Rhodium and Iridium Complexes with a New Scorpionate Phosphane Ligand

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), CNtBu, 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 κNP-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 κNP2-CC binding mode in the TBPY-5 complexes [Ir­(κ3-A2BPN)­(L)­(L′)] [L = L′ = 1/2cod (3), CNtBu (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)­(CNtBu)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 TpMe2 ligand in the κNP mode but comparable to Tp if coordinated in the κNP2-CC mode.