Reactivities Study Of Isothiocyanates By Digallane Compounds With Non-innocent α-diimine Ligands

While the chemistry of single-bond cleavage promoted by main-group element compounds has gained some development in recent years,the cleavage of multiple bonds remains underexplored.Here we report the reactions of two digallanes with α-diimine ligands,[LGa-Ga L](1,L = dpp-dad = [(2,6-i Pr2C6H3)NC(CH3)]2)with isothiocyanates.The reaction of 1 with isothiocyanates in 1:2 molar ratio proceeded via [2+4] cycloaddition of C=S bond across the C=C-N-Ga fragment to afford [L(RN=C-S)Ga-Ga(S-C=NR)L](2,R = Me;3,R = Ph)with formation of the C-C and S-Ga single bonds.Interestingly,both cycloaddition and oxidative cleavage of Ga-Ga bond as well as reductive cleavage of the C=S bond occurred in the reaction of 1 with phenyl-isothiocyanate(Ph NCS),resulting in the mono-or di-S-bridged digallium complexes [L(Ph N=C-S)Ga(m-S)Ga(S-C=NPh)L](4)and [Na(THF)]2[L(Ph N=C-S)Ga(m-S)2Ga(S-C=NPh)L](6).The di-S-bridged digallium compounds [LGa(μ-S)2Ga L][Na(THF)3]2(5)were also obtained via cleavage of C=S double bond without cycloaddition.The products 2-6 have been characterized by NMR(1H,13C)and IR spectroscopy,elemental analysis,and X-ray diffraction,and their electronic structures were studied by DFT calculations.The first section,Simply introduce the history,synthesis methods and crystal structure of the typical metal-metal bond compound.In addition,synopically introduced the reaction properties of some metal-metal bond compounds.The second section,A Ga-Ga-bonded compound [LGa-Ga L](L = [(2,6-i Pr2C6H3)NC(Me)]2)(1),which is a example of Ga-Ga-bonded complex with α-diimine ligand,reacted with methyl-isothiocyanate(Me NCS)or phenyl-isothiocyanate(Ph NCS)in toluene afforded the [2+4] cycloaddition products [L(Me N=C-S)Ga-Ga(S-C=NMe)L](2)and [L(Ph N=C-S)Ga-Ga(S-C=NPh)L](3)with the [2.2.1] bicycle.When the amount of Ph NCS was increased to 3.0 equivalents,the reaction with 1 led to a different dinuclear product [L(Ph N=C-S)Ga-S-Ga(S-C=NPh)L](4).Besides cycloaddition of two N=C=S moieties to the metal-ligand backbones as in 2 and 3,a unique reductive C=S bond cleavage occurred to the third Ph NCS molecule with accompanying breaking of the Ga-Ga bond,yielding the digallium species 4 bridged by a sulfur atom.The di-S-bridged digallium compound [LGa(μ-S)2Ga L][Na(THF)3]2(5)with a four-membered Ga2S2 central core was obtained in good yield by the reaction of digallane 1 with 2.0 equiv of Ph NCS in the presence of Na metal.In this case no cycloaddition of the isothiocyanate occurred but only cleavage of C=S was observed to generate the bridging sulfur ligands.The reaction of precursor 1 with even more(4.0 equiv.)phenyl isothiocyanate followed by treatment with 2 equiv.of Na proceeded smoothly,affording the unique centrosymmetric dimer 6 that is bridged by two sulfur atoms resulted from the C=S bond cleavage.