Rh and Ir β‑Diiminate Complexes of Boranes, Silanes, Germanes, and Stannanes

Reported
here are several new adducts of the type (RBDI)­M­(HE)2 where RBDI is the β-diiminate
ligand [2,6-R2C6H3NCMe]2CH (R = Me, Et, MeO; M = Rh, Ir; HE = HSiEt3, HGeEt3, HSnnBu3, HBPin).
DFT calculations are used to analyze the bonding in these and related
Cp* complexes, in particular with respect to the degree of oxidative
addition (OA) of the H–E bonds: this increases in the order
H2 < HBPin < HSiEt3 ≈ HGeEt3 ≈ HSnnBu3,
it proceeds further for Ir than for Rh, and Cp* promotes OA to a larger
degree in comparison to the BDI ligand. The first metal–HE dissociation energy is rather sensitive to steric
effects and increases in the order CH4 ≪ H2 ≈ HBPin ≈ HSiMe3 ≈ HGeMe3 < HSnMe3, with Ir uniformly binding HE more strongly
than Rh by about 10 kcal/mol. M–HE dissociation is the first
step of the intramolecular ligand functionalization first reported
for (MeBDI)­Rh­(HSiEt3)2. Such functionalization
was not observed for any of the new complexes reported here. On the
basis of the idea that stannane dissociation might be prohibitive,
we obtained evidence that it is possible to effect such functionalization
via generation of a stannane within the coordination sphere of the
metal: treatment of (MeBDI)­Rh­(COE)­(N2) with
SnMe4 and H2 produced a mixture of (MeBDI)­Rh­(HSnMe3)2 and its functionalized derivative
(MeBDI∧SnHMe2)­Rh­(HSnMe3) via
Sn–C cleavage.