Square-Planar Pt(II) and Ir(I) Complexes as the Lewis Bases: Donor–Acceptor Adducts with Group 13 Trihalides and Trihydrides

The stability and
properties of donor–acceptor adducts of square-planar Pt­(II)
and Ir­(I) complexes (designated as PtX, IrX, or generally MX complexes)
with trihydrides and trihalides of group 13 elements of general formula
YZ3 (Y = B, Al, Ga; Z = H, F, Cl, Br) were studied theoretically
using DFT methodology in the gas phase. MX complexes were represented
by wide range of the ligand environment which included model complexes
[Ir­(NH3)3X]0 and cis-[Pt­(NH3)2X2]0 (X = H,
CH3, F, Cl, Br) and isoelectronic complexes [Ir­(NNN)­(CH3)]0 and [Pt­(NCN)­(CH3)]0 with
tridentate NNN and NCN pincer ligands. MX complexes acted as the Lewis
bases donating electron density from the doubly occupied 5dz2 atomic orbital of the metal M atom to
the empty valence pz orbital of Y whose
evidence was clearly provided by the natural atomic orbital (NAO)
analysis. This charge transfer led to the formation of pentacoordinated
square pyramidal MX·(YZ3) adducts with M·Y dative
bond. Binding energies were −44.7 and −75.2 kcal/mol
for interaction of GaF3 as the strongest acid with PtNCN
and IrNNN pincer ligands complexes. Only M·B bonds had covalent
character although MX·BZ3 adducts were the least stable
due to large values of Pauli repulsion and deformation energies. The
highest degree of covalent character was found for adducts of BH3 in all series of structures studied. Al and Ga adducts showed
remarkably similar behavior with respect to geometry and binding energies.