A series of alkylammonium-imidazolium chloride salts [RImH(CH 2) n NMe 2 ]Cl•HCl (R = Me, t-Bu, Mes, n = 2, 3) have been prepared by alkylation of 1-substituted imidazole compounds with the corresponding chloro-alkyl-dimethylamine hydrochloride. These salts are precursors for the synthesis of a library of rhodium (I) complexes containing amino-alkyl functionalized N-heterocyclic carbene (NHC) ligands with hemilabile character by varying the substituent on the heterocyclic ring and the length of the linker with the dimethylamino moiety. The monodeprotonation of alkylammoniumimidazolium salts with NaH in the presence of [{Rh(µ-Cl)(cod)} 2 ] gave the amino-imidazolium salts [RImH(CH 2) n NMe 2 ][RhCl 2 (cod)]. Further deprotonation with NaH under non anhydrous conditions gave the neutral complexes [RhCl(cod)(RIm(CH 2) n NMe 2)] in good yields. The abstraction of the chloro ligand by silver salts rendered the cationic complexes [Rh(cod)(κ 2 C,N-RIm(CH 2) 3 NMe 2)][BF 4 ] (R = Me, Mes) by coordination of the NMe 2 fragment of the sidearm of the functionalized NHC ligands. The catalytic activity of the rhodium complexes in the hydrosilylation of terminal alkynes using HSiMe 2 Ph has been investigated with Ph-C≡CH, t-Bu-C≡CH, n-Bu-C≡CH, and Et 3 Si-C≡CH as substrates. Higher activities were achieved using neutral complexes having small substituents at the heterocyclic ring (R = Me). Excellent selectivities in the β-(Z)-vinylsilane isomer were found in the hydrosilylation of 1hexyne and predominantly the β-(E) and α-bis(silyl)alkene isomers were obtained in the hydrosilylation of triethylsilylacetylene.

A series of cationic complexes [Rh(diene){Ph 2 P(CH 2 ) n Z}] [BF 4 ] (diene = 1,5-cyclooctadiene (cod), tetrafluorobenzobarralene (tfb) or 2,5-norbonadiene (nbd)) containing functionalized phosphine ligands of the type Ph 2 P(CH 2 ) n Z (n = 2, or 3; Z = OMe, NMe 2 , SMe) have been prepared and characterized. These complexes have shown a great catalytic activity for phenylacetylene (PA) polymerization. Catalyst screening and optimization have determined the superior performance of complexes containing a P,N-functionalyzed phosphine ligand, [Rh(diene){Ph 2 P(CH 2 ) 3 NMe 2 }][BF 4 ] (diene = cod 5, tfb 6, nbd 7), and tetrahydrofuran as solvent. The influence of the diene ligand and the effect of temperature, PA to rhodium molar ratio, addition of water or a co-catalyst, DMAP (4-(dimethylamino)pyridine), have been studied. Diene ligands strongly influence the catalytic activity and complexes 6 and 7 are far more active than 5. Both complexes gave polyphenylacetylene (PPA) with very high number-average molecular weights (M n ) of 970 000 (6) and 1 420 000 (7). The addition of DMAP resulted in a dramatic drop in the PPA molecular weight, 106 000 (6) and 233 000 (7,). The PPA obtained with the system 6/DMAP showed a narrow molecular weight distribution (M w /M n = 1.20) and incremental monomer addition experiments have demonstrated the quasi-living nature of the polymerization reaction under these conditions. The PPA obtained with these catalytic systems has been characterized by 1 H and 13 C{ 1 H} NMR spectroscopy and shows a cis-transoidal configuration with a high level of steroregularity (cis content superior to 99%). TGA, DSC, and IR analysis have revealed a thermal cis↔trans

Characterization of poly(phenylacetylene) (PPA) samples produced using Rh(I) complexes featuring hemi-labile phosphine ligands by size exclusion chromatography, multi-angle light scattering, (SEC-MALS), or asymmetric field flow fractionation (A4F)-MALS has revealed that some of these PPA samples contain a mixture of linear and branched polymer. The occurrence and extent of branching is dependent on both catalyst structure and polymerization conditions. The levels of branching are consistent with either terminal branching through copolymerization of macro-monomer or chain transfer to polymer, where the branched species are less reactive towards further polymerization than the linear chains. The MM dependence of B, the number of branches per molecule, or λ, the number of branches per repeat unit, suggests that the latter explanation may be correct but further work is needed.

Cationic rhodium(I) complexes containing the flexible hemilabile phosphine ligand (3-ethoxypropyl)diphenylphosphine efficiently catalyzed the anti-Markovnikov oxidative amination of styrene in tetrahydrofurane at 80 degrees C to produce (E)-1-styrylpiperidine with turnover frequencies up to 75 h(-1) with excellent enamine selectivity (96%).

A series of novel functionalized phosphines of hemilabile character, R 2 P(CH 2 ) n Z, have been prepared from diarylphosphines using several synthetic methodologies. The synthetic methods include the alkylation of lithium diarylphosphide or diarylphosphino-borane adducts with functionalized halogenoalkanes, X-(CH 2 ) n -Z, and the photochemical hydrophosphination of suitable functionalized allyl or vinyl derivatives, CH 2 =CH-Z or CH 2 =CH-CH 2 -Z, using white light. A range of R 2 PH (R = C 6 H 5 -CH 2 , p-CH 3 O-C 6 H 4 , p-CH 3 -C 6 H 4 , o-CH 3 -C 6 H 4 , C 6 H 5 , p-CF 3 -C 6 H 4 ) has been used in order to tune the electronic density on the P donor atom. The coordination ability of the hemilabile fragment was modified by selection of the donor group (Z = OMe, OEt, OnBu, NMe 2 ) or the length of the flexible carbon chain (n = 2, 3). Hemilabile fluorinated allyl phosphines, R 2 PCH 2 CH=CH 2 (R = p-F-C 6 H 4 , C 6 F 5 ), have been prepared from diarylchlorophosphines and allymagnesiun bromide.

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and excellent enamine selectivity (96%).

Abstract:Cationic rhodium(I) complexes having P,O-functionalized arylphosphine ligands are efficient catalysts for the regioselective antiMarkovnikov oxidative amination of styrene with piperidine. The mechanism of the catalytic reaction has been investigated by spectroscopic means under stoichiometric and catalytic conditions. In the presence of piperidine the catalyst precursor [Rh{κ 2 -P,O-Ph 2 P(CH 2 ) 3 OEt} 2 ] + (5) gives the piperidine complex [Rh{κ 1 -PPh 2 P(CH 2 ) 3 OEt} 2 (HNC 5 H 10 ) 2 ] + (8) that was transformed into the neutral amidopiperidine species [Rh{κ 1 -PPh 2 P(CH 2 ) 3 OEt} 2 (NC 5 H 10 )(HNC 5 H 10 )] (9) under thermal conditions. NMR studies carried out in the presence of styrene under catalytic conditions showed that 9 is a key species in the catalytic oxidative amination of styrene. Related cyclooctadiene-containing catalyst precursors [Rh(cod){κ 1 -PPh 2 P(CH 2 ) 3 OEt} n ] + (n = 1, 2) also gave 9 under the same conditions. The proposed catalytic cycle has been established by a series of DFT calculations including the transition states of the key steps that have been found and characterized. These studies have shown that, after the elimination of the enamine, the regeneration of catalytic active species takes place by direct transfer of the proton of a piperidine ligand to the alkyl group, resulting from the insertion of styrene into Rh-H bond, with formation of ethylbenzene. Against the expectations, the formation of a dihydride intermediate by NH oxidative addition is a highly energy-demanding process. Catalyst 5 has also been applied for the oxidative amination of substituted vinylarenes with several secondary cyclic and acyclic amines.