Metal-assisted, facile syntheses of chelating triphosphine ligands on platinum

Abstract

Chelated unsymmetrical triphosphine ligands of the type R2PCH2CH2CH2P(Ph)CH,CH2PR'2 and R2PCH2CH2CH2P-(Ph)CH2CH2CH2PRt2 (R = R' = C&; R = R' = C6Hll; R = C6Hl1, R' = C6H5) can be synthesized rapidly on platinum by Et3N-catalyzed condensation of simpler phosphine units onto a coordinated secondary phosphine. The resulting [PtCl(triphos)]X (X = C1, AsF6) complexes are characterized by elemental analyses and by 'H, 3'P, and lssPt NMR spectroscopy. For those complexes that contain a five-membered chelate ring, the IgSPt 6 values are shifted to higher fields, whereas the 6 values are shifted to lower fields, when compared with analogous phosphino groups in six-membered chelate rings.

Development of a Synthetic Route to Unsymmetrical Triphosphine Ligands and an Investigation of Their Coordination Chemistry with Nickel and Palladium

“…The complexes are also ideally suited to 31 P NMR studies. The only complexes reported by Meek and co-workers , were [Pt(eptp)Cl]AsF 6 and [RhNO(eptp)]. In this study we report analogous nickel(II) and palladium(II) complexes.…”

“…It was prepared on a small scale by heating (3-(diphenylphosphino)propyl)phenylphosphine with vinyldiphenylphosphine in the presence of 2,2-azoisobutyronitrile (AIBN). Later it was shown that the ligand could also be synthesized rapidly on platinum by an Et 3 N-catalyzed reaction of vinyldiphenylphosphine with the coordinated secondary phosphine:

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“…It is able to chelate to three of the four coordination sites of a square planar complex. Unlike the much studied symmetrical “ttp” ligand, PhP[(CH 2 ) 3 PPh 2 ] 2 , − the ligand eptp contains a chiral phosphorus center and three nonequivalent phosphorus nuclei. These features are of course imparted to its square planar complexes which could therefore have applications as homogeneous catalysts for asymmetric syntheses since molecular models show that the third group on the central phosphorus atom must be directed to one side of the square plane.…”

A Novel Asymmetric Hydroarsination Reaction Promoted by a Chiral Organopalladium Complex

“…Indeed, the protonolysis of the P−C carbon may be initiated by the proton of the methanol solvent, which may be regenerated subsequently by proton transfer from the As−H moiety. A similar stepwise proton-transfer process involving a coordinated secondary phosphine has been described previously …”

Asymmetric synthesis of chiral arsine ligands promoted by organopalladium complexes

“…al. observed that the reaction between PtCI 2 (cyppH) 168 (cyppH = CY2P(CH2)3PHPh) with diphenylvinylphosphine 169 in ethanol without any catalyst such as Et3N or KOt-Bu occurs but in a much slower rate than when Et3N is present 106. It appears that ethanol stabilizes the phosphido nucleophile that was formed, which then attacks the vinyl group and may have subsequently undergone a proton exchange (Scheme 4.8).…”