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.