Rhodium(I) and Iridium(I) Complexes with β-Keto Phosphine or Phosphino Enolate Ligands. Catalytic Transfer Dehydrogenation of Cyclooctane

Abstract

The synthesis of new metal complexes containing the keto phosphine ligands R 1 2 PCH 2 C- 2) was obtained (PkO = η 2 (P,O)-chelated ligand). Reaction of 2 with TlPF 6 afforded the cationic compound [Rh(PkO) 2 ][PF 6 ] (3). The X-ray crystal structure determination of 3‚H 2 O shows a distorted-square-planar geometry with the two phosphorus atoms (and oxygen atoms) in cis positions. Treatment of [RhCl(CO)(PPh 3 ) 2 ] with 1 equiv of L gave [RhCl(CO)(P∼O)(PPh 3 )] (5). In the presence of TlPF 6 the cationic complex [Rh(CO)(PkO)(PPh 3 )][PF 6 ] (6) was obtained. The X-ray crystal structure determination of 6 shows a slightly distorted square planar geometry with the two phosphorus atoms in trans positions. The reaction of 5 or 6 with 1 equiv of NaOMe produced the phosphino enolate

Room-temperature C–H activation of the phosphino-ketone Ph2PCH2C(O)Ph leading to an iridium(III) complex with a hybrid phosphino-enolate ligand

“…The P-CH 2 bond length is slightly longer (P1-C13 1.843(7) Å ) than that of the P-CH bond (P2-C33 1.757(8) Å ). All these metrical data are consistent with values reported for related complexes containing chelating phosphino-enolates or P-bound ketophosphines, respectively [8,9].…”

“…. O)Ph,kP,kO}] was observed at 27.6 ppm [8]. The 1 H NMR spectrum of 5, recorded at 203 K for a better resolution, indicated the disappearance of the hydride resonance and the presence of two PCH 2 protons at 2.61 and 3.61 ppm (ABX spin system (A = B = H, X = P), partly overlapping with cod signals, with (Fig.…”

“…. O)Ph group, with a 2 J(H,P) coupling of 4.6 Hz [8]. Accordingly, the 1 H{ 31 P} NMR spectrum showed only one singlet for this proton.…”

“…With the objective to prepare a neutral iridium complex that would have a better solubility in coa, and thus facilitate the activation of its C-H bonds, we envisaged replacing the neutral cod ligand of complex 2 with an anionic P,O-chelating phosphino-enolate ligand since we have previously observed that their Rh(I)/Ir(I) complexes catalysed the transfer dehydrogenation of coa [8]. The Ir(III) dihydride complex [Ir(cod)(H) 2 {Ph 2 PCH .…”

“…. O) Ph,kP,kO}] was moderately stable in toluene solution [8]. In general, phosphino-enolate functionalities can be readily generated under basic conditions from a bketophosphine ligand, such as Ph 2 PCH 2 C(O)Ph, coordinated or not [9].…”