The behaviour of P-phenyl dinaphthophosphole (L), the first phosphole with axial chirality, towards some d* metal centres has been investigated. L acts as a monodentate phosphorus ligand and readily substitutes neutral or anionic ligands coordinated to Pd" and Pt" centres. New complexes L,MCl, with exclusive (M = Pt) or predominant (M = Pd) cis geometry have been obtained by reaction with KJPtC1.J and (PhCN),PdCl,. Reaction of L with ortho-metallated chloride bridged dinuclear [CC-NIMCl], complexes (HC-N = 2-benzylpyridine, M = Pt; HC-N = N,N-dimethyl_(methylbenzylamine, M = Pd) promotes bridge split- ting leading to the mononuclear species UC-N)MCl with a trans P-M-N arrangement. The X-ray structure of the Pd complex shows that the coordination around the metal is essentially square planar with normal bond distances. The dihedral angle between the average planes of the naphthyl groups of the phosphole (33") and Tolman's cone angle 0 of the ligand (136") have been determined. In some complexes, the phosphole ligand is fluxional at room temperature and undergoes rapid atropisomerization of the binaphthyl framework even in the bound state. Key words: Platinum; Palladium; Chirality; Phosphane ligands 1. Introduction During the last 3 years optically active phosphacyclic ligands have been introduced with remarkable success in enantioselective hydrogenation and hydroformyla- tion of olefins with rhodium [ll and platinum-tin cata- lysts [2], respectively. A few different phospholanes and phospholes have been synthesized for this purpose. All the ligands of this kind reported so far in the literature owe their chirality to the presence of stereogenic cen- tres in the carbon backbone [1,2]. The preparation of dinaphthophospholes [3] has been accomplished recently. These compounds are Correspondence to: Profs. S. Gladiali and G. Banditelli. 0022-328X/94/$7.00 SSDI 0022-328X3(94)24524-M characterized by the inclusion of the phosphorus atom in a cyclic structure and by the axial chirality of the molecule. They constitute the first representatives of a new class of axially dissymmetric phosphacyclic ligands. On the way to exploring the efficiency of dinaph- thophosphole derivatives as chiral ligands in enantiose- lective catalysis, we were interested in the coordination chemistry around transition metal centres. In particu- lar, this work was aimed at finding out the extent of the conformational stability of these ligands in the bound state. This is essential for the transmission of the chiral information to the substrate and is a basic requisite for establishing an efficient resolution protocol of the racemic ligand. In previous papers on this subject, [3a,b], it has been demonstrated that, in solution, free dinaphthophos- 0 1994 - Elsevier Science S.A. All rights reserved
Atropisomeric Diaryl-Core Phosphole Ligands: Pd(II) and Pt(II) Complexes with P-Phenyl Binaphthophosphole
Fabbri D;
1994
Abstract
The behaviour of P-phenyl dinaphthophosphole (L), the first phosphole with axial chirality, towards some d* metal centres has been investigated. L acts as a monodentate phosphorus ligand and readily substitutes neutral or anionic ligands coordinated to Pd" and Pt" centres. New complexes L,MCl, with exclusive (M = Pt) or predominant (M = Pd) cis geometry have been obtained by reaction with KJPtC1.J and (PhCN),PdCl,. Reaction of L with ortho-metallated chloride bridged dinuclear [CC-NIMCl], complexes (HC-N = 2-benzylpyridine, M = Pt; HC-N = N,N-dimethyl_(methylbenzylamine, M = Pd) promotes bridge split- ting leading to the mononuclear species UC-N)MCl with a trans P-M-N arrangement. The X-ray structure of the Pd complex shows that the coordination around the metal is essentially square planar with normal bond distances. The dihedral angle between the average planes of the naphthyl groups of the phosphole (33") and Tolman's cone angle 0 of the ligand (136") have been determined. In some complexes, the phosphole ligand is fluxional at room temperature and undergoes rapid atropisomerization of the binaphthyl framework even in the bound state. Key words: Platinum; Palladium; Chirality; Phosphane ligands 1. Introduction During the last 3 years optically active phosphacyclic ligands have been introduced with remarkable success in enantioselective hydrogenation and hydroformyla- tion of olefins with rhodium [ll and platinum-tin cata- lysts [2], respectively. A few different phospholanes and phospholes have been synthesized for this purpose. All the ligands of this kind reported so far in the literature owe their chirality to the presence of stereogenic cen- tres in the carbon backbone [1,2]. The preparation of dinaphthophospholes [3] has been accomplished recently. These compounds are Correspondence to: Profs. S. Gladiali and G. Banditelli. 0022-328X/94/$7.00 SSDI 0022-328X3(94)24524-M characterized by the inclusion of the phosphorus atom in a cyclic structure and by the axial chirality of the molecule. They constitute the first representatives of a new class of axially dissymmetric phosphacyclic ligands. On the way to exploring the efficiency of dinaph- thophosphole derivatives as chiral ligands in enantiose- lective catalysis, we were interested in the coordination chemistry around transition metal centres. In particu- lar, this work was aimed at finding out the extent of the conformational stability of these ligands in the bound state. This is essential for the transmission of the chiral information to the substrate and is a basic requisite for establishing an efficient resolution protocol of the racemic ligand. In previous papers on this subject, [3a,b], it has been demonstrated that, in solution, free dinaphthophos- 0 1994 - Elsevier Science S.A. All rights reservedI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
