Palladium Complexes of the Heterodiphosphineo-C₆H₄(CH₂P^tBu₂)(CH₂PPh₂) Are Highly Selective and Robust Catalysts for the Hydromethoxycarbonylation of Ethene

Abstract

The coordination chemistry and ethene hydromethoxycarbonylation catalysis with the diphosphine o-C 6 H 4 (CH 2 P t Bu 2 )(CH 2 PPh 2 ) (L 3 ) is reported and the results compared with the analogous chemistry of the symmetrical diphosphines o-C 6 H 4 (CH 2 P t Bu 2 ) 2 (L 1 ) and o-C 6 H 4 (CH 2 PPh 2 ) 2 (L 2 ). Palladium-catalyzed ethene hydromethoxycarbonylation studies under the commercial catalytic conditions are reported. The results obtained using L 1-3 as supporting ligands show that the catalysts derived from L 3 and L 1 have similar activity and selectivity for methyl propanoate (MeP). In addition, the Pd-L 3 catalyst has much greater longevity than the Pd- 6), and [PtCl(CH 3 )(L 3 )] (9). At equilibrium, complex 9 is a 90:1 mixture of geometric isomers 9a (with CH 3 trans to the t Bu 2 P) and 9b (with Cl trans to the t Bu 2 P). The fluxionality of complex 3, detected by 1 H NMR, is interpreted in terms of the conformation of the seven-membered chelate. The complexes [Pt(CH 3 )(PMe 3 )(L 3 )]Cl (10b) and [PtH(PPh 3 )(L 3 )]Cl (12b) are formed as essentially single isomers with CH 3 /H trans to the Ph 2 P group. The palladium complexes [PdCl 2 (L 3 )] ( 13), [PdCl(CH 3 )(L 3 )] (14a/14b), and [PdH(PCy 3 )-(L 3 )]BF 4 (15b) have been made by similar methods to their platinum analogues. The factors controlling the relative isomer stabilities are explored experimentally and computationally. The complexes [PtCl 2 (L 4 )] ( 16) and [PtCl(CH 3 )(L 4 )] (17a/17b) where L 4 = o-C 6 H 4 (CH 2 P n Bu 2 )(CH 2 PPh 2 ) are reported, and the geometric isomers of 17 are almost isoenergetic. The crystal structures of 3, 14a, 15b, and 16 have been determined by X-ray crystallography. DFT calculations on complexes of the type [Pt(X)(Y)(L 3 )] gave only small calculated differences in energy between the geometrical isomers (0-4 kcal mol -1 ), which are consistent with the experimental observations. It is suggested that repulsive intramolecular H 3 3 3 H interactions (between the Pt-CH 3 and PC(CH 3 ) 3 groups) determine which isomer predominates. The reasons for the favorable catalytic properties of the Pd-L 3 catalyst are probed by 13 CO reactions with the model complexes 9a/9b and 14a/14b, and the structures of the resulting acyl complexes are assigned on the basis of 13 C and 31 P NMR and IR spectroscopy. From these studies, it is suggested that the reason for the Pd-L 3 catalyst resembling the Pd-L 1 catalyst in terms of selectivity is that the crucial acyl intermediates are similar.

An Empirical Study of Phosphine Ligands for the Methoxycarbonylation of Medium‐Chain Alkenes

“…These results can be compared with those obtained by Pringle20a et al. by using ligands A , Q , and R (Figure 4) for the methoxycarbonylation of ethylene.…”

“…The first two were very active for the production of methyl propionate, and the latter resulted in a sluggish reaction rate and afforded ethene/CO co‐oligomers and polyketone 10j. 20 Notably, the Pd catalyst based on ligand Q had a longer lifetime than the Pd complex derived from ligand A 20a. This is another demonstration that both steric and electronic properties of the ligand are important.…”

Polymer precursors from catalytic reactions of natural oils

“…111 The field of hydro/methoxycarbonylation of ethylene to methyl propanoate using BTDPMB-based systems and variations of the ligand has been recently reviewed by Fanjul and co-workers. [112][113][114] Drent and Jager have shown the BTDPMB/palladium system to give methyl pentanoate from 2-butene in 97% selectivity at 65 bar and 100℃, 115 showing the methoxycarbonylation of a carbon chain longer than ethylene was possible. The same authors desired to increase the selectivity to the linear ester and found that using a mixture anisole/methanol : 2/1 as a solvent for the methoxycarbonylation of 2-butene and 1-octene yielded a full conversion to the ester with high selectivity to the linear species (97%).…”

[Pd(L)Cl2]‐Catalyzed Selective Hydroxylation of Arylboronic Acids to Phenols

“…Table 2. S2) match well with those of an analogous molecule containing a diphosphanylamine ligand moiety. [11] The mononuclear form of 1 in powdered bulk samples as well as in solution has been established by different experimental techniques. The 31 P NMR spectrum of L in CDCl 3 exhibits two signals at 60.60 and -21.8 ppm corresponding to P1/P2 and P3, respectively ( Figure S2a) Figure S2b).…”