Exploring the Utility of Neutral Rhodium and Iridium κ2-P,O and κ2-P(S),O Complexes as Catalysts for Alkene Hydrogenation and Hydrosilylation

Heating of [(COD)M(κ2-3-PiPr2-2-NMe2-indene)]+X- (M = Rh or Ir; X = BF4, PF6; COD = η4-1,5-cyclooctadiene) in a mixture of water and THF (48 h, 60 °C) afforded the neutral (COD)M(κ2-P,O) complexes (M = Rh, 5a, 80%; M = Ir, 5b, 74%). Similarly, thermolysis of [(COD)M(κ2-3-P(S)iPr2-2-NMe2-indene)]+BF4- (M = Rh or Ir) in a mixture of water and CH2Cl2 (14 h, 60 °C) produced the neutral (COD)M(κ2-P(S),O) complexes (M = Rh, 13a, 91%; M = Ir, 13b, 90%). Subsequent preparation of 1-PiPr2-2-indanone (8, 91%) enabled the non-hydrolytic synthesis of 5b in 70% isolated yield via treatment with 0.5[(COD)IrCl]2 in the presence of NEt3. Lithiation of (o-PiPr2)phenol followed by quenching with 0.5[(COD)IrCl]2 afforded the neutral (COD)Ir(κ2-P,O) complex 10 (91%). Single-crystal X-ray diffraction data are provided for 5b, 10, 13a, and 13b. Whereas 5a, 13a, and 13b performed poorly as catalysts for the hydrogenation of alkenes, the known complex (COD)Ir(OPh)(PCy3) 2 as well as 5b and 10 proved to be excellent catalysts for hydrogenation of mono-, di-, and trisubstituted alkene substrates under mild conditions (22 °C, ∼1 atm H2). Complexes 13a,b were also shown to be competent catalysts for addition of triethylsilane to styrene.