Accessing delta-B-H Coordinated Complexes of Rh(I) and Ir(I) Using Mono- and Dihydroboranes: Cooperative Stabilization by a Phosphoramidate Coligand

Reactions of the four-membered irida(I)- and rhoda(I)heterocycles {[}M\{kappa(2)-N,O-Xyl(N)P(O)(OEt)(2)\}(eta(4)-COD)] (M = Rh (1), Ir (2)) with electrophilic borane reagents are investigated: Treatment of 1 or 2 with 9-borabicydo{[}3.3.1]nonane (HBC8H14) gives {[}M\{kappa(2)-N,H-Xyl(N)P(OH(BC8H14)(OEt)(2)\}(eta(4)-COD)] (M = Rh (5), Ir (6)). Complexes 1 and 2 display differing reactivity toward HBMes(2) and H(2)BMes: reaction With HBMes(2) provides an equilibrium mixture of {[}M\{kappa(2)-N,H-Xyl(N)P(OHB(Mes)(2))(OEt)(2)\}(eta(4)-COD)] (M = Rh (7), Ir (8)) and the precursor complex 1 or 2. For H(2)BMes, borane coordination was found to be irreversible and the five-coordinate bis(B, H) complexes {[}M\{kappa(3)-N,H,H-Xyl(N)P(OH(2)BMes)-(OEt)\}(2)(eta(4)-COD)] (M = Rh (9), Ir (10)) were accessed. Complexes 9 and 10 are highly fluxional in solution; this is ascribed to rapid rotation of the 1,5-Cydooctadiene (COD) coligand. Treatment of 1 or 2 with Piers' borane, HB(C6F5)(2), also provides the corresponding ring-expanded metalla(I)cydes {[}M\{kappa(2)-N,H-Xyl(N)P(OHB(C6H5)(2))(OEt)(2)\}(eta(4)-COD)] (M = Rh (11), Ir (12)). In the absence of a stabilizing {[}M]..H-B interaction, treatment of 1 or 2 with B(C6F5)(3) provides the corresponding eta(5)-iminocycrohexadienyl complexes {[}M\{eta(5)-Xyl(N)P(O..-B(C6F5)(3))(OEt)(2)\}(eta(4)-COD)] (M = Rh (21), Ir (22)), which result from phosphine oxide donation to the electron-deficient boron center.