Abstract:Reaction of (o-phenylene)magnesium (1) with CH3MCl2 (2; M = Al, Ga, In) gave access to
the corresponding methyl(o-phenylene)metal compounds 3 ((1,2-C6H4MCH3)
n
). These novel
1,2-dimetalated benzene derivatives of group 13 were characterized by their spectral data
and, in the case of 3b (M = Ga, n = 2), by a single-crystal X-ray structure determination.
“…It is noteworthy that gallium has rarely been incorporated in polyfunctional Lewis acids . The cyclization reaction leading to the formation of 2 is unexpected.…”
The reaction of equimolar quantities of 1,8bistrimethylstannylnaphthalene (1) and GaCl 3 in toluene yields a stannagallacycle, namely, bis(µ-1,8-naphthalenediyl)(µ-chloride)methyltin(IV)chlorogallium(III) (2). Compound 2 is insoluble in solvents of low polarity and has been characterized by EA, MSCI, and X-ray analysis. The latter revealed the existence of a folded eightmembered dimetallacycle as well as the presence of a chloride ligand bridging the two metals. When treated with pyridine, formation of a soluble bis(pyridine) adduct (3) occurs. Compound 3 has been characterized by EA and 1 H, 13 C, and 119 Sn NMR spectroscopy. As shown by X-ray single-crystal analysis of 3, the central eightmembered dimetallacycle of the molecule has remained intact on going from 2 to 3. Compound 3 does not feature a bridging chloride, and its structure is that of a Lewis acid-Lewis base adduct in which two independent pyridine molecules coordinate the metal centers.
“…It is noteworthy that gallium has rarely been incorporated in polyfunctional Lewis acids . The cyclization reaction leading to the formation of 2 is unexpected.…”
The reaction of equimolar quantities of 1,8bistrimethylstannylnaphthalene (1) and GaCl 3 in toluene yields a stannagallacycle, namely, bis(µ-1,8-naphthalenediyl)(µ-chloride)methyltin(IV)chlorogallium(III) (2). Compound 2 is insoluble in solvents of low polarity and has been characterized by EA, MSCI, and X-ray analysis. The latter revealed the existence of a folded eightmembered dimetallacycle as well as the presence of a chloride ligand bridging the two metals. When treated with pyridine, formation of a soluble bis(pyridine) adduct (3) occurs. Compound 3 has been characterized by EA and 1 H, 13 C, and 119 Sn NMR spectroscopy. As shown by X-ray single-crystal analysis of 3, the central eightmembered dimetallacycle of the molecule has remained intact on going from 2 to 3. Compound 3 does not feature a bridging chloride, and its structure is that of a Lewis acid-Lewis base adduct in which two independent pyridine molecules coordinate the metal centers.
“…While the 1 H and 13 C NMR spectrum reveals the presence of a symmetrically substituted naphthalene ring, the 119 Sn signal observed at −16 ppm corresponds to that of pure Me 3 SnCl in the same solvent. This observation suggests that 3 does not retain its structure in pyridine solutions but rather dissociates to give Me 3 SnCl·py and possibly solvent-stabilized molecules of the digallacyle. , 1 Structure of 3 in the crystal. Selected bond lengths (Å) and angles (deg): Sn(1)−C(33) 2.114(3), Sn(1)−C(31) 2.115(3), Sn(1)−C(32) 2.124(3), Sn(1)−Cl(1) 2.7444(7), Sn(1)−Cl(3A) 2.7578(7), Ga(1)−C(11) 1.955(3), Ga(1)−C(1) 1.957(3), Ga(1)−Cl(1) 2.2806(7), Ga(1)−Cl(2) 2.3803(7), Ga(2)−C(18) 1.962(3), Ga(2)−C(8) 1.965(3), Ga(2)−Cl(3) 2.2723(7), Ga(2)−Cl(2) 2.3743(7); C(33)−Sn(1)−C(31) 121.19(12), C(33)−Sn(1)−C(32) 115.34(12), C(31)−Sn(1)−C(32) 123.35(11), Cl(1)−Sn(1)−Cl(3A), 176.64(2), C(11)−Ga(1)−C(1) 132.28(11), Cl(1)−Ga(1)−Cl(2) 100.07(3), C(18)−Ga(2)−C(8) 134.43(11), Cl(3)−Ga(2)−Cl(2) 100.89(2), Ga(1)−Cl(1)−Sn(1) 111.73(3), Ga(2)−Cl(2)−Ga(1) 76.91(2), Ga(2)−Cl(3)−Sn(1A) 115.28(3).…”
The reaction of equimolar quantities of 1,8-bis(trimethylstannyl)naphthalene (1) and GaCl 3 in toluene at -25 °C yields the known stannagallacycle bis(µ-1,8-naphthalenediyl)(µ-chloride)methyltin(IV)chlorogallium(III) (2) and a new product which has been identified as the cyclic adduct formed between two molecules of bis(µ-1,8-naphthalenediyl)bis(gallium(III)chloride) and two molecules of trimethyltin chloride (3). Interestingly, when carried out at 25 °C and in the presence of water, this reaction leads to the formation of an additional product (4) that is a 12-membered macrocycle containing three gallium atoms linked by 1,8-naphthalenediyl ligands and arranged about a central oxygen atom. The charge balance of 4 is achieved by the presence of a chloride atom that occupies a bridging position between two of the gallium centers. Compounds 3 and 4 have been characterized by NMR, elemental analysis, and single-crystal X-ray analysis. In the crystal, 4 exists as a dimer wherein the monomers are bridged via a Ga-O-Ga-O four-membered ring. The solution structure of 4 in THF-d 8 has been investigated by pulse field gradient spin-echo (PGSE) methods and VT 1 H NMR spectroscopy. The PGSE measurements suggest that, in solution, 4 undergoes a rapid monomer-dimer equilibrium. VT 1 H NMR spectroscopy confirms the existence of a fluxional system. The high-temperature spectrum exhibits three sharp signals. Upon cooling, each of the three sharp signals decoalesces into three signals. Simulation of the spectra followed by an Eyring analysis afforded ∆H q ) 43 ( 3 kJ‚mol -1 and ∆S q ) -36 ( 9 J‚K -1 ‚mol -1 for this process. As a whole, these results support the existence of an exchange between the monomeric and dimeric form of 4. The high-temperature data suggest that upon dissociation into the monomer, the chloride anion undergoes rapid exchange leading to an apparent three-fold molecular symmetry.
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