Synthesis and Reactivity of Rhodium(III) Pentamethylcyclopentadienyl Complexes of N–B PTA(BH3) : X-ray crystal structures of [Cp*RhCl2(N–B–PTA(BH3)] and [Cp*Rh{N–B–PTA(BH3)}(η2- CH2=CHPh)]

The reaction between 1-boranyl-1,3,5-triaza-7-phosphaadamantane ligand N-B-PTA(BH3) and [Cp*RhCl(μ-Cl)]2 affords [Cp*Rh{N-B-PTA(BH3)}Cl2] (3) or [Cp*Rh{N-B-PTA(BH3)}2Cl]Cl (5) containing one or two P-bonded boronated PTA ligands. The hydride [Cp*Rh{N-B-PTA(BH3)}H2] (8) was also obtained by reaction of 3 with NaBH4 and alternatively by direct hydroboration of [Cp*Rh(PTA)Cl2] with excess NaBH4. Moderately slow hydrolysis of the N-boranyl rhodium complexes affords dihydrogen, H3BO3 and the corresponding PTA derivatives, including the water-soluble dihydride [Cp*Rh(PTA)H2] (9). Finally, the reaction of 8 with electron poor alkynes gives the alkene complexes [Cp*Rh{N-B-PTA(BH3)}(η2-CH2 = CHR)] (R = Ph, 10; C(O)OEt, 11) as a mixture of rotamers η2-coordinated to rhodium without affecting the N-BH3 moiety. The X-ray crystal structures of 3 and 10 were also obtained and are here discussed.