Dinuclear Phosphine-Amido [Rh₂(diene){μ-NH(CH₂)₃PPh₂}₂] Complexes as Efficient Catalyst Precursors for Phenylacetylene Polymerization

Abstract

Dinuclear phosphine-amido, [Rh 2 (diene){μ-NH(CH 2 ) 3 PPh 2 } 2 ], and cationic phosphine-amino complexes, [Rh(diene){Ph 2 P(CH 2 ) 3 NHR}] + (diene = cod, nbd, tfb) and [Rh{Ph 2 P(CH 2 ) 3 NHR} 2 ] + , have been prepared from the corresponding amino-functionalized phosphines Ph 2 P-(CH 2 ) 3 NHR (R = H, Me) and suitable rhodium(I) precursors. The dinuclear [Rh 2 (diene){μ-NH(CH 2 ) 3 PPh 2 } 2 ] complexes bearing π-acceptors diene ligands such as nbd or tfb exhibit a remarkable catalytic activity in phenylacetylene (PA) polymerization affording stereoregular polyphenylacetylenes with, unlike the cod precursor, unimodal molar mass distributions of very high molecular weights, M w up to ≈ 1.2 × 10 6 , and moderate polydispersity indexes. These complexes are more active than the mononuclear phosphino-anilido [Rh(diene){Ph 2 P(C 6 H 4 )NMe}] complexes, which are in turn more active than the cationic complexes [Rh(diene){Ph 2 P(CH 2 ) 3 NHMe}] + , [Rh(nbd){Ph 2 P(CH 2 ) 3 NH 2 }] + , and [Rh(nbd){Ph 2 P(C 6 H 4 )NHMe}] + bearing the same diene ligand. In contrast, complexes [Rh{Ph 2 P(CH 2 ) 3 NHR} 2 ] + (R = H, Me) without a diene ligand have been found to be inactive in PA polymerization. The excellent catalytic performance of [Rh 2 (diene){μ-NH(CH 2 ) 3 PPh 2 } 2 ] (diene = nbd, tfb) complexes is a consequence of the mode of activation of PA that likely results in the formation of unsaturated alkynyl species [Rh(diene)(CC-Ph)L] (L = PA, THF), which may be competent for PA polymerization.

Variation on the π‐Acceptor Ligand within a RhI−N‐Heterocyclic Carbene Framework: Divergent Catalytic Outcomes for Phenylacetylene‐Methanol Transformations

“…A rational explanation could arise from the presence of an extra vacant site with regard to neutral counterparts which allows the coordination of a second molecule of alkyne to yield a [2+2] coupling with the alkoxycarbene intermediate resulting in the formation of dienol ethers [33] . As previously described, [29] Rh‐cod complexes 1 , 7 , and 11 , lacking a π ‐acceptor ligand, promoted the polymerization of phenylacetylene.…”

“…The catalytic outcome is strongly dependent on the catalyst. In addition to the expected alkyne hydroalkoxylation to enol ethers ( 16 ), alkyne polymerization ( 13 ), [29] cyclotrimerization ( 14 ) [30] or dimerization ( 15 ) [12c] were also observed. The new dienol ethers ( 17 ) [31] resulting from formal addition of methanol to enynes 15 were also formed in some cases.…”

Silicon Promoted Cationic Polymerization of Phenylacetylenes

“…Early transition metal catalysts include Ziegler–Natta catalysts and group 6 metal carbene complexes of molybdenum and tungsten, , while for late-transition-metal catalysts, the best studied are rhodium and palladium complexes. Since 1969, Kern’s first report on the use of a Rh catalyst, (Ph 3 P) 3 RhCl, to polymerize PA, the late-transition-metal catalysts have drawn particular attention thanks to their high activity, stability, and the relatively wide monomer scope …”

“…Since 1969, Kern's first report on the use of a Rh catalyst, (Ph 3 P) 3 RhCl, to polymerize PA, 27 the late-transition-metal catalysts have drawn particular attention thanks to their high activity, stability, and the relatively wide monomer scope. 28 The main disadvantages of metal-based catalysts are related to their high cost and complicated synthesis. 29 Moreover, the residual metal complexes in polymeric products might be problematic especially for plastic electronic applications.…”

Rhodium-Catalyzed Stitching Polymerization of Alkynylsilylacetylenes

“…Rhodium-catalyzed polymerization of terminal alkynes such as phenylacetylene is one of the well explored chain polymerizations to give π-conjugated polymers (Scheme a) . In addition to the development of highly effective catalyst systems as well as the detailed studies on the polymerization mechanism, applications toward functional materials possessing various properties such as helix-induced chirality, fluorescent characteristics, liquid crystallinity, and gas permeability have also been actively investigated through introduction of appropriately functionalized substituents to the monomers. However, only carbon-substituted alkynes have been employed as monomers to date, and the reported polymerization patterns were either simple coordination–insertion of monoynes or cyclopolymerization of diynes until recently, which significantly limited the accessible structures of the main chain repeating unit.…”