This paper is concerned with an evaluation of the factors which influence the facility of the oxidative addition of chelating substrates. Spectrophotometrically we determined the [Ir(III)]/[Ir(I)] ratios resulting from the oxidative addition of C6H5XH and o-Ph2PC6H4XH (X = O, CO2) to trans-IrCl(CO)(EPh3)2 (E = P, 1; E = As, 2). The measured [Ir(III)]/[Ir(I)] ratios for the chelating substrates were 103–104 greaterthan those for the nonchelating substrates. While benzaldehyde does not detectably add to 1, o-Ph2PC6H4CHO (PCHO) does so quantitatively (K ≃ 5 × 104) affording a stable acyl hydride, [formula omitted]. Related stable acyl hydrides prepared in this way are [formula omitted] and [formula omitted] the last compound being derived from (phenylphosphino)dibenzaldehyde (P(CHO)2). Equilibrium measurements using 1, 2, PCHO, and the analogous arsine, AsCHO, established a strong dependence of the facility of the oxidative addition on the nature of the ancillary donor ligands. An attempted synthesis of a nonchelated acyl hydride from the reaction of “IrH(CO)(PPh3)2” and PhCOCl gave only 1 and PhCHO. This result establishes that the differing facilities for oxidative addition of PhCHO and PCHO to 1 is a thermodynamic and not a kinetic effect. The single-crystal X-ray diffraction study of PCHO itself revealed an unexceptional structure which closely resembles that of PPh3. o-Ph2PC6H4CHO crystallizes in the triclinic space group Ci1-P1̄ with cell dimensions of a = 10.663 (3) Å, b = 11.065 (3) Å, c = 8.585 (2) Å, α = 103.20 (2)°, β = 105.95 (2)°, γ = 118.67 (2)°, V = 772.8 (3) Å3, and Z = 2.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry