Bimetallic aluminum alkyl and iodide complexes stabilized by a bulky bis-guanidinate ligand

Abstract

A series of bulky bis-guanidine ligands such as $$\hbox {L}^{1}\hbox {(2H)}$$ , $$\hbox {L}^{2}\hbox {(2H)}$$ and $$\hbox {L}^{3}\hbox {(2H)}$$ , where $$\hbox {L} = \{\hbox {ArNCNAr}\}_{2}\{\upmu {\text {-}}\hbox {N(C}_{2}\hbox {H}_{4})_{2}\hbox {N}\}$$ , for $$\hbox {L}^{1}\hbox {(2H)}\text { (Ar} = 2, \hbox {6-Me}_{2}$$ - $$\hbox {C}_{6}\hbox {H}_{3})$$ , $$\hbox {L}^{2}\hbox {(2H)}\text { (Ar} = 2, 4, \hbox {6-Me}_{3}$$ - $$\hbox {C}_{6}\hbox {H}_{2})$$ and $$\hbox {(L}^{3}\hbox {(2H)}$$ ) ( $$\hbox {Ar} = 2, 6{\text {-}}^{i}\hbox {Pr}_{2}$$ - $$\hbox {C}_{6}\hbox {H}_{3})$$ have been utilized to synthesize four-membered dinuclear aluminum heterocycles. Deprotonation of $$\hbox {L}^{1-3 }$$ (2H) (1.0 equiv.) upon treatment with trimethyl aluminum (2.1 equiv.) in toluene led to the formation of bimetallic aluminum alkyls: $$\hbox {[L}^{1}\hbox {(AlMe}_{2})_{2}]$$ (1), $$\hbox {[L}^{2}\hbox {(AlMe}_{2})_{2}]$$ (2) and $$\hbox {[L}^{3}(\hbox {AlMe}_{2})_{2}]$$ (3). Aluminum halide complex i.e., $$[\hbox {L}^{3}\hbox {(AlI}_{2})_{2}$$ ](4) was obtained by the reaction of compound 3 with four equivalents of molecular iodine in toluene at 80 $${^{\circ }}\hbox {C}$$ , in which alkyl-halide exchange occurred. All the compounds (1–4) were confirmed by multinuclear ( $$^{1}\hbox {H}$$ and $$^{13}\hbox {C}$$ ) magnetic resonance spectroscopy. Furthermore, compounds 2–4 were confirmed by single crystal X-ray structural analysis. All the compounds 1–4 display the expected number of signals in the $$^{1}\hbox {H}$$ and $$^{13}\hbox {C}$$ NMR spectra and are consistent with their compositions. The solid state structures of 1–4 reveal that each aluminum center is bonded to the monoanionic guanidinate ligand in $$N{,}N'$$ -chelated fashion and the other two sites are occupied by alkyl or halide ligands, resulting in a distorted tetrahedral geometry. Synopsis Bulky bigunidinate-supported dinuclear aluminum alkyl and halide complexes have been synthesized and structurally characterized. Synthesis of aluminum alkyls was achieved by the deprotonation of free ligand upon treatment with metal reagent. Aluminum halide has been accessed by the treatment of aluminum alkyl with molecular iodine.