Rhodium
and Iridium Complexes with a New Scorpionate
Phosphane Ligand

Serrano, Angel
L.; Casado, Miguel A.; López, José A.; Tejel, Cristina

doi:10.1021/ic400684s.s001

ic400684s_si_001.pdf (785.58 kB)

Rhodium and Iridium Complexes with a New Scorpionate Phosphane Ligand

journal contribution

posted on 2013-07-01, 00:00 authored by Angel L. Serrano, Miguel A. Casado, José A. López, Cristina Tejel

A straightforward synthesis of a new hybrid scorpionate ligand [(allyl)₂B(CH₂PPh₂)(Pz)]⁻ ([A₂BPN]⁻) is reported. Coordination to rhodium resulted in square-planar complexes [Rh(κ²-A₂BPN)(L)(L′)] [L = L′ = ¹/₂cod (1,5-cyclooctadiene), CN^tBu, CO (6); L = CO, L′ = NH₃, pyridine, PPh₃, PMe₃] for which spectroscopic data and the molecular structure of [Rh(κ²-A₂BPN)(CO)PPh₃] (11) indicate the ligand to be κN,κP-bound to rhodium with two dangling free allyl groups. Studies in solution point out that the six-membered Rh–N–N–B–C–P metallacycle undergoes a fast inversion in all of them. The bis(carbonyl) complex 6 easily loses a CO group to give [{Rh(A₂BPN)(CO)}₂], a dinuclear compound in which two mononuclear subunits are brought together by two bridging allyl groups. Coordination to iridium is dominated by a tripodal κN,κP,η²-CC binding mode in the TBPY-5 complexes [Ir(κ³-A₂BPN)(L)(L′)] [L = L′ = ¹/₂cod (3), CN^tBu (5), CO (7); L = CO, L′ = PPh₃ (13), PMe₃ (14), H₂CCH₂, (17), MeO₂CCCCO₂Me (dmad, 18)], as confirmed by the single-crystal structure determination of complexes 3 and 18. A fast exchange between the two allyl arms is observed for complexes having L = L′ (3, 5, and 7), while those having CO and L ligands (14, 17, and 18) were found to be nonfluxional species. An exception is complex 13, which establishes an equilibrium with the SP-4 configuration. Protonation reactions on complexes 13 and 14 with HCl yielded the hydride complex [Ir(κ²-A₂BPN)(CO)(Cl)(H)PPh₃] (15) and the C-alkyl compound [Ir{κ³-(allyl)B(CH₂CHCH₃)(CH₂PPh₂)(Pz)}(Cl)(CO)PMe₃] (16), respectively. The bis(isocyanide) complex 5 reacts with dmad to form [Ir(κ²-A₂BPN)(CN^tBu)₂(dmad)]. On the whole, the electronic density provided to the metal by the [A₂BPN]⁻ ligand is very sensitive to the coordination mode. The basicity of the new ligand is similar to that of the Tp^Me2 ligand in the κN,κP mode but comparable to Tp if coordinated in the κN,κP,η²-CC mode.