Intramolecular hydrophosphination

Douglass, M.R. and Marks, T.J., Organolanthanide-catalyzed intramolecular hydrophosphination/cyclization of phosphinoalkenes and phosphi-noalkynes, /. Am. Chem. Soc., 122, 1824, 2000. 

Lanthanide metals catalyze intramolecular hydrophosphination-cyclization of alkenyl- and alkynylphosphines rapidly at room temperature [19]. As summarized in Table 3, the reaction is quite general. 

Table 3 Intramolecular hydrophosphination with Cp" 2YCH(SiMe3)2 precatalyst...

A mechanism that involves ytterbium phosphide species has been proposed, similarly to the foregoing intramolecular hydrophosphination. Generation of the phosphide species is supported by the formation of Ph2CDNHPh (after aqueous quench) upon treatment of the imine complex with Ph2PD (Scheme 15). Lanthanide phosphide is known to react with THF, forming a 4-diphenylphosphino-l-butoxyl species [21], which was indeed found as a side product in the catalytic hydrophosphination of disubstituted aliphatic alkynes run in THF, supporting further the ytterbium-phosphide intermediate (Scheme 16). 

The amide [Sm(45a) N(SiMe3)2 ] was a catalyst for an aUene-based hydroamination/ cyclisation. As an illustration, one such product upon hydrogenation yielded a naturally occurring alkaloid. Scheme 4.8. " " The same samarium(lll) amide was also active for the intramolecular hydrophosphination/cyclisation of phosphino-alkenes or -alkynes e.g., H2P(CH2)3C=CPh was transformed into 76. " ... 

The phosphirene complex 26, as generated from a terminal phosphinidene complex and 4-phenylbut-3-yn-l-ol, reacts with a second molecule of the phosphinidine complex giving an intermediate phosphirene 27 with additional secondary alkoxyphosphine functionality. An intramolecular hydrophosphination yields then the complex 28 as a mixture of two diastereomers (Scheme 7) <20050M696>. 

Homoleptic lanthanide alkyls of the form Ln[GH(SiMe3)2]3 (Ln = Y, La, Nd, Sm, Lu) serve as efficient precatalysts for intramolecular homogeneous hydrophosphination. Both phosphinoalkenes and phosphinoalkynes undergo cyclization to the corresponding heterocyclic structures.1055 The catalytic intramolecular hydrophosphination/cycli-zation of phosphinoalkenes and phosphinoalkynes using organolanthanide precatalysts of the type... 

Significant progress in organolanthanide-catalyzedhydroamination over the last two decades has sparked the interest in the development of analogous catalytic hydrofunctionalization protocols. Catalytic hydrophosphination of unsaturated carbon-carbon linkages offers an attractive atom-economic route to phosphines [87,177], It should be noted that inter- and intramolecular hydrophosphinations are also... 

The mechanism and scope of rare-earth metal-catalyzed intramolecular hydrophosphination has been studied in detail by Marks and coworkers [147,178-181]. The hydrophosphination of phosphinoalkenes is believed to proceed through a mechanism analogous to that of hydroamination. The rate-determining alkene insertion into the Ln-P bond is nearly thermoneutral, while the faster protolytic o-bond metathesis step is exothermic (Fig. 22) [179,181]. The experimental observation of a first-order rate dependence on catalyst concentration and zero-order rate dependence on substrate concentration are supportive of this mechanism. A notable feature is a significant product inhibition observed after the first half-life of the reaction. This is apparently caused by a competitive binding of a cyclic phosphine to the metal center that impedes coordination of the phosphinoalkene substrate and, therefore, diminishes catalytic performance [179]. 

Another recent advance is the synthesis of P-stereogenic ferrocenepho-spholanes, simultaneously reported by two independent groups. Pugin, Pfaltz and co-workers studied the intramolecular hydrophosphination in a racemic secondary phosphine (Scheme 2.51). 

Platinum catalysts of the preceding section activate only the nucleophile (a secondary phosphine), which then reacts with the electrophile (an activated alkene). There are, however, interesting examples of lanthanide complexes activating both the nucleophile and the electrophile towards intramolecular diastereoselective hydrophosphination/cyclisations. In 2000 Marks and co-workers found that certain lanthanide complexes catalyse the intramolecular hydrophosphination of alkenes and alkynes (Scheme 6.13). 

Diastereomerically pure catalysts 33 were obtained after recrystallisation and tested in intramolecular hydrophosphination of alkenes to yield phospholanes 35 (Scheme 6.14). 

A route to non-racemic P-stereogenic vinylphosphine-boranes, e.g., (100), is afforded by the addition of methylphenylphosphine-borane with alkynes in the presence of a chiral diphosphine-palladium catalyst. The ehiral diphosphine-platinum complex-catalysed addition of diethylphosphine to the diene cis,cis-muco-nitrile has given the new diphosphine (101) as a 3 2 mixture of diastereoisomers. Further work has been reported on the use of cyclopentadienyliron complexes that act as metal templates for the intramolecular hydrophosphination of coordinated vinylphosphines with 1,2-diphosphino-alkanes and -benzenes, leading to 1,4,7-triphosphacyclononanes, e.g., (102), capable of further elaboration to form new cyclic phosphines. 

Benzo[b]phosphole oxides were prepared by the intramolecular hydrophosphination of 2-alkynylphenyl-phenylphosphine oxides (Scheme 17-1). ° A variation leading to bis(phosphole oxides) is shown in Scheme 17-2. °... 

Scheme 8.47 Proposed mechanism of intramolecular hydrophosphination of phosphinealkenes using Cp LnE(TMS)2...

Douglass MR, Marks TJ (2000) Organolanthanide-catalyzed intramolecular hydrophosphination/ cyclization of phosphinoalkenes and phosphinoalkynes. J Am Chem Soc 122 1824—1825... 

Douglass MR, Stem ChL, Marks TJ (2001) Intramolecular hydrophosphination/cyclization of phosphinoalkenes and phosphinoalkynes catalyzed by organolanthanides scope, selectivity, and mechanism. J Am Chem Soc 123 10221-10238... 

A related radical-initiated iron-template reaction between l,2-bis(phos-phino)ethane and diallylphosphines gave complex 12 with nonsymmetric 3-methyl-1,4,7-triphosphacyclodecane ligand (Scheme 12.5). This macrocycle is the result of two intramolecular hydrophosphination reactions the first one generates a five-membered (chelate) ring with an exo-methyl group and the second gives a six-membered chelate. 

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