The present study first describes the reactivity of low valent Al(ii) and Ga(ii) complexes of the type (dpp-bian)M-M(dpp-bian) (1, M = Al; 2, Ga; dpp-bian2- = 1,2-bis-(2,6-iPr2-C6H3)-acenaphthenequinonediamido) with cyclic esters/carbonates such as ε-caprolactone (CL) and trimethylene carbonate (TMC). CL and TMC both readily coordinate to the Al(ii) species 1 to form the corresponding bis-adducts (dpp-bian)Al(L)-(L)Al(dpp-bian) (3, L = CL; 4, L = TMC), which were structurally characterized confirming that the Al(ii)-Al(ii) dimetallic backbone retains its integrity in the presence of such cyclic polar substrates. In contrast, the less Lewis acidic Ga(ii) analogue 2 shows no reaction in the presence of stoichiometric amounts of CL and TMC at room temperature. In combination with BnOH, the dinuclear Al(ii) species 1 revealed to be an extremely active Al(ii) initiator for the controlled ROP of CL at room temperature, outperforming all its Al(iii) congeners reported thus far. Detailed DFT studies on the ROP mechanism are consistent with a process occurring thanks to the metallic cooperativity between the two Al(ii) proximal (since directly bonded) metal centers in 1, which undoubtedly favors the ROP process through bimetallic activation and thus rationalizes the unusually high CL ROP activity at room temperature.
Treatment of (dpp-Bian)Ga−Ga(dpp-Bian) (1) (dpp-Bian = 1,2-bis [(2,6-diisopropylphenyl)imino]acenaphthene) with iodine gives (dpp-Bian)Ga(I)−Ga(I)-(dpp-Bian) (2 ), wh ich re act s in sit u wit h K-(C 5 H 4 CH 2 CH 2 NMe 2 ) (KCp Do ) or K(OCH 2 CH 2 NMe 2 ) (KOR Do ) to produce the monomeric species (dpp-Bian)-GaCp Do (3) and (dpp-Bian)GaOR Do (4), respectively. Complex 3 reacts with PhCCH to give the paramagnetic derivative (dpp-Bian)Ga(CCPh) 2 (5), while compound 4 is inert toward this alkyne. In contrast, monomeric (dpp-Bian)Ga(S 2 CNMe 2 ) (6) reacts with PhCCH and HCCH to give the cycloaddition products [dpp-Bian(PhC CH)]Ga(S 2 CNMe 2 ) ( 7) and [dpp-Bian(HCCH)]Ga(S 2 CNMe 2 ) (8). The related compounds [dpp-Bian(MeCCC(O)-OMe)]Ga(S 2 CNMe 2 ) ( 9) and [dpp-Bian(CH 2 CHC(Me)O)]Ga(S 2 CNMe 2 ) (10) have been obtained in the reactions of complex 6 with methyl 2-butynoate and methyl vinyl ketone, respectively. New complexes have been characterized by 1 H NMR (3, 4, and 7−10) and ESR (5) spectroscopy; their molecular structures have been established by single-crystal X-ray analysis. The catalytic activity of complex 6 in the hydroamination and hydroarylation of alkynes has been examined.
A titanium(IV) alkoxido complex, (dpp-bian)Ti(OBn) 2 (2), as well as alkoxido chlorido complexes (dpp-bian)-TiCl(OCH 2 CH 2 OMe) (3) and (dpp-bian)TiCl 2 OBn (4), were synthesized from the titanium(IV) dichloride precursor [(dppbian)TiCl 2 ] 2 (1) by exchange with corresponding sodium salts (comps. 2 and 3) or by the alcoholysis with BnOH (comp. 4). The compounds 2-4 were fully characterized by elemental analysis, NMR or EPR, and IR spectroscopy. Molecular structures of the metal complexes in the solid state have been determined[a] G.A. Razuvaev
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