Efficient and Selective Rhodium‐Catalyzed Hydrophosphorylation of Dienes

Abstract

Abstract:The hydrophosphorylation of a model 1,6-diene having a terminal and an internal alkene function has been investigated. Free radical protocols lead invariably to mixtures of cyclic phosphonate products, due to rapid cyclization of the intermediary radical species. Rhodium catalysis using a cyclic pinacol-derived phosphonate provides an efficient technique for the highly selective (> 99 %) hydrophosphorylation at the terminal alkene function. In situ modification of Wilkinsons complex by addition of 2-50 equivalents (vs. Rh) of a monophosphine (PCy 3 > PPh 3 ) or carbene ligand greatly improves the catalyst performances (TON up to 2250 mol phosphonate/mol Rh). An even more efficient system was obtained with 2 equivalents (vs. Rh) of the bidentate 1,6-bis(diphenylphosphino)hexane ligand, which affords so far unprecedented high catalytic productivity (TON up to 4 550 mol phosphonate/mol Rh) and activity (TOF up to 250 h À1 ).

Functional Elastomers via Sequential Selective Diene Copolymerization/Hydrophosphorylation Catalysis

“…A preliminary control experiment performed with 1,4-cis-homopolyisoprene (using 2.5 mol% of Rh vs. internal C=C bonds) ( Table 2, entry 1) confirmed that (i) no hydrophosphorylation takes place on the poly- Following the conditions optimized for the hydrophosphorylation of the model molecular substrate, [9] initial experiments with PA C H T U N G T R E N N U N G (IP-co-OT) copolymers were conducted using 1,4-dioxane as the solvent (Table 2, entries 2 and 3). However, moderate conversions of the vinyl functions were observed in these conditions, even in the presence of an excess of 2, a phenomenon which is assumed to arise from the poor solubility of the copolymers in this solvent at 100 8C.…”

“…[9] In fact, the linear (anti-Markovnikov) hydrophosphorylation product of the vinyl bond was the only product observed under these conditions; i.e., the catalyst system operates via steric discrimination between internal (substituted) and terminal olefins. This result suggested us that internal C=C bonds such as those present in polyisoprene/polyoctatriene backbones should not be affected.…”

“…[8] Such a copolymerization should lead to polydienes with pendant vinyl groups, offering unique opportunities for further chemical functionalization. In a preliminary study, [9] we explored and defined the optimal conditions for the highly effective rhodium-catalyzed hydrophosphorylation [10] of 2-methyl-2,7-octadiene, a model molecular diene that bears one terminal and one trisubstituted C=C bond which mimics a polydiene with pending vinyl groups.…”

Recent Advances in Metal-Catalyzed C–P Bond Formation

“…The observed A Rh catalyst mediated anti-Markovnikov hydrophosphonylation of alkenes in a polymer to give a linear product (Scheme 16). A catalyst formed from Wilkinson's complex and four equiv of dpph was the most active; this ligand was suggested to be bidentate, but the active Rh species was not identified [26,27].…”

Recent Progress in Transition Metal-Catalyzed Addition Reactions of H–P(O) Compounds with Unsaturated Carbon Linkages

“…No publication has appeared to disclose addition reactions of a phosphine oxide except for cyclopropenes (vide infra). The rhodium-catalyzed addition of pinacol phosphonate has been revisited, focusing on the effect of the ligands using nonconjugated terminal-internal dienes [52]. Only the terminal double bond participates in the reaction to furnish linear products.…”