Easy Access to Hydride Chemistry on a Tripodal P-Based Rhodium Scaffold

Abstract

The TBPY-5 rhodium complex [(PhBP3)Rh(CH2═CH2)(NCMe)] (1; PhBP3 = PhB(CH2PPh2)3), which contains ethylene in the equatorial plane and a labile acetonitrile ligand at one of the axial positions, provides a simple entry into the chemistry of the fac-[P3Rh] scaffold. DFT calculations using the model compound [(MeB(CH2PMe2)3)Rh(CH2═CH2)(NCMe)] (1′) reproduce well the crystallographic geometry of 1 and converge to the isolated conformer, in which the strong π back-donation from the metal to the π* orbital of ethylene fixes it coplanar with the equatorial plane. Oxidation of 1 is electrochemically irreversible (at 0.080 V vs SCE), and 1 was effectively oxidized with [Cp2Fe]+ in acetonitrile to [(PhBP3)Rh(NCMe)3]2+. Reaction of 1 with hydrogen in toluene gives the dihydride [(PhBP3)Rh(H)2(NCMe)] (3), which loses acetonitrile to give the insoluble hydride [{(PhBP3)Rh(H)(μ-H)}2] (4), while 1 in THF with BHT (2,6-bis(1,1-dimethylethyl)-4-methylphenol) results in the mixed-valence paramagnetic hydride [{(PhBP3)Rh}2(...