Reactions of a phosphinoaldehyde with Pd(II), Rh(I), and Ir(I) precursors, including the formation of complexes containing a P,OH-chelated phosphinohemiacetal ligand: a new bonding mode.

The complexes trans-PdCl(2)eta(1)-P-(Ph(2)P)CH(Ph)CH(Me)CH(OMe)(2) (1) and M(H)Cl[eta(2)-P,OH-(Ph(2)P)CH(Ph)CH(Me)CH(OH)OMe][eta(2)-P,C(O)-(Ph(2)P)CH(Ph)CH(Me)C(O)], M = Rh (3) and Ir (4), are synthesized by reacting the phosphinoaldehyde [3-(diphenylphosphino)-3-phenyl-2-methyl]propionaldehyde [(Ph(2)P)(2)CH(Ph)CH(Me)CHO] with trans-PdCl(2)(PhCN)(2), RhCl(COD), and IrCl(COD), respectively, in MeOH; trans-PdCl(2)eta(1)-P-(Ph(2)P)CH(Ph)CH(Me)CHO (2) is isolated from the same reaction in CH(2)Cl(2). One diastereomer of each of the complexes 1, 3 x MeOH, and 4 x MeOH was characterized by X-ray analysis. The stereochemistry of such complexes in the solid state and in solution (MeOH and CH(2)Cl(2)) is discussed. In CD(2)Cl(2), NMR data suggest that the coordinated hemiacetal moiety of 3 (but not 4) undergoes reversible loss of MeOH; this process is associated with equilibria between various diastereomers of 3 that were investigated by (31)P{(1)H}, (13)C{(1)H}, (1)H, (1)H{(31)P}, and HSQC and HMBC (1)H/(31)P{(1)H} and (1)H/(13)C{(1)H} NMR spectroscopies. Complexes 3 and 4 reveal a new chelate bonding mode via a P atom and the hydroxyl O atom of a hemiacetal. Solvent-dependent stereochemical changes within solution species imply that such chiral phosphinoaldehydes are not likely to be useful ligands for applications in asymmetric catalysis, although conditions are suggested for testing the complexes as potential precursors for nonasymmetric catalytic processes.