Salicylaldehyde compound containing an ammonium salt unit, [2-(HO)-3-tBu-5-{Bu3N+(CH2)3Si(Me2)}C6H2C(O)H][BF4 -], is prepared from which a Salen-type ligand and its cobalt(III) complex, (Salen-1)CoX (1:  Salen-1 = [trans-N,N‘-bis(3-tBu-5-(Bu3N+(CH2)3Si(Me2)-salicylidene)-1,2-cyclohexanediamine)]X2; X = 2,4-dinitrophenolate), is prepared. Complex 1 shows high activity for CO2/(propylene oxide) copolymerization even at a condition of high [propylene oxide]/[catalyst] ratio and high temperature up to 90 °C, at which conditions a typical binary system of [(Salen)CoX]/[PPNCl] does not yield any copolymer. A very high TOF (up to 3500 h-1) and TON (up to 14500) are achieved, which have never been attained with other catalytic systems. The high selectivity (>84%) for the formation of copolymer over cyclic carbonate and the high molecular weight of the obtained polymers (M n = 53000−95000) are the other merits of the catalyst.

Salen-type ligands comprised of ethylenediamine or 1,2-cyclohexenediamine, along with an salicylaldehyde bearing a methyl substituent on its 3-position and a -[CR(CH(2)CH(2)CH(2)N(+)Bu(3))(2)] (R = H or Me) on its 5-position, unexpectedly afford cobalt(III) complexes with uncoordinated imines. In these complexes, two salen-phenoxys and two 2,4-dinitrophenolates (DNPs), which counter the quaternary ammonium cations, coordinate persistently with cobalt, while two other DNPs are fluxional between a coordinated and an uncoordinated state in THF at room temperature. The complexes of this binding mode show excellent activities in carbon dioxide/propylene oxide copolymerization (TOF, 8300-13,000 h(-1)) but with some fluctuation in induction times (1-10 h), depending on how dry the system is. The induction time is shortened (<1.0 h) and activity is increased approximately 1.5 times upon the replacement of the two fluxional DNPs with 2,4-dinitrophenol-2,4-dinitrophenolate homoconjugation ([DNP...H...DNP](-)). Imposing steric congestion either by replacing the methyl substituent on the salicylaldehyde with tert-butyl or by employing H(2)NCMe(2)CMe(2)NH(2) instead of ethylenediamine or 1,2-cyclohexenediamine results in conventional imine-coordinating complexes, which show lower activities than uncoordinated imine complexes.

Copolymerization of CO 2 and epoxide catalyzed by metal complexes has drawn much attention recently.[1] In the initial report by Inoue and co-workers in 1969 the catalyst activity was poor (turnover number (TON): 6; turnover frequency (TOF): 0.12 h À1 ), [2] but by the early 2000s it had been significantly improved by using binary catalytic systems of [Co(salen)] [3] or [Cr(salen)] complexes [4] with an onium salt or base (1; salen = N,N'-bis(salicylidene)ethylenediamine,[5] It was proposed that the two components or the two zinc centers participated in the propagation reaction, and therefore binding of the two metal centers or the two components further improved catalysis to the maximum reported TON and TOF of 14 500 and 4600 h À1 , respectively. [6,7] These values, which were achieved with 2 in the copolymerization of CO 2 and propylene oxide, are still low enough to warrant further improvement, [7] because low activity means higher catalyst cost and higher levels of catalyst-derived metal residue in the resin.[8] This metal residue either colors the resin or causes toxicity. For the TON of 14 500 attained with 2, the residual cobalt level in the resin reached 40 ppm unless it was removed.[9] Herein, we report a highly active catalytic system for CO 2 /propylene oxide copolymerization and an efficient recovery strategy of the catalyst.We prepared various cobalt-salen complexes by varying either the ortho substituent or the number of attached quaternary ammonium groups (Scheme 1). Thus, the Friedel-Crafts acylation of ortho-substituted phenol using 4-chlorobutyryl chloride and subsequent hydrogenation attached a (CH 2 ) 4 Cl group in the para position. In a similar manner, attack by 1,7-dichloroheptan-4-one on lithium 2-alkyl-4-lithiophenolate yielded a tertiary benzylic alcohol, and subsequent hydrogenation attached CH[(CH 2 ) 3 Cl] 2 . After formylation, the chloro substituent, that was not susceptible to nucleophilic substitution with tributylamine, was transformed into a more reactive iodo substituent. Formation of the quaternary ammonium salt occurred in nearly quantitative yields after generation of the salen-type ligand. Because the halide ion interfered with the metalation reaction, we replaced it with inert BF 4 À . Following metalation by a routine method, an active 2,4-dinitrophenolate anion replaced this BF 4 À ion.[3a]We screened the newly prepared complexes for CO 2 / propylene oxide copolymerization under the following conditions: [propylene oxide (PO)]/[catalyst (cat.)] = 25 000, 80 8C, and CO 2 pressure 2.0-1.7 MPa (Table 1). The polymerization was terminated before 25 % conversion was reached, because after this time the solution became highly viscous, thus making stirring and diffusion difficult. The identity of the ortho substituent strongly influenced the activity. Contrary to other reports, [3] the bulky tert-butyl group was not the best choice in this study, and replacing it with a small methyl group significantly enhanced TOF. The TOF also increased dramat-

An approach to the design of nido-carborane-based luminescent compounds that can exhibit thermally activated delayed fluorescence (TADF) is proposed. 7,8-Dicarba-nido-undecaboranes (nido-carboranes) having various 8-R groups (R=H, Me, i-Pr, Ph) are appended to the meta or para position of the phenyl ring of the dimesitylphenylborane (PhBMes ) acceptor, forming donor-acceptor compounds (nido-m1-m4 and nido-p1-p4). The bulky 8-R group and meta substitution of the nido-carborane are essential to attain a highly twisted arrangement between the donor and acceptor moieties, leading to a very small energy splitting between the singlet and triplet excited states (ΔE <0.05 eV for nido-m2, -m3, and -p3). These compounds exhibit efficient TADF with microsecond-range lifetimes. In particular, nido-m2 and -m3 display aggregation-induced emission (AIE) with TADF properties.

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