Phosphaalkene-oxazoline copolymers with styrene as chiral ligands for rhodium(i)

Abstract

The radical-initiated copolymerization of phosphaalkene-oxazoline, MesP[double bond, length as m-dash]C(Ph)CMe2Ox [1, Ox = CNOCH(iPr)CH2] with different loadings of styrene affords poly(methylenephosphine-co-styrene)s [2a (1 : S = 1 : 2): Mw = 7400 g mol(-1), PDI = 1.1; 2b (1 : S = 1 : 5): Mw = 18 000 g mol(-1), PDI = 1.2; 2c (1 : S = 1 : 10): Mw = 16 000 g mol(-1), PDI = 1.3]. Copolymers 2a-2c are demonstrated as viable macromolecular ligands for rhodium(i). By comparison with the crystallographically characterized model P,N-bidentate complex, [Mes(Me)P-CH(Ph)CMe2Ox·Rh(cod)]BF4, the polymer complexes [2·Rh(cod)]BF4 were prepared. The macromolecular metal complexes were characterized by GPC {for [2a·Rh(cod)]BF4: Mw = 14 000 g mol(-1), PDI = 1.2}, UV/Vis spectroscopy, (1)H, (13)C and (31)P NMR spectroscopy. Integration of the (31)P NMR spectra of mixtures of 2 and [Rh(cod)2]BF4 permitted the determination of the mol% of incorporation of monomer 1 in copolymer 2 (2a: 17%; 2b: 5%; 2c: 4%). These results compared favorably with those determined by elemental analysis (2a: 17%; 2b: 6%).

An Addition–Isomerization Mechanism for the Anionic Polymerization of MesP═CPh2 and m-XylP═CPh2

“…The field of functional polymers featuring inorganic elements in the main chain has grown dramatically due to their unique properties and potential applications. − As part of a broad program to synthesize phosphorus-containing macromolecules, we have been interested in extending addition polymerization to PC bonds. In particular, the close analogy between phosphaalkenes and olefins in molecular chemistry has inspired us to develop the addition polymerization of the monomer MesPCPh 2 ( A , R = Ph) and related phosphaalkenes. − On the basis of NMR spectroscopic investigations, the resultant poly­(methylene­phosphine)­s were originally assigned a microstructure that was consistent with a simple head-to-tail propagation analogous to that observed for polyolefins (i.e., B , x = 0 in Scheme ). Recently, we discovered that the nitroxide-mediated radical polymerization of A (R = Ph) gives a polymer with a fascinating and unexpected microstructure that is presumably derived from regioregular C–H activation processes (i.e., B , x ≫ y ) .…”

“…Recently, we discovered that the nitroxide-mediated radical polymerization of A (R = Ph) gives a polymer with a fascinating and unexpected microstructure that is presumably derived from regioregular C–H activation processes (i.e., B , x ≫ y ) . Follow-up studies revealed that this novel addition–isomerization mechanism of propagation for phosphaalkenes might be more general. − …”

A “masked” source for the phosphaalkene MesP=CH2: Trapping, rearrangement, and oligomerization

“…In particular, the analogy between the P=C bond of a phosphaalkene and the C=C bond of an olefin has been exploited to generate an entirely new class of functional phosphine polymers . The principle monomers for polymerization studies have employed bulky substituents at both carbon and phosphorus (ie, MesP=CAr 2 ) . The presence of sterically encumbering substituents greatly reduces the reactivity of the P=C bond toward polymerization.…”

A C-Pyrenyl Poly(methylenephosphine): Oxidation “Turns On” Blue Photoluminescence in Solution and the Solid State

“…Living anionic methods of initiation may be employed to afford homopolymers and block copolymers with controlled architectures. , Additionally, the P moieties within PMPs can be functionalized to give materials that undergo self-assembly in block-selective solvents. , Radical-initiated copolymerization of phosphaalkenes with styrene can be achieved to access random copolymers that are effective ligands for Pd-catalyzed Suzuki–Miyaura cross-coupling reactions . Recently, we have shown that PMP copolymers derived from an enantiomerically pure phosphaalkene and styrene can be used as chiral macromolecular ligands for rhodium­(I) …”