Generation and reactivity of {(ethane-1,2-diyl)bis[diisopropylphosphine-kappa P]}-{[2,4,6-tri(tert-butyl)phenyl]phosphino-kappa P}rhodium ([Rh[PH((Bu3C6H2)-Bu-t)]((Pr2PCH2CH2PPr2)-Pr-i-Pr-i)]): Catalytic C-P bond formation via intramolecular C-H/P-H dehydrogenative cross-coupling

The complex [Rh(eta (3)-benzyl)(dippe)] (1: dippe = bis(diisopropylphosphin o)ethane = (ethane-1,2-diyl)bis-[diisopropylphosphine]) reacted cleanly wit h Mes*PH2 (2; Mes* = 2,4,6-'Bu3C6H2) to provide a new Rh species [Rh(H)(dip pe)(L)] (3). L being the 2,3-dihydro-3-3-dimethyl-1H-phosphindole ligind4(= 'Bu2C6H2(CMe2CH2PH)) (Scheme 1). Complex 3 was converted to the correspond ing chloride [Rh(Cl)(dippe)(L)] (6) when treated with CH2Cl2, whereas the d imeric species [Rh-2{mu-'Bu2C6H2(CMe2CH2P)}(mu -H)(dippe)(2)] (7) was forme d upon thermolysis in toluene (Scheme 2). The structures of 6 and 7(.)C(7)H (8) were determined by X-ray crystallography. Complexes 1 and 3 served as c atalyst precursors for the dehydrogenative coupling of C-H and P-H bonds in the conversion of 2 to 4 (Scheme 3). Deuteration studies with Mes* PD2 exp osed a complex series of bond-activation pathways that appear to involve C- H activation of the dippe ligand by the Rh-atom (Schemes 4 and 5).