrast, for the arsenic derivatives 1 b and 2 b, no coupling reaction is observed. The underlying chemical processes are elucidated by quantum chemical computations.