To study the influence of electronics on catalytic polymerization properties independent from sterics, phosphinesulfonato Pd(II) complexes bearing remotely located substituents on the nonchelating P-bound aryls [κ 2 -(P,O)-(4-R-2-anisyl) 2 PC 6 H 4 SO 2 O]Pd(Me)(dmso) (1a−edmso: 1a, R = CF 3 ; 1b, R = Cl; 1c, R = H; 1d, R = CH 3 ; 1e, R = OCH 3 ) were prepared. The electron-poor complex 1admso (4-CF 3 ) undergoes the fastest insertion of methyl acrylate (MA) and is the most active for ethylene polymerization. The polyethylene molecular weight increases by a factor of 2 for the more electron rich complex 1e-dmso (4-OCH 3 ) (M n = 17 × 10 3 vs 8 × 10 3 for 1a-dmso (4-CF 3 )). MA/ ethylene copolymerization experiments revealed that the MA incorporation ratio and copolymer molecular weights are largely independent of the electronic nature of the remote substituents. These trends were further confirmed by studies of two mixed Paryl/-alkyl complexes 1f-dmso ([κ 2 -(2,4,6-(OMe) 3 C 6 H 2 )( t Bu)PC 6 H 4 SO 2 O]Pd(Me)(dmso)) and 1g-dmso ([κ 2 -(C 6 H 5 )( t Bu) PC 6 H 4 SO 2 O]Pd(Me)(dmso)). In ethylene/MA copolymerization, 1f-dmso affords a significantly higher molecular weight polymer with reasonable MA incorporation (M n = 12 × 10 3 and 7.7 mol % MA) and activities similar to those observed for complexes 1a−e-dmso.

In modern methods for the preparation of small molecules and polymers, the insertion of substrate carbon-carbon double bonds into metal-carbon bonds is a fundamental step of paramount importance. This issue is illustrated by Mizoroki-Heck coupling as the most prominent example in organic synthesis and also by catalytic insertion polymerization. For unsymmetric substrates H 2 C ¼ CHX the regioselectivity of insertion is decisive for the nature of the product formed. Electron-deficient olefins insert selectively in a 2,1-fashion for electronic reasons. A means for controlling this regioselectivity is lacking to date. In a combined experimental and theoretical study, we now report that, by destabilizing the transition state of 2,1-insertion via steric interactions, the regioselectivity of methyl acrylate insertion into palladiummethyl and phenyl bonds can be inverted entirely to yield the opposite "regioirregular" products in stoichiometric reactions. Insights from these experiments will aid the rational design of complexes which enable a catalytic and regioirregular MizorokiHeck reaction of electron-deficient olefins.density functional theory calculation | homogeneous catalysis | organometallic | regiochemistry W hereas the palladium-catalyzed Mizoroki-Heck coupling is an established powerful strategy for the formation of carbon-carbon bonds from electron-deficient and electron-rich olefins (1-5), insertion (co)polymerization (6-8) of acceptor or donor substituted olefins has only been demonstrated since the mid-1990s, and only a few catalyst motifs are known to promote such polymerizations (9, 10), which are based on palladium. The regioselectivity of insertion follows the same pattern for both reactions. Electron-deficient olefins [e.g., methyl acrylate (MA)] selectively insert in a 2,1-fashion (6, 9-11), whereas electron-rich olefins (e.g., vinyl ethers) insert in a 1,2-fashion (3, 6, 12-14, †) (Fig. 1). Finally, apolar olefins (e.g., α-olefins) commonly afford mixtures of both insertion modes in palladium-catalyzed Mizoroki-Heck (15) and polymerization reactions (16), whereas closely related nickel-catalyzed polymerizations of α-olefins can proceed with high selectivity by 1,2-insertion (17)-e.g., under kinetically controlled low-temperature conditions when sterically demanding ligands coordinate to nickel (16,18).The accepted rationale for these reactivity patterns is that electronic effects govern the regiochemistry of insertion for polarized carbon-carbon double bond substrates: In the Cossée-Arlman-type insertion step, the metal-bound, nucleophilic carbon atom migrates to the lower electron-density carbon atom of the double bond, while the electrophilic palladium atom migrates to the higher electron-density carbon atom of the double bond. In contrast, the insertion regiochemistry of apolar carbon-carbon double bonds is rather determined by steric effects (given that there is little electronic discrimination of the two olefinic carbon atoms), and under strict kinetic control the 1,2-insertion mode may preva...

N-Isopropyl acrylamide (NIPAM), N,N-dimethyl acrylamide (DMAA), and 2-acetamidoethyl acrylate (AcAMEA) were copolymerized with ethylene employing [(P^O)PdMe(DMSO)] (1-DMSO; P^O = κ(2)-P,O-Ar(2)PC(6)H(4)SO(2)O with Ar = 2-MeOC(6)H(4)) as a catalyst precursor. Inhibition studies with nonpolymerizable polar additives show that reversible κ-O-coordination of free amide retards polymerization significantly. Retardation of polymerization increases in the order ethyl acetate ≪ methyl ethyl sulfone < acetonitrile < N,N-dimethylacetamide ≈ N-methylacetamide ≈ propionic acid < dimethylsulfoxide. Pseudo-first-order rate constants for the insertion into 1-DMSO were determined to increase in the order DMAA < AcAMEA < NIPAM < methyl acrylate. Exposure of 1-DMSO to NIPAM resulted in the formation of consecutive insertion products [(P^O)Pd(C(6)H(11)NO(2))(n)Me] (n ≤ 3), as determined by electrospray ionization mass spectrometry. The solid-state structure of the methanol adduct of the 2,1-insertion product of NIPAM into 1-DMSO, [(P^O)Pd{η(1)-CH(CONHiPr)CH(2)CH(3)}(κ(1)-O-MeOD)] (2-MeOD), was determined by single crystal X-ray diffraction. Both 2,1- and 1,2-insertions of DMAA into the Pd-Me bond of a [(P^O)PdMe] fragment occur to afford a ca. 4:1 mixture of chelates [(P^O)Pd{κ(2)-C,O-C(CH(2)CH(3))C(O)NMe(2)}] (3) and [(P^O)Pd{κ(2)-C,O-CH(2)C(CH(3))C(O)NMe(2)}] (4). The four-membered chelate of 3 is opened by coordination of 2,6-lutidine (3 + 2,6-lutidine ⇌ 3-LUT) with ΔH° = -41.8(10.5) kJ and ΔS° = -115(37) J mol(-1) K(-1).

To investigate the impact of the linker on the electronic and photophysical properties of diboryl compounds, three new diboryl compounds that contain two BMes2 groups (Mes = mesityl) have been synthesized, including a planar 1,6-(BMes2)2pyrene (1), a V-shaped bis(p-BMes2phenyl)diphenylsilane (4), and a U-shaped 1,8-bis(p-BMes2phenyl)naphthalene (5). For comparison, two previously known compounds, p-(BMes2)2benzene (3) and 1,8-bis(p-BMes2-biphenyl)naphthalene (6), were also investigated. The aromatic linkers in these molecules have been found to have a dramatic impact on the electron-accepting ability and Lewis acidity of the diboryl compounds through their distinct steric and electronic properties. Compound 1 has the most positive reduction potential (E 1/2 red1 = −1.81 V, relative to FeCp2 0/+), while 5 has the most negative reduction potential (E 1/2 red1 = −2.34 V). All compounds are blue emitters with considerable variation of emission energy and efficiencies (e.g., λem = 446, 402, 395 nm, Φ = ∼1.0, 0.17, ∼1.0 for 1, 4, and 5, respectively), and each displays a distinct and selective response toward fluoride ions. Upon addition of fluoride ions, compound 1 displays an unusual red shift and an on−off response in both absorption and fluorescent spectra. By comparing the behavior of 1 to that of the monoboryl compound 1-BMes2pyrene (2) and 3, and with TD-DFT computations on 1 and its fluoride adducts 1F and 1F 2 , it has been found that the peculiar response of 1 toward fluoride ions is caused by the dominance of pyrene π orbitals at the HOMO level of 1F and the relatively low-energy charge transfer from the pyrene ring to the three-coordinate boron center in 1F. The crystal structures of 2, 4, 1F 2 , and 5F 2 were determined by X-ray diffraction analyses. The potential use of compound 1 as either a blue emitter or a bifunctional emitter in OLEDs has been demonstrated by the successful fabrication of double- and triple-layer electroluminescent devices.