Phosphino amine

All attempts to prepare (CH3)2PNH2 have met with failure [19, 20] but (Cp3)2PNH2 [14],Ph2PNH2 [21] and Bu2PNH2 [22] are moderately stable. Although bis(phosphino)amines have occasionally been claimed to exist in two isomeric forms, R N(PR 2)2 R 2P-P(=NR R [23, 24], they have been... 

The bis(phosphino)amines are versatile ligands and an extensive coordination chemistry, based on variable coordination patterns (Scheme 30), has been developed on this basis... 

Bis(phosphino)amines (R = H) can be easily deprotonated with lithium alkyls or sodium hydride in THF or other basic solvents (Scheme 31), and the N-lithiated derivatives react with metal and organometaUic hahdes to give a broad variety of metal compounds. 

Catalytic applications of metal complexes with (phosphino) amines 289... 

Phosphino)amines, ligands containing one, two or three P—N bonds, have attracted much interest due to their ease of preparation, their diverse coordination chemistry, and their catalytic applications. There are several synthetic routes now available, as highlighted below. 

A common synthetic strategy involves reaction of an appropriate chlorophosphine and the amine (primary, secondary, aliphatic, aromatic) in the presence of base (usually triethylamine, pyridine, or DBU (l,8-diazabicyclo[5.4.0]undec-7-ene). Care is often required during these syntheses to exclude water, thereby preventing the formation of Ph2PP(0)Ph2. Work-up procedures are similar to those for the preparation of phosphites, phosphonites, etc. and yields are often high. In some cases this strategy may yield mixtures of (phosphino)amines in which both full and partial aminolysis has resulted. 

The (phosphino)amines (198) and (199), closely related to Ph2PN(H)C6H5, were readily synthesized (Equation (48)) from Ph2PCl and o-H2NC6I I4X (X = C(0)CH3 or C(0)Ph) in ca. 70% yields (<5(P) ca. 26 ppm).444 In a similar manner ether- (200),445 amine- (201),446 pyridine- (202),447 hydra-zinopyridine- (203),448 or tertiary phosphine-functionalized (204)4 9 aminophosphines have also been reported (Scheme 13). Alternatively, dialkylchlorophosphines have been used to prepare bulky electron-rich phosphino(amines) such as (205).450... 

Bis(phosphino)amines (208)-(211) were readily prepared by condensation of Ph2PCl and the appropriate secondary amine in diethyl ether, tetrahydrofuran, dichloromethane, or benzene, with triethylamine as base.454-457 Polymer-supported phosphine-phosphino(amines) (212) have also been reported.458 Hersh and co-workers have described a novel series of bis(p-toluenesulfonylamino) phosphines (213) and (214) from bis(dichlorophosphino) starting materials and A,vV -(ditoluenesul-fonyl)-l, 2-diaminoethane.459... 

Chiral phosphino(amines) based on amino-acid (215)460 t62 or partially hydrogenated binaphthyl (216)463 units have been prepared from Ph2PCl, the amine precursor (in the case of (215) from readily available amino ester hydrochlorides) and triethylamine as base. These compounds can be isolated as (off) white solids or oils in yields of up to 90%. 

Probably the most widely studied (phosphino)amine is Ph2PN(H)PPh2 (222), which is readily prepared by heating a toluene solution of Me3SiN(H)SiMe3 and Ph2PCl. 8 In contrast, bis(phos-phino)amines such as (223) are accessible via experimental conditions outlined in Section 1.12.2.14.1.469 Compound (222) is a versatile starting material for many other phosphorus(III) and phosphorus(V) compounds and has an extensive coordination chemistry. 

The coordination chemistry of (phosphino)amines has received widespread attention, with emphasis on complexes with late transition-metal centers (especially those of Ru, Rh, Pd, Pt, Ag, and Au) but also with Cr, Ni, Cu, Mo, and W. Recently the homoleptic complex [Ni Ph2PN(H)Ph 4] was described and prepared by the reaction of NiCL-61 LO with Ph2PN(H)Ph in the presence of zinc dust.473 Of particular interest is Ph2PN(H)PPh2 (222), which has been extensively studied.474-477... 

One particularly interesting reaction of coordinated (phosphino)amines is their ability to undergo orthometallation, as observed for ligands (198) and (199) at platinum(ll) and rhodium(III) metal centers.444 These constitute the first examples of CH activation of a (phosphino)amine, in... 

Phosphino)amines and their complexes have been shown to be efficient catalysts for the palladium-catalyzed Suzuki coupling reaction of chloroarenes,449 rhodium-catalyzed hydroformy-lations458 and asymmetric hydrogenations,463,466 allylic substitution reactions,47, 472 conversion of isocyanates to isocyanurates,478 and as ethylene polymerization catalysts.479... 

An unusual reaction takes place when 1,2,4,5-tetrabromobenzene reacts with NaPPh2 in liquid ammonia.383 Although sodium bromide is formed, the products are benzene and HN(PPh2)2, and not the expected tetrasubstituted benzene. The chloramination of similar N-substituted bis(phosphino)amines gives phosphonium salts [Ph2P(NHR)NPPh2(NH2)]Cl, and a mechanism for this interesting reaction has been discussed.384... 

Bulky electron rich phosphino-amines as ligands for the Suzuki coupling reaction of aryl chlorides... 

BULKY ELECTRON RICH PHOSPHINO-AMINES AS LIGANDS FOR THE SUZUKI COUPLING REACTION OF ARYL CHLORIDES... 

If we substitnte a carbon substituent of a tertiary phosphane by an amino group, we would expect a downfleld shift simply because nitrogen is more electronegative than carbon. In Fig. 5.2, we see phosphorus chemical shifts of 19.4ppm to r p=28.6ppm downfleld of most tertiary phosphanes. We note that all three phosphino amines depicted in Fig. 5.2 still have an NH functionality. We suspect that deprotonation will resnlt in a further upheld shift. 

Note Phosphino amines have phosphorus chemical shifts downfleld from the respective phosphanes. 

Note Lithiation of a phosphino amine can cause a downfleld chemical shift due to coordination of the nitrogen atoms to two lithium atoms each. 

Not all phosphino amides resonate downfield from their respective phosphino amines. In Fig. 5.4, we see an example for an upfield shift of A< =-12ppm upon deprotonation. The upfield shift is very modest due to intermolecular hydrogen bonding (explained below). In the heterocyclic structure of the amide, the additional electron density due to deprotonation stays on the nitrogen atom. The potassium atom is coordinated by the oxygen and sulfur atoms. 

Note N-acylation of phosphino amines causes a downfield shift in the phosphorus resonance. 

Fig. 5.5 Comparison of phosphorus chemical shifts between phosphino amines, phosphino amides, and phosphino ureas...

However, acylation does not always result in a downfield shift of the phosphorus resonance, as we can see in Fig. 5.6. Direct acylation of NH PPh yields PPh2NHC(0)Me. The latter has a P-NMR chemical shift of < p=21.6ppm, and thus A< =-0.9ppm upheld of the phosphino amine NHPhPPh. For some reason, the N-acylated phosphino amine PPh2NHC(0)Me, Jp=21.6ppm, has a phosphorus chemical shift A< =-33.5ppm upheld from the phosphorus resonance of PPh2NMeC(0)Me, =55.1 ppm. 

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