Synthesis and reactivity of rhodium(III) pentamethylcyclopentadienyl complexes of N– B–PTA(BH 3): X-ray crystal structures of [Cp ∗RhCl 2{ N– B}–PTA(BH 3)] and [Cp ∗Rh{ N– B–PTA(BH 3)}(η 2-CH 2 = CHPh)

Abstract

The reaction between 1-boranyl-1,3,5-triaza-7-phosphaadamantane ligand N– B–PTA(BH 3) and [Cp ∗RhCl(μ-Cl)] 2 affords [Cp ∗Rh{ N– B–PTA(BH 3)}Cl 2] ( 3) or [Cp ∗Rh{ N– B–PTA(BH 3)} 2Cl]Cl ( 5) containing one or two P-bonded boronated PTA ligands. The hydride [Cp ∗Rh{ N– B–PTA(BH 3)}H 2] ( 8) was also obtained by reaction of 3 with NaBH 4 and alternatively by direct hydroboration of [Cp ∗Rh(PTA)Cl 2] with excess NaBH 4. Moderately slow hydrolysis of the N-boranyl rhodium complexes affords dihydrogen, H 3BO 3 and the corresponding PTA derivatives, including the water-soluble dihydride [Cp ∗Rh(PTA)H 2] ( 9). Finally, the reaction of 8 with electron poor alkynes gives the alkene complexes [Cp ∗Rh{ N– B–PTA(BH 3)}(η 2-CH 2 = CHR)] (R = Ph, 10; C(O)OEt, 11) as a mixture of rotamers η 2-coordinated to rhodium without affecting the N–BH 3 moiety. The X-ray crystal structures of 3 and 10 were also obtained and are here discussed.