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Digallane [L 1 Ga-GaL 1 ] (1, L 1 =dpp-bian=1,2-[(2,6-iPr 2 C 6 H 3 )NC] 2 C 12 H 6 ) reacts with RN=C=O (R=Ph or Tos) by [2+4] cycloaddition of the isocyanate C=N bonds across both of its C=C-N-Ga fragments to afford [L 1 (O=C-NR)Ga-Ga(RN-C=O)L 1 ] (R=Ph, 3; R=Tos, 4). The reactions with both isocyanates result in new C-C and N-Ga single bonds. In the case of allyl isocyanate, the [2+4] cycloaddition across one C=C-N-Ga fragment of 1 is accompanied by insertion of a second allyl isocyanate molecule into the Ga-N bond of the same fragment to afford compound [L 1 Ga-Ga(AllN- C=O) 2 L 1 ] (5) (All=allyl). In the presence of Na metal, the related digallane [L 2 Ga-GaL 2 ] (2; L 2 =dpp-dad=[(2,6-iPr 2 C 6 H 3 )NC(CH 3 )] 2 ) is converted into the gallium(I) carbene analogue [L 2 Ga:] - (2 A), which undergoes a variety of reactions with isocyanate substrates. These include the cycloaddition of ethyl isocyanate to 2 A affording [Na 2 (THF) 5 ]{L 2 Ga[EtN-C(O)] 2 GaL 2 } (6), cleavage of the N=C bond with release of 1 equiv. of CO to give [Na(THF) 2 ] 2 [L 2 Ga(p-MeC 6 H 4 )(N-C(O)) 2 -N(p-MeC 6 H 4 )] 2 (7), cleavage of the C=O bond to yield the di-O-bridged digallium compound [Na(THF) 3 ] 2 [L 2 Ga-(μ-O) 2 -GaL 2 ] (8), and generation of the further addition product [Na 2 (THF) 5 ][L 2 Ga(CyNCO 2 )] 2 (9). Complexes 3-9 have been characterized by NMR ( 1 H, 13 C), IR spectroscopy, elemental analysis, and X-ray diffraction analysis. Their electronic structures have been examined by DFT calculations., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Whereas the chemistry of single-bond activation by compounds of the main group elements has undergone some development in recent years, the cleavage of multiple bonds remains underexplored. Herein, the reactions of two digallanes bearing α-diimine ligands, namely, [L 1 Ga-GaL 1 ] (1, L 1 =dpp-dad=[(2,6-iPr 2 C 6 H 3 )NC(CH 3 )] 2 ) and [L 2 Ga-GaL 2 ] (2, L 2 =dpp-bian=1,2-[(2,6-iPr 2 C 6 H 3 )NC] 2 C 10 H 6 ), with isothiocyanates are reported. Reactions of 1 or 2 with isothiocyanates in 1:2 molar ratio proceeded with [2+4] cycloaddition of the C=S bond across the C 2 N 2 Ga metallacycle with formation of C-C and S-Ga single bonds to afford [L 1 (RN=C-S)Ga-Ga(S-C=NR)L 1 ] (3, R=Me; 4, R=Ph) and [L 2 (RN=C-S)Ga-Ga(S-C=NR)L 2 ] (8, R=allyl; 9, R=Ph). In the cases of 8 and 9, this cycloaddition is reversible. The digallanes reacted with 2 equiv of PhNCS in the presence of Na metal or at high temperatures through a unique reductive cleavage of the C=S bond to yield the disulfide-bridged digallium species [Na(THF) 3 ] 2 [L 1 Ga(μ-S) 2 GaL 1 ] (5), [L 2 Ga(μ-S) 2 GaL 2 ] (10), and [Na(DME) 3 ][L 2 Ga(μ-S) 2 GaL 2 ] (11). Moreover, products 4 and 5 can further react with an excess of isothiocyanate, through cleavage of the C=S bond or cycloaddition, to give the bis- or mono-S-bridged complexes [Na(THF) 2 ] 2 [L 1 (PhN=C-S)Ga(μ-S) 2 Ga(S-C=NPh)L 1 ] (6) and [L 1 (PhN=C-S)Ga(μ-S)Ga(S-C=NPh)L 1 ] (7). All the newly prepared compounds were characterized by elemental analysis, single-crystal X-ray diffraction, IR spectroscopy, NMR (3-9) or ESR spectroscopy (11), and DFT calculations., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The reaction of digallane (dpp-bian)Ga-Ga(dpp-bian) (2) (dpp-bian=1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with allyl chloride (AllCl) proceeded by a two-electron oxidative addition to afford paramagnetic complexes (dpp-bian)Ga(η 1 -All)Cl (3) and (dpp-bian)(Cl)Ga-Ga(Cl)(dpp-bian) (4). Treatment of complex 4 with pyridine induced an intramolecular redox process, which resulted in the diamagnetic complex (dpp-bian)Ga(Py)Cl (5). In reaction with allyl bromide, complex 2 gave metal- and ligand-centered addition products (dpp-bian)Ga(η 1 -All)Br (6) and (dpp-bian-All)(Br)Ga-Ga(Br)(dpp-bian-All) (7). The reaction of digallane 2 with Ph 3 SnNCO afforded (dpp-bian)Ga(SnPh 3 ) 2 (8) and (dpp-bian)(NCO)Ga-Ga(NCO)(dpp-bian) (9). Treatment of GaCl 3 with (dpp-bian)Na in diethyl ether resulted in the formation of (dpp-bian)GaCl 2 (10). Diorganylgallium derivatives (dpp-bian)GaR 2 (R=Ph, 11; tBu, 14; Me, 15; Bn, 16) and (dpp-bian)Ga(η 1 -All)R (R=nBu, 12; Cp, 13) were synthesized from complexes 3, 10, Bn 2 GaCl, or tBu 2 GaCl by salt metathesis. The salt elimination reaction between (dpp-bian)GaI 2 (17) and tBuLi was accompanied by reduction of both the metal and the dpp-bian ligand, which resulted in digallane 2 as the final product. Similarly, the reaction of complex 10 with MentMgCl (Ment=menthyl) proceeded with reduction of the dpp-bian ligand to give the diamagnetic complex [(dpp-bian)GaCl 2 ][Mg 2 Cl 3 (THF) 6 ] (18). Compounds 11, 12, 13, 15, and 16 were thermally robust, whereas compound 14 decomposed when heated at reflux in toluene to give complex (dpp-bian-tBu)GatBu 2 (19). Both complexes 7 and 19 contain R-substituted dpp-bian ligand: in the former compound the allyl group was attached to the imino-carbon atom, whereas in complex 19, the tBu group was situated on the naphthalene ring. Crystal structures of complexes 3, 8, 9, 10, 13, 14, 18, and 19 were determined by single-crystal X-ray analysis. The presence of dpp-bian radical anions in 3, 6, 8, and 10-16 was determined by ESR spectroscopy., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)