P.N ligands

Among recently described new Pd-catalysed enantioselective reactions, the ring opening of meso oxabicyclic alkenes with dialkyl zinc reagents in the presence of chiral P/P and P/N ligands reported by Tautens el al. constitutes a synthetically outstanding C-C bond-forming desymmetrization reaction. 

A combination of P- and N- donors is another useful approach to potentially reactive (and cataly-tically active) Ni species. Similar to O- donors, N is a hard donor capable of stabilizing metal ions in higher oxidation states, whereas the soft donor P is best suited to stabilize medium or low oxidation states. A neutral bidentate P,N ligand combining a hard dimethylamino and a soft phosphine donor in /V,/V -dimethyl-2-(diphenylphosphino)aniline (241) affords the neutral trigonal bipyramidal and the... 

Figure 32 The first P,N-ligand shown in Figure 32 can form five-membered ring chelates, in allylic alkylation with Pd the second is a chelating (phosphinomethyl)oxazoline P,N-type ligand, that catalyzes...

The reaction of [Au2(/i-Cl2)Me4] with 3,7-dimethyl-l,5,7-triaza-3-phosphabicyclo[3.3.1]nonane (L) gives [AuMe2L][AuMe2Cl2] (339) with a chelate P,N ligand.1973... 

A highly thermostable palladium-phosphine oxazoline catalytic system, shown in Eq. (11.37), has recently been reported to yield high ee under single-mode micro-wave irradiation [54, 55]. The use of this P,N-ligand catalytic system resulted in even higher ee than the P,P-ligand BINAP [56], The reactions were performed in acetonitrile (b.p. 81-82 °C) and superheating increased the temperatures up to 145 °C, as measured by means of a fluoroptic probe. 

In the framework of this concept a series of new mixed P/N ligands was prepared, employing the phosphorus-analogous Mannich reaction (Scheme 9). This transformation permits the substitution of primary or secondary amines by methylenephos-phine residues -CH2PRR (R, R = alkyl, aryl) through reaction with a secondary phosphine and formaldehyde (46). Based on the... 

Fig. 8. Mo/W dinitrogen complex with the P/N ligand N,N,N, N -tetrakis-(diphenylphosphinomethyl)-2,6-diaminopyridine (pyN2P

A most significant advance in the alkyne hydration area during the past decade has been the development of Ru(n) catalyst systems that have enabled the anti-Markovnikov hydration of terminal alkynes (entries 6 and 7). These reactions involve the addition of water to the a-carbon of a ruthenium vinylidene complex, followed by reductive elimination of the resulting hydridoruthenium acyl intermediate (path C).392-395 While the use of GpRuGl(dppm) in aqueous dioxane (entry 6)393-396 and an indenylruthenium catalyst in an aqueous medium including surfactants has proved to be effective (entry 7),397 an Ru(n)/P,N-ligand system (entry 8) has recently been reported that displays enzyme-like rate acceleration (>2.4 x 1011) (dppm = bis(diphenylphosphino)methane).398... 

However, by far the most common approach toward catalytic asymmetric hydroboration is to use a chiral catalyst and an achiral borane source. Both homobidentate F Pand heterobidentate P,N ligand classes have been employed in this transformation with varying degrees of success. 

Figure 12 Planar chiral pyrazole containing P,N ligands.

The 1-t-butylphospholane sulfide intermediate to TangPhos was also used to prepare the P,N ligands 48 by reacting the lithium complex with C02 and then oxazoline formation with a range of chiral amino alcohols [69b, 74]. The Ir complexes of these ligands have been successfully used in the reduction of / -methylcinnamic esters (80-99% ee) and methylstilbene derivatives (75-95% ee), a particularly challenging class of unfunctionalized olefins [4 c]. 

The oxazoline-derived P,N ligands can be classified into four groups according to structure phosphino-oxazolines phosphite- and phosphinite-oxazolines catalysts containing a P-N bond and structurally related non-oxazoline catalysts. 

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