Nicholas Sheng Loong Tan

The synthesis of the Rh(I)-aryl complex, Rh(I)(nbd)(BiPh)(P(4-FC₆H₄)₃) is reported and its efficacy as an initiator for the (co)polymerization of phenylacetylenes established. The X-ray crystal structure indicates that the complex adopts a slightly distorted square planar geometry whose purity and structure was also confirmed by elemental analysis and ¹H, ¹³C, ³¹P, ¹⁹F, ¹⁰³Rh, and ³¹P-¹⁰³Rh{¹H} HMQC NMR spectroscopy. We demonstrate that Rh(I)(nbd)(BiPh)(P(4-FC₆H₄)₃) mediates the (co)polymerization of phenylacetylenes in a controlled fashion with initiation efficiencies as high as 0.98, as evidenced by the pseudo-first-order kinetic and number-average molecular weight versus conversion profiles. The ability to form well-defined AB diblock copolymers, in a stereoregular manner, by sequential monomer addition is verified in the block copolymerization of phenylacetylene with 4-fluorophenylacetylene with quantitative crossover efficiency, as determined by size exclusion chromatography.

The synthesis of a novel Rh(I)-aryl complex is detailed and its ability to serve as an initiator in the stereospecific polymerisation of phenylacetylene evaluated. Targeting the Rh(I) species, (2-phenylnaphthalen-1-yl)rhodium(I)(2,5-norbornadiene)tris(para-fluorophenylphosphine), Rh(nbd)(P(4-FC₆H₄)₃)(2-PhNapth), following recrystallization we obtained the isomeric (2-(naphthalen-2-yl)phenyl)rhodium(I) complex, Rh(nbd)(P(4-FC₆H₄)₃)(2-NapthPh), as determined by X-ray single-crystal structure analysis, and confirmed by X-ray powder diffraction. The isolation of the latter species was proposed to occur from the target (2-PhNapth) derivative via an intramolecular 1,4-Rh atom migration. This supposition was supported by density functional theory (DFT) calculations that indicated the isolated (2-NapthPh) derivative has lower energy (−19 kJ mol⁻¹) than the targeted complex. The structure of the isolated (2-NapthPh) species was confirmed by multinuclear NMR spectroscopy including 2D ³¹P–¹⁰³Rh{¹H, ¹⁰³Rh}, heteronuclear multiple-quantum correlation (HMQC) experiments; however, NMR analysis indicated the presence of a second, minor species in solution in an approximate 1 : 4 ratio with the 2-NapthPh complex. The minor species was identified as a second structural isomer, the 3-phenylnaphthyl derivative, proposed to be formed under a dynamic equilibrium with the 2-NapthPh derivative via a second 1,4-Rh atom migration. DFT calculations indicate that this 1,4-migration proceeds through a low-energy pathway involved in the oxidative addition of a C–H bond to Rh followed by a reductive elimination with the distribution of the products being thermodynamically controlled. The recrystallized Rh(nbd)(P(4-FC₆H₄)₃)(2-NapthPh) complex was subsequently evaluated as an initiator in the polymerisation of phenylacetylene (PA); gratifyingly, the Rh(I) species was an active initiating species with the pseudo-first-order kinetic and molecular weight evolution vs time plots both linear implying a controlled polymerisation while yielding (co)polymers with low dispersities (Đ = M_w/M_n typically ≤1.25) and high cis-transoidal stereoregularity (>95%). Typical initiation efficiencies, while not quantitative (as judged by size exclusion chromatography), were nonetheless high at ca. 0.8. The presence of the minor 3-phenylnaphthyl species when in solution is proposed to be the cause of the observed non-quantitative initiation.

Dieser Kurzaufsatz präsentiert den aktuellen Stand von (Co)polymerisationen, die von definierten Ethinyl‐, Vinyl‐ und Aryl‐Rh^I‐Komplexen vermittelt werden. Dabei konzentrieren wir uns auf Rh^I‐Verbindungen, die sich für die (Co)polymerisation von Phenylacetylenen, Arylisocyaniden sowie Propargylestern und ‐amiden eignen.

The synthesis, characterization and use, as initiators for phenylacetylene polymerizations, of three new rhodium(I)‐vinyl complexes containing fluorenyl functionality with fluorine‐functionalized phosphine ligands is described. Rh(nbd)(CPh=CFlu)P(4‐FC₆H₄)₃, Rh(nbd)(CPh=CFlu)P(4‐CF₃C₆H₄)₃, and Rh(nbd)(CPh=CFlu)P[3,5‐(CF₃)₂C₆H₃]₃ (nbd: 2,5‐norbornadiene; Flu: fluorenyl) were prepared and isolated as discrete, orange compounds and were readily recrystallized yielding X‐ray quality crystals. All complexes were characterized by a combination of ¹H, ³¹P, ¹⁹F, ¹⁰³Rh NMR spectroscopy and 2D ³¹P‐¹⁰³Rh/³¹P‐¹⁰³Rh{¹⁰³Rh} heteronuclear multiple‐quantum correlation (HMQC) experiments, elemental analysis, and single‐crystal X‐ray analysis. The complexes were active as initiators in the co‐ordination insertion polymerization of phenylacetylene, with initiation efficiencies spanning the range 13–56 %, and yielded polyphenylacetylenes of low dispersity (Ð = M_w/M_n) with high cis‐transoidal stereoregularity.