Rh(I) and Ir(I) Derivatives of a P(S),N-Substituted Indene Ligand: Synthetic, Structural, and Catalytic Alkene Hydrosilylation Studies

Treatment of 1-PiPr2-indene or 1-PiPr2-2-NMe2-indene (1a) with elemental sulfur afforded 3-iPr2P(S)-indene or 1-iPr2P(S)-2-NMe2-indene (4a) in 81% and 85% isolated yield, respectively. Addition of 4a to [(COD)M(THF)2]+BF4-
afforded the corresponding [(COD)M(κ2-N,S-4a)]+BF4- complexes (M = Rh, 5a, 76%; M = Ir, 5b, 59%; COD =
η4-1,5-cyclooctadiene), which were found to exhibit temperature-dependent NMR spectral features that were
rationalized in terms of a dynamic process involving M-NMe2 dissociation, rotation about the indenyl-NMe2 bond,
inversion at nitrogen, and re-coordination to M. Analysis of variable-temperature NMR data collected for 5a and 5b
each yielded a value for ΔG‡ of ca. 14 kcal/mol for this process. Exposure of 5a or 5b to NaN(SiMe3)2 generated
the corresponding (COD)M(κ2-C,S-1-iPr2P(S)-2-NMe2-(C1-indenyl)) complex (M = Rh, 6a, 70%; M = Ir, 6b, 86%)
in which the metal is incorporated into an M−C−P−S ring via coordination to the indenyl ring in an η1-fashion, as
well as to sulfur. Alternatively, complex 6b was prepared cleanly via lithiation of 4a followed by treatment with 0.5
equiv of [(COD)IrCl]2. The ability of 5a,b and 6a,b to mediate the addition of triethylsilane to styrene was also
explored, and their performance was compared with that of Wilkinson's Catalyst ((PPh3)3RhCl) and Crabtree's
catalyst ([(COD)Ir(PCy3)(Py)]+PF6-; Cy = cyclohexyl; Py = pyridine). Single-crystal X-ray diffraction data are provided
for 4a, 2-NMe2-3-iPr2P(S)-indene (4b), 6a, and 6b.