Dihydrogen Complexes of Rhodium: [RhH2(H2)x(PR3)2]+ (R = Cy, iPr; x = 1, 2)

Abstract

Addition of H-2 (4 atm at 298 K) to [Rh(nbd)(PR3)(2)][BAr4F] [R = Cy, Pr-i] affords Rh(III) dihydride/dihydrogen complexes. For R = Cy, complex la results, which has been shown by low-temperature NMR experiments to be the bisdihydrogen/bis-hydride complex [Rh(H)(2)(eta(2) -H-2)(2)(PCY3)(2)][BAr4F]. An X-ray diffraction study on la confirmed the {Rh(PCY3)(2)} core structure, but due to a poor data set, the hydrogen ligands were not located. DFT calculations at the B3LYP/DZVP level support the formulation as a Rh(III) dihydride/dihydrogen complex with cis hydride ligands. For R = Pr-i, the equivalent species, [Rh(H)(2) (eta(2) -H-2)(2)((PPr3)-Pr-i)(2)][BAr4F] 2a, is formed, along with another complex that was spectroscopically identified as the mono-dihydrogen, bis-hydride solvent complex [Rh(H)(2) (eta(2) - H-2) (CD2Cl2)((PPr3)-Pr-i)(2)] [BAr (F)(4)] 2b. The analogous complex with PCy3 ligands, [Rh(H)(2)(eta(2)-H-2)(CD2Cl2)(PCy3)(2)][BAr4F] 1b, can be observed by reducing the H-2 pressure to 2 atm (at 298 K). Under vacuum, the dihydrogen ligands are lost in these complexes to form the spectroscopically characterized species, tentatively identified as the bis hydrides [Rh(H)(2)(L)(2)(PR3)(2)][BAr (F)(4)] (1c R = Cy; 2c R = Pr-i; L = CD2Cl2 or agostic interaction). Exposure of 1c or 2c to a H2 atmosphere regenerates the dihydrogen/bis-hydride complexes, while adding acetonitrile affords the bis-hydride MeCN adduct complexes [Rh(H)(2)(NCMe)(2)(PR3)(2)][BAr4F]. The clihydrogen complexes lose [HPR3][BAr4F] at or just above ambient temperature, suggested to be by heterolytic splitting of coordinated H2, to ultimately afford the dicationic cluster compounds of the type [Rh-6(PR3)(6)(mu-H)(12)][BAr4F](2) in moderate yield