No abstract

A diamine-bis(phenolate) chromium(III) complex, {CrCl[O(2)NN'](BuBu)}(2) catalyzes the copolymerization of cyclohexene oxide with carbon dioxide. The synthesis of this metal complex is straightforward, and it can be obtained in high yields. This catalyst incorporates a tripodal amine-bis(phenolate) ligand, which differs from the salen or salan ligands typically used with Cr and Co complexes that have been employed as catalysts for the synthesis of such polycarbonates. The catalyst reported herein yields low molecular weight polymers with narrow polydispersities. Structural and spectroscopic details of this complex along with its copolymerization activity for cyclohexene oxide and carbon dioxide are presented.

The reduction of [P(2)N(2)]NbCl (where [P(2)N(2)] = PhP(CH(2)SiMe(2)NSiMe(2)CH(2))(2)PPh) with KC(8) under a dinitrogen atmosphere generates the paramagnetic dinuclear dinitrogen complex ([P(2)N(2)]Nb)(2)(mu-N(2)) (2). Complex 2 has been characterized crystallographically and by EPR spectroscopy. Variable-temperature magnetic susceptibility measurements indicate that 2 displays antiferromagnetic coupling between two Nb(IV) (d(1)) centers. A density functional theory calculation on the model complex [(PH(3))(2)(NH(2))(2)Nb](2)(mu-N(2)) was performed. Thermolysis of ([P(2)N(2)]Nb)(2)(mu-N(2)) in toluene generates the paramagnetic bridging nitride species where one N atom of the dinitrogen ligand inserts into the macrocycle backbone to form [P(2)N(2)]Nb(mu-N)Nb[PN(3)] (3) (where [PN(3)] = PhPMe(CHSiMe(2)NSiMe(2)CH(2)P(Ph)CH(2)SiMe(2)NSiMe(2)N)). Complex 3 has been characterized in the solid state as well as by variable-temperature magnetic susceptibility measurements. The reaction of ([P(2)N(2)]Nb)(2)(mu-N(2)) with phenylacetylene displaces the dinitrogen fragment to generate a paramagnetic eta(2)-alkyne complex, [P(2)N(2)]Nb(eta(2)-HCCPh) (4).

Catalytic cross-coupling of aryl Grignard reagents with primary and secondary alkyl halides bearing beta-hydrogens is achieved using Fe(III) amine-bis(phenolate) halide complexes.

A diamino-bis(phenolate) chromium(III) complex, CrCl(THF)[L], 1, where [L] = dimethylaminoethylamino- N, N-bis(2-methylene-4,6- tert-butylphenolate), has been synthesized in high yield and characterized by MALDI-TOF mass spectrometry, elemental analysis, UV-vis spectroscopy and single crystal X-ray diffraction. This complex combined with 4-dimethylaminopyridine (DMAP) or bis(triphenylphosphoranylidene)ammonium chloride or azide salts (PPNCl or PPNN) shows improved activity over previously reported amine-bis(phenolate) chromium(III) complexes for copolymerization of cyclohexene oxide (CHO) and CO to yield poly(cyclohexene) carbonate (PCHC). Kinetic studies of the complex/DMAP system showed the activation energy for polycarbonate formation to be 62 kJ/mol. End group analysis of resulting polycarbonates by MALDI-TOF MS reveals either the chloride of the Cr(III) complex or the external nucleophile initiates the copolymerization reaction.