Phosphinoalkenes, hydrophosphination

In the most recent developments in this area, organometallic lanthanide complexes have been utilized for hydrophosphination/cyclization reactions of phosphinoalkenes.202,203... 

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

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... 

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]. 

Scheme 12 Diastereoselective hydrophosphination/cyclization of chiral phosphinoalkenes [147,179]...

The generation of a phosphine-functionalized substrate and its coordination to the chiral metal template in order to activate the unsaturated C=C bond toward nucleophilic attack is a prerequisite for the hydrophosphination reactions seen in previous sections. However, in the case of activated alkynes such as dimethyl acetylenedicarboxylate or its diketone analogue, this pre-preparation of the phosphinoalkene is not necessary, and a direct hydrophosphination using two equivalents of diphenylphosphine in the presence of trace amounts of base was found to promote the two-stage hydrophosphination in a one-pot process with diastereoselectivity of 6 1 and in quantitative yield (Scheme 15) [73],... 

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... 

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