[Ir(PCy 3 ) 2 (H) 2 (H 2 BNMe 2 )] + as a Latent Source of Aminoborane: Probing the Role of Metal in the Dehydrocoupling of H 3 B⋅NMe 2 H and Retrodimerisation of [H 2 BNMe 2 ] 2

The Ir III fragment {Ir(PCy 3 ) 2 (H) 2 } + has been used to probe the role of the metal centre in the catalytic dehydrocoupling of H 3 B⋅NMe 2 H ( A ) to ultimately give dimeric aminoborane [H 2 BNMe 2 ] 2 ( D ). Addition of A to [Ir(PCy 3 ) 2 (H) 2 (H 2 ) 2 ][BAr F 4 ] ( 1 ; Ar F =(C 6 H 3 (CF 3 ) 2 ), gives the amine‐borane complex [Ir(PCy 3 ) 2 (H) 2 (H 3 B⋅NMe 2 H)][BAr F 4 ] ( 2 a ), which slowly dehydrogenates to afford the aminoborane complex [Ir(PCy 3 ) 2 (H) 2 (H 2 BNMe 2 )][BAr F 4 ] ( 3 ). DFT calculations have been used to probe the mechanism of dehydrogenation and show a pathway featuring sequential BH activation/H 2 loss/NH activation. Addition of D to 1 results in retrodimerisation of D to afford 3 . DFT calculations indicate that this involves metal trapping of the monomer–dimer equilibrium, 2 H 2 BNMe 2 ⇌ [H 2 BNMe 2 ] 2 . Ruthenium and rhodium analogues also promote this reaction. Addition of MeCN to 3 affords [Ir(PCy 3 ) 2 (H) 2 (NCMe) 2 ][BAr F 4 ] ( 6 ) liberating H 2 BNMe 2 ( B ), which then dimerises to give D . This is shown to be a second‐order process. It also allows on‐ and off‐metal coupling processes to be probed. Addition of MeCN to 3 followed by A gives D with no amine‐borane intermediates observed. Addition of A to 3 results in the formation of significant amounts of oligomeric H 3 B⋅NMe 2 BH 2 ⋅NMe 2 H ( C ), which ultimately was converted to D . These results indicate that the metal is involved in both the dehydrogenation of A , to give B , and the oligomerisation reaction to afford C . A mechanism is suggested for this latter process. The reactivity of oligomer C with the Ir complexes is also reported. Addition of excess C to 1 promotes its transformation into D , with 3 observed as the final organometallic product, suggesting a BN bond cleavage mechanism. Complex 6 does not react with C , but in combination with B oligomer C is consumed to eventually give D , suggesting an additional role for free aminoborane in the formation of D from C .